These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
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  

Microsoft Academic Search

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

J. B. Vos

1986-01-01

3

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

NASA Technical Reports Server (NTRS)

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

Thompson, Anne M.; Stewart, Richard W.

1991-01-01

4

NISt Chemical Kinetics Database  

NSDL National Science Digital Library

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.

5

Chemical Calculations  

NSDL National Science Digital Library

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

Goodman, Jonathan

6

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.

7

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.

David N. Blauch

8

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

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.

David N. Blauch

11

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

12

Chemical kinetics on extrasolar planets.  

PubMed

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

Moses, Julianne I

2014-04-28

13

Chemical Kinetics: half-life  

NSDL National Science Digital Library

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

David N. Blauch

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

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

16

Reduced chemical kinetic mechanisms for hydrocarbon fuels  

Microsoft Academic Search

Using CARM (Computer Aided Reduction Method), a computer program that automates the mechanism reduction process, a variety of different reduced chemical kinetic mechanisms for ethylene and n-heptane have been generated. The reduced mechanisms have been compared to detailed chemistry calculations in simple homogeneous reactors and experiments. Reduced mechanisms for combustion of ethylene having as few as 10 species were found

C J Montgomery; M A Cremer; M P Heap; J-Y Chen; C K Westbrook; L Q Maurice

1999-01-01

17

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

18

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

19

Microreactor for fast chemical kinetics  

E-print Network

The chemical reaction process in a T-shaped microchannel is studied experimentally through the reaction of Ca++ with a fluorescent tracer, Calcium-green. For thin channels (10 um), diffusion of species is found to behave in a way independent of the thickness direction. In such a situation, simulations of a two-dimensional reaction-diffusion model agree remarkably well with the experimental measurements. The comparison of experiments and simulations is used to measure the chemical kinetic constant, which we find to be k=3.2 x 10^5 dm^3/(mol s). Applications of the analysis to faster reactions and to micro-titration are also discussed.

Baroud, C N; Menetrier, L; Tabeling, P; Baroud, Charles N.; Okkels, Fridolin; Menetrier, Laure; Tabeling, Patrick

2003-01-01

20

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.

21

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

22

Detailed Chemical Kinetic Modeling of Cyclohexane Oxidation  

Microsoft Academic Search

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

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

2006-01-01

23

Detailed chemical kinetic modeling of butylbenzene pyrolysis  

Microsoft Academic Search

The gas phase pyrolysis of butylbenzene is modeled using a detailed chemical kinetic approach. A 60-reaction, free radical mechanism is used. The thermodynamics of the chemical species and the kinetic rate parameters for the reactions are taken from the literature or estimated from closely related species or reactions. There was no fitting of these parameters to better match the butylbenzene

H. Freund; W. N. Olmstead

1988-01-01

24

Enhancing Thai Students' Learning of Chemical Kinetics  

ERIC Educational Resources Information Center

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

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

2009-01-01

25

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

26

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

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 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.

David N. Blauch

29

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

30

Chemical kinetics in the coma  

SciTech Connect

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

Huebner, W.F.

1980-01-01

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 Mechanisms for Combustion  

Microsoft Academic Search

Stricter emissions legislation combined with the need to reduce greenhouse gas emissions drives fundamental research to produce cleaner more efficient systems. Chemical kinetic mechanisms together with CFD codes are used to design more efficient and clean systems and optimize the operating behaviour of practical combustion devices such as internal combustion engines, gas turbines and other combustion devices. However, in order

H. J. Curran

33

Chemical Dosing and First-Order Kinetics  

ERIC Educational Resources Information Center

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

Hladky, Paul W.

2011-01-01

34

Method of invariant manifold for chemical kinetics  

Microsoft Academic Search

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

Alexander N. Gorban; Iliya V. Karlin

2002-01-01

35

Method of invariant manifold for chemical kinetics  

Microsoft Academic Search

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

Alexander N. Gorban; Iliya V. Karlina

2003-01-01

36

Chemical kinetics and modeling of planetary atmospheres  

NASA Technical Reports Server (NTRS)

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

Yung, Yuk L.

1990-01-01

37

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

38

Visualization Methods in Analysis of Detailed Chemical Kinetics Modelling  

Microsoft Academic Search

Sensitivity analysis, principal component analysis of the sensitivity matrix, and rate-of-production analysis are useful tools in interpreting detailed chemical kinetics calculations. This paper deals with the practical use and communication of the sensitivity analysis and the related methods are discussed. Some limitations of sensitivity analysis, originating from the mathematical concept (e.g. first-order or brute force methods) or from the software-specific

Anders Broe Bendtsen; Peter Glarborg; Kim Dam-johansen

2001-01-01

39

Chemical Kinetic Modeling of HMX and TATB Laser Ignition Tests  

Microsoft Academic Search

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

CRAIG M. TARVER

2004-01-01

40

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

41

A Detailed Chemical Kinetic Model for TNT  

Microsoft Academic Search

A detailed chemical kinetic mechanism for 2,4,6-tri-nitrotoluene (TNT) has been developed to explore problems of explosive performance and soot formation during the destruction of munitions. The TNT mechanism treats only gas-phase reactions. Reactions for the decomposition of TNT and for the consumption of intermediate products formed from TNT are assembled based on information from the literature and on current understanding

W J Pitz; C K Westbrook

2005-01-01

42

Point kinetics calculations with fully coupled thermal fluids reactivity feedback  

SciTech Connect

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

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

2013-07-01

43

Spreadsheet Templates for Chemical Equilibrium Calculations.  

ERIC Educational Resources Information Center

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

Joshi, Bhairav D.

1993-01-01

44

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

45

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

46

Calculation of Kinetics Parameters for the NBSR  

SciTech Connect

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

Hanson A. L.; Diamond D.

2012-03-06

47

Bio-butanol: Combustion properties and detailed chemical kinetic model  

SciTech Connect

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

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

2010-02-15

48

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

49

SUPERSONIC COMBUSTION SIMULATIONS USING REDUCED CHEMICAL KINETIC MECHANISMS AND ISAT  

Microsoft Academic Search

Reduced chemical kinetic mechanisms for hydrogen and ethylene combustion, created using the CARM (Computer Aided Reduction Method) software have been implemented into the Vulcan CFD code and used for simulations of a supersonic jet flame. CFD simulations using reduced chemical kinetic mechanisms for hydrogen\\/air combustion show better agreement with detailed chemistry simulations and with experiments than existing models using the

Christopher J. Montgomery; Wei Zhao; Bradley R. Adams; Dean R. Eklund

50

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

51

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

52

Problems in rarefied flows and chemical kinetics  

NASA Astrophysics Data System (ADS)

In Part I, a theory on weakly rarefied, low Mach number flows with surface reactions based on small sticking coefficients was first formulated for a binary gas mixture with an irreversible surface reaction, and then extended to a multicomponent mixture with multi-step surface reactions for situation in which all chemically active species are small in concentration compared to a major inert species. Particular interest was placed on the interaction between the Knudsen layer and the surface reactions. Results show that the Knudsen layer modifies not only the incident flux of the molecules striking the surface, but also the temperature-sensitive sticking coefficients and consequently the surface reaction rates. The surface reactions in turn modify the flow structure in the Knudsen layer through the non-zero net flux at the surface. Rate expressions for the surface reactions based on sticking coefficients were derived, and slip boundary conditions for temperature and species concentration suitable for application were established. The widely-used Motz-Wise correction formula for the surface reaction rate was revised and the underlying assumptions leading to its derivation were shown to be incorrect. As an application of the theory, an activation energy asymptotic analysis with one-step overall reaction was performed for the stabilization and extinction of a premixed flame over a rotating disk at sufficiently low pressures, for its relevance in low-pressure CVD (chemical vapor deposition) operations in which the flow is weakly rarefied. Extinction criteria based on the critical Damkohler number were obtained through the S-curve concept, parametrically demonstrating the influence of the CVD operating conditions, such as the spin rate and temperature of the disk, on flame extinction. It is further shown that, while decreasing pressure and hence the reactivity of the mixture tends to extinguish the flame, the trend can be substantially weakened by taking into account of the influence of the Knudsen layer, which reduces the heat loss to the disk as well as the flow stretch rate at the flame. In Part II, a theoretical analysis was performed for the head-on collision of two identical droplets in a gaseous environment, with the attendant bouncing and coalescence outcomes, for situations in which the extent of droplet deformation upon collision is comparable to the original droplet radius, corresponding to O(1--10) of the droplet Weber number. The model embodies the essential physics that describes the substantial amount of droplet deformation, the viscous loss through droplet internal motion induced by the deformation, the dynamics and rarefied nature of the gas film between the interfaces of the colliding droplets, and the potential destruction and thereby merging of these interfaces due to the van der Waals attraction force. The theoretical model was applied to investigate collisions involving hydrocarbon and water droplets at sub- and super-atmospheric pressures. In Part III, a fitting formula was first proposed to approximate the fall-off curves of the pressure- and temperature-dependent unimolecular reaction rate constants. Compared with the widely used Troe's formula, the present expression has the potential to substantially reduce the computation time in its evaluation because of the mathematical simplicity. Four testing reactions from the VariFlex program package were used to examine the accuracy of the present formula, showing improved performance as compared with previous expressions. Furthermore, the present formula shows improved computational efficiency compared to Troe's formula by savings of more than 60% computation time on its evaluation. Studies on chemical kinetics have also included a separate analysis on the decomposition kinetics of CH3NHNH2 (Monomethylhydrazine) with the ab initio transition state theory based master equation analyses. The simple NN and CN bond fissions to produce the radicals CH 3NH + NH2 or CH3 + NHNH2 are expected to dominate the decomposition kinetics. The transition states for these two b

Zhang, Peng

53

Using Excel to Calculate Mineral Chemical Analyses  

NSDL National Science Digital Library

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

54

Calculating Shocks In Flows At Chemical Equilibrium  

NASA Technical Reports Server (NTRS)

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

Eberhardt, Scott; Palmer, Grant

1988-01-01

55

Detailed chemical kinetic mechanisms for combustion of oxygenated fuels  

Microsoft Academic Search

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

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

2000-01-01

56

Detailed chemical kinetic oxidation mechanism for a biodiesel Olivier Herbineta  

E-print Network

Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate Olivier Herbineta , William of methyl decanoate, a surrogate for biodiesel fuels. This model has been built by following the rules and biodiesel fuels to predict overall reactivity, but some kinetic details, including early CO2 production from

Paris-Sud XI, Université de

57

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

58

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

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

59

Understanding the kinetics of spin-forbidden chemical reactions.  

PubMed

Many chemical reactions involve a change in spin-state and are formally forbidden. This article summarises a number of previously published applications showing that a form of Transition State Theory (TST) can account for the kinetics of these reactions. New calculations for the emblematic spin-forbidden reaction HC + N(2) are also reported. The observed reactivity is determined by two factors. The first is the critical energy required for reaction to occur, which in spin-forbidden reactions is often defined by the relative energy of the Minimum Energy Crossing Point (MECP) between potential energy surfaces corresponding to the different spin states. The second factor is the probability of hopping from one surface to the other in the vicinity of the crossing region, which is largely defined by the spin-orbit coupling matrix element between the two electronic wavefunctions. The spin-forbidden transition state theory takes both factors into account and gives good results. The shortcomings of the theory, which are largely analogous to those of standard TST, are discussed. Finally, it is shown that in cases where the surface-hopping probability is low, the kinetics of spin-forbidden reactions will be characterised by unusually unfavourable entropies of activation. As a consequence, reactions involving a spin-state change can be expected to compete poorly with spin-allowed reactions at high temperatures (or energies). PMID:17199148

Harvey, Jeremy N

2007-01-21

60

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

61

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

62

An efficient chemical kinetics solver using high dimensional model representation  

Microsoft Academic Search

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

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

1999-01-01

63

Development of a reduced chemical kinetic mechanism for a gasoline surrogate for gasoline HCCI combustion  

Microsoft Academic Search

A reduced chemical kinetic mechanism consisting of 48 species and 67 reactions is developed and validated for a gasoline surrogate fuel. The surrogate fuel is modeled as a blend of iso-octane, n-heptane, and toluene. The mechanism reduction is performed using sensitivity analysis, investigation of species concentrations, and consideration of the main reaction path. Comparison between ignition delay times calculated using

Kyeonghyeon Lee; Yongrae Kim; Kyoungdoug Min

2010-01-01

64

Fluid flow and chemical reaction kinetics in metamorphic systems  

SciTech Connect

The treatment and effects of chemical reaction kinetics during metamorphism are developed along with the incorporation of fluid flow, diffusion, and thermal evolution. The interplay of fluid flow and surface reaction rates, the distinction between steady state and equilibrium, and the possible overstepping of metamorphic reactions are discussed using a simple analytic model. This model serves as an introduction to the second part of the paper, which develops a reaction model that solves the coupled temperature-fluid flow-chemical composition differential equations relevant to metamorphic processes. Consideration of stable isotopic evidence requires that such a kinetic model be considered for the chemical evolution of a metamorphic aureole. A general numerical scheme is discussed to handle the solution of the model. The results of this kinetic model allow us to reach several important conclusions regarding the factors controlling the chemical evolution of mineral assemblages during a metamorphic event. 41 refs., 19 figs., 5 tabs.

Lasaga, A.C.; Rye, D.M. (Yale Univ., New Haven, CT (United States))

1993-05-01

65

Recent Developments in Detailed Chemical Kinetic Mechanisms  

Microsoft Academic Search

Mechanism reduction must work for the mechanisms being used in current kinetics research. Recent mechanisms and their uses in combustion research are reviewed, attempting to quantify and limit the needs of new mechanism reduction techniques. These mechanisms also provide an ongoing challenge to reduction practitioners.

Charles K. Westbrook; William J. Pitz; Marco Mehl

66

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

67

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

68

A kinetic and equilibrium analysis of silicon carbide chemical vapor deposition on monofilaments  

NASA Technical Reports Server (NTRS)

Chemical kinetics of atmospheric pressure silicon carbide (SiC) chemical vapor deposition (CVD) from dilute silane and propane source gases in hydrogen is numerically analyzed in a cylindrical upflow reactor designed for CVD on monofilaments. The chemical composition of the SiC deposit is assessed both from the calculated total fluxes of carbon and silicon and from chemical equilibrium considerations for the prevailing temperatures and species concentrations at and along the filament surface. The effects of gas and surface chemistry on the evolution of major gas phase species are considered in the analysis.

Gokoglu, S. A.; Kuczmarski, M. A.

1993-01-01

69

A Detailed Chemical Kinetics Simulation of Engine Knock  

Microsoft Academic Search

Abstract–Engine knock was simulated for a stoichiometric ethane-air mixture in which the ethane oxidized according to the detailed chemical kinetics mechanism of Westbrook, Dryer, an co-workers. The simulation, using experimental temperature and pressure histories to drive the reaction kinetics, predicted times of knock occurrence that agreed to within two crank-angle degrees of available experimental engine data. In add ition, general

William. R. Leppard

1985-01-01

70

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

71

Modeling of homogeneous mercury speciation using detailed chemical kinetics  

Microsoft Academic Search

Homogeneous mercury speciation in combustion-generated flue gases was modeled by a detailed kinetic model consisting of 107 reactions and 30 species. This kinetic model includes the oxidation and chlorination of key flue-gas components, as well as six mercury reactions involving HgO with new reaction rate constants calculated neither from experimental data nor by estimated, which was commonly used by other

Minghou Xu; Yu Qiaoa; Chuguang Zheng; Laicai Lib; Jing Liu

2003-01-01

72

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

73

Atrazine sorption kinetics in a characterized soil: predictive calculations.  

PubMed

The use and risks of agricultural pesticides will continue. It is proposed here that better control and possibly some prevention of environmental and health problems should replace the arbitrary standards and post- event monitoring that are still current practice. Mathematical models have been developed for atrazine in a characterized soil from outside Ottawa, Ontario. Experimental data obtained bythe on line HPLC microextraction method were used for the development of the models. The labile sorption sites were treated as a reactant and the number of sites per gram of soil was used to define stoichiometry. This allowed a second-order kinetics integral rate law to be used for sorption from solution onto labile sorption sites, and a first order kinetics integral rate law to be used for bound residue formation. An experimental check and error analyses indicate that the type of model can be used for predictive calculations. The physical meaning of the distribution coefficient K(D) is also considered. The model suggests some practical implications for leaching through soil and for transport by storm runoff. The type of model would be best used for providing input data for fate and transport hydrology models. PMID:18441800

Gamble, Donald S

2008-03-01

74

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

75

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

76

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

77

Detailed chemical kinetic models for the combustion of hydrocarbon fuels  

Microsoft Academic Search

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

John M. Simmie

2003-01-01

78

Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate  

Microsoft Academic Search

A detailed chemical kinetic mechanism has been developed and used to study the oxidation of methyl decanoate, a surrogate for biodiesel fuels. This model has been built by following the rules established by Curran 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

O Herbinet; W J Pitz; C K Westbrook

2007-01-01

79

Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate  

Microsoft Academic Search

A detailed chemical kinetic mechanism has been developed and used to study the oxidation of methyl decanoate, a surrogate for biodiesel fuels. This model has been built by following the rules established by Curran and co-workers for the oxidation of n-heptane and it includes all the reactions known to be pertinent to both low and high temperatures. Computed results have

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

2008-01-01

80

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

81

Detailed chemical kinetic modeling of diesel combustion with oxygenated fuels  

Microsoft Academic Search

The influence of oxygenated hydrocarbons as additives to diesel fuels on ignition, NOx emissions and soot production has been examined using a detailed chemical kinetic reaction mechanism. N-heptane was used as a representative diesel fuel, and methanol, ethanol, dimethyl ether and dimethoxymethane were used as oxygenated fuel additives. It was found that addition of oxygenated hydrocarbons reduced NOx levels and

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

1999-01-01

82

Chemical Kinetics at the Single-Molecule Level  

ERIC Educational Resources Information Center

For over a century, chemists have investigated the rates of chemical reactions using experimental conditions involving huge numbers of molecules. As a consequence, the description of the kinetics of the reaction in terms of average values was good enough for all practical purposes. From the pedagogical point of view, such a description misses the…

Levitus, Marcia

2011-01-01

83

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

84

Chemkin-II: A Fortran chemical kinetics package for the analysis of gas-phase chemical kinetics  

SciTech Connect

This document is the user's manual for the second-generation Chemkin package. Chemkin is a software package for whose purpose is to facilitate the formation, solution, and interpretation of problems involving elementary gas-phase chemical kinetics. It provides an especially flexible and powerful tool for incorporating complex chemical kinetics into simulations of fluid dynamics. The package consists of two major software components: an Interpreter and Gas-Phase Subroutine Library. The Interpreter is a program that reads a symbolic description of an elementary, user-specified chemical reaction mechanism. One output from the Interpreter is a data file that forms a link to the Gas-Phase Subroutine Library. This library is a collection of about 100 highly modular Fortran subroutines that may be called to return information on equation of state, thermodynamic properties, and chemical production rates.

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

1989-09-01

85

Chemical kinetic reaction mechanism for the combustion of propane  

NASA Technical Reports Server (NTRS)

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

Jachimowski, C. J.

1984-01-01

86

Chemical kinetic performance losses for a hydrogen laser thermal thruster  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

87

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

88

Chemical Dynamics, Molecular Energetics, and Kinetics at the Synchrotron  

SciTech Connect

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

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

2010-03-14

89

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

Microsoft Academic Search

A detailed chemical kinetic mechanism for propene oxidation is developed and used to model reactions in a static reactor at temperatures of 575-715 K, equivalence ratios of 0.8 - 2.0, and a pressure of 600 torr. Modeling of hydrocarbon oxidation in this temperature range is important for the validation of detailed models to be used for performing calculations related to

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

1987-01-01

90

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

91

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

E-print Network

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

Vladimirsky, Alexander

92

Detailed chemical kinetic mechanism for surrogates of alternative jet fuels  

Microsoft Academic Search

Blends of n- and iso-alkane components are employed as surrogates for Fischer–Tropsch (F–T) and biomass-derived jet fuels. The composition of the blends has been determined based on data available for two F–T fuel samples obtained from different sources, using a systematic optimization approach. A detailed chemical kinetic mechanism for combustion of the surrogate blends has been assembled. The mechanism has

Chitralkumar V. Naik; Karthik V. Puduppakkam; Abhijit Modak; Ellen Meeks; Yang L. Wang; Qiyao Feng; Theodore T. Tsotsis

2011-01-01

93

Chemical Kinetic Modeling of Combustion of Automotive Fuels  

SciTech Connect

The objectives of this report are to: (1) Develop detailed chemical kinetic reaction models for components of fuels, including olefins and cycloalkanes used in diesel, spark-ignition and HCCI engines; (2) Develop surrogate mixtures of hydrocarbon components to represent real fuels and lead to efficient reduced combustion models; and (3) Characterize the role of fuel composition on production of emissions from practical automotive engines.

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

2006-11-10

94

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

95

Ab initio NMR Chemical Shift Calculations for Biomolecular Systems  

E-print Network

molecular structures in the framework of NMR spectroscopy. Our work is concerned with the development4 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

96

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

97

Modeling of chemical inhibition from amyloid protein aggregation kinetics  

PubMed Central

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

2014-01-01

98

Calculation of coupling coefficients for equations of multipoint kinetics  

NASA Astrophysics Data System (ADS)

The multipoint kinetics equations for fission reaction rate are developed. The algorithm for computation of coupling coefficients is implemented within the MCU-5 code. Results from approbation of the method using the model problem and experimental data are presented.

Ioannisian, M. V.

2013-12-01

99

Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate  

SciTech Connect

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

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

2008-08-15

100

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

101

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

102

A Computer Generated Reduced Iso-Octane Chemical Kinetic Mechanism Applied to Simulation of HCCI Combustion  

Microsoft Academic Search

This paper shows how a computer can systematically remove non-essential chemical reactions from a large chemical kinetic mechanism. The computer removes the reactions based upon a single solution using a detailed mechanism. The resulting reduced chemical mechanism produces similar numerical predictions significantly faster than predictions that use the detailed mechanism. Specifically, a reduced chemical kinetics mechanism for iso-octane has been

S M Aceves; J Martinez-Frias; D Flowers; J R Smith; R Dibble; J Y Chen

2002-01-01

103

Chemical-kinetic prediction of critical parameters in gaseous detonations  

SciTech Connect

A theoretical model including a detailed chemical kinetic reaction mechanism for hydrogen and hydrocarbon oxidation is used to examine the effects of variations in initial pressure and temperature on the detonation properties of gaseous fuel-oxidizer mixtures. Fuels considered include hydrogen, methane, ethane, ethylene, and acetylene. Induction lengths are computed for initial pressures between 0.1 and 10.0 atmospheres and initial temperatures between 200K and 500K. These induction lengths are then compared with available experimental data for critical energy and critical tube diameter for initiation of spherical detonation, as well as detonation limits in linear tubes. Combined with earlier studies concerning variations in fuel-oxidizer equivalence ratio and degree of dilution with N/sub 2/, the model provides a unified treatment of fuel oxidation kinetics in detonations. 4 figures, 1 table.

Westbrook, C.K.; Urtiew, P.A.

1982-01-12

104

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

105

Engineering model reduction of bio-chemical kinetic David Csercsik, Katalin M. Hangos  

E-print Network

, Hungary Significance and Aim Bio-chemical kinetic models of enzyme kinetic processes, as well on the dynamic modeling of signal transduction pathways [2] and enzyme kinetics [3], but no one has tried.: The total quasi-steady-state approximation is valid for reversible enzyme kinetics. Journal of Theoretical

Gorban, Alexander N.

106

Comparison of engine knock predictions using a fully-detailed and a reduced chemical kinetic mechanism  

Microsoft Academic Search

Two different chemical kinetic models are used to interpret engine knock data obtained in a laboratory internal combustion engine. These consisted of a detailed chemical kinetic model and a global kinetic model, both calibrated to be able to describe these conditions. Both models are found to provide accurate simulations of the experimental data, but both models required calibration and\\/or updating.

J. S. Cowart; J. C. Keck; J. B. Heywood; C. K. Westbrook; W. J. Pitz

1989-01-01

107

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

Microsoft Academic Search

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

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

2001-01-01

108

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

Microsoft Academic Search

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

P. Pepiot-Desjardins; H. Pitsch

2008-01-01

109

Surface complex structures modelled with quantum chemical calculations: carbonate, phosphate,  

E-print Network

Surface complex structures modelled with quantum chemical calculations: carbonate, phosphate to provide good agree- ment with experimental observations for the oxyanions carbonate, phosphate, sulphate, the interaction of species such as carbon- ate, phosphate, sulphate, arsenate and arsenite with metal oxide

Sparks, Donald L.

110

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

Microsoft Academic Search

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

Christopher J. Montgomery; Chongguan Yang; Alan R. Parkinson; J.-Y. Chen

2006-01-01

111

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

Microsoft Academic Search

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

W. Pitz; C. K. Westbrook

1986-01-01

112

Symmetry relations in chemical kinetics arising from microscopic reversibility.  

PubMed

It is shown that the kinetics of time-reversible chemical reactions having the same equilibrium constant but different initial conditions are closely related to one another by a directly measurable symmetry relation analogous to chemical detailed balance. In contrast to detailed balance, however, this relation does not require knowledge of the elementary steps that underlie the reaction, and remains valid in regimes where the concept of rate constants is ill defined, such as at very short times and in the presence of low activation barriers. Numerical simulations of a model of isomerization in solution are provided to illustrate the symmetry under such conditions, and potential applications in protein folding or unfolding are pointed out. PMID:16486660

Adib, Artur B

2006-01-20

113

Maximum Probability Reaction Sequences in Stochastic Chemical Kinetic Systems  

PubMed Central

The detailed behavior of many molecular processes in the cell, such as protein folding, protein complex assembly, and gene regulation, transcription and translation, can often be accurately captured by stochastic chemical kinetic models. We investigate a novel computational problem involving these models – that of finding the most-probable sequence of reactions that connects two or more states of the system observed at different times. We describe an efficient method for computing the probability of a given reaction sequence, but argue that computing most-probable reaction sequences is EXPSPACE-hard. We develop exact (exhaustive) and approximate algorithms for finding most-probable reaction sequences. We evaluate these methods on test problems relating to a recently-proposed stochastic model of folding of the Trp-cage peptide. Our results provide new computational tools for analyzing stochastic chemical models, and demonstrate their utility in illuminating the behavior of real-world systems. PMID:21629860

Salehi, Maryam; Perkins, Theodore J.

2010-01-01

114

Maximum Probability Reaction Sequences in Stochastic Chemical Kinetic Systems  

PubMed Central

The detailed behavior of many molecular processes in the cell, such as protein folding, protein complex assembly, and gene regulation, transcription and translation, can often be accurately captured by stochastic chemical kinetic models. We investigate a novel computational problem involving these models – that of finding the most-probable sequence of reactions that connects two or more states of the system observed at different times. We describe an efficient method for computing the probability of a given reaction sequence, but argue that computing most-probable reaction sequences is EXPSPACE-hard. We develop exact (exhaustive) and approximate algorithms for finding most-probable reaction sequences. We evaluate these methods on test problems relating to a recently-proposed stochastic model of folding of the Trp-cage peptide. Our results provide new computational tools for analyzing stochastic chemical models, and demonstrate their utility in illuminating the behavior of real-world systems. PMID:21441987

Salehi, Maryam; Perkins, Theodore J.

2010-01-01

115

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

E-print Network

1 Detailed chemical kinetic mechanism for the oxidation of biodiesel fuels blend surrogate of biodiesel fuels in diesel and homogeneous charge compression ignition engines. Keywords: Methyl decanoate; Methyl decenoate; Surrogate; Oxidation; Biodiesel fuels; Kinetic modeling; Engine; Low

Paris-Sud XI, Université de

116

Theory of Chemical Kinetics and Charge Transfer based on Nonequilibrium Thermodynamics  

E-print Network

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 ...

Bazant, Martin Z.

117

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

PubMed Central

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

2012-01-01

118

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

119

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

120

Stochastic chemical kinetics with energy Guy Fayolle, Vadim Malyshev, Serguei Pirogov  

E-print Network

Stochastic chemical kinetics with energy parameters Guy Fayolle, Vadim Malyshev, Serguei Pirogov ABSTRACT: We introduce new models of energy redistribution in stochas- tic chemical kinetics with several biology are chains or networks of chemical reac- tions providing redistribution of energy, in particular

Paris-Sud XI, Université de

121

Kinetics of Soil Chemical Reactions: Relationships between Empirical Equations and Diffusion Models  

E-print Network

Kinetics of Soil Chemical Reactions: Relationships between Empirical Equations and Diffusion Models equation has been used by several workers to describe soil chemical reaction rates (Chien and Clayton, 1980-diffusion equa- tions have been used to describe the kinetics of soil chemical processes. Often, several

Sparks, Donald L.

122

Quasi-analytic point reactor kinetics calculations using individual precursor data  

Microsoft Academic Search

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

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

1985-01-01

123

Calculation of viscoelastic beadrod flow mediated by a homogenised kinetic scale with holonomic constraints  

E-print Network

Calculation of viscoelastic bead­rod flow mediated by a homogenised kinetic scale with holonomic with a finite volume Godunov-projection algorithm. We demonstrate the computation of viscoelastic stress divergence using this multiscale approach. Keywords: viscoelasticity; complex fluids; multiscale

124

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

125

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

SciTech Connect

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

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

1996-05-01

126

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

127

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

128

Infrared Absorption Spectroscopy and Chemical Kinetics of Free Radicals  

SciTech Connect

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

Curl, Robert F; Glass, Graham

2004-11-01

129

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

130

Hyperpolarizability calculation and kinetic effect of impurities on LVP.  

PubMed

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. PMID:25233029

Liu, Xiaojing; Xu, Xijin; Zhang, Changwen

2015-02-25

131

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

132

Engine knock predictions using a fully-detailed and a reduced chemical kinetic mechanism  

Microsoft Academic Search

Two chemical kinetic models are used to interpret engine knock data obtained in a laboratory internal combustion engine. These consisted of a detailed kinetic model and a reduced kinetic model, both calibrated to describe engine conditions. Comparisons of both models with experimental results are discussed. Relationships between the reaction steps of the detailed and reduced models are examined in detail,

J. S. Cowart; J. C. Keck; J. B. Heywood; C. K. Westbrook; W. J. Pitz

1989-01-01

133

Core Physics and Kinetics Calculations for the Fissioning Plasma Core Reactor  

NASA Technical Reports Server (NTRS)

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

Butler, C.; Albright, D.

2007-01-01

134

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

135

Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels  

E-print Network

Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels C.K. Westbrooka chemical kinetic reaction mechanism is developed for the five major components of soy biodiesel and rapeseed biodiesel fuels. These components, methyl stearate, methyl oleate, methyl linoleate, methyl

Paris-Sud XI, Université de

136

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

137

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

E-print Network

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

Van Den Eijnden, Eric

138

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

PubMed

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

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

2013-11-15

139

Thermodynamics and Kinetics of Chemical Equilibrium in Solution.  

ERIC Educational Resources Information Center

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

Leenson, I. A.

1986-01-01

140

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

141

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

142

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. PMID:25685503

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

2013-01-01

143

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

PubMed

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

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

2014-05-01

144

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

145

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

146

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

Microsoft Academic Search

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

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

2008-01-01

147

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

E-print Network

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

Sparks, Donald L.

148

Kinetics calculation of cascade in K p and K d atoms by Monte-Carlo method  

Microsoft Academic Search

method. The x-ray yields due to the radiative transitions during the cascade processes are calculated. The evolution of the kinetic energy distribution during the atomic cascade is very important, because many collisional processes are energy dependence(2). we have taken into account the energy dependence of collisional processes and we have not used any tuning parameters in the Coulomb transition and

S. Z. Kalantari; M. G. Raeisi

149

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 ...

150

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

Microsoft Academic Search

We present an ab initio study of the thermodynamics and kinetics of LixC6 , relevant for anode Li intercalation in rechargeable Li batteries. In graphite, the interlayer interactions are dominated by Van der Waals forces, which are not captured with standard density-functional theory (DFT). By calculating the voltage profile for Li intercalation into graphite and comparing it to experimental results,

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

2010-01-01

151

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

1998-01-01

152

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 ...

153

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

154

Chemical Kinetic Data Base for Combustion Chemistry Part 4. Isobutane  

Microsoft Academic Search

This publication contains evaluated and estimated data on the kinetics of reactions involving isobutane, t-butyl radical and isobutyl radical and various small inorganic and organic species which are of importance for the proper understanding of isobutane combustion and pyrolysis. It is meant to be used in conjunction with the kinetic data given in earlier publications, which is of direct pertinence

Wing Tsang

1990-01-01

155

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

156

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

PubMed

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

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

2014-03-21

157

Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels  

Microsoft Academic Search

A detailed chemical kinetic reaction mechanism is developed for the five major components of soy biodiesel and rapeseed biodiesel fuels. These components, methyl stearate, methyl oleate, methyl linoleate, methyl linolenate, and methyl palmitate, are large methyl ester molecules, some with carboncarbon double bonds, and kinetic mechanisms for them as a family of fuels have not previously been available. Of particular

C. K. Westbrook; C. V. Naik; O. Herbinet; W. J. Pitz; M. Mehl; S. M. Sarathy; H. J. Curran

2011-01-01

158

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

E-print Network

and mi- croscopic elements of modern physical chemistry. The bulk properties displayed by gases. The course will use our standard text for physical chemistry at Waterloo, Physical Chemistry - A Molecular the kinetic theory of gases and the core elements of chemical kinetics, the rate law and the reaction

Nazar, Linda F.

159

Analysis of the Computational Singular Perturbation Reduction Method for Chemical Kinetics  

Microsoft Academic Search

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

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

2004-01-01

160

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

Microsoft Academic Search

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

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

1994-01-01

161

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

162

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

163

An efficient storage scheme for reduced chemical kinetics based on orthogonal polynomials  

Microsoft Academic Search

Simplified chemical kinetic schemes are a crucial prerequisite for the simulation of complex three-dimensional turbulent flows, and various methods for the generation of reduced mechanisms have been developed in the past. The method of intrinsic low-dimensional manifolds (ILDM), e.g., provides a mathematical tool for the automatic simplification of chemical kinetics, but one problem of this method is the fact that

H. Hiemann; D. Schmidt; U. Maas

1997-01-01

164

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

165

Toward the quantum chemical calculation of nuclear magnetic resonance chemical shifts of proteins.  

PubMed

Despite the many protein structures solved successfully by nuclear magnetic resonance (NMR) spectroscopy, quality control of NMR structures is still by far not as well established and standardized as in crystallography. Therefore, there is still the need for new, independent, and unbiased evaluation tools to identify problematic parts and in the best case also to give guidelines that how to fix them. We present here, quantum chemical calculations of NMR chemical shifts for many proteins based on our fragment-based quantum chemical method: the adjustable density matrix assembler (ADMA). These results show that (13)C chemical shifts of reasonable accuracy can be obtained that can already provide a powerful measure for the structure validation. (1)H and even more (15)N chemical shifts deviate more strongly from experiment due to the insufficient treatment of solvent effects and conformational averaging. PMID:21557322

Frank, Andrea; Onila, Ionut; Möller, Heiko M; Exner, Thomas E

2011-07-01

166

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

167

Calculation of the chemical behavior of highly concentrated geothermal brines  

SciTech Connect

In this report, the authors describe the development of a chemical equilibrium model for hydrothermal waters based on the semiempirical equations of aqueous electrolyte solutions recently introduced by Pitzer and co-workers. Accurate solubility predictions (usually within 5-10% of experimental results) can be made for ionic strengths 0-20m. Comparison with experimental data indicates that a theory parameterized by binary and ternary data can be used to accurately predict solubilities in much more complex mixtures. Mineral solubilities calculated with this model are compared with those calculated from other currently available models. Whereas the predictions are typically within 5%, the ion pairing models are substantially in error at low ionic strengths. Recent results parameterizing the H{sub 2}S and SiO{sub 2} systems will be presented.

Moller-Weare, Nancy; Weare, John H.

1982-10-08

168

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

Microsoft Academic Search

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

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

2005-01-01

169

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

SciTech Connect

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

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

2007-11-15

170

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

171

Chemical glycan conjugation controls the biodistribution and kinetics of proteins in live animals.  

PubMed

The biodistributions and in vivo kinetics of chemically prepared neoglycoproteins have been examined previously and are reviewed here. A variety of mono- and oligosaccharides may be conjugated onto a protein surface using chemical methods. The kinetics and organ-specific accumulation profiles of these glycoconjugates, introduced through intravenous injection, have been analyzed using conventional dissection studies as well as noninvasive methods, such as SPECT, PET, or fluorescence imaging. These studies have revealed glycan-dependent protein distribution kinetics that may be useful for pharmacological and diagnostic applications. PMID:25441835

Ogura, A; Kurbangalieva, A; Tanaka, K

2015-01-01

172

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

PubMed

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

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

2014-04-01

173

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

174

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

175

Integration of large chemical kinetic mechanisms via exponential methods with Krylov approximations to Jacobian matrix functions  

Microsoft Academic Search

Recent trends in hydrocarbon fuel research indicate that the number of species and reactions in chemical kinetic mechanisms is rapidly increasing in an effort to provide predictive capabilities for fuels of practical interest. In order to cope with the computational cost associated with the time integration of stiff, large chemical systems, a novel approach is proposed. The approach combines an

Fabrizio Bisetti

2011-01-01

176

Detailed Chemical Kinetic Reaction Mechanisms for Combustion of Isomers of Heptane  

Microsoft Academic Search

Detailed chemical kinetic reaction mechanisms are developed for all nine chemical isomers of heptane (CH), following techniques and models developed previously for other smaller alkane hydrocarbon species. These reaction mechanisms are tested at high temperatures by computing shock tube ignition delay times and at lower temperatures by simulating ignition in a rapid compression machine. Although the corresponding experiments have not

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

2001-01-01

177

Integration of large chemical kinetic mechanisms via exponential methods with Krylov approximations to Jacobian matrix functions  

Microsoft Academic Search

Recent trends in hydrocarbon fuel research indicate that the number of species and reactions in chemical kinetic mechanisms is rapidly increasing in an effort to provide predictive capabilities for fuels of practical interest. In order to cope with the computational cost associated with the time integration of stiff, large chemical systems, a novel approach is proposed. The approach combines an

Fabrizio Bisetti

2012-01-01

178

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

179

Spin-selective recombination kinetics of a model chemical magnetoreceptor.  

PubMed

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

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

2011-06-21

180

Beyond Traditional Chemical Kinetics Formulas: Group-Theoretic Approach  

E-print Network

obtains by the traditional formulas. For example, Michaelis and Menten shows that for enzyme kinetics different ways to describe their values. For example, temperature can be measures in degrees Fahrenheit is, in effect, a logarithm of this energy), etc. Numerical values x and x of the same quantity

Kreinovich, Vladik

181

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

ERIC Educational Resources Information Center

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

Weston, Ralph E., Jr.

1988-01-01

182

Calculation of f? and m? at finite chemical potential  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

183

Chemical Kinetic Data Base for Combustion Chemistry Part 4. Isobutane  

SciTech Connect

This publication contains evaluated and estimated data on the kinetics of reactions involving isobutane, {ital t}-butyl radical and isobutyl radical and various small inorganic and organic species which are of importance for the proper understanding of isobutane combustion and pyrolysis. It is meant to be used in conjunction with the kinetic data given in earlier publications, which is of direct pertinence to the understanding of methane, ethane, methanol and propane pyrolysis and combustion, but which also contains a large volume of data that are applicable to the isobutane system. The temperature range covered is 300--2500 K and the density range 1{times}10{sup 16} to 1{times}10{sup 21} molecules cm{sup {minus}3}.

Tsang, W. (Chemical Kinetics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (USA))

1990-01-01

184

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

NASA Astrophysics Data System (ADS)

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

Kolesnichenko, Evgeniy G.; Gorbachev, Yuriy E.

2014-12-01

185

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

186

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...

187

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

NASA Technical Reports Server (NTRS)

The efficiency of several algorithms used for numerical integration of stiff ordinary differential equations was compared. The methods examined included two general purpose codes EPISODE and LSODE and three codes (CHEMEQ, CREK1D and GCKP84) developed specifically to integrate chemical kinetic rate equations. The codes were applied to two test problems drawn from combustion kinetics. The comparisons show that LSODE is the fastest code available for the integration of combustion kinetic rate equations. It is shown that an iterative solution of the algebraic energy conservation equation to compute the temperature can be more efficient then evaluating the temperature by integrating its time-derivative.

Radhakrishnan, K.

1984-01-01

188

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

NASA Technical Reports Server (NTRS)

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

Radhakrishnan, K.

1985-01-01

189

Validity conditions for moment closure approximations in stochastic chemical kinetics.  

PubMed

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. PMID:25173001

Schnoerr, David; Sanguinetti, Guido; Grima, Ramon

2014-08-28

190

Accurate calculation of (31)P NMR chemical shifts in polyoxometalates.  

PubMed

We search for the best density functional theory strategy for the determination of (31)P nuclear magnetic resonance (NMR) chemical shifts, ?((31)P), in polyoxometalates. Among the variables governing the quality of the quantum modelling, we tackle herein the influence of the functional and the basis set. The spin-orbit and solvent effects were routinely included. To do so we analysed the family of structures ?-[P2W18-xMxO62](n-) with M = Mo(VI), V(V) or Nb(V); [P2W17O62(M'R)](n-) with M' = Sn(IV), Ge(IV) and Ru(II) and [PW12-xMxO40](n-) with M = Pd(IV), Nb(V) and Ti(IV). The main results suggest that, to date, the best procedure for the accurate calculation of ?((31)P) in polyoxometalates is the combination of TZP/PBE//TZ2P/OPBE (for NMR//optimization step). The hybrid functionals (PBE0, B3LYP) tested herein were applied to the NMR step, besides being more CPU-consuming, do not outperform pure GGA functionals. Although previous studies on (183)W NMR suggested that the use of very large basis sets like QZ4P were needed for geometry optimization, the present results indicate that TZ2P suffices if the functional is optimal. Moreover, scaling corrections were applied to the results providing low mean absolute errors below 1 ppm for ?((31)P), which is a step forward in order to confirm or predict chemical shifts in polyoxometalates. Finally, via a simplified molecular model, we establish how the small variations in ?((31)P) arise from energy changes in the occupied and virtual orbitals of the PO4 group. PMID:25738630

Pascual-Borràs, Magda; López, Xavier; Poblet, Josep M

2015-04-14

191

Chemical kinetics of homogeneous atmospheric oxidation of sulfur dioxide  

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

192

Vibrational and chemical kinetics in plasma of CO containing gases  

NASA Astrophysics Data System (ADS)

This paper discusses the experimental results pointing to the efficient channel of the CO vibrational to the C2 electron energy transfer. The radiation spectra of e3?, C1?, D1? states of C2 molecules were investigated and the relation of their kinetics to vibrational excitation of CO (X1?, v) molecules in the He-CO-O2 gas discharge plasma was discussed. The rate constant for VE- process CO (X1?, v>= 25) + C2 ? CO(X1?) + C2(D1?u), was estimated, and kvE ~ 10-14 cm3/c.

Grigorian, G. M.; Cenian, A.

2014-08-01

193

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

194

CHEMKIN2. General Gas-Phase Chemical Kinetics  

SciTech Connect

CHEMKIN is a high-level tool for chemists to use to describe arbitrary gas-phase chemical reaction mechanisms and systems of governing equations. It remains, however, for the user to select and implement a solution method; this is not provided. It consists of two major components: the Interpreter and the Gas-phase Subroutine Library. The Interpreter reads a symbolic description of an arbitrary, user-specified chemical reaction mechanism. A data file is generated which forms a link to the Gas-phase Subroutine Library, a collection of about 200 modular subroutines which may be called to return thermodynamic properties, chemical production rates, derivatives of thermodynamic properties, derivatives of chemical production rates, or sensitivity parameters. Both single and double precision versions of CHEMKIN are included. Also provided is a set of FORTRAN subroutines for evaluating gas-phase transport properties such as thermal conductivities, viscosities, and diffusion coefficients. These properties are an important part of any computational simulation of a chemically reacting flow. The transport properties subroutines are designed to be used in conjunction with the CHEMKIN Subroutine Library. The transport properties depend on the state of the gas and on certain molecular parameters. The parameters considered are the Lennard-Jones potential well depth and collision diameter, the dipole moment, the polarizability, and the rotational relaxation collision number.

Rupley, F.M. [Sandia National Labs., Livermore, CA (United States)

1992-01-24

195

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

196

Chemical kinetics and the environment: Studies at SRI International  

Microsoft Academic Search

The description of our research that appeared in the issue of Chemical and Engineering news that announced this award mentioned four general areas of research. The author would like to address each of them in this presentation. Bond Dissociation Energy Measurements: In recent years there has been some controversy as to the values of the heats of formation of some

Golden

1990-01-01

197

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

198

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...

199

Equilibrium, chemical kinetic, and transport limitations to diamond growth  

Microsoft Academic Search

Because of their extreme properties, diamond films have found some industrial applications, i.e., heat sinks and tool coatings. However, to increase their economic attractiveness, the growth rate must be increased, the deposition temperature must be lowered, and single crystal films must be achieved. We have studied two types of chemical vapor deposition systems, hot-filament and microwave assisted, in order to

Edward Anthony Evans

1998-01-01

200

Using dynamic frequencies for overcoming the stiffness of the neutronic space-time kinetic calculations  

SciTech Connect

One of the major computational difficulties in space-time kinetics is the [open quotes]stiffness[close quotes] of the kinetic equations, which is caused by the orders-of-magnitude difference between the prompt neutron and delayed neutron lifetimes. As a result, the time discretization step size in the numerical solution of the equations has to be very small to reflect the very fast response of the prompt neutrons. The idea of the [open quotes]stiffness confinement method[close quotes] was introduced and successfully demonstrated in Ref. I to alleviate the stiffness problem. The method uses a time-dependent [open quotes]dynamic frequency[close quotes] to replace the time-derivative term in the kinetic equations and calculates the dynamic frequencies iteratively in solving the equations. If the dynamic frequency for the prompt neutron is set to zero, the method reduces to the prompt jump approximation but also extends the validity of the prompt jump approximation into the prompt supercritical regime. Otherwise, if the dynamic frequency for the prompt neutron is retained, then no approximation is introduced, and the time discretization step size can be significantly enlarged.

Chao, Y.A.; Risher, D.H. (Westinghouse Electric Corp., Pittsburgh, PA (United States))

1993-01-01

201

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

202

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

203

Kinetic and chemical mechanisms of homocitrate synthase from Thermus thermophilus.  

PubMed

The homocitrate synthase from Thermus thermophilus (TtHCS) is a metal-activated enzyme with either Mg(2+) or Mn(2+) capable of serving as the divalent cation. The enzyme exhibits a sequential kinetic mechanism. The mechanism is steady state ordered with ?-ketoglutarate (?-Kg) binding prior to acetyl-CoA (AcCoA) with Mn(2+), whereas it is steady state random with Mg(2+), suggesting a difference in the competence of the E·Mn·?-Kg·AcCoA and E·Mg·?-Kg·AcCoA complexes. The mechanism is supported by product and dead-end inhibition studies. The primary isotope effect obtained with deuterioacetylCoA (AcCoA-d(3)) in the presence of Mg(2+) is unity (value 1.0) at low concentrations of AcCoA, whereas it is 2 at high concentrations of AcCoA. Data suggest the presence of a slow conformational change induced by binding of AcCoA that accompanies deprotonation of the methyl group of AcCoA. The solvent kinetic deuterium isotope effect is also unity at low AcCoA, but is 1.7 at high AcCoA, consistent with the proposed slow conformational change. The maximum rate is pH independent with either Mg(2+) or Mn(2+) as the divalent metal ion, whereas V/K(?-Kg) (with Mn(2+)) decreases at low and high pH giving pK values of about 6.5 and 8.0. Lysine is a competitive inhibitor that binds to the active site of TtHCS, and shares some of the same binding determinants as ?-Kg. Lysine binding exhibits negative cooperativity, indicating cross-talk between the two monomers of the TtHCS dimer. Data are discussed in terms of the overall mechanism of TtHCS. PMID:21733842

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

2011-08-19

204

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

SciTech Connect

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

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

2010-01-22

205

Analysis of Premixed Charge Compression Ignition Combustion with a Sequential Fluid Mechanics-Multizone Chemical Kinetics Model  

SciTech Connect

We have developed a methodology for analysis of PCCI engines that applies to conditions in which there is some stratification in the air-fuel distribution inside the cylinder at the time of combustion. Our analysis methodology consists of two stages: first, a fluid mechanics code is used to determine temperature and equivalence ratio distributions as a function of crank angle, assuming motored conditions. The distribution information is then used for grouping the mass in the cylinder into a two-dimensional (temperature-equivalence ratio) array of zones. The zone information is then handed on to a detailed chemical kinetics model that calculates combustion, emissions and engine efficiency information. The methodology applies to situations where chemistry and fluid mechanics are weakly linked. The results of the multi-zone model have been compared to the results obtained from a fully integrated code, in which a chemical kinetics code is directly linked into a fluid mechanics code to calculate chemistry in every cell of the grid. The results show that the multi-zone model predicts burn duration and peak cylinder pressure with good accuracy. However, ignition timing predicted by the multi-zone model is sensitive to the transition angle between the fluid mechanics code and the chemical kinetics code. The paper explores the possibility of using three different criteria for determining the transition angle: fraction of heat release at the time of ignition, temperature of the hottest cell at the time of ignition, and a fixed crank angle of transition. The results show that the three criteria have some validity as transition criteria. Further research is necessary to investigate the effect of fuel properties and operating conditions on transition angle.

Aceves, S M; Flowers, D L; Espinosa-Loza, F; Babajimopoulos, A; Assanis, D N

2004-09-30

206

Calculation of the growth kinetics and dispersity of K2SO4 crystals in drops of an evaporating solution  

NASA Astrophysics Data System (ADS)

Experimental data on the evaporation kinetics of saturated K2SO4 solution drops and the nucleation kinetics of the first crystals are used to develop a simple procedure for the calculation of the solution concentration and the number, size, and dispersity of growing crystals. The calculation results agree well with the experimental data on the growth kinetics of K2SO4 crystals and their dispersity after complete evaporation of water. The dispersity of crystals is shown to linearly depend on the reciprocal time of evaporation of drops having different initial heights.

Fedorov, V. Yu.

2010-07-01

207

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

E-print Network

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 for computing kinetic isotope effects for chemical reactions in solution and in enzymes. In the ensemble

Minnesota, University of

208

Comparison of self-consistent field treatments of kinetic couplings in calculations on polyatomic molecules  

NASA Astrophysics Data System (ADS)

The accuracy of the vibrational self-consistent field (VSCF) and time-dependent self-consistent field (TDSCF) approximations for studies of vibrational dynamics of polyatomic systems is investigated for systems in which the most important off-diagonal coupling terms in the Hamiltonian are in the kinetic energy operator. To lowest order, these terms are zero in the VSCF treatment. This leads to large differences between the energies calculated using this approximation, compared to those obtained from a variational calculation. In contrast, the energy levels, obtained using the TDSCF approximation, are in good agreement with variational results. These questions are investigated using a collinear model of HCN in an internal coordinate representation.

McCoy, Anne B.

1998-08-01

209

Kinetics and chemical equilibrium of the hydration of formaldehyde  

Microsoft Academic Search

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

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

2002-01-01

210

Kinetics and thermodynamics of chemical reactions in Li/SOCl2 cells  

NASA Technical Reports Server (NTRS)

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

Hansen, Lee D.; Frank, Harvey

1987-01-01

211

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

E-print Network

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

Ben O'Shaughnessy; Dimitrios Vavylonis

1998-12-21

212

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

NASA Astrophysics Data System (ADS)

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.

2014-02-01

213

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

214

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

NASA Astrophysics Data System (ADS)

Sensitivity analysis is a powerful tool in determining parameters to which the system output is most responsive, in assessing robustness of the system to extreme circumstances or unusual environmental conditions, in identifying rate limiting pathways as a candidate for drug delivery, and in parameter estimation for calculating the Hessian of the objective function. Anderson [SIAM J. Numer. Anal. 50, 2237 (2012)], 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.

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

2013-02-01

215

Reduced Chemical Kinetic Model for the Ignition Delay of Hydrocarbon Fuels and DME  

Microsoft Academic Search

A reduced chemical kinetic model that consists of 19 reactions and 17 species was derived to apply an autoignition model of hydrocarbon fuels. Given the initial fuel-air mixture concentration, temperature, and pressure, the present model was used to predict temperature, pressure, and species concentrations as a function of time. The model was validated with the experimental data where the ignition

Hyunguk Kim; Sangsoo Pae; Kyoungdoug Min

2002-01-01

216

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

Microsoft Academic Search

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

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

2001-01-01

217

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

Microsoft Academic Search

Detailed chemical kinetic mechanisms were developed and used to study the oxidation of two large unsaturated esters: methyl-5-decenoate and methyl-9-decenoate. These models were built from a previous methyl decanoate mechanism and were compared with rapeseed oil methyl esters oxidation experiments in a jet stirred reactor. A comparative study of the reactivity of these three oxygenated compounds was performed and the

O Herbinet; W J Pitz; C K Westbrook

2009-01-01

218

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

Microsoft Academic Search

New chemical kinetic reaction mechanisms are developed for two of the five major components of biodiesel fuel, methyl stearate and methyl oleate. The mechanisms are produced using existing reaction classes and rules for reaction rates, with additional reaction classes to describe other reactions unique to methyl ester species. Mechanism capabilities were examined by computing fuel\\/air autoignition delay times and comparing

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

2010-01-01

219

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

Microsoft Academic Search

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

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

2007-01-01

220

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

221

Post-processing of detailed chemical kinetic mechanisms onto CFD simulations  

Microsoft Academic Search

A new general method to combine computational fluid dynamics tools and detailed chemical kinetic mechanisms is presented. The method involves post-processing of data extracted from computational fluid dynamics (CFD) simulations obtained by using a simple reaction model to generate an overall estimate of the temperature and flow field in the computational domain. In post-processing of the data, the individual cells

M. S. Skjøth-rasmussen; O. Holm-christensen; M. Østberg; T. S. Christensen; T. Johannessen; A. D. Jensen; P. Glarborg; H. Livbjerg

2004-01-01

222

Detailed chemical kinetic reaction mechanism for biodiesel components methyl stearate and methyl oleate  

Microsoft Academic Search

New chemical kinetic reaction mechanisms are developed for two of the five major components of biodiesel fuel, methyl stearate and methyl oleate. The mechanisms are produced using existing reaction classes and rules for reaction rates, with additional reaction classes to describe other reactions unique to methyl ester species. Mechanism capabilities were examined by computing fuel\\/air autoignition delay times and comparing

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

2011-01-01

223

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

Microsoft Academic Search

A detailed chemical kinetic reaction mechanism is described which simulates the oxidation of the primary reference fuels n-heptane and iso-octane. The high temperature subset of these mechanisms is identified, and the extensions to deal with low temperature conditions are also explained. The algorithms used to assign reaction rates to elementary steps in the reaction mechanism are described, and the means

C. K. Westbrook; W. J. Pitz

1993-01-01

224

Developing simplified models of combustion chemistry by simulation with detailed chemical kinetics models  

Microsoft Academic Search

Simulations with detailed chemical kinetics mechanisms were used to develop simplified models for the oxidation of simple fuels, with emphasis on methane. The first simplification was based on the observation that the concentrations of several radical species were in steady state so that they formed a ''radical pool'' where the concentrations of pool species track one another. During the induction

Creighton

1986-01-01

225

Does co burn in a fluidized bed?—a detailed chemical kinetic modeling study  

Microsoft Academic Search

One important issue in fluidized bed combustion is the effect of the fluidized particles on the homogeneous oxidation of both the volatiles and CO from char combustion. These surfaces are thought to quench the radicals and thus lower the rate of combustion significantly. In this work the quenching of the radicals is introduced in a detailed chemical kinetic mechanism to

G. Loeffler; H. Hofbauer

2002-01-01

226

The Bailey criterion: Statistical derivation and applications to interpretations of durability tests and chemical kinetics  

Microsoft Academic Search

The Bailey durability criterion, well known in mechanics of materials, has also been used in other flelds of study such as the kinetics of chemical reactions. This paper rationalizes the wide applicability of this criterion in terms of Markovian statistical properties of systems. Two particular cases are discussed as examples of the general approach: durability of a wide class of

A. D. Freeds; A. I. Leonov

2002-01-01

227

The Teaching and Learning of Chemical Kinetics Supported with MS Excel  

ERIC Educational Resources Information Center

Students in 12 secondary schools in three states of Malaysia were taught to use worksheets on the chemical kinetics topic which had been pre-created using the MS Excel worksheets. After the teaching, an opinion survey of 612 Form Six students from these schools was conducted. The results showed that almost all the students felt that MS Excel…

Zain, Sharifuddin Md; Rahman, Noorsaadah Abdul; Chin, Lee Sui

2013-01-01

228

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

229

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

E-print Network

1 Combustion chemical kinetics of biodiesel and related compounds (methyl and ethyl esters transportation fuel dedicated to the diesel engine, biodiesel, with an emphasis on ethyl esters because of biodiesel and related components, the main gaps in the field are highlighted to facilitate the convergence

Paris-Sud XI, Université de

230

Detailed chemical kinetic reaction mechanism for biodiesel components methyl stearate and methyl oleate  

E-print Network

Detailed chemical kinetic reaction mechanism for biodiesel components methyl stearate and methyl are developed for two of the five major components of biodiesel fuel, methyl stearate and methyl oleate renewable sources, can reduce net emissions of greenhouse gases. An important class of biodiesel fuels

Paris-Sud XI, Université de

231

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

232

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

Microsoft Academic Search

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

Brian W. Sheldon

1990-01-01

233

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

Microsoft Academic Search

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

Brian W. Sheldon; Theodore M. Besmann

1991-01-01

234

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

235

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

236

Investigation of the carbonation front shape on cementitious materials: Effects of the chemical kinetics  

Microsoft Academic Search

Carbonation depth-profiles have been determined by thermogravimetric analysis and by gammadensitometry after accelerated carbonation tests on ordinary Portland cement (OPC) pastes and concretes. These methods support the idea that carbonation does not exhibit a sharp reaction front. From analytical modelling, this feature is explained by the fact that the kinetics of the chemical reactions become the rate-controlling processes, rather than

M. Thiery; G. Villain; P. Dangla; G. Platret

2007-01-01

237

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 layers on silicon substrates during nucleation and the early stages of diamond deposition have been of carbon atoms into the silicon carbide layer and the morphology and orientation of the diamond film

Dandy, David

238

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

239

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

PubMed Central

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

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

1991-01-01

240

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

241

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

242

Chemical kinetic modeling of a methane opposed flow diffusion flame and comparison to experiments  

SciTech Connect

The chemical structure of an opposed flow, methane diffusion flame is studied using a chemical kinetic model and the results are compared to experimental measurements. The chemical kinetic paths leading to aromatics and polycyclic aromatics hydrocarbons (PAHs) in the diffusion flame are identified. These paths all involve resonantly stabilized radicals which include propargyl, allyl, cyclopentadienyl, and benzyl radicals. The modeling results show reasonable agreement with the experimental measurements for the large hydrocarbon aliphatic compounds, aromatics, and PAHs. the benzene was predicted to be formed primarily by the reaction sequence of Allyl plus Propargyl equals Fulvene plus H plus H followed by fulvene isomerization to benzene. Naphthalene was modeled using the reaction of benzyl with propargyl, while the combination of cyclopentadienyl radicals were shown to be a minor contributor in the diffusion flame. The agreement between the model and experiment for the four-ring PAHs was poor.

Marinov, N.M., Pitz, W.J.; Westbrook, C.K. [Lawrence Livermore National Lab., CA (United States); Vincitore, A.M.; Senka, S.M. [Univ. of California, Los Angeles, CA (United States); Lutz, A.E. [Sandia National Labs., Livermore, CA (United States)

1998-01-01

243

Reaction of phenyl radicals with acetylene: quantum chemical investigation of the mechanism and master equation analysis of the kinetics.  

PubMed

The mechanism of the C(6)H(5) + C(2)H(2) reaction has been investigated by various quantum chemical methods. Electrophilic addition to the CC triple bond is found to be the only important mode of phenyl radical attack on acetylene. The initially formed chemically activated C(6)H(5)C(2)H(2) adducts may follow several isomerization pathways in competition with collisional stabilization and H-elimination. Thermochemistry of various decomposition and isomerization channels is evaluated by the G2M method. For key intermediates, the following standard enthalpies of formation have been deduced from isodesmic reactions: 94.2 +/- 2.0 kcal/mol (C(6)H(5)CHCH), 86.4 +/- 2.0 kcal/mol (C(6)H(5)CCH(2)), and 95.5 +/- 1.8 kcal/ mol (o-C(6)H(4)C(2)H(3)). The accuracy of theoretical predictions was examined through extensive comparisons with available experimental and theoretical data. The kinetics and product branching of the C(6)H(5) + C(2)H(2) reaction have been evaluated by weak collision master equation/Rice-Ramsperger-Kassel-Marcus (RRKM) analysis of the truncated kinetic model including only kinetically important transformations of the isomeric C(8)H(7) radicals. Available experimental kinetic data can be quantitatively reproduced by calculation with a minor adjustment of the C(6)H(5) addition barrier from 3.7 to 4.1 kcal/mol. Our predicted total rate constant, k(R1) = (1.29 x 10(10))T(0.834) exp(-2320/T) cm(3) mol(-)(1) s(-)(1), is weakly dependent on P and corresponds to the phenylation process under combustion conditions (T > 1000 K). PMID:16220963

Tokmakov, I V; Lin, M C

2003-09-17

244

Kinetic Demonstration.  

ERIC Educational Resources Information Center

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

Burgardt, Erik D.; Ryan, Hank

1996-01-01

245

Origin of the Chemical and Kinetic Stability of Graphene Oxide  

PubMed Central

At moderate temperatures (? 70°C), thermal reduction of graphene oxide is inefficient and after its synthesis the material enters in a metastable state. Here, first-principles and statistical calculations are used to investigate both the low-temperature processes leading to decomposition of graphene oxide and the role of ageing on the structure and stability of this material. Our study shows that the key factor underlying the stability of graphene oxide is the tendency of the oxygen functionalities to agglomerate and form highly oxidized domains surrounded by areas of pristine graphene. Within the agglomerates of functional groups, the primary decomposition reactions are hindered by both geometrical and energetic factors. The number of reacting sites is reduced by the occurrence of local order in the oxidized domains, and due to the close packing of the oxygen functionalities, the decomposition reactions become – on average – endothermic by more than 0.6?eV. PMID:23963517

Zhou, Si; Bongiorno, Angelo

2013-01-01

246

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

Microsoft Academic Search

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

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

2010-01-01

247

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

248

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

249

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

PubMed

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

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

2014-06-30

250

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

NASA Technical Reports Server (NTRS)

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

Radhakrishnan, K.

1984-01-01

251

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

252

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

253

Quantum chemical calculations for polymers and organic compounds  

NASA Technical Reports Server (NTRS)

The relativistic effects of the orbiting electrons on a model compound were calculated. The computational method used was based on 'Modified Neglect of Differential Overlap' (MNDO). The compound tetracyanoplatinate was used since empirical measurement and calculations along "classical" lines had yielded many known properties. The purpose was to show that for large molecules relativity effects could not be ignored and that these effects could be calculated and yield data in closer agreement to empirical measurements. Both the energy band structure and molecular orbitals are depicted.

Lopez, J.; Yang, C.

1982-01-01

254

Quantum Chemical Calculations of Sulfate Adsorption at the Al-and  

E-print Network

Quantum Chemical Calculations of Sulfate Adsorption at the Al- and Fe-(Hydr)oxide-H2O Interfaces, The Pennsylvania State University, University Park, Pennsylvania 16802 Quantum chemical calculations were performed-(hydr)oxides. Sulfate adsorption is influenced, to a varying extent, by pH, ionic strength, hydration state, and mineral

Sparks, Donald L.

255

Quantum chemical calculations of (31)P NMR chemical shifts: scopes and limitations.  

PubMed

The aim of this work is to convince practitioners of (31)P NMR methods to regard simple GIAO quantum chemical calculations as a safe tool in structural analysis of organophosphorus compounds. A comparative analysis of calculated GIAO versus experimental (31)P NMR chemical shifts (CSs) for a wide range of phosphorus containing model compounds was carried out. A variety of combinations (at the HF, DFT (B3LYP and PBE1PBE), and MP2 levels using 6-31G(d), 6-31+G(d), 6-31G(2d), 6-31G(d,p), 6-31+G(d,p), 6-311G(d), 6-311G(2d,2p), 6-311++G(d,p), 6-311++G(2d,2p), and 6-311++G(3df,3pd) basis sets) were tested. On the whole, it is shown that, in contrast to what is claimed in the literature, high level of theory is not needed to obtain rather accurate predictions of (31)P CSs by the GIAO method. The PBE1PBE/6-31G(d)//PBE1PBE/6-31G(d) level can be recommended for express estimation of (31)P CSs. The PBE1PBE/6-31G(2d)//PBE1PBE/6-31G(d) combination can be recommended for routine applications. The PBE1PBE/6-311G(2d,2p)//PBE1PBE/6-31+G(d) level can be proposed to obtain better results at a reasonable cost. Scaling by linear regression parameters significantly improves results. The results obtained using these combinations were demonstrated in (31)P CS calculations for a variety of medium (large) size organic compounds of practical interest. Care has to be taken for compounds that may be involved in exchange between different structural forms (self-associates, associates with solvent, tautomers, and conformers). For phosphorus located near the atoms of third period elements ((CH3)3PS and P(SCH3)3) the impact of relativistic effects may be notable. PMID:25683906

Latypov, Shamil K; Polyancev, Fedor M; Yakhvarov, Dmitry G; Sinyashin, Oleg G

2015-02-25

256

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

NASA Astrophysics Data System (ADS)

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

Justi, Rosária; Gilbert, John K.

257

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

NASA Technical Reports Server (NTRS)

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

Radhakrishnan, K.

1985-01-01

258

Double-focusing mixing jet for XFEL study of chemical kinetics  

PubMed Central

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

2014-01-01

259

New integration techniques for chemical kinetic rate equations. II - Accuracy comparison  

NASA Technical Reports Server (NTRS)

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

Radhakrishnan, K.

1986-01-01

260

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

Microsoft Academic Search

A new on-grid dynamic multi-timescale (MTS) method is presented to increase significantly the computation efficiency involving multi-physical and chemical processes using detailed and reduced kinetic mechanisms. The methodology of the MTS method using the instantaneous timescales of different species is introduced. The definition of the characteristic time for species is examined and compared with that of the computational singular perturbation

Xiaolong Gou; Wenting Sun; Zheng Chen; Yiguang Ju

2010-01-01

261

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

Microsoft Academic Search

Ignition delay time measurements were recorded at equivalence ratios of 0.3, 0.5, 1, and 2 for n-butane at pressures of approximately 1, 10, 20, 30 and 45 atm at temperatures from 690 to 1430 K in both a rapid compression machine and in a shock tube. A detailed chemical kinetic model consisting of 1328 reactions involving 230 species was constructed

D. Healy; H. J. Curran; N. S. Donato; C. J. Aul; E. L. Petersen; C. M. Zinner; G. Bourque

2010-01-01

262

A detailed chemical kinetic model for gas phase combustion of TNT  

Microsoft Academic Search

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

William J. Pitz; Charles K. Westbrook

2007-01-01

263

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

Microsoft Academic Search

Ignition delay time measurements were recorded at equivalence ratios of 0.3, 0.5, 1, and 2 for n-butane at pressures of approximately 1, 10, 20, 30 and 45atm at temperatures from 690 to 1430K in both a rapid compression machine and in a shock tube. A detailed chemical kinetic model consisting of 1328 reactions involving 230 species was constructed and used

D. Healy; N. S. Donato; C. J. Aul; E. L. Petersen; C. M. Zinner; G. Bourque; H. J. Curran

2010-01-01

264

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

Microsoft Academic Search

Detailed chemical kinetic mechanisms were developed and used to study the oxidation of two large unsaturated esters: methyl-5-decenoate and methyl-9-decenoate. These models were built from a previous methyl decanoate mechanism and were compared with rapeseed oil methyl esters oxidation experiments in a jet-stirred reactor. A comparative study of the reactivity of these three oxygenated compounds was performed and the differences

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

2010-01-01

265

MultiDimensional Modeling of Natural Gas Autoignition using Detailed Chemical Kinetics  

Microsoft Academic Search

The autoignition of natural gas injected into a combustion bomb at pressures and temperatures typical of top-dead-center conditions in compression ignition engines is studied by combining a detailed chemical kinetic mechanism, consisting of 22 species and 104 elementary reactions, with a multi-dimensional reactive flow code. The effect of natural gas composition, ambient density and temperature on the ignition process is

APOORVA AGARWAL; DENNIS N. ASSANIS

2001-01-01

266

Detailed chemical kinetic reaction mechanism for oxidation of n-octane and iso-octane  

Microsoft Academic Search

The development of detailed chemical kinetic reaction mechanisms for oxidation of n-octane and iso-octane is described, with emphasis on the factors which are specific to many large hydrocarbon fuel molecules. Elements which are of particular importance are found to include site-specific abstraction of H atoms, radical isomerization of alkyl radicals by internal H atom abstraction, and rapid ..beta..-scission of the

E. I. Axelsson; K. Brezinsky; F. L. Dryer; W. J. Pitz; C. K. Westbrook

1986-01-01

267

Modeling Instabilities in Lean Premixed Turbulent Combustors Using Detailed Chemical Kinetics  

Microsoft Academic Search

The development of non-conventional combustion technology with ultra-low emissions and the safe operation of combustion systems require a thorough understanding of the mechanisms of combustion instabilities. The objective of the present work is to investigate the role of unmixedness and chemical kinetics in driving combustion instabilities. The reaction-rate responses of different species to inlet flow variations have been studied using

Bjørn Lilleberg; Ivar S. Ertesvåg; Kjell Erik Rian

2009-01-01

268

On inelastic reactive collisions in kinetic theory of chemically reacting gas mixtures  

Microsoft Academic Search

A kinetic theory for a simple reversible reaction–characterized by a binary mixture of ideal gases whose constituents denoted by A and B undergo a reaction of the type A+A?B+B–is developed by considering the reactive collisions as inelastic ones. The geometry of the collision is taken into account in the line-of-centers differential cross section by allowing that a chemical reaction may

Gilberto M. Kremer; Adriano W. Silva; Giselle M. Alves

2010-01-01

269

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

270

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

271

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

272

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

Microsoft Academic Search

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

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

1996-01-01

273

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

E-print Network

Basics of Chemical Kinetics - 1 Rate of reaction = rate of disappearance of A = # of moles/volume) ; 1 mole = 6.023x1023 molecules rA = -k [A] rA = -k [A]2 rA = -k1 [A]/(1+k2[A]) Reaction rate law is an algebraic equation involving concentrations (not a differential equation) For a given reaction, the rate law

Albert, Réka

274

Analysis of RDX-TAGzT pseudo-propellant combustion with detailed chemical kinetics  

Microsoft Academic Search

A detailed model of steady-state combustion of a pseudo-propellant containing cyclotrimethylene trinitramine (RDX) and triaminoguanidinium azotetrazolate (TAGzT) is presented. The physicochemical processes occurring within the foam layer, comprised of a liquid and gas bubbles, and a gas-phase region above the burning surface are considered. The chemical kinetics is represented by a global thermal decomposition mechanism within the liquid by considering

Neeraj Kumbhakarna; Stefan T. Thynell; Arindrajit Chowdhury; Ping Lin

2011-01-01

275

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

PubMed Central

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

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

1971-01-01

276

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.

277

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

278

Tocopheramines and tocotrienamines as antioxidants: ESR spectroscopy, rapid kinetics and DFT calculations.  

PubMed

Tocopheramines (TNH2) and tocotrienamines (T3NH2) are analogues of tocopherols (TOH) and tocotrienols in which phenolic OH is replaced by NH2. It was shown in previous studies that TNH2 and T3NH2 act as potent antioxidants. In this study we compared the one-electron oxidation of TNH2/T3NH2 by diphenyl picryl hydrazyl (DPPH) and galvinoxyl (GOX) radicals with the one of ?-TOH as a reference compound using ESR spectroscopy, stopped flow spectrophotometry and density functional theory (DFT) calculations. ESR spectroscopy revealed the presence of tocopheramine radicals during electrochemical oxidation of ?-TNH2. Kinetic measurements demonstrated that in apolar n-hexane TNH2/T3NH2 derivatives reacted two to three orders of magnitude slower than ?-TOH with the model radicals. DFT calculations indicated that this correlates well with the higher bond dissociation energy (BDE) for N-H in TNH2 than for O-H in ?-TOH in pure H-atom transfer (HAT). In the more polar medium ethanol TNH2/T3NH2 derivatives partially reacted faster than ?-TOH depending on the reaction partner. DFT calculations suggest that this is due to reaction mechanisms alternative to HAT. According to thermochemistry data sequential proton loss and electron transfer (SPLET) is more favored for ?-TOH in ethanol than for TNH2. Therefore, for TNH2 a contribution of the alternative mechanism of sequential electron transfer-proton transfer (SET-PT) could be a possible explanation. These data show that the antioxidant reactivity strongly depends on the structure, reaction partners and environment. According to these findings TNH2/T3NH2 should be superior as antioxidants over ?-TOH in polar head group regions of membranes but not in the apolar core of lipid bilayers. PMID:23876337

Bamonti, Luca; Hosoya, Takashi; Pirker, Katharina F; Böhmdorfer, Stefan; Mazzini, Francesco; Galli, Francesco; Netscher, Thomas; Rosenau, Thomas; Gille, Lars

2013-09-01

279

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

PubMed

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

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

2014-03-27

280

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

281

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

282

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

283

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

Microsoft Academic Search

The source of conspicuous disagreement between theory and experiment for the chemical shift of C? in the 1-cyclopropylcyclopropylidenemethyl cation is identified as an inadequate treatment of electron correlation effects in a previous theoretical study. When the sophisticated CCSD(T) method is used, all calculated 13C chemical shifts agree with the experimental values to within 2.2 ppm. These findings undermine the basis

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

1996-01-01

284

Calculation of Plasma Radiation in Electrothermal-Chemical Launcher  

NASA Astrophysics Data System (ADS)

A numerical model of radiation has been adopted for electrothermal-chemical (ETC) launcher, in which Monte Carlo method and statistical physics are employed to simulate the process of a capillary plasma source in an ETC launcher. The effect on propellant grains with different average absorption coefficients is discussed. The plasma-propellant interaction is also discussed when combined with a thermal model. Results show that the strong instantaneous radiation is responsible for the transmission of energy to the propellant grains leading to ignition. The efficiency of energy absorption in the propellant bed always maintains a high level. Radiant energy caused by plasma is concentrated around the plasma injector. And the “hot zone” efficiency is mainly affected by the properties of propellant grains within a small field around the plasma injector.

Jin, Yong; Li, Baoming

2014-01-01

285

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

286

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

287

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

288

Mineral growth in metamorphic rocks: relationships between chemical patterns, mineral microstructure and reaction kinetics  

NASA Astrophysics Data System (ADS)

Mineral growth in metamorphic rocks is governed by kinetic processes, which are strongly related to geometrical and physical properties of the chemical pathways involved. Information on the nature of chemical pathways and potential effects of deformation on kinetic processes is stored in chemical patterns and mineral microstruture. By using high-resolution analytical techniques (i.e. EBSD, FE-EMPA and TEM/FIB) and numerical simulations we explored natural and experimental samples in order to reveal the kinetics and the microstrutural evolution of both transport controlled mineral reactions and exchange reactions. We found reaction rims between reactant minerals, which are composed of several grains. These grains are subdivided into subgrains perpendicular to the reaction fronts. The subgrains often show a systematic lateral orienation change, which is possibly caused by grain-scale plastic deformation in the form of creep polygonization. Such an arrangment of grain boundaries allows for short-circuit diffusion and amplifies the necessary mass transfer across reaction rims. Information about the contribution of grain boundary diffusion to bulk material flow in Grt is stored during the formation of asymmetric growth zonings and during micron- scale compositional variations along grain and phase boundaries. Our evaluation of these compositional patterns by diffusion modelling allows for the derivation of Digb/Divol ratios and rim growth rates. Information about phase boundary material properties is also stored in the zoning of Grt porphyroblasts, which formed during the retrograde Fe-Mg exchange between Grt and biotite. If temperature falls below a limiting value during cooling, non-equilibrated rim compositions start to develop along Grt-Qtz phase boundaries due to insufficient chemical transport rates. As the extent of non-equilibrated rim compositions reflects the transport capacity of the present interganular medium, our simulations by diffusion modelling of observed compositional patterns formed during cooling at Grt-Bt-Qtz triple junctions allows for the extraction of boundary material properties.

Keller, L. M.

2008-12-01

289

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

290

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

SciTech Connect

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

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

2010-05-15

291

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

SciTech Connect

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

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

2009-07-21

292

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

293

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.

294

Chemical Kinetic Simulation of the Combustion of Bio-based Fuels  

SciTech Connect

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

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

2007-10-01

295

Computing minimal entropy production trajectories: an approach to model reduction in chemical kinetics.  

PubMed

Advanced experimental techniques in chemistry and physics provide increasing access to detailed deterministic mass action models for chemical reaction kinetics. Especially in complex technical or biochemical systems the huge amount of species and reaction pathways involved in a detailed modeling approach call for efficient methods of model reduction. These should be automatic and based on a firm mathematical analysis of the ordinary differential equations underlying the chemical kinetics in deterministic models. A main purpose of model reduction is to enable accurate numerical simulations of even high dimensional and spatially extended reaction systems. The latter include physical transport mechanisms and are modeled by partial differential equations. Their numerical solution for hundreds or thousands of species within a reasonable time will exceed computer capacities available now and in a foreseeable future. The central idea of model reduction is to replace the high dimensional dynamics by a low dimensional approximation with an appropriate degree of accuracy. Here I present a global approach to model reduction based on the concept of minimal entropy production and its numerical implementation. For given values of a single species concentration in a chemical system all other species concentrations are computed under the assumption that the system is as close as possible to its attractor, the thermodynamic equilibrium, in the sense that all modes of thermodynamic forces are maximally relaxed except the one, which drives the remaining system dynamics. This relaxation is expressed in terms of minimal entropy production for single reaction steps along phase space trajectories. PMID:15267587

Lebiedz, D

2004-04-15

296

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

297

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

SciTech Connect

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

Huckaby, James L.

2006-09-26

298

A hybrid genetic algorithm approach to calculating chemical equilibrium and detonation parameters in condensed energetic materials  

Microsoft Academic Search

We discuss the implementation of genetic algorithms for modelling chemical equilibrium and detonation parameters at the Chapman–Jouguet (CJ) state. This strategy has the advantage that no initial estimate of the equilibrium product distribution needs to be made. It is also an efficient method for finding the global minimum, since for highly non-ideal condensed energetic materials, the calculation of the chemical

A. Zayer; U. Riedel; J. Warnatz

2006-01-01

299

A Detailed Chemical Kinetic Analysis of Low Temperature Non-Sooting Diesel Combustion  

SciTech Connect

We have developed a model of the diesel fuel injection process for application to analysis of low temperature non-sooting combustion. The model uses a simplified mixing correlation and detailed chemical kinetics, and analyzes a parcel of fuel as it moves along the fuel jet, from injection into evaporation and ignition. The model predicts chemical composition and soot precursors, and is applied at conditions that result in low temperature non-sooting combustion. Production of soot precursors is the first step toward production of soot, and modeling precursor production is expected to give insight into the overall evolution of soot inside the engine. The results of the analysis show that the model has been successful in describing many of the observed characteristics of low temperature combustion. The model predicts results that are qualitatively similar to those obtained for soot formation experiments at conditions in which the EGR rate is increased from zero to very high values as the fueling rate is kept constant. The model also describes the two paths to achieve non-sooting combustion. The first is smokeless rich combustion and the second is modulated kinetics (MK). The importance of the temperature after ignition and the equivalence ratio at the time of ignition is demonstrated, as these parameters can be used to collapse onto a single line all the results for soot precursors for multiple fueling rates. A parametric analysis indicates that precursor formation increases considerably as the gas temperature in the combustion chamber and the characteristic mixing time are increased. The model provides a chemical kinetic description of low temperature diesel combustion that improves the understanding of this clean and efficient regime of operation.

Aceves, S M; Flowers, D L

2004-10-01

300

Comparison of two gas-phase chemical kinetic mechanisms of ozone formation over Europe  

Microsoft Academic Search

Two recent gas-phase chemical kinetic mechanisms for tropospheric ozone formation, one based on the lumped-structure approach\\u000a (CB05) and the other based on the lumped-molecule approach (RACM2), are compared for simulations of ozone over Europe. The\\u000a host air quality model is POLAIR3D of the Polyphemus modeling platform. A one-month period (15 July to 15 August 2001) is\\u000a simulated. Model performance is

Youngseob Kim; Karine Sartelet; Christian Seigneur

2009-01-01

301

Chemical kinetics and mechanisms of complex systems: a perspective on recent theoretical advances.  

PubMed

This Perspective presents a personal overview of the current status of the theory of chemical kinetics and mechanisms for complex processes. We attempt to assess the status of the field for reactions in the gas phase, at gas-solid interfaces, in liquid solutions, in enzymes, and for protein folding. Some unifying concepts such as potential energy surfaces, free energy, master equations, and reaction coordinates occur in more than one area. We hope this Perspective will be useful for highlighting recent advances and for identifying important areas for future research. PMID:24283502

Klippenstein, Stephen J; Pande, Vijay S; Truhlar, Donald G

2014-01-15

302

Characterizing acid diffusion lengths in chemically amplified resists from measurements of deprotection kinetics  

NASA Astrophysics Data System (ADS)

The acid-catalyzed deprotection of glassy poly(4-hydroxystyrene-co-tertbutyl acrylate) films was studied with infrared absorbance spectroscopy and stochastic simulations. Experimental data were interpreted with a simple description of subdiffusive acid transport coupled to second-order acid loss. This model predicts key attributes of observed deprotection rates, such as fast reaction at short times, slow reaction at long times, and a nonlinear dependence on acid loading. Fickian diffusion is approached by increasing the postexposure bake temperature or adding plasticizing agents to the polymer resin. These findings demonstrate that acid mobility and overall deprotection kinetics are coupled to glassy matrix dynamics. To complement the analysis of bulk kinetics, acid diffusion lengths were calculated from the anomalous transport model and compared with nanopattern line widths. The consistent scaling between experiments and simulations suggests that the anomalous diffusion model could be further developed into a predictive lithography tool.

Patil, Abhijit A.; Pandey, Yogendra Narayan; Doxastakis, Manolis; Stein, Gila E.

2014-10-01

303

Forward, Tangent Linear, and Adjoint Runge Kutta Methods in KPP2.2 for Efficient Chemical Kinetic Simulations  

E-print Network

Forward, Tangent Linear, and Adjoint Runge Kutta Methods in KPP­2.2 for Efficient Chemical Kinetic implicit three-stage Runge Kutta methods, and the second family are singly diagonally-implicit Runge Kutta and of the discrete adjoint sensitivity method with Runge Kutta methods. Numerical experiments with a chemical system

Sandu, Adrian

304

The role of detailed chemical kinetics on CFD diesel spray ignition and combustion modelling  

Microsoft Academic Search

Spray ignition and flame stabilisation in the frame of diesel-like combustion conditions combine fundamental and complex physical and chemical processes. In this work, a numerical investigation has been performed to evaluate the potential of integrating detailed chemistry into CFD calculations, in order to improve predictions and gain more insight in involved processes. This work has been carried out using the

R. Novella; A. García; J. M. Pastor; V. Domenech

2011-01-01

305

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

306

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

307

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

308

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

E-print Network

The main aim of the paper was performing test of our (chemical and kinetic) codes, which will be used during self-consistent modelling of dynamics and chemistry in the winds from C-rich AGB stars. We use the thermodynamical equilibrium code to test the different databases of dissociation constants. We also calculate the equilibrium content of the gas using the kinetic code, which includes the chemical network of neutral--neutral reactions studied by Willacy & Cherchneff (1998). The influence of reaction rates updated using the UMIST database for Astrochemistry 2005 (UDFA05), was tested. The local thermodynamical equilibrium calculations have shown that the NIST database reproduces fairly well equilibrium concentrations of Willacy & Cherchneff (1998), while agreement in case of Tsuji (1973) dissociation constants is much worse. The most important finding is that the steady state solution obtained with the kinetic code for reaction network of Willacy & Cherchneff (1998) is different from the thermodynamical equilibrium solution. In particular, CN and C2, which are important opacity sources are underabundant relative to hermodynamical equilibrium, while O-bearing molecules (like SiO, H2O, and OH) are overabundant. After updating the reaction rates by data from the UDFA05 database consistency in O-bearing species becomes much better, however the disagreement in C-bearing species is still present.

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

2007-02-24

309

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

SciTech Connect

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

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

2010-08-15

310

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

311

Accelerating moderately stiff chemical kinetics in reactive-flow simulations using GPUs  

NASA Astrophysics Data System (ADS)

The chemical kinetics ODEs arising from operator-split reactive-flow simulations were solved on GPUs using explicit integration algorithms. Nonstiff chemical kinetics of a hydrogen oxidation mechanism (9 species and 38 irreversible reactions) were computed using the explicit fifth-order Runge-Kutta-Cash-Karp method, and the GPU-accelerated version performed faster than single- and six-core CPU versions by factors of 126 and 25, respectively, for 524,288 ODEs. Moderately stiff kinetics, represented with mechanisms for hydrogen/carbon-monoxide (13 species and 54 irreversible reactions) and methane (53 species and 634 irreversible reactions) oxidation, were computed using the stabilized explicit second-order Runge-Kutta-Chebyshev (RKC) algorithm. The GPU-based RKC implementation demonstrated an increase in performance of nearly 59 and 10 times, for problem sizes consisting of 262,144 ODEs and larger, than the single- and six-core CPU-based RKC algorithms using the hydrogen/carbon-monoxide mechanism. With the methane mechanism, RKC-GPU performed more than 65 and 11 times faster, for problem sizes consisting of 131,072 ODEs and larger, than the single- and six-core RKC-CPU versions, and up to 57 times faster than the six-core CPU-based implicit VODE algorithm on 65,536 ODEs. In the presence of more severe stiffness, such as ethylene oxidation (111 species and 1566 irreversible reactions), RKC-GPU performed more than 17 times faster than RKC-CPU on six cores for 32,768 ODEs and larger, and at best 4.5 times faster than VODE on six CPU cores for 65,536 ODEs. With a larger time step size, RKC-GPU performed at best 2.5 times slower than six-core VODE for 8192 ODEs and larger. Therefore, the need for developing new strategies for integrating stiff chemistry on GPUs was discussed.

Niemeyer, Kyle E.; Sung, Chih-Jen

2014-01-01

312

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

313

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

314

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

315

Premixed hydrocarbon stagnation flames : experiments and simulations to validate combustion chemical-kinetic models  

NASA Astrophysics Data System (ADS)

A methodology based on the comparison of flame simulations relying on reacting flow models with experiment is applied to C1-C3 stagnation flames. The work reported targets the assessment and validation of the modeled reactions and reaction rates relevant to (C1-C3)-flame propagation in several detailed combustion kinetic models. A concensus does not, as yet, exist on the modeling of the reasonably well-understood oxidation of C1-C2 flames, and a better knowledge of C3 hydrocarbon combustion chemistry is required before attempting to bridge the gap between the oxidation of C1-C2 hydrocarbons and the more complex chemistry of heavier hydrocarbons in a single kinetic model. Simultaneous measurements of velocity and CH-radical profiles were performed in atmospheric propane(C3H8)- and propylene(C3H6)-air laminar premixed stagnation flames stabilized in a jet-wall configuration. These nearly-flat flames can be modeled by one-dimensional simulations, providing a means to validate kinetic models. Experimental data for these C3 flames and similar experimental data for atmospheric methane(CH4)-, ethane(C2H6)-, and ethylene(C2H4)-air flames are compared to numerical simulations performed with a one-dimensional hydrodynamic model, a multi-component transport formulation including thermal diffusion, and different detailed-chemistry models, in order to assess the adequacy of the models employed. A novel continuation technique between kinetic models was developed and applied successfully to obtain solutions with the less-robust models. The 2005/12 and 2005/10 releases of the San Diego mechanism are found to have the best overall performance in C3H8 and C3H6 flames, and in CH4, C2H6, and C2H4 flames, respectively. Flame position provides a good surrogate for flame speed in stagnation-flow stabilized flames. The logarithmic sensitivities of the simulated flame locations to variations in the kinetic rates are calculated via the "brute-force" method for fifteen representative flames covering the five fuels under study and the very lean, stoichiometric, and very rich burning regimes, in order to identify the most-important reactions for each flame investigated. The rates of reactions identified in this manner are compared between the different kinetic models. Several reaction-rate differences are thus identified that are likely responsible for the variance in flame-position (or flame-speed) predictions in C1-C2 flames.

Benezech, Laurent Jean-Michel

316

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

317

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

318

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

319

Quantum Chemical 13Ca Chemical Shift Calculations for Protein NMR Structure Determination, Refinement, and Validation  

SciTech Connect

A recently determined set of 20 NMR-derived conformations of a 48-residue all-?-helical protein, (PDB ID code 2JVD), is validated here by comparing the observed 13C? chemical shifts with those computed at the density functional level of theory. In addition, a recently introduced physics-based method, aimed at determining protein structures by using NOE-derived distance constraints together with observed and computed 13C? chemical shifts, was applied to determine a new set of 10 conformations, (Set-bt), as a blind test for the same protein. A cross-validation of these two sets of conformations in terms of the agreement between computed and observed 13C? chemical shifts, several stereochemical quality factors, and some NMR quality assessment scores reveals the good quality of both sets of structures. We also carried out an analysis of the agreement between the observed and computed 13C? chemical shifts for a slightly longer construct of the protein solved by x-ray crystallography at 2.0-A resolution (PDB ID code 3BHP) with an identical amino acid residue sequence to the 2JVD structure for the first 46 residues. Our results reveal that both of the NMR-derived sets, namely 2JVD and Set-bt, are somewhat better representations of the observed 13C? chemical shifts in solution than the 3BHP crystal structure. In addition, the 13C?-based validation analysis appears to be more sensitive to subtle structural differences across the three sets of structures than any other NMR quality-assessment scores used here, and, although it is computationally intensive, this analysis has potential value as a standard procedure to determine, refine, and validate protein structures.

Vila, J.; Aramini, J; Rossi, P; Kuzin, A; Su, M; Seetharaman, J; Xiao, R; Tong, L; Montelione, G; Scheraga, H

2008-01-01

320

Decay-ratio calculation in the frequency domain with the LAPUR code using 1D-kinetics  

SciTech Connect

This paper deals with the problem of computing the Decay Ratio in the frequency domain codes as the LAPUR code. First, it is explained how to calculate the feedback reactivity in the frequency domain using slab-geometry i.e. 1D kinetics, also we show how to perform the coupling of the 1D kinetics with the thermal-hydraulic part of the LAPUR code in order to obtain the reactivity feedback coefficients for the different channels. In addition, we show how to obtain the reactivity variation in the complex domain by solving the eigenvalue equation in the frequency domain and we compare this result with the reactivity variation obtained in first order perturbation theory using the 1D neutron fluxes of the base case. Because LAPUR works in the linear regime, it is assumed that in general the perturbations are small. There is also a section devoted to the reactivity weighting factors used to couple the reactivity contribution from the different channels to the reactivity of the entire reactor core in point kinetics and 1D kinetics. Finally we analyze the effects of the different approaches on the DR value. (authors)

Munoz-Cobo, J. L.; Escriva, A.; Garcia, C.; Berna, C. [Instituto de Ingenieria Energetica, Universitat Politecnica de Valencia, Camino de Vera s/n, Valencia 46022 (Spain); Melara, J. [IBERDROLA Ingenieria Y Construccion, C/ Jose Bardasano Baos 9, 28016 Madrid (Spain)

2012-07-01

321

Capillary Viscometry: Analysis of Kinetic Energy and Hydrostatic Head Corrections and a More Exact Calculation  

Microsoft Academic Search

An extensive experimental investigation and an analysis of previous results on capillary viscometry have resolved many of the contradictory results and conclusions concerning the constancy of the kinetic-energy correction factor, usually denoted m. This factor is shown to be constant within experimental error at flow rates corresponding to Reynolds numbers from 50 to 1500. The reported gross changes in m,

R. E. Wellman; R. DeWitt; R. B. Ellis

1966-01-01

322

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

323

An efficient error-propagation-based reduction method for large chemical kinetic mechanisms  

SciTech Connect

Production rates obtained from a detailed chemical mechanism are analyzed in order to quantify the coupling between the various species and reactions involved. These interactions can be represented by a directed relation graph. A geometric error propagation strategy applied to this graph accurately identifies the dependencies of specified targets and creates a set of increasingly simplified kinetic schemes containing only the chemical paths deemed the most important for the targets. An integrity check is performed concurrently with the reduction process to avoid truncated chemical paths and mass accumulation in intermediate species. The quality of a given skeletal model is assessed through the magnitude of the errors introduced in the target predictions. The applied error evaluation is variable-dependent and unambiguous for unsteady problems. The technique yields overall monotonically increasing errors, and the smallest skeletal mechanism that satisfies a user-defined error tolerance over a selected domain of applicability is readily obtained. An additional module based on life-time analysis identifies a set of species that can be modeled accurately by quasi-steady state relations. An application of the reduction procedure is presented for autoignition using a large iso-octane mechanism. The whole process is automatic, is fast, has moderate CPU and memory requirements, and compares favorably to other existing techniques. (author)

Pepiot-Desjardins, P.; Pitsch, H. [Department of Mechanical Engineering, Stanford University, Stanford, CA (United States)

2008-07-15

324

Extracting chemical information from plane wave calculations by a 3D 'fuzzy atoms' analysis  

NASA Astrophysics Data System (ADS)

Bond order and valence indices have been calculated by the method of the three-dimensional 'fuzzy atoms' analysis, using the numerical molecular orbitals obtained from plane wave DFT calculations, i.e., without introducing any external atom-centered functions. Weight functions of both Hirshfeld and Becke types have been applied. The results are rather close to the similar 'fuzzy atoms' ones obtained by using atom-centered basis sets and agree well with the chemical expectations, stressing the power of the genuine chemical concepts.

Bakó, I.; Stirling, A.; Seitsonen, A. P.; Mayer, I.

2013-03-01

325

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

PubMed

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

de Carvalho, Luiz Pedro S; Blanchard, John S

2006-07-25

326

Reactibodies generated by kinetic selection couple chemical reactivity with favorable protein dynamics  

PubMed Central

Igs offer a versatile template for combinatorial and rational design approaches to the de novo creation of catalytically active proteins. We have used a covalent capture selection strategy to identify biocatalysts from within a human semisynthetic antibody variable fragment library that uses a nucleophilic mechanism. Specific phosphonylation at a single tyrosine within the variable light-chain framework was confirmed in a recombinant IgG construct. High-resolution crystallographic structures of unmodified and phosphonylated Fabs display a 15-Å-deep two-chamber cavity at the interface of variable light (VL) and variable heavy (VH) fragments having a nucleophilic tyrosine at the base of the site. The depth and structure of the pocket are atypical of antibodies in general but can be compared qualitatively with the catalytic site of cholinesterases. A structurally disordered heavy chain complementary determining region 3 loop, constituting a wall of the cleft, is stabilized after covalent modification by hydrogen bonding to the phosphonate tropinol moiety. These features and presteady state kinetics analysis indicate that an induced fit mechanism operates in this reaction. Mutations of residues located in this stabilized loop do not interfere with direct contacts to the organophosphate ligand but can interrogate second shell interactions, because the H3 loop has a conformation adjusted for binding. Kinetic and thermodynamic parameters along with computational docking support the active site model, including plasticity and simple catalytic components. Although relatively uncomplicated, this catalytic machinery displays both stereo- and chemical selectivity. The organophosphate pesticide paraoxon is hydrolyzed by covalent catalysis with rate-limiting dephosphorylation. This reactibody is, therefore, a kinetically selected protein template that has enzyme-like catalytic attributes. PMID:21896761

Smirnov, Ivan; Carletti, Eugénie; Kurkova, Inna; Nachon, Florian; Nicolet, Yvain; Mitkevich, Vladimir A.; Débat, Hélène; Avalle, Bérangère; Belogurov, Alexey A.; Kuznetsov, Nikita; Reshetnyak, Andrey; Masson, Patrick; Tonevitsky, Alexander G.; Ponomarenko, Natalia; Makarov, Alexander A.; Friboulet, Alain; Tramontano, Alfonso; Gabibov, Alexander

2011-01-01

327

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

328

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

PubMed

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

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

2014-10-01

329

Use of detailed chemical kinetics to study HCCI engine combustionwith consideration of turbulent mixing effects  

Microsoft Academic Search

Detailed chemical kinetics was used in an engine CFD code to study\\u000d\\u000a\\u0009the combustion process in HCCI engines. The CHEMKIN code was implemented\\u000d\\u000a\\u0009in KIVA such that the chemistry and flow solutions were coupled.\\u000d\\u000a\\u0009The reaction mechanism consists of hundreds of reactions and species\\u000d\\u000a\\u0009and is derived from fundamental flame chemistry. Effects of turbulent\\u000d\\u000a\\u0009mixing on the reaction rates were

S.-C. Kong; R. D. Reitz

2002-01-01

330

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

331

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

SciTech Connect

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

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

1993-10-01

332

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

333

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

SciTech Connect

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

Sheps, Leonid; Chandler, David W.

2013-04-01

334

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

PubMed Central

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. PMID:24619066

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

2014-01-01

335

Use of a pressuremeter to measure the kinetics of carbon dioxide evolution in chemically leavened wheat flour dough.  

PubMed

Among a number of impediments to a wider use of chemical leavening agents in bakery applications is the lack of standardized instrumentation capable of providing information on the rates of CO2 production from chemical leaveners in a format that is meaningful to both the technologist (i.e., the dough rate of reaction or DRR) and the researcher (e.g., in terms of fundamental unitskmol CO2 per kg of dough per s). This paper presents an original methodology to carry out the DRR test using a commercial pressuremeter, the Gassmart apparatus, and to model the kinetics of CO2 evolution of chemically leavened dough. Lean formula doughs were leavened at 27 and 39 degrees C with four chemical leavening systems containing sodium bicarbonate and one of four leavening acids, sodium acid pyrophosphate 40 (SAPP), adipic acid (ADA), potassium acid tartrate (KAT), and glucono-delta-lactone (GDL). Chemical kinetics theory was used to gain an insight into the reaction mechanisms responsible for the evolution of carbon dioxide from the leaveners. A first-order reaction kinetics model was found to be suitable for describing the neutralizing properties of GDL and ADA leavening systems, whereas a first-order reaction kinetics model for irreversible parallel reactions better described the leavening properties of the acidic salts KAT and SAPP. PMID:18841986

Bellido, Guillermo G; Scanlon, Martin G; Sapirstein, Harry D; Page, John H

2008-11-12

336

Kinetic Formulation of the Kohn-Sham Equations for ab initio Electronic Structure Calculations  

NASA Astrophysics Data System (ADS)

We introduce a new connection between density functional theory and kinetic theory. In particular, we show that the Kohn-Sham equations can be reformulated as a macroscopic limit of the steady-state solution of a suitable single-particle kinetic equation. We derive a Boltzmann-like equation for a gas of quasiparticles, where the potential plays the role of an external source that generates and destroys particles, so as to drive the system towards its ground state. The ions are treated as classical particles by using either the Born-Oppenheimer dynamics or by imposing concurrent evolution with the electronic orbitals. In order to provide quantitative support to our approach, we implement a discrete (lattice) kinetic model and compute the exchange and correlation energies of simple atoms and the geometrical configuration of the methane molecule. Moreover, we also compute the first vibrational mode of the hydrogen molecule, with both Born-Oppenheimer and concurrent dynamics. Excellent agreement with values in the literature is found in all cases.

Mendoza, M.; Succi, S.; Herrmann, H. J.

2014-08-01

337

Calculations of protective action distance for toxic chemical spills using nomographs  

Microsoft Academic Search

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

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

1995-01-01

338

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

339

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

340

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

341

Calculations of protective action distance for toxic chemical spills using nomographs  

SciTech Connect

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

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

1995-04-01

342

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

343

Quantum Chemical Calculations of the Influence of Anchor-Cum-Spacer Groups on Femtosecond Electron  

E-print Network

Quantum Chemical Calculations of the Influence of Anchor-Cum-Spacer Groups on Femtosecond Electron different anchor-cum-spacer groups, have been studied theoretically using density functional theory (DFT injection rate depends strongly on the ability of the anchor-cum-spacer unit that separates the d

Goddard III, William A.

344

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

345

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

346

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

347

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

348

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

SciTech Connect

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

Andrew, VINCENT

2005-04-22

349

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

350

Kinetics of chemical degradation of isoxaflutole: influence of the nature of aqueous buffers (alkanoic acid/sodium salt vs phosphate).  

PubMed

A kinetic study of the chemical degradation of isoxaflutole (5-cyclopropyl-1,2-oxazol-4-yl alpha alpha alpha-trifluoro-2-mesyl-p-tolyl ketone) into its diketonitrile derivative (DKN), which is its active herbicide principle, in organic buffers at different pH values was carried out using a HPLC/UV detection method. The values of the pseudo-first-order rate constants Kobs for the reaction were calculated and compared with those previously obtained in inorganic buffers. In both cases, Kobs was found to be dependent on pH and temperature, but at pH 5.2 the degradation of isoxaflutole in CH3COOH/CH3COONa buffers was considerably faster than in KH2PO4/Na2HPO4 buffers, indicating that the compound was sensitive to the nature of the reagents used to prepare buffered solutions. The influence of phosphate and acetate concentrations and the influence of the R-substituent in RCOOH/RCOONa buffers were investigated. For the HA/A- buffers studied, the values of Kobs were linearly dependent on HA and A- concentrations, which meant that the degradation of isoxaflutole was subject to general catalysis. The values of Kobs were also found to be dependent on the number and the position of the CH3 groups of the R-substituent. The known degradation product of DKN (a benzoic acid derivative) was not detected throughout this study. PMID:11455816

Beltran, E; Fenet, H; Cooper, J F; Coste, C M

2001-04-01

351

Extraction of the suppression effects of oxygenated fuels on soot formation using a detailed chemical kinetic model  

Microsoft Academic Search

The influence of oxygenated fuels on the soot formation process inside a burning diesel jet plume was examined using a detailed chemical kinetic reaction mechanism. Normal heptane was selected as a representative diesel fuel, and methanol, ethanol and dimethyl ether were used as oxygenated fuels. It was found that the production of soot precursors, such as small unsaturated hydrocarbons and

Takaaki Kitamura; Takayuki Ito; Jiro Senda; Hajime Fujimoto

2001-01-01

352

A detailed chemical kinetic reaction mechanism for oxidation of four small alkyl esters in laminar premixed flames  

Microsoft Academic Search

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

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

2009-01-01

353

Improved understanding of thermal agent fire suppression mechanisms from detailed chemical kinetic modeling with idealized surrogate agents  

Microsoft Academic Search

Fire suppression agents that derive their entire effectiveness from physical processes are known as thermal agents. Thermal agents operate by lowering the flame temperature through dilution, heat absorption, and thermal diffusion. Two aspects of these mechanisms are investigated using detailed chemical-kinetic modeling of methane opposed-jet laminar diffusion flames burning in air mixed with two idealized surrogate agents. “X” has the

William M. Pitts

2009-01-01

354

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

Microsoft Academic Search

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

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

2008-01-01

355

Volume 76. number 1 CHEMICAL PHYSICS LETTERS 15 November 1980 THE KINETICS OF VIBRATIONAL ENERGY TRANSFER AND RELAXATION PROCESSES  

E-print Network

Volume 76. number 1 CHEMICAL PHYSICS LETTERS 15 November 1980 THE KINETICS OF VIBRATIONAL ENERGY to be the overtones of v3 of which the iirst overtone transltlon has a large oscillator strength and is there- fore was connected to a glass vacuum syste

Apkarian, V. Ara

356

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

Microsoft Academic Search

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

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

2002-01-01

357

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

ERIC Educational Resources Information Center

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

Salvador, F.; And Others

1984-01-01

358

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

359

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

360

A study of natural gas\\/DME combustion in HCCI engines using CFD with detailed chemical kinetics  

Microsoft Academic Search

Combustion characteristics of natural gas and dimethyl ether (DME) mixture in a homogeneous charge compression ignition (HCCI) engine were studied numerically. Detailed chemical kinetics with 83 species and 360 reactions was used with an engine CFD code to simulate the combustion process. Operating conditions with different fuel compositions were simulated. Combustion, nitrogen oxides emissions and effects of fuel compositions on

Song-Charng Kong

2007-01-01

361

Numerical simulation of thermal conversion of aromatic hydrocarbons in the presence of hydrogen and steam using a detailed chemical kinetic model  

Microsoft Academic Search

A detailed chemical kinetic model with a reaction mechanism consisting of thousands of elementary step-like reactions has been successfully applied to predict the combustion and pyrolysis characteristics of hydrocarbon fuels. This approach, however, has seldom been used for predicting steam reforming of aromatic hydrocarbons. In this study, the predictive capability of an existing detailed chemical kinetic model was critically evaluated

Koyo Norinaga; Yasuhiro Sakurai; Ryota Sato; Jun-ichiro Hayashi

362

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

PubMed

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

Jung, Moon Chul; Weber, Stephen G

2005-02-15

363

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

PubMed

A simultaneous use of the full molecular symmetry and of an exact kinetic energy operator (KEO) is of key importance for accurate predictions of vibrational levels at a high energy range from a potential energy surface (PES). An efficient method that permits a fast convergence of variational calculations would allow iterative optimization of the PES parameters using experimental data. In this work, we propose such a method applied to tetrahedral AB4 molecules for which a use of high symmetry is crucial for vibrational calculations. A symmetry-adapted contracted angular basis set for six redundant angles is introduced. Simple formulas using this basis set for explicit calculation of the angular matrix elements of KEO and PES are reported. The symmetric form (six redundant angles) of vibrational KEO without the sin(q)(-2) type singularity is derived. The efficient recursive algorithm based on the tensorial formalism is used for the calculation of vibrational matrix elements. A good basis set convergence for the calculations of vibrational levels of the CH4 molecule is demonstrated. PMID:25747072

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

2015-03-01

364

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

365

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

SciTech Connect

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 R/sub 2/ and I/sub 2/. Laser- and rf-discharge-based methods for regenerating starting materials from by-products are evaluated experimentally. For economical operation of large iodine laser systems, CF/sub 3/I 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 CF/sub 3/I molecule using pulsed rf-discharge techniques is 5.8 eV.

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

1980-01-01

366

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

367

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

SciTech Connect

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

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

2010-06-15

368

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

SciTech Connect

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

Gou, Xiaolong; Sun, Wenting; Chen, Zheng; Ju, Yiguang

2010-01-01

369

The release behavior and kinetic evaluation of tramadol HCl from chemically cross linked Ter polymeric hydrogels  

PubMed Central

Background and the purpose of the study Hydrogels, being stimuli responsive are considered to be effective for targeted and sustained drug delivery. The main purpose for this work was to study the release behavior and kinetic evaluation of Tramadol HCl from chemically cross linked ter polymeric hydrogels. Methods Ter-polymers of methacrylate, vinyl acetate and acrylic acid cross linked with ethylene glycol dimethacrylate (EGDMA) were prepared by free radical polymerization. The drug release rates, dynamic swelling behavior and pH sensitivity of hydrogels ranging in composition from 1-10 mol% EGDMA were studied. Tramadol HCl was used as model drug substance. The release behavior was investigated at pH 8 where all formulations exhibited non-Fickian diffusion mechanism. Results and major conclusion Absorbency was found to be more than 99% indicating good drug loading capability of these hydrogels towards the selected drug substance. Formulations designed with increasing amounts of EGDMA had a decreased equilibrium media content as well as media penetrating velocity and thus exhibited a slower drug release rate. Fitting of release data to different kinetic models indicate that the kinetic order shifts from the first to zero order as the concentration of drug was increased in the medium, showing gradual independency of drug release towards its concentration. Formulations with low drug content showed best fitness with Higuchi model whereas those with higher concentration of drug followed Hixson-Crowell model with better correlation values indicating that the drug release from these formulations depends more on change in surface area and diameter of tablets than that on concentration of the drug. Release exponent (n) derived from Korse-Meyer Peppas equation implied that the release of Tramadol HCl from these formulations was generally non-Fickian (n?>?0.5?>?1) showing swelling controlled mechanism. The mechanical strength and controlled release capability of the systems indicate that these co-polymeric hydrogels have a great potential to be used as colon drug delivery device through oral administration. PMID:23351340

2013-01-01

370

The Influence of Chemical Mechanisms on PDF Calculations of Non-Premixed Piloted Jet Flames The Influence of Chemical Mechanisms on PDF  

E-print Network

The Influence of Chemical Mechanisms on PDF Calculations of Non-Premixed Piloted Jet Flames The Influence of Chemical Mechanisms on PDF Calculations of Non-Premixed Piloted Jet Flames Supplementary Engineering, Cornell University, Ithaca, NY 14853, USA Supplementary material Page 1 of 385 #12;The Influence

371

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

372

Projected and Hidden Markov Models for calculating kinetics and metastable states of complex molecules  

E-print Network

Markov state models (MSMs) have been successful in computing metastable states, slow relaxation timescales and associated structural changes, and stationary or kinetic experimental observables of complex molecules from large amounts of molecular dynamics simulation data. However, MSMs approximate the true dynamics by assuming a Markov chain on a clusters discretization of the state space. This approximation is difficult to make for high-dimensional biomolecular systems, and the quality and reproducibility of MSMs has therefore been limited. Here, we discard the assumption that dynamics are Markovian on the discrete clusters. Instead, we only assume that the full phase- space molecular dynamics is Markovian, and a projection of this full dynamics is observed on the discrete states, leading to the concept of Projected Markov Models (PMMs). Robust estimation methods for PMMs are not yet available, but we derive a practically feasible approximation via Hidden Markov Models (HMMs). It is shown how various molecula...

Noe, Frank; Prinz, Jan-Hendrik; Plattner, Nuria

2013-01-01

373

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.

374

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

NASA Astrophysics Data System (ADS)

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

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

1999-05-01

375

OXIDATION OF 1METHYLNAPHTHALENE AT 1–13 ATM: EXPERIMENTAL STUDY IN A JSR AND DETAILED CHEMICAL KINETIC MODELING  

Microsoft Academic Search

The kinetics of oxidation of 1-methylnaphthalene have been studied in a jet stirred reactor (800 ? T\\/K ? 1421, 1 ? P\\/atm ? 10, 0.5 ? equivalence ratio ? 1.5). Molecular species concentration profiles of reactants, stable intermediates and final products were measured by sonic probe sampling followed by on-line GC-MS analyses and off-line GC-TCD-FID and GC-MS analyses. The oxidation of 1-methylnaphthalene was modeled using a detailed chemical kinetic reaction mechanism (146

KARIM MATI; ALAIN RISTORI; GAËLLE PENGLOAN; PHILIPPE DAGAUT

2007-01-01

376

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

PubMed

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

Görlitz, Linus; Gao, Zhenglei; Schmitt, Walter

2011-05-15

377

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

PubMed Central

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

Haque, Imran S.; Walters, W. Patrick

2010-01-01

378

SIML: a fast SIMD algorithm for calculating LINGO chemical similarities on GPUs and CPUs.  

PubMed

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

Haque, Imran S; Pande, Vijay S; Walters, W Patrick

2010-04-26

379

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

PubMed

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

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

2014-02-18

380

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

381

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

382

Modeling miRNA-mRNA interactions: fitting chemical kinetics equations to microarray data  

PubMed Central

Background The miRNAs are small non-coding RNAs of roughly 22 nucleotides in length, which can bind with and inhibit protein coding mRNAs through complementary base pairing. By degrading mRNAs and repressing proteins, miRNAs regulate the cell signaling and cell functions. This paper focuses on innovative mathematical techniques to model gene interactions by algorithmic analysis of microarray data. Our goal was to elucidate which mRNAs were actually degraded or had their translation inhibited by miRNAs belonging to a very large pool of potential miRNAs. Results We proposed two chemical kinetics equations (CKEs) to model the interactions between miRNAs, mRNAs and the associated proteins. In order to reduce computational cost, we used a non linear profile clustering method named minimal net clustering and efficiently condensed the large set of expression profiles observed in our microarray data sets. We determined unknown parameters of the CKE models by minimizing the discrepancy between model prediction and data, using our own fast non linear optimization algorithm. We then retained only the CKE models for which the optimized fit to microarray data is of high quality and validated multiple miRNA-mRNA pairs. Conclusion The implementation of CKE modeling and minimal net clustering reduces drastically the potential set of miRNA-mRNA pairs, with a high gain for further experimental validations. The minimal net clustering also provides good miRNA candidates that have similar regulatory roles. PMID:24548346

2014-01-01

383

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

384

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

385

Kinetics of chemical leaching of chalcopyrite from low grade copper ore: behavior of different size fractions  

NASA Astrophysics Data System (ADS)

The kinetics of the chemical leaching of copper from low grade ore in ferric sulfate media was investigated using the constrained least square optimization technique. The experiments were carried out for different particle sizes in both the reactor and column at constant oxidation-reduction potential ( E h), pH values, and temperature. The main copper mineral was chalcopyrite. About 40% of Cu recovery is obtained after 7 d of reactor leaching at 85°C using -0.5 mm size fraction, while the same recovery is obtained at 75°C after 24 d. Also, about 23% of Cu recovery is obtained after 60 d of column leaching for +4--8 mm size fraction whereas the Cu recovery is as low as about 15% for +8--12.7 and +12.7--25 mm size fractions. A 4-stage model for chalcopyrite dissolution was used to explain the observed dissolution behaviors. The results show that thick over-layers of sulphur components cause the parabolic behavior of chalcopyrite dissolution and the precipitation of Fe3+ plays the main role in chalcopyrite passivation. In the case of coarse particles, transformation from one stage to another takes a longer time, thus only two stages including the initial reaction on fresh surfaces and S0 deposition are observed.

Naderi, H.; Abdollahy, M.; Mostoufi, N.; Koleini, M. J.; Shojaosadati, S. A.; Manafi, Z.

2011-12-01

386

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

387

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

388

An integrated fingerprinting and kinetic approach to accelerated shelf-life testing of chemical changes in thermally treated carrot puree.  

PubMed

To have a better understanding of chemical reactions during shelf-life, an integrated analytical and engineering toolbox: "fingerprinting-kinetics" was used. As a case study, a thermally sterilised carrot puree was selected. Sterilised purees were stored at four storage temperatures as a function of time. Fingerprinting enabled selection of volatiles clearly changing during shelf-life. Only these volatiles were identified and studied further. Next, kinetic modelling was performed to investigate the suitability of these volatiles as quality indices (markers) for accelerated shelf-life testing (ASLT). Fingerprinting enabled selection of terpenoids, phenylpropanoids, fatty acid derivatives, Strecker aldehydes and sulphur compounds as volatiles clearly changing during shelf-life. The amount of Strecker aldehydes increased during storage, whereas the rest of the volatiles decreased. Out of the volatiles, based on the applied kinetic modelling, myristicin, ?-terpinolene, ?-pinene, ?-terpineol and octanal were identified as potential markers for ASLT. PMID:25722143

Kebede, Biniam T; Grauwet, Tara; Magpusao, Johannes; Palmers, Stijn; Michiels, Chris; Hendrickx, Marc; Loey, Ann Van

2015-07-15

389

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

390

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

NASA Astrophysics Data System (ADS)

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

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

2007-07-01

391

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

PubMed

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

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

2010-12-01

392

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

PubMed

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. PMID:23181301

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

2012-11-21

393

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

394

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

NASA Astrophysics Data System (ADS)

Mathematical models play an important role in physical chemistry. This paper describes the use of Mathcad software in a series of exercises that explore the mathematical models for reversible first order and series first order reactions. In this approach students learn to use the Mathcad software while exploring kinetics models in an open ended format. Other objectives of the exercises include helping students to develop higher order thinking skills and to foster deeper chemical thinking processes. The method uses the Perry model of student development as the pedagogical framework. This approach to teaching chemical kinetics is an easily implemented alternative to traditional lecture presentations. This is important as retention of material learned through immediate use of the learning in teaching others rises to 90% in group work. The student pair interaction that these exercises require provides the opportunity for teaching that increases learning. Positive student responses to the method and the advantages of this approach are given in the paper.

Zielinski, Theresa Julia

1995-07-01

395

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

PubMed

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

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

2010-03-25

396

Detailed Chemical Kinetic Reaction Mechanisms for Primary Reference Fuels for Diesel Cetane Number and Spark-Ignition Octane Number  

Microsoft Academic Search

For the first time, a detailed chemical kinetic reaction mechanism is developed for primary reference fuel mixtures of n-hexadecane and 2,2,4,4,6,8,8-heptamethyl nonane for diesel cetane ratings. The mechanisms are constructed using existing rules for reaction pathways and rate expressions developed previously for the primary reference fuels for gasoline octane ratings, n-heptane and iso-octane. These reaction mechanisms are validated by comparisons

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

2010-01-01

397

Detailed chemical kinetic reaction mechanisms for primary reference fuels for diesel cetane number and spark-ignition octane number  

Microsoft Academic Search

A detailed chemical kinetic reaction mechanism is developed for primary reference fuel mixtures of n-hexadecane and 2,2,4,4,6,8,8-heptamethyl nonane for diesel cetane ratings. The mechanisms are constructed using existing rules for reaction pathways and rate expressions developed previously for the primary reference fuels for gasoline octane ratings, n-heptane and iso-octane. These reaction mechanisms are validated by comparisons between computed and experimental

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

2011-01-01

398

A G-equation Combustion Model Incorporating Detailed Chemical Kinetics for PFI\\/DI SI Engine Simulations  

Microsoft Academic Search

A G-equation-based combustion model incorporating detailed chemical kinetics has been developed and implemented in KIVA-3V for Spark-Ignition (SI) engine simulations for better predictions of flame propa- gation and pollutant formation. A progress variable concept is introduced into the turbulent flame speed correlation to account for the laminar to turbulent evolution of the spark kernel flame. The flame front in the

Long Liang; D. Reitz; Jianwen Yi; Claudia O. Iyer

399

The development of a detailed chemical kinetic mechanism for diisobutylene and comparison to shock tube ignition times  

Microsoft Academic Search

Shock tube experiments and chemical kinetic modeling were carried out on 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene, the two isomers of diisobutylene, a compound intended for use as an alkene component in a surrogate diesel. Ignition delay times were obtained behind reflected shock waves at 1 and 4atm, and between temperatures of 1200 and 1550K. Equivalence ratios ranging from 1.0 to 0.25 were

Wayne K. Metcalfe; William J. Pitz; Henry J. Curran; John M. Simmie; Charles K. Westbrook

2007-01-01

400

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

Microsoft Academic Search

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

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

2009-01-01

401

Calculator.  

ERIC Educational Resources Information Center

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

Parma City School District, OH.

402

Chemical reaction- and particle diffusion-based kinetic modeling of metal biosorption by a Phormidium sp.-dominated cyanobacterial mat  

Microsoft Academic Search

The present study explores the suitability of chemical reaction-based and diffusion-based kinetic models for defining the biosorption of Cu(II), Cd(II) and Pb(II) by Phormidium sp.-dominated mat. The time-course data of metal sorption by the test mat significantly (r2=0.932–0.999) fitted to the chemical reaction-based models namely pseudo-first-order, -second-order, and the general rate law. However, these models fail to accurately describe the

Dhananjay Kumar; J. P. Gaur

2011-01-01

403

Construction of environment states in quantum-chemical density-matrix renormalization group calculations.  

PubMed

The application of the quantum-chemical density-matrix renormalization group (DMRG) algorithm is cumbersome for complex electronic structures with many active orbitals. The high computational cost is mainly due to the poor convergence of standard DMRG calculations. A factor which affects the convergence behavior of the calculations is the choice of the start-up procedure. In this start-up step matrix representations of operators have to be calculated in a guessed many-electron basis of the DMRG environment block. Different possibilities for the construction of these basis states exist, and we first compare four procedures to approximate the environment states using Slater determinants explicitly. These start-up procedures are applied to DMRG calculations on a sophisticated test system: the chromium dimer. It is found that the converged energies and the rate of convergence depend significantly on the choice of the start-up procedure. However, since already the most simple start-up procedure, which uses only the Hartree-Fock determinant, is comparatively good, Slater determinants, in general, appear not to be a good choice as approximate environment basis states for convergence acceleration. Based on extensive test calculations it is demonstrated that the computational cost can be significantly reduced if the number of total states m is successively increased. This is done in such a way that the environment states are built up stepwise from system states of previous truncated DMRG sweeps for slowly increasing m values. PMID:16438563

Moritz, Gerrit; Reiher, Markus

2006-01-21

404

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

PubMed

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

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

2015-06-15

405

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

PubMed Central

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

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

2012-01-01

406

Peroxone mineralization of chemical oxygen demand for direct potable water reuse: Kinetics and process control.  

PubMed

Mineralization of organics in secondary effluent by the peroxone process was studied at a direct potable water reuse research treatment system serving an occupied four-bedroom, four bath university residence hall apartment. Organic concentrations were measured as chemical oxygen demand (COD) and kinetic runs were monitored at varying O3/H2O2 dosages and ratios. COD degradation could be accurately described as the parallel pseudo-1st order decay of rapidly and slowly-oxidizable fractions, and effluent COD was reduced to below the detection limit (<0.7 mg/L). At dosages ?4.6 mg L(-1) h(-1), an O3/H2O2 mass ratio of 3.4-3.8, and initial COD <20 mg/L, a simple first order decay was indicated for both single-passed treated wastewater and recycled mineral water, and a relationship is proposed and demonstrated to estimate the pseudo-first order rate constant for design purposes. At this O3/H2O2 mass ratio, ORP and dissolved ozone were found to be useful process control indicators for monitoring COD mineralization in secondary effluent. Moreover, an average second order rate constant for OH oxidation of secondary effluent organics (measured as MCOD) was found to be 1.24 × 10(7) ± 0.64 × 10(7) M(-1) S(-1). The electric energy demand of the peroxone process is estimated at 1.73-2.49 kW h electric energy for removal of one log COD in 1 m(3) secondary effluent, comparable to the energy required for desalination of medium strength seawater. Advantages/disadvantages of the two processes for municipal wastewater reuse are discussed. PMID:25704155

Wu, Tingting; Englehardt, James D

2015-04-15

407

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

408

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

409

Ozonolysis of Mixed Oleic-Acid/Stearic-Acid Particles: Reaction Kinetics and Chemical Morphology  

NASA Astrophysics Data System (ADS)

Atmospheric particles directly and indirectly affect global climate and have a primary role in regional issues of air pollution, visibility, and human health. Atmospheric particles have a variety of shapes, dimensions, and chemical compositions, and these physicochemical properties evolve (i.e., "age") during transport of the particles through the atmosphere, in part because of the chemical reactions of particle-phase organic molecules with gas-phase atmospheric oxidants. As a global average, hydroxyl radical (OH) and ozone (O3) are responsible quantitatively for most oxidant aging of atmospheric particles. The reactions of the hydroxyl radical occur in the surface region of a particle because of the nearly diffusion-limited bimolecular rate constant of OH with a variety of organic molecules. Ozone, on the other hand, is a selective agent for the unsaturated bonds of organic molecules and may diffuse a considerable distance into particles prior to reaction. The reaction of oleic acid with ozone has recently emerged as a model system to better understand the atmospheric chemical oxidation processes affecting organic particles. The ozonolysis of mixed oleic-acid/stearic-acid (OL/SA) aerosol particles from 0/100 to 100/0 weight percent composition is studied. The magnitude of the divergence of the particle beam inside an aerosol mass spectrometer shows that, in the concentration range 100/0 to 60/40, the mixed OL/SA particles are liquid prior to reaction. Upon ozonolysis, particles with SA composition greater than 25% change shape, indicating that they have solidified. Transmission electron micrographs show that SA(s) forms needles. For SA compositions greater than 10%, the reaction kinetics exhibit an initial fast decay of OL for low O3 exposure with no further loss of OL at higher O3 exposures. For compositions from 50/50 to 10/90, the residual OL concentration remains at 28+/-2% of its initial value. The initial reactive uptake coefficient for O3, as determined by OL loss, decreases linearly from 1.25(+/-0.2) 10-3 to 0.60(+/-0.15) 10-3 for composition changes of 100/0 to 60/40. At 50/50 composition, the uptake coefficient drops abruptly to 0.15(+/-0.1) 10-3, and there are no further changes with increased SA content. The amount of SA in the particles also decreases during OL ozonolysis. The stabilized Criegee intermediate (SCI) formed by OL ozonolysis attacks the carboxylic acid group of SA to yield an acyloxyalkyl hydroperoxide product. The experimental observations of this study can be explained by the following two postulates: (1) unreacted mixed particles remain as supersatured liquids up to 60/40 composition and (2) SA, as it solidifies, locks in a significant amount of oleic acid. The results of this study point out the important effects of particle phase, composition, and morphology on chemical reactivity. Oleic acid in liquid regions of a particle reacts rapidly with O3 whereas OL trapped inside solid SA is essentially unavailable for reaction with O3. These results contribute to the continuing development of the scientific community's understanding of particle aging process in the atmosphere, for which the ultimate goal is to provide quantitative mechanistic models of physicochemical transformations under atmospheric conditions.

Martin, S. T.; Katrib, Y.; Biskos, G.; Buseck, P. R.; Davidovits, P.; Jayne, J. T.; Mochida, M.; Wise, M. E.; Worsnop, D. R.

2005-12-01

410

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

ERIC Educational Resources Information Center

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

Elias, Horst; Zipp, Arden P.

1988-01-01

411

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

412

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

413

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

PubMed

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

Li, Yue; Fang, De-Cai

2014-08-01

414

A study of the accuracy of moment-closure approximations for stochastic chemical kinetics  

NASA Astrophysics Data System (ADS)

Moment-closure approximations have in recent years become a popular means to estimate the mean concentrations and the variances and covariances of the concentration fluctuations of species involved in stochastic chemical reactions, such as those inside cells. The typical assumption behind these methods is that all cumulants of the probability distribution function solution of the chemical master equation which are higher than a certain order are negligibly small and hence can be set to zero. These approximations are ad hoc and hence the reliability of the predictions of these class of methods is presently unclear. In this article, we study the accuracy of the two moment approximation (2MA) (third and higher order cumulants are zero) and of the three moment approximation (3MA) (fourth and higher order cumulants are zero) for chemical systems which are monostable and composed of unimolecular and bimolecular reactions. We use the system-size expansion, a systematic method of solving the chemical master equation for monostable reaction systems, to calculate in the limit of large reaction volumes, the first- and second-order corrections to the mean concentration prediction of the rate equations and the first-order correction to the variance and covariance predictions of the linear-noise approximation. We also compute these corrections using the 2MA and the 3MA. Comparison of the latter results with those of the system-size expansion shows that: (i) the 2MA accurately captures the first-order correction to the rate equations but its first-order correction to the linear-noise approximation exhibits the wrong dependence on the rate constants. (ii) the 3MA accurately captures the first- and second-order corrections to the rate equation predictions and the first-order correction to the linear-noise approximation. Hence while both the 2MA and the 3MA are more accurate than the rate equations, only the 3MA is more accurate than the linear-noise approximation across all of parameter space. The analytical results are numerically validated for dimerization and enzyme-catalyzed reactions.

Grima, Ramon

2012-04-01

415

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

416

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

NASA Technical Reports Server (NTRS)

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

Palmer, Grant

1987-01-01

417

Using Calculator-Based Laboratory Technology to Conduct Undergraduate Chemical Research  

NASA Astrophysics Data System (ADS)

Calculator-based laboratory (CBL) technology can be used to initiate a viable undergraduate research program and at the same time teach ethical behavior in science and research. One research project, utilizing buckminsterfullerene, is described as a prototype of the quality and scope of such chemical research programs. Eight original research project ideas are presented for undergraduates to pursue using readily available materials and pH, colorimeter, relative humidity, temperature, light, carbon dioxide, and dissolved oxygen probes.

See Letter re: this article.

Sales, Cynthia L.; Ragan, Nicole M.; Kendrick Murphy, Maureen

2001-05-01

418

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

PubMed Central

Univalent cations and pH influence the UV-visible absorption spectrum of the tryptophan tryptophylquinone (TTQ) enzyme, aromatic amine dehydrogenase (AADH). Little spectral perturbation was observed when pH was varied in the absence of univalent cations. The addition of alkali metal univalent cations (K+, Na+, Li+, Rb+ or Cs+) to oxidized AADH caused significant changes in its absorption spectrum. The apparent Kd for each cation, determined from titrations of the spectral perturbation, decreased with increasing pH. Transient kinetic studies involving rapid mixing of AADH with cations and pH jump revealed that the rate of the cation-induced spectral changes initially decreased with increasing cation concentration to a minimum value, then increased with increasing cation concentration. A kinetic model was developed to fit these data, determine the true pH-independent Kd values for K+ and Na+, and explain the pH-dependence of the apparent Kd. A chemical reaction mechanism, based on the kinetic data, is presented in which the metallic univalent cation facilitates the chemical modification of the TTQ prosthetic group to form an hydroxide adduct which gives rise to the spectral change. Addition of NH4(+)/NH3 to AADH caused changes in the absorption spectrum which were very different form those caused by addition of the metallic univalent cations. The kinetics of the reaction induced by addition of NH4+/NH3 were also different, being simple saturation kinetics. Another reaction mechanism is proposed for the NH4+/NH3-induced spectral change that involves nucleophilic addition of the unprotonated NH3 to TTQ. The general relevance of these data and models to the physiological reactions of TTQ-dependent enzymes and to the roles of univalent cations in modulating enzyme activity are discussed. PMID:9405291

Zhu, Z; Davidson, V L

1998-01-01

419

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

SciTech Connect

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

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

2011-01-01

420

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

421

Free energy calculations, enhanced by a Gaussian ansatz, for the "chemical work" distribution.  

PubMed

The evaluation of the free energy is essential in molecular simulation because it is intimately related with the existence of multiphase equilibrium. Recently, it was demonstrated that it is possible to evaluate the Helmholtz free energy using a single statistical ensemble along an entire isotherm by accounting for the "chemical work" of transforming each molecule, from an interacting one, to an ideal gas. In this work, we show that it is possible to perform such a free energy perturbation over a liquid vapor phase transition. Furthermore, we investigate the link between a general free energy perturbation scheme and the novel nonequilibrium theories of Crook's and Jarzinsky. We find that for finite systems away from the thermodynamic limit the second law of thermodynamics will always be an inequality for isothermal free energy perturbations, resulting always to a dissipated work that may tend to zero only in the thermodynamic limit. The work, the heat, and the entropy produced during a thermodynamic free energy perturbation can be viewed in the context of the Crooks and Jarzinsky formalism, revealing that for a given value of the ensemble average of the "irreversible" work, the minimum entropy production corresponded to a Gaussian distribution for the histogram of the work. We propose the evaluation of the free energy difference in any free energy perturbation based scheme on the average irreversible "chemical work" minus the dissipated work that can be calculated from the variance of the distribution of the logarithm of the work histogram, within the Gaussian approximation. As a consequence, using the Gaussian ansatz for the distribution of the "chemical work," accurate estimates for the chemical potential and the free energy of the system can be performed using much shorter simulations and avoiding the necessity of sampling the computational costly tails of the "chemical work." For a more general free energy perturbation scheme that the Gaussian ansatz may not be valid, the free energy calculation can be expressed in terms of the moment generating function of the "chemical work" distribution. PMID:24664967

Boulougouris, Georgios C

2014-05-15

422

Model-based analysis of coupled equilibrium-kinetic processes: indirect kinetic studies of thermodynamic parameters using the dynamic data.  

PubMed

Thermodynamic studies of equilibrium chemical reactions linked with kinetic procedures are mostly impossible by traditional approaches. In this work, the new concept of generalized kinetic study of thermodynamic parameters is introduced for dynamic data. The examples of equilibria intertwined with kinetic chemical mechanisms include molecular charge transfer complex formation reactions, pH-dependent degradation of chemical compounds and tautomerization kinetics in micellar solutions. Model-based global analysis with the possibility of calculating and embedding the equilibrium and kinetic parameters into the fitting algorithm has allowed the complete analysis of the complex reaction mechanisms. After the fitting process, the optimal equilibrium and kinetic parameters together with an estimate of their standard deviations have been obtained. This work opens up a promising new avenue for obtaining equilibrium constants through the kinetic data analysis for the kinetic reactions that involve equilibrium processes. PMID:25723920

Emami, Fereshteh; Maeder, Marcel; Abdollahi, Hamid

2015-05-01

423

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

SciTech Connect

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

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

1988-07-12

424

Efficient stochastic simulation of chemical kinetics networks using a weighted ensemble of trajectories  

PubMed Central

We apply the “weighted ensemble” (WE) simulation strategy, previously employed in the context of molecular dynamics simulations, to a series of systems-biology models that range in complexity from a one-dimensional system to a system with 354 species and 3680 reactions. WE is relatively easy to implement, does not require extensive hand-tuning of parameters, does not depend on the details of the simulation algorithm, and can facilitate the simulation of extremely rare events. For the coupled stochastic reaction systems we study, WE is able to produce accurate and efficient approximations of the joint probability distribution for all chemical species for all time t. WE is also able to efficiently extract mean first passage times for the systems, via the construction of a steady-state condition with feedback. In all cases studied here, WE results agree with independent “brute-force” calculations, but significantly enhance the precision with which rare or slow processes can be characterized. Speedups over “brute-force” in sampling rare events via the Gillespie direct Stochastic Simulation Algorithm range from ?1012 to ?1018 for characterizing rare states in a distribution, and ?102 to ?104 for finding mean first passage times. PMID:24070313

Donovan, Rory M.; Sedgewick, Andrew J.; Faeder, James R.; Zuckerman, Daniel M.

2013-01-01

425

Efficient Stochastic Simulation of Chemical Kinetics Networks using a Weighted Ensemble of Trajectories  

E-print Network

We apply the "weighted ensemble" (WE) simulation strategy, previously employed in the context of molecular dynamics simulations, to a series of systems-biology models that range in complexity from one-dimensional to a system with 354 species and 3680 reactions. WE is relatively easy to implement, does not require extensive hand-tuning of parameters, does not depend on the details of the simulation algorithm, and can facilitate the simulation of extremely rare events. For the coupled stochastic reaction systems we study, WE is able to produce accurate and efficient approximations of the joint probability distribution for all chemical species for all time t. WE is also able to efficiently extract mean first passage times for the systems, via the construction of a steady-state condition with feedback. In all cases studied here, WE results agree with independent calculations, but significantly enhance the precision with which rare or slow processes can be characterized. Speedups over "brute-force" in sampling rar...

Donovan, Rory M; Faeder, James R; Zuckerman, Daniel M

2013-01-01

426

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

427

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

428

Molecular structure and spectroscopic characterization of Carbamazepine with experimental techniques and DFT quantum chemical calculations.  

PubMed

A systematic vibrational spectroscopic assignment and analysis of Carbamazepine has been carried out by using FT-IR, FT-Raman and UV spectral data. The vibrational analysis were aided by electronic structure calculations - ab initio (RHF) and hybrid density functional methods (B3LYP) performed with standard basis set 6-31G(d,p). Molecular equilibrium geometries, electronic energies, natural bond order analysis, harmonic vibrational frequencies and IR intensities have been computed. A detailed interpretation of the vibrational spectra of the molecule has been made on the basis of the calculated Potential Energy Distribution (PED) by VEDA program. UV-visible spectrum of the compound was also recorded and the electronic properties, such as HOMO and LUMO energies and ?max were determined by HF/6-311++G(d,p) Time-Dependent method. The thermodynamic functions of the title molecule were also performed using the RHF and DFT methods. The restricted Hartree-Fock and density functional theory-based nuclear magnetic resonance (NMR) calculation procedure was also performed, and it was used for assigning the (13)C and (1)H NMR chemical shifts of Carbamazepine. PMID:25682215

Suhasini, M; Sailatha, E; Gunasekaran, S; Ramkumaar, G R

2015-04-15

429

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

430

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

PubMed Central

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

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

2013-01-01

431

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

432

Computer Program for the Calculation of Multicomponent Convective Diffusion Deposition Rates from Chemically Frozen Boundary Layer Theory  

NASA Technical Reports Server (NTRS)

The computer program based on multicomponent chemically frozen boundary layer (CFBL) theory for calculating vapor and/or small particle deposition rates is documented. A specific application to perimter-averaged Na2SO4 deposition rate calculations on a cylindrical collector is demonstrated. The manual includes a typical program input and output for users.

Gokoglu, S. A.; Chen, B. K.; Rosner, D. E.

1984-01-01

433

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

Microsoft Academic Search

Detailed chemical kinetic reaction mechanisms have been developed to describe the pyrolysis and oxidation of the n-alkanes, including n-octane (n-CH), n-nonane (n-CH), n-decane (n-CH), n-undecane (n-CH), n-dodecane (n-CH), n-tridecane (n-CH), n-tetradecane (n-CH), n-pentadecane (n-CH), and n-hexadecane (n-CH). These mechanisms include both high temperature and low temperature reaction pathways. The mechanisms are based on previous mechanisms for n-heptane, using the same

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

2007-01-01

434

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

Microsoft Academic Search

Detailed chemical kinetic reaction mechanisms have been developed to describe the pyrolysis and oxidation of nine n-alkanes larger than n-heptane, including n-octane (n-CH), n-nonane (n-CH), n-decane (n-CH), n-undecane (n-CH), n-dodecane (n-CH), n-tridecane (n-CH), n-tetradecane (n-CH), n-pentadecane (n-CH), and n-hexadecane (n-CH). These mechanisms include both high temperature and low temperature reaction pathways. The mechanisms are based on our previous mechanisms for

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

2008-01-01

435

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

436

The Submillimeter-Wave Spectrum and Quantum Chemical Calculations of Glyoxylic Acid.  

PubMed

Glyoxylic acid is a possible candidate for interstellar detection. Many transitions of the submillimeter wave spectrum of the ground vibrational state of its most stable conformer have been measured for the first time. These transitions have been used together with microwave transitions measured previously to obtain accurate spectroscopic constants that should facilitate a search for this compound in interstellar space. High-level quantum chemical calculations of the structure, quartic centrifugal distortion constants, inertial defect, and energy difference between the two low-energy conformers of glyoxylic acid have also been made. Accurate predictions of the equilibrium structures of the most stable forms of glyoxylic, as well as of formic acid, are reported. Copyright 2001 Academic Press. PMID:11437557

Bakri, B.; Demaison, J.; Margulès, L.; Møllendal, H.

2001-07-01

437

QSPR models for various physical properties of carbohydrates based on molecular mechanics and quantum chemical calculations.  

PubMed

Quantitative Structure-Property Relationships (QSPR) have been developed for a series of monosaccharides, including the physical properties of partial molar heat capacity, heat of solution, melting point, heat of fusion, glass-transition temperature, and solid state density. The models were based on molecular descriptors obtained from molecular mechanics and quantum chemical calculations, combined with other types of descriptors. Saccharides exhibit a large degree of conformational flexibility, therefore a methodology for selecting the energetically most favorable conformers has been developed, and was used for the development of the QSPR models. In most cases good correlations were obtained for monosaccharides. For five of the properties predictions were made for disaccharides, and the predicted values for the partial molar heat capacities were in excellent agreement with experimental values. PMID:14698885

Dyekjaer, Jane Dannow; Jónsdóttir, Svava Osk

2004-01-22

438

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

NASA Technical Reports Server (NTRS)

The Brinkley, Huff, and White methods for chemical-equilibrium calculations were modified and extended in order to permit an analytical comparison. The extended forms of these methods permit condensed species as reaction products, include temperature as a variable in the iteration, and permit arbitrary estimates for the variables. It is analytically shown that the three extended methods can be placed in a form that is independent of components. In this form the Brinkley iteration is identical computationally to the White method, while the modified Huff method differs only'slightly from these two. The convergence rates of the modified Brinkley and White methods are identical; and, further, all three methods are guaranteed to converge and will ultimately converge quadratically. It is concluded that no one of the three methods offers any significant computational advantages over the other two.

Zeleznik, Frank J.; Gordon, Sanford

1960-01-01

439

Kinetics of evaporation of barium THD precursors used for organometallic chemical vapor deposition (OMCVD) thin films  

NASA Astrophysics Data System (ADS)

Various methods have been used to synthesize Ba(THD) 2 and its molecular structure has been studied using nuclear magnetic resonance. Compared with Raman and infrared spectroscopy it was found that NMR is very useful to determine quantitatively the decomposition through aging of Ba(THD) 2. The transport kinetics of Ba(THD) 2 has been studied under experimental conditions of a OMCVD reactor. It has been found that the freshly prepared Ba(THD) 2 by the reaction of Ba metal with THD ligand in anhydrous conditions with subsequent crystallization from methanol transported quantitatively without decomposition. A simple model shows that the transport kinetics corresponds to a diffusion controlled process.

Burtman, V.; Schieber, M.; Yitzchaik, S.; Yaroslavsky, Y.

1997-04-01

440

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

441

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

442

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

443

On extensions of approaches for heat recovery calculations in integrated chemical process systems  

PubMed

This paper deals with heat recovery calculations in integrated chemical process systems. A level of heat recovery in a heat exchanger network (HEN) determines the cost of heat energy consumed in a total system and influences environmental pollution. Even though well established approaches to the problem of calculating minimum cost of utilities in a HEN are available at present, they do not fully account for complex industrial scenarios. The aim of methods developed in this work is to extend applications for the following cases: 1. multiple utilities of great temperature spans (so called non-point utilities), and 2. disturbances of flow-rates of heat exchanging streams. To solve the problems, methods have been developed based on optimisation models. The models are linear though one of them involves mixed-integer variables. Linearity ensures the possibility of solving the models to global optimum, even for large-scale industrial problems. The description of solution methods and examples of applications are presented in this paper. PMID:10890369

Jezowski; Shethna; Bochenek; Castillo

2000-07-01

444

Quantum chemical calculations of bond dissociation energies for COOH scission and electronic structure in some acids  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations are performed to investigate the equilibrium C—COOH bond distances and the bond dissociation energies (BDEs) for 15 acids. These compounds are studied by utilizing the hybrid density functional theory (DFT) (B3LYP, B3PW91, B3P86, PBE1PBE) and the complete basis set (CBS—Q) method in conjunction with the 6-311G** basis as DFT methods have been found to have low basis sets sensitivity for small and medium molecules in our previous work. Comparisons between the computational results and the experimental values reveal that CBS—Q method, which can produce reasonable BDEs for some systems in our previous work, seems unable to predict accurate BDEs here. However, the B3P86 calculated results accord very well with the experimental values, within an average absolute error of 2.3 kcal/mol. Thus, B3P86 method is suitable for computing the reliable BDEs of C—COOH bond for carboxylic acid compounds. In addition, the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of studied compounds are estimated, based on which the relative thermal stabilities of the studied acids are also discussed.

Zeng, Hui; Zhao, Jun; Xiao, Xun

2013-02-01

445

CHEMICAL KINETICS MODELS FOR THE FATIGUE BEHAVIOR OF FUSED SILICA OPTICAL FIBER  

E-print Network

Department of Ceramic and Materials Engineering, Rutgers University, Piscataway, NJ 08854, mjohnm of stress, temperature and activity of the corroding species (e.g. water). A power law degradation kinetics to be the same as the proof test environment when making lifetime predictions, thus avoiding the need

Matthewson, M. John

446

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

447

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

448

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

449

Thermogravimetric Analysis of Modified Hematite by Methane (CH{sub 4}) for Chemical-Looping Combustion: A Global Kinetics Mechanism  

SciTech Connect

Iron oxide (Fe{sub 2}O{sub 3}) or in its natural form (hematite) is a potential material to capture CO{sub 2} through the chemical-looping combustion (CLC) process. It is known that magnesium (Mg) is an effective methyl cleaving catalyst and as such it has been combined with hematite to assess any possible enhancement to the kinetic rate for the reduction of Fe{sub 2}O{sub 3} with methane. Therefore, in order to evaluate its effectiveness as a hematite additive, the behaviors of Mg-modified hematite samples (hematite –5% Mg(OH){sub 2}) have been analyzed with regard to assessing any enhancement to the kinetic rate process. The Mg-modified hematite was prepared by hydrothermal synthesis. The reactivity experiments were conducted in a thermogravimetric analyzer (TGA) using continuous stream of CH{sub 4} (5, 10, and 20%) at temperatures ranging from 700 to 825 {degrees}C over ten reduction cycles. The mass spectroscopy analysis of product gas indicated the presence of CO{sub 2}, H{sub 2}O, H{sub 2} and CO in the gaseous product. The kinetic data at reduction step obtained by isothermal experiments could be well fitted by two parallel rate equations. The modified hematite samples showed higher reactivity as compared to unmodified hematite samples during reduction at all investigated temperatures.

Monazam, Esmail R.; Breault, Ronald W.; Siriwardane, Ranjani; Miller, Duane D.

2013-10-01

450

Kinetics of NF(a1delta), NF(X3E), and chemically pumped NF(b1E)  

NASA Astrophysics Data System (ADS)

We have been investigating kinetics issues associated with the development of a new chemical laser in the green based on the b-X transition of NF at 529 nm. The proposed scheme involves energy pooling of NF(a1(Delta) ) with I*(2P1/2) to form NF(b1(Sigma) ). The kinetics of NF(a) and NF(X) have a strong impact on the relative populations of NF(X) and NF(b) and therefore play a central role in this system. We have measured the rate coefficients for the reactions of NF(a) and NF(X) with several relevant species including O2, NF2, N2F4, and I2. We have also carried out a series of measurements on the energy pooling of I* with NF(a) by photolyzing mixtures of HI and NF2 at 193 nm to produce H atoms and NF(a). Using a flashlamp-pumped I* laser, we optically prepared I* to create a steady-state ratio of [I*]/[I] during the 30 microsecond(s) laser pulse. This greatly simplifies the kinetics and allows us to extract rate constants for: NF(a) + I* yields NF(b) + I, NF(b) + I yields NF(a) + I*, and NF(b) + I yields other products.

Weiller, Bruce H.; Heidner, Raymond F., III; Koffend, J. B.

1993-06-01

451

Fast Prediction of HCCI and PCCI Combustion with an Artificial Neural Network-Based Chemical Kinetic Model  

SciTech Connect

We have added the capability to look at in-cylinder fuel distributions using a previously developed ignition model within a fluid mechanics code (KIVA3V) that uses an artificial neural network (ANN) to predict ignition (The combined code: KIVA3V-ANN). KIVA3V-ANN was originally developed and validated for analysis of Homogeneous Charge Compression Ignition (HCCI) combustion, but it is also applicable to the more difficult problem of Premixed Charge Compression Ignition (PCCI) combustion. PCCI combustion refers to cases where combustion occurs as a nonmixing controlled, chemical kinetics dominated, autoignition process, where the fuel, air, and residual gas mixtures are not necessarily as homogeneous as in HCCI combustion. This paper analyzes the effects of introducing charge non-uniformity into a KIVA3V-ANN simulation. The results are compared to experimental results, as well as simulation results using a more physically representative and computationally intensive code (KIVA3V-MPI-MZ), which links a fluid mechanics code to a multi-zone detailed chemical kinetics solver. The results indicate that KIVA3V-ANN produces reasonable approximations to the more accurate KIVA3V-MPI-MZ at a much reduced computational cost.

Piggott, W T; Aceves, S M; Flowers, D L; Chen, J Y

2007-09-26

452

Exact results in nonequilibrium statistical mechanics: Formalism and applications in chemical kinetics and single-molecule free energy estimation  

NASA Astrophysics Data System (ADS)

In the last two decades or so, a collection of results in nonequilibrium statistical mechanics that departs from the traditional near-equilibrium framework introduced by Lars Onsager in 1931 has been derived, yielding new fundamental insights into far-from-equilibrium processes in general. Apart from offering a more quantitative statement of the second law of thermodynamics, some of these results---typified by the so-called "Jarzynski equality"---have also offered novel means of estimating equilibrium quantities from nonequilibrium processes, such as free energy differences from single-molecule "pulling" experiments. This thesis contributes to such efforts by offering three novel results in nonequilibrium statistical mechanics: (a) The entropic analog of the Jarzynski equality; (b) A methodology for estimating free energies from "clamp-and-release" nonequilibrium processes; and (c) A directly measurable symmetry relation in chemical kinetics similar to (but more general than) chemical detailed balance. These results share in common the feature of remaining valid outside Onsager's near-equilibrium regime, and bear direct applicability in protein folding kinetics as well as in single-molecule free energy estimation.

Adib, Artur B.

453

In vitro release kinetics and physical, chemical and mechanical characterization of a POVIAC®/CaCO3/HAP-200 composite.  

PubMed

Coralline calcium-hydroxyapatite and calcium carbonate from Porites Porites coral were added to a polymeric matrix based on polyvinyl acetate (POVIAC(®)), to obtain a novel bone substitute composite as well as a system for the controlled drug (cephalexin) release. Composite samples with different compositions were characterized by physical-chemical and mechanical methods. Furthermore, the in vitro release profile of cephalexin and the kinetic behavior of its release from these composites were analyzed by appropriate mathematical models. It was shown that there is no chemical interaction between the inorganic filler and the polymer matrix, each conserving the original properties of the raw materials. The compressive mechanical strength and Young modulus of the composite with 17.5% of POVIAC(®), has better mechanical properties than those of cancellous bone. The variation of POVIAC(®) content can affect the cephalexin release kinetic in the composite. The cephalexin release mechanism from the composites can be considered as the result of the joint contribution of a prevailing Fickian diffusion and of polymer chain relaxation. It was also demonstrated that cephalexin is occluded inside the composites and not on their surface. PMID:22201028

Aragón, Javier; González, Ramón; Fuentes, Gastón; Palin, Luca; Croce, Gianluca; Viterbo, Davide

2012-02-01

454

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

455

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

Microsoft Academic Search

A direct path flux analysis (PFA) method for kinetic mechanism reduction is proposed and validated by using high temperature ignition, perfect stirred reactors, and steady and unsteady flame propagations of n-heptane and n-decane\\/air mixtures. The formation and consumption fluxes o