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Sample records for agency reaction rate

  1. Applications of Reaction Rate

    ERIC Educational Resources Information Center

    Cunningham, Kevin

    2007-01-01

    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…

  2. What Is a Reaction Rate?

    ERIC Educational Resources Information Center

    Schmitz, Guy

    2005-01-01

    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.

  3. Renormalized reaction and relaxation rates

    NASA Astrophysics Data System (ADS)

    Gorbachev, Yuriy E.

    2016-06-01

    Impact of the non-equilibrium on the reaction and relaxation rates (called as generalized relaxation rates - GRR), for the spatially inhomogeneous gas mixture is considered. Discarding the assumption that the 'chemical' part of the collisional integral is a small correction to non-reactive part, the expression for the zero-order GRR is derived. They are represented as a renormalization of the traditional reaction and relaxation rates, which means mixing of all corresponding processes. Thus all reactions and relaxation processes are entangled.

  4. Nova reaction rates and experiments

    NASA Astrophysics Data System (ADS)

    Bishop, S.; Herlitzius, C.; Fiehl, J.

    2011-04-01

    Oxygen-neon novae form a subset of classical novae events known to freshly synthesize nuclei up to mass number A≲40. Because several gamma-ray emitters lie in this mass range, these novae are also interesting candidates for gamma-ray astronomy. The properties of excited states within those nuclei in this mass region play a critical role in determining the resonant (p,γ) reaction rates, themselves, largely unknown for the unstable nuclei. We describe herein a new Doppler shift lifetime facility at the Maier-Leibnitz tandem laboratory, Technische Universität München, with which we will map out important resonant (p,γ) nova reaction rates.

  5. The Rate Laws for Reversible Reactions.

    ERIC Educational Resources Information Center

    King, Edward L.

    1986-01-01

    Provides background information for teachers on the rate laws for reversible reactions. Indicates that although prediction of the form of the rate law for a reverse reaction given the rate law for the forward reaction is not certain, the number of possibilities is limited because of relationships described. (JN)

  6. Method of controlling fusion reaction rates

    DOEpatents

    Kulsrud, Russell M.; Furth, Harold P.; Valeo, Ernest J.; Goldhaber, Maurice

    1988-03-01

    A method of controlling the reaction rates of the fuel atoms in a fusion reactor comprises the step of polarizing the nuclei of the fuel atoms in a particular direction relative to the plasma confining magnetic field. Fusion reaction rates can be increased or decreased, and the direction of emission of the reaction products can be controlled, depending on the choice of polarization direction.

  7. Method of controlling fusion reaction rates

    DOEpatents

    Kulsrud, Russell M.; Furth, Harold P.; Valeo, Ernest J.; Goldhaber, Maurice

    1988-01-01

    A method of controlling the reaction rates of the fuel atoms in a fusion reactor comprises the step of polarizing the nuclei of the fuel atoms in a particular direction relative to the plasma confining magnetic field. Fusion reaction rates can be increased or decreased, and the direction of emission of the reaction products can be controlled, depending on the choice of polarization direction.

  8. Reaction Order Ambiguity in Integrated Rate Plots

    ERIC Educational Resources Information Center

    Lee, Joe

    2008-01-01

    Integrated rate plots are frequently used in reaction kinetics to determine orders of reactions. It is often emphasised, when using this methodology in practice, that it is necessary to monitor the reaction to a substantial fraction of completion for these plots to yield unambiguous orders. The present article gives a theoretical and statistical…

  9. pH & Rate of Enzymatic Reactions.

    ERIC Educational Resources Information Center

    Clariana, Roy B.

    1991-01-01

    A quantitative and inexpensive way to measure the rate of enzymatic reaction is provided. The effects of different pH levels on the reaction rate of an enzyme from yeast are investigated and the results graphed. Background information, a list of needed materials, directions for preparing solutions, procedure, and results and discussion are…

  10. Effective reaction rates for diffusion-limited reaction cycles

    NASA Astrophysics Data System (ADS)

    Nałecz-Jawecki, Paweł; Szymańska, Paulina; Kochańczyk, Marek; Miekisz, Jacek; Lipniacki, Tomasz

    2015-12-01

    Biological signals in cells are transmitted with the use of reaction cycles, such as the phosphorylation-dephosphorylation cycle, in which substrate is modified by antagonistic enzymes. An appreciable share of such reactions takes place in crowded environments of two-dimensional structures, such as plasma membrane or intracellular membranes, and is expected to be diffusion-controlled. In this work, starting from the microscopic bimolecular reaction rate constants and using estimates of the mean first-passage time for an enzyme-substrate encounter, we derive diffusion-dependent effective macroscopic reaction rate coefficients (EMRRC) for a generic reaction cycle. Each EMRRC was found to be half of the harmonic average of the microscopic rate constant (phosphorylation c or dephosphorylation d), and the effective (crowding-dependent) motility divided by a slowly decreasing logarithmic function of the sum of the enzyme concentrations. This implies that when c and d differ, the two EMRRCs scale differently with the motility, rendering the steady-state fraction of phosphorylated substrate molecules diffusion-dependent. Analytical predictions are verified using kinetic Monte Carlo simulations on the two-dimensional triangular lattice at the single-molecule resolution. It is demonstrated that the proposed formulas estimate the steady-state concentrations and effective reaction rates for different sets of microscopic reaction rates and concentrations of reactants, including a non-trivial example where with increasing diffusivity the fraction of phosphorylated substrate molecules changes from 10% to 90%.

  11. Astrophysical Reaction Rates Obtained By Indirect Techniques

    SciTech Connect

    Tribble, R. E.; Al-Abdullah, T.; Alharbi, A.; Banu, A.; Chen, X.; Clark, H. L.; Fu, C.; Gagliardi, C. A.; Hardy, J. C.; Iacob, V. E.; Lui, Y.-W.; McCleskey, M.; Mukhamedzhanov, A.; Nica, N.; Park, H. I.; Roeder, B.; Simmons, E.; Tabacaru, G.; Tokimoto, Y.; Trache, L.

    2010-08-12

    Indirect techniques have been used to obtain information about reaction rates for several proton capture reactions that occur on short-lived nuclei. The techniques used to carry out the measurements are reviewed and the results obtained are presented. Also future prospects for further measurements with a new facility, T-REX are discussed.

  12. The Kinetic Rate Law for Autocatalytic Reactions.

    ERIC Educational Resources Information Center

    Mata-Perez, Fernando; Perez-Benito, Joaquin F.

    1987-01-01

    Presented is a method of obtaining accurate rate constants for autocatalytic reactions. The autocatalytic oxidation of dimethylamine by permanganate ion in aqueous solution is used as an example. (RH)

  13. Critical reaction rates in hypersonic combustion chemistry

    SciTech Connect

    Oldenborg, R.C.; Harradine, D.M.; Loge, G.W.; Lyman, J.L.; Schott, G.L.; Winn, K.R.

    1989-01-01

    High Mach number flight requires that the scramjet propulsion system operate at a relatively low static inlet pressure and a high inlet temperature. These two constraints can lead to extremely high temperatures in the combustor, yielding high densities of radical species and correspondingly poor chemical combustion efficiency. As the temperature drops in the nozzle expansion, recombination of these excess radicals can produce more product species, higher heat yield, and potentially more thrust. The extent to which the chemical efficiency can be enhanced in the nozzle expansion depends directly on the rate of the radical recombination reactions. A comprehensive assessment of the important chemical processes and an experimental validation of the critical rate parameters is therefore required if accurate predictions of scramjet performance are to be obtained. This report covers the identification of critical reactions, and the critical reaction rates in hypersonic combustion chemistry. 4 refs., 2 figs.

  14. Universal reaction rates for ultracold molecular collisions

    NASA Astrophysics Data System (ADS)

    Julienne, Paul; Idziaszek, Zbigniew

    2010-03-01

    We offer a simple yet general model of reactive collisions using a quantum defect framework based on the separation of the collision dynamics into long-range and a short-range parts [1]. Two dimensionless quantum defect parameters s and y are used to characterize the S-matrix for a given entrance channel; s represents a phase parameter and y the probability of short-range reaction. The simple analytic expressions we obtain give universal values for s-wave and p-wave collision rates for a van der Waals potential when y approaches unity. In this limit, reaction rates are governed entirely by the threshold laws governing the quantum transmission of the long range potential and depend only on the van der Waals coefficient. The universal rate constants explain the magnitude of the observed rate constants for reactive collisions of fermionic KRb + KRb or K + KRb [2]. In contrast, reaction rates will be non-universal and depend strongly on the phase parameter s if the short range reaction probability is low, y << 1. [1] Z. Idziaszek and P. S. Julienne, arXiv:0912.0370. [2] S. Ospelkaus, K.-K. Ni, D. Wang, M. H. G. de Miranda, B. Neyenhuis, G. Qu'em'ener, P. S. Julienne, J. L. Bohn, D. S. Jin, and J. Ye, arXiv:0912.3854.

  15. Enhanced aqueous photochemical reaction rates after freezing.

    PubMed

    Grannas, Amanda M; Bausch, Alexandra R; Mahanna, Kendell M

    2007-11-01

    Sunlit snow/ice is known to play an important role in the processing of atmospheric species, including photochemical production of NO(x), HONO, molecular halogens, alkyl halides, and carbonyl compounds, among others. It has been shown that a liquid-like (quasi-liquid or disordered) layer exists on the surface of pure ice and that this quasi-liquid layer is also found on the surface of ambient snow crystals and ice at temperatures similar to polar conditions. However, it is unclear what role the liquid-like fractions present in and on frozen water play in potential photochemical reactions, particularly with regard to organic substrates. Here, we report a detailed study of enhanced rates of photochemical nucleophilic substitution of p-nitroanisole (PNA) with pyridine, a well-characterized and commonly used actinometer system. Reaction rates were enhanced by a factor of up to approximately 40 when frozen at temperatures between 236 and 272 K. Reaction rates were dependent on temperature and solute concentration, both variables that control the nature of the liquid-like fraction in frozen water. The results obtained indicate that a major portion of the organic solutes is excluded to the liquid-like layer, significantly impacting the rate of the photochemical nucleophilic substitution reaction studied here. Also, the direct comparison of liquid-phase kinetics to reactions occurring in frozen water systems is drawn into question, indicating that a simple extrapolation of liquid-phase mechanisms to snow/ice may not be valid for certain reactions. PMID:17918916

  16. Reaction rates for a generalized reaction-diffusion master equation

    PubMed Central

    Hellander, Stefan; Petzold, Linda

    2016-01-01

    It has been established that there is an inherent limit to the accuracy of the reaction-diffusion master equation. Specifically, there exists a fundamental lower bound on the mesh size, below which the accuracy deteriorates as the mesh is refined further. In this paper we extend the standard reaction-diffusion master equation to allow molecules occupying neighboring voxels to react, in contrast to the traditional approach in which molecules react only when occupying the same voxel. We derive reaction rates, in two dimensions as well as three dimensions, to obtain an optimal match to the more fine-grained Smoluchowski model, and show in two numerical examples that the extended algorithm is accurate for a wide range of mesh sizes, allowing us to simulate systems that are intractable with the standard reaction-diffusion master equation. In addition, we show that for mesh sizes above the fundamental lower limit of the standard algorithm, the generalized algorithm reduces to the standard algorithm. We derive a lower limit for the generalized algorithm which, in both two dimensions and three dimensions, is on the order of the reaction radius of a reacting pair of molecules. PMID:26871190

  17. Reaction rates for a generalized reaction-diffusion master equation

    NASA Astrophysics Data System (ADS)

    Hellander, Stefan; Petzold, Linda

    2016-01-01

    It has been established that there is an inherent limit to the accuracy of the reaction-diffusion master equation. Specifically, there exists a fundamental lower bound on the mesh size, below which the accuracy deteriorates as the mesh is refined further. In this paper we extend the standard reaction-diffusion master equation to allow molecules occupying neighboring voxels to react, in contrast to the traditional approach, in which molecules react only when occupying the same voxel. We derive reaction rates, in two dimensions as well as three dimensions, to obtain an optimal match to the more fine-grained Smoluchowski model and show in two numerical examples that the extended algorithm is accurate for a wide range of mesh sizes, allowing us to simulate systems that are intractable with the standard reaction-diffusion master equation. In addition, we show that for mesh sizes above the fundamental lower limit of the standard algorithm, the generalized algorithm reduces to the standard algorithm. We derive a lower limit for the generalized algorithm which, in both two dimensions and three dimensions, is of the order of the reaction radius of a reacting pair of molecules.

  18. Thermodynamic limitations on microbially catalyzed reaction rates

    NASA Astrophysics Data System (ADS)

    LaRowe, Douglas E.; Dale, Andrew W.; Amend, Jan P.; Van Cappellen, Philippe

    2012-08-01

    Quantification of global biogeochemical cycles requires knowledge of the rates at which microorganisms catalyze chemical reactions. In order for models that describe these processes to capture global patterns of change, the underlying formulations in them must account for biogeochemical transformations over seasonal and millennial time scales in environments characterized by different energy levels. Building on existing models, a new thermodynamic limiting function is introduced. With only one adjustable parameter, this function that can be used to model microbial metabolism throughout the range of conditions in which organisms are known to be active. The formulation is based on a comparison of the amount of energy available from any redox reaction to the energy required to maintain a membrane potential, a proxy for the minimum amount of energy required by an active microorganism. This function does not require species- or metabolism-specific parameters, and can be used to model metabolisms that capture any amount of energy. The utility of this new thermodynamic rate limiting term is illustrated by applying it to three low-energy processes: fermentation, methanogenesis and sulfate reduction. The model predicts that the rate of fermentation will be reduced by half once the Gibbs energy of the catalyzed reaction reaches -12 kJ (mol e-)-1, and then slowing exponentially until the energy yield approaches zero. Similarly, the new model predicts that the low energy yield of methanogenesis, -4 to -0.5 kJ (mol e-)-1, for a partial pressure of H2 between 11 and 0.6 Pa decreases the reaction rate by 95-99%. Finally, the new function's utility is illustrated through its ability to accurately model sulfate concentration data in an anoxic marine sediment.

  19. Pycnonuclear reaction rates for binary ionic mixtures

    NASA Technical Reports Server (NTRS)

    Ichimaru, S.; Ogata, S.; Van Horn, H. M.

    1992-01-01

    Through a combination of compositional scaling arguments and examinations of Monte Carlo simulation results for the interparticle separations in binary-ionic mixture (BIM) solids, we have derived parameterized expressions for the BIM pycnonuclear rates as generalizations of those in one-component solids obtained previously by Salpeter and Van Horn and by Ogata et al. We have thereby discovered a catalyzing effect of the heavier elements, which enhances the rates of reactions among the lighter elements when the charge ratio exceeds a critical value of approximately 2.3.

  20. An approximate classical unimolecular reaction rate theory

    NASA Astrophysics Data System (ADS)

    Zhao, Meishan; Rice, Stuart A.

    1992-05-01

    We describe a classical theory of unimolecular reaction rate which is derived from the analysis of Davis and Gray by use of simplifying approximations. These approximations concern the calculation of the locations of, and the fluxes of phase points across, the bottlenecks to fragmentation and to intramolecular energy transfer. The bottleneck to fragment separation is represented as a vibration-rotation state dependent separatrix, which approximation is similar to but extends and improves the approximations for the separatrix introduced by Gray, Rice, and Davis and by Zhao and Rice. The novel feature in our analysis is the representation of the bottlenecks to intramolecular energy transfer as dividing surfaces in phase space; the locations of these dividing surfaces are determined by the same conditions as locate the remnants of robust tori with frequency ratios related to the golden mean (in a two degree of freedom system these are the cantori). The flux of phase points across each dividing surface is calculated with an analytic representation instead of a stroboscopic mapping. The rate of unimolecular reaction is identified with the net rate at which phase points escape from the region of quasiperiodic bounded motion to the region of free fragment motion by consecutively crossing the dividing surfaces for intramolecular energy exchange and the separatrix. This new theory generates predictions of the rates of predissociation of the van der Waals molecules HeI2, NeI2 and ArI2 which are in very good agreement with available experimental data.

  1. Fusion Reaction Rate in an Inhomogeneous Plasma

    SciTech Connect

    S. Son; N.J. Fisch

    2004-09-03

    The local fusion rate, obtained from the assumption that the distribution is a local Maxwellian, is inaccurate if mean-free-paths of fusing particles are not sufficiently small compared with the inhomogeneity length of the plasma. We calculate the first order correction of P0 in terms of the small spatial gradient and obtain a non-local modification of P(sub)0 in a shock region when the gradient is not small. Use is made of the fact that the fusion reaction cross section has a relatively sharp peak as a function of energy.

  2. Indirect techniques for astrophysical reaction rates determinations

    NASA Astrophysics Data System (ADS)

    Hammache, F.; Oulebsir, N.; Benamara, S.; De Séréville, N.; Coc, A.; Laird, A.; Stefan, I.; Roussel, P.

    2016-05-01

    Direct measurements of nuclear reactions of astrophysical interest can be challenging. Alternative experimental techniques such as transfer reactions and inelastic scattering reactions offer the possibility to study these reactions by using stable beams. In this context, I will present recent results that were obtained in Orsay using indirect techniques. The examples will concern various astrophysical sites, from the Big-Bang nucleo synthesis to the production of radioisotopes in massive stars.

  3. Representing Rate Equations for Enzyme-Catalyzed Reactions

    ERIC Educational Resources Information Center

    Ault, Addison

    2011-01-01

    Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of…

  4. Impact of THM reaction rates for astrophysics

    NASA Astrophysics Data System (ADS)

    Lamia, L.; Spitaleri, C.; Tognelli, E.; Degl'Innocenti, S.; Pizzone, R. G.; Moroni, P. G. Prada; Puglia, S. M. R.; Romano, S.; Sergi, M. L.

    2015-10-01

    Burning reaction S(E)-factor determinations are among the key ingredients for stellar models when one has to deal with energy generation evaluation and the genesis of the elements at stellar conditions. To by pass the still present uncertainties in extrapolating low-energies values, S(E)-factor measurements for charged-particle induced reactions involving light elements have been made available by devote Trojan Horse Method (THM) experiments. The recent results are here discussed together with their impact in astrophysics.

  5. Typewriting rate as a function of reaction time.

    PubMed

    Hayes, V; Wilson, G D; Schafer, R L

    1977-12-01

    This study was designed to determine the relationship between reaction time and typewriting rate. Subjects were 24 typists ranging in age from 19 to 39 yr. Reaction times (.001 sec) to a light were recorded for each finger and to each alphabetic character and three punctuation marks. Analysis of variance yielded significant differences in reaction time among subjects and fingers. Correlation between typewriting rate and average reaction time to the alphabetic characters and three punctuation marks was --.75. Correlation between typewriting rate and the difference between the reaction time of the hands was --.42. Factors influencing typewriting rate may include reaction time of the fingers, difference between the reaction time of the hands, and reaction time to individual keys on the typewriter. Implications exist for instructional methodology and further research. PMID:604897

  6. Multidimensional reaction rate theory with anisotropic diffusion

    NASA Astrophysics Data System (ADS)

    Berezhkovskii, Alexander M.; Szabo, Attila; Greives, Nicholas; Zhou, Huan-Xiang

    2014-11-01

    An analytical expression is derived for the rate constant that describes diffusive transitions between two deep wells of a multidimensional potential. The expression, in contrast to the Kramers-Langer formula for the rate constant, is valid even when the diffusion is highly anisotropic. Our approach is based on a variational principle for the reactive flux and uses a trial function for the splitting probability or commitor. The theoretical result is validated by Brownian dynamics simulations.

  7. DSMC predictions of non-equilibrium reaction rates.

    SciTech Connect

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

    2010-04-01

    A set of Direct Simulation Monte Carlo (DSMC) chemical-reaction models recently proposed by Bird and based solely on the collision energy and the vibrational energy levels of the species involved is applied to calculate nonequilibrium chemical-reaction rates for atmospheric reactions in hypersonic flows. The DSMC non-equilibrium model predictions are in good agreement with theoretical models and experimental measurements. The observed agreement provides strong evidence that modeling chemical reactions using only the collision energy and the vibrational energy levels provides an accurate method for predicting non-equilibrium chemical-reaction rates.

  8. On the rate of relativistic surface chemical reactions.

    PubMed

    Veitsman, E V

    2004-07-15

    On the basis of special relativity and the classical theory of chemical reaction rates it is shown how the surface chemical reaction rates vary as v --> c, where v is the velocity of the object under study and c is the velocity of light. PMID:15178286

  9. Empirical rate equation for association reactions and ion-molecule reactions

    NASA Astrophysics Data System (ADS)

    Sato, Shin

    2016-05-01

    Temperature dependence of the rate constants of many association reactions is now available. In order to express the rate constants at temperatures from very low to high, we tried to use the sum of new empirical rate equations for association reactions and Arrhenius equations. Temperature dependence of a number of radical-molecule and some ion-molecule reactions could be successfully demonstrated. A new procedure to analyze ion-molecule reactions was proposed. This might suggest a new viewpoint to understanding chemical reactions.

  10. Estimating the Backup Reaction Wheel Orientation Using Reaction Wheel Spin Rates Flight Telemetry from a Spacecraft

    NASA Technical Reports Server (NTRS)

    Rizvi, Farheen

    2013-01-01

    A report describes a model that estimates the orientation of the backup reaction wheel using the reaction wheel spin rates telemetry from a spacecraft. Attitude control via the reaction wheel assembly (RWA) onboard a spacecraft uses three reaction wheels (one wheel per axis) and a backup to accommodate any wheel degradation throughout the course of the mission. The spacecraft dynamics prediction depends upon the correct knowledge of the reaction wheel orientations. Thus, it is vital to determine the actual orientation of the reaction wheels such that the correct spacecraft dynamics can be predicted. The conservation of angular momentum is used to estimate the orientation of the backup reaction wheel from the prime and backup reaction wheel spin rates data. The method is applied in estimating the orientation of the backup wheel onboard the Cassini spacecraft. The flight telemetry from the March 2011 prime and backup RWA swap activity on Cassini is used to obtain the best estimate for the backup reaction wheel orientation.

  11. Theory of Crowding Effects on Bimolecular Reaction Rates.

    PubMed

    Berezhkovskii, Alexander M; Szabo, Attila

    2016-07-01

    An analytical expression for the rate constant of a diffusion-influenced bimolecular reaction in a crowded environment is derived in the framework of a microscopic model that accounts for: (1) the slowdown of diffusion due to crowding and the dependence of the diffusivity on the distance between the reactants, (2) a crowding-induced attractive short-range potential of mean force, and (3) nonspecific reversible binding to the crowders. This expression spans the range from reaction to diffusion control. Crowding can increase the reaction-controlled rate by inducing an effective attraction between reactants but decrease the diffusion-controlled rate by reducing their relative diffusivity. PMID:27096470

  12. An Improved Reaction Rate Equation for Simulating the Ignition and Growth of Reaction in High Explosives

    SciTech Connect

    Murphy, M J

    2010-03-08

    We describe an improved reaction rate equation for simulating ignition and growth of reaction in high explosives. It has been implemented into CALE and ALE3D as an alternate to the baseline the Lee-Tarver reactive flow model. The reactive flow model treats the explosive in two phases (unreacted/reactants and reacted/products) with a reaction rate equation to determine the fraction reacted, F. The improved rate equation has fewer parameters, is continuous with continuous derivative, results in a unique set of reaction rate parameters for each explosive while providing the same functionality as the baseline rate equation. The improved rate equation uses a cosine function in the ignition term and a sine function in the growth and completion terms. The improved rate equation is simpler with fewer parameters.

  13. Gas-solid reaction-rate enhancement by pressure cycling

    NASA Astrophysics Data System (ADS)

    Sohn, H. Y.; Aboukheshem, M. B.

    1992-06-01

    An experimental study and mathematical modeling of the effects of external pressure cycling on gas-solid reactions have been conducted using the reduction of nickel oxide pellets by hy-drogen. Experiments were carried out in two phases: In the first phase, the intrinsic kinetic parameters were measured, and in the second phase, the gas-solid reaction was carried out under a constant or cycling external pressure. The effects of the frequency and amplitude of pressure cycling were studied at various reaction conditions. Pressure cycling substantially increases the overall rate of the reaction. A mathematical model was developed from the first principles to establish the extent of the overall reaction-rate enhancement and subsequently to analyze the experimental observations. The calculated values from the mathematical model are in good agreement with the experimental results. The effects are most pronounced when the overall rate under a constant pressure is controlled by diffusion. Depending on the reaction condition, a very large degree of rate enhancement could be achieved. Furthermore, low-amplitude pressure waves, like acoustic waves, could significantly increase the rates of gas-solid reactions.

  14. Non-resonant triple alpha reaction rate at low temperature

    SciTech Connect

    Itoh, T.; Tamii, A.; Aoi, N.; Fujita, H.; Hashimoto, T.; Miki, K.; Ogata, K.; Carter, J.; Donaldson, L.; Sideras-Haddad, E.; Furuno, T.; Kawabata, T.; Kamimura, M.; Nemulodi, F.; Neveling, R.; Smit, F. D.; Swarts, C.

    2014-05-02

    Our experimental goal is to study the non-resonant triple alpha reaction rate at low temperture (T < 10{sup 8} K). The {sup 13}C(p,d) reaction at 66 MeV has been used to probe the alpha-unbound continuum state in {sup 12}C just below the 2{sup nd} 0{sup +} state at 7.65 MeV. The transition strength to the continuum state is predicted to be sensitive to the non-resonant triple alpha reaction rate. The experiment has been performed at iThemba LABS. We report the present status of the experiment.

  15. Rate of reaction between molecular hydrogen and molecular oxygen

    NASA Technical Reports Server (NTRS)

    Brokaw, R. S.

    1973-01-01

    The shock tube data of Jachimowski and Houghton were rigorously analyzed to obtain rate constants for the candidate initiation reactions H2 + O2 yields H + HO2, H2 + O2 yields H2O + O, and H2 + O2 yields OH + OH. Reaction (01) is probably not the initiation process because the activation energy obtained is less than the endothermicity and because the derived rates greatly exceed values inferred in the literature from the reverse of reaction (01). Reactions (02) and (03) remain as possibilities, with reaction (02) slightly favored on the basis of steric and statistical considerations. The solution of the differential equations is presented in detail to show how the kinetics of other ignition systems may be solved.

  16. Analysis of reaction schemes using maximum rates of constituent steps.

    PubMed

    Motagamwala, Ali Hussain; Dumesic, James A

    2016-05-24

    We show that the steady-state kinetics of a chemical reaction can be analyzed analytically in terms of proposed reaction schemes composed of series of steps with stoichiometric numbers equal to unity by calculating the maximum rates of the constituent steps, rmax,i, assuming that all of the remaining steps are quasi-equilibrated. Analytical expressions can be derived in terms of rmax,i to calculate degrees of rate control for each step to determine the extent to which each step controls the rate of the overall stoichiometric reaction. The values of rmax,i can be used to predict the rate of the overall stoichiometric reaction, making it possible to estimate the observed reaction kinetics. This approach can be used for catalytic reactions to identify transition states and adsorbed species that are important in controlling catalyst performance, such that detailed calculations using electronic structure calculations (e.g., density functional theory) can be carried out for these species, whereas more approximate methods (e.g., scaling relations) are used for the remaining species. This approach to assess the feasibility of proposed reaction schemes is exact for reaction schemes where the stoichiometric coefficients of the constituent steps are equal to unity and the most abundant adsorbed species are in quasi-equilibrium with the gas phase and can be used in an approximate manner to probe the performance of more general reaction schemes, followed by more detailed analyses using full microkinetic models to determine the surface coverages by adsorbed species and the degrees of rate control of the elementary steps. PMID:27162366

  17. Analysis of reaction schemes using maximum rates of constituent steps

    NASA Astrophysics Data System (ADS)

    Hussain Motagamwala, Ali; Dumesic, James A.

    2016-05-01

    We show that the steady-state kinetics of a chemical reaction can be analyzed analytically in terms of proposed reaction schemes composed of series of steps with stoichiometric numbers equal to unity by calculating the maximum rates of the constituent steps, rmax,i, assuming that all of the remaining steps are quasi-equilibrated. Analytical expressions can be derived in terms of rmax,i to calculate degrees of rate control for each step to determine the extent to which each step controls the rate of the overall stoichiometric reaction. The values of rmax,i can be used to predict the rate of the overall stoichiometric reaction, making it possible to estimate the observed reaction kinetics. This approach can be used for catalytic reactions to identify transition states and adsorbed species that are important in controlling catalyst performance, such that detailed calculations using electronic structure calculations (e.g., density functional theory) can be carried out for these species, whereas more approximate methods (e.g., scaling relations) are used for the remaining species. This approach to assess the feasibility of proposed reaction schemes is exact for reaction schemes where the stoichiometric coefficients of the constituent steps are equal to unity and the most abundant adsorbed species are in quasi-equilibrium with the gas phase and can be used in an approximate manner to probe the performance of more general reaction schemes, followed by more detailed analyses using full microkinetic models to determine the surface coverages by adsorbed species and the degrees of rate control of the elementary steps.

  18. Nonlinear dynamical effects on reaction rates in thermally fluctuating environments.

    PubMed

    Kawai, Shinnosuke; Komatsuzaki, Tamiki

    2010-07-21

    A framework to calculate the rate constants of condensed phase chemical reactions of manybody systems is presented without relying on the concept of transition state. The theory is based on a framework we developed recently adopting a multidimensional underdamped Langevin equation in the region of a rank-one saddle. The theory provides a reaction coordinate expressed as an analytical nonlinear functional of the position coordinates and velocities of the system (solute), the friction constants, and the random force of the environment (solvent). Up to moderately high temperature, the sign of the reaction coordinate can determine the final destination of the reaction in a thermally fluctuating media, irrespective of what values the other (nonreactive) coordinates may take. In this paper, it is shown that the reaction probability is analytically derived as the probability of the reaction coordinate being positive, and that the integration with the Boltzmann distribution of the initial conditions leads to the exact reaction rate constant when the local equilibrium holds and the quantum effect is negligible. Because of analytical nature of the theory taking into account all nonlinear effects and their combination with fluctuation and dissipation, the theory naturally provides us with the firm mathematical foundation of the origin of the reactivity of the reaction in a fluctuating media. PMID:20544104

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

    NASA Technical Reports Server (NTRS)

    Liechty, Derek S.; Lewis, Mark J.

    2010-01-01

    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.

  20. A Transition in the Cumulative Reaction Rate of Two Species Diffusion with Bimolecular Reaction

    NASA Astrophysics Data System (ADS)

    Rajaram, Harihar; Arshadi, Masoud

    2015-04-01

    Diffusion and bimolecular reaction between two initially separated reacting species is a prototypical small-scale description of reaction induced by transverse mixing. It is also relevant to diffusion controlled transport regimes as encountered in low-permeability matrix blocks in fractured media. In previous work, the reaction-diffusion problem has been analyzed as a Stefan problem involving a distinct moving boundary (reaction front), which predicts that front motion scales as √t, and the cumulative reaction rate scales as 1/√t-. We present a general non-dimensionalization of the problem and a perturbation analysis to show that there is an early time regime where the cumulative reaction rate scales as √t- rather than 1/√t. The duration of this early time regime (where the cumulative rate is kinetically rather than diffusion controlled) depends on the rate parameter, in a manner that is consistently predicted by our non-dimensionalization. We also present results on the scaling of the reaction front width. We present numerical simulations in homogeneous and heterogeneous porous media to demonstrate the limited influence of heterogeneity on the behavior of the reaction-diffusion system. We illustrate applications to the practical problem of in-situ chemical oxidation of TCE and PCE by permanganate, which is employed to remediate contaminated sites where the DNAPLs are largely dissolved in the rock matrix.

  1. Benchmark calculations of thermal reaction rates. I - Quantal scattering theory

    NASA Technical Reports Server (NTRS)

    Chatfield, David C.; Truhlar, Donald G.; Schwenke, David W.

    1991-01-01

    The thermal rate coefficient for the prototype reaction H + H2 yields H2 + H with zero total angular momentum is calculated by summing, averaging, and numerically integrating state-to-state reaction probabilities calculated by time-independent quantum-mechanical scattering theory. The results are very carefully converged with respect to all numerical parameters in order to provide high-precision benchmark results for confirming the accuracy of new methods and testing their efficiency.

  2. Diagrammatic algorithm for evaluating finite-temperature reaction rates

    NASA Astrophysics Data System (ADS)

    Ashida, Naoki; Nakkagawa, Hisao; Niégawa, Akira; Yokota, Hiroshi

    1992-05-01

    In this paper, by following the procedure of statistical mechanics we present the systematic calculational rules for evaluating the reaction rate of a generic dynamical process taking place in a heat bath. These rules are formulated within the framework of real-time thermal field theory (RTFT), in terms of the Feynman-like diagrams, the so-called circled diagrams. With the machinery developed in this paper we can establish the finite temperature generalization of the Cutkosky, or the cutting rules in quantum field theory at zero temperature. We have also studied the relation between the imaginary part of forward RTFT amplitude and the reaction rates; the imaginary part consists of various reaction rates. This is a finite temperature generalization of the optical theorem.

  3. A transition in the spatially integrated reaction rate of bimolecular reaction-diffusion systems

    NASA Astrophysics Data System (ADS)

    Arshadi, Masoud; Rajaram, Harihar

    2015-09-01

    Numerical simulations of diffusion with bimolecular reaction demonstrate a transition in the spatially integrated reaction rate—increasing with time initially, and transitioning to a decrease with time. In previous work, this reaction-diffusion problem has been analyzed as a Stefan problem involving a distinct moving boundary (reaction front), leading to predictions that front motion scales as √t, and correspondingly the spatially integrated reaction rate decreases as the square root of time 1/√t. We present a general nondimensionalization of the problem and a perturbation analysis to show that there is an early time regime where the spatially integrated reaction rate scales as √t rather than 1/√t. The duration of this early time regime (where the spatially integrated reaction rate is kinetically rather than diffusion controlled) is shown to depend on the kinetic rate parameters, diffusion coefficients, and initial concentrations of the two species. Numerical simulation results confirm the theoretical estimates of the transition time. We present illustrative calculations in the context of in situ chemical oxidation for remediation of fractured rock systems where contaminants are largely dissolved in the rock matrix. We consider different contaminants of concern (COCs), including TCE, PCE, MTBE, and RDX. While the early time regime is very short lived for TCE, it can persist over months to years for MTBE and RDX, due to slow oxidation kinetics.

  4. Reaction rate uncertainties and the ν p-process

    NASA Astrophysics Data System (ADS)

    Fröhlich, C.; Rauscher, T.

    2012-11-01

    Current hydrodynamical simulations of core collapse supernovae find proton-rich early ejecta. At the same time, the models fail to eject neutron-rich matter, thus leaving the origin of the main r-process elements unsolved. However, the proton-rich neutrino-driven winds from supernovae have been identified as a possible production site for light n-capture elements beyond iron (such as Ge, Sr, Y, Zr) through the νp-process. The detailed nucleosynthesis patterns of the νp-process depend on the hydrodynamic conditions and the nuclear reaction rates of key reactions. We investigate the impact of reaction rate uncertainties on the νp-process nucleosynthesis.

  5. Semiclassical Calculation of Reaction Rate Constants for Homolytical Dissociations

    NASA Technical Reports Server (NTRS)

    Cardelino, Beatriz H.

    2002-01-01

    There is growing interest in extending organometallic chemical vapor deposition (OMCVD) to III-V materials that exhibit large thermal decomposition at their optimum growth temperature, such as indium nitride. The group III nitrides are candidate materials for light-emitting diodes and semiconductor lasers operating into the blue and ultraviolet regions. To overcome decomposition of the deposited compound, the reaction must be conducted at high pressures, which causes problems of uniformity. Microgravity may provide the venue for maintaining conditions of laminar flow under high pressure. Since the selection of optimized parameters becomes crucial when performing experiments in microgravity, efforts are presently geared to the development of computational OMCVD models that will couple the reactor fluid dynamics with its chemical kinetics. In the present study, we developed a method to calculate reaction rate constants for the homolytic dissociation of III-V compounds for modeling OMCVD. The method is validated by comparing calculations with experimental reaction rate constants.

  6. A transport equation for reaction rate in turbulent flows

    NASA Astrophysics Data System (ADS)

    Sabelnikov, V. A.; Lipatnikov, A. N.; Chakraborty, N.; Nishiki, S.; Hasegawa, T.

    2016-08-01

    New transport equations for chemical reaction rate and its mean value in turbulent flows have been derived and analyzed. Local perturbations of the reaction zone by turbulent eddies are shown to play a pivotal role even for weakly turbulent flows. The mean-reaction-rate transport equation is shown to involve two unclosed dominant terms and a joint closure relation for the sum of these two terms is developed. Obtained analytical results and, in particular, the closure relation are supported by processing two widely recognized sets of data obtained from earlier direct numerical simulations of statistically planar 1D premixed flames associated with both weak large-scale and intense small-scale turbulence.

  7. Reaction rate uncertainties and the {nu}p-process

    SciTech Connect

    Froehlich, C.; Rauscher, T.

    2012-11-12

    Current hydrodynamical simulations of core collapse supernovae find proton-rich early ejecta. At the same time, the models fail to eject neutron-rich matter, thus leaving the origin of the main r-process elements unsolved. However, the proton-rich neutrino-driven winds from supernovae have been identified as a possible production site for light n-capture elements beyond iron (such as Ge, Sr, Y, Zr) through the {nu}p-process. The detailed nucleosynthesis patterns of the {nu}p-process depend on the hydrodynamic conditions and the nuclear reaction rates of key reactions. We investigate the impact of reaction rate uncertainties on the {nu}p-process nucleosynthesis.

  8. Quantum and semiclassical theories of chemical reaction rates

    SciTech Connect

    Miller, W.H. |

    1995-09-01

    A rigorous quantum mechanical theory (and a semiclassical approximation thereto) is described for calculating chemical reaction rates ``directly``, i.e., without having to solve the complete state-to-state reactive scattering problem. The approach has many vestiges of transition state theory, for which it may be thought of as the rigorous generalization.

  9. Prediction of Rate Constants for Catalytic Reactions with Chemical Accuracy.

    PubMed

    Catlow, C Richard A

    2016-08-01

    Ex machina: A computational method for predicting rate constants for reactions within microporous zeolite catalysts with chemical accuracy has recently been reported. A key feature of this method is a stepwise QM/MM approach that allows accuracy to be achieved while using realistic models with accessible computer resources. PMID:27329206

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

    SciTech Connect

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

    2010-06-01

    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.

  11. Code System to Calculate Integral Parameters with Reaction Rates from WIMS Output.

    Energy Science and Technology Software Center (ESTSC)

    1994-10-25

    Version 00 REACTION calculates different integral parameters related to neutron reactions on reactor lattices, from reaction rates calculated with WIMSD4 code, and comparisons with experimental values.

  12. Rate of reaction of OH with HNO3

    NASA Technical Reports Server (NTRS)

    Wine, P. H.; Ravishankara, A. R.; Kreutter, N. M.; Shah, R. C.; Nicovich, J. M.; Thompson, R. L.; Wuebbles, D. J.

    1981-01-01

    Measurements of the kinetics of the reaction of OH with HNO3, and mechanisms of HNO3 removal from the stratosphere, are reported. Bimolecular rate constants were determined at temperatures between 224 and 366 K by monitoring the concentrations of OH radicals produced by HNO3 photolysis and HNO3 according to their resonance fluorescence and 184.9-nm absorption, respectively. The rate constant measured at 298 K is found to be somewhat faster than previously accepted values, with a negative temperature dependence. Calculations of a one-dimensional transport-kinetic atmospheric model on the basis of the new rate constant indicate reductions in O3 depletion due to chlorofluoromethane release and NOx injection, of magnitudes dependent on the nature of the reaction products.

  13. Reaction rate and products for the reaction O/3P/ + H2CO

    NASA Technical Reports Server (NTRS)

    Chang, J. S.; Barker, J. R.

    1979-01-01

    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.

  14. Scaling of geochemical reaction rates via advective solute transport.

    PubMed

    Hunt, A G; Ghanbarian, B; Skinner, T E; Ewing, R P

    2015-07-01

    Transport in porous media is quite complex, and still yields occasional surprises. In geological porous media, the rate at which chemical reactions (e.g., weathering and dissolution) occur is found to diminish by orders of magnitude with increasing time or distance. The temporal rates of laboratory experiments and field observations differ, and extrapolating from laboratory experiments (in months) to field rates (in millions of years) can lead to order-of-magnitude errors. The reactions are transport-limited, but characterizing them using standard solute transport expressions can yield results in agreement with experiment only if spurious assumptions and parameters are introduced. We previously developed a theory of non-reactive solute transport based on applying critical path analysis to the cluster statistics of percolation. The fractal structure of the clusters can be used to generate solute distributions in both time and space. Solute velocities calculated from the temporal evolution of that distribution have the same time dependence as reaction-rate scaling in a wide range of field studies and laboratory experiments, covering some 10 decades in time. The present theory thus both explains a wide range of experiments, and also predicts changes in the scaling behavior in individual systems with increasing time and/or length scales. No other theory captures these variations in scaling by invoking a single physical mechanism. Because the successfully predicted chemical reactions include known results for silicate weathering rates, our theory provides a framework for understanding changes in the global carbon cycle, including its effects on extinctions, climate change, soil production, and denudation rates. It further provides a basis for understanding the fundamental time scales of hydrology and shallow geochemistry, as well as the basis of industrial agriculture. PMID:26232976

  15. Scaling of geochemical reaction rates via advective solute transport

    NASA Astrophysics Data System (ADS)

    Hunt, A. G.; Ghanbarian, B.; Skinner, T. E.; Ewing, R. P.

    2015-07-01

    Transport in porous media is quite complex, and still yields occasional surprises. In geological porous media, the rate at which chemical reactions (e.g., weathering and dissolution) occur is found to diminish by orders of magnitude with increasing time or distance. The temporal rates of laboratory experiments and field observations differ, and extrapolating from laboratory experiments (in months) to field rates (in millions of years) can lead to order-of-magnitude errors. The reactions are transport-limited, but characterizing them using standard solute transport expressions can yield results in agreement with experiment only if spurious assumptions and parameters are introduced. We previously developed a theory of non-reactive solute transport based on applying critical path analysis to the cluster statistics of percolation. The fractal structure of the clusters can be used to generate solute distributions in both time and space. Solute velocities calculated from the temporal evolution of that distribution have the same time dependence as reaction-rate scaling in a wide range of field studies and laboratory experiments, covering some 10 decades in time. The present theory thus both explains a wide range of experiments, and also predicts changes in the scaling behavior in individual systems with increasing time and/or length scales. No other theory captures these variations in scaling by invoking a single physical mechanism. Because the successfully predicted chemical reactions include known results for silicate weathering rates, our theory provides a framework for understanding changes in the global carbon cycle, including its effects on extinctions, climate change, soil production, and denudation rates. It further provides a basis for understanding the fundamental time scales of hydrology and shallow geochemistry, as well as the basis of industrial agriculture.

  16. Stellar Evolution Constraints on the Triple-α Reaction Rate

    NASA Astrophysics Data System (ADS)

    Suda, Takuma; Hirschi, Raphael; Fujimoto, Masayuki Y.

    2011-11-01

    We investigate the quantitative constraint on the triple-α reaction rate based on stellar evolution theory, motivated by the recent significant revision of the rate proposed by nuclear physics calculations. Targeted stellar models were computed in order to investigate the impact of that rate in the mass range of 0.8 <= M/M sun <= 25 and in the metallicity range between Z = 0 and Z = 0.02. The revised rate has a significant impact on the evolution of low- and intermediate-mass stars, while its influence on the evolution of massive stars (M >~ 10 M sun) is minimal. We find that employing the revised rate suppresses helium shell flashes on asymptotic giant branch phase for stars in the initial mass range 0.8 <= M/M sun <= 6, which is contradictory to what is observed. The absence of helium shell flashes is due to the weak temperature dependence of the revised triple-α reaction cross section at the temperature involved. In our models, it is suggested that the temperature dependence of the cross section should have at least ν > 10 at T = (1-1.2) × 108 K where the cross section is proportional to T ν. We also derive the helium ignition curve to estimate the maximum cross section to retain the low-mass first red giants. The semi-analytically derived ignition curves suggest that the reaction rate should be less than ~10-29 cm6 s-1 mole-2 at ≈107.8 K, which corresponds to about three orders of magnitude larger than that of the NACRE compilation. In an effort to compromise with the revised rates, we calculate and analyze models with enhanced CNO cycle reaction rates to increase the maximum luminosity of the first giant branch. However, it is impossible to reach the typical red giant branch tip luminosity even if all the reaction rates related to CNO cycles are enhanced by more than 10 orders of magnitude.

  17. STELLAR EVOLUTION CONSTRAINTS ON THE TRIPLE-{alpha} REACTION RATE

    SciTech Connect

    Suda, Takuma; Fujimoto, Masayuki Y.; Hirschi, Raphael

    2011-11-01

    We investigate the quantitative constraint on the triple-{alpha} reaction rate based on stellar evolution theory, motivated by the recent significant revision of the rate proposed by nuclear physics calculations. Targeted stellar models were computed in order to investigate the impact of that rate in the mass range of 0.8 {<=} M/M{sub sun} {<=} 25 and in the metallicity range between Z = 0 and Z = 0.02. The revised rate has a significant impact on the evolution of low- and intermediate-mass stars, while its influence on the evolution of massive stars (M {approx}> 10 M{sub sun}) is minimal. We find that employing the revised rate suppresses helium shell flashes on asymptotic giant branch phase for stars in the initial mass range 0.8 {<=} M/M{sub sun} {<=} 6, which is contradictory to what is observed. The absence of helium shell flashes is due to the weak temperature dependence of the revised triple-{alpha} reaction cross section at the temperature involved. In our models, it is suggested that the temperature dependence of the cross section should have at least {nu} > 10 at T = (1-1.2) Multiplication-Sign 10{sup 8} K where the cross section is proportional to T {sup {nu}}. We also derive the helium ignition curve to estimate the maximum cross section to retain the low-mass first red giants. The semi-analytically derived ignition curves suggest that the reaction rate should be less than {approx}10{sup -29} cm{sup 6} s{sup -1} mole{sup -2} at Almost-Equal-To 10{sup 7.8} K, which corresponds to about three orders of magnitude larger than that of the NACRE compilation. In an effort to compromise with the revised rates, we calculate and analyze models with enhanced CNO cycle reaction rates to increase the maximum luminosity of the first giant branch. However, it is impossible to reach the typical red giant branch tip luminosity even if all the reaction rates related to CNO cycles are enhanced by more than 10 orders of magnitude.

  18. The astrophysical reaction rate for the {sup 18}F(p,{alpha}){sup 15}O reaction

    SciTech Connect

    Rehm, K.E.; Paul, M.; Roberts, A.D.

    1996-03-01

    Proton and alpha widths for a 3/2{sup +} ({ell}{sub p} = 0) state in {sup 19}Ne at E{sub x} = 7.1 MeV have been extracted using the results of recent measurements of the {sup 18}F(p,{alpha}){sup 15}O reaction. This {ell}{sub p} = 0 resonance dominates the astrophysical reaction rates at temperatures T{sub 9} > 0.5.

  19. Pore size and the lab-field reaction rate riddle

    NASA Astrophysics Data System (ADS)

    Emmanuel, S.; Ague, J. J.; Walderhaug, O.

    2009-12-01

    Pore size is usually thought to influence the rate of crystal growth during diagenesis and metamorphism by controlling the ratio of surface area to fluid volume. However, theory suggests that in micron-scale to nanometer-scale pores, interfacial energy effects can also become important. We used mercury porosimetry to investigate the pore-size distributions in naturally cemented sandstone adjacent to stylolites and found that quartz precipitation was inhibited in pores smaller than 10 microns in diameter. We demonstrate that standard kinetic models cannot reproduce the observed pore-size patterns in mineralized samples; by contrast, excellent fits with the data are obtained when interfacial energy effects are taken into account. Moreover, as such micron-scale pores comprise the overwhelming majority of surface area in the sandstone, average reaction rates for the rock are significantly reduced. Reaction rates in geological media determined in field studies can be orders of magnitude lower than those measured in laboratory experiments, and we propose that reduced reaction rates in rocks with micron-scale porosity could account for the apparent paradox.

  20. A model for reaction rates in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Chinitz, W.; Evans, J. S.

    1984-01-01

    To account for the turbulent temperature and species-concentration fluctuations, a model is presented on the effects of chemical reaction rates in computer analyses of turbulent reacting flows. The model results in two parameters which multiply the terms in the reaction-rate equations. For these two parameters, graphs are presented as functions of the mean values and intensity of the turbulent fluctuations of the temperature and species concentrations. These graphs will facilitate incorporation of the model into existing computer programs which describe turbulent reacting flows. When the model was used in a two-dimensional parabolic-flow computer code to predict the behavior of an experimental, supersonic hydrogen jet burning in air, some improvement in agreement with the experimental data was obtained in the far field in the region near the jet centerline. Recommendations are included for further improvement of the model and for additional comparisons with experimental data.

  1. Suppression of excited-state contributions to stellar reaction rates

    NASA Astrophysics Data System (ADS)

    Rauscher, T.

    2013-09-01

    It has been shown in previous work [Kiss , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.101.191101 101, 191101 (2008); Rauscher , Phys. Rev. C10.1103/PhysRevC.80.035801 80, 035801 (2009)] that a suppression of the stellar enhancement factor (SEF) occurs in some endothermic reactions at and far from stability. This effect is re-evaluated using the ground-state contributions to the stellar reaction rates, which were shown to be better suited to judging the importance of excited-state contributions than the previously applied SEFs. An update of the tables shown in the latter work is given. The new evaluation finds 2350 cases (out of a full set of 57 513 reactions) for which the ground-state contribution is larger in the reaction direction with a negative reaction Q value than in the exothermic direction, thus providing exceptions to the commonly applied Q value rule. The results confirm the Coulomb suppression effect but lead to a larger number of exceptions than previously found. This is due to the fact that often a large variation in the g.s. contribution does not lead to a sizable change in the SEF. On the other hand, several previously identified cases do not appear anymore because it is found that their g.s. contribution is smaller than inferred from the SEF.

  2. Triple-α reaction rate constrained by stellar evolution models

    NASA Astrophysics Data System (ADS)

    Suda, Takuma; Hirschi, Raphael; Fujimoto, Masayuki Y.

    2012-11-01

    We investigate the quantitative constraint on the triple-α reaction rate based on stellar evolution theory, motivated by the recent significant revision of the rate proposed by nuclear physics calculations. Targeted stellar models were computed in order to investigate the impact of that rate in the mass range of 0.8<=M/Msolar<=25 and in the metallicity range between Z = 0 and Z = 0.02. The revised rate has a significant impact on the evolution of low-and intermediate-mass stars, while its influence on the evolution of massive stars (M > 10Msolar) is minimal. We find that employing the revised rate suppresses helium shell flashes on AGB phase for stars in the initial mass range 0.8<=M/Msolar<=6, which is contradictory to what is observed. The absence of helium shell flashes is due to the weak temperature dependence of the revised triple-α reaction cross section at the temperature involved. In our models, it is suggested that the temperature dependence of the cross section should have at least ν > 10 at T = 1-1.2×108K where the cross section is proportional to Tν. We also derive the helium ignition curve to estimate the maximum cross section to retain the low-mass first red giants. The semi-analytically derived ignition curves suggest that the reaction rate should be less than ~ 10-29 cm6 s-1 mole-2 at ~ 107.8 K, which corresponds to about three orders of magnitude larger than that of the NACRE compilation.

  3. Triple-{alpha} reaction rate constrained by stellar evolution models

    SciTech Connect

    Suda, Takuma; Hirschi, Raphael; Fujimoto, Masayuki Y.

    2012-11-12

    We investigate the quantitative constraint on the triple-{alpha} reaction rate based on stellar evolution theory, motivated by the recent significant revision of the rate proposed by nuclear physics calculations. Targeted stellar models were computed in order to investigate the impact of that rate in the mass range of 0.8{<=}M/M{sub Circled-Dot-Operator }{<=}25 and in the metallicity range between Z= 0 and Z= 0.02. The revised rate has a significant impact on the evolution of low-and intermediate-mass stars, while its influence on the evolution of massive stars (M > 10M{sub Circled-Dot-Operator }) is minimal. We find that employing the revised rate suppresses helium shell flashes on AGB phase for stars in the initial mass range 0.8{<=}M/M{sub Circled-Dot-Operator }{<=}6, which is contradictory to what is observed. The absence of helium shell flashes is due to the weak temperature dependence of the revised triple-{alpha} reaction cross section at the temperature involved. In our models, it is suggested that the temperature dependence of the cross section should have at least {nu} > 10 at T = 1-1.2 Multiplication-Sign 10{sup 8}K where the cross section is proportional to T{sup {nu}}. We also derive the helium ignition curve to estimate the maximum cross section to retain the low-mass first red giants. The semi-analytically derived ignition curves suggest that the reaction rate should be less than {approx} 10{sup -29} cm{sup 6} s{sup -1} mole{sup -2} at Almost-Equal-To 10{sup 7.8} K, which corresponds to about three orders of magnitude larger than that of the NACRE compilation.

  4. Application of semiclassical methods to reaction rate theory

    SciTech Connect

    Hernandez, R.

    1993-11-01

    This work is concerned with the development of approximate methods to describe relatively large chemical systems. This effort has been divided into two primary directions: First, we have extended and applied a semiclassical transition state theory (SCTST) originally proposed by Miller to obtain microcanonical and canonical (thermal) rates for chemical reactions described by a nonseparable Hamiltonian, i.e. most reactions. Second, we have developed a method to describe the fluctuations of decay rates of individual energy states from the average RRKM rate in systems where the direct calculation of individual rates would be impossible. Combined with the semiclassical theory this latter effort has provided a direct comparison to the experimental results of Moore and coworkers. In SCTST, the Hamiltonian is expanded about the barrier and the ``good`` action-angle variables are obtained perturbatively; a WKB analysis of the effectively one-dimensional reactive direction then provides the transmission probabilities. The advantages of this local approximate treatment are that it includes tunneling effects and anharmonicity, and it systematically provides a multi-dimensional dividing surface in phase space. The SCTST thermal rate expression has been reformulated providing increased numerical efficiency (as compared to a naive Boltzmann average), an appealing link to conventional transition state theory (involving a ``prereactive`` partition function depending on the action of the reactive mode), and the ability to go beyond the perturbative approximation.

  5. A Study of the Comparability of Speaking Proficiency Interview Ratings across Three Government Language Training Agencies.

    ERIC Educational Resources Information Center

    Clark, John L. D.

    A study of the reliability of the proficiency ratings scale and techniques used by three federal government agencies--the Central Intelligence Agency, the Defense Language Institute, and the Foreign Service Institute (FSI)--to test employees' oral language proficiency in French and German had two randomly selected two-person teams of testers from…

  6. 75 FR 61050 - Removal From Regulation FD of the Exemption for Credit Rating Agencies

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-10-04

    ... From the Federal Register Online via the Government Publishing Office SECURITIES AND EXCHANGE COMMISSION 17 CFR Part 243 Removal From Regulation FD of the Exemption for Credit Rating Agencies AGENCY... Regulation FD. Due to the removal of Rule 100(b)(2)(iii), we are re- designating Rule 100(b)(2)(iv) as...

  7. Omphacite breakdown reactions and relation to eclogite exhumation rates

    NASA Astrophysics Data System (ADS)

    Anderson, Eric D.; Moecher, David P.

    2007-09-01

    Clinopyroxene + plagioclase (±Hbl ± Qtz) symplectites after omphacite are widely cited as evidence for prior eclogite-facies or high-pressure (HP) metamorphism. Precursor omphacite compositions of retrograde eclogites, used for reconstructing retrograde P- T paths, are commonly estimated by reintegrating symplectite phases with the assumption that the symplectite-forming reactions were isochemical. Comparisons of broadbeam symplectite compositions to adjacent unreacted pyroxene from various symplectites after clinopyroxene from the Appalachian Blue Ridge (ABR) and Western Gneiss Region (WGR) suggest that the symplectite forming reactions are largely isochemical. Endmember calculations based on reintegrated symplectite compositions from the ABR and WGR suggest that a minor Ca-Eskola (CaEs) component (XCaEs = 0.04-0.15) was present in precursor HP clinopyroxene. WGR symplectites consist of fine-grained (˜1 μm-scale), vermicular intergrowths of Pl + Cpx II ± Hbl that occur at grain boundaries or internally. ABR symplectites contain coarser (˜10 μm-scale) planar lamellae and rods of Pl + Cpx II + Qtz + Hbl within clinopyroxene cores. The contrasting textures correlate with decompression and cooling rate, and degree of overstepping of the retrograde reaction (lamellar: slow, erosionally controlled exhumation with slow/low overstepping; fine-grained, grainboundary symplectite: rapid, tectonic exhumation with rapid/high overstepping). Variations in XCaEs, Xjd, and XCaTs of precursor HP omphacite are related to the symplectic mineral assemblages that result from decompression. Quartz-normative symplectities indicate quartz-producing retrograde reactions (e.g., breakdown of precursor CaEs); quartz-free symplectities (e.g., diopside + plagioclase after omphacite) indicate quartz-consuming reactions (jd, CaTs breakdown) outpaced quartz-producing reactions.

  8. Rate constant for the reaction of atomic chlorine with methane

    NASA Technical Reports Server (NTRS)

    Lin, C. L.; Leu, M. T.; Demore, W. B.

    1978-01-01

    The rate constant and temperature dependence of the Cl + CH4 reaction have been investigated by the techniques of competitive chlorination of CH4/C2H6 mixtures and by discharge-flow/mass spectroscopy. The objectives were to determine an accurate value for the rate constant for use in stratospheric modeling, and to clarify discrepancies in results previously obtained by different techniques. The results deduced from the competitive chlorination study are in good agreement with the absolute values measured by the mass spectrometric method, and at temperatures above 300 K are in good agreement with measurements by other techniques based on resonance fluorescence detection of atomic chlorine. However, in the 220-300 K region, the competitive experiments indicate lower rate constants than those obtained by resonance fluorescence methods, and do not reproduce the curved Arrhenius plots seen in some of those studies.

  9. r-PROCESS Reaction Rates for the Actinides and Beyond

    NASA Astrophysics Data System (ADS)

    Panov, I. V.; Korneev, I. Yu.; Rauscher, T.; Thielemann, F.-K.

    2011-10-01

    We discuss the importance of different fission rates for the formation of heavy and superheavy nuclei in the astrophysical r-process. Neutron-induced reaction rates, including fission and neutron capture, are calculated in the temperature range 108 ≤ T(K) ≤ 1010 within the framework of the statistical model for targets with the atomic number 84 ≤ Z ≤ 118 (from Po to Uuo) from the neutron to the proton drip-line for different mass and fission barrier predictions based on Thomas-Fermi (TF), Extended Thomas-Fermi plus Strutinsky Integral (ETFSI), Finite-Range Droplet Model (FRDM) and Hartree-Fock-Bogolyubov (HFB) approaches. The contribution of spontaneous fission as well as beta-delayed fission to the recycling r-process is discussed. We also discuss the possibility of rate tests, based on mini r-processed yields in nuclear explosions.

  10. Primordial lithium: New reaction rates, new abundances, new constraints

    SciTech Connect

    Kawano, L.; Schramm, D.; Steigman, G.

    1986-12-01

    Newly measured nuclear reaction rates for /sup 3/H(..cap alpha..,..gamma..)/sup 7/Li (higher than previous values) and /sup 7/Li(p,..cap alpha..)/sup 4/He (lower than previous values) are shown to increase the /sup 7/Li yield from big bang nucleosynthesis for lower baryon to photon ratio (eta less than or equal to 4 x 10/sup -10/); the yield for higher eta is not affected. New, independent determinations of Li abundances in extreme Pop II stars are in excellent agreement with the earlier work of the Spites and give continued confidence in the use of /sup 7/Li in big bang baryon density determinations. The new /sup 7/Li constraints imply a lower limit on eta of 2 x 10/sup -10/ and an upper limit of 5 x 10/sup -10/. This lower limit to eta is concordant with that obtained from considerations of D + /sup 3/He. The upper limit is consistent with, but even more restrictive than, the D bound. With the new rates, any observed primordial Li/H ratio below 10/sup -10/ would be inexplicable by the standard big bang nucleosynthesis. A review is made of the strengths and possible weaknesses of utilizing conclusions drawn from big bang lithium considerations. An appendix discusses the null effect of a factor of 32 increase in the experimental rate for the D(d,..gamma..)/sup 4/He reaction. 28 refs., 1 fig.

  11. RPMDRATE: Bimolecular chemical reaction rates from ring polymer molecular dynamics

    NASA Astrophysics Data System (ADS)

    Suleimanov, Yu. V.; Allen, J. W.; Green, W. H.

    2013-03-01

    We present RPMDRATE, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH4, OH+CH4 and H+C2H6 reactions. Catalogue identifier: AENW_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AENW_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: MIT license No. of lines in distributed program, including test data, etc.: 94512 No. of bytes in distributed program, including test data, etc.: 1395674 Distribution format: tar.gz Programming language: Fortran 90/95, Python (version 2.6.x or later, including any version of Python 3, is recommended). Computer: Not computer specific. Operating system: Any for which Python, Fortran 90/95 compiler and the required external routines are available. Has the code been vectorized or parallelized?: The program can efficiently utilize 4096+ processors, depending on problem and available computer. At low temperatures, 110 processors are reasonable for a typical umbrella integration run with an analytic potential energy function and gradients on the latest x86-64 machines.

  12. Rate-Controlled Constrained-Equilibrium Theory of Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Keck, James C.

    2008-08-01

    The Rate-Controlled Constrained-Equilibrium (RCCE) method for simplifying the treatment of reactions in complex systems is summarized and the selection of constraints for both close-to and far-from equilibrium systems is discussed. Illustrative examples of RCCE calculations of carbon monoxide concentrations in the exhaust products of an internal combustion engine and ignition delays for methane-oxygen mixtures in a constant volume adiabatic chamber are given and compared with "detailed" calculations. The advantages of RCCE calculations over "detailed" calculations are discussed.

  13. Kinetics of Imidazole Catalyzed Ester Hydrolysis: Use of Buffer Dilutions to Determine Spontaneous Rate, Catalyzed Rate, and Reaction Order.

    ERIC Educational Resources Information Center

    Lombardo, Anthony

    1982-01-01

    Described is an advanced undergraduate kinetics experiment using buffer dilutions to determine spontaneous rate, catalyzed rate, and reaction order. The reaction utilized is hydrolysis of p-nitro-phenyl acetate in presence of imidazole, which has been shown to enhance rate of the reaction. (Author/JN)

  14. Primordial lithium - New reaction rates, new abundances, new constraints

    NASA Technical Reports Server (NTRS)

    Kawano, Lawrence; Schramm, David; Steigman, Gary

    1988-01-01

    Newly measured nuclear reaction rates for H-3(alpha, gamma)Li-7 (higher than previous values) and Li-7(p, alpha)He-4 (lower than previous values) are shown to increase the Li-7 yield from big band nucleosynthesis for lower baryon-to-photon ratio (less than about 4 x 10 to the 10th). Recent revisions in the He-3(alpha, gamma)Be-7 and the D(p, gamma)He-3 rates enhance the high (greater than 4 x 10 to the 10th) Li-7(Be) production. New, independent determinations of Li abundances in extreme population II stars are in excellent agreement with the work of Spites and give continued confidence in the use of Li-7 in big bang baryon density determinations.

  15. Constraining kinetic rates of mineral reactions using reactive transport models

    NASA Astrophysics Data System (ADS)

    Bolton, E. W.; Wang, Z.; Ague, J.; Bercovici, D.; Cai, Z.; Karato, S.; Oristaglio, M. L.; Qiu, L.

    2012-12-01

    We use a reactive transport model to better understand results of experiments to obtain kinetic rates of mineral reactions in closed systems. Closed system experiments pose special challenges in that secondary minerals may form that modify the fluid composition evolution and may grow on the dissolving minerals thus armoring the surface. Even so, such closed system experiments provide critical data for what minerals would actually form in field applications and how coupled dissolution and precipitation mineral reactions are strongly linked. Comparing to experimental observations can test the reactive transport model, and the experimental observations can be better understood by comparing the results to the modeling. We apply a 0D end member of the model to understand the dissolution of single crystals of forsterite in a variety of settings (low pH, high pH, or NaHCO3 initial fluids, at 100 C and 1 bar, or 200 C and 150 bar). Depending on the initial conditions, we observe the precipitation of talc, brucite, amorphous silica, chrysotile, or magnesite, in various combinations. We compare simulation results to fluid compositions and the presence of secondary minerals experimentally sampled at various times. Insight from the simulations helped create an inverse model to extract the rates of forsterite dissolution and to create a simple forward model useful for exploring the influence of system size, secondary mineral surface areas, etc. Our reactive transport model allows secondary minerals to armor the forsterite surface, which can strongly decrease the dissolution rate as the system evolves. Tuning our model with experimentally derived rates and assuring relevant processes are included so as to reproduce experimental observations is necessary before upscaling to heterogeneous field conditions. The reactive transport model will be used for field-scale sequestration simulations and coupled with a geomechanical model that includes the influence of deformation.

  16. Nucleation and reaction rates controlled by local reaction volume and reaction-induced stress - spinel layer growth as an example

    NASA Astrophysics Data System (ADS)

    Götze, Lutz C.; Milke, Ralf; Dohmen, Ralf; Wirth, Richard

    2014-05-01

    We observed the growth of spinel sensu stricto (MgAl2O4) between periclase (MgO) and corundum (Al2O3) in thin films deposited by the pulsed laser deposition method on crystallographically oriented single crystal substrates. The starting samples consisted of cut and ultra polished single crystals of either corundum (parallel (0001)) or periclase (parallel (111)) and an amorphous source layer of the respective reactant that in the very first stages of the experiments became polycrystalline. The cutting direction in the substrate minerals ensures that the substrate phases start to react along their close-packed hexagonal oxygen layers which allows topotactical growth of the newly formed spinel. The entire layer setup on the substrate crystals was only a few 100 nm thick. The growth of these spinel product layers was monitored in-situ using a heating attachment and synchrotron X-ray diffraction. From the reacted samples we took electron transparent foils by the focused ion beam method and analysed them ex-situ by TEM. At 1000°C we found a difference in spinel growth rate between one and two orders of magnitude between the two substrates, all other parameters held constant. At 900 and 1000 °C spinel had formed after one hour by 0.004 nm/s (900°C) and 0.034 nm/s (1000°C) on corundum substrate, while on periclase substrate the reaction had gone completely through the Al2O3 source layer transforming it to spinel by at least 15-30 times higher reaction rates (boundary values) and probably even faster. At 800°C no reaction occurred between periclase layers and corundum single crystals, whereas spinel crystallized at a (linearized) rate of 46 nm/h on periclase single crystals. We explain our findings by the local reaction volume at the periclase-corundum interface. Many studies (including this one) have established that spinel grows by cation exchange in a rather immobile oxygen sublattice. This mechanism implies a negative volume change at the Sp-Per interface (by -13

  17. Rate Constant for the OH + CO Reaction at Low Temperatures.

    PubMed

    Liu, Yingdi; Sander, Stanley P

    2015-10-01

    Rate constants for the reaction of OH + CO → products (1) have been measured using laser photolysis/laser-induced fluorescence (LP/LIF) over the temperature range 193–296 K and at pressures of 50–700 Torr of Ar and N2. The reaction was studied under pseudo-first-order conditions, monitoring the decay of OH in the presence of a large excess of CO. The rate constants can be expressed as a combination of bimolecular and termolecular components. The bimolecular component was found to be temperature-independent with an expression given by kbi(T) = (1.54 ± 0.14) × 10(–13)[e(–(13±17)/T)] cm(3) molecule(–1) s(–1), with an error of one standard deviation. The termolecular component was fitted to the expression, kter = k0(T)[M]/[1 + (k0(T)[M]/k∞(T)] × 0.6({1+[log10(k0(T)[M]/k∞(T))]2}−1) where k0(T) = k0(300)(T/300)(−n) and k∞(T) = k∞(300)(T/300)(−m). The parameters for k0(T) were determined to be k0(300) = (6.0±0.5) × 10(−33) cm(6) molecule(–2) s(–1) in N2 and k0(300) = (3.4 ± 0.3) × 10(–33) cm(6) molecule(–2) s(–1) in Ar, with n = 1.9±0.5 and 2.0±0.4 in N2 and Ar, respectively. These parameters were determined using k0(T) and m from the NASA kinetics data evaluation (JPL Publication No. 10-6) since the experimental pressure range was far from the high-pressure limit. Addition of low concentrations of O2 had no discernible effect on the mechanism of the OH + CO reaction but resulted in secondary reactions which regenerated OH. PMID:26305192

  18. In Search of Reaction Rate Scaling Law for Supersonic Combustion

    NASA Astrophysics Data System (ADS)

    Ladeinde, Foluso; Lou, Zhipeng; Li, Wenhai

    2015-11-01

    As a way of employing the flamelet approach, which was developed essentially for incompressible flows, to model supersonic combustion, the role ascribed to pressure has not been very convincing. That is, the reaction rate is often scaled on the square of the pressure in the finite Mach number flow field relative to the usually atmospheric static pressure field used in the generation of the flamelet library. This scaling assumption is quite simple and will therefore be very attractive if it has a sound theoretical basis and it works for a large selection of high-speed combustion flows. We try to find some justifications for different scaling laws, with the hope of coming up with a more universally-acceptable flamelet procedure for supersonic combustion.

  19. The effects of vacuum polarization on thermonuclear reaction rates

    NASA Technical Reports Server (NTRS)

    Gould, Robert J.

    1990-01-01

    Added to the pure Coulomb potential, the contribution from vacuum polarization increases the barrier, reducing the wave function (u) for reacting nuclei within the range of nuclear forces. The cross section and reaction rate are then reduced accordingly by a factor proportional to u squared. The effect is treated by evaluating the vacuum polarization potential as a small correction to the Coulomb term, then computing u in a WKB formulation. The calculation is done analytically employing the small r power-series expansion for the Uehling potential to express the final result in terms of convenient parameters. At a temperature of 1.4 x 10 to the 7th K the (negative) correction is 1.3 percent for the fundamental fusion process p + p yields d + e(+) + nu.

  20. Measurement of sulfur dioxide reaction rates in wintertime orographic clouds

    SciTech Connect

    Snider, J.R.

    1989-01-01

    Releases of SO2 into the wintertime orographic clouds at Elk Mountain in southeastern Wyoming were utilized to accelerate the rate of SO2 oxidation to cloud-water dissolved sulfate (SO4(-2)). Background SO2 mixing ratios were 0.6 parts-per-billion by volume (ppbv) and were consistent with the remote location of the experimental site and with supplemental cloud water, snow, and aerosol composition measurements. Background mixing ratios of hydrogen peroxide (H2O2) and the organohydroperoxides, expressed as methyl hydroperoxide (MHP), were 0.15 and 0.17 ppbv, respectively. The concentration of H2O2 in cloud water, obtained as rime, was also monitored. Analysis of these findings suggests that both reactive loss of H2O2 and volatilization during riming are mechanisms for H2O2 loss. The pseudo first-order SO2 depletion rates varied between 2 and 72 percent /hr (x=32 plus or minus 22 percent/hr, n=10). Observed depletions of H2O2 (x=0.030 ppbv) were consistent with observed yields of SO4(-2) (x=0.027 ppbv) and with model predictions. Observed depletions of MHP were not significantly different from 0.0 ppbv. This observation is both consistent with the much smaller solubility of MHP, compared with H2O2, and with the results of 16 model simulations. Reactions between dissolved SO2 and O3, between SO2 and O2, and between SO2 and HCHO were calculated to contribute less than 40 percent to the total amount of SO4(-2). These reactions were inferred to be inhibited by the low pH (less than 5) of the Elk Mountain cloud water. It is concluded that H2O2 is the dominant SO2 oxidant in these clouds, and that the laboratory measurements form an adequate basis for predicting the rate of in-cloud oxidation of SO2 by H2O2.

  1. An Experiment To Demonstrate How a Catalyst Affects the Rate of a Reaction.

    ERIC Educational Resources Information Center

    Copper, Christine L.; Koubeck, Edward

    1999-01-01

    Describes a chemistry experiment that allows students to calculate rates of reaction, orders of reaction, and activation energies. The activity demonstrates that to increase a reaction's rate, a catalyst need only provide any additional pathway for the reaction, not necessarily a pathway having lower activation energy. (WRM)

  2. Pressure Dependence of Gas-Phase Reaction Rates

    ERIC Educational Resources Information Center

    De Persis, Stephanie; Dollet, Alain; Teyssandier, Francis

    2004-01-01

    It is presented that only simple concepts, mainly taken from activated-complex or transition-state theory, are required to explain and analytically describe the influence of pressure on gas-phase reaction kinetics. The simplest kind of elementary gas-phase reaction is a unimolecular decomposition reaction.

  3. Photonuclear and radiative capture reaction rates for Nuclear Astrophysics

    NASA Astrophysics Data System (ADS)

    Beard, Mary; Frauendorf, S.; Kaempfer, B.; Scwengner, R.; Wiescher, M.

    2011-10-01

    The vast majority of nuclei heavier than iron are synthesisized via the capture of neutrons. There are however 35 naturally occurring nuclei, including isotopes of Mo and La, located on the neutron-deficient size of the valley of stability. It has been proposed that these nuclei, referred to as p-nuclei, are produced via sequential photo-dissociation reactions in the oxygen-neon shell burning regions of a pre-supernova star. As such, cross sections for p-nuclei production are particularly sensitive to the gamma-ray strength function, which, though dominated by the giant dipole resonance, may contain extra strength contributions near to the neutron threshold. Recently new (γ, γ') cross section measurements have been performed at the ELBE facility at Helmholtz-Zentrum Dresden-Rossendorf for the nuclei ^92-100Mo, ^88Sr, ^90Zr and ^139La probing the photo-absorption cross section over an energy range 4.5 - 6 MeV, up to the neutron separation threshold. The use of these measurements as a test of existing gamma-ray strength function models, and the consequent impact on p-nuclei production rates, will be discussed.

  4. Enhanced reaction rates in NDP analysis with neutron scattering

    SciTech Connect

    Downing, R. Gregory

    2014-04-15

    Neutron depth profiling (NDP) makes accessible quantitative information on a few isotopic concentration profiles ranging from the surface into the sample a few micrometers. Because the candidate analytes for NDP are few, there is little interference encountered. Furthermore, neutrons have no charge so mixed chemical states in the sample are of no direct concern. There are a few nuclides that exhibit large probabilities for neutron scattering. The effect of neutron scattering on NDP measurements has not previously been evaluated as a basis for either enhancing the reaction rates or as a source of measurement error. Hydrogen is a common element exhibiting large neutron scattering probability found in or around sample volumes being analyzed by NDP. A systematic study was conducted to determine the degree of signal change when neutron scattering occurs during analysis. The relative signal perturbation was evaluated for materials of varied neutron scattering probability, concentration, total mass, and geometry. Signal enhancements up to 50% are observed when the hydrogen density is high and in close proximity to the region of analysis with neutron beams of sub thermal energies. Greater signal enhancements for the same neutron number density are reported for thermal neutron beams. Even adhesive tape used to position the sample produces a measureable signal enhancement. Because of the shallow volume, negligible distortion of the NDP measured profile shape is encountered from neutron scattering.

  5. Reaction mechanism and rate constants of the CH+CH4 reaction: a theoretical study

    NASA Astrophysics Data System (ADS)

    Ribeiro, Joao Marcelo; Mebel, Alexander M.

    2015-07-01

    Ab initio and density functional calculations have been performed to elucidate the mechanism of CH radical insertion into methane. The results show that the reaction can be viewed to occur via two stages. On the first stage, the CH radical approaches methane without large structural changes to acquire proper positioning for the subsequent stage, where H-migration occurs from CH4 to CH, along with a C-C bond formation. Where the first stage ends and the second begins, a tight transition state was located using the B3LYP/6-311G(d,p) and MP4(SDQ)/6-311++G(d,p) methods. Using a rigid rotor - harmonic oscillator approach within transition state theory, we show that at the MP5/6-311++G(d,p)//MP4(SDQ)/6-311++G(d,p) level the calculated rate constants are in a reasonably good agreement with experiment in a broad temperature range of 145-581 K. Even at low temperatures, the insertion reaction bottleneck is found about the location of the tight transition state, rather than at long separations between the CH and CH4 reactants. In addition, high level CCSD(T)-F12/CBS calculations of the remainder of the C2H5 potential energy surface predict the CH+CH4 reaction to proceed via the initial insertion step to the ethyl radical which then can emit a hydrogen atom to form highly exothermic C2H4+H products.

  6. Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows.

    SciTech Connect

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

    2009-08-01

    This report summarizes the work completed during FY2009 for the LDRD project 09-1332 'Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows'. The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates 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 nonequilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological non-equilibrium 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, the difference between the two models can exceed 10 orders of magnitude. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates. Extensions of the model to reactions typically found in combustion flows and ionizing reactions are also found to be in very good agreement with available measurements, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

  7. On the ambiguity of the reaction rate constants in multivariate curve resolution for reversible first-order reaction systems.

    PubMed

    Schröder, Henning; Sawall, Mathias; Kubis, Christoph; Selent, Detlef; Hess, Dieter; Franke, Robert; Börner, Armin; Neymeyr, Klaus

    2016-07-13

    If for a chemical reaction with a known reaction mechanism the concentration profiles are accessible only for certain species, e.g. only for the main product, then often the reaction rate constants cannot uniquely be determined from the concentration data. This is a well-known fact which includes the so-called slow-fast ambiguity. This work combines the question of unique or non-unique reaction rate constants with factor analytic methods of chemometrics. The idea is to reduce the rotational ambiguity of pure component factorizations by considering only those concentration factors which are possible solutions of the kinetic equations for a properly adapted set of reaction rate constants. The resulting set of reaction rate constants corresponds to those solutions of the rate equations which appear as feasible factors in a pure component factorization. The new analysis of the ambiguity of reaction rate constants extends recent research activities on the Area of Feasible Solutions (AFS). The consistency with a given chemical reaction scheme is shown to be a valuable tool in order to reduce the AFS. The new methods are applied to model and experimental data. PMID:27237834

  8. Optimal reconstruction of reaction rates from particle distributions

    NASA Astrophysics Data System (ADS)

    Fernandez-Garcia, Daniel; Sanchez-Vila, Xavier

    2010-05-01

    Random walk particle tracking methodologies to simulate solute transport of conservative species constitute an attractive alternative for their computational efficiency and absence of numerical dispersion. Yet, problems stemming from the reconstruction of concentrations from particle distributions have typically prevented its use in reactive transport problems. The numerical problem mainly arises from the need to first reconstruct the concentrations of species/components from a discrete number of particles, which is an error prone process, and then computing a spatial functional of the concentrations and/or its derivatives (either spatial or temporal). Errors are then propagated, so that common strategies to reconstruct this functional require an unfeasible amount of particles when dealing with nonlinear reactive transport problems. In this context, this article presents a methodology to directly reconstruct this functional based on kernel density estimators. The methodology mitigates the error propagation in the evaluation of the functional by avoiding the prior estimation of the actual concentrations of species. The multivariate kernel associated with the corresponding functional depends on the size of the support volume, which defines the area over which a given particle can influence the functional. The shape of the kernel functions and the size of the support volume determines the degree of smoothing, which is optimized to obtain the best unbiased predictor of the functional using an iterative plug-in support volume selector. We applied the methodology to directly reconstruct the reaction rates of a precipitation/dissolution problem involving the mixing of two different waters carrying two aqueous species in chemical equilibrium and moving through a randomly heterogeneous porous medium.

  9. Cross sections and reaction rates of relevance to aeronomy

    SciTech Connect

    Fox, J.L. )

    1991-01-01

    Experimental and theoretical data relevant to models and measurements of the chemical and thermal structures and luminosity of the thermospheres of the earth and planets published during the last four years are surveyed. Among chemical processes, attention is given to ion-molecule reactions, dissociative recombination of molecular ions, and reactions between neutral species. Both reactions between ground state species and species in excited states are considered, including energy transfer and quenching. Measured and calculated cross sections for interactions of solar radiation with atmospheric species, such as photoabsorption, photoionization, and photodissociation and related processes are surveyed.

  10. Rates of primary electron transfer reactions in the photosystem I reaction center reconstituted with different quinones as the secondary acceptor

    SciTech Connect

    Kumazaki, Shigeichi; Kandori, Hideki; Yoshihara, Keitaro ); Iwaki, Masayo; Itoh, Shigeru ); Ikegamu, Isamu )

    1994-10-27

    Rates of sequential electron transfer reactions from the primary electron donor chlorophyll dimer (P700) to the electron acceptor chlorophyll a-686 (A[sub 0]) and to the secondary acceptor quinone (Q[sub [phi

  11. Interactive Program System for Integration of Reaction Rate Equations.

    ERIC Educational Resources Information Center

    Chesick, John P.

    1988-01-01

    Describes a Pascal-language based kinetics rate package for the microcomputer. Considers possible ecological uses for the program and illustrates results for several rate laws. Discusses hardware and software needs for adequate operation. (ML)

  12. Reaction rate oscillations during catalytic CO oxidation: A brief overview

    NASA Technical Reports Server (NTRS)

    Tsotsis, T. T.; Sane, R. C.

    1987-01-01

    It is not the intent here to present a comprehensive review of the dynamic behavior of the catalytic oxidation of CO. This reaction is one of the most widely studied in the field of catalysis. A review paper by Engel and Ertl has examined the basic kinetic and mechanistic aspects, and a comprehensive paper by Razon and Schmitz was recently devoted to its dynamic behavior. Those interested in further study of the subject should consult these reviews and a number of general review papers on catalytic reaction dynamics. The goal is to present a brief overview of certain interesting aspects of the dynamic behavior of this reaction and to discuss a few questions and issues, which are still the subject of study and debate.

  13. Quick and Easy Rate Equations for Multistep Reactions

    ERIC Educational Resources Information Center

    Savage, Phillip E.

    2008-01-01

    Students rarely see closed-form analytical rate equations derived from underlying chemical mechanisms that contain more than a few steps unless restrictive simplifying assumptions (e.g., existence of a rate-determining step) are made. Yet, work published decades ago allows closed-form analytical rate equations to be written quickly and easily for…

  14. Women's Self-Disclosure of HIV Infection: Rates, Reasons, Reactions.

    ERIC Educational Resources Information Center

    Simoni, Jane M.; And Others

    1995-01-01

    A survey of 65 ethnically diverse women revealed relatively low rates of disclosure of HIV-positive serostatus to extended family members, somewhat higher rates for immediate family members, and highest rates for lovers or friends. Spanish-speaking Latinas were less likely to disclose their serostatus than English-speaking Latinas, African…

  15. Development of the new approach to the diffusion-limited reaction rate theory

    SciTech Connect

    Veshchunov, M. S.

    2012-04-15

    The new approach to the diffusion-limited reaction rate theory, recently proposed by the author, is further developed on the base of a similar approach to Brownian coagulation. The traditional diffusion approach to calculation of the reaction rate is critically analyzed. In particular, it is shown that the traditional approach is applicable only in the special case of reactions with a large reaction radius and the mean inter-particle distances, and become inappropriate in calculating the reaction rate in the case of a relatively small reaction radius. In the latter case, most important for chemical reactions, particle collisions occur not in the diffusion regime but mainly in the kinetic regime characterized by homogeneous (random) spatial distribution of particles on the length scale of the mean inter-particle distance. The calculated reaction rate for a small reaction radius in three dimensions formally (and fortuitously) coincides with the expression derived in the traditional approach for reactions with a large reaction radius, but notably deviates at large times from the traditional result in the planar two-dimensional geometry. In application to reactions on discrete lattice sites, new relations for the reaction rate constants are derived for both three-dimensional and two-dimensional lattices.

  16. 41 CFR 102-117.45 - What other factors must I consider when using another agency's contract or rate tender?

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 41 Public Contracts and Property Management 3 2011-01-01 2011-01-01 false What other factors must I consider when using another agency's contract or rate tender? 102-117.45 Section 102-117.45 Public... tender? When using another agency's contract or rate tender, you must: (a) Assure that the contract...

  17. 41 CFR 102-117.45 - What other factors must I consider when using another agency's contract or rate tender?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false What other factors must I consider when using another agency's contract or rate tender? 102-117.45 Section 102-117.45 Public... tender? When using another agency's contract or rate tender, you must: (a) Assure that the contract...

  18. 41 CFR 102-117.45 - What other factors must I consider when using another agency's contract or rate tender?

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 41 Public Contracts and Property Management 3 2014-01-01 2014-01-01 false What other factors must I consider when using another agency's contract or rate tender? 102-117.45 Section 102-117.45 Public... tender? When using another agency's contract or rate tender, you must: (a) Assure that the contract...

  19. 41 CFR 102-117.45 - What other factors must I consider when using another agency's contract or rate tender?

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 41 Public Contracts and Property Management 3 2012-01-01 2012-01-01 false What other factors must I consider when using another agency's contract or rate tender? 102-117.45 Section 102-117.45 Public... tender? When using another agency's contract or rate tender, you must: (a) Assure that the contract...

  20. 41 CFR 102-117.45 - What other factors must I consider when using another agency's contract or rate tender?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 41 Public Contracts and Property Management 3 2013-07-01 2013-07-01 false What other factors must I consider when using another agency's contract or rate tender? 102-117.45 Section 102-117.45 Public... tender? When using another agency's contract or rate tender, you must: (a) Assure that the contract...

  1. Fluctuation enhanced electrochemical reaction rates at the nanoscale.

    PubMed

    García-Morales, Vladimir; Krischer, Katharina

    2010-03-01

    The electrode potential constitutes a dynamical variable whenever an electrode is resistively coupled to the electric circuit. We show that at the nanoscale, the discreteness and stochasticity of an electron transfer event causes fluctuations of the electrode potential that render all elementary electrochemical reactions to be faster on a nanoelectrode than predicted by the macroscopic (Butler-Volmer) electrochemical kinetics. This phenomenon is substantiated by means of a generalized (electro)chemical master equation. PMID:20176966

  2. Error Rate Comparison during Polymerase Chain Reaction by DNA Polymerase.

    PubMed

    McInerney, Peter; Adams, Paul; Hadi, Masood Z

    2014-01-01

    As larger-scale cloning projects become more prevalent, there is an increasing need for comparisons among high fidelity DNA polymerases used for PCR amplification. All polymerases marketed for PCR applications are tested for fidelity properties (i.e., error rate determination) by vendors, and numerous literature reports have addressed PCR enzyme fidelity. Nonetheless, it is often difficult to make direct comparisons among different enzymes due to numerous methodological and analytical differences from study to study. We have measured the error rates for 6 DNA polymerases commonly used in PCR applications, including 3 polymerases typically used for cloning applications requiring high fidelity. Error rate measurement values reported here were obtained by direct sequencing of cloned PCR products. The strategy employed here allows interrogation of error rate across a very large DNA sequence space, since 94 unique DNA targets were used as templates for PCR cloning. The six enzymes included in the study, Taq polymerase, AccuPrime-Taq High Fidelity, KOD Hot Start, cloned Pfu polymerase, Phusion Hot Start, and Pwo polymerase, we find the lowest error rates with Pfu, Phusion, and Pwo polymerases. Error rates are comparable for these 3 enzymes and are >10x lower than the error rate observed with Taq polymerase. Mutation spectra are reported, with the 3 high fidelity enzymes displaying broadly similar types of mutations. For these enzymes, transition mutations predominate, with little bias observed for type of transition. PMID:25197572

  3. Error Rate Comparison during Polymerase Chain Reaction by DNA Polymerase

    DOE PAGESBeta

    McInerney, Peter; Adams, Paul; Hadi, Masood Z.

    2014-01-01

    As larger-scale cloning projects become more prevalent, there is an increasing need for comparisons among high fidelity DNA polymerases used for PCR amplification. All polymerases marketed for PCR applications are tested for fidelity properties (i.e., error rate determination) by vendors, and numerous literature reports have addressed PCR enzyme fidelity. Nonetheless, it is often difficult to make direct comparisons among different enzymes due to numerous methodological and analytical differences from study to study. We have measured the error rates for 6 DNA polymerases commonly used in PCR applications, including 3 polymerases typically used for cloning applications requiring high fidelity. Errormore » rate measurement values reported here were obtained by direct sequencing of cloned PCR products. The strategy employed here allows interrogation of error rate across a very large DNA sequence space, since 94 unique DNA targets were used as templates for PCR cloning. The six enzymes included in the study, Taq polymerase, AccuPrime-Taq High Fidelity, KOD Hot Start, cloned Pfu polymerase, Phusion Hot Start, and Pwo polymerase, we find the lowest error rates with Pfu , Phusion, and Pwo polymerases. Error rates are comparable for these 3 enzymes and are >10x lower than the error rate observed with Taq polymerase. Mutation spectra are reported, with the 3 high fidelity enzymes displaying broadly similar types of mutations. For these enzymes, transition mutations predominate, with little bias observed for type of transition.« less

  4. Error Rate Comparison during Polymerase Chain Reaction by DNA Polymerase

    PubMed Central

    McInerney, Peter; Adams, Paul; Hadi, Masood Z.

    2014-01-01

    As larger-scale cloning projects become more prevalent, there is an increasing need for comparisons among high fidelity DNA polymerases used for PCR amplification. All polymerases marketed for PCR applications are tested for fidelity properties (i.e., error rate determination) by vendors, and numerous literature reports have addressed PCR enzyme fidelity. Nonetheless, it is often difficult to make direct comparisons among different enzymes due to numerous methodological and analytical differences from study to study. We have measured the error rates for 6 DNA polymerases commonly used in PCR applications, including 3 polymerases typically used for cloning applications requiring high fidelity. Error rate measurement values reported here were obtained by direct sequencing of cloned PCR products. The strategy employed here allows interrogation of error rate across a very large DNA sequence space, since 94 unique DNA targets were used as templates for PCR cloning. The six enzymes included in the study, Taq polymerase, AccuPrime-Taq High Fidelity, KOD Hot Start, cloned Pfu polymerase, Phusion Hot Start, and Pwo polymerase, we find the lowest error rates with Pfu, Phusion, and Pwo polymerases. Error rates are comparable for these 3 enzymes and are >10x lower than the error rate observed with Taq polymerase. Mutation spectra are reported, with the 3 high fidelity enzymes displaying broadly similar types of mutations. For these enzymes, transition mutations predominate, with little bias observed for type of transition. PMID:25197572

  5. Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes, Cycloalkanes, and Dimethyl Ether

    NASA Technical Reports Server (NTRS)

    DeMore, W.; Bayes, K.

    1998-01-01

    Relative rate experiements were used to measure rate constants and temperature denpendencies of the reactions of OH with propane, n-butane, n-pentane, n-hexane, cyclopropane, cyclobutane, cyclopentane, and dimethyl ether.

  6. Effect of temperature oscillation on chemical reaction rates in the atmosphere

    NASA Technical Reports Server (NTRS)

    Eberstein, I. J.

    1974-01-01

    The effect of temperature fluctuations on atmospheric ozone chemistry is examined by considering the Chapman photochemical theory of ozone transport to calculate globally averaged ozone production rates from mean reaction rates, activation energies, and recombination processes.

  7. Upper atmosphere research: Reaction rate and optical measurements

    NASA Technical Reports Server (NTRS)

    Stief, L. J.; Allen, J. E., Jr.; Nava, D. F.; Payne, W. A., Jr.

    1990-01-01

    The objective is to provide photochemical, kinetic, and spectroscopic information necessary for photochemical models of the Earth's upper atmosphere and to examine reactions or reactants not presently in the models to either confirm the correctness of their exclusion or provide evidence to justify future inclusion in the models. New initiatives are being taken in technique development (many of them laser based) and in the application of established techniques to address gaps in the photochemical/kinetic data base, as well as to provide increasingly reliable information.

  8. Hospital cost-containment strategies that earn the respect of rating agencies.

    PubMed

    Dopoulos, Jason

    2016-01-01

    To confirm that hospitals have the necessary structures and strategies in place to reduce costs and secure future market share, credit rating agencies analyze a variety of quantitative and qualitative criteria, including: Salaries and benefits, bad debt, age of plant and depreciation, and other line items that may point to inefficiencies in a hospital's expense structure. Cost-benefit analyses, strategic plans, and leadership qualities that show the long-term value of expense cuts, capital investments, and mergers and acquisitions. Cost-effective and clinically appropriate shifts in a hospital's outpatient-to-inpatient ratio. Liquidity and market share. PMID:26863833

  9. Interlaboratory reaction rate program. 12th progress report, November 1976-October 1979

    SciTech Connect

    Lippincott, E.P.; McElroy, W.N.; Preston, C.C.

    1980-09-01

    The Interlaboratory Reaction Rate UILRR) program is establishing the capability to accurately measure neutron-induced reactions and reaction rates for reactor fuels and materials development programs. The goal for the principal fission reactions, /sup 235/U, /sup 238/U and /sup 239/Pu, is an accuracy to within +- 5% at the 95% confidence level. Accurate measurement of other fission and nonfission reactions is also required, but to a lesser accuracy, between +- 5% and 10% at the 95% confidence level. A secondary program objective is improvement in knowledge of the nuclear parameters involved in the standarization of fuels and materials dosimetry measurements of neutron flux, spectra, fluence and burnup.

  10. Controlling the emotional heart: heart rate biofeedback improves cardiac control during emotional reactions.

    PubMed

    Peira, Nathalie; Fredrikson, Mats; Pourtois, Gilles

    2014-03-01

    When regulating negative emotional reactions, one goal is to reduce physiological reactions. However, not all regulation strategies succeed in doing that. We tested whether heart rate biofeedback helped participants reduce physiological reactions in response to negative and neutral pictures. When viewing neutral pictures, participants could regulate their heart rate whether the heart rate feedback was real or not. In contrast, when viewing negative pictures, participants could regulate heart rate only when feedback was real. Ratings of task success paralleled heart rate. Participants' general level of anxiety, emotion awareness, or cognitive emotion regulation strategies did not influence the results. Our findings show that accurate online heart rate biofeedback provides an efficient way to down-regulate autonomic physiological reactions when encountering negative stimuli. PMID:24373886

  11. The Gaseous Explosive Reaction : the Effect of Pressure on the Rate of Propagation of the Reaction Zone and upon the Rate of Molecular Transformation

    NASA Technical Reports Server (NTRS)

    Stevens, F W

    1932-01-01

    This study of gaseous explosive reaction has brought out a number of important fundamental characteristics of the explosive reaction indicating that the basal processes of the transformation are much simpler and corresponds more closely to the general laws and principles of ordinary transformations than is usually supposed. The report calls attention to the point that the rate of molecular transformation within the zone was found in all cases to be proportional to pressure, that the transformation within the zone is the result of binary impacts. This result is of unusual interest in the case of the reaction of heavy hydrocarbon fuels and the reaction mechanism proposed by the recent kinetic theory of chain reactions.

  12. 34 CFR 222.40 - How does a local educational agency select a local contribution rate based on generally...

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 34 Education 1 2012-07-01 2012-07-01 false How does a local educational agency select a local contribution rate based on generally comparable local educational agencies? 222.40 Section 222.40 Education Regulations of the Offices of the Department of Education OFFICE OF ELEMENTARY AND SECONDARY EDUCATION, DEPARTMENT OF EDUCATION IMPACT...

  13. 34 CFR 222.41 - How does a State educational agency compute local contribution rates based upon generally...

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 34 Education 1 2012-07-01 2012-07-01 false How does a State educational agency compute local contribution rates based upon generally comparable local educational agencies? 222.41 Section 222.41 Education Regulations of the Offices of the Department of Education OFFICE OF ELEMENTARY AND SECONDARY EDUCATION, DEPARTMENT OF EDUCATION IMPACT...

  14. Simulation of Transport and Reaction Using Random Walks: Reactions Without Concentrations and the Automatic Simulation of Drastically Different Thermodynamic--- Versus Diffusion---Limited Reaction Rates

    NASA Astrophysics Data System (ADS)

    Benson, D. A.; Meerschaert, M. M.

    2008-12-01

    We extend the advantages of Lagrangian random walk particle tracking (RWPT) methods that have long been used to simulate advection and dispersion in highly heterogeneous media. By formulating dissolution as a random, independent decay process, the classical continuum rate law is recovered. A novel formulation of the random precipitation process requires a consideration of the probability that two nearby particles will occupy the same differential volume in a given time period. This depends on local mixing (as by diffusion) and the total domain particle number density, which are fixed and therefore easy to calculate. The result is that the effective reaction rate follows two regimes. First, for high thermodynamic reaction probability and/or fast mixing, the classical continuum rate laws are reproduced. These are coded in the Gillespie method. This implies an exponentially fast approach to equilibrium. Second, for diffusion (mixing) limited reaction rates, equilibrium is approached much more slowly, following a power law that differs for 1-, 2-, or 3-d. At long enough times, the classical law of mass action for equilibrium reactions is reproduced, in an ensemble sense, for either rate regime. The same number of parameters for A+B ⇌ C are needed in a probabilistic versus continuum reaction simulation---one each for forward and backward probabilities that correspond to continuum thermodynamic rates. The random nature of the simulations allows for significant disequilibrium in any given region at any time that is independent of the numerical details such as time stepping or particle density. This is exemplified by nearby or intermingled groups of reactants and little or no product---a result that is often noted in the field that is difficult to reconcile with continuum methods or coarse-grained Eulerian models. Our results support both the recent experiments that show mixing-limited reactions and the results of perturbed advection-dispersion-reaction continuum models

  15. Simulation of biochemical reactions with time-dependent rates by the rejection-based algorithm

    SciTech Connect

    Thanh, Vo Hong; Priami, Corrado

    2015-08-07

    We address the problem of simulating biochemical reaction networks with time-dependent rates and propose a new algorithm based on our rejection-based stochastic simulation algorithm (RSSA) [Thanh et al., J. Chem. Phys. 141(13), 134116 (2014)]. The computation for selecting next reaction firings by our time-dependent RSSA (tRSSA) is computationally efficient. Furthermore, the generated trajectory is exact by exploiting the rejection-based mechanism. We benchmark tRSSA on different biological systems with varying forms of reaction rates to demonstrate its applicability and efficiency. We reveal that for nontrivial cases, the selection of reaction firings in existing algorithms introduces approximations because the integration of reaction rates is very computationally demanding and simplifying assumptions are introduced. The selection of the next reaction firing by our approach is easier while preserving the exactness.

  16. The effect of temperature fluctuations of reaction rate constants in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Chinitz, W.; Antaki, P. J.; Kassar, G. M.

    1981-01-01

    Current models of turbulent reacting flows frequently use Arrhenius reaction rate constants obtained from static or laminar flow theory and/or experiments, or from best fits of static, laminar, and turbulent data. By treating the reaction rate constant as a continuous random variable which is temperature-dependent, the present study assesses the effect of turbulent temperature fluctuations on the reaction rate constant. This model requires that a probability density function (PDF) describing the nature of the fluctuations be specified. Three PDFs are examined: the clipped Gaussian, the beta PDF, and the ramp model. All the models indicate that the reaction rate constant is greater in a turbulent flow field than in an equivalent laminar flow. In addition, an amplification ratio, which is the ratio of the turbulent rate constant to the laminar rate constant, is defined and its behavior as a function of the mean temperature fluctuations is described

  17. VizieR Online Data Catalog: Brussels nuclear reaction rate library (Aikawa+, 2005)

    NASA Astrophysics Data System (ADS)

    Aikawa, M.; Arnould, M.; Goriely, S.; Jorissen, A.; Takahashi, K.

    2005-07-01

    The present data is part of the Brussels nuclear reaction rate library (BRUSLIB) for astrophysics applications and concerns nuclear reaction rate predictions calculated within the statistical Hauser-Feshbach approximation and making use of global and coherent microscopic nuclear models for the quantities (nuclear masses, nuclear structure properties, nuclear level densities, gamma-ray strength functions, optical potentials) entering the rate calculations. (4 data files).

  18. Chiral polymerization in open systems from chiral-selective reaction rates.

    PubMed

    Gleiser, Marcelo; Nelson, Bradley J; Walker, Sara Imari

    2012-08-01

    We investigate the possibility that prebiotic homochirality can be achieved exclusively through chiral-selective reaction rate parameters without any other explicit mechanism for chiral bias. Specifically, we examine an open network of polymerization reactions, where the reaction rates can have chiral-selective values. The reactions are neither autocatalytic nor do they contain explicit enantiomeric cross-inhibition terms. We are thus investigating how rare a set of chiral-selective reaction rates needs to be in order to generate a reasonable amount of chiral bias. We quantify our results adopting a statistical approach: varying both the mean value and the rms dispersion of the relevant reaction rates, we show that moderate to high levels of chiral excess can be achieved with fairly small chiral bias, below 10%. Considering the various unknowns related to prebiotic chemical networks in early Earth and the dependence of reaction rates to environmental properties such as temperature and pressure variations, we argue that homochirality could have been achieved from moderate amounts of chiral selectivity in the reaction rates. PMID:22610131

  19. A simple expression for the apparent reaction rate of large wood char gasification with steam.

    PubMed

    Umeki, Kentaro; Roh, Seon-Ah; Min, Tai-Jin; Namioka, Tomoaki; Yoshikawa, Kunio

    2010-06-01

    A simple expression for the apparent reaction rate of large wood char gasification with steam is proposed. Large char samples were gasified under steam atmosphere using a thermo-balance reactor. The apparent reaction rate was expressed as the product of the intrinsic rate and the effective factor. The effective factor was modified to include the effect of change in char diameter and intrinsic reaction rate during the reaction. Assuming uniform conversion ratio throughout a particle, the simplified reaction scheme was divided into three stages. In the initial stage, the local conversion ratio increases without particle shrinkage. In the middle stage, the particle shrinks following the shrinking core model without change in the local conversion ratio. In the final stage, the local conversion ratio increases without particle shrinkage. The validity of the modified effective value was confirmed by comparison with experimental results. PMID:20144863

  20. Determination of the Temperature Dependence of the Rate Constants for HO2/Acetonylperoxy Reaction and Acetonylperoxy Self-Reaction

    NASA Astrophysics Data System (ADS)

    Darby, E. C.; Grieman, F. J.; Hui, A. O.; Okumura, M.; Sander, S. P.

    2014-12-01

    Reactions of hydroperoxy radical, HO2, with carbonyl containing RO2 can play an important role in the oxidation chemistry of the troposphere. Discovered radical product channels in addition to radical termination channels have resulted in increased study of these important reactions. In our continued study of HO2 reactions with acetonylperoxy and acetylperoxy radicals, we report here our first results on the kinetics of the acetonylperoxy system. Previous studies have resulted in conflicting results and no temperature dependence of the rate constants. Using the Infrared Kinetic Spectroscopy (IRKS) method in which a temperature-controlled slow-flow tube apparatus and laser flash photolysis of Cl2 are used to produce HO2 and CH3C(O)CH2O2 from methanol and acetone, respectively, we studied the chemical kinetics involved over the temperature range of 295 to 240 K. Rates of chemical reaction were determined by monitoring the HO2 concentration as a function of time by sensitive near-IR diode laser wavelength modulation spectroscopy while simultaneously measuring the disappearance of [CH3C(O)CH2O2] in the ultraviolet at 300 nm. The simultaneous fits resulted in the determination of the temperature dependence of the rate constants for the HO2/acetonylperoxy reaction and the acetonylperoxy self-reaction. At the lower temperatures, the reactions of HO2 and CH3C(O)CH2O2 with the adducts HO2•CH3OH and HO2•CH3C(O)CH3 formed in significant concentrations needed to be included in the fitting models.

  1. Viscosity Dependence of Some Protein and Enzyme Reaction Rates: Seventy-Five Years after Kramers.

    PubMed

    Sashi, Pulikallu; Bhuyan, Abani K

    2015-07-28

    Kramers rate theory is a milestone in chemical reaction research, but concerns regarding the basic understanding of condensed phase reaction rates of large molecules in viscous milieu persist. Experimental studies of Kramers theory rely on scaling reaction rates with inverse solvent viscosity, which is often equated with the bulk friction coefficient based on simple hydrodynamic relations. Apart from the difficulty of abstraction of the prefactor details from experimental data, it is not clear why the linearity of rate versus inverse viscosity, k ∝ η(-1), deviates widely for many reactions studied. In most cases, the deviation simulates a power law k ∝ η(-n), where the exponent n assumes fractional values. In rate-viscosity studies presented here, results for two reactions, unfolding of cytochrome c and cysteine protease activity of human ribosomal protein S4, show an exceedingly overdamped rate over a wide viscosity range, registering n values up to 2.4. Although the origin of this extraordinary reaction friction is not known at present, the results indicate that the viscosity exponent need not be bound by the 0-1 limit as generally suggested. For the third reaction studied here, thermal dissociation of CO from nativelike cytochrome c, the rate-viscosity behavior can be explained using Grote-Hynes theory of time-dependent friction in conjunction with correlated motions intrinsic to the protein. Analysis of the glycerol viscosity-dependent rate for the CO dissociation reaction in the presence of urea as the second variable shows that the protein stabilizing effect of subdenaturing amounts of urea is not affected by the bulk viscosity. It appears that a myriad of factors as diverse as parameter uncertainty due to the difficulty of knowing the exact reaction friction and both mode and consequences of protein-solvent interaction work in a complex manner to convey as though Kramers rate equation is not absolute. PMID:26135219

  2. Temperature trends for reaction rates, hydrogen generation, and partitioning of iron during experimental serpentinization of olivine

    NASA Astrophysics Data System (ADS)

    McCollom, Thomas M.; Klein, Frieder; Robbins, Mark; Moskowitz, Bruce; Berquó, Thelma S.; Jöns, Niels; Bach, Wolfgang; Templeton, Alexis

    2016-05-01

    A series of laboratory experiments were conducted to examine how partitioning of Fe among solid reaction products and rates of H2 generation vary as a function of temperature during serpentinization of olivine. Individual experiments were conducted at temperatures ranging from 200 to 320 °C, with reaction times spanning a few days to over a year. The extent of reaction ranged from <1% to ∼23%. Inferred rates for serpentinization of olivine during the experiments were 50-80 times slower than older studies had reported but are consistent with more recent results, indicating that serpentinization may proceed more slowly than previously thought. Reaction products were dominated by chrysotile, brucite, and magnetite, with minor amounts of magnesite, dolomite, and iowaite. The chrysotile contained only small amounts of Fe (XFe = 0.03-0.05, with ∼25% present as ferric Fe in octahedral sites), and displayed little variation in composition with reaction temperature. Conversely, the Fe contents of brucite (XFe = 0.01-0.09) increased steadily with decreasing reaction temperature. Analysis of the reaction products indicated that the stoichiometry of the serpentinization reactions varied with temperature, but remained constant with increasing reaction progress at a given temperature. The observed distribution of Fe among the reaction products does not appear to be entirely consistent with existing equilibrium models of Fe partitioning during serpentinization, suggesting improved models that include kinetic factors or multiple reaction steps need to be developed. Rates of H2 generation increased steeply from 200 to 300 °C, but dropped off at higher temperatures. This trend in H2 generation rates is attributable to a combination of the overall rate of serpentinization reactions and increased partitioning of Fe into brucite rather than magnetite at lower temperatures. The results suggest that millimolal concentration of H2 could be attained in moderately hot hydrothermal

  3. Estimation of the prevalence and rate of acute transfusion reactions occurring in Windhoek, Namibia

    PubMed Central

    Meza, Benjamin P.L.; Lohrke, Britta; Wilkinson, Robert; Pitman, John P.; Shiraishi, Ray W.; Bock, Naomi; Lowrance, David W.; Kuehnert, Matthew J.; Mataranyika, Mary; Basavaraju, Sridhar V.

    2014-01-01

    Background Acute transfusion reactions are probably common in sub-Saharan Africa, but transfusion reaction surveillance systems have not been widely established. In 2008, the Blood Transfusion Service of Namibia implemented a national acute transfusion reaction surveillance system, but substantial under-reporting was suspected. We estimated the actual prevalence and rate of acute transfusion reactions occurring in Windhoek, Namibia. Methods The percentage of transfusion events resulting in a reported acute transfusion reaction was calculated. Actual percentage and rates of acute transfusion reactions per 1,000 transfused units were estimated by reviewing patients’ records from six hospitals, which transfuse >99% of all blood in Windhoek. Patients’ records for 1,162 transfusion events occurring between 1st January – 31st December 2011 were randomly selected. Clinical and demographic information were abstracted and Centers for Disease Control and Prevention National Healthcare Safety Network criteria were applied to categorize acute transfusion reactions1. Results From January 1 – December 31, 2011, there were 3,697 transfusion events (involving 10,338 blood units) in the selected hospitals. Eight (0.2%) acute transfusion reactions were reported to the surveillance system. Of the 1,162 transfusion events selected, medical records for 785 transfusion events were analysed, and 28 acute transfusion reactions were detected, of which only one had also been reported to the surveillance system. An estimated 3.4% (95% confidence interval [CI]: 2.3–4.4) of transfusion events in Windhoek resulted in an acute transfusion reaction, with an estimated rate of 11.5 (95% CI: 7.6–14.5) acute transfusion reactions per 1,000 transfused units. Conclusion The estimated actual rate of acute transfusion reactions is higher than the rate reported to the national haemovigilance system. Improved surveillance and interventions to reduce transfusion-related morbidity and mortality

  4. A mesoscopic reaction rate model for shock initiation of multi-component PBX explosives.

    PubMed

    Liu, Y R; Duan, Z P; Zhang, Z Y; Ou, Z C; Huang, F L

    2016-11-01

    The primary goal of this research is to develop a three-term mesoscopic reaction rate model that consists of a hot-spot ignition, a low-pressure slow burning and a high-pressure fast reaction terms for shock initiation of multi-component Plastic Bonded Explosives (PBX). Thereinto, based on the DZK hot-spot model for a single-component PBX explosive, the hot-spot ignition term as well as its reaction rate is obtained through a "mixing rule" of the explosive components; new expressions for both the low-pressure slow burning term and the high-pressure fast reaction term are also obtained by establishing the relationships between the reaction rate of the multi-component PBX explosive and that of its explosive components, based on the low-pressure slow burning term and the high-pressure fast reaction term of a mesoscopic reaction rate model. Furthermore, for verification, the new reaction rate model is incorporated into the DYNA2D code to simulate numerically the shock initiation process of the PBXC03 and the PBXC10 multi-component PBX explosives, and the numerical results of the pressure histories at different Lagrange locations in explosive are found to be in good agreements with previous experimental data. PMID:27258213

  5. The sonochemical degradation of azobenzene and related azo dyes: Rate enhancements via Fenton's reactions

    SciTech Connect

    Joseph, J.M.; Destaillats, H.; Hung, H.M.; Hoffmann, M.R.

    2000-01-20

    The sonochemical degradation of aqueous solutions of azobenzene and related azo dyes (methyl orange, o-methyl red, and p-methyl red) was performed at 500 kHz and 50 W, under air, O{sub 2}, or Ar saturation at 288 K. Reaction products and intermediates were identified by HPLC-ES-MS. Total organic carbon (TOC) was also determined as a function of reaction time. The authors propose a reaction mechanism based on the observed species and the extent and rate of TOC depletion. The effects of the dye structures and of the background gas on the sonochemical bleaching rates were also investigated. The reaction rates for o-methyl red were approximately 30--40% faster than those for the other compounds. Saturating with Ar instead of air or O{sub 2} increased the pseudo first-order rate constants for the degradation by 10%. The acceleration of the sonochemical bleaching and the mineralization process upon addition of Fe(II) was also investigated in Ar-saturated methyl orange solutions. A 3-fold increase in the reaction rate was observed at optimal Fe(II) concentrations. This kinetic effect is quantitatively accounted for by a simple kinetic model based on the reaction of Fe(II) with sonochemically produced H{sub 2}O{sub 2} (Fenton's reaction). This latter effect illustrates a simple way of achieving a substantial improvement in the efficiency of sonochemical degradation reactions.

  6. Evidence of reaction rate influencing cubic and hexagonal phase formation process in CdS nanocrystals

    NASA Astrophysics Data System (ADS)

    Deka, Kuldeep; Kalita, M. P. C.

    2016-05-01

    CdS nanocrystals are synthesized by co-precipitation method using 2-mercaptoethanol (ME) as capping agent. Cubic, hexagonal and their mixture are obtained by varying the ME concentration. Lower (higher) ME concentration results in cubic (hexagonal) phase. The crystallite sizes are in the range 3-7 nm. Increase in ME concentration lead to lower reaction rate between Cd2+ and S2- of the precursors, and slower reaction rate is found to favor hexagonal phase formation over the cubic one in CdS nanocrystals. Role of reaction rate in the phase formation process provides a way to synthesize CdS nanocrystals in desired crystal phase.

  7. Thermonuclear reaction rate of 18Ne(α ,p ) 21Na from Monte Carlo calculations

    NASA Astrophysics Data System (ADS)

    Mohr, P.; Longland, R.; Iliadis, C.

    2014-12-01

    The 18Ne(α ,p ) 21Na reaction impacts the break-out from the hot CNO cycles to the r p process in type-I x-ray bursts. We present a revised thermonuclear reaction rate, which is based on the latest experimental data. The new rate is derived from Monte Carlo calculations, taking into account the uncertainties of all nuclear physics input quantities. In addition, we present the reaction rate uncertainty and probability density versus temperature. Our results are also consistent with estimates obtained using different indirect approaches.

  8. Sensitivity study of explosive nucleosynthesis in type Ia supernovae: Modification of individual thermonuclear reaction rates

    NASA Astrophysics Data System (ADS)

    Bravo, Eduardo; Martínez-Pinedo, Gabriel

    2012-05-01

    Background: Type Ia supernovae contribute significantly to the nucleosynthesis of many Fe-group and intermediate-mass elements. However, the robustness of nucleosynthesis obtained via models of this class of explosions has not been studied in depth until now.Purpose: We explore the sensitivity of the nucleosynthesis resulting from thermonuclear explosions of massive white dwarfs with respect to uncertainties in nuclear reaction rates. We put particular emphasis on indentifying the individual reactions rates that most strongly affect the isotopic products of these supernovae.Method: We have adopted a standard one-dimensional delayed detonation model of the explosion of a Chandrasekhar-mass white dwarf and have postprocessed the thermodynamic trajectories of every mass shell with a nucleosynthetic code to obtain the chemical composition of the ejected matter. We have considered increases (decreases) by a factor of 10 on the rates of 1196 nuclear reactions (simultaneously with their inverse reactions), repeating the nucleosynthesis calculations after modification of each reaction rate pair. We have computed as well hydrodynamic models for different rates of the fusion reactions of 12C and of 16O. From the calculations we have selected the reactions that have the largest impact on the supernova yields, and we have computed again the nucleosynthesis using two or three alternative prescriptions for their rates, taken from the JINA REACLIB database. For the three reactions with the largest sensitivity we have analyzed as well the temperature ranges where a modification of their rates has the strongest effect on nucleosynthesis.Results: The nucleosynthesis resulting from the type Ia supernova models is quite robust with respect to variations of nuclear reaction rates, with the exception of the reaction of fusion of two 12C nuclei. The energy of the explosion changes by less than ˜4% when the rates of the reactions 12C+12C or 16O+16O are multiplied by a factor of ×10 or

  9. ACTIVE: a program to calculate and plot reaction rates from ANISN calculated fluxes

    SciTech Connect

    Judd, J.L.

    1981-12-01

    The ACTIVE code calculates spatial heating rates, tritium production rates, neutron reaction rates, and energy spectra from particle fluxes calculated by ANISN. ACTIVE has a variety of input options including the capability to plot all calculated spatial distributions. The code was primarily designed for use with fusion first wall/blanket systems, but could be applied to any one-dimensional problem.

  10. Rate constants measured for hydrated electron reactions with peptides and proteins

    NASA Technical Reports Server (NTRS)

    Braams, R.

    1968-01-01

    Effects of ionizing radiation on the amino acids of proteins and the reactivity of the protonated amino group depends upon the pK subscript a of the group. Estimates of the rate constants for reactions involving the amino acid side chains are presented. These rate constants gave an approximate rate constant for three different protein molecules.

  11. A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reaction flows

    NASA Technical Reports Server (NTRS)

    Magnotti, F.; Diskin, G.; Matulaitis, J.; Chinitz, W.

    1984-01-01

    The use of silane (SiH4) as an effective ignitor and flame stabilizing pilot fuel is well documented. A reliable chemical kinetic mechanism for prediction of its behavior at the conditions encountered in the combustor of a SCRAMJET engine was calculated. The effects of hydrogen addition on hydrocarbon ignition and flame stabilization as a means for reduction of lengthy ignition delays and reaction times were studied. The ranges of applicability of chemical kinetic models of hydrogen-air combustors were also investigated. The CHARNAL computer code was applied to the turbulent reaction rate modeling.

  12. Comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reaction flows

    SciTech Connect

    Magnotti, F.; Diskin, G.; Matulaitis, J.; Chinitz, W.

    1984-01-01

    The use of silane (SiH4) as an effective ignitor and flame stabilizing pilot fuel is well documented. A reliable chemical kinetic mechanism for prediction of its behavior at the conditions encountered in the combustor of a SCRAMJET engine was calculated. The effects of hydrogen addition on hydrocarbon ignition and flame stabilization as a means for reduction of lengthy ignition delays and reaction times were studied. The ranges of applicability of chemical kinetic models of hydrogen-air combustors were also investigated. The CHARNAL computer code was applied to the turbulent reaction rate modeling.

  13. Astrophysical S-Factors and Reaction Rates of Threshold (p, n)-Reactions on {sup 99-102}Ru

    SciTech Connect

    Skakun, Ye.; Rauscher, T.

    2010-08-12

    Astrophysical S-factors of (p, n) reactions on {sup 99}Ru, {sup 100}Ru, {sup 101}Ru, and {sup 102}Ru were derived from the sum of experimental isomeric and ground states cross sections measured in the incident proton energy range of 5-9 MeV. They were compared with Hauser-Feshbach statistical model predictions of the NON-SMOKER code. Good agreement was found in the majority of cases. Reaction rates were derived up to 8.7 GK stellar temperature by combining experiment and theory.

  14. Nonequilibrium Contribution to the Rate of Reaction. III. Isothermal Multicomponent Systems

    DOE R&D Accomplishments Database

    Shizgal, B.; Karplus, M.

    1970-10-01

    The nonequilibrium contribution to the reaction rate of an isothermal multicomponent system is obtained by solution of the appropriate Chapman-Enskog equation; the system is composed of reactive species in contact with a heat bath of inert atoms M.

  15. Determining astrophysical three-body radiative capture reaction rates from inclusive Coulomb break-up measurements

    NASA Astrophysics Data System (ADS)

    Casal, J.; Rodríguez-Gallardo, M.; Arias, J. M.; Gómez-Camacho, J.

    2016-04-01

    A relationship between the Coulomb inclusive break-up probability and the radiative capture reaction rate for weakly bound three-body systems is established. This direct link provides a robust procedure to estimate the reaction rate for nuclei of astrophysical interest by measuring inclusive break-up processes at different energies and angles. This might be an advantageous alternative to the determination of reaction rates from the measurement of B (E 1 ) distributions through exclusive Coulomb break-up experiments. In addition, it provides a reference to assess the validity of different theoretical approaches that have been used to calculate reaction rates. The procedure is applied to 11Li (9Li+n +n ) and 6He (4He+n +n ) three-body systems for which some data exist.

  16. Anticipatory Heart Rate Deceleration and Reaction Time in Children with and without Referral for Learning Disability

    ERIC Educational Resources Information Center

    Sroufe, L. Alan; And Others

    1973-01-01

    The finding of major significance in this study concerns the effect of stimulant drug medication on the relationship between heart rate deceleration and reaction time with the clinic children. (Authors)

  17. Reaction mechanisms and rate constants of waste degradation in landfill bioreactor systems with enzymatic-enhancement.

    PubMed

    Jayasinghe, P A; Hettiaratchi, J P A; Mehrotra, A K; Kumar, S

    2014-06-01

    Augmenting leachate before recirculation with peroxidase enzymes is a novel method to increase the available carbon, and therefore the food supply to microorganisms at the declining phase of the anaerobic landfill bioreactor operation. In order to optimize the enzyme-catalyzed leachate recirculation process, it is necessary to identify the reaction mechanisms and determine rate constants. This paper presents a kinetic model developed to ascertain the reaction mechanisms and determine the rate constants for enzyme catalyzed anaerobic waste degradation. The maximum rate of reaction (Vmax) for MnP enzyme-catalyzed reactors was 0.076 g(TOC)/g(DS).day. The catalytic turnover number (k(cat)) of the MnP enzyme-catalyzed was 506.7 per day while the rate constant (k) of the un-catalyzed reaction was 0.012 per day. PMID:24759644

  18. Method and apparatus for obtaining enhanced production rate of thermal chemical reactions

    DOEpatents

    Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Wegeng, Robert S [Richland, WA; Gao, Yufei [Kennewick, WA

    2003-04-01

    The present invention is a method and apparatus (vessel) for providing a heat transfer rate from a reaction chamber through a wall to a heat transfer chamber substantially matching a local heat transfer rate of a catalytic thermal chemical reaction. The key to the invention is a thermal distance defined on a cross sectional plane through the vessel inclusive of a heat transfer chamber, reaction chamber and a wall between the chambers. The cross sectional plane is perpendicular to a bulk flow direction of the reactant stream, and the thermal distance is a distance between a coolest position and a hottest position on the cross sectional plane. The thermal distance is of a length wherein the heat transfer rate from the reaction chamber to the heat transfer chamber substantially matches the local heat transfer rate.

  19. Controlling the rates of biochemical reactions and signaling networks by shape and volume changes.

    PubMed

    Lizana, L; Bauer, B; Orwar, O

    2008-03-18

    In biological systems, chemical activity takes place in micrometer- and nanometer-sized compartments that constantly change in shape and volume. These ever-changing cellular compartments embed chemical reactions, and we demonstrate that the rates of such incorporated reactions are directly affected by the ongoing shape reconfigurations. First, we show that the rate of product formation in an enzymatic reaction can be regulated by simple volume contraction-dilation transitions. The results suggest that mitochondria may regulate the dynamics of interior reaction pathways (e.g., the Krebs cycle) by volume changes. We then show the effect of shape changes on reactions occurring in more complex and structured systems by using biomimetic networks composed of micrometer-sized compartments joined together by nanotubes. Chemical activity was measured by implementing an enzymatic reaction-diffusion system. During ongoing reactions, the network connectivity is changed suddenly (similar to the dynamic tube formations found inside Golgi stacks, for example), and the effect on the reaction is registered. We show that spatiotemporal properties of the reaction-diffusion system are extremely sensitive to sudden changes in network topology and that chemical reactions can be initiated, or boosted, in certain nodes as a function of connectivity. PMID:18337513

  20. A Unified Equation for the Reaction Rate in Dense Matter Stars

    SciTech Connect

    Gasques, L. R.; Wiescher, M.; Yakovlev, D. G.

    2007-10-26

    We analyze thermonuclear and pycnonuclear reaction rates in multi-component dense stellar plasma. First we describe calculations of the astrophysical S-factor at low energies using the Sao Paulo potential on the basis of the barrier penetration model. Then we present a simple phenomenological expression for a reaction rate. The expression contains several fit parameters which we adjust to reproduce the best microscopic calculations available in the literature.

  1. Shell and explosive hydrogen burning. Nuclear reaction rates for hydrogen burning in RGB, AGB and Novae

    NASA Astrophysics Data System (ADS)

    Boeltzig, A.; Bruno, C. G.; Cavanna, F.; Cristallo, S.; Davinson, T.; Depalo, R.; deBoer, R. J.; Di Leva, A.; Ferraro, F.; Imbriani, G.; Marigo, P.; Terrasi, F.; Wiescher, M.

    2016-04-01

    The nucleosynthesis of light elements, from helium up to silicon, mainly occurs in Red Giant and Asymptotic Giant Branch stars and Novae. The relative abundances of the synthesized nuclides critically depend on the rates of the nuclear processes involved, often through non-trivial reaction chains, combined with complex mixing mechanisms. In this paper, we summarize the contributions made by LUNA experiments in furthering our understanding of nuclear reaction rates necessary for modeling nucleosynthesis in AGB stars and Novae explosions.

  2. Up-Scaling Geochemical Reaction Rates for Carbon Dioxide (CO2) in Deep Saline Aquifers

    SciTech Connect

    Lindquist, W Brent

    2009-03-03

    The overall goal of the project was to bridge the gap between our knowledge of small-scale geochemical reaction rates and reaction rates meaningful for modeling transport at core scales. The working hypothesis was that reaction rates, determined from laboratory measurements based upon reactions typically conducted in well mixed batch reactors using pulverized reactive media may be significantly changed in in situ porous media flow due to rock microstructure heterogeneity. Specifically we hypothesized that, generally, reactive mineral surfaces are not uniformly accessible to reactive fluids due to the random deposition of mineral grains and to the variation in flow rates within a pore network. Expected bulk reaction rates would therefore have to be correctly up-scaled to reflect such heterogeneity. The specific objective was to develop a computational tool that integrates existing measurement capabilities with pore-scale network models of fluid flow and reactive transport. The existing measurement capabilities to be integrated consisted of (a) pore space morphology, (b) rock mineralogy, and (c) geochemical reaction rates. The objective was accomplished by: (1) characterizing sedimentary sandstone rock morphology using X-ray computed microtomography, (2) mapping rock mineralogy using back-scattered electron microscopy (BSE), X-ray dispersive spectroscopy (EDX) and CMT, (3) characterizing pore-accessible reactive mineral surface area, and (4) creating network models to model acidic CO{sub 2} saturated brine injection into the sandstone rock samples.

  3. Elementary/Secondary Education Data Redesign Project: Letters, Comments, Reactions from Organizations and Agencies.

    ERIC Educational Resources Information Center

    1985

    The following organizations and agencies sent their suggestions and comments on the National Center for Education Statistics (NCES) Elementary/Secondary Education Data Redesign Project: American Association for Counseling and Development, American Association of Colleges for Teacher Education, American Library Association, Indiana University,…

  4. Thick target measurement of the 40Ca(alpha,gamma)44Ti reaction rate

    SciTech Connect

    Sheets, S A; Burke, J T; Scielzo, N D; Phair, L; Bleuel, D; Norman, E B; Grant, P G; Hurst, A M; Tumey, S; Brown, T A; Stoyer, M

    2009-02-06

    The thick-target yield for the {sup 40}Ca({alpha},{gamma}){sup 44}Ti reaction has been measured for E{sub beam} = 4.13, 4.54, and 5.36 MeV using both an activation measurement and online {gamma}-ray spectroscopy. The results of the two measurements agree. From the measured yield a reaction rate is deduced that is smaller than statistical model calculations. This implies a smaller {sup 44}Ti production in supernova compared to recently measured {sup 40}Ca({alpha},{gamma}){sup 44}Ti reaction rates.

  5. Rate coefficients from quantum and quasi-classical cumulative reaction probabilities for the S(1D) + H2 reaction

    NASA Astrophysics Data System (ADS)

    Jambrina, P. G.; Lara, Manuel; Menéndez, M.; Launay, J.-M.; Aoiz, F. J.

    2012-10-01

    Cumulative reaction probabilities (CRPs) at various total angular momenta have been calculated for the barrierless reaction S(1D) + H2 → SH + H at total energies up to 1.2 eV using three different theoretical approaches: time-independent quantum mechanics (QM), quasiclassical trajectories (QCT), and statistical quasiclassical trajectories (SQCT). The calculations have been carried out on the widely used potential energy surface (PES) by Ho et al. [J. Chem. Phys. 116, 4124 (2002), 10.1063/1.1431280] as well as on the recent PES developed by Song et al. [J. Phys. Chem. A 113, 9213 (2009), 10.1021/jp903790h]. The results show that the differences between these two PES are relatively minor and mostly related to the different topologies of the well. In addition, the agreement between the three theoretical methodologies is good, even for the highest total angular momenta and energies. In particular, the good accordance between the CRPs obtained with dynamical methods (QM and QCT) and the statistical model (SQCT) indicates that the reaction can be considered statistical in the whole range of energies in contrast with the findings for other prototypical barrierless reactions. In addition, total CRPs and rate coefficients in the range of 20-1000 K have been calculated using the QCT and SQCT methods and have been found somewhat smaller than the experimental total removal rates of S(1D).

  6. High-precision (p,t) reaction to determine {sup 25}Al(p,{gamma}){sup 26}Si reaction rates

    SciTech Connect

    Matic, A.; Berg, A. M. van den; Harakeh, M. N.; Woertche, H. J.; Berg, G. P. A.; Couder, M.; Goerres, J.; LeBlanc, P.; O'Brien, S.; Wiescher, M.; Fujita, K.; Hatanaka, K.; Sakemi, Y.; Shimizu, Y.; Tameshige, Y.; Tamii, A.; Yosoi, M.; Adachi, T.; Fujita, Y.; Shimbara, Y.

    2010-08-15

    Since the identification of ongoing {sup 26}Al production in the universe, the reaction sequence {sup 24}Mg(p,{gamma}){sup 25}Al({beta}{sup +{nu}}){sup 25}Mg(p,{gamma}){sup 26}Al has been studied intensively. At temperatures where the radiative capture on {sup 25}Al (t{sub 1/2}=7.2 s) becomes faster than the {beta}{sup +} decay, the production of {sup 26}Al can be reduced due to the depletion of {sup 25}Al. To determine the resonances relevant for the {sup 25}Al(p,{gamma}){sup 26}Si bypass reaction, we measured the {sup 28}Si(p,t){sup 26}Si reaction with high-energy precision using the Grand Raiden spectrometer at the Research Center for Nuclear Physics, Osaka. Several new energy levels were found above the p threshold and for known states excitation energies were determined with smaller uncertainties. The calculated stellar rates of the bypass reaction agree well with previous results, suggesting that these rates are well established.

  7. Rate constants of reactions of bromine with phenols in aqueous solution.

    PubMed

    Gallard, Hervé; Pellizzari, Fabien; Croué, Jean Philippe; Legube, B

    2003-07-01

    The kinetics of bromination of six ortho- and para-substituted phenols was investigated between pH 5 and pH 12 in aqueous solution. Kinetics was followed with a continuous-flow reactor previously validated by studying the fast reaction between chlorine and ammonia. The overall reaction rate between bromine and phenols is controlled by the reaction of HOBr with the phenoxide ion between pH 6 and pH 10. The reaction of HOBr with the undissociated phenols and the reaction of BrO(-) with the phenoxide ions become only significant for pH<6 and pH>10, respectively. The second-order rate constants for the reaction of HOBr with phenoxide ions vary between 1.4(+/-0.1)x10(3) and 2.1(+/-0.5)x10(8)M(-1)s(-1) for 2,4,6-trichlorophenol and 4-methylphenol, respectively. Hammett-type correlation was obtained for the reaction of HOBr with the phenoxide ions (log(k)=8.0-3.33 x Sigmasigma) and was compared with Hammett-type correlations of HOCl and HOI. The reaction rate of bromine with phenol-like organic compounds was estimated to be about 10(3)-fold higher than with chlorine and 10(3)-fold lower than with ozone in drinking water treatment conditions. PMID:12767291

  8. Recent Augmentations of the Functionality of the Thermonuclear Reaction Rate Calculator (TReRaC)

    NASA Astrophysics Data System (ADS)

    Thomsen, Kyle; Smith, Michael

    2011-10-01

    The chemical variety of our universe can be explained by stellar nucleosynthesis. Many thermonuclear reactions are studied by reproducing them in accelerator experiments and determining their rates. Using the codes available through the Computational Infrastructure for Nuclear Astrophysics (CINA), researchers can process the results of these experiments. One such program is the Thermonuclear Reaction Rate Calculator (TReRaC), which uses various experimental inputs including resonant energies, strengths, channel widths, and information on non-resonant contributions to calculate reaction rates. Presently, TReRaC is capable of quickly generating accurate rates which closely match those given in a number of publications. This adds to CINA capabilities by enabling a wider variety of nuclear information to generate rates. The next step in TReRaC's evolution is integration into the existing CINA complex so that it can be used by researchers worldwide.

  9. Pore-Scale Process Coupling and Effective Surface Reaction Rates in Heterogeneous Subsurface Materials

    SciTech Connect

    Liu, Chongxuan; Liu, Yuanyuan; Kerisit, Sebastien N.; Zachara, John M.

    2015-09-01

    This manuscript provides a review of pore-scale researches in literature including experimental and numerical approaches, and scale-dependent behavior of geochemical and biogeochemical reaction rates in heterogeneous porous media. A mathematical equation that can be used to predict the scale-dependent behavior of geochemical reaction rates in heterogeneous porous media has been derived. The derived effective rate expression explicitly links the effective reaction rate constant to the intrinsic rate constant, and to the pore-scale variations in reactant concentrations in porous media. Molecular simulations to calculate the intrinsic rate constants were provided. A few examples of pore-scale simulations were used to demonstrate the application of the equation to calculate effective rate constants in heterogeneous materials. The results indicate that the deviation of effective rate constant from the intrinsic rate in heterogeneous porous media is caused by the pore-scale distributions of reactants and their correlation, which are affected by the pore-scale coupling of reactions and transport.

  10. Reaction Rates of Semi-Volatile Organic Compounds with the Hydroxyl Radical.

    NASA Astrophysics Data System (ADS)

    Anderson, Philip Neal

    1995-01-01

    The atmosphere is the primary route of global dispersion of many semi-volatile organic compounds (SOCs), including polychlorinated biphenyls, dibenzo-p-dioxins, and dibenzofurans. While the long-distance atmospheric transport of these compounds has been well established, the importance of chemical reactions that may occur while SOCs are in the atmosphere is largely unknown. For most semi-volatile organic compounds in the vapor phase, the most significant atmospheric reaction is likely to be attack by the hydroxyl radical (OH). The importance of this removal pathway, relative to other loss mechanisms from the atmosphere, is dependent on the reaction rate of a given semi-volatile organic compound with OH. A system was constructed and validated to measure the reaction rate of OH with semi-volatile organic compounds in the laboratory. The system featured a small, heated, quartz chamber with on-line detection of reactants by mass spectrometry. OH radicals were generated by the 254 nm photolysis of O _3 in the presence of H_2 O. The temperature dependent reaction rates of OH with 15 polychlorinated biphenyl congeners (PCBs), containing 0-5 chlorines, were measured. Calculated atmospheric lifetimes of PCBs due to OH-initiated reactions ranged from 2 days for biphenyl to 34 days for a pentachlorobiphenyl. Using an average of reaction rates extrapolated to atmospheric temperatures, the lifetime in the atmosphere for total PCBs due to OH reaction was calculated. A model for the vertical concentration gradient of PCBs in the troposphere was developed and used to calculate the flux (16 mug m^{-2} yr^{-1}) and total global flow (8,300 tonnes yr^{-1}) of PCBs removed from the atmosphere by OH-PCB reaction. This pathway is very large in comparison to any other known permanent PCB loss processes from the environment, such as deep ocean sediment burial (240 tonnes yr^ {-1}). The reaction of PCBs with OH may be the dominant removal mechanism of PCBs from the natural environment.

  11. STARLIB: A Next-generation Reaction-rate Library for Nuclear Astrophysics

    NASA Astrophysics Data System (ADS)

    Sallaska, A. L.; Iliadis, C.; Champange, A. E.; Goriely, S.; Starrfield, S.; Timmes, F. X.

    2013-07-01

    STARLIB is a next-generation, all-purpose nuclear reaction-rate library. For the first time, this library provides the rate probability density at all temperature grid points for convenient implementation in models of stellar phenomena. The recommended rate and its associated uncertainties are also included. Currently, uncertainties are absent from all other rate libraries, and, although estimates have been attempted in previous evaluations and compilations, these are generally not based on rigorous statistical definitions. A common standard for deriving uncertainties is clearly warranted. STARLIB represents a first step in addressing this deficiency by providing a tabular, up-to-date database that supplies not only the rate and its uncertainty but also its distribution. Because a majority of rates are lognormally distributed, this allows the construction of rate probability densities from the columns of STARLIB. This structure is based on a recently suggested Monte Carlo method to calculate reaction rates, where uncertainties are rigorously defined. In STARLIB, experimental rates are supplemented with: (1) theoretical TALYS rates for reactions for which no experimental input is available, and (2) laboratory and theoretical weak rates. STARLIB includes all types of reactions of astrophysical interest to Z = 83, such as (p, γ), (p, α), (α, n), and corresponding reverse rates. Strong rates account for thermal target excitations. Here, we summarize our Monte Carlo formalism, introduce the library, compare methods of correcting rates for stellar environments, and discuss how to implement our library in Monte Carlo nucleosynthesis studies. We also present a method for accessing STARLIB on the Internet and outline updated Monte Carlo-based rates.

  12. Reaction rate and composition dependence of the stability of thermonuclear burning on accreting neutron stars

    SciTech Connect

    Keek, L.; Cyburt, R. H.; Heger, A.

    2014-06-01

    The stability of thermonuclear burning of hydrogen and helium accreted onto neutron stars is strongly dependent on the mass accretion rate. The burning behavior is observed to change from Type I X-ray bursts to stable burning, with oscillatory burning occurring at the transition. Simulations predict the transition at a 10 times higher mass accretion rate than observed. Using numerical models we investigate how the transition depends on the hydrogen, helium, and CNO mass fractions of the accreted material, as well as on the nuclear reaction rates of 3α and the hot-CNO breakout reactions {sup 15}O(α, γ){sup 19}Ne and {sup 18}Ne(α, p){sup 21}Na. For a lower hydrogen content the transition is at higher accretion rates. Furthermore, most experimentally allowed reaction rate variations change the transition accretion rate by at most 10%. A factor 10 decrease of the {sup 15}O(α, γ){sup 19}Ne rate, however, produces an increase of the transition accretion rate of 35%. None of our models reproduce the transition at the observed rate, and depending on the true {sup 15}O(α, γ){sup 19}Ne reaction rate, the actual discrepancy may be substantially larger. We find that the width of the interval of accretion rates with marginally stable burning depends strongly on both composition and reaction rates. Furthermore, close to the stability transition, our models predict that X-ray bursts have extended tails where freshly accreted fuel prolongs nuclear burning.

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    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.

  14. Estimation of the reaction rate constant of HOCl by SMILES observation

    NASA Astrophysics Data System (ADS)

    Kuribayashi, Kouta; Kasai, Yasuko; Sato, Tomohiro; Sagawa, Hideo

    2012-07-01

    Hypochlorous acid, HOCl plays an important role to link the odd ClOx and the odd HOx in the atmospheric chemistry with the reaction: {ClO} + {HO_{2}} \\longrightarrow {HOCl} + {O_{2}} Quantitative understanding of the rate constant of the reaction (1.1) is essential for understanding the ozone loss in the mid-latitude region because of a view point of its rate controlling role in the ozone depletion chemistry. Reassessment of the reaction rate constant was pointed out from MIPAS/Envisat observations (von Clarmann et al., 2011) and balloon-borne observations (Kovalenko et al., 2007). Several laboratory studies had been reported, although the reaction rate constants have large uncertainties, as k{_{HOCl}} = (1.75 ± 0.52) × 10^{-12} exp[(368 ± 78)/T] (Hickson et al., 2007), and large discrepancies (Hickson et al., 2007;Stimpfle et al., 1979). Moreover, theoretical ab initio studies pointed out the pressure dependence of the reaction (1.1) (Xu et al., 2003). A new high-sensitive remote sensing technology named Superconducting SubMillimeter-wave Limb-Emission Sounder (SMILES) on the International Space Station (ISS) had observed diurnal variations of HOCl in the upper stratosphere/lower mesosphere (US/LM) region for the first time. ClO and HO_{2} were slso observed simultaneously with HOCl. SMILES performed the observations between 12^{{th}} October 2009 and 21^{{th}} April 2010. The latitude coverage of SMILES observation is normally 38°S-65°N. The altitude region of HOCl observation is about 28-70 km. We estimated the time period in which the reaction (1.1) becomes dominant in the ClO_{y} diurnal chemistry in US/LM. The reaction rate constant was directly estimated by decay of [ClO] and [HO_{2}] amounts in that period. The derived reaction rate constant represented well the increase of [HOCl] amount.

  15. [Incidence rate of adverse reaction/event by Qingkailing injection: a Meta-analysis of single rate].

    PubMed

    Ai, Chun-ling; Xie, Yan-ming; Li, Ming-quan; Wang, Lian-xin; Liao, Xing

    2015-12-01

    To systematically review the incidence rate of adverse drug reaction/event by Qingkailing injection. Such databases as the PubMed, EMbase, the Cochrane library, CNKI, VIP WanFang data and CBM were searched by computer from foundation to July 30, 2015. Two reviewers independently screened literature according to the inclusion and exclusion criteria, extracted data and cross check data. Then, Meta-analysis was performed by using the R 3.2.0 software, subgroup sensitivity analysis was performed based on age, mode of medicine, observation time and research quality. Sixty-three studies involving 9,793 patients with Qingkailing injection were included, 367 cases of adverse reactions/events were reported in total. The incidence rate of adverse reaction in skin and mucosa group was 2% [95% CI (0.02; 0.03)]; the digestive system adverse reaction was 6% [95% CI(0.05; 0.07); the injection site adverse reaction was 4% [95% CI (0.02; 0.07)]. In the digestive system as the main types of adverse reactions/events, incidence of children and adults were 4.6% [0.021 1; 0.097 7] and 6.9% [0.053 5; 0.089 8], respectively. Adverse reactions to skin and mucous membrane damage as the main performance/event type, the observation time > 7 days and ≤ 7 days incidence of 3% [0.012 9; 0.068 3] and 1.9% [0.007 8; 0.046 1], respectively. Subgroup analysis showed that different types of adverse reactions, combination in the incidence of adverse reactions/events were higher than that of single drug, the difference was statistically significant (P < 0.05). This study suggested the influence factors of adverse reactions occur, and clinical rational drug use, such as combination, age and other fators, and the influence factors vary in different populations. Therefore, clinical doctors for children and the elderly use special care was required for a clear and open spirit injection, the implementation of individualized medication. PMID:27245021

  16. REACLIB: A Reaction Rate Library for the Era of Collaborative Science

    NASA Astrophysics Data System (ADS)

    Meisel, Zachary

    2008-10-01

    Thermonuclear reaction rates and weak decay rates are of great importance to modern nuclear astrophysics. They are critical in the study of many topics such as Big Bang Nucleosynthesis, X-ray bursts, Supernovae, and S-process element formation, among others. The Joint Institute for Nuclear Astrophysics (JINA) has been created to increase connectivity amongst nuclear astrophysicists in our modern age of highly collaborative science. Within JINA there has been an effort to create a frequently updated and readily accessible database of thermonuclear reactions and weak decay rates. This database is the REACLIB library, which can be accessed at the web address: http://www.nscl.msu.edu/˜nero/db/. Here I will discuss the JINA REACLIB Project, including a new procedure to fit reaction rates as a function of temperature that takes full advantage of physicality. With these updated reaction rates, astrophysical modelers will no longer have to worry about the adverse effects of using obsolete reaction rate libraries lacking physical behavior.

  17. EFFECTS OF RING STRAIN ON GAS-PHASE RATE CONSTANTS. 2. OH RADICAL REACTIONS WITH CYCLOALKENES

    EPA Science Inventory

    Relative rate constants for the gas phase reactions of OH radicals with a series of cycloalkenes have been determined at 298 + or - 2 K, using methyl nitrite photolysis in air as a source of OH radicals. The data show that the rate constants for the nonconjugated cycloalkenes stu...

  18. Method and apparatus for obtaining enhanced production rate of thermal chemical reactions

    DOEpatents

    Tonkovich, Anna Lee Y.; Wang, Yong; Wegeng, Robert S.; Gao, Yufei

    2003-09-09

    Reactors and processes are disclosed that can utilize high heat fluxes to obtain fast, steady-state reaction rates. Porous catalysts used in conjunction with microchannel reactors to obtain high rates of heat transfer are also disclosed. Reactors and processes that utilize short contact times, high heat flux and low pressure drop are described. Improved methods of steam reforming are also provided.

  19. Method and apparatus for obtaining enhanced production rate of thermal chemical reactions

    DOEpatents

    Tonkovich, Anna Lee Y.; Wang, Yong; Wegeng, Robert S.; Gao, Yufei

    2006-05-16

    Reactors and processes are disclosed that can utilize high heat fluxes to obtain fast, steady-state reaction rates. Porous catalysts used in conjunction with microchannel reactors to obtain high rates of heat transfer are also disclosed. Reactors and processes that utilize short contact times, high heat flux and low pressure drop are described. Improved methods of steam reforming are also provided.

  20. Field measurement of slow metamorphic reaction rates at temperatures of 500 degrees to 600 degrees C

    PubMed

    Baxter; DePaolo

    2000-05-26

    High-temperature metamorphic reaction rates were measured using strontium isotopic ratios of garnet and whole rock from a field site near Simplon Pass, Switzerland. For metamorphic conditions of cooling from 612 degrees +/- 17 degrees C to 505 degrees +/- 15 degrees C at pressures up to 9.1 kilobars, the inferred bulk fluid-rock exchange rate is 1.3(-0.4)(+1.1) x 10(-7) grams of solid reacted per gram of solid per year, several orders of magnitude lower than laboratory-based estimates. The inferred reaction rate suggests that mineral chemistry may lag the evolving conditions in Earth's crust during mountain building. PMID:10827949

  1. Venus volcanism: Rate estimates from laboratory studies of sulfur gas-solid reactions

    NASA Technical Reports Server (NTRS)

    Ehlers, K.; Fegley, B., Jr.; Prinn, R. G.

    1989-01-01

    Thermochemical reactions between sulfur-bearing gases in the atmosphere of Venus and calcium-, iron-, magnesium-, and sulfur-bearing minerals on the surface of Venus are an integral part of a hypothesized cycle of thermochemical and photochemical reactions responsible for the maintenance of the global sulfuric acid cloud cover on Venus. SO2 is continually removed from the Venus atmosphere by reaction with calcium bearing minerals on the planet's surface. The rate of volcanism required to balance SO2 depletion by reactions with calcium bearing minerals on the Venus surface can therefore be deduced from a knowledge of the relevant gas-solid reaction rates combined with reasonable assumptions about the sulfur content of the erupted material (gas + magma). A laboratory program was carried out to measure the rates of reaction between SO2 and possible crustal minerals on Venus. The reaction of CaCO3(calcite) + SO2 yields CaSO4 (anhydrite) + CO was studied. Brief results are given.

  2. Rate Coefficient Measurements of the Reaction CH3 + O2 = CH3O + O

    NASA Technical Reports Server (NTRS)

    Hwang, S. M.; Ryu, Si-Ok; DeWitt, K. J.; Rabinowitz, M. J.

    1999-01-01

    Rate coefficients for the reaction CH3 + O2 = CH3O + O were measured behind reflected shock waves in a series of lean CH4-O2-Ar mixtures using hydroxyl and methyl radical diagnostics. The rate coefficients are well represented by an Arrhenius expression given as k = (1.60(sup +0.67, sub -0.47 ) x 10(exp 13) e(-15813 +/- 587 K/T)/cubic cm.mol.s. This expression, which is valid in the temperature range 1575-1822 K, supports the downward trend in the rate coefficients that has been reported in recent determinations. All measurements to date, including the present study, have been to some extent affected by secondary reactions. The complications due to secondary reactions, choice of thermochemical data, and shock-boundary layer interactions that affect the determination of the rate coefficients are examined.

  3. Rate Coefficient Measurements of the Reaction CH3+O2+CH3O+O

    NASA Technical Reports Server (NTRS)

    Hwang, S. M.; Ryu, Si-Ok; DeWitt, K. J.; Rabinowitz, M. J.

    1999-01-01

    Rate coefficients for the reaction CH3 + O2 = CH3O + O were measured behind reflected shock waves in a series of lean CH4-O2-Ar mixtures using hydroxyl and methyl radical diagnostics. The rate coefficients are well represented by an Arrhenius expression given as k = (1.60(sup +0.67, -0.47)) X 10(exp 13) exp(- 15813 +/- 587 K/T)cc/mol s. This expression, which is valid in the temperature range 1575-1822 K, supports the downward trend in the rate coefficients that has been reported in recent determinations. All measurements to date, including the present study, have been to some extent affected by secondary reactions. The complications due to secondary reactions, choice of thermochemical data, and shock-boundary layer interactions that affect the determination of the rate coefficients are examined.

  4. Rate Constant Change of Photo Reaction of Bacteriorhodopsin Observed in Trimeric Molecular System.

    PubMed

    Tsujiuchi, Yutaka; Masumoto, Hiroshi; Goto, Takashi

    2016-04-01

    To elucidate the time evolution of photo reaction of bacteriorhodopsin in glycerol mixed purple membrane at around 196 K under irradiation by red light, a kinetic model was constructed. The change of absorption with irradiation at times of 560 nm and 412 nm was analyzed for the purpose of determining reaction rates of photo reaction of bacteriorhodopsin and its product M intermediate. In this study it is shown that reaction rates of conversion from bacteriorhodopsin to the M intermediate can be explained by a set of linear differential equations. This model analysis concludes that bacteriorhodopsin in which constitutes a trimer unit with other two bacteriorhodopsin molecules changes into M intermediates in the 1.73 of reaction rate, in the initial step, and according to the number of M intermediate in a trimer unit, from three to one, the reaction rate of bacteriorhodopsin into M intermediates smaller as 1.73, 0.80, 0.19 which caused by influence of inter-molecular interaction between bacteriorhodopsin. PMID:27451646

  5. Effective reaction rates in diffusion-limited phosphorylation-dephosphorylation cycles

    NASA Astrophysics Data System (ADS)

    Szymańska, Paulina; Kochańczyk, Marek; Miekisz, Jacek; Lipniacki, Tomasz

    2015-02-01

    We investigate the kinetics of the ubiquitous phosphorylation-dephosphorylation cycle on biological membranes by means of kinetic Monte Carlo simulations on the triangular lattice. We establish the dependence of effective macroscopic reaction rate coefficients as well as the steady-state phosphorylated substrate fraction on the diffusion coefficient and concentrations of opposing enzymes: kinases and phosphatases. In the limits of zero and infinite diffusion, the numerical results agree with analytical predictions; these two limits give the lower and the upper bound for the macroscopic rate coefficients, respectively. In the zero-diffusion limit, which is important in the analysis of dense systems, phosphorylation and dephosphorylation reactions can convert only these substrates which remain in contact with opposing enzymes. In the most studied regime of nonzero but small diffusion, a contribution linearly proportional to the diffusion coefficient appears in the reaction rate. In this regime, the presence of opposing enzymes creates inhomogeneities in the (de)phosphorylated substrate distributions: The spatial correlation function shows that enzymes are surrounded by clouds of converted substrates. This effect becomes important at low enzyme concentrations, substantially lowering effective reaction rates. Effective reaction rates decrease with decreasing diffusion and this dependence is more pronounced for the less-abundant enzyme. Consequently, the steady-state fraction of phosphorylated substrates can increase or decrease with diffusion, depending on relative concentrations of both enzymes. Additionally, steady states are controlled by molecular crowders which, mostly by lowering the effective diffusion of reactants, favor the more abundant enzyme.

  6. Unbound states of (32)Cl andthe (31)S(p,gamma)(32)Cl reaction rate

    SciTech Connect

    Matos, M.; Blackmon, Jeff C; Linhardt, Laura; Bardayan, Daniel W; Nesaraja, Caroline D; Clark, Jason; Diebel, C.; O'Malley, Patrick; Parker, P.D.

    2011-01-01

    The {sup 31}S(p,{gamma}){sup 32}Cl reaction is expected to provide the dominant break-out path from the SiP cycle in novae and is important for understanding enrichments of sulfur observed in some nova ejecta. We studied the {sup 32}S(3He,t){sup 32}Cl charge-exchange reaction to determine properties of proton-unbound levels in {sup 32}Cl that have previously contributed significant uncertainties to the {sup 31}S(p,{gamma}){sup 32}Cl reaction rate. Measured triton magnetic rigidities were used to determine excitation energies in {sup 32}Cl. Proton-branching ratios were obtained by detecting decay protons from unbound {sup 32}Cl states in coincidence with tritons. An improved {sup 31}S(p,{gamma}){sup 32}Cl reaction rate was calculated including robust statistical and systematic uncertainties.

  7. Ab Initio Calculation of Rate Constants for Molecule-Surface Reactions with Chemical Accuracy.

    PubMed

    Piccini, GiovanniMaria; Alessio, Maristella; Sauer, Joachim

    2016-04-18

    The ab initio prediction of reaction rate constants for systems with hundreds of atoms with an accuracy that is comparable to experiment is a challenge for computational quantum chemistry. We present a divide-and-conquer strategy that departs from the potential energy surfaces obtained by standard density functional theory with inclusion of dispersion. The energies of the reactant and transition structures are refined by wavefunction-type calculations for the reaction site. Thermal effects and entropies are calculated from vibrational partition functions, and the anharmonic frequencies are calculated separately for each vibrational mode. This method is applied to a key reaction of an industrially relevant catalytic process, the methylation of small alkenes over zeolites. The calculated reaction rate constants (free energies), pre-exponential factors (entropies), and enthalpy barriers show that our computational strategy yields results that agree with experiment within chemical accuracy limits (less than one order of magnitude). PMID:27008460

  8. Ab Initio Calculation of Rate Constants for Molecule–Surface Reactions with Chemical Accuracy

    PubMed Central

    Piccini, GiovanniMaria; Alessio, Maristella

    2016-01-01

    Abstract The ab initio prediction of reaction rate constants for systems with hundreds of atoms with an accuracy that is comparable to experiment is a challenge for computational quantum chemistry. We present a divide‐and‐conquer strategy that departs from the potential energy surfaces obtained by standard density functional theory with inclusion of dispersion. The energies of the reactant and transition structures are refined by wavefunction‐type calculations for the reaction site. Thermal effects and entropies are calculated from vibrational partition functions, and the anharmonic frequencies are calculated separately for each vibrational mode. This method is applied to a key reaction of an industrially relevant catalytic process, the methylation of small alkenes over zeolites. The calculated reaction rate constants (free energies), pre‐exponential factors (entropies), and enthalpy barriers show that our computational strategy yields results that agree with experiment within chemical accuracy limits (less than one order of magnitude). PMID:27008460

  9. Generalization of the Activated Complex Theory of Reaction Rates. I. Quantum Mechanical Treatment

    DOE R&D Accomplishments Database

    Marcus, R. A.

    1964-01-01

    In its usual form activated complex theory assumes a quasi-equilibrium between reactants and activated complex, a separable reaction coordinate, a Cartesian reaction coordinate, and an absence of interaction of rotation with internal motion in the complex. In the present paper a rate expression is derived without introducing the Cartesian assumption. The expression bears a formal resemblance to the usual one and reduces to it when the added assumptions of the latter are introduced.

  10. Exploiting time-resolved magnetic field effects for determining radical ion reaction rates

    NASA Astrophysics Data System (ADS)

    Bessmertnykh, A. O.; Borovkov, V. I.; Bagryansky, V. A.; Molin, Yu N.

    2016-07-01

    The capabilities of the method of time-resolved magnetic field effect in determining the rates of charge transfer reactions between radical ions and molecules on a nanosecond time scale have been investigated. The approach relies on the electron spin coherence in radical pair's partners generated by ionizing radiation. The spin evolution of the pair is sensitive to the reaction since the latter results in changing magnetic interactions of the unpaired electron. This process can be monitored by magnetic-field-sensitive fluorescence from an irradiated sample that is illustrated using reactions involving alkane radical cations. The accuracy and limitations of the approach are discussed.

  11. Absolute rate parameters for the reaction of ground state atomic oxygen with dimethyl sulfide and episulfide

    NASA Technical Reports Server (NTRS)

    Lee, J. H.; Timmons, R. B.; Stief, L. J.

    1976-01-01

    It is pointed out that the investigated reaction of oxygen with dimethyl sulfide may play an important role in photochemical smog formation and in the chemical evolution of dense interstellar clouds. Kinetic data were obtained with the aid of the flash photolysis-resonance fluorescence method. The photodecomposition of molecular oxygen provided the oxygen atoms for the experiments. The decay of atomic oxygen was studied on the basis of resonance fluorescence observations. Both reactions investigated were found to be fast processes. A negative temperature dependence of the rate constants for reactions with dimethyl sulfide was observed.

  12. Considerations Based on Reaction Rate on Char Gasification Behavior in Two-stage Gasifier for Biomass

    NASA Astrophysics Data System (ADS)

    Taniguchi, Miki; Nishiyama, Akio; Sasauchi, Kenichi; Ito, Yusuke; Akamatsu, Fumiteru

    In order to develop a small-scale gasifier in which biomass can be converted to energy with high efficiency, we planned a gasification process that consists of two parts: pyrolysis part (rotary kiln) and gasification part (downdraft gasifier). We performed fundamental experiments on gasification part and discussed the appropriate conditions such as air supply location, air ratio, air temperature and hearth load. We considered the results by calculating reaction rates of representative reactions on char gasification part and found that water gas reaction is dominant in the reduction area and its behavior gives important information to decide the adequate length of the char layer.

  13. Rate constants for chemical reactions in high-temperature nonequilibrium air

    NASA Technical Reports Server (NTRS)

    Jaffe, R. L.

    1986-01-01

    In the nonequilibrium atmospheric chemistry regime that will be encountered by the proposed Aeroassisted Orbital Transfer Vehicle in the upper atmosphere, where air density is too low for thermal and chemical equilibrium to be maintained, the detailed high temperature air chemistry plays a critical role in defining radiative and convective heating loads. Although vibrational and electronic temperatures remain low (less than 15,000 K), rotational and translational temperatures may reach 50,000 K. Attention is presently given to the effects of multiple temperatures on the magnitudes of various chemical reaction rate constants, for the cases of both bimolecular exchange reactions and collisional excitation and dissociation reactions.

  14. Reaction Rates for the Formation of Deuterium Tritide from Deuterium and Tritium

    SciTech Connect

    McConville, G. T.; Menke, D. A.; Ellefson, R. E.

    1985-04-01

    The rates of formation of DT in a mixture of D2 and T2 have been measured as a function of initial T2 concentration, pressure, temperature,and methane concentration in a stainless steel reaction container which had been treated to inhibit protium ingrowth. An attempt has been made to explain the experimental resuts on the basis of ion-molecule chain reactions. Some of the observations are consistent with a gas-phase ion, ground-state molecule reaction, but some of the more interesting observations require more complicated models. The addition of excited state molecules or heterogeneous catalytic effects are possibilities that will need further experiments for confirmation.

  15. Matching of experimental and statistical-model thermonuclear reaction rates at high temperatures

    NASA Astrophysics Data System (ADS)

    Newton, Joseph; Longland, Richard; Iliadis, Christian

    2009-05-01

    Reliable reaction rates at high stellar temperatures are necessary for the study of advanced stellar burning stages, supernovae and x-ray bursts. We suggest a new procedure for extrapolating experimental thermonuclear reaction rates to these higher temperatures (T > 1 GK) using statistical model (Hauser-Feshbach) results. Current, generally accepted, procedures involve the use of the Gamow peak, which has been shown to be unreliable for narrow resonances at high stellar temperatures [1]. Our new approach defines the effective thermonuclear energy range (ETER) by using the 8^th, 50^th and 92^nd percentiles of the cumulative distribution of fractional resonant reaction contributions. The ETER is then used to define a reliable temperature for matching experimental rates to Hauser-Feshbach rates. The resulting matching temperature is often well above the previous result using the Gamow peak concept. Our new method should provide more accurate extrapolated rates since Hauser-Feshbach rates are more reliable at higher temperatures. These ideas are applied to 21 (p,γ), (p,α) and (α,γ) reactions on a range of A = 20-40 target nuclei and results will be presented. [0pt] [1] J. R. Newton, C. Iliadis, A. E. Champagne, A. Coc, Y. Parpottas and R. Ugalde, Phys. Rev. C 75, 045801 (2007).

  16. Determination of the rate constant of hydroperoxyl radical reaction with phenol

    NASA Astrophysics Data System (ADS)

    Kozmér, Zsuzsanna; Arany, Eszter; Alapi, Tünde; Takács, Erzsébet; Wojnárovits, László; Dombi, András

    2014-09-01

    The rate constant of HO2rad reaction with phenol (kHO2rad +phenol) was investigated. The primary radical set produced in water γ radiolysis (rad OH, eaq- and Hrad ) was transformed to HO2rad /O2rad - by using dissolved oxygen and formate anion (in the form of either formic acid or sodium formate). The concentration ratio of HO2rad /O2rad - was affected by the pH value of the solution: under acidic conditions (using HCOOH) almost all radicals were converted to HO2rad , while under alkaline conditions (using HCOONa) to O2rad -. The degradation rate of phenol was significantly higher using HCOOH. From the ratio of reaction rates under the two reaction conditions kHO2rad +phenol was estimated to be (2.7±1.2)×103 L mol-1 s-1.

  17. Triple-alpha reaction rate studied with the Faddeev three-body formalism

    SciTech Connect

    Ishikawa, Souichi

    2012-11-12

    The triple-alpha (3{alpha}) reaction, {sup 4}He+{sup 4}He+{sup 4}He{yields}{sup 12}C+{gamma}, which plays a significant role in the stellar evolution scenarios, is studied in terms of a three-alpha (3-{alpha}) model. The reaction rate of the process is calculated via an inverse process, 3-{alpha} photodisintegration of a {sup 12}C nucleus. Both of 3-{alpha} bound and-continuum states are calculated by a Faddeev method with accommodating the long range Coulomb interaction. With being adjusted to the empirical E2-strength for {sup 12}C(0{sub 2}{sup +}){yields}{sup 12}C(2{sub 1}{sup +}) transition, results of the 3{alpha} reaction rate <{alpha}{alpha}{alpha}> at higher temperature (T > 10{sup 8} K), where the reaction proceeds mainly through the {sup 8}Be and {sup 12}C(0{sub 2}{sup +}) resonant states, almost agree with those of the Nuclear Astrophysics Compilation of Reaction Rates (NACRE). On the other hand, calculated values of <{alpha}{alpha}{alpha}> are about 10{sup 3} times larger than the NACRE rate at a low temperature (T= 10{sup 7} K), which means our results are remarkably smaller than recent CDCC results.

  18. Determination of Global Reaction Rate During Laser-Induced Decomposition at Static High Pressures

    NASA Astrophysics Data System (ADS)

    Russell, Thomas. P.; Pangilinan, Gerardo I.

    1998-03-01

    The laser induced decomposition of hexahydro-1,3,5-trinitro-1,3,5 triazine (C_3H_6N_6O_6, RDX), trinitro azetidine (C_3H_4N_3O_6, TNAZ) and ammonium perchlorate (NH_4ClO_4, AP) at static high pressure in the range of 0.6 - 2.0 GPa is presented. The samples are loaded in a gem anvil cell and the reaction is induced with a single laser pulse (514 nm, 6 μs duration, 3-22 J/cm^2). The dynamic chemical processes are probed using time resolved uv-Vis absorption spectroscopy, during and up to 20 μs after the laser pulse. In all three materials, decomposition is characterized by a time-dependent increase in absorbance from 300-500 nm. This absorption change is directly proportional to the mole fraction of reaction and provides a measurement of the global reaction rate. The reaction rate is determined to be dependent on the sample, the initial pressure, and the laser fluence. The chemical decomposition is modeled using a three term reaction rate equation encompassing initiation, growth, and coalescence. A description of the differences in the decomposition kinetics for each material will be provided. Finally, the implications of these measurements to models of macroscopic energy release rates will be addressed.

  19. The 25Al(p,g)26Si Reaction Rate in Novae

    NASA Astrophysics Data System (ADS)

    Bardayan, Dan; Blackmon, J. C.; Hix, W. R.; Liang, J. F.; Smith, M. S.; Howard, J. A.; Kozub, R. L.; Brune, C. R.; Chae, K. Y.; Lingerfelt, E. J.; Scott, J. P.; Johnson, M. S.; Jones, K. L.; Pain, S. D.; Thomas, J. S.; Livesay, R. J.; Wisser, D. W.

    The production of 26Al in novae is uncertain, in part, because of the uncertain rate of the 25 Al(p,γ)26Si reaction at novae temperatures. This reaction is thought to be dominated by a long- sought 3+ level in 26Si, and the calculated reaction rate varies by orders of magnitude depending on the energy of this resonance. We present evidence concerning the spin of a level at 5.914 MeV in 26Si from the 28Si(p,t)26Si reaction studied at the Holifield Radioactive Beam Facility at ORNL. We find that the angular distribution for this level implies either a 2+ or 3+ assignment, with only a 3+ being consistent with the mirror nucleus, 26Mg. Additionally, we have used the updated 25Al(p,γ)26Si reaction rate in a nova nucleosynthesis calculation and have addressed the effects of the remaining uncertainties in the rate on 26Al production.

  20. Impact of strange quark matter nuggets on pycnonuclear reaction rates in the crusts of neutron stars

    SciTech Connect

    Golf, B.; Hellmers, J.; Weber, F.

    2009-07-15

    This article presents an investigation into the pycnonuclear reaction rates in dense crustal matter of neutron stars contaminated with strange quark matter nuggets. The presence of such nuggets in the crustal matter of neutron stars would be a natural consequence if Witten's strange quark matter hypothesis is correct. The methodology presented in this article is a recreation of a recent representation of nuclear force interactions embedded within pycnonuclear reaction processes. The study then extends the methodology to incorporate distinctive theoretical characteristics of strange quark matter nuggets, like their low charge-per-baryon ratio, and then assesses their effects on the pycnonuclear reaction rates. Particular emphasis is put on the impact of color superconductivity on the reaction rates. Depending on whether quark nuggets are in this novel state of matter, their electric charge properties vary drastically, which turns out to have a dramatic effect on the pycnonuclear reaction rates. Future nuclear fusion network calculations may thus have the potential to shed light on the existence of strange quark matter nuggets and on whether they are in a color superconducting state, as suggested by QCD.

  1. Rates of various reactions catalyzed by ATP synthase as related to the mechanism of ATP synthesis

    SciTech Connect

    Berkich, D.A.; Williams, G.D.; Masiakos, P.T.; Smith, M.B.; Boyer, P.D.; LaNoue, K.F. )

    1991-01-05

    The forward and reverse rates of the overall reaction catalyzed by the ATP synthase in intact rat heart mitochondria, as measured with 32P, were compared with the rates of two partial steps, as measured with 18O. Such rates have been measured previously, but their relationship to one another has not been determined, nor have the partial reactions been measured in intact mitochondria. The partial steps measured were the rate of medium Pi formation from bound ATP (in state 4 this also equals the rate of medium Pi into bound ATP) and the rate of formation of bound ATP from bound Pi within the catalytic site. The rates of both partial reactions can be measured by 31P NMR analysis of the 18O distribution in Pi and ATP released from the enzyme during incubation of intact mitochondria with highly labeled (18O)Pi. Data were obtained in state 3 and 4 conditions with variation in substrate concentrations, temperature, and mitochondrial membrane electrical potential gradient (delta psi m). Although neither binding nor release of ATP is necessary for phosphate/H2O exchange, in state 4 the rate of incorporation of at least one water oxygen atom into phosphate is approximately twice the rate of the overall reaction rate under a variety of conditions. This can be explained if the release of Pi or ATP at one catalytic site does not occur, unless ATP or Pi is bound at another catalytic site. Such coupling provides strong support for the previously proposed alternating site mechanism. In state 3 slow reversal of ATP synthesis occurs within the mitochondrial matrix and can be detected as incorporation of water oxygen atoms into medium Pi even though medium (32P)ATP does not give rise to 32Pi in state 3. These data can be explained by lack of translocation of ATP from the medium to the mitochondrial matrix.

  2. Astrophysical reaction rate for Be9 formation within a three-body approach

    NASA Astrophysics Data System (ADS)

    Casal, J.; Rodríguez-Gallardo, M.; Arias, J. M.; Thompson, I. J.

    2014-10-01

    The structure of the Borromean nucleus Be9 (α+α+n) is addressed within a three-body approach using the analytical transformed harmonic oscillator method. The three-body formalism provides an accurate description of the radiative capture reaction rate for the entire temperature range relevant in astrophysics. At high temperatures, results match the calculations based on two-step sequential processes. At low temperatures, where the particles have no access to intermediate two-body resonances, the three-body direct capture leads to reaction rates larger than the sequential processes. These results support the reliability of the method for systems with several charged particles.

  3. Photochemistry of solutes in/on ice: reaction rate dependence on sample orientation and photon flux

    NASA Astrophysics Data System (ADS)

    Hullar, T.; Anastasio, C.

    2015-12-01

    Particularly in polar regions, photochemical reactions in snowpacks can be an important mechanism for transforming organic and inorganic compounds. Chemicals within snow and ice are found in three different compartments: distributed in the bulk ice, concentrated in liquid-like regions (LLRs) within the ice matrix (such as at grain boundaries), or present in quasi-liquid layers (QLLs) at the air-ice interface. While some previous work suggested reaction rates may vary in these different compartments, our preliminary experiments found similar reaction rates in all three compartments, as well as in aqueous solution. Previous work also suggested reaction rate constants may be independent of photon flux under certain illumination conditions. Here, we extend our investigations to measure reaction rate constants in ice samples with different orientations to the illumination source, which our work thus far suggests may impact the measured rate constants. Polycyclic aromatic hydrocarbons (PAHs) are common pollutants in snow and ice. We first prepared aqueous solutions of a single PAH. We then froze these samples using various methods previously shown to segregate the solute into known locations in the ice matrix. With simulated polar sunlight, we illuminated these samples and measured photon flux (using 2-nitrobenzaldehyde as a chemical actinometer) and photodecay of the PAH. Using this information, we normalized the rate of PAH loss to the photon flux and calculated the rate constants for PAH photodegradation under various freezing conditions, photon fluxes, and sample orientations. We will report on the impact of these variables on PAH photodegradation as well as the effect of varying the photon flux.

  4. Assessing hydrodynamic effects on jarosite dissolution rates, reaction products, and preservation on Mars

    NASA Astrophysics Data System (ADS)

    Dixon, Emily M.; Elwood Madden, Andrew S.; Hausrath, Elisabeth M.; Elwood Madden, Megan E.

    2015-04-01

    Jarosite flow-through dissolution experiments were conducted in ultrapure water (UPW), pH 2 sulfuric acid, and saturated NaCl and CaCl2 brines at 295-298 K to investigate how hydrologic variables may affect jarosite preservation and reaction products on Mars. K+-based dissolution rates in flowing UPW did not vary significantly with flow rate, indicating that mineral surface reactions control dissolution rates over the range of flow rates investigated. In all of the solutions tested, hydrologic variables do not significantly affect extent of jarosite alteration; therefore, jarosite is equally likely to be preserved in flowing or stagnant waters on Mars. However, increasing flow rate did affect the mineralogy and accumulation of secondary reaction products. Iron release rates in dilute solutions increased as the flow rate increased, likely due to nanoscale iron (hydr)oxide transport in flowing water. Anhydrite formed in CaCl2 brine flow-through experiments despite low temperatures, while metastable gypsum and bassanite were observed in batch experiments. Therefore, observations of the hydration state of calcium sulfate minerals on Mars may provide clues to unravel past salinity and hydrologic conditions as well as temperatures and vapor pressures.

  5. Direct use of the mass output of a thermobalance for controlling the reaction rate of solid-state reactions

    NASA Astrophysics Data System (ADS)

    Diánez, M. J.; Pérez Maqueda, L. A.; Criado, J. M.

    2004-08-01

    Sample controlled thermal analysis equipment has been developed constituted by an electrobalance in which the mass output (TG signal) is directly used for monitoring the temperature of thermal decomposition reactions under constant rate thermal analysis (CRTA) or stepwise isothermal analysis (SIA) control. The sample weight is programmed to follow a preset linear decrease as a function of the time by means of a conventional controller, that at the time control a second conventional temperature programmer. The CRTA control is achieved by controlling the temperature is such a way that if the mass input is higher than the setpoint, the temperature increases at a predefined heating rate; while if the mass input is lower than the setpoint, the temperature decreases at a predefined cooling rate. The SIA control is achieved by selecting the run-hold command from the menu of the digital input of the temperature programmer. In such a case, the programmed linear heating schedule is in progress while the sample weight is higher than the setpoint and an isothermal dwell is maintained as soon as the weight becomes lower than the setpoint. The direct use of the mass output for the control provides a higher sensitivity for selecting very low values of constant reaction rates than the more conventional methods using the DTG output as control parameter. The thermal degradation of polyvinye chloride (PVC) has been used for checking the behavior of the equipment here developed, showing that the dehydrochlorination of PVC is controlled either by a nucleation and growth of nuclei or by a random scission of the main chain of the polymer.

  6. Degradation of (14)C-labeled few layer graphene via Fenton reaction: Reaction rates, characterization of reaction products, and potential ecological effects.

    PubMed

    Feng, Yiping; Lu, Kun; Mao, Liang; Guo, Xiangke; Gao, Shixiang; Petersen, Elijah J

    2015-11-01

    Graphene has attracted considerable commercial interest due to its numerous potential applications. It is inevitable that graphene will be released into the environment during the production and usage of graphene-enabled consumer products, but the potential transformations of graphene in the environment are not well understood. In this study, (14)C-labeled few layer graphene (FLG) enabled quantitative measurements of FLG degradation rates induced by the iron/hydrogen peroxide induced Fenton reaction. Quantification of (14)CO2 production from (14)C-labeled FLG revealed significant degradation of FLG after 3 days with high H2O2 (200 mmol L(-1)) and iron (100 μmol L(-1)) concentrations but substantially lower rates under environmentally relevant conditions (0.2-20 mmol L(-1) H2O2 and 4 μmol L(-1) Fe(3+)). Importantly, the carbon-14 labeling technique allowed for quantification of the FLG degradation rate at concentrations nearly four orders of magnitude lower than those typically used in other studies. These measurements revealed substantially faster degradation rates at lower FLG concentrations and thus studies with higher FLG concentrations may underestimate the degradation rates. Analysis of structural changes to FLG using multiple orthogonal methods revealed significant FLG oxidation and multiple reaction byproducts. Lastly, assessment of accumulation of the degraded FLG and intermediates using aquatic organism Daphnia magna revealed substantially decreased body burdens, which implied that the changes to FLG caused by the Fenton reaction may dramatically impact its potential ecological effects. PMID:26210029

  7. Reaction rate modeling in the deflagration to detonation transition of granular energetic materials

    SciTech Connect

    Son, S.F.; Asay, B.W.; Bdzil, J.B.; Kober, E.M.

    1996-07-01

    The problem of accidental initiation of detonation in granular material has been the initial focus of the Los Alamos explosives safety program. Preexisting models of deflagration-to-detonation transition (DDT) in granular explosives, especially the Baer and Nunziato (BN) model, have been examined. The main focus of this paper is the reaction rate model. Comparison with experiments are made using the BN rate model. Many features are replicated by the simulations. However, some qualitative features, such as inert plug formation in DDT tube-test experiments and other trends, are not produced in the simulations. By modifying the reaction rate model the authors show inert plug formation that more closely replicates the qualitative features of experimental observations. Additional improvements to the rate modeling are suggested.

  8. Scale-Dependent Rates of Uranyl Surface Complexation Reaction in Sediments

    SciTech Connect

    Liu, Chongxuan; Shang, Jianying; Kerisit, Sebastien N.; Zachara, John M.; Zhu, Weihuang

    2013-03-15

    Scale-dependency of uranyl[U(VI)] surface complexation rates was investigated in stirred flow-cell and column systems using a U(VI)-contaminated sediment from the US Department of Energy, Hanford site, WA. The experimental results were used to estimate the apparent rate of U(VI) surface complexation at the grain-scale and in porous media. Numerical simulations using molecular, pore-scale, and continuum models were performed to provide insights into and to estimate the rate constants of U(VI) surface complexation at the different scales. The results showed that the grain-scale rate constant of U(VI) surface complexation was over 3 to 10 orders of magnitude smaller, dependent on the temporal scale, than the rate constant calculated using the molecular simulations. The grain-scale rate was faster initially and slower with time, showing the temporal scale-dependency. The largest rate constant at the grain-scale decreased additional 2 orders of magnitude when the rate was scaled to the porous media in the column. The scaling effect from the grain-scale to the porous media became less important for the slower sorption sites. Pore-scale simulations revealed the importance of coupled mass transport and reactions in both intragranular and inter-granular domains, which caused both spatial and temporal dependence of U(VI) surface complexation rates in the sediment. Pore-scale simulations also revealed a new rate-limiting mechanism in the intragranular porous domains that the rate of coupled diffusion and surface complexation reaction was slower than either process alone. The results provided important implications for developing models to scale geochemical/biogeochemical reactions.

  9. Rate constant calculations of H-atom abstraction reactions from ethers by HȮ2 radicals.

    PubMed

    Mendes, Jorge; Zhou, Chong-Wen; Curran, Henry J

    2014-02-27

    In this work, we detail hydrogen atom abstraction reactions from six ethers by the hydroperoxyl radical, including dimethyl ether, ethyl methyl ether, propyl methyl ether, isopropyl methyl ether, butyl methyl ether, and isobutyl methyl ether, in order to test the effect of the functional group on the rate constant calculations. The Møller-Plesset (MP2) method with the 6-311G(d,p) basis set has been employed in the geometry optimizations and frequency calculations of all of the species involved in the above reaction systems. The connections between each transition state and the corresponding local minima have been determined by intrinsic reaction coordinate calculations. Energies are reported at the CCSD(T)/cc-pVTZ level of theory and include the zero-point energy corrections. As a benchmark in the electronic energy calculations, the CCSD(T)/CBS extrapolation was used for the reactions of dimethyl ether + HȮ2 radicals. A systematic calculation of the high-pressure limit rate constants has been performed using conventional transition-state theory, including asymmetric Eckart tunneling corrections, in the temperature range of 500-2000 K. The one dimensional hindrance potentials obtained at MP2/6-311G(d,p) for the reactants and transition states have been used to describe the low frequency torsional modes. Herein, we report the calculated individual, average, and total rate constants. A branching ratio analysis for every reaction site has also been performed. PMID:24483837

  10. Evaluation of reaction rates in streambed sediments with seepage flow: a novel code

    NASA Astrophysics Data System (ADS)

    Boano, Fulvio; De Falco, Natalie; Arnon, Shai

    2015-04-01

    Streambed interfaces represent hotspots for nutrient transformations because they host different microbial species which perform many heterotrophic and autotrophic reactions. The evaluation of these reaction rates is crucial to assess the fate of nutrients in riverine environments, and it is often performed through the analysis of concentrations from water samples collected along vertical profiles. The most commonly employed evaluation tool is the Profile code developed by Berg et al. (1998), which determines reaction rates by fitting observed concentrations to a diffusion-reaction equation that neglects the presence of water flow within sediments. However, hyporheic flow is extremely common in streambeds, where solute transport is often controlled by advection rather than diffusion. There is hence a pressing need to develop new methods that can be applied even to advection-dominated sediments. This contribution fills this gap by presenting a novel approach that extends the method proposed by Berg et al. (1998). This new approach includes the influence of vertical solute transport by upwelling or downwelling water, and it is this suited to the typical flow conditions of stream sediments. The code is applied to vertical profiles of dissolved oxygen from a laboratory flume designed to mimic the complex flow conditions of real streams. The results show that it is fundamental to consider water flow to obtain reliable estimates of reaction rates in streambeds. Berg, P., N. Risgaard-Petersen, and S. Rysgaard, 1998, Interpretation of measured concentration profiles in the sediment porewater, Limnology and Oceanography, 43:1500-1510.

  11. Modeling of atmospheric OH reaction rates using newly developed variable distance weighted zero order connectivity index

    NASA Astrophysics Data System (ADS)

    Markelj, Jernej; Pompe, Matevž

    2016-04-01

    A new variable distance weighted zero order connectivity index was used for development of structure-activity relationship for modeling reactivity of OH radical with alkanes and non-conjugated alkenes in the atmosphere. The proposed model is based on the assumptions that the total reaction rate can be obtained by summing all partial reaction rates and that all reaction sites are interrelated by influencing each other. The results suggest that these assumptions are justified. The model was compared with the EPA implemented model in the studied application domain and showed superior prediction capabilities. Further, optimized values of the weights that were used in our model permit some insight into mechanisms that govern the reaction OH + alkane/alkene. The most important conclusion is that the branching degree of the forming radical seems to play a major role in site specific reaction rates. Relative qualitative structural interpretation is possible, e.g. allylic site is suggested to be much more reactive than even tertiary sp3 carbon. Novel modeling software MACI, which was developed in our lab and is now available for research purposes, was used for calculations. Various variable topological indices that are again starting to be recognized because of their great potentials in simplicity, fast calculations, very good correlations and structural information, were implemented in the program.

  12. Acid–base chemical reaction model for nucleation rates in the polluted atmospheric boundary layer

    PubMed Central

    Chen, Modi; Titcombe, Mari; Jiang, Jingkun; Jen, Coty; Kuang, Chongai; Fischer, Marc L.; Eisele, Fred L.; Siepmann, J. Ilja; Hanson, David R.; Zhao, Jun; McMurry, Peter H.

    2012-01-01

    Climate models show that particles formed by nucleation can affect cloud cover and, therefore, the earth's radiation budget. Measurements worldwide show that nucleation rates in the atmospheric boundary layer are positively correlated with concentrations of sulfuric acid vapor. However, current nucleation theories do not correctly predict either the observed nucleation rates or their functional dependence on sulfuric acid concentrations. This paper develops an alternative approach for modeling nucleation rates, based on a sequence of acid–base reactions. The model uses empirical estimates of sulfuric acid evaporation rates obtained from new measurements of neutral molecular clusters. The model predicts that nucleation rates equal the sulfuric acid vapor collision rate times a prefactor that is less than unity and that depends on the concentrations of basic gaseous compounds and preexisting particles. Predicted nucleation rates and their dependence on sulfuric acid vapor concentrations are in reasonable agreement with measurements from Mexico City and Atlanta. PMID:23091030

  13. Reaction rate constants of H-abstraction by OH from large ketones: measurements and site-specific rate rules.

    PubMed

    Badra, Jihad; Elwardany, Ahmed E; Farooq, Aamir

    2014-06-28

    Reaction rate constants of the reaction of four large ketones with hydroxyl (OH) are investigated behind reflected shock waves using OH laser absorption. The studied ketones are isomers of hexanone and include 2-hexanone, 3-hexanone, 3-methyl-2-pentanone, and 4-methl-2-pentanone. Rate constants are measured under pseudo-first-order kinetics at temperatures ranging from 866 K to 1375 K and pressures near 1.5 atm. The reported high-temperature rate constant measurements are the first direct measurements for these ketones under combustion-relevant conditions. The effects of the position of the carbonyl group (C=O) and methyl (CH3) branching on the overall rate constant with OH are examined. Using previously published data, rate constant expressions covering, low-to-high temperatures, are developed for acetone, 2-butanone, 3-pentanone, and the hexanone isomers studied here. These Arrhenius expressions are used to devise rate rules for H-abstraction from various sites. Specifically, the current scheme is applied with good success to H-abstraction by OH from a series of n-ketones. Finally, general expressions for primary and secondary site-specific H-abstraction by OH from ketones are proposed as follows (the subscript numbers indicate the number of carbon atoms bonded to the next-nearest-neighbor carbon atom, the subscript CO indicates that the abstraction is from a site next to the carbonyl group (C=O), and the prime is used to differentiate different neighboring environments of a methylene group): PMID:24817270

  14. Pore and Continuum Scale Study of the Effect of Subgrid Transport Heterogeneity on Redox Reaction Rates

    SciTech Connect

    Liu, Yuanyuan; Liu, Chongxuan; Zhang, Changyong; Yang, Xiaofan; Zachara, John M.

    2015-08-01

    A micromodel system with a pore structure for heterogeneous flow and transport was used to investigate the effect of subgrid transport heterogeneity on redox reaction rates. Hematite reductive dissolution by injecting a reduced form of flavin mononucleotide (FMNH2) at variable flow rates was used as an example to probe the variations of redox reaction rates in different subgrid transport domains. Experiments, pore-scale simulations, and macroscopic modeling were performed to measure and simulate in-situ hematite reduction and to evaluate the scaling behavior of the redox reaction rates from the pore to macroscopic scales. The results indicated that the measured pore-scale rates of hematite reduction were consistent with the predictions from a pore scale reactive transport model. A general trend is that hematite reduction followed reductant transport pathways, starting from the advection-dominated pores toward the interior of diffusion-dominated domains. Two types of diffusion domains were considered in the micromodel: a micropore diffusion domain, which locates inside solid grains or aggregates where reactant transport is limited by diffusion; and a macropore diffusion domain, which locates at wedged, dead-end pore spaces created by the grain-grain contacts. The rate of hematite reduction in the advection-dominated domain was faster than those in the diffusion-controlled domains, and the rate in the macropore diffusion domain was faster than that in the micropore domain. The reduction rates in the advection and macropore diffusion domains increased with increasing flow rate, but were affected by different mechanisms. The rate increase in the advection domain was controlled by the mass action effect as a faster flow supplied more reactants, and the rate increase in the macropore domain was more affected by the rate of mass exchange with the advection domain, which increased with increasing flow rate. The hematite reduction rate in the micropore domain was, however

  15. Solid-gas reaction with adsorption as the rate limiting step.

    PubMed

    Wróbel, Rafał; Arabczyk, Walerian

    2006-07-27

    The model of nucleation where adsorption of reactant is a rate-limiting step has been considered. Assuming the adsorption range model, a numerical simulation has been made. The dependency of bulk concentration and surface coverage versus time and thermogravimetric curves are presented. The crystallite size is suggested to be the key factor of the nucleation rate. Theoretical considerations have been compared with the experimental results of the iron nitriding reaction. PMID:16854036

  16. Estimating the effective rate of fast chemical reactions with turbulent mixing of reactants

    SciTech Connect

    Vorotilin, V. P. Yanovskii, Yu. G.

    2015-07-15

    On the basis of representation of a turbulent fluid as an aggregation of independent turbulent particles (vortexes), we derive relations for the effective rate of chemical reactions and obtain a closed system of equations describing reactions with turbulent mixing of reactants. A variant of instantaneous reactions is considered that explains the proposed approach simply. In particular, the turbulent mixing events according to this approach are uniquely related to the acts of chemical interaction, which makes it possible to exclude from consideration the mixing of inert impurities–the most difficult point of the theory formulated using classical notions. The obtained system of equations is closed without introducing arbitrarily adopted correlations, by naturally introducing the concept of effective reaction and writing the equations of conservation for both the concentrations of reactants and their volumes.

  17. Estimating the effective rate of fast chemical reactions with turbulent mixing of reactants

    NASA Astrophysics Data System (ADS)

    Vorotilin, V. P.; Yanovskii, Yu. G.

    2015-07-01

    On the basis of representation of a turbulent fluid as an aggregation of independent turbulent particles (vortexes), we derive relations for the effective rate of chemical reactions and obtain a closed system of equations describing reactions with turbulent mixing of reactants. A variant of instantaneous reactions is considered that explains the proposed approach simply. In particular, the turbulent mixing events according to this approach are uniquely related to the acts of chemical interaction, which makes it possible to exclude from consideration the mixing of inert impurities-the most difficult point of the theory formulated using classical notions. The obtained system of equations is closed without introducing arbitrarily adopted correlations, by naturally introducing the concept of effective reaction and writing the equations of conservation for both the concentrations of reactants and their volumes.

  18. New Approach for Investigating Reaction Dynamics and Rates with Ab Initio Calculations.

    PubMed

    Fleming, Kelly L; Tiwary, Pratyush; Pfaendtner, Jim

    2016-01-21

    Herein, we demonstrate a convenient approach to systematically investigate chemical reaction dynamics using the metadynamics (MetaD) family of enhanced sampling methods. Using a symmetric SN2 reaction as a model system, we applied infrequent metadynamics, a theoretical framework based on acceleration factors, to quantitatively estimate the rate of reaction from biased and unbiased simulations. A systematic study of the algorithm and its application to chemical reactions was performed by sampling over 5000 independent reaction events. Additionally, we quantitatively reweighed exhaustive free-energy calculations to obtain the reaction potential-energy surface and showed that infrequent metadynamics works to effectively determine Arrhenius-like activation energies. Exact agreement with unbiased high-temperature kinetics is also shown. The feasibility of using the approach on actual ab initio molecular dynamics calculations is then presented by using Car-Parrinello MD+MetaD to sample the same reaction using only 10-20 calculations of the rare event. Owing to the ease of use and comparatively low-cost of computation, the approach has extensive potential applications for catalysis, combustion, pyrolysis, and enzymology. PMID:26690335

  19. Rate constant for the reaction Cl + HO2NO2 yielding products. [in stratospheric chemistry

    NASA Technical Reports Server (NTRS)

    Simonaitis, R.; Leu, M. T.

    1985-01-01

    The rates for the reaction of Cl atoms iwth HO2NO2 were calculated from data obtained by the use of the discharge flow/resonance fluorescence (DF/RF) and the discharge flow/mass spectrometric (DF/MS) techniques. The total rate constant, k1, for the overall reaction: 1a (Cl + HO2NO2 yielding HCl + NO2 +O2), 1b (yielding HO2 + ClNO2), and the two possible additional channels was found to be less than 1.0 x 10 to the -13th cu cm/s at 296 K. The value of (k1a + k1b) was found to be 3.4 + or - 1.4) x 10 to the -14th cu cm/s. Thus, the reaction of Cl with peroxynitric acid is too slow, by a factor of 100, to contribute significantly to the hydrogen abstraction by Cl in the stratosphere.

  20. Toward a reaction rate model of condensed-phase RDX decomposition under high temperatures

    NASA Astrophysics Data System (ADS)

    Schweigert, Igor

    2015-06-01

    Shock ignition of energetic molecular solids is driven by microstructural heterogeneities, at which even moderate stresses can result in sufficiently high temperatures to initiate material decomposition and chemical energy release. Mesoscale modeling of these ``hot spots'' requires a reaction rate model that describes the energy release with a sub-microsecond resolution and under a wide range of temperatures. No such model is available even for well-studied energetic materials such as RDX. In this presentation, I will describe an ongoing effort to develop a reaction rate model of condensed-phase RDX decomposition under high temperatures using first-principles molecular dynamics, transition-state theory, and reaction network analysis. This work was supported by the Naval Research Laboratory, by the Office of Naval Research, and by the DoD High Performance Computing Modernization Program Software Application Institute for Multiscale Reactive Modeling of Insensitive Munitions.

  1. Reaction rates and kinetic isotope effects of H2 + OH → H2O + H.

    PubMed

    Meisner, Jan; Kästner, Johannes

    2016-05-01

    We calculated reaction rate constants including atom tunneling of the reaction of dihydrogen with the hydroxy radical down to a temperature of 50 K. Instanton theory and canonical variational theory with microcanonical optimized multidimensional tunneling were applied using a fitted potential energy surface [J. Chen et al., J. Chem. Phys. 138, 154301 (2013)]. All possible protium/deuterium isotopologues were considered. Atom tunneling increases at about 250 K (200 K for deuterium transfer). Even at 50 K the rate constants of all isotopologues remain in the interval 4 ⋅ 10(-20) to 4 ⋅ 10(-17) cm(3) s(-1), demonstrating that even deuterated versions of the title reaction are possibly relevant to astrochemical processes in molecular clouds. The transferred hydrogen atom dominates the kinetic isotope effect at all temperatures. PMID:27155636

  2. Reaction rates and kinetic isotope effects of H2 + OH → H2O + H

    NASA Astrophysics Data System (ADS)

    Meisner, Jan; Kästner, Johannes

    2016-05-01

    We calculated reaction rate constants including atom tunneling of the reaction of dihydrogen with the hydroxy radical down to a temperature of 50 K. Instanton theory and canonical variational theory with microcanonical optimized multidimensional tunneling were applied using a fitted potential energy surface [J. Chen et al., J. Chem. Phys. 138, 154301 (2013)]. All possible protium/deuterium isotopologues were considered. Atom tunneling increases at about 250 K (200 K for deuterium transfer). Even at 50 K the rate constants of all isotopologues remain in the interval 4 ṡ 10-20 to 4 ṡ 10-17 cm3 s-1, demonstrating that even deuterated versions of the title reaction are possibly relevant to astrochemical processes in molecular clouds. The transferred hydrogen atom dominates the kinetic isotope effect at all temperatures.

  3. Rate constant for the reaction of atomic oxygen with phosphine at 298 K

    NASA Technical Reports Server (NTRS)

    Stief, L. J.; Payne, W. A.; Nava, D. F.

    1987-01-01

    The rate constant for the reaction of atomic oxygen with phosphine has been measured at 298 K using flash photolysis combined with time-resolved detection of O(3P) via resonance fluorescence. Atomic oxygen was produced by flash photolysis of N2O or NO highly diluted in argon. The results were shown to be independent of (PH3), (O), total pressure and the source of O(3P). The mean value of all the experiments is k1 = (3.6 + or -0.8) x 10 to the -11th cu cm/s (1 sigma). Two previous measurements of k1 differed by more than an order of magnitude, and the results support the higher value obtained in a discharge flow-mass spectrometry study. A comparison with rate data for other atomic and free radical reactions with phosphine is presented, and the role of these reactions in the aeronomy or photochemistry of Jupiter and Saturn is briefly considered.

  4. Thermonuclear Reaction Rate Libraries and Software Tools for Nuclear Astrophysics Research

    NASA Astrophysics Data System (ADS)

    Smith, Michael S.; Cyburt, Richard; Schatz, Hendrik; Wiescher, Michael; Smith, Karl; Warren, Scott; Ferguson, Ryan; Lingerfelt, Eric; Buckner, Kim; Nesaraja, Caroline D.

    2008-05-01

    Thermonuclear reaction rates are a crucial input for simulating a wide variety of astrophysical environments. A new collaboration has been formed to ensure that astrophysical modelers have access to reaction rates based on the most recent experimental and theoretical nuclear physics information. To reach this goal, a new version of the REACLIB library has been created by the Joint Institute for Nuclear Astrophysics (JINA), now available online at http://www.nscl.msu.edu/~nero/db. A complementary effort is the development of software tools in the Computational Infrastructure for Nuclear Astrophysics, online at nucastrodata.org, to streamline, manage, and access the workflow of the reaction evaluations from their initiation to peer review to incorporation into the library. Details of these new projects will be described.

  5. Reaction Rate Acceleration and Tg Depression of Polycyanurate Under Nanopore Confinement

    NASA Astrophysics Data System (ADS)

    Lopez, Evelyn; Simon, Sindee L.

    2015-03-01

    Material properties such as Tg and the reaction kinetics are known to deviate from the bulk when subjected to nano-sized confinement. Previous work from our laboratory on the trimerization of cyanate esters found that the reaction kinetics were faster for a monofunctional reactant compared to a difunctional monomer, whereas the Tg depression was greater for the crosslinked product of the latter compared to the low molecular weight trimer of the former. The origin of the changes in nanoconfined reaction rates differs from those that govern changes in the Tg. The research objective is to further explore the effect that confinement has on reaction kinetics and Tg using a mixture consisting of mono- and di- cyanate ester monomers. The product is an uncrosslinked polycyanurate with Mn = 5240 g/mol and PDI = 1.78. The confinement mediums are controlled pore glasses with diameters ranging from 8.1 to 111.1 nm. The nanopore-confined material was synthesized in-situ and the reaction kinetics are followed by DSC; after the reaction, the Tg values of the nanoconfined polymer where also measured by DSC. An acceleration factor of 13 and a Tg depression of 38 °C are observed for the material confined in the smallest 8.1 nm-diameter pores. The Tg depression is between those of the trimer and network previously studied, while the acceleration of the reaction rate is lower. Our results are consistent with the reaction acceleration arising from packing effects at the pore wall and the Tg depression arising from intrinsic size effects.

  6. Oscillations in the reaction rate of nitric oxide reduction by ammonia over polycrystalline platinum foil catalysts

    SciTech Connect

    Katona, T. |; Somorjai, G.A.

    1992-06-25

    Self-sustained oscillations were obtained in the No + NH{sub 3} reaction at atmospheric pressure with reactant partial pressures of 133-600 Pa (1-4.5 Torr), in the temperature range of 603-673 K. The effects of reaction parameters, temperature, partial pressure, and reactant gas velocity were studied. The onset temperature of the oscillations (603 K) was slightly dependent on the partial pressure of nitric oxide in the feed gas. Near this temperature the oscillations were uncontrolled (chaotic), while increasing the temperature resulted in periodic oscillations in the reaction rates. The oscillation phenomena were studied in both isothermic and adiabatic modes. The oscillations, when initiated by a temperature increase, start up only after an induction period during which the rates of NO consumption and N{sub 2} formation sharply increase as opposed to the slow enhancement of the rate of N{sub 2}O formation. The two reaction branches found at the high- and low-temperature regimes in the batch mode have product distributions which are similar to those found at the extremes of the amplitudes of rate oscillations. 36 refs., 13 figs.

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

    ERIC Educational Resources Information Center

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

    2007-01-01

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

  8. Calibration of reaction rates for the CREST reactive-burn model

    NASA Astrophysics Data System (ADS)

    Handley, Caroline

    2015-06-01

    In recent years, the hydrocode-based CREST reactive-burn model has had success in modelling a range of shock initiation and detonation propagation phenomena in polymer bonded explosives. CREST uses empirical reaction rates that depend on a function of the entropy of the non-reacted explosive, allowing the effects of initial temperature, porosity and double-shock desensitisation to be simulated without any modifications to the model. Until now, the sixteen reaction-rate coefficients have been manually calibrated by trial and error, using hydrocode simulations of a subset of sustained-shock initiation gas-gun experiments and the detonation size-effect curve for the explosive. This paper will describe the initial development of an automatic method for calibrating CREST reaction-rate coefficients, using the well-established Particle Swarm Optimisation (PSO) technique. The automatic method submits multiple hydrocode simulations for each ``particle'' and analyses the results to determine the ``misfit'' to gas-gun and size-effect data. Over ~40 ``generations,'' the PSO code finds a best set of reaction-rate coefficients that minimises the misfit. The method will be demonstrated by developing a new CREST model for EDC32, a conventional high explosive.

  9. Measurement of proton transfer reaction rates in a microwave cavity discharge flowing afterglow

    NASA Astrophysics Data System (ADS)

    Brooke, George M., IV

    The reaction rate coefficients between the hydronium ion and the molecules ethene (C2H4), propene (C 3H6), 1-butene (C4H8) and hydrogen sulfide (H2S) were measured at 296 K. The measured reaction rates were compared to collision rates calculated using average dipole orientation (ADO) theory. Reaction efficiency depends primarily upon the proton affinity of the molecules. All the measurements were obtained using the newly developed microwave cavity discharge flowing afterglow (MCD-FA) apparatus. This device uses an Asmussen-type microwave cavity discharge ion source that is spatially separated from the flow tube, eliminating many of the problems inherent with the original FA devices. In addition to measuring reaction rate coefficients, the MCD-FA was shown to be an effective tool for measuring trace compounds in atmospheric air. This method has many advantages over current detection techniques since compounds can be detected in almost real time, large mass ranges can be scanned quickly, and repeated calibration is not required. Preliminary measurements were made of car exhaust and exhaled alveolar air. Car exhaust showed the presence of numerous hydrocarbons, such as butene, benzene and toluene while the exhaled alveolar air showed the presence of various volatile organic compounds such as methanol and acetone.

  10. Generalization of the Activated Complex Theory of Reaction Rates. II. Classical Mechanical Treatment

    DOE R&D Accomplishments Database

    Marcus, R. A.

    1964-01-01

    In its usual classical form activated complex theory assumes a particular expression for the kinetic energy of the reacting system -- one associated with a rectilinear motion along the reaction coordinate. The derivation of the rate expression given in the present paper is based on the general kinetic energy expression.

  11. Relative Reaction Rates of Sulfamic Acid and Hydroxylamine with Nitric Acid

    SciTech Connect

    Karraker, D.G.

    2001-03-28

    This report describes a study of comparative reaction rates where the reductant is in excess, as in the 1B bank in the Purex process. The results of this work apply to planned plant tests to partially substitute HAN for the ferrous sulfamate reductant in the Purex 1B bank.

  12. Effect of Conceptual Change Approach on Students' Understanding of Reaction Rate Concepts

    ERIC Educational Resources Information Center

    Kingir, Sevgi; Geban, Omer

    2012-01-01

    The purpose of the present study was to investigate the effect of conceptual change text oriented instruction compared to traditional instruction on 10th grade students' understanding of reaction rate concepts. 45 students from two classes of the same teacher in a public high school participated in this study. Students in the experimental group…

  13. Rate of reaction of superoxide radical with chloride-containing species

    SciTech Connect

    Long, C.A.; Bielski, B.H.J.

    1980-01-01

    This paper evaluates the rate constants for the reaction of superoxide radical with five common chloride-containing species (Cl/sup -/, ClO/sup -/, ClO/sub 2//sup -/, ClO/sub 3//sup -/, and ClO/sub 4//sup -/ and proposes a mechanism for those which react.

  14. Should thermostatted ring polymer molecular dynamics be used to calculate thermal reaction rates?

    SciTech Connect

    Hele, Timothy J. H.; Suleimanov, Yury V.

    2015-08-21

    We apply Thermostatted Ring Polymer Molecular Dynamics (TRPMD), a recently proposed approximate quantum dynamics method, to the computation of thermal reaction rates. Its short-time transition-state theory limit is identical to rigorous quantum transition-state theory, and we find that its long-time limit is independent of the location of the dividing surface. TRPMD rate theory is then applied to one-dimensional model systems, the atom-diatom bimolecular reactions H + H{sub 2}, D + MuH, and F + H{sub 2}, and the prototypical polyatomic reaction H + CH{sub 4}. Above the crossover temperature, the TRPMD rate is virtually invariant to the strength of the friction applied to the internal ring-polymer normal modes, and beneath the crossover temperature the TRPMD rate generally decreases with increasing friction, in agreement with the predictions of Kramers theory. We therefore find that TRPMD is approximately equal to, or less accurate than, ring polymer molecular dynamics for symmetric reactions, and for certain asymmetric systems and friction parameters closer to the quantum result, providing a basis for further assessment of the accuracy of this method.

  15. Rate Coefficients for the OH + (CHO)2 (Glyoxal) Reaction Between 240 and 400 K

    NASA Astrophysics Data System (ADS)

    Feierabend, K. J.; Talukdar, R. K.; Zhu, L.; Ravishankara, A. R.; Burkholder, J. B.

    2006-12-01

    Glyoxal (CHO)2, the simplest dialdehyde, is an end product formed in the atmospheric oxidation of biogenic hydrocarbons, for example, isoprene. As such, glyoxal plays a role in regional air quality and ozone production in certain locations. Glyoxal is lost in the atmosphere via UV photolysis and reaction with OH. However, the currently available rate coefficient data for the OH + glyoxal reaction is limited to a single room- temperature measurement made using the relative rate method. A determination of the rate coefficient temperature dependence is therefore needed for a more complete interpretation of the atmospheric processing of glyoxal. This study reports the rate coefficient for the OH + (CHO)2 reaction measured under pseudo- first-order conditions in OH ([(CHO)2] > 1000 [OH]0). OH radicals were produced using 248 nm pulsed laser photolysis of H2O2 or HNO3 and detected by pulsed laser induced fluorescence. The concentration of glyoxal in the reactor was determined using three independent techniques; gas flow rates as well as in situ UV and IR absorption. The total pressure in the reactor was varied from 40 to 300 Torr (He), and the rate coefficient was found to be independent of pressure over the temperature range studied. The rate coefficient exhibits a negative temperature dependence between 240 and 400 K consistent with the dependence previously observed for many other aldehydes. Our room-temperature rate coefficient is smaller than the relative rate value that is currently recommended for use in atmospheric model calculations. Our measured rate coefficients are discussed with respect to those for other aldehydes. The atmospheric implications of our work will also be discussed.

  16. Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer

    USGS Publications Warehouse

    Green, C.T.; Böhlke, J.K.; Bekins, B.A.; Phillips, S.P.

    2010-01-01

    Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field-scale (apparent) estimated reaction rates and isotopic fractionations and local-scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and field observations were used to study the effects of physical heterogeneity on reaction parameter estimates. Field measurements included major ions, age tracers, stable isotopes, and dissolved gases. Parameters were estimated for the O2 reduction rate, denitrification rate, O 2 threshold for denitrification, and stable N isotope fractionation during denitrification. For multiple geostatistical realizations of the aquifer, inverse modeling was used to establish reactive transport simulations that were consistent with field observations and served as a basis for numerical experiments to compare sample-based estimates of "apparent" parameters with "true" (intrinsic) values. For this aquifer, non-Gaussian dispersion reduced the magnitudes of apparent reaction rates and isotope fractionations to a greater extent than Gaussian mixing alone. Apparent and true rate constants and fractionation parameters can differ by an order of magnitude or more, especially for samples subject to slow transport, long travel times, or rapid reactions. The effect of mixing on apparent N isotope fractionation potentially explains differences between previous laboratory and field estimates. Similarly, predicted effects on apparent O2 threshold values for denitrification are consistent with previous reports of higher values in aquifers than in the laboratory. These results show that hydrogeological complexity substantially influences the interpretation and prediction of reactive transport. ?? 2010 by the American Geophysical Union.

  17. Product distributions, rate constants, and mechanisms of LiH +H reactions

    NASA Astrophysics Data System (ADS)

    Defazio, Paolo; Petrongolo, Carlo; Gamallo, Pablo; González, Miguel

    2005-06-01

    We present a quantum-mechanical investigation of the LiH depletion reaction LiH +H→Li+H2 and of the H exchange reaction LiH +H'→LiH'+H. We report product distributions, rate constant, and mechanism of the former, and rate constant and mechanism of the latter reaction. We use the potential-energy surface by Dunne et al. [Chem. Phys. Lett. 336, 1 (2001)], the real-wave-packet method by Gray and Balint-Kurti [J. Chem. Phys. 108, 950 (1998)], and the J-shifting approximation. The H21 nuclear-spin statistics and progressions of vib-rotational states (v',j') rule both initial-state-resolved and thermal product distributions, which have saw-toothed shapes with odd j' preferred with respect to even j'. At high collision energies and temperatures, we obtain a regular 3-to-1 intensity alternation of rotational states. At low collision energies and temperatures, the degeneracy and density of many H2 levels can, however, give more irregular distributions. During the collision, the energy flows from the reactant translational mode to the product vibration and recoil ones. The rate constants of both reactions are not Arrhenius type because the reactions are barrier-less. The low-temperature, LiH depletion rate constant is larger than the H exchange one, whereas the contrary holds at high temperature. The real-time mechanisms show the nuclear rearrangements of the nonreactive channel and of the reactive ones, and point out that the LiH depletion is preferred over the H exchange at short times. This confirms the rate-constant results.

  18. Automated Prediction of Catalytic Mechanism and Rate Law Using Graph-Based Reaction Path Sampling.

    PubMed

    Habershon, Scott

    2016-04-12

    In a recent article [ J. Chem. Phys. 2015 , 143 , 094106 ], we introduced a novel graph-based sampling scheme which can be used to generate chemical reaction paths in many-atom systems in an efficient and highly automated manner. The main goal of this work is to demonstrate how this approach, when combined with direct kinetic modeling, can be used to determine the mechanism and phenomenological rate law of a complex catalytic cycle, namely cobalt-catalyzed hydroformylation of ethene. Our graph-based sampling scheme generates 31 unique chemical products and 32 unique chemical reaction pathways; these sampled structures and reaction paths enable automated construction of a kinetic network model of the catalytic system when combined with density functional theory (DFT) calculations of free energies and resultant transition-state theory rate constants. Direct simulations of this kinetic network across a range of initial reactant concentrations enables determination of both the reaction mechanism and the associated rate law in an automated fashion, without the need for either presupposing a mechanism or making steady-state approximations in kinetic analysis. Most importantly, we find that the reaction mechanism which emerges from these simulations is exactly that originally proposed by Heck and Breslow; furthermore, the simulated rate law is also consistent with previous experimental and computational studies, exhibiting a complex dependence on carbon monoxide pressure. While the inherent errors of using DFT simulations to model chemical reactivity limit the quantitative accuracy of our calculated rates, this work confirms that our automated simulation strategy enables direct analysis of catalytic mechanisms from first principles. PMID:26938837

  19. Refinement of the aeronomically determined rate coefficient for the reaction of N2/+/ with O

    NASA Technical Reports Server (NTRS)

    Torr, D. G.

    1979-01-01

    An earlier aeronomic determination of the rate coefficient for the reaction N2(+) + O yields NO(+) + N using Atmosphere Explorer data indicated a small increase in the rate coefficient with ion temperature, contrary to laboratory observations. This was incorrectly attributed to neglect of an increase in the N2(+) recombination rate with vibrational excitation. Recent aeronomical results have shown that the rate coefficient for charge exchange of O(+)(2D) with N2 is about an order of magnitude smaller at thermal temperatures than at energies greater than 0.5 eV (i.e., energies at which laboratory measurements have been made). It is shown that the use of the smaller charge exchange rate coefficient coupled with recent results on N2 quenching of O(+)(2D) yields a temperature dependence in excellent agreement with the laboratory results for the rate coefficient.

  20. Correcting reaction rates measured by saturation-transfer magnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Gabr, Refaat E.; Weiss, Robert G.; Bottomley, Paul A.

    2008-04-01

    Off-resonance or spillover irradiation and incomplete saturation can introduce significant errors in the estimates of chemical rate constants measured by saturation-transfer magnetic resonance spectroscopy (MRS). Existing methods of correction are effective only over a limited parameter range. Here, a general approach of numerically solving the Bloch-McConnell equations to calculate exchange rates, relaxation times and concentrations for the saturation-transfer experiment is investigated, but found to require more measurements and higher signal-to-noise ratios than in vivo studies can practically afford. As an alternative, correction formulae for the reaction rate are provided which account for the expected parameter ranges and limited measurements available in vivo. The correction term is a quadratic function of experimental measurements. In computer simulations, the new formulae showed negligible bias and reduced the maximum error in the rate constants by about 3-fold compared to traditional formulae, and the error scatter by about 4-fold, over a wide range of parameters for conventional saturation transfer employing progressive saturation, and for the four-angle saturation-transfer method applied to the creatine kinase (CK) reaction in the human heart at 1.5 T. In normal in vivo spectra affected by spillover, the correction increases the mean calculated forward CK reaction rate by 6-16% over traditional and prior correction formulae.

  1. Reaction and internal energy relaxation rates in viscous thermochemically non-equilibrium gas flows

    SciTech Connect

    Kustova, E. V.; Oblapenko, G. P.

    2015-01-15

    In the present paper, reaction and energy relaxation rates as well as the normal stress are studied for viscous gas flows with vibrational and chemical non-equilibrium. Using the modified Chapman-Enskog method, multi-temperature models based on the Treanor and Boltzmann vibrational distributions are developed for the general case taking into account all kinds of vibrational energy transitions, exchange reactions, dissociation, and recombination. Integral equations specifying the first-order corrections to the normal mean stress and reaction rates are derived, as well as approximate systems of linear equations for their numerical computation. Generalized thermodynamic driving forces associated with all non-equilibrium processes are introduced. It is shown that normal stresses and rates of non-equilibrium processes can be expressed in terms of the same driving forces; the symmetry of kinetic coefficients in these expressions is proven. The developed general model is applied to a particular case of a pure N{sub 2} viscous flow with slow VT relaxation. Normal stress and rates of vibrational relaxation are studied for various ratios of vibrational and translational temperatures. The cross effects between different vibrational transitions in viscous flows are evaluated, along with the influence of anharmonicity and flow compressibility on the first-order corrections to the relaxation rate. Limits of validity for the widely used Landau–Teller model of vibrational relaxation are indicated.

  2. Rate Constant and Reaction Coordinate of Trp-Cage Folding in Explicit Water

    PubMed Central

    Juraszek, Jarek; Bolhuis, Peter G.

    2008-01-01

    We report rate constant calculations and a reaction coordinate analysis of the rate-limiting folding and unfolding process of the Trp-cage mini-protein in explicit solvent using transition interface sampling. Previous transition path sampling simulations revealed that in this (un)folding process the protein maintains its compact configuration, while a (de)increase of secondary structure is observed. The calculated folding rate agrees reasonably with experiment, while the unfolding rate is 10 times higher. We discuss possible origins for this mismatch. We recomputed the rates with the forward flux sampling method, and found a discrepancy of four orders of magnitude, probably caused by the method's higher sensitivity to the choice of order parameter with respect to transition interface sampling. Finally, we used the previously computed transition path-sampling ensemble to screen combinations of many order parameters for the best model of the reaction coordinate by employing likelihood maximization. We found that a combination of the root mean-square deviation of the helix and of the entire protein was, of the set of tried order parameters, the one that best describes the reaction coordination. PMID:18676648

  3. Estimating Reaction Rate Coefficients Within a Travel-Time Modeling Framework

    SciTech Connect

    Gong, R; Lu, C; Luo, Jian; Wu, Wei-min; Cheng, H.; Criddle, Craig; Kitanidis, Peter K.; Gu, Baohua; Watson, David B; Jardine, Philip M; Brooks, Scott C

    2011-03-01

    A generalized, efficient, and practical approach based on the travel-time modeling framework is developed to estimate in situ reaction rate coefficients for groundwater remediation in heterogeneous aquifers. The required information for this approach can be obtained by conducting tracer tests with injection of a mixture of conservative and reactive tracers and measurements of both breakthrough curves (BTCs). The conservative BTC is used to infer the travel-time distribution from the injection point to the observation point. For advection-dominant reactive transport with well-mixed reactive species and a constant travel-time distribution, the reactive BTC is obtained by integrating the solutions to advective-reactive transport over the entire travel-time distribution, and then is used in optimization to determine the in situ reaction rate coefficients. By directly working on the conservative and reactive BTCs, this approach avoids costly aquifer characterization and improves the estimation for transport in heterogeneous aquifers which may not be sufficiently described by traditional mechanistic transport models with constant transport parameters. Simplified schemes are proposed for reactive transport with zero-, first-, nth-order, and Michaelis-Menten reactions. The proposed approach is validated by a reactive transport case in a two-dimensional synthetic heterogeneous aquifer and a field-scale bioremediation experiment conducted at Oak Ridge, Tennessee. The field application indicates that ethanol degradation for U(VI)-bioremediation is better approximated by zero-order reaction kinetics than first-order reaction kinetics.

  4. 5 CFR 530.306 - Evaluating agency requests for new or increased special rates.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... problems, including the superior qualifications and special needs pay-setting authority in 5 CFR 531.212 and recruitment, relocation, and retention incentives under 5 CFR part 575; (7) The degree to which an agency has considered relevant non-pay solutions to staffing problems, such as conducting an...

  5. Rate constant for the reaction of atomic chlorine with formaldehyde from 200 to 500 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Nava, D. F.; Payne, W. A.

    1979-01-01

    The absolute rate constant for the reaction of atomic chlorine with formaldehyde has been measured from 200 to 500 K using the flash photolysis-resonance fluorescence technique. The results were independent of substantial variations in (H2CO), total pressure (Ar), and flash intensity (i.e., initial (Cl)). The rate constant was shown to be invariant with temperature, the best representation for this temperature range being k-sub-1 = (7.48 + or - 0.50) times 10 to the -11 cu cm/molecule sec, where the error is one standard deviation. This result is compared with the only previous determination of k-sub-1, which was a relative value obtained at 298 K. The rate constant is theoretically discussed, and the potential importance of the reaction in stratospheric chemistry is considered.

  6. Reaction rate kinetics for in situ combustion retorting of Michigan Antrim oil shale

    USGS Publications Warehouse

    Rostam-Abadi, M.; Mickelson, R.W.

    1984-01-01

    The intrinsic reaction rate kinetics for the pyrolysis of Michigan Antrim oil shale and the oxidation of the carbonaceous residue of this shale have been determined using a thermogravimetric analysis method. The kinetics of the pyrolysis reaction were evaluated from both isothermal and nonisothermal rate data. The reaction was found to be second-order with an activation energy of 252.2 kJ/mole, and with a frequency factor of 9.25 ?? 1015 sec-1. Pyrolysis kinetics were not affected by heating rates between 0.01 to 0.67??K/s. No evidence of any reactions among the oil shale mineral constituents was observed at temperatures below 1173??K. However, it was found that the presence of pyrite in oil shale reduces the primary devolatilization rate of kerogen and increases the amount of residual char in the spent shale. Carbonaceous residues which were prepared by heating the oil shale at a rate of 0.166??K/s to temperatures between 923??K and 1073??K, had the highest reactivities when oxidized at 0.166??K/s in a gas having 21 volume percent oxygen. Oxygen chemisorption was found to be the initial precursor to the oxidation process. The kinetics governing oxygen chemisorption is (Equation Presented) where X is the fractional coverage. The oxidation of the carbonaceous residue was found also to be second-order. The activation energy and the frequency factor determined from isothermal experiments were 147 kJ/mole and 9.18??107 sec-1 respectively, while the values of these parameters obtained from a nonisothermal experiment were 212 kJ/mole and 1.5??1013 sec-1. The variation in the rate constants is attributed to the fact that isothermal and nonisothermal analyses represent two different aspects of the combustion process.

  7. Rate constants for the slow Mu + propane abstraction reaction at 300 K by diamagnetic RF resonance.

    PubMed

    Fleming, Donald G; Cottrell, Stephen P; McKenzie, Iain; Ghandi, Khashayar

    2015-08-14

    The study of kinetic isotope effects for H-atom abstraction rates by incident H-atoms from the homologous series of lower mass alkanes (CH4, C2H6 and, here, C3H8) provides important tests of reaction rate theory on polyatomic systems. With a mass of only 0.114 amu, the most sensitive test is provided by the rates of the Mu atom. Abstraction of H by Mu can be highly endoergic, due to the large zero-point energy shift in the MuH bond formed, which also gives rise to high activation energies from similar zero-point energy corrections at the transition state. Rates are then far too slow near 300 K to be measured by conventional TF-μSR techniques that follow the disappearance of the spin-polarised Mu atom with time. Reported here is the first measurement of a slow Mu reaction rate in the gas phase by the technique of diamagnetic radio frequency (RF) resonance, where the amplitude of the MuH product formed in the Mu + C3H8 reaction is followed with time. The measured rate constant, kMu = (6.8 ± 0.5) × 10(-16) cm(3) s(-1) at 300 K, is surprisingly only about a factor of three slower than that expected for H + C3H8, indicating a dominant contribution from quantum tunneling in the Mu reaction, consistent with elementary transition state theory calculations of the kMu/kH kinetic isotope effect. PMID:26165545

  8. Determination of reaction rates and activation energy in aerobic composting processes for yard waste.

    PubMed

    Uma, R N; Manjula, G; Meenambal, T

    2007-04-01

    The reaction rates and activation energy in aerobic composting processes for yard waste were determined using specifically designed reactors. Different mixture ratios were fixed before the commencement of the process. The C/N ratio was found to be optimum for a mixture ratio of 1:6 containing one part of coir pith to six parts of other waste which included yard waste, yeast sludge, poultry yard waste and decomposing culture (Pleurotosis). The path of stabilization of the wastes was continuously monitored by observing various parameters such as temperature, pH, Electrical Conductivity, C.O.D, VS at regular time intervals. Kinetic analysis was done to determine the reaction rates and activation energy for the optimum mixture ratio under forced aeration condition. The results of the analysis clearly indicated that the temperature dependence of the reaction rates followed the Arrhenius equation. The temperature coefficients were also determined. The degradation of the organic fraction of the yard waste could be predicted using first order reaction model. PMID:18476403

  9. Solvation effect on kinetic rate constant of reactions in supercritical solvents

    SciTech Connect

    Chialvo, A.A.; Cummings, P.T. |; Kalyuzhnyi, Yu.V.

    1998-03-01

    A statistical mechanical analysis of the solvation effects on the kinetic rate constants of reactions in near and supercritical solvents is presented to understand the experimental findings regarding the thermodynamic pressure effects. This is an extension of the solvation formalism of Chialvo and Cummings to the analysis of the microscopic basis for the macroscopic pressure and temperature effects on the kinetic rate constants of reactions conducted in the compressible region of the solvent phase diagram. This analysis is illustrated with integral equations calculations involving Lennard-Jones infinitely dilute quaternary systems to describe the species in solution during the reaction of triplet benzophenone ({sup 3}BP) with a cosolvent (either O{sub 2} or 1,4-cyclohexadiene) in supercritical CO{sub 2} along the supercritical isotherms T{sub r} = 1.01 and 1.06. The role of the species molecular asymmetries and consequently their solvation behavior in determining the thermodynamic pressure and temperature effects on the kinetic rate constant of reactions at near-critical conditions are discussed.

  10. Benchmark experiments for validation of reaction rates determination in reactor dosimetry

    NASA Astrophysics Data System (ADS)

    Rataj, J.; Huml, O.; Heraltova, L.; Bily, T.

    2014-11-01

    The precision of Monte Carlo calculations of quantities of neutron dosimetry strongly depends on precision of reaction rates prediction. Research reactor represents a very useful tool for validation of the ability of a code to calculate such quantities as it can provide environments with various types of neutron energy spectra. Especially, a zero power research reactor with well-defined core geometry and neutronic properties enables precise comparison between experimental and calculated data. Thus, at the VR-1 zero power research reactor, a set of benchmark experiments were proposed and carried out to verify the MCNP Monte Carlo code ability to predict correctly the reaction rates. For that purpose two frequently used reactions were chosen: He-3(n,p)H-3 and Au-197(n,γ)Au-198. The benchmark consists of response measurement of small He-3 gas filled detector in various positions of reactor core and of activated gold wires placed inside the core or to its vicinity. The reaction rates were calculated in MCNP5 code utilizing a detailed model of VR-1 reactor which was validated for neutronic calculations at the reactor. The paper describes in detail the experimental set-up of the benchmark, the MCNP model of the VR-1 reactor and provides a comparison between experimental and calculated data.

  11. Rate Constant and Temperature Dependence for the Reaction of Hydroxyl Radicals with 2-Flouropropane (FC-281ea) and Comparison with an Estimated Rate Constant

    NASA Technical Reports Server (NTRS)

    DeMore, W.; Wilson, E., Jr.

    1998-01-01

    Relative rate experiments were used to measure the rate constant and temperature dependence of the reaction of OH radicals with 2-fluoropropane (HFC-281ea), using ethane, propane, ethyl chloride as reference standards.

  12. Theoretical investigation on H abstraction reaction mechanisms and rate constants of Isoflurane with the OH radical

    NASA Astrophysics Data System (ADS)

    Ren, Hongjiang; Li, Xiaojun

    2015-12-01

    The mechanism of H abstraction reactions for Isoflurane with the OH radical was investigated using density functional theory and G3(MP2) duel theory methods. The geometrical structures of all the species were fully optimised at B3LYP/6-311++G** level of theory. Thermochemistry data were obtained by utilising the high accurate model chemistry method G3(MP2) combined with the standard statistical thermodynamic calculations. Gibbs free energies were used for the reaction channels analysis. All the reaction channels were confirmed throughout the intrinsic reaction coordinate analysis. The results show that two channels were obtained, which correspond to P(1) and P(2) with the respective activation barriers of 63.03 and 54.82 kJ/mol. The rate constants for the two channels over a wide temperature range of 298.15-2000 K were predicted and the calculated data are in agreement with the experimental one. The results show that P(2) is the dominant reaction channel under 800 K and above 800 K, it can be found that P(1) will be more preferable reaction channel.

  13. Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction

    SciTech Connect

    Scott C. Brooks; Wenming Dong; Sue Carroll; James K. Fredrickson; Kenneth M. Kemner; Shelly D. Kelly

    2006-06-01

    The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. (2) Elucidate the controls on the rate and extent of contaminant reactivity. (3) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions.

  14. A new theoretical approach to thermonuclear radiative-capture reaction rate

    SciTech Connect

    Funaki, Yasuro; Yabana, Kazuhiro; Akahori, Takahiko

    2012-11-12

    We propose a new computational method for astrophysical reaction rate of radiative capture process, which does not require any solution of scattering problem. It is tested for twobody radiative caputure reaction {sup 16}O({alpha},{gamma}){sup 20}Ne and a comparison is made with an ordinary method solving two-body scattering problem. The method is shown to work well in practice and thus will be useful for problems in which an explicit construction of scattering solution is difficult such as the triple-alpha capture process.

  15. Rates for neutron-capture reactions on tungsten isotopes in iron meteorites. [Abstract only

    NASA Technical Reports Server (NTRS)

    Masarik, J.; Reedy, R. C.

    1994-01-01

    High-precision W isotopic analyses by Harper and Jacobsen indicate the W-182/W-183 ratio in the Toluca iron meteorite is shifted by -(3.0 +/- 0.9) x 10(exp -4) relative to a terrestrial standard. Possible causes of this shift are neutron-capture reactions on W during Toluca's approximately 600-Ma exposure to cosmic ray particles or radiogenic growth of W-182 from 9-Ma Hf-182 in the silicate portion of the Earth after removal of W to the Earth's core. Calculations for the rates of neutron-capture reactions on W isotopes were done to study the first possibility. The LAHET Code System (LCS) which consists of the Los Alamos High Energy Transport (LAHET) code and the Monte Carlo N-Particle(MCNP) transport code was used to numerically simulate the irradiation of the Toluca iron meteorite by galactic-cosmic-ray (GCR) particles and to calculate the rates of W(n, gamma) reactions. Toluca was modeled as a 3.9-m-radius sphere with the composition of a typical IA iron meteorite. The incident GCR protons and their interactions were modeled with LAHET, which also handled the interactions of neutrons with energies above 20 MeV. The rates for the capture of neutrons by W-182, W-183, and W-186 were calculated using the detailed library of (n, gamma) cross sections in MCNP. For this study of the possible effect of W(n, gamma) reactions on W isotope systematics, we consider the peak rates. The calculated maximum change in the normalized W-182/W-183 ratio due to neutron-capture reactions cannot account for more than 25% of the mass 182 deficit observed in Toluca W.

  16. Reaction of atomic bromine with acetylene and loss rate of atmospheric acetylene due to reaction with OH, Cl, O, and Br

    NASA Technical Reports Server (NTRS)

    Payne, W. A.; Nava, D. F.; Brunning, J.; Stief, L. J.

    1986-01-01

    The first-order, diffusion, and bimolecular rate constants for the reaction Br + C2H2 yields C2H3Br are evaluated. The rate constants are measured at 210, 248, 298, and 393 K and at pressures between 15-100 torr Ar using flash photolysis combined with time-resolved detection of atomic bromine via Br resonance radiation. It is observed that the reaction is not affected by pressure or temperature and the bimolecular constant = (4.0 + or - 0.8) x 10 to the -15th cu cm/sec with an error of two standard deviations. The C2H2 + Br reaction rates are compared with reactions of C2H2 with Cl, OH, NH2, and H. The loss rates for atmospheric C2H2 for reactions with OH, Cl, O, and Br are calculated as a function of altitude.

  17. Accurate label-free reaction kinetics determination using initial rate heat measurements

    PubMed Central

    Ebrahimi, Kourosh Honarmand; Hagedoorn, Peter-Leon; Jacobs, Denise; Hagen, Wilfred R.

    2015-01-01

    Accurate label-free methods or assays to obtain the initial reaction rates have significant importance in fundamental studies of enzymes and in application-oriented high throughput screening of enzyme activity. Here we introduce a label-free approach for obtaining initial rates of enzyme activity from heat measurements, which we name initial rate calorimetry (IrCal). This approach is based on our new finding that the data recorded by isothermal titration calorimetry for the early stages of a reaction, which have been widely ignored, are correlated to the initial rates. Application of the IrCal approach to various enzymes led to accurate enzyme kinetics parameters as compared to spectroscopic methods and enabled enzyme kinetic studies with natural substrate, e.g. proteases with protein substrates. Because heat is a label-free property of almost all reactions, the IrCal approach holds promise in fundamental studies of various enzymes and in use of calorimetry for high throughput screening of enzyme activity. PMID:26574737

  18. Substituent effects on the reaction rates of hydrogen abstraction in the pyrolysis of phenethyl phenyl ethers

    SciTech Connect

    Beste, Ariana; Buchanan III, A C

    2010-01-01

    We report reaction profiles and forward rate constants for hydrogen abstraction reactions occurring in the pyrolysis of methoxy-substituted derivatives of phenethyl phenyl ether (PhCH{sub 2}CH{sub 2}OPh, PPE), where the substituents are located on the aryl ether ring (PhCH{sub 2}CH{sub 2}OPh-X). We use density functional theory in combination with transition-state theory, and anharmonic corrections are included within the independent mode approximation. PPE is the simplest model of the abundant {beta}-O-4 linkage in lignin. The mechanism of PPE pyrolysis and overall product selectivities have been studied experimentally by one of us, which was followed by computational analysis of key individual hydrogen-transfer reaction steps. In the previous work, we have been able to use a simplified kinetic model based on quasi-steady-state conditions to reproduce experimental {alpha}/{beta} selectivities for PPE and PPEs with substituents on the phenethyl ring (X-PhCH{sub 2}CH{sub 2}OPh). This model is not applicable to PPE derivatives where methoxy substituents are located on the phenyl ring adjacent to the ether oxygen because of the strongly endothermic character of the hydrogen abstraction by substituted phenoxy radicals as well as the decreased kinetic chain lengths resulting from enhanced rates of the initial C?O homolysis step. Substituents decelerate the hydrogen abstraction by the phenoxy radical, while the influence on the benzyl abstraction is less homogeneous. The calculations provide insight into the contributions of steric and polar effects in these important hydrogen-transfer steps. We emphasize the importance of an exhaustive conformational space search to calculate rate constants and product selectivities. The computed rate constants will be used in future work to numerically simulate the pyrolysis mechanism, pending the calculation of the rate constants of all participating reactions.

  19. Light elements burning reaction rates at stellar temperatures as deduced by the Trojan Horse measurements

    SciTech Connect

    Lamia, L.; Spitaleri, C.; La Cognata, M.; Palmerini, S.; Sergi, M. L.; Puglia, S. M. R.

    2015-02-24

    Experimental nuclear astrophysics aims at determining the reaction rates for astrophysically relevant reactions at their Gamow energies. For charged-particle induced reactions, the access to these energies is usually hindered, in direct measurements, by the presence of the Coulomb barrier between the interacting particles or by electron screening effects, which make hard the determination of the bare-nucleus S(E)-factor of interest for astrophysical codes. The use of the Trojan Horse Method (THM) appears as one of the most suitable tools for investigating nuclear processes of interest for astrophysics. Here, in view of the recent TH measurements, the main destruction channels for deuterium ({sup 2}H), for the two lithium {sup 6,7}Li isotopes, for the {sup 9}Be and the one for the two boron {sup 10,11}B isotopes will be discussed.

  20. On the Rate and Mechanism of Proton Transfer Reactions in Proteins

    NASA Astrophysics Data System (ADS)

    Xie, Aihua; Li, Yunxing; Manda, Edward; Nie, Beining; Hoff, Wouter; Martin, Richard

    2009-03-01

    One of the fundamental processes in molecular biology is proton transfer reactions in proteins. Proton transfer is essential for the biological functions of proteins responsible in bioenergetics, biological signaling, and enzymatic catalysis. The mechanism of proton transfer is of great interests in order to understand the structural basis of biological functions. Despite of extensive experimental and computational efforts, it remains elusive what causes a proton to move from the proton donor to the proton acceptor. We will report a proof of concept study regarding a general mechanism of internal proton transfer reactions in proteins. Density functional theory, B3LYP/6-311+G(2d,p), is employed in this study. The results of our study provide deep insights into the structural basis to the rate and mechanism of proton transfer reactions in proteins, such as bacteriorhodopsin and green fluorescence protein.

  1. Light elements burning reaction rates at stellar temperatures as deduced by the Trojan Horse measurements

    NASA Astrophysics Data System (ADS)

    Lamia, L.; Spitaleri, C.; La Cognata, M.; Palmerini, S.; Puglia, S. M. R.; Sergi, M. L.

    2015-02-01

    Experimental nuclear astrophysics aims at determining the reaction rates for astrophysically relevant reactions at their Gamow energies. For charged-particle induced reactions, the access to these energies is usually hindered, in direct measurements, by the presence of the Coulomb barrier between the interacting particles or by electron screening effects, which make hard the determination of the bare-nucleus S(E)-factor of interest for astrophysical codes. The use of the Trojan Horse Method (THM) appears as one of the most suitable tools for investigating nuclear processes of interest for astrophysics. Here, in view of the recent TH measurements, the main destruction channels for deuterium (2H ), for the two lithium 6,7Li isotopes, for the 9Be and the one for the two boron 10,11B isotopes will be discussed.

  2. 5 CFR 591.229 - How does OPM inform agencies and employees of COLA rate changes?

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... COLA rate changes? OPM publishes COLA area survey summary reports, MEG and PEG indexes, and COLA rates in the Federal Register. OPM makes survey data and other information available to the public to...

  3. 5 CFR 591.229 - How does OPM inform agencies and employees of COLA rate changes?

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... COLA rate changes? OPM publishes COLA area survey summary reports, MEG and PEG indexes, and COLA rates in the Federal Register. OPM makes survey data and other information available to the public to...

  4. 5 CFR 591.229 - How does OPM inform agencies and employees of COLA rate changes?

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... COLA rate changes? OPM publishes COLA area survey summary reports, MEG and PEG indexes, and COLA rates in the Federal Register. OPM makes survey data and other information available to the public to...

  5. 5 CFR 591.229 - How does OPM inform agencies and employees of COLA rate changes?

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... COLA rate changes? OPM publishes COLA area survey summary reports, MEG and PEG indexes, and COLA rates in the Federal Register. OPM makes survey data and other information available to the public to...

  6. 5 CFR 591.229 - How does OPM inform agencies and employees of COLA rate changes?

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... COLA rate changes? OPM publishes COLA area survey summary reports, MEG and PEG indexes, and COLA rates in the Federal Register. OPM makes survey data and other information available to the public to...

  7. Rate coefficients of hydroxyl radical reactions with pesticide molecules and related compounds: A review

    NASA Astrophysics Data System (ADS)

    Wojnárovits, László; Takács, Erzsébet

    2014-03-01

    Rate coefficients published in the literature on hydroxyl radical reactions with pesticides and related compounds are discussed together with the experimental methods and the basic reaction mechanisms. Recommendations are made for the most probable values. Most of the molecules whose rate coefficients are discussed have aromatic ring: their rate coefficients are in the range of 2×109-1×1010 mol-1 dm3 s-1. The rate coefficients show some variation with the electron withdrawing-donating nature of the substituent on the ring. The rate coefficients for triazine pesticides (simazine, atrazine, prometon) are all around 2.5×109 mol-1 dm3 s-1. The values do not show variation with the substituent on the s-triazine ring. The rate coefficients for the non-aromatic molecules which have C=C double bonds or several C-H bonds may also be above 1×109 mol-1 dm3 s-1. However, the values for molecules without C=C double bonds or several C-H bonds are in the 1×107-1×109 mol-1 dm3 s-1 range.

  8. Rate constants for reactions between atmospheric reservoir species. 2. H sub 2 O

    SciTech Connect

    Hatakeyama, Shiro; Leu, Mingtaun )

    1989-07-27

    The kinetics of the reactions of H{sub 2}O with ClONO{sub 2}, N{sub 2}O{sub 5}, O{sub 3}, and COCl{sub 2} have been investigated by using a large-volume static cell and a Fourier transform infrared spectrometer at 296 K. Upper limits for the homogeneous gas-phase reaction rate constants of the ClONO{sub 2} + H{sub 2}O, N{sub 2}O{sub 5} + H{sub 2}O, O{sub 3} + H{sub 2}O, and COCl{sub 2} + H{sub 2}O reactions were found to be 3.4 {times} 10{sup {minus}21}, 2.8 {times} 10{sup {minus}21}, 1.1 {times} 10{sup {minus}22}, and 1.2 {times} 10{sup {minus}23}, respectively (all in units of cm{sup 3} s{sup {minus}1}), based on the observed decay rates of ClONO{sub 2}, N{sub 2}O{sub 5}, O{sub 3}, and COCl{sub 2}. Product analyses gave 0.82 {plus minus} 0.07 for the yield of HNO{sub 3} in the ClONO{sub 2} + H{sub 2}O {yields} HOCl + HNO{sub 3} reaction and 1.1 {plus minus} 0.3 for the yield of HNO{sub 3} from the N{sub 2}O{sub 5} + H{sub 2}O {yields} 2HNO{sub 3} reaction. The quoted error represents one standard deviation of the measurement. An attempt was also made to monitor possible reaction products such as H{sub 2}O{sub 2} for the O{sub 3} + H{sub 2}O reaction, and CO{sub 2} or HCl for the COCl{sub 2} + H{sub 2}O reaction. These results may be important in the elucidation of the springtime Antarctic ozone depletion over the past decade. The implication for NO{sub x} chemistry in the nighttime troposphere based on their results of the N{sub 2}O{sub 5} + H{sub 2}O reaction will be discussed.

  9. The effects of physical and geochemical heterogeneities on hydro-geochemical transport and effective reaction rates

    NASA Astrophysics Data System (ADS)

    Atchley, Adam L.; Navarre-Sitchler, Alexis K.; Maxwell, Reed M.

    2014-09-01

    The role of coupled physical and geochemical heterogeneities in hydro-geochemical transport is investigated by simulating three-dimensional transport in a heterogeneous system with kinetic mineral reactions. Ensembles of 100 physically heterogeneous realizations were simulated for three geochemical conditions: 1) spatially homogeneous reactive mineral surface area, 2) reactive surface area positively correlated to hydraulic heterogeneity, and 3) reactive surface area negatively correlated to hydraulic heterogeneity. Groundwater chemistry and the corresponding effective reaction rates were calculated at three transverse planes to quantify differences in plume evolution due to heterogeneity in mineral reaction rates and solute residence time (τ). The model is based on a hypothetical CO2 intrusion into groundwater from a carbon capture utilization and storage (CCUS) operation where CO2 dissolution and formation of carbonic acid created geochemical dis-equilibrium between fluids and the mineral galena that resulted in increased aqueous lead (Pb2 +) concentrations. Calcite dissolution buffered the pH change and created conditions of galena oversaturation, which then reduced lead concentrations along the flow path. Near the leak kinetic geochemical reactions control the release of solutes into the fluid, but further along the flow path mineral solubility controls solute concentrations. Simulation results demonstrate the impact of heterogeneous distribution of geochemical reactive surface area in coordination with physical heterogeneity on the effective reaction rate (Krxn,eff) and Pb2 + concentrations within the plume. Dissimilarities between ensemble Pb2 + concentration and Krxn,eff are attributed to how geochemical heterogeneity affects the time (τeq) and therefore advection distance (Leq) required for the system to re-establish geochemical equilibrium. Only after geochemical equilibrium is re-established, Krxn,eff and Pb2 + concentrations are the same for all three

  10. The effects of physical and geochemical heterogeneities on hydro-geochemical transport and effective reaction rates.

    PubMed

    Atchley, Adam L; Navarre-Sitchler, Alexis K; Maxwell, Reed M

    2014-09-01

    The role of coupled physical and geochemical heterogeneities in hydro-geochemical transport is investigated by simulating three-dimensional transport in a heterogeneous system with kinetic mineral reactions. Ensembles of 100 physically heterogeneous realizations were simulated for three geochemical conditions: 1) spatially homogeneous reactive mineral surface area, 2) reactive surface area positively correlated to hydraulic heterogeneity, and 3) reactive surface area negatively correlated to hydraulic heterogeneity. Groundwater chemistry and the corresponding effective reaction rates were calculated at three transverse planes to quantify differences in plume evolution due to heterogeneity in mineral reaction rates and solute residence time (τ). The model is based on a hypothetical CO2 intrusion into groundwater from a carbon capture utilization and storage (CCUS) operation where CO2 dissolution and formation of carbonic acid created geochemical dis-equilibrium between fluids and the mineral galena that resulted in increased aqueous lead (Pb(2+)) concentrations. Calcite dissolution buffered the pH change and created conditions of galena oversaturation, which then reduced lead concentrations along the flow path. Near the leak kinetic geochemical reactions control the release of solutes into the fluid, but further along the flow path mineral solubility controls solute concentrations. Simulation results demonstrate the impact of heterogeneous distribution of geochemical reactive surface area in coordination with physical heterogeneity on the effective reaction rate (Krxn,eff) and Pb(2+) concentrations within the plume. Dissimilarities between ensemble Pb(2+) concentration and Krxn,eff are attributed to how geochemical heterogeneity affects the time (τeq) and therefore advection distance (Leq) required for the system to re-establish geochemical equilibrium. Only after geochemical equilibrium is re-established, Krxn,eff and Pb(2+) concentrations are the same for all

  11. Rate constants of chemical reactions from semiclassical transition state theory in full and one dimension

    NASA Astrophysics Data System (ADS)

    Greene, Samuel M.; Shan, Xiao; Clary, David C.

    2016-06-01

    Semiclassical Transition State Theory (SCTST), a method for calculating rate constants of chemical reactions, offers gains in computational efficiency relative to more accurate quantum scattering methods. In full-dimensional (FD) SCTST, reaction probabilities are calculated from third and fourth potential derivatives along all vibrational degrees of freedom. However, the computational cost of FD SCTST scales unfavorably with system size, which prohibits its application to larger systems. In this study, the accuracy and efficiency of 1-D SCTST, in which only third and fourth derivatives along the reaction mode are used, are investigated in comparison to those of FD SCTST. Potential derivatives are obtained from numerical ab initio Hessian matrix calculations at the MP2/cc-pVTZ level of theory, and Richardson extrapolation is applied to improve the accuracy of these derivatives. Reaction barriers are calculated at the CCSD(T)/cc-pVTZ level. Results from FD SCTST agree with results from previous theoretical and experimental studies when Richardson extrapolation is applied. Results from our implementation of 1-D SCTST, which uses only 4 single-point MP2/cc-pVTZ energy calculations in addition to those for conventional TST, agree with FD results to within a factor of 5 at 250 K. This degree of agreement and the efficiency of the 1-D method suggest its potential as a means of approximating rate constants for systems too large for existing quantum scattering methods.

  12. Rate constants of chemical reactions from semiclassical transition state theory in full and one dimension.

    PubMed

    Greene, Samuel M; Shan, Xiao; Clary, David C

    2016-06-28

    Semiclassical Transition State Theory (SCTST), a method for calculating rate constants of chemical reactions, offers gains in computational efficiency relative to more accurate quantum scattering methods. In full-dimensional (FD) SCTST, reaction probabilities are calculated from third and fourth potential derivatives along all vibrational degrees of freedom. However, the computational cost of FD SCTST scales unfavorably with system size, which prohibits its application to larger systems. In this study, the accuracy and efficiency of 1-D SCTST, in which only third and fourth derivatives along the reaction mode are used, are investigated in comparison to those of FD SCTST. Potential derivatives are obtained from numerical ab initio Hessian matrix calculations at the MP2/cc-pVTZ level of theory, and Richardson extrapolation is applied to improve the accuracy of these derivatives. Reaction barriers are calculated at the CCSD(T)/cc-pVTZ level. Results from FD SCTST agree with results from previous theoretical and experimental studies when Richardson extrapolation is applied. Results from our implementation of 1-D SCTST, which uses only 4 single-point MP2/cc-pVTZ energy calculations in addition to those for conventional TST, agree with FD results to within a factor of 5 at 250 K. This degree of agreement and the efficiency of the 1-D method suggest its potential as a means of approximating rate constants for systems too large for existing quantum scattering methods. PMID:27369506

  13. Investigation of Mixing and Chemical Reaction Interactions Using Rate-Controlled Constrained-Equilibrium

    NASA Astrophysics Data System (ADS)

    Hadi, Fatemeh; Janbozorgi, Mohammad; Sheikhi, Reza H.; Metghalchi, Hameed

    2014-11-01

    The Rate-Controlled Constrained-Equilibrium (RCCE) method is applied to study the interaction between mixing and chemical reaction in a constant pressure Partially-Stirred Reactor (PaSR). The objective is to understand the influence of mixing on RCCE predictions. The RCCE is a computationally efficient method based on thermodynamics to implement the combustion chemistry. In the RCCE the dynamics of reacting systems is described by a small number of rate-controlling reactions and slowly-varying constraints. The method is applied to study methane combustion via 12 constraints and 133 reaction steps. Simulations are carried out over a wide range of initial temperatures and equivalence ratios. The RCCE predictions are assessed by comparing with those of detailed kinetics model, in which the same kinetics, involving 29 species and 133 reaction steps, is integrated directly. Chemical kinetics and mixing interactions are studied for different residence and mixing time scales. Results show that the RCCE accurately represents the effect of mixing with different mixing strengths. An assessment of numerical performance of the RCCE is also performed. It is shown that the method is effective to reduce the stiffness of the kinetics and thus allows simulations with much lower computation costs.

  14. Up-Scaling Geochemical Reaction Rates for Carbon Dioxide (CO2) in Deep Saline Aquifers

    SciTech Connect

    Peters, Catherine A

    2013-02-28

    Geochemical reactions in deep subsurface environments are complicated by the consolidated nature and mineralogical complexity of sedimentary rocks. Understanding the kinetics of these reactions is critical to our ability to make long-term predictions about subsurface processes such as pH buffering, alteration in rock structure, permeability changes, and formation of secondary precipitates. In this project, we used a combination of experiments and numerical simulation to bridge the gap between our knowledge of these reactions at the lab scale and rates that are meaningful for modeling reactive transport at core scales. The focus is on acid-driven mineral dissolution, which is specifically relevant in the context of CO2-water-rock interactions in geological sequestration of carbon dioxide. The project led to major findings in three areas. First, we modeled reactive transport in pore-network systems to investigate scaling effects in geochemical reaction rates. We found significant scaling effects when CO2 concentrations are high and reaction rates are fast. These findings indicate that the increased acidity associated with geological sequestration can generate conditions for which proper scaling tools are yet to be developed. Second, we used mathematical modeling to investigate the extent to which SO2, if co-injected with CO2, would acidify formation brines. We found that there exist realistic conditions in which the impact on brine acidity will be limited due to diffusion rate-limited SO2 dissolution from the CO2 phase, and the subsequent pH shift may also be limited by the lack of availability of oxidants to produce sulfuric acid. Third, for three Viking sandstones (Alberta sedimentary basin, Canada), we employed backscattered electron microscopy and energy dispersive X-ray spectroscopy to statistically characterize mineral contact with pore space. We determined that for reactive minerals in sedimentary consolidated rocks, abundance alone is not a good predictor of

  15. Rate of reactions between D 2O and Ca xAl yO z

    NASA Astrophysics Data System (ADS)

    Christensen, A. Nørlund; Lehmann, M. S.

    1984-02-01

    The rate of the reaction between D 2O and the calcium aluminum oxides Ca 3Al 2O 6, Ca 5Al 6O 14, CaAl 2O 4, and CaAl 4O 7 was investigated by on-line neutron diffraction powder methods at temperatures from room temperature to 100°C. The rate of the reaction increases with increasing calcium content of the compounds and with increasing temperature for each of the compounds. The crystallographic stable hydrate Ca 3Al 2(OD) 12 is obtained from CaAl 4O 7 and CaAl 2O 4 at temperatures above 63°C, from Ca 5Al 6O 14 at temperatures above 49°C, and from Ca 3Al 2O 6 at temperatures as low as 7°C.

  16. Reacting gas mixtures in the state-to-state approach: The chemical reaction rates

    SciTech Connect

    Kustova, Elena V.; Kremer, Gilberto M.

    2014-12-09

    In this work chemically reacting mixtures of viscous flows are analyzed within the framework of Boltzmann equation. By applying a modified Chapman-Enskog method to the system of Boltzmann equations general expressions for the rates of chemical reactions and vibrational energy transitions are determined as functions of two thermodynamic forces: the velocity divergence and the affinity. As an application chemically reacting mixtures of N{sub 2} across a shock wave are studied, where the first lowest vibrational states are taken into account. Here we consider only the contributions from the first four single quantum vibrational-translational energy transitions. It is shown that the contribution to the chemical reaction rate related to the affinity is much larger than that of the velocity divergence.

  17. Absolute rate of the reaction of bromine atoms with ozone from 200-360 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Lee, J. H.; Payne, W. A.; Stief, L. J.

    1978-01-01

    The rate constant for the reaction Br + O3 yields BrO + O2 was measured from 200 to 360 K by the technique of flash photolysis coupled to time resolved detection of bromine atoms by resonance fluorescence (FP-RF). Br atoms were produced by the flash photolysis of CH3Br at lambda 165nm.O3 was monitored continuously under reaction conditions by absorption at 253.7 nm. At each of five temperatures the results were independent of substantial variations in O3, total pressure and limited variations in flash intensity. The measured rate constants obeyed the Arrhenius expression, where the error quoted is two standard deviations. Results are compared with previous determinations which employed the discharge flow-mass spectrometric technique.

  18. Absolute rate of the reaction of bromine atoms with ozone from 200 to 360 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Lee, J. H.; Payne, W. A.; Stief, L. J.

    1978-01-01

    The rate constant for the reaction Br + O3 yields BrO + O2 has been measured from 200 to 360 K by the technique of flash photolysis coupled to time resolved detection of bromine atoms by resonance fluorescence (FP-RF). Br atoms were produced by the flash photolysis of CH3Br at a wavelength of 165 nm. O3 concentration was monitored continuously under reaction conditions by absorption at 253.7 nm. At each of five temperatures the results were independent of substantial variations in O3 concentration, total pressure (Ar), and limited variations in flash intensity (i.e., initial Br concentration). The measured rate constants obey the Arrhenius expression, k = (7.74 plus or minus 0.50) x 10 to the -12th exp(-603 plus or minus 16/T) cu cm/molecule/sec, where the error quoted is two standard deviations.

  19. Absolute rate parameters for the reaction of atomic hydrogen with hydrazine

    NASA Technical Reports Server (NTRS)

    Stief, L. J.; Payne, W. A.

    1976-01-01

    Absolute rate parameters for the reaction of atomic hydrogen with hydrazine H + N2H4 yields H2 + N2H3 have been determined in a direct manner using flash photolysis of dilute mixtures of hydrazine in helium and time dependent observation of H via resonance fluorescence. By measuring the H-atom decay under pseudo-first-order conditions, the bimolecular rate constant K sub 1 was obtained over the temperature range 228-400 K. The data were fitted with good linearity to the Arrhenius expression K sub 1 = (9.87 plus or minus 1.17) x 10 to the -12th exp(-2380 plus or minus 100/RT) cu cm/molecule/s. The data were shown to be free of any contributions from secondary reactions involving H as a reactant or product.

  20. 23Na (α,p )26Mg Reaction Rate at Astrophysically Relevant Energies

    NASA Astrophysics Data System (ADS)

    Howard, A. M.; Munch, M.; Fynbo, H. O. U.; Kirsebom, O. S.; Laursen, K. L.; Diget, C. Aa.; Hubbard, N. J.

    2015-07-01

    The production of 26Al in massive stars is sensitive to the 23Na (α,p )26Mg cross section. Recent experimental data suggest the currently recommended cross sections are underestimated by a factor of ˜40 . We present here differential cross sections for the 23Na (α,p )26Mg reaction measured in the energy range Ec .m .=1.7 - 2.5 MeV . Concurrent measurements of Rutherford scattering provide absolute normalizations that are independent of variations in target properties. Angular distributions are measured for both p0 and p1 permitting the determination of total cross sections. The results show no significant deviation from the statistical model calculations upon which the recommended rates are based. We therefore retain the previous recommendation without the increase in cross section and resulting stellar reaction rates by a factor of 40, impacting the 26Al yield from massive stars by more than a factor of 3.

  1. Computational Approach for Ranking Mutant Enzymes According to Catalytic Reaction Rates

    PubMed Central

    Kumarasiri, Malika; Baker, Gregory A.; Soudackov, Alexander V.

    2009-01-01

    A computationally efficient approach for ranking mutant enzymes according to the catalytic reaction rates is presented. This procedure requires the generation and equilibration of the mutant structures, followed by the calculation of partial free energy curves using an empirical valence bond potential in conjunction with biased molecular dynamics simulations and umbrella integration. The individual steps are automated and optimized for computational efficiency. This approach is used to rank a series of 15 dihydrofolate reductase mutants according to the hydride transfer reaction rate. The agreement between the calculated and experimental changes in the free energy barrier upon mutation is encouraging. The computational approach predicts the correct direction of the change in free energy barrier for all mutants, and the correlation coefficient between the calculated and experimental data is 0.82. This general approach for ranking protein designs has implications for protein engineering and drug design. PMID:19235997

  2. Hydrolysis of lanthanide dicarbides: Rates of reaction of cubic and tetragonal solid solutions with water

    SciTech Connect

    McColm, I.J. )

    1993-05-01

    Two series of solid solutions, Ho[sub 1[minus]x]La[sub x]C[sub 2] and Nd[sub 1[minus]x]LaC[sub 2], have been made and their X-ray unit cell parameters measured. The Ho[sub 1[minus]x]La[sub x]C[sub 2] series contains two tetragonal phases and a cubic solid solution series which has enabled the reaction rate constants for the water hydrolysis reaction of a cubic dicarbide phase to be determined for the first time. By comparing the linear rate constants and the activation energies across the two series the nature of bonding in general and the structure of the cubic phase are elucidated. A comparison with microhardness data is made and the change in M-C[sub 2] bonding as a function of composition is considered. 10 refs., 9 figs., 3 tabs.

  3. Rate constant for formation of chlorine nitrate by the reaction ClO + NO2 + M

    NASA Technical Reports Server (NTRS)

    Leu, M. T.; Lin, C. L.; Demore, W. B.

    1977-01-01

    The pseudo-first-order decay of ClO in a large excess of NO2 was monitored in a discharge flow/mass-spectrometer apparatus in order to measure the rate constant of the reaction ClO + NO2 + M yields ClONO2 + M for M = He, Ar, and N2 over the temperature range from 248 to 417 K. Numerical results are given for He at 248, 299, 360, and 417 K (1 to 9 torr); for Ar at 298 K (1 to 4 torr); and for N2 at 299, 360, and 417 K (1 to 6 torr). Systematic errors are estimated, and identification of the reaction product is discussed. The results obtained are shown to be in excellent agreement with other recent measurements of the same rate constant.

  4. Quantitative determination of the steady-state kinetics of multienzyme reactions using the algebraic rate equations for the component single-enzyme reactions.

    PubMed Central

    Stoner, C D

    1993-01-01

    Methods are given whereby the steady-state kinetic characteristics of multienzyme reactions consisting of individual single-enzyme reactions linked by freely diffusible intermediates can be determined quantitatively from the experimentally determined complete algebraic rate equations for the individual reactions. The approach is based on the fact that a valid steady-state rate equation for such a multienzyme reaction, in terms of the rate equations for the individual reactions, can be obtained simply from knowledge of the relative rates of the individual reactions when the multienzyme reaction is in the steady state. A number of model multienzyme reactions, which differ as to structural arrangement of the individual reactions, are examined by this approach. Simple mathematical methods which are applicable to most of these models are given for direct calculation of dependent variables. It is either pointed out or demonstrated with Mathematica that the rate equations for all of these models can be handled very easily with the aid of a personal computer equipped with appropriate equation-solving software. Since the approach permits evaluation of all dependent variables for any specific combination of values for the kinetic parameters and independent variables, numerical values for the flux control coefficients of the individual enzymes can be obtained by direct calculation for a wide variety of conditions and can be compared with those obtained according to the methods of Metabolic Control Analysis. Several such comparisons have been made and in all cases identical results were obtained. The intuitive notion that the individual enzymes of a multienzyme reaction would be equally rate limiting if the total amount of enzyme were being used with maximum efficiency is tested and shown to be incorrect. In the course of this test the flux control coefficient for the individual enzymes were found to be appropriate indicators of relative rate limitation or control by the

  5. Turnover rate, reaction order, and elementary steps for the hydrodechlorination of chlorofluorocarbon compounds on palladium catalysts

    SciTech Connect

    Thompson, C.D.; Rioux, R.M.; Chen, N.; Ribeiro, F.H.

    2000-04-13

    The rates of hydrodechlorination catalyzed by Pd supported on carbon for four chlorofluorocarbons spanned a range of 7 orders of magnitude. The rates scaled up to the bond strength of the carbon-chlorine bond for the gas-phase reactant. This finding demonstrates that the rate-determining step involves the scission of the C-Cl bond and suggests, through Polanyi and linear free-energy relationships, that rates for other compounds can be estimated if the C-Cl bond strength is known. The reaction orders for the most abundant products are approximately first-order for the chlorine-containing compound, half-order in H{sub 2}, and inverse first-order in HCl. The reaction steps consistent with these orders include a rate-determining step involving the adsorption of the chlorofluorocarbon to a single site (which could be a single surface palladium atom) and equilibrated steps between gas-phase H{sub 2}, gas-phase HCl, and adsorbed hydrogen and chlorine atoms. The rates on the supported catalysts are comparable to the ones reported before on a Pd foil, indicating that the support does not play a role in the reaction. The product distribution is independent of conversion, implying that the various products are formed from a single visit of the reactant on the surface and not from readsorption of gas-phase products. The four compounds studied were chloropentafluoroethane (CF{sub 3}-CF{sub 2}Cl), 2-chloro-1,1,1,2-tetrafluoroethane (CF{sub 3}-CFClH), 1,1-dichlorotetrafluoroethane (CF{sub 3}-CFCl{sub 2}), and 1,1,1-trichloro-2,2,2-trifluoroethane (CF{sub 3}-CCl{sub 3}).

  6. A Review of the Thermodynamic, Transport, and Chemical Reaction Rate Properties of High-temperature Air

    NASA Technical Reports Server (NTRS)

    Hansen, C Frederick; Heims, Steve P

    1958-01-01

    Thermodynamic and transport properties of high temperature air, and the reaction rates for the important chemical processes which occur in air, are reviewed. Semiempirical, analytic expressions are presented for thermodynamic and transport properties of air. Examples are given illustrating the use of these properties to evaluate (1) equilibrium conditions following shock waves, (2) stagnation region heat flux to a blunt high-speed body, and (3) some chemical relaxation lengths in stagnation region flow.

  7. Absolute rate of the reaction of hydrogen atoms with ozone from 219-360 K

    NASA Technical Reports Server (NTRS)

    Lee, J. H.; Michael, J. V.; Payne, W. A.; Stief, L. J.

    1978-01-01

    Absolute rate constants for the reaction of atomic hydrogen with ozone were obtained over the temperature range 219-360 K by the flash photolysis-resonance fluorescence technique. The results can be expressed in Arrhenius form by K = (1.33 plus or minus 0.32)x10 to the minus 10 power exp (-449 plus or minus 58/T) cu cm/molecule/s (two standard deviations). The present work is compared to two previous determinations and is discussed theoretically.

  8. Rate constants for reactions of ClO/x/ of atmospheric interest

    NASA Technical Reports Server (NTRS)

    Watson, R. T.

    1977-01-01

    Chemical kinetics measurements on 82 gas phase reactions of chlorine containing species are reviewed. Recommended rate constants are given. The principal species of interest are Cl, Cl2, ClO, Cl2O, ClOO, OClO, CINO, HCl and halo derivatives of methane and ethane. Absorption spectra are given for 21 species. In addition the chemical kinetics methods used to obtain these data are discussed with regard to their applicability and reliability.

  9. The Rate Constant for the Reaction H + C2H5 at T = 295 - 150K

    NASA Technical Reports Server (NTRS)

    Pimentel, Andre S.; Payne, Walter A.; Nesbitt, Fred L.; Cody, Regina J.; Stief, Louis J.

    2004-01-01

    The reaction between the hydrogen atom and the ethyl (C2H3) radical is predicted by photochemical modeling to be the most important loss process for C2H5 radicals in the atmospheres of Jupiter and Saturn. This reaction is also one of the major sources for the methyl radicals in these atmospheres. These two simplest hydrocarbon radicals are the initial species for the synthesis of larger hydrocarbons. Previous measurements of the rate constant for the H + C2H5 reaction varied by a factor of five at room temperature, and some studies showed a dependence upon temperature while others showed no such dependence. In addition, the previous studies were at higher temperatures and generally higher pressures than that needed for use in planetary atmospheric models. The rate constant for the reaction H + C2H5 has been measured directly at T = 150, 202 and 295 K and at P = 1.0 Torr He for all temperatures and additionally at P = 0.5 and 2.0 Torr He at T = 202 K. The measurements were performed in a discharge - fast flow system. The decay of the C2H5 radical in the presence of excess hydrogen was monitored by low-energy electron impact mass spectrometry under pseudo-first order conditions. H atoms and C2H5 radicals were generated rapidly and simultaneously by the reaction of fluorine atoms with H2 and C2H6, respectively. The total rate constant was found to be temperature and pressure independent. The measured total rate constant at each temperature are: k(sub 1)(295K) = (1.02+/-0.24)x10(exp -10), k(sub 1)(202K) = (1.02+/-0.22)x10(exp -10) and k(sub 1)(150K) = (0.93+/-0.21)x10(exp -10), all in units of cu cm/molecule/s. The total rate constant derived from all the combined measurements is k(sub 1) = (l.03+/-0.17)x10(exp -10) cu cm/molecule/s. At room temperature our results are about a factor of two higher than the recommended rate constant and a factor of three lower than the most recently published study.

  10. Rate of the reaction of atomic hydrogen with propyne over an extended pressure and temperature range

    NASA Technical Reports Server (NTRS)

    Whytock, D. A.; Payne, W. A.; Stief, L. J.

    1976-01-01

    The technique of flash photolysis coupled with time resolved detection of H via resonance fluorescence has been used to obtain rate constants for the reaction of atomic hydrogen with propyne at temperatures from 215 to 460 K and at pressures in the range 5-600 torr. The rate constants are strongly pressure dependent and the high pressure limiting values give rise to the Arrhenius expression K = approximately 6 x 10 to the minus 11th exp(-2450T) cu cm per molecule per sec. The results are discussed and compared with those of previous studies

  11. Foaming and the Rate of the Carbon-Iron Oxide Reaction in Slag

    NASA Astrophysics Data System (ADS)

    Corbari, Rodrigo; Matsuura, Hiroyuki; Halder, Sabuj; Walker, Matthew; Fruehan, Richard J.

    2009-12-01

    Foaming in the electric arc furnace is achieved by injecting carbon into slag, where the resulting reaction of the carbon with FeO dissolved in the slag generates gas (CO) that causes the slag to foam. In this research, the rate of the reaction of FeO in slag with carbon and the resulting foam height were measured. In these experiments, the FeO content of the slag ranged from 15 to 45 mass pct, and several different types of carbon were used including graphite, coals, and chars. The rate of the slag-carbon reaction and the consequent CO generation increased with FeO content of the slag from 15 to 45 mass pct. However, the slag foam height reached a maximum at about 25 mass pct FeO and decreased at higher FeO contents. The decrease in foaming is apparently due to a decrease in the foam index or foamability caused by a decrease in viscosity and an increase in density of the slag with FeO content. The results of this work indicate that the foam height is influenced more significantly by the decrease in the foam index compared to the increase in the CO gas generation rate at higher FeO contents. The decrease in the foam index with FeO agrees with that predicted from the slag properties.

  12. Rates and mechanisms of the atomic oxygen reaction with nickel at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Christian, J. D.; Gilbreath, W. P.

    1973-01-01

    The oxidation of nickel by atomic oxygen at pressure from 1 to 45 N/sq m between 1050 and 1250 K was investigated. In these ranges, the oxidation was found to follow the parobolic rate law, viz., K sub p = 0.0000114 exp(-13410/T) g squared/cm4/sec for films of greater than 1 micron thickness and was pressure independent. The activation enthalpy for the oxidation reaction was 112 + or - 11 kj/mole (27 + or - 3 kcal/mole). Of a number of possible mechanisms and defect structures considered, it was shown that the most likely was a saturated surface defect model for atomic oxidation, based on reaction activation enthalpies, impurity effects, pressure independence, and magnitudes of rates. A model judged somewhat less likely was one having doubly ionized cationic defects rate controlling in both atomic and molecular oxygen. From comparisons of the appropriate processes, the following enthalpy values were derived: enthalpy of activation (Ni diffusion in Ni0) = 110 + or - 30 kj/mole and standard enthalpy change for reaction formation (doubly ionized cation vacancies in Ni0 from atomic oxygen)= -9 + or - 25 kj/mole.

  13. Rate and product measurements for the reactions of OH with I/sub 2/ and ICl at 298 K: separation of gas-phase and surface reaction components

    SciTech Connect

    Loewenstein, L.M.; Anderson, J.G.

    1985-12-05

    The kinetic behavior of OH with I/sub 2/ and ICl is reported within the context of a series of radical-halogen reactions to investigate the mechanism of such reactions through studies of reactivity trends. Atomic I and Cl products of the title reactions are measured by resolved resonance fluorescence vapor lamps. IO and ClO are detected by chemically converting them, using NO, to I and Cl, respectively. The rate constant of the reaction H + ICl has been measured at 298 K; its only product channel is I + HCl. Magnitudes of the rate constants of these OH reactions substantiate the reactivity trends in the OH-halogen system based on an electron-transfer mechanism from the highest occupied molecular orbital of the halogen to the lowest unoccupied orbital of the hydroxyl. The rapidity of the OH + I/sub 2/ reaction makes it a possible source of HOI for photochemical studies. 31 references, 11 figures, 2 tables.

  14. A reinvestigation of the rate of the C/+/ + H2 radiative association reaction. [interstellar chemistry

    NASA Technical Reports Server (NTRS)

    Herbst, E.

    1982-01-01

    It is noted that new experimental results and statistical theories have prompted a reinvestigation of the rate coefficient of the interstellar reaction in which C(+) + H2 yields CH2(+) + h(nu) in the 10-100 K temperature range. The results presented here indicate a rate coefficient between 10 to the -16 and 10 to the -15 cu cm/s at all temperatures studied. In applying the modified thermal and phase space theories, it is expected that they will be as accurate as for radiative association as for three-body association, provided the ab initio value for the radiative decay rate is correct. It is expected that the calculated values of the rate coefficient will be accurate to within an order of magnitude and will have the correct temperature dependence.

  15. Relative rate constants for the reactions of OH with methane and methyl chloroform

    NASA Technical Reports Server (NTRS)

    Demore, W. B.

    1992-01-01

    Atmospheric lifetimes of methane and methyl chloroform are largely determined by the rates of their reactions with hydroxyl radical. The relative lifetimes for this loss path are inversely proportional to the ratio of the corresponding rate coefficients. The relative rate constants were measured in a slow-flow, temperature-controlled photochemical reactor, and were based on rates of disappearance of the parent compounds as measured by FTIR spectroscopy. The temperature range was 277-356 K. Hydroxyl radicals were generated by 254 nm photolysis of O3 in the presence of water vapor. The preferred Arrhenius expression for the results is k(CH3CCl3)/k(CH4) = 0.62 exp (291/T), corresponding to a value of 1.65 at 298 K and 1.77 at 277 K. The respective uncertainties are 5 and 7 percent.

  16. 34 CFR 694.11 - What is the maximum indirect cost rate for an agency of a State or local government?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... indirect cost rate for an agency of a State or local government? Notwithstanding 34 CFR 75.560-75.562 and 34 CFR 80.22, the maximum indirect cost rate that an agency of a State or local government receiving funds under GEAR UP may use to charge indirect costs to these funds is the lesser of— (a) The...

  17. 34 CFR 694.11 - What is the maximum indirect cost rate for an agency of a State or local government?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... indirect cost rate for an agency of a State or local government? Notwithstanding 34 CFR 75.560-75.562 and 34 CFR 80.22, the maximum indirect cost rate that an agency of a State or local government receiving funds under GEAR UP may use to charge indirect costs to these funds is the lesser of— (a) The...

  18. 34 CFR 694.11 - What is the maximum indirect cost rate for an agency of a State or local government?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... indirect cost rate for an agency of a State or local government? Notwithstanding 34 CFR 75.560-75.562 and 34 CFR 80.22, the maximum indirect cost rate that an agency of a State or local government receiving funds under GEAR UP may use to charge indirect costs to these funds is the lesser of— (a) The...

  19. Upscaling of reaction rates in reactive transport using pore-scale reactive transport model

    NASA Astrophysics Data System (ADS)

    Yoon, H.; Dewers, T. A.; Arnold, B. W.; Major, J. R.; Eichhubl, P.; Srinivasan, S.

    2013-12-01

    Dissolved CO2 during geological CO2 storage may react with minerals in fractured rocks, confined aquifers, or faults, resulting in mineral precipitation and dissolution. The overall rate of reaction can be affected by coupled processes among hydrodynamics, transport, and reactions at the (sub) pore-scale. In this research pore-scale modeling of coupled fluid flow, reactive transport, and heterogeneous reaction at the mineral surface is applied to account for permeability alterations caused by precipitation-induced pore-blocking. This work is motivated by the observed CO2 seeps from a natural analog to geologic CO2 sequestration at Crystal Geyser, Utah. A key observation is the lateral migration of CO2 seep sites at a scale of ~ 100 meters over time. A pore-scale model provides fundamental mechanistic explanations of how calcite precipitation alters flow paths by pore plugging under different geochemical compositions and pore configurations. In addition, response function of reaction rates will be constructed from pore-scale simulations which account for a range of reaction regimes characterized by the Damkohler and Peclet numbers. Newly developed response functions will be used in a continuum scale model that may account for large-scale phenomena mimicking lateral migration of surface CO2 seeps. Comparison of field observations and simulations results will provide mechanistic explanations of the lateral migration and enhance our understanding of subsurface processes associated with the CO2 injection. This work is supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security

  20. Assessing the Effects of New Reaction Rates and Convection Theory on Studies of Supernova Progenitors

    NASA Astrophysics Data System (ADS)

    Starrfield, Sumner

    We request funding to carry out a systematic evaluation of nuclear reaction rates and convection on the pre-explosion evolution of core-collapse (SN II) and thermonuclear (SN Ia) supernovae. We will use MESA (Modules for Experiments in Stellar Astrophysics) a new stellar evolution computer code that is co-authored by Co-PI Timmes. One goal of this proposal is to determine the effects of new thermonuclear reaction rates, taken from the next-generation library STARLIB developed by Co-PI Iliadis, on the resulting evolution. Another goal is to test the effects of the latest convection theory, microphysics changes, and numerical techniques on the results. STARLIB is a first-of-its-kind nuclear reaction rate library and, unlike all other libraries, it contains the full reaction rate probability densities at all stellar temperatures. It is publicly available as of June 2013. Consequently, we are now in a unique position to model stellar evolution and nucleosynthesis in a quantitative manner that makes predictions for key observations by NASA ground-based and satellite observatories. We will use two complementary strategies. First, we will take the modern and multiple prescriptions of convection that are implemented in MESA, together with the recommended thermonuclear reaction rates provided by STARLIB, to generate new hydrodynamic simulations of SN Ia and SN II progenitor evolution. Second, we will take the temperature-density-time trajectories from the evolutionary results and do Monte Carlo post-processing nucleosynthesis calculations by sampling over the reaction rate probability densities. This procedure could not be applied previously and has only become feasible with the availability of STARLIB. Calculations of pre-supernova evolution with the STARLIB reaction rates and new convection prescriptions will provide, for the first time, statistically rigorous estimates for both their evolutionary structures and resulting nucleosynthesis. Significant insight into pre

  1. Reaction rate of a composite core-shell nanoreactor with multiple nanocatalysts.

    PubMed

    Galanti, Marta; Fanelli, Duccio; Angioletti-Uberti, Stefano; Ballauff, Matthias; Dzubiella, Joachim; Piazza, Francesco

    2016-07-27

    We present a detailed theory for the total reaction rate constant of a composite core-shell nanoreactor, consisting of a central solid core surrounded by a hydrogel layer of variable thickness, where a given number of small catalytic nanoparticles are embedded at prescribed positions and are endowed with a prescribed surface reaction rate constant. Besides the precise geometry of the assembly, our theory accounts explicitly for the diffusion coefficients of the reactants in the hydrogel and in the bulk as well as for their transfer free energy jump upon entering the hydrogel shell. Moreover, we work out an approximate analytical formula for the overall rate constant, which is valid in the physically relevant range of geometrical and chemical parameters. We discuss in depth how the diffusion-controlled part of the rate depends on the essential variables, including the size of the central core. In particular, we derive some simple rules for estimating the number of nanocatalysts per nanoreactor for an efficient catalytic performance in the case of small to intermediate core sizes. Our theoretical treatment promises to provide a very useful and flexible tool for the design of superior performing nanoreactor geometries with optimized nanoparticle load. PMID:27411947

  2. Characterization of the reaction rate coefficient of DNA with the hydroxyl radical

    SciTech Connect

    Milligan, J.R.; Ward, J.F.; Aguilera, J.A.

    1996-11-01

    Using agarose gel electrophoresis, we have measured the yield of single-strand breaks (SSBs) induced by {sup 137}Cs {gamma} irradiation in a variety of plasmid DNA substrates ranging in size from 2.7 kb to 38 kb irradiated in aerobic aqueous solution in the presence of the hydroxyl radical scavenger dimethyl sulfoxide (DMSO). Under these conditions DNA SSBs are caused mainly by the hydroxyl radical. Using the competition between DMSO and DNA for the hydroxyl radical, we have estimated the rate coefficient for the reaction of the hydroxyl radical with DNA. The results cannot be characterized by conventional steady-state competition kinetics. However, it is possible to describe the second-order rate constant for the reaction as a function of the scavenging capacity of the solution. The second-order rate constant increases with increasing scavenging capacity, rising from about 5x10{sup 8} dm{sup 3} mol{sup -1} s{sup -1} at 10{sup 5} s{sup -1} to about 10{sup 10} dm{sup 3} mol{sup -1} s{sup -1} at 10{sup 10} s{sup -1}. This dependence of the second-order rate constant on the scavenging capacity appears to be more pronounced for larger plasmids. 17 refs., 4 figs.

  3. Equation of state and reaction rate for condensed-phase explosives

    NASA Astrophysics Data System (ADS)

    Wescott, B. L.; Stewart, D. Scott; Davis, W. C.

    2005-09-01

    The wide-ranging equation of state is a nonideal equation of state based on empirical fitting forms argued from thermodynamic considerations that yield the proper physical features of detonation. The complete equation of state forms are presented and the equation of state and a reaction rate are calibrated for the condensed-phase explosive PBX-9502. Experimental overdriven Hugoniot data are used to calibrate the products equation of state off the principal isentrope passing through the Chapman-Jouguet state. Shock Hugoniot data are used to calibrate the reactants equation of state. The normal detonation shock speed-shock curvature data (Dn-κ) from rate-stick measurements and shock initiation data from wedge tests are used to calibrate the reaction rate. Simulations are carried out that predict detailed particle velocity transients that are measured experimentally with embedded electromagnetic gauge measurements from gas-gun experiments. Multidimensional simulations of steady detonation in a right circular cylinder rate stick are carried out and compared with experiment.

  4. Nova Nucleosynthesis with a New 18F(p,alpha) Reaction Rate

    NASA Astrophysics Data System (ADS)

    Smith, Michael; Kozub, Raymond; Brune, Carl; Starrfield, Sumner

    2005-04-01

    The long-lived radionuclide ^18F is synthesized in nova outbursts and its decay may serve as an observational tracer of the explosion mechanism. Because the ^18F(p,α)^15O reaction is the dominant destruction mechanism for ^18F, the flux of gamma rays from ^18F decay is very sensitive to the rate of this reaction. A revised ^18F(p,α)^15O rate was determined from recent ORNL measurements of ^1H(^18F,p)^18F and ^2H(^18F,p)^19F, combined with a reanalysis of archival ^15N(α,α)^15N data. We used this new rate in nova element synthesis calculations and compared new predictions of the synthesized abundance ^18F (and other nuclides) to that obtained using the two most recent (p,α) rates. We used a post- processing approach with temperature and density histories of 28 zones of ejected material determined from separate hydrodynamics calculations. The implications for satellite observations of novae will be discussed. These calculations were performed and visualized with the Computational Infrastructure for Nuclear Astrophysics, an online suite of codes available at nucastrodata.org.

  5. A study of the photocatalytic effects of aqueous suspensions of platinized semiconductor materials on the reaction rates of candidate redox reactions

    NASA Technical Reports Server (NTRS)

    Miles, A. M.

    1982-01-01

    The effectiveness of powdered semiconductor materials in photocatalyzing candidate redox reactions was investigated. The rate of the photocatalyzed oxidation of cyanide at platinized TiO2 was studied. The extent of the cyanide reaction was followed directly using an electroanalytical method (i.e. differential pulse polarography). Experiments were performed in natural or artificial light. A comparison was made of kinetic data obtained for photocatalysis at platinized powders with rate data for nonplatinized powders.

  6. Charge-exchange reactions and electron-capture rates for presupernova stellar evolution

    NASA Astrophysics Data System (ADS)

    Zegers, Remco

    2015-04-01

    Weak reaction rates such as electron captures and beta decays play major roles in a variety of astrophysical phenomena, such as core-collapse and thermonuclear supernovae and accreting neutron stars. Consequently, the use of accurate weak reaction rates in astrophysical simulations to understand these phenomena is important. Unfortunately, the number of relevant nuclei is typically very large, and, except for a few special cases, it is impossible to rely on experimental results only: theoretical models must be used to estimate the weak reaction rates. These models can then be benchmarked and improved on the basis of a limited number of experimental data. The most important nuclear structure input that is required for calculating weak reaction rates are Gamow-Teller transition strengths. Although these can be extracted from beta and electron-capture decay data, the energy window accessible by such experiments is limited, if accessible at all. However, at the high temperatures and densities that occur in massive stars prior to the cataclysmic demise, transitions to final states at high excitation energies are important. In addition, to properly test theory, full Gamow-Teller transition strength distributions are very valuable. Fortunately, nature is kind: charge-exchange experiments at intermediate energies can provide the relevant strength distributions over a wide energy window and a variety of charge-exchange probes, such as (p,n), (n,p), (d,2 He) and (t,3 He) have been used to extract strengths of relevance for astrophysics (and for other purposes). This presentation will focus on efforts to validate electron capture rates calculated based on nuclear structure models for nuclei with masses ranging from A ~ 40-65, and on studies aimed at testing astrophysical sensitivities to uncertainties/deviations in the theoretical rates. These efforts include experiments with unstable isotopes, and special gamma-ray coincidence techniques to localize very weak, but

  7. Experimental and Estimated Rate Constants for the Reactions of Hydroxyl Radicals with Several Halocarbons

    NASA Technical Reports Server (NTRS)

    DeMore, W.B.

    1996-01-01

    Relative rate experiments are used to measure rate constants and temperature dependencies of the reactions of OH with CH3F (41), CH2FCl (31), CH2BrCl (30B1), CH2Br2 (3OB2), CHBr3 (2OB3), CF2BrCHFCl (123aBl(alpha)), and CF2ClCHCl2 (122). Rate constants for additional compounds of these types are estimated using an empirical rate constant estimation method which is based on measured rate constants for a wide range of halocarbons. The experimental data are combined with the estimated and previously reported rate constants to illustrate the effects of F, Cl, and Br substitution on OH rate constants for a series of 19 halomethanes and 25 haloethanes. Application of the estimation technique is further illustrated for some higher hydrofluorocarbons (HFCs), including CHF2CF2CF2CF2H (338pcc), CF3CHFCHFCF2CF3 (43-10mee), CF3CH2CH2CF3 (356ffa), CF3CH2CF2CH2CF3 (458mfcf), CF3CH2CHF2 (245fa), and CF3CH2CF2CH3 (365mfc). The predictions are compared with literature data for these compounds.

  8. Measuring OH Reaction Rate Constants and Estimating the Atmospheric Lifetimes of Trace Gases.

    NASA Astrophysics Data System (ADS)

    Orkin, Vladimir; Kurylo, Michael

    2015-04-01

    Reactions with hydroxyl radicals and photolysis are the main processes dictating a compound's residence time in the atmosphere for a majority of trace gases. In case of very short-lived halocarbons their reaction with OH dictates both the atmospheric lifetime and active halogen release. Therefore, the accuracy of OH kinetic data is of primary importance for the comprehensive modeling of a compound's impact on the atmosphere, such as in ozone depletion (i.e., the Ozone Depletion Potential, ODP) and climate change (i.e., the Global Warming Potential, GWP), each of which are dependent on the atmospheric lifetime of the compound. We have demonstrated the ability to conduct very high accuracy determinations of OH reaction rate constants over the temperature range of atmospheric interest, thereby decreasing the uncertainty of kinetic data to 2-3%. The atmospheric lifetime of a well-mixed compound due to its reaction with tropospheric hydroxyl radicals can be estimated by using a simple scaling procedure that is based on the results of field observations of methyl chloroform concentrations and detailed modeling of the OH distribution in the atmosphere. The currently available modeling results of the atmospheric fate of various trace gases allow for an improved understanding of the ability and accuracy of simplified semi-empirical estimations of atmospheric lifetimes. These aspects will be illustrated in this presentation for a variety of atmospheric trace gases.

  9. Measuring OH Reaction Rate Constants and Estimating the Atmospheric Lifetimes of Trace Gases.

    NASA Astrophysics Data System (ADS)

    Orkin, V. L.; Kurylo, M. J., III

    2014-12-01

    Reactions with hydroxyl radicals and photolysis are the main processes dictating a compound's residence time in the atmosphere for a majority of trace gases. In case of very short-lived halocarbons their reaction with OH dictates both the atmospheric lifetime and active halogen release. Therefore, the accuracy of OH kinetic data is of primary importance for the comprehensive modeling of a compound's impact on the atmosphere, such as in ozone depletion (i.e., the Ozone Depletion Potential, ODP) and climate change (i.e., the Global Warming Potential, GWP), each of which are dependent on the atmospheric lifetime of the compound. We have demonstrated the ability to conduct very high accuracy determinations of OH reaction rate constants over the temperature range of atmospheric interest, thereby decreasing the uncertainty of kinetic data to 2-3%. The atmospheric lifetime of a tropospherically well-mixed compound due to its reaction with tropospheric hydroxyl radicals can be estimated by using a simple scaling procedure that is based on the results of field observations of methyl chloroform concentrations and detailed modeling of the OH distribution in the atmosphere. The currently available modeling results of the atmospheric fate of various trace gases allow for an improved understanding of the ability and accuracy of simplified semi-empirical estimations of atmospheric lifetimes. These aspects will be illustrated in this presentation for a variety of atmospheric trace gases.

  10. Reaction kinetics, P-T-t paths and rates of tectonic processes

    SciTech Connect

    Bohlen, S.R.; Hankins, W.B.; Eckert, J.O. Jr.; Kirby, S.H.; Liu, J. ); Hacker, B.R.; Mosenfelder, J.L. . Dept. of Geology)

    1992-01-01

    The interpretation of portions of P-T-time (t) paths in metamorphic rocks assumes that continuous and discontinuous reactions record local equilibrium as P-T conditions change, implying that the kinetics of many reactions are rapid relative to dT/dt and dP/dt. Occurrence of eclogite veins in granulites from Bergen, Norway as well as occurrences of coesite and diamond in crustal rocks imply that, under certain conditions, this assumption is wrong. Knowledge of the kinetics of important reactions under appropriate conditions would provide limits on the duration of relatively narrowly defined P-T conditions, allow inference of the rates of exhumation of rocks containing high-pressure phases, and allow the calculation of the time required for the conversion of gabbro to eclogite in the lower crust as a function of P-T-t. The authors are currently assessing the rates of key phase transformations: calcite to aragonite, albite to jadeite + quartz, coesite to quartz, opx[sub Fs[sup 80

  11. Effective reaction rate for porous surfaces under strong shear: Beyond Damkohler

    NASA Astrophysics Data System (ADS)

    Shaqfeh, Eric S. G.; Shah, Preyas

    2014-11-01

    Traditonally, surface reactive porous media are modeled via an effective reaction/mass transfer rate based on the original ansatz of Damkohler, i.e, reaction limited transport at the microscale in the absence of flow. We are interested in modeling the microscale mass transfer to porous surfaces occuring in leaky tumor vasculature, where the Damkohler number can be O(1) and the Peclet number may be large. We model it as a uniform bath of a species in unbound shear flow over a wall with first order reactive circular patches (pores). We analyze the flux through a single pore using both analytic and boundary element simulations and observe the formation of a 3-D depletion region (wake) downstream of the pore. Wake sharing between adjacent pores in a multibody setting such as 2 pores aligned in the shear direction leads to a smaller flux per pore. Obtaining this interaction length scale and using the renormalized periodic Green's function, we study the flux through a periodic and disordered distribution of pores. This flux appears as the reaction rate in an effective boundary condition, valid up to non-dilute pore area fractions, and applicable at a wall-normal effective slip distance. It replaces the details of the surface and can be used directly in large scale physics simulations.

  12. Absolute rate constants of alkoxyl radical reactions in aqueous solution. [Tert-butyl hydroperoxide

    SciTech Connect

    Erben-Russ, M.; Michel, C.; Bors, W.; Saran, M.

    1987-04-23

    The pulse radiolysis technique was used to generate the alkoxyl radical derived from tert-butyl hydroperoxide (/sup t/BuOOH) in aqueous solution. The reactions of this radical with 2,2'-azinobis(3-ethyl-6-benzothiazolinesulfonate) (ABTS) and promethazine were monitored by kinetic spectroscopy. The unimolecular decay rate constant of the tert-butoxyl radical (/sup t/BuO) was determined to be 1.4 x 10/sup 6/ s/sup -1/. On the basis of this value, the rate constants for /sup t/BuO attack on quercetin, crocin, crocetin, ascorbate, isoascorbate, trolox c, glutathione, thymidine, adenosine, guanosine, and unsaturated fatty acids were determined. In addition, the reaction of /sup t/BuO with the polyunsaturated fatty acids (PUFA) was observed by directly monitoring the formation of the fatty acid pentadienyl radicals. Interestingly, the attack of /sup t/BuO on PUFA was found to be faster by about one order of magnitude as compared to the same reaction in a nonpolar solvent.

  13. Contribution of 19F resonances on 18O( p, α)15N reaction rate

    NASA Astrophysics Data System (ADS)

    Benmeslem, Meriem; Chafa, Azzedine; Barhoumi, Slimane; Tribeche, Mouloud

    2014-08-01

    The 18O( p, α)15N reaction influences the isotopes production such as 19F, 18O, and 15N which can be used to test the models of stellar evolution. 19F is synthesized in both asymptotic giant branch (AGB) and metal-rich Wolf-Rayet (WR) stars. Using R-matrix theory we allow new values of resonances parameters in 19F. We show that the most important contribution to the differential and total cross section at low energies, comes from the levels in 19F situated at resonances energies E R =151, 680 and 840 keV with spin and parity 1/2+. The total width of the 680 keV resonance is badly known. So, we have focused on this broad resonance corresponding to the 8.65 MeV level in 19F. We delimit the temperature range in which each resonance contribution to the total reaction rate occurs by analyzing the ratio ( N A < σν> i / N A < σν>). This allowed us to show that the 680 and 840 keV broad resonances strongly dominate the reaction rate over the stellar temperature range T 9=0.02-0.06 and T 9=0.5-5. Finally, these results were compared to NACRE and Iliadis astrophysical compilations.

  14. Absolute rate of the reaction of Cl(p-2) with molecular hydrogen from 200 - 500 K

    NASA Technical Reports Server (NTRS)

    Whytock, D. A.; Lee, J. H.; Michael, J. V.; Payne, W. A.; Stief, L. J.

    1976-01-01

    Rate constants for the reaction of atomic chlorine with hydrogen are measured from 200 - 500 K using the flash photolysis-resonance fluorescence technique. The results are compared with previous work and are discussed with particular reference to the equilibrium constant for the reaction and to relative rate data for chlorine atom reactions. Theoretical calculations, using the BEBO method with tunneling, give excellent agreement with experiment.

  15. THE IMPACT OF HELIUM-BURNING REACTION RATES ON MASSIVE STAR EVOLUTION AND NUCLEOSYNTHESIS

    SciTech Connect

    West, Christopher; Heger, Alexander; Austin, Sam M. E-mail: alexander.heger@monash.edu

    2013-05-20

    We study the sensitivity of presupernova evolution and supernova nucleosynthesis yields of massive stars to variations of the helium-burning reaction rates within the range of their uncertainties. The current solar abundances from Lodders are used for the initial stellar composition. We compute a grid of 12 initial stellar masses and 176 models per stellar mass to explore the effects of independently varying the {sup 12}C({alpha}, {gamma}){sup 16}O and 3{alpha} reaction rates, denoted R{sub {alpha},12} and R{sub 3{alpha}}, respectively. The production factors of both the intermediate-mass elements (A = 16-40) and the s-only isotopes along the weak s-process path ({sup 70}Ge, {sup 76}Se, {sup 80}Kr, {sup 82}Kr, {sup 86}Sr, and {sup 87}Sr) were found to be in reasonable agreement with predictions for variations of R{sub 3{alpha}} and R{sub {alpha},12} of {+-}25%; the s-only isotopes, however, tend to favor higher values of R{sub 3{alpha}} than the intermediate-mass isotopes. The experimental uncertainty (one standard deviation) in R{sub 3{alpha}}(R{sub {alpha},12}) is approximately {+-}10%({+-}25%). The results show that a more accurate measurement of one of these rates would decrease the uncertainty in the other as inferred from the present calculations. We also observe sharp changes in production factors and standard deviations for small changes in the reaction rates, due to differences in the convection structure of the star. The compactness parameter was used to assess which models would likely explode as successful supernovae, and hence contribute explosive nucleosynthesis yields. We also provide the approximate remnant masses for each model and the carbon mass fractions at the end of core-helium burning as a key parameter for later evolution stages.

  16. A reaction-diffusion-based coding rate control mechanism for camera sensor networks.

    PubMed

    Yamamoto, Hiroshi; Hyodo, Katsuya; Wakamiya, Naoki; Murata, Masayuki

    2010-01-01

    A wireless camera sensor network is useful for surveillance and monitoring for its visibility and easy deployment. However, it suffers from the limited capacity of wireless communication and a network is easily overflown with a considerable amount of video traffic. In this paper, we propose an autonomous video coding rate control mechanism where each camera sensor node can autonomously determine its coding rate in accordance with the location and velocity of target objects. For this purpose, we adopted a biological model, i.e., reaction-diffusion model, inspired by the similarity of biological spatial patterns and the spatial distribution of video coding rate. Through simulation and practical experiments, we verify the effectiveness of our proposal. PMID:22163620

  17. Development of the GEM-MSTPC for studies of astrophysical nuclear reaction rates

    SciTech Connect

    Yamaguchi, K.; Arai, I.; Ishiyama, H.; Watanabe, Y. X.; Tanaka, M. H.; Miyatake, H.; Hirayama, Y.; Imai, N.; Fuchi, Y.; Jeong, S. C.; Nomura, T.; Mizoi, Y.; Das, S. K.; Fukuda, T.; Hashimoto, T.; Yamaguchi, H.; Kubono, S.; Hayakawa, S.; Makii, H.; Mitsuoka, S.

    2010-08-12

    We have developed an active-target type gas-detector, a Gas Electron Multiplier Multiple-Sampling and Tracking Proportional Chamber (GEM-MSTPC) operating with low-pressure He-base mixed gas, where He is used as a target for studies of astrophysical nuclear reaction rates. Different kinds of 400 {mu}m thick GEMs were examined. The gain stability was examined with a configuration of GEMs of 400 {mu}m in thickness fabricated in different ways, against the injection rate of low-energy heavy ions of 10{sup 5} particles per second. The gain of GEM with Cu electrodes coated by Au was observed to be stable up to the injection rate of 10{sup 5} particles per second.

  18. The rate constant for the reaction of oxygen /3P/ atoms with dichlorine monoxide

    NASA Technical Reports Server (NTRS)

    Miziolek, A. W.; Molina, M. J.

    1978-01-01

    A fast flow discharge apparatus was used to measure the rate constant for the reaction of ground state oxygen atoms with dichlorine monoxide in the temperature range 236-295 K. The air afterflow technique (NO2 chemiluminescence) was used for detection of oxygen atoms. The Arrhenius expression for the rate constant was found to be 2.7 plus or minus 0.3 times 10 to the -11th power exp(-560 plus or minus 80/T) cu cm per molecule per sec. At 295 K the rate constant is 4.1 plus or minus 0.5 times 10 to the -12th power cu cm per molecule per sec.

  19. Channel specific rate constants for reactions of O(1D) with HCl and HBr

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

    The absolute rate coefficients and product yields for reactions of O(1D) with HCl(1) and HBr(2) at 287 K are presently determined by means of the time-resolved resonance fluorescence detection of O(3P) and H(2S) in conjunction with pulsed laser photolysis of O3/HX/He mixtures. Total rate coefficients for O(1D) removal are found to be, in units of 10 to the -10th cu cm/molecule per sec, k(1) = 1.50 + or - 0.18 and k(2) 1.48 + or - 0.16; the absolute accuracy of these rate coefficients is estimated to be + or - 20 percent.

  20. CNO and 6Li from big-bang nucleosynthesis-Impact of unmeasured reaction rates

    NASA Astrophysics Data System (ADS)

    Madsen, Jes

    1990-04-01

    Rates for a number of nuclear reactions not studied in the laboratory are crucial for predicting the outcome of big-bang nucleosynthesis. It is shown in the present investigation that the mass fraction of CNO elements produced in neutron-rich zones in inhomogeneous nucleosynthesis (other parameters fixed) spans almost 3 orders of magnitude depending on the unmeasured rate of 8Li(α,n)11B. The possibility of producing observable quantities of primordial 6Li via 3H(3He,γ)6Li is discussed for the first time, and finally it is reported that helium production through 2H(2H, γ)4He is negligible in all nucleosynthesis scenarios, in spite of recent measurements increasing the low-energy rate by a factor 32.

  1. A Reaction-Diffusion-Based Coding Rate Control Mechanism for Camera Sensor Networks

    PubMed Central

    Yamamoto, Hiroshi; Hyodo, Katsuya; Wakamiya, Naoki; Murata, Masayuki

    2010-01-01

    A wireless camera sensor network is useful for surveillance and monitoring for its visibility and easy deployment. However, it suffers from the limited capacity of wireless communication and a network is easily overflown with a considerable amount of video traffic. In this paper, we propose an autonomous video coding rate control mechanism where each camera sensor node can autonomously determine its coding rate in accordance with the location and velocity of target objects. For this purpose, we adopted a biological model, i.e., reaction-diffusion model, inspired by the similarity of biological spatial patterns and the spatial distribution of video coding rate. Through simulation and practical experiments, we verify the effectiveness of our proposal. PMID:22163620

  2. Internal Thermodynamical Equilibrium And Consequences For Rate Law Expressions For Elementary Chemical And Physical Reactions

    NASA Astrophysics Data System (ADS)

    Jesudason, Christopher G.

    2009-07-01

    By viewing reactant species to be in a state of thermodynamical equilibrium with its various members which constitutes a set within a set of topological parameters various states of internal equilibrium within the same species would exist subject to the Gibbs thermodynamical criteria. Some examples from actual ab initio computer simulations show that there exists an empirical relationship between the activity coefficient ratio and the so-called reactivity coefficients, defined as a measure of departure of the rate constant with varying concentration of reactants in a system at equilibrium, where forward and backward rates can still be measured. These ideas are applied to charged reaction dynamics where a generalization of the Brönsted and Bjerrum rate expression is obtained.

  3. Linear free energy relationships between aqueous phase hydroxyl radical reaction rate constants and free energy of activation.

    PubMed

    Minakata, Daisuke; Crittenden, John

    2011-04-15

    The hydroxyl radical (HO(•)) is a strong oxidant that reacts with electron-rich sites on organic compounds and initiates complex radical chain reactions in aqueous phase advanced oxidation processes (AOPs). Computer based kinetic modeling requires a reaction pathway generator and predictions of associated reaction rate constants. Previously, we reported a reaction pathway generator that can enumerate the most important elementary reactions for aliphatic compounds. For the reaction rate constant predictor, we develop linear free energy relationships (LFERs) between aqueous phase literature-reported HO(•) reaction rate constants and theoretically calculated free energies of activation for H-atom abstraction from a C-H bond and HO(•) addition to alkenes. The theoretical method uses ab initio quantum mechanical calculations, Gaussian 1-3, for gas phase reactions and a solvation method, COSMO-RS theory, to estimate the impact of water. Theoretically calculated free energies of activation are found to be within approximately ±3 kcal/mol of experimental values. Considering errors that arise from quantum mechanical calculations and experiments, this should be within the acceptable errors. The established LFERs are used to predict the HO(•) reaction rate constants within a factor of 5 from the experimental values. This approach may be applied to other reaction mechanisms to establish a library of rate constant predictions for kinetic modeling of AOPs. PMID:21410278

  4. A kinetic-theory approach for computing chemical-reaction rates in upper-atmosphere hypersonic flows.

    PubMed

    Gallis, Michael A; Bond, Ryan B; Torczynski, John R

    2009-09-28

    Recently proposed 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 investigated for chemical reactions occurring in upper-atmosphere hypersonic flows. The new models are in good agreement with the measured Arrhenius rates for near-equilibrium conditions and with both measured rates and other theoretical models for far-from-equilibrium conditions. Additionally, the new models are applied to representative combustion and ionization reactions and are in good agreement with available measurements and theoretical models. Thus, molecular-level chemistry modeling provides an accurate method for predicting equilibrium and nonequilibrium chemical-reaction rates in gases. PMID:19791885

  5. A kinetic-theory approach for computing chemical-reaction rates in upper-atmosphere hypersonic flows

    NASA Astrophysics Data System (ADS)

    Gallis, Michael A.; Bond, Ryan B.; Torczynski, John R.

    2009-09-01

    Recently proposed 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 investigated for chemical reactions occurring in upper-atmosphere hypersonic flows. The new models are in good agreement with the measured Arrhenius rates for near-equilibrium conditions and with both measured rates and other theoretical models for far-from-equilibrium conditions. Additionally, the new models are applied to representative combustion and ionization reactions and are in good agreement with available measurements and theoretical models. Thus, molecular-level chemistry modeling provides an accurate method for predicting equilibrium and nonequilibrium chemical-reaction rates in gases.

  6. A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Foy, E.; Ronan, G.; Chinitz, W.

    1982-01-01

    A principal element to be derived from modeling turbulent reacting flows is an expression for the reaction rates of the various species involved in any particular combustion process under consideration. A temperature-derived most-likely probability density function (pdf) was used to describe the effects of temperature fluctuations on the Arrhenius reaction rate constant. A most-likely bivariate pdf described the effects of temperature and species concentrations fluctuations on the reaction rate. A criterion is developed for the use of an "appropriate" temperature pdf. The formulation of models to calculate the mean turbulent Arrhenius reaction rate constant and the mean turbulent reaction rate is considered and the results of calculations using these models are presented.

  7. Size dependence of surface thermodynamic properties of nanoparticles and its determination method by reaction rate constant

    NASA Astrophysics Data System (ADS)

    Li, Wenjiao; Xue, Yongqiang; Cui, Zixiang

    2016-08-01

    Surface thermodynamic properties are the fundamental properties of nanomaterials, and these properties depend on the size of nanoparticles. In this paper, relations of molar surface thermodynamic properties and surface heat capacity at constant pressure of nanoparticles with particle size were derived theoretically, and the method of obtaining the surface thermodynamic properties by reaction rate constant was put forward. The reaction of nano-MgO with sodium bisulfate solution was taken as a research system. The influence regularities of the particle size on the surface thermodynamic properties were discussed theoretically and experimentally, which show that the experimental regularities are in accordance with the corresponding theoretical relations. With the decreasing of nanoparticle size, the molar surface thermodynamic properties increase, while the surface heat capacity decreases (the absolute value increases). In addition, the surface thermodynamic properties are linearly related to the reciprocal of nanoparticle diameter, respectively.

  8. Rate of reaction of the hydrogen atom with nitrous oxide in ambient water

    NASA Astrophysics Data System (ADS)

    Kazmierczak, Lukasz; Swiatla-Wojcik, Dorota; Szala-Bilnik, Joanna; Wolszczak, Marian

    2016-08-01

    The reaction of the hydrogen atom with nitrous oxide has been investigated by pulse radiolysis of N2O-saturated 0.1 M HCl solution at room temperature (24±1 °C). The value of (9±2)×104 M-1 s-1 obtained for the reaction rate constant is between the early estimates 1×104 M-1 s-1 by Czapski and Jortner (1960) and 4.3×105 M-1 s-1 by Thomas (1969), and is much lower than 2×106 M-1 s-1 used recently (Janik et al., 2007; Ismail et al., 2013; Liu et al., 2015; Meesungnoen et al., 2015).

  9. Process for the oxidation of materials in water at supercritical temperatures utilizing reaction rate enhancers

    SciTech Connect

    Swallow, K.C.; Killilea, W.R.; Hong, G.T.; Bourhis, A.L.

    1993-08-03

    A method is described for substantially completely oxidizing combustible materials in which an aqueous stream bearing the combustible materials is reacted in the presence of an oxidant comprising diatomic oxygen and at a temperature greater than the critical temperature of water and at a pressure greater than about 25 bar, within a reactor for a period of less than about 5 minutes to produce a reaction product stream, wherein the reaction is initiated in the presence of a rate enhancer comprising at least one oxidizing agent in addition to said oxidant selected from the group consisting of ozone, hydrogen peroxide, salts containing persulfate, salts containing permanganate, nitric acid, salts containing nitrate, oxyacids of chlorine and their corresponding salts, hypochlorous acid, salts containing hypochlorite, chlorous acid, salts containing chlorite, chloric acid, salts containing chlorate, perchloric acid, and salts containing perchlorate.

  10. Estimates of neutron reaction rates in three portable He-3 proportional counters

    SciTech Connect

    Descalle, M; Labov, S

    2007-03-01

    The goal of this study is to obtain Monte Carlo estimates of neutron reaction rates for the {sup 3}He(n,p){sup 3}H reaction in two portable He-3 proportional counters in several configurations to quantify contributions from the environment, and optimize the tube characteristics. The smallest tube (0.5-inch diameter, 2-inch long, P = 10 atm) will not meet requirements. The largest tube (1-inch diameter, 4-inch long, P = 6 or 10 atm) will meet requirements and the tube length could be decreased to 2-inch at 6 atm and 1-inch at 10 atm. The 'medium' tube (3/4-inch diameter, 2-inch long, P = 10 atm) will meet requirements for the parallelepiped body, but will not for the cylindrical body.

  11. Structural and dynamical control of the reaction rate in protein electron transfer

    NASA Astrophysics Data System (ADS)

    Balabin, Ilya A.

    Electron transfer (ET) reactions in proteins are key steps in many vital bioenergetic processes, and the reaction rate is known to be highly sensitive to the protein structure in some cases. For most bioenergetic reactions, as described by the Fermi Golden rule, the rate is proportional to a product of the average square of the effective electronic donor to acceptor coupling and a Franck-Condon factor, which accounts for the nuclear control of the energy gap. The nuclear factor is reasonably well described in Marcus theory and its modifications, and this work is focused on the mechanisms that control the effective coupling. About ten years ago, the Pathways model described for the first time how protein environment may control the effective coupling. In this work, a novel theoretical approach is developed to explore the mechanisms of structural and dynamical control beyond the qualitative level of the Pathways model. In Chapter 1, the assumptions of the Pathways model, its limitations and effects of the structure and the electronic Hamiltonian are investigated for model chain-like bridges using the Dyson's equations. In Chapter II, the framework to explore the sensitivity of the effective coupling to quality of the electronic Hamiltonian, the interference among the dominant pathways and the bridge dynamics is presented. This analysis employs the Green's function technique and includes combined molecular dynamics and electronic structure calculations. Finally, in Chapter III, this framework is tested on the bacterial photosynthetic reaction center, and the mechanisms of the structural and dynamical control for different ET steps are discussed.

  12. Effects of arsenic incorporation on jarosite dissolution rates and reaction products

    NASA Astrophysics Data System (ADS)

    Kendall, Matthew R.; Madden, Andrew S.; Elwood Madden, Megan E.; Hu, Qinhong

    2013-07-01

    Batch dissolution experiments were undertaken on synthetic arsenojarosites at pH 2, pH 8, and in ultra-pure water to better understand the influence of As incorporation on the kinetics and reaction products of jarosite dissolution. Incongruent jarosite dissolution was observed in all experiments. Arsenojarosite lacks the pH dependency observed in K-jarosite dissolution, likely the result of surface arsenate-iron complexes preventing protonation at low pH and repelling hydroxyls at high pH. The stronger bonding of arsenate to iron, compared to sulfate to iron, leads to an enrichment of surface layer arsenate-iron complex sites, inhibiting the dissolution of jarosite with time. The secondary reaction products formed during the dissolution of arsenojarosite include maghemite, goethite, and hematite in ultra-pure water, and ferrihydrite in pH 8 Tris buffered solution. Maghemite initially forms and transitions to hematite with time in ultra-pure water, but increasing arsenic concentrations slow this transition. At pH >3.5, arsenic from the dissolution of arsenojarosite adsorbs onto newly formed reaction products. Arsenic also inhibits the formation of goethite and reduces the crystallinity of the observed maghemite reaction products. The coprecipitation of iron oxides with increasing amounts of arsenic results in a change from spherical to "worm-like" aggregate morphology and provides a sink for arsenic released during arsenojarosite dissolution. This study shows that in open systems with a flush of fresh solution, arsenic incorporation in jarosite results in an increase in dissolution rates. In closed systems, however, increasing surface arsenate-iron complexes inhibit further dissolution of the underlying bulk material, causing a reduction in dissolution rates as arsenic incorporation increases.

  13. 31Cl beta decay and the 30P31S reaction rate in nova nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Bennett, Michael; Wrede, C.; Brown, B. A.; Liddick, S. N.; Pérez-Loureiro, D.; NSCL e12028 Collaboration

    2016-03-01

    The 30P31S reaction rate is critical for modeling the final isotopic abundances of ONe nova nucleosynthesis, identifying the origin of presolar nova grains, and calibrating proposed nova thermometers. Unfortunately, this rate is essentially experimentally unconstrained because the strengths of key 31S proton capture resonances are not known, due to uncertainties in their spins and parities. Using a 31Cl beam produced at the National Superconducting Cyclotron Laboratory, we have populated several 31S states for study via beta decay and devised a new decay scheme which includes updated beta feedings and gamma branchings as well as multiple states previously unobserved in 31Cl beta decay. Results of this study, including the unambiguous identification due to isospin mixing of a new l = 0 , Jπ = 3 /2+ 31S resonance directly in the middle of the Gamow Window, will be presented, and significance to the evaluation of the 30P31S reaction rate will be discussed. Work supported by U.S. Natl. Sci. Foundation (Grants No. PHY-1102511, PHY-1404442, PHY-1419765, and PHY-1431052); U.S. Dept. of Energy, Natl. Nucl. Security Administration (Award No. DE-NA0000979); Nat. Sci. and Eng. Research Council of Canada.

  14. New reaction rates for improved primordial D /H calculation and the cosmic evolution of deuterium

    NASA Astrophysics Data System (ADS)

    Coc, Alain; Petitjean, Patrick; Uzan, Jean-Philippe; Vangioni, Elisabeth; Descouvemont, Pierre; Iliadis, Christian; Longland, Richard

    2015-12-01

    Primordial or big bang nucleosynthesis (BBN) is one of the three historically strong evidences for the big bang model. Standard BBN is now a parameter-free theory, since the baryonic density of the Universe has been deduced with an unprecedented precision from observations of the anisotropies of the cosmic microwave background radiation. There is a good agreement between the primordial abundances of 4He, D, 3He, and 7Li deduced from observations and from primordial nucleosynthesis calculations. However, the 7Li calculated abundance is significantly higher than the one deduced from spectroscopic observations and remains an open problem. In addition, recent deuterium observations have drastically reduced the uncertainty on D /H , to reach a value of 1.6%. It needs to be matched by BBN predictions whose precision is now limited by thermonuclear reaction rate uncertainties. This is especially important as many attempts to reconcile Li observations with models lead to an increased D prediction. Here, we reevaluate the d (p ,γ )3He, d (d ,n ) 3H3, and d (d ,p ) 3H reaction rates that govern deuterium destruction, incorporating new experimental data and carefully accounting for systematic uncertainties. Contrary to previous evaluations, we use theoretical ab initio models for the energy dependence of the S factors. As a result, these rates increase at BBN temperatures, leading to a reduced value of D /H =(2.45 ±0.10 )×10-5 (2 σ ), in agreement with observations.

  15. Rate Equations and Kinetic Parameters of the Reactions Involved in Pyrite Oxidation by Thiobacillus ferrooxidans.

    PubMed

    Lizama, H M; Suzuki, I

    1989-11-01

    Rate equations and kinetic parameters were obtained for various reactions involved in the bacterial oxidation of pyrite. The rate constants were 3.5 muM Fe per min per FeS(2) percent pulp density for the spontaneous pyrite dissolution, 10 muM Fe per min per mM Fe for the indirect leaching with Fe, 90 muM O(2) per min per mg of wet cells per ml for the Thiobacillus ferrooxidans oxidation of washed pyrite, and 250 muM O(2) per min per mg of wet cells per ml for the T. ferrooxidans oxidation of unwashed pyrite. The K(m) values for pyrite concentration were similar and were 1.9, 2.5, and 2.75% pulp density for indirect leaching, washed pyrite oxidation by T. ferrooxidans, and unwashed pyrite oxidation by T. ferrooxidans, respectively. The last reaction was competitively inhibited by increasing concentrations of cells, with a K(i) value of 0.13 mg of wet cells per ml. T. ferrooxidans cells also increased the rate of Fe production from Fe plus pyrite. PMID:16348054

  16. Temperature dependent rate coefficients for the reaction of OH radicals with dimethylbenzoquinones

    NASA Astrophysics Data System (ADS)

    Bejan, Iustinian; Barnes, Ian; Wiesen, Peter; Wenger, John C.

    2015-10-01

    Rate coefficients for the gas-phase reaction of hydroxyl (OH) radicals with two methylated benzoquinones have been measured at atmospheric pressure over the temperature range 284-313 K using the relative rate method. The following Arrhenius expressions (in cm3 molecule-1 s-1) have been obtained: k(25DMBQ) = (8.59 ± 4.70) × 10-12exp[(228 ± 163)/T] and k(26DMBQ) = (5.11 ± 2.79) × 10-12exp[(399 ± 165)/T] for 2,5-dimethylbenzoquinone (2,5DMBQ) and 2,6-dimethylbenzoquinone (2,6DMBQ), respectively, with corresponding values at 298 K: k(25DMBQ) = (2.05 ± 0.46) × 10-11 and k(26DMBQ) = (1.93 ± 0.12) × 10-11. The rate coefficients are compared to those reported for similar compounds and discussed in terms of structure-activity relationships. The results are also used to calculate atmospheric lifetimes for 2,5DMBQ and 2,6DMBQ with respect to reaction with OH radicals.

  17. Nuclear reaction rates and their influence on nucleosynthesis in the neutrino-p-process

    NASA Astrophysics Data System (ADS)

    Hatcher, Daniel; Frohlich, Carla; Perdikakis, Georgios

    2015-10-01

    The synthesis of elements heavier than iron in the early stages of galactic evolution is commonly attributed to Type II (core collapse) supernova explosions. However, the currently accepted mechanisms of heavy element synthesis through neutron capture processes (r-process and s-process) cannot explain the abundance patterns seen in very old galactic halo stars. A proposed solution to this problem is the neutrino-p-process, which takes place in the strong neutrino winds of core-collapse supernovae. In the neutrino-p-process, antineutrinos absorbed by protons yield neutrons that are quickly captured by the surrounding, proton-rich nuclei through (n,p) reactions. Such interactions allow for the nucleosynthesis of elements with atomic mass numbers greater than 64 (this includes Sr, Y, Zr and others possibly up to Sn). We study the sensitivity of the νp-process abundance pattern to (n,p), (p, γ), and (n, γ) rates for nuclei between Ni and Sn. We illustrate our findings for three different initial electron fractions and two representative trajectories. We discuss how these rates influence the abundance pattern and the nuclear flow. We observe the effects of predicted reaction rates on the abundance pattern and nuclear flow.

  18. Test of the quantum instanton approximation for thermal rate constants for some collinear reactions.

    PubMed

    Ceotto, Michele; Miller, William H

    2004-04-01

    Two variants of the recently developed quantum instanton (QI) model for calculating thermal rate constants of chemical reactions are applied to several collinear atom-diatom reactions with various skew angles. The results show that the original QI version of the model is consistently more accurate than the "simplest" quantum instanton version (both being applied here with one "dividing surface") and thus to be preferred. Also, for these examples (as with other earlier applications) the QI results agree well with the correct quantum rates (to within approximately 20% or better) for all temperatures >200 K, except for situations where dynamical corrections to transition state theory (i.e., "re-crossing" dynamics) are evident. (Since re-crossing effects are substantially reduced in higher dimensionality, this is not a cause for serious concern.) A procedure is also described which facilitates use of the METROPOLIS algorithm for evaluating all quantities that appear in the QI rate expression by Monte Carlo path integral methods. PMID:15267524

  19. 77 FR 64759 - Rescission of 10-Day Agency Discretionary Period in Assigning Unsatisfactory Safety Ratings

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-23

    ... Statutory History The Motor Carrier Safety Act of 1990 (1990 Act) (section 15 of the Sanitary Food... Fitness procedures; Safety Ratings, 56 FR 40801, 40802, 40806 (Aug. 18, 1991) (FHWA final rule). \\3\\ http... Federal Motor Carrier Safety Administration 49 CFR Part 385 RIN 2126-AB55 Rescission of 10-Day...

  20. Pyrite oxidation in unsaturated aquifer sediments. Reaction stoichiometry and rate of oxidation.

    PubMed

    Andersen, M S; Larsen, F; Postma, D

    2001-10-15

    The oxidation of pyrite (FeS2) contained in unsaturated aquifer sediment was studied by sediment incubation in gas impermeable polymer laminate bags. Reaction progress was followed over a period of nearly 2 months by monitoring the gas composition within the laminate bag. The gas phase in the incubation bags became depleted in O2 and enriched in CO2 and N2 and was interpreted as due to pyrite oxidation in combination with calcite dissolution. Sediment incubation provides a new method to estimate low rates of pyrite oxidation in unsaturated zone aquifer sediments. Oxidation rates of up to 9.4 x 10(-10) mol FeS2/g x s are measured, and the rates are only weakly correlated with the sediment pyrite content. The reactivity of pyrite, including the inhibition by FeOOH layers formed on its surface, apparently has a major effect on the rate of oxidation. The code PHREEQC 2.0 was used to calculate the reaction stoichiometry and partitioning of gases between the solution and the gas phase. Pyrite oxidation with concurrent calcite dissolution was found to be consistent with the experimental data while organic carbon oxidation was not. The reaction involves changes in the total volume of the gas phase. The reaction scheme predicts the volume of O2 gas consumed to be larger than of CO2 produced. In addition the solubility of CO2 in water is about 30 times larger than of O2 causing a further decrease in total gas volume. The change in total gas volume therefore also depends on the gas/water volume ratio and the lower the ratio the more pronounced the loss of volume will be. Under field conditions the change in total volume may amount up to 20% in the absence of calcite and over 10% in the presence of calcite. Such changes in gas volume during the oxidation of pyrite are expected to result in pressure gradients causing advective transport of gaseous oxygen. PMID:11686369

  1. Redox reaction rates in shallow aquifers: Implications for nitrate transport in groundwater and streams

    USGS Publications Warehouse

    Tesoriero, Anthony J.

    2012-01-01

    Groundwater age and water chemistry data along flow paths from recharge areas to streams were used to evaluate the trends and transformations of agricultural chemicals. Results from this analysis indicate that median nitrate recharge concentrations in these agricultural areas have increased markedly over the last 50 years from 4 mg N/L in samples collected prior to 1983 to 7.5 mg N/L in samples collected since 1983. The effect that nitrate accumulation in shallow aquifers will have on drinking water quality and stream ecosystems is dependent on the rate of redox reactions along flow paths and on the age distribution of nitrate discharging to supply wells and streams.

  2. Novel technique for constraining r-process (n, γ) reaction rates.

    PubMed

    Spyrou, A; Liddick, S N; Larsen, A C; Guttormsen, M; Cooper, K; Dombos, A C; Morrissey, D J; Naqvi, F; Perdikakis, G; Quinn, S J; Renstrøm, T; Rodriguez, J A; Simon, A; Sumithrarachchi, C S; Zegers, R G T

    2014-12-01

    A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r process. As a proof of principle, the γ spectra from the β decay of ^{76}Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and γ-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the ^{75}Ge(n,γ)^{76}Ge cross section and reaction rate. PMID:25526121

  3. Optimal choice of dividing surface for the computation of quantum reaction rates.

    PubMed

    Predescu, Cristian; Miller, William H

    2005-04-14

    We consider the calculation of quantum mechanical rate constants for chemical reactions via algorithms that utilize short-time values of the symmetrized flux-flux correlation function. We argue that the dividing surface that makes optimal use of the short-time quantum information is the surface that minimizes the value at the origin of the symmetrized flux-flux correlation function. We also demonstrate that, in the classical limit, this quantum variational criterion produces the same dividing surface as Wigner's variational principle. Finally, we argue that the quantum variational criterion behaves in a nearly optimal fashion with respect to the minimization of the extent of re-crossing flux. PMID:16851728

  4. First Results of Reaction Propagation Rates in HMX at High Pressure

    SciTech Connect

    Farber, D L; Esposito, A; Zaug, J M; Aracne-Ruddle, C

    2001-06-15

    The authors have measured the reaction propagation rate (RPR) in weapons-grade, ultrafine octahydro-1,3,57-tetranitro-1,3,5,7-tetrazocine (HMX) powder in a diamond anvil cell over the pressure range 0.7-35 GPa. In order to have a cross-comparison of their experiments, they carried out a series of experiments on nitromethane (NM) up to 15 GPa. The results on NM are indistinguishable from previous measurements of Rice and Folz. In comparison to high-pressure, NM, the burn process for solid HMX is not spatially uniform.

  5. First Results of Reaction Propagation Rates in HMX at High Pressure

    SciTech Connect

    Farber, D L; Esposito, A; Zaug, J M; Aracne-Ruddle, C

    2001-06-15

    The authors have measured the reaction propagation rate (RPR) in weapons-grade, ultrafine octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) powder in a diamond anvil cell over the pressure range 0.7-35 GPa. In order to have a cross-comparison of their experiments, they carried out a series of experiments on nitromethane (NM) up to 15 GPa. The results on NM are indistinguishable from previous measurements of Rice and Folz. In comparison to high-pressure NM, the burn process for solid HMX is between 5-10 times faster at pressures above 10 GPa.

  6. Chemical reaction rates using the semiclassical Van-Vleck initialvalue representation

    SciTech Connect

    Venkataraman, Charulatha; Miller, William H.

    2006-11-29

    A semiclassical IVR formulation using the Van-Vleck propagator has been used to calculate the flux correlation function and thereby reaction rate constants. This Van-Vleck formulation of the flux-flux correlation function is computationally as simple as the classical Wigner model. However unlike the latter, it has the ability to capture quantum interference/coherence effects. Classical trajectories are evolved starting from the dividing surface that separates reactants and products, and are evolved negatively in time. This formulation has been tested on model problems ranging from the Eckart barrier, double well to the collinear H + H{sub 2}.

  7. Measurement of (α,n) reaction cross sections of erbium isotopes for testing astrophysical rate predictions

    NASA Astrophysics Data System (ADS)

    Kiss, G. G.; Szücs, T.; Rauscher, T.; Török, Zs; Csedreki, L.; Fülöp, Zs; Gyürky, Gy; Halász, Z.

    2015-05-01

    The γ-process in core-collapse and/or type Ia supernova explosions is thought to explain the origin of the majority of the so-called p nuclei (the 35 proton-rich isotopes between Se and Hg). Reaction rates for γ-process reaction network studies have to be predicted using Hauser-Feshbach statistical model calculations. Recent investigations have shown problems in the prediction of α-widths at astrophysical energies which are an essential input for the statistical model. It has an impact on the reliability of abundance predictions in the upper mass range of the p nuclei. With the measurement of the 164,166Er(α,n)167,169Yb reaction cross sections at energies close to the astrophysically relevant energy range we tested the recently suggested low energy modification of the α+nucleus optical potential in a mass region where γ-process calculations exhibit an underproduction of the p nuclei. Using the same optical potential for the α-width which was derived from combined 162Er(α,n) and 162Er(α,γ) measurement makes it plausible that a low-energy modification of the optical α+nucleus potential is needed.

  8. Breakdown of the reaction-diffusion master equation with nonelementary rates

    NASA Astrophysics Data System (ADS)

    Smith, Stephen; Grima, Ramon

    2016-05-01

    The chemical master equation (CME) is the exact mathematical formulation of chemical reactions occurring in a dilute and well-mixed volume. The reaction-diffusion master equation (RDME) is a stochastic description of reaction-diffusion processes on a spatial lattice, assuming well mixing only on the length scale of the lattice. It is clear that, for the sake of consistency, the solution of the RDME of a chemical system should converge to the solution of the CME of the same system in the limit of fast diffusion: Indeed, this has been tacitly assumed in most literature concerning the RDME. We show that, in the limit of fast diffusion, the RDME indeed converges to a master equation but not necessarily the CME. We introduce a class of propensity functions, such that if the RDME has propensities exclusively of this class, then the RDME converges to the CME of the same system, whereas if the RDME has propensities not in this class, then convergence is not guaranteed. These are revealed to be elementary and nonelementary propensities, respectively. We also show that independent of the type of propensity, the RDME converges to the CME in the simultaneous limit of fast diffusion and large volumes. We illustrate our results with some simple example systems and argue that the RDME cannot generally be an accurate description of systems with nonelementary rates.

  9. Noise-induced convergence of the low flow rate chaos in the Belousov-Zhabotinsky reaction

    NASA Astrophysics Data System (ADS)

    Yoshimoto, Minoru; Nakaiwa, Masaru; Akiya, Takaji; Ohmori, Takao; Yamaguchi, Tomohiko

    The effect of noise on the low flow-rate chaos in the Belousov-Zhabotinsky (BZ) reaction was studied. The chaos was simulated using the three-variable model of Györgyi and Field. Gaussian white noise was imposed on the flow-rate of the reactant solutions fed into CSTR to simulate the so-called type P noise. The range of average noise amplitudes was chosen between 0.01% and 1% related to the inverse residence time. The calculated time series were analyzed on the basis of their Fourier spectra, maximum Lyapunov exponent, Kolmogorov entropies, return maps and invariant density. We found that the noise induces partial order of the period-3-like oscillations in the low flowrate chaos.

  10. Absolute rate constants for the reaction of atomic hydrogen with ketene from 298 to 500 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Nava, D. F.; Payne, W. A.; Stief, L. J.

    1979-01-01

    Rate constants for the reaction of atomic hydrogen with ketene have been measured at room temperature by two techniques, flash photolysis-resonance fluorescence and discharge flow-resonance fluorescence. The measured values are (6.19 + or - 1.68) x 10 to the -14th and (7.3 + or - 1.3) x 10 to the -14th cu cm/molecule/s, respectively. In addition, rate constants as a function of temperature have been measured over the range 298-500 K using the FP-RF technique. The results are best represented by the Arrhenius expression k = (1.88 + or - 1.12) x 10 to the -11th exp(-1725 + or - 190/T) cu cm/molecule/s, where the indicated errors are at the two standard deviation level.

  11. Elementary reaction rate measurements at high temperatures by tunable-laser flash-absorption

    SciTech Connect

    Hessler, J.P.

    1993-12-01

    The major objective of this program is to measure thermal rate coefficients and branching ratios of elementary reactions. To perform these measurements, the authors constructed an ultrahigh-purity shock tube to generate temperatures between 1000 and 5500 K. The tunable-laser flash-absorption technique is used to measure the rate of change of the concentration of species which absorb below 50,000 cm{sup {minus}1} e.g.: OH, CH, and CH{sub 3}. This technique is being extended into the vacuum-ultraviolet spectral region where one can measure atomic species e.g.: H, D, C, O, and N; and diatomic species e.g.: O{sub 2}, CO, and OH.

  12. Solvent effects on the rate constants for reaction of trichloromethylperoxyl radicals with organic reductants

    SciTech Connect

    Alfassi, Z.B.; Huie, R.E.; Neta, P. )

    1993-07-15

    Absolute rate constants for the reactions of trichloromethylperoxyl radicals with chloropromazine and trolox have been determined by pulse radiolysis in 16 different solvents. The rate constants were found to vary over two orders of magnitude (10[sup 7]-10[sup 9] L mol[sup [minus]1] s[sup [minus]1]) and to correlate with the Hildebrand solubility parameter (cohesive energy density) of the solvent better than with any other single solvent parameter. The correlation was satisfactory for ClPz and did not improve significantly by including additional parameters. For trolox, however, the correlation was relatively poor but was improved considerably by taking into account the basicity of the solvent. This effect is due to the transfer of a proton upon the oxidation of trolox. 21 refs., 3 figs., 2 tabs.

  13. Informing Neutron-Capture Rates through (d,p) Reactions on Neutron-Rich Tin Isotopes

    NASA Astrophysics Data System (ADS)

    Manning, B.; Cizewski, J. A.; Kozub, R. L.; Ahn, S.; Allmond, J. M.; Bardayan, D. W.; Chae, K. Y.; Chipps, K. A.; Howard, M. E.; Jones, K. L.; Liang, J. F.; Matos, M.; Nunes, F. M.; Nesaraja, C. D.; O'Malley, P. D.; Pain, S. D.; Peters, W. A.; Pittman, S. T.; Ratkiewicz, A.; Schmitt, K. T.; Shapira, D.; Smith, M. S.; Titus, L.

    2014-03-01

    Level energies and spectroscopic information for neutron-rich nuclei provide important input for r-process nucleosynthesis calculations; specifically, the location and strength of single-neutron l = 1 states when calculating neutron-capture rates. Surman and collaborators have performed sensitivity studies to show that varying neutron-capture rates can significantly alter final r-process abundances. However, there are many nuclei important to the r-process that cannot be studied. Extending studies to more neutron-rich nuclei will help constrain the nuclear shell-model in extrapolating to nuclei even further from stability. The (d,p) reaction has been measured with radioactive ion beams of 126Sn and 128Sn to complete the set of (d,p) studies on even mass tin isotopes from doubly-magic 132 to stable 124Sn. Work supported in part by the U.S. Department of Energy and National Science Foundation.

  14. PH-dependence of the steady-state rate of a two-step enzymic reaction.

    PubMed

    Brocklehurst, K; Dixon, H B

    1976-04-01

    1. The pH-dependence is considered of a reaction between E and S that proceeds through an intermediate ES under "Briggs-Haldane' conditions, i.e. there is a steady state in ES and [S]o greater than [E]T, where [S]o is the initial concentration of S and [E]T is the total concentration of all forms of E. Reactants and intermediates are assumed to interconvert in three protonic states (E equilibrium ES; EH equilibrium EHS; EH2 equilibrium EH2S), but only EHS provides products by an irreversible reaction whose rate constant is kcat. Protonations are assumed to be so fast that they are all at equilibrium. 2. The rate equation for this model is shown to be v = d[P]/dt = (kcat.[E]T[S]o/A)/[(KmBC/DA) + [S]o], where Km is the usual assembly of rate constants around EHS and A-D are functions of the form (1 + [H]/K1 + K2/[H]), in which K1 and K2 are: in A, the molecular ionization constants of ES; in B, the analogous constants of E; in C and D, apparent ionization constants composed of molecular ionization constants (of E or ES) and assemblies of rate constants. 3. As in earlier treatments of this type of reaction which involve either the assumption that the reactants and intermediate are in equilibrium or the assumption of Peller & Alberty [(1959) J. Am. Chem. Soc. 81, 5907-5914] that only EH and EHS interconvert directly, the pH-dependence of kcat. is determined only by A. 4. The pH-dependence of Km is determined in general by B-C/A-D, but when reactants and intermediate are in equilibrium, C identical to D and this expression simplifies to B/A. 5. The pH-dependence of kcat./Km, i.e. of the rate when [S]o less than Km, is not necessarily a simple bell-shaped curve characterized only by the ionization constants of B, but is a complex curve characterized by D/B-C. 6. Various situations are discussed in which the pH-dependence of kcat./Km is determined by assemblies simpler than D/B-C. The special situation in which a kcat./Km-pH profile provides the molecular pKa values of

  15. Scanning electrochemical microscopy of metallic biomaterials: reaction rate and ion release imaging modes.

    PubMed

    Gilbert, J L; Smith, S M; Lautenschlager, E P

    1993-11-01

    The Scanning Electrochemical Microscope (SECM) is a nonoptical scanning microscopic instrument capable of imaging highly localized electrical currents associated with charge transfer reactions on metallic biomaterials surfaces. The SECM operates as an aqueous electrochemical cell under bipotentiostatic control with a microelectrode and sample independently biased as working electrodes. Microelectrode current and position is recorded as it is scanned very near a metallurgically polished planar sample surface. To date, the SECM has imaged metallic biomaterials surfaces in oxygen reaction rate imaging (ORRI) and ion release and deposition imaging (IRDI) modes. In ORRI, sample and microelectrode are biased at sufficiently negative potentials to reduce absorbed oxygen. As the microelectrode scans areas of active oxygen reduction, localized diffusion fields with decreased oxygen solution concentrations are encountered and resultant decrements in microelectrode current are observed. In IRDI mode the sample is positively biased and the microelectrode is negatively biased. The microelectrode detects anodic dissolution products with highest currents being observed over the most active areas. Performance of the SECM has been evaluated on Ni minigrids, gamma-1 Hg-Ag dental amalgam crystals, and sintered beads of Co-Cr-Mo alloy which represent significantly different geometries and corrosion processes to help demonstrate the potential of this instrument. The SECM is a valuable tool for imaging microelectrochemical processes on the surfaces of metallurgically polished metallic biomaterials samples and a wide variety of other surfaces of biological interest where charge transfer reactions occur. The SECM allows selective biasing of metallic biomaterials surfaces and Faradaic reactions can be selectively imaged while the surface is in the active, passive, or transpassive state. PMID:8262998

  16. Reaction Rate Theory of Radiation Exposure and Scaling Hypothesis in Mutation Frequency

    NASA Astrophysics Data System (ADS)

    Manabe, Yuichiro; Nakamura, Issei; Bando, Masako

    2014-11-01

    We have developed a kinetic reaction model for cells with irradiated DNA molecules due to ionizing radiation exposure. Our theory simultaneously accounts for the time-dependent reactions of DNA damage, DNA mutation and DNA repair, and the proliferation and apoptosis of cells in a tissue with a minimal set of model parameters. In contrast to existing theories of radiation exposition, we do not assume the relationships between the total dose and the induced mutation frequency. Our theory provides a universal scaling function that reasonably explains the mega-mouse experiments by Russell and Kelly [Proc. Natl. Acad. Sci. U.S.A. 79, 542 (1982)] with different dose rates. Furthermore, we have estimated the effective dose rate, which is biologically equivalent to the ionizing effects other than those caused by artificial irradiation. This value is 1.11 × 10-3 Gy/h, which is significantly larger than the effect caused by natural background radiation.

  17. The application of the Reaction Rate Analyser LKB 8600 as an automatic coagulometer.

    PubMed

    Andersen, I; Thorsen, S

    1977-02-01

    The application of the Reaction Rate Analyser LKB 8600 (RRA) as an automatic coagulometer is described. The RRA was slightly modified without interfering with its function as an enzyme reaction rate analyser. The endpoint of coagulation was recorded when the increase in absorbance exceeded 0.047 at lambda = 340 nm. The coagulation time was monitored by a counter with automatic print-out or by a recorder. The analytical dispersion, s(x)x, ranged between 0.01 and 0.05. Results (x, y) of the determination of the quantity of plasma coagulation factors (II + VII + X) by RRA and manually by visual recording could be expressed by y = 0.93x + 0.04, r = 0.96, n = 66 (method of Owren & Aas) or by y = 1.00x + 0.02, r = 0.98, n = 49 (Normotest). Similarly, plasma activated partial thromboplastin time (Activated Thrombofax) could be expressed by y = 0.99x + 5.00, r = 0.99, n = 23. PMID:616030

  18. Dissolution Dynamic Nuclear Polarization Instrumentation for Real-time Enzymatic Reaction Rate Measurements by NMR.

    PubMed

    Balzan, Riccardo; Fernandes, Laetitia; Comment, Arnaud; Pidial, Laetitia; Tavitian, Bertrand; Vasos, Paul R

    2016-01-01

    The main limitation of NMR-based investigations is low sensitivity. This prompts for long acquisition times, thus preventing real-time NMR measurements of metabolic transformations. Hyperpolarization via dissolution DNP circumvents part of the sensitivity issues thanks to the large out-of-equilibrium nuclear magnetization stemming from the electron-to-nucleus spin polarization transfer. The high NMR signal obtained can be used to monitor chemical reactions in real time. The downside of hyperpolarized NMR resides in the limited time window available for signal acquisition, which is usually on the order of the nuclear spin longitudinal relaxation time constant, T1, or, in favorable cases, on the order of the relaxation time constant associated with the singlet-state of coupled nuclei, TLLS. Cellular uptake of endogenous molecules and metabolic rates can provide essential information on tumor development and drug response. Numerous previous hyperpolarized NMR studies have demonstrated the relevancy of pyruvate as a metabolic substrate for monitoring enzymatic activity in vivo. This work provides a detailed description of the experimental setup and methods required for the study of enzymatic reactions, in particular the pyruvate-to-lactate conversion rate in presence of lactate dehydrogenase (LDH), by hyperpolarized NMR. PMID:26967906

  19. Reaction Rate Measurement at the Californium User Facility (CUF) for unfolding the neutron spectrum

    NASA Astrophysics Data System (ADS)

    Hannan, Mohammad; Ortega, Ruben

    2011-03-01

    Neutron Activation Analysis was used to determine Reaction Rate measurement of several activation detectors at the ORNL Californium User Facility (CUF). The irradiations were performed with 34 mg Cf 252 neutron source strength.. Ten source capsules > 34 mgwerepositionedconcentricallyaroundasamplecavity . Wehavedeterminedabsoluteactivityperatomof 9 detectors : Au 197 (n , γ) Au 198 , Al 27 (n , α) Na 24 , Al 27 (n , p) Mg 27 , Fe 56 (n , p) Mn 5 , Fe 54 (n , p) Mn 54 , In 115 (n , γ) In 116 , Ti 46 (n , p) Sc 46 , Ni 60 (n , p) Co 60 , Fe 58 (n , γ) Fe 59 . Theerrorsarewithin 1.5 - 8 60 and Fe 58 have errors of 46% and 32 %. These high errors may be attributed to the counting statistics. These reaction rate values will be used to unfold the neutron spectrum of the CUF using the MAXED 2000, a computer code for the de convolution of multi sphere neutron spectrometer data and the results are discussed. The authors acknowledge help, advise, and using facility at ORNL-CUF to Dr. Rodger martin and Mr. David C. Galsgow.

  20. Relationship between the surface coverage of spectator species and the rate of electrocatalytic reactions.

    SciTech Connect

    Strmcnik, D. S.; Rebec, P.; Gaberscek, M.; Tripkovic, D.; Stamenkovic, V.; Lucas, C.; Markovic, N. M.; Materials Science Division; Univ. of Chicago; National Inst. of Chemistry; Univ. of Liverpool

    2007-12-20

    Relationships between the surface coverage of spectator (blocking) species and the rate of the hydrogen oxidation reaction (HOR), the oxygen reduction reaction (ORR), and the bulk oxidation of dissolved CO on Pt(100) and Pt(111) single crystals in acidic electrolytes has been probed by cyclic voltammetry, in situ surface X-ray scattering (SXS), and ex situ scanning tunneling microscopy (STM) techniques. It is shown that the surface coverage by spectator species during the HOR and the ORR are the same as for the corresponding coverage obtained in the inert (Ar-saturated) environment. This observation is consistent with the proposition that the availability of active sites for H{sub 2} and O{sub 2} is determined almost entirely by the coverage of adsorbates from the supporting electrolyte and not by the active intermediates. Related electrochemical-SXS studies undertaken for bulk CO oxidation reveal that the maximum rate above the ignition potential is reached on a surface that is covered by {approx}90% of an ordered CO adlayer. The nature of the active sites in this case is determined by a combination of electrochemical and STM results. It is found that the active sites in this potential region are steps, which appear to be active sites for OH adsorption. To get insight into the relationship between the diffusion-limiting current and the surface coverage by the inactive CO adlayer, we introduce the concept of a partially blocked electrode surface with active and inactive areas. On the basis of the calculations and experimental results, it is proposed that the active sites for given electrochemical reactions on Pt electrodes are arrays of adsorbate-free nanoscale patches embedded in an inactive adlayer of nonreactive molecular species.

  1. Reactions of OH with Butene Isomers. Measurements of the Overall Rates and a Theoretical Study

    SciTech Connect

    Vasu, Subith; Huynh, Lam; Davidson, David F.; Hanson, Ronald K.; Golden, David

    2011-03-09

    Reactions of hydroxyl (OH) radicals with 1-butene (k1), trans-2-butene (k2), and cis-2-butene (k3) were studied behind reflected shock waves over the temperature range 880-1341 K and at pressures near 2.2 atm. OH radicals were produced by shock-heating tert-butyl hydroperoxide, (CH3)3-CO-OH, and monitored by narrow-line width ring dye laser absorption of the well-characterized R1(5) line of the OH A-X (0, 0) band near 306.7 nm. OH time histories were modeled using a comprehensive C5 oxidation mechanism, and rate constants for the reaction of OH with butene isomers were extracted by matching modeled and measured OH concentration time histories. We present the first high-temperature measurement of OH + cis-2-butene and extend the temperature range of the only previous high-temperature study for both 1-butene and trans-2-butene. With the potential energy surface calculated using CCSD(T)/6-311++G(d,p)//QCISD/6-31G(d), the rate constants and branching fractions for the H-abstraction channels of the reaction of OH with 1-butene were calculated in the temperature range 300-1500 K. Corrections for variational and tunneling effects as well as hindered-rotation treatments were included. The calculations are in good agreement with current and previous experimental data and with a recent theoretical study.

  2. Thermal behaviors, nonisothermal decomposition reaction kinetics, thermal safety and burning rates of BTATz-CMDB propellant.

    PubMed

    Yi, Jian-Hua; Zhao, Feng-Qi; Wang, Bo-Zhou; Liu, Qian; Zhou, Cheng; Hu, Rong-Zu; Ren, Ying-Hui; Xu, Si-Yu; Xu, Kang-Zhen; Ren, Xiao-Ning

    2010-09-15

    The composite modified double base (CMDB) propellants (nos. RB0601 and RB0602) containing 3,6-bis (1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine (BTATz) without and with the ballistic modifier were prepared and their thermal behaviors, nonisothermal decomposition reaction kinetics, thermal safety and burning rates were investigated. The results show that there are three mass-loss stages in TG curve and two exothermic peaks in DSC curve for the BTATz-CMDB propellant. The first two mass-loss stages occur in succession and the temperature ranges are near apart, and the decomposition peaks of the two stages overlap each other, inducing only one visible exothermic peak appear in DSC curve during 350-550 K. The reaction mechanisms of the main exothermal decomposition processes of RB0601 and RB0602 are all classified as chemical reaction, the mechanism functions are f(alpha)=(1-alpha)(2), and the kinetic equations are dalpha/dt = 10(19.24)(1-alpha)(2)e(-2.32x10(4)/T) and dalpha/dt = 10(20.32)(1-alpha)(2)e(-2.32x10(4)/T). The thermal safety evaluation on the BTATz-CMDB propellants was obtained. With the substitution of 26% RDX by BTATz and with the help of the ballistic modifier in the CMDB propellant formulation, the burning rate can be improved by 89.0% at 8 MPa and 47.1% at 22 MPa, the pressure exponent can be reduced to 0.353 at 14-20 MPa. PMID:20542638

  3. Product distributions and rate constants for ion-molecule reactions in water, hydrogen sulfide, ammonia, and methane

    NASA Technical Reports Server (NTRS)

    Huntress, W. T., Jr.; Pinizzotto, R. F., Jr.

    1973-01-01

    The thermal energy, bimolecular ion-molecule reactions occurring in gaseous water, hydrogen sulfide, ammonia, and methane have been identified and their rate constants determined using ion cyclotron resonance methods. Absolute rate constants were determined for the disappearance of the primary ions by using the trapped ion method, and product distributions were determined for these reactions by using the cyclotron ejection method. Previous measurements are reviewed and compared with the results using the present methods. The relative rate constants for hydrogen-atom abstraction, proton transfer, and charge transfer are also determined for reactions of the parent ions.

  4. Ground reaction forces and loading rates associated with parkour and traditional drop landing techniques.

    PubMed

    Puddle, Damien L; Maulder, Peter S

    2013-01-01

    Due to the relative infancy of Parkour there is currently a lack of empirical evidence on which to base specific technique instruction upon. The purpose of this study was to compare the ground reaction forces and loading rates involved in two Parkour landing techniques encouraged by local Parkour instructors and a traditional landing technique recommended in the literature. Ten male participants performed three different drop landing techniques (Parkour precision, Parkour roll, and traditional) onto a force plate. Compared to the traditional technique the Parkour precision technique demonstrated significantly less maximal vertical landing force (38%, p < 0.01, ES = 1.76) and landing loading rate (54%, p < 0.01, ES = 1.22). Similarly, less maximal vertical landing force (43%, p < 0.01, ES = 2.04) and landing loading rate (63%, p < 0.01, ES = 1.54) were observed in the Parkour roll technique compared to the traditional technique. It is unclear whether or not the Parkour precision technique produced lower landing forces and loading rates than the Parkour roll technique as no significant differences were found. The landing techniques encouraged by local Parkour instructors such as the precision and roll appear to be more appropriate for Parkour practitioners to perform than a traditional landing technique due to the lower landing forces and loading rates experienced. Key pointsParkour precision and Parkour roll landings were found to be safer than a traditional landing technique, resulting in lower maximal vertical forces, slower times to maximal vertical force and ultimately lesser loading rates.Parkour roll may be more appropriate (safer) to utilize than the Parkour precision during Parkour landing scenarios.The Parkour landing techniques investigated n this study may be beneficial for landing by non-Parkour practitioners in everyday life. PMID:24149735

  5. Ground Reaction Forces and Loading Rates Associated with Parkour and Traditional Drop Landing Techniques

    PubMed Central

    Puddle, Damien L.; Maulder, Peter S.

    2013-01-01

    Due to the relative infancy of Parkour there is currently a lack of empirical evidence on which to base specific technique instruction upon. The purpose of this study was to compare the ground reaction forces and loading rates involved in two Parkour landing techniques encouraged by local Parkour instructors and a traditional landing technique recommended in the literature. Ten male participants performed three different drop landing techniques (Parkour precision, Parkour roll, and traditional) onto a force plate. Compared to the traditional technique the Parkour precision technique demonstrated significantly less maximal vertical landing force (38%, p < 0.01, ES = 1.76) and landing loading rate (54%, p < 0.01, ES = 1.22). Similarly, less maximal vertical landing force (43%, p < 0.01, ES = 2.04) and landing loading rate (63%, p < 0.01, ES = 1.54) were observed in the Parkour roll technique compared to the traditional technique. It is unclear whether or not the Parkour precision technique produced lower landing forces and loading rates than the Parkour roll technique as no significant differences were found. The landing techniques encouraged by local Parkour instructors such as the precision and roll appear to be more appropriate for Parkour practitioners to perform than a traditional landing technique due to the lower landing forces and loading rates experienced. Key points Parkour precision and Parkour roll landings were found to be safer than a traditional landing technique, resulting in lower maximal vertical forces, slower times to maximal vertical force and ultimately lesser loading rates. Parkour roll may be more appropriate (safer) to utilize than the Parkour precision during Parkour landing scenarios. The Parkour landing techniques investigated n this study may be beneficial for landing by non-Parkour practitioners in everyday life. PMID:24149735

  6. 34 CFR 694.9 - What is the maximum indirect cost rate for an agency of a State or local government?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... AWARENESS AND READINESS FOR UNDERGRADUATE PROGRAMS (GEAR UP) § 694.9 What is the maximum indirect cost rate for an agency of a State or local government? Notwithstanding 34 CFR 75.560-75.562 and 34 CFR...

  7. Rate and reaction probability of the surface reaction between ozone and dihydromyrcenol measured in a bench scale reactor and a room-sized chamber

    NASA Astrophysics Data System (ADS)

    Shu, Shi; Morrison, Glenn C.

    2012-02-01

    Low volatility terpenoids emitted from consumer products can react with ozone on surfaces and may significantly alter concentrations of ozone, terpenoids and reaction products in indoor air. We measured the reaction probability and a second-order surface-specific reaction rate for the ozonation of dihydromyrcenol, a representative indoor terpenoid, adsorbed onto polyvinylchloride (PVC), glass, and latex paint coated spheres. The reaction probability ranged from (0.06-8.97) × 10 -5 and was very sensitive to humidity, substrate and mass adsorbed. The average surface reaction probability is about 10 times greater than that for the gas-phase reaction. The second-order surface-specific rate coefficient ranged from (0.32-7.05) × 10 -15 cm 4 s -1 molecule -1and was much less sensitive to humidity, substrate, or mass adsorbed. We also measured the ozone deposition velocity due to adsorbed dihydromyrcenol on painted drywall in a room-sized chamber, Based on that, we calculated the rate coefficient ((0.42-1.6) × 10 -15 cm 4 molecule -1 s -1), which was consistent with that derived from bench-scale experiments for the latex paint under similar conditions. We predict that more than 95% of dihydromyrcenol oxidation takes place on indoor surfaces, rather than in building air.

  8. Shock tube measurements of specific reaction rates in the branched chain CH4-CO-O2 system

    NASA Technical Reports Server (NTRS)

    Brabbs, T. A.; Brokaw, R. S.

    1974-01-01

    Rate constants of two elementary bimolecular reactions involved in the oxidation of methane have been determined by monitoring the exponential growth of CO flame band emission behind incident shocks in three suitably chosen gas mixtures. The data do not support a mechanism which invokes the four center process CH3 + O2 yields CH2O + OH for the reaction of methyl with oxygen.

  9. Stress-associated cardiovascular reaction masks heart rate dependence on physical load in mice.

    PubMed

    Andreev-Andrievskiy, A A; Popova, A S; Borovik, A S; Dolgov, O N; Tsvirkun, D V; Custaud, M; Vinogradova, O L

    2014-06-10

    When tested on the treadmill mice do not display a graded increase of heart rate (HR), but rather a sharp shift of cardiovascular indices to high levels at the onset of locomotion. We hypothesized that under test conditions cardiovascular reaction to physical load in mice is masked with stress-associated HR increase. To test this hypothesis we monitored mean arterial pressure (MAP) and heart rate in C57BL/6 mice after exposure to stressful stimuli, during spontaneous locomotion in the open-field test, treadmill running or running in a wheel installed in the home cage. Mice were treated with β1-adrenoblocker atenolol (2mg/kg ip, A), cholinolytic ipratropium bromide (2mg/kg ip, I), combination of blockers (A+I), anxiolytic diazepam (5mg/kg ip, D) or saline (control trials, SAL). MAP and HR in mice increased sharply after handling, despite 3weeks of habituation to the procedure. Under stressful conditions of open field test cardiovascular parameters in mice were elevated and did not depend on movement speed. HR values did not differ in I and SAL groups and were reduced with A or A+I. HR was lower at rest in D pretreated mice. In the treadmill test HR increase over speeds of 6, 12 and 18m/min was roughly 1/7-1/10 of HR increase observed after placing the mice on the treadmill. HR could not be increased with cholinolytic (I), but was reduced after sympatholytic (A) or A+I treatment. Anxiolytic (D) reduced heart rate at lower speeds of movement and its overall effect was to unmask the dependency of HR on running speed. During voluntary running in non-stressful conditions of the home cage HR in mice linearly increased with increasing running speeds. We conclude that in test situations cardiovascular reactions in mice are governed predominantly by stress-associated sympathetic activation, rendering efforts to evaluate HR and MAP reactions to workload unreliable. PMID:24802359

  10. The role of advanced reactive surface area characterization in improving predictions of mineral reaction rates

    NASA Astrophysics Data System (ADS)

    Beckingham, L. E.; Zhang, S.; Mitnick, E.; Cole, D. R.; Yang, L.; Anovitz, L. M.; Sheets, J.; Swift, A.; Kneafsey, T. J.; Landrot, G.; Mito, S.; Xue, Z.; Steefel, C. I.; DePaolo, D. J.; Ajo Franklin, J. B.

    2014-12-01

    Geologic sequestration of CO2 in deep sedimentary formations is a promising means of mitigating carbon emissions from coal-fired power plants but the long-term fate of injected CO2 is challenging to predict. Reactive transport models are used to gain insight over long times but rely on laboratory determined mineral reaction rates that have been difficult to extrapolate to field systems. This, in part, is due to a lack of understanding of mineral reactive surface area. Many models use an arbitrary approximation of reactive surface area, applying orders of magnitude scaling factors to measured BET or geometric surface areas. Recently, a few more sophisticated approaches have used 2D and 3D image analyses to determine mineral-specific reactive surface areas that account for the accessibility of minerals. However, the ability of these advanced surface area estimates to improve predictions of mineral reaction rates has yet to be determined. In this study, we fuse X-ray microCT, SEM QEMSCAN, XRD, SANS, and SEM-FIB analysis to determine mineral-specific accessible reactive surface areas for a core sample from the Nagaoka pilot CO2 injection site (Japan). This sample is primarily quartz, plagioclase, smectite, K-feldspar, and pyroxene. SEM imaging shows abundant smectite cement and grain coatings that decrease the fluid accessibility of other minerals. However, analysis of FIB-SEM images reveals that smectite nano-pores are well connected such that access to underlying minerals is not occluded by smectite coatings. Mineral-specific accessible surfaces are determined, accounting for the connectivity of the pore space with and without connected smectite nano-pores. The large-scale impact of variations in accessibility and dissolution rates are then determined through continuum scale modeling using grid-cell specific information on accessible surface areas. This approach will be compared with a traditional continuum scale model using mineral abundances and common surface area

  11. Mixed quantum classical calculation of proton transfer reaction rates: From deep tunneling to over the barrier regimes

    SciTech Connect

    Xie, Weiwei; Xu, Yang; Zhu, Lili; Shi, Qiang

    2014-05-07

    We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula.

  12. Mixed quantum classical calculation of proton transfer reaction rates: from deep tunneling to over the barrier regimes.

    PubMed

    Xie, Weiwei; Xu, Yang; Zhu, Lili; Shi, Qiang

    2014-05-01

    We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula. PMID:24811623

  13. The interplay between transport and reaction rates as controls on nitrate attenuation in permeable, streambed sediments

    NASA Astrophysics Data System (ADS)

    Lansdown, K.; Heppell, C. M.; Trimmer, M.; Binley, A.; Heathwaite, A. L.; Byrne, P.; Zhang, H.

    2015-06-01

    Anthropogenic nitrogen fixation and subsequent use of this nitrogen as fertilizer have greatly disturbed the global nitrogen cycle. Rivers are recognized hot spots of nitrogen removal in the landscape as interaction between surface water and sediments creates heterogeneous redox environments conducive for nitrogen transformations. Our understanding of riverbed nitrogen dynamics to date comes mainly from shallow sediments or hyporheic exchange flow pathways with comparatively little attention paid to groundwater-fed, gaining reaches. We have used 15N techniques to quantify in situ rates of nitrate removal to 1 m depth within a groundwater-fed riverbed where subsurface hydrology ranged from strong upwelling to predominantly horizontal water fluxes. We combine these rates with detailed hydrologic measurements to investigate the interplay between biogeochemical activity and water transport in controlling nitrogen attenuation along upwelling flow pathways. Nitrate attenuation occurred via denitrification rather than dissimilatory nitrate reduction to ammonium or anammox (range = 12 to >17,000 nmol 15N L-1 h-1). Overall, nitrate removal within the upwelling groundwater was controlled by water flux rather than reaction rate (i.e., Damköhler numbers <1) with the exception of two hot spots of biogeochemical activity. Deep sediments were as important a nitrate sink as shallow sediments with fast rates of denitrification and short water residence time close to the riverbed surface balanced by slower rates of denitrification and water flux at depth. Within this permeable riverbed >80% of nitrate removal occurs within sediments not exposed to hyporheic exchange flows under base flow conditions, illustrating the importance of deep sediments as nitrate sinks in upwelling systems.

  14. Shock tube measurements of specific reaction rates in branched chain CH4-CO-O2 system

    NASA Technical Reports Server (NTRS)

    Brabbs, T. A.; Brokaw, R. S.

    1974-01-01

    Rate constants of two elementary bimolecular reactions involved in the oxidation of methane were determined by monitoring the exponential growth of CO flame band emission behind incident shocks in three suitably chosen gas mixtures.

  15. A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Chinitz, W.; Foy, E.; Rowan, G.; Goldstein, D.

    1982-01-01

    The use of probability theory to determine the effects of turbulent fluctuations on reaction rates in turbulent combustion systems is briefly reviewed. Results are presented for the effect of species fluctuations in particular. It is found that turbulent fluctuations of species act to reduce the reaction rates, in contrast with the temperature fluctuations previously determined to increase Arrhenius reaction rate constants. For the temperature fluctuations, a criterion is set forth for determining if, in a given region of a turbulent flow field, the temperature can be expected to exhibit ramp like fluctuations. Using the above results, along with results previously obtained, a model is described for testing the effects of turbulent fluctuations of temperature and species on reaction rates in computer programs dealing with turbulent reacting flows. An alternative model which employs three variable probability density functions (temperature and two species) and is currently being formulated is discussed as well.

  16. Revised Production Rates for Na-22 and Mn-54 in Meteorites Using Cross Sections Measured for Neutron-induced Reactions

    NASA Technical Reports Server (NTRS)

    Sisterson, J. M.; Kim, K. J.; Reedy, R. C.

    2004-01-01

    The interactions of galactic cosmic rays (GCR) with extraterrestrial bodies produce small amounts of radionuclides and stable isotopes. The production rates of many relatively short-lived radionuclides, including 2.6-year Na-22 and 312-day Mn-54, have been measured in several meteorites collected very soon after they fell. Theoretical models used to calculate production rates for comparison with the measured values rely on input data containing good cross section measurements for all relevant reactions. Most GCR particles are protons, but secondary neutrons make most cosmogenic nuclides. Calculated production rates using only cross sections for proton-induced reactions do not agree well with measurements. One possible explanation is that the contribution to the production rate from reactions initiated by secondary neutrons produced in primary GCR interactions should be included explicitly. This, however, is difficult to do because so few of the relevant cross sections for neutron-induced reactions have been measured.

  17. Analysis of turbulent free jet hydrogen-air diffusion flames with finite chemical reaction rates

    NASA Technical Reports Server (NTRS)

    Sislian, J. P.

    1978-01-01

    The nonequilibrium flow field resulting from the turbulent mixing and combustion of a supersonic axisymmetric hydrogen jet in a supersonic parallel coflowing air stream is analyzed. Effective turbulent transport properties are determined using the (K-epsilon) model. The finite-rate chemistry model considers eight reactions between six chemical species, H, O, H2O, OH, O2, and H2. The governing set of nonlinear partial differential equations is solved by an implicit finite-difference procedure. Radial distributions are obtained at two downstream locations of variables such as turbulent kinetic energy, turbulent dissipation rate, turbulent scale length, and viscosity. The results show that these variables attain peak values at the axis of symmetry. Computed distributions of velocity, temperature, and mass fraction are also given. A direct analytical approach to account for the effect of species concentration fluctuations on the mean production rate of species (the phenomenon of unmixedness) is also presented. However, the use of the method does not seem justified in view of the excessive computer time required to solve the resulting system of equations.

  18. Early diagenetic processes, fluxes, and reaction rates in sediments of the South Atlantic

    SciTech Connect

    Schulz, H.D.; Dahmke, A.; Schinzel, U.; Wallmann, K.; Zabel, M. )

    1994-05-01

    Porewaters recovered from sediment cores (gravity corers, box corers, and multicorers) from various subregions of the South Atlantic (Amazon River mouth, equatorial upwelling, Congo River mouth, Benguela coastal upwelling area, and Angola Basin) were investigated geochemically. Objectives included determination of Eh, pH, oxygen, nitrate, sulfate, alkalinity, phosphate, ammonium, fluoride, sulfide, Ca, Mg, Sr, Fe, Mn, and Si, in order to quantify organic matter diagenesis and related mineral precipitation and dissolution processes. Porewater profiles from the eastern upwelling areas of the South Atlantic suggest that sulfate reduction in the deeper parts of the sediment may be attributed mainly to methane oxidation, whereas organic matter degradation by sulfate reduction is restricted to the near-surface sediments. Further, a prominent concentration gradient change of sulfate and related mineralization products occurred typically in the upwelling sediments at a depth of 4 to 8 m, far below the zone of bioturbation or bioirrigation. Because other sedimentological reasons seem to fail as explanations, an early diagenetic sulfide oxidation to sulfate within the anoxic environment is discussed. Porewater profiles from the sediments of the Amazon fan area are mainly influenced by reactions with Fe(III)-phases. The remarkable linearity of the concentration gradients of sulfate supports the idea of distinct reaction layers in these sediments. In contrast to the upwelling sediments, the sulfate gradient develops from the sediment surface to a sulfate reduction zone at a depth of 5.3 m, probably because a reoxidation of sulfide is prevented by the reaction with iron oxides and the formation of iron sulfide minerals. A comparison of organic matter degradation rates from the different areas of the South Atlantic show the expected relationship to primary productivity.

  19. Actinometric measurement of solar ultraviolet and development of a weighted solar UV integral. [photochemical reaction rate determination

    NASA Technical Reports Server (NTRS)

    Gupta, A.; Coulbert, C.

    1978-01-01

    An actinometer has been developed to measure outdoor irradiance in the range 295-400 nm. Actinometric measurements of radiation are based on determination of photochemical reaction rates for reactions of known quantum efficiency. Actinometers have the advantage of providing irradiance data over surfaces of difficult accessibility; in addition, actinometrically determined irradiance data are wavelength weighted and therefore provide a useful means of assessing the degradation rates of polymers employed in solar energy systems.

  20. Analytical Solution of Steady State Equations for Chemical Reaction Networks with Bilinear Rate Laws

    PubMed Central

    Halász, Ádám M.; Lai, Hong-Jian; McCabe, Meghan M.; Radhakrishnan, Krishnan; Edwards, Jeremy S.

    2014-01-01

    True steady states are a rare occurrence in living organisms, yet their knowledge is essential for quasi-steady state approximations, multistability analysis, and other important tools in the investigation of chemical reaction networks (CRN) used to describe molecular processes on the cellular level. Here we present an approach that can provide closed form steady-state solutions to complex systems, resulting from CRN with binary reactions and mass-action rate laws. We map the nonlinear algebraic problem of finding steady states onto a linear problem in a higher dimensional space. We show that the linearized version of the steady state equations obeys the linear conservation laws of the original CRN. We identify two classes of problems for which complete, minimally parameterized solutions may be obtained using only the machinery of linear systems and a judicious choice of the variables used as free parameters. We exemplify our method, providing explicit formulae, on CRN describing signal initiation of two important types of RTK receptor-ligand systems, VEGF and EGF-ErbB1. PMID:24334389

  1. Path-integral virial estimator for reaction rate calculation basedon the quantum instanton aproximation

    SciTech Connect

    Yang, Sandy; Yamamoto, Takeshi; Miller, William H.

    2005-11-28

    The quantum instanton approximation is a type of quantum transition state theory that calculates the chemical reaction rate using the reactive flux correlation function and its low order derivatives at time zero. Here we present several path-integral estimators for the latter quantities, which characterize the initial decay profile of the flux correlation function. As with the internal energy or heat capacity calculation, different estimators yield different variances (and therefore different convergence properties) in a Monte Carlo calculation. Here we obtain a virial(-type) estimator by using a coordinate scaling procedure rather than integration by parts, which allows more computational benefits. We also consider two different methods for treating the flux operator, i.e., local-path and global-path approaches, in which the latter achieves a smaller variance at the cost of using second-order potential derivatives. Numerical tests are performed for a one-dimensional Eckart barrier and a model proton transfer reaction in a polar solvent, which illustrates the reduced variance of the virial estimator over the corresponding thermodynamic estimator.

  2. Pressure dependence on the reaction propagation rate of PETN at high pressure

    SciTech Connect

    Foltz, M.F.

    1993-04-01

    The reaction propagation rate (RPR) of the sensitive high explosive pentaerythritol tetranitrate (PETN) was measured in a diamond anvil cell (DAC) over the pressure range of 2--20 GPa. The experimental technique used is the same as that previously reported. The RPR data shows that it burns one to two orders of magnitude faster in the DAC than 1,3,5,-triamino-2,4,6-trinitrobenzene (TATB) and nitromethane (CH{sub 3}NO{sub 2}) respectively. The PETN RPR curve did not show sample pressure-dependent behavior like that of nitromethane, but instead varied abruptly like the RPR curve of TATB. In order to interpret these changes, static-pressure DAC mid-IR FTIR spectra were taken of micro-pellets of PETN embedded in KBr. The relationship between changes in the spectra, the RPR curve, and published single crystal PETN wedge test data are discussed.

  3. Temperature dependence of the NO + O3 reaction rate from 195 to 369 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Allen, J. E., Jr.; Brobst, W. D.

    1981-01-01

    The temperature dependence of the NO + O3 reaction rate was examined by means of the fast flow technique. Several different experimental conditions and detection schemes were employed. With excess NO or excess O3, NO2 chemiluminescence was monitored. In addition, with excess O3, NO was followed by fluorescence induced by an NO microwave discharge lamp. The results of the three independent sets of data are compared and found to agree within experimental error, indicating the absence of secondary chemistry which might complicate the kinetics. The data exhibit curvature on an Arrhenius plot; however, the simple Arrhenius expression k = (2.6 + or - 0.8) x 10 to the -12th exp(-1435 + or - 64/T) cu cm/molecule s is an adequate description for T between 195 and 369 K. This result is compared to earlier determinations.

  4. Relative rate constants for the reactions of atomic oxygen with HO2 anad OH radicals

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1983-01-01

    Relative rate constants for the reactions O + HO2 - OH + O2 (1) and O + OH - H + O2 (2) were obtained by using the discharge-flow resonance fluorescence technique at 2 torr total pressure and 299 K. HO2 radicals were generated by reacting atomic hydrogen with an excess of O2. Quasi-steady-state concentrations of OH and HO2 were established in the presence of excess atomic oxygen. Observed concentration ratios, namely the ratio of the OH concentration to the HO2 concentration, resulted in a value of 1.7 + or 0.2 for k1/k2. The error limits are twice the standard deviation obtained from the data analysis. Overall experimental error is estimated to be + or - 25 percent. This result confirms earlier direct measurements of k1 and k2 which required knowledge of absolute radical or atomic oxygen concentrations.

  5. Partial reactions of the Na,K-ATPase: determination of rate constants

    PubMed Central

    1994-01-01

    Experiments were designed to characterize several partial reactions of the Na,K-ATPase and to demonstrate that a model can be defined that reproduces most of the transport features of the pump with a single set of kientic parameters. We used the fluorescence label 5- iodoacetamidofluorescein, which is thought to be sensitive to conformational changes, and the styryl dye RH 421, which can be applied to detect ion-binding and -release reactions. In addition transient electric currents were measured, which are associated mainly with the E1-->E2 conformational transition. Numerical simulations were performed on the basis of a reaction model, that has been developed from the Post- Albers cycle. Analysis of the experimental data allows the determination of several rate constants of the pump cycle. Our conclusions may be summarized as follows: (a) binding of one Na+ ion at the cytoplasmic face is electrogenic. This Na+ ion is specifically bound to a neutral binding site with an affinity of 8 mM in the presence of 10 mM Mg2+. In the absence of divalent cations, the intrinsic binding affinity was found to be 0.7 mM. (b) The analysis of fluorescence experiments with the cardiotonic steroid strophanthidin indicates that the 5-iodoacetamidofluorescein label monitors the conformational transition (Na3)E1-P-->P-E2(Na2), which is accompanied by the release of one Na+ ion. 5-IAF does not respond to the release of the subsequent two Na+ ions, which can be monitored by the RH 421 dye. These experiments indicate further that the conformational transition E1P-->P-E2 is the rate limiting process of the Na+ translocation. The corresponding rate constant was determined to be 22 s-1 at 20 degrees C. From competition experiments with cardiotonic steroids, we estimated that the remaining 2 Na+ ions are released subsequently with a rate constant of at least 5,000 s-1 from their negatively charged binding sites. (c) Comparing the fluorescence experiments with electric current transients

  6. Cybersickness provoked by head-mounted display affects cutaneous vascular tone, heart rate and reaction time.

    PubMed

    Nalivaiko, Eugene; Davis, Simon L; Blackmore, Karen L; Vakulin, Andrew; Nesbitt, Keith V

    2015-11-01

    Evidence from studies of provocative motion indicates that motion sickness is tightly linked to the disturbances of thermoregulation. The major aim of the current study was to determine whether provocative visual stimuli (immersion into the virtual reality simulating rides on a rollercoaster) affect skin temperature that reflects thermoregulatory cutaneous responses, and to test whether such stimuli alter cognitive functions. In 26 healthy young volunteers wearing head-mounted display (Oculus Rift), simulated rides consistently provoked vection and nausea, with a significant difference between the two versions of simulation software (Parrot Coaster and Helix). Basal finger temperature had bimodal distribution, with low-temperature group (n=8) having values of 23-29 °C, and high-temperature group (n=18) having values of 32-36 °C. Effects of cybersickness on finger temperature depended on the basal level of this variable: in subjects from former group it raised by 3-4 °C, while in most subjects from the latter group it either did not change or transiently reduced by 1.5-2 °C. There was no correlation between the magnitude of changes in the finger temperature and nausea score at the end of simulated ride. Provocative visual stimulation caused prolongation of simple reaction time by 20-50 ms; this increase closely correlated with the subjective rating of nausea. Lastly, in subjects who experienced pronounced nausea, heart rate was elevated. We conclude that cybersickness is associated with changes in cutaneous thermoregulatory vascular tone; this further supports the idea of a tight link between motion sickness and thermoregulation. Cybersickness-induced prolongation of reaction time raises obvious concerns regarding the safety of this technology. PMID:26340855

  7. High-precision {sup 28}Si(p,t){sup 26}Si reaction to determine {sup 22}Mg({alpha},p){sup 25}Al reaction rates

    SciTech Connect

    Matic, A.; Berg, A. M. van den; Harakeh, M. N.; Woertche, H. J.; Beard, M.; Berg, G. P. A.; Goerres, J.; LeBlanc, P.; O'Brien, S.; Wiescher, M.; Fujita, K.; Hatanaka, K.; Sakemi, Y.; Shimizu, Y.; Tameshige, Y.; Tamii, A.; Yosoi, M.; Adachi, T.; Fujita, Y.; Shimbara, Y.

    2011-08-15

    The rise time of stellar x-ray bursts is a signature of thermonuclear runaway processes in the atmosphere of neutron stars and is highly sensitive to a series of ({alpha},p) reactions via high-lying resonances in sd-shell nuclei. Lacking data for the relevant resonance levels, the stellar reaction rates have been calculated using statistical, Hauser-Feshbach models, assuming a high-level density. This assumption may not be correct in view of the selectivity of the ({alpha},p) reaction to natural parity states. We measured the {sup 28}Si(p,t){sup 26}Si reaction with a high-resolution spectrometer to identify resonance levels in {sup 26}Si above the {alpha}-emission threshold at 9.164 MeV excitation energy. These resonance levels are used to calculate the stellar reaction rate of the {sup 22}Mg({alpha},p){sup 25}Al reaction and to test the validity of the statistical assumption.

  8. Helium effects on microstructural change in RAFM steel under irradiation: Reaction rate theory modeling

    NASA Astrophysics Data System (ADS)

    Watanabe, Y.; Morishita, K.; Nakasuji, T.; Ando, M.; Tanigawa, H.

    2015-06-01

    Reaction rate theory analysis has been conducted to investigate helium effects on the formation kinetics of interstitial type dislocation loops (I-loops) and helium bubbles in reduced-activation-ferritic/martensitic steel during irradiation, by focusing on the nucleation and growth processes of the defect clusters. The rate theory model employs the size and chemical composition dependence of thermal dissociation of point defects from defect clusters. In the calculations, the temperature and the production rate of Frenkel pairs are fixed to be T = 723 K and PV = 10-6 dpa/s, respectively. And then, only the production rate of helium atoms was changed into the following three cases: PHe = 0, 10-7 and 10-5 appm He/s. The calculation results show that helium effect on I-loop formation quite differs from that on bubble formation. As to I-loops, the loop formation hardly depends on the existence of helium, where the number density of I-loops is almost the same for the three cases of PHe. This is because helium atoms trapped in vacancies are easily emitted into the matrix due to the recombination between the vacancies and SIAs, which induces no pronounced increase or decrease of vacancies and SIAs in the matrix, leading to no remarkable impact on the I-loop nucleation. On the other hand, the bubble formation depends much on the existence of helium, in which the number density of bubbles for PHe = 10-7 and 10-5 appm He/s is much higher than that for PHe = 0. This is because helium atoms trapped in a bubble increase the vacancy binding energy, and suppress the vacancy dissociation from the bubble, resulting in a promotion of the bubble nucleation. And then, the helium effect on the promotion of bubble nucleation is very strong, even the number of helium atoms in a bubble is not so large.

  9. Reaction rates, depositional history and sources of indium in sediments from Appalachian and Canadian Shield lakes

    NASA Astrophysics Data System (ADS)

    Tessier, André; Gobeil, Charles; Laforte, Lucie

    2014-07-01

    Sediment cores were collected at the deepest site of twelve headwater lakes from the Province of Québec, Canada that receive contaminants only from atmospheric deposition, either directly to the lake surface or indirectly from the watershed. Several of the lakes are located within relatively short distance (<40 km) and others at more than 200 km from potential sources of contamination. The sediments were dated and analyzed for In and other elements including Fe, Mn, Al and organic C. Fe-rich authigenic material was collected on Teflon sheets inserted vertically into the sediments at the only study site whose hypolimnion remains perennially oxic. Porewater samples collected at the coring site of four of the lakes were also analyzed for In and other solutes including sulfide, sulfate, Fe, Mn, inorganic and organic C and major ions. The porewater In profiles display concentration gradients at or below the sediment-water interface. Modeling these profiles with a one-dimensional transport-reaction equation assuming steady state allows definition of depth intervals (zones) where In is either released to or removed from porewater and quantification of net In reactions rates in each zone. The position of the In consumption zones, the shape of the vertical profiles of dissolved In, sulfide and iron, as well as thermodynamic calculations of saturation states collectively suggest that In(OH)3(s) and In2S3(s) do not precipitate in the sediments and that adsorption of In onto sedimentary FeS(s) does not occur. However, similarities in the In and Fe porewater profiles, and the presence of In in the authigenic Fe-rich solids, reveal that part of the In becomes associated with authigenic Fe oxyhydroxides in the perennially oxic lake and is coupled to the Fe redox cycling. Comparison of the In/Corg and In/Fe molar ratios in the authigenic Fe-rich material and in surface sediments (0-0.5 cm) of this lake suggests that most non-lithogenic In was bound to humic substances. From the

  10. Rate Coefficient for the (4)Heμ + CH4 Reaction at 500 K: Comparison between Theory and Experiment.

    PubMed

    Arseneau, Donald J; Fleming, Donald G; Li, Yongle; Li, Jun; Suleimanov, Yury V; Guo, Hua

    2016-03-01

    The rate constant for the H atom abstraction reaction from methane by the muonic helium atom, Heμ + CH4 → HeμH + CH3, is reported at 500 K and compared with theory, providing an important test of both the potential energy surface (PES) and reaction rate theory for the prototypical polyatomic CH5 reaction system. The theory used to characterize this reaction includes both variational transition-state (CVT/μOMT) theory (VTST) and ring polymer molecular dynamics (RPMD) calculations on a recently developed PES, which are compared as well with earlier calculations on different PESs for the H, D, and Mu + CH4 reactions, the latter, in particular, providing for a variation in atomic mass by a factor of 36. Though rigorous quantum calculations have been carried out for the H + CH4 reaction, these have not yet been extended to the isotopologues of this reaction (in contrast to H3), so it is important to provide tests of less rigorous theories in comparison with kinetic isotope effects measured by experiment. In this regard, the agreement between the VTST and RPMD calculations and experiment for the rate constant of the Heμ + CH4 reaction at 500 K is excellent, within 10% in both cases, which overlaps with experimental error. PMID:26484648

  11. Chemical mechanisms and reaction rates for the initiation of hot corrosion of IN-738

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Kohl, F. J.; Stearns, C. A.

    1984-01-01

    Sodium-sulfate-induced hot corrosion of preoxidized IN-738 was studied at 975 C with special emphasis placed on the processes occurring during the long induction period. Thermogravimetric tests were run for predetermined periods of time, and then one set of specimens was washed with water. Chemical analysis of the wash solutions yielded information about water soluble metal salts and residual sulfate. A second set of samples was cross sectioned dry and polished in a nonaqueous medium. Element distributions within the oxide scale were obtained from electron microprobe X-ray micrographs. Evolution of SO was monitored throughout the thermogravimetric tests. Kinetic rate studies were performed for several pertinent processes; appropriate rate constants were obtained from the following chemical reactions: Cr2O3 + 2 Na2SO4(1) + 3/2 O2 yields 2 Na2CrO4(1) + 2 SO3(g)n TiO2 + Na2SO4(1) yields Na2O(TiO2)n + SO3(g)n TiO2 + Na2CrO4(1) yields Na2O(TiO2)n + CrO3(g).

  12. The influence of the reaction rate of explosives on blast effects

    NASA Astrophysics Data System (ADS)

    Williams, Pharis E.

    1996-05-01

    Many of the tools developed for the study of shock physics for weapons related work have direct application in industry. For example, instrumentation developed in the study of shock physics has been used to good advantage in the commercial explosives industry. The development of additional sensors is ongoing, though the manner in which these sensors are used and the data analyzed are slightly different because of the application. On the other hand, some of the tools, procedures, and methodologies need some changes in order to provide the best utility to the industrial community. Take reactive hydrocode modeling as an example. The use of reaction rate laws which are very good at modeling the ideal explosives used in shock physics are not universally applicable to industry uses of explosives because of the need to use the energy release rates to tailor the explosive to the job at hand. For example, warheads typically use ideal explosives which release their energy very rapidly and under shock conditions while the commercial composite explosives needed for open pit mining must release the major part of their energy very slowly in order to allow time to over come the inertia of the overburden in heaving it off the ore body. These, and other applications of shock physics techniques will be discussed.

  13. The effect of particle size on hydrolysis reaction rates and rheological properties in cellulosic slurries.

    PubMed

    Dasari, Rajesh K; Eric Berson, R

    2007-04-01

    The effect of varying initial particle sizes on enzymatic hydrolysis rates and rheological properties of sawdust slurries is investigated. Slurries with four particle size ranges (33 microm < x < or = 75 microm, 150 microm < x < or = 180 microm, 295 microm < x < or = 425 microm, and 590 microm < x < or = 850 microm) were subjected to enzymatic hydrolysis using an enzyme dosage of 15 filter paper units per gram of cellulose at 50 degrees C and 250 rpm in shaker flasks. At lower initial particle sizes, higher enzymatic reaction rates and conversions of cellulose to glucose were observed. After 72 h 50 and 55% more glucose was produced from the smallest size particles than the largest size ones, for initial solids concentration of 10 and 13% (w/w), respectively. The effect of initial particle size on viscosity over a range of shear was also investigated. For equivalent initial solids concentration, smaller particle sizes result in lower viscosities such that at a concentration of 10% (w/w), the viscosity decreased from 3000 cP for 150 microm < x < or = 180 microm particle size slurries to 61.4 cP for 33 microm < x < or = 75 microm particle size slurries. Results indicate particle size reduction may provide a means for reducing the long residence time required for the enzymatic hydrolysis step in the conversion of biomass to ethanol. Furthermore, the corresponding reduction in viscosity may allow for higher solids loading and reduced reactor sizes during large-scale processing. PMID:18478396

  14. Analysis of turbulent free-jet hydrogen-air diffusion flames with finite chemical reaction rates

    NASA Technical Reports Server (NTRS)

    Sislian, J. P.; Glass, I. I.; Evans, J. S.

    1979-01-01

    A numerical analysis is presented of the nonequilibrium flow field resulting from the turbulent mixing and combustion of an axisymmetric hydrogen jet in a supersonic parallel ambient air stream. The effective turbulent transport properties are determined by means of a two-equation model of turbulence. The finite-rate chemistry model considers eight elementary reactions among six chemical species: H, O, H2O, OH, O2 and H2. The governing set of nonlinear partial differential equations was solved by using an implicit finite-difference procedure. Radial distributions were obtained at two downstream locations for some important variables affecting the flow development, such as the turbulent kinetic energy and its dissipation rate. The results show that these variables attain their peak values on the axis of symmetry. The computed distribution of velocity, temperature, and mass fractions of the chemical species gives a complete description of the flow field. The numerical predictions were compared with two sets of experimental data. Good qualitative agreement was obtained.

  15. Evaporation Rate Study and NDMA Formation from UDMH/NO2 Reaction Products

    NASA Technical Reports Server (NTRS)

    Buchanan, Vanessa D.; Dee, Louis A.; Baker, David L.

    2003-01-01

    Laboratory samples of uns-dimethylhydrazine (UDMH) fuel/oxidizer (nitrogen dioxide) non-combustion reaction products (UFORP) were prepared using a unique permeation tube technology. Also, a synthetic UFORP was prepared from UDMH, N-nitrosodimethylamine (NDMA), dimethylammonium nitrate, sodium nitrite and purified water. The evaporation rate of UFORP and synthetic UFORP was determined under space vacuum (approx 10(exp -3) Torr) at -40 ?C and 0 ?C. The material remaining was analyzed and showed that the UFORP weight and NDMA concentration decreased over time; however, NDMA had not completely evaporated. Over 85% of the weight was removed by subjecting the UFORP to 10(-3) Torr for 7 hours at -40 ?C and 4 hours at 0 ?C. A mixture of dimethylammonium nitrate and sodium nitrite formed NDMA at a rapid rate in a moist air environment. A sample of UFORP residue was analyzed for formation of NDMA under various conditions. It was found that NDMA was not formed unless nitrite was added.

  16. Potential chlorofluorocarbon replacements: OH reaction rate constants between 250 and 315 K and infrared absorption spectra

    SciTech Connect

    Garland, N.L.; Medhurst, L.J.; Nelson, H.H.

    1993-12-20

    The authors measured the rate constant for reactions of the OH radical with several potential chlorofluorocarbon replacements over the temperature range 251-314 K using laser photolysis laser-induced fluorescence techniques. The compounds studied and Arrhenius parameters determined from fits to the measured rate constants are as follows: CHF{sub 2}OCHF{sub 2} (E 134), k(T) = (5.4 {+-} 3.5) x 10{sup {minus}13} cm{sup 3} s{sup {minus}1} exp [({minus}3.1 {+-} 0.4 kcal mol{sup {minus}1})/RT]; CF{sub 3}CH{sub 2}CF{sub 3} (FC 236fa), k(T) = (2.0 {+-} 1.0) x 10{sup {minus}14} cm{sup 3} s{sup {minus}1} exp [({minus}1.8 {+-} 0.3 kcal mol{sup {minus}1})/RT]; CF{sub 3}CHFCHF{sub 2} (FC 236ea), k(T) = (2.0 {+-} 0.9) x 10{sup {minus}13} cm{sup 3} s{sup {minus}1} exp [({minus}2.0 {+-} 0.3 kcal mol{sup {minus}1})/RT]; and CF{sub 3}CF{sub 2}CH{sub 2}F (FC 236cb), k(T) = (2.6 {+-} 1.6) x 10{sup {minus}13} cm{sup 3} s{sup {minus}1} exp [({minus}2.2 {+-} 0.4 kcal mol{sup {minus}1})/RT]. The measured activation energies (2-3 kcal mol{sup {minus}1}) are consistent with a mechanism of H atom abstraction. The tropospheric lifetimes, estimated from the measured OH reaction rates, and measured integrated infrared absorption cross sections over the range 770 to 1430 cm{sup {minus}1} suggest that E 134 and FC 236fa may have significant global warming potential, while FC 236ea and FC 236cb do not. 17 refs., 4 figs., 3 tabs.

  17. The TDF System for Thermonuclear Plasma Reaction Rates, Mean Energies and Two-Body Final State Particle Spectra

    SciTech Connect

    Warshaw, S I

    2001-07-11

    The rate of thermonuclear reactions in hot plasmas as a function of local plasma temperature determines the way in which thermonuclear ignition and burning proceeds in the plasma. The conventional model approach to calculating these rates is to assume that the reacting nuclei in the plasma are in Maxwellian equilibrium at some well-defined plasma temperature, over which the statistical average of the reaction rate quantity {sigma}v is calculated, where {sigma} is the cross-section for the reaction to proceed at the relative velocity v between the reacting particles. This approach is well-understood and is the basis for much nuclear fusion and astrophysical nuclear reaction rate data. The Thermonuclear Data File (TDF) system developed at the Lawrence Livermore National Laboratory (Warshaw 1991), which is the topic of this report, contains data on the Maxwellian-averaged thermonuclear reaction rates for various light nuclear reactions and the correspondingly Maxwellian-averaged energy spectra of the particles in the final state of those reactions as well. This spectral information closely models the output particle and energy distributions in a burning plasma, and therefore leads to more accurate computational treatments of thermonuclear burn, output particle energy deposition and diagnostics, in various contexts. In this report we review and derive the theoretical basis for calculating Maxwellian-averaged thermonuclear reaction rates, mean particle energies, and output particle spectral energy distributions for these reactions in the TDF system. The treatment of the kinematics is non-relativistic. The current version of the TDF system provides exit particle energy spectrum distributions for two-body final state reactions only. In a future report we will discuss and describe how output particle energy spectra for three- and four-body final states can be developed for the TDF system. We also include in this report a description of the algorithmic implementation of the

  18. Evaluating rates and yields of second-order, photoinitiated reactions under conditons of Gaussian-profile excitation

    SciTech Connect

    Cambron, R.T.; Zhu, X.R.; Harris, J.M.

    1994-09-01

    Under conditions of Gaussian radial profile excitation, a mixed-order kinetic model is used to interpret the rates and yields of photoinitiated reactions. This model is used to determine the triplet-triplet annihilation rate constant for benzophenone in acetonitrile and anthracene at room temperature. 34 refs., 9 figs.

  19. Bimolecular electron transfer reactions in coumarin amine systems: Donor acceptor orientational effect on diffusion-controlled reaction rates

    NASA Astrophysics Data System (ADS)

    Satpati, A. K.; Nath, S.; Kumbhakar, M.; Maity, D. K.; Senthilkumar, S.; Pal, H.

    2008-04-01

    Electron transfer (ET) reactions between excited coumarin dyes and different aliphatic amine (AlA) and aromatic amine (ArA) donors have been investigated in acetonitrile solution using steady-state (SS) and time-resolved (TR) fluorescence quenching measurements. No ground state complex or emissive exciplex formation has been indicated in these systems. SS and TR measurements give similar quenching constants ( kq) for each of the coumarin-amine pairs, suggesting dynamic nature of interaction in these systems. On correlating kq values with the free energy changes (Δ G0) of the ET reactions show the typical Rehm-Weller type of behavior as expected for bimolecular ET reactions under diffusive condition, where kq increases with -Δ G0 at the lower exergonicity (-Δ G0) region but ultimately saturate to a diffusion-limited value (kqDC) at the higher exergonicity region. It is, however, interestingly observed that the kqDC values vary largely depending on the type of the amines used. Thus, kqDC is much higher with ArAs than AlAs. Similarly, the kqDC for cyclic monoamine 1-azabicyclo-[2,2,2]-octane (ABCO) is distinctly lower and that for cyclic diamine 1,4-diazabicyclo-[2,2,2]-octane (DABCO) is distinctly higher than the kqDC value obtained for other noncyclic AlAs. These differences in the kqDC values have been rationalized on the basis of the differences in the orientational restrictions involved in the ET reactions with different types of amines. As understood, n-type donors (AlAs) introduce large orientational restriction and thus significantly reduces the ET efficiency in comparison to the π-type donors (ArAs). Structural constrains are inferred to be the reason for the differences in the kqDC values involving ABCO, DABCO donors in comparison to other noncyclic AlAs. Supportive evidence for the orientational restrictions involving different types of amines donors has also been obtained from DFT based quantum chemical calculations on the molecular orbitals of

  20. A sensitivity study of s-process: the impact of uncertainties from nuclear reaction rates

    NASA Astrophysics Data System (ADS)

    Vinyoles, N.; Serenelli, A.

    2016-01-01

    The slow neutron capture process (s-process) is responsible for the production of about half the elements beyond the Fe-peak. The production sites and the conditions under which the different components of s-process occur are relatively well established. A detailed quantitative understanding of s-process nucleosynthesis may yield light in physical processes, e.g. convection and mixing, taking place in the production sites. For this, it is important that the impact of uncertainties in the nuclear physics is well understood. In this work we perform a study of the sensitivity of s-process nucleosynthesis, with particular emphasis in the main component, on the nuclear reaction rates. Our aims are: to quantify the current uncertainties in the production factors of s-process elements originating from nuclear physics and, to identify key nuclear reactions that require more precise experimental determinations. In this work we studied two different production sites in which s-process occurs with very different neutron exposures: 1) a low-mass extremely metal-poor star during the He-core flash (nn reaching up to values of ∼ 1014cm-3); 2) the TP-AGB phase of a M⊙, Z=0.01 model, the typical site of the main s-process component (nn up to 108 — 109cm-3). In the first case, the main variation in the production of s-process elements comes from the neutron poisons and with relative variations around 30%-50%. In the second, the neutron poison are not as important because of the higher metallicity of the star that actually acts as a seed and therefore, the final error of the abundances are much lower around 10%-25%.

  1. Early diagenetic processes, fluxes, and reaction rates in sediments of the South Atlantic

    NASA Astrophysics Data System (ADS)

    Schulz, Horst D.; Dahmke, Andreas; Schinzel, Uwe; Wallmann, Klaus; Zabel, Matthias

    1994-05-01

    Porewaters recovered from sediment cores (gravity corers, box corers, and multicorers) from various subrogions of the South Atlantic (Amazon River mouth, equatorial upwelling, Congo River mouth, Benguela coastal upwelling area, and Angola Basin) were investigated geochemically. Objectives included determination of Eh, pH, oxygen, nitrate, sulfate, alkalinity, phosphate, ammonium, fluoride, sulfide, Cal, Mg, Sr, Fe, Mn, and Si, in order to quantify organic matter diagenesis and related mineral precipitation and dissolution processes. Porewater profiles from the eastern upwelling areas of the South Atlantic suggest that sulfate reduction in the deeper parts of the sediment may be attributed mainly to methane oxidation, whereas organic matter degradation by sulfate reduction is restricted to the near-surface sediments. Further, a prominent concentration gradient change of sulfate and related mineralization products occurred typically in the upwelling sediments at a depth of 4 to 8 m, far below the zone of bioturbation or bioirrigation. Because other sedimentological reasons seem to fail as explanations, an early diagenetic sulfide oxidation to sulfate within the anoxic environment is discussed. Porewater profiles from the sediments of the Amazon fan area are mainly influenced by reactions with Fe(III)-phases. The remarkable linearity of the concentration gradients of sulfate supports the idea of distinct reaction layers in these sediments. In contrast to the upwelling sediments, the sulfate gradient develops from the sediment surface to a sulfate reduction zone at a depth of 5.3 m, probably because a reoxidation of sulfide is prevented by the reaction with iron oxides and the formation of iron sulfide minerals. A comparison of organic matter degradation rates from the different areas of the South Atlantic show the expected relationship to primary productivity. Oxygen is the dominating oxidant, whereas organic matter degradation by nitrate, Mn(IV)- and probably also Fe

  2. Quantum mechanical reaction rate constants by vibrational configuration interaction: the OH + H2->H2O + H reaction as a function of temperature.

    PubMed

    Chakraborty, Arindam; Truhlar, Donald G

    2005-05-10

    The thermal rate constant of the 3D OH + H(2)-->H(2)O + H reaction was computed by using the flux autocorrelation function, with a time-independent square-integrable basis set. Two modes that actively participate in bond making and bond breaking were treated by using 2D distributed Gaussian functions, and the remaining (nonreactive) modes were treated by using harmonic oscillator functions. The finite-basis eigenvalues and eigenvectors of the Hamiltonian were obtained by solving the resulting generalized eigenvalue equation, and the flux autocorrelation function for a dividing surface optimized in reduced-dimensionality calculations was represented in the basis formed by the eigenvectors of the Hamiltonian. The rate constant was obtained by integrating the flux autocorrelation function. The choice of the final time to which the integration is carried was determined by a plateau criterion. The potential energy surface was from Wu, Schatz, Lendvay, Fang, and Harding (WSLFH). We also studied the collinear H + H(2) reaction by using the Liu-Siegbahn-Truhlar-Horowitz (LSTH) potential energy surface. The calculated thermal rate constant results were compared with reported values on the same surfaces. The success of these calculations demonstrates that time-independent vibrational configuration interaction can be a very convenient way to calculate converged quantum mechanical rate constants, and it opens the possibility of calculating converged rate constants for much larger reactions than have been treated until now. PMID:15774583

  3. Selective determination of rate constants of reactions of atomic hydrogen with various functional groups of a complex molecule

    NASA Astrophysics Data System (ADS)

    Brauer, G. B.; Pugachev, D. V.; Azatyan, V. V.

    2016-05-01

    The possibility of determining absolute values of the rate constants of reactions of active intermediate species with different functional groups of molecules is demonstrated by measuring macrokinetic combustion characteristics. The Arrhenius parameters of the rate constant of the reaction between atomic hydrogen with the methylene group of ethanol and molecular oxygen within the temperature range of 830-970 K are determined. The reasons for the differences between the rate constants of reactions with the methylene and methyl groups of an ethanol molecule are discussed using thermochemical data. It is found that the obtained values of activation energies and preexponential factors of rate constants are in good agreement with the literature data on the region of lower temperatures.

  4. Application of the compensated Arrhenius formalism to explain the dielectric constant dependence of rates for Menschutkin reactions.

    PubMed

    Petrowsky, Matt; Glatzhofer, Daniel T; Frech, Roger

    2013-11-21

    The dependence of the reaction rate on solvent dielectric constant is examined for the reaction of trihexylamine with 1-bromohexane in a series of 2-ketones over the temperature range 25-80 °C. The rate constant data are analyzed using the compensated Arrhenius formalism (CAF), where the rate constant assumes an Arrhenius-like equation that also contains a dielectric constant dependence in the exponential prefactor. The CAF activation energies are substantially higher than those obtained using the simple Arrhenius equation. A master curve of the data is observed by plotting the prefactors against the solvent dielectric constant. The master curve shows that the reaction rate has a weak dependence on dielectric constant for values approximately less than 10 and increases more rapidly for dielectric constant values greater than 10. PMID:24156502

  5. Experimental measurements of low temperature rate coefficients for neutral-neutral reactions of interest for atmospheric chemistry of Titan, Pluto and Triton: reactions of the CN radical.

    PubMed

    Morales, Sébastien B; Le Picard, Sébastien D; Canosa, André; Sims, Ian R

    2010-01-01

    The kinetics of the reactions of cyano radical, CN (X2sigma+) with three hydrocarbons, propane (CH3CH2CH3), propene (CH3CH=CH2) and 1-butyne (CH[triple band]CCH2CH3) have been studied over the temperature range of 23-298 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. These reactions are of interest for the cold atmospheres of Titan, Pluto and Triton, as they might participate in the formation of nitrogen and carbon bearing molecules, including nitriles, that are thought to play an important role in the formation of hazes and biological molecules. All three reactions are rapid with rate coefficients in excess of 10(-10) cm3 molecule(-1) s(-1) at the lowest temperatures of this study and show behaviour characteristic of barrierless reactions. Temperature dependences, different for each reaction, are compared to those used in the most recent photochemical models of Titan's atmosphere. PMID:21302546

  6. Direct Measurement of the Effective Rate Constant for Primary Charge Separation in Isolated Photosystem II Reaction Centers

    SciTech Connect

    Greenfield, S. R.; Seibert, M.; Govindjee; Wasielewski, M. R.

    1997-03-27

    Transient absorption measurements of the pheophytin a anion band and Qx band bleach region using preferential excitation of P680 are performed on isolated photosystem II reaction centers to determine the effective rate constant for charge separtion. A novel analysis of the Qx band bleach region explicity takes the changing background into account in order to directly measure the rate of growth of the bleach. Both spectral regions reveal biphasic kinetics, with a ca. (8 ps)-1 rate constant for the faster component, and a ca. (50 ps)-1 rate constant for the slower component. We propose that the fster component corresponds to the effective rate constant for charge separation from within the equilibrated reaction center core and provides a lower limit for the intrinsic rate constant for charge separation. The slower component corresponds to charge separation that is limited by slow energy transfer from a long-wavelength accessory chlorophyll a.

  7. On the time dependence of rate coefficients of irreversible reactions between reactants with anisotropic reactivity in liquid solutions

    NASA Astrophysics Data System (ADS)

    Ivanov, Konstantin L.; Lukzen, Nikita N.; Doktorov, Alexander B.

    2016-08-01

    Time dependence of the rate coefficients of sterically specific reactions is analyzed theoretically. Generally, such reactions exhibit a non-trivial dependence of their rate constant on the steric factor, f < 1, which is defined as the fraction of reactive surface area. Notably, the rate constant of a diffusion-controlled reaction is proportional not to f but, counter-intuitively, to √{ f } due to partial averaging of the reaction anisotropy by translational diffusion. Here we demonstrate that the effective steric factor of a diffusion-influenced reaction is strongly time-dependent, increasing from f to √{ f } . When reactants have several active sites, these sites "interfere" each other in the sense that the rate constant depends on their relative positions. We demonstrate that such an interference effect is strongly time-dependent as well: it is absent at t = 0 but builds up with time. We argue that the outlined effects are also of importance for calculating the fluorescence quenching rate constants.

  8. Effect of Buddhist meditation on serum cortisol and total protein levels, blood pressure, pulse rate, lung volume and reaction time.

    PubMed

    Sudsuang, R; Chentanez, V; Veluvan, K

    1991-09-01

    Serum cortisol and total protein levels, blood pressure, heart rate, lung volume, and reaction time were studied in 52 males 20-25 years of age practicing Dhammakaya Buddhist meditation, and in 30 males of the same age group not practicing meditation. It was found that after meditation, serum cortisol levels were significantly reduced, serum total protein level significantly increased, and systolic pressure, diastolic pressure and pulse rate significantly reduced. Vital capacity, tidal volume and maximal voluntary ventilation were significantly lower after meditation than before. There were also significant decreases in reaction time after mediation practice. The percentage decrease in reaction time during meditation was 22%, while in subjects untrained in meditation, the percentage decrease was only 7%. Results from these studies indicate that practising Dhammakaya Buddhist meditation produces biochemical and physiological changes and reduces the reaction time. PMID:1801007

  9. Proteolysis inside the membrane is a rate-governed reaction not driven by substrate affinity

    PubMed Central

    Dickey, Seth W.; Baker, Rosanna P.; Cho, Sangwoo; Urban, Siniša

    2013-01-01

    SUMMARY Enzymatic cleavage of transmembrane anchors to release proteins from the membrane controls diverse signaling pathways and is implicated in over a dozen diseases. How catalysis works within the viscous, water-excluding, two-dimensional membrane is unknown. We developed an inducible reconstitution system to interrogate rhomboid proteolysis quantitatively within the membrane in real time. Remarkably, rhomboid proteases displayed no physiological affinity for substrates (Kd ~190 μM, or 0.1 mol%). Instead, ~10,000-fold differences in proteolytic efficiency with substrate mutants and diverse rhomboid proteases were reflected in kcat values alone. Analysis of gate-open mutant and solvent isotope effects revealed that substrate gating, not hydrolysis, is rate limiting. Ultimately a single proteolytic event within the membrane normally takes minutes. Rhomboid intramembrane proteolysis is thus a slow, kinetically controlled reaction not driven by transmembrane protein-protein affinity. These properties are unlike those of other studied proteases or membrane proteins but strikingly reminiscent of one subset of DNA-repair enzymes, raising important mechanistic and drug-design implications. PMID:24315097

  10. Astrophysical Reaction Rate for the Neutron-Generator Reaction {sup 13}C({alpha},n){sup 16}O in Asymptotic Giant Branch Stars

    SciTech Connect

    Johnson, E. D.; Rogachev, G. V.; Baby, L. T.; Cluff, W. T.; Crisp, A. M.; Diffenderfer, E.; Green, B. W.; Hinners, T.; Hoffman, C. R.; Kemper, K. W.; Momotyuk, O.; Peplowski, P.; Pipidis, A.; Reynolds, R.; Roeder, B. T.; Mukhamedzhanov, A. M.; Goldberg, V. Z.; Brown, S.

    2006-11-10

    The reaction {sup 13}C({alpha},n) is considered to be the main source of neutrons for the s process in asymptotic giant branch stars. At low energies, the cross section is dominated by the 1/2{sup +} 6.356 MeV subthreshold resonance in {sup 17}O whose contribution at stellar temperatures is uncertain by a factor of 10. In this work, we performed the most precise determination of the low-energy astrophysical S factor using the indirect asymptotic normalization (ANC) technique. The {alpha}-particle ANC for the subthreshold state has been measured using the sub-Coulomb {alpha}-transfer reaction ({sup 6}Li,d). Using the determined ANC, we calculated S(0), which turns out to be an order of magnitude smaller than in the nuclear astrophysics compilation of reaction rates.

  11. Absolute Rate Constants for the Reaction of OH with [|#11#|]Cyclopentane and Cycloheptane from 230-350 K

    NASA Astrophysics Data System (ADS)

    Dransfield, T. J.; Gennaco, M. M.; Huang, Y.; Hannun, R. A.

    2011-12-01

    We report absolute measurements of the rate constants of the reaction of hydroxyl radical (OH) with cyclopentane and cycloheptane in 6-8 Torr of nitrogen from 230-350 K using Harvard's High Pressure Flow System. Ethane's reactivity was simultaneously measured as a test of experimental performance. Hydroxyl concentrations were measured using Laser-Induced Fluorescence, and alkane concentrations were measured using Fourier-Transform Infrared Spectroscopy. Recent work on this flow system has suggested that cyclohexane has a significantly higher activation energy to reaction with OH than does cyclo-octane, a result which is not suggested by our understanding of hydrocarbon reactivity nor predicted by structure-activity relationships. This work examines the temperature dependent rates for two other similarly-sized cycloalkanes to determine whether they behave as cyclohexane or as cyclooctane. While several previous experiments have studied the reaction with cyclopentane, there is significant scatter in the room temperature rates, and only four absolute rate measurements are available at non-ambient temperatures. There are only two absolute rate measurements available for the reaction with cycloheptane; only one of these reports a temperature dependence, and that study is limited to temperatures above 298 K. Thus, this work significantly expands the available data set for both reactions. The data for the reactions of OH with ethane, cyclopentane, cyclohexane, and cycloheptane are all modeled using a simple Arrhenius fit, and also with a modified Arrhenius equation based on transition state theory, ignoring tunneling. Results from the latter fit indicate that the activation barriers for both title reactions are greater than that of OH + cyclo-octane. The measured activation energy for OH + cyclopentane actually exceeds that of OH + cyclohexane.

  12. Asn-150 of Murine Erythroid 5-Aminolevulinate Synthase Modulates the Catalytic Balance between the Rates of the Reversible Reaction.

    PubMed

    Stojanovski, Bosko M; Ferreira, Gloria C

    2015-12-25

    5-Aminolevulinate synthase (ALAS) catalyzes the first step in mammalian heme biosynthesis, the pyridoxal 5'-phosphate (PLP)-dependent and reversible reaction between glycine and succinyl-CoA to generate CoA, CO2, and 5-aminolevulinate (ALA). Apart from coordinating the positioning of succinyl-CoA, Rhodobacter capsulatus ALAS Asn-85 has a proposed role in regulating the opening of an active site channel. Here, we constructed a library of murine erythroid ALAS variants with substitutions at the position occupied by the analogous bacterial asparagine, screened for ALAS function, and characterized the catalytic properties of the N150H and N150F variants. Quinonoid intermediate formation occurred with a significantly reduced rate for either the N150H- or N150F-catalyzed condensation of glycine with succinyl-CoA during a single turnover. The introduced mutations caused modifications in the ALAS active site such that the resulting variants tipped the balance between the forward- and reverse-catalyzed reactions. Although wild-type ALAS catalyzes the conversion of ALA into the quinonoid intermediate at a rate 6.3-fold slower than the formation of the same quinonoid intermediate from glycine and succinyl-CoA, the N150F variant catalyzes the forward reaction at a mere 1.2-fold faster rate than that of the reverse reaction, and the N150H variant reverses the rate values with a 1.7-fold faster rate for the reverse reaction than that for the forward reaction. We conclude that the evolutionary selection of Asn-150 was significant for optimizing the forward enzymatic reaction at the expense of the reverse, thus ensuring that ALA is predominantly available for heme biosynthesis. PMID:26511319

  13. Accurate measurements of OH reaction rate constants over atmospheric temperatures and the atmospheric lifetime of trace gases

    NASA Astrophysics Data System (ADS)

    Orkin, V. L.; Khamaganov, V. G.; Martynova, L. E.; Kurylo, M. J.

    2013-12-01

    Reactions with hydroxyl radicals and photolysis are the main processes dictating the compound residence time in the atmosphere for a majority of trace gases. In case of very short lived compounds their reaction with OH dictates both the atmospheric lifetime and active halogen release. Therefore, the accuracy of OH kinetic data is of primary importance for the purpose of comprehensive atmospheric modeling of compound's impact on the atmosphere, such as in ozone depletion (ODP) and climate change (GWP). The currently recommended uncertainties of OH reaction rate constants (NASA/JPL Publications and IUPAC Publications) exceed 10% at room temperature for the majority of compounds to be larger at lower temperatures of atmospheric interest. Thus, uncertainties in the photochemical properties of potential and current atmospheric trace gases obtained under controlled laboratory conditions may constitute a major source of uncertainty in estimating the compound's environmental impact. We will present the higher accuracy results of OH reaction rate constant determinations between 220 K and 370 K. A statistical analysis of the data will be discussed. The high precision of kinetic measurements performed at low temperatures allows reliable determination of temperature dependences of the rate constants. This is especially important because we found that many OH reactions exhibit the curvature of the Arrhenius plots. A detailed inventory of sources of instrumental uncertainties related to our experiment proves a total uncertainty of the OH reaction rate constant to be as small as ~2-3%. The estimation of the atmospheric lifetime of a compound based on its OH reaction rate constant will be discussed.

  14. The reaction H + C4H2 - Absolute rate constant measurement and implication for atmospheric modeling of Titan

    NASA Astrophysics Data System (ADS)

    Nava, D. F.; Mitchell, M. B.; Stief, L. J.

    1986-04-01

    The absolute rate constant for the reaction H + C4H2 has been measured over the temperature (T) interval 210-423 K, using the technique of flash photolysis-resonance fluorescence. At each of the five temperatures employed, the results were independent of variations in C4H2 concentration, total pressure of Ar or N2, and flash intensity (i.e., the initial H concentration). The rate constant, k, was found to be equal to 1.39 x 10 to the -10th exp (-1184/T) cu cm/s, with an error of one standard deviation. The Arrhenius parameters at the high pressure limit determined here for the H + C4H2 reaction are consistent with those for the corresponding reactions of H with C2H2 and C3H4. Implications of the kinetic carbon chemistry results, particularly those at low temperature, are considered for models of the atmospheric carbon chemistry of Titan. The rate of this reaction, relative to that of the analogous, but slower, reaction of H + C2H2, appears to make H + C4H2 a very feasible reaction pathway for effective conversion of H atoms to molecular hydrogen in the stratosphere of Titan.

  15. The Impact of Reaction Rate Uncertainties (and other nuclear physics inputs) on Nucleosynthesis in the Neutrino-p Process

    NASA Astrophysics Data System (ADS)

    Frohlich, Carla; Tang, X.; Truran, J. W.

    2009-10-01

    The neutrino-p (νp) process has been shown to be an important nucleosynthesis process, occurring in core collapse supernovae, that contributes to the synthesis of nuclei in the mass region 64<=A<=120. Such a nucleosynthesis process (in addition to the r- and s-processes) is needed to explain the observed abundance patterns in this mass region - particularly in very low metallicity stars. The νp-process consists of a sequence of (p,γ) and (n,p) or β^+ reactions, where the slowest reactions set the timescale. Nucleosynthesis studies of such events as the νp-process typically involve the use of reaction networks that include several thousand nuclei and associated reaction cross sections and lifetimes, most of which are only known theoretically. A majority of the nuclei involved are unstable and hence pose a challenge for experimental nuclear physicists. With improvements in existing facilities such as NSCL at MSU and ATLAS at ANL and with a future FRIB facility, experimental investigations of reaction rates and other nuclear quantities involving unstable nuclei will become feasible. In this talk, we will demonstrate how uncertainties in the reaction rates influence the resulting nucleosynthesis. In addition, we will identify important reactions and nuclei to be studied experimentally with upcoming techniques at the new facilities.

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

    NASA Astrophysics Data System (ADS)

    Mincer, Joshua S.; Schwartz, Steven D.

    2004-04-01

    A model is presented for coupled hydrogen-electron transfer reactions in condensed phase in the presence of a rate promoting vibration. Large kinetic isotope effects (KIEs) are found when the hydrogen is substituted with deuterium. While these KIEs are essentially temperature independent, reaction rates do exhibit temperature dependence. These findings agree with recent experimental data for various enzyme-catalyzed reactions, such as the amine dehydrogenases and soybean lipoxygenase. Consistent with earlier results, turning off the promoting vibration results in an increased KIE. Increasing the barrier height increases the KIE, while increasing the rate of electron transfer decreases it. These results are discussed in light of other views of vibrationally enhanced tunneling in enzymes.

  17. Shell Model Based Reaction Rates for rp-PROCESS Nuclei in the Mass Range A=44-63

    NASA Astrophysics Data System (ADS)

    Fisker, J. L.; Barnard, V.; Görres, J.; Langanke, K.; Martínez-Pinedo, G.; Wiescher, M. C.

    2001-11-01

    We have used large-scale shell-model diagonalization calculations to determine the level spectra, proton spectroscopic factors, and electromagnetic transition probabilities for proton rich nuclei in the mass range A=44-63. Based on these results and the available experimental data, we calculated the resonances for proton capture reactions on neutron deficient nuclei in this mass range. We also calculated the direct capture processes on these nuclei in the framework of a Woods-Saxon potential model. Taking into account both resonant and direct contributions, we determined the ground-state proton capture reaction rates for these nuclei under hot hydrogen burning conditions for temperatures between 108 and 1010 K. The calculated compound-nucleus level properties and the reaction rates are presented here; the rates are also available in computer-readable format from the authors.

  18. Determination of the astrophysical 12N(p,γ)13O reaction rate from the 2H(12N,13O)n reaction and its astrophysical implications

    NASA Astrophysics Data System (ADS)

    Guo, B.; Su, J.; Li, Z. H.; Wang, Y. B.; Yan, S. Q.; Li, Y. J.; Shu, N. C.; Han, Y. L.; Bai, X. X.; Chen, Y. S.; Liu, W. P.; Yamaguchi, H.; Binh, D. N.; Hashimoto, T.; Hayakawa, S.; Kahl, D.; Kubono, S.; He, J. J.; Hu, J.; Xu, S. W.; Iwasa, N.; Kume, N.; Li, Z. H.

    2013-01-01

    The evolution of massive stars with very low-metallicities depends critically on the amount of CNO nuclides which they produce. The 12N(p,γ)13O reaction is an important branching point in the rap processes, which are believed to be alternative paths to the slow 3α process for producing CNO seed nuclei and thus could change the fate of massive stars. In the present work, the angular distribution of the 2H(12N, 13O)n proton transfer reaction at Ec.m.=8.4 MeV has been measured for the first time. Based on the Johnson-Soper approach, the square of the asymptotic normalization coefficient (ANC) for the virtual decay of 13Og.s. → 12N+p was extracted to be 3.92±1.47 fm-1 from the measured angular distribution and utilized to compute the direct component in the 12N(p,γ)13O reaction. The direct astrophysical S factor at zero energy was then found to be 0.39±0.15 keV b. By considering the direct capture into the ground state of 13O, the resonant capture via the first excited state of 13O and their interference, we determined the total astrophysical S factors and rates of the 12N(p,γ)13O reaction. The new rate is two orders of magnitude slower than that from the REACLIB compilation. Our reaction network calculations with the present rate imply that 12N(p,γ)13O will only compete successfully with the β+ decay of 12N at higher (˜2 orders of magnitude) densities than initially predicted.

  19. Phosphorus-31 NMR magnetization transfer measurements of metabolic reaction rates in the rat heart and kidney in vivo

    SciTech Connect

    Koretsky, A.P.

    1984-01-01

    /sup 31/P NMR is a unique tool to study bioenergetics in living cells. The application of magnetization transfer techniques to the measurement of steady-state enzyme reaction rates provides a new approach to understanding the regulation of high energy phosphate metabolism. This dissertation is concerned with the measurement of the rates of ATP synthesis in the rat kidney and of the creatine kinase catalyzed reaction in the rat heart in situ. The theoretical considerations of applying magnetization transfer techniques to intact organs are discussed with emphasis on the problems associated with multiple exchange reactions and compartmentation of reactants. Experimental measurements of the ATP synthesis rate were compared to whole kidney oxygen consumption and Na/sup +/ reabsorption rates to derive ATP/O values. The problems associated with ATP synthesis rate measurements in kidney, e.g. the heterogeneity of the inorganic phosphate resonance, are discussed and experiments to overcome these problems proposed. In heart, the forward rate through creatine kinase was measured to be larger than the reverse rate. To account for the difference in forward and reverse rates a model is proposed based on the compartmentation of a small pool of ATP.

  20. EFFECTS OF PORE STRUCTURE CHANGE AND MULTI-SCALE HETEROGENEITY ON CONTAMINANT TRANSPORT AND REACTION RATE UPSCALING

    SciTech Connect

    Peters, Catherine A

    2013-05-15

    This project addressed the scaling of geochemical reactions to core and field scales, and the interrelationship between reaction rates and flow in porous media. We targeted reactive transport problems relevant to the Hanford site specifically the reaction of highly caustic, radioactive waste solutions with subsurface sediments, and the immobilization of 90Sr and 129I through mineral incorporation and passive flow blockage, respectively. We addressed the correlation of results for pore-scale fluid-soil interaction with field-scale fluid flow, with the specific goals of (i) predicting attenuation of radionuclide concentration; (ii) estimating changes in flow rates through changes of soil permeabilities; and (iii) estimating effective reaction rates. In supplemental work, we also simulated reactive transport systems relevant to geologic carbon sequestration. As a whole, this research generated a better understanding of reactive transport in porous media, and resulted in more accurate methods for reaction rate upscaling and improved prediction of permeability evolution. These scientific advancements will ultimately lead to better tools for management and remediation of DOE legacy waste problems.

  1. Voluntary Control of Human Heart Rate: Effect on Reaction to Aversive Stimulation: A Replication and Extension

    ERIC Educational Resources Information Center

    Sirota, Alan D.; And Others

    1976-01-01

    Hypothesized that biofeedback training for fear-relevant physiological changes might provide a useful therapeutic strategy to influence directly a person's reaction to anxiety-inducing situations. (Author)

  2. High-precision (p,t) reaction measurement to determine {sup 18}Ne({alpha},p){sup 21}Na reaction rates

    SciTech Connect

    Matic, A.; Berg, A. M. van den; Harakeh, M. N.; Woertche, H. J.; Berg, G. P. A.; Couder, M.; Fisker, J. L.; Goerres, J.; LeBlanc, P.; O'Brien, S.; Wiescher, M.; Fujita, K.; Hatanaka, K.; Sakemi, Y.; Shimizu, Y.; Tameshige, Y.; Tamii, A.; Yosoi, M.; Adachi, T.; Fujita, Y.

    2009-11-15

    x-ray bursts are identified as thermonuclear explosions in the outer atmosphere of accreting neutron stars. The thermonuclear runaway is fueled by the {alpha}p process that describes a sequence of ({alpha},p) reactions triggered by the {sup 18}Ne({alpha},p){sup 21}Na breakout reaction from the hot CNO cycles. We studied the level structure of the compound nucleus {sup 22}Mg by measuring the {sup 24}Mg(p,t){sup 22}Mg reaction at the Grand Raiden spectrometer at Research Center for Nuclear Physics, Osaka. A large number of {alpha}-unbound states was identified and precise excitation energies were determined. Based on shell model and {alpha}-cluster model calculations we predict the level parameters for determining the stellar reaction rate of {sup 18}Ne({alpha},p){sup 21}Na for a wide temperature range. x-ray burst simulations have been performed to study the impact of the reaction on the x-ray burst luminosity.

  3. Rate constant measurements for the reaction Cl + CH2O yields HCl + CHO Implications regarding the removal of stratospheric chlorine

    NASA Technical Reports Server (NTRS)

    Anderson, P. C.; Kurylo, M. J.

    1979-01-01

    The flash photolysis resonance fluorescence technique was employed to investigate the rate constant for the reaction Cl + CH2O yields HCl + CHO from 223 to 323 K. An Arrhenius fit of the data gives a rate constant equal to (1.09 + or - 0.40) x 10 to the -10th exp/-(131 + or - 98)/T/ in units of cu cm/molecule per sec. The results are compared to two very recent kinetic studies and are assessed in view of the reaction's role in disrupting the Cl-ClO stratospheric ozone depletion chain.

  4. The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

    SciTech Connect

    Maher, K.; Steefel, C. I.; White, A.F.; Stonestrom, D.A.

    2009-02-25

    In order to explore the reasons for the apparent discrepancy between laboratory and field weathering rates and to determine the extent to which weathering rates are controlled by the approach to thermodynamic equilibrium, secondary mineral precipitation and flow rates, a multicomponent reactive transport model (CrunchFlow) was used to interpret soil profile development and mineral precipitation and dissolution rates at the 226 ka marine terrace chronosequence near Santa Cruz, CA. Aqueous compositions, fluid chemistry, transport, and mineral abundances are well characterized (White et al., 2008, GCA) and were used to constrain the reaction rates for the weathering and precipitating minerals in the reactive transport modeling. When primary mineral weathering rates are calculated with either of two experimentally determined rate constants, the nonlinear, parallel rate law formulation of Hellmann and Tisser and [2006] or the aluminum inhibition model proposed by Oelkers et al. [1994], modeling results are consistent with field-scale observations when independently constrained clay precipitation rates are accounted for. Experimental and field rates, therefore, can be reconciled at the Santa Cruz site. Observed maximum clay abundances in the argillic horizons occur at the depth and time where the reaction fronts of the primary minerals overlap. The modeling indicates that the argillic horizon at Santa Cruz can be explained almost entirely by weathering of primary minerals and in situ clay precipitation accompanied by undersaturation of kaolinite at the top of the profile. The rate constant for kaolinite precipitation was also determined based on model simulations of mineral abundances and dissolved Al, SiO{sub 2}(aq) and pH in pore waters. Changes in the rate of kaolinite precipitation or the flow rate do not affect the gradient of the primary mineral weathering profiles, but instead control the rate of propagation of the primary mineral weathering fronts and thus total

  5. SISGR - In situ characterization and modeling of formation reactions under extreme heating rates in nanostructured multilayer foils

    SciTech Connect

    Hufnagel, Todd C.

    2014-06-09

    Materials subjected to extreme conditions, such as very rapid heating, behave differently than materials under more ordinary conditions. In this program we examined the effect of rapid heating on solid-state chemical reactions in metallic materials. One primary goal was to develop experimental techniques capable of observing these reactions, which can occur at heating rates in excess of one million degrees Celsius per second. One approach that we used is x-ray diffraction performed using microfocused x-ray beams and very fast x-ray detectors. A second approach is the use of a pulsed electron source for dynamic transmission electron microscopy. With these techniques we were able to observe how the heating rate affects the chemical reaction, from which we were able to discern general principles about how these reactions proceed. A second thrust of this program was to develop computational tools to help us understand and predict the reactions. From atomic-scale simulations were learned about the interdiffusion between different metals at high heating rates, and about how new crystalline phases form. A second class of computational models allow us to predict the shape of the reaction front that occurs in these materials, and to connect our understanding of interdiffusion from the atomistic simulations to measurements made in the laboratory. Both the experimental and computational techniques developed in this program are expected to be broadly applicable to a wider range of scientific problems than the intermetallic solid-state reactions studied here. For example, we have already begun using the x-ray techniques to study how materials respond to mechanical deformation at very high rates.

  6. Temperature and pressure dependence of the absolute rate constant for the reactions of NH2 radicals with acetylene and ethylene

    NASA Technical Reports Server (NTRS)

    Bosco, S. R.; Nava, D. F.; Brobst, W. D.; Stief, L. J.

    1984-01-01

    The absolute rate constants for the reaction between the NH2 free radical and acetylene and ethylene is measured experimentally using a flash photolysis technique. The constant is considered to be a function of temperature and pressure. At each temperature level of the experiment, the observed pseudo-first-order rate constants were assumed to be independent of flash intensity. The results of the experiment indicate that the bimolecular rate constant for the NH2 + C2H2 reaction increases with pressure at 373 K and 459 K but not at lower temperatures. Results near the pressure limit conform to an Arrhenius expression of 1.11 (+ or -) 0.36 x 10 to the -13th over the temperature range from 241 to 459 K. For the reaction NH2 + C2H4, a smaller rate of increase in the bimolecular rate constant was observed over the temperature range 250-465 K. The implications of these results for current theoretical models of NH2 + C2H2 (or H4) reactions in the atmospheres of Jupiter and Saturn are discussed.

  7. A rate-determining proton relay in the pyruvate kinase reaction

    SciTech Connect

    Rose, I.A.; Kuo, D.J.; Warms, J.V.B. )

    1991-01-22

    This study ascribes the large steady-state D{sub 2}O isotope effect on k{sub cat} of pyruvate kinase (PEP + ADP {yields} pyruvate + ATP) to the reprotonation of the product form of the enzyme for use in forming pyruvate. Previous tritium trapping experiments with muscle pyruvate kinase showed that the proton used for ketonization of enolpyruvate is derived from an enzyme pool that contains three kinetically equivalent hydrogens that could be trapped in a nontritiated chase medium by high levels of ADP and PEP. The exchange of this pool with the medium was rapid in the free enzyme prior to addition of PEP, and apparently much less in the completed complex. The present study shows that the competition constant, K{sub 1/2}, is decreased by {approximately}5-fold in D{sub 2}O, the same effect seen on k{sub cat} under conditions where k{sub cat}/K{sub m}, measured in the steady state, is not changed. The common effect of D{sub 2}O on k{sub cat} in the steady state and k{sub off}{sup T} in pulse/chase suggests that the forward reaction rate is determined by hydrogen transfer to the enzyme. Further evidence indicates that the kinetically important proton in question is the proton used for ketonization of enolpyruvate, the substrate proton. With Co, roughly three T of the pool can be trapped. With Mg, only one T can be trapped from the same pulse solution at the highest concentrations of PEP. Apparently two positions, possibly from a bound water molecule, are rapidly exchanged with water of the chase. The inference that lysine NH{sub 3{sup +}} is the proton donor group on the basis of the three T trapped is open to question by evidence that one or two of these come from relay positions.

  8. Optimal reconstruction of concentrations, gradients and reaction rates from particle distributions

    NASA Astrophysics Data System (ADS)

    Fernàndez-Garcia, D.; Sanchez-Vila, X.

    2011-03-01

    Random walk particle tracking methodologies to simulate solute transport of conservative species constitute an attractive alternative for their computational efficiency and absence of numerical dispersion. Yet, problems stemming from the reconstruction of concentrations from particle distributions have typically prevented its use in reactive transport problems. The numerical problem mainly arises from the need to first reconstruct the concentrations of species/components from a discrete number of particles, which is an error prone process, and then computing a spatial functional of the concentrations and/or its derivatives (either spatial or temporal). Errors are then propagated, so that common strategies to reconstruct this functional require an unfeasible amount of particles when dealing with nonlinear reactive transport problems. In this context, this article presents a methodology to directly reconstruct this functional based on kernel density estimators. The methodology mitigates the error propagation in the evaluation of the functional by avoiding the prior estimation of the actual concentrations of species. The multivariate kernel associated with the corresponding functional depends on the size of the support volume, which defines the area over which a given particle can influence the functional. The shape of the kernel functions and the size of the support volume determines the degree of smoothing, which is optimized to obtain the best unbiased predictor of the functional using an iterative plug-in support volume selector. We applied the methodology to directly reconstruct the reaction rates of a precipitation/dissolution problem involving the mixing of two different waters carrying two aqueous species in chemical equilibrium and moving through a randomly heterogeneous porous medium.

  9. An Interactive Classroom Activity Demonstrating Reaction Mechanisms and Rate-Determining Steps

    ERIC Educational Resources Information Center

    Jennings, Laura D.; Keller, Steven W.

    2005-01-01

    An interactive classroom activity that includes two-step reaction of unwrapping and eating chocolate candies is described which brings not only the reaction intermediate, but also the reactants and products into macroscopic view. The qualitative activation barriers of both steps can be adjusted independently.

  10. Charting an Alternate Pathway to Reaction Orders and Rate Laws in Introductory Chemistry Courses

    ERIC Educational Resources Information Center

    Rushton, Gregory T.; Criswell, Brett A.; McAllister, Nicole D.; Polizzi, Samuel J.; Moore, Lamesha A.; Pierre, Michelle S.

    2014-01-01

    Reaction kinetics is an axiomatic topic in chemistry that is often addressed as early as the high school course and serves as the foundation for more sophisticated conversations in college-level organic, physical, and biological chemistry courses. Despite the fundamental nature of reaction kinetics, students can struggle with transforming their…

  11. Determination of the reaction rate coefficient of sulphide mine tailings deposited under water.

    PubMed

    Awoh, Akué Sylvette; Mbonimpa, Mamert; Bussière, Bruno

    2013-10-15

    The efficiency of a water cover to limit dissolved oxygen (DO) availability to underlying acid-generating mine tailings can be assessed by calculating the DO flux at the tailings-water interface. Fick's equations, which are generally used to calculate this flux, require knowing the effective DO diffusion coefficient (Dw) and the reaction (consumption) rate coefficient (Kr) of the tailings, or the DO concentration profile. Whereas Dw can be accurately estimated, few studies have measured the parameter Kr for submerged sulphide tailings. The objective of this study was to determine Kr for underwater sulphide tailings in a laboratory experiment. Samples of sulphide mine tailings (an approximately 6 cm layer) were placed in a cell under a water cover (approximately 2 cm) maintained at constant DO concentration. Two tailings were studied: TA1 with high sulphide content (83% pyrite) and TA2 with low sulphide content (2.8% pyrite). DO concentration was measured with a microelectrode at various depths above and below the tailings-water interface at 1 mm intervals. Results indicate that steady-state condition was rapidly attained. As expected, a diffusive boundary layer (DBL) was observed in all cases. An iterative back-calculation process using the numerical code POLLUTEv6 and taking the DBL into account provided the Kr values used to match calculated and experimental concentration profiles. Kr obtained for tailings TA1 and TA2 was about 80 d(-1) and 6.5 d(-1), respectively. For comparison purposes, Kr obtained from cell tests on tailings TA1 was lower than Kr calculated from the sulphate production rate obtained from shake-flask tests. Steady-state DO flux at the water-tailings interface was then calculated with POLLUTEv6 using tailings characteristics Dw and Kr. For the tested conditions, DO flux ranged from 608 to 758 mg O2/m(2)/d for tailings TA1 and from 177 to 221 mg O2/m(2)/d for tailings TA2. The impact of placing a protective layer of inert material over

  12. Mapped interpolation scheme for single-point energy corrections in reaction rate calculations and a critical evaluation of dual-level reaction path dynamics methods

    SciTech Connect

    Chuang, Y.Y.; Truhlar, D.G.; Corchado, J.C.

    1999-02-25

    Three procedures for incorporating higher level electronic structure data into reaction path dynamics calculations are tested. In one procedure, variational transition state theory with interpolated single-point energies, which is denoted VTST-ISPE, a few extra energies calculated with a higher level theory along the lower level reaction path are used to correct the classical energetic profile of the reaction. In the second procedure, denoted variational transition state theory with interpolated optimized corrections (VTST-IOC), which the authors introduced earlier, higher level corrections to energies, frequencies, and moments of inertia are based on stationary-point geometries reoptimized at a higher level than the reaction path was calculated. The third procedure, called interpolated optimized energies (IOE), is like IOC except it omits the frequency correction. Three hydrogen-transfer reactions, CH{sub 3} + H{prime}H {r_arrow} CH{sub 3}H{prime} + H (R1), OH + H{prime}H {r_arrow} HOH{prime} + H (R2), and OH + H{prime}CH{sub 3} {r_arrow} HOH{prime} + CH{sub 3} (R3), are used to test and validate the procedures by comparing their predictions to the reaction rate evaluated with a full variational transition state theory calculation including multidimensional tunneling (VTST/MT) at the higher level. The authors present a very efficient scheme for carrying out VTST-ISPE calculations, which are popular due to their lower computational cost. They also show, on the basis of calculations of the reactions R1--R3 with eight pairs of higher and lower levels, that VTST-IOC with higher level data only at stationary points is a more reliable dual-level procedure than VTST-ISPE with higher level energies all along the reaction path. Although the frequencies along the reaction path are not corrected in the IOE scheme, the results are still better than those from VTST-ISPE; this indicates the importance of optimizing the geometry at the highest possible level.

  13. Measurements of the O+ plus N2 and O+ plus O2 reaction rates from 300 to 900 K

    NASA Technical Reports Server (NTRS)

    Chen, A.; Johnsen, R.; Biondi, M. A.

    1977-01-01

    Rate coefficients for the O(+) + N2 atom transfer and O(+) + O2 charge transfer reactions are determined at thermal energies between 300 K and 900 K difference in a heated drift tube mass spectrometer apparatus. At 300 K the values K(O(+) + N2) = (1.2 plus or minus 0.1) x 10 to the negative 12 power cubic cm/sec and k(O(+) + O2) = (2.1 plus or minus 0.2) x 10 to the negative 11 power cubic cm/sec were obtained, with a 50% difference decrease in the reaction rates upon heating to 700 K. These results are in good agreement with heated flowing afterglow results, but the O(+) + O2 thermal rate coefficients are systematically lower than equivalent Maxwellian rates inferred by conversion of nonthermal drift tube and flow drift data.

  14. Rate constants for the reactions OH + HOCl. -->. H/sub 2/O + ClO and H + HOCl. -->. products

    SciTech Connect

    Ennis, C.A.; Birks, J.W.

    1988-03-10

    A new laboratory source of gaseous hypochlorous acid (HOCl) has been used in two kinetics investigations in a mass spectrometry-resonance fluorescence discharge flow system. Two potential removal reactions of stratospheric HOCl were studied. The rate constant for the reaction OH + HOCl ..-->.. H/sub 2/O + ClO (1) at 298 K was found to be lower than the NASA estimate by a factor of about 2-12; a value in the range (1.7-9.5) x 10/sup -13/ cm/sup 3/ molecule/sup -1/ s/sup -1/ for k/sub 1/ is reported here. The reaction of Cl/sub 2/O + OH interfered in the study of k/sub 1/ and was the subject of a preliminary investigation. Its rate constant was determined to be (9.4 +/- 1.0) x 10/sup -12/ cm/sup 3/ molecule/sup -1/ s/sup -1/ at 298 K. The rate constant for the reaction H + HOCl ..-->.. products (2) was determined to be (5.0 +/- 1.4) x 298 K. Although branching ratios for three possible products channels could not be determined, OH was identified as a product. The results of this work imply that reactions 1 and 2 are not competitive with direct photolysis in the removal of HOCl from the stratosphere.

  15. EFFECTS OF REACTION PARAMETERS ON ELECTROCHEMICAL DECHLORINATION OF TRICHLOROETHYLENE RATE AND BY-PRODUCTS

    EPA Science Inventory

    Trichloroethylene (TCE) was electrochemically dechlorinated in aqueous environments using granular graphite cathode in a mixed reactor. Effects of pH, current, electrolyte type, and flow rate on TCE dechlorination rate were evaluated. TCE dechlorination rate constant and gas prod...

  16. Evaluating free vs bound oxygen on ignition of nano-aluminum based energetics leads to a critical reaction rate criterion

    NASA Astrophysics Data System (ADS)

    Zhou, Wenbo; DeLisio, Jeffery B.; Wang, Xizheng; Egan, Garth C.; Zachariah, Michael R.

    2015-09-01

    This study investigates the ignition of nano-aluminum (n-Al) and n-Al based energetic materials (nanothermites) at varying O2 pressures (1-18 atm), aiming to differentiate the effects of free and bound oxygen on ignition and to assess if it is possible to identify a critical reaction condition for ignition independent of oxygen source. Ignition experiments were conducted by rapidly heating the samples on a fine Pt wire at a heating rate of ˜105 °C s-1 to determine the ignition time and temperature. The ignition temperature of n-Al was found to reduce as the O2 pressure increased, whereas the ignition temperatures of nanothermites (n-Al/Fe2O3, n-Al/Bi2O3, n-Al/K2SO4, and n-Al/K2S2O8) had different sensitivities to O2 pressure depending on the formulations. A phenomenological kinetic/transport model was evaluated to correlate the concentrations of oxygen both in condensed and gaseous phases, with the initiation rate of Al-O at ignition temperature. We found that a constant critical reaction rate (5 × 10-2 mol m-2 s-1) for ignition exists which is independent to ignition temperature, heating rate, and free vs bound oxygen. Since for both the thermite and the free O2 reaction the critical reaction rate for ignition is the same, the various ignition temperatures are simply reflecting the conditions when the critical reaction rate for thermal runaway is achieved.

  17. Absolute rate of the reaction of atomic hydrogen with ethylene from 198 to 320 K at high pressure

    NASA Technical Reports Server (NTRS)

    Lee, J. H.; Michael, J. V.; Payne, W. A.; Stief, L. J.

    1978-01-01

    The rate constant for the H+C2H4 reaction has been measured as a function of temperature. Experiments were performed with high pressures of Ar heat bath gas at seven temperatures from 198 to 320 K with the flash photolysis-resonance fluorescence (FP-RF) technique. Pressures were chosen so as to isolate the addition rate constant k1. The results are well represented by an Arrhenius expression. The results are compared with other studies and are theoretically discussed.

  18. Shock tube measurements of specific reaction rates in the branched chain CH4-CO-O2 system

    NASA Technical Reports Server (NTRS)

    Brabbs, T. A.; Brokaw, R. S.

    1975-01-01

    Growth constants, obtained by measuring the blue CO flame band emission behind incident shock waves, were obtained for two elementary bimolecular reactions involved in the oxidation of methane. Gas mixtures containing small amounts of CH4 with varying amounts of CO, O2, and in one case CO2, diluted with argon, were investigated, and exponential growth constants were derived from plots of the logarithm of observed light intensity versus gas time. The rate constant for the reaction O + CH4 yields CH3 + OH was found to be 1.9 times 10 to the 14th exp(-5900/T) cu cm per mole per sec in the range 1300-2000 K; for the reaction CH3 + O2 yields CH3O + O, the rate constant was determined to be 2.4 times 10 to the 13th exp(-14,500/T) cu cm per mole per sec in the range 1200 to 1900 K.

  19. Improved 192,194,195,196Pt(n,γ) and 192Ir(n,γ) astrophysical reaction rates

    NASA Astrophysics Data System (ADS)

    Koehler, P. E.; Guber, K. H.

    2013-09-01

    192Pt is produced solely by the slow neutron capture (s) nucleosynthesis process and hence an accurate (n,γ) reaction rate for this nuclide would allow its use as an important calibration point near the termination of the s-process nucleosynthesis flow. For this reason, we have measured neutron capture and total cross sections for 192,194,195,196,natPt in the energy range from 10 eV to several hundred keV at the Oak Ridge Electron Linear Accelerator. Measurements on the other Pt isotopes were, in part, necessitated by the fact that only a relatively small 192Pt sample of modest enrichment was available. Astrophysical 192,194,195,196Pt(n,γ) reaction rates, accurate to approximately 3%-5%, were calculated from these data. No accurate reaction rates have been published previously for any of these isotopes. At s-process temperatures, previously recommended rates are larger (by as much as 35%) and have significantly different shapes as functions of temperature than our new rates. We used our new Pt results, together with 191,193Ir(n,γ) data, to calibrate nuclear statistical model calculations and hence obtain an improved rate for the unmeasured s-process branching-point isotope 192Ir.

  20. TECHNIQUES AFFECTING PRECISION AND ACCURACY IN HYDROLYSIS RATE CONSTANT DETERMINATIONS OF VOLATILE ORGANIC COMPOUNDS USING JEFFERS' ZERO HEADSPACE REACTION BULBS

    EPA Science Inventory

    A recently published method for measurement of hydrolysis rate constants for volatile organic compounds in aqueous samples was adapted for use in our laboratory. n applying the method, we developed the capability to make the zero-headspace reaction bulbs and used them to measure ...

  1. Revised Calculations of the Production Rates for Co Isotopes in Meteorites Using New Cross Sections for Neutron-induced Reactions

    NASA Technical Reports Server (NTRS)

    Sisterson, J. M.; Brooks, F. D.; Buffler, A.; Allie, M. S.; Herbert, M. S.; Nchodu, M. R.; Makupula, S.; Ullmann, J.; Reedy, R. C.; Jones, D. T. L.

    2002-01-01

    New cross section measurements for reactions induced by neutrons with energies greater than 70 MeV are used to calculate the production rates for cobalt isotopes in meteorites and these new calculations are compared to previous estimates. Additional information is contained in the original extended abstract.

  2. Rate constant and mechanism of the reaction between Cl and CH{sub 3}OCl at 295 K

    SciTech Connect

    Carl, S.A.; Roehl, C.M.; Moortgat, G.K.; Crowley, J.N.; Mueller, C.M. |

    1996-10-24

    The reaction between Cl atoms and CH{sub 3}OCl was investigated at 295 K in both air and N{sub 2} bath gases at total pressures between 100 and 850 Torr by the relative rate method. The rate constant of the title reaction was found to be a factor 1.07{+-}0.02 (2{sigma}) greater than that of Cl+C{sub 2}H{sub 6} at room temperature and independent of pressure between 100 and 750 Torr. This yields a rate constant of (6.1{+-}0.6)x10{sup -11} cm{sup 3} molecule{sup -1} s{sup -1}. The products of the reaction were detected by FTIR and UV absorption spectroscopy. Analysis of Cl{sub 2} and HCl products allowed branching ratios of 0.2{+-}0.1 for HCl+CH{sub 2}OCl formation and 0.8{+-}0.2 for Cl{sub 2}+CH{sub 3}O formation to be determined. The high rate constant implies that reaction with Cl atoms is an important loss process for CH{sub 3}OCl in the polar stratosphere. 37 refs., 9 figs., 3 tabs.

  3. Relationship between severity of the local skin reactions and the rate of local skin reaction resolution in patients treated with ingenol mebutate gel

    PubMed Central

    Jim On, Shelbi C; Knudsen, Kim Mark; Skov, Torsten; Lebwohl, Mark

    2016-01-01

    Background Ingenol mebutate gel is a topical field treatment for actinic keratosis (AK). The treatment elicits application-site reactions in most patients. This analysis evaluated the relationship between the severity of reactions and the speed of their resolution. Methods Patients in Phase III studies were treated for AKs on the face (n=218), scalp (n=56), and trunk and extremities (n=209). All of the patients were treated with either ingenol mebutate gel 0.015% once daily for three consecutive days (face/scalp) or ingenol mebutate gel 0.05% once daily for two consecutive days (trunk/extremities). Local skin reactions (LSRs) were assessed on a 5-point scale from 0 to 4 in six categories, yielding composite scores in the range of 0 to 24. Results The composite LSR score on the day after the last application of ingenol mebutate gel was an important predictor of the speed of resolution of LSRs. The rate of resolution was greatest for AKs treated on the face, followed by the scalp, and then the trunk and extremities. All patients were expected to have minimal LSR scores for the face and scalp at 2 weeks, and for the trunk and extremities at 4 weeks. Conclusion The absolute reduction in LSR scores was proportional to the composite LSR score on the day after the last application of ingenol mebutate gel treatment. The rate of resolution for LSRs was dependent on the anatomic site treated as well as the day 4 composite score. PMID:27601928

  4. 34 CFR 694.11 - What is the maximum indirect cost rate for an agency of a State or local government?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 34 Education 4 2012-07-01 2012-07-01 false What is the maximum indirect cost rate for an agency of a State or local government? 694.11 Section 694.11 Education Regulations of the Offices of the Department of Education (Continued) OFFICE OF POSTSECONDARY EDUCATION, DEPARTMENT OF EDUCATION (CONTINUED) GAINING EARLY AWARENESS AND READINESS...

  5. 41 CFR 102-117.40 - When is it advantageous for me to use another agency's contract or rate tender for transportation...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false When is it advantageous for me to use another agency's contract or rate tender for transportation services? 102-117.40 Section 102-117.40 Public Contracts and Property Management Federal Property Management Regulations...

  6. 41 CFR 102-117.40 - When is it advantageous for me to use another agency's contract or rate tender for transportation...

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 41 Public Contracts and Property Management 3 2011-01-01 2011-01-01 false When is it advantageous for me to use another agency's contract or rate tender for transportation services? 102-117.40 Section 102-117.40 Public Contracts and Property Management Federal Property Management Regulations...

  7. 41 CFR 102-117.40 - When is it advantageous for me to use another agency's contract or rate tender for transportation...

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 41 Public Contracts and Property Management 3 2012-01-01 2012-01-01 false When is it advantageous for me to use another agency's contract or rate tender for transportation services? 102-117.40 Section 102-117.40 Public Contracts and Property Management Federal Property Management Regulations...

  8. 41 CFR 102-117.40 - When is it advantageous for me to use another agency's contract or rate tender for transportation...

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 41 Public Contracts and Property Management 3 2014-01-01 2014-01-01 false When is it advantageous for me to use another agency's contract or rate tender for transportation services? 102-117.40 Section 102-117.40 Public Contracts and Property Management Federal Property Management Regulations...

  9. 41 CFR 102-117.40 - When is it advantageous for me to use another agency's contract or rate tender for transportation...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 41 Public Contracts and Property Management 3 2013-07-01 2013-07-01 false When is it advantageous for me to use another agency's contract or rate tender for transportation services? 102-117.40 Section 102-117.40 Public Contracts and Property Management Federal Property Management Regulations...

  10. The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

    NASA Astrophysics Data System (ADS)

    Maher, Kate; Steefel, Carl I.; White, Art F.; Stonestrom, Dave A.

    2009-05-01

    In order to explore the reasons for the apparent discrepancy between laboratory and field weathering rates and to determine the extent to which weathering rates are controlled by the approach to thermodynamic equilibrium, secondary mineral precipitation, and flow rates, a multicomponent reactive transport model (CrunchFlow) was used to interpret soil profile development and mineral precipitation and dissolution rates at the 226 ka Marine Terrace Chronosequence near Santa Cruz, CA. Aqueous compositions, fluid chemistry, transport, and mineral abundances are well characterized [White A. F., Schulz M. S., Vivit D. V., Blum A., Stonestrom D. A. and Anderson S. P. (2008) Chemical weathering of a Marine Terrace Chronosequence, Santa Cruz, California. I: interpreting the long-term controls on chemical weathering based on spatial and temporal element and mineral distributions. Geochim. Cosmochim. Acta72 (1), 36-68] and were used to constrain the reaction rates for the weathering and precipitating minerals in the reactive transport modeling. When primary mineral weathering rates are calculated with either of two experimentally determined rate constants, the nonlinear, parallel rate law formulation of Hellmann and Tisserand [Hellmann R. and Tisserand D. (2006) Dissolution kinetics as a function of the Gibbs free energy of reaction: An experimental study based on albite feldspar. Geochim. Cosmochim. Acta70 (2), 364-383] or the aluminum inhibition model proposed by Oelkers et al. [Oelkers E. H., Schott J. and Devidal J. L. (1994) The effect of aluminum, pH, and chemical affinity on the rates of aluminosilicate dissolution reactions. Geochim. Cosmochim. Acta58 (9), 2011-2024], modeling results are consistent with field-scale observations when independently constrained clay precipitation rates are accounted for. Experimental and field rates, therefore, can be reconciled at the Santa Cruz site. Additionally, observed maximum clay abundances in the argillic horizons occur at the

  11. The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

    USGS Publications Warehouse

    Maher, K.; Steefel, Carl; White, A.F.; Stonestrom, D.A.

    2009-01-01

    In order to explore the reasons for the apparent discrepancy between laboratory and field weathering rates and to determine the extent to which weathering rates are controlled by the approach to thermodynamic equilibrium, secondary mineral precipitation, and flow rates, a multicomponent reactive transport model (CrunchFlow) was used to interpret soil profile development and mineral precipitation and dissolution rates at the 226 ka Marine Terrace Chronosequence near Santa Cruz, CA. Aqueous compositions, fluid chemistry, transport, and mineral abundances are well characterized [White A. F., Schulz M. S., Vivit D. V., Blum A., Stonestrom D. A. and Anderson S. P. (2008) Chemical weathering of a Marine Terrace Chronosequence, Santa Cruz, California. I: interpreting the long-term controls on chemical weathering based on spatial and temporal element and mineral distributions. Geochim. Cosmochim. Acta 72 (1), 36-68] and were used to constrain the reaction rates for the weathering and precipitating minerals in the reactive transport modeling. When primary mineral weathering rates are calculated with either of two experimentally determined rate constants, the nonlinear, parallel rate law formulation of Hellmann and Tisserand [Hellmann R. and Tisserand D. (2006) Dissolution kinetics as a function of the Gibbs free energy of reaction: An experimental study based on albite feldspar. Geochim. Cosmochim. Acta 70 (2), 364-383] or the aluminum inhibition model proposed by Oelkers et al. [Oelkers E. H., Schott J. and Devidal J. L. (1994) The effect of aluminum, pH, and chemical affinity on the rates of aluminosilicate dissolution reactions. Geochim. Cosmochim. Acta 58 (9), 2011-2024], modeling results are consistent with field-scale observations when independently constrained clay precipitation rates are accounted for. Experimental and field rates, therefore, can be reconciled at the Santa Cruz site. Additionally, observed maximum clay abundances in the argillic horizons occur at

  12. Inter-and intraspecific variation in excited-state triplet energy transfer rates in reaction centers of photosynthetic bacteria.

    SciTech Connect

    Laible, P. D.; Morris, Z. S.; Thurnauer, M. C.; Schiffer, M.; Hanson, D. K.

    2003-08-01

    In protein-cofactor reaction center (RC) complexes of purple photosynthetic bacteria, the major role of the bound carotenoid (C) is to quench the triplet state formed on the primary electron donor (P) before its sensitization of the excited singlet state of molecular oxygen from its ground triplet state. This triplet energy is transferred from P to C via the bacteriochlorophyll monomer B{sub B}. Using time-resolved electron paramagnetic resonance (TREPR), we have examined the temperature dependence of the rates of this triplet energy transfer reaction in the RC of three wild-type species of purple nonsulfur bacteria. Species-specific differences in the rate of transfer were observed. Wild-type Rhodobacter capsulatus RCs were less efficient at the triplet transfer reaction than Rhodobacter sphaeroides RCs, but were more efficient than Rhodospirillum rubrum RCs. In addition, RCs from three mutant strains of R. capsulatus carrying substitutions of amino acids near P and B{sub B} were examined. Two of the mutant RCs showed decreased triplet transfer rates compared with wild-type RCs, whereas one of the mutant RCs demonstrated a slight increase in triplet transfer rate at low temperatures. The results show that site-specific changes within the RC of R. capsulatus can mimic interspecies differences in the rates of triplet energy transfer. This application of TREPR was instrumental in defining critical energetic and coupling factors that dictate the efficiency of this photoprotective process.

  13. Gas-Phase Reaction Pathways and Rate Coefficients for the Dichlorosilane-Hydrogen and Trichlorosilane-Hydrogen Systems

    NASA Technical Reports Server (NTRS)

    Dateo, Christopher E.; Walch, Stephen P.

    2002-01-01

    As part of NASA Ames Research Center's Integrated Process Team on Device/Process Modeling and Nanotechnology our goal is to create/contribute to a gas-phase chemical database for use in modeling microelectronics devices. In particular, we use ab initio methods to determine chemical reaction pathways and to evaluate reaction rate coefficients. Our initial studies concern reactions involved in the dichlorosilane-hydrogen (SiCl2H2--H2) and trichlorosilane-hydrogen (SiCl2H-H2) systems. Reactant, saddle point (transition state), and product geometries and their vibrational harmonic frequencies are determined using the complete-active-space self-consistent-field (CASSCF) electronic structure method with the correlation consistent polarized valence double-zeta basis set (cc-pVDZ). Reaction pathways are constructed by following the imaginary frequency mode of the saddle point to both the reactant and product. Accurate energetics are determined using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations (CCSD(T)) extrapolated to the complete basis set limit. Using the data from the electronic structure calculations, reaction rate coefficients are obtained using conventional and variational transition state and RRKM theories.

  14. 59Fe(n,g)60Fe and 60Fe(n,g)61Fe Reaction Rates from Local Systematics

    SciTech Connect

    Kelley, K; Hoffman, R D; Drake, M

    2005-04-25

    We present modeled neutron capture cross sections relevant to stellar production of {sup 60}Fe. Systematics for the input parameters required by the Hauser-Feshbach statistical model are developed based on measured data in the local region of the isotopic plane (20 {le} Z {le} 29, 43 {le} A {le} 65). These parameters and used to calculate reaction cross sections and rates for select target isotopes. Modeled cross sections are compared to experimental data where available. The {sup 59}Fe(n,{gamma}){sup 60}Fe and {sup 60}Fe(n, {gamma}){sup 61}Fe rates are compared to previous calculations. A brief discussion of errors related to the modeling is provided. We conclude by investigating the sensitivity of stellar production of {sup 26}Al and {sup 60}Fe to the {sup 59}Fe(n,{gamma}){sup 60}Fe and {sup 60}Fe(n,{gamma})61Fe reaction rates using a single zone model.

  15. Significance of vapor phase chemical reactions on CVD rates predicted by chemically frozen and local thermochemical equilibrium boundary layer theories

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.

    1988-01-01

    This paper investigates the role played by vapor-phase chemical reactions on CVD rates by comparing the results of two extreme theories developed to predict CVD mass transport rates in the absence of interfacial kinetic barrier: one based on chemically frozen boundary layer and the other based on local thermochemical equilibrium. Both theories consider laminar convective-diffusion boundary layers at high Reynolds numbers and include thermal (Soret) diffusion and variable property effects. As an example, Na2SO4 deposition was studied. It was found that gas phase reactions have no important role on Na2SO4 deposition rates and on the predictions of the theories. The implications of the predictions of the two theories to other CVD systems are discussed.

  16. Theoretical study of the rate constants for the hydrogen atom abstraction reactions of esters with (•)OH radicals.

    PubMed

    Mendes, Jorge; Zhou, Chong-Wen; Curran, Henry J

    2014-07-10

    A systematic investigation of the rate constants for hydrogen atom abstraction reactions by hydroxyl radicals on esters has been performed. The geometry optimizations and frequency calculations were obtained using the second-order Møller-Plesset method with the 6-311G(d,p) basis set. The same method was also used in order to determine the dihedral angle potential for each individual hindered rotor in each reactant and transition state. Intrinsic reaction coordinate calculations were used in order to connect each transition state to the corresponding local minimum. For the reactions of methyl ethanoate with an (•)OH radical, the relative electronic energies were calculated using the G3 and the CCSD(T)/cc-pVXZ (where X = D, T, and Q) methods, which were extrapolated to the complete basis set (CBS) limit. The electronic energies obtained using the G3 method were then benchmarked against the CBS results and were found to be within 1 kcal mol(-1) of one another. The high-pressure limit rate constants for every reaction channel were calculated by conventional transition-state theory, with an asymmetric Eckart tunneling correction, using the energies obtained with the G3 method. We report the individual, average, and total rate constants in the temperature range from 500 to 2200 K. Our calculated results are within a factor of 2 for methyl ethanoate and between 40% to 50% for methyl propanoate and methyl butanoate when compared to previously reported experimental data. PMID:24878337

  17. Dynamic Linkages between Denitrification Functional Genes/Enzymes and Biogeochemical Reaction Rates of Nitrate and Its Reduction Products

    NASA Astrophysics Data System (ADS)

    Li, M.; Shi, L.; Qian, W.; Gao, Y.; Liu, Y.; Liu, C.

    2015-12-01

    Denitrification is a respiratory process in which oxidized nitrogen compounds are used as alternative electron acceptors for energy production when oxygen is limited. Denitrification is an important process that not only accounts for the significant loss of nitrogen fertilizers from soils but also leads to NO, N2O and CO2 emissions, which are important greenhouse gas species. In this study, denitrification was investigated in Columbia River sediments, focusing on the dynamic linkages between functional genes/enzymes and biogeochemical reaction rates of nitrate and its reduction products. NO3-, NO2- and N2O were assayed in different incubation time. DNA was extracted from the sediments and functional genes were quantified as a function of time during the denitrification. Functional enzymes were extracted from the sediments and measured using a newly developed, targeted protein method. The biogeochemical, functional gene, and enzyme data were collectively used to establish the dynamic correlation of functional genes/enzymes and biogeochemical reaction rates. The results provide fundamental insights regarding the dynamic regulation of functional genes and enzymes in the processes of denitrification and greenhouse gas production, and also provide experimental data critical for the development of biogeochemical reaction models that incorporate genome-scale insights and describe macroscopic biogeochemical reaction rates in ecosystems.

  18. The effects of finite-rate reactions at the gas/surface interface in support of thermal protection system design

    NASA Astrophysics Data System (ADS)

    Beerman, Adam Farrell

    2011-12-01

    Gas-surface modeling is dependent on material type and atmospheric reentry conditions. Lower molecular collisions at the low pressure trajectories make it more likely for occurrences of nonequilibrium, or finite-rate, reactions. Equilibrium is often assumed at the surface of a material as it is a subset of nonequilibrium and is easier to compute, though it can lead to overly conservative predictions. A case where a low density material experiences a low pressure trajectory and designed for equilibrium is the Stardust Return Capsule (SRC) with the Phenolic Impregnated Carbon Ablator (PICA) as its heatshield. Post-flight analysis of the recession on the SRC found that the prediction from the equilibrium model can be more than 50% larger than the measured recession. The Modified Park Model was chosen as the finite-rate model as it contains simple four reactions (oxidation, sublimation, and nitridation) and has been previously used to study individual points of the SRC trajectory. The Modified Park Model cannot model equilibrium so a model BFIAT was developed that allows finite-rate reactions to be applied to the surface for a certain length of time. Finite-rate sublimation was determined to be reaction of importance in the Park Model for SRC-like conditions. The predicted recession on the SRC heatshield experienced a reduction in its overprediction; the finite-rate predictions fall with the measurement error of the recession at three points on the heatshield. The recession reduction was driven by a significant reduction in char formation. There was little change in the pyrolysis gas rate. The finite-rate model was also applied to simulations of various arc-jet tests that covered a range of heating conditions on the surface of the PICA material. Comparison to this experimental data further showed the role of finite-rate reactions and sublimation in the Park Model and conditions that favor the nonequilibrium assumption (heating over 1000 W/cm2). For the emerging PICA

  19. The effect of nuclear reaction rates and convective mixing on the evolution of a 6M{sub ȯ} star

    SciTech Connect

    Halabi, Ghina M.

    2014-05-09

    We present the evolution of a 6M{sub ȯ} star, of solar-like initial metallicity, and investigate the effects of key nuclear reaction rates, as well as the treatment of the convective mixing on its evolution along the Cepheid instability strip. In particular, we study the effect of recent estimates of the {sup 14}N(p,γ){sup 15}O reaction on the formation and extension of the blue loop during core helium burning. We also investigate the effects induced on this blue loop by the adoption of non-standard convective mixing prescriptions, as well as the implications of modifying the Mixing Length Theory.

  20. Determination of redox reaction rates and orders by in situ liquid cell electron microscopy of Pd and Au solution growth

    SciTech Connect

    Sutter, Eli A.; Sutter, Peter W.

    2014-11-19

    In-situ liquid cell transmission and scanning transmission electron microscopy (TEM/STEM) experiments are important as they provide direct insight into processes in liquids, such as solution growth of nanoparticles among others. In liquid cell TEM/STEM redox reaction experiments the hydrated electrons e⁻aq created by the electron beam are responsible for the reduction of metal-ion complexes. Here we investigate the rate equation of redox reactions involving reduction by e⁻aq generated by the electron beam during in-situ liquid TEM/STEM. Specifically we consider the growth of Pd on Au seeds in aqueous solutions containing Pd-chloro complexes. From the quantification of the rate of Pd deposition at different electron beam currents and as a function of distance from a stationary, nanometer-sized exciting beam, we determine that the reaction is first order with respect to the concentration of hydrated electrons, [e⁻aq]. In addition, by comparing Pd- and Au-deposition, we further demonstrate that measurements of the local deposition rate on nanoparticles in the solution via real-time imaging can be used to measure not only [e⁻aq] but also the rate of reduction of a metal-ion complex to zero-valent metal atoms in solution.

  1. Determination of redox reaction rates and orders by in situ liquid cell electron microscopy of Pd and Au solution growth

    DOE PAGESBeta

    Sutter, Eli A.; Sutter, Peter W.

    2014-11-19

    In-situ liquid cell transmission and scanning transmission electron microscopy (TEM/STEM) experiments are important as they provide direct insight into processes in liquids, such as solution growth of nanoparticles among others. In liquid cell TEM/STEM redox reaction experiments the hydrated electrons e⁻aq created by the electron beam are responsible for the reduction of metal-ion complexes. Here we investigate the rate equation of redox reactions involving reduction by e⁻aq generated by the electron beam during in-situ liquid TEM/STEM. Specifically we consider the growth of Pd on Au seeds in aqueous solutions containing Pd-chloro complexes. From the quantification of the rate of Pdmore » deposition at different electron beam currents and as a function of distance from a stationary, nanometer-sized exciting beam, we determine that the reaction is first order with respect to the concentration of hydrated electrons, [e⁻aq]. In addition, by comparing Pd- and Au-deposition, we further demonstrate that measurements of the local deposition rate on nanoparticles in the solution via real-time imaging can be used to measure not only [e⁻aq] but also the rate of reduction of a metal-ion complex to zero-valent metal atoms in solution.« less

  2. The OXYGEN-15(ALPHA, GAMMA)NEON-19 Reaction Rate and the Rapid-Proton Capture Process

    NASA Astrophysics Data System (ADS)

    Magnus, Paul Vogt

    The energetics and the rates of the various nuclear reaction chains active in stars play a critical role in the stars' evolution and in the isotopic abundances resulting from this nucleosynthesis. One can therefore gain information about the structure and evolution of stars by examining these nuclear reaction chains and the resulting elemental and isotopic abundances. The abundances of a number of isotopes (e.g., 13C and ^ {15}N) point to the importance of explosive hydrogen burning which takes place on time scales which are short compared to the relevant beta-decay lifetimes. Explosive hydrogen burning is expected to occur at high temperatures (rm T>2times10^8K) in many astrophysical environments such as super-massive stars, accreting neutron stars, red giants with neutron star cores, novae, and supernovae. In these environments it is usually assumed that hydrogen burning occurs via the Hot-CNO (HCNO) cycle which is responsible for the observed abundance of 15N. At sufficiently high temperatures, however, the ^ {15}O(alpha,gamma)^{19 }Ne reaction can break the HCNO cycle and initiate a reaction chain called the rapid-proton capture (rp) process. The rp process transforms CNO nuclei to heavier nuclei (up to iron and nickel) by a chain of successive proton captures and beta decays. Hydrogen and helium-burning reactions, including the 15O( alpha,gamma)19Ne breakout reaction and the subsequent rp process, are thought to be the energy source for novae on the surface of accreting neutron stars and are possibly responsible for the unusual concentrations of heavy elements recently observed in novae. At astrophysically important temperatures, the 15O(alpha,gamma) 19Ne reaction rate is determined by the properties of several resonances just above the alpha-particle threshold in 19 Ne (Ecm<1.2 MeV). This thesis involves a series of experiments which determine the reaction rate for the 15O(alpha,gamma)^ {19}Ne reaction by measuring the properties of these resonances. The ^{15

  3. Reduction of Large Detailed Chemical Kinetic Mechanisms for Autoignition Using Joint Analyses of Reaction Rates and Sensitivities

    SciTech Connect

    Saylam, A; Ribaucour, M; Pitz, W J; Minetti, R

    2006-11-29

    A new technique of reduction of detailed mechanisms for autoignition, which is based on two analysis methods is described. An analysis of reaction rates is coupled to an analysis of reaction sensitivity for the detection of redundant reactions. Thresholds associated with the two analyses have a great influence on the size and efficiency of the reduced mechanism. Rules of selection of the thresholds are defined. The reduction technique has been successfully applied to detailed autoignition mechanisms of two reference hydrocarbons: n-heptane and iso-octane. The efficiency of the technique and the ability of the reduced mechanisms to reproduce well the results generated by the full mechanism are discussed. A speedup of calculations by a factor of 5.9 for n-heptane mechanism and by a factor of 16.7 for iso-octane mechanism is obtained without losing accuracy of the prediction of autoignition delay times and concentrations of intermediate species.

  4. The Effects of Thermonuclear Reaction Rate Variations on 26Al Production in Massive Stars: A Sensitivity Study

    NASA Astrophysics Data System (ADS)

    Iliadis, Christian; Champagne, Art; Chieffi, Alessandro; Limongi, Marco

    2011-03-01

    We investigate the effects of thermonuclear reaction rate variations on 26Al production in massive stars. The dominant production sites in such events were recently investigated by using stellar model calculations: explosive neon-carbon burning, convective shell carbon burning, and convective core hydrogen burning. Post-processing nucleosynthesis calculations are performed for each of these sites by adopting temperature-density-time profiles from recent stellar evolution models. For each profile, we individually multiplied the rates of all relevant reactions by factors of 10, 2, 0.5, and 0.1, and analyzed the resulting abundance changes of 26Al. In total, we performed ≈900 nuclear reaction network calculations. Our simulations are based on a next-generation nuclear physics library, called STARLIB, which contains a recent evaluation of Monte Carlo reaction rates. Particular attention is paid to quantifying the rate uncertainties of those reactions that most sensitively influence 26Al production. For stellar modelers our results indicate to what degree predictions of 26Al nucleosynthesis depend on currently uncertain nuclear physics input, while for nuclear experimentalists our results represent a guide for future measurements. We also investigate equilibration effects of 26Al. In all previous massive star investigations, either a single species or two species of 26Al were taken into account, depending on whether thermal equilibrium was achieved or not. These are two extreme assumptions, and in a hot stellar plasma the ground and isomeric states may communicate via γ-ray transitions involving higher-lying 26Al levels. We tabulate the results of our reaction rate sensitivity study for each of the three distinct massive star sites referred to above. It is found that several current reaction rate uncertainties influence the production of 26Al. Particularly important reactions are 26Al(n,p)26Mg, 25Mg(α,n)28Si, 24Mg(n,γ)25Mg, and 23Na(α,p)26Mg. These reactions

  5. Rate constants and temperature dependences for the reactions of hydroxyl radical with several halogenated methanes, ethanes, and propanes by relative rate measurements

    NASA Technical Reports Server (NTRS)

    Hsu, K.-J.; DeMore, W. B.

    1995-01-01

    Rate constants of 15 OH reactions with halogen-substituted alkanes, C1 to C3, were studied using a relative rate technique in the temperature range 283-403 K. Compounds studied were CHF2Cl (22), CHF2Br (22B), CH3F (41), CH2F2 (32), CHF3 (23), CHClFCCl2F (122a), CHCl2CF3 (123), CHClFCF3 (124), CH3CF3 (143a), CH3CH2F (161), CF3CHFCF3 (227ea), CF3CH2CF3 (236fa), CF3CHFCHF2 (236ea), and CHF2CF2CH2F (245ca). Using CH4, CH3CCl3, CF3CF2H, and C2H6 as primary reference standards (JPL 92-20 rate constants), absolute rate constants are derived. Results are in good agreement with previous experimental results for six of the compounds studied, including CHF2Cl, CHF2Br, CH2F2, CH3CF3, CHFClCFCl2, and CF3CHFCF3. For the remainder the relative rate constants are lower than those derived from experiments in which OH loss was used to measure the reaction rate. Comparisons of the derived Arrhenius A factors with previous literature transition-state calculations show order of magnitude agreement in most cases. However, the experimental A factors show a much closer proportionality to the number of H atoms in the molecule than is evident from the transition state calculations. For most of the compounds studied, an A factor of (8 +/- 3)E-13 cm(exp 3)/(molecule s) per C-H bond is observed. A new measurement of the ratio k(CH3CCl3)/k(CH4) is reported that is in good agreement with previous data.

  6. Muonium Addition Reactions and Kinetic Isotope Effects in the Gas Phase: k∞ Rate Constants for Mu + C2H2.

    PubMed

    Arseneau, Donald J; Garner, David M; Reid, Ivan D; Fleming, Donald G

    2015-07-16

    The kinetics of the addition reaction of muonium (Mu) to acetylene have been studied in the gas phase at N2 moderator pressures mainly from ∼800 to 1000 Torr and over the temperature range from 168 to 446 K, but also down to 200 Torr at 168 K and over a much higher range of pressures, from 10 to 44 bar at 295 K, demonstrating pressure-independent rate constants, kMu(T). Even at 200 Torr moderator pressure, the kinetics for Mu + C2H2 addition behave as if effectively in the high-pressure limit, giving k∞ = kMu due to depolarization of the muon spin in the MuC2H2 radical formed in the addition step. The rate constants kMu(T) exhibit modest Arrhenius curvature over the range of measured temperatures. Comparisons with data and with calculations for the corresponding H(D) + C2H2 addition reactions reveal a much faster rate for the Mu reaction at the lowest temperatures, by 2 orders of magnitude, in accord with the propensity of Mu to undergo quantum tunneling. Moreover, isotopic atom exchange, which contributes in a major way to the analogous D atom reaction, forming C2HD + H, is expected to be unimportant in the case of Mu addition, a consequence of the much higher zero-point energy and hence weaker C-Mu bond that would form, meaning that the present report of the Mu + C2H2 reaction is effectively the only experimental study of kinetic isotope effects in the high-pressure limit for H-atom addition to acetylene. PMID:25664674

  7. Experimental and theoretical studies of rate coefficients for the reaction O(3P)+CH3OH at high temperatures.

    PubMed

    Lu, Chih-Wei; Chou, Shen-Long; Lee, Yuan-Pern; Xu, Shucheng; Xu, Z F; Lin, M C

    2005-06-22

    Rate coefficients of the reaction O((3)P) + CH(3)OH in the temperature range of 835-1777 K were determined using a diaphragmless shock tube. O atoms were generated by photolysis of SO(2) with a KrF excimer laser at 248 nm or an ArF excimer laser at 193 nm; their concentrations were monitored via atomic resonance absorption excited by emission from a microwave-discharged mixture of O(2) and He. The rate coefficients determined for the temperature range can be represented by the Arrhenius equation, k(T) = (2.29 +/- 0.18) x 10(-10) exp[-(4210 +/- 100)T] cm(3) molecule(-1) s(-1); unless otherwise noted, all the listed errors represent one standard deviation in fitting. Combination of these and previous data at lower temperature shows a non-Arrhenius behavior described as the three-parameter equation, k(T) = (2.74 +/- 0.07) x 10(-18)T(2.25 +/- 0.13) exp[-(1500 +/- 90)T] cm(3)molecule(-1) s(-1). Theoretical calculations at the Becke-3-Lee-Yang-Parr (B3LYP)6-311 + G(3df,2p) level locate three transition states. Based on the energies computed with coupled clusters singles, doubles (triples) [CCSD(T)]/6-311 + G(3df,2p)B3LYP6-311 + G(3df,2p), the rate coefficients predicted with canonical variational transition state theory with small curvature tunneling corrections agree satisfactorily with the experimental observations. The branching ratios of two accessible reaction channels forming OH + CH(2)OH (1a) and OH + CH(3)O (1b) are predicted to vary strongly with temperature. At 300 K, reaction (1a) dominates, whereas reaction (1b) becomes more important than reaction (1a) above 1700 K. PMID:16035764

  8. Determination of rates of reaction in the gas-phase in the troposphere. Theory and practice. 5. Rate of indirect photoreaction

    SciTech Connect

    Leifer, A.

    1993-01-01

    The document contains a critical review of the Atmospheric Oxidation Computer Program (AOP) for estimating the second-order rate constant k[sub OH] for the reaction of an organic chemical with hydroxyl radicals in the gas-phase in the troposphere. AOP is being used to regulate industrial chemicals under Sections 4 and 5 of the Toxic Substances Control Act. It describes the computerization of the structure/reactivity relationships of Atkinson of the University of California/Riverside by Syracuse Research Corporation. The only input needed to operate AOP is the SMILES notation, a computerized notation of the molecular structure of the chemical. The computer program will estimate k(sub OH) and the associated halflife for the reaction of organic chemicals in the atmosphere. AOP will also list an experimental value of k[sub OH] if it is available in the scientific literature.

  9. Reply to 'Comments on upscaling geochemical reaction rates usingpore-scale network modeling' by Peter C. Lichtner and Qinjun Kang

    SciTech Connect

    Li, Li; Peters, Catherine A.; Celia, Michael A.

    2006-05-03

    Our paper "Upscaling geochemical reaction rates usingpore-scale network modeling" presents a novel application of pore-scalenetwork modeling to upscale mineral dissolution and precipitationreaction rates from the pore scale to the continuum scale, anddemonstrates the methodology by analyzing the scaling behavior ofanorthite and kaolinite reaction kinetics under conditions related to CO2sequestration. We conclude that under highly acidic conditions relevantto CO2 sequestration, the traditional continuum-based methodology may notcapture the spatial variation in concentrations from pore to pore, andscaling tools may be important in correctly modeling reactive transportprocesses in such systems. This work addresses the important butdifficult question of scaling mineral dissolution and precipitationreaction kinetics, which is often ignored in fields such as geochemistry,water resources, and contaminant hydrology. Although scaling of physicalprocesses has been studied for almost three decades, very few studieshave examined the scaling issues related to chemical processes, despitetheir importance in governing the transport and fate of contaminants insubsurface systems.

  10. Rate constant for the reaction of hydroxyl radical with formaldehyde over the temperature range 228-362 K

    NASA Technical Reports Server (NTRS)

    Stief, L. J.; Nava, D. F.; Payne, W. A.; Michael, J. V.

    1980-01-01

    Absolute rate constants for the reaction OH ? H2CO measured over the temperature range 228-362 K using the flash photolysis-resonance fluorescence technique are given. The results are independent of variations in H2CO concentration, total pressure Ar concentration, and flash intensity (i.e., initial OH concentration). The rate constant is found to be invariant with temperature in this range, the best representation being k sub 1 = (1.05 ? or - 0.11) x 10 to the 11th power cu cm molecule(-1) s(-1) where the error is two standard deviations. This result is compared with previous absolute and relative determinations of k sub 1. The reaction is also discussed from a theoretical point of view.

  11. Rate constant for the reaction of hydroxyl radical with formaldehyde over the temperature range 228-362 K

    NASA Technical Reports Server (NTRS)

    Stief, L. J.; Nava, D. F.; Payne, W. A.; Michael, J. V.

    1980-01-01

    Absolute rate constants for the reaction OH + H2CO have been measured over the temperature range 228-362 K using the flash photolysis-resonance fluorescence technique. The results were independent of variations in forbidden H2CO, total pressure of forbidden Ar and flash intensity (i.e., initial forbidden OH). The rate constant was found to be invariant with temperature in this range, the best representation being k1 = (1.05 + or - 0.11) x 10 to the -11th cu cm/molecule sec where the error is two standard deviations. This result is compared with previous absolute and relative determinations of k1. The reaction is also discussed from a theoretical point of view.

  12. Quantum reaction rate from higher derivatives of the thermal flux-flux autocorrelation function at time zero.

    PubMed

    Ceotto, Michele; Yang, Sandy; Miller, William H

    2005-01-22

    A quantum theory of thermal reaction rates is presented which may be viewed as an extension of the recently developed "quantum instanton" (QI) model [W. H. Miller, Y. Zhao, M. Ceotto, and S. Yang, J. Chem. Phys. 119, 1329 (2003)]. It is based on using higher derivatives of the flux-flux autocorrelation function C(t) (as given by Miller, Schwartz, and Tromp) at t=0 to construct a short time approximation for C(t). Tests of this theory on 1d and collinear reactions, both symmetric and asymmetric, show it to be more accurate than the original QI model, giving rate constants to approximately 5% for a wide range of temperature. PMID:15740237

  13. Quantum reaction rate from higher derivatives of the thermal flux-flux autocorrelation function at time zero

    NASA Astrophysics Data System (ADS)

    Ceotto, Michele; Yang, Sandy; Miller, William H.

    2005-01-01

    A quantum theory of thermal reaction rates is presented which may be viewed as an extension of the recently developed "quantum instanton" (QI) model [W. H. Miller, Y. Zhao, M. Ceotto, and S. Yang, J. Chem. Phys. 119, 1329 (2003)]. It is based on using higher derivatives of the flux-flux autocorrelation function C(t) (as given by Miller, Schwartz, and Tromp) at t=0 to construct a short time approximation for C(t). Tests of this theory on 1d and collinear reactions, both symmetric and asymmetric, show it to be more accurate than the original QI model, giving rate constants to ˜5% for a wide range of temperature.

  14. A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Goldstein, D.; Magnotti, F.; Chinitz, W.

    1983-01-01

    Reaction rates in turbulent, reacting flows are reviewed. Assumed probability density functions (pdf) modeling of reaction rates is being investigated in relation to a three variable pdf employing a 'most likely pdf' model. Chemical kinetic mechanisms treating hydrogen air combustion is studied. Perfectly stirred reactor modeling of flame stabilizing recirculation regions was used to investigate the stable flame regions for silane, hydrogen, methane, and propane, and for certain mixtures thereof. It is concluded that in general, silane can be counted upon to stabilize flames only when the overall fuel air ratio is close to or greater than unity. For lean flames, silane may tend to destabilize the flame. Other factors favoring stable flames are high initial reactant temperatures and system pressure.

  15. Rate constants for the reactions of free radicals with oxygen in solution

    SciTech Connect

    Maillard, B.; Ingold, K.U.; Scaiano, J.C.

    1983-07-27

    The kinetics of the rections of several free radicals with oxygen have been examined in solution at 300 K using laser flash photolysis techniques. The reactions of resonance-stabilized radicals are only slightly slower than those of nonstabilized radicals: for example, for tert-butyl (in cyclohexane), 4.93 x 10/sup 9/; benzyl, 2.36 x 10/sup 9/ (in cyclohexane); cyclohexadienyl (in benzene), 1.64 x 10/sup 9/ M/sup -1/ s/sup -1/. The reaction of butyl-tin (n-Bu/sub 3/Sn.) radicals is unusually fast (7.5 x 10/sup 9/ M/sup -1/ s/sup -1/), a fact that has been tentatively attributed to a relaxation of spin selection rules due to heavy atom effects. 1 table.

  16. Gas-phase rate coefficients of the reaction of ozone with four sesquiterpenes at 295 ± 2 K.

    PubMed

    Richters, Stefanie; Herrmann, Hartmut; Berndt, Torsten

    2015-05-01

    The rate coefficients of the reaction of ozone with the four atmospherically relevant sesquiterpenes β-caryophyllene, α-humulene, α-cedrene and isolongifolene were investigated at 295 ± 2 K and atmospheric pressure by at least two independent experimental investigations for each reaction. Relative rate experiments were carried out in a flow tube using two different experimental approaches with GC-MS detection (RR 1) and PTR-MS analysis (RR 2) as the analytical techniques. Absolute rate coefficients were determined in a stopped-flow experiment following the ozone depletion by means of UV spectroscopy. The average rate coefficients from the combined investigations representing the mean values of the different experimental methods are (unit: cm(3) molecule(-1) s(-1)): k(O3+β-caryophyllene) = (1.1 ± 0.3) × 10(-14) (methods: RR 1, RR 2, absolute), k(O3+α-humulene) = (1.2 ± 0.3) × 10(-14) (RR 1, RR 2), k(O3+α-cedrene) = (1.7 ± 0.5) × 10(-16) (RR 2, absolute) and k(O3+isolongifolene) = (1.1 ± 0.5) × 10(-17) (RR 2, absolute). The high ozonolysis rate coefficients for β-caryophyllene and α-humulene agree well with the results by Shu and Atkinson (Int. J. Chem. Kinet., 1994, 26) and lead to short atmospheric lifetimes of about two minutes with respect to the ozone reaction. The relatively small rate coefficients for α-cedrene and isolongifolene differ from the available literature values by a factor of about 2.5-6. Possible reasons for the deviations are discussed. Finally, calibrated sesquiterpene FT-IR spectra were recorded for the first time. PMID:25866852

  17. IWTS metal-water reaction rate evaluation (Fauske and Associates report 99-26)

    SciTech Connect

    DUNCAN, D.R.

    1999-07-29

    The report presents a thermal stability analysis of partially metallic particulate in two IWTS components, the knock out pot and settlers. Particulate in the knock out pot is thermally stable for combinations of average particle size and metal mass fraction which appear realistic. Particulate in the settlers is thermally stable when a realistic account of particle reactions over time, metal fraction, and size distribution is considered.

  18. Does electron-transfer theory explain large rate differences in singlet and triplet excited state electron-transfer reactions?

    SciTech Connect

    Zusman, L.D.; Kurnikov, I.V.; Beratan, D.N.

    1995-12-31

    Gray and coworkers have shown that intramolecular electron-transfer rates from singlet and triplet excited states in iridium(spacer)pyridinium complexes can be vastly different (>5 orders of magnitude). We have analyzed the possible sources of these differences, including effects that may arise from reorganization energies, free energies, and tunneling matrix elements. When distance dependent reorganization energies and energy dependent tunneling matrix elements are included, a systematic framework emerges to describe these electron-transfer reactions.

  19. Three-body calculation of the rate of the reaction p+p+e→d+νe in the Sun

    NASA Astrophysics Data System (ADS)

    Irgaziev, B. F.; Belyaev, V. B.; Nabi, Jameel-Un

    2013-03-01

    Using expansion of the three-body wave function of the pep system in the initial state on hyperharmonic functions, the rate of the p+p+e-→d+νe reaction in the Sun is calculated. The results of calculation of the flux at 1 AU are compared with the results of a measurement made by the Borexino collaboration and Bahcall theoretical predictions.

  20. Rates and temperature dependences of the reaction of OH with isoprene, its oxidation products, and selected terpenes

    SciTech Connect

    Kleindienst, T.E.; Harris, G.W.; Pitts, J.N. Jr.

    1982-12-01

    Absolute rate constants determined by using the flash photolysis-resonance fluorescence technique are reported for the reactions of hydroxyl radicals with isoprene, ..cap alpha.., and ..beta..-pinene, methyl vinyl ketone, and methacrolein in the temperature range 297-424 K, and with methylglyoxal at 297 K. These results contribute to a more quantitative understanding of the tropospheric fate of gas-phase biomass-related organics and serve as input to models of the chemistry of the natural troposphere.

  1. Revision of the 15N(p, γ)16O reaction rate and oxygen abundance in H-burning zones

    NASA Astrophysics Data System (ADS)

    Caciolli, A.; Mazzocchi, C.; Capogrosso, V.; Bemmerer, D.; Broggini, C.; Corvisiero, P.; Costantini, H.; Elekes, Z.; Formicola, A.; Fülöp, Zs.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, Gy.; Imbriani, G.; Junker, M.; Lemut, A.; Marta, M.; Menegazzo, R.; Palmerini, S.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.; Vomiero, A.

    2011-09-01

    Context. The NO cycle takes place in the deepest layer of a H-burning core or shell, when the temperature exceeds T ≃ 30 × 106 K. The O depletion observed in some globular cluster giant stars, always associated with a Na enhancement, may be due to either a deep mixing during the red giant branch (RGB) phase of the star or to the pollution of the primordial gas by an early population of massive asymptotic giant branch (AGB) stars, whose chemical composition was modified by the hot bottom burning. In both cases, the NO cycle is responsible for the O depletion. Aims: The activation of this cycle depends on the rate of the 15N(p, γ)16O reaction. A precise evaluation of this reaction rate at temperatures as low as experienced in H-burning zones in stellar interiors is mandatory to understand the observed O abundances. Methods: We present a new measurement of the 15N(p, γ)16O reaction performed at LUNA covering for the first time the center of mass energy range 70-370 keV, which corresponds to stellar temperatures between 65 × 106 K and 780 × 106 K. This range includes the 15N(p, γ)16O Gamow-peak energy of explosive H-burning taking place in the external layer of a nova and the one of the hot bottom burning (HBB) nucleosynthesis occurring in massive AGB stars. Results: With the present data, we are also able to confirm the result of the previous R-matrix extrapolation. In particular, in the temperature range of astrophysical interest, the new rate is about a factor of 2 smaller than reported in the widely adopted compilation of reaction rates (NACRE or CF88) and the uncertainty is now reduced down to the 10% level.

  2. Corneal ulcer and adverse reaction rates in premarket contact lens studies.

    PubMed

    MacRae, S; Herman, C; Stulting, R D; Lippman, R; Whipple, D; Cohen, E; Egan, D; Wilkinson, C P; Scott, C; Smith, R

    1991-04-15

    We analyzed clinical data on 22,739 contact lens wearers who were studied and whose lenses were approved under 48 manufacturer-sponsored studies for the Food and Drug Administration between 1980 and 1988. The incidence of corneal ulcers was low in the cosmetic (nontherapeutic) daily-wear soft and rigid gas-permeable lens wearers (1/1,923 and 1/1,471 patient-years, respectively). Corneal ulcers and severe adverse reactions occurred two to four times more frequently in extended-wear cosmetic soft and rigid gas-permeable lens wearers than in cosmetic daily-wear lens wearers. Aphakic extended-wear soft lens users were nine times more likely to develop a corneal ulcer when compared to the soft daily-wear cosmetic group. Corneal abrasions and keratitis accounted for 81 of 159 severe adverse reactions, whereas corneal ulcers accounted for 28 of 159 adverse reactions. The data indicate that overnight extended wear of contact lenses is associated with a greater risk of serious, sight-threatening complications than daily wear. PMID:2012148

  3. Rate Coefficients of the HCl + OH → Cl + H2O Reaction from Ring Polymer Molecular Dynamics.

    PubMed

    Zuo, Junxiang; Li, Yongle; Guo, Hua; Xie, Daiqian

    2016-05-26

    Thermal rate coefficients at temperatures between 200 and 1000 K are calculated for the HCl + OH → Cl + H2O reaction on a recently developed permutation invariant potential energy surface, using ring polymer molecular dynamics (RPMD). Large deviations from the Arrhenius limit are found at low temperatures, suggesting significant quantum tunneling. Agreement with available experimental rate coefficients is generally satisfactory, although the deviation becomes larger at lower temperatures. The theory-experiment discrepancy is attributed to the remaining errors in the potential energy surface, which is known to slightly overestimate the barrier. In the deep tunneling region, RPMD performs better than traditional transition-state theory with semiclassical tunneling corrections. PMID:27149243

  4. Absolute rate constant of the reaction between chlorine /2P/ atoms and hydrogen peroxide from 298 to 424 K

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1980-01-01

    The absolute rate constant of the reaction between chlorine (2P) atoms and hydrogen peroxide was determined from 298 to 424 K, using the discharge flow resonance fluorescence technique. Pseudo-first-order conditions were used with hydrogen peroxide in large excess. A fast flow-sampling procedure limited hydrogen peroxide decomposition to less than 5% over the temperature range studied. At 298 K, the rate constant is (4.1 plus or minus 0.2) x 10 to the minus 13th cu cm/molecule-sec.

  5. The H2 + CO ↔ H2CO Reaction: Rate Constants and Relevance to Hot and Dense Astrophysical Media

    NASA Astrophysics Data System (ADS)

    Vichietti, R. M.; Spada, R. F. K.; da Silva, A. B. F.; Machado, F. B. C.; Haiduke, R. L. A.

    2016-07-01

    A theoretical thermochemical and kinetic investigation of the thermal H2 + CO ↔ H2CO reaction was performed for a temperature range from 200 to 4000 K. Geometries and vibrational frequencies of reactants, product, and transition state (TS) were obtained at CCSD/cc-pVxZ (x = T and Q) levels and scaling factors were employed to consider anharmonicity effects on vibrational frequencies, zero-point energies, and thermal corrections provided by these methodologies. Enthalpies Gibbs energies, and rate constants for this reaction were determined by including a complete basis set extrapolation correction for the electronic properties calculated at CCSD(T)/cc-pVyZ (y = Q and 5) levels. Our study indicates that enthalpy changes for this reaction are highly dependent on temperature. Moreover, forward and reverse (high-pressure limit) rate constants were obtained from variational TS theory with quantum tunneling corrections. Thus, modified Arrhenius’ equations were fitted by means of the best forward and reverse rate constant values, which provide very reliable estimates for these quantities within the temperature range between 700 and 4000 K. To our knowledge, this is the first kinetic study done for the forward H2 + CO \\to H2CO process in a wide temperature range. Finally, these results can be used to explain the formaldehyde abundance in hot and dense interstellar media, possibly providing data about the physical conditions associated with H2CO masers close to massive star-forming regions.

  6. Variations of boundary reaction rate and particle size on the diffusion-induced stress in a phase separating electrode

    SciTech Connect

    Zhang, Lei; He, Linghui; Ni, Yong; Song, Yicheng

    2014-10-14

    In contrast to the case of single-phase delithiation wherein faster discharging leads to higher diffusion-induced stress (DIS), this paper reports nonmonotonous dependency of the boundary reaction rate on the DIS in nanosized spherical electrode accompanying phase separation. It is attributed to a transition from two-phase to single-phase delithiation driven by increase of the boundary reaction rate leading to narrowing and vanishing of the miscibility gap in a range of the particle size. The profiles of lithium concentration and the DIS are identified during the transition based on a continuum model. The resultant maximum DIS first decreases in the region of two-phase delithiation and later returns to increase in the region of single-phase delithiation with the increase of the boundary reaction rate. A map for the failure behavior in the spherical electrode particle is constructed based on the Tresca failure criterion. These results indicate that the failure caused by the DIS can be avoided by appropriate selection of the said parameters in such electrodes.

  7. The physiological basis of reaction norms: the interaction among growth rate, the duration of growth and body size.

    PubMed

    Davidowitz, Goggy; Nijhout, H Frederik

    2004-12-01

    The general effects of temperature and nutritional quality on growth rate and body size are well known. We know little, however, about the physiological mechanisms by which an organism translates variation in diet and temperature into reaction norms of body size or development time. We outline an endocrine-based physiological mechanism that helps explain how this translation occurs in the holometabolous insect Manduca sexta (Sphingidae). Body size and development time are controlled by three factors: (i) growth rate, (ii) the timing of the cessation of juvenile hormone secretion (measured by the critical weight) and (iii) the timing of ecdysteroid secretion leading to pupation (the interval to cessation of growth [ICG] after reaching the critical weight). Thermal reaction norms of body size and development time are a function of how these three factors interact with temperature. Body size is smaller at higher temperatures, because the higher growth rate decreases the ICG, thereby reducing the amount of mass that can accumulate. Development time is shorter at higher temperatures because the higher growth rate decreases the time required to attain the critical weight and, independently, controls the duration of the ICG. Life history evolution along altitudinal, latitudinal and seasonal gradients may occur through differential selection on growth rate and the duration of the two independently controlled determinants of the growth period. PMID:21676730

  8. Flow rates and reaction rates in the Galapagos Rise spreading center hydrothermal system as inferred from 228Ra/226Ra in vesicomyid clam shells

    PubMed Central

    Turekian, Karl K.; Cochran, J. Kirk

    1986-01-01

    The 228Ra/226Ra ratios in a previously dated vesicomyid clam shell were used to determine that seawater was in contact with mid-oceanic-ridge basalt glass for 22-45 years prior to arrival to the surface at 350°C at the Galapagos Rise Spreading Center. The minimum rate of reaction for the 45-year sojourn time, based on a water/rock ratio of 2.8 derived from 226Ra concentrations, is 8 g of basalt altered per kg of seawater per year. PMID:16593746

  9. Finite Element Analysis of the Time-Dependent Smoluchowski Equation for Acetylcholinesterase Reaction Rate Calculations

    PubMed Central

    Cheng, Yuhui; Suen, Jason K.; Zhang, Deqiang; Bond, Stephen D.; Zhang, Yongjie; Song, Yuhua; Baker, Nathan A.; Bajaj, Chandrajit L.; Holst, Michael J.; McCammon, J. Andrew

    2007-01-01

    This article describes the numerical solution of the time-dependent Smoluchowski equation to study diffusion in biomolecular systems. Specifically, finite element methods have been developed to calculate ligand binding rate constants for large biomolecules. The resulting software has been validated and applied to the mouse acetylcholinesterase (mAChE) monomer and several tetramers. Rates for inhibitor binding to mAChE were calculated at various ionic strengths with several different time steps. Calculated rates show very good agreement with experimental and theoretical steady-state studies. Furthermore, these finite element methods require significantly fewer computational resources than existing particle-based Brownian dynamics methods and are robust for complicated geometries. The key finding of biological importance is that the rate accelerations of the monomeric and tetrameric mAChE that result from electrostatic steering are preserved under the non-steady-state conditions that are expected to occur in physiological circumstances. PMID:17307827

  10. Reaction rate constant for dry air oxidation of K Basin fuel

    SciTech Connect

    Trimble, D.J.

    1998-04-29

    The rate of oxidation of spent nuclear fuel stored in the K Basin water is an important parameter when assessing the processes and accident scenarios for preparing the fuel for dry storage. The literature provides data and rate laws for the oxidation of unirradiated uranium in various environments. Measurement data for the dry air oxidation of K Basin fuel is compared to the literature data for linear oxidation in dry air. Equations for the correlations and statistical bounds to the K Basin fuel data and the literature data are selected for predicting nominal and bounding rates for the dry air oxidation of the K Basin fuel. These rate equations are intended for use in the Spent Nuclear Fuel Project Technical Data book.

  11. Solubility and Reaction Rates of Aluminum Solid Phases Under Geothermal Conditions

    SciTech Connect

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

    2000-05-28

    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.

  12. Hydrogenation of O and OH on Pt(111): A comparison between the reaction rates of the first and the second hydrogen addition steps

    SciTech Connect

    Näslund, L.-Å.

    2014-03-14

    The formation of water through hydrogenation of oxygen on platinum occurs at a surprisingly low reaction rate. The reaction rate limited process for this catalytic reaction is, however, yet to be settled. In the present work, the reaction rates of the first and the second hydrogen addition steps are compared when hydrogen is obtained through intense synchrotron radiation that induces proton production in a water overlayer on top of the adsorbed oxygen species. A substantial amount of the produced hydrogen diffuses to the platinum surface and promotes water formation at the two starting conditions O/Pt(111) and (H{sub 2}O+OH)/Pt(111). The comparison shows no significant difference in the reaction rate between the first and the second hydrogen addition steps, which indicates that the rate determining process of the water formation from oxygen on Pt(111) is neither the first nor the second H addition step or, alternatively, that both H addition steps exert rate control.

  13. Adverse drug reactions caused by drug-drug interactions reported to Croatian Agency for Medicinal Products and Medical Devices: a retrospective observational study

    PubMed Central

    Mirošević Skvrce, Nikica; Macolić Šarinić, Viola; Mucalo, Iva; Krnić, Darko; Božina, Nada; Tomić, Siniša

    2011-01-01

    Aim To analyze potential and actual drug-drug interactions reported to the Spontaneous Reporting Database of the Croatian Agency for Medicinal Products and Medical Devices (HALMED) and determine their incidence. Methods In this retrospective observational study performed from March 2005 to December 2008, we detected potential and actual drug-drug interactions using interaction programs and analyzed them. Results HALMED received 1209 reports involving at least two drugs. There were 468 (38.7%) reports on potential drug-drug interactions, 94 of which (7.8% of total reports) were actual drug-drug interactions. Among actual drug-drug interaction reports, the proportion of serious adverse drug reactions (53 out of 94) and the number of drugs (n = 4) was significantly higher (P < 0.001) than among the remaining reports (580 out of 1982; n = 2, respectively). Actual drug-drug interactions most frequently involved nervous system agents (34.0%), and interactions caused by antiplatelet, anticoagulant, and non-steroidal anti-inflammatory drugs were in most cases serious. In only 12 out of 94 reports, actual drug-drug interactions were recognized by the reporter. Conclusion The study confirmed that the Spontaneous Reporting Database was a valuable resource for detecting actual drug-drug interactions. Also, it identified drugs leading to serious adverse drug reactions and deaths, thus indicating the areas which should be in the focus of health care education. PMID:21990078

  14. Synchronizing Substrate Activation Rates in Multicomponent Reactions with Metal-Organic Framework Catalysts.

    PubMed

    Aguirre-Díaz, Lina María; Iglesias, Marta; Snejko, Natalia; Gutiérrez-Puebla, Enrique; Monge, M Ángeles

    2016-05-01

    A study on the influence of the cation coordination number, number of Lewis acid centers, concurrent existence of Lewis base sites, and structure topology on the catalytic activity of six new indium MOFs, has been carried out for multicomponent reactions (MCRs). The new indium polymeric frameworks, namely [In8 (OH)6 (popha)6 (H2 O)4 ]⋅3 H2 O (InPF-16), [In(popha)(2,2'-bipy)]⋅3 H2 O (InPF-17), [In3 (OH)3 (popha)2 (4,4'-bipy)]⋅4 H2 O (InPF-18), [In2 (popha)2 (4,4'-bipy)2 ]⋅3 H2 O (InPF-19), [In(OH)(Hpopha)]⋅0.5 (1,7-phen) (InPF-20), and [In(popha)(1,10-phen)]⋅4 H2 O (InPF-21) (InPF=indium polymeric framework, H3 popha=5-(4-carboxy-2-nitrophenoxy)isophthalic acid, phen=phenanthroline, bipy=bipyridine), have been hydrothermally obtained by using both conventional heating (CH) and microwave (MW) procedures. These indium frameworks show efficient Lewis acid behavior for the solvent-free cyanosilylation of carbonyl compounds, the one pot Passerini 3-component (P-3CR) and the Ugi 4-component (U-4CR) reactions. In addition, InPF-17 was found to be a highly reactive, recyclable, and environmentally benign catalyst, which allows the efficient synthesis of α-aminoacyl amides. The relationship between the Lewis base/acid active site and the catalytic performance is explained by the 2D seven-coordinated indium framework of the catalyst InPF-17. This study is an attempt to highlight the main structural and synthetic factors that have to be taken into account when planning a new, effective MOF-based heterogeneous catalyst for multicomponent reactions. PMID:27010759

  15. Neutrino-Induced Charged-Current Reaction Rates for r-PROCESS Nuclei

    NASA Astrophysics Data System (ADS)

    Langanke, K.; Kolbe, E.

    2001-11-01

    Neutrino-induced reactions play an important role during and after the r-process if it occurs in an environment with extreme neutrino fluxes, as in the neutrino-driven wind model or neutron star mergers. The neutrino reactions can excite the daughter nucleus above the neutron threshold, which is quite low for r-process nuclei. Thus the daughter nucleus will decay by emission of one or several neutrons. We have calculated the relevant total (νe, e-) cross sections as well as the partial neutron spallation cross sections for r-process nuclei with neutron numbers N=41-135 and proton numbers Z=21-82. The supernova neutrino spectrum is described by a Fermi-Dirac distribution with various temperature parameters between T=2.8 MeV and T=10 MeV and with the degeneracy parameters α=0 and α=3. Our calculations of the nuclear response are based on the random phase approximation and consider allowed as well as forbidden transitions.

  16. Surface-active ionic liquids in micellar catalysis: impact of anion selection on reaction rates in nucleophilic substitutions.

    PubMed

    Cognigni, Alice; Gaertner, Peter; Zirbs, Ronald; Peterlik, Herwig; Prochazka, Katharina; Schröder, Christian; Bica, Katharina

    2016-05-21

    A series of surface-active ionic liquids based on the 1-dodecyl-3-methylimidazolium cation and different anions such as halides and alkylsulfates was synthesized. The aggregation behavior of these ionic liquids in water was characterized by surface tension, conductivity measurements and UV-Vis spectroscopy in order to determine the critical micelle concentration (CMC) and to provide aggregation parameters. The determination of surface activity and aggregation properties of amphiphilic ionic liquids was accompanied by SAXS studies on selected surface-active ionic liquids. The application of these surface-active ionic liquids with different anions was tested in nucleophilic substitution reactions for the degradation of organophosphorus compounds. Kinetic studies via UV-Vis spectrophotometry showed a strong acceleration of the reaction in the micellar system compared to pure water. In addition, an influence of the anion was observed, resulting in a correlation between the anion binding to the micelle and the reaction rate constants, indicating that the careful choice of the surface-active ionic liquid can considerably affect the outcome of reactions. PMID:27121134

  17. Pressure dependence of the absolute rate constant for the reaction Cl + C2H2 from 210-361 K

    NASA Technical Reports Server (NTRS)

    Brunning, J.; Stief, L. J.

    1985-01-01

    In recent years, considerable attention has been given to the role of chlorine compounds in the catalytic destruction of stratospheric ozone. However, while some reactions have been studied extensively, the kinetic data for the reaction of Cl with C2H2 is sparse with only three known determinations of the rate constant k3. The reactions involved are Cl + C2H2 yields reversibly ClC2H2(asterisk) (3a) and ClC2H2(asterisk) + M yields ClC2H2 + M (3b). In the present study, flash photolysis coupled with chlorine atomic resonance fluorescence have been employed to determine the pressure and temperature dependence of k3 with the third body M = Ar. Room temperature values are also reported for M = N2. The pressure dependence observed in the experiments confirms the expectation that the reaction involves addition of Cl to the unsaturated C2H2 molecule followed by collisional stabilization of the resulting adduct radical.

  18. A simplified method for determining reactive rate parameters for reaction ignition and growth in explosives

    SciTech Connect

    Miller, P.J.

    1996-07-01

    A simplified method for determining the reactive rate parameters for the ignition and growth model is presented. This simplified ignition and growth (SIG) method consists of only two adjustable parameters, the ignition (I) and growth (G) rate constants. The parameters are determined by iterating these variables in DYNA2D hydrocode simulations of the failure diameter and the gap test sensitivity until the experimental values are reproduced. Examples of four widely different explosives were evaluated using the SIG model. The observed embedded gauge stress-time profiles for these explosives are compared to those calculated by the SIG equation and the results are described.

  19. Local mode excitation and direct unimolecular reaction rate measurements in tetramethyldioxetane

    SciTech Connect

    Cannon, B.D.; Crim, F.F.

    1981-08-15

    Direct excitation of overtone vibrations combined with time-resolved detection of product chemiluminescence produces both overtone vibration excitation spectra and directly measured unimolecular decay rates of tetramethyldioxetane. The spectra show increasingly pure local mode character in higher vibrational levels and exhibit splittings which arise from nonequivalent sites occupied by methyl hydrogens. The temporal evolution of the signal reflects the unimolecular decomposition rate of the highly vibrationally excited molecule, and comparing the observed behavior to Rice--Ramsperger--Kassel--Marcus theory calculations shows that they adequately describe the decomposition if properly averaged over the thermal vibrational energy content of the molecule.

  20. Modulation of lead-induced performance deficit in children by varying signal rate in a serial choice reaction task

    SciTech Connect

    Winneke, G.; Brockhaus, A.; Collet, W.; Kraemer, U. )

    1989-11-01

    Evidence is presented showing that serial choice reaction performance is disrupted at low blood lead levels (PbB), and that parametric variation of task characteristics modulates the degree of disruption. This evidence is based on two independent studies in 6- to 9-year-old children living in two lead smelter areas in the cities of Nordenham (N = 114) and Stolberg (N = 109) in West Germany. Average PbB was 8.2 micrograms/100 ml (4.4-23.8 micrograms/100 ml) in the Nordenham sample and 7.4 micrograms/100 ml (4.2-18.0 micrograms/100 ml) in the Stolberg sample. Serial choice reaction performance was assessed by means of the Vienna reaction device in which a random sequence of light and tone signals has to be answered by pressing appropriate response buttons. Correct (hits) and false responses (errors) were evaluated as performance measures, and signal rate was varied in order to achieve easy and difficult task conditions. Exposure-related performance deficit was more pronounced for errors than for hits, more clearcut for high than for low signal rates, and proved significant in both studies after correction for confounding using confounder models of different complexities. Some features of the observed deficit resemble clinical observations in children presenting with attention deficit disorder.

  1. Hydrogen Abstraction Reactions from Phenolic Compounds by Peroxyl Radicals: Multireference Character and Density Functional Theory Rate Constants.

    PubMed

    Galano, Annia; Muñoz-Rugeles, Leonardo; Alvarez-Idaboy, Juan Raul; Bao, Junwei Lucas; Truhlar, Donald G

    2016-07-14

    An assessment of multireference character in transition states is considered to be an important component in establishing the expected reliability of various electronic structure methods. In the present work, the multireference characters of the transition states and the forming and breaking of bonds for a large set of hydrogen abstraction reactions from phenolic compounds by peroxyl radicals have been analyzed using the T1, M, B1, and GB1 diagnostics. The extent of multireference character depends on the system and on the conditions under which the reaction takes place, and some systematic trends are observed. In particular, the multireference character is found to be reduced by solvation, the size of the phenolic compound, and deprotonation in aqueous solution. However, the deviations of calculated rate constants from experimental ones are not correlated with the extent of multireference character. The performance of single-determinant density functional theory was investigated for the kinetics of these reactions by comparing calculated rate constants to experimental data; the results from these analyses showed that the M05 functional performs well for the task at hand. PMID:26378461

  2. An efficient nonclassical quadrature for the calculation of nonresonant nuclear fusion reaction rate coefficients from cross section data

    NASA Astrophysics Data System (ADS)

    Shizgal, Bernie D.

    2016-08-01

    Nonclassical quadratures based on a new set of half-range polynomials, Tn(x) , orthogonal with respect to w(x) =e - x - b /√{ x } for x ∈ [ 0 , ∞) are employed in the efficient calculation of the nuclear fusion reaction rate coefficients from cross section data. The parameter b = B /√{kB T } in the weight function is temperature dependent and B is the Gamow factor. The polynomials Tn(x) satisfy a three term recurrence relation defined by two sets of recurrence coefficients, αn and βn. These recurrence coefficients define in turn the tridiagonal Jacobi matrix whose eigenvalues are the quadrature points and the weights are calculated from the first components of the eigenfunctions. For nonresonant nuclear reactions for which the astrophysical function can be expressed as a lower order polynomial in the relative energy, the convergence of the thermal average of the reactive cross section with this nonclassical quadrature is extremely rapid requiring in many cases 2-4 quadrature points. The results are compared with other libraries of nuclear reaction rate coefficient data reported in the literature.

  3. An investigation of the effect of pore scale flow on average geochemical reaction rates using direct numerical simulation

    SciTech Connect

    Rafa, S. Molins; Trebotich, D.; Steefel, C. I.; Shen, C.

    2012-02-01

    The scale-dependence of geochemical reaction rates hinders their use in continuum scale models intended for the interpretation and prediction of chemical fate and transport in subsurface environments such as those considered for geologic sequestration of CO{sub 2}. Processes that take place at the pore scale, especially those involving mass transport limitations to reactive surfaces, may contribute to the discrepancy commonly observed between laboratory-determined and continuum-scale or field rates. Here, the dependence of mineral dissolution rates on the pore structure of the porous media is investigated by means of pore scale modeling of flow and multicomponent reactive transport. The pore scale model is comprised of high performance simulation tools and algorithms for incompressible flow and conservative transport combined with a general-purpose multicomponent geochemical reaction code. The model performs direct numerical simulation of reactive transport based on an operator-splitting approach to coupling transport and reactions. The approach is validated with a Poiseuille flow single-pore experiment and verified with an equivalent 1D continuum-scale model of a capillary tube packed with calcite spheres. Using the case of calcite dissolution as an example, the high resolution model is used to demonstrate that non-uniformity in the flow field at the pore scale has the effect of decreasing the overall reactivity of the system, even when systems with identical reactive surface area are considered. The effect becomes more pronounced as the heterogeneity of the reactive grain packing increases, particularly where the flow slows sufficiently such that the solution approaches equilibrium locally and the average rate becomes transport-limited.

  4. Regulating emotions uniquely modifies reaction time, rate of force production, and accuracy of a goal-directed motor action.

    PubMed

    Beatty, Garrett F; Fawver, Bradley; Hancock, Gabriella M; Janelle, Christopher M

    2014-02-01

    We investigated how emotion regulation (ER) strategies influence the execution of a memory guided, ballistic pinch grip. Participants (N=33) employed ER strategies (expressive suppression, emotional expression, and attentional deployment) while viewing emotional stimuli (IAPS images). Upon stimulus offset, participants produced a targeted pinch force aimed at 10% of their maximum voluntary contraction. Performance measures included reaction time (RT), rate of force production, and performance accuracy. As hypothesized, attentional deployment resulted in the slowest RT, largest rate of force production, and poorest performance accuracy. In contrast, expressive suppression reduced the rate of force production and increased performance accuracy relative to emotional expression and attentional deployment. Findings provide evidence that emotion regulation strategies uniquely influence human movement. Future work should further delineate the interacting role that emotion regulation strategies have in modulating both affective experience and motor performance. PMID:24576703

  5. Thermonuclear Reaction Rate of T(t,2n) α Measured in ICF Plasmas

    NASA Astrophysics Data System (ADS)

    Brune, C. R.; Casey, D. T.; Caggiano, J. A.; Hatarik, R.; McNabb, D. P.; Sayre, D. B.; Smalyuk, V. A.; Bacher, A. D.; Frenje, J. A.; Gatu-Johnson, M.; Zylstra, A. B.; Couder, M.

    2014-09-01

    Measurements of charged-particle reactivity have been performed in inertial confinement fusion experiments at the National Ignition Facility. Time-of-flight detectors were used to measure neutrons from the T(t,2n) and T(d,n) reactions produced by implosions with tritium-filled targets (0.1% deuterium). Along with the measured target fuel composition and reactant ion temperature, the well-known T(d,n) reactivity was used to convert the measured neutron yields into a T(t,2n) reactivity. The ion temperature was determined to be 3.3(3) keV, corresponding to an effective energy of 16 keV. In comparison to accelerator measurements of the low-energy T(t,2n) cross section, the source of all previous data, our experiment has resulted in T(t,2n) data with better statistics and lower backgrounds.

  6. USE OF ROUGH SETS AND SPECTRAL DATA FOR BUILDING PREDICTIVE MODELS OF REACTION RATE CONSTANTS

    EPA Science Inventory

    A model for predicting the log of the rate constants for alkaline hydrolysis of organic esters has been developed with the use of gas-phase min-infrared library spectra and a rule-building software system based on the mathematical theory of rough sets. A diverse set of 41 esters ...

  7. Continuum Diffusion Reaction Rate Calculations of Wild-Type and Mutant Mouse Acetylcholinesterase: Adaptive Finite Element Analysis

    PubMed Central

    Song, Yuhua; Zhang, Yongjie; Bajaj, Chandrajit L.; Baker, Nathan A.

    2004-01-01

    As described previously, continuum models, such as the Smoluchowski equation, offer a scalable framework for studying diffusion in biomolecular systems. This work presents new developments in the efficient solution of the continuum diffusion equation. Specifically, we present methods for adaptively refining finite element solutions of the Smoluchowski equation based on a posteriori error estimates. We also describe new, molecular-surface-based models, for diffusional reaction boundary criteria and compare results obtained from these models with the traditional spherical criteria. The new methods are validated by comparison of the calculated reaction rates with experimental values for wild-type and mutant forms of mouse acetylcholinesterase. The results show good agreement with experiment and help to define optimal reactive boundary conditions. PMID:15345536

  8. Observation of K-dependent Reaction Rates in Pulsed Uniform Supersonic Flows by Chirped-Pulse Microwave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Broderick, Bernadette; Ariyasingha, Nuwandi; Suits, Arthur; University of Missouri Team

    Chirped-pulse Fourier-transform microwave spectroscopy was used to interrogate the reaction of Cl atoms with propyne in a pulsed uniform supersonic flow. The technique, termed ``CPUF'', utilizes broad-band microwave spectroscopy to extract structural information with MHz resolution and near universal detection, in conjunction with a Laval flow system, which offers thermalized conditions at low temperatures and high number densities. Previous studies have exploited this approach to obtain multichannel product branching fractions in a number of polyatomic systems, with isomer and often vibrational level specificity. This report highlights an additional capability of the CPUF technique: here, the state-specific reactant depletion is directly monitored on a microsecond timescale. In doing so, a clear dependence on the rotational quantum number K in the rate of the reaction between Cl atoms and propyne is revealed. Future prospects for the technique will be discussed.

  9. On progress and rate of the peritectic reaction Fo + SiO2 → En in natural andesitic arc magmas

    NASA Astrophysics Data System (ADS)

    Zellmer, Georg F.; Sakamoto, Naoya; Matsuda, Nozomi; Iizuka, Yoshiyuki; Moebis, Anja; Yurimoto, Hisayoshi

    2016-07-01

    Using a high resolution ion microprobe with SCAPS imaging, the peritectic reaction of forsterite + silica to enstatite was studied down to submicron level in a natural andesitic tephra from the Central Plateau of North Island, New Zealand. The fayalitic component of natural olivines is stable in high-silica melts, and therefore the reaction is in fact a two-step progress: 1. Dissolution of Mg-rich olivine, rate-limited by Fe-Mg interdiffusion at the crystal rim, results in enrichment of Fe in the crystal rim and of Mg in the c. 1 μm wide melt boundary layer around the crystal. 2. Magnesian pyroxenes preferentially but not exclusively nucleate in the melt boundary layer and grow; as soon as these microlites touch the rim of the dissolving olivine, they shield the crystals from the silica-rich melt, thereby preventing further olivine dissolution. At this point, Fe-Mg interdiffusion begins to destroy the Fe-enrichment of the olivine rim. The reaction is completed when the dissolving olivine crystal is completely mantled by magnesian pyroxene microlites. Thick pyroxene mantles are likely the result of pyroxene overgrowth rather than due to peritectic transformation. The morphology of the olivine rim preserves information about the reaction history of the grain. Modeling of Fe-Mg interdiffusion in the olivine rim following its shielding from the melt by pyroxene overgrowth may yield the rates of olivine dissolution and the rates of pyroxene growth if temperature is known. For the tephra we have studied, microlite thermometry yields a temperature of 1137 (±41) °C, indicating an olivine dissolution rate of 3-6 × 10-11 ms-1 and an initially volumetric pyroxene growth rate of 2.2-5.6 × 10-21 m3 s-1. This points to timescales between olivine crystal uptake into the SiO2-rich melt and explosive eruption at the surface of a few hours to at most a day.

  10. Ozone-Induced Dissociation of Conjugated Lipids Reveals Significant Reaction Rate Enhancements and Characteristic Odd-Electron Product Ions

    NASA Astrophysics Data System (ADS)

    Pham, Huong T.; Maccarone, Alan T.; Campbell, J. Larry; Mitchell, Todd W.; Blanksby, Stephen J.

    2013-02-01

    Ozone-induced dissociation (OzID) is an alternative ion activation method that relies on the gas phase ion-molecule reaction between a mass-selected target ion and ozone in an ion trap mass spectrometer. Herein, we evaluated the performance of OzID for both the structural elucidation and selective detection of conjugated carbon-carbon double bond motifs within lipids. The relative reactivity trends for [M + X]+ ions (where X = Li, Na, K) formed via electrospray ionization (ESI) of conjugated versus nonconjugated fatty acid methyl esters (FAMEs) were examined using two different OzID-enabled linear ion-trap mass spectrometers. Compared with nonconjugated analogues, FAMEs derived from conjugated linoleic acids were found to react up to 200 times faster and to yield characteristic radical cations. The significantly enhanced reactivity of conjugated isomers means that OzID product ions can be observed without invoking a reaction delay in the experimental sequence (i.e., trapping of ions in the presence of ozone is not required). This possibility has been exploited to undertake neutral-loss scans on a triple quadrupole mass spectrometer targeting characteristic OzID transitions. Such analyses reveal the presence of conjugated double bonds in lipids extracted from selected foodstuffs. Finally, by benchmarking of the absolute ozone concentration inside the ion trap, second order rate constants for the gas phase reactions between unsaturated organic ions and ozone were obtained. These results demonstrate a significant influence of the adducting metal on reaction rate constants in the fashion Li > Na > K.

  11. Application of chemometrics methods with kinetic constraints for estimation of rate constants of second order consecutive reactions.

    PubMed

    Kompany-Zareh, Mohsen; Khoshkam, Maryam

    2008-05-01

    To determine the rate constants for the second order consecutive reactions of the form U + V -(k1)--> W -(k2)--> P, a number of chemometrics and hard modeling-based methods are described. The absorption spectroscopic data from the reaction were utilized for performing the analysis. Concentrations and extinctions of components were comparable, and all of them were absorbing species. The number of steps in the reaction was less than the number of absorbing species, which resulted in a rank-deficient response matrix. This can cause difficulties for some of the methods described in the literature. The standard MATLAB functions were used for determining the solutions of the differential equations as well as for finding the optimal rate constants to describe the kinetic profiles. The available knowledge about the system determines the approaches described in this paper. The knowledge includes the spectra of reactants and products, the initial concentrations, and the exact kinetics. Some of this information is sometimes not available or is hard to estimate. Multiple linear regression for fitting the kinetic parameters to the obtained concentration profiles, rank augmentation using multiple batch runs, a mixed spectral approach which treats the reaction using a pseudo species concept, and principal components regression are the four groups of methods discussed in this study. In one of the simulated datasets the spectra are quite different, and in the other one the spectra of one reactant and of the product share a high degree of overlap. Instrumental noise, sampling error are the sources of error considered. Our aim was the investigation of the relative merits of each method. PMID:18469471

  12. Temperature-Dependent Rate Constants and Substituent Effects for the Reactions of Hydroxyl Radicals With Three Partially Fluorinated Ethers

    NASA Technical Reports Server (NTRS)

    Hsu, K.-J.; DeMore, W. B.

    1995-01-01

    Rate constants and temperature dependencies for the reactions of OH with CF3OCH3 (HFOC-143a), CF2HOCF2H (HFOC-134), and CF3OCF2H (HFOC-125) were studied using a relative rate technique in the temperature range 298-393 K. The following absolute rate constants were derived: HFOC-143a, 1.9E-12 exp(-1555/T); HFOC-134, 1.9E-12 exp(-2006/T); HFOC-125, 4.7E-13 exp(-2095/T). Units are cm(exp 3)molecule(exp -1) s(exp -1). Substituent effects on OH abstraction rate constants are discussed, and it is shown that the CF3O group has an effect on the OH rate constants similar to that of a fluorine atom. The effects are related to changes in the C-H bond energies of the reactants (and thereby the activation energies) rather than changes in the preexponential factors. On the basis of a correlation of rate constants with bond energies, the respective D(C-H) bond strengths in the three ethers are found to be 102, 104, and 106 kcal/mol, with an uncertainty of about 1 kcal/mol.

  13. Recommended Thermal Rate Coefficients for the C + H3+ Reaction and Some Astrochemical Implications

    NASA Astrophysics Data System (ADS)

    Vissapragada, Shreyas; Buzard, Cam; Miller, Kenneth A.; O'Connor, Aodh; De Ruette, Nathalie; Urbain, Xavier; Savin, Daniel Wolf

    2016-06-01

    We have incorporated our experimentally derived thermal rate coefficients for C + H3+ forming CH+ and CH2+ into a commonly used astrochemical model. We find that the Arrhenius-Kooij equation typically used in chemical models does not accurately fit our data and use instead a more versatile fitting formula. At a temperature of 10 K and a density of 104 cm-3, we find no significant differences in the predicted abundances, but at higher temperatures of 50, 100, and 300 K we find up to factor of 2 changes. Additionally, we find that the relatively small error on our measurements (~15%) significantly reduces the uncertainties on the predicted abundances compared to those obtained using the currently implemented Langevin rate coefficient with its estimated factor of 2 uncertainty.

  14. Biomolecular folding rates as understood from single-reaction-coordinate Langevin dynamics and Kramers' theory

    NASA Astrophysics Data System (ADS)

    Kabir, Md Adnan

    Langevin dynamics was used to model the folding and unfolding of simple, hairpin-like biomolecules whose ends are attached to laser-trapped beads, as occurs in optical tweezers experiments. The Langevin process was evolved numerically, using parameters motivated by real experimental systems. Folding trajectories were generated and analyzed to extract the folding rate as a function of the force applied to the beads. The observed rate was compared to the analytical predictions of Kramers' theory. Strong discrepancies were noted. The failure of the Kramers' theory was attributed to the slow dynamical response of the beads, which it does not account for. The results of this work highlight the necessity to include in the modeling the experimental systems that mediate force along the length of the biomolecule.

  15. Reaction of lymphoid organs to laser radiation with different pulsation rates

    NASA Astrophysics Data System (ADS)

    Kapinosov, Ivan K.; Bugaeva, Irine O.; Kolokolov, George R.; Provozina, Helen J.

    1996-05-01

    Experimental studies were performed on 220 male rats of Wistar line to reveal optimal parameters of laser radiation causing positive changes in biotissues and to select methods of laser therapy. Irradiation of the ventral abdominal wall performed by arsenide-gallium injector (710 - 890 nm, exposure - 128 sec) in pulse rate: 3000 Hz, 1500 Hz, 80 Hz. Content of lymphoblasts, medium and small lymphocytes, plasmocytes, T-lymphocytes and T-helpers as well as the activity of chromatin and lysosomal enzymes were determined in the dynamics of thymus, spleen and lymph nodes. During irradiation with the rate of 3000 Hz prevailing inhibiting influence on the immumocytopoesis and functional activity of lymphocytes in all organs studied was state, the effect being manifested by the decrease in the number of all forms of lymphocytes particular on the 3rd-5th-7th day followed by normalization on the 15th- 21st-30th day. Irradiation with the rate of 1500 Hz produced stimulating effect on the immune organs accompanied by reliable excess of control indices of lymphocyte content particularly of poorly differentiated forms (blasts and medium ones), as well as by the increase of the number of plasmocytes, T-lymphocytes, T-helpers with maximum manifestation on the 7th day. On the 15th day there is a decrease, and on the 21st-30th day--there is normalization. Irradiation with the rate of 80 Hz produced the smallest but most marked effect, particularly on the number of lymphoblasts. Peculiarities in kinetics of cellular elements studied were revealed in different lymphoid organs and in different functional zones of these organs.

  16. Low-energy enhancement of nuclear γ strength and its impact on astrophysical reaction rates

    NASA Astrophysics Data System (ADS)

    Larsen, A. C.; Blasi, N.; Bracco, A.; Bürger, A.; Camera, F.; Eriksen, T. K.; Giacoppo, F.; Goriely, S.; Guttormsen, M.; Görgen, A.; Hagen, T. W.; Harissopulos, S.; Koehler, P. E.; Leoni, S.; Million, B.; Nyhus, H. T.; Renstrøm, T. T.; Rose, S.; Ruud, I. E.; Schiller, A.; Siem, S.; Tornyi, T.; Tveten, G. M.; Voinov, A. V.; Wiedeking, M.

    2014-03-01

    An unexpected enhancement in the low-energy part of the γ-strength function for light and medium-mass nuclei has been discovered at the Oslo Cyclotron Laboratory. This enhancement could lead to an increase in the neutron-capture rates up to two orders of magnitude for very exotic, neutron-rich nuclei. However, it is still an open question whether this structure persists when approaching the neutron drip line.

  17. Cryopreservation of human spermatozoa with pentoxifylline improves the post-thaw agonist-induced acrosome reaction rate.

    PubMed

    Esteves, S C; Sharma, R K; Thomas, A J; Agarwal, A

    1998-12-01

    Cryopreservation causes extensive damage to spermatozoa, thereby impairing their fertilizing ability. The purpose of this study was to determine if the direct addition of pentoxifylline to the seminal plasma before cryopreservation improved sperm motility and acrosome reaction. Semen specimens from 15 healthy volunteers were divided into two aliquots. One aliquot was treated by adding 5 mM pentoxifylline directly to the seminal plasma (treatment group) and the other aliquot received no treatment (control group). Both aliquots were then cryopreserved by using the liquid nitrogen freezing method. The percentage of motile spermatozoa and various motion characteristics were then evaluated by performing computer-assisted semen analysis. The sperm viability was determined with a supra-vital dye, Hoechst-33258, and the acrosome reaction (spontaneous and calcium ionophore-induced) was monitored using fluorescein isothiocyanate-conjugated peanut lectin (FITC-PNA) binding assays. Pentoxifylline treatment significantly increased the sperm motility, the amplitude of lateral head displacement, the hyperactivation status, and the frequency of spontaneous acrosome reactions before freezing (P < 0.05). After post-thaw, no difference in motion characteristics (except percentage motility) between treated and control groups were observed. Acrosome loss due to the freeze-thaw process was less in the pentoxifylline-treated group (P = 0.0003). In addition, the percentage of cryopreserved acrosome-intact spermatozoa that underwent further acrosome reactions in response to calcium-ionophore challenge was significantly higher in the treated group (P = 0.03). Pentoxifylline treatment before freezing improved the acrosome reaction to ionophore challenge in cryopreserved spermatozoa. Treatment with pentoxifylline appears to minimize sperm damage during the freeze-thaw process and may improve fertilization rates with assisted reproductive procedures such as intrauterine insemination or in

  18. Photocatalytic degradation of 2-chlorophenol in TiO{sub 2} aqueous suspension: Modeling of reaction rate

    SciTech Connect

    Rideh, L.; Wehrer, A.; Ronze, D.; Zoulalian, A.

    1997-11-01

    The photoassisted oxidation of a dilute aqueous solution of 2-chlorophenol (2-CP) was investigated, over a heterogeneous catalyst of TiO{sub 2}, in an annular photocatalytic reactor. The effects of some physical and chemical parameters such as 2-CP concentration, catalyst concentration, dissolved oxygen concentration, pH, temperature, and absorbed light intensity were studied in order to optimize the process. The experiment, carried out in the presence of electron scavengers such as metallic ions, shows that the reaction rate is significantly higher than that obtained when oxygen is used alone. The results obtained in this study have led the authors, on the basis of experimentally determined adsorption, to propose a kinetic approach in which the rate-determining step is the reaction of OH{sup {sm_bullet}} radicals, identified by a spin trapping technique (EPR), with adsorbed 2-CP. A kinetic model proposed was based on a Langmuir type adsorption involving a competition between solvent and substrate with a supplementary assumption that the further oxygen adsorption sites were different from those of 2-CP and the oxygen adsorption obeys the Freundlich isotherm. This model is able to justify the observed dependence of the pollutant disappearance rate on dissolved 2-CP concentration, oxygen partial pressure, and absorbed light intensity.

  19. Modeling Ignition of a Heptane Isomer: Improved Thermodynamics, Reaction Pathways, Kinetics, and Rate Rule Optimizations for 2-Methylhexane.

    PubMed

    Mohamed, Samah Y; Cai, Liming; Khaled, Fethi; Banyon, Colin; Wang, Zhandong; Al Rashidi, Mariam J; Pitsch, Heinz; Curran, Henry J; Farooq, Aamir; Sarathy, S Mani

    2016-04-14

    Accurate chemical kinetic combustion models of lightly branched alkanes (e.g., 2-methylalkanes) are important to investigate the combustion behavior of real fuels. Improving the fidelity of existing kinetic models is a necessity, as new experiments and advanced theories show inaccuracies in certain portions of the models. This study focuses on updating thermodynamic data and the kinetic reaction mechanism for a gasoline surrogate component, 2-methylhexane, based on recently published thermodynamic group values and rate rules derived from quantum calculations and experiments. Alternative pathways for the isomerization of peroxy-alkylhydroperoxide (OOQOOH) radicals are also investigated. The effects of these updates are compared against new high-pressure shock tube and rapid compression machine ignition delay measurements. It is shown that rate constant modifications are required to improve agreement between kinetic modeling simulations and experimental data. We further demonstrate the ability to optimize the kinetic model using both manual and automated techniques for rate parameter tunings to improve agreement with the measured ignition delay time data. Finally, additional low temperature chain branching reaction pathways are shown to improve the model's performance. The present approach to model development provides better performance across extended operating conditions while also strengthening the fundamental basis of the model. PMID:26998618

  20. Applying constraints on model-based methods: estimation of rate constants in a second order consecutive reaction.

    PubMed

    Kompany-Zareh, Mohsen; Khoshkam, Maryam

    2013-02-01

    This paper describes estimation of reaction rate constants and pure ultraviolet/visible (UV-vis) spectra of the component involved in a second order consecutive reaction between Ortho-Amino benzoeic acid (o-ABA) and Diazoniom ions (DIAZO), with one intermediate. In the described system, o-ABA was not absorbing in the visible region of interest and thus, closure rank deficiency problem did not exist. Concentration profiles were determined by solving differential equations of the corresponding kinetic model. In that sense, three types of model-based procedures were applied to estimate the rate constants of the kinetic system, according to Levenberg/Marquardt (NGL/M) algorithm. Original data-based, Score-based and concentration-based objective functions were included in these nonlinear fitting procedures. Results showed that when there is error in initial concentrations, accuracy of estimated rate constants strongly depends on the type of applied objective function in fitting procedure. Moreover, flexibility in application of different constraints and optimization of the initial concentrations estimation during the fitting procedure were investigated. Results showed a considerable decrease in ambiguity of obtained parameters by applying appropriate constraints and adjustable initial concentrations of reagents. PMID:23220674