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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.
Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a glass like'' material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.
Nguyen, H.D.
Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a ``glass like`` material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.
Nguyen, H.D.
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.
Chemical Kinetics: Isolation Method
NSDL National Science Digital Library
This site offers an interactive tutorial that guides the student through the Method of Isolation used for the determination of chemical reaction rate laws and rate constants. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.
Blauch, David N.
LLNL Chemical Kinetics Modeling Group
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
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)
Chemical Kinetics: Rate of Reaction
NSDL National Science Digital Library
This site offers an interactive tutorial that emphasizes graphical interpretation of chemical kinetics. The stoichiometric coefficients for a chemical equation are determined by comparing the slopes of concentration-time plots for the reactants and products. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.
Blauch, David N.
Chemical kinetics on extrasolar planets.
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
NSDL National Science Digital Library
This site offers an interactive tutorial that emphasizes graphical interpretation of chemical kinetics. The half-life is measured for various initial concentrations for zero-, first-, and second-order reactions. The data is analyzed graphically to determine the relationship between the half-life and reactant concentration for each order reaction and to determine the rate constant for each reaction. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.
Blauch, David N.
Kinetic studies of elementary chemical reactions
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)
Chemical kinetics and combustion modeling
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)
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.
Detailed Chemical Kinetic Modeling of Cyclohexane Oxidation
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
Thermochemical and chemical kinetic data for fluorinated hydrocarbons
A comprehensive, detailed chemical kinetic mechanism was developed and is presented for C1 and C2 fluorinated hydrocarbon destruction and flame suppression. Existing fluorinated hydrocarbon thermochemistry and kinetics were compiled from the literature and evaluated. For species where no or incomplete thermochemistry was available, these data were calculated through application of ab initio molecular orbital theory. Group additivity values were determined
D. R. Burgess; M. R. Zachariah; W. Tsang; P. R. Westmoreland
Reduced chemical kinetics for propane combustion
NASA Technical Reports Server (NTRS)
It is pointed out that a detailed chemical kinetics mechanism for the combustion of propane consists of 40 chemical species and 118 elementary chemical reactions. An attempt is made to reduce the number of chemical species and elementary chemical reactions so that the computer run times and storage requirements may be greatly reduced in three-dimensional gas turbine combustion flow calculations, while maintaining accurate predictions of the propane combustion and exhaust emissions. By way of a sensitivity analysis, the species of interest and chemical reactions are classified in descending order of importance. Nineteen species are chosen, and their pressure, temperature, and concentration profiles are presented for the reduced mechanisms, which are then compared with those from the full 118 reactions. It is found that 45 reactions involving 27 species have to be kept for comparable agreement. A comparison of the results obtained from the 45 reactions to that of the full 118 shows that the pressure and temperature profiles and concentrations of C3H8, O2, N2, H2O, CO, and CO2 are within 10 percent of maximum change.
Ying, Shuh-Jing; Nguyen, Hung Lee
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.
Fast algorithms for combustion kinetics calculations: A comparison
NASA Technical Reports Server (NTRS)
To identify the fastest algorithm currently available for the numerical integration of chemical kinetic rate equations, several algorithms were examined. Findings to date are summarized. The algorithms examined include two general-purpose codes EPISODE and LSODE and three special-purpose (for chemical kinetic calculations) codes CHEMEQ, CRK1D, and GCKP84. In addition, an explicit Runge-Kutta-Merson differential equation solver (IMSL Routine DASCRU) is used to illustrate the problems associated with integrating chemical kinetic rate equations by a classical method. Algorithms were applied to two test problems drawn from combustion kinetics. These problems included all three combustion regimes: induction, heat release and equilibration. Variations of the temperature and species mole fraction are given with time for test problems 1 and 2, respectively. Both test problems were integrated over a time interval of 1 ms in order to obtain near-equilibration of all species and temperature. Of the codes examined in this study, only CREK1D and GCDP84 were written explicitly for integrating exothermic, non-isothermal combustion rate equations. These therefore have built-in procedures for calculating the temperature.
Radhakrishnan, K.
Chemical kinetics and oil shale process design
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.
Chemical Kinetics in Flames�a Review
The importance of chemical kinetics (heat release rates) in the laminar flame front are discussed. The need and possibilities of studying complex reactions in the flame front for large extents of conversion are considered.
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.
Chemical kinetics of Estane aging in PBX
The Plastic-Bonded Explosive PBX 9501 is about 95% HMX, 2.5% Estane 5703, 2.5% nitroplasticizer (NP), and 0.1% stabilizer by weight. The NP, BDNPA/F, is a eutectic mixture of bis(2,2-dinitropropyl) acetal and bis(2,2-dinitropropyl)formal. The stabilizer is diphenylamine (DPA) or Irganox 1010. The Estane, a polyester-polyurethane, slowly degrades with time. Knowledge of the effect of the Estane aging on the mechanical properties of the PBX 9501 is required to predict with confidence the useful lifetime of the explosive with respect to safety and reliability. A detailed master equation model of the chemical mechanisms and kinetics of the aging of Estane 5703 in PBX 9501 is being developed. Its output will be used as input into other models being developed to calculate the changes in the mechanical properties of the PBX.
Pack, R.T.; Hanson, D.E.; Redondo, A. [Los Alamos National Lab., NM (United States). Theoretical Div.
Chemical kinetic modelling of hydrocarbon ignition
Chemical kinetic modeling of hydrocarbon ignition is discussed with reference to a range of experimental configurations, including shock tubes, detonations, pulse combustors, static reactors, stirred reactors and internal combustion engines. Important conditions of temperature, pressure or other factors are examined to determine the main chemical reaction sequences responsible for chain branching and ignition, and kinetic factors which can alter the rate of ignition are identified. Hydrocarbon ignition usually involves complex interactions between physical and chemical factors, and it therefore is a suitable and often productive subject for computer simulations. In most of the studies to be discussed below, the focus of the attention is placed on the chemical features of the system. The other physical parts of each application are generally included in the form of initial or boundary conditions to the chemical kinetic parts of the problem, as appropriate for each type of application being addressed.
Westbrook, C.K.; Pitz, W.J.; Curran, H.J.; Gaffuri, P.; Marinov, N.M.
Chemical Kinetics: Method of Initial Rates
NSDL National Science Digital Library
This site offers an interactive tutorial to assist in the understanding of how the Method of Initial Rates is employed to determine rate constants for chemical reactions. The student runs a series of experiments to create graphical data that is analyzed. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.
Blauch, David N.
Chemical Oscillations in Enzyme Kinetics
The Higgins model is a two variable model in enzyme kinetics. In contrast with other popular simple dynamical models like the Lotka-Volterra model, the Higgins model shows steady states, damped oscillations and stable limit cycles. For these three dynamical behaviors, stability analysis yields expressions of the eigenvalues, which are easy to obtain either analytically or with the use of Mathematica.
Katherine L. Queeney; Ethan P. Marin; Cory M. Campbell; Enrique Peacock-Lopez
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.
Detailed chemical kinetic model for ethanol oxidation
A detailed chemical kinetic model for ethanol oxidation has been developed and validated against a variety of experimental data sets. Laminar flame speed data obtained from a constant volume bomb, ignition delay data behind reflected shock waves, and ethanol oxidation product profiles from a turbulent flow reactor were used in this study. Very good agreement was found in modeling the data sets obtained from the three different experimental systems. The computational modeling results show that high temperature ethanol oxidation exhibits strong sensitivity to the fall-off kinetics of ethanol decomposition, branching ratio selection for c2h5oh+oh=products, and reactions involving the hydroperoxyl (HO2) radical.
Marinov, N.
Sensitivity, robustness, and identifiability in stochastic chemical kinetics models.
We present a novel and simple method to numerically calculate Fisher information matrices for stochastic chemical kinetics models. The linear noise approximation is used to derive model equations and a likelihood function that leads to an efficient computational algorithm. Our approach reduces the problem of calculating the Fisher information matrix to solving a set of ordinary differential equations. This is the first method to compute Fisher information for stochastic chemical kinetics models without the need for Monte Carlo simulations. This methodology is then used to study sensitivity, robustness, and parameter identifiability in stochastic chemical kinetics models. We show that significant differences exist between stochastic and deterministic models as well as between stochastic models with time-series and time-point measurements. We demonstrate that these discrepancies arise from the variability in molecule numbers, correlations between species, and temporal correlations and show how this approach can be used in the analysis and design of experiments probing stochastic processes at the cellular level. The algorithm has been implemented as a Matlab package and is available from the authors upon request. PMID:21551095
Komorowski, Micha?; Costa, Maria J; Rand, David A; Stumpf, Michael P H
Chemical kinetic effects in nonpremixed flames of H[sub 2]\\/CO[sub 2] fuel
Finite rate chemical kinetic effects are investigated in diffusion flames of H[sub 2]\\/CO[sub 2] fuel. The CO[sub 2] diluent is not totally inert since a high temperature some of it will react to give CO. In this paper calculations of laminar flames and measurements in turbulent flames are presented. The calculations are performed, using a detailed chemical kinetic mechanism with
A. R. Masri; R. W. Dibble; R. S. Barlow
Perspective: Stochastic algorithms for chemical kinetics
We outline our perspective on stochastic chemical kinetics, paying particular attention to numerical simulation algorithms. We first focus on dilute, well-mixed systems, whose description using ordinary differential equations has served as the basis for traditional chemical kinetics for the past 150 years. For such systems, we review the physical and mathematical rationale for a discrete-stochastic approach, and for the approximations that need to be made in order to regain the traditional continuous-deterministic description. We next take note of some of the more promising strategies for dealing stochastically with stiff systems, rare events, and sensitivity analysis. Finally, we review some recent efforts to adapt and extend the discrete-stochastic approach to systems that are not well-mixed. In that currently developing area, we focus mainly on the strategy of subdividing the system into well-mixed subvolumes, and then simulating diffusional transfers of reactant molecules between adjacent subvolumes together with chemical reactions inside the subvolumes. PMID:23656106
Gillespie, Daniel T.; Hellander, Andreas; Petzold, Linda R.
The standard chemical oxygen-iodine laser kinetics package
This report presents the Air Force Weapons Laboratory Standard Chemical Oxygen-Iodine Laser Kinetics Package. A complete reaction scheme including recommended rate coefficients for modeling the gas phase kinetics of chemical oxygen-iodine lasers (COIL) was established to provide a common basis for the research and development of COIL devices. A review of the experimental kinetic data base from which this model
Glen P. Perram; Gordon D. Hager
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.
action chemical kinetics conserves mass and renders non-negative solutions; a good numerical simulation-negative quantities; · for stability of the chemical system; · an operator-split solution of convectionA POSITIVE NUMERICAL INTEGRATION METHOD FOR CHEMICAL KINETIC SYSTEMS ADRIAN SANDU Abstract. Mass
Sandu, Adrian
Theory of homogeneous nucleation - A chemical kinetic view
NASA Technical Reports Server (NTRS)
A simple function with two undetermined parameters has been used in place of the Thomson-Gibbs relation to relate the activation energy of the vaporization reaction to cluster size. The parameters are iterated to assume optimum values in numerical computation so experimental data may be correlated. Calculations show this approach closely predicts and correlates available data for water, benzene, and ethanol. The nucleation formulism is redeveloped with an emphasis on the chemical kinetic view. Surface tension of the liquid and free energy of droplet formation are not used in its derivation.
Yang, C. H.; Qiu, H.
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
A Chemical Kinetic Model of Transcriptional Elongation
A chemical kinetic model of the elongation dynamics of RNA polymerase along a DNA sequence is introduced. The proposed model governs the discrete movement of the RNA polymerase along a DNA template, with no consideration given to elastic effects. The model's novel concept is a ``look-ahead'' feature, in which nucleotides bind reversibly to the DNA prior to being incorporated covalently into the nascent RNA chain. Results are presented for specific DNA sequences that have been used in single-molecule experiments of the random walk of RNA polymerase along DNA. By replicating the data analysis algorithm from the experimental procedure, the model produces velocity histograms, enabling direct comparison with these published results.
Yujiro Richard Yamada; Charles S. Peskin
Calculation of kinetic spatial weighting factors in power reactors
Ex-core neutron detector kinetic (frequency-dependent) spatial sensitivities (weighting factors) for in-core neutron sources were determined by performing space-dependent, transport and diffusion theory, kinetic detector adjoint calculations in which both source propagation through fission processes and the frequency dependence of the reactivity-to-power transfer function were considered. This study was pursued to overcome the shortcomings of previous calculations of ex-core detector weighting factors for in-core neutron sources using discrete-ordinate shielding or point kernel techniques.
Sweeney, F.J.; Renier, J.P.
Benchmarking kinetic calculations of resistive wall mode stability
NASA Astrophysics Data System (ADS)
Validating the calculations of kinetic resistive wall mode (RWM) stability is important for confidently predicting RWM stable operating regions in ITER and other high performance tokamaks for disruption avoidance. Benchmarking the calculations of the Magnetohydrodynamic Resistive Spectrum�Kinetic (MARS-K) [Y. Liu et al., Phys. Plasmas 15, 112503 (2008)], Modification to Ideal Stability by Kinetic effects (MISK) [B. Hu et al., Phys. Plasmas 12, 057301 (2005)], and Perturbed Equilibrium Nonambipolar Transport PENT) [N. Logan et al., Phys. Plasmas 20, 122507 (2013)] codes for two Solov'ev analytical equilibria and a projected ITER equilibrium has demonstrated good agreement between the codes. The important particle frequencies, the frequency resonance energy integral in which they are used, the marginally stable eigenfunctions, perturbed Lagrangians, and fluid growth rates are all generally consistent between the codes. The most important kinetic effect at low rotation is the resonance between the mode rotation and the trapped thermal particle's precession drift, and MARS-K, MISK, and PENT show good agreement in this term. The different ways the rational surface contribution was treated historically in the codes is identified as a source of disagreement in the bounce and transit resonance terms at higher plasma rotation. Calculations from all of the codes support the present understanding that RWM stability can be increased by kinetic effects at low rotation through precession drift resonance and at high rotation by bounce and transit resonances, while intermediate rotation can remain susceptible to instability. The applicability of benchmarked kinetic stability calculations to experimental results is demonstrated by the prediction of MISK calculations of near marginal growth rates for experimental marginal stability points from the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)].
Berkery, J. W.; Liu, Y. Q.; Wang, Z. R.; Sabbagh, S. A.; Logan, N. C.; Park, J.-K.; Manickam, J.; Betti, R.
This paper updates and extends a previous critical evaluation of the kinetics and photochemistry of gas phase chemical reactions of neutral species involved in middle atmosphere chemistry (10�55 km altitude) [J. Phys. Chem. Ref. Data 9, 295 (1980)]. The work has been carried out by the authors under the auspices of the CODATA Task Group on Chemical Kinetics. Data sheets
D. L. Baulch; R. A. Cox; P. J. Crutzen; R. F. Hampson; J. A. Kerr; J. Troe; R. T. Watson
Effects of impurities on wake chemical kinetics and electron density
NASA Astrophysics Data System (ADS)
The present paper studies the effects of impurities on wake chemical kinetics and wake ionization. Such effects are examined through computation of wake flows composed of H2O, F2, CaF4, and Na-containing species added to the air constituents. A 26-species, 36-reaction chemical system is considered. An exact finite difference method for solving the axisymmetric boundary layer equations for chemical nonequilibrium wake flow is employed for both laminar and turbulent flows regions. In order to ascertain a variety of effects separately. nine different chemical subsystems of increasing complexity are treated. These are pure air, air-Na, air-F2, air-C2F4, air-F2-C2F4, air-H2O-Na, air-F2-Na, air-C2F4-Na, and air-C2F4-F2-Na. Calculated results demonstrate that impurities exert significant influences on wake ionization. Sodium can enhance electron concentration of pure air by 1-3 orders of magnitude and the electron decay mechanism of the air-C2F4 chemical subsystem results in production of negative F ions and removes most of the electrons.
Zhou, Xuehua
Elimination kinetic model for organic chemicals in earthworms.
Mechanistic understanding of bioaccumulation in different organisms and environments should take into account the influence of organism and chemical depending factors on the uptake and elimination kinetics of chemicals. Lipophilicity, metabolism, sorption (bioavailability) and biodegradation of chemicals are among the important factors that may significantly affect the bioaccumulation process in soil organisms. This study attempts to model elimination kinetics of organic chemicals in earthworms by accounting for the effects of both chemical and biological properties, including metabolism. The modeling approach that has been developed is based on the concept for simulating metabolism used in the BCF base-line model developed for predicting bioaccumulation in fish. Metabolism was explicitly accounted for by making use of the TIMES engine for simulation of metabolism and a set of principal transformations. Kinetic characteristics of transformations were estimated on the basis of observed kinetics data for the elimination of organic chemicals from earthworms. PMID:20185163
Dimitrova, N; Dimitrov, S; Georgieva, D; Van Gestel, C A M; Hankard, P; Spurgeon, D; Li, H; Mekenyan, O
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.
Light nuclei at room temperature and below exhibit a kinetic energy which significantly deviates from the predictions of classical statistical mechanics. This quantum kinetic energy is responsible for a wide variety of isotope effects of interest in fields ranging from chemistry to climatology. It also furnishes the second moment of the nuclear momentum distribution, which contains subtle information about the chemical environment and has recently become accessible to deep inelastic neutron scattering experiments. Here we show how, by combining imaginary time path integral dynamics with a carefully designed generalized Langevin equation, it is possible to dramatically reduce the expense of computing the quantum kinetic energy. We also introduce a transient anisotropic Gaussian approximation to the nuclear momentum distribution which can be calculated with negligible additional effort. As an example, we evaluate the structural properties, the quantum kinetic energy, and the nuclear momentum distribution for a ...
Ceriotti, Michele
Quantum mechanical calculations to chemical accuracy
NASA Technical Reports Server (NTRS)
The accuracy of current molecular-structure calculations is illustrated with examples of quantum mechanical solutions for chemical problems. Two approaches are considered: (1) the coupled-cluster singles and doubles (CCSD) with a perturbational estimate of the contribution of connected triple excitations, or CCDS(T); and (2) the multireference configuration-interaction (MRCI) approach to the correlation problem. The MRCI approach gains greater applicability by means of size-extensive modifications such as the averaged-coupled pair functional approach. The examples of solutions to chemical problems include those for C-H bond energies, the vibrational frequencies of O3, identifying the ground state of Al2 and Si2, and the Lewis-Rayleigh afterglow and the Hermann IR system of N2. Accurate molecular-wave functions can be derived from a combination of basis-set saturation studies and full configuration-interaction calculations.
Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.
Detailed chemical kinetic oxidation mechanism for a biodiesel Olivier Herbineta
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
NIST Standard Reference Database 17 NIST Chemical Kinetics Database
NIST Standard Reference Database 17 __________________________________________________________ NIST Chemical Kinetics Database WindowsTM Version 2Q98 Users' Guide (NIST) uses its best efforts to deliver a high quality copy of the Database and to verify that the data
Polymerization dynamics of double-stranded biopolymers: chemical kinetic approach
The polymerization dynamics of double-stranded polymers, such as actin filaments, is investigated theoretically using simple chemical kinetic models that explicitly take into account some microscopic details of the polymer structure and the lateral interactions between the protofilaments. By considering all possible molecular configurations, the exact analytical expressions for the growth velocity and dispersion for two-stranded polymers are obtained in the case of the growing at only one end, and for the growth from both polymer ends. Exact theoretical calculations are compared with the predictions of approximate multi-layer models that consider only a finite number of the most relevant polymer configurations. Our theoretical approach is applied to analyze the experimental data on the growth and fluctuations dynamics of individual single actin filaments.
Evgeny B. Stukalin; Anatoly B. Kolomeisky
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.
Basic Chemical Principles 1: Reaction Kinetics
with radiation can cause chemical events: bonds broken, molecules excited { Creation of radicals Molecular state: Lowest energy con#12;guration of electrons in orbitals #15; To form chemical bond, combine atomic, photo-chemical reactions are important: reactions initiated by light #12; { Interaction of matter
Schofield, Jeremy
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
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.
A kinetic-theory approach to turbulent chemically reacting flows
NASA Technical Reports Server (NTRS)
The paper examines the mathematical and physical foundations for the kinetic theory of reactive turbulent flows, discussing the differences and relation between the kinetic and averaged equations, and comparing some solutions of the kinetic equations obtained by the Green's function method with those obtained by the approximate bimodal method. The kinetic method described consists essentially in constructing the probability density functions of the chemical species on the basis of solutions of the Langevin stochastic equation for the influence of eddies on the behavior of fluid elements. When the kinetic equations are solved for the structure of the diffusion flame established in a shear layer by the bimodal method, discontinuities in gradients of the mean concentrations at the two flame edges appear. This is a consequence of the bimodal approximation of all distribution functions by two dissimilar half-Maxwellian functions, which is a very crude approximation. These discontinuities do not appear when the solutions are constructed by the Green's function method described here.
Chung, P. M.
Chemical and kinetic equilibrations via radiative parton transport
A hot and dense partonic system can be produced in the early stage of a relativistic heavy ion collision. How it equilibrates is important for the extraction of Quark-Gluon Plasma properties. We study the chemical and kinetic equilibrations of the Quark-Gluon Plasma using a radiative transport model. Thermal and Color-Glass-Condensate motivated initial conditions are used. We observe that screened parton interactions always lead to partial pressure isotropization. Different initial pressure anisotropies result in the same asymptotic evolution. Comparison of evolutions with and without radiative processes shows that chemical equilibration interacts with kinetic equilibration and radiative processes can contribute significantly to pressure isotropization.
Bin Zhang; Warner A. Wortman
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.
Chemical kinetics in hydrogen-air flames
This report describes a chemical reaction mechanism for hydrogen-air flames. The mechanism includes the minimum number of elementary reactions that are necessary to reproduce macroscopic flame properties. The elementary reactions, their rate coefficients, and a qualitative description of their contributions to the structure of the flame are given. It is suggested that the flammability limits are determined primarily by the
Dissolution kinetics of chemically amplified resists
NASA Astrophysics Data System (ADS)
The dissolution rate characteristics of two typical DUV chemically amplified resists (negative resist A and positive resist B) were investigated, by comparing with an i-line novolac resist (resist C). The negative resist A here was based on crosslinking between phenolic resin and melamine derivatives, and the positive resist B was composed of tert-BOC protected phenolic resin.
Itani, Toshiro; Itoh, Katsuyuki; Kasama, Kunihiko
Ernest Rutherford, Avogadro's Number, and Chemical Kinetics
NASA Astrophysics Data System (ADS)
The paper presents a way for students to use data from Rutherford's works (1908 - 1911) in order to determine one of the most precise values of Avogadro Constant available at the beginning of the century. A brief discussion of earlier and modern methods for the determination of this fundamental constant is followed by vast quotations from the works of Rutherford, Boltwood and Geiger. Then there are given a dozen of problems and questions for students about these classical experiments; they vary in complexity from rather simple to quite challenging. Additional information and hints are provided to help the students in solving the problems. The last part contains detailed answers and solutions to all problems. The article will be useful for students of general chemistry, radiochemistry and physical chemistry (kinetics).
Leenson, I. A.
Constant chemical potential approach for quantum chemical calculations in electrocatalysis.
In order to simulate electrochemical reactions in the framework of quantum chemical methods, density functional theory, methods can be devised that explicitly include the electrochemical potential. In this work we discuss a Grand Canonical approach in the framework of density functional theory in which fractional numbers of electrons are used to represent an open system in contact with an electrode at a given electrochemical potential. The computational shortcomings and the additional effort in such calculations are discussed. An ansatz for a SCF procedure is presented, which can be applied routinely and only marginally increases the computational effort of standard constant electron number approaches. In combination with the common implicit solvent models this scheme can become a powerful tool, especially for the investigation of omnipresent non-faradaic effects in electrochemistry. PMID:24991504
Schneider, Wolfgang B; Auer, Alexander A
PLASMAKIN: A chemical kinetics library for plasma physics modeling
PLASMAKIN is a package to handle physical and chemical data used in plasma physics modeling and to compute kinetics data from the reactions taking place in the gas or at the surfaces: particle production and loss rates, photon spectra and energy exchange rates. It has no limits on the number of species and reactions that can be handled, is independent
Nuno Pinhao
Polymerization dynamics of double-stranded biopolymers: Chemical kinetic approach
Polymerization dynamics of double-stranded biopolymers: Chemical kinetic approach Evgeny B 19 November 2004; accepted 20 December 2004; published online 10 March 2005 The polymerization, the exact analytical expressions for the growth velocity and dispersion for two-stranded polymers
HTheorems in some kinetic models of chemically reacting dense gases
and Reaction Dynamics and Chemical Reactivity, 1987, or M.J.Pilling, P.W.Seakins, Reaction Kinetics, 1995 by C.F.Curtiss (1949) for very simple reactions where the presence of reaction products were ignoredlike) equation for the density distribution of particles A. . Often the cross sections of (gas) reactions
Polewczak, Jacek
Experimental characterization and chemical kinetics study of chemical looping combustion
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
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.
A pared-down gas-phase kinetics for the chemical oxygen-iodine laser medium
NASA Astrophysics Data System (ADS)
Kinetic data obtained in the last decade has resulted in revisions of some mechanisms of excitation and deactivation of excited states in the chemical oxygen-iodine laser (COIL) medium. This review considers new kinetic data and presents analyses of the mechanisms of pumping and quenching of electronically and vibrationally excited states in the oxygen-iodine laser media. An effective three-level model of I2 molecule excitation and relaxation has been developed. The calculated effective rate constants for deactivation of I2(X,11 ? ? ? 24) by O2, N2, He and CO2 are presented. A simplified kinetic package for the COIL active medium is recommended. This model consists of a 30-reaction set with 14 species. The results of calculations utilizing simplified model are in good agreement with the experimental data.
Pichugin, S. Yu.; Heaven, M. C.
Infrared absorption spectroscopy and chemical kinetics of free radicals
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)
Numerical Simulation of SNCR Technology with Simplified Chemical Kinetics Model
NASA Astrophysics Data System (ADS)
The paper deals with numerical simulation of SNCR method. For numerical modelling was used CFD code Ansys/CFX. SNCR method was described by dominant chemical reaction, which were look up NIST Chemical database. The reactions including reduction of NOx and concentration change of pollutants, like N2O and CO in flue gas too. Proposed chemical kinetics and CFD model was applied to two boilers. Both simulations were compared with experimental measurements. First simulation was used to validation of chemical mechanism. Second simulation was based on first simulation and it was used to verification of compiled SNCR chemical mechanism. Next the new variant of the reagent penetration lance was proposed and compared with the original variants.
Blejcha?, T.; Doln�?kov�, D.
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
Combustion of hydrocarbon fuels has been a very challenging scientific and engineering problem due to the complexity of turbulent flows and hydrocarbon reaction kinetics. There is an urgent need to develop an efficient modeling capability to accurately predict the combustion of complex fuels. Detailed chemical kinetic models for the surrogates of fuels such as gasoline, diesel and JP-8 consist of thousands of chemical species and Arrhenius reaction steps. Oxygenated fuels such as bio-fuels and heavier hydrocarbons, such as from newer fossil fuel sources, are expected to have a much more complex chemistry requiring increasingly larger chemical kinetic models. Such models are beyond current computational capability, except for homogeneous or partially stirred reactor type calculations. The advent of highly parallel multi-core processors and graphical processing units (GPUs) promises a steep increase in computational performance in the coming years. This paper will present a software framework that translates the detailed chemical kinetic models to high-performance code targeted for GPU accelerators.
Sankaran, R.; Grout, R.
Chemical kinetic modeling of propene oxidation at low and intermediate temperatures
A detailed chemical kinetic mechanism for propene oxidation is developed and used to model reactions in a static reactor at temperatures of 590 to 740°K, equivalence ratios of 0.8 to 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
R. D. Wilk; N. P. Cernansky; W. J. Pitz; C. K. Westbrook
Single-molecule chemical reaction reveals molecular reaction kinetics and dynamics.
Understanding the microscopic elementary process of chemical reactions, especially in condensed phase, is highly desirable for improvement of efficiencies in industrial chemical processes. Here we show an approach to gaining new insights into elementary reactions in condensed phase by combining quantum chemical calculations with a single-molecule analysis. Elementary chemical reactions in liquid-phase, revealed from quantum chemical calculations, are studied by tracking the fluorescence of single dye molecules undergoing a reversible redox process. Statistical analyses of single-molecule trajectories reveal molecular reaction kinetics and dynamics of elementary reactions. The reactivity dynamic fluctuations of single molecules are evidenced and probably arise from either or both of the low-frequency approach of the molecule to the internal surface of the SiO2 nanosphere or the molecule diffusion-induced memory effect. This new approach could be applied to other chemical reactions in liquid phase to gain more insight into their molecular reaction kinetics and the dynamics of elementary steps. PMID:24963600
Zhang, Yuwei; Song, Ping; Fu, Qiang; Ruan, Mingbo; Xu, Weilin
Chemical Kinetic Models for HCCI and Diesel Combustion
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
NASA Astrophysics Data System (ADS)
Chemical equilibrium calculations are essential for many environmental problems. It is also a fundamental tool for chemical kinetics and reactive transport modelling, since these applications may require hundreds to billions equilibrium calculations in a single simulation. Therefore, an equilibrium method for such critical applications must be very efficient, robust and accurate. In this work we demonstrate the potential effectiveness of a novel Gibbs energy minimisation algorithm for reactive transport simulations. The algorithm includes strategies to converge from poor initial guesses; capabilities to specify non-linear equilibrium constraints such as pH of an aqueous solution and activity or fugacity of a species; a rigorous phase stability test to determine the unstable phases; and a strategy to boost the convergence speed of the calculations to quadratic rates, requiring only few iterations to converge. We use this equilibrium method to solve geochemical problems relevant to carbon storage in saline aquifers, where aqueous, gaseous and minerals phases are present. The problems are formulated to mimic the ones found in kinetics and transport simulations, where a sequence of equilibrium calculations are performed, each one using the previous solution as the initial guess. The efficiency and convergence rates of the calculations are presented, which require an average of 1-2 iterations. These results indicate that critical applications such as chemical kinetics and reactive transport modelling can potentially benefit by using this multiphase equilibrium algorithm.
Leal, Allan M. M.; Blunt, Martin J.; LaForce, Tara C.
Modeling of chemical inhibition from amyloid protein aggregation kinetics
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
Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate
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
Detailed chemical kinetic oxidation mechanism for a biodiesel surrogate
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
Chemical kinetic modeling of chlorinated hydrocarbons under stirred-reactor conditions
The combustin of chloroethane is modeled as a stirred reactor so that we can study critical emission characteristics of the reactor as a function of residence time. We examine important operating conditions such as pressure, temperature, and equivalence ratio and their influence on destructive efficiency of chloroethane and production of other chlorinated products. The model uses a detailed chemical kinetic mechanism that we have developed previously for C{sub 3} hydrocarbons. We have added to this mechanism the chemical kinetic mechanism for C{sub 2} chlorinated hydrocarbons developed by Senkan and coworkers. Some reactions have been added to Senkan's mechanism and some of the reaction-rate expressions have been updated to reflect recent developments in the literature. In the modeling calculations, sensitivity coefficients are determined to find which reaction-rate constants have the largest effect on destructive efficiency. 25 refs., 6 figs., 1 tab.
Pitz, W.J.; Westbrook, C.K.
Towards cleaner combustion engines through groundbreaking detailed chemical kinetic models
In the context of limiting the environmental impact of transportation, this paper reviews new directions which are being followed in the development of more predictive and more accurate detailed chemical kinetic models for the combustion of fuels. In the first part, the performance of current models, especially in terms of the prediction of pollutant formation, is evaluated. In the next parts, recent methods and ways to improve these models are described. An emphasis is given on the development of detailed models based on elementary reactions, on the production of the related thermochemical and kinetic parameters, and on the experimental techniques available to produce the data necessary to evaluate model predictions under well defined conditions. PMID:21597604
Battin-Leclerc, Frederique; Blurock, Edward; Bounaceur, Roda; Fournet, Rene; Glaude, Pierre-Alexandre; Herbinet, Olivier; Sirjean, Baptiste; Warth, V.
Progress in Chemical Kinetic Modeling for Surrogate Fuels
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
Calculation of Chemical Shift Anisotropy in Proteins
Individual peptide groups in proteins must exhibit some variation in the chemical shift anisotropy (CSA) of their constituent atoms, but not much is known about the extent or origins of this dispersion. Direct spectroscopic measurement of CSA remains technically challenging, and theoretical methods can help to overcome these limitations by estimating shielding tensors for arbitrary structures. Here we use an automated fragmentation quantum mechanics/molecular mechanics (AF-QM/MM) approach to compute 15N, 13C? and 1H chemical shift tensors for human ubiquitin and the GB1 and GB3 fragments of staphylococcal protein G. The average and range of variation of the anisotropies is in good agreement with experimental estimates from solid-state NMR, and the variation among residues is somewhat smaller than that estimated from solution-state measurements. Hydrogen-bond effects account for much of the variation, both between helix and sheet regions, and within elements of secondary structure, but other effects (including variations in torsion angles) may play a role as well. PMID:21866436
Tang, Sishi; Case, David A.
Analytical Derivation of Moment Equations in Stochastic Chemical Kinetics
The master probability equation captures the dynamic behavior of a variety of stochastic phenomena that can be modeled as Markov processes. Analytical solutions to the master equation are hard to come by though because they require the enumeration of all possible states and the determination of the transition probabilities between any two states. These two tasks quickly become intractable for all but the simplest of systems. Instead of determining how the probability distribution changes in time, we can express the master probability distribution as a function of its moments, and, we can then write transient equations for the probability distribution moments. In 1949, Moyal defined the derivative, or jump, moments of the master probability distribution. These are measures of the rate of change in the probability distribution moment values, i.e. what the impact is of any given transition between states on the moment values. In this paper we present a general scheme for deriving analytical moment equations for any N-dimensional Markov process as a function of the jump moments. Importantly, we propose a scheme to derive analytical expressions for the jump moments for any N-dimensional Markov process. To better illustrate the concepts, we focus on stochastic chemical kinetics models for which we derive analytical relations for jump moments of arbitrary order. Chemical kinetics models are widely used to capture the dynamic behavior of biological systems. The elements in the jump moment expressions are a function of the stoichiometric matrix and the reaction propensities, i.e the probabilistic reaction rates. We use two toy examples, a linear and a non-linear set of reactions, to demonstrate the applicability and limitations of the scheme. Finally, we provide an estimate on the minimum number of moments necessary to obtain statistical significant data that would uniquely determine the dynamics of the underlying stochastic chemical kinetic system. The first two moments only provide limited information, especially when complex, non-linear dynamics are involved. PMID:21949443
Sotiropoulos, Vassilios; Kaznessis, Yiannis N.
Incorporation of chemical kinetic models into process control
An important consideration in chemical process control is to determine the precise rationing of reactant streams, particularly when a large time delay exists between the mixing of the reactants and the measurement of the product. In this paper, a method is described for incorporating chemical kinetic models into the control strategy in order to achieve optimum operating conditions. The system is first characterized by determining a reaction rate surface as a function of all input reactant concentrations over a feasible range. A nonlinear constrained optimization program is then used to determine the combination of reactants which produces the specified yield at minimum cost. This operating condition is then used to establish the nominal concentrations of the reactants. The actual operation is determined through a feedback control system employing a Smith predictor. The method is demonstrated on a laboratory bench scale enzyme reactor.
Herget, C.J.; Frazer, J.W.
Laboratory Kinetics of Chemical Reactions occurring in Astrophysical Environments
NASA Astrophysics Data System (ADS)
To model the dynamics and molecular evolution of interstellar clouds, a great deal of information on chemical kinetics is required, preferably under the appropriate conditions of kinetic temperature and internal excitation. This kinetics includes (i) gas phase ionic (ion-molecule and electron-ion) and (ii) neutral-neutral reactions and (iii) heterogeneous surface catalysis, all from simple species to those as complex as polyaromatic hydrocarbons and pre-life molecules. The current situation in these three areas will be briefly reviewed with more emphasis on ionic reactions for which the most data are available. The classes of reactions will include charge and proton transfer, atom insertion and abstraction, radiative association, electron-ion and ion-ion recombination, reactions with atoms, reactions involving isotopes, reaction and production of structural isomers, ring formation and destruction, and condensation. Information on rates of reaction, product identity and state of excitation will be presented wherever possible. Some mention will also be made of the reactions of negative ions. Most recent data will be presented, specifically involving the understudied process of electron-ion recombination. Some possible future directions will also be suggested. Funding of my research program by ACF-PRF, NASA and NSF is gratefully acknowledged.
Adams, N. G.; Babcock, L. M.
The design process for an experimental platform measuring reaction kinetics in a chemical looping combustion (CLC) process is documented and justified. To enable an experiment designed to characterize the reaction kinetics ...
Jester-Weinstein, Jack (Jack L.)
Theory of Chemical Kinetics and Charge Transfer based on Nonequilibrium Thermodynamics
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.
Detailed chemical kinetic mechanism for the oxidation of biodiesel fuels blend surrogate
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
Kinetics of cyanogen chloride destruction by chemical reduction methods.
In this study, membrane introduction mass spectrometry (MIMS) was applied to evaluate the kinetics of cyanogen chloride (ClCN) destruction by chemical reduction methods, using thiosulfate, sulfite, metabisulfite, ferrous ions and zero-valent iron at various concentrations and pH. The ClCN destruction followed second-order reaction kinetics in all cases of using sulfur compounds, though the second-order rate constants varied substantially from approximately 0.3-25.7 M(-1)s(-1) under different experimental conditions. The destruction of ClCN was primarily attributable to the chemical reduction pathway. Hydroxide-assisted ClCN hydrolysis was only significant at pH 9 and also when the observed reduction rate was relatively slow. The second-order rate constants achieved by sulfur(IV) compounds in the form of sulfite were found to be higher than those obtained with thiosulfate and S(IV) compounds in the form of bisulfite. Ferrous ions and zero-valent iron demonstrated slow or no ClCN reduction up to dosages of 1000 mgL(-1) and 100 gL(-1), respectively. These findings suggest that applying moderately high dosages of S(IV) compounds under neutral or alkali conditions with sufficient contact time is required for wastewater ClCN destruction. In addition, ClCN losses during long-term preservation with excess reducing sulfur compounds prior to analysis can be substantial and should be avoided. PMID:15893356
Shang, Chii; Qi, Yinan; Xie, Li; Liu, Wei; Yang, Xin
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
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 (14)C-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 (14)C 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
Ashauer, Roman; Hintermeister, Anita; O'Connor, Isabel; Elumelu, Maline; Hollender, Juliane; Escher, Beate I
A chemical kinetics software package Peter Kirkegaard, Erling Bjergbakke, Jens V. Olsen
CHEMSIMUL: A chemical kinetics software package Peter Kirkegaard, Erling Bjergbakke, Jens V. Olsen: CHEMSIMUL: A chemical kinetics software package Division: IT-Service Risø-R-1630(EN) December 2008 ISSN 0106 Tables: 6 References: 23 Abstract CHEMSIMUL is a computer program system for simulation of chemical
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.
Free energy calculations: Applications to chemical and biochemical phenomena
The author will review the applications of free energy calculations employing molecular dynamics or Monte Carlo methods to a variety of chemical and biochemical phenomena. The focus is on the applications of such calculations to molecular solvation, molecular association, macromolecular stability, and enzyme catalysis. The molecules discussed range from monovalent ions and small molecules to proteins and nucleic acids.
Peter. Kollman
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.
Thermodynamic and Kinetic Properties of Metal Hydrides from First-Principles Calculations
NASA Astrophysics Data System (ADS)
In an effort to minimize the worldwide dependence on fossil fuels, much research has focused on the development of hydrogen fuel cell vehicles. Among the many challenges currently facing the transition to such an alternative energy economy is the storage of hydrogen in an economical and practical way. One class of materials that has presented itself as a possible candidate is solid metal hydrides. These materials chemically bind hydrogen and on heating, release the gas which can then be used to generate power as needed for the vehicle. In order to meet guidelines that have been set for such a storage system, hydrogen must be released rapidly in a narrow temperature range of -40 to 80�C with all reactions being reversible. This sets both thermodynamic and kinetic requirements for the design of candidate metal hydrides. First-principles calculations are well-suited for the task of exploring reactions involving metal hydrides. Here, density-functional theory is used to calculate properties of these materials at the quantum mechanical level of accuracy. In particular, three systems have been investigated: 1. Li-Mg-N-H. Reactions between all known compounds in this system are systematically investigated in order to predict thermodynamically allowed reactions that release hydrogen. The properties of these reactions are compared to the requirements set for hydrogen storage systems. Additionally, ground-state structures are predicted for Li2Mg(NH)2 and Li 4Mg(NH)3. 2. Na-Al-H. The kinetics of mass transport during the (de)hydrogenation of the well-known metal hydride NaAlH4 are investigated. A model is developed to study the flux of native defects through phases involved in these reactions. Since it is also known that titanium is an effective catalyst for both dehydrogenation and rehydrogenation, the effect of Ti substitution in bulk lattices on the kinetics of mass transport is investigated. Results are compared to experiments in order to determine if mass transport represents the rate-limiting process during de- or rehydrogenation and what the effect of Ti may be. 3. Si-H. Properties of the recently synthesized compound SiH4(H 2)2 are investigated. Under high pressures, hydrogen binding to SiH4 exhibits characteristics of both physical and chemical bonds. A ground-state structure is predicted for this phase and the vibrational and bonding properties are investigated in order to determine the origin of the unusual binding between H2 and SiH4.
Michel, Kyle Jay
High Temperature Chemical Kinetic Combustion Modeling of Lightly Methylated Alkanes
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
and Isothermal Calorimetry Xueyu Panga *, Dale P. Bentzb , Christian Meyerc , Gary P. Funkhousera , Robert Darbea methods of evaluating cement hydration kinetics, namely chemical shrinkage and isothermal calorimetry in the experiments. Keywords: Cement hydration; chemical shrinkage; heat of hydration; isothermal calorimetry
Bentz, Dale P.
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.
Sequential Voronoi diagram calculations using simple chemical reactions
In our recent paper [de Lacy Costello et al. 2010] we described the formation of complex tessellations of the plane arising from the various reactions of metal salts with potassium ferricyanide and ferrocyanide loaded gels. In addition to producing colourful tessellations these reactions are naturally computing generalised Voronoi diagrams of the plane. The reactions reported previously were capable of the calculation of three distinct Voronoi diagrams of the plane. As diffusion coupled with a chemical reaction is responsible for the calculation then this is achieved in parallel. Thus an increase in the complexity of the data input does not utilise additional computational resource. Additional benefits of these chemical reactions is that a permanent record of the Voronoi diagram calculation (in the form of precipitate free bisectors) is achieved, so there is no requirement for further processing to extract the calculation results. Previously it was assumed that the permanence of the results was also a potenti...
Costello, Ben de Lacy; Adamatzky, Andy
Calculation, measurement and sensitivity analysis of kinetic parameters of Tehran Research Reactor
Effective delayed neutron fraction ?eff and neutron generation time ? are important factors in reactor physics calculation and transient analysis. In the first stage of this research, these kinetic parameters have been calculated for two states of Tehran Research Reactor (TRR), i.e. cold (fuel, clad and coolant temperatures equal to 20�C) and hot (fuel, clad and coolant temperatures of 65,
S. A. Hosseini; N. Vosoughi; M. B. Ghofrani; M. Gharib
Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels
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
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.
Chemical kinetic analysis of hydrogen-air ignition and reaction times
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.
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.
Uptake and release kinetics of 22 polar organic chemicals in the Chemcatcher passive sampler.
The Chemcatcher passive sampler, which uses Empore� disks as sampling phase, is frequently used to monitor polar organic chemicals in river water and effluents. Uptake kinetics need to be quantified to calculate time-weighted average concentrations from Chemcatcher field deployments. Information on release kinetics is needed if performance reference compounds (PRCs) are used to quantify the influence of environmental conditions on the uptake. In a series of uptake and elimination experiments, we used Empore� SDB disks (poly(styrenedivinylbenzene) copolymer modified with sulfonic acid groups) as a sampling phase and 22 compounds with a logK(ow) (octanol-water partitioning coefficient) range from -2.6 to 3.8. Uptake experiments were conducted in river water or tap water and lasted up to 25 days. Only 1 of 22 compounds (sulfamethoxazole) approached equilibrium in the uptake trials. Other compounds showed continuing non-linear uptake, even after 25 days. All compounds could be released from SDB disks, and desorption was proportionally higher in disks loaded for shorter periods. Desorption showed two-phase characteristics, and desorption was proportionally higher for passively sorbed compounds compared to actively loaded compounds (active loading was performed by pulling spiked river water over SDB disks using vacuum). We hypothesise that the two-phase kinetics and better retention of actively loaded compounds--and compounds loaded for a longer period--may be caused by slow diffusion of chemicals within the polymer. As sorption and desorption did not show isotropic kinetics, it is not possible to develop robust PRCs for adsorbent material like SDB disks. PMID:23532391
Vermeirssen, Eti�nne L M; Dietschweiler, Conrad; Escher, Beate I; van der Voet, J�rgen; Hollender, Juliane
Coupled-cluster calculations of nuclear magnetic resonance chemical shifts
NASA Astrophysics Data System (ADS)
Theory and implementation of the gauge-including atomic orbital (GIAO) ansatz for the gauge-invariant calculation of nuclear magnetic resonance chemical shifts are described for the coupled-cluster singles and doubles (CCSD) approach. Results for the shielding constants of the hydrides HF, H2O, NH3, and CH4 as well as for a few multiply bonded systems such as CO, N2, and HCN demonstrate the importance of higher-order correlation corrections, as good agreement with experiment is only obtained at the CCSD level and to some extent at partial fourth-order many-body perturbation theory [SDQ-MBPT(4)] with the latter slightly overestimating correlation effects due to single and double excitations. For relative chemical shifts, GIAO-CCSD calculations provide in difficult cases (e.g., CO and CF4) more accurate results than previous GIAO-MBPT(2) calculations. But, it seems that it is often more important to include rovibrational effects (as well as possible molecule-solvent interactions) than higher-order correlation corrections. Despite that, GIAO-CCSD proves to be a powerful tool for the accurate calculation of NMR chemical shifts. Its capabilities as well as its limitations are demonstrated in shielding calculations for formaldehyde, diazomethane, and ozone. At least for the latter, the description provided by the CCSD ansatz is not sufficient and even higher excitations need to be considered.
Gauss, J�rgen; Stanton, John F.
Chemical-equilibrium calculations for aqueous geothermal brines
Results from four chemical-equilibrium computer programs, REDEQL.EPAK, GEOCHEM, WATEQF, and SENECA2, have been compared with experimental solubility data for some simple systems of interest with geothermal brines. Seven test cases involving solubilities of CaCO/sub 3/, amorphous SiO/sub 2/, CaSO/sub 4/, and BaSO/sub 4/ at various temperatures from 25 to 300/sup 0/C and in NaCl or HCl solutions of 0 to 4 molal have been examined. Significant differences between calculated results and experimental data occurred in some cases. These differences were traced to inaccuracies in free-energy or equilibrium-constant data and in activity coefficients used by the programs. Although currently available chemical-equilibrium programs can give reasonable results for these calculations, considerable care must be taken in the selection of free-energy data and methods of calculating activity coefficients.
Kerrisk, J.F.
Calculating kinetics parameters and reactivity changes with continuous-energy Monte Carlo
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
Thermodynamic and kinetic consistency of calculated binary nucleation rates
To establish the accuracy and applicability of analytical expressions for the steady state rate of binary nucleation, we numerically solved the birth-death equations for the vapor-to-liquid transition. These calculations were performed using rate coefficients that are consistent with the principle of detailed balance and a new self-consistent form of the equilibrium distribution function for binary cluster concentrations. We found that the customary saddle point and growth path approximations are almost always valid and can fail only if the nucleating solution phase is significantly nonideal. For example, problems can arise when the vapor composition puts the system on the verge of partial liquid phase miscibility. When this occurs for comparable monomer impingement rates, nucleation still occurs through the saddle point, but the usual quadratic expansion for the cluster free energy is inadequate. When the two impingement rates differ significantly, however, the major particle flux may bypass the saddle point and cross a low ridge on the free energy surface. The dependence of the saddle point location on the gas phase composition is also important in initiating or terminating ridge crossing nucleation.
Wilemski, G. [Lawrence Livermore National Lab., CA (United States); Wyslouzil, B.E. [Worcester Polytechnic Institute, MA (United States)
PLASMAKIN: A chemical kinetics library for plasma physics modeling
NASA Astrophysics Data System (ADS)
PLASMAKIN is a package to handle physical and chemical data used in plasma physics modeling and to compute kinetics data from the reactions taking place in the gas or at the surfaces: particle production and loss rates, photon spectra and energy exchange rates. It has no limits on the number of species and reactions that can be handled, is independent of problem dimensions and can be used in both steady-state and time-dependent problems. A broad range of species properties and reaction types are supported: gas or electron temperature dependent rate coefficients, vibrational and cascade levels, branching ratios, superelastic and other reverse processes, three-body collisions, radiation imprisonment and photoelectric emission. Non-standard rate coefficient functions can be handled by a user-supplied shared library. Reaction data is supplied in text files and is independent of the user's program. Recent additions include the simulation of emission spectra taking line broadening into account; reactions with excited ionic species; 3-body reactions with species with different efficiencies as 3rd body; a species properties database and a Python interface for rapid scripting and debugging.
Pinhao, Nuno
Detailed and global chemical kinetics model for hydrogen
Detailed and global chemical kinetic computations for hydrogen-air mixtures have been performed to describe flame propagation, flame structure and ignition phenomena. Simulations of laminar flame speeds, flame compositions and shock tube ignition delay times have been successfully performed. Sensitivity analysis was applied to determine the governing rate-controlling reactions for the experimental data sets examined. In the flame propagation and structure studies, the reactions, OH + H{sub 2} = H{sub 2}0 + H, 0 + H{sub 2} = OH + H and 0 + OH = 0{sub 2} + H were the most important in flames. The shock tube ignition delay time study indicated the H + 0{sub 2} + M = H0{sub 2} + M (M = N{sub 2}, H{sub 2}) and 0 + OH = 0{sub 2} + H reactions controlled ignition. A global rate expression for a one-step overall reaction was developed and validated against experimental hydrogen-air laminar flame speed data. The global reaction expression was determined to be 1.8 {times} 10{sup 13} exp({minus}17614K/T)[H{sub 2}]{sup 1.0}[O{sub 2}]{sup 0.5} for the single step reaction H{sub 2} + 1/2O{sub 2} = H{sub 2}O.
Marinov, N.M.; Westbrook, C.K.; Pitz, W.J.
Cometary impact and amino acid survival - Chemical kinetics and thermochemistry
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.
Effect of humidity on deprotection kinetics in chemically amplified resists
NASA Astrophysics Data System (ADS)
Water is known to play a key role in the solubility switching reaction of novolac-diazonaphthoquinone photoresists and certain chemically amplified resists. In order to quantitatively study these effects, an environmental chamber was built in which the % RH could be controlled while the extent of acid catalyzed deprotection was monitored during the post exposure bake by reflectance FTIR spectroscopy. The extent of acid catalyzed deprotection of tBOC, KRS-XE, UV6, and a tBOC-poly(hydroxystyrene) copolymer have been measured as a function of time over a range of 0-60 % RH. For tBOC, the deprotection reaction rate was found to slow considerably as the %RH was increased. Also, the relative film shrinkage varied considerably with varying % RH. Several possible mechanisms for the dependence of the reaction rate and thickness loss on % RH were investigated. For KRS-XE, the deprotection reaction kinetics were found to increase as the % RH was increased, which was an expected trend. For UV6 and the tBOC-PHOST copolymer, no change in deprotection reaction rate was observed with changes in %RH.
Burns, Sean D.; Medeiros, David R.; Johnson, Heather F.; Wallraff, Gregory M.; Hinsberg, William D.; Willson, C. Grant
GPU Accelerated Chemical Similarity Calculation for Compound Library Comparison
Chemical similarity calculation plays an important role in compound library design, virtual screening, and �lead� optimization. In this manuscript, we present a novel GPU-accelerated algorithm for all-vs-all Tanimoto matrix calculation and nearest neighbor search. By taking advantage of multi-core GPU architecture and CUDA parallel programming technology, the algorithm is up to 39 times superior to the existing commercial software that runs on CPUs. Because of the utilization of intrinsic GPU instructions, this approach is nearly 10 times faster than existing GPU-accelerated sparse vector algorithm, when Unity fingerprints are used for Tanimoto calculation. The GPU program that implements this new method takes about 20 minutes to complete the calculation of Tanimoto coefficients between 32M PubChem compounds and 10K Active Probes compounds, i.e., 324G Tanimoto coefficients, on a 128-CUDA-core GPU. PMID:21692447
Ma, Chao; Wang, Lirong; Xie, Xiang-Qun
NASA Astrophysics Data System (ADS)
A one-dimensional hydro-kinetic model is developed to study arc extinction in a low-voltage breaking device. In part 1 of this double paper, the data necessary for the implementation of the hydro-kinetic model are presented. The equilibrium composition of the plasma is derived from the law of mass action. Mixtures of air and materials ablated from the thermoplastic wall (PA66, monomer C12H22O2N2) and from the contacts (copper) are considered. Thermodynamic properties such as mass density, enthalpy and specific heat at constant pressure are then calculated. Transport coefficients (viscosity, electrical conductivity and thermal conductivity) are determined with the Chapman-Enskog theory. Concerning radiation, the net emission coefficient, corresponding to the power radiated per unit volume and per unit solid angle, is calculated. Finally, for chemical kinetics, a reliable set of reaction rate coefficients linking the chemical species of the plasma is compiled. Particular attention is paid to ionization and recombination of atomic species which are obtained with the 'bottleneck' method.
Teulet, Ph; Gonzalez, J. J.; Mercado-Cabrera, A.; Cressault, Y.; Gleizes, A.
Fundamental Chemical Kinetic And Thermodynamic Data For Purex Process Models
To support either the continued operations of current reprocessing plants or the development of future fuel processing using hydrometallurgical processes, such as Advanced Purex or UREX type flowsheets, the accurate simulation of Purex solvent extraction is required. In recent years we have developed advanced process modeling capabilities that utilize modern software platforms such as Aspen Custom Modeler and can be run in steady state and dynamic simulations. However, such advanced models of the Purex process require a wide range of fundamental data including all relevant basic chemical kinetic and thermodynamic data for the major species present in the process. This paper will summarize some of these recent process chemistry studies that underpin our simulation, design and testing of Purex solvent extraction flowsheets. Whilst much kinetic data for actinide redox reactions in nitric acid exists in the literature, the data on reactions in the diluted TBP solvent phase is much rarer. This inhibits the accurate modelization of the Purex process particularly when species show a significant extractability in to the solvent phase or when cycling between solvent and aqueous phases occurs, for example in the reductive stripping of Pu(IV) by ferrous sulfamate in the Magnox reprocessing plant. To support current oxide reprocessing, we have investigated a range of solvent phase reactions: - U(IV)+HNO{sub 3}; - U(IV)+HNO{sub 2}; - U(IV)+HNO{sub 3} (Pu catalysis); - U(IV)+HNO{sub 3} (Tc catalysis); - U(IV)+ Np(VI); - U(IV)+Np(V); - Np(IV)+HNO{sub 3}; - Np(V)+Np(V); Rate equations have been determined for all these reactions and kinetic rate constants and activation energies are now available. Specific features of these reactions in the TBP phase include the roles of water and hydrolyzed intermediates in the reaction mechanisms. In reactions involving Np(V), cation-cation complex formation, which is much more favourable in TBP than in HNO{sub 3}, also occurs and complicates the redox chemistry. Whilst some features of the redox chemistry in TBP appear similar to the corresponding reactions in aqueous HNO{sub 3}, there are notable differences in rates, the forms of the rate equations and mechanisms. Secondly, to underpin the development of advanced single cycle flowsheets using the complexant aceto-hydroxamic acid, we have also characterised in some detail its redox chemistry and solvent extraction behaviour with both Np and Pu ions. We find that simple hydroxamic acids are remarkably rapid reducing agents for Np(VI). They also reduce Pu(VI) and cause a much slower reduction of Pu(IV) through a complex mechanism involving acid hydrolysis of the ligand. AHA is a strong hydrophilic and selective complexant for the tetravalent actinide ions as evidenced by stability constant and solvent extraction data for An(IV), M(III) and U(VI) ions. This has allowed the successful design of U/Pu+Np separation flowsheets suitable for advanced fuel cycles. (authors)
Taylor, R.J.; Fox, O.D.; Sarsfield, M.J.; Carrott, M.J.; Mason, C.; Woodhead, D.A.; Maher, C.J. [British Technology Centre, Nexia Solutions, Sellafield, Seascale, CA20 1PG (United Kingdom); Steele, H. [Nexia Solutions, inton House, Risley, Warrington, WA3 6AS (United Kingdom); Koltunov, V.S. [A.A. Bochvar All-Russia Institute of Inorganic Materials, VNIINM, PO Box 369, Moscow 123060 (Russian Federation)
A Shock Tube and Chemical Kinetic Modeling Study of the Oxidation of 2,5-Dimethylfuran
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, Rene; Glaude, Pierre-Alexandre; Battin-Leclerc, Frederique; Wang, Weijing; Oehlschlaeger, Matthew A.
Experimental and chemical kinetic modeling study of 3-pentanone oxidation.
Shock tube ignition delay times have been measured for 3-pentanone at a reflected shock pressure of 1 atm (�2%), in the temperature range 1250-1850 K, at equivalence ratios of 0.5-2.0 for O(2) mixtures in argon with fuel concentrations varying from 0.875 to 1.3125%. Laminar flame speeds have also been measured at an initial pressure of 1 atm over an equivalence ratio range. Complementary to previous studies [Pichon S., Black, G., Chaumeix, N., Yahyaoui, M., Simmie, J. M., Curran, H. J., Donohue, R. Combust. Flame, 2009, 156, 494-504; Serinyel, Z.; Black, G.; Curran, H. J.; Simmie, J. M. Combustion Sci. Tech., 2010, 182, 574-587], laminar flame speeds of 2-butanone have also been measured, and relative reactivities of these ketones have been compared and discussed. A chemical kinetic submechanism describing the oxidation of 3-pentanone has been developed and detailed in this paper; rate constants for unimolecular fuel decomposition reactions have been treated for falloff in pressure with nine-parameter fits using the Troe Formulism. Both compounds treated in this work may be used as fuel tracers, thus further ignition delay time measurements have been carried out by adding 3-pentanone to n-heptane in order to test the effect of the blend on ignition delay timing. It was found that the autoignition characteristics of n-heptane remained unaffected in the presence of 15% 3-pentanone in the fuel, consistent with results obtained using acetone and 2-butanone [Pichon S., Black, G., Chaumeix, N., Yahyaoui, M., Simmie, J. M., Curran, H. J., Donohue, R. Combust. Flame, 2009, 156, 494-504; Serinyel, Z.; Black, G.; Curran, H. J.; Simmie, J. M. Combustion Sci. Tech., 2010, 182, 574-587]. PMID:21033754
Serinyel, Z; Chaumeix, N; Black, G; Simmie, J M; Curran, H J
Fundamental Kinetic Modeling: ab initio rate constant calculations of elementary reactions
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
A complete model of baryon production in an expanding, primordially symmetric hot Universe is constructed in the framework of general-relativistic kinetic theory. In this model specific model for a baryon is calculated and graphs of the value dependence are constructed.
Yu. G. Ignatyev; K. Alsmadi
A pressure correction method for the calculation of compressible chemical reacting flows
NASA Technical Reports Server (NTRS)
A recently developed noniterative method for the solution of the transient fluid flow equations at all speed is extended to handle chemical reacting flows. The species conservation equations are loosely coupled into the predictor/multicorrector sequence of the solution procedure. A split-operator method separates the chemical kinetics terms from the fluid-dynamical terms, as well as an implicit differencing method enhance the numerical stability. The method was applied for turbulent diffusion flame calculations and for the analyses of high pressure, axisymmetric turbulent hypersonic nozzle flows. The diffusion flame results were compared with a similar pressure method for fast chemistry integration scheme without operator-splitting. Simulations of the nozzle flow indicated that the nonideal intermolecular effects must be included in the analysis and design of high pressure hypersonic nozzle.
Chen, Z. J.; Chen, C. P.; Chen, Y. S.
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
Review of chemical-kinetic problems of future NASA missions. I - Earth entries
NASA Technical Reports Server (NTRS)
A number of chemical-kinetic problems related to phenomena occurring behind a shock wave surrounding an object flying in the earth atmosphere are discussed, including the nonequilibrium thermochemical relaxation phenomena occurring behind a shock wave surrounding the flying object, problems related to aerobraking maneuver, the radiation phenomena for shock velocities of up to 12 km/sec, and the determination of rate coefficients for ionization reactions and associated electron-impact ionization reactions. Results of experiments are presented in form of graphs and tables, giving data on the reaction rate coefficients for air, the ionization distances, thermodynamic properties behind a shock wave, radiative heat flux calculations, Damkoehler numbers for the ablation-product layer, together with conclusions.
Park, Chul
Numerical simulation of Jet-A combustion approximated by improved propane chemical kinetics
NASA Technical Reports Server (NTRS)
Through the effort devoted to the chemical kinetics for propane air combustion, three mechanisms are developed. The full mechanism consists of 131 reactions. This mechanism is used as a guide for the evaluation of other mechanisms, but because of the long expected cpu time, it is not to be incorporated into the computer code KIVA-II for actual simulation. Through the sensitivity analysis, a reduced mechanism of 45 reactions is produced. But the calculated results from the 45 reaction mechanism are always low in temperature. Some efforts are devoted to correct this situation and details are included in this report. A simplified mechanism of reactions is successfully improved and computed results are compared with experimental data. Contour plots of physical parameters and species concentrations and results for emission indices of CO and NOx are presented.
Ying, Shuh-Jing; Nguyen, Hung Lee
Chemical kinetic modeling of propene oxidation at low and intermediate temperatures
A detailed chemical kinetic mechanism for propene oxidation is developed and used to model reactions in a static reactor at temperatures of 590 to 740/sup 0/K, equivalence ratios of 0.8 to 2.0, and a pressure of 600 torr. Modeling of hydrocarbon oxidation in this temperature range is important for the validation of detailed models to be used for performing calculations related to automotive engine knock. The model predicted induction periods and species concentrations for all the species measured experimentally in a static reactor by Wilk, Cernansky, and Cohen. The detailed model predicted a temperature region of approximately constant induction period which corresponded very closely to the region of negative temperature coefficient behavior found in the experiment. Overall, the calculated concentrations of acetaldehyde, ethene, and methane were somewhat low compared to the experimental measurements, and the calculated concentrations of formaldehyde and methanol were high. The characteristic s-shape of the fuel concentration history was well predicted. The importance of OH+C/sub 3/H/sub 6/ and related rections in determining product distributions and the importance of consumption reactions for allyl radicals was demonstrated by the modeling calculations. 18 refs., 4 figs., 1 tab.
Wilk, R.D.; Cernansky, N.P.; Pitz, W.J.; Westbrook, C.K.
Chemical kinetics parameters and model validation for the gasification of PCEA nuclear graphite
NASA Astrophysics Data System (ADS)
A series of gasification experiments, using two right cylinder specimens (?12.7 � 25.4 mm and 25.4 � 25.4 mm) of PCEA nuclear graphite in ambient airflow, measured the total gasification flux at weight losses up to 41.5% and temperatures (893-1015 K) characteristics of those for in-pores gasification Mode (a) and in-pores diffusion-limited Mode (b). The chemical kinetics parameters for the gasification of PCEA graphite are determined using a multi-parameters optimization algorithm from the measurements of the total gasification rate and transient weight loss in experiments. These parameters are: (i) the pre-exponential rate coefficients and the Gaussian distributions and values of specific activation energies for adsorption of oxygen and desorption of CO gas; (ii) the specific activation energy and pre-exponential rate coefficient for the breakup of stable un-dissociated C(O2) oxygen radicals to form stable (CO) complexes; (iii) the specific activation energy and pre-exponential coefficient for desorption of CO2 gas and; (iv) the initial surface area of reactive free sites per unit mass. This area is consistently 13.5% higher than that for nuclear graphite grades of NBG-25 and IG-110 and decreases inversely proportional with the square root of the initial mass of the graphite specimens in the experiments. Experimental measurements successfully validate the chemical-reactions kinetics model that calculates continuous Arrhenius curves of the total gasification flux and the production rates of CO and CO2 gases. The model results at different total weight losses agree well with measurements and expand beyond the temperatures in the experiments to the diffusion-limited mode of gasification. Also calculated are the production rates of CO and CO2 gases and their relative contributions to the total gasification rate in the experiments as functions of temperature, for total weight losses of 5% and 10%.
El-Genk, Mohamed S.; Tournier, Jean-Michel P.; Contescu, Cristian I.
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.
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.
NASA Astrophysics Data System (ADS)
Jet-A spray combustion has been evaluated in gas turbine combustion with the use of propane chemical kinetics as the first approximation for the chemical reactions. Here, the numerical solutions are obtained by using the KIVA-2 computer code. The KIVA-2 code is the most developed of the available multidimensional combustion computer programs for application of the in-cylinder combustion dynamics of internal combustion engines. The released version of KIVA-2 assumes that 12 chemical species are present; the code uses an Arrhenius kinetic-controlled combustion model governed by a four-step global chemical reaction and six equilibrium reactions. Researchers efforts involve the addition of Jet-A thermophysical properties and the implementation of detailed reaction mechanisms for propane oxidation. Three different detailed reaction mechanism models are considered. The first model consists of 131 reactions and 45 species. This is considered as the full mechanism which is developed through the study of chemical kinetics of propane combustion in an enclosed chamber. The full mechanism is evaluated by comparing calculated ignition delay times with available shock tube data. However, these detailed reactions occupy too much computer memory and CPU time for the computation. Therefore, it only serves as a benchmark case by which to evaluate other simplified models. Two possible simplified models were tested in the existing computer code KIVA-2 for the same conditions as used with the full mechanism. One model is obtained through a sensitivity analysis using LSENS, the general kinetics and sensitivity analysis program code of D. A. Bittker and K. Radhakrishnan. This model consists of 45 chemical reactions and 27 species. The other model is based on the work published by C. K. Westbrook and F. L. Dryer.
Nguyen, H. L.; Ying, S.-J.
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)
The reaction mechanism of 12 antimalarial artemisinin compounds with two competitive pathways was studied by means of quantum chemical calculations using the IMOMO(B3LYP\\/6-31(d,p):HF\\/3-21G) method. The oxygen-centered radicals, carbon-centered radicals, and transition states (TS) in both pathways were geometrically optimized. The obtained kinetic and thermodynamic energy profiles show that homolytic C�C cleavage reaction (pathway 2) is energetically more preferable than an
Somsak Tonmunphean; Vudhichai Parasuk; Sirirat Kokpol
EQ6 Calculations for Chemical Degradation of Navy Waste Packages
The Monitored Geologic Repository Waste Package Operations of the Civilian Radioactive Waste Management System Management & Operating Contractor (CRWMS M&O) performed calculations to provide input for disposal of spent nuclear fuel (SNF) from the Navy (Refs. 1 and 2). The Navy SNF has been considered for disposal at the potential Yucca Mountain site. For some waste packages, the containment may breach (Ref. 3), allowing the influx of water. Water in the waste package may moderate neutrons, increasing the likelihood of a criticality event within the waste package. The water may gradually leach the fissile components and neutron absorbers out of the waste package. In addition, the accumulation of silica (SiO{sub 2}) in the waste package over time may further affect the neutronics of the system. This study presents calculations of the long-term geochemical behavior of waste packages containing the Enhanced Design Alternative (EDA) II inner shell, Navy canister, and basket components. The calculations do not include the Navy SNF in the waste package. The specific study objectives were to determine the chemical composition of the water and the quantity of silicon (Si) and other solid corrosion products in the waste package during the first million years after the waste package is breached. The results of this calculation will be used to ensure that the type and amount of criticality control material used in the waste package design will prevent criticality.
S. LeStrange
A detailed chemical kinetic reaction mechanism is developed to describe incineration of the chemical warfare nerve agent sarin (GB), based on commonly used principles of bond additivity and hierarchical reaction mechanisms. The mechanism is based on previous kinetic models of organophosphorus compounds such as TMP, DMMP and DIMP that are often used as surrogates to predict incineration of GB. Kinetic models of the three surrogates and GB are then used to predict their consumption in a perfectly stirred reactor fueled by natural gas to simulate incineration of these chemicals. Computed results indicate that DIMP is the only one of these surrogates that adequately describes combustion of GB under comparable conditions. The kinetic pathways responsible for these differences in reactivity are identified and discussed. The most important reaction in GB and DIMP that makes them more reactive than TMP or DMMP is found to be a six-center molecular elimination reaction producing propene.
Glaude, P A; Melius, C; Pitz, W J; Westbrook, C K
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.
Integrating chemical kinetics with CFD modeling for autothermal reforming of biogas
Using biogas for hydrogen production via autothermal reforming (ATR) can potentially increase the energy conversion efficiency and correspondingly reduce environmental impact. The present study aimed to investigate the performance and characteristics of biogas ATR. A two-dimensional numerical model was developed based on the integration of computational fluid dynamics (CFD) and chemical kinetics. The mass transport, chemical reactions and heat transfer
Jin Xuan; Michael K. H. Leung; Dennis Y. C. Leung; Meng Ni
Abstract�A detailed chemical kinetic reaction mechanism is developed to describe the oxidation and pyrolysis of propane and propene. The mechanism consists of 163 elementary reactions among 4l chemical species. New rate expressions are developed for a number of reactions of propane, propene, and intermediate hydrocarbon species with radicals including H, 0, and OH. The mechanism is tested by comparisons between
A comprehensive detailed chemical kinetic reaction mechanism for combustion of nalkane
A comprehensive detailed chemical kinetic reaction mechanism for combustion of nalkane 94550, USA b University College of Ireland, Galway, Ireland Abstract Detailed chemical, published in "Combustion and Flame 156 (2008) 181-199" DOI : 10.1016/j.combustflame.2008.07.014 #12
Paris-Sud XI, Université de
Solutions of the chemical kinetic equations for initially inhomogeneous mixtures.
NASA Technical Reports Server (NTRS)
Following the recent discussions by O'Brien (1971) and Donaldson and Hilst (1972) of the effects of inhomogeneous mixing and turbulent diffusion on simple chemical reaction rates, the present report provides a more extensive analysis of when inhomogeneous mixing has a significant effect on chemical reaction rates. The analysis is then extended to the development of an approximate chemical sub-model which provides much improved predictions of chemical reaction rates over a wide range of inhomogeneities and pathological distributions of the concentrations of the reacting chemical species. In particular, the development of an approximate representation of the third-order correlations of the joint concentration fluctuations permits closure of the chemical sub-model at the level of the second-order moments of these fluctuations and the mean concentrations.
Hilst, G. R.
Validity conditions for moment closure approximations in stochastic chemical kinetics
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 CME, 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 numbe...
Schnoerr, David; Grima, Ramon
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
The initiation mechanisms and kinetics of pyrolysis and combustion of n-dodecane are investigated by using the reactive molecular dynamics (ReaxFF MD) simulation and chemical kinetic modeling. From ReaxFF MD simulations, we find the initiation mechanisms of pyrolysis of n-dodecane are mainly through two pathways, (1) the cleavage of C-C bond to form smaller hydrocarbon radicals, and (2) the dehydrogenation reaction
Quan-De Wang; Jing-Bo Wang; Juan-Qin Li; Ning-Xin Tan; Xiang-Yuan Li
The initiation mechanisms and kinetics of pyrolysis and combustion of n-dodecane are investigated by using the reactive molecular dynamics (ReaxFF MD) simulation and chemical kinetic modeling. From ReaxFF MD simulations, we find the initiation mechanisms of pyrolysis of n-dodecane are mainly through two pathways, (1) the cleavage of C�C bond to form smaller hydrocarbon radicals, and (2) the dehydrogenation reaction
Quan-De Wang; Jing-Bo Wang; Juan-Qin Li; Ning-Xin Tan; Xiang-Yuan Li
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...
Validity conditions for moment closure approximations in stochastic chemical kinetics
NASA Astrophysics Data System (ADS)
Approximations based on moment-closure (MA) are commonly used to obtain estimates of the mean molecule numbers and of the variance of fluctuations in the number of molecules of chemical systems. The advantage of this approach is that it can be far less computationally expensive than exact stochastic simulations of the chemical master equation. Here, we numerically study the conditions under which the MA equations yield results reflecting the true stochastic dynamics of the system. We show that for bistable and oscillatory chemical systems with deterministic initial conditions, the solution of the MA equations can be interpreted as a valid approximation to the true moments of the chemical master equation, only when the steady-state mean molecule numbers obtained from the chemical master equation fall within a certain finite range. The same validity criterion for monostable systems implies that the steady-state mean molecule numbers obtained from the chemical master equation must be above a certain threshold. For mean molecule numbers outside of this range of validity, the MA equations lead to either qualitatively wrong oscillatory dynamics or to unphysical predictions such as negative variances in the molecule numbers or multiple steady-state moments of the stationary distribution as the initial conditions are varied. Our results clarify the range of validity of the MA approach and show that pitfalls in the interpretation of the results can only be overcome through the systematic comparison of the solutions of the MA equations of a certain order with those of higher orders.
Schnoerr, David; Sanguinetti, Guido; Grima, Ramon
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.
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 is presented. Different integration methods are tested by application of the packaged code LSODE to four practical combustion kinetics problems. The problems describe adiabatic, 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 of this result to the development of fast integration techniques for combustion kinetic rate equations are discussed.
Radhakrishnan, K.
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.
Uncovering Oscillations, Complexity, and Chaos in Chemical Kinetics Using Mathematica
NASA Astrophysics Data System (ADS)
Unlike reactions with no peculiar temporal behavior, in oscillatory reactions concentrations can rise and fall spontaneously in a cyclic or disorganized fashion. In this article, the software Mathematica is used for a theoretical study of kinetic mechanisms of oscillating and chaotic reactions. A first simple example is introduced through a three-step reaction, called the Lotka model, which exhibits a temporal behavior characterized by damped oscillations. The phase plane method of dynamic systems theory is introduced for a geometric interpretation of the reaction kinetics without solving the differential rate equations. The equations are later numerically solved using the built-in routine NDSolve and the results are plotted. The next example, still with a very simple mechanism, is the Lotka-Volterra model reaction, which oscillates indefinitely. The kinetic process and rate equations are also represented by a three-step reaction mechanism. The most important difference between this and the former reaction is that the undamped oscillation has two autocatalytic steps instead of one. The periods of oscillations are obtained by using the discrete Fourier transform (DFT)-a well-known tool in spectroscopy, although not so common in this context. In the last section, it is shown how a simple model of biochemical interactions can be useful to understand the complex behavior of important biological systems. The model consists of two allosteric enzymes coupled in series and activated by its own products. This reaction scheme is important for explaining many metabolic mechanisms, such as the glycolytic oscillations in muscles, yeast glycolysis, and the periodic synthesis of cyclic AMP. A few of many possible dynamic behaviors are exemplified through a prototype glycolytic enzymatic reaction proposed by Decroly and Goldbeter. By simply modifying the initial concentrations, limit cycles, chaos, and birhythmicity are computationally obtained and visualized.
Ferreira, M. M. C.; Ferreira, W. C., Jr.; Lino, A. C. S.; Porto, M. E. G.
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.
This report presents the development of a mixed chemical Kinetic and Equilibrium MODel in which every chemical species can be treated either as a equilibrium-controlled or as a kinetically controlled reaction. The reaction processes include aqueous complexation, adsorption/desorption, ion exchange, precipitation/dissolution, oxidation/reduction, and acid/base reactions. Further development and modification of KEMOD can be made in: (1) inclusion of species switching solution algorithms, (2) incorporation of the effect of temperature and pressure on equilibrium and rate constants, and (3) extension to high ionic strength.
Yeh, G.T.; Iskra, G.A. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Civil Engineering; Szecsody, J.E.; Zachara, J.M.; Streile, G.P. [Pacific Northwest Lab., Richland, WA (United States)
A detailed chemical kinetic reaction mechanism is described which simulates the oxidation of the primary reference fuels n-heptane and iso-octane. The high temperature subset of these mechanisms is identified, and the extensions to deal with low temperature conditions are also explained. The algorithms used to assign reaction rates to elementary steps in the reaction mechanism are described, and the means of identifying the different chemical species and the relevant reactions are outlined. Finally, we show how interested kinetic modeling researchers can obtain copies of this reaction mechanism.
Westbrook, C.K.; Pitz, W.J.
The Role of Comprehensive Detailed Chemical Kinetic Reaction Mechanisms in Combustion Research
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
A Piagetian Learning Cycle for Introductory Chemical Kinetics.
ERIC Educational Resources Information Center
Described is a Piagetian learning cycle based on Monte Carlo modeling of several simple reaction mechanisms. Included are descriptions of learning cycle phases (exploration, invention, and discovery) and four BASIC-PLUS computer programs to be used in the explanation of chemical reacting systems. (Author/DS)
Batt, Russell H.
Kinetic and Chemical Mechanisms of Homocitrate Synthase from Thermus thermophilus*
The homocitrate synthase from Thermus thermophilus (TtHCS) is a metal-activated enzyme with either Mg2+ or Mn2+ capable of serving as the divalent cation. The enzyme exhibits a sequential kinetic mechanism. The mechanism is steady state ordered with ?-ketoglutarate (?-Kg) binding prior to acetyl-CoA (AcCoA) with Mn2+, whereas it is steady state random with Mg2+, suggesting a difference in the competence of the E�Mn�?-Kg�AcCoA and E�Mg�?-Kg�AcCoA complexes. The mechanism is supported by product and dead-end inhibition studies. The primary isotope effect obtained with deuterioacetylCoA (AcCoA-d3) in the presence of Mg2+ is unity (value 1.0) at low concentrations of AcCoA, whereas it is 2 at high concentrations of AcCoA. Data suggest the presence of a slow conformational change induced by binding of AcCoA that accompanies deprotonation of the methyl group of AcCoA. The solvent kinetic deuterium isotope effect is also unity at low AcCoA, but is 1.7 at high AcCoA, consistent with the proposed slow conformational change. The maximum rate is pH independent with either Mg2+ or Mn2+ as the divalent metal ion, whereas V/K?-Kg (with Mn2+) decreases at low and high pH giving pK values of about 6.5 and 8.0. Lysine is a competitive inhibitor that binds to the active site of TtHCS, and shares some of the same binding determinants as ?-Kg. Lysine binding exhibits negative cooperativity, indicating cross-talk between the two monomers of the TtHCS dimer. Data are discussed in terms of the overall mechanism of TtHCS. PMID:21733842
Kumar, Vidya Prasanna; West, Ann H.; Cook, Paul F.
Including the relativistic kinetic energy in a spline-augmented plane-wave band calculation
The first-order relativistic correction to the kinetic energy of an electron, the mass-velocity term, is not bounded from below. It can, therefore, not be used within a variational framework. To overcome this deficiency we developed a method to include the entire relativistic kinetic energy {radical}(p{sup 2}c{sup 2}+m{sub 0}{sup 2}c{sup 4}){minus}m{sub 0}c{sup 2} in a spline-augmented plane-wave band calculation. The first results for silver are quite promising, especially for d and p states: The analysis of the energies of the core states as well as of the valence band structure suggests that the energies of d bands are reproduced within 1 mRy. However, the combination of the relativistic kinetic energy with the Darwin term leads to energies which are too low for s-like valence states by 10 mRy. Therefore, the s and d valence band complex is spread out and the Fermi level is lowered by the same amount as the s states. We expect to overcome these deficiencies in future investigations by using a alternative form of the relativistic potential correction along the lines proposed by Douglas and Kroll. {copyright} {ital 1997} {ital The American Physical Society}
Fehrenbach, G.M.; Schmidt, G. [Sektion Physik der Ludwig Maximilians Universitaet Muenchen, Theresienstrae 37, 80333 Munich (Federal Republic of Germany)] [Sektion Physik der Ludwig Maximilians Universitaet Muenchen, Theresienstrae 37, 80333 Munich (Federal Republic of Germany)
The kinetic behavior of a laboratory population of bluegill (Lepomis macrochirus) under defined laboratory conditions is shown to be analogous to the reaction kinetics described by a population of molecules engaged in an opposed (reversible) first-order reaction. Thus as in chemical kinetics, the locomotor activity of fish can be described quantitatively in the form of rate constants.
Erik G. Ellgaard; Kerry S. Bloom; Anthony A. Malizia JR; Gerald E. Gunning; Richard E. Jensen
The subtle business of model reduction for stochastic chemical kinetics
This paper addresses the problem of simplifying chemical reaction networks by adroitly reducing the number of reaction channels and chemical species. The analysis adopts a discrete-stochastic point of view and focuses on the model reaction set S1?S2?S3, whose simplicity allows all the mathematics to be done exactly. The advantages and disadvantages of replacing this reaction set with a single S3-producing reaction are analyzed quantitatively using novel criteria for measuring simulation accuracy and simulation efficiency. It is shown that in all cases in which such a model reduction can be accomplished accurately and with a significant gain in simulation efficiency, a procedure called the slow-scale stochastic simulation algorithm provides a robust and theoretically transparent way of implementing the reduction. PMID:19222263
Gillespie, Dan T.; Cao, Yang; Sanft, Kevin R.; Petzold, Linda R.
Elimination of the Translational Kinetic Energy Contamination in pre-Born-Oppenheimer Calculations
In this paper we present a simple strategy for the elimination of the translational kinetic energy contamination of the total energy in pre-Born--Oppenheimer calculations carried out in laboratory-fixed Cartesian coordinates (LFCCs). The simple expressions for the coordinates and the operators are thus preserved throughout the calculations, while the mathematical form and the parametrisation of the basis functions are chosen so that the translational and rotational invariances are respected. The basis functions are constructed using explicitly correlated Gaussian functions (ECGs) and the global vector representation. First, we observe that it is not possible to parametrise the ECGs so that the system is at rest in LFCCs and at the same time the basis functions are square-integrable with a non-vanishing norm. Then, we work out a practical strategy to circumvent this problem by making use of the properties of the linear transformation between the LFCCs and translationally invariant and center-of-mass Cartesian ...
Simmen, Benjamin; Reiher, Markus
A reduced kinetic mechanism is constructed taking into account various boundary conditions and the considerable spread of data on rate constant of elementary steps. Kinetic schemes describing the chemical structure of flame with various degrees of accuracy are considered. The �shortest� mechanism consists of 83 steps and 29 species. The heat fluxes, temperature profiles, and concentration profiles of the main
N. E. Ermolin; V. E. Zarko
The influence of changes in the contracted Gaussian basis set used for ab initio calculations of nuclear magnetic resonance (NMR) phosphorous chemical shift anisotropy (CSA) tensors was investigated. The isotropic chemical shitl and chemical shift anisotropy were found to converge with increasing complexity of the basis set at the Hartree-Fock @IF) level. The addition of d polarization function on the phosphorous nucIei was found to have a major impact of the calculated chemical shi~ but diminished with increasing number of polarization fimctions. At least 2 d polarization fimctions are required for accurate calculations of the isotropic phosphorous chemical shift. The introduction of density fictional theory (DFT) techniques through tie use of hybrid B3LYP methods for the calculation of the phosphorous chemical shift tensor resulted in a poorer estimation of the NMR values, even though DFT techniques result in improved energy and force constant calculations. The convergence of the W parametem with increasing basis set complexity was also observed for the DFT calculations, but produced results with consistent large deviations from experiment. The use of a HF 6-31 l++G(242p) basis set represents a good compromise between accuracy of the simulation and the complexity of the calculation for future ab initio calculations of 31P NMR parameters in larger complexes.
Alam, T.M.
A Sequential Fluid-mechanic Chemical-kinetic Model of Propane HCCI Combustion
We have developed a methodology for predicting combustion and emissions in a Homogeneous Charge Compression Ignition (HCCI) Engine. This methodology combines a detailed fluid mechanics code with a detailed chemical kinetics code. Instead of directly linking the two codes, which would require an extremely long computational time, the methodology consists of first running the fluid mechanics code to obtain temperature
S M Aceves; D L Flowers; J Martinez-Frias; J R Smith; C Westbrook; W Pitz; R Dibble; J F Wright; W C Akinyemi; R P Hessel
brakes are frequently made of carbon/carbon (C=C) compos- ites. To deposit the composite interphaseINTERACTION BETWEEN GAS DIFFUSION AND MULTISTABLE HETEROGENEOUS CHEMICAL KINETICS IN C=C COMPOSITE PROCESSING G#19;erard L. VIGNOLES Universit#19;e Bordeaux 1, Laboratoire des Composites ThermoStructuraux 3
Recanati, Catherine
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.
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
the concentration, temperature and other dependences of a chemical reaction, and the subsequent formulation biochemically-relevant enzyme kinetics. The course will conclude with a brief foray into reaction dynamics of Temperature on Reaction Rates, Collision Theory, Transition State Theory (Sections 28.6 - 28.8 of M & S) Week
Nazar, Linda F.
Kinetic analyses of energy storage in a chemically pumped iodine laser
A set of 16 kinetic rate equations is numerically integrated to yield energy storage lifetimes in a chemically pumped iodine laser (CPIL) for various experimental parameters. Storage times greater than 3 ms are possible at room temperature, making the CPIL an interesting candidate for a high efficiency pulsed fusion laser. At low temperatures, storage times may even exceed 1 s.
G. E. Busch
Research in chemical kinetics. Progress report, August 1, 1987--July 20, 1988
This paper describes chemical kinetics research in the following areas: reactions of thermalized tritium atoms with organo-tin compounds; studies on the hydrolysis of OCS and CS{sub 2}; thermal chlorine 38 reactions with 2,3-dichloro-hexafluoro-2-butene; and thermal T reactions with fluoroethylenes.
Rowland, F.S.
H-Theorems in some kinetic models of chemically reacting dense gases
and Reaction Dynamics and Chemical Reactivity, 1987, or M.J.Pilling, P.W.Seakins, Reaction Kinetics, 1995 by C.F.Curtiss (1949) for very simple reactions where the presence of reaction products were ignored-like) equation for the density distribution of particles A. · Often the cross sections of (gas) reactions
Polewczak, Jacek
An experimental and detailed chemical kinetic modelling study of 2methyl furan oxidation
An experimental and detailed chemical kinetic modelling study of 2methyl furan oxidation Abstract An experimental ignition delay time study for the promising biofuel 2methyl furan promoting reactivity and hydrogen atom addition to the furan ring inhibiting reactivity. This work
Paris-Sud XI, Université de
Numerical modeling of D-mappings with applications to chemical kinetics
NASA Technical Reports Server (NTRS)
Numerical modeling of D-mappings was studied and applied to solving nonlinear stiff systems. These mappings were locally linearized for convergence analysis, and some applications were made to chemical kinetics. The technique avoids using multistep implicit codes that require inversion of Jacobian matrices, but depends on the Jacobians for its convergence analysis.
Dey, S. K.
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
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
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
Thermochemical analysis and kinetics aspects for a chemical model for camphene ozonolysis
NASA Astrophysics Data System (ADS)
In this work, a chemical model for the camphene ozonolysis, leading to carbonyl final products, is proposed and discussed on the basis of the thermochemical properties and kinetic data obtained at density functional theory levels of calculation. The mechanism is initiated by the electrophilic attack of ozone to the double bond in camphene leading to a 1,2,3-trioxolane intermediate, which decomposes to peroxy radicals and carbonyl compounds in a total of 10 elementary reactions. The thermodynamic properties (enthalpy and entropies differences) are calculated at 298 K. For the thermochemical evaluation, theoretical calculations are performed with the B3LYP, MPW1PW91, and mPW1K density functionals and the basis sets 6-31G(d), 6-31G(2d,2p), 6-31+G(d,p), and 6-31+G(2d,2p). Eventually, single point calculations adopting the 6-311++G(2d,2p) basis set are performed in order to improve the electronic energies. The enthalpy profiles suggest highly exothermic reactions for the individual steps, with a global enthalpy difference of -179.18 kcal mol-1, determined at the B3LYP/6-31+G(2d,2p) level. The Gibbs free energy differences for each step, at 298 K, calculated at the B3LYP/6-311++G(2d,2p)//B3LYP/6-31+G(2d,2p) level, are used to estimate the composition of a final product mixture under equilibrium conditions as 58% of camphenilone and 42% of 6,6-dimethyl-?-caprolactone-2,5-methylene. For the reaction kinetics, the bimolecular O3 + camphene step is assumed to be rate determining in the global mechanism. A saddle point for the ozone addition to the double bond is located and rate constants are determined on the basis of the transition state theory. This saddle point is well represented by a loosely bound structure and corrections for the basis set superposition error (BSSE) are calculated, either by considering the effect over the geometry optimization procedure (here referred as CP1 procedure), or the effect of the BSSE over the electronic energy of a previously optimized geometry, included a posteriori (here referred as CP2). The rate constants, calculated at 298 K from the data obtained at the mPW1K/6-31+G(d,p), CP1/B3LYP//6-31+G(2d,2p), and CP2/B3LYP//6-31+G(2d,2p) levels (3.62 � 10-18, 1.12 � 10-18, and 1.39 � 10-18 cm3 molecule-1 s-1), are found in good agreement with the available experimental data at the same temperature, 0.9 � 10-18 cm3 molecule-1 s-1 [R. Atkinson, S. M. Aschmann, and J. Arey, Atmos. Environ. 24, 2647 (1990)]. The importance of the BSSE corrections for the final rate constants must be pointed out. Furthermore, this work will contribute to a better understanding of the chemistry of monoterpenes in the atmosphere, as well as the implications for the phenomena of pollution.
Oliveira, R. C. de M.; Bauerfeldt, G. F.
The bioconcentration of two chlorobenzenes (CBs) and of seven polychlorobiphenyls (PCBs) to Selenastrum capricornutum and Microcystis aeruginosa was studied with accumulation experiments followed by gas purge elimination experiments. Henry's law constants at 10 C were needed to interpret the gas purge results and were measured in control experiments. For the M. aerogunisa culture, steady-state uptake was reached within days, whereas uptake by S. capricornutum took several weeks. The relationships between the log bioconcentration factors (BCF) and log octanol-water partition coefficients (K[sub OW]) were nonlinear, with relatively low values for the more hydrophobic PCBs. Rate constants for the elimination of CBs and PCBs from the algal cells were shown to be larger than 1 per day when calculated with a one-compartment model. With such large rate constants, it is unlikely that the curvature observed for these species is caused by slow kinetics or that algal growth affects BCF by dilution of CB or PCB concentrations. The log BCF-log K[sub OW] relationships could be described by a simple three-phase model that accounted for the binding of CBs and PCBs to dissolved organic carbon (DOC). Modeling bioconcentration of hydrophobic chemicals in phytoplankton should account for the binding to DOC.
Koelmans, A.A.; Woude, H. van der; Hattink, J.; Niesten, D.J.M. (Wageningen Agricultural Univ. (Netherlands). Aquatic Ecology and Water Quality Management Group)
An analytical kinetic model for chemical-vapor deposition of pureB layers from diborane
NASA Astrophysics Data System (ADS)
In this paper, an analytical model is established to describe the deposition kinetics and the deposition chamber characteristics that determine the deposition rates of pure boron (PureB-) layers grown by chemical-vapor deposition (CVD) from diborane (B2H6) as gas source on a non-rotating silicon wafer. The model takes into consideration the diffusion mechanism of the diborane species through the stationary boundary layer over the wafer, the gas phase processes and the related surface reactions by applying the actual parabolic gas velocity and temperature gradient profiles in the reactor. These are calculated theoretically and also simulated with fluent software. The influence of an axial and lateral diffusion of diborane species and the validity of the model for laminar flow in experimental CVD processes are also treated. This model is based on a wide range of input parameters, such as initial diborane partial pressure, total gas flow, axial position on the wafer, deposition temperature, activation energy of PureB deposition from diborane, surface H-coverage, and reactor dimensions. By only adjusting these reactor/process parameters, the model was successfully transferred from the ASM Epsilon One to the Epsilon 2000 reactor which has totally different reactor conditions. The model's predictive capabilities have been verified by experiments performed at 700 �C in these two different ASM CVD reactors.
Mohammadi, V.; de Boer, W. B.; Nanver, L. K.
NASA Astrophysics Data System (ADS)
Sensitivity analysis is a powerful tool in determining parameters to which the system output is most responsive, in assessing robustness of the system to extreme circumstances or unusual environmental conditions, in identifying rate limiting pathways as a candidate for drug delivery, and in parameter estimation for calculating the Hessian of the objective function. Anderson [SIAM J. Numer. Anal. 50, 2237 (2012)] shows the advantages of the newly developed coupled finite difference (CFD) estimator over the common reaction path (CRP) [M. Rathinam, P. W. Sheppard, and M. Khammash, J. Chem. Phys. 132, 034103 (2010)] estimator. In this paper, we demonstrate the superiority of the CFD estimator over the common random number (CRN) estimator in a number of scenarios not considered previously in the literature, including the sensitivity of a negative log likelihood function for parameter estimation, the sensitivity of being in a rare state, and a sensitivity with fast fluctuating species. In all examples considered, the superiority of CFD over CRN is demonstrated. We also provide an example in which the CRN method is superior to the CRP method, something not previously observed in the literature. These examples, along with Anderson's results, lead to the conclusion that CFD is currently the best estimator in the class of finite difference estimators of stochastic chemical kinetic models.
Srivastava, Rishi; Anderson, David F.; Rawlings, James B.
The initiation mechanisms and kinetics of pyrolysis and combustion of n-dodecane are investigated by using the reactive molecular dynamics (ReaxFF MD) simulation and chemical kinetic modeling. From ReaxFF MD simulations, we find the initiation mechanisms of pyrolysis of n-dodecane are mainly through two pathways, (1) the cleavage of C-C bond to form smaller hydrocarbon radicals, and (2) the dehydrogenation reaction to form an H radical and the corresponding n-C{sub 12}H{sub 25} radical. Another pathway is the H-abstraction reactions by small radicals including H, CH{sub 3}, and C{sub 2}H{sub 5}, which are the products after the initiation reaction of n-dodecane pyrolysis. ReaxFF MD simulations lead to reasonable Arrhenius parameters compared with experimental results based on first-order kinetic analysis of n-dodecane pyrolysis. The density/pressure effects on the pyrolysis of n-dodecane are also analyzed. By appropriate mapping of the length and time from macroscopic kinetic modeling to ReaxFF MD, a simple comparison of the conversion of n-dodecane from ReaxFF MD simulations and that from kinetic modeling is performed. In addition, the oxidation of n-dodecane is studied by ReaxFF MD simulations. We find that formaldehyde molecule is an important intermediate in the oxidation of n-dodecane, which has been confirmed by kinetic modeling, and ReaxFF leads to reasonable reaction pathways for the oxidation of n-dodecane. These results indicate that ReaxFF MD simulations can give an atomistic description of the initiation mechanism and product distributions of pyrolysis and combustion for hydrocarbon fuels, and can be further used to provide molecular based robust kinetic reaction mechanism for chemical kinetic modeling of hydrocarbon fuels. (author)
Wang, Quan-De [College of Chemistry, Sichuan University, Chengdu (China); Wang, Jing-Bo; Li, Juan-Qin; Tan, Ning-Xin; Li, Xiang-Yuan [College of Chemical Engineering, Sichuan University, Chengdu (China)
Chemical kinetics at very high pressures. I. Two experimental techniques
NASA Astrophysics Data System (ADS)
Two methods of following chemical reaction rates at very high pressures by means of the electrical conductivity are described. In the first, opposed circular tungsten-carbide anvils are used, with 12-?m sheets of platinum silver soldered to them if the solution is too corrosive for unprotected carbide or if electrode polarization is too high, and the sample is confined by a gasket of epoxy resin and fiberglass. It can be used at pressures up to �100 kbar. In the second, a conductance cell was built into a hydraulic piston-cylinder apparatus, and the hydraulic fluid was pressurized by a piston. Measurements were made to 27 kbar and could be made to 45 or 50 kbar if a pressure vessel having a greater ratio of outside to inside diameter were used.
Saluja, Preet P. S.; Cameron, Colin; Floriano, M. Antonio; Lavergne, Aurele; McLaurin, Graham E.; Whalley, Edward
Chemical kinetic modeling of a methane opposed flow diffusion flame and comparison to experiments
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)
Ab initio NMR Chemical Shift Calculations for Biomolecular Systems
magnetic field B and nuclear magnetic moment . The gauge origin dependence is eliminated by using field, the chemical shift describes the dependence of nuclear magnetic energy levels on the electronic environment between nuclei placed in different molecular environments. This means that the chemical shift is sensitive
Furui, Sadaoki
NASA Astrophysics Data System (ADS)
Rainfall erosivity is a key component in soil erosion by water. While kinetic energy and momentum are used to describe the erosivity of rainfall, and both are derived from mass and velocity of raindrops, it is not clear how different substrates transform this energy. In our study we conducted rainfall simulation experiments to determine splash detachment amounts of five substrates (coarse sand, medium sand, fine sand, PE balls, silt) for seven different rainfall intensities (52-116 mm h-1). We used linear mixed-effect modeling (LME) to calculate erosivity predictors for each substrate. Additionally, we separated drop-size-velocity relationship into lower left and upper right quarter to investigate the effect of small and slow just as big and fast raindrops on splash detachment amounts. We suggest using momentum divided by drop diameter as a substrate-independent erosivity predictor. To consider different substrates specific erosivity parameters are needed. Heavier substrates like sand are best described by kinetic energy multiplied by diameter whereas lighter substrates like silt point to momentum divided by diameter to the power of 1.5. Furthermore, our results show that substrates are differently affected by the size and velocity of drops. While splash detachment of light substances can be reliably predicted by drop size and velocity for small and slow drops, drop size and velocity loses its predictive power in heavier substrates like sand.
Goebes, Philipp; Seitz, Steffen; Gei�ler, Christian; Lassu, Tam�s; Peters, Piet; Seeger, Manuel; Nadrowski, Karin; Scholten, Thomas
NASA Astrophysics Data System (ADS)
The methods to calculate the kinetics parameters of ?eff and ? with the differential operator sampling have been reviewed. The comparison of the results obtained with the differential operator sampling and iterated fission probability approaches has been performed. It is shown that the differential operator sampling approach gives the same results as the iterated fission probability approach within the statistical uncertainty. In addition, the prediction accuracy of the evaluated nuclear data library JENDL-4.0 for the measured ?eff/? and ?eff values is also examined. It is shown that JENDL-4.0 gives a good prediction except for the uranium-233 systems. The present results imply the need for revisiting the uranium-233 nuclear data evaluation and performing the detailed sensitivity analysis.
Nagaya, Yasunobu
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.
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.
Double-focusing mixing jet for XFEL study of chemical kinetics.
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?�s, 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
Double-focusing mixing jet for XFEL study of chemical kinetics
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?�s, 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
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.
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.
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.
NASA Astrophysics Data System (ADS)
De-icing chemicals that contain propylene glycol are used at Oslo airport during winter time. A fraction of these chemicals is spilled on the runway and can be transported rapidly in the sandy soil in spring during snowmelt. Better insight into the chemical and physical processes that govern the fate of these chemicals in soil will help to estimate potential effects on the large unconfined aquifer in this area, and makes it possible to evaluate potential remedial actions. Micro-organisms in the soil can degrade propylene glycol, for which they need electron-acceptors. Under aerobic conditions, oxygen will be used as an electron-acceptor. From experiments, it is known that also anaerobic degradation occurs in this soil. During snowmelt, high infiltration rates can lead to locally saturated soil. In these parts, oxygen diffusion is limited and thus anaerobic conditions will occur. In these anaerobic regions, other electron-acceptors, such as manganese-oxides that are present in this soil, are used. However, frequent propylene glycol application may lead to a depletion of manganese-oxides and so to increased persistence and migration of propylene glycol in soil. To prevent this depletion and to enhance biodegradation, other electron-acceptors can be applied at the soil surface. Examples are the application of nitrate to the soil surface, and air injection. Model calculations could help to estimate required concentrations. The objectives of this study are 1) to create the reactive model, 2) to use this model to evaluate which parameters are determining leaching fluxes of propylene glycol from the soil, and 3) to evaluate the effectiveness of the different remediation strategies. Therefore, transient water flow, kinetic degradation, and redox chemistry were combined in one model. Degradation is modelled with Monod kinetics using multiple electron-acceptors. Oxygen diffusion in the gas phase, biomass growth, and oxidation and reduction of the important electron-acceptors are included.
Schotanus, D.; Meeussen, J. C. L.; van der Ploeg, M. J.; van der Zee, S. E. A. T. M.
Molecular Design Using Quantum Chemical Calculations for Property Estimation
. In both examples, a genetic algorithm is applied to generate and screen candidate molecules. The molecular (calculations from first principles) obtain molecular properties from the most fundamental level of molecular
Maranas, Costas
Chemical Kinetic Reaction Mechanisms for Combustion of Hydrocarbon and Other Types of Chemical Fuels
Reaction mechanisms have been tested and validated extensively through comparisons between computed results and measured data from laboratory experiments (e.g., shock tubes, laminar flames, rapid compression machines, flow reactors, stirred reactors) and from practical systems (e.g., diesel engines, spark-ignition engines, homogeneous charge, compression ignition (HCCI) engines). These kinetic models are used to examine a wide range of combustion systems.[Taken from https://www-pls.llnl.gov/?url=science_and_technology-chemistry-combustion
React. Kinet. Catal. Lett., Vol. 15, No. 2,245-250 (1980) DYNAMICS OF CHEMICAL REACTIONS behavior of chemical reactions,in particular,the reasonsfor slow relaxa- tions. IIoKa3aHo, qTO 14[HdpKcaum~. Prolonged transientregimes were found experimentally in chemical reactions in greatlydifferenthomogeneous
Gorban, Alexander N.
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
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.
Quantum chemical calculations of vibrational spectra of para-ethylbenzenesulfonic acid
NASA Astrophysics Data System (ADS)
Quantum chemical calculations of vibrational spectra of para-ethylbenzenesulfonic acid have been conducted by means of a non-empirical SCF MO LCAO method with the use of the 6-31G( d) basis set. Calculated IR and Raman frequencies are assigned to vibrations of specific atomic groups. It is shown that para-ethylbenzenesulfonic acid can serve as a reasonable quantum chemical model in calculations of vibrational spectra for polystyrene sulfonic resins of various degrees of hydration.
Zelenkovskii, V. M.; Bezyazychnaya, T. V.; Soldatov, V. S.
Errors in the Calculation of 27Al Nuclear Magnetic Resonance Chemical Shifts
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
NASA Astrophysics Data System (ADS)
Widely different time scales are common in systems of chemical reactions and can be exploited to obtain reduced models applicable to the time scales of interest. These reduced models enable more efficient computation and simplify analysis. A classic example is the irreversible enzymatic reaction, for which separation of time scales in a deterministic mass action kinetics model results in approximate rate laws for the slow dynamics, such as that of Michaelis-Menten. Recently, several methods have been developed for separation of slow and fast time scales in chemical master equation (CME) descriptions of stochastic chemical kinetics, yielding separate reduced CMEs for the slow variables and the fast variables. The paper begins by systematizing the preliminary step of identifying slow and fast variables in a chemical system from a specification of the slow and fast reactions in the system. The authors then present an enhanced time-scale-separation method that can extend the validity and improve the accuracy of existing methods by better accounting for slow reactions when equilibrating the fast subsystem. The resulting method is particularly accurate in systems such as enzymatic and protein interaction networks, where the rates of the slow reactions that modify the slow variables are not a function of the slow variables. The authors apply their methodology to the case of an irreversible enzymatic reaction and show that the resulting improvements in accuracy and validity are analogous to those obtained in the deterministic case by using the total quasi-steady-state approximation rather than the classical Michaelis-Menten. The other main contribution of this paper is to show how mass fluctuation kinetics models, which give approximate evolution equations for the means, variances, and covariances of the concentrations in a chemical system, can feed into time-scale-separation methods at a variety of stages.
G�mez-Uribe, Carlos A.; Verghese, George C.; Tzafriri, Abraham R.
Control of Mass Transport and Chemical Reaction Kinetics in Ultrasmall Volumes
NASA Astrophysics Data System (ADS)
This talk will describe means for triggering chemical reactions for studying reaction kinetics under extreme confinement with sub-millisecond temporal resolution, including on-demand generation and fusion of femtoliter (10-15 L) volume water-in-oil droplets, and triggering reactions in femtoliter chambers microfabricated in poly(dimethylsiloxane) (PDMS). We demonstrated a reversible chemical toggle switch, which lays the groundwork for exploring more complex chemical and biochemical reaction sequences triggered and monitored in real time in discrete ultrasmall reactors, such as sequential and coupled enzymatic reactions. We are also developing methods to vary confinement and macromolecular crowding in ultrasmall, water-in-oil droplets and chambers micromolded in PDMS as biomimetic reaction vessels containing minimal synthetic gene circuits, in order to better understand how confinement, reduced dimensionality and macromolecular crowding affect molecular mechanisms involved in the operation and regulation of genetic circuits in living cells.
Collier, Charles
Calibration of Chemical Kinetic Models Using Simulations of Small-Scale Cookoff Experiments
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
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.
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.
Detailed chemical kinetic mechanism for the oxidation of biodiesel fuels blend surrogate.
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
Chemical oxidation of aniline and N-methylaniline: A kinetic study by Raman spectroscopy
NASA Astrophysics Data System (ADS)
For the first time, chemical oxidation of aniline and N-methylaniline with dichromate as oxidant has been studied by Raman spectroscopy with 785 nm laser beam excitation, and the suitability of this technique for kinetic study of this process was demonstrated. For both monomers used, a sigmoidal growth of the intensities for most prominent Raman bands was observed, showing a self-accelerating character of this reaction. Self-acceleration appears most clearly expressed for aniline, and for the low oxidant-to-monomer molar ratio used. After reaching their maximum values, the intensities of Raman bands drop almost to zero, most probably due to increase in opacity and optical absorbance of reaction mixture. The kinetics of an increase, and the next following decrease of band intensities depend on the monomer used, and oxidant-to-monomer molar ratio.
Ma�eikien?, Regina; Niaura, Gediminas; Malinauskas, Albertas
Detailed chemical kinetic mechanism for the oxidation of biodiesel fuels blend surrogate
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)
Kinetics studies of a variety of positive and negative ions reacting with the GX surrogate, dimethyl methylphosphonate (DMMP), were performed. All protonated species reacted rapidly, that is, at the collision limit. The protonated reactant ions created from neutrals with proton affinities (PAs) less than or equal to the PA for ammonia reacted exclusively by nondissociative proton transfer. Hydrated H(3)O(+) ions also reacted rapidly by proton transfer, with 25% of the products from the second hydrate, H(3)O(+)(H(2)O)(2), forming the hydrated form of protonated DMMP. Both methylamine and triethylamine reacted exclusively by clustering. NO(+) also clustered with DMMP at about 70% of the collision rate constant. O(+) and O(2)(+) formed a variety of products in reactions with DMMP, with O(2)(+) forming the nondissociative charge transfer product about 50% of the time. On the other hand, many negative ions were less reactive, particularly, SF(5)(-), SF(6)(-), CO(3)(-), and NO(3)(-). However, F(-), O(-), and O(2)(-) all reacted rapidly to generate m/z = 109 amu anions (PO(3)C(2)H(6)(-)). In addition, product ions with m/z = 122 amu from H(2)(+) loss to form H(2)O were the dominant ions produced in the O(-) reaction. NO(2)(-) underwent a slow association reaction with DMMP at 0.4 Torr. G3(MP2) calculations of the ion energetics properties of DMMP, sarin, and soman were also performed. The calculated ionization potentials, proton affinities, and fluoride affinities were consistent with the trends in the measured kinetics and product ion branching ratios. The experimental results coupled with the calculated ion energetics helped to predict which ion chemistry would be most useful for trace detection of the actual chemical agents. PMID:19385679
Midey, Anthony J; Miller, Thomas M; Viggiano, A A
Chemical Kinetic Simulation of the Combustion of Bio-based Fuels
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
NASA Astrophysics Data System (ADS)
Vector methods have been developed for the computation of the kinetic energy (reciprocal reduced mass) expressions for the ring-twisting and ring-bending vibrations of bicyclic molecules in the tetralin family. The definitions of the bond vectors in terms of these coordinates are presented. Both one- and two-dimensional kinetic energy surfaces have been calculated for tetralin and 1,4-benzodioxan and both are significantly coordinate dependent. The results for the S0 electronic ground states and S1(?, ?*) excited states are presented.
Yang, Juan; Laane, Jaan
Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics.
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
A Detailed Chemical Kinetic Analysis of Low Temperature Non-Sooting Diesel Combustion
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
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 of Chemical Mechanisms on PDF Calculations of Non-Premixed Piloted Jet Flames Table of Contents DESCRIPTION
Chemical Dynamic Kinetic Resolution and S/R?Interconversion of Unprotected ?-Amino Acids.
Reported herein is the first purely chemical method for the dynamic kinetic resolution (DKR) of unprotected racemic ?-amino acids (?-AAs), a method which can rival the economic efficiency of the enzymatic reactions. The DKR reaction principle can be readily applied for S/R?interconversions of ?-AAs, the methodological versatility of which is unmatched by biocatalytic approaches. The presented process features a virtually complete stereochemical outcome, fully recyclable source of chirality, and operationally simple and convenient reaction conditions, thus allowing its ready scalability. A quite unique and novel mode of the thermodynamic control over the stereochemical outcome, including an exciting interplay between axial, helical, and central elements of chirality is proposed. PMID:25244328
Takeda, Ryosuke; Kawamura, Akie; Kawashima, Aki; Sato, Tatsunori; Moriwaki, Hiroki; Izawa, Kunisuke; Akaji, Kenichi; Wang, Shuni; Liu, Hong; Ace�a, Jos� Luis; Soloshonok, Vadim A
Effect of off-design operation of MHD generators on NO/x/ chemical kinetics
NASA Technical Reports Server (NTRS)
The purpose of this study is to provide a capability for determining the chemical kinetic behavior of one family of pollutants, the nitrogen oxides, in the flow of a coal-fired MHD generator facility. The method used in the study allows the prediction of the nonequilibrium concentration of the minor NO(x) species in a flow otherwise assumed in equilibrium. Consideration is given to the effect of preheat, stoichiometry, and oxygen enrichment of the NO(x) concentration. The effect of preheat and stoichiometry is found to have a significant influence on the NO(x) concentration at the exit of the radiant boiler.
Simmons, G. A.; Wilson, D. R.
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.
A review of the physics and modelling of mass diffusion involving different gaseous chemical species is firstly proposed. Both accurate and simplified models for mass diffusion involve the calculation of individual species diffusion coefficients. Since these are computationally expensive, in CFD they are commonly estimated by assuming constant Lewis or Schmidt numbers for each chemical species. The constant Lewis number
E. Giacomazzi; F. R. Picchia; N. Arcidiacono
Both experimental and theoretical investigations are reported on the infrared spectrum of vinylphosphine-borane (CH(2)=CHPH(2) x BH(3)), a donor-acceptor complex. The gas phase infrared spectra (3500-600 cm(-1)) have been recorded at 0.5 cm(-1) resolution. This first primary alpha,beta-unsaturated phosphine-borane synthesized up to now is kinetically very unstable in the gas phase and decomposes rapidly into two fragments: the free vinylphosphine CH(2)=CHPH(2) and the monoborane BH(3) which dimerizes to form the more stable diborane B(2)H(6). Spectra of free CH(2)=CHPH(2) and B(2)H(6) compounds were also recorded to assign some vibration modes of the complex in very dense spectral regions. The analysis was completed by carrying out quantum mechanical calculations by density functional theory method at the B3LYP/6-31+G(**) level. Anharmonic frequencies and infrared intensities of the two predicted gauche and syn conformers of the vinylphosphine-borane complex were calculated in the 3500-100 cm(-1) region with the use of a variational approach, implemented in the P_ANHAR_V1.2 code. Because of the relatively weak interaction between the vinylphosphine and the monoborane, the vibrations of the complex can easily be subdivided into modes localized in the CH(2)=CHPH(2) and BH(3) moieties and into "intermolecular" modes. Localized modes are unambiguously correlated with the modes of the isolated monomers. Therefore, they are described in terms of the monomer vibrations, and the complexation shifts are defined as Delta nu = nu(complex) - nu(monomer) to make the effect of the complexation precise on each localized mode. In this objective, anharmonic frequencies and infrared intensities of the BH(3) monomer and the stable gauche and syn conformers of the free vinylphosphine were obtained at the same level of theory. In the gas phase, only the syn form of the complex was observed and assigned. All theoretically predicted frequencies and complexation shifts in magnitude and direction are in good agreement with experiment. By infrared spectroscopy assisted by quantum chemical calculations, the consequences of the complexation of an alpha,beta-unsaturated phosphine by borane on the physicochemical properties of the formed 12-atom complex have been efficiently evaluated. PMID:19071917
Khater, Brahim; Guillemin, Jean-Claude; Benidar, Abdessamad; B�gu�, Didier; Pouchan, Claude
The role of detailed chemical kinetics on CFD diesel spray ignition and combustion modelling
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. Garc�a; J. M. Pastor; V. Domenech
Protein folding kinetics: barrier effects in chemical and thermal denaturation experiments
Recent experimental work on fast protein folding brings about an intriguing paradox. Microsecond-folding proteins are supposed to fold near or at the folding speed limit (downhill folding), but yet their folding behavior seems to comply with classical two-state analyses, which imply the crossing of high free energy barriers. However, close inspection of chemical and thermal denaturation kinetic experiments in fast-folding proteins reveals systematic deviations from two-state behavior. Using a simple one-dimensional free energy surface approach we find that such deviations are indeed diagnostic of marginal folding barriers. Furthermore, the quantitative analysis of available fast-kinetic data indicates that many microsecond-folding proteins fold downhill in native conditions. All of these proteins are then promising candidates for an atom-by-atom analysis of protein folding using nuclear magnetic resonance1. We also find that the diffusion coefficient for protein folding is strongly temperature dependent, corresponding to an activation energy of ~1 kJ.mol?1 per protein residue. As a consequence, the folding speed limit at room temperature is about an order of magnitude slower than the ~ 1?s estimates from high temperature T-jump experiments. Our analysis is quantitatively consistent with the available thermodynamic and kinetic data on two-state folding proteins, and provides a straightforward explanation for the apparent fast-folding paradox. PMID:17419630
Naganathan, Athi N.; Doshi, Urmi; Mu�oz, Victor
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.
Reduction Kinetics of a CasO4 Based Oxygen Carrier for Chemical-Looping Combustion
NASA Astrophysics Data System (ADS)
The CaSO4 based oxygen carrier has been proposed as an alternative low cost oxygen carrier for Chemical-looping combustion (CLC) of coal. The reduction of CaSO4 to CaS is an important step for the cyclic process of reduction/oxidation in CLC of coal with CaSO4 based oxygen carrier. Thermodynamic analysis of CaSO4 oxygen carrier with CO based on the principle of Gibbs free energy minimization show that the essentially high purity of CO2 can be obtained, while the solid product is CaS instead of CaO. The intrinsic reduction kinetics of a CaSO4 based oxygen carrier with CO was investigated in a differential fixed bed reactor. The effects of gas partial pressure (20%-70%) and temperature (880-950�C) on the reduction were investigated. The reduction was described with shrinking unreacted core model. Experimental results of CO partial pressure on the solid conversion show that the reduction of fresh oxygen carriers is of first order with respect to the CO partial pressure. Both chemical reaction control and product layer diffusion control determine the reduction rate. The dependences of reaction rate constant and effective diffusivity with temperature were both obtained. The kinetic equation well predicted the experimental data.
Xiao, R.; Song, Q. L.; Zheng, W. G.; Deng, Z. Y.; Shen, L. H.; Zhang, M. Y.
Edge-controlled growth and kinetics of single-crystal graphene domains by chemical vapor deposition
The controlled growth of large-area, high-quality, single-crystal graphene is highly desired for applications in electronics and optoelectronics; however, the production of this material remains challenging because the atomistic mechanism that governs graphene growth is not well understood. The edges of graphene, which are the sites at which carbon accumulates in the two-dimensional honeycomb lattice, influence many properties, including the electronic properties and chemical reactivity of graphene, and they are expected to significantly influence its growth. We demonstrate the growth of single-crystal graphene domains with controlled edges that range from zigzag to armchair orientations via growth�etching�regrowth in a chemical vapor deposition process. We have observed that both the growth and the etching rates of a single-crystal graphene domain increase linearly with the slanted angle of its edges from 0� to ?19� and that the rates for an armchair edge are faster than those for a zigzag edge. Such edge-structure�dependent growth/etching kinetics of graphene can be well explained at the atomic level based on the concentrations of the kinks on various edges and allow the evolution and control of the edge and morphology in single-crystal graphene following the classical kinetic Wulff construction theory. Using these findings, we propose several strategies for the fabrication of wafer-sized, high-quality, single-crystal graphene. PMID:24297886
Ma, Teng; Ren, Wencai; Zhang, Xiuyun; Liu, Zhibo; Gao, Yang; Yin, Li-Chang; Ma, Xiu-Liang; Ding, Feng; Cheng, Hui-Ming
Thermal rate constants and H\\/D kinetic isotope effects for the Cl+C2H6-->HCl+C2H5 reaction were computed by microcanonical variational transition state theory on a high-level ab initio potential energy surface (PES). The calculations show that the reaction proceeds through a ``loose'' transition state, and so the consideration of variational effects is important. The PES presents a van der Waals minimum in the
A. Fern�ndez-Ramos; E. Mart�nez-N��ez; J. M. C. Marques; S. A. V�zquez
Thermal rate constants and H\\/D kinetic isotope effects for the Cl+C2H6?HCl+C2H5 reaction were computed by microcanonical variational transition state theory on a high-level ab initio potential energy surface (PES). The calculations show that the reaction proceeds through a �loose� transition state, and so the consideration of variational effects is important. The PES presents a van der Waals minimum in the
A. Ferna�ndez-Ramos; J. M. C. Marques; S. A. Va�zquez
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.; P�schl, U.
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. P�schl, Atmos. Chem. Phys, 2012, 12, 2777.
Arangio, Andrea; Slade, Jonathan H.; Berkemeier, Thomas; Knopf, Daniel A.; Shiraiwa, Manabu
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.
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.
Modeling of the HiPco process for carbon nanotube production. I. Chemical kinetics.
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. PMID:12908291
Dateo, Christopher E; G�k�en, Tahir; Meyyappan, M
Comparative kinetic calculations of turbulent combustion of air mixtures of hydrogen and methane
The authors compare several mathematical models describing the combustion kinetics of hydrogen-air and methane-air mixtures under conditions of turbulence in the flame propagation region. The process considered is based on homogeneous combustion with jet stabilization of the flame. The participation of 18 elements and compounds in a total of 35 reactions occurring in both forward and reverse directions is tabulated.
V. Ya. Basevich; V. P. Volodin; S. M. Kogarko; N. I. Peregudov
Review of recent experiments and calculations relevant to the kinetics of the HF laser
An abbreviated review of rate coefficients relevant to HF laser kinetics modeling is presented. The literature has been surveyed from the last published review in 1983 to the present. Updated HF Einstein emission coefficients are tabulated. This brief summary of a more detailed review addresses rate coefficients relevant to HF generation, reactive quenching, self-relaxation, and vibrational relaxation by a selection
Gerald C. Manke; Gordon D. Hager
A Review of Recent Experiments and Calculations Relevant to the Kinetics of the HF Laser
A review of rate coefficients relevant to HF laser kinetics modeling is presented. The literature has been surveyed from the last published review in 1983 to the present. Updated HF Einstein emission coefficients are tabulated. Rate coefficients are categorized according to their role in the HF laser model: HF generation, reactive quenching, self-relaxation, V�V energy transfer, vibrational relaxation by atoms
Gerald C. Manke; Gordon D. Hager
The formation of H{sub 3}{sup +} from saturated hydrocarbon molecules represents a prototype of a complex chemical process, involving the breaking and the making of chemical bonds. We present a combined theoretical and experimental investigation providing for the first time an understanding of the mechanism of H{sub 3}{sup +} formation at the molecular level. The experimental approach involves femtosecond laser pulse ionization of ethane leading to H{sub 3}{sup +} ions with kinetic energies on the order of 4 to 6.5 eV. The theoretical approach involves high-level quantum chemical calculation of the complete reaction path. The calculations confirm that the process takes place on the potential energy surface of the ethane dication. A surprising result of the theoretical investigation is, that the transition state of the process can be formally regarded as a H{sub 2} molecule attached to a C{sub 2}H{sub 4}{sup 2+} entity but IRC calculations show that it belongs to the reaction channel yielding C{sub 2}H{sub 3}{sup +}+ H{sub 3}{sup +}. Experimentally measured kinetic energies of the correlated H{sub 3}{sup +} and C{sub 2}H{sub 3}{sup +} ions confirm the reaction path suggested by theory.
Kraus, Peter M.; Schwarzer, Martin C.; Schirmel, Nora; Urbasch, Gunter; Frenking, Gernot; Weitzel, Karl-Michael [Fachbereich Chemie, Physikalische Chemie, Philipps-Universitaet Marburg, Hans-Meerwein-Strasse, D-35032 Marburg (Germany)
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.
NASA Astrophysics Data System (ADS)
We present a computationally efficient adaptive method for calculating the time evolution of the concentrations of chemical species in global 3-D models of atmospheric chemistry. Our strategy consists of partitioning the computational domain into fast and slow regions for each chemical species at every time step. In each grid box, we group the fast species and solve for their concentration in a coupled fashion. Concentrations of the slow species are calculated using a simple semi-implicit formula. Separation of species between fast and slow is done on the fly based on their local production and loss rates. This allows for example to exclude short-lived volatile organic compounds (VOCs) and their oxidation products from chemical calculations in the remote troposphere where their concentrations are negligible, letting the simulation determine the exclusion domain and allowing species to drop out individually from the coupled chemical calculation as their production/loss rates decline. We applied our method to a 1-year simulation of global tropospheric ozone-NO x-VOC-aerosol chemistry using the GEOS-Chem model. Results show a 50% improvement in computational performance for the chemical solver, with no significant added error.
Santillana, Mauricio; Le Sager, Philippe; Jacob, Daniel J.; Brenner, Michael P.
A quantitative study of chemical kinetics for the synthesis of doped oxide nanocrystals using FTIR
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
Kinetic models for autopoietic chemical systems: the role of fluctuations in a homeostatic regime.
Two kinetic models describing the emergence of autopoietic chemical units are presented and discussed: the single reagent autopoietic mechanism (SRAM) and a reduced version (rSRAM). The proposed schemes are inspired to the autopoietic vesicles studied by Zepik et al (2001 Angew. Chem., Int. Ed. Engl. 40 199-202). Deterministic and stochastic analyses are then performed in order to obtain conditions for growth, homeostasis and decay time behaviours of the overall amphiphiles concentration. Only the reduced SRAM is able to exhibit all the three regimes as experimentally observed and in order to obtain details on the time evolution of the aggregates' size distribution, stochastic simulations are carried out. What emerges from the rSRAM simulation outcomes is that random fluctuations can act as selection rules for the size of the autopoietic units in the homeostatic regime suggesting how, in a prebiotic scenario, stochastic fluctuations can select the more robust, in this case larger, as the fittest 'organisms'. PMID:20130341
Mavelli, Fabio; Stano, Pasquale
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
NASA Technical Reports Server (NTRS)
LSENS, the Lewis General Chemical Kinetics and Sensitivity Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part 3 of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part 3 explains the kinetics and kinetics-plus-sensitivity analysis problems supplied with LSENS and presents sample results. These problems illustrate the various capabilities of, and reaction models that can be solved by, the code and may provide a convenient starting point for the user to construct the problem data file required to execute LSENS. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions.
Bittker, David A.; Radhakrishnan, Krishnan
Elucidating the interaction of H2O2 with polar amino acids - Quantum chemical calculations
NASA Astrophysics Data System (ADS)
Quantum chemical calculations have been carried out to investigate the interaction motifs of H2O2 with polar amino acid residues. Binding energies obtained from gas phase and continuum solvent phase calculations range between 2 and 30 kcal/mol. H2O2 interacts with the side chain of polar amino acids chiefly through the formation of hydrogen bonds. The sbnd CH group in side chains of a few residues provides additional stabilization to H2O2.
Karmakar, Tarak; Balasubramanian, Sundaram
An unsymmetrical fluoran dye, 3-diethylamino-6-methyl-7-chlorofluoran (DEAMCF) is one of the leuco dyes which shows the coloring-to-decoloring reversible reaction with acidity. We calculated the 13C chemical shieldings of the DEAMCF with the frame model compounds using ab initio gauge invariant atomic orbital methods, and compared it with the experimental shifts. The calculated values of the frame compounds are in good agreement
T. Hoshiba; T Ida; M Mizuno; T Otsuka; K Takaoka; K Endo
NASA Astrophysics Data System (ADS)
Quantum-chemical methods are used to calculate electronic-absorption spectra, dipole moments, and atomic-charge distributions of aromatic amino acids in aqueous solutions at various concentrations. The electronic-absorption spectra are analyzed and compared with the spectra that are calculated for gas phase. The bathochromic shift of the spectral position is shown for the long-wavelength absorption peak of the singlet-singlet transition for aqueous solutions of amino acids.
Migovich, M. I.; Kel'man, V. A.
Atomic-scale kinetic Monte Carlo simulations of diamond chemical vapor deposition
NASA Astrophysics Data System (ADS)
Diamond's superb mechanical, thermal, optical, and electronic properties are ideally suited for use in protective coatings, thermal management components, cold cathode emitters, and high-performance electronic devices, among others. Diamond can be chemically vapor deposited (CVD) to produce coatings and thin films, but this technique is currently expensive and difficult to control, and the details of the molecular processes that lead to diamond deposition remain unclear. The goal of this work is to construct a tool by which the nano-scale processes that lead to diamond growth, and their effects on film properties, can be examined. This is accomplished through the development of a kinetic Monte Carlo simulation method that treats diamond deposition on the atomic length scale using established chemical reaction rate data as input, while addressing deposition time scales that correspond directly to real growth experiments. The impact of the atomic-scale surface reaction processes on the growth kinetics, surface morphologies, and defect densities of single crystal CVD diamond are examined. In this way, a clearer understanding of the connection between atomic-scale deposition processes and CVD diamond film properties can be obtained. The growth kinetics and surface morphologies that develop during deposition are found to depend primarily on the details of the atomic surface features and their effects on bonding during deposition. The (110) and (111) surfaces facet under certain growth conditions. The (100) surface grows fastest and roughens, in contradiction to experimental observations. This can be rectified by the introduction of a mechanism for the preferential etching of monatomic islands on (100) facets, whereby the simulations predict slow-growing smooth (100) faces in accord with experimental observations. The trapping of H atoms is enhanced at higher substrate temperatures where the flux of larger Csb2Hsb2 molecules to the surface is high. Incorporation of spsp2 defects is highest for high-CHsb4 feeds which generate less H, since H is required to convert sp2-bonded C on the surface to spsp3-bonded material. Vacancy incorporation is not substantial. The ratio of simulated growth rate to defect concentration is maximized around 800-950sp�C and 1% inlet CHsb4, for which experiments also produce the best quality CVD diamond.
Battaile, Corbett Chandler
The hydration of isoamylenes to produce 2-methyl-2-butanol (tert-amyl alcohol, or TAA) is strongly limited by chemical equilibrium to olefin conversions of less than 50%. The general goal of this work was to determine whether reactive distillation would be a valid method to enhance the yield of TAA. The first step was to study the reaction kinetics and chemical equilibrium, using
J. Castor Gonz�lez; James R. Fair
Research in chemical kinetics. Progress report, July 20, 1988--August 30, 1989
A major aspect of our research over the past decade under this contract has been the application of radioisotopes generated by nuclear reactions for the study of various kinetic mechanisms. Two general theoretical concepts have been explored in detail by this technique: (a) The addition of halogen atoms to olefins, which have been described for fifty years by the phrase {open_quotes}anti-Markownikoff{close_quotes} to indicate that the preference for one or the other end of an unsymmetric olefin is opposite to that ({open_quotes}Markownikoff addition{close_quotes}) for hydrogen halide addition. (b) The redistribution of internal energy within a molecule after an energetic addition reaction, for which the usual assumption is rapid equilibration into all available degrees of freedom, as calculated by the Rice-Rarnsperger-Kassel-Marcus (RRKM) model. In both instances, significant results have been obtained which expand the overall view of each of these two concepts.
Rowland, F.S.
A detailed chemical kinetic reaction mechanism has been developed for a group of four small alkyl ester fuels, consisting of methyl formate, methyl acetate, ethyl formate and ethyl acetate. This mechanism is validated by comparisons between computed results and recently measured intermediate species mole fractions in fuel-rich, low pressure, premixed laminar flames. The model development employs a principle of similarity of functional groups in constraining the H atom abstraction and unimolecular decomposition reactions in each of these fuels. As a result, the reaction mechanism and formalism for mechanism development are suitable for extension to larger oxygenated hydrocarbon fuels, together with an improved kinetic understanding of the structure and chemical kinetics of alkyl ester fuels that can be extended to biodiesel fuels. Variations in concentrations of intermediate species levels in these flames are traced to differences in the molecular structure of the fuel molecules.
Westbrook, C K; Pitz, W J; Westmoreland, P R; Dryer, F L; Chaos, M; Osswald, P; Kohse-Hoinghaus, K; Cool, T A; Wang, J; Yang, B; Hansen, N; Kasper, T
Although arguably the most important reaction in glycoscience, chemical glycosylations are among the least well understood of organic chemical reactions resulting in an unnecessarily high degree of empiricism and a brake on rational development in this critical area. To address this problem primary 13C kinetic isotope effects now have been determined for the formation of ?- and ?-manno- and glucopyranosides by a natural abundance NMR method. In contrast to the common current assumption, for three of the four cases studied the experimental values concur with those computed for associative displacement of the intermediate covalent glycosyl trifluoromethanesulfonates. For the formation of the ?-mannopyranosides the experimentally determined KIE differs significantly from that computed for an associative displacement, which is strongly suggestive of a dissociative mechanism that approaches the intermediacy of a glycosyl oxocarbenium ion. The application of comparable experiments to other glycosylation systems should shed further light on their glycosylation mechanisms and thus assist in the design of better reactions conditions with improved stereoselectivity. PMID:22824899
Huang, Min; Garrett, Graham E.; Birlirakis, Nicolas; Boh�, Luis
921 A TIGHT-BINDING CALCULATION OF THE CHEMICAL SHIFT IN TRIGONAL SELENIUM AND TELLURIUM M in trigonal selenium and tellurium is presented. It is based on a tight-binding model where interactions for trigonal selenium [2]. From this it follows that there are three distinct sites in the primitive cell
Paris-Sud XI, Université de
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
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
SIML: A Fast SIMD Algorithm for Calculating LINGO Chemical Similarities on GPUs Imran S. Haque,
of chemical similarity based on text comparison of SMILES strings. We present a new algorithm for calculating than existing methods when run on a GPU. INTRODUCTION The continuing exponential increase in computer methods are required to handle the increasing computational load. The GPU revolution in computing offers
Pratt, Vaughan
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.
Oxidation (off state) and reduction (on state) of a single azurin molecule is monitored, one electron at a time, which depend on the chemical redox potential. By analysing the fluorescence time traces from individual azurin molecules, reaction kinetics and redox thermodynamics were determined. PMID:25302565
Akkilic, Namik; van der Grient, Fenna; Kamran, Muhammad; Sanghamitra, Nusrat J M
Volume 76. number 1 CHEMICAL PHYSICS LETTERS 15 November 1980 THE KINETICS OF VIBRATIONAL ENERGY of the experimental apparatus is presented #12;Volume 76, number 1 CHELIICAL PHYSICS LETTERS I.5 November 1980 1 COW Received 11 August 1980 Subsequenttoe\\cmn_e1.~ b>--nCO 1 laser pulse,U~oiesccnceh~beenderccted,rom 1v3 of
Apkarian, V. Ara
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
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
The extinction limits of diffusion flames have been measured experimentally and computed numerically for fuels of three different molecular structures pertinent to surrogate fuel formulation: n-alkanes, alkyl benzenes, and iso-octane. The focus of this study is to isolate the thermal and mass transport effects from chemical kinetic contributions to diffusion flame extinction, allowing for a universal correlation of extinction limit
Sang Hee Won; Stephen Dooley; Frederick L. Dryer; Yiguang Ju
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
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
The theory of absorbance measurements on a system (e.g., chromophore(s) in a protein) that undergoes a sequence of reactions initiated by a linearly polarized light pulse is developed for excitation pulses of arbitrary intensity. This formalism is based on a set of master equations describing the time evolution of the orientational distribution function of the various species resulting from excitation, reorientational dynamics, and chemical kinetics. For intense but short excitation pulses, the changes in absorbance (for arbitrary polarization directions of the excitation and probe pulses) and the absorption anisotropy are expressed in terms of reorientational correlation functions. The influence of the internal motions of the chromophore as well as the overall motions of the molecules is considered. When the duration of the excitation pulse is long compared to the time-scale of internal motions but comparable to the overall correlation time of the molecule that is reorienting isotropically, the problem of calculating the changes in absorbance is reduced to the solution of a set of first-order coupled differential equations. Emphasis is placed on obtaining explicit results for quantities that are measured in photolysis and fluorescence experiments so as to facilitate the analysis of experimental data. PMID:8471729
Ansari, A; Szabo, A
First principle chemical kinetics in zeolites: the methanol-to-olefin process as a case study.
To optimally design next generation catalysts a thorough understanding of the chemical phenomena at the molecular scale is a prerequisite. Apart from qualitative knowledge on the reaction mechanism, it is also essential to be able to predict accurate rate constants. Molecular modeling has become a ubiquitous tool within the field of heterogeneous catalysis. Herein, we review current computational procedures to determine chemical kinetics from first principles, thus by using no experimental input and by modeling the catalyst and reacting species at the molecular level. Therefore, we use the methanol-to-olefin (MTO) process as a case study to illustrate the various theoretical concepts. This process is a showcase example where rational design of the catalyst was for a long time performed on the basis of trial and error, due to insufficient knowledge of the mechanism. For theoreticians the MTO process is particularly challenging as the catalyst has an inherent supramolecular nature, for which not only the Br�nsted acidic site is important but also organic species, trapped in the zeolite pores, must be essentially present during active catalyst operation. All these aspects give rise to specific challenges for theoretical modeling. It is shown that present computational techniques have matured to a level where accurate enthalpy barriers and rate constants can be predicted for reactions occurring at a single active site. The comparison with experimental data such as apparent kinetic data for well-defined elementary reactions has become feasible as current computational techniques also allow predicting adsorption enthalpies with reasonable accuracy. Real catalysts are truly heterogeneous in a space- and time-like manner. Future theory developments should focus on extending our view towards phenomena occurring at longer length and time scales and integrating information from various scales towards a unified understanding of the catalyst. Within this respect molecular dynamics methods complemented with additional techniques to simulate rare events are now gradually making their entrance within zeolite catalysis. Recent applications have already given a flavor of the benefit of such techniques to simulate chemical reactions in complex molecular environments. PMID:25054453
Van Speybroeck, Veronique; De Wispelaere, Kristof; Van der Mynsbrugge, Jeroen; Vandichel, Matthias; Hemelsoet, Karen; Waroquier, Michel
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
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.
Postcolumn derivatization reactions can enhance detector sensitivity and selectivity, but their successful combination with capillary liquid chromatography has been limited because of the small peak volumes in capillary chromatography. A capillary Taylor reactor (CTR), developed in our laboratory, provides simple and effective mixing and reaction in a 25-?m-radius postcolumn capillary. Homogenization of reactant streams occurs by radial diffusion, and a chemical reaction follows. Three characteristic times for a given reaction process can be predicted using simple physical and chemical parameters. Two of these times are the homogenization time, which governs how long it takes the molecules in the analyte and reagent streams to mix, and the reaction time, which governs how long the molecules in a homogeneous solution take to react. The third characteristic time is an adjustment to the reaction time called the start time, which represents an estimate of the average time the analyte stream spends without exposure to reagent. In this study, laser-induced fluorescence monitored the extent of the postcolumn reaction (reduction of Os(bpy)33+ by analyte to the photoluminescent Os(bpy)32+) in a CTR. The reaction time depends on the reaction rates. Analysis of product versus time data yielded second-order reaction rate constants between the PFET reagent, tris(2,2?-bipyridine)osmium, and standards ((ferrocenylmethyl)trimethylammonium cation and p-hydroquinone) or catechols (dopamine, epinephrine, norepinephrine, 3, 4-dihydroxyphenylacetic acid. The extent of the reactions in a CTR were then predicted from initial reaction conditions and compared to experimental results. Both the theory and experimental results suggested the reactions of catechols were generally kinetically controlled, while those of the standards were controlled by mixing time (1�2 s). Thus, the extent of homogenization can be monitored in a CTR using the relatively fast reaction of the reagent and p-hydroquinone. Kinetically controlled reactions of catechols, however, could be also completed in a reasonable time at increased reagent concentration. A satisfactory reactor, operating at 1.7 cm/s (2 ?L/min) velocity with solutes having diffusion coefficients in the 5 � 10?6 cm2/s range, can be constructed from 8.0 cm of 25-?m-radius capillary. Slower reactions require longer reaction times, but theoretical calculations expect that a CTR does not broaden a chromatographic peak (N = 14 000) from a 100-?m-capillary chromatography column by 10% if the pseudo-first-order rate constant is larger than 0.1 s?1. PMID:15858975
Jung, Moon Chul; Weber, Stephen G.
Effects of chemical kinetics of the performance of the atomic iodine laser system
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.
NASA Astrophysics Data System (ADS)
We investigate the chemical evolution model explaining the chemical composition and the star formation histories (SFHs) simultaneously for the dwarf spheroidal galaxies (dSphs). Recently, wide imaging photometry and multi-object spectroscopy give us a large number of data. Therefore, we start to develop the chemical evolution model based on an SFH given by photometric observations and estimates a metallicity distribution function (MDF) comparing with spectroscopic observations. With this new model we calculate the chemical evolution for 4 dSphs (Fornax, Sculptor, Leo II, Sextans), and then we found that the model of 0.1 Gyr for the delay time of type Ia SNe is too short to explain the observed [alpha /Fe] vs. [Fe/H] diagrams.
Homma, H.; Murayama, T.
A novel circulating jet loop bioreactor adapted for organic matter oxidation has been designed and constructed. In this study, the input was leachate samples collected from Kemerburgaz Odayeri waste landfill site located on the European side of Istanbul. Controlling the jet loop bioreactor to realize high rates of purification depends on maintaining the appropriate loadings and operating conditions. This requires collecting various system data to estimate the dynamics of the system satisfactorily with the aim of keeping certain parameters within the specified range. The differential transform method (DTM) based solution of the state equations reveals the current state of the process so that any deviation in the system parameters can be immediately detected and regulated accordingly. The respirometric method for kinetic parameter calculations for biodegradation has been used for some time. In many studies, the respirometer was designed separately, usually in bench-scale. However, when a separate respirometer is used, the scale effect and parameters that affect the hydrodynamic structure of the system should be taken into consideration. In this study, therefore, the jet loop reactor itself was used as a respirometer. Thus, the kinetic parameters found reflecting the characteristics of microorganisms used for biodegradation would be more realistic. If the main reactor, here the jet loop reactor, would be used as the respirometer, the kinetic parameter changes can easily be monitored in the long run. Using the bioreactor as a respirometer, the most important kinetic parameters, Ks, kd and micromax were found to be 11,000 mg L(-1), 0.019 day(-1), and 0.21 day(-1), respectively. The stoichiometric coefficient, Y, was found to be 0.28 gr gr(-1) for the present system. PMID:17997217
Ince, M; Yildiz, F; Engin, G Onkal; Engin, S N; Keskinler, B
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
Ab initio chemical kinetics of methyl formate decomposition: the simplest model biodiesel.
The energetics and kinetics of methyl formate decomposition have been investigated by high-level ab initio calculations with rate constant predictions. The paucity of reliable experimental data for methyl formate has been circumvented by studying a very similar system, namely, the decarboxylation of acetic acid, in order to help validate the theoretical calculations. Our study shows that methyl formate decomposes to methanol and carbon monoxide, almost exclusively, with a high pressure limit rate constant of k(1)(infinity) = 2.128 x 10(12)T(0.735) exp(-34,535/T) s(-1), and the decomposition of acetic acid to methane and carbon dioxide proceeds with a rate constant, k(4)(infinity), of 1.668 x 10(10)T(1.079) exp -35,541/T s(-1). Experimental values for the formation enthalpy of methyl formate are discussed, and it is shown that these can be reconciled with our computed value for DeltaH(f) (298.15 K) of -360.1 +/- 2.2 kJ mol(-1). In turn, bond dissociation energies for all single bonds in the molecule are presented. PMID:20380414
Metcalfe, Wayne K; Simmie, John M; Curran, Henry J
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
NASA Astrophysics Data System (ADS)
Some of the most difficult chemical systems, either to observe or produce in significant quantities, are polynitrogen molecules. One example of this type of molecules in the early stages of investigation is cyclic-N3, whose molecular geometry and promising technological applications have attracted our attention to define optimal experimental conditions for being photoproduced. High-resolution synchrotron-radiation-based Photoionization Mass Spectrometry (PIMS) was applied to study the dissociative photoionization of three azide precursors for cyclic-N3; chlorine azide (ClN3), hydrogen azide (HN3), and methyl azide (CH3N3). In our attempts to detect cyclic-N3, the thermochemistry derived in the PIMS studies stimulated our work to perform photodissociation dynamics experiments of CH3N3 at 193 nm using Photofragment Translational Spectroscopy (PTS) with electron impact (EI) detection under collision-free conditions, and chemical kinetic studies based on Infrared Spectroscopy (IR) in matrix-isolated ices formed from rare gases (Argon, Nitrogen and Xenon). PTS experiments lead us to derive the branching ratio between reactions CH 3+N3 (radical channel) vs CH3N+N2 (molecular channel), and to conclude that cyclic-N3 is the dominant product in the radical channel. In contrast, in the matrix isolation experiments we found no evidence of the radical channel, possibly due to barrier-less recombination. However, since no mechanistic reports of methyl azide dissociation exist at these conditions, these studies could have significant implications for future experiments addressed to detect cylic-N3 under matrix environments.
Quinto Hernandez, Alfredo
Autoignition of toluene reference fuels at high pressures modeled with detailed chemical kinetics
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 for a mixture consisting of 35% n-heptane and 65% toluene by liquid volume. Important features of the autoignition of the mixture proved to be cross-acceleration effects, where hydroperoxy radicals produced during n-heptane oxidation dramatically increased the oxidation rate of toluene compared to the case when toluene alone was oxidized. Rate constants for the reaction of benzyl and hydroperoxyl radicals previously used in the modeling of the oxidation of toluene alone were untenably high for modeling of the mixture. To model both systems it was found necessary to use a lower rate and introduce an additional branching route in the reaction between benzyl radicals and O{sub 2}. Good agreement between experiments and predictions was found when the model was validated against shock tube autoignition delay data for gasoline surrogate fuels consisting of mixtures of 63-69% isooctane, 14-20% toluene, and 17% n-heptane by liquid volume. Cross reactions such as hydrogen abstractions between toluene and alkyl and alkylperoxy radicals and between the PRF were introduced for completion of chemical description. They were only of small importance for modeling autoignition delays from shock tube experiments, even at low temperatures. A single-zone engine model was used to evaluate how well the validated mechanism could capture autoignition behavior of toluene reference fuels in a homogeneous charge compression ignition (HCCI) engine. The model could qualitatively predict the experiments, except in the case with boosted intake pressure, where the initial temperature had to be increased significantly in order to predict the point of autoignition. (author)
Andrae, J.C.G. [Department of Chemical Engineering and Technology, Royal Institute of Technology, SE-100 44 Stockholm (Sweden); Shell Global Solutions, P.O. Box 1, Chester CH1 3SH (United Kingdom); Bjoernbom, P. [Department of Chemical Engineering and Technology, Royal Institute of Technology, SE-100 44 Stockholm (Sweden); Cracknell, R.F.; Kalghatgi, G.T. [Shell Global Solutions, P.O. Box 1, Chester CH1 3SH (United Kingdom)
A Simple Model for Calculating the Kinetics of Protein Folding from Three-Dimensional Structures
An elementary statistical mechanical model was used to calculate the folding rates for 22 proteins from their known three-dimensional structures. In this model, residues come into contact only after all of the intervening chain is in the native conformation. An additional simplifying assumption is that native structure grows from localized regions that then fuse to form the complete native molecule.
Victor Munoz; William A. Eaton
Chemical accuracy in QM/MM calculations on enzyme-catalysed reactions
Combined quantum mechanics/molecular mechanics (QM/MM) modelling has the potential to answer fundamental questions about enzyme mechanisms and catalysis. Calculations using QM/MM methods can now predict barriers for enzyme-catalysed reactions with unprecedented, near chemical accuracy, i.e. to within 1 kcal/mol in the best cases. Quantitative predictions from first-principles calculations were only previously possible for very small molecules. At this level, quantitative, reliable predictions can be made about the mechanisms of enzyme-catalysed reactions. This development signals a new era of computational biochemistry. PMID:17880750
Mulholland, Adrian J
Quantum-chemical calculations on a novel reaction mechanism of CNN with NO
NASA Astrophysics Data System (ADS)
Quantum-chemical calculations of the possible interaction between CNN and NO have been performed at the CCSD(T)/aug-cc-PVTZ//B3LYP/6-31++G(d,p) level of theory. Fourteen conformers corresponding to local minima of potential energy and sixteen transition structures are located, and various possible reaction paths are probed. Products P3 - NCO + N 2 - and P4 - N 2O + CN - were the two leading channels with slight energy barriers as compared to the reactants CNN + NO. Employing the Fukui functions and HSAB theory, we are able to rationalize the calculated outcomes.
Chen, Hui-Lung; Li, Han-Jung; Ho, Jia-Jen
CFD analysis of municipal solid waste combustion using detailed chemical kinetic modelling.
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
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
A path flux analysis method for the reduction of detailed chemical kinetic mechanisms
A direct path flux analysis (PFA) method for kinetic mechanism reduction is proposed and validated by using high temperature ignition, perfect stirred reactors, and steady and unsteady flame propagations of n-heptane and n-decane/air mixtures. The formation and consumption fluxes of each species at multiple reaction path generations are analyzed and used to identify the important reaction pathways and the associated species. The formation and consumption path fluxes used in this method retain flux conservation information and are used to define the path indexes for the first and the second generation reaction paths related to a targeted species. Based on the indexes of each reaction path for the first and second generations, different sized reduced chemical mechanisms which contain different number of species are generated. The reduced mechanisms of n-heptane and n-decane obtained by using the present method are compared to those generated by the direct relation graph (DRG) method. The reaction path analysis for n-decane is conducted to demonstrate the validity of the present method. The comparisons of the ignition delay times, flame propagation speeds, flame structures, and unsteady spherical flame propagation processes showed that with either the same or significantly less number of species, the reduced mechanisms generated by the present PFA are more accurate than that of DRG in a broad range of initial pressures and temperatures. The method is also integrated with the dynamic multi-timescale method and a further increase of computation efficiency is achieved. (author)
Sun, Wenting; Ju, Yiguang [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544 (United States); Chen, Zheng [State Key Laboratory for Turbulence and Complex Systems, College of Engineering, Peking University, Beijing 100871 (China); Gou, Xiaolong [School of Power Engineering, Chongqing University, Chongqing 400044 (China)
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.
Markov state models (MSMs) have been successful in computing metastable states, slow relaxation timescales and associated structural changes, and stationary or kinetic experimental observables of complex molecules from large amounts of molecular dynamics simulation data. However, MSMs approximate the true dynamics by assuming a Markov chain on a clusters discretization of the state space. This approximation is difficult to make for high-dimensional biomolecular systems, and the quality and reproducibility of MSMs has, therefore, been limited. Here, we discard the assumption that dynamics are Markovian on the discrete clusters. Instead, we only assume that the full phase-space molecular dynamics is Markovian, and a projection of this full dynamics is observed on the discrete states, leading to the concept of Projected Markov Models (PMMs). Robust estimation methods for PMMs are not yet available, but we derive a practically feasible approximation via Hidden Markov Models (HMMs). It is shown how various molecular observables of interest that are often computed from MSMs can be computed from HMMs/PMMs. The new framework is applicable to both, simulation and single-molecule experimental data. We demonstrate its versatility by applications to educative model systems, a 1 ms Anton MD simulation of the bovine pancreatic trypsin inhibitor protein, and an optical tweezer force probe trajectory of an RNA hairpin. PMID:24320261
No�, Frank; Wu, Hao; Prinz, Jan-Hendrik; Plattner, Nuria
.��?A new method for an increased numerical efficiency of ab initio calculations is proposed. It is based on the assumption that\\u000a in most cases chemical properties of functional groups in molecules are mainly controlled by a few electrons. This statement\\u000a allows one to distinguish between two classes of nuclei and electrons: active and inactive ones. The effective group potential\\u000a (EGP)
Fabienne Alary; Romuald Poteau; Jean-Louis Heully; Jean-Claude Barthelat; Jean-Pierre Daudey
SIML: A Fast SIMD Algorithm for Calculating LINGO Chemical Similarities on GPUs and CPUs
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
In the study of the role of allyl type radicals in the pyrolysis of hydrocarbons it is of interest to investigate the conditions of formation, structure, and reactivity of 2-methylallyl radical (C/sub 4/H/sub 7//sup ./). The authors performed theoretical assignment of the bands, which were observed in the lattice spectra of the pyrolysis products, to the vibrations of the C/sub 4/H/sub 7//sup ./ radical by means of calculation of the frequencies and shapes of the normal vibrations. Since the necessary geometrical parameters and force coefficients of C/sub 4/H/sub 7//sup ./ are not known, they determined them by means of nonempirical quantum chemical calculation. The quantum chemical calculation of C/sub 4/H/sub 7//sup ./ was performed by means of the unrestricted Hartree-Fock method using STO-4G (geometry optimization taking into account the characteristics of calculation of radicals in minimal bases and calculation of the force coefficients by means of numerical differentiation) and 4-31G bases (electron density distribution) by means of GAUSSIAN-70 program. For comparison of the energy and electron density distribution they performed calculations also for the 2-methylallyl cation C/sub 4/H/sub 7//sup ./. From the calculation of the difference of the total energies of C/sub 4/H/sub 7//sup ./ and C/sub 4/H/sub 7//sup ./ in the 4-31G basis was 7.4 eV, which is comparable to the ionization energy of the 2-methylallyl radical, 7.95 eV.
Avakyan, V.G.; Volkova, V.V.; Gusel'nikov, L.E.; Ziegler, U.; Zimmermann, G.; Ondurshka, B.; Nametkin, N.S.
-flux correlation function for calculating the thermal rate constants of chemical reactions in solutionA combined quantum-classical dynamics method for calculating thermal rate constants of chemical reactions in solution Thanh N. Truong,") J. Andrew McCammon, and Donald J. Kouri Department of Chemistry
Truong, Thanh N.
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.
Effect of kinetics on the nucleation of thin InAs films on InP by chemical beam epitaxy
The authors present a study on the nucleation of thin InAs films on InP by Chemical Beam Epitaxy. Analysis by Atomic Force microscopy shows that the islanding process is kinetically-controlled; the onset of this process and the island shape are also dependent on the misorientation of the substrate. The island distribution along step edges prior to vertical growth indicates the existence of a step edge barrier altering the diffusion dynamics on the surface.
Cotta, M.A.; Mendonca, C.A.C. de; Ito-Landers, K.M.; Carvalho, M.M.G. de [UNICAMP, Campinas, Sao Paulo (Brazil); Martins, R.B. [Centro de Pesquisa e Desenvolvimento Telebras, Campinas, Sao Paulo (Brazil)
A simple method for the preparation of the biocatalyst with whole cells is presented, and the applicability of the technique\\u000a for biodegradation of phenol in wastewater from the chemical industries using the basidomycetes yeast Trichosporon cutaneum is explored. Kinetic studies of the influence of other compounds contained in wastewater as naphthalene, benzene, toluene\\u000a and pyridine indicate that apart from oil
Lyubov Yotova; Irene Tzibranska; Filadia Tileva; G. H. Markx; Nelly Georgieva
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
DFT calculations of 1H and 13C NMR chemical shifts in transition metal hydrides.
Transition metal hydrides are of great interest in chemistry because of their reactivity and their potential use as catalysts for hydrogenation. Among other available techniques, structural properties in transition metal (TM) complexes are often probed by NMR spectroscopy. In this paper we will show that it is possible to establish a viable methodological strategy in the context of density functional theory, that allows the determination of 1H NMR chemical shifts of hydride ligands attached to transition metal atoms in mononuclear systems and clusters with good accuracy with respect to experiment. 13C chemical shifts have also been considered in some cases. We have studied mononuclear ruthenium complexes such as Ru(L)(H)(dppm)2 with L = H or Cl, cationic complex [Ru(H)(H2O)(dppm)2]+ and Ru(H)2(dppm)(PPh3)2, in which hydride ligands are characterized by a negative 1H NMR chemical shift. For these complexes all calculations are in relatively good agreement compared to experimental data with errors not exceeding 20% except for the hydrogen atom in Ru(H)2(dppm)(PPh3)2. For this last complex, the relative error increases to 30%, probably owing to the necessity to take into account dynamical effects of phenyl groups. Carbonyl ligands are often encountered in coordination chemistry. Specific issues arise when calculating 1H or 13C NMR chemical shifts in TM carbonyl complexes. Indeed, while errors of 10 to 20% with respect to experiment are often considered good in the framework of density functional theory, this difference in the case of mononuclear carbonyl complexes culminates to 80%: results obtained with all-electron calculations are overall in very satisfactory agreement with experiment, the error in this case does not exceed 11% contrary to effective core potentials (ECPs) calculations which yield errors always larger than 20%. We conclude that for carbonyl groups the use of ECPs is not recommended, although their use could save time for very large systems, for instance in cluster chemistry. The reliance of NMR chemical shielding on dynamical effects, such as intramolecular rearrangements or trigonal twists, is also examined for H2Fe(CO)4, K+[HFe(CO)](-), HMn(CO)5 and HRe(CO)5. The accuracy of the theory is also examined for complexes with two dihydrogen ligands (Tp*RuH(H2)2 and [FeH(H2)(DMPE)2]+) and a ruthenium cluster, [H3Ru4(C6H6)4(CO)]+. It is shown that for all complexes studied in this work, the effect of the ligands on the chemical shielding of hydrogen coordinated to metal is suitably calculated, thus yielding a very good correlation between experimental chemical shifts and theoretical chemical shielding. PMID:18648699
del Rosal, I; Maron, L; Poteau, R; Jolibois, F
NASA Astrophysics Data System (ADS)
We study the effects of atomic vibrations on the solid-state chemical shielding tensor using first principles density functional theory calculations. At the harmonic level, we use a Monte Carlo method and a perturbative expansion. The Monte Carlo method is accurate but computationally expensive, while the perturbative method is computationally more efficient, but approximate. We find excellent agreement between the two methods for both the isotropic shift and the shielding anisotropy. The effects of zero-point quantum mechanical nuclear motion are important up to relatively high temperatures: at 500 K they still represent about half of the overall vibrational contribution. We also investigate the effects of anharmonic vibrations, finding that their contribution to the zero-point correction to the chemical shielding tensor is small. We exemplify these ideas using magnesium oxide and the molecular crystals L-alanine and ?-aspartyl-L-alanine. We therefore propose as the method of choice to incorporate the effects of temperature in solid state chemical shielding tensor calculations using the perturbative expansion within the harmonic approximation. This approach is accurate and requires a computational effort that is about an order of magnitude smaller than that of dynamical or Monte Carlo approaches, so these effects might be routinely accounted for.
Monserrat, Bartomeu; Needs, Richard J.; Pickard, Chris J.
We study the effects of atomic vibrations on the solid-state chemical shielding tensor using first principles density functional theory calculations. At the harmonic level, we use a Monte Carlo method and a perturbative expansion. The Monte Carlo method is accurate but computationally expensive, while the perturbative method is computationally more efficient, but approximate. We find excellent agreement between the two methods for both the isotropic shift and the shielding anisotropy. The effects of zero-point quantum mechanical nuclear motion are important up to relatively high temperatures: at 500 K they still represent about half of the overall vibrational contribution. We also investigate the effects of anharmonic vibrations, finding that their contribution to the zero-point correction to the chemical shielding tensor is small. We exemplify these ideas using magnesium oxide and the molecular crystals L-alanine and ?-aspartyl-L-alanine. We therefore propose as the method of choice to incorporate the effects of temperature in solid state chemical shielding tensor calculations using the perturbative expansion within the harmonic approximation. This approach is accurate and requires a computational effort that is about an order of magnitude smaller than that of dynamical or Monte Carlo approaches, so these effects might be routinely accounted for. PMID:25296790
Monserrat, Bartomeu; Needs, Richard J; Pickard, Chris J
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.
A study of the accuracy of moment-closure approximations for stochastic chemical kinetics.
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. PMID:22519313
Grima, Ramon
Calculation of the mixing chamber of an ejector chemical oxygen - iodine laser
Gas parameters are calculated at the outlet of the mixing chamber of an ejector chemical oxygen-iodine laser with a nozzle unit consisting of nozzles of three types, which provides a total pressure of the active medium that substantially exceeds a pressure in the generator of singlet oxygen. This technique of forming the laser active medium substantially facilitates the ejection of the exhaust gas to the atmosphere by using a diffuser and single-stage vacuum systems based on water circulating pumps. (lasers, active media)
Zagidullin, M V; Nikolaev, V D [Samara Branch of the P.N. Lebedev Physics Institute, Russian Academy of Sciences, Samara (Russian Federation)
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 Ag?Se 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
NASA Astrophysics Data System (ADS)
The vibrational spectra of pentafluoroethyliminosulfur difluoride, CF 3CF 2N dbnd SF 2, were recorded in the gas phase with IR spectroscopy and in the liquid state with Raman spectroscopy. Quantum chemical calculations at the B3LYP (6-311+G(d) and 6-311+G(2df) basis sets) and MP2 levels of theory (6-31+G(d) and 6-311G(d) basis sets) were performed. According to all calculations the lowest energy conformer possesses C1 symmetry with syn orientation of the SF 2 group relative to the C sbnd N bond and near- trans orientation of the CF 3 group relative to the N dbnd S bond ( syn- trans). Calculations predict the hypothetical presence of a second stable conformer with anti-orientation of the SF 2 group ( anti- trans) which, however, possesses considerably higher energy and is therefore not observed in the analysis of the experimental spectra. The vibrational spectra were assigned for a single conformer in agreement with these calculations.
Robles, Norma L.; Cutin, Edgardo H.; Mews, R�diger; Della V�dova, Carlos O.
Basics of Chemical Kinetics -1 Rate of reaction = rate of disappearance of A =
Kinetics - 4 Reaction Stoichiometry + Law of Conservation of Mass rA -a rB -b rC c rD d = = = (Irrespective Michaelis-Menten model of enzymatic reactions #12;Michaelis-Menten kinetics Mass conservation: Assumption/volume) ; 1 mole = 6.023x1023 molecules rA = -k [A] rA = -k [A]2 rA = -k1 [A]/(1+k2[A]) Reaction rate law
Albert, Réka
HCCI experiments with gasoline surrogate fuels modeled by a semidetailed chemical kinetic model
Experiments in a homogeneous charge compression ignition (HCCI) engine have been conducted with four gasoline surrogate fuel blends. The pure components in the surrogate fuels consisted of n-heptane, isooctane, toluene, ethanol and diisobutylene and fuel sensitivities (RON-MON) in the fuel blends ranged from two to nine. The operating conditions for the engine were p{sub in}=0.1 and 0.2 MPa, T{sub in}=80 and 250 C, {phi}=0.25 in air and engine speed 1200 rpm. A semidetailed chemical kinetic model (142 species and 672 reactions) for gasoline surrogate fuels, validated against ignition data from experiments conducted in shock tubes for gasoline surrogate fuel blends at 1.0{<=} p{<=}5.0MPa, 700{<=} T{<=}1200 K and {phi}=1.0, was successfully used to qualitatively predict the HCCI experiments using a single zone modeling approach. The fuel blends that had higher fuel sensitivity were more resistant to autoignition for low intake temperature and high intake pressure and less resistant to autoignition for high intake temperature and low intake pressure. A sensitivity analysis shows that at high intake temperature the chemistry of the fuels ethanol, toluene and diisobutylene helps to advance ignition. This is consistent with the trend that fuels with the least Negative Temperature Coefficient (NTC) behavior show the highest octane sensitivity, and become less resistant to autoignition at high intake temperatures. For high intake pressure the sensitivity analysis shows that fuels in the fuel blend with no NTC behavior consume OH radicals and acts as a radical scavenger for the fuels with NTC behavior. This is consistent with the observed trend of an increase in RON and fuel sensitivity. With data from shock tube experiments in the literature and HCCI modeling in this work, a correlation between the reciprocal pressure exponent on the ignition delay to the fuel sensitivity and volume percentage of single-stage ignition fuel in the fuel blend was found. Higher fuel sensitivity and single-stage fuel content generally gives a lower value of the pressure exponent. This helps to explain the results obtained while boosting the intake pressure in the HCCI engine. (author)
Andrae, J.C.G. [Dept. of Chemical Engineering and Technology, Royal Institute of Technology (KTH), SE-100 44 Stockholm (Sweden); Head, R.A. [Shell Technology Centre Thornton, P.O. Box 1, Chester CH1 3SH (United Kingdom)
NASA Astrophysics Data System (ADS)
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.
Donovan, Rory M.; Sedgewick, Andrew J.; Faeder, James R.; Zuckerman, Daniel M.
Combining quantum-chemical calculations and ultrahigh-field NMR measurements of (29)Si chemical shielding (CS) tensors has provided a powerful approach for probing the fine details of zeolite crystal structures. In previous work, the quantum-chemical calculations have been performed on 'molecular fragments' extracted from the zeolite crystal structure using Hartree-Fock methods (as implemented in Gaussian). Using recently acquired ultrahigh-field (29) Si NMR data for the pure silica zeolite ITQ-4, we report the results of calculations using recently developed quantum-chemical calculation methods for periodic crystalline solids (as implemented in CAmbridge Serial Total Energy Package (CASTEP) and compare these calculations to those calculated with Gaussian. Furthermore, in the context of NMR crystallography of zeolites, we report the completion of the NMR crystallography of the zeolite ITQ-4, which was previously solved from NMR data. We compare three options for the 'refinement' of zeolite crystal structures from 'NMR-solved' structures: (i) a simple target-distance based geometry optimization, (ii) refinement of atomic coordinates in which the differences between experimental and calculated (29)Si CS tensors are minimized, and (iii) refinement of atomic coordinates to minimize the total energy of the lattice using CASTEP quantum-chemical calculations. All three refinement approaches give structures that are in remarkably good agreement with the single-crystal X-ray diffraction structure of ITQ-4. PMID:20623826
Brouwer, Darren H; Moudrakovski, Igor L; Darton, Richard J; Morris, Russell E
The calculation of molecular electric moments, polarizabilities, and electrostatic potentials is a widespread application of quantum chemistry. Although a range of wave function and density functional theory (DFT) methods have been applied in these calculations, combined with a variety of basis sets, there has not been a comprehensive evaluation of how accurate these methods are. To benchmark the accuracy of these methods, the dipole moments and polarizabilities of a set of 46 molecules were calculated using a broad set of quantum chemical methods and basis sets. Wave function methods Hartree-Fock (HF), second-order M�ller-Plesset (MP2), and coupled cluster-singles and doubles (CCSD) were evaluated, along with the PBE, TPSS, TPSSh, PBE0, B3LYP, M06, and B2PLYP DFT functionals. The cc-pVDZ, cc-pVTZ, aug-cc-pVDZ, aug-cc-pVTZ, and Sadlej cc-pVTZ basis sets were tested. The aug-cc-pVDZ, Sadlej cc-pVTZ, and aug-cc-pVTZ basis sets all yield results with comparable accuracy, with the aug-cc-pVTZ calculations being the most accurate. CCSD, MP2, or hybrid DFT methods using the aug-cc-pVTZ basis set are all able to predict dipole moments with RMSD errors in the 0.12-0.13 D range and polarizabilities with RMSD errors in the 0.30-0.38 �(3) range. Calculations using Hartree-Fock theory systematically overestimated dipole moments and underestimate polarizabilities. The pure DFT functionals included in this study (PBE and TPSS) slightly underestimate dipole moments and overestimate polarizability. Polarization anisotropy and implications for charge fitting are discussed. PMID:24796376
Hickey, A Leif; Rowley, Christopher N
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.
Calculation of the equation of state of QCD at finite chemical and zero temperature
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)
NASA Astrophysics Data System (ADS)
Simplification of chemical kinetics description through dimensional reduction is particularly important to achieve an accurate numerical treatment of complex reacting systems, especially when stiff kinetics are considered and a comprehensive picture of the evolving system is required. To this aim several tools have been proposed in the past decades, such as sensitivity analysis, lumping approaches, and exploitation of time scales separation. In addition, there are methods based on the existence of the so-called slow manifolds, which are hyper-surfaces of lower dimension than the one of the whole phase-space and in whose neighborhood the slow evolution occurs after an initial fast transient. On the other hand, all tools contain to some extent a degree of subjectivity which seems to be irremovable. With reference to macroscopic and spatially homogeneous reacting systems under isothermal conditions, in this work we shall adopt a phenomenological approach to let self-emerge the dimensional reduction from the mathematical structure of the evolution law. By transforming the original system of polynomial differential equations, which describes the chemical evolution, into a universal quadratic format, and making a direct inspection of the high-order time-derivatives of the new dynamic variables, we then formulate a conjecture which leads to the concept of an ``attractiveness'' region in the phase-space where a well-defined state-dependent rate function ? has the simple evolution ??=-?2 along any trajectory up to the stationary state. This constitutes, by itself, a drastic dimensional reduction from a system of N-dimensional equations (being N the number of chemical species) to a one-dimensional and universal evolution law for such a characteristic rate. Step-by-step numerical inspections on model kinetic schemes are presented. In the companion paper [P. Nicolini and D. Frezzato, J. Chem. Phys. 138, 234102 (2013)] this outcome will be naturally related to the appearance (and hence, to the definition) of the slow manifolds.
Nicolini, Paolo; Frezzato, Diego
NASA Astrophysics Data System (ADS)
An algorithm proposed by Chen ( Combust. Sci. Technol.57,89 (1988)) for the construction of reduced chemical kinetic mechanisms is reviewed. It is shown that the algorithm can be formally used only with the steady state approximation. A new algorithm is presented which can accept more general assumptions. However, for the new algorithm to be successful these assumptions must meet a certain condition which is presented. The reduced mechanisms generated by both algorithms do not provide optimum accuracy and stability in numerical simulations. This can be achieved by a specific refinement of these reduced mechanisms according to the CSP method.
Goussis, D. A.
A catalyst is an agent that modifies the kinetics of a chemical reaction, making it occur faster, but is not itself consumed as part of the reaction. Catalysts are essential for commercial production of a number of economically important commodity and specialty chemicals. For transition metals, oxidation states are related
Kinetic roughening during hot-wire chemical vapor deposition of hydrogenated amorphous silicon
NASA Astrophysics Data System (ADS)
Despite the widespread use of hydrogenated amorphous silicon (a-Si:H), the fundamental surface processes during film growth are not well understood. One approach to studying these mechanisms is to analyze the surface morphology that results from their action. In this dissertation, hot-wire chemical vapor deposition is used to deposit a-Si:H thin films. Both post-deposition atomic force microscopy (AFM) and in situ spectroscopic ellipsometry (SE) are used to characterize the surface morphology and its dynamics. Results of this work indicate that the surface morphology is shaped by geometric shadowing of growth particles and thermally-activated smoothening mechanisms. For films grown at low temperature, the local slope of the surface is found to exhibit power law scaling with time that is consistent with anomalous roughening behavior also observed in models that include shadowing. A temperature-dependent transition in roughening behavior is observed, and an activation energy is extracted that agrees with previous estimates for SiH3 surface diffusion. Additionally, a-Si:H grown on rough substrates is examined. Smoothening at short lateral length scales is observed simultaneously with global roughening. Behavior is found to generally agree with deterministic models in the literature. This work also explores the difference between SE and AFM in how roughness is measured. Rayleigh-Rice theory (vector perturbation theory) is used to calculate ellipsometric data that is subsequently compared to the usual method of using an effective medium layer to approximate roughness. SE measurements are found to critically depend on both the vertical extent of roughness and the root-mean-squared slope of the surface.
Sperling, Brent Andrew
The promising chemical kinetics for the simulation of propane-air combustion with KIVA-II code
NASA Technical Reports Server (NTRS)
The development of chemical kinetics for the simulation of propane-air combustion with the use of computer code KIVA-II since 1989 is summarized here. In order to let readers understand the general feature well, a brief description of the KIVA-II code, specially related with the chemical reactions is also given. Then the results of recent work with 20 reaction mechanism is presented. It is also compared with the 5 reaction mechanism. It may be expected that the numerical stability of the 20 reaction mechanism is better as compared to that of 5 reaction mechanism, but the CPU time of the CRAY computer is much longer. Details are presented in the paper.
Ying, S. J.; Gorla, Rama S. R.; Kundu, Krishna P.
Recently proposed molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction-rate information) are investigated for chemical reactions occurring in upper-atmosphere hypersonic flows. The new models are in good agreement with the measured Arrhenius rates for near-equilibrium conditions and with both measured rates and other theoretical models for far-from-equilibrium conditions. Additionally, the new models are applied to representative combustion and ionization reactions and are in good agreement with available measurements and theoretical models. Thus, molecular-level chemistry modeling provides an accurate method for predicting equilibrium and nonequilibrium chemical-reaction rates in gases. PMID:19791885
Gallis, Michael A; Bond, Ryan B; Torczynski, John R
A Rule-Based Approach for Automated Generation of Kinetic Chemical Mechanisms
Several software systems have been developed recently for the automated generation of combustion reactions kinetic mechanisms using different representations of species and reactions and different gen- eration algorithms. In parallel, several software systems based on rewrit- ing have been developed for the easy modeling and prototyping of sys- tems using rules controlled by strategies. This paper presents our current experience
Olivier Bournez; Guy-marie C�me; Val�rie Conraud; H�l�ne Kirchner; Liliana Ibanescu
The influence of enthalpy of mixing and elemental mechanical characteristics on the kinetics of mechanical alloying (MA) of 80 at.% Ni-20 at.% bcc transition metals (Fe, Cr, W, Nb, and Ta) has been studied. The features and structures of milled powders were characterized by X-ray diffraction, optical microscopy, and particle size analysis. Powder caking of the grinding media � in
A. N Streletskii; T. H Courtney
The organocatalytic kinetic resolution of 4-substituted oxazinones has been optimised (selectivity factor S up to 98, chiral oxazinone ee values up to 99.6?% (1?a-g) and product ee values up to 90?% (3?a-g)) in a rational way by applying the Design of Experiments (DoE) approach. PMID:25078283
Renzi, Polyssena; Kronig, Christel; Carlone, Armando; Er�ks�z, Serap; Berkessel, Albrecht; Bella, Marco
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
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.
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
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.
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.
Burnup calculations and chemical analysis of irradiated fuel samples studied in LWR-PROTEUS phase II
The isotopic compositions of 5 UO{sub 2} samples irradiated in a Swiss PWR power plant, which were investigated in the LWR-PROTEUS Phase II programme, were calculated using the CASMO-4 and BOXER assembly codes. The burnups of the samples range from 50 to 90 MWd/kg. The results for a large number of actinide and fission product nuclides were compared to those of chemical analyses performed using a combination of chromatographic separation and mass spectrometry. A good agreement of calculated and measured concentrations is found for many of the nuclides investigated with both codes. The concentrations of the Pu isotopes are mostly predicted within {+-}10%, the two codes giving quite different results, except for {sup 242}Pu. Relatively significant deviations are found for some isotopes of Cs and Sm, and large discrepancies are observed for Eu and Gd. The overall quality of the predictions by the two codes is comparable, and the deviations from the experimental data do not generally increase with burnup. (authors)
Grimm, P.; Guenther-Leopold, I. [Paul Scherrer Inst., CH-5232 Villigen PSI (Switzerland); Berger, H. D. [AREVA NP GmbH, FEEP, Bunsenstrasse 43, D-91058 Erlangen (Germany)
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.
The hydration of isoamylenes to produce 2-methyl-2-butanol (tert-amyl alcohol, or TAA) is strongly limited by chemical equilibrium to olefin conversions of less than 50%. The general goal of this work was to determine whether reactive distillation would be a valid method to enhance the yield of TAA. The first step was to study the reaction kinetics and chemical equilibrium, using a polymeric acid catalyst (Amberlyst-15). Acetone was identified as a suitable medium to enable single liquid phase operation and also to enhance the reaction rate. It was found that the intraparticle mass-transfer resistance is negligible at temperatures below 70 C. A kinetic expression, based on Langmuir-Hinshelwood formalism, is proposed. The forward and reverse reactions show first-order dependence on isoamylenes and TAA, respectively, while water is essentially an inhibitor of the reaction in both directions. The temperature effect on the forward reaction is quantified with an activation energy of 69.5 kJ/mol.
Gonzalez, J.C.; Fair, J.R. [Univ. of Texas, Austin, TX (United States). Separations Research Program] [Univ. of Texas, Austin, TX (United States). Separations Research Program
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.
This paper reports the removal of a basic dye (rhodamine-B) by the activated carbon prepared from Parthenium biomass by sulphuric acid treatment method (SWC). The effectiveness of the prepared adsorbent has been studied as a function of agitation time, adsorbent dosage, initial dye concentration and pH. The removal of rhodamine-B by SWC followed second order kinetic model. The second order
Hem Lata; V. K. Garg; R. K. Gupta
Novel trajectory based concepts for model and complexity reduction in (bio)chemical kinetics
Summary. Based on increasing availability of high-accuracy data from high- throughput experimental techniques, detailed kinetic models for complex reaction mechanisms come more and more into applications. They are for instance used in computer simulations aimed at optimization of technical process operation or for virtual experiments in a systems biology approach to cellular biochemistry. Since high-dimensional models from large-scale mechanisms are
Dirk Lebiedz; Volkmar Reinhardt; Julia Kammerer
The authors employed detailed numerical models with a one-step finite-rate chemical reaction to investigate the kinetic rate effect (through the variation of the pre-exponential factor) on concurrent flame spread rates over thin solids. It is found that flames in forced flow are less sensitive to the change of kinetics than flames in buoyant flow, and narrow samples are more sensitive
Sheng-Yen Hsu; James S. Tien
Multi-step, gas-phase chemical kinetics are introduced into flame spread modeling efforts. An unsteady multi-step, gas-phase kinetics model both with and without steady-state species assumptions, and including nonunit Lewis number, is compared with a model including a single, finite-rate gas-phase reaction, which has been the usual approach in flame spread modeling. Laminar diffusion flames over a thin fuel in an opposing
M. Katherine Wolverton; Robert A. Altenkirch; Lin Tang
Model calculations of kinetic isotope effects in the Menschutkin-type S\\/sub N\\/2 reaction of benzyl arenesulfonates with N,N-dimethyl-p-toluidine have been carried out by use of the program BEBOVIB-IV. Transition-state models encompassing the region of n� + n� less than or equal to 1.0 were considered, where n� and n� are the bond orders of the breaking C\\/sub ..cap alpha..\\/-O bond and
H. Yamataka; T. Ando
NASA Astrophysics Data System (ADS)
The sources of uncertainty associated with the calculation of rainfall kinetic energy and rainfall erosivity were investigated when the USLE R factor was operationally calculated for a mountainous river basin (504 km2) in the Southeastern Pyrenees. Rainfall kinetic energy was first obtained at the scale of the rainfall event by means of sub-hourly precipitation tipping-bucket rain gauge records and updates of the Kinnell (1981) equation. Annual erosivity values for the nearby pluviometric stations were then derived from the linear regressions between daily rainfall erosivity and daily precipitation, obtained for two different seasons. Finally, maps for rainfall erosivity estimates were obtained from the station values with Thiessen polygons. The sources of uncertainty analysed were i) the tipping-bucket instrumental errors, ii) the efficiency of the Kinnell (1981) equation, iii) the efficiency of the regressions between daily precipitation and kinetic energy, iv) the temporal variability of annual rainfall erosivity values, and the spatial variability of v) annual rainfall erosivity values and vi) long-term R factor values. The results showed that the uncertainty associated with the calculation of rainfall kinetic energy from rainfall intensity at the event and station scales is highly relevant and must be taken into account for experimental or modelling purposes; for longer temporal scales, the relevance of this source of uncertainty remains high if there is a low variability of the types of rain. Temporal variability of precipitation at wider spatial scales is the main source of uncertainty when rainfall erosivity is to be calculated on an annual basis, whereas the uncertainty associated with the long-term R factor is rather low and less important than the uncertainty associated with the other RUSLE factors when operationally used for long-term soil erosion modelling.
Catari, G.; Latron, J.; Gallart, F.
Nuclei-selected NMR shielding calculations: a sublinear-scaling quantum-chemical method.
An ab initio method for the direct calculation of NMR shieldings for selected nuclei at the Hartree-Fock and density-functional theory level is presented. Our method shows a computational effort scaling only sublinearly with molecular size, as it is motivated by the physical consideration that the chemical shielding is dominated by its local environment. The key feature of our method is to avoid the conventionally performed calculation of all NMR shieldings but instead to solve directly for specific nuclear shieldings. This has important implications not only for the study of large molecules, but also for the simulation of solvent effects and molecular dynamics, since often just a few shieldings are of interest. Our theory relies on two major aspects both necessary to provide a sublinear scaling behavior: First, an alternative expression for the shielding tensor is derived, which involves the response density matrix with respect to the nuclear magnetic moment instead of the response to the external magnetic field. Second, as unphysical long-range contributions occur within the description of distributed gauge origin methods that do not influence the final expectation value, we present a screening procedure to truncate the B-field dependent basis set, which is crucial in order to ensure an early onset of the sublinear scaling. The screening is in line with the r(-2) distance decay of Biot-Savarts law for induced magnetic fields. Our present truncation relies on the introduced concept of "individual gauge shielding contributions" applied to a reformulated shielding tensor, the latter consisting of gauge-invariant terms. The presented method is generally applicable and shows typical speed-ups of about one order of magnitude; moreover, due to the reduced scaling behavior of O(1) as compared to O(N), the wins become larger with increasing system size. We illustrate the validity of our method for several test systems, including ring-current dominated systems and biomolecules with more than 1000 atoms. PMID:21341823
Beer, Matthias; Kussmann, J�rg; Ochsenfeld, Christian
High temperature chemical kinetic study of the H2-CO-CO2-NO reaction system
NASA Technical Reports Server (NTRS)
An experimental study of the kinetics of the H2-CO-CO2-NO reaction system was made behind incident shock waves at temperatures of 2460 and 2950 K. The overall rate of the reaction was measured by monitoring radiation from the CO + O yields CO2 + h upoilon reaction. Correlation of these data with a detailed reaction mechanism showed that the high-temperature rate of the reaction N + OH yields NO + H can be described by the low-temperature (320 K) rate coefficient. Catalytic dissociation of molecular hydrogen was an important reaction under the tests conditions.
Jachimowski, C. J.
[Determination of trace amounts of nitrite and its chemical reaction kinetics].
A catalytic kinetic spectrophotometric method for the determination of nitrite, NO2(-)-S2O8(2-)-MR, was developed. It is based on the fading reaction of methyl red (MR) oxidized by potassium persulfate which can be catalyzed by NO2- in the medium of dilute HCl. The optimum experimental conditions were gained by combining single factor experiments with orthogonal experiments. Calibration curve, detection limit, precision, and anti-interference under the optimum experimental conditions were researched. Its kinetics principles and parameters were discussed. Its quantitative principle was investigated. The results show that the optimum experimental conditions of this method should be as follows: 1.0 mL 0.3 mol x L(-1) HCl, 1.0 mL 0.01 mol x L(-1) K2S2O8, 0.6 mL 0.2 g x L(-1) MR, reaction temperature 80 degrees C and reaction time 9 min. The principles for the quantitative determination of trace nitrite is that variation of MR concentration at the maximum absorption wavelength of 518 nm, ln(A0/A), shows a good linear relationship with the concentration of NO2- under the optimum experimental conditions. Its determination range is 0.01-0.80 mg x L(-1) and its detection limit is 0.007 mg x L(-1). The kinetic characteristics are that the reaction order in NO2- is 1 and the fading reaction is a pseudo first order reaction. Its apparent activation energy is 85.04 kJ x mol(-1). Its apparent rate constant is 0.021 4 min(-1), and the half-life is 32.39 min at 80 degrees C. The kinetic principle is that the variation of MR concentration is directly proportional to the concentration of NO2-, ln(A0/A) = kc(NO2-). This new method for the determination of trace nitrite has never previously been reported in the published literature so far. It is highly sensitive and selective. Most of the common ions don't interfere with the determination of nitrite. This method has the advantages of convenient operation and the regents used are cheap and nontoxic. It was applied to the determination of trace nitrite in food and water samples with satisfactory results. PMID:25358175
Luo, Zhi-yong; Zheng, Huai-li
Chemical Kinetic Data Base for Combustion Chemistry. Part I. Methane and Related Compounds
This document contains evaluated data on the kinetics and thermodynamic properties of species that are of importance in methane pyrolysis and combustion. Specifically, the substances considered include H, H2, O, O2, OH, HO2, H2O2, H2O, CH4, C2H6, HCHO, CO2, CO, HCO, CH3, C2H5, C2H4, C2H3, C2H2, C2H, CH3CO, CH3O2, CH3O, singlet CH2, and triplet CH2. All possible reactions are considered.
W. Tsang; R. F. Hampson
The correlation analysis of the calculated by means of GIAO PBE\\/3? method and experimental (2D NMR INADEQUATE) 13C NMR chemical shifts of C60 derivatives was performed. It was shown that the computational method with sufficient accuracy (r.m.s.?5ppm) reproduces the experimental 13C NMR chemical shifts of the sp2-fullerene carbon atoms uncoupled with the sp3-fullerene carbons. By quality description the GIAO method
Arthur R. Tulyabaev; Leonard M. Khalilov
NASA Astrophysics Data System (ADS)
The search for organic carbon at the surface of Mars, as clues of past habitability or remnants of life, is a major science goal of Mars� exploration. Understanding the chemical evolution of organic molecules under current martian environmental conditions is essential to support the analyses performed in situ. What molecule can be preserved? What is the timescale of organic evolution at the surface? This paper presents the results of laboratory investigations dedicated to monitor the evolution of organic molecules when submitted to simulated Mars surface ultraviolet radiation (190-400 nm), mean temperature (218 � 2 K) and pressure (6 � 1 mbar) conditions. Experiments are done with the MOMIE simulation setup (for Mars Organic Molecules Irradiation and Evolution) allowing both a qualitative and quantitative characterization of the evolution the tested molecules undergo (Poch, O. et al. [2013]. Planet. Space Sci. 85, 188-197). The chemical structures of the solid products and the kinetic parameters of the photoreaction (photolysis rate, half-life and quantum efficiency of photodecomposition) are determined for glycine, urea, adenine and chrysene. Mellitic trianhydride is also studied in order to complete a previous study done with mellitic acid (Stalport, F., Coll, P., Szopa, C., Raulin, F. [2009]. Astrobiology 9, 543-549), by studying the evolution of mellitic trianhydride. The results show that solid layers of the studied molecules have half-lives of 10-103 h at the surface of Mars, when exposed directly to martian UV radiation. However, organic layers having aromatic moieties and reactive chemical groups, as adenine and mellitic acid, lead to the formation of photoresistant solid residues, probably of macromolecular nature, which could exhibit a longer photostability. Such solid organic layers are found in micrometeorites or could have been formed endogenously on Mars. Finally, the quantum efficiencies of photodecomposition at wavelengths from 200 to 250 nm, determined for each of the studied molecules, range from 10-2 to 10-6 molecule photon-1 and apply for isolated molecules exposed at the surface of Mars. These kinetic parameters provide essential inputs for numerical modeling of the evolution of Mars� current reservoir of organic molecules. Organic molecules adsorbed on martian minerals may have different kinetic parameters and lead to different endproducts. The present study paves the way for the interpretation of more complex simulation experiments where organics will be mixed with martian mineral analogs.
Poch, O.; Kaci, S.; Stalport, F.; Szopa, C.; Coll, P.
The interactions between ionic liquids (ILs) and acetone have been studied to obtain a further understanding of the behavior of their mixtures, which generally give place to an exothermic process, mutual miscibility, and negative deviation of Raoult's law. COSMO-RS was used as a suitable computational method to systematically analyze the excess enthalpy of IL-acetone systems (>300), in terms of the intermolecular interactions contributing to the mixture behavior. Spectroscopic and COSMO-RS results indicated that acetone, as a polar compound with strong hydrogen bond acceptor character, in most cases, establishes favorable hydrogen bonding with ILs. This interaction is strengthened by the presence of an acidic cation and an anion with dispersed charge and non-HB acceptor character in the IL. COSMO-RS predictions indicated that gas-liquid and vapor-liquid equilibrium data for IL-acetone systems can be finely tuned by the IL selection, that is, acting on the intermolecular interactions between the molecular and ionic species in the liquid phase. NMR measurements for IL-acetone mixtures at different concentrations were also carried out. Quantum-chemical calculations by using molecular clusters of acetone and IL species were finally performed. These results provided additional evidence of the main role played by hydrogen bonding in the behavior of systems containing ILs and HB acceptor compounds, such as acetone. PMID:23688030
Ruiz, Elia; Ferro, Victor R; Palomar, Jose; Ortega, Juan; Rodriguez, Juan Jose
Nuclear methods in chemical kinetics. Technical progress report, October 1, 1981-September 30, 1982
The 1982-83 DOE research proposal included the following projects: (1) The recoil /sup 18/F vs CF/sub 4/ reaction system; (2) The recoil /sup 18/F vs C/sub 2/F/sub 6/ reaction system; (3) Recoil /sup 18/F vs CF/sub 4//M mixture experiments; (4) Other recoil /sup 18/F rections producing CF/sub 31//sup 8/F; and (5) The 11th International Hot Atom Chemistry Symposium. As detailed in this report, the proposed gas phase recoil /sup 18/F experiments with pure CF/sub 4/ and C/sub 2/F/sub 6/ were completed, and new studies were initiated pertaining to the mechanism of the thermal /sup 18/F + C/sub 2/H/sub 4/ reaction, to the steady state kinetic theory of hot atom reactions, and to the kinetic theory of bimolecular collision processes under realistic potential. The 11th IHAC Symposium was covered at Davis during the period June 27 through July 2, 1982.
Not Available
NASA Astrophysics Data System (ADS)
The complete vibrational assignment and analysis of the fundamental modes of 2-bromo-5-nitrothiazole (BNT) 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 for the optimized geometry of the compound from the ab initio HF and DFT-B3LYP gradient calculations employing 6-311++G(d,p) basis set. Thermodynamic properties like entropy, heat capacity and zero point energy 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 BNT have been computed using B3LYP quantum chemical calculation.
Gobinath, E.; Xavier, R. John
In this work simulation of a turbulent H2\\/N2 jet diffusion flame with flamelet modelling has been presented. The favre-averaged mixture fraction has been employed to model the combustion. Favre-averaged scalar quantities have been calculated from flamelet libraries by making use of a presumed Probability Density Function (PDF) method. The predicted flame temperature profiles and chemical species concentrations are compared with
M. A. Alim; W. Malalasekera
Kinetic results obtained in cationic and anionic emulsions show for the first time that pseudophase kinetic models give reasonable estimates of the partition constants of reactants, here t-butylhydroquinone (TBHQ) between the oil and interfacial region, P(O)(I), and the water and interfacial region, P(W)(I), and of the interfacial rate constant, k(I), for the reaction with an arenediazonium ion in emulsions containing a 1:1 volume ratio of a medium chain length triglyceride, MCT, and aqueous acid or buffer. The results provide: (a) an explanation for the large difference in pH, >4 pH units, required to run the reaction in CTAB (pH 1.54, added HBr) and SDS (pH 5.71, acetate buffer) emulsions; (b) reasonable estimates of PO(I) and k(I) in the CTAB emulsions; (c) a sensible interpretation of added counterion effects based on ion exchange in SDS emulsions (Na(+)/H3O(+) ion exchange in the interfacial region) and Donnan equilibrium in CTAB emulsions (Br(-) increasing the interfacial H3O(+)); and (d) the significance of the effect of the much greater solubility of TBHQ in MCT versus octane, 1000/1, as the oil. These results should aid in interpreting the effects of ionic surfactants on chemical reactivity in emulsions in general and in selecting the most efficient antioxidant for particular food applications. PMID:23545243
Gu, Qing; Bravo-D�az, Carlos; Romsted, Laurence S
NASA Technical Reports Server (NTRS)
One of the goals of the original proposal was to study how cross-linking affects the properties of an ion exchange material(IEM) developed at Lewis Research Center. However, prior to the start of this work, other workers at LERC investigated the effect of cross-linking on the properties of this material. Other than variation in the ion exchange capacity, the chemical characteristics were shown to be independent of the cross-linking agent, and the degree of cross-linking. New physical forms of the film were developed (film, supported film, various sizes of beads, and powder). All showed similar properties with respect to ion exchange equilibria but the kinetics of ion exchange depended on the surface area per unit mass; the powder form of the IEM exchanging much more rapidly than the other forms. The research performed under this grant was directed towards the application of the IEM to the analysis of metal ions at environmental concentrations.
Tanner, Stephen P.
Kinetic characterization of the enzymatic and chemical oxidation of the catechins in green tea.
The oxidation of green tea catechins by polyphenol oxidase/O2 and peroxidase/H2O2 gives rise to o-quinones and semiquinones, respectively, which inestability, until now, have hindered the kinetic characterization of enzymatic oxidation of the catechins. To overcome this problem, ascorbic acid (AH2) was used as a coupled reagent, either measuring the disappearance of AH2 or using a chronometric method in which the time necessary for a fixed quantity of AH2 to be consumed was measured. In this way, it was possible to determine the kinetic constants characterizing the action of polyphenol oxidase and peroxidase toward these substrates. From the results obtained, (-) epicatechin was seen to be the best substrate for both enzymes with the OH group of the C ring in the cis position with respect to the B ring. The next best was (+) catechin with the OH group of the C ring in the trans position with respect to the B ring. Epigallocatechin, which should be in first place because of the presence of three vecinal hydroxyls in its structure (B ring), is not because of the steric hindrance resulting from the hydroxyl in the cis position in the C ring. The epicatechin gallate and epigallocatechin gallate are very poor substrates due to the presence of sterified gallic acid in the OH group of the C ring. In addition, the production of H2O2 in the auto-oxidation of the catechins by O2 was seen to be very low for (-) epicatechin and (+) catechin. However, its production from the o-quinones generated by oxidation with periodate was greater, underlining the importance of the evolution of the o-quinones in this process. When the [substrate] 0/[IO4 (-)] 0 ratio = 1 or >1, H2O2 formation increases in cases of (-) epicatechin and (+) catechin and practically is not affected in cases involving epicatechin gallate, epigallocatechin, or epigallocatechin gallate. Moreover, the antioxidant power is greater for the gallates of green tea, probably because of the greater number of hydroxyl groups in its structure capable of sequestering and neutralizing free radicals. Therefore, we kinetically characterized the action of polyphenol oxidase and peroxidase on green tea catechins. Furthermore, the formation of H2O2 during the auto-oxidation of these compounds and during the evolution of their o-quinones is studied. PMID:18788750
Munoz-Munoz, J L; Garc�a-Molina, F; Molina-Alarc�n, M; Tudela, J; Garc�a-C�novas, F; Rodr�guez-L�pez, J N
Kinetics of endothermic decomposition reactions. I. Steady-state chemical steps
When the solid product of an endothermic decomposition reaction is porous, the rate-limiting chemical step is usually assumed to be a surface step of the gaseous product or of a precursor of that product. It is shown here that the rate of such a reaction may also depend upon rates of diffusion in the reactant phase, the rate of transfer
Alan W. Searcy; Dario Beruto
This dissertation presents a series of studies that describe the impacts of, among other things, temperature and kinematics on inter-level dielectric (ILD) and metal chemical mechanical planarization (CMP) processes. The performance of CMP is often evaluated in terms of removal rate, uniformity, planarization length, step height, defects and resulting topography such as erosion and dishing. The assessment of these parameters
Jamshid Sorooshian
Mercury (Hg) speciation in combustion-generated flue gas is modeled using a detailed chemical mechanism consisting of 60 reactions and 21 species. This speciation model accounts for chlorination and oxidation of key flue-gas components, including elemental mercury. Results indica...
Acetylcholinesterase has been attached covalently to the inner surface of nylon tubing. An experimental study has been carried out on the flow kinetics; solutions of acetylthiocholine at various concentrations were passed through tubing at various flow rates, and measurements made of the rates of formation of product. The results were analyzed in the light of the theoretical treatment of Kobayashi and Laidler, four different methods of analysis being employed. It is found that at lower substrate concentrations and flow rates the reactions are largely diffusion controlled. The Km(app) values are substantially higher than the Km value for diffusion-free conditions, but approach it as the flow rate is increased, when the diffusion layer becomes less important. The results are entirely consistent with the Kobayaski-Laidler theory, and provide guidelines for the design of open tubular heterogeneous enzyme reactors, both for industrial and analytic purposes. PMID:1168075
Ngo, T T; Laidler, K J
Relevance of Chemical Kinetics for Medicine: The Case of Nitric Oxide
NASA Astrophysics Data System (ADS)
Nitric oxide, NO, is central to many physiological processes including regulation of blood pressure and nerve signal transmission. Enzymes in endothelial cells and in the brain of mammals continuously synthesize it�generally in low and carefully regulated concentrations. The well known reaction of NO with oxygen to produce toxic nitrogen dioxide, NO2, has a rate which is bimolecular in NO. High concentrations of NO, as are found often in industrial plants or cigarettes, react rapidly with oxygen to produce toxic NO2. However, the half-life of NO at low NO concentrations as found in solutions and gases occurring in blood vessels, brains, and lungs is sufficiently long for biochemical purposes. Kinetics, then, determines the harmful versus helpful aspects of nitric oxide. At concentrations below 80 ppm NO is used in hospitals for lung vasodilation of preterm newborns and patients with pulmonary distress.
Balaban, Alexandru T.; Seitz, William
We conducted the title reaction using a crossed molecular-beam apparatus, quantum-chemical calculations, and RRKM calculations. Synchrotron radiation from an undulator served to ionize selectively reaction products by advantage of negligibly small dissociative ionization. We observed two products with gross formula C(2)H(3)N and C(2)H(2)N associated with loss of one and two hydrogen atoms, respectively. Measurements of kinetic-energy distributions, angular distributions, low-resolution photoionization spectra, and branching ratios of the two products were carried out. Furthermore, we evaluated total branching ratios of various exit channels using RRKM calculations based on the potential-energy surface of reaction N((2)D)+C(2)H(4) established with the method CCSD(T)/6-311+G(3df,2p)//B3LYP/6-311G(d,p)+ZPE[B3LYP/6-311G(d,p)]. The combination of experimental and computational results allows us to reveal the reaction dynamics. The N((2)D) atom adds to the C=C ?-bond of ethene (C(2)H(4)) to form a cyclic complex c-CH(2)(N)CH(2) that directly ejects a hydrogen atom or rearranges to other intermediates followed by elimination of a hydrogen atom to produce C(2)H(3)N; c-CH(2)(N)CH+H is the dominant product channel. Subsequently, most C(2)H(3)N radicals, notably c-CH(2)(N)CH, further decompose to CH(2)CN+H. This work provides results and explanations different from the previous work of Balucani et al. [J. Phys. Chem. A, 2000, 104, 5655], indicating that selective photoionization with synchrotron radiation as an ionization source is a good choice in chemical dynamics research. PMID:21437304
Lee, Shih-Huang; Chin, Chih-Hao; Chen, Wei-Kan; Huang, Wen-Jian; Hsieh, Chu-Chun
NASA Astrophysics Data System (ADS)
The program HYPER-FORM permits the input and calculation of a mineral formula from wet chemical and electron microprobe analysis. It includes autosaving of data, search routines, and other database functions. The calculated formula can be exported to wordprocessing programs such as MacWrite� or Microsoft Word� and can be edited as required. It also is possible to export the calculated data to graphic programs such as Cricket Graph� or Kaleidagraph� for a graphic representation of the data. HYPER-FORM is an interactive program written in HyperTalk� (HyperCard� environment) and is designed to correspond to the Macintosh� interface.
de Bjerg, Silvia C.; Mogessie, Aberra; Bjerg, Ernesto
NASA Astrophysics Data System (ADS)
The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K3) having C s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.
Khaikin, L. S.; Tikhonov, D. S.; Grikina, O. E.; Rykov, A. N.; Stepanov, N. F.
Reduction Kinetics of a CasO4 Based Oxygen Carrier for Chemical-Looping Combustion
The CaSO4 based oxygen carrier has been proposed as an alternative low cost oxygen carrier for Chemical-looping combustion (CLC) of coal. The reduction of CaSO4 to CaS is an important step for the cyclic process of reduction\\/oxidation in CLC of coal with CaSO4 based oxygen carrier. Thermodynamic analysis of CaSO4 oxygen carrier with CO based on the principle of Gibbs
R. Xiao; Q. L. Song; W. G. Zheng; Z. Y. Deng; L. H. Shen; M. Y. Zhang
The pyrolytic and oxidative behaviour of the biofuel 2,5-dimethylfuran (25DMF) has been studied in a range of experimental facilities in order to investigate the relatively unexplored combustion chemistry of the title species and to provide combustor relevant experimental data. The pyrolysis of 25DMF has been re-investigated in a shock tube using the single-pulse method for mixtures of 3% 25DMF in argon, at temperatures from 1200�1350 K, pressures from 2�2.5 atm and residence times of approximately 2 ms. Ignition delay times for mixtures of 0.75% 25DMF in argon have been measured at atmospheric pressure, temperatures of 1350�1800 K at equivalence ratios (?) of 0.5, 1.0 and 2.0 along with auto-ignition measurements for stoichiometric fuel in air mixtures of 25DMF at 20 and 80 bar, from 820�1210 K. This is supplemented with an oxidative speciation study of 25DMF in a jet-stirred reactor (JSR) from 770�1220 K, at 10.0 atm, residence times of 0.7 s and at ? = 0.5, 1.0 and 2.0. Laminar burning velocities for 25DMF-air mixtures have been measured using the heat-flux method at unburnt gas temperatures of 298 and 358 K, at atmospheric pressure from ? = 0.6�1.6. These laminar burning velocity measurements highlight inconsistencies in the current literature data and provide a validation target for kinetic mechanisms. A detailed chemical kinetic mechanism containing 2768 reactions and 545 species has been simultaneously developed to describe the combustion of 25DMF under the experimental conditions described above. Numerical modelling results based on the mechanism can accurately reproduce the majority of experimental data. At high temperatures, a hydrogen atom transfer reaction is found to be the dominant unimolecular decomposition pathway of 25DMF. The reactions of hydrogen atom with the fuel are also found to be important in predicting pyrolysis and ignition delay time experiments. Numerous proposals are made on the mechanism and kinetics of the previously unexplored intermediate temperature combustion pathways of 25DMF. Hydroxyl radical addition to the furan ring is highlighted as an important fuel consuming reaction, leading to the formation of methyl vinyl ketone and acetyl radical. The chemically activated recombination of H?2 or CH3?2 with the 5-methyl-2-furanylmethyl radical, forming a 5-methyl-2-furylmethanoxy radical and ?H or CH3? radical is also found to exhibit significant control over ignition delay times, as well as being important reactions in the prediction of species profiles in a JSR. Kinetics for the abstraction of a hydrogen atom from the alkyl side-chain of the fuel by molecular oxygen and H?2 radical are found to be sensitive in the estimation of ignition delay times for fuel-air mixtures from temperatures of 820�1200 K. At intermediate temperatures, the resonantly stabilised 5-methyl-2-furanylmethyl radical is found to predominantly undergo bimolecular reactions, and as a result sub-mechanisms for 5-methyl-2-formylfuran and 5-methyl-2-ethylfuran, and their derivatives, have also been developed with consumption pathways proposed. This study is the first to attempt to simulate the combustion of these species in any detail, although future refinements are likely necessary. The current study illustrates both quantitatively and qualitatively the complex chemical behavior of what is a high potential biofuel. Whilst the current work is the most comprehensive study on the oxidation of 25DMF in the literature to date, the mechanism cannot accurately reproduce laminar burning velocity measurements over a suitable range of unburnt gas temperatures, pressures and equivalence ratios, although discrepancies in the experimental literature data are highlighted. Resolving this issue should remain a focus of future work. PMID:24273333
Somers, Kieran P.; Simmie, John M.; Gillespie, Fiona; Conroy, Christine; Black, Grainne; Metcalfe, Wayne K.; Battin-Leclerc, Frederique; Dirrenberger, Patricia; Herbinet, Olivier; Glaude, Pierre-Alexandre; Dagaut, Philippe; Togbe, Casimir; Yasunaga, Kenji; Fernandes, Ravi X.; Lee, Changyoul; Tripathi, Rupali; Curran, Henry J.
The chemical speciation of 2-amino-N-hydroxypropanamide (?-alaninohydroxamic acid, HL) and vanadium (V) in aqueous solution has been investigated through calculations of the thermodynamic properties and the (51)V nuclear magnetic resonance (NMR) chemical shifts of the species formed at equilibrium. The results have been compared directly with the experimental (51)V NMR data. The (51)V NMR chemical shifts have been calculated by using a density functional theory (DFT) approach accounting for relativistic corrections and solvent effects. All tautomers of the 1:1 and 1:2 VO2(+)/?-ala complexes with different degrees of protonation have been calculated and thermodynamic and structural properties are presented for the most stable species. The system is better modeled as tautomeric equilibria, and species lying down in the range of 10 kcal�mol(-1) cannot be neglected at the BP/TZ2P/COSMO approach. In fact, the metal complex speciation in aqueous solution should not be investigated based solely on the thermodynamic analysis, but together with spectroscopic calculations such as NMR. PMID:23971999
Duarte, H�lio Anderson; Vankova, Nina; Ferreira, Isabella Pires; Paniago, Eucler B; Heine, Thomas
The association reaction between C2H and 1-butyne: a computational chemical kinetics study.
The potential energy surfaces (PES) for the reaction of the C(2)H radical with 1-butyne (C(4)H(6)) have been studied using the CBS-QB3 method. Density functional B3LYP/cc-pVTZ and M06-2X/6-311++G(d,p) calculations have also been performed to analyze the reaction energetics. For detailed theoretical calculation on the total reaction mechanism, the initial association reactions on more and less substituted C atoms of 1-butyne are treated separately followed by a variational transition state theory (VTST) calculation to obtain reaction rates. The successive unimolecular reactions from the association reaction complexes are subjected to Rice-Ramsperger-Kassel-Marcus (RRKM) calculations for reaction rate constants and product branching ratios. The calculated rate constants in the temperature range 70-295 K for both the association reactions are found to be highly temperature dependent at low temperatures, which is contrary to the experimental findings of temperature independent association rates. We have explained this observation with the help of variational nature of the transition states, and we found a "loose" transition state at low temperatures. The calculated product branching ratios for the unimolecular reactions generally agree with the available experimental data, although some channels show a significant method dependency and therefore the correlation with experiment is lost to some extent. Our detailed reaction energetics calculations confirm that the C(2)H + C(4)H(6) reaction proceeds without an entrance barrier and leads to the important products ethynylallene + CH(3), 1,3-hexadiyne + H, 3,4-hexadiene-1-yne + H, 2-ethynyl-1,3-butadiene + H, 3,4-dimethylenecyclobut-1-ene + H and fulvene + H exothermic by 25-75 kcal mol(-1), with strong dependence of the product distribution on the association mode of C(2)H with C(4)H(6), making these reactions fast under low temperature conditions of Titan's atmosphere. Therefore this study can provide a detailed picture of the complex hydrocarbon formation mechanism in the upper atmosphere. PMID:21279199
Mandal, Debasish; Mondal, Bhaskar; Das, Abhijit K
Chlorite dismutase carries out the heme-catalyzed decomposition of ClO2� to Cl� and O2, an unusual transformation with biotechnological and bioremediative applications. The enzyme has been successfully overexpressed for the first time in highly functional form in Escherichia coli and its steady state kinetics studied. The purified enzyme is abundant (55 mg/L cell culture), highly active (~4.7 � 103 ?mol of ClO2� min�1 mg�1 subunit) and nearly stoichiometric in heme; further, it shares spectroscopic and physicochemical features with chlorite dismutases previously isolated from three organisms. A careful study of the enzyme's steady state kinetics has been carried out. ClO2� consumption and O2 release rates were measured, yielding comparable values of kcat (4.5 � 105 min�1), Km (~215 ?M), and kcat/Km (3.5 � 107 M�1 s�1) via either method (4 �C, pH 6.8; all values referenced per heme-containing subunit). ClO2�:O2 stoichiometry exhibited a 1:1 relationship under all conditions measured. Though the value of kcat/Km indicates near diffusion control of the reaction, viscosogens had no effect on kcat/Km or Vmax. The product O2 did not inhibit the reaction at saturating [O2], but Cl� is a mixed inhibitor with relatively high values of KI (225 mM for enzyme and 95.6 mM for the enzyme�substrate complex), indicating a relatively low affinity of the heme iron for halogen ions. Chlorite irreversibly inactivates the enzyme after ~1.7 � 104 turnovers (per heme) and with a half-life of 0.39 min, resulting in bleaching of the heme chromophore. The inactivation KI (Kinact) of 166 ?M is similar in magnitude to Km, consistent with a common Michaelis complex on the pathway to both reaction and inactivation. The one-electron peroxidase substrate guaiacol offers incomplete protection of the enzyme from inactivation. Mechanisms in keeping with the available data and the properties of other well-described heme enzymes are proposed. PMID:18422344
Streit, Bennett R.; DuBois, Jennifer L.
Aim of this study was to evaluate the feasibility of the use of clinoptilolite as a barrier material to eliminate heavy metals from roof runoff. The effect of chemical conditioning with 1 M NaCl solution upon the ion exchange capacity and on kinetic of zinc uptake by clinoptilolite has been investigated. According to the batch experiments the modified clinoptilolite has up to 100% higher sorption capacity, regarding Zn than the natural material. The pre-treatment of clinoptilolite results in an acceleration of the ion exchange process up to 40% regarding zinc. In order to define the reasons of this behaviour, both materials, modified and natural, were analysed for: (i) chemical composition, (ii) density, (iii) pore size distribution and (iv) zeta potential. The clogging of the pores, the charge of the grain surface, the pH of the initial metal solution and the ion metal concentration are the factors which are mainly affecting the ion exchange capacity and the rate of zinc uptake by clinoptilolite. PMID:15878024
Athanasiadis, Konstantinos; Helmreich, Brigitte
NASA Astrophysics Data System (ADS)
Understanding of the factors which influence proton chemical shifts in nuclear magnetic resonance (NMR) spectra of proteins has advanced steadily as the number of proteins, for which assignments in conjunction with high resolution structures have been obtained, has increased. Progress has been made in both the calculation of chemical shifts from given coordinates, both empirically for 1H (Williamson & Asakura J. Magn. Reson. (1991) 94, 557) and using ab initio approaches for calculation of 13C (De Dios et al. Science (1993) 260, 1491). Concomitantly Wishart et al. (J. Mol. Biol. (1992) 222, 311), using statistical methods have clarified the relationship between H? chemical shift and regular secondary structure in proteins to a high degree of accuracy. We recently demonstrated the significant amount of structural information present in the H? chemical shift through the use of chemical shift restrained molecular dynamics simulations (Harvey & van Gunsteren Techniques in Protein Chemistry IV (1993) 615, Academic Press). Here we apply a similar methodology to the stereospecific assignment of methylene and methyl proton resonances in proteins. Stereospecific assignment of such 1H resonances dramatically increases the degree of precision of ensembles of structures derived from NMR data. However, this is often a cumbersome process, requiring detailed analysis of large amounts of data. Furthermore, experimental considerations such as poor signal-to-noise ratios, spectral overlap and spin diffusion combine to make this process somewhat unreliable. We present calculations of the chemical shifts for the known structures of bovine pancreatic trypsin inhibitor (Mw 6.5 kDa) and the ?-amylase inhibitor tendamistat (Mw 8 kDa), for which stereospecific assignments and high resolution structures from both NMR and crystallographic studies are available. The methods described are also applied to the ensemble of structures obtained for protein S (Mw 19 kDa) for both structure evaluation, stereospecific assignment and subsequent refinement using chemical shift restrained molecular dynamics simulations. The structure of protein S has been determined by NMR but no x-ray structure is available.
Harvey, Timothy S.; van Gunsteren, Wilfred F.; Ikura, Mitsuhiko
ERIC Educational Resources Information Center
An experiment in chemical kinetics as part of our Discovery Chemistry curriculum is described. Discovery Chemistry is a pedagogical philosophy that makes the laboratory the key center of learning for students in their first two years of undergraduate instruction. Questions are posed in the pre-laboratory discussion and assessed using pooled�
Herrick, Richard S.; Mills, Kenneth V.; Nestor, Lisa P.
Bioconcentration kinetics of hydrophobic chemicals in different densities of Chlorella pyrenoidosa
Algal density-dependent bioconcentration factors and rate constants were determined for a series of hydrophobic compounds in Chlorella pyrenoidosa. The apparent uptake rate constants of the hydrophobic compounds in algae varied between 200 and 710,000 L/kg/d, slightly increased with hydrophobicity within an experiment, were relatively constant for each algal density, and fitted fairly within existing allometric relationships. The bioavailability of the hydrophobic test compounds was significantly reduced by sorption by algal exudates. The sorption coefficients of the hydrophobic compounds to the algal exudates were between 80 and 1,200 L/kg, and were for most algal densities in the same order of magnitude as the apparent bioconcentration factors to the algae, that is, between 80 and 60,200 L/kg. In typical field situations, however, no significant reduction in bioavailability due to exudates is expected. The apparent elimination rate constants of the hydrophobic compounds were high and fairly constant for each algal density and varied between 2 and 190/d. Because the apparent elimination rate constants were higher than the growth rate constant, and were independent of hydrophobicity, the authors speculated that other factors dominate excretion, such as exudate excretion-enhanced elimination. Bioconcentration factors increased less than proportional with hydrophobicity, i.e., the octanol-water partition coefficient [K{sub ow}]. The role of algal composition in bioconcentration is evaluated. Bioconcentrations (kinetics) of hydrophobic compounds that are determined at high algal densities should be applied with caution to field situations.
Sijm, D.T.H.M.; Broersen, K.W.; Roode, D.F. de; Mayer, P. [Utrecht Univ. (Netherlands)
Cometary impact and amino acid survival--chemical kinetics and thermochemistry.
The Arrhenius parameters for the initiating reactions in butane thermolysis and the formation of soot, reliable to at least 3000 K, have been applied to the question of the survival of amino acids in cometary impacts on early Earth. The pressure/temperature/time course employed here was that developed in hydrocode simulations for kilometer-sized comets (Pierazzo and Chyba, 1999), with attention to the track below 3000 K where it is shown that potential stabilizing effects of high pressure become unimportant kinetically. The question of survival can then be considered without the need for assignment of activation volumes and the related uncertainties in their application to extreme conditions. The exercise shows that the characteristic times for soot formation in the interval fall well below the cooling periods for impacts ranging from fully vertical down to about 9 degrees above horizontal. Decarboxylation, which emerges as more rapid than soot formation below 2000-3000 K, continues further down to extremely narrow impact angles, and accordingly cometary delivery of amino acids to early Earth is highly unlikely. PMID:16722675
Ross, David S
A catalytic kinetic method is described for the determination of Se(IV), Se(VI) and total inorganic selenium in water based on the catalytic effect of Se(IV) on the reduction of bromate by hydrazine dihydrochloride in acidic media. The generated bromine decolorized methyl orange (MO) and the reaction was monitored spectrophotometrically at 507 nm as a function of time. The initial rate and fixed time methods were adopted for the determination and speciation of inorganic selenium. Under two optimum conditions, the calibration graphs are linear in the range 0-126.3 and 0-789.6 microg L(-1) of Se(IV) for the initial rate method and 0-315.8 and 0-789.6 microg L(-1) of Se(IV) for the fixed time method. The detection limits were 1.3 and 14.7 microg L(-1) for the initial rate and fixed time methods, respectively. The proposed methods were validated statistically and through recovery studies in environmental water samples. The relative standard deviation in the determination of 31.6-94.8 microg L(-1) of Se(IV) and Se(VI) was less than 6%. Analyses of standard reference materials for selenium using initial rate and fixed time methods showed that the proposed methods have good accuracy. Se(IV), Se(VI) and total inorganic selenium in environmental water samples have been successfully determined by this method after selective reduction of Se(VI) to Se(IV). PMID:19091465
Chand, Vimlesh; Prasad, Surendra
Chemical Kinetics and Properties from the Radiation Chemistry Data Center (RCDC)
The Radiation Chemistry Data Center (RCDC) is a focal point for the compilation and evaluation of kinetic, spectroscopic and thermodynamic data for processes in solution involving reactive intermediates, including free radicals and excited states. These data are primarily derived from the published literature on radiation chemistry and quantitative aspects of photochemistry. The compilations are presented as individual groups of pages corresponding to each published work. Each compilation consists of an introductory article, describing the scope of the compilation, with the considerations and criteria for data evaluation discussed. Nomenclature for the compilation is also described here. For several compilations the introduction is followed by one or more pages of links organized as an index or table of contents to the individual pages of the compilation. These links allow the browsing of the data by species name. Each page tabulates the reaction of a transient species with a particular reactant. RCDC was established at the Notre Dame Radiation Laboratory in 1965, as part of the National Standard Reference Data System.
The chemical kinetics and thermodynamics of sodium species in oxygen-rich hydrogen flames
NASA Technical Reports Server (NTRS)
Results are presented which, it is claimed, lead to a correction of previous misconceptions over the relative importance and kinetics of NaO2. It is shown that its rapid conversion to NaO and NaOH is such that it can severely perturb the NaOH/Na ratio and produce significant concentration overshoots over that predicted from the balance of the reaction of Na with H2O. This becomes increasingly the case in flames of large O2 concentrations and temperatures below 2500 K; and the corresponding large rate constants for the termolecular formation of the other alkali peroxides imply that similar considerations will be necessary for them. Depending on the rate constants for the exothermic conversions of MO2 to MO or MOH, the steady-state concentrations of MO2 could be more or less significant than for sodium. Owing to numerous reactions that produce these conversions, the MOH species will probably be the dominant species in all cases in oxygen-rich hydrogen or hydrocarbon flames, with MO concentrations at not greater than 1 percent of the bound metal.
Hynes, A. J.; Steinberg, M.; Schofield, K.
Mathematical description of complex chemical kinetics and application to CFD modeling codes
NASA Technical Reports Server (NTRS)
A major effort in combustion research at the present time is devoted to the theoretical modeling of practical combustion systems. These include turbojet and ramjet air-breathing engines as well as ground-based gas-turbine power generating systems. The ability to use computational modeling extensively in designing these products not only saves time and money, but also helps designers meet the quite rigorous environmental standards that have been imposed on all combustion devices. The goal is to combine the very complex solution of the Navier-Stokes flow equations with realistic turbulence and heat-release models into a single computer code. Such a computational fluid-dynamic (CFD) code simulates the coupling of fluid mechanics with the chemistry of combustion to describe the practical devices. This paper will focus on the task of developing a simplified chemical model which can predict realistic heat-release rates as well as species composition profiles, and is also computationally rapid. We first discuss the mathematical techniques used to describe a complex, multistep fuel oxidation chemical reaction and develop a detailed mechanism for the process. We then show how this mechanism may be reduced and simplified to give an approximate model which adequately predicts heat release rates and a limited number of species composition profiles, but is computationally much faster than the original one. Only such a model can be incorporated into a CFD code without adding significantly to long computation times. Finally, we present some of the recent advances in the development of these simplified chemical mechanisms.
Bittker, D. A.
Reduction Kinetics of a CasO 4 Based Oxygen Carrier for Chemical-Looping Combustion
\\u000a The CaSO4 based oxygen carrier has been proposed as an alternative low cost oxygen carrier for Chemical-looping combustion (CLC) of\\u000a coal. The reduction of CaSO4 to CaS is an important step for the cyclic process of reduction\\/oxidation in CLC of coal with CaSO4 based oxygen carrier. Thermodynamic analysis of CaSO4 oxygen carrier with CO based on the principle of Gibbs
R. Xiao; Q. L. Song; W. G. Zheng; Z. Y. Deng; L. H. Shen; M. Y. Zhang
Chemical structure and kinetic modeling of 1,2-dichloroethane\\/methane fuel-rich flames
The chemical structure of atmospheric, premixed, one-dimensional, laminar, fuel-rich flames of 1,2-dichloroethane (1,2-DCE)\\/CH�\\/O�\\/Ar have been explored using a flat flame burner facility. The flames investigated have an equivalence ratio of about 2.0 and they are varied in the fuel ratios (0.3-1.5) together with the chlorine\\/hydrogen ratios (0.1-0.3). A number of important flame species have been identified and quantified for the
Measurements of HO2 chemical kinetics with a new detection method
NASA Technical Reports Server (NTRS)
Research for the period from December 1, 1985 to May 31, 1986 is discussed, i.e., the reaction rate constant of HO2+O3 has been measured with a discharge-flow-tube apparatus. The HO2 radical was detected by the OH(A-X) photofragment emission produced from photodissociative excitation of HO2 at 147 nm. In the meantime, the optical emissions produced by the vacuum ultraviolet excitation of chemical species in the flow tube were investigated and used to examine the possibility for their interference with the HO2 detection. The research results are summarized below.
Lee, L. C.; Suto, M.
NASA Astrophysics Data System (ADS)
Advances in high-speed digital electronics have enabled a new generation of molecular rotational spectroscopy techniques that provide instantaneous broadband spectral coverage. These techniques use a chirped excitation pulse to coherently excite the molecular sample over a spectral bandwidth of 10 GHz or larger through rapid passage. The subsequent time-domain emission is recorded using high-speed digitizers (up to 100 Gigasample/s) and the frequency domain spectrum is produced by fast Fourier transformation. The chirped-pulse Fourier transform (CP-FT) method has been implemented in the microwave frequency range (2-40 GHz) for studies of cold samples in pulsed jet sources and in the mm-wave/terahertz (THz) frequency range for studies of samples at room-temperature. The method has opened new applications for molecular rotational spectroscopy in the area of chemical kinetics where dynamic rotational spectroscopy is used to measure the rates of unimolecular isomerization reactions in highly excited molecules prepared by pulsed infrared laser excitation. In these applications, the isomerization rate is obtained from an analysis of the overall line shapes which are modified by chemical exchange leading to coalescence behavior similar to the effect in NMR spectroscopy. The sensitivity of the method and the ability to extend it to low frequency (2-8 GHz) have significantly increased the size range of molecules and molecular clusters for structure determination using isotopic substitution to build up the 3D molecular structures atom-by-atom. Application to the structure of water clusters with up to 15 water molecules will be presented. When coupled with advances in solid-state mm-wave/THz devices, this method provides a direct digital technique for analytical chemistry of room-temperature gases based on molecular rotational spectroscopy. These high-throughput methods can analyze complex sample mixtures with unmatched chemical selectivity and short analysis times.
Pate, Brooks
This thesis is an investigation of two topics in the area of molecular and chemical dynamics phenomena. The first topic, Sensitivity Analysis in Molecular Dynamics and Chemical Kinetics, explores the response of the numerical solutions to variation in the input information. After a brief consideration of elementary sensitivity coefficients (i.e. partial derivatives of observables with respect to model parameters), attention is focused on an entire new family of derived coefficients capable of exhibiting important aspects of the underlying dynamics. Each derived sensitivity coefficient has a unique physical interpretation in terms of an experiment or modeling calculation. Also, a fitting model for rotationally inelastic cross sections that accurately predicts cross sections away from the region of parameter space used in the fitting is presented. The global behavior of cross sections in parameter space is examined, and a nonlinear interpolation formula is suggested which utilizes sensitivity information. The second topic, A Theory of Intramolecular Energy Transfer in the Presence of Intense Radiation Fields, represents a theoretical formulation of energy redistribution based on stochastic considerations. The fundamental assumption is that a random phase approximation is valid at specific time intervals. This results in the replacement of the Schrodinger equation by a master-type equation, which is further approximated by a Fokker-Planck diffusion like equation. Energy transfer is described as a flow of probability among the quantum states, and the dissociation of dynamics are embodied in the boundary conditions. By virtue of the continuous character of the Fokker-Planck equation, the computational difficulty of its numerical solution depends only on the number of degrees of freedom and not on the number of states.
Eslava, L.A.
Kinetic bottlenecks to chemical exchange rates for deep-sea animals - Part 1: Oxygen
NASA Astrophysics Data System (ADS)
Ocean warming will reduce dissolved oxygen concentrations which can pose challenges to marine life. Oxygen limits are traditionally reported simply as a static concentration thresholds with no temperature, pressure or flow rate dependency. Here we treat the oceanic oxygen supply potential for heterotrophic consumption as a dynamic molecular exchange problem analogous to familiar gas exchange processes at the sea surface. A combination of the purely physico-chemical oceanic properties temperature, hydrostatic pressure, and oxygen concentration defines the ability of the ocean to supply oxygen to any given animal. This general oceanic oxygen supply potential is modulated by animal specific properties such as the diffusive boundary layer thickness to define and limit maximal oxygen supply rates. Here we combine all these properties into formal, mechanistic equations defining novel oceanic properties that subsume various relevant classical oceanographic parameters to better visualize, map, comprehend, and predict the impact of ocean deoxygenation on aerobic life. By explicitly including temperature and hydrostatic pressure into our quantities, various ocean regions ranging from the cold deep-sea to warm, coastal seas can be compared. We define purely physico-chemical quantities to describe the oceanic oxygen supply potential, but also quantities that contain organism-specific properties which in a most generalized way describe general concepts and dependencies. We apply these novel quantities to example oceanic profiles around the world and find that temperature and pressure dependencies of diffusion and partial pressure create zones of greatest physical constriction on oxygen supply typically at around 1000 m depth, which coincides with oxygen concentration minimum zones. In these zones, which comprise the bulk of the world ocean, ocean warming and deoxygenation have a clear negative effect for aerobic life. In some shallow and warm waters the enhanced diffusion and higher partial pressure due to higher temperatures might slightly overcompensate for oxygen concentration decreases due to decreases in solubility.
Hofmann, A. F.; Peltzer, E. T.; Brewer, P. G.
Solid State Kinetic Parameters and Chemical Mechanism of the Dehydration of CoCl2.6H2O.
ERIC Educational Resources Information Center
Presents an experimental example illustrating the most common methods for the determination of kinetic parameters. Discusses the different theories and equations to be applied and the mechanism derived from the kinetic results. (CW)
Ribas, Joan; And Others
Kinetics and Extent of Mineralization of Organic Chemicals at Trace Levels in Freshwater and Sewage
A sensitive and rapid method was developed to measure the mineralization of 14C-labeled organic compounds at picogram-per-milliliter or lower levels in samples of natural waters and sewage. Mineralization was considered to be equivalent to the loss of radioactivity from solutions. From 93 to 98% of benzoate, benzylamine, aniline, phenol, and 2,4-dichlorophenoxyacetate at one or more concentrations below 300 ng/ml was mineralized in samples of lake waters and sewage, indicating little or no incorporation of carbon into microbial cells. Assimilation of 14C by the cells mineralizing benzylamine in lake water was not detected. Mineralization in lake waters was linear with time for aniline at 5.7 pg to 500 ng/ml, benzylamine at 310 ng/ml, phenol at 102 fg to 10 mg/ml, 2,4-dichlorophenoxyacetate at 1.5 pg/ml, and di-(2-ethylhexyl) phthalate at 21 pg to 200 ng/ml, but it was exponential at several p-nitrophenol concentrations. The rate of mineralization of 50 and 500 ng of aniline per ml and 200 pg and 2.0 ng of the phthalate per ml increased with time in lake waters. The phthalate and 2,4-dichlorophenoxyacetate were mineralized in samples from a eutrophic but not an oligotrophic lake. Addition to eutrophic lake water of a benzoate-utilizing bacterium did not increase the rate of benzoate mineralization at 34 and 350 pg/ml but did so at 5 and 50 ng/ml. Glucose and phenol reduced the percentage of p-nitrophenol mineralized at p-nitrophenol concentrations of 200 ng/ml but not at 22.6 pg/ml and inhibited the rates of mineralization at both concentrations. These results show that the kinetics of mineralization, the capacity of the aquatic community to assimilate carbon from the substrate or the extent of assimilation, and the sensitivity of the mineralizing populations to organic compounds are different at trace levels than at higher concentrations of organic compounds. PMID:16346011
Subba-Rao, R. V.; Rubin, Howard E.; Alexander, Martin
HCCI experiments with toluene reference fuels modeled by a semidetailed chemical kinetic model
A semidetailed mechanism (137 species and 633 reactions) and new experiments in a homogeneous charge compression ignition (HCCI) engine on the autoignition of toluene reference fuels are presented. Skeletal mechanisms for isooctane and n-heptane were added to a detailed toluene submechanism. The model shows generally good agreement with ignition delay times measured in a shock tube and a rapid compression machine and is sensitive to changes in temperature, pressure, and mixture strength. The addition of reactions involving the formation and destruction of benzylperoxide radical was crucial to modeling toluene shock tube data. Laminar burning velocities for benzene and toluene were well predicted by the model after some revision of the high-temperature chemistry. Moreover, laminar burning velocities of a real gasoline at 353 and 500 K could be predicted by the model using a toluene reference fuel as a surrogate. The model also captures the experimentally observed differences in combustion phasing of toluene/n-heptane mixtures, compared to a primary reference fuel of the same research octane number, in HCCI engines as the intake pressure and temperature are changed. For high intake pressures and low intake temperatures, a sensitivity analysis at the moment of maximum heat release rate shows that the consumption of phenoxy radicals is rate-limiting when a toluene/n-heptane fuel is used, which makes this fuel more resistant to autoignition than the primary reference fuel. Typical CPU times encountered in zero-dimensional calculations were on the order of seconds and minutes in laminar flame speed calculations. Cross reactions between benzylperoxy radicals and n-heptane improved the model predictions of shock tube experiments for {phi}=1.0 and temperatures lower than 800 K for an n-heptane/toluene fuel mixture, but cross reactions had no influence on HCCI simulations. (author)
Andrae, J.C.G. [Department of Chemical Engineering and Technology, Royal Institute of Technology (KTH), SE-100 44 Stockholm (Sweden); Brinck, T. [Department of Physical Chemistry, Royal Institute of Technology (KTH), SE-100 44 Stockholm (Sweden); Kalghatgi, G.T. [Shell Global Solutions (UK), P.O. Box 1, Chester CH1 3SH (United Kingdom)
NASA Astrophysics Data System (ADS)
The molecular structure and conformational properties of 1,3-dimethoxybenzene (1,3-DMB) have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 methods with 6-31G(d,p) and cc-pVTZ basis sets). The differences between geometrical parameters were constrained at values calculated at B3LYP/cc-pVTZ and MP2/cc-pVTZ levels. Quantum chemical calculations predict three stable planar conformers for 1,3-DMB: syn-anti ( Cs symmetry), anti-anti ( C2v symmetry), and syn-syn ( C2v symmetry) with abundances of about 65%, 20%, and 15%, respectively ( syn and anti describe the orientation of the O-CH 3 bonds relative to the C1-C2 and C2-C3 bonds, respectively). The GED analysis results in a mixture of 46(19)% syn-anti, 31(15)% anti-anti, and 23% syn-syn conformers, close to the contributions predicted by theoretical calculations. The experimental structural parameters agree well with results of B3LYP/cc-pVTZ and MP2/cc-pVTZ calculations.
Dorofeeva, Olga V.; Shishkov, Igor F.; Rykov, Anatoliy N.; Vilkov, Lev V.; Oberhammer, Heinz
Growth kinetics and yield study on Chlorella pyrenoidosa in chemically defined media
A Chlorella culture free from heterotrophic bacteria was obtained by eliminating the bacteria with successive use of antibiotics and agar plants. The purified Chlorella was cultured in chemically defined media. Under a photon flux (16.7 mw/cmS) similar to insolation, both heterotrophic and mixotrophic cultures were luxurious but the growth rates of autotrophic cultures were reduced substantially. The Chlorella culture grew most rapidly at 30 C in the absence of heterotrophic bacteria, and the highest specific growth rates were 1.43 x 10 h and 0.46 x 10 h for mixotrophic and autotrophic cultures, respectively. The highest photosynthetic efficiency over its growth period was 2.9% for autotrophic cultures. Elimination of heterotrophic bacteria from Chlorella cultures improved the algal growth rate as well as biomass yield significantly. A parasite of 0.1- m size was identified. The motile microorganism played an important role in the growth of the Chlorella and appeared to be common to green algae. 16 references, 2 tables.
Joung, J.J.; Akin, C.
Kinetic roughening of amorphous silicon during hot-wire chemical vapor deposition at low temperature
NASA Astrophysics Data System (ADS)
We use postdeposition atomic force microscopy and in situ spectroscopic ellipsometry to analyze the roughening of hydrogenated amorphous silicon films deposited by hot-wire chemical vapor deposition at 150�C. From the atomic force microscopy data, the root-mean-squared roughness w increases with deposition time t as w ?t? with ? =0.37�0.02, and the correlation length ? increases as ? ?t1/z with 1/z=0.31�0.02. From the height-difference correlation function, we obtain a roughness exponent ? =0.87�0.04 and a root-mean-squared local slope ?, which increases as ? ?t? with ? =0.17�0.03. These measurements are indicative of anomalous growth, which we attribute to geometric shadowing. However, the roughening behavior we observe using atomic force microscopy is not reproduced in the spectroscopic ellipsometry data. This contradicts previous reports which found a linear relationship between the thickness of the optical roughness layer and the root-mean-squared roughness. We discuss the discrepancy between the two techniques in terms of short-range roughness and vector perturbation theory.
Sperling, Brent A.; Abelson, John R.
Background Biochemical systems with relatively low numbers of components must be simulated stochastically in order to capture their inherent noise. Although there has recently been considerable work on discrete stochastic solvers, there is still a need for numerical methods that are both fast and accurate. The Bulirsch-Stoer method is an established method for solving ordinary differential equations that possesses both of these qualities. Results In this paper, we present the Stochastic Bulirsch-Stoer method, a new numerical method for simulating discrete chemical reaction systems, inspired by its deterministic counterpart. It is able to achieve an excellent efficiency due to the fact that it is based on an approach with high deterministic order, allowing for larger stepsizes and leading to fast simulations. We compare it to the Euler ?-leap, as well as two more recent ?-leap methods, on a number of example problems, and find that as well as being very accurate, our method is the most robust, in terms of efficiency, of all the methods considered in this paper. The problems it is most suited for are those with increased populations that would be too slow to simulate using Gillespie�s stochastic simulation algorithm. For such problems, it is likely to achieve higher weak order in the moments. Conclusions The Stochastic Bulirsch-Stoer method is a novel stochastic solver that can be used for fast and accurate simulations. Crucially, compared to other similar methods, it better retains its high accuracy when the timesteps are increased. Thus the Stochastic Bulirsch-Stoer method is both computationally efficient and robust. These are key properties for any stochastic numerical method, as they must typically run many thousands of simulations. PMID:24939084
Modelling cycle to cycle variations in an SI engine with detailed chemical kinetics
This paper presents experimental results and a new computational model that investigate cycle to cycle variations (CCV) in a spark ignition (SI) engine. An established stochastic reactor model (SRM) previously used to examine homogeneous charge compression ignition (HCCI) combustion has been extended by spark initiation, flame propagation and flame termination sub-models in order to simulate combustion in SI engines. The model contains a detailed chemical mechanism but relatively short computation times are achieved. The flame front is assumed to be spherical and centred at the spark location, and a pent roof and piston bowl geometry are accounted for. The model is validated by simulating the pressure profile and emissions from an iso-octane fuelled single cylinder research engine that showed low CCV. The effects of key parameters are investigated. Experimental results that show cycle to cycle fluctuations in a four-cylinder naturally aspirated gasoline fuelled SI engine are presented. The model is then coupled with GT-Power, a one-dimensional engine simulation tool, which is used to simulate the breathing events during a multi-cycle simulation. This allows an investigation of the cyclic fluctuations in peak pressure. The source and magnitude of nitric oxide (NO) emissions produced by different cycles are then investigated. It was found that faster burning cycles result in increased NO emissions compared with cycles that have a slower rate of combustion and that more is produced in the early stages of combustion compared with later in the cycle. The majority of NO was produced via the thermal mechanism just after combustion begins. (author)
Etheridge, Jonathan; Mosbach, Sebastian; Kraft, Markus [Department of Chemical Engineering and Biotechnology, University of Cambridge (United Kingdom); Wu, Hao; Collings, Nick [Department of Engineering, University of Cambridge (United Kingdom)
Chemical kinetic modeling of benzene and toluene oxidation behind shock waves
NASA Technical Reports Server (NTRS)
The oxidation of stoichiometric mixtures of benzene and toluene behind incident shock waves was studied for a temperature range from 1700 to 2800 K and a pressure range from 1.1 to 1.7 atm. The concentration of CO and CO2 produced were measured as well as the product of the oxygen atom and carbon monoxide concentrations. Comparisons between the benzene experimental data and results calculated by use of a reaction mechanism published in the open literature were carried out. With some additional reactions and changes in rate constants to reflect the pressure-temperature range of the experimental data, a good agreement was achieved between computed and experimental results. A reaction mechanism was developed for toluene oxidation based on analogous rate steps from the benzene mechanism. Measurements of NOx levels in an actual flame device, a jet-stirred combustor, were reproduced successfully by use of the reaction mechanism developed from the shock-tube experiments on toluene. These experimental measurements of NOx levels were reproduced from a computer simulation of a jet-stirred combustor.
Mclain, A. G.; Jachimowski, C. J.; Wilson, C. H.
Solvent effects in the GIAO-DFT calculations of the (15) N NMR chemical shifts of azoles and azines.
The calculation of (15) N NMR chemical shifts of 27 azoles and azines in 10 different solvents each has been carried out at the gauge including atomic orbitals density functional theory level in gas phase and applying the integral equation formalism polarizable continuum model (IEF-PCM) and supermolecule solvation models to account for solvent effects. In the calculation of (15) N NMR, chemical shifts of the nitrogen-containing heterocycles dissolved in nonpolar and polar aprotic solvents, taking into account solvent effect is sufficient within the IEF-PCM scheme, whereas for polar protic solvents with large dielectric constants, the use of supermolecule solvation model is recommended. A good agreement between calculated 460 values of (15) N NMR chemical shifts and experiment is found with the IEF-PCM scheme characterized by MAE of 7.1?ppm in the range of more than 300?ppm (about 2%). The best result is achieved with the supermolecule solvation model performing slightly better (MAE 6.5?ppm). Copyright � 2014 John Wiley & Sons, Ltd. PMID:25102971
Semenov, Valentin A; Samultsev, Dmitry O; Krivdin, Leonid B
NASA Technical Reports Server (NTRS)
Quantitative values were computed which show the effects of the presence of small amounts of oxygen, hydrogen, and hydroxyl radicals on the finite-rate chemical kinetics of premixed hydrogen-air mixtures undergoing isobaric autoignition and combustion. The free radicals were considered to be initially present in hydrogen-air mixtures at equivalence ratios of 0.2, 0.6, 1.0, and 1.2. Initial mixture temperatures were 1100 K, 1200 K, and 1500 K, and pressures were 0.5, 1.0, 2.0, and 4.0 atm. Of the radicals investigated, atomic oxygen was found to be the most effective for reducing induction time, defined as the time to 5 percent of the total combustion temperature rise. The reaction time, the time between 5 percent and 95 percent of the temperature rise, is not decreased by the presence of free radicals in the initial hydrogen-air mixture. Fuel additives which yield free radicals might be used to effect a compact supersonic combustor design for efficient operation in an otherwise reaction-limited combustion regime.
Carson, G. T., Jr.
NASA Astrophysics Data System (ADS)
Experimental results of electron paramagnetic resonance spectra, X-ray diffraction, scanning electron microscopy and infrared spectroscopy demonstrate that the kinetic of the physical and chemical processes that takes place during prolonged intensive mechanical processing (MP, 0
Kakazey, M.; Vlasova, M.; Dominguez-Pati�o, M.; Juarez-Arellano, E. A.; Bykov, A.; Leon, I.; Siqueiros-Diaz, A.
Conventional petroleum jet and diesel fuels, as well as alternative Fischer-Tropsch (FT) fuels and hydrotreated renewable jet (HRJ) fuels, contain high molecular weight lightly branched alkanes (i.e., methylalkanes) and straight chain alkanes (n-alkanes). Improving the combustion of these fuels in practical applications requires a fundamental understanding of large hydrocarbon combustion chemistry. This research project presents a detailed and reduced chemical kinetic mechanism for singly methylated iso-alkanes (i.e., 2-methylalkanes) ranging from C{sub 8} to C{sub 20}. The mechanism also includes an updated version of our previously published C{sub 8} to C{sub 16} n-alkanes model. The complete detailed mechanism contains approximately 7,200 species 31,400 reactions. The proposed model is validated against new experimental data from a variety of fundamental combustion devices including premixed and nonpremixed flames, perfectly stirred reactors and shock tubes. This new model is used to show how the presence of a methyl branch affects important combustion properties such as laminar flame propagation, ignition, and species formation.
Sarathy, S M; Westbrook, C K; Pitz, W J; Mehl, M; Togbe, C; Dagaut, P; Wang, H; Oehlschlaeger, M; NIemann, U; Seshadri, K; Veloo, P S; Ji, C; Egolfopoulos, F; Lu, T
Breadnut skin, in both its unmodified (KS) and base-modified (BM-KS) forms, was investigated for its potential use as a low-cost adsorbent for the removal of toxic dye, malachite green (MG). Characterization of the adsorbents was carried out using scanning electron microscope, X-ray fluorescence and Fourier transform infra-red spectroscopy. Batch adsorption experiments, carried out under optimized conditions, for the adsorption of MG were fitted using five isotherm models (Langmuir, Freundlich, Dubinin-Radushkevich, Temkin and Sips) and six error functions to determine the best-fit model. The adsorption capacity was greatly enhanced when breadnut skin was chemically modified with NaOH, leading to an adsorption capacity of 353.0�mg�g(-1), that was far superior to most reported adsorbents for the removal of MG. Thermodynamics studies indicated that the adsorption of MG was spontaneous on KS and BM-KS, and the reactions were endothermic and exothermic, respectively. Kinetics studies showed that both followed the pseudo-second order. Regeneration experiments on BM-KS indicated that its adsorption capacity was still maintained at>90% even after five cycles. It can be concluded that NaOH-modified breadfruit skin has great potential to be utilized in real-life application as a low-cost adsorbent for the removal of MG in wastewater treatment. PMID:25409587
Chieng, Hei Ing; Lim, Linda B L; Priyantha, Namal
The exquisite sensitivity of chemical shifts as reporters of structural information, and the ability to measure them routinely and accurately, gives great import to formulations that elucidate the structure-chemical-shift relationship. Here we present a new and highly accurate, precise, and robust formulation for the prediction of NMR chemical shifts from protein structures. Our approach, shAIC (shift prediction guided by Akaikes Information Criterion), capitalizes on mathematical ideas and an information-theoretic principle, to represent the functional form of the relationship between structure and chemical shift as a parsimonious sum of smooth analytical potentials which optimally takes into account short-, medium-, and long-range parameters in a nuclei-specific manner to capture potential chemical shift perturbations caused by distant nuclei. shAIC outperforms the state-of-the-art methods that use analytical formulations. Moreover, for structures derived by NMR or structures with novel folds, shAIC delivers better overall results; even when it is compared to sophisticated machine learning approaches. shAIC provides for a computationally lightweight implementation that is unimpeded by molecular size, making it an ideal for use as a force field. PMID:22293396
Nielsen, Jakob T.; Eghbalnia, Hamid R.; Nielsen, Niels Chr.
NASA Astrophysics Data System (ADS)
We studied four substituted mercaptotetrazoles using IR- and Raman-spectroscopy on the bulk substance and surface enhanced Raman spectroscopy (SERS) on a silver colloid. Semiempirical and ab initio calculations with various basis sets were performed to establish an assignment of the experimentally observed bands to the calculated ones. We found a satisfactory agreement between the calculated and observed frequencies of CH/CC-vibrations in the phenyl ring and encountered problems with the tetrazole ring vibrations. The PM3 hamiltonian failed for the SH group.
S�gm�ller, Bernd; Freunscht, Peter; Schneider, Siegfried
Step-Scan FTIR spectroscopy and quantum chemical calculations of xanthone in the triplet state
NASA Astrophysics Data System (ADS)
Step-Scan-FTIR spectroscopy has been used to measure the infrared spectrum of xanthone in the triplet state using chloroform as solvent. Xanthone is an important triplet sensitizer and therefore suitable as model system. Xanthone was excited at 266 nm and its IR triplet spectrum measured in the range 1000-1750 cm-1. The spectrum was analyzed by comparison with DFT/B3LYP/TZVP/COSMO calculations. Further on the results were compared to gas phase IR measurements of triplet xanthone and calculations of isolated xanthone. Mainly based on the calculations we tried to identify the geometry changes from the electronic ground state to the first triplet state.
Buschhaus, L.; Kleinermanns, K.
NASA Technical Reports Server (NTRS)
LSENS, the Lewis General Chemical Kinetics and Sensitivity Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part II of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part II describes the code, how to modify it, and its usage, including preparation of the problem data file required to execute LSENS. Code usage is illustrated by several example problems, which further explain preparation of the problem data file and show how to obtain desired accuracy in the computed results. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions. Part I (NASA RP-1328) derives the governing equations and describes the numerical solution procedures for the types of problems that can be solved by LSENS. Part III (NASA RP-1330) explains the kinetics and kinetics-plus-sensitivity-analysis problems supplied with LSENS and presents sample results.
Radhakrishnan, Krishnan; Bittker, David A.
Quantum chemical calculation of the equilibrium structures of small metal atom clusters
NASA Technical Reports Server (NTRS)
Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches. Because these large 'molecular' systems pose special practical computational problems in the application of the quantum mechanical methods, there is a special need to find simplifying techniques that do not compromise the reliability of the calculations. Research is therefore directed towards various aspects of the implementation of the effective core potential technique for the removal of the metal atom core electrons from the calculations.
Kahn, L. R.
We have performed a quantum-chemical MP2/6-31G* calculation for the hemagglutinin (HA) antigen-antibody system of the H3N2 influenza virus with the fragment molecular orbital method, which provides one of the world's largest ab initio electron-correlated calculations for biomolecular systems. On the basis of the calculated interfragment interaction energies (IFIEs) representing the molecular interactions between the amino acid residues in the antigen-antibody complex, we have identified those residues in the antigenic region E of HA protein that are significantly recognized by the Fab fragment of antibody with strongly attractive interactions. Combining these IFIE results with those of hemadsorption experiments by which the mutation-prohibited sites are specified has enabled us to explain most of the historical mutation data (five of six residues), which would thus provide a promising method for predicting the HA residues that have a high probability of forthcoming mutation. PMID:19323468
Takematsu, Kazutomo; Fukuzawa, Kaori; Omagari, Katsumi; Nakajima, Setsuko; Nakajima, Katsuhisa; Mochizuki, Yuji; Nakano, Tatsuya; Watanabe, Hirofumi; Tanaka, Shigenori
The calculation of polar surface areas (PSA) from the electron density using quantum chemical topology (QCT) and a newly developed algorithm to determine isodensity surface areas is described. PSA values were calculated from the atomic partitioning of B3LYP/6-311G* wavefunctions and the results described herein represent the first application of this new algorithm. PSA values were calculated for forty drugs and compared to the topological polar surface area (TPSA) and those calculated by the QikProp program. Oral bioavailabilities predicted from the QCT PSA values for a subset of twenty drugs (the Palm set) were similar to those predicted by the dynamic polar surface area (DPSA) and in general, are in agreement with the observed values. Overall, PSA values obtained from QCT were generally similar to the DPSA, TPSA, and QikProp values, though differences in fragment contributions were found, with nitrogen-bearing functional groups showing the largest variation between methods. Differences between methods showed how the calculation of the PSA is dependent on the method used and, therefore, judicious application of the upper limits used in the prediction of oral bioavailability is warranted. These results also indicate that, because of the differences in the way PSA values are calculated, values from the different methods should not be used interchangeably. PMID:18161739
Bytheway, Ian; Darley, Michael G; Popelier, Paul L A
NASA Astrophysics Data System (ADS)
An application of the finite element method to calculation of the adhesive joints of D16AT alloy plates, which are subjected to the effect of shear and bend, is justified on the basis of complex theoretical and experimental analysis. The possibility of extension of the developed models on a linear fracture mechanics field for laminated metal polymer composites is shown and experimentally confirmed. The influence of some mechanical characteristics of the polymeric binder on the fracture nature in the area of through and surface cracks is estimated by calculation for organometallic plastics.
Semin, M. I.; Safonov, P. K.
A box model representative for a mesoscale volume and three different plume models are used to estimate the chemical conversion of exhaust species of a subsonic aircraft at cruise altitude. Clearly deviating results have been obtained for instantaneous mixing of the exhaust in a box and gradual dispersion of a plume. The effect of varying daytime of release as well
H. Petry; J. Hendricks; M. M�llhoff; E. Lippert; A. Meier; A. Ebel; R. Sausen
of fullerene derivatives than in parent C60 and C70 spectra. It is difficult, even impossible, to assign the 13-Encapsulated Fullerenes and Fullerene Derivatives Guan-Wu Wang,*, Xin-Hao Zhang, Huan Zhan, Qing-Xiang Guo-3 NMR chemical shifts of various 3 He-encapsulated fullerenes (3 He@Cn) and their derivatives have
Wang, Guan-Wu
Homogeneous Decomposition Mechanisms of Diethylzinc by Raman Spectroscopy and Quantum Chemical. The homogeneous thermal decomposition of DEZn in N2 carrier was followed in an impinging-jet, up-flow reactor dissociation between zinc and carbon atoms is the dominant homogeneous thermal decomposition pathway
Anderson, Timothy J.
NASA Astrophysics Data System (ADS)
The kinetics and mechanism for the reaction of ClOO with NO have been investigated by ab initio molecular orbital theory calculations based on the CCSD(T)/6-311+G(3df)//PW91PW91/6-311+G(3df) method, employed to evaluate the energetics for the construction of potential energy surfaces and prediction of reaction rate constants. The results show that the reaction can produce two key low energy products ClNO + 3O2 via the direct triplet abstraction path and ClO + NO2 via the association and decomposition mechanism through long-lived singlet pc-ClOONO and ClONO2 intermediates. The yield of ClNO + O2 (1?) from any of the singlet intermediates was found to be negligible because of their high barriers and tight transition states. As both key reactions initially occur barrierlessly, their rate constants were evaluated with a canonical variational approach in our transition state theory and Rice-Ramspergen-Kassel-Marcus/master equation calculations. The rate constants for ClNO + 3O2 and ClO + NO2 production from ClOO + NO can be given by 2.66 � 10-16 T1.91 exp(341/T) (200-700 K) and 1.48 � 10-24 T3.99 exp(1711/T) (200-600 K), respectively, independent of pressure below atmospheric pressure. The predicted total rate constant and the yields of ClNO and NO2 in the temperature range of 200-700 K at 10-760 Torr pressure are in close agreement with available experimental results.
Raghunath, P.; Lin, M. C.
Multi-step, gas-phase chemical kinetics are introduced into flame spread modeling efforts. An unsteady multi-step, gas-phase kinetics model both with and without steady-state species assumptions, and including nonunit Lewis number, is compared with a model including a single, finite-rate gas-phase reaction, which has been the usual approach in flame spread modeling. Laminar diffusion flames over a thin fuel in an opposing O{sub 2}/N{sub 2} flow are considered with the solution in two-dimensional space of momentum, energy, and 12 gas-phase species. Results for the multi-step models show detailed flame structure in terms of species and heat release distributions throughout the flame and the role of chemical kinetics as a controlling mechanism in flame spread. Of particular interest is the potential of multi-step chemical kinetics in solutions at near-extinction limit conditions. While the incorporation of nonunit Le alone affords more detailed species transport, in high opposing flows it was found to give only minor structural differences form the single-step unit Le model. The multi-step chemistry allows for the gas kinetics to be self-adjusting to environmental conditions. As a result, the distribution of endothermicity and exothermicity throughout the flame and for particular reversible reactions is found to be a function of the flow environment, which overcomes a major drawback of single-step models, namely a fixed heat of combustion independent of environmental conditions, or one that must be determined separately from the model itself.
Wolverton, M.K.; Altenkirch, R.A.; Tang, L. [Mississippi State Univ., MS (United States)] [Mississippi State Univ., MS (United States)
The torsional energy levels of CH3OH(+), CH3OD(+), and CD3OD(+) have been determined for the first time using one-photon zero kinetic energy photoelectron spectroscopy. The adiabatic ionization energies for CH3OH, CH3OD, and CD3OD are determined as 10.8396, 10.8455, and 10.8732 eV with uncertainties of 0.0005 eV, respectively. Theoretical calculations have also been performed to obtain the torsional energy levels for the three isotopologues using a one-dimensional model with approximate zero-point energy corrections of the torsional potential energy curves. The calculated values are in good agreement with the experimental data. The barrier height of the torsional potential energy without zero-point energy correction was calculated as 157 cm(-1), which is about half of that of the neutral (340 cm(-1)). The calculations showed that the cation has eclipsed conformation at the energy minimum and staggered one at the saddle point, which is the opposite of what is observed in the neutral molecule. The fundamental C-O stretch vibrational energy level for CD3OD(+) has also been determined. The energy levels for the combinational excitation of the torsional vibration and the fundamental C-O stretch vibration indicate a strong torsion-vibration coupling. PMID:25318721
Dai, Zuyang; Gao, Shuming; Wang, Jia; Mo, Yuxiang
NASA Astrophysics Data System (ADS)
In this paper the relationship between the chemical structure and fluorescence characteristics of 30 phenylquinolinylethyne (PhQE), and phenylisoquinolinylethyne (PhIE) derivatives compounds employing ab initio calculations have been elucidated. Quantum chemical calculations (6-31G) were carried out to obtain: the optimized geometry, energy levels, charges and dipole moments of these compounds, in the singlet (steady and excited states) and triplet states. The relationship between quantum chemical descriptors, and wavelength of maximum excitation and emission indicated that these two parameters have the most correlation with quantum chemical hardness ( ?). Also, stokes shift has the most correlation with the square of difference between the maximum of positive charges in the singlet steady and singlet excited states. The quantitative structure-property relationship (QSPR) of PhQE and PhIE was studied for relative fluorescence intensity (RFI). The genetic algorithm (GA) was applied to select the variables that resulted in the best-fit models. After the variable selection, multiple linear regression (MLR) and support vector machine (SVM) were both utilized to construct linear and non-linear QSPR models, respectively. The SVM model demonstrated a better performance than that of the MLR model. The route mean square error (RMSE) in the training and the test sets for the SVM model was 0.195 and 0.324, and the correlation coefficients were 0.965 and 0.960, respectively, thus revealing the reliability of this model. The resulting data indicated that SVM could be used as a powerful modeling tool for QSPR studies. According to the best of our knowledge, this is the first research on QSPR studies to predict RFI for a series of PhQE and PhIE derivative compounds using SVM.
Riahi, Siavash; Beheshti, Abolghasem; Ganjali, Mohammad Reza; Norouzi, Parviz
Ab initio quantum chemical calculations of aluminum substitution in zeolite ZSM-5
The authors have performed ab initio quantum mechanical calculations in monomeric clusters modeling the 12 different T sites of zeolite ZSM-5. By comparing the results of calculations that use minimum basis sets with those that employ valence double-[zeta] bases, the authors conclude that minimum basis sets are unreliable for predicting relative replacement energies for the substitution of silicon by aluminum atoms at the T sites of the zeolite. From these calculations, it is also concluded that small differences in the bond lengths and angles can significantly alter the order of the sites with respect to the replacement energies. From calculations using valence double-[zeta] basis sets on T(OH)[sub 4] monomers, it is concluded that in the absence of protons or other ions, the most favorable sites for Al substitution in zeolite ZSM-5 are the T[sub 6], T[sub 12], and T[sub 9] sites, whereas the least favorable site is T[sub 3]. However, the least favorable and most favorable sites only differ by 3.3 kcal/mol. The authors also present a simple empirical model that is capable of reproducing the results of the ab initio calculations. This model gives the replacement energy in terms of the bond lengths and bond angles about each site.
Alvarado-Swaisgood, A.E.; Barr, M.K. (Amoco Research Center, Naperville, IL (United States)); Hay, P.J.; Redondo, A. (Los Alamos National Lab., NM (United States))
NASA Astrophysics Data System (ADS)
For numerically predicting the combustion processes in homogeneous charge compression ignition (HCCI) engines, practical chemical kinetic models have been explored. A genetic algorithm (GA) has been applied to the optimization of the rate constants in detailed chemical kinetic models, and a detailed kinetic model (592 reactions) for gasoline reference fuels with arbitrary octane number between 60 and 100 has been obtained from the detailed reaction schemes for iso-octane and n-heptane proposed by Golovitchev. The ignition timing in a gasoline HCCI engine has been predicted reasonably well by zero-dimensional simulation using the CHEMKIN code with this detailed kinetic model. An original reduced reaction scheme (45 reactions) for dimethyl ether (DME) has been derived from Curran�s detailed scheme, and the combustion process in a DME HCCI engine has been predicted reasonably well in a practical computation time by three-dimensional simulation using the authors� GTT code, which has been linked to the CHEMKIN subroutines with the proposed reaction scheme and also has adopted a modified eddy dissipation combustion model.
Kim, Sang-Kyu; Ito, Kazuma; Yoshihara, Daisuke; Wakisaka, Tomoyuki
Quantum chemical calculation of the equilibrium structures of small metal atom clusters
NASA Technical Reports Server (NTRS)
The application of ab initio quantum mechanical approaches in the study of metal atom clusters requires simplifying techniques that do not compromise the reliability of the calculations. Various aspects of the implementation of the effective core potential (ECP) technique for the removal of the metal atom core electrons from the calculation were examined. The ECP molecular integral formulae were modified to bring out the shell characteristics as a first step towards fulfilling the increasing need to speed up the computation of the ECP integrals. Work on the relationships among the derivatives of the molecular integrals that extends some of the techniques pioneered by Komornicki for the calculation of the gradients of the electronic energy was completed and a formulation of the ECP approach that quite naturally unifies the various state-of-the-art "shape- and Hamiltonian-consistent" techniques was discovered.
Kahn, L. R.
For description of the chemical structure of RDX flames, key reactions and species are selected by numerical solution of the system of equations describing one�dimensional flows of a viscous, heat�conducting, reacting gas at pressures of 0.5�90 atm. The kinetic mechanism consists of 263 elementary steps and 43 species. Literature data on rate constants of elementary steps are considered. Flame structure
N. E. Ermolin; V. E. Zarko
The ability of pseudo-detailed chemical kinetic modeling to simulate the oxidation behavior of Exxsol D-80, a paraffin blend whose oxidative characteristics are representative of severely hydrotreated jet fuels, is assessed. The effects of temperature and initial dissolved O2 concentration on oxidation are considered. A 17-step pseudo-detailed mechanism is shown to provide reasonable simulations of Exxsol D-80 oxidation over a range
Nicholas J. Kuprowicz; Jamie S. Ervin; Steven Zabarnick
NASA Technical Reports Server (NTRS)
LSENS, the Lewis General Chemical Kinetics and Sensitivity Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part 1 of a series of three reference publications that describe LENS, provide a detailed guide to its usage, and present many example problems. Part 1 derives the governing equations and describes the numerical solution procedures for the types of problems that can be solved. The accuracy and efficiency of LSENS are examined by means of various test problems, and comparisons with other methods and codes are presented. 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.
Radhakrishnan, Krishnan
NASA Technical Reports Server (NTRS)
An addition to the computer program of NASA SP-273 is given that permits transport property calculations for the gaseous phase. Approximate mixture formulas are used to obtain viscosity and frozen thermal conductivity. Reaction thermal conductivity is obtained by the same method as in NASA TN D-7056. Transport properties for 154 gaseous species were selected for use with the program.
Gordon, S.; Mcbride, B.; Zeleznik, F. J.
NASA Astrophysics Data System (ADS)
In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 3500-100 cm-1 and 4000-400 cm-1, respectively, for 3-Bromodiphenylamine (3BDPA). Theoretical calculations were performed by using Density Functional Theory (DFT) method with 6-31G(d,p) and 6-311++G(d,p) basis sets. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The calculated wavenumbers were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. The frontier orbital energy gap and dipole moment illustrates the high reactivity of the title molecule. The first order hyperpolarizability (?0) and related properties (?, ? and ??) of the molecule were also calculated. Stability of the molecule arising from hyperconjugative interactions and charge delocalization were analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the ?* and ?* anti-bonding orbitals and second order delocalization energies (E2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. Molecular electrostatic potential (MEP) and HOMO-LUMO energy levels are also constructed. The thermodynamic properties of the title compound were calculated at different temperatures and the results reveals the heat capacity (C), and entropy (S) increases with rise in temperature.
Sudharsan, A.; Seshadri, S.; Gnanasambandan, T.; Saravanan, R. R.
Theoretical calculations of the thermal rate constants for the gas-phase chemical reactions H + NH
Rate constants for the title reactions are computed by using variational transition-state theory with semiclassical ground-state adiabatic transmission coefficients for the temperature range from 200 to 2,400 K. The rates are computed from selected information about the potential energy surface along the minimum energy path as parameters of the reaction path Hamiltonian. The potential information is obtained from ab initio electronic structure calculations with an empirical bond additivity correction. The accuracy of this semiempirical technique for obtaining the potential information is tested by comparing the results of the underlying ab initio calculations with higher quality multiconfiguration SCF and multireference CI calculations and by using increasingly higher quality ab initio electronic structure calculations before applying the bond additivity correction. For the reactions H + NH{sub 3} {yields} H{sub 2} + NH{sub 2}, H{sub 2} + NH{sub 2} {yields} H + NH{sub 3}, and D + ND{sub 3} {yields} D{sub 2} + ND{sub 2}, the ultimate test is given by comparison with recent experimental results. Although the agreement is good in general, the comparisons of experiment and theory indicate that the computed barrier height is overestimated by about 1 kcal/mol.
Garrett, B.C. (Chemical Dynamics Corp., Marlboro, MD (USA)); Koszykowski, M.L.; Melius, C.F. (Sandia National Lab., Livermore, CA (USA)); Page, M. (Naval Research Lab., Washington, DC (USA))
for the calculation of activation energies by the Ynitial rise Rportion of glow curves is given. The method is shown of finding the activation energy of a trap by using the "initial rise" range of thermoluminescence (TL A is a constant, E the activation energy, T the absolute temperature and k the Boltzmann constant. By plotting
Chen, Reuven
NASA Astrophysics Data System (ADS)
Single crystals of N-Succinopyridine (NSP) have been grown from water using solution growth method by isothermal solvent evaporation technique. The solid state Fourier Transform Infrared (FTIR) spectrum of the grown crystal shows a broad absorption extending from 3450 down to 400 cm-1, due to H-bond vibrations and other characteristic vibrations. Fourier Transform Raman (FT-Raman) spectrum of NSP single crystal shows Raman intensities ranging from 3100 to 100 cm-1 due the characteristics vibrations of functional groups present in NSP. The proton and carbon positions of NSP have been described by 1H and 13C NMR spectrum respectively. Ab initio quantum chemical calculations on NSP have been performed by density functional theory (DFT) calculations using B3LYP method with 6-311++G(d,p) basis set. The predicted first hyperpolarizability is found to be 1.29 times greater than that of urea and suggests that the title compound could be an attractive material for nonlinear optical applications. The calculated HOMO-LUMO energies show that charge transfers occur within the molecule and other related molecular properties. Molecular properties such as Mulliken population analysis, thermodynamic functions and perturbation theory energy analysis have also been reported. Electrostatic potential map (ESP) of NSP obtained by electron density isosurface provided the information about the size, shape, charge density distribution and site of chemical reactivity of the title molecule. The molecular stability and bond strength have been investigated through the Natural Bond Orbital (NBO) analysis.
Kannan, V.; Thirupugalmani, K.; Brahadeeswaran, S.
The objective of this study was to evaluate the impact of whole- and sub-population-related variabilities on the determination of the human kinetic adjustment factor (HKAF) used in risk assessment of inhaled volatile organic chemicals (VOCs). Monte Carlo simulations were applied to a steady-state algorithm to generate population distributions for blood concentrations (CAss) and rates of metabolism (RAMs) for inhalation exposures to benzene (BZ) and 1,4-dioxane (1,4-D). The simulated population consisted of various proportions of adults, elderly, children, neonates and pregnant women as per the Canadian demography. Subgroup-specific input parameters were obtained from the literature and P3M software. Under the "whole population" approach, the HKAF was computed as the ratio of the entire population's upper percentile value (99th, 95th) of dose metrics to the median value in either the entire population or the adult population. Under the "distinct subpopulation" approach, the upper percentile values in each subpopulation were considered, and the greatest resulting HKAF was retained. CAss-based HKAFs that considered the Canadian demography varied between 1.2 (BZ) and 2.8 (1,4-D). The "distinct subpopulation" CAss-based HKAF varied between 1.6 (BZ) and 8.5 (1,4-D). RAM-based HKAFs always remained below 1.6. Overall, this study evaluated for the first time the impact of underlying assumptions with respect to the interindividual variability considered (whole population or each subpopulation taken separately) when determining the HKAF. PMID:22523487
Valcke, M; Nong, A; Krishnan, K
Kinetic-fluid dynamics modeling of I{sub 2} dissociation in supersonic chemical oxygen-iodine lasers
The mechanism of I{sub 2} dissociation in supersonic chemical oxygen-iodine lasers (COILs) is studied applying kinetic-fluid dynamics modeling, where pathways involving the excited species I{sub 2}(X {sup 1}SIGMA{sub g}{sup +},10<=v<25), I{sub 2}(X {sup 1}SIGMA{sub g}{sup +},25<=v<=47), I{sub 2}(A{sup '} {sup 3}PI{sub 2u}), I{sub 2}(A {sup 3}PI{sub 1u}), O{sub 2}(X {sup 3}SIGMA{sub g}{sup -},v), O{sub 2}(a {sup 1}DELTA{sub g},v), O{sub 2}(b {sup 1}SIGMA{sub g}{sup +},v), and I({sup 2}P{sub 1/2}) as intermediate reactants are included. The gist of the model is adding the first reactant and reducing the contribution of the second as compared to previous models. These changes, recently suggested by Azyazov, et al. [J. Chem. Phys. 130, 104306 (2009)], significantly improve the agreement with the measurements of the gain in a low pressure supersonic COIL for all I{sub 2} flow rates that have been tested in the experiments. In particular, the lack of agreement for high I{sub 2} flow rates, which was encountered in previous models, has been eliminated in the present model. It is suggested that future modeling of the COIL operation should take into account the proposed contribution of the above mentioned reactants.
Waichman, K. [Department of Physics, NRCN, P.O. Box 9001, Beer Sheva 89140 (Israel); Barmashenko, B. D.; Rosenwaks, S. [Department of Physics, Ben-Gurion University of the Negev, Beer Sheva 84105 (Israel)
NASA Technical Reports Server (NTRS)
We have previously developed a chemical conversion model of the carbothermal processing of lunar regolith using methane to predict the rate of production of carbon monoxide. In this carbothermal process, gaseous methane is pyrolyzed as it flows over the hot surface of a molten zone of lunar regolith and is converted to carbon and hydrogen. Hydrogen is carried away by the exiting stream of gases and carbon is deposited on the melt surface. The deposited carbon mixes with the melt and reacts with the metal oxides in it to produce carbon monoxide that bubbles out of the melt. In our model, we assume that the flux of carbon deposited is equal to the product of the surface reaction rate constant gamma and the concentration of methane adjacent to the melt surface. Similarly, the rate of consumption of carbon per unit volume in the melt is equal to the product of the melt reaction rate constant k and the concentrations of carbon and metal oxide in the melt. In this paper, we describe our effort to determine gamma and k by comparison of the predictions from our model with test data obtained by ORBITEC (Orbital Technologies Corporation). The concentration of methane adjacent to the melt surface is a necessary input to the model. It is inferred from the test data by a mass balance of methane, adopting the usual assumptions of the continuously-stirred-tank-reactor model, whereby the average concentration of a given gaseous species equals its exit concentration. The reaction rates gamma and k have been determined by a non-linear least-squares fit to the test data for the production of carbon monoxide and the fraction of the incoming methane that is converted. The comparison of test data with our model predictions using the determined chemical kinetic rate constants provides a consistent interpretation of the process over the full range of temperatures, pressures, and methane flow rates used in the tests, thereby increasing our confidence to use the model for scale-up purposes.
Balasubramaniam, R; Gokoglu, S.; Hegde, U.
in Solution and in Enzymes Jiali Gao,*,a Dan T. Major, Yao Fan, Yen-lin Lin, Shuhua Ma, and Kin-Yiu Wong Isotope Effects, Enzyme Kinetics, and Solvent Effects. Abstract: A method for incorporating quantum mechanics into enzyme kinetics modeling is presented. Three aspects are emphasized: (1) combined quantum
Minnesota, University of
Quantum chemical and conventional TST calculations of rate constants for the OH + alkane reaction
NASA Astrophysics Data System (ADS)
Reactions of OH with methane, ethane, propane, i-butane, and n-butane have been modeled using ab initio (MP2) and hybrid DFT (BHandHLYP) methods, and the 6-311G(d,p) basis set. Furthermore, single-point calculations at the CCSD(T) level were carried out at the optimized geometries. The rate constants have been calculated using the conventional transition-state theory (CTST). Arrhenius equations are proposed in the temperature range of 250-650 K. Hindered Internal Rotation partition functions calculations were explicitly carried out and included in the total partition functions. These corrections showed to be relevant in the determination of the pre-exponential parameters, although not so important as in the NO 3 + alkane reactions [G. Bravo-P�rez, J.R. Alvarez-Idaboy, A. Cruz-Torres, M.E. Ru�z, J. Phys. Chem. A 106 (2002) 4645]. The explicit participation of the tunnel effect has been taken into account. The calculated rate coefficients provide a very good agreement with the experimental data. The best agreement for the overall alkane + OH reactions seemed to occur when the BHandHLYP geometries and partition functions are used. For propane and i-butane, in addition to the respective secondary and tertiary H-abstraction channels, the primary one has been considered. These pathways are confirmed to be significant in spite of the large differences in activation energies between primary and secondary or primary and tertiary channels, respectively of propane and i-butane reactions and should not be disregarded.
Bravo-P�rez, Graciela; Alvarez-Idaboy, J. Ra�l; Jim�nez, Annia Galano; Cruz-Torres, Armando
This report contains sections on the reaction of chlorine atoms with 1,1,1,2-terafluoroethane, abstraction reactions by thermal chlorine atoms with hfc-134a, and chlorine atom reactions with vinyl bromide.
Rowland, F.S.
The team will examine how the incorporation of actinide species important for mixed oxide (MOX) and other advanced fuel designs impacts thermodynamic quantities of the host UO2 nuclear fuel and how Pu, Np, Cm and Am influence oxygen mobility. In many cases, the experimental data is either insufficient or missing. For example, in the case of pure NpO2, there is essentially no experimental data on the hyperstoichiometric form it is not even known if hyperstoichiometry NpO2+x is stable. The team will employ atomistic modeling tools to calculate these quantities
Chaitanya Deo; Davis Adnersson; Corbett Battaile; Blas uberuaga
NASA Astrophysics Data System (ADS)
Several new substituted amidine derivatives of benzanthrone were synthesized by a condensation reaction from 3-aminobenzo[de]anthracen-7-one and appropriate aromatic and aliphatic amides. The obtained derivatives have a bright yellow or orange fluorescence in organic solvents and in solid state. The novel benzanthrone derivatives were characterized by TLC analysis, 1H NMR, IR, MS, UV/vis, and fluorescence spectroscopy. The solvent effect on photophysical behaviors of these dyes was investigated, and the results showed that the Stoke's shift increased, whereas quantum yield decreased with the growth of the solvent polarity. The structure of some dyes was confirmed by the X-ray single crystal structure analysis. AM1, ZINDO/S and ab initio calculations using Gaussian software were carried out to estimate the electron system of structures. The calculations show planar configurations for the aromatic core of these compounds and two possible orientations of amidine substituents. The calculation results correlate well with red-shifted absorption and emission spectra of compounds.
Gonta, Svetlana; Utinans, Maris; Kirilov, Georgii; Belyakov, Sergey; Ivanova, Irena; Fleisher, Mendel; Savenkov, Valerij; Kirilova, Elena
Major element, minor element, and gas composition data are tabulated for 15 springs and wells in Honey Lake Valley, California. Wendel and Amedee hot springs issue Na-S04-C1 waters at boiling or near boiling temperatures; the remaining springs and wells issue Na-HC03 waters at temperatures ranging from 14 to 33 deg C. Gases escaping from the hot springs are principally nitrogen with minor amounts of methane. The geothermometers calculated from the chemical data are also tabulated for each spring. (Woodard-USGS)
Mariner, R.H.; Presser, T.S.; Evans, W.C.
Fluid/mineral equilibrium calculations for geothermal fluids and chemical geothermometry
Aquifer temperatures of 13 geothermal wells in Iceland whose measured reservoir temperatures range from 47 to 325 C have been estimated from the chemical composition of the discharged fluid by considering simultaneously temperature dependent equilibria between many mineral phases and the solution. This approach to chemical geothermometry was initially proposed by Reed and Spycher. Its advantage over individual solute geothermometers such as the silica and the Na-K and Na-K-Ca geothermometers is that it allows a distinction to be made between equilibrated and non-equilibrated waters. However, care should be taken in interpreting the results of multi-mineral/solute equilibria as the results depend on both the thermodynamic data base used for mineral solubilities and the activities of end-member minerals in solid solutions. When using old analytical data attention has to be paid to analytical methods, especially in the case of important constituents present at low concentrations in the fluid, such as aluminium, for which analytical results obtained by two methods yielded very different equilibrium temperatures. The results for selected wells in Iceland, presented here, indicate that the geothermometry results are with few exceptions within 20 C of measured aquifer temperatures, and within 10 C for about half the wells considered. The method responds rapidly to changes such as cooling or mixing.
Tole, M.P. (Moi Univ., Eldoret (Kenya). School of Environmental Studies); Armannsson, H. (National Energy Authority, Reykjavik (Iceland)); Pang Zhonghe (Inst. of Geology, Beijing (China). Lab. for Geothermal); Arnorsson, S. (Univ. of Iceland, Reykjavik (Iceland). Science Inst.)
The chemical shift tensors of the acetate anions in cadmium acetate dihydrate are calculated using a cluster approach, the embedded ion method (EIM), and a combination of the two in the EIM/cluster method. The results of these calculations are compared with those completed on the isolated acetate anion and show the need for the inclusion of intermolecular interactions. The RMS difference between experiment and theory improves from over 60 ppm when the calculation is completed on an isolated anion, to below 10 ppm when interactions to nearby atoms are included. The best cluster model includes three cadmium acetate dihydrate and gives an RMS result of 4.4 ppm. The EIM method, which uses point charges to account for the intermolecular effects, achieves an RMS of 7.7 ppm on individual anions alone. A combination of the two, the EIM/cluster method, shows that the only necessary atom to explicitly add is the nearest cadmium; this addition results in an RMS of 4.1 ppm. These results are also discussed in terms of the computational cost of the different calculations. PMID:16477671
Orendt, Anita M
Vibrational spectra, DFT quantum chemical calculations and conformational analysis of P-iodoanisole.
The solid phase FT-IR and FT-Raman spectra of P-iodoanisole (P-IA) have been recorded in the regions 400-4000 and 50-4000 cm(-1), respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by ab initio (HF) and density functional theory (B3LYP) methods with LanL2DZ as basis set. The potential energy surface scan for the selected dihedral angle of P-IA has been performed to identify stable conformer. The optimized structure parameters and vibrational wavenumbers of stable conformer have been predicted by density functional B3LYP method with LanL2DZ (with effective core potential representations of electrons near the nuclei for post-third row atoms) basis set. The nucleophilic and electrophilic sites obtained from the molecular electrostatic potential (MEP) surface were calculated. The temperature dependence of thermodynamic properties has been analyzed. Several thermodynamic parameters have been calculated using B3LYP with LanL2DZ basis set. PMID:23727676
Arivazhagan, M; Anitha Rexalin, D; Geethapriya, J
Flow modeling of alkaline dissolution by a thermodynamic or by a kinetic approach
This paper presents a calculation of the propagation of basic pH in a reservoir rock based on either a kinetically controlled reaction or a thermodynamic equilibrium assumption. Results demonstrate that the kinetic approach is the only way to analyze the interactions of alkaline chemicals with clayey sandstones properly.
Labrid, J.; Bazin, B. (Inst. Francais du Petrole, Rueil-Malmaison (France))
Norm-conserving pseudopotentials with chemical accuracy compared to all-electron calculations
By adding a non-linear core correction to the well established Dual Space Gaussian type pseudopotentials, we construct improved pseudopotentials for the Perdew Burke Ernzerhof (PBE) functional and demonstrate that they exhibit excellent accuracy. Our benchmarks for the G2-1 test set show average atomization energy errors of only half a kcal/mol. The pseudopotentials also remain highly reliable for high pressure phases of crystalline solids. When supplemented by empirical dispersion corrections the average error in the interaction energy between molecules is also about half a kcal/mol. The accuracy that can be obtained by these pseudopotentials in combination with a systematic basis set is well superior to the accuracy that can be obtained by commonly used medium size Gaussian basis sets in all-electron calculations.
Willand, Alexander; Genovese, Luigi; V�zquez-Mayagoitia, �lvaro; Deb, Arpan Krishna; Sadeghi, Ali; Deutsch, Thierry; Goedecker, Stefan
NASA Astrophysics Data System (ADS)
In recent years, the role of halogen species (e.g. Br, Cl) in the troposphere of polar regions is investigated after the discovery of their importance for boundary layer ozone destruction in the polar spring. Halogen species take part in an auto-catalytic chemical cycle including key self reactions. In this study, several chemical reaction schemes are investigated, and the importance of specific reactions and their rate constants is identified by a sensitivity analysis. A category of heterogeneous reactions related to HOBr activate halogen ions from sea salt aerosols, fresh sea ice or snow pack, driving the "bromine explosion". In the Arctic, a small amount of NOx may exist, which comes from nitrate contained in the snow, and this NOx may have a strong impact on ozone depletion. The heterogeneous reaction rates are parameterized by considering the aerodynamic resistance, a reactive surface ratio, ?, i.e. ratio of reactive surface area to total ground surface area, and the boundary layer height, Lmix. It is found that for ? = 1, the ozone depletion process starts after five days and lasts for 40 h for Lmix = 200 m. Ozone depletion duration becomes independent of the height of the boundary layer for about ??20, and it approaches a value of two days for ?=100. The role of nitrogen and chlorine containing species on the ozone depletion rate is studied. The calculation of the time integrated bromine and chlorine atom concentrations suggests a value in the order of 103 for the [Br] / [Cl] ratio, which reveals that atomic chlorine radicals have minor direct influence on the ozone depletion. The NOx concentrations are influenced by different chemical cycles over different time periods. During ozone depletion, the reaction cycle involving the BrONO2 hydrolysis is dominant. A critical value of 0.002 of the uptake coefficient of the BrONO2 hydrolysis reaction at the aerosol and saline surfaces is identified, beyond which the existence of NOx species accelerate the ozone depletion event - for lower values, deceleration occurs.
Cao, L.; Sihler, H.; Platt, U.; Gutheil, E.
Uncovering the chemical and physical links between natural environments and microbial communities is becoming increasingly amenable owing to geochemical observations and metagenomic sequencing. At the hot spring known as Bison Pool in Yellowstone National Park, the cooling of the water in the outflow channel is associated with an increase in oxidation potential estimated from multiple field-based measurements. Representative groups of proteins whose sequences were derived from metagenomic data also exhibit an increase in average oxidation state of carbon in the protein molecules with distance from the hot-spring source. The energetic requirements of reactions to form selected proteins used in the model were computed using amino-acid group additivity for the standard molal thermodynamic properties of the proteins, and the relative chemical stabilities of the proteins were investigated by varying temperature, pH and oxidation state, expressed as activity of dissolved hydrogen. The relative stabilities of the proteins were found to track the locations of the sampling sites when the calculations included a function for hydrogen activity that increases with temperature and is higher, or more reducing, than values consistent with measurements of dissolved oxygen, sulfide and oxidation-reduction potential in the field. These findings imply that spatial patterns in the amino acid compositions of proteins can be linked, through energetics of overall chemical reactions representing the formation of the proteins, to the environmental conditions at this hot spring, even if microbial cells maintain considerably different internal conditions. Further applications of the thermodynamic calculations are possible for other natural microbial ecosystems. PMID:21853048
Dick, Jeffrey M; Shock, Everett L
Uncovering the chemical and physical links between natural environments and microbial communities is becoming increasingly amenable owing to geochemical observations and metagenomic sequencing. At the hot spring known as Bison Pool in Yellowstone National Park, the cooling of the water in the outflow channel is associated with an increase in oxidation potential estimated from multiple field-based measurements. Representative groups of proteins whose sequences were derived from metagenomic data also exhibit an increase in average oxidation state of carbon in the protein molecules with distance from the hot-spring source. The energetic requirements of reactions to form selected proteins used in the model were computed using amino-acid group additivity for the standard molal thermodynamic properties of the proteins, and the relative chemical stabilities of the proteins were investigated by varying temperature, pH and oxidation state, expressed as activity of dissolved hydrogen. The relative stabilities of the proteins were found to track the locations of the sampling sites when the calculations included a function for hydrogen activity that increases with temperature and is higher, or more reducing, than values consistent with measurements of dissolved oxygen, sulfide and oxidation-reduction potential in the field. These findings imply that spatial patterns in the amino acid compositions of proteins can be linked, through energetics of overall chemical reactions representing the formation of the proteins, to the environmental conditions at this hot spring, even if microbial cells maintain considerably different internal conditions. Further applications of the thermodynamic calculations are possible for other natural microbial ecosystems. PMID:21853048
Dick, Jeffrey M.; Shock, Everett L.
Detailed chemical kinetic reaction mechanisms have been developed to describe the pyrolysis and oxidation of the n-alkanes, including n-octane (n-C{sub 8}H{sub 18}), n-nonane (n-C{sub 9}H{sub 20}), n-decane (n-C{sub 10}H{sub 22}), n-undecane (n-C{sub 11}H{sub 24}), n-dodecane (n-C{sub 12}H{sub 26}), n-tridecane (n-C{sub 13}H{sub 28}), n-tetradecane (n-C{sub 14}H{sub 30}), n-pentadecane (n-C{sub 15}H{sub 32}), and n-hexadecane (n-C{sub 16}H{sub 34}). These mechanisms include both high temperature and low temperature reaction pathways. The mechanisms are based on previous mechanisms for n-heptane, using the same reaction class mechanism construction developed initially for n-heptane. Individual reaction class rules are as simple as possible in order to focus on the parallelism between all of the n-alkane fuels included in the mechanisms, and there is an intent to develop these mechanisms further in the future to incorporate greater levels of accuracy and predictive capability. Several of these areas for improvement are identified and explained in detail. These mechanisms are validated through comparisons between computed and experimental data from as many different sources as possible. In addition, numerical experiments are carried out to examine features of n-alkane combustion in which the detailed mechanisms can be used to compare processes in all of the n-alkane fuels. The mechanisms for all of these n-alkanes are presented as a single detailed mechanism, which can be edited to produce efficient mechanisms for any of the n-alkanes included, and the entire mechanism, with supporting thermochemical and transport data, together with an explanatory glossary explaining notations and structural details, will be available on our web page when the paper is accepted for publication.
Westbrook, C K; Pitz, W J; Herbinet, O; Silke, E J; Curran, H J
Detailed chemical kinetic reaction mechanisms have been developed to describe the pyrolysis and oxidation of nine n-alkanes larger than n-heptane, including n-octane (n-C{sub 8}H{sub 18}), n-nonane (n-C{sub 9}H{sub 20}), n-decane (n-C{sub 10}H{sub 22}), n-undecane (n-C{sub 11}H{sub 24}), n-dodecane (n-C{sub 12}H{sub 26}), n-tridecane (n-C{sub 13}H{sub 28}), n-tetradecane (n-C{sub 14}H{sub 30}), n-pentadecane (n-C{sub 15}H{sub 32}), and n-hexadecane (n-C{sub 16}H{sub 34}). These mechanisms include both high temperature and low temperature reaction pathways. The mechanisms are based on our previous mechanisms for the primary reference fuels n-heptane and iso-octane, using the reaction class mechanism construction first developed for n-heptane. Individual reaction class rules are as simple as possible in order to focus on the parallelism between all of the n-alkane fuels included in the mechanisms, and these mechanisms will be refined further in the future to incorporate greater levels of accuracy and predictive capability. These mechanisms are validated through extensive comparisons between computed and experimental data from a wide variety of different sources. In addition, numerical experiments are carried out to examine features of n-alkane combustion in which the detailed mechanisms can be used to compare reactivities of different n-alkane fuels. The mechanisms for all of these n-alkanes are presented as a single detailed mechanism, which can be edited to produce efficient mechanisms for any of the n-alkanes included, and the entire mechanism, with supporting thermochemical and transport data, together with an explanatory glossary explaining notations and structural details, will be available for download from our web page.
Westbrook, C K; Pitz, W J; Herbinet, O; Curran, H J; Silke, E J
februari 2011 Department of Chemical Engineering
februari 2011 Department of Chemical Engineering Thermal and Flow Engineering Laboratory Ron 8. Mass transfer with chemical reaction 8.1 Overview 8.2 First order, homogeneous kinetics 8.5 Design calculations 13.6 Concentrated solutions; distillation 14. Extraction and leaching 14.1 Liquid
Zevenhoven, Ron
The effectiveness of the VVER-1000 reactor scram system is analyzed using ionization chamber currents with different sets of kinetic parameters with allowance for the isotopic composition in the calculation of these parameters. The most 'correct, aesthetically acceptable' results are obtained using the eight-group constants of the ROSFOND (BNAB-RF) library. The difference between the maximum and minimum values of the scram system effectiveness calculated with different sets of kinetic parameters slightly exceeds 2{beta}. The problems of introducing corrections due to spatial effects are not considered in this study.
Zizin, M. N., E-mail: firstname.lastname@example.com [Russian Research Centre Kurchatov Institute (Russian Federation); Zizina, S. N.; Kryakvin, L. V.; Pitilimov, V. A.; Tereshonok, V. A. [JSC VNIIAES (Russian Federation)
Details of the mechanism of asymmetric transfer hydrogenation of ketones catalyzed by two chiral bifunctional ruthenium complexes, (S)-RuH[(R,R)-OCH(Ph)CH(Ph)NH(2)](?(6)-benzene) (Ru-1) or (S)-RuH[(R,R)-p-TsNCH(Ph)CH(Ph)NH(2)](?(6)-mesitylene) (Ru-2), were studied computationally by density functional theory, accounting for the solvation effects by using continuum, discrete, and mixed continuum/discrete solvation models via "solvated supermolecules" approach. In contrast to gas phase quantum chemical calculations, where the reactions were found to proceed via a concerted three-bond asynchronous process through a six-membered pericyclic transition state, incorporation of the implicit and/or explicit solvation into the calculations suggests that the same reactions proceed via two steps in solution: (i) enantio-determining hydride transfer and (ii) proton transfer through the contact ion-pair intermediate, stabilized primarily by ionic hydrogen bonding between the cation and the anion. The calculations suggest that the proton source for neutralizing the chiral RO(-) anion may be either the amine group of the cationic Ru complex or, more likely, a protic solvent molecule. In the latter case, the reaction may not necessarily proceed via the 16e amido complex Ru[(R,R)-XCH(Ph)CH(Ph)NH](?(6)-arene). The origin of enantioselectivity is discussed in terms of the newly formulated mechanism. PMID:23336817
Dub, Pavel A; Ikariya, Takao
of Chemical Mechanisms on PDF Calculations of Nonpremixed Piloted Jet Flames Renfeng Cao and Stephen B. Pope of the chemical mechanism that is employed. In this work, focusing on flame F (which has significant local piloted jet flames (flames D, E and F) [4]. While there is at least partial understanding of the influence
The objective of this work was first to investigate the chemical degradation of the sesquiterpene lactone nobilin and determine its solubility under conditions of concurrent degradation for partially amorphous starting material; second, to determine the effect of biorelevant media used in the in vitro measurement of intestinal absorption on degradation and solubility of nobilin. Purely aqueous medium (aq-TMCaco ), fasted and fed state simulated intestinal fluid (FaSSIF-TMCaco and FeSSIF-TMCaco ), and two liposomal formulations (LiposomesFaSSIF and LiposomesFeSSIF ) with the same lipid concentration as FaSSIF-TMCaco and FeSSIF-TMCaco were used. Degradation products were identified by nuclear magnetic resonance and X-ray crystallography and the order of reaction kinetics was determined. Solubility was deduced with a mathematical model encompassing dissolution, degradation, and reprecipitatio