Sample records for chemical kinetics calculations

  1. LLNL Chemical Kinetics Modeling Group

    SciTech Connect

    Pitz, W J; Westbrook, C K; Mehl, M; Herbinet, O; Curran, H J; Silke, E J

    2008-09-24

    The LLNL chemical kinetics modeling group has been responsible for much progress in the development of chemical kinetic models for practical fuels. The group began its work in the early 1970s, developing chemical kinetic models for methane, ethane, ethanol and halogenated inhibitors. Most recently, it has been developing chemical kinetic models for large n-alkanes, cycloalkanes, hexenes, and large methyl esters. These component models are needed to represent gasoline, diesel, jet, and oil-sand-derived fuels.

  2. Chemical Looping Combustion Kinetics

    SciTech Connect

    Edward Eyring; Gabor Konya

    2009-03-31

    One of the most promising methods of capturing CO{sub 2} emitted by coal-fired power plants for subsequent sequestration is chemical looping combustion (CLC). A powdered metal oxide such as NiO transfers oxygen directly to a fuel in a fuel reactor at high temperatures with no air present. Heat, water, and CO{sub 2} are released, and after H{sub 2}O condensation the CO{sub 2} (undiluted by N{sub 2}) is ready for sequestration, whereas the nickel metal is ready for reoxidation in the air reactor. In principle, these processes can be repeated endlessly with the original nickel metal/nickel oxide participating in a loop that admits fuel and rejects ash, heat, and water. Our project accumulated kinetic rate data at high temperatures and elevated pressures for the metal oxide reduction step and for the metal reoxidation step. These data will be used in computational modeling of CLC on the laboratory scale and presumably later on the plant scale. The oxygen carrier on which the research at Utah is focused is CuO/Cu{sub 2}O rather than nickel oxide because the copper system lends itself to use with solid fuels in an alternative to CLC called 'chemical looping with oxygen uncoupling' (CLOU).

  3. Chemical kinetics on extrasolar planets.

    PubMed

    Moses, Julianne I

    2014-04-28

    Chemical kinetics plays an important role in controlling the atmospheric composition of all planetary atmospheres, including those of extrasolar planets. For the hottest exoplanets, the composition can closely follow thermochemical-equilibrium predictions, at least in the visible and infrared photosphere at dayside (eclipse) conditions. However, for atmospheric temperatures approximately <2000K, and in the uppermost atmosphere at any temperature, chemical kinetics matters. The two key mechanisms by which kinetic processes drive an exoplanet atmosphere out of equilibrium are photochemistry and transport-induced quenching. I review these disequilibrium processes in detail, discuss observational consequences and examine some of the current evidence for kinetic processes on extrasolar planets. PMID:24664912

  4. Stochastic simulation of chemical kinetics.

    PubMed

    Gillespie, Daniel T

    2007-01-01

    Stochastic chemical kinetics describes the time evolution of a well-stirred chemically reacting system in a way that takes into account the fact that molecules come in whole numbers and exhibit some degree of randomness in their dynamical behavior. Researchers are increasingly using this approach to chemical kinetics in the analysis of cellular systems in biology, where the small molecular populations of only a few reactant species can lead to deviations from the predictions of the deterministic differential equations of classical chemical kinetics. After reviewing the supporting theory of stochastic chemical kinetics, I discuss some recent advances in methods for using that theory to make numerical simulations. These include improvements to the exact stochastic simulation algorithm (SSA) and the approximate explicit tau-leaping procedure, as well as the development of two approximate strategies for simulating systems that are dynamically stiff: implicit tau-leaping and the slow-scale SSA. PMID:17037977

  5. Computer Simulation in Chemical Kinetics

    ERIC Educational Resources Information Center

    Anderson, Jay Martin

    1976-01-01

    Discusses the use of the System Dynamics technique in simulating a chemical reaction for kinetic analysis. Also discusses the use of simulation modelling in biology, ecology, and the social sciences, where experimentation may be impractical or impossible. (MLH)

  6. Detailed Chemical Kinetic Modeling of Cyclohexane Oxidation

    SciTech Connect

    Silke, E J; Pitz, W J; Westbrook, C K; Ribaucour, M

    2006-11-10

    A detailed chemical kinetic mechanism has been developed and used to study the oxidation of cyclohexane at both low and high temperatures. Reaction rate constant rules are developed for the low temperature combustion of cyclohexane. These rules can be used for in chemical kinetic mechanisms for other cycloalkanes. Since cyclohexane produces only one type of cyclohexyl radical, much of the low temperature chemistry of cyclohexane is described in terms of one potential energy diagram showing the reaction of cyclohexyl radical + O{sub 2} through five, six and seven membered ring transition states. The direct elimination of cyclohexene and HO{sub 2} from RO{sub 2} is included in the treatment using a modified rate constant of Cavallotti et al. Published and unpublished data from the Lille rapid compression machine, as well as jet-stirred reactor data are used to validate the mechanism. The effect of heat loss is included in the simulations, an improvement on previous studies on cyclohexane. Calculations indicated that the production of 1,2-epoxycyclohexane observed in the experiments can not be simulated based on the current understanding of low temperature chemistry. Possible 'alternative' H-atom isomerizations leading to different products from the parent O{sub 2}QOOH radical were included in the low temperature chemical kinetic mechanism and were found to play a significant role.

  7. The induction plasma chemical reactor: Part II. Kinetic model

    Microsoft Academic Search

    G. Y. Zhao; J. Mostaghimi; M. I. Boulos

    1990-01-01

    A kinetic model has been developed for the prediction of the concentration gelds in an rf plasma reactor. A sample calculation for a SiCl4\\/H2 system is then performed. The model considers the mixing processes along with the kinetics of seven reactions involving the decomposition of these reactants. The results obtained are compared to those assuming chemical equilibrium. The predictions indicate

  8. Chemical Weathering Kinetics of Basalt on Venus

    NASA Technical Reports Server (NTRS)

    Fegley, Bruce, Jr.

    1997-01-01

    The purpose of this project was to experimentally measure the kinetics for chemical weathering reactions involving basalt on Venus. The thermochemical reactions being studied are important for the CO2 atmosphere-lithosphere cycle on Venus and for the atmosphere-surface reactions controlling the oxidation state of the surface of Venus. These reactions include the formation of carbonate and scapolite minerals, and the oxidation of Fe-bearing minerals. These experiments and calculations are important for interpreting results from the Pioneer Venus, Magellan, Galileo flyby, Venera, and Vega missions to Venus, for interpreting results from Earth-based telescopic observations, and for the design of new Discovery class (e.g., VESAT) and New Millennium missions to Venus such as geochemical landers making in situ elemental and mineralogical analyses, and orbiters, probes and balloons making spectroscopic observations of the sub-cloud atmosphere of Venus.

  9. Chemical kinetics of Estane aging in PBX

    SciTech Connect

    Pack, R.T.; Hanson, D.E.; Redondo, A. [Los Alamos National Lab., NM (United States). Theoretical Div.

    1997-12-01

    The Plastic-Bonded Explosive PBX 9501 is about 95% HMX, 2.5% Estane 5703, 2.5% nitroplasticizer (NP), and 0.1% stabilizer by weight. The NP, BDNPA/F, is a eutectic mixture of bis(2,2-dinitropropyl) acetal and bis(2,2-dinitropropyl)formal. The stabilizer is diphenylamine (DPA) or Irganox 1010. The Estane, a polyester-polyurethane, slowly degrades with time. Knowledge of the effect of the Estane aging on the mechanical properties of the PBX 9501 is required to predict with confidence the useful lifetime of the explosive with respect to safety and reliability. A detailed master equation model of the chemical mechanisms and kinetics of the aging of Estane 5703 in PBX 9501 is being developed. Its output will be used as input into other models being developed to calculate the changes in the mechanical properties of the PBX.

  10. Nonlinear response theory in chemical kinetics

    PubMed Central

    Kryvohuz, Maksym; Mukamel, Shaul

    2014-01-01

    A theory of nonlinear response of chemical kinetics, in which multiple perturbations are used to probe the time evolution of nonlinear chemical systems, is developed. Expressions for nonlinear chemical response functions and susceptibilities, which can serve as multidimensional measures of the kinetic pathways and rates, are derived. A new class of multidimensional measures that combine multiple perturbations and measurements is also introduced. Nonlinear fluctuation-dissipation relations for steady-state chemical systems, which replace operations of concentration measurement and perturbations, are proposed. Several applications to the analysis of complex reaction mechanisms are provided. PMID:25669367

  11. Chemical kinetics models for semiconductor processing

    SciTech Connect

    Coltrin, M.E.; Creighton, J.R. [Sandia National Labs., Albuquerque, NM (United States); Meeks, E.; Grcar, J.F.; Houf, W.G. [Sandia National Labs., Livermore, CA (United States); Kee, R.J. [Colorado School of Mines, Golden, CO (United States)

    1997-12-31

    Chemical reactions in the gas-phase and on surfaces are important in the deposition and etching of materials for microelectronic applications. A general software framework for describing homogeneous and heterogeneous reaction kinetics utilizing the Chemkin suite of codes is presented. Experimental, theoretical and modeling approaches to developing chemical reaction mechanisms are discussed. A number of TCAD application modules for simulating the chemically reacting flow in deposition and etching reactors have been developed and are also described.

  12. Chemical Kinetic Modeling of Advanced Transportation Fuels

    SciTech Connect

    PItz, W J; Westbrook, C K; Herbinet, O

    2009-01-20

    Development of detailed chemical kinetic models for advanced petroleum-based and nonpetroleum based fuels is a difficult challenge because of the hundreds to thousands of different components in these fuels and because some of these fuels contain components that have not been considered in the past. It is important to develop detailed chemical kinetic models for these fuels since the models can be put into engine simulation codes used for optimizing engine design for maximum efficiency and minimal pollutant emissions. For example, these chemistry-enabled engine codes can be used to optimize combustion chamber shape and fuel injection timing. They also allow insight into how the composition of advanced petroleum-based and non-petroleum based fuels affect engine performance characteristics. Additionally, chemical kinetic models can be used separately to interpret important in-cylinder experimental data and gain insight into advanced engine combustion processes such as HCCI and lean burn engines. The objectives are: (1) Develop detailed chemical kinetic reaction models for components of advanced petroleum-based and non-petroleum based fuels. These fuels models include components from vegetable-oil-derived biodiesel, oil-sand derived fuel, alcohol fuels and other advanced bio-based and alternative fuels. (2) Develop detailed chemical kinetic reaction models for mixtures of non-petroleum and petroleum-based components to represent real fuels and lead to efficient reduced combustion models needed for engine modeling codes. (3) Characterize the role of fuel composition on efficiency and pollutant emissions from practical automotive engines.

  13. Chemical kinetics in the coma

    SciTech Connect

    Huebner, W.F.

    1980-01-01

    Physical and chemical conditions in the coma of a bright new comet are related to the composition of the nucleus. Chemical and photolytic processes are described and related to distance in the coma above the nucleus and to heliocentric distance of the comet. Comparison of the model with coma observations leads to some restrictions about the nucleus composition. It is expected that these restrictions become more stringent as coma models are developed further and as observations become more detailed.

  14. Chemical Dosing and First-Order Kinetics

    ERIC Educational Resources Information Center

    Hladky, Paul W.

    2011-01-01

    College students encounter a variety of first-order phenomena in their mathematics and science courses. Introductory chemistry textbooks that discuss first-order processes, usually in conjunction with chemical kinetics or radioactive decay, stop at single, discrete dose events. Although single-dose situations are important, multiple-dose events,…

  15. Biodiesel combustion: Advances in chemical kinetic modeling

    Microsoft Academic Search

    Jason Y. W. Lai; Kuang C. Lin; Angela Violi

    2011-01-01

    Burgeoning global demand for energy has increased concerns about the fuel security issues and deleterious environmental impacts that result from the ubiquitous use of fossil fuels to meet these needs. This article is a review of completed work towards the goal of creating chemical kinetic mechanisms for biodiesel, which will aid in the development of clean and efficient combustors that

  16. Chemical kinetics and modeling of planetary atmospheres

    NASA Technical Reports Server (NTRS)

    Yung, Yuk L.

    1990-01-01

    A unified overview is presented for chemical kinetics and chemical modeling in planetary atmospheres. The recent major advances in the understanding of the chemistry of the terrestrial atmosphere make the study of planets more interesting and relevant. A deeper understanding suggests that the important chemical cycles have a universal character that connects the different planets and ultimately link together the origin and evolution of the solar system. The completeness (or incompleteness) of the data base for chemical kinetics in planetary atmospheres will always be judged by comparison with that for the terrestrial atmosphere. In the latter case, the chemistry of H, O, N, and Cl species is well understood. S chemistry is poorly understood. In the atmospheres of Jovian planets and Titan, the C-H chemistry of simple species (containing 2 or less C atoms) is fairly well understood. The chemistry of higher hydrocarbons and the C-N, P-N chemistry is much less understood. In the atmosphere of Venus, the dominant chemistry is that of chlorine and sulfur, and very little is known about C1-S coupled chemistry. A new frontier for chemical kinetics both in the Earth and planetary atmospheres is the study of heterogeneous reactions. The formation of the ozone hole on Earth, the ubiquitous photochemical haze on Venus and in the Jovian planets and Titan all testify to the importance of heterogeneous reactions. It remains a challenge to connect the gas phase chemistry to the production of aerosols.

  17. Application of the ICE-PIC method for the dimension reduction of chemical kinetics

    E-print Network

    Application of the ICE-PIC method for the dimension reduction of chemical kinetics Zhuyin Ren the computational burden imposed by the direct use of detailed chemical kinetics in reactive flow calculations- ful (and which can be used in combination) are: the devel- opment of skeletal mechanisms from large

  18. Chemical Kinetic Modeling of HMX and TATB Laser Ignition Tests

    Microsoft Academic Search

    CRAIG M. TARVER

    2004-01-01

    Recent high-power laser deposition experiments on octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) produced ignition times from milliseconds to seconds. Global chemical kinetic thermal decomposition models for HMX and TATB developed to predict thermal explosion experiments lasting seconds to days are applied to these laser ignition experimental data. Excellent agreement was obtained for TATB, while the calculated ignition times were longer than

  19. PUBLISHED VERSION Benchmarking kinetic calculations of resistive wall mode stability

    E-print Network

    PUBLISHED VERSION Benchmarking kinetic calculations of resistive wall mode stability Berkery J W://scitation.aip.org/content/aip/journal/pop/21/5?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Drift kinetic (Received 17 March 2014; accepted 17 April 2014; published online 15 May 2014) Validating the calculations

  20. PACKAGE (Plasma Analysis, Chemical Kinetics and Generator Efficiency): a computer program for the calculation of partial chemical equilibrium/partial chemical rate controlled composition of multiphased mixtures under one dimensional steady flow

    SciTech Connect

    Yousefian, V.; Weinberg, M.H.; Haimes, R.

    1980-02-01

    The NASA CEC Code was the starting point for PACKAGE, whose function is to evaluate the composition of a multiphase combustion product mixture under the following chemical conditions: (1) total equilibrium with pure condensed species; (2) total equilibrium with ideal liquid solution; (3) partial equilibrium/partial finite rate chemistry; and (4) fully finite rate chemistry. The last three conditions were developed to treat the evolution of complex mixtures such as coal combustion products. The thermodynamic variable pairs considered are either pressure (P) and enthalpy, P and entropy, at P and temperature. Minimization of Gibbs free energy is used. This report gives detailed discussions of formulation and input/output information used in the code. Sample problems are given. The code development, description, and current programming constraints are discussed. (DLC)

  1. A chemical kinetic modeling study of chlorinated hydrocarbon combustion

    SciTech Connect

    Pitz, W.J.; Westbrook, C.K.

    1990-09-05

    The combustion of chloroethane is modeled as a stirred reactor so that we can study critical emission characteristics of the reactor as a function of residence time. We examine important operating conditions such as pressure, temperature, and equivalence ratio and their influence on destructive efficiency of chloroethane. The model uses a detailed chemical kinetic mechanism that we have developed previously for C{sub 3} hydrocarbons. We have added to this mechanism the chemical kinetic mechanism for C{sub 2} chlorinated hydrocarbons developed by Senkan and coworkers. In the modeling calculations, sensitivity coefficients are determined to find which reaction-rate constants have the largest effect on destructive efficiency. 24 refs., 6 figs., 1 tab.

  2. Perspective: Stochastic algorithms for chemical kinetics.

    PubMed

    Gillespie, Daniel T; Hellander, Andreas; Petzold, Linda R

    2013-05-01

    We outline our perspective on stochastic chemical kinetics, paying particular attention to numerical simulation algorithms. We first focus on dilute, well-mixed systems, whose description using ordinary differential equations has served as the basis for traditional chemical kinetics for the past 150 years. For such systems, we review the physical and mathematical rationale for a discrete-stochastic approach, and for the approximations that need to be made in order to regain the traditional continuous-deterministic description. We next take note of some of the more promising strategies for dealing stochastically with stiff systems, rare events, and sensitivity analysis. Finally, we review some recent efforts to adapt and extend the discrete-stochastic approach to systems that are not well-mixed. In that currently developing area, we focus mainly on the strategy of subdividing the system into well-mixed subvolumes, and then simulating diffusional transfers of reactant molecules between adjacent subvolumes together with chemical reactions inside the subvolumes. PMID:23656106

  3. The Deterministic Limit of Stochastic Chemical Kinetics

    PubMed Central

    Gillespie, Daniel T.

    2009-01-01

    An analysis is presented of the approximating assumptions that underlie a recently proposed derivation of the traditional deterministic reaction rate equation from a discrete-stochastic formulation of chemical kinetics. It is shown that if the system is close enough to the thermodynamic limit, in which the molecular populations and the containing volume all approach infinity in such a way that the molecular concentrations remain finite, then the required approximating assumptions will be justified for practically all spatially homogeneous systems that one is likely to encounter. PMID:19159264

  4. Deterministic limit of stochastic chemical kinetics.

    PubMed

    Gillespie, Daniel T

    2009-02-12

    An analysis is presented of the approximating assumptions that underlie a recently proposed derivation of the traditional deterministic reaction rate equation from a discrete-stochastic formulation of chemical kinetics. It is shown that if the system is close enough to the thermodynamic limit, in which the molecular populations and the containing volume all approach infinity in such a way that the molecular concentrations remain finite, then the required approximating assumptions will be justified for practically all spatially homogeneous systems that one is likely to encounter. PMID:19159264

  5. Point kinetics calculations with fully coupled thermal fluids reactivity feedback

    SciTech Connect

    Zhang, H.; Zou, L.; Andrs, D.; Zhao, H.; Martineau, R. [Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83406 (United States)

    2013-07-01

    The point kinetics model has been widely used in the analysis of the transient behavior of a nuclear reactor. In the traditional nuclear reactor system safety analysis codes such as RELAP5, the reactivity feedback effects are calculated in a loosely coupled fashion through operator splitting approach. This paper discusses the point kinetics calculations with the fully coupled thermal fluids and fuel temperature feedback implemented into the RELAP-7 code currently being developed with the MOOSE framework. (authors)

  6. Spreadsheet Templates for Chemical Equilibrium Calculations.

    ERIC Educational Resources Information Center

    Joshi, Bhairav D.

    1993-01-01

    Describes two general spreadsheet templates to carry out all types of one-equation chemical equilibrium calculations encountered by students in undergraduate chemistry courses. Algorithms, templates, macros, and representative examples are presented to illustrate the approach. (PR)

  7. Bio-butanol: Combustion properties and detailed chemical kinetic model

    SciTech Connect

    Black, G.; Curran, H.J.; Pichon, S.; Simmie, J.M.; Zhukov, V. [Combustion Chemistry Centre, National University of Ireland, Galway (Ireland)

    2010-02-15

    Autoignition delay time measurements were performed at equivalence ratios of 0.5, 1 and 2 for butan-1-ol at reflected shock pressures of 1, 2.6 and 8 atm at temperatures from 1100 to 1800 K. High-level ab initio calculations were used to determine enthalpies of formation and consequently bond dissociation energies for each bond in the alcohol. A detailed chemical kinetic model consisting of 1399 reactions involving 234 species was constructed and tested against the delay times and also against recent jet-stirred reactor speciation data with encouraging results. The importance of enol chemistry is highlighted. (author)

  8. A Chemical Kinetic Model of Transcriptional Elongation

    E-print Network

    Yujiro Richard Yamada; Charles S. Peskin

    2006-05-23

    A chemical kinetic model of the elongation dynamics of RNA polymerase along a DNA sequence is introduced. The proposed model governs the discrete movement of the RNA polymerase along a DNA template, with no consideration given to elastic effects. The model's novel concept is a ``look-ahead'' feature, in which nucleotides bind reversibly to the DNA prior to being incorporated covalently into the nascent RNA chain. Results are presented for specific DNA sequences that have been used in single-molecule experiments of the random walk of RNA polymerase along DNA. By replicating the data analysis algorithm from the experimental procedure, the model produces velocity histograms, enabling direct comparison with these published results.

  9. A kinetic mechanism inducing oscillations in simple chemical reactions networks

    E-print Network

    Altafini, Claudio

    A kinetic mechanism inducing oscillations in simple chemical reactions networks J. Coatl´even and C of oscillations in sufficiently simple reaction networks. Keywords: chemical reaction networks, oscillations, Hopf. Altafini September 10, 2009 Abstract It is known that a kinetic reaction network in which one or more

  10. Kinetic Analyses Combining Quantum Chemical and Quantum Statistical Methods: Some Case Studies

    E-print Network

    Nguyen, Minh Tho

    Kinetic Analyses Combining Quantum Chemical and Quantum Statistical Methods: Some Case Studies Minh quantum chemical calculations with a quantum statistical treatment of rate constants. We first briefly methods employed. We then discuss a sampling of the studies recently carried out in the Laboratory

  11. Calculations of the effect of nitrogen vibrational kinetics on laminar flame temperature profiles

    SciTech Connect

    Fisher, E.M. [Cornell Univ., Ithaca, NY (United States). Sibley School of Mechanical and Aerospace Engineering] [Cornell Univ., Ithaca, NY (United States). Sibley School of Mechanical and Aerospace Engineering

    1997-01-01

    Calculations of several premixed and nonpremixed laminar flames have been performed using two chemical kinetics mechanisms: (1) a vibrational kinetics mechanism treating nitrogen as a number of distinct species corresponding to different vibrational energy levels, with reactions representing transitions between energy levels; and (2) a traditional mechanism that treats nitrogen as being in vibrational equilibrium. In the vibrational kinetics calculations, translational/vibrational and vibrational/vibrational energy transfers are included, as is the effect of collisions with CO{sub 2} and H{sub 2}O on N{sub 2} vibrational excitation. Vibrational temperatures are calculated from the populations of various N{sub 2} species. For a stoichiometric, atmospheric-pressure premixed methane/air flame, the vibrational temperature is 40 K lower than the rotational/translational temperature in the region of high temperature gradient. The lag in filling upper vibrational energy levels of nitrogen also results in a lower effective heat capacity for the mixture in the vibrational kinetics case than in the vibrational equilibrium case. Rotational/translational temperatures exceed those calculated with the traditional mechanism by as much as 15 K in the region of steep temperature gradient. For diffusion flames over the range of strain rates investigated here, the effect of vibrational kinetics is much smaller. Sensitivity analysis indicates that, among the vibrational Kinetics reactions, the initial vibrational excitation of N{sub 2} by CO{sub 2} and H{sub 2}O has the greatest impact on the temperature results.

  12. CHAPTER 9. CHEMICAL KINETICS In the following chapters we will present various chemical reaction

    E-print Network

    Jacob, Daniel J.

    AND CHEMICAL EQUILIBRIA Reactions are re155 CHAPTER 9. CHEMICAL KINETICS In the following chapters we will present various chemical reaction mechanisms controlling the abundance of stratospheric ozone, the oxidizing power of the atmosphere

  13. A Detailed Chemical Kinetic Model for TNT

    SciTech Connect

    Pitz, W J; Westbrook, C K

    2005-01-13

    A detailed chemical kinetic mechanism for 2,4,6-tri-nitrotoluene (TNT) has been developed to explore problems of explosive performance and soot formation during the destruction of munitions. The TNT mechanism treats only gas-phase reactions. Reactions for the decomposition of TNT and for the consumption of intermediate products formed from TNT are assembled based on information from the literature and on current understanding of aromatic chemistry. Thermodynamic properties of intermediate and radical species are estimated by group additivity. Reaction paths are developed based on similar paths for aromatic hydrocarbons. Reaction-rate constant expressions are estimated from the literature and from analogous reactions where the rate constants are available. The detailed reaction mechanism for TNT is added to existing reaction mechanisms for RDX and for hydrocarbons. Computed results show the effect of oxygen concentration on the amount of soot precursors that are formed in the combustion of RDX and TNT mixtures in N{sub 2}/O{sub 2} mixtures.

  14. Using Excel to Calculate Mineral Chemical Analyses

    NSDL National Science Digital Library

    In this assignment, students are provided instructions to make an Excel spreadsheet to calculate mineral chemical analyses from weight percent to atoms per given number of oxygen atoms. This skill will be useful for the major rock-forming mineral groups.

  15. Calculating Shocks In Flows At Chemical Equilibrium

    NASA Technical Reports Server (NTRS)

    Eberhardt, Scott; Palmer, Grant

    1988-01-01

    Boundary conditions prove critical. Conference paper describes algorithm for calculation of shocks in hypersonic flows of gases at chemical equilibrium. Although algorithm represents intermediate stage in development of reliable, accurate computer code for two-dimensional flow, research leading up to it contributes to understanding of what is needed to complete task.

  16. Kinetic parameters of sintering of chemically enriched magnesium oxide

    Microsoft Academic Search

    V. L. Noviov; V. G. Abbakumov; S. I. Vikhman

    1993-01-01

    A kinetic investigation of sinetring of chemically enriched magnesium oxide was made for the purpose of finding a mathematical model of the process and determination of its kinetic parameters, knowledge of which makes it possible to solve problems of optimization of the firing method in design of firing equipment. in the investigations two varieties of pure magnesium oxide produced by

  17. Quantum mechanical calculations to chemical accuracy

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1991-01-01

    The accuracy of current molecular-structure calculations is illustrated with examples of quantum mechanical solutions for chemical problems. Two approaches are considered: (1) the coupled-cluster singles and doubles (CCSD) with a perturbational estimate of the contribution of connected triple excitations, or CCDS(T); and (2) the multireference configuration-interaction (MRCI) approach to the correlation problem. The MRCI approach gains greater applicability by means of size-extensive modifications such as the averaged-coupled pair functional approach. The examples of solutions to chemical problems include those for C-H bond energies, the vibrational frequencies of O3, identifying the ground state of Al2 and Si2, and the Lewis-Rayleigh afterglow and the Hermann IR system of N2. Accurate molecular-wave functions can be derived from a combination of basis-set saturation studies and full configuration-interaction calculations.

  18. Chemical Kinetic Modeling of HMX and TATB Laser Ignition Tests

    SciTech Connect

    Tarver, C M

    2004-03-02

    Recent laser ignition experiments on octahydro-1,3,5,7-tetranitro-1,3,5,7-terrazocine (HMX) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) subjected to laser fluxes ranging from 10 to 800 W/cm{sup 2} produced ignition times from seconds to milliseconds. Global chemical kinetic thermal decomposition models for HMX and TATB have been developed to calculate times to thermal explosion for experiments in the seconds to days time frame. These models are applied to the laser ignition experimental data in this paper. Excellent agreement was obtained for TATB, while the calculated ignition times were longer than experiment for HMX at lower laser fluxes. At the temperatures produced in the laser experiments, HMX melts. Melting generally increases condensed phase reaction rates so faster rates were used for three of the HMX reaction rates. This improved agreement with experiments at the lower laser fluxes but yielded very fast ignition at high fluxes. The calculated times to ignition are in reasonable agreement with the laser ignition experiments, and this justifies the use of these models for estimating reaction times at impact and shock ''hot spot'' temperatures.

  19. Chemical Kinetics: As Important As The Second Law Of Thermodynamics?

    Microsoft Academic Search

    FRANK L. LAMBERT

    1998-01-01

    The second law may be ‘time’s arrow’ but activation energies (chemical kinetics) prevent second law predictions from occurring for femtoseconds to eons. This is humanly important: Activation energies not only protect all the organic chemicals in our bodies and our oxidizable possessions from instant combustion in air, but also our breakable skis and surfboards (and legs) from disastrous fracture. Murphy’s

  20. An efficient chemical kinetics solver using high dimensional model representation

    Microsoft Academic Search

    Jeffrey A. Shorter; Precila C. Ip; Herschel A. Rabitz

    1999-01-01

    A high dimensional model representation (HDMR) technique is introduced to capture the input-output behavior of chemical kinetic models. The HDMR expresses the output chemical species concentrations as a rapidly convergent hierarchical correlated function expansion in the input variables. In this paper, the input variables are taken as the species concentrations at time t{sub i} and the output is the concentrations

  1. Chemical & Biochemical Engineering 441 (14:155:441) Chemical Engineering Kinetics

    E-print Network

    Chemical & Biochemical Engineering 441 (14:155:441) Chemical Engineering Kinetics Fall 2013 Tuesday is emphasized. The relationship of reaction mechanisms to rate laws is investigated. Prerequisites: 14:155:304: Transport Phenomena in Chemical Eng. II 14:155:307: Chemical Engineering Analysis II 01:160:328: Physical

  2. Chemical kinetics study of a nanosecond pulsed He-O2 plasma Jet

    NASA Astrophysics Data System (ADS)

    Xia, Shengguo; Jiang, Chunqi

    2011-10-01

    Atmospheric-pressure, nanosecond pulsed plasma jets have shown promising applications in biomedical and dental fields. In order to better understand the mechanisms associated to the plasma processes, a zero-dimensional plasma chemistry model was used to study the chemical kinetics of an atmospheric-pressure, nanosecond pulsed He-O2 plasma jet. Density kinetics of the charged and neutral species in the plasma jet as a function of the input parameters including the oxygen concentration and the electric field are calculated. The roles played by different reactions in the kinetics schemes are assessed. In addition, both of He-O2 and He-O2-N2 plasma chemical kinetics reaction schemes are discussed to examine the effects of air entrainment on the characteristics of the plasma jet.

  3. 3D nozzle flow simulations including state-to-state kinetics calculation

    NASA Astrophysics Data System (ADS)

    Cutrone, L.; Tuttafesta, M.; Capitelli, M.; Schettino, A.; Pascazio, G.; Colonna, G.

    2014-12-01

    In supersonic and hypersonic flows, thermal and chemical non-equilibrium is one of the fundamental aspects that must be taken into account for the accurate characterization of the plasma. In this paper, we present an optimized methodology to approach plasma numerical simulation by state-to-state kinetics calculations in a fully 3D Navier-Stokes CFD solver. Numerical simulations of an expanding flow are presented aimed at comparing the behavior of state-to-state chemical kinetics models with respect to the macroscopic thermochemical non-equilibrium models that are usually used in the numerical computation of high temperature hypersonic flows. The comparison is focused both on the differences in the numerical results and on the computational effort associated with each approach.

  4. A tool model for predicting atmospheric chemical kinetics with sensitivity analysis.

    PubMed

    Shen, J

    2001-01-01

    A package(a tool model) for program of predicting atmospheric chemical kinetics with sensitivity analysis is presented. The new direct method of calculating the first order sensitivity coefficients using sparse matrix technology to chemical kinetics is included in the tool model, it is only necessary to triangularize the matrix related to the Jacobian matrix of the model equation. The Gear type procedure is used to integrate a model equation and its coupled auxiliary sensitivity coefficient equations. The FORTRAN subroutines of the model equation, the sensitivity coefficient equations, and their Jacobian analytical expressions are generated automatically from a chemical mechanism. The kinetic representation for the model equation and its sensitivity coefficient equations, and their Jacobian matrix is presented. Various FORTRAN subroutines in packages, such as SLODE, modified MA28, Gear package, with which the program runs in conjunction are recommended. The photo-oxidation of dimethyl disulfide is used for illustration. PMID:11590724

  5. A kinetic-theory approach to turbulent chemically reacting flows

    NASA Technical Reports Server (NTRS)

    Chung, P. M.

    1976-01-01

    The paper examines the mathematical and physical foundations for the kinetic theory of reactive turbulent flows, discussing the differences and relation between the kinetic and averaged equations, and comparing some solutions of the kinetic equations obtained by the Green's function method with those obtained by the approximate bimodal method. The kinetic method described consists essentially in constructing the probability density functions of the chemical species on the basis of solutions of the Langevin stochastic equation for the influence of eddies on the behavior of fluid elements. When the kinetic equations are solved for the structure of the diffusion flame established in a shear layer by the bimodal method, discontinuities in gradients of the mean concentrations at the two flame edges appear. This is a consequence of the bimodal approximation of all distribution functions by two dissimilar half-Maxwellian functions, which is a very crude approximation. These discontinuities do not appear when the solutions are constructed by the Green's function method described here.

  6. Kinetics of Heterogeneous Chemical Reactions, II*

    PubMed Central

    Lin, S. H.; Eyring, H.

    1970-01-01

    The first-order and zero-order kinetics of heterogeneous reactions coupled with the diffusion process are studied. The differential equations of these reaction systems are solved for the cases in which the fluid is not stirred and the fluid is well stirred. It is shown that both the rate constants and the diffusion coefficient can be determined in various ways depending on the experimental conditions. PMID:5263761

  7. Computational fluid dynamics coupled with chemical kinetics, combustion and thermodynamics

    NASA Astrophysics Data System (ADS)

    Jokilaakso, A.

    This volume contains the proceedings of papers presented at the Colloquium on Process Simulation held at Helsinki University of Technology, Espoo, Finland, August 3-4, 1994. The presentations at the colloquium were all invited as this was the first meeting organized on the topic covering process modelling and computational fluid dynamics involving chemical kinetics, combustion and thermodynamics. Thermodynamic modelling and heat transfer problems in metallurgical processes have been studied at the Laboratory of Materials Processing and Powder Metallurgy, Helsinki University of Technology since 1970s. Combining chemical kinetics, combustion and thermodynamics with CFD-modelling have been studied at the laboratory during the last few years. Therefore, an annual colloquium was initiated for bringing together researchers in different process simulation fields to discuss the present status of the process modelling and, especially, the CFD-modelling involving chemical kinetics, combustion and thermodynamics.

  8. Chemical Kinetic Models for HCCI and Diesel Combustion

    SciTech Connect

    Pitz, W J; Westbrook, C K; Mehl, M; Sarathy, S M

    2010-11-15

    Predictive engine simulation models are needed to make rapid progress towards DOE's goals of increasing combustion engine efficiency and reducing pollutant emissions. These engine simulation models require chemical kinetic submodels to allow the prediction of the effect of fuel composition on engine performance and emissions. Chemical kinetic models for conventional and next-generation transportation fuels need to be developed so that engine simulation tools can predict fuel effects. The objectives are to: (1) Develop detailed chemical kinetic models for fuel components used in surrogate fuels for diesel and HCCI engines; (2) Develop surrogate fuel models to represent real fuels and model low temperature combustion strategies in HCCI and diesel engines that lead to low emissions and high efficiency; and (3) Characterize the role of fuel composition on low temperature combustion modes of advanced combustion engines.

  9. Chemical and kinetic equilibrations via radiative parton transport

    E-print Network

    Bin Zhang; Warner A. Wortman

    2011-02-21

    A hot and dense partonic system can be produced in the early stage of a relativistic heavy ion collision. How it equilibrates is important for the extraction of Quark-Gluon Plasma properties. We study the chemical and kinetic equilibrations of the Quark-Gluon Plasma using a radiative transport model. Thermal and Color-Glass-Condensate motivated initial conditions are used. We observe that screened parton interactions always lead to partial pressure isotropization. Different initial pressure anisotropies result in the same asymptotic evolution. Comparison of evolutions with and without radiative processes shows that chemical equilibration interacts with kinetic equilibration and radiative processes can contribute significantly to pressure isotropization.

  10. Fractal chemical kinetics: Simulations and experiments

    NASA Astrophysics Data System (ADS)

    Anacker, L. W.; Kopelman, R.

    1984-12-01

    We relate the effective order X of the elementary binary reaction, A+A? products, on a fractal, to the spectral dimension. For ds<2: X=1+2/ds. We regain the calsssical value (X=2) for the cubic lattice but get X=3 for the linear lattice. Supercomputer simulations (transient and steady state) and exciton fusion experiments are in quantitative agreement with the above. For percolating clusters X=2.5 and for the Sierpinski gasket X=2.45. Relevance to heterogeneous kinetics is discussed.

  11. Chemical kinetics modeling of engine knock: preliminary results

    Microsoft Academic Search

    W. J. Pitz; C. K. Westbrook

    1983-01-01

    A theoretical model, including a detailed kinetic mechanism for propane oxidation, is used to examine the ignition of propane-air mixtures under conditions of pressure and temperature encountered in knocking engines. Purely kinetic calculations are used to evaluate relative time scales for the fuel-air ignition process, varying the initial pressure, temperature, and fuel-air equivalence ratio. A one dimensional model is then

  12. Model reduction for chemical kinetics: An optimization approach

    SciTech Connect

    Petzold, L. [Univ. of California, Santa Barbara, CA (United States). Dept. of Mechanical and Environmental Engineering] [Univ. of California, Santa Barbara, CA (United States). Dept. of Mechanical and Environmental Engineering; Zhu, W. [Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Computer Science] [Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Computer Science

    1999-04-01

    The kinetics of a detailed chemically reacting system can potentially be very complex. Although the chemist may be interested in only a few species, the reaction model almost always involves a much larger number of species. Some of those species are radicals, which are very reactive species and can be important intermediaries in the reaction scheme. A large number of elementary reactions can occur among the species; some of these reactions are fast and some are slow. The aim of simplified kinetics modeling is to derive the simplest reaction system which retains the essential features of the full system. An optimization-based method for reduction of the number of species and reactions in chemical kinetics model is described. Numerical results for several reaction mechanisms illustrate the potential of this approach.

  13. Sensitivity, robustness, and identifiability in stochastic chemical kinetics models

    E-print Network

    Millar, Andrew J.

    Sensitivity, robustness, and identifiability in stochastic chemical kinetics models Michal' performances is sensitivity analysis (2). Large sensitivity to a parameter suggests that the system's output in an insensitive parameter will have little effect on the behavior. Traditionally, the concept of sensitivity has

  14. A note on the kinetic theory of chemically reacting gases

    Microsoft Academic Search

    A. Rossani; G. Spiga

    1999-01-01

    A kinetic approach to a mixture of gases whose particles interact by elastic scattering and by a bimolecular chemical reaction is analyzed by means of the relevant Boltzmann-like equation. Conservation laws and moment equations are considered, and, improving previous results in the literature, equilibria under collision are studied in detail, by providing in particular a strict stability result, which shows

  15. Calculation of a safe reentry time into an orchard treated with a pesticide chemical which produces a measurable physiological response

    Microsoft Academic Search

    William F. Serat

    1973-01-01

    A mathematical equation is presented for the calculation of a safe reentry time into an orange orchard which has been treated with a pesticide chemical, the residues of which produce a dose—dependent response in humans. The equation relates the kinetics of the rate of loss of pesticide residues, which remain on the foliage of pesticide—treated trees, and the kinetics of

  16. Combustion Research Program: Flame studies, laser diagnostics, and chemical kinetics

    SciTech Connect

    Crosley, D.R.

    1992-09-01

    This project has comprised laser flame diagnostic experiments, chemical kinetics measurements, and low pressure flame studies. Collisional quenching has been investigated for several systems: the OH radical, by H{sub 2}0 in low pressure flames; the rotational level dependence for NH, including measurements to J=24; and of NH{sub 2} at room temperature. Transition probability measurements for bands involving v{prime} = 2 and 3 of the A-X system of OH were measured in a flame. Laser-induced fluorescence of vinyl radicals was unsuccessfully attempted. RRKM and transition state theory calculations were performed on the OH + C{sub 2}H{sub 4} reaction, on the t-butyl radical + HX; and transition state theory has been applied to a series of bond scission reactions. OH concentrations were measured quantitatively in low pressure H{sub 2}/N{sub 2}O and H{sub 2}/O{sub 2} flames, and the ability to determine spatially precise flame temperatures accurately using OH laser-induced fluorescence was studied.

  17. Integration Strategies for Efficient Multizone Chemical Kinetics Models

    SciTech Connect

    McNenly, M J; Havstad, M A; Aceves, S M; Pitz, W J

    2009-10-15

    Three integration strategies are developed and tested for the stiff, ordinary differential equation (ODE) integrators used to solve the fully coupled multizone chemical kinetics model. Two of the strategies tested are found to provide more than an order of magnitude of improvement over the original, basic level of usage for the stiff ODE solver. One of the faster strategies uses a decoupled, or segregated, multizone model to generate an approximate Jacobian. This approach yields a 35-fold reduction in the computational cost for a 20 zone model. Using the same approximate Jacobian as a preconditioner for an iterative Krylov-type linear system solver, the second improved strategy achieves a 75-fold reduction in the computational cost for a 20 zone model. The faster strategies achieve their cost savings with no significant loss of accuracy. The pressure, temperature and major species mass fractions agree with the solution from the original integration approach to within six significant digits; and the radical mass fractions agree with the original solution to within four significant digits. The faster strategies effectively change the cost scaling of the multizone model from cubic to quadratic, with respect to the number of zones. As a consequence of the improved scaling, the 40 zone model offers more than a 250-fold cost savings over the basic calculation.

  18. Constant chemical potential approach for quantum chemical calculations in electrocatalysis

    PubMed Central

    Schneider, Wolfgang B

    2014-01-01

    Summary In order to simulate electrochemical reactions in the framework of quantum chemical methods, density functional theory, methods can be devised that explicitly include the electrochemical potential. In this work we discuss a Grand Canonical approach in the framework of density functional theory in which fractional numbers of electrons are used to represent an open system in contact with an electrode at a given electrochemical potential. The computational shortcomings and the additional effort in such calculations are discussed. An ansatz for a SCF procedure is presented, which can be applied routinely and only marginally increases the computational effort of standard constant electron number approaches. In combination with the common implicit solvent models this scheme can become a powerful tool, especially for the investigation of omnipresent non-faradaic effects in electrochemistry. PMID:24991504

  19. Experimental characterization and chemical kinetics study of chemical looping combustion

    E-print Network

    Chen, Tianjiao, S.M. Massachusetts Institute of Technology

    2014-01-01

    Chemical looping combustion (CLC) is one of the most promising technologies to achieve carbon capture in fossil fuel power generation plants. A novel rotary-bed reactor concept was proposed by Zhao et. al. [1] in 2013. It ...

  20. Chemical zonation in garnet: kinetics or chemical equilibrium?

    NASA Astrophysics Data System (ADS)

    Ague, Jay; Chu, Xu; Axler, Jennifer

    2015-04-01

    Chemical zonation in garnet is widely used to reconstruct the pressure (P), temperature (T), time (t), and fluid (f) histories of mountain belts. Zonation is thought to result largely from changing P - T - t - f conditions during growth as well as post-growth intracrystalline diffusion. Chemical zonation is conventionally interpreted to mean that at least some of the garnet interior was out of chemical equilibrium with the matrix during metamorphism. In this case, thermally-activated diffusion in garnet is too slow to equalize chemical potentials. However, in their groundbreaking paper, Tajčmanová et al. (2014) postulate that in high-grade rocks, chemical zonation may actually reflect attainment of equilibrium. In this scenario, diffusion is fast but viscous relaxation is slow such that the zonation patterns directly mirror internal pressure gradients within garnet. Such zoning would likely be very different than typical concentric growth zonation. Furthermore, Baumgartner et al. (2010) hypothesize that given significant variations in the molar volumes of garnet endmembers, diffusional relaxation may produce internal pressure gradients if the garnet behaves as a near constant-volume system. Consequently, growth zoning could be preserved by pressure variations within the garnet that equalize chemical potentials and slow or stop diffusion (i.e., the garnet is chemically heterogeneous but maintains internal chemical equilibrium due to the pressure variations). This mechanism predicts that areas of garnet with small compositional contrasts would undergo more diffusional relaxation than areas with large contrasts. Moreover, generation of large internal pressure gradients approaching 1 GPa would be expected to induce deformation (e.g., fracturing) in regions of large compositional gradients. Strongly growth-zoned amphibolite facies garnet from the Barrovian zones, Scotland (Ague and Baxter, 2007) shows neither of these features. The sharp compositional gradients are instead interpreted to reflect short residence times at peak-T conditions. Existing diffusion coefficient calibrations predict shockingly short peak-T residence times

  1. On The Theory of Time dilation in Chemical Kinetics

    E-print Network

    Mirza Wasif Baig

    2012-03-17

    The rates of chemical reactions are not absolute but their magnitude depends upon the relative speeds of the moving observers. This has been proved by unifying theories of chemical kinetics, which are transition state theory, collision theory and Marcus theory, with the special theory of relativity. Boltzmann constant and energy spacing between permitted quantum levels of molecules are quantum mechanically proved to be Lorentz variant. The relativistic statistical thermodynamics has been developed to explain quasiequilibrium existing between reactants and activated complex. The newly formulated Lorentz transformation of the rate constant from Arrhenius Equation, of the collision frequency and of the Eyring and Marcus equations renders the rate law also Lorentz variant. For a moving observer moving at fractions of the speed of light along the reaction coordinate the transition state possess less kinetic energy to sweep translation over it. This results in the slower transformation of reactants into products and in a stretched time frame for the chemical reaction. Lorentz transformation of the half-life equation explains time dilation of the half life period of chemical reactions and proves special theory of relativity and presents theory of relativistic chemical kinetics in accord with each other. To demonstrate the effectiveness of the present theory, the enzymatic reaction of methylamine dehydrogenase and radioactive disintegration of Astatine are considered as numerical examples.

  2. Chemical kinetic reaction mechanism for the combustion of propane

    NASA Technical Reports Server (NTRS)

    Jachimowski, C. J.

    1984-01-01

    A detailed chemical kinetic reaction mechanism for the combustion of propane is presented and discussed. The mechanism consists of 27 chemical species and 83 elementary chemical reactions. Ignition and combustion data as determined in shock tube studies were used to evaluate the mechanism. Numerical simulation of the shock tube experiments showed that the kinetic behavior predicted by the mechanism for stoichiometric mixtures is in good agrement with the experimental results over the entire temperature range examined (1150-2600K). Sensitivity and theoretical studies carried out using the mechanism revealed that hydrocarbon reactions which are involved in the formation of the HO2 radical and the H2O2 molecule are very important in the mechanism and that the observed nonlinear behavior of ignition delay time with decreasing temperature can be interpreted in terms of the increased importance of the HO2 and H2O2 reactions at the lower temperatures.

  3. Infrared absorption spectroscopy and chemical kinetics of free radicals

    SciTech Connect

    Curl, R.F.; Glass, G.P. [Rice Univ., Houston, TX (United States)

    1993-12-01

    This research is directed at the detection, monitoring, and study of chemical kinetic behavior by infrared absorption spectroscopy of small free radical species thought to be important intermediates in combustion. During the last year, infrared kinetic spectroscopy using excimer laser flash photolysis and color-center laser probing has been employed to study the high resolution spectrum of HCCN, the rate constant of the reaction between ethynyl (C{sub 2}H) radical and H{sub 2} in the temperature region between 295 and 875 K, and the recombination rate of propargyl (CH{sub 2}CCH) at room temperature.

  4. DNA as a universal substrate for chemical kinetics

    PubMed Central

    Soloveichik, David; Seelig, Georg; Winfree, Erik

    2010-01-01

    Molecular programming aims to systematically engineer molecular and chemical systems of autonomous function and ever-increasing complexity. A key goal is to develop embedded control circuitry within a chemical system to direct molecular events. Here we show that systems of DNA molecules can be constructed that closely approximate the dynamic behavior of arbitrary systems of coupled chemical reactions. By using strand displacement reactions as a primitive, we construct reaction cascades with effectively unimolecular and bimolecular kinetics. Our construction allows individual reactions to be coupled in arbitrary ways such that reactants can participate in multiple reactions simultaneously, reproducing the desired dynamical properties. Thus arbitrary systems of chemical equations can be compiled into real chemical systems. We illustrate our method on the Lotka–Volterra oscillator, a limit-cycle oscillator, a chaotic system, and systems implementing feedback digital logic and algorithmic behavior. PMID:20203007

  5. Chemical Dynamics, Molecular Energetics, and Kinetics at the Synchrotron

    SciTech Connect

    Leone, Stephen R.; Ahmed, Musahid; Wilson, Kevin R.

    2010-03-14

    Scientists at the Chemical Dynamics Beamline of the Advanced Light Source in Berkeley are continuously reinventing synchrotron investigations of physical chemistry and chemical physics with vacuum ultraviolet light. One of the unique aspects of a synchrotron for chemical physics research is the widely tunable vacuum ultraviolet light that permits threshold ionization of large molecules with minimal fragmentation. This provides novel opportunities to assess molecular energetics and reaction mechanisms, even beyond simple gas phase molecules. In this perspective, significant new directions utilizing the capabilities at the Chemical Dynamics Beamline are presented, along with an outlook for future synchrotron and free electron laser science in chemical dynamics. Among the established and emerging fields of investigations are cluster and biological molecule spectroscopy and structure, combustion flame chemistry mechanisms, radical kinetics and product isomer dynamics, aerosol heterogeneous chemistry, planetary and interstellar chemistry, and secondary neutral ion-beam desorption imaging of biological matter and materials chemistry.

  6. Accelerating the Computation of Detailed Chemical Reaction Kinetics for Simulating Combustion of Complex Fuels

    SciTech Connect

    Sankaran, R.; Grout, R.

    2012-01-01

    Combustion of hydrocarbon fuels has been a very challenging scientific and engineering problem due to the complexity of turbulent flows and hydrocarbon reaction kinetics. There is an urgent need to develop an efficient modeling capability to accurately predict the combustion of complex fuels. Detailed chemical kinetic models for the surrogates of fuels such as gasoline, diesel and JP-8 consist of thousands of chemical species and Arrhenius reaction steps. Oxygenated fuels such as bio-fuels and heavier hydrocarbons, such as from newer fossil fuel sources, are expected to have a much more complex chemistry requiring increasingly larger chemical kinetic models. Such models are beyond current computational capability, except for homogeneous or partially stirred reactor type calculations. The advent of highly parallel multi-core processors and graphical processing units (GPUs) promises a steep increase in computational performance in the coming years. This paper will present a software framework that translates the detailed chemical kinetic models to high-performance code targeted for GPU accelerators.

  7. The invariant constrained equilibrium edge preimage curve method for the dimension reduction of chemical kinetics

    E-print Network

    Vladimirsky, Alexander

    The invariant constrained equilibrium edge preimage curve method for the dimension reduction of chemical kinetics Zhuyin Rena and Stephen B. Pope Sibley School of Mechanical and Aerospace Engineering manifolds to simplify complex chemical kinetics. Typically, chemical kinetic systems have a wide range

  8. On the theory of time dilation in chemical kinetics

    E-print Network

    Baig, Mirza Wasif

    2012-01-01

    The rates of chemical reactions are not absolute but their magnitude depends upon the relative speeds of the moving observers. This has been proved by unifying theories of chemical kinetics, which are transition state theory, collision theory and Marcus theory, with the special theory of relativity. Lorentz transformations of Boltzmann constant and energy spacing between permitted quantum levels of molecules are quantum mechanically proved to be Lorentz variant. The relativistic statistical thermodynamics has been developed to explain quasiequilibrium existing between reactants and activated complex. The newly formulated Lorentz transformation of the rate constant from Arrhenius Equation, of the collision frequency and of the Eyring and Marcus equations renders the rate law also Lorentz variant. For a moving observer moving at fractions of the speed of light along the reaction coordinate the transition state possess less kinetic energy to sweep translation over it. This results in the slower transformation of...

  9. Injectivity of chemical reaction networks with mass action kinetics revisited

    E-print Network

    Feliu, Elisenda

    2011-01-01

    In this work we extend the characterization of injectivity via the Jacobian criterion first developed by Craciun and Feinberg for chemical reaction networks with outflow reactions to arbitrary chemical reaction networks taken with mass action kinetics. Injective chemical reaction networks do not have the capacity to admit multiple positive steady states for any rate constants and within each stoichiometric class. It is shown that a network is injective if and only if the determinant of the Jacobian of the system of ordinary differential equations associated to the network never vanishes. The determinant is a polynomial on the species concentrations and the rate constants, and its coefficients are fully determined. Previous works apply to chemical reaction networks whose stoichiometric space has maximal dimension. Here we present a direct route, independent of the dimension of the stoichiometric space which precludes at the same time the existence of degenerate steady states.

  10. Chemical Kinetic Models for HCCI and Diesel Combustion

    SciTech Connect

    Pitz, W J; Westbook, C K; Mehl, M

    2008-10-30

    Hydrocarbon fuels for advanced combustion engines consist of complex mixtures of hundreds or even thousands of different components. These components can be grouped into a number of chemically distinct classes, consisting of n-paraffins, branched paraffins, cyclic paraffins, olefins, oxygenates, and aromatics. Biodiesel contains its own unique chemical class called methyl esters. The fractional amounts of these chemical classes are quite different in gasoline, diesel fuel, oil-sand derived fuels and bio-derived fuels, which contributes to the very different combustion characteristics of each of these types of combustion systems. The objectives of this project are: (1) Develop detailed chemical kinetic models for fuel components used in surrogate fuels for diesel and HCCI engines; (2) Develop surrogate fuel models to represent real fuels and model low temperature combustion strategies in HCCI and diesel engines that lead to low emissions and high efficiency; and (3) Characterize the role of fuel composition on low temperature combustion modes of advanced combustion engines.

  11. Modeling of chemical inhibition from amyloid protein aggregation kinetics

    PubMed Central

    2014-01-01

    Backgrounds The process of amyloid proteins aggregation causes several human neuropathologies. In some cases, e.g. fibrillar deposits of insulin, the problems are generated in the processes of production and purification of protein and in the pump devices or injectable preparations for diabetics. Experimental kinetics and adequate modelling of chemical inhibition from amyloid aggregation are of practical importance in order to study the viable processing, formulation and storage as well as to predict and optimize the best conditions to reduce the effect of protein nucleation. Results In this manuscript, experimental data of insulin, A?42 amyloid protein and apomyoglobin fibrillation from recent bibliography were selected to evaluate the capability of a bivariate sigmoid equation to model them. The mathematical functions (logistic combined with Weibull equation) were used in reparameterized form and the effect of inhibitor concentrations on kinetic parameters from logistic equation were perfectly defined and explained. The surfaces of data were accurately described by proposed model and the presented analysis characterized the inhibitory influence on the protein aggregation by several chemicals. Discrimination between true and apparent inhibitors was also confirmed by the bivariate equation. EGCG for insulin (working at pH?=?7.4/T?=?37°C) and taiwaniaflavone for A?42 were the compounds studied that shown the greatest inhibition capacity. Conclusions An accurate, simple and effective model to investigate the inhibition of chemicals on amyloid protein aggregation has been developed. The equation could be useful for the clear quantification of inhibitor potential of chemicals and rigorous comparison among them. PMID:24572069

  12. Using hyperheuristics to improve the determination of the kinetic constants of a chemical reaction in

    E-print Network

    Giménez, Domingo

    Using hyperheuristics to improve the determination of the kinetic constants of a chemical reaction constants of a chemical reaction Kinetic parameters of a chemical reaction are determined with metaheuristic of a chemical reaction that occurs in heterogeneous phase involves the simulation of the processes occurring

  13. Chemical kinetic modeling of chlorinated hydrocarbons under stirred-reactor conditions

    SciTech Connect

    Pitz, W.J.; Westbrook, C.K.

    1990-10-04

    The combustin of chloroethane is modeled as a stirred reactor so that we can study critical emission characteristics of the reactor as a function of residence time. We examine important operating conditions such as pressure, temperature, and equivalence ratio and their influence on destructive efficiency of chloroethane and production of other chlorinated products. The model uses a detailed chemical kinetic mechanism that we have developed previously for C{sub 3} hydrocarbons. We have added to this mechanism the chemical kinetic mechanism for C{sub 2} chlorinated hydrocarbons developed by Senkan and coworkers. Some reactions have been added to Senkan's mechanism and some of the reaction-rate expressions have been updated to reflect recent developments in the literature. In the modeling calculations, sensitivity coefficients are determined to find which reaction-rate constants have the largest effect on destructive efficiency. 25 refs., 6 figs., 1 tab.

  14. Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate

    SciTech Connect

    Herbinet, Olivier; Pitz, William J.; Westbrook, Charles K. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States)

    2008-08-15

    A detailed chemical kinetic mechanism has been developed and used to study the oxidation of methyl decanoate, a surrogate for biodiesel fuels. This model has been built by following the rules established by Curran and co-workers for the oxidation of n-heptane and it includes all the reactions known to be pertinent to both low and high temperatures. Computed results have been compared with methyl decanoate experiments in an engine and oxidation of rapeseed oil methyl esters in a jet-stirred reactor. An important feature of this mechanism is its ability to reproduce the early formation of carbon dioxide that is unique to biofuels and due to the presence of the ester group in the reactant. The model also predicts ignition delay times and OH profiles very close to observed values in shock tube experiments fueled by n-decane. These model capabilities indicate that large n-alkanes can be good surrogates for large methyl esters and biodiesel fuels to predict overall reactivity, but some kinetic details, including early CO{sub 2} production from biodiesel fuels, can be predicted only by a detailed kinetic mechanism for a true methyl ester fuel. The present methyl decanoate mechanism provides a realistic kinetic tool for simulation of biodiesel fuels. (author)

  15. Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate

    SciTech Connect

    Herbinet, O; Pitz, W J; Westbrook, C K

    2007-09-17

    A detailed chemical kinetic mechanism has been developed and used to study the oxidation of methyl decanoate, a surrogate for biodiesel fuels. This model has been built by following the rules established by Curran et al. for the oxidation of n-heptane and it includes all the reactions known to be pertinent to both low and high temperatures. Computed results have been compared with methyl decanoate experiments in an engine and oxidation of rapeseed oil methyl esters in a jet stirred reactor. An important feature of this mechanism is its ability to reproduce the early formation of carbon dioxide that is unique to biofuels and due to the presence of the ester group in the reactant. The model also predicts ignition delay times and OH profiles very close to observed values in shock tube experiments fueled by n-decane. These model capabilities indicate that large n-alkanes can be good surrogates for large methyl esters and biodiesel fuels to predict overall reactivity, but some kinetic details, including early CO2 production from biodiesel fuels, can be predicted only by a detailed kinetic mechanism for a true methyl ester fuel. The present methyl decanoate mechanism provides a realistic kinetic tool for simulation of biodiesel fuels.

  16. Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate

    SciTech Connect

    Herbinet, O; Pitz, W J; Westbrook, C K

    2007-09-20

    A detailed chemical kinetic mechanism has been developed and used to study the oxidation of methyl decanoate, a surrogate for biodiesel fuels. This model has been built by following the rules established by Curran et al. for the oxidation of n-heptane and it includes all the reactions known to be pertinent to both low and high temperatures. Computed results have been compared with methyl decanoate experiments in an engine and oxidation of rapeseed oil methyl esters in a jet stirred reactor. An important feature of this mechanism is its ability to reproduce the early formation of carbon dioxide that is unique to biofuels and due to the presence of the ester group in the reactant. The model also predicts ignition delay times and OH profiles very close to observed values in shock tube experiments fueled by n-decane. These model capabilities indicate that large n-alkanes can be good surrogates for large methyl esters and biodiesel fuels to predict overall reactivity, but some kinetic details, including early CO{sub 2} production from biodiesel fuels, can be predicted only by a detailed kinetic mechanism for a true methyl ester fuel. The present methyl decanoate mechanism provides a realistic kinetic tool for simulation of biodiesel fuels.

  17. Towards cleaner combustion engines through groundbreaking detailed chemical kinetic models

    PubMed Central

    Battin-Leclerc, Frédérique; Blurock, Edward; Bounaceur, Roda; Fournet, René; Glaude, Pierre-Alexandre; Herbinet, Olivier; Sirjean, Baptiste; Warth, V.

    2013-01-01

    In the context of limiting the environmental impact of transportation, this paper reviews new directions which are being followed in the development of more predictive and more accurate detailed chemical kinetic models for the combustion of fuels. In the first part, the performance of current models, especially in terms of the prediction of pollutant formation, is evaluated. In the next parts, recent methods and ways to improve these models are described. An emphasis is given on the development of detailed models based on elementary reactions, on the production of the related thermochemical and kinetic parameters, and on the experimental techniques available to produce the data necessary to evaluate model predictions under well defined conditions. PMID:21597604

  18. Progress in Chemical Kinetic Modeling for Surrogate Fuels

    SciTech Connect

    Pitz, W J; Westbrook, C K; Herbinet, O; Silke, E J

    2008-06-06

    Gasoline, diesel, and other alternative transportation fuels contain hundreds to thousands of compounds. It is currently not possible to represent all these compounds in detailed chemical kinetic models. Instead, these fuels are represented by surrogate fuel models which contain a limited number of representative compounds. We have been extending the list of compounds for detailed chemical models that are available for use in fuel surrogate models. Detailed models for components with larger and more complicated fuel molecular structures are now available. These advancements are allowing a more accurate representation of practical and alternative fuels. We have developed detailed chemical kinetic models for fuels with higher molecular weight fuel molecules such as n-hexadecane (C16). Also, we can consider more complicated fuel molecular structures like cyclic alkanes and aromatics that are found in practical fuels. For alternative fuels, the capability to model large biodiesel fuels that have ester structures is becoming available. These newly addressed cyclic and ester structures in fuels profoundly affect the reaction rate of the fuel predicted by the model. Finally, these surrogate fuel models contain large numbers of species and reactions and must be reduced for use in multi-dimensional models for spark-ignition, HCCI and diesel engines.

  19. An automatic chemical lumping method for the reduction of large chemical kinetic mechanisms

    Microsoft Academic Search

    P. Pepiot-Desjardins; H. Pitsch

    2008-01-01

    A novel approach to the lumping of species in large chemical kinetic mechanisms is presented. Species with similar composition and functionalities are lumped into one single representative species. Simulations using the detailed scheme are used to gather statistical information on the distribution of the isomers within each lump group. These distributions are functions of space and time. Closure is performed

  20. Chemical kinetics of the high pressure oxidation of n-butane and its relation to engine knock

    Microsoft Academic Search

    W. Pitz; C. K. Westbrook

    1986-01-01

    A chemical kinetic oxidation mechanism for n-butane is employed to study hydrocarbon autoignition related to engine knock. A low temperature submechanism has been added to a previously developed high temperature mechanism in order to examine the importance of low temperature reaction paths in autoignition. Numerical calculations follow reactions taking place in a sample of end gas and are used to

  1. Progress in an oxygen-carrier reaction kinetics experiment for rotary-bed chemical looping combustion

    E-print Network

    Jester-Weinstein, Jack (Jack L.)

    2013-01-01

    The design process for an experimental platform measuring reaction kinetics in a chemical looping combustion (CLC) process is documented and justified. To enable an experiment designed to characterize the reaction kinetics ...

  2. Theory of Chemical Kinetics and Charge Transfer based on Nonequilibrium Thermodynamics

    E-print Network

    Bazant, Martin Z.

    Advances in the fields of catalysis and electrochemical energy conversion often involve nanoparticles, which can have kinetics surprisingly different from the bulk material. Classical theories of chemical kinetics assume ...

  3. Significance of Xenobiotic Metabolism for Bioaccumulation Kinetics of Organic Chemicals in Gammarus pulex

    PubMed Central

    2012-01-01

    Bioaccumulation and biotransformation are key toxicokinetic processes that modify toxicity of chemicals and sensitivity of organisms. Bioaccumulation kinetics vary greatly among organisms and chemicals; thus, we investigated the influence of biotransformation kinetics on bioaccumulation in a model aquatic invertebrate using fifteen 14C-labeled organic xenobiotics from diverse chemical classes and physicochemical properties (1,2,3-trichlorobenzene, imidacloprid, 4,6-dinitro-o-cresol, ethylacrylate, malathion, chlorpyrifos, aldicarb, carbofuran, carbaryl, 2,4-dichlorophenol, 2,4,5-trichlorophenol, pentachlorophenol, 4-nitrobenzyl-chloride, 2,4-dichloroaniline, and sea-nine (4,5-dichloro-2-octyl-3-isothiazolone)). We detected and identified metabolites using HPLC with UV and radio-detection as well as high resolution mass spectrometry (LTQ-Orbitrap). Kinetics of uptake, biotransformation, and elimination of parent compounds and metabolites were modeled with a first-order one-compartment model. Bioaccumulation factors were calculated for parent compounds and metabolite enrichment factors for metabolites. Out of 19 detected metabolites, we identified seven by standards or accurate mass measurements and two via pathway analysis and analogies to other compounds. 1,2,3-Trichlorobenzene, imidacloprid, and 4,6-dinitro-o-cresol were not biotransformed. Dietary uptake contributed little to overall uptake. Differentiation between parent and metabolites increased accuracy of bioaccumulation parameters compared to total 14C measurements. Biotransformation dominated toxicokinetics and strongly affected internal concentrations of parent compounds and metabolites. Many metabolites reached higher internal concentrations than their parents, characterized by large metabolite enrichment factors. PMID:22321051

  4. Mission Fuel Kinetics Input and RELAP-like Calculations

    SciTech Connect

    Pavlovichev, A.M.

    2001-09-28

    In this document issued according to ''Work Release 02. P. 99-4b'' the neutronics parameters intended for use in 1-point kinetics RELAP model are presented. They are obtained for equilibrium 30% MOX fueled core of VVER-1000 containing boron burnable poison rods.

  5. Basics of Chemical Kinetics -1 Rate of reaction = rate of disappearance of A =

    E-print Network

    Albert, Réka

    Basics of Chemical Kinetics - 1 Rate of reaction = rate of disappearance of A = # of moles of Chemical Kinetics - 3 Elementary Reaction: Reaction order of each species is identical reactions: Forward Reaction Backward Reaction CBA + 2 CBA + 2 CBA + 2 CBA + 2 #12;Basics of Chemical

  6. Grad's distribution functions in the kinetic equations for a chemical reaction

    E-print Network

    Spiga, Giampiero

    Grad's distribution functions in the kinetic equations for a chemical reaction Marzia Bisi, Maria of four species undergoing a bimolecular reversible chemical reaction, along with all possible elastic] and Prigogine-Xhrouet [2], kinetic approaches to chemical reactions in a gas have gained interest and importance

  7. CHEMKIN-III: A FORTRAN chemical kinetics package for the analysis of gas-phase chemical and plasma kinetics

    SciTech Connect

    Kee, R.J.; Rupley, F.M.; Meeks, E.; Miller, J.A.

    1996-05-01

    This document is the user`s manual for the third-generation CHEMKIN package. CHEMKIN is a software package whose purpose is to facilitate the formation, solution, and interpretation of problems involving elementary gas-phase chemical kinetics. It provides a flexible and powerful tool for incorporating complex chemical kinetics into simulations of fluid dynamics. The package consists of two major software components: an Interpreter and a Gas-Phase Subroutine Library. The Interpreter is a program that reads a symbolic description of an elementary, user-specified chemical reaction mechanism. One output from the Interpreter is a data file that forms a link to the Gas-Phase Subroutine Library. This library is a collection of about 100 highly modular FORTRAN subroutines that may be called to return information on equations of state, thermodynamic properties, and chemical production rates. CHEMKIN-III includes capabilities for treating multi-fluid plasma systems, that are not in thermal equilibrium. These new capabilities allow researchers to describe chemistry systems that are characterized by more than one temperature, in which reactions may depend on temperatures associated with different species; i.e. reactions may be driven by collisions with electrons, ions, or charge-neutral species. These new features have been implemented in such a way as to require little or no changes to CHEMKIN implementation for systems in thermal equilibrium, where all species share the same gas temperature. CHEMKIN-III now has the capability to handle weakly ionized plasma chemistry, especially for application related to advanced semiconductor processing.

  8. Free energy calculations: Applications to chemical and biochemical phenomena

    Microsoft Academic Search

    Peter. Kollman

    1993-01-01

    The author will review the applications of free energy calculations employing molecular dynamics or Monte Carlo methods to a variety of chemical and biochemical phenomena. The focus is on the applications of such calculations to molecular solvation, molecular association, macromolecular stability, and enzyme catalysis. The molecules discussed range from monovalent ions and small molecules to proteins and nucleic acids.

  9. Free energy calculations: Applications to chemical and biochemical phenomena

    SciTech Connect

    Kollman, P. [Univ. of California, San Francisco, CA (United States). Dept. of Pharmaceutical Chemistry

    1993-11-01

    The author will review the applications of free energy calculations employing molecular dynamics or Monte Carlo methods to a variety of chemical and biochemical phenomena. The focus is on the applications of such calculations to molecular solvation, molecular association, macromolecular stability, and enzyme catalysis. The molecules discussed range from monovalent ions and small molecules to proteins and nucleic acids.

  10. Free-Electron Lasers, Thermal Diffusion, Chemical Kinetics, and Surgery

    NASA Astrophysics Data System (ADS)

    Edwards, Glenn; Hutson, M. Shane

    2001-11-01

    Experiments demonstrate that the Mark-III FEL is a particularly effective tool for etching soft matter with remarkably little damage surrounding the site when tuned to wavelengths near 6.45 microns. Based on these observatons, human neuorsurgical and ophthalmic procedures were developed and have been performed successfully. A thermodynamic model was proposed to account for the wavelength dependence; however, the dynamics have not been well understood. We have theoretically investigated thermal diffusion and chemical kinetics in a system of alternating layers of protein and water as heated by a Mark-III FEL. The model is representative of cornea and the exposure conditions are comparable to previous experimental FEL investigations. A substantial temperature enhancement develops in the surface layer on the ten-nanosecond time scale. We consider the onset of both the helix-coil transition and chemical bond breaking of collagen in terms of the thermal, chemical, and structural properties of the system as well as laser wavelength and pulse structure.

  11. KINETICS: A computer program to analyze chemical reaction data. Revision 2

    SciTech Connect

    Braun, R.L.; Burnham, A.K.

    1994-09-01

    KINETICS (Version 3.2) is a copyrighted, user-friendly kinetics analysis computer program designed for reactions such-as kerogen or polymer decomposition. It can fit rate parameters to chemical reaction data (rate or cumulative reacted) measured at a series of constant temperatures, constant heating rates, or arbitrary thermal histories. The program uses two models with conversion-dependent Azrhenius parameters and two models with activation energy distributions. The discrete distribution model fits an average frequency factor and relative fractions and activation energies for up to 25 parallel, fast-order reactions. The Gaussian distribution model fits a frequency factor, activation energy, Gaussian distribution parameter, and reaction order for up to 3 parallel reactions. For both distribution models, if the experiments are at a series of constant heating rates, the program uses a very fast approximate fitting procedure to determine possible initial parameter-estimates for the subsequent nonlinear regression analysis. This increases the probability that the regression analysis will properly. converge with a minimum of computer time. Once convergence is reached by the discrete model, the parameter space is further systematically searched to achieve global convergence. With the Gaussian model, the calculated rates or integrals can be convoluted with an experimental tracer signal during the nonlinear regression to account for dispersion effects often found in real chemical reaction data. KINETICS can also be used in an application mode to calculate reaction rates and integrals for previously determined Gaussian or discrete, parameters, using an arbitrary thermal history. Four additional models have been incorporated for the kinetics analysis of polymers and other materials, including some kerogens, which have a reaction-rate profile that is narrower than that for a single first-order reaction.

  12. Kinetic and Chemical Mechanism of ?–Isopropylmalate Synthase from Mycobacterium tuberculosis

    PubMed Central

    de Carvalho, Luiz Pedro S.; Blanchard, John S.

    2008-01-01

    Mycobacterium tuberculosis ?–isopropylmalate synthase (MtIPMS) catalyzes the condensation of AcCoA with ?–ketoisovalerate (?–KIV) and the subsequent hydrolysis of ?–isopropylmalyl-CoA to generate the products CoA and ?–isopropylmalate (?–IPM). This is the first committed step in L–leucine biosynthesis. We have purified recombinant MtIPMS and characterized it using a combination of steady-state kinetics, isotope effects, isotopic labeling, and 1H-NMR spectroscopy. The ?–keto acid specificity of the enzyme is narrow and the acyl-CoA specificity is absolute for AcCoA. In the absence of ?–KIV MtIPMS does not enolize the ?–protons of AcCoA, but slowly hydrolyzes acyl-CoA analogs. Initial velocity studies, product inhibition, and dead-end inhibition studies indicate that MtIPMS follows a nonrapid equilibrium random Bi Bi kinetic mechanism, with a preferred pathway to the ternary complex. MtIPMS requires two catalytic bases for maximal activity (both with pKa values of ca. 6.7), and we suggest that one catalyzes deprotonation and enolization of AcCoA and the other activates the water molecule involved in the hydrolysis of ?–isopropylmalyl-CoA. Primary deuterium and solvent kinetic isotope effects indicate that there is a step after chemistry that is rate limiting, although with poor substrates such as pyruvate, hydrolysis becomes partially rate-limiting. Our data is inconsistent with the suggestion that a metal-bound water is involved in hydrolysis. Finally, our results indicate that the hydrolysis of ?–isopropylmalyl-CoA is direct, without the formation of a cyclic anhydride intermediate. Based on these results, a chemical mechanism for the MtIPMS-catalyzed reaction is proposed. PMID:16846242

  13. Infrared Absorption Spectroscopy and Chemical Kinetics of Free Radicals

    SciTech Connect

    Curl, Robert F; Glass, Graham

    2004-11-01

    This research was directed at the detection, monitoring, and study of the chemical kinetic behavior by infrared absorption spectroscopy of small free radical species thought to be important intermediates in combustion. Work on the reaction of OH with acetaldehyde has been completed and published and work on the reaction of O({sup 1}D) with CH{sub 4} has been completed and submitted for publication. In the course of our investigation of branching ratios of the reactions of O({sup 1}D) with acetaldehyde and methane, we discovered that hot atom chemistry effects are not negligible at the gas pressures (13 Torr) initially used. Branching ratios of the reaction of O({sup 1}D) with CH{sub 4} have been measured at a tenfold higher He flow and fivefold higher pressure.

  14. High Temperature Chemical Kinetic Combustion Modeling of Lightly Methylated Alkanes

    SciTech Connect

    Sarathy, S M; Westbrook, C K; Pitz, W J; Mehl, M

    2011-03-01

    Conventional petroleum jet and diesel fuels, as well as alternative Fischer-Tropsch (FT) fuels and hydrotreated renewable jet (HRJ) fuels, contain high molecular weight lightly branched alkanes (i.e., methylalkanes) and straight chain alkanes (n-alkanes). Improving the combustion of these fuels in practical applications requires a fundamental understanding of large hydrocarbon combustion chemistry. This research project presents a detailed high temperature chemical kinetic mechanism for n-octane and three lightly branched isomers octane (i.e., 2-methylheptane, 3-methylheptane, and 2,5-dimethylhexane). The model is validated against experimental data from a variety of fundamental combustion devices. This new model is used to show how the location and number of methyl branches affects fuel reactivity including laminar flame speed and species formation.

  15. Plasma parameters and chemical kinetics of an HCl DC glow discharge

    Microsoft Academic Search

    A. M. Efremov; G. H. Kim; D. I. Balashov; C. I. Kim

    2006-01-01

    The investigations of plasma parameters and active particles kinetics in an HCl DC glow discharge system were carried out. The investigation combines plasma diagnostics by electric probes and plasma modeling based on the self-consistent solution of Boltzmann kinetic equation and the balance equation of chemical kinetic for neutral and charged particles. It was shown that the direct electron impact dissociation

  16. Non-meanfield deterministic limits in chemical reaction kinetics R. E. Lee DeVille

    E-print Network

    Van Den Eijnden, Eric

    Non-meanfield deterministic limits in chemical reaction kinetics R. E. Lee DeVille Courant is demonstrated for the kinetic Monte Carlo version of the Schnakenberg reaction where we identified a scaling, and it is at the very heart of the majority of macroscopic models of physical, chemical, and biological systems

  17. Surface Reaction Kinetics of Ga 1x In x P Growth During Pulsed Chemical Beam Epitaxy

    E-print Network

    Surface Reaction Kinetics of Ga 1­x In x P Growth During Pulsed Chemical Beam Epitaxy N. Dietz 1 growth has been a slow process because little is known about chemical reaction properties and reaction into the surface reaction kinetics during an organometallic deposition process. These insights will allow us

  18. System Theory Applications in Biology: From Stochastic Chemical Kinetics to Deterministic Model Invalidation

    Microsoft Academic Search

    Mustafa Khammash; Brian Munsky

    Ideas from System Theory lie behind many of the new powerful methods being developed in the burgeoning field of Systems Biology. In this paper, we show two examples of this: one in the area of stochastic chemical kinetics, and the other in biological model invalidation. Stochastic chemical kinetics has gained a lot of attention in the last few years. In

  19. Core Physics and Kinetics Calculations for the Fissioning Plasma Core Reactor

    NASA Technical Reports Server (NTRS)

    Butler, C.; Albright, D.

    2007-01-01

    Highly efficient, compact nuclear reactors would provide high specific impulse spacecraft propulsion. This analysis and numerical simulation effort has focused on the technical feasibility issues related to the nuclear design characteristics of a novel reactor design. The Fissioning Plasma Core Reactor (FPCR) is a shockwave-driven gaseous-core nuclear reactor, which uses Magneto Hydrodynamic effects to generate electric power to be used for propulsion. The nuclear design of the system depends on two major calculations: core physics calculations and kinetics calculations. Presently, core physics calculations have concentrated on the use of the MCNP4C code. However, initial results from other codes such as COMBINE/VENTURE and SCALE4a. are also shown. Several significant modifications were made to the ISR-developed QCALC1 kinetics analysis code. These modifications include testing the state of the core materials, an improvement to the calculation of the material properties of the core, the addition of an adiabatic core temperature model and improvement of the first order reactivity correction model. The accuracy of these modifications has been verified, and the accuracy of the point-core kinetics model used by the QCALC1 code has also been validated. Previously calculated kinetics results for the FPCR were described in the ISR report, "QCALC1: A code for FPCR Kinetics Model Feasibility Analysis" dated June 1, 2002.

  20. Chemical Kinetics of Polycyclic Aromatic Hydrocarbons in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Kress, Monika; Tran, T.; Chiar, J.; Tielens, A. G. G. M.

    2012-05-01

    Polycyclic aromatic hydrocarbons (PAHs) comprise about 10% of the carbon in the interstellar medium. There is evidence of modification of PAHs in protoplanetary disks. What happens to these molecules as they are incorporated into protoplanetary disks? We address this question by investigating the chemical kinetics of PAHs in the disk environment. Kress et al. (2010) investigated the chemical behavior of PAHs at temperatures from 1000 to 2000 K at a pressure of 1e-6 bar, and proposed the concept of the 'soot line', analogous to the 'snow line' in the solar nebula. Inside of the soot line, PAHs are irreversibly destroyed via thermally-driven reactions. We will extend this study to more realistic disk conditions and timescales. In a related project (see poster by Tran, Chiar, et al.), we are investigating the differences in the PAH physical characteristics in quiescent dense clouds versus the environment around embedded protostars. Together, these studies will help us understand (1) the fate of interstellar PAHs in planet-forming disks and (2) the relationship between interstellar and solar system PAHs. We also will investigate the soot line in disks around sub-solar mass stars (e.g. M dwarfs). This work has been supported by the NASA Astrobiology Institute's Virtual Planetary Laboratory (PI: V. Meadows) and the NASA/EPOESS program (PI: C. Phillips).

  1. Sequential Voronoi diagram calculations using simple chemical reactions

    E-print Network

    Costello, Ben de Lacy; Adamatzky, Andy

    2012-01-01

    In our recent paper [de Lacy Costello et al. 2010] we described the formation of complex tessellations of the plane arising from the various reactions of metal salts with potassium ferricyanide and ferrocyanide loaded gels. In addition to producing colourful tessellations these reactions are naturally computing generalised Voronoi diagrams of the plane. The reactions reported previously were capable of the calculation of three distinct Voronoi diagrams of the plane. As diffusion coupled with a chemical reaction is responsible for the calculation then this is achieved in parallel. Thus an increase in the complexity of the data input does not utilise additional computational resource. Additional benefits of these chemical reactions is that a permanent record of the Voronoi diagram calculation (in the form of precipitate free bisectors) is achieved, so there is no requirement for further processing to extract the calculation results. Previously it was assumed that the permanence of the results was also a potenti...

  2. THE JOURNAL OF CHEMICAL PHYSICS 135, 024113 (2011) A weak second order tau-leaping method for chemical kinetic systems

    E-print Network

    Li, Tiejun

    2011-01-01

    THE JOURNAL OF CHEMICAL PHYSICS 135, 024113 (2011) A weak second order tau-leaping method with weak second order accuracy. We extend their work to the discrete chemical jump processes. With slight modification, the method can also solve dis- crete chemical kinetic systems with weak second order accuracy

  3. Thermodynamics and Kinetics of Chemical Equilibrium in Solution.

    ERIC Educational Resources Information Center

    Leenson, I. A.

    1986-01-01

    Discusses theory of thermodynamics of the equilibrium in solution and dissociation-dimerization kinetics. Describes experimental procedure including determination of molar absorptivity and equilibrium constant, reaction enthalpy, and kinetics of the dissociation-dimerization reaction. (JM)

  4. Quantum dynamics of chemical reactions by converged algebraic variational calculations

    Microsoft Academic Search

    Donald G. Truhlar; David W. Schwenke; Donald J. Kouri

    1990-01-01

    This paper describes recent progress in using algebraic variational methods and L² basis sets for converged quantum mechanical calculations of chemical reaction dynamics of the H + Hâ, O + Hâ, H + HBr, and F + Hâ reactions and the isotopically substituted reactions D + Hâ and O + HD and some of the reverse reactions. The paper emphasizes

  5. Chemical-equilibrium calculations for aqueous geothermal brines

    SciTech Connect

    Kerrisk, J.F.

    1981-05-01

    Results from four chemical-equilibrium computer programs, REDEQL.EPAK, GEOCHEM, WATEQF, and SENECA2, have been compared with experimental solubility data for some simple systems of interest with geothermal brines. Seven test cases involving solubilities of CaCO/sub 3/, amorphous SiO/sub 2/, CaSO/sub 4/, and BaSO/sub 4/ at various temperatures from 25 to 300/sup 0/C and in NaCl or HCl solutions of 0 to 4 molal have been examined. Significant differences between calculated results and experimental data occurred in some cases. These differences were traced to inaccuracies in free-energy or equilibrium-constant data and in activity coefficients used by the programs. Although currently available chemical-equilibrium programs can give reasonable results for these calculations, considerable care must be taken in the selection of free-energy data and methods of calculating activity coefficients.

  6. Calculating kinetics parameters and reactivity changes with continuous-energy Monte Carlo

    SciTech Connect

    Kiedrowski, Brian C [Los Alamos National Laboratory; Brown, Forrest B [Los Alamos National Laboratory; Wilson, Paul [UNIV. WISCONSIN

    2009-01-01

    The iterated fission probability interpretation of the adjoint flux forms the basis for a method to perform adjoint weighting of tally scores in continuous-energy Monte Carlo k-eigenvalue calculations. Applying this approach, adjoint-weighted tallies are developed for two applications: calculating point reactor kinetics parameters and estimating changes in reactivity from perturbations. Calculations are performed in the widely-used production code, MCNP, and the results of both applications are compared with discrete ordinates calculations, experimental measurements, and other Monte Carlo calculations.

  7. Cometary impact and amino acid survival - Chemical kinetics and thermochemistry

    USGS Publications Warehouse

    Ross, D.S.

    2006-01-01

    The Arrhenius parameters for the initiating reactions in butane thermolysis and the formation of soot, reliable to at least 3000 K, have been applied to the question of the survival of amino acids in cometary impacts on early Earth. The pressure/temperature/time course employed here was that developed in hydrocode simulations for kilometer-sized comets (Pierazzo and Chyba, 1999), with attention to the track below 3000 K where it is shown that potential stabilizing effects of high pressure become unimportant kinetically. The question of survival can then be considered without the need for assignment of activation volumes and the related uncertainties in their application to extreme conditions. The exercise shows that the characteristic times for soot formation in the interval fall well below the cooling periods for impacts ranging from fully vertical down to about 9?? above horizontal. Decarboxylation, which emerges as more rapid than soot formation below 2000-3000 K, continues further down to extremely narrow impact angles, and accordingly cometa??ry delivery of amino acids to early Earth is highly unlikely. ?? 2006 American Chemical Society.

  8. Chemical kinetic simulation of kerosene combustion in an individual flame tube.

    PubMed

    Zeng, Wen; Liang, Shuang; Li, Hai-Xia; Ma, Hong-An

    2014-05-01

    The use of detailed chemical reaction mechanisms of kerosene is still very limited in analyzing the combustion process in the combustion chamber of the aircraft engine. In this work, a new reduced chemical kinetic mechanism for fuel n-decane, which selected as a surrogate fuel for kerosene, containing 210 elemental reactions (including 92 reversible reactions and 26 irreversible reactions) and 50 species was developed, and the ignition and combustion characteristics of this fuel in both shock tube and flat-flame burner were kinetic simulated using this reduced reaction mechanism. Moreover, the computed results were validated by experimental data. The calculated values of ignition delay times at pressures of 12, 50 bar and equivalence ratio is 1.0, 2.0, respectively, and the main reactants and main products mole fractions using this reduced reaction mechanism agree well with experimental data. The combustion processes in the individual flame tube of a heavy duty gas turbine combustor were simulated by coupling this reduced reaction mechanism of surrogate fuel n-decane and one step reaction mechanism of surrogate fuel C12H23 into the computational fluid dynamics software. It was found that this reduced reaction mechanism is shown clear advantages in simulating the ignition and combustion processes in the individual flame tube over the one step reaction mechanism. PMID:25685503

  9. Chemical kinetic simulation of kerosene combustion in an individual flame tube

    PubMed Central

    Zeng, Wen; Liang, Shuang; Li, Hai-xia; Ma, Hong-an

    2013-01-01

    The use of detailed chemical reaction mechanisms of kerosene is still very limited in analyzing the combustion process in the combustion chamber of the aircraft engine. In this work, a new reduced chemical kinetic mechanism for fuel n-decane, which selected as a surrogate fuel for kerosene, containing 210 elemental reactions (including 92 reversible reactions and 26 irreversible reactions) and 50 species was developed, and the ignition and combustion characteristics of this fuel in both shock tube and flat-flame burner were kinetic simulated using this reduced reaction mechanism. Moreover, the computed results were validated by experimental data. The calculated values of ignition delay times at pressures of 12, 50 bar and equivalence ratio is 1.0, 2.0, respectively, and the main reactants and main products mole fractions using this reduced reaction mechanism agree well with experimental data. The combustion processes in the individual flame tube of a heavy duty gas turbine combustor were simulated by coupling this reduced reaction mechanism of surrogate fuel n-decane and one step reaction mechanism of surrogate fuel C12H23 into the computational fluid dynamics software. It was found that this reduced reaction mechanism is shown clear advantages in simulating the ignition and combustion processes in the individual flame tube over the one step reaction mechanism. PMID:25685503

  10. Propene oxidation at low and intermediate temperatures: A detailed chemical kinetic study

    SciTech Connect

    Wilk, R.D.; Cernansky, N.P.; Pitz, W.J.; Westbrook, C.K.

    1987-03-24

    A detailed chemical kinetic mechanism for propene oxidation is developed and used to model reactions in a static reactor at temperatures of 575-715 K, equivalence ratios of 0.8 - 2.0, and a pressure of 600 torr. Modeling of hydrocarbon oxidation in this temperature range is important for the validation of detailed models to be used for performing calculations related to automotive engine knock. The model predicted induction periods and species concentrations for all the species and all conditions measured experimentally in the static reactor. Overall, the calculated concentrations of carbon monoxide, acetaldehyde, acrolein, and propane oxide agreed well with those measured. The calculated concentrations of ethane are low compared to the experimental measurements, and the calculated concentrations of formaldehyde are high. Agreement for concentrations of carbon dioxide, methane, and methanol is mixed. The characteristic s-shape of the fuel concentration history is well predicted. Modeling calculations identified some of the key reaction steps at the present conditions. Addition of OH to propene and H atom abstraction by OH from propene are important steps in determining the subsequent distributions of intermediate products, such as acetaldehyde, acrolein and formaldehyde. Allyl radicals are very abundant in propene oxidation, and the primary steps found to be responsible for their consumption are reaction with CH/sub 3/O/sub 2/ and HO/sub 2/. 37 refs., 5 figs., 1 tab.

  11. Propene oxidation at low and intermediate temperatures: A detailed chemical kinetic study

    SciTech Connect

    Wilk, R.D.; Gernansky, N.P.; Pitz, W.J.; Westbrook, C.K.

    1987-01-01

    A detailed chemical kinetic mechanism for propene oxidation is developed and used to model reactions in a static reactor at temperatures of 575-715 K, equivalence ratios of 0.8 - 2.0, and a pressure of 600 torr. Modeling of hydrocarbon oxidation in this temperature range is important for the validation of detailed models to be used for performing calculations related to automotive engine knock. The model predicted induction periods and species concentrations for all the species and all conditions measured experimentally in the static reactor. Overall, the calculated concentrations of carbon monoxide, acetaldehyde, acrolein, and propene oxide agreed well with those measured. The calculated concentrations of ethene are low compared to the experimental measurements, and the calculated concentrations of formaldehyde are high. Agreement for concentrations of carbon dioxide, methane, and methanol is mixed. The characteristic s-shape of the fuel concentration history is well predicted. Modeling calculations identified some of the key reaction steps at the present conditions. Addition of OH to propene and H atom abstraction by OH from propene are important steps in determining the subsequent distributions of intermediate products, such as acetaldehyde, acrolein and formaldehyde. Allyl radicals are very abundant in propene oxidation, and the primary steps found to be responsible for their consumption are reaction with CH/sub 3/O/sub 2/ and HO/sub 2/.

  12. Atmospheric chemical reactions of monoethanolamine initiated by OH radical: mechanistic and kinetic study.

    PubMed

    Xie, Hong-Bin; Li, Chao; He, Ning; Wang, Cheng; Zhang, Shaowen; Chen, Jingwen

    2014-02-01

    Monoethanolamine (MEA) is a benchmark and widely utilized solvent in amine-based postcombustion CO2 capture (PCCC), a leading technology for reducing CO2 emission from fossil fuel power plants. The large-scale implementation of PCCC would lead to inevitable discharges of amines to the atmosphere. Therefore, understanding the kinetics and mechanisms of the transformation of representative amine MEA in the atmosphere is of great significance for risk assessment of the amine-based PCCC. In this study, the H-abstraction reaction of MEA with ·OH, and ensuing reactions of produced MEA-radicals, including isomerization, dissociation, and bimolecular reaction MEA-radicals+O2, were investigated by quantum chemical calculation [M06-2X/aug-cc-pVTZ//M06-2X/6-311++G(d,p)] and kinetic modeling. The calculated overall rate constant [(7.27 × 10(-11)) cm(3) molecule(-1) s(-1)] for H-abstraction is in excellent agreement with the experimental value [(7.02 ± 0.46) × 10(-11) cm(3) molecule(-1) s(-1)]. The results show that the product branching ratio of NH2CH2 · CHOH (MEA-?) (43%) is higher than that of NH2 · CHCH2OH (MEA-?) (39%), clarifying that MEA-? is not an exclusive product. On the basis of the unveiled reaction mechanisms of MEA-radicals + O2, the proton transfer reaction mass spectrometry signal (m/z 60.044), not recognized in the experiment, was identified. PMID:24438015

  13. A Shock Tube and Chemical Kinetic Modeling Study of the Oxidation of 2,5-Dimethylfuran

    PubMed Central

    Sirjean, Baptiste; Fournet, René; Glaude, Pierre-Alexandre; Battin-Leclerc, Frédérique; Wang, Weijing; Oehlschlaeger, Matthew A.

    2013-01-01

    A detailed kinetic model describing the oxidation of 2,5-dimethylfuran (DMF), a potential second-generation biofuel, is proposed. The kinetic model is based upon quantum chemical calculations for the initial DMF consumption reactions and important reactions of intermediates. The model is validated by comparison to new DMF shock tube ignition delay time measurements (over the temperature range 1300 – 1831 K and at nominal pressures of 1 and 4 bar) and the DMF pyrolysis speciation measurements of Lifshitz et al. [J. Phys. Chem. A 102 (52) (1998) 10655-10670] Globally, modeling predictions are in good agreement with the considered experimental targets. In particular, ignition delay times are predicted well by the new model, with model experiment deviations of at most a factor of two, and DMF pyrolysis conversion is predicted well, to within experimental scatter of the Lifshitz et al. data. Additionally, comparisons of measured and model predicted pyrolysis speciation provides validation of theoretically calculated channels for the oxidation of DMF. Sensitivity and reaction flux analyses highlight important reactions as well as the primary reaction pathways responsible for the decomposition of DMF and formation and destruction of key intermediate and product species. PMID:23327724

  14. A weak second order tau-leaping method for chemical kinetic systems

    Microsoft Academic Search

    Yucheng Hu; Tiejun Li; Bin Min

    2011-01-01

    Recently Anderson and Mattingly [Comm. Math. Sci. 9, 301 (2011)] proposed a method which can solve chemical Langevin equations with weak second order accuracy. We extend their work to the discrete chemical jump processes. With slight modification, the method can also solve discrete chemical kinetic systems with weak second order accuracy in the large volume scaling. Especially, this method achieves

  15. "Kinetics of Chemical Reactions in Environmental Systems: Research Needs and Challenges"

    E-print Network

    Sparks, Donald L.

    "Kinetics of Chemical Reactions in Environmental Systems: Research Needs and Challenges" Donald(oid)s, nutrients, radionuclides, and organic chemicals have shown that reaction rates are initially rapid followed by a slow approach to a steady state. The rapid reaction has been ascribed to chemical reactions and film

  16. On persistence of chemical reaction networks with time-dependent kinetics and no global conservation laws

    E-print Network

    Sontag, Eduardo

    On persistence of chemical reaction networks with time-dependent kinetics and no global for persistence of chemical reaction networks are proposed, which extend those obtained by the authors in previous. Interpreted for chemical reactions and population models, this translates into a "non-extinction property

  17. Fundamental Chemical Kinetic And Thermodynamic Data For Purex Process Models

    SciTech Connect

    Taylor, R.J.; Fox, O.D.; Sarsfield, M.J.; Carrott, M.J.; Mason, C.; Woodhead, D.A.; Maher, C.J. [British Technology Centre, Nexia Solutions, Sellafield, Seascale, CA20 1PG (United Kingdom); Steele, H. [Nexia Solutions, inton House, Risley, Warrington, WA3 6AS (United Kingdom); Koltunov, V.S. [A.A. Bochvar All-Russia Institute of Inorganic Materials, VNIINM, PO Box 369, Moscow 123060 (Russian Federation)

    2007-07-01

    To support either the continued operations of current reprocessing plants or the development of future fuel processing using hydrometallurgical processes, such as Advanced Purex or UREX type flowsheets, the accurate simulation of Purex solvent extraction is required. In recent years we have developed advanced process modeling capabilities that utilize modern software platforms such as Aspen Custom Modeler and can be run in steady state and dynamic simulations. However, such advanced models of the Purex process require a wide range of fundamental data including all relevant basic chemical kinetic and thermodynamic data for the major species present in the process. This paper will summarize some of these recent process chemistry studies that underpin our simulation, design and testing of Purex solvent extraction flowsheets. Whilst much kinetic data for actinide redox reactions in nitric acid exists in the literature, the data on reactions in the diluted TBP solvent phase is much rarer. This inhibits the accurate modelization of the Purex process particularly when species show a significant extractability in to the solvent phase or when cycling between solvent and aqueous phases occurs, for example in the reductive stripping of Pu(IV) by ferrous sulfamate in the Magnox reprocessing plant. To support current oxide reprocessing, we have investigated a range of solvent phase reactions: - U(IV)+HNO{sub 3}; - U(IV)+HNO{sub 2}; - U(IV)+HNO{sub 3} (Pu catalysis); - U(IV)+HNO{sub 3} (Tc catalysis); - U(IV)+ Np(VI); - U(IV)+Np(V); - Np(IV)+HNO{sub 3}; - Np(V)+Np(V); Rate equations have been determined for all these reactions and kinetic rate constants and activation energies are now available. Specific features of these reactions in the TBP phase include the roles of water and hydrolyzed intermediates in the reaction mechanisms. In reactions involving Np(V), cation-cation complex formation, which is much more favourable in TBP than in HNO{sub 3}, also occurs and complicates the redox chemistry. Whilst some features of the redox chemistry in TBP appear similar to the corresponding reactions in aqueous HNO{sub 3}, there are notable differences in rates, the forms of the rate equations and mechanisms. Secondly, to underpin the development of advanced single cycle flowsheets using the complexant aceto-hydroxamic acid, we have also characterised in some detail its redox chemistry and solvent extraction behaviour with both Np and Pu ions. We find that simple hydroxamic acids are remarkably rapid reducing agents for Np(VI). They also reduce Pu(VI) and cause a much slower reduction of Pu(IV) through a complex mechanism involving acid hydrolysis of the ligand. AHA is a strong hydrophilic and selective complexant for the tetravalent actinide ions as evidenced by stability constant and solvent extraction data for An(IV), M(III) and U(VI) ions. This has allowed the successful design of U/Pu+Np separation flowsheets suitable for advanced fuel cycles. (authors)

  18. Study of the thermooxidative degradation kinetics of poly(tetrafluoroethene) using iso-conversional calculation procedure

    Microsoft Academic Search

    S. D. Genieva; L. T. Vlaev; A. N. Atanassov

    2010-01-01

    The thermooxidative degradation kinetics of poly(tetrafluoroethene) (PTFE) in air flow has been studied at different heating\\u000a rates (6, 10, 12 and 15 K min?1) by non-isothermal differential thermal analysis (DTA). Six calculation procedures based on single TG curves and iso-conversional\\u000a method, as well as 27 mechanism functions were used. The comparison of the results obtained with these calculation procedures\\u000a showed that they

  19. The complete relativistic kinetic model of symmetry violation in isotopic expanding plasma. III. Specific entropy calculation

    E-print Network

    Yu. G. Ignatyev; K. Alsmadi

    2010-12-27

    A complete model of baryon production in an expanding, primordially symmetric hot Universe is constructed in the framework of general-relativistic kinetic theory. In this model specific model for a baryon is calculated and graphs of the value dependence are constructed.

  20. Dynamics calculations of kinetic isotope effects for the reactions of muonium atoms with Fâ and Clâ

    Microsoft Academic Search

    Rozeanne Steckler; Donald G. Truhlar; Bruce C. Garrett

    1986-01-01

    Variational-transition-state theory with semiclassical ground-state transmission coefficients is applied to calculate reaction rate constants, activation energies, and kinetic isotope effects for the protium (H) and muonium (Mu) cases of H + Fâ to HF + F and H + Clâ to HCl + Cl. The authors examine four potential energy surfaces for H + Fâ and two for H +

  1. Development of chemical kinetic models for lean NOx traps.

    SciTech Connect

    Larson, Richard S.

    2010-04-01

    Overall project goal: Obtain the fundamental surface chemistry knowledge needed for the design and optimal utilization of NOx trap catalysts, thereby helping to speed the widespread adoption of this technology. Relevance to VT Program goals: Effective, durable advanced aftertreatment systems for lean-burn engines must be available if the fuel economy advantages of these engines are to be realized. Specific current year objective: Identify and correct any deficiencies in the previously developed reaction mechanism describing normal storage/regeneration cycles, and complete development of a supplementary mechanism accounting for the effects of sulfation. A fundamental understanding of LNT chemistry is needed to realize the full potential of this aftertreatment technology, which could lead to greater use of fuel-efficient lean-burn engines. We have used a multi-tiered approach to developing an elementary chemical mechanism benchmarked against experimental data: (1) Simulate a set of steady flow experiments, with storage effects minimized, to infer a tentative mechanism for chemistry on precious metal sites (completed). (2) Simulate a set of long cycle experiments to infer a mechanism for NOx and oxygen storage sites while simultaneously finalizing precious metal chemistry (completed). (3) Simulate a simplified sulfation/desulfation protocol to obtain a supplementary set of reactions involving sulfur on all three kinds of sites (nearly completed). (4) Investigate the potential role of reductants other than CO and H{sub 2}. While simulation of isothermal experiments is the preferred way to extract kinetic parameters, simulation of realistic storage/regeneration cycles requires that exotherms be considered. Our ultimate goal is to facilitate improved designs for LNT-based aftertreatment systems and to assist in the development of improved catalysts.

  2. Oxidation kinetics of chemically vapor-deposited silicon carbide in wet oxygen

    Microsoft Academic Search

    Elizabeth J. Opila

    1994-01-01

    The oxidation kinetics of chemically vapor-deposited SiC in dry oxygen and wet oxygen at temperatures between 1,200 and 1,400 C were monitored using thermogravimetric analysis. It was found that in a clean environment, 10% water vapor enhanced the oxidation kinetics of SiC only very slightly compared to rates found in dry oxygen. Oxidation kinetics were examined in terms of the

  3. The pyrolysis of 2-methylfuran: a quantum chemical, statistical rate theory and kinetic modelling study.

    PubMed

    Somers, Kieran P; Simmie, John M; Metcalfe, Wayne K; Curran, Henry J

    2014-03-21

    Due to the rapidly growing interest in the use of biomass derived furanic compounds as potential platform chemicals and fossil fuel replacements, there is a simultaneous need to understand the pyrolysis and combustion properties of such molecules. To this end, the potential energy surfaces for the pyrolysis relevant reactions of the biofuel candidate 2-methylfuran have been characterized using quantum chemical methods (CBS-QB3, CBS-APNO and G3). Canonical transition state theory is employed to determine the high-pressure limiting kinetics, k(T), of elementary reactions. Rice-Ramsperger-Kassel-Marcus theory with an energy grained master equation is used to compute pressure-dependent rate constants, k(T,p), and product branching fractions for the multiple-well, multiple-channel reaction pathways which typify the pyrolysis reactions of the title species. The unimolecular decomposition of 2-methylfuran is shown to proceed via hydrogen atom transfer reactions through singlet carbene intermediates which readily undergo ring opening to form collisionally stabilised acyclic C5H6O isomers before further decomposition to C1-C4 species. Rate constants for abstraction by the hydrogen atom and methyl radical are reported, with abstraction from the alkyl side chain calculated to dominate. The fate of the primary abstraction product, 2-furanylmethyl radical, is shown to be thermal decomposition to the n-butadienyl radical and carbon monoxide through a series of ring opening and hydrogen atom transfer reactions. The dominant bimolecular products of hydrogen atom addition reactions are found to be furan and methyl radical, 1-butene-1-yl radical and carbon monoxide and vinyl ketene and methyl radical. A kinetic mechanism is assembled with computer simulations in good agreement with shock tube speciation profiles taken from the literature. The kinetic mechanism developed herein can be used in future chemical kinetic modelling studies on the pyrolysis and oxidation of 2-methylfuran, or the larger molecular structures for which it is a known pyrolysis/combustion intermediate (e.g. cellulose, coals, 2,5-dimethylfuran). PMID:24496403

  4. Kinetics of chemical decolorization of the azo dye C.I. Reactive Orange 96 by sulfide

    Microsoft Academic Search

    E. S. Yoo

    2002-01-01

    The mechanism of decolorization of azo dyes based on the extracellular chemical reduction with sulfide (H2S, HS?, S2?) was postulated for sulfate reducing environments. To design technical decolorization processes of textile wastewater treatment with sulfide produced by sulfate reducing bacteria (SRB), kinetics is of great significance. Batch experiments were made in order to investigate the kinetics of abiotic decolorization of

  5. Analysis of the Computational Singular Perturbation Reduction Method for Chemical Kinetics

    Microsoft Academic Search

    A. Zagaris; H. G. Kaper; T. J. Kaper

    2004-01-01

    This article is concerned with the asymptotic accuracy of the Computational Singular Perturbation (CSP) method developed by Lam and Goussis [The CSP method for simplifying kinetics, Int. J. Chem. Kin. 26 (1994) 461–486] to reduce the dimensionality of a system of chemical kinetics equations. The method, which is generally applicable to multiple-time scale problems arising in a broad array of

  6. A Comparison Study of Portland Cement Hydration Kinetics as Measured by Chemical Shrinkage and Isothermal Calorimetry

    E-print Network

    Bentz, Dale P.

    at various temperatures. For a given cement paste, the hydration kinetics curves measured by the two methods properties of a hydrating cement paste, such as the non-evaporable water content, the cumulative heat1 A Comparison Study of Portland Cement Hydration Kinetics as Measured by Chemical Shrinkage

  7. Recent Advances in Detailed Chemical Kinetic Models for Large Hydrocarbon and Biodiesel Transportation Fuels

    SciTech Connect

    Westbrook, C K; Pitz, W J; Curran, H J; Herbinet, O; Mehl, M

    2009-03-30

    n-Hexadecane and 2,2,4,4,6,8,8-heptamethylnonane represent the primary reference fuels for diesel that are used to determine cetane number, a measure of the ignition property of diesel fuel. With the development of chemical kinetics models for these two primary reference fuels for diesel, a new capability is now available to model diesel fuel ignition. Also, we have developed chemical kinetic models for a whole series of large n-alkanes and a large iso-alkane to represent these chemical classes in fuel surrogates for conventional and future fuels. Methyl decanoate and methyl stearate are large methyl esters that are closely related to biodiesel fuels, and kinetic models for these molecules have also been developed. These chemical kinetic models are used to predict the effect of the fuel molecule size and structure on ignition characteristics under conditions found in internal combustion engines.

  8. Chemical kinetics parameters and model validation for the gasification of PCEA nuclear graphite

    NASA Astrophysics Data System (ADS)

    El-Genk, Mohamed S.; Tournier, Jean-Michel P.; Contescu, Cristian I.

    2014-01-01

    A series of gasification experiments, using two right cylinder specimens (?12.7 × 25.4 mm and 25.4 × 25.4 mm) of PCEA nuclear graphite in ambient airflow, measured the total gasification flux at weight losses up to 41.5% and temperatures (893-1015 K) characteristics of those for in-pores gasification Mode (a) and in-pores diffusion-limited Mode (b). The chemical kinetics parameters for the gasification of PCEA graphite are determined using a multi-parameters optimization algorithm from the measurements of the total gasification rate and transient weight loss in experiments. These parameters are: (i) the pre-exponential rate coefficients and the Gaussian distributions and values of specific activation energies for adsorption of oxygen and desorption of CO gas; (ii) the specific activation energy and pre-exponential rate coefficient for the breakup of stable un-dissociated C(O2) oxygen radicals to form stable (CO) complexes; (iii) the specific activation energy and pre-exponential coefficient for desorption of CO2 gas and; (iv) the initial surface area of reactive free sites per unit mass. This area is consistently 13.5% higher than that for nuclear graphite grades of NBG-25 and IG-110 and decreases inversely proportional with the square root of the initial mass of the graphite specimens in the experiments. Experimental measurements successfully validate the chemical-reactions kinetics model that calculates continuous Arrhenius curves of the total gasification flux and the production rates of CO and CO2 gases. The model results at different total weight losses agree well with measurements and expand beyond the temperatures in the experiments to the diffusion-limited mode of gasification. Also calculated are the production rates of CO and CO2 gases and their relative contributions to the total gasification rate in the experiments as functions of temperature, for total weight losses of 5% and 10%.

  9. Chemical kinetics parameters and model validation for the gasification of PCEA nuclear graphite

    SciTech Connect

    El-Genk, Mohamed S [University of New Mexico, Albuquerque] [University of New Mexico, Albuquerque; Tournier, Jean-Michel [University of New Mexico, Albuquerque] [University of New Mexico, Albuquerque; Contescu, Cristian I [ORNL] [ORNL

    2014-01-01

    A series of gasification experiments, using two right cylinder specimens (~ 12.7 x 25.4 mm and 25.4 x 25.4 mm) of PCEA nuclear graphite in ambient airflow, measured the total gasification flux at weight losses up to 41.5% and temperatures (893-1015 K) characteristics of those for in-pores gasification Mode (a) and in-pores diffusion-limited Mode (b). The chemical kinetics parameters for the gasification of PCEA graphite are determined using a multi-parameters optimization algorithm from the measurements of the total gasification rate and transient weight loss in experiments. These parameters are: (i) the pre-exponential rate coefficients and the Gaussian distributions and values of specific activation energies for adsorption of oxygen and desorption of CO gas; (ii) the specific activation energy and pre-exponential rate coefficient for the breakup of stable un-dissociated C(O2) oxygen radicals to form stable (CO) complexes; (iii) the specific activation energy and pre-exponential coefficient for desorption of CO2 gas and; (iv) the initial surface area of reactive free sites per unit mass. This area is consistently 13.5% higher than that for nuclear graphite grades of NBG-25 and IG-110 and decreases inversely proportional with the square root of the initial mass of the graphite specimens in the experiments. Experimental measurements successfully validate the chemical-reactions kinetics model that calculates continuous Arrhenius curves of the total gasification flux and the production rates of CO and CO2 gases. The model results at different total weight losses agree well with measurements and expand beyond the temperatures in the experiments to the diffusion-limited mode of gasification. Also calculated are the production rates of CO and CO2 gases and their relative contributions to the total gasification rate in the experiments as functions of temperature, for total weight losses of 5% and 10%.

  10. Critical evaluation of Jet-A spray combustion using propane chemical kinetics in gas turbine combustion simulated by KIVA-2

    NASA Technical Reports Server (NTRS)

    Nguyen, H. L.; Ying, S.-J.

    1990-01-01

    Jet-A spray combustion has been evaluated in gas turbine combustion with the use of propane chemical kinetics as the first approximation for the chemical reactions. Here, the numerical solutions are obtained by using the KIVA-2 computer code. The KIVA-2 code is the most developed of the available multidimensional combustion computer programs for application of the in-cylinder combustion dynamics of internal combustion engines. The released version of KIVA-2 assumes that 12 chemical species are present; the code uses an Arrhenius kinetic-controlled combustion model governed by a four-step global chemical reaction and six equilibrium reactions. Researchers efforts involve the addition of Jet-A thermophysical properties and the implementation of detailed reaction mechanisms for propane oxidation. Three different detailed reaction mechanism models are considered. The first model consists of 131 reactions and 45 species. This is considered as the full mechanism which is developed through the study of chemical kinetics of propane combustion in an enclosed chamber. The full mechanism is evaluated by comparing calculated ignition delay times with available shock tube data. However, these detailed reactions occupy too much computer memory and CPU time for the computation. Therefore, it only serves as a benchmark case by which to evaluate other simplified models. Two possible simplified models were tested in the existing computer code KIVA-2 for the same conditions as used with the full mechanism. One model is obtained through a sensitivity analysis using LSENS, the general kinetics and sensitivity analysis program code of D. A. Bittker and K. Radhakrishnan. This model consists of 45 chemical reactions and 27 species. The other model is based on the work published by C. K. Westbrook and F. L. Dryer.

  11. A description of chemical and diffusion control in isothermal kinetics of cure kinetics

    Microsoft Academic Search

    J. E. K. Schawe

    2002-01-01

    During isothermal polymerization reaction, a thermosetting resin vitrifies if the reaction temperature is lower than the maximum glass transition temperature of the fully reacted material. Due to the vitrification process, the kinetics become diffusion-controlled. The kinetics of such reactions can be described using a diffusion control function. The actual reaction rate can be expressed as a product of the reaction

  12. Leaching Kinetics of Atrazine and Inorganic Chemicals in Tilled and Orchard Soils

    NASA Astrophysics Data System (ADS)

    Szajdak, Lech W.; Lipiec, Jerzy; Siczek, Anna; Nosalewicz, Artur; Majewska, Urszula

    2014-04-01

    The aim of this study was to verify first-order kinetic reaction rate model performance in predicting of leaching of atrazine and inorganic compounds (K+1, Fe+3, Mg+2, Mn+2, NH4 +, NO3 - and PO4 -3) from tilled and orchard silty loam soils. This model provided an excellent fit to the experimental concentration changes of the compounds vs. time data during leaching. Calculated values of the first-order reaction rate constants for the changes of all chemicals were from 3.8 to 19.0 times higher in orchard than in tilled soil. Higher first-order reaction constants for orchard than tilled soil correspond with both higher total porosity and contribution of biological pores in the former. The first order reaction constants for the leaching of chemical compounds enables prediction of the actual compound concentration and the interactions between compound and soil as affected by management system. The study demonstrates the effectiveness of simultaneous chemical and physical analyses as a tool for the understanding of leaching in variously managed soils.

  13. IMPACT OF TOXIC ORGANIC CHEMICALS ON THE KINETICS OF ACETOCLASTICMETHOGENESIS

    EPA Science Inventory

    A knowledge of the effect of toxic organic chemicals on thebiotransformation characteristics of organic co-susbstrates isessential for predicting the impact of these chemicals in anaerobicprocesses. ench-scale tests were conducted to assess the impactof toxic organic chemicals on...

  14. Theory of chemical kinetics. Technical report, January 16, 1980-January 15, 1981

    SciTech Connect

    Ross, J.

    1981-01-01

    Progress made in research in the theory of chemical kinetics is described. The work in the past year has been primarily concerned with the efficiency of thermal and chemical engines, the role of inertial effect in thermal engines, the behavior of harmonically driven oscillatory reactions and a detailed analysis of glycolysis including its mechanism, its control features and its resonance effects.

  15. Implicit Second Order Weak Taylor Tau-Leaping Methods for the Stochastic Simulation of Chemical Kinetics

    Microsoft Academic Search

    T.-H. Ahn; A. Sandu

    2011-01-01

    For biochemical systems, when some chemical species are represented by small numbers of molecules, discrete and stochastic approaches are more appropriate than continuous and deterministic approaches. The stochastic simulation algorithm (SSA), proposed by Gillespie, is a cardinal simulation method for the chemical kinetics. Because the SSA simulates every reaction event, the amount of the computational time is huge when models

  16. Modeling particle formation during low-pressure silane oxidation: Detailed chemical kinetics and aerosol dynamics

    E-print Network

    Zachariah, Michael R.

    10 October 2000; accepted 22 January 2001 A detailed chemical kinetic model is presented for silicon-pressure chemical vapor deposition LPCVD of SiO2 films from silane and oxygen is widely used in micro- electronics fabrication. SiO2 is used in electronic compo- nents because of its insulating properties and as a barrier

  17. Mechanistic, kinetic, and processing aspects of tungsten chemical mechanical polishing

    NASA Astrophysics Data System (ADS)

    Stein, David

    This dissertation presents an investigation into tungsten chemical mechanical polishing (CMP). CMP is the industrially predominant unit operation that removes excess tungsten after non-selective chemical vapor deposition (CVD) during sub-micron integrated circuit (IC) manufacture. This work explores the CMP process from process engineering and fundamental mechanistic perspectives. The process engineering study optimized an existing CMP process to address issues of polish pad and wafer carrier life. Polish rates, post-CMP metrology of patterned wafers, electrical test data, and synergy with a thermal endpoint technique were used to determine the optimal process. The oxidation rate of tungsten during CMP is significantly lower than the removal rate under identical conditions. Tungsten polished without inhibition during cathodic potentiostatic control. Hertzian indenter model calculations preclude colloids of the size used in tungsten CMP slurries from indenting the tungsten surface. AFM surface topography maps and TEM images of post-CMP tungsten do not show evidence of plow marks or intergranular fracture. Polish rate is dependent on potassium iodate concentration; process temperature is not. The colloid species significantly affects the polish rate and process temperature. Process temperature is not a predictor of polish rate. A process energy balance indicates that the process temperature is predominantly due to shaft work, and that any heat of reaction evolved during the CMP process is negligible. Friction and adhesion between alumina and tungsten were studied using modified AFM techniques. Friction was constant with potassium iodate concentration, but varied with applied pressure. This corroborates the results from the energy balance. Adhesion between the alumina and the tungsten was proportional to the potassium iodate concentration. A heuristic mechanism, which captures the relationship between polish rate, pressure, velocity, and slurry chemistry, is presented. In this mechanism, the colloid reacts with the chemistry of the slurry to produce active sites. These active sites become inactive by removing tungsten from the film. The process repeats when then inactive sites are reconverted to active sites. It is shown that the empirical form of the heuristic mechanism fits all of the data obtained. The mechanism also agrees with the limiting cases that were investigated.

  18. An investigation on the catalytic capacity of dolomite in transesterification and the calculation of kinetic parameters.

    PubMed

    Niu, Sheng-Li; Huo, Meng-Jia; Lu, Chun-Mei; Liu, Meng-Qi; Li, Hui

    2014-04-01

    The catalytic capacity of dolomite in transesterification was investigated and the kinetic parameters were calculated. The activated dolomites as transesterification catalyst were characterized by X-ray diffraction, nitrogen adsorption and desorption and Hammett indicator method, where the original dolomite was analyzed by thermogravimetric and X-ray fluorescence in advance. Its potential catalytic capacity was validated from aspects of the activated temperature and the reused property, where the reliability of the experimental system was also examined. Then, influences of the catalyst added amount, the mole ratio of methanol to oil, the transesterification temperature and the transesterification time on the catalytic capacity were investigated. Finally, kinetic parameters of the transesterification catalyzed by the activated dolomite were calculated. PMID:24583217

  19. EBR-II time constant calculation using the EROS kinetics code

    SciTech Connect

    Grimm, K.N.; Meneghetti, D.

    1986-01-01

    System time constants are important parameters in determining the dynamic behavior of reactors. One method of determining basic time constants is to apply a step change in power level and determine the resulting temperature change. This methodology can be done using any computer code that calculates temperature versus time given either a power input or a reactivity input. In the current analysis this is done using the reactor kinetics code EROS. As an example of this methodology, the time constant is calculated for an Experimental Breeder Reactor II (EBR-II) fuel pin.

  20. Chemical and kinetic factors related to hydrogen removal from aluminum

    Microsoft Academic Search

    G. K. Sigworth; T. A. Engh

    1982-01-01

    The available data on hydrogen solubility in aluminum are reviewed. Then a mathematical analysis of the kinetics of hydrogen removal is presented. A rather complicated general equation for the hydrogen removal in batch reactors is shown to reduce to more simple expressions for certain values of anew dimensionless group, Psi\\/[pct H]. This ``dimensionless hydrogen concentration'' can be understood to represent

  1. Beyond Traditional Chemical Kinetics Formulas: Group-Theoretic Approach

    E-print Network

    Kreinovich, Vladik

    obtains by the traditional formulas. For example, Michaelis and Menten shows that for enzyme kinetics different ways to describe their values. For example, temperature can be measures in degrees Fahrenheit the temperature tC in Celsius, then we can compute the temperature tF in Fahrenheit as tF = f(tC), where f(x) = 32

  2. The influence of chemical mechanisms on PDF calculations of nonpremixed piloted jet flames

    SciTech Connect

    Cao, Renfeng Richard; Pope, Stephen B. [Mechanical and Aerospace Engineering, Cornell University, 245 Upson Hall, Ithaca, NY 14853 (United States)

    2005-12-01

    Seven different chemical mechanisms for methane are used in PDF model calculations of the Barlow and Frank flames D, E, and F in order to investigate the ability of these mechanisms to represent the local extinction, reignition, and other chemical phenomena observed in these nonpremixed piloted jet flames. The mechanisms studied range from a 5-step reduced mechanism to the GRI3.0 mechanism which involves 53 species. As in several other recent studies, we use the PDF method based on the joint probability density function of velocity, turbulence frequency, and composition. Extensive tests are performed to ensure the numerical accuracy of the calculations, to relate them to previous calculations based on the same model, and to reexamine the sensitivity of the calculations (especially of flame F) to uncertainties in the pilot temperature and the treatment of radiation. As has been observed in other studies of laminar and turbulent nonpremixed flames, we find that the GRI3.0 mechanism overpredicts the levels of NO, typically by a factor of 2. Apart from this, the GRI3.0 and GRI2.11 mechanisms yield comparably good agreement with the experimental data for all three flames, including the level of local extinction and the conditional means of major and other minor species. Two augmented reduce mechanism (ARM1 and ARM2) based on GRI2.11 and containing 16 and 19 species are slightly less accurate; while the 5-step reduced mechanism and two C{sub 1} skeletal mechanisms containing 16 species display significant inaccuracies. An examination of the autoignition and laminar-flame behavior of the different mechanisms confirms (with some exceptions) expected trends: there is an association between long ignition delay times, small extinction strain rates, and high levels of local extinction. This study again demonstrates the ability of the joint PDF method to represent accurately the strong turbulence-chemistry interactions in these flames, and it clarifies the necessary level of description of the chemical kinetics.

  3. Spectroscopic analysis of cinnamic acid using quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Vinod, K. S.; Periandy, S.; Govindarajan, M.

    2015-02-01

    In this present study, FT-IR, FT-Raman, 13C NMR and 1H NMR spectra for cinnamic acid have been recorded for the vibrational and spectroscopic analysis. The observed fundamental frequencies (IR and Raman) were assigned according to their distinctiveness region. The computed frequencies and optimized parameters have been calculated by using HF and DFT (B3LYP) methods and the corresponding results are tabulated. On the basis of the comparison between computed and experimental results assignments of the fundamental vibrational modes are examined. A study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, were performed by HF and DFT methods. The alternation of the vibration pattern of the pedestal molecule related to the substitutions was analyzed. The 13C and 1H NMR spectra have been recorded and the chemical shifts have been calculated using the gauge independent atomic orbital (GIAO) method. The Mulliken charges, UV spectral analysis and HOMO-LUMO analysis of have been calculated and reported. The molecular electrostatic potential (MEP) was constructed.

  4. Kinetic-quantum chemical model for catalytic cycles: the Haber-Bosch process and the effect of reagent concentration.

    PubMed

    Kozuch, Sebastian; Shaik, Sason

    2008-07-01

    A combined kinetic-quantum chemical model is developed with the goal of estimating in a straightforward way the turnover frequency (TOF) of catalytic cycles, based on the state energies obtained by quantum chemical calculations. We describe how the apparent activation energy of the whole cycle, so-called energetic span (delta E), is influenced by the energy levels of two species: the TOF determining transition state (TDTS) and the TOF determining intermediate (TDI). Because these key species need not be adjoining states, we conclude that for catalysis there are no rate-determining steps, only rate determining states. In addition, we add here the influence of reactants concentrations. And, finally, the model is applied to the Haber-Bosch process of ammonia synthesis, for which we show how to calculate which catalyst will be the most effective under specific reagents conditions. PMID:18537227

  5. Chemical gas-dynamics beyond Wang Chang-Uhlenbeck's kinetics

    NASA Astrophysics Data System (ADS)

    Kolesnichenko, Evgeniy G.; Gorbachev, Yuriy E.

    2014-12-01

    Wang Chang-Uhlenbeck equation does not give possibility to take into account intermolecular processes such as redistribution of the energy among different degrees of freedom. The modification of the generalized Wang Chang-Uhlenbeck equation including such processes is proposed. It allows to study for instance the kinetics of non-radiative transitions. Limitations of this approach are connected with the requirements of absence of polarization of rotational momentum and phases of intermolecular vibrations.

  6. Chemical and kinetic factors related to hydrogen removal from aluminum

    Microsoft Academic Search

    G. K. Sigworth; T. A. Engh

    1982-01-01

    The available data on hydrogen solubility in aluminum are reviewed. Then a mathematical analysis of the kinetics of hydrogen\\u000a removal is presented. A rather complicated general equation for the hydrogen removal in batch reactors is shown to reduce\\u000a to more simple expressions for certain values of anew dimensionless group, ?\\/[pct H]. This “dimensionless hydrogen concentration”\\u000a can be understood to represent

  7. Chemical and kinetic factors related to hydrogen removal from aluminum

    Microsoft Academic Search

    G. K. Sigworth; T. A. Engh

    1991-01-01

    The available data on hydrogen solubility in aluminum are reviewed. Then a mathematical analysis of the kinetics of hydrogen removal is presented. A rather complicated general equation for the hydrogen removal in batch reactors is shown to reduce to more simple expressions for certain values of a new dimensionless group, psi\\/[pct H]. This ``dimensionless hydrogen concentration≓ can be understood to

  8. Selecting the optimum quasi-steady-state species for reduced chemical kinetic mechanisms using a genetic algorithm

    SciTech Connect

    Montgomery, Christopher J.; Yang, Chongguan [Reaction Engineering International, 77 West 200 South, Suite 210, Salt Lake City, UT 84101 (United States); Parkinson, Alan R. [Department of Mechanical Engineering, Brigham Young University, 270 Clyde Building, Provo, UT 84602 (United States); Chen, J.-Y. [Department of Mechanical Engineering, University of California-Berkeley, 6163 Etcheverry Hall, Berkeley, CA 94720 (United States)

    2006-01-01

    A genetic optimization algorithm has been applied to the selection of quasi-steady-state (QSS) species in reduced chemical kinetic mechanisms. The algorithm seeks to minimize the error between reduced and detailed chemistry for simple reactor calculations approximating conditions of interest for a computational fluid dynamics simulation. The genetic algorithm does not guarantee that the global optimum will be found, but much greater accuracy can be obtained than by choosing QSS species through a simple kinetic criterion or by human trial and error. The algorithm is demonstrated for methane-air combustion over a range of temperatures and stoichiometries and for homogeneous charge compression ignition engine combustion. The results are in excellent agreement with those predicted by the baseline mechanism. A factor of two reduction in the number of species was obtained for a skeletal mechanism that had already been greatly reduced from the parent detailed mechanism.

  9. Data quality in predictive toxicology: identification of chemical structures and calculation of chemical properties.

    PubMed Central

    Helma, C; Kramer, S; Pfahringer, B; Gottmann, E

    2000-01-01

    Every technique for toxicity prediction and for the detection of structure-activity relationships relies on the accurate estimation and representation of chemical and toxicologic properties. In this paper we discuss the potential sources of errors associated with the identification of compounds, the representation of their structures, and the calculation of chemical descriptors. It is based on a case study where machine learning techniques were applied to data from noncongeneric compounds and a complex toxicologic end point (carcinogenicity). We propose methods applicable to the routine quality control of large chemical datasets, but our main intention is to raise awareness about this topic and to open a discussion about quality assurance in predictive toxicology. The accuracy and reproducibility of toxicity data will be reported in another paper. PMID:11102292

  10. Chemical kinetic mechanism for the oxidation of paraffinic hydrocarbons needed for primary reference fuels

    SciTech Connect

    Westbrook, C.K.; Pitz, W.J.

    1993-03-01

    A detailed chemical kinetic reaction mechanism is described which simulates the oxidation of the primary reference fuels n-heptane and iso-octane. The high temperature subset of these mechanisms is identified, and the extensions to deal with low temperature conditions are also explained. The algorithms used to assign reaction rates to elementary steps in the reaction mechanism are described, and the means of identifying the different chemical species and the relevant reactions are outlined. Finally, we show how interested kinetic modeling researchers can obtain copies of this reaction mechanism.

  11. PDF calculations of turbulent nonpremixed flames of H[sub 2]/CO[sub 2] using reduced chemical mechanisms. [Probability Density Function

    SciTech Connect

    Taing, S.; Masri, A.R. (Univ. of Sydney (Australia). Dept. of Mechanical Engineering); Pope, S.B. (Cornell Univ., Ithaca, NY (United States). Sibley School of Mechanical and Aerospace Engineering)

    1993-10-01

    A three-step chemical kinetic scheme, reduced systematically from a more detailed mechanism is used to represent chemical reaction in the Monte Carlo calculations of the joint velocity-composition probability density function (PDF) for pilot-stabilized turbulent jet nonpremixed flames of H[sub 2]/CO[sub 2] fuel mixtures. Flames with a range of fuel jet velocities and hence varying degrees of finite rate chemical kinetic effects have been calculated. Three multidimensional look-up tables are generated for density, other dependent properties and the composition increments due to chemical reaction. Terms representing the effects of pressure fluctuations, mechanical dissipation, and scalar dissipation are modeled using an improved particle interaction model. Solutions are obtained on a Sun-Sparc1 station using 30,000 Monte Carlo particles for the low jet velocity flames and this number is increased to 50,000 at high jet velocities. The calculated mixing field compares well with experimental data and the calculated flame length is slightly shorter than the observed visible flame length. For the low- intermediate-velocity flames, the calculated temperature and mass fractions of the stable species agree reasonably well with instantaneous experimental data collected in similar flames. At high jet velocities, when the flames are close to blowoff and finite rate chemical kinetic effects are very significant, discrepancies occur between measurements and computations and blowoff jet velocity is underpredicted by about 20%.

  12. First-Principles-Based Development of Kinetic Mechanisms in Chemically Active Light-Emitting Nonthermal Plasmas and Gases

    NASA Astrophysics Data System (ADS)

    Astapenko, Valerie; Bagatur'yants, Alexander; Chernishova, Irina; Deminsky, Maxim; Eletskii, Alexander; Kirillov, Igor; Knizhnik, Andrei; Potapkin, Boris; Rykova, Elena; Umanskii, Stanislaw; Zaitsevskii, Andrei; Strelkova, Marina; Sukhanov, Leonid; Safonov, Andrei; Cotzas, George M.; Dean, Anthony; Michael, J. Darryl; Midha, Vikas; Smith, David J.; Sommerer, Timothy J.; Varatharajan, Bala; Tentner, Adrian

    2007-04-01

    Recent progress in several related research areas such as first-principles electronic-structure calculations of atoms and diatomic molecules, theory of elementary processes, kinetics, and numerical engineering, and also continued exponential growth in computational resources enhanced by recent advances in massively parallel computing have opened the possibility of directly designing kinetics mechanisms to describe chemical processes and light emission in such complex media as nonequilibrium plasmas and reacting gases. It is important that plasma and combustion kinetics can be described in the framework of this direct approach to a sufficiently high accuracy, which makes it an independent predictive research tool complementary to experimental techniques. This paper demonstrates the capabilities of the first-principles based approach to develop kinetic mechanisms. Two examples are discussed in detail: (1) the mechanism of hydrocarbon fuel combustion at high temperatures and (2) light emission in non-thermal glow discharge plasma of metal halides; special attention is paid to a comparison of the results obtained at every level of system description with the appropriate experimental data. In house software tools that can be used in such multilevel theoretical works are discussed as well.

  13. First-Principles-Based Development of Kinetic Mechanisms in Chemically Active Light-Emitting Nonthermal Plasmas and Gases

    SciTech Connect

    Astapenko, Valerie; Bagatur'yants, Alexander; Chernishova, Irina; Deminsky, Maxim; Eletskii, Alexander; Knizhnik, Andrei; Potapkin, Boris; Rykova, Elena; Umanskii, Stanislaw; Zaitsevskii, Andrei; Safonov, Andrei [Kinetics Technologies, Moscow (Russian Federation); Kirillov, Igor; Strelkova, Marina; Sukhanov, Leonid [RRC Kurchatov Institute, Moscow (Russian Federation); Cotzas, George M.; Dean, Anthony; Michael, J. Darryl; Midha, Vikas; Smith, David J.; Sommerer, Timothy J. [GE Global Research, Niskayuna, New York (United States)] (and others)

    2007-04-06

    Recent progress in several related research areas such as first-principles electronic-structure calculations of atoms and diatomic molecules, theory of elementary processes, kinetics, and numerical engineering, and also continued exponential growth in computational resources enhanced by recent advances in massively parallel computing have opened the possibility of directly designing kinetics mechanisms to describe chemical processes and light emission in such complex media as nonequilibrium plasmas and reacting gases. It is important that plasma and combustion kinetics can be described in the framework of this direct approach to a sufficiently high accuracy, which makes it an independent predictive research tool complementary to experimental techniques. This paper demonstrates the capabilities of the first-principles based approach to develop kinetic mechanisms. Two examples are discussed in detail: (1) the mechanism of hydrocarbon fuel combustion at high temperatures and (2) light emission in non-thermal glow discharge plasma of metal halides; special attention is paid to a comparison of the results obtained at every level of system description with the appropriate experimental data. In house software tools that can be used in such multilevel theoretical works are discussed as well.

  14. Detailed Chemical Kinetic Reaction Mechanism for Biodiesel Components Methyl Stearate and Methyl Oleate

    SciTech Connect

    Naik, C; Westbrook, C K; Herbinet, O; Pitz, W J; Mehl, M

    2010-01-22

    New chemical kinetic reaction mechanisms are developed for two of the five major components of biodiesel fuel, methyl stearate and methyl oleate. The mechanisms are produced using existing reaction classes and rules for reaction rates, with additional reaction classes to describe other reactions unique to methyl ester species. Mechanism capabilities were examined by computing fuel/air autoignition delay times and comparing the results with more conventional hydrocarbon fuels for which experimental results are available. Additional comparisons were carried out with measured results taken from jet-stirred reactor experiments for rapeseed methyl ester fuels. In both sets of computational tests, methyl oleate was found to be slightly less reactive than methyl stearate, and an explanation of this observation is made showing that the double bond in methyl oleate inhibits certain low temperature chain branching reaction pathways important in methyl stearate. The resulting detailed chemical kinetic reaction mechanism includes more approximately 3500 chemical species and more than 17,000 chemical reactions.

  15. KINETICS OF CHEMICAL WEATHERING IN B-HORIZON SPODOSOL FRACTION

    EPA Science Inventory

    Studies on a B horizon soil from Maine have been conducted to etermine the weathering rate dependence on hydrogen ion concentration in soil solution. Effects of soil concentration and solution chemistry on chemical weathering rate were also investigated. he studies used a laborat...

  16. Effect of humidity on deprotection kinetics in chemically amplified resists

    Microsoft Academic Search

    Sean D. Burns; David R. Medeiros; Heather F. Johnson; Gregory M. Wallraff; William D. Hinsberg; C. Grant Willson

    2002-01-01

    Water is known to play a key role in the solubility switching reaction of novolac-diazonaphthoquinone photoresists and certain chemically amplified resists. In order to quantitatively study these effects, an environmental chamber was built in which the % RH could be controlled while the extent of acid catalyzed deprotection was monitored during the post exposure bake by reflectance FTIR spectroscopy. The

  17. Recent Results in Quantum Chemical Kinetics from High Resolution Spectroscopy

    SciTech Connect

    Quack, Martin [ETH Zuerich, Physical Chemistry, Wolfgang-Pauli-Str. 10, CH-8093 Zurich (Switzerland)

    2007-12-26

    We outline the approach of our group to derive intramolecular kinetic primary processes from high resolution spectroscopy. We then review recent results on intramolecular vibrational redistribution (IVR) and on tunneling processes. Examples are the quantum dynamics of the C-H-chromophore in organic molecules, hydrogen bond dynamics in (HF){sub 2} and stereomutation dynamics in H{sub 2}O{sub 2} and related chiral molecules. We finally discuss the time scales for these and further processes which range from 10 fs to more than seconds in terms of successive symmetry breakings, leading to the question of nuclear spin symmetry and parity violation as well as the question of CPT symmetry.

  18. Infrared absorption spectroscopy and chemical kinetics of free radicals

    SciTech Connect

    Curl, R.F.; Glass, G.P.

    1992-04-01

    Propargyl radical has recently attracted interest because of its possible role in combustion and soot formation. At high temperatures it is not easily destroyed by dissociation nor by reaction with oxygen thus, it has been observed in significant concentrations in numerous pyrolysis and oxidation processes. During the last year, we have obtained the high resolution spectrum of the v{sub 1} acetylenic CH stretch of propargyl radical (HCCCH{sub 2}) near 3322 cm{sup {minus}1} using infrared laser kinetic spectroscopy at Doppler limited resolution. Propargyl is prepared by flash photolysis of propargyl bromide (or propargyl chloride) at 193 nm (ArFexcimer) and its transient infrared absorption probed by a cw color center laser. We are beginning to investigate the kinetics of propargyl radical. The decay of the radical after the flash appears to be second order. The fine structure transition of the Br atom is accessible and when monitored under the same conditions appears to exhibit a simple first order decay suggesting that the Br atom is reacting with precursor propargyl bromide. Ketenyl radicals were produced by 193 nm excimer laser photolysis of ketene and probed with a tunable diode laser operating at 2014 cm{sup {minus}1}. Under these conditions, any singlet methylene which may be formed should react with the precursor, ketene, at a rate fast enough to ensure its total removal from the photolysis cell within 1 {mu}s. In the presence of 2 to 8 Torr of O{sub 2}, the ketenyl radical was observed to decay exponentially with time constants that ranged fro 20 to 5 {mu}s.

  19. Kinetics and thermodynamics of chemical reactions in Li/SOCl2 cells

    NASA Technical Reports Server (NTRS)

    Hansen, Lee D.; Frank, Harvey

    1987-01-01

    Work is described that was designed to determine the kinetic constants necessary to extrapolate kinetic data on Li/SOCl2 cells over the temperature range from 25 to 75 C. A second objective was to characterize as far as possible the chemical reactions that occur in the cells since these reactions may be important in understanding the potential hazards of these cells. The kinetics of the corrosion processes in undischarged Li/SOCl2 cells were determined and separated according to their occurrence at the anode and cathode; the effects that switching the current on and off has on the corrosion reactions was determined; and the effects of discharge state on the kinetics of the corrosion process were found. A thermodynamic analysis of the current-producing reactions in the cell was done and is included.

  20. Reactions at Polymer Interfaces: Transitions from Chemical to Diffusion-Control and Mixed Order Kinetics

    E-print Network

    Ben O'Shaughnessy; Dimitrios Vavylonis

    1998-12-21

    We study reactions between end-functionalized chains at a polymer-polymer interface. For small chemical reactivities (the typical case) the number of diblocks formed, $R_t$, obeys 2nd order chemically controlled kinetics, $R_t \\sim t$, until interfacial saturation. For high reactivities (e.g. radicals) a transition occurs at short times to 2nd order diffusion-controlled kinetics, with $R_t \\sim t/\\ln t$ for unentangled chains while $t/\\ln t$ and $t^{1/2}$ regimes occur for entangled chains. Long time kinetics are 1st order and controlled by diffusion of the more dilute species to the interface: $R_t \\sim t^{1/4}$ for unentangled cases, while $R_t \\sim t^{1/4}$ and $t^{1/8}$ regimes arise for entangled systems. The final 1st order regime is governed by center of gravity diffusion, $R_t \\sim t^{1/2}$.

  1. The subtle business of model reduction for stochastic chemical kinetics.

    PubMed

    Gillespie, Dan T; Cao, Yang; Sanft, Kevin R; Petzold, Linda R

    2009-02-14

    This paper addresses the problem of simplifying chemical reaction networks by adroitly reducing the number of reaction channels and chemical species. The analysis adopts a discrete-stochastic point of view and focuses on the model reaction set S(1)<=>S(2)-->S(3), whose simplicity allows all the mathematics to be done exactly. The advantages and disadvantages of replacing this reaction set with a single S(3)-producing reaction are analyzed quantitatively using novel criteria for measuring simulation accuracy and simulation efficiency. It is shown that in all cases in which such a model reduction can be accomplished accurately and with a significant gain in simulation efficiency, a procedure called the slow-scale stochastic simulation algorithm provides a robust and theoretically transparent way of implementing the reduction. PMID:19222263

  2. The subtle business of model reduction for stochastic chemical kinetics

    PubMed Central

    Gillespie, Dan T.; Cao, Yang; Sanft, Kevin R.; Petzold, Linda R.

    2009-01-01

    This paper addresses the problem of simplifying chemical reaction networks by adroitly reducing the number of reaction channels and chemical species. The analysis adopts a discrete-stochastic point of view and focuses on the model reaction set S1?S2?S3, whose simplicity allows all the mathematics to be done exactly. The advantages and disadvantages of replacing this reaction set with a single S3-producing reaction are analyzed quantitatively using novel criteria for measuring simulation accuracy and simulation efficiency. It is shown that in all cases in which such a model reduction can be accomplished accurately and with a significant gain in simulation efficiency, a procedure called the slow-scale stochastic simulation algorithm provides a robust and theoretically transparent way of implementing the reduction. PMID:19222263

  3. INFLUENCE OF ORGANIC COSOLVENTS ON THE SORPTION KINETICS OF HYDROPHOBIC ORGANIC CHEMICALS

    EPA Science Inventory

    A quantitative examination of the kinetics of sorption of hydrophobic organic chemicals by soils from mixed solvents reveals that the reverse sorption rate constant (k2) increases log-linearly with increasing volume fraction of organic cosolvent (fc). This relationship was expec...

  4. A Sequential Fluid-mechanic Chemical-kinetic Model of Propane HCCI Combustion

    Microsoft Academic Search

    S M Aceves; D L Flowers; J Martinez-Frias; J R Smith; C Westbrook; W Pitz; R Dibble; J F Wright; W C Akinyemi; R P Hessel

    2000-01-01

    We have developed a methodology for predicting combustion and emissions in a Homogeneous Charge Compression Ignition (HCCI) Engine. This methodology combines a detailed fluid mechanics code with a detailed chemical kinetics code. Instead of directly linking the two codes, which would require an extremely long computational time, the methodology consists of first running the fluid mechanics code to obtain temperature

  5. Kinetic effect of Pd additions on the hydrogen uptake of chemically activated, ultramicroporous carbon

    SciTech Connect

    Bhat, Vinay V [ORNL; Contescu, Cristian I [ORNL; Gallego, Nidia C [ORNL

    2010-01-01

    The effect of mixing chemically-activated ultramicroporous carbon (UMC) with Pd nanopowder is investigated. Results show that Pd addition doubles the rate of hydrogen uptake, but does not enhance the hydrogen capacity or improve desorption kinetics. The effect of Pd on the rate of hydrogen adsorption supports the occurrence of the hydrogen spillover mechanism in the Pd - UMC system.

  6. The Database of Quantitative Cellular Signaling: management and analysis of chemical kinetic models of signaling networks

    Microsoft Academic Search

    Sudhir Sivakumaran; Sridhar Hariharaputran; Jyoti Mishra; Upinder S. Bhalla

    2003-01-01

    Motivation: Analysis of cellular signaling interactions is expected to pose an enormous informatics challenge, per- haps even larger than analyzing the genome. The complex networks arising from signaling processes are traditionally represented as block diagrams. A key step in the evolu- tion toward a more quantitative understanding of signal- ing is to explicitly specify the kinetics of all chemical reac-

  7. CHEM 350 -CHEMICAL KINETICS RCH 204, MWF 9:30 -10:20

    E-print Network

    Nazar, Linda F.

    the concentration, temperature and other dependences of a chemical reaction, and the subsequent formulation biochemically-relevant enzyme kinetics. The course will conclude with a brief foray into reaction dynamics of Temperature on Reaction Rates, Collision Theory, Transition State Theory (Sections 28.6 - 28.8 of M & S) Week

  8. Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels

    E-print Network

    Paris-Sud XI, Université de

    Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels C.K. Westbrooka and rapeseed biodiesel fuels. These components, methyl stearate, methyl oleate, methyl linoleate, methyl properties between the two biodiesel fuels, derived from soy and rapeseed oils, are traced to the differences

  9. A New Shock-Tube Facility for the Study of High-Temperature Chemical Kinetics 

    E-print Network

    Vivanco, Jose E

    2014-09-30

    A new stainless steel shock-tube facility designed for the study of chemical kinetics at elevated temperatures and pressures is described. It consists of a single-pulse shock tube capable of using both lexan diaphragms and die-scored aluminum disks...

  10. A RAPID COMPRESSION MACHINE FOR CHEMICAL KINETICS STUDIES AT ELEVATED PRESSURES AND TEMPERATURES

    Microsoft Academic Search

    GAURAV MITTAL; CHIH-JEN SUNG

    2007-01-01

    A rapid compression machine (RCM) has been designed and fabricated for the purpose of chemical kinetics studies at elevated pressures and temperatures. The present RCM is pneumatically driven and hydraulically actuated and stopped. Stroke of the machine varies from 7 to 10 inches and clearance is also adjustable. Compression ratio of up to 21 can be obtained. The optically-accessible reaction

  11. Combustion chemical kinetics of biodiesel and related compounds (methyl and ethyl esters): Experiments and

    E-print Network

    Paris-Sud XI, Université de

    1 Combustion chemical kinetics of biodiesel and related compounds (methyl and ethyl esters and reduced exhaust emissions have led to the emergence of new fuels and combustion devices. Over the past ten years, considerable effort has gone into understanding combustion phenomena in relation to emerging fuel

  12. Planarization mechanism of alkaline copper CMP slurry based on chemical mechanical kinetics

    NASA Astrophysics Data System (ADS)

    Shengli, Wang; Kangda, Yin; Xiang, Li; Hongwei, Yue; Yunling, Liu

    2013-08-01

    The planarization mechanism of alkaline copper slurry is studied in the chemical mechanical polishing (CMP) process from the perspective of chemical mechanical kinetics. Different from the international dominant acidic copper slurry, the copper slurry used in this research adopted the way of alkaline technology based on complexation. According to the passivation property of copper in alkaline conditions, the protection of copper film at the concave position on a copper pattern wafer surface can be achieved without the corrosion inhibitors such as benzotriazole (BTA), by which the problems caused by BTA can be avoided. Through the experiments and theories research, the chemical mechanical kinetics theory of copper removal in alkaline CMP conditions was proposed. Based on the chemical mechanical kinetics theory, the planarization mechanism of alkaline copper slurry was established. In alkaline CMP conditions, the complexation reaction between chelating agent and copper ions needs to break through the reaction barrier. The kinetic energy at the concave position should be lower than the complexation reaction barrier, which is the key to achieve planarization.

  13. 10.1098/rsta.2003.1364 Microfluidic systems for chemical kinetics

    E-print Network

    Ismagilov, Rustem F.

    10.1098/rsta.2003.1364 Microfluidic systems for chemical kinetics that rely on chaotic mixing-ismagilov@uchicago.edu) Published online 18 March 2004 This paper reviews work on a microfluidic system that relies on chaotic and straight sections, winding microfluidic channels create unsteady fluid flows that rapidly mix the multiple

  14. A New Shock-Tube Facility for the Study of High-Temperature Chemical Kinetics

    E-print Network

    Vivanco, Jose E

    2014-09-30

    A new stainless steel shock-tube facility designed for the study of chemical kinetics at elevated temperatures and pressures is described. It consists of a single-pulse shock tube capable of using both lexan diaphragms and die-scored aluminum disks...

  15. Degradation kinetics of glass-reinforced polyesters in chemical environments

    Microsoft Academic Search

    S. P. Sonawala; R. J. Spontak

    1996-01-01

    Glass-reinforced polyesters (GRPs) are attractive in structural applications due to their strength-to-weight ratio and resistance to chemical attack. For marine and processing applications, in particular, GRPs must withstand long-term exposure to brine and either highly acidic or basic aqueous solutions. In this work, we report on the degradation of two GRP laminates, a pultruded isophthalic polyester (IPE) and a hand-moulded

  16. Kinetics and chemical equilibrium of the hydration of formaldehyde

    Microsoft Academic Search

    J. G. M. Winkelman; O. K. Voorwinde; M. Ottens; A. A. C. M. BeenackersX; L. P. B. M. Janssen

    2002-01-01

    The reaction rate of the hydration of formaldehyde is obtained from the measured, chemically enhanced absorption rate of formaldehyde gas into water in a stirred cell with a plane gas–liquid interface, and mathematically modelling of the transfer processes. Experiments were performed at the conditions prevailing in industrial formaldehyde absorbers, i.e. at temperatures of 293–333K and at pH values between 5

  17. Kinetics of halide chemical vapor deposition of silicon carbide film

    Microsoft Academic Search

    Rong Wang; Ronghui Ma

    2007-01-01

    Halide chemical vapor deposition (HCVD) emerges as a promising method for growing thick silicon carbide (SiC) epilayers, due to its ability to deposit SiC film at a high growth rate. In this paper, we develop a comprehensive model for HCVD of SiC film using silicon tetrachloride and propane as precursors. The model includes gas flow, heat and mass transfer, gas-phase

  18. Kinetically constrained ring-polymer molecular dynamics for non-adiabatic chemical reactions.

    PubMed

    Menzeleev, Artur R; Bell, Franziska; Miller, Thomas F

    2014-02-14

    We extend ring-polymer molecular dynamics (RPMD) to allow for the direct simulation of general, electronically non-adiabatic chemical processes. The kinetically constrained (KC) RPMD method uses the imaginary-time path-integral representation in the set of nuclear coordinates and electronic states to provide continuous equations of motion that describe the quantized, electronically non-adiabatic dynamics of the system. KC-RPMD preserves the favorable properties of the usual RPMD formulation in the position representation, including rigorous detailed balance, time-reversal symmetry, and invariance of reaction rate calculations to the choice of dividing surface. However, the new method overcomes significant shortcomings of position-representation RPMD by enabling the description of non-adiabatic transitions between states associated with general, many-electron wavefunctions and by accurately describing deep-tunneling processes across asymmetric barriers. We demonstrate that KC-RPMD yields excellent numerical results for a range of model systems, including a simple avoided-crossing reaction and condensed-phase electron-transfer reactions across multiple regimes for the electronic coupling and thermodynamic driving force. PMID:24527896

  19. Long-term bioconcentration kinetics of hydrophobic chemicals in Selenastrum capricornutum and Microcystis aeruginosa

    SciTech Connect

    Koelmans, A.A.; Woude, H. van der; Hattink, J.; Niesten, D.J.M. (Wageningen Agricultural Univ. (Netherlands). Aquatic Ecology and Water Quality Management Group)

    1999-06-01

    The bioconcentration of two chlorobenzenes (CBs) and of seven polychlorobiphenyls (PCBs) to Selenastrum capricornutum and Microcystis aeruginosa was studied with accumulation experiments followed by gas purge elimination experiments. Henry's law constants at 10 C were needed to interpret the gas purge results and were measured in control experiments. For the M. aerogunisa culture, steady-state uptake was reached within days, whereas uptake by S. capricornutum took several weeks. The relationships between the log bioconcentration factors (BCF) and log octanol-water partition coefficients (K[sub OW]) were nonlinear, with relatively low values for the more hydrophobic PCBs. Rate constants for the elimination of CBs and PCBs from the algal cells were shown to be larger than 1 per day when calculated with a one-compartment model. With such large rate constants, it is unlikely that the curvature observed for these species is caused by slow kinetics or that algal growth affects BCF by dilution of CB or PCB concentrations. The log BCF-log K[sub OW] relationships could be described by a simple three-phase model that accounted for the binding of CBs and PCBs to dissolved organic carbon (DOC). Modeling bioconcentration of hydrophobic chemicals in phytoplankton should account for the binding to DOC.

  20. Thermochemical analysis and kinetics aspects for a chemical model for camphene ozonolysis.

    PubMed

    Oliveira, R C de M; Bauerfeldt, G F

    2012-10-01

    In this work, a chemical model for the camphene ozonolysis, leading to carbonyl final products, is proposed and discussed on the basis of the thermochemical properties and kinetic data obtained at density functional theory levels of calculation. The mechanism is initiated by the electrophilic attack of ozone to the double bond in camphene leading to a 1,2,3-trioxolane intermediate, which decomposes to peroxy radicals and carbonyl compounds in a total of 10 elementary reactions. The thermodynamic properties (enthalpy and entropies differences) are calculated at 298 K. For the thermochemical evaluation, theoretical calculations are performed with the B3LYP, MPW1PW91, and mPW1K density functionals and the basis sets 6-31G(d), 6-31G(2d,2p), 6-31+G(d,p), and 6-31+G(2d,2p). Eventually, single point calculations adopting the 6-311++G(2d,2p) basis set are performed in order to improve the electronic energies. The enthalpy profiles suggest highly exothermic reactions for the individual steps, with a global enthalpy difference of -179.18 kcal mol(-1), determined at the B3LYP?6-31+G(2d,2p) level. The Gibbs free energy differences for each step, at 298 K, calculated at the B3LYP?6-311++G(2d,2p)??B3LYP?6-31+G(2d,2p) level, are used to estimate the composition of a final product mixture under equilibrium conditions as 58% of camphenilone and 42% of 6,6-dimethyl-?-caprolactone-2,5-methylene. For the reaction kinetics, the bimolecular O(3) + camphene step is assumed to be rate determining in the global mechanism. A saddle point for the ozone addition to the double bond is located and rate constants are determined on the basis of the transition state theory. This saddle point is well represented by a loosely bound structure and corrections for the basis set superposition error (BSSE) are calculated, either by considering the effect over the geometry optimization procedure (here referred as CP1 procedure), or the effect of the BSSE over the electronic energy of a previously optimized geometry, included a posteriori (here referred as CP2). The rate constants, calculated at 298 K from the data obtained at the mPW1K?6-31+G(d,p), CP1?B3LYP??6-31+G(2d,2p), and CP2?B3LYP??6-31+G(2d,2p) levels (3.62 × 10(-18), 1.12 × 10(-18), and 1.39 × 10(-18) cm(3) molecule(-1) s(-1)), are found in good agreement with the available experimental data at the same temperature, 0.9 × 10(-18) cm(3) molecule(-1) s(-1) [R. Atkinson, S. M. Aschmann, and J. Arey, Atmos. Environ. 24, 2647 (1990)]. The importance of the BSSE corrections for the final rate constants must be pointed out. Furthermore, this work will contribute to a better understanding of the chemistry of monoterpenes in the atmosphere, as well as the implications for the phenomena of pollution. PMID:23039598

  1. Parallel Reacting Flow Calculations for Chemical Vapor Deposition Reactor Design 1

    E-print Network

    Devine, Karen

    Parallel Reacting Flow Calculations for Chemical Vapor Deposition Reactor Design 1 Andrew G Computer modeling of chemical vapor deposition (CVD) reactors can greatly aid in the understanding, design of Energy under contract no. DE­AC04­94AL85000. #12; Parallel Reacting Flow Calculations for Chemical Vapor

  2. Ab Initio Calculation of Nuclear Magnetic Resonance Chemical Shift Anisotropy Tensors 1. Influence of Basis Set on the Calculation of 31P Chemical Shifts

    SciTech Connect

    Alam, T.M.

    1998-09-01

    The influence of changes in the contracted Gaussian basis set used for ab initio calculations of nuclear magnetic resonance (NMR) phosphorous chemical shift anisotropy (CSA) tensors was investigated. The isotropic chemical shitl and chemical shift anisotropy were found to converge with increasing complexity of the basis set at the Hartree-Fock @IF) level. The addition of d polarization function on the phosphorous nucIei was found to have a major impact of the calculated chemical shi~ but diminished with increasing number of polarization fimctions. At least 2 d polarization fimctions are required for accurate calculations of the isotropic phosphorous chemical shift. The introduction of density fictional theory (DFT) techniques through tie use of hybrid B3LYP methods for the calculation of the phosphorous chemical shift tensor resulted in a poorer estimation of the NMR values, even though DFT techniques result in improved energy and force constant calculations. The convergence of the W parametem with increasing basis set complexity was also observed for the DFT calculations, but produced results with consistent large deviations from experiment. The use of a HF 6-31 l++G(242p) basis set represents a good compromise between accuracy of the simulation and the complexity of the calculation for future ab initio calculations of 31P NMR parameters in larger complexes.

  3. Structural and kinetic aspects of chemical reactions in DNA duplexes. Information on DNA local structure obtained from chemical ligation data.

    PubMed Central

    Dolinnaya, N G; Tsytovich, A V; Sergeev, V N; Oretskaya, T S; Shabarova, Z A

    1991-01-01

    Chemical ligation of oligonucleotides in double-stranded helices has been considered in its structural-kinetic aspect. A study was made of (i) two series of DNA duplexes with various arrangements of reacting groups in the ligation junction induced by mispairing or by alteration of furanose structure (the replacement of dT unit with rU, aU, IU, xU, dxT ones) and of (ii) eight synthetic water-soluble carbodiimides with different substituents at N1 and N3 atoms. We assumed that some information on the local structure of modified sites in the duplex can be obtained from kinetic parameters of oligonucleotide coupling reaction. The ratio of kinetic constants k3/(k2 + k3) for productive and nonproductive decomposition of the activated phosphomonoester derivative apparently reflects the reaction site structure: for a given duplex this parameter is virtually independent of the condensing agent composition. Based on the analysis of the chemical ligation kinetics a suggestion has been made about the conformation of some modified units in the double helix. Images PMID:2057363

  4. Effect of reactant size on discrete stochastic chemical kinetics.

    PubMed

    Gillespie, Dan T; Lampoudi, Sotiria; Petzold, Linda R

    2007-01-21

    This paper is aimed at understanding what happens to the propensity functions (rates) of bimolecular chemical reactions when the volume occupied by the reactant molecules is not negligible compared to the containing volume of the system. For simplicity our analysis focuses on a one-dimensional gas of N hard-rod molecules, each of length l. Assuming these molecules are distributed randomly and uniformly inside the real interval [0,L] in a nonoverlapping way, and that they have Maxwellian distributed velocities, the authors derive an expression for the probability that two rods will collide in the next infinitesimal time dt. This probability controls the rate of any chemical reaction whose occurrence is initiated by such a collision. The result turns out to be a simple generalization of the well-known result for the point molecule case l=0: the system volume L in the formula for the propensity function in the point molecule case gets replaced by the "free volume" L-Nl. They confirm the result in a series of one-dimensional molecular dynamics simulations. Some possible wider implications of this result are discussed. PMID:17249866

  5. Transport Properties of a Kinetic Model for Chemical Reactions without Barriers

    SciTech Connect

    Alves, Giselle M. [Escola Tecnica, Universidade Federal do Parana, Curitiba (Brazil); Kremer, Gilberto M. [Departamento de Fisica, Universidade Federal do Parana, Curitiba (Brazil); Soares, Ana Jacinta [Departamento de Matematica, Universidade do Minho, Braga (Portugal)

    2011-05-20

    A kinetic model of the Boltzmann equation for chemical reactions without energy barrier is considered here with the aim of evaluating the reaction rate and characterizing the transport coefficient of shear viscosity for the reactive system. The Chapman-Enskog solution of the Boltzmann equation is used to compute the chemical reaction effects, in a flow regime for which the reaction process is close to the final equilibrium state. Some numerical results are provided illustrating that the considered chemical reaction without energy barrier can induce an appreciable influence on the reaction rate and on the transport coefficient of shear viscosity.

  6. Nonequilibrium kinetic processes with chemical reactions and complex structures in open systems

    NASA Astrophysics Data System (ADS)

    Aristov, Vladimir; Frolova, Anna; Zabelok, Sergey

    2014-04-01

    The study of the nonequilibrium distributions in open systems with complex kinetic processes is performed. The nonuniform relaxation problems (NRP) are solved. Previous solutions of NRP have demonstrated nonclassical transfer properties in the relaxation zones for monatomic simple gases, for mixtures of simple gases and for molecular gases. In the present paper for the first time more complex structures for mixtures of four chemically reacting gases are investigated by means of kinetic model equations. Nonclassical effects are observed in simulations. It is discussed how this can allow us to simulate properties of complex nonequilibrium systems and, in particular, the role of the nonequilibrium entropy (-H-function) is also considered.

  7. DSMC Simulation of Entry Vehicle Flowfields Using a Collision-Based Chemical Kinetics Approach

    NASA Astrophysics Data System (ADS)

    Wilmoth, R. G.; VanGilder, D. B.; Papp, J. L.

    2011-05-01

    A study of high-altitude, nonequilibrium flows about an Orion Command Module (CM) is conducted using the collision-based chemical kinetics approach introduced by Bird in 2008. DSMC simulations are performed for Earth entry flow conditions and show significant differences in molecular dissociation in the shock layer from those obtained using traditional temperature-based procedures with an attendant reduction in the surface heat flux. Reaction rates derived from equilibrium simulations are also presented for selected reactions relevant to entry flow kinetics, and comparisons to various experimental and theoretical results are presented.

  8. Kinetic study of magnesium oxide/water chemical heat pump

    SciTech Connect

    Kato, Yukitaka; Inoue, Shinzo; Nanmoku, Wataru; Yoshizawa, Yoshio [Tokyo Inst. of Technology (Japan). Research Lab. for Nuclear Reactors

    1995-12-31

    A laboratory scale system of magnesium oxide/water chemical heat pump was designed for the heat output of 100W class, and the performance of the system was demonstrated. The fraction of magnesium oxide reacted and the heat output were measured directly and simultaneously in the experiment. The former was performed by measuring weight change with a load cell. The latter was measured with a heating tube installed in the reactor. It was shown that the system was able to store thermal energy at about 400 C and to supply thermal energy at 75--120 C, and that the thermal power exceeded 50--100W per 1 kilogram of initial magnesium hydroxide during the first 60 minutes. The profile of reaction rate and heat transfer in the reactor were simulated by two-dimensional numerical analysis. The results of the experiments and the simulations showed that the heat pump had enough thermal storage capacity and thermal power as a commercial system.

  9. Momentum or kinetic energy - How do substrate properties influence the calculation of rainfall erosivity?

    NASA Astrophysics Data System (ADS)

    Goebes, Philipp; Seitz, Steffen; Geißler, Christian; Lassu, Tamás; Peters, Piet; Seeger, Manuel; Nadrowski, Karin; Scholten, Thomas

    2014-09-01

    Rainfall erosivity is a key component in soil erosion by water. While kinetic energy and momentum are used to describe the erosivity of rainfall, and both are derived from mass and velocity of raindrops, it is not clear how different substrates transform this energy. In our study we conducted rainfall simulation experiments to determine splash detachment amounts of five substrates (coarse sand, medium sand, fine sand, PE balls, silt) for seven different rainfall intensities (52-116 mm h-1). We used linear mixed-effect modeling (LME) to calculate erosivity predictors for each substrate. Additionally, we separated drop-size-velocity relationship into lower left and upper right quarter to investigate the effect of small and slow just as big and fast raindrops on splash detachment amounts. We suggest using momentum divided by drop diameter as a substrate-independent erosivity predictor. To consider different substrates specific erosivity parameters are needed. Heavier substrates like sand are best described by kinetic energy multiplied by diameter whereas lighter substrates like silt point to momentum divided by diameter to the power of 1.5. Furthermore, our results show that substrates are differently affected by the size and velocity of drops. While splash detachment of light substances can be reliably predicted by drop size and velocity for small and slow drops, drop size and velocity loses its predictive power in heavier substrates like sand.

  10. Kinetics analysis and quantitative calculations for the successive radioactive decay process

    NASA Astrophysics Data System (ADS)

    Zhou, Zhiping; Yan, Deyue; Zhao, Yuliang; Chai, Zhifang

    2015-01-01

    The general radioactive decay kinetics equations with branching were developed and the analytical solutions were derived by Laplace transform method. The time dependence of all the nuclide concentrations can be easily obtained by applying the equations to any known radioactive decay series. Taking the example of thorium radioactive decay series, the concentration evolution over time of various nuclide members in the family has been given by the quantitative numerical calculations with a computer. The method can be applied to the quantitative prediction and analysis for the daughter nuclides in the successive decay with branching of the complicated radioactive processes, such as the natural radioactive decay series, nuclear reactor, nuclear waste disposal, nuclear spallation, synthesis and identification of superheavy nuclides, radioactive ion beam physics and chemistry, etc.

  11. Oxidation Kinetics of Chemically Vapor-Deposited Silicon Carbide in Wet Oxygen

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.

    1994-01-01

    The oxidation kinetics of chemically vapor-deposited SiC in dry oxygen and wet oxygen (P(sub H2O) = 0.1 atm) at temperatures between 1200 C and 1400 C were monitored using thermogravimetric analysis. It was found that in a clean environment, 10% water vapor enhanced the oxidation kinetics of SiC only very slightly compared to rates found in dry oxygen. Oxidation kinetics were examined in terms of the Deal and Grove model for oxidation of silicon. It was found that in an environment containing even small amounts of impurities, such as high-purity Al2O3 reaction tubes containing 200 ppm Na, water vapor enhanced the transport of these impurities to the oxidation sample. Oxidation rates increased under these conditions presumably because of the formation of less protective sodium alumino-silicate scales.

  12. Thermoreversible Associating Polymer Networks: I. Interplay of Thermodynamics, Chemical Kinetics, and Polymer Physics

    E-print Network

    Robert S. Hoy; Glenn H. Fredrickson

    2009-11-06

    Hybrid molecular dynamics/Monte Carlo simulations used to study melts of unentangled, thermoreversibly associating supramolecular polymers. In this first of a series of papers, we describe and validate a model that is effective in separating the effects of thermodynamics and chemical kinetics on the dynamics and mechanics of these systems, and is extensible to arbitrarily nonequilibrium situations and nonlinear mechanical properties. We examine the model's quiescent (and heterogeneous) dynamics, nonequilibrium chemical dynamics, and mechanical properties. Many of our results may be understood in terms of the crossover from diffusion-limited to kinetically-limited sticky bond recombination, which both influences and is influenced by polymer physics, i. e. the connectivity of the parent chains.

  13. Double-focusing mixing jet for XFEL study of chemical kinetics

    PubMed Central

    Wang, Dingjie; Weierstall, Uwe; Pollack, Lois; Spence, John

    2014-01-01

    Several liquid sample injection methods have been developed to satisfy the requirements for serial femtosecond X-ray nanocrystallography, which enables radiation-damage-free determination of molecular structure at room temperature. Time-resolved nanocrystallography would combine structure analysis with chemical kinetics by determining the structures of the transient states and chemical kinetic mechanisms simultaneously. A windowless liquid mixing jet device has been designed for this purpose. It achieves fast uniform mixing of substrates and enzymes in the jet within 250?µs, with an adjustable delay between mixing and probing by the X-ray free-electron laser beam of up to 1?s for each frame of a ‘movie’. The principle of the liquid mixing jet device is illustrated using numerical simulation, and experimental results are presented using a fluorescent dye. PMID:25343806

  14. Double-focusing mixing jet for XFEL study of chemical kinetics.

    PubMed

    Wang, Dingjie; Weierstall, Uwe; Pollack, Lois; Spence, John

    2014-11-01

    Several liquid sample injection methods have been developed to satisfy the requirements for serial femtosecond X-ray nanocrystallography, which enables radiation-damage-free determination of molecular structure at room temperature. Time-resolved nanocrystallography would combine structure analysis with chemical kinetics by determining the structures of the transient states and chemical kinetic mechanisms simultaneously. A windowless liquid mixing jet device has been designed for this purpose. It achieves fast uniform mixing of substrates and enzymes in the jet within 250?µs, with an adjustable delay between mixing and probing by the X-ray free-electron laser beam of up to 1?s for each frame of a `movie'. The principle of the liquid mixing jet device is illustrated using numerical simulation, and experimental results are presented using a fluorescent dye. PMID:25343806

  15. Modelling transport and degradation of de-icing chemicals in soil, assuming Monod kinetics with multiple electron-acceptors

    NASA Astrophysics Data System (ADS)

    Schotanus, D.; Meeussen, J. C. L.; van der Ploeg, M. J.; van der Zee, S. E. A. T. M.

    2012-04-01

    De-icing chemicals that contain propylene glycol are used at Oslo airport during winter time. A fraction of these chemicals is spilled on the runway and can be transported rapidly in the sandy soil in spring during snowmelt. Better insight into the chemical and physical processes that govern the fate of these chemicals in soil will help to estimate potential effects on the large unconfined aquifer in this area, and makes it possible to evaluate potential remedial actions. Micro-organisms in the soil can degrade propylene glycol, for which they need electron-acceptors. Under aerobic conditions, oxygen will be used as an electron-acceptor. From experiments, it is known that also anaerobic degradation occurs in this soil. During snowmelt, high infiltration rates can lead to locally saturated soil. In these parts, oxygen diffusion is limited and thus anaerobic conditions will occur. In these anaerobic regions, other electron-acceptors, such as manganese-oxides that are present in this soil, are used. However, frequent propylene glycol application may lead to a depletion of manganese-oxides and so to increased persistence and migration of propylene glycol in soil. To prevent this depletion and to enhance biodegradation, other electron-acceptors can be applied at the soil surface. Examples are the application of nitrate to the soil surface, and air injection. Model calculations could help to estimate required concentrations. The objectives of this study are 1) to create the reactive model, 2) to use this model to evaluate which parameters are determining leaching fluxes of propylene glycol from the soil, and 3) to evaluate the effectiveness of the different remediation strategies. Therefore, transient water flow, kinetic degradation, and redox chemistry were combined in one model. Degradation is modelled with Monod kinetics using multiple electron-acceptors. Oxygen diffusion in the gas phase, biomass growth, and oxidation and reduction of the important electron-acceptors are included.

  16. Coupling between chemical kinetics and mechanics that is both nonlinear and compatible with thermodynamics.

    PubMed

    Klika, Václav; Grmela, Miroslav

    2013-01-01

    Motivated by biological applications (e.g., bone tissue development and regeneration) we investigate coupling between mesoscopic mechanics and chemical kinetics. Governing equations of both dynamical systems are first written in a form expressing manifestly their compatibility with microscopic mechanics and thermodynamics. The same form is then required from governing equations of the coupled dynamics. The main result of the paper is an admissible form of the coupled dynamics. PMID:23410317

  17. Heat Diffusion and Chemical Kinetics in Mark-III FEL Tissue Ablation

    Microsoft Academic Search

    Glenn S. Edwards; M. Shane Hutson; Susanne Hauger

    We present in some detail a theoretical model that provides a dynamical account for the experimentally observed ablative properties of an FEL tuned near 6.45 microns. The model is based on thermal diffusion and chemical kinetics in a system of alternating layers of protein and saline as heated by an infrared Mark-III FEL. We compare exposure at 3.0 microns, where

  18. Role of Thermal Diffusion and Chemical Kinetics in Infrared Tissue Ablation

    Microsoft Academic Search

    Glenn Edwards; M. Shane Hutson

    2003-01-01

    We have theoretically investigated the role of dynamic processes, specifically thermal diffusion and chemical kinetics, to account for experimental observations of the preferential ablative properties of infrared radiation from a tunable Mark-III free-electron laser (FEL). The model is based on a laminar system composed of alternating layers of protein and saline. The picosecond pulses of the Mark-III superpulse are teated

  19. Heat diffusion and chemical kinetics in Mark-III FEL tissue ablation

    Microsoft Academic Search

    Glenn S. Edwards; M. Shane Hutson; Susanne Hauger

    2002-01-01

    We present in some detail a theoretical model that provides a dynamical account for the experimentally observed ablative properties of an FEL tuned near 6.45 microns. The model is based on thermal diffusion and chemical kinetics in a system of alternating layers of protein and saline as heated by an infrared Mark-III FEL. We compare exposure at 3.0 microns, where

  20. In situ measurements and modeling of carbon nanotube array growth kinetics during chemical vapor deposition

    Microsoft Academic Search

    Alexander A Puretzky; David B Geohegan; Stephen Jesse; Ilia N Ivanov; Gyula Eres

    2005-01-01

    Direct measurements of carbon nanotube growth kinetics are described based upon time-resolved reflectivity (TRR) of a HeNe laser beam from vertically aligned nanotube arrays (VANTAs) as they grow during chemical vapor deposition (CVD). Growth rates and terminal lengths were measured in situ for VANTAs growing during CVD between 535 °C and 900 °C on Si substrates with evaporated Al\\/Fe\\/Mo multi-layered catalysts and

  1. Quantum-chemical evaluation of energy quantities governing electron transfer kinetics: applications to intramolecular processes

    Microsoft Academic Search

    M. V. Basilevsky; G. E. Chudinov; I. V. Rostov; Yi-Ping Liu; M. D. Newton

    1996-01-01

    Important energy quantities governing electron transfer (ET) kinetics in polar solutions (reorganization energy, Er, and net free energy change, ?U) are evaluated on the basis of quantum-chemical self-consistent reaction-field (SCRF) models. Either self-consistent field (SCF) or configuration interaction (CI) wavefunctions are used for the solute, which occupies a molecular cavity of realistic shape in a dielectric continuum. A classical SCRF

  2. Kinetic study of the hydration of magnesium oxide for a chemical heat pump

    Microsoft Academic Search

    Yukitaka Kato; Norimichi Yamashita; Kei Kobayashi; Yoshio Yoshizawa

    1996-01-01

    A kinetic study of the hydration of magnesium oxide was performed to test the possibility of developing a magnesium oxide\\/water chemical heat pump. The hydration rate of magnesium oxide was measured by a gravimetric analysis with a sample of average particle size 10 ?m for the reaction temperature 373–423 K and the reaction vapor pressure 12.3–47.4 kPa. It was a

  3. Coupling between chemical kinetics and mechanics that is both nonlinear and compatible with thermodynamics

    NASA Astrophysics Data System (ADS)

    Klika, Václav; Grmela, Miroslav

    2013-01-01

    Motivated by biological applications (e.g., bone tissue development and regeneration) we investigate coupling between mesoscopic mechanics and chemical kinetics. Governing equations of both dynamical systems are first written in a form expressing manifestly their compatibility with microscopic mechanics and thermodynamics. The same form is then required from governing equations of the coupled dynamics. The main result of the paper is an admissible form of the coupled dynamics.

  4. High-Temperature Kinetics of AlCl3 Decomposition in the Presence of Additives for Chemical Vapor Deposition

    E-print Network

    Swihart, Mark T.

    the chemical vapor deposition CVD of alumina from AlCl3 /CO2 /H2 mixtures. The purpose is to answer whether-phase combustion synthesis of particles and for chemical vapor deposition CVD of films and coatings. DependingHigh-Temperature Kinetics of AlCl3 Decomposition in the Presence of Additives for Chemical Vapor

  5. Reduced and simplified chemical kinetics for air dissociation using Computational Singular Perturbation

    NASA Technical Reports Server (NTRS)

    Goussis, D. A.; Lam, S. H.; Gnoffo, P. A.

    1990-01-01

    The Computational Singular Perturbation CSP methods is employed (1) in the modeling of a homogeneous isothermal reacting system and (2) in the numerical simulation of the chemical reactions in a hypersonic flowfield. Reduced and simplified mechanisms are constructed. The solutions obtained on the basis of these approximate mechanisms are shown to be in very good agreement with the exact solution based on the full mechanism. Physically meaningful approximations are derived. It is demonstrated that the deduction of these approximations from CSP is independent of the complexity of the problem and requires no intuition or experience in chemical kinetics.

  6. Kinetics of Heterogeneous Chemical Reactions: A Theoretical Model for the Accumulation of Pesticides in Soil

    PubMed Central

    Lin, S. H.; Sahai, R.; Eyring, H.

    1971-01-01

    A theoretical model for the accumulation of pesticides in soil has been proposed and discussed from the viewpoint of heterogeneous reaction kinetics with a basic aim to understand the complex nature of soil processes relating to the environmental pollution. In the bulk of soil, the pesticide disappears by diffusion and a chemical reaction; the rate processes considered on the surface of soil are diffusion, chemical reaction, vaporization, and regular pesticide application. The differential equations involved have been solved analytically by the Laplace-transform method. PMID:5279519

  7. A weak second order tau-leaping method for chemical kinetic systems

    NASA Astrophysics Data System (ADS)

    Hu, Yucheng; Li, Tiejun; Min, Bin

    2011-07-01

    Recently Anderson and Mattingly [Comm. Math. Sci. 9, 301 (2011)] proposed a method which can solve chemical Langevin equations with weak second order accuracy. We extend their work to the discrete chemical jump processes. With slight modification, the method can also solve discrete chemical kinetic systems with weak second order accuracy in the large volume scaling. Especially, this method achieves higher order accuracy than both the Euler ?-leaping and mid-point ?-leaping methods in the sense that the local truncation error for the covariance is of order ?3V-1 when ? = V-? (0 < ? < 1) and the system size V ? ?. We present the convergence analysis, numerical stability analysis, and numerical examples. Overall, in the authors' opinion, the new method is easy to be implemented and good in performance, which is a good candidate among the highly accurate ?-leaping type schemes for discrete chemical reaction systems.

  8. Parameter estimation in stochastic chemical kinetic models using derivative free optimization and bootstrapping

    PubMed Central

    Srivastava, Rishi; Rawlings, James B.

    2014-01-01

    Recent years have seen increasing popularity of stochastic chemical kinetic models due to their ability to explain and model several critical biological phenomena. Several developments in high resolution fluorescence microscopy have enabled researchers to obtain protein and mRNA data on the single cell level. The availability of these data along with the knowledge that the system is governed by a stochastic chemical kinetic model leads to the problem of parameter estimation. This paper develops a new method of parameter estimation for stochastic chemical kinetic models. There are three components of the new method. First, we propose a new expression for likelihood of the experimental data. Second, we use sample path optimization along with UOBYQA-Fit, a variant of of Powell’s unconstrained optimization by quadratic approximation, for optimization. Third, we use a variant of Efron’s percentile bootstrapping method to estimate the confidence regions for the parameter estimates. We apply the parameter estimation method in an RNA dynamics model of E. coli. We test the parameter estimates obtained and the confidence regions in this model. The testing of the parameter estimation method demonstrates the efficiency, reliability, and accuracy of the new method. PMID:24920866

  9. Reactive properties of chemically modified Pd(100) surface revealed by Kinetic Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Alfonso, Dominic

    2009-03-01

    The interaction of H2 and CO with sulfur-covered Pd(100) surface represents a prototype model for understanding the various reasons for the poisoning of palladium by sulfur compounds. The use of Kinetic Monte Carlo method to investigate this system was explored. A Kinetic Monte Carlo code was developed and used to monitor the hosts of competing elementary steps associated with the adsorption, diffusion and desorption of H2 and CO on the metal surface. The input parameters such as rate of reactions and lateral interactions were obtained from density functional theory calculations within the generalized gradient approximation. We demonstrate that Kinetic Monte Carlo simulation is a powerful tool for elucidating the microscopic details of the behavior of H2 and CO on the poisoned surface.

  10. CH?NH? + O? and CH?CHNH? + O? reaction kinetics: photoionization mass spectrometry experiments and master equation calculations.

    PubMed

    Rissanen, Matti P; Eskola, Arkke J; Nguyen, Thanh Lam; Barker, John R; Liu, Jingjing; Liu, Jingyao; Halme, Erkki; Timonen, Raimo S

    2014-03-27

    Two carbon centered amino radical (CH2NH2 and CH3CHNH2) reactions with O2 were scrutinized by means of laboratory gas kinetics experiments together with quantum chemical computations and master equation modeling. In the experiments, laser photolysis of alkylamine compounds at 193 nm was used for the radical production and photoionization mass spectrometry was employed for the time-resolved detection of the reactants and products. The investigations were performed in a tubular, uncoated borosilicate glass flow reactor. The rate coefficients obtained were high, ranging from 2.4 × 10(-11) to 3.5 × 10(-11) cm(3) molecule(-1) s(-1) in the CH2NH2 + O2 reaction and from 5.5 × 10(-11) to 7.5 × 10(-11) cm(3) molecule(-1) s(-1) in the CH3CHNH2 + O2 reaction, showed negative temperature dependence with no dependence on the helium bath gas pressure (0.5 to 2.5 Torr He). The measured rate coefficients can be expressed as a function of temperature with: k(CH2NH2 + O2) = (2.89 ± 0.13) × 10(-11) (T/300 K)(-(1.10±0.47)) cm(3) molecule(-1) s(-1) (267-363 K) and k(CH3CHNH2 + O2) = (5.92 ± 0.23) × 10(-11) (T/300 K)(-(0.50±0.42)) cm(3) molecule(-1) s(-1) (241-363 K). The reaction paths and mechanisms were characterized using quantum chemical calculations and master equation modeling. Master equation computations, constrained by experimental kinetic results, were employed to model pressure-dependencies of the reactions. The constrained modeling results reproduce the experimentally observed negative temperature dependence and the dominant CH2NH imine production in the CH2NH2 + O2 reaction at the low pressures of the present laboratory investigation. In the CH3CHNH2 + O2 reaction, similar qualitative behavior was observed both in the rate coefficients and in the product formation, although the fine details of the mechanism were observed to change according to the different energetics in this system. In conclusion, the constrained modeling results predict significant imine + HO2 production for both reactions even at atmospheric pressure. PMID:24592923

  11. Chemical Kinetic Reaction Mechanisms for Combustion of Hydrocarbon and Other Types of Chemical Fuels

    DOE Data Explorer

    Reaction mechanisms have been tested and validated extensively through comparisons between computed results and measured data from laboratory experiments (e.g., shock tubes, laminar flames, rapid compression machines, flow reactors, stirred reactors) and from practical systems (e.g., diesel engines, spark-ignition engines, homogeneous charge, compression ignition (HCCI) engines). These kinetic models are used to examine a wide range of combustion systems.

  12. Enhanced identification and exploitation of time scales for model reduction in stochastic chemical kinetics

    PubMed Central

    Gómez-Uribe, Carlos A.; Verghese, George C.; Tzafriri, Abraham R.

    2008-01-01

    Widely different time scales are common in systems of chemical reactions and can be exploited to obtain reduced models applicable to the time scales of interest. These reduced models enable more efficient computation and simplify analysis. A classic example is the irreversible enzymatic reaction, for which separation of time scales in a deterministic mass action kinetics model results in approximate rate laws for the slow dynamics, such as that of Michaelis–Menten. Recently, several methods have been developed for separation of slow and fast time scales in chemical master equation (CME) descriptions of stochastic chemical kinetics, yielding separate reduced CMEs for the slow variables and the fast variables. The paper begins by systematizing the preliminary step of identifying slow and fast variables in a chemical system from a specification of the slow and fast reactions in the system. The authors then present an enhanced time-scale-separation method that can extend the validity and improve the accuracy of existing methods by better accounting for slow reactions when equilibrating the fast subsystem. The resulting method is particularly accurate in systems such as enzymatic and protein interaction networks, where the rates of the slow reactions that modify the slow variables are not a function of the slow variables. The authors apply their methodology to the case of an irreversible enzymatic reaction and show that the resulting improvements in accuracy and validity are analogous to those obtained in the deterministic case by using the total quasi-steady-state approximation rather than the classical Michaelis–Menten. The other main contribution of this paper is to show how mass fluctuation kinetics models, which give approximate evolution equations for the means, variances, and covariances of the concentrations in a chemical system, can feed into time-scale-separation methods at a variety of stages. PMID:19123500

  13. Kinetics of intramolecular chemical exchange by initial growth rates of spin saturation transfer difference experiments (SSTD NMR).

    PubMed

    Quirós, M Teresa; Angulo, Jesús; Muñoz, María Paz

    2015-06-25

    We report here the Initial Growth Rates SSTD NMR method, as a new powerful tool to obtain the kinetic parameters of intramolecular chemical exchange in challenging small organic and organometallic molecules. PMID:26022614

  14. Chemical and Biochemical Engineering 441 (14:155:441) Chemical Engineering Kinetics

    E-print Network

    Muzzio, Fernando J.

    ) of your own hand-written notes for quizzes. All backpacks, cellphones, calculators, textbooks, notebooks, problem sets etc. must be left against the wall in the front of the classroom. Write your name on the page, calculators, textbooks, notebooks, problem sets etc. must be left against the wall in the front

  15. First principles calculations in iron: structure and mobility of defect clusters and defect complexes for kinetic modelling

    Microsoft Academic Search

    Chu Chun Fu; F. Willaime

    2008-01-01

    Predictive simulations of the defect population evolution in materials under or after irradiation can be performed in a multi-scale approach, where the atomistic properties of defects are determined by electronic structure calculations based on the Density Functional Theory and used as input for kinetic simulations covering macroscopic time and length scales. Recent advances obtained in iron are presented. The determination

  16. Calculation of chemical and phase equilibria via simulated annealing

    Microsoft Academic Search

    David Reynolds; Anthony J. Mulholland; Jagannathan Gomatam

    1997-01-01

    We present a new class of techniques for the solution of the chemical and phase equilibria problem for reacting species in\\u000a a closed system. The minimisation of the Gibbs free energy for all the species in the system is conducted using the technique\\u000a of simulated annealing (SA). The SA objective function incorporates non?ideal equations of state. This new approach is

  17. Heat diffusion and chemical kinetics in Mark-III FEL tissue ablation

    NASA Astrophysics Data System (ADS)

    Edwards, Glenn S.; Hutson, M. Shane; Hauger, Susanne

    2002-04-01

    We present in some detail a theoretical model that provides a dynamical account for the experimentally observed ablative properties of an FEL tuned near 6.45 microns. The model is based on thermal diffusion and chemical kinetics in a system of alternating layers of protein and saline as heated by an infrared Mark-III FEL. We compare exposure at 3.0 microns, where water is the sole absorber, to that at 6.45 microns, where both protein and water absorb. The picosecond pulses of the Mark-III superpulse are treated as a train of impulses. We consider the onset of both the helix-coil transition and chemical bond breaking in terms of the thermal, chemical, and mechanical properties of the system as well as laser wavelength and pulse structure.

  18. Detailed chemical kinetic mechanism for the oxidation of biodiesel fuels blend surrogate

    SciTech Connect

    Herbinet, Olivier [Lawrence Livermore National Laboratory, CA 94550 (United States); Departement de Chimie Physique des Reactions, UMR 7630 CNRS, Nancy Universite-ENSIC, 1 rue Grandville, 54000 Nancy (France); Pitz, William J.; Westbrook, Charles K. [Lawrence Livermore National Laboratory, CA 94550 (United States)

    2010-05-15

    Detailed chemical kinetic mechanisms were developed and used to study the oxidation of two large unsaturated esters: methyl-5-decenoate and methyl-9-decenoate. These models were built from a previous methyl decanoate mechanism and were compared with rapeseed oil methyl esters oxidation experiments in a jet-stirred reactor. A comparative study of the reactivity of these three oxygenated compounds was performed and the differences in the distribution of the products of the reaction were highlighted showing the influence of the presence and the position of a double bond in the chain. Blend surrogates, containing methyl decanoate, methyl-5-decenoate, methyl-9-decenoate and n-alkanes, were tested against rapeseed oil methyl esters and methyl palmitate/n-decane experiments. These surrogate models are realistic kinetic tools allowing the study of the combustion of biodiesel fuels in diesel and homogeneous charge compression ignition engines. (author)

  19. Tuning kinetics to control droplet shapes on chemically striped patterned surfaces.

    PubMed

    Jansen, H Patrick; Sotthewes, Kai; Ganser, Christian; Teichert, Christian; Zandvliet, Harold J W; Kooij, E Stefan

    2012-09-18

    The typically elongated shape of droplets on chemically microstriped surfaces has been suggested to depend strongly on the kinetics during deposition. Here, we unequivocally establish the importance of impact kinetics by comparing the geometry of pico- to microliter droplets deposited from an inkjet nozzle with those obtained by conventional deposition from a syringe. For large Weber numbers, the strongly enhanced spreading during the impact in combination with direction-dependent pinning of the contact line gives rise to more spherical droplets with a low aspect ratio. The impact energy can be minimized by the prolonged firing of small picoliter droplets to form larger droplets or, as shown in the past, by using high-viscosity liquids. In the first case, the impact energy is absorbed by the liquid already present, therewith reducing the impact diameter and consequently forming markedly more elongated droplets. PMID:22954443

  20. Detailed chemical kinetic mechanism for the oxidation of biodiesel fuels blend surrogate.

    SciTech Connect

    Herbinet, O; Pitz, W J; Westbrook, C K

    2009-07-21

    Detailed chemical kinetic mechanisms were developed and used to study the oxidation of two large unsaturated esters: methyl-5-decenoate and methyl-9-decenoate. These models were built from a previous methyl decanoate mechanism and were compared with rapeseed oil methyl esters oxidation experiments in a jet stirred reactor. A comparative study of the reactivity of these three oxygenated compounds was performed and the differences in the distribution of the products of the reaction were highlighted showing the influence of the presence and the position of a double bond in the chain. Blend surrogates, containing methyl decanoate, methyl-5-decenoate, methyl-9-decenoate and n-alkanes, were tested against rapeseed oil methyl esters and methyl palmitate/n-decane experiments. These surrogate models are realistic kinetic tools allowing the study of the combustion of biodiesel fuels in diesel and homogeneous charge compression ignition engines.

  1. Chemical Kinetic Simulation of the Combustion of Bio-based Fuels

    SciTech Connect

    Ashen, Ms. Refuyat [Oak Ridge High School; Cushman, Ms. Katherine C. [Oak Ridge High School

    2007-10-01

    Due to environmental and economic issues, there has been an increased interest in the use of alternative fuels. However, before widespread use of biofuels is feasible, the compatibility of these fuels with specific engines needs to be examined. More accurate models of the chemical combustion of alternative fuels in Homogeneous Charge Compression Ignition (HCCI) engines are necessary, and this project evaluates the performance of emissions models and uses the information gathered to study the chemical kinetics involved. The computer simulations for each alternative fuel were executed using the Chemkin chemical kinetics program, and results from the runs were compared with data gathered from an actual engine that was run under similar conditions. A new heat transfer mechanism was added to the existing model's subroutine, and simulations were then conducted using the heat transfer mechanism. Results from the simulation proved to be accurate when compared with the data taken from the actual engine. The addition of heat transfer produced more realistic temperature and pressure data for biodiesel when biodiesel's combustion was simulated in an HCCI engine. The addition of the heat transfer mechanism essentially lowered the peak pressures and peak temperatures during combustion of all fuels simulated in this project.

  2. Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics.

    PubMed

    Bazant, Martin Z

    2013-05-21

    Advances in the fields of catalysis and electrochemical energy conversion often involve nanoparticles, which can have kinetics surprisingly different from the bulk material. Classical theories of chemical kinetics assume independent reactions in dilute solutions, whose rates are determined by mean concentrations. In condensed matter, strong interactions alter chemical activities and create variations that can dramatically affect the reaction rate. The extreme case is that of a reaction coupled to a phase transformation, whose kinetics must depend not only on the order parameter but also on its gradients at phase boundaries. Reaction-driven phase transformations are common in electrochemistry, when charge transfer is accompanied by ion intercalation or deposition in a solid phase. Examples abound in Li-ion, metal-air, and lead-acid batteries, as well as metal electrodeposition-dissolution. Despite complex thermodynamics, however, the standard kinetic model is the Butler-Volmer equation, based on a dilute solution approximation. The Marcus theory of charge transfer likewise considers isolated reactants and neglects elastic stress, configurational entropy, and other nonidealities in condensed phases. The limitations of existing theories recently became apparent for the Li-ion battery material LixFePO4 (LFP). It has a strong tendency to separate into Li-rich and Li-poor solid phases, which scientists believe limits its performance. Chemists first modeled phase separation in LFP as an isotropic "shrinking core" within each particle, but experiments later revealed striped phase boundaries on the active crystal facet. This raised the question: What is the reaction rate at a surface undergoing a phase transformation? Meanwhile, dramatic rate enhancement was attained with LFP nanoparticles, and classical battery models could not predict the roles of phase separation and surface modification. In this Account, I present a general theory of chemical kinetics, developed over the past 7 years, which is capable of answering these questions. The reaction rate is a nonlinear function of the thermodynamic driving force, the free energy of reaction, expressed in terms of variational chemical potentials. The theory unifies and extends the Cahn-Hilliard and Allen-Cahn equations through a master equation for nonequilibrium chemical thermodynamics. For electrochemistry, I have also generalized both Marcus and Butler-Volmer kinetics for concentrated solutions and ionic solids. This new theory provides a quantitative description of LFP phase behavior. Concentration gradients and elastic coherency strain enhance the intercalation rate. At low currents, the charge-transfer rate is focused on exposed phase boundaries, which propagate as "intercalation waves", nucleated by surface wetting. Unexpectedly, homogeneous reactions are favored above a critical current and below a critical size, which helps to explain the rate capability of LFP nanoparticles. Contrary to other mechanisms, elevated temperatures and currents may enhance battery performance and lifetime by suppressing phase separation. The theory has also been extended to porous electrodes and could be used for battery engineering with multiphase active materials. More broadly, the theory describes nonequilibrium chemical systems at mesoscopic length and time scales, beyond the reach of molecular simulations and bulk continuum models. The reaction rate is consistently defined for inhomogeneous, nonequilibrium states, for example, with phase separation, large electric fields, or mechanical stresses. This research is also potentially applicable to fluid extraction from nanoporous solids, pattern formation in electrophoretic deposition, and electrochemical dynamics in biological cells. PMID:23520980

  3. Solidphase crystallization kinetics in doped aSi chemical-vapor-deposition films

    Microsoft Academic Search

    R. Bisaro; J. Magario; K. Zellama; S. Squelard; P. Germain; J. F. Morhange

    1985-01-01

    Solid-phase crystallization kinetics of undoped, phosphorus-doped (0<[PH3]\\/[SiH4]<2×1 0-3), and boron-doped (0<[B2H6]\\/[SiH4 ]<2×10-3) amorphous silicon films prepared by chemical-vapor deposition (CVD) of silane have been studied with use of conductivity measurements. The crystallization growth rates (Vg) and their activation energies (Ev) are obtained during isothermal annealings in a large temperature range (510

  4. Reaction Kinetics and Catalysis Letters, Vol. 1, No. 2/1974/209-213 STOCHASTIC SIMULATION OF CHEMICAL REACTIONS BY

    E-print Network

    Tóth, János

    OF CHEMICAL REACTIONS BY DIGITAL COMPUTER, H. APPLICATIONS T. Sipos1, J.TSth 2 and P. ~.rdi1 1. Danube Oil chemical reactions (especially those of biological interest, e.g. reactions exhibiting oscillationReaction Kinetics and Catalysis Letters, Vol. 1, No. 2/1974/209-213 STOCHASTIC SIMULATION

  5. An Alternative Treatment of Trace Chemical Constituents in Calculated Chemical Source Terms for Hanford Tank Farms Safety Analsyes

    SciTech Connect

    Huckaby, James L.

    2006-09-26

    Hanford Site high-level radioactive waste tank accident analyses require chemical waste toxicity source terms to assess potential accident consequences. Recent reviews of the current methodology used to generate source terms and the need to periodically update the sources terms has brought scrutiny to the manner in which trace waste constituents are included in the source terms. This report examines the importance of trace constituents to the chemical waste source terms, which are calculated as sums of fractions (SOFs), and recommends three changes to the manner in which trace constituents are included in the calculation SOFs.

  6. Physically consistent simulation of mesoscale chemical kinetics: The non-negative FIS-{alpha} method

    SciTech Connect

    Dana, Saswati, E-mail: saswatid@rishi.serc.iisc.ernet.in [Supercomputer Education and Research Centre, Indian Institute of Science, Bangalore 560012 (India); Raha, Soumyendu, E-mail: raha@serc.iisc.ernet.in [Supercomputer Education and Research Centre, Indian Institute of Science, Bangalore 560012 (India)

    2011-10-01

    Biochemical pathways involving chemical kinetics in medium concentrations (i.e., at mesoscale) of the reacting molecules can be approximated as chemical Langevin equations (CLE) systems. We address the physically consistent non-negative simulation of the CLE sample paths as well as the issue of non-Lipschitz diffusion coefficients when a species approaches depletion and any stiffness due to faster reactions. The non-negative Fully Implicit Stochastic {alpha} (FIS {alpha}) method in which stopped reaction channels due to depleted reactants are deleted until a reactant concentration rises again, for non-negativity preservation and in which a positive definite Jacobian is maintained to deal with possible stiffness, is proposed and analysed. The method is illustrated with the computation of active Protein Kinase C response in the Protein Kinase C pathway.

  7. Computational singular perturbation with non-parametric tabulation of slow manifolds for time integration of stiff chemical kinetics

    Microsoft Academic Search

    Bert J. Debusschere; Youssef M. Marzouk; Habib N. Najm; Blane Rhoads; Dimitris A. Goussis; Mauro Valorani

    2012-01-01

    This paper presents a novel tabulation strategy for the adaptive numerical integration of chemical kinetics using the computational singular perturbation (CSP) method. The strategy stores and reuses CSP quantities required to filter out fast dissipative processes, resulting in a non-stiff chemical source term. In particular, non-parametric regression on low-dimensional slow invariant manifolds (SIMs) in the chemical state space is used

  8. Computational singular perturbation with non-parametric tabulation of slow manifolds for time integration of stiff chemical kinetics

    Microsoft Academic Search

    Bert J. Debusschere; Youssef M. Marzouk; Habib N. Najm; Blane Rhoads; Dimitris A. Goussis; Mauro Valorani

    2011-01-01

    This paper presents a novel tabulation strategy for the adaptive numerical integration of chemical kinetics using the computational singular perturbation (CSP) method. The strategy stores and reuses CSP quantities required to filter out fast dissipative processes, resulting in a non-stiff chemical source term. In particular, non-parametric regression on low-dimensional slow invariant manifolds (SIMs) in the chemical state space is used

  9. Colloquium on Process Simulation. Computational Fluid Dynamics Coupled With Chemical Kinetics, Combustion and Thermodynamics

    NASA Astrophysics Data System (ADS)

    Jokilaakso, Ari

    This volume contains the proceedings of the Colloquium on Process Simulation held at Helsinki University of Technology, Espoo, Finland, 3-4 Aug. 1994. The range of applications for computational fluid dynamics (CFD) is wide. This is mainly due to the great development of computer performance together with the diversification of modelling software and built-in options included in the software. Furthermore, the modelling tools have become more user friendly and thus easier to learn. As a result of all this the experts of different fields have been able to start using the CFD-tools to simulate and analyse their own cases. This, in turn, has brought a strong demand for addition of user developed sub-routines to the CFD-codes. Also, more and more precise models for turbulence, radiation heat transfer, two-phase flow etc. are needed in the CFD modelling. Thermodynamic modelling and heat transfer problems in metallurgical processes have been studied at the Laboratory of Materials Processing and Powder Metallurgy, Helsinki University of Technology since 1970s. Combining chemical kinetics, combustion, and thermodynamics with CFD-modelling have been studied at the laboratory during the last few years. Therefore, an annual colloquium was initiated for bringing together researchers in different process simulation fields to discuss the present status of the process modelling and, especially, the CFD-modelling involving chemical kinetics, combustion and thermodynamics.

  10. Edge-controlled growth and kinetics of single-crystal graphene domains by chemical vapor deposition

    PubMed Central

    Ma, Teng; Ren, Wencai; Zhang, Xiuyun; Liu, Zhibo; Gao, Yang; Yin, Li-Chang; Ma, Xiu-Liang; Ding, Feng; Cheng, Hui-Ming

    2013-01-01

    The controlled growth of large-area, high-quality, single-crystal graphene is highly desired for applications in electronics and optoelectronics; however, the production of this material remains challenging because the atomistic mechanism that governs graphene growth is not well understood. The edges of graphene, which are the sites at which carbon accumulates in the two-dimensional honeycomb lattice, influence many properties, including the electronic properties and chemical reactivity of graphene, and they are expected to significantly influence its growth. We demonstrate the growth of single-crystal graphene domains with controlled edges that range from zigzag to armchair orientations via growth–etching–regrowth in a chemical vapor deposition process. We have observed that both the growth and the etching rates of a single-crystal graphene domain increase linearly with the slanted angle of its edges from 0° to ?19° and that the rates for an armchair edge are faster than those for a zigzag edge. Such edge-structure–dependent growth/etching kinetics of graphene can be well explained at the atomic level based on the concentrations of the kinks on various edges and allow the evolution and control of the edge and morphology in single-crystal graphene following the classical kinetic Wulff construction theory. Using these findings, we propose several strategies for the fabrication of wafer-sized, high-quality, single-crystal graphene. PMID:24297886

  11. Coherent chemical kinetics as quantum walks I: Reaction operators for radical pairs

    E-print Network

    A. Chia; A. Gorecka; K. C. Tan; L. Pawela; P. Kurzynski; T. Paterek; D. Kaszlikowski

    2015-06-13

    Classical chemical kinetics use rate-equation models to describe how a reaction proceeds in time. Such models are sufficient for describing state transitions in a reaction where coherences between different states do not arise, or in other words, a reaction which contain only incoherent transitions. A prominent example reaction containing coherent transitions is the radical-pair model. The kinetics of such reactions is defined by the so-called reaction operator which determines the radical-pair state as a function of intermediate transition rates. We argue that the well-known concept of quantum walks from quantum information theory is a natural and apt framework for describing multisite chemical reactions. By composing Kraus maps that act only on two sites at a time, we show how the quantum-walk formalism can be applied to derive a reaction operator for the standard avian radical-pair reaction. Our reaction operator predicts a recombination dephasing rate consistent with recent experiments [J. Chem. Phys. {\\bf 139}, 234309 (2013)], in contrast to previous work by Jones and Hore [Chem. Phys. Lett. {\\bf 488}, 90 (2010)]. The standard radical-pair reaction has conventionally been described by either a normalised density operator incorporating both the radical pair and reaction products, or by a trace-decreasing density operator that considers only the radical pair. We demonstrate a density operator that is both normalised and refers only to radical-pair states. Generalisations to include additional dephasing processes and an arbitrary number of sites are also discussed.

  12. Isobutane ignition delay time measurements at high pressure and detailed chemical kinetic simulations

    SciTech Connect

    Healy, D.; Curran, H.J. [Combustion Chemistry Centre, School of Chemistry, NUI Galway (Ireland); Donato, N.S.; Aul, C.J.; Petersen, E.L. [Department of Mechanical Engineering, Texas A and M University, College Station, TX (United States); Zinner, C.M. [Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, FL (United States); Bourque, G. [Rolls-Royce Canada Limited, 9500 Cote de Liesse, Lachine, Quebec (Canada)

    2010-08-15

    Rapid compression machine and shock-tube ignition experiments were performed for real fuel/air isobutane mixtures at equivalence ratios of 0.3, 0.5, 1, and 2. The wide range of experimental conditions included temperatures from 590 to 1567 K at pressures of approximately 1, 10, 20, and 30 atm. These data represent the most comprehensive set of experiments currently available for isobutane oxidation and further accentuate the complementary attributes of the two techniques toward high-pressure oxidation experiments over a wide range of temperatures. The experimental results were used to validate a detailed chemical kinetic model composed of 1328 reactions involving 230 species. This mechanism has been successfully used to simulate previously published ignition delay times as well. A thorough sensitivity analysis was performed to gain further insight to the chemical processes occurring at various conditions. Additionally, useful ignition delay time correlations were developed for temperatures greater than 1025 K. Comparisons are also made with available isobutane data from the literature, as well as with 100% n-butane and 50-50% n-butane-isobutane mixtures in air that were presented by the authors in recent studies. In general, the kinetic model shows excellent agreement with the data over the wide range of conditions of the present study. (author)

  13. Calculation of the basic kinetic parameters of thermo-oxidative degradation of polyethylene and its copper-containing composites

    Microsoft Academic Search

    E. S Trofimchuk; M. Y Yablokova

    2001-01-01

    Calculation of the basic kinetic parameters of thermo-oxidative destruction of initial, porous HDPE and copper-containing composites based on porous HDPE was carried out by the IKP method. It was shown that thermo-oxidation of these materials consisted of three stages: (1) the migration of oxygen molecules to the active oxidising centres and the beginning of chain oxidation; (2) destruction of polymer

  14. Chemical Equilibrium, Unit 3: Chemical Equilibrium Calculations. A Computer-Enriched Module for Introductory Chemistry. Student's Guide and Teacher's Guide.

    ERIC Educational Resources Information Center

    Jameson, Cynthia J.

    Presented are the teacher's guide and student materials for one of a series of self-instructional, computer-based learning modules for an introductory, undergraduate chemistry course. The student manual for this unit on chemical equilibrium calculations includes objectives, prerequisites, a discussion of the equilibrium constant (K), and ten…

  15. Molecular corridors and kinetic regimes in the multiphase chemical evolution of secondary organic aerosol

    NASA Astrophysics Data System (ADS)

    Shiraiwa, M.; Berkemeier, T.; Schilling-Fahnestock, K.; Seinfeld, J.; Poeschl, U.

    2014-12-01

    The dominant component of atmospheric organic aerosol is that derived from the oxidation of volatile organic compounds (VOCs), so-called secondary organic aerosol (SOA). SOA consists of a multitude of organic compounds, only a small fraction of which has historically been identified. Formation and evolution of SOA is a complex process involving coupled chemical reaction and mass transport in the gas and particle phases. Current SOA models do not embody the full spectrum of reaction and transport processes nor do they identify the dominant rate-limiting steps in SOA formation. Based on molecular identification of SOA oxidation products, we show here that the chemical evolution of SOA from a variety of VOC precursors adheres to characteristic "molecular corridors" with a tight inverse correlation between volatility and molar mass. The slope of these corridors corresponds to the increase in molar mass required to decrease volatility by one order of magnitude (-dM/dlogC0). It varies in the range of 10-30 g mol-1 depending on the molecular size of the SOA precursor and the O:C ratio of the reaction products. Sequential and parallel reaction pathways of oxidation and dimerization or oligomerization progressing along these corridors pass through characteristic regimes of reaction-, diffusion-, or accommodation-limited multiphase chemical kinetics that can be classified according to reaction location, degree of saturation, and extent of heterogeneity of gas and particle phases. The molecular corridors and kinetic regimes help to constrain and described the properties of the products, pathways and rates of SOA evolution, thereby facilitating the further development of aerosol models for air quality and climate.

  16. Molecular conformational stability and Spectroscopic analysis of Parared with experimental techniques and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Srinivasaraghavan, R.; Thamaraikannan, S.; Seshadri, S.; Gnanasambandan, T.

    2015-02-01

    The complete vibrational assignment and analysis of the fundamental modes of Parared was carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically from the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G(d,p) and 6-311++G(d,p) basis sets. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of Parared have been computed using B3LYP quantum chemical calculations. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated.

  17. Stabilization of the Simplest Criegee Intermediate from the Reaction between Ozone and Ethylene: A High-Level Quantum Chemical and Kinetic Analysis of Ozonolysis.

    PubMed

    Nguyen, Thanh Lam; Lee, Hyunwoo; Matthews, Devin A; McCarthy, Michael C; Stanton, John F

    2015-06-01

    The fraction of the collisionally stabilized Criegee species CH2OO produced from the ozonolysis of ethylene is calculated using a two-dimensional (E, J)-grained master equation technique and semiclassical transition-state theory based on the potential energy surface obtained from high-accuracy quantum chemical calculations. Our calculated yield of 42 ± 6% for the stabilized CH2OO agrees well, within experimental error, with available (indirect) experimental results. Inclusion of angular momentum in the master equation is found to play an essential role in bringing the theoretical results into agreement with the experiment. Additionally, yields of HO and HO2 radical products are predicted to be 13 ± 6% and 17 ± 6%, respectively. In the kinetic simulation, the HO radical product is produced mostly from the stepwise decomposition mechanism of primary ozonide rather than from dissociation of hot CH2OO. PMID:25945650

  18. Unusual mechanism for H{sub 3}{sup +} formation from ethane as obtained by femtosecond laser pulse ionization and quantum chemical calculations

    SciTech Connect

    Kraus, Peter M.; Schwarzer, Martin C.; Schirmel, Nora; Urbasch, Gunter; Frenking, Gernot; Weitzel, Karl-Michael [Fachbereich Chemie, Physikalische Chemie, Philipps-Universitaet Marburg, Hans-Meerwein-Strasse, D-35032 Marburg (Germany)

    2011-03-21

    The formation of H{sub 3}{sup +} from saturated hydrocarbon molecules represents a prototype of a complex chemical process, involving the breaking and the making of chemical bonds. We present a combined theoretical and experimental investigation providing for the first time an understanding of the mechanism of H{sub 3}{sup +} formation at the molecular level. The experimental approach involves femtosecond laser pulse ionization of ethane leading to H{sub 3}{sup +} ions with kinetic energies on the order of 4 to 6.5 eV. The theoretical approach involves high-level quantum chemical calculation of the complete reaction path. The calculations confirm that the process takes place on the potential energy surface of the ethane dication. A surprising result of the theoretical investigation is, that the transition state of the process can be formally regarded as a H{sub 2} molecule attached to a C{sub 2}H{sub 4}{sup 2+} entity but IRC calculations show that it belongs to the reaction channel yielding C{sub 2}H{sub 3}{sup +}+ H{sub 3}{sup +}. Experimentally measured kinetic energies of the correlated H{sub 3}{sup +} and C{sub 2}H{sub 3}{sup +} ions confirm the reaction path suggested by theory.

  19. Thermal Decomposition of Some Chemical Compounds Used As Food Preservatives and Kinetic Parameters of This Process

    Microsoft Academic Search

    J. Mas?owska; M. Wi?d?ocha

    2000-01-01

    Thermal decomposition processes of selected chemicals used as food preservatives such as sodium formate, sodium propionate,\\u000a sodium nitrates(V and III) and sodium sulphate(IV) were examined by the derivatographic method. Based on the curves obtained,\\u000a the number of decomposition stages and characteristic temperatures of these compounds have been found. Mass decrements calculated\\u000a from TG curves ranged from 28.9% for sodium formate

  20. Trimesitylsilylium cation verification of a free silylium cation in solution by NMR chemical shift calculations

    NASA Astrophysics Data System (ADS)

    Kraka, Elfi; Sosa, Carlos P.; Gräfenstein, Jürgen; Cremer, Dieter

    1997-11-01

    NMR chemical shift calculations at the SOS-DFPT/PW91/[9s6p2d/5s4pld/5s4pld/3s]//B3LYP/6-31G(d) level of theory were used to describe the trimesitylsilylium cation 1, recently synthesized in benzene solution and investigated by NMR spectroscopy. The conformation of cation 1 is characterized by mesityl rings rotated by 47° in a propeller-like form. Contrary to other silylium cations investigated, cation 1 forms a weak Van der Waals complex 3 with benzene rather than a Wheland ?-complex. The calculated 29Si NMR chemical shifts for 1 and 3 are 226 and 227 ppm, compared to the experimental value of 225.5 ppm. The agreement between calculated and measured NMR chemical shifts provides evidence that cation 1 presents the first free silylium cation synthesized.

  1. n-Butane: Ignition delay measurements at high pressure and detailed chemical kinetic simulations

    SciTech Connect

    Healy, D.; Curran, H.J. [Combustion Chemistry Centre, School of Chemistry, NUI Galway (Ireland); Donato, N.S.; Aul, C.J.; Petersen, E.L. [Department of Mechanical Engineering, Texas A and M University, College Station, TX (United States); Zinner, C.M. [Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, FL (United States); Bourque, G. [Rolls-Royce Canada Limited, 9500 Cote de Liesse, Lachine, Quebec, H8T 1A2 (Canada)

    2010-08-15

    Ignition delay time measurements were recorded at equivalence ratios of 0.3, 0.5, 1, and 2 for n-butane at pressures of approximately 1, 10, 20, 30 and 45 atm at temperatures from 690 to 1430 K in both a rapid compression machine and in a shock tube. A detailed chemical kinetic model consisting of 1328 reactions involving 230 species was constructed and used to validate the delay times. Moreover, this mechanism has been used to simulate previously published ignition delay times at atmospheric and higher pressure. Arrhenius-type ignition delay correlations were developed for temperatures greater than 1025 K which relate ignition delay time to temperature and concentration of the mixture. Furthermore, a detailed sensitivity analysis and a reaction pathway analysis were performed to give further insight to the chemistry at various conditions. When compared to existing data from the literature, the model performs quite well, and in several instances the conditions of earlier experiments were duplicated in the laboratory with overall good agreement. To the authors' knowledge, the present paper presents the most comprehensive set of ignition delay time experiments and kinetic model validation for n-butane oxidation in air. (author)

  2. Time-resolved simplified chemical kinetics modelling using computational singular perturbation

    NASA Technical Reports Server (NTRS)

    Lam, S. H.; Goussis, D. A.; Konopka, D.

    1989-01-01

    A CO-CH4-air reaction system is used to demonstrate the computational singular perturbation (CSP) method for deriving time-resolved simplified chemical kinetics models. CSP provides a programmable algorithm to group the given collection of elementary reactions into reaction groups which are ordered according to their speed. The concept of Importance Index k(m)exp s is introduced: k(m)exp s is defined to be a number between 0 and 1 which measures the importance of the m-th reaction group to the s-th reactant and can readily be computed from data generated by CSP. It is suggested that the robustness of the solutions of the reaction system can be qualitatively assessed by inspecting the Importance Index data.

  3. Time-resolved broadband cavity-enhanced absorption spectroscopy for chemical kinetics.

    SciTech Connect

    Sheps, Leonid; Chandler, David W.

    2013-04-01

    Experimental measurements of elementary reaction rate coefficients and product branching ratios are essential to our understanding of many fundamentally important processes in Combustion Chemistry. However, such measurements are often impossible because of a lack of adequate detection techniques. Some of the largest gaps in our knowledge concern some of the most important radical species, because their short lifetimes and low steady-state concentrations make them particularly difficult to detect. To address this challenge, we propose a novel general detection method for gas-phase chemical kinetics: time-resolved broadband cavity-enhanced absorption spectroscopy (TR-BB-CEAS). This all-optical, non-intrusive, multiplexed method enables sensitive direct probing of transient reaction intermediates in a simple, inexpensive, and robust experimental package.

  4. Optimization of chemical reactor feed by simulations based on a kinetic approach.

    PubMed

    Guinand, Charles; Dabros, Michal; Roduit, Bertrand; Meyer, Thierry; Stoessel, Francis

    2014-10-01

    Chemical incidents are typically caused by loss of control, resulting in runaway reactions or process deviations in different stages of the production. In the case of fed-batch reactors, the problem generally encountered is the accumulation of heat. This is directly related to the temperature of the process, the reaction kinetics and adiabatic temperature rise, which is the maximum temperature attainable in the event of cooling failure. The main possibility to control the heat accumulation is the use of a well-controlled adapted feed. The feed rate can be adjusted by using reaction and reactor dynamic models coupled to Model Predictive Control. Thereby, it is possible to predict the best feed profile respecting the safety constraints. PMID:25437170

  5. Chemical Kinetic Data Base for Propellant Combustion. II. Reactions Involving CN, NCO, and HNCO

    NASA Astrophysics Data System (ADS)

    Tsang, Wing

    1992-07-01

    This paper contains evaluated chemical kinetic data on single step elementary reactions involving small polyatomic molecules which are of importance in propellant combustion. The work consists of the collection and evaluation of mechanistic and rate information and the use of various methods for the extrapolation and estimation of rate data where information does not exist. The conditions covered range from 500-2500 K and 1017-1022 particles cm-3. The results of the second year's effort add to the existing data base reactions involving CN, NCO, and HNCO with each other and the following species: H, H2, H2O, O, OH, HCHO, CHO, CO, NO, NO2, HNO, HNO2, HCN, and N2O.

  6. XCHEM-1D: A Heat Transfer/Chemical Kinetics Computer Program for multilayered reactive materials

    SciTech Connect

    Gross, R.J.; Baer, M.R.; Hobbs, M.L.

    1993-10-01

    An eXplosive CHEMical kinetics code, XCHEM, has been developed to solve the reactive diffusion equations associated with thermal ignition of energetic materials. This method-of-lines code uses stiff numerical methods and adaptive meshing to resolve relevant combustion physics. Solution accuracy is maintained between multilayered materials consisting of blends of reactive components and/or inert materials. Phase change and variable properties are included in one-dimensional slab, cylindrical and spherical geometries. Temperature-dependent thermal properties have been incorporated and the modification of thermal conductivities to include decomposition effects are estimated using solid/gas volume fractions determined by species fractions. Gas transport properties, including high pressure corrections, have also been included. Time varying temperature, heat flux, convective and thermal radiation boundary conditions, and layer to layer contact resistances have also been implemented.

  7. Quantum chemical 13Calpha chemical shift calculations for protein NMR structure determination, refinement, and validation

    Microsoft Academic Search

    Jorge A. Vila; James M. Aramini; Paolo Rossi; Alexandre Kuzin; Min Su; Jayaraman Seetharaman; Rong Xiao; Liang Tong; Gaetano T. Montelione; Harold A. Scheraga

    2008-01-01

    A recently determined set of 20 NMR-derived conformations of a 48-residue all-alpha-helical protein, (PDB ID code 2JVD), is validated here by comparing the observed 13Calpha chemical shifts with those computed at the density functional level of theory. In addition, a recently introduced physics-based method, aimed at determining protein structures by using NOE-derived distance constraints together with observed and computed 13Calpha

  8. Ab initio quantum chemical calculation as a tool of evaluating diamagnetic susceptibility of magnetically levitating substances

    Microsoft Academic Search

    Y. Fujiwara; Y. Tanimoto

    2009-01-01

    On magnetic force evaluation necessary for magnetically levitated diamagnetic substances, isotropic diamagnetic susceptibility estimation by the ab initio quantum chemical calculation using Gaussian03W was verified for more than 300 molecules in a viewpoint of the accuracy in the absolute value and the calculation level affording good cost performance. From comparison, the method of B3PW91 \\/ 6-311+G(d,p) was found to give

  9. Chemical bond as a test of density-gradient expansions for kinetic and exchange energies

    SciTech Connect

    Perdew, J.P.; Levy, M.; Painter, G.S.; Wei, S.; Lagowski, J.B.

    1988-01-15

    Errors in kinetic and exchange contributions to the molecular bonding energy are assessed for approximate density functionals by reference to near-exact Hartree-Fock values. From the molecular calculations of Allan et al. and of Lee and Ghosh, it is demonstrated that the density-gradient expansion does not accurately describe the noninteracting kinetic contribution to the bonding energy, even when this expansion is carried to fourth order and applied in its spin-density-functional form to accurate Hartree-Fock densities. In a related study, it is demonstrated that the overbinding of molecules such as N/sub 2/ and F/sub 2/, which occurs in the local-spin-density (LSD) approximation for the exchange-correlation energy, is not attributable to errors in the self-consistent LSD densities. Contrary to expectations based upon the Gunnarsson-Jones nodality argument, it is found that the LSD approximation for the exchange energy can seriously overbind a molecule even when bonding does not create additional nodes in the occupied valence orbitals. LSD and exact values for the exchange contribution to the bonding energy are displayed and discussed for several molecules.

  10. Calculation of solid-propellant burning rates from condensed-phase decomposition kinetics

    Microsoft Academic Search

    R. H. W. Waesche; J. Wenograd

    2000-01-01

    Kinetic rates of thermal decomposition reactions of three ammonium perchlorate composite propellants have been determined\\u000a by the techniques of differential scanning calorimetry and thermogravimetric analysis at pressures to 500 psi (1 psi=6894.7\\u000a Pa=0.068 atm; 1 atm=14.7 psi). The results of these experiments were extrapolated to give heat-evolution rates at temperatures\\u000a that are believed to prevail at the surface of burning

  11. Shock tube study of the fuel structure effects on the chemical kinetic mechanisms responsible for soot formation, part 2

    NASA Technical Reports Server (NTRS)

    Frenklach, M.; Clary, D. W.; Ramachandra, M. K.

    1985-01-01

    Soot formation in oxidation of allene, 1,3-butadiene, vinylacetylene and chlorobenzene and in pyrolysis of ethylene, vinylacetylene, 1-butene, chlorobenzene, acetylen-hydrogen, benzene-acetylene, benzene-butadiene and chlorobenzene-acetylene argon-diluted mixtures was studied behind reflected shock waves. The results are rationalized within the framework of the conceptual models. It is shown that vinylacetylene is much less sooty than allene, which indicates that conjugation by itself is not a sufficient factor for determining the sooting tendency of a molecule. Structural reactivity in the context of the chemical kinetics is the dominant factor in soot formation. Detailed chemical kinetic modeling of soot formation in pyrolysis of acetylene is reported. The main mass growth was found to proceed through a single dominant route composed of conventional radical reactions. The practically irreversible formation reactions of the fused polycyclic aromatics and the overshoot by hydrogen atom over its equilibrium concentration are the g-driving kinetic forces for soot formation.

  12. A Detailed Chemical Kinetic Reaction Mechanism for Oxidation of Four Small Alkyl Esters in Laminar Premixed Flames

    SciTech Connect

    Westbrook, C K; Pitz, W J; Westmoreland, P R; Dryer, F L; Chaos, M; Osswald, P; Kohse-Hoinghaus, K; Cool, T A; Wang, J; Yang, B; Hansen, N; Kasper, T

    2008-02-08

    A detailed chemical kinetic reaction mechanism has been developed for a group of four small alkyl ester fuels, consisting of methyl formate, methyl acetate, ethyl formate and ethyl acetate. This mechanism is validated by comparisons between computed results and recently measured intermediate species mole fractions in fuel-rich, low pressure, premixed laminar flames. The model development employs a principle of similarity of functional groups in constraining the H atom abstraction and unimolecular decomposition reactions in each of these fuels. As a result, the reaction mechanism and formalism for mechanism development are suitable for extension to larger oxygenated hydrocarbon fuels, together with an improved kinetic understanding of the structure and chemical kinetics of alkyl ester fuels that can be extended to biodiesel fuels. Variations in concentrations of intermediate species levels in these flames are traced to differences in the molecular structure of the fuel molecules.

  13. COIL chemical kinetics package revisited: a re-analysis of molecular iodine dissociation rate data

    NASA Astrophysics Data System (ADS)

    Paschkewitz, John S.; Heaven, Michael C.

    2000-05-01

    New fits to the molecular iodine dissociation rate data of Heidner et al. Were obtained with the goals of achieving a better overall representation of the experimental data and determining a set of rate constants compatible with the assumption that the dissociation intermediate I2dagger is vibrationally excited I2. Improved rate constants were obtained that are significantly different from those used in current computational models of COIL systems. While the new rate constants provided a better representation of the experimental dat, troubling discrepancies remain. New reactions involving electronically excited iodine (I2*) were then added to the model in an attempt to resolve these discrepancies. Preliminary calculations indicate that I2* kinetics provide only a minor path to dissociation and that these model deficiencies will not be resolved by adding electronically excited iodine channels.

  14. Promoting Higher-Order Thinking Skills: Uses of Mathcad and Classical Chemical Kinetics To Foster Student Development.

    ERIC Educational Resources Information Center

    Zielinski, Theresa Julia

    1995-01-01

    Explains how the Mathcad computer program can promote the development of higher-order chemical thinking skills of students taking junior-level physical chemistry courses. The kinetics of first-order series and reversible reactions is used as an example of how this can be implemented within an interactive laboratory or lecture format. (PVD)

  15. Thermal diffusion and chemical kinetics in laminar biomaterial due to heating by a free-electron laser

    Microsoft Academic Search

    M. Shane Hutson; Susanne A. Hauger; Glenn Edwards

    2002-01-01

    We have theoretically investigated the role of thermal diffusion and chemical kinetics as a possible dynamic explanation for the preferential ablative properties of infrared radiation from a free-electron laser ~FEL!. The model is based on a laminar system composed of alternating layers of protein and saline. We have compared exposure to 3 mm where water is the main absorber and

  16. Is case-based learning an effective teaching strategy to challenge students’ alternative conceptions regarding chemical kinetics?

    Microsoft Academic Search

    Eylem Yalç?nkaya; Özgecan Ta?tan-K?r?k; Yezdan Boz; Demet Y?ld?ran

    2012-01-01

    Background: Case-based learning (CBL) is simply teaching the concept to the students based on the cases. CBL involves a case, which is a scenario based on daily life, and study questions related to the case, which allows students to discuss their ideas. Chemical kinetics is one of the most difficult concepts for students in chemistry. Students have generally low levels

  17. EFFECTS OF STUDENT TEAMS-ACHIEVEMENT DIVISIONS STRATEGY AND MATHEMATICS KNOWLEGDE ON LEARNING OUTCOMES IN CHEMICAL KINETICS

    Microsoft Academic Search

    Francis A. ADESOJI; Tunde L. IBRAHEEM

    The study investigated effects of Student Teams-Achievement Divisions strategy and mathematics ability on senior secondary school chemistry students' learning outcome in chemical kinetics. A pretest, posttest control group quasi experimental design was adopted for the study. Data were collected from a sample of 300 students made up of 110 males and 190 females from six senior secondary schools in Epe

  18. A Microscale Approach to Chemical Kinetics in the General Chemistry Laboratory: The Potassium Iodide Hydrogen Peroxide Iodine-Clock Reaction

    ERIC Educational Resources Information Center

    Sattsangi, Prem D.

    2011-01-01

    A microscale laboratory for teaching chemical kinetics utilizing the iodine clock reaction is described. Plastic pipets, 3 mL volume, are used to store and deliver precise drops of reagents and the reaction is run in a 24 well plastic tray using a total 60 drops of reagents. With this procedure, students determine the rate of reaction and the…

  19. Combustion Research Program: Flame studies, laser diagnostics, and chemical kinetics. Final report, 15 July 1987--15 June 1992

    SciTech Connect

    Crosley, D.R.

    1992-09-01

    This project has comprised laser flame diagnostic experiments, chemical kinetics measurements, and low pressure flame studies. Collisional quenching has been investigated for several systems: the OH radical, by H{sub 2}0 in low pressure flames; the rotational level dependence for NH, including measurements to J=24; and of NH{sub 2} at room temperature. Transition probability measurements for bands involving v{prime} = 2 and 3 of the A-X system of OH were measured in a flame. Laser-induced fluorescence of vinyl radicals was unsuccessfully attempted. RRKM and transition state theory calculations were performed on the OH + C{sub 2}H{sub 4} reaction, on the t-butyl radical + HX; and transition state theory has been applied to a series of bond scission reactions. OH concentrations were measured quantitatively in low pressure H{sub 2}/N{sub 2}O and H{sub 2}/O{sub 2} flames, and the ability to determine spatially precise flame temperatures accurately using OH laser-induced fluorescence was studied.

  20. Investigations of spontaneous ignition of high-pressure hydrogen release based on detailed chemical kinetics

    NASA Astrophysics Data System (ADS)

    Terashima, Hiroshi; Koshi, Mitsuo; Mogi, Toshio; Dobashi, Ritsu

    2013-11-01

    A numerical simulation of spontaneous ignition of high-pressure release in a length of duct is performed to explore ignition mechanisms. The present study adopts a rectangular duct and focuses on effects of initial diaphragm shape on spontaneous ignitions. The Navier-Stokes equations with a detailed chemical kinetics mechanism are solved in a manner of direct numerical simulation. A conventional numerical approach is used for solving the Navier-Stokes equations, while the chemical source term is integrated by a dynamic multi-timescale method for alleviating the stiffness. Detailed mechanisms of spontaneous ignitions are discussed for various initial diaphragm shapes. For a straight diaphragm shape, the ignition occurs only near the wall region due to the adiabatic wall condition, while, for a largely deformed diaphragm shape, the three ignition events: ignition due to leading shock wave reflection at the wall, hydrogen penetration into shock-heated air near the wall, and deep penetration of hydrogen into shock-heated air behind the leading shock wave, are identified.

  1. Chemical kinetic model of hydrocarbon generation, expulsion, and destruction applied to the Maracaibo basin, Venezuela

    SciTech Connect

    Sweeney, J.J.; Braun, R.L.; Burnham, A.K. [Lawrence Livermore National Lab., CA (United States)] [and others

    1995-10-01

    This paper describes the development and application of a compositional chemical model of hydrocarbon generation, expulsion,a nd destruction for the Cretaceous La Luna Formation source rock of the Maraciabo basin, Venezuela. Applications include both laboratory and geological settings. Laboratory pyrolysis experiments were used to study bulk oil generation, expulsion, and associated changes in composition of the kerogen, extractable organic matter, and expelled and unexpelled hydrocarbons. The laboratory experiments were also used to determine kinetic parameters to quantitatively describe organic reactions, via a computer model that also includes simulation of pressure-driven primary expulsion, over widely varying conditions. We show that the chemical model accuratley simulates the experimental results. Thermal history models for wells in the Maraciabo basin were used to simulate hydrocarbon generation and pore pressure development in the La Luna Formation and expulsion into nearby Cretaceous reservoirs. Results of the modeling indicate that both compaction disequilibrium and organic maturation play important roles in the development of excess pore pressure in the La Luna Formation. The model simulation of the variation of indicators such as Rock-Eval parameters and extract and oil compositions shows generally good agreement with measurements from remaining kerogen, oils, and extracts recovered from the La Luna Formation and from nearby Cretaceous reservoirs.

  2. Dissecting the Mechanisms of a Class of Chemical Glycosylation Using Primary 13C Kinetic Isotope Effects

    PubMed Central

    Huang, Min; Garrett, Graham E.; Birlirakis, Nicolas; Bohé, Luis

    2012-01-01

    Although arguably the most important reaction in glycoscience, chemical glycosylations are among the least well understood of organic chemical reactions resulting in an unnecessarily high degree of empiricism and a brake on rational development in this critical area. To address this problem primary 13C kinetic isotope effects now have been determined for the formation of ?- and ?-manno- and glucopyranosides by a natural abundance NMR method. In contrast to the common current assumption, for three of the four cases studied the experimental values concur with those computed for associative displacement of the intermediate covalent glycosyl trifluoromethanesulfonates. For the formation of the ?-mannopyranosides the experimentally determined KIE differs significantly from that computed for an associative displacement, which is strongly suggestive of a dissociative mechanism that approaches the intermediacy of a glycosyl oxocarbenium ion. The application of comparable experiments to other glycosylation systems should shed further light on their glycosylation mechanisms and thus assist in the design of better reactions conditions with improved stereoselectivity. PMID:22824899

  3. Analysis of chemical kinetics at the gas-aqueous interface for submicron aerosols.

    PubMed

    Remorov, R G; George, C

    2006-11-14

    The effect of kinetics of chemical reactions in the gas-liquid interface between atmospheric gases and reactive solute in dilute aqueous aerosols is analysed in order to see if such processes will affect the overall uptake rate. Accordingly, a parameterization of such heterogeneous reactions was derived, taking into account interfacial reactions. Gibbs surface excess concentration of both reactive compounds and stable compounds leads to higher heterogeneous reaction rates in comparison to aqueous phase bulk reactions. An analytical formulation shows that the surface reactions may be of considerable importance for the uptake process in the case of small liquid aerosols even in the absence of organic film on the surface. In particular, we demonstrate that the uptake rate of atmospheric gas-phase oxidants (such as OH, NO(3) or O(3)) reacting with volatile organic compounds (such as ethanol or methanol) is increased by more than 10% for atmospheric aerosols with diameters lower than 0.1 microm. This effect is in addition intensified in the case of reactions of atmospheric oxidants with liquid aerosols containing organic surfactants, such as semi-volatile organic compounds, i.e., the chemical reactions at the gas-liquid interface may be dominant in the main uptake process for atmospheric submicron aerosols. PMID:17066179

  4. Numerical Study on Spark Ignition Characteristics of a Methane-Air Mixture Using Detailed Chemical Kinetics

    NASA Astrophysics Data System (ADS)

    Han, Jilin; Yamashita, Hiroshi; Yamamoto, Kazuhiro

    Spark ignition is considered one of the most difficult and complex problems because it involves complicated physical and chemical processes, and it has not yet been explained sufficiently. The minimum ignition energy (MIE) is an important parameter for judging the ignition ability of combustion systems. In the present study, the spark ignition characteristics of a methane-air mixture were investigated by numerical analysis using detailed chemical kinetics consisting of 53 species and 325 elementary reactions. Two different analytical models, with and without electrodes, were applied to research the effect of electrode temperature and energy channel length on flame propagation and the relationship between the MIE and equivalence ratio. The electrode temperature was set as 300 K, 1000 K, and 2000 K for analytical models with electrodes, and the energy channel length was set as 1 mm, 2 mm, and 3 mm for analytical models without electrodes. The obtained computational results showed good agreement with experimental results. We determined that with increasing electrode temperature, the minima of the curve indicating the relationship between the MIE and equivalence ratio move toward the leaner side, that a leaner mixture is more sensitive to heat loss to the cold surrounding gas, and that heat loss to the electrodes is an unignorable factor for the initial formation of the flame kernel.

  5. Kinetics of cadmium, chromium, and lead sorption onto chemically modified sugarcane bagasse and wheat straw.

    PubMed

    Mahmood-Ul-Hassan, M; Suthar, V; Rafique, E; Ahmad, R; Yasin, M

    2015-07-01

    In this study, cadmium (Cd), chromium (Cr), and lead (Pb) adsorption potential of unmodified and modified sugarcane bagasse and ground wheat straw was explored from aqueous solution through batch equilibrium technique. Both the materials were chemically modified by treating with sodium hydroxide (NaOH) alone and in combination with nitric acid (HNO3) and sulfuric acid (H2SO4). Two kinetic models, pseudo-first order and pseudo-second order were used to follow the adsorption process and reaction fallowed the later model. The Pb removal by both the materials was highest and followed by Cr and Cd. The chemical treatment invariably increased the adsorption capacity and NaOH treatment proved more effective than others. Langmuir maximum sorption capacity (q m) of Pb was utmost (12.8-23.3 mg/g of sugarcane bagasse, 14.5-22.4 mg/g of wheat straw) and of Cd was least (1.5-2.2 mg/g of sugarcane bagasse, 2.5-3.8 mg/g of wheat straw). The q m was in the order of Pb > Cr > Cd for all the three adsorbents. Results demonstrate that agricultural waste materials used in this study could be used to remediate the heavy metal-polluted water. PMID:26116198

  6. First principle chemical kinetics in zeolites: the methanol-to-olefin process as a case study.

    PubMed

    Van Speybroeck, Veronique; De Wispelaere, Kristof; Van der Mynsbrugge, Jeroen; Vandichel, Matthias; Hemelsoet, Karen; Waroquier, Michel

    2014-11-01

    To optimally design next generation catalysts a thorough understanding of the chemical phenomena at the molecular scale is a prerequisite. Apart from qualitative knowledge on the reaction mechanism, it is also essential to be able to predict accurate rate constants. Molecular modeling has become a ubiquitous tool within the field of heterogeneous catalysis. Herein, we review current computational procedures to determine chemical kinetics from first principles, thus by using no experimental input and by modeling the catalyst and reacting species at the molecular level. Therefore, we use the methanol-to-olefin (MTO) process as a case study to illustrate the various theoretical concepts. This process is a showcase example where rational design of the catalyst was for a long time performed on the basis of trial and error, due to insufficient knowledge of the mechanism. For theoreticians the MTO process is particularly challenging as the catalyst has an inherent supramolecular nature, for which not only the Brønsted acidic site is important but also organic species, trapped in the zeolite pores, must be essentially present during active catalyst operation. All these aspects give rise to specific challenges for theoretical modeling. It is shown that present computational techniques have matured to a level where accurate enthalpy barriers and rate constants can be predicted for reactions occurring at a single active site. The comparison with experimental data such as apparent kinetic data for well-defined elementary reactions has become feasible as current computational techniques also allow predicting adsorption enthalpies with reasonable accuracy. Real catalysts are truly heterogeneous in a space- and time-like manner. Future theory developments should focus on extending our view towards phenomena occurring at longer length and time scales and integrating information from various scales towards a unified understanding of the catalyst. Within this respect molecular dynamics methods complemented with additional techniques to simulate rare events are now gradually making their entrance within zeolite catalysis. Recent applications have already given a flavor of the benefit of such techniques to simulate chemical reactions in complex molecular environments. PMID:25054453

  7. Ab initio quantum chemical calculation as a tool of evaluating diamagnetic susceptibility of magnetically levitating substances

    NASA Astrophysics Data System (ADS)

    Fujiwara, Y.; Tanimoto, Y.

    2009-03-01

    On magnetic force evaluation necessary for magnetically levitated diamagnetic substances, isotropic diamagnetic susceptibility estimation by the ab initio quantum chemical calculation using Gaussian03W was verified for more than 300 molecules in a viewpoint of the accuracy in the absolute value and the calculation level affording good cost performance. From comparison, the method of B3PW91 / 6-311+G(d,p) was found to give the adequate absolute value by the relation of (observed) = (1.03 ± 0.005) x (calculated) - (1.22 ± 0.60) x 10-6 in a unit of cm3 mol-1 and good cost performance.

  8. Performance test of multicomponent quantum mechanical calculation with polarizable continuum model for proton chemical shift.

    PubMed

    Kanematsu, Yusuke; Tachikawa, Masanori

    2015-05-21

    Multicomponent quantum mechanical (MC_QM) calculations with polarizable continuum model (PCM) have been tested against liquid (1)H NMR chemical shifts for a test set of 80 molecules. Improvement from conventional quantum mechanical calculations was achieved for MC_QM calculations. The advantage of the multicomponent scheme could be attributed to the geometrical change from the equilibrium geometry by the incorporation of the hydrogen nuclear quantum effect, while that of PCM can be attributed to the change of the electronic structure according to the polarization by solvent effects. PMID:25915075

  9. Chemical composition and calculated nutritive value of commonly available feedstuffs for ruminants in Burundi

    E-print Network

    Paris-Sud XI, Université de

    Chemical composition and calculated nutritive value of commonly available feedstuffs for ruminants Louvain, Place Croix du Sud2 (Boite 14),1348 Louvain-la-Neuve, Belgique Burundese domestic ruminants, in : Alimentation des ruminants, INRA ed, Versailles, 469-584) and Xandé et al (1989, in : Paturages et alimentation

  10. A Simple Method to Calculate the Temperature Dependence of the Gibbs Energy and Chemical Equilibrium Constants

    ERIC Educational Resources Information Center

    Vargas, Francisco M.

    2014-01-01

    The temperature dependence of the Gibbs energy and important quantities such as Henry's law constants, activity coefficients, and chemical equilibrium constants is usually calculated by using the Gibbs-Helmholtz equation. Although, this is a well-known approach and traditionally covered as part of any physical chemistry course, the required…

  11. Influence of Chemical Kinetics on Postcolumn Reaction in a Capillary Taylor Reactor with Catechol Analytes and Photoluminescence Following Electron Transfer

    PubMed Central

    Jung, Moon Chul; Weber, Stephen G.

    2006-01-01

    Postcolumn derivatization reactions can enhance detector sensitivity and selectivity, but their successful combination with capillary liquid chromatography has been limited because of the small peak volumes in capillary chromatography. A capillary Taylor reactor (CTR), developed in our laboratory, provides simple and effective mixing and reaction in a 25-?m-radius postcolumn capillary. Homogenization of reactant streams occurs by radial diffusion, and a chemical reaction follows. Three characteristic times for a given reaction process can be predicted using simple physical and chemical parameters. Two of these times are the homogenization time, which governs how long it takes the molecules in the analyte and reagent streams to mix, and the reaction time, which governs how long the molecules in a homogeneous solution take to react. The third characteristic time is an adjustment to the reaction time called the start time, which represents an estimate of the average time the analyte stream spends without exposure to reagent. In this study, laser-induced fluorescence monitored the extent of the postcolumn reaction (reduction of Os(bpy)33+ by analyte to the photoluminescent Os(bpy)32+) in a CTR. The reaction time depends on the reaction rates. Analysis of product versus time data yielded second-order reaction rate constants between the PFET reagent, tris(2,2?-bipyridine)osmium, and standards ((ferrocenylmethyl)trimethylammonium cation and p-hydroquinone) or catechols (dopamine, epinephrine, norepinephrine, 3, 4-dihydroxyphenylacetic acid. The extent of the reactions in a CTR were then predicted from initial reaction conditions and compared to experimental results. Both the theory and experimental results suggested the reactions of catechols were generally kinetically controlled, while those of the standards were controlled by mixing time (1–2 s). Thus, the extent of homogenization can be monitored in a CTR using the relatively fast reaction of the reagent and p-hydroquinone. Kinetically controlled reactions of catechols, however, could be also completed in a reasonable time at increased reagent concentration. A satisfactory reactor, operating at 1.7 cm/s (2 ?L/min) velocity with solutes having diffusion coefficients in the 5 × 10?6 cm2/s range, can be constructed from 8.0 cm of 25-?m-radius capillary. Slower reactions require longer reaction times, but theoretical calculations expect that a CTR does not broaden a chromatographic peak (N = 14 000) from a 100-?m-capillary chromatography column by 10% if the pseudo-first-order rate constant is larger than 0.1 s?1. PMID:15858975

  12. Kinetic analysis of chemical reactions coupled to an enzymic step. Application to acid phosphatase assay with Fast Red.

    PubMed Central

    Escribano, J; García-Carmona, F; García-Cánovas, F; Iborra, J L; Lozano, J A

    1984-01-01

    Acid phosphatase assay with alpha-naphthyl phosphate as substrate and the use of diazonium salt (Fast Red TR) for chromophore formation was kinetically analysed as a system of two chemical reactions coupled to an enzymic reaction. This system follows a mechanism defined as enzymic-chemical-chemical (EzCC). The accumulation of chromophore with reaction time presented a marked lag period, which was only dependent on the rate constants of the chemical reactions and was independent of the enzymic step. The specific rate constants of each chemical step were determined in 3.8-5.0 pH and 10-35 degrees C temperature ranges. Thermodynamic parameters of the chemical steps were also obtained. Measurement of acid phosphatase activity can be carried out in the pH range 3.8-5.0 (4.8 was optimal pH) without the need to eliminate the lag period. PMID:6508735

  13. Kinetic distribution model for chemicals based on results from a standard environmental system

    SciTech Connect

    Figge, K.; Klahn, J.; Koch, J.

    1986-06-01

    In order to reduce potential hazards to the environment resulting from production and use of chemicals, the German law on hazardous substances, and the regulation regarding submission of test data on physiochemical properties of new substances, have been ratified by the Federal Republic of Germany legislation in 1980 and 1981, respectively. This implies that before production, marketing, and use of a new chemical, its potential hazard to human beings and the environment has to be checked. Therefore it is necessary to have available accurate information about the probable fate of this new chemical in the environment, i.e., its distribution among the different environmental compartments. To this end, the submission of basic physiochemical data of a new chemical, such as boiling point, vapor pressure, water solubility, fat solubility, and partition coefficient in the system n-octanol/water, is mandatory for its registration. These data are meant to be used by the official evaluating department as a basis for describing the distribution behavior of the substance in the environment. However, there is no generally accepted procedure yet which would allow the reliable prediction. Such a calculation procedure should comprise all factors decisive for distribution and degradation of chemicals in the environment, according to their significance. We have taken a first step in this direction by carrying out the following experiments, with the aim of developing such a distribution model as well as identifying the physicochemical properties of chemicals required for the prediction of distribution patterns. The distribution patterns of 12 selected substances, having significant differences with respect to their physiochemical properties, were determined via radiotracer technique, in a defined, standardized, terrestrial ecosystem.

  14. NASA Data Evaluation: Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies

    NASA Astrophysics Data System (ADS)

    Burkholder, J. B.; Sander, S. P.; Abbatt, J.; Barker, J. R.; Fleming, E. L.; Friedl, R.; Huie, R. E.; Jackman, C. H.; Kolb, C. E., Jr.; Kurylo, M. J., III; Orkin, V. L.; Wine, P. H.

    2014-12-01

    Atmospheric chemistry models must include a large number of processes to accurately describe the temporal and spatial behavior of atmospheric composition. They require a wide range of chemical and physical data (parameters) that describe elementary gas-phase and heterogeneous processes. The review and evaluation of chemical and physical data has, therefore, played an important role in the development of chemical models and in their use in environmental assessment activities. The NASA data panel was originally established in 1977 by the NASA Upper Atmosphere Research Program Office to provide a critical evaluation of kinetic and photochemical data for use in laboratory studies and in atmospheric modeling of stratospheric ozone. Today, the NASA data panel evaluations have a broader atmospheric focus and include Ox, O(1D), singlet O2, HOx, NOx, Organic, FOx, ClOx, BrOx, IOx, SOx, and Na reactions, three-body reactions, equilibrium constants, photochemistry, aqueous chemistry, heterogeneous chemistry and processes, and thermodynamic parameters. The 2011 evaluation (JPL 10-6 available at http://jpldataeval.jpl.nasa.gov.) includes the comprehensive coverage of ~670 bimolecular reactions, 75 three-body reactions, 24 equilibrium constants, 215 photochemical species, 355 aqueous and heterogeneous processes, thermodynamic parameters for 590 species, and over 4000 literature citations. Each evaluation includes (1) recommended values (e.g. rate coefficients, absorption cross sections, and uptake coefficients) with estimated uncertainty factors and (2) a note describing the available experimental and theoretical data and explanation for the recommendation. As new studies have become available over the years the recommendations are critically reviewed and updated as warranted (the next evaluation is scheduled for release in early 2015). This presentation provides an overview of the NASA data panel evaluation process and the methodology used to estimate uncertainties. Examples on the current use of a 2-D model to help set evaluation priorities will be illustrated. Evaluation users are encouraged to discuss/suggest potential improvements in analysis and the communication of the evaluation results to the modeling community.

  15. Ab Initio Molecular Orbital Calculations of Electronic Effects on the Kinetics of Cyclopropylcarbinyl Radical Ring Openings

    E-print Network

    Schlegel, H. Bernhard

    of Cyclopropylcarbinyl Radical Ring Openings Felix N. Martinez, H. Bernhard Schlegel,* and Martin Newcomb* Department orbital calculations have been performed on the ring-opening reactions of cyclopropylcarbinyl radical substituents on the radical center. Barrier heights were calculated at the UHF/6-31G*, UMP2/6-31G*//UHF/6-31G

  16. Computer program for calculation of complex chemical equilibrium compositions and applications. Part 1: Analysis

    NASA Technical Reports Server (NTRS)

    Gordon, Sanford; Mcbride, Bonnie J.

    1994-01-01

    This report presents the latest in a number of versions of chemical equilibrium and applications programs developed at the NASA Lewis Research Center over more than 40 years. These programs have changed over the years to include additional features and improved calculation techniques and to take advantage of constantly improving computer capabilities. The minimization-of-free-energy approach to chemical equilibrium calculations has been used in all versions of the program since 1967. The two principal purposes of this report are presented in two parts. The first purpose, which is accomplished here in part 1, is to present in detail a number of topics of general interest in complex equilibrium calculations. These topics include mathematical analyses and techniques for obtaining chemical equilibrium; formulas for obtaining thermodynamic and transport mixture properties and thermodynamic derivatives; criteria for inclusion of condensed phases; calculations at a triple point; inclusion of ionized species; and various applications, such as constant-pressure or constant-volume combustion, rocket performance based on either a finite- or infinite-chamber-area model, shock wave calculations, and Chapman-Jouguet detonations. The second purpose of this report, to facilitate the use of the computer code, is accomplished in part 2, entitled 'Users Manual and Program Description'. Various aspects of the computer code are discussed, and a number of examples are given to illustrate its versatility.

  17. A Comparison of EPIcode and ALOHA Calculations for Pool Evaporation and Chemical Atmospheric Transport and Dispersion.

    SciTech Connect

    Andrew, VINCENT

    2005-04-22

    EPIcode (version 7.0) and ALOHA (version 5.2.3) are two of the designated toolbox codes identified in the Department of Energy's Implementation Plan for DNFSB Recommendation 2002-1 on Software Quality Assurance issues in the DOE Complex. Both have the capability to estimate evaporation rates from pools formed from chemical spills and to predict subsequent atmospheric transport and dispersion. This paper provides an overview of the algorithms used by EPIcode and ALOHA to calculate evaporation rates and downwind plume concentrations. The technical bases for these algorithms are briefly discussed, and differences in the EPIcode and ALOHA methodologies highlighted. In addition, sample calculations are performed using EPIcode and ALOHA for selected chemicals under various environmental conditions. Side-by-side comparisons of results from sample calculations are analyzed to illustrate the impact that the different methodologies used by EPIcode and ALOHA have on predicted evaporation rates and downwind concentrations.

  18. Dimesitylketone O-oxide: verification of an unusually stable carbonyl oxide by NMR chemical shift calculations

    NASA Astrophysics Data System (ADS)

    Kraka, Elfi; Sosa, Carlos P.; Cremer, Dieter

    1996-09-01

    NMR chemical shift calculations in combination with geometry optimizations both based on density functional theory were used to identify and to describe dimesitylketone O-oxide ( 6), which is the first carbonyl oxide that could be generated in solution at - 78°C and investigated by NMR spectroscopy. The conformation of carbonyl oxide 6 is characterized by two orthogonal mesityl rings and a close O,H contact between one of the H atoms of the mesityl methyl groups and the terminal O atom of the carbonyl oxide. The calculated geometry and conformation of 6 are verified by the agreement of calculated and measured NMR chemical shifts. The unusual rearrangement of 6 to an alcohol is explained.

  19. An efficient method for energy levels calculation using full symmetry and exact kinetic energy operator: Tetrahedral molecules

    NASA Astrophysics Data System (ADS)

    Nikitin, A. V.; Rey, M.; Tyuterev, Vl. G.

    2015-03-01

    A simultaneous use of the full molecular symmetry and of an exact kinetic energy operator (KEO) is of key importance for accurate predictions of vibrational levels at a high energy range from a potential energy surface (PES). An efficient method that permits a fast convergence of variational calculations would allow iterative optimization of the PES parameters using experimental data. In this work, we propose such a method applied to tetrahedral AB4 molecules for which a use of high symmetry is crucial for vibrational calculations. A symmetry-adapted contracted angular basis set for six redundant angles is introduced. Simple formulas using this basis set for explicit calculation of the angular matrix elements of KEO and PES are reported. The symmetric form (six redundant angles) of vibrational KEO without the sin(q)-2 type singularity is derived. The efficient recursive algorithm based on the tensorial formalism is used for the calculation of vibrational matrix elements. A good basis set convergence for the calculations of vibrational levels of the CH4 molecule is demonstrated.

  20. Infrared absorption spectroscopy and chemical kinetics of free radicals. Final performance report, August 1, 1985--July 31, 1994

    SciTech Connect

    Curl, R.F.; Glass, G.P.

    1995-06-01

    This research was directed at the detection, monitoring, and study (by infrared absorption spectroscopy) of the chemical kinetic behavior of small free radical species thought to be important intermediates in combustion. The work typically progressed from the detection and analysis of the infrared spectrum of combustion radical to the utilization of the infrared spectrum thus obtained in the investigation of chemical kinetics of the radical species. The methodology employed was infrared kinetic spectroscopy. In this technique the radical is produced by UV flash photolysis using an excimer laser and then its transient infrared absorption is observed using a single frequency cw laser as the source of the infrared probe light. When the probe laser frequency is near the center of an absorption line of the radical produced by the flash, the transient infrared absorption rises rapidly and then decays as the radical reacts with the precursor or with substances introduced for the purpose of studying the reaction kinetics or with itself. The decay times observed in these studies varied from less than one microsecond to more than one millisecond. By choosing appropriate time windows after the flash and the average infrared detector signal in a window as data channels, the infrared spectrum of the radical may be obtained. By locking the infrared probe laser to the center of the absorption line and measuring the rate of decay of the transient infrared absorption signal as the chemical composition of the gas mixture is varied, the chemical kinetics of the radical may be investigated. In what follows the systems investigated and the results obtained are outlined.

  1. Using CBL Technology and a Graphing Calculator To Teach the Kinetics of Consecutive First-Order Reactions

    NASA Astrophysics Data System (ADS)

    Cortés-Figueroa, José E.; Moore, Deborah A.

    1999-05-01

    The Calculator-Based Laboratory (CBL) system is an inexpensive data-collection instrument that feeds tabular and graphical information directly into either a graphing calculator or a computer. The CBL system and a graphing calculator permit hands-on experiences in both classroom and laboratory settings. This work proposes a demonstration to introduce first-order reactions using the CBL system. It then presents the analysis of two consecutive first-order reactions. The values of the rate constants that govern each reaction's rate are determined using the graphing and statistical capabilities of a TI-83 calculator. The rate constant values are used to obtain a regression equation that models the entire process, predicting the behavior of absorbance versus time as the reactions progress. This technique is useful because it allows instructors to engage students in an in-class activity analyzing data. It permits rigorous discussion of complex kinetics behavior without overemphasizing tedious mathematical manipulations. The example discussed in this article involves two consecutive first-order reactions whose progress is monitored by observing the change in the absorbance intensity of the solution with time. This example is challenging particularly because all the species in solution contribute to the value of the absorbance.

  2. Quantum chemical calculation of the equilibrium structures of small metal atom clusters

    NASA Technical Reports Server (NTRS)

    Kahn, L. R.

    1981-01-01

    A decomposition of the molecular energy is presented that is motivated by the atom superposition and electron delocalization physical model of chemical binding. The energy appears in physically transparent form consisting of a classical electrostatic interaction, a zero order two electron exchange interaction, a relaxation energy, and the atomic energies. Detailed formulae are derived in zero and first order of approximation. The formulation extends beyond first order to any chosen level of approximation leading, in principle, to the exact energy. The structure of this energy decomposition lends itself to the fullest utilization of the solutions to the atomic sub problems to simplify the calculation of the molecular energy. If nonlinear relaxation effects remain minor, the molecular energy calculation requires at most the calculation of two center, two electron integrals. This scheme thus affords the prospects of substantially reducing the computational effort required for the calculation of molecular energies.

  3. From the Cover: Force-dependent chemical kinetics of disulfide bond reduction observed with single-molecule techniques

    NASA Astrophysics Data System (ADS)

    Wiita, Arun P.; Rama Koti Ainavarapu, Sri; Huang, Hector H.; Fernandez, Julio M.

    2006-05-01

    The mechanism by which mechanical force regulates the kinetics of a chemical reaction is unknown. Here, we use single-molecule force-clamp spectroscopy and protein engineering to study the effect of force on the kinetics of thiol/disulfide exchange. Reduction of disulfide bonds through the thiol/disulfide exchange chemical reaction is crucial in regulating protein function and is known to occur in mechanically stressed proteins. We apply a constant stretching force to single engineered disulfide bonds and measure their rate of reduction by DTT. Although the reduction rate is linearly dependent on the concentration of DTT, it is exponentially dependent on the applied force, increasing 10-fold over a 300-pN range. This result predicts that the disulfide bond lengthens by 0.34 Å at the transition state of the thiol/disulfide exchange reaction. Our work at the single bond level directly demonstrates that thiol/disulfide exchange in proteins is a force-dependent chemical reaction. Our findings suggest that mechanical force plays a role in disulfide reduction in vivo, a property that has never been explored by traditional biochemistry. Furthermore, our work also indicates that the kinetics of any chemical reaction that results in bond lengthening will be force-dependent. atomic force microscopy | mechanochemistry

  4. Role of Thermal Diffusion and Chemical Kinetics in Infrared Tissue Ablation

    NASA Astrophysics Data System (ADS)

    Edwards, Glenn; Hutson, M. Shane

    2003-03-01

    We have theoretically investigated the role of dynamic processes, specifically thermal diffusion and chemical kinetics, to account for experimental observations of the preferential ablative properties of infrared radiation from a tunable Mark-III free-electron laser (FEL). The model is based on a laminar system composed of alternating layers of protein and saline. The picosecond pulses of the Mark-III superpulse are teated as a train of impulses with a 3-GHz repetition rate. We find that the heating rates are sufficient to superheat the outer saline layers on the nanosecond time scale, leading to explosive vaporization. We also find that the competition between the layer specific heating rates and thermal diffusion results in wavelength-dependent separation in layer temperatures. There is no evidence for thermal bond breaking on relevant time scales. At 6.45 microns, but not 3.0 microns, there is evidence for a significant helix-coil transition. While the native protein is ductile, the denatured protein exhibits brittle fracture. This model provides a dynamic account of the preferential ablative properties experimentally observed with a Mark-III FEL tuned near 6.45 microns. See Phys. Rev. E 65, 061906 (2002).

  5. A multiple shock tube and chemical kinetic modeling study of diethyl ether pyrolysis and oxidation.

    PubMed

    Yasunaga, K; Gillespie, F; Simmie, J M; Curran, H J; Kuraguchi, Y; Hoshikawa, H; Yamane, M; Hidaka, Y

    2010-09-01

    The pyrolysis and oxidation of diethyl ether (DEE) has been studied at pressures from 1 to 4 atm and temperatures of 900-1900 K behind reflected shock waves. A variety of spectroscopic diagnostics have been used, including time-resolved infrared absorption at 3.39 mum and time-resolved ultraviolet emission at 431 nm and absorption at 306.7 nm. In addition, a single-pulse shock tube was used to measure reactant, intermediate, and product species profiles by GC samplings at different reaction times varying from 1.2 to 1.8 ms. A detailed chemical kinetic model comprising 751 reactions involving 148 species was assembled and tested against the experiments with generally good agreement. In the early stages of reaction the unimolecular decomposition and hydrogen atom abstraction of DEE and the decomposition of the ethoxy radical have the largest influence. In separate experiments at 1.9 atm and 1340 K, it is shown that DEE inhibits the reactivity of an equimolar mixture of hydrogen and oxygen (1% of each). PMID:20690588

  6. Effect of excluded volume on 2D discrete stochastic chemical kinetics

    SciTech Connect

    Lampoudi, Sotiria [Dept. of Computer Science, University of California, Santa Barbara, CA 93106 (United States)], E-mail: slampoud@cs.ucsb.edu; Gillespie, Dan T. [Dan T Gillespie Consulting, 30504 Cordoba Place, Castaic, CA 91384 (United States); Petzold, Linda R. [Dept. of Computer Science, University of California, Santa Barbara, CA 93106 (United States)

    2009-06-01

    The stochastic simulation algorithm (SSA) is widely used in the discrete stochastic simulation of chemical kinetics. The propensity functions which play a central role in this algorithm have been derived under the point-molecule assumption, i.e., that the total volume of the molecules is negligible compared to the volume of the container. It has been shown analytically that for a one-dimensional system and the A + A reaction, when the point-molecule assumption is relaxed, the propensity function need only be adjusted by replacing the total volume of the system with the free volume of the system. In this paper we investigate via numerical simulations the impact of relaxing the point-molecule assumption in two dimensions. We find that the distribution of times to the first collision is close to exponential in most cases, so that the formalism of the propensity function is still applicable. In addition, we find that the area excluded by the molecules in two dimensions is usually higher than their close-packed area, requiring a larger correction to the propensity function than just the replacement of the total volume by the free volume.

  7. Effect of excluded volume on 2D discrete stochastic chemical kinetics

    PubMed Central

    Lampoudi, Sotiria; Gillespie, Dan T.; Petzold, Linda R.

    2009-01-01

    The Stochastic Simulation Algorithm (SSA) is widely used in the discrete stochastic simulation of chemical kinetics. The propensity functions which play a central role in this algorithm have been derived under the point-molecule assumption, i.e., that the total volume of the molecules is negligible compared to the volume of the container. It has been shown analytically that for a one dimensional system and the A+A reaction, when the point molecule assumption is relaxed, the propensity function need only be adjusted by replacing the total volume of the system with the free volume of the system. In this paper we investigate via numerical simulations the impact of relaxing the point-molecule assumption in two dimensions. We find that the distribution of times to the first collision is close to exponential in most cases, so that the formalism of the propensity function is still applicable. In addition, we find that the area excluded by the molecules in two dimensions is usually higher than their close-packed area, requiring a larger correction to the propensity function than just the replacement of the total volume by the free volume. PMID:19360139

  8. Fundamental Kinetic Modeling: ab initio rate constant calculations of elementary reactions 

    E-print Network

    Jenks, Richard Lee

    1998-01-01

    . The following discussion follows that of Benson (1976). Group Additivity Group additivity is a simple way to estimate the heat capacity, entropy and standard heat of formation for chemical species in a reaction. Each molecule is broken up into groups... method. The table containing the values of the fee-radical group are available as well. If these properties are required at temperatures other than 298 K, heat capacity data at several temperatures are given, and equations (7) and (8) are used...

  9. Fundamental Kinetic Modeling: ab initio rate constant calculations of elementary reactions

    E-print Network

    Jenks, Richard Lee

    1998-01-01

    . . . IV . . . . . . 3 . . . . . . 4 . . 7 . . . . . . 9 . . 15 . . . 15 . . . 15 . . . 17 17 24 Addition of Phosgene to Aniline to Form Arylcarbamoyl Chloride . . . . . . . 26 Elimination of Hydrogen Chloride from Arylcarbamoyl Chloride... to aniline. . . . . . . . . . . . 26 Table 13. Calculated reaction parameters for reaction (5), phosgene addition to aniline , . . . . 28 Table 14. AS"" of various species. Table 15. Rate constants for reaction (6), conversion of carbamoyl chloride...

  10. Calculation of NMR chemical shifts. 7. Gauge-invariant INDO method

    NASA Astrophysics Data System (ADS)

    Fukui, H.; Miura, K.; Hirai, A.

    A gauge-invariant INDO method based on the coupled Hartree-Fuck perturbation theory is presented and applied to the calculation of 1H and 13C chemical shifts of hydrocarbons including ring compounds. Invariance of the diamagnetic and paramagnetic shieldings with respect to displacement of the coordinate origin is discussed. Comparison between calculated and experimental results exhibits fairly good agreement, provided that the INDO parameters of Ellis et al. (J. Am. Chem. Soc.94, 4069 (1972)) are used with the inclusion of all multicenter one-electron integrals.

  11. Chemical accuracy in QM/MM calculations on enzyme-catalysed reactions

    PubMed Central

    Mulholland, Adrian J

    2007-01-01

    Combined quantum mechanics/molecular mechanics (QM/MM) modelling has the potential to answer fundamental questions about enzyme mechanisms and catalysis. Calculations using QM/MM methods can now predict barriers for enzyme-catalysed reactions with unprecedented, near chemical accuracy, i.e. to within 1 kcal/mol in the best cases. Quantitative predictions from first-principles calculations were only previously possible for very small molecules. At this level, quantitative, reliable predictions can be made about the mechanisms of enzyme-catalysed reactions. This development signals a new era of computational biochemistry. PMID:17880750

  12. A Chemical Kinetic Modeling Study of the Effects of Oxygenated Hydrocarbons on Soot Emissions from Diesel Engines

    SciTech Connect

    Westbrook, C K; Pitz, W J; Curran, H J

    2005-11-14

    A detailed chemical kinetic modeling approach is used to examine the phenomenon of suppression of sooting in diesel engines by addition of oxygenated hydrocarbon species to the fuel. This suppression, which has been observed experimentally for a few years, is explained kinetically as a reduction in concentrations of soot precursors present in the hot products of a fuel-rich diesel ignition zone when oxygenates are included. Oxygenates decrease the overall equivalence ratio of the igniting mixture, producing higher ignition temperatures and more radical species to consume more soot precursor species, leading to lower soot production. The kinetic model is also used to show how different oxygenates, ester structures in particular, can have different soot-suppression efficiencies due to differences in molecular structure of the oxygenated species.

  13. LocalSCF method for semiempirical quantum-chemical calculation of ultralarge biomolecules

    Microsoft Academic Search

    N. A. Anikin; V. M. Anisimov; V. L. Bugaenko; V. V. Bobrikov; A. M. Andreyev

    2004-01-01

    A linear-scaling semiempirical method, LocalSCF, has been proposed for the quantum-chemical calculations of ultralarge molecular systems by treating the large-scale molecular task as a variational problem. The method resolves the self-consistent field task through the finite atomic expansion of weakly nonorthogonal localized molecular orbitals. The inverse overlap matrix arising from the nonorthogonality of the localized orbitals is approximated by preserving

  14. Determination of atropisomeric configurations of macrocyclic bisbibenzyls by HPLC-CD/UV and quantum chemical calculations.

    PubMed

    Wang, Li-Ning; Xie, Chun-Feng; Zhu, Xiao-Song; Fan, Pei-Hong; Lou, Hong-Xiang

    2011-04-01

    Isoriccardin C (1) and riccardin D (2), isolated from the liverwort Reboulia hemisphaerica, were first characterized to be a mixture of two enantiomeric atropisomers by online chiral high-performance liquid chromatography-circular dichroism (HPLC-CD) analysis. Exemplarily for bisbibenzyls of the diarylether-biphenyl type, the absolute atropisomeric configurations of compunds 1 and 2 were determined by the analysis of their CD data coupled with quantum chemical CD calculations. PMID:21462034

  15. SIML: A Fast SIMD Algorithm for Calculating LINGO Chemical Similarities on GPUs and CPUs

    PubMed Central

    Haque, Imran S.; Walters, W. Patrick

    2010-01-01

    LINGOs are a holographic measure of chemical similarity based on text comparison of SMILES strings. We present a new algorithm for calculating LINGO similarities amenable to parallelization on SIMD architectures (such as GPUs and vector units of modern CPUs). We show that it is nearly 3 times as fast as existing algorithms on a CPU, and over 80 times faster than existing methods when run on a GPU. PMID:20218693

  16. Effect of kinetic and configurational thermostats on calculations of the first normal stress coefficient in nonequilibrium molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Daivis, Peter J.; Dalton, Benjamin A.; Morishita, Tetsuya

    2012-11-01

    Thermostats for homogeneous nonequilibrium molecular dynamics simulations are usually designed to control the kinetic temperature, but it is now possible control any combination of many different types of temperature, including the configurational and kinetic temperatures and their directional components. It is well known that these temperatures can become unequal in homogeneously thermostatted shearing steady states. The microscopic expressions for these temperatures are all derived from equilibrium distribution functions, and it is pertinent to ask, what are the consequences of using these equilibrium microscopic expressions for temperature in thermostats for shearing nonequilibrium steady states? Here we show that the answer to this question depends on which properties are being investigated. We present numerical results showing that the value of the zero shear rate viscosity obtained by extrapolating results of nonequilibrium molecular dynamics simulations of shearing steady states is the same, regardless of the type of temperature that is controlled. It also agrees with the value obtained from the equilibrium stress autocorrelation function via the Green-Kubo relation. However, the values of the limiting zero shear rate first normal stress coefficient obtained from nonequilibrium molecular dynamics simulations of shearing steady states are strongly dependent on the choice of temperature being controlled. They also differ from the value of the first normal stress coefficient that is calculated from the equilibrium stress autocorrelation function. We show that even when all of the directional components of the kinetic and configurational temperatures are simultaneously controlled to the same value, the agreement with the result obtained from the equilibrium stress autocorrelation function is poor.

  17. Effect of kinetic and configurational thermostats on calculations of the first normal stress coefficient in nonequilibrium molecular dynamics simulations.

    PubMed

    Daivis, Peter J; Dalton, Benjamin A; Morishita, Tetsuya

    2012-11-01

    Thermostats for homogeneous nonequilibrium molecular dynamics simulations are usually designed to control the kinetic temperature, but it is now possible control any combination of many different types of temperature, including the configurational and kinetic temperatures and their directional components. It is well known that these temperatures can become unequal in homogeneously thermostatted shearing steady states. The microscopic expressions for these temperatures are all derived from equilibrium distribution functions, and it is pertinent to ask, what are the consequences of using these equilibrium microscopic expressions for temperature in thermostats for shearing nonequilibrium steady states? Here we show that the answer to this question depends on which properties are being investigated. We present numerical results showing that the value of the zero shear rate viscosity obtained by extrapolating results of nonequilibrium molecular dynamics simulations of shearing steady states is the same, regardless of the type of temperature that is controlled. It also agrees with the value obtained from the equilibrium stress autocorrelation function via the Green-Kubo relation. However, the values of the limiting zero shear rate first normal stress coefficient obtained from nonequilibrium molecular dynamics simulations of shearing steady states are strongly dependent on the choice of temperature being controlled. They also differ from the value of the first normal stress coefficient that is calculated from the equilibrium stress autocorrelation function. We show that even when all of the directional components of the kinetic and configurational temperatures are simultaneously controlled to the same value, the agreement with the result obtained from the equilibrium stress autocorrelation function is poor. PMID:23214906

  18. Kinetics of chemical ordering in a Ag-Pt nanoalloy particle via first-principles simulations

    NASA Astrophysics Data System (ADS)

    Negreiros, F. R.; Taherkhani, F.; Parsafar, G.; Caro, A.; Fortunelli, A.

    2012-11-01

    The energetics and kinetic energy barriers of vacancy/atom exchange in a 37-atom truncated octahedron Ag-Pt binary cluster in the Ag-rich range of compositions are investigated via a first-principles atomistic approach. The energy of the local minima obtained considering various distributions of a single vacancy and a few Pt atoms within the cluster and the energy barriers connecting them are evaluated using accurate density-functional calculations. The effects of the simultaneous presence of a vacancy and Pt atoms are found to be simply additive when their distances are larger than first-neighbors, whereas when they can be stabilizing at low Pt content due to the release of strain by the Pt/vacancy interaction or destabilizing close to a perfect Pt(core)/Ag(shell) arrangement. It is found that alloying with Pt appreciably increases the barriers for homotops transformations, thus rationalizing the issues encountered at the experimental level in producing Ag-Pt equilibrated nanoparticles and bulk phase diagram.

  19. Kinetics of chemical ordering in a Ag-Pt nanoalloy particle via first-principles simulations

    SciTech Connect

    Negreiros, F. R.; Fortunelli, A. [CNR-IPCF, Istituto per i Processi Chimico-Fisici del Consiglio Nazionale delle Ricerche, Molecular Modeling Laboratory, via G. Moruzzi 1, Pisa I56124 (Italy); Taherkhani, F. [Department of Chemistry, Razi University, Kermanshah (Iran, Islamic Republic of); Parsafar, G. [Department of Chemistry and Nanotechnology Center, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Caro, A. [Los Alamos National Laboratories, Division of Materials Science and Technology, Los Alamos, New Mexico 87545 (United States)

    2012-11-21

    The energetics and kinetic energy barriers of vacancy/atom exchange in a 37-atom truncated octahedron Ag-Pt binary cluster in the Ag-rich range of compositions are investigated via a first-principles atomistic approach. The energy of the local minima obtained considering various distributions of a single vacancy and a few Pt atoms within the cluster and the energy barriers connecting them are evaluated using accurate density-functional calculations. The effects of the simultaneous presence of a vacancy and Pt atoms are found to be simply additive when their distances are larger than first-neighbors, whereas when they can be stabilizing at low Pt content due to the release of strain by the Pt/vacancy interaction or destabilizing close to a perfect Pt(core)/Ag(shell) arrangement. It is found that alloying with Pt appreciably increases the barriers for homotops transformations, thus rationalizing the issues encountered at the experimental level in producing Ag-Pt equilibrated nanoparticles and bulk phase diagram.

  20. Substantiation of the two-temperature kinetic model by comparing calculations within the kinetic and fluid models of the positive column plasma of a dc oxygen discharge

    Microsoft Academic Search

    E. A. Bogdanov; A. A. Kudryavtsev; L. D. Tsendin; R. R. Arslanbekov; V. I. Kolobov; V. V. Kudryavtsev

    2003-01-01

    Results from kinetic and fluid simulations of the positive column plasma of a dc oxygen discharge are compared using commercial\\u000a CFDRC software (http:\\/\\/www.cfdrc.com\\/?cfdplasma), which enables one to perform numerical simulations in an arbitrary 3D geometry with the use of both the fluid equations\\u000a for all the components (fluid model) and the kinetic equation for the electron energy distribution function (kinetic

  1. Kinetic lattice grand canonical Monte Carlo simulation for ion current calculations in a model ion channel system

    NASA Astrophysics Data System (ADS)

    Hwang, Hyonseok; Schatz, George C.; Ratner, Mark A.

    2007-07-01

    An algorithm in which kinetic lattice grand canonical Monte Carlo simulations are combined with mean field theory (KLGCMC/MF) is presented to calculate ion currents in a model ion channel system. In this simulation, the relevant region of the system is treated by KLGCMC simulations, while the rest of the system is described by modified Poisson-Boltzmann mean field theory. Calculation of reaction field due to induced charges on the channel/water and membrane/water boundaries is carried out using a basis-set expansion method [Im and Roux, J. Chem. Phys. 115, 4850 (2001)]. Calculation of ion currents, electrostatic potentials, and ion concentrations, as obtained from the KLGCMC/MF simulations, shows good agreement with Poisson-Nernst-Planck (PNP) theory predictions when the channel and membrane have the same dielectric constant as water. If the channel and membrane have a lower dielectric constant than water, however, there is a considerable difference between the KLGCMC/MF and PNP predictions. This difference is attributed to the reaction field, which is missing in PNP theory. It is demonstrated that the reaction field as well as fixed charges in the channel play key roles in selective ion transport. Limitations and further development of the current KLGCMC/MF approach are also discussed.

  2. A combined quantum-classical dynamics method for calculating thermal rate constants of chemical reactions in solution

    E-print Network

    Truong, Thanh N.

    -flux correlation function for calculating the thermal rate constants of chemical reactions in solution in this study would provide a complete tool for studying the quantum dynamics of chemical reactions the thermal chemical reaction rate constants. Furthermore, we also employ an efficient and accurate quantum

  3. Chemical kinetic study of the oxidation of a biodiesel-bioethanol surrogate fuel: methyl octanoate-ethanol mixtures.

    PubMed

    Togbé, C; May-Carle, J-B; Dayma, G; Dagaut, P

    2010-03-25

    There is a growing interest for using bioethanol-biodiesel fuel blends in diesel engines but no kinetic data and model for their combustion were available. Therefore, the kinetics of oxidation of a biodiesel-bioethanol surrogate fuel (methyl octanoate-ethanol) was studied experimentally in a jet-stirred reactor at 10 atm and constant residence time, over the temperature range 560-1160 K, and for several equivalence ratios (0.5-2). Concentration profiles of reactants, stable intermediates, and final products were obtained by probe sampling followed by online FTIR, and off-line gas chromatography analyses. The oxidation of this fuel in these conditions was modeled using a detailed chemical kinetic reaction mechanism consisting of 4592 reversible reactions and 1087 species. The proposed kinetic reaction mechanism yielded a good representation of the kinetics of oxidation of this biodiesel-bioethanol surrogate under the JSR conditions. The modeling was used to delineate the reactions triggering the low-temperature oxidation of ethanol important for diesel engine applications. PMID:20235606

  4. Mathematical and computational science issues in high precision Hylleraas–configuration interaction variational calculations: II. Kinetic energy and electron–nucleus interaction integrals

    Microsoft Academic Search

    James S Sims; Stanley A Hagstrom

    2007-01-01

    Three-electron kinetic energy and electron–nucleus interaction integrals arising in Hylleraas–configuration interaction (Hy–CI) calculations are discussed. We show that the electron–nucleus interaction operators introduce no new integral complications and that the kinetic energy operators lead to integrals which have much in common with electron interaction integrals treated in the first paper of this series. We discuss the efficient evaluation of the

  5. Surftherm: A program to analyze thermochemical and kinetic data in gas-phase and surface chemical reaction mechanisms

    SciTech Connect

    Coltrin, M.E.; Moffat, H.K.

    1994-06-01

    This report documents the Surftherm program that analyzes transport coefficient, thermochemical- and kinetic rate information in complex gas-phase and surface chemical reaction mechanisms. The program is designed for use with the Chemkin (gas-phase chemistry) and Surface Chemkin (heterogeneous chemistry) programs. It was developed as a ``chemist`s companion`` in using the Chemkin packages with complex chemical reaction mechanisms. It presents in tabular form detailed information about the temperature and pressure dependence of chemical reaction rate constants and their reverse rate constants, reaction equilibrium constants, reaction thermochemistry, chemical species thermochemistry and transport properties. This report serves as a user`s manual for use of the program, explaining the required input and the output.

  6. Accelerated Stability and Chemical Kinetics of Ethanol Extracts of Fruit of Piper sarmentosum Using High Performance Liquid Chromatography

    PubMed Central

    Khalid, Hussain; Zhari, Ismail; Amirin, Sadikun; Pazilah, Ibrahim

    2011-01-01

    The extracts of Piper sarmentosum, a medicinal plant, are being used to prepare phytopharmaceuticals while the information about chemical kinetics of constituents of the extract is unavailable to assign precise shelf life (t90) and find optimum storage conditions of the product for patient safety, and to avoid economic repercussions of launching an unstable product. The extract was exposed to three different conditions of high temperature and relative humidity (RH) for six months. The samples were then analyzed at 0, 1, 2, 4 and 6 months by high performance liquid chromatography (HPLC) using pellitorine, sarmentine and sarmentosine as markers. Different chemical kinetic parameters of the markers were evaluated by Arrhenius equation to predict shelf life (t90) at different storage conditions and at room temperature. The markers in the extract followed the zero order degradation, and the activation energy, pre exponential factor and rate constant of the reaction of the markers were found to be varying in samples stored at different conditions. The contents of the markers were found to be decreasing at high temperature and humidity with the passage of time. The predicted shelf life (t90) of the markers at room temperature was found to be 16 months approximately. Results of this study indicate that extracts of the plant are stable at room temperature for 16 months. Moreover, the chemical kinetic data of the markers and the analytical method used to quantify the markers may be useful for phytopharmaceutical industry to produce efficacious and stable products from extracts of the plant. PMID:24250372

  7. Accelerated Stability and Chemical Kinetics of Ethanol Extracts of Fruit of Piper sarmentosum Using High Performance Liquid Chromatography.

    PubMed

    Khalid, Hussain; Zhari, Ismail; Amirin, Sadikun; Pazilah, Ibrahim

    2011-01-01

    The extracts of Piper sarmentosum, a medicinal plant, are being used to prepare phytopharmaceuticals while the information about chemical kinetics of constituents of the extract is unavailable to assign precise shelf life (t90) and find optimum storage conditions of the product for patient safety, and to avoid economic repercussions of launching an unstable product. The extract was exposed to three different conditions of high temperature and relative humidity (RH) for six months. The samples were then analyzed at 0, 1, 2, 4 and 6 months by high performance liquid chromatography (HPLC) using pellitorine, sarmentine and sarmentosine as markers. Different chemical kinetic parameters of the markers were evaluated by Arrhenius equation to predict shelf life (t90) at different storage conditions and at room temperature. The markers in the extract followed the zero order degradation, and the activation energy, pre exponential factor and rate constant of the reaction of the markers were found to be varying in samples stored at different conditions. The contents of the markers were found to be decreasing at high temperature and humidity with the passage of time. The predicted shelf life (t90) of the markers at room temperature was found to be 16 months approximately. Results of this study indicate that extracts of the plant are stable at room temperature for 16 months. Moreover, the chemical kinetic data of the markers and the analytical method used to quantify the markers may be useful for phytopharmaceutical industry to produce efficacious and stable products from extracts of the plant. PMID:24250372

  8. Catalytic mechanism of porphobilinogen synthase: the chemical step revisited by QM/MM calculations.

    PubMed

    Tian, Bo-Xue; Erdtman, Edvin; Eriksson, Leif A

    2012-10-11

    Porphobilinogen synthase (PBGS) catalyzes the asymmetric condensation and cyclization of two 5-aminolevulinic acid (5-ALA) substrate molecules to give porphobilinogen (PBG). The chemical step of PBGS is herein revisited using QM/MM (ONIOM) calculations. Two different protonation states and several different mechanisms are considered. Previous mechanisms based on DFT-only calculations are shown unlikely to occur. According to these new calculations, the deprotonation step rather than ring closure is rate-limiting. Both the C-C bond formation first mechanism and the C-N bond formation first mechanism are possible, depending on how the A-site ALA binds to the enzyme. We furthermore propose that future work should focus on the substrate binding step rather than the enzymatic mechanism. PMID:22974111

  9. Phosphorus chemical shifts in a nucleic acid backbone from combined molecular dynamics and density functional calculations.

    PubMed

    P?ececht?lová, Jana; Novák, Petr; Munzarová, Markéta L; Kaupp, Martin; Sklená?, Vladimír

    2010-12-01

    A comprehensive quantum chemical analysis of the influence of backbone torsion angles on (31)P chemical shifts in DNAs has been carried out. An extensive DFT study employed snapshots obtained from the molecular dynamics simulation of [d(CGCGAATTCGCG)]2 to construct geometries of a hydrated dimethyl phosphate, which was used as a model for the phosphodiester linkage. Our calculations provided differences of 2.1 ± 0.3 and 1.6 ± 0.3 ppm between the B(I) and B(II) chemical shifts in two B-DNA residues of interest, which is in a very good agreement with the difference of 1.6 ppm inferred from experimental data. A more negative (31)P chemical shift for a residue in pure BI conformation compared to residues in mixed B(I)/B(II) conformation states is provided by DFT, in agreement with the NMR experiment. Statistical analysis of the MD/DFT data revealed a large dispersion of chemical shifts in both B(I) and B(II) regions of DNA structures. ?P ranges within 3.5 ± 0.8 ppm in the B(I) region and within 4.5 ± 1.5 ppm in the B(II) region. While the (31)P chemical shift becomes more negative with increasing ? in B(I)-DNA, it has the opposite trend in B(II)-DNA when both ? and ? increase simultaneously. The (31)P chemical shift is dominated by the torsion angles ? and ?, while an implicit treatment of ? and ? is sufficient. The presence of an explicit solvent leads to a damping and a 2-3 ppm upfield shift of the torsion angle dependences. PMID:21073198

  10. Three-dimensional kinetic Monte Carlo simulations of diamond chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Rodgers, W. J.; May, P. W.; Allan, N. L.; Harvey, J. N.

    2015-06-01

    A three-dimensional kinetic Monte Carlo model has been developed to simulate the chemical vapor deposition of a diamond (100) surface under conditions used to grow single-crystal diamond (SCD), microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films. The model includes adsorption of CHx (x = 0, 3) species, insertion of CHy (y = 0-2) into surface dimer bonds, etching/desorption of both transient adsorbed species and lattice sidewalls, lattice incorporation, and surface migration but not defect formation or renucleation processes. A value of ˜200 kJ mol-1 for the activation Gibbs energy, ?G‡etch, for etching an adsorbed CHx species reproduces the experimental growth rate accurately. SCD and MCD growths are dominated by migration and step-edge growth, whereas in NCD and UNCD growths, migration is less and species nucleate where they land. Etching of species from the lattice sidewalls has been modelled as a function of geometry and the number of bonded neighbors of each species. Choice of appropriate parameters for the relative decrease in etch rate as a function of number of neighbors allows flat-bottomed etch pits and/or sharp-pointed etch pits to be simulated, which resemble those seen when etching diamond in H2 or O2 atmospheres. Simulation of surface defects using unetchable, immobile species reproduces other observed growth phenomena, such as needles and hillocks. The critical nucleus for new layer growth is 2 adjacent surface carbons, irrespective of the growth regime. We conclude that twinning and formation of multiple grains rather than pristine single-crystals may be a result of misoriented growth islands merging, with each island forming a grain, rather than renucleation caused by an adsorbing defect species.

  11. Kinetics of laser chemical vapor deposition of carbon and refractory metals

    NASA Astrophysics Data System (ADS)

    Gao, Feng

    2000-10-01

    Three-dimensional laser chemical vapor deposition (3D-LCVD) has been used to grow rods of carbon, tungsten, titanium, and hafnium from a variety of hydrocarbons and metal halide-based precursors. A novel computerized 3D-LCVD system was designed and successfully used in the experiments. A focused Nd:Yag laser beam (lambda = 1.06 mum) was utilized to locally heat up a substrate to deposition temperature. The rods, which grew along the axis of the laser beam, had a typical diameter of 30--80 mum and a length of about 1 mm. The precursors for carbon deposition were the alkynes: propyne, butyne, pentyne, hexyne, and octyne. Propyne gave the highest deposition rate, in excess 3 mm/s at high laser powers (0.45 W) and high partial pressures (3000 mbar). the temperature dependence and pressure dependence were both non-linear functions of the growth rate. the temperature dependence could be separated into two regions---the kinetically limited region, which obeys the Arrhenius relationship, and the transport limited region, which is explained by diffusion of the precursors to the reaction zone. The pressure dependence showed that the reaction order for the different precursors varied from 2.5 for propyne to 1.3 for octyne. The precursors used deposit the refractory metals were tungsten hexafloride, titanium tetraiodide and hafnium chloride. The only successful precursor was tungsten hexafluoride, which readily produced tungsten rods when mixed with hydrogen. Rod diameters typically ranged from 50 mum to 400 mum and the average length of the rods were about 1 mm. Much lower deposition rates, less than 4.5 mum/s were obtained in this case as compared to carbon deposition. By an optimization of the LCVD process, it was possible to deposit high-quality single crystal tungsten rods. They were all oriented in the <100> direction.

  12. Three-dimensional kinetic Monte Carlo simulations of diamond chemical vapor deposition.

    PubMed

    Rodgers, W J; May, P W; Allan, N L; Harvey, J N

    2015-06-01

    A three-dimensional kinetic Monte Carlo model has been developed to simulate the chemical vapor deposition of a diamond (100) surface under conditions used to grow single-crystal diamond (SCD), microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films. The model includes adsorption of CHx (x = 0, 3) species, insertion of CHy (y = 0-2) into surface dimer bonds, etching/desorption of both transient adsorbed species and lattice sidewalls, lattice incorporation, and surface migration but not defect formation or renucleation processes. A value of ?200 kJ mol(-1) for the activation Gibbs energy, ?G(‡) etch, for etching an adsorbed CHx species reproduces the experimental growth rate accurately. SCD and MCD growths are dominated by migration and step-edge growth, whereas in NCD and UNCD growths, migration is less and species nucleate where they land. Etching of species from the lattice sidewalls has been modelled as a function of geometry and the number of bonded neighbors of each species. Choice of appropriate parameters for the relative decrease in etch rate as a function of number of neighbors allows flat-bottomed etch pits and/or sharp-pointed etch pits to be simulated, which resemble those seen when etching diamond in H2 or O2 atmospheres. Simulation of surface defects using unetchable, immobile species reproduces other observed growth phenomena, such as needles and hillocks. The critical nucleus for new layer growth is 2 adjacent surface carbons, irrespective of the growth regime. We conclude that twinning and formation of multiple grains rather than pristine single-crystals may be a result of misoriented growth islands merging, with each island forming a grain, rather than renucleation caused by an adsorbing defect species. PMID:26049516

  13. The Study of a Simple Redox Reaction as an Experimental Approach to Chemical Kinetics.

    ERIC Educational Resources Information Center

    Elias, Horst; Zipp, Arden P.

    1988-01-01

    Recommends using iodide ions and peroxodisulfate ions for studying rate laws instead of the standard iodine clock for kinetic study. Presents the methodology and a discussion of the kinetics involved for a laboratory experiment for a high school or introductory college course. (ML)

  14. Living poly(?-methylstyrene) near the polymerization line 6. Chemical kinetics

    Microsoft Academic Search

    Juewen Zhuang; S. Sarkar Das; M. D. Nowakowski; S. C. Greer

    1997-01-01

    We present new measurements of the kinetics of polymerization near the polymerization line of poly(?-methylstyrene) in the solvent tetrahydrofuran, initiated by sodium naphthalide or cesium naphthalide. We develop a computer model of the kinetics of the reversible polymerization of this system. We fit the model to the experimental data to obtain rate constants for propagation and depropagation.

  15. DFT calculations of 1H and 13C NMR chemical shifts in transition metal hydrides.

    PubMed

    del Rosal, I; Maron, L; Poteau, R; Jolibois, F

    2008-08-14

    Transition metal hydrides are of great interest in chemistry because of their reactivity and their potential use as catalysts for hydrogenation. Among other available techniques, structural properties in transition metal (TM) complexes are often probed by NMR spectroscopy. In this paper we will show that it is possible to establish a viable methodological strategy in the context of density functional theory, that allows the determination of 1H NMR chemical shifts of hydride ligands attached to transition metal atoms in mononuclear systems and clusters with good accuracy with respect to experiment. 13C chemical shifts have also been considered in some cases. We have studied mononuclear ruthenium complexes such as Ru(L)(H)(dppm)2 with L = H or Cl, cationic complex [Ru(H)(H2O)(dppm)2]+ and Ru(H)2(dppm)(PPh3)2, in which hydride ligands are characterized by a negative 1H NMR chemical shift. For these complexes all calculations are in relatively good agreement compared to experimental data with errors not exceeding 20% except for the hydrogen atom in Ru(H)2(dppm)(PPh3)2. For this last complex, the relative error increases to 30%, probably owing to the necessity to take into account dynamical effects of phenyl groups. Carbonyl ligands are often encountered in coordination chemistry. Specific issues arise when calculating 1H or 13C NMR chemical shifts in TM carbonyl complexes. Indeed, while errors of 10 to 20% with respect to experiment are often considered good in the framework of density functional theory, this difference in the case of mononuclear carbonyl complexes culminates to 80%: results obtained with all-electron calculations are overall in very satisfactory agreement with experiment, the error in this case does not exceed 11% contrary to effective core potentials (ECPs) calculations which yield errors always larger than 20%. We conclude that for carbonyl groups the use of ECPs is not recommended, although their use could save time for very large systems, for instance in cluster chemistry. The reliance of NMR chemical shielding on dynamical effects, such as intramolecular rearrangements or trigonal twists, is also examined for H2Fe(CO)4, K+[HFe(CO)](-), HMn(CO)5 and HRe(CO)5. The accuracy of the theory is also examined for complexes with two dihydrogen ligands (Tp*RuH(H2)2 and [FeH(H2)(DMPE)2]+) and a ruthenium cluster, [H3Ru4(C6H6)4(CO)]+. It is shown that for all complexes studied in this work, the effect of the ligands on the chemical shielding of hydrogen coordinated to metal is suitably calculated, thus yielding a very good correlation between experimental chemical shifts and theoretical chemical shielding. PMID:18648699

  16. Activation dependence and kinetics of force and stiffness inhibition by aluminiofluoride, a slowly dissociating analogue of inorganic phosphate, in chemically skinned fibres from rabbit psoas muscle

    Microsoft Academic Search

    P. Bryant Chase; Donald A. Martyn; James D. Hannon

    1994-01-01

    To examine the mechanism by which aluminiofluoride, a tightly binding analogue of inorganic phosphate, inhibits force in single, chemically skinned fibres from rabbit psoas muscle, we measured the Ca2+-dependence of the kinetics of inhibitor dissociation and the kinetics of actomyosin interactions when aluminiofluoride was bound to the crossbridges. The relation between stiffness and the speed of stretch during small amplitude

  17. Redesigning combustion modelingnext term algorithms for the Graphics Processing Unit (GPU): Chemical kinetic rate evaluation and ordinary differential equation integration

    SciTech Connect

    Shi, Y.; Green, W. H.; Wong, H. W.; Oluwole, O. O.

    2011-01-01

    Detailed modeling of complex combustion kinetics remains challenging and often intractable, due to prohibitive computational costs incurred when solving the associated large kinetic mechanisms. The Graphics Processing Unit (GPU), originally designed for graphics rendering on computer and gaming systems, has recently emerged as a powerful, cost-effective supplement to the Central Processing Unit (CPU) for dramatically accelerating scientific computations. Complex scientific computations are now being performed on the GPU in several research fields, such as quantum chemistry, molecular dynamics, and atmospheric modeling. Here, we present methods for exploiting the highly parallel structure of GPUs for combustion modeling. This paper outlines simple algorithm revisions that can be applied to the majority of existing combustion modeling algorithms for GPU computations. Significant simulation acceleration and predictive capability enhancements were obtained by using these GPU-enhanced algorithms for reaction rate evaluation and in ODE integration. For the demonstrations, we implemented the rate evaluation revisions in CHEMKIN and the ODE integration revisions in DASAC and DVODE and we tested the performance for simulating constant-volume ignition using SENKIN. The simulations using the revised algorithms are more than an order of magnitude faster than the corresponding CPU-only simulations, even for a low-end (double-precision) graphics card. Additionally, the computational time scales less than quadratically with the number of chemical species in the kinetic mechanism when using the GPU, as compared to the super-quadratic scaling normally seen with CPU-only chemical kinetics computations; and the GPU-based revisions do not involve approximations to the detailed kinetics. An analysis of the growth rates of combustion mechanism sizes versus computational capabilities of CPUs and GPUs further reveals the important role that GPUs are expected to play in the future of combustion modeling. Finally, we briefly outline practical steps for effectively transitioning from CPU-only to GPU-enhanced combustion modeling.

  18. Temperature effects in first-principles solid state calculations of the chemical shielding tensor made simple.

    PubMed

    Monserrat, Bartomeu; Needs, Richard J; Pickard, Chris J

    2014-10-01

    We study the effects of atomic vibrations on the solid-state chemical shielding tensor using first principles density functional theory calculations. At the harmonic level, we use a Monte Carlo method and a perturbative expansion. The Monte Carlo method is accurate but computationally expensive, while the perturbative method is computationally more efficient, but approximate. We find excellent agreement between the two methods for both the isotropic shift and the shielding anisotropy. The effects of zero-point quantum mechanical nuclear motion are important up to relatively high temperatures: at 500 K they still represent about half of the overall vibrational contribution. We also investigate the effects of anharmonic vibrations, finding that their contribution to the zero-point correction to the chemical shielding tensor is small. We exemplify these ideas using magnesium oxide and the molecular crystals L-alanine and ?-aspartyl-L-alanine. We therefore propose as the method of choice to incorporate the effects of temperature in solid state chemical shielding tensor calculations using the perturbative expansion within the harmonic approximation. This approach is accurate and requires a computational effort that is about an order of magnitude smaller than that of dynamical or Monte Carlo approaches, so these effects might be routinely accounted for. PMID:25296790

  19. FragIt: A Tool to Prepare Input Files for Fragment Based Quantum Chemical Calculations

    PubMed Central

    Steinmann, Casper; Ibsen, Mikael W.; Hansen, Anne S.; Jensen, Jan H.

    2012-01-01

    Near linear scaling fragment based quantum chemical calculations are becoming increasingly popular for treating large systems with high accuracy and is an active field of research. However, it remains difficult to set up these calculations without expert knowledge. To facilitate the use of such methods, software tools need to be available to support these methods and help to set up reasonable input files which will lower the barrier of entry for usage by non-experts. Previous tools relies on specific annotations in structure files for automatic and successful fragmentation such as residues in PDB files. We present a general fragmentation methodology and accompanying tools called FragIt to help setup these calculations. FragIt uses the SMARTS language to locate chemically appropriate fragments in large structures and is applicable to fragmentation of any molecular system given suitable SMARTS patterns. We present SMARTS patterns of fragmentation for proteins, DNA and polysaccharides, specifically for D-galactopyranose for use in cyclodextrins. FragIt is used to prepare input files for the Fragment Molecular Orbital method in the GAMESS program package, but can be extended to other computational methods easily. PMID:23028546

  20. Crystal structure, spectroscopic investigations and quantum chemical calculational studies of N-diphenylphosphino-4-methylpiperidine sulfide

    NASA Astrophysics Data System (ADS)

    Saraço?lu, Hanife; Sariöz, Özlem; Öznergiz, Sena

    2014-04-01

    The title molecule, N-diphenylphosphino-4-methylpiperidine sulfide (I), has been synthesized and characterized by elemental analysis, 1H NMR, 31P NMR, IR and X-ray single-crystal determination. The molecular geometry from X-ray determination, vibrational frequencies and gauge, including atomic orbital (GIAO) 1H NMR and 31P NMR chemical shift values of the title compound (I) in the ground state have been calculated using the density functional theory with the 6-31G(d), 6-31G(d,p) and 6-311G(d,p) basis sets. The calculated results show that the optimized geometry can well reproduce the crystal structure, and theoretical vibrational frequencies and chemical shift values show good agreement with experimental values. The predicted nonlinear optical properties of the title compound are greater than those of urea. In addition, DFT calculations of the molecular electrostatic potentials, frontier molecular orbitals of the title compound were carried out at the B3LYP/6-31G(d) level of theory.

  1. Molecular structure, vibrational, electronic and thermal properties of 4-vinylcyclohexene by quantum chemical calculations.

    PubMed

    Nagabalasubramanian, P B; Periandy, S; Karabacak, Mehmet; Govindarajan, M

    2015-06-15

    The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000-100cm(-1). The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV-Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated. PMID:25795608

  2. Molecular structure, vibrational, electronic and thermal properties of 4-vinylcyclohexene by quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Nagabalasubramanian, P. B.; Periandy, S.; Karabacak, Mehmet; Govindarajan, M.

    2015-06-01

    The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000-100 cm-1. The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV-Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated.

  3. Stability of an anti-stroke peptide: driving forces and kinetics in chemical degradation.

    PubMed

    Li, Rui; Wang, Fengzhen; Chen, Li; Zhu, Shuning; Wu, Lin; Jiang, Sunmin; Xu, Qunwei; Zhu, Dongya

    2014-09-10

    NR2B9c (Lys-Leu-Ser-Ser-Ile-Glu-Ser-Asp-Val) is a 9-amino acid peptide that has been illustrated to be a potential anti-stroke drug. For more effective treatment, suitable drug delivery systems should be developed. However, little is known about the stability of NR2B9c which is essential to its formulation. In this study, a reversed-phase high-performance liquid chromatography (HPLC) was applied to study the forced degradation behavior and stability of NR2B9c. HPLC studies were performed with an C8 column using a mobile phase consisting of acetonitrile (14.5:85.5, v/v) and aqueous solution (0.1% trifluoroacetic acid (TFA) and 0.05 M KH2PO4). The flow rate and the wavelength set during HPLC detection were 1.0 mL/min and 205 nm, respectively. The degradation pattern of NR2B9c aqueous solution followed pseudo first-order kinetics. The degradation rate at pH 7.5 was the slowest according to the plotting V-shaped pH-rate profile. The influence of temperature on the rate of reactions was interpreted in terms of Arrhenius equation (r(2)>0.98). Thermodynamic parameters were calculated based on Eyring equation (r(2)>0.98). The concentrations of drug, buffer species, buffer concentrations, oxidation and organic solvents have noticeable effects on the degradation of NR2B9c while ultrasound shows little impact under the experimental conditions. In a word, this study may give a detailed description of stability of NR2B9c. PMID:24929015

  4. Kinetic studies of chemical shrinkage and residual stress formation in thermoset epoxy adhesives under confined curing conditions

    NASA Astrophysics Data System (ADS)

    Schumann, M.; Geiß, P. L.

    2015-05-01

    Faultless processing of thermoset polymers in demanding applications requires a profound mastering of the curing kinetics considering both the physico-chemical changes in the transition from the liquid to the solid state and the consolidation of the polymers network in the diffusion controlled curing regime past the gel point. Especially in adhesive joints shrinkage stress occurring at an early state of the curing process under confined conditions is likely to cause defects due to local debonding and thus reduce their strength and durability1. Rheometry is considered the method of choice to investigate the change of elastic and viscous properties in the progress of curing. Drawbacks however relate to experimental challenges in accessing the full range of kinetic parameters of thermoset resins with low initial viscosity from the very beginning of the curing reaction to the post-cure consolidation of the polymer due to the formation of secondary chemical bonds. Therefore the scope of this study was to interrelate rheological data with results from in-situ measurements of the shrinkage stress formation in adhesive joints and with the change of refractive index in the progress of curing. This combination of different methods has shown to be valuable in gaining advanced insight into the kinetics of the curing reaction. The experimental results are based on a multi component thermoset epoxy-amine adhesive.

  5. Horizontal mixing coefficients for two-dimensional chemical models calculated from National Meteorological Center Data

    NASA Technical Reports Server (NTRS)

    Newman, P. A.; Schoeberl, M. R.; Plumb, R. A.

    1986-01-01

    Calculations of the two-dimensional, species-independent mixing coefficients for two-dimensional chemical models for the troposphere and stratosphere are performed using quasi-geostrophic potential vorticity fluxes and gradients from 4 years of National Meteorological Center data for the four seasons in both hemispheres. Results show that the horizontal mixing coefficient values for the winter lower stratosphere are broadly consistent with those currently employed in two-dimensional models, but the horizontal mixing coefficient values in the northern winter upper stratosphere are much larger than those usually used.

  6. Validation of hypersonic chemical equilibrium flow calculations using ballistic-range data

    NASA Astrophysics Data System (ADS)

    Sawada, K.; Dendou, E.

    The hypersonic flow field over a sphere flying in a ballistic-range is numerically simulated for the purpose of validating a hypersonic chemical equilibrium flow solver. The numerical results obtained are compared with available experimental data on the stand-off distance and the shape of the detached bow shock wave. In the calculation, an adaptive mesh is employed for a crisp capturing of the shock wave. Comparison with the experimental data reveals that the equilibrium flow solver can yield a fairly accurate prediction of the flow field.

  7. An implicit flux-split algorithm to calculate hypersonic flowfields in chemical equilibrium

    NASA Technical Reports Server (NTRS)

    Palmer, Grant

    1987-01-01

    An implicit, finite-difference, shock-capturing algorithm that calculates inviscid, hypersonic flows in chemical equilibrium is presented. The flux vectors and flux Jacobians are differenced using a first-order, flux-split technique. The equilibrium composition of the gas is determined by minimizing the Gibbs free energy at every node point. The code is validated by comparing results over an axisymmetric hemisphere against previously published results. The algorithm is also applied to more practical configurations. The accuracy, stability, and versatility of the algorithm have been promising.

  8. Technical Note: The MESSy-submodel AIRSEA calculating the air-sea exchange of chemical species

    NASA Astrophysics Data System (ADS)

    Pozzer, A.; Jöckel, P.; Sander, R.; Williams, J.; Ganzeveld, L.; Lelieveld, J.

    2006-12-01

    The new submodel AIRSEA for the Modular Earth Submodel System (MESSy) is presented. It calculates the exchange of chemical species between the ocean and the atmosphere with a focus on organic compounds. The submodel can be easily extended to a large number of tracers, including highly soluble ones. It is demonstrated that the application of explicitly calculated air-sea exchanges with AIRSEA can induce substantial changes in the simulated tracer distributions in the troposphere in comparison to a model setup in which this process is neglected. For example, the simulations of acetone, constrained with measured oceanic concentrations, shows relative changes in the atmospheric surface layer mixing ratios over the Atlantic Ocean of up to 300%.

  9. Technical note: The MESSy-submodel AIRSEA calculating the air-sea exchange of chemical species

    NASA Astrophysics Data System (ADS)

    Pozzer, A.; Jöckel, P.; Sander, R.; Ganzeveld, L.; Lelieveld, J.

    2006-08-01

    The new submodel AIRSEA for the Modular Earth Submodel System (MESSy) is presented. It calculates the exchange of chemical species between the ocean and the atmosphere with a focus on organic compounds. The submodel can be easily extended to a large number of tracers, including highly soluble ones. It is demonstrated that application of explicitly calculated air-sea exchanges with AIRSEA can induce substantial changes in the simulated tracer distributions in the troposphere in comparison to a model version in which this process is neglected. For example, the simulations of acetone, constrained with measured oceanic concentrations, shows relative changes in the atmospheric surface layer mixing ratios over the Atlantic Ocean up to 300%.

  10. Rotational isomers, NBO and spectral analyses of N-(2-hydroxyethyl) phthalimide based on quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Lakshmi, A.; Balachandran, V.

    2013-02-01

    FT-IR and FT-Raman spectra of N-(2-hydroxyethyl)phthalimide (NHEP) have been recorded and analyzed. The stable isomer of NHEP is determined. The optimization geometry, intermolecular hydrogen bonding, and harmonic vibrational wavenumber of NHEP have been investigated with the help of B3LYP scaled quantum mechanical (SQM) method. The infrared and Raman spectra were predicted theoretically from the calculated intensities. Natural bond orbital (NBO) analysis indicates the presence of Cdbnd O⋯H in the molecule. The calculated HOMO and LUMO are important in determining such properties as molecular reactivity. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with electrostatic potential (ESP).

  11. Evaluation of uncertainties in solid-aqueous-gas chemical equilibrium calculations

    NASA Astrophysics Data System (ADS)

    Novoselov, Alexey A.; Popov, Serguei; de Souza Filho, Carlos Roberto

    2015-06-01

    Thermodynamic calculations are traditionally carried out under the assumption of specified input parameters. Errors associated to the results are not often estimated. Here, we propose a novel algorithm that propagates the uncertainty intervals on thermodynamic constants to the uncertainty in chemical equilibrium compositions. The computing uses a dataset of uncertainties on thermodynamic parameters for minerals, solution species and gases consistent with the SUPCRT92 database. Also the algorithm of nonlinear optimization is thoroughly described and realized on a base of the CRONO software. This code can be incorporated into reactive mass transport models as a core for calculating equilibrium compositions. The performance of the algorithm is tested in an experimental system involving Mont Terri's Opalinus Clay interacting with pore water. Its effectiveness is also evaluated against Monte Carlo simulations and Latin Hypercube sampling.

  12. Large scale application of kinetic ART, a near order-1 topologically- based off-lattice kinetic Monte-Carlo algorithm with on-the-fly calculation of events

    Microsoft Academic Search

    Laurent Karim Beland; Fedwa El-Mellouhi; Normand Mousseau

    2010-01-01

    Using a topological classification of eventsfootnotetextB. D. McKay, Congressus Numerantium 30, 45 (1981). combined with the Activation-Relaxation Technique (ART nouveau) for the generation of diffusion pathways, the kinetic ART (k-ART)footnotetextF. El-Mellouhi, N. Mousseau and L. J. Lewis, Phys Rev B, 78,15 (2008). lifts many restrictions generally associated with standard kinetic Monte Carlo algorithms. In particular, it can treat on and

  13. Deuterium-Hydrogen Exchange Kinetics: Implications for Early Chemical Evolution of Chondritic Insoluble Organic Matter

    NASA Astrophysics Data System (ADS)

    Kebukawa, Y.; Cody, G. D.

    2012-03-01

    We report D-H exchange kinetics obtained using laboratory synthesized organic polymers, in order to evaluate the D-H exchange between D enriched organic polymers and D depleted water. Our results explain well the known chondritic ?D values.

  14. Sidedness and chemical and kinetic properties of the vesamicol receptor of cholinergic synaptic vesicles

    SciTech Connect

    Kornreich, W.D.; Parsons, S.M.

    1988-07-12

    Cholinergic synaptic vesicles isolated from Torpedo electric organ contain a receptor for the compound l-2-(4-phenylpiperidino)cyclohexanol (vesamicol, formerly AH5183), which then occupied blocks storage of acetylcholine (AcCh). The inside or outside orientation of the receptor and its chemical and ligand binding kinetics characteristics were studied. Binding of (/sup 3/H)vesamicol to the receptor is inhibited efficiently by the protein modification reagents 4-(chloromercuri)benzenesulfonate and N,N'-dicyclohexylcarbodiimide and by protease treatment of cholate-solubilized receptor. The receptor in native vesicles is resistant to irreversible inactivation by proteases, elevated temperature, or pH extremes. (/sup 3/H)Vesamicol binding depends on deprotonation of a group of pK/sub a/sub 1// = 6.26 +/- 0.03 and protonation of a group of pK/sub a/sub 2// = 10.60 +/- 0.04, which is probably the tertiary amine of the drug molecule itself. The membrane-impermeant zwitterionic vesamicol analgoue dl-trans-4-oxo-4-((5,6,7,8-tetrahydro-6-hydroxy-7-(4-phenyl-1-piperidinyl)-1-naphthalenyl)amino)butanoic acid (TPNB) is an effective inhibitor of AcCh active transport. At 0/sup 0/C, 10 ..mu..M unlabeled vesamicol displaced 36 +/- 2% of a low concentration of bound (/sup 3/H)vesamicol at 0.16 +/- 0.02 min/sup -1/ and 64 +/- 2% at 0.013 +/- 0.001 min/sup -1/. One micromolar unlabeled vesamicol behaved similarly. Several types of receptor heterogeneity are consistent with the data. It is concluded that the vesamicol receptor is a stable protein often exhibiting heterogeneity, which faces the cytoplasmic compartment of the cholinergic nerve terminal. It probably contains a binding site carboxylate in a hydrophobic environment, which ion pairs with the protonated tertiary ammonium group of the drug. It also contains a cytoplasmically oriented sulfhydryl group, which is linked to but not part of the binding site.

  15. Kinetics of gas-phase chemical reactions in a remote RF plasma reactor with electron spin resonance

    SciTech Connect

    Janca, J.; Talsky, A.; Zvonicek, V. [Masaryk Univ., Brno (Czech Republic)

    1995-12-31

    A remote RF plasma reactor is inherently a reactive gas flow system in which the gas-phase chemical reactions of interest occur outside (downstream) the plasma and involve paramagnetic ground state or excited species (e.g. H, O, O{sub 2}, N, NO). Consequently, the kinetics of the gas-phase reactions can be quantitatively characterized by electron spin resonance (ESR). Gas flows and tube pressure are essential parameters for quantitative analysis. The ESR measurements provides the absolute value of paramagnetic species, the determination of recombination and rate coefficients of selected reactions. The goal of the measurements described in the present paper was to find the wall recombination coefficient in pure nitrogen and oxygen and to explain the effect of impurities on both dissociation and recombination of N and O. Next the reaction of atomic oxygen with the molecules of tetraethoxysilane (TEOS) was studied and the kinetic coefficient of this reaction was determined.

  16. Primary Ion Depletion Kinetics (PIDK) Studies as a New Tool for Investigating Chemical Ionization Fragmentation Reactions with PTR-MS

    PubMed Central

    Schuhfried, Erna; Märk, Tilmann D.; Biasioli, Franco

    2013-01-01

    We report on a new approach for studying fragmentation channels in Proton Transfer Reaction-Mass Spectrometry (PTR-MS), which we name primary ion depletion kinetics (PIDK). PTR-MS is a chemical ionization mass spectrometric (CIMS) technique deploying hydronium ions for the chemical ionization. Induced by extremely high concentrations of analyte M, depletion of the primary ions in the drift tube occurs. This is observed as quasi zero concentration of the primary ion H3O+, and constant MH+. Under these non-standard conditions, we find an overall changed fragmentation. We offer two explanations. Either the changed fragmentation pattern is the result of secondary proton transfer reactions. Or, alternatively, the fast depletion of H3O+ leads to reduced heating of H3O+ in the drift field, and consequently changed fragmentation following protonation of the analyte M. In any case, we use the observed changes in fragmentation as a successful new approach to fragmentation studies, and term it primary ion depletion kinetics, PIDK. PIDK easily yields an abundance of continuous data points with little deviation, because they are obtained in one experimental run, even for low abundant fragments. This is an advantage over traditional internal kinetic energy variation studies (electric field per number density (E/N) variation studies). Also, some interpretation on the underlying fragmentation reaction mechanisms can be gleamed. We measure low occurring fragmentation (<2% of MH+) of the compounds dimethyl sulfide, DMS, a compound that reportedly does not fragment, diethyl sulfide DES, and dipropyl sulfide DPS. And we confirm and complement the results with traditional E/N studies. Summing up, the new approach of primary ion depletion kinetics allows for the identification of dehydrogenation [MH+ -H2] and adduct formation (RMH+) as low abundant fragmentation channels in monosulfides. PMID:23840555

  17. Theoretical chemical kinetic study of the H-atom abstraction reactions from aldehydes and acids by ? atoms and ?H, H?2, and ?H3 radicals.

    PubMed

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

    2014-12-26

    We have performed a systematic, theoretical chemical kinetic investigation of H atom abstraction by ? atoms and ?H, H?2, and ?H3 radicals from aldehydes (methanal, ethanal, propanal, and isobutanal) and acids (methanoic acid, ethanoic acid, propanoic acid, and isobutanoic acid). The geometry optimizations and frequencies of all of the species in the reaction mechanisms of the title reactions were calculated using the MP2 method and the 6-311G(d,p) basis set. The one-dimensional hindered rotor treatment for reactants and transition states and the intrinsic reaction coordinate calculations were also determined at the MP2/6-311G(d,p) level of theory. For the reactions of methanal and methanoic acid with ? atoms and ?H, H?2, and ?H3 radicals, the calculated relative electronic energies were obtained with the CCSD(T)/cc-pVXZ (where X = D, T, and Q) method and were extrapolated to the complete basis set limit. The electronic energies obtained with the CCSD(T)/cc-pVTZ method were benchmarked against the CCSD(T)/CBS energies and were found to be within 1 kcal mol(-1) of one another. Thus, the energies calculated using the less expensive CCSD(T)/cc-pVTZ method were used in all of the reaction mechanisms and in calculating our high-pressure limit rate constants for the title reactions. Rate constants were calculated using conventional transition state theory with an asymmetric Eckart tunneling correction, as implemented in Variflex. Herein, we report the individual and average rate constants, on a per H atom basis, and total rate constants in the temperature range 500-2000 K. We have compared some of our rate constant results to available experimental and theoretical data, and our results are generally in good agreement. PMID:25387985

  18. Assessing the sources of uncertainty associated with the calculation of rainfall kinetic energy and erosivity - application to the Upper Llobregat Basin, NE Spain

    Microsoft Academic Search

    G. Catari; J. Latron; F. Gallart

    2011-01-01

    The diverse sources of uncertainty associated with the calculation of rainfall kinetic energy and rainfall erosivity, calculated from precipitation data, were investigated at a range of temporal and spatial scales in a mountainous river basin (504 km2) in the south-eastern Pyrenees. The sources of uncertainty analysed included both methodological and local sources of uncertainty and were (i) tipping-bucket rainfall gauge

  19. Theoretical study of the dynamics and kinetics of the O + CS ? CO + S chemical laser reaction, where CO shows a very high vibrational excitation.

    PubMed

    Gamallo, Pablo; Francia, Rafael; Martínez, Rodrigo; Sayós, Ramón; González, Miguel

    2012-12-01

    The dynamics and kinetics of the O((3)P) + CS(X(1)?(+)) ? CO(X(1)?(+)) + S((3)P) chemical laser reaction was studied theoretically in detail for the first time, as a function of collision energy (0.0388-2.0 eV) and rovibrational excitation of CS. This was made using the quasi-classical trajectory (QCT) method and employing the best ab initio analytical ground potential energy surface (1(3)A' PES) available. A broad set of properties was determined, including scalar and vector properties, and the reaction mode. The behaviors observed and the considerable formation of OCS collision complexes were interpreted from some characteristics of the PES (early barrier, shallow minimum in the exit channel, and high exoergicity (mainly channeled into CO vibration; up to ?81% of the available energy)) and the kinematics. The QCT vibrational and rotational CO populations and the vector properties show a quite good agreement with experiments, but the QCT rate constants disagree. To better account for the kinetics, we performed CASPT2/aug-cc-pVTZ ab initio calculations on the stationary points along the minimum energy path of the ground and first excited (1(3)A'') PESs. The transition state theory, which can be satisfactorily applied here, leads to rate constants (100-2000 K) that are quite close to the measured ones, where comparison is possible (150-300 K). We expect that these results will encourage further theoretical and experimental developments. PMID:23131012

  20. Chemical enthalpies of hydration calculated for the ions of astatine, francium, and radium by the hyperbola method

    Microsoft Academic Search

    A. I. Cherkesov; N. P. Sadovnikov

    2009-01-01

    Calculations by the hyperbola method are presented on the chemical enthalpies of hydration for the ions of astatine, francium, and radium. Values are also given for the enthalpies of hydration for ions of the hypothetical elements 117, 119, and 120.

  1. S3 and S4 abundances and improved chemical kinetic model for the lower atmosphere of Venus

    NASA Astrophysics Data System (ADS)

    Krasnopolsky, Vladimir A.

    2013-07-01

    Mixing ratios of S3 and S4 are obtained from reanalysis of the spectra of true absorption in the visible range retrieved by Maiorov et al. (Maiorov, B.S. et al. [2005]. Solar Syst. Res. 39, 267-282) from the Venera 11 observations. These mixing ratios are fS3 = 11 ± 3 ppt at 3-10 km and 18 ± 3 ppt at 10-19 km, fS4 = 4 ± 4 ppt at 3-10 km and 6 ± 2 ppt at 10-19 km, and show a steep decrease in both S3 and S4 above 19 km. Photolysis rates of S3 and S4 at various altitudes are calculated using the Venera 11 spectra and constant photolysis yields as free parameters. The chemical kinetic model for the Venus lower atmosphere (Krasnopolsky, V.A. [2007]. Icarus 191, 25-37) has been improved by inclusion of the S4 cycle from Yung et al. (Yung, Y.L. et al. [2009]. J. Geophys. Res. 114, E00B34), reduction of the H2SO4 and CO fluxes at the upper boundary of 47 km by a factor of 4 in accord with the recent photochemical models for the middle atmosphere, by using a closed lower boundary for OCS instead of a free parameter for this species at the surface, and some minor updates. Our model with the S4 cycle but without the SO3 + 2 OCS reaction suggested by Krasnopolsky and Pollack (Krasnopolsky, V.A., Pollack, J.B. [1994]. Icarus 109, 58-78) disagrees with the observations of OCS, CO, S3, and S4. However, inclusion of the S4 cycle improves the model fit to all observational constraints. The best-fit activation energy of 7800 K for thermolysis of S4 supports the S4 enthalpy from Mills (Mills, K.C. [1974]. Thermodynamic Data for Inorganic Sulfides, Selenides and Tellurides. Butterworths, London). Chemistry of the Venus lower atmosphere is initiated by disequilibrium products H2SO4 and CO from the middle atmosphere, photolysis of S3 and S4, and thermochemistry in the lowest scale height. The chemistry is mostly driven by sulfur that is formed in a slow reaction SO + SO, produces OCS, and results in dramatic changes in abundances of OCS, CO, and free sulfur allotropes. The SX + OCS fraction is constant and equal to 20 ppm in the lower atmosphere. A source of free sulfur on Venus is in the lower atmosphere, and the calculated S8 mixing ratio is 2.5 ppm above 40 km and results in condensation and formation of aerosol sulfur near 50 km. Therefore the model does not support sulfur as the NUV absorber that was observed by Venera 14 above 58 km. Sources and sinks of the major chemical products in the model are briefly discussed. The model predicts a significant abundance of 3.5 ppb for SO2Cl2 above 25 km. This prediction of SO2Cl2 as well as that in the photochemical model for the middle atmosphere (Krasnopolsky, V.A. [2012]. Icarus 218, 230-246) may stimulate search for this species. A modified concept of the fast and slow sulfur cycles in the middle and lower atmospheres, respectively, has been presented and discussed. Some sources of the model uncertainty are briefly discussed.

  2. Recommendations on adopting the values and correlations for calculating the thermophysical and kinetic properties of liquid lead

    NASA Astrophysics Data System (ADS)

    Savchenko, I. V.; Lezhnin, S. I.; Mosunova, N. A.

    2015-06-01

    Recent years have seen an essentially increased interest in studying the properties of liquid lead, which is primarily connected with the possibility of using it as coolant in nuclear power installations, first of all, in reactors based on fission of heavy nuclei by fast neutrons. The article presents an analysis of published data on the thermophysical and kinetic properties of lead in liquid state, the results of which served as a basis for selecting and recommending correlations to be used in carrying out scientific and engineering calculations. A general assessment of the state of experimental investigations into the thermophysical properties of liquid lead is presented. The presented value of lead solidification temperature is the maximally reliable one. The data on the boiling temperature, melting and vaporization enthalpies, and saturated vapor pressure have been determined with satisfactory accuracy. The published data on the liquid lead heat capacity differ considerably from each other; therefore, the recommended values should be experimentally checked and determined more exactly. The available experimental data on surface tension density, volumetric expansion coefficient, sound velocity, viscosity, and thermal conductivity do not cover the entire range of liquid phase existence temperatures. The temperature region above 1200 K and the crystal-liquid phase transition region are the least studied ones. Additional investigations of these properties in the above-mentioned temperature intervals are necessary. The question about the influence of impurities on the thermophysical properties of lead still remains to be answered and requires experimental investigations.

  3. Kinetics of the Reduction of Wüstite by Hydrogen and Carbon Monoxide for the Chemical Looping Production of Hydrogen

    E-print Network

    Liu, Wen; Lim, Jin Yang; Saucedo, Marco A.; Hayhurst, Allan N.; Scott, Stuart A.; Dennis, J. S.

    2014-08-13

    produced could be stored, e.g. by geological sequestration, making the overall process “carbon-neutral”, or “carbon-negative” when biomass is used as fuel. In addition, the hydrogen produced during the oxidation of FexO and metallic Fe in steam can be kept... Kinetics of the reduction of wüstite by hydrogen and carbon monoxide for the chemical looping production of hydrogen Wen Liu a,n, Jin Yang Lim b, Marco A. Saucedo a, Allan N. Hayhurst b, Stuart A. Scott a, J.S. Dennis b a Department of Engineering...

  4. Calculation of the equation of state of QCD at finite chemical and zero temperature

    SciTech Connect

    Zong Hongshi; Sun Weimin [Department of Physics, Nanjing University, Nanjing 210093 (China); Joint Center for Particle, Nuclear Physics and Cosmology, Nanjing 210093 (China)

    2008-09-01

    In this paper, we give a direct method for calculating the partition function, and hence the equation of state (EOS) of quantum chromodynamics (QCD) at finite chemical potential and zero temperature. In the EOS derived in this paper the pressure density is the sum of two terms: the first term P({mu})|{sub {mu}}{sub =0} (the pressure density at {mu}=0) is a {mu}-independent constant; the second term, which is totally determined by G{sub R}[{mu}](p) (the renormalized dressed quark propagator at finite {mu}), contains all the nontrivial {mu}-dependence. By applying a general result in the rainbow-ladder approximation of the Dyson-Schwinger approach obtained in our previous study [Phys. Rev. C 71, 015205 (2005)], G{sub R}[{mu}](p) is calculated from the meromorphic quark propagator proposed in [Phys. Rev. D 70, 014014 (2004)]. From this the full analytic expression of the EOS of QCD at finite {mu} and zero T is obtained (apart from the constant term P({mu})|{sub {mu}}{sub =0} which can in principle be calculated from the Cornwall-Jackiw-Tomboulis effective action). A comparison between our EOS and the cold, perturbative EOS of QCD of Fraga, Pisarski, and Schaffner-Bielich is made. It is expected that our EOS can provide a possible new approach for the study of neutron stars.

  5. Molecular structure and spectroscopic characterization of Carbamazepine with experimental techniques and DFT quantum chemical calculations.

    PubMed

    Suhasini, M; Sailatha, E; Gunasekaran, S; Ramkumaar, G R

    2015-04-15

    A systematic vibrational spectroscopic assignment and analysis of Carbamazepine has been carried out by using FT-IR, FT-Raman and UV spectral data. The vibrational analysis were aided by electronic structure calculations - ab initio (RHF) and hybrid density functional methods (B3LYP) performed with standard basis set 6-31G(d,p). Molecular equilibrium geometries, electronic energies, natural bond order analysis, harmonic vibrational frequencies and IR intensities have been computed. A detailed interpretation of the vibrational spectra of the molecule has been made on the basis of the calculated Potential Energy Distribution (PED) by VEDA program. UV-visible spectrum of the compound was also recorded and the electronic properties, such as HOMO and LUMO energies and ?max were determined by HF/6-311++G(d,p) Time-Dependent method. The thermodynamic functions of the title molecule were also performed using the RHF and DFT methods. The restricted Hartree-Fock and density functional theory-based nuclear magnetic resonance (NMR) calculation procedure was also performed, and it was used for assigning the (13)C and (1)H NMR chemical shifts of Carbamazepine. PMID:25682215

  6. Detailed chemical kinetic models for large n-alkanes and iso-alkanes found in conventional and F-T diesel fuels

    SciTech Connect

    Westbrook, C K; Pitz, W J; Mehl, M; Curran, H J

    2009-03-09

    n-Hexadecane and 2,2,4,4,6,8,8-heptamethylnonane represent the primary reference fuels for diesel that are used to determine cetane number, a measure of the ignition property of diesel fuel. With the development of chemical kinetics models for both primary reference fuels, a new capability is now available to model diesel fuel ignition. Additionally, we have developed chemical kinetic models for a whole series of large n-alkanes and a large iso-alkane to represent these chemical classes in fuel surrogates for conventional and future fuels. These chemical kinetic models are used to predict the effect of the aforementioned fuel components on ignition characteristics under conditions found in internal combustion engines.

  7. 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

  8. Computer Program for the Calculation of Multicomponent Convective Diffusion Deposition Rates from Chemically Frozen Boundary Layer Theory

    NASA Technical Reports Server (NTRS)

    Gokoglu, S. A.; Chen, B. K.; Rosner, D. E.

    1984-01-01

    The computer program based on multicomponent chemically frozen boundary layer (CFBL) theory for calculating vapor and/or small particle deposition rates is documented. A specific application to perimter-averaged Na2SO4 deposition rate calculations on a cylindrical collector is demonstrated. The manual includes a typical program input and output for users.

  9. Turbulent Chemically Reacting Flows According to a Kinetic Theory. Ph.D. Thesis; [statistical analysis/gas flow

    NASA Technical Reports Server (NTRS)

    Hong, Z. C.

    1975-01-01

    A review of various methods of calculating turbulent chemically reacting flow such as the Green Function, Navier-Stokes equation, and others is presented. Nonequilibrium degrees of freedom were employed to study the mixing behavior of a multiscale turbulence field. Classical and modern theories are discussed.

  10. Detailed Chemical Kinetic Reaction Mechanisms for Primary Reference Fuels for Diesel Cetane Number and Spark-Ignition Octane Number

    SciTech Connect

    Westbrook, C K; Pitz, W J; Mehl, M; Curran, H J

    2010-03-03

    For the first time, a detailed chemical kinetic reaction mechanism is developed for primary reference fuel mixtures of n-hexadecane and 2,2,4,4,6,8,8-heptamethyl nonane for diesel cetane ratings. The mechanisms are constructed using existing rules for reaction pathways and rate expressions developed previously for the primary reference fuels for gasoline octane ratings, n-heptane and iso-octane. These reaction mechanisms are validated by comparisons between computed and experimental results for shock tube ignition and for oxidation under jet-stirred reactor conditions. The combined kinetic reaction mechanism contains the submechanisms for the primary reference fuels for diesel cetane ratings and submechanisms for the primary reference fuels for gasoline octane ratings, all in one integrated large kinetic reaction mechanism. Representative applications of this mechanism to two test problems are presented, one describing fuel/air autoignition variations with changes in fuel cetane numbers, and the other describing fuel combustion in a jet-stirred reactor environment with the fuel varying from pure 2,2,4,4,6,8,8-heptamethyl nonane (Cetane number of 15) to pure n-hexadecane (Cetane number of 100). The final reaction mechanism for the primary reference fuels for diesel fuel and gasoline is available on the web.

  11. The Fizz Keeper, a Case Study in Chemical Education, Equilibrium, and Kinetics.

    ERIC Educational Resources Information Center

    Howald, Reed A.

    1999-01-01

    The loss of carbon dioxide from carbonated beverages provides an interesting case of the combination of equilibrium and kinetic principles. Adding air with a commercial device (the Fizz Keeper) has a negligible effect on various equilibria present but will slow diffusion in the gas space of a resealed bottle, decreasing the rate at which…

  12. The Utility of the Lambert Function W[a exp(a - bt)] in Chemical Kinetics

    ERIC Educational Resources Information Center

    Williams, Brian Wesley

    2010-01-01

    The mathematical Lambert function W[a exp(a - bt)] is used to find integrated rate laws for several examples, including simple enzyme and Lindemann-Christiansen-Hinshelwood (LCH) unimolecular decay kinetics. The results derived here for the well-known LCH mechanism as well as for a dimer-monomer reaction mechanism appear to be novel. A nonlinear…

  13. An Analytical Investigation of Three General Methods of Calculating Chemical-Equilibrium Compositions

    NASA Technical Reports Server (NTRS)

    Zeleznik, Frank J.; Gordon, Sanford

    1960-01-01

    The Brinkley, Huff, and White methods for chemical-equilibrium calculations were modified and extended in order to permit an analytical comparison. The extended forms of these methods permit condensed species as reaction products, include temperature as a variable in the iteration, and permit arbitrary estimates for the variables. It is analytically shown that the three extended methods can be placed in a form that is independent of components. In this form the Brinkley iteration is identical computationally to the White method, while the modified Huff method differs only'slightly from these two. The convergence rates of the modified Brinkley and White methods are identical; and, further, all three methods are guaranteed to converge and will ultimately converge quadratically. It is concluded that no one of the three methods offers any significant computational advantages over the other two.

  14. Exact results in nonequilibrium statistical mechanics: Formalism and applications in chemical kinetics and single-molecule free energy estimation

    NASA Astrophysics Data System (ADS)

    Adib, Artur B.

    In the last two decades or so, a collection of results in nonequilibrium statistical mechanics that departs from the traditional near-equilibrium framework introduced by Lars Onsager in 1931 has been derived, yielding new fundamental insights into far-from-equilibrium processes in general. Apart from offering a more quantitative statement of the second law of thermodynamics, some of these results---typified by the so-called "Jarzynski equality"---have also offered novel means of estimating equilibrium quantities from nonequilibrium processes, such as free energy differences from single-molecule "pulling" experiments. This thesis contributes to such efforts by offering three novel results in nonequilibrium statistical mechanics: (a) The entropic analog of the Jarzynski equality; (b) A methodology for estimating free energies from "clamp-and-release" nonequilibrium processes; and (c) A directly measurable symmetry relation in chemical kinetics similar to (but more general than) chemical detailed balance. These results share in common the feature of remaining valid outside Onsager's near-equilibrium regime, and bear direct applicability in protein folding kinetics as well as in single-molecule free energy estimation.

  15. Kinetics of the biodegradation of phenol in wastewaters from the chemical industry by covalently immobilized Trichosporon cutaneum cells.

    PubMed

    Yotova, Lyubov; Tzibranska, Irene; Tileva, Filadia; Markx, G H; Georgieva, Nelly

    2009-03-01

    A simple method for the preparation of the biocatalyst with whole cells is presented, and the applicability of the technique for biodegradation of phenol in wastewater from the chemical industries using the basidomycetes yeast Trichosporon cutaneum is explored. Kinetic studies of the influence of other compounds contained in wastewater as naphthalene, benzene, toluene and pyridine indicate that apart from oil fraction, which is removed, the phenol concentration is the only major factor limiting the growth of immobilized cells. Mathematical models are applied to describe the kinetic behavior of immobilized yeast cells. From the analysis of the experimental curves was shown that the obtained values for the apparent rate parameters vary depending on the substrate concentration (mu(maxapp) from 0.35 to 0.09 h(-1) and K (sapp) from 0.037 to 0.4 g dm(-3)). The inhibitory effect of the phenol on the obtained yield coefficients was investigated too. It has been shown that covalent immobilization of T. cutaneum whole cells to plastic carrier beads is possible, and that cell viability and phenol degrading activity are maintained after the chemical modification of cell walls during the binding procedure. The results obtained indicate a possible future application of immobilized T. cutaneum for destroying phenol in industrial wastewaters. PMID:19052785

  16. Parametric Investigation of the Kinetics of Growth of Carbon-Nanotube Arrays on Iron Nanoparticles in the Process of Chemical Vapor Deposition of Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Futko, S. I.; Shulitski, B. G.; Labunov, V. A.; Ermolaevaa, E. M.

    2015-03-01

    On the basis of the kinetic model of synthesis of carbon nanotubes on iron nanoparticles in the process of chemical vapor deposition of hydrocarbons, the parametric dependences of characteristics of arrays of vertically oriented nanotubes on the temperature of their synthesis, the concentration of acetylene in a reactor, and the diameter of the catalyst nanoparticles were investigated. It is shown that the maximum on the temperature dependence of the rate of growth of carbon nanotubes, detected in experiments at a temperature of ~700oC is due to the competing processes of increasing the catalytic activity of iron nanoparticles and decreasing the acetylene concentration because of the signifi cant gas-phase decomposition of acetylene in the reactor before it enters the substrate with the catalyst. Our calculations have shown that the indicated maximum arises near the transition point separating the low-temperature region where multiwall nanotubes are predominantly synthesized from the higher-temperature region of generation of single-wall nanotubes in the process of chemical vapor deposition of hydrocarbons.

  17. Parametric Investigation of the Kinetics of Growth of Carbon-Nanotube Arrays on Iron Nanoparticles in the Process of Chemical Vapor Deposition of Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Futko, S. I.; Shulitski, B. G.; Labunov, V. A.; Ermolaevaa, E. M.

    2015-04-01

    On the basis of the kinetic model of synthesis of carbon nanotubes on iron nanoparticles in the process of chemical vapor deposition of hydrocarbons, the parametric dependences of characteristics of arrays of vertically oriented nanotubes on the temperature of their synthesis, the concentration of acetylene in a reactor, and the diameter of the catalyst nanoparticles were investigated. It is shown that the maximum on the temperature dependence of the rate of growth of carbon nanotubes, detected in experiments at a temperature of ~700oC is due to the competing processes of increasing the catalytic activity of iron nanoparticles and decreasing the acetylene concentration because of the signifi cant gas-phase decomposition of acetylene in the reactor before it enters the substrate with the catalyst. Our calculations have shown that the indicated maximum arises near the transition point separating the low-temperature region where multiwall nanotubes are predominantly synthesized from the higher-temperature region of generation of single-wall nanotubes in the process of chemical vapor deposition of hydrocarbons.

  18. Chemical Kinetics, Heat Transfer, and Sensor Dynamics Revisited in a Simple Experiment

    ERIC Educational Resources Information Center

    Sad, Maria E.; Sad, Mario R.; Castro, Alberto A.; Garetto, Teresita F.

    2008-01-01

    A simple experiment about thermal effects in chemical reactors is described, which can be used to illustrate chemical reactor models, the determination and validation of their parameters, and some simple principles of heat transfer and sensor dynamics. It is based in the exothermic reaction between aqueous solutions of sodium thiosulfate and…

  19. Vibrational spectra, structural conformations, scaled quantum chemical calculations and NBO analysis of 3-acetyl-7-methoxycoumarin

    NASA Astrophysics Data System (ADS)

    Joseph, Lynnette; Sajan, D.; Reshmy, R.; Arun Sasi, B. S.; Erdogdu, Y.; Thomas, K. Kurien

    2012-12-01

    The powder form NIR-FT Raman and FT-IR spectra of 3-acetyl-7-methoxycoumarin (3A7MC) have been recorded in the regions 4000-400 and 3500-100 cm-1, respectively. The equilibrium geometry, vibrational frequencies, band intensities, NMR spectra, NBO analysis and UV-Vis spectral studies of the most stable conformer have been calculated by density functional B3LYP method with the 6-311G(d,p) basis set. A complete vibrational analysis has been attempted on the basis of experimental infrared and Raman spectra, the calculated wavenumber and intensity of the vibrational bands and the potential energy distribution over the internal coordinates. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping the electron density isosurface with electrostatic potential surfaces (ESP). Natural bond orbital analysis has been carried out to understand the nature of different interactions responsible for the electron delocalization and the intramolecular charge transfer between the orbitals (n ? ??, n ? ??, ? ? ??).

  20. Noise-Induced Modulation of the Relaxation Kinetics around a Non-Equilibrium Steady State of Non-Linear Chemical Reaction Networks

    Microsoft Academic Search

    Rajesh Ramaswamy; Ivo F. Sbalzarini; Nélido González-Segredo

    2011-01-01

    Stochastic effects from correlated noise non-trivially modulate the kinetics of non-linear chemical reaction networks. This is especially important in systems where reactions are confined to small volumes and reactants are delivered in bursts. We characterise how the two noise sources confinement and burst modulate the relaxation kinetics of a non-linear reaction network around a non-equilibrium steady state. We find that

  1. Adsorptive removal of basic dye by chemically activated Parthenium biomass: equilibrium and kinetic modeling

    Microsoft Academic Search

    Hem Lata; V. K. Garg; R. K. Gupta

    2008-01-01

    This paper reports the removal of a basic dye (rhodamine-B) by the activated carbon prepared from Parthenium biomass by sulphuric acid treatment method (SWC). The effectiveness of the prepared adsorbent has been studied as a function of agitation time, adsorbent dosage, initial dye concentration and pH. The removal of rhodamine-B by SWC followed second order kinetic model. The second order

  2. Non-meanfield deterministic limits in chemical reaction kinetics far from equilibrium

    E-print Network

    R. E. Lee DeVille; Cyrill B. Muratov; Eric Vanden-Eijnden

    2005-12-25

    A general mechanism is proposed by which small intrinsic fluctuations in a system far from equilibrium can result in nearly deterministic dynamical behaviors which are markedly distinct from those realized in the meanfield limit. The mechanism is demonstrated for the kinetic Monte-Carlo version of the Schnakenberg reaction where we identified a scaling limit in which the global deterministic bifurcation picture is fundamentally altered by fluctuations. Numerical simulations of the model are found to be in quantitative agreement with theoretical predictions.

  3. Chemical reaction kinetics leading to the first Stober silica nanoparticles – NMR and SAXS investigation

    Microsoft Academic Search

    D. L Green; S Jayasundara; Yui-Fai Lam; M. T Harris

    2003-01-01

    29Si-NMR and 13C-NMR were used in methanol and ethanol to monitor the intermediates or hydrolyzed monomers that lead to the formation of the first primary particles as detected by small angle X-ray scattering. This identification was facilitated by using initial NH3 and H2O levels at the lower end of those experienced in Stober synthesis to slow the reaction kinetics. We

  4. Sensitivity of Polar Stratospheric Ozone Loss to Uncertainties in Chemical Reaction Kinetics

    NASA Astrophysics Data System (ADS)

    Kawa, S. R.; Rex, M.; Stolarski, R. S.; Douglass, A. R.; Newman, P. A.; Frieler, K.

    2008-12-01

    Several recent observational and laboratory studies of processes involved in polar stratospheric ozone loss have prompted a reexamination of aspects of our understanding for this key indicator of global change. To a large extent, our confidence in understanding and projecting changes in polar and global ozone is based on our ability to simulate these processes in numerical models of chemistry and transport. The fidelity of the models is assessed in comparison with a wide range of observations. These models depend on laboratory- measured kinetic reaction rates and photolysis cross sections to simulate molecular interactions. The rates of all of these reactions are subject to uncertainty, some substantial. Given the complexity of the models, however, it is difficult to quantify uncertainties in many aspects of system. In this study we use trajectory box- model simulations for Antarctic and Arctic ozone to estimate the uncertainty in loss attributable to known reaction kinetic uncertainties. Following the method of earlier work, rates and uncertainties from the latest laboratory evaluations are applied in random combinations. We determine the key reactions and rates contributing the largest potential errors and compare the results with observations to evaluate which combinations are consistent with atmospheric data. Comparisons with ozone sonde and MLS data in the Antarctic and MATCH observations in the Arctic present a consistent picture of seasonal ozone loss and chlorine partitioning vis-a-vis the kinetic rates and their uncertainties. Implications for our theoretical and practical understanding of polar ozone loss will be assessed.

  5. Sample Handling and Chemical Kinetics in an Acoustically Levitated Drop Microreactor

    PubMed Central

    2009-01-01

    Accurate measurement of enzyme kinetics is an essential part of understanding the mechanisms of biochemical reactions. The typical means of studying such systems use stirred cuvettes, stopped-flow apparatus, microfluidic systems, or other small sample containers. These methods may prove to be problematic if reactants or products adsorb to or react with the container’s surface. As an alternative approach, we have developed an acoustically-levitated drop reactor eventually intended to study enzyme-catalyzed reaction kinetics related to free radical and oxidative stress chemistry. Microliter-scale droplet generation, reactant introduction, maintenance, and fluid removal are all important aspects in conducting reactions in a levitated drop. A three capillary bundle system has been developed to address these needs. We report kinetic measurements for both luminol chemiluminescence and the reaction of pyruvate with nicotinamide adenine dinucleotide, catalyzed by lactate dehydrogenase, to demonstrate the feasibility of using a levitated drop in conjunction with the developed capillary sample handling system as a microreactor. PMID:19769373

  6. Kinetic mechanism of molecular energy transfer and chemical reactions in low-temperature air-fuel plasmas.

    PubMed

    Adamovich, Igor V; Li, Ting; Lempert, Walter R

    2015-08-13

    This work describes the kinetic mechanism of coupled molecular energy transfer and chemical reactions in low-temperature air, H2-air and hydrocarbon-air plasmas sustained by nanosecond pulse discharges (single-pulse or repetitive pulse burst). The model incorporates electron impact processes, state-specific N2 vibrational energy transfer, reactions of excited electronic species of N2, O2, N and O, and 'conventional' chemical reactions (Konnov mechanism). Effects of diffusion and conduction heat transfer, energy coupled to the cathode layer and gasdynamic compression/expansion are incorporated as quasi-zero-dimensional corrections. The model is exercised using a combination of freeware (Bolsig+) and commercial software (ChemKin-Pro). The model predictions are validated using time-resolved measurements of temperature and N2 vibrational level populations in nanosecond pulse discharges in air in plane-to-plane and sphere-to-sphere geometry; temperature and OH number density after nanosecond pulse burst discharges in lean H2-air, CH4-air and C2H4-air mixtures; and temperature after the nanosecond pulse discharge burst during plasma-assisted ignition of lean H2-mixtures, showing good agreement with the data. The model predictions for OH number density in lean C3H8-air mixtures differ from the experimental results, over-predicting its absolute value and failing to predict transient OH rise and decay after the discharge burst. The agreement with the data for C3H8-air is improved considerably if a different conventional hydrocarbon chemistry reaction set (LLNL methane-n-butane flame mechanism) is used. The results of mechanism validation demonstrate its applicability for analysis of plasma chemical oxidation and ignition of low-temperature H2-air, CH4-air and C2H4-air mixtures using nanosecond pulse discharges. Kinetic modelling of low-temperature plasma excited propane-air mixtures demonstrates the need for development of a more accurate 'conventional' chemistry mechanism. PMID:26170427

  7. Chemical Conversion Pathways and Kinetic Modeling for the OH-Initiated Reaction of Triclosan in Gas-Phase

    PubMed Central

    Zhang, Xue; Zhang, Chenxi; Sun, Xiaomin; Kang, Lingyan; Zhao, Yan

    2015-01-01

    As a widely used antimicrobial additive in daily consumption, attention has been paid to the degradation and conversion of triclosan for a long time. The quantum chemistry calculation and the canonical variational transition state theory are employed to investigate the mechanism and kinetic property. Besides addition and abstraction, oxidation pathways and further conversion pathways are also considered. The OH radicals could degrade triclosan to phenols, aldehydes, and other easily degradable substances. The conversion mechanisms of triclosan to the polychlorinated dibenzopdioxin and furan (PCDD/Fs) and polychlorinated biphenyls (PCBs) are clearly illustrated and the toxicity would be strengthened in such pathways. Single radical and diradical pathways are compared to study the conversion mechanism of dichlorodibenzo dioxin (DCDD). Furthermore, thermochemistry is discussed in detail. Kinetic property is calculated and the consequent ratio of kadd/ktotal and kabs/ktotal at 298.15 K are 0.955 and 0.045, respectively. Thus, the OH radical addition reactions are predominant, the substitute position of OH radical on triclosan is very important to generate PCDD and furan, and biradical is also a vital intermediate to produce dioxin. PMID:25867482

  8. Ab initio chemical kinetics for the hydrolysis of N2O4 isomers in the gas phase.

    PubMed

    Zhu, R S; Lai, Ke-Yu; Lin, M C

    2012-05-10

    The mechanism and kinetics for the gas-phase hydrolysis of N(2)O(4) isomers have been investigated at the CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++G(3df,2p) level of theory in conjunction with statistical rate constant calculations. Calculated results show that the contribution from the commonly assumed redox reaction of sym-N(2)O(4) to the homogeneous gas-phase hydrolysis of NO(2) can be unequivocally ruled out due to the high barrier (37.6 kcal/mol) involved; instead, t-ONONO(2) directly formed by the association of 2NO(2), was found to play the key role in the hydrolysis process. The kinetics for the hydrolysis reaction, 2NO(2) + H(2)O ? HONO + HNO(3) (A) can be quatitatively interpreted by the two step mechanism: 2NO(2) ? t-ONONO(2), t-ONONO(2) + H(2)O ? HONO + HNO(3). The predicted total forward and reverse rate constants for reaction (A), k(tf) = 5.36 × 10(-50)T(3.95) exp(1825/T) cm(6) molecule(-2) s(-1) and k(tr) = 3.31 × 10(-19)T(2.478) exp(-3199/T) cm(3) molecule(-1) s(-1), respectively, in the temperature range 200-2500 K, are in good agreement with the available experimental data. PMID:22506560

  9. Chemical conversion pathways and kinetic modeling for the OH-initiated reaction of triclosan in gas-phase.

    PubMed

    Zhang, Xue; Zhang, Chenxi; Sun, Xiaomin; Kang, Lingyan; Zhao, Yan

    2015-01-01

    As a widely used antimicrobial additive in daily consumption, attention has been paid to the degradation and conversion of triclosan for a long time. The quantum chemistry calculation and the canonical variational transition state theory are employed to investigate the mechanism and kinetic property. Besides addition and abstraction, oxidation pathways and further conversion pathways are also considered. The OH radicals could degrade triclosan to phenols, aldehydes, and other easily degradable substances. The conversion mechanisms of triclosan to the polychlorinated dibenzopdioxin and furan (PCDD/Fs) and polychlorinated biphenyls (PCBs) are clearly illustrated and the toxicity would be strengthened in such pathways. Single radical and diradical pathways are compared to study the conversion mechanism of dichlorodibenzo dioxin (DCDD). Furthermore, thermochemistry is discussed in detail. Kinetic property is calculated and the consequent ratio of k add/k total and k abs/k total at 298.15 K are 0.955 and 0.045, respectively. Thus, the OH radical addition reactions are predominant, the substitute position of OH radical on triclosan is very important to generate PCDD and furan, and biradical is also a vital intermediate to produce dioxin. PMID:25867482

  10. Institution: Reaction Engineering International Award Number: DMI0091593 Program: SBIR Phase II Project Title: A Problem Solving Environment for Reduced Kinetic Mechanisms Reduced Chemical Kinetic Mechanisms: Application to CFD Codes and Optimization

    Microsoft Academic Search

    Christopher J. Montgomery; Darren M. Shino; Chonguan Yang; Shane D. Brunson; Alan R. Parkinson; Graham M. Goldin

    Reduced chemical kinetic mechanisms developed and tested using the CARM- PSE software have been implemented into a variety of CFD codes. When used in the commercial code Fluent, a CARM -PSE created reduced mechanism performs well for predicting the major species and temperature of the Sandia D flame. Predictions for radical and pollutant species are not as good. Much of

  11. Surface Runoff Contamination by Soil Chemicals: Simulations for Equilibrium and First-Order Kinetics

    Microsoft Academic Search

    Rony Wallach; Rina Shabtai

    1992-01-01

    A model was developed to predict the potential contamination of overland flow by chemicals removed from soil water by rainfall on sloping soil. The model accounts for transient water infiltration and convective-dispersive solute transport in the soil and also considers rate-limited mass transfer through a laminar boundary layer at the soil surface\\/runoff water interface. Sorption-desorption interactions between soil and chemicals

  12. Kinetic models with chemical reactions and nonequilibrium entropy in open systems

    NASA Astrophysics Data System (ADS)

    Aristov, Vladimir; Frolova, Anna; Zabelok, Sergey

    2014-12-01

    Nonuniform relaxation problems are applied to simulate complex non-equilibrium processes with chemical reactions in open systems. The present paper is a continuation of our studies at a new level, in particular, 2D flows are considered. Besides the slow chemical reactions, the so-called fast reactions are studied. A special attention is paid to studying the behavior of non-equilibrium entropy and entropy flux in such complex open systems.

  13. Assessing the sources of uncertainty associated with the calculation of rainfall kinetic energy and erosivity - application to the Upper Llobregat Basin, NE Spain

    NASA Astrophysics Data System (ADS)

    Catari, G.; Latron, J.; Gallart, F.

    2011-03-01

    The diverse sources of uncertainty associated with the calculation of rainfall kinetic energy and rainfall erosivity, calculated from precipitation data, were investigated at a range of temporal and spatial scales in a mountainous river basin (504 km2) in the south-eastern Pyrenees. The sources of uncertainty analysed included both methodological and local sources of uncertainty and were (i) tipping-bucket rainfall gauge instrumental errors, (ii) the efficiency of the customary equation used to derive rainfall kinetic energy from intensity, (iii) the efficiency of the regressions obtained between daily precipitation and rainfall erosivity, (iv) the temporal variability of annual rainfall erosivity values, and the spatial variability of (v) annual rainfall erosivity values and (vi) long-term erosivity values. The differentiation between systematic (accuracy) and random (precision) errors was taken into account in diverse steps of the analysis. The results showed that the uncertainty associated with the calculation of rainfall kinetic energy from rainfall intensity at the event and station scales was as high as 30%, because of insufficient information on rainfall drop size distribution. This methodological limitation must be taken into account for experimental or modelling purposes when rainfall kinetic energy is derived solely from rainfall intensity data. For longer temporal scales, the relevance of this source of uncertainty remained high if low variability in the types of rain was supposed. Temporal variability of precipitation at wider spatial scales was the main source of uncertainty when rainfall erosivity was calculated on an annual basis, whereas the uncertainty associated with long-term erosivity was rather low and less important than the uncertainty associated with other model factors such as those in the RUSLE, when operationally used for long-term soil erosion modelling.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  15. Chemical Kinetics of Reaction Systems Carbon Monoxide + Hydroxy Radical and Methyl Radical + Oxygen

    NASA Astrophysics Data System (ADS)

    Yu, Ching-Len

    Experimental and modeling studies were carried out on kinetics and mechanism of two key reactions of natural gas combustion. Five mixtures of hydrogen, oxygen, and carbon dioxide diluted in argon were studied behind reflected -shock waves in the temperature range from 1420 to 2640 K. The production of CO molecules and OH radicals was measured in-situ by laser absorption. The rate coefficient of reaction CO + OH --> CO_2 + H was derived by detailed kinetic modeling, expressed as 4.76 times 10 ^7T^{1.228}{rm e} ^{-35/T}{rm cm}^3 {rm mol}^{-1}{rm s}^{-1}. Theoretical analysis of the CO + OH reaction was performed by using Rice-Ramsperger -Kassel-Marcus (RRKM) theory and the master equation approach by fitting the experimental rate coefficient. The resulting entrance and exit barrier heights, relative to the CO + OH energy level, are 0.92 and 0.72 kcal/mol, respectively. Oxidation of methyl radicals by molecular oxygen were studied by using four shock-heated fuel-lean methane -oxygen-argon mixtures at temperatures from 1550 to 2200 K. The reaction progress was monitored by laser absorption of OH radicals and CO molecules. The rate coefficients of the CH_3+O_2 reactions were determined via kinetic modeling and the RRKM-master equation approach: 2.87 times 10^ {13}{rm e}^{-15340/T } for reaction CH_3+O _2 --> CH_3O + O and 1.85 times 10^{12 }{rm e}^{-10224/T} for reaction CH_3+O_2 --> CH_2O + OH, in the units of cm^3mol^ {-1}s^{-1}. The former was found to be in agreement with that computed based on the canonical variational transition state theory. The derived reaction model was shown to be consistent with essentially all available experimental data. The discrepancy among literature studies results from data interpretation and experimental design.

  16. [Determination of trace amounts of nitrite and its chemical reaction kinetics].

    PubMed

    Luo, Zhi-yong; Zheng, Huai-li

    2014-06-01

    A catalytic kinetic spectrophotometric method for the determination of nitrite, NO2(-)-S2O8(2-)-MR, was developed. It is based on the fading reaction of methyl red (MR) oxidized by potassium persulfate which can be catalyzed by NO2- in the medium of dilute HCl. The optimum experimental conditions were gained by combining single factor experiments with orthogonal experiments. Calibration curve, detection limit, precision, and anti-interference under the optimum experimental conditions were researched. Its kinetics principles and parameters were discussed. Its quantitative principle was investigated. The results show that the optimum experimental conditions of this method should be as follows: 1.0 mL 0.3 mol x L(-1) HCl, 1.0 mL 0.01 mol x L(-1) K2S2O8, 0.6 mL 0.2 g x L(-1) MR, reaction temperature 80 degrees C and reaction time 9 min. The principles for the quantitative determination of trace nitrite is that variation of MR concentration at the maximum absorption wavelength of 518 nm, ln(A0/A), shows a good linear relationship with the concentration of NO2- under the optimum experimental conditions. Its determination range is 0.01-0.80 mg x L(-1) and its detection limit is 0.007 mg x L(-1). The kinetic characteristics are that the reaction order in NO2- is 1 and the fading reaction is a pseudo first order reaction. Its apparent activation energy is 85.04 kJ x mol(-1). Its apparent rate constant is 0.021 4 min(-1), and the half-life is 32.39 min at 80 degrees C. The kinetic principle is that the variation of MR concentration is directly proportional to the concentration of NO2-, ln(A0/A) = kc(NO2-). This new method for the determination of trace nitrite has never previously been reported in the published literature so far. It is highly sensitive and selective. Most of the common ions don't interfere with the determination of nitrite. This method has the advantages of convenient operation and the regents used are cheap and nontoxic. It was applied to the determination of trace nitrite in food and water samples with satisfactory results. PMID:25358175

  17. Kinetics of chemical marker formation in whey protein gels for studying microwave sterilization

    Microsoft Academic Search

    M. H. Lau; J. Tang; I. A. Taub; T. C. S. Yang; C. G. Edwards; R. Mao

    2003-01-01

    The kinetics of 4-hydroxy-5-methy-3(2H)-furanone (M-2) formation in a model food system (20% whey protein gel) was determined for studying cumulative time–temperature effects in high-temperature-short-time processes. M-2 was formed from d-ribose and amines through non-enzymatic browning reactions and enolization under low acid conditions (pH>5). The order of the reaction for M-2 formation was determined by non-linear regression analysis and further confirmed

  18. Chemical Kinetic Data Base for Combustion Chemistry. Part I. Methane and Related Compounds

    Microsoft Academic Search

    W. Tsang; R. F. Hampson

    1986-01-01

    This document contains evaluated data on the kinetics and thermodynamic properties of species that are of importance in methane pyrolysis and combustion. Specifically, the substances considered include H, H2, O, O2, OH, HO2, H2O2, H2O, CH4, C2H6, HCHO, CO2, CO, HCO, CH3, C2H5, C2H4, C2H3, C2H2, C2H, CH3CO, CH3O2, CH3O, singlet CH2, and triplet CH2. All possible reactions are considered.

  19. High temperature chemical kinetic study of the H2-CO-CO2-NO reaction system

    NASA Technical Reports Server (NTRS)

    Jachimowski, C. J.

    1975-01-01

    An experimental study of the kinetics of the H2-CO-CO2-NO reaction system was made behind incident shock waves at temperatures of 2460 and 2950 K. The overall rate of the reaction was measured by monitoring radiation from the CO + O yields CO2 + h upoilon reaction. Correlation of these data with a detailed reaction mechanism showed that the high-temperature rate of the reaction N + OH yields NO + H can be described by the low-temperature (320 K) rate coefficient. Catalytic dissociation of molecular hydrogen was an important reaction under the tests conditions.

  20. Thermal Decomposition of NCN: Shock-Tube Study, Quantum Chemical Calculations, and Master-Equation Modeling.

    PubMed

    Busch, Anna; González-García, Núria; Lendvay, György; Olzmann, Matthias

    2015-07-16

    The thermal decomposition of cyanonitrene, NCN, was studied behind reflected shock waves in the temperature range 1790-2960 K at pressures near 1 and 4 bar. Highly diluted mixtures of NCN3 in argon were shock-heated to produce NCN, and concentration-time profiles of C atoms as reaction product were monitored with atomic resonance absorption spectroscopy at 156.1 nm. Calibration was performed with methane pyrolysis experiments. Rate coefficients for the reaction (3)NCN + M ? (3)C + N2 + M (R1) were determined from the initial slopes of the C atom concentration-time profiles. Reaction R1 was found to be in the low-pressure regime at the conditions of the experiments. The temperature dependence of the bimolecular rate coefficient can be expressed with the following Arrhenius equation: k1(bim) = (4.2 ± 2.1) × 10(14) exp[-242.3 kJ mol(-1)/(RT)] cm(3) mol(-1) s(-1). The rate coefficients were analyzed by using a master equation with specific rate coefficients from RRKM theory. The necessary molecular data and energies were calculated with quantum chemical methods up to the CCSD(T)/CBS//CCSD/cc-pVTZ level of theory. From the topography of the potential energy surface, it follows that reaction R1 proceeds via isomerization of NCN to CNN and subsequent C-N bond fission along a collinear reaction coordinate without a tight transition state. The calculations reproduce the magnitude and temperature dependence of the rate coefficient and confirm that reaction R1 is in the low-pressure regime under our experimental conditions. PMID:25853321

  1. Enskog's kinetic theory of dense gases for chemically reacting binary mixtures. I. Reaction rate and viscosity coefficients

    Microsoft Academic Search

    Adriano W. Silva; Giselle M. Alves; Gilberto M. Kremer

    2008-01-01

    The symmetric moderately dense reaction A+A&rlhar2;B+B is analyzed within the framework of Enskog's equation by using the Chapman Enskog method. For the last stage of a chemical reaction where the affinity is considered a small quantity the constitutive equations for the reaction rate densities and the pressure tensor of the mixture are calculated in terms of the thermodynamic forces: affinity,

  2. Enskog’s kinetic theory of dense gases for chemically reacting binary mixtures. I. Reaction rate and viscosity coefficients

    Microsoft Academic Search

    Adriano W. Silva; Giselle M. Alves; Gilberto M. Kremer

    2008-01-01

    The symmetric moderately dense reaction A+A?B+B is analyzed within the framework of Enskog’s equation by using the Chapman–Enskog method. For the last stage of a chemical reaction–where the affinity is considered a small quantity–the constitutive equations for the reaction rate densities and the pressure tensor of the mixture are calculated in terms of the thermodynamic forces: affinity, divergence and gradient

  3. Chemical Kinetic and Molecular Genetic Study of Selenium Oxyanion Reduction by Enterobactor cloacae SLD1a-1

    SciTech Connect

    Ma,J.; Kobayashi, D.; Yee, N.

    2007-01-01

    Microbial processes play an important role in the redox transformations of toxic selenium oxyanions. In this study, we employed chemical kinetic and molecular genetic techniques to investigate the mechanisms of Se(IV) and Se(VI) reduction by the facultative anaerobe Enterobacter cloacae SLD1a-1. The rates of microbial selenium oxyanion reduction were measured as a function of initial selenium oxyanion concentration (0-1.0 mM) and temperature (10-40 C), and mutagenesis studies were performed to identify the genes involved in the selenium oxyanion reduction pathway. The results indicate that Se(IV) reduction is significantly more rapid than the reduction of Se(VI). The kinetics of the reduction reactions were successfully quantified using the Michaelis-Menten kinetic equation. Both the rates of Se(VI) and Se(IV) reduction displayed strong temperature-dependence with Ea values of 121 and 71.2 kJ/mol, respectively. X-ray absorption near-edge spectra collected for the precipitates formed by Se(VI) and Se(IV) reduction confirmed the formation of Se(0). A miniTn5 transposon mutant of E. cloacae SLD1a-1 was isolated that had lost the ability to reduce Se(VI) but was not affected in Se(IV) reduction activity. Nucleotide sequence analysis revealed the transposon was inserted within a tatC gene, which encodes for a central protein in the twin arginine translocation system. Complementation by the wild-type tatC sequence restored the ability of mutant strains to reduce Se(VI). The results suggest that Se(VI) reduction activity is dependent on enzyme export across the cytoplasmic membrane and that reduction of Se(VI) and Se(IV) are catalyzed by different enzymatic systems.

  4. Evaluated Chemical Kinetic Data for the Reactions of Atomic Oxygen O(3P) with Sulfur Containing Compounds

    NASA Astrophysics Data System (ADS)

    Singleton, D. L.; Cvetanovi?, R. J.

    1988-10-01

    Chemical kinetic data for reactions of O(3P) atoms with sulfur containing compounds are compiled and critically evaluated. Specifically, the reactions considered include the interactions of the ground electronic state of oxygen atoms, O(3P), with S2, SF2, SF5, SOF, S2O, SO, SO2, SO3, SH, H2S, D2S, H2SO4, CS, CS2, COS, CH3SH, C2H5SH, C4H9SH, C5H11SH, CH3SCH3, cy-CH2SCH2, cy-CHCHSCHCH, CH3SSCH3, SCF2, SCCl2, and cy-CF2SCF2S. With one exception, the liquid phase reaction O(3P)+H2SO4?products, all the data considered were for gas phase reactions. Where possible, ``Recommended'' values of the rate parameters have been assessed and conservative uncertainty limits assigned to them.

  5. Chemical kinetics of mobile-proton generation and annihilation in SiO{sub 2} thin films

    SciTech Connect

    Vanheusden, K. [US Air Force Research Laboratory, Kirtland Air Force Base, New Mexico 87117-5776 (United States)] [US Air Force Research Laboratory, Kirtland Air Force Base, New Mexico 87117-5776 (United States); Warren, W.L.; Fleetwood, D.M.; Schwank, J.R.; Shaneyfelt, M.R.; Draper, B.L.; Winokur, P.S. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)] [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Devine, R.A. [France Telecom/CNET, Meylan Cedex (France)] [France Telecom/CNET, Meylan Cedex (France); Archer, L.B.; Brown, G.A.; Wallace, R.M. [Texas Instruments Inc., 13588 North Central Expressway, Dallas, Texas 75243 (United States)] [Texas Instruments Inc., 13588 North Central Expressway, Dallas, Texas 75243 (United States)

    1998-08-01

    The chemical kinetics of mobile-proton reactions in the SiO{sub 2} film of Si/SiO{sub 2}/Si structures were analyzed as a function of forming-gas anneal parameters in the 300{endash}600thinsp{degree}C temperature range. Our data show that the initial buildup of mobile protons is limited by the rate of lateral hydrogen diffusion into the SiO{sub 2} films. The final density of mobile protons is determined by the cooling rate which terminates the annealing process and, in the case of subsequent anneals, by the temperature of the final anneal. To explain the observations, we propose a dynamical equilibrium model which assumes a reversible interfacial reaction with a temperature-dependent balance. {copyright} {ital 1998 American Institute of Physics.}

  6. Nuclear quantum effects in chemical reactions via higher-order path-integral calculations

    NASA Astrophysics Data System (ADS)

    Engel, Hamutal; Eitan, Reuven; Azuri, Asaf; Major, Dan Thomas

    2015-04-01

    A practical approach to treat nuclear quantum mechanical effects in simulations of condensed phases, such as enzymes, is via Feynman path integral (PI) formulations. Typically, the standard primitive approximation (PA) is employed in enzymatic PI simulations. Nonetheless, these PI simulations are computationally demanding due to the large number of beads required to obtain converged results. The efficiency of PI simulations may be greatly improved if higher-order factorizations of the density matrix operator are employed. Herein, we compare the results of model calculations obtained employing the standard PA, the improved operator of Takahashi and Imada (TI), and a gradient-based forward corrector algorithm due to Chin (CH). The quantum transmission coefficient is computed for the Eckart potential while the partition functions and rate constant are computed for the H2 + H hydrogen transfer reaction. These potentials are simple models for chemical reactions. The study of the different factorization methods reveals that in most cases the higher-order action converges faster than the PA and TI approaches, at a moderate computational cost.

  7. Humic Acid Metal Cation Interaction Studied by Spectromicroscopy Techniques in Combination with Quantum Chemical Calculations

    SciTech Connect

    Plaschke, M.; Rothe, J; Armbruster, M; Denecke, M; Naber, A; Geckeis, H

    2010-01-01

    Humic acids (HA) have a high binding capacity towards traces of toxic metal cations, thus affecting their transport in aquatic systems. Eu(III)-HA aggregates are studied by synchrotron-based scanning transmission X-ray microscopy (STXM) at the carbon K-edge and laser scanning luminescence microscopy (LSLM) at the {sup 5}D{sub 0} {yields} {sup 7}F{sub 1,2} fluorescence emission lines. Both methods provide the necessary spatial resolution in the sub-micrometre range to resolve characteristic aggregate morphologies: optically dense zones embedded in a matrix of less dense material in STXM images correspond to areas with increased Eu(III) luminescence yield in the LSLM micrographs. In the C 1s-NEXAFS of metal-loaded polyacrylic acid (PAA), used as a HA model compound, a distinct complexation effect is identified. This effect is similar to trends observed in the dense fraction of HA/metal cation aggregates. The strongest complexation effect is observed for the Zr(IV)-HA/PAA system. This effect is confirmed by quantum chemical calculations performed at the ab initio level for model complexes with different metal centres and complex geometries. Without the high spatial resolution of STXM and LSLM and without the combination of molecular modelling with experimental results, the different zones indicating a 'pseudo'-phase separation into strong complexing domains and weaker complexing domains of HA would never have been identified. This type of strategy can be used to study metal interaction with other organic material.

  8. Predicting new, simple inorganic species by quantum chemical calculations: some successes.

    PubMed

    Pyykkö, Pekka

    2012-11-21

    A combination of ab initio calculations with the isoelectronic principle and chemical intuition is a useful way to predict new species. Some experimentally verified examples are (1) the transition-metal hydrides, MH(n) (n = 4-12), (2) new members of the multiply-bonded 2nd- or 3rd-period species A?B, A=B=C, A=B=C=D or A?B-C?D, and A=B=C=D=E classes, the last-mentioned class including the cations N and OCNCO(+), (3) new members of the uranyl isoelectronic series, (4) actinyls where one of the oxygens is replaced by a 5d transition-metal (TM), (5) certain systems with noble-gas-noble-metal bonds, (6) the first argon compound HArF, (7) the cluster series of WAu(12), (8) TM-centred polyazide anions, (9) covalent molecules with a central -Zn-Zn- bond, (10) tetrahedral clusters of zinc and cadmium, (11) model systems for otherwise missing multiple bonds and (12) certain endohedral A@B systems. Further series of hypothetical species were used as a tool for developing recent sets of covalent radii, for studying the endohedral intermolecular interactions in A@B systems, or for finding examples of a 32-electron rule, corresponding to the well-known 8e- and 18e-rules. For obvious reasons, much of the molecular chemistry of the superheavy elements is based on studies of hypothetical model systems. PMID:22334093

  9. Elucidating triplet-sensitized photolysis mechanisms of sulfadiazine and metal ions effects by quantum chemical calculations.

    PubMed

    Wang, Se; Song, Xuedan; Hao, Ce; Gao, Zhanxian; Chen, Jingwen; Qiu, Jieshan

    2015-03-01

    Sulfadiazine (SDZ) mainly proceeds triplet-sensitized photolysis with dissolved organic matter (DOM) in the aquatic environment. However, the mechanisms underlying the triplet-sensitized photolysis of SDZ with DOM have not been fully worked out. In this study, we investigated the mechanisms of triplet-sensitized photolysis of SDZ(0) (neutral form) and SDZ(-) (anionic form) with four DOM analogues, i.e., fluorenone (FL), thioxanthone (TX), 2-acetonaphthone (2-AN), and 4-benzoylbenzoic acid (CBBP), and three metal ions (i.e., Mg(2+), Ca(2+), and Zn(2+)) effects using quantum chemical calculations. Results indicated that the triplet-sensitized photolysis mechanism of SDZ(0) with FL, TX, and 2-AN was hydrogen transfer, and with CBBP was electron transfer along with proton transfer (for complex SDZ(0)-CBBP2) and hydrogen transfer (for complex SDZ(0)-CBBP1). The triplet-sensitized photolysis mechanisms of SDZ(-) with FL, TX, and CBBP was electron transfer along with proton transfer, and with 2-AN was hydrogen transfer. The triplet-sensitized photolysis product of both SDZ(0) and SDZ(-) was a sulfur dioxide extrusion product (4-(2-iminopyrimidine-1(2H)-yl)aniline), but the formation routs of the products for SDZ(0) and SDZ(-) were different. In addition, effects of the metal ions on the triplet-sensitized photolysis of SDZ(0) and SDZ(-) were different. The metal ions promoted the triplet-sensitized photolysis of SDZ(0), but inhibited the triplet-sensitized photolysis of SDZ(-). PMID:25496743

  10. Calculating NMR chemical shifts using the augmented plane-wave method

    NASA Astrophysics Data System (ADS)

    Laskowski, Robert; Blaha, Peter

    2014-01-01

    Density functional theory (DFT) calculations of the magnetic shielding for solid state nuclear magnetic resonance (NMR) provide an important contribution for the understanding of the experimentally observed chemical shifts. Therefore, methods allowing us to compute those parameters with high precision are very valuable. Recently, we have presented a formalism for computing the NMR parameters in solids based on the augmented plane wave (APW) method [Phys. Rev. B 85, 035132 (2012), 10.1103/PhysRevB.85.035132]. In the present work we derive an improvement of the original schema, which greatly boosts its precision and efficiency. Although the APW method is virtually an exact method for the ground state wave functions in a solid, its optimized basis set is incomplete and we need to extend it by including basis functions containing the radial derivative of the standard APW basis functions in order to efficiently describe the perturbation due to a magnetic field. In addition we also include the core states in the first-order perturbation formula correcting an error resulting from separation of the core and valence states. These allow us to obtain the NMR parameters that are nearly numerically exact within a given DFT functional.

  11. Sister-chromatid exchange and cell replication kinetics in fetal and maternal cells after treatment with chemical teratogens.

    PubMed

    Sharma, R K; Jacobson-Kram, D; Lemmon, M; Bakke, J; Galperin, I; Blazak, W F

    1985-12-01

    Effects of selected chemical teratogens on sister-chromatid exchange (SCE) frequencies and cell replication kinetics (CRK) in pregnant mice and their fetuses were investigated. Maternal and fetal cells were analyzed for SCE and classified as to whether they had gone through 1 (M1), 2 (M2), or 3 or more (M3+) cell cycles for quantifying cell replication kinetics and estimating average generation time (AGT). The teratogens tested in this system were mitomycin C (MMC), cyclophosphamide (CP), ethylnitrosourea (ENU), dimethylnitrosamine (DMN), lead acetate (LA), benzene (BEN), diethylstilbestrol (DES), diphenyldantoin (DPH), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and dimethyl sulfoxide (DMSO). MMC, CP, ENU, DMN, LA and BEN induced significant increases in SCE in both maternal and fetal cells compared with control values. DES and DPH induced increases in SCE in fetal cells only, whereas MNNG and DMSO did not induce any increase in SCE in either maternal or fetal cells. Chi-square analysis of the relative numbers of M1, M2 and M2+ cells revealed significant heterogeneity among test chemical doses in both maternal and fetal cells treated with all of the chemicals except DES. DES had an effect on fetal cells but not on maternal cells. A significant linear relationship between AGT and test chemical dose was noted for ENU and DMSO in maternal cells and DPH and MNNG in fetal cells. Although statistically significant, the effects of DPH, MNNG, and DMSO on AGT were small, with increases in AGT of only 1 h or less at the highest doses tested. ENU, however, resulted in more than a 2-h increase in the AGT of maternal cells. Average generation time was consistently lower in fetal cells as compared with maternal cells (overall mean AGT +/- S.D. from solvent controls was 8.6 +/- 0.3 h for fetal cells and 11.6 +/- 0.7 h for maternal cells). The results indicate that SCE induction and cell replication inhibition can occur independently, and that the assessment of SCE and CRK in maternal and fetal cells may be a promising approach to the identification of teratogenic agents. PMID:4079953

  12. Comparison of direct and quasi-static methods for neutron kinetic calculations with the EDF R and D COCAGNE code

    SciTech Connect

    Girardi, E.; Guerin, P. [Electricite de France - RandD, 1 av. du General de Gaulle, 92141, Clamart (France); Dulla, S.; Nervo, M.; Ravetto, P. [Dipartimento di Energetica, Politecnico di Torino, 24, c.so Duca degli Abruzzi, 10129, Torino (Italy)

    2012-07-01

    Quasi-Static (QS) methods are quite popular in the reactor physics community and they exhibit two main advantages. First, these methods overcome both the limits of the Point Kinetic (PK) approach and the issues of the computational effort related to the direct discretization of the time-dependent neutron transport equation. Second, QS methods can be implemented in such a way that they can be easily coupled to very different external spatial solvers. In this paper, the results of the coupling between the QS methods developed by Politecnico di Torino and the EDF R and D core code COCAGNE are presented. The goal of these activities is to evaluate the performances of QS methods (in term of computational cost and precision) with respect to the direct kinetic solver (e.g. {theta}-scheme) already available in COCAGNE. Additionally, they allow to perform an extensive cross-validation of different kinetic models (QS and direct methods). (authors)

  13. A STUDY OF GAS-PHASE MERCURY SPECIATION USING DETAILED CHEMICAL KINETICS

    EPA Science Inventory

    Mercury (Hg) speciation in combustion-generated flue gas is modeled using a detailed chemical mechanism consisting of 60 reactions and 21 species. This speciation model accounts for chlorination and oxidation of key flue-gas components, including elemental mercury. Results indica...

  14. A chemical kinetics software package Peter Kirkegaard, Erling Bjergbakke, Jens V. Olsen

    E-print Network

    Risø-R-1630(EN) Risø National Laboratory for Sustainable Energy Technical University of Denmark Tables: 6 References: 23 Abstract CHEMSIMUL is a computer program system for simulation of chemical. Homepage: http://chemsimul.dk Information Service Department Risø National Laboratory for Sustainable

  15. A Study of Gas-Phase Mercury Speciation Using Detailed Chemical Kinetics

    Microsoft Academic Search

    Jack R. Edwards; Ravi K. Srivastava; James D. Kilgroe

    2001-01-01

    Mercury speciation in combustion-generated flue gas was modeled using a detailed chemical mechanism consisting of 60 reactions and 21 species. This speciation model accounts for the chlorination and oxidation of key flue-gas components, including elemental mercury (Hg). Results indicated that the performance of the model is very sensitive to temperature. Starting with pure HCl, for lower reactor temperatures (less than

  16. Numerical Study on Spark Ignition Characteristics of a Methane-Air Mixture Using Detailed Chemical Kinetics

    Microsoft Academic Search

    Jilin Han; Hiroshi Yamashita; Kazuhiro Yamamoto

    2009-01-01

    Spark ignition is considered one of the most difficult and complex problems because it involves complicated physical and chemical processes, and it has not yet been explained sufficiently. The minimum ignition energy (MIE) is an important parameter for judging the ignition ability of combustion systems. In the present study, the spark ignition characteristics of a methane-air mixture were investigated by

  17. INTERACTION BETWEEN GAS DIFFUSION AND MULTISTABLE HETEROGENEOUS CHEMICAL KINETICS IN C/C COMPOSITE

    E-print Network

    Paris-Sud XI, Université de

    ]. In the case of silicon carbide deposition from CH3SiCl3/H2 on a plane substrate (i.e. CVD), chemical fibers, an interphase which coats them (usually carbon or hexagonal boron nitride), and a matrix which

  18. Detailed chemical kinetics study of the role of pressure in butane pyrolysis

    SciTech Connect

    Mallinson, R.G. (Oklahoma Univ., Norman, OK (United States). School of Chemical Engineering and Materials Science); Braun, R.L.; Westbrook, C.K.; Burnham, A.K. (Lawrence Livermore National Lab., CA (United States))

    1992-01-01

    This paper reports on a detailed free-radical kinetic model that has been developed to represent the pyrolysis of n-butane and has been used to study the role of pressure on the pyrolysis. THe temperature range covered is from 200 to 600{degrees}C with pressures from 1 to 1000 atm. Simulations were conducted for isothermal, isobaric, homogeneous systems with pure n-butane as the initial reactant. At high temperature, increasing the pressure increases the decomposition rate of butane, as well as increasing the breadth of the carbon number distribution and decreasing the olefins content. Model results agree well with the literature. At low temperature, the rate of decomposition of butane is inhibited by increasing pressures until relatively high pressures, above 100 atm, when the rate increases with higher pressures. Increased pressures at lower temperatures also favor larger products and fewer olefins, but different mechanistic pathways control the decomposition.

  19. Infrared absorption spectroscopy and chemical kinetics of free radicals. Progress report

    SciTech Connect

    Curl, R.F.; Glass, G.P.

    1992-04-01

    Propargyl radical has recently attracted interest because of its possible role in combustion and soot formation. At high temperatures it is not easily destroyed by dissociation nor by reaction with oxygen thus, it has been observed in significant concentrations in numerous pyrolysis and oxidation processes. During the last year, we have obtained the high resolution spectrum of the v{sub 1} acetylenic CH stretch of propargyl radical (HCCCH{sub 2}) near 3322 cm{sup {minus}1} using infrared laser kinetic spectroscopy at Doppler limited resolution. Propargyl is prepared by flash photolysis of propargyl bromide (or propargyl chloride) at 193 nm (ArFexcimer) and its transient infrared absorption probed by a cw color center laser. We are beginning to investigate the kinetics of propargyl radical. The decay of the radical after the flash appears to be second order. The fine structure transition of the Br atom is accessible and when monitored under the same conditions appears to exhibit a simple first order decay suggesting that the Br atom is reacting with precursor propargyl bromide. Ketenyl radicals were produced by 193 nm excimer laser photolysis of ketene and probed with a tunable diode laser operating at 2014 cm{sup {minus}1}. Under these conditions, any singlet methylene which may be formed should react with the precursor, ketene, at a rate fast enough to ensure its total removal from the photolysis cell within 1 {mu}s. In the presence of 2 to 8 Torr of O{sub 2}, the ketenyl radical was observed to decay exponentially with time constants that ranged fro 20 to 5 {mu}s.

  20. Dissolution kinetics of polycrystalline calcium sulfate-based materials: influence of chemical modification.

    PubMed

    Fisher, Robin D; Mbogoro, Michael M; Snowden, Michael E; Joseph, Maxim B; Covington, James A; Unwin, Patrick R; Walton, Richard I

    2011-09-01

    Using a channel flow cell (CFC) system, the dissolution kinetics of polycrystalline gypsum-based materials have been examined with the aim of understanding their interaction with water, a property that limits the applications of the material in many situations. ICP (inductively coupled plasma) analysis of elemental concentrations in solution as a function of time yields surface fluxes by using a finite element modeling approach to simulate the hydrodynamic behavior within the CFC. After correction for surface roughness, a value for the intrinsic dissolution flux into water of pure polycrystalline gypsum, CaSO(4).2H(2)O, of 1.1 (±0.4) × 10(-8) mol cm(-2) s(-1) has been obtained. The addition of known humid creep inhibitors to the gypsum samples, including boric acid, tartaric acid and 3,4,5-trihydroxybenzoic acid (gallic acid), was found to have little measurable effect on the dissolution kinetics of gypsum: all yielded dissolution fluxes of 1.4 (±0.6) × 10(-8) mol cm(-2) s(-1). However, trisodium trimetaphosphate (STMP) was found to have a small detectable inhibitory effect relative to pure gypsum yielding a flux of 7.4 (±2.0) × 10(-9) mol cm(-2) s(-1). The data strongly suggest that models for humid creep inhibition that involve dissolution-crystallization of gypsum crystallites are less likely than those that involve a hindered ingress of water into the gypsum matrix. For comparison, composite materials that comprised of calcium sulfate anhydrite (CaSO(4)) crystallites bound by a polyphosphate matrix were also studied. For some of these samples, Ca(2+) surface fluxes were observed to be ?1 order of magnitude lower than values for polycrystalline gypsum control substrates, suggesting a useful way to impart water resistance to gypsum-based materials. PMID:21861513

  1. Molecular simulations of Hugoniots of detonation products mixtures at chemical equilibrium: Microscopic calculation

    E-print Network

    Paris-Sud XI, Université de

    Molecular simulations of Hugoniots of detonation products mixtures at chemical equilibrium and chemical equilibrium of mixtures of detonation products on the Hugoniot curve. The ReMC method (W. R. Smith and B. Triska, J. Chem. Phys. 100, pp 3019-3027 (1994)) allows to reach the chemical equilibrium

  2. On the prediction of thermal stability of nitroaromatic compounds using quantum chemical calculations

    E-print Network

    Paris-Sud XI, Université de

    ranks at top of physicochemical hazards that may be feared from the use of a given chemical [11 On the prediction of thermal stability of nitroaromatic compounds using quantum chemical a new approach to predict thermal stability of nitroaromatic compounds based on quantum chemical

  3. Object Kinetic Monte Carlo calculations of irradiated Fe-Cr dilute alloys: The effect of the interaction radius between substitutional Cr and self-interstitial Fe

    NASA Astrophysics Data System (ADS)

    Gámez, L.; Gámez, B.; Caturla, M. J.; Terentyev, D.; Perlado, J. M.

    2011-07-01

    Object Kinetic Monte Carlo models allow for the study of the evolution of the damage created by irradiation to time scales that are comparable to those achieved experimentally. Therefore, the essential Object Kinetic Monte Carlo parameters can be validated through comparison with experiments. However, this validation is not trivial since a large number of parameters is necessary, including migration energies of point defects and their clusters, binding energies of point defects in clusters, as well as the interaction radii. This is particularly cumbersome when describing an alloy, such as the Fe-Cr system, which is of interest for fusion energy applications. In this work we describe an Object Kinetic Monte Carlo model for Fe-Cr alloys in the dilute limit. The parameters used in the model come either from density functional theory calculations or from empirical interatomic potentials. This model is used to reproduce isochronal resistivity recovery experiments of electron irradiated dilute Fe-Cr alloys performed by Abe and Kuramoto. The comparison between the calculated results and the experiments reveal that an important parameter is the capture radius between substitutional Cr and self-interstitial Fe atoms. A parametric study is presented on the effect of the capture radius on the simulated recovery curves.

  4. A comprehensive experimental and detailed chemical kinetic modelling study of 2,5-dimethylfuran pyrolysis and oxidation

    PubMed Central

    Somers, Kieran P.; Simmie, John M.; Gillespie, Fiona; Conroy, Christine; Black, Gráinne; Metcalfe, Wayne K.; Battin-Leclerc, Frédérique; Dirrenberger, Patricia; Herbinet, Olivier; Glaude, Pierre-Alexandre; Dagaut, Philippe; Togbé, Casimir; Yasunaga, Kenji; Fernandes, Ravi X.; Lee, Changyoul; Tripathi, Rupali; Curran, Henry J.

    2013-01-01

    The pyrolytic and oxidative behaviour of the biofuel 2,5-dimethylfuran (25DMF) has been studied in a range of experimental facilities in order to investigate the relatively unexplored combustion chemistry of the title species and to provide combustor relevant experimental data. The pyrolysis of 25DMF has been re-investigated in a shock tube using the single-pulse method for mixtures of 3% 25DMF in argon, at temperatures from 1200–1350 K, pressures from 2–2.5 atm and residence times of approximately 2 ms. Ignition delay times for mixtures of 0.75% 25DMF in argon have been measured at atmospheric pressure, temperatures of 1350–1800 K at equivalence ratios (?) of 0.5, 1.0 and 2.0 along with auto-ignition measurements for stoichiometric fuel in air mixtures of 25DMF at 20 and 80 bar, from 820–1210 K. This is supplemented with an oxidative speciation study of 25DMF in a jet-stirred reactor (JSR) from 770–1220 K, at 10.0 atm, residence times of 0.7 s and at ? = 0.5, 1.0 and 2.0. Laminar burning velocities for 25DMF-air mixtures have been measured using the heat-flux method at unburnt gas temperatures of 298 and 358 K, at atmospheric pressure from ? = 0.6–1.6. These laminar burning velocity measurements highlight inconsistencies in the current literature data and provide a validation target for kinetic mechanisms. A detailed chemical kinetic mechanism containing 2768 reactions and 545 species has been simultaneously developed to describe the combustion of 25DMF under the experimental conditions described above. Numerical modelling results based on the mechanism can accurately reproduce the majority of experimental data. At high temperatures, a hydrogen atom transfer reaction is found to be the dominant unimolecular decomposition pathway of 25DMF. The reactions of hydrogen atom with the fuel are also found to be important in predicting pyrolysis and ignition delay time experiments. Numerous proposals are made on the mechanism and kinetics of the previously unexplored intermediate temperature combustion pathways of 25DMF. Hydroxyl radical addition to the furan ring is highlighted as an important fuel consuming reaction, leading to the formation of methyl vinyl ketone and acetyl radical. The chemically activated recombination of H?2 or CH3?2 with the 5-methyl-2-furanylmethyl radical, forming a 5-methyl-2-furylmethanoxy radical and ?H or CH3? radical is also found to exhibit significant control over ignition delay times, as well as being important reactions in the prediction of species profiles in a JSR. Kinetics for the abstraction of a hydrogen atom from the alkyl side-chain of the fuel by molecular oxygen and H?2 radical are found to be sensitive in the estimation of ignition delay times for fuel-air mixtures from temperatures of 820–1200 K. At intermediate temperatures, the resonantly stabilised 5-methyl-2-furanylmethyl radical is found to predominantly undergo bimolecular reactions, and as a result sub-mechanisms for 5-methyl-2-formylfuran and 5-methyl-2-ethylfuran, and their derivatives, have also been developed with consumption pathways proposed. This study is the first to attempt to simulate the combustion of these species in any detail, although future refinements are likely necessary. The current study illustrates both quantitatively and qualitatively the complex chemical behavior of what is a high potential biofuel. Whilst the current work is the most comprehensive study on the oxidation of 25DMF in the literature to date, the mechanism cannot accurately reproduce laminar burning velocity measurements over a suitable range of unburnt gas temperatures, pressures and equivalence ratios, although discrepancies in the experimental literature data are highlighted. Resolving this issue should remain a focus of future work. PMID:24273333

  5. Quantum-chemical calculations and electron diffraction study of the equilibrium molecular structure of vitamin K3

    NASA Astrophysics Data System (ADS)

    Khaikin, L. S.; Tikhonov, D. S.; Grikina, O. E.; Rykov, A. N.; Stepanov, N. F.

    2014-05-01

    The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K3) having C s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.

  6. Layer selection effect on solid state 13C and 15N chemical shifts calculation using ONIOM approach.

    PubMed

    Shaghaghi, Hoora; Ebrahimi, Hossein Pasha; Bahrami Panah, Niloufar; Tafazzoli, Mohsen

    2013-01-01

    Solid state (13)C and (15)N chemical shifts of uracil and imidazole have been calculated using a 2-layer ONIOM approach at 32 levels of theory. The effect of electron correlation between two layers has been investigated by choosing two different kinds of layer selection. Factorial design has been applied as a multivariate technique to analyze the effect of wave function and layer selection on solid state (13)C and (15)N chemical shifts calculations. PBEPBE/6-311+G(d,p) was recommended as an optimally selected level of theory for high layer in both models. It is illustrated that considering the electron correlation of two layers of ONIOM models is important factor to calculate solid state (15)N chemical shifts. The agreement between the calculated and experimental values of solid state (13)C and (15)N chemical shifts using ONIOM (PBEPBE/6-311+G(d,p):AM1) for both uracil and imidazole confirmed the reliability of the selected wave functions and layer selection. PMID:23414630

  7. Measurement of HO2 chemical kinetics with a new detection method

    NASA Technical Reports Server (NTRS)

    Lee, Long C.; Suto, Masako

    1986-01-01

    Reaction rate constants of HO2+O3 were measured at various temperatures using a newly developed HO2 detection method. HO2 was detected by the OH(A-X) emission produced from photodissociative excitation of HO2 at 147 nm. In order to examine the possible interference of other emitting species with the HO2 detection, the photoexcitation processes of all the chemical species existing in the discharge flow tube were also investigated. The results are summarized.

  8. Effect of silicon source gas on silicon-germanium chemical vapor deposition kinetics at atmospheric pressure

    Microsoft Academic Search

    T. I. Kamins; D. J. Meyer

    1992-01-01

    Epitaxial Si1?xGex alloy layers have been deposited in an atmospheric-pressure, chemical-vapor-deposition reactor using dichlorosilane, silane, and disilane, along with germane. The deposition rate increases and the Ge content decreases with increasing reactivity of the silicon-containing gas. The rate increases monotonically with increasing Ge content in the layer for all three gases, in contrast to the behavior seen in systems operating

  9. Chemical vapor deposition of epitaxial silicon-germanium from silane and germane. 1: Kinetics

    Microsoft Academic Search

    S. M. Jang; K. Liao; R. Reif

    1995-01-01

    The authors report measured germanium incorporation and growth rate for Si{sub 1-x}Geâ grown by very low pressure chemical vapor deposition in the temperature range of 570 to 700 C. The growth rate of Si{sub 1-x}Geâ shows different germanium dependencies at different temperatures. They found that the growth rate decrease at 700 C and increase at 570 C with the addition

  10. Kinetics of silicon-germanium deposition by atmospheric-pressure chemical vapor deposition

    Microsoft Academic Search

    T. I. Kamins; D. J. Meyer

    1991-01-01

    The deposition of Si1?xGex alloy layers in an atmospheric-pressure, chemical vapor deposition reactor has been studied by separately examining the silicon and the germanium components of the deposition rate. The overall deposition rate increases approximately linearly with GeH4 partial pressure, but is relatively independent of SiH2Cl2 partial pressure. The silicon component of the deposition rate increases rapidly with increasing temperature

  11. Kinetics and mechanisms of high-temperature creep in silicon carbide: II, chemically vapor deposited

    Microsoft Academic Search

    C. H. Carter; J. Bentley; R. F. Davis

    1984-01-01

    Chemically vapor deposited (CVD) silicon carbide was subjected to constant compressive stresses (110 to 220 MN\\/m²) at high temperatures (1848 to 2023 K) in order to determine the controlling steady-state creep mechanisms under these conditions. An extensive TEM study was also conducted to facilitate this determination. The strong preferred crystallographic orientation of this material causes the creep rate to be

  12. Chemical and elemental depth profiling of very thin organic layers by constant kinetic energy XPS: a new synchrotron XPS analysis strategy.

    PubMed

    Girard-Lauriault, Pierre-Luc; Gross, Thomas; Lippitz, Andreas; Unger, Wolfgang E S

    2012-07-17

    We present a new synchrotron X-ray photoelectron spectroscopy strategy for surface chemical analysis of materials. Our approach is based on the acquisition of photoelectron spectra at constant kinetic energies with the help of a tunable synchrotron X-radiation source. This ensures both constant and tunable information depth for all elements in a very thin organic layer. Many of the problems known to XPS depth profiling using laboratory equipment are thereby avoided. Using our methodology, the 95% information depth, z(95%), can be tuned down to about 0.7 nm in organic materials. The upper limit in our study at the HE-SGM monochromator dipole magnet beamline at the synchrotron radiation source BESSY II is about 4.3 nm. Elemental quantification is achieved through relative sensitivity factors (RSF) specific to the measurement conditions, determined either with the help of calculated photoionization cross sections and inelastic mean free paths or experimentally. The potential of the technique is demonstrated for the in-depth analysis of plasma deposited nitrogen-rich organic thin films used in biomedical applications. PMID:22686444

  13. The kinetics of cytokine production by draining lymph node cells following primary exposure of mice to chemical allergens.

    PubMed Central

    Hope, J C; Dearman, R J; Kimber, I; Hopkins, S J

    1994-01-01

    Skin sensitization with chemical allergens is associated with the activation and proliferation of lymphocytes in lymph nodes draining the site of exposure. As lymphocyte activation is regulated by the action of cytokines, we have investigated the nature and kinetics of cytokine production by draining lymph node cells (LNC) from mice, following their primary exposure to chemical allergens. Both interleukin-1 (IL-1) and IL-6 were induced in a biphasic manner following primary exposure of mice to oxazolone or to dicyclohexylmethane-4,4'-diisocyanate (HMDI). The initial phase of production occurred when LNC were prepared from mice 8-20 hr following exposure, while the second peak was coincident with the maximal proliferative response at 72 hr. Increased IL-4 production was observed only when LNC were prepared 96 hr following sensitization. Despite vigorous lymphocyte proliferation there was no evidence for IL-2 production by draining LNC. The ordered and transient pattern of cytokine production that occurs during the afferent phase of contact sensitization suggests that sequential cytokine signals may be involved in regulating the characteristics of the response generated within the draining lymph node. PMID:7835943

  14. Chemical and Steady-State Kinetic Analyses of a Heterologously Expressed Heme Dependent Chlorite Dismutase†

    PubMed Central

    Streit, Bennett R.; DuBois, Jennifer L.

    2013-01-01

    Chlorite dismutase carries out the heme-catalyzed decomposition of ClO2– to Cl– and O2, an unusual transformation with biotechnological and bioremediative applications. The enzyme has been successfully overexpressed for the first time in highly functional form in Escherichia coli and its steady state kinetics studied. The purified enzyme is abundant (55 mg/L cell culture), highly active (~4.7 × 103 ?mol of ClO2– min–1 mg–1 subunit) and nearly stoichiometric in heme; further, it shares spectroscopic and physicochemical features with chlorite dismutases previously isolated from three organisms. A careful study of the enzyme's steady state kinetics has been carried out. ClO2– consumption and O2 release rates were measured, yielding comparable values of kcat (4.5 × 105 min–1), Km (~215 ?M), and kcat/Km (3.5 × 107 M–1 s–1) via either method (4 °C, pH 6.8; all values referenced per heme-containing subunit). ClO2–:O2 stoichiometry exhibited a 1:1 relationship under all conditions measured. Though the value of kcat/Km indicates near diffusion control of the reaction, viscosogens had no effect on kcat/Km or Vmax. The product O2 did not inhibit the reaction at saturating [O2], but Cl– is a mixed inhibitor with relatively high values of KI (225 mM for enzyme and 95.6 mM for the enzyme–substrate complex), indicating a relatively low affinity of the heme iron for halogen ions. Chlorite irreversibly inactivates the enzyme after ~1.7 × 104 turnovers (per heme) and with a half-life of 0.39 min, resulting in bleaching of the heme chromophore. The inactivation KI (Kinact) of 166 ?M is similar in magnitude to Km, consistent with a common Michaelis complex on the pathway to both reaction and inactivation. The one-electron peroxidase substrate guaiacol offers incomplete protection of the enzyme from inactivation. Mechanisms in keeping with the available data and the properties of other well-described heme enzymes are proposed. PMID:18422344

  15. Earle K. Plyler Prize for Molecular Spectroscopy & Dynamics Lecture: Broadband Rotational Spectroscopy for Chemical Kinetics, Molecular Structure, and Analytical Chemistry

    NASA Astrophysics Data System (ADS)

    Pate, Brooks

    2013-03-01

    Advances in high-speed digital electronics have enabled a new generation of molecular rotational spectroscopy techniques that provide instantaneous broadband spectral coverage. These techniques use a chirped excitation pulse to coherently excite the molecular sample over a spectral bandwidth of 10 GHz or larger through rapid passage. The subsequent time-domain emission is recorded using high-speed digitizers (up to 100 Gigasample/s) and the frequency domain spectrum is produced by fast Fourier transformation. The chirped-pulse Fourier transform (CP-FT) method has been implemented in the microwave frequency range (2-40 GHz) for studies of cold samples in pulsed jet sources and in the mm-wave/terahertz (THz) frequency range for studies of samples at room-temperature. The method has opened new applications for molecular rotational spectroscopy in the area of chemical kinetics where dynamic rotational spectroscopy is used to measure the rates of unimolecular isomerization reactions in highly excited molecules prepared by pulsed infrared laser excitation. In these applications, the isomerization rate is obtained from an analysis of the overall line shapes which are modified by chemical exchange leading to coalescence behavior similar to the effect in NMR spectroscopy. The sensitivity of the method and the ability to extend it to low frequency (2-8 GHz) have significantly increased the size range of molecules and molecular clusters for structure determination using isotopic substitution to build up the 3D molecular structures atom-by-atom. Application to the structure of water clusters with up to 15 water molecules will be presented. When coupled with advances in solid-state mm-wave/THz devices, this method provides a direct digital technique for analytical chemistry of room-temperature gases based on molecular rotational spectroscopy. These high-throughput methods can analyze complex sample mixtures with unmatched chemical selectivity and short analysis times. Advances in high-speed digital electronics have enabled a new generation of molecular rotational spectroscopy techniques that provide instantaneous broadband spectral coverage. These techniques use a chirped excitation pulse to coherently excite the molecular sample over a spectral bandwidth of 10 GHz or larger through rapid passage. The subsequent time-domain emission is recorded using high-speed digitizers (up to 100 Gigasample/s) and the frequency domain spectrum is produced by fast Fourier transformation. The chirped-pulse Fourier transform (CP-FT) method has been implemented in the microwave frequency range (2-40 GHz) for studies of cold samples in pulsed jet sources and in the mm-wave/terahertz (THz) frequency range for studies of samples at room-temperature. The method has opened new applications for molecular rotational spectroscopy in the area of chemical kinetics where dynamic rotational spectroscopy is used to measure the rates of unimolecular isomerization reactions in highly excited molecules prepared by pulsed infrared laser excitation. In these applications, the isomerization rate is obtained from an analysis of the overall line shapes which are modified by chemical exchange leading to coalescence behavior similar to the effect in NMR spectroscopy. The sensitivity of the method and the ability to extend it to low frequency (2-8 GHz) have significantly increased the size range of molecules and molecular clusters for structure determination using isotopic substitution to build up the 3D molecular structures atom-by-atom. Application to the structure of water clusters with up to 15 water molecules will be presented. When coupled with advances in solid-state mm-wave/THz devices, this method provides a direct digital technique for analytical chemistry of room-temperature gases based on molecular rotational spectroscopy. These high-throughput methods can analyze complex sample mixtures with unmatched chemical selectivity and short analysis times. Work Supported by the NSF MRI Program.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    The solubility of ozone and the kinetics of its decomposition and interaction with chloride ions in a 1 M aqueous solution of NaCl at 20°C and pH 8.4-10.8 were studied. The ratio between the concentration of O3 in solution and the gas phase was found to be 0.16 at pH 8.4-9.8. The concentration of dissolved ozone decreased sharply as pH increased to 10.8 because of a substantial increase in the rate of its decomposition. It was observed for the first time that the interaction of O3 with Cl- in alkaline media resulted in the formation of ClO{3/-} chlorate ions. The dependence of the rate of formation of ClO{3/-} on pH was determined; its maximum value was found to be 9.6 × 10-6 mol l-1 min-1 at pH 10.0 and the concentration of ozone at the entrance of the reactor 30.0 g/m3. A spectrophotometric method for the determination of chlorate ions (concentrations 1 × 10-5-3 × 10-4 M) in aqueous solutions was suggested.

  17. Cometary impact and amino acid survival--chemical kinetics and thermochemistry.

    PubMed

    Ross, David S

    2006-06-01

    The Arrhenius parameters for the initiating reactions in butane thermolysis and the formation of soot, reliable to at least 3000 K, have been applied to the question of the survival of amino acids in cometary impacts on early Earth. The pressure/temperature/time course employed here was that developed in hydrocode simulations for kilometer-sized comets (Pierazzo and Chyba, 1999), with attention to the track below 3000 K where it is shown that potential stabilizing effects of high pressure become unimportant kinetically. The question of survival can then be considered without the need for assignment of activation volumes and the related uncertainties in their application to extreme conditions. The exercise shows that the characteristic times for soot formation in the interval fall well below the cooling periods for impacts ranging from fully vertical down to about 9 degrees above horizontal. Decarboxylation, which emerges as more rapid than soot formation below 2000-3000 K, continues further down to extremely narrow impact angles, and accordingly cometary delivery of amino acids to early Earth is highly unlikely. PMID:16722675

  18. Self-consistent nonlocal feedback theory for electrocatalytic swimmers with heterogeneous surface chemical kinetics

    NASA Astrophysics Data System (ADS)

    Nourhani, Amir; Crespi, Vincent H.; Lammert, Paul E.

    2015-06-01

    We present a self-consistent nonlocal feedback theory for the phoretic propulsion mechanisms of electrocatalytic micromotors or nanomotors. These swimmers, such as bimetallic platinum and gold rods catalyzing decomposition of hydrogen peroxide in aqueous solution, have received considerable theoretical attention. In contrast, the heterogeneous electrochemical processes with nonlocal feedback that are the actual "engines" of such motors are relatively neglected. We present a flexible approach to these processes using bias potential as a control parameter field and a locally-open-circuit reference state, carried through in detail for a spherical motor. While the phenomenological flavor makes meaningful contact with experiment easier, required inputs can also conceivably come from, e.g., Frumkin-Butler-Volmer kinetics. Previously obtained results are recovered in the weak-heterogeneity limit and improved small-basis approximations tailored to structural heterogeneity are presented. Under the assumption of weak inhomogeneity, a scaling form is deduced for motor speed as a function of fuel concentration and swimmer size. We argue that this form should be robust and demonstrate a good fit to experimental data.

  19. Chemical Kinetics and Properties from the Radiation Chemistry Data Center (RCDC)

    DOE Data Explorer

    The Radiation Chemistry Data Center (RCDC) is a focal point for the compilation and evaluation of kinetic, spectroscopic and thermodynamic data for processes in solution involving reactive intermediates, including free radicals and excited states. These data are primarily derived from the published literature on radiation chemistry and quantitative aspects of photochemistry. The compilations are presented as individual groups of pages corresponding to each published work. Each compilation consists of an introductory article, describing the scope of the compilation, with the considerations and criteria for data evaluation discussed. Nomenclature for the compilation is also described here. For several compilations the introduction is followed by one or more pages of links organized as an index or table of contents to the individual pages of the compilation. These links allow the browsing of the data by species name. Each page tabulates the reaction of a transient species with a particular reactant. RCDC was established at the Notre Dame Radiation Laboratory in 1965, as part of the National Standard Reference Data System.

  20. M A N U A L A Program to Calculate Chemical Speciation Equilibria,

    E-print Network

    Wehrli, Bernhard

    of the program. Another library with more than 300 solubility constants allows easy introduction of solid phases, Dissolution, Precipitation, Adsorption, Kinetics, pX-pY Diagrams, Solubility Diagrams. Libraries with Complexation Constants For MacOSX, Windows, Linux, Solaris Beat Müller Limnological Research Center EAWAG

  1. Measurements of HO2 chemical kinetics with a new detection method

    NASA Technical Reports Server (NTRS)

    Lee, L. C.; Suto, M.

    1986-01-01

    Research for the period from December 1, 1985 to May 31, 1986 is discussed, i.e., the reaction rate constant of HO2+O3 has been measured with a discharge-flow-tube apparatus. The HO2 radical was detected by the OH(A-X) photofragment emission produced from photodissociative excitation of HO2 at 147 nm. In the meantime, the optical emissions produced by the vacuum ultraviolet excitation of chemical species in the flow tube were investigated and used to examine the possibility for their interference with the HO2 detection. The research results are summarized below.

  2. Binomial tau-leap spatial stochastic simulation algorithm for applications in chemical kinetics

    NASA Astrophysics Data System (ADS)

    Marquez-Lago, Tatiana T.; Burrage, Kevin

    2007-09-01

    In cell biology, cell signaling pathway problems are often tackled with deterministic temporal models, well mixed stochastic simulators, and/or hybrid methods. But, in fact, three dimensional stochastic spatial modeling of reactions happening inside the cell is needed in order to fully understand these cell signaling pathways. This is because noise effects, low molecular concentrations, and spatial heterogeneity can all affect the cellular dynamics. However, there are ways in which important effects can be accounted without going to the extent of using highly resolved spatial simulators (such as single-particle software), hence reducing the overall computation time significantly. We present a new coarse grained modified version of the next subvolume method that allows the user to consider both diffusion and reaction events in relatively long simulation time spans as compared with the original method and other commonly used fully stochastic computational methods. Benchmarking of the simulation algorithm was performed through comparison with the next subvolume method and well mixed models (MATLAB), as well as stochastic particle reaction and transport simulations (CHEMCELL, Sandia National Laboratories). Additionally, we construct a model based on a set of chemical reactions in the epidermal growth factor receptor pathway. For this particular application and a bistable chemical system example, we analyze and outline the advantages of our presented binomial ?-leap spatial stochastic simulation algorithm, in terms of efficiency and accuracy, in scenarios of both molecular homogeneity and heterogeneity.

  3. Kinetic and chemical characterization of aldehyde oxidation by fungal aryl-alcohol oxidase.

    PubMed

    Ferreira, Patricia; Hernández-Ortega, Aitor; Herguedas, Beatriz; Rencoret, Jorge; Gutiérrez, Ana; Martínez, María Jesús; Jiménez-Barbero, Jesús; Medina, Milagros; Martínez, Angel T

    2010-02-01

    Fungal AAO (aryl-alcohol oxidase) provides H2O2 for lignin biodegradation. AAO is active on benzyl alcohols that are oxidized to aldehydes. However, during oxidation of some alcohols, AAO forms more than a stoichiometric number of H2O2 molecules with respect to the amount of aldehyde detected due to a double reaction that involves aryl-aldehyde oxidase activity. The latter reaction was investigated using different benzylic aldehydes, whose oxidation to acids was demonstrated by GC-MS. The steady- and presteady state kinetic constants, together with the chromatographic results, revealed that the presence of substrate electron-withdrawing or electron-donating substituents had a strong influence on activity; the highest activity was with p-nitrobenzaldehyde and halogenated aldehydes and the lowest with methoxylated aldehydes. Moreover, activity was correlated to the aldehyde hydration rates estimated by 1H-NMR. These findings, together with the absence in the AAO active site of a residue able to drive oxidation via an aldehyde thiohemiacetal, suggested that oxidation mainly proceeds via the gem-diol species. The reaction mechanism (with a solvent isotope effect, 2H2Okred, of approx. 1.5) would be analogous to that described for alcohols, the reductive half-reaction involving concerted hydride transfer from the alpha-carbon and proton abstraction from one of the gem-diol hydroxy groups by a base. The existence of two steps of opposite polar requirements (hydration and hydride transfer) explains some aspects of aldehyde oxidation by AAO. Site-directed mutagenesis identified two histidine residues strongly involved in gem-diol oxidation and, unexpectedly, suggested that an active-site tyrosine residue could facilitate the oxidation of some aldehydes that show no detectable hydration. Double alcohol and aldehyde oxidase activities of AAO would contribute to H2O2 supply by the enzyme. PMID:19891608

  4. Chemical bonding in view of electron charge density and kinetic energy density descriptors.

    PubMed

    Jacobsen, Heiko

    2009-05-01

    Stalke's dilemma, stating that different chemical interpretations are obtained when one and the same density is interpreted either by means of natural bond orbital (NBO) and subsequent natural resonance theory (NRT) application or by the quantum theory of atoms in molecules (QTAIM), is reinvestigated. It is shown that within the framework of QTAIM, the question as to whether for a given molecule two atoms are bonded or not is only meaningful in the context of a well-defined reference geometry. The localized-orbital-locator (LOL) is applied to map out patterns in covalent bonding interaction, and produces results that are consistent for a variety of reference geometries. Furthermore, LOL interpretations are in accord with NBO/NRT, and assist in an interpretation in terms of covalent bonding. PMID:19090572

  5. Validity conditions for stochastic chemical kinetics in diffusion-limited systems.

    PubMed

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

    2014-02-01

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

  6. Validity conditions for stochastic chemical kinetics in diffusion-limited systems

    PubMed Central

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

    2014-01-01

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

  7. Calculation of eddy viscosity in a compressible turbulent boundary layer with mass injection and chemical reaction

    NASA Technical Reports Server (NTRS)

    Omori, S.; Gross, K. W.

    1973-01-01

    The turbulent kinetic energy equation is coupled with boundary layer equations to solve the characteristics of compressible turbulent boundary layers with mass injection and combustion. The Reynolds stress is related to the turbulent kinetic energy using the Prandtl-Wieghardt formulation. When a lean mixture of hydrogen and nitrogen is injected through a porous plate into the subsonic turbulent boundary layer of air flow and ignited by external means, the turbulent kinetic energy increases twice as much as that of noncombusting flow with the same mass injection rate of nitrogen. The magnitudes of eddy viscosity between combusting and noncombusting flows with injection, however, are almost the same due to temperature effects, while the distributions are different. The velocity profiles are significantly affected by combustion. If pure hydrogen as a transpiration coolant is injected into a rocket nozzle boundary layer flow of combustion products, the temperature drops significantly across the boundary layer due to the high heat capacity of hydrogen. At a certain distance from the wall hydrogen reacts with the combustion products, liberating an extensive amount of heat.

  8. The researchers are using kinetics and quantum mechanical calculations to elucidate the catalytic reaction mechanism of hydrocarbon epoxidation.

    E-print Network

    Ottino, Julio M.

    Theory (DFT) and a quantum/classical ONIOM model. For the DFT calculations and for the high-level part of ONIOM, PW91 exchange-correlation functional is used, and the LANL2DZ basis set is employed. For the low-level part of the ONIOM calculations of epoxidation, the UFF force field is utilized. Results: The Broadbelt

  9. Chemical kinetics and atmospheric modification. Final report, 31 August 1989-31 December 1993

    SciTech Connect

    McFadden, D.L.

    1994-05-01

    Electron attachment rate constants were obtained and negative ion product analysis was performed over the temperature between 300 and 1200 degrees range for a series of seventeen halomethane molecules that undergo dissociative electron attachment. The reactant molecules include CH3Cl, CH3Br, CH3I, CF3Cl, CF3Br, CF3I, CF2Cl2, CFCl3, CCl4, CF3H, CF2H2, CH3F, CF2HCl, CHFCl2, CH2Br2, CCl2H2, and CC13H. Positive activation energies were observed for most of the reactions. The results of molecular structure calculations for both the neutral and anionic species suggest that the magnitude of the rate constants and of the temperature coefficients for dissociative electron attachment in these systems can be understood in terms of the geometrical reorganization associated with negative ion formation.

  10. Molecular structure, spectroscopic characterization of (S)-2-Oxopyrrolidin-1-yl Butanamide and ab initio, DFT based quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Ramya, T.; Gunasekaran, S.; Ramkumaar, G. R.

    2015-10-01

    The experimental and theoretical spectra of (S)-2-Oxopyrrolidin-1-yl Butanamide (S2OPB) were studied. FT-IR and FT-Raman spectra of S2OPB in the solid phase were recorded and analyzed in the range 4000-450 and 5000-50 cm-1 respectively. The structural and spectroscopic analyses of S2OPB were calculated using ab initio Hartree Fock (HF) and density functional theory calculations (B3PW91, B3LYP) with 6-31G(d,p) basis set. A complete vibrational interpretation has been made on the basis of the calculated Potential Energy Distribution (PED). The HF, B3LYP and B3PW91 methods based NMR calculation has been used to assign the 1H NMR and 13C NMR chemical shift of S2OPB. Comparative study on UV-Vis spectral analysis between the experimental and theoretical (B3PW91, B3LYP) methods and the global chemical parameters and local descriptor of reactivity through the Fukui function were performed. Finally the thermodynamic properties of S2OPB were calculated at different temperatures and the corresponding relations between the properties and temperature were also studied.

  11. Chemical vapor deposition of epitaxial silicon-germanium from silane and germane. 1: Kinetics

    SciTech Connect

    Jang, S.M.; Liao, K.; Reif, R. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Microsystems Technology Labs.

    1995-10-01

    The authors report measured germanium incorporation and growth rate for Si{sub 1{minus}x}Ge{sub x} grown by very low pressure chemical vapor deposition in the temperature range of 570 to 700 C. The growth rate of Si{sub 1{minus}x}Ge{sub x} shows different germanium dependencies at different temperatures. They found that the growth rate decrease at 700 C and increase at 570 C with the addition of germanium. The observed nonlinear Arrhenius behavior of the growth rate as a function of germanium content suggests that germanium modifies the activation energy for Si{sub 1{minus}x}Ge{sub x} deposition, possibly by enhancing hydrogen desorption. The possible rate-limiting steps controlling Si{sub 1{minus}x}Ge{sub x} deposition were examined by varying the hydrogen flow rate and the total deposition pressure, and it was found that hydrogen suppresses Si{sub 1{minus}x}Ge{sub x} deposition rate when the germanium content is low. The consistent growth-rate enhancement observed by increasing total deposition pressure is dependent on germanium incorporation and becomes more pronounced as the germanium content is increased. A model is proposed to explain the observations.

  12. Mass spectrometric and kinetic study of low-pressure chemical vapor deposition of Si[sub 3]N[sub 4] thin films from SiH[sub 2]Cl[sub 2] and NH[sub 3

    SciTech Connect

    Sorita, Tetsuji; Satake, Tetsuya; Adachi, Hiroshi; Ogata, Tamotsu; Kobayashi, Kiyoteru (Mitsubishi Electric Corp., Hyogo (Japan))

    1994-12-01

    The deposition mechanism of Si[sub 3]N[sub 4] films from dichlorosilane (DCS) and ammonia, formed by a conventional low-pressure chemical vapor deposition system, was studied, combining mass spectrometric analysis and the macrocavity method''. The dominant neutral species in the gas phase are NH[sub 3] and aminochlorosilane (ACS), which was produced by the gas-phase reaction of DCS, in a high NH[sub 3] (a large NH[sub 3]/DCS ratio) condition, while DCS dominantly exists in a low NH[sub 3] condition. Contrary to the mass spectrometric results, there is not a major dependence of the kinetic constants of the deposition precursors on the gas-mixture ratio. By fitting the growth-rate profiles to an optimal theoretical profile, both of the two kinds of precursor are estimated to have low activity. The conformal step coverage quality agrees with the small sticking probabilities estimated as 10[sup [minus]4] and 10[sup [minus]6]. Those precursors can be assigned to DCS and ACS, so that the mass spectrometric data would be consistent with the growth profiles. The conversion to ACS is calculated based on an assumed simple kinetic form and leads to a qualitative interpretation for gas-mixture ratio-dependence of conversion. A kinetic model including precursor molecules is presented to correlate the mass spectrometric results, the growth-rate profiles, and the step coverage quality.

  13. Effects of Ca and Sr chemical doping on the average superconducting kinetic energy of YBa2Cu3O7-?

    NASA Astrophysics Data System (ADS)

    Vieira, V. N.; Mendonça, A. P. A.; Dias, F. T.; Hneda, M. L.; Pureur, P.; Schaf, J.; Mesquita, F.

    2015-03-01

    In this brief communication we applied the MZFC(T) and MFCC(T) reversible dc magnetizations to get the average superconducting kinetic energy density, kS(T,B) of YBa2Cu3O7-?, Y0.95Ca0.05Ba2Cu3O7-? and YBa1.75Sr0.25Cu3O7-? ceramic samples with the aim of study the effects of Ca and Sr doping on the kS(T,B). The MZFC(T) and MFCC(T) measurements were performed with a SQUID magnetometer from quantum design to dc magnetic fields up to 50kOe. The determination of the kS(T,B) from reversible dc magnetization is supported by virial theorem of superconductivity [kS(T,B) = – MB]. The kS(T,B) results show an common temperature profile for all the samples which is smoothly affected by the magnetic field. On the other hand the kS(T,B) results to T > Tc could not be associated to the pseudogap phenomenon. The Ca doping affects more effectively the kS(T,B) behaviour then Sr doping. A possible explanation to this feature could be associated to the fact that the hole doping promoted by Ca doping depress more considerably the superconducting state and enhances the granular character of the YBa2Cu3O7-? superconductor than the chemical pressure effect promoted by Sr doping.

  14. Comprehensive chemical kinetic modeling of the oxidation of C8 and larger n-alkanes and 2-methylalkanes

    SciTech Connect

    Sarathy, S M; Westbrook, C K; Pitz, W J; Mehl, M; Togbe, C; Dagaut, P; Wang, H; Oehlschlaeger, M; NIemann, U; Seshadri, K; Veloo, P S; Ji, C; Egolfopoulos, F; Lu, T

    2011-03-16

    Conventional petroleum jet and diesel fuels, as well as alternative Fischer-Tropsch (FT) fuels and hydrotreated renewable jet (HRJ) fuels, contain high molecular weight lightly branched alkanes (i.e., methylalkanes) and straight chain alkanes (n-alkanes). Improving the combustion of these fuels in practical applications requires a fundamental understanding of large hydrocarbon combustion chemistry. This research project presents a detailed and reduced chemical kinetic mechanism for singly methylated iso-alkanes (i.e., 2-methylalkanes) ranging from C{sub 8} to C{sub 20}. The mechanism also includes an updated version of our previously published C{sub 8} to C{sub 16} n-alkanes model. The complete detailed mechanism contains approximately 7,200 species 31,400 reactions. The proposed model is validated against new experimental data from a variety of fundamental combustion devices including premixed and nonpremixed flames, perfectly stirred reactors and shock tubes. This new model is used to show how the presence of a methyl branch affects important combustion properties such as laminar flame propagation, ignition, and species formation.

  15. Analytical chemical kinetic investigation of the effects of oxygen, hydrogen, and hydroxyl radicals on hydrogen-air combustion

    NASA Technical Reports Server (NTRS)

    Carson, G. T., Jr.

    1974-01-01

    Quantitative values were computed which show the effects of the presence of small amounts of oxygen, hydrogen, and hydroxyl radicals on the finite-rate chemical kinetics of premixed hydrogen-air mixtures undergoing isobaric autoignition and combustion. The free radicals were considered to be initially present in hydrogen-air mixtures at equivalence ratios of 0.2, 0.6, 1.0, and 1.2. Initial mixture temperatures were 1100 K, 1200 K, and 1500 K, and pressures were 0.5, 1.0, 2.0, and 4.0 atm. Of the radicals investigated, atomic oxygen was found to be the most effective for reducing induction time, defined as the time to 5 percent of the total combustion temperature rise. The reaction time, the time between 5 percent and 95 percent of the temperature rise, is not decreased by the presence of free radicals in the initial hydrogen-air mixture. Fuel additives which yield free radicals might be used to effect a compact supersonic combustor design for efficient operation in an otherwise reaction-limited combustion regime.

  16. Si nanowires by a single-step metal-assisted chemical etching process on lithographically defined areas: formation kinetics

    PubMed Central

    2011-01-01

    In this paper, we investigate the formation kinetics of Si nanowires [SiNWs] on lithographically defined areas using a single-step metal-assisted chemical etching process in an aqueous HF/AgNO3 solution. We show that the etch rate of Si, and consequently, the SiNW length, is much higher on the lithographically defined areas compared with that on the non-patterned areas. A comparative study of the etch rate in the two cases under the same experimental conditions showed that this effect is much more pronounced at the beginning of the etching process. Moreover, it was found that in both cases, the nanowire formation rate is linear with temperature in the range from 20°C to 50°C, with almost the same activation energy, as obtained from an Arrhenius plot (0.37 eV in the case of non-patterned areas, while 0.38 eV in the case of lithographically patterned areas). The higher etch rate on lithographically defined areas is mainly attributed to Si surface modification during the photolithographic process. PACS: 68; 68.65-k. PMID:22087735

  17. Enhancing adsorption capacity of toxic malachite green dye through chemically modified breadnut peel: equilibrium, thermodynamics, kinetics and regeneration studies.

    PubMed

    Chieng, Hei Ing; Lim, Linda B L; Priyantha, Namal

    2015-01-01

    Breadnut skin, in both its unmodified (KS) and base-modified (BM-KS) forms, was investigated for its potential use as a low-cost adsorbent for the removal of toxic dye, malachite green (MG). Characterization of the adsorbents was carried out using scanning electron microscope, X-ray fluorescence and Fourier transform infra-red spectroscopy. Batch adsorption experiments, carried out under optimized conditions, for the adsorption of MG were fitted using five isotherm models (Langmuir, Freundlich, Dubinin-Radushkevich, Temkin and Sips) and six error functions to determine the best-fit model. The adsorption capacity was greatly enhanced when breadnut skin was chemically modified with NaOH, leading to an adsorption capacity of 353.0 mg g(-1), that was far superior to most reported adsorbents for the removal of MG. Thermodynamics studies indicated that the adsorption of MG was spontaneous on KS and BM-KS, and the reactions were endothermic and exothermic, respectively. Kinetics studies showed that both followed the pseudo-second order. Regeneration experiments on BM-KS indicated that its adsorption capacity was still maintained at>90% even after five cycles. It can be concluded that NaOH-modified breadfruit skin has great potential to be utilized in real-life application as a low-cost adsorbent for the removal of MG in wastewater treatment. PMID:25409587

  18. Modelling cycle to cycle variations in an SI engine with detailed chemical kinetics

    SciTech Connect

    Etheridge, Jonathan; Mosbach, Sebastian; Kraft, Markus [Department of Chemical Engineering and Biotechnology, University of Cambridge (United Kingdom); Wu, Hao; Collings, Nick [Department of Engineering, University of Cambridge (United Kingdom)

    2011-01-15

    This paper presents experimental results and a new computational model that investigate cycle to cycle variations (CCV) in a spark ignition (SI) engine. An established stochastic reactor model (SRM) previously used to examine homogeneous charge compression ignition (HCCI) combustion has been extended by spark initiation, flame propagation and flame termination sub-models in order to simulate combustion in SI engines. The model contains a detailed chemical mechanism but relatively short computation times are achieved. The flame front is assumed to be spherical and centred at the spark location, and a pent roof and piston bowl geometry are accounted for. The model is validated by simulating the pressure profile and emissions from an iso-octane fuelled single cylinder research engine that showed low CCV. The effects of key parameters are investigated. Experimental results that show cycle to cycle fluctuations in a four-cylinder naturally aspirated gasoline fuelled SI engine are presented. The model is then coupled with GT-Power, a one-dimensional engine simulation tool, which is used to simulate the breathing events during a multi-cycle simulation. This allows an investigation of the cyclic fluctuations in peak pressure. The source and magnitude of nitric oxide (NO) emissions produced by different cycles are then investigated. It was found that faster burning cycles result in increased NO emissions compared with cycles that have a slower rate of combustion and that more is produced in the early stages of combustion compared with later in the cycle. The majority of NO was produced via the thermal mechanism just after combustion begins. (author)

  19. Molecular simulations of Hugoniots of detonation product mixtures at chemical equilibrium: microscopic calculation of the Chapman-Jouguet state.

    PubMed

    Bourasseau, Emeric; Dubois, Vincent; Desbiens, Nicolas; Maillet, Jean-Bernard

    2007-08-28

    In this work, we used simultaneously the reaction ensemble Monte Carlo (ReMC) method and the adaptive Erpenbeck equation of state (AE-EOS) method to directly calculate the thermodynamic and chemical equilibria of mixtures of detonation products on the Hugoniot curve. The ReMC method [W. R. Smith and B. Triska, J. Chem. Phys. 100, 3019 (1994)] allows us to reach the chemical equilibrium of a reacting mixture, and the AE-EOS method [J. J. Erpenbeck, Phys. Rev. A 46, 6406 (1992)] constrains the system to satisfy the Hugoniot relation. Once the Hugoniot curve of the detonation product mixture is established, the Chapman-Jouguet (CJ) state of the explosive can be determined. A NPT simulation at P(CJ) and T(CJ) is then performed in order to calculate direct thermodynamic properties and the following derivative properties of the system using a fluctuation method: calorific capacities, sound velocity, and Gruneisen coefficient. As the chemical composition fluctuates, and the number of particles is not necessarily constant in this ensemble, a fluctuation formula has been developed to take into account the fluctuations of mole number and composition. This type of calculation has been applied to several usual energetic materials: nitromethane, tetranitromethane, hexanitroethane, PETN, and RDX. PMID:17764275

  20. Investigating chemical changes during shelf-life of thermal and high-pressure high-temperature sterilised carrot purees: A 'fingerprinting kinetics' approach.

    PubMed

    Kebede, Biniam T; Grauwet, Tara; Palmers, Stijn; Michiels, Chris; Hendrickx, Marc; Van Loey, Ann

    2015-10-15

    This work investigates chemical changes during shelf-life of thermally and high pressure high temperature (HPHT) sterilised carrot purees using a 'fingerprinting kinetics' approach. Fingerprinting enabled selection of Strecker aldehydes, terpenes, phenylpropanoids, fatty acid derivatives and carotenoid degradation products as volatiles clearly changing during shelf-life. Next, kinetic modelling of these volatiles was performed to compare their reaction kinetics during storage in differently sterilised samples. Immediately after processing, the Strecker aldehydes were detected at higher levels in thermally sterilised samples. During storage, the compounds increased at a comparable rate in thermally and HPHT processed samples. In contrast, immediately after processing, most of the naturally occurring terpenes and phenylpropanoids were better preserved in HPHT treated samples. Nevertheless, by the end of storage, the concentration of these compounds decreased to almost the same level in both thermal and HPHT samples (with a higher degradation rate in HPHT samples). PMID:25952849

  1. Step-Scan FTIR spectroscopy and quantum chemical calculations of xanthone in the triplet state

    NASA Astrophysics Data System (ADS)

    Buschhaus, L.; Kleinermanns, K.

    2014-10-01

    Step-Scan-FTIR spectroscopy has been used to measure the infrared spectrum of xanthone in the triplet state using chloroform as solvent. Xanthone is an important triplet sensitizer and therefore suitable as model system. Xanthone was excited at 266 nm and its IR triplet spectrum measured in the range 1000-1750 cm-1. The spectrum was analyzed by comparison with DFT/B3LYP/TZVP/COSMO calculations. Further on the results were compared to gas phase IR measurements of triplet xanthone and calculations of isolated xanthone. Mainly based on the calculations we tried to identify the geometry changes from the electronic ground state to the first triplet state.

  2. Transport calculations of chemically sputtered carbon near a plasma divertor surface

    SciTech Connect

    Brooks, J.N.

    1992-01-01

    The transport of chemically sputtered carbon near a tokamak divertor surface has been analyzed with the Monte Carlo code WBC. The code follows the motion of sputtered methane atoms and the resulting carbon and hydrocarbon derivatives. Ion transport due to the magnetic field, sheath electric field, and collisions with the plasma is computed. Redeposition fractions, impinging species type, charge state, and velocity have been analyzed. For plasma temperatures {ge} 10 eV, and for typical divertor plasma densities, local redeposition of chemically sputtered carbon approaches 100%. Redeposition fractions are lower ({approximately}80%) for lower temperatures and/or lower density. Physical sputtering of carbon due to redeposition of chemically sputtered material is low but a hydrocarbon reflection cascade due to redeposition may be high.

  3. Kinetics of distribution and adipose tissue storage as a function of lipophilicity and chemical structure. II. Benzodiazepines.

    PubMed

    Xie, X; Steiner, S H; Bickel, M H

    1991-01-01

    Distribution kinetics of flurazepam, medazepam, prazepam, and clobazam were determined in rats. Concentration-time curves of unchanged drugs and non-polar metabolites in plasma, adipose tissue, liver, brain, and muscle after a single iv administration were obtained using GLC/electron capture detector analysis. Pharmacokinetic parameters were calculated for plasma and tissues. Adipose tissue storage was quantified with the adipose storage index (ASI). Including data of benzodiazepines from the literature, a correlation between ASI and log P (over a range 1.6-3.8) was nonexistent and the influence of individual functional groups was not easily discernible. However, benzodiazepines with a pKa (base) within the range 1.6-6.2 were stored in adipose tissue (ASI greater than 1), whereas those with pKa greater than 7 were not (ASI less than 1). Since many other basic lipophilic drugs with pKa greater than 7 are not stored in adipose tissue, and this is likely due to lysosomal trapping in lean tissues, which requires a pKa value above 7, it is suggested that within the series of benzodiazepines, adipose tissue storage is mainly influenced by the basicity of the drugs. PMID:1673390

  4. Torsional energy levels of CH?OH?/CH?OD?/CD?OD? studied by zero-kinetic energy photoelectron spectroscopy and theoretical calculations.

    PubMed

    Dai, Zuyang; Gao, Shuming; Wang, Jia; Mo, Yuxiang

    2014-10-14

    The torsional energy levels of CH3OH(+), CH3OD(+), and CD3OD(+) have been determined for the first time using one-photon zero kinetic energy photoelectron spectroscopy. The adiabatic ionization energies for CH3OH, CH3OD, and CD3OD are determined as 10.8396, 10.8455, and 10.8732 eV with uncertainties of 0.0005 eV, respectively. Theoretical calculations have also been performed to obtain the torsional energy levels for the three isotopologues using a one-dimensional model with approximate zero-point energy corrections of the torsional potential energy curves. The calculated values are in good agreement with the experimental data. The barrier height of the torsional potential energy without zero-point energy correction was calculated as 157 cm(-1), which is about half of that of the neutral (340 cm(-1)). The calculations showed that the cation has eclipsed conformation at the energy minimum and staggered one at the saddle point, which is the opposite of what is observed in the neutral molecule. The fundamental C-O stretch vibrational energy level for CD3OD(+) has also been determined. The energy levels for the combinational excitation of the torsional vibration and the fundamental C-O stretch vibration indicate a strong torsion-vibration coupling. PMID:25318721

  5. Calculation of diamond chemical vapor deposition region in C–H–O phase diagram

    Microsoft Academic Search

    E. G. Rakov

    1996-01-01

    Thermodynamic calculations of graphite yield at the interaction of gaseous components of the C–H–O system were performed. Their results proved to be in satisfactory agreement with experimental data published on the lower concentration boundary of the diamond deposition region. The calculations indicate an influence of the substrate temperature, total pressure, and concentrations of inert and active additives on this boundary’s

  6. Quantum chemical calculation of the equilibrium structures of small metal atom clusters

    NASA Technical Reports Server (NTRS)

    Kahn, L. R.

    1982-01-01

    Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches. Because these large 'molecular' systems pose special practical computational problems in the application of the quantum mechanical methods, there is a special need to find simplifying techniques that do not compromise the reliability of the calculations. Research is therefore directed towards various aspects of the implementation of the effective core potential technique for the removal of the metal atom core electrons from the calculations.

  7. ChemSage—A computer program for the calculation of complex chemical equilibria

    Microsoft Academic Search

    Gunnar Eriksson; Klaus Hack

    1990-01-01

    An extensive computer program called ChemSage, based upon the SOLGASMIX Gibbs energy minimizer, is presented together with\\u000a several examples which illustrate its use. ChemSage was designed to perform three types of thermochemical calculations in\\u000a complex systems involving phases exhibiting nonideal mixing properties. These are the calculation of thermodynamic functions,\\u000a heterogeneous phase equilibria, and steady-state conditions for the simulation of simple

  8. Calculated simulation of the kinetics of a crack propagation in the bearing sheets of the glued laminated structures

    NASA Astrophysics Data System (ADS)

    Semin, M. I.; Safonov, P. K.

    1994-07-01

    An application of the finite element method to calculation of the adhesive joints of D16AT alloy plates, which are subjected to the effect of shear and bend, is justified on the basis of complex theoretical and experimental analysis. The possibility of extension of the developed models on a linear fracture mechanics field for laminated metal polymer composites is shown and experimentally confirmed. The influence of some mechanical characteristics of the polymeric binder on the fracture nature in the area of through and surface cracks is estimated by calculation for organometallic plastics.

  9. Miniature free-piston homogeneous charge compression ignition engine-compressor concept—Part II: modeling HCCI combustion in small scales with detailed homogeneous gas phase chemical kinetics

    Microsoft Academic Search

    H. T. Aichlmayr; D. B. Kittelson; M. R. Zachariah

    2002-01-01

    Operational maps for crankshaft-equipped miniature homogeneous charge compression ignition engines are established using performance estimation, detailed chemical kinetics, and diffusion models for heat transfer and radical loss. In this study, radical loss was found to be insignificant. In contrast, heat transfer was found to be increasingly significant for 10, 1, and 0.1W engines, respectively. Also, temperature–pressure trajectories and ignition delay

  10. An Integrated Path Integral and Free-Energy Perturbation?Umbrella Sampling Method for Computing Kinetic Isotope Effects of Chemical Reactions in Solution and in Enzymes

    Microsoft Academic Search

    Dan Thomas Major; Jiali Gao

    2007-01-01

    An integrated centroid path integral and free-energy perturbation-umbrella sampling (PI-FEP\\/UM) method for computing kinetic isotope effects (KIEs) for chemical reactions in solution and in enzymes is presented. The method is based on the bisection quantized classical path sampling in centroid path integral simulations to include nuclear quantum corrections in the classical potential of mean force. The required accuracy for computing

  11. Ab-initio calculation of magnetic susceptibility and NMR chemical shifts in solids and liquids

    Microsoft Academic Search

    Francesco Mauri

    1997-01-01

    I will present a novel theory for the ab-initio computation of the magnetic susceptibility (F. Mauri and S.G. Louie, Phys. Rev. Lett. 76, 4246 (1996).) and of the NMR chemical shifts (F. Mauri, B. Pfrommer, and S. G. Louie, Phys. Rev. Lett., in press.) in condensed matter systems. The new formalism overcomes the limitations of previous approaches, which could handle

  12. Chemical Kinetic Influences of Alkyl Chain Structure on the High Pressure and Temperature Oxidation of a Representative Unsaturated Biodiesel: Methyl Nonenoate.

    PubMed

    Fridlyand, Aleksandr; Goldsborough, S Scott; Brezinsky, Kenneth

    2015-07-16

    The high pressure and temperature oxidation of methyl trans-2-nonenoate, methyl trans-3-nonenoate, 1-octene, and trans-2-octene are investigated experimentally to probe the influence of the double bond position on the chemical kinetics of long esters and alkenes. Single pulse shock tube experiments are performed in the ranges p = 3.8-6.2 MPa and T = 850-1500 K, with an average reaction time of 2 ms. Gas chromatographic measurements indicate increased reactivity for trans-2-octene compared to 1-octene, whereas both methyl nonenoate isomers have reactivities similar to that of 1-octene. A difference in the yield of stable intermediates is observed for the octenes when compared to the methyl nonenoates. Chemical kinetic models are developed with the aid of the Reaction Mechanism Generator to interpret the experimental results. The models are created using two different base chemistry submodels to investigate the influence of the foundational chemistry (i.e., C0-C4), whereas Monte Carlo simulations are performed to examine the quality of agreement with the experimental results. Significant uncertainties are found in the chemistry of unsaturated esters with the double bonds located close to the ester groups. This work highlights the importance of the foundational chemistry in predictive chemical kinetics of biodiesel combustion at engine relevant conditions. PMID:25710595

  13. Establishment of a finite element model for extracting chemical reaction kinetics in a micro-flow injection system with high throughput sampling.

    PubMed

    Wu, Zeng-Qiang; Du, Wen-Bin; Li, Jin-Yi; Xia, Xing-Hua; Fang, Qun

    2015-08-01

    Numerical simulation can provide valuable insights for complex microfluidic phenomena coupling mixing and diffusion processes. Herein, a novel finite element model (FEM) has been established to extract chemical reaction kinetics in a microfluidic flow injection analysis (micro-FIA) system using high throughput sample introduction. To reduce the computation burden, the finite element mesh generation is performed with different scales based on the different geometric sizes of micro-FIA. In order to study the contribution of chemical reaction kinetics under non-equilibrium condition, a pseudo-first-order chemical kinetics equation is adopted in the numerical simulations. The effect of reactants diffusion on reaction products is evaluated, and the results demonstrate that the Taylor dispersion plays a determining role in the micro-FIA system. In addition, the effects of flow velocity and injection volume on the reaction product are also simulated. The simulated results agree well with the ones from experiments. Although gravity driven flow is used to the numerical model in the present study, the FEM model also can be applied into the systems with other driving forces such as pressure. Therefore, the established FEM model will facilitate the understanding of reaction mechanism in micro-FIA systems and help us to optimize the manifold of micro-FIA systems. PMID:26048839

  14. Quantum chemical calculation of the equilibrium structures of small metal atom clusters

    NASA Technical Reports Server (NTRS)

    Kahn, L. R.

    1981-01-01

    The application of ab initio quantum mechanical approaches in the study of metal atom clusters requires simplifying techniques that do not compromise the reliability of the calculations. Various aspects of the implementation of the effective core potential (ECP) technique for the removal of the metal atom core electrons from the calculation were examined. The ECP molecular integral formulae were modified to bring out the shell characteristics as a first step towards fulfilling the increasing need to speed up the computation of the ECP integrals. Work on the relationships among the derivatives of the molecular integrals that extends some of the techniques pioneered by Komornicki for the calculation of the gradients of the electronic energy was completed and a formulation of the ECP approach that quite naturally unifies the various state-of-the-art "shape- and Hamiltonian-consistent" techniques was discovered.

  15. Modelling the Distributions of Dissolved Zn and Ni in the Tamar Estuary Using Hydrodynamics Coupled with Chemical Kinetics

    NASA Astrophysics Data System (ADS)

    Liu, Y. P.; Millward, G. E.; Harris, J. R. W.

    1998-11-01

    Suspended particulate matter (SPM) from the Tamar Estuary was separated into permanent SPM (PSPM) and temporary SPM (TSPM) by settling experiments. Both particulate fractions were chemically characterized and used to study the kinetics of adsorption and desorption of Zn and Ni. The results showed that the adsorption of Zn and Ni at salinity=0 was biphasic, with an initial rapid step, completed in <5 min, followed by a slower progression to equilibrium. The PSPM adsorbed relatively more Zn and Ni than the TSPM, which had a smaller specific surface area and lower acetic acid-leachable Fe and Mn content. Labile Zn and Ni desorbed biphasically, when the metal-laden particles were suspended in seawater (salinity=30) and a greater amount of metal was desorbed from TSPM than PSPM. The sorption mechanisms were described by reversible, first order reactions, from which reaction constants were estimated for the slow step. The response time for the adsorption of dissolved Zn during the slow step (i.e. time to achieve 63% of the new equilibrium) was 3-5 h, whereas during desorption of Zn it was approximately 25 h. For dissolved Ni, the response time for the slow step was about 13 h and in the range 33-50 h for the desorption reaction. Sorption reaction constants for Zn and Ni were incorporated into the estuarine contaminant simulator (ECoS) and used to predict dissolved Zn and Ni distributions in the Tamar Estuary. The predicted trends in dissolved metal concentrations were in general agreement with published field observations.

  16. Corrigendum to "Si 2p and O 1s photoemission from oxidized Si(0 0 1) surfaces depending on translational kinetic energy of incident O2 molecules" [Appl. Surf. Sci. 190 (2002) 75-79

    NASA Astrophysics Data System (ADS)

    Teraoka, Yuden; Yoshigoe, Akitaka

    2015-07-01

    We have performed experiments on surface chemical reactions using a supersonic O2 molecular beam and O2 gas. Translational kinetic energy values of the O2 molecules have been estimated by calculations. We had made a mistake in the calculations. In this article, the translational kinetic energy of the O2 molecules had been calculated by the following equation,

  17. ONIOM as an efficient tool for calculating NMR chemical shielding constants in large molecules

    Microsoft Academic Search

    Peter B. Karadakov; Keiji Morokuma

    2000-01-01

    The ONIOM approach is used to derive an expression for the NMR chemical shielding tensor in a molecule subdivided into n-layers, each of which can be described at a different level of theory. The two-layer ONIOM2(MP2-GIAO:HF-GIAO) variant, in which a small part of the molecule containing the nuclei of interest is described at the MP2-GIAO level of theory, and the

  18. Determination of the absolute configurations using electronic and vibrational circular dichroism measurements and quantum chemical calculations

    Microsoft Academic Search

    Prasad L. Polavarapu; Jadwiga Frelek; Magdalena Wo?nica

    The stereochemistry of products obtained via a chemical reaction may not always be obvious from the reaction scheme utilized. The identification of convenient methods to determine the stereochemistry in such cases is highly desirable. To identify these methods, we considered a substituted 4-vinyl-1-azabicyclo[3.2.0]hept-3-en-7-one that undergoes spontaneous oxidation in the atmosphere at room temperature, yielding an epoxide with unknown absolute configuration.

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  20. Quantum chemical investigation on the mechanism and kinetics of OH radical-initiated atmospheric oxidation of PCB-47.

    PubMed

    Sun, Yanhui; Zhang, Qingzhu; Wang, Hui; Wang, Wenxing

    2015-08-01

    The OH radical-initiated atmospheric oxidation degradation of 2,2',4,4'-tetrachlorobiphenyl (PCB-47) was investigated by using quantum chemical calculations. All possible pathways involved in the oxidation process were discussed. Potential barriers and reaction heats have been obtained to assess the energetically favorable reaction pathways and the relatively stable products. The study shows that the OH radicals are more likely to attack the C3 and C5 atom of the aromatic ring in the PCB-47 molecule to form PCB-OH adducts. Subsequent reactions are the addition of O2 or NO2 molecule to the PCB-OH adducts at the ortho position of the OH group. Water molecule plays an important role during the whole degradation process. The individual and overall rate constants were calculated by using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory over the temperature range of 180-370K. At 298K, the atmospheric lifetime of PCB-47 determined by OH radicals is about 9.1d. The computational results are crucial to risk assessment and pollution prevention of PCBs. PMID:25898309

  1. Studies on vibrational, NMR spectra and quantum chemical calculations of N-Succinopyridine: An organic nonlinear optical material

    NASA Astrophysics Data System (ADS)

    Kannan, V.; Thirupugalmani, K.; Brahadeeswaran, S.

    2013-10-01

    Single crystals of N-Succinopyridine (NSP) have been grown from water using solution growth method by isothermal solvent evaporation technique. The solid state Fourier Transform Infrared (FTIR) spectrum of the grown crystal shows a broad absorption extending from 3450 down to 400 cm-1, due to H-bond vibrations and other characteristic vibrations. Fourier Transform Raman (FT-Raman) spectrum of NSP single crystal shows Raman intensities ranging from 3100 to 100 cm-1 due the characteristics vibrations of functional groups present in NSP. The proton and carbon positions of NSP have been described by 1H and 13C NMR spectrum respectively. Ab initio quantum chemical calculations on NSP have been performed by density functional theory (DFT) calculations using B3LYP method with 6-311++G(d,p) basis set. The predicted first hyperpolarizability is found to be 1.29 times greater than that of urea and suggests that the title compound could be an attractive material for nonlinear optical applications. The calculated HOMO-LUMO energies show that charge transfers occur within the molecule and other related molecular properties. Molecular properties such as Mulliken population analysis, thermodynamic functions and perturbation theory energy analysis have also been reported. Electrostatic potential map (ESP) of NSP obtained by electron density isosurface provided the information about the size, shape, charge density distribution and site of chemical reactivity of the title molecule. The molecular stability and bond strength have been investigated through the Natural Bond Orbital (NBO) analysis.

  2. Tungsten-dependent formaldehyde ferredoxin oxidoreductase: Reaction mechanism from quantum chemical calculations

    E-print Network

    Liao, Rongzhen

    theory Enzyme catalysis Formaldehyde ferredoxin oxidoreductase from Pyrococcus furiosus is a tungsten-ray crystal structure of the native enzyme. Based on the calculations, we propose a new mechanism in which, and the nature of the axial ligands, tungsten enzymes have been divided into three different families: aldehyde

  3. Spectroscopic analysis of 3-Bromodiphenylamine with experimental techniques and quantum chemical calculations.

    PubMed

    Sudharsan, A; Seshadri, S; Gnanasambandan, T; Saravanan, R R

    2014-10-15

    In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 3500-100cm(-1) and 4000-400cm(-1), respectively, for 3-Bromodiphenylamine (3BDPA). Theoretical calculations were performed by using Density Functional Theory (DFT) method with 6-31G(d,p) and 6-311++G(d,p) basis sets. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The calculated wavenumbers were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. The frontier orbital energy gap and dipole moment illustrates the high reactivity of the title molecule. The first order hyperpolarizability (?0) and related properties (?, ? and ??) of the molecule were also calculated. Stability of the molecule arising from hyperconjugative interactions and charge delocalization were analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the ?(*) and ?(*) anti-bonding orbitals and second order delocalization energies (E2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. Molecular electrostatic potential (MEP) and HOMO-LUMO energy levels are also constructed. The thermodynamic properties of the title compound were calculated at different temperatures and the results reveals the heat capacity (C), and entropy (S) increases with rise in temperature. PMID:24835947

  4. Quantum chemical calculations predict biological function: The case of T cell receptor interaction with a peptide/MHC class I

    NASA Astrophysics Data System (ADS)

    Antipas, Georgios S. E.; Germenis, Anastasios

    2015-02-01

    A combination of atomic correlation statistics and quantum chemical calculations are shown to predict biological function. In the present study, various antigenic peptide-Major Histocompatibility Complex (pMHC) ligands with near-identical stereochemistries, in complexation with the same T cell receptor (TCR), were found to consistently induce distinctly different quantum chemical behavior, directly dependent on the peptide’s electron spin density and intrinsically expressed by the protonation state of the peptide’s N-terminus. Furthermore, the cumulative coordination difference of any variant in respect to the native peptide was found to accurately reflect peptide biological function and immerges as the physical observable which is directly related to the immunological end-effect of pMHC-TCR interaction.

  5. Quantum chemical calculations predict biological function: the case of T cell receptor interaction with a peptide/MHC class I

    PubMed Central

    Antipas, Georgios S. E.; Germenis, Anastasios E.

    2015-01-01

    A combination of atomic correlation statistics and quantum chemical calculations are shown to predict biological function. In the present study, various antigenic peptide-Major Histocompatibility Complex (pMHC) ligands with near-identical stereochemistries, in complexation with the same T cell receptor (TCR), were found to consistently induce distinctly different quantum chemical behavior, directly dependent on the peptide's electron spin density and intrinsically expressed by the protonation state of the peptide's N-terminus. Furthermore, the cumulative coordination difference of any variant in respect to the native peptide was found to accurately reflect peptide biological function and immerges as the physical observable which is directly related to the immunological end-effect of pMHC-TCR interaction. PMID:25713797

  6. Quantum instanton calculation of rate constant for CH4 + OH ? CH3 + H2O reaction: Torsional anharmonicity and kinetic isotope effect

    NASA Astrophysics Data System (ADS)

    Wang, Wenji; Zhao, Yi

    2012-12-01

    Thermal rate constants for the title reaction are calculated by using the quantum instanton approximation within the full dimensional Cartesian coordinates. The results reveal that the quantum effect is remarkable for the reaction at both low and high temperatures, and the obtained rates are in good agreement with experimental measurements at high temperatures. Compared to the harmonic approximation, the torsional anharmonic effect of the internal rotation has a little influence on the rates at low temperatures, however, it enhances the rate by about 20% at 1000 K. In addition, the free energy barriers for the isotopic reactions and the temperature dependence of kinetic isotope effects are also investigated. Generally speaking, for the title reaction, the replacement of OH with OD will reduce the free energy barrier, while substituting D for H (connected to C) will increase the free energy barrier.

  7. Research in chemical kinetics

    SciTech Connect

    Rowland, F.S.

    1991-01-01

    This report contains sections on the reaction of chlorine atoms with 1,1,1,2-terafluoroethane, abstraction reactions by thermal chlorine atoms with hfc-134a, and chlorine atom reactions with vinyl bromide.

  8. Phenylazoindole dyes - Part I: The syntheses, characterizations, crystal structures, quantum chemical calculations and antimicrobial properties

    NASA Astrophysics Data System (ADS)

    Sefero?lu, Zeynel; Yalç?n, Ergin; Babür, Banu; Sefero?lu, Nurgül; Hökelek, Tuncer; Y?lmaz, Ebru; ?ahin, Ertan

    2013-09-01

    In this study, the synthesis of four new phenylazo indole dyes (dye 1-4) were carried out by diazotization of 4-aminoacetophenone and coupling with various 2- and 1,2-disubstituted indole derivatives. The dyes were characterized by UV-vis, FT-IR, 1H NMR, HRMS and X-ray single crystal diffraction methods. Azo-hydrazone tautomeric bahavior of the dyes in different solvents (DMSO, methanol, acetic acid and chloroform) was investigated by using 1H NMR and UV-vis results. The experimental results were compared with the corresponding calculated values. The results of experimental data and theoretical calculations showed that the azo tautomer is more stable than hydrazone tautomer. In addition to this, the antimicrobial activity of the dyes was also evaluated.

  9. ELECTRONIC STRUCTURE AND CHEMICAL BONDING IN ALKALINE EARTH METAL SUBNITRIDES: PHOTOEMISSION STUDIES AND BAND STRUCTURE CALCULATIONS

    Microsoft Academic Search

    U. Steinbrenner; P. Adler; W. Hölle; A. Simon

    1998-01-01

    The electronic structure of various alkaline earth metal subnitrides has been studied by X-ray and ultraviolet photoelectron spectroscopy and by LMTO band structure calculations. Improved methods for the synthesis of several of the materials are described. The electronic structure of compounds with discrete clusters (Na22Ba14SrN6) or Ba3N chains (Ba3N, NaBa3N, Na5Ba3N) in the crystal structure is characterized by a narrow

  10. Quantum-chemical calculations of the structure and vibration spectrum of methyl nitrate

    NASA Astrophysics Data System (ADS)

    Shaikhullina, R. M.; Khrapkovskii, G. M.; Sarvarov, F. S.

    2014-12-01

    Methyl nitrate vibration spectra theoretical analysis data within the B3LYP density functional theory method in the 6 -31G (d) basis are represented. When optimizing the geometry of the molecule it was found out that methyl nitrate is characterized by one stable conformation: trans – form. Frequency, intensity and forms of normal vibrations are calculated, their comparative analysis with well-known from the literature experimental data is given.

  11. Valence XPS, IR, and C13 NMR spectral analysis of 6 polymers by quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Endo, Kazunaka; Ida, Tomonori; Shimada, Shingo; Ortiz, Joseph Vincent; Deguchi, Kenzo; Shimizu, Tadashi; Yamada, Kazuhiko

    2012-11-01

    Valence XPS (VXPS), IR, and C13 NMR spectra of 6 polymers (PE, PS, PMMA, PET, Nylon6, PVC) have been analyzed using the model oligomers from B3LYP/6-31+G(d,p) basis calculations in GAUSSIAN 09. We simulated VXPS of the polymers by the negative of the orbital energies of the ground electronic state at the geometry-optimization of the model oligomers. The simulated VXPS spectra by B3LYP/6-31+G(d,p) basis level were compared with simulated spectra by calculations of SAOP method of ADF program. Simulated IR, and C13 NMR spectra of polymers were obtained from the other SCF calculations of B3LYP/6-31+G(d,p) basis using atomic coordinates of the model molecules at the geometry optimization, in order to gain the vibrational frequencies and nuclear magnetic shielding tensors, respectively. We have clarified the electronic states of the polymers from the good accordance of simulated VXPS, IR, and C13 NMR spectra of polymer models molecules with the experimental ones of the polymers.

  12. Development of Multiscale Simulator for Dye-Sensitized TiO2 Nanoporous Electrode Based on Quantum Chemical Calculation

    NASA Astrophysics Data System (ADS)

    Ogiya, Kei; Lv, Chen; Suzuki, Ai; Sahnoun, Riadh; Koyama, Michihisa; Tsuboi, Hideyuki; Hatakeyama, Nozomu; Endou, Akira; Takaba, Hiromitsu; Kubo, Momoji; Del Carpio, Carlos A.; Miyamoto, Akira

    2008-04-01

    In this study, we have developed a novel multiscale simulator for a dye-sensitized TiO2 porous electrode. In the simulator, we can estimate the properties of the dye-sensitized TiO2 porous electrode using the three-dimensional mesoscopic structure model constructed on the basis of our original porous structure simulator. The microscopic physical properties of the materials were estimated by quantum chemistry calculation using a tight-binding quantum chemical molecular dynamics program. From the calculation results, we determined the absorption coefficient and the diffusion coefficient of excited carriers used in the macroscopic simulation for photoelectrode characteristics. By using this multiscale simulator, we will be able to determine the best electrode system efficiently.

  13. Fractal-like kinetics of intracellular enzymatic reactions: a chemical framework of endotoxin tolerance and a possible non-specific contribution of macromolecular crowding to cross-tolerance

    PubMed Central

    2013-01-01

    Background The response to endotoxin (LPS), and subsequent signal transduction lead to the production of cytokines such as tumor necrosis factor-? (TNF-?) by innate immune cells. Cells or organisms pretreated with endotoxin enter into a transient state of hyporesponsiveness, referred to as endotoxin tolerance (ET) which represents a particular case of negative preconditioning. Despite recent progress in understanding the molecular basis of ET, there is no consensus yet on the primary mechanism responsible for ET and for the more complex cases of cross tolerance. In this study, we examined the consequences of the macromolecular crowding (MMC) and of fractal-like kinetics (FLK) of intracellular enzymatic reactions on the LPS signaling machinery. We hypothesized that this particular type of enzyme kinetics may explain the development of ET phenomenon. Method Our aim in the present study was to characterize the chemical kinetics framework in ET and determine whether fractal-like kinetics explains, at least in part, ET. We developed an ordinary differential equations (ODE) mathematical model that took into account the links between the MMC and the LPS signaling machinery leading to ET. We proposed that the intracellular fractal environment (MMC) contributes to ET and developed two mathematical models of enzyme kinetics: one based on Kopelman’s fractal-like kinetics framework and the other based on Savageau’s power law model. Results Kopelman’s model provides a good image of the potential influence of a fractal intracellular environment (MMC) on ET. The Savageau power law model also partially explains ET. The computer simulations supported the hypothesis that MMC and FLK may play a role in ET. Conclusion The model highlights the links between the organization of the intracellular environment, MMC and the LPS signaling machinery leading to ET. Our FLK-based model does not minimize the role of the numerous negative regulatory factors. It simply draws attention to the fact that macromolecular crowding can contribute significantly to the induction of ET by imposing geometric constrains and a particular chemical kinetic for the intracellular reactions. PMID:24034421

  14. Development of a Multi-Scale Electromigration Simulator Based on a Combination of Ultra Accelerated Quantum Chemical Molecular Dynamics and Kinetic Monte Carlo Methods Application to Cu Interconnects Lifetime Simulation

    NASA Astrophysics Data System (ADS)

    Tsuboi, Hideyuki; Kato, Asami; Sato, Hiromi; Hasekura, Fumie; Oda, Saori; Setogawa, Hiroshi; Abe, Chie; Chutia, Arnubhiram; Lv, Chen; Zhu, Zigang; Miura, Ryuji; Suzuki, Ai; Sahnoun, Riadh; Koyama, Michihisa; Hatakeyama, Nozomu; Endou, Akira; Takaba, Hiromitsu; Del Carpio, Carlos A.; Deka, Ramesh C.; Kubo, Momoji; Miyamoto, Akira

    2009-04-01

    We present a novel study on electromigration (EM) phenomena in Cu interconnects using a newly developed multi-scale simulator that consists on a combination of a device scale simulator based on a kinetic Monte Carlo (KMC) method and an atomic scale simulator based on ultra accelerated quantum chemical molecular dynamics (UA-QCMD). We have firstly demonstrated the simulation of the lifetime of Cu interconnects using the newly developed device scale simulator setting some suitable KMC probabilities for the void movement according to the regions in which it can be divided, i.e., the crystal grain and the grain boundary. The simulated values are shown to be in good agreement with experimental values. In an attempt to connect the device scale studies to quantum chemical instances of the system - since the correlation of probability of the void movement with, for example, activation energies or diffusion coefficients is important - we have developed an atomic scale simulator based on our original UA-QCMD method. In this atomic scale simulation, the electron wind force was evaluated using our original electrical conductivity prediction simulator based on KMC method which uses the electronic states from tight-binding quantum chemical (TBQC) calculation. Using this atomic scale simulator under the conditions of 475 K of temperature and 2.5 ×1010 A/m2 of current density, we were able to successfully simulate the migration of a Cu atom from a lattice site to a vacant site by evaluating the electron wind force.

  15. An interactive computer code for calculation of gas-phase chemical equilibrium (EQLBRM)

    NASA Technical Reports Server (NTRS)

    Pratt, B. S.; Pratt, D. T.

    1984-01-01

    A user friendly, menu driven, interactive computer program known as EQLBRM which calculates the adiabatic equilibrium temperature and product composition resulting from the combustion of hydrocarbon fuels with air, at specified constant pressure and enthalpy is discussed. The program is developed primarily as an instructional tool to be run on small computers to allow the user to economically and efficiency explore the effects of varying fuel type, air/fuel ratio, inlet air and/or fuel temperature, and operating pressure on the performance of continuous combustion devices such as gas turbine combustors, Stirling engine burners, and power generation furnaces.

  16. Lattice dynamics and chemical bonding in Sb2Te3 from first-principles calculations.

    PubMed

    Wang, Bao-Tian; Souvatzis, Petros; Eriksson, Olle; Zhang, Ping

    2015-05-01

    Pressure effects on the lattice dynamics and the chemical bonding of the three-dimensional topological insulator, Sb2Te3, have been studied from a first-principles perspective in its rhombohedral phase. Where it is possible to compare, theory agrees with most of the measured phonon dispersions. We find that the inclusion of relativistic effects, in terms of the spin-orbit interaction, affects the vibrational features to some extend and creates large fluctuations on phonon density of state in high frequency zone. By investigations of structure and electronic structure, we analyze in detail the semiconductor to metal transition at ?2 GPa followed by an electronic topological transition at a pressure of ?4.25 GPa. PMID:25956111

  17. Adsorption of carbon monoxide on ZSM-5 zeolites. Infrared spectroscopic study and quantum-chemical calculations

    SciTech Connect

    Kustov, L.M.; Kazansky, V.B.; Beran, S.; Kubelkova, L.; Jiru, P.

    1987-09-24

    Low temperature adsorption of CO was studied on H-ZSM-5 zeolites modified by dehydroxylation, ionic exchange with Al/sup 3 +/, and impregnation with Al/sub 2/O/sub 3/ and on Na-ZSM-5 and CaH-ZSM-5 zeolites. It was found that interaction of CO with framework OH groups results in the formation of a hydrogen-bonded CO complex whose OH bond frequency is decreased by 310-320 cm/sup -1/ compared with that of free hydroxyls. For the less acidic framework hydroxyls in large cavities of H/sub 70/Na/sub 30/-Y zeolite the observed shift is 275 cm/sup -1/. With ZSM-5 zeolites, at least six types of electron-accepting sites are observed originating from nonframework Al species (band of CO in the interaction complex: 2132, 2222, 2202, 2195, and 2198 cm/sup -1/) and the Al/sub 2/O/sub 3/ microcrystalline phase (CO band at 2153 cm/sup -1/). The CO bond orders calculated by the CNDO/2 method for the CO interaction complexes with models of surface sites increase in the following order: > O-CO < > OH-CO approx. ..-->.. Al-CO approx. = Na-CO < alumina-CO approx. = Ca-CO < ..-->.. Si-CO < Al(cationic)-CO. A correlation between the calculated bond orders of CO and the observed vibrational frequencies of CO-forming interaction complexes is drawn.

  18. Complementing high-throughput X-ray powder diffraction data with quantum-chemical calculations: Application to piroxicam form III.

    PubMed

    Naelapää, Kaisa; van de Streek, Jacco; Rantanen, Jukka; Bond, Andrew D

    2012-11-01

    High-throughput crystallisation and characterisation platforms provide an efficient means to carry out solid-form screening during the pre-formulation phase. To determine the crystal structures of identified new solid phases, however, usually requires independent crystallisation trials to produce single crystals or bulk samples of sufficient quantity to carry out high-quality X-ray diffraction measurements. This process could be made more efficient by a robust procedure for crystal structure determination directly from high-throughput X-ray powder diffraction (XRPD) data. Quantum-chemical calculations based on dispersion-corrected density functional theory (DFT-D) have now become feasible for typical small organic molecules used as active pharmaceutical ingredients. We demonstrate how these calculations can be applied to complement high-throughput XRPD data by determining the crystal structure of piroxicam form III. These combined experimental/quantum-chemical methods can provide access to reliable structural information in the course of an intensive experimentally based solid-form screening activity or in other circumstances wherein single crystals might never be viable, for example, for polymorphs obtained only during high-energy processing such as spray drying or milling. PMID:22886472

  19. A Detailed Chemical Kinetic Reaction Mechanism for n-Alkane Hydrocarbons from n-Octane to n-Hexadecane

    SciTech Connect

    Westbrook, C K; Pitz, W J; Herbinet, O; Silke, E J; Curran, H J

    2007-09-25

    Detailed chemical kinetic reaction mechanisms have been developed to describe the pyrolysis and oxidation of the n-alkanes, including n-octane (n-C{sub 8}H{sub 18}), n-nonane (n-C{sub 9}H{sub 20}), n-decane (n-C{sub 10}H{sub 22}), n-undecane (n-C{sub 11}H{sub 24}), n-dodecane (n-C{sub 12}H{sub 26}), n-tridecane (n-C{sub 13}H{sub 28}), n-tetradecane (n-C{sub 14}H{sub 30}), n-pentadecane (n-C{sub 15}H{sub 32}), and n-hexadecane (n-C{sub 16}H{sub 34}). These mechanisms include both high temperature and low temperature reaction pathways. The mechanisms are based on previous mechanisms for n-heptane, using the same reaction class mechanism construction developed initially for n-heptane. Individual reaction class rules are as simple as possible in order to focus on the parallelism between all of the n-alkane fuels included in the mechanisms, and there is an intent to develop these mechanisms further in the future to incorporate greater levels of accuracy and predictive capability. Several of these areas for improvement are identified and explained in detail. These mechanisms are validated through comparisons between computed and experimental data from as many different sources as possible. In addition, numerical experiments are carried out to examine features of n-alkane combustion in which the detailed mechanisms can be used to compare processes in all of the n-alkane fuels. The mechanisms for all of these n-alkanes are presented as a single detailed mechanism, which can be edited to produce efficient mechanisms for any of the n-alkanes included, and the entire mechanism, with supporting thermochemical and transport data, together with an explanatory glossary explaining notations and structural details, will be available on our web page when the paper is accepted for publication.

  20. A Detailed Chemical Kinetic Reaction Mechanism for n-Alkane Hydrocarbons From n-Octane to n-Hexadecane

    SciTech Connect

    Westbrook, C K; Pitz, W J; Herbinet, O; Curran, H J; Silke, E J

    2008-02-08

    Detailed chemical kinetic reaction mechanisms have been developed to describe the pyrolysis and oxidation of nine n-alkanes larger than n-heptane, including n-octane (n-C{sub 8}H{sub 18}), n-nonane (n-C{sub 9}H{sub 20}), n-decane (n-C{sub 10}H{sub 22}), n-undecane (n-C{sub 11}H{sub 24}), n-dodecane (n-C{sub 12}H{sub 26}), n-tridecane (n-C{sub 13}H{sub 28}), n-tetradecane (n-C{sub 14}H{sub 30}), n-pentadecane (n-C{sub 15}H{sub 32}), and n-hexadecane (n-C{sub 16}H{sub 34}). These mechanisms include both high temperature and low temperature reaction pathways. The mechanisms are based on our previous mechanisms for the primary reference fuels n-heptane and iso-octane, using the reaction class mechanism construction first developed for n-heptane. Individual reaction class rules are as simple as possible in order to focus on the parallelism between all of the n-alkane fuels included in the mechanisms, and these mechanisms will be refined further in the future to incorporate greater levels of accuracy and predictive capability. These mechanisms are validated through extensive comparisons between computed and experimental data from a wide variety of different sources. In addition, numerical experiments are carried out to examine features of n-alkane combustion in which the detailed mechanisms can be used to compare reactivities of different n-alkane fuels. The mechanisms for all of these n-alkanes are presented as a single detailed mechanism, which can be edited to produce efficient mechanisms for any of the n-alkanes included, and the entire mechanism, with supporting thermochemical and transport data, together with an explanatory glossary explaining notations and structural details, will be available for download from our web page.

  1. The Renner-Teller effect in HCCCl(+)(X?(2)?) studied by zero-kinetic energy photoelectron spectroscopy and ab initio calculations.

    PubMed

    Sun, Wei; Dai, Zuyang; Wang, Jia; Mo, Yuxiang

    2015-05-21

    The spin-vibronic energy levels of the chloroacetylene cation up to 4000 cm(-1) above the ground state have been measured using the one-photon zero-kinetic energy photoelectron spectroscopic method. The spin-vibronic energy levels have also been calculated using a diabatic model, in which the potential energy surfaces are expressed by expansions of internal coordinates, and the Hamiltonian matrix equation is solved using a variational method with harmonic basis functions. The calculated spin-vibronic energy levels are in good agreement with the experimental data. The Renner-Teller (RT) parameters describing the vibronic coupling for the H-C?C bending mode (?4), Cl-C?C bending mode (?5), the cross-mode vibronic coupling (?45) of the two bending vibrations, and their vibrational frequencies (?4 and ?5) have also been determined using an effective Hamiltonian matrix treatment. In comparison with the spin-orbit interaction, the RT effect in the H-C?C bending (?4) mode is strong, while the RT effect in the Cl-C?C bending mode is weak. There is a strong cross-mode vibronic coupling of the two bending vibrations, which may be due to a vibronic resonance between the two bending vibrations. The spin-orbit energy splitting of the ground state has been determined for the first time and is found to be 209 ± 2 cm(-1). PMID:26001458

  2. The Renner-Teller effect in HCCCl + ( X ˜ 2 ? ) studied by zero-kinetic energy photoelectron spectroscopy and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Sun, Wei; Dai, Zuyang; Wang, Jia; Mo, Yuxiang

    2015-05-01

    The spin-vibronic energy levels of the chloroacetylene cation up to 4000 cm-1 above the ground state have been measured using the one-photon zero-kinetic energy photoelectron spectroscopic method. The spin-vibronic energy levels have also been calculated using a diabatic model, in which the potential energy surfaces are expressed by expansions of internal coordinates, and the Hamiltonian matrix equation is solved using a variational method with harmonic basis functions. The calculated spin-vibronic energy levels are in good agreement with the experimental data. The Renner-Teller (RT) parameters describing the vibronic coupling for the H—C?C bending mode (?4), Cl—C?C bending mode (?5), the cross-mode vibronic coupling (?45) of the two bending vibrations, and their vibrational frequencies (?4 and ?5) have also been determined using an effective Hamiltonian matrix treatment. In comparison with the spin-orbit interaction, the RT effect in the H—C?C bending (?4) mode is strong, while the RT effect in the Cl—C?C bending mode is weak. There is a strong cross-mode vibronic coupling of the two bending vibrations, which may be due to a vibronic resonance between the two bending vibrations. The spin-orbit energy splitting of the ground state has been determined for the first time and is found to be 209 ± 2 cm-1.

  3. Recycling of metal-organic chemical vapor deposition waste of GaN based power device and LED industry by acidic leaching: Process optimization and kinetics study

    NASA Astrophysics Data System (ADS)

    Swain, Basudev; Mishra, Chinmayee; Kang, Leeseung; Park, Kyung-Soo; Lee, Chan Gi; Hong, Hyun Seon; Park, Jeung-Jin

    2015-05-01

    Recovery of metal values from GaN, a metal-organic chemical vapor deposition (MOCVD) waste of GaN based power device and LED industry is investigated by acidic leaching. Leaching kinetics of gallium rich MOCVD waste is studied and the process is optimized. The gallium rich waste MOCVD dust is characterized by XRD and ICP-AES analysis followed by aqua regia digestion. Different mineral acids are used to find out the best lixiviant for selective leaching of the gallium and indium. Concentrated HCl is relatively better lixiviant having reasonably faster kinetic and better leaching efficiency. Various leaching process parameters like effect of acidity, pulp density, temperature and concentration of catalyst on the leaching efficiency of gallium and indium are investigated. Reasonably, 4 M HCl, a pulp density of 50 g/L, 100 °C and stirring rate of 400 rpm are the effective optimum condition for quantitative leaching of gallium and indium.

  4. Calculation of the Relative Chemical Stabilities of Proteins as a Function of Temperature and Redox Chemistry in a Hot Spring

    PubMed Central

    Dick, Jeffrey M.; Shock, Everett L.

    2011-01-01

    Uncovering the chemical and physical links between natural environments and microbial communities is becoming increasingly amenable owing to geochemical observations and metagenomic sequencing. At the hot spring known as Bison Pool in Yellowstone National Park, the cooling of the water in the outflow channel is associated with an increase in oxidation potential estimated from multiple field-based measurements. Representative groups of proteins whose sequences were derived from metagenomic data also exhibit an increase in average oxidation state of carbon in the protein molecules with distance from the hot-spring source. The energetic requirements of reactions to form selected proteins used in the model were computed using amino-acid group additivity for the standard molal thermodynamic properties of the proteins, and the relative chemical stabilities of the proteins were investigated by varying temperature, pH and oxidation state, expressed as activity of dissolved hydrogen. The relative stabilities of the proteins were found to track the locations of the sampling sites when the calculations included a function for hydrogen activity that increases with temperature and is higher, or more reducing, than values consistent with measurements of dissolved oxygen, sulfide and oxidation-reduction potential in the field. These findings imply that spatial patterns in the amino acid compositions of proteins can be linked, through energetics of overall chemical reactions representing the formation of the proteins, to the environmental conditions at this hot spring, even if microbial cells maintain considerably different internal conditions. Further applications of the thermodynamic calculations are possible for other natural microbial ecosystems. PMID:21853048

  5. Thermal cure kinetics of epoxidized linseed oil with anhydride hardener

    Microsoft Academic Search

    Arunjunai Raj Mahendran; Günter Wuzella; Andreas Kandelbauer; Nicolai Aust

    The thermal cure kinetics of an epoxidized linseed oil with methyl nadic anhydride as curing agent and 1-methyl imidazole\\u000a as catalyst was studied by differential scanning calorimetry (DSC). The curing process was evaluated by non-isothermal DSC\\u000a measurements; three iso-conversional methods for kinetic analysis of the original thermo-chemical data were applied to calculate\\u000a the changes in apparent activation energy in dependence

  6. The extent of disorder and properties of silicate glasses, melts and layer-silicates: Spectroscopic analysis and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Lee, Sung Keun

    Silicate glasses and melts have long been studied not only because of their geologic relevance to natural magmas but also because of their technological applications to the glass industry. The inherent aspect of silicate glasses and melts are extent of disorder among framework units and the distribution of internal structural variables. This dissertation is for a systematic exploration of the extent of disorder in silicate glasses, melts and layer-silicates using NMR spectroscopy and analysis both by theoretical prediction based on statistical thermodynamics and by quantum chemical calculations. The objective of the dissertation includes exploration of the consequences of the degree of disorder of the system on physical properties of interest to geologists and material scientists. The degree of randomness in framework in silicate glasses including borosilicate and aluminosilicates was quantified using the models introducing order parameters such as the degree of Al avoidance and the degree of inter-mixing. The model in conjunction with input from high-resolution NMR and quantum chemical calculations was used to calculate the configurational thermodynamic properties in these glasses. We presented general framework for understanding the extent of short-range order in framework silicates, demonstrating that a more complete description of the macroscopic thermodynamic properties of silicates can be derived from information on the degree of framework disorder and provides another strong link between structures of melts and properties. Bond angle and length distributions, one aspect of topological disorder in this system, were also quantified using these methods. 17O MQ (multiple quantum) MAS NMR at high fields were applied to better understand reactivity of oxygen sites in layer silicates which are one of the most dominant constituents of the Earth's surfaces. Several basal and apical oxygen sites in model clay minerals were resolved, providing improved prospects for atomic scale understanding on the geochemical processes such as weathering.

  7. FAF-Drugs3: a web server for compound property calculation and chemical library design.

    PubMed

    Lagorce, David; Sperandio, Olivier; Baell, Jonathan B; Miteva, Maria A; Villoutreix, Bruno O

    2015-07-01

    Drug attrition late in preclinical or clinical development is a serious economic problem in the field of drug discovery. These problems can be linked, in part, to the quality of the compound collections used during the hit generation stage and to the selection of compounds undergoing optimization. Here, we present FAF-Drugs3, a web server that can be used for drug discovery and chemical biology projects to help in preparing compound libraries and to assist decision-making during the hit selection/lead optimization phase. Since it was first described in 2006, FAF-Drugs has been significantly modified. The tool now applies an enhanced structure curation procedure, can filter or analyze molecules with user-defined or eight predefined physicochemical filters as well as with several simple ADMET (absorption, distribution, metabolism, excretion and toxicity) rules. In addition, compounds can be filtered using an updated list of 154 hand-curated structural alerts while Pan Assay Interference compounds (PAINS) and other, generally unwanted groups are also investigated. FAF-Drugs3 offers access to user-friendly html result pages and the possibility to download all computed data. The server requires as input an SDF file of the compounds; it is open to all users and can be accessed without registration at http://fafdrugs3.mti.univ-paris-diderot.fr. PMID:25883137

  8. FAF-Drugs3: a web server for compound property calculation and chemical library design

    PubMed Central

    Lagorce, David; Sperandio, Olivier; Baell, Jonathan B.; Miteva, Maria A.; Villoutreix, Bruno O.

    2015-01-01

    Drug attrition late in preclinical or clinical development is a serious economic problem in the field of drug discovery. These problems can be linked, in part, to the quality of the compound collections used during the hit generation stage and to the selection of compounds undergoing optimization. Here, we present FAF-Drugs3, a web server that can be used for drug discovery and chemical biology projects to help in preparing compound libraries and to assist decision-making during the hit selection/lead optimization phase. Since it was first described in 2006, FAF-Drugs has been significantly modified. The tool now applies an enhanced structure curation procedure, can filter or analyze molecules with user-defined or eight predefined physicochemical filters as well as with several simple ADMET (absorption, distribution, metabolism, excretion and toxicity) rules. In addition, compounds can be filtered using an updated list of 154 hand-curated structural alerts while Pan Assay Interference compounds (PAINS) and other, generally unwanted groups are also investigated. FAF-Drugs3 offers access to user-friendly html result pages and the possibility to download all computed data. The server requires as input an SDF file of the compounds; it is open to all users and can be accessed without registration at http://fafdrugs3.mti.univ-paris-diderot.fr. PMID:25883137

  9. Structure and vibrational spectra of melaminium bis(trifluoroacetate) trihydrate: FT-IR, FT-Raman and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Sangeetha, V.; Govindarajan, M.; Kanagathara, N.; Marchewka, M. K.; Gunasekaran, S.; Anbalagan, G.

    Melaminium bis(trifluoroacetate) trihydrate (MTFA), an organic material has been synthesized and single crystals of MTFA have been grown by the slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms that MTFA crystal belongs to the monoclinic system with space group P2/c. The molecular geometry, vibrational frequencies and intensity of the vibrational bands have been interpreted with the aid of structure optimization based on density functional theory (DFT) B3LYP method with 6-311G(d,p) and 6-311++G(d,p) basis sets. The X-ray diffraction data have been compared with the data of optimized molecular structure. The theoretical results show that the crystal structure can be reproduced by optimized geometry and the vibrational frequencies show good agreement with the experimental values. The nuclear magnetic resonance (NMR) chemical shift of the molecule has been calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. HOMO-LUMO, and other related molecular and electronic properties are calculated. The Mulliken and NBO charges have also been calculated and interpreted.

  10. Structure and vibrational spectra of melaminium bis(trifluoroacetate) trihydrate: FT-IR, FT-Raman and quantum chemical calculations.

    PubMed

    Sangeetha, V; Govindarajan, M; Kanagathara, N; Marchewka, M K; Gunasekaran, S; Anbalagan, G

    2014-05-01

    Melaminium bis(trifluoroacetate) trihydrate (MTFA), an organic material has been synthesized and single crystals of MTFA have been grown by the slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms that MTFA crystal belongs to the monoclinic system with space group P2/c. The molecular geometry, vibrational frequencies and intensity of the vibrational bands have been interpreted with the aid of structure optimization based on density functional theory (DFT) B3LYP method with 6-311G(d,p) and 6-311++G(d,p) basis sets. The X-ray diffraction data have been compared with the data of optimized molecular structure. The theoretical results show that the crystal structure can be reproduced by optimized geometry and the vibrational frequencies show good agreement with the experimental values. The nuclear magnetic resonance (NMR) chemical shift of the molecule has been calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. HOMO-LUMO, and other related molecular and electronic properties are calculated. The Mulliken and NBO charges have also been calculated and interpreted. PMID:24556134

  11. Ring planarity problem of 2-oxazoline revisited using microwave spectroscopy and quantum chemical calculations.

    PubMed

    Samdal, Svein; Møllendal, Harald; Reine, Simen; Guillemin, Jean-Claude

    2015-05-21

    In a previous infrared, Raman, and microwave spectroscopic work,1 it was claimed that 2-oxazoline has a planar ring equilibrium conformation, and the ring-puckering potential function V(z) = 22.2(z(4) + 1.31z(2)) cm(-1), where z is a dimensionless reduced coordinate, was derived. This function poorly reproduces the rotational constants of the lowest and most important puckering states. The microwave spectrum has been reinvestigated and largely extended to include more than 4600 transitions of the ground state and six excited states of the ring-puckering vibration allowing accurate centrifugal distortion constants to be obtained for the first time. A new potential function V(z) = 38.8(z(4) - 0.65z(2)) cm(-1) has been determined. This function yields much better agreement between calculated and observed rotational constants, especially for the lowest puckering states, than the previous function and predicts a nonplanar ring equilibrium conformation. The barrier to ring planarity is determined to be 49(8) J/mol. The ground-state energy level is 35 cm(-1) above the barrier maximum. Theory predicts that three of the five Watson centrifugal distortion constants, ?JK, ?K, and ?K, should vary with the puckering state, whereas ?J and ?J should be unaffected. It was found that ?JK and ?K indeed behave in the expected manner, while deviations were seen for the three other centrifugal distortion constants. The ab initio methods HF, MP2, CCSD, CCSD(T), and CCSD(T)-F12 with large basis sets as well as several DFT methods were used in an attempt to reproduce the low experimental barrier to the planar ring. Only the MP2 method yielded a satisfactory prediction of the barrier. The CCSD and the CCSD(T) calculations predict a planar ring, whereas the energy differences between a planar and a nonplanar ring obtained in the CCSD(T)-F12 computations are so small that a definite conclusion cannot be drawn. PMID:25874960

  12. Quantum chemical calculations of the reorganization energy of blue-copper proteins.

    PubMed Central

    Olsson, M. H.; Ryde, U.; Roos, B. O.

    1998-01-01

    The inner-sphere reorganization energy for several copper complexes related to the active site in blue-copper protein has been calculated with the density functional B3LYP method. The best model of the blue-copper proteins, Cu(Im)2(SCH3)(S(CH3)2)(0/+), has a self-exchange inner-sphere reorganization energy of 62 kJ/mol, which is at least 120 kJ/mol lower than for Cu(H2O)4(+/2+). This lowering of the reorganization energy is caused by the soft ligands in the blue-copper site, especially the cysteine thiolate and the methionine thioether groups. Soft ligands both make the potential surfaces of the complexes flatter and give rise to oxidized structures that are quite close to a tetrahedron (rather than tetragonal). Approximately half of the reorganization energy originates from changes in the copper-ligand bond lengths and half of this contribution comes from the Cu-S(Cys) bond. A tetragonal site, which is present in the rhombic type 1 blue-copper proteins, has a slightly higher (16 kJ/mol) inner-sphere reorganization energy than a trigonal site, present in the axial type 1 copper proteins. A site with the methionine ligand replaced by an amide group, as in stellacyanin, has an even higher reorganization energy, about 90 kJ/mol. PMID:9865961

  13. Reaction Kinetics and Catalysis Letters, Vol. 1, No. 1, 113-117/1974/ STOCHASTIC SIMULATION OF CHEMICAL REACTION BY

    E-print Network

    Tóth, János

    OF CHEMICAL REACTION BY DIGITAL COMPUTER, I. THE MODEL T. Sipos, 1 j. T6th, 2 and P. l~rdi 1 1. Danube Oil Received November 9, 1972 A stochastic model of complex chemical reactions is outlined. A discrete Markovprocess corresponds to the complex chemical reaction in the model i.e. the concentrations

  14. Surface CHEMKIN (Version 4. 0): A Fortran package for analyzing heterogeneous chemical kinetics at a solid-surface---gas-phase interface

    SciTech Connect

    Coltrin, M.E. (Sandia National Labs., Albuquerque, NM (United States)); Kee, R.J.; Rupley, F.M. (Sandia National Labs., Livermore, CA (United States))

    1991-07-01

    Heterogeneous reaction at the interface between a solid surface and adjacent gas is central to many chemical processes. Our purpose for developing the software package SURFACE CHEMKIN was motivated by our need to understand the complex surface chemistry in chemical vapor deposition systems involving silicon, silicon nitride, and gallium arsenide. However, we have developed the approach and implemented the software in a general setting. Thus, we expect it will find use in such diverse applications as chemical vapor deposition, chemical etching, combustion of solids, and catalytic processes, and for a wide range of chemical systems. We believe that it provides a powerful capability to help model, understand, and optimize important industrial and research chemical processes. The SURFACE CHEMKIN software is designed to work in conjunction with the CHEMKIN-2 software, which handles the chemical kinetics in the gas phase. It may also be used in conjunction with the Transport Property Package, which provides information about molecular diffusion. Thus, these three packages provide a foundation on which a user can build applications software to analyze gas-phase and heterogeneous chemistry in flowing systems. These packages should not be considered programs'' in the ordinary sense. That is, they are not designed to accept input, solve a particular problem, and report the answer. Instead, they are software tools intended to help a user work efficiently with large systems of chemical reactions and develop Fortran representations of systems of equations that define a particular problem. It is up the user to solve the problem and interpret the answer. 11 refs., 15 figs., 5 tabs.

  15. Computer-Oriented Treatment of High Symmetry in Quantum-Chemical Calculations of Correlated Electronic States

    NASA Astrophysics Data System (ADS)

    Kuprievich, V. A.; Kapitanchuk, O. L.; Shramko, O. V.

    2003-04-01

    Recent achievements in the synthesis of novel substances and materials raise specific problems in computational quantum chemistry demanding to consider electronic structure multiatomic molecular systems in excited and ionic states beyond one-electron approaches. The proposed computational treatment of problem of electron correlation with emphasis on the symmetry-induced degeneracy of molecular states is discussed. It is essentially based on the theory of symmetry molecular invariants that supposes (i) use of fixed reference symmetry base and (ii) determination of invariant expansions for two-electron integrals and energies. The method successively takes full advantage of the relations between the integrals defined on symmetry molecular orbitals (MO). Using the symmetry-similarity principle within the model with two-center electron - electron interaction a simple computational technique is elaborated enabling to represent each integral from complete set as an expansion of a few independent integrals [1,2]. The technique is specified for the most complicated case of icosahedral (Ih) symmetry which is inherent to fullerene C60. It is considered for (i) the configurations (t1u + t1g), the symmetries of two lowest vacant MOs and (ii) for upper occupied hu-shell. The reference symmetry basis sets (mostly with integer components) are presented enabling to obtain the most results in a mathematically rigorous form thus avoiding round-off errors. Energy functionals constructed for all multiplet states of multi-charged ions are reduced to simple form involving only five (h-shell) or six ((t1u + t1g) case) independent integrals (instead of 120 or 231, respectively, in the general case) thus enabling to reduce full-CI or multiconfigurational self-consistent-field calculations of multicharged ions within the corresponding orbital spaces. Applications of the proposed approach are presented to the C60 anion states, which are the case in superconducting fullerides K3C60 and Rb3C60. Some effects of electron interactions within quasi-pi-electron model with different interelectron potentials are considered [3].

  16. Molecular dynamics simulation and quantum chemical calculations for the adsorption of some Azo-azomethine derivatives on mild steel

    NASA Astrophysics Data System (ADS)

    Shokry, H.

    2014-02-01

    The adsorption mechanism and inhibition performance of some Azo-azomethine derivatives [2-hydroxyphenylazo-2?,4?-dihydroxy-3?-formylbenzene(Azo-1), 2-carboxyphenylazo-2?,4?-dihydroxy-3?-formylbenzene (Azo-II), 2-hydroxyphenylazo-2?,4?-dihydroxy-3?-{2-hydroxyphenylazomethine}(Azo-I-azomethine I) and 2-carboxyphenylazo-2?,4?-dihydroxy-3?-{2-hydroxyazo methane} (Azo-II-azomethine II) on mild steel at temperatures ranging from 298 K to 333 K have been studied using molecular dynamics (MD) simulation and quantum chemical computational methods. The results obtained revealed that these molecules could effectively adsorb on Fe (0 0 1) surface and the active adsorption sites of these molecules are the nitrogen, oxygen atoms and special negatively charged carbon atoms. All the inhibitors studied had unique corrosion inhibition performance with Azo-II-azomethine II showing the highest inhibition performance at lower temperature ranges from 298 K to 313 K and Azo-II displaying the highest inhibition performance at higher temperature ranges of 323 K and 333 K. Some quantum chemical parameters and the Mulliken charge densities on the optimized structure of inhibitors were calculated using the 6-31?G basis set method to provide further insight into the mechanism of the corrosion inhibition process. The local reactivity was analyzed through the Fukui function and condensed softness indices in order to know the possible sites of nucleophillic and electrophillic attacks.

  17. Noise-Induced Modulation of the Relaxation Kinetics around a Non-Equilibrium Steady State of Non-Linear Chemical Reaction Networks

    PubMed Central

    Ramaswamy, Rajesh; Sbalzarini, Ivo F.; González-Segredo, Nélido

    2011-01-01

    Stochastic effects from correlated noise non-trivially modulate the kinetics of non-linear chemical reaction networks. This is especially important in systems where reactions are confined to small volumes and reactants are delivered in bursts. We characterise how the two noise sources confinement and burst modulate the relaxation kinetics of a non-linear reaction network around a non-equilibrium steady state. We find that the lifetimes of species change with burst input and confinement. Confinement increases the lifetimes of all species that are involved in any non-linear reaction as a reactant. Burst monotonically increases or decreases lifetimes. Competition between burst-induced and confinement-induced modulation may hence lead to a non-monotonic modulation. We quantify lifetime as the integral of the time autocorrelation function (ACF) of concentration fluctuations around a non-equilibrium steady state of the reaction network. Furthermore, we look at the first and second derivatives of the ACF, each of which is affected in opposite ways by burst and confinement. This allows discriminating between these two noise sources. We analytically derive the ACF from the linear Fokker–Planck approximation of the chemical master equation in order to establish a baseline for the burst-induced modulation at low confinement. Effects of higher confinement are then studied using a partial-propensity stochastic simulation algorithm. The results presented here may help understand the mechanisms that deviate stochastic kinetics from its deterministic counterpart. In addition, they may be instrumental when using fluorescence-lifetime imaging microscopy (FLIM) or fluorescence-correlation spectroscopy (FCS) to measure confinement and burst in systems with known reaction rates, or, alternatively, to correct for the effects of confinement and burst when experimentally measuring reaction rates. PMID:21297975

  18. Molecular structure analysis and spectroscopic characterization of carbimazole with experimental (FT-IR, FT-Raman and UV-Vis) techniques and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Gnanasambandan, T.; Gunasekaran, S.; Seshadri, S.

    2013-11-01

    The complete vibrational assignment and analysis of the fundamental modes of carbimazole (CBZ) was carried out using the experimental FTIR, FT-Raman and UV-Vis data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G(d,p) and 6-311++G(d,p) basis sets. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of CBZ have been computed using B3LYP quantum chemical calculation. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated.

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

    Microsoft Academic Search

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

    2012-01-01

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

  20. 227-0684-00L Control Methods in Systems Biology March 31, 2011 Lecture 5: Introduction to Chemical Kinetics

    E-print Network

    Lygeros, John

    227-0684-00L Control Methods in Systems Biology March 31, 2011 Lecture 5: Introduction to Chemical. Definition 1 Consider a set of chemical species or agents A = {A1, . . . , An} and a relation M(A) × R+ × M but a normal set, e.g. A, can not. Definition 2 A multiset can equivalently be described in terms