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1

Fast algorithm for calculating chemical kinetics in turbulent reacting flow  

NASA Technical Reports Server (NTRS)

This paper addresses the need for a fast batch chemistry solver to perform the kinetics part of a split operator formulation of turbulent reacting flows, with special attention focused on the solution of the ordinary differential equations governing a homogeneous gas-phase chemical reaction. For this purpose, a two-part predictor-corrector algorithm which incorporates an exponentially fitted trapezoidal method was developed. The algorithm performs filtering of ill-posed initial conditions, automatic step-size selection, and automatic selection of Jacobi-Newton or Newton-Raphson iteration for convergence to achieve maximum computational efficiency while observing a prescribed error tolerance. The new algorithm, termed CREK1D (combustion reaction kinetics, one-dimensional), compared favorably with the code LSODE when tested on two representative problems drawn from combustion kinetics, and is faster than LSODE.

Radhakrishnan, K.; Pratt, D. T.

1986-01-01

2

APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems  

SciTech Connect

Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a glass like'' material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

Nguyen, H.D.

1991-11-01

3

APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems  

SciTech Connect

Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a ``glass like`` material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

Nguyen, H.D.

1991-11-01

4

Iteration Scheme for Implicit Calculations of Kinetic and Equilibrium Chemical Reactions in Fluid Dynamics  

NASA Astrophysics Data System (ADS)

An iteration scheme for the implicit treatment of equilibrium chemical reactions in partial equilibrium flow has previously been described (J. D. Ramshaw and A. A. Amsden, J. Comput. Phys.59, 484 (1985); 71 , 224 (1987)). Here we generalize this scheme to kinetic reactions as well as equilibrium reactions. This extends the applicability of the scheme to problems with kinetic reactions that are fast in some regions of the flow field but slow in others. The resulting scheme thereby provides a single unified framework for the implicit treatment of an arbitrary number of coupled equilibrium and kinetic reactions in chemically reacting fluid flow.

Ramshaw, J. D.; Chang, C. H.

1995-02-01

5

Iteration scheme for implicit calculations of kinetic and equilibrium chemical reactions in fluid dynamics  

SciTech Connect

An iteration scheme for the implicit treatment of equilibrium chemical reactions in partial equilibrium flow has previously been described. Here we generalize this scheme to kinetic reactions as well as equilibrium reactions. This extends the applicability of the scheme to problems with kinetic reactions that are fast in regions of the flow field but slow in others. The resulting scheme thereby provides a single unified framework for the implicit treatment of an arbitrary number of coupled equilibrium and kinetic reactions in chemically reacting fluid flow. 10 refs., 2 figs.

Ramshaw, J.D.; Chang, C.H. [Idaho National Engineering Lab., ID (United States)] [Idaho National Engineering Lab., ID (United States)

1995-02-01

6

Learning Chemical Kinetics with Spreadsheets.  

ERIC Educational Resources Information Center

Presented are several simple kinetic systems together with the spreadsheets used to solve them. A set of exercises in chemical kinetics appropriate for an introductory course in physical chemistry is given. Error propagation calculations with experimental data are illustrated. (CW)

Blickensderfer, Roger

1990-01-01

7

Influence of the environment on kinetics and electronic structure of asymmetric azobenzene derivatives — experiment and quantum-chemical calculations  

NASA Astrophysics Data System (ADS)

The kinetics of thermally driven cis- trans isomerisation of asymmetrically substituted azobenzenes dissolved in solvents of various polarities was measured spectrophotometrically. The solvatochromic effect was observed in 4-nitro-4'-aminoazobenzene as well as in 4-nitro-4'methoxyazobenzene. The experiment has been supplemented with quantum-chemical calculations. The solvent effect was taken into account using the quantum-mechanical Langevin dipoles/Monte Carlo (QM/LD/MC) approach. Calculations of first-order hyperpolarizability tensors of investigated molecules have been performed within a sum-over-states (SOS) method. Both methods were implemented in the all-valence method, GRINDOL.

Matczyszyn, K.; Bartkowiak, W.; Leszczynski, J.

2001-05-01

8

Effect of chemical kinetics uncertainties on calculated constituents in a tropospheric photochemical model  

NASA Technical Reports Server (NTRS)

Random photochemical reaction rates are employed in a 1D photochemical model to examine uncertainties in tropospheric concentrations and thereby determine critical kinetic processes and significant correlations. Monte Carlo computations are used to simulate different chemical environments and their related imprecisions. The most critical processes are the primary photodissociation of O3 (which initiates ozone destruction) and NO2 (which initiates ozone formation), and the OH/methane reaction is significant. Several correlations and anticorrelations between species are discussed, and the ozone/transient OH correlation is examined in detail. One important result of the modeling is that estimates of global OH are generally about 25 percent uncertain, limiting the precision of photochemical models. Techniques for reducing the imprecision are discussed which emphasize the use of species and radical species measurements.

Thompson, Anne M.; Stewart, Richard W.

1991-01-01

9

Chemical Calculations  

NSDL National Science Digital Library

This site contains many chemistry applets created by Jonathan Goodman and his group at Cambridge University. An example of an applet available is the Molecular Weight Calculation; whereby entering in a molecular formula, users are able to discover the HRMS weight, the molecular weight, the element percents, and the Molecular Ion Isotope Pattern. Interactive graphs are also available to assist chemistry students with concepts such as boiling points, pressure, and Consecutive First Step Reversible Reactions. Educators and students will also find many three dimensional depictions of the molecules including fused rings, aromatic rings, and Fullerenes.

Goodman, Jonathan

10

Chemical Kinetics Database  

National Institute of Standards and Technology Data Gateway

SRD 17 NIST Chemical Kinetics Database (Web, free access)   The NIST Chemical Kinetics Database includes essentially all reported kinetics results for thermal gas-phase chemical reactions. The database is designed to be searched for kinetics data based on the specific reactants involved, for reactions resulting in specified products, for all the reactions of a particular species, or for various combinations of these. In addition, the bibliography can be searched by author name or combination of names. The database contains in excess of 38,000 separate reaction records for over 11,700 distinct reactant pairs. These data have been abstracted from over 12,000 papers with literature coverage through early 2000.

11

Evaluation of the catalytic mechanism of AICAR transformylase by pH-dependent kinetics, mutagenesis, and quantum chemical calculations.  

PubMed

The catalytic mechanism of 5-aminoimidazole-4-carboxamide ribonucleotide transformylase (AICAR Tfase) is evaluated with pH dependent kinetics, site-directed mutagenesis, and quantum chemical calculations. The chemistry step, represented by the burst rates, was not pH-dependent, which is consistent with our proposed mechanism that the 4-carboxamide of AICAR assists proton shuttling. Quantum chemical calculations on a model system of 5-amino-4-carboxamide imidazole (AICA) and formamide using the B3LYP/6-31G level of theory confirmed that the 4-carboxamide participated in the proton-shuttling mechanism. The result also indicated that the amide-assisted mechanism is concerted such that the proton transfers from the 5-amino group to the formamide are simultaneous with nucleophilic attack by the 5-amino group. Because the process does not lead to a kinetically stable intermediate, the intramolecular proton transfer from the 5-amino group through the 4-carboxamide to the formamide proceeds in the same transition state. Interestingly, the calculations predicted that protonation of the N3 of the imidazole of AICA would reduce the energy barrier significantly. However, the pK(a) of the imidazole of AICAR was determined to be 3.23 +/- 0.01 by NMR titration, and AICAR is likely to bind to the enzyme with its imidazole in the free base form. An alternative pathway was suggested by modeling Lys266 to have a hydrogen-bonding interaction with the N3 of the imidazole of AICAR. Lys266 has been implicated in catalysis based on mutagenesis studies and the recent X-ray structure of AICAR Tfase. The quantum chemical calculations on a model system that contains AICA complexed with CH3NH3+ as a mimic of the Lys residue confirmed that such an interaction lowered the activation energy of the reaction and likewise implicated the 4-carboxamide. To experimentally verify this hypothesis, we prepared the K266R mutant and found that its kcat is reduced by 150-fold from that of the wild type without changes in substrate and cofactor Km values. The kcat-pH profile indicated virtually no pH-dependence in the pH range 6-10.5. The results suggest that the ammonium moiety of Lys or Arg is important in catalysis, most likely acting as a general acid catalyst with a pK(a) value greater than 10.5. The H267A mutant was also prepared since His267 has been found in the active site and implicated in catalysis. The mutant enzyme showed no detectable activity while retaining its binding affinity for substrate, indicating that it plays a critical role in catalysis. We propose that His267 interacts with Lys266 to aid in the precise positioning of the general acid catalyst to the N3 of the imidazole of AICAR. PMID:11457277

Shim, J H; Wall, M; Benkovic, S J; Díaz, N; Suárez, D; Merz, K M

2001-05-23

12

Chemical kinetics and dynamics.  

PubMed

Chemical reactions correspond to irreversible processes creating entropy. Chemistry belongs to the class of nonintegrable Poincare systems. In general, chemistry is associated with resonances-transitions of quantum states. We have studied some very simple examples of such processes, like decay of an unstable state, in detail. (In such cases, there are always multiple time scales.) We obtain a nonunitary ("star unitary"), invertible, nondistributive operator Lambda (which reduces to the unitary transformation operator U for integrable systems). The explicit form of Lambda depends on the interaction of each species with all other types of molecules in the system including the solvent. The basic property that results from Lambda is that the fundamental description of nonintegrable systems is no longer in terms of Hamiltonian equations, but in terms of kinetic equations with broken time symmetry. Once we have the kinetic equations, it is easy to show that we have irreversible processes and entropy production. PMID:12796095

Prigogine, Ilya

2003-05-01

13

Chemical Kinetics: Rate of Reaction  

NSDL National Science Digital Library

This site offers an interactive tutorial that emphasizes graphical interpretation of chemical kinetics. The stoichiometric coefficients for a chemical equation are determined by comparing the slopes of concentration-time plots for the reactants and products. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.

Blauch, David N.

14

Stochastic Simulation of Chemical Kinetics  

Microsoft Academic Search

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

Daniel T. Gillespie

2007-01-01

15

Chemical Looping Combustion Kinetics  

SciTech Connect

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).

Edward Eyring; Gabor Konya

2009-03-31

16

Accurate quantum chemical calculations  

NASA Technical Reports Server (NTRS)

An important goal of quantum chemical calculations is to provide an understanding of chemical bonding and molecular electronic structure. A second goal, the prediction of energy differences to chemical accuracy, has been much harder to attain. First, the computational resources required to achieve such accuracy are very large, and second, it is not straightforward to demonstrate that an apparently accurate result, in terms of agreement with experiment, does not result from a cancellation of errors. Recent advances in electronic structure methodology, coupled with the power of vector supercomputers, have made it possible to solve a number of electronic structure problems exactly using the full configuration interaction (FCI) method within a subspace of the complete Hilbert space. These exact results can be used to benchmark approximate techniques that are applicable to a wider range of chemical and physical problems. The methodology of many-electron quantum chemistry is reviewed. Methods are considered in detail for performing FCI calculations. The application of FCI methods to several three-electron problems in molecular physics are discussed. A number of benchmark applications of FCI wave functions are described. Atomic basis sets and the development of improved methods for handling very large basis sets are discussed: these are then applied to a number of chemical and spectroscopic problems; to transition metals; and to problems involving potential energy surfaces. Although the experiences described give considerable grounds for optimism about the general ability to perform accurate calculations, there are several problems that have proved less tractable, at least with current computer resources, and these and possible solutions are discussed.

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

1989-01-01

17

Chemical kinetics on extrasolar planets.  

PubMed

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

Moses, Julianne I

2014-04-28

18

Computer Simulation in Chemical Kinetics  

ERIC Educational Resources Information Center

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)

Anderson, Jay Martin

1976-01-01

19

Chemical Kinetics: half-life  

NSDL National Science Digital Library

This site offers an interactive tutorial that emphasizes graphical interpretation of chemical kinetics. The half-life is measured for various initial concentrations for zero-, first-, and second-order reactions. The data is analyzed graphically to determine the relationship between the half-life and reactant concentration for each order reaction and to determine the rate constant for each reaction. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.

Blauch, David N.

20

Surprisingly slow reaction of dimethylsilylene with dimethylgermane: time-resolved kinetic studies and related quantum chemical calculations.  

PubMed

Time-resolved studies of silylene, SiH2, and dimethylsilylene, SiMe2, generated by the 193 nm laser flash photolysis of appropriate precursor molecules have been carried out to obtain rate constants for their bimolecular reactions with dimethylgermane, Me2GeH2, in the gas phase. SiMe2 + Me2GeH2 was studied at five temperatures in the range 299-555 K. Problems of substrate UV absorption at 193 nm at temperatures above 400 K meant that only three temperatures could be used reliably for rate constant measurement. These rate constants gave the Arrhenius parameters log(A/cm3 molecule(-1) s(-1)) = -13.25 +/- 0.16 and E(a) = -(5.01 +/- 1.01) kJ mol(-1). Only room temperature studies of SiH2 were carried out. These gave values of (4.05 +/- 0.06) x 10(-10) cm3 molecule(-1) s(-1) (SiH2 + Me2GeH2 at 295 K) and also (4.41 +/- 0.07) x 10(-10) cm3 molecule(-1) s(-1) (SiH2 + MeGeH3 at 296 K). Rate constant comparisons show the surprising result that SiMe2 reacts 12.5 times slower with Me2GeH2 than with Me2SiH2. Quantum chemical calculations (G2(MP2,SVP)//B3LYP level) of the model Si-H and Ge-H insertion processes of SiMe2 with SiH4/MeSiH3 and GeH4/MeGeH3 support these findings and show that the lower reactivity of SiMe2 with Ge-H bonds is caused by a higher secondary barrier for rearrangement of the initially formed complexes. Full details of the structures of intermediate complexes and the discussion of their stabilities are given in the paper. Other, related, comparisons of silylene reactivity are also presented. PMID:18193853

Becerra, Rosa; Boganov, Sergey E; Egorov, Mikhail P; Faustov, Valery I; Krylova, Irina V; Nefedov, Oleg M; Promyslov, Vladimir M; Walsh, Robin

2008-02-01

21

Modeling chemical kinetic aspects of engine knock  

Microsoft Academic Search

A chemical kinetics 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. A series of calculations follows reactions taking place in a sample of end-gas that is subjected

W. J. Pitz; C. K. Westbrook

1984-01-01

22

Chemical Kinetic Characterization of Combustion Toluene  

SciTech Connect

A study is performed to elucidate the chemical kinetic mechanism of combustion of toluene. A detailed chemical kinetic mechanism for toluene was improved by adding a more accurate description of the phenyl + O{sub 2} reaction channels. Results of the chemical kinetic mechanism are compared with experimental data obtained from premixed and nonpremixed systems. Under premixed conditions, predicted ignition delay times are compared with new experimental data obtained in shock tube. Also, calculated species concentration histories are compared to experimental flow reactor data from the literature. Critical conditions of extinction and ignition were measured in strained laminar flows under nonpremixed conditions in the counterflow configuration. Numerical calculations are performed using the chemical kinetic mechanism at conditions corresponding to those in the experiments. Critical conditions of extinction and ignition are predicted and compared with the experimental data. For both premixed and nonpremixed systems, sensitivity analysis was used to identify the reaction rate constants that control the overall rate of oxidation in each of the systems considered.

Pitz, W J; Seiser, R; Bozzelli, J W; Da Costa, I; Fournet, R; Billaud, F; Battin-Leclerc, F; Seshadri, K; Westbrook, C K

2001-03-20

23

Chemical Kinetic Modeling of Hydrogen Combustion Limits  

SciTech Connect

A detailed chemical kinetic model is used to explore the flammability and detonability of hydrogen mixtures. In the case of flammability, a detailed chemical kinetic mechanism for hydrogen is coupled to the CHEMKIN Premix code to compute premixed, laminar flame speeds. The detailed chemical kinetic model reproduces flame speeds in the literature over a range of equivalence ratios, pressures and reactant temperatures. A series of calculation were performed to assess the key parameters determining the flammability of hydrogen mixtures. Increased reactant temperature was found to greatly increase the flame speed and the flammability of the mixture. The effect of added diluents was assessed. Addition of water and carbon dioxide were found to reduce the flame speed and thus the flammability of a hydrogen mixture approximately equally well and much more than the addition of nitrogen. The detailed chemical kinetic model was used to explore the detonability of hydrogen mixtures. A Zeldovich-von Neumann-Doring (ZND) detonation model coupled with detailed chemical kinetics was used to model the detonation. The effectiveness on different diluents was assessed in reducing the detonability of a hydrogen mixture. Carbon dioxide was found to be most effective in reducing the detonability followed by water and nitrogen. The chemical action of chemical inhibitors on reducing the flammability of hydrogen mixtures is discussed. Bromine and organophosphorus inhibitors act through catalytic cycles that recombine H and OH radicals in the flame. The reduction in H and OH radicals reduces chain branching in the flame through the H + O{sub 2} = OH + O chain branching reaction. The reduction in chain branching and radical production reduces the flame speed and thus the flammability of the hydrogen mixture.

Pitz, W J; Westbrook, C K

2008-04-02

24

Chemical Kinetic Study of Toluene Oxidation  

SciTech Connect

A study was performed to elucidate the chemical-kinetic mechanism of combustion of toluene. A detailed chemical-kinetic mechanism for toluene was improved by adding a more accurate description of the phenyl + O{sub 2} reaction channels, toluene decomposition reactions and the benzyl + 0 reaction. Results of the chemical kinetic mechanism are compared with experimental data obtained from premixed and nonpremixed systems. Under premixed conditions, predicted ignition delay times are compared with new experimental data obtained in shock tube. Also, calculated species concentration histories are compared to experimental flow reactor data from the literature. Under nonpremixed conditions, critical conditions of extinction and autoignition were measured in strained laminar flows in the counterflow configuration. Numerical calculations are performed using the chemical-kinetic mechanism at conditions corresponding to those in the experiments. Critical conditions of extinction and autoignition are predicted and compared with the experimental data. Comparisons between the model predictions and experimental results of ignition delay times in shock tube, and extinction and autoignition in nonpremixed systems show that the chemical-kinetic mechanism predicts that toluene/air is overall less reactive than observed in the experiments. For both premixed and nonpremixed systems, sensitivity analysis was used to identify the reaction rate constants that control the overall rate of oxidation in each of the systems considered. Under shock tube conditions, the reactions that influence ignition delay time are H + O{sub 2} chain branching, the toluene decomposition reaction to give an H atom, and the toluene + H abstraction reaction. The reactions that influence autoignition in nonpremixed systems involve the benzyl + HO{sub 2} reaction and the phenyl + O{sub 2} reaction.

Pitz, W J; Seiser, R; Bozzelli, J W; Seshadri, K; Chen, C-J; Da Costa, I; Fournet, R; Billaud, F; Battin-Leclerc, F; Westbrook, C K

2001-12-17

25

Calculating Kinetics of a Student Designed Machine  

NSDL National Science Digital Library

This activity is a project-based inquiry where students design and create a machine to complete a task. Then students will be asked to calculate velocities, kinetic energy and potential energies of various parts of their machine.

26

Thermochemical and chemical kinetic data for fluorinated hydrocarbons  

Microsoft Academic Search

A comprehensive, detailed chemical kinetic mechanism was developed and is presented for C1 and C2 fluorinated hydrocarbon destruction and flame suppression. Existing fluorinated hydrocarbon thermochemistry and kinetics were compiled from the literature and evaluated. For species where no or incomplete thermochemistry was available, these data were calculated through application of ab initio molecular orbital theory. Group additivity values were determined

D. R. Burgess; M. R. Zachariah; W. Tsang; P. R. Westmoreland

1995-01-01

27

Updated Chemical Kinetics and Sensitivity Analysis Code  

NASA Technical Reports Server (NTRS)

An updated version of the General Chemical Kinetics and Sensitivity Analysis (LSENS) computer code has become available. A prior version of LSENS was described in "Program Helps to Determine Chemical-Reaction Mechanisms" (LEW-15758), NASA Tech Briefs, Vol. 19, No. 5 (May 1995), page 66. To recapitulate: LSENS solves complex, homogeneous, gas-phase, chemical-kinetics problems (e.g., combustion of fuels) that are represented by sets of many coupled, nonlinear, first-order ordinary differential equations. LSENS has been designed for flexibility, convenience, and computational efficiency. The present version of LSENS incorporates mathematical models for (1) a static system; (2) steady, one-dimensional inviscid flow; (3) reaction behind an incident shock wave, including boundary layer correction; (4) a perfectly stirred reactor; and (5) a perfectly stirred reactor followed by a plug-flow reactor. In addition, LSENS can compute equilibrium properties for the following assigned states: enthalpy and pressure, temperature and pressure, internal energy and volume, and temperature and volume. For static and one-dimensional-flow problems, including those behind an incident shock wave and following a perfectly stirred reactor calculation, LSENS can compute sensitivity coefficients of dependent variables and their derivatives, with respect to the initial values of dependent variables and/or the rate-coefficient parameters of the chemical reactions.

Radhakrishnan, Krishnan

2005-01-01

28

Chemical kinetics and modeling of combustion processes  

Microsoft Academic Search

Chemical kinetic modeling is an important tool in the analysis of many combustion systems. The use of detailed kinetic models in the interpretation of fundamental kinetics experiments in shock tubes and plug flow reactors is widespread. Recently these models, coupled with fluid mechanical models, have become valuable in helping to understand complex phenomena in practical combustion devices. This study reviews

C. K. Westbrook; F. L. Dryer

1981-01-01

29

Reduced chemical kinetics for propane combustion  

NASA Technical Reports Server (NTRS)

It is pointed out that a detailed chemical kinetics mechanism for the combustion of propane consists of 40 chemical species and 118 elementary chemical reactions. An attempt is made to reduce the number of chemical species and elementary chemical reactions so that the computer run times and storage requirements may be greatly reduced in three-dimensional gas turbine combustion flow calculations, while maintaining accurate predictions of the propane combustion and exhaust emissions. By way of a sensitivity analysis, the species of interest and chemical reactions are classified in descending order of importance. Nineteen species are chosen, and their pressure, temperature, and concentration profiles are presented for the reduced mechanisms, which are then compared with those from the full 118 reactions. It is found that 45 reactions involving 27 species have to be kept for comparable agreement. A comparison of the results obtained from the 45 reactions to that of the full 118 shows that the pressure and temperature profiles and concentrations of C3H8, O2, N2, H2O, CO, and CO2 are within 10 percent of maximum change.

Ying, Shuh-Jing; Nguyen, Hung Lee

1990-01-01

30

Inflation Rates, Car Devaluation, and Chemical Kinetics.  

ERIC Educational Resources Information Center

Describes the inflation rate problem and offers an interesting analogy with chemical kinetics. Presents and solves the car devaluation problem as a normal chemical kinetic problem where the order of the rate law and the value of the rate constant are derived. (JRH)

Pogliani, Lionello; Berberan-Santos, Mario N.

1996-01-01

31

Enhancing Thai Students' Learning of Chemical Kinetics  

ERIC Educational Resources Information Center

Chemical kinetics is an extremely important concept for introductory chemistry courses. The literature suggests that instruction in chemical kinetics is often teacher-dominated at both the secondary school and tertiary levels, and this is the case in Thailand--the educational context for this inquiry. The work reported here seeks to shift students…

Chairam, Sanoe; Somsook, Ekasith; Coll, Richard K.

2009-01-01

32

A chemical kinetic model of vitrinite maturation and reflectance  

Microsoft Academic Search

A chemical kinetic model is presented that uses Arrhenius rate constants to calculate vitrinite elemental composition as a function of time and temperature. The model uses distributions of activation energies for each of four reactions: elimination of water, carbon dioxide, methane and higher hydrocarbons. The resulting composition is used to calculate vitrinite reflectance via correlations between elemental composition and reflectance.

Alan K. Burnham; Jerry J. Sweeney

1989-01-01

33

Chemical Weathering Kinetics of Basalt on Venus  

NASA Technical Reports Server (NTRS)

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.

Fegley, Bruce, Jr.

1997-01-01

34

Chemical Weathering Kinetics of Basalt on Venus.  

National Technical Information Service (NTIS)

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 atmo...

B. Fegley

1997-01-01

35

Chemical kinetic modelling of hydrocarbon ignition  

SciTech Connect

Chemical kinetic modeling of hydrocarbon ignition is discussed with reference to a range of experimental configurations, including shock tubes, detonations, pulse combustors, static reactors, stirred reactors and internal combustion engines. Important conditions of temperature, pressure or other factors are examined to determine the main chemical reaction sequences responsible for chain branching and ignition, and kinetic factors which can alter the rate of ignition are identified. Hydrocarbon ignition usually involves complex interactions between physical and chemical factors, and it therefore is a suitable and often productive subject for computer simulations. In most of the studies to be discussed below, the focus of the attention is placed on the chemical features of the system. The other physical parts of each application are generally included in the form of initial or boundary conditions to the chemical kinetic parts of the problem, as appropriate for each type of application being addressed.

Westbrook, C.K.; Pitz, W.J.; Curran, H.J.; Gaffuri, P.; Marinov, N.M.

1995-08-25

36

Fully equivalent operational models for atmospheric chemical kinetics within global chemistry-transport models  

Microsoft Academic Search

A major portion of the computational effort in simulations by three-dimensional (3-D) chemistry-transport models is consumed in chemical kinetics calculations which repeatedly solve coupled ordinary differential equations. To address this burden, this paper introduces a high-speed fully equivalent operational model (FEOM) for chemical kinetics calculations. The FEOM consists of a hierarchical correlated-function expansion capturing the input-output relationships of chemical kinetics.

S. W. Wang; G. Li; H. Rabitz

1999-01-01

37

Mass Conservation and Chemical Kinetics.  

ERIC Educational Resources Information Center

Presents a method for obtaining all mass conservation conditions implied by a given mechanism in which the conditions are used to simplify integration of the rate equations and to derive stoichiometric relations. Discusses possibilities of faulty inference of kinetic information from a given stoichiometry. (CS)

Barbara, Thomas M.; Corio, P. L.

1980-01-01

38

Chemical Kinetics: Method of Initial Rates  

NSDL National Science Digital Library

This site offers an interactive tutorial to assist in the understanding of how the Method of Initial Rates is employed to determine rate constants for chemical reactions. The student runs a series of experiments to create graphical data that is analyzed. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.

Blauch, David N.

39

Improved General Chemical-Kinetics Program  

NASA Technical Reports Server (NTRS)

New general chemical-kinetics code, GCKP84, developed to compute progress of many types of complex gas-phase chemical reactions. Replaces original GCKP code and offers greatly improved efficiency, additional capabilities, and greater convenience. New code written in FORTRAN IV.

Bittker, David A.; Scullin, Vincent J.

1987-01-01

40

Chemical Kinetic Modeling of Advanced Transportation Fuels  

SciTech Connect

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.

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

2009-01-20

41

Method of invariant manifold for chemical kinetics  

Microsoft Academic Search

In this paper, we review the construction of low-dimensional manifolds of reduced description for equations of chemical kinetics from the standpoint of the method of invariant manifold (MIM). The MIM is based on a formulation of the condition of invariance as an equation, and its solution by Newton iterations. A review of existing alternative methods is extended by a thermodynamically

Alexander N. Gorban; Iliya V. Karlina

2003-01-01

42

Chemical kinetics and modeling of planetary atmospheres  

NASA Technical Reports Server (NTRS)

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.

Yung, Yuk L.

1990-01-01

43

Perspective: Stochastic algorithms for chemical kinetics  

PubMed Central

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.

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

2013-01-01

44

Exploring 1,2-Hydrogen Shift in Silicon Nanoparticles: Reaction Kinetics from Quantum Chemical Calculations and Derivation of Transition State Group Additivity Database  

NASA Astrophysics Data System (ADS)

Accurate rate coefficients for 35 1,2-hydrogen shift reactions for hydrides containing up to 10 silicon atoms have been calculated using G3//B3LYP. The overall reactions exhibit two distinct barriers. Overcoming the first barrier results in the formation of a hydrogen-bridged intermediate species from a substituted silylene and is characterized by a low activation energy. Passing over the second barrier converts this stable intermediate into the double-bonded silene. Values for the single event Arrhenius pre-exponential factor, Ã, and the activation energy, Ea, were calculated from the G3//B3LYP rate coefficients, and a group additivity scheme was developed to predict à and Ea. The values predicted by group additivity are more accurate than structure/reactivity relationships currently used in the literature, which rely on a representative à value and the Evans-Polanyi correlation to predict Ea. The structural factors that have the most pronounced effect on à and Ea were considered, and the presence of rings was shown to influence these values strongly.

Adamczyk, Andrew J.; Reyniers, Marie-Francoise; Marin, Guy B.; Broadbelt, Linda J.

2009-09-01

45

Exploring 1,2-hydrogen shift in silicon nanoparticles: reaction kinetics from quantum chemical calculations and derivation of transition state group additivity database.  

PubMed

Accurate rate coefficients for 35 1,2-hydrogen shift reactions for hydrides containing up to 10 silicon atoms have been calculated using G3//B3LYP. The overall reactions exhibit two distinct barriers. Overcoming the first barrier results in the formation of a hydrogen-bridged intermediate species from a substituted silylene and is characterized by a low activation energy. Passing over the second barrier converts this stable intermediate into the double-bonded silene. Values for the single event Arrhenius pre-exponential factor, A, and the activation energy, E(a), were calculated from the G3//B3LYP rate coefficients, and a group additivity scheme was developed to predict A and E(a). The values predicted by group additivity are more accurate than structure/reactivity relationships currently used in the literature, which rely on a representative A value and the Evans-Polanyi correlation to predict E(a). The structural factors that have the most pronounced effect on A and E(a) were considered, and the presence of rings was shown to influence these values strongly. PMID:19764804

Adamczyk, Andrew J; Reyniers, Marie-Francoise; Marin, Guy B; Broadbelt, Linda J

2009-10-15

46

A Detailed Chemical Kinetic Model for TNT  

Microsoft Academic Search

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

W J Pitz; C K Westbrook

2005-01-01

47

Promoting Graphical Thinking: Using Temperature and a Graphing Calculator to Teach Kinetics Concepts  

ERIC Educational Resources Information Center

A combination of graphical thinking with chemical and physical theories in the classroom is encouraged by using the Calculator-Based Laboratory System (CBL) with a temperature sensor and graphing calculator. The theory of first-order kinetics is logically explained with the aid of the cooling or heating of the metal bead of the CBL's temperature…

Cortes-Figueroa, Jose E.; Moore-Russo, Deborah A.

2004-01-01

48

The kinetic preprocessor KPP-a software environment for solving chemical kinetics  

Microsoft Academic Search

The kinetic preprocessor (KPP) is a software tool that assists the computer simulation of chemical kinetic systems. The concentrations of a chemical system evolve in time according to the differential law of mass action kinetics. A computer simulation requires the implementation of the differential system and its numerical integration in time. KPP translates a specification of the chemical mechanism into

Valeriu Damian; Adrian Sandu; Mirela Damian; Florian Potra; Gregory R. Carmichael

2002-01-01

49

Spreadsheet Templates for Chemical Equilibrium Calculations.  

ERIC Educational Resources Information Center

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)

Joshi, Bhairav D.

1993-01-01

50

Sensitivity, robustness, and identifiability in stochastic chemical kinetics models  

PubMed Central

We present a novel and simple method to numerically calculate Fisher information matrices for stochastic chemical kinetics models. The linear noise approximation is used to derive model equations and a likelihood function that leads to an efficient computational algorithm. Our approach reduces the problem of calculating the Fisher information matrix to solving a set of ordinary differential equations. This is the first method to compute Fisher information for stochastic chemical kinetics models without the need for Monte Carlo simulations. This methodology is then used to study sensitivity, robustness, and parameter identifiability in stochastic chemical kinetics models. We show that significant differences exist between stochastic and deterministic models as well as between stochastic models with time-series and time-point measurements. We demonstrate that these discrepancies arise from the variability in molecule numbers, correlations between species, and temporal correlations and show how this approach can be used in the analysis and design of experiments probing stochastic processes at the cellular level. The algorithm has been implemented as a Matlab package and is available from the authors upon request.

Komorowski, Michal; Costa, Maria J.; Rand, David A.; Stumpf, Michael P. H.

2011-01-01

51

Spatial Kinetics Calculations of MOX Fueled Core: Variant 22  

Microsoft Academic Search

This work is part of a Joint US\\/Russian Project with Weapons-Grade Plutonium Disposition in VVER Reactors and presents the results of spatial kinetics calculational benchmarks. The examinations were carried out with the following purposes: to verify one of spatial neutronic kinetics model elaborated in KI, to understand sensibility of the model to neutronics difference of UOX and MOX cores, to

Pavlovichev

2001-01-01

52

Point kinetics calculations with fully coupled thermal fluids reactivity feedback  

SciTech Connect

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)

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

2013-07-01

53

The standard chemical oxygen-iodine laser kinetics package  

Microsoft Academic Search

This report presents the Air Force Weapons Laboratory Standard Chemical Oxygen-Iodine Laser Kinetics Package. A complete reaction scheme including recommended rate coefficients for modeling the gas phase kinetics of chemical oxygen-iodine lasers (COIL) was established to provide a common basis for the research and development of COIL devices. A review of the experimental kinetic data base from which this model

Glen P. Perram; Gordon D. Hager

1988-01-01

54

Calculation of Kinetics Parameters for the NBSR  

SciTech Connect

The delayed neutron fraction and prompt neutron lifetime have been calculated at different times in the fuel cycle for the NBSR when fueled with both high-enriched uranium (HEU) and low-enriched uranium (LEU) fuel. The best-estimate values for both the delayed neutron fraction and the prompt neutron lifetime are the result of calculations using MCNP5-1.60 with the most recent ENDFB-VII evaluations. The best-estimate values for the total delayed neutron fraction from fission products are 0.00665 and 0.00661 for the HEU fueled core at startup and end-of-cycle, respectively. For the LEU fuel the best estimate values are 0.00650 and 0.00648 at startup and end-of-cycle, respectively. The present recommendations for the delayed neutron fractions from fission products are smaller than the value reported previously of 0.00726 for the HEU fuel. The best-estimate values for the contribution from photoneutrons will remain as 0.000316, independent of the fuel or time in the cycle.The values of the prompt neutron lifetime as calculated with MCNP5-1.60 are compared to values calculated with two other independent methods and the results are in reasonable agreement with each other. The recommended, conservative values of the neutron lifetime for the HEU fuel are 650 {micro}s and 750 {micro}s for the startup and end-of-cycle conditions, respectively. For LEU fuel the recommended, conservative values are 600 {micro}s and 700 {micro}s for the startup and end-of-cycle conditions, respectively. In all three calculations, the prompt neutron lifetime was determined to be longer for the end-of-cycle equilibrium condition when compared to the startup condition. The results of the three analyses were in agreement that the LEU fuel will exhibit a shorter prompt neutron lifetime when compared to the HEU fuel.

Hanson A. L.; Diamond D.

2012-03-06

55

Chemical Kinetic Modeling of Biofuel Combustion  

NASA Astrophysics Data System (ADS)

Bioalcohols, such as bioethanol and biobutanol, are suitable replacements for gasoline, while biodiesel can replace petroleum diesel. Improving biofuel engine performance requires understanding its fundamental combustion properties and the pathways of combustion. This study's contribution is experimentally validated chemical kinetic combustion mechanisms for biobutanol and biodiesel. Fundamental combustion data and chemical kinetic mechanisms are presented and discussed to improve our understanding of biofuel combustion. The net environmental impact of biobutanol (i.e., n-butanol) has not been studied extensively, so this study first assesses the sustainability of n-butanol derived from corn. The results indicate that technical advances in fuel production are required before commercializing biobutanol. The primary contribution of this research is new experimental data and a novel chemical kinetic mechanism for n-butanol combustion. The results indicate that under the given experimental conditions, n-butanol is consumed primarily via abstraction of hydrogen atoms to produce fuel radical molecules, which subsequently decompose to smaller hydrocarbon and oxygenated species. The hydroxyl moiety in n-butanol results in the direct production of the oxygenated species such as butanal, acetaldehyde, and formaldehyde. The formation of these compounds sequesters carbon from forming soot precursors, but they may introduce other adverse environmental and health effects. Biodiesel is a mixture of long chain fatty acid methyl esters derived from fats and oils. This research study presents high quality experimental data for one large fatty acid methyl ester, methyl decanoate, and models its combustion using an improved skeletal mechanism. The results indicate that methyl decanoate is consumed via abstraction of hydrogen atoms to produce fuel radicals, which ultimately lead to the production of alkenes. The ester moiety in methyl decanoate leads to the formation of low molecular weight oxygenated compounds such as carbon monoxide, formaldehyde, and ketene. The study concludes that the oxygenated molecules in biofuels follow similar combustion pathways to the hydrocarbons in petroleum fuels. The oxygenated moiety's ability to sequester carbon from forming soot precursors is highlighted. However, the direct formation of oxygenated hydrocarbons warrants further investigation into the environmental and health impacts of practical biofuel combustion systems.

Sarathy, Subram Maniam

56

Calculating Shocks In Flows At Chemical Equilibrium  

NASA Technical Reports Server (NTRS)

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.

Eberhardt, Scott; Palmer, Grant

1988-01-01

57

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.

58

Benchmarking kinetic calculations of resistive wall mode stability  

NASA Astrophysics Data System (ADS)

Validating the calculations of kinetic resistive wall mode (RWM) stability is important for confidently predicting RWM stable operating regions in ITER and other high performance tokamaks for disruption avoidance. Benchmarking the calculations of the Magnetohydrodynamic Resistive Spectrum—Kinetic (MARS-K) [Y. Liu et al., Phys. Plasmas 15, 112503 (2008)], Modification to Ideal Stability by Kinetic effects (MISK) [B. Hu et al., Phys. Plasmas 12, 057301 (2005)], and Perturbed Equilibrium Nonambipolar Transport (PENT) [N. Logan et al., Phys. Plasmas 20, 122507 (2013)] codes for two Solov'ev analytical equilibria and a projected ITER equilibrium has demonstrated good agreement between the codes. The important particle frequencies, the frequency resonance energy integral in which they are used, the marginally stable eigenfunctions, perturbed Lagrangians, and fluid growth rates are all generally consistent between the codes. The most important kinetic effect at low rotation is the resonance between the mode rotation and the trapped thermal particle's precession drift, and MARS-K, MISK, and PENT show good agreement in this term. The different ways the rational surface contribution was treated historically in the codes is identified as a source of disagreement in the bounce and transit resonance terms at higher plasma rotation. Calculations from all of the codes support the present understanding that RWM stability can be increased by kinetic effects at low rotation through precession drift resonance and at high rotation by bounce and transit resonances, while intermediate rotation can remain susceptible to instability. The applicability of benchmarked kinetic stability calculations to experimental results is demonstrated by the prediction of MISK calculations of near marginal growth rates for experimental marginal stability points from the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)].

Berkery, J. W.; Liu, Y. Q.; Wang, Z. R.; Sabbagh, S. A.; Logan, N. C.; Park, J.-K.; Manickam, J.; Betti, R.

2014-05-01

59

Kinetics calculations for near Ne-like ions  

NASA Astrophysics Data System (ADS)

The purpose of the present work is to systematically test the sensitivity of steady-state kinetics to variations in the atomic modeling for plasmas in a near Ne-like state. The effect of 2s vacancies autoionizing states, high lying excited states and electron density is studied. In addition, kinetics calculations using configuration average modeling are compared to similar calculations using detailed fine structure levels. Results are presented mainly for the charge state distribution of selenium. However, relative gain coefficients are calculated for both selenium and silver. These calculations predict somewhat larger gains for the J = 2 to 1 lasing transitions than for the 0 to 1 transitions, which agrees with experimental trends.

Abdallah, J., Jr.; Clark, R. E. H.; Peek, J. M.; Fontes, C. J.

1994-02-01

60

Chemomechanics: chemical kinetics for multiscale phenomena.  

PubMed

The purpose of this critical review is to introduce the reader to an increasingly important class of phenomena: enormous changes in rates of simple chemical reactions within macromolecules as they are stretched by interactions with the environment. In these chemomechanical, or mechanochemical, phenomena the effect of the macromolecular environment can be visualized as a spring (harmonic or anharmonic) bridging and pulling apart a pair of atoms of the macromolecule. Being able to predict how the parameters of this spring affect the kinetics of the reactions occurring between the constrained atoms may create revolutionary opportunities for designing new reactions, molecules and materials that would capture large-scale deformations to drive useful chemistry or, conversely, that would propel autonomous micro- and nanomechanical devices by coupling them to the concerted motion of atoms that convert reactants into products. Although chemists have long studied and exploited coupling between molecular strain and reactivity in small molecules, a quantitative understanding of the relationship between large-scale (>50 nm) strain and localized reactivity presents unique conceptual and experimental challenges. Below we discuss both the phenomenology and the interpretive framework of chemomechanical phenomena (102 references). PMID:21283850

Huang, Zhen; Boulatov, Roman

2011-05-01

61

A Detailed Chemical Kinetic Model for TNT  

SciTech Connect

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.

Pitz, W J; Westbrook, C K

2005-01-13

62

Evaluated Kinetic and Photochemical Data for Atmospheric Chemistry: Supplement I CODATA Task Group on Chemical Kinetics  

Microsoft Academic Search

This paper updates and extends a previous critical evaluation of the kinetics and photochemistry of gas phase chemical reactions of neutral species involved in middle atmosphere chemistry (10–55 km altitude) [J. Phys. Chem. Ref. Data 9, 295 (1980)]. The work has been carried out by the authors under the auspices of the CODATA Task Group on Chemical Kinetics. Data sheets

D. L. Baulch; R. A. Cox; P. J. Crutzen; R. F. Hampson; J. A. Kerr; J. Troe; R. T. Watson

1982-01-01

63

Efficient first-principles calculation of the quantum kinetic energy and momentum distribution of nuclei.  

PubMed

Light nuclei at room temperature and below exhibit a kinetic energy which significantly deviates from the predictions of classical statistical mechanics. This quantum kinetic energy is responsible for a wide variety of isotope effects of interest in fields ranging from chemistry to climatology. It also furnishes the second moment of the nuclear momentum distribution, which contains subtle information about the chemical environment and has recently become accessible to deep inelastic neutron scattering experiments. Here, we show how, by combining imaginary time path integral dynamics with a carefully designed generalized Langevin equation, it is possible to dramatically reduce the expense of computing the quantum kinetic energy. We also introduce a transient anisotropic Gaussian approximation to the nuclear momentum distribution which can be calculated with negligible additional effort. As an example, we evaluate the structural properties, the quantum kinetic energy, and the nuclear momentum distribution for a first-principles simulation of liquid water. PMID:23005275

Ceriotti, Michele; Manolopoulos, David E

2012-09-01

64

Chemical Kinetic Model for the Lower Atmosphere of Venus  

NASA Astrophysics Data System (ADS)

A self-consistent chemical kinetic model of the Venus atmosphere at 0-47 km has been calculated for the first time. The model involves 82 reactions of 26 species. Chemical processes in the atmosphere below the clouds are initiated by photochemical products from the middle atmosphere (H2SO4, CO, Sx), thermochemistry in the lowest 10 km, and photolysis of S3. The sulfur bonds in OCS and Sx are weaker than the bonds of other elements in the basic atmospheric species on Venus; therefore the chemistry is mostly sulfur-driven. The calculated abundances of CO, OCS, H2SO4, and S3 are in good agreement with the observations. The model predicts the H2S abundance of ~150 ppb and does not support some controversial detections of H2S as well as some expectations of significant abundances of ClSO2 and SO2Cl2. The existing concept of the atmospheric sulfur cycles is incompatible with the observations of the OCS profile and has been revised.A self-consistent chemical kinetic model of the Venus atmosphere at 0-47 km has been calculated for the first time. The model involves 82 reactions of 26 species. Chemical processes in the atmosphere below the clouds are initiated by photochemical products from the middle atmosphere (H2SO4, CO, Sx), thermochemistry in the lowest 10 km, and photolysis of S3. The sulfur bonds in OCS and Sx are weaker than the bonds of other elements in the basic atmospheric species on Venus; therefore the chemistry is mostly sulfur-driven. The calculated abundances of CO, OCS, H2SO4, and S3 are in good agreement with the observations. The model predicts the H2S abundance of ~150 ppb and does not support some controversial detections of H2S as well as some expectations of significant abundances of ClSO2 and SO2Cl2. The existing concept of the atmospheric sulfur cycles is incompatible with the observations of the OCS profile and has been revised.

Krasnopolsky, V. A.

65

Detailed chemical kinetic mechanisms for combustion of oxygenated fuels  

Microsoft Academic Search

Thermodynamic properties and detailed chemical kinetic models have been developed for the combustion of two oxygenates: methyl butanoate, a model compound for biodiesel fuels, and methyl formate, a related simpler molecule. Bond additivity methods and rules for estimating kinetic parameters were adopted from hydrocarbon combustion and extended. The resulting mechanisms have been tested against the limited combustion data available in

E. M. Fisher; W. J. Pitz; H. J. Curran; C. K. Westbrook

2000-01-01

66

Chemical Kinetic Model for the Lower Atmosphere of Venus  

NASA Astrophysics Data System (ADS)

A self-consistent chemical kinetic model of the Venus atmosphere at 0-47 km has been calculated for the first time. The model involves 76 reactions of 27 species. Chemical processes in the atmosphere below the clouds are initiated by photochemical products from the middle atmosphere (SO3, CO, Sn), thermochemistry in the lowest 10 km, and photolysis of S3. The sulfur bonds in OCS and Sn are weaker than the bonds of other elements in the basic atmospheric species on Venus; therefore the chemistry is sulfur-driven. Sulfur chemistry activates some H and Cl atoms and radicals, though their effect on the chemical composition is weak. The lack of kinetic data for many reactions presents a problem that has been solved using some similar reactions and thermodynamic calculations of inverse processes. Column rates of some reactions in the lower atmosphere exceed the highest rates in the middle atmosphere by two orders of magnitude. However, many reactions are balanced by the inverse processes, and their net rates are comparable to those in the middle atmosphere. The calculated profile of CO is in excellent agreement with the Pioneer Venus and Venera 12 gas chromatographic measurements and slightly above the value from the nightside spectroscopy at 2.3 ?m. The OCS profile also agrees with the nightside spectroscopy which is the only source of data for this species. The model predicts 1.5 ppm of H2S confirming the questionable detection by the Pioneer Venus mass spectrometer. While the calculated mean S3 abundance agrees with the Venera 11-14 observations, a steep decrease in S_3 from the surface to 20 km is not expected from the observations. The ClSO2and SO2Cl2 mixing ratios are ~10-11 in the lowest scale height. The existing concept of the atmospheric sulfur cycles is incompatible with the observations of the OCS profile. A scheme suggested in the current work involves the basic photochemical cycle that transforms CO2and SO2into SO3, CO, and Sn and a minor photochemical cycle which forms SO2and Sn from OCS. The net effect of thermochemistry in the lowest 10 km is formation of OCS from CO and Sn. Chemistry at 30-40 km removes the downward flux of SO3 and the upward flux of OCS and increases the downward fluxes of CO and Sn. The geological cycle of sulfur remains unchanged.

Krasnopolsky, V. A.

2007-05-01

67

Chemical kinetic model for the lower atmosphere of Venus  

NASA Astrophysics Data System (ADS)

A self-consistent chemical kinetic model of the Venus atmosphere at 0-47 km has been calculated for the first time. The model involves 82 reactions of 26 species. Chemical processes in the atmosphere below the clouds are initiated by photochemical products from the middle atmosphere (H 2SO 4, CO, S x), thermochemistry in the lowest 10 km, and photolysis of S 3. The sulfur bonds in OCS and S x are weaker than the bonds of other elements in the basic atmospheric species on Venus; therefore the chemistry is mostly sulfur-driven. Sulfur chemistry activates some H and Cl atoms and radicals, though their effect on the chemical composition is weak. The lack of kinetic data for many reactions presents a problem that has been solved using some similar reactions and thermodynamic calculations of inverse processes. Column rates of some reactions in the lower atmosphere exceed the highest rates in the middle atmosphere by two orders of magnitude. However, many reactions are balanced by the inverse processes, and their net rates are comparable to those in the middle atmosphere. The calculated profile of CO is in excellent agreement with the Pioneer Venus and Venera 12 gas chromatographic measurements and slightly above the values from the nightside spectroscopy at 2.3 ?m. The OCS profile also agrees with the nightside spectroscopy which is the only source of data for this species. The abundance and vertical profile of gaseous H 2SO 4 are similar to those observed by the Mariner 10 and Magellan radio occultations and ground-based microwave telescopes. While the calculated mean S 3 abundance agrees with the Venera 11-14 observations, a steep decrease in S 3 from the surface to 20 km is not expected from the observations. The ClSO 2 and SO 2Cl 2 mixing ratios are ˜10 -11 in the lowest scale height. The existing concept of the atmospheric sulfur cycles is incompatible with the observations of the OCS profile. A scheme suggested in the current work involves the basic photochemical cycle, that transforms CO 2 and SO 2 into SO 3, CO, and S x, and a minor photochemical cycle which forms CO and S x from OCS. The net effect of thermochemistry in the lowest 10 km is formation of OCS from CO and S x. Chemistry at 30-40 km removes the downward flux of SO 3 and the upward flux of OCS and increases the downward fluxes of CO and S x. The geological cycle of sulfur remains unchanged.

Krasnopolsky, Vladimir A.

2007-11-01

68

A hybrid computer program for rapidly solving flowing or static chemical kinetic problems involving many chemical species  

NASA Technical Reports Server (NTRS)

A hybrid chemical kinetic computer program was assembled which provides a rapid solution to problems involving flowing or static, chemically reacting, gas mixtures. The computer program uses existing subroutines for problem setup, initialization, and preliminary calculations and incorporates a stiff ordinary differential equation solution technique. A number of check cases were recomputed with the hybrid program and the results were almost identical to those previously obtained. The computational time saving was demonstrated with a propane-oxygen-argon shock tube combustion problem involving 31 chemical species and 64 reactions. Information is presented to enable potential users to prepare an input data deck for the calculation of a problem.

Mclain, A. G.; Rao, C. S. R.

1976-01-01

69

The Multiplexed Chemical Kinetic Photoionization Mass Spectrometer: A New Approach To Isomer-resolved Chemical Kinetics  

SciTech Connect

We have developed a multiplexed time- and photon-energy?resolved photoionizationmass spectrometer for the study of the kinetics and isomeric product branching of gasphase, neutral chemical reactions. The instrument utilizes a side-sampled flow tubereactor, continuously tunable synchrotron radiation for photoionization, a multi-massdouble-focusing mass spectrometer with 100percent duty cycle, and a time- and positionsensitive detector for single ion counting. This approach enables multiplexed, universal detection of molecules with high sensitivity and selectivity. In addition to measurement of rate coefficients as a function of temperature and pressure, different structural isomers can be distinguished based on their photoionization efficiency curves, providing a more detailed probe of reaction mechanisms. The multiplexed 3-dimensional data structure (intensity as a function of molecular mass, reaction time, and photoionization energy) provides insights that might not be available in serial acquisition, as well as additional constraints on data interpretation.

Osborne, David L.; Zou, Peng; Johnsen, Howard; Hayden, Carl C.; Taatjes, Craig A.; Knyazev, Vadim D.; North, Simon W.; Peterka, Darcy S.; Ahmed, Musahid; Leone, Stephen R.

2008-08-28

70

The multiplexed chemical kinetic photoionization mass spectrometer: A new approach to isomer-resolved chemical kinetics  

SciTech Connect

We have developed a multiplexed time- and photon-energy-resolved photoionization mass spectrometer for the study of the kinetics and isomeric product branching of gas phase, neutral chemical reactions. The instrument utilizes a side-sampled flow tube reactor, continuously tunable synchrotron radiation for photoionization, a multimass double-focusing mass spectrometer with 100% duty cycle, and a time- and position-sensitive detector for single ion counting. This approach enables multiplexed, universal detection of molecules with high sensitivity and selectivity. In addition to measurement of rate coefficients as a function of temperature and pressure, different structural isomers can be distinguished based on their photoionization efficiency curves, providing a more detailed probe of reaction mechanisms. The multiplexed three-dimensional data structure (intensity as a function of molecular mass, reaction time, and photoionization energy) provides insights that might not be available in serial acquisition, as well as additional constraints on data interpretation.

Osborn, David L.; Zou Peng; Johnsen, Howard; Hayden, Carl C.; Taatjes, Craig A. [Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, California 94551-0969 (United States); Knyazev, Vadim D. [Research Center for Chemical Kinetics, Department of Chemistry, Catholic University of America, Washington, DC 20064 (United States); North, Simon W. [Department of Chemistry, Texas A and M University, P.O. Box 30012, College Station, Texas 77842 (United States); Peterka, Darcy S.; Ahmed, Musahid [Chemical Sciences Division, Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Leone, Stephen R. [Chemical Sciences Division, Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Departments of Chemistry and Physics, University of California, Berkeley, California 94720 (United States)

2008-10-15

71

A hydrocode calculation coupled with reaction kinetics of carbon compounds within an impact vapor plume and its implications for cometary impacts on Galilean satellites  

Microsoft Academic Search

The synthesis of organic molecules via chemical reactions within impact vapor plumes has been proposed as a mechanism to supply organics on a planet. However, the kinetics of chemical reactions within a rapidly expanding vapor plume or quenching process of the reactions has not been studied extensively. In this study, we constructed a new numerical model that calculates kinetics of

Ryo Ishimaru; Hiroki Senshu; Seiji Sugita; Takafumi Matsui

2010-01-01

72

Chemical kinetics of water-rock interactions  

Microsoft Academic Search

The recent literature on the kinetics of water-rock interactions is reviewed. The data are then extended to provide a quantitative framework for the description of weathering and alteration. The available experimental data on dissolution of silicates verifies quantitatively the usual mineral stability series in sedimentary petrology. The rate of hydration of carbonic acid is shown to be a possible limiting

Antonio C. Lasaga

1984-01-01

73

Hungarian University Students' Misunderstandings in Thermodynamics and Chemical Kinetics  

ERIC Educational Resources Information Center

The misunderstandings related to thermodynamics (including chemical equilibrium) and chemical kinetics of first and second year Hungarian students of chemistry, environmental science, biology and pharmacy were investigated. We demonstrated that Hungarian university students have similar misunderstandings in physical chemistry to those reported in…

Turanyi, Tamas; Toth, Zoltan

2013-01-01

74

Kinetics of Chemical Weathering in B Horizon Spodosol Fraction.  

National Technical Information Service (NTIS)

The purpose of this study is to investigate the rate and kinetic formulation of chemical weathering on an isolated fraction of whole soil, specifically, whether the rate of chemical weathering is proportional to a fractional power of the hydrogen ion acti...

S. R. Asolekar R. L. Valentine J. L. Schnoor

1991-01-01

75

Chemical kinetics of hydrocarbon ignition in practical combustion systems  

Microsoft Academic Search

Chemical kinetic factors of hydrocarbon oxidation are examined in a variety of ignition problems. Ignition is related to the presence of a dominant chain-branching reaction mechanism that can drive a chemical system to completion in a very short period of time. Ignition in laboratory environments is studied for problems including shock tubes and rapid compression machines. Modeling of the laboratory

Charles K. Westbrook

2000-01-01

76

Chemical kinetics computer program for static and flow reactions  

NASA Technical Reports Server (NTRS)

General chemical kinetics computer program for complex gas mixtures has been developed. Program can be used for any homogeneous reaction in either one dimensional flow or static system. It is flexible, accurate, and easy to use. It can be used for any chemical system for which species thermodynamic data and reaction rate constant data are known.

Bittker, D. A.; Scullin, V. J.

1972-01-01

77

An efficient chemical kinetics solver using high dimensional model representation  

Microsoft Academic Search

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

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

1999-01-01

78

Chemical Kinetics of Polycyclic Aromatic Hydrocarbons in Comet Impacts  

NASA Astrophysics Data System (ADS)

Polycyclic aromatic hydrocarbons (PAHs) are stable, robust organic compounds that would have been an important constituent of the early atmospheres of terrestrial planets. These strongly-bound molecules readily absorb ultraviolet light and may play a role in aerosol formation. PAHs are one of the predominant carriers of carbon in interstellar space, after CO. They are common in carbonaceous chondrites, and quite likely in comets as well. Impacts of volatile-rich planetesimals such as carbonaceous chondrites and comets would have been common during the late stages of planet formation. Theoretical studies of impact chemistry typically assume that the chemical composition of the post-impact material is given by thermodynamic equilibrium at 2000 K. These calculations also typically ignore the formation of aromatic compounds because the closure of the first aromatic ring is kinetically inhibited, although thermodynamically favorable at the temperatures and pressures of an impact fireball. Do the PAHs present in a comet or asteroid survive impact? If so, how are these PAHs modified during impact? To address these questions, we model the chemical kinetics of PAH survival, formation, growth and destruction within a parameter space consisting of impact fireball cooling timescales, pressures, temperatures, C/O ratios and other factors. The chemistry of PAHs has been well studied under conditions present in plug flow reactors and sooting flames (P ? 1atm, T? 1000 K). We hope that our results will motivate more experimental investigation of reaction mechanisms and rate coefficients for a broader range of temperatures and pressures than those heretofore studied for industrial applications. This work has been supported by the NASA Astrobiology Institute's Virtual Planetary Laboratory and the Institute for Geophysics and Planetary Physics at Lawrence Livermore National Laboratory.

Kress, M. E.; McKay, C.; Tielens, A. G.; Frenklach, M.

2004-12-01

79

Constant chemical potential approach for quantum chemical calculations in electrocatalysis  

PubMed Central

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.

Schneider, Wolfgang B

2014-01-01

80

Chemical kinetics of a bipalladium complex.  

PubMed

A theoretical model is presented, for reductive elimination in a bipalladium complex, based on the model of Ariafard et al. (2011). This reaction is of particular interest due to the novel Pd(III) intermediate. A thermo-kinetic model is proposed for this reaction scheme, and the rate laws and energy balance are given as a system of ordinary differential equations. A simplified model is then derived that only involves two key variables, so that the system can be analyzed completely in a phase plane. It is shown that kinetic oscillations do not occur, but that there are multiple steady states for the reaction. These new features are confirmed by a numerical analysis of the full model scheme. The predictions provide a mechanism to test the model and the underlying computational chemistry. PMID:23244399

Doddridge, Edward W; Forbes, Larry K; Yates, Brian F

2013-01-24

81

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

NASA Astrophysics Data System (ADS)

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.

Xia, Shengguo; Jiang, Chunqi

2011-11-01

82

A Gas-Kinetic Scheme for Multimaterial Flows and Its Application in Chemical Reaction  

NASA Technical Reports Server (NTRS)

This paper concerns the extension of the multicomponent gas-kinetic BGK-type scheme to multidimensional chemical reactive flow calculations. In the kinetic model, each component satisfies its individual gas-kinetic BGK equation and the equilibrium states of both components are coupled in space and time due to the momentum and energy exchange in the course of particle collisions. At the same time, according to the chemical reaction rule one component can be changed into another component with the release of energy, where the reactant and product could have different gamma. Many numerical test cases are included in this paper, which show the robustness and accuracy of kinetic approach in the description of multicomponent reactive flows.

Lian, Yongsheng; Xu, Kun

1999-01-01

83

A kinetic-theory approach to turbulent chemically reacting flows  

NASA Technical Reports Server (NTRS)

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.

Chung, P. M.

1976-01-01

84

The chemical shock tube as a tool for studying high-temperature chemical kinetics  

NASA Technical Reports Server (NTRS)

Although the combustion of hydrocarbons is our primary source of energy today, the chemical reactions, or pathway, by which even the simplest hydro-carbon reacts with atmospheric oxygen to form CO2 and water may not always be known. Furthermore, even when the reaction pathway is known, the reaction rates are always under discussion. The shock tube has been an important and unique tool for building a data base of reaction rates important in the combustion of hydrocarbon fuels. The ability of a shock wave to bring the gas sample to reaction conditions rapidly and homogeneously makes shock-tube studies of reaction kinetics extremely attractive. In addition to the control and uniformity of reaction conditions achieved with shock-wave methods, shock compression can produce gas temperatures far in excess of those in conventional reactors. Argon can be heated to well over 10 000 K, and temperatures around 5000 K are easily obtained with conventional shock-tube techniques. Experiments have proven the validity of shock-wave theory; thus, reaction temperatures and pressures can be calculated from a measurement of the incident shock velocity. A description is given of the chemical shock tube and auxiliary equipment and of two examples of kinetic experiments conducted in a shock tube.

Brabbs, Theodore A.

1986-01-01

85

The applications of chemical thermodynamics and chemical kinetics to planetary atmospheres research  

NASA Technical Reports Server (NTRS)

A review of the applications of chemical thermodynamics and chemical kinetics to planetary atmospheres research during the past four decades is presented with an emphasis on chemical equilibrium models and thermochemical kinetics. Several current problems in planetary atmospheres research such as the origin of the atmospheres of the terrestrial planets, atmosphere-surface interactions on Venus and Mars, deep mixing in the atmospheres of the gas giant planets, and the origin of the atmospheres of outer planet satellites all require laboratory data on the kinetics of thermochemical reactions for their solution.

Fegley, Bruce, Jr.

1990-01-01

86

Ernest Rutherford, Avogadro's Number, and Chemical Kinetics  

NASA Astrophysics Data System (ADS)

The paper presents a way for students to use data from Rutherford's works (1908 - 1911) in order to determine one of the most precise values of Avogadro Constant available at the beginning of the century. A brief discussion of earlier and modern methods for the determination of this fundamental constant is followed by vast quotations from the works of Rutherford, Boltwood and Geiger. Then there are given a dozen of problems and questions for students about these classical experiments; they vary in complexity from rather simple to quite challenging. Additional information and hints are provided to help the students in solving the problems. The last part contains detailed answers and solutions to all problems. The article will be useful for students of general chemistry, radiochemistry and physical chemistry (kinetics).

Leenson, I. A.

1998-08-01

87

LSENS - GENERAL CHEMICAL KINETICS AND SENSITIVITY ANALYSIS CODE  

NASA Technical Reports Server (NTRS)

LSENS has been developed for solving complex, homogeneous, gas-phase, chemical kinetics problems. The motivation for the development of this program is the continuing interest in developing detailed chemical reaction mechanisms for complex reactions such as the combustion of fuels and pollutant formation and destruction. A reaction mechanism is the set of all elementary chemical reactions that are required to describe the process of interest. Mathematical descriptions of chemical kinetics problems constitute sets of coupled, nonlinear, first-order ordinary differential equations (ODEs). The number of ODEs can be very large because of the numerous chemical species involved in the reaction mechanism. Further complicating the situation are the many simultaneous reactions needed to describe the chemical kinetics of practical fuels. For example, the mechanism describing the oxidation of the simplest hydrocarbon fuel, methane, involves over 25 species participating in nearly 100 elementary reaction steps. Validating a chemical reaction mechanism requires repetitive solutions of the governing ODEs for a variety of reaction conditions. Analytical solutions to the systems of ODEs describing chemistry are not possible, except for the simplest cases, which are of little or no practical value. Consequently, there is a need for fast and reliable numerical solution techniques for chemical kinetics problems. In addition to solving the ODEs describing chemical kinetics, it is often necessary to know what effects variations in either initial condition values or chemical reaction mechanism parameters have on the solution. Such a need arises in the development of reaction mechanisms from experimental data. The rate coefficients are often not known with great precision and in general, the experimental data are not sufficiently detailed to accurately estimate the rate coefficient parameters. The development of a reaction mechanism is facilitated by a systematic sensitivity analysis which provides the relationships between the predictions of a kinetics model and the input parameters of the problem. LSENS provides for efficient and accurate chemical kinetics computations and includes sensitivity analysis for a variety of problems, including nonisothermal conditions. LSENS replaces the previous NASA general chemical kinetics codes GCKP and GCKP84. LSENS is designed for flexibility, convenience and computational efficiency. A variety of chemical reaction models can be considered. The models include static system, steady one-dimensional inviscid flow, reaction behind an incident shock wave including boundary layer correction, and the perfectly stirred (highly backmixed) reactor. In addition, computations of equilibrium properties can be performed for the following assigned states, enthalpy and pressure, temperature and pressure, internal energy and volume, and temperature and volume. For static problems LSENS computes sensitivity coefficients with respect to the initial values of the dependent variables and/or the three rates coefficient parameters of each chemical reaction. To integrate the ODEs describing chemical kinetics problems, LSENS uses the packaged code LSODE, the Livermore Solver for Ordinary Differential Equations, because it has been shown to be the most efficient and accurate code for solving such problems. The sensitivity analysis computations use the decoupled direct method, as implemented by Dunker and modified by Radhakrishnan. This method has shown greater efficiency and stability with equal or better accuracy than other methods of sensitivity analysis. LSENS is written in FORTRAN 77 with the exception of the NAMELIST extensions used for input. While this makes the code fairly machine independent, execution times on IBM PC compatibles would be unacceptable to most users. LSENS has been successfully implemented on a Sun4 running SunOS and a DEC VAX running VMS. With minor modifications, it should also be easily implemented on other platforms with FORTRAN compilers which support NAMELIST input. LSENS required 4Mb of RAM under Sun

Bittker, D. A.

1994-01-01

88

Chemical oxidation kinetics of pyrite in bioleaching processes  

Microsoft Academic Search

Bio-oxidation experiments with Leptospirillum bacteria were used to determine the chemical oxidation kinetics of pyrite in acidic ferric sulphate solutions (0.1–0.2 M) at 30°C and pH 1.6. The proposed method is applicable because the oxidation of pyrite with Leptospirillum bacteria consists of two sub-processes: (i) Pyrite is chemically oxidized with ferric iron to sulphate and ferrous iron, (ii) Ferric iron

M Boon; J. J Heijnen

1998-01-01

89

Kinetic and Chemical Mechanism of Malate Synthase from Mycobacterium tuberculosis  

PubMed Central

Malate synthase catalyzes the Claisen-like condensation of acetyl-coenzyme A and glyoxylate in the glyoxylate shunt of the citric acid cycle. The Mycobacterium tuberculosis malate synthase G gene, glcB, was cloned, and the N-terminal His6 tagged 80 kDa protein was expressed in soluble form and purified by metal affinity chromatography. A chromogenic 4,4?-dithiodipyridine assay did not yield linear kinetics, but the generation of an active site directed mutant, C619S, gave an active enzyme and linear kinetics. The resulting mutant exhibited comparable kinetics to wild type and was used for the full kinetic analysis. Initial velocity studies were intersecting suggesting a sequential mechanism, which was confirmed by product and dead-end inhibition. The inhibition studies delineated the ordered binding of glyoxylate followed by AcCoA and the ordered release of CoA followed by malate. The pH dependence of kcat and kcat/Kgly are both bell-shaped and catalysis depends on a general base (pK 5.3) and a general acid (pK 9.2). Primary kinetic isotope effects determined using [C2H3-methyl] acetyl-CoA suggested that proton removal and carbon-carbon bond formation were partially rate-limiting. Solvent kinetic isotope effects on kcat suggested the hydrolysis of the malyl-CoA intermediate was also partially rate-limiting. Multiple kinetic isotope effects, utilizing D2O and [C2H3-methyl] acetyl-CoA, confirmed a stepwise mechanism in which the step exhibiting primary kinetic isotope effects precedes the step exhibiting the solvent isotope effects. The kinetic data and the pH dependence of the kinetic parameters were combined with existing structural and mutagenesis data to propose a chemical mechanism for malate synthase from Mycobacterium tuberculosis.

Quartararo, Christine E.; Blanchard, John S.

2011-01-01

90

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

SciTech Connect

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.

Crosley, D.R.

1992-09-01

91

Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate  

Microsoft Academic Search

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

Olivier Herbinet; William J. Pitz; Charles K. Westbrook

2008-01-01

92

A small detailed chemical-kinetic mechanism for hydrocarbon combustion  

Microsoft Academic Search

A chemical-kinetic mechanism is presented that is designed to be used for autoignition, deflagrations, detonations, and diffusion flames of a number of different fuels. To keep the mechanism small, attention is restricted to pressures below about 100 atm, temperatures above about 1000 K, and equivalence ratios less than about 3 for the premixed systems, thereby excluding soot formation and low-temperature

M. V. Petrova; F. A. Williams

2006-01-01

93

Chemical Kinetic Studies on Dry Sorbents. Final Report.  

National Technical Information Service (NTIS)

The scope of this research investigation has included a review of potential additives suitable for dry flue-gas desulfurization (FGD) and a bench scale laboratory study to determine the chemical kinetics for the reaction of five different sorbents with su...

T. C. Keener W. T. Davis

1982-01-01

94

Prospective Chemistry Teachers' Conceptions of Chemical Thermodynamics and Kinetics  

ERIC Educational Resources Information Center

This study aimed at identifying specifically prospective chemistry teachers' difficulties in determining the differences between the concepts of chemical thermodynamics and kinetics. Data were collected from 67 prospective chemistry teachers at Kazim Karabekir Education Faculty of Ataturk University in Turkey during 2005-2006 academic year. Data…

Sozbilir, Mustafa; Pinarbasi, Tacettin; Canpolat, Nurtac

2010-01-01

95

Kinetics of chemical interactions between zirconium alloys and stainless steels.  

National Technical Information Service (NTIS)

The chemical interaction kinetics of reactor core component zirconium alloys and stainless steels at high temperatures was examined. Interaction of as-received and preoxidized Zr1%Nb with X18H10T stainless steel used in WWER type nuclear reactors, and als...

J. Frecska L. Maroti L. Matus

1995-01-01

96

Model reduction for chemical kinetics: An optimization approach  

Microsoft Academic Search

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

Linda Petzold; Wenjie Zhu

1999-01-01

97

Chemical kinetics of hydrocarbon oxidation in gaseous detonations  

Microsoft Academic Search

A theoretical model including a detailed chemical kinetic reaction mechanism for hydrocarbon oxidation is used to examine detonation properties for mixtures of fuel-air, fuel-oxygen diluted with varying amounts of nitrogen. Fuels considered are methane, ethane, acetylene, and methanol. Computed induction lengths are compared with available experimental data for critical tube diameter for initiation of detonation, as well as detonation limits

C WESTBROOK

1982-01-01

98

Detailed chemical kinetic models for the combustion of hydrocarbon fuels  

Microsoft Academic Search

The status of detailed chemical kinetic models for the intermediate to high-temperature oxidation, ignition, combustion of hydrocarbons is reviewed in conjunction with the experiments that validate them.All classes of hydrocarbons are covered including linear and cyclic alkanes, alkenes, alkynes as well as aromatics.

John M. Simmie

2003-01-01

99

Binomial leap methods for simulating stochastic chemical kinetics  

Microsoft Academic Search

This paper discusses efficient simulation methods for stochastic chemical kinetics. Based on the tau-leap and midpoint tau-leap methods of Gillespie [D. T. Gillespie, J. Chem. Phys. 115, 1716 (2001)], binomial random variables are used in these leap methods rather than Poisson random variables. The motivation for this approach is to improve the efficiency of the Poisson leap methods by using

Tianhai Tian; Kevin Burrage

2004-01-01

100

Evaluated Chemical Kinetic Rate Constants for Various Gas Phase Reactions  

Microsoft Academic Search

The available information, up to mid-1972, for the rate constants of a series of gas phase chemical reactions has been evaluated critically. For each reaction, relevant thermodynamic data are presented and values for the equilibrium constant expressed in mathematical form. Kinetic data are presented in tabular and graphical form together with a discussion of the pertinent details. Recommended rate constant

Keith Schofield

1973-01-01

101

EQLBRM: A Computer Program to Calculate High Temperature Chemical Equilibrium.  

National Technical Information Service (NTIS)

The report describes a program written to calculate the equilibrium composition of high temperature chemical systems. The program is generally applicable to systems for which the appropriate thermodynamic data is available. The method of calculation is ou...

A. D. Cross

1977-01-01

102

Chemical kinetic performance losses for a hydrogen laser thermal thruster  

NASA Technical Reports Server (NTRS)

Projected requirements for efficient, economical, orbit-raising propulsion systems have generated investigations into several potentially high specific impulse, moderate thrust, advanced systems. One of these systems, laser thermal propulsion, utilizes a high temperature plasma as the enthalpy source. The plasma is sustained by a focused laser beam which maintains the plasma temperature at levels near 20,000 K. Since such temperature levels lead to total dissociation and high ionization, the plasma thruster system potentially has a high specific impulse decrement due to recombination losses. The nozzle flow is expected to be sufficiently nonequilibrium to warrant concern over the achievable specific impluse. This investigation was an attempt at evaluation of those losses. The One-Dimensional Kinetics (ODK) option of the Two-Dimensional Kinetics (TDK) Computer Program was used with a chemical kinetics rate set obtained from available literature to determine the chemical kinetic energy losses for typical plasma thruster conditions. The rates were varied about the nominal accepted values to band the possible losses. Kinetic losses were shown to be highly significant for a laser thermal thruster using hydrogen. A 30 percent reduction in specific impulse is possible simply due to the inability to completely extract the molecular recombination energy.

Mccay, T. D.; Dexter, C. E.

1985-01-01

103

Detailed chemical kinetic modeling of diesel combustion with oxygenated fuels  

SciTech Connect

The influence of oxygenated hydrocarbons as additives to diesel fuels on ignition, NOx emissions and soot production has been examined using a detailed chemical kinetic reaction mechanism. N-heptane was used as a representative diesel fuel, and methanol, ethanol, dimethyl ether and dimethoxymethane were used as oxygenated fuel additives. It was found that addition of oxygenated hydrocarbons reduced NOx levels and reduced the production of soot precursors. When the overall oxygen content in the fuel reached approximately 25% by mass, production of soot precursors fell effectively to zero, in agreement with experimental studies. The kinetic factors responsible for these observations are discussed.

Pitz, W J; Curran, H J; Fisher, E; Glaude, P A; Marinov, N M; Westbrook, C K

1999-10-28

104

A pared-down gas-phase kinetics for the chemical oxygen-iodine laser medium  

NASA Astrophysics Data System (ADS)

Kinetic data obtained in the last decade has resulted in revisions of some mechanisms of excitation and deactivation of excited states in the chemical oxygen-iodine laser (COIL) medium. This review considers new kinetic data and presents analyses of the mechanisms of pumping and quenching of electronically and vibrationally excited states in the oxygen-iodine laser media. An effective three-level model of I2 molecule excitation and relaxation has been developed. The calculated effective rate constants for deactivation of I2(X,11 ? ? ? 24) by O2, N2, He and CO2 are presented. A simplified kinetic package for the COIL active medium is recommended. This model consists of a 30-reaction set with 14 species. The results of calculations utilizing simplified model are in good agreement with the experimental data.

Pichugin, S. Yu.; Heaven, M. C.

2013-11-01

105

DNA as a universal substrate for chemical kinetics  

PubMed Central

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.

Soloveichik, David; Seelig, Georg; Winfree, Erik

2010-01-01

106

Numerical Simulation of SNCR Technology with Simplified Chemical Kinetics Model  

NASA Astrophysics Data System (ADS)

The paper deals with numerical simulation of SNCR method. For numerical modelling was used CFD code Ansys/CFX. SNCR method was described by dominant chemical reaction, which were look up NIST Chemical database. The reactions including reduction of NOx and concentration change of pollutants, like N2O and CO in flue gas too. Proposed chemical kinetics and CFD model was applied to two boilers. Both simulations were compared with experimental measurements. First simulation was used to validation of chemical mechanism. Second simulation was based on first simulation and it was used to verification of compiled SNCR chemical mechanism. Next the new variant of the reagent penetration lance was proposed and compared with the original variants.

Blejcha?, T.; Dolní?ková, D.

2013-04-01

107

Chemical Kinetic Study of Toluene Oxidation Under Premixed and Nonpremixed Conditions  

SciTech Connect

A study was performed to elucidate the chemical-kinetic mechanism of combustion of toluene. A detailed chemical-kinetic mechanism for toluene was improved by adding a more accurate description of the phenyl + O{sub 2} reaction channels, toluene decomposition reactions and the benzyl + O reaction. Results of the chemical kinetic mechanism are compared with experimental data obtained from premixed and non-premixed systems. Under premixed conditions, predicted ignition delay times are compared with new experimental data obtained in shock tube. Also, calculated species concentration histories are compared to experimental flow reactor data from the literature. Under non-premixed conditions, critical conditions of extinction and autoignition were measured in strained laminar flows in the counterflow configuration. Numerical calculations are performed using the chemical-kinetic mechanism at conditions corresponding to those in the experiments. Critical conditions of extinction and autoignition are predicted and compared with the experimental data. Comparisons between the model predictions and experimental results of ignition delay times in shock tube, and extinction and autoignition in non-premixed systems show that the chemical-kinetic mechanism predicts that toluene/air is overall less reactive than observed in the experiments. For both premixed and non-premixed systems, sensitivity analysis was used to identify the reaction rate constants that control the overall rate of oxidation in each of the systems considered. Under shock tube conditions, the reactions that influence ignition delay time are H + O{sub 2} chain branching, the toluene decomposition reaction to give an H atom, and the toluene + H abstraction reaction. The reactions that influence autoignition in non-premixed systems involve the benzyl + HO{sub 2} reaction and the phenyl + O{sub 2} reaction.

Costa, I D; Bozzelli, J W; Seiser, R; Pitz, W J; Westbrook, C K; Chen, C -; Fournet, R; Seshadri, K; Battin-Leclerc, F; Billaud, F

2003-12-10

108

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

SciTech Connect

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.

Grout, Ray W [ORNL

2012-01-01

109

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

SciTech Connect

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.

Sankaran, R.; Grout, R.

2012-01-01

110

Chemical kinetic modeling of jet fuel autoxidation and antioxidant chemistry  

SciTech Connect

Chemical kinetic modeling has been performed in order to simulate the chemical processes that occur during the autoxidation of jet fuels at temperatures near 200[degree] C. Rate parameters are estimated for the elementary reactions that comprise the mechanism. The mechanism used treats the fuel and antioxidant species as single compounds. The model is able to reproduce the autoxidation chain mechanism that is responsible for oxygen removal in the fuel. The inhibition of oxygen removal by antioxidants is reproduced successfully by the model. Also, the model predicts that the thermal decomposition of alkyl hydroperoxides, even at very small conversions, can play a crucial role in the oxidation mechanism.

Zabarnick, S. (Univ. of Dayton Research Inst., OH (United States). Applied Physics Division)

1993-06-01

111

Chemical Kinetic Models for HCCI and Diesel Combustion  

SciTech Connect

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.

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

2008-10-30

112

Single-molecule chemical reaction reveals molecular reaction kinetics and dynamics.  

PubMed

Understanding the microscopic elementary process of chemical reactions, especially in condensed phase, is highly desirable for improvement of efficiencies in industrial chemical processes. Here we show an approach to gaining new insights into elementary reactions in condensed phase by combining quantum chemical calculations with a single-molecule analysis. Elementary chemical reactions in liquid-phase, revealed from quantum chemical calculations, are studied by tracking the fluorescence of single dye molecules undergoing a reversible redox process. Statistical analyses of single-molecule trajectories reveal molecular reaction kinetics and dynamics of elementary reactions. The reactivity dynamic fluctuations of single molecules are evidenced and probably arise from either or both of the low-frequency approach of the molecule to the internal surface of the SiO2 nanosphere or the molecule diffusion-induced memory effect. This new approach could be applied to other chemical reactions in liquid phase to gain more insight into their molecular reaction kinetics and the dynamics of elementary steps. PMID:24963600

Zhang, Yuwei; Song, Ping; Fu, Qiang; Ruan, Mingbo; Xu, Weilin

2014-01-01

113

Calculation of kinetic rate constants from thermodynamic data  

NASA Technical Reports Server (NTRS)

A new scheme for relating the absolute value for the kinetic rate constant k to the thermodynamic constant Kp is developed for gases. In this report the forward and reverse rate constants are individually related to the thermodynamic data. The kinetic rate constants computed from thermodynamics compare well with the current kinetic rate constants. This method is self consistent and does not have extensive rules. It is first demonstrated and calibrated by computing the HBr reaction from H2 and Br2. This method then is used on other reactions.

Marek, C. John

1995-01-01

114

Evaluated Kinetic and Photochemical Data for Atmospheric Chemistry: Supplement II. CODATA Task Group on Gas Phase Chemical Kinetics  

Microsoft Academic Search

This paper updates and extends previous critical evaluations of the kinetics and photochemistry of gas phase chemical reactions of neutral species involved in atmosphere chemistry [J. Phys. Chem. Ref. Data 9, 295 (1980); 11 327 (1982)]. The work has been carried out by the authors under the auspices of the CODATA Task Group on Gas Phase Chemical Kinetics. Data sheets

D. L. Baulch; R. A. Cox; R. F. Hampson; J. Troe; R. T. Watson

1984-01-01

115

Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate  

SciTech Connect

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.

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

2007-09-17

116

Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate  

SciTech Connect

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)

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

2008-08-15

117

Simplifying chemical kinetics intrinsic low-dimensional manifoldsin composition space  

Microsoft Academic Search

A general procedure for simplifying chemical kinetics is developed,\\u000d\\u000a\\u0009based on the dynamical systems approach. In contrast to conventional\\u000d\\u000a\\u0009reduced mechanisms no information is required concerning which reactions\\u000d\\u000a\\u0009are to be assumed to be in partial equilibrium nor which species\\u000d\\u000a\\u0009are assumed to be in steady state. The only “inputs” to the procedure\\u000d\\u000a\\u0009are the detailed kinetics mechanism and the

U. Maas; S. B. Pope

1992-01-01

118

QUANTUM CHEMICAL CALCULATIONS IN INDUSTRIAL LIQUID CRYSTAL RESEARCH  

Microsoft Academic Search

In advance to syntheses in the laboratory, it is very useful, to have quick and easy procedures available, allowing the calculation of physical properties of liquid crystal materials without any experimental basis. Using different quantum chemical methods, it is possible to calculate molecular data like electrical dipole moment and polarizability including the anisotropy of these data. By comparison of the

Dietrich Demus; Takashi Inukai

2003-01-01

119

Carbon Footprint Calculations: An Application of Chemical Principles  

ERIC Educational Resources Information Center

Topics commonly taught in a general chemistry course can be used to calculate the quantity of carbon dioxide emitted into the atmosphere by various human activities. Each calculation begins with the balanced chemical equation for the reaction that produces the CO[subscript 2] gas. Stoichiometry, thermochemistry, the ideal gas law, and dimensional…

Treptow, Richard S.

2010-01-01

120

Sparse matrix methods for chemical process separation calculations on supercomputers  

Microsoft Academic Search

For many complex chemical processes, multistage, multicornponent separation calculations dominate the computation time in a plantwide simulation. This paper focuses on using the frontal method on supercomputers to solve the large, sparse linear equation systems arising in process separation calculations. The motivation is that the frontal method takes advantage of vector computers by treating parts of the sparse matrix asfdl

Stephen E. Zitney

1992-01-01

121

Analytical Derivation of Moment Equations in Stochastic Chemical Kinetics  

PubMed Central

The master probability equation captures the dynamic behavior of a variety of stochastic phenomena that can be modeled as Markov processes. Analytical solutions to the master equation are hard to come by though because they require the enumeration of all possible states and the determination of the transition probabilities between any two states. These two tasks quickly become intractable for all but the simplest of systems. Instead of determining how the probability distribution changes in time, we can express the master probability distribution as a function of its moments, and, we can then write transient equations for the probability distribution moments. In 1949, Moyal defined the derivative, or jump, moments of the master probability distribution. These are measures of the rate of change in the probability distribution moment values, i.e. what the impact is of any given transition between states on the moment values. In this paper we present a general scheme for deriving analytical moment equations for any N-dimensional Markov process as a function of the jump moments. Importantly, we propose a scheme to derive analytical expressions for the jump moments for any N-dimensional Markov process. To better illustrate the concepts, we focus on stochastic chemical kinetics models for which we derive analytical relations for jump moments of arbitrary order. Chemical kinetics models are widely used to capture the dynamic behavior of biological systems. The elements in the jump moment expressions are a function of the stoichiometric matrix and the reaction propensities, i.e the probabilistic reaction rates. We use two toy examples, a linear and a non-linear set of reactions, to demonstrate the applicability and limitations of the scheme. Finally, we provide an estimate on the minimum number of moments necessary to obtain statistical significant data that would uniquely determine the dynamics of the underlying stochastic chemical kinetic system. The first two moments only provide limited information, especially when complex, non-linear dynamics are involved.

Sotiropoulos, Vassilios; Kaznessis, Yiannis N.

2011-01-01

122

Detailed Chemical Kinetic Modeling of Diesel Combustion with Oxygenated Fuels  

SciTech Connect

Emission standards for diesel engines in vehicles have been steadily reduced in recent years, and a great deal of research and development effort has been focused on reducing particulate and nitrogen oxide emissions. One promising approach to reducing emissions involves the addition of oxygen to the fuel, generally by adding an oxygenated compound to the normal diesel fuel. Miyamoto et al. [1] showed experimentally that particulate levels can be significantly reduced by adding oxygenated species to the fuel. They found the Bosch smoke number (a measure of the particulate or soot levels in diesel exhaust) falls from about 55% for conventional diesel fuel to less than 1% when the oxygen content of the fuel is above about 25% by mass, as shown in Figure 1. It has been well established that addition of oxygenates to automotive fuel, including both diesel fuel as well as gasoline, reduces NOx and CO emissions by reducing flame temperatures. This is the basis for addition of oxygenates to produce reformulated gasoline in selected portions of the country. Of course, this is also accompanied by a slight reduction in fuel economy. A new overall picture of diesel combustion has been developed by Dec [2], in which laser diagnostic studies identified stages in diesel combustion that had not previously been recognized. These stages are summarized in Figure 2. The evolution of the diesel spray is shown, starting as a liquid jet that vaporizes and entrains hot air from the combustion chamber. This relatively steady process continues as long as fuel is being injected. In particular, Dec showed that the fuel spray vaporizes and mixes with air and products of earlier combustion to provide a region in which a gas phase, premixed fuel-rich ignition and burn occurs. The products of this ignition are then observed experimentally to lead rapidly to formation of soot particles, which subsequently are consumed in a diffusion flame. Recently, Flynn et al. [3] used a chemical kinetic and mixing model to study the premixed, rich ignition process. Using n-heptane as a representative diesel fuel, they showed that addition of an oxygenated additive, methanol, to the fuel reduced the concentrations of a number of hydrocarbon species in the products of the rich ignition. Specifically, methanol addition reduced the total concentrations of acetylene, ethylene and 1,3-butadiene, as well as propargyl and vinyl radicals, in the ignition products. These are the same species shown in a number of studies [4-6] to be responsible for formation of aromatic and polycyclic aromatic species in flames, species which lead eventually to production of soot. Flynn et al. did not, however, examine the kinetic processes responsible for the computed reduction in production of soot precursor species. At least two hypotheses have been advanced to explain the role that oxygenated species play in diesel ignition and the reduction in the concentrations of these species. The first is that the additive, methanol in the case of Flynn et al., does not contain any C-C bonds and cannot then produce significant levels of the species such as acetylene, ethylene or the unsaturated radicals which are known to lead to aromatic species. The second hypothesis is that the product distribution changes very naturally as oxygen is added and the overall equivalence ratio is reduced. In the present study, we repeat the ignition calculations of Flynn et al. and include a number of other oxygenated species to determine which of these theories is more applicable to this model.

Curran, H J; Fisher, E M; Glaude, P-A; Marinov, N M; Pitz, W J; Westbrook, C K; Flynn, P F; Durrett, R P; zur Loye, A O; Akinyemi, O C; Dryer, F L

2000-01-11

123

Detailed Chemical Kinetic Reaction Mechanisms for Incineration of Organophosphorus and Fluoro-Organophosphorus Compounds  

Microsoft Academic Search

A detailed chemical kinetic reaction mechanism is developed to describe incineration of the chemical warfare nerve agent sarin (GB), based on commonly used principles of bond additivity and hierarchical reaction mechanisms. The mechanism is based on previous kinetic models of organophosphorus compounds such as TMP, DMMP and DIMP that are often used as surrogates to predict incineration of GB. Kinetic

P A Glaude; C Melius; W J Pitz; C K Westbrook

2001-01-01

124

Maximum Probability Reaction Sequences in Stochastic Chemical Kinetic Systems  

PubMed Central

The detailed behavior of many molecular processes in the cell, such as protein folding, protein complex assembly, and gene regulation, transcription and translation, can often be accurately captured by stochastic chemical kinetic models. We investigate a novel computational problem involving these models – that of finding the most-probable sequence of reactions that connects two or more states of the system observed at different times. We describe an efficient method for computing the probability of a given reaction sequence, but argue that computing most-probable reaction sequences is EXPSPACE-hard. We develop exact (exhaustive) and approximate algorithms for finding most-probable reaction sequences. We evaluate these methods on test problems relating to a recently-proposed stochastic model of folding of the Trp-cage peptide. Our results provide new computational tools for analyzing stochastic chemical models, and demonstrate their utility in illuminating the behavior of real-world systems.

Salehi, Maryam; Perkins, Theodore J.

2010-01-01

125

Detailed Chemical Kinetic Mechanisms for Combustion of Oxygenated Fuels  

SciTech Connect

Thermodynamic properties and detailed chemical kinetic models have been developed for the combustion of two oxygenates: methyl butanoate, a model compound for biodiesel fuels, and methyl formate, a related simpler molecule. Bond additivity methods and rules for estimating kinetic parameters were adopted from hydrocarbon combustion and extended. The resulting mechanisms have been tested against the limited combustion data available in the literature, which was obtained at low temperature, subatmospheric conditions in closed vessels, using pressure measurements as the main diagnostic. Some qualitative agreement was obtained, but the experimental data consistently indicated lower overall reactivities than the model, differing by factors of 10 to 50. This discrepancy, which occurs for species with well-established kinetic mechanisms as well as for methyl esters, is tentatively ascribed to the presence of wall reactions in the experiments. The model predicts a region of weak or negative dependence of overall reaction rate on temperature for each methyl ester. Examination of the reaction fluxes provides an explanation of this behavior, involving a temperature-dependent competition between chain-propagating unimolecular decomposition processes and chain-branching processes, similar to that accepted for hydrocarbons. There is an urgent need to obtain more complete experimental data under well-characterized conditions for thorough testing of the model.

Fisher, E.M.; Pitz, W.J.; Curran, H.J.; Westbrook, C.K.

2000-01-11

126

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

Microsoft Academic Search

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

W. Pitz; C. K. Westbrook

1986-01-01

127

Computational study of graphene growth on copper by first-principles and kinetic Monte Carlo calculations.  

PubMed

In this work the growth of a graphene monolayer on copper substrate, as typically achieved via chemical vapor deposition of propene (C3H6), was investigated by first-principles and kinetic Monte Carlo calculations. A comparison between calculated C1s core-level binding energies and electron spectroscopy measurements showed that graphene nucleates from isolated carbon atoms adsorbed on surface defects or sub-superficial layers upon hydrocarbon fragmentation. In this respect, ab initio nudged elastic band simulations yield the energetic barriers characterizing the diffusion of elemental carbon on the Cu(111) surface and atomic carbon uptake by the growing graphene film. Our calculations highlight a strong interaction between the growing film edges and the copper substrate, indicative of the importance of the grain boundaries in the epitaxy process. Furthermore, we used activation energies to compute the reaction rates for the different mechanisms occurring at the carbon-copper interface via harmonic transition state theory. Finally, we simulated the long-time system growth evolution through a kinetic Monte Carlo approach for different temperatures and coverage. Our ab initio and Monte Carlo simulations of the out-of-equilibrium system point towards a growth model strikingly different from that of standard film growth. Graphene growth on copper turns out to be a catalytic, thermally-activated process that nucleates from carbon monomers, proceeds by adsorption of carbon atoms, and is not self-limiting. Furthermore, graphene growth seems to be more effective at carbon supersaturation of the surface-a clear fingerprint of a large activation barrier for C attachment. Our growth model and computational results are in good agreement with recent X-ray photoelectron spectroscopy experimental measurements. PMID:24939464

Taioli, Simone

2014-07-01

128

A Hybrid Computer Program for Rapidly Solving Flowing or Static Chemical Kinetic Problems Involving Many Chemical Species.  

National Technical Information Service (NTIS)

A hybrid chemical kinetic computer program was assembled which provides a rapid solution to problems involving flowing or static, chemically reacting, gas mixtures. The computer program uses existing subroutines for problem setup, initialization, and prel...

A. G. Mclain C. S. R. Rao

1976-01-01

129

Quasi-analytic point reactor kinetics calculations using individual precursor data  

Microsoft Academic Search

It has become an industry standard to use the classic six-group delayed neutron representation in reactor kinetics calculations. The purpose of this work is to modify the point reactor kinetics equations to consider each of the 105 precursors explicitly, and compare the results for simple step changes in reactivity (e.g., as in control rod calibration curves) using 105 precursors to

M. C. Brady; R. T. Perry; W. B. Wilson; T. R. England

1985-01-01

130

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

PubMed Central

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.

2012-01-01

131

Thermodynamic and Kinetic Properties of Metal Hydrides from First-Principles Calculations  

NASA Astrophysics Data System (ADS)

In an effort to minimize the worldwide dependence on fossil fuels, much research has focused on the development of hydrogen fuel cell vehicles. Among the many challenges currently facing the transition to such an alternative energy economy is the storage of hydrogen in an economical and practical way. One class of materials that has presented itself as a possible candidate is solid metal hydrides. These materials chemically bind hydrogen and on heating, release the gas which can then be used to generate power as needed for the vehicle. In order to meet guidelines that have been set for such a storage system, hydrogen must be released rapidly in a narrow temperature range of -40 to 80°C with all reactions being reversible. This sets both thermodynamic and kinetic requirements for the design of candidate metal hydrides. First-principles calculations are well-suited for the task of exploring reactions involving metal hydrides. Here, density-functional theory is used to calculate properties of these materials at the quantum mechanical level of accuracy. In particular, three systems have been investigated: 1. Li-Mg-N-H. Reactions between all known compounds in this system are systematically investigated in order to predict thermodynamically allowed reactions that release hydrogen. The properties of these reactions are compared to the requirements set for hydrogen storage systems. Additionally, ground-state structures are predicted for Li2Mg(NH)2 and Li 4Mg(NH)3. 2. Na-Al-H. The kinetics of mass transport during the (de)hydrogenation of the well-known metal hydride NaAlH4 are investigated. A model is developed to study the flux of native defects through phases involved in these reactions. Since it is also known that titanium is an effective catalyst for both dehydrogenation and rehydrogenation, the effect of Ti substitution in bulk lattices on the kinetics of mass transport is investigated. Results are compared to experiments in order to determine if mass transport represents the rate-limiting process during de- or rehydrogenation and what the effect of Ti may be. 3. Si-H. Properties of the recently synthesized compound SiH4(H 2)2 are investigated. Under high pressures, hydrogen binding to SiH4 exhibits characteristics of both physical and chemical bonds. A ground-state structure is predicted for this phase and the vibrational and bonding properties are investigated in order to determine the origin of the unusual binding between H2 and SiH4.

Michel, Kyle Jay

132

On a so-called "kinetic anomeric effect" in chemical glycosylation.  

PubMed

Commentary on diastereoselectivity in chemical glycosylation reactions, and dismissal of the influence of stereoelectronic effects analogous to the anomeric effect in kinetically controlled reactions. PMID:22336963

Cumpstey, Ian

2012-04-01

133

Kinetic and Chemical Mechanism of ?-Isopropylmalate Synthase from Mycobacterium tuberculosis  

PubMed Central

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.

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

2008-01-01

134

High Temperature Chemical Kinetic Combustion Modeling of Lightly Methylated Alkanes  

SciTech Connect

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.

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

2011-03-01

135

Fluidity dependence of deprotonation kinetics of chemically amplified resist  

NASA Astrophysics Data System (ADS)

Chemically amplified resists have been widely used in the mass production line. An acid generation mechanism induced by ionizing radiation with extreme ultraviolet (EUV) and electron beam is an important issue for improvement of the resist performance such as sensitivity, roughness, and resolution below 16 nm. However, the details of deprotonation kinetics from the ionized resist solid film immediately after the ionization have been still unclear. In this study, pulse radiolysis of highly concentrated poly(4-hydroxystylene) (PHS) solutions was performed. The viscosity dependence on the deprotonation dynamics of the ionized concentrated solutions was investigated to clarify the proton generation of ionized PHS in a medium with low mobility. The deprotonation from the PHS radical cation becomes slower with increasing PHS concentration. It is suggested that the deprotonation reaction is slower in a less mobile medium because of decrease of the molecular motions.

Okamoto, Kazumasa; Ishida, Takuya; Yamamoto, Hiroki; Kozawa, Takahiro; Fujiyoshi, Ryoko; Umegaki, Kikuo

2014-03-01

136

Infrared Absorption Spectroscopy and Chemical Kinetics of Free Radicals  

SciTech Connect

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.

Curl, Robert F; Glass, Graham

2004-11-01

137

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

SciTech Connect

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.

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

1994-09-01

138

Calculation, measurement and sensitivity analysis of kinetic parameters of Tehran Research Reactor  

Microsoft Academic Search

Effective delayed neutron fraction ?eff and neutron generation time ? are important factors in reactor physics calculation and transient analysis. In the first stage of this research, these kinetic parameters have been calculated for two states of Tehran Research Reactor (TRR), i.e. cold (fuel, clad and coolant temperatures equal to 20°C) and hot (fuel, clad and coolant temperatures of 65,

S. A. Hosseini; N. Vosoughi; M. B. Ghofrani; M. Gharib

2010-01-01

139

A small detailed chemical-kinetic mechanism for hydrocarbon combustion  

SciTech Connect

A chemical-kinetic mechanism is presented that is designed to be used for autoignition, deflagrations, detonations, and diffusion flames of a number of different fuels. To keep the mechanism small, attention is restricted to pressures below about 100 atm, temperatures above about 1000 K, and equivalence ratios less than about 3 for the premixed systems, thereby excluding soot formation and low-temperature fuel-peroxide chemistry. Under these restrictions, hydrogen combustion is included with 21 steps among 8 chemical species, combustion of carbon monoxide with 30 steps among 11 species, methane, methanol, ethane, ethylene, and acetylene combustion with 134 steps among 30 species, and propane, propene, allene, and propyne combustion with 177 steps among 37 species. The mechanism has been extensively tested previously for all of these fuels except propane, propene, allene, and propyne. Tests are reported here for these last four fuels through comparisons with experiments and with predictions of other mechanisms for deflagration velocities and shock-tube ignition. (author)

Petrova, M.V.; Williams, F.A. [Center for Energy Research, Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States)

2006-02-01

140

Standard chemical oxygen-iodine laser kinetics package. Revision. Final report, August 1987March 1988  

Microsoft Academic Search

It has been long recognized that continuous-wave (CW) chemical lasers represent an extremely complex interaction between fluid mechanics, chemical kinetics, and optical physics. The chemical oxygen-iodine laser presents additional problems in that the energy-storage medium, singlet oxygen, is generated by a liquid-gas phase reaction. The kinetics of chemical oxygen-iodine lasers can be divided into five categories: (1) the chemistry of

G. P. Perram; G. D. Hager

1988-01-01

141

Vibrational spectroscopic studies of Isoleucine by quantum chemical calculations.  

PubMed

In this work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of Isoleucine (2-Amino-3-methylpentanoic acid). The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments, thermodynamics properties, NBO analyses, NMR chemical shifts and ultraviolet-visible spectral interpretation of Isoleucine have been studied by performing MP2 and DFT/cc-pVDZ level of theory. The FTIR, FT-Raman spectra were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. The UV-visible absorption spectra of the compound were recorded in the range of 200-800 nm. Computational calculations at MP2 and B3LYP level with basis set of cc-pVDZ is employed in complete assignments of Isoleucine molecule on the basis of the potential energy distribution (PED) of the vibrational modes, calculated using VEDA-4 program. The calculated wavenumbers are compared with the experimental values. The difference between the observed and calculated wavenumber values of most of the fundamentals is very small. (13)C and (1)H nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method and compared with experimental results. The formation of hydrogen bond was investigated in terms of the charge density by the NBO calculations. Based on the UV spectra and TD-DFT calculations, the electronic structure and the assignments of the absorption bands were carried out. Besides, molecular electrostatic potential (MEP) were investigated using theoretical calculations. PMID:24508874

Moorthi, P P; Gunasekaran, S; Ramkumaar, G R

2014-04-24

142

Chemical kinetic analysis of hydrogen-air ignition and reaction times  

NASA Technical Reports Server (NTRS)

An anaytical study of hydrogen air kinetics was performed. Calculations were made over a range of pressure from 0.2 to 4.0 atm, temperatures from 850 to 2000 K, and mixture equivalence ratios from 0.2 to 2.0. The finite rate chemistry model included 60 reactions in 20 species of the H2-O2-N2 system. The calculations also included an assessment of how small amounts of the chemicals H2O, NOx, H2O2, and O3 in the initial mixture affect ignition and reaction times, and how the variation of the third body efficiency of H2O relative of N2 in certain key reactions may affect reaction time. The results indicate that for mixture equivalence ratios between 0.5 and 1.7, ignition times are nearly constant; however, the presence of H2O and NO can have significant effects on ignition times, depending on the mixture temperature. Reaction time is dominantly influenced by pressure but is nearly independent of initial temperature, equivalence ratio, and the addition of chemicals. Effects of kinetics on reaction at supersonic combustor conditions are discussed.

Rogers, R. C.; Schexnayder, C. J., Jr.

1981-01-01

143

Path-integral Monte Carlo calculation of the kinetic energy of condensed lithium  

Microsoft Academic Search

We report path-integral Monte Carlo calculations of the kinetic energy of condensed lithium for several temperatures in both the solid and liquid phases. The excess kinetic energy of lithium decreases from about 10.4% of the classical value at 300 K to 3.2% at 520 K indicating a very slow decay with temperature. A Wigner-Kirkwood perturbation treatment of quantum effects to

Claudia Filippi; David M. Ceperley

1998-01-01

144

Melting behavior of typical thermoplastic materials--an experimental and chemical kinetics study.  

PubMed

A medium-scale melting experiment rig was designed and constructed in this study. A detailed experimental study was conducted on the melting behavior and the chemical kinetic characteristics of three typical thermoplastic materials, including polypropylene (PP), polyethylene (PE) and polystyrene (PS). It is observed that the thermal decomposition of the thermoplastic materials mainly consists of three stages: the initial heating stage, the melting-dominated stage and the gasification-dominated stage. Melting of the materials examined takes place within a certain temperature range. The melting temperature of PS is the lowest, moreover, it takes the shortest time to be completely liquefied. To quantitatively represent the chemical kinetics, an nth-order reaction model was employed to interpret the thermal decomposition behavior of the materials. The calculated reaction order is largely in accordance with the small-scale thermal gravimetric analysis (TGA). The small difference between the results and TGA data suggests that there are some limitations in the small-scale experiments in simulating the behavior of thermoplastic materials in a thermal hazard. Therefore, investigating the thermal physical and chemical properties of the thermoplastic materials and their thermal hazard prevention in medium or large-scale experiments is necessary for the fire safety considerations of polymer materials. PMID:24007994

Wang, Nan; Tu, Ran; Ma, Xin; Xie, Qiyuan; Jiang, Xi

2013-11-15

145

Chemical kinetics of an argon/methane plasma in a hydrogen reforming reactor  

NASA Astrophysics Data System (ADS)

We have studied the characteristics of a plasma reactor for the promotion of chemical reactions aimed to hydrogen reforming from gaseous hydrocarbons. A plasma torch-like electrode configuration was powered by a limited current, high voltage DC source. Using as process gas an argon/methane mixture at atmospheric pressure, we have produced an intermittent spark discharge which has been investigated at different operating parameters. Experimental information on the discharge have been used to perform a numerical simulation of the plasma chemical kinetics. The evolution of the gas-phase composition during and after the interaction in the discharge region was calculated under different operating conditions. The results have been used to predict the hydrogen production yield in the experiments and to study the role played by the different discharge parameters in order to determine the optimal interaction between plasma and gas mixture.

Barni, R.; Benocci, R.; Broggi, C.; Riccardi, C.

2006-08-01

146

Standard Chemical Oxygen-Iodine Laser Kinetics Package. Final report, August 1987March 1988  

Microsoft Academic Search

This report presents the Air Force Weapons Laboratory Standard Chemical Oxygen-Iodine Laser Kinetics Package. A complete reaction scheme including recommended rate coefficients for modeling the gas-phase kinetics of chemical oxygen-iodine lasers (COIL) was established to provide a common basis for the research and development of COIL devices. A review of the experimental kinetic data base from which this model was

G. P. Perram; G. D. Hager

1988-01-01

147

Thermodynamics and Kinetics of Chemical Equilibrium in Solution.  

ERIC Educational Resources Information Center

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)

Leenson, I. A.

1986-01-01

148

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

DOE Data Explorer

The central feature of the Combustion Chemistry project at LLNL is the development, validation, and application of detailed chemical kinetic reaction mechanisms for the combustion of hydrocarbon and other types of chemical fuels. For the past 30 years, LLNL's Chemical Sciences Division has built hydrocarbon mechanisms for fuels from hydrogen and methane through much larger fuels including heptanes and octanes. Other classes of fuels for which models have been developed include flame suppressants such as halons and organophosphates, and air pollutants such as soot and oxides of nitrogen and sulfur. 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.[Taken from https://www-pls.llnl.gov/?url=science_and_technology-chemistry-combustion

149

Cometary impact and amino acid survival - Chemical kinetics and thermochemistry  

USGS Publications Warehouse

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.

Ross, D. S.

2006-01-01

150

Development and validation of a model for the chemical kinetics of graphite oxidation  

NASA Astrophysics Data System (ADS)

A model of the chemical kinetics and primary reactions of graphite oxidation is developed and successfully validated for pyrolytic carbon thin films. The model uses Gaussian distributions of the activation energies for adsorption and desorption and the measured active surface area (ASA) as a function of burn-off. The activation energies distributions and the pre-exponential rate coefficients for the four elementary oxidation kinetics reactions in the model are obtained from the reported measurements of the gases yields and adsorbed oxygen using a multi-parameter optimization algorithm. The model calculates the production rates of CO and CO 2 and the gasification rate as functions of temperature and oxygen partial pressure, and its predictions are in excellent agreement with reported experimental measurements. Results for pyrolytic carbon thin films show that when the oxygen pressure is kept constant, the gasification rate depends on both temperature and ASA until a full burn-off is reached. By contrast, in a depleting oxygen environment, only partial burn-off is possible; gasification ceases following the consumption of the free oxygen in the enclosure. This model represents the first phase in an ongoing effort to develop a model for predicting the oxidation kinetics of nuclear graphite following a massive air ingress in high temperature reactors.

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

2011-04-01

151

A pressure correction method for the calculation of compressible chemical reacting flows  

NASA Technical Reports Server (NTRS)

A recently developed noniterative method for the solution of the transient fluid flow equations at all speed is extended to handle chemical reacting flows. The species conservation equations are loosely coupled into the predictor/multicorrector sequence of the solution procedure. A split-operator method separates the chemical kinetics terms from the fluid-dynamical terms, as well as an implicit differencing method enhance the numerical stability. The method was applied for turbulent diffusion flame calculations and for the analyses of high pressure, axisymmetric turbulent hypersonic nozzle flows. The diffusion flame results were compared with a similar pressure method for fast chemistry integration scheme without operator-splitting. Simulations of the nozzle flow indicated that the nonideal intermolecular effects must be included in the analysis and design of high pressure hypersonic nozzle.

Chen, Z. J.; Chen, C. P.; Chen, Y. S.

1992-01-01

152

Graphing Calculator Strategies for Solving Chemical Equilibrium Problems  

NASA Astrophysics Data System (ADS)

Polynomial equations arising from analysis of the chemical equilibrium state present computational difficulties for many introductory chemistry students. A general method for finding the roots of these polynomial equations using the ubiquitous and inexpensive graphing calculator is presented. It is suggested that important reactions, which are not discussed in introductory chemistry courses because of computational considerations, may now be discussed. Also, complete treatments of equilibrium systems may be given so that students will not have to deal with a complex array of approximate methods.

Donato, Henry, Jr.

1999-05-01

153

A Convenient Spreadsheet Approach to the Calculation of Stability Constants and the Simulation of Kinetics  

Microsoft Academic Search

The described spreadsheet approach is a versatile method for processing data on metal ligand complexes in solution. It provides not only speciations vs pH, but also simulates potentiometric and spectroscopic titrations. Furthermore, metal ligand stability constants can be calculated from potentiometric or spectroscopic data. The approach puts no extra constraints on the experimental conditions of the titrations. Kinetics can be

Jurriaan Huskens; Herman Van Bekkum; Joop A. Peters

1995-01-01

154

Detailed and reduced chemical-kinetic descriptions for hydrocarbon combustion  

NASA Astrophysics Data System (ADS)

Numerical and theoretical studies of autoignition processes of fuels such as propane are in need of realistic simplified chemical-kinetic descriptions that retain the essential features of the detailed descriptions. These descriptions should be computationally feasible and cost-effective. Such descriptions are useful for investigating ignition processes that occur, for example, in homogeneous-charge compression-ignition engines, for studying the structures and dynamics of detonations and in fields such as multi-dimensional Computational Fluid Dynamics (CFD). Reduced chemistry has previously been developed successfully for a number of other hydrocarbon fuels, however, propane has not been considered in this manner. This work focuses on the fuels of propane, as well propene, allene and propyne, for several reasons. The ignition properties of propane resemble those of other higher hydrocarbons but are different from those of the lower hydrocarbons (e.g. ethylene and acetylene). Propane, therefore, may be the smallest hydrocarbon that is representative of higher hydrocarbons in ignition and detonation processes. Since the overall activation energy and ignition times for propane are similar to those of other higher hydrocarbons, including liquid fuels that are suitable for many applications, propane has been used as a model fuel for several numerical and experimental studies. The reason for studying elementary chemistry of propene and C3H4 (allene or propyne) is that during the combustion process, propane breaks down to propene and C3H4 before proceeding to products. Similarly, propene combustion includes C3H4 chemistry. In studying propane combustion, it is therefore necessary to understand the underlying combustion chemistry of propene as well as C3H 4. The first part of this thesis focuses on obtaining and testing a detailed chemical-kinetic description for autoignition of propane, propene and C 3H4, by comparing predictions obtained with this detailed mechanism against numerous experimental data available from shock-tube studies and flame-speed measurements. To keep the detailed mechanism small, attention is restricted to pressures below about 100 atm, temperatures above about 1000 K and equivalence ratios less than about 3. Based on this detailed chemistry description, short (or skeletal) mechanisms are then obtained for each of the three fuels by eliminating reactions that are unimportant for the autoignition process under conditions presented above. This was achieved by utilizing tools such as sensitivity and reaction pathway analyses. Two distinct methodologies were then used in order to obtain a reduced mechanism for autoignition from the short mechanisms. A Systematic Reduction approach is first taken that involves introducing steady-state approximations to as many species as analytically possible. To avoid resorting to numerical methods, the analysis for obtaining ignition times for heptane, presented by Peters and co-workers is followed in order to obtain a rough estimate for an expression of propane ignition time. The results from this expression are then compared to the ignition times obtained computationally with the detailed mechanism. The second method is an Empirical Approach in which chemistry is not derived formally, but rather postulated empirically on the basis of experimental, computational and theoretical observations. As a result, generalized reduced mechanisms are proposed for autoignition of propane, propene and C3H 4. Expressions for ignition times obtained via this empirical approach are compared to the computational results obtained from the detailed mechanism.

Petrova, Maria V.

155

EQ6 Calculations for Chemical Degradation of Navy Waste Packages  

SciTech Connect

The Monitored Geologic Repository Waste Package Operations of the Civilian Radioactive Waste Management System Management & Operating Contractor (CRWMS M&O) performed calculations to provide input for disposal of spent nuclear fuel (SNF) from the Navy (Refs. 1 and 2). The Navy SNF has been considered for disposal at the potential Yucca Mountain site. For some waste packages, the containment may breach (Ref. 3), allowing the influx of water. Water in the waste package may moderate neutrons, increasing the likelihood of a criticality event within the waste package. The water may gradually leach the fissile components and neutron absorbers out of the waste package. In addition, the accumulation of silica (SiO{sub 2}) in the waste package over time may further affect the neutronics of the system. This study presents calculations of the long-term geochemical behavior of waste packages containing the Enhanced Design Alternative (EDA) II inner shell, Navy canister, and basket components. The calculations do not include the Navy SNF in the waste package. The specific study objectives were to determine the chemical composition of the water and the quantity of silicon (Si) and other solid corrosion products in the waste package during the first million years after the waste package is breached. The results of this calculation will be used to ensure that the type and amount of criticality control material used in the waste package design will prevent criticality.

S. LeStrange

1999-11-15

156

Development of chemical kinetic models for lean NOx traps.  

SciTech Connect

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.

Larson, Richard S.

2010-04-01

157

Shock tube and chemical kinetic modeling study of the oxidation of 2,5-dimethylfuran.  

PubMed

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 1998 , 102 ( 52 ), 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 2, 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

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

2013-02-21

158

Application of Chemical Kinetics to Deterioration of Foods.  

ERIC Educational Resources Information Center

Possible modes of food deterioration (such as microbial decay, nonenzymatic browning, senescence, lipid oxidation) are reviewed. A basic mathematical approach to the kinetics of food deterioration, kinetic approach to accelerating shelf-life deterioration, and shelf-life predictions are discussed. (JN)

Labuza, T. P.

1984-01-01

159

Necessary and sufficient conditions for complex balancing in chemical kinetics  

Microsoft Academic Search

In a recent publication (Horn & Jackson [1]) it was shown that complex balancing together with mass action type rate laws ensures certain stability properties of a kinetic system, thereby precluding sustained oscillations, bistability and other types of irregular dynamics. In this paper a necessary condition for complex balancing in general kinetics and necessary and sufficient conditions for complex balancing

F. Horn

1972-01-01

160

Chemical Kinetic Data Base for Combustion Chemistry. Part 2. Methanol  

Microsoft Academic Search

This publication contains evaluated and estimated data on the kinetics of reactions involving methanol and hydroxymethyl radicals and various small inorganic and organic species which are of importance for the proper understanding of methanol combustion and pyrolysis. It is meant to be used in conjunction with the kinetic data given in an earlier publication pertaining to methane pyrolysis and combustion,

Wing Tsang

1987-01-01

161

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

Microsoft Academic Search

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

Yucheng Hu; Tiejun Li; Bin Min

2011-01-01

162

Chemical kinetic modeling of component mixtures relevant to gasoline  

SciTech Connect

Detailed kinetic models of pyrolysis and combustion of hydrocarbon fuels are nowadays widely used in the design of internal combustion engines and these models are effectively applied to help meet the increasingly stringent environmental and energetic standards. In previous studies by the combustion community, such models not only contributed to the understanding of pure component combustion, but also provided a deeper insight into the combustion behavior of complex mixtures. One of the major challenges in this field is now the definition and the development of appropriate surrogate models able to mimic the actual features of real fuels. Real fuels are complex mixtures of thousands of hydrocarbon compounds including linear and branched paraffins, naphthenes, olefins and aromatics. Their behavior can be effectively reproduced by simpler fuel surrogates containing a limited number of components. Aside the most commonly used surrogates containing iso-octane and n-heptane only, the so called Primary Reference Fuels (PRF), new mixtures have recently been suggested to extend the reference components in surrogate mixtures to also include alkenes and aromatics. It is generally agreed that, including representative species for all the main classes of hydrocarbons which can be found in real fuels, it is possible to reproduce very effectively in a wide range of operating conditions not just the auto-ignition propensity of gasoline or Diesel fuels, but also their physical properties and their combustion residuals [1]. In this work, the combustion behavior of several components relevant to gasoline surrogate formulation is computationally examined. The attention is focused on the autoignition of iso-octane, hexene and their mixtures. Some important issues relevant to the experimental and modeling investigation of such fuels are discussed with the help of rapid compression machine data and calculations. Following the model validation, the behavior of mixtures is discussed on the basis of computational results.

Mehl, M; Curran, H J; Pitz, W J; Dooley, S; Westbrook, C K

2008-05-29

163

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

Microsoft Academic Search

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

Elizabeth J. Opila

1994-01-01

164

Heterogeneous chemical kinetics and particle nucleation in interstellar and atmospheric environments  

NASA Astrophysics Data System (ADS)

Dust is believed to play a significant role in the evolution of interstellar clouds and hence in processes such as star formation. The physics involved is similar to that responsible for terrestrial aerosols. Certain chemical reactions in interstellar conditions may only occur on the surface of a host particle and are not viable purely in the gas phase. The traditionally used rate equations approach to describe these reactions fail to account for the statistical fluctuations in the reactant populations, which would be significant in situations where the mean population may be well below unity. This can easily occur in interstellar conditions and quite often in reactions catalysed by terrestrial aerosols. This thesis considers a master equation approach that provides a stochastic description of heterogeneous chemical kinetics and demonstrates that classical kinetics may have been overestimating the reaction rates by one order of magnitude under interstellar conditions. The same idea can be extended to study mantle growth on dust surfaces. Traditionally, this is described using a classical description of nucleation kinetics, generally suitable for large systems. Again, this can be unreliable for heterogeneous nucleation taking place on small particles under low vapour concentration where the mean population of adsorbed nucleating species could be of order unity or less. The the-sis explores a stochastic description of heterogeneous nucleation kinetics and solves the arising equations numerically to demonstrate that the stochastic nucleation rate could be significantly different from that derived using the traditional approach. The chemical composition of interstellar dust has for long puzzled experts. The key to determining this lies in an accurate description of the physical processes underlying the formation of these particles. Magnesium oxide is considered to be one of the major candidates as the primary nucleating material, but recently doubts have been cast over this. However, the models employed in reaching that conclusion seem to be rather inaccurate. The thesis attempts to calculate free energies of molecular clusters using newly designed potential models for MgO. It is found that MgO is probably not the primary nucleating dust species in stellar winds.

Bhatt, Jayesh

165

Review of chemical-kinetic problems of future NASA missions. I - Earth entries  

NASA Technical Reports Server (NTRS)

A number of chemical-kinetic problems related to phenomena occurring behind a shock wave surrounding an object flying in the earth atmosphere are discussed, including the nonequilibrium thermochemical relaxation phenomena occurring behind a shock wave surrounding the flying object, problems related to aerobraking maneuver, the radiation phenomena for shock velocities of up to 12 km/sec, and the determination of rate coefficients for ionization reactions and associated electron-impact ionization reactions. Results of experiments are presented in form of graphs and tables, giving data on the reaction rate coefficients for air, the ionization distances, thermodynamic properties behind a shock wave, radiative heat flux calculations, Damkoehler numbers for the ablation-product layer, together with conclusions.

Park, Chul

1993-01-01

166

Numerical simulation of Jet-A combustion approximated by improved propane chemical kinetics  

NASA Technical Reports Server (NTRS)

Through the effort devoted to the chemical kinetics for propane air combustion, three mechanisms are developed. The full mechanism consists of 131 reactions. This mechanism is used as a guide for the evaluation of other mechanisms, but because of the long expected cpu time, it is not to be incorporated into the computer code KIVA-II for actual simulation. Through the sensitivity analysis, a reduced mechanism of 45 reactions is produced. But the calculated results from the 45 reaction mechanism are always low in temperature. Some efforts are devoted to correct this situation and details are included in this report. A simplified mechanism of reactions is successfully improved and computed results are compared with experimental data. Contour plots of physical parameters and species concentrations and results for emission indices of CO and NOx are presented.

Ying, Shuh-Jing; Nguyen, Hung Lee

1991-01-01

167

Evaluation of Isothermal Chemical-Vapor Infiltration with Langmuir-Hinshelwood Type Kinetics  

Microsoft Academic Search

A model has been developed for the mathematical description of isothermal chemical vapor infiltration (ICVI) processes. Three types of adsorption of the reactive species are incorporated into the kinetic equations: weak associative adsorption, strong associative adsorption, and dissociative adsorption. The kinetic models are based on Langmuir-Hinshelwood equations. Weak associative adsorption of the reactive species gives rise to an exponentially shaped

R. Moene; J. P. Dekker; M. Makkee; J. Schoonman; J. A. Moulijn

1994-01-01

168

Calibration of Chemical Kinetic Models Using Simulations of Small-Scale Cookoff Experiments  

Microsoft Academic Search

Establishing safe handling limits for explosives in elevated temperature environments is a difficult problem that often requires extensive simulation. The largest influence on predicting thermal cookoff safety lies in the chemical kinetic model used in these simulations, and these kinetic model reaction sequences often contain multiple steps. Several small-scale cookoff experiments, notably Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), One-Dimensional

A P Wemhoff; R C Becker; A K Burnham

2008-01-01

169

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

SciTech Connect

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.

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

2009-03-30

170

Chemical Kinetics of Nitrogen-Hydrogen-Fluorine Systems of Interest as Rocket Propellants.  

National Technical Information Service (NTIS)

The principle objective of the program was the study of the chemical kinetics of elementary reactions important in the combustion of several gas phase systems containing nitrogen, hydrogen and fluorine. Combustion system were selected with a view to provi...

D. I. MacLean

1972-01-01

171

Development of AGNES, a Kinetics Code for Fissile Solutions, 1. Calculation of the Radiolytic Gas Void by 'Pressure Model'.  

National Technical Information Service (NTIS)

A kinetics code for fissile solutions, AGNES (Accidentally Generated Nuclear Excursion Simulation code), has been developed. This code calculates the radiolytic gas void effect as a reactivity feedback. Physical and calculative models of the radiolytic ga...

K. Nakajima N. Ohnishi

1986-01-01

172

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

SciTech Connect

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%.

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

173

Chemical kinetic considerations for postflame synthesis of carbon nanotubes in premixed flames using a support catalyst  

SciTech Connect

Multiwalled carbon nanotubes (MWCNTs) on a grid supported cobalt nanocatalyst were grown, by exposing it to combustion gases from ethylene/air rich premixed flames. Ten equivalence ratios ({phi}) were investigated, as follows: 1.37, 1.44, 1.47, 1.50, 1.55, 1.57, 1.62, 1.75, 1.82, and 1.91. MWCNT growth could be observed for the range of equivalence ratios between 1.45 and 1.75, with the best yield restricted to the range 1.5-1.6. A one-dimensional premixed flame code with a postflame heat loss model, including detailed chemistry, was used to estimate the gas phase chemical composition that favors MWCNT growth. The results of the calculations show that the mixture, including the water gas shift reaction, is not even in partial chemical equilibrium. Therefore, past discussions of compositional parameters that relate to optimum carbon nanotube (CNT) growth are revised to include chemical kinetic effects. Specifically, rapid departures of the water gas shift reaction from partial equilibrium and changes in mole fraction ratios of unburned C{sub 2} hydrocarbons to hydrogen correlate well with experimentally observed CNT yields. (author)

Gopinath, Prarthana; Gore, Jay [School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907 (United States)

2007-11-15

174

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

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

175

Calculation of f? and m? at finite chemical potential  

NASA Astrophysics Data System (ADS)

Based on the previous work in Y. Jiang, Y. M. Shi, H. T. Feng, W. M. Sun, and H. S. Zong, Phys. Rev. C 78, 025214 (2008)PRVCAN0556-281310.1103/PhysRevC.78.025214 on the quark-meson vertex and pion properties at finite quark chemical potential, we provide an analytical analysis of the weak decay constant of the pion (f?[?]) and the pion mass (m?[?]) at finite quark chemical potential using the model quark propagator proposed in R. Alkofer, W. Detmold, C. S. Fischer, and P. Maris, Phys. Rev. D 70, 014014 (2004)PRVDAQ0556-282110.1103/PhysRevD.70.014014. It is found that when ? is below a threshold value ?0 (which equals 0.350, 0.377, and 0.341 GeV, for the 2CC, 1R1CC, and 3R parametrizations of the model quark propagator, respectively), f?[?] and m?[?] are kept unchanged from their vacuum values. The value of ?0 is intimately connected with the pole distribution of the model quark propagator and is found to coincide with the threshold value below which the quark-number density vanishes identically. Numerical calculations show that when ? becomes larger than ?0, f?[?] exhibits a sharp decrease whereas m?[?] exhibits a sharp increase. A comparison is given between the results obtained in this paper and those obtained in previous literature.

Jiang, Yu; Shi, Yuan-Mei; Li, Hua; Sun, Wei-Min; Zong, Hong-Shi

2008-12-01

176

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

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

177

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

NASA Astrophysics Data System (ADS)

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.

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

1990-07-01

178

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...

179

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

NASA Astrophysics Data System (ADS)

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.

Stein, David

180

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

PubMed

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

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

2014-04-01

181

Chemical kinetic modeling of propane oxidation behind shock waves  

NASA Technical Reports Server (NTRS)

The stoichiometric combustion of propane behind incident shock waves was studied experimentally and analytically over a temperature range from 1700 K to 2600 K and a pressure range from 1.2 to 1.9 atm. Measurements of the concentrations of carbon monoxide (CO) and carbon dioxide (CO2) and the product of the oxygen atom and carbon dioxide concentrations (O)(CO) were made after passage of the incident shock wave. A kinetic mechanism was developed which, when used in a computer program for a flowing, reacting gas behind an incident shock wave predicted experimentally measured results quite well. Ignition delay times from the literature were also predicted quite well. The kinetic mechanism consisted of 59 individual kinetic steps.

Mclain, A. G.; Jachimowski, C. J.

1977-01-01

182

Equilibrium, chemical kinetic, and transport limitations to diamond growth  

NASA Astrophysics Data System (ADS)

Because of their extreme properties, diamond films have found some industrial applications, i.e., heat sinks and tool coatings. However, to increase their economic attractiveness, the growth rate must be increased, the deposition temperature must be lowered, and single crystal films must be achieved. We have studied two types of chemical vapor deposition systems, hot-filament and microwave assisted, in order to understand the factors limiting diamond growth rate. From simultaneous microbalance growth rate measurements and mass spectrometer measurements, changes in growth rate are correlated with changes in gas phase composition. Measured reaction orders support the proposal that diamond growth occurs through a single-carbon-atom species, e.g., CHsb3. When a two-carbon atom source gas is used, it is likely that the dissociation to two, single-carbon atom species occurs on the substrate surface (dissociative adsorption). Furthermore, a shift to zero-order suggests that the diamond growth is a surface-site limited process at higher hydrocarbon concentrations. The diamond growth rate maximum with pressure is explained by transport limitations of species within the reaction zone. The reported diamond growth rates in the hot-filament reactor are several times higher than those reported by other research groups. These higher growth rates result from surrounding the substrate with the filament. We have used the measured growth rates, filament temperatures, and thermocouple measurements to calculate activation energies for diamond growth. When the filament temperature is used for the calculation, an activation energy of 73 kcal per mole is obtained; however, based on estimated substrate temperatures, an activation energy of 18 kcal per mole is determined. A dimensional analysis approach was developed to select the most important gas phase reactions occurring during diamond CVD. Steady-state analysis of these reactions and the application of mass transport equations lead to the conclusion that diamond growth, in current hot-filament and microwave assisted CVD processes, is occurring in a partial equilibrium environment in which diffusion of atomic hydrogen controls the overall diamond growth rate. The initial stages of diamond growth on non-diamond substrates correspond to carburization, nucleation and growth. When polycrystalline or single crystal diamond is used as a substrate, the carburization and nucleation stages are not observed and growth begins immediately. The nucleation rate depends sensitively on the radiative heat transfer to the substrate. Adding ozone to the hot-filament CVD charge increases the production of carbon monoxide and carbon dioxide; this increase is observed with or without the filament being activated. A consistent effect on the diamond growth rate was not observed when ozone was added to the hot-filament reactor.

Evans, Edward Anthony

183

Calculations of kinetic behavior in the supersonic expansion of a helium plasma in a Laval nozzle  

Microsoft Academic Search

The problem of the expansion of a dense, low-temperature helium plasma in a Laval nozzle is considered. The equations of level-by-level kinetics are solved numerically together with the equations of plasma dynamics in a quasi-one-dimensional approximation. The results of the calculations and the dependence of the solutions on the initial conditions in the critical cross section are discussed. The solutions

N. V. Zakrevskii; G. A. Lukyanov; S. I. Tserkovnyi

1982-01-01

184

Chemical compounds in the remote Pacific troposphere: Comparison between MLOPEX measurements and chemical transport model calculations  

NASA Astrophysics Data System (ADS)

A global three-dimensional chemical transport model, called MOZART (Model of OZone And Related species in the Troposphere), is used to compare calculated abundances of chemical species and their seasonal evolution in the remote Pacific troposphere near Hawaii with values observed during the Mauna Loa Observatory Photochemistry Experiments (MLOPEX 1 and 2). MOZART is a fully diurnal model which calculates the time evolution of about 30 chemical species from the surface to the upper stratosphere. It accounts for surface emissions of source gases, wet and dry depositions, photochemical transformations and transport processes. The dynamical variables are provided by the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM2) at T42 resolution (2.8° × 2.8°) and 18 levels in the vertical. Simulated abundances of 222Rn reveal an underestimate of the transport of continental emissions to the remote Pacific troposphere, more particularly during winter and summer. Calculated concentrations of chemical species are generally in fair agreement with observations. However, the abundances of soluble species are overestimated, leading, for example, to concentrations of nitric acid (HNO3) and hydrogen peroxide (H2O2) which are overpredicted by a factor of 3-8, depending on the season. This feature is attributed to insufficient washout by clouds and precipitation in the model. MOZART succesfully reproduces the development of high-NOx episodes at Mauna Loa Observatory (MLO) associated with anticyclonic conditions to the north of Hawaii and breakdown of the polar jet which tends to deflect to the central Pacific the flow of NOx transported from eastern Asia (China, Japan). During high NOx episodes, the calculated NOx mixing ratio in the vicinity of the MLO increases by about a factor of 3 over its background level (reaching 90-100 pptv) within 3-5 days.

Brasseur, G. P.; Hauglustaine, D. A.; Walters, S.

1996-06-01

185

Detailed Chemical Kinetic Reaction Mechanisms for Incineration of Organophosphorus and Fluoro-Organophosphorus Compounds  

SciTech Connect

A detailed chemical kinetic reaction mechanism is developed to describe incineration of the chemical warfare nerve agent sarin (GB), based on commonly used principles of bond additivity and hierarchical reaction mechanisms. The mechanism is based on previous kinetic models of organophosphorus compounds such as TMP, DMMP and DIMP that are often used as surrogates to predict incineration of GB. Kinetic models of the three surrogates and GB are then used to predict their consumption in a perfectly stirred reactor fueled by natural gas to simulate incineration of these chemicals. Computed results indicate that DIMP is the only one of these surrogates that adequately describes combustion of GB under comparable conditions. The kinetic pathways responsible for these differences in reactivity are identified and discussed. The most important reaction in GB and DIMP that makes them more reactive than TMP or DMMP is found to be a six-center molecular elimination reaction producing propene.

Glaude, P A; Melius, C; Pitz, W J; Westbrook, C K

2001-12-13

186

The toroidal momentum diffusivity in a tokamak plasma: A comparison of fluid and kinetic calculations  

SciTech Connect

Fluid and gyrokinetic calculations of the toroidal momentum diffusivity in a tokamak are compared. The four-moment gyrofluid model predicts the Prandtl number connected with the ion temperature gradient mode reasonably well provided the drift term is kept in the momentum balance. Without the drift term in the momentum balance, some previous gyrofluid models predicted small values of the Prandtl number in the range of experimental observations. It is shown that the drift term enters in the fluid equations through the gyroviscosity. Gyrokinetic calculations of the ion temperature gradient mode with kinetic electrons, and for experimentally relevant parameters yield a Prandtl number in the range 0.7-1.2.

Strintzi, D. [Department of Electrical and Computer Engineering, National Technical University of Athens, GR-157 73 Athens (Greece); Peeters, A. G. [Center for Fusion, Space and Astrophysics, Physics Department, University of Warwick, CV4 7AL, Coventry (United Kingdom); Weiland, J. [Chalmers University of Technology, S-412 96 Goetenborg (Sweden)

2008-04-15

187

A Case Study in Chemical Kinetics: The OH + CO Reaction.  

ERIC Educational Resources Information Center

Reviews some important properties of the bimolecular reaction between the hydroxyl radical and carbon monoxide. Investigates the kinetics of the reaction, the temperature and pressure dependence of the rate constant, the state-to-state dynamics of the reaction, and the reverse reaction. (MVL)

Weston, Ralph E., Jr.

1988-01-01

188

A kinetic mechanism inducing oscillations in simple chemical reactions networks.  

PubMed

It is known that a kinetic reaction network in which one or more secondary substrates are acting as cofactors may exhibit an oscillatory behavior. The aim of this work is to provide a description of the functional form of such a cofactor action guaranteeing the onset of oscillations in sufficiently simple reaction networks. PMID:20462291

Coatleven, Julien; Altafini, Claudio

2010-04-01

189

Spin-selective recombination kinetics of a model chemical magnetoreceptor.  

PubMed

We determine the spin-selective kinetics of a carotenoid-porphyrin-fullerene triad that has previously been used to establish the principle that a photochemical reaction could form the basis of the magnetic compass sensor of migratory birds and show that its magnetic sensitivity can be understood without invoking quantum Zeno effects. PMID:21562681

Maeda, Kiminori; Wedge, Christopher J; Storey, Jonathan G; Henbest, Kevin B; Liddell, Paul A; Kodis, Gerdenis; Gust, Devens; Hore, P J; Timmel, Christiane R

2011-06-21

190

Efficient Implementation of Fully Implicit Methods for Atmospheric Chemical Kinetics  

Microsoft Academic Search

Implicit integrators are very useful in efficiently solving stiff systems of ODEs arising from atmospheric chemistry kinetics, provided that they are modified to take full advantage of the structure of the problem. A systematic way of treating sparsity for reducing the linear algebra cost is presented.

A. Sandu; F. A. Potra; G. R. Carmichael; V. Damian

1996-01-01

191

Solutions of the chemical kinetic equations for initially inhomogeneous mixtures.  

NASA Technical Reports Server (NTRS)

Following the recent discussions by O'Brien (1971) and Donaldson and Hilst (1972) of the effects of inhomogeneous mixing and turbulent diffusion on simple chemical reaction rates, the present report provides a more extensive analysis of when inhomogeneous mixing has a significant effect on chemical reaction rates. The analysis is then extended to the development of an approximate chemical sub-model which provides much improved predictions of chemical reaction rates over a wide range of inhomogeneities and pathological distributions of the concentrations of the reacting chemical species. In particular, the development of an approximate representation of the third-order correlations of the joint concentration fluctuations permits closure of the chemical sub-model at the level of the second-order moments of these fluctuations and the mean concentrations.

Hilst, G. R.

1973-01-01

192

A Comprehensive Chemical Kinetic Reaction Mechanism for Oxidation and Pyrolysis of Propane and Propene  

Microsoft Academic Search

Abstract—A detailed chemical kinetic reaction mechanism is developed to describe the oxidation and pyrolysis of propane and propene. The mechanism consists of 163 elementary reactions among 4l chemical species. New rate expressions are developed for a number of reactions of propane, propene, and intermediate hydrocarbon species with radicals including H, 0, and OH. The mechanism is tested by comparisons between

CHARLES K. WESTBROOK; WILLIAM J. PITZ

1984-01-01

193

From Chemical Kinetics to Streamer Corona Reactor and Voltage Pulse Generator  

Microsoft Academic Search

This paper discusses the global chemical kinetics of corona plasma-induced chemical reactions for pollution control. If there are no significant radical termination reactions, the pollution removal linearly depends on the corona energy density and\\/or the energy yield is a constant. If linear radical termination reactions play a dominant role, the removal rate shows experimental functions in terms of the corona

K. Yan; E. J. M. van Heesch; A. J. M. Pemen; P. A. H. J. Huijbrechts

2001-01-01

194

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

Microsoft Academic Search

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

T.-H. Ahn; A. Sandu

2011-01-01

195

Electrostatic calculations for an ion channel. II. Kinetic behavior of the gramicidin A channel.  

PubMed Central

A theoretical model of the gramicidin A channel is presented and the kinetic behavior of the model is derived and compared with previous experimental results. The major assumption of the model is that the only interaction between ions in a multiply-occupied channel is electrostatic. The electrostatic calculations indicate in a multiply-occupied channel is electrostatic. The electrostatic calculations indicate that there will be potential wells at each end of the channel and, at high concentrations, that both wells can be occupied. The kinetics are based on two reaction steps: movement of the ion from the bulk solution to the well and movement between the two wells. The kinetics for this reaction rate approach are identical to those based on the Nernst-Planck equation in the limit where the movement between the two wells is rate limiting. The experimental results for sodium and potassium are consistent with a maximum of two ions per channel. To explain the thallium results it is necessary to allow three ions per channel. It is shown that this case is compatible with the electrostatic calculations if the presence of an anion is included. The theoretical kinetics are in reasonable quantitative agreement with the following experimental measurements: single channel conductance of sodium, potassium, and thallium; bi-ionic potential and permeability ratio between sodium-potassium and potassium-thallium; the limiting conductance of potassium and thallium at high applied voltages; current-voltage curves for sodium and potassium at low (but not high) concentrations; and the inhibition of sodium conductance by thallium. The results suggest that the potential well is located close to the channel mouth and that the conductance is partially limited by the rate going from the bulk solution to the well. For thallium, this entrance rate is probably diffusion limited.

Levitt, D G

1978-01-01

196

General chemical kinetics computer program for static and flow reactions, with application to combustion and shock-tube kinetics  

NASA Technical Reports Server (NTRS)

A general chemical kinetics program is described for complex, homogeneous ideal-gas reactions in any chemical system. Its main features are flexibility and convenience in treating many different reaction conditions. The program solves numerically the differential equations describing complex reaction in either a static system or one-dimensional inviscid flow. Applications include ignition and combustion, shock wave reactions, and general reactions in a flowing or static system. An implicit numerical solution method is used which works efficiently for the extreme conditions of a very slow or a very fast reaction. The theory is described, and the computer program and users' manual are included.

Bittker, D. A.; Scullin, V. J.

1972-01-01

197

Kinetics of SiC chemical vapor deposition from methylsilane  

Microsoft Academic Search

The kinetics of heterogeneous decomposition of methylsilane in a pumped hot-wall reactor were studied just below the critical\\u000a partial pressure for homogeneous decomposition. The activation energies of the process derived from gas-phase conversion measurements\\u000a and from deposition rates of SiC were found to be equal (about 230 kJ\\/mol). The nature of the diluent (H2, He, or Ar) has only a

A. M. Abyzov; E. P. Smirnov

2000-01-01

198

Semi-gas kinetics model for performance modeling of flowing chemical oxygen-iodine lasers (COIL)  

NASA Astrophysics Data System (ADS)

A semi-gas kinetics (SGK) model for performance analyses of flowing chemical oxygen-iodine laser (COIL) is presented. In this model, the oxygen-iodine reaction gas flow is treated as a continuous medium, and the effect of thermal motions of particles of different laser energy levels on the performances of the COIL is included and the velocity distribution function equations are solved by using the double-parameter perturbational method. For a premixed flow, effects of different chemical reaction systems, different gain saturation models and temperature, pressure, yield of excited oxygen, iodine concentration and frequency-shift on the performances of the COIL are computed, and the calculated output power agrees well with the experimental data. The results indicate that the power extraction of the SGK model considering 21 reactions is close to those when only the reversible pumping reaction is considered, while different gain saturation, models and adjustable parameters greatly affect the output power, the optimal threshold gain range, and the length of power extraction.

Gao, Zhi; Hu, Limin; Shen, Yiqing

2004-05-01

199

Deuterium isotope effects during HMX combustion: Chemical kinetic burn-rate control mechanism verified  

Microsoft Academic Search

The appearance of a significant deuterium isotope effect during the combustion of the solid HMX compound verifies that the chemical reaction kinetics is a major contributor in determining the experimentally observed or global burn rate. Burn rate comparison of HMX and its deuterium labeled HMX-d(8) analogue reveals a primary kinetic deuterium isotope effect (1 deg. KDIE) at 500 psig (3.55

S. A. Shackelford; B. B. Goshgarian; R. D. Chapman; R. E. Askins; D. A. Flanigan; R. N. Rogers

1989-01-01

200

Anomalous Kinetic Roughening by Chemical Reaction-Limited Aggregation  

NASA Astrophysics Data System (ADS)

The evolution of rough fronts in the early growth stage of poly(chloro-p-xylylene) films on Si/SiO2 substrates was measured using atomic force microscopy, and analyzed in detail according to the dynamic scaling theories of kinetic roughening. While the growth of the interface width and the correlation length were reduced as the system entered into the three-dimensional growth mode, both the global and the local roughness exponents remained at ?=1.39 and ?loc=0.74. The scaling behavior, ?=?s\

Lee, InJae; Park, Euldoo

2011-12-01

201

Chemical kinetics of homogeneous atmospheric oxidation of sulfur dioxide  

NASA Technical Reports Server (NTRS)

A systematic evaluation of known homogeneous SO2 reactions which might be important in air pollution chemistry is carried out. A mechanism is developed to represent the chemistry of NOx/hydrocarbon/SO2 systems, and the mechanism is used to analyze available experimental data appropriate for quantitative analysis of SO2 oxidation kinetics. Detailed comparisons of observed and predicted concentration behavior are presented. In all cases, observed SO2 oxidation rates cannot be explained solely on the basis of those SO2 reactions for which rate constants have been measured. The role of ozone-olefin reactions in SO2 oxidation is elucidated.

Sander, S. P.; Seinfeld, J. H.

1976-01-01

202

Chemical Kinetics in Support of Syngas Turbine Combustion  

SciTech Connect

This document is the final report on an overall program formulated to extend our prior work in developing and validating kinetic models for the CO/hydrogen/oxygen reaction by carefully analyzing the individual and interactive behavior of specific elementary and subsets of elementary reactions at conditions of interest to syngas combustion in gas turbines. A summary of the tasks performed under this work are: 1. Determine experimentally the third body efficiencies in H+O{sub 2}+M = HO{sub 2}+M (R1) for CO{sub 2} and H{sub 2}O. 2. Using published literature data and the results in this program, further develop the present H{sub 2}/O{sub 2}/diluent and CO/H{sub 2}/O{sub 2}/diluent mechanisms for dilution with CO{sub 2}, H{sub 2}O and N{sub 2} through comparisons with new experimental validation targets for H{sub 2}-CO-O{sub 2}-N{sub 2} reaction kinetics in the presence of significant diluent fractions of CO{sub 2} and/or H{sub 2}O, at high pressures. (task amplified to especially address ignition delay issues, see below). 3. Analyze and demonstrate issues related to NOx interactions with syngas combustion chemistry (task amplified to include interactions of iron pentacarbonyl with syngas combustion chemistry, see below). 4. Publish results, including updated syngas kinetic model. Results are summarized in this document and its appendices. Three archival papers which contain a majority of the research results have appeared. Those results not published elsewhere are highlighted here, and will appear as part of future publications. Portions of the work appearing in the above publications were also supported in part by the Department of Energy under Grant No. DE-FG02-86ER-13503. As a result of and during the research under the present contract, we became aware of other reported results that revealed substantial differences between experimental characterizations of ignition delays for syngas mixtures and ignition delay predictions based upon homogenous kinetic modeling. We adjusted emphasis of Task 2 to understand the source of these noted disparities because of their key importance to developing lean premixed combustion technologies of syngas turbine applications. In performing Task 3, we also suggest for the first time the very significant effect that metal carbonyls may have on syngas combustion properties. This work is fully detailed. The work on metal carbonyl effects is entirely computational in nature. Pursuit of experimental verification of these interactions was beyond the scope of the present work.

Dryer, Frederick

2007-07-31

203

Integrating chemical kinetic rate equations by selective use of stiff and nonstiff methods  

NASA Technical Reports Server (NTRS)

The effect of switching between nonstiff and stiff methods on the efficiency of algorithms for integrating chemical kinetic rate equations was examined. Different integration methods were tested by application of the packaged code LSODE to four practical combustion kinetics problems. The problems describe adiabatic, and homogeneous gas phase combustion reactions. It is shown that selective use of nonstiff and stiff methods in different regimes of a typical batch combustion problem is faster than the use of either method for the entire problem. The implications which result in the development of fast integration techniques for combustion kinetic rate equations are discussed.

Radhakrishnan, K.

1985-01-01

204

Calculations of kinetic behavior in the supersonic expansion of a helium plasma in a Laval nozzle  

SciTech Connect

The problem of the expansion of a dense, low-temperature helium plasma in a Laval nozzle is considered. The equations of level-by-level kinetics are solved numerically together with the equations of plasma dynamics in a quasi-one-dimensional approximation. The results of the calculations and the dependence of the solutions on the initial conditions in the critical cross section are discussed. The solutions are compared with a model approximation of a stationary sink and experimental results, showing their satisfactory agreement.

Zakrevskii, N.V.; Luk'yanov, G.A.; Tserkovnyi, S.I.

1982-07-01

205

Parameter Estimates in Differential Equation Models for Chemical Kinetics  

ERIC Educational Resources Information Center

We discuss the need for devoting time in differential equations courses to modelling and the completion of the modelling process with efforts to estimate the parameters in the models using data. We estimate the parameters present in several differential equation models of chemical reactions of order n, where n = 0, 1, 2, and apply more general…

Winkel, Brian

2011-01-01

206

A Piagetian Learning Cycle for Introductory Chemical Kinetics.  

ERIC Educational Resources Information Center

Described is a Piagetian learning cycle based on Monte Carlo modeling of several simple reaction mechanisms. Included are descriptions of learning cycle phases (exploration, invention, and discovery) and four BASIC-PLUS computer programs to be used in the explanation of chemical reacting systems. (Author/DS)

Batt, Russell H.

1980-01-01

207

Combinatorial and topological methods in nonlinear chemical kinetics  

Microsoft Academic Search

Combinatorial and topological techniques are developed to classify nonlinear chemical reaction networks in terms of their qualitative dynamics. A class of N coupled equations, based on a hypothesis concerning biological control by Monod and Jacob is derived. Transitions between volumes in concentration space for these equations are represented as directed edges on N cubes (hypercubes in N dimensions). A classification

Leon Glass

1975-01-01

208

Asymptotic expansions of slow invariant manifolds and reduction of chemical kinetics models  

NASA Astrophysics Data System (ADS)

Methods of the geometric theory of singular perturbations are used to reduce the dimensions of problems in chemical kinetics. The methods are based on using slow invariant manifolds. As a result, the original system is replaced by one on an invariant manifold, whose dimension coincides with that of the slow subsystem. Explicit and implicit representations of slow invariant manifolds are applied. The mathematical apparatus described is used to develop N.N. Semenov's fundamental ideas related to the method of quasi-stationary concentrations and is used to study particular problems in chemical kinetics.

Sobolev, V. A.; Tropkina, E. A.

2012-01-01

209

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

SciTech Connect

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.

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

1993-03-01

210

Rotational and Vibrational Kinetic Energies Should be Included in Mass-Energy Calculations  

NASA Astrophysics Data System (ADS)

Conversion of mass to energy involves more than rest mass. At the subatomic, nuclear, atomic and molecular levels there are rotational, spin and vibratory kinetic energies although small may account for some discrepancies between theory and experiment. In pair annhilation spin and vibratory kinetic energies should be included in calculations. Thus, [ E0= 2m0c^2 + .5I 2?rp+ .52?re+ (n + 1/2) ?vp+ (n + 1/2) ?ve+ 1/2mv^2p+ 1/2mv^2e] if the positron and electron are going slowly. The ?r and the ?v are the rotational angular velocity iand vibrational angular frequency. The mass energy equation for a nucleus and a molecule is therefore [E0= m0c^2 +1/2I?r^2 + (n +1/2)?v+ 1/2mv^2]. On a universal scale planets, stars, galaxies and galactic groups will have rotational Orbital and vibrational factors which should be included in any mass-energy conversions. Some of the energy attributed to binding energy on a nuclear level may actually be vibrational and rotational kinetic energy.

Brekke, Stewart

2007-03-01

211

Role of plasma activation in kinetics of carbon nanotube growth in plasma-enhanced chemical vapor deposition  

NASA Astrophysics Data System (ADS)

The effect of the acceleration of carbon nanotube (CNT) growth from methane via modification of the gas composition with plasma discharge is studied by means of kinetic modeling. A model of CNT growth describing the detailed gas-phase and surface kinetics of hydrocarbons in catalytic chemical vapor deposition is used. It is shown that the effect of plasma is related to the formation of active species in the gas phase that can easily adsorb and dissociate on the catalyst surface. It is also demonstrated that in addition to the adsorption of carbon precursors, the CNT growth rate can be limited by the gas-phase diffusion of carbon species to the catalyst surface. The critical energy input above which the dominant contribution to CNT growth is provided by non-radical neutral species is calculated and confirmed by analytic estimates.

Lebedeva, Irina V.; Knizhnik, Andrey A.; Gavrikov, Alexey V.; Baranov, Alexey E.; Potapkin, Boris V.; Smith, David J.; Sommerer, Timothy J.

2012-04-01

212

Recent Results in Quantum Chemical Kinetics from High Resolution Spectroscopy  

SciTech Connect

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.

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

2007-12-26

213

Chemical kinetic modeling of component mixtures relevant to gasoline  

SciTech Connect

Real fuels are complex mixtures of thousands of hydrocarbon compounds including linear and branched paraffins, naphthenes, olefins and aromatics. It is generally agreed that their behavior can be effectively reproduced by simpler fuel surrogates containing a limited number of components. In this work, a recently revised version of the kinetic model by the authors is used to analyze the combustion behavior of several components relevant to gasoline surrogate formulation. Particular attention is devoted to linear and branched saturated hydrocarbons (PRF mixtures), olefins (1-hexene) and aromatics (toluene). Model predictions for pure components, binary mixtures and multi-component gasoline surrogates are compared with recent experimental information collected in rapid compression machine, shock tube and jet stirred reactors covering a wide range of conditions pertinent to internal combustion engines. Simulation results are discussed focusing attention on the mixing effects of the fuel components.

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

2009-02-13

214

Infrared absorption spectroscopy and chemical kinetics of free radicals  

SciTech Connect

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.

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

1992-04-01

215

Kinetic and Chemical Mechanisms of Homocitrate Synthase from Thermus thermophilus*  

PubMed Central

The homocitrate synthase from Thermus thermophilus (TtHCS) is a metal-activated enzyme with either Mg2+ or Mn2+ capable of serving as the divalent cation. The enzyme exhibits a sequential kinetic mechanism. The mechanism is steady state ordered with ?-ketoglutarate (?-Kg) binding prior to acetyl-CoA (AcCoA) with Mn2+, whereas it is steady state random with Mg2+, suggesting a difference in the competence of the E·Mn·?-Kg·AcCoA and E·Mg·?-Kg·AcCoA complexes. The mechanism is supported by product and dead-end inhibition studies. The primary isotope effect obtained with deuterioacetylCoA (AcCoA-d3) in the presence of Mg2+ is unity (value 1.0) at low concentrations of AcCoA, whereas it is 2 at high concentrations of AcCoA. Data suggest the presence of a slow conformational change induced by binding of AcCoA that accompanies deprotonation of the methyl group of AcCoA. The solvent kinetic deuterium isotope effect is also unity at low AcCoA, but is 1.7 at high AcCoA, consistent with the proposed slow conformational change. The maximum rate is pH independent with either Mg2+ or Mn2+ as the divalent metal ion, whereas V/K?-Kg (with Mn2+) decreases at low and high pH giving pK values of about 6.5 and 8.0. Lysine is a competitive inhibitor that binds to the active site of TtHCS, and shares some of the same binding determinants as ?-Kg. Lysine binding exhibits negative cooperativity, indicating cross-talk between the two monomers of the TtHCS dimer. Data are discussed in terms of the overall mechanism of TtHCS.

Kumar, Vidya Prasanna; West, Ann H.; Cook, Paul F.

2011-01-01

216

The Role of Comprehensive Detailed Chemical Kinetic Reaction Mechanisms in Combustion Research  

SciTech Connect

Recent developments by the authors in the field of comprehensive detailed chemical kinetic reaction mechanisms for hydrocarbon fuels are reviewed. Examples are given of how these mechanisms provide fundamental chemical insights into a range of combustion applications. Practical combustion consists primarily of chemical heat release from reactions between a fuel and an oxidizer, and computer simulations of practical combustion systems have become an essential tool of combustion research (Westbrook et al., 2005). At the heart of most combustion simulations, the chemical kinetic submodel frequently is the most detailed, complex and computationally costly part of a system model. Historically, the chemical submodel equations are solved using time-implicit numerical algorithms, due to the extreme stiffness of the coupled rate equations, with a computational cost that varies roughly with the cube of the number of chemical species in the model. While early mechanisms (c. 1980) for apparently simple fuels such as methane (Warnatz, 1980) or methanol (Westbrook and Dryer, 1979) included perhaps 25 species, current detailed mechanisms for much larger, more complex fuels such as hexadecane (Fournet et al., 2001; Ristori et al., 2001; Westbrook et al., 2008) or methyl ester methyl decanoate (Herbinet et al., 2008) have as many as 2000 or even 3000 species. Rapid growth in capabilities of modern computers has been an essential feature in this rapid growth in the size and complexity of chemical kinetic reaction mechanisms.

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

2008-07-16

217

Constrained-equilibrium calculations for chemical systems subject to generalized linear constraints using the NASA and STANJAN equilibrium programs  

NASA Astrophysics Data System (ADS)

Fast efficient numerical programs for determining the equilibrium composition of large chemical systems subject to generalized linear constraints are needed for chemical kinetic calculations involving both the conventional local thermodynamic equilibrium (LTE) and the more general rate-controlled constrained-equilibrium RCCE assumptions. For this purpose two callable subroutines based on the well known NASA and STANJAN equilibrium codes have been developed by a simple modification of their input files. To evaluate the performance of these subroutines, test calculations have been made for the hydrogen - oxygen (H - O) and carbon - hydrogen - oxygen - nitrogen (C - H - O - N) systems with various combinations of constraints on the elements, the total moles and the free valence (number of unpaired electrons) in the system. The allowed domain of the constraints was determined and both interior and boundary points were investigated for several temperature and pressure conditions. The results showed that STANJAN was superior to NASA both in convergence and speed under all conditions investigated.

Bishnu, Partha S.; Hamiroune, Djamel; Metghalchi, Mohamad; Keck, James C.

1997-09-01

218

Chemical kinetics in the coma. [of sun grazing comet  

NASA Technical Reports Server (NTRS)

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 correlated to distance in the coma above the nucleus and to heliocentric distance of the comet. Two classes for the composition of comets are considered based on their place of origin: in the environs of the giant planets or in a companion fragment of the presolar nebula. Comparison of model results 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. Composition based on an origin of comets in the presolar nebula yields abundances of C2, C3, and CN that are in agreement with observations.

Huebner, W. F.

1981-01-01

219

Kinetics and chemical equilibrium of the hydration of formaldehyde  

Microsoft Academic Search

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

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

2002-01-01

220

Degradation kinetics of glass-reinforced polyesters in chemical environments  

Microsoft Academic Search

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

S. P. Sonawala; R. J. Spontak

1996-01-01

221

Studies on the kinetic response of mosquitos to chemicals*  

PubMed Central

An apparatus is described for study of the activity of mosquitos either with or without stimulation by exposure to insecticides or other chemicals such as repellents. Batches of up to 30 mosquitos can be used and they can be studied for a longer time than is possible with, for instance, the method put forward in 1960 by the WHO Expert Committee on Insecticides. Random activity by the test insects, in the absence of directional stimuli due to light or chemicals, is converted to progress through baffles in the partitions separating a series of four boxes and is expressed as a percentage of the total possible activity that would be shown if all the insects passed all the baffles. Exposure to chemicals, by exposure to impregnated papers, can take place before the mosquitos are put in the apparatus, or in the first box. In the experiments described, the activity of recently fed female Anopheles was studied over periods of up to 20 hours. Comparison of the method described with other methods shows that it shares the high variance characteristic of all current procedures for studying mosquito behaviour, although the use of large numbers of insects over long periods has some advantages. The method does, however, give information on mortality under conditions of facultative contact that may be a valuable supplement to the results of conventional susceptibility tests.

Elliott, R.

1964-01-01

222

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

SciTech Connect

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.

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

223

Chemical pathway and kinetics of phenol oxidation by Fenton's reagent.  

PubMed

Phenol oxidation by Fenton's reagent (H2O2 + Fe2+) in aqueous solution has been studied in depth for the purpose of learning more about the reactions involved and the extent of the oxidation process, under various operating conditions. An initial phenol concentration of 100 mg/L was used as representative of a phenolic industrial wastewater. Working temperatures of 25 and 50 degrees C were tested, and the initial pH was set at 3. The H2O2 and the Fe2+ doses were varied in the range of 500-5000 and 1-100 mg/L, respectively, corresponding to 1-10 times the stoichiometric ratio. A series of intermediates were identified, corresponding mainly to ring compounds and short-chain organic acids. Most significant among the former were catechol, hydroquinone, and p-benzoquinone; the main organic acids were maleic, acetic, oxalic, and formic, with substantially lower amounts of muconic, fumaric, and malonic acids. Under milder operating conditions (H2O2 and Fe2+ at lower concentrations), a great difference was found between the measured total organic carbon (TOC) and the amount of carbon in all analyzed species in the reaction medium. This difference decreased as the doses of H2O2 and Fe2+ increased, indicating that the unidentified compounds must correspond to oxidation intermediates between phenol and the organic acids. To establish a complete oxidation pathway, experiments were carried out using each of the identified intermediates as starting compounds. Dihydroxybenzenes were identified in the earlier oxidation stages. Muconic acid was detected in catechol but not in the hydroquinone and p-benzoquinone oxidation runs; the last two compounds were oxidized to maleic acid. Oxalic and acetic acid appeared to be fairly refractory to this oxidation treatment. A detailed knowledge of the time evolution of the oxidation intermediates is of environmental interest particularly in the case of hydroquinone and p-benzoquinone because their toxicities are several orders of magnitudes higher than that of phenol itself. The time evolution of the intermediates and TOC was fitted to a simple second-order kinetic equation, and the values of the kinetic constants were determined. This provides a simplified approach useful for design purposes. PMID:16382955

Zazo, J A; Casas, J A; Mohedano, A F; Gilarranz, M A; Rodríguez, J J

2005-12-01

224

Stability and Control of Lean Blowout in Chemical Kinetics-Controlled Combustion Systems  

Microsoft Academic Search

This study is motivated by lean-blowout (LBO) detection and control in dry-low-emission (DLE) combustion systems. However, this analysis is confined to chemical kinetics-controlled combustion. Despite its simplicity, some useful insight may still be shed on near-LBO combustion systems, as the chemical reaction rates are rather low near LBO. A third-order linear well-stirred reactor (WSR) model is derived to examine a

Tongxun Yi; Ephraim J. Gutmark; Bruce K. Walker

2009-01-01

225

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

PubMed

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

Oliveira, R C de M; Bauerfeldt, G F

2012-10-01

226

Kinetics and thermodynamics of chemical reactions in Li/SOCl2 cells  

NASA Technical Reports Server (NTRS)

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.

Hansen, Lee D.; Frank, Harvey

1987-01-01

227

Chemical Cycle Kinetics: Removing the Limitation of Linearity of a Non-equilibrium Thermodynamic Description  

NASA Astrophysics Data System (ADS)

Chemical cycle kinetics is customarily analyzed by means of the law of mass action which describes how the concentrations of the substances vary with time. The connection of this approach with non-equilibrium thermodynamics (NET) has traditionally been restricted to the linear domain close to equilibrium in which the reaction rates are linear functions of the affinities. We show, by a pertinent formulation of the concept of local equilibrium in the mesoscopic description along the reaction coordinates, that the connection between kinetic and thermodynamic approaches is deeper than thought and holds in the nonlinear domain far from equilibrium, for higher values of the affinity. This new perspective indicates how to overcome the inherent limitation of classical NET in treating cyclic reactions, providing a description of closed and open cycles operating far from equilibrium, in accordance with thermodynamic principles. We propose that the new set of equations are tested and used for data reduction in chemical reaction kinetics.

Rubi, J. M.; Bedeaux, D.; Kjelstrup, S.; Pagonabarraga, I.

2013-07-01

228

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

PubMed

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

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

2014-02-14

229

Comparison of finite difference based methods to obtain sensitivities of stochastic chemical kinetic models  

NASA Astrophysics Data System (ADS)

Sensitivity analysis is a powerful tool in determining parameters to which the system output is most responsive, in assessing robustness of the system to extreme circumstances or unusual environmental conditions, in identifying rate limiting pathways as a candidate for drug delivery, and in parameter estimation for calculating the Hessian of the objective function. Anderson [SIAM J. Numer. Anal. 50, 2237 (2012)] shows the advantages of the newly developed coupled finite difference (CFD) estimator over the common reaction path (CRP) [M. Rathinam, P. W. Sheppard, and M. Khammash, J. Chem. Phys. 132, 034103 (2010)] estimator. In this paper, we demonstrate the superiority of the CFD estimator over the common random number (CRN) estimator in a number of scenarios not considered previously in the literature, including the sensitivity of a negative log likelihood function for parameter estimation, the sensitivity of being in a rare state, and a sensitivity with fast fluctuating species. In all examples considered, the superiority of CFD over CRN is demonstrated. We also provide an example in which the CRN method is superior to the CRP method, something not previously observed in the literature. These examples, along with Anderson's results, lead to the conclusion that CFD is currently the best estimator in the class of finite difference estimators of stochastic chemical kinetic models.

Srivastava, Rishi; Anderson, David F.; Rawlings, James B.

2013-02-01

230

Inactivation kinetics of various chemical disinfectants on Aeromonas hydrophila planktonic cells and biofilms.  

PubMed

The present article focuses on the inactivation kinetics of various disinfectants including ethanol, sodium hypochlorite, hydrogen peroxide, peracetic acid, and benzalkonium chloride against Aeromonas hydrophila biofilms and planktonic cells. Efficacy was determined by viable plate count and compared using a modified Weibull model. The removal of the biofilms matrix was determined by the crystal violet assay and was confirmed by field-emission scanning electron microscope. The results revealed that all the experimental data and calculated Weibull ? (scale) and ? (shape) parameters had a good fit, as the R(2) values were between 0.88 and 0.99. Biofilms are more resistant to disinfectants than planktonic cells. Ethanol (70%) was the most effective in killing cells in the biofilms and significantly reduced (p<0.05) the biofilms matrix. The Weibull parameter b-value correlated (R(2)=0.6835) with the biofilms matrix removal. The present findings deduce that the Weibull model is suitable to determine biofilms matrix reduction as well as the effectiveness of chemical disinfectants on biofilms. The study showed that the Weibull model could successfully be used on food and food contact surfaces to determine the exact contact time for killing biofilms-forming foodborne pathogens. PMID:24552163

Jahid, Iqbal Kabir; Ha, Sang-Do

2014-05-01

231

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

SciTech Connect

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.

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

2010-01-01

232

Reaction and diffusion kinetics during the initial stages of isothermal chemical vapor infiltration  

Microsoft Academic Search

This paper reports that individual bundles of ceramic fibers were infiltrated with SiC to study the reaction and diffusion kinetics during isothermal chemical vapor infiltration (CVI). More uniform infiltration was observed in samples where baffles were placed in the reactor and when HC1 was added to the inlet gases. The evolution of the microstructure was modeled using an analytical expression

Brian W. Sheldon; Theodore M. Besmann

1991-01-01

233

The control of gas phase kinetics to maximize densification during chemical vapor infiltration  

Microsoft Academic Search

A serious problem during the fabrication of composite materials by isothermal chemical vapor infiltration is that the matrix forms more rapidly at the external edges of the body and traps a large amount of porosity inside. In theory, this problem can be eliminated by controlling the gas-phase kinetics to obtain densification which is more rapid in the center of a

Brian W. Sheldon

1990-01-01

234

A Chemical Kinetics Model to Predict Lubricant Performance in a Diesel Engine. Part I: Simulation Methodology  

Microsoft Academic Search

The ability of a lubricant to protect increasingly complex diesel engines directly affects engine durability and warranty costs and is becoming increasingly costly to validate. This paper presents a novel approach combining a chemical kinetic model using rate constants determined by a set of laboratory bench tests and a finite-difference computer program to predict lubricant performance in a given diesel

Chun-I Chen; Stephen M. Hsu

2003-01-01

235

Fitness Diversity Based Adaptive Memetic Algorithm for solving inverse problems of chemical kinetics  

Microsoft Academic Search

This paper proposes the fitness diversity based adaptive memetic algorithm (FIDAMA) for solving the problem of the inverse type consisting of retrieving chemical kinetics reaction rate coefficients in the generalised Arrhenius form based on the observed concentrations in a given range of temperatures of a limited set of species which describe the reaction mechanism. FIDAMA consists of the evolutionary framework

Anna V. Kononova; Kevin J. Hughes; Mohamed Pourkashanian; Derek B. Ingham

2007-01-01

236

Cooperative Learning Instruction for Conceptual Change in the Concepts of Chemical Kinetics  

ERIC Educational Resources Information Center

Learning is a social event and so the students need learning environments that enable them to work with their peers so that they can learn through their interactions. This study discusses the effectiveness of cooperative learning compared to traditional instruction in terms of students' motivation and understanding of chemical kinetics in a high…

Kirik, Ozgecan Tastan; Boz, Yezdan

2012-01-01

237

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

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

238

Autoignition of toluene reference fuels at high pressures modeled with detailed chemical kinetics  

Microsoft Academic Search

A detailed chemical kinetic model for the autoignition of toluene reference fuels (TRF) is presented. The toluene submechanism added to the Lawrence Livermore Primary Reference Fuel (PRF) mechanism was developed using recent shock tube autoignition delay time data under conditions relevant to HCCI combustion. For two-component fuels the model was validated against recent high-pressure shock tube autoignition delay time data

J. C. G. Andrae; P. Björnbom; R. F. Cracknell; G. T. Kalghatgi

2007-01-01

239

Laser absorption techniques for spectroscopy and chemical kinetics studies in a shock tube  

Microsoft Academic Search

Recent laboratory work to develop advanced laser-based diagnostics for shock tube applications is overviewed. Tunable laser absorption techniques have received primary emphasis, with applications to fundamental studies of spectroscopic parameters and investigations of chemical kinetics. Laser sources have included a discretely tunable CO infrared laser, a continuously tunable infrared diode laser and a continuously tunable ultraviolet\\/visible ring dye laser.

R. K. Hanson; S. Salimian; E. C. Rea Jr.

1984-01-01

240

A. G. Vernon Harcourt: A Founder of Chemical Kinetics and a Friend of "Lewis Carroll."  

ERIC Educational Resources Information Center

Outlines the life of A. G. Vernon Harcourt, a founder of chemical kinetics, contributor to the purification of coal gas from sulfur compounds, inventor of the percentage chloroform inhaler, friend to Lewis Carroll, and instructor to the Prince of Wales. (CS)

Shorter, John

1980-01-01

241

Chemical Kinetic Modeling of Dimethyl Carbonate in an Opposed-Flow Diffusion Flame.  

National Technical Information Service (NTIS)

Dimethyl carbonate (DMC) has been of interest as an oxygenate additive to diesel fuel because of its high oxygen content. In this study, a chemical kinetic mechanism for DMC was developed for the first time and used to understand its combustion under cond...

P. A. Glaude W. J. Pitz M. J. Thomson

2003-01-01

242

New integration techniques for chemical kinetic rate equations. I - Efficiency comparison  

NASA Technical Reports Server (NTRS)

A comparison of the efficiency of several recently developed numerical techniques for solving chemical kinetic rate equations is presented. The solution procedures examined include two general-purpose codes, EPISODE and LSODE, developed as multipurpose differential equation solvers, and three specialzed codes, CHEMEQ, CREK1D, and GCKP84, developed specifically for chemical kinetics. The efficiency comparison is made by applying these codes to two practical combustion kinetics problems. Both problems describe adiabatic, constant-pressure, gas-phase chemical reactions and include all three combustion regimes: induction, heat release, and equilibration. The comparison shows that LSODE is the fastest routine currently available for solving chemical kinetic rate equations. An important finding is that an iterative solution of the algebraic enthalpy conservation equation for temperature can be significantly faster than evaluation of the temperature by integration of its time derivative. Significant increases in computational speed are realized by updating the reaction rate constants only when the temperature change exceeds an amount Delta-T that is problem dependent. An approximate expression for the automatic evaluation of Delta-T is presented and is shown to result in increased computational speed.

Radhakrishnan, K.

1986-01-01

243

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

Microsoft Academic Search

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-

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

2003-01-01

244

Numerical modeling of D-mappings with applications to chemical kinetics  

NASA Technical Reports Server (NTRS)

Numerical modeling of D-mappings was studied and applied to solving nonlinear stiff systems. These mappings were locally linearized for convergence analysis, and some applications were made to chemical kinetics. The technique avoids using multistep implicit codes that require inversion of Jacobian matrices, but depends on the Jacobians for its convergence analysis.

Dey, S. K.

1984-01-01

245

Thermodynamic and kinetic properties of the Li-graphite system from first-principles calculations  

NASA Astrophysics Data System (ADS)

We present an ab initio study of the thermodynamics and kinetics of LixC6 , relevant for anode Li intercalation in rechargeable Li batteries. In graphite, the interlayer interactions are dominated by Van der Waals forces, which are not captured with standard density-functional theory (DFT). By calculating the voltage profile for Li intercalation into graphite and comparing it to experimental results, we find that only by correcting for vdW interactions between the graphene planes is it possible to reproduce the experimentally observed sequence of phases, as a function of Li content. At higher Li content the interlayer binding forces are increasingly due to Li-C interactions, which are well characterized by DFT. Using the calculated energies, corrected for the vdW interactions, we derive an ab initio lattice model, based on the cluster-expansion formalism, that accounts for interactions among Li ions in LixC6 having a stage I and stage II structure. We find that the resulting cluster expansions are dominated by Li-Li repulsive interactions. The phase diagram, obtained from Monte Carlo simulations, agrees well with experiments except at low Li concentrations as we exclude stage III and stage IV compounds. Furthermore, we calculate Li migration barriers for stage I and stage II compounds and identify limiting factors for Li mobility in the in-plane dilute as well as in the high Li concentration range. The Li diffusivity, obtained through kinetic Monte Carlo simulations, slowly decreases as a function of Li content, consistent with increasing Li-Li repulsions. However, overall we find very fast Li diffusion in bulk graphite, which may have important implications for Li battery anode optimizations.

Persson, Kristin; Hinuma, Yoyo; Meng, Ying Shirley; van der Ven, Anton; Ceder, Gerbrand

2010-09-01

246

Chemical-kinetic problems of future NASA missions  

NASA Technical Reports Server (NTRS)

Thermochemical nonequilibrium in the shock layer surrounding vehicles entering the atmospheres of earth and Mars at superescape velocities is studied, deriving reaction rate coefficients that reproduce experimental data obtained in shock tubes. Thermodynamic properties and emitted radiation intensities are obtained for shock tube flow and flow in a shock layer over a blunt body. The results indicate that the viscous layer of the ablation product over an ablating heat shield is likely to be in chemical nonequilbrium. For earth entry flight, the thickness of the nonequilbrium region is between and 2 cm at the expected peak radiation point in the aerobraking trajectory, For Martian entry flight it is between 8 and 23 cm. For the earth entry case, nonequilibrium phenomena reduce radiative heating rate, while the opposite occurs for the Martian case. The radiative heat transfer rates are significant for the Mars entry conditions at entry velocities equal to or greater than 7 km/s.

Park, Chul; Howe, John T.; Jaffe, Richard L.; Candler, Graham V.

1991-01-01

247

Chemical Kinetic Modeling of Dimethyl Carbonate in an Opposed-Flow Diffusion Flame  

SciTech Connect

Dimethyl carbonate (DMC) has been of interest as an oxygenate additive to diesel fuel because of its high oxygen content. In this study, a chemical kinetic mechanism for DMC was developed for the first time and used to understand its combustion under conditions in an opposed flow diffusion flame. Computed results were compared to experimental results from an opposed flow diffusion flame. It was found that the decomposition rate DMC {yields} H{sub 3}COC(=O)O. + CH{sub 3} in the flame was much slower than originally thought because resonance stabilization in the H{sub 3}COC(=O)O. radical was less than expected. Also, a new molecular elimination path for DMC is proposed and its rate calculated by quantum chemical methods. In the simulations of DMC in the flame, it was determined that much of the oxygen in dimethyl carbonate goes directly to CO{sub 2}. This characteristic indicates that DMC would not be an effective oxygenate additive for reducing soot emissions from diesel engines. In an ideal oxygenate additive for diesel fuel, each oxygen atom stays bonded to one carbon atom in the products thereby preventing the formation of carbon-carbon bonds that can lead to soot. When CO2 is formed directly, two oxygen atoms are bonded to one carbon atom thereby wasting one oxygen atom in the oxygenate additive. To determine how much CO{sub 2} is formed directly, the branching ratio of the key reaction, CH{sub 3}OC.=O going to the products CH{sub 3} + CO{sub 2} or CH{sub 3}O + CO was determined by ab initio methods. The A-factors of the rate constant of this reaction were found to be about 20 times higher than previous factors estimates. The new reaction rate constants obtained can be used as reaction rate rules for all oxygenates that contain the ester moiety including biodiesel.

Glaude, P A; Pitz, W J; Thomson, M J

2003-12-08

248

Ab initio chemical kinetics for the HCCO + OH reaction  

NASA Astrophysics Data System (ADS)

The mechanism for the reaction of HCCO and OH has been investigated at different high-levels of theory. The reaction was found to occur on singlet and triplet potential energy surfaces with multiple accessible paths. Rate constants predicted by variational RRKM/ME calculations show that the reaction on both surfaces occurs primarily by barrierless OH attack at both C atoms producing excited intermediates which fragment to produce predominantly CO and 1,3HCOH with kS = 3.12 × 10-8T-0.59exp[-73.0/T] and kT = 6.29 × 10-11T0.13exp[108/T] cm3 molecule-1 s-1 at T = 300-2000 K, independent of pressure at P < 76 000 Torr.

Mai, Tam V.-T.; Raghunath, P.; Le, Xuan T.; Huynh, Lam K.; Nam, Pham-Cam; Lin, M. C.

2014-01-01

249

Origin of the Chemical and Kinetic Stability of Graphene Oxide  

NASA Astrophysics Data System (ADS)

At moderate temperatures (<= 70°C), thermal reduction of graphene oxide is inefficient and after its synthesis the material enters in a metastable state. Here, first-principles and statistical calculations are used to investigate both the low-temperature processes leading to decomposition of graphene oxide and the role of ageing on the structure and stability of this material. Our study shows that the key factor underlying the stability of graphene oxide is the tendency of the oxygen functionalities to agglomerate and form highly oxidized domains surrounded by areas of pristine graphene. Within the agglomerates of functional groups, the primary decomposition reactions are hindered by both geometrical and energetic factors. The number of reacting sites is reduced by the occurrence of local order in the oxidized domains, and due to the close packing of the oxygen functionalities, the decomposition reactions become - on average - endothermic by more than 0.6 eV.

Zhou, Si; Bongiorno, Angelo

2013-08-01

250

Transport Properties of a Kinetic Model for Chemical Reactions without Barriers  

SciTech Connect

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.

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

251

Chemical kinetics simulation for atmospheric pressure air plasmas in a streamer regime  

SciTech Connect

We present a theoretical analysis of air discharges at high pressure which operates in a streamer regime. The aim is to provide a simplified framework to study the chemical kinetics in the discharge gas phase. We have tried to model the characteristics of actually existing devices, such as dc and ac discharges in sharp point-plane, point to point, or coaxial cylinder configuration, dielectric barrier discharges. Within such scheme it is possible to perform numerical simulations in order to predict the evolution of the gas-phase chemical composition. As a first application we have chosen to simulate the chemical kinetics induced in a single isolated streamer and the results of this approach are examined within this paper. In particular, we have studied the detailed temporal evolution of the discharge gas phase using reference values for the simulation free parameters. The interplay between different time scale processes is shown. The effect due to charged as well as metastable species on chemical kinetics has been discussed too. Then we have studied the dependence of chemical species density on discharge parameters such as the electron temperature, the electron density, the transverse radius of the streamer, and the streamer formation time. Many results can be proven relevant for a better understanding of the operating conditions during technological sensible processing based on atmospheric pressure plasma.

Barni, R.; Esena, P.; Riccardi, C. [Dipartimento di Fisica G. Occhialini, Universita degli Studi di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milan (Italy)

2005-04-01

252

LSENS, a general chemical kinetics and sensitivity analysis code for gas-phase reactions: User's guide  

NASA Technical Reports Server (NTRS)

A general chemical kinetics and sensitivity analysis code for complex, homogeneous, gas-phase reactions is described. The main features of the code, LSENS, are its flexibility, efficiency and convenience in treating many different chemical reaction models. The models include static system, steady, one-dimensional, inviscid flow, shock initiated reaction, and a perfectly stirred reactor. In addition, equilibrium computations can be performed for several assigned states. An implicit numerical integration method, which works efficiently for the extremes of very fast and very slow reaction, is used for solving the 'stiff' differential equation systems that arise in chemical kinetics. For static reactions, sensitivity coefficients of all dependent variables and their temporal derivatives with respect to the initial values of dependent variables and/or the rate coefficient parameters can be computed. This paper presents descriptions of the code and its usage, and includes several illustrative example problems.

Radhakrishnan, Krishnan; Bittker, David A.

1993-01-01

253

Consistency of field-theoretical and kinetic calculations of viscous transport coefficients for a relativistic fluid  

NASA Astrophysics Data System (ADS)

We investigate the ratios ???/? and ???/?, i.e., the ratios of shear, ?, and bulk, ?, viscosities to the relaxation times ?, ? of the shear stress tensor and bulk viscous pressure, respectively, in the framework of causal relativistic dissipative fluid dynamics. These viscous transport coefficients are computed both in a field-theoretical and a kinetic approach based on the Boltzmann equation. Our results differ from those of the traditional Boltzmann calculation by Israel and Stewart. The new expressions for the viscous transport coefficients agree with the results obtained in the field-theoretical approach when the contributions from pair annihilation and creation (PAC) are neglected. The latter induce non-negligible corrections to the viscous transport coefficients.

Denicol, Gabriel S.; Huang, Xu-Guang; Koide, Tomoi; Rischke, Dirk H.

2012-02-01

254

Calculation of Reactor Kinetics Parameters ?eff and ? with Monte Carlo Differential Operator Sampling  

NASA Astrophysics Data System (ADS)

The methods to calculate the kinetics parameters of ?eff and ? with the differential operator sampling have been reviewed. The comparison of the results obtained with the differential operator sampling and iterated fission probability approaches has been performed. It is shown that the differential operator sampling approach gives the same results as the iterated fission probability approach within the statistical uncertainty. In addition, the prediction accuracy of the evaluated nuclear data library JENDL-4.0 for the measured ?eff/? and ?eff values is also examined. It is shown that JENDL-4.0 gives a good prediction except for the uranium-233 systems. The present results imply the need for revisiting the uranium-233 nuclear data evaluation and performing the detailed sensitivity analysis.

Nagaya, Yasunobu

2014-06-01

255

The determination of the kinetic parameters of electrochemical reaction in chemical power sources: A critical review  

Microsoft Academic Search

The derivation and proposal of major electrochemical techniques used to determine and calculate the electrochemical kinetic parameters is basically based on the electrochemical reaction taking place at liquid\\/solid or liquid\\/liquid interface in which all the reactants and products are soluble in liquid aqueous solution or liquid mercury electrode, or are volatile gas. Such electrochemical reaction system is classical and traditional

Yanhui Xu; Ying Chen; Jun Wu; Decheng Li; Hua Ju; Junwei Zheng

2010-01-01

256

Chemically reacting supersonic flow calculation using an assumed PDF model  

NASA Technical Reports Server (NTRS)

This work is motivated by the need to develop accurate models for chemically reacting compressible turbulent flow fields that are present in a typical supersonic combustion ramjet (SCRAMJET) engine. In this paper the development of a new assumed probability density function (PDF) reaction model for supersonic turbulent diffusion flames and its implementation into an efficient Navier-Stokes solver are discussed. The application of this model to a supersonic hydrogen-air flame will be considered.

Farshchi, M.

1990-01-01

257

Calculating chemical concentrations during the initiation of crevice corrosion  

Microsoft Academic Search

Numerical simulations of solution chemistry and electrochemical potential variations within crevice corrosion sites on stainless steel have been carried out using a method recently developed by Friedly and Rubin. Potential differences in the crevice solution have been calculated via the Nernst–Planck equation rather than by making the usual assumption of electroneutrality at any point, although this assumption is proven to

Stephen P. White; Graham J. Weir; N. J. Laycock

2000-01-01

258

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

NASA Astrophysics Data System (ADS)

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.

Aristov, Vladimir; Frolova, Anna; Zabelok, Sergey

2014-04-01

259

Ab initio path-integral calculations of kinetic and equilibrium isotope effects on base-catalyzed RNA transphosphorylation models.  

PubMed

Detailed understandings of the reaction mechanisms of RNA catalysis in various environments can have profound importance for many applications, ranging from the design of new biotechnologies to the unraveling of the evolutionary origin of life. An integral step in the nucleolytic RNA catalysis is self-cleavage of RNA strands by 2'-O-transphosphorylation. Key to elucidating a reaction mechanism is determining the molecular structure and bonding characteristics of transition state. A direct and powerful probe of transition state is measuring isotope effects on biochemical reactions, particularly if we can reproduce isotope effect values from quantum calculations. This article significantly extends the scope of our previous joint experimental and theoretical work in examining isotope effects on enzymatic and nonenzymatic 2'-O-transphosphorylation reaction models that mimic reactions catalyzed by RNA enzymes (ribozymes), and protein enzymes such as ribonuclease A (RNase A). Native reactions are studied, as well as reactions with thio substitutions representing chemical modifications often used in experiments to probe mechanism. Here, we report and compare results from eight levels of electronic-structure calculations for constructing the potential energy surfaces in kinetic and equilibrium isotope effects (KIE and EIE) computations, including a "gold-standard" coupled-cluster level of theory [CCSD(T)]. In addition to the widely used Bigeleisen equation for estimating KIE and EIE values, internuclear anharmonicity and quantum tunneling effects were also computed using our recently developed ab initio path-integral method, that is, automated integration-free path-integral method. The results of this work establish an important set of benchmarks that serve to guide calculations of KIE and EIE for RNA catalysis. © 2014 Wiley Periodicals, Inc. PMID:24841935

Wong, Kin-Yiu; Xu, Yuqing; York, Darrin M

2014-06-30

260

Errors in the Calculation of 27Al Nuclear Magnetic Resonance Chemical Shifts  

PubMed Central

Computational chemistry is an important tool for signal assignment of 27Al nuclear magnetic resonance spectra in order to elucidate the species of aluminum(III) in aqueous solutions. The accuracy of the popular theoretical models for computing the 27Al chemical shifts was evaluated by comparing the calculated and experimental chemical shifts in more than one hundred aluminum(III) complexes. In order to differentiate the error due to the chemical shielding tensor calculation from that due to the inadequacy of the molecular geometry prediction, single-crystal X-ray diffraction determined structures were used to build the isolated molecule models for calculating the chemical shifts. The results were compared with those obtained using the calculated geometries at the B3LYP/6-31G(d) level. The isotropic chemical shielding constants computed at different levels have strong linear correlations even though the absolute values differ in tens of ppm. The root-mean-square difference between the experimental chemical shifts and the calculated values is approximately 5 ppm for the calculations based on the X-ray structures, but more than 10 ppm for the calculations based on the computed geometries. The result indicates that the popular theoretical models are adequate in calculating the chemical shifts while an accurate molecular geometry is more critical.

Wang, Xianlong; Wang, Chengfei; Zhao, Hui

2012-01-01

261

Direct and adjoint sensitivity analysis of chemical kinetic systems with KPP: Part I—theory and software tools  

Microsoft Academic Search

The analysis of comprehensive chemical reactions mechanisms, parameter estimation techniques, and variational chemical data assimilation applications require the development of efficient sensitivity methods for chemical kinetics systems. The new release (KPP-1.2) of the kinetic preprocessor (KPP) contains software tools that facilitate direct and adjoint sensitivity analysis. The direct-decoupled method, built using BDF formulas, has been the method of choice for

Adrian Sandu; Dacian N. Daescu; Gregory R. Carmichael

2003-01-01

262

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

NASA Technical Reports Server (NTRS)

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.

Opila, Elizabeth J.

1994-01-01

263

A comparison of the efficiency of numerical methods for integrating chemical kinetic rate equations  

NASA Technical Reports Server (NTRS)

A comparison of the efficiency of several algorithms recently developed for the efficient numerical integration of stiff ordinary differential equations is presented. The methods examined include two general-purpose codes EPISODE and LSODE and three codes (CHEMEQ, CREK1D, and GCKP84) developed specifically to integrate chemical kinetic rate equations. The codes are applied to two test problems drawn from combustion kinetics. The comparisons show that LSODE is the fastest code currently available for the integration of combustion kinetic rate equations. An important finding is that an iterative solution of the algebraic energy conservation equation to compute the temperature can be more efficient than evaluating the temperature by integrating its time-derivative.

Radhakrishnan, K.

1984-01-01

264

Kinetic Demonstration.  

ERIC Educational Resources Information Center

Presents a unit on chemical reaction kinetics that consists of a predemonstration activity, the demonstration, and a set of postdemonstration activities that help students transfer the concepts to actual chemical reactions. Simulates various aspects of chemical reaction kinetics. (JRH)

Burgardt, Erik D.; Ryan, Hank

1996-01-01

265

Calculation of eddy viscosity in a compressible turbulent boundary layer with mass injection and chemical reaction, volume 2. [computer programs  

NASA Technical Reports Server (NTRS)

As described in Vol. 1, the eddy viscosity is calculated through the turbulent kinetic energy, in order to include the history of the flow and the effect of chemical reaction on boundary layer characteristics. Calculations can be performed for two different cooling concepts; that is, transpiration and regeneratively cooled wall cases. For the regenerative cooling option, coolant and gas side wall temperature and coolant bulk temperature in a rocket engine can be computed along the nozzle axis. Thus, this computer program is useful in designing coolant flow rate and cooling tube geometry, including the tube wall thickness as well as in predicting the effects of boundary layers along the gas side wall on thrust performances.

Omori, S.

1973-01-01

266

History and Philosophy of Science through Models: The Case of Chemical Kinetics  

NASA Astrophysics Data System (ADS)

The case for a greater role for the history and philosophy of science in science education is reviewed. It is argued that such a role can only be realised if it is based on both a credible analytical approach to the history and philosophy of science and if the evolution of a sufficient number of major themes in science is known in suitable detail. Adopting Lakatos' Theory of Scientific Research Programmes as the analytical approach, it is proposed that the development, use, and replacement, of specific models forms the core of such programmes.Chemical kinetics was selected as an exemplar major topic in chemistry. Eight models which have played a central role in the evolution of the study of chemical kinetics were identified by an analysis of the literature. The implications that these models have for the teaching and learning of chemistry today are discussed.

Justi, Rosária; Gilbert, John K.

267

New integration techniques for chemical kinetic rate equations. 2: Accuracy comparison  

NASA Technical Reports Server (NTRS)

A comparison of the accuracy of several techniques recently developed for solving stiff differential equations is presented. The techniques examined include two general purpose codes EEPISODE and LSODE developed for an arbitrary system of ordinary differential equations, and three specialized codes CHEMEQ, CREKID, and GCKP84 developed specifically to solve chemical kinetic rate equations. The accuracy comparisons are made by applying these solution procedures to two practical combustion kinetics problems. Both problems describe adiabatic, homogeneous, gas phase chemical reactions at constant pressure, and include all three combustion regimes: induction, heat release, and equilibration. The comparisons show that LSODE is the most efficient code - in the sense that it requires the least computational work to attain a specified accuracy level. An important finding is that an iterative solution of the algebraic enthalpy conservation equation for the temperature can be more accurate and efficient than computing the temperature by integrating its time derivative.

Radhakrishnan, K.

1985-01-01

268

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

SciTech Connect

Detailed chemical kinetic reaction mechanisms are developed for combustion of all nine isomers of heptane (C{sub 7}H{sub 16}), and these mechanisms are tested by simulating autoignition of each isomer under rapid compression machine conditions. The reaction mechanisms focus on the manner in which the molecular structure of each isomer determines the rates and product distributions of possible classes of reactions. The reaction pathways emphasize the importance of alkylperoxy radical isomerizations and addition reactions of molecular oxygen to alkyl and hydroperoxyalkyl radicals. A new reaction group has been added to past models, in which hydroperoxyalkyl radicals that originated with abstraction of an H atom from a tertiary site in the parent heptane molecule are assigned new reaction sequences involving additional internal H atom abstractions not previously allowed. This process accelerates autoignition in fuels with tertiary C-H bonds in the parent fuel. In addition, the rates of hydroperoxyalkylperoxy radical isomerization reactions have all been reduced so that they are now equal to rates of analogous alkylperoxy radical isomerizations, significantly improving agreement between computed and experimental ignition delay times in the rapid compression machine. Computed ignition delay times agree well with experimental results in the few cases where experiments have been carried out for specific heptane isomers, and predictive model calculations are reported for the remaining isomers. The computed results fall into three general groups; the first consists of the most reactive isomers, including n-heptane, 2-methyl hexane and 3-methyl hexane. The second group consists of the least reactive isomers, including 2,2-dimethyl pentane, 3,3-dimethyl pentane, 2,3-dimethyl pentane, 2,4-dimethyl pentane and 2,2,3-trimethyl butane. The remaining isomer, 3-ethyl pentane, was observed computationally to have an intermediate level of reactivity. These observations are generally consistent with knocking tendencies of these isomers, as measured by octane ratings, although the correlations are only approximate.

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

2001-12-17

269

A detailed chemical kinetic model for gas phase combustion of TNT  

Microsoft Academic Search

A detailed chemical kinetic mechanism for gas phase combustion of 2,4,6-tri-nitrotoluene (TNT) has been developed to explore problems of explosive performance and of soot formation during the destruction of munitions. Thermodynamic properties of intermediate and radical species are estimated by group additivity. Reactions for the decomposition and oxidation of TNT and its intermediate products are assembled, based on information from

William J. Pitz; Charles K. Westbrook

2007-01-01

270

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

Microsoft Academic Search

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

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

2005-01-01

271

Kinetics of the chemical oxidation of polysulfide anions in aqueous solution  

Microsoft Academic Search

The kinetic properties of the chemical oxidation of aqueous polysulfide solutions have been studied in phosphate-buffered systems at pH 7–12, at temperatures between 20 and 40°C, and ionic strength between 0.05 and 0.50M. Polysulfide solutions were mixed with a buffer solution of known dissolved oxygen concentration, after which the decrease in the oxygen concentration of the solution was measured in

Wilfred E. Kleinjan; Arie de Keizer; Albert J. H. Janssen

2005-01-01

272

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

PubMed

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

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

2014-03-27

273

Thermodynamics and kinetics of apoazurin folding under macromolecular crowding effect and chemical interference  

NASA Astrophysics Data System (ADS)

Proteins fold in a cellular milieu crowded by different kinds of macromolecules. They exert volume exclusion impacting protein folding processes in vivo. Folding processes, however, has been studied by chemical denaturation under in vitro conditions. The impact of the two factors as an attempt to advance the understanding of folding mechanism in vivo is not understood. Here, we investigate the folding mechanisms of apoazurin affected by the macromolecular crowding and chemical interference by using coarse-grained molecular simulations. Crowding agents are modeled as hard-spheres and the chemical denaturation effects are implemented into an energy function of the side chain and backbone interactions. Protein folding stability, mechanism, and kinetics rates of apoazurin under chemical interference and macromolecular crowding conditions are being investigated.

Zegarra, Fabio; Cheung, Margaret

2013-03-01

274

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

NASA Astrophysics Data System (ADS)

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.

Hu, Yucheng; Li, Tiejun; Min, Bin

2011-07-01

275

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

NASA Astrophysics Data System (ADS)

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.

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

2012-04-01

276

On Validity of Linear Phenomenological Nonequilibrium Thermodynamics Equations in Chemical Kinetics  

NASA Astrophysics Data System (ADS)

The chemical equilibrium state is treated as a fundamental ``reference frame'' in description of chemical reaction. In a definition of reactive absolute activities for components in chemical reaction the difference of chemical potential and its value in the equilibrium is used. The chemical reaction rate is shown to be proportional to the force Xnew defined as the difference of reactive absolute activities of reactants and products. The force Xnew is shown to be equivalent to the force following from chemical kinetics equations and compared with the reduced affinity X as well as with the force of Ross and Mazur XRM = 1 - {exp}(-X). The force Xnew coincides with X and XRM near to the chemical equilibrium state. A range of the molar fraction of product, in which a difference between the forces Xnew and X is relatively small, is larger than it would be for the forces XRM and X. It means that for some chemical reactions the formalism of linear nonequilibrium thermodynamics can be used in wider ranges than usually expected. Particular analysis is presented for simple reactions.

Cukrowski, A. S.; Kolbus, A.

2005-05-01

277

Kinetics Calculation Under Space-Dependent Feedback in Analytic Function Expansion Nodal Method via Solution Decomposition and Galerkin Scheme  

SciTech Connect

To develop kinetics calculational capability of the analytic function expansion nodal methodology for space-dependent feedback problems, a novel method with the time-dependent solution decomposed into an analytic part and a polynomial correction part is proposed. The analytic part consists of the analytic solutions of the 'quasi-static' diffusion equation and the polynomial part is determined by applying a Galerkin scheme. The results tested on several benchmark problems (two-dimensional and three-dimensional) show that 1 node/assembly calculation and a large time-step size can be used for high accuracy. The new feedback calculation method removes almost all the errors induced from space-dependent feedback. Also, it is shown that the coarse group rebalance acceleration scheme and conventional techniques for kinetics calculation (exponential transformation for time variable and bilinear weighting for control rod cusping problem) can be easily incorporated into the method.

Kim, Do Sam; Cho, Nam Zin [Korea Advanced Institute of Science and Technology (Korea, Republic of)

2002-03-15

278

Calibration of Chemical Kinetic Models Using Simulations of Small-Scale Cookoff Experiments  

SciTech Connect

Establishing safe handling limits for explosives in elevated temperature environments is a difficult problem that often requires extensive simulation. The largest influence on predicting thermal cookoff safety lies in the chemical kinetic model used in these simulations, and these kinetic model reaction sequences often contain multiple steps. Several small-scale cookoff experiments, notably Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), One-Dimensional Time-to-Explosion (ODTX), and the Scaled Thermal Explosion (STEX) have been performed on various explosives to aid in cookoff behavior determination. Past work has used a single test from this group to create a cookoff model, which does not guarantee agreement with the other experiments. In this study, we update the kinetic parameters of an existing model for the common explosive 2,4,6-Trinitrotoluene (TNT) using DSC and ODTX experimental data at the same time by minimizing a global Figure of Merit based on hydrodynamic simulated data. We then show that the new kinetic model maintains STEX agreement, reduces DSC agreement, and improves ODTX and TGA agreement when compared to the original model. In addition, we describe a means to use implicit hydrodynamic simulations of DSC experiments to develop a reaction model for TNT melting.

Wemhoff, A P; Becker, R C; Burnham, A K

2008-02-26

279

Chemical Kinetics of the TPS and Base Bleeding During Flight Test  

NASA Technical Reports Server (NTRS)

The present research deals with thermal degradation of polyurethane foam (PUF) during flight test. Model of thermal decomposition was developed that accounts for polyurethane kinetics parameters extracted from thermogravimetric analyses and radial heat losses to the surrounding environment. The model predicts mass loss of foam, the temperature and kinetic of release of the exhaust gases and char as function of heat and radiation loads. When PUF is heated, urethane bond break into polyol and isocyanate. In the first stage, isocyanate pyrolyses and oxidizes. As a result, the thermo-char and oil droplets (yellow smoke) are released. In the second decomposition stage, pyrolysis and oxidization of liquid polyol occur. Next, the kinetics of chemical compound release and the information about the reactions occurring in the base area are coupled to the CFD simulations of the base flow in a single first stage motor vertically stacked vehicle configuration. The CFD simulations are performed to estimate the contribution of the hot out-gassing, chemical reactions, and char oxidation to the temperature rise of the base flow. The results of simulations are compared with the flight test data.

Osipov, Viatcheslav; Ponizhovskaya, Ekaterina; Hafiychuck, Halyna; Luchinsky, Dmitry; Smelyanskiy, Vadim; Dagostino, Mark; Canabal, Francisco; Mobley, Brandon L.

2012-01-01

280

CCSD(T) calculation of NMR chemical shifts: consistency of calculated and measured 13C chemical shifts in the 1-cyclopropylcyclopropylidenemethyl cation  

NASA Astrophysics Data System (ADS)

The source of conspicuous disagreement between theory and experiment for the chemical shift of C ? in the 1-cyclopropylcyclopropylidenemethyl cation is identified as an inadequate treatment of electron correlation effects in a previous theoretical study. When the sophisticated CCSD(T) method is used, all calculated 13C chemical shifts agree with the experimental values to within 2.2 ppm. These findings undermine the basis of an earlier suggestion that the selectively poor performance of theory for the C ? nucleus can be attributed to environmental effects in which solvent interactions significantly perturb the geometrical structure of the cation.

Stanton, John F.; Gauss, Jürgen; Siehl, Hans-Ullrich

1996-11-01

281

Model calculations of kinetic and fluid dynamic processes in diode pumped alkali lasers  

NASA Astrophysics Data System (ADS)

Kinetic and fluid dynamic processes in diode pumped alkali lasers (DPALs) are analyzed in detail using a semianalytical model, applicable to both static and flowing-gas devices. The model takes into account effects of temperature rise, excitation of neutral alkali atoms to high lying electronic states and their losses due to ionization and chemical reactions, resulting in a decrease of the pump absorption, slope efficiency and lasing power. Effects of natural convection in static DPALs are also taken into account. The model is applied to Cs DPALs and the results are in good agreement with measurements in a static [B.V. Zhdanov, J. Sell and R.J. Knize, Electron. Lett. 44, 582 (2008)] and 1-kW flowing-gas [A.V. Bogachev et al., Quantum Electron. 42, 95 (2012)] DPALs. It predicts the dependence of power on the flow velocity in flowing-gas DPALs and on the buffer gas composition. The maximum values of the laser power can be substantially increased by optimization of the flowing-gas DPAL parameters. In particular for the aforementioned 1 kW DPAL, 6 kW maximum power is achievable just by increasing the pump power and the temperature of the wall and the gas at the flow inlet (resulting in increase of the alkali saturated vapor density). Dependence of the lasing power on the pump power is non-monotonic: the power first increases, achieves its maximum and then decreases. The decrease of the lasing power with increasing pump power at large values of the latter is due to the rise of the aforementioned losses of the alkali atoms as a result of ionization. Work in progress applying two-dimensional computational fluid dynamics modeling of flowing-gas DPALs is also reported.

Barmashenko, Boris D.; Rosenwaks, Salman; Waichman, Karol

2013-10-01

282

The multiconfiguration time-dependent Hartree-Fock method for quantum chemical calculations  

Microsoft Academic Search

We apply the multiconfiguration time-dependent Hartree-Fock method to electronic structure calculations and show that quantum chemical information can be obtained with this explicitly time-dependent approach. Different equations of motion are discussed, as well as the numerical cost. The two-electron integrals are calculated using a natural potential expansion, of which we describe the convergence behavior in detail.

M. Nest; T. Klamroth; P. Saalfrank

2005-01-01

283

Controls on chemical weathering kinetics: Implications from modelling of stable isotope fractionations  

NASA Astrophysics Data System (ADS)

The kinetic controls on silicate chemical weathering rates are thought central to the feedback process that regulates global climate on geological time scales. However the nature and magnitude of these kinetic controls are controversial. In particular the importance of physical erosion rates is uncertain with some arguing that there is an upper limit on chemical weathering fluxes irrespective of physical erosion rates (e.g. Dixon and von Blackenburg, 2012). Others argue that it is the hydrology of catchments which determines flow path lengths and fluid residence times which are critical to chemical weathering fluxes (e.g. Maher, 2011). Understanding these physical controls is essential to predicting how chemical weathering fluxes will respond the key climatic controls. Chemical weathering fluxes are best estimated by the integrated riverine outputs from catchments as soil profiles may not integrate all the flow paths. However the interpretation of chemical weathering processes based solely on flux data is difficult, because of both the multiple processes acting and multiple phases dissolving that contribute to these fluxes. Fractionations of stable isotopes of the soluble elements including Li, Mg, Si and Ca should place additional constraints on chemical weathering processes. Here we use a simple reactive-transport model to interpret stable isotope fractionations. Although still a simplification of the natural system, this offers a much closer representation than simple batch and Rayleigh models. The isotopic fractionations are shown to be a function of the ratio of the amount of the element supplied by mineral dissolution to that lost to secondary mineral formation and the extent of reaction down the flow path. The modelling is used to interpret the evolution of dissolved Li, Mg and Si-isotope ratios in Ganges river system. The evolution of Si isotopic ratios in the rapidly eroding Himalayan catchments is distinct from that in the flood planes. Critically the extent of the isotopic fractionations is a measure of the approach of the system to chemical equilibrium, a key indicator of the temperature sensitivity of the chemical weathering rate and hence important to understanding the climate-weathering feedback. Dixon JL, & von Blanckenburg, F, (2012) Soils as pacemakers and limiters of global silicate weathering. Comptes Rendus Geoscience, 344:597-609. Maher, K (2011) The role of fluid residence time and topographic scales in determining chemical fluxes from landscapes. Earth and Planetary Science Letters, 312:48-58.

Bickle, M. J.; Tipper, E.; De La Rocha, C. L.; Galy, A.; Li, S.

2013-12-01

284

Reaction and diffusion kinetics during the initial stages of isothermal chemical vapor infiltration  

SciTech Connect

This paper reports that individual bundles of ceramic fibers were infiltrated with SiC to study the reaction and diffusion kinetics during isothermal chemical vapor infiltration (CVI). More uniform infiltration was observed in samples where baffles were placed in the reactor and when HC1 was added to the inlet gases. The evolution of the microstructure was modeled using an analytical expression for impinging cylindrical fibers. The transport of reactants was treated using classical descriptions of molecular and Knudsen diffusion in a porous body and also by considering the existence of a percolation threshold. All of these models predict that infiltration should be more uniform than the results that were obtained experimentally. It is possible that this discrepancy occurs because mass transport is more complex than the descriptions that were used. However, a more likely explanation is that the deposition kinetics are significantly more complex than the simple first-order reaction that was used for these models.

Sheldon, B.W. (Brown Univ., Providence, RI (United States). Div. of Engineering); Besmann, T.M. (Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.)

1991-12-01

285

Communication: Kinetics of chemical ordering in Ag-Au and Ag-Ni nanoalloys  

NASA Astrophysics Data System (ADS)

The energy landscape and kinetics of medium-sized Ag-Au and Ag-Ni nanoalloy particles are explored via a discrete path sampling approach, focusing on rearrangements connecting regions differing in chemical order. The highly miscible Ag27Au28 supports a large number of nearly degenerate icosahedral homotops. The transformation from reverse core-shell to core-shell involves large displacements away from the icosahedron through elementary steps corresponding to surface diffusion and vacancy formation. The immiscible Ag42Ni13 naturally forms an asymmetric core-shell structure, and about 10 eV is required to extrude the nickel core to the surface. The corresponding transformation occurs via a long and smooth sequence of surface displacements. For both systems the rearrangement kinetics exhibit Arrhenius behavior. These results are discussed in the light of experimental observations.

Calvo, F.; Fortunelli, A.; Negreiros, F.; Wales, D. J.

2013-09-01

286

Chemical kinetics and interactions involved in horseradish peroxidase-mediated oxidative polymerization of phenolic compounds.  

PubMed

The primary objective of this research was to evaluate various factors that affect the reaction rate of oxidative coupling (OXC) reaction of phenolic estrogens catalyzed by horseradish peroxidase (HRP). Kinetic parameters were obtained for the conversion of phenol as well as natural and synthetic estrogens estrone (E(1)), 17?-estradiol (E(2)), estriol (E(3)), and 17?-ethinylestradiol (EE(2)). Molecular orbital theory and Autodock software were employed to analyze chemical properties and substrate binding characteristics. Reactions were first order with respect to phenolic concentration and reaction rate constants (k(r)) were determined for phenol, E(3), E(1), E(2) and EE(2) (in increasing order). Oxidative coupling was controlled by enzyme-substrate interactions, not collision frequency. Docking simulations show that higher binding energy and a shorter binding distance both promote more favorable kinetics. This research is the first to show that the OXC of phenolics is an entropy-driven and enthalpy-retarded process. PMID:22305176

Cheng, Wenjing; Harper, Willie F

2012-03-10

287

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

SciTech Connect

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)

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

288

Calculation of NMR chemical shifts in organic solids: accounting for motional effects.  

PubMed

NMR chemical shifts were calculated from first principles for well defined crystalline organic solids. These density functional theory calculations were carried out within the plane-wave pseudopotential framework, in which truly extended systems are implicitly considered. The influence of motional effects was assessed by averaging over vibrational modes or over snapshots taken from ab initio molecular dynamics simulations. It is observed that the zero-point correction to chemical shifts can be significant, and that thermal effects are particularly noticeable for shielding anisotropies and for a temperature-dependent chemical shift. This study provides insight into the development of highly accurate first principles calculations of chemical shifts in solids, highlighting the role of motional effects on well defined systems. PMID:19292543

Dumez, Jean-Nicolas; Pickard, Chris J

2009-03-14

289

Probing the cruzain S2 recognition subsite: a kinetic and binding energy calculation study.  

PubMed

Cysteine proteases are relevant to several aspects of the parasite life cycle and the parasite-host relationship. Moreover, they appear as promising targets for antiparasite chemotherapy. Here, a quantitative investigation on the catalytic properties of cruzain, the papain-like cysteine protease from epimastigotes of Trypanosoma cruzi, is reported. The results indicate that kinetics for the cruzain catalyzed hydrolysis of N-alpha-benzyloxycarbonyl-l-arginyl-l-alanine-(7-amino-4-methylcoumarin), N-alpha-benzyloxycarbonyl-l-phenylalanyl-l-alanine-(7-amino-4-methylcoumarin), and N-alpha-benzyloxycarbonyl-l-tyrosyl-l-alanine-(7-amino-4-methylcoumarin) can be consistently fitted to the minimum three-step mechanism of cysteine proteases involving the acyl.enzyme intermediate E.P; the deacylation step is rate-limiting in enzyme catalysis. Remarkably, these substrates show identical catalytic parameters. This reflects the ability of the cruzain Glu205 residue, located at the bottom of the S(2) subsite, to neutralize the substrate/inhibitor polar P(2) residues (e.g., Arg or Tyr) and to be solvent-exposed when substrate/inhibitor nonpolar P(2) residues (e.g., Phe) fit the S(2) subsite. More complex catalytic mechanisms are also discussed. Binding free-energy calculation provides a quantitative framework for the interpretation of these results; in particular, direct evidence for the compensatory effect between Coulomb interaction(s) and solvation effect(s) is reported. These results appear of general significance for a deeper understanding of (macro)molecular recognition and for the rational design of novel inhibitors of parasitic cysteine proteases. PMID:15723522

Polticelli, Fabio; Zaini, Germano; Bolli, Alessandro; Antonini, Giovanni; Gradoni, Luigi; Ascenzi, Paolo

2005-03-01

290

Kinetics of ion-molecule reactions with dimethyl methylphosphonate at 298 K for chemical ionization mass spectrometry detection of GX.  

PubMed

Kinetics studies of a variety of positive and negative ions reacting with the GX surrogate, dimethyl methylphosphonate (DMMP), were performed. All protonated species reacted rapidly, that is, at the collision limit. The protonated reactant ions created from neutrals with proton affinities (PAs) less than or equal to the PA for ammonia reacted exclusively by nondissociative proton transfer. Hydrated H(3)O(+) ions also reacted rapidly by proton transfer, with 25% of the products from the second hydrate, H(3)O(+)(H(2)O)(2), forming the hydrated form of protonated DMMP. Both methylamine and triethylamine reacted exclusively by clustering. NO(+) also clustered with DMMP at about 70% of the collision rate constant. O(+) and O(2)(+) formed a variety of products in reactions with DMMP, with O(2)(+) forming the nondissociative charge transfer product about 50% of the time. On the other hand, many negative ions were less reactive, particularly, SF(5)(-), SF(6)(-), CO(3)(-), and NO(3)(-). However, F(-), O(-), and O(2)(-) all reacted rapidly to generate m/z = 109 amu anions (PO(3)C(2)H(6)(-)). In addition, product ions with m/z = 122 amu from H(2)(+) loss to form H(2)O were the dominant ions produced in the O(-) reaction. NO(2)(-) underwent a slow association reaction with DMMP at 0.4 Torr. G3(MP2) calculations of the ion energetics properties of DMMP, sarin, and soman were also performed. The calculated ionization potentials, proton affinities, and fluoride affinities were consistent with the trends in the measured kinetics and product ion branching ratios. The experimental results coupled with the calculated ion energetics helped to predict which ion chemistry would be most useful for trace detection of the actual chemical agents. PMID:19385679

Midey, Anthony J; Miller, Thomas M; Viggiano, A A

2009-04-30

291

17O NMR investigation of rigid polycyclic systems: experimental and calculated chemical shifts  

NASA Astrophysics Data System (ADS)

In this work we describe a systematic and comparative study of the 17O NMR and related parameters of 17 polycyclic compounds: bicyclic, tricyclic, tetracyclic ( endo-endo and endo-exo fusion), pentacyclic compounds (ketone; endo and exo-alcohols), hexacyclic alcohol. Concentration, temperature and solvent effects on the 17O NMR chemical shifts and the relaxation rate are also described. We compare all experimental 17O NMR chemical shifts with chemical shifts calculated from gauge-independent atomic orbitals within density functional theory (GIAO-DFT). Correlations between calculated and experimental 17O NMR chemical shifts for respective functional groups were carried out and linear equations for chemical shift predictions were generated.

Uberti Costa, Valentim E.; Grunewald Nichele, Aline; Carneiro, José Walkimar de M.

2004-09-01

292

Minimal curvature trajectories: Riemannian geometry concepts for slow manifold computation in chemical kinetics  

NASA Astrophysics Data System (ADS)

In dissipative ordinary differential equation systems different time scales cause anisotropic phase volume contraction along solution trajectories. Model reduction methods exploit this for simplifying chemical kinetics via a time scale separation into fast and slow modes. The aim is to approximate the system dynamics with a dimension-reduced model after eliminating the fast modes by enslaving them to the slow ones via computation of a slow attracting manifold. We present a novel method for computing approximations of such manifolds using trajectory-based optimization. We discuss Riemannian geometry concepts as a basis for suitable optimization criteria characterizing trajectories near slow attracting manifolds and thus provide insight into fundamental geometric properties of multiple time scale chemical kinetics. The optimization criteria correspond to a suitable mathematical formulation of "minimal relaxation" of chemical forces along reaction trajectories under given constraints. We present various geometrically motivated criteria and the results of their application to four test case reaction mechanisms serving as examples. We demonstrate that accurate numerical approximations of slow invariant manifolds can be obtained.

Lebiedz, Dirk; Reinhardt, Volkmar; Siehr, Jochen

2010-09-01

293

Multiphase chemical kinetics of NO3 radicals reacting with organic aerosol components from biomass burning.  

PubMed

Multiphase reactions with nitrate radicals are among the most important chemical aging processes of organic aerosol particles in the atmosphere especially at nighttime. Reactive uptake of NO(3) by organic compounds has been observed in a number of studies, but the pathways of mass transport and chemical reaction remained unclear. Here we apply kinetic flux models to experimental NO(3) exposure studies. The model accounts for gas phase diffusion within a cylindrical flow tube, reversible adsorption of NO(3), surface-bulk exchange, bulk diffusion, and chemical reactions from the gas-condensed phase interface to the bulk. We resolve the relative contributions of surface and bulk reactions to the uptake of NO(3) by levoglucosan and abietic acid, which serve as surrogates and molecular markers of biomass burning aerosol (BBA). Applying the kinetic flux model, we provide the first estimate of the diffusion coefficient of NO(3) in amorphous solid organic matrices (10(-8)-10(-7) cm(2) s(-1)) and show that molecular markers are well-conserved in the bulk of solid BBA particles but undergo rapid degradation upon deliquescence/liquefaction at high relative humidity, indicating that the observed concentrations and subsequent apportionment of the biomass burning source could be significantly underestimated. PMID:22594762

Shiraiwa, Manabu; Pöschl, Ulrich; Knopf, Daniel A

2012-06-19

294

Chemical Kinetic Simulation of the Combustion of Bio-based Fuels  

SciTech Connect

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.

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

2007-10-01

295

Effect of off-design operation of MHD generators on NO/x/ chemical kinetics  

NASA Technical Reports Server (NTRS)

The purpose of this study is to provide a capability for determining the chemical kinetic behavior of one family of pollutants, the nitrogen oxides, in the flow of a coal-fired MHD generator facility. The method used in the study allows the prediction of the nonequilibrium concentration of the minor NO(x) species in a flow otherwise assumed in equilibrium. Consideration is given to the effect of preheat, stoichiometry, and oxygen enrichment of the NO(x) concentration. The effect of preheat and stoichiometry is found to have a significant influence on the NO(x) concentration at the exit of the radiant boiler.

Simmons, G. A.; Wilson, D. R.

1980-01-01

296

A numerical scheme for optimal transition paths of stochastic chemical kinetic systems  

NASA Astrophysics Data System (ADS)

We present a new framework for finding the optimal transition paths of metastable stochastic chemical kinetic systems with large system size. The optimal transition paths are identified to be the most probable paths according to the Large Deviation Theory of stochastic processes. Dynamical equations for the optimal transition paths are derived using the variational principle. A modified Minimum Action Method (MAM) is proposed as a numerical scheme to solve the optimal transition paths. Applications to Gene Regulatory Networks such as the toggle switch model and the Lactose Operon Model in Escherichia coli are presented as numerical examples.

Liu, Di

2008-10-01

297

A Chemical Kinetic Mechanism for the Ignition of Silane/Hydrogen Mixtures  

NASA Technical Reports Server (NTRS)

A chemical kinetic reaction mechanism for the oxidation of silane/hydrogen mixtures is presented and discussed. Shock-tube ignition delay time data were used to evaluate and refine the mechanism. Good agreement between experimental results and the results predicted by the mechanism was obtained by adjusting the rate coefficient for the reaction SiH3 + O2 yields SiH2O + OH. The reaction mechanism was used to theoretically investigate the ignition characteristics of silane/hydrogen mixtures. The results revealed that over the entire range of temperature examined (800 K to 1200 K), substantial reduction in ignition delay times is obtained when silane is added to hydrogen.

Jachimowski, C. J.; Mclain, A. G.

1983-01-01

298

A simplified chemical kinetic model for slightly ionized, atmospheric pressure nitrogen plasmas  

NASA Astrophysics Data System (ADS)

Nitrogen plasmas at atmospheric pressure produced by 2.45 GHz microwaves at a power density of approximately 10 MW m-3 have a degree of ionization less than about 10-7. Nevertheless they have interesting and potentially important effects on polymer and metal surfaces exposed to them. An experimental programme is underway to identify the active species in the plasma and its afterglow. This paper describes a simplified model of the chemical kinetics in the plasma that allows species concentrations to be estimated in a range of conditions, for comparison with experimental data. It predicts a high degree of dissociation combined with low gas temperature in microwave-generated plasmas.

Hugill, J.; Saktioto, T.

2001-02-01

299

Chemical composition and growing kinetics of titanium nitrided layers under CO2 laser irradiation  

NASA Astrophysics Data System (ADS)

The growth and morphology of nitrided layers formed during the solid phase nitriding of pure titanium by CO2 laser were investigated. In the case of a laser treatment carried out under isothermal conditions, it was shown that CO2 photons irradiation of the substrate does not produce any specific assisted nitride growth: nitriding kinetics, nitride composition and structure were similar to those obtained after nitriding using a classical heating system. From the nitriding kinetics, nitrogen diffusion coefficients were determined using an analytical solution of Fick's equation. This allows to plot the evolution of the nitrogen concentration with respect to depth and to compare calculated profiles to those determined experimentally by Nuclear Reaction Microanalysis.

Laurens, Patricia; L'Enfant, Herve; Dubois, Thierry; Saint Catherine, Marie C.

1997-08-01

300

Momentum Transfer Approximation for the Calculation of Molecular Transition Probabilities in High Temperature Gas Kinetic Collisions.  

National Technical Information Service (NTIS)

A straightforward method, the momentum transfer approximation, is proposed for the determination of the probabilities of inelastic (non-electronic) processes in high temperature gas kinetic collisions. The approximation is applicable to polyatomic as well...

A. P. Proudian

1965-01-01

301

Kinetics  

NSDL National Science Digital Library

Conceptual questions about kinetics. For example, "[w]hat are the reaction velocity, the rates of formation of N2 and H2, and the rate of decomposition of ammonia for the decomposition of ammonia on a tungsten surface under the conditions reflected in the figure."

Nurrenbern, Susan C.; Robinson, William R.

2008-02-27

302

Critical Evaluation of Jet-a Spray Combustion Using Propane Chemical Kinetics in Gas Turbine Combustion Simulated by KIVA-2.  

National Technical Information Service (NTIS)

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 c...

H. L. Nguyen S. Ying

1990-01-01

303

FORTRAN 4 computer program for calculation of thermodynamic and transport properties of complex chemical systems  

NASA Technical Reports Server (NTRS)

A FORTRAN IV computer program for the calculation of the thermodynamic and transport properties of complex mixtures is described. The program has the capability of performing calculations such as:(1) chemical equilibrium for assigned thermodynamic states, (2) theoretical rocket performance for both equilibrium and frozen compositions during expansion, (3) incident and reflected shock properties, and (4) Chapman-Jouguet detonation properties. Condensed species, as well as gaseous species, are considered in the thermodynamic calculation; but only the gaseous species are considered in the transport calculations.

Svehla, R. A.; Mcbride, B. J.

1973-01-01

304

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

PubMed Central

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.

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

2012-01-01

305

Kinetics of gas-phase reactions relevant to the chemical vapor deposition of indium compounds  

SciTech Connect

Compounds containing indium are of interest for electronic and optical applications. These compounds include III-V semiconductors such as InP and InAs used in both electronic devices and solar cells, and indium tin oxide, which can be used for optical memory and antireflection coatings. Chemical vapor deposition (CVD) techniques can be used to deposit these materials on a variety of substrates. At the temperatures typically employed (550--900 K), gas-phase chemical reactions involving the indium-containing precursor can occur. The kinetics of trimethylindium pyrolysis are investigated in a flow reactor equipped with a molecular-beam mass-spectrometric sampling system. Data are analyzed using a new computational approach that accounts for heat and mass transport in the reactor. The measured activation energy, 46.2 kcal/mol, is in good agreement with previously reported values.

Allendorf, M.D.; McDaniel, A.H.

1998-03-01

306

Using NMR chemical shifts to calculate the propensity for structural order and disorder in proteins.  

PubMed

NMR spectroscopy offers the unique possibility to relate the structural propensities of disordered proteins and loop segments of folded peptides to biological function and aggregation behaviour. Backbone chemical shifts are ideally suited for this task, provided that appropriate reference data are available and idiosyncratic sensitivity of backbone chemical shifts to structural information is treated in a sensible manner. In the present paper, we describe methods to detect structural protein changes from chemical shifts, and present an online tool [ncSPC (neighbour-corrected Structural Propensity Calculator)], which unites aspects of several current approaches. Examples of structural propensity calculations are given for two well-characterized systems, namely the binding of ?-synuclein to micelles and light activation of photoactive yellow protein. These examples spotlight the great power of NMR chemical shift analysis for the quantitative assessment of protein disorder at the atomic level, and further our understanding of biologically important problems. PMID:22988857

Tamiola, Kamil; Mulder, Frans A A

2012-10-01

307

Kinetics Calculation Under Space-Dependent Feedback in Analytic Function Expansion Nodal Method via Solution Decomposition and Galerkin Scheme  

Microsoft Academic Search

To develop kinetics calculational capability of the analytic function expansion nodal methodology for space-dependent feedback problems, a novel method with the time-dependent solution decomposed into an analytic part and a polynomial correction part is proposed. The analytic part consists of the analytic solutions of the 'quasi-static' diffusion equation and the polynomial part is determined by applying a Galerkin scheme. The

Do Sam Kim; Nam Zin Cho

2002-01-01

308

A kinetic Monte Carlo study of proton diffusion in disordered perovskite structured lattices based on first-principles calculations  

Microsoft Academic Search

A jump-diffusion model is introduced to describe proton diffusion in cubic perovskites. It is solved using both an analytical matrix approach and kinetic Monte Carlo simulations. The model is applied to In-doped BaZrO3 and we use first-principles calculations to determine binding energies and diffusion barriers. We find that dopants act as traps and reduce the diffusion coefficient with about one

Mårten E. Björketun; Per G. Sundell; Göran Wahnström; Dennis Engberg

2005-01-01

309

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

PubMed Central

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.

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

2013-01-01

310

Respirometric evaluation of a mixture of organic chemicals with different biodegradation kinetics.  

PubMed

The study evaluated the biodegradation characteristics of a mixture of organics with different biodegradation characteristics in an integrated chemical plant effluent. The wastewater had a total chemical oxygen demand (COD) content of 12,800mg/L, mostly soluble and 93% biodegradable. The evaluation was based on respirometry, and mainly consisted on model calibration and interpretation of the oxygen uptake rate data, which exhibited an original and specific profile with a sequence of two peaks and three plateaus. A specific model was defined for this purpose, which identified four different biodegradable COD components with significantly different process kinetics. The major fraction accounting for 57% of the total biodegradable COD in the wastewater had to be hydrolyzed before biodegradation with a low hydrolysis rate of 1.3day(-1). The analysis of the experimental data showed that the oxygen utilization started with a delayed response after substrate addition. The delayed logarithmic phase could be characterized by a Haldane type of inhibition kinetics. PMID:18439757

Cokgor, Emine Ubay; Insel, Güçlü; Aydin, Egemen; Orhon, Derin

2009-01-15

311

Reduction Kinetics of a CasO4 Based Oxygen Carrier for Chemical-Looping Combustion  

NASA Astrophysics Data System (ADS)

The CaSO4 based oxygen carrier has been proposed as an alternative low cost oxygen carrier for Chemical-looping combustion (CLC) of coal. The reduction of CaSO4 to CaS is an important step for the cyclic process of reduction/oxidation in CLC of coal with CaSO4 based oxygen carrier. Thermodynamic analysis of CaSO4 oxygen carrier with CO based on the principle of Gibbs free energy minimization show that the essentially high purity of CO2 can be obtained, while the solid product is CaS instead of CaO. The intrinsic reduction kinetics of a CaSO4 based oxygen carrier with CO was investigated in a differential fixed bed reactor. The effects of gas partial pressure (20%-70%) and temperature (880-950°C) on the reduction were investigated. The reduction was described with shrinking unreacted core model. Experimental results of CO partial pressure on the solid conversion show that the reduction of fresh oxygen carriers is of first order with respect to the CO partial pressure. Both chemical reaction control and product layer diffusion control determine the reduction rate. The dependences of reaction rate constant and effective diffusivity with temperature were both obtained. The kinetic equation well predicted the experimental data.

Xiao, R.; Song, Q. L.; Zheng, W. G.; Deng, Z. Y.; Shen, L. H.; Zhang, M. Y.

312

Self-consistent treatment of dynamics and chemistry in the winds from carbon-rich AGB stars. I. Tests of the equilibrium and kinetic chemical codes  

NASA Astrophysics Data System (ADS)

Aims:The main aim of this paper was to test our (chemical and kinetic) codes, which will be used during self-consistent modelling of dynamics and chemistry in the winds from C-rich AGB stars. Methods: We used the thermodynamical equilibrium code to test the different databases of dissociation constants. We also calculated the equilibrium content of the gas using the kinetic code that includes the chemical network of neutral-neutral reactions. The influence of reaction rates updated using the UMIST database for Astrochemistry 2005 (UDFA05) was tested. Results: The local thermodynamical equilibrium calculations show that the NIST database reproduces equilibrium concentrations fairly well in comparison with previous computations, while consistency for the other, commonly used, dissociation constants is worse. The most important finding is that the steady state solution obtained with the kinetic code for the reactions network is different from the thermodynamical equilibrium solution. In particular, the important opacity sources CN and C2 are underabundant relative to thermodynamical equilibrium, while O-bearing molecules (like SiO, H{2}O, and OH) are overabundant. After updating the reaction rates by data from the UDFA05 database, the consistency in O-bearing species becomes much better, however the disagreement in C-bearing species is still present. Figures 3-5 and 7 are only available in electronic form at http://www.aanda.org

Pu?ecka, M.; Schmidt, M. R.; Shematovich, V. I.; Szczerba, R.

2007-07-01

313

Turbulence interacting with chemical kinetics in airbreathing combustion of ducted rockets  

NASA Astrophysics Data System (ADS)

Physical interactions between turbulence and shock waves are very complex phenomena. If these interactions take place in chemically reacting flows the degree of complexity increases dramatically. Examples of applications may be cited in the area of supersonic combustion, in which the controlled generation of turbulence and/or large scale vortices in the mixing and flame holding zones is crucial for efficient combustion. Equally important, shock waves interacting with turbulence and chemical reactions affect the combustor flowfield resulting in enhanced relaxation and chemical reaction rates. Chemical reactions in turn contribute to dispersion of shock waves and reduction of turbulent kinetic energies. Computational schemes to address these physical phenomena must be capable of resolving various length and time scales. These scales are widely disparate and the most optimum approach is found in explicit/ implicit adjustable schemes for the Navier-Stokes solver. This is accomplished by means of the generalized Taylor-Galerkin (GTG) finite element formulations. Adaptive meshes are used in order to assure efficiency and accuracy of solutions. Various benchmark problems are presented for illustration of the theory and applications. Geometries of ducted rockets, supersonic diffusers, flame holders, and hypersonic inlets are included. Merits of proposed schemes are demonstrated through these example problems.

Chung, T. J.; Yoon, W. S.

1992-10-01

314

Fast semiempirical calculations for nuclear magnetic resonance chemical shifts: A divide-and-conquer approach  

NASA Astrophysics Data System (ADS)

A new approach to calculate nuclear magnetic resonance chemical shifts has been implemented at the semiempirical modified neglect of diatomic overlap level using gauge-including atomic orbitals. The perturbed density matrix with respect to the magnetic field is obtained by the diagonalization of the complex Fock matrix using the divide and conquer (DC) method, instead of by solving the computationally expensive coupled perturbed Hartree-Fock equations. Adopting the Patchkovskii and Thiel parameters [S. Patchkovskii and W. Thiel J. Comput. Chem. 20, 1220 (1999)], we were able to reproduce their results for small organic molecules. The errors introduced by DC method are negligible, as shown by the calculations on a series of polyalaine structures. Test calculations on proteins have demonstrated that our approach makes it possible to calculate chemical shifts routinely on systems with hundreds of atoms with good accuracy.

Wang, Bing; Brothers, Edward N.; van der Vaart, Arjan; Merz, Kenneth M.

2004-06-01

315

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

SciTech Connect

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 profiles as a function of time. These temperature profiles are then used as input to a multi-zone chemical kinetics code. The advantage of this procedure is that a small number of zones (10) is enough to obtain accurate results. This procedure achieves the benefits of linking the fluid mechanics and the chemical kinetics codes with a great reduction in the computational effort, to a level that can be handled with current computers. The success of this procedure is in large part a consequence of the fact that for much of the compression stroke the chemistry is inactive and thus has little influence on fluid mechanics and heat transfer. Then, when chemistry is active, combustion is rather sudden, leaving little time for interaction between chemistry and fluid mixing and heat transfer. This sequential methodology has been capable of explaining the main characteristics of HCCI combustion that have been observed in experiments. In this paper, we use our model to explore an HCCI engine running on propane. The paper compares experimental and numerical pressure traces, heat release rates, and hydrocarbon and carbon monoxide emissions. The results show an excellent agreement, even in parameters that are difficult to predict, such as chemical heat release rates. Carbon monoxide emissions are reasonably well predicted, even though it is intrinsically difficult to make good predictions of CO emissions in HCCI engines. The paper includes a sensitivity study on the effect of the heat transfer correlation on the results of the analysis. Importantly, the paper also shows a numerical study on how parameters such as swirl rate, crevices and ceramic walls could help in reducing HC and CO emissions from HCCI engines.

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

2000-11-29

316

Gas phase chemical kinetics at high temperature of carbonaceous molecules: application to circumstellar envelopes  

NASA Astrophysics Data System (ADS)

Circumstellar shells of evolved stars are a theater of extremely rich physical and chemical processes. More than seventy molecules of varied nature have been identified in the envelopes through their spectral fingerprints in the microwave or far infrared regions. Many of them are carbon chain molecules and radicals and a significant number are unique to the circumstellar medium. However, observational data remain scarce and more than half of the detected species have been observed in only one object, the nearby carbon star IRC + 10216. Chemical kinetic models are needed to describe the formation of molecules in evolved circumstellar outflows. Upcoming terrestrial telescopes such as ALMA will increase the spatial resolution by several orders of magnitude and provide a wealth of data. The determination of relevant laboratory kinetics data is critical to keep up with the development of the observations and of the refinement of chemical models. Today, the majority of reactions studied in the laboratory are the ones involved in combustion and concerning light hydrocarbons. Our objective is to provide the scientific community with rate coefficients of reactions between abundant species in these warm environments. Cyanopolyynes from HC_2N to HC_9N have all been detected in carbon rich circumstellar envelopes in up to 10 sources for HC_3N. Neutral-neutral reactions of the CN radical with unsaturated hydrocarbons could be a dominant route in the formation of cyanopolyynes, even at low temperatures. Our approach aims to bridge the temperature gap between resistively heated flow tubes and shock tubes. The present kinetic measurements are obtained using a new reactor combining a high enthalpy source (Moudens et al. 2011) with a flow tube and a pulsed laser photolysis and laser induced fluorescence system to probe the undergoing chemical reactions. The high enthalpy flow tube has been used to measure the rate constant of the reaction of the CN radical with propane, propene, propadiene, 1,3-butadiene, and butyne over a temperature range extending from 300 to 1200 K. The majority of the reactions studied are rapid, with rate constants greater than 10-10 cm^3 molecule-1 s-1.

Biennier, L.; Gardez, A.; Saidani, G.; Georges, R.; Rowe, B.; Reddy, K. P. J.

2011-05-01

317

Finite volume method for the calculation of compressible chemically reacting flows  

SciTech Connect

Several efficient pseudo time techniques have been developed for calculating steady state chemically reacting flows. The techniques include the implicit treatment of the chemical source term, point implicit multiple grid accelerator and a constant CFL condition. It turns out that these methods can be viewed as ways of rescaling the equations in time such that all chemical and convective phenomena evolve at comparable pseudo time scales. Consequently the number of iterations needed to solve reacting problems is approximately the same as for non-reacting problems. The techniques are demonstrated for a simple dissociation model and a nontrivial H2 - Air combustion model.

Bussing, T.R.A.; Murman, E.M.

1983-01-01

318

Modeling Multiphase Chemical Kinetics of OH Radical Reacting with Biomass Burning Organic Aerosol  

NASA Astrophysics Data System (ADS)

Levoglucosan, abietic acid and nitroguaiacol are commonly used as molecular tracers of biomass burning in source apportionment. Recent studies have demonstrated the decay of levoglucosan when the particles were exposed to atmospherically relevant concentration of OH radicals [1-3]. However, multiphase chemical kinetics of OH radical reacting with such compounds has not fully understood. Here we apply the kinetic multi-layer model for gas-particle interactions (KM-GAP) [4] to experimental data of OH exposure to levoglucosan, abietic acid and nitroguaiacol [1]. KM-GAP resolves the following mass transport and chemical reactions explicitly: gas-phase diffusion, reversible surface adsorption, surface reaction, surface-bulk transport, bulk diffusion and reaction. The particle shrink due to the evaporation of volatile reaction products is also considered. The time- and concentration-dependence of reactive uptake coefficient of OH radicals were simulated by KM-GAP. The measured OH uptake coefficients were fitted by a Monte Carlo (MC) filtering coupled with a genetic algorithm (GA) to derive physicochemical parameters such as bulk diffusion coefficient, Henry's law coefficient and desorption lifetime of OH radicals. We assessed the relative contribution of surface and bulk reactions to the overall uptake of OH radicals. Chemical half-life and the evaporation time scale of these compounds are estimated in different scenarios (dry, humid and cloud processing conditions) and at different OH concentrations. REFERENCES [1] J. H. Slade, D. A. Knopf, Phys. Chem. Chem. Phys., 2013, 15, 5898. [2] S. H. Kessler, J. D. Smith, D.L. Che, D.R. Worsnop, K. R. Wilson, J. H. Kroll, Environ. Sci. Technol., 2010, 44, 7005. [3] C. J. Hennigan, A. P. Sullivan, J. L. Collett Jr, A. L. Robinson, Geophys. Res. Lett., 2010, 37, L09806. [4] M. Shiraiwa, C. Pfrang, T. Koop, U. Pöschl, Atmos. Chem. Phys, 2012, 12, 2777.

Arangio, Andrea; Slade, Jonathan H.; Berkemeier, Thomas; Knopf, Daniel A.; Shiraiwa, Manabu

2014-05-01

319

Numerical Modeling of Lead Oxidation in Controlled Lead Bismuth Eutectic Systems: Chemical Kinetics and Hydrodynamic Effects  

SciTech Connect

Using liquid Lead-Bismuth Eutectic (LBE) as coolant in nuclear systems has been studied for more than 50 years. And LBE has many unique nuclear, thermo physical and chemical attributes which are attractive for practical application. But, corrosion is one of the greatest concerns in using liquid Lead-Bismuth Eutectic (LBE) as spallation target in the Accelerator-driven Transmutation of Waste (ATW) program. Los Alamos National Laboratory has designed and built the Liquid Lead-Bismuth Materials Test Loop (MTL) to study the materials behavior in a flow of molten LBE. A difference of 100 deg. C was designed between the coldest and the hottest parts at a nominal flow rate of 8.84 GPM. Liquid LBE flow was activated by a mechanical sump pump or by natural convection. In order to maintain a self-healing protective film on the surface of the stainless steel pipe, a certain concentration of oxygen has to be maintained in the liquid metal. Therefore, it is of importance to understand what the oxygen concentrations are in the LBE loop related to the corrosion effects on the metal surface, the temperature profiles, the flow rates, and diffusion rates through the metal surface. The chemical kinetics also needs to be fully understood in the corrosion processes coupled with the hydrodynamics. The numerical simulation will be developed and used to analyze the system corrosion effects with different kind of oxygen concentrations, flow rates, chemical kinetics, and geometries. The hydrodynamics modeling of using computational fluid dynamics will provide the necessary the levels of oxygen and corrosion products close to the boundary or surface. This paper presents an approach towards the above explained tasks by analyzing the reactions between the Lead and oxygen at a couple of sections in the MTL. Attempt is also made to understand the surface chemistry by choosing an example model and estimating the near wall surface concentration values for propane and oxygen. (authors)

Wu, Chao; Kanthi Kiran Dasika; Chen, Yitung; Moujaes, Samir [Department of Mechanical Engineering, University of Nevada, Las Vegas, 4505 Maryland Parkway, Las Vegas NV, 89154-4027 (United States)

2002-07-01

320

Chemical shifts in nucleic acids studied by density functional theory calculations and comparison with experiment.  

PubMed

NMR chemical shifts are highly sensitive probes of local molecular conformation and environment and form an important source of structural information. In this study, the relationship between the NMR chemical shifts of nucleic acids and the glycosidic torsion angle, ?, has been investigated for the two commonly occurring sugar conformations. We have calculated by means of DFT the chemical shifts of all atoms in the eight DNA and RNA mono-nucleosides as a function of these two variables. From the DFT calculations, structures and potential energy surfaces were determined by using constrained geometry optimizations at the BP86/TZ2P level of theory. The NMR parameters were subsequently calculated by single-point calculations at the SAOP/TZ2P level of theory. Comparison of the (1)H and (13)C NMR shifts calculated for the mono-nucleosides with the shifts determined by NMR spectroscopy for nucleic acids demonstrates that the theoretical shifts are valuable for the characterization of nucleic acid conformation. For example, a clear distinction can be made between ? angles in the anti and syn domains. Furthermore, a quantitative determination of the ? angle in the syn domain is possible, in particular when (13)C and (1)H chemical shift data are combined. The approximate linear dependence of the C1' shift on the ? angle in the anti domain provides a good estimate of the angle in this region. It is also possible to derive the sugar conformation from the chemical shift information. The DFT calculations reported herein were performed on mono-nucleosides, but examples are also provided to estimate intramolecularly induced shifts as a result of hydrogen bonding, polarization effects, or ring-current effects. PMID:22899588

Fonville, Judith M; Swart, Marcel; Voká?ová, Zuzana; Sychrovský, Vladimír; Šponer, Judit E; Šponer, Ji?í; Hilbers, Cornelis W; Bickelhaupt, F Matthias; Wijmenga, Sybren S

2012-09-24

321

Importance of variable time-step algorithms in spatial kinetics calculations  

Microsoft Academic Search

The use of spatial kinetics codes in conjunction with advanced thermal-hydraulics codes is becoming more widespread as better methods and faster computers appear. The integrated code packages are being used for routine nuclear power plant design and analysis, including simulations with instrumentation and control systems initiating system perturbations such as rod motion and scrams. As a result, it is important

Aviles

1994-01-01

322

Enskog-Landau kinetic equation. Calculation of the transport coefficients for charged hard spheres  

Microsoft Academic Search

Using the charged hard sphere model as an example, the dense one-component plasma is considered. For this model, the Enskog-Landau kinetic equation is obtained and its normal solution is found using the Chapman-Enskog method. Transport coefficients are obtained numerically and analytically which are then compared with the experimental data available.

A. E. Kobryn; V. G. Morozov; I. P. Omelyan; M. V. Tokarchuk

1996-01-01

323

Systematic Approach to Calculate the Concentration of Chemical Species in Multi-Equilibrium Problems  

ERIC Educational Resources Information Center

A general systematic approach is proposed for the numerical calculation of multi-equilibrium problems. The approach involves several steps: (i) the establishment of balances involving the chemical species in solution (e.g., mass balances, charge balance, and stoichiometric balance for the reaction products), (ii) the selection of the unknowns (the…

Baeza-Baeza, Juan Jose; Garcia-Alvarez-Coque, Maria Celia

2011-01-01

324

Calculations of protective action distance for toxic chemical spills using nomographs  

SciTech Connect

This document was produced for emergency use following a spill of liquid gas or finely divided solid (<100 micron) toxic chemicals. The information on the next few pages was kept deliberately terse and is limited to data and graphic aids needed for calculation of plume distance (protective action distance). All supporting material is provided as Appendices.

Lee, L.G.; Vail, J.A.; Gibeault, G.L.

1995-04-01

325

Numerical Methods for Two-Dimensional CW Chemical Laser Power Calculations.  

National Technical Information Service (NTIS)

The current status of two-dimensional chemical laser modeling at Los Alamos is reviewed, with emphasis on numerical methods for coupling the radiation field to the fluid dynamics so that laser power can be calculated. The primary computational model is em...

J. D. Ramshaw T. D. Butler

1977-01-01

326

Stereoelectronic effects in silicon, phosphorus, and sulfur molecules. Quantum-chemical calculations and qualitative orbital models  

NASA Astrophysics Data System (ADS)

The results of non-empirical quantum-chemical calculations for silicon, phosphorus, and sulfur compounds of different structure are discussed. Qualitative orbital models, which establish a relation between the distribution of electrons and molecular structure and properties, are analysed. A general definition of stereoelectronic effects is presented. The bibliography includes 176 references.

Korkin, A. A.

1992-05-01

327

{ital Ab initio} quantum chemical calculation of electron transfer matrix elements for large molecules  

SciTech Connect

Using a diabatic state formalism and pseudospectral numerical methods, we have developed an efficient {ital ab initio} quantum chemical approach to the calculation of electron transfer matrix elements for large molecules. The theory is developed at the Hartree{endash}Fock level and validated by comparison with results in the literature for small systems. As an example of the power of the method, we calculate the electronic coupling between two bacteriochlorophyll molecules in various intermolecular geometries. Only a single self-consistent field (SCF) calculation on each of the monomers is needed to generate coupling matrix elements for all of the molecular pairs. The largest calculations performed, utilizing 1778 basis functions, required {approximately}14h on an IBM 390 workstation. This is considerably less cpu time than would be necessitated with a supermolecule adiabatic state calculation and a conventional electronic structure code. {copyright} {ital 1997 American Institute of Physics.}

Zhang, L.Y.; Friesner, R.A. [Department of Chemistry, Columbia University, New York, New York 10027 (United States)] [Department of Chemistry, Columbia University, New York, New York 10027 (United States); Murphy, R.B. [Schroedinger, Inc., Portland, Oregon 97204 (United States)] [Schroedinger, Inc., Portland, Oregon 97204 (United States)

1997-07-01

328

ChemSage—A computer program for the calculation of complex chemical equilibria  

NASA Astrophysics Data System (ADS)

An extensive computer program called ChemSage, based upon the SOLGASMIX Gibbs energy minimizer, is presented together with several examples which illustrate its use. ChemSage was designed to perform three types of thermochemical calculations in complex systems involving phases exhibiting nonideal mixing properties. These are the calculation of thermodynamic functions, heterogeneous phase equilibria, and steady-state conditions for the simulation of simple multistage reactors. The thermodynamic functions module calculates specific heat, enthalpy, entropy, and Gibbs energy with respect to a chosen reference state for a given phase and, if this phase is a mixture, the partial properties of its components. Chemical equilibrium calculations can be made for a system which has been uniquely defined with respect to temperature, pressure (or volume), and composition. One of these quantities may also be replaced by an extensive property or phase target, e.g., for the calculation of adiabatic and liquidus temperatures, respectively.

Eriksson, Gunnar; Hack, Klaus

1990-12-01

329

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

NASA Technical Reports Server (NTRS)

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.

Gordon, Sanford; Mcbride, Bonnie J.

1994-01-01

330

Modeling of the HiPco process for carbon nanotube production. I. Chemical kinetics  

NASA Technical Reports Server (NTRS)

A chemical kinetic model is developed to help understand and optimize the production of single-walled carbon nanotubes via the high-pressure carbon monoxide (HiPco) process, which employs iron pentacarbonyl as the catalyst precursor and carbon monoxide as the carbon feedstock. The model separates the HiPco process into three steps, precursor decomposition, catalyst growth and evaporation, and carbon nanotube production resulting from the catalyst-enhanced disproportionation of carbon monoxide, known as the Boudouard reaction: 2 CO(g)-->C(s) + CO2(g). The resulting detailed model contains 971 species and 1948 chemical reactions. A second model with a reduced reaction set containing 14 species and 22 chemical reactions is developed on the basis of the detailed model and reproduces the chemistry of the major species. Results showing the parametric dependence of temperature, total pressure, and initial precursor partial pressures are presented, with comparison between the two models. The reduced model is more amenable to coupled reacting flow-field simulations, presented in the following article.

Dateo, Christopher E.; Gokcen, Tahir; Meyyappan, M.

2002-01-01

331

High-Throughput Microwave Spectroscopy for Chemical Kinetics and Trace Detection  

NASA Astrophysics Data System (ADS)

Recent developments in high-speed digital electronics have made it possible to develop a new generation of broadband microwave spectrometers for molecular spectroscopy. These spectrometers acquire a broadband microwave spectrum (up to 12 GHz bandwidth in the current designs) in a single data acquisition event. Chirped pulse excitation is employed to efficiently polarize a molecular gas sample over the 12 GHz bandwidth using a pulse duration of about 1 microsecond. Following sample polarization, the free induction decay signal from the molecular rotational spectrum is directly digitized using a high-speed digital oscilloscope. The frequency domain spectrum is obtained by Fourier transform following coherent, time-domain signal averaging. The spectrometer design provides new capabilities for high-throughput chemical analysis. Applications to chemical identification of molecules of astrochemical interest will be presented. The broadband technique is well-suited to laser experiments where isomerization kinetics of highly excited molecules can be measured on the picosecond time scale through line shape analysis. Microwave-laser experiments for chemical reaction dynamics in pulsed jet samples and room-temperature gases will be presented.

Pate, Brooks

2009-05-01

332

Uncertainties in Kinetic and Photochemical Parameters of Ozone Depleting Substances and the Impact on Atmospheric Lifetime Calculations  

NASA Astrophysics Data System (ADS)

The SPARC (Stratospheric Processes And their Role in Climate) initiative "Reevaluation of the Lifetimes of Dominant Stratospheric Ozone-Depleting Substances (ODSs)" is aimed toward providing a critical evaluation of atmospheric lifetimes for a number of key compounds. The atmospheric lifetimes of ODSs and greenhouse gases play a key role in the evaluation of ozone loss/recovery and climate change. Therefore, it is critically important to have accurate estimates of lifetimes as well as their uncertainty. The initiative has identified 26 key compounds to be included in this study. The compounds were chosen primarily due to their contribution to ozone depletion, their use as ODS replacements, and their contribution as climate forcing agents. Model calculated atmospheric lifetimes rely on kinetic and photochemical input parameters that are obtained from laboratory studies. Important gas-phase loss processes include reaction with OH, O(1D), and Cl atoms as well as EUV (Lyman-?) and UV photolysis where the relative importance of these processes depends on the properties of the individual compound. As part of the initiative, an evaluation of the model kinetic input parameters and their uncertainties was performed. Here, an assessment of the atmospheric loss processes and associated uncertainties for the target compounds will be presented. Two-dimensional (2D) atmospheric model calculations are used to characterize the globally/annually averaged vertical profiles of the target compounds, loss processes and uncertainties, and their atmospheric lifetimes. The 2D model results are used to highlight the limitations of atmospheric lifetime calculations due to uncertainties in the kinetic and photochemical input parameters, which in some cases are substantial. This component of the initiative also identifies areas where more accurate laboratory studies are needed in order to reduce uncertainties in calculated atmospheric lifetimes for these key species.

Burkholder, J. B.; Kurylo, M. J.; Wallington, T.; Fleming, E. L.; Jackman, C. H.

2011-12-01

333

Kinetic and chemical mechanism of alpha-isopropylmalate synthase from Mycobacterium tuberculosis.  

PubMed

Mycobacterium tuberculosis alpha-isopropylmalate synthase (MtIPMS) catalyzes the condensation of acetyl-coenzyme A (AcCoA) with alpha-ketoisovalerate (alpha-KIV) and the subsequent hydrolysis of alpha-isopropylmalyl-CoA to generate the products CoA and alpha-isopropylmalate (alpha-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 (1)H-NMR spectroscopy. The alpha-keto acid specificity of the enzyme is narrow, and the acyl-CoA specificity is absolute for AcCoA. In the absence of alpha-KIV, MtIPMS does not enolize the alpha protons of AcCoA but slowly hydrolyzes acyl-CoA analogues. 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 pK(a) 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 alpha-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 alpha-isopropylmalyl-CoA is direct, without the formation of a cyclic anhydride intermediate. On the basis of these results, a chemical mechanism for the MtIPMS-catalyzed reaction is proposed. PMID:16846242

de Carvalho, Luiz Pedro S; Blanchard, John S

2006-07-25

334

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

Microsoft Academic Search

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

R. H. W. Waesche; J. Wenograd

2000-01-01

335

Time-resolved simplified chemical kinetics modelling using computational singular perturbation  

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

336

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

SciTech Connect

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.

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

1993-10-01

337

Modeling of simulated photochemical smog with kinetic mechanisms. Volume 2. Chemk: a computer modeling scheme for chemical kinetics. Final report, July 1978-September 1979  

SciTech Connect

Mechanisms that describe the formation of photochemical smog are developed using a computer modeling technique directed toward the simulation of data collected in two smog chambers: an indoor chamber and a dual outdoor chamber. Individual compounds for which specific experiments were simulated and mechanisms developed include the following: formaldehyde, acetaldehyde, ethylene, propylene, butane, and toluene. Volume 2 contains the user's manual and coding for a chemical kinetics computer program, CHEMK.

Whitten, G.Z.; Hogo, H.

1980-02-01

338

LSENS: A General Chemical Kinetics and Sensitivity Analysis Code for homogeneous gas-phase reactions. Part 3: Illustrative test problems  

NASA Technical Reports Server (NTRS)

LSENS, the Lewis General Chemical Kinetics and Sensitivity Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part 3 of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part 3 explains the kinetics and kinetics-plus-sensitivity analysis problems supplied with LSENS and presents sample results. These problems illustrate the various capabilities of, and reaction models that can be solved by, the code and may provide a convenient starting point for the user to construct the problem data file required to execute LSENS. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions.

Bittker, David A.; Radhakrishnan, Krishnan

1994-01-01

339

Equivalence of on-Lattice Stochastic Chemical Kinetics with the Well-Mixed Chemical Master Equation in the Limit of Fast Diffusion  

PubMed Central

Well-mixed and lattice-based descriptions of stochastic chemical kinetics have been extensively used in the literature. Realizations of the corresponding stochastic processes are obtained by the Gillespie stochastic simulation algorithm and lattice kinetic Monte Carlo algorithms, respectively. However, the two frameworks have remained disconnected. We show the equivalence of these frameworks whereby the stochastic lattice kinetics reduces to effective well-mixed kinetics in the limit of fast diffusion. In the latter, the lattice structure appears implicitly, as the lumped rate of bimolecular reactions depends on the number of neighbors of a site on the lattice. Moreover, we propose a mapping between the stochastic propensities and the deterministic rates of the well-mixed vessel and lattice dynamics that illustrates the hierarchy of models and the key parameters that enable model reduction.

Stamatakis, Michail; Vlachos, Dionisios G.

2011-01-01

340

Respiratory uptake kinetics of neutral hydrophobic organic chemicals in a marine benthic fish, Pseudopleuronectes yokohamae.  

PubMed

We investigated the respiratory uptake kinetics of polychlorinated biphenyls (PCBs), organohalogen pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), and 2,2',4,4'-tetrabrominated diphenyl ether (BDE #47) in a marine benthic fish, Pseudopleuronectes yokohamae. The respiratory uptake efficiencies (EW) of the chemicals, of which there have been no reports for the majority of persistent organic pollutants (POPs), were obtained by measuring the respiratory uptake rate constants (k1) and the oxygen consumption rates of fish. Fish were exposed to water in which these chemicals were dissolved at environmentally relevant concentrations for 28 d, followed by 168 d of depuration in clean seawater. The k1 and EW values for 99 compounds were obtained, and they ranged from 2000 to 42000 L kg-lipid(-1) d(-1) and from 0.060 to 1.3, respectively. The EW values of the chemicals, except for PAHs, tended to increase with increasing values of the log octanol-water partition coefficients (KOW) of the chemicals up to a log KOW of 5. For log KOW in the range 3-5, the EW values in this study were much lower than those in a published study (about one-third). As a result of analysis by a two-phase resistance model, the resistance of transport rates to the lipid phase in this study was lower than was the case in the published study. These findings indicate that the EW predicted by the published study for log KOW in the range 3-5 may differ among fish species and water temperature, and further study is needed. PMID:23962382

Kobayashi, Jun; Sakurai, Takeo; Mizukawa, Kaoruko; Kinoshita, Kyoko; Ito, Nozomi; Hashimoto, Shunji; Nakajima, Daisuke; Kawai, Toru; Imaizumi, Yoshitaka; Takada, Hideshige; Suzuki, Noriyuki

2013-11-01

341

Analysis of long-term bacterial vs. chemical Fe(III) oxide reduction kinetics  

NASA Astrophysics Data System (ADS)

Data from studies of dissimilatory bacterial (10 8 cells mL -1 of Shewanella putrefaciens strain CN32, pH 6.8) and ascorbate (10 mM, pH 3.0) reduction of two synthetic Fe(III) oxide coated sands and three natural Fe(III) oxide-bearing subsurface materials (all at ca. 10 mmol Fe(III) L -1) were analyzed in relation to a generalized rate law for mineral dissolution (J t/m 0 = k'(m/m 0) ?, where J t is the rate of dissolution and/or reduction at time t, m 0 is the initial mass of oxide, and m/m 0 is the unreduced or undissolved mineral fraction) in order to evaluate changes in the apparent reactivity of Fe(III) oxides during long-term biological vs. chemical reduction. The natural Fe(III) oxide assemblages demonstrated larger changes in reactivity (higher ? values in the generalized rate law) compared to the synthetic oxides during long-term abiotic reductive dissolution. No such relationship was evident in the bacterial reduction experiments, in which temporal changes in the apparent reactivity of the natural and synthetic oxides were far greater (5-10 fold higher ? values) than in the abiotic reduction experiments. Kinetic and thermodynamic considerations indicated that neither the abundance of electron donor (lactate) nor the accumulation of aqueous end-products of oxide reduction (Fe(II), acetate, dissolved inorganic carbon) are likely to have posed significant limitations on the long-term kinetics of oxide reduction. Rather, accumulation of biogenic Fe(II) on residual oxide surfaces appeared to play a dominant role in governing the long-term kinetics of bacterial crystalline Fe(III) oxide reduction. The experimental findings together with numerical simulations support a conceptual model of bacterial Fe(III) oxide reduction kinetics that differs fundamentally from established models of abiotic Fe(III) oxide reductive dissolution, and indicate that information on Fe(III) oxide reactivity gained through abiotic reductive dissolution techniques cannot be used to predict long-term patterns of reactivity toward enzymatic reduction at circumneutral pH.

Roden, Eric E.

2004-08-01

342

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

SciTech Connect

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.

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

1988-01-15

343

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

NASA Technical Reports Server (NTRS)

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.

Kahn, L. R.

1981-01-01

344

Kinetics of chemical degradation in monoclonal antibodies: relationship between rates at the molecular and peptide levels.  

PubMed

This article describes a method to analyze the kinetics of monoclonal antibody degradation and to determine the quantitative relationship between the degradation rates observed at the molecular and peptide levels. The proposed model can be applied to any degradation pathway that can be well approximated by a first order reaction; if several pathways exist, the model assumes that they are independent. Three examples are presented to illustrate the benefits of this approach. For each case, the calculated fractions of species were compared to one or more data sets to demonstrate the good agreement between experimental results and model prediction. This method can serve as a valuable tool in interpreting chromatograms of degraded samples and predicting the population of species present at the molecular level when only data from degradation observed at the peptide level is available. This method further demonstrates how deviations from predictions of simple models can be used to unravel additional, unforeseen reactions. PMID:20302349

Ionescu, Roxana; Vlasak, Josef

2010-04-15

345

Detailed chemical kinetic models for large n-alkanes and iso-alkanes found in conventional and FT diesel fuels  

Microsoft Academic Search

Detailed chemical kinetic models are needed to simulate the combustion of current and future transportation fuels. These models should represent the various chemical classes in these fuels. Conventional diesel fuels are composed of n-alkanes, iso-alkanes, cycloalkanes and aromatics (Farrell et al. 2007). For future fuels, there is a renewed interest in Fischer-Tropsch (F-T) processes which can be used to synthesize

C K Westbrook; W J Pitz; H J Curran; M Mehl

2008-01-01

346

Detailed Chemical Kinetic Reaction Mechanisms for Combustion of Isomers of Heptane  

SciTech Connect

Detailed chemical kinetic reaction mechanisms are developed for all nine chemical isomers of heptane (C{sub 7}H{sub 16}), following techniques and models developed previously for other smaller alkane hydrocarbon species. These reaction mechanisms are tested at high temperatures by computing shock tube ignition delay times and at lower temperatures by simulating ignition in a rapid compression machine. Although the corresponding experiments have not been reported in the literature for most of these isomers of heptane, intercomparisons between the computed results for these isomers and comparisons with available experimental results for other alkane fuels are used to validate the reaction mechanisms as much as possible. Differences in the overall reaction rates of these fuels are discussed in terms of differences in their molecular structure and the resulting variations in rates of important elementary reactions. Reaction mechanisms in this study are works in progress and the results reported here are subject to change, based on model improvements and corrections of errors not yet discovered.

Westbrook, C K; Pitz, W J; Curran, H C; Boercker, J; Kunrath, E

2001-03-26

347

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

SciTech Connect

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.

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

1995-10-01

348

Quantum-chemical calculations on the electronic circular dichroism of (-)-dibromophakellin and (-)-dibromophakell-statin.  

PubMed

The CD spectra of the pyrrole-imidazole alkaloids, (-)-dibromophakellin and (-)-dibromophakellstatin, have been calculated employing the quantum-chemical time-dependent density functional theory. Comparison of calculated and measured spectra showed that this well-established method is also a useful tool to elucidate the absolute stereochemistry of this class of compounds. The computational results have further been used to analyze the spectra measured in methanol and to explain the remarkable red shift of one CD band when trifluoroethanol is used as a solvent instead of methanol. PMID:17487888

Atodiresei, Iuliana; Zöllinger, Michael; Lindel, Thomas; Fleischhauer, Jörg; Raabe, Gerhard

2007-07-01

349

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

SciTech Connect

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.

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

350

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

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

351

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

SciTech Connect

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.

Crosley, D.R.

1992-09-01

352

Investigation of the ICT state of DPA-DSB using spectroscopic experiments and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

The excited states of a symmetric D- ?-D structure two-photon excited fluorescence material 1,4-di (4'- N, N-diphenylaminostyryl) benzene (DPA-DSB) have been investigated by spectroscopic experiments and quantum chemical calculations. The solvent polarity dependent fluorescence properties indicate that upon photoexcitation, a radiative intramolecular charge-transfer (ICT) state is formed resulting from the ICT process. The molecular structure does not have large change during the ICT process, which is confirmed by the quantum chemical calculations performed by G AUSSIAN 03 software. The planar structure of the fluorescent ICT state results in the high fluorescence quantum yield which is important in the two-photon excited fluorescence application.

He, Xing; Wang, Yang; Liu, Weilong; Yang, Zhenling; Du, Xin; Liu, Yuqiang; Yang, Yanqiang

2011-01-01

353

Calculation of 19F NMR chemical shifts in uranium complexes using density functional theory and pseudopotentials  

NASA Astrophysics Data System (ADS)

The 19F NMR nuclear shieldings of fluoride ligands in uranium complexes UF nCl 6 - n ( n = 1-6) have been studied quantum chemically, using different exchange-correlation functionals and a relativistic small-core pseudopotential on uranium. In contrast to a recent study [G. Schreckenbach, S.W. Wolff, T. Ziegler, J. Phys. Chem. A 104 (2000) 8244] we find that pseudopotential methods are well suited for calculations of ligand chemical shifts in actinide compounds, provided that a sufficiently small core-size definition is used. With modern relativistic small-core pseudopotentials and gradient-corrected density functionals we obtain results of the same accuracy as were found with all-electron density functional ZORA or Pauli calculations. The unusually large dependence of the shifts on the exchange-correlation functional is discussed in the context of the description of ?- and ?-bonding, and also with respect to the accuracy of the optimized structures.

Straka, Michal; Kaupp, Martin

2005-04-01

354

Is Case-Based Learning an Effective Teaching Strategy to Challenge Students' Alternative Conceptions regarding Chemical Kinetics?  

ERIC Educational Resources Information Center

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…

Yalcinkaya, Eylem; Tastan-Kirik, Ozgecan; Boz, Yezdan; Yildiran, Demet

2012-01-01

355

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

Microsoft Academic Search

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

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

2002-01-01

356

A reduced chemical kinetic model for HCCI combustion of primary reference fuels in a rapid compression machine  

Microsoft Academic Search

A model for the Homogeneous Charge Compression Ignition (HCCI) of Primary Reference Fuels (PRFs) in a Rapid Compression Machine (RCM) has been developed. A reduced chemical kinetic model that included 32 species and 55 reactions was used and the affect of wall heat transfer on the temperature of the adiabatic core gas was taken into account by adding the displacement

Shigeyuki Tanaka; Ferran Ayala; James C. Keck

2003-01-01

357

Non-Isothermic Chemical Kinetics in the Undergraduate Laboratory: Arrhenius Parameters from Experiments with Hyperbolic Temperature Variation.  

ERIC Educational Resources Information Center

Describes a method which adapts itself to the characteristics of the kinetics of a chemical reaction in solution, enabling students to determine the Arrhenius parameters with satisfactory accuracy by means of a single non-isothermic experiment. Both activation energy and the preexponential factor values can be obtained by the method. (JN)

Salvador, F.; And Others

1984-01-01

358

A new method for modelling spectator chemical groups in ab initio calculations: effective group potentials  

Microsoft Academic Search

.  ?A new method for an increased numerical efficiency of ab initio calculations is proposed. It is based on the assumption that\\u000a in most cases chemical properties of functional groups in molecules are mainly controlled by a few electrons. This statement\\u000a allows one to distinguish between two classes of nuclei and electrons: active and inactive ones. The effective group potential\\u000a (EGP)

Fabienne Alary; Romuald Poteau; Jean-Louis Heully; Jean-Claude Barthelat; Jean-Pierre Daudey

2000-01-01

359

Electronic Structure Theory and Multi-Structural Statistical Thermodynamics for Computational Chemical Kinetics  

NASA Astrophysics Data System (ADS)

This thesis involves the development and application of methods for accurate computational thermochemistry. It consists of two parts. The first part focuses on the accuracy of the electronic structure methods. In particular, various augmentation schemes for one-electron basis sets are presented and tested for density functional theory (DFT) calculations and for wave function theory (WFT) calculations. The relationship between diffuse basis functions and basis set superposition error is discussed. For WFT, we also compare the efficiency of conventional one-electron basis-sets to that of newly developed explicitly correlated methods. Various ways of approaching the complete basis set limit of WFT calculations are explained, and recommendations are made for the best ways of achieving balance between the basis set size, higher-order correlation, and relativistic corrections. Applications of this work include computation of barrier heights, reaction and bond energies, electron affinities, ionization potentials, and noncovalent interactions. The second part of this thesis focuses on the problem of incorporating multi-structural effects and anharmonicity effects in the torsional modes into partition function calculations, especially by using a new multi-structural torsion (MS-T) method. Applications of the MS-T method include partition functions of molecules and radicals important for combustion research. These partition functions are used to obtain thermodynamic functions that are the most reliable results available to date for these molecules. The multi-structural approach is also applied to two kinetics problems: The hydrogen abstraction from carbon-3 of 1-butanol by hydroperoxyl radical; The 1,5-hydrogen shift isomerization of the 1-butoxyl radical. In both cases multi-structural effects play an important role in the final results.

Papajak, Ewa

360

Fragment formula calculator (FFC): determination of chemical formulas for fragment ions in mass spectrometric data.  

PubMed

The accurate determination of mass isotopomer distributions (MID) is of great significance for stable isotope-labeling experiments. Most commonly, MIDs are derived from gas chromatography/electron ionization mass spectrometry (GC/EI-MS) measurements. The analysis of fragment ions formed during EI, which contain only specific parts of the original molecule can provide valuable information on the positional distribution of the label. The chemical formula of a fragment ion is usually applied to derive the correction matrix for accurate MID calculation. Hence, the correct assignment of chemical formulas to fragment ions is of crucial importance for correct MIDs. Moreover, the positional distribution of stable isotopes within a fragment ion is of high interest for stable isotope-assisted metabolomics techniques. For example, (13)C-metabolic flux analyses ((13)C-MFA) are dependent on the exact knowledge of the number and position of retained carbon atoms of the unfragmented molecule. Fragment ions containing different carbon atoms are of special interest, since they can carry different flux information. However, the process of mass spectral fragmentation is complex, and identifying the substructures and chemical formulas for these fragment ions is nontrivial. For that reason, we developed an algorithm, based on a systematic bond cleavage, to determine chemical formulas and retained atoms for EI derived fragment ions. Here, we present the fragment formula calculator (FFC) algorithm that can calculate chemical formulas for fragment ions where the chemical bonding (e.g., Lewis structures) of the intact molecule is known. The proposed algorithm is able to cope with general molecular rearrangement reactions occurring during EI in GC/MS measurements. The FFC algorithm is able to integrate stable isotope labeling experiments into the analysis and can automatically exclude candidate formulas that do not fit the observed labeling patterns.1 We applied the FFC algorithm to create a fragment ion repository that contains the chemical formulas and retained carbon atoms of a wide range of trimethylsilyl and tert-butyldimethylsilyl derivatized compounds. In total, we report the chemical formulas and backbone carbon compositions for 160 fragment ions of 43 alkylsilyl-derivatives of primary metabolites. Finally, we implemented the FFC algorithm in an easy-to-use graphical user interface and made it publicly available at http://www.ffc.lu . PMID:24498896

Wegner, André; Weindl, Daniel; Jäger, Christian; Sapcariu, Sean C; Dong, Xiangyi; Stephanopoulos, Gregory; Hiller, Karsten

2014-02-18

361

Influence of chemical kinetics on postcolumn reaction in a capillary Taylor reactor with catechol analytes and photoluminescence following electron transfer.  

PubMed

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-microm-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)3(3+) by analyte to the photoluminescent Os(bpy)3(2+)) 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 microL/min) velocity with solutes having diffusion coefficients in the 5 x 10(-6) cm2/s range, can be constructed from 8.0 cm of 25-microm-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-microm-capillary chromatography column by 10% if the pseudo-first-order rate constant is larger than 0.1 s(-1). PMID:15858975

Jung, Moon Chul; Weber, Stephen G

2005-02-15

362

A dynamic multi-timescale method for combustion modeling with detailed and reduced chemical kinetic mechanisms  

SciTech Connect

A new on-grid dynamic multi-timescale (MTS) method is presented to increase significantly the computation efficiency involving multi-physical and chemical processes using detailed and reduced kinetic mechanisms. The methodology of the MTS method using the instantaneous timescales of different species is introduced. The definition of the characteristic time for species is examined and compared with that of the computational singular perturbation (CSP) and frozen reaction rate methods by using a simple reaction system. A hybrid multi-timescale (HMTS) algorithm is constructed by integrating the MTS method with an implicit Euler scheme, respectively, for species with and without the requirement of accurate time histories at sub-base timescales. The efficiency and the robustness of the MTS and HMTS methods are demonstrated by comparing with the Euler and VODE solvers for homogenous ignition and unsteady flame propagation of hydrogen, methane, and n-decane-air mixtures. The results show that both MTS and HMTS reproduce well the species and temperature histories and are able to decrease computation time by about one-order with the same kinetic mechanism. Compared to MTS, HMTS has slightly better computation efficiency but scarifies the stability at large base time steps. The results also show that with the increase of mechanism size and the decrease of time step, the computation efficiency of multi-timescale method increases compared to the VODE solver. In addition, it is shown that the integration of the multi-timescale method with the path flux analysis based mechanism reduction approach can further increase the computation efficiency. Unsteady simulations of outwardly propagating spherical n-decane-air premixed flames demonstrate that the multi-timescale method is rigorous for direct numerical simulations with both detailed and reduced chemistry and can dramatically improve the computation efficiency. (author)

Gou, Xiaolong [Department of Mechanical and Aerospace Engineering, Princeton University, NJ 08544 (United States); College of Power Engineering, Chongqing University, Chongqing 400030 (China); Sun, Wenting; Ju, Yiguang [Department of Mechanical and Aerospace Engineering, Princeton University, NJ 08544 (United States); Chen, Zheng [Department of Mechanical and Aerospace Engineering, Princeton University, NJ 08544 (United States); School of Engineering, Peking University, Beijing 100871 (China)

2010-06-15

363

The chemical mechanism generation programme CHEMATA—Part 2: Comparison of four chemical mechanisms for mesoscale calculation of atmospheric pollution  

NASA Astrophysics Data System (ADS)

RACM and the three new mechanisms described in the companion paper (the extended, reduced and small mechanisms) are implemented in a mesoscale 3D transport-chemistry model (TAPOM for Transport and Air POllution Model) in order to find an optimum between calculation speed and mechanism detail. The 3D tests are performed in the domains of Milan, Mexico City and Bogota. The three domains present different chemical and meteorological conditions, which are used to test the behaviour of the four mechanisms in different situations. Three emission scenarios are simulated: the whole emission inventory, 35% NO x reduction and 35% VOC reduction. The comparison of the four mechanisms is performed for O 3, NO x , aldehydes and peroxy radicals. Only the small mechanism presents significant differences in ozone concentrations. RO 2 and aldehyde differences are important with the reduced and the small mechanism, which share a new RO 2 parameterisation. Compared to RACM, the small mechanism shows very large differences for aldehydes and RO 2. The extended mechanism and RACM show almost the same ozone response to emissions reduction strategies, and the reduced mechanism presents differences in the range of 10% with respect to the extended mechanisms. The small mechanism is found to be the most VOC sensitive and therefore presents very different results from the other when emissions are modified. The results indicate a strong restriction to the use of the small mechanism in 3D models. Finally, the calculation time required for the calculation of a simulation with the four mechanisms is compared.

Junier, Martin; Kirchner, Frank; Clappier, Alain; van den Bergh, Hubert

364

A METHOD FOR CALCULATING THE EFFECTIVE PERMITTIVITY OF A MIXTURE SOLUTION DURING A CHEMICAL REACTION BY EXPERIMENTAL RESULTS  

Microsoft Academic Search

Usually, an effective permittivity can be used to describe the molecular polarization of a mixture during a chemical reaction and consequently be used to calculate the transmission and absorption of microwave in the mixture. In this paper, we propose a method to calculate the effective permittivity of a mixture solution during a chemical reaction by means of the experimental results.

Kama Huang; Xiaoqing Yang

2008-01-01

365

Calculator.  

ERIC Educational Resources Information Center

Five activities are presented in this student workbook on using the electronic calculator. Following the directions for using the machine, problems are given on multiplying and dividing, finding percentages, calculating the area of assorted polygons, changing fractions to decimals, and finding squares and square roots. (JH)

Parma City School District, OH.

366

Calculation of chemical potentials of chain molecules by the incremental gauge cell method  

NASA Astrophysics Data System (ADS)

The gauge cell Monte Carlo method is extended to calculations of the incremental chemical potentials and free energies of linear chain molecules. The method was applied to chains of Lennard-Jones beads with stiff harmonic bonds up to 500 monomers in length. We show that the suggested method quantitatively reproduces the modified Widom particle insertion method of Kumar et al. [S. K. Kumar, I. Szleifer, and A. Z. Panagiotopoulos, Phys. Rev. Lett. 66(22), 2935 (1991)], and is by an order of magnitude more efficient for long chains in terms of the computational time required for the same accuracy of chemical potential calculations. The chain increment ansatz, which suggests that the incremental chemical potential is independent of the chain length, was tested at different temperatures. We confirmed that the ansatz holds only for coils above the ? temperature. Special attention is paid to the effects of the magnitude of adsorption potential and temperature on the behavior of single chains in confinements that are comparable in size with the free chain radius of gyration. At sufficiently low temperatures, the dependence of the incremental chemical potential on the chain length in wetting pores is superficially similar to a capillary condensation isotherm, reflecting monolayer formation following by pore volume filling, as the chain length increases. We find that the incremental gauge cell method is an accurate and efficient technique for calculations of the free energies of chain molecules in bulk systems and nanoconfinements alike. The suggested method may find practical applications, such as modeling polymer partitioning on porous substrates and dynamics of chain translocation into nanopores.

Rasmussen, Christopher J.; Vishnyakov, Aleksey; Neimark, Alexander V.

2011-12-01

367

Projected and hidden Markov models for calculating kinetics and metastable states of complex molecules  

NASA Astrophysics Data System (ADS)

Markov state models (MSMs) have been successful in computing metastable states, slow relaxation timescales and associated structural changes, and stationary or kinetic experimental observables of complex molecules from large amounts of molecular dynamics simulation data. However, MSMs approximate the true dynamics by assuming a Markov chain on a clusters discretization of the state space. This approximation is difficult to make for high-dimensional biomolecular systems, and the quality and reproducibility of MSMs has, therefore, been limited. Here, we discard the assumption that dynamics are Markovian on the discrete clusters. Instead, we only assume that the full phase-space molecular dynamics is Markovian, and a projection of this full dynamics is observed on the discrete states, leading to the concept of Projected Markov Models (PMMs). Robust estimation methods for PMMs are not yet available, but we derive a practically feasible approximation via Hidden Markov Models (HMMs). It is shown how various molecular observables of interest that are often computed from MSMs can be computed from HMMs/PMMs. The new framework is applicable to both, simulation and single-molecule experimental data. We demonstrate its versatility by applications to educative model systems, a 1 ms Anton MD simulation of the bovine pancreatic trypsin inhibitor protein, and an optical tweezer force probe trajectory of an RNA hairpin.

Noé, Frank; Wu, Hao; Prinz, Jan-Hendrik; Plattner, Nuria

2013-11-01

368

A reaction-based paradigm to model reactive chemical transport in groundwater with general kinetic and equilibrium reactions  

NASA Astrophysics Data System (ADS)

This paper presents a reaction-based water quality transport model in subsurface flow systems. Transport of chemical species with a variety of chemical and physical processes is mathematically described by M partial differential equations (PDEs). Decomposition via Gauss-Jordan column reduction of the reaction network transforms M species reactive transport equations into two sets of equations: a set of thermodynamic equilibrium equations representing NE equilibrium reactions and a set of reactive transport equations of M- NE kinetic-variables involving no equilibrium reactions (a kinetic-variable is a linear combination of species). The elimination of equilibrium reactions from reactive transport equations allows robust and efficient numerical integration. The model solves the PDEs of kinetic-variables rather than individual chemical species, which reduces the number of reactive transport equations and simplifies the reaction terms in the equations. A variety of numerical methods are investigated for solving the coupled transport and reaction equations. Simulation comparisons with exact solutions were performed to verify numerical accuracy and assess the effectiveness of various numerical strategies to deal with different application circumstances. Two validation examples involving simulations of uranium transport in soil columns are presented to evaluate the ability of the model to simulate reactive transport with complex reaction networks involving both kinetic and equilibrium reactions.

Zhang, Fan; Yeh, Gour-Tsyh; Parker, Jack C.; Brooks, Scott C.; Pace, Molly N.; Kim, Young-Jin; Jardine, Philip M.; Watson, David B.

2007-06-01

369

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

PubMed

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

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

2008-08-14

370

Statistical analysis of chemical transformation kinetics using Markov-Chain Monte Carlo methods.  

PubMed

For the risk assessment of chemicals intentionally released into the environment, as, e.g., pesticides, it is indispensable to investigate their environmental fate. Main characteristics in this context are transformation rates and partitioning behavior. In most cases the relevant parameters are not directly measurable but are determined indirectly from experimentally determined concentrations in various environmental compartments. Usually this is done by fitting mathematical models, which are usually nonlinear, to the observed data and such deriving estimates of the parameter values. Statistical analysis is then used to judge the uncertainty of the estimates. Of particular interest in this context is the question whether degradation rates are significantly different from zero. Standard procedure is to use nonlinear least-squares methods to fit the models and to estimate the standard errors of the estimated parameters from Fisher's Information matrix and estimated level of measurement noise. This, however, frequently leads to counterintuitive results as the estimated probability distributions of the parameters based on local linearization of the optimized models are often too wide or at least differ significantly in shape from the real distribution. In this paper we identify the shortcoming of this procedure and propose a statistically valid approach based on Markov-Chain Monte Carlo sampling that is appropriate to determine the real probability distribution of model parameters. The effectiveness of this method is demonstrated on three data sets. Although it is generally applicable to different problems where model parameters are to be inferred, in the present case for simplicity we restrict the discussion to the evaluation of metabolic degradation of chemicals in soil. It is shown that the method is successfully applicable to problems of different complexity. We applied it to kinetic data from compounds with one and five metabolites. Additionally, using simulated data, it is shown that the MCMC method estimates the real probability distributions of parameters well and much better than the standard optimization approach. PMID:21526818

Görlitz, Linus; Gao, Zhenglei; Schmitt, Walter

2011-05-15

371

Spectroscopic Studies of Azide compounds: Thermochemistry, Chemical Kinetics and Photodissociation Dynamics  

NASA Astrophysics Data System (ADS)

Some of the most difficult chemical systems, either to observe or produce in significant quantities, are polynitrogen molecules. One example of this type of molecules in the early stages of investigation is cyclic-N3, whose molecular geometry and promising technological applications have attracted our attention to define optimal experimental conditions for being photoproduced. High-resolution synchrotron-radiation-based Photoionization Mass Spectrometry (PIMS) was applied to study the dissociative photoionization of three azide precursors for cyclic-N3; chlorine azide (ClN3), hydrogen azide (HN3), and methyl azide (CH3N3). In our attempts to detect cyclic-N3, the thermochemistry derived in the PIMS studies stimulated our work to perform photodissociation dynamics experiments of CH3N3 at 193 nm using Photofragment Translational Spectroscopy (PTS) with electron impact (EI) detection under collision-free conditions, and chemical kinetic studies based on Infrared Spectroscopy (IR) in matrix-isolated ices formed from rare gases (Argon, Nitrogen and Xenon). PTS experiments lead us to derive the branching ratio between reactions CH 3+N3 (radical channel) vs CH3N+N2 (molecular channel), and to conclude that cyclic-N3 is the dominant product in the radical channel. In contrast, in the matrix isolation experiments we found no evidence of the radical channel, possibly due to barrier-less recombination. However, since no mechanistic reports of methyl azide dissociation exist at these conditions, these studies could have significant implications for future experiments addressed to detect cylic-N3 under matrix environments.

Quinto Hernandez, Alfredo

372

Decomposition kinetics of dimethyl methylphospate (chemical agent simulant) by supercritical water oxidation.  

PubMed

Supercritical water oxidation (SCWO) has been drawing much attention due to effectively destroy a large variety of high-risk wastes resulting from munitions demilitarization and complex industrial chemical. An important design consideration in the development of supercritical water oxidation is the information of decomposition rate. In this paper, the decomposition rate of dimethyl methylphosphonate (DMMP), which is similar to the nerve agent VX and GB (Sarin) in its structure, was investigated under SCWO conditions. The experiments were performed in an isothermal tubular reactor with a H2O2 as an oxidant. The reaction temperatures were ranged from 398 to 633 degrees C at a fixed pressure of 24 MPa. The conversion of DMMP was monitored by analyzing total organic carbon (TOC) on the liquid effluent samples. It is found that the oxidative decomposition of DMMP proceeded rapidly and a high TOC decomposition up to 99.99% was obtained within 11 s at 555 degrees C. On the basis of data derived from experiments, a global kinetic equation for the decomposition of DMMP was developed. The model predictions agreed well with the experimental data. PMID:20050541

Veriansyah, Bambang; Kim, Jae-Duck; Lee, Youn-Woo

2006-01-01

373

Numerical Simulation of Compressible Viscous Magneto-Hydrodynamics Equations with Chemical Kinetics  

NASA Astrophysics Data System (ADS)

Most of the objectives of this research project have been achieved. In this first phase of the AFOSR grant (1 October 1998 - 30 September 2002), the principal investigator and his students have developed a 2-D unsteady compressible viscous magnetohydrodynamic code designated MHD2D which has been validated for 2-D internal and external flow & The code solves the coupled MHD equations (mass. momentum and energy equations of fluid flow including MHD effects (Lorentz force and Joule heating), magnetic induction equations and Maxwell equations) and includes an equilibrium air model for re gas effects, a finite-rate chemical kinetics model for dissociated air, several electrical conductivity models and a bi-temperature model. I-his code has been employed to investigate the concept of supersonic drag and heat transfer reduction by modification/dissipation of shock waves in the presence of strong magnetic fields. A series of numerical experiments for blunt body flows and scramjet inlet flow fields have been conducted by varying the Mach number, Reynolds number, degree of ionization of the air plasma and the intensity of the magnetic field to understand the physics of the phenomena and its potential for supersonic drag reduction in practical applications.

Agarwal, Ramesh K.

2002-09-01

374

The Coupling of Related Demonstrations to Illustrate Principles in Chemical Kinetics and Equilibrium  

NASA Astrophysics Data System (ADS)

Two very simple lecture demonstrations, both involving the reaction of magnesium with one or more dilute acids, are linked together to illustrate principles in chemical kinetics and equilibrium. In the first, crumpled Mg ribbon is placed in the nipple of a baby bottle holding 200 mL of 0.40 M HCl. The bottle is inverted into a large beaker of water, and the volume of H2 gas generated in one minute is measured. the experiment is repeated with 0.60 M HCl. The rate law, Rate = k[H+]n, is developed from the data. In the second, equal lengths of Mg ribbon are placed in small beakers or Petri dishes, on an overhead projector, containing equal (0.80 to 1.0 M) concentrations of HCl, H3BO3, and CH3CO2H. Acids are not identified; students are merely told that 'Acids A, B, and C are of the same molarity.' Students are then asked to explain why the rates are so different, which serves as a lead-in for the instructor to explain the meaning of a Ka value. Students readily conclude that one of the acids must be a strong acid, but are puzzled by the other two. [The enormous difference in the Ka values of acetic and boric acids results in a striking difference in their reaction rates.

Pacer, Richard A.

1997-05-01

375

Rapid chemical kinetic techniques for investigations of neurotransmitter receptors expressed in Xenopus oocytes.  

PubMed

Xenopus laevis oocytes have been used extensively during the past decade to express and study neurotransmitter receptors of various origins and subunit composition and also to express and study receptors altered by site-specific mutations. Interpretations of the effects of structural differences on receptor mechanisms were, however, hampered by a lack of rapid chemical reaction techniques suitable for use with oocytes. Here we describe flow and photolysis techniques, with 2-ms and 100-microseconds time resolution, respectively, for studying neurotransmitter receptors in giant (approximately 20-microns diameter) patches of oocyte membranes, using muscle and neuronal acetylcholine receptors as examples. With these techniques, we find that the muscle receptor in BC3H1 cells and the same receptor expressed in oocytes have comparable kinetic properties. This finding is in contrast to previous studies and raises questions regarding the interpretations of the many studies of receptors expressed in oocytes in which an insufficient time resolution was available. The results obtained indicate that the rapid reaction techniques described here, in conjunction with the oocyte expression system, will be useful in answering many outstanding questions regarding the structure and function of diverse neurotransmitter receptors. PMID:8917527

Niu, L; Vazquez, R W; Nagel, G; Friedrich, T; Bamberg, E; Oswald, R E; Hess, G P

1996-11-12

376

Kinetic and Thermodynamic Control of Protonation in Atmospheric Pressure Chemical Ionization  

NASA Astrophysics Data System (ADS)

For p-(dimethylamino)chalcone ( p-DMAC), the N atom is the most basic site in the liquid phase, whereas the O atom possesses the highest proton affinity in the gas phase. A novel and interesting observation is reported that the N- and O-protonated p-DMAC can be competitively produced in atmospheric pressure chemical ionization (APCI) with the change of solvents and ionization conditions. In neat methanol or acetonitrile, the protonation is always under thermodynamic control to form the O-protonated ion. When methanol/water or acetonitrile/water was used as the solvent, the protonation is kinetically controlled to form the N-protonated ion under conditions of relatively high infusion rate and high concentration of water in the mixed solvent. The regioselectivity of protonation of p-DMAC in APCI is probably attributed to the bulky solvent cluster reagent ions (SnH+) and the analyte having different preferred protonation sites in the liquid phase and gas phase.

Chai, Yunfeng; Hu, Nan; Pan, Yuanjiang

2013-07-01

377

A path flux analysis method for the reduction of detailed chemical kinetic mechanisms  

SciTech Connect

A direct path flux analysis (PFA) method for kinetic mechanism reduction is proposed and validated by using high temperature ignition, perfect stirred reactors, and steady and unsteady flame propagations of n-heptane and n-decane/air mixtures. The formation and consumption fluxes of each species at multiple reaction path generations are analyzed and used to identify the important reaction pathways and the associated species. The formation and consumption path fluxes used in this method retain flux conservation information and are used to define the path indexes for the first and the second generation reaction paths related to a targeted species. Based on the indexes of each reaction path for the first and second generations, different sized reduced chemical mechanisms which contain different number of species are generated. The reduced mechanisms of n-heptane and n-decane obtained by using the present method are compared to those generated by the direct relation graph (DRG) method. The reaction path analysis for n-decane is conducted to demonstrate the validity of the present method. The comparisons of the ignition delay times, flame propagation speeds, flame structures, and unsteady spherical flame propagation processes showed that with either the same or significantly less number of species, the reduced mechanisms generated by the present PFA are more accurate than that of DRG in a broad range of initial pressures and temperatures. The method is also integrated with the dynamic multi-timescale method and a further increase of computation efficiency is achieved. (author)

Sun, Wenting; Ju, Yiguang [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544 (United States); Chen, Zheng [State Key Laboratory for Turbulence and Complex Systems, College of Engineering, Peking University, Beijing 100871 (China); Gou, Xiaolong [School of Power Engineering, Chongqing University, Chongqing 400044 (China)

2010-07-15

378

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

PubMed Central

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.

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

2012-01-01

379

Identifying Stereoisomers by ab-initio Calculation of Secondary Isotope Shifts on NMR Chemical Shieldings.  

PubMed

We present ab-initio calculations of secondary isotope effects on NMR chemical shieldings. The change of the NMR chemical shift of a certain nucleus that is observed if another nucleus is replaced by a different isotope can be calculated by computing vibrational corrections on the NMR parameters using electronic structure methods. We demonstrate that the accuracy of the computational results is sufficient to even distinguish different conformers. For this purpose, benchmark calculations for fluoro(2-2H)ethane in gauche and antiperiplanar conformation are carried out at the HF, MP2 and CCSD(T) level of theory using basis sets ranging from double- to quadruple-zeta quality. The methodology is applied to the secondary isotope shifts for 2-fluoronorbornane in order to resolve an ambiguity in the literature on the assignment of endo- and exo-2-fluoronorbornanes with deuterium substituents in endo-3 and exo-3 positions, also yielding insight into mechanistic details of the corresponding synthesis. PMID:24762967

Böhm, Karl-Heinz; Banert, Klaus; Auer, Alexander A

2014-01-01

380

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

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

381

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

PubMed

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

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

2012-11-01

382

Chemical mechanism and kinetics study on the ocimene ozonolysis reaction in atmosphere  

NASA Astrophysics Data System (ADS)

The ocimene ozonolysis reaction is one of the most important processes for the formation of secondary organic aerosol (SOA). In this paper, molecular orbital theory has been performed for the reaction of ocimene with O 3, and the detailed reaction mechanisms of active intermediates with H 2O or NO are also presented. The geometry parameters and vibrational frequencies of the stationary points are calculated at the MPWB1K level with the 6-31G(d,p) basis set. Single-point energy calculations are carried out at the MPWB1K/6-311+G(3df,2p) level. On the basis of the quantum chemical information, the Rice-Ramsperger-Kassel-Marcus (RRKM) theory and the canonical variational transition state theory (CVT) with small-curvature tunneling effect (SCT) are used to calculate the rate constants over the temperature range of 200-800 K. The arrhenius formulas of rate constants with the temperature are fitted, which can provide helpful information for the model simulation study. The atmospheric lifetimes of the reaction species are estimated according to the rate constants.

Sun, Xiaomin; Bai, Jing; Zhao, Yuyang; Zhang, Chenxi; Wang, Yudong; Hu, Jingtian

2011-11-01

383

LSENS, a general chemical kinetics and sensitivity analysis code for homogeneous gas-phase reactions. 2: Code description and usage  

NASA Technical Reports Server (NTRS)

LSENS, the Lewis General Chemical Kinetics Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part 2 of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part 2 describes the code, how to modify it, and its usage, including preparation of the problem data file required to execute LSENS. Code usage is illustrated by several example problems, which further explain preparation of the problem data file and show how to obtain desired accuracy in the computed results. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions. Part 1 (NASA RP-1328) derives the governing equations describes the numerical solution procedures for the types of problems that can be solved by lSENS. Part 3 (NASA RP-1330) explains the kinetics and kinetics-plus-sensitivity-analysis problems supplied with LSENS and presents sample results.

Radhakrishnan, Krishnan; Bittker, David A.

1994-01-01

384

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

NASA Technical Reports Server (NTRS)

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.

Palmer, Grant

1987-01-01

385

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

SciTech Connect

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.

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

2005-11-14

386

Highly effective pincer-ligated iridium catalysts for alkane dehydrogenation. DFT calculations of relevant thermodynamic, kinetic, and spectroscopic properties.  

PubMed

The p-methoxy-substituted pincer-ligated iridium complexes, (MeO-(tBu)PCP)IrH(4) ((R)PCP = kappa(3)-C(6)H(3)-2,6-(CH(2)PR(2))(2)) and (MeO-(iPr)PCP)IrH(4), are found to be highly effective catalysts for the dehydrogenation of alkanes (both with and without the use of sacrificial hydrogen acceptors). These complexes offer an interesting comparison with the recently reported bis-phosphinite "POCOP" ((R)POCOP = kappa(3)-C(6)H(3)-2,6-(OPR(2))(2)) pincer-ligated catalysts, which also show catalytic activity higher than unsubstituted PCP analogues (Gottker-Schnetmann, I.; White, P.; Brookhart, M. J. Am. Chem. Soc. 2004, 126, 1804). On the basis of nu(CO) values of the respective CO adducts, the MeO-PCP complexes appear to be more electron-rich than the parent PCP complexes, whereas the POCOP complexes appear to be more electron-poor. However, the MeO-PCP and POCOP ligands are calculated (DFT) to show effects in the same directions, relative to the parent PCP ligand, for the kinetics and thermodynamics of a broad range of reactions including the addition of C-H and H-H bonds and CO. In general, both ligands favor (relative to unsubstituted PCP) addition to the 14e (pincer)Ir fragments but disfavor addition to the 16e complexes (pincer)IrH(2) or (pincer)Ir(CO). These kinetic and thermodynamic effects are all largely attributable to the same electronic feature: O --> C(aryl) pi-donation, from the methoxy or phosphinito groups of the respective ligands. DFT calculations also indicate that the kinetics (but not the thermodynamics) of C-H addition to (pincer)Ir are favored by sigma-withdrawal from the phosphorus atoms. The high nu(CO) value of (POCOP)Ir(CO) is attributable to electrostatic effects, rather than decreased Ir-CO pi-donation or increased OC-Ir sigma-donation. PMID:15469303

Zhu, Keming; Achord, Patrick D; Zhang, Xiawei; Krogh-Jespersen, Karsten; Goldman, Alan S

2004-10-13

387

Hyperspherical analysis of kinetic paths for elementary chemical reactions and their angular momentum dependence  

NASA Astrophysics Data System (ADS)

Exploiting the hyperspherical mapping of potential energy surfaces, the evolutions of minima (valley bottoms) and saddles (ridges) as a function of the kinetic radius are identified as kinetic paths for studying reaction mechanisms and dynamics. The effect of angular momentum is investigated quantum-mechanically in a hyperspherical harmonic basis and a lower bound to adiabatic evolution is established. By a classical stability analysis, the dependence of angular momentum effects on configuration is studied. Some features of kinetic paths (such as the occurrence of symmetry degeneracies and bifurcations related to elementary catastrophes) are briefly illustrated for kinetic paths on surfaces for H 3 and H 3+.

Aquilanti, Vincenzo; Cavalli, Simonetta

1987-11-01

388

Physical and numerical sources of computational inefficiency in integration of chemical kinetic rate equations: Etiology, treatment and prognosis  

NASA Technical Reports Server (NTRS)

The design of a very fast, automatic black-box code for homogeneous, gas-phase chemical kinetics problems requires an understanding of the physical and numerical sources of computational inefficiency. Some major sources reviewed in this report are stiffness of the governing ordinary differential equations (ODE's) and its detection, choice of appropriate method (i.e., integration algorithm plus step-size control strategy), nonphysical initial conditions, and too frequent evaluation of thermochemical and kinetic properties. Specific techniques are recommended (and some advised against) for improving or overcoming the identified problem areas. It is argued that, because reactive species increase exponentially with time during induction, and all species exhibit asymptotic, exponential decay with time during equilibration, exponential-fitted integration algorithms are inherently more accurate for kinetics modeling than classical, polynomial-interpolant methods for the same computational work. But current codes using the exponential-fitted method lack the sophisticated stepsize-control logic of existing black-box ODE solver codes, such as EPISODE and LSODE. The ultimate chemical kinetics code does not exist yet, but the general characteristics of such a code are becoming apparent.

Pratt, D. T.; Radhakrishnan, K.

1986-01-01

389

DFT calculations on kinetic data for some [4+2] reactions in solution.  

PubMed

The reaction mechanisms of [4+2] cycloaddition reactions between dienes and dienophiles have been investigated with several density functional theory (DFT) methods, such as CAM-B3LYP, BMK, M062x wB97x and wB97xd, and the obtained results show that most of the reactions are synchronous or asynchronous. The stability of the transition state is moderated by the interaction of frontier molecular orbitals (FMOs), in which a diene acts as an electron-donating partner and a dienophile acts as an electron-acceptor from the charge transfer direction in the transition state. The activation free energy barriers have been calculated with both gas-phase translational entropy and solution translational entropy, in which those from gas-phase translational entropy (output of the Gaussian job) are far away from the experimental estimations. It has been found that free-energy barriers generated from solution translational entropies with CAM-B3LYP+IDSCRF/6-31G(d), BMK+IDSCRF/6-31G(d) and wB97x+IDSCRF/6-31G(d) are very close to the experimental measurements, but both M062x and wB97xd methods predict too low free-energy barriers for most of the studied reactions. The substituent and solvent effects on reaction dynamic data have also been addressed. PMID:24938221

Li, Yue; Fang, De-Cai

2014-08-01

390

Chemical kinetic analysis of thermal decay of rhodopsin reveals unusual energetics of thermal isomerization and hydrolysis of Schiff base.  

PubMed

The thermal properties of rhodopsin, which set the threshold of our vision, have long been investigated, but the chemical kinetics of the thermal decay of rhodopsin has not been revealed in detail. To understand thermal decay quantitatively, we propose a kinetic model consisting of two pathways: 1) thermal isomerization of 11-cis-retinal followed by hydrolysis of Schiff base (SB) and 2) hydrolysis of SB in dark state rhodopsin followed by opsin-catalyzed isomerization of free 11-cis-retinal. We solve the kinetic model mathematically and use it to analyze kinetic data from four experiments that we designed to assay thermal decay, isomerization, hydrolysis of SB using dark state rhodopsin, and hydrolysis of SB using photoactivated rhodopsin. We apply the model to WT rhodopsin and E181Q and S186A mutants at 55 °C, as well as WT rhodopsin in H(2)O and D(2)O at 59 °C. The results show that the hydrogen-bonding network strongly restrains thermal isomerization but is less important in opsin and activated rhodopsin. Furthermore, the ability to obtain individual rate constants allows comparison of thermal processes under various conditions. Our kinetic model and experiments reveal two unusual energetic properties: the steep temperature dependence of the rates of thermal isomerization and SB hydrolysis in the dark state and a strong deuterium isotope effect on dark state SB hydrolysis. These findings can be applied to study pathogenic rhodopsin mutants and other visual pigments. PMID:21921035

Liu, Jian; Liu, Monica Yun; Fu, Li; Zhu, Gefei Alex; Yan, Elsa C Y

2011-11-01

391

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

PubMed

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

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

2010-03-25

392

Calculation of free energies and chemical potentials for gas hydrates using Monte Carlo simulations.  

PubMed

We describe a method for calculating free energies and chemical potentials for molecular models of gas hydrate systems using Monte Carlo simulations. The method has two components: (i) thermodynamic integration to obtain the water and guest molecule chemical potentials as functions of the hydrate occupancy; (ii) calculation of the free energy of the zero-occupancy hydrate system using thermodynamic integration from an Einstein crystal reference state. The approach is applicable to any classical molecular model of a hydrate. We illustrate the methodology with an application to the structure-I methane hydrate using two molecular models. Results from the method are also used to assess approximations in the van der Waals-Platteeuw theory and some of its extensions. It is shown that the success of the van der Waals-Platteeuw theory is in part due to a cancellation of the error arising from the assumption of a fixed configuration of water molecules in the hydrate framework with that arising from the neglect of methane-methane interactions. PMID:17530795

Wierzchowski, S J; Monson, P A

2007-06-28

393

Structure of acidic haloaluminate melts: Neutron diffraction and quantum chemical calculations  

SciTech Connect

The structure of molten mixtures of (KX){sub {ital y}}(AlX{sub 3}){sub 1{minus}{ital y}} was investigated by neutron diffraction for X=Cl and Br and {ital y}=0.25 and 0.33. These melts, known as acidic haloaluminates, contain different ionic species such as AlX{sup {minus}}{sub 4},Al{sub 2}X{sup {minus}}{sub 7}, Al{sub 3}X{sup {minus}}{sub 10}. The diffraction patterns were similar, although not identical, for the same halide pairs and showed features indicative of short-range and intermediate-range order. Quantum chemical calculations were carried out on AlX{sup {minus}}{sub 4}, Al{sub 2}X{sup {minus}}{sub 7}, and Al{sub 3}X{sup {minus}}{sub 10} to provide information needed to interpret the structural results within the framework of the random packing of structural units model. It is shown that the bent Al--X--Al bridge for Al{sub 2}X{sup {minus}}{sub 7}, obtained from the quantum chemical calculations, is necessary to represent well the structure, and that the values of the bond angles at the central halide atoms are around 110{degree}. Aluminum atoms are found to be tetrahedrally coordinated by the halide atoms, and information on the orientational correlations of neighboring Al{sub 2}X{sup {minus}}{sub 7} is derived.

Blander, M.; Bierwagen, E.; Calkins, K.G.; Curtiss, L.A.; Price, D.L.; Saboungi, M. (Argonne National Laboratory, Argonne, Illinois 60439 (United States))

1992-08-15

394

Kinetics of thermal gradient chemical vapor infiltration of large-size carbon\\/carbon composites with vaporized kerosene  

Microsoft Academic Search

Large-size samples of carbon\\/carbon composites were prepared using thermal gradient chemical vapor infiltration with kerosene precursor at 950, 1020, 1100, 1180 and 1250°C. The temperature gradient, kinetics and density distribution of these samples were studied and the microstructure of pyrolytic carbon was examined by polarized light microscopy. The results show that the initial infiltration rate increased from 5.81 to 21.32gmin?1

Xiaowen Wu; Ruiying Luo; Jincao Zhang; Qiang Li; Yongfeng Ni

2009-01-01

395

Acetylcholine Receptor (from Electrophorus electricus): A Comparison of Single-Channel Current Recordings and Chemical Kinetic Measurements  

Microsoft Academic Search

We report a direct comparison between two types of measurements of the dynamic properties of the acetylcholine receptor: single-channel currents recorded using the patch-clamp technique and chemical kinetic measurements. Electrophorus electricus electroplax cells, and membrane vesicles prepared from these cells, were used. Such a comparison, and single-channel currents recorded from these cells, have not previously been reported. We first give

George P. Hess; Hans-Albert Kolb; Peter Lauger; Ernest Schoffeniels; Werner Schwarze

1984-01-01

396

A kinetic Monte Carlo simulation of chemical vapor deposition: non-monotonic variation of surface roughness with growth temperature  

Microsoft Academic Search

We have implemented a 2D+1 solid-on-solid kinetic Monte Carlo model to explore aspects of thin film growth via chemical vapor deposition (CVD) that may differ from growth via physical vapor deposition. This model is a minimal extension to CVD of models that have previously been used by others to successfully simulate growth by molecular beam epitaxy. This extension involves the

Martine Kalke; David V. Baxter

2001-01-01

397

The role of monovalent phosphate anions in the crossbridge kinetics of chemically skinned rabbit psoas fibers.  

PubMed

The role of phosphate ions (Pi) in crossbridge kinetics is investigated by parallel measurements of the ATP hydrolysis rate and the tension transients in maximally activated, chemically skinned rabbit psoas fibers. The tension transients are induced by sinusoidal length oscillations, and resulting time courses are analyzed in terms of three exponential processes (A), (B), and (C). The ATP hydrolysis rate is measured by the NADH fluorscence method coupled with enzymatic reactions which rephosphorylate ADP and oxidize NADH. The hydrolysis rate of the standard activation at 20 degrees C is measured at 0.61 mM/sec. The isometric tension, stiffness, and the ATPase rate progressively decrease with increasing concentrations of Pi (0-16 mM). The decrease is most notably observed with tension, followed by stiffness and the ATPase rate. Both the apparent rate constant and the magnitude parameters of exponential process (B) increase with Pi concentration resulting in a large increase in the oscillatory power output. The active species of Pi which causes this effect is found to be the monovalent anion H2PO4-. The effects of Pi on processes (A) and (C) are only marginal. When fibers are oscillated at 1 Hz, no increase in the ATP hydrolysis rate is observed; a small increase is noticed at 10 Hz (1%), and at 100 Hz (6%). We interpret these results in terms of a crossbridge scheme which adds a branch pathway to the conventional hydrolysis cycle: the number of crossbridges entering the branch pathway increases at higher Pi concentrations and in the presence of oscillations. PMID:2970207

Kawai, M; Güth, K; Cornacchia, T W

1988-01-01

398

Combustion in Homogeneous Charge Compression Ignition Engines: Experiments and Detailed Chemical Kinetic Simulations  

SciTech Connect

Homogeneous charge compression ignition (HCCI) engines are being considered as an alternative to diesel engines. The HCCI concept involves premixing fuel and air prior to induction into the cylinder (as is done in current spark-ignition engine) then igniting the fuel-air mixture through the compression process (as is done in current diesel engines). The combustion occurring in an HCCI engine is fundamentally different from a spark-ignition or Diesel engine in that the heat release occurs as a global autoignition process, as opposed to the turbulent flame propagation or mixing controlled combustion used in current engines. The advantage of this global autoignition is that the temperatures within the cylinder are uniformly low, yielding very low emissions of oxides of nitrogen (NO{sub x}, the chief precursors to photochemical smog). The inherent features of HCCI combustion allows for design of engines with efficiency comparable to, or potentially higher than, diesel engines. While HCCI engines have great potential, several technical barriers exist which currently prevent widespread commercialization of this technology. The most significant challenge is that the combustion timing cannot be controlled by typical in-cylinder means. Means of controlling combustion have been demonstrated, but a robust control methodology that is applicable to the entire range of operation has yet to be developed. This research focuses on understanding basic characteristics of controlling and operating HCCI engines. Experiments and detailed chemical kinetic simulations have been applied to the characterize some of the fundamental operational and design characteristics of HCCI engines. Experiments have been conducted on single and multi-cylinder engines to investigate general features of how combustion timing affects the performance and emissions of HCCI engines. Single-zone modeling has been used to characterize and compare the implementation of different control strategies. Multi-zone modeling has been applied to investigate combustion chamber design with respect to increasing efficiency and reducing emissions in HCCI engines.

Flowers, D L

2002-06-07

399

Chemical kinetic behavior of chlorogenic acid in protecting erythrocyte and DNA against radical-induced oxidation.  

PubMed

As an abundant ingredient in coffee, chlorogenic acid (CGA) is a well-known antioxidant. Although some works have dealt with its radical-scavenging property, the present work investigated the protective effects of CGA on the oxidation of DNA and on the hemolysis of human erythrocytes induced by 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH) by means of chemical kinetics. The inhibition period (t(inh)) derived from the protective effect of CGA on erythrocyte and DNA was proportional to its concentration, t(inh) = (n/R(i))[CGA], where R(i) refers to the radical-initiation rate, and n indicates the number of radical-propagation chains terminated by CGA. It was found that the n of CGA to protect erythrocytes was 0.77, lower than that of vitamin E (2.0), but higher than that of vitamin C (0.19). Furthermore, CGA facilitated a mutual protective effect with VE and VC on AAPH-induced hemolysis by increasing n of VE and VC. CGA was also found to be a membrane-stabilizer to protect erythrocytes against hemin-induced hemolysis. Moreover, the n of CGA was only 0.41 in the process of protecting DNA. This fact revealed that CGA served as an efficient antioxidant to protect erythrocytes more than to protect DNA. Finally, the reaction between CGA and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) radical cation (ABTS(+*)) or 2,2'-diphenyl-1-picrylhydrazyl (DPPH) revealed that CGA was able to trap radicals by reducing radicals more than by donating its hydrogen atoms to radicals. PMID:18983165

Tang, You-Zhi; Liu, Zai-Qun

2008-11-26

400

Mass fluctuation kinetics: Capturing stochastic effects in systems of chemical reactions through coupled mean-variance computations  

NASA Astrophysics Data System (ADS)

The intrinsic stochastic effects in chemical reactions, and particularly in biochemical networks, may result in behaviors significantly different from those predicted by deterministic mass action kinetics (MAK). Analyzing stochastic effects, however, is often computationally taxing and complex. The authors describe here the derivation and application of what they term the mass fluctuation kinetics (MFK), a set of deterministic equations to track the means, variances, and covariances of the concentrations of the chemical species in the system. These equations are obtained by approximating the dynamics of the first and second moments of the chemical master equation. Apart from needing knowledge of the system volume, the MFK description requires only the same information used to specify the MAK model, and is not significantly harder to write down or apply. When the effects of fluctuations are negligible, the MFK description typically reduces to MAK. The MFK equations are capable of describing the average behavior of the network substantially better than MAK, because they incorporate the effects of fluctuations on the evolution of the means. They also account for the effects of the means on the evolution of the variances and covariances, to produce quite accurate uncertainty bands around the average behavior. The MFK computations, although approximate, are significantly faster than Monte Carlo methods for computing first and second moments in systems of chemical reactions. They may therefore be used, perhaps along with a few Monte Carlo simulations of sample state trajectories, to efficiently provide a detailed picture of the behavior of a chemical system.

Gómez-Uribe, Carlos A.; Verghese, George C.

2007-01-01

401

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

PubMed Central

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.

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

2011-01-01

402

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

ERIC Educational Resources Information Center

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)

Elias, Horst; Zipp, Arden P.

1988-01-01

403

Removal of 2,4-dichlorophenoxyacetic acid from aqueous solutions by partially characterized organophilic sepiolite: thermodynamic and kinetic calculations.  

PubMed

The adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) on organophilic sepiolite (dodecylammonium sepiolite, DAS) was studied as a function of solution concentration and temperature. The observed adsorption rates were found to be equal to the first-order kinetics. The rate constants were calculated for temperatures ranging between 25 and 40 degrees C at constant concentration. The adsorption energies, E, and adsorption capacity, q(m), for 2,4-D adsorption on organophilic sepiolite was estimated using the Dubinin-Radushkevic equation. Thermodynamic parameters (Deltag(a), Deltah(a), Deltas(a)) were determined by a new approximation from the isotherm of 2,4-D adsorption on DAS. Also, DeltaS(0) and DeltaH(0) values were calculated from the van't Hoff equation. These isotherms were modeled according to the Freundlich and Dubinin-Radushkevic adsorption equations. The amount of adsorption of this herbicide on organophilic sepiolite was found to be dependent on the relative energies of adsorbent-adsorbate, adsorbate-solvent, and adsorbate-adsorbate interaction. PMID:15567376

Akçay, Gülten; Akçay, Mehmet; Yurdakoç, Kadir

2005-01-01

404

Benchmarking quantum chemical methods for the calculation of molecular dipole moments and polarizabilities.  

PubMed

The calculation of molecular electric moments, polarizabilities, and electrostatic potentials is a widespread application of quantum chemistry. Although a range of wave function and density functional theory (DFT) methods have been applied in these calculations, combined with a variety of basis sets, there has not been a comprehensive evaluation of how accurate these methods are. To benchmark the accuracy of these methods, the dipole moments and polarizabilities of a set of 46 molecules were calculated using a broad set of quantum chemical methods and basis sets. Wave function methods Hartree-Fock (HF), second-order Møller-Plesset (MP2), and coupled cluster-singles and doubles (CCSD) were evaluated, along with the PBE, TPSS, TPSSh, PBE0, B3LYP, M06, and B2PLYP DFT functionals. The cc-pVDZ, cc-pVTZ, aug-cc-pVDZ, aug-cc-pVTZ, and Sadlej cc-pVTZ basis sets were tested. The aug-cc-pVDZ, Sadlej cc-pVTZ, and aug-cc-pVTZ basis sets all yield results with comparable accuracy, with the aug-cc-pVTZ calculations being the most accurate. CCSD, MP2, or hybrid DFT methods using the aug-cc-pVTZ basis set are all able to predict dipole moments with RMSD errors in the 0.12-0.13 D range and polarizabilities with RMSD errors in the 0.30-0.38 Å(3) range. Calculations using Hartree-Fock theory systematically overestimated dipole moments and underestimate polarizabilities. The pure DFT functionals included in this study (PBE and TPSS) slightly underestimate dipole moments and overestimate polarizability. Polarization anisotropy and implications for charge fitting are discussed. PMID:24796376

Hickey, A Leif; Rowley, Christopher N

2014-05-22

405

The Development of a Detailed Chemical Kinetic Mechanism for Diisobutylene and Comparison to Shock Tube Ignition Times  

SciTech Connect

There is much demand for chemical kinetic models to represent practical fuels such as gasoline, diesel and aviation fuel. These blended fuels contain hundreds of components whose identity and amounts are often unknown. A chemical kinetic mechanism that would represent the oxidation of all these species with accompanying chemical reactions is intractable with current computational capabilities, chemical knowledge and manpower resources. The use of surrogate fuels is an approach to make the development of chemical kinetic mechanisms for practical fuels tractable. A surrogate fuel model consists of a small number of fuel components that can be used to represent the practical fuel and still predict desired characteristics of the practical fuel. These desired fuel characteristics may include ignition behavior, burning velocity, fuel viscosity, fuel vaporization, and fuel emissions (carbon monoxide, hydrocarbons, soot and nitric oxides). Gasoline consists of many different classes of hydrocarbons including n-alkanes, alkenes, iso-alkanes, cycloalkanes, cycloalkenes, and aromatics. One approach is to use a fuel surrogate that has a single component from each class of hydrocarbon in gasoline so that the unique molecular structure of each class is represented. This approach may lead to reliable predictions of many of the combustion properties of the practical fuel. In order to obtain a fuel surrogate mechanism, detailed chemical kinetic mechanisms must be developed for each component in the surrogate. In this study, a detailed chemical kinetic mechanism is developed for diisobutylene, a fuel intended to represent alkenes in practical fuels such as gasoline, diesel, and aviation fuel. The fuel component diisobutylene usually consists of a mixture of two conjugate olefins of iso-octane: 1- or 2-pentene, 2,4,4-trimethyl. Diisobutylene has a similar molecular structure to iso-octane, so that its kinetics offers insight into the effect of including a double bond in the carbon skeletal structure of iso-octane. There are few previous studies on diisobutylene. Kaiser et al. [1] examined the exhaust emission from a production spark ignition engine with neat diisobutylene and with it mixed with gasoline. They found the exhaust emissions of diisobutylene to be similar to that of iso-octane. They saw a significant increase in the amount of 2-methyl-1,3-butadiene measured in the exhaust of the engine. They also found appreciable amount of propene in the exhaust, but could not explain the source of this product as they did others in terms of C-C bond beta scission of alkyl radicals. Risberg et al. [2] studied a number of fuel blends to evaluate their autoignition quality for use in a homogeneous charge compression ignition engine, using diisobutylene to represent olefins in one of their test fuels. In this study, experiments on the shock tube ignition of both isomers of diisobutylene will be described. Then, the development of a detailed chemical kinetic mechanism for the two isomers of diisobutylene will be discussed.

Metcalfe, W; Curran, H J; Simmie, J M; Pitz, W J; Westbrook, C K

2005-01-21

406

Silicon Oxysulfide, OSiS: Rotational Spectrum, Quantum-Chemical Calculations, and Equilibrium Structure  

NASA Astrophysics Data System (ADS)

Silicon oxysulfide, OSiS, and seven of its minor isotopic species have been characterized for the first time in the gas phase at high spectral resolution by means of Fourier transform microwave spectroscopy. The equilibrium structure of OSiS has been determined from the experimental data using calculated vibration-rotation interaction constants. The structural parameters (rO-Si = 1.5064 Angstrom and rSi-S = 1.9133 Angstrom) are in very good agreement with values from high-level quantum chemical calculations using coupled-cluster techniques together with sophisticated additivity and extrapolation schemes. The bond distances in OSiS are very short in comparison with those in SiO and SiS. This unexpected finding is explained by the partial charges calculated for OSiS via a natural population analysis. The results suggest that electrostatic effects rather than multiple bonding are the key factors in determining bonding in this triatomic molecule. The data presented provide the spectroscopic information needed for radio astronomical searches for OSiS.

Thorwirth, S.; Mück, L. A.; Gauss, J.; Tamassia, F.; Lattanzi, V.; McCarthy, M. C.

2011-05-01

407

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

PubMed

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 0.05M KH2PO4). The flow rate and the wavelength set during HPLC detection were 1.0mL/min and 205nm, 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

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

2014-09-10

408

An experimental and kinetic calculation of the promotion effect of hydrocarbons on the NO-NO 2 conversion in a flow reactor  

Microsoft Academic Search

Experimental and detailed chemical kinetic modeling work has been performed to investigate the role of hydrocarbon oxidation in NO-NO2 conversion. An atmospheric pressure, quartz flow reactor was used to examine the dependence of NO oxidation to NO2 by hydrocarbon type, reaction temperature, and residence time. The five hydrocarbons examined were methane, ethylene, ethane, propene, and propane. In the experiment, probe

Morio Hori; Naoki Matsunaga; Nick Marinov; Pitz William; Westbrook Charles

1998-01-01

409

Kinetic and chemical mechanisms for the effects of univalent cations on the spectral properties of aromatic amine dehydrogenase.  

PubMed Central

Univalent cations and pH influence the UV-visible absorption spectrum of the tryptophan tryptophylquinone (TTQ) enzyme, aromatic amine dehydrogenase (AADH). Little spectral perturbation was observed when pH was varied in the absence of univalent cations. The addition of alkali metal univalent cations (K+, Na+, Li+, Rb+ or Cs+) to oxidized AADH caused significant changes in its absorption spectrum. The apparent Kd for each cation, determined from titrations of the spectral perturbation, decreased with increasing pH. Transient kinetic studies involving rapid mixing of AADH with cations and pH jump revealed that the rate of the cation-induced spectral changes initially decreased with increasing cation concentration to a minimum value, then increased with increasing cation concentration. A kinetic model was developed to fit these data, determine the true pH-independent Kd values for K+ and Na+, and explain the pH-dependence of the apparent Kd. A chemical reaction mechanism, based on the kinetic data, is presented in which the metallic univalent cation facilitates the chemical modification of the TTQ prosthetic group to form an hydroxide adduct which gives rise to the spectral change. Addition of NH4(+)/NH3 to AADH caused changes in the absorption spectrum which were very different form those caused by addition of the metallic univalent cations. The kinetics of the reaction induced by addition of NH4+/NH3 were also different, being simple saturation kinetics. Another reaction mechanism is proposed for the NH4+/NH3-induced spectral change that involves nucleophilic addition of the unprotonated NH3 to TTQ. The general relevance of these data and models to the physiological reactions of TTQ-dependent enzymes and to the roles of univalent cations in modulating enzyme activity are discussed.

Zhu, Z; Davidson, V L

1998-01-01

410

Cluster models and ab initio calculations of (19)F NMR isotropic chemical shifts for inorganic fluorides.  

PubMed

(19)F NMR isotropic chemical shift (delta(iso)) calculations are performed in crystallized compounds using the GIAO method with the B3LYP hybrid functional at DFT level. Clusters centered on the studied fluorine atoms mimic the crystalline structures. The 6-311+G(d) basis set is chosen for the central fluorine atom, and the LanL2DZ basis set for the others. The metal atoms are described by the 3-21G(2d) basis set or, when not available, by the CRENBL basis set with the corresponding ECP, and augmented with 2d polarization functions when existing. First, for high-symmetry systems (MF, MF(2), and MF(3) compounds), a systematization of the cluster building up from coordination spheres is proposed, generalized to fluoroperovskites and fluoroaluminates KAlF(4) and RbAlF(4). When applied to rather low symmetry systems such as barium fluorometalates BaMgF(4), BaZnF(4), and Ba(2)ZnF(6), the definition of the coordination spheres is far from easy. Then, for structures built up from a MF(6) octahedron network, we may define different "starting clusters": [FM(2)F(8)] for the shared fluorine atoms, [FMF(4)] for the unshared ones, and [FBa(4)](7+) for the "free" ones. Analogous "starting clusters" are then tested on compounds from the NaF-AlF(3), BaF(2)-AlF(3), and CaF(2)-AlF(3) binary systems and for alpha-BaCaAlF(7) that are also built up from a MF(6) octahedron network. For each of these corresponding fluorine sites, delta(iso) values are calculated with the "starting clusters" and several larger clusters and compared to the experimental delta(iso) values. For the barium-containing clusters, the RMS deviation is equal to 51 ppm. It is suggested that this result may be related to the poor quality of the barium basis sets for which no polarization functions are available for the moment. In total, chemical shifts were calculated for 122 fluorine sites, in a various range of compounds. For the clusters without barium, the ab initio method leads to a RMS equal to 22 ppm, which is a quite nice result keeping in mind that the (19)F chemical shift range is larger than 200 ppm. PMID:16852244

Body, Monique; Silly, Gilles; Legein, Christophe; Buzaré, Jean-Yves

2005-05-26

411

An Analytical Investigation of Three General Methods of Calculating Chemical-Equilibrium Compositions  

NASA Technical Reports Server (NTRS)

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.

Zeleznik, Frank J.; Gordon, Sanford

1960-01-01

412

Combined ab initio/DFT and Monte Carlo calculation of relative standard chemical potentials in solution.  

PubMed

A method has been proposed for pure theoretical estimation of relative standard chemical potentials (1 mol/dm(3) standard state) and related K(c) equilibrium constants for tautomers/conformers dissolved in some solvents. The relative internal free energy could be obtained by means of in-solution ab initio/DFT methods. Using the free energy perturbation method for the transformation of the involved species, the solvation contribution to the relative standard chemical potential can be determined by considering 1 M solution models. Comparison of the ?G(solv)/MC value calculated for the 1 M solution with those obtained for the system at other concentrations helps explore the ratio of the activity coefficients in nonstandard states. The method has been applied for the study of the tautomeric pair of formaldoxime and nitrosomethane with large structural differences. It was pointed out that the ?G(solv)/MC values for the 1 and 0.11 M solutions differ by up to 0.2 kcal/mol, when atomic charges are derived on the basis of the in-solution IEF-PCM/B3LYP/aug-cc-pvtz molecular electrostatic potential. On the basis of calculated free energy differences, the ratio of the CH(3)NO and CH(2)NOH activity coefficients in 0.11 molar aqueous and dichloromethane solutions were predicted as of 1.4 and 0.8, respectively. The 0.11 M model is hypothetical by assuming that only one of the tautomers exists in the solution box. As an extension of the method, a procedure has been outlined where contributions to the change of the solvation free energy by terms related to relative activity coefficients might be assessed at physically relevant concentrations for the equilibrated tautomers. PMID:21682330

Nagy, Peter I

2011-08-11

413

HCCI experiments with gasoline surrogate fuels modeled by a semidetailed chemical kinetic model  

SciTech Connect

Experiments in a homogeneous charge compression ignition (HCCI) engine have been conducted with four gasoline surrogate fuel blends. The pure components in the surrogate fuels consisted of n-heptane, isooctane, toluene, ethanol and diisobutylene and fuel sensitivities (RON-MON) in the fuel blends ranged from two to nine. The operating conditions for the engine were p{sub in}=0.1 and 0.2 MPa, T{sub in}=80 and 250 C, {phi}=0.25 in air and engine speed 1200 rpm. A semidetailed chemical kinetic model (142 species and 672 reactions) for gasoline surrogate fuels, validated against ignition data from experiments conducted in shock tubes for gasoline surrogate fuel blends at 1.0{<=} p{<=}5.0MPa, 700{<=} T{<=}1200 K and {phi}=1.0, was successfully used to qualitatively predict the HCCI experiments using a single zone modeling approach. The fuel blends that had higher fuel sensitivity were more resistant to autoignition for low intake temperature and high intake pressure and less resistant to autoignition for high intake temperature and low intake pressure. A sensitivity analysis shows that at high intake temperature the chemistry of the fuels ethanol, toluene and diisobutylene helps to advance ignition. This is consistent with the trend that fuels with the least Negative Temperature Coefficient (NTC) behavior show the highest octane sensitivity, and become less resistant to autoignition at high intake temperatures. For high intake pressure the sensitivity analysis shows that fuels in the fuel blend with no NTC behavior consume OH radicals and acts as a radical scavenger for the fuels with NTC behavior. This is consistent with the observed trend of an increase in RON and fuel sensitivity. With data from shock tube experiments in the literature and HCCI modeling in this work, a correlation between the reciprocal pressure exponent on the ignition delay to the fuel sensitivity and volume percentage of single-stage ignition fuel in the fuel blend was found. Higher fuel sensitivity and single-stage fuel content generally gives a lower value of the pressure exponent. This helps to explain the results obtained while boosting the intake pressure in the HCCI engine. (author)

Andrae, J.C.G. [Dept. of Chemical Engineering and Technology, Royal Institute of Technology (KTH), SE-100 44 Stockholm (Sweden); Head, R.A. [Shell Technology Centre Thornton, P.O. Box 1, Chester CH1 3SH (United Kingdom)

2009-04-15

414

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

SciTech Connect

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 orienta