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1

Reactions at supercritical conditions: Applications and fundamentals  

Microsoft Academic Search

Supercritical fluids possess properties that make them attractive as media for chemical reactions. Conducting chemical reactions at supercritical conditions affords opportunities to manipulate the reaction environment (Solvent properties) by manipulating pressure, to enhance the solubilities of reactants and products, to eliminate interphase transport limitations on reaction rates, and to integrate reaction and separation unit operations. Supercritical conditions may be advantageous

Phillip E. Savage; Sudhama Gopalan; Thamid I. Mizan; Christopher J. Martino; Eric E. Brock

1995-01-01

2

Reactions at supercritical conditions: Applications and fundamentals  

SciTech Connect

Supercritical fluids possess properties that make them attractive as media for chemical reactions. Conducting chemical reactions at supercritical conditions affords opportunities to manipulate the reaction environment (Solvent properties) by manipulating pressure, to enhance the solubilities of reactants and products, to eliminate interphase transport limitations on reaction rates, and to integrate reaction and separation unit operations. Supercritical conditions may be advantageous for reactions involved in fuels processing, biomass conversion, biocatalysis, homogeneous and heterogeneous catalysis, environmental control, polymerization, materials synthesis, and chemical synthesis. Moreover, supercritical fluids can be used profitably in fundamental chemical investigations of intermolecular interactions and their influence on chemical processes. Work on chemical reactions in and with supercritical fluids is reviewed. The authors discuss both fundamental studies and applications of reactions at supercritical conditions, with focus on work published after 1985. 425 refs.

Savage, P.E.; Gopalan, S.; Mizan, T.I.; Martino, C.J.; Brock, E.E. [Univ. of Michigan, Ann Arbor, MI (United States). Chemical Engineering Dept.] [Univ. of Michigan, Ann Arbor, MI (United States). Chemical Engineering Dept.

1995-07-01

3

'GREENER' CHEMICAL SYNTHESES USING ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

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

4

Expert system for predicting reaction conditions: the Michael reaction case.  

PubMed

A generic chemical transformation may often be achieved under various synthetic conditions. However, for any specific reagents, only one or a few among the reported synthetic protocols may be successful. For example, Michael ?-addition reactions may proceed under different choices of solvent (e.g., hydrophobic, aprotic polar, protic) and catalyst (e.g., Brønsted acid, Lewis acid, Lewis base, etc.). Chemoinformatics methods could be efficiently used to establish a relationship between the reagent structures and the required reaction conditions, which would allow synthetic chemists to waste less time and resources in trying out various protocols in search for the appropriate one. In order to address this problem, a number of 2-classes classification models have been built on a set of 198 Michael reactions retrieved from literature. Trained models discriminate between processes that are compatible and respectively processes not feasible under a specific reaction condition option (feasible or not with a Lewis acid catalyst, feasible or not in hydrophobic solvent, etc.). Eight distinct models were built to decide the compatibility of a Michael addition process with each considered reaction condition option, while a ninth model was aimed to predict whether the assumed Michael addition is feasible at all. Different machine-learning methods (Support Vector Machine, Naive Bayes, and Random Forest) in combination with different types of descriptors (ISIDA fragments issued from Condensed Graphs of Reactions, MOLMAP, Electronic Effect Descriptors, and Chemistry Development Kit computed descriptors) have been used. Models have good predictive performance in 3-fold cross-validation done three times: balanced accuracy varies from 0.7 to 1. Developed models are available for the users at http://infochim.u-strasbg.fr/webserv/VSEngine.html . Eventually, these were challenged to predict feasibility conditions for ?50 novel Michael reactions from the eNovalys database (originally from patent literature). PMID:25588070

Marcou, G; Aires de Sousa, J; Latino, D A R S; de Luca, A; Horvath, D; Rietsch, V; Varnek, A

2015-02-23

5

Fractionating Recalcitrant Lignocellulose at Modest Reaction Conditions  

SciTech Connect

Effectively releasing the locked polysaccharides from recalcitrant lignocellulose to fermentable sugars is among the greatest technical and economic barriers to the realization of lignocellulose biorefineries because leading lignocellulose pre-treatment technologies suffer from low sugar yields, and/or severe reaction conditions, and/or high cellulase use, narrow substrate applicability, and high capital investment, etc. A new lignocellulose pre-treatment featuring modest reaction conditions (50 C and atmospheric pressure) was demonstrated to fractionate lignocellulose to amorphous cellulose, hemicellulose, lignin, and acetic acid by using a non-volatile cellulose solvent (concentrated phosphoric acid), a highly volatile organic solvent (acetone), and water. The highest sugar yields after enzymatic hydrolysis were attributed to no sugar degradation during the fractionation and the highest enzymatic cellulose digestibility ({approx}97% in 24 h) during the hydrolysis step at the enzyme loading of 15 filter paper units of cellulase and 60 IU of beta-glucosidase per gram of glucan. Isolation of high-value lignocellulose components (lignin, acetic acid, and hemicellulose) would greatly increase potential revenues of a lignocellulose biorefinery.

Zhang, Y.-H. Percival [Virginia Polytechnic Institute and State University (Virginia Tech); Ding, Shi-You [National Energy Renewable Laboratory; Mielenz, Jonathan R [ORNL; Cui, Jing-Biao [Dartmouth College; Elander, Richard T. [Dartmouth College; Laser, Mark [Dartmouth College; Himmel, Michael [ORNL; McMillan, James R. [National Energy Renewable Laboratory; Lynd, L. [Dartmouth College

2007-01-01

6

Accelerated glass reaction under PCT conditions  

SciTech Connect

Static leach tests similar to PCT (Product Consistency Test) were performed for up to 2 years to assess long-term reaction behavior of high-level nuclear waste glasses similar to those at Defense Waste Processing Facility. These tests show the reaction rate to decrease with the reaction time from an initially high rate to a low rate, but then to accelerate to a higher rate after reaction times of about 1 year, depending on glass surface area/leachant volume ratio used. Solution concentrations of soluble glass components increase as the reaction is accelerated, while release of other glass components into solution is controlled by secondary phases. Net result is that transformation of glass to stable phases is accelerated while the solution becomes enriched in soluble components not effectively contained in secondary phases. Rate becomes linear in time after the acceleration and may be similar to the initial forward rate. A current model of glass reaction predicts that the glass reaction will be accelerated upon the formation of secondary phases which lower the silicic acid solution concentration. These tests show total Si concentration to increase upon reaction acceleration, however, which may be due to the slightly higher pH attained with the acceleration. The sudden change in the reaction rate is likely due to secondary phase formation. 17 refs, 2 tabs, 3 figs.

Ebert, W.L.; Bates, J.K.; Buck, E.C.; Bradley, C.R.

1992-01-01

7

Accelerated glass reaction under PCT conditions  

SciTech Connect

Static leach tests similar to PCT (Product Consistency Test) were performed for up to 2 years to assess long-term reaction behavior of high-level nuclear waste glasses similar to those at Defense Waste Processing Facility. These tests show the reaction rate to decrease with the reaction time from an initially high rate to a low rate, but then to accelerate to a higher rate after reaction times of about 1 year, depending on glass surface area/leachant volume ratio used. Solution concentrations of soluble glass components increase as the reaction is accelerated, while release of other glass components into solution is controlled by secondary phases. Net result is that transformation of glass to stable phases is accelerated while the solution becomes enriched in soluble components not effectively contained in secondary phases. Rate becomes linear in time after the acceleration and may be similar to the initial forward rate. A current model of glass reaction predicts that the glass reaction will be accelerated upon the formation of secondary phases which lower the silicic acid solution concentration. These tests show total Si concentration to increase upon reaction acceleration, however, which may be due to the slightly higher pH attained with the acceleration. The sudden change in the reaction rate is likely due to secondary phase formation. 17 refs, 2 tabs, 3 figs.

Ebert, W.L.; Bates, J.K.; Buck, E.C.; Bradley, C.R.

1992-12-31

8

NO/CHAR REACTIONS AT PULVERIZED COAL FLAME CONDITIONS  

EPA Science Inventory

The paper discusses nitrogen oxide (NO)/char reactions at pulverized-coal flame conditions. he effective rate of the NO/char reaction, measured over the temperature range 1250 to 1750 K, was found to be retarded by water vapor and enhanced by carbon monoxide (CO) by amounts that ...

9

GREEN CHEMICAL SYNTHESIS THROUGH CATALYSIS AND ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

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

10

High explosive violent reaction (HEVR) from slow heating conditions  

SciTech Connect

The high explosives (HEs) developed and used at the Los Alamos National Laboratory are designed to be insensitive to impact and thermal insults under all but the most extreme conditions. Nevertheless, violent reactions do occasionally occur when HE is involved in an accident. The HE response is closely dependent on the type of external stimulus that initiates the reaction. For example, fast heating of conventional HE will probably result in fairly benign burning, while long-term, slow heating of conventional HE is more likely to produce an HEVR that will do much more damage to the immediate surroundings. An HEVR (High Explosive Violent Reaction) can be defined as the rapid release of energy from an explosive that ranges from slightly faster than a deflagration (very rapid burning) to a reaction that approaches a detonation. A number of thermal analyses have been done to determine slow heat/cook-off conditions that produce HE self-heating that can build up to a catastrophic runaway reaction. The author specifies the conditions that control reaction violence, describes experiments that produced an HEVR, describes analyses done to determine a heating rate threshold for HEVR, and lists possible HEVR situations.

Vigil, A.S.

1999-03-01

11

Fulleranes by Direct Reaction with Hydrogen Gas at Elevated Conditions  

NASA Astrophysics Data System (ADS)

Reaction of solid fullerenes with hydrogen gas occurs with or without catalysts at elevated conditions. Composition of hydrofullerene mixture obtained in this reaction depends strongly on temperature (350-450°C), hydrogen pressure (typically 10-120 bar) and duration of treatment. Saturation of hydrogenation occurs after tens of hours, depending on temperature of reaction. In case of extra strong hydrogenation prolonged reaction leads to formation of fulleranes with composition C60Hx approaching number of hydrogen atoms X = 60. These fulleranes are highly unstable and decompose first with formation of fragmented hydrofullerenes with progressively smaller number of carbon atoms C59, C58, C57 etc., followed by collapse of cage structure. Since the collapse occurs at the conditions of high temperature and high hydrogen pressure, all breaking C-C bonds are saturated immediately with hydrogen and new C-H bonds are formed. Therefore, large fragments of fullerane molecules are able to survive and large polycyclic aromatic hydrocarbons (PAH's) formed as a result of cage structure collapse.

Talyzin, Alexandr V.

12

Reactions of animals and people under conditions of brief weightlessness  

NASA Technical Reports Server (NTRS)

It has been shown that under brief weightlessness sensory reactions arise in a number of people, mainly those under these conditions for the first time, in the form of spatial and visual illusions, motor excitation, in which tonic and motor components can be distinguished, and vestibular-vegetative disturbances (nausea, vomiting, etc.). In repeated flights with creation of weightlessness, a decrease in the extent of expression and, then, disappearance of these reactions occurred in a significant majority of those studied. Experiments in weightlessness with the vision cut off and with the absence of vestibular functions in the subjects confirm the hypothesis that spatial conceptions of people in weightlessness depend on predominance of gravireceptor or visual afferent signals under these conditions.

Kitayev-Smik, L. A.

1975-01-01

13

Homogeneous-Heterogeneous Reactions in Peristaltic Flow with Convective Conditions  

PubMed Central

This article addresses the effects of homogeneous-heterogeneous reactions in peristaltic transport of Carreau fluid in a channel with wall properties. Mathematical modelling and analysis have been carried out in the presence of Hall current. The channel walls satisfy the more realistic convective conditions. The governing partial differential equations along with long wavelength and low Reynolds number considerations are solved. The results of temperature and heat transfer coefficient are analyzed for various parameters of interest. PMID:25460608

Hayat, Tasawar; Tanveer, Anum; Yasmin, Humaira; Alsaedi, Ahmed

2014-01-01

14

An age extended progress variable for conditioning reaction rates  

NASA Astrophysics Data System (ADS)

An aging progress variable (APV) is proposed as a convenient tool for conditioning quantities used to calculate reaction rates in premixed turbulent combustion. The APV is defined to obey an advection-diffusion-reaction equation where the source term is linearly related to the fuel consumption rate when the APV is less than a threshold representative of the trailing edge of the fuel consumption layer. Above this threshold, the APV has a constant source term. To test the proposal, three-dimensional fully compressible direct numerical simulation (DNS) is performed in an inflow-outflow configuration with inlet turbulence forcing using a modified version of the DNS code SENGA. A model chemical mechanism involving two steps and four species is used which has an order of magnitude difference between the time scales associated with the two steps. The inlet Taylor scale Reynolds number is 51 and the Damköhler numbers are 2.0 and 0.29 for the two steps. When conditionally averaged on the proposed APV the scalar fluctuations about the conditional average are negligible. Further, it is shown that the probability density function of the APV can be reasonably approximated based on the first two moments of the APV and the fuel mass fraction. The APV probability density function (PDF) is approximated on rectangular slabs of cells normal to the flow direction using only these moments as a test case. Convolution of the PDF so approximated with conditional mean reaction rates—calculated from conditionally averaged scalar fields where the averaging was carried out over the entire domain—leads to an approximation for the unconditional mean reaction rates on each of these slabs typically within 10% of the true value for both steps. That the correlation between the reaction rates and the APV is strong, and that the PDF can be approximated for a situation where approximating the PDF for a product based progress variable is nontrivial, makes the proposed APV a strong alternative to traditional progress variables for both flamelet models and premixed conditional moment closure (CMC) approaches.

Grout, R. W.

2007-10-01

15

Effects of Meteorological Conditions on Reactions to Noise Exposure  

NASA Technical Reports Server (NTRS)

More than 80,000 residents' responses to transportation noise at different times of year provide the best, but imprecise, statistical estimates of the effects of season and meteorological conditions on community response to noise. Annoyance with noise is found to be slightly statistically significantly higher in the summer than in the winter in a seven-year study in the Netherlands. Analyses of 41 other surveys drawn from diverse countries, climates, and times of year find noise annoyance is increased by temperature, and may be increased by more sunshine, less precipitation, and reduced wind speeds. Meteorological conditions on the day of the interview or the immediately preceding days do not appear to have any more effect on reactions than do the conditions over the immediately preceding weeks or months.

Shepherd, Kevin P. (Technical Monitor); Fields, James M.

2004-01-01

16

Reactions of aminomalononitrile with electrophiles. [simulating prebiotic conditions  

NASA Technical Reports Server (NTRS)

Aminomalononitrile (HCN trimer) reacts with electrophiles such as aldehydes and acrylonitrile under very mild conditions of temperature and pH to produce intermediates which, after acid hydrolysis, yield amino acids. The following amino acids have been identified and quantitated: glycine, D,L-erythro- and D,L-threo-beta-hydroxyaspartic acids, D,L glutamic acid, and D,L-threonine and allo-threonine. The mechanism of their formation and the possible significance of these reactions in prebiotic syntheses are discussed.

Thanassi, J. W.

1975-01-01

17

Experimental assessment of the probabilistic maturation reaction norm: condition matters  

PubMed Central

The probabilistic maturation reaction norm (PMRN) describes an individual's probability of maturing at a given age as a function of size and other relevant phenotypic traits. Population-level shifts in the PMRN are often interpreted to indicate genetic as opposed to phenotypic changes in maturation in fish. Inferences derived from trends in the PMRN have been challenged, warranting an experimental assessment of the method. This was accomplished in a laboratory experiment using zebrafish (Danio rerio). Fish were reared under different food levels to induce variation in growth and maturation. Plasticity in maturation was not entirely captured by the demographic age- and length-based PMRN. Adding condition to the PMRN captured a greater amount of environmental variation in maturation probability. Nevertheless, significant differences in the PMRNs among the food levels remained after accounting for the influences of age, size and condition on maturation probability indicating plasticity of the PMRN. This was particularly pronounced between fish held on low food levels as compared with fish experiencing abundant resources, with the latter experiencing higher size-specific maturation probabilities. Our analysis emphasizes the need for incorporating salient physiological traits influencing maturation, such as condition, to make accurate inferences about documented shifts observed in the position of PMRNs on maturation trends in wild fish stocks. PMID:20861054

Uusi-Heikkilä, S.; Kuparinen, A.; Wolter, C.; Meinelt, T.; O'Toole, A. C.; Arlinghaus, R.

2011-01-01

18

MICROWAVE-ACCELERATED MULTICOMPONENT REACTIONS UNDER SOLVENT-FREE CONDITIONS  

EPA Science Inventory

The application of microwave-accelerated solventless synthetic protocols in multicomponent (MCC) reactions will be exemplified by several condensation and cyclization reactions including the rapid one-pot assembly of valuable heterocyclic compounds from in situ generated intermed...

19

Impact of reaction conditions on grafting acrylamide onto starch  

Technology Transfer Automated Retrieval System (TEKTRAN)

We have explored the radical initiated graft polymerization reaction of acrylamide onto starch where the solvent, concentration, temperature and reaction times were varied. We have found that the morphology of the resulting grafted polymer is dramatically different and is dependent on the reaction c...

20

Reaction pathways of glucose oxidation by ozone under acidic conditions.  

PubMed

The ozonation of d-glucose-1-(13)C, 2-(13)C, and 6-(13)C was carried out at pH 2.5 in a semi-batch reactor at room temperature. The products present in the liquid phase were analyzed by GC-MS, HPAEC-PAD, and (13)C NMR spectroscopy. Common oxidation products of glucose have also been submitted to identical ozonation conditions. For the first time, a pentaric acid was identified and its formation quantitatively correlated to the loss of C-6 of glucose in the form of carbon dioxide. Potential mechanisms for the formation of this pentaric acid are discussed. The well-accepted pathway involving the anomeric position in glucose, gluconic acid, arabinose, and carbon dioxide is reinvestigated. The origin of small molecules such as tartaric, erythronic, and oxalic acids is clarified. Finally, new reaction pathways and tentative mechanisms consistent with the formation of ketoaldonic acids and smaller acids are proposed. PMID:19524217

Marcq, Olivier; Barbe, Jean-Michel; Trichet, Alain; Guilard, Roger

2009-07-27

21

MICROWAVE-FACILITATED MULTICOMPONENT REACTIONS UNDER SOLVENT-FREE CONDITIONS  

EPA Science Inventory

The application of microwave-expedited solvent-free synthetic protocols in multi-component (MCC) reactions will be exemplified by several condensation and cyclization reactions including the rapid one-pot assembly of heterocyclic compounds from in situ generated intermediates. R...

22

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

ERIC Educational Resources Information Center

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

Tellinghuisen, Joel

2006-01-01

23

REACTIONS TO SUFFERING OF OTHERS UNDER CONDITIONS OF INDIRECT RESPONSIBILITY  

Microsoft Academic Search

PRESENTED AS A STUDY OF PAIRED-ASSOCIATE LEARNING TO 66 FEMALE UNDERGRADUATES WHO PARTICIPATED IN PAIRS. EACH S, WITH THE EXCEPTION OF THOSE IN A CONTROL CONDITION, WAS LED TO BELIEVE THAT HER PARTNER WAS TO RECEIVE A STRONG ELECTRICAL SHOCK AND THAT S WOULD BE IN A MORE DESIRABLE CONDITION (CONTROL OR MONEY). WHEN S PERCEIVED THAT THE OTHER PERSON

MELVIN J. LERNER; GAIL MATTHEWS

1967-01-01

24

Chemical reactions in viscous liquids under space conditions  

Microsoft Academic Search

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

A. Kondyurin; B. Lauke; E. Richter

2004-01-01

25

Uranium plasma emission at gas-core reaction conditions  

NASA Technical Reports Server (NTRS)

The results of uranium plasma emission produced by two methods are reported. For the first method a ruby laser was focused on the surface of a pure U-238 sample to create a plasma plume with a peak plasma density of about 10 to the 20th power/cu cm and a temperature of about 38,600 K. The absolute intensity of the emitted radiation, covering the range from 300 to 7000 A was measured. For the second method, the uranium plasma was produced in a 20 kilovolt, 25 kilojoule plasma-focus device. The 2.5 MeV neutrons from the D-D reaction in the plasma focus are moderated by polyethylene and induce fissions in the U-235. Spectra of both uranium plasmas were obtained over the range from 30 to 9000 A. Because of the low fission yield the energy input due to fissions is very small compared to the total energy in the plasma.

Williams, M. D.; Jalufka, N. W.; Hohl, F.; Lee, J. H.

1976-01-01

26

Characteristics of uranium carbonitride microparticles synthesized using different reaction conditions  

SciTech Connect

Three sets of different experimental conditions by changing the cover gases during the sample preparation were tested to synthesize uranium carbonitride (UC1-xNx) microparticles. In the first two sets of experiments using (N2 to N2-4%H2 to Ar) and (Ar to N2 to Ar) environments, single phase UC1-xNx was synthesized. When reducing environments (Ar-4%H2 to N2-4%H2 to Ar-4%H2) were utilized, theoretical densities up to 97% of single phase UC1-xNx kernels were obtained. Physical and chemical characteristics such as density, phase purity, and chemical compositions of the synthesized UC1-xNx materials for the diferent experimental conditions used are provided. In-depth analysis of the microstrutures of UC1-xNx has been carried out and is discussed with the objective of large batch fabrication of high density UC1-xNx kernels.

Silva, Chinthaka M [ORNL; Lindemer, Terrence [Harbach Engineering and Solutions; Voit, Stewart L [ORNL; Hunt, Rodney Dale [ORNL; Besmann, Theodore M [ORNL; Terrani, Kurt A [ORNL; Snead, Lance Lewis [ORNL

2014-01-01

27

Impact of reaction conditions on architecture and rheological properties of starch graft polyacrylamide polymers  

Technology Transfer Automated Retrieval System (TEKTRAN)

We carried out experiments examining the impact that solvent selection and reaction conditions have on the radical initiated graft polymerization reaction of acrylamide onto starch. We have also evaluated the rheological properties the starch graftpolyacrylamide product when a gel is formed in water...

28

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

E-print Network

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

Kjelstrup, Signe

29

Characteristics of uranium carbonitride microparticles synthesized using different reaction conditions  

NASA Astrophysics Data System (ADS)

Three sets of experimental conditions were tested to synthesize uranium carbonitride (UC1-xNx) kernels from gel-derived urania-carbon microspheres. Primarily, three sequences of gases were used, N2 to N2-4%H2 to Ar, Ar to N2 to Ar, and Ar-4%H2 to N2-4%H2 to Ar-4%H2. Physical and chemical characteristics such as geometrical density, phase purity, and chemical compositions of the synthesized UC1-xNx were measured. Single-phase kernels were commonly obtained with densities generally ranging from 85% to 93% TD and values of x as high as 0.99. In-depth analysis of the microstrutures of UC1-xNx has been carried out and is discussed with the objective of large batch fabrication of high density UC1-xNx kernels.

Silva, Chinthaka M.; Lindemer, Terrence B.; Voit, Stewart R.; Hunt, Rodney D.; Besmann, Theodore M.; Terrani, Kurt A.; Snead, Lance L.

2014-11-01

30

Kinetics of OH + CO reaction under atmospheric conditions  

NASA Technical Reports Server (NTRS)

A pulsed laser photolysis-pulsed laser-induced fluorescence technique is used to directly measure the temperature, pressure, and H2O concentration dependence on k1 in air. K1 is found to increase linearly with increasing pressure at pressures of not greater than 1 atm, and the pressure dependence of k1 at 299 K is the same in N2 buffer gas as in O2 buffer gas. The rate constant in the low-pressure limit and the slope of the k1 versus pressure dependence are shown to be the same at 262 K as at 299 K. The present results significantly reduce the current atmospheric model uncertainties in the temperature dependence under atmospheric conditions, in the third body efficiency of O2, and in the effect of water vapor on k1.

Hynes, A. J.; Wine, P. H.; Ravishankara, A. R.

1986-01-01

31

One-pot three-component Mannich reaction catalyzed by iodine under solvent-free conditions  

Microsoft Academic Search

One-pot three-component Mannich reactions of ketones with aromatic aldehydes and aromatic amines are effectively catalyzed\\u000a by molecular iodine at room temperature under solvent-free conditions to afford the corresponding ?-amino carbonyl compounds\\u000a with moderate to excellent yields. The method has the following advantages: no use of solvent, mild condition, high reaction\\u000a speed and small quantity of catalyst.

Li Gang; Long Ruiling; Yang Jiangli

2011-01-01

32

An investigation of a Friedel-Crafts alkylation reaction in homogeneous supercritical CO 2 and under subcritical and splitphase reaction conditions  

Microsoft Academic Search

This study investigates the Friedel-Crafts alkylation reaction of triphenylmethanol with methoxybenzene (anisole) in supercritical and subcritical carbon dioxide, and under two-phase (gas\\/liquid) reaction conditions at moderate pressures and temperatures. The reaction was initiated using trifluoroacetic acid to produce triphenylmethlycarbocation as the reaction intermediate. Isolated product yields of the Friedel-Crafts product, p-methoxytetraphenylmethane, are reported.

John E. Chateauneuf; Kan Nie

2000-01-01

33

A transferable predator avoidance reaction may account for the conditioned and naive coho salmon  

E-print Network

Rathbun, a brachyuran crab, occurs on the continental shelf from Puget Sound in Washington StateA transferable predator avoidance reaction may account for the conditioned and naive coho salmon acting as a homogeneous group in the present study. Conditioned coho salmon had learned to avoid torrent

34

Characterization of reaction conditions providing rapid and specific cysteine alkylation for peptide-based mass spectrometry.  

PubMed

Alkylation converts Cys thiols to thioethers and prevents unwanted side reactions, thus facilitating mass spectrometric identification of Cys-containing peptides. Alkylation occurs preferentially at Cys due to its high nucleophilicity, however reactions at other such sites are possible. N-ethylmaleimide (NEM) shows rapid reaction kinetics with Cys and careful definition of reaction conditions results in little reactivity at other sites. Analysis of a protein standard alkylated under differing reaction conditions (pH, NEM concentrations and reaction times) was performed using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) and selected reaction monitoring (SRM) of NEM-modified and unmodified peptide pairs. Mis-alkylation sites at primary and secondary amines were identified and limited to one equivalent of NEM. No evidence for hydroxyl or thioether alkylation was observed. Improved specificity was achieved by restricting the pH below neutral, NEM concentration below 10mM and/or reaction time to below 5min. Maximal removal of Cys activity was observed in tissue homogenates at 40mM NEM within 1min, dependent upon efficient protein denaturation. SRM assays identified peptide-specific levels of mis-alkylation, indicating that NEM-modified to unmodified ratios did not exceed 10%, with the exception of Cys alkylation that proceeded to 100%, and some Lys residues that resulted in tryptic missed cleavages. High reactivity was observed for His residues considering their relatively low abundance. These data indicate that rapid and specific Cys alkylation is possible with NEM under relatively mild conditions, with more abrasive conditions leading to increased non-specific alkylation without appreciable benefit for MS-based proteomics. PMID:22910378

Paulech, Jana; Solis, Nestor; Cordwell, Stuart J

2013-01-01

35

Onset conditions for gas phase reaction and nucleation in the CVD of transition metal oxides  

NASA Technical Reports Server (NTRS)

A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No vapor phase ignition has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw = 1700 K). The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.

Collins, J.; Rosner, D. E.; Castillo, J.

1992-01-01

36

Macromolecular crowding conditions enhance glycation and oxidation of whey proteins in ultrasound-induced Maillard reaction.  

PubMed

High intensity ultrasound (HIUS) can promote Maillard reaction (MR). Macromolecular crowding conditions accelerate reactions and stabilise protein structure. The aim of this study was to investigate if combined application of ultrasound and macromolecular crowding can improve efficiency of MR. The presence of crowding agent (polyethylene glycol) significantly increased ultrasound-induced whey protein (WP) glycation by arabinose. An increase in glycation efficiency results only in slight change of WP structure. Macromolecular crowding intensifies oxidative modifications of WP, as well as formation of amyloid-like structures by enhancement of MR. Solubility at different pH, thermal stability and antioxidative capacity of glycated WP were increased, especially in the presence of crowding agent, compared to sonicated nonglycated proteins. The application of HIUS under crowding conditions can be a new approach for enhancement of reactions in general, enabling short processing time and mild conditions, while preserving protein structure and minimising protein aggregation. PMID:25660883

Perusko, Marija; Al-Hanish, Ayah; Cirkovic Velickovic, Tanja; Stanic-Vucinic, Dragana

2015-06-15

37

Experimental Studies of Hydrogenation and Other Reactions on Surfaces Under Astrophysically Relevant Conditions  

NASA Technical Reports Server (NTRS)

The goal of our project is to study hydrogen recombination reactions on solid surfaces under conditions that are relevant in astrophysics. Laboratory experiments were conducted using low-flux, cold atomic H and D beams impinging on a sample kept under ultra high vacuum conditions. Realistic analogues of interstellar dust grains were used. Our results show that current models for hydrogen recombination reactions have to be modified to take into account the role of activated diffusion of H on surfaces even at low temperature.

Vidali, Gianfranco

1998-01-01

38

Using Group-Inquiry to Study Differing Reaction Conditions in the E2 Elimination of Cyclohexyl Halides  

ERIC Educational Resources Information Center

In this experiment, students individually conduct one of several variations of an E2 dehydrohalogenation reaction on a cyclohexyl halide substrate for 30 min, which is sufficient only for a partial reaction to occur. The variations examine reaction conditions including different leaving groups, decreased reaction temperature, or reduced base…

Long, Robert D.

2012-01-01

39

Studies of the reactions of dibenzyl ether under preconversion processing conditions  

SciTech Connect

The occurrence of retrogressive reactions during direct coal liquefaction processing is harmful because these reactions result in the formation of high molecular weight material that is refractory to further processing. Therefore, the yields of desired products are decreased, downstream processing conditions must be more severe than if retrogressive reactions did not occur, and in some cases, an accumulation of solids causes process shutdown. The objectives of this research project are (1) to determine the causes of retrogressive reactions during the initial processing of coal (known as preconversion processing) in direct liquefaction and (2) to devise methods for minimizing these undesired reactions. The first objective involves evaluating the effects of process conditions and additives on retrogressive reactions. The approach to completing this objective is twofold. Initial scoping studies have been done using the model compound dibenzyl ether (DBE). Subsequent work will use coal. Work on the second research objective will be performed in conjunction with the evaluation of the effects of process variables and additives on coal. Research for completing the second objective will involve several different approaches such as the use of cleaned coals, and the use of different coal pretreatments.

Stohl, F.V.; Kottenstette, R.J.

1991-12-31

40

Carboxymethylation of Cassava Starch in Different Solvents and Solvent-Water Mixtures: Optimization of Reaction Conditions  

NASA Astrophysics Data System (ADS)

The influence of reaction medium on carboxymethylation process was investigated by treating cassava starch with sodium monochloroacetate in different solvents and solvent-water mixtures under alkaline conditions. The amount of carboxyl groups introduced into the starch moiety was determined titrimetrically and used to calculate the Degree of Substitution (DS) and Reaction Efficiency (RE). The results showed that carboxymethylation is significantly affected by the nature of reaction medium at p<0.05. Carboxymethylation in different solvent-water mixtures showed that aqueous 80% n-propanol offered the best medium for carboxymethylation. Optimization of reaction conditions in aqueous 80% n-propanol showed that the best condition for carboxymethylation was at starch-liquor ratio of 1:3, NaOH/reagent molar ratio of 4.0 and reagent-starch molar ratio of 0.35. An increase in temperature was required to effect the reaction at shorter time. At 55°C the highest values of DS and RE achieved in 0.5 h would require three hours to achieve the same values of DS and RE at 45°C.

Nwokocha, Louis M.; Ogunmola, Gabiel B.

41

Decarboxylative ketone aldol reactions: development and mechanistic evaluation under metal-free conditions.  

PubMed

Malonic acid half thioesters (MAHTs) and malonic acid half oxyesters (MAHOs) are shown to undergo decarboxylative nucleophilic addition reactions with ketone and aldehyde electrophiles in the presence of stoichiometric or catalytic quantities of triethylamine at room temperature. The ability to perform these reactions under metal-free conditions has enabled a detailed mechanistic analysis of the reaction pathway leading to the (1)H NMR spectroscopic characterization of a postnucleophilic addition/predecarboxylation intermediate and experimental evidence for a reversible formation of this intermediate followed by an irreversible decarboxylation. Rate constants for each of the bond forming/bond breaking steps in the reaction pathway were also determined, casting light on the differing reactivity between MAHO and MAHT nucleophiles in these processes. Finally, the mechanistic insights gained through these studies have been employed in the development of a new decarboxylative coumarin synthesis. PMID:20560569

Blaquiere, Nicole; Shore, Daniel G; Rousseaux, Sophie; Fagnou, Keith

2009-08-21

42

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

NASA Technical Reports Server (NTRS)

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

Johnson, R. E.

1986-01-01

43

Sharper graph-theoretical conditions for the stabilization of complex reaction networks.  

PubMed

Across the landscape of all possible chemical reaction networks there is a surprising degree of stable behavior, despite what might be substantial complexity and nonlinearity in the governing differential equations. At the same time there are reaction networks, in particular those that arise in biology, for which richer behavior is exhibited. Thus, it is of interest to understand network-structural features whose presence enforces dull, stable behavior and whose absence permits the dynamical richness that might be necessary for life. We present conditions on a network's Species-Reaction Graph that ensure a high degree of stable behavior, so long as the kinetic rate functions satisfy certain weak and natural constraints. These graph-theoretical conditions are considerably more incisive than those reported earlier. PMID:25600138

Knight, Daniel; Shinar, Guy; Feinberg, Martin

2015-04-01

44

Tyrosinase-catalyzed modification of Bombyx mori silk fibroin: Grafting of chitosan under heterogeneous reaction conditions  

Microsoft Academic Search

The capability of mushroom tyrosinase to catalyze the oxidation of tyrosine residues of Bombyx mori silk fibroin was studied under heterogeneous reaction conditions, by using a series of silk substrates differing in surface and bulk morphology and structure, i.e. hydrated and insoluble gels, mechanically generated powder and fibre. Tyrosinase was able to oxidize 10–11% of the tyrosine residues of silk

Giuliano Freddi; Anna Anghileri; Sandra Sampaio; Johanna Buchert; Patrizia Monti; Paola Taddei

2006-01-01

45

Runaway reactions, their courses and the methods to establish safe process conditions  

NASA Astrophysics Data System (ADS)

Much of the literature on runaway reactions deals with the consequences such as mechanical damage toxic and flammable release. The DIERS literature provides effective methods for vent sizing where experimental information is requested. Thermal stability measurements provide information on the onset temperature and kinetic data for chemical reactions. There is less information on the way the runaway reactions occur whereas the runaway reactions may have different causes. The purpose of this paper is to describe the various process deviations which can cause a runaway reaction to occur and to discuss the experimental information necessary for risk assessment, the choice of a safe process and the mitigation of the consequences of the runaway reaction. Each possible hazardous process deviation is illustrated by examples from the process industry and/or relevant experimental information obtained from laboratory experiments. The typical hazardous situations to be considered are the following: 1) The homogeneous thermal runaway due to too high a temperature. 2) The homogeneous runaway reaction by unintended introduction of additional reactants or catalyst. 3) The heterogeneous runaway reaction due to too high a local temperature. 4) The heterogeneous runaway reaction caused by slow heat conduction to the outside. 5) The runaway reaction caused by excess residence time at the process temperature (autocatalytic reactions). 6) The runaway reaction caused by reactant accumulation. The controling reactant feed rate is higher than the consumption rate perhaps because the temperature is too low, or the catalyst is absent. 7) The runaway reaction due to the pressurization of the enclosure by gaseous oxidizing intermediates (typical of nitric oxidations). 8) The runaway reaction due to phase separation of unstable species (liquids, solids) by loss of mixing or on cooling. 9) The runaway reaction on mixing of fast reacting chemicals in separate phases. 10)The runaway reaction due to fire or external heating. Considering the various runaway situations, the effectiveness of the following approaches is discussed: - Theoretical and experimental information required for hazard assessment. - Choice of adequate process conditions. - Choice of adequate methods for process control. - Experimental information required for vent sizing. La plus grande partie de la littérature sur les emballements thermiques traite des conséquences de l'accident telles que les effets mécaniques, les émissions toxiques et inflammables. Les travaux publiés par le DIERS fournissent des méthodes permettant le dimensionnement d'évents, nécessitant des déterminations expérimentales. Il y a moins d'information sur la manière dont les emballements thermiques peuvent survenir alors que ceux-ci peuvent avoir différentes causes. Le propos de cet article est de décrire les différentes dérives de procédé qui peuvent entraîner un emballement thermique et de déterminer l'information expérimentale nécessaire pour l'analyse des risques du procédé, le choix de conditions opératoires sûres et la réduction des conséquences de l'emballement thermique. Chaque dérive de procédé dangereuse, est illustrée par des exemples connus dans l'industrie chimique et par des données expérimentales obtenues dans des essais de laboratoire. Les conditions de procédé dangereuses prises en compte sont les suivantes: 1)L'emballement thermique homogène dû à une température excessive; 2) L'emballement thermique homogène par introduction d'un catalyseur ou d'un réactif contrôlant; 3) L'emballement thermique hétérogène dû à une température locale excessive; 4)L'emballement thermique hétérogène dû à une faible conduction thermique vers l'extérieur; 5) L'emballement thermique dû à un temps de séjour excessif à la température du procédé (Réactions autocatalytiques); 6) L'emballement thermique par accumulation de réactifs. La vitesse d'introduction d'un réactif contrôlant est supérieure à la vitesse de consommation de ce réactif, parce que la temp

Gustin, J. L.

1991-08-01

46

Radiolytic reactions of nitro blue tetrazolium under oxidative and reductive conditions: a pulse radiolysis study  

NASA Astrophysics Data System (ADS)

The radiolytic reactions of the ditetrazolium salt nitro blue tetrazolium chloride (NBTCl 2) were studied by pulse radiolysis technique in aqueous solution under reducing and oxidising conditions with the aim of potential dosimetry application. Under reducing conditions the fast formation of the tetrazolinyl radical is observed that is followed by the appearance of monoformazan (MF +), i.e. one of the tetrazolium rings is reduced to formazan. The formation of the water-insoluble diformazan, i.e. the result of the second reduction step was not observed in pulse radiolysis. Formazan formation was not found under oxidative conditions.

Kovacs, A.; Wojnarovits, L.; Baranyai, M.; Moussa, A.; Othman, I.; McLaughlin, W. L.

1999-08-01

47

Reaction of dopa decarboxylase with L-aromatic amino acids under aerobic and anaerobic conditions.  

PubMed Central

Analysis of the reaction of dopa decarboxylase (DDC) with L-dopa reveals that loss of decarboxylase activity with time is observed at enzyme concentrations approximately equal to the binding constant, K(d), of the enzyme for pyridoxal 5'-phosphate (PLP). Instead, at enzyme concentrations higher than K(d) the course of product formation proceeds linearly until complete consumption of the substrate. Evidence is provided that under both experimental conditions no pyridoxamine 5'-phosphate (PMP) is formed during the reaction and that dissociation of coenzyme occurs at low enzyme concentration, leading to the formation of a PLP-L-dopa Pictet-Spengler cyclic adduct. Taken together, these results indicate that decarboxylation-dependent transamination does not accompany the decarboxylation of L-dopa proposed previously [O'Leary and Baughn (1977) J. Biol. Chem. 252, 7168-7173]. Nevertheless, when the reaction of DDC with L-dopa is studied under anaerobic conditions at an enzyme concentration higher than K(d), we observe that (1) the enzyme is gradually inactivated and inactivation is associated with PMP formation and (2) the initial velocity of decarboxylation is approximately half of that in the presence of O(2). Similar behaviour is observed by comparing the reaction with L-5-hydroxytryptophan occurring in aerobiosis or in anaerobiosis. Therefore the reaction of DDC with L-aromatic amino acids seems to be under O(2) control. In contrast, the reactivity of the enzyme with L-aromatic amino acids does not change in the presence or absence of O(2). These and other results, together with previous results on the effect exerted by O(2) on reaction specificity of DDC towards aromatic amines [Bertoldi, Frigeri, Paci and Borri Voltattorni (1999) J. Biol. Chem. 274, 5514-5521], suggest a productive effect of O(2) on an intermediate complex of the reaction of the enzyme with L-aromatic amino acids or aromatic amines. PMID:11085948

Bertoldi, M; Borri Voltattorni, C

2000-01-01

48

Influence of reaction conditions on the composition of liquid products from two-stage catalytic hydrothermal processing of lignin.  

PubMed

The influence of reaction conditions on the composition of liquid products during two-stage hydrothermal conversion of alkali lignin has been investigated in a batch reactor. Reactions were carried out in the presence of formic acid (FA) and Pt/Al2O3 catalyst. The two different sets of reaction conditions involved alternative reaction times of 1h and 5h at 265°C and 350°C, respectively. These provided different contributions to reaction severity, which affected the compositions of liquid products. Yields of liquid products reached up to 40wt% (on lignin feed basis) in the presence of FA under the less severe reaction condition. With 5h reaction time at 350°C, alkylphenols, alkylguaiacols and hydrocarbons were the dominant liquid products. However, with 5h reaction time at 265°C, phenol and methanol became dominant. The two-stage hydrothermal process led to improved lignin conversion, with the potential to manipulate the liquid product range. PMID:25840361

Onwudili, Jude A

2015-07-01

49

Method and apparatus for measuring coupled flow, transport, and reaction processes under liquid unsaturated flow conditions  

DOEpatents

The present invention is a method and apparatus for measuring coupled flow, transport and reaction processes under liquid unsaturated flow conditions. The method and apparatus of the present invention permit distinguishing individual precipitation events and their effect on dissolution behavior isolated to the specific event. The present invention is especially useful for dynamically measuring hydraulic parameters when a chemical reaction occurs between a particulate material and either liquid or gas (e.g. air) or both, causing precipitation that changes the pore structure of the test material.

McGrail, Bernard P. (Pasco, WA); Martin, Paul F. (Richland, WA); Lindenmeier, Clark W. (Richland, WA)

1999-01-01

50

Knoevenagel condensation reaction catalyzed by task-specific ionic liquid under solvent-free conditions  

Microsoft Academic Search

A task-specific ionic liquid, [H3N+–CH2–CH2–OH][CH3COO?] was synthesized and used as catalyst in the Knoevenagel condensation reaction of various kinds of aromatic aldehydes with ethyl cyanoacetate or malononitrile. ?,?-Unsaturated carbonyl compounds were obtained in reasonable yields when the [H3N+–CH2–CH2–OH][CH3COO?] catalyzed Knoevenagel reaction was carried out at room temperature for several to 60min under solvent-free conditions. Only E-isomers were detected. The task-specific

Caibo Yue; Aiqin Mao; Yunyang Wei; Minjie Lü

2008-01-01

51

A proposed abiotic reaction scheme for hydroxylamine and monochloramine under chloramination relevant drinking water conditions.  

PubMed

Drinking water monochloramine (NH2Cl) use may promote ammonia-oxidizing bacteria (AOB). AOB use (i) ammonia monooxygenase for biological ammonia (NH3) oxidation to hydroxylamine (NH2OH) and (ii) hydroxylamine oxidoreductase for NH2OH oxidation to nitrite. NH2Cl and NH2OH may react, providing AOB potential benefits and detriments. The NH2Cl/NH2OH reaction would benefit AOB by removing the disinfectant (NH2Cl) and releasing their growth substrate (NH3), but the NH2Cl/NH2OH reaction would also provide a possible additional inactivation mechanism besides direct NH2Cl reaction with cells. Because biological NH2OH oxidation supplies the electrons required for biological NH3 oxidation, the NH2Cl/NH2OH reaction provides a direct mechanism for NH2Cl to inhibit NH3 oxidation, starving the cell of reductant by preventing biological NH2OH oxidation. To investigate possible NH2Cl/NH2OH reaction implications on AOB, an understanding of the underlying abiotic reaction is first required. The present study conducted a detailed literature review and proposed an abiotic NH2Cl/NH2OH reaction scheme (RS) for chloramination relevant drinking water conditions (?M concentrations, air saturation, and pH 7-9). Next, RS literature based kinetics and end-products were evaluated experimentally between pHs 7.7 and 8.3, representing (i) the pH range for future experiments with AOB and (ii) mid-range pHs typically found in chloraminated drinking water. In addition, a (15)N stable isotope experiment was conducted to verify nitrous oxide and nitrogen gas production and their nitrogen source. Finally, the RS was slightly refined using the experimental data and an AQUASIM implemented kinetic model. A chloraminated drinking water relevant RS is proposed and provides the abiotic reaction foundation for future AOB biotic experiments. PMID:24862953

Wahman, David G; Speitel, Gerald E; Machavaram, Madhav V

2014-09-01

52

Influence of reaction conditions on the enantioselectivity of biocatalyzed C-C bond formations under high pressure conditions.  

PubMed

Benzoylformate decarboxylase (BFD, EC 4.1.1.7) is a homotetrameric thiamine diphosphate (ThDP)-dependent enzyme which catalyzes the synthesis of chiral 2-hydroxyketones accepting a broad range of aldehydes as substrates. In this study the synthesis of 2-hydroxypropiophenone (2-HPP) from benzaldehyde and acetaldehyde was catalyzed by three BFD variants namely BFD F464I, BFD A460I and BFD A460I-F464I. This paper reports the effect of hydrostatic pressure up to 290 MPa when the reactions were carried out at different benzaldehyde concentrations (5-40 mM) as well as at different pH values (7.0-8.5). Acetaldehyde concentration was fixed at 400 mM in all biotransformations. Reactions performed at high benzaldehyde concentrations and at high hydrostatic pressures showed an increase in (R)-2-HPP formation catalyzed by all BFD variants. For BFD A460I-F464I we observed an increase in the ee of (R)-2-HPP up to 80%, whereas at atmospheric conditions this variant synthesizes (R)-2-HPP with an ee of only 50%. Alkaline conditions (up to pH 8.5) and high hydrostatic pressures resulted in an increase of (R)-2-HPP synthesis, especially in the case of BFD A460I and BFD F464I. PMID:21295624

Kara, Selin; Long, Wei Sing; Berheide, Marco; Peper, Stephanie; Niemeyer, Bernd; Liese, Andreas

2011-03-20

53

Correlation changes in EEG, conditioned and behavioral reactions with various degrees of oxygen insufficiency  

NASA Technical Reports Server (NTRS)

The dynamics of change in bioelectric activity of the brain during acute hypoxia are studied for the time that working capacity and active consciousness are preserved, and to establish the correlation between EEG changes and behavioral reactions under oxygen starvation. Changes in body functions and behavioral disturbances are related to the degree of oxygen saturation in the blood, to bioelectric activity of the brain, and to an increase in conditioned reflexes. The capacity for adequate reaction to external signals and for coordinated psychomotor activity after loss of consciousness returns to man after 30 seconds. Repeated effects of hypoxia produce changes in the physiological reactions of the body directed toward better adaptation to changing gaseous environments.

Agadzhanyan, N. A.; Zakharova, I. N.; Kalyuzhnyy, L. V.; Dvorzhak, I. I.; Moravek, M.; Tsmiral, Y. I.

1974-01-01

54

Reaction Mechanisms in Petroleum: From Experimentation to Upgrading and Geological Conditions  

E-print Network

Among the numerous questions that arise concerning the exploitation of petroleum from unconventional reservoirs, lie the questions of the composition of hydrocarbons present in deep seated HP-HT reservoirs or produced during in-situ upgrading steps of heavy oils and oil shales. Our research shows that experimental hydrocarbon cracking results obtained in the laboratory cannot be extrapolated to geological reservoir conditions in a simple manner. Our demonstration is based on two examples: 1) the role of the hydrocarbon mixture composition on reaction kinetics (the "mixing effect") and the effects of pressure (both in relationship to temperature and time). The extrapolation of experimental data to geological conditions requires investigation of the free-radical reaction mechanisms through a computed kinetic model. We propose a model that takes into account 52 reactants as of today, and which can be continuously improved by addition of new reactants as research proceeds. This model is complete and detailed enou...

Lannuzel, Frédéric; Bounaceur, Roda; Marquaire, Paul-Marie; Michels, Raymond

2009-01-01

55

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

PubMed

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

Sgarlata, Carmelo; Zito, Valeria; Arena, Giuseppe

2013-01-01

56

The kinetics of dolomite reaction rim growth under isostatic and non-isostatic pressure conditions  

NASA Astrophysics Data System (ADS)

During burial and exhumation, rocks are simultaneously exposed to metamorphic reactions and tectonic stresses. Therefore, the reaction rate of newly formed minerals may depend on chemical and mechanical driving forces. Here, we investigate the reaction kinetics of dolomite (CaMg[CO3]2) rim growth by solid-state reactions experiments on oriented calcite (CaCO3) and magnesite (MgCO3) single crystals under isostatic and non-isostatic pressure conditions. Cylindrical samples of 3-5 mm length and 7 mm diameter were drilled and polished perpendicular to the rhombohedral cleavage planes of natural clear crystals. The tests were performed using a Paterson-type deformation apparatus at P = 400 MPa confining pressure, temperatures, T, between 750 and 850°C, and reaction durations, t, of 2 - 146 h to calculate the kinetic parameters of dolomite rim growth under isostatic stress conditions. For non-isostatic reaction experiments we applied in addition differential stresses, ?, up to 40 MPa perpendicular to the contact interface at T = 750°C for 4 - 171 h duration, initiating minor inelastic deformation of calcite. The thickness of the resulting dolomite reaction rims increases linearly with the square root of time, indicating a diffusion-controlled reaction. The rims consist of two different textural domains. Granular dolomite grains (? 2 -5 ?m grain size) form next to calcite and elongated palisade-shaped grains (1-6 ?m diameter) grow perpendicular to the magnesite interface. Texture measurements with the electron backscatter diffraction technique indicate that the orientations of dolomite grains are mainly influenced by the orientation of the calcite educt crystal, in particular in the granular rim. To some extent, the texture of dolomite palisades is also influenced by the orientation of magnesite. The thickness of the two individual layers increases with temperature. At 400 MPa isostatic pressure, T = 750°C and t = 29 hours, a 5 ?m thick granular dolomite layer and a 7 ?m thick palisade-shaped layer evolve. At similar conditions and a differential stress of 30 MPa, the rim thickness remains similar; consequently the effect of non-isostatic stress on dolomite rim growth is negligible. Platinum markers show that the initial calcite-magnesite interface is located between granular and palisade-forming dolomite, indicating that rim growth occurs by counter diffusion of MgO and CaO. Diffusion of MgO across the dolomite reaction rim into calcite forms additionally magnesio-calcite grains with diameters of ? 13 - 46 ?m, depending on the experimental conditions and increasing with increasing distance to the dolomite boundary. At T = 750°C, t = 29 hours, the thickness of the magnesio-calcite layer is 32 ?m (isostatic) - 35 ?m (? = 30 MPa). The experiments indicate that solid-state reaction rim growth of dolomite between calcite and magnesite is primarily controlled by diffusion of MgO and CaO, forming layers with different microstructures during growth into the educt phases. The kinetics of the reaction in the carbonate system are not significantly changed by differential stresses up to 40 MPa. We suggest that volume diffusion is the dominant transport mechanism, which is presumably less affected by non-isostatic stresses than grain boundary diffusion.

Helpa, V.; Rybacki, E.; Morales, L. G.; Abart, R.; Dresen, G. H.

2013-12-01

57

Effects of cannabinoids on lithium-induced conditioned rejection reactions in a rat model of nausea  

Microsoft Academic Search

  \\u000a \\u000a Rationale. Marijuana has been reported to suppress nausea produced by chemotherapy treatment in human cancer patients. Although there\\u000a is abundant evidence that cannabinoid agonists attenuate vomiting in emetic species, there has been little experimental evidence\\u000a of their anti-nausea potential. Considerable evidence suggests that conditioned rejection reactions in rats reflect nausea.\\u000a The present experiments evaluated the potential of low doses

Linda A. Parker; Raphael Mechoulam; Coralynn Schlievert; Laura Abbott; Melissa L. Fudge; Page Burton

2003-01-01

58

Kinetics of the reaction between hydrogen and sulfur under high-temperature Claus furnace conditions  

Microsoft Academic Search

The reaction Hâ + (1\\/2)Sâ {r equilibrium}HâS has been studied as a function of temperature and residence time over the ranges 602--1290°C and 0.03--1.5 s in the absence of a catalyst. This paper shows that the combination of Hâ and elemental sulfur vapor under the high-temperature conditions typical of a Claus sulfur recovery unit proceeds via a reversible homogeneous gas-phase

Norman I. Dowling; James B. Hyne; Dennis M. Brown

1990-01-01

59

Effects of Maillard reaction conditions on the functional properties of WPI chitosan oligosaccharide conjugates.  

PubMed

Whey proteins are widely used as food material, but their functional properties are affected by processing conditions, in which Maillard reaction commonly occurs. The objective of this study was to investigate the effects of reaction conditions (saccharide rate (SR), setting time and setting temperature) on the functional properties of conjugates of whey protein isolates (WPI) - chitosan oligosaccharide (COS), which were produced by Maillard reaction. Response surface methodology (RSM) was used in this study, models for solubility, heat stability (HS), emulsifying activity (EA) and emulsifying stability (ES) of WPI-COS were established. Results indicated that the solubility of WPI-COS was 98.8 % at 29.8 % SR, 17.4 h, 46.7 °C; the heat stability of WPI-COS was 92.95 % at 27.2 % SR, 18.1 h, 48.7 °C; the EA of WPI-COS was 1.87 at 25.3 % SR, 20.0 h, 46.1 °C; the ES of WPI-COS was 13.28 min at 32.5 % SR, 12.0 h, 35.0 °C and setting temperature was the major factor affecting EA and ES while SR was the major factor affecting solubility and heat stability. Conditions were optimized for the preparation of WPI-COS to obtain improved functional properties. PMID:25477646

Zheng, Zhe; Luo, Yongkang; Yao, Lei; Lu, Jing; Bu, Guanhao

2014-12-01

60

Search for reaction conditions and catalyst for selective prebiotic formation of Aldopentoses from Glycolaldehyde and Formaldehyde  

NASA Astrophysics Data System (ADS)

Formation of organic compounds from simple precursors appears to have been one of the first steps from geochemistry towards modern biochemistry. The Earth lagoons, hydrothermal springs, cosmic dust, meteorites, protoplanetary disk, etc. has been considered as the possible ``reactors'' in which the prebiotic synthesis could have taken place. The finding of reactions and reaction conditions which allow to produce the high yields of the biologically relevant substances from simple compounds could help us to verify different hypothesis of plausible prebotic conditions. In this work we have studied the formation of vitally important sugars, namely aldopentoses (ribose, xylose, lyxose and arabinose), from glycolaldehyde and formaldehyde over catalysts. Aldopentoses nowadays play the important roles as the components of polysaccharides, glycosides, nucleic acids and ATP. Glycolaldehyde is the simplest monosaccharide, which was found in the interstellar space [1], where it could be generated as a result of several processes, for instance, condensation of formaldehyde under UV-radiation [2]. In this work the peculiarities of interaction between glycolaldehyde and formaldehyde in the presence of soluble (phosphate and borate buffers) and solid (minerals apatite and montmorillonites) catalysts were studied. The dependences of composition of the reaction products on the catalyst nature, molar ratio of substrates, pH value of reaction mixture were revealed. The yields of aldopentoses amount to ca. 60-65% in the presence of borate catalyst under optimized reaction conditions. Borate acts not only as a catalyst, but also as the stabilizer of active intermediates and aldopentoses from side reactions [3]. Borates are present in some mineral and clays (serpentine, montmorillonite etc.) and in water of Cityhot springs (Geyser valley, placeKamchatka) in rather high concentrations. Therefore catalysis by borates could be considered as plausible prebotic condition. Acknowledgements. We thank Dr. S. Yashnik for providing the montmorillonite clays. The financial support of Program RAS (program ``Origin of biosphere and evolution biogeology systems'') is gratefully acknowledged. Hollis, J., Jewell, P., Lovas, F., et al., The Astrophysical Journal. 613, L45--L48, 2004 Pestunova, O., Simonov, A., Snytnikov, V., et al., Adv. Space Res. 36/2, 214-219, 2005. Ricardo, A., Carrigan, M.A., Olcott, A.N., Benner, S.A. Science. 303, 5655, 196, 2004.

Delidovich, Irina; Taran, Oxana; Parmon, Valentin; Gromov, Nikolay

2012-07-01

61

Organocatalytic acetylation of starch: effect of reaction conditions on DS and characterisation of esterified granules.  

PubMed

Starch acetates with varying degree of substitution (DS) were prepared by a novel solvent-free organocatalytic methodology. The acetylation protocol involved a non-toxic biobased ?-hydroxycarboxylic acid as catalyst, and proceeded with high efficiency in absence of solvents. The effect of reaction conditions including reaction temperature (90-140 °C), catalyst load (0-2.3 g/g starch), acetic anhydride/starch weight ratio (6.5-13.5 g/g), and starch moisture content (0.6-14.8%) on the DS of the esters was evaluated. The analysis performed showed that the increase of temperature and catalyst concentration resulted in higher DS values, and evidenced a beneficial contribution of native starch moisture content on the substitution level achieved. Variation of reaction conditions allowed starch esters to be obtained with DS in the 0.03-2.93 range. Starch esters were characterised in terms of morphology, chemical structure, thermal properties, and distribution in polar/non polar liquid systems. PMID:25306348

Tupa, Maribel Victoria; Ávila Ramírez, Jhon Alejandro; Vázquez, Analía; Foresti, María Laura

2015-03-01

62

Temperature-dependent reaction-rate expression for oxygen recombination at Shuttle entry conditions  

NASA Technical Reports Server (NTRS)

A temperature-dependent oxygen surface reaction-rate coefficient has been determined from experimental STS-2 heating and wall temperature data at altitudes of 77.91 km, 74.98 km, and 71.29 km. The coefficient is presented in an Arrhenius form and is shown to be less temperature dependent than previous results. Finite-rate viscous-shock-layer heating rates based on this present expression have been compared with predicted heating rates using the previous rate coefficients and with experimental heating data obtained over an extensive range of STS-2 and STS-3 entry conditions. A substantial improvement is obtained in comparison of experimental data and predicted heating rates using the present oxygen reaction-rate expression.

Zoby, E. V.; Simmonds, A. L.; Gupta, R. N.

1984-01-01

63

Specificity of psychomotor reactions in the conditions of support deprivation including effects of countermeasures  

NASA Astrophysics Data System (ADS)

Activity of the cosmonaut demands high level of psychomotor reactions (PMR) which can vary during space flight under the influences of psychophysiological state’s variability and unusual inhabitancy that causes the necessity of PMR estimation’s inclusion into quality monitoring of capacity for work (CW). A main objective of research was a study of features of visual-motor reactions (VMR) and elements of CW of the person within simulation of microgravity effects via 7-day dry immersion (DI) in healthy male-volunteers 20-35 years old. The experimental data were received which testified to peculiarities of VMR and recognition of simple figures of main colors of a visible spectrum (red, green, blue, the RGB-standard) in the conditions of the DI characterized by support deprivation and decreased proprioceptive afferentation - in a control series and in a series with use of mioelectrostimulation as a countermeasure.

Nichiporuk, Igor; Ivanov, Oleg

64

Method of experimental determination of the kinetic constants in fast polymerization reactions in nonisothermal diffusion conditions  

SciTech Connect

A new method for the experimental determination of the kinetic constants k/sub p/ and k/sub t/ in fast polymerization reactions on the example of cationic (under the effect of AlCl/sub 3/, BF/sub 3/, and other catalysts) liquid phase polymerization of isobutylene in a flow was suggested. The study of the macrokinetic features of low-temperature polymerization of isobutylene revealed the specific conditions of the occurrence of the process (quasi-ideal displacement) which are characterized by the relative constancy and uniformity of the distribution of the concentrations of the reacting substances along the flow section.

Prochukhan, Yu.A.; Berlin, A.A.; Enikolopyan, N.S.

1986-09-01

65

Growth and characterizations of magnetic nanoparticles under hydrothermal conditions: Reaction time and temperature  

NASA Astrophysics Data System (ADS)

Magnetic iron oxide nanoparticles with various sizes and magnetic properties were synthesized by using a hydrothermal method. The initial nanoparticles were obtained by co-precipitation of ferric and ferrous salts and then treated under a hydrothermal condition for 1-120 h at 160 °C. At reaction time of 12 h, further treatment on the particles was performed at 200 °C. The resultant nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffractometer (XRD) and vibrating sample magnetometer. The images obtained by TEM showed that the particles are around spherical in shape. The mean size of particles increased from 14±4 nm to 74±9 nm as the reaction time was increased from 1 h to 120 h. From the XRD patterns, high crystalline iron oxide nanoparticles were obtained with increasing reaction time and temperature. The saturation magnetizations obtained from magnetization curves were found to be rising from 74.9 to 93.5 emu/g that is consistent with the bulk value of the magnetite.

Ozel, Fatmahan; Kockar, Hakan

2015-01-01

66

Reaction of perfluoroalkylpolyethers (PFPE) with 440C steel in vacuum under sliding conditions at room temperature  

NASA Technical Reports Server (NTRS)

Reactions of perfluoroalkylpolyethers (PFPE: Fomblin, Demnum and Krytox) were studied during the sliding contact of stainless steel specimens under ultrahigh vacuum conditions. All three fluids reacted with the steel specimens during sliding. Fomblin, which has acetal linkages, decomposed under the sliding conditions generating gaseous products, (COF2 and fluorinated carbons) which were detected by a quadrupole mass spectrometer. Gaseous products were not detected for the Demnum and Krytox fluids. The amount of gaseous products from Fomblin increased with increasing sliding speed. At the end of the sliding experiments, the wear scar and deposits on the specimens were examined by small spot size XPS. The oxide layer on the specimen surface was removed during sliding, and metal fluorides were formed on the worn surface. The surface of the wear scar and deposits were covered with adsorbed PFPE. Based on these results, it was concluded that the decomposition reaction on Fomblin was initiated by contacting the fluid with a fresh metal surface which was formed during sliding.

Mori, Shigeyuki; Morales, Wilfredo

1989-01-01

67

In-situ observations of catalytic surface reactions with soft x-rays under working conditions  

NASA Astrophysics Data System (ADS)

Catalytic chemical reactions proceeding on solid surfaces are an important topic in fundamental science and industrial technologies such as energy conversion, pollution control and chemical synthesis. Complete understanding of the heterogeneous catalysis and improving its efficiency to an ultimate level are the eventual goals for many surface scientists. Soft x-ray is one of the prime probes to observe electronic and structural information of the target materials. Most studies in surface science using soft x-rays have been performed under ultra-high vacuum conditions due to the technical limitation, though the practical catalytic reactions proceed under ambient pressure conditions. However, recent developments of soft x-ray based techniques operating under ambient pressure conditions have opened a door to the in-situ observation of materials under realistic environments. The near-ambient-pressure x-ray photoelectron spectroscopy (NAP-XPS) using synchrotron radiation enables us to observe the chemical states of surfaces of condensed matters under the presence of gas(es) at elevated pressures, which has been hardly conducted with the conventional XPS technique. Furthermore, not only the NAP-XPS but also ambient-pressure compatible soft x-ray core-level spectroscopies, such as near-edge absorption fine structure (NEXAFS) and x-ray emission spectroscopy (XES), have been significantly contributing to the in-situ observations. In this review, first we introduce recent developments of in-situ observations using soft x-ray techniques and current status. Then we present recent new findings on catalytically active surfaces using soft x-ray techniques, particularly focusing on the NAP-XPS technique. Finally we give a perspective on the future direction of this emerging technique.

Toyoshima, Ryo; Kondoh, Hiroshi

2015-03-01

68

Kinetics and mechanisms of the reaction of zoisite to anorthite under hydrothermal conditions: reaction phenomenology away from the equilibrium region  

NASA Astrophysics Data System (ADS)

The kinetics and mechanisms of the dehydration reactions of zoisite have been studied at 635° 792° C, 1 2 kbar. The equilibrium reaction does not occur and is replaced by metastable reactions involving the formation of gehlenite and a calcium tri-octahedral mica, instead of corundum: zoisite ? anorthite+grossular+gehlenite +calcium 3T mica+H2O. The experimental data can be interpreted by zero-order equations dX An/ dt=k ( X An=fractional extent of reaction, t=time, k=zero-order rate constant). These relations hold for variations in P, T, A initial(the initial surface area of zoisite) and also in the presence of seed crystals, which enhance the reaction rate. No induction period is evident and only at advanced stages of reaction are sharp decreases observed in the rate, which are attributed to physical affects (shrinking particles, armouring). SEM studies show that dissolution of zoisite is anisotropic, occurring preferentially parallel to the crystallographic b-axis, with the result that a characteristic ‘sawtooth’ etch structure develops. Garnet grows as euhedral crystals located in cavities or on ‘teeth’ of dissolving zoisite, whereas anorthite forms as clusters of coalescing grains which spread over and enclose the zoisite. In seeded runs, garnet growth initiates on both seeds and on zoisite surfaces whereas anorthite growth is more closely tied to the seeds, resulting in the development of clusters of smaller grains. The experimental evidence favours dissolution and nucleation-controlled growth as rate-determining processes. The preservation of zero-order kinetics in the face of shrinking particles is attributed to the anisotropic dissolution mechanism, which effectively preserves a constant reaction interface. The rate effects of nucleation appear to accord with the classic model in which growth of crystal layers is initiated by the formation of coherent nuclei. The temperature dependence of rate constants reflects both thermally activated Arrhenius-type behaviour and the rate-depressing influences of approach to equilibrium. Similarly pressure affects on reaction rate can be interpreted in terms of competition between rate enhancement due to pressure increase and rate-depression accompanying the approach to equilibrium. Although the equilibrium-approach effects accord with current treatments of reaction kinetics, a problem exists in deriving an exact relation coupling dissolution and nucleation rate control. Consequently an overall-reaction rate equation, such as that of Fisher and Lasaga (1981), is only partially successful in interpreting the temperature dependence of rates. The data suggest that the surface reaction equation of Wood and Walther (1983) only applies when nuclei are present.

Matthews, Alan

1985-04-01

69

reactions  

Microsoft Academic Search

Gene regulatory, signal transduction and metabolic networks are major areas of interest in the newly emerging field of systems biology. In living cells, stochastic dynamics play an important role; however, the kinetic parameters of biochemical reactions necessary for modelling these processes are often not accessible directly through experiments. The problem of estimating stochastic reaction constants from molecule count data measured,

S. Reinker; R. M. Altman; J. Timmer

70

Palladium(II)-catalyzed Heck reaction of aryl halides and arylboronic acids with olefins under mild conditions  

PubMed Central

Summary A series of general and selective Pd(II)-catalyzed Heck reactions were investigated under mild reaction conditions. The first protocol has been developed employing an imidazole-based secondary phosphine oxide (SPO) ligated palladium complex (6) as a precatalyst. The catalytic coupling of aryl halides and olefins led to the formation of the corresponding coupled products in excellent yields. A variety of substrates, both electron-rich and electron-poor olefins, were converted smoothly to the targeted products in high yields. Compared with the existing approaches employing SPO–Pd complexes in a Heck reaction, the current strategy features mild reaction conditions and broad substrate scope. Furthermore, we described the coupling of arylboronic acids with olefins, which were catalyzed by Pd(OAc)2 and employed N-bromosuccinimide as an additive under ambient conditions. The resulted biaryls have been obtained in moderate to good yields. PMID:23946858

Shaikh, Tanveer Mahamadali

2013-01-01

71

A more robust model of the biodiesel reaction, allowing identification of process conditions for significantly enhanced rate and water tolerance.  

PubMed

A more robust kinetic model of base-catalysed transesterification than the conventional reaction scheme has been developed. All the relevant reactions in the base-catalysed transesterification of rapeseed oil (RSO) to fatty acid methyl ester (FAME) were investigated experimentally, and validated numerically in a model implemented using MATLAB. It was found that including the saponification of RSO and FAME side reactions and hydroxide-methoxide equilibrium data explained various effects that are not captured by simpler conventional models. Both the experiment and modelling showed that the "biodiesel reaction" can reach the desired level of conversion (>95%) in less than 2min. Given the right set of conditions, the transesterification can reach over 95% conversion, before the saponification losses become significant. This means that the reaction must be performed in a reactor exhibiting good mixing and good control of residence time, and the reaction mixture must be quenched rapidly as it leaves the reactor. PMID:24508659

Eze, Valentine C; Phan, Anh N; Harvey, Adam P

2014-03-01

72

Combined temperature-programmed reaction and in situ x-ray scattering studies of size-selected silver clusters under realistic reaction conditions in the epoxidation of propene  

NASA Astrophysics Data System (ADS)

The catalytic activity and dynamical shape changes in size-selected nanoclusters at work are studied under realistic reaction conditions by using a combination of simultaneous temperature-programmed reaction with in situ grazing-incidence small angle x-ray scattering. This approach allows drawing a direct correlation between nanocatalyst size, composition, shape, and its function under realistic reaction conditions for the first time. The approach is illustrated in a chemical industry highly relevant selective partial oxidation of propene on a monodisperse silver nanocatalyst. The shape of the catalyst undergoes rapid change already at room temperature upon the exposure to the reactants, followed by a complex evolution of shape with increasing temperature. Acrolein formation is observed around 50 °C while the formation of the propylene oxide exhibits a sharp onset at 80 °C and is leveling off at 150 °C. At lower temperatures acrolein is produced preferentially to propylene oxide; at temperatures above 100 °C propylene oxide is favored.

Vajda, Stefan; Lee, Sungsik; Sell, Kristian; Barke, Ingo; Kleibert, Armin; von Oeynhausen, Viola; Meiwes-Broer, Karl-Heinz; Rodríguez, Arantxa Fraile; Elam, Jeffrey W.; Pellin, Michael M.; Lee, Byeongdu; Seifert, Sönke; Winans, Randall E.

2009-09-01

73

A Comparison Between the Burn Condition of Deuterium-Tritium and Deuterium-Helium-3 Reaction and Stability Limits  

NASA Astrophysics Data System (ADS)

The nuclear reaction of deuterium-tritium (D-T) fusion by the usual magnetic or inertial confinement suffers from a number of difficulties and problems caused by tritium handling, neutron damage to materials and neutron-induced radioactivity, etc. The study of the nuclear synthesis reaction of deuterium-helium-3 (D-3He) at low collision energies (below 1 keV) is of interest for its applications in nuclear physics and astrophysics. Spherical tokamak (ST) reactors have a low aspect ratio and can confine plasma with ??1. These capabilities of ST reactors are due to the use of the alternative D-3He reaction. In this work, the burn condition of D-3He reaction was calculated by using zero-dimensional particles and power equations, and, with the use of the parameters of the ST reactor, the stability limit of D-3He reaction was calculated and then the results were compared with those of D-T reaction. The obtained results show that the burn conditions of D-3He reaction required a higher temperature and had a much more limited temperature range in comparison to those of D-T reaction.

Motevalli, Seyed Mohammad; Fadaei, Fereshteh

2015-02-01

74

Study of the optimal reaction conditions for assay of the mouse alternative complement pathway.  

PubMed

The optimal reaction conditions for hemolytic assay of alternative complement pathway activity in mouse serum were investigated. A microtiter system was used, in which a number of 7.5 X 10(6) rabbit erythrocytes per test well appeared to be optimal. Rabbit erythrocytes were superior as target cells over erythrocytes from a number of other animal species. The optimal conditions were as follows: an incubation temperature of 39 degrees C, an ionic strength of about 200 mM, and a magnesium concentration of 2.5 mM. Incubation during 60 min was not sufficient for an end-point titration. Addition of 1 mg of zymosan A per test well, however, enhanced and accelerated the hemolytic activity of mouse serum via the alternative pathway resulting in a maximum value after 45 min. This, most probably, proceeded by a mechanism involving the formation of a zymosan-C5-convertase and bystander lysis of the target cells. In contrast to the normal alternative pathway assay the zymosan-potentiated test did, most probably, not involve natural antibodies. Cobra venom factor was more efficient in enhancing the sensitivity of the assay for the mouse alternative complement pathway than zymosan. This makes this factor very useful for testing C-poor body fluids. PMID:4078314

Van Dijk, H; Rademaker, P M; Klerx, J P; Willers, J M

1985-12-27

75

Reactions of adsorbed pyrene and perylene with gaseous N 2O 5 under simulated atmospheric conditions  

NASA Astrophysics Data System (ADS)

We report here results of studies concerning the reactions of two representative polycyclic aromatic hydrocarbons (PAH), pyrene and perylene, adsorbed on glass fiber filters, towards gaseous N 2O 5, NO 3 radicals, NO 2 and HNO 3 at part-per-million or lower concentrations and at ? 5% relative humidity. These exposures were carried out in a passive mode in an ~ 6400-? all-Teflon environmental chamber. As is the case for naphthalene vapor, neither adsorbed pyrene nor perylene reacted to any observable extent with the NO 3 radical. However, pyrene reacted rapidly with N 2O 3 to form 1-nitropyrene (1-NP) with a 60-70% yield after 50 min exposure to an initial N 2O 5 concentration of 1.5 ppm. Under these conditions, no reaction of perylene with N 2O 5 was observed. In control runs of the same duration, neither pyrene nor perylene reacted significantly ( < 0.5%) with 1.7 ppm of gaseous HNO 3 but, consistent with earlier studies, a ~ 3% yield of 3-nitroperylene (and < 0.5 % 1-NP) was formed when they were exposed to a mixture of 0.5 ppm NO2 + 0.35 ppm HNO3. These data show for the first time that gas phase N 2O 5 can be a strong nitrating agent for adsorbed pyrene to produce 1-nitropyrene, a powerful bacterial mutagen. Clearly, uncertainties occur in extrapolating our laboratory data to ambient atmospheres. However, when our results are combined with estimated N 2O 5 concentrations of up to ~ 15 ppb in polluted night-time atmospheres, they suggest that nitro-PAH, could be formed at significant rates in ambient air.

Pitts, James N.; Zielinska, Barbara; Sweetman, Janet A.; Atkinson, Roger; Winer, Arthur M.

76

Kinetics and mechanism of the reaction of aminoguanidine with the ?-oxoaldehydes glyoxal, methylglyoxal, and 3-deoxyglucosone under physiological conditions  

Microsoft Academic Search

Aminoguanidine (AG), a prototype agent for the preventive therapy of diabetic complications, reacts with the physiological ?-oxoaldehydes glyoxal, methylglyoxal, and 3-deoxyglucosone (3-DG) to form 3-amino-1,2,4-triazine derivatives (T) and prevent glycation by these agents in vitro and in vivo. The reaction kinetics of these ?-oxoaldehydes with AG under physiological conditions pH 7.4 and 37° was investigated. The rate of reaction of

Paul J Thornalley; Alexander Yurek-George; Ongian K Argirov

2000-01-01

77

Toward safer methodologies for the synthesis of polyheterocyclic systems: intramolecular arylation of arenes under Mizoroki-Heck reaction conditions.  

PubMed

[reaction: see text] A straightforward synthesis of ibudilast-related pyrazolo[1,5-f]phenanthridines is accomplished by a tandem amine-exchange/heterocyclization of arylenaminones followed by an intramolecular biaryl coupling of the so-formed diarylpyrazoles. The direct, environmentally convenient ring-closure of the latter pyrazole intermediates, which show a close resemblance to the antiinflammatory drug celecoxib, is efficiently performed under Mizoroki-Heck reaction conditions. PMID:12659582

Hernández, Susana; SanMartin, Raul; Tellitu, Imanol; Domínguez, Esther

2003-04-01

78

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

Microsoft Academic Search

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

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

1965-01-01

79

A Knoevenagel Initiated Annulation Reaction Using Room Temperature or Microwave Conditions  

ERIC Educational Resources Information Center

An experiment is presented that has the student execute a Knoevenagel initiated annulation reaction. The reaction can be carried out either through use of a microwave reactor or by allowing the mixture to stand at room temperature for two days. The student is then challenged to identify the reaction product through a guided prelab exercise of the…

Cook, A. Gilbert

2007-01-01

80

Cardiac muscle ultrastructure and cyclic AMP reactions to altered gravity conditions  

SciTech Connect

Morphological and biochemical analyses of heart muscle of rats subjected to microgravity on Spacelab 3(SL-3) flight and rats born and reared under increased gravity (1.7 G) conditions were compared with 1-G controls. Electronmicroscopic studies showed an increase in the number of lipid droplets and in areas of glycogen storage. Distribution changes of microtubules and cytoskeletal elements from both SL-3 and 1.7-G groups were observed. The high K/sub m/(2,8-/sup 3/H) cyclic AMP phosphodiesterase activity was lower in SL-3 heart muscle, and low K/sub m/ activity was lower in 1.7-G males but was unaltered in females. Cyclic AMP-dependent protein kinase (cA-PK) activity was decreased in subcellular fractions of heart muscle of SL-3 animals. Recompartmentalization of cA-PK activity occurred in particulate tissue fraction of 1.7-g animals (70.3% of total for 1.7 G vs. 35.9% for controls). Phosphorylation of endogenous low-mobility proteins increased in SL-3 heart-soluble fractions. Photoaffinity labeling (18 h, 4/sup 0/C) decreased in type II cA-PK regulatory (R) subunits in both SL-3 and in 1.7-G male heart tissue particulate fractions. The 1.7-G female heart R subunit distribution did not differ from controls. These findings indicate that in heart muscle altered gravity conditions influenced physiological reactions similar to catecholamine-induced receptor-mediated hormonal responses.

Mednieks, M.I.; Fine, A.S.; Oyama, J.; Philpott, D.E.

1987-02-01

81

Optimization of reaction conditions by RSM and structure characterization of sulfated locust bean gum.  

PubMed

Sulfated derivatives of galactomannan from locust bean gum (LBG) with the degree of substitution (DS) of 0.34-1.07 were synthesized using chlorosulfonic acid/pyridine (CSA/Py) method. Box-Behnken design (BBD) of response surface methodology (RSM) was employed to optimize the reaction conditions. Results of FT-IR and X-ray photoelectron spectroscopy (XPS) indicated that SO3H groups were widely present in sulfated LBG (SLBG). (13)C NMR result revealed that sulfation had occurred and C-6 substitution was predominant in SLBG. All sulfated samples showed a decrease in Mw and more broad molar mass distribution in size exclusion chromatography combined with laser light scattering (SEC-LLS) analysis. Results of MW - [Formula: see text] showed a decrease in fractal dimension (df) value. Laser light scattering results also showed a conformation transition from a compact chain conformation of branched clusters to a random coil conformation of SLBG. Compared to LBG and SLBG with low DS and molecular weight, SLBG2 exhibited an internal structure of random coil with a DS of 1.07. DS and molecular weight had great influence on its conformation in aqueous solution. Our results confirmed that the degradation of polysaccharide and SO3H groups improved significantly the stiffness of the chains due to the electrostatic effect. PMID:25263904

Wang, Junlong; Yang, Ting; Tian, Jia; Liu, Wenxi; Jing, Fan; Yao, Jian; Zhang, Ji; Lei, Ziqiang

2014-12-19

82

Methods for quantifying the influences of pressure and temperature variation on metal hydride reaction rates measured under isochoric conditions.  

PubMed

Analysis techniques for determining gas-solid reaction rates from gas sorption measurements obtained under non-constant pressure and temperature conditions often neglect temporal variations in these quantities. Depending on the materials in question, this can lead to significant variations in the measured reaction rates. In this work, we present two new analysis techniques for comparison between various kinetic models and isochoric gas measurement data obtained under varying temperature and pressure conditions in a high pressure Sievert system. We introduce the integral pressure dependence method and the temperature dependence factor as means of correcting for experimental variations, improving model-measurement fidelity, and quantifying the effect that such variations can have on measured reaction rates. We use measurements of hydrogen absorption in LaNi5 and TiCrMn to demonstrate the effect of each of these methods and show that their use can provide quantitative improvements in interpretation of kinetics measurements. PMID:24289432

Voskuilen, Tyler G; Pourpoint, Timothée L

2013-11-01

83

Methods for quantifying the influences of pressure and temperature variation on metal hydride reaction rates measured under isochoric conditions  

NASA Astrophysics Data System (ADS)

Analysis techniques for determining gas-solid reaction rates from gas sorption measurements obtained under non-constant pressure and temperature conditions often neglect temporal variations in these quantities. Depending on the materials in question, this can lead to significant variations in the measured reaction rates. In this work, we present two new analysis techniques for comparison between various kinetic models and isochoric gas measurement data obtained under varying temperature and pressure conditions in a high pressure Sievert system. We introduce the integral pressure dependence method and the temperature dependence factor as means of correcting for experimental variations, improving model-measurement fidelity, and quantifying the effect that such variations can have on measured reaction rates. We use measurements of hydrogen absorption in LaNi5 and TiCrMn to demonstrate the effect of each of these methods and show that their use can provide quantitative improvements in interpretation of kinetics measurements.

Voskuilen, Tyler G.; Pourpoint, Timothée L.

2013-11-01

84

KINETICS AND MECHANISMS OF THE GAS-PHASE REACTIONS OF THE HYDROXYL RADICAL WITH ORGANIC COMPOUNDS UNDER ATMOSPHERIC CONDITIONS  

EPA Science Inventory

The available kinetic, mechanistic and product data for the gas phase reactions of the OH radical with organic compounds are discussed and evaluated with an emphasis upon these data under atmospheric conditions. In addition, a-priori predictive techniques for the estimation of ro...

85

Conditions for diffusion-limited and reaction-limited recombination in nanostructured solar cells  

SciTech Connect

The performance of Dye-sensitized solar cells (DSC) and related devices made of nanostructured semiconductors relies on a good charge separation, which in turn is achieved by favoring charge transport against recombination. Although both processes occur at very different time scales, hence ensuring good charge separation, in certain cases the kinetics of transport and recombination can be connected, either in a direct or an indirect way. In this work, the connection between electron transport and recombination in nanostructured solar cells is studied both theoretically and by Monte Carlo simulation. Calculations using the Multiple-Trapping model and a realistic trap distribution for nanostructured TiO{sub 2} show that for attempt-to-jump frequencies higher than 10{sup 11}–10{sup 13} Hz, the system adopts a reaction limited (RL) regime, with a lifetime which is effectively independent from the speed of the electrons in the transport level. For frequencies lower than those, and depending on the concentration of recombination centers in the material, the system enters a diffusion-limited regime (DL), where the lifetime increases if the speed of free electrons decreases. In general, the conditions for RL or DL recombination depend critically on the time scale difference between recombination kinetics and free-electron transport. Hence, if the former is too rapid with respect to the latter, the system is in the DL regime and total thermalization of carriers is not possible. In the opposite situation, a RL regime arises. Numerical data available in the literature, and the behavior of the lifetime with respect to (1) density of recombination centers and (2) probability of recombination at a given center, suggest that a typical DSC in operation stays in the RL regime with complete thermalization, although a transition to the DL regime may occur for electrolytes or hole conductors where recombination is especially rapid or where there is a larger dispersion of energies of electron acceptors.

Ansari-Rad, Mehdi, E-mail: ansari.rad@ut.ac.ir [Department of Physics, University of Tehran, 1439955961 Tehran (Iran, Islamic Republic of) [Department of Physics, University of Tehran, 1439955961 Tehran (Iran, Islamic Republic of); Department of Physics, University of Shahrood, Shahrood (Iran, Islamic Republic of); Anta, Juan A., E-mail: anta@upo.es [Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, 41013 Sevilla (Spain); Arzi, Ezatollah [Department of Physics, University of Tehran, 1439955961 Tehran (Iran, Islamic Republic of)] [Department of Physics, University of Tehran, 1439955961 Tehran (Iran, Islamic Republic of)

2014-04-07

86

Reaction rate of O + with O 2 , N 2 , and NO under highly disturbed auroral conditions  

Microsoft Academic Search

There are no published reaction rates of O + ions with 02, N2, and NO for ion temperatures in excess of 6000 K in the ionosphere. Yet, there are now documented cases of very strong perpendicular high-latitude ionospheric electric fields, with resulting ion temperatures well in excess of 10,000 K. We have therefore extended the calculations of O + reaction

J.-P. St.-Maurice; P. J. Laneville

1998-01-01

87

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

88

Mizoroki-heck cross-coupling reactions catalyzed by dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium under mild reaction conditions.  

PubMed

Dichloro-bis(aminophosphine) complexes of palladium with the general formula of [(P{(NC5H10)3-n(C6H11)n})2Pd(Cl)2] (where n = 0-2), belong to a new family of easy accessible, very cheap, and air stable, but highly active and universally applicable C-C cross-coupling catalysts with an excellent functional group tolerance. Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium [(P(NC5H10)3)2Pd(Cl)2] (1), the least stable complex within this series towards protons; e.g. in the form of water, allows an eased nanoparticle formation and hence, proved to be the most active Heck catalyst within this series at 100 °C and is a very rare example of an effective and versatile catalyst system that efficiently operates under mild reaction conditions. Rapid and complete catalyst degradation under work-up conditions into phosphonates, piperidinium salts and other, palladium-containing decomposition products assure an easy separation of the coupling products from catalyst and ligands. The facile, cheap, and rapid synthesis of 1,1',1"-(phosphinetriyl)tripiperidine and 1 respectively, the simple and convenient use as well as its excellent catalytic performance in the Heck reaction at 100 °C make 1 to one of the most attractive and greenest Heck catalysts available. We provide here the visualized protocols for the ligand and catalyst syntheses as well as the reaction protocol for Heck reactions performed at 10 mmol scale at 100 °C and show that this catalyst is suitable for its use in organic syntheses. PMID:24686532

Oberholzer, Miriam; Frech, Christian M

2014-01-01

89

Dynamics of morphological manifestations of reactions of the organism under conditions of hypergravitation  

NASA Technical Reports Server (NTRS)

The dynamics of the reaction of the hypothalamus-hypophysis-adrenal system to g-forces of 4 G's magnitude reveal a phasal nature of the adaptational system, dependent both on duration of force and position of the body.

Knyazeva, G. D.; Podymov, V. K.; Savina, Y. A.

1975-01-01

90

Indium(III) bromide-catalyzed preparation of dihydropyrimidinones: improved protocol conditions for the Biginelli reaction  

Microsoft Academic Search

Indium(III) bromide efficiently catalyzes the three-component coupling of ?-keto esters, aldehydes and urea (or thiourea) to afford the corresponding dihydropyrimidinones. This new protocol for the Biginelli reaction includes the following important features: produces excellent yields, allows the recycling of catalyst with no loss in its activity, and leads to zero-discharge during the process. The reaction of ethyl acetoacetate, salicylaldehyde and

Nan-Yan Fu; Yao-Feng Yuan; Zhong Cao; Shan-Wei Wang; Ji-Tao Wang; Clovis Peppe

2002-01-01

91

Preparation of Re(I)- and (99m)Tc(I)-metallocarboranes in water under weakly basic reaction conditions.  

PubMed

A new method for the preparation of Re- and (99m)Tc-metallocarboranes in water under mild reaction conditions was developed. Three nido-carborane ligands were reacted with [Re(CO)(3)Br(3)](2)(-) in the presence of aqueous potassium fluoride to give the corresponding eta(5)-Re(CO)(3)-carborane complexes. The use of KF as a base afforded the desired Re-metallocarboranes in good yields while avoiding the formation of Re clusters, which are byproducts commonly observed when reactions are carried out in the presence of strong aqueous bases. The reaction was also performed at the tracer level producing the first (99m)Tc-carborane complex, which was isolated in 80% radiochemical yield following a simple Sep-Pak purification process. The resulting organometallic complex was stable to cysteine and histidine challenges for more than 24 h. PMID:15132607

Sogbein, Oyebola O; Merdy, Patricia; Morel, Pierre; Valliant, John F

2004-05-17

92

Preparation of SiC particles coated with alumina hydrate: Effect of reaction condition on particle coalescence  

Microsoft Academic Search

Alumina-hydrate-coated SiC particles were prepared via a homogeneous precipitation method using urea, and the conditions for uniform coating and less coalescence of the particles were investigated. Coalescence of coated particles could be said to occur by collision and agglomeration followed by deposition of alumina hydrate on the agglomerated particles. Coalescence of coated particles was suppressed by use of low reaction

H. Nakamura; M. Yoshinaga; S. Nagashima; A. Kato

1996-01-01

93

An in situ XAS study of Cu\\/ZrO 2 catalysts under de-NO x reaction conditions  

Microsoft Academic Search

This paper reports an X-ray absorption spectroscopy investigation of the chemical state of copper in Cu\\/ZrO2 catalysts under reaction conditions. The catalysts were subjected to different treatments with hydrocarbons (CH4, C3H8, or C3H6) and hydrocarbon\\/NO and hydrocarbon\\/NO\\/O2 mixtures. The analysis was done for samples heated in situ at temperatures ranging from 298 to 773 K. The first derivative of the

Alfonso Caballero; Jose Jorge Morales; Ana Maria Cordon; Juan Pedro Holgado; Juan Pedro Espinos; Agustin R. Gonzalez-Elipe

2005-01-01

94

Specialty Fats from Beef Tallow and Canola Oil: Establishment of Reaction Conditions, Characterization of Products, and Evaluation of Crystal Stability  

Microsoft Academic Search

The effect of reaction time (0–90 min), catalyst concentration (0.2–0.5% CH3ONa powder), and temperature (60–90 °C) of chemical interesterification (CIE) was studied to determine the optimal conditions\\u000a for maximal change of solid fat content (SFC) in minimal time in a beef tallow (BT)\\/canola oil (CaO) blend (80:20, w\\/w, herein after referred to as BT\\/CaO blend 80:20). The optimal conditions were obtained as:

Zong Meng; Yuanfa Liu; Liang Shan; Qingzhe Jin; Fengyan Wang; Xingguo Wang

2011-01-01

95

Experimental Studies in Insect Parasitism. XI. The Haemocytic Reaction of a Caterpillar under Varied Conditions  

Microsoft Academic Search

Eggs or young larvae of an ichneumonid parasite, Nemeritis, injected into caterpillars of the tomato moth, Diataraxia, evoked a rapid reaction of the haemocytes, which led to the encapsulation of the parasite within 4 h. The further development of the capsule is described, and evidence is adduced that the encapsulated parasites were killed by asphyxiation. Encapsulation was blocked by injection

G. Salt

1960-01-01

96

Dynamic three-dimensional pore-scale imaging of reaction in a carbonate at reservoir conditions.  

PubMed

Quantifying CO2 transport and average effective reaction rates in the subsurface is essential to assess the risks associated with underground carbon capture and storage. We use X-ray microtomography to investigate dynamic pore structure evolution in situ at temperatures and pressures representative of underground reservoirs and aquifers. A 4 mm diameter Ketton carbonate core is injected with CO2-saturated brine at 50 °C and 10 MPa while tomographic images are taken at 15 min intervals with a 3.8 ?m spatial resolution over a period of 2(1)/2 h. An approximate doubling of porosity with only a 3.6% increase in surface area to volume ratio is measured from the images. Pore-scale direct simulation and network modeling on the images quantify an order of magnitude increase in permeability and an appreciable alteration of the velocity field. We study the uniform reaction regime, with dissolution throughout the core. However, at the pore scale, we see variations in the degree of dissolution with an overall reaction rate which is approximately 14 times lower than estimated from batch measurements. This work implies that in heterogeneous rocks, pore-scale transport of reactants limits dissolution and can reduce the average effective reaction rate by an order of magnitude. PMID:25738415

Menke, Hannah P; Bijeljic, Branko; Andrew, Matthew G; Blunt, Martin J

2015-04-01

97

Textured catalysts, methods of making textured catalysts, and methods of catalyzing reactions conducted in hydrothermal conditions  

DOEpatents

A textured catalyst having a hydrothermally-stable support, a metal oxide and a catalyst component is described. Methods of conducting aqueous phase reactions that are catalyzed by a textured catalyst are also described. The invention also provides methods of making textured catalysts and methods of making chemical products using a textured catalyst.

Werpy, Todd [West Richland, WA; Wang, Yong [Richland, WA

2003-12-30

98

Kinetics and Mechanism of the Reaction of Hydoxyl Radicals with Acetonitrile under Atmospheric Conditions  

NASA Technical Reports Server (NTRS)

The pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to determine absolute rate coefficients for the reaction OH + CH3CN (1) and its isotopic variants, OH + CD3CN (2), OD + CH3CN (3), and OD + CD3CN (4). Reactions 1 and 2 were studied as a function of pressure and temperature in N2, N2/O2, and He buffer gases. In the absence of O2 all four reactions displayed well-behaved kinetics with exponential OH decays and pseudo-first rate constants which were proportional to substrate concentration. Data obtained in N2 over the range 50-700 Torr at 298 K are consistent with k(sub 1), showing a small pressure dependence. The Arrhenius expression obtained by averaging data at all pressures in k(sub 1)(T) = (1.1(sup +0.5)/(sub -0.3)) x 10(exp -12) exp[(-1130 +/- 90)/T] cu cm /(molecule s). The kinetics of reaction 2 are found to be pressure dependent with k(sub 2) (298 K) increasing from (1.21 +/- 0.12) x 10(exp -14) to (2.16 +/- 0.11) x 10(exp -14) cm(exp 3)/ (molecule s) over the pressure range 50-700 Torr of N2 at 298 K. Data at pressures greater than 600 Torr give k(sub 2)(T) = (9.4((sup +13.4)(sub -5.0))) x 10(exp -13) exp[(-1180 +/- 250)/T] cu cm/(molecule s). The rates of reactions 3 and 4 are found to be independent of pressure over the range 50-700 Torr of N2 with 298 K rate coefficient given by k(sub 3) =(3.18 +/- 0.40) x 10(exp -14) cu cm/(molecule s) and k(sub 4) = (2.25 +/-0.28) x 10(exp -14) cu cm/(molecule s). In the presence of O2 each reaction shows complex (non-pseudo-first-order) kinetic behavior and/or an apparent decrease in the observed rate constant with increasing [O2], indicating the presence of significant OH or OD regeneration. Observation of regeneration of OH in (2) and OD in (3) is indicative of a reaction channel which proceeds via addition followed by reaction of the adduct, or one of its decomposition products, with O2. The observed OH and OD decay profiles have been modeled by using a simple mechanistic scheme to extract kinetic information about the adduct reations with O2 and branching ratios for OH regeneration. A plausible mechanism for OH regeneration in (2) involves OH addition to the nitrogen atom followed by O2 addition to the cyano carbon atom, isomeriazation and decomposition to D2CO + DOCN + OH. Our results suggest that the OH + CH3CN reaction occurs via a complex mechanism involving both bimolecular and termolecular pathways, analogous to the mechanisms for the the important atmospheric reactions of OH with CO and HNO3.

Hynes, A. J.; Wine, P. H.

1997-01-01

99

Evaluations of kinetic parameters and critical runaway conditions in the reaction system of hexamine-nitric acid to produce RDX in a non-isothermal batch reactor  

Microsoft Academic Search

In the production process of RDX from the reaction of hexamine and nitric acid, its reaction rate was evaluated and expressed as ?rA=1.234×106e?5671.062TCNOC1.28A, where T is the reaction temperature, CA is the concentration of hexamine and CNO is the initial concentration of added nitric acid. The critical condition of runaway reaction for the RDX production in a batch reactor is

Kuo-Ming Luo; Sheann-Huei Lin; Jih-Guang Chang; Tzung-Huei Huang

2002-01-01

100

Housing conditions influence cortical and behavioural reactions of sheep in response to videos showing social interactions of different valence.  

PubMed

Mood, as a long-term affective state, is thought to modulate short-term emotional reactions in animals, but the details of this interplay have hardly been investigated experimentally. Apart from a basic interest in this affective system, mood is likely to have an important impact on animal welfare, as bad mood may taint all emotional experience. In the present study about mood - emotion interaction, 29 sheep were kept under predictable, stimulus-rich or unpredictable, stimulus-poor housing conditions, to induce different mood states. In an experiment, the animals were confronted with video sequences of social interactions of conspecifics showing agonistic interactions, ruminating or tolerantly co-feeding as stimuli of different valences. Emotional reactions were assessed by measuring frontal brain activity using functional near-infrared spectroscopy and by recording behavioral reactions. Attentiveness of the sheep decreased from videos showing agonistic interactions to ruminating sheep to those displaying co-feeding sheep. Seeing agonistic interactions was also associated with a deactivation of the frontal cortex, specifically in animals living under predictable, stimulus-rich housing conditions. These sheep generally showed less attentiveness and locomotor activity and they had their ears in a forward position less often and in a backward position more often than the sheep from the unpredictable, stimulus-poor conditions. Housing conditions influenced how the sheep behaved, which can either be thought to be mediated by mood or by the animals' previous experience with stimulus-richness in their housing conditions. Frontal cortical activity may not depend on valence only, but also on the perceptual channel through which the stimuli were perceived. PMID:25680678

Vögeli, Sabine; Wolf, Martin; Wechsler, Beat; Gygax, Lorenz

2015-05-01

101

The influence of reaction conditions on SO2 oxidation in a discharge plasma reactor  

Microsoft Academic Search

In this paper, experimental approaches have been carried out to investigate the removal of sulfur dioxide (SO2) using pulsed discharge nonthermal plasma in the absence of ammonia (NH3). The gas-phase reaction was found to be less attractive due to its large energy cost. The increase in temperature decreased the SO2 removal rate, resulting in large energy cost. SO2 removal was

Hyun Ha Kim; Chunxi Wu; Youhei Kinoshita; Kazunori Takashima; Shinji Katsura; Akira Mizuno

2001-01-01

102

Hot-Fire Testing of 100 LB(sub F) LOX/LCH4 Reaction Control Engine at Altitude Conditions  

NASA Technical Reports Server (NTRS)

Liquid oxygen/liquid methane (LO2/LCH4 ) has recently been viewed as a potential green propulsion system for both the Altair ascent main engine (AME) and reaction control system (RCS). The Propulsion and Cryogenic Advanced Development Project (PCAD) has been tasked by NASA to develop these green propellant systems to enable safe and cost effective exploration missions. However, experience with LO2/LCH4 as a propellant combination is limited, so testing of these systems is critical to demonstrating reliable ignition and performance. A test program of a 100 lb f reaction control engine (RCE) is underway at the Altitude Combustion Stand (ACS) of the NASA Glenn Research Center, with a focus on conducting tests at altitude conditions. These tests include a unique propellant conditioning feed system (PCFS) which allows for the inlet conditions of the propellant to be varied to test warm to subcooled liquid propellant temperatures. Engine performance, including thrust, c* and vacuum specific impulse (I(sub sp,vac)) will be presented as a function of propellant temperature conditions. In general, the engine performed as expected, with higher performance at warmer propellant temperatures but better efficiency at lower propellant temperatures. Mixture ratio effects were inconclusive within the uncertainty bands of data, but qualitatively showed higher performance at lower ratios.

Marshall, William M.; Kleinhenz, Julie E.

2010-01-01

103

Prompt HO2 formation following the reaction of OH with aromatic compounds under atmospheric conditions.  

PubMed

The secondary formation of HO(2) radicals following OH + aromatic hydrocarbon reactions in synthetic air under normal pressure and temperature was investigated in the absence of NO after pulsed production of OH radicals. OH and HO(x) (=OH + HO(2)) decay curves were recorded using laser-induced fluorescence after gas-expansion. The prompt HO(2) yields (HO(2) formed without preceding NO reactions) were determined by comparison to results obtained with CO as a reference compound. This approach was recently introduced and applied to the OH + benzene reaction and was extended here for a number of monocyclic aromatic hydrocarbons. The measured HO(2) formation yields are as follows: toluene, 0.42 ± 0.11; ethylbenzene, 0.53 ± 0.10; o-xylene, 0.41 ± 0.08; m-xylene, 0.27 ± 0.06; p-xylene, 0.40 ± 0.09; 1,2,3-trimethylbenzene, 0.31 ± 0.06; 1,2,4-trimethylbenzene, 0.37 ± 0.09; 1,3,5-trimethylbenzene, 0.29 ± 0.08; hexamethylbenzene, 0.32 ± 0.08; phenol, 0.89 ± 0.29; o-cresol, 0.87 ± 0.29; 2,5-dimethylphenol, 0.72 ± 0.12; 2,4,6-trimethylphenol, 0.45 ± 0.13. For the alkylbenzenes HO(2) is the proposed coproduct of phenols, epoxides, and possibly oxepins formed in secondary reactions with O(2). In most product studies the only quantified coproducts were phenols whereas only a few studies reported yields of epoxides. Oxepins have not been observed so far. Together with the yields of phenols from other studies, the HO(2) yields determined in this work set an upper limit to the combined yields of epoxides and oxepins that was found to be significant (?0.3) for all investigated alkylbenzenes except m-xylene. For the hydroxybenzenes the currently proposed HO(2) coproducts are dihydroxybenzenes. For phenol and o-cresol the determined HO(2) yields are matching the previously reported dihydroxybenzene yields, indicating that these are the only HO(2) forming reaction channels. For 2,5-dimethylphenol and 2,4,6-trimethylphenol no complementary product studies are available. PMID:22195640

Nehr, Sascha; Bohn, Birger; Wahner, Andreas

2012-06-21

104

Reaction Norms in Natural Conditions: How Does Metabolic Performance Respond to Weather Variations in a Small Endotherm Facing Cold Environments?  

PubMed Central

Reaction norms reflect an organisms' capacity to adjust its phenotype to the environment and allows for identifying trait values associated with physiological limits. However, reaction norms of physiological parameters are mostly unknown for endotherms living in natural conditions. Black-capped chickadees (Poecile atricapillus) increase their metabolic performance during winter acclimatization and are thus good model to measure reaction norms in the wild. We repeatedly measured basal (BMR) and summit (Msum) metabolism in chickadees to characterize, for the first time in a free-living endotherm, reaction norms of these parameters across the natural range of weather variation. BMR varied between individuals and was weakly and negatively related to minimal temperature. Msum varied with minimal temperature following a Z-shape curve, increasing linearly between 24°C and ?10°C, and changed with absolute humidity following a U-shape relationship. These results suggest that thermal exchanges with the environment have minimal effects on maintenance costs, which may be individual-dependent, while thermogenic capacity is responding to body heat loss. Our results suggest also that BMR and Msum respond to different and likely independent constraints. PMID:25426860

Petit, Magali; Vézina, François

2014-01-01

105

Reaction norms in natural conditions: how does metabolic performance respond to weather variations in a small endotherm facing cold environments?  

PubMed

Reaction norms reflect an organisms' capacity to adjust its phenotype to the environment and allows for identifying trait values associated with physiological limits. However, reaction norms of physiological parameters are mostly unknown for endotherms living in natural conditions. Black-capped chickadees (Poecile atricapillus) increase their metabolic performance during winter acclimatization and are thus good model to measure reaction norms in the wild. We repeatedly measured basal (BMR) and summit (Msum) metabolism in chickadees to characterize, for the first time in a free-living endotherm, reaction norms of these parameters across the natural range of weather variation. BMR varied between individuals and was weakly and negatively related to minimal temperature. Msum varied with minimal temperature following a Z-shape curve, increasing linearly between 24°C and -10°C, and changed with absolute humidity following a U-shape relationship. These results suggest that thermal exchanges with the environment have minimal effects on maintenance costs, which may be individual-dependent, while thermogenic capacity is responding to body heat loss. Our results suggest also that BMR and Msum respond to different and likely independent constraints. PMID:25426860

Petit, Magali; Vézina, François

2014-01-01

106

The reaction of cell-free oxyhemoglobin with nitrite under physiologically relevant conditions: Implications for nitrite-based therapies  

PubMed Central

Nitric oxide (NO·) participates in the regulation of a wide array of biological processes and its deficit contributes to the severity of many diseases. Recently, a role of NO deficiency that occurs as a result of intravascular hemolysis and increases in levels of cell-free hemoglobin in the pathway of chronic anemic pathologies has been suggested. Experimental evidence for deoxyhemoglobin-catalyzed reduction of nitrite to NO· leads to the possibility of nitrite infusion-based therapies to correct NO· deficits. However, the presence of plasma hemoglobin also raises the possibility of deleterious free radical-mediated oxidative damage from the reaction between nitrite and oxyhemoglobin in the vasculature. We show that the conditions required for the reaction between nitrite and oxyhemoglobin to exhibit free radical-mediated autocatalytic kinetics are highly unlikely to occur in the plasma compartment, even during extensive hemolysis and with pharmacological nitrite doses. Although the presence of haptoglobin enhances the rate of the reaction between nitrite and oxyhemoglobin, common plasma antioxidants—ascorbate and urate, as well as catalase—prevent autocatalysis. Our findings suggest that pharmacological doses of nitrite are unlikely to cause free radical or ferrylhemoglobin formation in plasma originating from the reaction of nitrite with cell-free oxyhemoglobin in vivo. PMID:19010434

Piknova, Barbora; Keszler, Agnes; Hogg, Neil; Schechter, Alan N.

2009-01-01

107

Solubility and Reaction Rates of Aluminum Solid Phases Under Geothermal Conditions  

SciTech Connect

Experimental studies involving equilibrium solubility and dissolution/precipitation rates were initiated on aluminum hydroxide phases prevalent under geothermal reservoir conditions. A large capacity, hydrogen-electrode concentration cell (HECC) was constructed specifically for this purpose.

Benezeth, P.; Palmer, D.A.; Wesolowski, D.J.; Anovitz, L.M.

2000-05-28

108

Experiments on the high temperature graphite and steam reaction under LOCA condition  

SciTech Connect

The results of conceptual design activity of ITER (International Thermonuclear Experimental Reactor) gave graphite as a primarily candidate for the plasma facing materials in the first physics phase. In safety analysis of the fusion experimental reactor, release of radioactive tritium and activation product in the plasma-facing materials caused by a loss of coolant accident (LOCA) in a vacuum vessel is one of the severest accident scenarios. It is presumed that loss of coolant flow will generate an extremely high temperature spot, above 1000{degrees}C, on plasma-facing components such as armor tiles of the first wall and divertor plates. Thus coolant pipe made of copper will break or melt, then coolant water will blow out as steam into the vacuum vessel. High temperature graphite will react violently with the steam pouring into the vacuum vessel. Then safety analysis necessitate that the reactivity of the graphite materials should be precisely evaluated. To obtain fundamental data for safety analyses considering loss of coolant inside of the vessel, the rate of reaction between high temperature graphite and steam has been experimentally measured between 1000 and 1600{degrees}C. For experiments isotopic graphite and C/C composite ones were used. Reaction rate to a unit surface area was measured dividing the weight loss by inner surface area of tube type graphite specimen, and product gases were analyzed by gas-chromatography.

Uda, T.; Ogawa, M.; Seki, Y. [Japan Atomic Energy Research Inst., Ibaraki-ken (Japan)] [and others

1994-12-31

109

Palladium-Catalyzed ?-Arylation of Zinc Enolates of Esters: Reaction Conditions and Substrate Scope  

PubMed Central

The intermolecular ?-arylation of esters by palladium-catalyzed coupling of aryl bromides with zinc enolates of esters is reported. Reactions of three different types of zinc enolates have been developed. ?-Arylation of esters occurs in high yields with isolated Reformatsky reagents, with Reformatsky reagents generated from ?-bromo esters and activated zinc, and with zinc enolates generated by quenching lithium enolates of esters with zinc chloride. The use of zinc enolates, instead of alkali metal enolates, greatly expands the scope of the arylation of esters. The reactions occur at room temperature or at 70 °C with bromoarenes containing cyano, nitro, ester, keto, fluoro, enolizable hydrogen, hydroxyl or amino functionality and with bromopyridines. The scope of esters encompasses acyclic acetates, propionates, and isobutyrates, ?-alkoxyesters, and lactones. The arylation of zinc enolates of esters was conducted with catalysts bearing the hindered pentaphenylferrocenyl di-tert-butylphosphine (Q-phos) or the highly reactive dimeric Pd(I) complex {[P(t-Bu)3]PdBr}2. PMID:23931445

Hama, Takuo; Ge, Shaozhong; Hartwig, John F.

2013-01-01

110

The necessary and sufficient conditions of therapeutic personality change: Reactions to Rogers' 1957 article.  

PubMed

Carl Rogers' article (see record 2007-14639-002) on the necessary and sufficient conditions for personality change has had a significant impact on the field of psychotherapy and psychotherapy research. He emphasized the client as arbiter of his or her own subjective experience and tested his hypothesized therapist-offered conditions of change using recorded sessions. This aided in demystifying the therapeutic process and led to a radical shift in the listening stance of the therapist. I briefly outline my views regarding the influence of the ideas presented in this work, describe the intellectual and cultural context of the times, and discuss a number of ways in which the therapist-offered conditions for psychological transformation are neither necessary nor sufficient. (PsycINFO Database Record (c) 2010 APA, all rights reserved). PMID:22122256

Samstag, Lisa Wallner

2007-09-01

111

Optimisation of the reaction conditions for the production of cross-linked starch with high resistant starch content.  

PubMed

The optimum reaction conditions (temperature and pH) for the preparation of cross-linked (CL) corn and wheat starches with maximum resistant starch (RS) content were investigated by using response surface methodology (RSM). According to the preliminary results, five levels were selected for reaction temperature (38-70 °C) and pH (10-12) in the main study. RS contents of the CL corn and wheat starch samples increased with increasing temperature and pH, and pH had a greater influence on RS content than had temperature. The maximum RS content (with a maximum p value of 0.4%) was obtained in wheat starch cross-linked at 38 °C and pH 12. In the case of CL corn starch, the optimum condition was 70 °C and pH 12. CL corn and wheat starch samples were also produced separately under the optimum conditions and their RS contents were 80.4% and 83.9%, respectively. These results were also in agreement with the values predicted by RSM. PMID:25529667

Kahraman, Kevser; Koksel, Hamit; Ng, Perry K W

2015-05-01

112

Conditionals  

E-print Network

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

von Fintel, Kai

2011-01-01

113

Temperature effects of pad conditioning process on oxide CMP: Polishing pad, slurry characteristics, and surface reactions  

Microsoft Academic Search

Temperature effects were investigated on the improvement of silicon dioxide (oxide) chemical mechanical polishing performances including removal rate and surface morphology by controlling the pad conditioning temperature. The characteristics of silica slurry including potential of hydrogen (pH), conductivity, particle size, and zeta potential were changed by the frictional heat of the polishing process and the remaining heat after a high-temperature

Nam-Hoon Kim; Yong-Jin Seo; Woo-Sun Lee

2006-01-01

114

Hemispheric Processing Differences Revealed by Differential Conditioning and Reaction Time Performance  

ERIC Educational Resources Information Center

Two different experimental procedures were used to examine (a) information-processing differences between two groups of subjects (Cs versus Vs) identified by the form of their conditioned eyeblinks; (b) information-processing differences between the right and left cerebral hemispheres; and (c) parallels between hypothesized C-V differences and…

Hellige, Joseph

1975-01-01

115

Solubility and Reaction Rates of Aluminum Solid Phases Under Hydrothermal Conditions  

SciTech Connect

Experimental studies involving equilibrium solubility and dissolution/precipitation rates were initiated on boehmite (AIOOH) using a hydrogen-electrode concentration cell (HECC). This cell provides continuous, accurate in situ pH measurements of solid/solution mixtures to 295 C with provision for either removing solution samples for analysis of the metal content, or adding either of two titrants. This cell has been recently used to measure the solubility of minerals such as brucite; boehmite, zincite, arid magnetite. The ability to perturb pH, isothermally by addition of acidic or basic titrant opens the door for studies of the kinetics of dissolution/precipitation, even for relatively fast reactions. By monitoring the change in pH, with time, detailed kinetic information can be obtained without the need for sampling.

Benezeth, P.; Palmer, D.A.; Wesolowski, D.

1999-11-14

116

The effect of preparation conditions on the structure and mechanical properties of reaction-sintered silicon nitride  

NASA Technical Reports Server (NTRS)

The microstructure of reaction sintered silicon nitride (RSSN) was changed over a wide range by varying the grain density, grain size of the silicon starting powder, nitriding conditions, and by introducing artificial pores. The influence of single microstructural parameters on mechanical properties like room temperature strength, creep behavior, and resistance to thermal shock was investigated. The essential factors influencing these properties were found to be total porosity, pore size distribution, and the fractions of alpha and beta Si3N4. In view of high temperature engineering applications of RSSN, potentials for optimizing the material's properties by controlled processing are discussed.

Heinrich, J.

1980-01-01

117

Effects of relative humidity and temperature conditions on pollen fluorochromatic reaction of Rosmarinus officinalis L. (Lamiaceae)  

Microsoft Academic Search

Summary.  Mediterranean ecosystems are characterized by seasonal and annual fluctuations in humidity and temperature which are considered\\u000a limiting factors for plant growth and might have played a key role in the selection of species that compose the present vegetation.\\u000a After anther release, pollen is generally exposed to various changes of temperature and humidity conditions, therefore its\\u000a viability and consequently successful fruit

G. Aronne; V. De Micco; M. Scala

2006-01-01

118

QuadraPure-Supported Palladium Nanocatalysts for Microwave-Promoted Suzuki Cross-Coupling Reaction under Aerobic Condition  

PubMed Central

Cross-linked resin-captured palladium (XL-QPPd) was readily prepared by simple physical adsorption onto the high loading QuadraPure macroporous resin and a subsequent reduction process. To enhance the mechanical stability, entrapped palladium nanocatalysts were cross-linked with succinyl chloride. Both transmission electron microscopy images and X-ray diffraction analysis revealed that the palladium nanoparticles were well dispersed with diameters ranging in 4–10?nm. The catalyst performed good catalytic activity in microwave-promoted Suzuki cross-coupling reactions in water under aerobic condition with mild condition by using various aryl halides and phenylboronic acid. In addition, the catalyst showed an excellent recyclability without significant loss of catalytic activity. PMID:25054185

Loh, Poh Lee; Juan, Joon Ching; Yarmo, Mohd Ambar; Yusop, Rahimi M.

2014-01-01

119

Role of choline and glycine betaine in the formation of N,N-dimethylpiperidinium (mepiquat) under Maillard reaction conditions.  

PubMed

This study is the first to examine the role of choline and glycine betaine, naturally present in some foods, in particular in cereal grains, to generate N,N-dimethylpiperidinium (mepiquat) under Maillard conditions via transmethylation reactions involving the nucleophile piperidine. The formation of mepiquat and its intermediates piperidine - formed by cyclisation of free lysine in the presence of reducing sugars - and N-methylpiperidine were monitored over time (240°C, up to 180 min) using high-resolution mass spectrometry in a model system comprised of a ternary mixture of lysine/fructose/alkylating agent (choline or betaine). The reaction yield was compared with data recently determined for trigonelline, a known methylation agent present naturally in coffee beans. The role of choline and glycine betaine in nucleophilic displacement reactions was further supported by experiments carried out with stable isotope-labelled precursors ((13)C- and deuterium-labelled). The results unequivocally demonstrated that the piperidine ring of mepiquat originates from the carbon chain of lysine, and that either choline or glycine betaine furnishes the N-methyl groups. The kinetics of formation of the corresponding demethylated products of both choline and glycine betaine, N,N-demethyl-2-aminoethanol and N,N-dimethylglycine, respectively, were also determined using high-resolution mass spectrometry. PMID:25333319

Bessaire, Thomas; Tarres, Adrienne; Stadler, Richard H; Delatour, Thierry

2014-01-01

120

Gas-phase reaction of methyl isothiocyanate and methyl isocyanate with hydroxyl radicals under static relative rate conditions.  

PubMed

Gaseous methyl isothiocyanate (MITC), the principal breakdown product of the soil fumigant metam sodium (sodium N-methyldithiocarbamate), is an inhalation exposure concern to persons living near treated areas. Inhalation exposure also involves gaseous methyl isocyanate (MIC), a highly reactive and toxic transformation product of MITC. In this work, gas-phase hydroxyl (OH) radical reaction rate constants of MITC and MIC have been determined using a static relative rate technique under controlled laboratory conditions. The rate constants obtained are 15.36 × 10(-12) cm(3) molecule(-1) s(-1) for MITC and 3.62 × 10(-12) cm(3) molecule(-1) s(-1) for MIC. The average half-lives of MITC and MIC in the atmosphere are estimated to be 15.7 and 66.5 h, respectively. The molar conversion of MITC to MIC for OH radical reactions is 67% ± 8%, which indicates that MIC is the primary product of the MITC-OH reaction in the gas phase. PMID:24483206

Lu, Zhou; Hebert, Vincent R; Miller, Glenn C

2014-02-26

121

Condensation Reactions and Formation of Amides, Esters, and Nitriles Under Hydrothermal Conditions  

NASA Astrophysics Data System (ADS)

Hydrothermal pyrolysis experiments were performed to assess condensation (dehydration) reactions to amide, ester, and nitrile functionalities from lipid precursors. Beside product formation, organic compound alteration and stability were also evaluated. Mixtures of nonadecanoic acid, hexadecanedioic acid, or hexadecanamide with water, ammonium bicarbonate, and oxalic acid were heated at 300°C for 72 h. In addition, mixtures of ammonium bicarbonate and oxalic acid solutions were used to test the abiotic formation of organic nitrogen compounds at the same temperature. The resulting products were condensation compounds such as amides, nitriles, and minor quantities of N-methylalkyl amides, alkanols, and esters. Mixtures of alkyl amide in water or oxalic acid yielded mainly hydrolysis and dehydration products, and with ammonium bicarbonate and oxalic acid the yield of condensation products was enhanced. The synthesis experiments with oxalic acid and ammonium bicarbonate solutions yielded homologous series of alkyl amides, alkyl amines, alkanes, and alkanoic acids, all with no carbon number predominances. These organic nitrogen compounds are stable and survive under the elevated temperatures of hydrothermal fluids.

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

2004-06-01

122

Lipid synthesis under hydrothermal conditions by Fischer-Tropsch-type reactions  

NASA Technical Reports Server (NTRS)

Ever since their discovery in the late 1970's, mid-ocean-ridge hydrothermal systems have received a great deal of attention as a possible site for the origin of life on Earth (and environments analogous to mid-ocean-ridge hydrothermal systems are postulated to have been sites where life could have originated or Mars and elsewhere as well). Because no modern-day terrestrial hydrothermal systems are free from the influence of organic compounds derived from biologic processes, laboratory experiments provide the best opportunity for confirmation of the potential for organic synthesis in hydrothermal systems. Here we report on the formation of lipid compounds during Fischer-Tropsch-type synthesis from aqueous solutions of formic acid or oxalic acid. Optimum synthesis occurs in stainless steel vessels by heating at 175 degrees C for 2-3 days and produces lipid compounds ranging from C2 to > C35 which consist of n-alkanols, n-alkanoic acids, n-alkenes, n-alkanes and alkanones. The precursor carbon sources used are either formic acid or oxalic acid, which disproportionate to H2, CO2 and probably CO. Both carbon sources yield the same lipid classes with essentially the same ranges of compounds. The synthesis reactions were confirmed by using 13C labeled precursor acids.

McCollom, T. M.; Ritter, G.; Simoneit, B. R.

1999-01-01

123

Does back reaction enforce the averaged null energy condition in semiclassical gravity\\?  

NASA Astrophysics Data System (ADS)

The expectation value of the renormalized stress-energy tensor of quantum fields generically violates the classical, local positive energy conditions of general relativity. Nevertheless, it is possible that may still satisfy some nonlocal positive energy conditions. Most prominent among these nonlocal conditions is the averaged null energy condition (ANEC), which states that ?kakbd?>=0 along any complete null geodesic, where ka denotes the geodesic tangent, with affine parameter ?. If the ANEC holds, then traversable wormholes cannot occur. However, although the ANEC holds in Minkowski spacetime, it is known that the ANEC can be violated in curved spacetimes if one is allowed to choose the spacetime and quantum state arbitrarily, without imposition of the semiclassical Einstein equation, Gab=8?. In this paper, we investigate whether the ANEC holds for self-consistent solutions of the semiclassical Einstein equation. We study a free, linear, massless scalar field with arbitrary curvature coupling in the context of perturbation theory about the flat spacetime/vacuum solution, and we modify the perturbed semiclassical equations by the ``reduction of order'' procedure to eliminate spurious solutions. We also restrict attention to the limit in which the length scales determined by the state and metric are much larger than the Planck length. At first order in the metric and state perturbations, and for pure states of the scalar field, we find that the ANEC integral vanishes, as it must for any positivity result to hold. For mixed states, the ANEC integral can be negative. However, we prove that if we average the ANEC integral transverse to the geodesic, using a suitable Planck scale smearing function, a strictly positive result is obtained in all cases except for the trivial flat spacetime/vacuum solution. Similar results hold for pure states at second order in perturbation theory, when we additionally specialize to the situation where incoming classical gravitational radiation does not dominate the first-order metric perturbation. These results suggest-in agreement with conclusions drawn by Ford and Roman from entirely independent arguments-that if traversable wormholes do exist as self-consistent solutions of the semiclassical equations, they cannot be macroscopic but must be ``Planck scale.'' In the course of our analysis, we investigate a number of more general issues relevant to doing perturbative expansions of the semiclassical equations off of flat spacetime, including an analysis of the nature of the semiclassical Einstein equation and of prescriptions for extracting physically relevant solutions. A large portion of our paper is devoted to the treatment of these more general issues.

Flanagan, Éanna É.; Wald, Robert M.

1996-11-01

124

Effects of network dissolution changes on pore-to-core up-scaled reaction rates for kaolinite and anorthite reactions under acidic conditions  

E-print Network

1 Effects of network dissolution changes on pore-to-core up-scaled reaction rates for kaolinite present in the solid matrix Geometric and reaction rate law factors exert differential influence the effect of these changes on up-scaled (pore-scale to core-scale)5 reaction rates and compared against

New York at Stoney Brook, State University of

125

Calcium phosphate scaffold from biogenic calcium carbonate by fast ambient condition reactions  

NASA Astrophysics Data System (ADS)

Calcium phosphate biogenic materials are biocompatible and promote bioactivity and osteoconductivity, which implies their natural affinity and tendency to bond directly to bones subsequently replacing the host bone after implantation owing to its biodegradability. Calcium hydrogen phosphate dihydrate, CaHPO 4·2H 2O, is known to be a nucleation precursor, in aqueous solutions, for apatitic calcium phosphates and, hence, a potential starting material for bone substitutes. Numerous approaches, via hydrothermal and ambient synthetic routes, have been used to produce calcium phosphate from biogenic calcium carbonate, taking advantage of the peculiar architecture and composition of the latter. In this article, the lamellar region of the cuttlefish bone ( Sepia officinalis) was used as a framework for the organized deposition of calcium phosphate crystals, at ambient conditions via a fast procedure involving an amorphous calcium carbonate intermediate, and ending with a conversion to calcium phosphate and a fixation procedure, thereby resulting in direct conversion of biogenic calcium carbonate into calcium phosphates at ambient conditions from the scale of months to hours.

Dutta, Abhishek; Fermani, Simona; Arjun Tekalur, Srinivasan; Vanderberg, Abigail; Falini, Giuseppe

2011-12-01

126

Role of the caudate nucleus in performance of the conditioned reactions connected with sound localization.  

PubMed

The instrumental differentiation of left-right positions of sound-conditioned stimuli (series of clicks under dichotic stimulation) in 8 dogs was examined before and after the bilateral electrolytic lesions of various parts of the caudate nucleus (NCd). It was demonstrated that after damage of the NCd the correct differentiation of the side of monaural sound stimulation was preserved in all dogs. However, the differentiation of lateralization of sound produced by interaural time differences was selectively impaired. Lesions of the dorsal part of the NCd heads caused the absolute absence of the differentiation of the binaural sound image lateralization for 21-50 days after the operation. This function partially recovered but the percentage of correct responses remained significantly reduced in comparison with preoperative performance. Lesions of the ventral segment of the NCd heads of different parts of the NCd bodies had less influence on the performance of this behavioral task. In these cases there was no period of absolute absence of the differentiation, but the level of correct responses to the binaural signals was significantly reduced. It is suggested that the NCd is a part of the system of brain structures in which the parameters of the conditioned sound signals are compared with a reference system for recognition of sound location. The result of this comparison is used by the NCd for choosing a corresponding program of the motor response. PMID:3397320

Suvorov, N F; Gulyakov, M B

1988-06-01

127

Hydrothermal processing of duckweed: effect of reaction conditions on product distribution and composition.  

PubMed

Influences of operating conditions such as temperature (270-380 °C), time (10-120 min), reactor loading (0.5-5.5 g), and K2CO3 loading (0-50 wt.%) on the product (e.g. crude bio-oil, water soluble, gas and solid residue) distribution from the hydrothermal processing of duckweed were determined. Of the four variables, temperature and K2CO3 loading were always the most influential factors to the relative amount of each component. The presence of K2CO3 is unfavorable for the production of bio-oil and gas. Hydrothermal processing duckweed produces a bio-oil that is enriched in carbon and hydrogen and has reduced levels of O compared with the original duckweed feedstock. The higher heating values of the bio-oil were estimated within the range of 32-36 MJ/kg. Major bio-oil constituents include ketones and their alkylated derivatives, alcohols, heterocyclic nitrogen-containing compounds, saturated fatty acids and hydrocarbons. The gaseous products were mainly CO2 and H2, with lesser amounts of CH4 and CO. PMID:23021946

Duan, Peigao; Chang, Zhoufan; Xu, Yuping; Bai, Xiujun; Wang, Feng; Zhang, Lei

2013-05-01

128

Real-Time Optical Monitoring of Flow Kinetics and Gas Phase Reactions Under High-Pressure OMCVD Conditions  

NASA Technical Reports Server (NTRS)

This contribution addresses the real-time optical characterization of gas flow and gas phase reactions as they play a crucial role for chemical vapor phase depositions utilizing elevated and high pressure chemical vapor deposition (HPCVD) conditions. The objectives of these experiments are to validate on the basis of results on real-time optical diagnostics process models simulation codes, and provide input parameter sets needed for analysis and control of chemical vapor deposition at elevated pressures. Access to microgravity is required to retain high pressure conditions of laminar flow, which is essential for successful acquisition and interpretation of the optical data. In this contribution, we describe the design and construction of the HPCVD system, which include access ports for various optical methods of real-time process monitoring and to analyze the initial stages of heteroepitaxy and steady-state growth in the different pressure ranges. To analyze the onset of turbulence, provisions are made for implementation of experimental methods for in-situ characterization of the nature of flow. This knowledge will be the basis for the design definition of experiments under microgravity, where gas flow conditions, gas phase and surface chemistry, might be analyzed by remote controlled real-time diagnostics tools, developed in this research project.

Dietz, N.; McCall, S.; Bachmann, K. J.

2001-01-01

129

Size Reproducibility of Gadolinium Oxide Based Nanomagnetic Particles for Cellular Magnetic Resonance Imaging: Effects of Functionalization, Chemisorption and Reaction Conditions  

PubMed Central

We developed biofunctionalized nanoparticles with magnetic properties by immobilizing diethyleneglycol (DEG) on Gd2O3, and PEGilation of small particulate gadolinium oxide (SPGO) with two methoxy-polyethyleneglycol-silane (mPEG-Silane 550 and 2000 Da) using a new supervised polyol route, described recently. In conjunction to the previous study to achieve a high quality synthesis and increase in the product yield of nanoparticles; assessment of the effects of functionalization, chemisorption and altered reaction conditions, such as NaOH concentration, temperature, reaction time and their solubility, on size reproducibility were determined as the goals of this study. Moreover, the effects of centrifugation, filtration and dialysis of the solution on the nono magnetic particle size values and their stability against aggregation have been evaluated. Optimization of reaction parameters led to strong coating of magnetic nanoparticles with the ligands which increases the reproducibility of particle size measurements. Furthermore, the ligand-coated nanoparticles showed enhanced colloidal stability as a result of the steric stabilization function of the ligands grafted on the surface of particles. The experiments showed that DEG and mPEG-silane (550 and 2000 Dalton) are chemisorbed on the particle surfaces of Gd2O3 and SPGO which led to particle sizes of 5.9 ± 0.13 nm, 51.3 ± 1.46 nm and 194.2 ± 22.1 nm, respectively. The small size of DEG-Gd2O3 is acceptably below the cutoff of 6nm, enabling easy diffusion through lymphatics and filtration from kidney, and thus provides a great deal of potential for further in-vivo and in-vitro application PMID:25561907

Riyahi-Alam, Sadjad; Haghgoo, Soheila; Gorji, Ensieh; Riyahi-Alam, Nader

2015-01-01

130

Size reproducibility of gadolinium oxide based nanomagnetic particles for cellular magnetic resonance imaging: effects of functionalization, chemisorption and reaction conditions.  

PubMed

We developed biofunctionalized nanoparticles with magnetic properties by immobilizing diethyleneglycol (DEG) on Gd2O3, and PEGilation of small particulate gadolinium oxide (SPGO) with two methoxy-polyethyleneglycol-silane (mPEG-Silane 550 and 2000 Da) using a new supervised polyol route, described recently. In conjunction to the previous study to achieve a high quality synthesis and increase in the product yield of nanoparticles; assessment of the effects of functionalization, chemisorption and altered reaction conditions, such as NaOH concentration, temperature, reaction time and their solubility, on size reproducibility were determined as the goals of this study. Moreover, the effects of centrifugation, filtration and dialysis of the solution on the nono magnetic particle size values and their stability against aggregation have been evaluated. Optimization of reaction parameters led to strong coating of magnetic nanoparticles with the ligands which increases the reproducibility of particle size measurements. Furthermore, the ligand-coated nanoparticles showed enhanced colloidal stability as a result of the steric stabilization function of the ligands grafted on the surface of particles. The experiments showed that DEG and mPEG-silane (550 and 2000 Dalton) are chemisorbed on the particle surfaces of Gd2O3 and SPGO which led to particle sizes of 5.9 ± 0.13 nm, 51.3 ± 1.46 nm and 194.2 ± 22.1 nm, respectively. The small size of DEG-Gd2O3 is acceptably below the cutoff of 6nm, enabling easy diffusion through lymphatics and filtration from kidney, and thus provides a great deal of potential for further in-vivo and in-vitro application. PMID:25561907

Riyahi-Alam, Sadjad; Haghgoo, Soheila; Gorji, Ensieh; Riyahi-Alam, Nader

2015-01-01

131

Stress response in Pectobacterium atrosepticum SCRI1043 under starvation conditions: adaptive reactions at a low population density.  

PubMed

The adaptive reactions of plant pathogenic bacterium Pectobacterium atrosepticum SCRI1043 under starvation conditions were studied. The main emphasis was given to the peculiarities of stress responses depending on the bacterial population densities. When bacteria were subjected to starvation at high population densities (10(7)-10(9) CFU ml(-1)), their adaptive reactions conformed to the conventional conception of bacterial adaptation related to autolysis of part of the population, specific modification of cell ultrastructure, activation of expression of stress responsive genes and acquiring cross protection against other stress factors. In contrast, at low initial population densities (10(3)-10(5) CFU ml(-1)), as described in our recent work, the cell density increased due to multiple cell division despite the absence of exogenous growth substrate. Here we present data that demonstrate that such unconventional behavior is part of a stress response, which provides increased stress tolerance while retaining virulence. Cell morphology and gene expression in high- and low-cell-density starving Pba cultures were compared. Our investigation demonstrates the existence of alternative adaptive strategies enabling pathogenic bacteria to cope with a variety of stress factors, including starvation, especially necessary when residing outside of their host. PMID:24300393

Petrova, Olga; Gorshkov, Vladimir; Daminova, Amina; Ageeva, Marina; Moleleki, Lucy N; Gogolev, Yuri

2014-01-01

132

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

PubMed

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

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

2003-01-01

133

Ethanol Conversion to Hydrocarbons on HZSM-5: Effect of Reaction Conditions and Si/Al Ratio on the Product Distributions  

SciTech Connect

The Conversion of ethanol to hydrocarbon over HZSM-5 zeolite with different Si/Al ratios was investigated under various reaction conditions. The catalyst with a higher Si/Al ratio (low acid density) deactivated faster and generated more unsaturated compounds at a similar time-on-stream. Temperature affects the catalytic activity with respect to liquid hydrocarbon generation and the hydrocarbon product composition. At lower temperatures (~300°C), the catalyst deactivated faster with respect to the liquid hydrocarbon formation. Higher temperatures (~400°C) reduced the formation of liquid range hydrocarbons and formed more gaseous fractions. Weight hourly space velocity was also found to affect product selectivity with higher weight hourly space velocity leading to a higher extent of ethylene formation. The experimental results were analyzed in terms of the product composition and the coke content with respect to catalyst time-on-stream and compared with the catalyst lifetime with respect to the variables tested on the conversion of ethanol to hydrocarbon.

Ramasamy, Karthikeyan K.; Wang, Yong

2014-11-17

134

H2S-CO2 Reaction with Hydrated Class H Well Cement under Geologic Sequestration Conditions  

NASA Astrophysics Data System (ADS)

The technology to inject CO2 into geological formations is available and practiced at several locations in the world, e.g. Sleipner, Norway and the Weyburn project in Alberta, Canada. In addition to CO2, acid gas (a mixture of CO2 and H2S) injection is also currently employed and on the rise. For example, there are currently over 40 wells used for acid gas injection in Alberta, Canada. Few studies address the physical and chemical characteristics of well cement exposed to acid gas under geologic sequestration conditions. The objective of this study is to determine how oilwell cement is affected by the addition of H2S in a CO2 injection scenario. Laboratory experiments have been performed in order to determine the physical and chemical changes in cement exposed to acid gas vs. pure CO2 under simulated sequestration reservoir conditions, including both aqueous and supercritical CO2. Obvious differences were observed between the H2S-CO2 and CO2-only exposed cement. Differences were also observed between the submerged and headspace exposed portions of the samples. The H2S-CO2 exposed cement underwent a combination of carbonation and redox reactions that ultimately affected the physical properties. The outer rim of the cylindrical cement samples were characterized by a zone of carbonation and the sulfidation of tetracalcium aluminoferrites to pyrite. Beyond the carbonation rim is evidence of significant impact from the H2S in the form of ettringite and very small grains of pyrite. Ettringite is formed due to oxidation of H2S which produces sulfides which in turn reacts with Ca-compounds. The carbonation reaction lowers the pH in the cement matrix to allow dissolution of ettringite and the tetracalcium aluminoferrite for pyrite formation. Implications regarding geologic co-sequestration and wellbore integrity are significant.

Kutchko, B. G.; Hawthorne, S.; Strazisar, B. R.; Miller, D.

2009-12-01

135

Reaction and transport in wellbore interfaces under CO2 storage conditions: Experiments simulating debonded cement-casing interfaces  

NASA Astrophysics Data System (ADS)

Debonding-defects at the interfaces between wellbore casing and cement are widely recognized as providing potential pathways for CO2 escape from geological storage systems. This study addresses how chemical reaction between CO2, cement and steel may affect the transport properties of such defects under near-static conditions, representative for early stages in leakage pathway development, prior to the formation of a fully connected defect network. Debonded cement-steel interfaces were simulated by constructing composite samples, containing a spacer-imposed gap. These were reacted with CO2 and water, brine or a solution pre-saturated with cement. Each sample was subjected to 7 sequential batch reaction runs, namely 6 runs of 5 days duration, followed by a single extended run, of 42 days, to study long-term effects. The reaction runs were conducted at 80°C and 14 MPa applied CO2-pressure. Permeability was measured after each run and microstructural analyses were performed after completion of the experiment. We investigated two ranges in gap-width, namely 50-120 ?m (denoted SA samples) and 270-350 ?m (LA samples). Reaction-induced permeability changes were limited and less than 1 order in all samples, and occurred in the early stage of testing. Corrosion product or scale (mainly Fe-carbonates, with minor Fe-hydroxides) formed extensively within the open gap, on the surfaces of both the casing steel and cement. Lack of calcium carbonates in these areas suggests the corrosion scale which formed on the cement surface produced a significant reduction in cement carbonation rate, similar to the decrease in corrosion rate observed when these precipitates create a protective film on steel surfaces only. CaCO3 precipitation occurred extensively on the cement side at locations beneath the spacers used to create the gap between the cement and steel plates, where corrosion scale did not form. Our results imply that healing of debonding defects at casing-cement interfaces in wellbores will be slower and less effective than healing of fractures in cement under comparable, near-static conditions, due to the formation of thin corrosion scale films on the cement surfaces. These films inhibit release of calcium from the cement into the aperture and impede the precipitation of calcium carbonates that was previously found to promote sealing in fractured cement when only local transport is possible. If thin corrosion scale films of the type observed in our experiments form in real wellbore systems, local small debonding defects (gaps less than a few tens of micrometres) can be expected to heal due to clogging by corrosion scale film. In larger debonding defects, where scale film development is insufficient to produce sealing, their retarding effect on further reaction has the potential to maintain an open interfacial pathway, should long-range connectivity and transport ensue. It is, therefore, important to incorporate the effects of early corrosion scale film development in future analyses of long-range leakage pathways along cement-casing interfaces.

Wolterbeek, T. K.; Peach, C. J.; Spiers, C. J.

2013-12-01

136

Charge distribution analysis of catalysts under simulated reaction conditions. Final report, October 1, 1993--June 30, 1995  

SciTech Connect

A new technique has been developed to measure mobile charge carriers in dielectric materials, insulators and catalysts. The technique, Charge Distribution Analysis, is based on the measurement of the dielectric polarization in an electric field gradient, contact-free, at 0 Hertz under minimum perturbation conditions. The measured parameter is the force F{sup +-} experienced by the sample in a gradient of reversible polarity. CDA allows to determine the sign of the majority charge carriers and the density of surface charges which may be correlated to the chemical or catalytic activity. Throughout this work a microbalance has been used as a force-sensing device. CDA can be applied to any dielectric material, compact or porous, in inert or reactive and corrosive gas environments. To conduct CDA experiments under simulated reaction conditions that are relevant to coal liquefaction research, e.g. in reactive and in part chemically corrosive atmospheres, several modifications were introduced to the current design. In particular, the stainless steel sample chamber and furnace/electrode assembly were built, and the gas flow system was redesigned. The CDA instrument was equipped with new data acquisition capabilities. Tests were performed in inert gases and in reactive and corrosive atmosphere between ambient temperature and 500{degrees}C on iron oxide and partially sulfidized iron oxide catalysts as well as on pyrite (FeS{sub 2}) single crystals.

Freund, F.

1996-02-01

137

N8 (-) polynitrogen stabilized on multi-wall carbon nanotubes for oxygen-reduction reactions at ambient conditions.  

PubMed

Polynitrogen (PN) species (Nn , n from 3 to 8) as highly energetic materials have attracted many theoretical calculations and predictions. N3 , N4 , N5 or their ions were experimentally detected under high-pressure and high-temperature conditions. Herein, a N8 (-) PN stabilized on the positively charged sidewalls of multi-walled carbon nanotubes (MWNTs) has been synthesized using cyclic voltammetry (CV) under ambient conditions. ATR-FTIR and Raman spectroscopic data assigned on the basis of density functional theory (DFT) calculations support the successful synthesis of a C2h symmetry chain structure of the N8 anion stabilized as MWNT(+) N8 (-) . Temperature programmed desorption (TPD) data show that MWNT(+) N8 (-) is thermally stable up to 400?°C. Oxygen-reduction reaction (ORR) experiments carried out using MWNT(+) N8 (-) as the cathodic catalyst shows that it is very active for ORR with an even higher current density than that of a commercial Pt/carbon catalyst. PMID:25123821

Wu, Zhiyi; Benchafia, El Mostafa; Iqbal, Zafar; Wang, Xianqin

2014-11-10

138

Diagnosis of foot-and mouth disease by real time reverse transcription polymerase chain reaction under field conditions in Brazil  

PubMed Central

Background Foot-and-mouth disease (FMD) is an economically important and highly contagious viral disease that affects cloven-hoofed domestic and wild animals. Virus isolation and enzyme-linked immunosorbent assay (ELISA) are the gold standard tests for diagnosis of FMD. As these methods are time consuming, assays based on viral nucleic acid amplification have been developed. Results A previously described real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay with high sensitivity and specificity under laboratorial and experimental conditions was used in the current study. To verify the applicability of this assay under field conditions in Brazil, 460 oral swabs from cattle were collected in areas free of FMD (n = 200) and from areas with outbreaks of FMD (n = 260). Three samples from areas with outbreaks of FMD were positive by real-time RT-PCR, and 2 of those samples were positive by virus isolation and ELISA. Four other samples were considered inconclusive by real-time RT-PCR (threshold cycle [Ct] > 40); whereas all 200 samples from an area free of FMD were real-time RT-PCR negative. Conclusion real-time RT-PCR is a powerful technique for reliable detection of FMDV in a fraction of the time required for virus isolation and ELISA. However, it is noteworthy that lack of infrastructure in certain areas with high risk of FMD may be a limiting factor for using real-time RT-PCR as a routine diagnostic tool. PMID:19117507

Paixão, Tatiane A; Neta, Alcina V Carvalho; Paiva, Naimes O; Reis, Jorge R; Barbosa, Meirivan S; Serra, Claudia V; Silva, René R; Beckham, Tammy R; Martin, Barbara M; Clarke, Neville P; Adams, L Garry; Santos, Renato L

2008-01-01

139

Microscale imaging and identification of Fe speciation and distribution during fluid-mineral reactions under highly reducing conditions.  

PubMed

The oxidation state, speciation, and distribution of Fe are critical determinants of Fe reactivity in natural and engineered environments. However, it is challenging to follow dynamic changes in Fe speciation in environmental systems during progressive fluid-mineral interactions. Two common geological and aquifer materials-basalt and Fe(III) oxides-were incubated with saline fluids at 55 °C under highly reducing conditions maintained by the presence of Fe(0). We tracked changes in Fe speciation after 48 h (incipient water-rock reaction) and 10 months (extensive water-rock interaction) using synchrotron-radiation ?XRF maps collected at multiple energies (ME) within the Fe K-edge. Immediate PCA analysis of the ME maps was used to optimize ?XANES analyses; in turn, refitting the ME maps with end-member XANES spectra enabled us to detect and spatially resolve the entire variety of Fe-phases present in the system. After 48 h, we successfully identified and mapped the major Fe-bearing components of our samples (Fe(III) oxides, basalt, and rare olivine), as well as small quantities of incipient brucite associated with olivine. After 10 months, the Fe(III)-oxides remained stable in the presence of Fe(0), whereas significant alteration of basalt to minnesotaite and chlinochlore had occurred, providing new insights into heterogeneous Fe speciation in complex geological media under highly reducing conditions. PMID:21517061

Mayhew, L E; Webb, S M; Templeton, A S

2011-05-15

140

Highly Regio- and Stereoselective Diels-Alder Cycloadditions via Two-Step and Multicomponent Reactions Promoted by Infrared Irradiation under Solvent-Free Conditions  

PubMed Central

Infrared irradiation promoted the Diels-Alder cycloadditions of exo-2-oxazolidinone dienes 1–3 with the Knoevenagel adducts 4–6, as dienophiles, leading to the synthesis of new 3,5-diphenyltetrahydrobenzo[d]oxazol-2-one derivatives (7, 9, 11 and 13–17), under solvent-free conditions. These cycloadditions were performed with good regio- and stereoselectivity, favoring the para-endo cycloadducts. We also evaluated the one-pot three-component reaction of active methylene compounds 20, benzaldehydes 21 and exo-2-oxazolidinone diene 2 under the same reaction conditions. A cascade Knoevenagel condensation/Diels-Alder cycloaddition reaction was observed, resulting in the final adducts 13–16 in similar yields. These procedures are environmentally benign, because no solvent and no catalyst were employed in these processes. The regioselectivity of these reactions was rationalized by Frontier Molecular Orbital (FMO) calculations. PMID:22489113

Flores-Conde, Maria Ines; Reyes, Leonor; Herrera, Rafael; Rios, Hulme; Vazquez, Miguel A.; Miranda, Rene; Tamariz, Joaquin; Delgado, Francisco

2012-01-01

141

KINETICS AND MECHANISMS OF THE GAS-PHASE REACTIONS OF OZONE WITH ORGANIC COMPOUNDS UNDER ATMOSPHERIC CONDITIONS  

EPA Science Inventory

Literature kinetic and mechanistic data have been compiled and evaluated for the gas phase reactions of ozone with organics. Emphasis is placed upon the reaction kinetics and mechanisms in air in order to assess the atmospheric relevance of these reactions. Wherever possible, rec...

142

Reaction-Sheet Jump Conditions in Premixed Flames J.W. Dold, R.W. Thatcher, A.A. Shah  

E-print Network

. The strong thermal sensitivity of the reaction rate at high activation temperature is likely to overwhelm takes place on an infinitesimally thin free boundary, or sheet of reaction, at a rate that depends only gases. In cases where the activation temperature is large enough and the temperature at the reaction

143

The Combination of Salt Induced Peptide Formation Reaction and Clay Catalysis: A Way to Higher Peptides under Primitive Earth Conditions  

NASA Astrophysics Data System (ADS)

Two reactions with suggested prebiotic relevance for peptide evolution, the saltinduced peptide formation reaction and the peptide chain elongation/stabilization on clay minerals have been combined in experimental series starting from dipeptides and dipeptide/amino acid mixtures. The results show that both reactions can take place simultaneously in the same reaction environment and that the presence of mineral catalysts favours the formation of higher oligopeptides. These findings lend further support to the relevance of these reactions for peptide evolution on the primitive earth. The detailed effects of the specific clay mineral depend both on the nature of the mineral and the reactants in solution.

Rode, Bernd M.; Son, Hoang L.; Suwannachot, Yuttana; Bujdak, Juraj

1999-05-01

144

Selection of reference genes for quantitative reverse-transcription polymerase chain reaction normalization in Brassica napus under various stress conditions.  

PubMed

Data normalization is essential for reliable output of quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) assays, as the unsuitable choice of reference gene(s), whose expression might be influenced by exogenous treatments in plant tissues, could cause misinterpretation of results. To date, no systematic studies on reference genes have been performed in stressed Brassica napus. In this study, we investigated the expression variations of nine candidate reference genes in 40 samples of B. napus leaves subjected to various exogenous treatments. Parallel analyses by geNorm and NormFinder revealed that optimal reference genes differed across the different sets of samples. The best-ranked reference genes were PP2A and TIP41 for salt stress, TIP41 and ACT7 for heavy metal (Cr(6+)) stress, PP2A and UBC21 for drought stress, F-box and SAND for cold stress, F-box and ZNF for salicylic acid stress, TIP41, ACT7, and PP2A for methyl jasmonate stress, TIP41 and ACT7 for abscisic acid stress, and TIP41, UBC21, and PP2A for Sclerotinia sclerotiorum stress. Two newly employed reference genes, TIP41 and PP2A, showed better performances, suggesting their suitability in multiple conditions. To further validate the suitability of the reference genes, the expression patterns of BnWRKY40 and BnMKS1 were studied in parallel. This study is the first systematic analysis of reference gene selection for qRT-PCR normalization in B. napus, an agriculturally important crop, under different stress conditions. The results will contribute toward more accurate and widespread use of qRT-PCR in gene analysis of the genus Brassica. PMID:24770781

Wang, Zheng; Chen, Yu; Fang, Hedi; Shi, Haifeng; Chen, Keping; Zhang, Zhiyan; Tan, Xiaoli

2014-10-01

145

Emissions of volatile organic compounds from Quercus ilex L. measured by Proton Transfer Reaction Mass Spectrometry under different environmental conditions  

NASA Astrophysics Data System (ADS)

Volatile organic compound (VOC) emissions of the Mediterranean holm oak (Quercus ilex L.) were investigated using a fast Proton Transfer Reaction Mass Spectrometry (PTR-MS) instrument for analysis. This technique is able to measure compounds with a proton affinity higher than water with a high time resolution of 1 s per compound. Hence nearly all VOCs can be detected on-line. We could clearly identify the emission of methanol, acetaldehyde, ethanol, acetone, acetic acid, isoprene, monoterpenes, toluene, and C10-benzenes. Some other species could be tentatively denominated. Among these are the masses 67 (cyclo pentadiene), mass 71 (tentatively attributed to methyl vinyl ketone (MVK) and metacrolein (MACR)), 73 (attributed to methyl ethyl ketone (MEK)), 85 (C6H12 or hexanol), and 95 (vinylfuran or phenol). The emissions of all these compounds (identified as well as nonidentified) together represent 99% of all masses detected and account for a carbon loss of 0.7-2.9% of the net photosynthesis. Of special interest was a change in the emission behavior under changing environmental conditions such as flooding or fast light/dark changes. Flooding of the root system caused an increase of several VOCs between 60 and 2000%, dominated by the emission of ethanol and acetaldehyde, which can be explained by the well described production of ethanol under anoxic conditions of the root system and the recently described subsequent transport and partial oxidation to acetaldehyde within the green leaves. However, ethanol emissions were dominant. Additionally, bursts of acetaldehyde with lower ethanol emission were also found under fast light/dark changes. These bursts are not understood.

Holzinger, R.; Sandoval-Soto, L.; Rottenberger, S.; Crutzen, P. J.; Kesselmeier, J.

2000-08-01

146

In-Cylinder Reaction Chemistry and Kinetics During Negative Valve Overlap Fuel Injection Under Low-Oxygen Conditions  

SciTech Connect

Fuel injection into the negative valve overlap (NVO) period is a common method for controlling combustion phasing in homogeneous charge compression ignition (HCCI) as well as other forms of advanced combustion. During this event, at least a portion of the fuel hydrocarbons can be converted to products containing significant levels of H2 and CO, as well as other short chain hydrocarbons by means of thermal cracking, water-gas shift, and partial oxidation reactions, depending on the availability of oxygen and the time-temperature-pressure history. The resulting products alter the autoignition properties of the combined fuel mixture for HCCI. Fuel-rich chemistry in a partial oxidation environment is also relevant to other high efficiency engine concepts (e.g., the dedicated EGR (D-EGR) concept from SWRI). In this study, we used a unique 6-stroke engine cycle to experimentally investigate the chemistry of a range of fuels injected during NVO under low oxygen conditions. Fuels investigated included iso-octane, iso-butanol, ethanol, and methanol. Products from NVO chemistry were highly dependent on fuel type and injection timing, with iso-octane producing less than 1.5% hydrogen and methanol producing more than 8%. We compare the experimental trends with CHEMKIN (single zone, 0-D model) predictions using multiple kinetic mechanisms available in the current literature. Our primary conclusion is that the kinetic mechanisms investigated are unable to accurately predict the magnitude and trends of major species we observed.

Kalaskar, Vickey B [ORNL] [ORNL; Szybist, James P [ORNL] [ORNL; Splitter, Derek A [ORNL] [ORNL; Pihl, Josh A [ORNL] [ORNL; Gao, Zhiming [ORNL] [ORNL; Daw, C Stuart [ORNL] [ORNL

2013-01-01

147

CO2 reaction with hydrated class H well cement under geologic sequestration conditions: effects of flyash admixtures.  

PubMed

The rate and mechanism of reaction of pozzolan-amended Class H cement exposed to both supercritical CO2 and CO2-saturated brine were determined under geologic sequestration conditions to assess the potential impact of cement degradation in existing, wells on CO2 storage integrity. The pozzolan additive chosen, Type F flyash, is the most common additive used in cements for well sealing in oil-gas field operations. The 35:65 and 65:35 (v/v) pozzolan-cement blends were exposed to supercritical CO2 and CO2-saturated brine and underwent cement carbonation. Extrapolation of the carbonation rate for the 35:65 case suggests a penetration depth of 170-180 mm for both the CO2-saturated brine and supercritical CO2 after 30 years. Despite alteration in both pozzolan systems, the reacted cement remained relatively impermeable to fluid flow after exposure to brine solution saturated with CO2, with values well below the American Petroleum Institute recommended maximum well cement permeability of 200 microD. Analyses of 50: 50 pozzolan-cement cores from a production well in a sandstone reservoir exhibited carbonation and low permeability to brine solution saturated with CO2, which are consistent with our laboratory findings. PMID:19544912

Kutchko, Barbara G; Strazisar, Brian R; Huerta, Nicolas; Lowry, Gregory V; Dzombak, David A; Thaulow, Niels

2009-05-15

148

Optimization of reaction conditions to fabricate nano-silver using Couroupita guianensis Aubl. (leaf & fruit) and its enhanced larvicidal effect  

NASA Astrophysics Data System (ADS)

Currently bioactive principles of plants and their nanoproducts have been extensively studied in agriculture and medicine. In this study Couroupita guianensis Aubl. leaf and fruit extracts were selected for rapid and cost-effective synthesis of silver nanoparticles (leaf-LAgNPs and fruit-FAgNPs). Various physiological conditions such as temperature, pH, concentration of metal ions, stoichiometric proportion of reaction mixture and reaction time showed influence on the size, dispersity and synthesis rate of AgNPs. Generation of AgNPs was initially confirmed with the surface plasmon vibrations at 420 nm in UV-visible spectrophotometer. The results recorded from X-ray diffractometer (XRD) and Transmission electron microscope (TEM) supports the biosynthesis of cubic crystalline LAgNPs & FAgNPs with the size ranges between 10-45 nm and 5-15 nm respectively. Surface chemistry of synthesized AgNPs was studied with Fourier transform infrared spectroscopy (FTIR), it reveals that water soluble phenolic compounds present in the extracts act as reducing and stabilizing agent. Leaf, fruit extracts and synthesized AgNPs were evaluated against IV instar larvae of Aedes aegypti (Diptera; Culicidae). Furthermore, different extracts and synthesized AgNPs showed dose dependent larvicidal effect against A. aegypti after 24 h of treatment. Compare to all extracts such as ethyl acetate (leaf; LC50 - 44.55 ppm and LC90 - 318.39 ppm & fruit; LC50 - 49.96 ppm and LC90 - 568.84 ppm respectively) and Methanol (leaf; LC50 - 85.75 ppm and LC90 - 598.63 ppm & fruit; LC50 - 67.78 ppm and LC90 - 714.45 ppm respectively) synthesized AgNPs showed extensive mortality rate (LAgNPs; LC50 - 2.1 ppm and LC90 - 5.59 ppm & FAgNPs; LC50 - 2.09 ppm and LC90 - 5.7 ppm). Hence, this study proves that C. guianensis is a potential bioresource for stable, reproducible nanoparticle synthesis (AgNPs) and also can be used as an efficient mosquito control agent.

Vimala, R. T. V.; Sathishkumar, Gnanasekar; Sivaramakrishnan, Sivaperumal

2015-01-01

149

Optimization of reaction conditions to fabricate nano-silver using Couroupita guianensis Aubl. (leaf & fruit) and its enhanced larvicidal effect.  

PubMed

Currently bioactive principles of plants and their nanoproducts have been extensively studied in agriculture and medicine. In this study Couroupita guianensis Aubl. leaf and fruit extracts were selected for rapid and cost-effective synthesis of silver nanoparticles (leaf-LAgNPs and fruit-FAgNPs). Various physiological conditions such as temperature, pH, concentration of metal ions, stoichiometric proportion of reaction mixture and reaction time showed influence on the size, dispersity and synthesis rate of AgNPs. Generation of AgNPs was initially confirmed with the surface plasmon vibrations at 420 nm in UV-visible spectrophotometer. The results recorded from X-ray diffractometer (XRD) and Transmission electron microscope (TEM) supports the biosynthesis of cubic crystalline LAgNPs & FAgNPs with the size ranges between 10-45 nm and 5-15 nm respectively. Surface chemistry of synthesized AgNPs was studied with Fourier transform infrared spectroscopy (FTIR), it reveals that water soluble phenolic compounds present in the extracts act as reducing and stabilizing agent. Leaf, fruit extracts and synthesized AgNPs were evaluated against IV instar larvae of Aedes aegypti (Diptera; Culicidae). Furthermore, different extracts and synthesized AgNPs showed dose dependent larvicidal effect against A. aegypti after 24h of treatment. Compare to all extracts such as ethyl acetate (leaf; LC50 - 44.55 ppm and LC90 - 318.39 ppm & fruit; LC50 - 49.96 ppm and LC90 - 568.84 ppm respectively) and Methanol (leaf; LC50 - 85.75 ppm and LC90 - 598.63 ppm & fruit; LC50 - 67.78 ppm and LC90 - 714.45 ppm respectively) synthesized AgNPs showed extensive mortality rate (LAgNPs; LC50 - 2.1 ppm and LC90 - 5.59 ppm & FAgNPs; LC50 - 2.09 ppm and LC90 - 5.7 ppm). Hence, this study proves that C. guianensis is a potential bioresource for stable, reproducible nanoparticle synthesis (AgNPs) and also can be used as an efficient mosquito control agent. PMID:25062056

Vimala, R T V; Sathishkumar, Gnanasekar; Sivaramakrishnan, Sivaperumal

2015-01-25

150

The use of a microreactor for rapid screening of the reaction conditions and investigation of the photoluminescence mechanism of carbon dots.  

PubMed

A microreactor is applied and reported, for the first time, in the field of research of carbon dots (CDs), including rapid screening of the reaction conditions and investigation of the photoluminescence (PL) mechanism. Various carbonaceous precursors and solvents were selected and hundreds of reaction conditions were screened (ca. 15?min on average per condition). Through analyzing the screened conditions, tunable PL emission maxima, from about 330 to 550?nm with respectable PL quantum yields, were achieved. Moreover, the relationship between different developmental stages of the CDs and the PL properties was explored by using the microreactor. The PL emission was observed to be independent of the composition, carbonization extent, and morphology/size of the CDs. This study unambiguously presents that a microreactor could serve as a promising tool for the research of CDs. PMID:24623603

Lu, Yue; Zhang, Ling; Lin, Hengwei

2014-04-01

151

Molecular studies of model surfaces of metals from single crystals to nanoparticles under catalytic reaction conditions. Evolution from prenatal and postmortem studies of catalysts.  

PubMed

Molecular level studies of metal crystal and nanoparticle surfaces under catalytic reaction conditions at ambient pressures during turnover were made possible by the use of instruments developed at the University of California at Berkeley. Sum frequency generation vibrational spectroscopy (SFGVS), owing to its surface specificity and sensitivity, is able to identify the vibrational features of adsorbed monolayers of molecules. We identified reaction intermediates, different from reactants and products, under reaction conditions and for multipath reactions on metal single crystals and nanoparticles of varying size and shape. The high-pressure scanning tunneling microscope (HP-STM) revealed the dynamics of a catalytically active metallic surface by detecting the mobility of the adsorbed species during catalytic turnover. It also demonstrated the reversible and adsorbate-driven surface restructuring of platinum when exposed to molecules such as CO and ethylene. Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) detected the reversible changes of surface composition in rhodium-palladium, platinum-palladium, and other bimetallic nanoparticles as the reactant atmosphere changed from oxidizing to reducing. It was found that metal nanoparticles of less than 2 nm in size are present in higher oxidation states, which alters and enhances their catalytic activity. The catalytic nanodiode (CND) confirmed that a catalytic reaction-induced current flow exists at oxide-metal interfaces, which correlates well with the reaction turnover. PMID:20860409

Somorjai, Gabor A; Aliaga, Cesar

2010-11-01

152

REACTIONS OF PEROXYNITRITE WITH URIC ACID: FORMATION OF REACTIVE INTERMEDIATES, ALKYLATED PRODUCTS AND TRIURET, AND IN VIVO PRODUCTION OF TRIURET UNDER CONDITIONS OF OXIDATIVE STRESS  

PubMed Central

Hyperuricemia is associated with hypertension, metabolic syndrome, preeclampsia, cardiovascular disease and renal disease, all conditions associated with oxidative stress. We hypothesized that uric acid, a known antioxidant, might become prooxidative following its reaction with oxidants; and, thereby contribute to the pathogenesis of these diseases. Uric acid and 1,3-15N2-uric acid were reacted with peroxynitrite in different buffers and in the presence of alcohols, antioxidants and in human plasma. The reaction products were identified using liquid chromatography-mass spectrometry (LC-MS) analyses. The reactions generate reactive intermediates that yielded triuret as their final product. We also found that the antioxidant, ascorbate, could partially prevent this reaction. Whereas triuret was preferentially generated by the reactions in aqueous buffers, when uric acid or 1,3-15N2-uric acid was reacted with peroxynitrite in the presence of alcohols, it yielded alkylated alcohols as the final product. By extension, this reaction can alkylate other biomolecules containing OH groups and others containing labile hydrogens. Triuret was also found to be elevated in the urine of subjects with preeclampsia, a pregnancy-specific hypertensive syndrome that is associated with oxidative stress, whereas very little triuret is produced in normal healthy volunteers. We conclude that under conditions of oxidative stress, uric acid can form reactive intermediates, including potential alkylating species, by reacting with peroxynitrite. These reactive intermediates could possibly explain how uric acid contributes to the pathogenesis of diseases such as the metabolic syndrome and hypertension. PMID:19219741

Gersch, Christine; Palii, Sergiu P.; Imaram, Witcha; Kim, Kyung Mee; Karumanchi, S. Ananth; Angerhofer, Alexander; Johnson, Richard J.; Henderson, George N.

2009-01-01

153

CATALYST-FREE REACTIONS UNDER SOLVENT-FEE CONDITIONS: MICROWAVE-ASSISTED SYNTHESIS OF HETEROCYCLIC HYDRAZONES BELOW THE MELTING POINT OF NEAT REACTANTS: JOURNAL ARTICLE  

EPA Science Inventory

NRMRL-CIN-1437 Jeselnik, M., Varma*, R.S., Polanc, S., and Kocevar, M. Catalyst-free Reactions under Solvent-fee Conditions: Microwave-assisted Synthesis of Heterocyclic Hydrazones below the Melting Point of Neat Reactants. Published in: Chemical Communications 18:1716-1717 (200...

154

DATA COLLECTION CONSTRAINTS FOR THE USE OF LENGTH HETEROGENEITY POLYMERASE CHAIN REACTION (LH-PCR) AS AN INDICATOR OF STREAM SANITARY AND ECOLOGICAL CONDITION  

EPA Science Inventory

This study is part of a larger project for the development of bacterial indicators of stream sanitary and ecological condition. Here we report preliminary research on the use of Length Heterogeneity Polymerase Chain Reaction (LH-PCR), which discriminates among 16S rRNA genes bas...

155

Encouraging Conceptual Change: The Use of Bridging Analogies in the Teaching of Action-Reaction Forces and the "At Rest" Condition in Physics. Research Report  

ERIC Educational Resources Information Center

The qualitative study described in this paper examined the effectiveness of bridging analogies intended to bring about conceptual change as part of a constructivist approach to teaching about action-reaction forces in the 'at rest' condition in physics. Twenty-one 15-year-old students were involved in the investigation with subgroups previously…

Bryce, Tom; MacMillan, Kenneth

2005-01-01

156

Molecular Studies of Surfaces under Reaction Conditions; Sum Frequency Generation Vibrational Spectroscopy, Scanning Tunneling Microscopy and Ambient Pressure X-Ray Photoelectron Spectroscopy  

SciTech Connect

Instruments developed in our laboratory permit the atomic and molecular level study of NPs under reaction conditions (SFG, ambient pressure XPS and high pressure STM). These studies indicate continuous restructuring of the metal substrate and the adsorbate molecules, changes of oxidation states with NP size and surface composition variations of bimetallic NPs with changes of reactant molecules.

Somorjai, G.A.

2009-11-11

157

Influence of the reaction temperature on the electrochemical promoted catalytic behaviour of platinum impregnated catalysts for the reduction of nitrogen oxides under lean burn conditions  

Microsoft Academic Search

The aim of this work was to study the influence of the reaction temperature on the efficiency of the electrochemical promotion to improve the catalytic performance of a Pt impregnated catalyst for the reduction of nitrogen oxides under lean burn conditions. Open circuit catalytic and potential measurements were carried out in order to explain the potentiostatic behaviour of the electrochemical

Fernando Dorado; Antonio de Lucas-Consuegra; Carmen Jiménez; José Luis Valverde

2007-01-01

158

Parallel synthesis of dihydropyrimidinones using Yb(III)-resin and polymer-supported scavengers under solvent-free conditions. A green chemistry approach to the Biginelli reaction  

Microsoft Academic Search

An efficient synthesis of an array of 3,4-dihydropyrimidin-2-(1H)-ones using solid-supported ytterbium(III) reagent from aldehydes, 1,3-dicarbonyl compounds and urea (Biginelli reaction) under solvent-free conditions is described. Purification of each member of the library was carried out using a cocktail of acid and basic polymer-supported scavengers

Alessandro Dondoni; Alessandro Massi

2001-01-01

159

Effect of reaction conditions on methyl red degradation mediated by boron and nitrogen doped TiO2  

NASA Astrophysics Data System (ADS)

Nowadays the employment of renewable and sustainable energy sources, and solar light as main option, becomes an urgent need. Photocatalytic processes received great attention in wastewater treatment due to their cheapness, environmental compatibility and optimal performances. Despite the general low selectivity of the photocatalysts, an accurate optimisation of the operational parameters needs to be carried out in order to maximise the process yield. Because of this reason, the present contribution aims to deepen either the knowledge in boron and/or nitrogen doped TiO2-based systems and their employment in methyl red removal from aqueous solutions. The samples were obtained by coprecipitation and characterised by XRD, SEM, BET specific surface area, UV-vis and XPS techniques. The catalytic activity was for the first time carefully evaluated with respect to methyl red photodegradation in different conditions as a function of working pH, counter-ions and pre-adsorption time. An ad-hoc study was performed on the importance of the pre-adsorption of the dye, suggesting that an extended adsorption is useless for the catalyst photoactivity, while a partial coverage is preferable. The photocatalytic tests demonstrate the positive influence of boron doping in photo-activated reactions and the great importance of the operational parameters with respect to the simple methyl red bleaching rather than the overall pollutant mineralisation. It is proved, indeed, that different working pH, acidifying means and substrate pre-adsorption time can enhance or limit the catalyst performances with respect to the complete pollutant degradation rather than its partial breakage.

Galenda, A.; Crociani, L.; Habra, N. El; Favaro, M.; Natile, M. M.; Rossetto, G.

2014-09-01

160

Sonication effect on the reaction of 4-bromo-1-methylbenzene with sodium sulfide in liquid-liquid multi-site phase-transfer catalysis condition - kinetic study.  

PubMed

The synthesis of di-p-tolylsulfane from the reaction of 4-bromo-1-methylbenzene (BMB) with sodium sulfide was carried out using a multi-site phase-transfer catalyst (MPTC) viz., 1,4-dihexyl-1,4-diazoniabicyclo[2.2.2]octanium dibromide and ultrasonic irradiation in a liquid-liquid reaction condition. The overall reaction rate is greatly enhanced when catalyzed by multi-site phase-transfer catalyst (MPTC) combined with sonication (40 kHz, 300 W) in a batch reactor than catalyzed by MPTC without sonication. Effects on the reaction due to various operating conditions, such as agitation speed, different ultrasound frequencies, different phase-transfer catalysts, different organic solvents, the amount of MPTC, temperature, amount of sodium sulfide, effect of sodium hydroxide, volume of n-hexane and the concentration of 4-bromo-1-methylbenzene. The reaction obeys a pseudo first-order rate law and a suitable mechanism was proposed based on the experimental observation. PMID:25199442

Abimannan, Pachaiyappan; Selvaraj, Varathan; Rajendran, Venugopal

2015-03-01

161

Non-precious metals catalyze formal [4 + 2] cycloaddition reactions of 1,2-diazines and siloxyalkynes under ambient conditions.  

PubMed

Copper(I) and nickel(0) complexes catalyze the formal [4 + 2] cycloaddition reactions of 1,2-diazines and siloxyalkynes, a reaction hitherto best catalyzed by silver salts. These catalysts based on earth abundant metals are not only competent, but the copper catalyst, in particular, promotes cycloadditions of pyrido[2,3-d]pyridazine and pyrido[3,4-d]pyridazine, enabling a new synthesis of quinoline and isoquinoline derivatives, as well as the formal [2 + 2] cycloaddition reaction of cyclohexenone with a siloxyalkyne. PMID:24911346

Sumaria, Chintan S; Türkmen, Yunus E; Rawal, Viresh H

2014-06-20

162

Development of atom-economical catalytic asymmetric reactions under proton transfer conditions: construction of tetrasubstituted stereogenic centers and their application to therapeutics.  

PubMed

The development of atom-economical catalytic asymmetric reactions based on two distinct sets of catalyst, a rare earth metal/amide-based ligand catalyst and a soft Lewis acid/hard Brønsted base catalyst, is reviewed. These catalytic systems exhibit high catalytic activity and stereoselectivity by harnessing a cooperative catalysis through hydrogen bond/metal coordination and soft-soft interactions/hard-hard interactions, respectively. The effectiveness of these cooperative catalysts is clearly delineated by the high stereoselectivity in reactions with highly coordinative substrates, and the specific activation of otherwise low-reactive pronucleophiles under proton transfer conditions. The rare earth metal/amide-based ligand catalyst was successfully applied to catalytic asymmetric aminations, nitroaldol (Henry) reactions, Mannich-type reactions, and conjugate addition reactions, generating stereogenic tetrasubstituted centers. Catalytic asymmetric amination and anti-selective catalytic asymmetric nitroaldol reactions were successfully applied to the efficient enantioselective synthesis of therapeutic candidates, such as AS-3201 and the ?(3)-adrenoreceptor agonist, showcasing the practical utility of the present protocols. The soft Lewis acid/hard Brønsted base cooperative catalyst was specifically developed for the chemoselective activation of soft Lewis basic allylic cyanides and thioamides, which are otherwise low-reactive pronucleophiles. The cooperative action of the catalyst allowed for efficient catalytic generation of active carbon nucleophiles in situ, which were integrated into subsequent enantioselective additions to carbonyl-type electrophiles. PMID:21212541

Kumagai, Naoya

2011-01-01

163

HIGHLY DIASTEREOSELECTIVE MICHAEL REACTION UNDER SOLVENT-FREE CONDITIONS USING MICROWAVES: CONJUGATE ADDITION OF FLAVANONE TO ITS CHALCONE PRECURSOR  

EPA Science Inventory

Microwave-assisted reaction of 2'-hydroxychalcones in the presence of DBU resulted in the formation of hitherto unknown dimers by conjugate addition of the intermediate cyclic ketone to the starting enone....

164

Total Synthesis of Cephalosporolide E via a Tandem Radical/Polar Crossover Reaction. The Use of the Radical Cations under Nonoxidative Conditions in Total Synthesis.  

PubMed

The present work reports the first example of the use of the chemistry of radical cations under nonoxidative conditions in total synthesis. Using a late-stage tandem radical/polar crossover reaction, a highly stereoselective total synthesis of cephalosporolide E (which is typically obtained admixed with cephalosporolide F) was accomplished. The reaction of a phthalimido derivative with triphenyltin radical in refluxing toluene engenders a contact ion-pair (radical cation) that leads, in the first instance, to the cephalosporolide F, which is transformed into the cephalosporolide E via a stereocontrolled spiroketal isomerization promoted by the diphenylphosphate acid that is formed during the tandem transformation. PMID:25642728

Cortezano-Arellano, Omar; Quintero, Leticia; Sartillo-Piscil, Fernando

2015-03-01

165

An experimental investigation of the reaction of hydrogen chloride with lead oxide under simulated hazardous waste incineration conditions  

SciTech Connect

To simulate the behavior of lead during hazardous waste incineration, pellets of sintered lead oxide were treated with hydrogen chloride at concentrations of 2000 and 4000 ppm in air in a laboratory tube furnace. The chemical reaction kinetics and mass transfer properties of the solid-gas and solid-liquid reactions were examined at temperatures between 260 and 680{degrees}C. Lead dichloride was found to form and became more volatile at elevated temperatures. At temperatures above 300{degrees}C, chemical reaction kinetic limitations were absent and mass transfer resistance in the developing liquid lead oxide, lead dichloride eutectic phases were controlling. Above 590{degrees}C, a curious anomaly occurred: The observed global reaction rate appeared to increase slightly while the volatilization of lead dichloride dropped during the initial stages of the reaction. A thick film of a lead oxychloride compound was found which displayed low lead dichloride activity. Below 590{degrees}C, a different lead oxychloride compound was identified by x-ray diffraction in which lead dichloride activity was high, and this compound was much more volatile than the oxychloride formed above 5900{degrees}C.

Shor, J.T. [Oak Ridge National Lab., TN (United States); Frazier, G.C. [Univ. of Tennessee, Knoxville, TN (United States)

1996-04-01

166

How Pragmatic Interpretations Arise from Conditionals: Profiling the Affirmation of the Consequent Argument with Reaction Time and EEG Measures  

ERIC Educational Resources Information Center

Conditional reasoning consists in combining a conditional premise with a categorical premise and inferring a conclusion from them. Two well-known conditional arguments are Modus Ponens (MP: "If P then Q; P//"therefore Q), which is logically valid and Affirmation of the Consequent (AC: "If P then Q; Q//"therefore "P"), which is not. The latter is…

Bonnefond, Mathilde; Van der Henst, Jean-Baptiste; Gougain, Marion; Robic, Suzanne; Olsen, Matthew D.; Weiss, Oshri; Noveck, Ira

2012-01-01

167

Nucleoside azide-alkyne cycloaddition reactions under solvothermal conditions or using copper vials in a ball mill.  

PubMed

Novel nucleoside analogues containing photoswitchable moieties were prepared using 'click' cycloaddition reactions between 5'-azido-5'-deoxythymidine and mono- or bis-N-propargylamide-substituted azobenzenes. In solution, high to quantitative yields were achieved using 5 mol% Cu(I) in the presence of a stabilizing ligand. 'Click' reactions using the monopropargylamides were also effected in the absence of added cuprous salts by the application of liquid assisted grinding (LAG) in metallic copper reaction vials. Specifically, high speed vibration ball milling (HSVBM) using a 3/32(?) (2.38 mm) diameter copper ball (62 mg) at 60 Hz overnight in the presence of ethyl acetate lead to complete consumption of the 5'-azido nucleoside with clean conversion to the corresponding 1,3-triazole. PMID:25874944

Cummings, Andrew J; Ravalico, Francesco; McColgan-Bannon, Kegan I S; Eguaogie, Olga; Elliott, P Alain; Shannon, Matthew R; Bermejo, Iris A; Dwyer, Angus; Maginty, Amanda B; Mack, James; Vyle, Joseph S

2015-05-01

168

Efficient synthesis of functionalized dihydro-1H-indol-4(5H)-ones via one-pot three-component reaction under catalyst-free conditions.  

PubMed

A facile and efficient one-pot procedure for the preparation of functionalized dihydro-1H-indol-4(5H)-ones by a catalyst-free, three-component reaction of 1,3-dicarbonyl compounds, arylglyoxal monohydrate and enaminones under mild conditions in excellent yield is reported. This synthesis was confirmed to follow the group-assisted-purification (GAP) chemistry process, which can avoid traditional purifications, chromatography, and recrystallization. PMID:23597107

Wang, Hui-Yan; Shi, Da-Qing

2013-05-13

169

LENGTH-HETEROGENEITY POLYMERASE CHAIN REACTION (LH-PCR) AS AN INDICATOR OF STREAM SANITARY AND ECOLOGICAL CONDITION: OPTIMAL SAMPLE SIZE AND HOLDING CONDITIONS  

EPA Science Inventory

The use of coliform plate count data to assess stream sanitary and ecological condition is limited by the need to store samples at 4oC and analyze them within a 24-hour period. We are testing LH-PCR as an alternative tool to assess the bacterial load of streams, offering a cost ...

170

A model of silver–iodine reactions in a light water reactor containment sump under severe accident conditions  

Microsoft Academic Search

Metallic silver and iodine form insoluble AgI in the containment sump which has a major impact on iodine volatility and hence on the source term to the environment. Resistance-in-series models are developed and validated against separate-effects tests. The reaction between I2 and Ag is limited by mass transfer in the liquid. The rate does not follow a parabolic law for

Elisabeth Krausmann; Yannis Drossinos

1999-01-01

171

Reaction Condition Effects on Nickel Sorption Mechanisms in IlliteWater Suspensions E. J. Elzinga* and D. L. Sparks  

E-print Network

of to partial opening of the interlattice space (Bolt et al.,pH (4.5­8.0), reaction time (3 h, 24 h, and 1 wk) and ionic strength (I 0.1 and 0.003 M) using x-ray absorption spectroscopy (XAS) to 1979). characterize at lower pH (slower Ni sorption rate). Lowering the ionic strength re- of outer-sphere complexes

Sparks, Donald L.

172

Reaction rates for the oxidation of highly sulphurised petroleum cokes: the influence of thermogravimetric conditions and some coke properties  

Microsoft Academic Search

The reaction with air of a large number (22) of high-sulphur petroleum cokes was studied by temperature-ramped thermogravimetric analysis. The kinetic parameters for each coke were established, based on BET surface areas. The oxidation rates (kgCm?2s?1atm?1) were found to vary with sample mass. This was a result of limitations on oxygen transfer, despite the small masses and low heating rates

S. Salvador; J.-M. Commandré; B. R. Stanmore

2003-01-01

173

Acetylation of sugarcane bagasse using NBS as a catalyst under mild reaction conditions for the production of oil sorption-active materials.  

PubMed

Sugarcane bagasse was esterified with acetic anhydride using N-bromosuccinimide as a catalyst under mild conditions in a solvent free system. The extent of acetylation was measured by weight percent gain, which varied from 2.1% to 24.7% by changing the reaction temperature (25-130 degrees C) and duration (0.5-6.0 h). N-Bromosuccinimide was found to be a novel and highly effective catalyst for acetylation of hydroxyl groups in bagasse. At a concentration of 1% of the catalyst in acetic anhydride, a weight percent gain of 24.7% was achieved at 120 degrees C for 1 h, compared with 5.1% for the un-catalyst reaction under the same reaction condition. FT-IR and CP-MAS 13C-NMR studies produced evidence for acetylation. The thermal stability of the products decreased slightly upon chemical modification, but no significant decrease in thermal stability was observed for WPG > or = 24.7%. More importantly, the acetylation significantly increased hydrophobic properties of the bagasse. The oil sorption capacity of the acetylated bagasse obtained at 80 degrees C for 6 h, was 1.9 times higher than the commercial synthetic oil sorbents such as polypropylene fibres. Therefore, these oil sorption-active materials can be used to substitute non-biodegradable materials in oil spill cleanup. PMID:15288278

Sun, X F; Sun, R C; Sun, J X

2004-12-01

174

Externally controlled pressure and temperature microreactor for in situ x-ray diffraction, visual and spectroscopic reaction investigations under supercritical and subcritial conditions  

SciTech Connect

A microreactor has been developed for in situ, spectroscopic investigations of materials and reaction processes with full external pressure and temperature control from ambient conditions to 400 C and 310 bar. The sample chamber is in direct contact with an external manifold, whereby gases, liquids or fluids can be injected and their activities controlled prior to and under investigation conditions. The microreactor employs high strength, single crystal moissanite windows which allow direct probe beam interaction with a sample to investigate in situ reaction processes and other materials properties. The relatively large volume of the cell, along with full optical accessibility and external temperature and pressure control, make this reaction cell well suited for experimental investigations involving any combination of gas, fluid, and solid interactions. The microreactor's capabilities are demonstrated through an in situ x-ray diffraction study of the conversion of a meta-serpentine sample to magnesite under high pressure and temperature. Serpentine is one of the mineral candidates for the implementation of mineral carbonation, an intriguing carbon sequestration candidate technology.

Diefenbacher, J.; McKelvy, M.; Chizemeshya, A.V.; Wolf, G.H. (ASU)

2010-07-13

175

Externally controlled pressure and temperature microreactor for in situ x-ray diffraction, visual and spectroscopic reaction investigations under supercritical and subcritical conditions  

SciTech Connect

A microreactor has been developed for in situ, spectroscopic investigations of materials and reaction processes with full external pressure and temperature control from ambient conditions to 400 deg. C and 310 bar. The sample chamber is in direct contact with an external manifold, whereby gases, liquids or fluids can be injected and their activities controlled prior to and under investigation conditions. The microreactor employs high strength, single crystal moissanite windows which allow direct probe beam interaction with a sample to investigate in situ reaction processes and other materials properties. The relatively large volume of the cell, along with full optical accessibility and external temperature and pressure control, make this reaction cell well suited for experimental investigations involving any combination of gas, fluid, and solid interactions. The microreactor's capabilities are demonstrated through an in situ x-ray diffraction study of the conversion of a meta-serpentine sample to magnesite under high pressure and temperature. Serpentine is one of the mineral candidates for the implementation of mineral carbonation, an intriguing carbon sequestration candidate technology.

Diefenbacher, Jason; McKelvy, Michael; Chizmeshya, Andrew V.G.; Wolf, George H. [Center for Solid State Science, Arizona State University, Tempe, Arizona 85287-1704 (United States); Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1504 (United States)

2005-01-01

176

Rapid and efficient copper-catalyzed Finkelstein reaction of (hetero)aromatics under continuous-flow conditions.  

PubMed

A general, rapid, and efficient method for the copper-catalyzed Finkelstein reaction of (hetero)aromatics has been developed using continuous flow to generate a variety of aryl iodides. The described method can tolerate a broad spectrum of functional groups, including N-H and O-H groups. Additionally, in lieu of isolation, the aryl iodide solutions were used in two distinct multistep continuous-flow processes (amidation and Mg-I exchange/nucleophilic addition) to demonstrate the flexibility of this method. PMID:25378244

Chen, Mao; Ichikawa, Saki; Buchwald, Stephen L

2015-01-01

177

Efficient transfer hydrogenation reaction Catalyzed by a dearomatized PN 3P ruthenium pincer complex under base-free Conditions  

Microsoft Academic Search

A dearomatized complex [RuH(PN3P)(CO)] (PN3PN, N?-bis(di-tert-butylphosphino)-2,6-diaminopyridine) (3) was prepared by reaction of the aromatic complex [RuH(Cl)(PN3P)(CO)] (2) with t-BuOK in THF. Further treatment of 3 with formic acid led to the formation of a rearomatized complex (4). These new complexes were fully characterized and the molecular structure of complex 4 was further confirmed by X-ray crystallography. In complex 4, a

Li-Peng He; Tao Chen; Dong-Xu Xue; Mohamed Eddaoudi; Kuo-Wei Huang

178

Heat and mass exchange in films of a reacting mixture and a cooling liquid under exothermic-reaction conditions  

NASA Astrophysics Data System (ADS)

Conjugate turbulent heat and mass exchange in fast exothermic reactions in thin films has been investigated with allowance for the change in the pressure. A modification of the equal-flow-rate method, the most natural for problems of such a kind, has been constructed. Its distinctive feature is that it is constructed on formal passage to a rectangular domain of variation in variables. The modification obtained has been tested on the problem solved earlier by the well-known equal-flow-rate method. Despite the fact that the proposed mathematical model and the procedure of its investigation enjoy rather wide application, in the present work, it is oriented toward the cationic liquid-phase polymerization of isobutylene. The local concentration distributions of the monomer and the catalyst and the temperature distributions have been obtained in numerical investigations. The reaction and cooling zones have been singled out; it has been recorded that the process of the most active chemical transformation is localized by the narrow zone of entry into the film.

Kholpanov, L. P.; Zakiev, S. E.

2008-05-01

179

[The laboratory cultivation of Phlebotomus papatasi. The nature of the reaction of the sandflies to unfavorable environmental conditions].  

PubMed

The breeding of Phlebotomus papatasi in laboratory setting has been studied for 4 years. It has been found that in addition to the well-known factors such as temperature and humidity, sandfly development is affected by the features of reservoirs for their breeding, amount of nutrient substrate, duration of a diapause and developmental conditions of their parents. Ph. papatasi responds to deterioration of dwelling conditions with prolonged period of development, increased number of diapausing larvae and decreased number of emerged imagines, i.e. with development inhibition of different degree and movable transfer to diapause. PMID:1387189

Valevich, T A; Dergacheva, T I

1992-01-01

180

Direct conversion of cellulose to glucose and valuable intermediates in mild reaction conditions over solid acid catalysts  

Microsoft Academic Search

The direct hydrolysis of cellulose to glucose, HMF and other soluble by-products at 190°C in water solution using zeolites (H-BEA, H-MOR), sulphated zirconia supported over mesoporous silica (SBA-15), Amberlyst®15, heteropolyacids and AlCl3·6H2O as acid catalysts was studied using a high cellulose to catalyst ratio (10), not-pretreated (neither mechanically nor chemically) cellulose and a static (not mixed) autoclave. Under these conditions,

P. Lanzafame; D. M. Temi; S. Perathoner; A. N. Spadaro; G. Centi

181

Reaction and transport in debonded wellbore casing-cement interfaces under CO2 storage conditions: From batch reaction tests to flow-through experiments on the 2m length scale  

NASA Astrophysics Data System (ADS)

Debonding at interfaces between wellbore casing and cement is widely recognized as providing potential pathways for leakage from CO2 storage systems. This study addresses how the transport properties of such debonding-defects are affected by chemical reaction between cement, steel and CO2-bearing fluids. Our first set of experiments investigates near-static conditions, representative for stages prior to the formation of a fully connected defect network. Debonded cement-steel interfaces were simulated by constructing composite samples containing a spacer-imposed gap. Each sample was reacted with CO2 and an aqueous fluid, at 80°C and 14 MPa applied CO2 pressure, in seven sequential batch reaction runs (cumulative duration: 72 days). Permeability was measured after each run and microstructural analyses were performed after completion of the experiment. Reaction-induced permeability changes were limited, being less than one order of magnitude for all samples. Corrosion scale (Fe-carbonate, minor Fe-hydroxide) formed within the gap, on the surfaces of both the steel and cement. Here, the observed lack of Ca-carbonates suggests this corrosion scale produced a significant reduction in cement carbonation, similar to the decrease in corrosion rate observed when corrosion scale forms a protective film on steel. In contrast, Ca-carbonate did precipitate on the cement at locations beneath the spacers used to create the gap between the cement and steel plates, where corrosion scale did not form. Overall, the thin corrosion scale films on the cement surfaces seem to inhibit release of Ca from the cement into the gap and impede the precipitation of Ca- carbonates, which in other studies was found to promote sealing in fractured cement. Our batch reaction results imply that in local debonding-defects where corrosion scale development is insufficient to produce sealing, the scale's retarding effect on further reaction has the potential to maintain an open interfacial pathway. Ongoing changes in the temperature and stress state could lead these defects to propagate and connect, possibly resulting in a long-range pathway. Our second set of experiments is currently ongoing and addresses how such interconnected debonding-defects are affected by long-range chemical reaction and transport under flow-through conditions. Cement slurry was poured into a coil made of steel tube and was subsequently cured at 80°C. After curing, debonding was promoted by causing the steel tube to lift off the cement, providing us with a sample that contains a 2 m long section of (partially) debonded cement-steel interface. A flow-through permeameter, maintained at 80°C, will be used to one-sidedly flood the coil with CO2-bearing fluid, while continuously measuring sample permeability and pump/fluid volume (indicative for extent of reaction). Post-experiment microstructural analysis will be performed on the coil. To our knowledge, this will be the first experimental investigation of the cement-steel interface that includes reactive transport phenomena that occur on the metre length scale.

Wolterbeek, Tim; Peach, Colin; Spiers, Chris

2014-05-01

182

A Laboratory Test Setup for in Situ Measurements of the Dielectric Properties of Catalyst Powder Samples under Reaction Conditions by Microwave Cavity Perturbation: Set up and Initial Tests  

PubMed Central

The catalytic behavior of zeolite catalysts for the ammonia-based selective catalytic reduction (SCR) of nitrogen oxides (NOX) depends strongly on the type of zeolite material. An essential precondition for SCR is a previous ammonia gas adsorption that occurs on acidic sites of the zeolite. In order to understand and develop SCR active materials, it is crucial to know the amount of sorbed ammonia under reaction conditions. To support classical temperature-programmed desorption (TPD) experiments, a correlation of the dielectric properties with the catalytic properties and the ammonia sorption under reaction conditions appears promising. In this work, a laboratory test setup, which enables direct measurements of the dielectric properties of catalytic powder samples under a defined gas atmosphere and temperature by microwave cavity perturbation, has been developed. Based on previous investigations and computational simulations, a resonator cavity and a heating system were designed, installed and characterized. The resonator cavity is designed to operate in its TM010 mode at 1.2 GHz. The first measurement of the ammonia loading of an H-ZSM-5 zeolite confirmed the operating performance of the test setup at constant temperatures of up to 300 °C. It showed how both real and imaginary parts of the relative complex permittivity are strongly correlated with the mass of stored ammonia. PMID:25211199

Dietrich, Markus; Rauch, Dieter; Porch, Adrian; Moos, Ralf

2014-01-01

183

Phosphonic acid functionalized ordered mesoporous material: a new and ecofriendly catalyst for one-pot multicomponent Biginelli reaction under solvent-free conditions.  

PubMed

We report a new ordered 2D hexagonal mesoporous organosilica material (PAFMS-1) bearing phosphonic acid functionality at the surface. This hybrid material showed high Brunauer-Emmett-Teller surface area (565 m(2) g(-1)) and ordered assembly of mesoporoes with an average pore diameter of ca. 2.1 nm. This novel hybrid mesoporous material has been synthesized via cocondensation of (triethoxysilyl)(propyliminomethyl)biphenylmethyl phosphoester (PEFOS) and tetraethyl orthosilicate (TEOS) in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) at 373 K. The phosphoester-functionalized organosilane (PEFOS) precursor has been synthesized for the first time by a simple SN2 reaction followed by Suzuki coupling and a Mannich reaction. The material has been characterized by powder X-ray diffraction, N2 sorption, and transmission electron microscopy image analysis, whereas the presence of organic moieties (an aromatic biphenyl ring and an aliphatic side chain), phosphrous, and silicon in the pore wall of the material have been characterized by solid-state magic-angle-spinning NMR, X-ray photoelectron, and Fourier transform infrared (FT-IR) spectroscopic tools. Further, the surface acid strength of the hybrid material has been determined by FT-IR analysis of the samples via temperature-programmed pyridine adsorption studies. The material has been utilized as a reusable heterogeneous catalyst for the synthesis of biologically important and value added multifunctionalized 3,4-dihydropyridin-2-1H-(ones)/3,4-dihydropyridin-2-1H-(thiones) (DHPMs) through a multicomponent Biginelli condensation reaction under solvent-free conditions at 333 K. The phosphonic acid functionalized 2D hexagonal mesoporous material showed much higher catalytic activity in this multicomponent condensation reaction over sulfonic acid functionalized mesoporous silica (MCM-41-SO3H) bearing an aliphatic chain in the hybrid framework. PMID:24372168

Pramanik, Malay; Bhaumik, Asim

2014-01-22

184

A realistic kinetic Monte Carlo simulation of the faceting of a Pt(110) surface under reaction conditions.  

PubMed

The faceting process on Pt(110) is studied with the help of a kinetic Monte Carlo model taking into account realistic Pt-Pt, Pt-CO, and Pt-O interactions. The activation energies of the allowed atomic steps are estimated using available computational and experimental data. The model well reproduces the region in the parameter space where faceting occurs. Under kinetic instability conditions, the simulated faceted pattern forms a periodic hill and valley structure with a lateral periodicity of approximately 140-170 A, which is comparable with experimental data. The simulations reproduce the development of faceting on a realistic time scale. PMID:15634090

Monine, M I; Pismen, L M; Imbihl, R

2004-12-01

185

Formation of 6-methyl-1,4-dihydronaphthalene in the reaction of the p-tolyl radical with 1,3-butadiene under single-collision conditions.  

PubMed

Crossed molecular beam reactions of p-tolyl (C7H7) plus 1,3-butadiene (C4H6), p-tolyl (C7H7) plus 1,3-butadiene-d6 (C4D6), and p-tolyl-d7 (C7D7) plus 1,3-butadiene (C4H6) were carried out under single-collision conditions at collision energies of about 55 kJ mol(-1). 6-Methyl-1,4-dihydronaphthalene was identified as the major reaction product formed at fractions of about 94% with the monocyclic isomer (trans-1-p-tolyl-1,3-butadiene) contributing only about 6%. The reaction is initiated by barrierless addition of the p-tolyl radical to the terminal carbon atom of the 1,3-butadiene via a van der Waals complex. The collision complex isomerizes via cyclization to a bicyclic intermediate, which then ejects a hydrogen atom from the bridging carbon to form 6-methyl-1,4-dihydronaphthalene through a tight exit transition state located about 27 kJ mol(-1) above the separated products. This is the dominant channel under the present experimental conditions. Alternatively, the collision complex can also undergo hydrogen ejection to form trans-1-p-tolyl-1,3-butadiene; this is a minor contributor to the present experiment. The de facto barrierless formation of a methyl-substituted aromatic hydrocarbons by dehydrogenation via a single event represents an important step in the formation of polycyclic aromatic hydrocarbons (PAHs) and their partially hydrogenated analogues in combustion flames and the interstellar medium. PMID:25407848

Parker, Dorian S N; Dangi, Beni B; Kaiser, Ralf I; Jamal, Adeel; Ryazantsev, Mikhail; Morokuma, Keiji

2014-12-26

186

The ReactorSTM: Atomically resolved scanning tunneling microscopy under high-pressure, high-temperature catalytic reaction conditions  

NASA Astrophysics Data System (ADS)

To enable atomic-scale observations of model catalysts under conditions approaching those used by the chemical industry, we have developed a second generation, high-pressure, high-temperature scanning tunneling microscope (STM): the ReactorSTM. It consists of a compact STM scanner, of which the tip extends into a 0.5 ml reactor flow-cell, that is housed in a ultra-high vacuum (UHV) system. The STM can be operated from UHV to 6 bars and from room temperature up to 600 K. A gas mixing and analysis system optimized for fast response times allows us to directly correlate the surface structure observed by STM with reactivity measurements from a mass spectrometer. The in situ STM experiments can be combined with ex situ UHV sample preparation and analysis techniques, including ion bombardment, thin film deposition, low-energy electron diffraction and x-ray photoelectron spectroscopy. The performance of the instrument is demonstrated by atomically resolved images of Au(111) and atom-row resolution on Pt(110), both under high-pressure and high-temperature conditions.

Herbschleb, C. T.; van der Tuijn, P. C.; Roobol, S. B.; Navarro, V.; Bakker, J. W.; Liu, Q.; Stoltz, D.; Cañas-Ventura, M. E.; Verdoes, G.; van Spronsen, M. A.; Bergman, M.; Crama, L.; Taminiau, I.; Ofitserov, A.; van Baarle, G. J. C.; Frenken, J. W. M.

2014-08-01

187

The ReactorSTM: Atomically resolved scanning tunneling microscopy under high-pressure, high-temperature catalytic reaction conditions  

SciTech Connect

To enable atomic-scale observations of model catalysts under conditions approaching those used by the chemical industry, we have developed a second generation, high-pressure, high-temperature scanning tunneling microscope (STM): the ReactorSTM. It consists of a compact STM scanner, of which the tip extends into a 0.5 ml reactor flow-cell, that is housed in a ultra-high vacuum (UHV) system. The STM can be operated from UHV to 6 bars and from room temperature up to 600 K. A gas mixing and analysis system optimized for fast response times allows us to directly correlate the surface structure observed by STM with reactivity measurements from a mass spectrometer. The in situ STM experiments can be combined with ex situ UHV sample preparation and analysis techniques, including ion bombardment, thin film deposition, low-energy electron diffraction and x-ray photoelectron spectroscopy. The performance of the instrument is demonstrated by atomically resolved images of Au(111) and atom-row resolution on Pt(110), both under high-pressure and high-temperature conditions.

Herbschleb, C. T.; Tuijn, P. C. van der; Roobol, S. B.; Navarro, V.; Bakker, J. W.; Liu, Q.; Stoltz, D.; Cañas-Ventura, M. E.; Verdoes, G.; Spronsen, M. A. van; Bergman, M.; Crama, L.; Taminiau, I.; Frenken, J. W. M., E-mail: frenken@physics.leidenuniv.nl [Huygens-Kamerlingh Onnes Laboratory, Leiden University, P.O. box 9504, 2300 RA Leiden (Netherlands); Ofitserov, A.; Baarle, G. J. C. van [Leiden Probe Microscopy B.V., J.H. Oortweg 21, 2333 CH Leiden (Netherlands)

2014-08-15

188

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

189

The photostat-1 device for studying the reaction of organisms to physical conditions on the planet Mars  

NASA Technical Reports Server (NTRS)

A description of the photostat device which reproduces the basic parameters of the physical environment of the planet Mars is presented. Any given temperature may be maintained in its working chamber from -35 to +30 C with a maintenance accuracy of + or - 0.5 deg; it can produce a change in temperature with varying rates of cooling or heating and maintain any given pressure in a range from 5 to 95 mm Hg. The system of ultraviolet filters in the device permits irradiation with the following individual lines of the ultraviolet spectrum: 1-253.7, 280 and 356 nm, and 220-320 nm. All operational conditions of the device are maintained automatically for given programs and are recorded by automatic recording devices.

Zaar, E. I.; Zelikson, V. G.; Kitaygorodskiy, M. G.; Koshelev, I. V.; Lozina-Lozinskiy, L. K.; Rybin, M. A.

1973-01-01

190

Experimental Investigation of Augmented Spark Ignition of a LO2/LCH4 Reaction Control Engine at Altitude Conditions  

NASA Technical Reports Server (NTRS)

The use of nontoxic propellants in future exploration vehicles would enable safer, more cost-effective mission scenarios. One promising green alternative to existing hypergols is liquid methane (LCH4) with liquid oxygen (LO2). A 100 lbf LO2/LCH4 engine was developed under the NASA Propulsion and Cryogenic Advanced Development project and tested at the NASA Glenn Research Center Altitude Combustion Stand in a low pressure environment. High ignition energy is a perceived drawback of this propellant combination; so this ignition margin test program examined ignition performance versus delivered spark energy. Sensitivity of ignition to spark timing and repetition rate was also explored. Three different exciter units were used with the engine s augmented (torch) igniter. Captured waveforms indicated spark behavior in hot fire conditions was inconsistent compared to the well-behaved dry sparks. This suggests that rising pressure and flow rate increase spark impedance and may at some point compromise an exciter s ability to complete each spark. The reduced spark energies of such quenched deliveries resulted in more erratic ignitions, decreasing ignition probability. The timing of the sparks relative to the pressure/flow conditions also impacted the probability of ignition. Sparks occurring early in the flow could trigger ignition with energies as low as 1 to 6 mJ, though multiple, similarly timed sparks of 55 to 75 mJ were required for reliable ignition. Delayed spark application and reduced spark repetition rate both correlated with late and occasional failed ignitions. An optimum time interval for spark application and ignition therefore coincides with propellant introduction to the igniter.

Kleinhenz, Julie; Sarmiento, Charles; Marshall, William

2012-01-01

191

Formation and reactions of singlet oxygen, O[sub 2]([sup 1][Delta]g), under atmospheric conditions  

SciTech Connect

Singlet molecular oxygen, O[sub 2]([sup 1][Delta][sub g]), plays a significant role in photochemical air pollution as a reactive and a deleterious oxidant. Gas phase O[sub 2]([sup 1][Delta][sub g]) formation by homogeneous photosensitization at atmospheric pressure was studied using a variety of compounds found in the atmosphere. The formation of O[sub 2]([sup 1][Delta][sub g]) was demonstrated by observing its 1.27 [mu]m emission using a liquid nitrogen-cooled germanium photodiode detector, and by performing chemical trapping studies with 2,3-dimethyl-2-butene (TME) and quenching studies with triethylamine (TEA). The factors affecting O[sub 2]([sup 1][Delta][sub g]) formation included sensitizer concentration, gas composition (%N[sub 2]/%O[sub 2]), total gas flow rate, irradiation wavelength, and light intensity. The disappearance of seven polycyclic aromatic hydrocarbons (PAHs) adsorbed on zeolite particles was studied under simulated atmospheric conditions. Benzo[ghi]perylene, chrysene, and benzo[e]pyrene were less susceptible to photooxidation than benz[a]anthracene (B[a]A), pyrene, dibenz[ah]anthracene, and benzo[a]pyrene. The disappearance of B[a]A in the presence of light and air involved a self-sensitized photooxidation with the formation of O[sub 2]([sup 1][Delta][sub g]) as a major process. These studies were directed at identifying viable processes for forming atmospheric O[sub 2]([sup 1][Delta][sub g]) and deleterious substances that might be formed when environmental pollutants react with O[sub 2]([sup 1][Delta][sub g]).

deSilva, M.S.W.

1993-01-01

192

Catalytic reduction of NO by CO over rhodium catalysts. 2. Effect of oxygen on the nature, population, and reactivity of surface species formed under reaction conditions  

SciTech Connect

The effect of oxygen on the nature, population, and reactivity of surface species formed during reduction of NO by CO over Rh/TiO{sub 2} catalysts has been examined employing FTIR and transient MS techniques. It has been found that the activity of Rh is hindered by accumulation of surface oxygen originating from NO decomposition and gas-phase oxygen in the feed. Adsorbed CO and reduced TiO{sub 2{minus}x} species in the vicinity of Rh particles act as oxygen atom scavengers and, under fuel-rich conditions, remove atomic oxygen from the surface and restore the catalytic properties. Results of the present study provide additional evidence that production of N{sub 2} is related to dissociation of adsorbed Rh-NO{sup {minus}} while production of N{sub 2}O is related to the presence of Rh(NO){sub 2}. The presence of reduced RH{sup 0} sites is necessary for the formation of both reduction products. In the absence of oxygen in the feed, surface isocyanate species are also observed under reaction conditions. Their formation requires the presence of adjacent Rh{sup 0}-CO and reduced Rh{sup 0} sites. Although these species are favored under conditions in which NO conversion to reduction products is observed, there is no evidence that they are catalytically active species.

Kondarides, D.I.; Chafik, T.; Verykios, X.E.

2000-04-01

193

PAH formation under single collision conditions: reaction of phenyl radical and 1,3-butadiene to form 1,4-dihydronaphthalene.  

PubMed

The crossed beam reactions of the phenyl radical (C(6)H(5), X(2)A(1)) with 1,3-butadiene (C(4)H(6), X(1)A(g)) and D6-1,3-butadiene (C(4)D(6), X(1)A(g)) as well as of the D5-phenyl radical (C(6)D(5), X(2)A(1)) with 2,3-D2-1,3-butadiene and 1,1,4,4-D4-1,3-butadiene were carried out under single collision conditions at collision energies of about 55 kJ mol(-1). Experimentally, the bicyclic 1,4-dihydronaphthalene molecule was identified as a major product of this reaction (58 ± 15%) with the 1-phenyl-1,3-butadiene contributing 34 ± 10%. The reaction is initiated by a barrierless addition of the phenyl radical to the terminal carbon atom of the 1,3-butadiene (C1/C4) to form a bound intermediate; the latter underwent hydrogen elimination from the terminal CH(2) group of the 1,3-butadiene molecule leading to 1-phenyl-trans-1,3-butadiene through a submerged barrier. The dominant product, 1,4-dihydronaphthalene, is formed via an isomerization of the adduct by ring closure and emission of the hydrogen atom from the phenyl moiety at the bridging carbon atom through a tight exit transition state located about 31 kJ mol(-1) above the separated products. The hydrogen atom was found to leave the decomposing complex almost parallel to the total angular momentum vector and perpendicularly to the rotation plane of the decomposing intermediate. The defacto barrierless formation of the 1,4-dihydronaphthalene molecule involving a single collision between a phenyl radical and 1,3-butadiene represents an important step in the formation of polycyclic aromatic hydrocarbons (PAHs) and their partially hydrogenated counterparts in combustion and interstellar chemistry. PMID:22497458

Kaiser, R I; Parker, D S N; Zhang, F; Landera, A; Kislov, V V; Mebel, A M

2012-05-01

194

Co-formation of hydroperoxides and ultra-fine particles during the reactions of ozone with a complex VOC mixture under simulated indoor conditions  

NASA Astrophysics Data System (ADS)

In this study we examined the co-formation of hydrogen peroxide and other hydroperoxides (collectively presented as H 2O 2*) as well as submicron particles, including ultra-fine particles (UFP), resulting from the reactions of ozone (O 3) with a complex mixture of volatile organic compounds (VOCs) under simulated indoor conditions. The VOC mixture contained 23 compounds, including two terpenes ( d-limonene and ?-pinene), two unsaturated alkenes (1-decene and 1-octene), and 19 other saturated organic compounds. These compounds are commonly found in indoor air but their concentrations were higher than typical indoor levels. When O 3 was added to a 25-m 3 controlled environmental facility (CEF) containing the 23 VOC mixture, both H 2O 2* and submicron particles were formed. The 2-h average concentration of H 2O 2* was 1.89±0.30 ppb, and the average total particle number concentration was 46,000±12,000 particles cm -3. A small increase of UFP (0.02-0.1 ?m) occurred 5 min after the O 3 addition (17 min after the VOC addition) and a sharp increase of UFP occurred 13 min after the O 3 addition, suggesting homogeneous nucleation. The delayed onset of this event might reflect the time required to achieve saturated concentrations of the condensable organics. When the 2 terpenes were removed from the O 3/23 VOCs mixture, no H 2O 2* or particles were formed, indicating that the reactions of O 3 with the two terpenes were the key processes contributing to the formation of H 2O 2* and submicron particles in the O 3/23 VOCs system. The present study confirmed the findings of a previous study carried out in a real-world office and generated new findings regarding co-formation of UFP. Through a comparative analysis of H 2O 2* yields under different reaction conditions, this study demonstrates that VOCs co-present with the terpenes and O 3 may play a role in producing H 2O 2*.

Fan, Zhihua; Weschler, Charles J.; Han, In-Kyu; Zhang, Junfeng (Jim)

195

Si-rich layer formation on olivine surfaces during reaction with water and supercritical carbon dioxide under conditions relevant for geologic carbon storage  

NASA Astrophysics Data System (ADS)

The reaction of Mg-silicate minerals (i.e. olivine) with carbon dioxide (CO2) is a promising method for secure, long-term, geologic carbon storage. Several technical challenges must be overcome before implementing mineral carbonation technology on a large scale, one of which is slow reaction kinetics. This study probes surface reaction limitations of olivine carbonation, specifically the formation of a passivating, Si-rich layer on olivine surfaces upon exposure to water and CO2 under sequestration conditions (elevated temperature and pressure). A series of batch reactions were performed at 60°C and 100 bar CO2 pressure in Dickson-style rocker bombs, varying the length of reaction and the amount of mixing (rocking). The initial aqueous phase was spiked with 29Si. Fluid samples were taken periodically and analyzed for cation content, alkalinity, and dissolved inorganic carbon. At the end of each experiment, the solid products were analyzed with a Sensitive High Resolution Ion Microprobe Reverse Geometry (SHRIMP-RG) in order to measure the amount of 29Si incorporated into the Si-rich layer on reacted olivine grains. We also cut cross sections of reacted grains from each experiment using a Focused Ion Beam (FIB) which were thinned to <100nm and imaged using Transmission Electron Microscopy (TEM). SHRIMP-RG results show incorporation of 29Si on olivine grain surfaces reacted for 19 days with no mixing, and TEM images of olivine grains from the same experiment show an amorphous, Si-rich layer that is 30nm thick. Similarly, SHRIMP-RG results for olivine grains reacted for 19 days with mixing indicate 29SiO2 precipitation and TEM images reveal a Si-rich layer 60nm thick. In both experiments, EDS (energy dispersive spectroscopy) data show a step change in composition from the bulk rock to the surface layer in addition to the sharp crystalline/amorphous interface visible in the TEM images. Olivine from the unmixed experiment also has a slow decrease in Mg relative to Si before the step change, suggesting that, at least in this experiment, a Si-rich layer precipitated on top of a Mg-depleted layer that formed via a leaching process. SHRIMP-RG data also imply the presence of a precipitated Si-rich layer on top of a leached Si-rich layer, as the 29Si penetration depth is only 25-65% of the total Si-rich layer thickness. The combination of SHRIMP-RG and FIB/TEM analysis leads us to hypothesize that a Si-rich layer forms quickly on olivine surfaces due to preferential Mg removal from the surface (the traditional 'leached' layer), and as the reaction proceeds, amorphous silica reaches saturation in the fluid and precipitates on surfaces inside the reactor (including olivine grains).

Johnson, N. C.; Jackson, A.; Maher, K.; Bird, D. K.; Brown, G. E.

2013-12-01

196

Cobalt corrole catalyst for efficient hydrogen evolution reaction from H2O under ambient conditions: reactivity, spectroscopy, and density functional theory calculations.  

PubMed

The feasibility of a hydrogen-based economy relies very much on the availability of catalysts for the hydrogen evolution reaction (HER) that are not based on Pt or other noble elements. Significant breakthroughs have been achieved with certain first row transition metal complexes in terms of low overpotentials and large turnover rates, but the majority of reported work utilized purified and deoxygenated solvents (most commonly mixtures of organic solvents/acids). Realizing that the design of earth abundant metal catalysts that operate under truly ambient conditions remains an unresolved challenge, we have now developed an electronically tuned Co(III) corrole that can catalyze the HER from aqueous sulfuric acid at as low as -0.3 V vs NHE, with a turnover frequency of 600 s(-1) and ?10(7) catalytic turnovers. Under aerobic conditions, using H2O from naturally available sources without any pretreatment, the same complex catalyzes the reduction of H(+) with a Faradaic Yield (FY) of 52%. Density functional theory (DFT) calculations indicate that the electron density on a putative hydride species is delocalized off from the H atom into the macrocycle. This makes the protonation of a [Co(III)-H](-) species the rate determining step (rds) for the HER consistent with the experimental data. PMID:23445187

Mondal, Biswajit; Sengupta, Kushal; Rana, Atanu; Mahammed, Atif; Botoshansky, Mark; Dey, Somdatta Ghosh; Gross, Zeev; Dey, Abhishek

2013-03-18

197

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

PubMed

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

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

2014-05-01

198

JOURNALDEPHYSIQUE ColloqueCl,supplkmentauno1, Tome41,janvier 1980,page C1-341 A I@SSBAUERSTUDY OF THE IRON-CHROMIUM TYPE CATALYST FOR CO CONVERSION UNDER THE REACTION CONDITIONS  

E-print Network

@SSBAUERSTUDY OF THE IRON-CHROMIUM TYPE CATALYST FOR CO CONVERSION UNDER THE REACTION CONDITIONS Ding Ying-Ru, Yen Qi. 1. Introduction. - In carrying act the water-ga_s s h i f t reaction a t about 350°C. iron-chromium gases has been made, However, we have made some comparison between the structures of some iron-chromium

Boyer, Edmond

199

Synthesis, characterization and microwave-promoted catalytic activity of novel N-phenylbenzimidazolium salts in Heck-Mizoroki and Suzuki-Miyaura cross-coupling reactions under mild conditions.  

PubMed

A number of novel benzimidazolium salts having aryl substituents such as N-phenyl, 4-chlorophenyl and various alkyl substituents were synthesized. Their microwave-assisted catalytic activities were evaluated in Heck-Mizoroki and Suzuki-Miyaura cross-coupling reactions using a catalytic system consisting of Pd(OAc)(2)/K(2)CO(3) in DMF/H(2)O under mild reaction conditions with consistent high yields, except those of 2-bromopyridine. PMID:23439565

Y?lmaz, Ülkü; Küçükbay, Hasan; Deniz, Selma; ?ireci, Nihat

2013-01-01

200

Combinatorial synthesis of pyrrolo[3,2-f]quinoline and pyrrolo[3,2-a]acridine derivatives via a three-component reaction under catalyst-free conditions.  

PubMed

A combinatorial synthesis of pyrrolo[3,2-f]quinoline and pyrrolo[3,2-a]acridine derivatives is described as a three-component reaction of aromatic aldehyde, 1H-indol-5-amine, and 1,3-dicarbonyl compounds under catalyst-free conditions. The 1,3-dicarbonyl compounds include 5,5-dimethylcyclohexane-1,3-dione, cyclopentane-1,3-dione, and 2H-indene-1,3-dione. It is interesting that the designed reactions gave aromatized or unaromatized products, which depend on the reaction temperature and reactants of 1,3-dicarbonyl compounds. PMID:23914831

Zhou, Yu-Jing; Chen, Dong-Sheng; Li, Yu-Ling; Liu, Yun; Wang, Xiang-Shan

2013-09-01

201

Effect of coupled dissolution and redox reactions on Cr(VI)aq attenuation during transport in the sediments under hyperalkaline conditions.  

PubMed

Aluminum-rich, hyperalkaline (pH > 13.5) and saline high-level nuclear waste (HLW) fluids at elevated temperatures (>50 degrees C), that possibly contained as much as 0.41 mol L(-1) Cr(VI), accidentally leaked to the sediments at the Hanford Site, WA. These extreme conditions promote base-induced dissolution of soil minerals which may affect Cr(VI)aq mobility. Our objective was to investigate Cr(VI)aq transport in sediments leached with HLW simulants at 50 degrees C, under CO2 and O2 free conditions. Results demonstrated that Cr(VI)aq fate was closely related to dissolution, and Cr(VI)aq mass loss was negligible in the first pore volumes but increased significantly thereafter. Similar to dissolution, Cr(VI)aq attenuation increased with increasing fluid residence time and NaOH concentration but decreased with Al concentrations in the leaching solutions. Aqueous Cr(VI) removal rate half-lives varied from 1.2 to 230 h with the fastest at the highest base concentration, lowest Al concentration, greatest reaction time, and lowest Cr(VI) concentration in the leaching solution. The rate of Cr(VI) removal (normalized to 1 kg of solution) varied from 0.83 x 10(-9) (+/-0.44 x 10(-9)) to 9.16 x 10(-9) (+/-1.10 x 10(-9)) mol s(-1). The predominant mechanism responsible for removing Cr(VI) from the aqueous phase appears to be homogeneous Cr(VI) reduction to Cr(III) by Fe(II) released during mineral dissolution. Cr(VI)aq removal was time-limited probably because it was controlled by the rate of Fe(II) release into the soil solution upon mineral dissolution, which was also a time-limited process, and other processes that may act to lower Fe(II)aq activity. PMID:12953877

Qafoku, Nikolla P; Ainsworth, Calvin C; Szecsody, James E; Qafoku, Odeta S; Heald, Steve M

2003-08-15

202

Research on active particle distribution in the crop stalk plasma reaction under the condition of streaming and discharging micro electric current  

NASA Astrophysics Data System (ADS)

In order to further study sugar-production mechanism in the crop stalk plasma reaction under the condition of streaming and discharging micro electric current with N2 and H2O as the electro-discharging gases, the active particles distribution is researched and analyzed. Through the study of methods and theories of statistical mechanics and statistica thermodynamics, the ionization process of the mixed discharging gas and the distribution features of the active particles changing with temperature in the plasma reactor are discussed. The constant pressure form of Saha equation that applies to this experiment is deduced. And the active particles generated in the dense ionization discharging process and the crop stalk conversion processes are also analyzed. The experimental results show that N2 and H2 can ionize synchronously. And it is found that during the crop stalk conversion process, while one gas is ionised, the other gas will not take the energy away, which will not affect the conversion. Among the discharging gases consisting of water vapour and nitrogen, the main components are ions of H2O+, H+, N2+ and molecules of N2, H2O, which are all beneficial to a high sugar yield.

Song, C. L.; Pi, S. G.; Liu, X. Y.; Xu, H. B.

2013-03-01

203

Effects of heat-moisture treatment reaction conditions on the physicochemical and structural properties of maize starch: moisture and length of heating.  

PubMed

Changes in the properties of normal maize starch (NMS) and waxy maize starch (WMS) after heat-moisture treatment (HMT) under various reaction conditions were investigated. NMS and WMS were adjusted to moisture levels of 20%, 25% and 30% and heated at 100 °C for 2, 4, 8 and 16 h. The results showed that moisture content was the most important factor in determining pasting properties for NMS, whereas the heating length was more important for WMS. Swelling power decreased in NMS but increased in WMS, and while the solubility index decreased for both samples, the changes were largely determined by moisture content. The gelatinisation temperatures of both samples increased with increasing moisture content but remained unchanged with increasing heating length. The Fourier transform infrared (FT-IR) absorbance ratio was affected to different extents by the moisture levels but remained constant with increasing the heating length. The X-ray intensities increased but relative crystallinity decreased to a greater extent with increasing moisture content. This study showed that the levels of moisture content and length of heating had significant impacts on the structural and physicochemical properties of normal and waxy maize starches but to different extents. PMID:25466134

Sui, Zhongquan; Yao, Tianming; Zhao, Yue; Ye, Xiaoting; Kong, Xiangli; Ai, Lianzhong

2015-04-15

204

Kinetics of stabilised Criegee intermediates derived from alkene ozonolysis: reactions with SO2, H2O and decomposition under boundary layer conditions.  

PubMed

The removal of SO2 in the presence of alkene-ozone systems has been studied for ethene, cis-but-2-ene, trans-but-2-ene and 2,3-dimethyl-but-2-ene, as a function of humidity, under atmospheric boundary layer conditions. The SO2 removal displays a clear dependence on relative humidity for all four alkene-ozone systems confirming a significant reaction for stabilised Criegee intermediates (SCI) with H2O. The observed SO2 removal kinetics are consistent with relative rate constants, k(SCI + H2O)/k(SCI + SO2), of 3.3 (±1.1) × 10(-5) for CH2OO, 26 (±10) × 10(-5) for CH3CHOO derived from cis-but-2-ene, 33 (±10) × 10(-5) for CH3CHOO derived from trans-but-2-ene, and 8.7 (±2.5) × 10(-5) for (CH3)2COO derived from 2,3-dimethyl-but-2-ene. The relative rate constants for k(SCI decomposition)/k(SCI + SO2) are -2.3 (±3.5) × 10(11) cm(-3) for CH2OO, 13 (±43) × 10(11) cm(-3) for CH3CHOO derived from cis-but-2-ene, -14 (±31) × 10(11) cm(-3) for CH3CHOO derived from trans-but-2-ene and 63 (±14) × 10(11) cm(-3) for (CH3)2COO. Uncertainties are ±2? and represent combined systematic and precision components. These values are derived following the approximation that a single SCI is present for each system; a more comprehensive interpretation, explicitly considering the differing reactivity for syn- and anti-SCI conformers, is also presented. This yields values of 3.5 (±3.1) × 10(-4) for k(SCI + H2O)/k(SCI + SO2) of anti-CH3CHOO and 1.2 (±1.1) × 10(13) for k(SCI decomposition)/k(SCI + SO2) of syn-CH3CHOO. The reaction of the water dimer with CH2OO is also considered, with a derived value for k(CH2OO + (H2O)2)/k(CH2OO + SO2) of 1.4 (±1.8) × 10(-2). The observed SO2 removal rate constants, which technically represent upper limits, are consistent with decomposition being a significant, structure dependent, sink in the atmosphere for syn-SCI. PMID:25562069

Newland, Mike J; Rickard, Andrew R; Alam, Mohammed S; Vereecken, Luc; Muñoz, Amalia; Ródenas, Milagros; Bloss, William J

2015-01-28

205

Storage conditions of blood samples and primer selection affect the yield of cDNA polymerase chain reaction products of hepatitis C virus.  

PubMed Central

We have noticed that suboptimal specimen processing and storage conditions may cause false-negative results in the detection of hepatitis C virus (HCV) RNA in plasma or serum. To establish the influence of specimen handling in a serological laboratory on the rate of detection of HCV RNA by the cDNA polymerase chain reaction (cDNA-PCR), we tested routine serum samples and fresh-frozen plasma samples from the same bleeding from confirmed anti-HCV-positive blood donors. When primers from the NS3/NS4 region were used, HCV RNA was detected in fresh-frozen plasma from 67% of the donors, whereas positive results were obtained with only 50% of the serum samples that had been subjected to routine serological procedures. Analysis of the same samples with primers from the highly conserved 5'-terminal region (5'-TR) revealed an HCV RNA detection rate of 92% for both the routine and the fresh-frozen samples. However, the yield of the amplification product in routine samples was strongly reduced compared with that in fresh-frozen plasma. Comparison of both primer sets for cDNA-PCR showed that the 5'-TR primer set was 10- to 100-fold more effective in detecting HCV RNA. We also analyzed the effect of storage of whole EDTA-blood and serum at room temperature and at 4 degrees C on the yield of the amplification product. A rapid decline in detectable HCV RNA of 3 to 4 log units was observed within 14 days when whole blood and serum were stored at room temperature. By contrast, no perceptible reduction in the cDNA-PCR signal was found in freshly prepared serum stored at 4 degrees C. Images PMID:1333489

Cuypers, H T; Bresters, D; Winkel, I N; Reesink, H W; Weiner, A J; Houghton, M; van der Poel, C L; Lelie, P N

1992-01-01

206

Time dependent Monte Carlo simulations of H reactions on the diamond ^001(2 1) surface under chemical vapor deposition conditions  

E-print Network

species and the diamond surface. The growth process itself is initiated by the formation of a surfaceTime dependent Monte Carlo simulations of H reactions on the diamond ^001(2 1) surface under of a variety of H reactions at a diamond 001 2 1 surface exposed to gaseous atomic and molecular hydrogen under

207

Mechanisms of seed ageing under different storage conditions for Vigna radiata (L.) Wilczek: lipid peroxidation, sugar hydrolysis, Maillard reactions and their relationship to glass state transition  

Microsoft Academic Search

Two primary biochemical reactions in seed ageing (lipid peroxidation and non-enzymatic protein glyco- sylation with reducing sugars) have been studied under different seed water contents and storage tem- peratures, and the role of the glassy state in retard- ing biochemical deterioration examined. The viability loss of Vigna radiata seeds during storage is associ- ated with Maillard reactions; however, the contribu-

U. M. Narayana Murthy; Prakash P. Kumar; Wendell Q. Sun

2003-01-01

208

The reactions of N-methylformamide and N,N-dimethylformamide with OH and their photo-oxidation under atmospheric conditions: experimental and theoretical studies.  

PubMed

The reactions of OH radicals with CH3NHCHO (N-methylformamide, MF) and (CH3)2NCHO (N,N-dimethylformamide, DMF) have been studied by experimental and computational methods. Rate coefficients were determined as a function of temperature (T = 260-295 K) and pressure (P = 30-600 mbar) by the flash photolysis/laser-induced fluorescence technique. OH radicals were produced by laser flash photolysis of 2,4-pentanedione or tert-butyl hydroperoxide under pseudo-first order conditions in an excess of the corresponding amide. The rate coefficients obtained show negative temperature dependences that can be parameterized as follows: kOH+MF = (1.3 ± 0.4) × 10(-12) exp(3.7 kJ mol(-1)/(RT)) cm(3) s(-1) and kOH+DMF = (5.5 ± 1.7) × 10(-13) exp(6.6 kJ mol(-1)/(RT)) cm(3) s(-1). The rate coefficient kOH+MF shows very weak positive pressure dependence whereas kOH+DMF was found to be independent of pressure. The Arrhenius equations given, within their uncertainty, are valid for the entire pressure range of our experiments. Furthermore, MF and DMF smog-chamber photo-oxidation experiments were monitored by proton-transfer-reaction time-of-flight mass spectrometry. Atmospheric MF photo-oxidation results in 65% CH3NCO (methylisocyanate), 16% (CHO)2NH, and NOx-dependent amounts of CH2[double bond, length as m-dash]NH and CH3NHNO2 as primary products, while DMF photo-oxidation results in around 35% CH3N(CHO)2 as primary product and 65% meta-stable (CH3)2NC(O)OONO2 degrading to NOx-dependent amounts of CH3N[double bond, length as m-dash]CH2 (N-methylmethanimine), (CH3)2NNO (N-nitroso dimethylamine) and (CH3)2NNO2 (N-nitro dimethylamine). The potential for nitramine formation in MF photo-oxidation is comparable to that of methylamine whereas the potential to form nitrosamine and nitramine in DMF photo-oxidation is larger than for dimethylamine. Quantum chemistry supported atmospheric degradation mechanisms for MF and DMF are presented. Rate coefficients and initial branching ratios calculated with statistical rate theory based on molecular data from quantum chemical calculations at the CCSD(T*)-F12a/aug-cc-pVTZ//MP2/aug-cc-pVTZ level of theory show satisfactory agreement with the experimental results. It turned out that adjustment of calculated threshold energies by 0.2 to 8.8 kJ mol(-1) lead to agreement between experimental and predicted results. PMID:25687949

Bunkan, Arne Joakim C; Hetzler, Jens; Mikoviny, Tomáš; Wisthaler, Armin; Nielsen, Claus J; Olzmann, Matthias

2015-02-25

209

Green synthesis of Pd/CuO nanoparticles by Theobroma cacao L. seeds extract and their catalytic performance for the reduction of 4-nitrophenol and phosphine-free Heck coupling reaction under aerobic conditions.  

PubMed

We report the green synthesis of palladium/CuO nanoparticles (Pd/CuO NPs) using Theobroma cacao L. seeds extract and their catalytic activity for the reduction of 4-nitrophenol and Heck coupling reaction under aerobic conditions. The catalyst was characterized using the powder XRD, TEM, EDS, UV-vis and FT-IR. This method has the advantages of high yields, elimination of surfactant, ligand and homogeneous catalysts, simple methodology and easy work up. The catalyst can be recovered from the reaction mixture and reused several times without any significant loss of catalytic activity. PMID:25721860

Nasrollahzadeh, Mahmoud; Sajadi, S Mohammad; Rostami-Vartooni, Akbar; Bagherzadeh, Mojtaba

2015-06-15

210

Heterogeneous reaction of peroxyacetic acid and hydrogen peroxide on ambient aerosol particles under dry and humid conditions: kinetics, mechanism and implications  

NASA Astrophysics Data System (ADS)

Hydrogen peroxide (H2O2) and organic peroxides play important roles in the cycle of oxidants and the formation of secondary aerosols in the atmosphere. Recent field observations suggest that peroxyacetic acid (PAA, CH3C(O)OOH) is one of the most important organic peroxides in the atmosphere, whose budget is potentially related to the aerosols. Here we present the first laboratory measurements of the uptake coefficient of gaseous PAA and H2O2 onto the ambient fine particulate matter (PM2.5) as a function of relative humidity (RH) at 298 K. The results show that the PM2.5, which was collected in an urban area, can take up PAA and H2O2 at the uptake coefficient (?) of 10-4, and both ?PAA and ?H2O2 increase with increasing RH. However, ?PAA is more sensitive to the RH variation than is ?H2O2, which indicates that the enhanced uptake of peroxide compounds on PM2.5 under humid conditions is dominated by chemical processes rather than dissolution. Considering that mineral dust is one of the main components of PM2.5, we also determined the uptake coefficients of gaseous PAA and H2O2 on authentic Asian Dust Storm (ADS) and Arizona Test Dust (ATD) particles. Compared to ambient PM2.5, ADS shows a similar ? value and RH dependence in its uptake coefficient for PAA and H2O2, while ATD gives a negative dependence on RH. The present study indicates that in addition to the mineral dust in PM2.5, other components (e.g., inorganic soluble salts) are also important to the uptake of peroxide compounds. When the heterogeneous reaction of PAA on PM2.5 is considered, its atmospheric lifetime is estimated to be 3.3 h on haze days and 7.6 h on non-haze days, values which agree well with the field observed result.

Wu, Q. Q.; Huang, L. B.; Liang, H.; Zhao, Y.; Huang, D.; Chen, Z. M.

2015-02-01

211

Direct capture in the 130Sn(n,?)131Sn and 132Sn(n,?)133Sn reactions under r-process conditions  

NASA Astrophysics Data System (ADS)

The cross sections of the 130Sn(n,?)131Sn and 132Sn(n,?)133Sn reactions are calculated in the direct capture model at low energies below 1.5 MeV. Using recent data from (d,p) transfer experiments on 130Sn and 132Sn, it is possible to avoid global input parameters with their inherent uncertainties and to determine all inputs to the direct capture model by local adjustments. The calculated direct capture cross sections of 130Sn and 132Sn are almost identical and have uncertainties of less than a factor of 2. The stellar reaction rates NA?v show a slight increase with temperature. Finally, an estimate for the influence of low-lying resonances to the stellar reaction rates is given.

Mohr, Peter

2012-12-01

212

Measurement of mutation and repair in mammalian cells/action of specific mutagens and antimutagens/genome exposure reaction in cancer and other disease conditions. Final subcontract report, April 1, 1996- March 31, 1996  

SciTech Connect

This is the final report for the project dealing with the the measurement of mutation and repair in mammalian cells, action of specific mutagens and antimutagens, and genome exposure reaction in cancer and other disease conditions. The overall objectives of this research are threefold: to develop and improve methodology for measurement of mutation and repair in mammalian cells and to apply it to measurement of the effectiveness of mutagens, antimutagens, and other molecules to as to achieve greater power in prevention of cancer and genetic disease; to analyze theoretically and experimentally the action of specific mutagens and antimutagens; and to investigate the role of genome exposure reaction in cancer and other disease conditions to secure improve preventive and treatment modalities.

Puck, T.T. [Eleanor Roosevelt Institute for Cancer Research, Inc., Denver, CO (United States)

1996-09-01

213

Connecting the dots: Semi-analytical and random walk numerical solutions of the diffusion–reaction equation with stochastic initial conditions  

SciTech Connect

We study a system with bimolecular irreversible kinetic reaction A+B?? where the underlying transport of reactants is governed by diffusion, and the local reaction term is given by the law of mass action. We consider the case where the initial concentrations are given in terms of an average and a white noise perturbation. Our goal is to solve the diffusion–reaction equation which governs the system, and we tackle it with both analytical and numerical approaches. To obtain an analytical solution, we develop the equations of moments and solve them approximately. To obtain a numerical solution, we develop a grid-less Monte Carlo particle tracking approach, where diffusion is modeled by a random walk of the particles, and reaction is modeled by annihilation of particles. The probability of annihilation is derived analytically from the particles' co-location probability. We rigorously derive the relationship between the initial number of particles in the system and the amplitude of white noise represented by that number. This enables us to compare the particle simulations and the approximate analytical solution and offer an explanation of the late time discrepancies. - Graphical abstract:.

Paster, Amir, E-mail: paster@tau.ac.il [Environmental Fluid Mechanics Laboratories, Dept. of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN (United States); School of Mechanical Engineering, Tel Aviv University, Tel Aviv, 69978 (Israel); Bolster, Diogo [Environmental Fluid Mechanics Laboratories, Dept. of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN (United States); Benson, David A. [Hydrologic Science and Engineering, Colorado School of Mines, Golden, CO, 80401 (United States)

2014-04-15

214

Competing reactions in three-way catalytic converters: modelling of the NO x conversion maximum in the light-off curves under net oxidising conditions  

Microsoft Academic Search

Automobile exhaust gas conversion was simulated with a reactor model based on first principles. The monolithic reactor was modelled as adiabatically operating with a uniform flow distribution over the channels and with constant heat and mass transfer coefficients. The kinetic rate equations in the model were constructed from elementary step kinetics of the individual global reactions. The model predictions for

J. H. B. J. Hoebink; R. A. van Gemert; J. A. A. van den Tillaart; GBMM Marin

2000-01-01

215

CATALYST-FREE REACTIONS UNDER SOLVENT-FEE CONDITIONS: MICROWAVE-ASSISTED SYNTHESIS OF HETEROCYCLIC HYDRAZONES BELOW THE MELTING POINT OF NEAT REACTANTS  

EPA Science Inventory

The reaction of neat 5- or 8-oxobenzopyran-2(1H)-ones with a variety of aromatic and heteroaromatic hydrazines are remarkable accelerated upon irradiation in a household microwave oven in the absence of any catalyst, solid support or solvent thus providing an environmentally frie...

216

Aldehyde-alcohol reactions catalyzed under mild conditions by chromium(III) terephthalate metal organic framework (MIL-101) and phosphotungstic acid composites.  

PubMed

Porous materials based on chromium(III) terephthalate metal organic frameworks (MIL-101) and their composites with phosphotungstic acid (PTA) were studied as heterogeneous acid catalysts in aldehyde-alcohol reactions exemplified by acetaldehyde-phenol (A-P) condensation and dimethylacetal formation from benzaldehyde and methanol (B-M reaction). The MIL-101 was synthesized solvothermically in water, and the MIL101/PTA composite materials were obtained by either impregnation of the already prepared MIL-101 porous matrix with phosphotungstic acid solution or by solvothermic treatment of aqueous mixtures of Cr(NO(3))(3), and terephthalic and phosphotungstic acids. The MIL101/PTA materials appeared to be effective catalysts for both A-P and B-M reactions occurring at room temperature, with half-lives ranging from 0.5 h (A-P) to 1.5-2 h (B-M) and turnover numbers over 600 for A-P and over 2900 for the B-M reaction, respectively. A synergistic effect of the strong acidic moieties (PTA) addition to mildly acidic Brønsted and Lewis acid cites of the MIL-101 was observed with the MIL101/PTA composites. The ability of the PTA and MIL101/PTA materials to strongly absorb and condense acetaldehyde vapors was discovered, with the MIL101/PTA absorbing over 10-fold its dry weight of acetaldehyde condensate at room temperature. The acetaldehyde was converted rapidly to crotonaldehyde and higher-molecular-weight compounds while in contact with MIL-101 and MIL101/PTA materials. The stability of the MIL-101 and MIL101/PTA catalysts was assessed within four cycles of the 1-day alcohol-aldehyde reactions in terms of the overall catalyst recovery, PTA or Cr content, and reaction rate constants in each cycle. The loss of the catalyst over 4 cycles was approximately 10 wt % for all tested catalysts due to the incomplete recovery and minute dissolution of the components. The reaction rates in all cycles remained unchanged and the catalyst losses stopped after the third cycle. The developed MIL101/PTA composites appear to be feasible for industrial catalytic applications. PMID:22091761

Bromberg, Lev; Hatton, T Alan

2011-12-01

217

Studies in Reaction to Disability. XII: Structure of Attitudes toward the Physically Disabled; Disability Factor Scales--Amputation, Blindness, Cosmetic Conditions.  

ERIC Educational Resources Information Center

To describe and to develop instruments to measure attitudes toward amputees, the blind, and those with cosmetic conditions, three groups of subjects responded to one of three large pools of items tapping attitudes toward the three disability conditions. Three new groups of about 500 subjects of diverse demographic characteristics were given one of…

Siller, Jerome; And Others

218

The reaction rates of O2 with closed-shell and open-shell Al(x)? and Ga(x)? clusters under single-collision conditions: experimental and theoretical investigations toward a generally valid model for the hindered reactions of O2 with metal atom clusters.  

PubMed

In order to characterize the oxidation of metallic surfaces, the reactions of O2 with a number of Al(x)(-) and, for the first time, Ga(x)(-) clusters as molecular models have been investigated, and the results are presented here for x = 9-14. The rate coefficients were determined with FT-ICR mass spectrometry under single-collision conditions at O2 pressures of ~10(-8) mbar. In this way, the qualitatively known differences in the reactivities of the even- and odd-numbered clusters toward O2 could be quantified experimentally. To obtain information about the elementary steps, we additionally performed density functional theory calculations. The results show that for both even- and odd-numbered clusters the formation of the most stable dioxide species, [M(x)O2](-), proceeds via the less stable peroxo species, [M(x)(+)···O2(2-)](-), which contains M-O-O-M moieties. We conclude that the formation of these peroxo intermediates may be a reason for the decreased reactivity of the metal clusters toward O2. This could be one of the main reasons why O2 reactions with metal surfaces proceed more slowly than Cl2 reactions with such surfaces, even though O2 reactions with both Al metal and Al clusters are more exothermic than are reactions of Cl2 with them. Furthermore, our results indicate that the spin-forbidden reactions of (3)O2 with closed-shell clusters and the spin-allowed reactions with open-shell clusters to give singlet [M(x)(+)···O2(2-)](-) are the root cause for the observed even/odd differences in reactivity. PMID:24564371

Neumaier, Marco; Olzmann, Matthias; Kiran, Boggavarapu; Bowen, Kit H; Eichhorn, Bryan; Stokes, Sarah T; Buonaugurio, Angela; Burgert, Ralf; Schnöckel, Hansgeorg

2014-03-01

219

The role of Fe and redox conditions in olivine carbonation rates: An experimental study of the rate limiting reactions at 90 and 150 °C in open and closed systems  

NASA Astrophysics Data System (ADS)

The mechanisms and rates of olivine carbonation reactions have been the object of a number of studies, but the thermodynamic limitations and the kinetics of the elementary processes that control the overall reaction are still poorly understood and characterized. The main objective of this study is to probe the effect of Fe on the measured rates of olivine carbonation and its role in the formation of Si-rich surface layers, which can significantly inhibit olivine dissolution and limit the extent of the carbonation reaction. A series of batch and flow-through reactor experiments was conducted in pure water at 90 and 150 °C and under a CO2 partial pressure of 100 and 200 bar, using both a natural sample of Fe-bearing olivine (Fo88) and a synthetic sample of pure forsterite (Fo100). Experimental results show that Fe plays an ambivalent role in the carbonation rates of olivine. On one hand, the presence of Fe favors the formation of Fe-Si-rich protective layers at the interface between olivine and aqueous solution, slowing down the dissolution reaction and limiting the extent of carbonation, whereas pure silica coatings have little to no inhibiting effect on measured carbonation rates. On the other hand, Fe enhances olivine to carbonate conversion rates at low degrees of supersaturation, by promoting the formation of fast precipitating Mg-Fe carbonate solid solutions. The passivating properties of Fe-Si-rich layers originate from the strong Fe(III)-Si interaction and are linked to the permanence of oxidizing conditions in the aqueous fluid. As a consequence, under reducing conditions, olivine carbonation rates can be significantly increased by higher extents of dissolution and by the formation of ferroan magnesites (Mg,Fe)CO3, which nucleate faster than the pure Mg end-member. Forsterite and olivine carbonation reactions can be hindered by the formation of secondary Mg sheet-silicates but, at the conditions studied, the formation of such silicate phases was observed to be transitional and not affecting significantly the rates of carbonation at the end of one-month long experimental runs. This work presents new measurements of olivine carbonation rates and delivers relevant information that suggest new reference criteria for the assessment of the sequestration potential of CO2 repositories and the optimization of the mineral carbonation process in mafic and ultramafic rocks.

Saldi, Giuseppe D.; Daval, Damien; Morvan, Gilles; Knauss, Kevin G.

2013-10-01

220

Further studies of the temperature dependence of the rate coefficients for the reactions of OH with a series of ethers under simulated atmospheric conditions  

Microsoft Academic Search

The following temperature-dependent rate coefficients (k\\/cm3 molecule-1 s-1) of the reactions of hydroxyl radicals with aliphatic ethers have been determined over the temperature range 247–373 K by a competitive flow technique: diethyl ether,kOH=5.2×10-12 exp[(262±150)\\/T]; methyln-butyl ether,kOH=5.4×10-12 exp[(309±150)\\/T]; ethyln-butyl ether,kOH=7.3×10-12 exp[(335±150)\\/T]; di-n-butyl ether,kOH=5.5×10-12 exp[(502±150)\\/T] and di-n-pentyl ether,kOH=8.5×10-12 exp[(417±150)\\/T]. The data have been measured relative to the rate coefficientk(OH + 2,3-dimethylbutane)=6.2×10-12 cm3

Marco Semadeni; David W. Stocker; J. Alistair Kerr

1993-01-01

221

Reaction of ( SP4-2)-dichloro bis(2-hydroxyethylamine)platinum(II) with 5?GMP under simulated physiological conditions, a CZE-ESI-MS study  

Microsoft Academic Search

Capillary zone electrophoresis (CZE) has been applied for studying the binding behavior of the tumor inhibiting complex (SP-4-2)-dichlorobis(2-hydroxyethylamine)platinum(II) to the nucleotide 5?-GMP. Diode array UV detection enabled investigation of the time dependent behavior of 5?-GMP coordination under simulated physiological conditions. The binding behavior has shown to be dependent on the NaCl concentration as well as the pH value. For elucidation

Angelika Küng; Markus Galanski; Christian Baumgartner; Bernhard K. Keppler

2002-01-01

222

Lymphohematopoietic graft-vs.-host reactions can be induced without graft-vs.-host disease in murine mixed chimeras established with a cyclophosphamide-based nonmyeloablative conditioning regimen  

Microsoft Academic Search

Mixed hematopoietic chimerism can be induced in mice receiving allogeneic bone marrow transplantation (BMT) after nonmyeloablative host conditioning with depletion T cells with of anti-T cell monoclonal antibodies (mAbs), low-dose (3 Gy) total-body irradiation (TBI), and local thymic irradiation (7 Gy). These mice are specifically tolerant to donor and host antigens. When nontolerant donor T cells are given to chimeras

Michele R Pelot; Denise A Pearson; Kirsten Swenson; Guiling Zhao; Jessica Sachs; Yong-Guang Yang; Megan Sykes

1999-01-01

223

Reaction of uranyl nitrate with carboxylic diacids under hydrothermal conditions. Crystal structure of complexes with l(+)-tartaric and oxalic acids  

Microsoft Academic Search

l(+)-tartaric acid reacts with uranyl nitrate in the presence of KOH, under mild hydrothermal conditions, to give the complex [UO2(C4H4O6)(H2O)] (1), the first uranyl tartrate to be crystallographically characterized. Each tartrate ligand bridges three uranyl ions, one of them in chelating fashion through proximal carboxylate and hydroxyl groups. The resulting assemblage is two-dimensional, with the uranyl pentagonal bipyramidal coordination polyhedra

Pierre Thuéry

2007-01-01

224

Characterization of recombinant nitrile-specifier proteins (NSPs) of Arabidopsis thaliana: dependency on Fe(II) ions and the effect of glucosinolate substrate and reaction conditions.  

PubMed

Glucosinolates are plant secondary metabolites that are part of a plant defence system against pathogens and pests, the myrosinase-glucosinolate system, in which glucosinolates get activated by enzymic degradation through thioglucoside glucohydrolases called myrosinases. Epithiospecifier protein (ESP) and nitrile-specifier proteins (NSPs) divert myrosinase-catalyzed hydrolysis of a given glucosinolate from the formation of isothiocyanate to that of epithionitrile and/or nitrile. As the biological activity of glucosinolate hydrolysis products varies considerably, a detailed characterization of these specifier proteins is of utmost importance to understand their biological role. Therefore, the Arabidopsis thaliana AtNSP1, AtNSP2 and AtNSP5 and a supposed ancestor protein AtNSP-like1 were expressed in Escherichia coli and the activity of the purified recombinant proteins was tested in vitro on three highly different glucosinolates and compared to that of purified AtESP. As previously reported, only AtESP showed epithiospecifier activity on 2-propenylglucosinolate. We further confirmed that purified AtNSP1, AtNSP2 and AtNSP5, but not the ancestor AtNSP-like1 protein, show nitrile-specifier activity on 2-propenylglucosinolate and benzylglucosinolate. We now show for the first time that in vitro AtNSP1, AtNSP2 and AtNSP5 are able to generate nitrile from indol-3-ylmethylglucosinolate. We also tested the effect of different Fe(II) ion concentrations on the nitrile-specifier activity of purified AtNSP1, AtNSP2 and AtNSP5 on 2-propenylglucosinolate and benzylglucosinolate. AtNSP-related nitrile production was highly dependent on the presence of Fe(II) ions in the reaction assay. In the absence of added Fe(II) ions nitriles were only detected when benzylglucosinolate was incubated with AtNSP1. While AtNSP1 also exhibited overall higher nitrile-specifier activity than AtNSP2 and AtNSP5 at a given Fe(II) ion concentration, the pattern of nitrile formation in relation to Fe(II) ion concentrations depended on the AtNSP and the glucosinolate substrate. The pH of the solution also affected the reaction outcome, with a higher proportion of nitrile being produced at the higher pH for AtNSP2 and AtNSP5. PMID:22954730

Kong, Xiang Yi; Kissen, Ralph; Bones, Atle M

2012-12-01

225

Role of Anions and Reaction Conditions in the Preparation of Uranium(VI), Neptunium(VI), and Plutonium(VI) Borates  

SciTech Connect

U(VI), Np(VI), and Pu(VI) borates with the formula AnO{sub 2}[B{sub 8}O{sub 11}(OH){sub 4}] (An = U, Np, Pu) have been prepared via the reactions of U(VI) nitrate, Np(VI) perchlorate, or Pu(IV) or Pu(VI) nitrate with molten boric acid. These compounds are all isotypic and consist of a linear actinyl(VI) cation, AnO{sub 2}{sup 2+}, surrounded by BO{sub 3} triangles and BO{sub 4} tetrahedra to create an AnO{sub 8} hexagonal bipyramidal environment. The actinyl bond lengths are consistent with actinide contraction across this series. The borate anions bridge between actinyl units to create sheets. Additional BO{sub 3} triangles and BO{sub 4} tetrahedra extend from the polyborate layers and connect these sheets together to form a three-dimensional chiral framework structure. UV?vis?NIR absorption and fluorescence spectroscopy confirms the hexavalent oxidation state in all three compounds. Bond-valence parameters are developed for Np(VI).

Wang, Shuao; Villa, Eric M.; Diwu, J.; Alekseev, Evgeny V.; Depmeier, Wulf; Albrecht-Schmitt, Thomas E.

2011-01-01

226

Role of anions and reaction conditions in the preparation of uranium(VI), neptunium(VI), and plutonium(VI) borates.  

PubMed

U(VI), Np(VI), and Pu(VI) borates with the formula AnO(2)[B(8)O(11)(OH)(4)] (An = U, Np, Pu) have been prepared via the reactions of U(VI) nitrate, Np(VI) perchlorate, or Pu(IV) or Pu(VI) nitrate with molten boric acid. These compounds are all isotypic and consist of a linear actinyl(VI) cation, AnO(2)(2+), surrounded by BO(3) triangles and BO(4) tetrahedra to create an AnO(8) hexagonal bipyramidal environment. The actinyl bond lengths are consistent with actinide contraction across this series. The borate anions bridge between actinyl units to create sheets. Additional BO(3) triangles and BO(4) tetrahedra extend from the polyborate layers and connect these sheets together to form a three-dimensional chiral framework structure. UV-vis-NIR absorption and fluorescence spectroscopy confirms the hexavalent oxidation state in all three compounds. Bond-valence parameters are developed for Np(VI). PMID:21291194

Wang, Shuao; Villa, Eric M; Diwu, Juan; Alekseev, Evgeny V; Depmeier, Wulf; Albrecht-Schmitt, Thomas E

2011-03-21

227

Studying Biological Rhythms of Person's Skin-galvanic Reaction and Dynamics of Light Transmission by Isomeric Substance in Space Flight Conditions  

NASA Technical Reports Server (NTRS)

Intensity and amplitude of human functional systems and human most important organs are wavelike, rhythmic by nature. These waves have constant periodicity, phase and amplitude. The mentioned characteristics can vary, however their variations have a pronounced reiteration in the course of time. This indicates a hashing of several wave processes and their interference. Stochastic changes in wave processes characteristics of a human organism are explained either by 'pulsations' associated with hashing (superposition) of several wave processes and their interference, or by single influence of environmental physical factors on a human organism. Human beings have respectively periods of higher and lower efficiency, state of health and so on, depending not only of environmental factors, but also of 'internal' rhythmic factor. Sometimes peaks and falls periodicity of some or other characteristics is broken. Disturbance of steady-state biological rhythms is usually accompanied by reduction of activity steadiness of the most important systems of a human organism. In its turn this has an effect on organism's adaptation to changing living conditions as well as on general condition and efficiency of a human being. The latter factor is very important for space medicine. Biological rhythmology is a special branch of biology and medicine, it studies rhythmic activity mechanisms of organs, their systems, individuals and species. Appropriate researches were also carried out in space medicine.

Glushko, Vladimir

2004-01-01

228

CO2 Reaction Induced Wettability Alteration and its Impacts on CO2 Storage: Pore to Core Scale Reservoir Condition Experimental Studies  

NASA Astrophysics Data System (ADS)

Wettability of the mineral surfaces plays an important role in subsurface multiphase flow and transport. Wettability affects the capillary pressure-saturation (Pc- S) relations, relative permeability (kr) of each fluid phase, and relative phase occupancy in reservoir pores. Although wettability issues have been studied extensively in other fields, significant knowledge gaps remain when applying the existing understanding to geological carbon sequestration; due largely to the unique physical-chemical properties of supercritical (sc) CO2 relative to other common non-wetting fluids such as air and oil. Here, we report our recent progress on wettability alteration upon reaction with CO2 and the resulting differences in capillary trapping of CO2 versus air. (1) Pore Scale Studies. There are conflict predictions in the literature concerning the effect of wettability on capillary trapping; some find that larger contact angles lead to lower capillary trapping while others have found opposite behavior. We hypothesized that spontaneous imbibition becomes energetically unfavorable with decreased wettability, so that increased residual trapping of scCO2 should occur during the post-injection inbibition stage. We developed a laboratory high-pressure and elevated temperature microscopic-micromodel system that is capable of controlling fine scale capillary pressure of scCO2-brine, and enabled us to conduct imbibition under controlled capillary pressures at the pore scale. We found that the de-wetting enhanced scCO2 capillary trapping is significant. These results suggest that scCO2 reaction induced dewetting can result in higher degrees of CO2 residual trapping in the post-injection stage than previously predicted. (2) Core Scale Studies. Capillary scaling is used routinely to predict Pc(S) relations for scCO2-brine systems at field scale, based on relations measured with air-water or mercury porosimetry. However, scaling-based predictions for CO2-brine systems have not been fully tested. Current limitations include the fact that imbibition curves are seldom measured due to experimental difficulties in controlling capillary pressure, and wettability (contact angles) is usually unknown and applied as adjustable parameters. Applying a new laboratory system to accurately control Pc at high total P, and we measured Pc(S) of a homogeneous quartz sand (selected because its 'normal' hydraulic properties are very well constrained). Drainage and imbibition experiments were conducted to directly measure Pc(S) with air-brine, then with scCO2-brine. With scCO2, intermediate levels of S shifted to Pc values 30% to 90% lower than predicted based on scaling with interfacial tension. Capillary trapping of CO2 were measured at Pc = 0 during brine imbibition, with trapped volumes for scCO2 significantly greater than for trapped air. We conclude that the observed deviations from scaling predictions make predicting the hydraulic behavior of scCO2 in reservoirs more challenging, and that an understanding of scCO2-induced wettability change is needed.

Wan, J.; Tokunaga, T. K.; Kim, Y.; Jung, J.; Kim, T.; Dong, W.

2013-12-01

229

Allergic reactions  

MedlinePLUS

... more often in people who have a family history of allergies . Substances that don't bother most people ( ... reaction is getting worse. The person has a history of severe allergic reactions (check for a medical ID ...

230

Enzyme Reactions  

NSDL National Science Digital Library

This video shows an enzyme reaction lab. The teacher demonstrates how the enzyme, catalase, reacts with hydrogen peroxide (a substrate found in cells). The teacher first demonstrates a normal enzyme reaction. He or she then goes on to show how manipulating temperature and pH will affect the reaction of an enzyme.

Minerva Deland School

2011-10-03

231

Special Reactions  

NSDL National Science Digital Library

The basics of chemical reactions were covered in the first chemistry book, including how to write and balance chemical equations that represent those reactions. There is also a quick review of chemical reactions in Chapter 1 of this book. We're going to d

William C. Robertson, Ph.D.

2010-03-01

232

Chemical Reactions  

NSDL National Science Digital Library

We don't often stop to think about it, but underlying many of our everyday activities are chemical reactions. From the cooking of an egg to the growth of a child, chemical reactions make things happen. Although many of the reactions that support our lives

National Science Teachers Association (NSTA)

2009-05-01

233

Reaction efficiency effects on binary chemical reactions  

NASA Astrophysics Data System (ADS)

We study the effect of the variation of reaction efficiency in binary reactions. We use the well-known A + B ? 0 model, which has been extensively studied in the past. We perform simulations on this model where we vary the efficiency of reaction, i.e., when two particles meet they do not instantly react, as has been assumed in previous studies, but they react with a probability ?, where ? is in the range 0 < ? < 1. Our results show that at small ? values the system is reaction limited, but as ? increases it crosses over to a diffusion limited behavior. At early times, for small ? values, the particle density falls slower than for larger ? values. This fall-off goes over a crossover point, around the value of ? = 0.50 for high initial densities. Under a variety of conditions simulated, we find that the crossover point was dependent on the initial concentration but not on the lattice size. For intermediate and long times simulations, all ? values (in the depleted reciprocal density versus time plot) converge to the same behavior. These theoretical results are useful in models of epidemic reactions and epidemic spreading, where a contagion from one neighbor to the next is not always successful but proceeds with a certain probability, an analogous effect with the reaction probability examined in the current work.

Lazaridis, Filippos; Savara, Aditya; Argyrakis, Panos

2014-09-01

234

Reaction pathways in coprocessing  

SciTech Connect

The reaction pathways in the catalytic coprocessing of Illinois No. 6 and Wyodak coals with Lloydminster and Hondo resids have been investigated at low and high severity. The reactions of a selected set of representative compounds including several different hydrocarbons as well as phenols and alkylated phenols have also been studied to gain perspective on the manner in which structural elements of complex coal molecules transform under the reaction conditions. The results of these investigations will be discussed in this presentation which will focus on the transformations that take place to fragment the very complex coal molecules.

Stock, L.M.; Ettinger, M.D.; Gatsis, J.G. [Univ. of Chicago, IL (United States)

1995-12-01

235

Reaction rates in accreting neutron stars  

Microsoft Academic Search

Temperature conditions in the deep layers of neutron star crusts can be affected by the occurence of pycnonuclear reaction processes. To simulate the fate of accreted matter in neutron star binary systems, we have calculated pycnonuclear reactions for the ashes of rp-process nucleosynthesis at extreme density conditions. Building on the work of Salpeter and Van Horn, nuclear reactions between very

Mary Beard; Michael Wiescher

2002-01-01

236

Reaction Time  

NSDL National Science Digital Library

In this activity, learners explore reaction time and challenge themselves to improve their coordination. Do you want to move faster? Catch that ball that you never seem to see in time? Use a simple test to help you improve your reaction (or response) time.

2012-06-26

237

Named Reactions  

NSDL National Science Digital Library

This Web site lists 95 of the most important named reactions in organic chemistry. Each is linked to a Web page that gives the primary reference and equations for one or more recent literature examples that illustrate the use of the reaction.

238

Chemical Reactions  

NSDL National Science Digital Library

We are going go over a general view of reactions to prepare us for our unit on Chemical Reactions! Have fun learning! WARNING: If you are caught looking at ANY other site, without permission, you will be sent to the ALC, and you will not participate in any other computer activities for the rest of the year. Get your worksheet and begin! Overview Take this quiz and have me come over and sign off on your worksheet when you have completed the quiz! Overview Quiz Next let's take a look at what effect the rate of a chemical reaction. Rates of Reactions Another quiz, another check off by me! Rates of Reactions Quiz Now how do we measure how fast a ...

Mrs. Hicken

2009-05-04

239

FACILITATED CHEMICAL SYNTHESIS UNDER ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

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

240

Reaction Time Sound Explanation  

NSDL National Science Digital Library

This experiment presents auditory stimuli and requires the participant to respond after hearing target stimuli under different conditions. This experiment gives students the opportunity to determine whether their reaction times are reliably different for tasks that require slightly different decisions. This page provides guidance for faculty who wish to incorporate this activity into their classroom.

241

Fundamental reaction pathways during coprocessing  

SciTech Connect

The objective of this research was to investigate the fundamental reaction pathways in coal petroleum residuum coprocessing. Once the reaction pathways are defined, further efforts can be directed at improving those aspects of the chemistry of coprocessing that are responsible for the desired results such as high oil yields, low dihydrogen consumption, and mild reaction conditions. We decided to carry out this investigation by looking at four basic aspects of coprocessing: (1) the effect of fossil fuel materials on promoting reactions essential to coprocessing such as hydrogen atom transfer, carbon-carbon bond scission, and hydrodemethylation; (2) the effect of varied mild conditions on the coprocessing reactions; (3) determination of dihydrogen uptake and utilization under severe conditions as a function of the coal or petroleum residuum employed; and (4) the effect of varied dihydrogen pressure, temperature, and residence time on the uptake and utilization of dihydrogen and on the distribution of the coprocessed products. Accomplishments are described.

Stock, L.M.; Gatsis, J.G. (Chicago Univ., IL (United States). Dept. of Chemistry)

1992-12-01

242

Diamine ligands in copper-catalyzed reactions  

E-print Network

The utility of copper-mediated cross-coupling reactions has been significantly increased by the development of mild reaction conditions and the ability to employ catalytic amounts of copper. The use of diamine-based ligands ...

Surry, David S.

243

Drug Reactions  

MedlinePLUS

Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions. One problem is ...

244

Enzyme Reactions  

NSDL National Science Digital Library

The enzyme reaction rate activity allows students to simulate the effects of variables such as temperature and pH on the reaction rate of the enzyme catalase. This computer simulation is best used after the students have done a wet lab experiment. The value of the simulation is that it requires the students to interpret and analyze the graphical representation of data and it enables the running of mutiple experiments in a short amount of time.

Maryland Virtual High School

245

Geometric description of chemical reactions  

E-print Network

We use the formalism of Geometrothermodynamics to describe chemical reactions in the context of equilibrium thermodynamics. Any chemical reaction in a closed system is shown to be described by a geodesic in a $2-$dimensional manifold that can be interpreted as the equilibrium space of the reaction. We first show this in the particular cases of a reaction with only two species corresponding to either two ideal gases or two van der Waals gases. We then consider the case of a reaction with an arbitrary number of species. The initial equilibrium state of the geodesic is determined by the initial conditions of the reaction. The final equilibrium state, which follows from a thermodynamic analysis of the reaction, is shown to correspond to a coordinate singularity of the thermodynamic metric which describes the equilibrium manifold.

Hernando Quevedo; Diego Tapias

2013-01-02

246

Facile electrochemical co-deposition of a graphene-cobalt nanocomposite for highly efficient water oxidation in alkaline media: direct detection of underlying electron transfer reactions under catalytic turnover conditions.  

PubMed

A facile electrochemical co-deposition method has been developed for the fabrication of graphene-cobalt nanocomposite modified electrodes that achieve exceptionally efficient water oxidation in highly alkaline media. In the method reported, a graphene-cobalt nanocomposite film was deposited electrochemically from a medium containing 1 mg ml(-1) graphene oxide, 0.8 mM cobalt nitrate and 0.05 M phytic acid (pH 7). The formation of the nanocomposite film was confirmed using electrochemical, Raman spectroscopic and scanning electron microscopic techniques. The nanocomposite film exhibits excellent activity and stability towards water oxidation to generate oxygen in 1 M NaOH aqueous electrolyte media. A turn over frequency of 34 s(-1) at an overpotential of 0.59 V and a faradaic efficiency of 97.7% were deduced from analysis of data obtained by rotating ring disk electrode voltammetry. Controlled potential electrolysis data suggests that the graphene supported catalyst exhibits excellent stability under these harsh conditions. Phytate anion acts as stabilizer for the electrochemical formation of cobalt nanoparticles. Fourier transformed ac voltammetry allowed the redox chemistry associated with catalysis to be detected directly under catalytic turnover conditions. Estimates of formal reversible potentials obtained from this method and derived from the overall reactions 3Co(OH)2 + 2OH(-) ? Co3O4 + 4H2O + 2e(-), Co3O4 + OH(-) ? 3CoOOH + e(-) and CoOOH + OH(-) ? CoO2 + H2O + e(-) are 0.10, 0.44 and 0.59 V vs. Ag/AgCl, respectively. PMID:25093585

Guo, Si-Xuan; Liu, Yuping; Bond, Alan M; Zhang, Jie; Esakki Karthik, P; Maheshwaran, I; Senthil Kumar, S; Phani, K L N

2014-09-21

247

"Greening up" the Suzuki Reaction  

ERIC Educational Resources Information Center

This article describes the rapid, green synthesis of a biaryl compound (4-phenylphenol) via a Pd(0)-catalyzed Suzuki cross-coupling reaction in water. Mild reaction conditions and operational simplicity makes this experiment especially amenable to both mid- and upper-level undergraduates. The methodology exposes students to purely aqueous…

Aktoudianakis, Evangelos; Chan, Elton; Edward, Amanda R.; Jarosz, Isabel; Lee, Vicki; Mui, Leo; Thatipamala, Sonya S.; Dicks, Andrew P.

2008-01-01

248

Environmental Conditions Environmental Conditions  

E-print Network

in habitat conditions. Stream flows, water temperatures, substrate characteristics and other combined watershed processes and human activities that influence flow, water quality, upland and riparian conditions feet in one mile The watershed includes approximately 760 miles of perennial streams and 1,440 miles

249

SABIO Reaction Kinetics Database (Homepage)  

NSDL National Science Digital Library

The SABIO-RK (System for the Analysis of Biochemical Pathways - Reaction Kinetics) is a web-based application based on the SABIO relational database that contains information about biochemical reactions, their kinetic equations with their parameters, and the experimental conditions under which these parameters were measured. It aims to support modellers in the setting-up of models of biochemical networks, but it is also useful for experimentalists or researchers with interest in biochemical reactions and their kinetics. Information about reactions and their kinetics can be exported in SBML (Systems Biology Mark-Up Language) format.

Scientific Databases and Visualization Group at the EML Research in Heidelberg, Germany

250

Cutaneous reactions to vaccinations.  

PubMed

Vaccinations are important for infectious disease prevention; however, there are adverse effects of vaccines, many of which are cutaneous. Some of these reactions are due to nonspecific inflammation and irritation at the injection site, whereas other reactions are directly related to the live attenuated virus. Rarely, vaccinations have been associated with generalized hypersensitivity reactions, such as erythema multiforme, Stevens-Johnson syndrome, urticaria, acute generalized exanthematous pustulosis, and drug hypersensitivity syndrome. The onset of certain inflammatory dermatologic conditions, such as lichen planus, granuloma annulare, and pemphigoid, were reported to occur shortly after vaccine administration. Allergic contact dermatitis can develop at the injection site, typically due to adjuvant ingredients in the vaccine, such as thimerosal and aluminum. Vaccinations are important to promote development of both individual and herd immunity. Although most vaccinations are considered relatively safe, there may be adverse effects associated with any vaccine. Cutaneous manifestations make up a large portion of the types of reactions associated with vaccines. There are many different reasons for the development of a cutaneous reaction to a vaccination. Some are directly related to the injection of a live attenuated virus, such as varicella or vaccinia (for immunity to smallpox), whereas others cause more nonspecific erythema and swelling at the injection site, as a result of local inflammation or irritation. Vaccinations have also been associated in rare reports with generalized hypersensitivity reactions, such as erythema multiforme, Stevens-Johnson syndrome, urticaria, acute generalized exanthematous pustulosis, and drug hypersensitivity syndrome. There have been case reports associating the administration of a vaccine with the new onset of a dermatologic condition, such as lichen planus, granuloma annulare, and Sweet syndrome. Finally, allergic contact dermatitis can develop at the injection site, typically due to adjuvant ingredients in the vaccine, such as thimerosal and aluminum. PMID:25889134

Rosenblatt, Adena E; Stein, Sarah L

2015-01-01

251

Reaction Time  

NSDL National Science Digital Library

This lab is not an inquiry activity. There are some students whose reaction times will not allow them to catch a 12 inch ruler. They may use a dowel, stick, strip of cardboard, etc. Although the students are led to believe that the point of the lab is to

Michael Horton

2009-05-30

252

Reaction Time  

NSDL National Science Digital Library

In this activity, learners conduct an experiment to test how fast they can react. Learners try to catch a piece of paper with a ruler printed on it (or a ruler) as quickly as they can. Learners collect data and compare the reaction times of friends and family.

WGBH Boston

2003-01-01

253

Proton Transfer Reaction Time-of-Flight Mass Spectrometric (PTR-TOF-MS) determination of volatile organic compounds (VOCs) emitted from a biomass fire developed under stable nocturnal conditions  

NASA Astrophysics Data System (ADS)

Combustion of solid and liquid fuels is the largest source of potentially toxic volatile organic compounds (VOCs), which can strongly affect health and the physical and chemical properties of the atmosphere. Among combustion processes, biomass burning is one of the largest at global scale. We used a Proton Transfer Reaction “Time-of-Flight” Mass Spectrometer (PTR-TOF-MS), which couples high sensitivity with high mass resolution, for real-time detection of multiple VOCs emitted by burned hay and straw in a barn located near our measuring station. We detected 132 different organic ions directly attributable to VOCs emitted from the fire. Methanol, acetaldehyde, acetone, methyl vinyl ether (MVE), acetic acid and glycolaldehyde dominated the VOC mixture composition. The time-course of the 25 most abundant VOCs, representing ?85% of the whole mixture of VOCs, was associated with that of carbon monoxide (CO), carbon dioxide (CO2) and methane (CH4) emissions. The strong linear relationship between the concentrations of pyrogenic VOC and of a reference species (i.e. CO) allowed us to compile a list of emission ratios (ERs) and emission factors (EFs), but values of ER (and EF) were overestimated due to the limited mixing of the gases under the stable (non-turbulent) nocturnal conditions. In addition to the 25 most abundant VOCs, chemical formula and concentrations of the residual, less abundant VOCs in the emitted mixture were also estimated by PTR-TOF-MS. Furthermore, the evolution of the complex combustion process was described on the basis of the diverse types of pyrogenic gases recorded.

Brilli, Federico; Gioli, Beniamino; Ciccioli, Paolo; Zona, Donatella; Loreto, Francesco; Janssens, Ivan A.; Ceulemans, Reinhart

2014-11-01

254

A 3D-RISM-SCF method with dual solvent boxes for a highly polarized system: application to 1,6-anhydrosugar formation reaction of phenyl ?- and ?-D-glucosides under basic conditions.  

PubMed

One of the difficulties in application of the usual reference interaction site model self-consistent field (RISM-SCF) method to a highly polarized and bulky system arises from the approximate evaluation of electrostatic potential (ESP) with pure point charges. To improve this ESP evaluation, the ESP near a solute is directly calculated with a solute electronic wavefunction, that distant from a solute is approximately calculated with solute point charges, and they are connected with a switching function. To evaluate the fine solvation structure near the solute by incorporating the long-range solute-solvent Coulombic interaction with low computational cost, we introduced the dual solvent box protocol; one small box with the fine spacing is employed for the first and the second solvation shells and the other large box with the normal spacing is employed for long-range solute-solvent interaction. The levoglucosan formation from phenyl ?- and ?-d-glucosides under basic conditions is successfully inspected by this 3D-RISM-SCF method at the MP2 and SCS-MP2 levels, though the 1D-RISM-SCF could not be applied to this reaction due to the presence of highly polarized and bulky species. This 3D-RISM-SCF calculation reproduces the experimentally reported higher reactivity of the ?-anomer. The 3D-RISM-SCF-calculated activation free energy for the ?-anomer is closer to the experimental value than the PCM-calculated one. Interestingly, the solvation effect increases the difference in reactivity between these two anomers. The reason is successfully elucidated with 3D-RISM-SCF-calculated microscopic solvation structure and decomposition analysis of solute-solvent interaction. PMID:23525092

Aono, Shinji; Hosoya, Takashi; Sakaki, Shigeyoshi

2013-05-01

255

Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles  

NASA Technical Reports Server (NTRS)

Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

Liechty, Derek S.; Lewis, Mark J.

2010-01-01

256

Subdiffusion-reaction processes with A ?B reactions versus subdiffusion-reaction processes with A +B?B reactions  

NASA Astrophysics Data System (ADS)

We consider the subdiffusion-reaction process with reactions of a type A +B?B (in which particles A are assumed to be mobile, whereas B are assumed to be static) in comparison to the subdiffusion-reaction process with A ?B reactions which was studied by Sokolov, Schmidt, and Sagués [Phys. Rev. E 73, 031102 (2006), 10.1103/PhysRevE.73.031102]. In both processes a rule that reactions can only occur between particles which continue to exist is taken into account. Although in both processes a probability of the vanishing of particle A due to a reaction is independent of both time and space variables (assuming that in the system with the A +B?B reactions, particles B are distributed homogeneously), we show that subdiffusion-reaction equations describing these processes as well as their Green's functions are qualitatively different. The reason for this difference is as follows. In the case of the former reaction, particles A and B have to meet with some probability before the reaction occurs in contradiction with the case of the latter reaction. For the subdiffusion process with the A +B?B reactions we consider three models which differ in some details concerning a description of the reactions. We base the method considered in this paper on a random walk model in a system with both discrete time and discrete space variables. Then the system with discrete variables is transformed into a system with both continuous time and continuous space variables. Such a method seems to be convenient in analyzing subdiffusion-reaction processes with partially absorbing or partially reflecting walls. The reason is that within this method we can determine Green's functions without a necessity of solving a fractional differential subdiffusion-reaction equation with boundary conditions at the walls. As an example, we use the model to find the Green's functions for a subdiffusive reaction system (with the reactions mentioned above), which is bounded by a partially absorbing wall. This example shows how the model can be used to analyze the subdiffusion-reaction process in a system with partially absorbing or reflecting thin membranes. Employing a simple phenomenological model, we also derive equations related to the reaction parameters used in the considered models.

Koszto?owicz, Tadeusz; Lewandowska, Katarzyna D.

2014-09-01

257

Intermolecular reaction screening as a tool for reaction evaluation.  

PubMed

Synthetic organic chemistry underpins many scientific disciplines. The development of new synthetic methods proceeds with the ultimate intention of providing access to novel structural motifs or providing safer, increasingly efficient, or more economical chemical reactions. To facilitate the identification and application of new methods in solving real synthetic problems, this Account will highlight the benefits of providing a fuller picture of both the scope and limitations of new reactions, with a primary focus on the evaluation of functional group tolerance and stability of a reaction using intermolecular screens. This Account will begin with a discussion on reaction evaluation, specifically considering the suitability of a given reaction for application in target-oriented synthesis. A comparison of desirable and essential criteria when choosing a reaction is given, and a short discussion on the value of negative and qualitative data is provided. The concept of intermolecular reaction screening will be introduced, and a direct comparison with a traditional substrate scope highlights the benefits and limitations of each and thus the complementary nature of these approaches. In recent years, a number of ad hoc applications of intermolecular screens to evaluate the functional group tolerance of a reaction or the stability of functional groups to a given set of reaction conditions have been reported, and will be discussed. More recently, we have developed a formal high-throughput intermolecular screening protocol that can be utilized to rapidly evaluate new chemical reactions. This simple and rapid protocol enables a much broader evaluation of a reaction in terms of functional group tolerance and the stability of chemical motifs to the reaction conditions than is feasible with a typical reaction scope. The development, evaluation, and application of this method within our group will be discussed in detail, with both the potential benefits and limitations highlighted and discussed. In addition, we will discuss more recent applications of intermolecular screens from both industrial and academic groups. Modifications in protocols and applications will be highlighted, including problem based evaluations, assessment of biomolecule compatibility, establishment of relative rate data, and the identification of new reactivity. Such screens have been applied in diverse chemistries including C-H functionalization reactions, frustrated Lewis-pair-catalyzed hydrogenations, heterogeneous catalysis, photoredox catalysis, enantioselective organocatalysis, and polymer science. We feel that the application of intermolecular screens to such a diversity of reactions highlights the practical simplicity of such screens. A summary of the applications and potential utility of intermolecular reaction evaluation is provided. PMID:25699585

Collins, Karl D; Glorius, Frank

2015-03-17

258

Incidents of chemical reactions in cell equipment  

SciTech Connect

Strongly exothermic reactions can occur between equipment structural components and process gases under certain accident conditions in the diffusion enrichment cascades. This paper describes the conditions required for initiation of these reactions, and describes the range of such reactions experienced over nearly 50 years of equipment operation in the US uranium enrichment program. Factors are cited which can promote or limit the destructive extent of these reactions, and process operations are described which are designed to control the reactions to minimize equipment damage, downtime, and the possibility of material releases.

Baldwin, N.M.; Barlow, C.R. [Uranium Enrichment Organization, Oak Ridge, TN (United States)

1991-12-31

259

Formation of 5- and 6-methyl-1H-indene (C10H10) via the reactions of the para-tolyl radical (C6H4CH3) with allene (H2CCCH2) and methylacetylene (HCCCH3) under single collision conditions.  

PubMed

The reactions of the p-tolyl radical with allene-d4 and methylacetylene-d4 as well as of the p-tolyl-d7 radical with methylacetylene-d1 and methylacetylene-d3 were carried out under single collision conditions at collision energies of 44-48 kJ mol(-1) and combined with electronic structure and statistical (RRKM) calculations. Our experimental results indicated that the reactions of p-tolyl with allene-d4 and methylacetylene-d4 proceeded via indirect reaction dynamics with laboratory angular distributions spanning about 20° in the scattering plane. As a result, the center-of-mass translational energy distribution determined a reaction exoergicity of 149 ± 28 kJ mol(-1) and exhibited a pronounced maximum at around 20 to 30 kJ mol(-1). In addition, the center-of-mass angular flux distribution T(?) depicted a forward-backward symmetry and indicated geometric constraints upon the decomposing complex(es). Combining with calculations, these results propose that the bicyclic polycyclic aromatic hydrocarbons, 6-methyl-1H-indene () and 5-methyl-1H-indene (), are formed under single collision conditions at fractions of at least 85% in both reaction systems. For the p-tolyl-methylacetylene system, experiments with partially deuterated reactants also reveal the formation of a third isomer (1-methyl-4-(1-propynyl)benzene) at levels of 5-10%, highlighting the importance in conducting reactions with partially deuterated reactants to elucidate the underlying reaction pathways comprehensively. PMID:25806373

Yang, Tao; Parker, Dorian S N; Dangi, Beni B; Kaiser, Ralf I; Mebel, Alexander M

2015-04-01

260

Diamine Ligands in Copper-Catalyzed Reactions  

PubMed Central

The utility of copper-mediated cross-coupling reactions has been significantly increased by the development of mild reaction conditions and the ability to employ catalytic amounts of copper. The use of diamine-based ligands has been important in these advances and in this review we discuss these systems, including the choice of reaction conditions and applications in the synthesis of pharmaceuticals, natural products and designed materials. PMID:22384310

Surry, David S.

2012-01-01

261

Metal Reactions  

NSDL National Science Digital Library

This is written as a static display, but can easily be adapted to a hands-on experiment for learners to conduct. Sodium phosphate, a clear colorless solution, is combined with six different metal ion solutions. Each metal (copper, nickel, iron, silver, cobalt, and barium) forms a different color and texture precipitate. Learners discover that a chemical reaction can be identified by a color change, and formation of a precipitate. They also learn that metals can be identified by their precipitates. For safety reasons, this activity should be conducted as a demonstration for younger audiences.

Oregon Museum of Science and Industry

1997-01-01

262

Thermonuclear reaction rates. II  

Microsoft Academic Search

A revision and updating of charged particle reactions involving nuclei ; with A less than or approximately equal to 30, except for the $sup ; 2$H(d,$gamma$)⁴He reaction whose reaction rate is very uncertain, is ; presented. Reactions involving neutrons are treated as neutron-producing ; reactions but factors for calculating the reverse reaction rate are provided for ; all reactions. The

W. A. Fowler; G. R. Caughlan; B. A. Zimmerman

1975-01-01

263

Classical Conditioning  

NSDL National Science Digital Library

!!Classical Conditioning!! Classical conditioning is the use of Pavlovian conditioning procedures where a neutral stimulus becomes capable of evoking a response through pairing with an unconditioned stimulus. Click the link below to get an introduction into classical conditioning. Introduction to Classical Conditioning Now that you\\'ve been introduced to classical conditioning, view the clip at the link below, ...

Mrs. Palacios, Miss Miller, Mr. Rowser

2008-04-01

264

Catalytic Organometallic Reactions of Ammonia  

PubMed Central

Until recently, ammonia had rarely succumbed to catalytic transformations with homogeneous catalysts, and the development of such reactions that are selective for the formation of single products under mild conditions has encountered numerous challenges. However, recently developed catalysts have allowed several classes of reactions to create products with nitrogen-containing functional groups from ammonia. These reactions include hydroaminomethylation, reductive amination, alkylation, allylic substitution, hydroamination, and cross-coupling. This Minireview describes examples of these processes and the factors that control catalyst activity and selectivity. PMID:20857466

Klinkenberg, Jessica L.

2012-01-01

265

Stability of sharp reaction fronts in porous rocks and implications for non-sharp reaction zones  

NASA Astrophysics Data System (ADS)

The flow of reactive fluids in the subsurface, like for instance acids, may create reaction fronts. A sharp reaction front is an idealization of the narrow zone where the reaction takes place. Narrow reaction zones are studied with a one-component reaction transport model, where a first order reaction changes the porosity. The porosity field is coupled to the permeability field, where an increasing porosity leads to an increasing permeability. Therefore, the reaction has a feed-back on the flow field. We have derived 1D approximate solutions for the change in concentration and porosity across the reaction zone. These solutions are used to derive a condition for reaction fronts to be narrow. The condition gives a minimum reaction rate necessary for 90% of the reaction to be restricted to the given area. Sharp fronts are idealizations of narrow fronts that are more amendable for analytical treatment. A condition has recently been derived for the stability of sharp reaction fronts in homogeneous porous medium using linear stability analysis. The condition gives that a perturbation of a flat reaction front of any wave-length becomes unstable if the permeability behind the front increases. The front instability grows faster for short wave lengths than for long wave lengths. Similarly, the perturbations of the front will die out if the permeability behind the front decreases, and short wave length perturbations will die out faster than long wave length perturbations. It is a condition that applies for both 2D and 3D porous media. Numerical experiments are shown that demonstrate the front stability criterion, when the fronts are narrow, but not sharp. The sharp front approximation turns out to be useful for the interpretation of reactions that are not sufficiently fast to give narrow reaction zones, when the reaction alters the porosity- and the permeability fields. Dissolution is an important example of reactions that increase the porosity and therefore the permeability. Numerical modelling shows that the flow field becomes directed towards tip of the reaction zone, because of the increased permeability towards the tip. This becomes the place where the Darcy flux is largest and where the reaction runs fastest. The largest Darcy flux at the tip implies a larger supply of reactive fluid at the tip than for the other parts of the reaction zone. Dissolution reactions are therefore unstable reactions, and they may be difficult to predict even though the data for the reaction kinetics is accurate. The same argumentation leads to that precipitation reaction propagate in a stable manner, since the precipitated minerals direct the flow away towards areas that have received less precipitation.

Wangen, Magnus

2014-05-01

266

Fast pyrolysis of radiata pine in a bench scale plant with a fluidized bed: Influence of a char separation system and reaction conditions on the production of bio-oil  

Microsoft Academic Search

Sawdust of radiata pine was pyrolyzed in a bench scale plant equipped mainly with a fluidized bed, a char separation system, and a series of quenching columns. In the experiments, the influence of reaction temperature and feed size on the yield of bio-oil was investigated. In addition, the efficiency of the char separation system, which was composed of a cyclone,

Bo-Sung Kang; Kyung Hae Lee; Hyun Ju Park; Young-Kwon Park; Joo-Sik Kim

2006-01-01

267

Low Energy Nuclear Reactions?  

E-print Network

After an introduction to the controversial problem of Low Energy Nuclear Reactions (LENR) catalyzed by neutrons on metallic hydride surfaces we present the results of an experiment, made in collaboration with ENEA Labs in Frascati, to search neutrons from plasma discharges in electrolytic cells. The negative outcome of our experiment goes in the direction of ruling out those theoretical models expecting LENR to occur in condensed matter systems under specific conditions. Our criticism on the theoretical foundations of such models will also be presented.

CERN. Geneva; Faccini, R.

2014-01-01

268

Microphotometric measurement of initial maximum reaction rates in quantitative enzyme histochemistry in situ  

Microsoft Academic Search

Summary  Final reaction product formation was recorded microphotometrically for succinate dehydrogenase in cross-sectioned muscle fibres at initial rate conditions and during prolonged incubations. Incubations with gel films and aqueous reaction medium both showed a decline of reaction rates. Maximum reaction rates could only be determined at initial rate conditions during the first minute of the incubation. Reaction rates recorded in different

Dirk Pette; Universitfit Konstanz

1981-01-01

269

Chromosomal Conditions  

MedlinePLUS

... 150 babies is born with a chromosomal condition. Down syndrome is an example of a chromosomal condition. Because ... all pregnant women be offered prenatal tests for Down syndrome and other chromosomal conditions. A screening test is ...

270

Integrated Microreactors for Reaction Automation: New Approaches to Reaction Development  

NASA Astrophysics Data System (ADS)

Applications of microsystems (microreactors) in continuous-flow chemistry have expanded rapidly over the past two decades, with numerous reports of higher conversions and yields compared to conventional batch benchtop equipment. Synthesis applications are enhanced by chemical information gained from integrating microreactor components with sensors, actuators, and automated fluid handling. Moreover, miniaturized systems allow experiments on well-defined samples at conditions not easily accessed by conventional means, such as reactions at high pressure and temperatures. The wealth of synthesis information that could potentially be acquired through use of microreactors integrated with physical sensors and analytical chemistry techniques for online reaction monitoring has not yet been well explored. The increased efficiency resulting from use of continuous-flow microreactor platforms to automate reaction screening and optimization encourages a shift from current batchwise chemical reaction development to this new approach. We review advances in this new area and provide application examples of online monitoring and automation.

McMullen, Jonathan P.; Jensen, Klavs F.

2010-07-01

271

Reactions of stabilized Criegee Intermediates  

NASA Astrophysics Data System (ADS)

Carbonyl oxides (Criegee intermediates) were proposed as key intermediates in the gas phase ozonolysis of alkenes in 1975 by Rudolf Criegee. Despite the importance of ozonolysis in atmospheric chemistry, direct observation of these intermediates remained elusive, with only indirect experimental evidence for their role in the oxidation of hydrocarbons, e.g. through scavenging experiments. Direct experimental observation of stabilized CI has only been achieved since 2008. Since then, a concerted effort using experimental and theoretical means is in motion to characterize the chemistry and kinetics of these reactive intermediates. We present the results of theoretical investigations of the chemistry of Criegee intermediates with a series of coreactants which may be of importance in the atmosphere, in experimental setups, or both. This includes the CI+CI cross-reaction, which proceeds with a rate coefficient near the collision limit and can be important in experimental conditions. The CI + alkene reactions show strong dependence of the rate coefficient depending on the coreactants, but is generally found to be rather slow. The CI + ozone reaction is sufficiently fast to occur both in experiment and the free troposphere, and acts as a sink for CI. The reaction of CI with hydroperoxides, ROOH, is complex, and leads both to the formation of oligomers, as to the formation of reactive etheroxides, with a moderately fast rate coefficient. The importance of these reactions is placed in the context of the reaction conditions in different atmospheric environments ranging from unpolluted to highly polluted.

Vereecken, Luc; Harder, Hartwig; Novelli, Anna

2014-05-01

272

Factors augmenting allergic reactions.  

PubMed

Elicitors of anaphylactic reactions are any sources of protein with allergenic capacity. However, not all allergic reactions end up in the most severe form of anaphylaxis. Augmenting factors may explain why certain conditions lead to anaphylaxis. Augmenting factors may exhibit three effects: lowering the threshold, increasing the severity, and reversing acquired clinical tolerance. Common augmenting factors are physical exercise, menstruation, NSAIDs, alcohol, body temperature, acute infections, and antacids. Therapeutic options may address causative, preventive, pragmatic, or symptomatic considerations: avoid the eliciting food, take an antihistamine before any situation with a possible risk of augmentation, separate food and sport (at least for 2 h), and carry an adrenaline autoinjector at all times. Individual patterns include summation effects and specific patterns. In conclusion, in the case of a suggestive history but a negative oral challenge, one should consider the possible involvement of augmenting factors; after anaphylactic reactions, always ask for possible augmentation and other risk factors during the recent past; if augmentation is suspected, oral food challenges should be performed in combination with augmenting factors; and in the future, standardized challenge protocols including augmenting factors should be established. PMID:25306896

Niggemann, B; Beyer, K

2014-12-01

273

Intramolecular Anodic Olefin Coupling Reactions: Using Competition Studies to Probe the Mechanism of Oxidative Cyclization Reactions  

PubMed Central

A competition experiment was designed so that the relative rates of anodic cyclization reactions under various electrolysis conditions can be determined. Reactions with ketene dithioacetal and enol ether-based substrates that use lithium methoxide as a base were shown to proceed through radical cation intermediates that were trapped by a sulfonamide anion. Results for the oxidative coupling of a vinyl sulfide with a sulfonamide anion using the same conditions were consistent with the reaction proceeding through a nitrogen-radical. PMID:20302359

Xu, Hai-Chao; Moeller, Kevin D.

2014-01-01

274

Intramolecular anodic olefin coupling reactions: using competition studies to probe the mechanism of oxidative cyclization reactions.  

PubMed

A competition experiment was designed so that the relative rates of anodic cyclization reactions under various electrolysis conditions can be determined. Reactions with ketene dithioacetal and enol ether-based substrates that use lithium methoxide as a base were shown to proceed through radical cation intermediates that were trapped by a sulfonamide anion. Results for the oxidative coupling of a vinyl sulfide with a sulfonamide anion using the same conditions were consistent with the reaction proceeding through a nitrogen-radical. PMID:20302359

Xu, Hai-Chao; Moeller, Kevin D

2010-04-16

275

Experimental Study of Serpentinization Reactions  

NASA Technical Reports Server (NTRS)

Current carbonaceous chondrite parent-body thermal models [1-3] produce scenarios that are inconsistent with constraints on aqueous alteration conditions based on meteorite mineralogical evidence, such as phase stability relationships within the meteorite matrix minerals [4] and isotope equilibration arguments [5, 6]. This discrepancy arises principally because of the thermal runaway effect produced by silicate hydration reactions (here loosely called serpentinization, as the principal products are serpentine minerals), which are so exothermic as to produce more than enough heat to melt more ice and provide a self-sustaining chain reaction. One possible way to dissipate the heat of reaction is to use a very small parent body [e.g., 2] or possibly a rubble pile model. Another possibility is to release this heat more slowly, which depends on the alteration reaction path and kinetics.

Cohen, B. A.; Brearley, A. J.; Ganguly, J.; Liermann, H.-P.; Keil, K.

2004-01-01

276

Adalimumab induced pulmonary sarcoid reaction  

PubMed Central

Sarcoidosis is a multisystem granulomatous inflammatory disease of unknown etiology. There is evidence that Tumor Necrosis Factor alpha (TNF-?) antagonists are useful in the treatment of advanced or refractory disease. However, sarcoidosis-like reaction has been reported with TNF-? blockade in other inflammatory conditions. Here we report a case of sarcoid-like reaction in a patient with psoriatic arthritis shortly after initiation of adalimumab therapy. Stopping adalimumab and systemic anti-inflammatory therapy with corticosteroids resulted in resolution of pulmonary symptoms and chest radiographic findings. Though TNF-? plays a critical role in pathogenesis of sarcoidosis, the development of sarcoid reaction with TNF-? blockade is paradoxical and the mechanism of this response remains unknown. TNF-? induced sarcoid-reaction could involve multiple organs. Its development with one agent does not preclude therapy with other TNF-? blockers.

Bhargava, S.; Perlman, D.M.; Allen, T.L.; Ritter, J.H.; Bhargava, M.

2013-01-01

277

DownloadedBy:[CanadianResearchKnowledgeNetwork]At:10:3327May2008 Simulation of chemical reaction equilibria by the reaction ensemble Monte Carlo method  

E-print Network

equilibria by the reaction ensemble Monte Carlo method: a review C. Heath Turnera *, John K. Brennanb-ideal conditions is the reaction ensemble Monte Carlo method (RxMC). RxMC has been applied to reactions confined

Lisal, Martin

278

Mechanisms of reactions of open-shell, heavier group 14 derivatives with small molecules: n-?* back-bonding in isocyanide complexes, C-H activation under ambient conditions, CO coupling, and ancillary molecular interactions.  

PubMed

The main themes of this review are the mechanisms of the reactions of germanium and tin analogues of carbenes with isocyanides, CO, ammonia, and related molecules. The treatment of Ge(Ar(Me6))2 (Ar(Me6) = C6H3-2,6(C6H2-2,4,6-Me3)2) with MeNC or Bu(t)NC afforded 1:1 complexes, but the increase in the electron density at germanium leads to C-H activation at the isocyanide methyl or tert-butyl substituents. For MeNC, the initial adduct formation is followed by a migratory insertion of the MeNC carbon into a Ge-C(ipso) bond of an aryl substituent. The addition of excess MeNC led to sequential insertions of two further MeNC molecules. The third insertion led to methylisocyanide methyl group C-H activation, to afford an azagermacyclopentadienyl species. The Bu(t)NC complex (Ar(Me6))2GeCNBu(t) spontanously transforms into (Ar(Me6))2Ge(H)CN and isobutene with C-H activation of the Bu(t) substituent. The germylene Ge(Ar(Me6))(Ar(Pr(i)4)) [Ar(Pr(i)4) = C6H3-2,6(C6H3-2,6-Pr(i)2)2] reacted with CO to afford ?-germyloxyketones. The initial step is the formation of a 1:1 complex, followed by migratory insertion into the Ge-C bond of the Ar(Pr(i)4) ligand to give Ar(Me6)GeC(O)Ar(Pr(i)4). Insertion of a second CO gave Ar(Me6)GeC(O)C(O)Ar(Pr(i)4), which rearranges to afford ?-germyloxyketone. No reaction was observed for Sn(Ar(Me6))2 with RNC (R = Me, Bu(t)) or CO. Spectroscopic (IR) results and density functional theory (DFT) calculations showed that the reactivity can be rationalized on the basis of Ge-C (isocyanide or CO) Ge(n) ? ?* (ligand) back-bonding. The reaction of Ge(Ar(Me6))2 and Sn(Ar(Me6))2 with ammonia or hydrazines initially gave 1:1 adducts. However, DFT calculations show that there are ancillary N-H---N interactions with a second ammonia or hydrazine, which stabilizes the transition state to form germanium(IV) hydride (amido or hydrazido) products. For tin, arene elimination is favored by a buildup of electron density at the tin, as well as the greater polarity of the Sn-C(ipso) bond. Germanium(IV) products were observed upon reaction of Ge(Ar(Me6))2 with acids, whereas reactions of Sn(Ar(Me6))2 with acids did not give tin(II) products. In contrast to reactions with NH3, there is no buildup of negative charge at tin upon protonation, and its subsequent reaction with conjugate bases readily affords the tin(IV) products. PMID:23683137

Brown, Zachary D; Power, Philip P

2013-06-01

279

Assessment of reaction-rate predictions of a collision-energy approach for chemical reactions in atmospheric flows.  

SciTech Connect

A recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates is assessed for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological nonequilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, significant differences can be found. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

2010-06-01

280

Reaction rates of hydrochloric acid with chalks  

Microsoft Academic Search

The reaction rate of hydrochloric acid with carbonate rock at acid-fracturing conditions depends on controllable variables such as injection rate and acid concentration, and variables inherent to the carbonate rock (permeability, mineral composition, etc.). In a previous study, the effects of some controllable variables on reaction rates were investigated and the results correlated with theory. This paper presents the results

Naim A. Mumallah

1998-01-01

281

Catalysis of Photochemical Reactions.  

ERIC Educational Resources Information Center

Offers a classification system of catalytic effects in photochemical reactions, contrasting characteristic properties of photochemical and thermal reactions. Discusses catalysis and sensitization, examples of catalyzed reactions of excepted states, complexing ground state substrates, and catalysis of primary photoproducts. (JM)

Albini, A.

1986-01-01

282

Adsorption Isotherms and Surface Reaction Kinetics  

ERIC Educational Resources Information Center

Explains an error that occurs in calculating the conditions for a maximum value of a rate expression for a bimolecular reaction. The rate expression is derived using the Langmuir adsorption isotherm to relate gas pressures and corresponding surface coverages. (GS)

Lobo, L. S.; Bernardo, C. A.

1974-01-01

283

On Thermonuclear Reaction Rates  

E-print Network

Nuclear reactions govern major aspects of the chemical evolution od galaxies and stars. Analytic study of the reaction rates and reaction probability integrals is attempted here. Exact expressions for the reaction rates and reaction probability integrals for nuclear reactions in the case of nonresonant, modified nonresonant, screened nonresonant and resonant cases are given. These are expressed in terms of H-functions, G-functions and in computable series forms. Computational aspects are also discussed.

H. J. Haubold; A. M. Mathai

1996-12-02

284

Assessment of reaction-rate predictions of a collision-energy approach for chemical reactions in atmospheric flows  

Microsoft Academic Search

A recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates is assessed for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. DSMC non-equilibrium reaction

Michail A. Gallis; Ryan Bomar Bond; John Robert Torczynski

2010-01-01

285

Mathematical model to predict drivers' reaction speeds.  

PubMed

Mental distractions and physical impairments can increase the risk of accidents by affecting a driver's ability to control the vehicle. In this article, we developed a linear mathematical model that can be used to quantitatively predict drivers' performance over a variety of possible driving conditions. Predictions were not limited only to conditions tested, but also included linear combinations of these tests conditions. Two groups of 12 participants were evaluated using a custom drivers' reaction speed testing device to evaluate the effect of cell phone talking, texting, and a fixed knee brace on the components of drivers' reaction speed. Cognitive reaction time was found to increase by 24% for cell phone talking and 74% for texting. The fixed knee brace increased musculoskeletal reaction time by 24%. These experimental data were used to develop a mathematical model to predict reaction speed for an untested condition, talking on a cell phone with a fixed knee brace. The model was verified by comparing the predicted reaction speed to measured experimental values from an independent test. The model predicted full braking time within 3% of the measured value. Although only a few influential conditions were evaluated, we present a general approach that can be expanded to include other types of distractions, impairments, and environmental conditions. PMID:22431214

Long, Benjamin L; Gillespie, A Isabella; Tanaka, Martin L

2012-02-01

286

Thermodynamics of Random Reaction Networks  

PubMed Central

Reaction networks are useful for analyzing reaction systems occurring in chemistry, systems biology, or Earth system science. Despite the importance of thermodynamic disequilibrium for many of those systems, the general thermodynamic properties of reaction networks are poorly understood. To circumvent the problem of sparse thermodynamic data, we generate artificial reaction networks and investigate their non-equilibrium steady state for various boundary fluxes. We generate linear and nonlinear networks using four different complex network models (Erd?s-Rényi, Barabási-Albert, Watts-Strogatz, Pan-Sinha) and compare their topological properties with real reaction networks. For similar boundary conditions the steady state flow through the linear networks is about one order of magnitude higher than the flow through comparable nonlinear networks. In all networks, the flow decreases with the distance between the inflow and outflow boundary species, with Watts-Strogatz networks showing a significantly smaller slope compared to the three other network types. The distribution of entropy production of the individual reactions inside the network follows a power law in the intermediate region with an exponent of circa ?1.5 for linear and ?1.66 for nonlinear networks. An elevated entropy production rate is found in reactions associated with weakly connected species. This effect is stronger in nonlinear networks than in the linear ones. Increasing the flow through the nonlinear networks also increases the number of cycles and leads to a narrower distribution of chemical potentials. We conclude that the relation between distribution of dissipation, network topology and strength of disequilibrium is nontrivial and can be studied systematically by artificial reaction networks. PMID:25723751

Fischer, Jakob; Kleidon, Axel; Dittrich, Peter

2015-01-01

287

From stereodynamics to high-throughput screening of catalysed reactions.  

PubMed

Characterising chemical reactions by kinetic analysis is of fundamental importance to experimentally obtain insights into reaction mechanisms. Based on such investigations reactions can be optimised and improved catalysts designed. Enhanced reaction conditions may drastically increase the performance of the reaction in terms of yield and (enantio-) selectivity. Understanding reaction kinetics in more complex systems involving adaptive chemical and dynamic systems on a molecular level as shown here is even more challenging. Here we review recent developments in monitoring reactions including the dynamic interconversion of stereoisomers by integrating (catalysed) reactions and chemical analysis in on-column reaction chromatographic devices. These recent developments allow rapid screening of reactions in great detail and are a central tool in determining reaction pathways and to understand how to control the stereodynamics of chiral molecules. PMID:25102302

Stockinger, Skrollan; Gmeiner, Julia; Zawatzky, Kerstin; Troendlin, Johannes; Trapp, Oliver

2014-11-28

288

Related Conditions  

MedlinePLUS

... chronic digestive disease requires a lifelong restriction of gluten, which is found in wheat, rye, barley, and perhaps oats. People with celiac disease must strictly avoid these grains and their by-products. When people with celiac disease eat gluten, they experience an immune reaction in the small ...

289

Using Disproportionation Reaction  

E-print Network

Abstract: In this study, copper (II) oxide and copper/copper (I) oxide mixture nanoparticles have been prepared via copper disproportionation reaction in non-aqueous solution. The performance of disproportionation reaction in dimethyl solfoxide (DMSO) was used to synthesis a Nano metallic element without any modification for the first time. Copper (I) Iodide (CuI), DMSO and ethylene diamine (en) have been used as copper (I) ion source, solvent and ligand, respectively. In this investigation the experiments were performed at two conditions. The products were characterized using both X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis of the solids produced at ambient atmosphere depicts the formation of pure copper (II) oxide (CuO) phase. The results also indicate that the achievement of the process after removal of oxygen and at N2 0 atmosphere yields a mixture of metallic copper (Cu) and copper (I) oxide (Cu2O). The SEM images of both products showed that the particle sizes are less than 100 nm and are spherical in shape.

Preparation Of Nanosized Cu O; Cu Cu; O Mixture; Yousef Zeraatkish; Ezat Keshavarzi; Yousef Ghaeb; Kazem Karami; Saman Mousavian

290

Iodine Clock Reaction  

NSDL National Science Digital Library

This site allows the user to vary initial solution concentration and temperature for the iodine clock reaction. A simulation of the reaction lets reaction times be measured. The data can then be used to determine the order of reaction for the various components.

291

The Glyoxal Clock Reaction  

ERIC Educational Resources Information Center

Research on the glyoxal clock reaction has led to adaptation of the clock reaction to a general chemistry experiment. This particular reaction is just one of many that used formaldehyde in the past. The kinetics of the glyoxal clock makes the reaction suitable as a general chemistry lab using a Calculator Based Laboratory (CBL) or a LabPro. The…

Ealy, Julie B.; Negron, Alexandra Rodriguez; Stephens, Jessica; Stauffer, Rebecca; Furrow, Stanley D.

2007-01-01

292

Reaction theory for exotic nuclei  

SciTech Connect

Exotic nuclei are usually defined as those with unusual N/Z ratios. They can be found in the crust of neutron stars enbedded in a sea of electrons or created in laboratory by fragmentation of a primary beam (in-flight method) or of the target (ISOL method). They are extremely important for nuclear astrophysics, see for example Ref.[1]. Furthermore by studying them we can check the limits of validity of nuclear reaction and structure models. This contribution will be devoted to the understanding of how by using reaction theory and comparing to the data we can extract structure information. We shall discuss the differences between the mechanisms of transfer and breakup reactions, an we will try to explain how nowadays it is possible to do accurate spectroscopy in extreme conditions.

Bonaccorso, Angela [INFN, Sez. di Pisa, 56127 Pisa. (Italy)

2014-05-09

293

Thermodynamics in the limit of irreversible reactions  

NASA Astrophysics Data System (ADS)

For many complex real physicochemical systems, the detailed mechanism includes both reversible and irreversible reactions. Such systems are typical in homogeneous combustion and heterogeneous catalytic oxidation. Most complex enzyme reactions include irreversible steps. Classical thermodynamics has no limit for irreversible reactions, whereas kinetic equations may have such a limit. We represent systems with irreversible reactions as the limits of fully reversible systems when some of the equilibrium concentrations tend to zero. The structure of the limit reaction system crucially depends on the relative rates of this tendency to zero. We study the dynamics of the limit system and describe its limit behavior as t??. If the reversible systems obey the principle of detailed balance then the limit system with some irreversible reactions must satisfy the extended principle of detailed balance. It is formulated and proven in the form of two conditions: (i) the reversible part satisfies the principle of detailed balance and (ii) the convex hull of the stoichiometric vectors of the irreversible reactions does not intersect the linear span of the stoichiometric vectors of the reversible reactions. These conditions imply the existence of the global Lyapunov functionals and allow an algebraic description of the limit behavior. Thermodynamic theory of the irreversible limit of reversible reactions is illustrated by the analysis of hydrogen combustion.

Gorban, A. N.; Mirkes, E. M.; Yablonsky, G. S.

2013-03-01

294

Reaction rates for mesoscopic reaction-diffusion kinetics  

E-print Network

The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework, frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a mixed boundary condition at the reaction radius of two molecules. We also establish fundamental limits for the range of mesh resolutions for which this approach yields accurate results, and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics.

Stefan Hellander; Andreas Hellander; Linda Petzold

2015-01-28

295

Reaction rates for mesoscopic reaction-diffusion kinetics  

NASA Astrophysics Data System (ADS)

The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic scale-dependent reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a Robin boundary condition at the reaction radius of two molecules. We also establish fundamental limits on the range of mesh resolutions for which this approach yields accurate results and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics. We show that for mesh sizes below the fundamental lower limit, results are less accurate. Thus, the lower limit determines the mesh size for which we obtain the most accurate results.

Hellander, Stefan; Hellander, Andreas; Petzold, Linda

2015-02-01

296

Knoevenagel Reaction of Unprotected Sugars  

NASA Astrophysics Data System (ADS)

The Knoevenagel reaction of unprotected sugars was investigated in the 1950s using zinc chloride as promoter. The so-called Garcia Gonzalez reaction had been almost forgotten for 50 years, until the emergence of new water tolerant catalysts having Lewis acid behavior. The reaction was thus reinvestigated and optimal conditions have been found to prepare trihydroxylated furan derivatives from pentose or ?-tetrahydrofuranylfuran from hexoses with non-cyclic ?-keto ester or ?-diketones. Other valuable compounds such as ?-linked tetrahydrobenzofuranyl glycosides or hydroxyalkyl-3,3,6,6,-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione can be obtained using cyclic ?-dicarbonylic derivatives. Apart from one report in the 1950s, the Knoevenagel reaction of unprotected carbohydrate in basic condition has been studied only in the mid-1980s to prepare C-glycosyl barbiturates from barbituric acids and, later on, from non-cyclic ?-diketones, ?-C-glycosidic ketones. The efficient method exploited to prepare such compounds has found an industrial development in cosmetics.

Scherrmann, Marie-Christine

297

Quantifying mixing using equilibrium reactions  

SciTech Connect

A method of quantifying equilibrium reactions in a microchannel using a fluorometric reaction of Fluo-4 and Ca{sup 2+} ions is presented. Under the proper conditions, equilibrium reactions can be used to quantify fluid mixing without the challenges associated with constituent mixing measures such as limited imaging spatial resolution and viewing angle coupled with three-dimensional structure. Quantitative measurements of CaCl and calcium-indicating fluorescent dye Fluo-4 mixing are measured in Y-shaped microchannels. Reactant and product concentration distributions are modeled using Green's function solutions and a numerical solution to the advection-diffusion equation. Equilibrium reactions provide for an unambiguous, quantitative measure of mixing when the reactant concentrations are greater than 100 times their dissociation constant and the diffusivities are equal. At lower concentrations and for dissimilar diffusivities, the area averaged fluorescence signal reaches a maximum before the species have interdiffused, suggesting that reactant concentrations and diffusivities must be carefully selected to provide unambiguous, quantitative mixing measures. Fluorometric equilibrium reactions work over a wide range of pH and background concentrations such that they can be used for a wide variety of fluid mixing measures including industrial or microscale flows.

Wheat, Philip M. [Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, Arizona 85287-6106 (United States); Posner, Jonathan D. [Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, Arizona 85287-6106 (United States); Department of Chemical Engineering, Arizona State University, Tempe, Arizona 85287-6106 (United States)

2009-03-15

298

Imidazole-Catalyzed Henry Reactions in Aqueous Medium  

Microsoft Academic Search

2-Nitroalkanols can be efficiently synthesized using imidazole as a mild Lewis basic catalyst in aqueous medium as well as in organic solvents. The products have been found in good yields without purification (> 95% purity by H NMR) for aromatic aldehydes. Additionally, the very mild reaction conditions prevent the particular side reactions such as aldol condensation, Cannizzaro reaction, or dehydration of

Mridula Phukan; Kalyan Jyoti Borah; Ruli Borah

2008-01-01

299

Two-Body and Three-Body Atomic Recombination Reactions.  

ERIC Educational Resources Information Center

Discusses how, in some circumstances, a two-body reaction (association in absence of a third body) is the only possible association, and how reactions proceed in this case. Taking competition between two/three-body reactions into account, considers relative importance of such combinations and conditions under which the former can be competitive.…

Alvarino, Jose M.; Martinez, E.

1983-01-01

300

Conditional Immunomodulation  

Microsoft Academic Search

Interest in central nervous-immune system interactions was inspired largely by the work on conditional immunomodulation (Ader and Cohen, 1975, 1985). Ader and Cohen (1975) reported that rats trained such that a taste cue (saccharine, SAC) predicted an injection of an immunosuppressant (cyclophosphamide, CY) subsequently exhibited a conditional immunosuppression in response to SAC alone.\\u000aExperiments 1-3 were designed to evaluate reports

Glenda Marlene MacQueen

1989-01-01

301

Diels–Alder reaction of maldoxin with an isopropenylallene  

PubMed Central

The Diels–Alder reaction of maldoxin with an isopropenylallene at 60-75 °C afforded an adduct closely related to chloropestolide A (24%) and a second adduct (0-11%) that underwent an ene reaction to generate the chloropupukeanolide D (11-22%) skeleton. The Diels–Alder reaction occurred with good selectively (>5:1) from a single face of maldoxin under much milder conditions than previously reported for the analogous dimethoxycyclohexadienone. Furthermore, the ene reaction took place under mild conditions whereas the analogous Diels–Alder adduct from the dimethoxycyclohexadienone did not undergo an ene reaction. PMID:22518065

Yu, Min; Snider, Barry. B.

2011-01-01

302

Continuous detonation reaction engine  

NASA Technical Reports Server (NTRS)

Reaction engine operates on the principles of a controlled condensed detonation rather than on the principles of gas expansion. The detonation results in reaction products that are expelled at a much higher velocity.

Lange, O. H.; Stein, R. J.; Tubbs, H. E.

1968-01-01

303

Pulmonary Transfusion Reactions  

PubMed Central

Summary Background In recent years, pulmonary transfusion reactions have gained increasing importance as serious adverse transfusion events. Methods Review of the literature. Results Pulmonary transfusion reactions are not extremely rare and, according to hemovigilance data, important causes of transfusion-induced major morbidity and death. They can be classified as primary with predominant pulmonary injury and secondary as part of another transfusion reaction. Primary reactions include transfusion-related acute lung injury (TRALI), transfusion-associated circulatory overload (TACO) and transfusion-associated dyspnea (TAD). Secondary pulmonary reactions are often observed in the wake of hemolytic transfusion reactions, hypotensive/anaphylactic reactions, and transfusion-transmitted bacterial infections. Conclusion Knowledge and careful management of cases of pulmonary transfusion reactions are essential for correct reporting to blood services and hemovigilance systems. Careful differentiation between TRALI and TACO is important for taking adequate preventive measures. PMID:21512622

Bux, Jürgen; Sachs, Ulrich J. H.

2008-01-01

304

Microfluidic chemical reaction circuits  

DOEpatents

New microfluidic devices, useful for carrying out chemical reactions, are provided. The devices are adapted for on-chip solvent exchange, chemical processes requiring multiple chemical reactions, and rapid concentration of reagents.

Lee, Chung-cheng (Irvine, CA); Sui, Guodong (Los Angeles, CA); Elizarov, Arkadij (Valley Village, CA); Kolb, Hartmuth C. (Playa del Rey, CA); Huang, Jiang (San Jose, CA); Heath, James R. (South Pasadena, CA); Phelps, Michael E. (Los Angeles, CA); Quake, Stephen R. (Stanford, CA); Tseng, Hsian-rong (Los Angeles, CA); Wyatt, Paul (Tipperary, IE); Daridon, Antoine (Mont-Sur-Rolle, CH)

2012-06-26

305

Microscale Thermite Reactions.  

ERIC Educational Resources Information Center

Describes the adaptation of thermite (aluminum with metal oxides) reactions from whole-class demonstrations to student-run micro-reactions. Lists detailed directions and possible variations of the experiment. (WRM)

Arnaiz, Francisco J.; Aguado, Rafael; Arnaiz, Susana

1998-01-01

306

Chemical Reactions (Netorials)  

NSDL National Science Digital Library

Chemical Reactions: this is a resource in the collection "Netorials". The Netorials cover selected topics in first-year chemistry including: Chemical Reactions, Stoichiometry, Thermodynamics, Intermolecular Forces, Acids & Bases, Biomolecules, and Electrochemistry.

307

Enhanced sludge dewatering by dual polyelectrolytes conditioning  

Microsoft Academic Search

Sludge dewatering by dual polyelectrolytes conditioning was investigated in this study. Single polyelectrolyte is utilized in sludge conditioning conventionally, in which charge neutralization and bridging are involved in the reactions. In the current study, both cationic and non-ionic polyelectrolytes were utilized simultaneously in the conditioning. Waste activated sludge was sampled from a synthetic fiber plant, and used in the experiment.

C. H Lee; J. C Liu

2000-01-01

308

Conditional moment closure for turbulent combustion  

Microsoft Academic Search

This paper reviews the fundamentals of conditional moment closure (CMC) methods for the prediction of turbulent reacting flows, with particular emphasis on combustion. It also surveys several of the applications that have been made. CMC methods predict the conditional averages and higher moments of quantities such as species mass fractions and enthalpy, conditional on the mixture fraction or reaction progress

A. Y. Klimenko; R. W. Bilger

1999-01-01

309

Reactions of Stabilized Criegee intermediates  

NASA Astrophysics Data System (ADS)

Carbonyl oxides (Criegee intermediates) were proposed as key intermediates in the gas phase ozonolysis of alkenes in 1975 by Rudolf Criegee. Despite the importance of ozonolysis in atmopsheric chemistry, direct observation of these intermediates remained elusive, with only indirect experimental evidence for their role in the oxidation of hydrocarbons, e.g. through scavenging experiments. Only recently did Taatjes et al (2008) directly observe thermally stabilized Criegee intermediates (SCI), while work by Welz et al (2012) and others have finally started to elucidate the reaction kinetics and products of SCI with a subset of coreactants. Given the dearth of direct experimental data, theoretical analysis of the chemistry of SCI remains a prime source of information; in general, the predictions are in agreement with the scarce experimental data. We present a set of modern theoretical studies on the chemistry of SCI, with emphasis on high-level quantum chemical calculations and theoretical kinetic analysis as a function of the substitutions in the SCI. A broad range of co-reactants is examined, as well as the unimolecular re-arrangement of SCI. In the atmosphere, the fate of SCI was long assumed to be solely its reaction with H2O, or unimolecular decomposition. However, recent re-analysis (Vereecken et al. 2012) of the available data shows that this view may need to be adjusted, with other fast bimolecular reactions playing a role in the atmosphere, with a strong dependence of the rates on the substituents in the SCI. Based on the new experimental and theoretical data, we re-evaluate the possible sinks of SCI in the atmosphere, putting forward a set of reactions that might have an impact in atmospheric or experimental reaction conditions. The reaction of SCI with SO2 receives particular attention, as it is proposed in the literature to be of importance in the atmospheric formation of H2SO4 as an aerosol precursor.

Vereecken, Luc; Harder, Hartwig; Novelli, Anna

2013-04-01

310

Characteristics of vestibulosensory reactions studied by experimental caloric test  

NASA Technical Reports Server (NTRS)

Vestibulo-sensory reactions were studied in 135 workers who were in contact with nitroethers, by the method of an experimental caloric test. The response vestibulo-sensory reactions were recorded by means of an electroencephalograph. The changes in the sensory reaction depended on the duration of the workers' contact with toxic agents. A study of illusion reactions by the labyrinth calorization widens diagnostic possibilities in the examination of functional condition of the vestibular analyser considerably.

Kapranov, V. Z.

1980-01-01

311

Chemical Reactions and Stoichiometry  

NSDL National Science Digital Library

In this activity, students explore reactions in which chemical bonds are formed and broken. Students experiment with changing the temperature and the concentration of the atoms in order to see how these affect reaction rates. They also learn how to communicate what happens during a chemical reaction by writing the ratios of reactants and products, known as stoichiometry.

The Concord Consortium

2011-12-11

312

Chemical Reactions: Investigating Exothermic and Endothermic Reactions  

NSDL National Science Digital Library

This activity is an inquiry-based investigation where students discover the indicators of chemical reactions (endothermic and exothermic) by collecting data and using that data to develop a testable question for further experimentation.

313

Planetary Fluids Under Extreme Conditions  

Microsoft Academic Search

Knowledge of the behavior of a variety of fluids under extreme conditions of high pressures and temperatures provides a crucial starting point for understanding the evolution, structure, and dynamics of deep planetary interiors. These properties include the equations of state, sound velocities, phase separation, and chemical reactions are essential. Despite advances in both static and dynamic compression methods, as well

R. J. Hemley; B. Militzer

2006-01-01

314

Conditional Probability  

NSDL National Science Digital Library

This site, created by the Department of Statistics at Yale University gives an explanation, a definition and an example of conditional probability. Topics include the probabilities of intersections of events and Bayes' formula. Overall, this is a great resource for any mathematics classroom studying statistics.

Lacey, Michelle

315

Mukaiyama Aldol Reactions in Aqueous Media  

PubMed Central

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

Kitanosono, Taku; Kobayashi, Sh?

2013-01-01

316

Cascade enzymatic reactions for efficient carbon sequestration.  

PubMed

Thermochemical processes developed for carbon capture and storage (CCS) offer high carbon capture capacities, but are generally hampered by low energy efficiency. Reversible cascade enzyme reactions are examined in this work for energy-efficient carbon sequestration. By integrating the reactions of two key enzymes of RTCA cycle, isocitrate dehydrogenase and aconitase, we demonstrate that intensified carbon capture can be realized through such cascade enzymatic reactions. Experiments show that enhanced thermodynamic driving force for carbon conversion can be attained via pH control under ambient conditions, and that the cascade reactions have the potential to capture 0.5mol carbon at pH 6 for each mole of substrate applied. Overall it manifests that the carbon capture capacity of biocatalytic reactions, in addition to be energy efficient, can also be ultimately intensified to approach those realized with chemical absorbents such as MEA. PMID:25708541

Xia, Shunxiang; Zhao, Xueyan; Frigo-Vaz, Benjamin; Zheng, Wenyun; Kim, Jungbae; Wang, Ping

2015-04-01

317

Efficient catalysts for asymmetric Mannich reactions.  

PubMed

Efficient chiral catalysts for direct asymmetric three-component Mannich reactions of ketones, aldehydes and an amine (p-anisidine) have been developed. The corresponding ?-amino carbonyl compounds (Mannich adducts) were obtained in good chemical yields and excellent enantio- and diastereoselectivities. The reaction conditions have been optimized by invoking ultrasonication and the influence of some structural moieties of the catalysts on the chemical yield and stereoselectivity of the Mannich products has been evaluated. PMID:23685888

Rachwalski, Micha?; Leenders, Tim; Kaczmarczyk, Sylwia; Kie?basi?ski, Piotr; Le?niak, Stanis?aw; Rutjes, Floris P J T

2013-07-01

318

Homogenizability conditions for multicomponent reactive transport  

NASA Astrophysics Data System (ADS)

We consider multicomponent reactive transport in porous media involving three reacting species, two of which undergo a nonlinear homogeneous reaction, while a third precipitates on the solid matrix through a heterogeneous nonlinear reaction. The process is fully reversible and can be described with a reaction of the kind A+B?C?S. The system's behavior is fully controlled by Péclet (Pe) and three Damköhler (Daj,j={1,2,3}) numbers, which quantify the relative importance of the four key mechanisms involved in the transport process, i.e. advection, molecular diffusion, homogeneous and heterogeneous reactions. We use multiple-scale expansions to upscale the pore-scale system of equations to the macroscale, and establish sufficient conditions under which macroscopic local advection-dispersion-reaction equations (ADREs) provide an accurate representation of the pore-scale processes. These conditions reveal that (i) the heterogeneous reaction leads to more stringent constraints compared to the homogeneous reactions, and (ii) advection can favorably enhance pore-scale mixing in the presence of fast reactions and relatively low molecular diffusion. Such conditions are summarized by a phase diagram in the (Pe,Daj)-space, and verified through numerical simulations of multicomponent transport in a planar fracture with reacting walls. Our computations suggest that the constraints derived in our analysis are robust in identifying sufficient as well as necessary conditions for homogenizability.

Boso, Francesca; Battiato, Ilenia

2013-12-01

319

Mechanisms in knockout reactions  

E-print Network

We report on the first detailed study of the mechanisms involved in knockout reactions, via a coincidence measurement of the residue and fast proton in one-proton knockout reactions, using the S800 spectrograph in combination with the HiRA detector array at the NSCL. Results on the reactions $^9$Be($^9$C,$^8$B+X)Y and $^9$Be($^8$B,$^7$Be+X)Y are presented. They are compared with theoretical predictions for both the diffraction and stripping reaction mechanisms, as calculated in the eikonal model. The data shows a clear distinction between the two reaction mechanisms, and the observed respective proportions are very well reproduced by the reaction theory. This agreement supports the results of knockout reaction analyses and their applications to the spectroscopy of rare isotopes.

D. Bazin; R. J. Charity; R. T. de Souza; M. A. Famiano; A. Gade; V. Henzl; D. Henzlova; S. Hudan; J. Lee; S. Lukyanov; W. G. Lynch; S. McDaniel; M. Mocko; A. Obertelli; A. M. Rogers; L. G. Sobotka; J. R. Terry; J. A. Tostevin; M. B. Tsang; M. S. Wallace

2009-02-16

320

Cardiac conditions.  

PubMed

Cardiovascular disease (CVD) is the leading cause of death in the US. The growth of the older population in coming decades will inevitably increase the incidence of age-related cardiac disease. Increasing evidence has shown the prevalence of co-morbid mental health conditions in CVD patients. Specifically, depression and anxiety have been linked with CVD mortality. Due to the risk of psychosocial conditions with cardiac patients, mental health practitioners in health and gerontology need to be well-informed about CVD-related mental health comorbidity and current research developments. Accordingly, this article provides a systematic review of the clinical evidence about the efficacy, cost-effectiveness, and any potential risk of psychosocial intervention with cardiac patients. PMID:18924386

Peck, Michel D; Ai, Amy L

2008-01-01

321

Prebiotic condensation reactions using cyanamide  

NASA Technical Reports Server (NTRS)

Condensation reactions in cyanamide, 4-amino-5-imidazole-carboxamide and cyanamide, imidazole systems under dehydrating conditions at moderate temperatures (60 to 100 deg C) were investigated. The cyanamide, imidazole system was used for synthesis of palmitoylglycerols from ammonium palmitate and glycerol. With the addition of deoxythymidine to the former system, P1, P2-dideoxythymidine 5 prime-phosphate was obtained; the same cyanamide, 4-amino-5-imidazole-carboxamide system was used to synthesize deoxythymidine oligonucleotides using deoxythymidine 5 prime-phosphate and deoxythymidine 5 prime-triphosphate, and peptides using glycine, phenylalanine or isoleucine with adenosine 5 prime-triphosphate. The pH requirements for these reactions make their prebiotic significance questionable; however, it is conceivable that they could occur in stable pockets of low interlayer acidity in a clay such as montmorillonite.

Sherwood, E.; Nooner, D. W.; Eichberg, J.; Epps, D. E.; Oro, J.

1978-01-01

322

Magnetic nanocomposites by reaction milling  

SciTech Connect

Systems of small magnetic particles embedded in a nonmagnetic matrix were prepared by high energy ball milling. Besides carefully chosen milling conditions, in situ chemical reactions were used to control the properties of the product. Nanocomposites of iron particles in metal oxides (Al{sub 2}O{sub 3} and ZnO), and magnetite particles in copper metal were prepared by reaction milling. The samples were characterized by X-ray diffraction and magnetic methods. A few hours of ball milling resulted in the completion of most chemical changes. Iron nanoparticles were formed with lattice strains of about 0.005; coercivities up to 400 Oe were achieved. The magnetization of the iron particles is 25--40% less than that expected for bulk iron.

Pardavi-Horvath, M. [George Washington Univ., Washington, DC (United States). Institute of Magnetics Research] [George Washington Univ., Washington, DC (United States). Institute of Magnetics Research; Takacs, L. [Univ. of Maryland Baltimore County, Baltimore, MD (United States). Dept. of Physics] [Univ. of Maryland Baltimore County, Baltimore, MD (United States). Dept. of Physics

1995-12-01

323

Classes of Chemical Reactions Reactions in aqueous media  

E-print Network

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

Zakarian, Armen

324

Aldehyde Coupling Reactions Enantioselective Organocatalytic  

E-print Network

Aldehyde Coupling Reactions Enantioselective Organocatalytic Direct Aldol Reactions of a upon carbohydrate architecture[2] as an important platform for reaction design and methodological advance- ment.[3] Application of the aldol reaction[4] to the synthesis of carbohydrates is well

MacMillan, David W. C.

325

[Reactions after MMR vaccination].  

PubMed

Four months after introducing routine vaccination against measles, mumps and German measles (MMR-vaccination) in Denmark, a questionnaire study of reactions in vaccinated children was carried out. There were significantly fewer reactions in children who had previously developed immunity to measles, either by having had the disease or by vaccination. The reaction frequency after MMR-vaccination of children immune to measles was no greater than that after other vaccinations. Moreover, for all vaccinations, the frequency of reaction was found to decrease significantly with increasing age. The study suggests that a large proportion of the so-called reactions were not caused by vaccination, but were due to common viral infections occurring at random and concurrently with it. The reactions that arose in connection with MMR-vaccination are considered to be of minor importance when compared with often prolonged and more severe course of these diseases. PMID:2363211

Kaaber, K; Samuelsson, I S; Larsen, S O

1990-06-01

326

Reaction-diffusion textures  

Microsoft Academic Search

We present a method for texture synthesis based on the simulation of a process of local nonlinear interaction, called reaction-diffusion, which has been proposed as a model of biological pattern formation. We extend traditional reaction-diffusion systems by allowing anisotropic and spatially non-uniform diffusion, as well as multiple competing directions of diffusion. We adapt reaction-diffusion system to the needs of computer

Andrew P. Witkin; Michael Kass

1991-01-01

327

Classic Organic Reactions  

NSDL National Science Digital Library

Despite the fact that the Classic Organic Reactions Page was designed for commercial purposes, to demonstrate the capabilities of ChemPen chemical structure drawing software for Windows, the page offers a useful resource for chemistry students and professionals. The creator of this page, and author and proprietor of ChemPen, Dr. Hilton Evans, has cited the literature for each reaction. The site contains drawings for over 300 alphabetically listed classic organic reactions. The list begins with the Acetoacetic Ester Condensation and ends with the Zinke-Suhl Reaction.

328

Sleeve reaction chamber system  

DOEpatents

A chemical reaction chamber system that combines devices such as doped polysilicon for heating, bulk silicon for convective cooling, and thermoelectric (TE) coolers to augment the heating and cooling rates of the reaction chamber or chambers. In addition the system includes non-silicon-based reaction chambers such as any high thermal conductivity material used in combination with a thermoelectric cooling mechanism (i.e., Peltier device). The heat contained in the thermally conductive part of the system can be used/reused to heat the device, thereby conserving energy and expediting the heating/cooling rates. The system combines a micromachined silicon reaction chamber, for example, with an additional module/device for augmented heating/cooling using the Peltier effect. This additional module is particularly useful in extreme environments (very hot or extremely cold) where augmented heating/cooling would be useful to speed up the thermal cycling rates. The chemical reaction chamber system has various applications for synthesis or processing of organic, inorganic, or biochemical reactions, including the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction.

Northrup, M. Allen (Berkeley, CA); Beeman, Barton V. (San Mateo, CA); Benett, William J. (Livermore, CA); Hadley, Dean R. (Manteca, CA); Landre, Phoebe (Livermore, CA); Lehew, Stacy L. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA)

2009-08-25

329

Homogenizability Conditions in Multicomponent Reactive Transport Processes  

NASA Astrophysics Data System (ADS)

We consider multicomponent reactive transport in porous media involving three reacting species, two of which undergo a nonlinear homogenous reaction, while a third precipitates on the solid matrix through a heterogenous nonlinear reaction. The process is fully reversible and can be described with a reaction of the kind A+B?C?S. The system behavior is fully controlled by the Péclet (Pe) and three Damköhler (Daj, j={1,2,3}) numbers which quantify the relative importance of the four key mechanisms involved in the transport process, i.e. advection, molecular diffusion, homogeneous and heterogeneous reactions. By means of multiple-scale expansions we upscale the pore-scale system of equations to the macroscale, and establish sufficient conditions under which macroscopic local advection-dispersion-reaction equations (ADREs) provide an accurate representation of the pore-scale processes. These conditions reveal that i) the heterogeneous reaction leads to more stringent constraints compared to the homogenous reactions, and ii) advection can favourably enhance pore-scale mixing in presence of fast reaction and relatively low molecular diffusion. Such conditions are summarized by a phase diagram in the (Pe,Daj)-space, and verified through numerical simulations of multicomponent transport in a planar fracture with reacting walls.

Boso, F.; Battiato, I.

2012-12-01

330

EFFICIENT CHEMICAL TRANSFORMATIONS USING ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

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

331

Coupling nuclear reaction rates with temperature in explosive conditions  

Microsoft Academic Search

We present a straightforward integration method to compute the abundance and temperature evolution in explosive scenarios. In this approach the thermal equation is implicitely coupled with chemical equations in order to avoid instabilities and ensure a gentle transition from the normal combustion regime to the quasi (QSE) and complete nuclear statistical equilibrium (NSE). Two nuclear networks, with 14 nuclei (?-network)

Domingo García-Senz; Rubén M. Cabezón Gómez

2003-01-01

332

Interfacial reaction of reballed BGAs under isothermal aging conditions  

Microsoft Academic Search

Reballing involves removing the original solder balls and attaching new solder balls on the pads of ball grid array components. In this study, 676 I\\/O BGAs with Sn3.0Ag0.5Cu (SAC305) balls were reballed with eutectic tin-lead solder. The original metallization of the pads on the BGAs was Cu\\/Ni with immersion Au. Two solder ball removal methods were applied: the low-temperature wave

Lei Nie; Mingzhi Dong; Jian Cai; M. Osterman; M. Pecht

2009-01-01

333

GREENER CHEMICAL SYNTHESES USING ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

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

334

CHEMICAL SYNTHESIS USING 'GREENER' ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

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

335

REACTIONS OF FUEL NITROGEN COMPOUNDS UNDER CONDITIONS OF INERT PYROLYSIS  

EPA Science Inventory

The paper describes the pyrolysis of fossil fuels and model nitrogen compounds in helium in a small quartz plow reactor, as part of a study of the chemical mechanisms involved in the conversion of fuel-nitrogen compounds to nitric oxide (NO) during combustion. Hydrogen cyanide (H...

336

GREENER ORGANIC SYNTHESES USING ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

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

337

ENVIRONMENTALLY FRIENDLIER SYNTHESIS USING ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

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

338

ENVIRONMENTALLY FRIENDLIER SYNTHESES USING MICROWAVES AND ALTERNATIVE REACTION CONDITIONS  

EPA Science Inventory

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

339

Coupling nuclear reaction rates with temperature in explosive conditions  

E-print Network

We present a straightforward integration method to compute the abundance and temperature evolution in explosive scenarios. In this approach the thermal equation is implicitely coupled with chemical equations in order to avoid instabilities and ensure a gentle transition from the normal combustion regime to the quasi (QSE) and complete nuclear statistical equilibrium (NSE). Two nuclear networks, with 14 nuclei (alpha-network) and 86 nuclei (including protons and neutrons) respectively, have been considered. The scheme is suitable to cope with a variety of explosive burning regimes.

Domingo Garcia-Senz; Ruben M. Cabezon Gomez

2002-10-16

340

Comparison of Absolute Thresholds Derived from an Adaptive Forced-Choice Procedure and from Reaction Probabilities and Reaction Times in a Simple Reaction Time Paradigm  

Microsoft Academic Search

An understanding of the auditory system's operation requires knowledge of the mechanisms underlying thresholds. In this work we compare detection thresholds obtained with a three-interval-three-alternative forced-choice paradigm with reaction thresholds extracted from both reaction probabilities (RP) and reaction times (RT) in a simple RT paradigm from the same listeners under otherwise nearly identical experimental conditions. Detection thresholds, RP, and RT

Peter Heil; Heinrich Neubauer; Andreas Tiefenau; Hellmut von Specht

2006-01-01

341

Detailed Chemical Kinetic Reaction Mechanisms for Autoignition of Isomers of Heptane Under Rapid Compression  

Microsoft Academic Search

Detailed chemical kinetic reaction mechanisms are developed for combustion of all nine isomers of heptane (CH), and these mechanisms are tested by simulating autoignition of each isomer under rapid compression machine conditions. The reaction mechanisms focus on the manner in which the molecular structure of each isomer determines the rates and product distributions of possible classes of reactions. The reaction

C K Westbrook; W J Pitz; J E Boercker; H J Curran; J F Griffiths; C Mohamed; M Ribaucour

2001-01-01

342

Capture reactions on C-14 in nonstandard big bang nucleosynthesis  

NASA Technical Reports Server (NTRS)

Nonstandard big bang nucleosynthesis leads to the production of C-14. The further reaction path depends on the depletion of C-14 by either photon, alpha, or neutron capture reactions. The nucleus C-14 is of particular importance in these scenarios because it forms a bottleneck for the production of heavier nuclei A greater than 14. The reaction rates of all three capture reactions at big bang conditions are discussed, and it is shown that the resulting reaction path, leading to the production of heavier elements, is dominated by the (p, gamma) and (n, gamma) rates, contrary to earlier suggestions.

Wiescher, Michael; Gorres, Joachim; Thielemann, Friedrich-Karl

1990-01-01

343

Chemical dynamics of the CH(X2?) + C2H4(X1A1g), CH(X2?) + C2D4(X1A1g), and CD(X2?) + C2H4(X1A1g) reactions studied under single collision conditions.  

PubMed

The crossed beam reactions of the methylidyne radical with ethylene (CH(X(2)?) + C(2)H(4)(X(1)A(1g))), methylidyne with D4-ethylene (CH(X(2)?) + C(2)D(4)(X(1)A(1g))), and D1-methylidyne with ethylene (CD(X(2)?) + C(2)H(4)(X(1)A(1g))) were conducted at nominal collision energies of 17-18 kJ mol(-1) to untangle the chemical dynamics involved in the formation of distinct C(3)H(4) isomers methylacetylene (CH(3)CCH), allene (H(2)CCCH(2)), and cyclopropene (c-C(3)H(4)) via C(3)H(5) intermediates. By tracing the atomic hydrogen and deuterium loss pathways, our experimental data suggest indirect scattering dynamics and an initial addition of the (D1)-methylidyne radical to the carbon-carbon double bond of the (D4)-ethylene reactant forming a cyclopropyl radical intermediate (c-C(3)H(5)/c-C(3)D(4)H/c-C(3)H(4)D). The latter was found to ring-open to the allyl radical (H(2)CCHCH(2)/D(2)CCHCD(2)/H(2)CCDCH(2)). This intermediate was found to be long lived with life times of at least five times its rotational period and decomposed via atomic hydrogen/deuterium loss from the central carbon atom (C2) to form allene via a rather loose exit transition state in an overall strongly exoergic reaction. Based on the experiments with partially deuterated reactants, no compelling evidence could be provided to support the formation of the cyclopropene and methylacetylene isomers under single collision conditions. Likewise, hydrogen/deuterium shifts in the allyl radical intermediates or an initial insertion of the (D1)-methylidyne radical into the carbon-hydrogen/deuterium bond of the (D4)-ethylene reactant were found to be-if at all-of minor importance. Our experiments propose that in hydrocarbon-rich atmospheres of planets and their moons such as Saturn's satellite Titan, the reaction of methylidyne radicals should lead predominantly to the hitherto elusive allene molecule in these reducing environments. PMID:22108533

Zhang, Fangtong; Maksyutenko, Pavlo; Kaiser, Ralf I

2012-01-14

344

Smell the Maillard Reaction  

NSDL National Science Digital Library

In this activity, learners cook amino acids and sugar to explore the range of aromas released. When amino acids and sugars are heated, learners will observe a phenomenon known as the Maillard reaction, also known as the browning reaction. Caution!: Kids, please don't try this at home without the help of an adult. The corn syrup can get very hot, very quickly.

2012-10-03

345

Nuclear Reaction Data Centers  

SciTech Connect

The cooperating Nuclear Reaction Data Centers are involved in the compilation and exchange of nuclear reaction data for incident neutrons, charged particles and photons. Individual centers may also have services in other areas, e.g., evaluated data, nuclear structure and decay data, reactor physics, nuclear safety; some of this information may also be exchanged between interested centers. 20 refs., 1 tab.

McLane, V.; Nordborg, C.; Lemmel, H.D.; Manokhin, V.N.

1988-01-01

346

Clock Reaction: Outreach Attraction  

ERIC Educational Resources Information Center

Chemistry students are often introduced to the concept of reaction rates through demonstrations or laboratory activities involving the well-known iodine clock reaction. For example, a laboratory experiment involving thiosulfate as an iodine scavenger is part of the first-year general chemistry laboratory curriculum at Dalhousie University. With…

Carpenter, Yuen-ying; Phillips, Heather A.; Jakubinek, Michael B.

2010-01-01

347

Applications of Reaction Rate  

ERIC Educational Resources Information Center

This article presents an assignment in which students are to research and report on a chemical reaction whose increased or decreased rate is of practical importance. Specifically, students are asked to represent the reaction they have chosen with an acceptable chemical equation, identify a factor that influences its rate and explain how and why it…

Cunningham, Kevin

2007-01-01

348

The guaiol color reaction.  

PubMed

The common and biogenetically important sesquiterpene guaiol yields a deep purple color when treated with electrophilic bromine reagents. This interesting color reaction was observed over fifty years ago, but the chemistry of this process has not been investigated. Herein, we present the chemistry of the guaiol color reaction. PMID:12391567

Waddell, Thomas G; Arp, Nathan W; Bodine, Kyle D; Pagni, Richard M

2002-10-01

349

Oscillating Reactions: Two Analogies  

ERIC Educational Resources Information Center

Oscillating chemical reactions are truly spectacular phenomena, and demonstrations are always appreciated by the class. However, explaining such reactions to high school or first-year university students is problematic, because it may seem that no acceptable explanation is possible unless the students have profound knowledge of both physical…

Petruševski, Vladimir M.; Stojanovska, Marina I.; Šoptrajanov, Bojan T.

2007-01-01

350

Chemical burn or reaction  

MedlinePLUS

Chemicals that touch skin can lead to a reaction on the skin, throughout the body, or both. ... leave the person alone and watch carefully for reactions affecting the entire body. Note: If a chemical gets into the eyes, the eyes should be ...

351

Surface catalyzed mercury transformation reactions  

NASA Astrophysics Data System (ADS)

Mercury is a known pollutant that has detrimental effect on human health and environment. The anthropogenic emissions of mercury account for 10 to 30% of worldwide mercury emissions. There is a need to control/reduce anthropogenic mercury emissions. Many mercury control technologies are available but their effectiveness is dependent on the chemical form of mercury, because different chemical forms of mercury have different physical and chemical properties. Mercury leaves the boiler in its elemental form but goes through various transformations in the post-combustion zone. There is a need to understand how fly ash and flue gas composition affect speciation, partitioning, and reactions of mercury under the full range of post-combustion zone conditions. This knowledge can then be used to predict the chemical transformation of mercury (elemental, oxidized or particulate) in the post combustion zone and thus help with the control of mercury emissions from coal-burning power plants. To accomplish this goal present study was conducted using five coal fly ashes. These ashes were characterized and their catalytic activity was compared under selected reaction conditions in a fixed bed reactor. Based on the results from these fly ash experiments, three key components (carbon, iron oxide and calcium oxide) were chosen. These three components were then used to prepare model fly ashes. Silica/alumina was used as a base for these model fly ashes. One, two or three component model fly ashes were then prepared to investigate mercury transformation reactions. The third set of experiments was performed with five different oxidation catalysts to further understand the mercury oxidation process. Based on the results of these three studies the key components were predicted for different fly ash compositions under variety of flue gas conditions. A fixed bed reactor system was used to conduct this study. In all the experiments, the inlet concentration of Hg0(g) was maintained at 35 mug/m 3 using a diffusion tube as the source of Hg0(g). All experiments were conducted using 4% O2 in nitrogen mix as a reaction gas, and other reactants (HCl, H2O and SO2, NO 2, Br2) were added as required. The fixed bed reactor was operated over a temperature range of 200 to 400°C. In each experiment, the reactor effluent was analyzed using the modified Ontario-Hydro method. After each experiment, fly ash particles were also analyzed for mercury. The results show that the ability of fly ash to adsorb and/or oxidize mercury is primarily dependent on its carbon, iron and calcium content. There can be either one or more than one key component at a particular temperature and flue gas condition. Surface area played a secondary role in effecting the mercury transformations when compared to the concentration of the key component in the fly ash. Amount carbon and surface area played a key important role in the adsorption of mercury. Increased concentration of gases in the flue gas other than oxygen and nitrogen caused decreased the amount of mercury adsorbed on carbon surface. Mercury adsorption by iron oxide primarily depended on the crystalline structure of iron oxide. alpha-iron oxide had no effect on mercury adsorption or oxidation under most of the flue gas conditions, but gamma-iron oxide adsorbed mercury under most of the flue gas conditions. Bromine is a very good oxidizing agent for mercury. But in the presence of calcium oxide containing fly ashes, all the oxidized mercury would be reduced to elemental form. Among the catalysts, it was observed that presence of free lattice chlorine in the catalyst was very important for the oxidation of mercury. But instead of using the catalyst alone, using it along with carbon may better serve the purpose by providing the adsorption surface for mercury and also some extra surface area for the reaction to occur (especially for fly ashes with low surface area).

Varanasi, Patanjali

352

Heck reactions of steroidal alkenyl iodides.  

PubMed

Heck reactions of some steroid derivatives possessing iodo-alkenyl moiety (17-iodo-androst-16-ene, 1, 17-iodo-4-aza-4-methyl-androst-16-en-3-one, 2, 17-iodo-4-aza-androst-16-en-3-one, 3) were carried out in the presence of palladium catalysts using various olefins (methyl acrylate, ethyl methacrylate, allyl alcohol and allyl acetate) as coupling partners. With methyl acrylate, a side reaction was observed: the coupling product underwent a Diels-Alder reaction with the excess of methyl acrylate resulting in a six-membered carbocyclic E-ring. Reaction conditions of the synthesis of the Heck-product were optimized. Although the coupling with allyl alcohol led to the formation of 21-formyl-16-pregnene derivatives, the synthesis of the corresponding steroidal unsaturated alcohol could be achieved only via hydrolysis of the coupling product of the alkenyl iodide with allyl acetate. PMID:9516719

Skoda-Földes, R; Bodnár, M; Kollár, L; Horváth, J; Tuba, Z

1998-02-01

353

TRIMOLECULAR REACTIONS OF URANIUM HEXAFLUORIDE WITH WATER  

SciTech Connect

The hydrolysis reaction of uranium hexafluoride (UF{sub 6}) is a key step in the synthesis of uranium dioxide (UO{sub 2}) powder for nuclear fuels. Mechanisms for the hydrolysis reactions are studied here with density functional theory and the Stuttgart small-core scalar relativistic pseudopotential and associated basis set for uranium. The reaction of a single UF{sub 6} molecule with a water molecule in the gas phase has been previously predicted to proceed over a relatively sizeable barrier of 78.2 kJ {center_dot} mol{sup -1}, indicating this reaction is only feasible at elevated temperatures. Given the observed formation of a second morphology for the UO{sub 2} product coupled with the observations of rapid, spontaneous hydrolysis at ambient conditions, an alternate reaction pathway must exist. In the present work, two trimolecular hydrolysis mechanisms are studied with density functional theory: (1) the reaction between two UF{sub 6} molecules and one water molecule, and (2) the reaction of two water molecules with a single UF{sub 6} molecule. The predicted reaction of two UF{sub 6} molecules with one water molecule displays an interesting 'fluorine-shuttle' mechanism, a significant energy barrier of 69.0 kJ {center_dot} mol{sup -1} to the formation of UF{sub 5}OH, and an enthalpy of reaction ({Delta}H{sub 298}) of +17.9 kJ {center_dot} mol{sup -1}. The reaction of a single UF{sub 6} molecule with two water molecules displays a 'proton-shuttle' mechanism, and is more favorable, having a slightly lower computed energy barrier of 58.9 kJ {center_dot} mol{sup -1} and an exothermic enthalpy of reaction ({Delta}H{sub 298}) of -13.9 kJ {center_dot} mol{sup -1}. The exothermic nature of the overall UF{sub 6} + 2 {center_dot} H{sub 2}O trimolecular reaction and the lowering of the barrier height with respect to the bimolecular reaction are encouraging; however, the sizable energy barrier indicates further study of the UF{sub 6} hydrolysis reaction mechanism is warranted to resolve the remaining discrepancies between the predicted mechanisms and experimental observations.

Westbrook, M.; Becnel, J.; Garrison, S.

2010-02-25

354

Microwave assisted reactions of some azaheterocylic compounds.  

PubMed

A fast, general, environmentally friendly and facile method for preparation of five- and six-membered ring diazaheterocylic salts under microwave irradiation is presented. The N-alkylation reactions of imidazole, pyrimidine, pyridazine and phthalazine have been studied. The microwaves remarkably accelerated these N-alkylations, the reaction times decreased dramatically, the reaction conditions were milder, the consumed energy decreased considerably and the amount of solvents used was reduced substantially. Consequently, the microwave assisted alkylation of N-containing heterocycles could be considered eco-friendly. In some cases, under MW irradiation the yields are also higher. A comparative study of microwave vs. classical conditions (liquid solvents) has been done. Twelve new diazaheterocylic salts of potential practical interest were obtained. PMID:19145217

Zbancioc, Gheorghita; Bejan, Vasilichia; Risca, Marian; Moldoveanu, Costel; Mangalagiu, Ionel I

2009-01-01

355

Optimal temperature conditions in catalytic reforming reactors  

Microsoft Academic Search

The paper reports on an investigation of the optimal distribution of temperatures at the inlet to the reaction section under conditions simulating the operation of commercial reformers. For these studies, the researchers used a semiworks catalytic reformer with three reactors, operating under adiabatic conditions. The experiments were performed with a commmercial polymetal catalyst KR-106 (0.36% platinum by weight), distributed in

Yu. A. Skipin; A. P. Fedorov; G. N. Maslyanskii; E. A. Shkuratova

2009-01-01

356

The reaction rate in nuclear fusion  

Microsoft Academic Search

Summary  A method to evaluate the reaction rate in nuclear fusion is proposed. This method is obtained in the framework of the elastic\\u000a model for subbarrier fusion. Conditions for the validity of the method are given. Some examples are discussed.

A. Scalia

1988-01-01

357

Reactions of cresol in hot aqueous borate solutions  

SciTech Connect

Phenol and methylphenol (cresol) are constituents of certain waste streams being considered for underground injection. We studied reactions of these compounds in solutions with other constituents of the waste streams and suspended clay at concentrations and temperatures higher than expected in natural situations, i.e. at 200{degrees}C and 250{degrees}C. Under these conditions, the predominant reaction was the demethylation of cresol to form phenol. This reaction was catalyzed strongly by clay. We were able to quantify phenol production. Other important reactions were a variety of condensation reactions in which two cresol molecules fuse. We found evidence of the intermolecular migration of methyl groups from the molecular weights of some of these condensation reactions. By digesting a sample of reacted clay with hydrofluoric acid we determined that under these conditions phenol and cresol did not bind appreciably to clay but that the condensation products did.

Tsao, L. [Lawrence Berkeley Lab., CA (United States); Weres, O. [Sonoma Research Co., Vineburg, CA (United States)

1992-04-01

358

Reaction Spectroscopy of ? Hypernuclei  

NASA Astrophysics Data System (ADS)

Reaction spectroscopy as a tool to investigate ? hypernuclear structure and ?N interaction is discussed showing recent spectroscopic data obtained through the (?+, K+) reaction using a large acceptance high resolution spectrometer (SKS) at KEK 12 GeV PS. High quality spectra of light ? hypernuclei in the p-shell region are compared with the recent DWIA calculation, in which a good agreement are observed. Analysis of the spectral shapes for 16? O and 13? C and their comparison with (K-,?-) data provided information on the splitting of the spin-orbit partner states, suggesting they are small. Future prospects of hypernuclear reaction spectroscopy are also presented.

Hashimoto, Osamu

2000-09-01

359

Characterization and Reaction Studies of Silica Supported Platinum and Rhodium Model Catalysts  

E-print Network

(e.g. CO oxidation) allow a method to calculate the total active area on a per atom basis for silica supported platinum and rhodium model catalysts under reaction conditions. While structure sensitive reactions allow an estimate of the types...

Lundwall, Matthew James

2012-02-14

360

Eco-friendly polyethylene glycol promoted Michael addition reactions of a,ß-unsaturated carbonyl compounds  

EPA Science Inventory

Abstract- Intra- and inter-nucleophilic addition reactions of different unsaturated compounds were found to be highly effective without any additives in PEG-400 as a recyclable reaction medium under neutral conditions. ...

361

Automated microreactor system for reaction development and online optimization of chemical processes  

E-print Network

Developing the optimal conditions for chemical reactions that are common in fine chemical and pharmaceutics is a difficult and expensive task. Because syntheses in these fields have multiple reaction pathways, a significant ...

McMullen, Jonathan Patrick

2010-01-01

362

Elucidation of the Chemical Structure and Determination of the Production Conditions for a Bioactive Maillard Reaction Product, [5-(5,6-Dihydro-4H-pyridin-3-ylidenemethyl)furan-2-yl]methanol, Isolated from a Glucose-Lysine Heated Mixture.  

PubMed

We previously isolated a bioactive molecule, named F3-A, from an aqueous glucose (Glc) and lysine (Lys) Maillard reaction (MR) model system. Herein, F3-A was verified as [5-(5,6-dihydro-4H-pyridin-3-ylidenemethyl)furan-2-yl]methanol (5) and was subsequently synthesized for confirmation of bioactivity. Using Taguchi and factorial designs, we determined that the conditions which best increased the yield of F3-A were at pH 6 with a sugar:amino acid ratio of 2:1 and heating time of 12 h at 100 °C. The MR mixtures containing glucose produced highest yield, compared to fructose, lactose, and sucrose. Both the F3-A recovered from Glc-Lys MR mixture and the synthesized product exhibited significant (P < 0.05), dose dependent, nitric oxide (NO) inhibitory activity in Caco-2 cells that was comparable to aminoguanidine (AG) and pyrrolidine dithiocarbamate (PDTC), respectively. Finally, an additional inhibitory effect of F3-A was determined when coincubated with AG in cytokine-induced Caco-2 cells. This bioactivity points to a potential role in preventing intestinal inflammation. PMID:25608183

Chen, Xiu-Min; Chen, Gang; Chen, Hongwen; Zhang, Yilin; Kitts, David D

2015-02-18

363

Ultrasound assisted reactions of steroid analogous of anticipated biological activities.  

PubMed

A new, fast, efficient and general method for preparation of steroid analogous of anticipated biological activity under ultrasound irradiation and classical heating is reported. The reaction pathway involves two steps: quaternization of phthalazine heterocycle followed by a 3+2 dipolar cycloaddition of cycloimmonium ylides to dienophiles. Under ultrasound the reaction time decreases substantially, the yields are higher, the reaction conditions are milder. A comparative study ultrasound verses classical heating has been done. PMID:19081283

Bejan, Vasilichia; Moldoveanu, Costel; Mangalagiu, Ionel I

2009-03-01

364

Kinetics of the sodium carbonate-sulfur dioxide reaction  

Microsoft Academic Search

The kinetics of the SOâ-NaâCOâ reaction were studied at 353 to 413 K and atmospheric pressure with thermal gravimetric analysis data. Since the reaction is very fast, special precautions were taken to operate at conditions such that transport effects did not influence results. The data indicated that NaâSOâ was formed by two paths: direct reaction, and adsorption of SOâ followed

Shoichi Kimura; J. M. Smith

1987-01-01

365

Reaction thrust of water jet for conical nozzles  

Microsoft Academic Search

Clear knowledge on the reaction thrust of water jet is valuable for better design of water jet propulsion system. In this\\u000a paper, theoretical, numerical and experimental studies were carried out to investigate the effects of the nozzle geometry\\u000a as well as the inlet conditions on the reaction thrust of water jet. Comparison analyses reveal that the reaction thrust has\\u000a a

Guo-qin Huang; You-sheng Yang; Xiao-hui Li; Yu-quan Zhu

2009-01-01

366

CBr4 -Mediated Cross-Dehydrogenative Coupling Reaction of Amines.  

PubMed

A novel CBr4 -mediated dehydrogenative Povarov/aromatization tandem reaction of glycine derivatives with alkenes, leading to complex quinoline derivatives, and a CBr4 -mediated dehydrogenative C?H functionalization of N-aryl tetrahydroisoquinolines with nucleophiles to form C?C and C?P bonds are reported. The reactions were performed under very simple and mild reaction conditions; only CBr4 was used as a promoter. A plausible mechanism involving a radical process is proposed. PMID:25707447

Huo, Congde; Xie, Haisheng; Wu, Mingxia; Jia, Xiaodong; Wang, Xicun; Chen, Fengjuan; Tang, Jing

2015-04-01

367

Reactor for exothermic reactions  

DOEpatents

A liquid phase process is described for oligomerization of C[sub 4] and C[sub 5] isoolefins or the etherification thereof with C[sub 1] to C[sub 6] alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120 to 300 F. Wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

Smith, L.A. Jr.; Hearn, D.; Jones, E.M. Jr.

1993-03-02

368

Polymerase Chain Reaction  

NSDL National Science Digital Library

This interactive activity adapted from the University of Nebraska's Library of Crop Technologies depicts steps in the polymerase chain reaction (PCR) technique and explains how it is used to efficiently copy sections of DNA for analysis.

2009-09-08

369

Reactor for exothermic reactions  

DOEpatents

A liquid phase process for oligomerization of C.sub.4 and C.sub.5 isoolefins or the etherification thereof with C.sub.1 to C.sub.6 alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120.degree. to 300.degree. F. Wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

Smith, Jr., Lawrence A. (Bellaire, TX); Hearn, Dennis (Houston, TX); Jones, Jr., Edward M. (Friendswood, TX)

1993-01-01

370

Chemisorption And Precipitation Reactions  

EPA Science Inventory

The transport and bioavailability of chemical components within soils is, in part, controlled by partitioning between solids and solution. General terms used to describe these partitioning reactions include chemisorption and precipitation. Chemisorption is inclusive of the suit...

371

Untoward penicillin reactions  

PubMed Central

The literature on untoward reactions following the administration of penicillin is reviewed. These reactions, including a certain number of deaths which have been reported, are of particular interest to health administrations and to WHO in view of the large-scale programmes for controlling the treponematoses which are now under way—programmes affecting millions of people in many parts of the world. The most serious problems are anaphylactic sensitivity phenomena and superinfection or cross-infection with penicillin-resistant organisms, and the reactions involved range in intensity from the mildest to the fatal; the incidence of the latter is estimated at 0.1-0.3 per million injections. The authors point out that with increasing use of penicillin, more persons are likely to become sensitized and the number of reactions can therefore be expected to rise. The best prevention against such an increase is the restriction of the unnecessary use of penicillin. PMID:13596877

Guthe, T.; Idsöe, O.; Willcox, R. R.

1958-01-01

372

Iodine Clock Reaction.  

ERIC Educational Resources Information Center

Describes a combination of solutions that can be used in the study of kinetics using the iodine clock reaction. The combination slows down degradation of the prepared solutions and can be used successfully for several weeks. (JRH)

Mitchell, Richard S.

1996-01-01

373

Transfusion reaction - hemolytic  

MedlinePLUS

... transfusion reaction. Mild symptoms may be treated with: Acetaminophen, a pain reliever to reduce fever and discomfort Fluids given through a vein (intravenous) and other medicines to treat or prevent kidney ...

374

Ligase Chain Reaction  

Microsoft Academic Search

\\u000a Nucleic acid amplification technologies have greatly facilitated medical diagnostics for genetic and infectious diseases through\\u000a the exquisite sensitivity and specificity associated with these methods. Polymerase chain reaction (PCR) (see\\u000a Chapter 6) ushered in these technologies and was soon accompanied by numerous newly developed amplification techniques, including\\u000a ligase chain reaction (LCR). These nucleic acid amplification techniques result in the exponential increase

Carla Osiowy

375

Thermonuclear reaction rates V  

Microsoft Academic Search

Analytic expressions are given for the reaction rates of astrophysically important thermonuclear reactions involving low-mass nuclei (1less than or equal toZless than or equal to14). Numerical values of the rates are tabulated for the temperature range 10⁶less than or equal toTless than or equal to10¹° K. This provides a comprehensive update of our previous publications. copyright 1988 Academic Press, Inc.

G. R. Caughlan; W. A. Fowler

1988-01-01

376

Polymerase Chain Reaction  

NSDL National Science Digital Library

Polymerase chain reaction (PCR) enables researchers to produce millions of copies of a specific DNA sequence in approximately two hours. This automated process bypasses the need to use bacteria for amplifying DNA. This animation from Cold Spring Harbor Laboratory's Dolan DNA Learning Center presents Polymerase Chain Reaction through a series of illustrations of the processes involved. Users may view the animation online (Flash is required) or download it for PC or Mac.

377

Glucose reversion reaction kinetics.  

PubMed

The reversion reactions of glucose in mildly acidic aqueous solutions have been studied, and the kinetics of conversion to disaccharides has been modeled. The experiments demonstrate that, at high sugar loadings, up to 12 wt % of the glucose can be converted into reversion products. The reversion products observed are primarily disaccharides; no larger oligosaccharides were observed. Only disaccharides linked to the C1 carbon of one of the glucose residues were observed. The formation of 1,6-linked disaccharides was favored, and alpha-linked disaccharides were formed at higher concentrations than beta-linked disaccharides. This observation can be rationalized on the basis of steric effects. At temperatures >140 degrees C, the disaccharides reach equilibrium with glucose and the reversion reaction competes with dehydration reactions to form 5-hydroxymethylfurfural. As a result, disaccharide formation reaches a maximum at reaction times <10 min and decreases with time. At temperatures <130 degrees C, disaccharide formation reaches a maximum at reaction times >30 min. As expected, disaccharide formation exhibits a second-order dependence upon glucose concentration. Levoglucosan formation is also observed; because it shows a first-order dependence upon glucose concentration, its formation is more significant at low concentrations (10 mg mL(-1)), whereas disaccharide formation dominates at high concentrations (200 mg mL(-1)). Experiments conducted using glucose and its disaccharides were calibrated with readily available standards. The kinetic parameters for hydrolysis of some glucodisaccharides could be compared to published literature values. From these experiments, the kinetics and activation energies for the reversion reactions have been calculated. The rate parameters can be used to model the formation of the disaccharides as a function of reaction time and temperature. A new and detailed picture of the molecular mechanism of these industrially important reversion reactions has been developed. PMID:20429509

Pilath, Heidi M; Nimlos, Mark R; Mittal, Ashutosh; Himmel, Michael E; Johnson, David K

2010-05-26

378

Rates of Hydrothermal Reactions  

Microsoft Academic Search

The rates of reactions of silicates and aqueous fluids follow zero-order kinetics controlled by the reacting surface area with the rate constant given by the equation: log k\\/bumpeq -2900\\/T - 6.85, where T is temperature and where k has the unit's gram-atoms of oxygen per square centimeter per second. This expression appears to hold for all silicates and for reactions

Bernard J. Wood; John V. Walther

1983-01-01

379

Side conditions for ordinary differential equations  

E-print Network

We specialize Olver's and Rosenau's side condition heuristics for the determination of particular invariant sets of ordinary differential equations. It turns out that side conditions of so-called LaSalle type are of special interest. Moreover we put side condition properties of symmetric and partially symmetric equations in a wider context. In the final section we present an application to parameter-dependent systems, in particular to quasi-steady state for chemical reactions.

G. Cicogna; G. Gaeta; S. Walcher

2014-06-11

380

Microfluidic study of fast gas-liquid reactions.  

PubMed

We present a new concept for studies of the kinetics of fast gas-liquid reactions. The strategy relies on the microfluidic generation of highly monodisperse gas bubbles in the liquid reaction medium and subsequent analysis of time-dependent changes in bubble dimensions. Using reactions of CO(2) with secondary amines as an exemplary system, we demonstrate that the method enables rapid determination of reaction rate constant and conversion, and comparison of various binding agents. The proposed approach addresses two challenges in studies of gas-liquid reactions: a mass-transfer limitation and a poorly defined gas-liquid interface. The proposed strategy offers new possibilities in studies of the fundamental aspects of rapid multiphase reactions, and can be combined with throughput optimization of reaction conditions. PMID:22176612

Li, Wei; Liu, Kun; Simms, Ryan; Greener, Jesse; Jagadeesan, Dinesh; Pinto, Sascha; Günther, Axel; Kumacheva, Eugenia

2012-02-15

381

Reaction kinetics of hydrothermal carbonization of loblolly pine.  

PubMed

Hydrothermal carbonization (HTC) is a pretreatment process to convert diverse feedstocks to homogeneous energy-dense solid fuels. Understanding of reaction kinetics is necessary for reactor design and optimization. In this study, the reaction kinetics and effects of particle size on HTC were investigated. Experiments were conducted in a novel two-chamber reactor maintaining isothermal conditions for 15s to 30 min reaction times. Loblolly pine was treated at 200, 230, and 260°C. During the first few minutes of reaction, the solid-product mass yield decreases rapidly while the calorific value increases rapidly. A simple reaction mechanism is proposed and validated, in which both hemicellulose and cellulose degrade in parallel first-order reactions. Activation energy of hemicellulose and cellulose degradation were determined to be 30 and 73 kJ/mol, respectively. For short HTC times, both reaction and diffusion effects were observed. PMID:23651600

Reza, M Toufiq; Yan, Wei; Uddin, M Helal; Lynam, Joan G; Hoekman, S Kent; Coronella, Charles J; Vásquez, Victor R

2013-07-01

382

Kinetics of a Substitution Reaction of Sulfitopentaaminecobalt(III).  

ERIC Educational Resources Information Center

Describes a laboratory experiment to determine the rate law for a substitution reaction of a transition metal. Derives the corresponding rate law from the accepted mechanism for the reaction using the steady state approximation and determines the conditions under which the two agree. (CW)

Richards, Lynne

1988-01-01

383

N-acyl oxazolidin-2-selones promoted aldol reactions  

SciTech Connect

Selenocarbonyls that are housed in a chiral environment have been found to play a pivotal role aldol reactions. We have found that, in general,, the aldol reaction affords the non-Evans aldol syn products. However, the use of glycolate donors with glycoaldehydes, under proper conditions, gave rise to predominately the anti aldol.

Li, Zizhong; Wu, R. (Ruilian); Silks, L. A. (Louis A.), III; Michalczyk, R. (Ryszard)

2001-01-01

384

Measurement of product alignment in beam-gas chemiluminescent reactions  

E-print Network

Measurement of product alignment in beam-gas chemiluminescent reactions Michael G. Prisant, Charles of the chemiluminescent atom-diatom exchange reaction A + BC-.AB* + C under beam-gas conditions. The degree of product momentum appears as product rotational angular momentum. For beam-gas chemiluminescence, this implies

Zare, Richard N.

385

Elementary reaction modeling of solid oxide electrolysis cells: Main zones for heterogeneous chemical/electrochemical reactions  

NASA Astrophysics Data System (ADS)

A theoretical model of solid oxide electrolysis cells considering the heterogeneous elementary reactions, electrochemical reactions and the transport process of mass and charge is applied to study the relative performance of H2O electrolysis, CO2 electrolysis and CO2/H2O co-electrolysis and the competitive behavior of heterogeneous chemical and electrochemical reactions. In cathode, heterogeneous chemical reactions exist near the outside surface and the electrochemical reactions occur near the electrolyte. According to the mathematical analysis, the mass transfer flux D ?c determines the main zone size of heterogeneous chemical reactions, while the charge transfer flux ? ?V determines the other one. When the zone size of heterogeneous chemistry is enlarged, more CO2 could react through heterogeneous chemical pathway, and polarization curves of CO2/H2O co-electrolysis could be prone to H2O electrolysis. Meanwhile, when the zone size of electrochemistry is enlarged, more CO2 could react through electrochemical pathway, and polarization curves of CO2/H2O co-electrolysis could be prone to CO2 electrolysis. The relative polarization curves, the ratio of CO2 participating in electrolysis and heterogeneous chemical reactions, the mass and charge transfer flux and heterogeneous chemical/electrochemical reaction main zones are simulated to study the effects of cathode material characteristics (porosity, particle diameter and ionic conductivity) and operating conditions (gas composition and temperature).

Li, Wenying; Shi, Yixiang; Luo, Yu; Cai, Ningsheng

2015-01-01

386

Chemical reactions at aqueous interfaces  

NASA Astrophysics Data System (ADS)

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

Vecitis, Chad David

2009-12-01

387

Development of a Reaction Signature for Combined Concrete Materials  

E-print Network

Although concrete is widely considered a very durable material, if conditions are such, it can be vulnerable to deterioration and early distress development. Alkali-Silica Reaction (ASR) is a major durability problem in concrete structures. It is a...

Ghanem, Hassan A.

2010-07-14

388

Ab initio simulations of reactions occurring in molecular crystals   

E-print Network

Although the solid state may not usually be thought of as an environment suitable for chemical reactions under mild conditions, a growing number of organic compounds are known to undergo interesting and, in many cases, practically useful chemistry...

Kochman, Michal

2014-06-28

389

Transition metals as catalysts of "autoxidation" reactions.  

PubMed

Superoxide (O2-), hydrogen peroxide (H2O2), and hydroxyl radical (.OH) produced from the "autoxidation" of biomolecules, such as ascorbate, catecholamines, or thiols, have been implicated in numerous toxicities. However, the direct reaction of dioxygen with the vast majority of biomolecules, including those listed above, is spin forbidden, a condition which imposes a severe kinetic limitation on this reaction pathway. Therefore, an alternate mechanism must be invoked to explain the "autoxidations" reactions frequently reported. Transition metals are efficient catalysts of redox reactions and their reactions with dioxygen are not spin restricted. Therefore it is likely that the "autoxidation" observed for many biomolecules is, in fact, metal catalyzed. In this paper we discuss: 1) the quantum mechanic, thermodynamic, and kinetic aspects of the reactions of dioxygen with biomolecules; 2) the involvement of transition metals in biomolecule oxidation; and 3) the biological implications of metal catalyzed oxidations. We hypothesize that true autoxidation of biomolecules does not occur in biological systems, instead the "autoxidation" of biomolecules is the result of transition metals bound by the biomolecules. PMID:2182396

Miller, D M; Buettner, G R; Aust, S D

1990-01-01

390

Stellar evolution and the triple-? reactions  

SciTech Connect

Nuclear reaction rates play a crucial role in the evolution of stars. For low-mass stars, the triple-? reaction controls the helium burning stars in the red giant and asymptotic giant branch (AGB) phase. More importantly, the cross section of the triple-? reaction has a great impact on the helium ignition at the center of the electron degenerate helium core of red giants and on the helium shell flashes of AGB stars. It is to be noted that stellar evolution models are influenced not only by the value of the cross section, but also by the temperature dependence of the reaction rate. In this paper, I present the impact of the triple-? reaction rates on the evolution of low-mass metal-free stars and intermediate-mass AGB stars. According to the previous study, the constraint on the triple-? reaction rate is derived based on stellar evolution theory. It is found that the recent revisions of the rate proposed by nuclear physics calculations satisfy the condition for the ignition of the helium core flash in low-mass stars.

Suda, Takuma [Osawa 2-21-1, Mitaka, Tokyo, 181-8588 (Japan)

2014-05-02

391

[Cutaneous adverse drug reactions].  

PubMed

Cutaneous adverse drug reactions (CADR) represent a heterogeneous field including various clinical patterns without specific features suggesting drug causality. Exanthematous eruptions, urticaria and vasculitis are the most common forms of CADR. Fixed eruption is uncommon in western countries. Serious reactions (fatal outcome, sequelae) represent 2% of CADR: bullous reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), DRESS (drug reaction with eosinophilia and systemic symptoms or drug-induced hypersensitivity syndrome) and acute generalized exanthematous pustulosis (AGEP). These forms must be quickly diagnosed to guide their management. The main risk factors are immunosuppression, autoimmunity and some HLA alleles in bullous reactions and DRESS. Most systemic drugs may induce cutaneous adverse reactions, especially antibiotics, anticonvulsivants, antineoplastic drugs, non-steroidal anti-inflammatory drugs, allopurinol and contrast media. Pathogenesis includes immediate or delayed immunologic mechanism, usually not related to dose, and pharmacologic/toxic mechanism, commonly dose-dependent or time-dependent. In case of immunologic mechanism, allergologic exploration is possible to clarify drug causality, with a variable sensitivity according to the drug and to the CADR type. It includes epicutaneous patch testing, prick test and intradermal test. However, no in vivo or in vitro test can confirm the drug causality. To determine the cause of the eruption, a logical approach based on clinical characteristics, chronologic factors and elimination of differential diagnosis is required, completed with a literature search. A reporting to pharmacovigilance network is essential in case of a serious CADR whatever the suspected drug and in any case if the involved drug is a newly marketed one or unusually related to cutaneous reactions. PMID:25458866

Lebrun-Vignes, B; Valeyrie-Allanore, L

2015-04-01

392

Parallelization of photocatalytic gas-producing reactions.  

PubMed

High-throughput screening has been widely utilized in the pharmaceutical and manufacturing industry targeting the development of new molecules and materials for numerous applications. To enable more rapid progress in photocatalytic water-splitting reactions, the construction of high-throughput combinatorial photoreactors enabling the parallel optimization of relevant compositions under varieties of experimental conditions seems appropriate. This contribution describes a 16-photoreactor apparatus permitting the kinetic evaluation of photocatalytic gas-producing reactions using head-space pressure, gas chromatography, and mass spectrometry operating in parallel, illustrated with molecular-based homogeneous photocatalytic H2-generating compositions. PMID:25832247

Khnayzer, Rony S; Martin, Douglas R; Codding, Charles L; Castellano, Felix N

2015-03-01

393

Parallelization of photocatalytic gas-producing reactions  

NASA Astrophysics Data System (ADS)

High-throughput screening has been widely utilized in the pharmaceutical and manufacturing industry targeting the development of new molecules and materials for numerous applications. To enable more rapid progress in photocatalytic water-splitting reactions, the construction of high-throughput combinatorial photoreactors enabling the parallel optimization of relevant compositions under varieties of experimental conditions seems appropriate. This contribution describes a 16-photoreactor apparatus permitting the kinetic evaluation of photocatalytic gas-producing reactions using head-space pressure, gas chromatography, and mass spectrometry operating in parallel, illustrated with molecular-based homogeneous photocatalytic H2-generating compositions.

Khnayzer, Rony S.; Martin, Douglas R.; Codding, Charles L.; Castellano, Felix N.

2015-03-01

394

Reactions of butadiyne. 1: The reaction with hydrogen atoms  

NASA Technical Reports Server (NTRS)

The reaction of hydrogen (H) atoms with butadiene (C4H2) was studied at room temperature in a pressure range between w mbar and 10 mbar. The primary step was an addition of H to C4H2 which is in its high pressure range at p 1 mbar. Under these conditions the following addition of a second H atom lies in the transition region between low and high pressure range. Vibrationally excited C4H4 can be deactivated to form buten-(1)-yne-(3)(C4H4) or decomposes into two C2H2 molecules. The rate constant at room temperature for primary step is given. The second order rate constant for the consumption of buten-(1)-yne-(3) is an H atom excess at room temperature is given.

Schwanebeck, W.; Warnatz, J.

1984-01-01

395

Ion-Molecule Reactions  

NASA Astrophysics Data System (ADS)

The observation of ion-molecule reactions has a history that goes back to the beginning of the twentieth century, when J. J. Thomson discovered that operating his positive ray parabola apparatus in a hydrogen atmosphere produced signals at a mass to charge ratio of 3, which he correctly attributed to the species H3 [67.1]. Later studies showed that this species was produced by a reaction between the primary ionization product H2 + and molecular hydrogen. Most ion-molecule reactions proceed without an activation barrier and their cross sections are governed by the long range attractive potential of the approaching reactants (Sect. 64.2.4). Reaction rates based on long range potential capture models [67.2] predict rates in excess of 10-9 cm3molecule-1s-1, corresponding to thermal energy cross sections (Sect. 47.1.7) of 10-16-10-15 cm2. The importance of ion-molecule reactions in such widely diverse areas as planetary atmospheres, (Sect. 84.1), electrical discharges and plasmas (Sect. 87.1.4), particularly in semiconductor processing, in the formation of molecules in interstellar space (Chapt. 82), and in flames and combustion systems (Sect. 88.1), has borne out that prediction. This chapter discusses applications of single-collision scattering methods to the study of reactive collision dynamics of ionic species with neutral partners.

Farrar, James

396

Theoretical Study ofTheoretical Study of ReactionReaction  

E-print Network

. The program prints out the reaction rate in the Arrhenius form (k = A Tn exp(-Ea/RT)) over the temperature and enthalpy) in the polynomial form for 200-6000K temperature range. The reaction rate and the polynomial form was extended to a mechanism with 35 species and 1012 reactions. Rate constants for 117 elementary reactions

397

Movement as a signal during classical conditioning.  

PubMed

Analysis of the available data and that of the author disclosed the peculiarities of motor reaction when used as a conditioned stimulus. The author's data showed that if signal value is attributed to a motor reaction (passive movement or movement evoked by the direct stimulation of the motor cortex), the changes of excitability in the motor cortex representation of the dog's leg depend on the biological sign of the reinforcing stimulus during classic conditioning. They also remained the same during instrumental conditioning and were opposite in sign, showed increased excitability in the food situation, and decreased excitability in the defense situation. Using the movement as a conditional stimulus, we managed to uncover the commonality between classic and instrumental conditioning. This enabled us to answer questions, discussed by Pavlov and Guthrie, which, it seems to us, had not been convincingly answered during their time. PMID:3050824

Davydova, E K

1988-01-01

398

Phase and chemical equilibria in the transesterification reaction of vegetable oils with supercritical lower alcohols  

NASA Astrophysics Data System (ADS)

Calculations of thermodynamic data are performed for fatty acid triglycerides, free fatty acids, and fatty acid methyl esters, participants of the transesterification reaction of vegetable oils that occurs in methanol. Using the obtained thermodynamic parameters, the phase diagrams for the reaction mixture are constructed, and the chemical equilibria of the esterification reaction of free fatty acids and the transesterification reaction of fatty acid triglycerides attained upon treatment with supercritical methanol are determined. Relying on our analysis of the obtained equilibria for the esterification reaction of fatty acids and the transesterification reaction of triglycerides attained upon treatment with lower alcohols, we select the optimum conditions for performing the reaction in practice.

Anikeev, V. I.; Stepanov, D. A.; Ermakova, A.

2011-08-01

399

Reaction/Momentum Wheel  

NASA Technical Reports Server (NTRS)

CTA Space Systems, Inc. has been licensed to sell commercially a reaction/momentum wheel originally developed for NASA's scientific satellites. NASA originally identified a need for the wheel in its Small Explorer program. The Submillimeter Wave Astronomy Satellite required extremely low jitter and a reaction/momentum wheel with a torque greater than any comparably sized commercially available wheel to keep the instrument pointed at celestial objects to a high degree of precision. After development, a market assessment by Research Triangle Institute was completed, showing commercial potential for the flywheel technology. A license was granted to CTA in the fall of 1996. The company currently uses the technology in its complete spacecraft fabrication services and has built over 10 reaction/momentum wheels for commercial, scientific, and military customers.

1997-01-01

400

Flow Giese reaction using cyanoborohydride as a radical mediator  

PubMed Central

Summary Tin-free Giese reactions, employing primary, secondary, and tertiary alkyl iodides as radical precursors, ethyl acrylate as a radical trap, and sodium cyanoborohydride as a radical mediator, were examined in a continuous flow system. With the use of an automated flow microreactor, flow reaction conditions for the Giese reaction were quickly optimized, and it was found that a reaction temperature of 70 °C in combination with a residence time of 10–15 minutes gave good yields of the desired addition products. PMID:24062844

Fukuyama, Takahide; Kawamoto, Takuji; Kobayashi, Mikako

2013-01-01

401

Aqueous Oxidative Heck Reaction as a Protein-Labeling Strategy  

PubMed Central

An increasing number of chemical reactions are being employed for bio-orthogonal ligation of detection labels to protein-bound functional groups. Several of these strategies, however, are limited in their application to pure proteins and are ineffective in complex biological samples such as cell lysates. Here we present the palladium-catalyzed oxidative Heck reaction as a new and robust bio-orthogonal strategy for linking functionalized arylboronic acids to protein-bound alkenes in high yields and with excellent chemoselectivity even in the presence of complex protein mixtures from living cells. Advantageously, this reaction proceeds under aerobic conditions, whereas most other metal-catalyzed reactions require inert atmosphere. PMID:24376051

Ourailidou, Maria Eleni; van der Meer, Jan-Ytzen; Baas, Bert-Jan; Jeronimus-Stratingh, Margot; Gottumukkala, Aditya L; Poelarends, Gerrit J; Minnaard, Adriaan J; Dekker, Frank J

2014-01-01

402

Modular modification of xylan with UV-initiated thiol-ene reaction.  

PubMed

Birch xylan was functionalized with various thiols through UV initiated radical thiol-ene reaction under mild conditions. Xylan was allylated through etherification with allyl glycidyl ether under alkaline conditions. The allylated xylan was then reacted with thiols containing varying functional groups: trimethylbenzyl mercaptan, dodecanethiol, thioglycolic acid, l-cysteine and cysteamine hydrochloride. The reactions were conducted under homogeneous conditions at room temperature, either in water (hydrophilic thiols) or in DMF (hydrophobic thiols). The effect of reaction parameters to the functionalization efficiency was studied, including, for example, thiol excess, thiol character, initiator amount and reaction mixture concentration. The reactions were fast and 100% conversion of allyl groups was reached in most cases, sometimes already within 10min. Water as solvent resulted generally in faster reactions when compared to DMF, and it was possible to conduct the aqueous reaction even without added UV initiator. It was also possible to incorporate two functionalities simultaneously during one reaction into the xylan structure. PMID:25665780

Nurmi, Leena; Salminen, Reeta; Setälä, Harri

2015-03-01

403

Computational analysis of methyl transfer reactions in dengue virus methyltransferase.  

PubMed

S-Adenosyl-L-methionine (SAM) dependent methyltransferases (MTases) play crucial roles in many biological processes. The MTase of the dengue virus is of particular interest for the development of antiviral drugs against flaviviruses. It catalyzes two distinct methylation reactions at the N7 and the 2'O position of the viral RNA cap structure. Based on density functional theory (DFT) electronic structure calculations, the molecular basis of the underlying chemical reactions involved in the N7 and the 2'O methyl transfer reactions of this enzyme were investigated using model systems. Calculations in the condensed phase show that both reactions are exergonic with significant activation barriers of 13.7 and 17.6 kcal/mol and stable product states, stabilized by 23.5 and 16.9 kcal/mol compared to the reactant states for the N7 and the 2'O reaction, respectively. We find that the reaction rate for the 2'O reaction is significantly enhanced in the presence of the native proton acceptor group, which lowers the activation barrier in the catalyzed reaction by 3.8 kcal/mol compared to the uncatalyzed reaction in aqueous solution. Furthermore, the 2'O reaction involves a methyl and a proton transfer reaction. Our results suggest that these two reactions occur in a concerted fashion in which the methyl group and the proton are transferred simultaneously. From a therapeutic viewpoint, SAM analogues stable under physiological conditions are particularly relevant. One such compound in MeAzaSAM, an isostructural mimic of SAM, for which the present calculations suggest that the methyl transfer reaction is unlikely to occur under biologically relevant conditions. PMID:24809209

Schmidt, Tobias; Schwede, Torsten; Meuwly, Markus

2014-06-01

404

Positron Reaction Microscope  

NASA Astrophysics Data System (ADS)

We are developing a positron reaction microscope to measure kinematically complete ionization reactions of atoms and dissociative ionization of simple molecules by positron impact. The experiment is designed to use the slow positron beamline at the ARC Centre for Antimatter Matter Studies (CAMS) node at the Australian National University (ANU). This project is a collaboration among the University of North Texas, CAMS, and the Max Planck Insitute for Kern Phyzik in Heidelberg. Initial measurements and apparatus calibration will be performed using electrons. For positron measurements, the apparatus will be rolled into position on the slow positron beamline at the CAMS site at ANU.

Mueller, D. W.; Lee, C.; Vermet, C.; Armitage, S.; Slaughter, D.; Hargrave, L.; Dorn, A.; Brunton, J.; Buckman, S. J.; Sullivan, J. P.

2012-06-01

405

Velocity pump reaction turbine  

DOEpatents

An expanding hydraulic/two-phase velocity pump reaction turbine including a dual concentric rotor configuration with an inter-rotor annular flow channel in which the inner rotor is mechanically driven by the outer rotor. In another embodiment, the inner rotor is immobilized and provided with gas recovery ports on its outer surface by means of which gas in solution may be recovered. This velocity pump reaction turbine configuration is capable of potential energy conversion efficiencies of up to 70%, and is particularly suited for geothermal applications.

House, Palmer A. (Walnut Creek, CA)

1984-01-01

406

Velocity pump reaction turbine  

DOEpatents

An expanding hydraulic/two-phase velocity pump reaction turbine including a dual concentric rotor configuration with an inter-rotor annular flow channel in which the inner rotor is mechanically driven by the outer rotor. In another embodiment, the inner rotor is immobilized and provided with gas recovery ports on its outer surface by means of which gas in solution may be recovered. This velocity pump reaction turbine configuration is capable of potential energy conversion efficiencies of up to 70%, and is particularly suited for geothermal applications.

House, Palmer A. (Walnut Creek, CA)

1982-01-01

407

Reaction rate and products for the reaction O/3P/ + H2CO  

NASA Technical Reports Server (NTRS)

A study of reaction kinetics of O + H2CO in a discharge-flow system using mass spectrometric detection of reactants and products is presented. It was performed under both oxygen-atom-rich and formaldehyde-rich conditions over the 296 to 437 K range, showing that the global bimolecular rate constant is in agreement with other studies. This study differs from others in that the reaction products can be observed, and a substantial yield of a primary reaction product was measured with a mass spectral peak at m/e=44. This suggests that the global reaction rate probably consists of combination, as well as of simple abstraction. For the combination, one hypothesis is that triplet dioxymethylene is formed which polymerizes to triplet formic acid; the vibrationally excited triplet formic acid may decompose to form several sets of products, including HCO + OH and HCO2 + H.

Chang, J. S.; Barker, J. R.

1979-01-01

408

Gas Producing Micro-Reaction  

NSDL National Science Digital Library

In this chemistry activity, learners use common chemicals and metals to examine reactions that produce gaseous substances. Learners will identify the gases produced and write a balanced equation for each reaction. Use this activity to also introduce learners to single displacement and double displacement reactions, two types of chemical reactions.

2014-01-28

409

What Is a Reaction Rate?  

ERIC Educational Resources Information Center

The definition of reaction rate is derived and demonstrations are made for the care to be taken while using the term. Reaction rate can be in terms of a reaction property, the extent of reaction and thus it is possible to give a definition applicable in open and closed systems.

Schmitz, Guy

2005-01-01

410

Inorganic Reaction Mechanisms. Part I  

ERIC Educational Resources Information Center

Provides a collection of data on the mechanistic aspects of inorganic chemical reactions. Wherever possible includes procedures for classroom demonstration or student project work. The material covered includes gas phase reactions, reactions in solution, mechanisms of electron transfer, the reaction between iron III and iodine, and hydrolysis. (GS)

Cooke, D. O.

1976-01-01

411

Different reaction mechanisms for cis- and trans-prenyltransferases  

SciTech Connect

Octaprenyl diphosphate synthase (OPPs) and undecaprenyl diphosphate synthases (UPPs) catalyze consecutive condensation reactions of farnesyl diphosphate (FPP) with 5 and 8 isopentenyl diphosphate (IPP) to generate C{sub 40} and C{sub 55} products with trans- and cis-double bonds, respectively. In this study, we used IPP analogue, 3-bromo-3-butenyl diphosphate (Br-IPP), in conjunction with radiolabeled FPP, to probe the reaction mechanisms of the two prenyltransferases. Using this alternative substrate with electron-withdrawing bromo group at the C3 position to slow down the condensation step, trapping of farnesol in the OPPs reaction from radiolabeled FPP under basic condition was observed, consistent with a sequential mechanism. In contrast, UPPs reaction yielded no farnesyl carbocation intermediate under the same condition with radiolabeled FPP and Br-IPP, indicating a concerted mechanism. Our data demonstrate the different reaction mechanisms for cis- and tran-prenyltransferases although they share the same substrates.

Lu Yenpin [Institute of Biochemical Sciences, National Taiwan University, Taipei 106, Taiwan (China); Liu Hunge [Institute of Biological Chemistry, 128 Academia Rd. sec. 2, Academia Sinica, Taipei 115, Taiwan (China); Liang, P-H. [Institute of Biochemical Sciences, National Taiwan University, Taipei 106, Taiwan (China); Institute of Biological Chemistry, 128 Academia Rd. sec. 2, Academia Sinica, Taipei 115, Taiwan (China)], E-mail: phliang@gate.sinica.edu.tw

2009-02-06

412

A taxonomy of integral reaction path analysis  

SciTech Connect

W. C. Gardiner observed that achieving understanding through combustion modeling is limited by the ability to recognize the implications of what has been computed and to draw conclusions about the elementary steps underlying the reaction mechanism. This difficulty can be overcome in part by making better use of reaction path analysis in the context of multidimensional flame simulations. Following a survey of current practice, an integral reaction flux is formulated in terms of conserved scalars that can be calculated in a fully automated way. Conditional analyses are then introduced, and a taxonomy for bidirectional path analysis is explored. Many examples illustrate the resulting path analysis and uncover some new results about nonpremixed methane-air laminar jets.

Grcar, Joseph F.; Day, Marcus S.; Bell, John B.

2004-12-23

413

Atmospheric photooxidation reactions. Rates, reactivity, and mechanism for reaction of organic compounds with hydroxyl radicals  

Microsoft Academic Search

The photooxidation of a number of organic species, representing several classes of atmospheric pollutants, was studied in the presence of HONO, NO, and NOâ at parts per million concentrations. The experiments give information on the rate and mechanism of the reaction with organic molecules of HO radicals produced by photolysis of HONO under these conditions. The data allow evaluation of

Richard A. Cox; Richard G. Derwent; Michael R. Williams

1980-01-01

414

Activity, stability and deactivation behavior of Au\\/CeO 2 catalysts in the water gas shift reaction at increased reaction temperature (300 °C)  

Microsoft Academic Search

The effect of increasing the reaction temperature to 300°C on the activity, stability and deactivation behavior of a 4.5wt.% Au\\/CeO2 catalyst in the water gas shift (WGS) reaction in idealized reformate was studied by kinetic and spectroscopic measurements at 300°C and comparison with previously reported data for reaction at 180°C under similar reaction conditions [A. Karpenko, Y. Denkwitz, V. Plzak,

A. Abd El-Moemen; A. Karpenko; Y. Denkwitz; R. J. Behm

2009-01-01

415

A Principal's Reaction  

ERIC Educational Resources Information Center

This article presents a principal's reaction to Catherine Marshall and Michael Ward's article on research on social justice and training for leadership. The author applauds Marshall and Ward's efforts to address what is undoubtedly among the most fundamentally important issues facing principals today. Marshall and Ward illuminate the importance of…

Zaretsky, Lindy

2004-01-01

416

Exocharmic Reactions up Close  

ERIC Educational Resources Information Center

The exocharmic reactions that can be observed microscopically are discussed. The students can discover the optimal concentration of an acidic lead nitrate solution, so that a crystal of potassium iodide, nudged to the edge of a drop, results in glinting golden hexagons of lead iodide.

Ramette, R. W.

2007-01-01

417

Chemical Reactions at Surfaces  

SciTech Connect

Chemical reactions at surfaces underlie some of the most important processes of today, including catalysis, energy conversion, microelectronics, human health and the environment. Understanding surface chemical reactions at a fundamental level is at the core of the field of surface science. The Gordon Research Conference on Chemical Reactions at Surfaces is one of the premiere meetings in the field. The program this year will cover a broad range of topics, including heterogeneous catalysis and surface chemistry, surfaces in environmental chemistry and energy conversion, reactions at the liquid-solid and liquid-gas interface, electronic materials growth and surface modification, biological interfaces, and electrons and photons at surfaces. An exciting program is planned, with contributions from outstanding speakers and discussion leaders from the international scientific community. The conference provides a dynamic environment with ample time for discussion and interaction. Attendees are encouraged to present posters; the poster sessions are historically well attended and stimulate additional discussions. The conference provides an excellent opportunity for junior researchers (e.g. graduate students or postdocs) to present their work and interact with established leaders in the field.

Michael Henderson and Nancy Ryan Gray

2010-04-14

418

Organocatalytic Domino Reactions  

Microsoft Academic Search

Since the rediscovery of proline in 2000 as catalyst in aldol reaction by List, Barbas and Lerner and, soon after, the development of iminium catalysis by D. W. C. MacMillan, the emergence of organocatalysis as an important tool in organic synthesis is outstanding. During the last years, several research groups have worked in the development of new and powerful methodologies

Andrea-Nekane Alba; Xavier Companyo; Monica Viciano; Ramon Rios

2009-01-01

419

Rates of Chemical Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the third of four Science Objects in the Chemical Reactions SciPack. It demonstrates

National Science Teachers Association (NSTA)

1900-01-01

420

Two chamber reaction furnace  

Microsoft Academic Search

A vertical two chamber reaction furnace. The furnace comprises a lower chamber having an independently operable first heating means for heating the lower chamber and a gas inlet means for admitting a gas to create an ambient atmosphere, and an upper chamber disposed above the lower chamber and having an independently operable second heating means for heating the upper chamber.

Blaugher; Richard D

1998-01-01

421

Two chamber reaction furnace  

Microsoft Academic Search

A vertical two chamber reaction furnace is described. The furnace comprises a lower chamber having an independently operable first heating means for heating the lower chamber and a gas inlet means for admitting a gas to create an ambient atmosphere, and an upper chamber disposed above the lower chamber and having an independently operable second heating means for heating the

Blaugher

1998-01-01

422

Categorizing Chemical Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the second of four Science Objects in the Chemical Reactions SciPack. It provides an

National Science Teachers Association (NSTA)

2009-07-10

423

Polymerase chain reaction system  

DOEpatents

A portable polymerase chain reaction DNA amplification and detection system includes one or more chamber modules. Each module supports a duplex assay of a biological sample. Each module has two parallel interrogation ports with a linear optical system. The system is capable of being handheld.

Benett, William J.; Richards, James B.; Stratton, Paul L.; Hadley, Dean R.; Milanovich, Fred P.; Belgrader, Phil; Meyer, Peter L.

2004-03-02

424

Chain Reaction Polymerization.  

ERIC Educational Resources Information Center

The salient features and importance of chain-reaction polymerization are discussed, including such topics as the thermodynamics of polymerization, free-radical polymerization kinetics, radical polymerization processes, copolymers, and free-radical chain, anionic, cationic, coordination, and ring-opening polymerizations. (JN)

McGrath, James E.

1981-01-01

425

Activationless photoionization reactions  

NASA Astrophysics Data System (ADS)

The notion of an activationless zone appearing due to the space dispersion of the activation energy and vibronic excitation of reaction products is introduced. The effective radius viscosity dependence of pheophytin a quenching by toluquinone is compared with the theory, taking into account a strong interaction between them deep inside the activationless zone. The electron tunnelling probability is determined by fitting to experiment.

Burshtein, A. I.; Morozov, V. A.

1990-01-01

426

Reaction Formulation: A Bibliography.  

ERIC Educational Resources Information Center

Reaction formation was studied by Sigmund Freud. This defense mechanism may be related to repression, substitution, reversal, and compensation (or over-compensation). Alfred Adler considered compensation a basic process in his individual psychology. Anna Freud discussed some defense mechanisms, and Bibring, Dwyer, Huntington, and Valenstein…

Pedrini, D. T.; Pedrini, Bonnie C.

427

Organic Reactions and Biofuels  

NSDL National Science Digital Library

The Advanced Technology Environmental and Energy Center (ATEEC) provides this classroom activity on organic reactions and biofuels. The goal of the lesson is to react methanol with waste oil to synthesize biodiesel. Users must download this resource for viewing, which requires a free log-in. There is no cost to download the item.

428

Reaction product imaging  

SciTech Connect

Over the past few years the author has investigated the photochemistry of small molecules using the photofragment imaging technique. Bond energies, spectroscopy of radicals, dissociation dynamics and branching ratios are examples of information obtained by this technique. Along with extending the technique to the study of bimolecular reactions, efforts to make the technique as quantitative as possible have been the focus of the research effort. To this end, the author has measured the bond energy of the C-H bond in acetylene, branching ratios in the dissociation of HI, the energetics of CH{sub 3}Br, CD{sub 3}Br, C{sub 2}H{sub 5}Br and C{sub 2}H{sub 5}OBr dissociation, and the alignment of the CD{sub 3} fragment from CD{sub 3}I photolysis. In an effort to extend the technique to bimolecular reactions the author has studied the reaction of H with HI and the isotopic exchange reaction between H and D{sub 2}.

Chandler, D.W. [Sandia National Laboratories, Livermore, CA (United States)

1993-12-01

429

A World of Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the first of four Science Objects in the Chemical Reactions SciPack. It explains tha

National Science Teachers Association (NSTA)

2009-07-10

430

Plasmon-driven sequential chemical reactions in an aqueous environment  

PubMed Central

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

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

2014-01-01

431

Plasmon-driven sequential chemical reactions in an aqueous environment  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

432

Photoneutron reactions in astrophysics  

NASA Astrophysics Data System (ADS)

Among key problems in nuclear astrophysics, that of obtaining deeper insight into the mechanism of synthesis of chemical elements is of paramount importance. The majority of heavy elements existing in nature are produced in stars via radiative neutron capture in so-called s- and r processes, which are, respectively, slow and fast, in relation to competing ? --decay processes. At the same time, we know 35 neutron-deficient so-called bypassed p-nuclei that lie between 74Se and 196Hg and which cannot originate from the aforementioned s- and r-processes. Their production is possible in ( ?, n), ( ?, p), or ( ?, ?) photonuclear reactions. In view of this, data on photoneutron reactions play an important role in predicting and describing processes leading to the production of p-nuclei. Interest in determining cross sections for photoneutron reactions in the threshold energy region, which is of particular importance for astrophysics, has grown substantially in recent years. The use of modern sources of quasimonoenergetic photons obtained in processes of inverse Compton laser-radiation scattering on relativistic electronsmakes it possible to reveal rather interesting special features of respective cross sections, manifestations of pygmy E1 and M1 resonances, or the production of nuclei in isomeric states, on one hand, and to revisit the problem of systematic discrepancies between data on reaction cross sections from experiments of different types, on the other hand. Data obtained on the basis of our new experimental-theoretical approach to evaluating cross sections for partial photoneutron reactions are invoked in considering these problems.

Varlamov, V. V.; Ishkhanov, B. S.; Orlin, V. N.; Peskov, N. N.; Stopani, K. A.

2014-12-01

433

Citrus Peel Additives for One-Pot Triazole Formation by Decarboxylation, Nucleophilic Substitution, and Azide-Alkyne Cycloaddition Reactions  

ERIC Educational Resources Information Center

This undergraduate organic laboratory experiment consists of three different reactions occurring in the same flask: a cycloaddition reaction, preceded by decarboxylation and nucleophilic substitution reactions. The decarboxylation and cycloaddition reactions occur using identical Cu(I) catalyst and conditions. Orange, lemon, and other citrus fruit…

Mendes, Desiree E.; Schoffstall, Allen M.

2011-01-01

434

Lewis Acid and/or Lewis Base catalyzed [3+2] cycloaddition reaction: Synthesis of pyrazoles and pyrazolines  

E-print Network

1 Lewis Acid and/or Lewis Base catalyzed [3+2] cycloaddition reaction: Synthesis of pyrazoles is reported. All the reactions were carried out under no strong bases/acids, solvent free conditions+2] cycloaddition reaction strategy to form five membered ring systems through the reaction partners of 1,3-dipoles

Paris-Sud XI, Université de

435

Resilience in reaction-diffusion systems  

NASA Astrophysics Data System (ADS)

Reaction-diffusion systems with zero-flux Neumann boundaries are widely used to model various kinds of interaction in, for example, the scientific fields of ecology, biology, chemistry, medicine and industry. The physical systems within these fields are often known to be (conditionally or unconditionally) resilient with respect to shocks, disturbances or catastrophies in the immediate environment. In order to be good mathematical models of such situations the reaction-diffusion systems must have the same resilient or asymptotic behaviour as that of the physical situation. Three fundamentally different kinds of reaction terms are usually distinguished according to the entry signs of the reaction Jacobian: mutualism, mixed (predator-prey) interaction and competition. The asymptotic stability (in the Poincare sense) of mutualistic systems has already been studied extensively, but the results cannot be generalized (globally) to the other two fundamental types, which are not order-preserving. A partial (local) generalization is, however given here for these two types, involving simple Jacobian inequalities and knowledge (often prompted by the underlying physical situation) of invariant sets in solution space. The return time of resilient systems and the approach rate of asymptotically stable solutions are also estimated. Key words: reaction-diffusion system; competition; resilience; asymptotic stability.

van Vuuren, J. H.

1999-10-01

436

The effects of reward and punishment on reaction times and autonomic activity in hyperactive and normal children  

Microsoft Academic Search

The performance of hyperactive and control children was compared on a delayed reaction time task under three reinforcement conditions: reward, punishment, and reward plus punishment. Hyperactives had slower and more variable reaction times, suggesting an attentional deficit. Although each of the three reinforcement conditions was successful in improving reaction times for both subject groups, reward led to a significant increase

Philip Firestone; Virginia Douglas

1975-01-01

437

Reactions of inorganic nitrogen species in supercritical water  

SciTech Connect

Redox reactions of nitrate salts with NH3 and methanol were studied in near-critical and supercritical water at 350 to 530 C and constant pressure of 302 bar. Sodium nitrate decomposition reactions were investigated at similar conditions. Reactions were conducted in isothermal tubular reactor under plug flow. For kinetic modeling, nitrate and nitrite reactants were lumped into an NO{sub x}{sup -} reactant; kinetic expressions were developed for MNO{sub 3}/NH{sub 4}X and sodium nitrate decomposition reactions. The proposed elementary reaction mechanism for MNO{sub 3}/NH{sub 4}X reaction indicated that NO{sub 2} was the primary oxidizing species and that N{sub 2}/N{sub 2}O selectivities could be determined by the form of MNO{sub 3} used. This suggest a nitrogen control strategy for use in SCWO (supercritical water oxidation) processes; nitrate or NH3 could be used to remove the other, at reaction conditions far less severe than required by other methods. Reactions of nitrate with methanol indicated that nitrate was a better oxidant than oxygen in supercritical water. Nitrogen reaction products included NH3 and nitrite, while inorganic carbon was the major carbon reaction product. Analysis of excess experiments indicated that the reaction at 475 C was first order in methanol concentration and second order in NO{sub x}{sup -} concentration. In order to determine phase regimes for these reactions, solubility of sodium nitrate was determined for some 1:1 nitrate electrolytes. Solubilities were measured at 450 to 525 C, from 248 to 302 bar. A semi-empirical solvation model was shown to adequately describe the experimental sodium nitrate solubilities. Solubilities of Li, Na, and K nitrates revealed with cations with smaller ionic radii had greater solubilities with nitrate.

Dell`Orco, P.C. [Texas Univ., Austin, TX (United States)] [Texas Univ., Austin, TX (United States)

1994-12-31

438

Quasiglobal reaction model for ethylene combustion  

NASA Technical Reports Server (NTRS)

The objective of this study is to develop a reduced mechanism for ethylene oxidation. The authors are interested in a model with a minimum number of species and reactions that still models the chemistry with reasonable accuracy for the expected combustor conditions. The model will be validated by comparing the results to those calculated with a detailed kinetic model that has been validated against the experimental data.

Singh, D. J.; Jachimowski, Casimir J.

1994-01-01

439

Relativistic approach to one nucleon knockout reactions  

Microsoft Academic Search

We develop a fully relativistic distorted wave impulse approximation model\\u000afor electron- and photon-induced one proton knockout reactions. The\\u000arelativistic mean field for the bound state and the Pauli reduction for the\\u000ascattering state are used, including a fully relativistic electromagnetic\\u000acurrent operator. Results for 16O(e,e'p) cross section and structure functions\\u000aare shown in various kinematic conditions and compared with

Andrea Meucci; Carlotta Giusti; Franco Davide Pacati

2002-01-01

440

Relativistic Approach to One Nucleon Knockout Reactions  

Microsoft Academic Search

We develop a fully relativistic distorted wave impulse approximation model for electron- and photon-induced one proton knockout reactions. The relativistic mean field for the bound state and the Pauli reduction for the scattering state are used, including a fully relativistic electromagnetic current operator. Results for 16O(e, e'p) cross section and structure functions are shown in various kinematic conditions and compared

Andrea Meucci; Carlotta Giusti; Franco Davide Pacati

2003-01-01

441

Computational methods for analyzing bistability in biochemical reaction networks  

E-print Network

system, we define the functions cA1 (t) and cA2 (t) to be the molar concentrations of the species A1, A2 condition above guarantees that each complex appears in at least one reaction, and the third condition says

Craciun, Gheorghe

442

Intrapore reaction of carbon fibers with oxygen-containing gases  

SciTech Connect

A study has been made of the conditions of the internal reaction of carbon fiber obtained from polyacrylonitrile under various conditions of heat thermal treatment (the final temperature was varied from 880/sup 0/C to 2400/sup 0/C) with gaseous oxidizing agents: atmospheric oxygen, carbon dioxide, and steam.

Elchina, V.I.; Fridman, L.I.; Gurdzhiyants, V.M.; Ivin, V.D.; Levit, R.M.; Samoilova, N.A.; Yavorskii, I.A.

1983-01-01

443

The Reaction between Iron(II) Iodide and Potassium Dichromate(VI) in Acidified Aqueous Solution  

ERIC Educational Resources Information Center

This "Science note" teaching lesson explores the possible reaction between the ions in a reaction mixture consisting of iron(II) iodide and potassium dichromate(VI) in acidified aqueous solution. The electrode potentials will be used to deduce any spontaneous reactions under standard thermodynamic conditions (298 K, 1 bar (approximately…

Talbot, Christopher

2013-01-01

444

Dependence of Up-scaled Reaction Rate on Flow Rate in Porous Media  

E-print Network

1 Dependence of Up-scaled Reaction Rate on Flow Rate in Porous Media D. Kim · W. B. Lindquist to inherent heterogeneities in structure, mineral placement and fluid velocity in rock, bulk reaction rates conditions commensurate with CO2 sequestration, we compute up-scaled reaction rates at the core scale

New York at Stoney Brook, State University of

445

Microwave-Assisted Organic Synthesis in the Organic Teaching Lab: A Simple, Greener Wittig Reaction  

ERIC Educational Resources Information Center

A greener, microwave-assisted Wittig reaction has been developed for the second-semester organic teaching laboratory. Utilizing this microwave technique, a variety of styrene derivatives have been successfully synthesized from aromatic aldehydes in good yields (41-68%). The reaction not only occurs under neat reaction conditions, but also employs…

Martin, Eric; Kellen-Yuen, Cynthia

2007-01-01

446

How does aqueous solubility of organic reactant affect a water-promoted reaction?  

PubMed

It was widely reported that under the "on water" condition, various water-promoted organic reactions can proceed with very high speed. Thus, it is considered that the aqueous solubility of reactant is not an important issue in these reactions. Three types of water-promoted organic reactions were investigated in the current study to distinguish whether the reaction rate of an aqueous reaction was affected by the aqueous solubilities of the reactants. The results showed that, for a Diels-Alder reaction which was fast under the neat conditions, the aqueous solubilities of reactants had little influence on the reaction. However, for the reactions which proceeded slowly under the neat conditions, such as [2?+2?+2?] cycloaddition reactions and epoxide aminolysis reactions, the reactants with good aqueous solubilities proceeded fast in water. Poorly aqueous soluble reactants reacted slowly or did not react under the "on water" condition, and an appropriate amount of organic cosolvent was needed to make the reaction become efficient. This evidence suggested that for these two types of reactions, the dissolution of the reactants in water was required. PMID:25000435

Zuo, Yi-Jie; Qu, Jin

2014-08-01

447

Mechanisms and rates of plagioclase carbonation reactions  

NASA Astrophysics Data System (ADS)

Plagioclase is one of the most abundant sources of calcium in the earth’s crust, and it may play an important role for CO2 storage. This study address’ the carbonation of anorthite-rich plagioclase (An67-An73) in a system with fluid transport, and under stagnant conditions. A combined approach of flow-through column and batch experiments has been used. Experimental conditions ranging from 100 to 250 °C and 20 to 120 bar and different preparations of the starting material were applied. The overall carbonation reaction consists of plagioclase dissolution coupled to a number of precipitation reactions. The flow-through column experiments at 250 °C showed stoichiometric dissolution of the plagioclase. Al-hydroxide (“proto Al-hydroxide”) nucleated on the plagioclase as the first phase to precipitate. A secondary porosity developed between the shrinking plagioclase and the enclosing “proto Al-hydroxide”. Calcite, as the second phase to precipitate, filled the primary pore space. A reaction front was developed separating the zone at the inlet where all the plagioclase had dissolved and the less reacted outlet of the column. Redissolution of the calcite and formation of euhedral boehmite crystals occurred when a sufficient amount of plagioclase had dissolved. Clay minerals were not precipitated in the column experiments. Between 11% and 30% of the plagioclase was dissolved within 72-168 h of reaction. A much higher extent of plagioclase dissolution was observed in the high pressure experiments compared to the low pressure. However, a smaller share of the released Ca was trapped as calcite in the high pressure experiments. Both observations are consistent with a more rapid progression of the dissolution front at high pressure. The batch experiments showed conversion of the plagioclase to a mixture of Al-hydroxide, possibly gibbsite, clays and calcite. A range in conversion from below the detection limit to 91% was observed within reaction periods of 24-72 h. Crystallinity of the feldspar was the most important factor contributing to increased reaction rates. A general positive effect of increasing temperature on the conversion is observed for all materials, whereas pressure and the addition of CaCl2 did not have any effect. The carbonation of plagioclase at stagnant conditions is slow compared to olivine at temperatures around 200 °C. However, industrial operations involving high fluid flows of CO2-water mixtures induce gradients in pH or solute concentrations, which may lead to increased reaction rates and changes in porosity/permeability.

Munz, I. A.; Brandvoll, Ø.; Haug, T. A.; Iden, K.; Smeets, R.; Kihle, J.; Johansen, H.

2012-01-01

448

Reaction synthesis of intermetallics  

SciTech Connect

Exothermicity associated with the synthesis of aluminides was utilized to obtain nickel, iron, and cobalt aluminides. Combustion synthesis, extrusion, and hot pressing were utilized to obtain intermetallics and their composites. Extrusion conditions, reduction ratios, and hot-pressing conditions of the intermetallics and their composites are discussed.

Deevi, S.C.; Sikka, V.K.

1994-12-31

449

Enzyme catalysed tandem reactions.  

PubMed

To transfer to the laboratory, the excellent efficiency shown by enzymes in Nature, biocatalysis, had to mimic several synthetic strategies used by the living organisms. Biosynthetic pathways are examples of tandem catalysis and may be assimilated in the biocatalysis field for the use of isolated multi-enzyme systems in the homogeneous phase. The concurrent action of several enzymes that work sequentially presents extraordinary advantages from the synthetic point of view, since it permits a reversible process to become irreversible, to shift the equilibrium reaction in such a way that enantiopure compounds can be obtained from prochiral or racemic substrates, reduce or eliminate problems due to product inhibition or prevent the shortage of substrates by dilution or degradation in the bulk media, etc. In this review we want to illustrate the developments of recent studies involving in vitro multi-enzyme reactions for the synthesis of different classes of organic compounds. PMID:23490810

Oroz-Guinea, Isabel; García-Junceda, Eduardo

2013-04-01

450

Cascade reactions in nanoreactors.  

PubMed

In an attempt to mimic the biosynthetic efficiencies of nature and in a search for greener, more sustainable alternatives to nowadays ways of producing chemicals, one-pot cascade reactions have attracted a lot of attention in the past decade. Since most catalysts are not compatible with each other, compartmentalization techniques have often been applied to prevent catalyst inactivation. A various array of nanoreactors have been developed to meet the demand of having a site-isolated catalyst system, while maintaining the catalyst activity. Both multienzyme nanoreactors as well as enzyme/metal catalyst or organocatalyst systems have shown great potential in one-pot cascade reactions and hold promise for future developments in this field. PMID:24832069

van Oers, M C M; Rutjes, F P J T; van Hest, J C M

2014-08-01

451

Neutrons from Piezonuclear Reactions  

E-print Network

We report the results obtained by cavitating water solutions of iron salts (iron chloride and iron nitrate) with different concentrations at different ultrasound powers. In all cases we detected a neutron radiation well higher than the background level. The neutron production is perfectly reproducible and can at some extent be controlled. These evidences for neutron emission generated by cavitation support some preliminary clues for the possibility of piezonuclear reactions (namely nuclear reactions induced by pressure and shock waves) obtained in the last ten years. We have been able for the first time to state some basic features of such a neutron emission induced by cavitation, namely: 1) a marked threshold behavior in power, energy and time; 2) its occurring without a concomitant production of gamma radiation.

F. Cardone; G. Cherubini; R. Mignani; W. Perconti; A. Petrucci; F. Rosetto; G. Spera

2008-11-16

452

Reactions to dietary tartrazine.  

PubMed

Double blind challenges with tartrazine and benzoic acid were performed in hospital in 24 children whose parents gave a definite history of a purely behavioural immediate adverse reaction to one of these substances. The patients, whose ages ranged from 1.6 to 12.4 years, were on a diet that avoided these items, and in all there was a clear history that any lapse of the diet caused an obvious adverse behavioural reaction within two hours. In no patient was any change in behaviour noted either by the parents or the nursing staff after the administration of placebo or active substances. Twenty two patients returned to a normal diet without problems, but the parents of two children insisted on continuing the diet. While popular belief has it that additives may have harmful behavioural effects, objective verification is required to prevent overdiagnosis. PMID:3548601

David, T J

1987-02-01

453

Reaction chemistry of cerium  

SciTech Connect

It is truly ironic that a synthetic organic chemist likely has far greater knowledge of the reaction chemistry of cerium(IV) than an inorganic colleague. Cerium(IV) reagents have long since been employed as oxidants in effecting a wide variety of organic transformations. Conversely, prior to the late 1980s, the number of well characterized cerium(IV) complexes did not extend past a handful of known species. Though in many other areas, interest in the molecular chemistry of the 4f-elements has undergone an explosive growth over the last twenty years, the chemistry of cerium(IV) has for the most part been overlooked. This report describes reactions of cerium complexes and structure.

NONE

1997-01-01

454

Heat Speeds Up Reactions  

NSDL National Science Digital Library

In this activity, learners investigate the effect of heat on a reaction. Learners first model molecular motion by moving their bodies (running, moving slowly) and pretending to be molecules at different temperatures, then by using groups of cut-out shapes (not provided) which get rearranged when they collide. After this introduction, three glow sticks are activated—one is put in ice water, one in warm water, and one left at room temperature for 15 minutes. A comparison of which glow stick gives off the most light gives an indication of the speed of the molecules and the number of reactions occurring. (The activity was originally written as part of a kit to be checked out of the library, but the kit is not required.)

Maisie Shaw

2009-01-01

455

Pathobiology of transfusion reactions.  

PubMed

Antibody-induced hemolytic transfusion reactions were first described over 300 years ago. Indeed, during its early evolution, transfusion medicine focused almost exclusively on issues in immunohematology to prevent such events. However, despite the best of efforts to avoid them, incompatible transfusions still occur, through both error and an inability to obtain compatible red blood cells for patients who are alloimmunized against multiple antigens. Because transfusing units of incompatible blood is potentially lethal, studies on human volunteers are not ethical. Thus, understanding of hemolytic transfusion reactions is generated through clinical cases, animal models, inference from related human pathologies, or studies using small volumes of transfused red blood cells. Over the past several decades, substantial new knowledge has been accumulated regarding the mechanisms of hemolysis, the metabolism of products of hemolysis, and the effects of both on recipient biology. Using these data sources, this article traces the historical generation of this knowledge and describes recent advances. PMID:25621658

Zimring, James C; Spitalnik, Steven L

2015-01-24

456

Polymerase Chain Reaction  

NSDL National Science Digital Library

Teachers' Domain presents this interactive, adapted from the University of Nebraska's Library of Crop Technologies, with reading material and animations to help students learn the basic steps of polymerase chain reaction. Following the introduction, the lesson is divided four parts: Finding and Isolating