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1

ALTERNATIVE RBC (ROTATING BIOLOGICAL CONTACTOR) DESIGN - SECOND ORDER KINETICS

This paper presents an alternative method for designing rotating biological contactors (RBC) for use as a secondary treatment operation. The method uses a combination of chemical kinetics, good engineering practice, operational simplicity, and cost effectiveness to design a RBC s...

2

The second-order velocity distribution function was calculated from the second-order rf kinetic theory [Jaeger et al., Phys. Plasmas 7, 641 (2000)]. However, the nonresonant ponderomotive force in the radial direction derived from the theory is inconsistent with that from the fluid theory. The inconsistency arises from that the multiple-timescale-separation assumption fails when the second-order Vlasov equation is directly integrated along unperturbed particle orbits. A slowly ramped wave field including an adiabatic turn-on process is applied in the modified kinetic theory in this paper. Since this modification leads only to additional reactive/nonresonant response relevant with the secular resonant response from the previous kinetic theory, the correct nonresonant ponderomotive force can be obtained while all the resonant moments remain unchanged.

Chen, Jiale [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China) [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Center for Magnetic Fusion Theory, Chinese Academy of Sciences, Hefei (China); Gao, Zhe [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China) [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China); Center for Magnetic Fusion Theory, Chinese Academy of Sciences, Hefei (China)

2013-08-15

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REMOVAL OF LEAD(II) FROM EFFLUENTS BY SORPTION ON PEAT USING SECOND-ORDER KINETICS

The sorption of lead ions from aqueous solution onto peat has been studied. The kinetics of sorption of lead ion are described by a pseudo-second-order model modified with a new parameter, t0, included to account for an initial resistance due to the film boundary layer. Analysis of this model has been carried out at various experimental conditions to study the

Y. S. Ho; J. C. Y. Ng; G. McKay

2001-01-01

4

Second order fluid dynamics for the unitary Fermi gas from kinetic theory

We compute second order transport coefficients of the dilute Fermi gas at unitarity. The calculation is based on kinetic theory and the Boltzmann equation at second order in the Knudsen expansion. The second order transport coefficients describe the shear stress relaxation time, non-linear terms in the strain-stress relation, and non-linear couplings between vorticity and strain. An exact calculation in the dilute limit gives $\\tau_R=\\eta/P$, where $\\tau_R$ is the shear stress relaxation time, $\\eta$ is the shear viscosity, and $P$ is pressure. This relation is identical to the result obtained using the Bhatnagar-Gross-Krook (BGK) approximation to the collision term, but other transport coefficients are sensitive to the exact collision integral.

Thomas Schaefer

2014-10-15

5

Temporal Frequency Modulates Reaction Time Responses to First-Order and Second-Order Motion

ERIC Educational Resources Information Center

This study investigated the effect of temporal frequency and modulation depth on reaction times for discriminating the direction of first-order (luminance-defined) and second-order (contrast-defined) motion, equated for visibility using equal multiples of direction-discrimination threshold. Results showed that reaction times were heavily…

Hutchinson, Claire V.; Ledgeway, Tim

2010-01-01

6

The kinetics of the HCl-catalyzed deprotection of the Boc-protected amine, thioester 2 to liberate AZD3409 1 have been studied in a mixture of toluene and propan-2-ol. The reaction rate was found to exhibit a second-order dependence upon the HCl concentration. This behavior was found to have a degree of generality as the deprotection of a second Boc-protected amine, tosylate 3 to yield amine 4 using HCl, sulfuric acid, and methane sulfonic acid showed the same kinetic dependence. In contrast the deprotection of tosylate 3 with trifluoroacetic acid required a large excess of acid to obtain a reasonable rate of reaction and showed an inverse kinetic dependence upon the trifluoroacetate concentration. These observations are rationalized mechanistically in terms of a general acid-catalyzed separation of a reversibly formed ion-molecule pair arising from the fragmentation of the protonated tert-butyl carbamate. PMID:21067172

Ashworth, Ian W; Cox, Brian G; Meyrick, Brian

2010-12-01

7

The mass transport (advection-dispersion) equations allowing coupled second-order reaction (i.e. Omega sub 1, C sub 1) + (omega sub 2, C sub 2) (R sub 12) -> Re) between two constituents are derived and result in a set of coupled nonlinear partial differential equations. Neglecti...

8

Second order equation of motion for electromagnetic radiation back-reaction

We take the viewpoint that the physically acceptable solutions of the Lorentz-Dirac equation for radiation back-reaction are actually determined by a second order equation of motion in such a way that the self-force can be given as a function of spacetime location and velocity. This self-force function turns out to be determined by a first order partial differential equation. In view of possible practical difficulty in solving that partial differential equation, we propose two iteration methods, too, for obtaining the self-force function. For two example systems, the second order equation of motion is obtained exactly in the nonrelativistic regime via each of the three methods, and the three results are found to coincide. We reveal that, for both systems, back-reaction induces a damping proportional to velocity and, in addition, it decreases the effect of the external force.

Tamás Matolcsi; Tamás Fülöp; Mihály Weiner

2014-10-26

9

Implementing the Second-Order Fermi Process in a Kinetic Monte-Carlo Simulation

NASA Astrophysics Data System (ADS)

Kinetic Monte-Carlo test-particle simulations require a way to simulate the effects of turbulence on particles. One way to do this is to prescribe a phenomenological scattering mechanism based on an empirical and/or qualitative description of turbulent scattering. Previous incarnations of the simulation presented here parameterize a scattering mean free path proportional to some power of the particle’s momentum in agreement with observational evidence from many sources. The scattering itself was done by scattering of the particle’s local fluid frame velocity onto a sphere of radius |v| via either large of small angle scattering. However, in real plasmas the scattering centers (turbulent plasma waves) are not stationary in the local fluid frame and particle velocities should, instead, be randomized in the frame of the moving scattering centers (which presumably move with the Alfvén speed) to more accurately represent the effects of turbulence on particles. Allowing scattering centers to move introduces heating as particles now diffuse in momentum as well as space (receiving a random kick of order the Alfvén speed at each scattering event). In 1965, Eugene Parker considered this effect (then called fermi acceleration) for cosmic ray particles and (correctly) concluded that it was negligible for those highly energetic particles because the particle speed was so much larger than the Alfvén speed kick which it received. However, doing the same calculation for thermal particles embedded in the solar wind (for whom a single kick of an Alfvén speed is significant) yields a very different result and it becomes clear that this process, now called second-order Fermi acceleration, must be included to get an accurate picture of particle acceleration in the heliosphere. This presentation will highlight the theoretical argument for the importance of second-order fermi acceleration in both the solar wind and shock environs as well as problems in heliophysics to which it may be applicable and problems it creates for the conventional picture of first-order fermi shock acceleration. It will also discuss results from the kinetic Monte-Carlo simulation described above (including second-order fermi) in the vicinity of shocks.

Summerlin, E. J.

2010-12-01

10

An Activation Energy Experiment for a Second-Order Reaction in a Single Laboratory Period.

ERIC Educational Resources Information Center

Describes modification of a chemical reaction to a single 4 1/2-hour laboratory period. Reaction kinetics between 2, 4-initrochlorobenzene and piperidine to form 2, 4-dinitrophenyl-piperidine and piperidinium hydrochloride are followed conductometrically at three temperatures to obtain data to calculate activation parameters. (Author/JN)

Barile, Raymond C.; Michiels, Leo P.

1983-01-01

11

NASA Astrophysics Data System (ADS)

This paper describes estimation of reaction rate constants and pure ultraviolet/visible (UV-vis) spectra of the component involved in a second order consecutive reaction between Ortho-Amino benzoeic acid (o-ABA) and Diazoniom ions (DIAZO), with one intermediate. In the described system, o-ABA was not absorbing in the visible region of interest and thus, closure rank deficiency problem did not exist. Concentration profiles were determined by solving differential equations of the corresponding kinetic model. In that sense, three types of model-based procedures were applied to estimate the rate constants of the kinetic system, according to Levenberg/Marquardt (NGL/M) algorithm. Original data-based, Score-based and concentration-based objective functions were included in these nonlinear fitting procedures. Results showed that when there is error in initial concentrations, accuracy of estimated rate constants strongly depends on the type of applied objective function in fitting procedure. Moreover, flexibility in application of different constraints and optimization of the initial concentrations estimation during the fitting procedure were investigated. Results showed a considerable decrease in ambiguity of obtained parameters by applying appropriate constraints and adjustable initial concentrations of reagents.

Kompany-Zareh, Mohsen; Khoshkam, Maryam

2013-02-01

12

A comparison was made of the linear least-squares method and a trial-and-error non-linear method of the widely used pseudo-second-order kinetic model for the sorption of cadmium onto ground-up tree fern. Four pseudo-second-order kinetic linear equations are discussed. Kinetic parameters obtained from the four kinetic linear equations using the linear method differed but they were the same when using the non-linear

Yuh-Shan Ho

2006-01-01

13

A second-order accurate kinetic-theory-based method for inviscid compressible flows

NASA Technical Reports Server (NTRS)

An upwind method for the numerical solution of the Euler equations is presented. This method, called the kinetic numerical method (KNM), is based on the fact that the Euler equations are moments of the Boltzmann equation of the kinetic theory of gases when the distribution function is Maxwellian. The KNM consists of two phases, the convection phase and the collision phase. The method is unconditionally stable and explicit. It is highly vectorizable and can be easily made total variation diminishing for the distribution function by a suitable choice of the interpolation strategy. The method is applied to a one-dimensional shock-propagation problem and to a two-dimensional shock-reflection problem.

Deshpande, Suresh M.

1986-01-01

14

Glucose reversion reaction kinetics.

The reversion reactions of glucose in mildly acidic aqueous solutions have been studied, and the kinetics of conversion to disaccharides has been modeled. The experiments demonstrate that, at high sugar loadings, up to 12 wt % of the glucose can be converted into reversion products. The reversion products observed are primarily disaccharides; no larger oligosaccharides were observed. Only disaccharides linked to the C1 carbon of one of the glucose residues were observed. The formation of 1,6-linked disaccharides was favored, and alpha-linked disaccharides were formed at higher concentrations than beta-linked disaccharides. This observation can be rationalized on the basis of steric effects. At temperatures >140 degrees C, the disaccharides reach equilibrium with glucose and the reversion reaction competes with dehydration reactions to form 5-hydroxymethylfurfural. As a result, disaccharide formation reaches a maximum at reaction times <10 min and decreases with time. At temperatures <130 degrees C, disaccharide formation reaches a maximum at reaction times >30 min. As expected, disaccharide formation exhibits a second-order dependence upon glucose concentration. Levoglucosan formation is also observed; because it shows a first-order dependence upon glucose concentration, its formation is more significant at low concentrations (10 mg mL(-1)), whereas disaccharide formation dominates at high concentrations (200 mg mL(-1)). Experiments conducted using glucose and its disaccharides were calibrated with readily available standards. The kinetic parameters for hydrolysis of some glucodisaccharides could be compared to published literature values. From these experiments, the kinetics and activation energies for the reversion reactions have been calculated. The rate parameters can be used to model the formation of the disaccharides as a function of reaction time and temperature. A new and detailed picture of the molecular mechanism of these industrially important reversion reactions has been developed. PMID:20429509

Pilath, Heidi M; Nimlos, Mark R; Mittal, Ashutosh; Himmel, Michael E; Johnson, David K

2010-05-26

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of the human visual system by measuring forced-choice reaction times for dis- criminating the drift directionChoice reaction times for identifying the direction of first-order motion and different varieties to near-threshold levels. Psychophysical (behavioural) reaction time paradigms have been employed

Nottingham, University of

16

Oxidation of estrone by permanganate: Reaction kinetics and estrogenicity removal

Permanganate was used as an oxidant to control estrone in the present study. Kinetics was determined at pH 2.5–9.4 and temperature\\u000a 15–40°C for the reaction of estrone with potassium permanganate. It was found that the reaction is second-order overall and\\u000a first-order with respect to both estrone and permanganate. The second-order rate constant for the reaction at pH 5.8 and 25°C

XiaoLing Shao; Jun Ma; Gang Wen; JingJing Yang

2010-01-01

17

SABIO Reaction Kinetics Database (Homepage)

NSDL National Science Digital Library

The SABIO-RK (System for the Analysis of Biochemical Pathways - Reaction Kinetics) is a web-based application based on the SABIO relational database that contains information about biochemical reactions, their kinetic equations with their parameters, and the experimental conditions under which these parameters were measured. It aims to support modellers in the setting-up of models of biochemical networks, but it is also useful for experimentalists or researchers with interest in biochemical reactions and their kinetics. Information about reactions and their kinetics can be exported in SBML (Systems Biology Mark-Up Language) format.

Scientific Databases and Visualization Group at the EML Research in Heidelberg, Germany

18

NASA Astrophysics Data System (ADS)

The kinetics of free radical decay reactions of poly(L-Lactic acid), poly(DL-Lactic acid) and random copolymer of lactic and glycolic acid have been investigated for decays taking place in air and in vacuum. The change in ESR lines of ?-irradiated polymers have been followed over a long time period. The decay has been found to follow neither simple first-order nor second-order kinetics. Various kinetic approaches including composite first or second-order mechanisms and diffusion-controlled first or second-order equations were determined to be also unsatisfactory. The decay of radicals in bulk irradiated lactic acid homo and copolymers was found to be best described when the second-order non-classical equation with time dependent rate constant approach was used.

Kanto?lu, Ömer; Özbey, Turan; Güven, Olgun

1995-02-01

19

Kinetics of actinide complexation reactions

Though the literature records extensive compilations of the thermodynamics of actinide complexation reactions, the kinetics of complex formation and dissociation reactions of actinide ions in aqueous solutions have not been extensively investigated. In light of the central role played by such reactions in actinide process and environmental chemistry, this situation is somewhat surprising. The authors report herein a summary of what is known about actinide complexation kinetics. The systems include actinide ions in the four principal oxidation states (III, IV, V, and VI) and complex formation and dissociation rates with both simple and complex ligands. Most of the work reported was conducted in acidic media, but a few address reactions in neutral and alkaline solutions. Complex formation reactions tend in general to be rapid, accessible only to rapid-scan and equilibrium perturbation techniques. Complex dissociation reactions exhibit a wider range of rates and are generally more accessible using standard analytical methods. Literature results are described and correlated with the known properties of the individual ions.

Nash, K.L.; Sullivan, J.C.

1997-09-01

20

Combustion kinetics and reaction pathways

This project is focused on the fundamental chemistry of combustion. The overall objectives are to determine rate constants for elementary reactions and to elucidate the pathways of multichannel reactions. A multitechnique approach that features three independent experiments provides unique capabilities in performing reliable kinetic measurements over an exceptionally wide range in temperature, 300 to 2500 K. Recent kinetic work has focused on experimental studies and theoretical calculations of the methane dissociation system (CH{sub 4} + Ar {yields} CH{sub 3} + H + Ar and H + CH{sub 4} {yields} CH{sub 3} + H{sub 2}). Additionally, a discharge flow-photoionization mass spectrometer (DF-PIMS) experiment is used to determine branching fractions for multichannel reactions and to measure ionization thresholds of free radicals. Thus, these photoionization experiments generate data that are relevant to both reaction pathways studies (reaction dynamics) and fundamental thermochemical research. Two distinct advantages of performing PIMS with high intensity, tunable vacuum ultraviolet light at the National Synchrotron Light Source are high detection sensitivity and exceptional selectivity in monitoring radical species.

Klemm, R.B.; Sutherland, J.W. [Brookhaven National Laboratory, Upton, NY (United States)

1993-12-01

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NASA Astrophysics Data System (ADS)

The formation of transient species (OH·, NO2·, NO radicals) and long-lived chemical products (O3, H2O2, NO_{3}^{-} , NO_{2}^{-} ) produced by a gas discharge plasma at the gas-liquid interface and directly in the liquid was measured in dependence on the gas atmosphere (20% oxygen mixtures with nitrogen or with argon) and pH of plasma-treated water (controlled by buffers at pH 3.3, 6.9 or 10.1). The aqueous-phase chemistry and specific contributions of these species to the chemical and biocidal effects of air discharge plasma in water were evaluated using phenol as a chemical probe and bacteria Escherichia coli. The nitrated and nitrosylated products of phenol (4-nitrophenol, 2-nitrophenol, 4-nitrocatechol, 4-nitrosophenol) in addition to the hydroxylated products (catechol, hydroquinone, 1,4-benzoquinone, hydroxy-1,4-benzoquinone) evidenced formation of NO2·, NO· and OH· radicals and NO+ ions directly by the air plasma at the gas-liquid interface and through post-discharge processes in plasma-activated water (PAW) mediated by peroxynitrite (ONOOH). Kinetic study of post-discharge evolution of H2O2 and NO_{2}^{-} in PAW has demonstrated excellent fit with the pseudo-second-order reaction between H2O2 and NO_{2}^{-} . The third-order rate constant k = 1.1 × 103 M-2 s-1 for the reaction NO_{2}^{-} +H_{2}O_{2}+H^{+}\\to ONOOH+H_{2}O was determined in PAW at pH 3.3 with the rate of ONOOH formation in the range 10-8-10-9 M s-1. Peroxynitrite chemistry was shown to significantly participate in the antibacterial properties of PAW. Ozone presence in PAW was proved indirectly by pH-dependent degradation of phenol and detection of cis,cis-muconic acid, but contribution of ozone to the inactivation of bacteria by the air plasma was negligible.

Lukes, P.; Dolezalova, E.; Sisrova, I.; Clupek, M.

2014-02-01

22

Kinetics of fast reactions of excited species. Final report

This report contains brief summaries of findings in the following areas: gamma radiation induced decomposition of chloroform; proton transfer and ion neutralization reactions in gaseous hydrocarbons; kinetics of thremal D-atom reactions with CH/sub 4/ C/sub 2/H/sub 6/; the gamma radiation induced decomposition of liquid n-pentane; pulse radiolysis of rare gases and liquid n-pentane and n-pentane-O/sub 2/ solutions; rate constants and activation energies for second order decay of pentyl and peroxypentyl radicals; pulse radiolysis fo aromatic solutes in halogenated solvents; the gamma radiation induced decomposition of nitromethane; the radiolysis of heavy water vapor; pulse radiolysis of solvated electrons in binary liquid solutions; collisional quenching of rare gas excimers by small foreign molecules; kinetics and mechanism for decay of Paschen-1s argon atoms; detection and monitoring of excited atoms in pulse irradiated rare gases.

Firestone, R.F.

1986-09-01

23

Second-order Darboux displacements

NASA Astrophysics Data System (ADS)

The potentials for a one-dimensional Schrödinger equation that are displaced along the x-axis under second-order Darboux transformations, called 2-SUSY invariant, are characterized in terms of a differential-difference equation. The solutions of the Schrödinger equation with such potentials are given analytically for any value of the energy. The method is illustrated by a two-soliton potential. It is proved that a particular case of the periodic Lamé-Ince potential is 2-SUSY invariant. Both Bloch solutions of the corresponding Schrödinger equation are found for any value of the energy. A simple analytic expression for a family of two-gap potentials is derived.

Samsonov, B. F.; Glasser, M. L.; Negro, J.; Nieto, L. M.

2003-10-01

24

Virtual Instrument for Determining Rate Constant of Second-Order Reaction by pX Based on LabVIEW 8.0

The virtual instrument system based on LabVIEW 8.0 for ion analyzer which can measure and analyze ion concentrations in solution is developed and comprises homemade conditioning circuit, data acquiring board, and computer. It can calibrate slope, temperature, and positioning automatically. When applied to determine the reaction rate constant by pX, it achieved live acquiring, real-time displaying, automatical processing of testing data, generating the report of results; and other functions. This method simplifies the experimental operation greatly, avoids complicated procedures of manual processing data and personal error, and improves veracity and repeatability of the experiment results. PMID:19730752

Meng, Hu; Li, Jiang-Yuan; Tang, Yong-Huai

2009-01-01

25

We report reaction paths starting from N((2)D) + H2O for doublet spin states, D0 and D1. The potential energy surfaces are explored in an automated fashion using the global reaction route mapping strategy. The critical points and reaction paths have been fully optimized at the complete active space second order perturbation theory level taking all valence electrons in the active space. In addition to direct dissociation pathways that would be dominant, three roaming processes, two roaming dissociation, and one roaming isomerization: (1) H2ON ? H-O(H)N ? H-HON ? NO((2)?) + H2, (2) cis-HNOH ? HNO-H ? H-HNO ? NO + H2, (3) H2NO ? H-HNO ? HNO-H ? trans-HNOH, are confirmed on the D0 surface. PMID:25338892

Isegawa, Miho; Liu, Fengyi; Maeda, Satoshi; Morokuma, Keiji

2014-10-21

26

NASA Astrophysics Data System (ADS)

We report reaction paths starting from N(2D) + H2O for doublet spin states, D0 and D1. The potential energy surfaces are explored in an automated fashion using the global reaction route mapping strategy. The critical points and reaction paths have been fully optimized at the complete active space second order perturbation theory level taking all valence electrons in the active space. In addition to direct dissociation pathways that would be dominant, three roaming processes, two roaming dissociation, and one roaming isomerization: (1) H2ON ? H-O(H)N ? H-HON ? NO(2?) + H2, (2) cis-HNOH ? HNO-H ? H-HNO ? NO + H2, (3) H2NO ? H-HNO ? HNO-H ? trans-HNOH, are confirmed on the D0 surface.

Isegawa, Miho; Liu, Fengyi; Maeda, Satoshi; Morokuma, Keiji

2014-10-01

27

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)

1993-12-01

28

Ultracold Chemistry and its Reaction Kinetics

We study the reaction kinetics of chemical processes occurring in the ultracold regime and systematically investigate their dynamics. Quantum entanglement is found to play a key role in driving an ultracold reaction towards a dynamical equilibrium. In case of multiple concurrent reactions Hamiltonian chaos dominates the phase space dynamics in the mean field approximation.

Florian Richter; Daniel Becker; Cédric Bény; Torben A. Schulze; Silke Ospelkaus; Tobias J. Osborne

2015-01-08

29

Chemical Kinetics: Rate of Reaction

NSDL National Science Digital Library

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

David N. Blauch

30

Ammonia, oxidation leaching of chalcopyrite —reaction kinetics

The reaction for the ammonia, oxidation leaching of chalcopyrite, CuFeS2 + 4NH3 + 17\\/4 O2 + 2 OH- ? Cu(NH3)+2\\u000a 42 + l\\/2Fe2O3 + 2 SO4 + H2O was studied using monosize particles in an intensely stirred reactor under moderate pressures to determine the important\\u000a chemical factors which govern the kinetic response of the system. The reaction kinetics were studied

L. W. Beckstead; J. D. Miller

1977-01-01

31

Source of second order chromaticity in RHIC

In this note we will answer the following questions: (1) what is the source of second order chromaticities in RHIC? (2) what is the dependence of second order chromaticity on the on-momentum {beta}-beat? (3) what is the dependence of second order chromaticity on {beta}* at IP6 and IP8? To answer these questions, we use the perturbation theory to numerically calculate the contributions of each quadrupole and sextupole to the first, second, and third order chromaticities.

Luo, Y.; Gu, X.; Fischer, W.; Trbojevic, D.

2011-01-01

32

Binocular Combination of Second-Order Stimuli

Phase information is a fundamental aspect of visual stimuli. However, the nature of the binocular combination of stimuli defined by modulations in contrast, so-called second-order stimuli, is presently not clear. To address this issue, we measured binocular combination for first- (luminance modulated) and second-order (contrast modulated) stimuli using a binocular phase combination paradigm in seven normal adults. We found that the binocular perceived phase of second-order gratings depends on the interocular signal ratio as has been previously shown for their first order counterparts; the interocular signal ratios when the two eyes were balanced was close to 1 in both first- and second-order phase combinations. However, second-order combination is more linear than previously found for first-order combination. Furthermore, binocular combination of second-order stimuli was similar regardless of whether the carriers in the two eyes were correlated, anti-correlated, or uncorrelated. This suggests that, in normal adults, the binocular phase combination of second-order stimuli occurs after the monocular extracting of the second-order modulations. The sensory balance associated with this second-order combination can be obtained from binocular phase combination measurements. PMID:24404180

Zhou, Jiawei; Liu, Rong; Zhou, Yifeng; Hess, Robert F.

2014-01-01

33

Kinetic Isotope Effects in Asymmetric Reactions

Kinetic isotope effects are exquisitely sensitive probes of transition structure. As such, kinetic isotope effects offer a uniquely useful probe for the symmetry-breaking process that is inherent to stereoselective reactions. In this Concept article, we explore the role of steric and electronic effects in stereocontrol, and we relate these concepts to recent studies carried out in our laboratory. We also explore the way in which kinetic isotope effects serve as useful points of contact with computational models of transition structures. Finally, we discuss future opportunities for kinetic isotope effects to play a role in asymmetric catalyst development. PMID:20669194

Giagou, Thomas; Meyer, Matthew P.

2010-01-01

34

Factors Affecting Reaction Kinetics of Glucose Oxidase

Basic principles of enzyme kinetics are demonstrated using the enzyme glucose oxidase. The glucose oxidase enzymatic reaction is coupled to horseradish peroxidase, which in turn catalyzes the oxidation of a dye to a bright blue-green color. The appearance of the blue-green dye is used to monitor the course of the reaction and is quite visible in a classroom setting. A

Kristin A. Johnson

2002-01-01

35

Symmetry Properties of Second Order Hyperpolarizabilities

Time-reversal symmetry property of a second order nonlinear optical hyperpolarizability is examined in terms of the Manley-Rowe power relation to find relationship to the overall permutation symmetry. An extended symmetry relation is discovered reducing the independent number of the hyperpolarizability tensor components describing the second order nonlinear optical processes. Experimental implications are discussed.

J. W. Wu

1994-01-01

36

Porphyrins carrying either a primary alcohol, a tertiary alcohol or a primary bromide linker group were allowed to react with the surface silanol groups on silicate glass thermally at 80-240 °C to obtain a monolayer film. The kinetics of the reaction was analysed based on the pseudo-second order equation. The tertiary alcohol and the primary bromide reacted much slower than the primary alcohol. Arrhenius plots indicated that higher activation energies can account for the slower reaction of both tertiary alcohol and primary bromide linkers. The introduction of six dodecyl chains into hydroxyporphyrin accelerated the anchoring reaction by a factor of 50 owing to the larger frequency factor of the reaction, demonstrating that the dynamics of the interface is one of the dominant factors regulating the reaction kinetics. PMID:25658579

Fujimoto, Takahiro; Furuta, Nao; Mizutani, Tadashi

2015-03-01

37

Second-Order Gravitational Self-Force

NASA Astrophysics Data System (ADS)

In order to extract physical parameters from the waveform of an extreme-mass-ratio binary, one requires a second-order-accurate description of the motion of the smaller of the two objects in the binary. Using a method of matched asymptotic expansions, I derive the second-order equation of motion of a small, nearly spherical and non-rotating compact object in an arbitrary vacuum spacetime. I find that the motion is geodesic in a certain locally defined effective metric satisfying the vacuum Einstein equation through second order, and I outline a method of numerically determining this effective metric.

Pound, Adam

2015-01-01

38

Non-Markovian polymer reaction kinetics.

Describing the kinetics of polymer reactions, such as the formation of loops and hairpins in nucleic acids or polypeptides, is complicated by the structural dynamics of their chains. Although both intramolecular reactions, such as cyclization, and intermolecular reactions have been studied extensively, both experimentally and theoretically, there is to date no exact explicit analytical treatment of transport-limited polymer reaction kinetics, even in the case of the simplest (Rouse) model of monomers connected by linear springs. We introduce a new analytical approach to calculate the mean reaction time of polymer reactions that encompasses the non-Markovian dynamics of monomer motion. This requires that the conformational statistics of the polymer at the very instant of reaction be determined, which provides, as a by-product, new information on the reaction path. We show that the typical reactive conformation of the polymer is more extended than the equilibrium conformation, which leads to reaction times significantly shorter than predicted by the existing classical Markovian theory. PMID:22717443

Guérin, T; Bénichou, O; Voituriez, R

2012-07-01

39

Applications of Second-Order Cone Programming

In a second-Order cone program (SOCP) a linear function is minimized over the inter- section of an affine set and the product of second-Order (quadratic) cones. SOCPs are nonlinear convex Problems that include linear and (convex) quadratic programs as spe- cial cases, but are less general than semidefinite programs (SDPs). Several efficient pri- maldual interior-Point methods for SOCP have been

Miguel Sousa Lobo; Lieven Vandenberghe; Stephen Boyd; Hervé Lebret

1998-01-01

40

Kinetics of proton transfer reactions involving carbon

Enol protomers of ketones and aldehydes, carboxylic acids and esters, ketenes, as well as keto protomers of phenols are generated by flash photolysis to investigate their reaction kinetics in aqueous solution. pH-Rate profiles and buffer dilution plots provide absolute rate constants for acid and base catalysis of keto-enol protomeric reactions. Equilibrium constants of enolization spanning a range of 30 orders

Jakob Wirz

1998-01-01

41

The curvature perturbation at second order

NASA Astrophysics Data System (ADS)

We give an explicit relation, up to second-order terms, between scalar-field fluctuations defined on spatially-flat slices and the curvature perturbation on uniform-density slices. This expression is a necessary ingredient for calculating observable quantities at second-order and beyond in multiple-field inflation. We show that traditional cosmological perturbation theory and the `separate universe' approach yield equivalent expressions for superhorizon wavenumbers, and in particular that all nonlocal terms can be eliminated from the perturbation-theory expressions.

Dias, Mafalda; Elliston, Joseph; Frazer, Jonathan; Mulryne, David; Seery, David

2015-02-01

42

Second Order Symmetries of the Conformal Laplacian

NASA Astrophysics Data System (ADS)

Let (M,g) be an arbitrary pseudo-Riemannian manifold of dimension at least 3. We determine the form of all the conformal symmetries of the conformal (or Yamabe) Laplacian on (M,g), which are given by differential operators of second order. They are constructed from conformal Killing 2-tensors satisfying a natural and conformally invariant condition. As a consequence, we get also the classification of the second order symmetries of the conformal Laplacian. Our results generalize the ones of Eastwood and Carter, which hold on conformally flat and Einstein manifolds respectively. We illustrate our results on two families of examples in dimension three.

Michel, Jean-Philippe; Radoux, Fabian; Šilhan, Josef

2014-02-01

43

Paper # XXX Topic: Reaction Kinetics Eastern State Fall Technical Meeting

Paper # XXX Topic: Reaction Kinetics 1 Eastern State Fall Technical Meeting Chemical & Physical Â 1017 s-1 #12;Paper # XXX Topic: Reaction Kinetics 2 and activation energy values close to the C-C bond

Knyazev, Vadim D.

44

Second-Order Conditioning in "Drosophila"

ERIC Educational Resources Information Center

Associative conditioning in "Drosophila melanogaster" has been well documented for several decades. However, most studies report only simple associations of conditioned stimuli (CS, e.g., odor) with unconditioned stimuli (US, e.g., electric shock) to measure learning or establish memory. Here we describe a straightforward second-order conditioning…

Tabone, Christopher J.; de Belle, J. Steven

2011-01-01

45

Second-order eikonal exchange amplitudes

The analytic expressions of the second-order eikonal exchange amplitudes are derived for electron-hydrogen scattering in both post and prior forms. In the case of the Glauber exchange amplitude, these expressions are shown to be reducible to closed forms. The results are applied to the calculation of elastic e-H(1s) scattering. Useful conclusions are drawn.

Gien, T.T.

1986-11-01

46

A novel approach to modeling the reaction kinetics of tetracycline antibiotics with aqueous ozone.

Tetracycline antibiotics represent one of the most successful classes of pharmaceuticals and are extensively used around the world for human and veterinary health. Ozone-based processes have emerged as a selective water treatment process for many pharmaceuticals. The primary objective of this study was to determine the reaction kinetics for transformation of five tetracycline antibiotics (i.e., chlortetracycline, doxycycline, oxytetracycline, rolitetracycline, and tetracycline) by ozone across the pH2 to 9 range. The apparent second-order rate constant for tetracycline was on the order of 1-6 × 10(4) M(-1) s(-1) at low pH, and 0.6-2.0 × 10(6) M(-1) s(-1) at near neutral pH. The apparent second-order rate constants did not fit a conventional pKa-based model, presumably due to the complex acid/base speciation of tetracycline antibiotics. A model that considers the net charge on tetracycline molecules in solution provided a nice fit to experimental data for all five tetracyclines. The five tetracycline antibiotics demonstrated similar reaction kinetics with ozone, and a cumulative analysis of all kinetics data provides a baseline model for other tetracycline compounds. The ozone exposure required for complete transformation of tetracycline antibiotics (10(-5) M-s) is well below that achieved during ozone disinfection processes (10(-3) M-s), indicating that ozone is an effective treatment for tetracycline antibiotics. PMID:24041601

Hopkins, Zachary R; Blaney, Lee

2014-01-15

47

Kinetic analysis of complex reactions using FEMLAB

A finite element method software FEMALB has been implemented to the kinetic analysis of complex reaction systems. The established protocol provides fast solutions to the coupled differential-algebraic equations. It shows significant advantages over the conventional coding process with the standard implicit Runge-Kutta (IRK) method. The accuracy and high efficiency have been demonstrated in the simulation of the reaction processes such as glucose/fructose hydrogenation and catalytic cracking of gasoil. As model validation, the numerical results showed satisfactory agreement with the exact solutions. With the powerful capability of solving large matrixes of differential equations (both ODE and PDE) with nonlinear algebraic constrains, such an algorithm has greatly reduced the coding labor in reaction mechanistic studies and provided a unique tool in reactor design and optimization.

Cao, Chunshe; Wang, Yong

2005-06-07

48

Calculating Second-Order Effects in MOSFET's

NASA Technical Reports Server (NTRS)

Collection of mathematical models includes second-order effects in n-channel, enhancement-mode, metal-oxide-semiconductor field-effect transistors (MOSFET's). When dimensions of circuit elements relatively large, effects neglected safely. However, as very-large-scale integration of microelectronic circuits leads to MOSFET's shorter or narrower than 2 micrometer, effects become significant in design and operation. Such computer programs as widely-used "Simulation Program With Integrated Circuit Emphasis, Version 2" (SPICE 2) include many of these effects. In second-order models of n-channel, enhancement-mode MOSFET, first-order gate-depletion region diminished by triangular-cross-section deletions on end and augmented by circular-wedge-cross-section bulges on sides.

Benumof, Reuben; Zoutendyk, John A.; Coss, James R.

1990-01-01

49

Visualizing second order tensor fields with hyperstreamlines

NASA Technical Reports Server (NTRS)

Hyperstreamlines are a generalization to second order tensor fields of the conventional streamlines used in vector field visualization. As opposed to point icons commonly used in visualizing tensor fields, hyperstreamlines form a continuous representation of the complete tensor information along a three-dimensional path. This technique is useful in visulaizing both symmetric and unsymmetric three-dimensional tensor data. Several examples of tensor field visualization in solid materials and fluid flows are provided.

Delmarcelle, Thierry; Hesselink, Lambertus

1993-01-01

50

Reaction kinetics of catalyzed competitive heteropolymer cleavage.

A theoretical formulation for complete heteropolymer degradation is developed in terms of Michaelis-Menten reaction kinetics under the quasi-steady-state approximation. This allows the concentration of the entire intermediate decomposition cascade to be accounted for as well as each species of emerging final product. The formulation is implemented computationally and results in stable reaction kinetics across a range of orders of magnitude for K(M) and k(cat). The model is compared with experiment, specifically in vitro HIV-1 protease-catalyzed retroviral Gag-polyprotein processing. Using an experimentally determined cleavage-polypeptide parameter set, good qualitative agreement is reached with Gag degradation kinetics, given the difference in experimental conditions. A parameter search within 1 order of magnitude of variation of the experimental set results in the determination of an optimal parameter set in complete agreement with experiment which allows the time evolution of each individual as well as intermediate species in Gag to be accurately followed. Future investigations that determine the required enzymatic parameters to populate such a scheme will allow for the model to be refined in order to track the time for viral maturation and infectivity. PMID:21823648

Sadiq, S Kashif; Könnyü, Balázs; Müller, Viktor; Coveney, Peter V

2011-09-22

51

Kinetics of COCO2 reaction with iron oxide containing slags

The reaction between CO-CO2 gases and metallurgical slags is one of the most crucial reactions in metal production and refining processes. However, a full understanding of the reaction kinetics has not been achieved due to the complex effect of different variables. The aim of the present study was to obtain a consistent and comprehensive picture of the reaction kinetics. ^

Mansoor Barati Sedeh

2006-01-01

52

Understanding Arsenate Reaction Kinetics with Ferric Hydroxides

Understanding arsenic reactions with ferric hydroxides is important in understanding arsenic transport in the environment and in designing systems for removing arsenic from potable water. Many experimental studies have shown that the kinetics of arsenic adsorption on ferric hydroxides is biphasic, where a fraction of the arsenic adsorption occurs on a time scale of seconds while full equilibrium may require weeks to attain. This research employed density functional theory modeling in order to understand the mechanisms contributing to biphasic arsenic adsorption kinetics. The reaction energies and activation barriers for three modes of arsenate adsorption to ferric hydroxides were calculated. Gibbs free energies of reaction depended on the net charge of the complexes, which is a function of the system pH value. Physical adsorption of arsenate to ferric hydroxide proceeded with no activation barrier, with Gibbs free energies of reaction ranging from ?21 to ?58 kJ/mol. The highest Gibbs free energies of reaction for physical adsorption resulted from negative charge assisted hydrogen bonding between H atoms on the ferric hydroxide and O atoms in arsenate. The conversion of physically adsorbed arsenate into monodentate surface complexes had Gibbs free energies of activation ranging from 62 to 73 kJ/mol, and Gibbs free energies of reaction ranging from ?23 to ?38 kJ/mol. The conversion of monodentate surface complexes to bidentate, binuclear complexes had Gibbs free energies of activation ranging from 79 to 112 kJ/mol, and Gibbs free energies of reaction ranging from ?11 to ?55 kJ/mol. For release of arsenate from uncharged bidentate complexes, energies of activation as high as 167 kJ/mol were encountered. Increasingly negative charges on the complexes lowered the activation barriers for desorption of arsenate, and in complexes with ?2 charges, the highest activation barrier was 65 kJ/mol. This study shows that the slow kinetics associated with arsenic adsorption and desorption can be attributed to the high Gibbs free energies of activation for forming and breaking bonds with the ferric hydroxide. PMID:23806140

Farrell, James; Chaudhary, Binod K.

2015-01-01

53

Reaction rate kinetics for in situ combustion retorting of Michigan Antrim oil shale

The intrinsic reaction rate kinetics for the pyrolysis of Michigan Antrim oil shale and the oxidation of the carbonaceous residue of this shale have been determined using a thermogravimetric analysis method. The kinetics of the pyrolysis reaction were evaluated from both isothermal and nonisothermal rate data. The reaction was found to be second-order with an activation energy of 252.2 kJ/mole, and with a frequency factor of 9.25 ?? 1015 sec-1. Pyrolysis kinetics were not affected by heating rates between 0.01 to 0.67??K/s. No evidence of any reactions among the oil shale mineral constituents was observed at temperatures below 1173??K. However, it was found that the presence of pyrite in oil shale reduces the primary devolatilization rate of kerogen and increases the amount of residual char in the spent shale. Carbonaceous residues which were prepared by heating the oil shale at a rate of 0.166??K/s to temperatures between 923??K and 1073??K, had the highest reactivities when oxidized at 0.166??K/s in a gas having 21 volume percent oxygen. Oxygen chemisorption was found to be the initial precursor to the oxidation process. The kinetics governing oxygen chemisorption is (Equation Presented) where X is the fractional coverage. The oxidation of the carbonaceous residue was found also to be second-order. The activation energy and the frequency factor determined from isothermal experiments were 147 kJ/mole and 9.18??107 sec-1 respectively, while the values of these parameters obtained from a nonisothermal experiment were 212 kJ/mole and 1.5??1013 sec-1. The variation in the rate constants is attributed to the fact that isothermal and nonisothermal analyses represent two different aspects of the combustion process.

Rostam-Abadi, M.; Mickelson, R.W.

1984-01-01

54

Second-order (2 +1 ) -dimensional anisotropic hydrodynamics

NASA Astrophysics Data System (ADS)

We present a complete formulation of second-order (2 +1 ) -dimensional anisotropic hydrodynamics. The resulting framework generalizes leading-order anisotropic hydrodynamics by allowing for deviations of the one-particle distribution function from the spheroidal form assumed at leading order. We derive complete second-order equations of motion for the additional terms in the macroscopic currents generated by these deviations from their kinetic definition using a Grad-Israel-Stewart 14-moment ansatz. The result is a set of coupled partial differential equations for the momentum-space anisotropy parameter, effective temperature, the transverse components of the fluid four-velocity, and the viscous tensor components generated by deviations of the distribution from spheroidal form. We then perform a quantitative test of our approach by applying it to the case of one-dimensional boost-invariant expansion in the relaxation time approximation (RTA) in which case it is possible to numerically solve the Boltzmann equation exactly. We demonstrate that the second-order anisotropic hydrodynamics approach provides an excellent approximation to the exact (0+1)-dimensional RTA solution for both small and large values of the shear viscosity.

Bazow, Dennis; Heinz, Ulrich; Strickland, Michael

2014-11-01

55

Electromagnetically induced second-order Talbot effect

NASA Astrophysics Data System (ADS)

The electromagnetically induced Talbot effect (EITE) offers a nondestructive and lensless way to image ultracold atoms or molecules (Wen J. M. et al., Appl. Phys. Lett., 98 (2011) 081108). We study an atomic imaging scheme based on the second-order two-photon EITE. Entangled photon pairs are taken as the imaging light to realize coincidence recording. Compared to the previous self-imaging scheme, the present one has the characteristic of imaging nonlocally and of the controllable image variation in size, and thus, it is useful for facilitating the EITE application in imaging techniques.

Qiu, Tianhui; Yang, Guojian; Bian, Qing

2013-02-01

56

Reaction rates for mesoscopic reaction-diffusion kinetics

The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework, frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a mixed boundary condition at the reaction radius of two molecules. We also establish fundamental limits for the range of mesh resolutions for which this approach yields accurate results, and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics.

Stefan Hellander; Andreas Hellander; Linda Petzold

2015-01-28

57

Reaction rates for mesoscopic reaction-diffusion kinetics

NASA Astrophysics Data System (ADS)

The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic scale-dependent reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a Robin boundary condition at the reaction radius of two molecules. We also establish fundamental limits on the range of mesh resolutions for which this approach yields accurate results and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics. We show that for mesh sizes below the fundamental lower limit, results are less accurate. Thus, the lower limit determines the mesh size for which we obtain the most accurate results.

Hellander, Stefan; Hellander, Andreas; Petzold, Linda

2015-02-01

58

Robust stability of second-order systems

NASA Technical Reports Server (NTRS)

It has been shown recently how virtual passive controllers can be designed for second-order dynamic systems to achieve robust stability. The virtual controllers were visualized as systems made up of spring, mass and damping elements. In this paper, a new approach emphasizing on the notion of positive realness to the same second-order dynamic systems is used. Necessary and sufficient conditions for positive realness are presented for scalar spring-mass-dashpot systems. For multi-input multi-output systems, we show how a mass-spring-dashpot system can be made positive real by properly choosing its output variables. In particular, sufficient conditions are shown for the system without output velocity. Furthermore, if velocity cannot be measured then the system parameters must be precise to keep the system positive real. In practice, system parameters are not always constant and cannot be measured precisely. Therefore, in order to be useful positive real systems must be robust to some degrees. This can be achieved with the design presented in this paper.

Chuang, C.-H.

1995-01-01

59

Second order non-linear optical polyphosphazenes

NASA Astrophysics Data System (ADS)

In this contribution, we describe the synthesis and second-order optical properties of a series of mixed-substituent poly(organophosphazenes)that possess covalently attached donor-acceptor substituted, conjugated moieties. The general structure of the polymer is (NP(OCH2CF3)x(OR)(y))(n), where OR = -O(CH2O) (k)C6H4-CH=CH-C6H4NO2; where k = 1-3, and -OCH2CH2N(CH2CH3)C6H4-N=N-C6H4NO2, and x + y = 100 percent. The nonlinear optical properties of thin films of the polymers were investigated by using second harmonic generation, giving second-harmonic coefficients, d(33), in the range 4.1 to 34 pm/V.

Dembek, Alexa A.; Allcock, Harry R.; Kim, Chulhee; Steier, William H.; Spangler, Charles W.; Devine, Robert L. S.; Yongquiang, Shi

1990-03-01

60

Second-order superintegrable quantum systems

A classical (or quantum) superintegrable system on an n-dimensional Riemannian manifold is an integrable Hamiltonian system with potential that admits 2n - 1 functionally independent constants of the motion that are polynomial in the momenta, the maximum number possible. If these constants of the motion are all quadratic, then the system is second-order superintegrable, the most tractable case and the one we study here. Such systems have remarkable properties: multi-integrability and separability, a quadratic algebra of symmetries whose representation theory yields spectral information about the Schroedinger operator, and deep connections with expansion formulas relating classes of special functions. For n = 2 and for conformally flat spaces when n = 3, we have worked out the structure of the classical systems and shown that the quadratic algebra always closes at order 6. Here, we describe the quantum analogs of these results. We show that, for nondegenerate potentials, each classical system has a unique quantum extension.

Miller, W. [University of Minnesota, School of Mathematics (United States); Kalnins, E. G. [University of Waikato, Department of Mathematics and Statistics (New Zealand); Kress, J. M. [The University of New South Wales, School of Mathematics (Australia)], E-mail: j.kress@unsw.edu.au

2007-03-15

61

Kinetic analysis of free-radical reactions in the low-temperature autoxidation of triglycerides

The kinetics of the low-temperature autoxidation of triglycerides has been investigated by electron spin resonance spectroscopy. After initial radical production, four reaction stages are found in the overall autoxidation of unsaturated lipids: (1) formation of peroxyl radicals by addition of molecular oxygen to the initial carbon radicals, (2) consumption of oxygen in the autoxidation cycle, (3) decay of the lipid peroxyl radical into allylic and pentadienyl radicals, and (4) recombination of the carbon-centered radicals. Peroxyl radical decay in saturated lipids follows second-order kinetics with an apparent activation energy of ca. 50 kJ/mol. The authors find that, for polyunsaturated lipids, even at quite low temperatures (120 K), the autoxidation process occurs readily and must be considered in the storage of biological samples.

Zhu, Jingmin; Sevilla, M.D. (Oakland Univ., Rochester, MI (USA))

1990-02-22

62

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

Dhananjay Kumar; J. P. Gaur

2011-01-01

63

Second-order continuum traffic flow model

NASA Astrophysics Data System (ADS)

A second-order traffic flow model is derived from microscopic equations and is compared to existing models. In order to build in different driver characteristics on the microscopic level, we exploit the idea of an additional phase-space variable, called the desired velocity originally introduced by Paveri-Fontana [Trans. Res. 9, 225 (1975)]. By taking the moments of Paveri-Fontana's Boltzmann-like ansatz, a hierachy of evolution equations is found. This hierarchy is closed by neglecting cumulants of third and higher order in the cumulant expansion of the distribution function, thus leading to Euler-like traffic equations. As a consequence of the desired velocity, we find dynamical quantities, which are the mean desired velocity, the variance of the desired velocity, and the covariance of actual and desired velocity. Through these quantities an alternative explanation for the onset of traffic clusters can be given, i.e., a spatial variation of the variance of the desired velocity can cause the formation of a traffic jam. Furthermore, by taking into account the finite car length, Paveri-Fontana's equation is generalized to the high-density regime eventually producing corrections to the macroscopic equations. The relevance of the present dynamic quantities is demonstrated by numerical simulations.

Wagner, C.; Hoffmann, C.; Sollacher, R.; Wagenhuber, J.; Schürmann, B.

1996-11-01

64

A classical but new kinetic equation for hydride transfer reactions.

A classical but new kinetic equation to estimate activation energies of various hydride transfer reactions was developed according to transition state theory using the Morse-type free energy curves of hydride donors to release a hydride anion and hydride acceptors to capture a hydride anion and by which the activation energies of 187 typical hydride self-exchange reactions and more than thirty thousand hydride cross transfer reactions in acetonitrile were safely estimated in this work. Since the development of the kinetic equation is only on the basis of the related chemical bond changes of the hydride transfer reactants, the kinetic equation should be also suitable for proton transfer reactions, hydrogen atom transfer reactions and all the other chemical reactions involved with breaking and formation of chemical bonds. One of the most important contributions of this work is to have achieved the perfect unity of the kinetic equation and thermodynamic equation for hydride transfer reactions. PMID:23917398

Zhu, Xiao-Qing; Deng, Fei-Huang; Yang, Jin-Dong; Li, Xiu-Tao; Chen, Qiang; Lei, Nan-Ping; Meng, Fan-Kun; Zhao, Xiao-Peng; Han, Su-Hui; Hao, Er-Jun; Mu, Yuan-Yuan

2013-09-28

65

Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks

ERIC Educational Resources Information Center

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

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

2011-01-01

66

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

ERIC Educational Resources Information Center

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

Weston, Ralph E., Jr.

1988-01-01

67

A generalized kinetic model for heterogeneous gas-solid reactions.

We present a generalized kinetic model for gas-solid heterogeneous reactions taking place at the interface between two phases. The model studies the reaction kinetics by taking into account the reactions at the interface, as well as the transport process within the product layer. The standard unreacted shrinking core model relies on the assumption of quasi-static diffusion that results in a steady-state concentration profile of gas reactant in the product layer. By relaxing this assumption and resolving the entire problem, general solutions can be obtained for reaction kinetics, including the reaction front velocity and the conversion (volume fraction of reacted solid). The unreacted shrinking core model is shown to be accurate and in agreement with the generalized model for slow reaction (or fast diffusion), low concentration of gas reactant, and small solid size. Otherwise, a generalized kinetic model should be used. PMID:22920132

Xu, Zhijie; Sun, Xin; Khaleel, Mohammad A

2012-08-21

68

Second-Order Accurate Method for Solving Radiation-Hydrodynamics

Second-order discretization for radiation-hydrodynamics is currently an area of great interest. Second-order methods used to solve the respective single-physics problems often differ fundamentally, making it difficult to combine them in a second...

Edwards, Jarrod Douglas

2013-11-12

69

Effects of jump diffusion rates on reaction kinetics in solids

Applying Torrey’s treatment of jump diffusion in solids to the study of reaction kinetics, a method is presented to describe the dynamics of caging processes in solids in which the reactants are confined to the cages. We put our attention to the study of three measures of time-dependent reactivity; namely, the observed reaction rate, cumulative reaction rate, and the fraction

Lian-Pin Hwang

1982-01-01

70

Kinetic Study of the Heck Reaction: An Interdisciplinary Experiment

ERIC Educational Resources Information Center

The aim of this experiment is to study and calculate the kinetic constant of a Heck reaction: the arylation of but-3-en-2-ol by iodobenzene catalyzed by palladium acetate in presence of triethylamine in DMF. The reaction leads to a mixture of two ketones. Students use GC analysis to quantify reagents and products of reaction. They control the…

Gozzi, Christel; Bouzidi, Naoual

2008-01-01

71

A solvent-free, chemoenzymatic reaction sequence for the enantioselective synthesis of ?-amino acid esters has been kinetically and thermodynamically characterized. The coupled sequence comprises a thermal aza-Michael addition of cheap starting materials and a lipase catalyzed aminolysis for the kinetic resolution of the racemic ester. Excellent ee values of >99% were obtained for the ?-amino acid ester at 60% conversion. Kinetic constants for the aza-Michael addition were obtained by straightforward numerical integration of second-order rate equations and nonlinear fitting of the progress curves. A different strategy had to be devised for the biocatalytic reaction. Initially, a simplified Michaelis-Menten model including product inhibition was developed for the reaction running in THF as an organic solvent. Activity based parameters were used instead of concentrations in order to facilitate the transfer of the kinetic model to the solvent-free system. Observed solvent effects not accounted for by the use of thermodynamic activities were incorporated into the kinetic model. Enzyme deactivation was observed to depend on the ratio of the applied substrates and also included in the kinetic model. The developed simple model is in very good agreement with the experimental data and allows the simulation and optimization of the solvent-free process. PMID:22275046

Strompen, Simon; Weiss, Markus; Ingram, Thomas; Smirnova, Irina; Gröger, Harald; Hilterhaus, Lutz; Liese, Andreas

2012-06-01

72

Hydroxyalkyl radicals have been reported to induce lipid oxidation as the key aspect of the pathogenesis of alcoholic fatty liver disease and are responsible for the alkylation and cleavage of DNA during the metabolism of a wide range of genotoxic compounds. However, relevant kinetic data for the oxidation of unsaturated lipids by 1-hydroxyethyl radical (HER) has not been reported. In this study, the rate constants for the reaction of unsaturated fatty acid methyl esters and sterols with HER have been determined using a competitive kinetic approach employing the spin-trap ?-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) as the competitive substrate. Polyunsaturated fatty acid methyl ester is shown to react with HER with an apparent second-order rate constant ranging from (3.7 ± 0.1) × 10(6) L mol(-1) s(-1) for methyl linoleate to (2.7 ± 0.2) × 10(7) L mol(-1) s(-1) for methyl docosahexanoate at 25.0 ± 0.2 °C in ethanol. The apparent second-order rate constant for polyunsaturated fatty acid methyl ester oxidation by HER is dependent on the number of bisallylic hydrogen atoms rather than on the bond dissociation energy value for the weakest C-H bond as determined by ab initio density functional theory calculations. Sterols displayed higher reactivity compared to unsaturated fatty acid methyl esters with apparent second-order rate constants of (2.7 ± 0.1) × 10(6) and (5.2 ± 0.1) × 10(7) L mol(-1) s(-1) at 25.0 ± 0.2 °C in ethanol for cholesterol and ergosterol, respectively. Similar experiments with prenylflavonoids as potential herbal chemopreventive agents for preventing alcoholic liver diseases yield apparent second-order rate constants close to the diffusion control with kapp values of (1.5 ± 0.2) and (3.6 ± 0.1) × 10(9) L mol(-1)s(-1) for 6-prenylnarigerin and xanthohumol at 25.0 ± 0.2 °C in ethanol solution, respectively. Polyunsaturated lipids were revealed to be highly reactive oxidizable substrates toward HER-induced oxidation in biological systems leading to damage of membranes and sensitive structures. PMID:25409421

de Almeida, Natália E C; de Aguiar, Inara; de Zawadzki, Andressa; Cardoso, Daniel R

2014-12-11

73

Kinetic studies of isoprene reactions with hydroxyl and chlorine radicals

Kinetic studies of the isoprene oxidation reactions initiated by the hydroxyl radical OH and the chlorine atom Cl have been investigated using a fast-flow reactor in conjunction with chemical ionization mass spectrometry (CIMS) and using laser...

Suh, Inseon

2000-01-01

74

Kinetic and theoretical study of the reaction of Cl atoms with a series of linear thiols

The reactions of Cl with a series of linear thiols: 1-propanethiol (k{sub 1}), 1-butanethiol (k{sub 2}), and 1-pentanethiol (k{sub 3}) were investigated as a function of temperature (in the range of 268-379 K) and pressure (in the range of 50-200 Torr) by laser photolysis-resonance fluorescence. Only 1-propanethiol has previously been studied, but at 1 Torr of total pressure. The derived Arrhenius expressions obtained using our kinetic data were as follows: k{sub 1}=(3.97{+-}0.44)x10{sup -11} exp[(410{+-}36)/T], k{sub 2}=(1.01{+-}0.16)x10{sup -10} exp[(146{+-}23)/T], and k{sub 3}=(1.28{+-}0.10)x10{sup -10} exp[(129{+-}25)/T] (in units of cm{sup 3} molecule{sup -1} s{sup -1}). Moreover, a theoretical insight into mechanisms of these reactions has also been pursued through ab initio Moeller-Plesset second-order perturbation treatment calculations with 6-311G** basis set. Optimized geometries have been obtained for transition states and molecular complexes appearing along the different reaction pathways. Furthermore, molecular energies have been calculated at QCISD(T) level in order to get an estimation of the activation energies. Finally, the nature of the molecular complexes and transitions states is analyzed by using kinetic-potential and natural bond orbital total energy decomposition schemes.

Garzon, Andres; Albaladejo, Jose [Departamento de Quimica Fisica, Facultad de CC. Quimicas, Universidad de Castilla La Mancha, Avenida Camilo Jose Cela, s/n, 13071 Ciudad Real (Spain); Notario, Alberto [Departamento de Quimica Fisica, Instituto de Tecnologias Quimica y Medioambiental (ITQUIMA), Universidad de Castilla La Mancha, Avenida Camilo Jose Cela, s/n, 13071 Ciudad Real (Spain); Pena-Ruiz, Tomas; Fernandez-Gomez, Manuel [Departamento de Quimica Fisica y Analitica, Facultad de CC. Experimentales, Universidad de Jaen, Paraje las Lagunillas, s/n, 23071 Jaen (Spain)

2008-11-21

75

New approach for kinetic parameters determination for hydrothermal oxidation reaction

1 New approach for kinetic parameters determination for hydrothermal oxidation reaction David different methods, namely pseudo first order kinetics, multiple linear regression and Runge-Kutta algorithm for industrial or agricultural applications. In order to scale up reactors for HOT of industrial wastewaters

Paris-Sud XI, Université de

76

Kinetics of Acid Reactions: Making Sense of Associated Concepts

ERIC Educational Resources Information Center

In chemical kinetics, in addition to the concepts related to kinetics, stoichiometry, chemical equilibrium and the characteristics of the reactants are often involved when comparing the rates of different reactions, making such comparisons very challenging for students at all levels, as well as for pre-service science teachers. Consequently, four…

Tan, Kim Chwee Daniel; Treagust, David F.; Chandrasegaran, A. L.; Mocerino, Mauro

2010-01-01

77

GAS–LIQUID REACTION KINETICS: A REVIEW OF DETERMINATION METHODS

The aim of this article is to provide comprehensive insight into the determination and interpretation of reaction kinetics of two-phase (gas–liquid) systems. Various aspects of the methodologies used for the measurements of kinetic parameters (such as equipment design, corresponding theoretical background, main steps, advantages, and limitations) are discussed in detail. In addition, an illustrating example is provided based on an

Prakash D. Vaidya; Eugeny Y. Kenig

2007-01-01

78

Reaction kinetics of Ni\\/Sn soldering reaction

Soldering between solid Ni and liquid Sn is studied, including late stages of reflow. Only during the very early stages of the process, intermetallic grains grow with a 1\\/3 power dependence on time. Later, kinetics clearly changes to parabolic growth, but remarkably in two subsequent regimes distinguished by different rate constants. The observed kinetics is discussed with respect to recent

Jens Görlich; Dietmar Baither; Guido Schmitz

2010-01-01

79

A study of the Sabatier-methanation reaction kinetics

NASA Technical Reports Server (NTRS)

The kinetics of the Sabatier methanation reaction, the reduction of carbon dioxide with hydrogen to methane and water, was investigated for 58 percent nickel on kieselguhr catalyst and 20 percent ruthenium on alumina catalyst. Differential rate data from an experimental program were correlated with a power function rate equation both for forward and reverse reactions. The kinetic parameters of activation energy, frequency rate constant and reaction order were determined for the rate equation. The values of these parameters were obtained from an Arrhenius plot of the experimental differential rate data. Also the carbon monoxide side reaction effect was measured and included in the correlation of parameters. The reaction was found to fit the rate equation experimentally within the temperature range 421 K, where the reaction effectively begins, the 800 K where the reaction rate drops and departs from the rate equation form.

Verostko, C. E.; Forsythe, R. K.

1974-01-01

80

Reaction kinetics of hydrothermal carbonization of loblolly pine.

Hydrothermal carbonization (HTC) is a pretreatment process to convert diverse feedstocks to homogeneous energy-dense solid fuels. Understanding of reaction kinetics is necessary for reactor design and optimization. In this study, the reaction kinetics and effects of particle size on HTC were investigated. Experiments were conducted in a novel two-chamber reactor maintaining isothermal conditions for 15s to 30 min reaction times. Loblolly pine was treated at 200, 230, and 260°C. During the first few minutes of reaction, the solid-product mass yield decreases rapidly while the calorific value increases rapidly. A simple reaction mechanism is proposed and validated, in which both hemicellulose and cellulose degrade in parallel first-order reactions. Activation energy of hemicellulose and cellulose degradation were determined to be 30 and 73 kJ/mol, respectively. For short HTC times, both reaction and diffusion effects were observed. PMID:23651600

Reza, M Toufiq; Yan, Wei; Uddin, M Helal; Lynam, Joan G; Hoekman, S Kent; Coronella, Charles J; Vásquez, Victor R

2013-07-01

81

Aqueous reaction kinetics of ozone and dimethylsulfide and its atmospheric implications

In order to understand and predict the budgets and distributions of ozone (O{sub 3}) and dimethylsulfide (DMS) in the marine atmosphere, it is necessary to determine the rates of aqueous reactions in clouds and surface water that may influence the lifetimes of these species. The authors studied the kinetics of the aqueous phase reaction of O{sub 3} and DMS in the laboratory using a bubbler-type gas-liquid reactor at sub-parts-per-billion (ppb) gas phase concentrations. The steady state reaction rate was determined from the decrease of gas phase DMS concentration in the effluent gas as ozone was simultaneously added. The reaction stoichiometry was found to be 1:1 with respect to the two reagents. Fitting the data to a kinetics scheme appropriate for a gas-liquid reaction in the slow reaction regime where the reaction rate is governed by both chemical reaction and convective mass transfer, the authors determined an intrinsic second-order aqueous rate coefficient of O{sub 3}-DMS reaction of 4 x 10{sup 8} ({+-}40%) M{sup -1} s{sup -1} at 15.0{degrees}C. The implications of this reaction include (1) the atmospheric lifetime of DMS against in-cloud O{sub 3}-DMS reaction at 30 ppb of O{sub 3} and 1 g/m liquid water concentration is calculated to be {approximately}3 days and is comparable to that against the gas phase reaction with OH radicals at 1 x 10{sup 6} molecules cm{sup {minus}3}; (2) the deposition of atmospheric O{sub 3} to the ocean surface is only slightly enhanced by the O{sub 3}-DMS reaction at the highest reported surface DMS concentrations, ({approximately}40 nM); and (3) the sea to air flux of DMS is not affected by this reaction at O{sub 3} concentrations typical of the marine atmosphere. 43 refs., 6 figs., 3 tabs.

Lee, Y.N.; Zhou, X. [Brookhaven National Lab., Upton, NY (United States)] [Brookhaven National Lab., Upton, NY (United States)

1994-02-20

82

Kinetics of enzymatic reactions in lipid membranes containing domains

NASA Astrophysics Data System (ADS)

An appreciable part of enzymes operating in vivo is associated with lipid membranes. The function of such enzymes can be influenced by the presence of domains containing proteins and/or composed of different lipids. The corresponding experimental model-system studies can be performed under well controlled conditions, e.g., on a planar supported lipid bilayer or surface-immobilized vesicles. To clarify what may happen in such systems, we propose general kinetic equations describing the enzyme-catalyzed substrate conversion occurring via the Michaelis–Menten (MM) mechanism on a membrane with domains which do not directly participate in reaction. For two generic situations when a relatively slow reaction takes place primarily in or outside domains, we take substrate saturation and lateral substrate–substrate interactions at domains into account and scrutinize the dependence of the reaction rate on the average substrate coverage. With increasing coverage, depending on the details, the reaction rate reaches saturation via an inflection point or monotonously as in the conventional MM case. In addition, we show analytically the types of reaction kinetics occurring primarily at domain boundaries. In the physically interesting situation when the domain growth is fast on the reaction time scale, the latter kinetics are far from conventional. The opposite situation when the reaction is fast and controlled by diffusion has been studied by using the Monte Carlo technique. The corresponding results indicate that the dependence of the reaction kinetics on the domain size may be weak.

Zhdanov, Vladimir P.; Höök, Fredrik

2015-04-01

83

Second order perturbation theory for spin-orbit resonances

We implement Lie transform perturbation theory to second order for the planar spin-orbit problem. The perturbation parameter is the asphericity of the body, with the orbital eccentricity entering as an additional parameter. We study first and second order resonances for different values of these parameters. For nearly spherical bodies like Mercury and the Moon first order perturbation theory is adequate, whereas for highly aspherical bodies like Hyperion the spin is mostly chaotic and perturbation theory is of limited use. However, in between, we identify a parameter range where second order perturbation theory is useful and where as yet unidentified objects may be in second order resonances.

A. E. Flynn; P. Saha

2005-05-27

84

Fluid flow and chemical reaction kinetics in metamorphic systems

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

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

1993-05-01

85

Basic Chemical Principles 1: Reaction Kinetics

of reactants ! mobility (masses) and density { Di#11;usion-controlled reactions: prefactor A is the most that Oxygen atom and molecule O 2 are ground state triplets. #15; Important fact: Quantum mechanics tell us: Spin forbidden #15; Consequence: Reactions with ground state Oxygen are slow #15; Molecules can

Schofield, Jeremy

86

Oxidation of diclofenac by potassium ferrate (VI): reaction kinetics and toxicity evaluation.

The reaction kinetics and toxicity of diclofenac (DCF) oxidation by ferrate (VI) under simulated water disinfection conditions were investigated. Experimental results indicated that the reaction between DCF and Fe(VI) followed first-order kinetics with respect to each reactant. Furthermore, the effects of pH and temperature on DCF oxidation by Fe(VI) were elucidated using a systematic examination. The apparent second-order rate constants (kapp) increased significantly from 2.54 to 11.6M(-1)s(-1), as the pH of the solution decreased from 11.0 to 7.0, and the acid-base equilibriums of Fe(VI) and DCF were proposed to explain the pH dependence of kapp. The acute toxicity of DCF solution during Fe(VI) oxidation was evaluated using a Microtox bioassay. Overall, the DCF degradation process resulted in a rapid increase of the inhibition rate of luminescent bacteria. These toxicity tests suggest that the formation of enhanced toxic intermediates during the Fe(VI) disinfection process may pose potential health risk to consumers. PMID:25460958

Wang, Yingling; Liu, Haijin; Liu, Guoguang; Xie, Youhai; Gao, Shuyan

2015-02-15

87

The accessibility of immobilized DNA has been shown to depend more crucially on the method of immobilization than on the type of support used for fixation. When sonicated denatured DNA is coupled via diazotization or via cyanogen bromide reaction to solid Sephadex G-25 and Cellex 410 or to macroporous Sephacryl S-500 and Sepharose C1-6B its accessibility varies from 100 to 24 percent. Generally the loss of accessibility is linked to a depression of the melting temperature of DNA helices formed on the support. This correlation shows a characteristic course for a particular coupling method. DNA coupled under denaturing conditions may become totally inaccessible when only 3 percent of its bases are involved in the covalent linkage. Kinetic experiments with sonicated E.coli DNA have shown that the rate constants for renaturation or hybridization reactions are very similar for DNA immobilized by different methods to solid or macroporous supports. Generally the second order rate constant for a heterogeneous reaction (between mobile and immobilized DNA) is about one order of magnitude smaller than that of the analogous homogeneous reaction (in solution). PMID:6185922

Bünemann, H

1982-01-01

88

Kinetics of the sodium carbonate-sulfur dioxide reaction

The kinetics of the SOâ-NaâCOâ reaction were studied at 353 to 413 K and atmospheric pressure with thermal gravimetric analysis data. Since the reaction is very fast, special precautions were taken to operate at conditions such that transport effects did not influence results. The data indicated that NaâSOâ was formed by two paths: direct reaction, and adsorption of SOâ followed

Shoichi Kimura; J. M. Smith

1987-01-01

89

Kinetics and mechanisms of some atomic oxygen reactions

NASA Technical Reports Server (NTRS)

Mechanisms and kinetics of some reactions of the ground state of oxygen atoms, O(3P), are briefly summarized. Attention is given to reactions of oxygen atoms with several different types of organic and inorganic compounds such as alkanes, alkenes, alkynes, aromatics, and some oxygen, nitrogen, halogen and sulfur derivatives of these compounds. References to some recent compilations and critical evaluations of reaction rate constants are given.

Cvetanovic, R. J.

1987-01-01

90

NASA Technical Reports Server (NTRS)

A second-order theory for electrostatic instabilities driven by counterstreaming ion beams is developed which describes momentum coupling and heating of the plasma via wave-particle interactions. Exchange rates between the waves and particles are derived, which are suitable for the fluid equations simulating microscopic effects on macroscopic scales. Using a fully kinetic simulation, the electrostatic ion cyclotron instability due to counterstreaming H(+) beams has been simulated. A power spectrum from the kinetic simulation is used to evaluate second-order exchange rates. The calculated heating and momentum loss from second-order theory is compared to the numerical simulation.

Miller, Ronald H.; Winske, Dan; Gary, S. P.

1992-01-01

91

Adsorption Isotherms and Surface Reaction Kinetics

ERIC Educational Resources Information Center

Explains an error that occurs in calculating the conditions for a maximum value of a rate expression for a bimolecular reaction. The rate expression is derived using the Langmuir adsorption isotherm to relate gas pressures and corresponding surface coverages. (GS)

Lobo, L. S.; Bernardo, C. A.

1974-01-01

92

Kinetics of Chemical Reactions in Flames

NASA Technical Reports Server (NTRS)

In part I of the paper the theory of flame propagation is developed along the lines followed by Frank-Kamenetsky and one of the writers. The development of chain processes in flames is considered. A basis is given for the application of the method of stationary concentrations to reactions in flames; reactions with branching chains are analyzed. The case of a diffusion coefficient different from the coefficient of temperature conductivity is considered.

Zeldovich, Y.; Semenov, N.

1946-01-01

93

Second-Order Conditioning during a Compound Extinction Treatment

ERIC Educational Resources Information Center

Two conditioned taste aversion experiments with rats were conducted to establish if a target taste that had received a prior pairing with illness could be subject to second-order conditioning during extinction treatment in compound with a flavor that also received prior conditioning. In these experiments, the occurrence of second-order…

Pineno, Oskar; Zilski, Jessica M.; Schachtman, Todd R.

2007-01-01

94

A discussion of second order sampling for bandpass signal

Kohlenberg's second order sampling allows a bandpass signal to be sampled at the theoretical minimum rate of 2 times the bandwidth. The theoretical minimum sampling rate is impractical in the sense that any engineering imperfections in the implementation will cause aliasing. In this paper, second order sampling at above the theoretical minimum rate is studied, a guard-band will be included

Meng Xiangwei

1998-01-01

95

A Simple Second Order Cartesian Scheme for Compressible Flows

and Iaccarino [6]. In this paper we present a simple globally second order scheme inspired by ghost cell of the convective fluxes computation for the cells near the solid ensures the boundary condition at second order and a centered scheme for the diffusive term. At the cells located on the boundary, we solve an ad hoc Riemann

Paris-Sud XI, Université de

96

Multivariate curve resolution applied to second order data

Application of multivariate curve resolution to second order data from hyphenated liquid chromatography with spectrometric diode array detection is shown. Chromatographic analysis of samples giving unresolved mixtures produces different data structures depending on the reproducibility of the elution process: (a) second order data where elution peaks of the same component in the different chromatographic runs have the same shape and

Roma Tauler

1995-01-01

97

Dual Formulation of Second Order Target Problems H. Mete Soner

Dual Formulation of Second Order Target Problems H. Mete Soner Nizar Touzi Jianfeng Zhang April 1 ingredient enables us to prove a dual formulation of the target problem as the supremum of the solutions, 2010 Abstract This paper provides a new formulation of second order stochastic target problems

Touzi, Nizar

98

Dual Formulation of Second Order Target Problems H. Mete Soner

Dual Formulation of Second Order Target Problems H. Mete Soner Nizar Touzi Jianfeng Zhang September ingredient enables us to prove a dual formulation of the target problem as the supremum of the solutions 2, 2011 Abstract This paper provides a new formulation of second order stochastic target problems

Touzi, Nizar

99

Periodic perturbation of the kinetics of heterogeneous catalytic reactions

NASA Astrophysics Data System (ADS)

Periodic forcing of reaction kinetics via, e.g., variation of reactant pressure(s), temperature or flow reversal is one of the useful tools employed in basic and applied studies of heterogeneous catalytic processes. In the case of conventional (stable) kinetics, this strategy is used to clarify the mechanisms of reactions and obtain data on reaction rate constants or to improve the reaction performance, e.g., to increase reaction rate and/or selectivity with respect to desired products. In experiments, that are focused on oscillatory catalytic reactions, periodic perturbations are employed to stabilize period-1 oscillations. This is easily achieved if the external and internal frequencies are equal. In a more general context, periodic perturbation of chemical reactions, that exhibit period-1 oscillations, may result in complex reaction behaviour, including period doubling and irregular kinetics provided that the external and internal frequencies do not coincide. We consider in this review both the relevant data available in the literature and the results of systematic calculations for a few generic models.

Zhdanov, Vladimir P.

2004-09-01

100

Kinetics and Thermochemistry of the Cl((sup 2)P(sub J)) + C2Cl4 Association Reaction

NASA Technical Reports Server (NTRS)

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the Cl(sup 2)P(sub j) + C2Cl4 association reaction as a function of temperature (231-390 K) and pressure (3-700 Torr) in nitrogen buffer gas. The reaction is found to be in the falloff regime between third and second order over the range of conditions investigated, although the second-order limit is approached at the highest pressures and lowest temperatures. At temperatures below 300 K, the association reaction is found to be irreversible on the experimental time scale of approximately 20 m-s. The kinetic data at T is less than 300 K have been employed to obtain falloff parameters in a convenient format for atmospheric modeling. At temperatures above 330 K, reversible addition is observed, thus allowing equilibrium constants for C2Cl5 formation and dissociation to be determined. Second- and third-law analyses of the equilibrium data lead to the following thermochemical parameters for the association reaction: Delta-H(298) = -18.1 +/- 1.3 kcal/mol, Delta-H(0) = -17.6 +/- 1.3 kcal/mol, and Delta-S(298) = -27.7 +/- 3.0 cal/mol.K. In conjunction with the well-known heats of formation of Cl((sup 2)P(sub j)) and C2Cl4 the above Delta-H values lead to the following heats of formation for C2Cl5, at 298 and 0 K: Delta-H(f,298) = 8.0 +/- 1.3 kcal/mol and Delta-H(f,0) = 8.1 +/- 1.5 kcal/mol. The kinetic and thermochemical parameters reported above are compared with other reported values, and the significance of reported association rate coefficients for understanding tropospheric chlorine chemistry is discussed.

Nicovich, J. M.; Wang, S.; Mckee, M. L.; Wine, P. H.

1997-01-01

101

Reaction wheels for kinetic energy storage

NASA Technical Reports Server (NTRS)

In contrast to all existing reaction wheel implementations, an order of magnitude increase in speed can be obtained efficiently if power to the actuators can be recovered. This allows a combined attitude control-energy storage system to be developed with structure mounted reaction wheels. The feasibility of combining reaction wheels with energy storage wwheels is demonstrated. The power required for control torques is a function of wheel speed but this energy is not dissipated; it is stored in the wheel. The I(2)R loss resulting from a given torque is shown to be constant, independent of the design speed of the motor. What remains, in order to efficiently use high speed wheels (essential for energy storage) for control purposes, is to reduce rotational losses to acceptable levels. Progress was made in permanent magnet motor design for high speed operation. Variable field motors offer more control flexibility and efficiency over a broader speed range.

Studer, P. A.

1984-01-01

102

Kinetics of surface reactions in catalytic combustion

Catalytic combustion is a system which holds promise for dealing with a variety of modern combustion problems, including high efficiency, low emissions, alternate fuels and staged combustion. Since, however, the rapid reaction possible on a catalytic surface is often restricted by heat and mass transfer, measured performance cannot easily be extrapolated to other systems without an understanding of all the simultaneously-occurring processes. In the program to be described, tightly-controlled laboratory tests of ignition, temperature rise, and combustion efficiency were conducted for a variety of fuels and surfaces. Through reduction by an analytical program treating chemical reaction and heat and mass transfer, the laboratory data furnished the particular rate of reaction of fuel on the surface. 7 refs.

Marteney, P.J.; Kesten, A.S.

1981-01-01

103

Reaction kinetics between fiber and matrix

NASA Technical Reports Server (NTRS)

Interdiffusion and interdiffusion controlled intermediate phase formation in metal matrix composites can be of interest for the prolonged application of these systems at high temperatures. Methods are discussed that address the kinetics of interdiffusion in systems that exhibit solid solution intermixing or the formation of a third intermediate phase at the fiber/matrix interface, or both. The tungsten fiber reinforced niobium and tungsten fiber reinforced superalloy systems are employed as model systems for experimentation and discussion. In an effort to impede interdiffusion, the concept of ion implanted diffusion barriers have been examined. Preliminary results on the feasibility and effectiveness of ion implanted diffusion barriers are presented.

Kopp, M. W.; Tien, J. K.; Petrasek, D. W.

1988-01-01

104

Exercises in the Geochemical Kinetics of Mineral-Water Reactions

NSDL National Science Digital Library

This module consists of a laboratory exercise and related homework problems on geochemical kinetics of mineral-solution reactions for undergraduate mineralogy. Students measure the grain sizes of equant halite crystals, and the time for complete dissolution of each grain. From these data, students retrieve a rate law, from several possible. Additional homework problems allow various chemical and physical transport processes in mineral-fluid systems to be evaluated. The lab and homework illustrate several basic principles of chemical kinetics directly relevant to geology, including rate laws of reactions, diffusion, advective transport, and the relationship between rate-limiting mechanisms and crystal-surface morphology.

105

Reaction kinetics and diagnostics for oil-shale retorting

NASA Astrophysics Data System (ADS)

The advances in pyrolysis chemistry and kinetics and the resulting diagnostic methods based on effluent products for determining retort performance were reviewed. Kerogen pyrolysis kinetics and stoichiometry were generalized by further measurements on a larger number of samples. Analysis by capillary colunn gas chromatography of shale oil samples produced under a variety of field and laboratory conditions resulted in a method for determining the oil yield from a combustion retort. Measurement of sulfur products under a variety of conditions led to an understanding sulfur reactions both those of processing and environmental importance. Equations for estimating the heat of combustion of spent shale were developed by understanding oil shale composition and reactions.

Burnham, A. K.

1981-10-01

106

Reaction of silylene with sulfur dioxide: some gas-phase kinetic and theoretical studies.

Time-resolved kinetic studies of the reaction of silylene, SiH2, with SO2 have been carried out in the gas phase over the temperature range 297-609 K, using laser flash photolysis to generate and monitor SiH2. The second order rate coefficients at 1.3 kPa (SF6 bath gas) fitted the Arrhenius equation: log(k/cm(3) molecule(-1) s(-1)) = (-10.10 ± 0.06) + (3.46 ± 0.45 kJ mol(-1))/RT ln 10 where the uncertainties are single standard deviations. The collisional efficiency is 71% at 298 K, and in kinetic terms the reaction most resembles those of SiH2 with CH3CHO and (CH3)2CO. Quantum chemical calculations at the G3 level suggest a mechanism occurring via addition of SiH2 to one of the S=O double bonds leading to formation of the three-membered ring, thione-siloxirane which has a low energy barrier to ring expansion to yield the four-membered ring, 3-thia-2,4-dioxasiletane, the lowest energy adduct found on the potential energy (PE) surface. RRKM calculations, however, show that, if formed, this molecule would only be partially stabilised under the reaction conditions and the rate coefficients would be pressure dependent, in contrast with experimental findings. The G3 calculations reveal the complexity of possible intermediates and end products and taken together with the RRKM calculations indicate the most likely end products to be H2SiO + SO ((3)?(-)). The reaction is compared and contrasted with that of SiH2 + CO2. PMID:23903751

Becerra, Rosa; Cannady, J Pat; Goldberg, Nicola; Walsh, Robin

2013-09-21

107

Reaction kinetics of CO2 absorption in to phosphonium based anion-functionalized ionic liquids.

The reaction kinetics between CO2 and trihexyl(tetradecyl)phosphonium ([P66614])-based ionic liquids (ILs) with prolinate ([Pro]), 2-cyanopyrrolide ([2-CNpyr]), and 3-(trifluoromethyl)pyrazolide ([3-CF3pyra]) anions are studied at temperatures from 22-60 °C. The absorption of CO2 is carried out in a stirred reactor under pseudo first order conditions. ILs are diluted to concentrations of 0.05, 0.1 and 0.15 M with tetraglyme--a nonreactive, low volatility solvent with much lower viscosity than the ILs. Physical solubility of CO2 in the mixtures is calculated using correlations developed from CO2 solubility measurements in tetraglyme and the N2O-analogy for ILs and dilute IL solutions. The diffusivity of CO2 is estimated from viscosity-dependent correlations chosen after a thorough literature review. The results indicate partial first order reaction kinetics with respect to IL with values ranging from 19,500 L mol(-1) s(-1) ([P66614][Pro]) to 3200 L mol(-1) s(-1) ([P66614][3-CF3pyra]) at 22 °C. The second order reaction rate constants follow Arrhenius behavior with the highest activation energy of 43 kJ mol(-1) measured for [P66614][Pro]. ILs with aprotic heterocylic anions (AHA), on the other hand, show small activation energies of 18 and 11 kJ mol(-1) for [P66614][3-CF3pyra] and [P66614][2-CNpyr], respectively. The ILs studied in this work exhibit reactivity comparable to or higher than common aqueous amines. High reaction rates and tunable capacity make ILs, and AHA ILs in particular, attractive solvents for CO2 separations. PMID:23598368

Gurkan, Burcu E; Gohndrone, Thomas R; McCready, Mark J; Brennecke, Joan F

2013-05-28

108

Chemical kinetic reaction mechanism for the combustion of propane

NASA Technical Reports Server (NTRS)

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

Jachimowski, C. J.

1984-01-01

109

Second-order Raman scattering in CuO.

Polarized second-order Raman scattering spectra of CuO single crystals are reported. It is shown that for some scattering geometries the second-order processes dominate the inelastic light scattering spectra. Group-theoretical symmetry analysis of the selection rules for the first- and second-order scattering processes is performed and phonon dispersion relations are calculated within density functional theory. The main spectral features of the two-phonon spectra are assigned to overtones of the vibrational branches at various special points across the Brillouin zone. PMID:23388624

Litvinchuk, A P; Möller, A; Debbichi, L; Krüger, P; Iliev, M N; Gospodinov, M M

2013-03-13

110

Method to render second order beam optics programs symplectic

We present evidence that second order matrix-based beam optics programs violate the symplectic condition. A simple method to avoid this difficulty, based on a generating function approach to evaluating transfer maps, is described. A simple example illustrating the non-symplectricity of second order matrix methods, and the effectiveness of our solution to the problem, is provided. We conclude that it is in fact possible to bring second order matrix optics methods to a canonical form. The procedure for doing so has been implemented in the program DIMAT, and could be implemented in programs such as TRANSPORT and TURTLE, making them useful in multiturn applications. 15 refs.

Douglas, D.; Servranckx, R.V.

1984-10-01

111

Superposition rules and second-order differential equations

The main purpose of this work is to introduce and analyse some generalizations of diverse superposition rules for first-order differential equations to the setting of second-order differential equations. As a result, we find a way to apply the theories of Lie and quasi-Lie systems to analyse second-order differential equations. In order to illustrate our results, several second-order differential equations appearing in the physics and mathematical literature are analysed and some superposition rules for these equations are derived by means of our methods.

J. F. Carińena; J. de Lucas

2011-07-14

112

Kinetics and mechanism of substitution reactions of complexes, XX

Thermal decomposition of 21 complexes of the type [Co(DH)2(amine)2]NCS has been studied under the conditions of thermogravimetric analysis, by using different heating rates. From the thermogravimetric curves apparent kinetic parameters of the pyrolysis reaction have been derived by means of the modified Doyle method. Apparent reaction order increases and apparent activation energy decreases with increasing heating rate. Thus, the obtained

J. Zsakó; E. Kékedy; Cs. Várhelyi

1969-01-01

113

Kinetics of fast reactions of excited species. Final report

This report contains brief summaries of findings in the following areas: gamma radiation induced decomposition of chloroform; proton transfer and ion neutralization reactions in gaseous hydrocarbons; kinetics of thremal D-atom reactions with CHâ CâHâ; the gamma radiation induced decomposition of liquid n-pentane; pulse radiolysis of rare gases and liquid n-pentane and n-pentane-Oâ solutions; rate constants and activation energies for second

Firestone

1986-01-01

114

MEASURING FENTON'S REACTION KINETICS AT ONE-SECOND INTERVALS

The concept of quench flow has been implemented to design a simple and yet easy-to-operate device to measure Fenton's reaction kinetics at one-second intervals. 2,4-dinitrophenol (DNP) was used as a model compound in this study. Experimental results show that more than 40% of DNP can be decomposed within the first second, followed by a stagnant reaction for a period of

Lay-Ching Ong; Yen-Han Lin; Ten-Hsiu Wang

2001-01-01

115

NSDL National Science Digital Library

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

David N. Blauch

116

Penicillin Hydrolysis: A Kinetic Study of a Multistep, Multiproduct Reaction.

ERIC Educational Resources Information Center

Background, procedures used, and typical results are provided for an experiment in which students carry out the necessary measurements on the acid-catalysis of penicillin in two hours. By applying kinetic theory to the data obtained, the reaction pathways for the hydrolysis of potassium benzyl penicillin are elucidated. (JN)

McCarrick, Thomas A.; McLafferty, Fred W.

1984-01-01

117

REACTION KINETICS OF CA-BASED SORBENTS WITH HC1

The paper gives results of an investigation of the kinetics of the reaction between CaO and HC1 under conditions that minimize bulk mass transfer and pore diffusion limitations. eactivity data from 0.2 to 1 s exposure to 5000 ppm HC1 in a fixed-bed reactor were analyzed by a shri...

118

REACTION KINETICS OF CA-BASED SORBENTS WITH HC1

The kinetics of the reaction between CaO and HCl were investigated under conditions that minimize bulk mass transfer and pore diffusion limitations. Reactivity data from 0.2- to 1-s exposure to 5000 ppm HCl in a fixed bed reactor were analyzed by a shrinking core model of diffusi...

119

Reaction Kinetics in Food Extrusion: Methods and Results

Extrusion cooking is a highly efficient food processing technology. During the extrusion process, there are many desirable and undesirable reactions which will determine final product quality. While being heated and sheared simultaneously, food raw materials experience a non-isothermal process and their residence time in the extruder is distributed. All these factors contribute to the difficulties in determining the kinetic parameters

Xuewei Zhao; Yimin Wei; Zhangcun Wang; Fengliang Chen; Anthony Okhonlaye Ojokoh

2011-01-01

120

Reaction Kinetics in Food Extrusion-Methods and Results

Extrusion cooking is a highly efficient food processing technology. During extrusion process, there are many desirable and undesirable reactions which will determine final product quality. While being heated and sheared simultaneously, food raw materials experience a non-isothermal process and their residence time in extruder is distributed. All these factors contribute to the difficulties in determining the kinetic parameters for those

Xuewei Zhao; Yimin Wei; Zhangcun Wang; Fengliang Chen; Anthony Okhonlaye Ojokoh

2011-01-01

121

Understanding the kinetics of spin-forbidden chemical reactions.

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

Harvey, Jeremy N

2007-01-21

122

Second Order of Accuracy Difference Schemes for Ultra Parabolic Equations

NASA Astrophysics Data System (ADS)

In this paper, our interest is studying the stability of second order difference scheme for the approximate solution of the initial boundary value problem for ultra parabolic equations in an arbitrary Banach space E with a strongly positive operator A. For approximately solving the given problem, the second-order of accuracy difference scheme is presented. Numerical example is given to illustrate the applicability and efficiency of our method.

Ashyralyev, Allaberen; Yilmaz, Serhat

2011-09-01

123

Evaluation of supersingular integrals: Second-order boundary derivatives

SUMMARY The boundary integral representation of second-order derivatives of the primary function involves second- order (hypersingular) and third-order (supersingular) derivatives of the Green's function. By defining these highly singular integrals as a difference of boundary limits, interior minus exterior, the limiting values are shown to exist. With a Galerkin formulation, coincident and edge-adjacent supersingular integrals are separately divergent, but the

M. N. J. Moore; L. J. Gray; T. Kaplan

2006-01-01

124

NASA Technical Reports Server (NTRS)

A laser flash photolysis-long path absorption technique has been employed to study the kinetics of the reaction BrO + NO2 + M yields (k1) products as a function of temperature (248-346 K), pressure (16-800 torr), and buffer gas identity (N2,CF4) The reaction is found to be in the falloff regime between third and second-order over the entire range of conditions investigated This is the first study where temperature-dependent measurements of k1(P,T) have been reported at pressures greater than 12 torr; hence, our results help constrain choices of k1(P,T) for use in models of lower stratospheric BrO(x) chemistry. Approximate falloff parameters in a convenient form for atmospheric modeling are derived.

Thron, R. P.; Daykin, E. P.; Wine, P.H.

1997-01-01

125

Second-order-accurate radiative hydrodynamics and multidimensional protostellar collapse

NASA Astrophysics Data System (ADS)

A second-order-accurate numerical scheme for computing the radiative hydrodynamics of three-dimensional, collapsing protostellar clouds has been developed and implemented in both spherical and cartesian coordinates. The scheme employs spatially second-order-accurate advective fluxes based on van Leer monotonic interpolation and consistent advection. The advective fluxes also contain the terms necessary to make the scheme temporally second-order-accurate in the presence of spatially and temporally varying velocity fields. A predictor-corrector treatment of the source terms completes the requirements for second-order accuracy in time. The Poisson equation for the gravitational potential is solved by either a spherical harmonic expansion or a Green's function method. Radiative transfer in the Eddington approximation is handled through the solution of a mean intensity equation. The numerical scheme has been shown to be second-order-accurate through convergence testing and has been shown to improve the performance on a shock propagation problem compared to schemes that do not contain the spatially and temporally second-order-accurate terms.

Boss, Alan P.; Myhill, Elizabeth A.

1995-08-01

126

Hypothiocyanite is a major oxidant generated by mammalian peroxidases. Although reported to react specifically with thiol groups in biological molecules, a detailed mechanistic study of this reaction has not been conducted. We have investigated the reaction of hypothiocyanous acid/hypothiocyanite with 5-thio-2-nitrobenzoic acid and with reduced glutathione by stopped-flow spectroscopy. The observed bell-shaped pH profile established that the reaction with 5-thio-2-nitrobenzoic acid proceeds via the thiolate and hypothiocyanous acid in the 2.5 < pH < 8 region. The obtained second-order rate constant of the reaction is (1.26 + or - 0.02) x 10(8) M(-1) s(-1), and the effective rate constant at pH 7.4 is (4.37 + or - 0.03) x 10(5) M(-1) s(-1). Analysis of the kinetic data, using a value of 4.38 + or - 0.01 for the pK(a) of 5-thio-2-nitrobenzoic acid thiol (measured independently by spectroscopic analysis), gave a pK(a) of 4.85 + or - 0.01 for hypothiocyanous acid at physiological salt concentration (I = 120 mM; NaCl and phosphate buffer) and 25 degrees C. A second-order rate constant of (8.0 + or - 0.5) x 10(4) M(-1) s(-1) for the reaction of hypothiocyanous acid/hypothiocyanite with reduced glutathione at pH 7.4 was determined. The glutathione data are also consistent with the reaction proceeding via the thiolate and hypothiocyanous acid. Our results demonstrate that hypothiocyanous acid/hypothiocyanite has very high reactivity with thiols and will be short-lived in the presence of physiological concentrations of glutathione and thiol proteins. As the reaction occurs strictly with the thiolate, this oxidant should selectively target proteins containing low pK(a) thiols. PMID:19821602

Nagy, Péter; Jameson, Guy N L; Winterbourn, Christine C

2009-11-01

127

Pulsed ion beam investigation of the kinetics of surface reactions

NASA Technical Reports Server (NTRS)

Pulsed ion beam measurements of the kinetics of surface reactions are discussed for the case where the width of the ion pulse is comparable to the measured reaction time, but short compared to the time between successive pulses. Theoretical expressions are derived for the time dependence of the ion-induced signals for linear surface reactions. Results are presented for CO emission from surface carbon and CF emission from Teflon induced by oxygen ion bombardment. The strengths and limitations of this technique are described.

Horton, C. C.; Eck, T. G.; Hoffman, R. W.

1989-01-01

128

Kinetics of the aqueous-phase reaction between ozone and 2,4,6-trichlorophenol

Treatment of industrial and municipal wastewater containing organic pollutants is of primary concern. Ozonation of these wastewaters has been effective in oxidizing organic pollutants into harmless compounds (CO{sub 2} and H{sub 2}O) as well as breaking up refractory compounds into different compounds that are more easily treated with cheaper, more conventional methods such as biodegradation, ion exchange, and filtration. In order to effectively treat wastewater with ozone and design appropriate treatment processes, reaction kinetics and reaction products must be determined. In addition, ozone solubilities and diffusivities must be known in order to model the diffusion/reaction process in this gas-liquid system. A wetted-sphere absorber was used to measure absorption rates of ozone into aqueous-buffered solutions of 2,4,6-trichlorophenol (TCP). Gas consisting of approximately 2.5% ozone in oxygen was contacted with aqueous-buffered TCP solution flowing over a sphere in a laminar liquid film. Absorption data were obtained by measuring the change in the liquid-phase concentration of TCP from the inlet to the outlet of the absorber. A rigorous numerical model for this diffusion/reaction process was used to analyze the absorption data to determine the second-order rate constant of the reaction between ozone and TCP at 15--35 C and pH 2 and 7. The kinetic data indicate that the rate-limiting step for the reaction of aqueous TCP with ozone is the same at pH 2 and 7. Four reaction products that occur early in the reaction of ozone with aqueous TCP were identified by GCMS, including: 2,3,4,6-tetrachlorophenol (TRCP), 4,6-dichlorocatechol (DCC), 2,6-dichlorohydroquinone (DCHQ), and 2,6-dichloroquinone (DCQ). Only DCHQ and CDQ occurred in significant concentrations. Over the pH range of 2 to 5, both DCHQ and DCQ were detected in the reacted solutions, while for pH 6 and 7 only DCHQ was detected. Carbon-13 NMR analysis shows that over longer ozone exposure times short-chain carboxylic acids are the dominant species in the reacted TCP solutions.

Rinker, E.B.; Ashour, S.S.; Johnson, M.C.; Kott, G.J.; Rinker, R.G.; Sandall, O.C. [Univ. of California, Santa Barbara, CA (United States). Dept. of Chemical Engineering] [Univ. of California, Santa Barbara, CA (United States). Dept. of Chemical Engineering

1999-08-01

129

Kinetic Insight into Specific Features of the Autocatalytic Soai Reaction

NASA Astrophysics Data System (ADS)

The addition of diisopropylzinc to prochiral pyrimidine carbaldehydes (Soai reaction) is the only known example of spontaneous asymmetric synthesis in organic chemistry. It serves as a model system for the spontaneous occurrence of chiral asymmetry from achiral initial conditions. This review describes the possible kinetic origin of specific experimental features of this reaction. It is shown that generic kinetic models, including enantioselective autocatalysis and mutual inhibition between the enantiomers, are adequate to describe a variety of the astonishing properties of the Soai reaction. Namely, these are the unprecedented strong chiral amplification, extreme sensitivity to the presence of very small amounts of chiral initiator, mirror-symmetry breaking when starting from achiral conditions, and the reversal of enantioselectivity of chiral catalysts by addition of achiral additives. The described kinetic approach allows a closer insight into the nonlinear dynamics of the Soai reaction. It also reveals that a number of open questions concerning the detailed reaction mechanism are still to be solved and that further experimental studies are required.

Lavabre, Dominique; Micheau, Jean-Claude; Islas, Jesús Rivera; Buhse, Thomas

130

Evaluation of true kinetic parameters for reversible immobilized enzyme reactions

For a reversible one-substrate reaction system that follows the Haldane reaction mechanism, a new and effective method has been proposed to extract true or intrinsic kinetic parameters of immobilized enzymes from diffusion limited rate data. The method utilizes the effectiveness factors correlated in terms of the general modulus defined by Aris and Bischoff, and a new modulus defined in the present study. It requires a trial-and-error calculation, but only a few data points. Furthermore, it provides a saving of materials such as substrates and enzymes, and takes less time for experiments compared to the initial rate methods. The usefulness of the method is demonstrated by determining the kinetic parameters for membrane bound fumarase which catalyzes the reaction of the conversion of fumarate to L-malate, for which the equilibrium constant is circa 4. (Refs. 20).

Ishikawa, H.; Tanaka, T.; Kurose, K.; Hikita, H.

1987-06-01

131

A kinetics investigation of several reactions involving chlorine containing compounds

NASA Technical Reports Server (NTRS)

The technique of flash photolysis-resonance fluorescence was utilized to study nine reactions of stratospheric importance. The tropospheric degradation reactions of seven halogenated hydrocarbons were studied to assess their possible influx into the stratosphere. There are reactions of either Cl, OH, or O(3P) species with hydrogenated species, O3 or chlorinated compounds. Apart from the kinetic measurements, the quantum yield for the production of O(1D) from O3 in the crucial wavelength region of 293 to 316.5 nm was studied by utilizing a narrow wavelength laser as the photolysis source. The product formation was monitored by measuring the fluorescence of NO2 formed through O(1D) reaction with N2O followed by NO reaction with O3 to give NO2.

Davis, D. D.

1978-01-01

132

Reaction kinetics of cellulose hydrolysis in subcritical and supercritical water

NASA Astrophysics Data System (ADS)

The uncertainties in the continuous supply of fossil fuels from the crisis-ridden oil-rich region of the world is fast shifting focus on the need to utilize cellulosic biomass and develop more efficient technologies for its conversion to fuels and chemicals. One such technology is the rapid degradation of cellulose in supercritical water without the need for an enzyme or inorganic catalyst such as acid. This project focused on the study of reaction kinetics of cellulose hydrolysis in subcritical and supercritical water. Cellulose reactions at hydrothermal conditions can proceed via the homogeneous route involving dissolution and hydrolysis or the heterogeneous path of surface hydrolysis. The work is divided into three main parts. First, the detailed kinetic analysis of cellulose reactions in micro- and tubular reactors was conducted. Reaction kinetics models were applied, and kinetics parameters at both subcritical and supercritical conditions were evaluated. The second major task was the evaluation of yields of water soluble hydrolysates obtained from the hydrolysis of cellulose and starch in hydrothermal reactors. Lastly, changes in molecular weight distribution due to hydrothermolytic degradation of cellulose were investigated. These changes were also simulated based on different modes of scission, and the pattern generated from simulation was compared with the distribution pattern from experiments. For a better understanding of the reaction kinetics of cellulose in subcritical and supercritical water, a series of reactions was conducted in the microreactor. Hydrolysis of cellulose was performed at subcritical temperatures ranging from 270 to 340 °C (tau = 0.40--0.88 s). For the dissolution of cellulose, the reaction was conducted at supercritical temperatures ranging from 375 to 395 °C (tau = 0.27--0.44 s). The operating pressure for the reactions at both subcritical and supercritical conditions was 5000 psig. The results show that the rate-limiting step in converting cellulose to fermentable sugars in subcritical and supercritical water differs because of the difference in their activation energies. Cellulose and starch were both hydrolyzed in micro- and tubular reactors and at subcritical and supercritical conditions. Due to the difficulty involved in generating an aqueous based dissolved cellulose and having it reacted in subcritical water, dissolved starch was used instead. Better yield of water soluble hydrolysates, especially fermentable sugars, were observed from the hydrolysis of cellulose and dissolved starch in subcritical water than at supercritical conditions. The concluding phase of this project focuses on establishing the mode of scission of cellulose chains in the hydrothermal reactor. This was achieved by using the simulated degradation pattern generated based on different scission modes to fingerprint the degradation pattern obtained from experiment.

Olanrewaju, Kazeem Bode

133

Reactions of allylic radicals that impact molecular weight growth kinetics.

The reactions of allylic radicals have the potential to play a critical role in molecular weight growth (MWG) kinetics during hydrocarbon oxidation and/or pyrolysis. Due to their stability (when compared to alkyl radicals), they can accumulate to relatively high concentrations. Thus, even though the rate coefficients for their various reactions are small, the rates of these reactions may be significant. In this work, we use electronic structure calculations to examine the recombination, addition, and abstraction reactions of allylic radicals. For the recombination reaction of allyl radicals, we assign a high pressure rate rule that is based on experimental data. Once formed, the recombination product can potentially undergo an H-atom abstraction reaction followed by unimolecular cyclization and ?-scission reactions. Depending upon the conditions (e.g., higher pressures) these pathways can lead to the formation of stable MWG species. The addition of allylic radicals to olefins can also lead to MWG species formation. Once again, cyclization of the adduct followed by ?-scission is an important energy accessible route. Since the recombination and addition reactions produce chemically-activated adducts, we have explored the pressure- and temperature-dependence of the overall rate constants as well as that for the multiple product channels. We describe a strategy for estimating these pressure-dependencies for systems where detailed electronic structure information is not available. We also derive generic rate rules for hydrogen abstraction reactions from olefins and diolefins by methyl and allyl radicals. PMID:25648200

Wang, Kun; Villano, Stephanie M; Dean, Anthony M

2015-02-18

134

polydispersion in reaction kinetics. Here we use single-molecule fluorescence microscopy to study twoSingle-Molecule Kinetics Reveals a Hidden Surface Reaction Intermediate in Single is further resolvable by single-turnover kinetics at the subparticle level. Detailed single-molecule kinetic

Chen, Peng

135

The ease with which alpha-chloroacetanilide herbicides undergo displacement reactions with strong nucleophiles, and their recalcitrance toward weak ones, is intimately related to their herbicidal properties and environmental chemistry. In this study, we investigate the kinetics and mechanisms of nucleophilic substitution reactions of propachlor and alachlor in aqueous solution. The role played by the alpha-amide group was examined by including several structurally related analogs of propachlor possessing modified alpha substituents. The overall second-order nature of the reaction, the negative DeltaS(double dagger) values, the weak influence of ionic strength on reactivity, and structure-reactivity trends together support an intermolecular S(N)2 mechanism rather than an intramolecular reaction for alpha-chloroacetanilides as well as the alpha-chlorothioacetanilide analog of propachlor. In contrast, the alpha-methylene analog exhibits kinetics and a salt effect consistent with anchimeric assistance by the aniline nitrogen. Electronic interactions with the alpha-anilide substituent, rather than neighboring group participation, can be inferred to govern the reactivity of alpha-chloroacetanilides toward nucleophiles. PMID:15137847

Lippa, Katrice A; Demel, Sandra; Lau, Irvin H; Roberts, A Lynn

2004-05-19

136

The kinetics study of the S + S2 ? S3 reaction by the chaperone mechanism

NASA Astrophysics Data System (ADS)

The recombination of S atoms has been found to be stepwise from the smallest unit, the elemental S atom, to the most abundant molecule S8. The reaction between S + S2 ? S3 has not been reported either experimentally or by theory, but may be a key intermediate step in the formation of sulfur aerosols in low-O2 atmospheres. In this work, the kinetics of this reaction is reported with Ar gas used as the chaperone molecule in the production of S3 via two complex intermediates: SAr + S2 and S2Ar + S. Quasi-classical and classical trajectory methods are used. The rate constant of the S + S2 + Ar ? S3 + Ar reaction is determined to be 2.66 × 10-33 cm6 mol-1 s-1 at 298.15 K. The temperature dependence of the reaction is found to be 2.67 × 10-33 exp[143.56(1/T-1/298.15)]. The second-order rate constant of S + S2 ? S3 is 6.47 × 10-14 cm3 molecule-1 s-1 at 298.15 K and the Arrhenius-type rate constant is calculated to be 6.25 × 10-14 exp[450.15(1/T-1/298.15)] cm3 molecule-1 s-1. This work provides a rate coefficient for a key intermediate species in studies of sulfur formation in the modern Venus atmosphere and the primitive Earth atmosphere, for which assumed model rate coefficients have spanned nearly 4 orders of magnitude. Although a symmetry-induced mass-independent isotope effect is not expected for a chaperone mechanism, the present work is an important step toward evaluating whether mass-independence is expected for thiozone formation as is observed for ozone formation.

Du, Shiyu; Germann, Timothy C.; Francisco, Joseph S.; Peterson, Kirk A.; Yu, Hua-Gen; Lyons, James R.

2011-04-01

137

Kinetics of sulfur and nitrogen reactions in combustion systems

This volume is the second of a three volume set. Specifically, the activities reported herein cover investigations of the reactivity of sorbent materials toward SO{sub 2}. For the most part this focuses on the furnace injection of calcium-based sorbents, although some work also considers post-furnace injection and the use of alternative sorbents. Work is described in the following sections. Reactivity kinetics of calcium-based sorbents for SO{sub x}: this task provides experimental data on improving the reactivity of calcium-based sorbents to sulfur dioxide. It is designed to identify what limits calcium utilization and how to avoid these limitations. The focus is on the influence of sorbent structure on sulfation. Sorbent sulfation: the goal is to define the sulfation rate processes and sulfation mechanism for calcium-based sorbents under furnace conditions. The focus is on the reaction kinetics of sulfation. Alternative sorbents: the objective is to provide detailed kinetics of SO{sub x} absorption by minerals (other than calcium based) which have application in a dry sorbent SO{sub 2} process. This study also includes a modeling element for SO{sub 2} capture by calcium-based materials. Physical/chemical modeling of sulfur/sorbent reaction: this project utilized the kinetic and mechanistic data from the experimental studies to develop and apply a detailed process model of the sulfur gas and sorbent solid reactions. Low temperature capture of SO{sub 2}: this experimental study supplies kinetic and mechanistic information of the capture of SO{sub 2} by calcium-based sorbents under post-air heater conditions (e.g., in the flue gas duct, at or below 300{degree}F). 36 refs., 95 figs., 7 tabs.

Kramlich, J.C.; Seeker, W.R. (Energy and Environmental Research Corp., Irvine, CA (USA)); Sarofim, A.F.; Longwell, J.T. (Massachusetts Inst. of Tech., Cambridge, MA (USA)); Ham, D.; Simons, G.A. (Physical Sciences, Inc., Woburn, MA (USA))

1989-09-01

138

Kinetic Monte Carlo method for simulating reactions in solutions.

We present an off-lattice kinetic Monte Carlo method, which is useful to simulate reactions in solutions. We derive the method from first-principles. We assume that diffusion leads to a Gaussian distribution for the position of the particles. This allows us to deal with the diffusion analytically, and we only need to simulate the reactive processes. The rate constants of these reactions can be computed before a simulation is started, and need not be computed on-the-fly as in other off-lattice kinetic Monte Carlo methods. We show how solvent molecules can be removed from the simulations, which minimizes the number of particles that have to be simulated explicitly. We present the relation with the customary macroscopic rate equations, and compare the results of these equations and our method on a variation of the Lotka model. PMID:21230409

Zhang, X-Q; Jansen, A P J

2010-10-01

139

Maximum Probability Reaction Sequences in Stochastic Chemical Kinetic Systems

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

Salehi, Maryam; Perkins, Theodore J.

2010-01-01

140

Maximum Probability Reaction Sequences in Stochastic Chemical Kinetic Systems

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

Salehi, Maryam; Perkins, Theodore J.

2010-01-01

141

Second order closure for variable density free shear layer

NASA Technical Reports Server (NTRS)

A full second order closure turbulence model for the prediction of free shear flows with variable density is developed. The importance of density fluctuations due to inhomogeneities in fluid composition is emphasized. Some simplicity is achieved by using density weighted averaging to account implicitly for density fluctuation effects. Transport equations for various second order correlations - such as Reynolds stress, turbulent mass fluxes or density velocity correlations - are derived, modelled and solved, together with the mean equations for momentum and species conservation. Solutions of these equations are compared with the two different sets of experimental data for low speed free mixing layers (helium into nitrogen and freon 12 into air).

Vandromme, D.; Kollmann, W.

1982-01-01

142

DC current induced second order optical nonlinearity in graphene.

We calculate the dc current induced second harmonic generation in doped graphene using the semiconductor Bloch equations under relaxation time approximations. We find that the maximum value of the effective second order susceptibility appears when the fundamental photon energy matches the chemical potential. For a surface current density 1.1 × 10(3) A/m and a relaxation time at optical frequencies of 13 fs, the effective second order susceptibility ?eff(2);xxx can be as large as 10(-7)m/V for h?? = 0.2 eV or 10(-8) m/V for h?? = 0.53 eV. PMID:24977842

Cheng, J L; Vermeulen, N; Sipe, J E

2014-06-30

143

Elasto-plastic model with second order defect density tensor

NASA Astrophysics Data System (ADS)

The paper deals with a second order finite elasto-plastic model, which involves the defect density tensor, as a measure of the extra material defects existing in the damaged microstructure. The material behaviour is described with respect to an anholonomic configuration, which is introduced through the second order plastic deformation, consisting in plastic distortion and plastic connection. The defect density tensor enters the expression of the plastic connection through its gradient and represents a measure of non-metricity. The constitutive and evolution equations are derived to be compatible with the free energy imbalance. The evolution equation for the defect density tensor is non-local and coupled with the plastic distortion.

Cleja-?igoiu, Sanda

2011-05-01

144

Second-order Talbot self-imaging with pseudothermal light

The second-order Talbot effect with thermal light is both theoretically and experimentally investigated. Three kinds of experimental schemes are performed, one of which reproduces the classical Talbot self-imaging and the others show plentiful self-imaging effects, in which an object with a periodic structure can be enlarged or diminished. The theoretical analysis, in good agreement with the experimental results, testifies that the specificity in the second-order Talbot effect refers to the joint diffraction of two correlated beams.

Song Xinbing; Xiong Jun; Zhang Xiangdong; Wang Kaige [Department of Physics, Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875 (China)

2010-09-15

145

Second-order subsonic airfoil theory including edge effects

NASA Technical Reports Server (NTRS)

Several recent advances in plane subsonic flow theory are combined into a unified second-order theory for airfoil sections of arbitrary shape. The solution is reached in three steps: the incompressible result is found by integration, it is converted into the corresponding subsonic compressible result by means of the second-order compressibility rule, and it is rendered uniformly valid near stagnation points by further rules. Solutions for a number of airfoils are given and are compared with the results of other theories and of experiment. A straight-forward computing scheme is outlined for calculating the surface velocities and pressures on any airfoil at any angle of attack

Van Dyke, Milton D

1956-01-01

146

The Poisson equation at second order in relativistic cosmology

We calculate the relativistic constraint equation which relates the curvature perturbation to the matter density contrast at second order in cosmological perturbation theory. This relativistic ''second order Poisson equation'' is presented in a gauge where the hydrodynamical inhomogeneities coincide with their Newtonian counterparts exactly for a perfect fluid with constant equation of state. We use this constraint to introduce primordial non-Gaussianity in the density contrast in the framework of General Relativity. We then derive expressions that can be used as the initial conditions of N-body codes for structure formation which probe the observable signature of primordial non-Gaussianity in the statistics of the evolved matter density field.

Hidalgo, J.C. [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX (United Kingdom); Christopherson, Adam J. [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom); Malik, Karim A., E-mail: juan.hidalgo@port.ac.uk, E-mail: Adam.Christopherson@nottingham.ac.uk, E-mail: k.malik@qmul.ac.uk [Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS (United Kingdom)

2013-08-01

147

Kubo Formulas for Second-Order Hydrodynamic Coefficients

At second order in gradients, conformal relativistic hydrodynamics depends on the viscosity {eta} and on five additional ''second-order'' hydrodynamical coefficients {tau}{sub {Pi}}, {kappa}, {lambda}{sub 1}, {lambda}{sub 2}, and {lambda}{sub 3}. We derive Kubo relations for these coefficients, relating them to equilibrium, fully retarded three-point correlation functions of the stress tensor. We show that the coefficient {lambda}{sub 3} can be evaluated directly by Euclidean means and does not in general vanish.

Moore, Guy D.; Sohrabi, Kiyoumars A. [Department of Physics, McGill University, 3600 rue University, Montreal, Quebec H3A 2T8 (Canada)

2011-03-25

148

Electrochemically responsive heterogeneous catalysis for controlling reaction kinetics.

We report a method to control reaction kinetics using electrochemically responsive heterogeneous catalysis (ERHC). An ERHC system should possess a hybrid structure composed of an electron-conducting porous framework coated with redox-switchable catalysts. In contrast to other types of responsive catalysis, ERHC combines all the following desired characteristics for a catalysis control strategy: continuous variation of reaction rates as a function of the magnitude of external stimulus, easy integration into fixed-bed flow reactors, and precise spatial and temporal control of the catalyst activity. Herein we first demonstrate a facile approach to fabricating a model ERHC system that consists of carbon microfibers with conformal redox polymer coating. Second, using a Michael reaction whose kinetics depends on the redox state of the redox polymer catalyst, we show that use of different electrochemical potentials permits continuous adjustment of the reaction rates. The dependence of the reaction rate on the electrochemical potential generally agrees with the Nernstian prediction, with minor discrepancies due to the multilayer nature of the polymer film. Additionally, we show that the ERHC system can be employed to manipulate the shape of the reactant concentration-time profile in a batch reactor through applying customized potential-time programs. Furthermore, we perform COMSOL simulation for an ERHC-integrated flow reactor, demonstrating highly flexible manipulation of reactant concentrations as a function of both location and time. PMID:25563424

Mao, Xianwen; Tian, Wenda; Wu, Jie; Rutledge, Gregory C; Hatton, T Alan

2015-01-28

149

Bayesian experts in exploring reaction kinetics of transcription circuits

Motivation Biochemical reactions in cells are made of several types of biological circuits. In current systems biology, making differential equation (DE) models simulatable in silico has been an appealing, general approach to uncover a complex world of biochemical reaction dynamics. Despite of a need for simulation-aided studies, our research field has yet provided no clear answers: how to specify kinetic values in models that are difficult to measure from experimental/theoretical analyses on biochemical kinetics. Results: We present a novel non-parametric Bayesian approach to this problem. The key idea lies in the development of a Dirichlet process (DP) prior distribution, called Bayesian experts, which reflects substantive knowledge on reaction mechanisms inherent in given models and experimentally observable kinetic evidences to the subsequent parameter search. The DP prior identifies significant local regions of unknown parameter space before proceeding to the posterior analyses. This article reports that a Bayesian expert-inducing stochastic search can effectively explore unknown parameters of in silico transcription circuits such that solutions of DEs reproduce transcriptomic time course profiles. Availability: A sample source code is available at the URL http://daweb.ism.ac.jp/?yoshidar/lisdas/ Contact: yoshidar@ism.ac.jp PMID:20823326

Yoshida, Ryo; Saito, Masaya M.; Nagao, Hiromichi; Higuchi, Tomoyuki

2010-01-01

150

Carborane tuning on iridium complexes: redox-switchable second-order NLO responses.

Much effort has been devoted to investigating the molecular geometries, electronic structures, redox properties and nonlinear optical (NLO) properties of Ir complexes involving o-, m- or p-carborane groups by density functional theory (DFT) methods. Switchable second-order NLO properties were induced by redox processes involving these complexes, and it was found that mainly the coordination bonds of Ir complexes changed during the oxidation process. Our calculations revealed that oxidation reactions have a significant influence on the second-order NLO response owing to the change in charge transfer pattern. The ? tot values of oxidized species are at least ?9 times larger for set I and ?5 times larger for set II than those of the corresponding parent complexes. Introduction of carborane groups into ppy (phenylpyridine) ligands can enhance the second-order NLO response by 1.2-?1.6 times by a metal-to-ligand charge transfer (MLCT) transition between the Ir atom and carborane. The ? tot of complex 2 [(ppy)2Ir(phen)](+) (phen?=?phenanthroline) is 3.3 times larger than that of complex 1 (ppy)2Ir(acce) (acce?=?acetylacetonate), which is caused by ligand-to-ligand charge transfer (LLCT) between ppy ligands and the ancillary ligand. Therefore, it can be concluded that the second-order NLO response can be effectively enhanced by oxidation reactions. PMID:25791353

Wang, Jiao; Wang, Wen-Yong; Fang, Xin-Yan; Qiu, Yong-Qing

2015-04-01

151

Primary kinetic isotope effects (KIEs) on a series of carboxylic acid-catalyzed protonation reactions of aryl-substituted ?-methoxystyrenes (X-1) to form oxocarbenium ions have been computed using the Kleinert variational second-order perturbation theory (KP2) in the framework of Feynman path integrals (PI) along with the potential energy surface obtained at the B3LYP/6-31+G(d,p) level. Good agreement with the experimental data was obtained, demonstrating that this novel computational approach for computing KIEs of organic reactions is a viable alternative to the traditional method employing Bigeleisen equation and harmonic vibrational frequencies. Although tunneling makes relative small contributions to the lowering of the free energy barriers for the carboxylic acid catalyzed protonation reaction, it is necessary to include tunneling contributions to obtain quantitative estimates of the KIEs. Consideration of anharmonicity can further improve the calculated KIEs for the protonation of substituted ?-methoxystyrenes by chloroacetic acid, but for the reactions of the parent and 4-NO2 substituted ?-methoxystyrene with substituted carboxylic acids, the correction of anharmonicity overestimates the computed KIEs for strong acid catalysts. In agreement with experimental findings, the largest KIEs are found in nearly ergoneutral reactions, ?Go ? 0, where the transition structures are nearly symmetric and the reaction barriers are relatively low. Furthermore, the optimized transition structures are strongly dependent on the free energy for the formation of the carbocation intermediate, i.e., the driving force ?Go, along with a good correlation of Hammond shift in the transition state structure. PMID:19754046

Wong, Kin Yiu; Richard, John P.; Gao, Jiali

2009-01-01

152

Microdroplet fusion mass spectrometry for fast reaction kinetics.

We investigated the fusion of high-speed liquid droplets as a way to record the kinetics of liquid-phase chemical reactions on the order of microseconds. Two streams of micrometer-size droplets collide with one another. The droplets that fused (13 ?m in diameter) at the intersection of the two streams entered the heated capillary inlet of a mass spectrometer. The mass spectrum was recorded as a function of the distance x between the mass spectrometer inlet and the droplet fusion center. Fused droplet trajectories were imaged with a high-speed camera, revealing that the droplet fusion occurred approximately within a 500-?m radius from the droplet fusion center and both the size and the speed of the fused droplets remained relatively constant as they traveled from the droplet fusion center to the mass spectrometer inlet. Evidence is presented that the reaction effectively stops upon entering the heated inlet of the mass spectrometer. Thus, the reaction time was proportional to x and could be measured and manipulated by controlling the distance x. Kinetic studies were carried out in fused water droplets for acid-induced unfolding of cytochrome c and hydrogen-deuterium exchange in bradykinin. The kinetics of the former revealed the slowing of the unfolding rates at the early stage of the reaction within 50 ?s. The hydrogen-deuterium exchange revealed the existence of two distinct populations with fast and slow exchange rates. These studies demonstrated the power of this technique to detect reaction intermediates in fused liquid droplets with microsecond temporal resolution. PMID:25775573

Lee, Jae Kyoo; Kim, Samuel; Nam, Hong Gil; Zare, Richard N

2015-03-31

153

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

Jung, Moon Chul; Weber, Stephen G

2005-02-15

154

Generalized Second-Order Partial Derivatives of 1/r

ERIC Educational Resources Information Center

The generalized second-order partial derivatives of 1/r, where r is the radial distance in three dimensions (3D), are obtained using a result of the potential theory of classical analysis. Some non-spherical-regularization alternatives to the standard spherical-regularization expression for the derivatives are derived. The utility of a…

Hnizdo, V.

2011-01-01

155

HOW TO REPAIR A SECOND-ORDER SURFACE FOR COMPUTER

1 HOW TO REPAIR A SECOND-ORDER SURFACE FOR COMPUTER EXPERIMENTS BY KRIGING Astrid JOURDAN and analysis of computer experiments have been widely investigated in the past decade. Two approaches seem describes and compares them briefly in order to present a methodology for computer experiments based

Paris-Sud XI, UniversitĂ© de

156

A Second-Order Markov Gravity Anomaly Model

A second-order Markov process is proposed as a statistical model for gravity anomalies in a local region. The method is applied to the analysis of errors in an inertial navigation system caused by unknown gravity phenomena. Statistical models of vertical deflection obtained from the anomaly model by means of the Vening Meinesz equations yield predictions of rms position and velocity

Joseph F. Kasper

1971-01-01

157

Blind channel identification based on second order cyclostationary statistics

For finite impulse response (FIR), channels with uncorrelated input sequences, L. Tong et al. (1991, 1992) have proposed an identification method under the special rank condition. The relationship is established between the rank condition and identifiability of FIR channels using second-order cyclostationary statistics. The method is generalized to the FIR channels with correlated input sequences. For general autoregressive moving average

Y. Li; Z. Ding

1993-01-01

158

Forward and Backward Second-Order Pavlovian Conditioning in Honeybees

ERIC Educational Resources Information Center

Second-order conditioning (SOC) is the association of a neutral stimulus with another stimulus that had previously been combined with an unconditioned stimulus (US). We used classical conditioning of the proboscis extension response (PER) in honeybees ("Apis mellifera") with odors (CS) and sugar (US). Previous SOC experiments in bees were…

Hussaini, Syed Abid; Komischke, Bernhard; Menzel, Randolf; Lachnit, Harald

2007-01-01

159

Second-order accurate nonoscillatory schemes for scalar conservation laws

NASA Technical Reports Server (NTRS)

Explicit finite difference schemes for the computation of weak solutions of nonlinear scalar conservation laws is presented and analyzed. These schemes are uniformly second-order accurate and nonoscillatory in the sense that the number of extrema of the discrete solution is not increasing in time.

Huynh, Hung T.

1989-01-01

160

Correcting second-order contamination in low-resolution spectra

An empirical method for correcting low-resolution astronomical spectra for second-order contamination is presented. The method was developed for correcting spectra obtained with grism #4 of the ALFOSC spectrograph at the Nordic Optical Telescope and the performance is demonstrated on spectra of two nearby bright Type Ia supernovae.

V. Stanishev

2007-05-23

161

A second-order factor analysis of critical TQM factors

The quality management literature prescribes various critical quality improvement strategies. However, there have been few empirical studies that tested for the synergy or the relationships among these critical quality constructs. This study develops a second-order factor model to test whether a set of critical quality management factors load on an overall construct that may be termed “Total quality management”. Using

Nabil Tamimi

1998-01-01

162

Second-Order Conditioning of Human Causal Learning

ERIC Educational Resources Information Center

This article provides the first demonstration of a reliable second-order conditioning (SOC) effect in human causal learning tasks. It demonstrates the human ability to infer relationships between a cause and an effect that were never paired together during training. Experiments 1a and 1b showed a clear and reliable SOC effect, while Experiments 2a…

Jara, Elvia; Vila, Javier; Maldonado, Antonio

2006-01-01

163

SECOND ORDER PDES WITH DIRICHLET WHITE NOISE BOUNDARY CONDITIONS

SECOND ORDER PDES WITH DIRICHLET WHITE NOISE BOUNDARY CONDITIONS ZDZISLAW BRZE´ZNIAK, BEN GOLDYS. A large class of noises including Wiener and fractional Wiener space time white noise, homogeneous noise and L´evy noise is considered. Key words and phrases. Partial differential equations, white noise

Paris-Sud XI, Université de

164

SECOND ORDER PDES WITH DIRICHLET WHITE NOISE BOUNDARY CONDITIONS

SECOND ORDER PDES WITH DIRICHLET WHITE NOISE BOUNDARY CONDITIONS ZDZISLAW BRZEÂ´ZNIAK, BEN GOLDYS. A large class of noises including Wiener and fractional Wiener space time white noise, homogeneous noise and LÂ´evy noise is considered. Key words and phrases. Partial differential equations, white noise

Sydney, University of

165

Children's Understanding of Second-Order Mental States

ERIC Educational Resources Information Center

The most popular topic in theory-of-mind research has been first-order false belief: the realization that it is possible to hold false beliefs about events in the world. A more advanced development is second-order false belief: the realization that it is possible to hold a false belief about someone else's belief. This article reviews research…

Miller, Scott A.

2009-01-01

166

The second order Raman spectroscopy in carbon crystallinity

Cellulose was heated in the absence\\/presence of B to determine crystallinity changes due to heat treatment and B doping with the objectives of evaluating the characteristics of the second order Raman spectroscopy in comparison with X-ray diffraction (XRD) and the first order Raman spectroscopy. The crystallinity determined by XRD was similar to those of the first order Raman spectroscopy; crystallinity

Young-Jae Lee

2004-01-01

167

Chattering avoidance by second-order sliding mode control

Relying on the possibility of generating a second-order sliding motion by using, as control, the first derivative of the control signal instead of the actual control, a new solution to the problem of chattering elimination in variable structure control (VSC) is presented. Such a solution, inspired by the classical bang-bang optimal control strategy, is first depicted and expressed in terms

G. Bartolini; A. Ferrara; E. Usani

1998-01-01

168

Second order sliding mode controller for twin rotor MIMO system

In this paper a twisting algorithm based second order sliding mode controller (SMC) is proposed to control a laboratory helicopter called the twin rotor multi-input multi-output (MIMO) system (TRMS). The TRMS model is pseudo decomposed into two subsystems and the coupling between them is considered as an uncertainty. A proportional integral based sliding surface is used for the vertical subsystem

Sanjoy Mondal; Chitralekha Mahanta

2011-01-01

169

Adaptive observer for a class of second order nonlinear systems

óThe problem addressed in this paper is the design of an adaptive observer that can estimate the states and identify the parameters of a class of second order nonlinear systems. The purpose of the proposed method is to eliminate the restrictive dissipativity condition from the stability proof that is present in many previous works presented in the literature. In this

Jiang Zhu; Karim Khayati

2011-01-01

170

Second-Order Effects in Mental Health Treatment

ERIC Educational Resources Information Center

This article argues that mental health clients are typically processed through a fairly standardized, complex professional system which, in its pursuit of salutary helping'' goals may also be occasioning serious negative second-order effects for its clients. The intent of the present article is to direct attention to the professional implications…

Graziano, Anthony M.; Fink, Robert S.

1973-01-01

171

PREDICTIONS OF HIGHWAY EMISSIONS BY A SECOND ORDER CLOSURE MODEL

The dispersion of sulfur hexafluoride tracer and sulfate from automobile emissions in the immediate vicinity of a highway were estimated for conditions similar to those existing during the General Motors sulfate dispersion experiment conducted at a GM test track. A second-order c...

172

Solving Second-Order Differential Equations with Variable Coefficients

ERIC Educational Resources Information Center

A method is developed in which an analytical solution is obtained for certain classes of second-order differential equations with variable coefficients. By the use of transformations and by repeated iterated integration, a desired solution is obtained. This alternative method represents a different way to acquire a solution from classic power…

Wilmer, A., III; Costa, G. B.

2008-01-01

173

A New Factorisation of a General Second Order Differential Equation

ERIC Educational Resources Information Center

A factorisation of a general second order ordinary differential equation is introduced from which the full solution to the equation can be obtained by performing two integrations. The method is compared with traditional methods for solving these type of equations. It is shown how the Green's function can be derived directly from the factorisation…

Clegg, Janet

2006-01-01

174

Second Order Motion Compensation for Squinted Spotlight Synthetic Aperture Radar

Second Order Motion Compensation for Squinted Spotlight Synthetic Aperture Radar Minh Phuong Nguyen motion com- pensation (MoCom) algorithm for squinted spotlight synthetic aperture radar (SAR). A preciseRCMC will be inverted to retain the range compressed SAR data for the subsequent Omega-K processing. This paper

175

Modeling Ability Differentiation in the Second-Order Factor Model

ERIC Educational Resources Information Center

In this article we present factor models to test for ability differentiation. Ability differentiation predicts that the size of IQ subtest correlations decreases as a function of the general intelligence factor. In the Schmid-Leiman decomposition of the second-order factor model, we model differentiation by introducing heteroscedastic residuals,…

Molenaar, Dylan; Dolan, Conor V.; van der Maas, Han L. J.

2011-01-01

176

NO sub x -char reactions: Kinetics and transport aspects

The present project is motivated by the need to reduce NO{sub x} emissions from combustors, especially coal combustors. Reactions with carbon are known to be effective at reducing No to N{sub 2}, and remain interesting candidates in a wide variety of possible applications. These reactions are known to be important in reducing NO{sub x} emissions from fluidized bed coal combustors, in which the coal char itself serves as the reducing agent. The principal goal of this project is to develop a mechanistic understanding of the processes by which carbons reduce NO to N{sub 2}. The carbon was a char derived from phenol-formaldehyde resin. This material has been noted to be a reasonable model for coal chars in most respects, expect that its gasification behavior is not complicated by catalytic processes due to minerals. In the first phases of the project, the global kinetics of the process were established. In more recent work, attention has been turned to the individual steps in the mechanism. Recent quarterly reports have detailed the role of both chemisorption and desorption processes in determining the course and kinetics of the process. This report continues the reporting of results obtained along these lines, and draws an important new conclusion concerning the number of separate processes involved in determining the kinetics. 40 refs., 3 figs., 2 tabs.

Calo, J.M.; Suuberg, E.M.

1990-01-01

177

Kinetic approach to reaction and diffusion in many-particle systems

A derivation of hydrodynamic equations which describe diffusion in connection with reaction processes in many-particle systems is given on the basis of quantum kinetic theory. For this purpose kinetic equations are derived for a quantum gas with chemical reactions. Following Grad's method in a linear approximation reaction-diffusion equations can be obtained with explicit expressions for the diffusion and reaction rate

Iu. L. Klimontovich; M. Schlanges; T. Bornath

1990-01-01

178

NASA Astrophysics Data System (ADS)

An inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer has been employed in a systematic survey of the room-temperature kinetics of reactions of NO with 13 atomic lanthanide cations from Ce+ to Lu+ (excluding Pm+). The atomic ions are produced at ca. 5500 K in an ICP source and are allowed to decay radiatively and to thermalize by collisions with Ar and He atoms prior to reaction in helium buffer gas at 0.35 +/- 0.01 Torr and 295 +/- 2 K. All lanthanide cations were observed to exhibit some reactivity towards NO, almost exclusively resulting in LnO+ formation. Reactions were observed that are both first and second order in NO. Periodic trends in the measured reaction efficiencies for direct exothermic O atom transfer correlate with trends in the energy required to promote an electron in Ln+ to achieve either a d1s1 or a d2 excited electronic configuration in which two non-f-electrons are available for bonding. No such correlation is apparent for the remaining reactions.

Blagojevic, Voislav; Flaim, Eric; Jarvis, Michael J. Y.; Koyanagi, Gregory K.; Bohme, Diethard K.

2006-03-01

179

NASA Astrophysics Data System (ADS)

Rate constants, k A, for the aromatic nucleophilic substitution reaction of 2-chloro-3,5-dinitropyridine with aniline were determined in different compositions of 2-propanol mixed with hexane, benzene, and 2-methylpropan-2-ol and 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO4]) with dimethyl sulfoxide at 25°C. The obtained rate constants of the reaction in pure solvents are in the following order: 2-methylpropan-2-ol > dimethyl sulfoxide > 2-propanol > hexane > benzene > [Emim][EtSO4]. Molecularmicroscopic solvent parameters corresponding to the selected binary mixtures were utilized to study the kinetics of a nucleophilic substitution reaction in order to investigate and compare the effects of the solvents on a chemical process. The influence of solvent parameters including normalized polarity ( E {/T N }), dipolarity/polarizability (?*), hydrogen bond donor acidity (?), and hydrogen bond acceptor basicity (?) on the second-order rate constants were investigated and multiple linear regressions gave much better results with regard to single parameter regressions. The dipolarity/polarizability of media has a positive effect in all mixtures regarding zwitterionic character of the reaction intermediate and the hydrogen bond acceptor basicity of the solvent by stabilizing of activated complex increases the reaction rate.

Salari, Hadi; Pedervand, Mohsen; Sadeghzadeh-Darabi, Faramarz; Gholami, Mohammad Reza

2013-12-01

180

A study of switchgrass pyrolysis: Product variability and reaction kinetics

NASA Astrophysics Data System (ADS)

Samples of the same cultivar of cave-in-rock switchgrass were harvested from plots in Frankenmuth, Roger City, Cass County, and Grand Valley, Michigan. It was determined that variation exists, between locations, among the pyrolytic compounds which can lead to variability in bio-oil and increased processing costs at bio-refineries to make hydrocarbon fuels. Washed and extractives-free switchgrass samples, which contain a lower alkali and alkaline earth metals content than untreated samples, were shown to produce lower amounts of acids, esters, furans, ketones, phenolics, and saccharides and also larger amounts of aldehydes upon pyrolysis. Although the minerals catalyzed pyrolytic reactions, there was no evidence indicating their effect on reducing the production of anhydrosugars, specifically levoglucosan. To further link minerals present in the biomass to a catalytic pathway, mathematic models were employed to determine the kinetic parameters of the switchgrass. While the calculated activation energies of switchgrass, using the FWO and KAS methods, were 227.7 and 217.8 kJ/mol, correspondingly, it was concluded that the activation energies for the switchgrass hemicellulose and cellulose peaks were 115.5 and 158.2 kJ/mol, respectively, using a modified model-fitting method. The minerals that effect the production of small molecules and levoglucosan also have an observable catalytic effect on switchgrass reaction rate, which may be quantifiable through the use of reaction kinetics so as to determine activation energy.

Bovee, Jonathan Matthew

181

Second-order nonlinear optical metamaterials: ABC-type nanolaminates

Structuring optical materials on a nanometer scale can lead to artificial effective media, or metamaterials, with strongly altered optical behavior. Metamaterials can provide a wide range of linear optical properties such as negative refractive index, hyperbolic dispersion, or magnetic behavior at optical frequencies. Nonlinear optical properties, however, have only been demonstrated for patterned metallic films which suffer from high optical losses. Here we show that second-order nonlinear metamaterials can also be obtained from non-metallic centrosymmetric constituents with inherently low optical absorption. In our proof-of-principle experiments, we have iterated atomic-layer deposition (ALD) of three different constituents, A = Al$_2$O$_3$, B = TiO$_2$ and C = HfO$_2$. The centrosymmetry of the resulting ABC stack is broken since the ABC and the inverted CBA sequences are not equivalent - a necessary condition for non-zero second-order nonlinearity. To the best of our knowledge, this is the first realizati...

Alloatti, Luca; Froelich, Andreas; Lauermann, Matthias; Frenzel, Tobias; Koehnle, Kira; Freude, Wolfgang; Leuthold, Juerg; Wegener, Martin; Koos, Christian

2015-01-01

182

Second order modeling of boundary-free turbulent shear flows

NASA Technical Reports Server (NTRS)

A set of realizable second order models for boundary-free turbulent flows is presented. The constraints on second order models based on the realizability principle are re-examined. The rapid terms in the pressure correlations for both the Reynolds stress and the passive scalar flux equations are constructed to exactly satisfy the joint realizability. All other model terms (return-to-isotropy, third moments, and terms in the dissipation equations) already satisfy realizability. To correct the spreading rate of the axisymmetric jet, an extra term is added to the dissipation equation which accounts for the effect of mean vortex stretching on dissipation. The test flows used in this study are the mixing shear layer, plane jet, axisymmetric jet, and plane wake. The numerical solutions show that the unified model equations predict all these flows reasonably. It is expected that these models would be suitable for more complex and critical flows.

Shih, T.-H.; Chen, Y.-Y.; Lumley, J. L.

1991-01-01

183

Robust eigensystem assignment for second-order estimators

NASA Technical Reports Server (NTRS)

An approach for the robust eigensystem assignment of flexible structures using full state or output feedback is developed. Using the second-order dynamic equations, the approach can assign the eigenvalues of the system via velocity and displacement feedbacks, or acceleration and velocity feedbacks. The eigenvalues and eigenvectors of the system are assigned, via the second-order eigenvalue problem for the structural system, in two steps. First, an orthonormal basis spanning the attainable closed-loop eigenvector space corresponding to each desired closed-loop eigenvalue is generated using the Singular Value or QR decompositions. Second, a sequential procedure is used to choose a set of closed-loop eigenvectors that are as close as possible to the column space of a well-conditioned target matrix. Among the possible choices of the target matrix, the closest unitary matrix to the open-loop eigenvector matrix appears to be a suitable choice. A numerical example is given to illustrate the proposed algorithm.

Juang, Jer-Nan; Maghami, Peiman G.

1990-01-01

184

First- and second-order charged particle optics

Since the invention of the alternating gradient principle there has been a rapid evolution of the mathematics and physics techniques applicable to charged particle optics. In this publication we derive a differential equation and a matrix algebra formalism valid to second-order to present the basic principles governing the design of charged particle beam transport systems. A notation first introduced by John Streib is used to convey the essential principles dictating the design of such beam transport systems. For example the momentum dispersion, the momentum resolution, and all second-order aberrations are expressed as simple integrals of the first-order trajectories (matrix elements) and of the magnetic field parameters (multipole components) characterizing the system. 16 references, 30 figures.

Brown, K.L.; Servranckx, R.V.

1984-07-01

185

Bioethics as public discourse and second-order discipline.

Bioethics is best viewed as both a second-order discipline and also part of public discourse. Since their goals differ, some bioethical activities are more usefully viewed as advancing public discourse than academic disciplines. For example, the "Universal Declaration on Bioethics and Human Rights" sponsored by the United Nations Educational, Scientific, and Cultural Organization seeks to promote ethical guidance on bioethical issues. From the vantage of philosophical ethics, it fails to rank or specify its stated principles, justify controversial principles, clarify key terms, or say what is meant by calling potentially conflicting norms "foundational." From the vantage of improving the public discourse about bioethical problems and seeking ethical solutions in the public arena, however, this document may have an important role. The goals and relations between bioethics as a second-order discipline and public discourse are explored. PMID:19387001

Kopelman, Loretta M

2009-06-01

186

First and second order convex approximation strategies in structural optimization

NASA Technical Reports Server (NTRS)

In this paper, various methods based on convex approximation schemes are discussed that have demonstrated strong potential for efficient solution of structural optimization problems. First, the convex linearization method (Conlin) is briefly described, as well as one of its recent generalizations, the method of moving asymptotes (MMA). Both Conlin and MMA can be interpreted as first-order convex approximation methods that attempt to estimate the curvature of the problem functions on the basis of semiempirical rules. Attention is next directed toward methods that use diagonal second derivatives in order to provide a sound basis for building up high-quality explicit approximations of the behavior constraints. In particular, it is shown how second-order information can be effectively used without demanding a prohibitive computational cost. Various first-order and second-order approaches are compared by applying them to simple problems that have a closed form solution.

Fleury, C.

1989-01-01

187

Symmetries of second-order PDEs and conformal Killing vectors

We study the Lie point symmetries of a general class of partial differential equations (PDE) of second order. An equation from this class naturally defines a second-order symmetric tensor (metric). In the case the PDE is linear on the first derivatives we show that the Lie point symmetries are given by the conformal algebra of the metric modulo a constraint involving the linear part of the PDE. Important elements in this class are the Klein--Gordon equation and the Laplace equation. We apply the general results and determine the Lie point symmetries of these equations in various general classes of Riemannian spaces. Finally we study the type II\\ hidden symmetries of the wave equation in a Riemannian space with a Lorenzian metric.

Michael Tsamparlis; Andronikos Paliathanasis

2015-01-24

188

Second-order weak lensing from modified gravity

We explore the sensitivity of weak gravitational lensing to second-order corrections to the spacetime metric within a cosmological adaptation of the parameterized post-Newtonian framework. Whereas one might expect nonlinearities of the gravitational field to introduce non-Gaussianity into the statistics of the lensing convergence field, we show that such corrections are actually always small within a broad class of scalar-tensor theories of gravity. We show this by first computing the weak lensing convergence within our parameterized framework to second order in the gravitational potential, and then computing the relevant post-Newtonian parameters for scalar-tensor gravity theories. In doing so we show that this potential systematic factor is generically negligible, thus clearing the way for weak lensing to provide a direct tracer of mass on cosmological scales for a wide class of gravity theories despite uncertainties in the precise nature of the departures from general relativity.

R. Ali Vanderveld; Robert R. Caldwell; Jason Rhodes

2011-11-07

189

Second-order achromat design based on FODO cell

NASA Astrophysics Data System (ADS)

Two dipole doglegs are widely used to translate the beam axis horizontally or vertically. Quadrupoles are placed between the two consecutive dipoles to match first-order dispersion and provide betatron focusing. Similarly, a four dipole chicane is usually employed to form a bypass region, where the beam axis is transversely shifted first, then translated back to the original axis. In order to generate an isochronous section, quadrupoles are again needed to tune the first-order transfer matrix element R56 equaling zero. Usually sextupoles are needed to correct second-order dispersion in the bending plane, for both the dogleg optics and the chicane (with quad) optics. In this paper, an alternative optics design is introduced, which is based on a simple FODO cell and does not need sextupole assistance to form a second-order achromat. It may provide a similar function of either a dogleg or a bypass, by using two or four of such combined supercells.

Sun, Yipeng

2011-06-01

190

A Second-Order Achromat Design Based on FODO Cell

Two dipole doglegs are widely used to translate the beam axis horizontally or vertically. Quadrupoles are placed between the two consecutive dipoles to match first order dispersion and provide betatron focusing. Similarly a four dipole chicane is usually employed to form a bypass region, where the beam axis is transversely shifted first, then translated back to the original axis. In order to generate an isochronous section, quadrupoles are again needed to tune the first order transfer matrix element R{sub 56} equaling zero. Usually sextupoles are needed to correct second order dispersion in the bending plane, for both the dogleg optics and the chicane (with quad) optics. In this paper, an alternative optics design is introduced, which is based on a simple FODO cell and does not need sextupoles assistance to form a second-order achromat. It may provide a similar function of either a dogleg or a bypass, by using 2 or 4 of such combined supercells.

Sun, Yipeng; /SLAC

2011-08-19

191

Experimental second-order nonlinear optics in molecular switching

NASA Astrophysics Data System (ADS)

This paper focuses on a few of the intricacies when relating theoretical calculations of first hyperpolarizabilities to experimental observables in second-order nonlinear optics. This is important for both theoreticians and experimentalists, as it provides for a better understanding of what the level of sophistication should be for the theory versus the experimental precision attainable in nonlinear optical experiments with pulsed lasers, but also to appreciate that there are limitations and assumptions that are imposed by the nature of the experiment.

Clays, Koen

2015-01-01

192

Gaussian spectral rules for second order finite-difference schemes

Earlier the authors suggested an algorithm of grid optimization for a second order finite-difference approximation of a two-point problem. The algorithm yields exponential superconvergence of the Neumann-to-Dirichlet map (or the boundary impedance). Here we extend that approach to PDEs with piecewise-constant coefficients and rectangular homogeneous subdomains. Examples of the numerical solution of the 2-dimensional oscillatory Helmholtz equation exhibit exponential convergence

Vladimir Druskin; Leonid Knizhnerman

2000-01-01

193

Extensions and applications of a second-order landsurface parameterization

NASA Technical Reports Server (NTRS)

Extensions and applications of a second order land surface parameterization, proposed by Andreou and Eagleson are developed. Procedures for evaluating the near surface storage depth used in one cell land surface parameterizations are suggested and tested by using the model. Sensitivity analysis to the key soil parameters is performed. A case study involving comparison with an "exact" numerical model and another simplified parameterization, under very dry climatic conditions and for two different soil types, is also incorporated.

Andreou, S. A.; Eagleson, P. S.

1983-01-01

194

Second-order coupling of two Love waves

NASA Astrophysics Data System (ADS)

The second-order contradirectional coupling of two Love waves in the presence of a radiation of bulk elastic waves in a substrate is analyzed. In particular, attention is given to maximizing the coupling between two Love waves and between a Love wave and a bulk elastic wave. The excitation of two counterpropagating Love waves by an incident bulk elastic wave is also examined, and two ways to optimize the excitation coefficients are discussed.

Seshadri, S. R.

1984-06-01

195

Second-Order Facial Information Processing in Schizophrenia

This study investigated the processing of second-order relational face information in schizophrenia. Twenty-eight schizophrenic patients and 28 controls were asked to say whether the space between the eyes was the same in 2 side-by-side faces. The 2 faces were derived from the same original face, but the spacing between the eyes was either the same or differed by various distances.

Jean-Yves Baudouin; Mathilde Vernet; Nicolas Franck

2008-01-01

196

Second order filter response with series coupled silica microresonators

NASA Technical Reports Server (NTRS)

We have demonstrated an approach for fabricating a photonic filter with second order response function. The filter consists of two germania-doped silica microtoroidal or microspherical resonators cascaded in series. We use UV irradiation to tune the mode of one microcavity to bring it close to the mode of the second microcavity. This approach produces a filter function with much sharper rolloff than can be obtained with the individual microresonators.

Savchenkov, A.; Iitchenko, V. S.; Handley, T.; Maleki, L.

2002-01-01

197

On an Interpretation of Second Order Quanti cation in

Andrew.Pitts@cl.cam.ac.uki Abstract We prove the following surprising property of Heyting's intuitionistic propositional calculus, Ip be modelled in IpC, and there is an interpretation of the second order propositional calculus, IpC2, in Ip is the strengthening of the usual Interpolation Theorem for IpC to the statement that there are least and greatest in

Pitts, Andrew

198

Second Order Corrections to QED Coupling at Low Temperature

We calculate the second order corrections to vacuum polarization tensor of photons at low temperatures, i.e; T $\\le 10^{10}$ K ($T temperatures below the electron mass that is $Ttemperatures has explicitly been checked. The electromagnetic properties of such a thermal medium are modified. Parameters like electric permittivity and magnetic permeability of such a medium are no more constant and become functions of temperature.

Samina S. Masood; Mahnaz Q. Haseeb

2008-07-29

199

Second-Order Linear Homogeneous Differential Equations with Constant Coefficients

NSDL National Science Digital Library

Created by Lang Moore and David Smith for the Connected Curriculum Project, the purpose of this module is to investigate the qualitative behavior of second-order constant coefficient differential equations and corresponding initial value problems. In particular, to determine how solutions depend on the signs and magnitudes of the coefficients and on the initial conditions. This is one of a much larger set of learning modules hosted by Duke University.

Moore, Lang

200

Second-Order Linear Homogeneous Differential Equations with Constant Coefficients

NSDL National Science Digital Library

Created by Lang Moore and David Smith for the Connected Curriculum Project, the purpose of this module is to investigate the qualitative behavior of the solutions of initial value problems for second-order constant coefficient differential equations. In particular, to determine how solutions depend on the signs and magnitudes of the coefficients and on the initial conditions. This is part of a larger group of learning modules hosted by Duke University.

Moore, Lang

201

Superconvergent discontinuous Galerkin methods for second-order elliptic problems

We identify discontinuous Galerkin methods for second-order el- liptic problems in several space dimensions having superconvergence properties similar to those of the Raviart-Thomas and the Brezzi-Douglas-Marini mixed methods. These methods use polynomials of degree k ? 0 for both the po- tential as well as the flux. We show that the approximate flux converges in L2 with the optimal order

Bernardo Cockburn; Johnny Guzman; Haiying Wang

2009-01-01

202

Kinetic Study of the Austempering Reactions in Ductile Irons

NASA Astrophysics Data System (ADS)

Kinetics of the reaction that occur during the austempering heat treatment in unalloyed and alloyed ductile irons with 1Cu-0.25Mo, 1Ni-0.25Mo, and 0.7Cu-1Ni-0.25Mo, was studied. The austenitization and austempering cycles were achieved by isothermal dilatometry in cylindrical samples of 2 mm in diameter and 12 mm in length. The specimens were austenitized at 870 °C for 120 min, followed by isothermal holding for 300 min at temperatures between 270 and 420 °C. Kinetic parameters such as the order of reaction " n" and the rate of reaction " k" were calculated using the Johnson-Mehl equation while the empirical activation energy was calculated by means of the Arrhenius equation. It was found that the values of " k" decreased with the addition of Cu, Ni, and Mo as well as with the reduction of the isothermal temperature. The activation energy changes with the austempering temperature, in the range 30,348-58,250 J/mol when the heat treatment was carried out between 370 and 420 °C and 10,336-26,683 J/mol when the temperature varied from 270 to 350 °C. The microstructures in samples austempered at 370 and 315 °C were observed by transmission electron microscopy. No carbides precipitation was observed on samples heat treated at 370 °C for less than 120 min, while at 315 °C carbides of hexagonal structure ?(Fe2.4C) were found from the beginning of the transformation. The smallest value of activation energy and a slower kinetic transformation seem to be related with the presence of a carbide phase. Additionally, the time results obtained for transformation fractions of 0.05 and 0.95 by the dilatometry analysis were used to build the temperature-time-transformation diagrams for the irons.

Pérez, M. J.; Cisneros, M. M.; Almanza, E.; Haro, S.

2012-11-01

203

Kinetics and mechanisms of reactions involving small aromatic reactive intermediates

Small aromatic radicals such as C{sub 6}H{sub 5}, C{sub 6}H{sub 5}O and C{sub 6}H{sub 4} are key prototype species of their homologs. C{sub 6}H{sub 5} and its oxidation product, C{sub 6}H{sub 5}O are believed to be important intermediates which play a pivotal role in hydrocarbon combustion, particularly with regard to soot formation. Despite their fundamental importance, experimental data on the reaction mechanisms and reactivities of these species are very limited. For C{sub 6}H{sub 5}, most kinetic data except its reactions with NO and NO{sub 2}, were obtained by relative rate measurements. For C{sub 6}H{sub 5}O, the authors have earlier measured its fragmentation reaction producing C{sub 5}H{sub 5} + CO in shock waves. For C{sub 6}H{sub 4}, the only rate constant measured in the gas phase is its recombination rate at room temperature. The authors have proposed to investigate systematically the kinetics and mechanisms of this important class of molecules using two parallel laser diagnostic techniques--laser resonance absorption (LRA) and resonance enhanced multiphoton ionization mass spectrometry (REMPI/MS). In the past two years, study has been focused on the development of a new multipass adsorption technique--the {open_quotes}cavity-ring-down{close_quotes} technique for kinetic applications. The preliminary results of this study appear to be quite good and the sensitivity of the technique is at least comparable to that of the laser-induced fluorescence method.

Lin, M.C. [Emory Univ., Atlanta, GA (United States)

1993-12-01

204

Numerical treatment of interfaces for second-order wave equations

In this article we develop a numerical scheme to deal with interfaces between touching numerical grids when solving the second-order wave equation. We show that it is possible to implement an interface scheme of "penalty" type for the second-order wave equation, similar to the ones used for first-order hyperbolic and parabolic equations, and the second-order scheme used by Mattsson et al (2008). These schemes, known as SAT schemes for finite difference approximations and penalties for spectral ones, and ours share similar properties but in our case one needs to pass at the interface a smaller amount of data than previously known schemes. This is important for multi-block parallelizations in several dimensions, for it implies that one obtains the same solution quality while sharing among different computational grids only a fraction of the data one would need for a comparable (in accuracy) SAT or Mattsson et al.'s scheme. The semi-discrete approximation used here preserves the norm and uses standard finite-difference operators satisfying summation by parts. For the time integrator we use a semi-implicit IMEX Runge-Kutta method. This is crucial, since the explicit Runge-Kutta method would be impractical given the severe restrictions that arise from the stiff parts of the equations.

F. Parisi; M. Cécere; M. Iriondo; O. Reula

2014-06-12

205

Second-order reconstruction of the inflationary potential

NASA Technical Reports Server (NTRS)

To first order in the deviation from scale invariance the inflationary potential and its first two derivatives can be expressed in terms of the spectral indices of the scalar and tensor perturbations, n and n(sub T), and their contributions to the variance of the quadrupole CBR temperature anisotropy, S and T. In addition, there is a 'consistency relation' between these quantities: n(sub T) = (-1/ 7)(T/S). We derive the second-order expressions for the inflationary potential and its first two derivatives and the first-order expression for its third derivative, in terms, of n, n(sub T), S, T, and dn/d ln gamma. We also obtain the second-order consistency relation, n(sub T) = (-1/7)(T/S)(1 + 0.11(T/S) + 0.15(n-1)). As an example we consider the exponential potential, the only known case where exact analytic solutions for the perturbation spectra exist. We reconstruct the potential via Taylor expansion (with coefficients calculated at both first and second order), and introduce the Pade approximate as a greatly improved alternative.

Liddle, Andrew R.; Turner, Michael S.

1994-01-01

206

Dressed four-wave mixing second-order Talbot effect

NASA Astrophysics Data System (ADS)

We theoretically demonstrate second-order Talbot effect (SOTE) based on entangled photon pairs. The photon pairs are generated from the spontaneous parametric four-wave mixing (SPFWM) process in a cold atomic medium and can be taken as the imaging light in order to realize coincidence recording. A strong standing wave is used to create the electromagnetically induced grating in the entangled photon pairs channels. By changing the frequency detuning of the standing wave or the other optical fields participating in the process, we can manipulate the contrast of the second-order Talbot image. We use the second-order correlation function and the dressed-state picture to explain the SOTE occurring in the SPFWM process. Moreover, we demonstrate the scheme for SOTE based on the spatially correlated twin beams generated from the SPFWM process with injection. This scheme provides a convenient detection proposal for the SOTE at the cost of the image contrast. Compared to the previous self-imaging schemes, the present schemes have the characteristic of controllable image contrast and of nonlocal imaging, and thus, they might broaden their applications in imaging techniques and find applications in quantum lithography.

Chen, Haixia; Zhang, Xun; Zhu, Dayu; Yang, Chang; Jiang, Tao; Zheng, Huaibin; Zhang, Yanpeng

2014-10-01

207

Reaction Kinetics and Mechanism of Magnetic Field Effects in Cryptochrome

Creatures as varied as mammals, fish, insects, reptiles, and birds have an intriguing ‘sixth’ sense that allows them to orient themselves in the Earth's magnetic field. Despite decades of study, the physical basis of this magnetic sense remains elusive. A likely mechanism is furnished by magnetically sensitive radical pair reactions occurring in the retina, the light-sensitive part of animal eyes. A photoreceptor, cryptochrome, has been suggested to endow birds with magnetoreceptive abilities as the protein has been shown to exhibit the biophysical properties required for an animal magnetoreceptor to operate properly. Here, we propose a theoretical analysis method for identifying cryptochrome's signaling reactions involving comparison of measured and calculated reaction kinetics in cryptochrome. Application of the method yields an exemplary light-driven reaction cycle, supported through transient absorption and electron-spin-resonance observations together with known facts on avian magnetoreception. The reaction cycle permits one to predict magnetic field effects on cryptochrome activation and deactivation. The suggested analysis method gives insight into structural and dynamic design features required for optimal detection of the geomagnetic field by cryptochrome and suggests further experimental and theoretical studies. PMID:22171949

2012-01-01

208

Kinetic study of Nafion degradation by Fenton reaction

NASA Astrophysics Data System (ADS)

To predict the durability of polymer electrolyte membranes in fuel cells, the degradation reactions of Nafion 117 films were studied as oxidation reactions with hydroxyl radicals as oxidation accelerators. The radical species were generated by the Fenton reaction between hydrogen peroxide (H2O2) and iron ions (Fe2+). The Nafion degradation kinetics were estimated by fluorine ion (F-) generation. The H2O2 and Nafion degradation reactions fit a pseudo-first-order rate constant. The values of the activation energy and frequency factor are 85 kJ mol-1 and 3.97 × 108 s-1 for H2O2 decomposition in the presence of a Nafion film and 97 kJ mol-1 and 9.88 × 108 s-1 for F- generation. The Nafion surface morphology became rough after reaction for 12 h; small cracks, approximately 100 ?m in length, were observed at temperatures below 60 °C. These cracks connected to make larger gaps of approximately 1 mm at temperatures above 70 °C. We also found a linear relationship between H2O2 consumption and F- generation. The rate constant is temperature dependent and expressed as ln(d[F-]/d[decomposed H2O2]) = -19.5 × 103 K-1 + 42.8. F- generated and H2O2 consumed along with the Nafion degradation conditions can be predicted using this relation.

Sugawara, Tomoko; Kawashima, Norimichi; Murakami, Takurou N.

2011-03-01

209

NASA Technical Reports Server (NTRS)

Recently introduced 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 extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

Liechty, Derek S.; Lewis, Mark J.

2010-01-01

210

Differential approach to the memory-function reaction kinetics

NASA Astrophysics Data System (ADS)

A new formulation of the encounter theory for liquid-phase many-particle reacting systems (MPRS) is developed. This new formulation is based upon the notion of the pair distribution function and results in a set of partial differential equations equivalent to the integro-differential equations of the conventional approach. The solution is greatly improved by considering pair-particle interactions. The new formulation is applicable to arbitrary MPRS and allows for a general numerical solution. Applied to the Lotka-Volterra reaction, this approach revealed damping and increasing oscillations on the concentration, which cannot be seen in the framework of phenomenological chemical kinetics.

Frantsuzov, P. A.; Igoshin, O. A.; Krissinel, E. B.

2000-02-01

211

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

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

2001-01-01

212

Diffusion Controlled Reactions, Fluctuation Dominated Kinetics, and Living Cell Biochemistry

In recent years considerable portion of the computer science community has focused its attention on understanding living cell biochemistry and efforts to understand such complication reaction environment have spread over wide front, ranging from systems biology approaches, through network analysis (motif identification) towards developing language and simulators for low level biochemical processes. Apart from simulation work, much of the efforts are directed to using mean field equations (equivalent to the equations of classical chemical kinetics) to address various problems (stability, robustness, sensitivity analysis, etc.). Rarely is the use of mean field equations questioned. This review will provide a brief overview of the situations when mean field equations fail and should not be used. These equations can be derived from the theory of diffusion controlled reactions, and emerge when assumption of perfect mixing is used.

Konkoli, Zoran

2009-01-01

213

Optimal automatic reaction and species elimination in kinetic mechanisms

A known challenge for the simulation of reacting flow systems is that detailed chemical mechanisms contain hundreds to thousands of species and thousands of reactions, leading to high CPU requirements despite the use of state-of-the-art solvers. For specific conditions of interest (temperature, pressure, and composition), smaller mechanisms can predict the chemistry relatively accurately. One possibility for obtaining such mechanisms is species elimination from a detailed mechanism. Here, an automatic method for kinetic model reduction by simultaneous reaction and species elimination is proposed, based on an integer linear program (ILP) formulation. The solution of the ILP is an optimally reduced kinetic mechanism that reproduces the predictions of a reference mechanism within prespecified tolerances for finitely many reference points in the state space. The method is applied to generate optimally reduced models for isobaric, adiabatic homogeneous combustion. Case studies are presented for the combustion of n-heptane. Comparisons between the full and reduced models are shown and the tradeoff between species and reaction elimination is discussed. Tolerances in the ILP formulation control the error introduced by the model reduction. For increasing acceptable error, more species and/or reactions are eliminated. A method of quantifying this tradeoff between approximation error and reduction achieved is proposed, based on multiobjective optimization, and demonstrated in a case study. The effect of variable initial conditions is investigated. The mechanisms generated achieve significant reduction in the CPU requirement and can accurately predict the trajectories of the state variables (species mass fractions and temperature), as well as other metrics of interest, such as ignition time delay. (author)

Mitsos, A. [RES Group/Numerica Technology, Cambridge, MA 02142 (United States); Oxberry, G.M.; Barton, P.I.; Green, W.H. [Massachusetts Institute of Technology/Department of Chemical Engineering, Cambridge, MA 02139 (United States)

2008-10-15

214

Transport coefficients in second-order non-conformal viscous hydrodynamics

Based on the exact solution of Boltzmann kinetic equation in the relaxation-time approximation, the precision of the two most recent formulations of relativistic second-order non-conformal viscous hydrodynamics (14-moment approximation and causal Chapman-Enskog method), standard Israel-Stewart theory, and anisotropic hydrodynamics framework, in the simple case of one-dimensional Bjorken expansion, is tested. It is demonstrated that the failure of Israel-Stewart theory in reproducing exact solutions of the Boltzmann kinetic equation occurs due to neglecting and/or choosing wrong forms of some of the second-order transport coefficients. In particular, the importance of shear--bulk couplings in the evolution equations for dissipative quantities is shown. One finds that, in the case of the bulk viscous pressure correction, such coupling terms are as important as the corresponding first-order Navier-Stokes term and must be included in order to obtain, at least qualitative, overall agreement with the kinetic theory.

Radoslaw Ryblewski

2014-11-26

215

Kinetic study of the OH radical reaction with phenylacetylene.

The reaction of the OH radical with phenylacetylene is studied over the 298-423 K temperature range and 1-7.5 Torr pressure range in a quasi-static reaction cell. The OH radical is generated by 266 nm photolysis of hydrogen peroxide (H2O2) or 355 nm photolysis of nitrous acid (HONO), and its concentration monitored using laser-induced fluorescence. The measured reaction rates are found to strongly depend on laser fluence at 266 nm. The 266 nm absorption cross-section of phenylacetylene is measured to be 1.29 (±0.71) × 10(-17) cm(2), prohibiting any accurate kinetic measurements at this wavelength. The rates are independent of laser fluence at 355 nm with an average value of 8.75 (±0.73) × 10(-11) cm(3) s(-1). The reaction exhibits no pressure or temperature dependence over the studied experimental conditions and is much faster than the estimated values presently used in combustion models. These results are consistent with the formation of a short lifetime intermediate that stabilizes by collisional quenching with the buffer gas. The structures of the most likely formed products are discussed based on both the computed energies for the OH-addition intermediates and previous theoretical investigations on similar chemical systems. PMID:25111848

Abhinavam Kailasanathan, Ranjith Kumar; Thapa, Juddha; Goulay, Fabien

2014-09-11

216

NASA Astrophysics Data System (ADS)

We propose explicitly correlated Ansatz for four-component relativistic methods within the framework of the no-pair approximation. Kinetically balanced geminal basis is derived to satisfy the cusp conditions in the non-relativistic limit based on the Lévy-Leblend-like equation. Relativistic variants of strong-orthogonality projection operator (Ansätze 2? and 2?) suitable for practical calculations are introduced by exploiting the orthogonal complement of the large-component basis. A pilot implementation is performed for the second order Mřller-Plesset perturbation theory.

Ten-no, Seiichiro; Yamaki, Daisuke

2012-10-01

217

Constraints on general second-order scalar-tensor models from gravitational Cherenkov radiation

We demonstrate that the general second-order scalar-tensor theories, which have attracted attention as possible modified gravity models to explain the late time cosmic acceleration, could be strongly constrained from the argument of the gravitational Cherenkov radiation. To this end, we consider the purely kinetic coupled gravity and the extended galileon model on a cosmological background. In these models, the propagation speed of tensor mode could be less than the speed of light, which puts very strong constraints from the gravitational Cherenkov radiation.

Kimura, Rampei; Yamamoto, Kazuhiro, E-mail: rampei@theo.phys.sci.hiroshima-u.ac.jp, E-mail: kazuhiro@hiroshima-u.ac.jp [Department of Physical Science, Hiroshima University, Higashi-Hiroshima 739-8526 (Japan)

2012-07-01

218

Chaotic properties of spin lattices near second-order phase transitions

We numerically investigate Lyapunov spectra of chaotic dynamics in lattices of classical spins in the vicinity of second-order ferromagnetic and antiferromagnetic phase transitions. On the basis of this investigation, we identify a characteristic of the shape of the Lyapunov spectra, which exhibits a sharp peak as a function of temperature exactly at the phase transition, provided the order parameter is capable of strong dynamic fluctuations. As a part of this work, we also propose a general numerical algorithm for determining the temperature in many-particle systems, where kinetic energy is not defined.

A. S. de Wijn; B. Hess; B. V. Fine

2014-10-21

219

Non-Gaussianity from the second-order cosmological perturbation

Several conserved and/or gauge-invariant quantities described as the second-order curvature perturbation have been given in the literature. We revisit various scenarios for the generation of second-order non-Gaussianity in the primordial curvature perturbation {zeta}, employing for the first time a unified notation and focusing on the normalization f{sub NL} of the bispectrum. When {zeta} first appears a few Hubble times after horizon exit, |f{sub NL}| is much less than 1 and is, therefore, negligible. Thereafter {zeta} (and hence f{sub NL}) is conserved as long as the pressure is a unique function of energy density (adiabatic pressure). Nonadiabatic pressure comes presumably only from the effect of fields, other than the one pointing along the inflationary trajectory, which are light during inflation ('light noninflaton fields'). During single-component inflation f{sub NL} is constant, but multicomponent inflation might generate vertical bar f{sub NL} vertical bar {approx}1 or bigger. Preheating can affect f{sub NL} only in atypical scenarios where it involves light noninflaton fields. The simplest curvaton scenario typically gives f{sub NL}<<-1 or f{sub NL}=+5/4. The inhomogeneous reheating scenario can give a wide range of values for f{sub NL}. Unless there is a detection, observation can eventually provide a limit vertical bar f{sub NL} vertical bar or approx. 1, at which level it will be crucial to calculate the precise observational limit using second-order theory.

Lyth, David H. [Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom); Rodriguez, Yeinzon [Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom); Centro de Investigaciones, Universidad Antonio Narino, Cll 58A no. 37-94, Bogota D.C. (Colombia)

2005-06-15

220

Superquadric glyphs for symmetric second-order tensors.

Symmetric second-order tensor fields play a central role in scientific and biomedical studies as well as in image analysis and feature-extraction methods. The utility of displaying tensor field samples has driven the development of visualization techniques that encode the tensor shape and orientation into the geometry of a tensor glyph. With some exceptions, these methods work only for positive-definite tensors (i.e. having positive eigenvalues, such as diffusion tensors). We expand the scope of tensor glyphs to all symmetric second-order tensors in two and three dimensions, gracefully and unambiguously depicting any combination of positive and negative eigenvalues. We generalize a previous method of superquadric glyphs for positive-definite tensors by drawing upon a larger portion of the superquadric shape space, supplemented with a coloring that indicates the quadratic form (including eigenvalue sign). We show that encoding arbitrary eigenvalue magnitudes requires design choices that differ fundamentally from those in previous work on traceless tensors that arise in the study of liquid crystals. Our method starts with a design of 2-D tensor glyphs guided by principles of scale-preservation and symmetry, and creates 3-D glyphs that include the 2-D glyphs in their axis-aligned cross-sections. A key ingredient of our method is a novel way of mapping from the shape space of three-dimensional symmetric second-order tensors to the unit square. We apply our new glyphs to stress tensors from mechanics, geometry tensors and Hessians from image analysis, and rate-of-deformation tensors in computational fluid dynamics. PMID:20975202

Schultz, Thomas; Kindlmann, Gordon L

2010-01-01

221

Spectator Ions ARE Important! A Kinetic Study of the Copper-Aluminum Displacement Reaction

ERIC Educational Resources Information Center

Surprisingly, spectator ions are responsible for unexpected kinetics in the biphasic copper(II)-aluminum displacement reaction, with the rate of reaction dependent on the identity of the otherwise ignored spectator ions. Application of a published kinetic analysis developed for a reaction between a rotating Al disk and a Cu(II) ion solution to the…

Sobel, Sabrina G.; Cohen, Skyler

2010-01-01

222

The reaction CH + Nâ (hydrocarbon radical + nitrogen) ..-->.. products was studied at 297 K at total pressures between 25 and 787 torr. The second-order reaction rate constant was found to be pressure dependent, varying by a factor of 9.6 in this range. This reaction was also studied in the range 297 to 675 K at 100-torr total pressure.

M. R. Berman; M. C. Lin

1983-01-01

223

Supersonic second order analysis and optimization program user's manual

NASA Technical Reports Server (NTRS)

Approximate nonlinear inviscid theoretical techniques for predicting aerodynamic characteristics and surface pressures for relatively slender vehicles at supersonic and moderate hypersonic speeds were developed. Emphasis was placed on approaches that would be responsive to conceptual configuration design level of effort. Second order small disturbance theory was utilized to meet this objective. Numerical codes were developed for analysis and design of relatively general three dimensional geometries. Results from the computations indicate good agreement with experimental results for a variety of wing, body, and wing-body shapes. Case computational time of one minute on a CDC 176 are typical for practical aircraft arrangement.

Clever, W. C.

1984-01-01

224

Second-order nonlinear optical effects of spin currents

NASA Astrophysics Data System (ADS)

Pure spin currents, which carry information via spins in lieu of charges, are a key element in spintronics and signify the quantum spin Hall effect. However, they are hardly traceable as they bear neither net magnetization nor net charge currents, notwithstanding many "smoking-gun" evidences. We show that a pure spin current has measurable second-order nonlinear optical effects by symmetry analysis and microscopic calculations. These findings may be exploited for directly "seeing" spin currents in real-time and real-space with standard nonlinear optical spectroscopy.

Wang, Jing; Liu, Ren-Bao; Zhu, Bang-Fen

2011-12-01

225

Linear programming based optimal power flow using second order sensitivities

For the electric railway traction in Sweden, a system of 130 kV transmission lines connected parallel to the contact lines is being built. Within this system, the generation costs differs only slightly between different nodes with power injections. In order to optimize the power flow in the system, an extended optimal power flow algorithm based on successive linear programming, has been developed. To improve the convergence, a method based on a second order sensitivity approximation of the active power losses of the total system is applied. Numerical examples are given to show the enhanced convergence properties.

Olofsson, M.; Andersson, G.; Soeder, L. [Royal Inst. of Tech., Stockholm (Sweden). Electric Power Systems] [Royal Inst. of Tech., Stockholm (Sweden). Electric Power Systems

1995-08-01

226

Irreducible second order SUSY transformations between real and complex potentials

Second order SUSY transformations between real and complex potentials for three important from physical point of view Sturm-Liouville problems, namely, problems with the Dirichlet boundary conditions for a finite interval, for a half axis and for the whole real line are analyzed. For every problem conditions on transformation functions are formulated when transformations are irreducible, i.e. when either the intermediate Hamiltonian is not well defined in the same Hilbert space as the initial and final Hamiltonians or its eigenfunctions cannot be obtained by applying transformation operator either on eigenfunctions of the initial Hamiltonian or on these of the final Hamiltonian. Obtained results are illustrated by numerous simple examples.

B. F. Samsonov

2006-11-16

227

Octonic second-order equations of relativistic quantum mechanics

We demonstrate a generalization of relativistic quantum mechanics using eight-component value ''octons'' that generate an associative noncommutative spatial algebra. It is shown that the octonic second-order equation for the eight-component octonic wave function, obtained from the Einstein relation for energy and momentum, describes particles with spin 1/2. It is established that the octonic wave function of a particle in the state with defined spin projection has a specific spatial structure that takes the form of an octonic oscillator with two spatial polarizations: longitudinal linear and transverse circular.

Mironov, Victor L.; Mironov, Sergey V. [Institute for Physics of Microstructures, RAS, GSP-105, Nizhniy Novgorod 603950 (Russian Federation)

2009-01-15

228

A second-order closure analysis of turbulent diffusion flames. [combustion physics

NASA Technical Reports Server (NTRS)

A complete second-order closure computer program for the investigation of compressible, turbulent, reacting shear layers was developed. The equations for the means and the second order correlations were derived from the time-averaged Navier-Stokes equations and contain third order and higher order correlations, which have to be modeled in terms of the lower-order correlations to close the system of equations. In addition to fluid mechanical turbulence models and parameters used in previous studies of a variety of incompressible and compressible shear flows, a number of additional scalar correlations were modeled for chemically reacting flows, and a typical eddy model developed for the joint probability density function for all the scalars. The program which is capable of handling multi-species, multistep chemical reactions, was used to calculate nonreacting and reacting flows in a hydrogen-air diffusion flame.

Varma, A. K.; Fishburne, E. S.; Beddini, R. A.

1977-01-01

229

On the universal identity in second order hydrodynamics

NASA Astrophysics Data System (ADS)

We compute the 't Hooft coupling correction to the infinite coupling expression for the second order transport coefficient ? 2 in SU( N c ) supersymmetric Yang-Mills theory at finite temperature in the limit of infinite N c , which originates from the R 4 terms in the low energy effective action of the dual type IIB string theory. Using this result, we show that the identity involving the three second order transport coefficients, 2 ?? ? - 4 ? 1 - ? 2 = 0, previously shown by Haack and Yarom to hold universally in relativistic conformal field theories with string dual descriptions to leading order in supergravity approximation, holds also at next to leading order in this theory. We also compute corrections to transport coefficients in a (hypothetical) strongly interacting conformal fluid arising from the generic curvature squared terms in the corresponding dual gravity action (in particular, Gauss-Bonnet action), and show that the identity holds to linear order in the higher-derivative couplings. We discuss potential implications of these results for the near-equilibrium entropy production rate at strong coupling.

Grozdanov, S.; Starinets, A. O.

2015-03-01

230

Second-Order Coding Rates for Entanglement-Assisted Communication

The entanglement-assisted capacity of a quantum channel is known to provide the formal quantum generalization of Shannon's classical channel capacity theorem, in the sense that it admits a single-letter characterization in terms of the quantum mutual information and does not increase in the presence of a noiseless quantum feedback channel from receiver to sender. In this work, we investigate the second-order asymptotics of the entanglement-assisted communication task. That is, we consider how quickly the rates of entanglement-assisted codes converge to the entanglement-assisted capacity of a channel as a function of the number of channel uses and the error tolerance. We define a quantum generalization of the mutual information variance of a channel in the entanglement-assisted setting. For covariant channels, we show that this quantity is equal to the channel dispersion, and characterizes the convergence towards the entanglement-assisted capacity when the number of channel uses increases. More generally, we prove that the Gaussian approximation of the second-order coding rate is achievable for all quantum channels.

Nilanjana Datta; Marco Tomamichel; Mark M. Wilde

2014-05-08

231

Second-order near-wall turbulence closures - A review

NASA Technical Reports Server (NTRS)

Advances in second-order near-wall turbulence closures are summarized. All closures under consideration are based on high-Reynolds-number models. Most near-wall closures proposed to date attempt to modify the high-Reynolds-number models for the dissipation function and the pressure redistribution term so that the resultant models are applicable all the way to the wall. The asymptotic behavior of the near-wall closures is examined and compared with the proper near-wall behavior of the exact Reynolds-stress equations. It is found that three second-order near-wall closures give the best correlations with simulated turbulence statistics. However, their predictions of near-wall Reynolds-stress budgets are considered to be incorrect. A proposed modification to the dissipitation-rate equation remedies part of those predictions. It is concluded that further improvements are required if a complete replication of all the turbulence properties and Reynolds-stress budgets by a statistical model of turbulence is desirable.

So, R. M. C.; Lai, Y. G.; Zhang, H. S.; Hwang, B. C.

1991-01-01

232

Second order inverse born approximation for diffuse optical tomography

NASA Astrophysics Data System (ADS)

Diffuse Optical Tomography (DOT) involves a nonlinear optimization problem to find the tissue optical properties by measuring near-infrared light noninvasively. Many researchers used linearization methods to obtain the optical image in real time. However, the linearization procedure may neglect small but sometimes important regions such as small tumors at an early stage. Therefore, nonlinear optimization methods such as gradient- or Newton- type methods are exploited, resulting in better resolution image than that of linearization methods. But the disadvantage of nonlinear methods is that they need much computation time. To solve this trade-off dilemma between image resolution and computing time, we suggest second order inverse Born expansion algorithm in this paper. It is known that a small perturbation of photon density is represented by Born expansion with respect to the perturbation of optical coefficients, which is an infinite series of integral operators having Robin function kernel. Whereas, inverse Born expansion is an implicit representation of a small perturbation of optical coefficients by an infinite series of the integral operators with respect to the photon density and its perturbation, which is appropriate series expansion for inverse DOT problem. Solving the inverse Born expansion itself and the first order approximation correspond to nonlinear and linear method, respectively. We formulated a second order approximation of the inverse Born expansion explicitly to make numerical implementation possible and showed the convergence order of the proposed method is higher than the linear method.

Kwon, Kiwoon; Kim, Beop-Min

2008-02-01

233

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

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

2010-01-01

234

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

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

2011-01-01

235

Using an modern many-particle method for the derivation of non-Markovian binary kinetic equations, we have treated theoretically the applicability of the encounter theory (ET) (the prototype of the collision theory) concepts to the widely known diffusion assisted irreversible bulk reaction A+A-->product (for example, radical reaction) in dilute solutions. The method shows that the agreement with the ET is observed when the familiar integral ET is employed which in this method is just a step in the derivation of kinetic equations. It allows for two-particle correlations only, but fails to take account of correlation of reactant simultaneously with the partner of the encounter and the reactant in the bulk. However, the next step leading to the modified ET under transformation of equations to the regular form both extends the time range of the applicability of ET rate equation (as it was for reactions proceeding with one of the reactants in excess), and gives the equation of the generalized ET. In full agreement with physical considerations, this theory reveals macroscopic correlations induced by the encounters in the reservoir of free walks. This means that the encounters of reactants in solution are correlated on a rather large time interval of the reaction. Though any nonstationary (non-Markovian) effects manifest themselves rather weakly in the kinetics of the bimolecular reaction in question, just the existence of the revealed macroscopic correlations in the binary theory is of primary importance. In particular, it means that the well-known phenomena which are generally considered to be associated solely with correlation of particles on the encounter (for example, chemically induced dynamic nuclear polarization) may be induced by correlation in the reservoir of free random walks of radicals in solution. PMID:20515095

Doktorov, Alexander B; Kipriyanov, Alexander A; Kipriyanov, Alexey A

2010-05-28

236

Rationale Second-order schedules of reinforcement have been used extensively to model reward-seeking and drug-seeking behaviour. Second-order stimuli within second-order schedules have been shown to enhance response rates during operant responding for natural reinforcers and drug reinforcers. This has led some to view second-order schedules of drug reinforcement as a model maintained of drug-seeking in addicts by drug-associated stimuli. However, the

David I. G. Wilson; E. M. Bowman

2004-01-01

237

Radical Recombination Kinetics: An Experiment in Physical Organic Chemistry.

ERIC Educational Resources Information Center

Describes a student kinetic experiment involving second order kinetics as well as displaying photochromism using a wide variety of techniques from both physical and organic chemistry. Describes measurement of (1) the rate of the recombination reaction; (2) the extinction coefficient; and (3) the ESR spectrometer signal. (Author/JN)

Pickering, Miles

1980-01-01

238

Kinetics of boehmite precipitation from supersaturated sodium aluminate solutions

This work presents the effect of the most important parameters, the precipitation temperature, the sodium hydroxide concentration and the initial seed ratio (SR) in the solution, on the boehmite precipitation from supersaturated sodium aluminate solutions. A kinetic model that describes the experimental data was developed. According to that model, boehmite precipitation follows second order reaction kinetics and has activation energy

C. Skoufadis; D. Panias; I. Paspaliaris

2003-01-01

239

Magnetic Compensation for Second-Order Doppler Shift in LITS

NASA Technical Reports Server (NTRS)

The uncertainty in the frequency of a linear-ion-trap frequency standard (LITS) can be reduced substantially by use of a very small magnetic inhomogeneity tailored to compensate for the residual second-order Doppler shift. An effect associated with the relativistic time dilatation, one cause of the second-order Doppler shift, is ion motion that is attributable to the trapping radio-frequency (RF)electromagnetic field used to trap ions. The second-order Doppler shift is reduced by using a multi-pole trap; however it is still the largest source of systematic frequency shift in the latest generation of LITSs, which are among the most stable clocks in the world. The present compensation scheme reduces the frequency instability of the affected LITS to about a tenth of its previous value. The basic principles of prior generation LITSs were discussed in several prior NASA Tech Briefs articles. Below are recapitulated only those items of basic information necessary to place the present development in context. A LITS includes a microwave local oscillator, the frequency of which is stabilized by comparison with the frequency of the ground state hyperfine transition of 199Hg+ ions. The comparison involves a combination of optical and microwave excitation and interrogation of the ions in a linear ion trap in the presence of a nominally uniform magnetic field. In the current version of the LITS, there are two connected traps (see figure): (1) a quadrupole trap wherein the optical excitation and measurement take place and (2) a 12-pole trap (denoted the resonance trap), wherein the microwave interrogation takes place. The ions are initially loaded into the quadrupole trap and are thereafter shuttled between the two traps. Shuttling ions into the resonance trap allows sensitive microwave interrogation to take place well away from loading interference. The axial magnetic field for the resonance trap is generated by an electric current in a finely wound wire coil surrounded by magnetic shields. In the quadrupole and 12-pole traps, the potentials are produced by RF voltages applied to even numbers (4 and 12, respectively) of parallel rods equally spaced around a circle. The polarity of the voltage on each rod is opposite that of the voltage on the adjacent rod. As a result, the amplitude of the RF trapping field is zero along the centerline and increases, with radius, to a maximum value near the rods.

Burt, Eric; Tjoelker, Robert

2008-01-01

240

Quadratically consistent nodal integration for second order meshfree Galerkin methods

NASA Astrophysics Data System (ADS)

Robust and efficient integration of the Galerkin weak form only at the approximation nodes for second order meshfree Galerkin methods is proposed. The starting point of the method is the Hu-Washizu variational principle. The orthogonality condition between stress and strain difference is satisfied by correcting nodal derivatives. The corrected nodal derivatives are essentially linear functions which can exactly reproduce linear strain fields. With the known area moments, the stiffness matrix resulting from these corrected nodal derivatives can be exactly evaluated using only the nodes as quadrature points. The proposed method can exactly pass the quadratic patch test and therefore is named as quadratically consistent nodal integration. In contrast, the stabilized conforming nodal integration (SCNI) which prevails in the nodal integrations for meshfree Galerkin methods fails to pass the quadratic patch test. Better accuracy, convergence, efficiency and stability than SCNI are demonstrated by several elastostatic and elastodynamic examples.

Duan, Qinglin; Wang, Bingbing; Gao, Xin; Li, Xikui

2014-08-01

241

Invariant classification of second-order conformally flat superintegrable systems

NASA Astrophysics Data System (ADS)

In this paper we continue the work of Kalnins et al in classifying all second-order conformally-superintegrable (Laplace-type) systems over conformally flat spaces, using tools from algebraic geometry and classical invariant theory. The results obtained show, through Stäckel equivalence, that the list of known nondegenerate superintegrable systems over three-dimensional conformally flat spaces is complete. In particular, a seven-dimensional manifold is determined such that each point corresponds to a conformal class of superintegrable systems. This manifold is foliated by the nonlinear action of the conformal group in three dimensions. Two systems lie in the same conformal class if and only if they lie in the same leaf of the foliation. This foliation is explicitly described using algebraic varieties formed from representations of the conformal group. The proof of these results rely heavily on Gröbner basis calculations using the computer algebra software packages Maple and Singular.

Capel, J. J.; Kress, J. M.

2014-12-01

242

Reconstructing the inflaton potential: Perturbative reconstruction to second order

One method to reconstruct the scalar field potential of inflation is a perturbative approach, where the values of the potential and its derivatives are calculated as an expansion in departures from the slow-roll approximation. They can then be expressed in terms of observable quantities, such as the square of the ratio of the gravitational wave amplitude to the density perturbation amplitude, the deviation of the spectral index from the Harrison--Zel'dovich value, etc. Here, we calculate complete expressions for the second-order contributions to the coefficients of the expansion by including for the first time corrections to the standard expressions for the perturbation spectra. As well as offering an improved result, these corrections indicate the expected accuracy of the reconstruction. Typically the corrections are only a few percent.

Copeland, Edmund J.; Kolb, Edward W.; Liddle, Andrew R.; Lidsey, James E.

1993-08-01

243

Relativistic quantum transport coefficients for second-order viscous hydrodynamics

We express the transport coefficients appearing in the second-order evolution equations for bulk viscous pressure and shear stress tensor using Bose-Einstein, Boltzmann, and Fermi-Dirac statistics for the equilibrium distribution function and Grad's 14-moment approximation as well as the method of Chapman-Enskog expansion for the non-equilibrium part. Specializing to the case of boost-invariant and transversally homogeneous longitudinal expansion of the viscous medium, we compare the results obtained using the above methods with those obtained from the exact solution of massive 0+1d Boltzmann equation in the relaxation-time approximation. We show that compared to the 14-moment approximation, the hydrodynamic transport coefficients obtained using the Chapman-Enskog method result in better agreement with the exact solution of the Boltzmann equation in relaxation-time approximation.

Florkowski, Wojciech; Maksymiuk, Ewa; Ryblewski, Radoslaw; Strickland, Michael

2015-01-01

244

Absorbing boundary conditions for second-order hyperbolic equations

NASA Technical Reports Server (NTRS)

A uniform approach to construct absorbing artificial boundary conditions for second-order linear hyperbolic equations is proposed. The nonlocal boundary condition is given by a pseudodifferential operator that annihilates travelling waves. It is obtained through the dispersion relation of the differential equation by requiring that the initial-boundary value problem admits the wave solutions travelling in one direction only. Local approximation of this global boundary condition yields an nth-order differential operator. It is shown that the best approximations must be in the canonical forms which can be factorized into first-order operators. These boundary conditions are perfectly absorbing for wave packets propagating at certain group velocities. A hierarchy of absorbing boundary conditions is derived for transonic small perturbation equations of unsteady flows. These examples illustrate that the absorbing boundary conditions are easy to derive, and the effectiveness is demonstrated by the numerical experiments.

Jiang, Hong; Wong, Yau Shu

1989-01-01

245

K-inflationary power spectra at second order

Within the class of inflationary models, k-inflation represents the most general single field framework that can be associated with an effective quadratic action for the curvature perturbations and a varying speed of sound. The incoming flow of high-precision cosmological data, such as those from the Planck satellite and small scale Cosmic Microwave Background (CMB) experiments, calls for greater accuracy in the inflationary predictions. In this work, we calculate for the first time the next-to-next-to-leading order scalar and tensor primordial power spectra in k-inflation needed in order to obtain robust constraints on the inflationary theory. The method used is the uniform approximation together with a second order expansion in the Hubble and sound flow functions. Our result is checked in various limits in which it reduces to already known situations.

Martin, Jérôme; Vennin, Vincent [Institut d'Astrophysique de Paris, UMR 7095-CNRS, Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris (France); Ringeval, Christophe, E-mail: jmartin@iap.fr, E-mail: christophe.ringeval@uclouvain.be, E-mail: vennin@iap.fr [Centre for Cosmology, Particle Physics and Phenomenology, Institute of Mathematics and Physics, Louvain University, 2 Chemin du Cyclotron, 1348 Louvain-la-Neuve (Belgium)

2013-06-01

246

Regularized orbital-optimized second-order perturbation theory

Orbital-optimized second-order perturbation theory (OOMP2) optimizes the zeroth order wave function in the presence of correlations, removing the dependence of the method on Hartree–Fock orbitals. This is particularly important for systems where mean field orbitals spin contaminate to artificially lower the zeroth order energy such as open shell molecules, highly conjugated systems, and organometallic compounds. Unfortunately, the promise of OOMP2 is hampered by the possibility of solutions being drawn into divergences, which can occur during the optimization procedure if HOMO and LUMO energies approach degeneracy. In this work, we regularize these divergences through the simple addition of a level shift parameter to the denominator of the MP2 amplitudes. We find that a large level shift parameter of 400 mE{sub h} removes divergent behavior while also improving the overall accuracy of the method for atomization energies, barrier heights, intermolecular interactions, radical stabilization energies, and metal binding energies.

Stück, David; Head-Gordon, Martin [Department of Chemistry, University of California, Berkeley, California 94720 (United States)] [Department of Chemistry, University of California, Berkeley, California 94720 (United States)

2013-12-28

247

A second-order analytic analysis for frozen orbits

NASA Technical Reports Server (NTRS)

An analytical method for studying characteristics of frozen orbits using mean orbital elements is presented. By removing some of the approximations of Brouwer and Kosai (1959) and using the method of integration by parts, an analytic solution is obtained accurate to the second order in the sense of expansion of the perturbing potential of an aspherical approximation. The solution applies to orbits at and near the critical inclination as well as to frozen orbits and, of course, to unfrozen orbits. The analysis reveals that a frozen orbit can be interpreted as an orbit in which movements of the long-periodic part of the rate of change of periapsis cancels the secular part exactly at any time.

Tang, Charles C. H.

1988-01-01

248

Second Order Optical Nonlinearities in Thermally Poled Phosphate Glasses

Second order optical nonlinearities were induced in commercial phosphate glasses (Schott, IOG-1) by the thermal poling technique. The induced {chi}{sup (2)} was measured via second harmonic generation using a fundamental beam from a 1064 nm mode-locked Nd:YAG laser. The nonlinear regions were characterized using the Maker-Fringe technique, in which the second harmonic signals were observed as a function of incident angle of the fundamental beam. The results show that the {chi}{sup (2)} profile has contributions from two distinct regions: a near-anodic surface region and a bulk. We have modeled the induced profile to fit our experimental results. The dependence of the induced nonlinearity on applied poling fields, temperatures and poling time is discussed.

Thamboon, P; Krol, D

2001-12-14

249

Absorbing boundary conditions for second-order hyperbolic equations

NASA Technical Reports Server (NTRS)

A uniform approach to construct absorbing artificial boundary conditions for second-order linear hyperbolic equations is proposed. The nonlocal boundary condition is given by a pseudodifferential operator that annihilates travelling waves. It is obtained through the dispersion relation of the differential equation by requiring that the initial-boundary value problem admits the wave solutions travelling in one direction only. Local approximation of this global boundary condition yields an nth-order differential operator. It is shown that the best approximations must be in the canonical forms which can be factorized into first-order operators. These boundary conditions are perfectly absorbing for wave packets propagating at certain group velocities. A hierarchy of absorbing boundary conditions is derived for transonic small perturbation equations of unsteady flows. These examples illustrate that the absorbing boundary conditions are easy to derive, and the effectiveness is demonstrated by the numerical experiments.

Jiang, Hong; Wong, Yau Shu

1990-01-01

250

This work studies the absorption of carbon dioxide into aqueous solutions of piperazine in a wetted wall contactor. Absorption was studied from 298 to 333K in solutions of 0.6 and 0.2M aqueous piperazine. The apparent reaction rate is first order in both carbon dioxide and piperazine with a value of 53,700m3\\/kmols at 25°C. The apparent second-order rate constant follows an

Sanjay Bishnoi; Gary T. Rochelle

2000-01-01

251

Second order closure modeling of turbulent buoyant wall plumes

NASA Technical Reports Server (NTRS)

Non-intrusive measurements of scalar and momentum transport in turbulent wall plumes, using a combined technique of laser Doppler anemometry and laser-induced fluorescence, has shown some interesting features not present in the free jet or plumes. First, buoyancy-generation of turbulence is shown to be important throughout the flow field. Combined with low-Reynolds-number turbulence and near-wall effect, this may raise the anisotropic turbulence structure beyond the prediction of eddy-viscosity models. Second, the transverse scalar fluxes do not correspond only to the mean scalar gradients, as would be expected from gradient-diffusion modeling. Third, higher-order velocity-scalar correlations which describe turbulent transport phenomena could not be predicted using simple turbulence models. A second-order closure simulation of turbulent adiabatic wall plumes, taking into account the recent progress in scalar transport, near-wall effect and buoyancy, is reported in the current study to compare with the non-intrusive measurements. In spite of the small velocity scale of the wall plumes, the results showed that low-Reynolds-number correction is not critically important to predict the adiabatic cases tested and cannot be applied beyond the maximum velocity location. The mean and turbulent velocity profiles are very closely predicted by the second-order closure models. but the scalar field is less satisfactory, with the scalar fluctuation level underpredicted. Strong intermittency of the low-Reynolds-number flow field is suspected of these discrepancies. The trends in second- and third-order velocity-scalar correlations, which describe turbulent transport phenomena, are also predicted in general, with the cross-streamwise correlations better than the streamwise one. Buoyancy terms modeling the pressure-correlation are shown to improve the prediction slightly. The effects of equilibrium time-scale ratio and boundary condition are also discussed.

Zhu, Gang; Lai, Ming-Chia; Shih, Tsan-Hsing

1992-01-01

252

WEAK GALERKIN METHODS FOR SECOND ORDER ELLIPTIC INTERFACE PROBLEMS

Weak Galerkin methods refer to general finite element methods for partial differential equations (PDEs) in which differential operators are approximated by their weak forms as distributions. Such weak forms give rise to desirable flexibilities in enforcing boundary and interface conditions. A weak Galerkin finite element method (WG-FEM) is developed in this paper for solving elliptic PDEs with discontinuous coefficients and interfaces. Theoretically, it is proved that high order numerical schemes can be designed by using the WG-FEM with polynomials of high order on each element. Extensive numerical experiments have been carried to validate the WG-FEM for solving second order elliptic interface problems. High order of convergence is numerically confirmed in both L2 and L? norms for the piecewise linear WG-FEM. Special attention is paid to solve many interface problems, in which the solution possesses a certain singularity due to the nonsmoothness of the interface. A challenge in research is to design nearly second order numerical methods that work well for problems with low regularity in the solution. The best known numerical scheme in the literature is of order O(h) to O(h1.5) for the solution itself in L? norm. It is demonstrated that the WG-FEM of the lowest order, i.e., the piecewise constant WG-FEM, is capable of delivering numerical approximations that are of order O(h1.75) to O(h2) in the L? norm for C1 or Lipschitz continuous interfaces associated with a C1 or H2 continuous solution. PMID:24072935

MU, LIN; WANG, JUNPING; WEI, GUOWEI; YE, XIU; ZHAO, SHAN

2013-01-01

253

Weak Galerkin methods for second order elliptic interface problems

NASA Astrophysics Data System (ADS)

Weak Galerkin methods refer to general finite element methods for partial differential equations (PDEs) in which differential operators are approximated by their weak forms as distributions. Such weak forms give rise to desirable flexibilities in enforcing boundary and interface conditions. A weak Galerkin finite element method (WG-FEM) is developed in this paper for solving elliptic PDEs with discontinuous coefficients and interfaces. Theoretically, it is proved that high order numerical schemes can be designed by using the WG-FEM with polynomials of high order on each element. Extensive numerical experiments have been carried out to validate the WG-FEM for solving second order elliptic interface problems. High order of convergence is numerically confirmed in both L2 and L? norms for the piecewise linear WG-FEM. Special attention is paid to solve many interface problems, in which the solution possesses a certain singularity due to the nonsmoothness of the interface. A challenge in research is to design nearly second order numerical methods that work well for problems with low regularity in the solution. The best known numerical scheme in the literature is of order O(h) to O(h1.5) for the solution itself in L? norm. It is demonstrated that the WG-FEM of the lowest order, i.e., the piecewise constant WG-FEM, is capable of delivering numerical approximations that are of order O(h1.75) to O(h2) in the L? norm for C1 or Lipschitz continuous interfaces associated with a C1 or H2 continuous solution.

Mu, Lin; Wang, Junping; Wei, Guowei; Ye, Xiu; Zhao, Shan

2013-10-01

254

WEAK GALERKIN METHODS FOR SECOND ORDER ELLIPTIC INTERFACE PROBLEMS.

Weak Galerkin methods refer to general finite element methods for partial differential equations (PDEs) in which differential operators are approximated by their weak forms as distributions. Such weak forms give rise to desirable flexibilities in enforcing boundary and interface conditions. A weak Galerkin finite element method (WG-FEM) is developed in this paper for solving elliptic PDEs with discontinuous coefficients and interfaces. Theoretically, it is proved that high order numerical schemes can be designed by using the WG-FEM with polynomials of high order on each element. Extensive numerical experiments have been carried to validate the WG-FEM for solving second order elliptic interface problems. High order of convergence is numerically confirmed in both L 2 and L ? norms for the piecewise linear WG-FEM. Special attention is paid to solve many interface problems, in which the solution possesses a certain singularity due to the nonsmoothness of the interface. A challenge in research is to design nearly second order numerical methods that work well for problems with low regularity in the solution. The best known numerical scheme in the literature is of order [Formula: see text] to [Formula: see text] for the solution itself in L ? norm. It is demonstrated that the WG-FEM of the lowest order, i.e., the piecewise constant WG-FEM, is capable of delivering numerical approximations that are of order [Formula: see text] to [Formula: see text] in the L ? norm for C (1) or Lipschitz continuous interfaces associated with a C (1) or H (2) continuous solution. PMID:24072935

Mu, Lin; Wang, Junping; Wei, Guowei; Ye, Xiu; Zhao, Shan

2013-10-01

255

Aromatic compounds such as toluene and xylene are major components of many fuels. Accurate kinetic mechanisms for the combustion of toluene are, however, incomplete, as they do not accurately model experimental results such as strain rates and ignition times and consistently underpredict conversion. Current kinetic mechanisms for toluene combustion neglect the reactions of the methylphenyl radicals, and we believe that this is responsible, in part, for the shortcomings of these models. We also demonstrate how methylphenyl radical formation is important in the combustion and pyrolysis of other alkyl-substituted aromatic compounds such as xylene and trimethylbenzene. We have studied the oxidation reactions of the methylphenyl radicals with O2 using computational ab initio and density functional theory methods. A detailed reaction submechanism is presented for the 2-methylphenyl radical + O2 system, with 16 intermediates and products. For each species, enthalpies of formation are calculated using the computational methods G3 and G3B3, with isodesmic work reactions used to minimize computational errors. Transition states are calculated at the G3B3 level, yielding high-pressure limit elementary rate constants as a function of temperature. For the barrierless methylphenyl + O2 and methylphenoxy + O association reactions, rate constants are determined from variational transition state theory. Multichannel, multifrequency quantum Rice-Ramsperger-Kassel (qRRK) theory, with master equation analysis for falloff, provides rate constants as a function of temperature and pressure from 800 to 2400 K and 1 x 10(-4) to 1 x 10(3) atm. Analysis of our results shows that the dominant pathways for reaction of the three isomeric methylphenyl radicals is formation of methyloxepinoxy radicals and subsequent ring opening to methyl-dioxo-hexadienyl radicals. The next most important reaction pathway involves formation of methylphenoxy radicals + O in a chain branching process. At lower temperatures, the formation of stabilized methylphenylperoxy radicals becomes significant. A further important reaction channel is available only to the 2-methylphenyl isomer, where 6-methylene-2,4-cyclohexadiene-1-one (ortho-quinone methide, o-QM) is produced via an intramolecular hydrogen transfer from the methyl group to the peroxy radical in 2-methylphenylperoxy, with subsequent loss of OH. The decomposition of o-QM to benzene + CO reveals a potentially important new pathway for the conversion of toluene to benzene during combustion. A number of the important products of toluene combustion proposed in this study are known to be precursors of polyaromatic hydrocarbons that are involved in soot formation. Reactions leading to the important unsaturated oxygenated intermediates identified in this study, and the further reactions of these intermediates, are not included in current aromatic oxidation mechanisms. PMID:17696501

da Silva, Gabriel; Chen, Chiung-Chu; Bozzelli, Joseph W

2007-09-01

256

Kinetic effects of nuclear reactions in deuterium gas puffs

NASA Astrophysics Data System (ADS)

Deuterium gas puffs are the largest source of laboratory neutrons producing more than 10^13 neutrons on the Z machine at Sandia National Laboratories. However, the mechanisms producing these neutrons are poorly understood. In particular, the extent of non-thermal neutron production is an important issue for determining the scalability of the results to higher currents. In this work we present the results of a computational study of the nuclear reactions in a deuterium gas puff. We investigate this by simulating the gas puff implosion using the 3D MHD GORGON code. The data is post-processed with the addition of a kinetic species to model the non-thermal neutron production. Results show that non-thermal neutron production accounts for only a small fraction of total neutron production. The number of 14.1MeV neutrons produced by secondary DT reactions is also calculated. The ratio of secondary to primary neutrons is approximately 0.0001. Finally, the shape of the neutron spectra for both thermal and non-thermal plasmas are derived theoretically and compared with the composite neutron spectra produced by the code. The results show the sensitivity of the spectra to conditions of the deuterium plasma.

Appelbe, Brian; Vickers, Simon; Chittenden, Jeremy

2010-11-01

257

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

258

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, UniversitĂ© de

259

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

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

Van Den Eijnden, Eric

260

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

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

Sparks, Donald L.

261

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

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

2001-01-01

262

Kinetics and Mechanism of Iodide Oxidation by Iron(III): A Clock Reaction Approach

ERIC Educational Resources Information Center

A simple method for studying the kinetics of a chemical reaction is described and the significance of reaction orders in deducing reaction mechanisms is demonstrated. In this student laboratory experiment, oxidation of iodide by iron(III) ions in an acidic medium is transformed into a clock reaction. By means of the initial rates method, it is…

Bauer, Jurica; Tomisic, Vladislav; Vrkljan, Petar B. A.

2008-01-01

263

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

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

Sparks, Donald L.

264

Kinetics studies provide mechanistic insight regarding the formation of dinitrosyl iron complexes (DNICs) now viewed as playing important roles in the mammalian chemical biology of the ubiquitous bioregulator nitric oxide (NO). Reactions in deaerated aqueous solutions containing FeSO4, cysteine (CysSH), and NO demonstrate that both the rates and the outcomes are markedly pH dependent. The dinuclear DNIC Fe2(?-CysS)2(NO)4, a Roussin's red salt ester (Cys-RSE), is formed at pH 5.0 as well as at lower concentrations of cysteine in neutral pH solutions. The mononuclear DNIC Fe(NO)2(CysS)2(-) (Cys-DNIC) is produced from the same three components at pH 10.0 and at higher cysteine concentrations at neutral pH. The kinetics studies suggest that both Cys-RSE and Cys-DNIC are formed via a common intermediate Fe(NO)(CysS)2(-). Cys-DNIC and Cys-RSE interconvert, and the rates of this process depend on the cysteine concentration and on the pH. Flash photolysis of the Cys-RSE formed from Fe(II)/NO/cysteine mixtures in anaerobic pH 5.0 solution led to reversible NO dissociation and a rapid, second-order back reaction with a rate constant kNO = 6.9 × 10(7) M(-1) s(-1). In contrast, photolysis of the mononuclear-DNIC species Cys-DNIC formed from Fe(II)/NO/cysteine mixtures in anaerobic pH 10.0 solution did not labilize NO but instead apparently led to release of the CysS(•) radical. These studies illustrate the complicated reaction dynamics interconnecting the DNIC species and offer a mechanistic model for the key steps leading to these non-heme iron nitrosyl complexes. PMID:25479566

Pereira, José Clayston Melo; Iretskii, Alexei V; Han, Rui-Min; Ford, Peter C

2015-01-14

265

Cr stable isotope fractionation and reaction kinetics in aqueous milieu

NASA Astrophysics Data System (ADS)

Mass-dependent stable Cr isotope variations show great potential to monitor the natural attenuation of anthropogenic chromate pollution as well as to investigate changes in environmental conditions in the present and the past. However, accurate interpretation of mass-dependent Cr isotope variations requires profound knowledge of the Cr isotope fractionation behaviour during redox transitions and the isotope exchange kinetics of the reactions involved. Here, we present a comprehensive dataset of stable Cr isotope fractionation and reaction kinetics during Cr(III) oxidation, Cr(VI) reduction and isotopic exchange between soluble Cr(III) and Cr(VI) in aqueous milieu. All experiments were carried out with both oxidation states (i.e. Cr(III) and Cr(VI)) in solution, using H2O2 as oxidising as well as reducing agent. The pH conditions were varied to investigate the influence of the different Cr(III) and Cr(VI) species on the Cr isotope fractionation and on the reaction mechanisms during the enforced redox transitions. All Cr stable isotope measurements were performed by high-resolution MC-ICP-MS [1]. The reduction of Cr(VI) to Cr(III) with H2O2 under strongly acidic conditions shows an equilibrium isotope fractionation of ?(53,52Cr)Cr(III)-Cr(VI) of -3.54 ± 0.35 ‰. This value is within uncertainty equal to that of -3.4 ± 0.1 ‰ reported by Ellis et al. [2], who used natural sediment and magnetite as reducing agents at pH 6 to 7. At pH = 7 our reduction experiments show a unidirectional, kinetic isotope fractionation ?(53,52Cr)Cr(III)-Cr(VI) of approximately -5 ‰ for reduction rates of up to 80 %, but a strong deviation from this Rayleigh-type process for higher reduction rates. However, at a pH value of 7 H2O2 supports the temporary formation and decomposition of Cr(V)-peroxo complexes that might explain this fractionation behaviour and deviation from a single Rayleigh type trend. The oxidation experiments of Cr(III) to Cr(VI) were carried out in alkaline media using H2O2 as reducing agent. The observed, small Cr isotope fractionation can not be explained by one, unidirectional oxidation process. The high energy needed to oxidise Cr(III) to Cr(VI), potential Cr(III) oligomerisation and the formation of Cr(IV) and/or Cr(V) intermediates make the oxidation of Cr(III) to Cr(VI) a very complex fractionation mechanism. Our best-fit modelling points to an overall isotope fractionation ?(53,52Cr)Cr(VI)-Cr(III) of +0.15 ‰ during the different oxidation steps, which is overprinted by a much larger isotope fractionation ?(53,52Cr)Cr(III)-Cr(VI) of -3.4 ‰ during the back reduction of approximately 15 % of the chromium. No isotope exchange between soluble Cr(VI) and Cr(III) species at pH values of 5.5 and 7 was revealed by our experiments over a timescale of 120 hours. This observation is in good agreement with the lack of isotope exchange between oxygen bound in dissolved chromate CrO42- and that of the surrounding water [3]. [1] Schoenberg, R. et al. (2008) Chemical Geology, 249, 294ff. [2] Ellis, A. et al. (2002) Science, 295, 2060ff. [3] Bullen, T. et al. (2009) Geochim. Cosmochim. Acta, 73 (13), Suppl. 1, A173

Zink, S.; Schoenberg, R.; Staubwasser, M.

2009-12-01

266

Correction of the Chromaticity up to Second Order for MEIC

The proposed electron collider lattice exhibits low ?- functions at the Interaction Point (IP) (?x?100mm ? ?y? 20 mm) and rather large equilibrium momentum spread of the collider ring (?p/p = 0.00158). Both features make the chromatic corrections of paramount importance. Here the chromatic effects of the final focus quadruples are cor- rected both locally and globally. Local correction features symmetric sextupole families around the IP, the betatron phase advances from the IP to the sextupoles are chosen to eliminate the second order chromatic aberration. Global interleaved families of sextupoles are placed in the figure-8 arc sections, and non-interleaved families at straight sec- tion making use of the freely propagated dispersion wave from the arcs. This strategy minimizes the required sex- tupole strength and eventually leads to larger dynamic aper- ture of the collider. The resulting spherical aberrations induced by the sextupoles are mitigated by design; the straight and arc sections optics features an inverse identity transformation between sextupoles in each pair.

H. K. Sayed, S.A. Bogacz, P. Chevtsov

2010-03-01

267

Kinetics of Ethyl Acetate Synthesis Catalyzed by Acidic Resins

ERIC Educational Resources Information Center

A low-cost experiment to carry out the second-order reversible reaction of acetic acid esterification with ethanol to produce ethyl acetate is presented to illustrate concepts of kinetics and reactor modeling. The reaction is performed in a batch reactor, and the acetic acid concentration is measured by acid-base titration versus time. The…

Antunes, Bruno M.; Cardoso, Simao P.; Silva, Carlos M.; Portugal, Ines

2011-01-01

268

Kinetic Studies of the Solvolysis of Two Organic Halides

ERIC Educational Resources Information Center

Describes an undergraduate organic chemistry laboratory experiment which utilizes the solvolysis of organic halides to demonstrate first and second order reaction kinetics. The experiment also investigates the effect of a change of solvent polarity on reaction rate, common-ion and noncommon-ion salt effects, and the activation parameters of a…

Duncan, J. A.; Pasto, D. J.

1975-01-01

269

Ab initio study of the kinetics of hydrogen abstraction reactions on toluene and tetralin

Hydrogen abstraction reactions play a key role in many thermal and catalytic processes involved in the production of fuels and chemicals. In this paper, the reaction barriers and rate constants for the hydrogen abstraction reactions on toluene and tetralin by the benzyl radical are calculated by ab initio methods. These reactions are representatives of similar reactions occurring in the thermolysis of lignin model compounds containing the phenethyl phenyl ether (PPE) structural moiety. Thermolysis of PPE occurs by a free radical chain mechanism in which the product selectivity arises from competitive hydrogen abstraction at the benzylic and nonbenzylic methylen sites by chain carrying benzyl and phenoxyl radicals. The title reactions serve to calibrate the theoretical methods to be used in the study of PPE through comparison of the rate constants and the reaction enthalpies with reliable experimental values. In this study, we used two different hybrid density functionals (BHandHLYP, B3LYP) and second-order perturbation theory to obtain equilibrium and transition state geometries. Multiple transition states were found for both reactions. BHandHLYP underestimates and second-order perturbation theory overestimates the reaction barriers; B3LYP energy barriers agree well with experiment. Absolute and relative rate constants were calculated using transition state theory. We found that the relative rate constant using the B3LYP functional agrees within a factor of 2.0 with experiment at the experimental temperature of 333 K, indicating that the B3LYP functional will be successful in predicting relative rate constants for hydrogen abstraction reactions participating in the pyrolysis of PPE.

Beste, Ariana [ORNL; Britt, Phillip F [ORNL; Buchanan III, A C [ORNL; Harrison, Robert J [ORNL; Hathorn, Bryan C [ORNL

2008-01-01

270

Kinetics of exciplex formation/dissipation in reaction following Weller Scheme II

Creation of exciplexes from the charged products of photoionization is considered by means of Integral Encounter Theory. The general kinetic equations of such a reaction following the Weller scheme II are developed. The special attention is given to the particular case of irreversible remote ionization of primary excited electron donor. Kinetics of exciplex formation is considered at fast biexponential geminate transformation of exciplexes in cage that gives way to subsequent bulk reaction of equilibrated reaction products controlled by power law recombination of ions. It is shown that the initial geminate stage of exciplex kinetics is observed only in diffusion controlled regime of the reaction and disappears with increasing mobility of ions in passing to kinetic regime. The quantum yield of exciplexes is studied along with their kinetics.

Fedorenko, S. G. [Voevodsky Institute of Chemical Kinetics and Combustion, Novosibirsk (Russian Federation); Burshtein, A. I. [Weizmann Institute of Science, 76100, Rehovot (Israel)

2014-09-21

271

Kinetics of exciplex formation/dissipation in reaction following Weller Scheme II

NASA Astrophysics Data System (ADS)

Creation of exciplexes from the charged products of photoionization is considered by means of Integral Encounter Theory. The general kinetic equations of such a reaction following the Weller scheme II are developed. The special attention is given to the particular case of irreversible remote ionization of primary excited electron donor. Kinetics of exciplex formation is considered at fast biexponential geminate transformation of exciplexes in cage that gives way to subsequent bulk reaction of equilibrated reaction products controlled by power law recombination of ions. It is shown that the initial geminate stage of exciplex kinetics is observed only in diffusion controlled regime of the reaction and disappears with increasing mobility of ions in passing to kinetic regime. The quantum yield of exciplexes is studied along with their kinetics.

Fedorenko, S. G.; Burshtein, A. I.

2014-09-01

272

Further development and testing of a second-order bulk boundary layer model. Master's thesis

A one-layer bulk boundary layer model is developed. The model predicts the mixed layer values of the potential temperature, mixing ratio, and u- and v-momentum. The model also predicts the depth of the boundary layer and the vertically integrated turbulence kinetic energy (TKE). The TKE is determined using a second-order closure that relates the rate of dissipation to the TKE. The fractional area covered by rising motion sigma and the entrainment rate (E) are diagnostically determined. The model is used to study the clear convective boundary layer (CBL) using data from the Wangara, Australia boundary layer experiment. The Wangara data is also used as an observation base to validate model results. A further study is accomplished by simulating the planetary boundary layer (PBL) over an ocean surface. This study is designed to find the steady-state solutions of the prognostic variable.

Krasner, R.D.

1993-05-03

273

Fluctuating reaction rate and non-exponential blinking statistics in single-enzyme kinetics

NASA Astrophysics Data System (ADS)

Extending the Michaelis-Menten kinetic scheme, we consider a three-state diffusion-controlled reaction model to investigate the effects of fluctuating reaction rate on the blinking statistics of single-enzyme catalytic reactions. As a result of conformational changes, the barrier-height and the reaction rate for the bottleneck enzymatic reaction could fluctuate in time, leading to non-exponential blinking statistics. To illustrate model applications, some reported experimental data for single ?-galactosidase molecules were reanalyzed here to extract useful kinetic parameters.

Tang, Jau; Yeh, Yi-Cheun; Tai, Po-Tse

2008-09-01

274

H-Atom Reaction Kinetics in Solid Parahydrogen Followed by Rapid Scan FTIR

NASA Astrophysics Data System (ADS)

Reactions of migrating H-atoms in parahydrogen (pH2) matrices with trapped molecular species provide a relatively unexplored yet well-established experimental method to study the kinetics and mechanisms of atom tunneling reactions in the 1.5 to 5 K temperature range. My group has now completed a series of experimental studies on the kinetics of reactions of H-atoms with HCOOH, CH3OH, and N2O which all show a pronounced inverse temperature dependence over this small temperature range. Conversely, the analogous H-atom reaction with NO displays a more standard Arrhenius behavior. In this talk, I will present a brief summary of these results with the objective of developing a predictive understanding of the kinetics of these H-atom tunneling reactions. I will also emphasize the advantages of following the kinetics using rapid scan FTIR. Fredrick M. Mutunga, Shelby E. Follett, and David T. Anderson, J. Chem. Phys. 139, 151104 (2013).

Anderson, David T.

2014-06-01

275

ENZO: A Web Tool for Derivation and Evaluation of Kinetic Models of Enzyme Catalyzed Reactions

We describe a web tool ENZO (Enzyme Kinetics), a graphical interface for building kinetic models of enzyme catalyzed reactions. ENZO automatically generates the corresponding differential equations from a stipulated enzyme reaction scheme. These differential equations are processed by a numerical solver and a regression algorithm which fits the coefficients of differential equations to experimentally observed time course curves. ENZO allows rapid evaluation of rival reaction schemes and can be used for routine tests in enzyme kinetics. It is freely available as a web tool, at http://enzo.cmm.ki.si. PMID:21818304

Bevc, Staš; Konc, Janez; Stojan, Jure; Hodoš?ek, Milan; Penca, Matej; Praprotnik, Matej; Janeži?, Dušanka

2011-01-01

276

A Pore Scale Evaluation of the Kinetics of Mineral Dissolution and Precipitation Reactions (EMSI)

The chief goals for CEKA are to (1) collect and synthesize molecular-level kinetic data into a coherent framework that can be used to predict time evolution of environmental processes over a range of temporal and spatial scales; (2) train a cohort of talented and diverse students to work on kinetic problems at multiple scales; (3) develop and promote the use of new experimental techniques in environmental kinetics; (4) develop and promote the use of new modeling tools to conceptualize reaction kinetics in environmental systems; and (5) communicate our understanding of issues related to environmental kinetics and issues of scale to the broader scientific community and to the public.

Steefel, Carl I.

2006-06-01

277

The kinetics of the hydrogen abstraction at alkanes by formyl radicals is investigated using the reaction class transition\\u000a state theory (RC-TST) approach combined with the linear energy relationship (LER) or the barrier height grouping (BHG). The\\u000a rate constants of a reaction in this class can be estimated through those of the reference reaction, CHO + C2H6, which are obtained from

Lam K. Huynh; Thanh N. Truong

2008-01-01

278

NSDL National Science Digital Library

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

Nurrenbern, Susan C.

279

NASA Astrophysics Data System (ADS)

Tetracoordinated organophosphorous compounds were synthesized, characterized and nucleophilic substitution reaction were investigated by varying substituents around phosphorous centre or in nucleophile considering its utility in biological and environmental system. The reactivity is expressed in terms of second-order rate constant, k2 and measured conductometrically. Linear Free Energy Relationship (LFER) tools mainly Hammett (?), Brönsted (?) LFER coefficients and deuterium kinetic isotope effects (KIEs) being determined for the pyridinolysis of 4 - chlorophenyl 4 - methoxy phenyl chlorophosphate, 1 in acetonitrile at 5.0 °C. The experimental data's were compared with those of structurally similar organophosphorous compounds reported earlier in quest for the mechanistic information. Nice linear correlation being found for Hammett (logk2 vs ?x), having negative value of the ?X = -5.85 and Brönsted (logk2 vs pKa(x)) plots having large positive value for ?X = 1.18 for 1 can be interpreted as SN2 process with greater extent of bond formation in transition state (TS) of 1. The observed kH/kD values of 1 is 1.00 ± 0.05 and net KIE, 1.32 suggests the primary KIE and indicates frontside nucleophilic attack through the partial deprotonation of pyridine occurs by the hydrogen bonding in the rate-determining step.

Lumbiny, B. J.; Hui, Z.; Islam, M. A.; Quader, M. A.; Rahman, M.

2014-04-01

280

GRAVITY ERROR COMPENSATION USING SECOND-ORDER GAUSS-MARKOV PROCESSES

AAS 11-502 GRAVITY ERROR COMPENSATION USING SECOND-ORDER GAUSS-MARKOV PROCESSES Jason M. Leonard the use of a second-order Gauss-Markov process to compensate for higher order spherical harmonic gravity an improvement in POD through the use of a second-order Gauss-Markov process (GMP2) for modeling J3 gravity

Born, George

281

Research projects discussed include: the branching ratio for abstraction vs. exchange in the reaction D + HCl; kinetics of O + H/sub 2/; energy storage in polyatomic molecules; and optoacoustic measurements of ir absorption and relaxation in large molecules. (GHT)

Gordon, R J

1982-08-02

282

1 Chlorine Transfer Reactions between Chloramine and 1- Piperidine: Kinetic Reactivity-piperidine in a Raschig medium (8 of the two reactants. The influence of the pH on the interaction chloramine/piperidine was examined at a p

Boyer, Edmond

283

Kinetics and thermodynamics of chemical reactions in Li/SOCl2 cells

NASA Technical Reports Server (NTRS)

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

Hansen, Lee D.; Frank, Harvey

1987-01-01

284

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

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

2010-01-22

285

Model for reaction kinetics in pyrolysis of wood

A reaction model for the pyrolysis of small and large particles of wood Is developed. The chemical reactions that take place when biomass is pyrolyzed are the devolatilization reactions (primary) and due to the vapour-solid interactions (secondary). In the case of small particles, when the volatiles are immediately removed by the purge gas, only primary reactions occur and the reaction model is described by weight loss and char forming reactions. The of heterogeneous secondary reactions occur in the case of large particles due to the interaction between the volatiles and the hot nascent primary char. A chain reaction mechanism of secondary char formation is proposed. The model takes both the volatiles retention time and cracking and repolymerization reactions of the vapours with the decomposing solid as well as autocatalysis into consideration. 7 refs., 3 figs., 2 tabs.

Ahuja, P.; Singh, P.C.; Upadhyay, S.N.; Kumar, S. [Banaras Hindu Univ., Varanasi (India)

1996-12-31

286

Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels

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

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

2011-01-01

287

Utilization of the Recycle Reactor in Determining Kinetics of Gas-Solid Catalytic Reactions.

ERIC Educational Resources Information Center

Describes a laboratory scale reactor that determines the kinetics of a gas-solid catalytic reaction. The external recycle reactor construction is detailed with accompanying diagrams. Experimental details, application of the reactor to CO oxidation kinetics, interphase gradients, and intraphase gradients are discussed. (CS)

Paspek, Stephen C.; And Others

1980-01-01

288

The thermodynamic and kinetic modeling of char reduction reactions in a downdraft (biomass) gasifier has been presented. Mass and energy balance are coupled with equilibrium relations or kinetic rate parameters (using varying char reactivity factor) in order to predict status of un-converted char in addition to gas composition, calorific value, conversion efficiency, exit gas temperature, endothermic heat absorption rate and

Avdhesh Kr. Sharma

2008-01-01

289

ERIC Educational Resources Information Center

An undergraduate kinetic experiment of the thermal decomposition of solids by microscopic observation and thermal analysis was developed by investigating a suitable reaction, applicable techniques of thermal analysis and microscopic observation, and a reliable kinetic calculation method. The thermal decomposition of sodium hydrogen carbonate is…

Koga, Nobuyoshi; Goshi, Yuri; Yoshikawa, Masahiro; Tatsuoka, Tomoyuki

2014-01-01

290

A kinetic investigation of the reaction of dibutyl sodiophosphonate with n-butyl bromide

of Texn~ in partial fulfillment of the requirements for the de ree of MASTER OF SCIENCE August 1955 Major Subject: Chemistry A KINETIC INVESTIGATION OF THE REACTION OF DIBUTYL SODIOPHOSPHONATE WITH N-BUTYL BROMIDE A Thesis By James Howard Shaffer..., Although the reaction has been employed often for synthetic purposes, we have been unable to find any litera- ture reference to a kinetic study of the reaction, Believ- ing that the synthetic utility of the reaction would be enhanced by such knowled e...

Shaffer, James Howard

1955-01-01

291

Reaction kinetics of isomerization of n-butenes to isobutylene

A study was made of kinetics of skeletal isomerization of n-butenes to isobutylene at 350-425/sup 0/C and normal pressure on alumina, modified using carbon tetrachloride. A kinetic model was developed for isomerization, the process being carried out continuously, bearing in mind the variable activity of the catalyst. Calculations based on the kinetic model indicate that with a conventional contact time of 3.358 g.hr/mole stable conversion of n-butenes (33-35%) is carried out in 15 hr with the continuous use of the catalyst. Calculated results show satisfactory agreement with experimental ones.

Smirnova, I.M.; Fel'dblyum, V.S.; Tsailingol'd, T.A.

1981-01-01

292

Polyester acrylate inorganic\\/organic hybrids were prepared using a sol–gel precursor, coupling agent, and reactive diluent. The hybrids were cured via a UV-free radical initiator. Design of experiments (DOE) was utilized to investigate reaction kinetics and complex variable interactions. The effects of the silicate groups on the free radical photo-curing reaction kinetics were investigated utilizing a time-resolved Fourier transform infrared (FT–IR)

Ahmet Nebioglu; Mark D. Soucek

2007-01-01

293

Determination of Reaction Kinetics for a Two-Part Epoxy Adhesive

NSDL National Science Digital Library

In this exercise, you will use Fourier transform infrared spectroscopy (FTIR) to determine the reaction kinetics for a two-part polymer system. After in-class presentation, completion of hands-on laboratory experiment and review of the information provided, you should: • Be able to communicate effectively about the synthesis and mechanism for condensation polymerizations. • Be familiar with FTIR methods for determining the reaction kinetics for a 2-part polymer.

DeRosa, Rebecca L.

2008-09-26

294

Low energy ion-molecule reactions and chemiionization kinetics

NASA Astrophysics Data System (ADS)

Work over the past 3 years was directed toward the dynamics of elementary gas phase proton transfer reactions, particularly those of the O(sup -) ion. Such reactions are important in flames. Published work over the past 30 months was concerned with dynamics of reactions of O(sup -) with H2O, NH3, and HF. Results are enumerated here.

Farrar, James M.

1993-07-01

295

Second Order Catalytic Quasispecies Yields Discontinuous Mean Fitness at Error Threshold

NASA Astrophysics Data System (ADS)

The quasispecies model describes processes related to the origin of life and viral evolutionary dynamics. We discuss how the error catastrophe that reflects the transition from localized to delocalized quasispecies population is affected by catalytic replication of different reaction orders. Specifically, we find that second order mechanisms lead to a discontinuity in the mean fitness of the population at the error threshold. This is in contrast to the behavior of the first order, autocatalytic replication mechanism considered in the standard quasispecies model. This suggests that quasispecies models with higher order replication mechanisms produce discontinuities in the mean fitness, and hence the viable population fraction as well, at the error threshold, while lower order replication mechanisms yield a continuous mean fitness function. We discuss potential implications for understanding replication in the RNA world and in virology.

Wagner, Nathaniel; Tannenbaum, Emmanuel; Ashkenasy, Gonen

2010-05-01

296

The results from a kinetic investigation of a Cu-catalyzed oxidative coupling reaction between N-phenyl tetrahydroisoquinoline and a silyl enol ether using elemental oxygen as oxidant are presented. By using reaction progress kinetic analysis as an evaluation method for the obtained data, we discovered information regarding the reaction order of the substrates and catalysts. Based on this information and some additional experiments, a refined model for the initial oxidative activation of the amine substrate and the activation of the nucleophile by the catalyst was developed. The mechanistic information also helped to understand why silyl nucleophiles have previously failed in a related Cu-catalyzed reaction using tert-butyl hydroperoxide as oxidant and how to overcome this limitation. PMID:25203932

Scott, Martin; Sud, Abhishek; Boess, Esther; Klussmann, Martin

2014-12-19

297

Kinetics of liquid-solid reactions in naphthenic acid conversion and Kraft pulping

NASA Astrophysics Data System (ADS)

Two liquid-solid reactions, in which the morphology of the solid changes as the reactions proceeds, were examined. One is the NA conversion in oil by decarboxylation on metal oxides and carbonates, and the other is the Kraft pulping in which lignin removal by delignification reaction. In the study of the NA conversion, CaO was chosen as the catalyst for the kinetic study from the tested catalysts based on NA conversion. Two reaction mixtures, carrier oil plus commercial naphthenic acids and heavy vacuum gas oil (HVGO) from Athabasca bitumen, were applied in the kinetic study. The influence of TAN, temperature, and catalyst loading on the NA conversion and decarboxylation were studied systematically. The results showed that the removal rate of TAN and the decarboxylation of NA were both independent of the concentration of NA over the range studied, and significantly dependent on reaction temperature. The data from analyzing the spent catalyst demonstrated that calcium naphthenate was an intermediate of the decarboxylation reaction of NA, and the decomposition of calcium naphthenate was a rate-determining step. In the study on the delignification of the Kraft pulping, a new mechanism was proposed for the heterogeneous delignification reaction during the Kraft pulping process. In particular, the chemical reaction mechanism took into account the heterogeneous nature of Kraft pulping. Lignin reacted in parallel with sodium hydroxide and sodium sulfide. The mechanism consists of three key kinetic steps: (1) adsorption of hydroxide and hydrosulfide ions on lignin; (2) surface reaction on the solid surface to produce degraded lignin products; and (3) desorption of degradation products from the solid surface. The most important step for the delignification process is the surface reaction, rather than the reactions occurring in the liquid phase. A kinetic model has, thus, been developed based on the proposed mechanism. The derived kinetic model showed that the mechanism could be employed to predict the pulping behavior under a variety of conditions with good accuracy.

Yang, Ling

298

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

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

2008-01-01

299

Detailed Chemical Kinetic Reaction Mechanisms for Combustion of Isomers of Heptane

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

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

2001-01-01

300

Kinetic and infrared spectroscopic studies of ionic reactions of interest to various plasma media

A selected ion flow tube (SIFT) and a Flowing Afterglow (FA) with extensive spectroscopic facilities were used in the kinetic and dynamic studies of gas phase reactions between ions, electrons, and neutral atoms and molecules. Along with the interest, these reactions have importance in planetary atmospheres, interstellar gas clouds, circumstellar shells, comets, laser plasmas, combustion flames, and etchant plasmas. SIFT

Ted Lee Williams

1999-01-01

301

Accelerated Search Kinetics Mediated by Redox Reactions of DNA Repair Enzymes

Accelerated Search Kinetics Mediated by Redox Reactions of DNA Repair Enzymes Pak-Wing Fok and Tom to explain the localization of base excision repair (BER) enzymes to lesions on DNA. The CT mechanism relies on redox reactions of iron-sulfur cofactors that modify the enzyme's binding affinity. These redox

Chou, Tom

302

Kinetics of thermal regeneration reaction of activated carbons used in waste water treatment

The kinetics of the thermal regeneration of activated carbons used in the waste water treatment was analyzed on the basis of a model that the regeneration reaction consists of a set of many first-order reactions each of which has different activation energy and frequency factor. The frequency factors were correlated approximately by a function of the activation energy. The difference

Kenji Hashimoto; Kouichi Miura; Tsuneo Watanabe

1982-01-01

303

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

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

2010-01-01

304

Paper Number 15736-PA Title Reaction Kinetics of Fuel Formation for In-Situ Combustion

Paper Number 15736-PA Title Reaction Kinetics of Fuel Formation for In-Situ Combustion Authors Abu believed to cause fuel formation for in-situ combustion have been studied and modeled. A thin, packed bed the approach of a combustion front. Analysis of gases produced from the reaction cell revealed that pyrolysis

Abu-Khamsin, Sidqi

305

Oxygen reduction reaction kinetics and mechanism on platinum nanoparticles inside Nafion ®

The aim of this work is to study kinetic parameters and the mechanism of the oxygen reduction reaction (orr) on platinum nanoparticles supported on carbon, inside Nafion® (i.e. in PEMFC cathode conditions). Stationary and electrochemical impedance spectroscopy techniques were used to measure exchange current densities, Tafel slopes, and reaction orders with respect to O2 pressure and H+ activity. The platinum

Olivier Antoine; Yann Bultel; Robert Durand

2001-01-01

306

The reaction mechanisms and kinetics describing the formation and surface decomposition of lithium metazirconate pellets (Li2ZrO3) have been investigated during Li2ZrO3 formation via solid-state reaction. Samples were analysed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A metastable tetragonal Li2ZrO3 phase was synthesised at low temperatures, recrystallizing into a monoclinic structure when the temperature was increased above 800 °C.

Heriberto Pfeiffer; Kevin M. Knowles

2004-01-01

307

Comparison of kinetic and equilibrium reaction models insimulating the behavior of porous media

In this study we compare the use of kinetic and equilibriumreaction models in the simulation of gas (methane) hydrate behavior inporous media. Our objective is to evaluate through numerical simulationthe importance of employing kinetic versus equilibrium reaction modelsfor predicting the response of hydrate-bearing systems to externalstimuli, such as changes in pressure and temperature. Specifically, we(1) analyze and compare the responses simulated using both reactionmodels for natural gas production from hydrates in various settings andfor the case of depressurization in a hydrate-bearing core duringextraction; and (2) examine the sensitivity to factors such as initialhydrate saturation, hydrate reaction surface area, and numericaldiscretization. We find that for large-scale systems undergoing thermalstimulation and depressurization, the calculated responses for bothreaction models are remarkably similar, though some differences areobserved at early times. However, for modeling short-term processes, suchas the rapid recovery of a hydrate-bearing core, kinetic limitations canbe important, and neglecting them may lead to significantunder-prediction of recoverable hydrate. Assuming validity of the mostaccurate kinetic reaction model that is currently available, the use ofthe equilibrium reaction model often appears to be justified andpreferred for simulating the behavior of gas hydrates, given that thecomputational demands for the kinetic reaction model far exceed those forthe equilibrium reaction model.

Kowalsky, Michael B.; Moridis, George J.

2006-11-29

308

Kinetic and mechanistic studies of free-radical reactions in combustion

Combustion is driven by energy-releasing chemical reactions. Free radicals that participate in chain reactions carry the combustion process from reactants to products. Research in chemical kinetics enables us to understand the microscopic mechanisms involved in individual chemical reactions as well as to determine the rates at which they proceed. Both types of information are required for an understanding of how flames burn, why engines knock, how to minimize the production of pollutants, and many other important questions in combustion. In this program the authors emphasize accurate measurements over wide temperature ranges of the rates at which ubiquitous free radicals react with stable molecules. The authors investigate a variety of OH, CN, and CH + stable molecule reactions important to fuel conversion, emphasizing application of the extraordinarily precise technique of laser photolysis/continuous-wave laser-induced fluorescence (LP/cwLIF). This precision enables kinetic measurements to serve as mechanistic probes. Since considerable effort is required to study each individual reaction, prudent selection is critical. Two factors encourage selection of a specific reaction: (1) the rates and mechanisms of the subject reaction are required input to a combustion model; and (2) the reaction is a chemical prototype which, upon characterization, will provide fundamental insight into chemical reactivity, facilitate estimation of kinetic parameters for similar reactions, and constrain and test the computational limits of reaction-rate theory. Most studies performed in this project satisfy both conditions.

Tully, F.P. [Sandia National Laboratories, Livermore, CA (United States)

1993-12-01

309

Graphene liquid marbles as photothermal miniature reactors for reaction kinetics modulation.

We demonstrate the fabrication of graphene liquid marbles as photothermal miniature reactors with precise temperature control for reaction kinetics modulation. Graphene liquid marbles show rapid and highly reproducible photothermal behavior while maintaining their excellent mechanical robustness. By tuning the applied laser power, swift regulation of graphene liquid marble's surface temperature between 21-135?°C and its encapsulated water temperature between 21-74?°C are demonstrated. The temperature regulation modulates the reaction kinetics in our graphene liquid marble, achieving a 12-fold superior reaction rate constant for methylene blue degradation than at room temperature. PMID:25650763

Gao, Wei; Lee, Hiang Kwee; Hobley, Jonathan; Liu, Tianxi; Phang, In Yee; Ling, Xing Yi

2015-03-23

310

Kinetic and products of the BrO+CH 3SH reaction: temperature and pressure dependence

The kinetics and the mechanism of the reaction BrO+CH3SH?P (1) have been studied using the mass spectrometric discharge-flow method over the temperature range 259–333 K and at low total pressure between 0.5 and 3 Torr. The temperature dependence of the reaction rate constant has been determined under pseudo-first-order kinetic conditions in excess of CH3SH over BrO radicals, k=(2.2±1.9)×10?15exp[(827±255)\\/T]cm3molecule?1s?1. The reaction

Alfonso Aranda; Yolanda D??az de Mera; Diana Rodr??guez; Sagrario Salgado; Ernesto Mart??nez

2002-01-01

311

General theory of multistage geminate reactions of isolated pairs of reactants. I. Kinetic equations

General matrix approach to the consideration of multistage geminate reactions of isolated pairs of reactants depending on reactant mobility is formulated on the basis of the concept of “effective” particles. Various elementary reactions (stages of multistage reaction including physicochemical processes of internal quantum state changes) proceeding with the participation of isolated pairs of reactants (or isolated reactants) are taken into account. Investigation has been made in terms of kinetic approach implying the derivation of general (matrix) kinetic equations for local and mean probabilities of finding any of the reaction species in the sample under study (or for local and mean concentrations). The recipes for the calculation of kinetic coefficients of the equations for mean quantities in terms of relative coordinates of reactants have been formulated in the general case of inhomogeneous reacting systems. Important specific case of homogeneous reacting systems is considered.

Doktorov, Alexander B.; Kipriyanov, Alexey A. [Voevodsky Institute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Sciences, Novosibirsk State University, Novosibirsk 630090 (Russian Federation)] [Voevodsky Institute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Sciences, Novosibirsk State University, Novosibirsk 630090 (Russian Federation)

2014-05-14

312

Kinetics of sulfur and nitrogen reactions in combustion systems

This volume is the second of a three volume set. Specifically, the activities reported herein cover investigations of the reactivity of sorbent materials toward SOâ. For the most part this focuses on the furnace injection of calcium-based sorbents, although some work also considers post-furnace injection and the use of alternative sorbents. Work is described in the following sections. Reactivity kinetics

J. C. Kramlich; W. R. Seeker; A. F. Sarofim; J. T. Longwell; D. Ham; G. A. Simons

1989-01-01

313

Enzymatic Reactions in Microfluidic Devices: Michaelis-Menten Kinetics

in biochemistry, medicine, food science, and biochemical engineering. Many enzymatic reactions are characterized with a series of experiments at different sub- strate concentrations in a well-mixed container. Here we, and product. In a well-mixed system, the initial rate of product formation (i.e., the reaction "velocity

Bou-Zeid, Elie

314

Kinetics of a Substitution Reaction of Sulfitopentaaminecobalt(III).

ERIC Educational Resources Information Center

Describes a laboratory experiment to determine the rate law for a substitution reaction of a transition metal. Derives the corresponding rate law from the accepted mechanism for the reaction using the steady state approximation and determines the conditions under which the two agree. (CW)

Richards, Lynne

1988-01-01

315

Modulation of the Bulk Structure and Second-Order Statistical Properties of Ekman Layers by Buoyancy

NASA Astrophysics Data System (ADS)

Parameterization of turbulence in the atmospheric boundary layers (ABL), where buoyant forces enhance or destroy turbulent kinetic energy (TKE), remains a challenging and very important problem in geophysical fluid dynamics. In order to understand the difficulties associated with understanding and modeling ABL turbulence, especially under stable conditions, this dissertation presents an in-depth analysis of changes in the bulk structure and second order statistical properties due to buoyancy, using new-generation numerical techniques for solving the fundamental equations that include direct and large-eddy simulations. Using direct numerical simulations, changes in the mean profiles and second-order statistics due to variation in imposed surface temperature are examined. The mechanisms through which buoyancy affects turbulence and the flow are identified as primarily being related to the damping of turbulence production, rather than to direct destruction by buoyancy. Budget analyses that are crucial for researchers aiming to understand stably-stratified shear flows, and to develop higher-order closure models are performed. The results obtained shed light on what terms in the budgets are negligible and how to model the remaining important terms. Very strong stability is shown to result in global intermittency in the turbulence fields. Although this intermittency lacks simple mechanistic explanation, a method for parameterization of the duration over which these intermittent patches are seen is proposed using simple dynamical systems analysis. Subsequently, large-eddy simulations are used to explore buoyancy modulation of large scale structures that carry TKE and fluxes in the ABL. The largest eddies are found to consist of streamwise rolls with similarities to the very large scale structures reported in wind tunnel studies. These rolls however are strongly modulated by buoyancy: they are intensified under unstable conditions and weakened, sometimes completely damped, by stable conditions. Finally, simulations with heterogeneities in surface properties affecting the real world ABL dynamics are carried out with a special emphasis on the implications for the 1.5-order turbulence closures in coarse atmospheric models. Advection is shown to become a critical term in the turbulence kinetic energy budget, and unexpected impacts on the bulk flow are identified.

Shah, Stimit

316

Atmospheric chemistry: Laboratory studies of kinetics of important reactions

NASA Astrophysics Data System (ADS)

Experiments to measure the rate constants for some reactions of the atmospherically important nitrate radical (NO3) are described using the discharge-flow technique. The nitrate radical was monitored by optical absorption at lambda = 662 nm. The reactions of NO3 with some stable organic and inorganic substrates are reported. The temperature dependences of some of the rate constants were also determined (298 less than T less than 523 K). In most cases, computer simulation was used to extract the rate constant for the primary process because the time-dependent behavior of (NO3) was affected by secondary reactions of NO3 with products of the primary interaction. The Arrhenius parameter for the reactions of NO3 with CH3CH3, CH2CH2, CH3OH, CHCl3, and HCl were determined. The activation energies for the reactions studied between NO3 and some alkynes are presented along with the corresponding pre-exponential factors. Some reactions were studied at room temperature (298 plus or minus 2 K) only and the rate constants found (in units of cubic cm/molecule sec) are: buta-1,3-diene (1.8 x 10 (exp -13), isobutene (2.8 x 10 (exp -13), HBr (1.3 x 10 (exp -15) and hex-2-yne (3.0 x 10 (exp -14). Non-Arrhenius behavior was found in the reactions of NO3 with n-butane, isobutane and propene. The empirical variation of these rate constants with temperature is presented. The curvature of the Arrhenius plots is discussed in terms of (1) a temperature-dependent pre-exponential factor, and (2) the possibility that two competing channels, possessing differing activation energies, exist for each reaction. The atmospheric implications of these reactions are discussed with reference to the nighttime production of nitric acid and the importance of the these reactions as loss processes for NO3.

Smith, S. J.

317

The reaction kinetics of the oxygen carrier particles, which are used as bed material for a fluidized bed chemical looping\\u000a combustor (CLC), has been studied experimentally by a conventional thermal gravimetrical analysis technique. The weight percent of nickel\\u000a and nickel oxide in oxygen carrier particles and reaction temperature were considered as experimental variables. After oxidation\\u000a reaction, the pure nickel particle

Ho-Jung Ryu; Dal-Hee Bae; Keun-Hee Han; Seung-Yong Lee; Gyoung-Tae Jin; Jeong-Hoo Choi

2001-01-01

318

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

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

Albert, Réka

319

Kinetic parameters of the reaction of phenols with epichlorohydrin

The reaction of phenol, ..cap alpha..-naphthol, and hydroquinone with epichlorohydrin in the presence of catalytic amounts of (C/sub 2/H/sub 5/)/sub 3/N. C/sub 4/H/sub 9/OH in excess epichlorohydrin were investigated. It was established that under these conditions 3-chloro-2-oxypropyl esters of the phenols studied are formed. It was found that the reaction is first order with respect to the catalyst and with respect to the phenol component. The rate constants and activation energies of the reactions were determined.

Ragimov, A.V.; Ismailova, C.O.; Mamedov, B.A.; Seiidov, M.A.

1985-07-01

320

Towards the ultimate conservative difference scheme. V - A second-order sequel to Godunov's method

A method of second-order accuracy is described for integrating the equations of ideal compressible flow. The method is based on the integral conservation laws and is dissipative, so that it can be used across shocks. The heart of the method is a one-dimensional Lagrangean scheme that may be regarded as a second-order sequel to Godunov's method. The second-order accuracy is

B. van Leer

1979-01-01

321

Constrained Second-Order Recurrent Networks for Finite-State Automata Induction

This paper presents an improved training algorithm for second-order dynamicalrecurrent networks applied to the problem of finite-state automata(FSA) induction. Second-order networks allow for a natural encodingof finite-state automata in which each second-order connectionweight corresponds to one transition in a finite-state automaton. In practice,however, when trained using gradient descent, these networks seldomassume this type of encoding and sophisticated algorithms must be...

Stefan C. Kremer; Ramón P. Ńeco; Mikel L. Forcada

322

Kinetic Isotope Effects for Alkaline Phosphatase Reactions: Implications for the Role of Active@stanford.edu; hengge@cc.usu.edu Abstract: Enzyme-catalyzed phosphoryl transfer reactions have frequently been suggested kinetic isotope effects (KIEs) for AP-catalyzed hydrolysis reactions with several phosphate monoester

Herschlag, Dan

323

Literature kinetic and mechanistic data have been compiled and evaluated for the gas phase reactions of ozone with organics. Emphasis is placed upon the reaction kinetics and mechanisms in air in order to assess the atmospheric relevance of these reactions. Wherever possible, rec...

324

Kinetic Modeling of Large?Scale Reaction Systems

This review gives a brief account of basic ideas underlying approaches to analysis and modeling of large?scale reaction systems. The emphasis is on model simplification and mechanism\\/dimension reduction via heuristic concepts and formal mathematical techniques. Among the key topics discussed are: top?down and bottom?up modeling approaches, graph\\/matrix representation of chemical reactions, mechanistic vs. pathways models, quantitative structure?reactivity relationships, mathematical reduction

Teh C. Ho

2008-01-01

325

The known unknowns: neural representation of second-order uncertainty, and ambiguity

Predictions provided by action-outcome probabilities entail a degree of (first-order) uncertainty. However, these probabilities themselves can be imprecise and embody second-order uncertainty. Tracking second-order uncertainty is important for optimal decision making and reinforcement learning. Previous functional magnetic resonance imaging investigations of second-order uncertainty in humans have drawn on an economic concept of ambiguity, where action-outcome associations in a gamble are either known (unambiguous) or completely unknown (ambiguous). Here, we relaxed the constraints associated with a purely categorical concept of ambiguity and varied the second-order uncertainty of gambles continuously, quantified as entropy over second-order probabilities. We show that second-order uncertainty influences decisions in a pessimistic way by biasing second-order probabilities, and that second-order uncertainty is negatively correlated with posterior cingulate cortex activity. The category of ambiguous (compared to non-ambiguous) gambles also biased choice in a similar direction, but was associated with distinct activation of a posterior parietal cortical area; an activation that we show reflects a different computational mechanism. Our findings indicate that behavioural and neural responses to second-order uncertainty are distinct from those associated with ambiguity and may call for a reappraisal of previous data. PMID:21451019

Bach, Dominik R.; Hulme, Oliver; Penny, William D.; Dolan, Raymond J.

2011-01-01

326

Kinetics and mechanism of the IO + IO reaction

NASA Technical Reports Server (NTRS)

The flash photolysis-absorption technique has been used to measure the rate constant for the reaction IO + IO over the temperature range 250-373 K and pressure range 20-700 torr of N2. The rate constant for the overall reaction was found to be independent of pressure and equal to 1.73 x 10 to the -12th exp (1020 + or - 200)/T cu cm/molecule s. Branching ratios for the reaction channels forming 2I + O2, I2 + O2, and I2O2, were found to be pressure dependent, with the I2 channel accounting for less than 5 percent of the total reaction over the observed pressure range. A stable reaction product was observed between 230 and 300 nm which was formed on a long time scale compared to IO disappearance. The rate constant for the reaction I + O3 + yields to IO + O2 was measured at 298 K and found to be (9.5 + or - 1.5) x 10 to the -13th cu cm/molecule s.

Sander, S. P.

1986-01-01

327

Oxygen Diffusion and Reaction Kinetics in Continuous Fiber Ceramic Matrix Composites

NASA Technical Reports Server (NTRS)

Previous stressed oxidation tests of C/SiC composites at elevated temperatures (350 C to 1500 C) and sustained stresses (69 MPa and 172 MPa) have led to the development of a finite difference cracked matrix model. The times to failure in the samples suggest oxidation occurred in two kinetic regimes defined by the rate controlling mechanisms (i.e. diffusion controlled and reaction controlled kinetics). Microstructural analysis revealed preferential oxidation along as-fabricated, matrix microcracks and also suggested two regimes of oxidation kinetics dependent on the oxidation temperature. Based on experimental results, observation, and theory, a finite difference model was developed. The model simulates the diffusion of oxygen into a matrix crack bridged by carbon fibers. The model facilitates the study of the relative importance of temperature, the reaction rate constant, and the diffusion coefficient on the overall oxidation kinetics.

Halbig, Michael C.; Eckel, Andrew J.; Cawley, James D.

1999-01-01

328

Second-order work, kinetic energy and diffuse failure in granular materials

Failure in soils and the yielding mechanisms involved are essential to many civil engineering issues such as slope stability.\\u000a Sudden collapse affecting slopes can be observed after rainfalls, sometimes leading to the devastating flow of a soil–water\\u000a mixture. Although the notion of failure in soils was long described as a perfect plastic limit, the scientific community now\\u000a recognizes that failure

François Nicot; Ali Daouadji; Farid Laouafa; Félix Darve

2011-01-01

329

CHLORINE DEMAND AND TTHM FORMATION KINETICS: A SECOND-ORDER MODEL

Much effort has been expended in attempting to develop mathematical models for chlorine demand in water and wastewater. Most of these efforts have centered around the use of first-order functions or modifications of first-order functions. Recently there has also been interest i...

330

NASA Technical Reports Server (NTRS)

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

Radhakrishnan, Krishnan; Bittker, David A.

1993-01-01

331

Second-order structure function analysis of scatterometer winds over the Tropical Pacific

NASA Astrophysics Data System (ADS)

second-order structure functions are used to quantify and compare the small-scale information contained in near-surface ocean wind products derived from measurements by ASCAT on MetOp-A and SeaWinds on QuikSCAT. Two ASCAT and three SeaWinds products are compared in nine regions (classified as rainy or dry) in the tropical Pacific between 10°S and 10°N and 140° and 260°E for the period November 2008 to October 2009. Monthly and regionally averaged longitudinal and transverse structure functions are calculated using along-track samples. To ease the analysis, the following quantities were estimated for the scale range 50 to 300 km and used to intercompare the wind products: (i) structure function slopes, (ii) turbulent kinetic energies (TKE), and (iii) vorticity-to-divergence ratios. All wind products are in good qualitative agreement, but also have important differences. Structure function slopes and TKE differ per wind product, but also show a common variation over time and space. Independent of wind product, longitudinal slopes decrease when sea surface temperature exceeds the threshold for onset of deep convection (about 28°C). In rainy areas and in dry regions during rainy periods, ASCAT has larger divergent TKE than SeaWinds, while SeaWinds has larger vortical TKE than ASCAT. Differences between SeaWinds and ASCAT vortical TKE and vorticity-to-divergence ratios for the convectively active months of each region are large.

King, Gregory P.; Vogelzang, Jur; Stoffelen, Ad

2015-01-01

332

ACKS2: Atom-condensed Kohn-Sham DFT approximated to second order

NASA Astrophysics Data System (ADS)

A new polarizable force field (PFF), namely atom-condensed Kohn-Sham density functional theory approximated to second order (ACKS2), is proposed for the efficient computation of atomic charges and linear response properties of extended molecular systems. It is derived from Kohn-Sham density functional theory (KS-DFT), making use of two novel ingredients in the context of PFFs: (i) constrained atomic populations and (ii) the Legendre transform of the Kohn-Sham kinetic energy. ACKS2 is essentially an extension of the Electronegativity Equalization Method (EEM) [W. J. Mortier, S. K. Ghosh, and S. Shankar, J. Am. Chem. Soc. 108, 4315 (1986)], 10.1021/ja00275a013 in which two major EEM shortcomings are fixed: ACKS2 predicts a linear size-dependence of the dipole polarizability in the macroscopic limit and correctly describes the charge distribution when a molecule dissociates. All ACKS2 parameters are defined as atoms-in-molecules expectation values. The implementation of ACKS2 is very similar to that of EEM, with only a small increase in computational cost.

Verstraelen, T.; Ayers, P. W.; Van Speybroeck, V.; Waroquier, M.

2013-02-01

333

The kinetics of outer sphere electron transfer reaction of surfactant cobalt(III) complex ions, cis-[Co(en)2(C12H25NH2)2](3+) (1), cis-[Co(dp)2(C12H25NH2)2](3+) (2), cis-[Co(trien)(C12H25NH2)2](3+) (3), cis-[Co(bpy)2(C12H25NH2)2](3+) (4) and cis-[Co(phen)2(C12H25NH2)2](3+) (5) (en: ethylenediamine, dp: diaminopropane, trien : triethylenetetramine, bpy: 2,2'-bipyridyl, phen: 1,10-phenanthroline and C12H25NH2 : dodecylamine) have been interrogated by Fe(2+) ion in ionic liquid (1-butyl-3-methylimidazoliumbromide) medium at different temperatures (298, 303, 308, 313, 318 and 323K) by the spectrophotometry method under pseudo first order conditions using an excess of the reductant. Experimentally the reactions were found to be of second order and the electron transfer as outer sphere. The second order rate constant for the electron transfer reaction in ionic liquids was found to increase with increase in the concentration of all these surfactant cobalt(III) complexes. Among these complexes (from en to phen ligand), complex containing the phenanthroline ligand rate is higher compared to other complexes. By assuming the outer sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of ionic liquids formed by the surfactant cobalt(III) complexes in the reaction medium. The activation parameters (enthalpy of activation ?H(‡) and entropy of activation ?S(‡)) of the reaction have been calculated which substantiate the kinetics of the reaction. PMID:25721780

Nagaraj, Karuppiah; Senthil Murugan, Krishnan; Thangamuniyandi, Pilavadi; Sakthinathan, Subramanian

2015-05-15

334

Atmospheric Chemistry: Laboratory Studies of Kinetics of Important Reactions.

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. This thesis describes the experiments to measure the rate constants for some reactions of the atmospherically important nitrate radical (NO_3) using the discharge-flow technique. The nitrate radical was monitored by optical absorption at lambda = 662 nm. The reactions of NO_3 with some stable organic and inorganic substrates are reported. The temperature dependences of some of the rate constants have also been determined (298 < T < 523 K). In most cases, computer simulation was used to extract the rate constant for the primary process because the time-dependent behaviour of (NO_3) was affected by secondary reactions of NO_3 with products of the primary interaction. The Arrhenius parameter in parentheses (E _{rm a}/kJ mol^ {-1}, A/cm^3 molecule ^{-1}s^ {-1} respectively) for the following reactions have been determined: ethane (37, 6.7 times 10^{-12}), ethylene (25.8, 6.3 times 10^ {-12}), CH_3OH (21.3, 1.2 times 10^ {-12}), CHCiota_3 (23.4, 8.6 times 10 ^{-13}) and HCl (27.7, 4 times 10^{-12}). The activation energies for the reactions studied between NO_3 and some alkynes are represented well by the value 25 +/- 3 kJ mol^{-1} and the corresponding pre-exponential factors (expressed as ln(10 ^{13}A/cm^3 molecule^{-1}s ^{-1}) are as follows: C_2H_2 (1.6 +/- 1.4), C_3H _4 (5.0 +/- 1.4), 1-C_4H_6 (5.8 +/- 1.0), 1-C_5 H_8 (5.7 +/- 0.6) and 1-C_6H _{10} (4.5 +/- 0.4). Some reactions were studied at room temperature _3(298 +/- 2 K) only and the rate constants found (in units of cm ^3 molecule^{ -1}s^{-1}) are: buta-1,3-diene (1.8 times 10 ^{-13}), isobutene (2.8 times 10^{-13 }), HBr (1.3 times 10 ^{-15}) and hex-2-yne (3.0 times 10^{-14 }). Non-Arrhenius behaviour was found in the reactions of NO_3 with n-butane, isobutane and propene. The empirical variation of these rate constants with temperature is well represented by the three parameter expressions:. k(T) = 1.2 times 10 ^{-46}T^{11.4 }exp(-1131/T) for n-butane; k(T) = 1.6 times 10^ {-49}T^{12.3} exp(-1828/T) for isobutane; and for propene, k(T) = 2.4 times 10 ^{-19}T^ {2.25}exp(-700/T). The curvature of the Arrhenius plots is discussed in terms of (a) a temperature-dependent pre-exponential factor and (b) the possibility that two competing channels, possessing differing activation energies, exist for each reaction. The atmospheric implications of these reactions are discussed with reference to the nigh-time production of nitric acid and the importance of the these reactions as loss processes for NO_3.

Smith, S. J.

335

Decay reactions of rare gas cluster ions: Kinetic energy release distributions and binding energies

NASA Astrophysics Data System (ADS)

We have carried out measurements on metastable fragmentation of mass selected argon cluster ions which are produced by electron impact ionization of a neutral argon cluster beam. From the shape of the fragment ion peaks (MIKE scan technique) one can deduce information about the distribution of kinetic energy that is released in the decay reaction. In this study, for Ar5+ to Ar15+, it is Gaussian and thus we can calculate from the peak width the mean kinetic energy release

Parajuli, R.; Matt, S.; Echt, O.; Stamatovic, A.; Scheier, P.; Märk, T. D.

336

Second Order Parametric Processes in Nonlinear Silica Microspheres Yong Xu, Ming Han, and Anbo Wang

Second Order Parametric Processes in Nonlinear Silica Microspheres Yong Xu, Ming Han, and Anbo Wang; published 25 April 2008) We analyze second order parametric processes in a silica microsphere coated with radially aligned nonlinear optical molecules. In a high-Q nonlinear microsphere, we discover

Heflin, Randy

337

A second-order sliding mode controller for active suspension systems

This paper presents a second-order sliding mode controller for active suspension systems. The proposed controller, which occurs a limit cycle as the second-order sliding mode, is designed by the integral sliding mode control theory with the twisting algorithm. With the block diagram algebra, the proposed control system can be converted into a nonlinear feedback system consisting of a linear transfer

Shigehiro Toyama; Fujio Ikeda; Yoshio Sorimachi

2008-01-01

338

Grid travel{time tracing: second{order method for the rst arrivals in smooth media *

Grid travel{time tracing: second{order method for the #12;rst arrivals in smooth media * Lud#20;ek the #12;rst{arrival travel times on a rectangular grid of points is proposed. Whereas the former "#12;nite is of the second{order accu- racy. It means that the relative propagation{velocity error of calculated travel time

Cerveny, Vlastislav

339

Grid travel{time tracing: second{order method for the rst arrivals in smooth media

Grid travel{time tracing: second{order method for the #12;rst arrivals in smooth media Lud#20;ek{arrival travel times on a rectan- gular grid of points is proposed. The new proposed method is of second{order accuracy. This means that the error of the calculated travel time is proportional to the second power

Cerveny, Vlastislav

340

Second-Order Asymptotics for the Gaussian MAC with Degraded Message Sets

-order coding rates, Dispersion. I. INTRODUCTION In this paper, we revisit the Gaussian multiple-access channel1 Second-Order Asymptotics for the Gaussian MAC with Degraded Message Sets Jonathan Scarlett and Vincent Y. F. Tan Abstract This paper studies the second-order asymptotics of the Gaussian multiple

341

Second-Order Theoretical Analysis of Observations: Data Analysis Through the Study of Dilemmas

ERIC Educational Resources Information Center

This paper explains the principles and procedures of second-order theoretical analysis of observation data. The second-order theoretical procedure is illustrated by analysis of the student-teachers seminar on the subject of the Holocaust, focusing on dilemmas of Holocaust survivors. Analysing observational data allows two distinctive method of…

Shkedi, Asher; Harel, Miri

2004-01-01

342

Second-order structure function analysis of scatterometer winds over1 the Tropical Pacific

Second-order structure function analysis of scatterometer winds over1 2 3 4 5 6 7 8 9 10 11 12 13 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Kolmogorov second-order structure functions (second moment and regionally averaged longitudinal and transverse structure functions are calculated using along-track winds

Haak, Hein

343

Effectiveness of parallel second order model over second and first order models

The chlorine decay is usually described by the first order model (FOM) due to its easiness, although its weaknesses are well known. In this work, two better models, second order model (SOM) and parallel second order model (PSOM), are compared for their accuracy to predict chlorine residuals for a single dosing scenario. Results showed that SOM model provided a better

Ahmad Jabari Kohpaei; Arumugam Sathasivan; Hanieh Aboutalebi

2011-01-01

344

Second Order perturbation Theory: A covariant approach involving a barotropic equation of state

We first revisit the motivations for developing techniques to study Second-Order effects, before presenting the formalism. We study second-order tensor perturbations about FLRW with dust on the one hand, and with a general barotropic equation of state on the other. Solutions to the wave equations are presented.

Bob Osano

2015-04-07

345

Fundamental notions of analysis in subsystems of second-order arithmetic

Fundamental notions of analysis in subsystems of second-order arithmetic Jeremy Avigad Department, Hilbert, and Banach spaces in the context of subsystems of second-order arithmetic. In particular, we, and study the relationships between them. For example, we show that a natural formalization of the mean

Avigad, Jeremy

346

Uniqueness Results for Second Order Bellman-Isaacs Equations under Quadratic Growth Assumptions semicontinuous viscosity sub and supersolu- tions growing at most quadratically of second-order degenerate parabolic Hamilton-Jacobi-Bellman and Isaacs equations. As an application, we characterize the value

Paris-Sud XI, UniversitĂ© de

347

First estimates of the second-order ionospheric effect on radio occultation observations

This study examines the impact of the second-order ionospheric effect on radio occultation (RO) data products. We propose a new linear combination between dual frequency GPS observables, which retrieves slant total electron content free from the second-order ionospheric effect. Our STEC values differ from those obtained by independent techniques by a maximum of 3 total electron content units (TECU), depending

Panagiotis Vergados; Spiros D. Pagiatakis

2010-01-01

348

MULTIZONE NEAR-END SPEECH ENHANCEMENT UNDER OPTIMAL SECOND-ORDER MAGNITUDE DISTORTION

MULTIZONE NEAR-END SPEECH ENHANCEMENT UNDER OPTIMAL SECOND-ORDER MAGNITUDE DISTORTION Jo~ao B.c.hendriks@tudelft.nl ABSTRACT In this article, we address near-end speech enhancement for a sce- nario where there are several-end speech enhancement, multizone, second-order magnitude distortion, public address system 1. INTRODUCTION

349

Adaptation of Log Domain Second Order Filters Implemented by Floating Gate MOSFETs

Adaptation of Log Domain Second Order Filters Implemented by Floating Gate MOSFETs Yiming Zhai, MD 20742, USA ymzhai, pabshire@umd.edu Abstract--We describe an adaptive log domain second order transistors to realize on-line learning of quality factor and time constant. We use adaptive dynamical system

Maryland at College Park, University of

350

On group classification of normal systems of linear second-order ordinary differential equations

NASA Astrophysics Data System (ADS)

In this paper we study the general group classification of systems of linear second-order ordinary differential equations inspired from earlier works and recent results on the group classification of such systems. Some interesting results and subsequent theorem arising from this particular study are discussed here. This paper considers the study of irreducible systems of second-order ordinary differential equations.

Meleshko, S. V.; Moyo, S.

2015-05-01

351

A Comparison of Bifactor and Second-Order Models of Quality of Life

ERIC Educational Resources Information Center

Bifactor and second-order factor models are two alternative approaches for representing general constructs comprised of several highly related domains. Bifactor and second-order models were compared using a quality of life data set (N = 403). The bifactor model identified three, rather than the hypothesized four, domain specific factors beyond the…

Chen, Fang Fang; West, Stephen G.; Sousa, Karen H.

2006-01-01

352

Teacher's Corner: Testing Measurement Invariance of Second-Order Factor Models

ERIC Educational Resources Information Center

We illustrate testing measurement invariance in a second-order factor model using a quality of life dataset (n = 924). Measurement invariance was tested across 2 groups at a set of hierarchically structured levels: (a) configural invariance, (b) first-order factor loadings, (c) second-order factor loadings, (d) intercepts of measured variables,…

Chen, Fang Fang; Sousa, Karen H.; West, Stephen G.

2005-01-01

353

Operator Factorization and the Solution of Second-Order Linear Ordinary Differential Equations

ERIC Educational Resources Information Center

The theory and application of second-order linear ordinary differential equations is reviewed from the standpoint of the operator factorization approach to the solution of ordinary differential equations (ODE). Using the operator factorization approach, the general second-order linear ODE is solved, exactly, in quadratures and the resulting…

Robin, W.

2007-01-01

354

The effects of second-order hydrodynamics on a semisubmersible floating offshore wind turbine

NASA Astrophysics Data System (ADS)

The objective of this paper is to assess the second-order hydrodynamic effects on a semisubmersible floating offshore wind turbine. Second-order hydrodynamics induce loads and motions at the sum- and difference-frequencies of the incident waves. These effects have often been ignored in offshore wind analysis, under the assumption that they are significantly smaller than first-order effects. The sum- and difference-frequency loads can, however, excite eigenfrequencies of a floating system, leading to large oscillations that strain the mooring system or vibrations that cause fatigue damage to the structure. Observations of supposed second-order responses in wave-tank tests performed by the DeepCwind consortium at the Maritime Research Institute Netherlands (MARIN) offshore basin suggest that these effects might be more important than originally expected. These observations inspired interest in investigating how second-order excitation affects floating offshore wind turbines and whether second-order hydrodynamics should be included in offshore wind simulation tools like FAST. In this work, the effects of second-order hydrodynamics on a floating semisubmersible offshore wind turbine are investigated. Because FAST is currently unable to account for second-order effects, a method to assess these effects was applied in which linearized properties of the floating wind system derived from FAST (including the 6x6 mass and stiffness matrices) are used by WAMIT to solve the first- and second-order hydrodynamics problems in the frequency domain. The method was applied to the Offshore Code Comparison Collaboration Continuation OC4-DeepCwind semisubmersible platform, supporting the National Renewable Energy Laboratory's 5-MW baseline wind turbine. In this paper, the loads and response of the system caused by the second-order hydrodynamics are analysed and compared to the first-order hydrodynamic loads and induced motions in the frequency domain. Further, the second-order loads and induced response data are compared to the loads and motions induced by aerodynamic loading as solved by FAST.

Bayati, I.; Jonkman, J.; Robertson, A.; Platt, A.

2014-06-01

355

Effects of Second-Order Hydrodynamics on a Semisubmersible Floating Offshore Wind Turbine: Preprint

The objective of this paper is to assess the second-order hydrodynamic effects on a semisubmersible floating offshore wind turbine. Second-order hydrodynamics induce loads and motions at the sum- and difference-frequencies of the incident waves. These effects have often been ignored in offshore wind analysis, under the assumption that they are significantly smaller than first-order effects. The sum- and difference-frequency loads can, however, excite eigenfrequencies of the system, leading to large oscillations that strain the mooring system or vibrations that cause fatigue damage to the structure. Observations of supposed second-order responses in wave-tank tests performed by the DeepCwind consortium at the MARIN offshore basin suggest that these effects might be more important than originally expected. These observations inspired interest in investigating how second-order excitation affects floating offshore wind turbines and whether second-order hydrodynamics should be included in offshore wind simulation tools like FAST in the future. In this work, the effects of second-order hydrodynamics on a floating semisubmersible offshore wind turbine are investigated. Because FAST is currently unable to account for second-order effects, a method to assess these effects was applied in which linearized properties of the floating wind system derived from FAST (including the 6x6 mass and stiffness matrices) are used by WAMIT to solve the first- and second-order hydrodynamics problems in the frequency domain. The method has been applied to the OC4-DeepCwind semisubmersible platform, supporting the NREL 5-MW baseline wind turbine. The loads and response of the system due to the second-order hydrodynamics are analysed and compared to first-order hydrodynamic loads and induced motions in the frequency domain. Further, the second-order loads and induced response data are compared to the loads and motions induced by aerodynamic loading as solved by FAST.

Bayati, I.; Jonkman, J.; Robertson, A.; Platt, A.

2014-07-01

356

Reaction Mechanism and Kinetics of Enargite Oxidation at Roasting Temperatures

NASA Astrophysics Data System (ADS)

Roasting of enargite (Cu3AsS4) in the temperature range of 648 K to 898 K (375 °C to 625 °C) in atmospheres containing variable amounts of oxygen has been studied by thermogravimetric methods. From the experimental results of weight loss/gain data and X-ray diffraction (XRD) analysis of partially reacted samples, the reaction mechanism of the enargite oxidation was determined, which occurred in three sequential stages:

Padilla, Rafael; Aracena, Alvaro; Ruiz, Maria C.

2012-10-01

357

Reaction kinetics of resveratrol with tert-butoxyl radicals

NASA Astrophysics Data System (ADS)

The rate constant for the reaction of t-butoxyl radicals with resveratrol was studied under pseudo-first order conditions. The rate constant was determined by measuring the phenoxyl radical formation rate at 390 nm as function of resveratrol concentration in acetonitrile. The rate constant was determined to be 6.5×108 M-1s-1. This high value indicates the high reactivity consistent with the strong antioxidant activity of resveratrol.

Džeba, Iva; Pedzinski, Tomasz; Mihaljevi?, Branka

2012-09-01

358

NASA Astrophysics Data System (ADS)

The kinetics and mechanisms of the dehydration reactions of zoisite have been studied at 635° 792° C, 1 2 kbar. The equilibrium reaction does not occur and is replaced by metastable reactions involving the formation of gehlenite and a calcium tri-octahedral mica, instead of corundum: zoisite ? anorthite+grossular+gehlenite +calcium 3T mica+H2O. The experimental data can be interpreted by zero-order equations dX An/ dt=k ( X An=fractional extent of reaction, t=time, k=zero-order rate constant). These relations hold for variations in P, T, A initial(the initial surface area of zoisite) and also in the presence of seed crystals, which enhance the reaction rate. No induction period is evident and only at advanced stages of reaction are sharp decreases observed in the rate, which are attributed to physical affects (shrinking particles, armouring). SEM studies show that dissolution of zoisite is anisotropic, occurring preferentially parallel to the crystallographic b-axis, with the result that a characteristic ‘sawtooth’ etch structure develops. Garnet grows as euhedral crystals located in cavities or on ‘teeth’ of dissolving zoisite, whereas anorthite forms as clusters of coalescing grains which spread over and enclose the zoisite. In seeded runs, garnet growth initiates on both seeds and on zoisite surfaces whereas anorthite growth is more closely tied to the seeds, resulting in the development of clusters of smaller grains. The experimental evidence favours dissolution and nucleation-controlled growth as rate-determining processes. The preservation of zero-order kinetics in the face of shrinking particles is attributed to the anisotropic dissolution mechanism, which effectively preserves a constant reaction interface. The rate effects of nucleation appear to accord with the classic model in which growth of crystal layers is initiated by the formation of coherent nuclei. The temperature dependence of rate constants reflects both thermally activated Arrhenius-type behaviour and the rate-depressing influences of approach to equilibrium. Similarly pressure affects on reaction rate can be interpreted in terms of competition between rate enhancement due to pressure increase and rate-depression accompanying the approach to equilibrium. Although the equilibrium-approach effects accord with current treatments of reaction kinetics, a problem exists in deriving an exact relation coupling dissolution and nucleation rate control. Consequently an overall-reaction rate equation, such as that of Fisher and Lasaga (1981), is only partially successful in interpreting the temperature dependence of rates. The data suggest that the surface reaction equation of Wood and Walther (1983) only applies when nuclei are present.

Matthews, Alan

1985-04-01

359

Kinetic of antigent-antibody reactions with scattering method

NASA Astrophysics Data System (ADS)

The immune reactions of interaction antigen-antibody represent specific effect of an antigene with an antibody, which outcome are the complex immune aggregates forming precipitate in case of a soluble antigene, or agglutinate in case of a corpuscular antigene. Immunological methods which uses in the quality of carrier protein latex's polymeric microspheresis, gained name and method latex agglutination. Polymeric microspheresis have the array of advantages before biological carries, which consist in the opportunity of the variation of attributes surface and size microspheresis in the broad band of meanings with the preservation of narrow distribution particles behind measurements, the putting of functional groups, necessary for bunch with ligand on stage their synthesis, in ragidity at storage. The quantitative evaluation of parameters of a response of interaction antigen-antibody in immunology is possible by optical methods on a measurement of a modification of intensity of a light stream of a solution in an outcome of a course of a reaction. Concentration of immune complexes determine both on slacking a taking place stream of light, and on a modification of intensity of a stream of light scattering suspended particles in a solution. The process light scattering by colloidal aggregates are formed from suspension microspheresis with adsorbed on their surface protein is described. In report the physics principle of registration immune reaction by light scattering methods is concerned. The results of the effectiveness latex's preparation created on basis of the polymeric carries is described.

Bilyi, Olexander I.; Kiselyov, Yevgen M.; Novikov, Volodymyr P.

2001-07-01

360

Low Temperature Kinetics of the CH3OH + OH Reaction

The rate constant of the reaction between methanol and the hydroxyl radical has been studied in the temperature range 56-202 K by pulsed laser photolysis-laser induced fluorescence in two separate experiments using either a low temperature flow tube coupled to a time of flight mass spectrometer or a pulsed Laval nozzle apparatus. The two independent techniques yield rate constants which are in mutual agreement and consistent with the results reported previously below 82 K [Shannon et al., Nature Chemistry, 2013, 5, 745-749] and above 210 K [Dillon et al., Phys. Chem. Chem. 2005, 7, 349-355], showing a very sharp increase with decreasing temperature with an onset around 180 K. This onset is also signalled by strong chemiluminescence tentatively assigned to formaldehyde, which is consistent with the formation of the methoxy radical at low temperature by quantum tunnelling, and its subsequent reaction with H and OH. Our results add confidence to the previous low temperature rate constant measurements and consolidate the experimental reference dataset for further theoretical work required to describe quantitatively the tunnelling mechanism operating in this reaction. An additional measurement of the rate constant at 56 K yielded a value of (4.9 ± 0.8) × 10?11 cm3 molecule?1 s?1 (2?), showing that the rate constant is increasing less rapidly at temperatures below 70 K. PMID:24669816

Martín, J. C. Gómez; Caravan, R. L.; Blitz, M. A.; Heard, D. E.; Plane, J. M. C.

2014-01-01

361

Low temperature kinetics of the CH3OH + OH reaction.

The rate constant of the reaction between methanol and the hydroxyl radical has been studied in the temperature range 56-202 K by pulsed laser photolysis-laser induced fluorescence in two separate experiments using either a low temperature flow tube coupled to a time-of-flight mass spectrometer or a pulsed Laval nozzle apparatus. The two independent techniques yield rate constants that are in mutual agreement and consistent with the results reported previously below 82 K [Shannon et al. Nat. Chem. 2013, 5, 745-749] and above 210 K [Dillon et al. Phys. Chem. Chem. Phys. 2005, 7, 349-355], showing a very sharp increase with decreasing temperature with an onset around 180 K. This onset is also signaled by strong chemiluminescence tentatively assigned to formaldehyde, which is consistent with the formation of the methoxy radical at low temperature by quantum tunnelling, and its subsequent reaction with H and OH. Our results add confidence to the previous low temperature rate constant measurements and consolidate the experimental reference data set for further theoretical work required to describe quantitatively the tunnelling mechanism operating in this reaction. An additional measurement of the rate constant at 56 K yielded a value of (4.9 ± 0.8) × 10(-11) cm(3) molecule(-1) s(-1) (2?), showing that the rate constant is increasing less rapidly at temperatures below 70 K. PMID:24669816

Gómez Martín, J C; Caravan, R L; Blitz, M A; Heard, D E; Plane, J M C

2014-04-17

362

Reactions of Cl atoms with alkyl esters: kinetic, mechanism and atmospheric implications.

Rate coefficients have been measured for the reaction of Cl atoms with a series of alkyl esters at 298?±?2 K and atmospheric pressure in a large volume photoreactor using the relative kinetic technique. The kinetic data have been used in conjunction with other literature studies on the reactions of Cl atoms with esters to revise the existing values for ester substituent factors in a structure activity relationship (SAR) for Cl reactions. Product studies are reported for the reactions of Cl atoms with isopropyl ethanoate and methyl-2-methyl-propanoate under NO x -free conditions. These studies highlight the types of products that can be expected when oxidation occurs at R groups on the acyl (-C(O)OR) and oxy (RC(O)O-) sides of the ester functionality where R is a straight or branched chain alkyl entity. Possible atmospheric repercussions of the atmospheric chemistry of esters are considered. PMID:24809490

Ifang, Stefanie; Benter, Thorsten; Barnes, Ian

2015-04-01

363

Theoretical study of the kinetics of reactions of the monohalogenated methanes with atomic chlorine.

Ab initio calculations at the G2 level were used in a theoretical description of the kinetics and mechanism of the hydrogen abstraction reactions from fluoro-, chloro- and bromomethane by chlorine atoms. The profiles of the potential energy surfaces show that mechanism of the reactions under investigation is complex and consists of two - in the case of CH3F+Cl - and of three elementary steps for CH3Cl+Cl and CH3Br+Cl. The heights of the energy barrier related to the H-abstraction are of 8-10 kJ mol(-1), the lowest value corresponds to CH3Cl+Cl and the highest one to CH3F+Cl. The rate constants were calculated using the theoretical method based on the RRKM theory and the simplified version of the statistical adiabatic channel model. The kinetic equations derived in this study[Formula: see text]and[Formula: see text]allow a description of the kinetics of the reactions under investigation in the temperature range of 200-3000 K. The kinetics of reactions of the entirely deuterated reactants were also included in the kinetic analysis. Results of ab initio calculations show that D-abstraction process is related with the energy barrier of 5 kJ mol(-1) higher than the H-abstraction from the corresponding non-deuterated reactant molecule. The derived analytical equations for the reactions, CD3X+Cl, CH2X+HCl and CD2X+DCl (X = F, Cl and Br) are a substantial supplement of the kinetic data necessary for the description and modeling of the processes of importance in the atmospheric chemistry. PMID:23239396

Brudnik, Katarzyna; Twarda, Maria; Sarzy?ski, Dariusz; Jodkowski, Jerzy T

2013-04-01

364

Kinetic analysis of the interfacial reactions in Ni\\/Sn\\/Cu sandwich structures

The mutual interaction between Sn\\/Ni and Sn\\/Cu interfacial reactions in a Ni\\/Sn\\/Cu sandwich sample has been studied. The major\\u000a interfacial reaction product on the Cu side was Cu6Sn5, while on the Ni side, a ternary (Cu,Ni)6Sn5 compound layer was formed. We found that the growth kinetics of the interfacial compound layers on both sides reached a steady\\u000a state in the

S. J. Wang; C. Y. Liu

2006-01-01

365

Kinetic analysis of the interfacial reactions in Ni\\/Sn\\/Cu sandwich structures

The mutual interaction between Sn\\/Ni and Sn\\/Cu interfacial reactions in a Ni\\/Sn\\/Cu sandwich sample has been studied. The major interfacial reaction product on the Cu side was Cu6Sn5, while on the Ni side, a ternary (Cu,Ni)6Sn5 compound layer was formed. We found that the growth kinetics of the interfacial compound layers on both sides reached a steady state in the

S. J. Wang; C. Y. Liu

2006-01-01

366

Kinetics of Thermochemical Reactions Important in the Venus Atmospheric Sulfur Cycle

NASA Technical Reports Server (NTRS)

The purpose of this project was to experimentally measure the rates of several thermochemical gas-solid reactions between sulfur gases in the Venus atmosphere and reactive minerals on the hot Venus surface. Despite the great importance of these reactions for the maintenance of significant amounts of sulfur gases (and thus for the maintenance of the global cloud cover) in the atmosphere of Venus, essentially no kinetic data are currently available for them.

Fegley, Bruce, Jr.

1997-01-01

367

in the human stomach. Depending on the pH, there are three main ways in which the dissolution of calcium carbonate occurs: By reaction with acetic acid. CaCO3 + H3O+ Ca2+ + HCO- 3 + H2O By reaction with carbonic is simply the sum of all individual rates. So, the kinetic of dissolution of calcium carbonate is a function

Giménez, Domingo

368

The decay of the excited primary electron donor P* in bacterial photosynthetic reaction centers (both membrane-bound and detergent-isolated) has been observed to be nonexponential on a time scale of some tens of picoseconds. Although the multipicosecond nonexponentiality of P* has been ascribed to heterogeneity in teh rate of primary electron transfer (PET), the decay kinetics can be interpreted equally well using homogeneous models. To address this ambiguity, we studied the decay of excited bacteriochlorophyll (Bchl) in the membrane-bound core antenna/reaction center complexes of wild-type and mutant reaction center strains of Rhodobacter capsulatus. Reaction centers isolated from these same strains display a range of multiexponentiality in primary charge separation. The mutant strains carry substitutions of amino acids residing near the monomeric Bchl on the active and/or inactive sides of the reaction center. Transient absorption measurements monitoring the Qy bleach of antenna Bchls require at least two exponential components to fit all decays. The wild type was fitted with equal-amplitude components whose lifetimes are 24 and 65 ps. The shortest-lived component is relatively insensitive to mutation, in contrast to the longer-lived component(s) whose amplitude and magnitude were dramatically perturbed by amino acid substitutions. Unlike the situation with isolated reaction centers, here the only kinetic models consistent with the data are those in which the primary electron-transfer rate constant is heterogeneous, suggesting at least two structural populations of RCs. PET in the population with the shortest-lived antenna decay causes the kinetics to be transfer-to-trap-limited, whereas the kinetics in the other population(s)--having longer-lived antenna decays--are limited by the rate of PET. Observation of both types of kinetic limitation within a single light-harvesting system is unexpected and complicates any discussion of the rate-limiting step of light energy utilization in photosynthesis. PMID:9289013

Laible, P D; Greenfield, S R; Wasielewski, M R; Hansen, D K; Pearlstein, R M

1997-07-22

369

We study a class of methods for the numerical solution of the system of stochastic differential equations (SDEs) that arises in the modeling of turbulent combustion, specifically in the Monte Carlo particle method for the solution of the model equations for the composition probability density function (PDF) and the filtered density function (FDF). This system consists of an SDE for particle position and a random differential equation for particle composition. The numerical methods considered advance the solution in time with (weak) second-order accuracy with respect to the time step size. The four primary contributions of the paper are: (i) establishing that the coefficients in the particle equations can be frozen at the mid-time (while preserving second-order accuracy), (ii) examining the performance of three existing schemes for integrating the SDEs, (iii) developing and evaluating different splitting schemes (which treat particle motion, reaction and mixing on different sub-steps), and (iv) developing the method of manufactured solutions (MMS) to assess the convergence of Monte Carlo particle methods. Tests using MMS confirm the second-order accuracy of the schemes. In general, the use of frozen coefficients reduces the numerical errors. Otherwise no significant differences are observed in the performance of the different SDE schemes and splitting schemes.

Wang Haifeng [Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853 (United States)], E-mail: hw98@cornell.edu; Popov, Pavel P.; Pope, Stephen B. [Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853 (United States)

2010-03-01

370

This study highlights the effect of the aggregate state of a reactant on the reaction kinetics under the conditions of nanoconfinement. Our previous work (Phys. Chem. Chem. Phys., 2014, 16, 11409) has demonstrated considerable deceleration of the solid state trimerization of sodium dicyanamide in organically modified silica nanopores. In the present study we use FTIR, NMR, pXRD, TGA and DSC to analyze the kinetics and mechanism of the liquid state trimerization of potassium and rubidium dicyanamide under similar conditions of nanoconfinement. It is found that nanoconfinement accelerates dramatically the kinetics of the liquid state trimerization, whereas it does not appear to affect the reaction mechanism. Kinetic analysis indicates that the acceleration is associated with an increase in the preexponential factor. Although nanoconfinement has the opposite effects on the respective kinetics of solid and liquid state trimerization, both effects are linked to a change in the preexponential factor. The results obtained are consistent with our hypothesis that the effects differ because nanoconfinement may promote disordering of the solid and ordering of the liquid reaction media. PMID:25796991

Yancey, Benjamin; Vyazovkin, Sergey

2015-04-01

371

Studies of Reaction Kinetics of Methane Hydrate Dissocation in Porous Media

The objective of this study is the description of the kinetic dissociation of CH4-hydrates in porous media, and the determination of the corresponding kinetic parameters. Knowledge of the kinetic dissociation behavior of hydrates can play a critical role in the evaluation of gas production potential of gas hydrate accumulations in geologic media. We analyzed data from a sequence of tests of CH4-hydrate dissociation by means of thermal stimulation. These tests had been conducted on sand cores partially saturated with water, hydrate and CH4 gas, and contained in an x-ray-transparent aluminum pressure vessel. The pressure, volume of released gas, and temperature (at several locations within the cores) were measured. To avoid misinterpreting local changes as global processes, x-ray computed tomography scans provided accurate images of the location and movement of the reaction interface during the course of the experiments. Analysis of the data by means of inverse modeling (history matching ) provided estimates of the thermal properties and of the kinetic parameters of the hydration reaction in porous media. Comparison of the results from the hydrate-bearing porous media cores to those from pure CH4-hydrate samples provided a measure of the effect of the porous medium on the kinetic reaction. A tentative model of composite thermal conductivity of hydrate-bearing media was also developed.

Moridis, George J.; Seol, Yongkoo; Kneafsey, Timothy J.

2005-03-10

372

Characterization of reaction kinetics in a porous electrode

NASA Technical Reports Server (NTRS)

A continuum-model approach, analogous to porous electrode theory, was applied to a thin-layer cell of rectangular and cylindrical geometry. A reversible redox couple is assumed, and the local reaction current density is related to the potential through the formula of Hubbard and Anson for a uniformily accessible thin-layer cell. The placement of the reference electrode is also accounted for in the analysis. Primary emphasis is placed on the effect of the solution-phase ohmic potential drop on the voltammogram characteristics. Correlation equations for the peak-potential displacement from E(sup 0 prime) and the peak current are presented in terms of two dimensionless parameters.

Fedkiw, Peter S.

1990-01-01

373

Self-triggering reaction kinetics between nitrates and aluminium powder.

During the night between the 19 and 20 September 2003, a loud explosion occurred at about 3km from the town of Carignano that was clearly heard at a distance of some tens of kilometres. The explosion almost completely destroyed most of the laboratories of the Panzera Company that were used for the production of fireworks. The results of the research activities that were carried out using a differential scanning calorimeter (DSC) on the same raw materials that made up the pyrotechnical mixture that exploded are reported in this paper. This activity was carried out to identify the dynamics of the accident. It proved possible to verify how the event was produced because of a slow exothermic reaction which, after about 8h, caused the self-triggering of 120 kg of finished product. The detonation can therefore be put down to a runaway reaction in the solid phase, whose primogenial causes can be attributed to a still craftsman type production system, not conformed to the rigorous controls and inspections as those required by a safety management system for major risk plants, as the Panzera Company was. PMID:17400376

Demichela, Micaela

2007-09-01

374

Kinetics and mechanism of the degradation of two pesticides in aqueous solutions by ozonation

This study evaluated the reaction kinetics and degradation mechanism of the pesticides bromoxynil and trifluralin during conventional ozonation. The second-order rate constants for the direct molecular ozone and hydroxyl radical reactions with bromoxynil and trifluralin were determined using a rapid-scan stopped-flow spectrophotometry, competition kinetics, and an organic substrate monitoring method. High reactivity toward ozone and hydroxyl radicals was observed for

Pamela Chelme-Ayala; Mohamed Gamal El-Din; Daniel W. Smith

2010-01-01

375

NASA Astrophysics Data System (ADS)

In the literature, the combination of the second order slip and the second order jump conditions was mostly employed with the Burnett and BGK Burnett equations for hypersonic gas flows. In this paper, we will investigate both the first order and the second order slip/jump conditions, in which the combination of the second order slip and the second order jump conditions is implemented to work with the Navier-Stokes-Fourier equations for low speed nano/micro-scale and hypersonic rarefied gas flows such as the pressure driven backward facing step and 90-degree bend nano/micro-channels, the lid-driven micro-cavity, and hypersonic gas flow over the flat plate. The simulation results show that the combination of the second order slip condition and the second order jump condition predicts better surface pressure and gas temperature than those of the first order slip and jump conditions in all cases studied in comparing with experimental and DSMC data.

Le, Nam T. P.; Roohi, Ehsan

2014-12-01

376

Isotope Effects, Enzyme Kinetics, and Solvent Effects. Abstract: A method for incorporating quantum mechanics into enzyme kinetics modeling is presented. Three aspects are emphasized: (1) combined quantum for computing kinetic isotope effects for chemical reactions in solution and in enzymes. In the ensemble

Minnesota, University of

377

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, UniversitĂ© de

378

Kinetics of the reaction between ozone and phenolic acids present in agro-industrial wastewaters

The kinetics of the ozonation of three phenolic acids is investigated from ozone absorption experiments in a semi-continuous reactor. After the evaluation of stoichiometric ratios for the individual reactions between ozone and each phenolic acid, the oxidation of p-hydroxybenzoic acid by ozone is performed in a first stage. The influence of the operating variables on the degradation process is established,

Jesus Beltran-Heredia; Joaquin Torregrosa; Joaquin R. Dominguez; Jose A. Peres

2001-01-01

379

The decomposition reaction kinetics of the double-base (DB) rocket propellant composed of the mixed ester of triethyleneglycol dinitrate (TEGDN) and nitroglycerin (NG), and nitrocellulose (NC) with lanthanum citrate as a combustion catalyst was investigated by thermogravimetry and differential thermogravimetry (TG-DTG), and differential scanning calorimetry (DSC) under atmospheric pressure and flowing nitrogen gas conditions. The results showed that the thermal decomposition

Jianhua Yi; Fengqi Zhao; Siyu Xu; Hongxu Gao; Rongzu Hu; Haixia Hao; Qing Pei; Yin Gao

2007-01-01

380

Kinetics of Enol Formation from Reaction of OH with Propene Lam K. Huynh,,

Kinetics of Enol Formation from Reaction of OH with Propene Lam K. Huynh,, Hongzhi R. Zhang*, Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, UniVersity of Utah, Salt Lake City, Utah 84112, Department of Chemical Engineering, UniVersity of Utah, Salt Lake City, Utah 84112

Utah, University of

381

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

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

Brian W. Sheldon; Theodore M. Besmann

1991-01-01

382

Marcus Theory: Thermodynamics CAN Control the Kinetics of Electron Transfer Reactions

ERIC Educational Resources Information Center

Although it is generally true that thermodynamics do not influence kinetics, this is NOT the case for electron transfer reactions in solution. Marcus Theory explains why this is so, using straightforward physical chemical principles such as transition state theory, Arrhenius' Law, and the Franck-Condon Principle. Here the background and…

Silverstein, Todd P.

2012-01-01

383

An Inexpensive Kinetic Study: The Reaction of FD&C Red #3 (Erythrosin B) with Hypochlorite

ERIC Educational Resources Information Center

Kinetics constitutes a core topic in both the lecture and laboratory components of lower- level chemistry courses. While textbook examples can ignore issues of time, temperature and safety, the laboratory can not. Reactions must occur slowly enough to be detected by students, occur rapidly enough for data collection in the few hours assigned to a…

Henary, Maher M.; Russell, Arlene A.

2007-01-01

384

Interfacial reaction kinetics of coated SiC fibers with various titanium alloys

NASA Technical Reports Server (NTRS)

The kinetics of the reaction between the silicon carbide fibers and the titanium-based alloy matrix was investigated at temperatures from 800 to 1000 C for several titanium-based alloys (including Ti-1100 alloy and BETA 21S) and unalloyed Ti, reinforced with coated silicon carbide fiber SCS-6. The reaction zone growth kinetics was studied by exposing vacuum encapsulated samples to temperatures from 700 to 1000 C for times up to 150 hrs, followed by SAM observations of samples which were polished perpendicular to the fiber axis and etched. It was found that the reaction zone growth kinetics of the alpha (hcp) and beta (bcc) phases of unalloyed titanium reacting with SCS-6 fibers exhibited different values of the apparent activation energy and of the preexponential factor. Additions of other metals to Ti was found to slow down the reaction kinetics. Among the alloys studied, the Ti-1100 was the slowest reacting conventional alloy and the Ti-14Al-21Nb (in wt pct) was the slowest overall.

Gundel, D. B.; Wawner, F. E.

1991-01-01

385

Employing Magnetic Levitation to Monitor Reaction Kinetics and Measure Activation Energy

ERIC Educational Resources Information Center

This article describes a simple and inexpensive undergraduate-level kinetics experiment that uses magnetic levitation to monitor the progress and determine the activation energy of a condensation reaction on a polymeric solid support. The method employs a cuvette filled with a paramagnetic solution positioned between two strong magnets. The…

Benz, Lauren; Cesafsky, Karen E.; Le, Tran; Park, Aileen; Malicky, David

2012-01-01

386

Pulsed laser photolysis kinetics study of the O(3P) + ClO reaction

NASA Technical Reports Server (NTRS)

A pulsed laser photolysis technique was used to investigate the kinetics of the important stratospheric reaction O + ClO yields Cl + O2 in buffer gas over the temperature and pressure ranges of 231-367 K and 25-500 torr. The results indicate a lack of pressure dependence at 298 K over the 25-500 torr range.

Nicovich, J. M.; Wine, P. H.; Ravishankara, A. R.

1988-01-01

387

with high efficiency into the vacuum system of the single particle mass spectrometer using an aerodynamics in its infancy.1 Many such materials are produced by spray-pyrolysis techniques in which liquid dropletsMeasurement of Condensed-Phase Reaction Kinetics in the Aerosol Phase Using Single Particle Mass

Zachariah, Michael R.

388

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

1998-01-01

389

ERIC Educational Resources Information Center

Three experiments using merocyanine M suitable as an integrated laboratory experience for undergraduates are described. Experiments demonstrate: complete molecular cycle composed of photochemical, thermal, and protolytic reaction steps; kinetics of cis-trans isomerization of the dye; and mechanism of base catalysis for thermal isomerization of the…

Abdel-Kader, M. H.; Steiner, U.

1983-01-01

390

SurfKin: an ab initio kinetic code for modeling surface reactions.

In this article, we describe a C/C++ program called SurfKin (Surface Kinetics) to construct microkinetic mechanisms for modeling gas-surface reactions. Thermodynamic properties of reaction species are estimated based on density functional theory calculations and statistical mechanics. Rate constants for elementary steps (including adsorption, desorption, and chemical reactions on surfaces) are calculated using the classical collision theory and transition state theory. Methane decomposition and water-gas shift reaction on Ni(111) surface were chosen as test cases to validate the code implementations. The good agreement with literature data suggests this is a powerful tool to facilitate the analysis of complex reactions on surfaces, and thus it helps to effectively construct detailed microkinetic mechanisms for such surface reactions. SurfKin also opens a possibility for designing nanoscale model catalysts. PMID:25111729

Le, Thong Nguyen-Minh; Liu, Bin; Huynh, Lam K

2014-10-01

391

Form and motion processing of second-order stimuli in color vision.

We investigate whether there are second-order form and motion mechanisms in human color vision. Second-order stimuli are contrast modulations of a noise carrier. The contrast envelopes are static Gabors of different spatial frequencies (0.125-1 cycles/°) or drifting Gabors of different temporal frequencies (0.25 cycles/°, 0.5-4 Hz). Stimuli are isoluminant red-green or achromatic. Second-order form processing is measured using a simultaneous 2IFC (two-interval forced-choice) detection and orientation identification task, and direction identification is used for second-order motion processing. We find that for simple detection thresholds, chromatic performance is as good or better than achromatic performance, whereas for both motion and form tasks, chromatic performance is poorer than achromatic. Chromatic second-order form perception is very poor across all spatial and temporal frequencies measured and has a lowpass contrast modulation sensitivity function with a spatial cutoff of 1 cycle/° and temporal cutoff of 4 Hz. Chromatic second-order motion sensitivity is even poorer than for form and typically is limited to 1-2 Hz. To determine whether this residual motion processing might be based on feature tracking, we used the pedestal paradigm of Lu and Sperling (1995). We find that adding a static pedestal of the same spatial frequency as the drifting Gabor envelope, with its contrast set to 1-2 times its detection threshold, impairs motion direction performance for the chromatic stimuli but not the achromatic. This suggests that the motion of second-order chromatic stimuli is not processed by a second-order system but by a third-order, feature-tracking system, although a genuine second-order motion system exists for achromatic stimuli. PMID:23766541

Garcia-Suarez, Luis; Mullen, Kathy T

2013-01-01

392

Macroscopic Kinetic Effect of Cell-to-Cell Variation in Biochemical Reactions

NASA Astrophysics Data System (ADS)

Genetically identical cells under the same environmental conditions can show strong variations in protein copy numbers due to inherently stochastic events in individual cells. We here develop a theoretical framework to address how variations in enzyme abundance affect the collective kinetics of metabolic reactions observed within a population of cells. Kinetic parameters measured at the cell population level are shown to be systematically deviated from those of single cells, even within populations of homogeneous parameters. Because of these considerations, Michaelis-Menten kinetics can even be inappropriate to apply at the population level. Our findings elucidate a novel origin of discrepancy between in vivo and in vitro kinetics, and offer potential utility for analysis of single-cell metabolomic data.

Kim, Pan-Jun; Price, Nathan D.

2010-04-01

393

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

NASA Technical Reports Server (NTRS)

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

Lian, Yongsheng; Xu, Kun

1999-01-01

394

Bench-scale Kinetics Study of Mercury Reactions in FGD Liquors

This document is the final report for Cooperative Agreement DE-FC26-04NT42314, 'Kinetics Study of Mercury Reactions in FGD Liquors'. The project was co-funded by the U.S. DOE National Energy Technology Laboratory and EPRI. The objective of the project has been to determine the mechanisms and kinetics of the aqueous reactions of mercury absorbed by wet flue gas desulfurization (FGD) systems, and develop a kinetics model to predict mercury reactions in wet FGD systems. The model may be used to determine optimum wet FGD design and operating conditions to maximize mercury capture in wet FGD systems. Initially, a series of bench-top, liquid-phase reactor tests were conducted and mercury species concentrations were measured by UV/visible light spectroscopy to determine reactant and byproduct concentrations over time. Other measurement methods, such as atomic absorption, were used to measure concentrations of vapor-phase elemental mercury, that cannot be measured by UV/visible light spectroscopy. Next, a series of bench-scale wet FGD simulation tests were conducted. Because of the significant effects of sulfite concentration on mercury re-emission rates, new methods were developed for operating and controlling the bench-scale FGD experiments. Approximately 140 bench-scale wet FGD tests were conducted and several unusual and pertinent effects of process chemistry on mercury re-emissions were identified and characterized. These data have been used to develop an empirically adjusted, theoretically based kinetics model to predict mercury species reactions in wet FGD systems. The model has been verified in tests conducted with the bench-scale wet FGD system, where both gas-phase and liquid-phase mercury concentrations were measured to determine if the model accurately predicts the tendency for mercury re-emissions. This report presents and discusses results from the initial laboratory kinetics measurements, the bench-scale wet FGD tests, and the kinetics modeling efforts.

Gary Blythe; John Currie; David DeBerry

2008-03-31

395

Constraints on the second order transport coefficients of an uncharged fluid

In this note we have tried to determine how the existence of a local entropy current with non-negative divergence constrains the second order transport coefficients of an uncharged fluid, following the procedure described in \\cite{Romatschke:2009kr}. Just on symmetry ground the stress tensor of an uncharged fluid can have 15 transport coefficients at second order in derivative expansion. The condition of entropy-increase gives five relations among these 15 coefficients. So finally the relativistic stress tensor of an uncharged fluid can have 10 independent transport coefficients at second order.

Sayantani Bhattacharyya

2012-06-29

396

First and Second Order Necessary Conditions for Stochastic Optimal Control Problems

In this work we consider a stochastic optimal control problem with either convex control constraints or finitely many equality and inequality constraints over the final state. Using the variational approach, we are able to obtain first and second order expansions for the state and cost function, around a local minimum. This fact allows us to prove general first order necessary condition and, under a geometrical assumption over the constraint set, second order necessary conditions are also established. We end by giving second order optimality conditions for problems with constraints on expectations of the final state.

Bonnans, J. Frederic, E-mail: Frederic.Bonnans@inria.fr [Ecole Polytechnique, INRIA-Saclay and CMAP (France); Silva, Francisco J., E-mail: fsilva@mat.uniroma1.it [Dipartimento di Matematica Guido Castelnuovo (Italy)

2012-06-15

397

Second-Order Born Effect in Single Ionization of Argon by Electron Impact

NASA Astrophysics Data System (ADS)

We extend the standard distorted wave Born approximation (DWBA) to include the second-order Born amplitude in order to describe the multiple interactions between a projectile and an atomic target. Both the first- and second- order DWBA models are used to calculate triply differential cross sections (TDCS) of coplanar (e, 2e) on atomic argon with the scattered electron energy fixed at 500 eV, the scattering angle at 6° and the ejected electron energies at 37, 74 and 205 eV. Overall agreements with experimental measurements have been obtained in shape, and the second-order DWBA model improves the calculations as expected, especially for recoil peak of TDCS.

Wang, Yang; Zhou, Ya-Jun; Jiao, Li-Guang

2012-01-01

398

Second-order Born effect in coplanar doubly symmetric (e,2e) collisions for sodium

NASA Astrophysics Data System (ADS)

The second-order distorted wave Born approximation (DWBA) method is employed to investigate the triple differential cross sections (TDCS) of coplanar doubly symmetric (e,2e) collisions for alkali target sodium at excess energies of 6-60 eV. Comparing with the first-order DWBA calculations, the inclusion of second-order Born term in the scattering amplitude improves the degree of agreement with experiments, especially for backward scattering region of TDCS. This indicates the present second-order Born term is capable to give a reasonable correction to DWBA model in studying coplanar symmetric (e,2e) problems in low and intermediate energy range.

Wang, Yang; Jiao, Liguang; Zhou, Yajun

2012-06-01

399

ERIC Educational Resources Information Center

The effects of self-assembly on the hydrolysis kinetics of surfactants that contain ester bonds are discussed. A number of examples on how reaction rates and apparent reaction orders can be modulated by changes in the conditions, including an instance of apparent zero-order kinetics, are presented. Furthermore, it is shown that the examples on…

Lundberg, Dan; Stjerndahl, Maria

2011-01-01

400

Kinetics of SiC Formation During High P-T Reaction Between Diamond and Silicon

Time-resolved in situ X-ray diffraction at simultaneous high pressures (P) and high temperatures (T) was used to monitor kinetics of the reaction between diamond and silicon. Analysis of the data indicated that the reaction was diffusion controlled, and the diffusion was taking place through grain boundaries. For the nm size diamond the activation energy (170 kJ/mol) was smaller than that for {mu}m size diamond (260 kJ/mol), and the reaction started at a temperature below the melting point of silicon. These effects are attributed to nanocrystalline structure and strained bonds within grain boundaries.

Pantea,C.; Voronin, G.; Zerda, T.; Wang, L.; Zhao, Y.

2005-01-01

401

NASA Astrophysics Data System (ADS)

Ab initio and chemical kinetic study of the hydrogen abstraction reactions by the hydrogen radical on ethyl formate, ethyl acetate, ethyl propanoate, and ethyl butanoate have been performed at the CCSD(T)/CBS//B3LYP/6-311G(d, p) level of theory. High-pressure limit rate constants at temperatures from 300 to 2500 K have been calculated for all of the reaction channels using transition state theory with Eckart tunneling corrections, and the data are fitted to the modified three parameters Arrhenius expression using least-squares regression. A branching ratio analysis for each reaction site has also been investigated for all of the ethyl esters.

Wang, Quan-De; Wang, Xing-Jian; Liu, Zi-Wu; Kang, Guo-Jun

2014-11-01

402

The effects of wood species and treatment retention on kinetics of CCA-C fixation reactions

Reaction kinetics of fixation of CCA-C (chromated copper arsenate type C) preservative was studied at 30°C in ground wood\\u000a of trembling aspen, red pine, and red maple at treatment retentions of 4.0, 6.4, 9.6, and 30 kg\\/m3, and red maple pre-extracted with hot water at retentions of 6.4 and 30 kg\\/m3. Reaction orders of cumulative Cr, Cu, and As reactions decreased gradually

Suzana Radivojevic; Paul A. Cooper

2010-01-01

403

A comprehensive kinetic model for the COCO 2 reaction with iron oxide-containing slags

A comprehensive kinetic model has been developed that enables the rate of the CO-CO2 reaction with FeO\\u000a x\\u000a -containing slags to be predicted. The model was developed considering a reaction mechanism involving adsorption of CO2 at the surface, charge transfer to the adsorbed CO2, and, finally, dissociation of CO\\u000a 2\\u000a ?\\u000a . The rate-determining step of the reaction was found

Mansoor Barati; Kenneth S. Coley

2006-01-01

404

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

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

1971-01-01

405

This review seeks to bring together a selection of recent laboratory work on gas phase photochemistry, kinetics and reaction dynamics of radical species relevant to the understanding of planetary atmospheres other than that of Earth. A majority of work focuses on the rich organic chemistry associated with photochemically initiated reactions in the upper atmospheres of the giant planets. Reactions relevant to Titan, the largest moon of Saturn and with a nitrogen/methane dominated atmosphere, have also received much focus due to potential to explain the chemistry of Earth's prebiotic atmosphere. Analogies are drawn between the approaches of terrestrial and non-terrestrial atmospheric chemistry. PMID:22880207

Blitz, M A; Seakins, P W

2012-10-01

406

A second-order modelling of a stably stratified sheared turbulence submitted to a non-vertical shear

NASA Astrophysics Data System (ADS)

In this work, the evolution of homogeneous stably stratified turbulence submitted to a non-vertical shear is studied using second-order closure models. Two cases of turbulent flows are considered. Firstly, the case of a purely horizontal shear is considered. In this case, the evolution of the turbulence is studied according to the Richardson number Ri which is varied from 0.2 to 2.0 when other parameters are kept constant. In the second case, two components of shear are present. The turbulence is submitted to a vertical component Sv = partU1/partx3 = S cos(thgr) and a horizontal component Sh = partU1/partx2 = S sin(thgr). In this case, we study the influence of shear inclination angle thgr on the evolution of turbulence. In both cases, we are referred respectively to the recent direct numerical simulations of Jacobitz (2002 J. Turbulence 3 055) and Jacobitz and Sarkar (1998 Phys. Fluids 10 1158-68) which are, to our knowledge, the most recent results of the above-mentioned flows. Transport equations of second-order moments \\overline{u_{i} u_{j}} , \\overline{u_{i} \\rho } , \\overline{\\rho^{2}} are derived. The Shih-Lumley (SL) (Shih T H 1996 Turbulence Transition and Modeling ed H D S Henningson, A V Johansson and P H Alfredsson (Dordrecht: Kluwer); Shih and Lumley J L 1989 27th Aerospace Meeting 9-12 January, Center of Turbulent Research, Nevada) and the Craft-Launder (CL) (Craft T J and Launder B E 1989 Turbulent Shear Flow Stanford University, USA, pp 12-1-12-6 Launder B E 1996 Turbulence Transition and Modeling ed H D S Henningson, A V Johansson and P H Alfredsson (Dordrecht: Kluwer)) second-order models are retained for the pressure-strain correlation phgrij and the pressure-scalar gradient correlation phgrirgr. The corresponding models are also retained for the dissipation egr of the turbulent kinetic energy and an algebraic model is retained for the dissipation egrrgrrgr of the variance of the scalar. A fourth-order Runge-Kutta method is used for the numerical integration of the closed systems of non-linear dimensionless differential equations. A good agreement between the predictions of second-order models and values of direct numerical simulation of Jacobitz has been generally observed for the principal component of anisotropy b12. A qualitative agreement has been observed for the ratios K/E and Krgr/E of the kinetic and potential energies to the total energy E.

Bouzaiane, Mounir; Ben Abdallah, Hichem; Lili, Taieb

2004-09-01

407

Kinetics of the Br2-CH3CHO Photochemical Chain Reaction

NASA Technical Reports Server (NTRS)

Time-resolved resonance fluorescence spectroscopy was employed in conjunction with laser flash photolysis of Br2 to study the kinetics of the two elementary steps in the photochemical chain reaction nBr2 + nCH3CHO + hv yields nCH3CBrO + nHBr. In the temperature range 255-400 K, the rate coefficient for the reaction Br((sup 2)P(sub 3/2)) + CH3CHO yields CH3CO + HBr is given by the Arrhenius expression k(sub 6)(T) = (1.51 +/- 0.20) x 10(exp -11) exp(-(364 +/- 41)/T)cu cm/(molecule.s). At 298 K, the reaction CH3CO + Br2 yields CH3CBrO + Br proceeds at a near gas kinetic rate, k(sub 7)(298 K) = (1.08 +/- 0.38) x 10(exp -10)cu cm/(molecule.s).

Nicovich, J. M.; Shackelford, C. J.; Wine, P. H.

1997-01-01

408

Carbon kinetic isotope effect in the reaction of CH4 with HO

NASA Technical Reports Server (NTRS)

The carbon kinetic isotope effect in the CH4 + HO reaction is measured experimentally and the use of carbon isotope ratios to diagnose atmospheric methane is examined. The chemical, photolysis, and analytical experimental conditions and procedures are described. It is determined that the CH4 + HO reaction has a carbon kinetic isotope effect of 1.010 + or 0.007 for k(12)k(13) (rate constants ratio) at 297 + or - 3 K. This value is compared with the data of Rust and Stevens (1980). Causes for the poor correlation between the data at high methane conversions are discussed. It is supposed that the difference between the k(12) and k(13) values is due to a difference in the activation energy of the two reactions.

Davidson, J. A.; Cantrell, C. A.; Tyler, S. C.; Shetter, R. E.; Cicerone, R. J.

1987-01-01

409

Label-free measurements of reaction kinetics using a droplet-based optofluidic device.

Label-free measurements of the reaction kinetics of a small sample volume are essential for efficient drug discovery, requiring methods and systems that are rapid, accurate, and cost-effective. Herein, we present an integrated optofluidic system for label-free characterization of reactions in a nanoliter reagent volume. This system contains a droplet-based microfluidic sampling section and an optical fiber-based spectroscopy detection section. By manipulating droplets containing reagents at certain concentrations at different times, quantifiable measurements via absorption spectroscopy can be made in a simple, sensitive, and high-throughput manner. We have demonstrated our system's capability by performing potency (IC50) assays of an inhibitor in a TEM-1 ?-lactamase (enzyme) and nitrocefin (substrate) system. This integrated platform can potentially provide an automated, label-free, and low-cost method for many other assays of reaction kinetics. PMID:25249275

Mao, Zhangming; Guo, Feng; Xie, Yuliang; Zhao, Yanhui; Lapsley, Michael Ian; Wang, Lin; Mai, John D; Costanzo, Francesco; Huang, Tony Jun

2015-02-01

410

The oxidation reaction kinetics of thiocyanate by excess hydrogen peroxide has been studied by using capillary electrophoresis. The paper illustrates for the first time the use of capillary electrophoresis in studying reaction kinetics and provides a non-laborious way to determine the rate law and the rate constant for the above reaction in the pH range 6-8. Standard solutions of thiocyanate were mixed with buffer solutions of different pHs (6-8) and the reactions were initiated by adding appropriate volumes of hydrogen peroxide in capillary electrophoresis vials. Each reaction mixture was sampled at regular time intervals using an automatic injection programme to follow the progress of the reaction and identify the reaction products. The peak areas, representing the products, were integrated and their concentrations were quantified using calibration plots. The concentration profiles obtained from a series of experiments at a particular pH were then used to determine the rate law and the rate constant for the reaction. Furthermore, the rate of decomposition of hypothiocyanite formed during the reaction is determined for the first time. The rate law is zero order with respect to hypothiocyanite and first order with respect to hydrogen peroxide. The results indicate that the rate law for the oxidation reaction is zero order with respect to thiocyanate and first order with respect to hydrogen peroxide. The rate constant for the reaction at 25 degrees C and at zero ionic strength is 3.6(+/-0.2)x10((-4)) min(-1). PMID:18967936

Christy, A A; Egeberg, P K

2000-05-01

411

Kinetic Monte Carlo simulations of one-dimensionally diffusing interstitial clusters (dislocation loops) are used to gain insight into their role in microstructure evolution under irradiation. The simulations investigate the changes in reaction kinetics of these defects as a function of changes in the Burgers vector and variation in the size and density of randomly or periodically distributed sinks. In this paper

Howard L. Heinisch; Bachu N. Singh; Stanislav I. Golubov

2000-01-01

412

Kinetics and activation parameters of the reaction of organoarsenic(V) compounds with glutathione.

In this work the kinetics of the reaction of glutathione (GSH) with the organoarsenic(V) compounds phenylarsonic acid (PAA), 4-hydroxy-3-nitrophenylarsonic acid (HNPAA), p-aminophenylarsonic acid (p-APAA) and o-aminophenylarsonic acid (o-APAA) as well as monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) is investigated. The reaction progress is monitored in real time by (1)H NMR, allowing the determination of rate coefficients and half-lives as well as activation parameters. The reaction consists of two steps: redox reaction and conjugation. In all investigated systems the conjugation is fast compared to the redox reaction and, therefore, rate determining. All investigated phenylarsonic acids follow the same rate law, showing overall reaction orders of 3 and half-lives between 47.7 ± 0.2 and 71.0 ± 3.6 min. The methylated compounds react slower, showing half-lives of 76.6 ± 0.4 and 444 ± 10 min for DMAA and MMAA, respectively. Enthalpies of activation range from 20 to 36 (± 2) kJ mol(-1) and the entropies of activation are within -154 and -97(± 7)J mol(-1)K(-1). The results reveal a correlation of the toxicity of the arsenic compound and the reaction rate with GSH. This may pave the way for the estimation of the toxicity of such compounds by simple kinetic studies. PMID:25238190

Kretzschmar, Jerome; Brendler, Erica; Wagler, Jörg; Schmidt, Anne-Christine

2014-09-15

413

Thermodynamics and kinetics of reactions in protective coating systems

NASA Technical Reports Server (NTRS)

Investigations of fluoride activated packs with Al:Ni ratios greater than 50 a/o prove that the specimen surface is not in equilibrium with the pack at high Al:Ni ratios but that an activity gradient exists between pack and specimen. Therefore, gaseous diffusion and possibly surface reactions play a role in determining the overall rate of Al deposition in such packs. Noticeable differences in coating behavior have been obtained in packs activated with chloride and iodide, and it appears that poorest results are obtained with iodides, better with chlorides, and best with fluorides. A numerical method has been perfected for calculating rates of solid-state diffusion controlled coating formation, allowing for the variation of diffusivity with composition in the NiAl phase. Layer growth rates can now be accurately predicted from a knowledge of the surface and substrate compositions. Furthermore, the correct diffusion profiles are obtained by this method. These differ substantially from the profile obtained when the diffusivity is assumed constant.

Gupta, B.; Sarkhel, A.; Sivakumar, R.; Seigle, L.

1974-01-01

414

A kinetic study of the quenching reaction of singlet oxygen ((1)O(2)) with pyrroloquinolinequinol (PQQH(2), a reduced form of pyrroloquinolinequinone (PQQ)), PQQNa(2) (disodium salt of PQQ), and seven kinds of natural antioxidants (vitamin C (Vit C), uric acid (UA), epicatechin (EC), epigallocatechin (EGC), ?-tocopherol (?-Toc), ubiquinol-10 (UQ(10)H(2)), and ?-carotene (?-Car)) has been performed. The second-order rate constants k(Q) (k(Q) = k(q) + k(r), physical quenching and chemical reaction) for the reaction of (1)O(2) with PQQH(2), PQQNa(2), and seven kinds of antioxidants were measured in 5.0 wt % Triton X-100 micellar solution (pH 7.4), using UV-visible spectrophotometry. The k(Q) values decreased in the order of ?-Car > PQQH(2) > ?-Toc > UA > UQ(10)H(2) > Vit C ? EGC > EC ? PQQNa(2). PQQH(2) is a water-soluble antioxidant. The singlet oxygen-quenching activity of PQQH(2) was found to be 6.3, 2.2, 6.1, and 22 times as large as the corresponding those of water-soluble antioxidants (Vit C, UA, EGC, and EC). Further, the activity of PQQH(2) was found to be 2.2 and 3.1 times as large as the corresponding activity of lipid-soluble antioxidants (?-Toc and UQ(10)H(2)). On the other hand, the activity of PQQH(2) is 6.4 times as small as that of ?-Car. It was observed that the chemical reaction (k(r)) is almost negligible in the quenching reaction of (1)O(2) by PQQH(2). The result suggests that PQQH(2) may contribute to the protection of oxidative damage in biological systems, by quenching (1)O(2). PMID:21309575

Mukai, Kazuo; Ouchi, Aya; Nakano, Masahiko

2011-03-01

415

Least Squares Second Order Radiative Transfer Equation and Meshless Method Solution

To overcome the singularity problem of the SORTE [Numer. Heat Transfer B 51 (2007) 391-409] in dealing with inhomogeneous media where some position is with very small/zero extinction coefficient, a new second order formula of radiative transfer equation which owns the characteristics of least squares approach (termed here the Least squares Second Order Radiative Transfer Equation, LSORTE) is proposed. A diffusion (second order) term is naturally introduced in the LSORTE, which provides much better numerical property than the classic first order radiative transfer equation (RTE). The discretization of the LSORTE by weighted residual approach with standard Galerkin scheme leads to a formulation exactly the same as the least squares scheme discretization of the RTE. A problem of the second order form of RTE in dealing with inhomogeneous medium with discontinuity in distribution of extinction coefficient is observed and an amendment scheme is proposed. The collocation meshless methods based on the moving least sq...

Zhao, J M; Liu, L H

2011-01-01

416

In this paper a second-order method for blind source separation of noisy instantaneous linear mixtures is presented for the case where the signal order k is unknown. Its performance advantages are illustrated by simulations ...

Mueller, Amy V.

417

Second-order global consensus in multiagent networks with random directional link failure.

In this paper, we consider the second-order globally nonlinear consensus in a multiagent network with general directed topology and random interconnection failure by characterizing the behavior of stochastic dynamical system with the corresponding time-averaged system. A criterion for the second-order consensus is derived by constructing a Lyapunov function for the time-averaged network. By associating the solution of random switching nonlinear system with the constructed Lyapunov function, a sufficient condition for second-order globally nonlinear consensus in a multiagent network with random directed interconnections is also established. It is required that the second-order consensus can be achieved in the time-averaged network and the Lyapunov function decreases along the solution of the random switching nonlinear system at an infinite subsequence of the switching moments. A numerical example is presented to justify the correctness of the theoretical results. PMID:25095263

Li, Huaqing; Liao, Xiaofeng; Huang, Tingwen; Zhu, Wei; Liu, Yanbing

2015-03-01

418

B polarization of cosmic background radiation from second-order scattering sources

B-mode polarization of the cosmic background radiation is induced from purely scalar primordial sources at second order in perturbations of the homogeneous, isotropic universe. We calculate the B-mode angular power spectrum C{sub l}{sup BB} sourced by the second-order scattering term in the full second-order Boltzmann equations for the polarized radiation phase-space density, which have recently become available. We find that at l ? 200 the second-order effect is comparable to the first-order effect for a tensor-to-scalar ratio of r = 10{sup ?6}, and to about 2·10{sup ?4} at l ? 1000. It is always negligible relative to the weak-lensing induced contribution.

Beneke, M.; Fidler, C.; Klingmüller, K. [Institut für Theoretische Teilchenphysik und Kosmologie, RWTH Aachen University, D-52056 Aachen (Germany)

2011-04-01

419

Groups, Graphs, Languages, Automata, Games and Second-order Monadic Logic

In this paper we survey some surprising connections between group theory, the theory of automata and formal languages, the theory of ends, infinite games of perfect information, and monadic second-order logic.

Ceccherini-Silberstein, Tullio; Fiorenzi, Francesca; Schupp, Paul E

2012-01-01

420

Structure Theory for Second Order 2D Superintegrable Systems with 1-Parameter Potentials

The structure theory for the quadratic algebra generated by first and second order constants of the motion for 2D second order superintegrable systems with nondegenerate (3-parameter) and or 2-parameter potentials is well understood, but the results for the strictly 1-parameter case have been incomplete. Here we work out this structure theory and prove that the quadratic algebra generated by first and second order constants of the motion for systems with 4 second order constants of the motion must close at order three with the functional relationship between the 4 generators of order four. We also show that every 1-parameter superintegrable system is St\\"ackel equivalent to a system on a constant curvature space.

Ernest G. Kalnins; Jonathan M. Kress; Willard Miller Jr.; Sarah Post

2009-01-20

421

A boundary element method is derived for solving a class of boundary value problems governed by an elliptic second order linear partial differential equation with variable coefficients. Numerical results are given for a specific test problem.

D. L. Clements

1996-01-01

422

We have studied the excitation second-order nonlinearity through a triangular lattice perforated gold film instead of square lattice in many papers. Under the excitation of surface plasmas resonance effect, the second order nonlinearity exists in the noncentrosymmetric split-ring resonators arrays. Reflection of fundamental frequency wave through a triangular lattice perforated gold film is obtained. We also described the second harmonic conversion efficiencies in the second order nonlinear optical process with the spectra. Moreover, the electric field distributions of fundamental frequency above the gold film region are calculated. The light propagation through the holes results in the enhancement of the second order nonlinearity including second harmonic generation as well as the sum (difference) frequency generation. PMID:24693233

Chen, Xiaoshuang; Xiao, Yingyi; Zhou, Bingju; Wu, Lingxi; Liu, Xiaojuan; Gao, Yongyi; Zhan, Jie

2014-01-01

423

Prediction of stably stratified homogeneous shear flows with second-order turbulence models

NASA Astrophysics Data System (ADS)

The present study investigated the role of pressure-correlation second-order turbulence modelling schemes on the predicted behaviour of stably stratified homogeneous vertical-sheared turbulence. The pressure-correlation terms were modelled with a nonlinear formulation (Craft 1991), which was compared with a linear pressure-strain model and the 'isotropization of production' model for the pressure-scalar correlation. Two additional modelling issues were investigated: the influence of the buoyancy term in the kinetic energy dissipation rate equation and the time scale in the thermal production term in the scalar variance dissipation equation. The predicted effects of increasing the Richardson number on turbulence characteristics were compared against a comprehensive set of direct numerical simulation databases. The linear models provide a broadly satisfactory description of the major effects of the Richardson number on stratified shear flow. The buoyancy term in the dissipation equation of the turbulent kinetic energy generates excessively low levels of dissipation. For moderate and large Richardson numbers, the term yields unrealistic linear oscillations in the shear and buoyancy production terms, and therefore should be dropped in this flow (or at least their coefficient c?3 should be substantially reduced from its standard value). The mechanical dissipation time scale provides marginal improvements in comparison to the scalar time scale in the production. The observed inaccuracy of the linear model in predicting the magnitude of the effects on the velocity anisotropy was demonstrated to be attributed mainly to the defective behaviour of the pressure-correlation model, especially for stronger stratification. The turbulence closure embodying a nonlinear formulation for the pressure-correlations and specific versions of the dissipation equations failed to predict the tendency of the flow to anisotropy with increasing stratification. By isolating the effects of the dissipation rate equations, it was demonstrated that nonlinear closure provides an improved account of the normal components of the anisotropy tensor over the linear model; however, the vertical velocity correlation and the shear stress still present too large a discrepancy. The observed shortcomings may be intrinsic to the current structure of the pressure-correlation terms. None of the models were able to predict the ultimate collapse of the turbulent fluxes and counter-gradient fluxes. However, this weakness may be beyond the modelling of the redistribution processes, but instead in fundamental shortcomings in the energy dissipation rate equations and the dissipation tensor to adequately represent the phenomenology of the transition from shear- to buoyancy-dominated flows.

Pereira, J. C. F.; Rocha, J. M. P.

2010-08-01

424

Second-order Percus-Yevick theory for a confined hard-sphere fluid

A fluid of hard spheres confined between two hard walls and in equilibrium with a bulk hard-sphere fluid is studied using\\u000a a second-order Percus-Yevick approximation. We refer to this approximation as second-order because the correlations that are\\u000a calculated depend upon the position of two hard spheres in the confined fluid. However, because the correlation functions\\u000a depend upon the positions of

Douglas Henderson; Stefan Sokolowski; Darsh Wasan

1997-01-01

425

Short note on second-order gauge-invariant cosmological perturbation theory

The second order perturbations in Friedmann-Robertson-Walker universe filled with a perfect fluid are completely formulated in the gauge invariant manner without any gauge fixing. All components of the Einstein equations are derived neglecting the first order vector and tensor modes. These equations imply that the tensor and the vector mode of the second order metric perturbations may be generated by the non-linear effects of the Einstein equations from the first order density perturbations.

Kouji Nakamura

2006-12-07

426

Intermittent tethering of second-order chords after mitral valve repair for bileaflet prolapse.

Mitral valve regurgitation which occurs immediately after repair can be due to anatomic (failure of repair) or functional (systolic anterior motion) reasons. We report a case where a patient with bileaflet prolapse showed, after surgical correction of the disease, moderate to severe regurgitation after cardiopulmonary bypass was stopped. The regurgitation was due to second-order tethering and was successfully treated with second-order chordal cutting. PMID:24296225

Iacň, Angela L; Ahmed, Ahmed A; Al Zaharani, Gormallah; Al Amri, Hussein; Di Mauro, Michele; Calafiore, Antonio M

2013-12-01

427

A Second-Order Dual X-\\/Ka-Band Frequency Selective Surface

In this letter, a new technique for designing dual-band frequency selective surfaces with arbitrary bands of operation, with second-order band-pass responses at each band of operation, is presented and experimentally verified. The technique is based on utilizing a particular topology of a second-order band-pass microwave filter and synthesizing its constituting elements using periodic structures with inductive, capacitive, or resonant type

Mohsen Salehi; Nader Behdad

2008-01-01

428

A New Technique for Design of Low-Profile, Second-Order, Bandpass Frequency Selective Surfaces

In this study, a new method for designing low profile frequency selective surfaces (FSS) with second-order bandpass responses is presented. The FSSs designed using this technique utilize non-resonant subwavelength constituting unit cells with unit cell dimensions and periodicities in the order of 0.15lambda0. It is demonstrated that using the proposed technique, second-order FSSs with an overall thickness of lambda0\\/30 can

Mudar Al-Joumayly; Nader Behdad

2009-01-01

429

Derivation of directional ocean-wave spectra by integral inversion of second-order radar echoes

The derivation of sea-state from a single decameter radio wave-scatter observation requires the inversion of a two-dimensional nonlinear integral equation which gives the second-order radar cross section in terms of the ocean-wave spectrum. The second-order structure is sensitive to the directional properties of waves moving slower than the wind and the total nondirectional energy spectrum. We show how these properties,

Belinda Lipa

1977-01-01

430

In this study we compare the use of kinetic and equilibriumreaction models in the simulation of gas (methane) hydrate behavior inporous media. Our objective is to evaluate through numerical simulationthe importance of employing kinetic versus equilibrium reaction modelsfor predicting the response of hydrate-bearing systems to externalstimuli, such as changes in pressure and temperature. Specifically, we(1) analyze and compare the responses simulated using both reactionmodels for natural gas production from hydrates in various settings andfor the case of depressurization in a hydrate-bearing core duringextraction; and (2) examine the sensitivity to factors such as initialhydrate saturation, hydrate reaction surface area, and numericaldiscretization. We find that for large-scale systems undergoing thermalstimulation and depressurization, the calculated responses for bothreaction models are remarkably similar, though some differences areobserved at early times. However, for modeling short-term processes, suchas the rapid recovery of a hydrate-bearing core, kinetic limitations canbe important, and neglecting them may lead to significantunder-prediction of recoverable hydrate. The use of the equilibriumreaction model often appears to be justified and preferred for simulatingthe behavior of gas hydrates, given that the computational demands forthe kinetic reaction model far exceed those for the equilibrium reactionmodel.

Kowalsky, Michael B.; Moridis, George J.

2006-11-29

431

Kinetic parameters of radical reactions of 2-mercaptobenzothiazole with quinone imines

NASA Astrophysics Data System (ADS)

The chain reaction of N, N'-diphenyl-1,4-benzoquinone diimine with 2-mercaptobenzothiazole was studied by two methods developed earlier for the nonchain reaction of N-phenyl-1,4-benzoquinone monoimine with 2-mercaptobenzothiazole. In the methods used, the kinetic scheme of the reaction is simplified by creating conditions under which the rates of all stages except radical generation and decay can be neglected. One of the methods was updated. For the nonchain reaction of N-phenyl-1,4-benzoquinone monoimine with 2-mercaptobenzothiazole, both methods gave close results; for the chain reaction of N, N'-diphenyl-1,4-phenylenediamine with 2-mercaptobenzothiazole, the results differed by approximately one order of magnitude.

Varlamov, V. T.; Gadomska, A. V.

2014-09-01

432

Study Design Controlled laboratory study, cross sectional design. Objective To determine if sagittal kinematic variables can be used to estimate select running kinetics. Background Excessive loading during running has been implicated in a variety of injuries, yet this information is typically not assessed during a standard clinical examination. Developing a clinically feasible strategy to estimate ground reaction forces and joint kinetics may improve the ability to identify those at an increased risk of injury. Methods Three-dimensional kinematics and ground reaction forces of 45 participants were recorded during treadmill running at self-selected speed. Kinematic variables used to estimate specific kinetic metrics included: vertical excursion of the center of mass, foot inclination angle at initial contact, horizontal distance between the center of mass and heel at initial contact, knee flexion angle at initial contact, and peak knee flexion angle during stance. Linear mixed effects models were fitted to explore the association between the kinetic and kinematic measures, including step rate and gender, with final models created using backward variable selection. Results Models were developed to estimate peak knee extensor moment (R2=0.43), energy absorbed at the knee during loading response (R2=0.58), peak patellofemoral joint reaction force (R2=0.55), peak vertical ground reaction force (R2=0.48), braking impulse (R2=0.50), and average vertical loading rate (R2=0.04). Conclusions Our findings suggest that insights into important running kinetics can be obtained from a subset of sagittal plane kinematics common to a clinical running analysis. Of note, the limb posture at initial contact influenced subsequent loading patterns in stance. PMID:25156183

Wille, Christa; Lenhart, Rachel; Wang, Sijian; Thelen, Darryl; Heiderscheit, Bryan

2015-01-01

433

In this paper, methods are described that are used for studying first-order reaction kinetics by gas chromatography. Basic theory is summarized and illustrated using the interconversion of 1-chloro-2,2-dimethylaziridine enantiomers as a representative example. For the determination of the kinetic and thermodynamic activation data of interconversion the following methods are reviewed: (i) classical kinetic methods where samples of batch-wise kinetic studies are analyzed by enantioselective gas chromatography, (ii) stopped-flow methods performed on one chiral column, (iii) stopped-flow methods performed on an achiral column or empty capillary coupled in series with two chiral columns, (iv) on-flow method performed on an achiral column coupled in series with two chiral columns, and (v) reaction gas chromatography, known as a dynamic gas chromatography, where the interconversion is performed on chiral column during the separation process. The determination of kinetic and thermodynamic activation data by methods (i) through (iv) is straightforward as the experimental data needed for the evaluation (particularly the concentration of reaction constituents) are accessible from the chromatograms. The evaluation of experiments from reaction chromatography method (v) is complex as the concentration bands of reaction constituents are overlapped. The following procedures have been developed to determination peak areas of reaction constituents in such complex chromatograms: (i) methods based on computer-assisted simulations of chromatograms where the kinetic activation parameters for the interconversion of enantiomers are obtained by iterative comparison of experimental and simulated chromatograms, (ii) stochastic methods based on the simulation of Gaussian distribution functions and using a time-dependent probability density function, (iii) approximation function and unified equation, (iv) computer-assisted peak deconvolution methods. Evaluation of the experimental data permits the calculation of apparent rate constants for both the interconversion of the first eluted (k (A-->B)(app)) as well as the second eluted (k(B-->A)(app)) enantiomer. The mean value for all the rate constants (from all the reviewed methods) was found for 1-chloro-2,2-dimethylaziridine A-->B enantiomer interconversion at 100 degrees C: k (A-->B)(app)=21.2 x 10(-4)s(-1) with a standard deviation sigma=10.7 x 10(-4). Evaluating data for reaction chromatography at 100 degrees C {k (app)=k(A-->B)(app)=k(B-->A)(app)=13.9 x 10(-4)s(-1), sigma=3.0 x 10(-4)s(-1)} shows that differences between k(A-->B)(app) and k(B-->A)(app) are the same within experimental error. It was shown both theoretically and experimentally that the Arrhenius activation energy (E(a)) calculated from Arrhenius plots (lnk(app) versus 1/T) is proportional to the enthalpy of activation {E(a)=DeltaH+RT}. Statistical treatment of Gibbs activation energy values gave: DeltaG (app)=110.5kJmol(-1), sigma=2.4kJmol(-1), DeltaG (A-->B)(app)=110.5kJmol(-1), sigma=2.2kJmol(-1), DeltaG (B-->A)(app)=110.3kJmol(-1), sigma=2.8kJmol(-1). This shows that the apparent Gibbs energy barriers for the interconversion of 1-chloro-2,2-dimethylaziridine enantiomers are equal DeltaG (app)=DeltaG(A-->B)(app)=DeltaG(B-->A)(app) and within the given precision of measurement independent of the experimental method used. PMID:18243224

Krupcík, J; Mydlová, J; Májek, P; Simon, P; Armstrong, D W

2008-04-01

434

NASA Astrophysics Data System (ADS)

Kramers’ model for the rate of chemical reaction is generalized to explain the phenomena of dispersed kinetics and dynamic disorder in biochemical reactions, by incorporating the newly observed power-law friction kernel into the generalized Langevin equation for a one-dimensional reaction ordinate. This new model accounts for time scale overlap between conformational and chemical dynamics, and quantitatively describes the multi-exponential kinetics and memory effects of fluctuating rate constants, which have been revealed by recent single-molecule experiments.

Min, Wei; Xie, X. Sunney

2006-01-01

435

NASA Astrophysics Data System (ADS)

The mixing dynamics resulting from the combined action of diffusion, dispersion, and advective stretching of a reaction front in heterogeneous flows leads to reaction kinetics that can differ by orders of magnitude from those measured in well-mixed batch reactors. The reactive fluid invading a porous medium develops a filamentary or lamellar front structure. Fluid deformation leads to an increase of the front length by stretching and consequently a decrease of its width by compression. This advective front deformation, which sharpens concentration gradients across the interface, is in competition with diffusion, which tends to increase the interface width and thus smooth concentration gradients. The lamella scale dynamics eventually develop into a collective behavior through diffusive coalescence, which leads to a disperse interface whose width is controlled by advective dispersion. We derive a new approach that quantifies the impact of these filament scale processes on the global mixing and reaction kinetics. The proposed reactive filament model, based on the elementary processes of stretching, coalescence, and fluid particle dispersion, provides a new framework for predicting reaction front kinetics in heterogeneous flows.

de Anna, Pietro; Dentz, Marco; Tartakovsky, Alexandre; Le Borgne, Tanguy

2014-07-01

436

Chemical kinetic analysis of hydrogen-air ignition and reaction times

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

437

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

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

438

Estimation of kinetic equations on decomposition of trichloroethylene using Fenton's reaction

NASA Astrophysics Data System (ADS)

Soil and groundwater pollution from trichloroethylene has recently been noted. In the present work kinetics for decomposition of trichloroethylene using Fenton's reaction are discussed. This study found that the reaction was first-order for concentration of trichloroethylene, 0.8-order for concentration of iron ion and half-order for concentrations of hydrogen peroxide. The reaction rate constant was given as 0.205 (l · mol-1) 1.3 · s-1. Additional experiments were carried out in the presence of humic acid (HA), the most abundant organic compound in soil. The reaction with HA was first-order for concentrations of trichloroethylene and Fe (II) iron, and 0.8-order for concentration of hydrogen peroxide, and the reaction rate constant was 0.865 (l · mol-1) 1.8 · s-1. In spite of small difference in reaction order, these reaction rates are almost the same with and without humic acid under the present conditions. At the initial stage of these reactions, concentrations of trichloroethylene were found to be reduced rapidly. The correlation to calculate the reduction amounts is proposed. Finally, equations to predict the variation of trichloroethylene concentration using Fenton's reaction are suggested.

Takuma, Yasuhiko; Kato, Shigeru; Kojima, Toshinori

439

NASA Astrophysics Data System (ADS)

In considering the irreversible chemical reaction A+B\\to C+B in liquid solutions two many-particle approaches to the derivation of binary non-Markovian kinetic equations are compared: simple superposition decoupling and a method of extracting 'pair' channels from three-particle correlation evolution. It is shown that both methods provide an almost identical description of this reaction. However, in studies of reversible reactions in liquid solutions only the channel extraction method gives a correct physically clear description of the reaction though it consists of a sequence of steps: the development of integral encounter theory (IET), effective pairs approximation (EPA), modified encounter theory (MET), and the final regular form (RF) of kinetic equations. It is shown that the rate equations often encountered in the literature correspond to the independence of transient channels of 'scattering' in the bimolecular reversible reaction (A+B \\rightleftarrows C+ B ), while the independent transient channel of 'decay' in the reversible reaction A+B \\rightleftarrows C is defined solely by time integral convolution. In the general case transient channels in non-Markovian theory are not independent, and their interference manifests itself as a non-Markovian inhomogeneous source in binary non-Markovian kinetic equations in regular form. Based on the derived equations new universal kinetics (independent of models) of chemical equilibrium attainment have been obtained. It is shown that these kinetics can differ essentially from the kinetics corresponding to the kinetic law of mass action of formal chemical kinetics.

Doktorov, Alexander B.; Kipriyanov, Alexey A.

2007-02-01

440

Full-wave and half-wave processes in second-order motion and texture.

A theory of human second-order motion perception is proposed and further applied to the discrimination of texture slant. The computational algorithms for deriving the direction of left-right motion from a sequence of images are equivalent to the algorithms for deriving the direction of slant (e.g. from top left to bottom right or top right to bottom left) in a single 2D image. There is a broad range of phenomena for which Fourier analysis of the image plus a few simple rules gives a good account of human perception. The problem with this first-order analysis is that there exists a broad class of 'microbalanced' stimuli in which the motion or slant is completely obvious to human subjects but is invisible to first-order analysis. Microbalanced stimuli require second-order analysis which consists of non-linear preprocessing (spatiotemporal filtering followed by rectification of the input signal) before standard motion or slant analysis. To determine whether the second-order rectification is half-wave or full-wave, we construct two special microbalanced stimulus types: 'half-wave stimuli' whose motion (or texture slant) is interpretable by a half-wave rectifying system but not by full-wave or a first-order (Fourier) analysis and 'full-wave stimuli' which are interpretable only after full-wave rectification. Such experiments show that second-order texture-slant perception utilizes both half-wave and full-wave processes, second-order motion-direction discrimination depends predominantly on full-wave rectification and second-order spatial interactions such as lateral contrast-contrast inhibition and second-order Mach bands are exclusively full-wave. PMID:7882759

Sperling, G; Chubb, C; Solomon, J A; Lu, Z L

1994-01-01

441

The properties of pentaamine (5-cyano-2H-tetrazolato-N2) cobalt (III) perchlorate (CP), which was first synthesized in 1968, continues to be of interest for predicting behavior in handling, shipping, aging, and thermal cook-off situations. We report coefficient of thermal expansion (CTE) values over four specific temperature ranges, decomposition kinetics using linear heating rates, and the reaction to three different types of stimuli: impact, spark, and friction. The CTE was measured using a Thermal Mechanical Analyzer (TMA) for samples that were uniaxially compressed at 10,000 psi and analyzed over a dynamic temperature range of -20 C to 70 C. Using differential scanning calorimetry, DSC, CP was decomposed at linear heating rates of 1, 3, and 7 C/min and the kinetic triplet calculated using the LLNL code Kinetics05. Values are also reported for spark, friction, and impact sensitivity.

Weese, R K; Burnham, A K; Fontes, A T

2005-03-23

442

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

Ben O'Shaughnessy; Dimitrios Vavylonis

1998-12-21

443

Gene regulatory, signal transduction and metabolic networks are major areas of interest in the newly emerging field of systems biology. In living cells, stochastic dynamics play an important role; however, the kinetic parameters of biochemical reactions necessary for modelling these processes are often not accessible directly through experiments. The problem of estimating stochastic reaction constants from molecule count data measured,

S. Reinker; R. M. Altman; J. Timmer

444

NASA Astrophysics Data System (ADS)

A new spectrophotometric method for the determination of nicotine in mixtures without pre-separation has been proposed. Nicotine could react with 2,4-dinitrophenol through a charge-transfer reaction to form a colored complex. The second-order data from the visible absorption spectra of the complex in a series of ethanol-water binary solvents with various water volume fractions could be expressed as the combination of two bilinear data matrices. With the bilinear model, the second-order spectra data of mixtures containing nicotine and other interferents could be analysed by using second-order calibration algorithms, and the determination of nicotine in the mixtures could be achieved. The algorithm used here was parallel factor analysis. The method has been successfully used to determine nicotine in tobacco samples with satisfactory results.

Gao, Shuqin; Liao, Lifu; Xiao, Xilin; Zhao, Zhiyuan; Du, Nan; Du, Jiangfeng

2010-05-01

445

Kinetics of the Reaction of O((sup 3)P) with CF3NO

NASA Technical Reports Server (NTRS)

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction of O((sup 3)P) with CF3NO (k(2)) as a function of temperature. Our results are described by the Arrhenius expression k(2)(T) = (4.54 +/- 0.70) x 10(exp -l2)exp[(-560 +/- 46)/T] cu cm/molecule.s (243 K is less than or equal to T is less than or equal to 424 K); errors are 2 sigma and represent precision only. The O((sup 3)P) + CF3NO reaction is sufficiently rapid that CF3NO cannot be employed as a selective quencher for O2(alpha(1) Delta-g) in laboratory systems where O((sup 3)P) and O2(alpha 1 Delta g) coexist, and where O((sup 3)P) kinetics are being investigated.

Thorn, R. P.; Nicovich, J. M.; Cronkhite, J. M.; Wine, P. H.

1997-01-01

446

Conversion of waste cellulose to ethanol. Phase 2: Reaction kinetics with phosphoric acid

NASA Astrophysics Data System (ADS)

Waste cellulosic material can be hydrolyzed in dilute acid solution to produce fermentable sugars which can then be converted into ethanol. A laboratory investigation was made of the feasibility of using phosphoric acid as the hydrolysis catalyst. The hydrolysis reaction with phosphoric acid solutions was compared with the reaction employing the more conventional dilute sulfuric acid catalyst. The purpose of this research was to examine the hydrolysis step in a proposed process for the conversion of cellulose (from wood, newspapers, municipal solid waste, or other sources) into ethanol - by which a potentially valuable co-product, DICAL (dicalcium phosphate), might be made and sold with or without the lignin content as a fertilizer. The pertinent reaction kinetics for the acid catalyzed production of glucose from cellulose consists of consecutive, pseudo-first order reactions.

Moeller, M. B.; Isbell, R. E.

1982-05-01

447

A mathematical model describing chemical kinetics of transesterification of palm-based methyl esters with trimethylolpropane has been developed. The model was developed by utilizing nonlinear regression method, which is an efficient and powerful way to determine rate constants for both forward and reverse reactions. A comparison with previous study which excludes the reverse reactions was made. The model was based on the reverse mechanism of transesterification reactions and describes concentration changes of trimethylolpropane, monoesters and diesters production. The developed model was validated against data from the literature. The reaction rate constants were determined using MATLAB version 7.2 and the ratios of rate constants obtained were well in agreement with those reported in the literature. A good correlation between model simulations and experimental data was observed. It was proven that both methods were able to predict the rate constants with plausible accuracy. PMID:20304636

Kamil, Ruzaimah Nik Mohamad; Yusup, Suzana

2010-08-01

448

Kinetics of the reaction between Pu(III) and Fe(III) in nitric acid solution

The kinetics of the reaction between Pu/sup (III)/ and Fe/sup (III)/ in an aqueous nitric acid solution in the presence of persulfate ions at a constant ionic strength of the solution was studied spectrophotometrically. It was shown that the reaction is first order with respect to the reagents; its rate is practically independent of the concentration of the H/sup +/ and S/sub 2/O/sub 8//sup 2 -/ ions and with increase in the analytical HNO/sub 3/ concentration at variable ionic strength, it first increases, and then decreases. The temperature dependence of the reaction was determined, and its thermodynamic activation parameters were calculated. A possible mechanism for the reaction between Pu/sup (III)/ and Fe/sup (III)/ was proposed.

Koltunov, V.S.; Zhuravleva, G.I.

1988-01-01

449

We investigate the effective kinetics of a reaction front for mixing limited bimolecular reaction $A+B\\rightarrow C$ in a porous medium. While Fickian diffusion predicts a scaling of the cumulative mass produced as $M_C \\propto t^{1/2}$, we observe two time regimes in which the total product mass evolves faster then $t^{1/2}$. At early times the invading solute is organized in fingers of high velocity. Reactions take place only at the fingers boundaries whose surface grows linearly in time. We show that this configuration leads to a mass scaling $M_C \\propto t^2$. When diffusion mixes reactants and destroy these finger structures, the effective reaction rate slows down and we relate it to the longitudinal advective spreading providing $M_C \\propto \\sigma_x$. The transition time between these two regimes is characterized by the diffusion time over the transverse fingers cross section.

de Anna, Pietro; Dentz, Marco; Tartakovsky, Alexandre M.; Le Borgne, Tanguy

2014-07-08

450

On the Reaction Kinetics in a Mercury Photosensitized CVD of a-Si:H Films

NASA Astrophysics Data System (ADS)

The reaction kinetic processes for mercury photosensitized CVD (Hg*-CVD) in silane were analyzed using a time-dependent, one-dimensional calculation based on mass-, momentum- and energy-conservation equations, including simplified surface reactions such as radical adsorption and hydrogen elimination from the substrate. A good agreement between the measured and the calculated time-varying concentrations of species provides sufficient validity regarding the present model. It is also shown that the saturation of the SiH4 decomposition observed by many authors in closed systems can be explained by the abstraction of SiH4 from the surfaces by radicals peculiar to the Hg*-CVD (e.g., HgH); gas-phase reactions are significantly influenced by surface reactions when the volume-to-surface ratio becomes small.

Matsui, Yasuji; Yuuki, Akimasa; Morita, Noriko; Tachibana, Kunihide

1987-09-01

451

Kinetics of lime/bentonite pozzolanic reactions at 20 and 50 °C: Batch tests and modeling

The effects of duration (1–100 days) and temperature (20 and 50 °C) were assessed from batch tests for Ca-bentonite mixed with 10 wt.% lime. The pozzolanic processes were monitored over time by {sup 29}Si NMR (Cement Concr. Res. 42, 2012), TGA-DTA, XRD and chemical analysis. Modeling considered kinetics and thermodynamics of mineralogical transformations and cation exchange. Kinetic laws were dependent on pH and temperature (Arrhenius energy). Lime hydration occurs within hours, modifying the bentonite exchangeable population and increasing the pH. These alkaline conditions initiate the pozzolanic reactions in a second stage. The rate-limiting step is the dissolution kinetics of the bentonite minerals, i.e. a relatively fast and total consumption of cristobalite in parallel to a long-term slower dissolution of montmorillonite. First C–S–H and then C–A–S–H are formed consequently. Temperature speeds up the pozzolanic reaction kinetics by a factor 5 from 20 to 50 °C, corresponding to an apparent activation energy of 40–50 kJ/mol.

De Windt, Laurent, E-mail: laurent.dewindt@mines-paristech.fr [Mines-ParisTech (Ecole des Mines de Paris), Centre de Géosciences, 35 Rue St-Honoré, 77305 Fontainebleau Cedex (France); Deneele, Dimitri [LUNAM, IFSTTAR, Institut Français des Sciences et des Technologies des Transports, de l'Aménagement et des Réseaux, BP 4129, route de Bouaye, 44332 Bouguenais (France); Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS, 2 rue de la Houssiničre, BP 32229, 44322 Nantes Cedex 3 (France); Maubec, Nicolas [LUNAM, IFSTTAR, Institut Français des Sciences et des Technologies des Transports, de l'Aménagement et des Réseaux, BP 4129, route de Bouaye, 44332 Bouguenais (France)

2014-05-01

452

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

Grout, Ray W [ORNL

2012-01-01

453

Kinetics of the reactions of alkyl radicals with HBr and DBr

NASA Technical Reports Server (NTRS)

The kinetics of the reactions CH3 + HBr, CD3 + HBr, CH3 + DBr, C2H5 + HBr, C2H5 + DBr, t-C4H9 + HBr, and t-C4H9 + DBr is studied as a function of temperature (257-430 K) and pressure (10-300 Torr of N2). Time-resolved resonance fluorescence detection of Br atom appearance following laser flash photolysis of RI was used in the experiments. Results show that the rates of all reactions increased as the temperature decreased.

Nicovich, J. M.; Van Dijk, C. A.; Kreutter, K. D.; Wine, P. H.

1991-01-01

454

Investigation of reaction kinetics and interfacial phase formation in Ti3Al + Nb composites

NASA Technical Reports Server (NTRS)

Titanium aluminide metal matrix composites are prominent materials systems being considered for high temperature aerospace applications. One of the major problems with this material is the reactivity between existing reinforcements and the matrix after prolonged thermal exposure. This paper presents results from an investigation of reaction kinetics between Ti-14Al-21Nb (wt pct) and SCS-6 fibers and SiC fibers with surface coatings of TiB2, TiC, TiN, W, and Si. Microstructural evaluation of the reaction layers as well as matrix regions around the fibers is presented.

Wawner, F. E.; Gundel, D. B.

1992-01-01

455

A temperature dependent kinetic study of the reaction of the hydroxyl radical with CH2Br

NASA Technical Reports Server (NTRS)

Rate constants have been measured for the gas phase reaction of the hydroxyl radical (OH) with CH3Br over the temperature range 250 to 400 K. The Arrhenius expression k = (5.79 x 10 exp -12) exp(-1560/T) cu cm/molecule per sec was derived from the kinetic data. From the rate constant at 277 K, the tropospheric lifetime of CH3Br with respect to reaction with OH is estimated to be 2.2 years and the overall atmospheric lifetime to be 2.1 years.

Zhang, Zhengyu; Saini, Rameshwar D.; Kurylo, Michael; Huie, Robert E.

1992-01-01

456

Fundamental kinetics and mechanistic pathways for oxidation reactions in supercritical water

NASA Technical Reports Server (NTRS)

Oxidation of the products of human metabolism in supercritical water has been shown to be an efficient way to accomplish the on-board water/waste recycling in future long-term space flights. Studies of the oxidation kinetics of methane to carbon dioxide in supercritical water are presented in this paper in order to enhance the fundamental understanding of the oxidation of human waste compounds in supercritical water. It is concluded that, although the elementary reaction models remain the best hope for simulating oxidation in supercritical water, several modifications to existing mechanisms need to be made to account for the role of water in the reaction mechanism.

Webley, Paul A.; Tester, Jefferson W.

1988-01-01

457

Long-time kinetics of the excited-state association dissociation reaction with different lifetimes

NASA Astrophysics Data System (ADS)

We consider the long-time behaviour of the reversible diffusion-influenced reaction A+B\\rightleftharpoons C when A and C are immobile electronically excited states and B particles are in excess. A and C have different lifetimes. When C decays faster than A, the two leading terms of the asymptotic behaviour are obtained analytically by mapping this problem onto an effective irreversible reaction. The first term is exponential, and it coincides with that obtained from conventional rate equations with steady-state diffusion-influenced rate constants. The second term in the exponent is \\sqrt {t} , as in the Smoluchowski irreversible kinetics.

Gopich, Irina V.

2007-02-01

458

Study of the Reaction Stages and Kinetics of the Europium Oxide Carbochlorination

NASA Astrophysics Data System (ADS)

The europium oxide (Eu2O3(s)) chlorination reaction with sucrose carbon was studied by thermogravimetry between room temperature and 1223 K (950 °C). The nonisothermal thermogravimetry showed that the reaction consists of three stages, and their stoichiometries were studied. The product of the first stage was europium oxychloride, and it showed independence of the reaction kinetics with the carbon content. Subsequently, in the second stage, the EuOCl(s) was carbochlorinated with formation of EuCl3(l) and its evaporation is observed in the third stage. The analysis by Fourier transform infrared spectroscopy of gaseous species showed that the reaction at second stage occurs with the formation of CO2(g) and CO(g). Both reactants and products were analyzed by X-ray diffraction, scanning electron microscopy and wavelength-dispersive X-ray fluorescence spectroscopy. The influence of carbon content, total flow rate, sample initial mass, chlorine partial pressure, and temperature were evaluated. The second stage kinetics was analyzed, which showed an anomalous behavior caused by generation of chlorine radicals during interaction of Cl2(g) and carbon. It was found that the reaction rate at 933 K (660 °C) was proportional to a potential function of the chlorine partial pressure whose exponent is 0.56. The conversion curves were analyzed with the Avrami-Erofeev model and it was obtained an activation energy of 154 ± 5 kJ mol-1.

Pomiro, Federico J.; Fouga, Gastón G.; Gaviría, Juan P.; Bohé, Ana E.

2015-02-01

459

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

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

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

1986-01-01

460

The atmospheric chemistry of dimethylsulfoxide (DMSO) kinetics and mechanism of the OH+DMSO reaction

We have employed a pulsed laser photolysis-pulsed laser induced fluorescence technique to study the kinetics and mechanism of the reaction of OH with dimethylsulfoxide and its deuterated analogue. A rate coefficient of (1.0±0.3)×10-10 cm3 molecule-1 s-1 was obtained ar room temperature. The rate coefficient was independent of pressure over the range 25–700 Torr, showed no dependence on the nature of

A. J. Hynes; P. H. Wine

1996-01-01

461

Conventional equations for enzyme kinetics are based on mass-action laws, that may fail in low-dimensional and disordered media such as biological membranes. We present Monte Carlo simulations of an isolated Michaelis–Menten enzyme reaction on two-dimensional lattices with varying obstacle densities, as models of biological membranes. The model predicts that, as a result of anomalous diffusion on these low-dimensional media, the

Hugues Berry

2002-01-01

462

Origin of fatty acid synthesis: Thermodynamics and kinetics of reaction pathways

Summary The primitiveness of contemporary fatty acid biosynthesis was evaluated by using the thermodynamics and kinetics of its component\\u000a reactions to estimate the extent of its dependence on powerful and selective catalysis by enzymes. Since this analysis indicated\\u000a that the modern pathway is not primitive because it requires sophisticated enzymatic catalysis, we here propose an alternative\\u000a pathway of primitive fatty acid

Arthur L. Weber

1991-01-01

463

The thermal decomposition behavior and nonisothermal reaction kinetics of the double-base gun propellants containing the mixed ester of triethyleneglycol dinitrate(TEGDN) and nitroglycerin(NG) were investigated by thermogravimetry(TG) and differential thermogravimetry(DTG), and differential scanning calorimetry(DSC) under the high-pressure dynamic ambience. The results show that the thermal decomposition processes of the mixed nitric ester gun propellants have two mass-loss stages. Nitric ester evaporates

Jian-hua YI; Feng-qi ZHAO; Si-yu XU; Hong-xu GAO; Rong-zu HU

2008-01-01

464

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.

465

COAL CHAR GASIFICATION KINETICS IN A JET-FLUIDIZED BED (COMBUSTION, REACTION, RATE PHENOMENA)

The kinetics of gasification of -10 + 65 mesh coke and coal char with O(,2) and O(,2)-CO(,2) mixtures was studied in a continuous, bench scale, jet-fluidized reactor over a wide range of temperatures (900(DEGREES)C to > 1400(DEGREES)C) and bed depths under atmospheric pressure. The measured specific reaction rates of carbon ranged from 0.01 to 0.1 gram carbon reacting per gram

MING-YUAN KAO

1984-01-01

466

Non-meanfield deterministic limits in chemical reaction kinetics far from equilibrium

A general mechanism is proposed by which small intrinsic fluctuations in a system far from equilibrium can result in nearly deterministic dynamical behaviors which are markedly distinct from those realized in the meanfield limit. The mechanism is demonstrated for the kinetic Monte-Carlo version of the Schnakenberg reaction where we identified a scaling limit in which the global deterministic bifurcation picture is fundamentally altered by fluctuations. Numerical simulations of the model are found to be in quantitative agreement with theoretical predictions.

R. E. Lee DeVille; Cyrill B. Muratov; Eric Vanden-Eijnden

2005-12-25

467

ERIC Educational Resources Information Center

Described is an advanced undergraduate kinetics experiment using buffer dilutions to determine spontaneous rate, catalyzed rate, and reaction order. The reaction utilized is hydrolysis of p-nitro-phenyl acetate in presence of imidazole, which has been shown to enhance rate of the reaction. (Author/JN)

Lombardo, Anthony

1982-01-01

468

, 2004 An application of the Reaction Class Transition State Theory/Linear Energy Relationship (RC Polycyclic Aromatic Hydrocarbons (PAH). Two classes of reactions have been considered, namely hydrogen bondedKinetics of Hydrogen Abstraction Reactions from Polycyclic Aromatic Hydrocarbons by H Atoms Angela

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