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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

The calculation of chemically reacting turbulent boundary layers by means of finite chemical kinetics  

NASA Astrophysics Data System (ADS)

A computer program developed at Delft University of Technology to describe two-dimensional turbulent flows through channels with and without sudden expansion was extended by accounting for heat and mass transfer at the boundaries. The wall-function method of Chieng and Launder (1980) was adapted, allowing the calculation of the Von Karman constant E, which is a function of the local boundary-layer structure in the case of mass transfer. A finite-chemical-kinetics combustion model was implemented in this computer program. The equations for the mass fractions are solved in two steps. In the first step the convection and diffusion of mass fractions is accounted for. In the second step chemical reactions are taken into account by integrating the chemical source term with the integration method for Gear (1971) at each gridpoint in the flow domain. Results of calculations are presented.

Vos, J. B.

1986-06-01

3

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.

4

Chemical Kinetics: Isolation Method  

NSDL National Science Digital Library

This site offers an interactive tutorial that guides the student through the Method of Isolation used for the determination of chemical reaction rate laws and rate constants. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.

Blauch, David N.

5

Reversible Chemical Kinetics Model  

NSDL National Science Digital Library

The Reversible Chemical Kinetics Model illustrates the time evolution of a reversible chemical reaction, from a given set of initial reactants concentration until chemical equilibrium is reached. The concentrations are plotted against time and the respective numerical values are periodically displayed at the data Table. As chemical equilibrium is attained, the concentrations become constant, the reaction quotient (Q) equalizes the equilibrium constant and Gibbs's energy change (G/RT) approaches zero. The Reversible Chemical Kinetics Model was developed using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the jar file will run the program if Java is installed. You can modify this simulation if you have EJS installed by right-clicking within the map and selecting "Open Ejs Model" from the pop-up menu item.

Fernandes, Fernando S.

2012-10-20

6

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

7

LLNL Chemical Kinetics Modeling Group  

SciTech Connect

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

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

2008-09-24

8

Silicate precursors: chemical kinetics  

SciTech Connect

This study employed high resolution /sup 29/Si NMR spectroscopy to measure the time evolution of the chemical species in the acid catalyzed Si(OCH/sub 3/)/sub 4/:CH/sub 3/OH:H/sub 2/O sol-gel system. Results support a theoretical model in which the reaction kinetics are described by three functional group rate constants and appropriate statistical factors.

Kay, Bruce D.; Assink, R.A.

1987-01-01

9

Chemical kinetics modeling  

SciTech Connect

This project emphasizes numerical modeling of chemical kinetics of combustion, including applications in both practical combustion systems and in controlled laboratory experiments. Elementary reaction rate parameters are combined into mechanisms which then describe the overall reaction of the fuels being studied. Detailed sensitivity analyses are used to identify those reaction rates and product species distributions to which the results are most sensitive and therefore warrant the greatest attention from other experimental and theoretical research programs. Experimental data from a variety of environments are combined together to validate the reaction mechanisms, including results from laminar flames, shock tubes, flow systems, detonations, and even internal combustion engines.

Westbrook, C.K.; Pitz, W.J. [Lawrence Livermore National Laboratory, CA (United States)

1993-12-01

10

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.

11

Quantum Chemical Calculations  

NASA Technical Reports Server (NTRS)

The current methods of quantum chemical calculations will be reviewed. The accent will be on the accuracy that can be achieved with these methods. The basis set requirements and computer resources for the various methods will be discussed. The utility of the methods will be illustrated with some examples, which include the calculation of accurate bond energies for SiF$_n$ and SiF$_n^+$ and the modeling of chemical data storage.

Bauschlicher, Charles W.; Arnold, James O. (Technical Monitor)

1997-01-01

12

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

13

Kinetic studies of elementary chemical reactions  

SciTech Connect

This program concerning kinetic studies of elementary chemical reactions is presently focussed on understanding reactions of NH{sub x} species. To reach this goal, the author is pursuing experimental studies of reaction rate coefficients and product branching fractions as well as using electronic structure calculations to calculate transition state properties and reaction rate calculations to relate these properties to predicted kinetic behavior. The synergy existing between the experimental and theoretical studies allow one to gain a deeper insight into more complex elementary reactions.

Durant, J.L. Jr. [Sandia National Laboratories, Livermore, CA (United States)

1993-12-01

14

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

15

Chemical Kinetics Laboratory Discussion Worksheet.  

PubMed

A laboratory discussion worksheet and its answer key provide instructors and students a discussion model to further the students' understanding of chemical kinetics. This discussion worksheet includes a section for students to augment their previous knowledge about chemical kinetics measurements, an initial check on students' understanding of basic concepts, a group participation model where students work on solving complex-conceptual problems, and a conclusion to help students connect this discussion to their laboratory or lecture class. Additionally, the worksheet has a detailed solution to a more advanced problem to help students understand how the concepts they have put together relate to problems they will encounter during later formal assessments. PMID:24092948

Demoin, Dustin Wayne; Jurisson, Silvia S

2013-09-10

16

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

17

Chemical kinetics and combustion modeling  

SciTech Connect

The goal of this program is to gain qualitative insight into how pollutants are formed in combustion systems and to develop quantitative mathematical models to predict their formation rates. The approach is an integrated one, combining low-pressure flame experiments, chemical kinetics modeling, theory, and kinetics experiments to gain as clear a picture as possible of the process in question. These efforts are focused on problems involved with the nitrogen chemistry of combustion systems and on the formation of soot and PAH in flames.

Miller, J.A. [Sandia National Laboratories, Livermore, CA (United States)

1993-12-01

18

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.

19

Detailed Chemical Kinetic Modeling of Cyclohexane Oxidation  

SciTech Connect

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

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

2006-11-10

20

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

21

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

22

Fast algorithms for combustion kinetics calculations: A comparison  

NASA Technical Reports Server (NTRS)

To identify the fastest algorithm currently available for the numerical integration of chemical kinetic rate equations, several algorithms were examined. Findings to date are summarized. The algorithms examined include two general-purpose codes EPISODE and LSODE and three special-purpose (for chemical kinetic calculations) codes CHEMEQ, CRK1D, and GCKP84. In addition, an explicit Runge-Kutta-Merson differential equation solver (IMSL Routine DASCRU) is used to illustrate the problems associated with integrating chemical kinetic rate equations by a classical method. Algorithms were applied to two test problems drawn from combustion kinetics. These problems included all three combustion regimes: induction, heat release and equilibration. Variations of the temperature and species mole fraction are given with time for test problems 1 and 2, respectively. Both test problems were integrated over a time interval of 1 ms in order to obtain near-equilibration of all species and temperature. Of the codes examined in this study, only CREK1D and GCDP84 were written explicitly for integrating exothermic, non-isothermal combustion rate equations. These therefore have built-in procedures for calculating the temperature.

Radhakrishnan, K.

1984-01-01

23

Modelling Chemical Speciation: Thermodynamics, Kinetics and  

E-print Network

CHAPTER 4 Modelling Chemical Speciation: Thermodynamics, Kinetics and Uncertainty Jeanne M. VanBriesen, Mitchell Small, Chris Weber and Jessica Wilson 4.1 INTRODUCTION Chemical speciation refers the full speciation of a chemical in order to predict its behaviour in a system, it is generally

McGaughey, Alan

24

Model simplification of chemical kinetic systems under uncertainty  

E-print Network

This thesis investigates the impact of uncertainty on the reduction and simplification of chemical kinetics mechanisms. Chemical kinetics simulations of complex fuels are very computationally expensive, especially when ...

Coles, Thomas Michael Kyte

2011-01-01

25

Chemical kinetics and oil shale process design  

SciTech Connect

Oil shale processes are reviewed with the goal of showing how chemical kinetics influences the design and operation of different processes for different types of oil shale. Reaction kinetics are presented for organic pyrolysis, carbon combustion, carbonate decomposition, and sulfur and nitrogen reactions.

Burnham, A.K.

1993-07-01

26

Chemical kinetics of Estane aging in PBX  

SciTech Connect

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

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

1997-12-01

27

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

28

CHEMICAL THERMODYNAMICS AND KINETICS Class Meetings  

E-print Network

CHEM 6471 CHEMICAL THERMODYNAMICS AND KINETICS Class Meetings 9:35 ­ 10:55 am, Tuesday and Thursday of October 22-26 Textbooks Molecular Thermodynamics by D.A McQuarrie and J.D. Simon, University Science Books the laws of classical thermodynamics and some of their chemical applications. It also covers basic

Sherrill, David

29

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.

30

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

31

Ultrafast chemical kinetics: Elementary chemical act  

NASA Astrophysics Data System (ADS)

Predictions of the classical theory of chemical reaction rates are compared with experimental results obtained by ultrafast time-resolved X-ray diffraction techniques. Our analysis is illustrated with the reaction I + I = I2 in solution at times immediately preceding recombination. Main features of experimentally detected dynamics are discussed and are compared with what is expected according to Eyring and Kramers. It is emphasized that atomic dynamics are unexpectedly complex at very earliest times.

Bratos, S.; Wulff, M.; Leicknam, J.-Cl.; Kong, Q.

2015-01-01

32

Detailed chemical kinetic model for ethanol oxidation  

SciTech Connect

A detailed chemical kinetic model for ethanol oxidation has been developed and validated against a variety of experimental data sets. Laminar flame speed data obtained from a constant volume bomb, ignition delay data behind reflected shock waves, and ethanol oxidation product profiles from a turbulent flow reactor were used in this study. Very good agreement was found in modeling the data sets obtained from the three different experimental systems. The computational modeling results show that high temperature ethanol oxidation exhibits strong sensitivity to the fall-off kinetics of ethanol decomposition, branching ratio selection for c2h5oh+oh=products, and reactions involving the hydroperoxyl (HO2) radical.

Marinov, N.

1997-04-01

33

KinChem: A Computational Resource for Teaching and Learning Chemical Kinetics  

ERIC Educational Resources Information Center

This paper presents a piece of educational software covering a comprehensive number of topics of chemical kinetics, which is available free of charge in Portuguese and English. The software was developed to support chemistry educators and students in the teaching-learning process of chemical kinetics by using animations, calculations, and…

da Silva, Jose´ Nunes, Jr.; Sousa Lima, Mary Anne; Silva Sousa, Eduardo Henrique; Oliveira Alexandre, Francisco Serra; Melo Leite, Antonio Jose´, Jr.

2014-01-01

34

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

SciTech Connect

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

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

1980-02-01

35

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

36

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. PMID:23656106

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

2013-01-01

37

Determination of the kinetic parameters for the electrothermal atomization of gold with and without chemical modifiers  

Microsoft Academic Search

The effect of various experimental parameters and the presence of chemical modifiers on the atomization kinetics of gold have been investigated. The dissipation process of the atomic vapour is also studied and the diffusion parameters calculated in the absence and in the presence of chemical modifiers. The chemical modifiers studied are ascorbic acid, rhenium, palladium and rhodium. In the absence

Nikolaos S. Thomaidis; Efrosini A. Piperaki

1999-01-01

38

Detailed Chemical Kinetic Modeling of Hydrazine Decomposition  

NASA Technical Reports Server (NTRS)

The purpose of this research project is to develop and validate a detailed chemical kinetic mechanism for gas-phase hydrazine decomposition. Hydrazine is used extensively in aerospace propulsion, and although liquid hydrazine is not considered detonable, many fuel handling systems create multiphase mixtures of fuels and fuel vapors during their operation. Therefore, a thorough knowledge of the decomposition chemistry of hydrazine under a variety of conditions can be of value in assessing potential operational hazards in hydrazine fuel systems. To gain such knowledge, a reasonable starting point is the development and validation of a detailed chemical kinetic mechanism for gas-phase hydrazine decomposition. A reasonably complete mechanism was published in 1996, however, many of the elementary steps included had outdated rate expressions and a thorough investigation of the behavior of the mechanism under a variety of conditions was not presented. The current work has included substantial revision of the previously published mechanism, along with a more extensive examination of the decomposition behavior of hydrazine. An attempt to validate the mechanism against the limited experimental data available has been made and was moderately successful. Further computational and experimental research into the chemistry of this fuel needs to be completed.

Meagher, Nancy E.; Bates, Kami R.

2000-01-01

39

Michael Polanyi's pioneering contribution to the most successful theory in chemical kinetics  

Microsoft Academic Search

After a short discussion of early discoveries in chemical kinetics, the history of the attempt to calculate the rate coefficient from first principles is followed. Michael Polanyi's crucial role in the calculation of potential energy surfaces and the development of the transition state theory (TST) in a form that can be used to successfully calculate practically important rate constants is

ERNÕ KESZEI

2003-01-01

40

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

41

A Chemical Kinetic Model of Transcriptional Elongation  

E-print Network

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

Yujiro Richard Yamada; Charles S. Peskin

2006-03-12

42

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

E-print Network

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

Nguyen, Minh Tho

43

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

44

Benchmarking kinetic calculations of resistive wall mode stability  

SciTech Connect

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.; Sabbagh, S. A. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)] [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States); Liu, Y. Q. [Euratom/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom)] [Euratom/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Wang, Z. R.; Logan, N. C.; Park, J.-K.; Manickam, J. [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)] [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Betti, R. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States)] [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States)

2014-05-15

45

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

46

Quantum chemical calculations of KTN solid solutions  

Microsoft Academic Search

The results of semi-empirical calculations for perovskite KNbxTa1?xO3 (KTN) solid solutions are presented for x = 0.04, 0.11, 0.89, and 0.96. Quantum chemical method of the Intermediate Neglect of the Differential Overlap (INDO) was combined with 135- and 320-atom supercells. Analysis of the optimised atomic and electronic structure has clearly demonstrated that several nearest Nb atoms substituting for Ta in

R. I Eglitis; E. A Kotomin; G Borstel

1998-01-01

47

Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks  

ERIC Educational Resources Information Center

Chemical reaction kinetics and equilibrium are essential core concepts of chemistry but are challenging topics for many students, both at the high school and undergraduate university level. Visualization at the molecular level is valuable to aid understanding of reaction kinetics and equilibrium. This activity provides a discovery-based method to…

Cloonan, Carrie A.; Nichol, Carolyn A.; Hutchinson, John S.

2011-01-01

48

NIST Standard Reference Database 17 NIST Chemical Kinetics Database  

E-print Network

NIST Standard Reference Database 17 __________________________________________________________ NIST Chemical Kinetics Database WindowsTM Version 2Q98 Users' Guide (NIST) uses its best efforts to deliver a high quality copy of the Database and to verify that the data

49

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

50

The efficient calculation of chemically reacting flow  

NASA Technical Reports Server (NTRS)

A semi-implicit finite volume formulation is used to study flows with chemical reactions. In this formulation the source terms resulting from the chemical reactions are treated implicitly and the resulting system of partial differential equations is solved using two time-stepping schemes. The first is based on the Runge-Kutta method while the second is based on an Adams predictor-corrector method. Results show that improvements in computational efficiency depend to a large extent on the manner in which the source term is treated. Further, analysis and computation indicate that the Runge-Kutta method is more efficient than the Adams methods. Finally, an adaptive time stepping scheme is developed to study problems involving shock ignition. Calculations for a hydrogen-air system agree well with other methods.

Eklund, D. R.; Hassan, H. A.; Drummond, J. P.

1986-01-01

51

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

52

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

PubMed

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. PMID:19044733

Osborn, 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

2008-10-01

53

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

54

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

55

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

56

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

57

Chemical kinetics of discharge-driven oxygen-iodine lasers  

Microsoft Academic Search

Oxygen-iodine lasers that utilize electrical discharges to produce O2(a1Delta) are currently being developed. The discharge generators differ from those used in chemical oxygen-iodine lasers in that they produce significant amounts of atomic oxygen and traces of ozone. As a consequence of these differences, the chemical kinetics of the discharge laser are markedly different from those of a conventional chemical oxygen-iodine

Valeriy N. Azyazov; Ivan O. Antonov; Michael C. Heaven

2007-01-01

58

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

59

Chemical Kinetic Models for HCCI and Diesel Combustion  

SciTech Connect

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

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

2010-11-15

60

Chemical and kinetic equilibrations via radiative parton transport  

E-print Network

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

Bin Zhang; Warner A. Wortman

2011-02-21

61

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

62

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

63

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

64

Experimental characterization and chemical kinetics study of chemical looping combustion  

E-print Network

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

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

2014-01-01

65

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

66

Sensitivity, robustness, and identifiability in stochastic chemical kinetics models  

E-print Network

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

Millar, Andrew J.

67

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

68

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

69

On The Theory of Time dilation in Chemical Kinetics  

E-print Network

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

Mirza Wasif Baig

2012-03-17

70

Infrared absorption spectroscopy and chemical kinetics of free radicals  

SciTech Connect

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

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

1993-12-01

71

A chemical kinetic model of hydrocarbon generation from the Bakken Formation, Williston Basin, North Dakota  

SciTech Connect

This report describes a model of hydrocarbon generation and expulsion in the North Dakota portion of the Williston Basin. The modeling incorporates kinetic methods to simulate chemical reactions and 1-dimensional conductive heat flow models to simulate thermal histories of the Mississippian-Devonian Bakken Formation source rock. We developed thermal histories of the source rock for 53 wells in the basin using stratigraphic and heat flow data obtained by the University of North Dakota. Chemical kinetics for hydrocarbon generation, determined from Pyromat pyrolysis, were, then used with the diennal histories to calculate the present day value of the Rock-Eval T{sub max} for each well. The calculated Rock-Eval T{sub max} values agreed with measured values within amounts attributable to uncertainties in the chemical kinetics and the heat flow. These optimized thermal histories were then used with a more detailed chemical kinetic model of hydrocarbon generation and expulsion, modified from a model developed for the Cretaceous La Luna shale, to simulate pore pressure development and detailed aspects of the hydrocarbon chemistry. When compared to values estimated from sonic logs, the pore pressure calculation underestimates the role of hydrocarbon generation and overestimates the role of compaction disequilibrium, but it matches well the general areal extent of pore pressures of 0.7 times lithostatic and higher. The simulated chemistry agrees very well with measured values of HI, PI, H/C atomic ratio of the kerogen, and Rock-Eval S1. The model is not as successful in simulating the amount of extracted bitumen and its saturate content, suggesting that detailed hydrous pyrolysis experiments will probably be needed to further refine the chemical model.

Sweeney, J.J.; Braun, R.L.; Burnham, A.K. [Lawrence Livermore National Lab., CA (United States); Gosnold, W.D. [North Dakota Univ., Grand Forks, ND (United States)

1992-10-01

72

A chemical kinetic model of hydrocarbon generation from the Bakken Formation, Williston Basin, North Dakota  

SciTech Connect

This report describes a model of hydrocarbon generation and expulsion in the North Dakota portion of the Williston Basin. The modeling incorporates kinetic methods to simulate chemical reactions and 1-dimensional conductive heat flow models to simulate thermal histories of the Mississippian-Devonian Bakken Formation source rock. We developed thermal histories of the source rock for 53 wells in the basin using stratigraphic and heat flow data obtained by the University of North Dakota. Chemical kinetics for hydrocarbon generation, determined from Pyromat pyrolysis, were, then used with the diennal histories to calculate the present day value of the Rock-Eval T[sub max] for each well. The calculated Rock-Eval T[sub max] values agreed with measured values within amounts attributable to uncertainties in the chemical kinetics and the heat flow. These optimized thermal histories were then used with a more detailed chemical kinetic model of hydrocarbon generation and expulsion, modified from a model developed for the Cretaceous La Luna shale, to simulate pore pressure development and detailed aspects of the hydrocarbon chemistry. When compared to values estimated from sonic logs, the pore pressure calculation underestimates the role of hydrocarbon generation and overestimates the role of compaction disequilibrium, but it matches well the general areal extent of pore pressures of 0.7 times lithostatic and higher. The simulated chemistry agrees very well with measured values of HI, PI, H/C atomic ratio of the kerogen, and Rock-Eval S1. The model is not as successful in simulating the amount of extracted bitumen and its saturate content, suggesting that detailed hydrous pyrolysis experiments will probably be needed to further refine the chemical model.

Sweeney, J.J.; Braun, R.L.; Burnham, A.K. (Lawrence Livermore National Lab., CA (United States)); Gosnold, W.D. (North Dakota Univ., Grand Forks, ND (United States))

1992-10-01

73

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

74

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

75

On the theory of time dilation in chemical kinetics  

E-print Network

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

Baig, Mirza Wasif

2012-01-01

76

Detailed and reduced chemical-kinetic descriptions for hydrocarbon combustion  

Microsoft Academic Search

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

Maria V. Petrova

2005-01-01

77

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

78

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

79

Ab initio NMR Chemical Shift Calculations for Biomolecular Systems  

E-print Network

(i.e. J-coupling, relaxation time and NOE), can provide invaluable information on the three-dimensional4 Ab initio NMR Chemical Shift Calculations for Biomolecular Systems Using Fragment Molecular of fragment molecular orbital (FMO)-based NMR chemical shift calculation methods. They successfully lead

Furui, Sadaoki

80

Kinetic Monte Carlo method for simulating astrochemical kinetics: Test calculations of molecular hydrogen formation on interstellar dust particles  

NASA Astrophysics Data System (ADS)

Molecular hydrogen formation on the surfaces of interstellar dust grains has been studied numerically. Different stochastic methods (analogue Monte Carlo methods, direct solutions of the chemical master equation, continuous-time random-walk simulations, etc.) have been recently applied to the astrochemistry of hydrogen formation; however, the computational efficiency of these approaches is usually low because they are extremely time consuming (Herbst and Shematovich, 2003). A kinetic version of the Monte Carlo method based on splitting by physical processes is presented in the study. Each of the basic physical processes—adsorption of atomic hydrogen on the surface, thermal diffusion, formation of molecular hydrogen, and hydrogen desorption from the surface-are considered as independent random Markovian-type processes and are simulated using stochastic algorithms. The suggested numerical model is computationally efficient allowing calculations to be held on model surfaces with up to 106 active centers, which corresponds to interstellar grains of up to 0.4 ?m in diameter. Test calculations of the efficiency of molecular hydrogen formation were held for the two models of the surfaces of interplanetary grains, namely, for the homogeneous surfaces of olivine and amorphous carbon. It was confirmed that the effective formation of molecular hydrogen in diffuse molecular clouds is possible only within a narrow range of dust-particle temperatures. A comparison with the numerical results of other authors is presented.

Tsvetkov, A. G.; Shematovich, V. I.

2009-08-01

81

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 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.

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

2007-09-20

82

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

83

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

84

Towards cleaner combustion engines through groundbreaking detailed chemical kinetic models  

PubMed Central

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

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

2013-01-01

85

Progress in Chemical Kinetic Modeling for Surrogate Fuels  

SciTech Connect

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

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

2008-06-06

86

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. PMID:21949443

Sotiropoulos, Vassilios; Kaznessis, Yiannis N.

2011-01-01

87

Kinetics calculations for RIA experiments in the Capsule Driver Core. [Reactivity Initiated Accidents  

Microsoft Academic Search

Space-time kinetics calculations have been done for transient fuel behavior tests that were conducted during the late 1960's in the Capsule Driver Core in PBF. The purpose of the calculations was to determine the amount of energy deposited by delayed-neutron-fission in the test fuel after the power burst was terminated by control rod insertion. The kinetics calculations were done in

A. J. Scott; D. W. Nigg; J. L. Judd; S. A. Easson

1981-01-01

88

A chemical kinetics software package Peter Kirkegaard, Erling Bjergbakke, Jens V. Olsen  

E-print Network

CHEMSIMUL: A chemical kinetics software package Peter Kirkegaard, Erling Bjergbakke, Jens V. Olsen: CHEMSIMUL: A chemical kinetics software package Division: IT-Service Risø-R-1630(EN) December 2008 ISSN 0106 Tables: 6 References: 23 Abstract CHEMSIMUL is a computer program system for simulation of chemical

89

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

90

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

91

Free energy calculations: Applications to chemical and biochemical phenomena  

Microsoft Academic Search

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

Peter. Kollman

1993-01-01

92

Mars sample return orbiter: Detailed vibrational-chemical kinetics and heat transfer  

NASA Astrophysics Data System (ADS)

In the present paper, detailed state-to-state model of vibrational-chemical kinetic and transport processes is applied to study fluid dynamics and heat transfer in a non-equilibrium flow of a five-component mixture containing CO2 molecules and products of their dissociation near the surface of the Mars Sample Return Orbiter. For several test cases, vibrational distributions, chemical composition, specific vibrational energy profiles as well as the transport coefficients and different contributions to the heat flux are calculated along the stagnation line. For a non-catalytic surface, the role of thermal diffusion process is found to be important. Prandtl and Schmidt numbers are calculated along the stagnation line, and their influence on the diffusion velocities and heat flux is evaluated.

Armenise, I.; Kustova, E.

2014-12-01

93

Chemical kinetics of discharge-driven oxygen-iodine lasers  

NASA Astrophysics Data System (ADS)

Oxygen-iodine lasers that utilize electrical discharges to produce O II(a1?) are currently being developed. The discharge generators differ from those used in chemical oxygen-iodine lasers in that they produce significant amounts of atomic oxygen and traces of ozone. As a consequence of these differences, the chemical kinetics of the discharge laser are markedly different from those of a conventional chemical oxygen-iodine laser (COIL). The reactions of O with iodine include channels that are both beneficial and detrimental to the laser. The beneficial reactions result in the dissociation of I II while the detrimental processes cause direct and indirect removal of I(2P 1/2) (denoted I*, the upper level of the laser). We have examined kinetic processes relevant to the laser through studies of photo-initiated reactions in N IIO/CO II/I II mixtures. The reactions have been monitored using absorption spectroscopy, laser induced fluorescence and time-resolved emission spectroscopy. It has been established that deactivation of I* by O atoms is a critical energy loss process. We have determined a rate constant of (1.2+/-0.1)×10 -11 cm 3 s -1 for this reaction. As part of this effort the branching fraction for the formation of O II(a) from the reaction of O(1D) with N IIO was determined to be 0.38. This result has implications for lasers based on photolysis of O 3/N IIO/I II mixtures and the formation of O II(a) in the upper atmosphere.

Azyazov, Valeriy N.; Kabir, Md. Humayun; Antonov, Ivan O.; Heaven, Michael C.

2007-05-01

94

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

95

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

NASA Astrophysics Data System (ADS)

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

Edwards, Glenn; Hutson, M. Shane

2001-11-01

96

Reflected kinetics model for nuclear space reactor kinetics and control scoping calculations  

SciTech Connect

The objective of this research is to develop a model that offers an alternative to the point kinetics (PK) modelling approach in the analysis of space reactor kinetics and control studies. Modelling effort will focus on the explicit treatment of control drums as reactivity input devices so that the transition to automatic control can be smoothly done. The proposed model is developed for the specific integration of automatic control and the solution of the servo mechanism problem. The integration of the kinetics model with an automatic controller will provide a useful tool for performing space reactor scoping studies for different designs and configurations. Such a tool should prove to be invaluable in the design phase of a space nuclear system from the point of view of kinetics and control limitations.

Washington, K.E.

1986-05-01

97

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

98

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

99

Chemical kinetics for drug discovery to combat protein aggregation diseases.  

PubMed

Protein misfolding diseases are becoming increasingly prevalent, yet there are very few effective pharmacological treatments. The onset and progression of these diseases is associated with the aberrant aggregation of normally soluble proteins and peptides into amyloid fibrils. Because genetic and physiological findings suggest that protein aggregation is a key event in pathogenesis, an attractive therapeutic strategy against this class of disorders is the search for compounds able to interfere with this process, in particular by suppressing the formation of soluble toxic oligomeric aggregates. In this review, we discuss how chemical kinetics can contribute to the fundamental understanding of the molecular mechanism of aggregation, and speculate on the implications for the development of therapeutic molecules that inhibit specific steps in the aggregation pathway that are crucial for preventing toxicity. PMID:24560688

Arosio, Paolo; Vendruscolo, Michele; Dobson, Christopher M; Knowles, Tuomas P J

2014-03-01

100

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

101

Hyperpolarizability calculation and kinetic effect of impurities on LVP  

NASA Astrophysics Data System (ADS)

In order to investigate microscopic second order nonlinear optical properties of L-valinium picrate (LVP) crystals, the molecular dipole moment, polarizability, and first hyperpolarizability are estimated by density functional theory (DFT). Apart from that, a quantitative study using Atomic force microscopy (AFM) combined with crystal growth experiments on the effects of impurities (magnesium and copper) on LVP is presented. Two-dimensional (2D) nucleation growth mechanism and typical surface morphologies are described and discussed. In the presence of impurities, the decreasing of the size of 2D islands is probably incurred by the reducing of the step kinetic coefficient. From the supersaturation dependence of the normal growth rate, the effective step edge free energies are evaluated as ?0 = 2.90 kT, ?Mg = 2.76 kT, ?Cu = 2.95 kT.

Liu, Xiaojing; Xu, Xijin; Zhang, Changwen

2015-02-01

102

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

103

Identifying Alternative Conceptions of Chemical Kinetics among Secondary School and Undergraduate Students in Turkey  

ERIC Educational Resources Information Center

This study identifies some alternative conceptions of chemical kinetics held by secondary school and undergraduate students (N = 191) in Turkey. Undergraduate students who participated are studying to become chemistry teachers when they graduate. Students' conceptions about chemical kinetics were elicited through a series of written tasks and…

Cakmakci, Gultekin

2010-01-01

104

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

105

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

106

Chemical-equilibrium calculations for aqueous geothermal brines  

SciTech Connect

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

Kerrisk, J.F.

1981-05-01

107

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

108

Detailed and global chemical kinetics model for hydrogen  

SciTech Connect

Detailed and global chemical kinetic computations for hydrogen-air mixtures have been performed to describe flame propagation, flame structure and ignition phenomena. Simulations of laminar flame speeds, flame compositions and shock tube ignition delay times have been successfully performed. Sensitivity analysis was applied to determine the governing rate-controlling reactions for the experimental data sets examined. In the flame propagation and structure studies, the reactions, OH + H{sub 2} = H{sub 2}0 + H, 0 + H{sub 2} = OH + H and 0 + OH = 0{sub 2} + H were the most important in flames. The shock tube ignition delay time study indicated the H + 0{sub 2} + M = H0{sub 2} + M (M = N{sub 2}, H{sub 2}) and 0 + OH = 0{sub 2} + H reactions controlled ignition. A global rate expression for a one-step overall reaction was developed and validated against experimental hydrogen-air laminar flame speed data. The global reaction expression was determined to be 1.8 {times} 10{sup 13} exp({minus}17614K/T)[H{sub 2}]{sup 1.0}[O{sub 2}]{sup 0.5} for the single step reaction H{sub 2} + 1/2O{sub 2} = H{sub 2}O.

Marinov, N.M.; Westbrook, C.K.; Pitz, W.J.

1995-03-01

109

Chemical cartography: Finding the keys to the kinetic labyrinth  

SciTech Connect

Very high resolution lasers allow spectroscopic pictures to be taken following a collision between two molecular reactants. The features of these pictures are the electronic, vibrational, rotational, and translational motions of the atomic particles, which relate the quantum states of the reactants to the quantum states of the products. Such state-to-state kinetic information can be used to test the shape and nature of the interaction potential that controls the collision process. The potential itself is akin to a map of the terrain through mountains and valleys where elevation is a measure of energy instead of height. Accurate mapping of this potential surface leads to an understanding of the forces which control rates and mechanisms of chemical reactions. The application of four different advanced laser techniques to the study of collisions between hot hydrogen (H) atoms and carbon dioxide (CO{sub 2}) molecules has provided a wealth of information about both reactive and nonreactive collisions for this system. The availability of data for rotationally, vibrationally, and translationally inelastic excitation of CO{sub 2} by H atoms, when compared with data for reactive events producing OH + CO, provides insights into the dynamics of collisions between H and CO{sub 2} and illustrates the future promise of these powerful techniques for elucidating features of potential energy surfaces. 35 refs., 3 figs.

Flynn, G.W. (Columbia Univ., New York, NY (USA))

1989-11-24

110

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

SciTech Connect

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

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

2009-01-01

111

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

112

Chemical kinetic simulation of kerosene combustion in an individual flame tube  

PubMed Central

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

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

2013-01-01

113

A kinetic model for chemical reactions without barriers: transport coefficients and eigenmodes  

NASA Astrophysics Data System (ADS)

The kinetic model of the Boltzmann equation proposed in the work of Kremer and Soares 2009 for a binary mixture undergoing chemical reactions of symmetric type which occur without activation energy is revisited here, with the aim of investigating in detail the transport properties of the reactive mixture and the influence of the reaction process on the transport coefficients. Accordingly, the non-equilibrium solutions of the Boltzmann equations are determined through an expansion in Sonine polynomials up to the first order, using the Chapman-Enskog method, in a chemical regime for which the reaction process is close to its final equilibrium state. The non-equilibrium deviations are explicitly calculated for what concerns the thermal-diffusion ratio and coefficients of shear viscosity, diffusion and thermal conductivity. The theoretical and formal analysis developed in the present paper is complemented with some numerical simulations performed for different concentrations of reactants and products of the reaction as well as for both exothermic and endothermic chemical processes. The results reveal that chemical reactions without energy barrier can induce an appreciable influence on the transport properties of the mixture. Oppositely to the case of reactions with activation energy, the coefficients of shear viscosity and thermal conductivity become larger than those of an inert mixture when the reactions are exothermic. An application of the non-barrier model and its detailed transport picture are included in this paper, in order to investigate the dynamics of the local perturbations on the constituent number densities, and velocity and temperature of the whole mixture, induced by spontaneous internal fluctuations. It is shown that for the longitudinal disturbances there exist two hydrodynamic sound modes, one purely diffusive hydrodynamic mode and one kinetic mode.

Alves, Giselle M.; Kremer, Gilberto M.; Marques, Wilson, Jr.; Jacinta Soares, Ana

2011-03-01

114

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

PubMed Central

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

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

2013-01-01

115

DNA as a universal substrate for chemical kinetics David Soloveichika,1  

E-print Network

DNA as a universal substrate for chemical kinetics David Soloveichika,1 , Georg Seeliga,b,1 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

Winfree, Erik

116

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.

117

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

118

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

119

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

120

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

121

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

E-print Network

Fundamental Kinetic Model' provides an alternative method for collecting rate constant data of elementary reactions when experimental observation is unavailable. A standard procedure of PMP4/6-3 IG*//UHF/6-3 IG* ab initio calculations of reactants...

Jenks, Richard Lee

2012-06-07

122

CALCULATION OF RATES FOR ENZYME AND MICROBIAL KINETICS VIA A SPLINE TECHNIQUE  

Technology Transfer Automated Retrieval System (TEKTRAN)

In biocatalysis research, determination of enzyme kinetics, microbial growth rates, substrate utilization rates, and product accumulation rates sometime require derivatives to be calculated with a method that can be duplicated and yields consistent results. In this paper, several methods that have ...

123

Calculation of rates for enzyme and microbial kinetics via a spline technique  

Technology Transfer Automated Retrieval System (TEKTRAN)

In biocatalysis research, determination of enzyme kinetics, microbial growth rates, substrate utilization rates, and product accumulation rates sometime require derivatives to be calculated with a method that can be duplicated and yields consistent results. In this paper, several methods that have ...

124

Effects of pressure on the thermal decomposition kinetics, chemical reactivity and phase behavior of RDX  

Microsoft Academic Search

The effects of pressure on the thermal decomposition kinetics, chemical reactivity, and phase behavior of RDX have been studied by a combination of measurement techniques in conjunction with a high-pressure diamond anvil cell. These techniques include Fourier transform infrared (FTIR) spectroscopy for kinetic measurements and phase identification, energy dispersive x-ray powder diffraction for identification of the observed polymorphic forms and

P. J. Miller; S. Block; G. J. Piermarini

1991-01-01

125

Visualizing Chemical Compositions and Kinetics of Sol-Gel by Near-Infrared Multispectral Imaging  

E-print Network

Visualizing Chemical Compositions and Kinetics of Sol-Gel by Near-Infrared Multispectral Imaging, Milwaukee, Wisconsin 53201 Kinetics of sol-gel formation were studied using the recently developed near-infrared been studied extensively by many different spectroscopic techniques.4-15 Among them, the near-infrared

Reid, Scott A.

126

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

E-print Network

toward clean and efficient combustion in diesel engines. After briefly outlining the synergy between and ethyl biodiesels; Combustion; Diesel engine; Performance and emission; Chemical kinetics of oxidation energy and renewable materials. According to the International Energy Outlook of 2011, which

Paris-Sud XI, Université de

127

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

128

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

129

Chemical TOPAZ: Modifications to the heat transfer code TOPAZ: The addition of chemical reaction kinetics and chemical mixtures  

SciTech Connect

This is a report describing the modifications which have been made to the heat flow code TOPAZ to allow the inclusion of thermally controlled chemical kinetics. This report is broken into parts. The first part is an introduction to the general assumptions and theoretical underpinning that were used to develop the model. The second section describes the changes that have been implemented into the code. The third section is the users manual for the input for the code. The fourth section is a compilation of hints, common errors, and things to be aware of while you are getting started. The fifth section gives a sample problem using the new code. This manual addenda is written with the presumption that most readers are not fluent with chemical concepts. Therefore, we shall in this section endeavor to describe the requirements that must be met before chemistry can occur and how we have modeled the chemistry in the code.

Nichols, A.L. III.

1990-06-07

130

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

131

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

132

Chemical intermediates in dopamine oxidation by tyrosinase, and kinetic studies of the process.  

PubMed

A minor pathway for dopamine oxidation to dopaminochrome, by tyrosinase, is proposed. Characterization of intermediates in this oxidative reaction and stoichiometric determination have both been undertaken. After oxidizing dopamine with mushroom tyrosinase or sodium periodate in a pH range from 6.0 to 7.0, it was spectrophotometrically possible to detect o-dopaminoquinone-H+ as the first intermediate in this pathway. The steps for dopamine transformation to dopaminochrome are as follows: dopamine----o-dopaminequinone-H+----o-dopaminequinone---- leukodopaminochrome--- - dopaminochrome. No participation of oxygen was detected in the conversion of leukodopaminochrome to dopaminochrome. Scanning spectroscopy and graphical analysis of the obtained spectra also verified that dopaminequinone-H+ was transformed into aminochrome in a constant ratio. The stoichiometry equation for this conversion is 2 o-dopaminequinone-H+----dopamine + dopaminochrome. The pathway for dopamine oxidation to dopaminochrome by tyrosinase has been studied as a system of various chemical reactions coupled to an enzymatic reaction. A theoretical and experimental kinetic approach is proposed for such a system; this type of mechanism has been named "Enzymatic-chemical-chemical" (EzCC). Rate constants for the implied chemical steps at different pH and temperature values have been evaluated from the measurement of the lag period arising from the accumulation of dopaminochrome that took place when dopamine was oxidized at acid pH. The thermodynamic activation parameters of the chemical steps, the deprotonation of dopaminequinone-H+ to dopaminequinone, and the internal cyclization of dopaminequinone to leukodopaminochrome have been calculated. PMID:6097187

Jimenez, M; Garcia-Carmona, F; Garcia-Canovas, F; Iborra, J L; Lozano, J A; Martinez, F

1984-12-01

133

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...

134

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

135

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

136

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

137

Structure, Thermodynamics and Kinetics of Chemically Heterogeneous Interfaces  

NASA Astrophysics Data System (ADS)

In this work we have used atomistic computer simulations to examine the structure, thermodynamics and transport properties, for two models of chemically heterogeneous interfaces: an ideal model (repulsive soft spheres against a potential wall), and a metal alloy interface (Cu-Pb). In both systems, interfacial prefreezing (crystal formation above the melting point of the fluid) was observed and this prefreezing was seen to promote heterogeneous nucleation, when the systems were cooled below the melting temperature. In our study of inverse-power repulsive soft spheres, we found that the soft-sphere fluid exhibited prefreezing at the wall surface. Similar behavior was previously observed in hard-sphere fluids at hard wall [17, 18, 20], however, to our knowledge, this the first time that prefreezing is reported for soft spheres. The prediction of prefreezing is based on the calculation of interfacial free energies wall-crystal (gammawc) and wall-fluid (gammawf) using a variant of the cleaving wall method. With the calculated, gammawc and gamma wf together with gammacf, previously computed [79], the tendency to prefreeze was quantified by the wetting angle formed between the metastable crystal phase on the wall and the soft-sphere fluid. We found that all the closest packing orientations [(111) FCC and (110) BCC] developed prefreezing (complete wetting). A detailed atomic-level characterization of the structure, energetics and transport properties of the planar Cu/Pb solid-liquid interface in equilibrium was performed at a several temperatures (625K and 750K) above the melting point of Pb and for two Cu crystal orientations [(111) and (100)]. Among the most relevant findings are that the Cu(100)/Pb interfaces presents surfaces alloying and the Cu(111)/Pb exhibits a prefreezing layer of Pb crystal. It was also observed that both interfaces have a nucleation barrier that prevents heterogeneous nucleation and that the mechanisms by which each structure promotes heterogeneous nucleation are different. Both models, the inverse-power soft spheres and the EAM Cu-Pb, showed the connection between atomistic behavior and prefreezing. The crystalline layer formed above the melting point of the fluids showed to be influential in heterogeneous nucleation in both cases. In this way, the study of basic properties shed new light on the atomistic underlying nature of macroscopic events, such as wetting and nucleation.

Palafox Hernandez, Jesus Pablo

2011-12-01

138

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

E-print Network

On persistence of chemical reaction networks with time-dependent kinetics and no global work. The new results allow the consideration of reaction rates which are time-varying, thus for persistence of chemical reaction networks are proposed, which extend those obtained by the authors in previous

Sontag, Eduardo

139

Role of Chemical Heterogeneities on Oxygen Reduction Kinetics on the Surface of Thin Film Cathodes  

E-print Network

more space in the bulk of LSM for this relatively large cation. Localized chemical analysis by nanoRole of Chemical Heterogeneities on Oxygen Reduction Kinetics on the Surface of Thin Film Cathodes-probe Auger electron spectroscopy revealed the strong enrichment of Sr and Zr in particles that form

Yildiz, Bilge

140

Spectroscopic analysis of cinnamic acid using quantum chemical calculations  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

141

Spectroscopic analysis of cinnamic acid using quantum chemical calculations.  

PubMed

In this present study, FT-IR, FT-Raman, (13)C NMR and (1)H NMR spectra for cinnamic acid have been recorded for the vibrational and spectroscopic analysis. The observed fundamental frequencies (IR and Raman) were assigned according to their distinctiveness region. The computed frequencies and optimized parameters have been calculated by using HF and DFT (B3LYP) methods and the corresponding results are tabulated. On the basis of the comparison between computed and experimental results assignments of the fundamental vibrational modes are examined. A study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, were performed by HF and DFT methods. The alternation of the vibration pattern of the pedestal molecule related to the substitutions was analyzed. The (13)C and (1)H NMR spectra have been recorded and the chemical shifts have been calculated using the gauge independent atomic orbital (GIAO) method. The Mulliken charges, UV spectral analysis and HOMO-LUMO analysis of have been calculated and reported. The molecular electrostatic potential (MEP) was constructed. PMID:25315873

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

2015-02-01

142

Detailed chemical kinetic oxidation mechanism for a biodiesel Olivier Herbineta  

E-print Network

become interesting as an additive to diesel fuel for two main reasons. This renewable alternative fuel. Keywords: Methyl decanoate; Oxidation; Biodiesel fuels; Kinetic modeling; Engine; Low temperature by lowering net emissions of greenhouse gases. The use of biodiesel in diesel engines decreases emissions

Paris-Sud XI, Université de

143

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

144

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

145

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

PubMed Central

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

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

2000-01-01

146

Reactive molecular dynamics simulation and chemical kinetic modeling of pyrolysis and combustion of n-dodecane  

Microsoft Academic Search

The initiation mechanisms and kinetics of pyrolysis and combustion of n-dodecane are investigated by using the reactive molecular dynamics (ReaxFF MD) simulation and chemical kinetic modeling. From ReaxFF MD simulations, we find the initiation mechanisms of pyrolysis of n-dodecane are mainly through two pathways, (1) the cleavage of C-C bond to form smaller hydrocarbon radicals, and (2) the dehydrogenation reaction

Quan-De Wang; Jing-Bo Wang; Juan-Qin Li; Ning-Xin Tan; Xiang-Yuan Li

2011-01-01

147

Reactive molecular dynamics simulation and chemical kinetic modeling of pyrolysis and combustion of n-dodecane  

Microsoft Academic Search

The initiation mechanisms and kinetics of pyrolysis and combustion of n-dodecane are investigated by using the reactive molecular dynamics (ReaxFF MD) simulation and chemical kinetic modeling. From ReaxFF MD simulations, we find the initiation mechanisms of pyrolysis of n-dodecane are mainly through two pathways, (1) the cleavage of C–C bond to form smaller hydrocarbon radicals, and (2) the dehydrogenation reaction

Quan-De Wang; Jing-Bo Wang; Juan-Qin Li; Ning-Xin Tan; Xiang-Yuan Li

2011-01-01

148

KINETICS OF CHEMICAL & MICROBIAL CONTAMINANTS IN DISTRIBUTION SYSTEMS  

EPA Science Inventory

Once treated drinking water enters the distribution system, substantial microbial, chemical, and physical changes can occur. Examples of such changes can nclude loss of disinfectant residual, increases in disinfection byproducts (DBP), growth of microbial diversity and population...

149

Validity conditions for moment closure approximations in stochastic chemical kinetics  

NASA Astrophysics Data System (ADS)

Approximations based on moment-closure (MA) are commonly used to obtain estimates of the mean molecule numbers and of the variance of fluctuations in the number of molecules of chemical systems. The advantage of this approach is that it can be far less computationally expensive than exact stochastic simulations of the chemical master equation. Here, we numerically study the conditions under which the MA equations yield results reflecting the true stochastic dynamics of the system. We show that for bistable and oscillatory chemical systems with deterministic initial conditions, the solution of the MA equations can be interpreted as a valid approximation to the true moments of the chemical master equation, only when the steady-state mean molecule numbers obtained from the chemical master equation fall within a certain finite range. The same validity criterion for monostable systems implies that the steady-state mean molecule numbers obtained from the chemical master equation must be above a certain threshold. For mean molecule numbers outside of this range of validity, the MA equations lead to either qualitatively wrong oscillatory dynamics or to unphysical predictions such as negative variances in the molecule numbers or multiple steady-state moments of the stationary distribution as the initial conditions are varied. Our results clarify the range of validity of the MA approach and show that pitfalls in the interpretation of the results can only be overcome through the systematic comparison of the solutions of the MA equations of a certain order with those of higher orders.

Schnoerr, David; Sanguinetti, Guido; Grima, Ramon

2014-08-01

150

A Simple Model for Calculating the Kinetics of Protein Folding from Three-Dimensional Structures  

NASA Astrophysics Data System (ADS)

An elementary statistical mechanical model was used to calculate the folding rates for 22 proteins from their known three-dimensional structures. In this model, residues come into contact only after all of the intervening chain is in the native conformation. An additional simplifying assumption is that native structure grows from localized regions that then fuse to form the complete native molecule. The free energy function for this model contains just two contributions--conformational entropy of the backbone and the energy of the inter-residue contacts. The matrix of inter-residue interactions is obtained from the atomic coordinates of the three-dimensional structure. For the 18 proteins that exhibit two-state equilibrium and kinetic behavior, profiles of the free energy versus the number of native peptide bonds show two deep minima, corresponding to the native and denatured states. For four proteins known to exhibit intermediates in folding, the free energy profiles show additional deep minima. The calculated rates of folding the two-state proteins, obtained by solving a diffusion equation for motion on the free energy profiles, reproduce the experimentally determined values surprisingly well. The success of these calculations suggests that folding speed is largely determined by the distribution and strength of contacts in the native structure. We also calculated the effect of mutations on the folding kinetics of chymotrypsin inhibitor 2, the most intensively studied two-state protein, with some success.

Munoz, Victor; Eaton, William A.

1999-09-01

151

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

SciTech Connect

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

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

2006-01-01

152

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

153

KINETICS OF CHEMICAL WEATHERING IN B-HORIZON SPODOSOL FRACTION  

EPA Science Inventory

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

154

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

155

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

156

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

157

Clouds in Super-Earth Atmospheres: Chemical Equilibrium Calculations  

NASA Astrophysics Data System (ADS)

Recent studies have unequivocally proven the existence of clouds in super-Earth atmospheres (Kreidberg et al., 2014). However, the composition of these clouds remains unknown and is poorly constrained by theory. We provide a theoretical context for the formation of clouds in super-Earth atmospheres by determining which condensates are likely to form, under the assumption of chemical equilibrium. The composition of rocky planets is determined by the accretion of chondritic material. We model super-Earth atmospheres assuming that they are formed by degassing of volatile elements from a solid chondritic core. The atomic abundances of the atmospheres are then specified by the composition of volatiles released during the degassing process. Given the atomic make-up of the atmosphere, we minimize the Gibbs free energy of over 300 gases, condensed liquids, and solids, to obtain the molecular composition of the atmosphere. Clouds should form along the temperature-pressure boundaries where the condensed species appear in our calculation. Our results determine the plausible composition of clouds that could form in degassed super-Earth atmospheres.

Mbarek, Rostom; Kempton, Eliza

2015-01-01

158

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

NASA Astrophysics Data System (ADS)

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; Kirillov, Igor; Knizhnik, Andrei; Potapkin, Boris; Rykova, Elena; Umanskii, Stanislaw; Zaitsevskii, Andrei; Strelkova, Marina; Sukhanov, Leonid; Safonov, Andrei; Cotzas, George M.; Dean, Anthony; Michael, J. Darryl; Midha, Vikas; Smith, David J.; Sommerer, Timothy J.; Varatharajan, Bala; Tentner, Adrian

2007-04-01

159

Kinetic study on Zn(O,OH)S thin films deposited by chemical bath deposition  

Microsoft Academic Search

In this paper kinetic study for chemical bath deposition (CBD) of Zn(O,OH)S thin films was done. Zn(O,OH)S thin films were deposited from chemical bath containing thiourea, zinc acetate, sodium citrate and ammonia. The influence of synthesis conditions on the growth rate and morphological properties of the as-grown Zn(O,OH)S thin films are presented. The Avrami–Erofeev equation was used to study growth

W. Vallejo; M. Hurtado; G. Gordillo

2010-01-01

160

Kinetics of chemically modified lignin peroxidase and enzymatic oxidation of aromatic nitrogen-containing compounds  

Microsoft Academic Search

Lignin peroxidase from the white-rot fungus Phanerochaete chrysosporium was chemically modified by reductive alkylation with benzyl, naphthyl and anthracyl moieties, thereby increasing its superficial hydrophobicity. The three chemical modifications altered the kinetic behaviour of the enzyme in 10% acetonitrile with four different substrates: carbazole, pinacyanol, pyrene and veratryl alcohol. Benzyl modification of lignin peroxidase increased the catalytic efficiency (kcat\\/Km,app) 2.7

R. Vazquez-Duhalt; D. W. S. Westlake; P. M. Fedorak

1995-01-01

161

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

SciTech Connect

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

Alam, T.M.

1998-09-01

162

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

163

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

Microsoft Academic Search

This paper contains evaluated chemical kinetic data on single step elementary reactions involving small polyatomic molecules which are of importance in propellant combustion. The work consists of the collection and evaluation of mechanistic and rate information and the use of various methods for the extrapolation and estimation of rate data where information does not exist. The conditions covered range from

Wing Tsang

1992-01-01

164

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

165

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

166

Research in chemical kinetics. Progress report, August 1, 1987--July 20, 1988  

SciTech Connect

This paper describes chemical kinetics research in the following areas: reactions of thermalized tritium atoms with organo-tin compounds; studies on the hydrolysis of OCS and CS{sub 2}; thermal chlorine 38 reactions with 2,3-dichloro-hexafluoro-2-butene; and thermal T reactions with fluoroethylenes.

Rowland, F.S.

1996-09-01

167

A detailed chemical kinetic model of high-temperature ethylene glycol gasification  

Microsoft Academic Search

In recent experimental investigations, ethylene glycol is used as a model substance for biomass-based pyrolysis oil in an entrained flow gasifier. In order to gain a deeper insight into process sequences and to conduct parametric analysis, this study describes the development and validation of a detailed chemical kinetic model of high-temperature ethylene glycol gasification. A detailed reaction mechanism based on

Simon Hafner; Arash Rashidi; Georgiana Baldea; Uwe Riedel

2011-01-01

168

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

169

A kinetic model of diamond nucleation and silicon carbide interlayer formation during chemical vapor deposition  

E-print Network

A kinetic model of diamond nucleation and silicon carbide interlayer formation during chemical February 2005 Available online 7 April 2005 Abstract The presence of thin silicon carbide intermediate of carbon atoms into the silicon carbide layer and the morphology and orientation of the diamond film

Dandy, David

170

RADIATION KINETICS AND CHEMICAL REACTIVITY OF BARRIER DISCHARGES IN HUMID ARGON  

E-print Network

RADIATION KINETICS AND CHEMICAL REACTIVITY OF BARRIER DISCHARGES IN HUMID ARGON K.V. Kozlov1,a , E discharge in flowing humid argon at atmospheric pressure. Concentrations of two stable reaction products of H2O decomposition (H2 and O2) in argon plasma were determined experimentally as functions

Boyer, Edmond

171

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

EPA Science Inventory

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

172

An analytical kinetic model for chemical-vapor deposition of pureB layers from diborane  

NASA Astrophysics Data System (ADS)

In this paper, an analytical model is established to describe the deposition kinetics and the deposition chamber characteristics that determine the deposition rates of pure boron (PureB-) layers grown by chemical-vapor deposition (CVD) from diborane (B2H6) as gas source on a non-rotating silicon wafer. The model takes into consideration the diffusion mechanism of the diborane species through the stationary boundary layer over the wafer, the gas phase processes and the related surface reactions by applying the actual parabolic gas velocity and temperature gradient profiles in the reactor. These are calculated theoretically and also simulated with fluent software. The influence of an axial and lateral diffusion of diborane species and the validity of the model for laminar flow in experimental CVD processes are also treated. This model is based on a wide range of input parameters, such as initial diborane partial pressure, total gas flow, axial position on the wafer, deposition temperature, activation energy of PureB deposition from diborane, surface H-coverage, and reactor dimensions. By only adjusting these reactor/process parameters, the model was successfully transferred from the ASM Epsilon One to the Epsilon 2000 reactor which has totally different reactor conditions. The model's predictive capabilities have been verified by experiments performed at 700 °C in these two different ASM CVD reactors.

Mohammadi, V.; de Boer, W. B.; Nanver, L. K.

2012-12-01

173

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

SciTech Connect

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.

Menzeleev, Artur R.; Bell, Franziska; Miller, Thomas F., E-mail: tfm@caltech.edu [Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 (United States)

2014-02-14

174

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

PubMed Central

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)]10.1137/110849079 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)]10.1063/1.3280166 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. PMID:23445000

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

2013-01-01

175

Large eddy simulation of extinction and reignition with artificial neural networks based chemical kinetics  

SciTech Connect

Large eddy simulation (LES) of a non-premixed, temporally evolving, syngas/air flame is performed with special emphasis on speeding-up the sub-grid chemistry computations using an artificial neural networks (ANN) approach. The numerical setup for the LES is identical to a previous direct numerical simulation (DNS) study, which reported considerable local extinction and reignition physics, and hence, offers a challenging test case. The chemical kinetics modeling with ANN is based on a recent approach, and replaces the stiff ODE solver (DI) to predict the species reaction rates in the subgrid linear eddy mixing (LEM) model based LES (LEMLES). In order to provide a comprehensive evaluation of the current approach, additional information on conditional statistics of some of the key species and temperature are extracted from the previous DNS study and are compared with the LEMLES using ANN (ANN-LEMLES, hereafter). The results show that the current approach can detect the correct extinction and reignition physics with reasonable accuracy compared to the DNS. The syngas flame structure and the scalar dissipation rate statistics obtained by the current ANN-LEMLES are provided to further probe the flame physics. It is observed that, in contrast to H{sub 2}, CO exhibits a smooth variation within the region enclosed by the stoichiometric mixture fraction. The probability density functions (PDFs) of the scalar dissipation rates calculated based on the mixture fraction and CO demonstrate that the mean value of the PDF is insensitive to extinction and reignition. However, this is not the case for the scalar dissipation rate calculated by the OH mass fraction. Overall, ANN provides considerable computational speed-up and memory saving compared to DI, and can be used to investigate turbulent flames in a computationally affordable manner. (author)

Sen, Baris Ali; Menon, Suresh [School of Aerospace Engineering, Georgia Institute of Technology, 270 Ferst Drive, Atlanta, GA 30332-0150 (United States); Hawkes, Evatt R. [School of Photovoltaic and Renewable Energy Engineering, The University of New South Wales, NSW 2052 (Australia); School of Mechanical and Manufacturing Engineering, The University of New South Wales, NSW 2052 (Australia)

2010-03-15

176

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

177

A novel method to determine uptake and elimination kinetics of volatile chemicals in fish.  

PubMed

The development of an exposure system suitable for studying the uptake and elimination kinetics in fish of volatile chemicals is discussed. Static exposure of the fish is in a closed system containing water and air. Automated sampling and analysis of the air provides a concentration-time profile that is then fit to differential equations using numerical integration methods. Assumptions for the mathematical description of the system are a) instantaneous distribution of chemical between water and air and b) a first order one-compartment model describes the kinetics of chemical in fish. Uptake and elimination rate constants in fathead minnows (Pimephales promelas) were determined for a mixture of benzene, toluene, monochlorobenzene, monobromobenzene, and 1,3-dichlorobenzene. No significant biotransformation was observed for any of the compounds. Uptake rate constants increased with increasing octanol-water partition coefficient (Kow), whereas the elimination rate constants were inversely related to Kow. PMID:9519463

de Wolf, W; Lieder, P H

1998-04-01

178

Momentum or kinetic energy - how do substrate properties influence the calculation of rainfall erosivity?  

NASA Astrophysics Data System (ADS)

Rainfall erosivity is a key component in soil erosion by water. In principle, two ways exist to describe erosivity, namely kinetic energy and momentum. However, the role of mass and velocity of raindrops in relation to properties of the substrates to be eroded is not yet clear. In our study we conducted rainfall simulation experiments to determine splash detachment amounts of five substrates (coarse sand, medium sand, fine sand, PE balls, silt) for seven different rainfall intensities (52-116 mm/h). We used linear mixed-effect modeling (LME) to calculate erosivity predictors for each substrate. Additionally, we separated drop size distribution into 1st and 3rd quartile to investigate the effect of small and slow respectively big and fast raindrops on splash detachment amounts. We suggest using momentum divided by drop diameter as a substrate-independent erosivity predictor. To consider different substrates specific erosivity parameters are needed. Heavier substrates like sand are best described by kinetic energy multiplied by diameter whereas lighter substrates like silt point to momentum divided by diameter to the power of 1.5. Further, our results show that the first quartile of the drop size distribution is best in describing splash detachment rates of light substrates whereas for heavier substrates like sand the influence of drop size distribution is indifferent.

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

2014-05-01

179

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

180

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

181

Analysis of the computational singular perturbation reduction method for chemical kinetics.  

SciTech Connect

This article is concerned with the asymptotic accuracy of the Computational Singular Perturbation (CSP) method developed by Lam and Goussis [The CSP method for simplifying kinetics, Int. J. Chem. Kin. 26 (1994) 461-486] to reduce the dimensionality of a system of chemical kinetics equations. The method, which is generally applicable to multiple-time scale problems arising in a broad array of scientific disciplines, exploits the presence of disparate time scales to model the dynamics by an evolution equation on a lower-dimensional slow manifold. In this article it is shown that the successive applications of the CSP algorithm generate, order by order, the asymptotic expansion of a slow manifold. The results are illustrated on the Michaelis-Menten-Henri equations of enzyme kinetics.

Zagaris, A.; Kaper, H. G.; Kaper, T. J.; Mathematics and Computer Science; Boston Univ.

2004-01-01

182

Kinetics analysis and quantitative calculations for the successive radioactive decay process  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

183

Gas-phase reaction between calcium monocation and fluoromethane: Analysis of the potential energy hypersurface and kinetics calculations  

Microsoft Academic Search

The gas-phase reaction between calcium monocation and fluoromethane: Ca++CH3F-->CaF++CH3 was theoretically analyzed. The potential energy hypersurface was explored by using density functional theory methodology with different functionals and Pople's, Dunning's, Ahlrichs', and Stuttgart-Dresden basis sets. Kinetics calculations (energy and total angular momentum resolved microcanonical variational\\/conventional theory) were accomplished. The theoretically predicted range for the global kinetic rate constant values at

Adrián Varela-Álvarez; V. M. Rayón; P. Redondo; C. Barrientos; José A. Sordo

2009-01-01

184

Gas-phase reaction between calcium monocation and fluoromethane: Analysis of the potential energy hypersurface and kinetics calculations  

Microsoft Academic Search

The gas-phase reaction between calcium monocation and fluoromethane: Ca++CH3F?CaF++CH3 was theoretically analyzed. The potential energy hypersurface was explored by using density functional theory methodology with different functionals and Pople’s, Dunning’s, Ahlrichs’, and Stuttgart–Dresden basis sets. Kinetics calculations (energy and total angular momentum resolved microcanonical variational\\/conventional theory) were accomplished. The theoretically predicted range for the global kinetic rate constant values at

Adria´n Varela-A´lvarez; V. M. Rayo´n; P. Redondo; C. Barrientos; Jose´ A. Sordo

2009-01-01

185

Multilevel non-empirical approach to calculation of light emission properties of of chemically active non-equilibrium plasma  

NASA Astrophysics Data System (ADS)

A multi-level approach for calculation of the properties of non-equilibrium plasmas using first principles and theories of elementary processes is described in the paper. In the framework of this approach, unknown properties of molecules, ions and atoms (structure, energy curves, and transition dipole moments) are calculated using quantum-chemical methods. The calculation results are then used to determine emission probabilities, Frank-Condon factors of electronic-vibration transitions, cross sections for electron impact excitation, dissociation, dissociative recombination and attachment. Ion-molecular reactions are treated in terms of the statistical theory. The energy transfer processes involving electronically species are described through the asymptotic approach. The electron impact excitation cross sections for atoms and molecules are calculated using the modified Born approximation. The resulting kinetic state-to-state scheme is then used to compute the dependencies of the electron energy balance and the radiative emission efficiency as a function of the plasma parameters. As an example of this multilevel approach, the radiative emission properties of an Ar-InI DC glow discharge were calculated using the Chemical Workbench computational environment.

Potapkin, B.; Adamson, S.; Astapenko, V.; Chernysheva, I.; Deminsky, M.; Demura, A.; Dyatko, N.; Eletskii, A.; Knizhnik, A.; Kochetov, I.; Napartovich, A.; Rykova, E.; Umanskii, S.; Zaitsevskii, A.; Cotzas, G.; Mikhael, D.; Midha, V.; Smith, D.; Sommerer, T.

2006-10-01

186

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

PubMed

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

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

2014-11-01

187

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

188

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

Microsoft Academic Search

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

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

189

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

Microsoft Academic Search

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

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

2002-01-01

190

Role of Thermal Diffusion and Chemical Kinetics in Infrared Tissue Ablation  

Microsoft Academic Search

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

Glenn Edwards; M. Shane Hutson

2003-01-01

191

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

192

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

DOE Data Explorer

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

193

Errors in the calculation of (27)Al nuclear magnetic resonance chemical shifts.  

PubMed

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. PMID:23203134

Wang, Xianlong; Wang, Chengfei; Zhao, Hui

2012-01-01

194

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. PMID:23203134

Wang, Xianlong; Wang, Chengfei; Zhao, Hui

2012-01-01

195

Chemical kinetics of low pressure high density hydrogen plasmas: application to negative ion sources for ITER  

NASA Astrophysics Data System (ADS)

This paper presents a systematic kinetic characterization of a low pressure high power hydrogen plasma. The plasma physics is described with a global model coupled to a homogeneous kinetic model for hydrogen. This model involves reactions which describe the vibrational and electronic excited kinetics of H2, the positive ?ft( H{+}{,}H2{+}{,}H3{+} \\right) and negative (H?) ion kinetics and the H chemistry. This enables the estimation of the particle density and the electron temperature and their evolutions as a function of power (1–100 kW) and pressure (0.3–4 Pa). These very specific plasma conditions involve physical phenomena not occurring in more usual plasmas, such as gas depletion. To account for this gas depletion, we incorporate in the global model both the H neutral heat equation to calculate the H temperature, and the gas pumping. Indeed, the gas depletion is mainly due to H atom heating leading to a higher pumping loss for H atoms. The consideration of the gas depletion allows us to obtain similar behaviors to the experiments when varying power and pressure. From an accurate analysis of the main formation and destruction pathways for each particle, the species kinetics is discussed and a simplified kinetic model that may be used to describe the non-equilibrium plasma in the negative source for ITER is proposed. Finally, the results point to strong coupling existing between the H atom wall recombination coefficient ?H and the gas depletion. An increase of ?H reduces the gas depletion, affecting the electron temperature and the electron density as well as the whole plasma kinetics.

Gaboriau, F.; Boeuf, J. P.

2014-12-01

196

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

PubMed Central

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

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

2008-01-01

197

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

198

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

199

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

E-print Network

) of your own hand-written notes for quizzes. All backpacks, cellphones, calculators, textbooks, notebooks-written notes for midterms, two pages of hand-written notes for the final exam. All backpacks, cellphones

Muzzio, Fernando J.

200

The calculation of the chemical exergies of coal-based fuels by using the higher heating values  

Microsoft Academic Search

This paper demonstrates the application of exergy to gain a better understanding of coal properties, especially chemical exergy and specific chemical exergy. In this study, a BASIC computer program was used to calculation of the chemical exergies of the coal-based fuels. Calculations showed that the chemical composition of the coal influences strongly the values of the chemical exergy. The exergy

Selçuk Bilgen; Kamil Kaygusuz

2008-01-01

201

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

NASA Astrophysics Data System (ADS)

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

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

2002-04-01

202

Kinetic study of the transient phase of a chemical reaction system coupled to an enzymatically catalyzed step. Application to the oxidation of epinine by tyrosinase.  

PubMed

The present work deals with epinine oxidation by mushroom tyrosinase and sodium metaperiodate. Intermediates produced within short reaction times were characterized by repetitive scanning spectrophotometry and the stoichiometry of the appearance of the respective aminochrome was established. The oxidation pathway from epinine to aminochrome had the following steps: epinine----o-quinone-H+----o-quinone----leukoaminochrome----aminoc hrome. The stoichiometry for the conversion of o-quinone-H+ into the aminochrome of epinine followed the equation: 2 o-quinone-H+----epinine+aminochrome. A transient phase kinetic study has been developed for the system of chemical reactions coupled to an enzymatically catalyzed step, these taking place when epinine is oxidized by mushroom tyrosinase. Rate constants for the implied chemical steps at different temperature and pH values were calculated from analysis of the progress curves of aminochrome accumulation with time. The thermodynamic activation parameters of the chemical steps were also calculated. PMID:3111559

Escribano, J; García, M; García Cánovas, F; García Carmona, F; Varón, R; Tudela, J; Lozano, J A

1987-07-01

203

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

204

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

205

Calculations of the Chemical Composition of the Sacramento Urban Plume  

NASA Astrophysics Data System (ADS)

Recent measurements within the Sacramento urban plume have provided a detailed benchmark for testing our understanding of tropospheric chemistry. Available measurements include a wide suite of VOC and BVOC, NOy,i, O3, and CO at the source and at a receptor site five hours downwind. Further, the meteorology in the region is extremely regular making it possible to evaluate effects of temperature or day-of-week patterns with a single season of measurements. Here we use a Lagrangian model representing transport from Granite Bay, a suburb at the eastern edge of Sacramento, to the University of California Blodgett Forest Research Station (UC- BFRS). The model represents chemistry based on MCM v3.1 along with mixing and dilution. The model is initiated with concentrations of NOx, peroxynitrates, alkyl and multifunctional nitrates, HNO3, VOCs and O3 based on measurements at the edge of the Sacramento suburban sprawl east of the city. Biogenic VOC emissions throughout the transect are included. The outputs of the model are compared with ozone measurements at Cool three hours downwind, and detailed measurements of VOC, the speciation of the nitrogen oxides and O3 at UC-BFRS, 5 hours downwind of the Sacramento suburbs in the center of the Mountain counties air basin. The comparisons indicate 1) O3 at UC-BFRS and Cool is largely driven by the combination of rural biogenic emissions and urban NOx emissions, 2) that OH is underestimated by standard chemical models, 3) that partitioning of NOy is dominated by peroxy and other multifunctional nitrates that are not represented in standard chemical models and which have a strong impact on how much NO2 is available for ozone production. We also investigate model representation of temperature and weekend/weekday effects.

Perez, I. M.; Cohen, R. C.

2007-12-01

206

Quantum calculation of protein NMR chemical shifts based on the automated fragmentation method.  

PubMed

The performance of quantum mechanical methods on the calculation of protein NMR chemical shifts is reviewed based on the recently developed automatic fragmentation quantum mechanics/molecular mechanics (AF-QM/MM) approach. By using the Poisson-Boltzmann (PB) model and first solvation water molecules, the influence of solvent effect is also discussed. Benefiting from the fragmentation algorithm, the AF-QM/MM approach is computationally efficient, linear-scaling with a low pre-factor, and thus can be applied to routinely calculate the ab initio NMR chemical shifts for proteins of any size. The results calculated using Density Functional Theory (DFT) show that when the solvent effect is included, this method can accurately reproduce the experimental ¹H NMR chemical shifts, while the ¹³C NMR chemical shifts are less affected by the solvent. However, although the inclusion of solvent effect shows significant improvement for ¹?N chemical shifts, the calculated values still have large deviations from the experimental observations. Our study further demonstrates that AF-QM/MM calculated results accurately reflect the dependence of ¹³C(?) NMR chemical shifts on the secondary structure of proteins, and the calculated ¹H chemical shift can be utilized to discriminate the native structure of proteins from decoys. PMID:25387959

Zhu, Tong; Zhang, John Z H; He, Xiao

2015-01-01

207

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

208

Multiscale multiphysics nonempirical approach to calculation of light emission properties of chemically active nonequilibrium plasma: application to Ar GaI3 system  

NASA Astrophysics Data System (ADS)

Present-day computational techniques provide a possibility of evaluating properties of macrosystems using ab initio quantum chemistry and theories of elementary processes. Physical and chemical phenomena on very different timescales have to be taken into account (excitation, emission, chemical reactions, diffusion) at different levels of refining. This refining covers a very wide region of parameters starting from the structure of species up to the macro chemical mechanism of their conversion. This multilevel approach is described in detail in the paper and includes interaction and data transfer between different levels of phenomena description. In the framework of the approach, unknown properties of molecules, ions and atoms (structure, potential energy curves, transition dipole moments) are calculated based on quantum-chemical methods. The calculation results are used to evaluate rate characteristics of physical and chemical processes. The developed kinetic state-to-state scheme is then used to calculate the macro properties of the system under investigation. As an example of the multilevel approach, the emission properties of the Ar-GaI3 positive column discharge plasma were calculated using the Chemical Work Bench computational environment. The calculations yield the electron energy balance and emission efficiency as functions of plasma parameters.

Adamson, S.; Astapenko, V.; Chernysheva, I.; Chorkov, V.; Deminsky, M.; Demchenko, G.; Demura, A.; Demyanov, A.; Dyatko, N.; Eletzkii, A.; Knizhnik, A.; Kochetov, I.; Napartovich, A.; Rykova, E.; Sukhanov, L.; Umanskii, S.; Vetchinkin, A.; Zaitsevskii, A.; Potapkin, B.

2007-07-01

209

Effects of pressure on the thermal decomposition kinetics, chemical reactivity and phase behavior of RDX  

SciTech Connect

The effects of pressure on the thermal decomposition kinetics, chemical reactivity, and phase behavior of RDX have been studied by a combination of measurement techniques in conjunction with a high-pressure diamond anvil cell. These techniques include Fourier transform infrared (FTIR) spectroscopy for kinetic measurements and phase identification, energy dispersive x-ray powder diffraction for identification of the observed polymorphic forms and also compression measurements, and optical polarizing microscopy for visual detection and confirmation of phase transformations and determinations of transition pressures. The ruby method of pressure measurement was used in all methods employed. Studies were generally limited to the region where decomposition rates could be measured within reasonable laboratory time, i.e., below 10 GPa and 573 K. The P-T phase diagram for RDX was determined to 573 K and 7.0/GPa, delineating the stability fields of three solid phases, and the liquidus.

Miller, P.J. (Naval Surface Warfare Center, Silver Spring, MD (USA)); Block, S.; Piermarini, G.J. (Inst. for Materials Science and Engineering, National Inst. of Standards and Technology, Gaithersburg, MD (US))

1991-01-01

210

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

211

Water quality index calculated from biological, physical and chemical attributes.  

PubMed

To ensure a safe drinking water supply, it is necessary to protect water quality. To classify the suitability of the Orós Reservoir (Northeast of Brazil) water for human consumption, a Water Quality Index (WQI) was enhanced and refined through a Principal Component Analysis (PCA). Samples were collected bi-monthly at seven points (P1 - P7) from July 2009 to July 2011. Samples were analysed for 29 physico-chemical attributes and 4 macroinvertebrate metrics associated with the macrophytes Pistia stratiotes and Eichhornia crassipes. PCA allowed us to reduce the number of attributes from 33 to 12, and 85.32% of the variance was explained in five dimensions (C1 - C5). Components C1 and C3 were related to water-soluble salts and reflect the weathering process, while C2 was related to surface runoff. C4 was associated with macroinvertebrate diversity, represented by ten pollution-resistant families. C5 was related to the nutrient phosphorus, an indicator of the degree of eutrophication. The mean values for the WQIs ranged from 49 to 65 (rated as fair), indicating that water can be used for human consumption after treatment. The lowest values for the WQI were recorded at the entry points to the reservoir (P3, P1, P5, and P4), while the best WQIs were recorded at the exit points (P6 and P7), highlighting the reservoir's purification ability. The proposed WQI adequately expressed water quality, and can be used for monitoring surface water quality. PMID:25492707

Rocha, Francisco Cleiton; Andrade, Eunice Maia; Lopes, Fernando Bezerra

2015-01-01

212

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

PubMed

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

Bazant, Martin Z

2013-05-21

213

Model calculations of kinetic isotope effects for the solvolysis of neopentyl arenesulfonates  

SciTech Connect

Model calculations of ..cap alpha..-/sup 14/C, ..beta..-/sup 14/C, ..gamma..-/sup 14/C, ..cap alpha..-D/sub 2/, and ..gamma..-D/sub 3/ kinetic isotope effects in the acetolysis of neopentyl arenesulfonate were carried out for two possible pathways, concerted (k/sub ..delta../) and stepwise (k/sub c/). In the k/sub ..delta../ transition state (TS), four bond orders, n/sub ..cap alpha..-0/, n/sub ..cap alpha..-..beta../, n/sub ..beta..-..gamma../, and n/sup ..cap alpha..-..gamma../, were taken as independent parameters which define the model, whereas in the k/sub c/ model, n/sub ..cap alpha..-0/, n/sub ..cap alpha..-..beta../, n/sub ..beta..-..gamma../, and n/sub ..gamma..-H/ were taken as the parameters; other geometrical parameters and diagonal force constants were related to these four parameters by empirical expressions. One or more off-diagonal force constants were used to generate the reaction-coordiate frequency. The calculations suggested that the reaction proceeds via the k/sub ..delta../ pathway whose TS has a weak but significant ..cap alpha..-..gamma.. interaction; the alternative k/sub c/ pathway was shown to be less probable. The k/sub ..delta../ TS structure determined was then compared with that of the 2-methyl-2-phenylpropyl (neophyl) solvolysis. The calculated k/sub ..delta../ TS of the neopentyl solvolysis has (1) a stronger C/sub ..cap alpha../-O bond, (2) a stronger C/sub ..cap alpha../-C/sub ..beta../ bond, (3) a weaker C/sub ..beta../-C/sub ..gamma../ bond, and (4) a weaker C/sub ..cap alpha../-C/sub ..gamma../ bond than the TS of the neophyl solvolysis has. The results were interpreted in terms of the difference in the migrating group, methyl vs. phenyl, and it was concluded that the major mode of neighboring group participation by the phenyl is bridging whereas that by the methyl is hyperconjugation.

Yamataka, H.; Ando, T.

1982-04-07

214

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

215

Calculations of physical and chemical reactions with DNA in aqueous solution from Auger cascades  

SciTech Connect

Monte Carlo calculations are performed of the physical and chemical interactions in liquid water by electrons produced during Auger cascades resulting from the decay of various radionuclides. Estimates are also made of the number of direct physical and indirect chemical interactions that would be produced on DNA located near the decay site. 13 refs., 8 figs.

Wright, H.A.; Hamm, R.N.; Turner, J.E.; Howell, R.W.; Rao, D.V.; Sastry, K.S.R.

1989-01-01

216

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

Microsoft Academic Search

Seven different chemical mechanisms for methane are used in PDF model calculations of the Barlow and Frank flames D, E, and F in order to investigate the ability of these mechanisms to represent the local extinction, reignition, and other chemical phenomena observed in these nonpremixed piloted jet flames. The mechanisms studied range from a 5-step reduced mechanism to the GRI3.0

Renfeng Richard Cao; Stephen B. Pope

2005-01-01

217

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

218

Vinylphosphine-borane: synthesis, gas phase infrared spectroscopy, and quantum chemical vibrational calculations.  

PubMed

Both experimental and theoretical investigations are reported on the infrared spectrum of vinylphosphine-borane (CH(2)=CHPH(2) x BH(3)), a donor-acceptor complex. The gas phase infrared spectra (3500-600 cm(-1)) have been recorded at 0.5 cm(-1) resolution. This first primary alpha,beta-unsaturated phosphine-borane synthesized up to now is kinetically very unstable in the gas phase and decomposes rapidly into two fragments: the free vinylphosphine CH(2)=CHPH(2) and the monoborane BH(3) which dimerizes to form the more stable diborane B(2)H(6). Spectra of free CH(2)=CHPH(2) and B(2)H(6) compounds were also recorded to assign some vibration modes of the complex in very dense spectral regions. The analysis was completed by carrying out quantum mechanical calculations by density functional theory method at the B3LYP/6-31+G(**) level. Anharmonic frequencies and infrared intensities of the two predicted gauche and syn conformers of the vinylphosphine-borane complex were calculated in the 3500-100 cm(-1) region with the use of a variational approach, implemented in the P_ANHAR_V1.2 code. Because of the relatively weak interaction between the vinylphosphine and the monoborane, the vibrations of the complex can easily be subdivided into modes localized in the CH(2)=CHPH(2) and BH(3) moieties and into "intermolecular" modes. Localized modes are unambiguously correlated with the modes of the isolated monomers. Therefore, they are described in terms of the monomer vibrations, and the complexation shifts are defined as Delta nu = nu(complex) - nu(monomer) to make the effect of the complexation precise on each localized mode. In this objective, anharmonic frequencies and infrared intensities of the BH(3) monomer and the stable gauche and syn conformers of the free vinylphosphine were obtained at the same level of theory. In the gas phase, only the syn form of the complex was observed and assigned. All theoretically predicted frequencies and complexation shifts in magnitude and direction are in good agreement with experiment. By infrared spectroscopy assisted by quantum chemical calculations, the consequences of the complexation of an alpha,beta-unsaturated phosphine by borane on the physicochemical properties of the formed 12-atom complex have been efficiently evaluated. PMID:19071917

Khater, Brahim; Guillemin, Jean-Claude; Benidar, Abdessamad; Bégué, Didier; Pouchan, Claude

2008-12-14

219

Vinylphosphine-borane: Synthesis, gas phase infrared spectroscopy, and quantum chemical vibrational calculations  

NASA Astrophysics Data System (ADS)

Both experimental and theoretical investigations are reported on the infrared spectrum of vinylphosphine-borane (CH2=CHPH2?BH3), a donor-acceptor complex. The gas phase infrared spectra (3500-600 cm-1) have been recorded at 0.5 cm-1 resolution. This first primary ?,?-unsaturated phosphine-borane synthesized up to now is kinetically very unstable in the gas phase and decomposes rapidly into two fragments: the free vinylphosphine CH2=CHPH2 and the monoborane BH3 which dimerizes to form the more stable diborane B2H6. Spectra of free CH2=CHPH2 and B2H6 compounds were also recorded to assign some vibration modes of the complex in very dense spectral regions. The analysis was completed by carrying out quantum mechanical calculations by density functional theory method at the B3LYP/6-31+G?? level. Anharmonic frequencies and infrared intensities of the two predicted gauche and syn conformers of the vinylphosphine-borane complex were calculated in the 3500-100 cm-1 region with the use of a variational approach, implemented in the P_ANHAR_V1.2 code. Because of the relatively weak interaction between the vinylphosphine and the monoborane, the vibrations of the complex can easily be subdivided into modes localized in the CH2=CHPH2 and BH3 moieties and into "intermolecular" modes. Localized modes are unambiguously correlated with the modes of the isolated monomers. Therefore, they are described in terms of the monomer vibrations, and the complexation shifts are defined as ??=?complex-?monomer to make the effect of the complexation precise on each localized mode. In this objective, anharmonic frequencies and infrared intensities of the BH3 monomer and the stable gauche and syn conformers of the free vinylphosphine were obtained at the same level of theory. In the gas phase, only the syn form of the complex was observed and assigned. All theoretically predicted frequencies and complexation shifts in magnitude and direction are in good agreement with experiment. By infrared spectroscopy assisted by quantum chemical calculations, the consequences of the complexation of an ?,?-unsaturated phosphine by borane on the physicochemical properties of the formed 12-atom complex have been efficiently evaluated.

Khater, Brahim; Guillemin, Jean-Claude; Benidar, Abdessamad; Bégué, Didier; Pouchan, Claude

2008-12-01

220

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

221

Kinetics Study of Solid Ammonia Borane Hydrogen Release – Modeling and Experimental Validation for Chemical Hydrogen Storage  

SciTech Connect

Ammonia borane (AB), NH3BH3, is a promising material for chemical hydrogen storage with 19.6 wt% gravimetric hydrogen capacity of which 16.2 wt% hydrogen can be utilized below 200°C. We have investigated the kinetics of hydrogen release from AB and from an AB-methyl cellulose (AB/MC) composite at temperatures of 160-300°C using both experiments and modeling. The purpose of our study was to show safe hydrogen release without thermal runaway effects and to validate system model kinetics. AB/MC released hydrogen at ~20°C lower than neat AB and at a rate that is two times faster. Based on the experimental results, the kinetics equations were revised to better represent the growth and nucleation process during decomposition of AB. We explored two different reactor concepts; Auger and fixed bed. The current Auger reactor concept turned out to not be appropriate, however, we demonstrated safe self-propagation of the hydrogen release reaction of solid AB/MC in a fixed bed reactor.

Choi, Yong-Joon; Ronnebro, Ewa; Rassat, Scot D.; Karkamkar, Abhijeet J.; Maupin, Gary D.; Holladay, Jamelyn D.; Simmons, Kevin L.; Brooks, Kriston P.

2014-02-24

222

Kinetics of the single-electron chemical oxidation of rhenium(V) meso-phenyl-?-octaethylporphyrinate  

NASA Astrophysics Data System (ADS)

The states and reactions of rhenium(V) complexes with meso-monophenyl-?-octaethylporphines containing Cl- and OPh- as axial ligands O=Re(Cl)MPOEP and O=Re(OPh)MPOEP in concentrated sulfuric acid at 298-348 K are studied via spectral and kinetic methods. While stable along M-N bonds, O=Re(Cl)MPOEP is found to undergo slow oxidation after transforming into axial hydrosulfate complex O=Re(HSO4)MPOEP. It is shown that the sole electron oxidizing agent is atmospheric oxygen (with the assistance of highly concentrated protons) and the sites of reduction are aromatic ligands. The reaction product was identified as ?-radical cation O=Re(HSO4)MPOEP·+. Forward and inverse chemical kinetics solutions are used to obtain a full kinetic equation and the reaction rate parameters of elementary steps, and to establish the stoichiometric mechanism of the composite oxidation of the complex. Complex O=Re(OPh)MPOEP in the form O=Re(OPh)(O2)MPOEP with coordinated oxygen is shown experimentally to be stable with respect to oxidation. The obtained results are important for identifying intermediates in processes catalyzed by stable metal porphyrins.

Bichan, N. G.; Tyulyaeva, E. Yu.; Lomova, T. N.

2014-10-01

223

Chemical kinetic study of the oxidation of toluene and related cyclic compounds  

SciTech Connect

Chemical kinetic models of hydrocarbons found in transportation fuels are needed to simulate combustion in engines and to improve engine performance. The study of the combustion of practical fuels, however, has to deal with their complex compositions, which generally involve hundreds of compounds. To provide a simplified approach for practical fuels, surrogate fuels including few relevant components are used instead of including all components. Among those components, toluene, the simplest of the alkyl benzenes, is one of the most prevalent aromatic compounds in gasoline in the U.S. (up to 30%) and is a promising candidate for formulating gasoline surrogates. Unfortunately, even though the combustion of aromatics been studied for a long time, the oxidation processes relevant to this class of compounds are still matter of discussion. In this work, the combustion of toluene is systematically approached through the analysis of the kinetics of some important intermediates contained in its kinetic submechanism. After discussing the combustion chemistry of cyclopentadiene, benzene, phenol and, finally, of toluene, the model is validated against literature experimental data over a wide range of operating conditions.

Mehl, M; Frassoldati, A; Fietzek, R; Faravelli, T; Pitz, W; Ranzi, E

2009-10-01

224

Filtering ground reaction force data affects the calculation and interpretation of joint kinetics and energetics during drop landings.  

PubMed

An inverse dynamic analysis and subsequent calculation of joint kinetic and energetic measures is widely used to study the mechanics of the lower extremity. Filtering the kinematic and kinetic data input to the inverse dynamics equations affects the calculated joint moment of force (JMF). Our purpose was to compare selected integral values of sagittal plane ankle, knee, and hip joint kinetics and energetics when filtered and unfiltered GRF data are input to inverse dynamics calculations. Six healthy, active, injury-free university student (5 female, 1 male) volunteers performed 10 two-legged landings. JMFs were calculated after two methods of data filtering. Unfiltered: marker data were filtered at 10 Hz, GRF data unfiltered. Filtered: both GRF and marker data filtered at 10 Hz. The filtering of the GRF data affected the shape of the knee and hip joint moment-time curves, and the ankle, knee and hip joint mechanical power-time curves. We concluded that although the contributions of individual joints to the support moment and to total energy absorption were not affected, the attenuation of high-frequency oscillations in both JMF and JMP time curves will influence interpretation of CNS strategies during landing. PMID:23434732

McCaw, Steven T; Gardner, Jacob K; Stafford, Lindsay N; Torry, Michael R

2013-12-01

225

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. PMID:24297886

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

2013-01-01

226

Structure, Kinetic, and Chemical Mechanism of Isocitrate Dehydrogenase-1 from Mycobacterium tuberculosis  

PubMed Central

Mycobacterium tuberculosis (Mtb) is the leading cause of death due to a bacterial infection. The success of the Mtb pathogen has largely been attributed to the nonreplicating, persistence phase of the life cycle, for which the glyoxylate shunt is required. In Escherichia coli flux through the shunt is controlled by regulation of isocitrate dehydrogenase (ICDH). In Mtb, the mechanism of regulation is unknown, and currently there is no mechanistic or structural information on ICDH. We optimized expression and purification to a yield high enough to perform the first detailed kinetic and structural studies for Mtb ICDH-1. A large solvent kinetic isotope effect (D2OV = 3.0 ± 0.2, D2O[V/Kisocitrate] = 1.5 ± 0.3) and a smaller primary kinetic isotope effect (DV = 1.3 ± 0.1, D[V/K[2R-2H]isocitrate] = 1.5 ± 0.2) allowed us to perform the first multiple kinetic isotope effect studies on any ICDH and suggest a chemical mechanism. In this mechanism, protonation of the enolate to form product ?-ketoglutarate is the rate-limiting step. We report the first structure of Mtb ICDH-1 to 2.18 Å by X-ray crystallography with NADPH and Mn2+ bound. It is a homodimer in which each subunit has a Rossmann fold, and a common top domain of interlocking beta sheets. Mtb ICDH-1 is most structurally similar to the R132H mutant human ICDH found in glioblastomas. Similar to human R132H ICDH, Mtb ICDH-1 also catalyses the formation of ?-hydroxyglutarate. Our data suggest that regulation of Mtb ICDH-1 is novel. PMID:23409873

Quartararo, Christine E.; Hazra, Saugata; Hadi, Timin; Blanchard, John S.

2013-01-01

227

New chemical kinetics for description of chemical noise in small, heterogeneous biological systems: Beyond the paradigm of the rate constant concept  

NASA Astrophysics Data System (ADS)

We introduce a novel chemical kinetics for quantitative description of chemical fluctuations in a small, heterogeneous biological reaction system. At first, we discuss the recently proposed renewal chemical kinetics, and its application to quantitative interpretation of the randomness in fluctuating enzymatic turnover times of a-galactosidase. From the analysis of the randomness parameter data of the single enzyme reaction, one can extract valuable quantitative information about the enzyme reaction system, beyond the reach of the conventional Michaelis-Menten analysis. Next, we discuss a new universal behavior in the time dependence of the chemical fluctuation of product density for a small, heterogeneous reaction system, which is predicted from an exact analytic study for a general reaction model and confirmed by stochastic simulation results. We also discuss the dependence of the chemical noise on substrate concentrations for a heterogeneous enzyme reaction system, which turns out qualitatively different from that for a homogeneous enzyme reaction system.

Sung, Jaeyoung

2012-02-01

228

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

E-print Network

We present an ab initio study of the thermodynamics and kinetics of Li [subscript x]C[subscript 6], relevant for anode Li intercalation in rechargeable Li batteries. In graphite, the interlayer interactions are dominated ...

Ceder, Gerbrand

229

Study of ethane hydrate formation kinetics using the chemical affinity model with and without presence of surfactants  

NASA Astrophysics Data System (ADS)

In this article, we examine ethane hydrate formation kinetics with and without the presence of various surfactants. Firstly, the influences of stirring rate and initial pressure without the presence of surfactants are studied. The effects of four surfactants containing Sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), Polyoxyethylene (20) sorbitanmonopalmitate (Tween® 40), and TritonX-100 (TX-100) on ethane hydrate formation kinetics were experimentally investigated. Then the chemical affinity model is applied to model the ethane hydrate formation kinetics with and without surfactants. The kinetic parameters of the chemical affinity model were computed for the ethane hydrate formation with and without surfactants. We will see that the results of the modeling are in good agreement with the experimental data.

Karimi, Reza; Varaminian, Farshad; Izadpanah, Amir A.

2014-12-01

230

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

231

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

NASA Astrophysics Data System (ADS)

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

Shiraiwa, M.; Berkemeier, T.; Schilling-Fahnestock, K. A.; Seinfeld, J. H.; Pöschl, U.

2014-08-01

232

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

233

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

PubMed

The complete vibrational assignment and analysis of the fundamental modes of Parared was carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically from the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G(d,p) and 6-311++G(d,p) basis sets. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of Parared have been computed using B3LYP quantum chemical calculations. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated. PMID:25305611

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

2015-02-25

234

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

235

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

236

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

237

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

SciTech Connect

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 MPa) and 1000 psig (6.99 MPa) pressure and selectively identifies covalent carbon-hydrogen bond rupture as the mechanistic step which ultimately controls the further HMX burn rate under the static combustion conditions of this experiment. The 1 deg. KDIE value further suggests the rate-limiting C-H bond rupture occurs during the solid state HMX decomposition/deflagration portion of the overall combustion event and is supported by other independently published studies. A possible anomalous KDIE result at 1500 psig (10.4 MPa) is addressed. This condensed phase KDIE approach illustrates a direct link between lower temperature/pressure thermal decomposition and deflagration processes and their potential applicability to the combustion regime. Most importantly, a new general method is demonstrated for mechanistic combustion investigations which selectively permits an in-situ identification of the compound's burn rate-controlling step.

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

1989-01-01

238

miRNA Regulatory Circuits in ES Cells Differentiation: A Chemical Kinetics Modeling Approach  

PubMed Central

MicroRNAs (miRNAs) play an important role in gene regulation for Embryonic Stem cells (ES cells), where they either down-regulate target mRNA genes by degradation or repress protein expression of these mRNA genes by inhibiting translation. Well known tables TargetScan and miRanda may predict quite long lists of potential miRNAs inhibitors for each mRNA gene, and one of our goals was to strongly narrow down the list of mRNA targets potentially repressed by a known large list of 400 miRNAs. Our paper focuses on algorithmic analysis of ES cells microarray data to reliably detect repressive interactions between miRNAs and mRNAs. We model, by chemical kinetics equations, the interaction architectures implementing the two basic silencing processes of miRNAs, namely “direct degradation” or “translation inhibition” of targeted mRNAs. For each pair (M,G) of potentially interacting miRMA gene M and mRNA gene G, we parameterize our associated kinetic equations by optimizing their fit with microarray data. When this fit is high enough, we validate the pair (M,G) as a highly probable repressive interaction. This approach leads to the computation of a highly selective and drastically reduced list of repressive pairs (M,G) involved in ES cells differentiation. PMID:22039400

Luo, Zijun; Xu, Xuping; Gu, Peili; Lonard, David; Gunaratne, Preethi H.; Cooney, Austin J.; Azencott, Robert

2011-01-01

239

The Chemical Kinetics of Alkaline Extraction of Tellurium from Lead-Bismuth Eutectic  

SciTech Connect

Polonium-210 is an important radioactive product of neutron activation of molten lead-bismuth eutectic, a promising candidate coolant for advanced fast nuclear reactors. The radiological hazard potential associated with polonium can be significantly reduced by continuous online removal of polonium from the coolant. The removal method under investigation in this research is alkaline extraction. Chemical kinetic measurements were made to determine first and second order rate constants, activation energy, and heat of reaction at various temperatures using tellurium as a surrogate. First and second order alkaline extraction rate constants were measured to be: k1 = 10.05 e –52,274/RT and k2 = 167 e –97,224/RT. Alkaline extraction is dependent on temperature and was found to follow the Arrhenius rate law. The activation energy (Ea) ranged between 52,274 – 97,224 J mol-1. With a strong foundation of surrogate work completed, this work should be validated using polonium-210.

Laurence E. Auman; Eric P. Loewen; Thomas F. Gesell; Shuji Ohno

2005-07-01

240

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

241

A quantitative study of chemical kinetics for the synthesis of doped oxide nanocrystals using FTIR  

NASA Astrophysics Data System (ADS)

The synthesis of Mg-doped ZnO nanocrystals was employed as a model system to quantitatively study the chemical kinetics of the precursor conversion reactions at synthetic conditions and the correlations with the formation of doped nanocrystals. An accurate method using Fourier transform infrared spectroscopy was developed to explore the alcoholysis reactions of the cationic precursors. Our study showed that three independent factors, molar ratio of dopant precursor, reaction temperature and coordination ligands of cationic precursors influenced the relative reactivity of magnesium to zinc precursor, and in turn the formation of Mg-doped ZnO nanocrystals with defined shapes and properties. This understanding underpins the advancement of the syntheses of doped nanocrystals and should be useful for future rational design of new synthetic systems.

Zhang, Na; Wang, Xin; Ye, Zhizhen; Jin, Yizheng

2014-03-01

242

A cutoff phenomenon in accelerated stochastic simulations of chemical kinetics via flow averaging (FLAVOR-SSA).  

PubMed

We present a simple algorithm for the simulation of stiff, discrete-space, continuous-time Markov processes. The algorithm is based on the concept of flow averaging for the integration of stiff ordinary and stochastic differential equations and ultimately leads to a straightforward variation of the the well-known stochastic simulation algorithm (SSA). The speedup that can be achieved by the present algorithm [flow averaging integrator SSA (FLAVOR-SSA)] over the classical SSA comes naturally at the expense of its accuracy. The error of the proposed method exhibits a cutoff phenomenon as a function of its speed-up, allowing for optimal tuning. Two numerical examples from chemical kinetics are provided to illustrate the efficiency of the method. PMID:21197986

Bayati, Basil; Owhadi, Houman; Koumoutsakos, Petros

2010-12-28

243

Bis-BN Cyclohexane: A Remarkably Kinetically Stable Chemical Hydrogen Storage Material.  

PubMed

A critical component for the successful development of fuel cell applications is hydrogen storage. For back-up power applications, where long storage periods under extreme temperatures are expected, the thermal stability of the storage material is particularly important. Here, we describe the development of an unusually kinetically stable chemical hydrogen storage material with a H2 storage capacity of 4.7 wt%. The compound, which is the first reported parental BN isostere of cyclohexane featuring two BN units, is thermally stable up to 150 °C both in solution and as a neat material. Yet, it can be activated to rapidly desorb H2 at room temperature in the presence of a catalyst without releasing other detectable volatile contaminants. We also disclose the isolation and characterization of two cage compounds with S4 symmetry from the H2 desorption reactions. PMID:25494531

Chen, Gang; Zakharov, Lev N; Bowden, Mark E; Karkamkar, Abhijeet J; Whittemore, Sean M; Garner, Edward B; Mikulas, Tanya C; Dixon, David A; Autrey, Tom; Liu, Shih-Yuan

2015-01-14

244

Kinetic and microstructural study of titanium nitride deposited by laser chemical vapor deposition  

NASA Astrophysics Data System (ADS)

Titanium nitride (TiN) films were deposited onto Ti-6Al-4V substrates by laser chemical vapor deposition using a cw COsb2 laser and TiClsb4,\\ Nsb2, and Hsb2 reactant gases. In-situ laser induced fluorescence (LIF) and multi-wavelength pyrometry determined relative titanium gas phase atomic number density and deposition temperature, respectively. Deposited films were yellow to gold in color. Transmission electron microscopy on one sample revealed a face-centered cubic structure with a lattice parameter (0.4237 nm) expected for TiN. Auger electron spectroscopy found substoichiometric compositions with a N/Ti ratio between 0.7 and 0.9. Variables decreasing grain size (lower temperature, higher TiClsb4 input) decreased the N/Ti ratio. Higher Nsb2 input increased stoichiometry, while larger Hsb2 input decreased stoichiometry. The deposit substoichiometry is believed to be caused by diffusion of nitrogen through TiN grain boundaries to the titanium alloy substrate. The morphology starts as a dense polycrystalline structure evolving into a columnar structure having facets or nodules at the surface with crystallite sizes ranging from 10-1000 nm. TiClsb4 input had a inverse correlation with crystallite size, while Nsb2:Hsb2 ratio had minimal effect; the crystallite size (G) varied exponentially with temperature (T) for a given irradiation time, i.e., G = C exp (-28000/T), with constant C reflecting substrate roughness and gas composition. Microhardness tests revealed substrate contributions; nevertheless, films appeared to have a minimum hardness of 2000 Hsbv. The deposition apparent activation energy was calculated as 122 ± 9 kJ/mole using growth rates measured by film height and 117 ± 23 kJ/mole using growth rates measured by LIF signals. This puts the process in the surface kinetic growth regime over the temperature range 1370-1610 K. Above Nsb2 and Hsb2 levels of 1.25% and below TiClsb4 input of 4.5%, the growth rate has a half-order dependence on nitrogen and a linear dependence on hydrogen and is approximated by$r = {{kPsb{TiClsb4}Psb{Hsb2}Psbsp{Nsb2}{1/2}exp?ft({{-}Esb{a}/ {RT}right)}/{1 + Psb{Ar}}}}.Since nitrogen positively affects growth rate (when added to a TiClsb4+Hsb2 mixture), stepwise reduction of TiClsb4 to Ti by hydrogen does not occur. NHsb{x} complexes are clearly involved in the growth mechanism; a likely combination of rate determining steps is the formation of NH and the initial reduction of TiClsb4$ by hydrogen.

Egland, Keith Maynard

245

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

246

Elucidating the interaction of H2O2 with polar amino acids - Quantum chemical calculations  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations have been carried out to investigate the interaction motifs of H2O2 with polar amino acid residues. Binding energies obtained from gas phase and continuum solvent phase calculations range between 2 and 30 kcal/mol. H2O2 interacts with the side chain of polar amino acids chiefly through the formation of hydrogen bonds. The sbnd CH group in side chains of a few residues provides additional stabilization to H2O2.

Karmakar, Tarak; Balasubramanian, Sundaram

2014-10-01

247

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

248

Observation of Optical Chemical Shift by Precision Nuclear Spin Optical Rotation Measurements and Calculations  

E-print Network

and Calculations Junhui Shi, Suvi Ikalainen, Juha Vaara,¶ and Michael V. Romalis*,§ Department of Chemistry The rotation of light polarization is similar to the Faraday effect caused by a nuclear magnetic field to Faraday rotation changes by more than a factor of 2 for the simple chemicals studied. We apply the recent

Romalis, Mike

249

Mechanism of tungsten-dependent acetylene hydratase from quantum chemical calculations  

E-print Network

Mechanism of tungsten-dependent acetylene hydratase from quantum chemical calculations Rong hydratase is a tungsten-dependent enzyme that cata- lyzes the nonredox hydration of acetylene metalloenzyme cluster approach Tungsten is the heaviest metal in biology and plays prominent roles in carbon

Liao, Rongzhen

250

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

ERIC Educational Resources Information Center

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

Vargas, Francisco M.

2014-01-01

251

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

252

Kinetic of NO2 uptake by Phleum pratense pollen: Chemical and allergenic implications.  

PubMed

Phleum pratense pollen was exposed to NO2 in a reactor allowing a continuous analysis of NO2 concentration by FTIR. The uptake coefficient of NO2 on pollen was calculated postulating a first order kinetic reaction and a value of (1.1 ± 0.1) × 10(-7) was determined. NO2 uptake was faster when the pollen water content was increased and when the pollen was pre-treated with ozone. The effect of NO2 exposure on pollen allergic properties was investigated by quantifying Th2- and Th1-associated chemokines in a model of human dendritic cells. Cellular analysis clearly showed that cells exposed to fumigated pollen favored the production of chemokines known to promote Th2-cell responses. Altogether these data demonstrate that NO2 uptake by pollen directly correlates with increased Th2 response in human cells, and are in favor of the involvement of NO2 pollution in the increase of allergic diseases. PMID:25463703

Chassard, Guillaume; Choël, Marie; Gosselin, Sylvie; Vorng, Han; Petitprez, Denis; Shahali, Youcef; Tsicopoulos, Anne; Visez, Nicolas

2014-10-17

253

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

254

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

255

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

256

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

257

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

ERIC Educational Resources Information Center

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

Sattsangi, Prem D.

2011-01-01

258

A radical index for the determination of the chemical kinetic contribution to diffusion flame extinction of large hydrocarbon fuels  

Microsoft Academic Search

The extinction limits of diffusion flames have been measured experimentally and computed numerically for fuels of three different molecular structures pertinent to surrogate fuel formulation: n-alkanes, alkyl benzenes, and iso-octane. The focus of this study is to isolate the thermal and mass transport effects from chemical kinetic contributions to diffusion flame extinction, allowing for a universal correlation of extinction limit

Sang Hee Won; Stephen Dooley; Frederick L. Dryer; Yiguang Ju

259

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

260

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

261

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

262

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

PubMed Central

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

Jung, Moon Chul; Weber, Stephen G.

2006-01-01

263

Effects of chemical kinetics of the performance of the atomic iodine laser system  

NASA Astrophysics Data System (ADS)

Model calculations show that chemical reactions which take place in the active medium of a photolytically pumped iodine laser limit the efficiency with which pump photons are utilized and convert significant amounts of the starting material RI to the unwanted by-products R2 and I2. Laser- and RF-discharge-based methods for regenerating starting materials from by-products are evaluated experimentally. For economical operation of large iodine laser systems, CF3I is presently the best starting material, and a pulsed RF-discharge technique is presently the best one for chemical regeneration. The absorbed energy required to regenerate one CF3I molecule using pulsed RF-discharge techniques is 5.8 eV.

Fisk, G. A.; Truby, F. K.

1980-01-01

264

Gutzwiller electronic structure calculations applied to transition metals: Kinetic energy gain with ferromagnetic order in bcc Fe  

NASA Astrophysics Data System (ADS)

The Gutzwiller projector technique has long been known as a method to include correlations in electronic structure calculations. We describe a model implementation for a Gutzwiller +LDA calculation in a localized-orbital restricted basis framework, emphasizing the protocol step by step and illustrating our specific procedure for this and future applications. We demonstrate the method with a classic problem, the ferromagnetism of bulk bcc Fe, whose nature is attracting fresh interest. In the conventional Stoner-Wohlfarth model, and in spin-polarized LDA calculations, the ferromagnetic ordering of iron sets in so that the electrons can reduce their mutual Coulomb repulsion, at the cost of some increase of electron kinetic energy. This balance may, however, be altered by correlations, which are strong for localized d orbitals. The present localized basis Gutzwiller +LDA calculation demonstrates how the ferromagnetic ordering of Fe may, in fact, entrain a decrease of kinetic energy at the cost of some increase of potential energy. This happens because, as foreshadowed long ago by Goodenough and others and more recently supported by LDA-DMFT calculations, correlations cause eg and t2g d orbitals to behave differently, with the weakly propagating eg states fully spin polarized and almost localized, and only t2g states forming a broad partly filled itinerant band. Owing to an intra-atomic Hund's rule exchange that aligns eg and t2g spins, the propagation of itinerant t2g holes is favored when different atomic spins are ferromagnetically aligned. This suggests a strong analogy with double exchange in iron ferromagnetism.

Borghi, Giovanni; Fabrizio, Michele; Tosatti, Erio

2014-09-01

265

Correlation Between Testosterone and PSA Kinetics in Metastatic Prostate Cancer Patients Treated With Diverse Chemical Castrations.  

PubMed

To assess total testosterone and prostatic-specific antigen (PSA) kinetics among diverse chemical castrations, advanced-stage prostate cancer patients were randomized into three groups of 20: Group 1, Leuprolide 3.75 mg; Group 2, Leuprolide 7.5 mg; and Group 3, Goserelin 3.6 mg. All groups were treated with monthly application of the respective drugs. The patients' levels of serum total testosterone and PSA were evaluated at two time periods: before the treatment and 3 months after the treatment. Spearman's rank correlation coefficient was utilized to verify the hypothesis of linear correlation between total testosterone and PSA levels. At the beginning the patients' age, stage, grade, PSA, and total testosterone were similar within the three groups, with median age 72, 70, and 70 years in Groups 1, 2, and 3, respectively. Three months after the treatment, patients who received Leuprolide 7.5 mg presented significantly lower median total testosterone levels compared with Goserelin 3.6 mg and Leuprolide 3.75 mg (9.5 ng/dL vs. 20.0 ng/dL vs. 30.0 ng/dL, respectively; p = .0072), while those who received Goserelin 3.6 mg presented significantly lower PSA levels compared with Leuprolide 7.5 mg and Leuprolide 3.75 mg (0.67 vs. 1.86 vs. 2.57, respectively; p = .0067). There was no linear correlation between total testosterone and PSA levels. Overall, regarding castration levels of total testosterone, 28.77% of patients did not obtain levels ?50 ng/dL and 47.80% did not obtain levels ?20 ng/dL. There was no correlation between total testosterone and PSA kinetics and no equivalence among different pharmacological castrations. PMID:25294865

Reis, Leonardo O; Denardi, Fernandes; Faria, Eliney F; Silva, Elcio Dias

2014-10-01

266

Object Kinetic Monte Carlo calculations of electron and He irradiation of nickel  

NASA Astrophysics Data System (ADS)

We present results of an Object Kinetic Monte Carlo model (OKMC) of nucleation of He-vacancy complexes under irradiation of nickel. This OKMC model has been constructed using the existing atomistic information on migration energies and binding energies of vacancies, self-interstitials and He-vacancy interactions, as well as He migration from embedded atom interatomic potentials. We use this model to first study the different annealing stages of electron irradiated Ni and the influence of impurities in the recovery of damage during isochronal annealing. Then, He desorption from implanted Ni is studied for different doses and compared to existing experimental measurements.

Gámez, B.; Gámez, L.; Ortiz, C. J.; Caturla, M. J.; Perlado, J. M.

2009-04-01

267

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

268

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

NASA Astrophysics Data System (ADS)

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

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

269

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

270

A reduced chemical kinetic model for IC engine combustion simulations with primary reference fuels  

SciTech Connect

A reduced chemical kinetic mechanism for the oxidation of primary reference fuel (PRF) has been developed and applied to model internal combustion engines. Starting from an existing reduced reaction mechanism for n-heptane oxidation, a new reduced n-heptane mechanism was generated by including an additional five species and their relevant reactions, by updating the reaction rate constants of several reactions pertaining to oxidation of carbon monoxide and hydrogen, and by optimizing reaction rate constants of selected reactions. Using a similar approach, a reduced mechanism for iso-octane oxidation was built and combined with the n-heptane mechanism to form a PRF mechanism. The final version of the PRF mechanism consists of 41 species and 130 reactions. Validation of the present PRF mechanism was performed with measurements from shock tube tests, and HCCI and direct injection engine experiments available in the literature. The results show that the present PRF mechanism gives reliable performance for combustion predictions, as well as computational efficiency improvements for multidimensional CFD simulations. (author)

Ra, Youngchul; Reitz, Rolf D. [Engine Research Center, University of Wisconsin-Madison, 1500 Engineering Drive, ERB 1016B, Madison, WI 53706 (United States)

2008-12-15

271

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

272

Simulations of chemical vapor deposition diamond film growth using a kinetic Monte Carlo model  

NASA Astrophysics Data System (ADS)

A one-dimensional kinetic Monte Carlo model has been developed to simulate the chemical vapor deposition (CVD) of a diamond (100) surface. The model considers adsorption, etching/desorption, lattice incorporation, and surface migration along and across the dimer rows. The reaction rates for these processes are re-evaluated in detail and their effect upon the predicted growth rates and morphology are described. We find that for standard CVD diamond conditions, etching of sp3 carbon species from the growing surface is negligible. Surface migration occurs rapidly, but is mostly limited to CH2 species oscillating back and forth between two adjacent radical sites. Despite the average number of migration hops being in the thousands, the average surface diffusion length for a surface species—before it either adds to the diamond lattice or is removed back to the gas phase—is <2 sites. ?-scission helps to smooth the surface, but is only a relatively minor process removing <2% of adsorbed species. At low substrate temperature, migration is negligible with film growth being dominated by direct adsorption (Eley-Rideal) processes. The resulting films are rough and spiky, reminiscent of amorphous carbon. With increasing substrate temperature migration increases in significance until for temperatures >1000 K migration becomes the major process by which the surface becomes smoother. Langmuir-Hinshelwood processes are now the dominant growth mechanism, although 30% of growth still occurs via direct adsorption.

May, P. W.; Harvey, J. N.; Allan, N. L.; Richley, J. C.; Mankelevich, Yu. A.

2010-07-01

273

Features in chemical kinetics. II. A self-emerging definition of slow manifolds  

NASA Astrophysics Data System (ADS)

In the preceding paper of this series (Part I [P. Nicolini and D. Frezzato, J. Chem. Phys. 138, 234101 (2013)], 10.1063/1.4809592) we have unveiled some ubiquitous features encoded in the systems of polynomial differential equations normally applied in the description of homogeneous and isothermal chemical kinetics (mass-action law). Here we proceed by investigating a deeply related feature: the appearance of so-called slow manifolds (SMs) which are low-dimensional hyper-surfaces in the neighborhood of which the slow evolution of the reacting system occurs after an initial fast transient. Indeed a geometrical definition of SM, devoid of subjectivity, "naturally" follows in terms of a specific sub-dimensional domain embedded in the peculiar region of the concentrations phase-space that in Part I we termed as "attractiveness region." Numerical inspections on simple low-dimensional model cases are presented, including the benchmark case of Davis and Skodje [J. Chem. Phys. 111, 859 (1999)], 10.1063/1.479372 and the preliminary analysis of a simplified model mechanism of hydrogen combustion.

Nicolini, Paolo; Frezzato, Diego

2013-06-01

274

CFD analysis of municipal solid waste combustion using detailed chemical kinetic modelling.  

PubMed

Nitrogen oxides (NO x ) emissions from the combustion of municipal solid waste (MSW) in waste-to-energy (WtE) facilities are receiving renewed attention to reduce their output further. While NO x emissions are currently 60% below allowed limits, further reductions will decrease the air pollution control (APC) system burden and reduce consumption of NH3. This work combines the incorporation of the GRI 3.0 mechanism as a detailed chemical kinetic model (DCKM) into a custom three-dimensional (3D) computational fluid dynamics (CFD) model fully to understand the NO x chemistry in the above-bed burnout zones. Specifically, thermal, prompt and fuel NO formation mechanisms were evaluated for the system and a parametric study was utilized to determine the effect of varying fuel nitrogen conversion intermediates between HCN, NH3 and NO directly. Simulation results indicate that the fuel nitrogen mechanism accounts for 92% of the total NO produced in the system with thermal and prompt mechanisms accounting for the remaining 8%. Results also show a 5% variation in final NO concentration between HCN and NH3 inlet conditions, demonstrating that the fuel nitrogen intermediate assumed is not significant. Furthermore, the conversion ratio of fuel nitrogen to NO was 0.33, revealing that the majority of fuel nitrogen forms N2. PMID:25005043

Frank, Alex; Castaldi, Marco J

2014-08-01

275

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

276

Role of Thermal Diffusion and Chemical Kinetics in Infrared Tissue Ablation  

NASA Astrophysics Data System (ADS)

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

Edwards, Glenn; Hutson, M. Shane

2003-03-01

277

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

278

Quantum Chemical Calculation on the Interaction of Hydrogen Isotopes with Materials for Energy System  

Microsoft Academic Search

A series of our quantum chemical study on the interaction of hydrogen isotopes with defects in Li2O was reported. Three kinds of F-centers and lithium vacancy were considered. Stable positions of -OH in Li2O lattice with defects were calculated and the determined structures were well analyzed from the viewpoint of electron transfer between a proton and defects. In addition to

Satoru Tanaka; Hisashi Tanigawa

2003-01-01

279

Calculating excess chemical potentials using dynamic simulations in the fourth dimension  

SciTech Connect

A general method for computing excess chemical potentials is presented. The excess chemical potential of a solute or ligand molecule is estimated from the potential of mean-force (PMF) calculated along a nonphysical fourth spatial dimension, {ital w}, into which the molecule is gradually inserted or from which it is gradually abstracted. According to this {open_quotes}4D-PMF{close_quotes} (four dimensional) scheme, the free energy difference between two limiting states defines the excess chemical potential: At w={plus_minus}{infinity}, the molecule is not interacting with the rest of the system, whereas at w=0, it is fully interacting. Use of a fourth dimension avoids the numerical instability in the equations of motion encountered upon growing or shrinking solute atoms in conventional free energy perturbation simulations performed in three dimensions, while benefiting from the efficient sampling of configurational space afforded by PMF calculations. The applicability and usefulness of the method are illustrated with calculations of the hydration free energy of simple Lennard-Jones (LJ) solutes, a water molecule, and camphor, using molecular dynamics simulations and umbrella sampling. Physical insight into the nature of the PMF profiles is gained from a continuum treatment of short- and long-range interactions. The short-range barrier for dissolution of a LJ solute in the added dimension provides an apparent surface tension of the solute. An approximation to the long-range behavior of the PMF profiles is made in terms of a continuum treatment of LJ dispersion and electrostatic interactions. Such an analysis saves the need for configurational sampling in the long-range limit of the fourth dimension. The 4D-PMF method of calculating excess chemical potentials should be useful for neutral solute and ligand molecules with a wide range of sizes, shapes, and polarities. {copyright} {ital 1999 American Institute of Physics.}

Pomes, R. [Theoretical Biology and Biophysics Group T-10, Mail Stop K710, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Theoretical Biology and Biophysics Group T-10, Mail Stop K710, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Eisenmesser, E.; Post, C.B. [Department of Medical Chemistry, Purdue University, West Lafayette, Indiana 47901-1333 (United States)] [Department of Medical Chemistry, Purdue University, West Lafayette, Indiana 47901-1333 (United States); Roux, B. [Departements de Physique et de Chimie, Universite de Montreal, C.P. 6128, Succursalle Centre-Ville, Montreal (Quebec), H3C 3J7 (CANADA)] [Departements de Physique et de Chimie, Universite de Montreal, C.P. 6128, Succursalle Centre-Ville, Montreal (Quebec), H3C 3J7 (CANADA)

1999-08-01

280

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

281

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

282

A Simple Model for Calculating the Kinetics of Protein Folding from Three-Dimensional Structures  

Microsoft Academic Search

An elementary statistical mechanical model was used to calculate the folding rates for 22 proteins from their known three-dimensional structures. In this model, residues come into contact only after all of the intervening chain is in the native conformation. An additional simplifying assumption is that native structure grows from localized regions that then fuse to form the complete native molecule.

Victor Munoz; William A. Eaton

1999-01-01

283

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

284

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

SciTech Connect

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

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

2012-11-21

285

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

286

Rapid calculation of protein chemical shifts using bond polarization theory and its application to protein structure refinement.  

PubMed

Although difficult to analyze, NMR chemical shifts provide detailed information on protein structure. We have adapted the semi-empirical bond polarization theory (BPT) to protein chemical shift calculation and chemical shift driven protein structure refinement. A new parameterization for BPT amide nitrogen chemical shift calculation has been derived from MP2 ab initio calculations and successfully evaluated using crystalline tripeptides. We computed the chemical shifts of the small globular protein ubiquitin, demonstrating that BPT calculations can match the results obtained at the DFT level of theory at very low computational cost. In addition to the calculation of chemical shift tensors, BPT allows the calculation of chemical shift gradients and consequently chemical shift driven geometry optimizations. We applied chemical shift driven protein structure refinement to the conformational analysis of a set of Trypanosoma brucei (the causative agent of African sleeping sickness) tryparedoxin peroxidase Px III structures. We found that the interaction of Px III with its reaction partner Tpx seems to be governed by conformational selection rather than by induced fit. PMID:22868284

Jakovkin, Igor; Klipfel, Marco; Muhle-Goll, Claudia; Ulrich, Anne S; Luy, Burkhard; Sternberg, Ulrich

2012-09-21

287

Pyrolysis behaviors and kinetics of refining and chemicals wastewater, lignite and their blends through TGA.  

PubMed

Co-pyrolysis behaviors of refining and chemicals wastewater solid (RS) and Huolinhe lignite (HL) were investigated via thermogravimetric analysis (TGA). The thermal degradation process of RS and the blends proceeded in three stages, while two stages for HL. The increased percentage of RS in the blends reduced the characteristic temperature (Ti, Tp, Tf) and residual mass (Mr), while raised the characteristic reaction rate (Rp, Rv) and comprehensive devolatilization parameter (D). The results indicated that there existed some inhibitive interactions between RS and HL. The activation energies were calculated by using the Friedman and Starink method. The activation energy of RS increased first and then decreased with conversion degree, and the variation wasn't as great as that of the blends and lignite. No matter which conversion degree is, the activation energy decreased with the percentage of RS in the blends increasing. The minimum value was obtained by blending 75wt.% RS. PMID:25585257

Mu, Lin; Chen, Jianbiao; Yin, Hongchao; Song, Xigeng; Li, Aimin; Chi, Xiao

2015-03-01

288

Effect of heat-treatment on the physico-chemical properties of egg white proteins: A kinetic study  

Microsoft Academic Search

In this study, kinetic models were established to describe the heat-induced changes in selected physico-chemical properties of egg white proteins. These changes were studied in a temperature range of 50–85°C and two pH levels were selected, to mimic the pH of fresh (pH 7.6) and aged egg white (pH 8.8). The heat-induced decrease of residual denaturation enthalpy and amount of

Iesel Van der Plancken; Ann Van Loey; Marc E. Hendrickx

2006-01-01

289

Gas-phase reaction between calcium monocation and fluoromethane: Analysis of the potential energy hypersurface and kinetics calculations  

SciTech Connect

The gas-phase reaction between calcium monocation and fluoromethane: Ca{sup +}+CH{sub 3}F{yields}CaF{sup +}+CH{sub 3} was theoretically analyzed. The potential energy hypersurface was explored by using density functional theory methodology with different functionals and Pople's, Dunning's, Ahlrichs', and Stuttgart-Dresden basis sets. Kinetics calculations (energy and total angular momentum resolved microcanonical variational/conventional theory) were accomplished. The theoretically predicted range for the global kinetic rate constant values at 295 K (7.2x10{sup -11}-5.9x10{sup -10} cm{sup 3} molecule{sup -1} s{sup -1}) agrees reasonably well with the experimental value at the same temperature [(2.6{+-}0.8)x10{sup -10} cm{sup 3} molecule{sup -1} s{sup -1}]. Explicit consideration of a two transition state model, where the formation of a weakly bounded prereactive complex is preceded by an outer transition state (entrance channel) and followed by an inner transition state connecting with a second intermediate that finally leads to products, is mandatory. Experimental observations on the correlation, or lack of correlation, between reaction rate constants and second ionization energies of the metal might well be rationalized in terms of this two transition state model.

Varela-Alvarez, Adrian; Sordo, Jose A. [Departamento de Quimica Fisica y Analitica, Laboratorio de Quimica Computacional, Facultad de Quimica, Universidad de Oviedo, Julian Claveria, 8. 33006 Oviedo, Principado de Asturias (Spain); Rayon, V. M.; Redondo, P.; Barrientos, C. [Departamento de Quimica Fisica y Quimica Inorganica, Facultad de Ciencias, Universidad de Valladolid, 47005 Valladolid (Spain)

2009-10-14

290

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. PMID:24250372

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

2011-01-01

291

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

292

Chemical vapour deposition growth of carbon nanotube forests: kinetics, morphology, composition, and their mechanisms  

NASA Astrophysics Data System (ADS)

This thesis analyzes the chemical vapour deposition (CVD) growth of vertically aligned carbon nanotube (CNT) forests in order to understand how CNT forests grow, why they stop growing, and how to control the properties of the synthesized CNTs. in situ kinetics data of the growth of CNT forests are gathered by in situ optical microscopy. The overall morphology of the forests and the characteristics of the individual CNTs in the forests are investigated using scanning electron microscopy and Raman spectroscopy. The in situ data show that forest growth and termination are activated processes (with activation energies on the order of 1 eV), suggesting a possible chemical origin. The activation energy changes at a critical temperature for ethanol CVD (approximately 870°C). These activation energies and critical temperature are also seen in the temperature dependence of several important characteristics of the CNTs, including the defect density as determined by Raman spectroscopy. This observation is seen across several CVD processes and suggests a mechanism of defect healing. The CNT diameter also depends on the growth temperature. In this thesis, a thermodynamic model is proposed. This model predicts a temperature and pressure dependence of the CNT diameter from the thermodynamics of the synthesis reaction and the effect of strain on the enthalpy of formation of CNTs. The forest morphology suggests significant interaction between the constituent CNTs. These interactions may play a role in termination. The morphology, in particular a microscale rippling feature that is capable of diffracting light, suggest a non-uniform growth rate across the forest. A gas phase diffusion model predicts a non-uniform distribution of the source gas. This gas phase diffusion is suggested as a possible explanation for the non-uniform growth rate. The gas phase diffusion is important because growth by acetylene CVD is found to be very efficient (approximately 30% of the acetylene is converted to CNTs). It is seen that multiple mechanisms are active during CNT growth. The results of this thesis provide insight into both the basic understanding of the microscopic processes involved in CVD growth and how to control the properties of the synthesized CNTs.

Vinten, Phillip

293

Applying chemical kinetics to natural-gas combustion problems. Annual report, September 1984August 1985  

Microsoft Academic Search

Kinetic modeling techniques were applied to two GRI-supported programs. Computational analysis of the successive reignition of methane-air mixtures under conditions similar to those encountered in research pulse combustors has shown that the lean and rich limits of operation are, to a considerable extent, kinetically controlled. For mixtures outside these limits, the times required for reignition are too long to permit

Westbrook

1985-01-01

294

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

295

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

296

Magnetic properties of bcc Iron surfaces and the influence of the chemical environment: electronic structure calculations  

NASA Astrophysics Data System (ADS)

We have investigated the magnetic properties of low-indexed iron surfaces and the influence of the chemical environment on these properties. We have considered the (1?0?0), (1?1?0), (1?1?1), (2?1?1) and (3?1?0) surfaces, both, bare and with the presence of adsorbates. These were chosen to mimic realistic chemical synthesis environments, being H, Cl, HCl, NH3, NH4Cl, or CH3COOH. We have found an increased magnetization at all bare surfaces. Upon H adsorption the magnetization is generally reduced, but still above the bulk value. All other ligands and their dissociated parts alter the magnetic properties of the surfaces only weakly. Our calculations do not indicate that ligands are responsible for experimental observations of Fe nanoparticles with average magnetizations below the bulk value.

Fischer, Guntram; Gerber, Iann C.

2015-01-01

297

Magnetic properties of bcc Iron surfaces and the influence of the chemical environment: electronic structure calculations.  

PubMed

We have investigated the magnetic properties of low-indexed iron surfaces and the influence of the chemical environment on these properties. We have considered the (1?0?0), (1?1?0), (1?1?1), (2?1?1) and (3?1?0) surfaces, both, bare and with the presence of adsorbates. These were chosen to mimic realistic chemical synthesis environments, being H, Cl, HCl, NH3, NH4Cl, or CH3COOH. We have found an increased magnetization at all bare surfaces. Upon H adsorption the magnetization is generally reduced, but still above the bulk value. All other ligands and their dissociated parts alter the magnetic properties of the surfaces only weakly. Our calculations do not indicate that ligands are responsible for experimental observations of Fe nanoparticles with average magnetizations below the bulk value. PMID:25419872

Fischer, Guntram; Gerber, Iann C

2015-01-14

298

The chemically driven phase transformation in a memristive abacus capable of calculating decimal fractions  

PubMed Central

The accurate calculation of decimal fractions is still a challenge for the binary-coded computations that rely on von Neumann paradigm. Here, we report a kind of memristive abacus based on synaptic Ag-Ge-Se device, in which the memristive long-term potentiation and depression are caused by a chemically driven phase transformation. The growth and the rupture of conductive Ag2Se dendrites are confirmed via in situ transmission electron microscopy. By detecting the change in memristive synaptic weight, the quantity of input signals applied onto the device can be “counted”. This makes it possible to achieve the functions of abacus that is basically a counting frame. We demonstrate through experimental studies that this kind of memristive abacus can calculate decimal fractions in the light of the abacus algorithms. This approach opens up a new route to do decimal arithmetic in memristive devices without encoding binary-coded decimal. PMID:23390580

Xu, Hanni; Xia, Yidong; Yin, Kuibo; Lu, Jianxin; Yin, Qiaonan; Yin, Jiang; Sun, Litao; Liu, Zhiguo

2013-01-01

299

Reaction mechanism and kinetics for the chemical bath deposition of In(OH) x S y thin films  

Microsoft Academic Search

The solution chemistry of InCl3–CH3CSNH2–CH3COOH (InCl3–TA–HAcO) system has been studied and the species distribution diagrams, solubility and precipitation curves have been calculated. At an acidic pH (1–4), the (InCl3–TA–HAcO) solution contains mainly indium–chloro-complexes and In(OH)3 precipitation is not expected when HAcO is added. Kinetic calculations based on TA hydrolysis have shown that indium hydroxide–sulfide [In(OH)xSy] precipitation takes place through a

R. Bayón; J. Herrero

2001-01-01

300

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

301

A study on quantum chemical calculations of 3-, 4-nitrobenzaldehyde oximes  

NASA Astrophysics Data System (ADS)

The molecular geometry, vibrational frequencies, 1H and 13C NMR chemical shifts, UV-vis spectra, HOMO-LUMO analyses, molecular elektrostatic potantials (MEPs), thermodinamic properties and atomic charges of 3- and 4-Nitrobenzaldehyde oxime (C 7H 6N 2O 3) molecules have been investigated by using Hartree-Fock (HF) and density functional theory (DFT/B3LYP) methods with the 6-311++G(d, p) basis set. The calculated optimized geometric parameters (bond lenghts and bond angles), the vibrational frequencies calculated and 13C and 1H NMR chemical shifts values for the mentioned compounds are in a very good agreement with the experimental data. Futheremore, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) have been simulated and the transition states, energy band gaps and molecular electrostatic potantial (MEP) maps for each oxime compound have been determined. Additionally, we also report the infrared intensities and Raman activities for the compounds under study.

Gökce, Halil; Bahçeli, Semiha

2011-09-01

302

A study on quantum chemical calculations of 3-, 4-nitrobenzaldehyde oximes.  

PubMed

The molecular geometry, vibrational frequencies, 1H and 13C NMR chemical shifts, UV-vis spectra, HOMO-LUMO analyses, molecular electrostatic potentials (MEPs), , thermodynamic properties and atomic charges of 3- and 4-Nitrobenzaldehyde oxime (C7H6N2O3) molecules have been investigated by using Hartree-Fock (HF) and density functional theory (DFT/B3LYP) methods with the 6-311++G(d, p) basis set. The calculated optimized geometric parameters (bond lengths and bond angles), the vibrational frequencies calculated and 13C and 1H NMR chemical shifts values for the mentioned compounds are in a very good agreement with the experimental data. Furthermore, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) have been simulated and the transition states, energy band gaps and molecular electrostatic potential (MEP) maps for each oxime compound have been determined. Additionally, we also report the infrared intensities and Raman activities for the compounds under study. PMID:21683648

Gökce, Halil; Bahçeli, Semiha

2011-09-01

303

Comparing quantum-chemical calculation methods for structural investigation of zeolite crystal structures by solid-state NMR spectroscopy.  

PubMed

Combining quantum-chemical calculations and ultrahigh-field NMR measurements of (29)Si chemical shielding (CS) tensors has provided a powerful approach for probing the fine details of zeolite crystal structures. In previous work, the quantum-chemical calculations have been performed on 'molecular fragments' extracted from the zeolite crystal structure using Hartree-Fock methods (as implemented in Gaussian). Using recently acquired ultrahigh-field (29) Si NMR data for the pure silica zeolite ITQ-4, we report the results of calculations using recently developed quantum-chemical calculation methods for periodic crystalline solids (as implemented in CAmbridge Serial Total Energy Package (CASTEP) and compare these calculations to those calculated with Gaussian. Furthermore, in the context of NMR crystallography of zeolites, we report the completion of the NMR crystallography of the zeolite ITQ-4, which was previously solved from NMR data. We compare three options for the 'refinement' of zeolite crystal structures from 'NMR-solved' structures: (i) a simple target-distance based geometry optimization, (ii) refinement of atomic coordinates in which the differences between experimental and calculated (29)Si CS tensors are minimized, and (iii) refinement of atomic coordinates to minimize the total energy of the lattice using CASTEP quantum-chemical calculations. All three refinement approaches give structures that are in remarkably good agreement with the single-crystal X-ray diffraction structure of ITQ-4. PMID:20623826

Brouwer, Darren H; Moudrakovski, Igor L; Darton, Richard J; Morris, Russell E

2010-12-01

304

Chemical enthalpies of hydration calculated for the ions of astatine, francium, and radium by the hyperbola method  

Microsoft Academic Search

Calculations by the hyperbola method are presented on the chemical enthalpies of hydration for the ions of astatine, francium, and radium. Values are also given for the enthalpies of hydration for ions of the hypothetical elements 117, 119, and 120.

A. I. Cherkesov; N. P. Sadovnikov

2009-01-01

305

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

306

An upwind, kinetic flux-vector splitting method for flows in chemical and thermal non-equilibrium  

NASA Technical Reports Server (NTRS)

We have developed new upwind kinetic difference schemes for flows with non-equilibrium thermodynamics and chemistry. These schemes are derived from the Boltzmann equation with the resulting Euler schemes developed as moments of the discretized Boltzmann scheme with a locally Maxwellian velocity distribution. Splitting the velocity distribution at the Boltzmann level is seen to result in a flux-split Euler scheme and is called Kinetic Flux Vector Splitting (KFVS). Extensions to flows with finite-rate chemistry and vibrational relaxation is accomplished utilizing nonequilibrium kinetic theory. Computational examples are presented comparing KFVS with the schemes of Van Leer and Roe for a quasi-one-dimensional flow through a supersonic diffuser, inviscid flow through two-dimensional inlet, and viscous flow over a cone at zero angle-of-attack. Calculations are also shown for the transonic flow over a bump in a channel and the transonic flow over an NACA 0012 airfoil. The results show that even though the KFVS scheme is a Riemann solver at the kinetic level, its behavior at the Euler level is more similar to the existing flux-vector splitting algorithms than to the flux-difference splitting scheme of Roe.

Eppard, W. M.; Grossman, B.

1993-01-01

307

A hybrid kinetic Monte Carlo method for simulating silicon films grown by plasma-enhanced chemical vapor deposition  

NASA Astrophysics Data System (ADS)

We present a powerful kinetic Monte Carlo (KMC) algorithm that allows one to simulate the growth of nanocrystalline silicon by plasma enhanced chemical vapor deposition (PECVD) for film thicknesses as large as several hundreds of monolayers. Our method combines a standard n-fold KMC algorithm with an efficient Markovian random walk scheme accounting for the surface diffusive processes of the species involved in PECVD. These processes are extremely fast compared to chemical reactions, thus in a brute application of the KMC method more than 99% of the computational time is spent in monitoring them. Our method decouples the treatment of these events from the rest of the reactions in a systematic way, thereby dramatically increasing the efficiency of the corresponding KMC algorithm. It is also making use of a very rich kinetic model which includes 5 species (H, SiH3, SiH2, SiH, and Si2H5) that participate in 29 reactions. We have applied the new method in simulations of silicon growth under several conditions (in particular, silane fraction in the gas mixture), including those usually realized in actual PECVD technologies. This has allowed us to directly compare against available experimental data for the growth rate, the mesoscale morphology, and the chemical composition of the deposited film as a function of dilution ratio.

Tsalikis, D. G.; Baig, C.; Mavrantzas, V. G.; Amanatides, E.; Mataras, D.

2013-11-01

308

THE JOURNAL OF CHEMICAL PHYSICS 134, 204501 (2011) First-principles calculations of the structural and dynamic properties,  

E-print Network

such as iodine oxides are known to destroy chemical and biological agents efficiently, with potential defense@usc.edu. I2O6 are not available in literature. Thermodynamic data such as thermal expansion, heat capacityTHE JOURNAL OF CHEMICAL PHYSICS 134, 204501 (2011) First-principles calculations of the structural

Southern California, University of

309

Calculating the dermal flux of chemicals with OELs based on their molecular structure: An attempt to assign the skin notation  

Microsoft Academic Search

Our objectives included calculating the permeability coefficient and dermal penetration rates (flux value) for 112 chemicals with occupational exposure limits (OELs) according to the LFER (linear free-energy relationship) model developed using published methods. We also attempted to assign skin notations based on each chemical's molecular structure. There are many studies available where formulae for coefficients of permeability from saturated aqueous

Ma?gorzata Kupczewska-Dobecka; Marek Jakubowski; S?awomir Czerczak

2010-01-01

310

Theoretical Chemical Kinetic Study of the H-Atom Abstraction Reactions from Aldehydes and Acids by ? Atoms and ?H, H?2, and ?H3 Radicals.  

PubMed

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

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

2014-12-26

311

Calculation of the equation of state of QCD at finite chemical and zero temperature  

SciTech Connect

In this paper, we give a direct method for calculating the partition function, and hence the equation of state (EOS) of quantum chromodynamics (QCD) at finite chemical potential and zero temperature. In the EOS derived in this paper the pressure density is the sum of two terms: the first term P({mu})|{sub {mu}}{sub =0} (the pressure density at {mu}=0) is a {mu}-independent constant; the second term, which is totally determined by G{sub R}[{mu}](p) (the renormalized dressed quark propagator at finite {mu}), contains all the nontrivial {mu}-dependence. By applying a general result in the rainbow-ladder approximation of the Dyson-Schwinger approach obtained in our previous study [Phys. Rev. C 71, 015205 (2005)], G{sub R}[{mu}](p) is calculated from the meromorphic quark propagator proposed in [Phys. Rev. D 70, 014014 (2004)]. From this the full analytic expression of the EOS of QCD at finite {mu} and zero T is obtained (apart from the constant term P({mu})|{sub {mu}}{sub =0} which can in principle be calculated from the Cornwall-Jackiw-Tomboulis effective action). A comparison between our EOS and the cold, perturbative EOS of QCD of Fraga, Pisarski, and Schaffner-Bielich is made. It is expected that our EOS can provide a possible new approach for the study of neutron stars.

Zong Hongshi; Sun Weimin [Department of Physics, Nanjing University, Nanjing 210093 (China); Joint Center for Particle, Nuclear Physics and Cosmology, Nanjing 210093 (China)

2008-09-01

312

S3 and S4 abundances and improved chemical kinetic model for the lower atmosphere of Venus  

NASA Astrophysics Data System (ADS)

Mixing ratios of S3 and S4 are obtained from reanalysis of the spectra of true absorption in the visible range retrieved by Maiorov et al. (Maiorov, B.S. et al. [2005]. Solar Syst. Res. 39, 267-282) from the Venera 11 observations. These mixing ratios are fS3 = 11 ± 3 ppt at 3-10 km and 18 ± 3 ppt at 10-19 km, fS4 = 4 ± 4 ppt at 3-10 km and 6 ± 2 ppt at 10-19 km, and show a steep decrease in both S3 and S4 above 19 km. Photolysis rates of S3 and S4 at various altitudes are calculated using the Venera 11 spectra and constant photolysis yields as free parameters. The chemical kinetic model for the Venus lower atmosphere (Krasnopolsky, V.A. [2007]. Icarus 191, 25-37) has been improved by inclusion of the S4 cycle from Yung et al. (Yung, Y.L. et al. [2009]. J. Geophys. Res. 114, E00B34), reduction of the H2SO4 and CO fluxes at the upper boundary of 47 km by a factor of 4 in accord with the recent photochemical models for the middle atmosphere, by using a closed lower boundary for OCS instead of a free parameter for this species at the surface, and some minor updates. Our model with the S4 cycle but without the SO3 + 2 OCS reaction suggested by Krasnopolsky and Pollack (Krasnopolsky, V.A., Pollack, J.B. [1994]. Icarus 109, 58-78) disagrees with the observations of OCS, CO, S3, and S4. However, inclusion of the S4 cycle improves the model fit to all observational constraints. The best-fit activation energy of 7800 K for thermolysis of S4 supports the S4 enthalpy from Mills (Mills, K.C. [1974]. Thermodynamic Data for Inorganic Sulfides, Selenides and Tellurides. Butterworths, London). Chemistry of the Venus lower atmosphere is initiated by disequilibrium products H2SO4 and CO from the middle atmosphere, photolysis of S3 and S4, and thermochemistry in the lowest scale height. The chemistry is mostly driven by sulfur that is formed in a slow reaction SO + SO, produces OCS, and results in dramatic changes in abundances of OCS, CO, and free sulfur allotropes. The SX + OCS fraction is constant and equal to 20 ppm in the lower atmosphere. A source of free sulfur on Venus is in the lower atmosphere, and the calculated S8 mixing ratio is 2.5 ppm above 40 km and results in condensation and formation of aerosol sulfur near 50 km. Therefore the model does not support sulfur as the NUV absorber that was observed by Venera 14 above 58 km. Sources and sinks of the major chemical products in the model are briefly discussed. The model predicts a significant abundance of 3.5 ppb for SO2Cl2 above 25 km. This prediction of SO2Cl2 as well as that in the photochemical model for the middle atmosphere (Krasnopolsky, V.A. [2012]. Icarus 218, 230-246) may stimulate search for this species. A modified concept of the fast and slow sulfur cycles in the middle and lower atmospheres, respectively, has been presented and discussed. Some sources of the model uncertainty are briefly discussed.

Krasnopolsky, Vladimir A.

2013-07-01

313

Features in chemical kinetics. I. Signatures of self-emerging dimensional reduction from a general format of the evolution law  

NASA Astrophysics Data System (ADS)

Simplification of chemical kinetics description through dimensional reduction is particularly important to achieve an accurate numerical treatment of complex reacting systems, especially when stiff kinetics are considered and a comprehensive picture of the evolving system is required. To this aim several tools have been proposed in the past decades, such as sensitivity analysis, lumping approaches, and exploitation of time scales separation. In addition, there are methods based on the existence of the so-called slow manifolds, which are hyper-surfaces of lower dimension than the one of the whole phase-space and in whose neighborhood the slow evolution occurs after an initial fast transient. On the other hand, all tools contain to some extent a degree of subjectivity which seems to be irremovable. With reference to macroscopic and spatially homogeneous reacting systems under isothermal conditions, in this work we shall adopt a phenomenological approach to let self-emerge the dimensional reduction from the mathematical structure of the evolution law. By transforming the original system of polynomial differential equations, which describes the chemical evolution, into a universal quadratic format, and making a direct inspection of the high-order time-derivatives of the new dynamic variables, we then formulate a conjecture which leads to the concept of an "attractiveness" region in the phase-space where a well-defined state-dependent rate function ? has the simple evolution dot{? }= - ? ^2 along any trajectory up to the stationary state. This constitutes, by itself, a drastic dimensional reduction from a system of N-dimensional equations (being N the number of chemical species) to a one-dimensional and universal evolution law for such a characteristic rate. Step-by-step numerical inspections on model kinetic schemes are presented. In the companion paper [P. Nicolini and D. Frezzato, J. Chem. Phys. 138, 234102 (2013)], 10.1063/1.4809593 this outcome will be naturally related to the appearance (and hence, to the definition) of the slow manifolds.

Nicolini, Paolo; Frezzato, Diego

2013-06-01

314

Extreme tunnelling in methylamine dehydrogenase revealed by hybrid QM\\/MM calculations: potential energy surface profile for methylamine and ethanolamine substrates and kinetic isotope effect values  

Microsoft Academic Search

The rate-determining proton transfer step in the amine reduction reaction catalysed by the enzyme methylamine dehydrogenase has been studied using a hybrid quantum mechanical\\/molecular mechanical (QM\\/MM) model. Variational transition state theory, combined with multidimensional tunnelling corrections, has been employed to calculate reaction rate constants, and hence deuterium kinetic isotope effects (KIE). To render these calculations computationally feasible, the electronic structure

Gary Tresadern; Hong Wang; Paul F. Faulder; Neil A. Burton; Ian H. Hillier

2003-01-01

315

Application of the golden section search algorithm in the nonlinear isoconversional calculations to the determination of the activation energy from nonisothermal kinetic conversion data  

Microsoft Academic Search

In this study, the golden section search algorithm in the nonlinear isoconversional calculations to be used for the determination of the activation energy from nonisothermal kinetic conversion data has been introduced. The technique has been applied to two simulated processes (one corresponds to a constant activation energy process, and the other corresponds to a varying activation energy process) and cellulose

Junmeng Cai; Dong Han; Chenxi Chen; Siyu Chen

2010-01-01

316

Kinetics of growth and chemical composition of Fusarium moniliforme cultivated on carob aqueous extract for microbial protein production  

Microsoft Academic Search

The kinetics of growth and the chemical composition ofFusarium moniliforme cultivated on aqueous carob pod extract were investigated. The extract was adjusted to provide 0.5, 1.0, 2.0 and 4.0% carob sugars supplemented with inorganic salts at the ratio: carob sugar: NH4H2PO4: MgSO4.7H2O=1:0.6:0.012. The extract contained 16 mg tannic acid (Folin-Dennis) per g of carob sugar.

B. J. Macris; R. Kokke

1977-01-01

317

Convergence of calculated nuclear magnetic resonance chemical shifts in a protein with respect to quantum mechanical model size  

Microsoft Academic Search

An important aspect of mixed quantum mechanics and molecular mechanics (QM\\/MM) calculation of nuclear magnetic resonance chemical shifts in proteins is the choice of a sufficiently large QM region. This region must be large enough that the electronic structure of the chromophore in the QM\\/MM model is essentially the same as in the complete system. In this work, we calculate

Erin R. Johnson; Gino A. DiLabio

2009-01-01

318

Terahertz absorption spectra of oxidized polyethylene and their analysis by quantum chemical calculations  

NASA Astrophysics Data System (ADS)

Low-density polyethylene, either cross-linked or not, was oxidized and its absorption spectra were measured in the terahertz (THz) range and infrared range. The absorption was increased by the oxidation in the whole THz range. In accord with this, infrared absorption due to carbonyl groups appears. Although these results indicate that the increase in absorption is induced by oxidation, its attribution to resonance or relaxation is unclear. To clarify this point, the vibrational frequencies of three-dimensional polyethylene models with and without carbonyl groups were quantum chemically calculated. As a result, it was clarified that optically inactive skeletal vibrations in polyethylene become active upon oxidation. Furthermore, several absorption peaks due to vibrational resonances are induced by oxidation at wavenumbers from 20 to 100 cm-1. If these absorption peaks are broadened and are superimposed on each other, the absorption spectrum observed experimentally can be reproduced. Therefore, the absorption is ascribable to resonance.

Komatsu, Marina; Hosobuchi, Masashi; Xie, Xiaojun; Cheng, Yonghong; Furukawa, Yukio; Mizuno, Maya; Fukunaga, Kaori; Ohki, Yoshimichi

2014-09-01

319

13C chemical shift tensors of hydrogen bonded amino acids: Relations between experimental and calculated results  

NASA Astrophysics Data System (ADS)

A new interpretation of 13C chemical shift tensors of amino acid carboxyl groups is presented. It is based on NMR results for 50 crystalline complexes of ?-alanine, betaine, glycine and sarcosine with different inorganic and organic acids (XH), X-ray and vibrational data on the same systems and GIAO calculations for model complexes: (CH 3COO-HX) -. Sensitivity of the chemical shift tensors on the amino acid electronic structure, crystal lattice, kind and strength of the hydrogen bonds is characterised in this way. Four categories of the complexes and hydrogen bonds are considered: (i) MO - the molecular complexes with the bonding proton not transferred to the amino acid carboxylate group, COO -⋯H-X; (ii) IP - the hydrogen bonded ion pairs with the bonding proton localised at the amino acid oxygen atom, COO-H⋯X -; (iii) BHB - the homoconjugated amino acid complexes with the bonding proton in the central region of short hydrogen bond, (COO-H-OOC) -; (iv) low-barrier hydrogen bonds with disordered proton position. Properties of the last category bonds are discussed by means of Mulliken theory of CT complexes.

Ilczyszyn, Marek; Godzisz, Dorota; Ilczyszyn, Maria M.; Mierzwicki, Krzysztof

2006-04-01

320

GCKP84-general chemical kinetics code for gas-phase flow and batch processes including heat transfer effects  

NASA Technical Reports Server (NTRS)

A general chemical kinetics code is described for complex, homogeneous ideal gas reactions in any chemical system. The main features of the GCKP84 code are flexibility, convenience, and speed of computation for many different reaction conditions. The code, which replaces the GCKP code published previously, solves numerically the differential equations for complex reaction in a batch system or one dimensional inviscid flow. It also solves numerically the nonlinear algebraic equations describing the well stirred reactor. A new state of the art numerical integration method is used for greatly increased speed in handling systems of stiff differential equations. The theory and the computer program, including details of input preparation and a guide to using the code are given.

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

1984-01-01

321

Turbulent Chemically Reacting Flows According to a Kinetic Theory. Ph.D. Thesis; [statistical analysis/gas flow  

NASA Technical Reports Server (NTRS)

A review of various methods of calculating turbulent chemically reacting flow such as the Green Function, Navier-Stokes equation, and others is presented. Nonequilibrium degrees of freedom were employed to study the mixing behavior of a multiscale turbulence field. Classical and modern theories are discussed.

Hong, Z. C.

1975-01-01

322

Detailed chemical kinetic models for large n-alkanes and iso-alkanes found in conventional and F-T diesel 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 both primary reference fuels, a new capability is now available to model diesel fuel ignition. Additionally, we have developed chemical kinetic models for a whole series of large n-alkanes and a large iso-alkane to represent these chemical classes in fuel surrogates for conventional and future fuels. These chemical kinetic models are used to predict the effect of the aforementioned fuel components on ignition characteristics under conditions found in internal combustion engines.

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

2009-03-09

323

The Fizz Keeper, a Case Study in Chemical Education, Equilibrium, and Kinetics.  

ERIC Educational Resources Information Center

The loss of carbon dioxide from carbonated beverages provides an interesting case of the combination of equilibrium and kinetic principles. Adding air with a commercial device (the Fizz Keeper) has a negligible effect on various equilibria present but will slow diffusion in the gas space of a resealed bottle, decreasing the rate at which…

Howald, Reed A.

1999-01-01

324

The Utility of the Lambert Function W[a exp(a - bt)] in Chemical Kinetics  

ERIC Educational Resources Information Center

The mathematical Lambert function W[a exp(a - bt)] is used to find integrated rate laws for several examples, including simple enzyme and Lindemann-Christiansen-Hinshelwood (LCH) unimolecular decay kinetics. The results derived here for the well-known LCH mechanism as well as for a dimer-monomer reaction mechanism appear to be novel. A nonlinear…

Williams, Brian Wesley

2010-01-01

325

Consequences of the ion beam irradiation on the chemical durability of Thorium Phosphate Diphosphate Kinetics study.  

E-print Network

conditions (fluence, stopping power) then submitted to leaching tests in different media (pH, temperature, complexing reagents, flow rate, ...). The normalized dissolution rates depend significantly on the amorphous). On the contrary, the pre-irradiation of the samples does not affect the kinetic parameters of the dissolution

Paris-Sud XI, Université de

326

A Generalized Pre-Equilibrium Approximation in Chemical and Photophysical Kinetics  

ERIC Educational Resources Information Center

The pre-equilibrium approximation is one of the several useful approximation methods that allows one to go from complex systems of differential equations to simple approximation methods. It is shown that the longtime behavior of systems subjected to pre-equilibrium can be obtained by a simple kinetic reasoning.

Rae, Margaret; Berberan-Santos, Mario N.

2004-01-01

327

An Analogy Using Pennies and Dimes to Explain Chemical Kinetics Concepts  

ERIC Educational Resources Information Center

In this article, the authors present an analogy that uses coins and graphical analysis to teach kinetics concepts and resolve pseudo-first-order rate constants related to transition-metal complexes ligand-solvent exchange reactions. They describe an activity that is directed to upper-division undergraduate and graduate students. The activity…

Cortes-Figueroa, Jose E.; Perez, Wanda I.; Lopez, Jose R.; Moore-Russo, Deborah A.

2011-01-01

328

Kinetics study of solid ammonia borane hydrogen release--modeling and experimental validation for chemical hydrogen storage.  

PubMed

Ammonia borane (AB), NH3BH3, is a promising material for chemical hydrogen storage with 19.6 wt% gravimetric hydrogen capacity of which maximum 16.2 wt% hydrogen can be released via an exothermic thermal decomposition below 200 °C. We have investigated the kinetics of hydrogen release from AB and from an AB-methyl cellulose (AB/MC) composite at temperatures of 160-300 °C using both experiments and modeling. The hydrogen release rate at 300 °C is twice as fast as at 160 °C. The purpose of our study was to show safe hydrogen release without thermal runaway effects and to validate system model kinetics. AB/MC released hydrogen at ?20 °C lower than neat AB and at a faster release rate in that temperature range. Based on the experimental results, the kinetics equations were revised to better represent the growth and nucleation process during decomposition of AB. We explored two different reactor concepts; auger and fixed bed. The current auger reactor concept turned out to not be appropriate, however, we demonstrated safe self-propagation of the hydrogen release reaction of solid AB/MC in a fixed bed reactor. PMID:24647627

Choi, Young Joon; Rönnebro, Ewa C E; Rassat, Scot; Karkamkar, Abhi; Maupin, Gary; Holladay, Jamie; Simmons, Kevin; Brooks, Kriston

2014-05-01

329

Chemical Kinetics, Heat Transfer, and Sensor Dynamics Revisited in a Simple Experiment  

ERIC Educational Resources Information Center

A simple experiment about thermal effects in chemical reactors is described, which can be used to illustrate chemical reactor models, the determination and validation of their parameters, and some simple principles of heat transfer and sensor dynamics. It is based in the exothermic reaction between aqueous solutions of sodium thiosulfate and…

Sad, Maria E.; Sad, Mario R.; Castro, Alberto A.; Garetto, Teresita F.

2008-01-01

330

Uptake and toxicity of polycyclic aromatic hydrocarbons in terrestrial springtails--studying bioconcentration kinetics and linking toxicity to chemical activity.  

PubMed

Passive dosing applies a polymer loaded with test compound(s) to establish and maintain constant exposure in laboratory experiments. Passive dosing with the silicone poly(dimethylsiloxane) was used to control exposure of the terrestrial springtail Folsomia candida to six polycyclic aromatic hydrocarbons (PAHs) in bioconcentration and toxicity experiments. Folsomia candida could move freely on the PAH-loaded silicone, resulting in exposure via air and direct contact. The bioconcentration kinetics indicated efficient uptake of naphthalene, anthracene, and pyrene through air and (near) equilibrium partitioning of these PAHs to lipids and possibly the waxy layer of the springtail cuticle. Toxicities of naphthalene, phenanthrene, and pyrene were related to chemical activity, which quantifies the energetic level and drives spontaneous processes including diffusive biouptake. Chemical activity-response relationships yielded effective lethal chemical activities (La50s) well within the expected range for baseline toxicity (0.01-0.1). Effective lethal body burdens for naphthalene and pyrene exceeded the expected range of 2 to 8 mmol kg(-1) fresh weight, which again indicated the waxy layer to be a sorbing phase. Finally, chemical activities were converted into equilibrium partitioning concentrations in lipids yielding effective lethal concentrations for naphthalene and phenanthrene in good correspondence with the lethal membrane burden for baseline toxicity (40-160?mmol kg(-1) lipid). Passive dosing was a practical approach for tightly controlling PAH exposure, which in turn provided new experimental possibilities and findings. PMID:23147567

Schmidt, Stine Nørgaard; Smith, Kilian Eric Christopher; Holmstrup, Martin; Mayer, Philipp

2013-02-01

331

Stochastic mechano-chemical kinetics of molecular motors: a multidisciplinary enterprise from a physicist's perspective  

E-print Network

A molecular motor is made of either a single macromolecule or a macromolecular complex. Just like their macroscopic counterparts, molecular motors "transduce" input energy into mechanical work. All the nano-motors considered here operate under isothermal conditions far from equilibrium. Moreover, one of the possible mechanisms of energy transduction, called Brownian ratchet, does not even have any macroscopic counterpart. But, molecular motor is not synonymous with Brownian ratchet; a large number of molecular motors execute a noisy power stroke, rather than operating as Brownian ratchet. We review not only the structural design and stochastic kinetics of individual single motors, but also their coordination, cooperation and competition as well as the assembly of multi-module motors in various intracellular kinetic processes. Although all the motors considered here execute mechanical movements, efficiency and power output are not necessarily good measures of performance of some motors. Among the intracellular...

Chowdhury, Debashish

2013-01-01

332

Kinetic models with chemical reactions and nonequilibrium entropy in open systems  

NASA Astrophysics Data System (ADS)

Nonuniform relaxation problems are applied to simulate complex non-equilibrium processes with chemical reactions in open systems. The present paper is a continuation of our studies at a new level, in particular, 2D flows are considered. Besides the slow chemical reactions, the so-called fast reactions are studied. A special attention is paid to studying the behavior of non-equilibrium entropy and entropy flux in such complex open systems.

Aristov, Vladimir; Frolova, Anna; Zabelok, Sergey

2014-12-01

333

Nuclei-selected NMR shielding calculations: A sublinear-scaling quantum-chemical method  

NASA Astrophysics Data System (ADS)

An ab initio method for the direct calculation of NMR shieldings for selected nuclei at the Hartree-Fock and density-functional theory level is presented. Our method shows a computational effort scaling only sublinearly with molecular size, as it is motivated by the physical consideration that the chemical shielding is dominated by its local environment. The key feature of our method is to avoid the conventionally performed calculation of all NMR shieldings but instead to solve directly for specific nuclear shieldings. This has important implications not only for the study of large molecules, but also for the simulation of solvent effects and molecular dynamics, since often just a few shieldings are of interest. Our theory relies on two major aspects both necessary to provide a sublinear scaling behavior: First, an alternative expression for the shielding tensor is derived, which involves the response density matrix with respect to the nuclear magnetic moment instead of the response to the external magnetic field. Second, as unphysical long-range contributions occur within the description of distributed gauge origin methods that do not influence the final expectation value, we present a screening procedure to truncate the B-field dependent basis set, which is crucial in order to ensure an early onset of the sublinear scaling. The screening is in line with the r-2 distance decay of Biot-Savarts law for induced magnetic fields. Our present truncation relies on the introduced concept of "individual gauge shielding contributions" applied to a reformulated shielding tensor, the latter consisting of gauge-invariant terms. The presented method is generally applicable and shows typical speed-ups of about one order of magnitude; moreover, due to the reduced scaling behavior of O(1) as compared to O(N), the wins become larger with increasing system size. We illustrate the validity of our method for several test systems, including ring-current dominated systems and biomolecules with more than 1000 atoms.

Beer, Matthias; Kussmann, Jörg; Ochsenfeld, Christian

2011-02-01

334

Laboratory insights into the chemical and kinetic evolution of several organic molecules under simulated Mars surface UV radiation conditions  

NASA Astrophysics Data System (ADS)

The search for organic carbon at the surface of Mars, as clues of past habitability or remnants of life, is a major science goal of Mars' exploration. Understanding the chemical evolution of organic molecules under current martian environmental conditions is essential to support the analyses performed in situ. What molecule can be preserved? What is the timescale of organic evolution at the surface? This paper presents the results of laboratory investigations dedicated to monitor the evolution of organic molecules when submitted to simulated Mars surface ultraviolet radiation (190-400 nm), mean temperature (218 ± 2 K) and pressure (6 ± 1 mbar) conditions. Experiments are done with the MOMIE simulation setup (for Mars Organic Molecules Irradiation and Evolution) allowing both a qualitative and quantitative characterization of the evolution the tested molecules undergo (Poch, O. et al. [2013]. Planet. Space Sci. 85, 188-197). The chemical structures of the solid products and the kinetic parameters of the photoreaction (photolysis rate, half-life and quantum efficiency of photodecomposition) are determined for glycine, urea, adenine and chrysene. Mellitic trianhydride is also studied in order to complete a previous study done with mellitic acid (Stalport, F., Coll, P., Szopa, C., Raulin, F. [2009]. Astrobiology 9, 543-549), by studying the evolution of mellitic trianhydride. The results show that solid layers of the studied molecules have half-lives of 10-103 h at the surface of Mars, when exposed directly to martian UV radiation. However, organic layers having aromatic moieties and reactive chemical groups, as adenine and mellitic acid, lead to the formation of photoresistant solid residues, probably of macromolecular nature, which could exhibit a longer photostability. Such solid organic layers are found in micrometeorites or could have been formed endogenously on Mars. Finally, the quantum efficiencies of photodecomposition at wavelengths from 200 to 250 nm, determined for each of the studied molecules, range from 10-2 to 10-6 molecule photon-1 and apply for isolated molecules exposed at the surface of Mars. These kinetic parameters provide essential inputs for numerical modeling of the evolution of Mars' current reservoir of organic molecules. Organic molecules adsorbed on martian minerals may have different kinetic parameters and lead to different endproducts. The present study paves the way for the interpretation of more complex simulation experiments where organics will be mixed with martian mineral analogs.

Poch, O.; Kaci, S.; Stalport, F.; Szopa, C.; Coll, P.

2014-11-01

335

[Determination of trace amounts of nitrite and its chemical reaction kinetics].  

PubMed

A catalytic kinetic spectrophotometric method for the determination of nitrite, NO2(-)-S2O8(2-)-MR, was developed. It is based on the fading reaction of methyl red (MR) oxidized by potassium persulfate which can be catalyzed by NO2- in the medium of dilute HCl. The optimum experimental conditions were gained by combining single factor experiments with orthogonal experiments. Calibration curve, detection limit, precision, and anti-interference under the optimum experimental conditions were researched. Its kinetics principles and parameters were discussed. Its quantitative principle was investigated. The results show that the optimum experimental conditions of this method should be as follows: 1.0 mL 0.3 mol x L(-1) HCl, 1.0 mL 0.01 mol x L(-1) K2S2O8, 0.6 mL 0.2 g x L(-1) MR, reaction temperature 80 degrees C and reaction time 9 min. The principles for the quantitative determination of trace nitrite is that variation of MR concentration at the maximum absorption wavelength of 518 nm, ln(A0/A), shows a good linear relationship with the concentration of NO2- under the optimum experimental conditions. Its determination range is 0.01-0.80 mg x L(-1) and its detection limit is 0.007 mg x L(-1). The kinetic characteristics are that the reaction order in NO2- is 1 and the fading reaction is a pseudo first order reaction. Its apparent activation energy is 85.04 kJ x mol(-1). Its apparent rate constant is 0.021 4 min(-1), and the half-life is 32.39 min at 80 degrees C. The kinetic principle is that the variation of MR concentration is directly proportional to the concentration of NO2-, ln(A0/A) = kc(NO2-). This new method for the determination of trace nitrite has never previously been reported in the published literature so far. It is highly sensitive and selective. Most of the common ions don't interfere with the determination of nitrite. This method has the advantages of convenient operation and the regents used are cheap and nontoxic. It was applied to the determination of trace nitrite in food and water samples with satisfactory results. PMID:25358175

Luo, Zhi-yong; Zheng, Huai-li

2014-06-01

336

Chemical Kinetic Data Base for Combustion Chemistry. Part I. Methane and Related Compounds  

Microsoft Academic Search

This document contains evaluated data on the kinetics and thermodynamic properties of species that are of importance in methane pyrolysis and combustion. Specifically, the substances considered include H, H2, O, O2, OH, HO2, H2O2, H2O, CH4, C2H6, HCHO, CO2, CO, HCO, CH3, C2H5, C2H4, C2H3, C2H2, C2H, CH3CO, CH3O2, CH3O, singlet CH2, and triplet CH2. All possible reactions are considered.

W. Tsang; R. F. Hampson

1986-01-01

337

Elucidating triplet-sensitized photolysis mechanisms of sulfadiazine and metal ions effects by quantum chemical calculations.  

PubMed

Sulfadiazine (SDZ) mainly proceeds triplet-sensitized photolysis with dissolved organic matter (DOM) in the aquatic environment. However, the mechanisms underlying the triplet-sensitized photolysis of SDZ with DOM have not been fully worked out. In this study, we investigated the mechanisms of triplet-sensitized photolysis of SDZ(0) (neutral form) and SDZ(-) (anionic form) with four DOM analogues, i.e., fluorenone (FL), thioxanthone (TX), 2-acetonaphthone (2-AN), and 4-benzoylbenzoic acid (CBBP), and three metal ions (i.e., Mg(2+), Ca(2+), and Zn(2+)) effects using quantum chemical calculations. Results indicated that the triplet-sensitized photolysis mechanism of SDZ(0) with FL, TX, and 2-AN was hydrogen transfer, and with CBBP was electron transfer along with proton transfer (for complex SDZ(0)-CBBP2) and hydrogen transfer (for complex SDZ(0)-CBBP1). The triplet-sensitized photolysis mechanisms of SDZ(-) with FL, TX, and CBBP was electron transfer along with proton transfer, and with 2-AN was hydrogen transfer. The triplet-sensitized photolysis product of both SDZ(0) and SDZ(-) was a sulfur dioxide extrusion product (4-(2-iminopyrimidine-1(2H)-yl)aniline), but the formation routs of the products for SDZ(0) and SDZ(-) were different. In addition, effects of the metal ions on the triplet-sensitized photolysis of SDZ(0) and SDZ(-) were different. The metal ions promoted the triplet-sensitized photolysis of SDZ(0), but inhibited the triplet-sensitized photolysis of SDZ(-). PMID:25496743

Wang, Se; Song, Xuedan; Hao, Ce; Gao, Zhanxian; Chen, Jingwen; Qiu, Jieshan

2015-03-01

338

Electronically excited states of membrane fluorescent probe 4-dimethylaminochalcone. Results of quantum chemical calculations.  

PubMed

Quantum-chemical calculations of ground and excited states for membrane fluorescent probe 4-dimethylaminochalcone (DMAC) in vacuum were performed. Optimized geometries and dipole moments for lowest-lying singlet and triplet states were obtained. The nature of these electronic transitions and the relaxation path in the excited states were determined; changes in geometry and charge distribution were assessed. It was shown that in vacuum the lowest existed level is of (n, ?*) nature, and the closest to it is the level of (?, ?*) nature; the energy gap between them is narrow. This led to an effective (1)(?, ?*) ?(1)(n, ?*) relaxation. After photoexcitation the molecule undergoes significant transformations, including changes in bond orders, pyramidalization angle of the dimethylamino group, and planarity of the molecule. Its dipole moment rises from 5.5 Debye in the ground state to 17.1 Debye in the (1)(?, ?*) state, and then falls to 2 Debye in the (1)(n, ?*) state. The excited (1)(n, ?*) state is a short living state; it has a high probability of intersystem crossing into the (3)(?, ?*) triplet state. This relaxation path explains the low quantum yield of DMAC fluorescence in non-polar media. It is possible that (3)(?, ?*) is responsible for observed DMAC phosphorescence. PMID:21487602

Romanov, Alexey N; Gularyan, Samvel K; Polyak, Boris M; Sakovich, Ruslan A; Dobretsov, Gennady E; Sarkisov, Oleg M

2011-05-28

339

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

PubMed

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 microm where water is the main absorber and 6.45 microm where both water and protein absorb. The picosecond pulses of the superpulse are treated as a train of impulses. We find that the heating rates are sufficient to superheat the outer saline layers on the nanosecond time scale, leading to explosive vaporization. We also find that competition between the layer-specific heating rates and thermal diffusion results in a wavelength-dependent separation in layer temperatures. We consider the onset of both chemical bond breaking and the helix-coil transition of protein prior to vaporization in terms of the thermal, chemical, and structural properties of the system as well as laser wavelength and pulse structure. There is no evidence for thermal bond breaking on these time scales. At 6.45 microm, but not 3 microm, there is evidence for a significant helix-coil transition. While the native protein is ductile, the denatured protein exhibits brittle fracture. This model provides a dynamic mechanism to account for the preferential ablative properties observed with FEL radiation tuned near 6.45 microm. PMID:12188758

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

2002-06-01

340

Structure of molecular tweezer complexes in the solid state: NMR experiments, X-ray investigations, and quantum chemical calculations.  

PubMed

The structure of supramolecular complexes formed by a naphthalene-spaced tweezer molecule as host and 1,4-dicyanobenzene (DCNB), 1,2,4,5-tetracyanobenzene (TCNB), and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as aromatic, electron-deficient guests is investigated by solid-state NMR and X-ray diffraction measurements. Quantum chemical calculations using linear scaling methods are applied to predict and to assign the 1H NMR chemical shifts of the complexes. By combining experiment and theory, insights into intra- and intermolecular effects influencing the proton chemical shifts of the host-guest system are provided in the solid state. PMID:17263413

Schaller, Torsten; Büchele, Uta P; Klärner, Frank-Gerrit; Bläser, Dieter; Boese, Roland; Brown, Steven P; Spiess, Hans Wolfgang; Koziol, Felix; Kussmann, Jörg; Ochsenfeld, Christian

2007-02-01

341

Sensitivity of Polar Stratospheric Ozone Loss to Uncertainties in Chemical Reaction Kinetics  

NASA Technical Reports Server (NTRS)

Several recent observational and laboratory studies of processes involved in polar stratospheric ozone loss have prompted a reexamination of aspects of our understanding for this key indicator of global change. To a large extent, our confidence in understanding and projecting changes in polar and global ozone is based on our ability to simulate these processes in numerical models of chemistry and transport. The fidelity of the models is assessed in comparison with a wide range of observations. These models depend on laboratory-measured kinetic reaction rates and photolysis cross sections to simulate molecular interactions. A typical stratospheric chemistry mechanism has on the order of 50- 100 species undergoing over a hundred intermolecular reactions and several tens of photolysis reactions. The rates of all of these reactions are subject to uncertainty, some substantial. Given the complexity of the models, however, it is difficult to quantify uncertainties in many aspects of system. In this study we use a simple box-model scenario for Antarctic ozone to estimate the uncertainty in loss attributable to known reaction kinetic uncertainties. Following the method of earlier work, rates and uncertainties from the latest laboratory evaluations are applied in random combinations. We determine the key reactions and rates contributing the largest potential errors and compare the results to observations to evaluate which combinations are consistent with atmospheric data. Implications for our theoretical and practical understanding of polar ozone loss will be assessed.

Kawa, S. Randolph; Stolarksi, Richard S.; Douglass, Anne R.; Newman, Paul A.

2008-01-01

342

Sensitivity of Polar Stratospheric Ozone Loss to Uncertainties in Chemical Reaction Kinetics  

NASA Technical Reports Server (NTRS)

Several recent observational and laboratory studies of processes involved in polar stratospheric ozone loss have prompted a reexamination of aspect of out understanding for this key indicator of global change. To a large extent, our confidence in understanding and projecting changes in polar and global ozone is based on our ability to to simulate these process in numerical models of chemistry and transport. These models depend on laboratory-measured kinetic reaction rates and photlysis cross section to simulate molecular interactions. In this study we use a simple box-model scenario for Antarctic ozone to estimate the uncertainty in loss attributable to known reaction kinetic uncertainties. Following the method of earlier work, rates and uncertainties from the latest laboratory evaluation are applied in random combinations. We determine the key reaction and rates contributing the largest potential errors and compare the results to observations to evaluate which combinations are consistent with atmospheric data. Implications for our theoretical and practical understanding of polar ozone loss will be assessed.

Kawa, S. Randolph; Stolarski, Richard S.; Douglass, Anne R.; Newman, Paul A.

2008-01-01

343

Prediction of Hydrolysis Pathways and Kinetics for Antibiotics under Environmental pH Conditions: A Quantum Chemical Study on Cephradine.  

PubMed

Understanding hydrolysis pathways and kinetics of many antibiotics that have multiple hydrolyzable functional groups is important for their fate assessment. However, experimental determination of hydrolysis encounters difficulties due to time and cost restraint. We employed the density functional theory and transition state theory to predict the hydrolysis pathways and kinetics of cephradine, a model of cephalosporin with two hydrolyzable groups, two ionization states, two isomers and two nucleophilic attack directions. Results showed that the hydrolysis of cephradine at pH = 8.0 proceeds via opening of the ?-lactam ring followed by intramolecular amidation. The predicted rate constants at different pH conditions are of the same order of magnitude as the experimental values, and the predicted products are confirmed by experiment. This study identified a catalytic role of the carboxyl group in the hydrolysis, and implies that the carboxyl group also plays a catalytic role in the hydrolysis of other cephalosporin and penicillin antibiotics. This is a first attempt to quantum chemically predict hydrolysis of an antibiotic with complex pathways, and indicates that to predict hydrolysis products under the environmental pH conditions, the variation of the rate constants for different pathways with pH should be evaluated. PMID:25590945

Zhang, Haiqin; Xie, Hongbin; Chen, Jingwen; Zhang, Shushen

2015-02-01

344

Enskog’s kinetic theory of dense gases for chemically reacting binary mixtures, II: Light scattering and sound propagation  

NASA Astrophysics Data System (ADS)

Enskog’s kinetic theory for a symmetric moderately dense reaction A+A?B+B is used to determine Fick’s and Fourier’s law. The transport coefficients of diffusion, thermal-diffusion rate and thermal conductivity are represented graphically for endothermic and exothermic reactions and are analyzed as a function of the activation energy and of the density of the mixture. The Onsager reciprocity relations are numerically investigated and verified. The problems related to sound propagation and light scattering are investigated for such a mixture and it is shown that the influence of chemical reactions on phase velocity, attenuation coefficient and light scattering spectra is more pronounced for rarefied gases although there is a considerable change in these quantities as the mixture becomes denser.

Silva, Adriano W.; Alves, Giselle M.; Marques, Wilson; Kremer, Gilberto M.

2009-02-01

345

Ion Exchange Equilibrium and Kinetic Properties of Polyacrylate Films and Applications to Chemical Analysis and Environmental Decontamination  

NASA Technical Reports Server (NTRS)

One of the goals of the original proposal was to study how cross-linking affects the properties of an ion exchange material(IEM) developed at Lewis Research Center. However, prior to the start of this work, other workers at LERC investigated the effect of cross-linking on the properties of this material. Other than variation in the ion exchange capacity, the chemical characteristics were shown to be independent of the cross-linking agent, and the degree of cross-linking. New physical forms of the film were developed (film, supported film, various sizes of beads, and powder). All showed similar properties with respect to ion exchange equilibria but the kinetics of ion exchange depended on the surface area per unit mass; the powder form of the IEM exchanging much more rapidly than the other forms. The research performed under this grant was directed towards the application of the IEM to the analysis of metal ions at environmental concentrations.

Tanner, Stephen P.

1997-01-01

346

Modulation of a Ligand's Energy Landscape and Kinetics by the Chemical Environment  

E-print Network

-competent conformations. While Mg2+ is not cocrystallized in the UDP-GlcNAc 2-epimerase complex, the selectively stabilized Mg2+ /UDP-GlcNAc complex may be a template for the bound state, and Mg2+ may accompany the binding of the binding pocket5 in ribozymes. Understanding which effect the chemical environment has on the conformations

347

GRAD'S CLOSURE IN THE KINETIC THEORY OF A CHEMICALLY REACTING GAS  

E-print Network

, which accounts for the threshold effects in the exothermic reaction due to the activation energy for the chemical process. This determines also the cross section of the endothermic reaction by means here to the isotropic cross section for exothermic reaction 9 12 34(g) = 1 4 12 34 g 1 - 2 g2 U(g2 - 2

Spiga, Giampiero

348

INTERACTION BETWEEN GAS DIFFUSION AND MULTISTABLE HETEROGENEOUS CHEMICAL KINETICS IN C=C COMPOSITE  

E-print Network

nanotexture transition is addressed in terms of a possible hysteretical chemical deposition mechanism, based of ceramic or carbon #12;bers, an interphase which coats them (usually carbon or hexagonal boron nitride mechanical and optical properties. A key issue in pyrocarbon CVD/CVI is the control of pyrocarbon

Recanati, Catherine

349

Chemical kinetics and transport processes in supercritical fluid extraction of coal. Final report, August 10, 1990--December 30, 1992  

SciTech Connect

The overall objective of this project was to study the supercritical fluid extraction of hydrocarbons from coal. Beyond the practical concern of deriving products from coal, the research has provided insights into the structure, properties, and reactivities of coal. Information on engineering fundamentals of coal thermolysis and extraction, including physical and chemical processes, is presented in this final report. To accomplish the goals of the project we developed continuous-flow experiments for fixed-bed samples of coal that allow two types of analysis of the extract: continuous spectrophotometric absorbance measurements of the lumped concentration of extract, and chromatographic determinations of molecular-weight distributions as a function of time. Thermolysis of coal yields a complex mixture of many extract products whose molecular-weight distribution (MWD) varies with time for continuous-flow, semibatch experiments. The flow reactor with a differential, fixed bed of coal particles contacted by supercritical t-butanol was employed to provide dynamic MWD data by means of HPLC gel permeation chromatography of the extract. The experimental results, time-dependent MWDs of extract molecules, were interpreted by a novel mathematical model based on continuous-mixture kinetics for thermal cleavage of chemical bonds in the coal network. The parameters for the MWDs of extractable groups in the coal and the rate constants for one- and two-fragment reaction are determined from the experimental data. The significant effect of temperature on the kinetics of the extraction was explained in terms of one- and two-fragment reactions in the coal.

McCoy, B.J.; Smith, J.M.; Wang, M.; Zhang, C.J.

1993-02-01

350

On the interpretation of the inverted kinetics equation and space-time calculations of the effectiveness of the VVER-1000 reactor scram system  

NASA Astrophysics Data System (ADS)

In the present paper, an attempt is made to analyze the accuracy of calculating the effectiveness of the VVER-1000 reactor scram system by means of the inverted solution of the kinetics equation (ISKE). In the numerical studies in the intellectual ShIPR software system, the actuation of the reactor scram system with the possible jamming of one of the two most effective rods is simulated. First, the connection of functionals calculated in the space-time computation in different approximations with the kinetics equation is considered on the theoretical level. The formulas are presented in a manner facilitating their coding. Then, the results of processing of several such functions by the ISKE are presented. For estimating the effectiveness of the VVER-1000 reactor scram system, it is proposed to use the measured currents of ionization chambers (IC) jointly with calculated readings of IC imitators. In addition, the integral of the delayed neutron (DN) generation rate multiplied by the adjoint DN source over the volume of the reactor, calculated for the instant of time when insertion of safety rods ends, is used. This integral is necessary for taking into account the spatial reactivity effects. Reasonable agreement was attained for the considered example between the effectiveness of the scram system evaluated by this method and the values obtained by steady-state calculations as the difference of the reciprocal effective multiplication factors with withdrawn and inserted control rods. This agreement was attained with the use of eight-group DN parameters.

Zizin, M. N.; Ivanov, L. D.

2013-12-01

351

Thermal oxidation of single-crystal silicon carbide - Kinetic, electrical, and chemical studies  

NASA Technical Reports Server (NTRS)

This paper presents kinetic data from oxidation studies of the polar faces for 3C and 6H SiC in wet and dry oxidizing ambients. Values for the linear and parabolic rate constants were obtained, as well as preliminary results for the activation energies of the rate constants. Examples are presented describing how thermal oxidation can be used to map polytypes and characterize defects in epitaxial layers grown on low tilt angle 6H SiC substrates. Interface widths were measured using Auger electron spectroscopy (AES) with Ar ion beam depth profiling and variable angle spectroscopic ellipsometry (VASE) with effective medium approximation (EMA) models. Preliminary electrical measurements of MOS capacitors are also presented.

Petit, J. B.; Neudeck, P. G.; Matus, L. G.; Powell, J. A.

1992-01-01

352

The Spontaneous Hydrolysis of Methyl Chloroformate: A Physical Chemistry Experiment for Teaching Techniques in Chemical Kinetics  

NASA Astrophysics Data System (ADS)

As an experiment for the undergraduate physical chemistry laboratory, the spontaneous hydrolysis of methyl chloroformate has the following attractive features: the reagent is inexpensive, and its stock solution in acetonitrile can be safely handled; the experiment requires very little preparation and can be carried out in a single 4-hour laboratory period; data acquisition can be performed either manually or with a microcomputer. The concentration of one of the reaction products, HCl, is determined either directly by pH measurement or indirectly by conductance measurement or by following the decrease in absorbance of the basic form of the indicator bromophenol blue. The present experiment is used to exemplify the scope and variety of techniques that can be employed for rate measurements and to demonstrate important features of first-order kinetics. These subjects are usually addressed in the specialized literature.

El Seoud, Omar A.; Takashima, Keiko

1998-12-01

353

HYPER-FORM—A Hypercard® program for Macintosh® microcomputers to calculate mineral formulae from electron microprobe and wet chemical analysis  

NASA Astrophysics Data System (ADS)

The program HYPER-FORM permits the input and calculation of a mineral formula from wet chemical and electron microprobe analysis. It includes autosaving of data, search routines, and other database functions. The calculated formula can be exported to wordprocessing programs such as MacWrite® or Microsoft Word® and can be edited as required. It also is possible to export the calculated data to graphic programs such as Cricket Graph® or Kaleidagraph® for a graphic representation of the data. HYPER-FORM is an interactive program written in HyperTalk™ (HyperCard® environment) and is designed to correspond to the Macintosh® interface.

de Bjerg, Silvia C.; Mogessie, Aberra; Bjerg, Ernesto

1992-07-01

354

Quantum-chemical calculations and electron diffraction study of the equilibrium molecular structure of vitamin K3  

NASA Astrophysics Data System (ADS)

The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K3) having C s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.

Khaikin, L. S.; Tikhonov, D. S.; Grikina, O. E.; Rykov, A. N.; Stepanov, N. F.

2014-05-01

355

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

E-print Network

A combined quantum-classical dynamics method for calculating thermal rate constants of chemical February 1992) We present a combined quantum-classical-stochastic dynamics method based on the flux to combine classical and quantum dynamics have been pro- posed and have shown some encouraging results

Truong, Thanh N.

356

Chemical speciation of metal complexes from chemical shift calculations: the interaction of 2-amino-N-hydroxypropanamide with V(V) in aqueous solution.  

PubMed

The chemical speciation of 2-amino-N-hydroxypropanamide (?-alaninohydroxamic acid, HL) and vanadium (V) in aqueous solution has been investigated through calculations of the thermodynamic properties and the (51)V nuclear magnetic resonance (NMR) chemical shifts of the species formed at equilibrium. The results have been compared directly with the experimental (51)V NMR data. The (51)V NMR chemical shifts have been calculated by using a density functional theory (DFT) approach accounting for relativistic corrections and solvent effects. All tautomers of the 1:1 and 1:2 VO2(+)/?-ala complexes with different degrees of protonation have been calculated and thermodynamic and structural properties are presented for the most stable species. The system is better modeled as tautomeric equilibria, and species lying down in the range of 10 kcal·mol(-1) cannot be neglected at the BP/TZ2P/COSMO approach. In fact, the metal complex speciation in aqueous solution should not be investigated based solely on the thermodynamic analysis, but together with spectroscopic calculations such as NMR. PMID:23971999

Duarte, Hélio Anderson; Vankova, Nina; Ferreira, Isabella Pires; Paniago, Eucler B; Heine, Thomas

2013-10-01

357

Nuclear magnetic resonance, vibrational spectroscopic studies, physico-chemical properties and computational calculations on (nitrophenyl) octahydroquinolindiones by DFT method  

NASA Astrophysics Data System (ADS)

In the present study, 2?-nitrophenyloctahydroquinolinedione and its 3?-nitrophenyl isomer were synthesized and characterized by FT-IR, FT-Raman, 1H NMR and 13C NMR spectroscopy. The molecular geometry, vibrational frequencies, 1H and 13C NMR chemical shift values of the synthesized compounds in the ground state have been calculated by using the density functional theory (DFT) method with the 6-311++G (d,p) basis set and compared with the experimental data. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution using GAR2PED programme. Isotropic chemical shifts for 1H and 13C NMR were calculated using gauge-invariant atomic orbital (GIAO) method. The experimental vibrational frequencies, 1H and 13C NMR chemical shift values were found to be in good agreement with the theoretical values. On the basis of vibrational analysis, molecular electrostatic potential and the standard thermodynamic functions have been investigated.

Pasha, M. A.; Siddekha, Aisha; Mishra, Soni; Azzam, Sadeq Hamood Saleh; Umapathy, S.

2015-02-01

358

Measurement of HO2 chemical kinetics with a new detection method  

NASA Technical Reports Server (NTRS)

Reaction rate constants of HO2+O3 were measured at various temperatures using a newly developed HO2 detection method. HO2 was detected by the OH(A-X) emission produced from photodissociative excitation of HO2 at 147 nm. In order to examine the possible interference of other emitting species with the HO2 detection, the photoexcitation processes of all the chemical species existing in the discharge flow tube were also investigated. The results are summarized.

Lee, Long C.; Suto, Masako

1986-01-01

359

Kinetic and thermodynamic studies on biosorption of Cu(II) by chemically modified orange peel  

Microsoft Academic Search

Cu(II) biosorption by orange peel that was chemically modified with sodium hydroxide and calcium chloride was investigated. The effects of temperature, contact time, initial concentration of metal ions and pH on the biosorption of Cu(II) ions were assessed. Thermodynamic parameters including change of free energy), (?G?), enthalpy (?H?) and entropy (?S?) during the biosorption were determined. The results show that

Ning-chuan FENG; Xue-yi GUO; Sha LIANG

2009-01-01

360

Mechanism and kinetics of the chemical interaction between liquid aluminium and silicon-carbide single crystals  

Microsoft Academic Search

Previous investigations of phase equilibria in the ternary system Al-C-Si have shown that silicon carbide is attacked by pure aluminium at temperatures higher or equal to 923±3 K and up to about 1600 K, according to the chemical reaction: 4Al+3SiC ? Al4C3+3Si In the present work, a study has been carried out to obtain more detailed information on the mechanism

J. C. Viala; F. Bosselet; V. Laurent; Y. Lepetitcorps

1993-01-01

361

A comprehensive experimental and detailed chemical kinetic modelling study of 2,5-dimethylfuran pyrolysis and oxidation  

PubMed Central

The pyrolytic and oxidative behaviour of the biofuel 2,5-dimethylfuran (25DMF) has been studied in a range of experimental facilities in order to investigate the relatively unexplored combustion chemistry of the title species and to provide combustor relevant experimental data. The pyrolysis of 25DMF has been re-investigated in a shock tube using the single-pulse method for mixtures of 3% 25DMF in argon, at temperatures from 1200–1350 K, pressures from 2–2.5 atm and residence times of approximately 2 ms. Ignition delay times for mixtures of 0.75% 25DMF in argon have been measured at atmospheric pressure, temperatures of 1350–1800 K at equivalence ratios (?) of 0.5, 1.0 and 2.0 along with auto-ignition measurements for stoichiometric fuel in air mixtures of 25DMF at 20 and 80 bar, from 820–1210 K. This is supplemented with an oxidative speciation study of 25DMF in a jet-stirred reactor (JSR) from 770–1220 K, at 10.0 atm, residence times of 0.7 s and at ? = 0.5, 1.0 and 2.0. Laminar burning velocities for 25DMF-air mixtures have been measured using the heat-flux method at unburnt gas temperatures of 298 and 358 K, at atmospheric pressure from ? = 0.6–1.6. These laminar burning velocity measurements highlight inconsistencies in the current literature data and provide a validation target for kinetic mechanisms. A detailed chemical kinetic mechanism containing 2768 reactions and 545 species has been simultaneously developed to describe the combustion of 25DMF under the experimental conditions described above. Numerical modelling results based on the mechanism can accurately reproduce the majority of experimental data. At high temperatures, a hydrogen atom transfer reaction is found to be the dominant unimolecular decomposition pathway of 25DMF. The reactions of hydrogen atom with the fuel are also found to be important in predicting pyrolysis and ignition delay time experiments. Numerous proposals are made on the mechanism and kinetics of the previously unexplored intermediate temperature combustion pathways of 25DMF. Hydroxyl radical addition to the furan ring is highlighted as an important fuel consuming reaction, leading to the formation of methyl vinyl ketone and acetyl radical. The chemically activated recombination of H?2 or CH3?2 with the 5-methyl-2-furanylmethyl radical, forming a 5-methyl-2-furylmethanoxy radical and ?H or CH3? radical is also found to exhibit significant control over ignition delay times, as well as being important reactions in the prediction of species profiles in a JSR. Kinetics for the abstraction of a hydrogen atom from the alkyl side-chain of the fuel by molecular oxygen and H?2 radical are found to be sensitive in the estimation of ignition delay times for fuel-air mixtures from temperatures of 820–1200 K. At intermediate temperatures, the resonantly stabilised 5-methyl-2-furanylmethyl radical is found to predominantly undergo bimolecular reactions, and as a result sub-mechanisms for 5-methyl-2-formylfuran and 5-methyl-2-ethylfuran, and their derivatives, have also been developed with consumption pathways proposed. This study is the first to attempt to simulate the combustion of these species in any detail, although future refinements are likely necessary. The current study illustrates both quantitatively and qualitatively the complex chemical behavior of what is a high potential biofuel. Whilst the current work is the most comprehensive study on the oxidation of 25DMF in the literature to date, the mechanism cannot accurately reproduce laminar burning velocity measurements over a suitable range of unburnt gas temperatures, pressures and equivalence ratios, although discrepancies in the experimental literature data are highlighted. Resolving this issue should remain a focus of future work. PMID:24273333

Somers, Kieran P.; Simmie, John M.; Gillespie, Fiona; Conroy, Christine; Black, Gráinne; Metcalfe, Wayne K.; Battin-Leclerc, Frédérique; Dirrenberger, Patricia; Herbinet, Olivier; Glaude, Pierre-Alexandre; Dagaut, Philippe; Togbé, Casimir; Yasunaga, Kenji; Fernandes, Ravi X.; Lee, Changyoul; Tripathi, Rupali; Curran, Henry J.

2013-01-01

362

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

SciTech Connect

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 diesel and other transportation fuels from biomass, coal and natural gas. F-T diesel fuels are expected to be similar to F-T jet fuels which are commonly comprised of iso-alkanes with some n-alkanes (Smith and Bruno, 2008). Thus, n-alkanes and iso-alkanes are common chemical classes in these conventional and future fuels. This paper reports on the development of chemical kinetic models of large n-alkanes and iso-alkanes to represent these chemical classes in conventional and future fuels. Two large iso-alkanes are 2,2,4,4,6,8,8-heptamethylnonane, which is a primary reference fuel for diesel, and isooctane, a primary reference fuel for gasoline. Other iso-alkanes are branched alkanes with a single methyl side chain, typical of most F-T fuels. The chemical kinetic models are then used to predict the effect of these fuel components on ignition characteristics under conditions found in internal combustion engines.

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

2008-12-15

363

Integrated design of Nb-based superalloys: Ab initio calculations, computational thermodynamics and kinetics, and experimental results  

Microsoft Academic Search

An optimal integration of modern computational tools and efficient experimentation is presented for the accelerated design of Nb-based superalloys. Integrated within a systems engineering framework, we have used ab initio methods along with alloy theory tools to predict phase stability of solid solutions and intermetallics to accelerate assessment of thermodynamic and kinetic databases enabling comprehensive predictive design of multicomponent multiphase

G. Ghosh; G. B. Olson

2007-01-01

364

Chemical Kinetic Data Base for Propellant Combustion I. Reactions Involving NO, NO2, HNO, HNO2, HCN and N2O  

Microsoft Academic Search

This publication contains evaluated chemical kinetic data on a number of single step elementary reactions involving small polyatomic molecules which are of importance in propellant combustion. The work involves the collection and evaluation of mechanistic and rate information and the use of various methods for the extrapolation and estimation of rate data where information does not exist. The conditions covered

Wing Tsang; John T. Herron

1991-01-01

365

Data Pooling in a Chemical Kinetics Experiment: The Aquation of a Series of Cobalt(III) Complexes--A Discovery Chemistry Experiment  

ERIC Educational Resources Information Center

An experiment in chemical kinetics as part of our Discovery Chemistry curriculum is described. Discovery Chemistry is a pedagogical philosophy that makes the laboratory the key center of learning for students in their first two years of undergraduate instruction. Questions are posed in the pre-laboratory discussion and assessed using pooled…

Herrick, Richard S.; Mills, Kenneth V.; Nestor, Lisa P.

2008-01-01

366

The chemical kinetics and thermodynamics of sodium species in oxygen-rich hydrogen flames  

NASA Technical Reports Server (NTRS)

Results are presented which, it is claimed, lead to a correction of previous misconceptions over the relative importance and kinetics of NaO2. It is shown that its rapid conversion to NaO and NaOH is such that it can severely perturb the NaOH/Na ratio and produce significant concentration overshoots over that predicted from the balance of the reaction of Na with H2O. This becomes increasingly the case in flames of large O2 concentrations and temperatures below 2500 K; and the corresponding large rate constants for the termolecular formation of the other alkali peroxides imply that similar considerations will be necessary for them. Depending on the rate constants for the exothermic conversions of MO2 to MO or MOH, the steady-state concentrations of MO2 could be more or less significant than for sodium. Owing to numerous reactions that produce these conversions, the MOH species will probably be the dominant species in all cases in oxygen-rich hydrogen or hydrocarbon flames, with MO concentrations at not greater than 1 percent of the bound metal.

Hynes, A. J.; Steinberg, M.; Schofield, K.

1984-01-01

367

Chemical Kinetics and Properties from the Radiation Chemistry Data Center (RCDC)  

DOE Data Explorer

The Radiation Chemistry Data Center (RCDC) is a focal point for the compilation and evaluation of kinetic, spectroscopic and thermodynamic data for processes in solution involving reactive intermediates, including free radicals and excited states. These data are primarily derived from the published literature on radiation chemistry and quantitative aspects of photochemistry. The compilations are presented as individual groups of pages corresponding to each published work. Each compilation consists of an introductory article, describing the scope of the compilation, with the considerations and criteria for data evaluation discussed. Nomenclature for the compilation is also described here. For several compilations the introduction is followed by one or more pages of links organized as an index or table of contents to the individual pages of the compilation. These links allow the browsing of the data by species name. Each page tabulates the reaction of a transient species with a particular reactant. RCDC was established at the Notre Dame Radiation Laboratory in 1965, as part of the National Standard Reference Data System.

368

Object Kinetic Monte Carlo calculations of irradiated Fe-Cr dilute alloys: The effect of the interaction radius between substitutional Cr and self-interstitial Fe  

NASA Astrophysics Data System (ADS)

Object Kinetic Monte Carlo models allow for the study of the evolution of the damage created by irradiation to time scales that are comparable to those achieved experimentally. Therefore, the essential Object Kinetic Monte Carlo parameters can be validated through comparison with experiments. However, this validation is not trivial since a large number of parameters is necessary, including migration energies of point defects and their clusters, binding energies of point defects in clusters, as well as the interaction radii. This is particularly cumbersome when describing an alloy, such as the Fe-Cr system, which is of interest for fusion energy applications. In this work we describe an Object Kinetic Monte Carlo model for Fe-Cr alloys in the dilute limit. The parameters used in the model come either from density functional theory calculations or from empirical interatomic potentials. This model is used to reproduce isochronal resistivity recovery experiments of electron irradiated dilute Fe-Cr alloys performed by Abe and Kuramoto. The comparison between the calculated results and the experiments reveal that an important parameter is the capture radius between substitutional Cr and self-interstitial Fe atoms. A parametric study is presented on the effect of the capture radius on the simulated recovery curves.

Gámez, L.; Gámez, B.; Caturla, M. J.; Terentyev, D.; Perlado, J. M.

2011-07-01

369

Measurements of HO2 chemical kinetics with a new detection method  

NASA Technical Reports Server (NTRS)

Research for the period from December 1, 1985 to May 31, 1986 is discussed, i.e., the reaction rate constant of HO2+O3 has been measured with a discharge-flow-tube apparatus. The HO2 radical was detected by the OH(A-X) photofragment emission produced from photodissociative excitation of HO2 at 147 nm. In the meantime, the optical emissions produced by the vacuum ultraviolet excitation of chemical species in the flow tube were investigated and used to examine the possibility for their interference with the HO2 detection. The research results are summarized below.

Lee, L. C.; Suto, M.

1986-01-01

370

Improved potential energy surface for the HâCl system and its use for calculations of rate coefficients and kinetic isotope effects  

Microsoft Academic Search

We present a new potential energy surface (called G3) for the chemical reaction Cl+HââHCl+H. The new surface is based on a previous potential surface called GQQ, and it incorporates an improved bending potential that is fit to the results of ab initio electronic structure calculations. Calculations based on variational transition state theory with semiclassical transmission coefficients corresponding to an optimized

Thomas C. Allison; Gillian C. Lynch; Donald G. Truhlar; Mark S. Gordon

1996-01-01

371

Chemical Speciation and Oxidation Kinetics of Iron and Sulfur in Subseafloor Basement Fluids on the Juan de Fuca Ridge Flanks  

NASA Astrophysics Data System (ADS)

Redox reactive chemical species circulate throughout the upper oceanic crust, and are involved in a variety of abiotic and microbially-mediated reactions. Through exchange with bottom seawater, fluids circulating in the upper basement have the potential to influence scales ranging from global-scale biogeochemical cycling to micro-scale microbe-mineral interactions. Understanding fundamental chemical speciation, distribution, bioavailability, and rates of transformations for key chemical redox species is crucial to understanding processes in the subsurface. In-situ electrochemical analyses were conducted in real-time at CORK (Circulation Obviation Retrofit Kit) observatories affixed to Integrated Ocean Drilling Program (IODP) boreholes in Cascadia Basin on the Juan de Fuca Ridge Flanks. Voltammetric electrodes were mounted into a flow cell to allow for simultaneous detection of redox species (O2, H_{2}O2, HS^{-}, S(0), Sx^{2-}, S2O_{3}2-, S_{4}O6^{2-}, Fe(II), Fe(III), FeS$_{(aq)}) concurrent to sample filtering or fluid collection. During real-time voltammetric scanning, qualitative assessment of the integrity of fluids delivered through the Fluid Delivery Lines could be made, allowing for comparisons between CORK sites and various sampling strategies. Newly installed CORKs at IODP sites 1362A and 1362B are producing the highest-integrity basement fluids collected to date, deplete in oxygen (<3uM) and enriched in iron (>1uM). Here, we report results of in situ electrochemical measurements at multiple borehole observatories, including the newly installed 1362A & 1362B sites, and present results of speciation analyses and kinetics of oxidation for iron and sulfur in discrete samples.

Glazer, B. T.; Matzinger, M.; Cowen, J. P.

2011-12-01

372

The chemical potential for the inhomogeneous electron liquid in terms of its kinetic and potential parts with special consideration of the surface pote ntial step and BCS-BEC crossover  

E-print Network

The chemical potential $\\mu$ of a many-body system is valuable since it carries fingerprints of phase changes. Here, we summarize results for $\\mu$ for a thre e-dimensional electron liquid in terms of average kinetic and potential energie s per particle. The difference between $\\mu$ and the energy per particle is fou nd to be exactly the electrostatic potential step at the surface. We also prese nt calculations for an integrable one-dimensional many-body system with delta f unction interactions, exhibiting a BCS-BEC crossover. It is shown that in the B CS regime the chemical potential can be expressed solely in terms of the ground -state energy per particle. A brief discussion is also included of the strong c oupling BEC limit.

K. Morawetz; N. H. March; R. H. Squire

2007-09-24

373

Methane and methanol oxidation in supercritical water: Chemical kinetics and hydrothermal flame studies  

SciTech Connect

Supercritical water oxidation (SCWO) is an emerging technology for the treatment of wastes in the presence of a large concentration of water at conditions above water`s thermodynamic critical point. A high-pressure, optically accessible reaction cell was constructed to investigate the oxidation of methane and methanol in this environment. Experiments were conducted to examine both flame and non-flame oxidation regimes. Optical access enabled the use of normal and shadowgraphy video systems for visualization, and Raman spectroscopy for in situ measurement of species concentrations. Flame experiments were performed by steadily injecting pure oxygen into supercritical mixtures of water and methane or methanol at 270 bar and at temperatures from 390 to 510{degrees}C. The experiments mapped conditions leading to the spontaneous ignition of diffusion flames in supercritical water. Above 470{degrees}C, flames spontaneously ignite in mixtures containing only 6 mole% methane or methanol. This data is relevant to the design and operation of commercial SCWO processes that may be susceptible to inadvertent flame formation. Non-flame oxidation kinetics experiments measured rates of methane oxidation in supercritical water at 270 bar and at temperatures from 390 to 442{degrees}C. The initial methane concentration was nominally 0.15 gmol/L, a level representative of commercial SCWO processes. The observed methane concentration histories were fit to a one-step reaction rate expression indicating a reaction order close to two for methane and zero for oxygen. Experiments were also conducted with varying water concentrations (0 to 8 gmol/L) while temperature and initial reactant concentrations were held constant. The rate of methane oxidation rises steadily with water concentration up to about 5 gmol/L and then abruptly falls off at higher concentrations.

Steeper, R.R.

1996-01-01

374

A high temperature and atmospheric pressure experimental and detailed chemical kinetic modelling study of 2-methyl furan oxidation  

PubMed Central

An experimental ignition delay time study for the promising biofuel 2-methyl furan (2MF) was performed at equivalence ratios of 0.5, 1.0 and 2.0 for mixtures of 1% fuel in argon in the temperature range 1200–1800 K at atmospheric pressure. Laminar burning velocities were determined using the heat-flux method for mixtures of 2MF in air at equivalence ratios of 0.55–1.65, initial temperatures of 298–398 K and atmospheric pressure. A detailed chemical kinetic mechanism consisting of 2059 reactions and 391 species has been constructed to describe the oxidation of 2MF and is used to simulate experiment. Accurate reproduction of the experimental data has been obtained over all conditions with the developed mechanism. Rate of production and sensitivity analyses have been carried out to identify important consumption pathways of the fuel and key kinetic parameters under these conditions. The reactions of hydrogen atom with the fuel are highlighted as important under all experimental conditions studied, with abstraction by the hydrogen atom promoting reactivity and hydrogen atom addition to the furan ring inhibiting reactivity. This work, to the authors knowledge, is the first to combine theoretical and experimental work to describe the oxidation of any of the alkylated furans. The mechanism developed herein to describe 2MF combustion should also function as a sub-mechanism to describe the oxidation of 2,5-dimethyl furan whilst also providing key insights into the oxidation of this similar biofuel candidate. PMID:23814505

Somers, Kieran P.; Simmie, John M.; Gillespie, Fiona; Burke, Ultan; Connolly, Jessica; Metcalfe, Wayne K.; Battin-Leclerc, Frédérique; Dirrenberger, Patricia; Herbinet, Olivier; Glaude, Pierre-Alexandre; Curran, Henry J.

2013-01-01

375

Methyl Formate Oxidation: Speciation Data, Laminar Burning Velocities, Ignition Delay Times and a Validated Chemical Kinetic Model  

SciTech Connect

The oxidation of methyl formate (CH{sub 3}OCHO) has been studied in three experimental environments over a range of applied combustion relevant conditions: 1. A variable-pressure flow reactor has been used to quantify reactant, major intermediate and product species as a function of residence time at 3 atm and 0.5% fuel concentration for oxygen/fuel stoichiometries of 0.5, 1.0, and 1.5 at 900 K, and for pyrolysis at 975 K. 2. Shock tube ignition delays have been determined for CH{sub 3}OCHO/O{sub 2}/Ar mixtures at pressures of ? 2.7, 5.4, and 9.2 atm and temperatures of 1275–1935 K for mixture compositions of 0.5% fuel (at equivalence ratios of 1.0, 2.0, and 0.5) and 2.5% fuel (at an equivalence ratio of 1.0). 3. Laminar burning velocities of outwardly propagating spherical CH{sub 3}OCHO/air flames have been determined for stoichiometries ranging from 0.8–1.6, at atmospheric pressure using a pressure-release-type high-pressure chamber. A detailed chemical kinetic model has been constructed, validated against, and used to interpret these experimental data. The kinetic model shows that methyl formate oxidation proceeds through concerted elimination reactions, principally forming methanol and carbon monoxide as well as through bimolecular hydrogen abstraction reactions. The relative importance of elimination versus abstraction was found to depend on the particular environment. In general, methyl formate is consumed exclusively through molecular decomposition in shock tube environments, while at flow reactor and freely propagating premixed flame conditions, there is significant competition between hydrogen abstraction and concerted elimination channels. It is suspected that in diffusion flame configurations the elimination channels contribute more significantly than in premixed environments.

Dooley, S.; Burke, M. P.; Chaos, M.; Stein, Y.; Dryer, F. L.; Zhukov, V. P.; Finch, O.; Simmie, J. M.; Curran, H. J.

2010-01-01

376

Chemical Property Calculation through JavaScript and Applications in QSAR  

Microsoft Academic Search

The inorganic property (I) and organic property (O) values of general organic groups are re-proposed here. Both I and O values of drug and biological molecules or groups can be calculated based on their common group values. The calculation can be performed easily on-line through JavaScript. Similar calculation can be done for the drug and biological molecular group electronegativity (

Hanqing Wu

1999-01-01

377

Tungsten-dependent formaldehyde ferredoxin oxidoreductase: Reaction mechanism from quantum chemical calculations  

E-print Network

redox reactions, while the latter catalyzes a non-redox hydration of acetylene. In Pyrococcus furiosusTungsten-dependent formaldehyde ferredoxin oxidoreductase: Reaction mechanism from quantum chemical April 2011 Keywords: Tungstoenzyme Formaldehyde oxidoreductase Reaction mechanism Density functional

Liao, Rongzhen

378

Calculations of physical and chemical reactions produced in irradiated water containing DNA  

SciTech Connect

Initial results obtained with a Monte Carlo computer program designed to link initial physical events in irradiated liquid water with subsequent chemical and biological events are presented. 10 refs., 4 figs., 3 tabs.

Wright, H.A.; Magee, J.L.; Hamm, R.N.; Chatterjee, A.; Turner, J.E.; Klots, C.E.

1985-01-01

379

In Vivo Anti-Leukemia, Quantum Chemical Calculations and ADMET Investigations of Some Quaternary and Isothiouronium Surfactants  

PubMed Central

Anti-leukemia screening of previously prepared isothiouronium and quaternary salts was performed, and some salts exhibited promising activity as anticancer agents. Quantum chemical calculations were utilized to explore the electronic structure and stability of these compounds. Computational studies have been carried out at the PM3 semiempirical molecular orbitals level, to establish the HOMO-LUMO, IP and ESP mapping of these compounds. The ADMET properties were also studied to gain a clear view of the potential oral bioavailability of these compounds. The surface properties calculated included critical micelle concentration (CMC), maximum surface excess (?max), minimum surface area (Amin), free energy of micellization (?Gomic) and adsorption (?Goads). PMID:24276171

El-Henawy, Ahmed A.; Khowdiary, Manal M.; Badawi, Abdelfattah B.; Soliman, Hussein M.

2013-01-01

380

Chemical kinetics and atmospheric modification. Final report, 31 August 1989-31 December 1993  

SciTech Connect

Electron attachment rate constants were obtained and negative ion product analysis was performed over the temperature between 300 and 1200 degrees range for a series of seventeen halomethane molecules that undergo dissociative electron attachment. The reactant molecules include CH3Cl, CH3Br, CH3I, CF3Cl, CF3Br, CF3I, CF2Cl2, CFCl3, CCl4, CF3H, CF2H2, CH3F, CF2HCl, CHFCl2, CH2Br2, CCl2H2, and CC13H. Positive activation energies were observed for most of the reactions. The results of molecular structure calculations for both the neutral and anionic species suggest that the magnitude of the rate constants and of the temperature coefficients for dissociative electron attachment in these systems can be understood in terms of the geometrical reorganization associated with negative ion formation.

McFadden, D.L.

1994-05-01

381

HCCI experiments with toluene reference fuels modeled by a semidetailed chemical kinetic model  

SciTech Connect

A semidetailed mechanism (137 species and 633 reactions) and new experiments in a homogeneous charge compression ignition (HCCI) engine on the autoignition of toluene reference fuels are presented. Skeletal mechanisms for isooctane and n-heptane were added to a detailed toluene submechanism. The model shows generally good agreement with ignition delay times measured in a shock tube and a rapid compression machine and is sensitive to changes in temperature, pressure, and mixture strength. The addition of reactions involving the formation and destruction of benzylperoxide radical was crucial to modeling toluene shock tube data. Laminar burning velocities for benzene and toluene were well predicted by the model after some revision of the high-temperature chemistry. Moreover, laminar burning velocities of a real gasoline at 353 and 500 K could be predicted by the model using a toluene reference fuel as a surrogate. The model also captures the experimentally observed differences in combustion phasing of toluene/n-heptane mixtures, compared to a primary reference fuel of the same research octane number, in HCCI engines as the intake pressure and temperature are changed. For high intake pressures and low intake temperatures, a sensitivity analysis at the moment of maximum heat release rate shows that the consumption of phenoxy radicals is rate-limiting when a toluene/n-heptane fuel is used, which makes this fuel more resistant to autoignition than the primary reference fuel. Typical CPU times encountered in zero-dimensional calculations were on the order of seconds and minutes in laminar flame speed calculations. Cross reactions between benzylperoxy radicals and n-heptane improved the model predictions of shock tube experiments for {phi}=1.0 and temperatures lower than 800 K for an n-heptane/toluene fuel mixture, but cross reactions had no influence on HCCI simulations. (author)

Andrae, J.C.G. [Department of Chemical Engineering and Technology, Royal Institute of Technology (KTH), SE-100 44 Stockholm (Sweden); Brinck, T. [Department of Physical Chemistry, Royal Institute of Technology (KTH), SE-100 44 Stockholm (Sweden); Kalghatgi, G.T. [Shell Global Solutions (UK), P.O. Box 1, Chester CH1 3SH (United Kingdom)

2008-12-15

382

Efficient simulation of stochastic chemical kinetics with the Stochastic Bulirsch-Stoer extrapolation method  

PubMed Central

Background Biochemical systems with relatively low numbers of components must be simulated stochastically in order to capture their inherent noise. Although there has recently been considerable work on discrete stochastic solvers, there is still a need for numerical methods that are both fast and accurate. The Bulirsch-Stoer method is an established method for solving ordinary differential equations that possesses both of these qualities. Results In this paper, we present the Stochastic Bulirsch-Stoer method, a new numerical method for simulating discrete chemical reaction systems, inspired by its deterministic counterpart. It is able to achieve an excellent efficiency due to the fact that it is based on an approach with high deterministic order, allowing for larger stepsizes and leading to fast simulations. We compare it to the Euler ?-leap, as well as two more recent ?-leap methods, on a number of example problems, and find that as well as being very accurate, our method is the most robust, in terms of efficiency, of all the methods considered in this paper. The problems it is most suited for are those with increased populations that would be too slow to simulate using Gillespie’s stochastic simulation algorithm. For such problems, it is likely to achieve higher weak order in the moments. Conclusions The Stochastic Bulirsch-Stoer method is a novel stochastic solver that can be used for fast and accurate simulations. Crucially, compared to other similar methods, it better retains its high accuracy when the timesteps are increased. Thus the Stochastic Bulirsch-Stoer method is both computationally efficient and robust. These are key properties for any stochastic numerical method, as they must typically run many thousands of simulations. PMID:24939084

2014-01-01

383

Solvent effects in the GIAO-DFT calculations of the 15N NMR chemical shifts of azoles and azines.  

PubMed

The calculation of (15)N NMR chemical shifts of 27 azoles and azines in 10 different solvents each has been carried out at the gauge including atomic orbitals density functional theory level in gas phase and applying the integral equation formalism polarizable continuum model (IEF-PCM) and supermolecule solvation models to account for solvent effects. In the calculation of (15)N NMR, chemical shifts of the nitrogen-containing heterocycles dissolved in nonpolar and polar aprotic solvents, taking into account solvent effect is sufficient within the IEF-PCM scheme, whereas for polar protic solvents with large dielectric constants, the use of supermolecule solvation model is recommended. A good agreement between calculated 460 values of (15)N NMR chemical shifts and experiment is found with the IEF-PCM scheme characterized by MAE of 7.1?ppm in the range of more than 300?ppm (about 2%). The best result is achieved with the supermolecule solvation model performing slightly better (MAE 6.5?ppm). PMID:25102971

Semenov, Valentin A; Samultsev, Dmitry O; Krivdin, Leonid B

2014-11-01

384

Swelling/shrinking kinetics of chemically cross-linked poly(vinyl alcohol) gels in the presence of borate ions  

NASA Astrophysics Data System (ADS)

The swelling/shrinking kinetics of chemically cross-linked poly(vinyl alcohol) (PVA) gels with borate ions has been studied by measuring the gel size as a function of time. The experimental process consisted of two steps, i.e., (I) immersion of a gel in a mixture of NaOH and boric acid aqueous solutions, and (II) subsequent immersion in deionized water or in a NaOH solution without borate ions. In step I, the gel swelled or shrank depending on the borate ion concentration and reached individual equilibrium values within 5000 min. After equilibration, the gel was transferred to the second bath and step II was initiated. When a gel was immersed in deionized water, the gel swelled considerably and then deswelled gradually to the original size. On the other hand, when a gel was dipped in a bath containing NaOH, a reverse process of step I took place and the gel size gradually reduced to the original size. The diffusion coefficients in these steps are discussed in conjunction with those obtained by dynamic light scattering.

Shibayama, Mitsuhiro; Uesaka, Masao; Shiwa, Yasuhiro

1996-09-01

385

Kinetics of physico-chemical processes during intensive mechanical processing of ZnO-MnO 2 powder mixture  

NASA Astrophysics Data System (ADS)

Experimental results of electron paramagnetic resonance spectra, X-ray diffraction, scanning electron microscopy and infrared spectroscopy demonstrate that the kinetic of the physical and chemical processes that takes place during prolonged intensive mechanical processing (MP, 03120 min) of powder mixtures of 50%wt ZnO+50%wt MnO 2 can be described as a three stage process. (1) 030 min, particles destruction, formation of superficial defects, fast increment of sample average temperature (from 290 to ˜600 K) and annealing of defects with the lowest energy of activation Eac. (2) 30390 min, further particle destruction, slow increment of sample average temperature (from ˜600 to ˜700 K), formation and growth of a very disordered layer of ?-MnO2 around ZnO particles, dehydration of MnO 2, formation of solid solution of Mn 2+ ions in ZnO, formation of nano-quasiamorphous states in the ZnO-MnO 2 mixture and onset of the formation of the ZnMnO 3 phase. (3) 3903120 min, the sample average temperature remains constant ( ˜700 K), the reaction is completed and the spinel ZnMnO 3 phase with a unit cell a=8.431(1) Å and space group Fd3¯m is the only phase present in the sample. No ferromagnetism at room temperature was detected in this study.

Kakazey, M.; Vlasova, M.; Dominguez-Patiño, M.; Juarez-Arellano, E. A.; Bykov, A.; Leon, I.; Siqueiros-Diaz, A.

2011-10-01

386

Enhancing adsorption capacity of toxic malachite green dye through chemically modified breadnut peel: equilibrium, thermodynamics, kinetics and regeneration studies.  

PubMed

Breadnut skin, in both its unmodified (KS) and base-modified (BM-KS) forms, was investigated for its potential use as a low-cost adsorbent for the removal of toxic dye, malachite green (MG). Characterization of the adsorbents was carried out using scanning electron microscope, X-ray fluorescence and Fourier transform infra-red spectroscopy. Batch adsorption experiments, carried out under optimized conditions, for the adsorption of MG were fitted using five isotherm models (Langmuir, Freundlich, Dubinin-Radushkevich, Temkin and Sips) and six error functions to determine the best-fit model. The adsorption capacity was greatly enhanced when breadnut skin was chemically modified with NaOH, leading to an adsorption capacity of 353.0 mg g(-1), that was far superior to most reported adsorbents for the removal of MG. Thermodynamics studies indicated that the adsorption of MG was spontaneous on KS and BM-KS, and the reactions were endothermic and exothermic, respectively. Kinetics studies showed that both followed the pseudo-second order. Regeneration experiments on BM-KS indicated that its adsorption capacity was still maintained at>90% even after five cycles. It can be concluded that NaOH-modified breadfruit skin has great potential to be utilized in real-life application as a low-cost adsorbent for the removal of MG in wastewater treatment. PMID:25409587

Chieng, Hei Ing; Lim, Linda B L; Priyantha, Namal

2015-01-01

387

Kinetic, spectroscopic and chemical modification study of iron release from transferrin; iron(III) complexation to adenosine triphosphate  

SciTech Connect

Amino acids other than those that serve as ligands have been found to influence the chemical properties of transferrin iron. The catalytic ability of pyrophosphate to mediate transferrin iron release to a terminal acceptor is largely quenched by modification non-liganded histine groups on the protein. The first order rate constants of iron release for several partially histidine modified protein samples were measured. A statistical method was employed to establish that one non-liganded histidine per metal binding domain was responsible for the reduction in rate constant. These results imply that the iron mediated chelator, pyrophosphate, binds directly to a histidine residue on the protein during the iron release process. EPR spectroscopic results are consistent with this interpretation. Kinetic and amino acid sequence studies of ovotransferrin and lactoferrin, in addition to human serum transferrin, have allowed the tentative assignment of His-207 in the N-terminal domain and His-535 in the C-terminal domain as the groups responsible for the reduction in rate of iron release. The above concepts have been extended to lysine modified transferrin. Complexation of iron(II) to adenosine triphosphate (ATP) was also studied to gain insight into the nature of iron-ATP species present at physiological pH. /sup 31/P NMR spectra are observed when ATP is presented in large excess.

Thompson, C.P.

1985-01-01

388

Comprehensive chemical kinetic modeling of the oxidation of C8 and larger n-alkanes and 2-methylalkanes  

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 and reduced chemical kinetic mechanism for singly methylated iso-alkanes (i.e., 2-methylalkanes) ranging from C{sub 8} to C{sub 20}. The mechanism also includes an updated version of our previously published C{sub 8} to C{sub 16} n-alkanes model. The complete detailed mechanism contains approximately 7,200 species 31,400 reactions. The proposed model is validated against new experimental data from a variety of fundamental combustion devices including premixed and nonpremixed flames, perfectly stirred reactors and shock tubes. This new model is used to show how the presence of a methyl branch affects important combustion properties such as laminar flame propagation, ignition, and species formation.

Sarathy, S M; Westbrook, C K; Pitz, W J; Mehl, M; Togbe, C; Dagaut, P; Wang, H; Oehlschlaeger, M; NIemann, U; Seshadri, K; Veloo, P S; Ji, C; Egolfopoulos, F; Lu, T

2011-03-16

389

Transport calculations of chemically sputtered carbon near a plasma divertor surface  

SciTech Connect

The transport of chemically sputtered carbon near a tokamak divertor surface has been analyzed with the Monte Carlo code WBC. The code follows the motion of sputtered methane atoms and the resulting carbon and hydrocarbon derivatives. Ion transport due to the magnetic field, sheath electric field, and collisions with the plasma is computed. Redeposition fractions, impinging species type, charge state, and velocity have been analyzed. For plasma temperatures {ge} 10 eV, and for typical divertor plasma densities, local redeposition of chemically sputtered carbon approaches 100%. Redeposition fractions are lower ({approximately}80%) for lower temperatures and/or lower density. Physical sputtering of carbon due to redeposition of chemically sputtered material is low but a hydrocarbon reflection cascade due to redeposition may be high.

Brooks, J.N.

1992-01-01

390

LSENS, A General Chemical Kinetics and Sensitivity Analysis Code for Homogeneous Gas-Phase Reactions. Part 2; Code Description and Usage  

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 II of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part II 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 I (NASA RP-1328) derives the governing equations and describes the numerical solution procedures for the types of problems that can be solved by LSENS. Part III (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

391

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

NASA Technical Reports Server (NTRS)

Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches. Because these large 'molecular' systems pose special practical computational problems in the application of the quantum mechanical methods, there is a special need to find simplifying techniques that do not compromise the reliability of the calculations. Research is therefore directed towards various aspects of the implementation of the effective core potential technique for the removal of the metal atom core electrons from the calculations.

Kahn, L. R.

1982-01-01

392

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

Microsoft Academic Search

An extensive computer program called ChemSage, based upon the SOLGASMIX Gibbs energy minimizer, is presented together with\\u000a several examples which illustrate its use. ChemSage was designed to perform three types of thermochemical calculations in\\u000a complex systems involving phases exhibiting nonideal mixing properties. These are the calculation of thermodynamic functions,\\u000a heterogeneous phase equilibria, and steady-state conditions for the simulation of simple

Gunnar Eriksson; Klaus Hack

1990-01-01

393

The calculation of (29)Si NMR chemical shifts of tetracoordinated silicon compounds in the gas phase and in solution.  

PubMed

Aiming at the identification of an efficient computational protocol for the accurate NMR assessment of organosilanes in low-polarity organic solvents, (29)Si NMR chemical shifts of a selected set of such species relevant in organic synthesis have been calculated relative to tetramethylsilane (TMS, 1) using selected density functional and perturbation theory methods. Satisfactory results are obtained when using triple zeta quality basis sets such as IGLO-III. Solvent effects impact the calculated results through both, changes in substrate geometry as well as changes in the actual shieldings. Spin-orbit (SO) corrections are required for systems carrying more than one chlorine atom directly bonded to silicon. Best overall results are obtained using gas phase geometries optimized at MPW1K/6-31+G(d) level in combination with shielding calculations performed at MPW1K/IGLO-III level in the presence of the PCM continuum solvation model. PMID:24993980

Zhang, Cong; Patschinski, Pascal; Stephenson, David S; Panisch, Robin; Wender, Josef Heinrich; Holthausen, Max C; Zipse, Hendrik

2014-08-21

394

Chemical identification in the CuAu(1 0 0) surface using scanning tunneling microscopy and first-principles calculations  

NASA Astrophysics Data System (ADS)

We describe the geometric, energetic and electronic structure of the CuAu(1 0 0) surface using a combination of scanning tunneling microscopy (STM) and first-principles calculations based on density-functional theory (DFT). Our calculations show that the half-half Cu-Au termination is the one with lower surface energy, in agreement with experiments. The surface atomic rippling proposed by experimental data is also well reproduced by the calculations. STM images with atomic resolution display interesting voltage dependence, showing both types of atoms in the surface unit cell for lower voltages but just one type for higher voltages. Comparisons with theoretically simulated STM images and cross-sectional density of states profiles allows for an unambiguous assignment of Au atoms as the one appearing in higher-voltage images, thus providing chemical identification at the surface.

Dias, L. G.; Leitão, A. A.; Achete, C. A.; Blum, R.-P.; Niehus, H.; Capaz, Rodrigo B.

2007-12-01

395

CALCULATING THE CARBON FOOTPRINT OF A CHEMICAL PLANT: A CASE STUDY OF AKZONOBEL  

Microsoft Academic Search

Reduction of greenhouse gas emissions is one of the key requirements for sustainable production and consumption, but while the Canadian chemical industry has been very successful in reducing emissions to water and air, and while non-CO2 greenhouse gas emissions have been minimised as well, reduction of CO2 emissions has been less successful. The industry itself forecasts that further reduction of

MICHAEL STEIN; ANSHUMAN KHARE

2009-01-01

396

Calculation of Propulsive Nozzle Flowfields in Multidiffusing Chemically Reacting Environments. Ph.D. Thesis - Purdue Univ.  

NASA Technical Reports Server (NTRS)

An advanced engineering model has been developed to aid in the analysis and design of hydrogen/oxygen chemical rocket engines. The complete multispecies, chemically reacting and multidiffusing Navier-Stokes equations are modelled, including the Soret thermal diffusion and the Dufour energy transfer terms. In addition to the spectrum of multispecies aspects developed, the model developed in this study is also conservative in axisymmetric flow for both inviscid and viscous flow environments and the boundary conditions employ a viscous, chemically reacting, reference plane characteristics method. Demonstration cases are presented for a 1030:1 area ratio nozzle, a 25 lbf film cooled nozzle, and a transpiration cooled plug and spool rocket engine. The results indicate that the thrust coefficient predictions of the 1030:1 and the 25 lbf film cooled nozzle are within 0.2 to 0.5 percent, respectively, of experimental measurements when all of the chemical reaction and diffusion terms are considered. Further, the model's predictions agree very well with the heat transfer measurements made in all of the nozzle test cases. The Soret thermal diffusion term is demonstrated to have a significant effect on the predicted mass fraction of hydrogen along the wall of the nozzle in both the laminar flow 1030:1 nozzle and the turbulent flow plug and spool nozzle analysis cases performed. Further, the Soret term was shown to represent an important fraction of the diffusion fluxes occurring in a transpiration cooled rocket engine.

Kacynski, Kenneth John

1994-01-01

397

Chemically transferable coarse-grained potentials from conditional reversible work calculations.  

PubMed

The representability and transferability of effective pair potentials used in multiscale simulations of soft matter systems is ill understood. In this paper, we study liquid state systems composed of n-alkanes, the coarse-grained (CG) potential of which may be assumed pairwise additive and has been obtained using the conditional reversible work (CRW) method. The CRW method is a free-energy-based coarse-graining procedure, which, by means of performing the coarse graining at pair level, rigorously provides a pair potential that describes the interaction free energy between two mapped atom groups (beads) embedded in their respective chemical environments. The pairwise nature of the interactions combined with their dependence on the chemically bonded environment makes CRW potentials ideally suited in studies of chemical transferability. We report CRW potentials for hexane using a mapping scheme that merges two heavy atoms in one CG bead. It is shown that the model is chemically and thermodynamically transferable to alkanes of different chain lengths in the liquid phase at temperatures between the melting and the boiling point under atmospheric (1 atm) pressure conditions. It is further shown that CRW-CG potentials may be readily obtained from a single simulation of the liquid state using the free energy perturbation method, thereby providing a fast and versatile molecular coarse graining method for aliphatic molecules. PMID:23083154

Brini, E; van der Vegt, N F A

2012-10-21

398

Quantum chemical calculations to reveal the relationship between the chemical structure and the fluorescence characteristics of phenylquinolinylethynes and phenylisoquinolinylethynes derivatives, and to predict their relative fluorescence intensity.  

PubMed

In this paper the relationship between the chemical structure and fluorescence characteristics of 30 phenylquinolinylethyne (PhQE), and phenylisoquinolinylethyne (PhIE) derivatives compounds employing ab initio calculations have been elucidated. Quantum chemical calculations (6-31G) were carried out to obtain: the optimized geometry, energy levels, charges and dipole moments of these compounds, in the singlet (steady and excited states) and triplet states. The relationship between quantum chemical descriptors, and wavelength of maximum excitation and emission indicated that these two parameters have the most correlation with quantum chemical hardness (eta). Also, stokes shift has the most correlation with the square of difference between the maximum of positive charges in the singlet steady and singlet excited states. The quantitative structure-property relationship (QSPR) of PhQE and PhIE was studied for relative fluorescence intensity (RFI). The genetic algorithm (GA) was applied to select the variables that resulted in the best-fit models. After the variable selection, multiple linear regression (MLR) and support vector machine (SVM) were both utilized to construct linear and non-linear QSPR models, respectively. The SVM model demonstrated a better performance than that of the MLR model. The route mean square error (RMSE) in the training and the test sets for the SVM model was 0.195 and 0.324, and the correlation coefficients were 0.965 and 0.960, respectively, thus revealing the reliability of this model. The resulting data indicated that SVM could be used as a powerful modeling tool for QSPR studies. According to the best of our knowledge, this is the first research on QSPR studies to predict RFI for a series of PhQE and PhIE derivative compounds using SVM. PMID:19854100

Riahi, Siavash; Beheshti, Abolghasem; Ganjali, Mohammad Reza; Norouzi, Parviz

2009-12-01

399

Ab initio quantum chemical calculations of aluminum substitution in zeolite ZSM-5  

SciTech Connect

The authors have performed ab initio quantum mechanical calculations in monomeric clusters modeling the 12 different T sites of zeolite ZSM-5. By comparing the results of calculations that use minimum basis sets with those that employ valence double-[zeta] bases, the authors conclude that minimum basis sets are unreliable for predicting relative replacement energies for the substitution of silicon by aluminum atoms at the T sites of the zeolite. From these calculations, it is also concluded that small differences in the bond lengths and angles can significantly alter the order of the sites with respect to the replacement energies. From calculations using valence double-[zeta] basis sets on T(OH)[sub 4] monomers, it is concluded that in the absence of protons or other ions, the most favorable sites for Al substitution in zeolite ZSM-5 are the T[sub 6], T[sub 12], and T[sub 9] sites, whereas the least favorable site is T[sub 3]. However, the least favorable and most favorable sites only differ by 3.3 kcal/mol. The authors also present a simple empirical model that is capable of reproducing the results of the ab initio calculations. This model gives the replacement energy in terms of the bond lengths and bond angles about each site.

Alvarado-Swaisgood, A.E.; Barr, M.K. (Amoco Research Center, Naperville, IL (United States)); Hay, P.J.; Redondo, A. (Los Alamos National Lab., NM (United States))

1991-11-28

400

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

NASA Technical Reports Server (NTRS)

The application of ab initio quantum mechanical approaches in the study of metal atom clusters requires simplifying techniques that do not compromise the reliability of the calculations. Various aspects of the implementation of the effective core potential (ECP) technique for the removal of the metal atom core electrons from the calculation were examined. The ECP molecular integral formulae were modified to bring out the shell characteristics as a first step towards fulfilling the increasing need to speed up the computation of the ECP integrals. Work on the relationships among the derivatives of the molecular integrals that extends some of the techniques pioneered by Komornicki for the calculation of the gradients of the electronic energy was completed and a formulation of the ECP approach that quite naturally unifies the various state-of-the-art "shape- and Hamiltonian-consistent" techniques was discovered.

Kahn, L. R.

1981-01-01

401

Application of a Genetic Algorithm to the Optimization of Rate Constants in Chemical Kinetic Models for Combustion Simulation of HCCI Engines  

NASA Astrophysics Data System (ADS)

For numerically predicting the combustion processes in homogeneous charge compression ignition (HCCI) engines, practical chemical kinetic models have been explored. A genetic algorithm (GA) has been applied to the optimization of the rate constants in detailed chemical kinetic models, and a detailed kinetic model (592 reactions) for gasoline reference fuels with arbitrary octane number between 60 and 100 has been obtained from the detailed reaction schemes for iso-octane and n-heptane proposed by Golovitchev. The ignition timing in a gasoline HCCI engine has been predicted reasonably well by zero-dimensional simulation using the CHEMKIN code with this detailed kinetic model. An original reduced reaction scheme (45 reactions) for dimethyl ether (DME) has been derived from Curran’s detailed scheme, and the combustion process in a DME HCCI engine has been predicted reasonably well in a practical computation time by three-dimensional simulation using the authors’ GTT code, which has been linked to the CHEMKIN subroutines with the proposed reaction scheme and also has adopted a modified eddy dissipation combustion model.

Kim, Sang-Kyu; Ito, Kazuma; Yoshihara, Daisuke; Wakisaka, Tomoyuki

402

Nuclear magnetic resonance, vibrational spectroscopic studies, physico-chemical properties and computational calculations on (nitrophenyl) octahydroquinolindiones by DFT method.  

PubMed

In the present study, 2'-nitrophenyloctahydroquinolinedione and its 3'-nitrophenyl isomer were synthesized and characterized by FT-IR, FT-Raman, (1)H NMR and (13)C NMR spectroscopy. The molecular geometry, vibrational frequencies, (1)H and (13)C NMR chemical shift values of the synthesized compounds in the ground state have been calculated by using the density functional theory (DFT) method with the 6-311++G (d,p) basis set and compared with the experimental data. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution using GAR2PED programme. Isotropic chemical shifts for (1)H and (13)C NMR were calculated using gauge-invariant atomic orbital (GIAO) method. The experimental vibrational frequencies, (1)H and (13)C NMR chemical shift values were found to be in good agreement with the theoretical values. On the basis of vibrational analysis, molecular electrostatic potential and the standard thermodynamic functions have been investigated. PMID:25440584

Pasha, M A; Siddekha, Aisha; Mishra, Soni; Azzam, Sadeq Hamood Saleh; Umapathy, S

2015-02-01

403

Calculated simulation of the kinetics of a crack propagation in the bearing sheets of the glued laminated structures  

NASA Astrophysics Data System (ADS)

An application of the finite element method to calculation of the adhesive joints of D16AT alloy plates, which are subjected to the effect of shear and bend, is justified on the basis of complex theoretical and experimental analysis. The possibility of extension of the developed models on a linear fracture mechanics field for laminated metal polymer composites is shown and experimentally confirmed. The influence of some mechanical characteristics of the polymeric binder on the fracture nature in the area of through and surface cracks is estimated by calculation for organometallic plastics.

Semin, M. I.; Safonov, P. K.

1994-07-01

404

Vibrational spectra, quantum chemical calculations and spectral assignments of 1,1-difluoro-1-silacyclohexane  

NASA Astrophysics Data System (ADS)

Raman spectra of 1,1-difluoro-1-silacyclohexane as a liquid, and as a solid at 78 K were recorded and depolarization data obtained. The infrared spectra of the vapour, liquid and amorphous and crystalline solids have been studied. In the low temperature IR and Raman spectra eight and three bands, respectively, were shifted a few cm-1 when the sample crystallized. No bands vanished after crystallization in agreement with the assumption that only one conformer (chair) was present in all the states of aggregation. The compound exists in the stable chair conformation, whereas in the parent silacyclohexane a possible twist form should have more than 15 kJ mol-1 higher energies than the chair, as derived from various calculations. The wavenumbers of the vibrational modes were calculated in the harmonic and anharmonic approximation employing B3LYP/cc-pVTZ calculations. The 27 A? and 21 A? fundamentals were assigned on the basis of the calculations, infrared vapour contours, Raman depolarization measurements and infrared and Raman band intensities. An average, relative deviation of 1.5% was found between the observed and the anharmonic wavenumbers for the 48 modes.

Guirgis, Gamil A.; Dukes, Horace W.; Wyatt, Justin K.; Nielsen, Claus J.; Horn, Anne; Aleksa, Valdemaras; Klaeboe, Peter

2015-02-01

405

Vibrational spectra, quantum chemical calculations and spectral assignments of 1,1-difluoro-1-silacyclohexane.  

PubMed

Raman spectra of 1,1-difluoro-1-silacyclohexane as a liquid, and as a solid at 78K were recorded and depolarization data obtained. The infrared spectra of the vapour, liquid and amorphous and crystalline solids have been studied. In the low temperature IR and Raman spectra eight and three bands, respectively, were shifted a few cm(-1) when the sample crystallized. No bands vanished after crystallization in agreement with the assumption that only one conformer (chair) was present in all the states of aggregation. The compound exists in the stable chair conformation, whereas in the parent silacyclohexane a possible twist form should have more than 15kJmol(-1) higher energies than the chair, as derived from various calculations. The wavenumbers of the vibrational modes were calculated in the harmonic and anharmonic approximation employing B3LYP/cc-pVTZ calculations. The 27 A' and 21 A? fundamentals were assigned on the basis of the calculations, infrared vapour contours, Raman depolarization measurements and infrared and Raman band intensities. An average, relative deviation of 1.5% was found between the observed and the anharmonic wavenumbers for the 48 modes. PMID:24238936

Guirgis, Gamil A; Dukes, Horace W; Wyatt, Justin K; Nielsen, Claus J; Horn, Anne; Aleksa, Valdemaras; Klaeboe, Peter

2015-02-01

406

Spectroscopic analysis of 3-Bromodiphenylamine with experimental techniques and quantum chemical calculations  

NASA Astrophysics Data System (ADS)

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 3500-100 cm-1 and 4000-400 cm-1, respectively, for 3-Bromodiphenylamine (3BDPA). Theoretical calculations were performed by using Density Functional Theory (DFT) method with 6-31G(d,p) and 6-311++G(d,p) basis sets. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The calculated wavenumbers were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. The frontier orbital energy gap and dipole moment illustrates the high reactivity of the title molecule. The first order hyperpolarizability (?0) and related properties (?, ? and ??) of the molecule were also calculated. Stability of the molecule arising from hyperconjugative interactions and charge delocalization were analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the ?* and ?* anti-bonding orbitals and second order delocalization energies (E2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. Molecular electrostatic potential (MEP) and HOMO-LUMO energy levels are also constructed. The thermodynamic properties of the title compound were calculated at different temperatures and the results reveals the heat capacity (C), and entropy (S) increases with rise in temperature.

Sudharsan, A.; Seshadri, S.; Gnanasambandan, T.; Saravanan, R. R.

2014-10-01

407

Studies on vibrational, NMR spectra and quantum chemical calculations of N-Succinopyridine: An organic nonlinear optical material  

NASA Astrophysics Data System (ADS)

Single crystals of N-Succinopyridine (NSP) have been grown from water using solution growth method by isothermal solvent evaporation technique. The solid state Fourier Transform Infrared (FTIR) spectrum of the grown crystal shows a broad absorption extending from 3450 down to 400 cm-1, due to H-bond vibrations and other characteristic vibrations. Fourier Transform Raman (FT-Raman) spectrum of NSP single crystal shows Raman intensities ranging from 3100 to 100 cm-1 due the characteristics vibrations of functional groups present in NSP. The proton and carbon positions of NSP have been described by 1H and 13C NMR spectrum respectively. Ab initio quantum chemical calculations on NSP have been performed by density functional theory (DFT) calculations using B3LYP method with 6-311++G(d,p) basis set. The predicted first hyperpolarizability is found to be 1.29 times greater than that of urea and suggests that the title compound could be an attractive material for nonlinear optical applications. The calculated HOMO-LUMO energies show that charge transfers occur within the molecule and other related molecular properties. Molecular properties such as Mulliken population analysis, thermodynamic functions and perturbation theory energy analysis have also been reported. Electrostatic potential map (ESP) of NSP obtained by electron density isosurface provided the information about the size, shape, charge density distribution and site of chemical reactivity of the title molecule. The molecular stability and bond strength have been investigated through the Natural Bond Orbital (NBO) analysis.

Kannan, V.; Thirupugalmani, K.; Brahadeeswaran, S.

2013-10-01

408

The calculation of electron chemical potential and ion charge state and their influence on plasma conductivity in electrical explosion of metal wire  

SciTech Connect

The electron chemical potential and ion charge state (average ion charge and ion distribution) are important parameters in calculating plasma conductivity in electrical explosion of metal wire. In this paper, the calculating method of electron chemical potential and ion charge state is discussed at first. For the calculation of electron chemical potential, the ideal free electron gas model and Thomas-Fermi model are compared and analyzed in terms of the coupling constant of plasma. The Thomas-Fermi ionization model, which is used to calculate ion charge state, is compared with the method based on Saha equation. Furthermore, the influence of electron degenerated energy levels and ion excited states in Saha equation on the ion charge state is also analyzed. Then the influence of different calculating methods of electron chemical potential and ion charge state on plasma conductivity is discussed by applying them in the Lee-More conductivity model.

Shi, Zongqian; Wang, Kun; Li, Yao; Shi, Yuanjie; Wu, Jian; Jia, Shenli [State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Shanxi 710049 (China)] [State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Shanxi 710049 (China)

2014-03-15

409

Hybrid Quantum and Classical Methods for Computing Kinetic Isotope Effects of Chemical Reactions in Solution and in Enzymes  

E-print Network

in Solution and in Enzymes Jiali Gao,*,a Dan T. Major, Yao Fan, Yen-lin Lin, Shuhua Ma, and Kin-Yiu Wong Isotope Effects, Enzyme Kinetics, and Solvent Effects. Abstract: A method for incorporating quantum mechanics into enzyme kinetics modeling is presented. Three aspects are emphasized: (1) combined quantum

Minnesota, University of

410

Thermodynamic and kinetic properties of the Li-graphite system from first-principles calculations Kristin Persson,1 Yoyo Hinuma,2 Ying Shirley Meng,2 Anton Van der Ven,3 and Gerbrand Ceder4  

E-print Network

Thermodynamic and kinetic properties of the Li-graphite system from first-principles calculations interca- lation in rechargeable Li batteries. In graphite, the interlayer interactions are dominated . By calculating the voltage profile for Li intercalation into graphite and comparing it to experimental results

Ceder, Gerbrand

411

Chemical composition data and calculated aquifer temperature for selected wells and springs of Honey Lake Valley, California  

USGS Publications Warehouse

Major element, minor element, and gas composition data are tabulated for 15 springs and wells in Honey Lake Valley, California. Wendel and Amedee hot springs issue Na-S04-C1 waters at boiling or near boiling temperatures; the remaining springs and wells issue Na-HC03 waters at temperatures ranging from 14 to 33 deg C. Gases escaping from the hot springs are principally nitrogen with minor amounts of methane. The geothermometers calculated from the chemical data are also tabulated for each spring. (Woodard-USGS)

Mariner, R.H.; Presser, T.S.; Evans, W.C.

1976-01-01

412

Fluid/mineral equilibrium calculations for geothermal fluids and chemical geothermometry  

SciTech Connect

Aquifer temperatures of 13 geothermal wells in Iceland whose measured reservoir temperatures range from 47 to 325 C have been estimated from the chemical composition of the discharged fluid by considering simultaneously temperature dependent equilibria between many mineral phases and the solution. This approach to chemical geothermometry was initially proposed by Reed and Spycher. Its advantage over individual solute geothermometers such as the silica and the Na-K and Na-K-Ca geothermometers is that it allows a distinction to be made between equilibrated and non-equilibrated waters. However, care should be taken in interpreting the results of multi-mineral/solute equilibria as the results depend on both the thermodynamic data base used for mineral solubilities and the activities of end-member minerals in solid solutions. When using old analytical data attention has to be paid to analytical methods, especially in the case of important constituents present at low concentrations in the fluid, such as aluminium, for which analytical results obtained by two methods yielded very different equilibrium temperatures. The results for selected wells in Iceland, presented here, indicate that the geothermometry results are with few exceptions within 20 C of measured aquifer temperatures, and within 10 C for about half the wells considered. The method responds rapidly to changes such as cooling or mixing.

Tole, M.P. (Moi Univ., Eldoret (Kenya). School of Environmental Studies); Armannsson, H. (National Energy Authority, Reykjavik (Iceland)); Pang Zhonghe (Inst. of Geology, Beijing (China). Lab. for Geothermal); Arnorsson, S. (Univ. of Iceland, Reykjavik (Iceland). Science Inst.)

1993-02-01

413

The molecular structure of niobium pentachloride by quantum chemical calculations and gas electron diffraction  

NASA Astrophysics Data System (ADS)

The molecular structure of NbCl 5 was determined experimentally by gas electron diffraction and computationally by structure optimisation of D 3h models. The bond distances obtained by ab initio calculations with very large basis sets, relativistic effects included through the one-electron Douglas-Kroll method and all electrons correlated at the MP2 level and by gas electron diffraction are: (calc/exp) Nb-Cl ax=230.7/230.6(5) pm and Nb-Cl eq=227.0/227.5(4) pm.

Gove, S. K.; Gropen, O.; Fægri, K.; Haaland, A.; Martinsen, K.-G.; Strand, T. G.; Volden, H. V.; Swang, O.

1999-08-01

414

An interactive computer code for calculation of gas-phase chemical equilibrium (EQLBRM)  

NASA Technical Reports Server (NTRS)

A user friendly, menu driven, interactive computer program known as EQLBRM which calculates the adiabatic equilibrium temperature and product composition resulting from the combustion of hydrocarbon fuels with air, at specified constant pressure and enthalpy is discussed. The program is developed primarily as an instructional tool to be run on small computers to allow the user to economically and efficiency explore the effects of varying fuel type, air/fuel ratio, inlet air and/or fuel temperature, and operating pressure on the performance of continuous combustion devices such as gas turbine combustors, Stirling engine burners, and power generation furnaces.

Pratt, B. S.; Pratt, D. T.

1984-01-01

415

Electronic structure of silicon nitride according to ab initio quantum-chemical calculations and experimental data  

SciTech Connect

Charge transfer {Delta}Q = 0.35e at the Si-N bond in silicon nitride is determined experimentally using photoelectron spectroscopy, and the ionic formula of silicon nitride Si{sub 3}{sup +1.4}N{sub 4}{sup -1.05} is derived. The electronic structure of {alpha}-Si{sub 3}N{sub 4} is studied ab initio using the density functional method. The results of calculations (partial density of states) are compared with experimental data on X-ray emission spectroscopy of amorphous Si{sub 3}N{sub 4}. The electronic structure of the valence band of amorphous Si{sub 3}N{sub 4} is studied using synchrotron radiation at different excitation energies. The electron and hole effective masses m{sub e}{sup *} {approx} m{sub h}{sup *} {approx} 0.5m{sub e} are estimated theoretically. The calculated values correspond to experimental results on injection of electrons and holes into silicon nitride.

Nekrashevich, S. S., E-mail: nss@isp.nsc.ru; Gritsenko, V. A. [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Klauser, R. [Synchrotron Radiation Research Center (China); Gwo, S. [National Tsing-Hua University, Department of Physics (China)

2010-10-15

416

Atomistic Calculations of the Effect of Minor Actinides on Thermodynamic and Kinetic Properties of UO{sub 2{+-}x}  

SciTech Connect

The team will examine how the incorporation of actinide species important for mixed oxide (MOX) and other advanced fuel designs impacts thermodynamic quantities of the host UO{sub 2} nuclear fuel and how Pu, Np, Cm and Am influence oxygen mobility. In many cases, the experimental data is either insufficient or missing. For example, in the case of pure NpO2, there is essentially no experimental data on the hyperstoichiometric form it is not even known if hyperstoichiometry NpO{sub 2{+-}x} is stable. The team will employ atomistic modeling tools to calculate these quantities

Chaitanya Deo; Davis Adnersson; Corbett Battaile; Blas uberuaga

2012-10-30

417

Quantum instanton calculation of rate constant for CH4 + OH ? CH3 + H2O reaction: torsional anharmonicity and kinetic isotope effect.  

PubMed

Thermal rate constants for the title reaction are calculated by using the quantum instanton approximation within the full dimensional Cartesian coordinates. The results reveal that the quantum effect is remarkable for the reaction at both low and high temperatures, and the obtained rates are in good agreement with experimental measurements at high temperatures. Compared to the harmonic approximation, the torsional anharmonic effect of the internal rotation has a little influence on the rates at low temperatures, however, it enhances the rate by about 20% at 1000 K. In addition, the free energy barriers for the isotopic reactions and the temperature dependence of kinetic isotope effects are also investigated. Generally speaking, for the title reaction, the replacement of OH with OD will reduce the free energy barrier, while substituting D for H (connected to C) will increase the free energy barrier. PMID:23231230

Wang, Wenji; Zhao, Yi

2012-12-01

418

Calculation of the kinetics of heating and structural changes in the cartilaginous tissue under the action of laser radiation  

SciTech Connect

A theoretical model is developed for the calculation of the temperature fields and determination of the size of a zone with structural changes in the cartilaginous tissue. The model is based on a simultaneous analysis of the heat and mass transfer processes and it takes into account the bulk absorption of laser radiation by the tissue, surface evaporation of water, and temperature dependences of the diffusion coefficients. It is assumed that under the influence of a phase transition between free and bound water, caused by heating of the cartilage to 70{sup 0}C, the proteoglycans of the cartilage matrix become mobile and, as a result of such mass transfer, structural changes are induced in the cartilaginous tissue causing relaxation of stresses or denaturation. It is shown that the maximum temperature is then reached not on the irradiated surface but at some distance from it, and that the size of the zones of structural changes (denaturation depth) depends strongly on the energy density of the laser radiation and its wavelength, on the duration of the irradiation, and on the cartilage thickness. This model makes it possible to calculate the temperature fields and the depth of structural changes in laser-induced relaxation of stresses and changes in the shape of the cartilaginous tissue. (interaction of laser radiation with matter)

Sobol', E N; Kitai, M S [Institute of Laser and Information Technologies, Russian Academy of Sciences, Troitsk, Moscow Region (Russian Federation)

1998-07-31

419

Furan derivatives of substituted phenylthiourea: spectral studies, semi-empirical quantum-chemical calculations and X-ray structure analyses  

NASA Astrophysics Data System (ADS)

Fifty new derivatives of 1-(furan-2-carbonyl)- and 1-(furan-3-carbonyl)-3-phenyl substituted thiourea have been synthesised and identified. Intramolecular hydrogen bonds were investigated in detail, using IR spectroscopy. The three-level Fermi resonance effect in the IR spectra was analysed after deconvolution and band separation. Semi-empirical quantum-chemical calculations (AM1 and PM3) support the results of the IR spectroscopic studies. X-ray single crystal diffraction analyses of four selected compounds, namely 1-(furan-3-carbonyl)-3-(2-trifluoromethyl-phenyl)-thiourea ( 1e), 1-(2-methyl-furan-3-carbonyl)-3-(2-trifluoromethyl-phenyl)-thiourea ( 2e), 1-(2,6-dichloro-phenyl)-3-(2-methyl-furan-3-carbonyl)-thiourea ( 2n) and 1-(4-methoxyphenyl)-3-(3-methyl-2-furan-carbonyl)-thiourea ( 3e), corroborated the molecular and crystal structure of these compounds. Relatively strong intramolecular hydrogen bonds of the N-H⋯O dbnd6 C type as well as intermolecular two-centred and bifurcated three-centred hydrogen bonds were observed, confirming the results of the IR spectral study and the semi-empirical quantum-chemical calculations. A variety of intermolecular interactions, yielding the supramolecular architectures in the four crystalline compounds, are discussed in detail.

Hritzová, Ol'ga; ?ernák, Juraj; Šafa?, Peter; Fr?hlichová, Zdenka; Cs?regh, Ingeborg

2005-05-01

420

Chemical Bonding in Si52- and NaSi5- via Photoelectron Spectroscopy and Ab Initio Calculations  

SciTech Connect

Photoelectron spectroscopy and ab initio calculations are used to investigate the electronic structure and chemical bonding of Si5 - and Si5 2- in NaSi5 -. Photoelectron spectra of Si5 - and NaSi5 - are obtained at several photon energies and are compared with theoretical calculations at four different levels of theory, TD-B3LYP, R(U)OVGF, UCCSD(T), and EOM-CCSD(T), all with 6-311+G(2df) basis sets. Excellent agreement is observed between experiment and theory, confirming the obtained ground-state structures for Si5 - and Si5 2-, which are both found to be trigonal bipyramid with D3h symmetry at several levels of theory. Chemical bonding in Si5, Si5 -, and Si5 2- is analyzed using NPA, molecular orbitals, ELF, and NICS indices. The bonding in Si5 2- is compared with that in the isoelectronic and isostructural B5H5 2- species, but they are found to differ due to the involvement of electron densities, which are supposed to be lone pairs in the skeletal bonding in Si5 2-.

Yu, Dmitry; Boldyrev, Zubarev; Boldyrev, Alexander I.; Li, Xi; Cui, Lifeng; Wang, Lai S.

2005-12-22

421

Fractal-like kinetics of intracellular enzymatic reactions: a chemical framework of endotoxin tolerance and a possible non-specific contribution of macromolecular crowding to cross-tolerance  

PubMed Central

Background The response to endotoxin (LPS), and subsequent signal transduction lead to the production of cytokines such as tumor necrosis factor-? (TNF-?) by innate immune cells. Cells or organisms pretreated with endotoxin enter into a transient state of hyporesponsiveness, referred to as endotoxin tolerance (ET) which represents a particular case of negative preconditioning. Despite recent progress in understanding the molecular basis of ET, there is no consensus yet on the primary mechanism responsible for ET and for the more complex cases of cross tolerance. In this study, we examined the consequences of the macromolecular crowding (MMC) and of fractal-like kinetics (FLK) of intracellular enzymatic reactions on the LPS signaling machinery. We hypothesized that this particular type of enzyme kinetics may explain the development of ET phenomenon. Method Our aim in the present study was to characterize the chemical kinetics framework in ET and determine whether fractal-like kinetics explains, at least in part, ET. We developed an ordinary differential equations (ODE) mathematical model that took into account the links between the MMC and the LPS signaling machinery leading to ET. We proposed that the intracellular fractal environment (MMC) contributes to ET and developed two mathematical models of enzyme kinetics: one based on Kopelman’s fractal-like kinetics framework and the other based on Savageau’s power law model. Results Kopelman’s model provides a good image of the potential influence of a fractal intracellular environment (MMC) on ET. The Savageau power law model also partially explains ET. The computer simulations supported the hypothesis that MMC and FLK may play a role in ET. Conclusion The model highlights the links between the organization of the intracellular environment, MMC and the LPS signaling machinery leading to ET. Our FLK-based model does not minimize the role of the numerous negative regulatory factors. It simply draws attention to the fact that macromolecular crowding can contribute significantly to the induction of ET by imposing geometric constrains and a particular chemical kinetic for the intracellular reactions. PMID:24034421

2013-01-01

422

Model of the catalytic mechanism of human aldose reductase based on quantum chemical calculations.  

SciTech Connect

Aldose Reductase is an enzyme involved in diabetic complications, thoroughly studied for the purpose of inhibitor development. The structure of an enzyme-inhibitor complex solved at sub-atomic resolution has been used to develop a model for the catalytic mechanism. This model has been refined using a combination of Molecular Dynamics and Quantum calculations. It shows that the proton donation, the subject of previous controversies, is the combined effect of three residues: Lys 77, Tyr 48 and His 110. Lys 77 polarises the Tyr 48 OH group, which donates the proton to His 110, which becomes doubly protonated. His 110 then moves and donates the proton to the substrate. The key information from the sub-atomic resolution structure is the orientation of the ring and the single protonafion of the His 110 in the enzyme-inhibitor complex. This model is in full agreement with all available experimental data.

Cachau, R. C.; Howard, E. H.; Barth, P. B.; Mitschler, A. M.; Chevrier, B. C.; Lamour, V.; Joachimiak, A.; Sanishvili, R.; Van Zandt, M.; Sibley, E.; Moras, D.; Podjarny, A.; UPR de Biologie Structurale; National Cancer Inst.; Univ. Louis Pasteur; Inst. for Diabetes Discovery, Inc.

2000-01-01

423

Calculation of the Relative Chemical Stabilities of Proteins as a Function of Temperature and Redox Chemistry in a Hot Spring  

PubMed Central

Uncovering the chemical and physical links between natural environments and microbial communities is becoming increasingly amenable owing to geochemical observations and metagenomic sequencing. At the hot spring known as Bison Pool in Yellowstone National Park, the cooling of the water in the outflow channel is associated with an increase in oxidation potential estimated from multiple field-based measurements. Representative groups of proteins whose sequences were derived from metagenomic data also exhibit an increase in average oxidation state of carbon in the protein molecules with distance from the hot-spring source. The energetic requirements of reactions to form selected proteins used in the model were computed using amino-acid group additivity for the standard molal thermodynamic properties of the proteins, and the relative chemical stabilities of the proteins were investigated by varying temperature, pH and oxidation state, expressed as activity of dissolved hydrogen. The relative stabilities of the proteins were found to track the locations of the sampling sites when the calculations included a function for hydrogen activity that increases with temperature and is higher, or more reducing, than values consistent with measurements of dissolved oxygen, sulfide and oxidation-reduction potential in the field. These findings imply that spatial patterns in the amino acid compositions of proteins can be linked, through energetics of overall chemical reactions representing the formation of the proteins, to the environmental conditions at this hot spring, even if microbial cells maintain considerably different internal conditions. Further applications of the thermodynamic calculations are possible for other natural microbial ecosystems. PMID:21853048

Dick, Jeffrey M.; Shock, Everett L.

2011-01-01

424

Kinetics of the reaction of the heaviest hydrogen atom with H2, the 4He? + H2 ? 4He?H + H reaction: experiments, accurate quantal calculations, and variational transition state theory, including kinetic isotope effects for a factor of 36.1 in isotopic mass.  

PubMed

The neutral muonic helium atom (4)He?, in which one of the electrons of He is replaced by a negative muon, may be effectively regarded as the heaviest isotope of the hydrogen atom, with a mass of 4.115 amu. We report details of the first muon spin rotation (?SR) measurements of the chemical reaction rate constant of (4)He? with molecular hydrogen, (4)He? + H(2) ? (4)He?H + H, at temperatures of 295.5, 405, and 500 K, as well as a ?SR measurement of the hyperfine coupling constant of muonic He at high pressures. The experimental rate constants, k(He?), are compared with the predictions of accurate quantum mechanical (QM) dynamics calculations carried out on a well converged Born-Huang (BH) potential energy surface, based on complete configuration interaction calculations and including a Born-Oppenheimer diagonal correction. At the two highest measured temperatures the agreement between the quantum theory and experiment is good to excellent, well within experimental uncertainties that include an estimate of possible systematic error, but at 295.5 K the quantum calculations for k(He?) are below the experimental value by 2.1 times the experimental uncertainty estimates. Possible reasons for this discrepancy are discussed. Variational transition state theory calculations with multidimensional tunneling have also been carried out for k(He?) on the BH surface, and they agree with the accurate QM rate constants to within 30% over a wider temperature range of 200-1000 K. Comparisons between theory and experiment are also presented for the rate constants for both the D + H(2) and Mu + H(2) reactions in a novel study of kinetic isotope effects for the H + H(2) reactions over a factor of 36.1 in isotopic mass of the atomic reactant. PMID:22088068

Fleming, Donald G; Arseneau, Donald J; Sukhorukov, Oleksandr; Brewer, Jess H; Mielke, Steven L; Truhlar, Donald G; Schatz, George C; Garrett, Bruce C; Peterson, Kirk A

2011-11-14

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A Detailed Chemical Kinetic Reaction Mechanism for n-Alkane Hydrocarbons from n-Octane to n-Hexadecane  

SciTech Connect

Detailed chemical kinetic reaction mechanisms have been developed to describe the pyrolysis and oxidation of the n-alkanes, including n-octane (n-C{sub 8}H{sub 18}), n-nonane (n-C{sub 9}H{sub 20}), n-decane (n-C{sub 10}H{sub 22}), n-undecane (n-C{sub 11}H{sub 24}), n-dodecane (n-C{sub 12}H{sub 26}), n-tridecane (n-C{sub 13}H{sub 28}), n-tetradecane (n-C{sub 14}H{sub 30}), n-pentadecane (n-C{sub 15}H{sub 32}), and n-hexadecane (n-C{sub 16}H{sub 34}). These mechanisms include both high temperature and low temperature reaction pathways. The mechanisms are based on previous mechanisms for n-heptane, using the same reaction class mechanism construction developed initially for n-heptane. Individual reaction class rules are as simple as possible in order to focus on the parallelism between all of the n-alkane fuels included in the mechanisms, and there is an intent to develop these mechanisms further in the future to incorporate greater levels of accuracy and predictive capability. Several of these areas for improvement are identified and explained in detail. These mechanisms are validated through comparisons between computed and experimental data from as many different sources as possible. In addition, numerical experiments are carried out to examine features of n-alkane combustion in which the detailed mechanisms can be used to compare processes in all of the n-alkane fuels. The mechanisms for all of these n-alkanes are presented as a single detailed mechanism, which can be edited to produce efficient mechanisms for any of the n-alkanes included, and the entire mechanism, with supporting thermochemical and transport data, together with an explanatory glossary explaining notations and structural details, will be available on our web page when the paper is accepted for publication.

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

2007-09-25