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1

A Kinetic Study of the Diels-Alder Reaction. An Experiment Illustrating Simple Second-Order Reaction Kinetics.  

ERIC Educational Resources Information Center

Describes an organic chemistry experiment for teaching the basic concepts of chemical kinetics. Provides background information about first- and second-order reactions, experimental procedures of the Diels-Alder reaction between cyclopentadiene and dimethyl fumarate, and the experimental results. (YP)

Silvestri, Michael G.; Dills, Charles E.

1989-01-01

2

ROTATING BIOLOGICAL CONTACTORS - SECOND ORDER KINETICS  

EPA Science Inventory

Rotating biological contactors (RBC) have been employed for treating municipal wastewaters within the United States since 1970. The RBC process lends itself to kinetic interpretation because of the sequential stages employed in the operation. This mode of operation enables the su...

3

Modeling Second-Order Chemical Reactions using Cellular Automata  

NASA Astrophysics Data System (ADS)

Cellular automata (CA) are discrete, agent-based, dynamic, iterated, mathematical computational models used to describe complex physical, biological, and chemical systems. Unlike the more computationally demanding molecular dynamics and Monte Carlo approaches, which use "force fields" to model molecular interactions, CA models employ a set of local rules. The traditional approach for modeling chemical reactions is to solve a set of simultaneous differential rate equations to give deterministic outcomes. CA models yield statistical outcomes for a finite number of ingredients. The deterministic solutions appear as limiting cases for conditions such as a large number of ingredients or a finite number of ingredients and many trials. Here we present a 2-dimensional, probabilistic CA model of a second-order gas phase reaction A + B ? C, using a MATLAB basis. Beginning with a random distribution of ingredients A and B, formation of C emerges as the system evolves. The reaction rate can be varied based on the probability of favorable collisions of the reagents A and B. The model permits visualization of the conversion of reagents to products, and allows one to plot concentration vs. time for A, B and C. We test hypothetical reaction conditions such as: limiting reagents, the effects of reaction probabilities, and reagent concentrations on the reaction kinetics. The deterministic solutions of the reactions emerge as statistical averages in the limit of the large number of cells in the array. Modeling results for dynamic processes in the atmosphere will be presented.

Hunter, N. E.; Barton, C. C.; Seybold, P. G.; Rizki, M. M.

2012-12-01

4

Epidemic analysis of the second-order transition in the Ziff-Gulari-Barshad surface-reaction model  

E-print Network

Epidemic analysis of the second-order transition in the Ziff-Gulari-Barshad surface-reaction model-Gulari-Barshad irreversible surface-reaction model around its kinetic second-order phase transition, using both epidemic

Voigt, Chris

5

Second-order ion drift-kinetic equation  

NASA Astrophysics Data System (ADS)

A novel form of ion drift-kinetic equation is presented, well suited to close the fluid description of slow macroscopic dynamics in low-collisionality, magnetically confined plasmas. It features second-order accuracy in the gyroradius expansion, with diamagnetic-scale ordering of frequencies and flow velocities. This second-order drift-kinetic equation is derived in the moving reference frame of the ion macroscopic flow, which facilitates the precise consistency with the complementary fluid system, as well as the rigorous treatment of the electric field. Examples of intended applications are the precursor of the ``sawtooth'' internal disruption and the ``neoclassical tearing mode'' in fusion-relevant tokamak temperature regimes. With these applications to slow excursions from well confined equilibria in mind, the distribution function is assumed to be close to a Maxwellian. The Maxwellian part carries the density, mean flow and temperature in Chapman-Enskog-like fashion. The resulting drift-kinetic equation for the non-Maxwellian perturbation is shown to be automatically consistent with the required condition that the density, random parallel velocity and random kinetic energy moments of such non-Maxwellian part be equal to zero.

Ramos, J. J.

2010-11-01

6

Interference by second order reactions in activation analysis  

Microsoft Academic Search

Equations to calculate the second order reaction interferences in activation analysis have been derived. A simple approximation\\u000a as well as the exact solution have been investigated. A new algorithm is proposed for fast and accurate calculations, without\\u000a the need of a computer with high precision arithmetic. The method can be used for all higher order reaction chains.

W. Maenhaut; J. P. Op de Beeck

1970-01-01

7

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

EPA Science Inventory

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...

8

Second-order radio frequency kinetic theory revisited: Resolving inconsistency with conventional fluid theory  

SciTech Connect

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

9

Iron chelation by polyamidoamine dendrimers: a second-order kinetic model for metal-amine complexation.  

PubMed

This study presents a kinetic model of the chelation of iron ions by generation 4 hydroxyl-terminated polyamidoamine (PAMAM) with ethylenediamine core (G4-OH). The coordination processes of iron ions from ferric chloride, FeCl(3), and ferrous bromide, FeBr(2), to G4-OH dendrimers were analyzed using ultraviolet-visible (UV-vis) spectroscopy, proton nuclear magnetic resonance ((1)H NMR) spectroscopy, and liquid chromatography-mass spectrometry (LC-MS). In the visible region, a charge-transfer was observed when the dendrimer was added to a ferric chloride solution. This phenomenon is a ligand-to-metal charge-transfer (LMCT) between the free electron group of the dendrimer's internal amines and the dehalogenated iron ion that takes 2 h to complete at room temperature. Analysis of potential rate laws and diffusion effects led to a second-order kinetic model for this reaction. By measuring the rate coefficients as a function of temperature (22-37 °C), an apparent activation energy of 41.5 kJ/mol was obtained using the Arrhenius method. The results of this study will fuel research of PAMAM dendrimers for environmental, pharmaceutical, and materials applications. PMID:21995617

Mankbadi, Michael R; Barakat, Mohamed A; Ramadan, Mohamed H; Woodcock, H Lee; Kuhn, John N

2011-11-24

10

First-Order or Second-Order Kinetics? A Monte Carlo Answer  

ERIC Educational Resources Information Center

Monte Carlo computational experiments reveal that the ability to discriminate between first- and second-order kinetics from least-squares analysis of time-dependent concentration data is better than implied in earlier discussions of the problem. The problem is rendered as simple as possible by assuming that the order must be either 1 or 2 and that…

Tellinghuisen, Joel

2005-01-01

11

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

E-print Network

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

2014-04-28

12

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

E-print Network

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.

Schaefer, Thomas

2014-01-01

13

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

NASA Astrophysics Data System (ADS)

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, nonlinear terms in the strain-stress relation, and nonlinear couplings between vorticity and strain. An exact calculation in the dilute limit gives ?R=? /P , where ?R is the shear stress relaxation time, ? is the shear viscosity, and P is pressure. This relation is identical to the result obtained using the Bhatnagar-Gross-Krook approximation to the collision term, but other transport coefficients are sensitive to the exact collision integral.

Schäfer, Thomas

2014-10-01

14

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

15

Kinetics and mechanism of N-Boc cleavage: evidence of a second-order dependence upon acid concentration.  

PubMed

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

16

DECAY OF DISSOLVED SUBSTANCES BY SECOND-ORDER REACTION: PROBLEM DESCRIPTION AND BATCH-REACTOR SOLUTIONS  

EPA Science Inventory

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...

17

Second order equation of motion for electromagnetic radiation back-reaction  

E-print Network

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

2012-07-02

18

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

19

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

20

Pseudo-Second-Order Kinetic Model for Biosorption of Methylene Blue onto Tamarind Fruit Shell: Comparison of Linear and Nonlinear Methods  

Microsoft Academic Search

In this study, the sorption of methylene blue, a basic dye, onto tamarind fruit shell was studied by performing batch kinetic sorption experiments. The equilibrium kinetic data were analyzed using the pseudo-second-order kinetic model. A comparison between linear least squares method and nonlinear regression method of estimating the kinetic parameters was examined. Four pseudo-second-order kinetic linear equations were discussed. The

Shamik Chowdhury; Papita Saha

2010-01-01

21

Second-order kinetic model for the sorption of cadmium onto tree fern: A comparison of linear and non-linear methods  

Microsoft Academic Search

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

22

Second order kinetic modeling of headspace solid phase microextraction of flavors released from selected food model systems.  

PubMed

The application of headspace-solid phase microextraction (HS-SPME) has been widely used in various fields as a simple and versatile method, yet challenging in quantification. In order to improve the reproducibility in quantification, a mathematical model with its root in psychological modeling and chemical reactor modeling was developed, describing the kinetic behavior of aroma active compounds extracted by SPME from two different food model systems, i.e., a semi-solid food and a liquid food. The model accounted for both adsorption and release of the analytes from SPME fiber, which occurred simultaneously but were counter-directed. The model had four parameters and their estimated values were found to be more reproducible than the direct measurement of the compounds themselves by instrumental analysis. With the relative standard deviations (RSD) of each parameter less than 5% and root mean square error (RMSE) less than 0.15, the model was proved to be a robust one in estimating the release of a wide range of low molecular weight acetates at three environmental temperatures i.e., 30, 40 and 60 °C. More insights of SPME behavior regarding the small molecule analytes were also obtained through the kinetic parameters and the model itself. PMID:25255763

Zhang, Jiyuan; Cheong, Mun-Wai; Yu, Bin; Curran, Philip; Zhou, Weibiao

2014-01-01

23

Second order symmetry operators  

E-print Network

Using systematic calculations in spinor language, we obtain simple descriptions of the second order symmetry operators for the conformal wave equation, the Dirac-Weyl equation and the Maxwell equation on a curved four dimensional Lorentzian manifold. The conditions for existence of symmetry operators for the different equations are seen to be related. Computer algebra tools have been developed and used to systematically reduce the equations to a form which allows geometrical interpretation.

Lars Andersson; Thomas Bäckdahl; Pieter Blue

2014-02-25

24

Fractal reaction kinetics.  

PubMed

Classical reaction kinetics has been found to be unsatisfactory when the reactants are spatially constrained on the microscopic level by either walls, phase boundaries, or force fields. Recently discovered theories of heterogeneous reaction kinetics have dramatic consequences, such as fractal orders for elementary reactions, self-ordering and self-unmixing of reactants, and rate coefficients with temporal "memories." The new theories were needed to explain the results of experiments and supercomputer simulations of reactions that were confined to low dimensions or fractal dimensions or both. Among the practical examples of "fractal-like kinetics" are chemical reactions in pores of membranes, excitation trapping in molecular aggregates, exciton fusion in composite materials, and charge recombination in colloids and clouds. PMID:17820893

Kopelman, R

1988-09-23

25

Non-autonomous second order Hamiltonian systems  

NASA Astrophysics Data System (ADS)

We study the existence of periodic solutions for a second order non-autonomous dynamical system containing variable kinetic energy terms. Our assumptions balance the interaction between the kinetic energy and the potential energy with neither one dominating the other. We study sublinear problems and the existence of non-constant solutions.

Pipan, John; Schechter, Martin

2014-07-01

26

Reactive scalar field near the turbulent/non-turbulent interface in a planar jet with a second-order chemical reaction  

NASA Astrophysics Data System (ADS)

The reactive scalar field near the turbulent/non-turbulent (T/NT) interface is analyzed using a direct numerical simulation (DNS) of a planar jet with an isothermal second-order chemical reaction A + B ? P. Reactants A and B are supplied from the jet and ambient flows, respectively. The DNS of the reactive jet is performed for Damköhler numbers Da = 0.1, 1, and 10. A visualization of the T/NT interface shows that most of the product P is contained in the turbulent region. The conditional mean concentrations of the reactive species change sharply near the T/NT interface. The width of the jump in the conditional mean concentration is almost independent of the chemical species and the Damköhler number. For the slow reaction (Da = 0.1), the conditional average of the chemical production rate gradually increases from the non-turbulent region toward the turbulent region. In contrast, the conditional average of the production rate for Da = 1 and 10 has a large peak value slightly inside the T/NT interface. The chemical reaction near the T/NT interface strongly depends on the interface orientation. The reactant A is deficient near the T/NT interface. The production rate is large near the interface toward which the deficient reactant A is frequently transported by the velocity fields. The transport due to the velocity relative to the interface movement strongly depends on the relationship between the interface geometry and the mean flow field. The dependence of the chemical reaction on the interface orientation becomes strong as Da increases. When the interface propagates toward the non-turbulent region, the reactant A and product P are contained in the turbulent region although the molecular diffusion and reaction contribute to the increase in the concentrations of A (non-reactive case) and P in the non-turbulent region. In contrast, the interface propagation toward the turbulent region leaves the fluids containing A and P in the non-turbulent region.

Watanabe, T.; Sakai, Y.; Nagata, K.; Ito, Y.; Hayase, T.

2014-10-01

27

Second-order algebraic theories  

E-print Network

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 7 SECOND-ORDER FUNCTORIAL SEMANTICS 93 7.1 Clone Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 7.2 Classifying Clones... and Bendix, 1970]; (iv) algebraic theories come with an associated notion of algebraic translation [Lawvere, 2004], whose syntactic counterpart provides the right notion of syntactic translation between equational presenta- tions [Fujiwara, 1959, Fujiwara...

Mahmoud, Ola

2011-11-08

28

Relation of Turbojet and Ramjet Combustion Efficiency to Second-Order Reaction Kinetics and Fundamental Flame Speed  

NASA Technical Reports Server (NTRS)

Theoretical studies of the turbojet and ramjet combustion process are summarized and the resulting equations are applied to experimental data obtained from various combustor tests. The theoretical treatment assumes that one step in the over-all chain of processes which constitute jet-engine combustion is sufficiently slow to be the rate-controlling step that determines combustion efficiency.

Childs, J Howard; Reynolds, Thaine W; Graves, Charles C

1957-01-01

29

Second order transport from anomalies  

NASA Astrophysics Data System (ADS)

We study parity odd transport at second order in derivative expansion for a non-conformal charged fluid. We see that there are 27 parity odd transport coefficients, of which 12 are non-vanishing in equilibrium. We use the equilibrium partition function method to express 7 of these in terms of the anomaly, shear viscosity, charge diffusivity and thermodynamic functions. The remaining 5 are constrained by 3 relations which also involve the anomaly. We derive Kubo formulae for 2 of the transport coefficients and show these agree with that derived from the equilibrium partition function.

Bhattacharyya, Sayantani; David, Justin R.; Thakur, Somyadip

2014-01-01

30

Aqueous-phase chemistry and bactericidal effects from an air discharge plasma in contact with water: evidence for the formation of peroxynitrite through a pseudo-second-order post-discharge reaction of H2O2 and HNO2  

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

31

A Substituent Effects Study Reveals the Kinetic Pathway for an Interfacial Reaction  

E-print Network

effects study to understand the mechanistic basis for an interfacial Diels-Alder reaction that does not proceed with standard second-order kinetics. Cyclopentadiene (Cp) undergoes a Diels-Alder reaction with a chemisorbed mercaptobenzoquinone to yield an immobilized Diels-Alder adduct. The pseudo-first-order rate

Mrksich, Milan

32

Kinetics of actinide complexation reactions  

SciTech Connect

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

33

Combustion kinetics and reaction pathways  

SciTech Connect

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

34

Oxygen sag equation for second-order BOD decay  

Microsoft Academic Search

A dissolved oxygen (DO) equation for a stream is developed in which the biochemical oxygen demand (BOD) deoxygenation rate is described as a second-order reaction. Rate constants for a second-order BOD equation may be evaluated by graphical or numerical methods. The DO sag equation incorporates exponential integral functions. These functions are available in tabular form or they may be calculated

Donald Dean Adrian; Thomas G. Sanders

1998-01-01

35

Modelling reaction kinetics inside cells  

PubMed Central

In the past decade, advances in molecular biology such as the development of non-invasive single molecule imaging techniques have given us a window into the intricate biochemical activities that occur inside cells. In this article we review four distinct theoretical and simulation frameworks: (1) non-spatial and deterministic, (2) spatial and deterministic, (3) non-spatial and stochastic and (4) spatial and stochastic. Each framework can be suited to modelling and interpreting intracellular reaction kinetics. By estimating the fundamental length scales, one can roughly determine which models are best suited for the particular reaction pathway under study. We discuss differences in prediction between the four modelling methodologies. In particular we show that taking into account noise and space does not simply add quantitative predictive accuracy but may also lead to qualitatively different physiological predictions, unaccounted for by classical deterministic models. PMID:18793122

Grima, Ramon; Schnell, Santiago

2009-01-01

36

Communication: Electronic UV-Vis transient spectra of the .OH reaction products of uracil, thymine, cytosine, and 5,6-dihydrouracil by using the complete active space self-consistent field second-order perturbation (CASPT2//CASSCF) theory  

NASA Astrophysics Data System (ADS)

Addition of .OH radicals to pyrimidine nucleobases is a common reaction in DNA/RNA damage by reactive oxygen species. Among several experimental techniques, transient absorption spectroscopy has been during the last decades used to characterize such compounds. Discrepancies have however appeared in the assignment of the adduct or adducts responsible for the reported transient absorption UV-Vis spectra. In order to get an accurate assignment of the transient spectra and a unified description of the absorption properties of the .OH reaction products of pyrimidines, a systematic complete active space self-consistent field second-order perturbation (CASPT2//CASSCF) theory study has been carried out on the uracil, thymine, and cytosine .OH addition adducts, as well as on the 5,6-dihydrouracil hydrogen abstraction products. With the obtained findings, the C5OH contributions to the lowest-energy band can be finally discarded. Instead, a bright 2(?2) state of the C6OH adducts is determined to be the main responsible in all compounds for the absorption band in the Vis range.

Francés-Monerris, Antonio; Merchán, Manuela; Roca-Sanjuán, Daniel

2013-08-01

37

Kinetics of reactions occurring during polyurethane synthesis  

NASA Astrophysics Data System (ADS)

We have used Fourier transform IR spectroscopy to study the kinetics of reaction between phenylisocyanate and oligomeric polyols at room temperature. We have determined the degree of conversion and the reaction rate constants for urethane formation.

Volkova, E. R.; Tereshatov, V. V.; Karmanov, V. I.

2010-11-01

38

Source of second order chromaticity in RHIC  

SciTech Connect

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

39

Binocular Combination of Second-Order Stimuli  

PubMed Central

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

40

The kinetics of the esterification reaction between castor oil and oleic acid  

Microsoft Academic Search

In this study, esterification of castor oil with oleic acid was investigated in view of the reaction kinetics under various\\u000a conditions. Potassium hydroxide,p-toluenesulfonic acid and tin chloride (SnCl22H2O) were used as catalysts. Reaction was carried out at 200C, 225C and 250 C by using equivalent proportions of the reactants.\\u000a For tin chloride, experimental data fitted the second-order rate equation, while

A. T. Erciyes; L. Dandik; O. S. Kabasakal

1991-01-01

41

The second-order gravitational red shift  

NASA Technical Reports Server (NTRS)

The direct measurement of the nonlinear term of the gravitational field equations by using very stable clocks is discussed along with measuring the perhelion advance of a planet or satellite. These are considered measurements of the second-order gravitational red shift. The exact expression for the frequency shift of light in a gravitational field is derived. Other topics discussed include: The Doppler-cancelling technique; the second-order red shift in a spherically symmetric gravitational field; finite signal transit time; and the reality and interpretation of coordinates in the second-order red shift experiment.

Jaffe, J.

1973-01-01

42

First and Second Order Perturbations of Hypersurfaces  

E-print Network

In this paper we find the first and second order perturbations of the induced metric and the extrinsic curvature of a non-degenerate hypersurface $\\Sigma$ in a spacetime $(M,g)$, when the metric $g$ is perturbed arbitrarily to second order and the hypersurface itself is allowed to change perturbatively (i.e. to move within spacetime) also to second order. The results are fully general and hold in arbitrary dimensions and signature. An application of these results for the perturbed matching theory between spacetimes is presented.

Marc Mars

2005-07-01

43

Kinetic studies of elementary chemical reactions  

SciTech Connect

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

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

1993-12-01

44

Chemical Kinetics: Rate of Reaction  

NSDL National Science Digital Library

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

Blauch, David N.

45

Tensorial Calibration. 2. Second Order Tensorial Calibration.  

National Technical Information Service (NTIS)

Tensorial calibration provides a useful approach to calibration in general. For calibration of instruments that produce two dimensional (second order) data arrays of data per sample, tensorial concepts are a natural way of solving the calibration problems...

E. Sanchez, B. R. Kowalski

1987-01-01

46

Rapid biocatalytic polytransesterification: Reaction kinetics in an exothermic reaction  

Microsoft Academic Search

Biocatalytic polytransesterification at high concentrations of monomers proceeds rapidly and is accompanied by an increase in the temperature of the reaction mixture due to liberation of heat of reaction during the initial phase. The authors have used principles of reaction calorimetry to monitor the kinetics of polymerization during this initial phase, thus relating the temperature to the extent of polymerization.

A. K. Chaudhary; E. J. Beckman; A. J. Russell

1998-01-01

47

Kinetic studies of oxygen atom transfer reactions from trans-dioxoruthenium(VI) porphyrins to sulfides  

Microsoft Academic Search

The kinetics of the reactions of three trans-dioxoruthenium(VI) porphyrin derivatives with organic sulfides were measured. The dioxo systems studied were 5,10,15,20-tetramesityl porphyrin-dioxoruthenium(VI) (2a), 5,10,15,20-tetraphenylporphyrin-dioxoruthenium(VI) (2b), and 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin-dioxoruthenium(VI) (2c). Species 2 were competent oxidants and reacted rapidly with thioanisoles to generate the corresponding sulfoxides. Typical second-order rate constants determined from pseudo-first-order kinetic studies for sulfoxidation reactions are 8–60M?1s?1, which are 3

Chris Abebrese; Yan Huang; Alice Pan; Zhibo Yuan; Rui Zhang

2011-01-01

48

Rapid biocatalytic polytransesterification: Reaction kinetics in an exothermic reaction  

SciTech Connect

Biocatalytic polytransesterification at high concentrations of monomers proceeds rapidly and is accompanied by an increase in the temperature of the reaction mixture due to liberation of heat of reaction during the initial phase. The authors have used principles of reaction calorimetry to monitor the kinetics of polymerization during this initial phase, thus relating the temperature to the extent of polymerization. Rate of polymerization increases with the concentration of monomers. This is also reflected by the increase in the temperature of the reaction mixture. Using time-temperature-conversion contours, a differential method of kinetic analysis was used to calculate the energy of activation ({approximately} 15.1 Kcal/mol).

Chaudhary, A.K.; Beckman, E.J.; Russell, A.J. [Univ. of Pittsburgh, PA (United States)] [Univ. of Pittsburgh, PA (United States)

1998-08-20

49

Metric Independent Analysis of Second Order Stresses  

E-print Network

A metric independent geometric analysis of second order stresses in continuum mechanics is presented. For a vector bundle $W$ over the $n$-dimensional space manifold, the value of a second order stress at a point $x$ in space is represented mathematically by a linear mapping between the second jet space of $W$ at $x$ and the space of $n$-alternating tensors at $x$. While only limited analysis can be performed on second order stresses as such, they may be represented by non-holonomic stresses, whose values are linear mapping defined on the iterated jet bundle, $J^{1}(J^{1}W)$, and for which an iterated analysis for first order stresses may be performed. As expected, we obtain the surface interactions on the boundaries of regions in space.

Reuven Segev

2014-02-13

50

Kinetics of reaction of cyclopentadiene with sodium  

SciTech Connect

The kinetics of the topochemical reaction of cyclopentadiene with metallic sodium were studied in a toluene medium. It was found that the observed rate of the first-order reaction is proportional to the surface of sodium and the cyclopentadiene concentration. The values of the energy of activation and reaction-rate constants are: E = 31 kJ/mole; k = 7.4 x 10/sup -4/ liter/m/sup 2/ x sec at 40/sup 0/C.

Koshkina, S.B.; Krylov, A.V.; Rozovskii, V.Ya.; Zhitkov, I.V.

1987-08-01

51

OSCILLATION OF SECOND ORDER DELAY DYNAMIC EQUATIONS  

Microsoft Academic Search

In this paper we establish some sucien t con- ditions for oscillation of second order delay dynamic equations on time scales. Our results not only unify the oscillation of sec- ond order delay dieren tial and dierence equations but also are new for q-dierence equations and can be applied on any time scale. We illustrate our results with many examples.

R. P. AGARWAL; M. BOHNER; S. H. SAKER

52

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

53

Second order Sigma-Delta modulator realization  

Microsoft Academic Search

Sigma-Delta modulation is a very efficient technique for analog to digital conversion. In this paper the realization of second order Sigma-Delta modulators is considered, both with switched capacitor and active RC circuits. The resulting modulators are realized using discrete components and their performance is evaluated and compared

G. Bourdopoulos; A. Pneumatikakis; T. Deliyannis

1996-01-01

54

Urban Principals' Second Order Change Leadership  

ERIC Educational Resources Information Center

Urban school leaders have challenges in continually improving student achievement and making change as quickly as needed. To address this problem 37 non-Title I principals completed an on-line survey, Principal's Actions Survey (PAS), based on the seven responsibilities for second order change identified by Marzano, Waters, and McNulty (2005).…

Taylor, Rosemarye T.; La Cava, Gonzalo S.

2011-01-01

55

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

56

Calcite Reaction Kinetics in Saline Waters  

E-print Network

The effect of ionic strength (I), pCO2, and temperature on the reaction kinetics of calcite was investigated in magnesium-free, phosphate-free, low calcium (mCa^2 ? 0.01 – 0.02 molal) simple KCl and NaCl solutions from both undersaturated...

Finneran, David

2012-02-14

57

Reaction Kinetics and Transformation of Carbadox and  

E-print Network

systems is of a concern due to its carcinogenic and genotoxic effects. Until this study, the reactivity to be investigated in depth. Chemical reactivity, reaction kinetics, and transformation pathways of carbadox, for CDX ranges from 51.8 to 3.15 Ã? 104 M-1s-1 at pH 4-11). The high reactivity of CDX and DCDX to chlorine

Huang, Ching-Hua

58

Magnetic fields from second-order interactions  

E-print Network

It is well known that when two types of perturbations interact in cosmological perturbation theory, the interaction may lead to the generation of a third type. In this article we discuss the generation of magnetic fields from such interactions. We determine conditions under which the interaction of a first-order magnetic field with a first-order scalar-or vector-, or tensor-perturbations would lead to the generation of second order magnetic field. The analysis is done in a covariant-index-free approach, but could be done in the standard covariant indexed-approach.

Bob Osano

2014-03-21

59

Forecast Bias Correction: A Second Order Method  

E-print Network

The difference between a model forecast and actual observations is called forecast bias. This bias is due to either incomplete model assumptions and/or poorly known parameter values and initial/boundary conditions. In this paper we discuss a method for estimating corrections to parameters and initial conditions that would account for the forecast bias. A set of simple experiments with the logistic ordinary differential equation is performed using an iterative version of a first order version of our method to compare with the second order version of the method.

Crowell, Sean

2010-01-01

60

Style context with second-order statistics.  

PubMed

Patterns often occur as homogeneous groups or fields generated by the same source. In multisource recognition problems, such isogeny induces statistical dependencies between patterns (termed style context). We model these dependencies by second-order statistics and formulate the optimal classifier for normally distributed styles. We show that model parameters estimated only from pairs of classes suffice to train classifiers for any test field length. Although computationally expensive, the style-conscious classifier reduces the field error rate by up to 20 percent on quadruples of handwritten digits from standard NIST data sets. PMID:15628265

Veeramachaneni, Sriharsha; Nagy, George

2005-01-01

61

Unraveling reaction pathways and specifying reaction kinetics for complex systems.  

PubMed

Many natural and industrial processes involve a complex set of competing reactions that include several different species. Detailed kinetic modeling of such systems can shed light on the important pathways involved in various transformations and therefore can be used to optimize the process conditions for the desired product composition and properties. This review focuses on elucidating the various components involved in modeling the kinetics of pyrolysis and oxidation of polymers. The elementary free radical steps that constitute the chain reaction mechanism of gas-phase/nonpolar liquid-phase processes are outlined. Specification of the rate coefficients of the various reaction families, which is central to the theme of kinetics, is described. Construction of the reaction network on the basis of the types of end groups and reactive moieties in a polymer chain is discussed. Modeling frameworks based on the method of moments and kinetic Monte Carlo are evaluated using illustrations. Finally, the prospects and challenges in modeling biomass conversion are addressed. PMID:22468596

Vinu, R; Broadbelt, Linda J

2012-01-01

62

Manganese peroxidase from the lignin-degrading basidiomycete Phanerochaete chrysosporium: Transient state kinetics and reaction mechanism  

SciTech Connect

Stopped-flow techniques were used to investigate the kinetics of the formation of manganese peroxidase compound I (MnPI) and of the reactions of MnPI and manganese peroxidase compound II (MnPII) with p-cresol and Mn{sup II}. All of the rate data were obtained from single turnover experiments under pseudo-first order conditions. In the presence of H{sub 2}O{sub 2} the formation of MnPI is independent of pH over the range 3.12-8.29 with a second-order rate constant of (2.0{+-}0.1) {times} 10{sup 6} M{sup {minus}1} s{sup {minus}1}. The activation energy for MnPI formation is 20 kJ mol{sup {minus}1}. MnPI formation also occurs with organic peroxides such as peracetic acid, m-chloroperoxybenzoic acid, and p-nitroperoxybenzoic acid with second-order rate constants of 9.7 x 10{sup 5}, 9.5 {times} 10{sup 4}, and 5.9 {times} 10{sup 4} M{sup {minus}1} s{sup {minus}1}, respectively. The reactions of MnPI and MnPII with p-cresol strictly obeyed second-order kinetics. The second-order rate constant for the reaction of MnPII with p-cresol is extremely low, (9.5{+-}0.5) m{sup {minus}1} s{sup {minus}1}. Kinetic analysis of the reaction of Mn{sup II} with MnPI and MnPII showed a binding interaction with the oxidized enzymes which led to saturation kinetics. The first-order dissociation rate constants for the reaction of Mn{sup II} with MnPI and MnPII are (0.7{+-}0.1) and (0.14{+-}0.01) s{sup {minus}1}, respectively, when the reaction is conducted in lactate buffer. Rate constants are considerably lower when the reactions are conducted in succinate buffer. Single turnover experiments confirmed that Mn{sup II} serves as an obligatory substrate for MnPII and that both oxidized forms of the enzyme form productive complexes with Mn{sup II}. Finally, these results suggest the {alpha}-hydroxy acids such as lactate facilitate the dissociation of Mn{sup II} from the enzyme.

Wariishi, Hiroyuki; Gold, M.H. (Oregon Graduate Center, Beaverton (United States)); Dunford, H.B.; MacDonald, I.D. (Univ. of Alberta, Edmonton (Canada))

1989-02-25

63

Second order formalism in Poincare gauge theory  

E-print Network

Changing the set of independent variables of Poincare gauge theory and considering, in a manner similar to the second order formalism of general relativity, the Riemannian part of the Lorentz connection as function of the tetrad field, we construct theories that do not contain second or higher order derivatives in the field variables, possess a full general relativity limit in the absence of spinning matter fields, and allow for propagating torsion fields in the general case. A concrete model is discussed and the field equations are reduced by means of a Yasskin type ansatz to a conventional Einstein-Proca system. Approximate solutions describing the exterior of a spin polarized neutron star are prsented and the possibility of an experimental detection of the torsion fields is briefly discussed.

M. Leclerc

2005-06-14

64

Kinetic Element Fractionation in Orthopyroxene Reaction Rims  

NASA Astrophysics Data System (ADS)

The contact of Mg-rich rocks to Si-rich rocks or melts is a major geochemical contrast that leads to the formation and advancement of reaction fronts due to reactions like olivine + quartz = orthopyroxene. Detailed experimental investigation focused on this reaction showed that microtextures in Opx reaction rims give evidence of either dilative or compressive local growth regimes on the two sides of the rims caused by the total volume change of the reaction and the ratio of diffusive mass flow of the SiO2 and MgO components. If the reaction starts from olivine solid solutions in addition distinct microchemical patterns evolve. Thanks to advancements in microanalytical techniques like field emission electron microprobe, focused ion beam preparation, or dual beam techniques (ion beam/electron beam) we are now able to study the combination of microtextural and microchemical patterns in great detail. In rim growth experiments using natural Fo-rich Ol and Qtz as reactants the two most important minor and trace elements are Fe and Ni. According to equilibrium fractionation both should be enriched in Ol vs. Opx. Nevertheless, experimental evidence shows that these two elements do not behave in identical way. Ni is retained in Ol at the reaction front. Fe, in contrast, is expelled, and after transport along grain boundaries of the Opx rim is enriched at the Opx-Qtz interface, where the Fe-concentration in Opx is not buffered. Thus, there are two ways to maintain local equilibrium at the Ol/Opx interface - retain or expel. Which of the two is more efficient in energy minimization depends on the transport properties of the grain boundaries in the reaction rim. Thus, we can speak of kinetic fractionation in reaction rims. This kind of kinetic fractionation is followed as a general principle in diffusion-controlled reaction rim growth. For additional investigation, forsterite doped with various elements (like Cr, Ca, Zn) was synthesized and used in Opx rim growth experiments, where each dopand develops a distinct zonation pattern. Investigation of microtextures and microchemical patterns may have implications on global geological processes. Recently the hypothesis of large scale SiO2 metasomatism (Ol + SiO2 component = Opx) in the upper mantle due to eclogite-derived SiO2-rich melts became prominent and is supported by a growing amount of evidence. Little, however, is known about the actual mechanisms at work in diffusion-reaction metasomatism that are at the base of kinetic major and minor element fractionation.

Milke, R.; Abart, R.; Keller, L.; Rhede, D.; Keilonat, C.

2008-12-01

65

Kinetic analysis of complex reactions using FEMLAB  

SciTech Connect

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

66

Relaxations in Second Order Nonlinear Optical Polymeric Systems  

NASA Astrophysics Data System (ADS)

Second order nonlinear optical (NLO) materials are important for applications such as optical switching, frequency conversion, and electro-optic modulation. Polarized infrared reflection-absorption spectroscopy is employed as an approach to study the relaxation of the poled order in second order NLO materials using new characterization techniques. Both guest/host and photo-crosslinkable systems are investigated. This simple and common tool is used to monitor the decay of aligned chromophores by probing the intensity change as a function of time in specific chromophoric IR absorption peaks, such as nitro (-NO _2) and amino (-NH_2) functionalities. The relaxation behavior of the poled order from IR measurements is similar to that observed from second harmonic generation (SHG) measurements in all of the samples studied in this thesis. Temperature and frequency dependent dielectric spectroscopy is performed to study the nature of the relaxation processes in several second order NLO polymers. PVCN doped with CNNB-R samples appear to be homogeneous up to a 20% doping level, the highest dopant concentration studied. CNNB -R has a plasticizing effect on PVCN as indicated by a decrease of the alpha transition temperatures. The alpha transition temperatures are associated with the main chain motion, which has a great influence on the temporal stability of the second order nonlinearities. A UV-induced crosslinking reaction in the PVCN/CNNB-R system resulted in a significant decrease in both dielectric constants and losses leading to enhanced temporal stability due to an increased restriction of the chain mobility. Dielectric measurements were also used to monitor and optimize the curing reaction in both a phenoxysilicon polymer and a polyimide/inorganic composite. The results from both dielectric and dynamic mechanical measurements combined with those of the temporal stability of the polyimide/inorganic composite suggested that alpha relaxation plays an important role in the dipolar relaxation whereas beta relaxation makes no significant contribution. A second order NLO interpenetrating polymer network possessing excellent temporal stability has been designed and synthesized. The second harmonic coefficient (d _{33} = 33 pm/V) showed no decay after being treated at 110^circC for a week. The dipolar relaxation of the IPN was further investigated by the SHG technique in the temperature range from 120 to 170^circC. The relaxation behavior at temperatures close to the Tg (176 ^circC) of the material seemed to follow an Arrhenius type behavior. The nature of the relaxation process in the system was found to be inherently different from that in guest/host systems. A comprehensive strategy for the investigation of macroscopically ordered noncentrosymmetric polymeric systems containing polar components was thus established. (Abstract shortened by UMI.).

Chen, Jeng-I.

67

Reaction kinetics of dolomite rim growth  

NASA Astrophysics Data System (ADS)

Reaction rims of dolomite (CaMg[CO3]2) were produced by solid-state reactions at the contacts of oriented calcite (CaCO3) and magnesite (MgCO3) single crystals at 400 MPa pressure, 750-850 °C temperature, and 3-146 h annealing time to determine the reaction kinetics. The dolomite reaction rims show two different microstructural domains. Elongated palisades of dolomite grew perpendicular into the MgCO3 interface with length ranging from about 6 to 41 µm. At the same time, a 5-71 µm wide rim of equiaxed granular dolomite grew at the contact with CaCO3. Platinum markers showed that the original interface is located at the boundary between the granular and palisade-forming dolomite. In addition to dolomite, a 12-80 µm thick magnesio-calcite layer formed between the dolomite reaction rims and the calcite single crystals. All reaction products show at least an axiotactic crystallographic relationship with respect to calcite reactant, while full topotaxy to calcite prevails within the granular dolomite and magnesio-calcite. Dolomite grains frequently exhibit growth twins characterized by a rotation of 180° around one of the equivalent axis. From mass balance considerations, it is inferred that the reaction rim of dolomite grew by counter diffusion of MgO and CaO. Assuming an Arrhenius-type temperature dependence, activation energies for diffusion of CaO and MgO are E a (CaO) = 192 ± 54 kJ/mol and E a (MgO) = 198 ± 44 kJ/mol, respectively.

Helpa, V.; Rybacki, E.; Abart, R.; Morales, L. F. G.; Rhede, D.; Je?ábek, P.; Dresen, G.

2014-04-01

68

Kinetic study of the reaction of ebselen with peroxynitrite  

Microsoft Academic Search

The second-order rate constant for the reaction of ebselen with peroxynitrite (ONOO?) is (2.0±0.1) × 106 M?1s?1 at pH ? 8 and 25°C, 3–4 orders of magnitude higher than the rate constants observed for cysteine, ascorbate, or methionine. The activation energy is relatively low, 12.8 kJ\\/mol. This is the fastest reaction of peroxynitrite observed so far. It may allow Secontaining

Hiroshi Masumoto; Reinhard Kissner; Willem H. Koppenol; Helmut Sies

1996-01-01

69

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

USGS Publications Warehouse

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

70

Second-order splitting schemes for a class of reactive systems  

NASA Astrophysics Data System (ADS)

We consider the numerical time integration of a class of reaction-transport systems that are described by a set of ordinary differential equations for primary variables. In the governing equations, the terms involved may require the knowledge of secondary variables, which are functions of the primary variables. Specifically, we consider the case where, given the primary variables, the evaluation of the secondary variables is computationally expensive. To solve this class of reaction-transport equations, we develop and demonstrate several computationally efficient splitting schemes, wherein the portions of the governing equations containing chemical reaction terms are separated from those parts containing the transport terms. A computationally efficient solution to the transport sub-step is achieved through the use of linearization or predictor-corrector methods. The splitting schemes are applied to the reactive flow in a continuously stirred tank reactor (CSTR) with the Davis-Skodjie reaction model, to the CO+H oxidation in a CSTR with detailed chemical kinetics, and to a reaction-diffusion system with an extension of the Oregonator model of the Belousov-Zhabotinsky reaction. As demonstrated in the test problems, the proposed splitting schemes, which yield efficient solutions to the transport sub-step, achieve second-order accuracy in time.

Ren, Zhuyin; Pope, Stephen B.

2008-09-01

71

Second-Order Nonlinear Optical Imaging of Chiral Crystals  

PubMed Central

Second-order nonlinear optical imaging of chiral crystals (SONICC) is an emerging technique for crystal imaging and characterization. We provide a brief overview of the origin of second harmonic generation signals in SONICC and discuss recent studies using SONICC for biological applications. Given that they provide near-complete suppression of any background, SONICC images can be used to determine the presence or absence of protein crystals through both manual inspection and automated analysis. Because SONICC creates high-resolution images, nucleation and growth kinetics can also be observed. SONICC can detect metastable, homochiral crystalline forms of amino acids crystallizing from racemic solutions, which confirms Ostwald’s rule of stages for crystal growth. SONICC’s selectivity, based on order, and sensitivity, based on background suppression, make it a promising technique for numerous fields concerned with chiral crystal formation. PMID:21469954

Kissick, David J.; Wanapun, Debbie; Simpson, Garth J.

2012-01-01

72

Kinetic Roughening and Bifurcations in Reaction - Systems  

NASA Astrophysics Data System (ADS)

We study the dynamics of two reaction-diffusion phenomena driven by chemical activation and thermal dissipation and evolving, respectively, on a randomly distributed or continuous medium. The first system describes the process of slow combustion of a randomly distributed reactant. It is studied by a phase-field model built up from first principles and describes the evolution of thermal and reactant concentration fields. Our combustion model incorporates thermal diffusion, activation and dissipation. We examine it in a manner which makes a connection between the propagation of combustion fronts, their kinetic roughening and the percolation transition. In so doing, we examine slow combustion in the context phase transitions. The second system describes propagation of reaction fronts arising in transformations obeying the Arrhenius law of chemical reactions. It too is modelled by a set of phase-field equations describing the dynamics of both thermal and concentration fields. A typical example of this transformation is the crystallization of an amorphous material. In addition to the features of our combustion model, this model also incorporated a realistic treatment of mass diffusion. Front propagation of our model is shown to undergo period doubling bifurcations as one varies the background temperature at which the system is maintained. The signature of these bifurcations is the same as those of the logistics map. We study how the bifurcation structure changes as a function mass diffusion, focusing on changes of the background temperature for which period doubling first emerges. This temperature is the most easily obtained experimentally.

Provatas, Nikolas

1995-01-01

73

A Simple Second Order Cartesian Scheme for Compressible Flows  

E-print Network

of the convective fluxes computation for the cells near the solid ensures the boundary condition at second order and Iaccarino [6]. In this paper we present a simple globally second order scheme inspired by ghost cell

Paris-Sud XI, Université de

74

[Kinetics modeling and reaction mechanism of ferrate(VI) oxidation of triclosan].  

PubMed

Triclosan (TCS) is a broad-spectrum antibacterial agent widely used in many personal care products. We investigated oxidation of TCS by aqueous ferrate Fe(VI) to determine reaction kinetics, interpreted the reaction mechanism by a linear free-energy relationship, and evaluated the degradation efficiency. Second-order reaction kinetics was used to model Fe (VI) oxidation of TCS, with the apparent second-order rate constant (k(app)) being 531.9 L x (mol x s)(-1) at pH 8.5 and (24 +/- 1) degrees C. The half life (t1/2) is 25.8 s for an Fe( VI) concentration of 10 mg x L(-1). The rate constants of the reaction decrease with increasing pH values. These pH-dependent variations in k(app) could be distributed by considering species-specific reactions between Fe(VI) species and acid-base species of an ionizable TCS. Species-specific second-order reaction rate constants, k, were determined for reaction of HFeO4(-) with each of TCS's acid-base species. The value of k determined for neutral TCS was (4.1 +/- 3.5) x 10(2) L x (mol x s)(-1), while that measured for anionic TCS was (1.8 +/- 0.1) x 10(4) L x (mol x s)(-1). The reaction between HFeO4(-) and the dissociated TCS controls the overall reaction. A linear free-energy relationship illustrated the electrophilic oxidation mechanism. Fe (VI) reacts initially with TCS by electrophilic attack at the latter's phenol moiety. At a n[Fe(VI)]: n(TCS) > 7: 1, complete removal of TCS was achieved. And lower concentration of the humic acid could enhance the k(app) of Fe( VI) with TCS. In conclusion, Fe(VI) oxidation technology appears to be a promising tool for applications of WWTPs effluents and other decontamination processes. PMID:22165218

Yang, Bin; Ying, Guang-Guo; Zhao, Jian-Liang

2011-09-01

75

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

SciTech Connect

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

76

ENGI 2422 Second Order Linear ODEs Page 4-01 4. Second Order Linear Ordinary Differential Equations  

E-print Network

Newton's second law of motion: ( ) d d F mv m dt ENGI 2422 Second Order Linear ODEs Page 4-01 4. Second Order Linear Ordinary Differential Equations The general second order linear ordinary differential equation is of the form ( ) ( ) ( ) 2 2 d y dy P x Q x y

George, Glyn

77

A classical but new kinetic equation for hydride transfer reactions.  

PubMed

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

78

Second-order shallow flow equation for anisotropic aquifers  

NASA Astrophysics Data System (ADS)

Transient unconfined ground-water flow is described using the well-known Boussinesq equation, in which the Dupuit assumptions are implicit. When these assumptions fail, one must recur to the next level of approximation, which is the second-order theory for shallow flow in porous media, developed by Dagan (1967) for isotropic aquifers. When the soil is highly anisotropic Dagan's second-order theory can become invalid. Here we present the generalized second order theory that account for anisotropy. An analytical solution for the second-order theory with anisotropy is presented for the linearized equation that is used to illustrate this effect on the bank storage problem.

Castro-Orgaz, O.; Giraldez, J. V.; Mateos, L.

2013-09-01

79

Second order perturbation theory for spin-orbit resonances  

E-print Network

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

80

Design of optimal second-order state estimators  

NASA Technical Reports Server (NTRS)

The present consideration of the design of online computation-saving second-order state estimators for second-order vector-matrix differential systems proposes a class of such estimators which is proven to possess guaranteed convergence. A class of optimal second-order estimators is then obtained, and the conditions required for optimality are identified. The estimator proposed offers high performance in conjunction with online computation reductions sufficiently great to allow the estimation of the large number of state variables associated with control of large, flexible space structures represented by high-dimensional second-order systems.

Joshi, Suresh M.

1991-01-01

81

Approximate Calculation Method for Second Order Sensitivity Coefficient  

Microsoft Academic Search

A simple method has been developed for calculating the second order sensitivity coefficient of static and burnup-dependent core performance parameters. The method is applied to a small and a large fast breeder reactors. Changes in core performance parameters due to 10% cross section changes are compared with that predicted by the first and the second order sensitivity analyses. Numerical results

Kazuhisa MATSUMOTO; Toshikazu TAKEDA; Tomoaki MASUDA

1994-01-01

82

Some Steady MHD Flows of the Second Order Fluid  

Microsoft Academic Search

The exact analytic solutions of two problems of a second order fluid in presence of a uniform transverse magnetic field are investigated. The governing equation is of fourth order ordinary differential equation and is solved using perturbation method. In the first problem we discuss the flow of a second order fluid due to non-coaxial rotations of a porous disk and

T. Hayat; M. I. Hameed; S. Asghar; A. M. Siddiqui

2004-01-01

83

Second-order symmetric duality with cone constraints  

NASA Astrophysics Data System (ADS)

Wolfe and Mond-Weir type second-order symmetric duals are formulated and appropriate duality theorems are established under [eta]-bonvexity/[eta]-pseudobonvexity assumptions. This formulation removes several omissions in an earlier second-order primal dual pair introduced by Devi [Symmetric duality for nonlinear programming problems involving [eta]-bonvex functions, European J. Oper. Res. 104 (1998) 615-621].

Gulati, T. R.; Gupta, S. K.; Ahmad, I.

2008-10-01

84

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

85

Induction is not derivable in second order dependent type theory  

E-print Network

Induction is not derivable in second order dependent type theory Herman Geuvers ? Department-derivability of induction in second order dependent type theory (#21;P 2). This is done by providing a model construction extensional combinatory algebra. We give counter-models in which the induction principle over natural num

Geuvers, Herman

86

Evaluation of reaction kinetics for gas-powder systems  

Microsoft Academic Search

Kinetic models for the reaction between a gas and powder are presented and discussed. Rates from the progressive conversion model are dependent on the amount of material present. This model is described by an equation that yields both the rate constant and the reaction order. The phase boundary model produces rates for topochemical reactions which are dependent on the powder

J. L. Stakebake; G. E. Bixby

1979-01-01

87

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

88

Visualization of second order tensor fields and matrix data  

NASA Technical Reports Server (NTRS)

We present a study of the visualization of 3-D second order tensor fields and matrix data. The general problem of visualizing unsymmetric real or complex Hermitian second order tensor fields can be reduced to the simultaneous visualization of a real and symmetric second order tensor field and a real vector field. As opposed to the discrete iconic techniques commonly used in multivariate data visualization, the emphasis is on exploiting the mathematical properties of tensor fields in order to facilitate their visualization and to produce a continuous representation of the data. We focus on interactively sensing and exploring real and symmetric second order tensor data by generalizing the vector notion of streamline to the tensor concept of hyperstreamline. We stress the importance of a structural analysis of the data field analogous to the techniques of vector field topology extraction in order to obtain a unique and objective representation of second order tensor fields.

Delmarcelle, Thierry; Hesselink, Lambertus

1992-01-01

89

The surface reaction kinetics of salicylate on alumina  

SciTech Connect

The kinetics of reaction of salicylate with colloidal alumina in aqueous suspension and with Al(III) in homogeneous aqueous solution were studied by stopped-flow laser fluorescence spectroscopy. The emission spectra confirmed the formation of both monodentate complexes and more stable bidentate chelates. Temporal evolution of the spectra indicated that the reaction was fast (within first few minutes) for both the homogeneous and heterogeneous reactions but slowed down afterwards for the latter. Reactions completed within 10 minutes in homogeneous phase at pH 3.3 but took more than 12 hours in alumina suspension. Analysis of the fluorescence intensity within first four minutes showed that in homogeneous phase the reaction followed a single pseudo-first-order kinetics. In alumina suspension log plots were nonlinear and characteristic of multiple heterogeneous reaction paths. The kinetics are interpreted in terms of the simultaneous formation of multiple species as well as subsequent conversion between species.

Wang, Z.; Ainsworth, C.C.; Friedrich, D.M.; Joly, A.G.; Gassman, P.L. [Pacific Northwest National Lab., Richland, WA (United States)

1997-12-31

90

Ferrate(VI) oxidation of ?-lactam antibiotics: reaction kinetics, antibacterial activity changes, and transformation products.  

PubMed

Oxidation of ?-lactam antibiotics by aqueous ferrate(VI) was investigated to determine reaction kinetics, reaction sites, antibacterial activity changes, and transformation products. Apparent second-order rate constants (kapp) were determined in the pH range 6.0-9.5 for the reaction of ferrate(VI) with penicillins (amoxicillin, ampicillin, cloxacillin, and penicillin G), a cephalosporin (cephalexin), and several model compounds. Ferrate(VI) shows an appreciable reactivity toward the selected ?-lactams (kapp for pH 7 = 110-770 M(-1) s(-1)). The pH-dependent kapp could be well explained by considering species-specific reactions between ferrate(VI) and the ?-lactams (with reactions occurring at thioether, amine, and/or phenol groups). On the basis of the kinetic results, the thioether is the main reaction site for cloxacillin and penicillin G. In addition to the thioether, the amine is a reaction site for ampicillin and cephalexin, and amine and phenol are reaction sites for amoxicillin. HPLC/MS analysis showed that the thioether of ?-lactams was transformed to stereoisomeric (R)- and (S)-sulfoxides and then to a sulfone. Quantitative microbiological assay of ferrate(VI)-treated ?-lactam solutions indicated that transformation products resulting from the oxidation of cephalexin exhibited diminished, but non-negligible residual activity (i.e., ?24% as potent as the parent compound). For the other ?-lactams, the transformation products showed much lower (<5%) antibacterial potencies compared to the parent compounds. Overall, ferrate(VI) oxidation appears to be effective as a means of lowering the antibacterial activities of ?-lactams, although alternative approaches may be necessary to achieve complete elimination of cephalosporin activities. PMID:25073066

Karlesa, Anggita; De Vera, Glen Andrew D; Dodd, Michael C; Park, Jihye; Espino, Maria Pythias B; Lee, Yunho

2014-09-01

91

Superposition rules and second-order differential equations  

NASA Astrophysics Data System (ADS)

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, diverse 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.

Cariñena, J. F.; de Lucas, J.

2011-07-01

92

Method to render second order beam optics programs symplectic  

SciTech Connect

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

93

Kinetics and mechanism of reactions of the drug tiopronin with platinum(IV) complexes.  

PubMed

Tiopronin, a synthetic thiol-containing drug being used in treatments of cystinuria and certain types of rare arthritis, is also a hepatoprotective and a detoxifying agent. Many analytical methods have been developed based on its redox chemistry with metal ions/complexes, but the kinetic and mechanistic aspects are poorly understood. In this work, the oxidation of tiopronin by cisplatin prodrug and a model compound, cis-[Pt(NH3)2Cl4] and trans-[PtCl2(CN)4](2-), was investigated. The oxidation kinetics was followed by a stopped-flow spectrophotometer over a wide pH range under the pseudo first-order conditions of [Tiopronin]?[Pt(IV)]. Time-resolved spectra were also recorded for both Pt(IV) complexes, enabling to establish an overall second-order rate law: -d[Pt(IV)]/dt=k'[Tiopronin][Pt(IV)], where k' pertains to observed second-order rate constants. Under the kinetic conditions, tiopronin was oxidized to form the tiopronin-disulfide exclusively as identified by mass spectrometry. A reaction mechanism was proposed, involving parallel reductions of the Pt(IV) complexes by the three protolytic tiopronin species as rate-determining steps. The rate constants for the rate-determining steps were derived. The fully deprotonated tiopronin is about 4×10(4) more reactive than its corresponding thiol form for both Pt(IV) complexes; the huge reactivity difference orchestrates closely with the fact that the nucleophilicity of thiolate is much higher than the corresponding thiol. Hence, the attack of the sulfur atom in thiol/thiolate of tiopronin on the axially-coordinated chloride in the Pt(IV) complexes is nucleophilic in nature in the rate-determining steps, resulting in a bridge formation and a subsequent bridged electron-transfer. PMID:23665090

Huo, Shuying; Shi, Hongmei; Liu, Dongzhi; Shen, Shigang; Zhang, Jiong; Song, Changying; Shi, Tiesheng

2013-08-01

94

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

SciTech Connect

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

95

Reaction kinetics of selected micropollutants in ozonation and advanced oxidation processes.  

PubMed

Second-order reaction rate constants of micropollutants with ozone (k(O3)) and hydroxyl radicals (k(OH)) are essential for evaluating their removal efficiencies from water during ozonation and advanced oxidation processes. Kinetic data are unavailable for many of the emerging micropollutants. Twenty-four micropollutants with very diverse structures and applications including endocrine disrupting compounds, pharmaceuticals, and personal care products were selected, and their k(O3) and k(OH) values were determined using bench-scale reactors (at pH 7 and T = 20 °C). Reactions with molecular ozone are highly selective as indicated by their k(O3) values ranging from 10(-2)-10(7) M(-1) s(-1). The general trend of ozone reactivity can be explained by micropollutant structures in conjunction with the electrophilic nature of ozone reactions. All of the studied compounds are highly reactive with hydroxyl radicals as shown by their high k(OH) values (10(8)-10(10) M(-1) s(-1)) even though they are structurally very diverse. For compounds with a low reactivity toward ozone, hydroxyl radical based treatment such as O(3)/H(2)O(2) or UV/H(2)O(2) is a viable alternative. This study contributed to filling the data gap pertaining kinetic data of organic micropollutants while confirming results reported in the literature where available. PMID:23079129

Jin, Xiaohui; Peldszus, Sigrid; Huck, Peter M

2012-12-01

96

On the state estimation of structures with second order observers  

NASA Technical Reports Server (NTRS)

The use of Linear Quadratic Regulator (LQR) control synthesis techniques implies the availability of full state feedback. For vibration control of structures, usually only a limited number of states are measured from which an observer model reconstructs the full state. It is shown that using second order observers is a viable technique for reconstructing the unmeasured states of structures under mildly restrictive conditions. Moreover, the computational advantages of the second order observer as compared to a first order observer indicate that significantly larger observer models may be utilized. Numerical examples are used to demonstrate the performance of second order observers. The implications of second order observers in the development of Controls-Structures Interaction (CSI) technology is discussed.

Belvin, W. Keith; Park, K. C.

1989-01-01

97

Some nonlinear second order equation modelling rocket motion  

E-print Network

In this paper, we consider a nonlinear second order equation modelling rocket motion in the gravitational field obstructed by the drag force. The proofs of the main results are based on topological fixed point approach.

Dorota Bors; Robert Sta?czy

2012-12-23

98

The second-order sharpening of blurred smooth borders  

SciTech Connect

The problem is to approximate, with local second-order accuracy, the smooth boundary separating a black and a white region in the plane, given discretely located gray values associated with a blurring of that border. ''Second-order'', here, is with respect to the size /ital h/ of the scale of the prescribed blurring. The locally determined approximations are line segments. The algorithms discussed here can result in second-order accuracy, but they may not in certain geometric circumstances. Typical local curvature estimates based on adjacent line segments do not converge, but atypical one does. Consideration of a class of scaled blurrings leads to a type of blurring of borders which is particularly easy for a computer to undo locally, yielding a line which is locally second-order accurate. Some extensions to three (and more) dimensions are appended.

Swartz, B.

1989-04-01

99

Second-order susceptibility from a tight-binding Hamiltonian  

E-print Network

Using a new formalism that modifies a tight-binding Hamiltonian to include interaction with a time-dependent electromagnetic field, we have obtained an analytical expression for the second-order susceptibility. This expression has been used...

Dumitrica, T.; Graves, JS; Allen, Roland E.

1998-01-01

100

Second-order synchrosqueezing transform or invertible reassignment? Towards ideal  

E-print Network

Second-order synchrosqueezing transform or invertible reassignment? Towards ideal time of the modes. These two new transformations thus provide the benefits of both the synchrosqueezing transform transformations, and illustrate their differences. Index Terms time-frequency, reassignment, synchrosqueezing, AM

Paris-Sud XI, Université de

101

How is complex second-order motion processed?  

Microsoft Academic Search

Converging psychophysical and electrophysiological evidence suggests that first-order (luminance-defined) complex motion types i.e., radial and rotational motion, are processed by specialized extrastriate motion mechanisms. We ask whether radial and rota- tional second-order (texture-defined) motion patterns are processed in a similar manner. The motion sensitivity to translating, radiating and rotating motion patterns of both first-order (luminance-modulated noise) and second-order (contrast-modulated noise)

Armando Bertone; Jocelyn Faubert

2003-01-01

102

Modulation masking produced by second-order modulators  

Microsoft Academic Search

Recent studies suggest that an auditory nonlinearity converts second-order sinusoidal amplitude modulation (SAM) (i.e., modulation of SAM depth) into a first-order SAM component, which contributes to the perception of second-order SAM. However, conversion may also occur in other ways such as cochlear filtering. The present experiments explored the source of the first-order SAM component by investigating the ability to detect

Christian Füllgrabe; Brian C. J. Moore; Laurent Demany; Stephan D. Ewert; Stanley Sheft; Christian Lorenzi

2005-01-01

103

Generic Blind Source Separation Using Second-Order Local Statistics  

Microsoft Academic Search

Exploiting the fact that one is dealing with time signals, it is possible to formulate certain blind source (or signal) separation\\u000a tasks in terms of a simple generalized eigenvalue decomposition based on two matrices. Many of the techniques determine these\\u000a two matrices using second-order statistics, e.g., variance, covariance, autocorrelation, etc.\\u000a \\u000a In this work, we present a second-order, covariance-based method to

Marco Loog

2006-01-01

104

Kubo Formulae for Second-Order Hydrodynamic Coefficients  

E-print Network

At second order in gradients, conformal relativistic hydrodynamics depends on the viscosity eta and on five additional "second-order" hydrodynamical coefficients tauPi, kappa, lambda1, lambda2, and lambda3. We derive Kubo relations for these coefficients, relating them to equilibrium, fully retarded 3-point correlation functions of the stress tensor. We show that the coefficient lambda3 can be evaluated directly by Euclidean means and does not in general vanish.

Guy D. Moore; Kiyoumars A. Sohrabi

2010-07-29

105

[Second-order retrospective revaluation in human contingency learning].  

PubMed

We demonstrated second-order retrospective revaluation with three cues (T1, T2, and C) and an outcome, in human contingency learning. Experimental task, PC-controlled video game in which participants were required to observe about the relations between firing missiles and the tank destruction, consisted of three training phases and two rating phases. Groups C+ and C- consisted of same first two training phases, CT+ (cues C and T with an outcome) and T1T2+ followed by C+, or C- training for Groups C+, C-, respectively. In rating phases, it is clearly demonstrated that the judgment of predictive value for the outcome of the T2 were higher by C+ training (second-order unovershadowing) and lowered by C- training (second-order backward blocking). The results for Groups RC+ and RC-, in which the orders of the first two training phase for Groups C+ and C- were interchanged, also showed second-order unovershadowing and second-order backward blocking. These results, the robustness of second-order retrospective revaluation against the order of the first training phases, can be explained by the extended comparator hypothesis and probabilistic contrast model. However, these results cannot be explained by traditional associative learning models. PMID:19489431

Numata, Keitaro; Shimazaki, Tsuneo

2009-04-01

106

Kinetics of the Fischer-Tropsch reaction.  

PubMed

Long carbon chains: Self-assembly of monomeric carbon intermediates into long-chain hydrocarbons on catalytically reactive surface was studied when full reversibility of the chain growth is included in the kinetic model. Using Brønsted-Evans-Polanyi relations, the maximum chain growth as a function of the surface reactivity is predicted. PMID:22829559

Markvoort, Albert J; van Santen, Rutger A; Hilbers, Peter A J; Hensen, Emiel J M

2012-09-01

107

Basic Chemical Principles 1: Reaction Kinetics  

E-print Network

with radiation can cause chemical events: bonds broken, molecules excited { Creation of radicals Molecular state: Lowest energy con#12;guration of electrons in orbitals #15; To form chemical bond, combine atomic, photo-chemical reactions are important: reactions initiated by light #12; { Interaction of matter

Schofield, Jeremy

108

Reaction kinetics in a tight spot.  

PubMed

The standard analysis of reaction networks based on deterministic rate equations fails in confined geometries, commonly encountered in fields such as astrochemistry, thin-film growth and cell biology. In these systems the small reactant population implies anomalous behavior of reaction rates, which can be accounted for only by following the full distribution of reactant numbers. PMID:17193475

Biham, Ofer; Krug, Joachim; Lipshtat, Azi; Michely, Thomas

2005-05-01

109

Reaction Kinetics of Powdered Uranium and Deuteroammonia  

Microsoft Academic Search

A rate law for the nitridation of pyrophoric uranium with deuteroammonia was established for the entire course of the reaction. The rate of reaction between powdered uranium and deuteroammonia was determined to be a linear function of the initial Brunauer, Emmett, and Teller (BET) surface area and the fraction of unreacted uranium. Sintering of powdered uranium to a stable surface

R. M. Alire; J. H. McCrary

1966-01-01

110

Protein Reaction Kinetics in a Room-Temperature Glass  

Microsoft Academic Search

Protein reaction kinetics in aqueous solution at room temperature are often simplified by the thermal averaging of conformational substates. These substates exhibit widely varying reaction rates that are usually exposed by trapping in a glass at low temperature. Here, it is shown that the solvent viscosity, rather than the low temperature, is primarily responsible for the trapping. This was demonstrated

Stephen J. Hagen; James Hofrichter; William A. Eaton

1995-01-01

111

Second Order Perturbations of Monte Carlo Criticality Calculations  

SciTech Connect

Perturbation techniques are powerful tools for determining the effects of small changes, or perturbations, to a problem. Perturbations have long been problematic in Monte Carlo calculations because the effects of small changes to the problem are usually masked by the inherent statistical uncertainties. The recently released MCNP4B Monte Carlo computer code uses the differential operator technique, to calculate changes in tallies caused by perturbations in density and composition over given energy ranges and reaction types. This technique will allow for precise calculation of the changes in tallies even if the standard deviation of the unperturbed tally is larger than the change. The differential operator is approximated by a second order Taylor series. The implementation of the Taylor series expansion assumes that the coefficients are independent of any perturbed cross-sections. However, if the tally is multiplied by cross-section data this assumption is invalid and incorrect results will be generated. Of significant interest is the use of perturbations in criticality calculations. Although the criticality source feature for MCNP cannot directly calculate perturbed eigenvalues, a track-length estimate for Keff can be tallied and the perturbation feature can be applied to this tally. However, since the tally multiplies the flux by the macroscopic fission cross-section, this tally is dependent on perturbed cross-section data and incorrect results will be calculated by the perturbation feature. In order to compute the correct tally, a correction term is needed that will account for the dependence of the Taylor series coefficients on the perturbed cross-section data.

Densmore, J.D.; Hendricks, J.S.; McKinney, G.W.

1997-07-01

112

Extension of second-order Stokes theory to variable bathymetry  

NASA Astrophysics Data System (ADS)

In the present work second-order Stokes theory has been extended to the case of a generally shaped bottom profile connecting two half-strips of constant (but possibly different) depths, initiating a method for generalizing the Stokes hierarchy of second- and higher-order wave theory, without the assumption of spatial periodicity. In modelling the wave bottom interaction three partial problems arise: the first order, the unsteady second order and the steady second order. The three problems are solved by using appropriate extensions of the consistent coupled-mode theory developed by the present authors for the linearized problem. Apart from the Stokes small-amplitude expansibility assumption, no additional asymptotic assumptions have been introduced. Thus, bottom slope and curvature may be arbitrary, provided that the resulting wave dynamics is Stokes-compatible. Accordingly, the present theory can be used for the study of various wave phenomena (propagation, reflection, diffraction) arising from the interaction of weakly nonlinear waves with a general bottom topography, in intermediate water depth. An interesting phenomenon, that is also very naturally resolved, is the net mass flux induced by the depth variation, which is consistently calculated by means of the steady second-order potential. The present method has been validated against experimental results and fully nonlinear numerical solutions. It has been found that it correctly predicts the second-order harmonic generation, the amplitude nonlinearity, and the amplitude variation due to non-resonant first-and-second harmonic interaction, up to the point where the energy transfer to the third and higher harmonics can no longer be neglected. Under the restriction of weak nonlinearity, the present model can be extended to treat obliquely incident waves and the resulting second-order refraction patterns, and to study bichromatic and/or bidirectional wave wave interactions, with application to the transformation of second-order random seas in variable bathymetry regions.

Belibassakis, K. A.; Athanassoulis, G. A.

2002-08-01

113

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

114

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

115

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

116

Children's understanding of second-order mental states.  

PubMed

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 directed to second-order false belief and other forms of higher order, recursive mentalistic reasoning. Three general issues are considered. Research directed to developmental changes indicates that preschoolers typically fail second-order tasks and that success emerges at about age 5 or 6, although results vary some with method of assessment. Research directed to the consequences of second-order competence has revealed positive relations with a number of other aspects of children's development. Finally, measures of both language and executive function relate positively to performance on second-order tasks; the causal bases for the correlations, however, remain to be established. This article concludes with suggestions for future research. PMID:19702381

Miller, Scott A

2009-09-01

117

The Reaction of a Food Colorant with Sodium Hypochlorite: A Student-Designed Kinetics Experiment  

NASA Astrophysics Data System (ADS)

The kinetics of the reaction of the food colorant FD&C Blue #1 with sodium hypochlorite (Clorox) is described in a student-designed experimental format. In this format, students are guided- by means of questions- to make decisions regarding concentration of reagents, choice of equipment, and actual laboratory procedures to be followed. This format provides an opportunity for students to apply the concepts and skills learned in class and in previous laboratory sessions to a new problem. We have found that this experience helps students gain depth of understanding of all concepts involved. The reaction (with a large excess of NaOCl) is followed with a Spectronic 20 at the Blue #1 colorant lmax of 630 nm. The %T is measured over time and three graphs: A vs time, ln A vs time and 1/A vs time are plotted to find that the second one is linear and thus first order with respect to the Blue #1. When the concentration of NaOCl is reduced to one-half the original value, it is found that the rate is reduced by one-half, indicating that the reaction is first order with respect to NaOCl and second order overall. The rate constant of the reaction is determined from the slope of the curve and the mean obtained by our students is 17 M-1 min-1 at room temperature (about 28° C).

Arce, Josefina; Betancourt, Rosa; Rivera, Yamil; Pijem, Joan

1998-09-01

118

Reaction wheels for kinetic energy storage  

SciTech Connect

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 wheels 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.

1984-11-01

119

Superposition rules and second-order Riccati equations  

E-print Network

A superposition rule is a particular type of map that enables one to express the general solution of certain systems of first-order ordinary differential equations, the so-called Lie systems, out of generic families of particular solutions and a set of constants. The first aim of this work is to propose several generalisations of this notion to second-order differential equations. Next, several results on the existence of such generalisations are given and relations with the theories of Lie systems and quasi-Lie schemes are found. Finally, our methods are used to study second-order Riccati equations and other second-order differential equations of mathematical and physical interest.

J. F. Cariñena; J. de Lucas

2010-07-08

120

Conformal symmetry and non-relativistic second order fluid dynamics  

E-print Network

We study the constraints imposed by conformal symmetry on the equations of fluid dynamics at second order in gradients of the hydrodynamic variables. At zeroth order conformal symmetry implies a constraint on the equation of state, E=2/3 P, where E is the energy density and P is the pressure. At first order, conformal symmetry implies that the bulk viscosity must vanish. We show that at second order conformal invariance requires that two-derivative terms in the stress tensor must be traceless, and that it determines the relaxation of dissipative stresses to the Navier-Stokes form. We verify these results by solving the Boltzmann equation at second order in the gradient expansion. We find that only a subset of the terms allowed by conformal symmetry appear.

Jingyi Chao; Thomas Schaefer

2011-08-25

121

Spacecraft attitude determination using a second-order nonlinear filter  

NASA Technical Reports Server (NTRS)

The stringent attitude determination accuracy and faster slew maneuver requirements demanded by present-day spacecraft control systems motivate the development of recursive nonlinear filters for attitude estimation. This paper presents the second-order filter development for the estimation of attitude quaternion using three-axis gyro and star tracker measurement data. Performance comparisons have been made by computer simulation of system models and filter mechanization. It is shown that the second-order filter consistently performs better than the extended Kalman filter when the performance index of the root sum square estimation error of the quaternion vector is compared. The second-order filter identifies the gyro drift rates faster than the extended Kalman filter. The uniqueness of this algorithm is the online generation of the time-varying process and measurement noise covariance matrices, derived as a function or the process and measurement nonlinearity, respectively.

Vathsal, S.

1987-01-01

122

Laboratory Kinetics of Chemical Reactions occurring in Astrophysical Environments  

NASA Astrophysics Data System (ADS)

To model the dynamics and molecular evolution of interstellar clouds, a great deal of information on chemical kinetics is required, preferably under the appropriate conditions of kinetic temperature and internal excitation. This kinetics includes (i) gas phase ionic (ion-molecule and electron-ion) and (ii) neutral-neutral reactions and (iii) heterogeneous surface catalysis, all from simple species to those as complex as polyaromatic hydrocarbons and pre-life molecules. The current situation in these three areas will be briefly reviewed with more emphasis on ionic reactions for which the most data are available. The classes of reactions will include charge and proton transfer, atom insertion and abstraction, radiative association, electron-ion and ion-ion recombination, reactions with atoms, reactions involving isotopes, reaction and production of structural isomers, ring formation and destruction, and condensation. Information on rates of reaction, product identity and state of excitation will be presented wherever possible. Some mention will also be made of the reactions of negative ions. Most recent data will be presented, specifically involving the understudied process of electron-ion recombination. Some possible future directions will also be suggested. Funding of my research program by ACF-PRF, NASA and NSF is gratefully acknowledged.

Adams, N. G.; Babcock, L. M.

2005-05-01

123

Second order limit language in variants of splicing system  

NASA Astrophysics Data System (ADS)

The cutting and pasting processes that occur in DNA molecules have led to the formulation of splicing system. Since then, there are few models used to model the splicing system. The splicing language, which is the product of splicing system, can be categorized into two, namely the adult and limit language. In this research, limit language is extended to the second order limit language. Few problems are approached which lead to the formation of second order limit language which is then analyzed using various types of splicing system.

Ahmad, Muhammad Azrin; Sarmin, Nor Haniza; Heng, Fong Wan; Yusof, Yuhani

2014-07-01

124

Static second-order polarizabilities of aminobenzophenones and nitrobenzophenones  

NASA Technical Reports Server (NTRS)

Static-field theoretical studies on molecular second-order polarizabilities (beta) of benzophenone derivatives were performed. Calculations were based on the use of shaped electric fields and semiempirical Hamiltonians. Either an electron-donating (amine) or an electron-withdrawing (nitro) substituent was incorporated into a phenyl ring of benzophenone; the phenyl rings of benzophenone were oriented either coplanar or perpendicular to the carbonyl. The change in charge transfer with respect to the electrophilic character of the carbonyl group was monitored to determine its effect on the molecular second-order polarizability. Calculations were performed for all constitutional isomers of the two benzophenone derivatives.

Moore, Craig E.; Cardelino, Beatriz H.

1991-01-01

125

The Poisson equation at second order in relativistic cosmology  

SciTech Connect

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

126

An application of integral inequality to second order nonlinear oscillation  

NASA Astrophysics Data System (ADS)

A simple result concerning integral inequalities enables us to give an alternative proof of Waltman's theorem: lim t ? ? ? t0a( s) ds = ? implies oscillation of the second order nonlinear equation y?( t) + a( t) f( y( t)) = 0; to prove an analog of Wintner's theorem that relates the nonoscillation of the second order nonlinear equations to the existence of solutions of some integral equations, assuming that lim t ? ? ? t0a( s) ds exists; and to give an alternative proof and to extend a result of Butler. An often used condition on the coefficient a( t) is given a more familiar equivalent form and an oscillation criterion involving this condition is established.

Kwong, Man Kam; Wong, James S. W.

127

a Second-Order Adaptive Arbitrary Lagrangian-Eulerian Method for the Compressible Euler Equations  

NASA Astrophysics Data System (ADS)

Most of finite volume schemes in the Arbitrary Lagrangian-Eulerian (ALE) method are constructed on the staggered mesh, where the momentum is defined at the nodes and the other variables (density, pressure and specific internal energy) are cell-centered. However, this kind of schemes must use a cell-centered remapping algorithm twice which is very inefficient. Furthermore, there is inconsistent treatment of the kinetic and internal energies.1 Recently, a new class of cell-centered Lagrangian scheme for two-dimensional compressible flow problems has been proposed in Ref. 2. The main new feature of the algorithm is the introduction of four pressures on each edge, two for each node on each side of the edge. This scheme is only first-order accurate. In this paper, a second-order cell-centered conservative ENO Lagrangian scheme is constructed by using an ENO-type approach to extend the spatial second-order accuracy. Time discretization is based on a second-order Runge-Kutta scheme. Combining a conservative interpolation (remapping) method3,4 with the second-order Lagrangian scheme, a kind of cell-centered second-order ALE methods can be obtained. Some numerical experiments are made with this method. All results show that our method is effective and have second-order accuracy. At last, in order to further increase the resolution of shock regions, we use an adaptive mesh generation based on the variational principle5 as a rezoned strategy for developing a class of adaptive ALE methods. Numerical experiments are also presented to valid the performance of the proposed method.

Wang, Y. J.; Zhao, N.; Wang, C. W.; Wang, D. H.

128

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

129

A Second-Order Markov Gravity Anomaly Model  

Microsoft Academic Search

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

130

Multi dimensional second order defuzzification algorithm (M-SODA)  

Microsoft Academic Search

Multi dimensional second order defuzzification algorithm (SODA) minimizes the hardware requirement and ensures easier implementation of a fuzzy controller as compared to the LUT and the triangular membership approach when extended to multiple dimensions. In this paper we have put forward the extension of the SODA to multiple dimensions. Fuzzy controllers can handle multiple inputs and outputs however size of

Nirav Dharia; J. Gownipalli; B. M. Wilamowski; O. Kaynak

2002-01-01

131

Second order bibliometric operators in the Astrophysics Data System  

Microsoft Academic Search

Second order relational operators are functions which take lists which have been generated by a database query, and from those lists form sets of other lists, which can then be merged and sorted on the basis of one or more of the attributes of the items in the lists. The NASA Astrophysics Data System is unique among bibliometric information retrieval

M. J. Kurtz; Guenther Eichhorn; Alberto Accomazzi; C. S. Grant; Stephen S. Murray

2002-01-01

132

OPTIMAL MAGNETIC SHIELD DESIGN WITH SECOND-ORDER CONE PROGRAMMING  

E-print Network

of the MAGLEV train, a new bullet train under development in Japan, is formulated as the continuous convex words. second-order cone programming, interior-point methods, magnetic shielding, MAGLEV train, optimal as similar problems with different linear equality constraints [15]. The bullet train, which is called MAGLEV

Tsuchiya, Takashi

133

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

134

Second-Order Raman Spectrum of MgO.  

National Technical Information Service (NTIS)

The second-order Raman spectrum of MgO at room temperature is reported for different polarizations and crystal orientations. The parts of the scattering polarizability transforming as A(1g), E(g), and T(2g) are separated and compared with features in the ...

N. B. Manson, S. L. Chodos, W. Von der Ohe

1970-01-01

135

C*-algebras associated with some second order differential operators  

E-print Network

We compare two C*-algebras that have been used to study the essential spectrum. This is done by considering a simple second order elliptic differential operator acting in L^2(R^N), which is affiliated with one or both of the algebras depending on the behaviour of the coefficients.

E Brian Davies; Vladimir Georgescu

2011-03-20

136

A second order differential equation for a point charged particle  

E-print Network

A model for the dynamics of a classical point charged particle interacting with higher order jet electromagnetic fields is described by an implicit ordinary second order differential equation. We show that such equation is free of run-away and pre-accelerated solutions of Dirac's type. The theory is Lorentz invariant and is compatible with Newton's first law and Larmor's power radiation law.

Ricardo Gallego Torromé

2012-07-16

137

Pecuniary Effects, Second-Order Conditions, and the LRAC Curve.  

ERIC Educational Resources Information Center

Explores the importance of second-order conditions in the cost-minimization problem confronting the monopsonistic employer of factor inputs. Describes an alternative approach to the presence of pecuniary effects that does not depend on the assumption that firms are monopsonistic in factor markets. (CMK)

Comolli, Paul M.

2000-01-01

138

Proportional retarded control of a second order system  

Microsoft Academic Search

A strategy for the tuning of a second order system in closed loop with a proportional retarded control law, based on the root location analysis of the system, is proposed. It is validated by achieving a significant reduction of the oscillatory behavior of a cart pendulum experimental setup.

R. Villafuerte; S. Mondie; C. Vazquez; J. Collado

2009-01-01

139

SECOND ORDER ENTROPY DIMINISHING SCHEME FOR THE EULER EQUATIONS  

Microsoft Academic Search

In several papers of Bouchut, Bourdarias, Perthame and Coquel, Le Floch ((13), (7)...), a general methodology has been developed to construct second order flnite volume schemes for hyperbolic systems of conservation laws satisfying the entire family of entropy inequalities. This approach is mainly based on the construction of an entropy diminishing projection. Unfor- tunately, the explicit computation of this projection

F. COQUEL; P. HELLUY; J. SCHNEIDER

2007-01-01

140

Nonlinear second order ODE's: Factorizations and particular solutions  

E-print Network

We present particular solutions for the following important nonlinear second order differential equations: modified Emden, generalized Lienard, convective Fisher, and generalized Burgers-Huxley. For the latter two equations these solutions are obtained in the travelling frame. All these particular solutions are the result of extending a simple and efficient factorization method that we developed in Phys. Rev. E 71 (2005) 046607

O. Cornejo-Perez; H. C. Rosu

2005-04-18

141

A simple second order cartesian scheme for compressible Euler flows  

E-print Network

], [13]) were followed by many other extensions [40], [17], [26]. Ghost cells are cells in the solid at solid boundaries, is simple to implement and it is formally second order accurate. Error convergence developments ([23],[8],[7]), belong to this category: the solid is modeled as a porous medium with vanishing

Paris-Sud XI, Université de

142

HOW TO REPAIR A SECOND-ORDER SURFACE FOR COMPUTER  

E-print Network

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, Université de

143

Wiener crosses borders: interpolation based on second order models  

E-print Network

Wiener crosses borders: interpolation based on second order models Alvaro Guevara a and Rudolf to extend images beyond theirs borders such that no size reduction occurs if a linear filter. This gives a definite answer to the problem of how an image should be extended across its borders

Mester, Rudolf

144

Simulation of vector fields with arbitrary second-order correlations  

E-print Network

, and the spectrum of random electromagnetic beams on propagation," Opt. Lett. 28, 1078­1080 (2003). 5. P. Vahimaa: Temporally-stationary electromagnetic fields with arbitrary second-order coherence functions are simulated) (2005). 7. E. Wolf, "Invariance of the spectrum of light on propagation," Phys. Rev. Lett. 56, 1370

Bhargava, Rohit

145

PREDICTIONS OF HIGHWAY EMISSIONS BY A SECOND ORDER CLOSURE MODEL  

EPA Science Inventory

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...

146

Remarks on the second-order Seiberg-Witten maps  

SciTech Connect

In this brief report, we discuss the Seiberg-Witten maps up to the second order in the noncommutative parameter {theta}. They add to the recently published solutions in [A. Alboteanu, T. Ohl, and R. Rueckl, Phys. Rev. D 76, 105018 (2007).]. Expressions for the vector, fermion, and Higgs fields are given explicitly.

Trampetic, Josip [Theoretical Physics Division, Rudjer Boskovic Institute, Zagreb (Croatia); Wohlgenannt, Michael [Erwin Schroedinger International Institute for Mathematical Physics, Boltzmanngasse 9, 1090 Vienna (Austria)

2007-12-15

147

Stochastic groundwater flow modeling using the second-order method  

Microsoft Academic Search

Stochastic groundwater flow modeling by means of a second-order uncertainty analysis technique is discussed. This technique is based on a Taylor series expansion of the state variables of interest (hydraulic heads and Darcian velocities) about the expected values of the model parameters. The method has been incorporated into the computer code PORSTAT, which solves the two-dimensional stochastic groundwater flow equation

B. Sagar; P. M. Clifton

1984-01-01

148

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

149

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

150

Adaptive observer for a class of second order nonlinear systems  

Microsoft Academic Search

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

151

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

152

Second-order Schemes for Steady Weakly Compressible Liquid Flows  

E-print Network

with temperature. One may cite other related phenomena under liquid impact and jet cutting, which are responsible1 Second-order Schemes for Steady Weakly Compressible Liquid Flows I. J. Keshtiban , F. Belblidia of Non-Newtonian Fluid Mechanics, Department of Computer Science, University of Wales, Swansea, SA2 8PP

Grant, P. W.

153

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

154

Reaction kinetics of Ca-based sorbents with HC1  

Microsoft Academic Search

The paper gives results of an investigation of the kinetics of the reaction between CaO and HCl 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 diffusion and chemical reaction control, either singly or

B. K. Gulett; W. Jozewicz; L. A. Stefanski

1992-01-01

155

REACTION KINETICS OF CA-BASED SORBENTS WITH HC1  

EPA Science Inventory

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...

156

REACTION KINETICS OF CA-BASED SORBENTS WITH HC1  

EPA Science Inventory

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...

157

Reaction of hydrogen atom with benzene: kinetics and mechanism  

Microsoft Academic Search

The rate coefficients for the reactions H + CâHâ ..-->.. products (kâ) (1), H + CâDâ ..-->.. products (kâ) (2), D + CâHâ ..-->.. products (kâ) (3), and D + CâDâ ..-->.. products (kâ) (4) have been measured in the temperature range of 298-1000 K by using the pulsed photolysis-resonance fluorescence technique. On the basis of the obtained kinetic information,

J. M. Nicovich; A. R. Ravishankara

1984-01-01

158

Analysis of kinetic isotope effects for nonadiabatic reactions.  

PubMed

Factors influencing the rates of quantum mechanical particle transfer reactions in many-body systems are discussed. The investigations are carried out on a simple model for a proton transfer reaction that captures generic features seen in more realistic models of condensed phase systems. The model involves a bistable quantum oscillator coupled to a one-dimensional double-well reaction coordinate, which is in turn coupled to a bath of harmonic oscillators. Reactive-flux correlation functions that involve quantum-classical Liouville dynamics for chemical species operators and quantum equilibrium sampling are used to estimate the reaction rates. Approximate analytical expressions for the quantum equilibrium structure are derived. Reaction rates are shown to be influenced significantly by both the quantum equilibrium structure and nonadiabatic dynamics. Nonadiabatic dynamical effects are found to play the major role in determining the magnitude of the kinetic isotope effect for the model transfer reaction. PMID:16965031

Kim, Hyojoon; Hanna, Gabriel; Kapral, Raymond

2006-08-28

159

Kinetics of self-decomposition and hydrogen atom transfer reactions of substituted phthalimide N-oxyl radicals in acetic acid.  

PubMed

Kinetic data have been obtained for three distinct types of reactions of phthalimide N-oxyl radicals (PINO(.)) and N-hydroxyphthalimide (NHPI) derivatives. The first is the self-decomposition of PINO(.) which was found to follow second-order kinetics. In the self-decomposition of 4-methyl-N-hydroxyphthalimide (4-Me-NHPI), H-atom abstraction competes with self-decomposition in the presence of excess 4-Me-NHPI. The second set of reactions studied is hydrogen atom transfer from NHPI to PINO(.), e.g., PINO(.) + 4-Me-NHPI <=> NHPI + 4-Me-PINO(.). The substantial KIE, k(H)/k(D) = 11 for both forward and reverse reactions, supports the assignment of H-atom transfer rather than stepwise electron-proton transfer. These data were correlated with the Marcus cross relation for hydrogen-atom transfer, and good agreement between the experimental and the calculated rate constants was obtained. The third reaction studied is hydrogen abstraction by PINO(.) from p-xylene and toluene. The reaction becomes regularly slower as the ring substituent on PINO(.) is more electron donating. Analysis by the Hammett equation gave rho = 1.1 and 1.8 for the reactions of PINO(.) with p-xylene and toluene, respectively. PMID:15624928

Cai, Yang; Koshino, Nobuyoshi; Saha, Basudeb; Espenson, James H

2005-01-01

160

A Second-Order Achromat Design Based on FODO Cell  

SciTech Connect

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

161

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

162

Second-order envelope equation of graphene electrons  

NASA Astrophysics Data System (ADS)

A treatment of graphene's electronic states based on the tight-binding method is presented. Like Dirac equation, this treatment uses envelope functions to eliminate crystal potential. Besides, a density-functional-theory Kohn-Sham (KS) orbital of an isolated carbon atom is employed. By locally expanding envelope functions into second-order polynomials and by involving up to third-nearest atoms in calculating orbital integrals, the second-order envelope equation is obtained. This equation does not contain any experimental data except graphene's crystal structure, and its coefficients are determined through several kinds of integrals of the carbon KS orbital. As an improvement, it leads to more accurate energy dispersion than Dirac equation including the triangular warping effect and asymmetry for electrons and holes, and gives the Fermi velocity which is in good agreement with the experimental value.

Luo, Ji

2014-10-01

163

Second Order Corrections to QED Coupling at Low Temperature  

E-print Network

We calculate the second order corrections to vacuum polarization tensor of photons at low temperatures, i.e; T $\\le 10^{10}$ K ($T QED coupling constant are evaluated at temperatures below the electron mass that is $TQED at these temperatures 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.

Masood, S S; Haseeb, Mahnaz Q.; Masood, Samina S.

2006-01-01

164

Second Order Corrections to QED Coupling at Low Temperature  

E-print Network

We calculate the second order corrections to vacuum polarization tensor of photons at low temperatures, i.e; T $\\le 10^{10}$ K ($T QED coupling constant are evaluated at temperatures below the electron mass that is $TQED at these temperatures 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

2006-12-11

165

Direct blind MMSE channel equalization based on second order statistics  

Microsoft Academic Search

A family of new MMSE blind channel equalization algorithms based on second order statistics are proposed. Instead of estimating the channel impulse response, we directly estimate the cross-correlation function needed in Wiener-Hopf filters. We develop several different schemes to estimate the cross-correlation vector, with which different Wiener filters are derived according to minimum mean square error (MMSE). Unlike many known

J. Shen; Zhi Ding

1999-01-01

166

Semiempirical hybrid density functional with perturbative second-order correlation  

Microsoft Academic Search

A new hybrid density functional for general chemistry applications is proposed. It is based on a mixing of standard generalized gradient approximations (GGAs) for exchange by Becke (B) and for correlation by Lee, Yang, and Parr (LYP) with Hartree-Fock (HF) exchange and a perturbative second-order correlation part (PT2) that is obtained from the Kohn-Sham (GGA) orbitals and eigenvalues. This virtual

Stefan Grimme

2006-01-01

167

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

168

Significantly enhanced second order nonlinearity in domain walls of ferroelectrics  

E-print Network

Significantly enhanced second order nonlinearity resulting from local symmetry breaking in domain walls is reported. By this new giant nonlinearity, novel hexagonally, conically and trigonally distributed second harmonic beams closely related to domain wall patterns are generated without contribution of reciprocal vectors. Experimental results show that such nonlinearities have made important impact on quasi-phase-matching technique and electro-optic Solc filter, which needs careful reconsiderations.

Deng, Xuewei; Zheng, Yuanlin; Liu, Kun; Chen, Xianfeng

2010-01-01

169

Gaussian spectral rules for second order finite-difference schemes  

Microsoft Academic Search

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

170

athena: Tree code for second-order correlation functions  

NASA Astrophysics Data System (ADS)

athena is a 2d-tree code that estimates second-order correlation functions from input galaxy catalogues. These include shear-shear correlations (cosmic shear), position-shear (galaxy-galaxy lensing) and position-position (spatial angular correlation). Written in C, it includes a power-spectrum estimator implemented in Python; this script also calculates the aperture-mass dispersion. A test data set is available.

Kilbinger, Martin; Bonnett, Christopher; Coupon, Jean

2014-02-01

171

Periodic solutions for some second order Hamiltonian systems  

NASA Astrophysics Data System (ADS)

We use the saddle point theorem of Benci-Rabinowitz to study the existence of periodic solutions with a fixed energy for second order Hamiltonian conservative systems without any symmetry; the key difficulty of the proof is proving the Palais-Smale condition and the non-constant property for the minimax critical point. Dedicated to the memories of Professor Shi Shuzhong and all who died in the earthquake on 12 May 2008.

Zhang, Shiqing

2009-09-01

172

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

173

Stochastic Lindemann kinetics for unimolecular gas-phase reactions.  

PubMed

Lindemann, almost a century ago, proposed a schematic mechanism for unimolecular gas-phase reactions. Here, we present a new semiempirical method to calculate the effective rate constant in unimolecular gas-phase kinetics through a stochastic reformulation of Lindemann kinetics. Considering the rate constants for excitation and de-excitation steps in the Lindemann mechanism as temperature dependent empirical parameters, we construct and solve a chemical master equation for unimolecular gas-phase kinetics. The effective rate constant thus obtained shows excellent agreement with experimental data in the entire concentration range in which it is reported. The extrapolated values of the effective rate constant for very low and very high concentrations of inert gas molecules are in close agreement with values obtained using the Troe semiempirical method. Stochastic Lindemann kinetics, thus, provides a simple method to construct the full falloff curves and can be used as an alternative to the Troe semiempirical method of kinetic data analysis for unimolecular gas-phase reactions. PMID:23879409

Saha, Soma; Dua, Arti

2013-08-22

174

Kinetics of the BrO + NO2 Association Reaction. Temperature and Pressure Dependence in the Falloff Regime  

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

175

Computation of kinetic isotope effects for enzymatic reactions  

PubMed Central

We describe a computational approach, incorporating quantum mechanics into enzyme kinetics modeling with a special emphasis on computation of kinetic isotope effects. Two aspects are highlighted: (1) the potential energy surface is represented by a combined quantum mechanical and molecular mechanical (QM/MM) potential in which the bond forming and breaking processes are modeled by electronic structure theory, and (2) a free energy perturbation method in path integral simulation is used to determine both kinetic isotope effects (KIEs). In this approach, which is called the PI-FEP/UM method, a light (heavy) isotope is mutated into a heavy (light) counterpart in centroid path integral simulations. The method is illustrated in the study of primary and secondary KIEs in two enzyme systems. In the case of nitroalkane oxidase, the enzymatic reaction exhibits enhanced quantum tunneling over that of the uncatalyzed process in water. In the dopa delarboxylase reaction, there appears to be distinguishable primary carbon-13 and secondary deuterium KIEs when the internal proton tautomerism is in the N-protonated or in the O-protonated positions. These examples show that the incorporation of quantum mechanical effects in enzyme kinetics modeling offers an opportunity to accurately and reliably model the mechanisms and free energies of enzymatic reactions. PMID:23976893

GAO, JiaLi

2013-01-01

176

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

177

Transient state kinetic investigation of 5-aminolevulinate synthase reaction mechanism.  

PubMed

5-Aminolevulinate synthase (ALAS), a pyridoxal 5'-phosphate-dependent enzyme, catalyzes the first, and regulatory, step of the heme biosynthetic pathway in nonplant eukaryotes and some bacteria. 5-Aminolevulinate synthase is a dimeric protein having an ordered kinetic mechanism with glycine binding before succinyl-CoA and with aminolevulinate release after CoA and carbon dioxide. Rapid scanning stopped-flow absorption spectrophotometry in conjunction with multiple turnover chemical quenched-flow kinetic analyses and a newly developed CoA detection method were used to examine the ALAS catalytic reaction and identify the rate-determining step. The reaction of glycine with ALAS follows a three-step kinetic process, ascribed to the formation of the Michaelis complex and the pyridoxal 5'-phosphate-glycine aldimine, followed by the abstraction of the glycine pro-R proton from the external aldimine. Significantly, the rate associated with this third step (k(3) = 0.002 s(-1)) is consistent with the rate determined for the ALAS-catalyzed removal of tritium from [2-(3)H(2)]glycine. Succinyl-CoA and acetoacetyl-CoA increased the rate of glycine proton removal approximately 250,000- and 10-fold, respectively, supporting our previous proposal that the physiological substrate, succinyl-CoA, promotes a protein conformational change, which accelerates the conversion of the external aldimine into the initial quinonoid intermediate (Hunter, G. A., and Ferreira, G. C. (1999) J. Biol. Chem. 274, 12222-12228). Rapid scanning stopped-flow and quenched-flow kinetic analyses of the ALAS reaction under single turnover conditions lend evidence for two quinonoid reaction intermediates and a model of the ALAS kinetic mechanism in which product release is at least the partially rate-limiting step. Finally, the carbonyl and carboxylate groups of 5-aminolevulinate play a major protein-interacting role by inducing a conformational change in ALAS and, thus, possibly modulating product release. PMID:12191993

Zhang, Junshun; Ferreira, Gloria C

2002-11-22

178

A unifying kinetic framework for modeling oxidoreductase-catalyzed reactions  

PubMed Central

Motivation: Oxidoreductases are a fundamental class of enzymes responsible for the catalysis of oxidation–reduction reactions, crucial in most bioenergetic metabolic pathways. From their common root in the ancient prebiotic environment, oxidoreductases have evolved into diverse and elaborate protein structures with specific kinetic properties and mechanisms adapted to their individual functional roles and environmental conditions. While accurate kinetic modeling of oxidoreductases is thus important, current models suffer from limitations to the steady-state domain, lack empirical validation or are too specialized to a single system or set of conditions. Results: To address these limitations, we introduce a novel unifying modeling framework for kinetic descriptions of oxidoreductases. The framework is based on a set of seven elementary reactions that (i) form the basis for 69 pairs of enzyme state transitions for encoding various specific microscopic intra-enzyme reaction networks (micro-models), and (ii) lead to various specific macroscopic steady-state kinetic equations (macro-models) via thermodynamic assumptions. Thus, a synergistic bridge between the micro and macro kinetics can be achieved, enabling us to extract unitary rate constants, simulate reaction variance and validate the micro-models using steady-state empirical data. To help facilitate the application of this framework, we make available RedoxMech: a Mathematica™ software package that automates the generation and customization of micro-models. Availability: The Mathematica™ source code for RedoxMech, the documentation and the experimental datasets are all available from: http://www.igb.uci.edu/tools/sb/metabolic-modeling. Contact: pfbaldi@ics.uci.edu Supplementary information: Supplementary data are available at Bioinformatics online. PMID:23613486

Chang, Ivan; Baldi, Pierre

2013-01-01

179

Kinetics and mechanisms of the reaction of hypothiocyanous acid with 5-thio-2-nitrobenzoic acid and reduced glutathione.  

PubMed

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

180

Chemical Kinetics: half-life  

NSDL National Science Digital Library

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

Blauch, David N.

181

Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles  

Microsoft Academic Search

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

Derek S. Liechty; Mark J. Lewis

2011-01-01

182

Oxidation of triclosan by ferrate: reaction kinetics, products identification and toxicity evaluation.  

PubMed

The oxidation of triclosan by commercial grade aqueous ferrate (Fe(VI)) was investigated and the reaction kinetics as a function of pH (7.0-10.0) were experimentally determined. Intermediate products of the oxidation process were characterized using both GC-MS and RRLC-MS/MS techniques. Changes in toxicity during the oxidation process of triclosan using Fe(VI) were investigated using Pseudokirchneriella subcapitata growth inhibition tests. The results show that triclosan reacted rapidly with Fe(VI), with the apparent second-order rate constant, k(app), being 754.7 M(-1) s(-1) at pH 7. At a stoichiometric ratio of 10:1 (Fe(VI):triclosan), complete removal of triclosan was achieved. Species-specific rate constants, k, were determined for reaction of Fe(VI) with both the protonated and deprotonated triclosan species. The value of k determined for neutral triclosan was 6.7(±1.9)×10(2) M(-1) s(-1), while that measured for anionic triclosan was 7.6(±0.6)×10(3) M(-1) s(-1). The proposed mechanism for the oxidation of triclosan by the Fe(VI) involves the scission of ether bond and phenoxy radical addition reaction. Coupling reaction may also occur during Fe(VI) degradation of triclosan. Overall, the degradation processes of triclosan resulted in a significant decrease in algal toxicity. The toxicity tests showed that Fe(VI) itself dosed in the reaction did not inhibit green algae growth. PMID:21093982

Yang, Bin; Ying, Guang-Guo; Zhao, Jian-Liang; Zhang, Li-Juan; Fang, Yi-Xiang; Nghiem, Long Duc

2011-02-15

183

Kinetics of diffusion-assisted reactions in microheterogeneous systems.  

PubMed

This review is focused on the basic theory of diffusion-assisted reactions in microheterogeneous systems, from porous solids to self-organized colloids and biomolecules. Rich kinetic behaviors observed experimentally are explained in a unified fashion using simple concepts of competing distance and time scales of the reaction and the embedding structure. We mainly consider pseudo-first-order reactions, such as luminescence quenching, described by the Smoluchowski type of equation for the reactant pair distribution function with a sink term defined by the reaction mechanism. Microheterogeneity can affect the microscopic rate constant. It also enters the evolution equation through various spatial constraints leading to complicated boundary conditions and, possibly, to the reduction of dimensionality of the diffusion space. The reaction coordinate and diffusive motion along this coordinate are understood in a general way, depending on the problem at hand. Thus, the evolution operator can describe translational and rotational diffusion of molecules in a usual sense, it can be a discrete random walk operator when dealing with hopping of adsorbates in solids, or it can correspond to conformational fluctuations in proteins. Mathematical formulation is universal but physical consequences can be different. Understanding the principal features of reaction kinetics in microheterogeneous systems enables one to extract important structural and dynamical information about the host environments by analyzing suitably designed experiments, it helps building effective strategies for computer simulations, and ultimately opens possibilities for designing systems with controllable reactivity properties. PMID:11215811

Barzykin, A V; Seki, K; Tachiya, M

2001-01-29

184

Second-order generation of point defects in highly irradiated float zone silicon—annealing studies  

Microsoft Academic Search

Isothermal and isochronal annealing experiments have shown that the I defect (the main cause for the changes in silicon diodes characteristics after high levels of gamma-irradiation) is stable up to 325–350°C. Possible reactions, which can explain the behavior of different defects formed during the annealing experiments, are discussed. All the experimental results concerning the I center (second-order irradiation induced defect,

I. Pintilie; E. Fretwurst; G. Kramberger; G. Lindstroem; Z. Li; J. Stahl

2003-01-01

185

Kinetics, kinetic deuterium isotope effects, and mechanism of nitrous oxide reaction with hydrogen on supported precious-metal catalysts  

Microsoft Academic Search

The kinetics and kinetic deuterium isotope effects have been precisely measured for the reaction of nitrous oxide with hydrogen on Ru\\/AlâOâ, Rh\\/AlâOâ, Ir\\/AlâOâ, and Pt\\/AlâOâ catalysts. The reaction apparently proceeds through the two following elementary steps: NâO + M ..-->.. Nâ + M=O (reaction 1) and M=O + Hâ ..-->.. M + HâO (reaction 2). In reaction 1, an NâO

A. Mlyamoto; Shigeo Baba; Mitsushi Mori; Yuichi Murakami

1981-01-01

186

Non-Gaussianity from the second-order cosmological perturbation  

SciTech Connect

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

187

Second-Order Corrections to QED Coupling at Low Temperature  

NASA Astrophysics Data System (ADS)

We calculate the second-order corrections to vacuum polarization tensor of photons at low temperatures, i.e. T ? 1010 K (T ? me). The thermal contributions to the QED coupling constant are evaluated at temperatures below the electron mass that is T < me. Renormalization of QED at these temperatures 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.

Masood, Samina S.; Haseeb, Mahnaz

188

Oscillation theory for linear second-order differential systems  

SciTech Connect

This article is concerned with the oscillatory behavior at infinity of the solution y:(a,infinity) ..-->.. R/sup n/ of a system of second-order differential equations, y''(t) + Q(t)y(t) = 0, t epsilon(a,infinity); Q is a continuous function on (a,infinity), whose values are real symmetric matrices of order n. It is shown that the solution is oscillatory at infinity if the largest eigenvalue of the matrix ..integral../sub a/ Q(t) dt is sufficiently large on a sufficiently large set of t-values. 11 refs.

Kaper, H.G.; Kwong, Man Kam

1987-01-01

189

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

190

A second order differential equation for a point charged particle  

E-print Network

A model for the dynamical evolution of a point charged particle interacting with higher order fields is described by an ordinary second order implicit differential equation. We show that such equation is free of run-away and pre-accelerated solutions of Dirac's type. The theory is Lorentz invariant, causal, and compatible with Newton's first law and energy-momentum conservation. However, it is not a local theory in the usual sense. In our model for point charged particles, covariant uniform acceleration motion is unstable and must be understood as an approximation.

Torromé, Ricardo Gallego

2012-01-01

191

Second order hydrodynamics for a special class of gravity duals  

E-print Network

The sound mode hydrodynamic dispersion relation is computed up to order $q^3$ for a class of gravitational duals which includes both Schwarzschild $AdS$ and Dp-Brane metrics. The implications for second order transport coefficients are examined within the context of Israel-Stewart theory. These sound mode results are compared with previously known results for the shear mode. This comparison allows one to determine the third order hydrodynamic contributions to the shear mode for the class of metrics considered here.

T. Springer

2009-02-15

192

The kinetics of phosphotriester condensation reactions on solid support.  

PubMed Central

A study has been made of the kinetics of condensation reactions in phosphotriester synthesis of oligonucleotides on polystyrene copolymer resin support, using monomers, dimers, and trimers as the coupling units. The condensations follow pseudo first order kinetics, with a rate constant that decreases from monomers to dimers to trimers. Arrhenius plots indicate a nearly constant activation energy of around 10.4 kcal mol-1. Extrapolation to find the Arrhenius preexponential factor, A, is inaccurate because of the limited temperature range studied. But if the assumption is made that Ea is the same for monomer, dimer, and trimer reactions, then the A values are inversely proportional to the surface areas of the coupling units, reinforcing the interpretation of A as a collision efficiency factor. PMID:6473109

Ikuta, S; Chattopadhyaya, R; Dickerson, R E

1984-01-01

193

Progress in an oxygen-carrier reaction kinetics experiment for rotary-bed chemical looping combustion  

E-print Network

The design process for an experimental platform measuring reaction kinetics in a chemical looping combustion (CLC) process is documented and justified. To enable an experiment designed to characterize the reaction kinetics ...

Jester-Weinstein, Jack (Jack L.)

2013-01-01

194

Mechanisms and kinetics of reaction-bonded aluminium oxide ceramics  

Microsoft Academic Search

Reaction-bonded Al[sub 2]O[sub 3] (RBAO) ceramics were fabricated starting from mechanically alloyed Al[sub 2]O[sub 3]\\/Al, Al[sub 2]O[sub 3]\\/Al\\/ZrO[sub 2], and Al[sub 2]O[sub 3]\\/Al\\/ZrO[sub 2]\\/Zr mixtures. Isopressed compacts were heat-treated in air up to 1,550 C. Reaction-bonding mechanisms, kinetics, and the influence of ZrO[sub 2] and Zr additions are investigated. Independent of additive, oxidation of Al proceeds both as solid\\/gas and

Suxing Wu; Dietmar Holz; Nils Claussen

1993-01-01

195

High temperature heterogeneous reaction kinetics and mechanisms of tungsten oxidation  

NASA Astrophysics Data System (ADS)

Tungsten, which is a material used in many high temperature applications, is limited by its susceptibility to oxidation at elevated temperatures. Although tungsten has the highest melting temperature of any metal, at much lower temperatures volatile oxides are formed during oxidation with oxygen containing species. This differs from many heterogeneous oxidation reactions involving metals since most reactions form very stable oxides that have higher melting or boiling points than the pure metal (e.g., aluminum, iron). Understanding heterogeneous oxidation and vaporization processes may allow for the expansion and improvement of high temperature tungsten applications. In order to increase understanding of the oxidation processes of tungsten, there is a need to develop reaction mechanisms and kinetics for oxidation processes involving oxidizers and environmental conditions of interest. Tungsten oxidation was thoroughly studied in the past, and today there is a good phenomenological understanding of these processes. However, as the design of large scale systems increasingly relies on computer modeling there becomes a need for improved descriptions of chemical reactions. With the increase in computing power over the last several decades, and the development of quantum chemistry and physics theories, heterogeneous systems can be modeled in detail at the molecular level. Thermochemical parameters that may not be measured experimentally may now be determined theoretically, a tool that was previously unavailable to scientists and engineers. Additionally, chemical kinetic modeling software is now available for both homogeneous and heterogeneous reactions. This study takes advantage of these new theoretical tools, as well as a thermogravimetric (TG) flow reactor developed as part of this study to learn about mechanisms and kinetics of tungsten oxidation. Oxidizers of interest are oxygen (O2), carbon dioxide (CO 2), water (H2O), and other oxidizers present in combustion and energy systems. The primary application for this research topic is the migration of erosion processes in solid rocket motor nozzles. Since oxidation is the primary erosion mechanism of tungsten based nozzles, mitigation of this process through improved comprehension of the chemical mechanisms will increase performance of future rocket systems. In this dissertation, results of the high temperature reaction rates of bulk tungsten are studied using TG analysis in oxidizing atmospheres of O2, CO2, and H2O using helium (He) as an inert carrier gas. Isothermal reaction rates were determined at temperatures up to 1970 K, and oxidizing species partial pressures up to 64.6 torr. Kinetic parameters such as activation energies, frequency factors, and pressure exponents were determined for each reactive system. An important contribution of this work was quantifying the effects of carbon monoxide (CO) on the CO2 reaction, and hydrogen (H2) on the H2O reaction. In both cases the non-oxidizing species significantly reduced oxidation rates. Results have led to new interpretations and thought processes for limiting nozzle erosion in rocket motors. Combined with the TG analysis, as well as recent theoretical interpretations of reaction thermodynamics and kinetics, a new mechanism for tungsten and O2 oxidation has been developed using a one-dimensional numerical model of the TG flow reactor. Important chemical processes and species are also identified for reaction systems involving H2O and CO2. In the future, additional studies are needed to improve our understanding of these chemical species and processes so that more advanced kinetic mechanisms may be developed. In addition to a detailed analysis of high temperature tungsten corrosion processes, synthetic graphite corrosion processes are studied in detail as well. Details of these studies are presented in an attached appendix of this dissertation. These studies considered not only oxidation processes, but decomposition of synthetic graphite in the presence of reducing and inert gas environments.

Sabourin, Justin L.

196

Kinetics of Enol Formation from Reaction of OH with Propene  

Microsoft Academic Search

Kinetics of enol generation from propene has been predicted in an effort to understand the presence of enols in flames. A potential energy surface for reaction of OH with propene was computed by CCSD(T)\\/cc-pVDZ\\/\\/ B3LYP\\/cc-pVTZ calculations. Rate constants of different product channels and branching ratios were then calculated using the Master Equation formulation ( J. Phys. Chem. A 2006 ,

Lam K. Huynh; Hongzhi R. Zhang; Shaowen Zhang; Eric Eddings; Adel Sarofim; Matthew E. Law; Phillip R. Westmoreland; Thanh N. Truong

2009-01-01

197

Ab initio kinetics of gas phase decomposition reactions.  

PubMed

The thermal and kinetic aspects of gas phase decomposition reactions can be extremely complex due to a large number of parameters, a variety of possible intermediates, and an overlap in thermal decomposition traces. The experimental determination of the activation energies is particularly difficult when several possible reaction pathways coexist in the thermal decomposition. Ab initio calculations intended to provide an interpretation of the experiment are often of little help if they produce only the activation barriers and ignore the kinetics of the decomposition process. To overcome this ambiguity, a theoretical study of a complete picture of gas phase thermo-decomposition, including reaction energies, activation barriers, and reaction rates, is illustrated with the example of the ?-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) molecule by means of quantum-chemical calculations. We study three types of major decomposition reactions characteristic of nitramines: the HONO elimination, the NONO rearrangement, and the N-NO(2) homolysis. The reaction rates were determined using the conventional transition state theory for the HONO and NONO decompositions and the variational transition state theory for the N-NO(2) homolysis. Our calculations show that the HMX decomposition process is more complex than it was previously believed to be and is defined by a combination of reactions at any given temperature. At all temperatures, the direct N-NO(2) homolysis prevails with the activation barrier at 38.1 kcal/mol. The nitro-nitrite isomerization and the HONO elimination, with the activation barriers at 46.3 and 39.4 kcal/mol, respectively, are slow reactions at all temperatures. The obtained conclusions provide a consistent interpretation for the reported experimental data. PMID:21077597

Sharia, Onise; Kuklja, Maija M

2010-12-01

198

Second-order analytic solutions for re-entry trajectories  

NASA Astrophysics Data System (ADS)

With the development of aeroassist technology, either for near-earth orbital transfer with or without a plane change or for planetary aerocapture, it is of interest to have accurate analytic solutions for reentry trajectories in an explicit form. Starting with the equations of motion of a non-thrusting aerodynamic vehicle entering a non-rotating spherical planetary atmosphere, a normalization technique is used to transform the equations into a form suitable for an analytic integration. Then, depending on the type of planar entry modes with a constant angle-of-attack, namely, ballistic fly-through, lifting skip, and equilibrium glide trajectories, the first-order solutions are obtained with the appropriate simplification. By analytic continuation, the second-order solutions for the altitude, speed, and flight path angle are derived. The closed form solutions lead to explicit forms for the physical quantities of interest, such as the deceleration and aerodynamic heating rates. The analytic solutions for the planar case are extended to three-dimensional skip trajectories with a constant bank angle. The approximate solutions for the heading and latitude are developed to the second order. In each type of trajectory examined, explicit relations among the principal variables are in a form suitable for guidance and navigation purposes. The analytic solutions have excellent agreement with the numerical integrations. They also provide some new results which were not reported in the existing classical theory.

Kim, Eun-Kyou

1993-01-01

199

Gravity actions, boundary terms and second-order field equations  

NASA Astrophysics Data System (ADS)

The Lovelock action is a natural generalization of the Einstein-Hilbert gravity action in higher (more than four) dimensions. Certain boundary terms have to be added to this action because of various reasons which we briefly review. Explicit expressions of these boundary terms can already be found in Chern's famous paper [6] on the generalization of the Gauss-Bonnet theorem. Dimensional reduction of the Lovelock action leads to a generalized Einstein-Yang-Mills (+ scalar field or ?-models) action in lower dimensions. Since the field equations derived from the Lovelock action are of second order only, the same holds for the dimensionally reduced action. The necessary boundary terms for the latter action are then obtained by dimensional reduction of the boundary terms in the Lovelock action. We consider reduction from n to n -1 dimensions in some detail and obtain generalizations of Horndeski's non-minimally coupled Einstein-Maxwell action with second-order field equations in more than four dimensions.

Müller-Hoissen, Folkert

1990-06-01

200

Stochastic evaluation of second-order Dyson self-energies.  

PubMed

A stochastic method is proposed that evaluates the second-order perturbation corrections to the Dyson self-energies of a molecule (i.e., quasiparticle energies or correlated ionization potentials and electron affinities) directly and not as small differences between two large, noisy quantities. With the aid of a Laplace transform, the usual sum-of-integral expressions of the second-order self-energy in many-body Green's function theory are rewritten into a sum of just four 13-dimensional integrals, 12-dimensional parts of which are evaluated by Monte Carlo integration. Efficient importance sampling is achieved with the Metropolis algorithm and a 12-dimensional weight function that is analytically integrable, is positive everywhere, and cancels all the singularities in the integrands exactly and analytically. The quasiparticle energies of small molecules have been reproduced within a few mEh of the correct values with 10(8) Monte Carlo steps. Linear-to-quadratic scaling of the size dependence of computational cost is demonstrated even for these small molecules. PMID:23635115

Willow, Soohaeng Yoo; Kim, Kwang S; Hirata, So

2013-04-28

201

Reaction Path Optimization with Holonomic Constraints and Kinetic Energy Potentials  

SciTech Connect

Two methods are developed to enhance the stability, efficiency, and robustness of reaction path optimization using a chain of replicas. First, distances between replicas are kept equal during path optimization via holonomic constraints. Finding a reaction path is, thus, transformed into a constrained optimization problem. This approach avoids force projections for finding minimum energy paths (MEPs), and fast-converging schemes such as quasi-Newton methods can be readily applied. Second, we define a new objective function - the total Hamiltonian - for reaction path optimization, by combining the kinetic energy potential of each replica with its potential energy function. Minimizing the total Hamiltonian of a chain determines a minimum Hamiltonian path (MHP). If the distances between replicas are kept equal and a consistent force constant is used, then the kinetic energy potentials of all replicas have the same value. The MHP in this case is the most probable isokinetic path. Our results indicate that low-temperature kinetic energy potentials (<5 K) can be used to prevent the development of kinks during path optimization and can significantly reduce the required steps of minimization by 2-3 times without causing noticeable differences between a MHP and MEP. These methods are applied to three test cases, the C?eq-to-Cax isomerization of an alanine dipeptide, the ?C?- to-¹C? transition of an ?-D-glucopyranose, and the helix-to-sheet transition of a GNNQQNY heptapeptide. By applying the methods developed in this work, convergence of reaction path optimization can be achieved for these complex transitions, involving full atomic details and a large number of replicas (>100). For the case of helix-to-sheet transition, we identify pathways whose energy barriers are consistent with experimental measurements. Further, we develop a method based on the work energy theorem to quantify the accuracy of reaction paths and to determine whether the atoms used to define a path are enough to provide quantitative estimation of energy barriers.

Brokaw, Jason B.; Haas, Kevin R.; Chu, Jhih-wei

2009-08-11

202

Kinetic Studies on the Reaction between Dicyanocobinamide and Hypochlorous Acid  

PubMed Central

Hypochlorous acid (HOCl) is a potent oxidant generated by myeloperoxidase (MPO), which is an abundant enzyme used for defense against microbes. We examined the potential role of HOCl in corrin ring destruction and subsequent formation of cyanogen chloride (CNCl) from dicyanocobinamide ((CN)2-Cbi). Stopped-flow analysis revealed that the reaction consists of at least three observable steps, including at least two sequential transient intermediates prior to corrin ring destruction. The first two steps were attributed to sequential replacement of the two cyanide ligands with hypochlorite, while the third step was the destruction of the corrin ring. The formation of (OCl)(CN)-Cbi and its conversion to (OCl)2-Cbi was fitted to a first order rate equation with second order rate constants of 0.002 and 0.0002 µM?1s?1, respectively. The significantly lower rate of the second step compared to the first suggests that the replacement of the first cyanide molecule by hypochlorite causes an alteration in the ligand trans effects changing the affinity and/or accessibility of Co toward hypochlorite. Plots of the apparent rate constants as a function of HOCl concentration for all the three steps were linear with Y-intercepts close to zero, indicating that HOCl binds in an irreversible one-step mechanism. Collectively, these results illustrate functional differences in the corrin ring environments toward binding of diatomic ligands. PMID:25375773

Maitra, Dhiman; Ali, Iyad; Abdulridha, Rasha M.; Shaeib, Faten; Khan, Sana N.; Saed, Ghassan M.; Pennathur, Subramaniam; Abu-Soud, Husam M.

2014-01-01

203

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

204

Cascaded second order nonlinearities in lithium niobate waveguides  

NASA Astrophysics Data System (ADS)

All-optical switching has drawn attention since the early days of nonlinear optics. Many different all-optical switching formats have been suggested and realized using third order nonlinear materials relying on the intensity dependent refractive index change. However, it turned out that it required too much power or too long device lengths to be implemented into real devices using presently available ?(3) material. Therefore an alternative approach using second order nonlinear materials has started. In this dissertation cascaded second order nonlinearities have been studied extensively in lithium niobate waveguides. As an initial stage, nonlinear phase shift measurements were performed in channel waveguides. More than ? phase shift was obtained with a peak input power of 300W. Moreover, this large nonlinear phase shift was achieved with less than 5% of the fundamental depletion due to the nonuniform wavevector mismatch profile along the propagation distance. Based on nonlinear phase shift measurements, two types of integrated all-optical devices, Mach Zehnder interferometer and directional coupler, were designed and switchings were demonstrated successfully. A better switching ratio than is usually achieved with third order nonlinear materials was obtained because of the specific nonlinear dependence of the phase shift on the input power characteristic of cascaded second order nonlinearities. All of these experiments have proven that cascaded nonlinearities can be used in realizing all- optical switching devices. On the basic physics side, the existence of one- dimensional quadratic spatial solitons based on cascaded nonlinearities was also studied in planar waveguides. Solitary waves could be generated with only small depletion of the fundamental due to the nonuniform wavevector mismatch profile. In addition, quadratic solitary waves near the phase matching condition were observed with significant fundamental depletion. In this case, simultaneous generation of the second harmonic component of the solitary waves was observed. Interactions of two quadratic solitons were investigated. To investigate a spectrum of the interactions between quadratic solitons, the experiments were performed in two different regimes-one with small depletion (<10%) and the other with large fundamental depletion (~45%). The observed interactions between quadratic solitons depend strongly on the relative phase difference between two fundamental input beams and different interaction behaviors were observed depending on the amounts of second harmonic generation. Overall, the interactions between quadratic solitons were similar to those known for solitons in saturable Kerr media.

Baek, Yongsoon

1997-12-01

205

Spatial optical solitons in second-order nonlinear materials  

NASA Astrophysics Data System (ADS)

Solitary waves have fascinated the world of nonlinear optics since they were first predicted more than 30 years ago. Predicted initially for spatial self-focusing in Kerr-type materials, they were also predicted-and discovered-in a variety of situations: temporal pulses propagating in optical fibers, photorefractive materials and second-order nonlinear materials, commonly used for second harmonic generation. In this dissertation, cascaded second order nonlinearities were investigated in second-harmonic geometries leading to solitary wave formation. The research presented here started with the investigation of interactions of solitary waves in Type I quadratically nonlinear media, for moderate phase mismatches. To simplify the problem, only one-dimensional geometries were considered. When the phase difference between the input fundamental waves was varied, the results of the collisions exhibited a threshold behavior at a negative phase mismatch and a critical phase difference was identified which marked the transition from attractive (and beam fusion) to repulsive behavior. It was shown that this feature persists even if the fields launched at the input are not exactly solitons. The influence of various parameters was investigated extensively, although not completely. The stability of solitary waves was also investigated, with a focus on the stability of highly asymmetric inputs (elliptic input beams and strip waves). It was found that even if the strip waves are analytical solutions which are stable in an one dimensional geometry, small modulations (periodic or just noise) will lead to the break-up of the beam into a periodic sequence of solitary waves. In the absence of noise, a highly elliptic beam was shown to reshape into a circular solitary wave. However, even a small amount of noise will trigger the breakup of the beam due to modulational instability, given that enough power is present at the input. Although this work is primarily theoretical and several simplifying assumptions were made, many new phenomena were predicted, some of which were observed experimentally. The wealth of new phenomena-including threshold phenomena-open the path to new classes of all-optical devices. Overall, cascaded nonlinearities provide a rich variety of applications for second-order nonlinearities, not yet fully explored.

Baboiu, Daniel-Marian

1998-12-01

206

Kinetics of the reaction of nitric oxide with hydrogen  

NASA Technical Reports Server (NTRS)

Mixtures of NO and H2 diluted in argon or krypton were heated by incident shock waves, and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The reaction kinetics were studied in the temperature range 2400-4500 K using a shock-tube technique. The decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principle result of the study was the determination of the rate constant for the reaction H + NO yields N + OH, which may be the rate-limiting step for NO removal in some combustion systems. Experimental values of k sub 1 were obtained for each test through comparisons of measured and numerically predicted NO profiles.

Flower, W. L.; Hanson, R. K.; Kruger, C. H.

1974-01-01

207

Regularized orbital-optimized second-order perturbation theory  

SciTech Connect

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

208

Second-order closure analysis of turbulent reacting flows  

NASA Technical Reports Server (NTRS)

A reacting shear layer program for a complete second-order closure of turbulent reacting flows is developed. The program uses a typical eddy box model and many of the fluid mechanical turbulence models developed in earlier studies. The computer program actually solves a total of 30 equations, where the numerical integration of the equations is performed by a forward-time-centered space quasi-implicit upwind finite-difference scheme. Results for nonreacting and simple isothermal reacting flows are presented along with preliminary results for propane-air flames. It is shown that the program predictions for simple nonreacting flows are in good agreement with available data. The calculations for isothermal reacting flows demonstrate the importance of including a mixedness correlation in finite rate chemistry calculations, where significant errors in the flowfield properties can result from neglect of the interaction between turbulence and the chemistry. Results for propane-air diffusion flames further support this conclusion.

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

1976-01-01

209

Riccati-parameter solutions of nonlinear second-order ODEs  

E-print Network

It has been proven by Rosu and Cornejo-Perez in 2005 that for some nonlinear second-order ODEs it is a very simple task to find one particular solution once the nonlinear equation is factorized with the use of two first-order differential operators. Here, it is shown that an interesting class of parametric solutions is easy to obtain if the proposed factorization has a particular form, which happily turns out to be the case in many problems of physical interest. The method that we exemplify with a few explicitly solved cases consists in using the general solution of the Riccati equation, which contributes with one parameter to this class of parametric solutions. For these nonlinear cases, the Riccati parameter serves as a `growth' parameter from the trivial null solution up to the particular solution found through the factorization procedure

M. A. Reyes; H. C. Rosu

2005-10-20

210

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

211

Second-order quantum nonlinear optical processes in graphene nanostructures  

E-print Network

Intense efforts have been made in recent years to realize nonlinear optical interactions at the single-photon level. Much of this work has focused on achieving strong third-order nonlinearities, such as by using single atoms or other quantum emitters, while the possibility of achieving strong second-order nonlinearities remains unexplored. Here, we describe a novel technique to realize such nonlinearities using graphene, exploiting the strong per-photon fields associated with tightly confined graphene plasmons in combination with spatially non-local nonlinear optical interactions. Under realistic conditions, we show that the interactions are strong enough to observe the generation of non-classical light and allow near-deterministic down-conversion of a single plasmon into an entangled plasmon pair.

Manzoni, Marco T; de Abajo, F Javier García; Chang, Darrick E

2014-01-01

212

Regularized orbital-optimized second-order perturbation theory  

NASA Astrophysics Data System (ADS)

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 mEh 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

2013-12-01

213

Cosmologies in Horndeski's second-order vector-tensor theory  

NASA Astrophysics Data System (ADS)

Horndeski derived a most general vector-tensor theory in which the vector field respects the gauge symmetry and the resulting dynamical equations are of second order. The action contains only one free parameter, ?, that determines the strength of the non-minimal coupling between the gauge field and gravity. We investigate the cosmological consequences of this action and discuss observational constraints. For ? < 0 we identify singularities where the deceleration parameter diverges within a finite proper time. This effectively rules out any sensible cosmological application of the theory for a negative non-minimal coupling. We also find a range of parameter that gives a viable cosmology and study the phenomenology for this case. Observational constraints on the value of the coupling are rather weak since the interaction is higher-order in space-time curvature.

Barrow, John D.; Thorsrud, Mikjel; Yamamoto, Kei

2013-02-01

214

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

215

Second-order nonlinear optical effects of spin currents.  

PubMed

Pure spin currents carry information in spintronics and signify novel quantum spin phenomena such as topological insulators. Measuring pure spin currents, however, is difficult since they have no direct electromagnetic induction. Noticing that a longitudinal spin current, in which electrons move along their spin directions, is a chiral quantity, we envisage that it has a chiral sum-frequency optical effect. A systematic symmetry analysis confirms this idea and reveals the second-order optical effects of general spin currents with unique polarization dependence. Microscopic calculations based on the eight-band model of III-V compound semiconductors show that the susceptibility is sizable under realistic conditions. These findings form a basis for "seeing" spin currents where and while they flow with standard nonlinear optical spectroscopy, providing a toolbox to explore a wealth of physics connecting spins and photons. PMID:20867405

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

2010-06-25

216

Second-Order Analysis of Semiparametric Recurrent Event Processes  

PubMed Central

Summary A typical recurrent event dataset consists of an often large number of recurrent event processes, each of which contains multiple event times observed from an individual during a followup period. Such data have become increasingly available in medical and epidemiological studies. In this paper, we introduce novel procedures to conduct second-order analysis for a flexible class of semiparametric recurrent event processes. Such an analysis can provide useful information regarding the dependence structure within each recurrent event process. Specifically, we will use the proposed procedures to test whether the individual recurrent event processes are all Poisson processes and to suggest sensible alternative models for them if they are not. We apply these procedures to a well-known recurrent event dataset on chronic granulomatous disease and an epidemiological dataset on Meningococcal disease cases in Merseyside, UK to illustrate their practical value. PMID:21361885

Guan, Yongtao

2011-01-01

217

WEAK GALERKIN METHODS FOR SECOND ORDER ELLIPTIC INTERFACE PROBLEMS  

PubMed Central

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

218

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

PubMed Central

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

Jung, Moon Chul; Weber, Stephen G.

2006-01-01

219

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

220

Studies on the Reaction Kinetics and Mechanism of Iron(II) Reduction of the cis -Halogeno(cetylamine)bis(ethylenediamine)cobalt(III) Complex Ion in Aqueous Perchlorate Medium  

Microsoft Academic Search

The electron-transfer kinetics of the ionic surfactant complex cis-chloro\\/bromo(cetylamine)bis(ethylenediamine)cobalt(III) by iron(II) in aqueous perchlorate medium at ?=1.0 mol?dm?3 ionic strength have been studied at 303, 308 and 313 K by spectrophotometry under pseudo-first-order conditions using an\\u000a excess of the reductant. The effects of [H+], ionic strength and [Fe2+] on the rate were determined. The reaction was found to be second order and

N. Kumaraguru; K. Santhakumar

2009-01-01

221

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

222

Kinetics and mechanisms of reactions involving small aromatic reactive intermediates  

SciTech Connect

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

223

Kinetic and Dynamic Investigations of OH Reaction with Styrene.  

PubMed

The kinetics of hydroxyl radical reaction with styrene has been studied at 240-340 K and a total pressure of 1-3 Torr using the relative rate/discharge flow/mass spectrometry technique. In addition, the dynamics of the reaction was also studied using the ab initio molecular orbital method. The reaction was found to be essentially pressure independent over 1-3 Torr at both 298 and 340 K. At 298 K, the average rate constant was determined, using four different reference compounds, to be kstyrene+OH = (5.80 ± 0.49) × 10(-11) cm(3) molecule(-1) s(-1). At 240-340 K, the rate constant of this reaction was found to be negatively dependent on temperature with an Arrhenius expression determined to be kstyrene+OH = (1.02 ± 0.10) × 10(-11) exp[(532 ± 28)/T] cm(3) molecule(-1) s(-1). Observation of mass spectral evidence of adduct products and their respective fragment ions suggests that the reaction proceeds with addition of the OH to the vinyl carbons of the styrene molecule. Ab initio calculations of both the addition and the abstraction pathways predict that the addition pathways are more energetically favorable because of large exothermicity and essentially barrierless transition state associated with the additions, which is consistent with the experimental observations. Using the styrene + OH rate constant determined at 277 K in the present work, the atmospheric lifetime of styrene was estimated to be 4.9 h. PMID:25215459

Cho, Joeson; Roueintan, Masoud; Li, Zhuangjie

2014-10-01

224

Reaction Kinetics and Mechanism of Magnetic Field Effects in Cryptochrome  

PubMed Central

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

225

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

PubMed

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

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

2014-01-01

226

Modal cost analysis for linear matrix-second-order systems  

NASA Technical Reports Server (NTRS)

Reduced models and reduced controllers for systems governed by matrix-second-order differential equations are obtained by retaining those modes which make the largest contributions to quadratic control objectives. Such contributions, expressed in terms of modal data, used as mode truncation criteria, allow the statement of the specific control objectives to influence the early model reduction from very high order models which are available, for example, from finite element methods. The relative importance of damping, frequency, and eigenvector in the mode truncation decisions are made explicit for each of these control objectives: attitude control, vibration suppression and figure control. The paper also shows that using modal cost analysis (MCA) on the closed loop modes of the optimally controlled system allows the construction of reduced control policies which feedback only those closed loop modal coordinates which are most critical to the quadratic control performance criterion. In this way, the modes which should be controlled (and hence the modes which must be observable by choice of measurements), are deduced from truncations of the optimal controller.

Skelton, R. E.; Hughes, P. C.

1980-01-01

227

Photonic second-order duty-cycle modulator  

NASA Astrophysics Data System (ADS)

The delta sigma modulator (DSM) is a device which transforms the amplitude information of an analog input signal to the duty cycle and frequency of a binary output. This device, typically employed in oversampled analog-to-digital converters, is based on a feedback loop which includes at least one integrator and one quantizer in the forward path. In this paper, a novel photonic second-order DSM is proposed and experimentally demonstrated. The system is composed of two inverted leaky integrator and one electro-optic quantizer. The maximum input frequency is around 2 MHz, limited by the fiber length of the accumulator and feedback loops, and the quantizer rise/fall times. The system is characterized at different input frequencies and waveforms (sinusoidal and saw tooth) to analyze the modulator performance and linearity. The binary output is acquired, processed and demodulated using a personal computer, in order to reconstruct the input analog signal. The reported fiber-optic DSM is very promising for future integration increasing the operation frequency up to GHz range.

Costanzo-Caso, Pablo A.; Reeves, Erin; Jin, Yiye; Granieri, Sergio; Siahmakoun, Azad

2011-09-01

228

First- and Second-order Fermi Acceleration at Parallel Shocks  

E-print Network

We report on a new Monte Carlo method for simulating diffusive shock acceleration (DSA) of solar energetic particles at upstream and downstream regions of quasi-parallel collisionless shock waves under the influence of self-generated turbulence. By way of example, we apply the model to a fast 1500 km \\mathrm{s}^{-1} coronal mass ejection at ten solar radii. Results indicate that the maximum energies at outer corona are likely to be limited to few MeV, due to lack of suprathermal protons for appreciable wave growth, and insufficient time required acceleration. We find that the second-order Fermi acceleration, although being a too slow process to have a notable effect at the highest energies, significantly flattens energy spectra at low energy end. Simulations indicate that protons continue to damp waves efficiently several solar radii from the shock in the downstream region, which may be an important mechanism for heating suprathermals. Our simulations also suggest that models assuming a simple isotropic scatt...

Sandroos, Arto; Zhao, Lulu

2014-01-01

229

Novel Architecture of Feedforward Second-Order Multibit ??AD Modulator  

NASA Astrophysics Data System (ADS)

This paper proposes novel feedforward architecture of the second-order multibit ??AD modulator with single DAC-feedback topology. The ??AD modulator realizes high resolution by oversampling and noise shaping techniques. However, its SNDR (Signal to Noise and Distortion Ratio) is limited by the dynamic range of the input signal and non-idealities of circuit building blocks, particularly by the harmonic distortion in amplifier circuits. A full feedforward ??AD modulator structure has the signal transfer function of unity under ideal circumstances, which means that the signal swings through the loop filter become smaller compared with a feedbacked ??AD modulator. Therefore, the harmonic distortion generated inside the loop filter can be significantly reduced in the feedforward structure because the effect of non-idealities in amplifiers can be suppressed when signal swing is small. Moreover, the reduction of the internal signal swings also relaxes output swing requirements for amplifiers with low supply voltage. However, in conventional feedforward ??AD modulator, an analog adder is needed before quantizer, and especially in a multibit modulator, an additional amplifier is necessary to realize the summation of feedforward signals, which leads to extra chip area and power dissipation. In this paper, we propose a novel architecture of a feedforward ??AD modulator which realizes the summation of feedforward signals without additional amplifier. The proposed architecture is functionally equivalent to the conventional one but with smaller chip area and lower power dissipation. We conducted MATLAB and SPICE simulations to validate the proposed architecture and modulator circuits.

San, Hao; Konagaya, Hajime; Xu, Feng; Motozawa, Atsushi; Kobayashi, Haruo; Ando, Kazumasa; Yoshida, Hiroshi; Murayama, Chieto; Miyazawa, Kanichi

230

Second order sliding mode control for a quadrotor UAV.  

PubMed

A method based on second order sliding mode control (2-SMC) is proposed to design controllers for a small quadrotor UAV. For the switching sliding manifold design, the selection of the coefficients of the switching sliding manifold is in general a sophisticated issue because the coefficients are nonlinear. In this work, in order to perform the position and attitude tracking control of the quadrotor perfectly, the dynamical model of the quadrotor is divided into two subsystems, i.e., a fully actuated subsystem and an underactuated subsystem. For the former, a sliding manifold is defined by combining the position and velocity tracking errors of one state variable, i.e., the sliding manifold has two coefficients. For the latter, a sliding manifold is constructed via a linear combination of position and velocity tracking errors of two state variables, i.e., the sliding manifold has four coefficients. In order to further obtain the nonlinear coefficients of the sliding manifold, Hurwitz stability analysis is used to the solving process. In addition, the flight controllers are derived by using Lyapunov theory, which guarantees that all system state trajectories reach and stay on the sliding surfaces. Extensive simulation results are given to illustrate the effectiveness of the proposed control method. PMID:24751475

Zheng, En-Hui; Xiong, Jing-Jing; Luo, Ji-Liang

2014-07-01

231

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

E-print Network

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

232

Second order multidimensional sign-preserving remapping for ALE methods  

SciTech Connect

A second-order conservative sign-preserving remapping scheme for Arbitrary Lagrangian-Eulerian (ALE) methods is developed utilising concepts of the Multidimensional Positive Definite Advection Transport Algorithm (MPDATA). The algorithm is inherently multidimensional, and so does not introduce splitting errors. The remapping is implemented in a two-dimensional, finite element ALE solver employing staggered quadrilateral meshes. The MPDATA remapping uses a finite volume discretization developed for volume coordinates. It is applied for the remapping of density and internal energy arranged as cell centered, and velocity as nodal, dependent variables. In the paper, the advection of scalar fields is examined first for test cases with prescribed mesh movement. A direct comparison of MPDATA with the performance of the van Leer MUSCL scheme indicates advantages of a multidimensional approach. Furthermore, distinctly different performance between basic MPDATA and the infinite gauge option is illustrated using benchmarks involving transport of a sign changing velocity field. Further development extends the application of MPDATA remapping to the full ALE solver with a staggered mesh arrangement for density, internal energy and momentum using volume coordinates. At present, two options of the algorithm - basic and infinite gauge - are implemented. To ensure a meaningful assessment, an identical Lagrangian solver and computational mesh update routines are used with either MPDATA or van Leer MUSCL remapping. The evaluation places particular focus on the abilities of both schemes to accurately model multidimensional problems. Theoretical considerations are supported with numerical examples. In addition to the prescribed mesh movement cases for advection of scalars, the demonstrations include two-dimensional Eulerian and ALE flow simulations on quadrilateral meshes with both fixed and variable timestep control. The key comparisons include the standard test cases of Sod and Noh for single material problems. The results demonstrate that the MPDATA gauge option is suitable for providing accurate ALE remapping and preserves the multidimensionality and sign of both scalar and vector fields.

Hill, Ryan N [Los Alamos National Laboratory; Szmelter, J. [LOUGHBOROUGH UNIV.

2010-12-15

233

Kinetics research on fast exothermic reaction between cyclohexanecarboxylic acid and oleum in microreactor  

Microsoft Academic Search

Microreactors are effective tools for the intensification of fast exothermic chemical reactions. In this work, we focus on the kinetics study of a microreacting process to provide a deeper understanding of the transport and reaction performance within microreactors. An experimental setup incorporating an online kinetic measurement method was developed based on the temperature–conversion relationship in the cyclohexanecarboxylic acid–oleum reaction –

K. Wang; Y. C. Lu; Y. Xia; H. W. Shao; G. S. Luo

2011-01-01

234

RIS-M-2366 KINETICS OF THE REACTION OF HYDROXYL RADICALS WITH ETHANE AND  

E-print Network

RISÃ?-M-2366 KINETICS OF THE REACTION OF HYDROXYL RADICALS WITH ETHANE AND A SERIES OF CI- AND F phase reactions of hydroxyl radicals with ethane and a series of CI- and F-substituted methanes were-descriptors; AIR POLLUTION? CHEMICAL REACTION KINETICS? ETHANE? HYDROXYL RADICALS? METHYL RADICALS? ORGANIC HALOGEN

235

Kinetics of enol formation from reaction of OH with propene.  

PubMed

Kinetics of enol generation from propene has been predicted in an effort to understand the presence of enols in flames. A potential energy surface for reaction of OH with propene was computed by CCSD(T)/cc-pVDZ//B3LYP/cc-pVTZ calculations. Rate constants of different product channels and branching ratios were then calculated using the Master Equation formulation (J. Phys. Chem. A 2006, 110, 10528). Of the two enol products, ethenol is dominant over propenol, and its pathway is also the dominant pathway for the OH + propene addition reactions to form bimolecular products. In the temperature range considered, hydrogen abstraction dominated propene + OH consumption by a branching ratio of more than 90%. Calculated rate constants of enol formation were included in the Utah Surrogate Mechanism to model the enol profile in a cyclohexane premixed flame. The extended model shows consistency with experimental data and gives 5% contribution of ethenol formation from OH + propene reaction, the rest coming from ethene + OH. PMID:19271758

Huynh, Lam K; Zhang, Hongzhi R; Zhang, Shaowen; Eddings, Eric; Sarofim, Adel; Law, Matthew E; Westmoreland, Phillip R; Truong, Thanh N

2009-04-01

236

Reactions of chlorine with inorganic and organic compounds during water treatment-Kinetics and mechanisms: a critical review.  

PubMed

Numerous inorganic and organic micropollutants can undergo reactions with chlorine. However, for certain compounds, the expected chlorine reactivity is low and only small modifications in the parent compound's structure are expected under typical water treatment conditions. To better understand/predict chlorine reactions with micropollutants, the kinetic and mechanistic information on chlorine reactivity available in literature was critically reviewed. For most micropollutants, HOCl is the major reactive chlorine species during chlorination processes. In the case of inorganic compounds, a fast reaction of ammonia, halides (Br(-) and I(-)), SO(3)(2-), CN(-), NO(2)(-), As(III) and Fe(II) with HOCl is reported (10(3)-10(9)M(-1)s(-1)) whereas low chlorine reaction rates with Mn(II) were shown in homogeneous systems. Chlorine reactivity usually results from an initial electrophilic attack of HOCl on inorganic compounds. In the case of organic compounds, second-order rate constants for chlorination vary over 10 orders of magnitude (i.e. <0.1-10(9)M(-1)s(-1)). Oxidation, addition and electrophilic substitution reactions with organic compounds are possible pathways. However, from a kinetic point of view, usually only electrophilic attack is significant. Chlorine reactivity limited to particular sites (mainly amines, reduced sulfur moieties or activated aromatic systems) is commonly observed during chlorination processes and small modifications in the parent compound's structure are expected for the primary attack. Linear structure-activity relationships can be used to make predictions/estimates of the reactivity of functional groups based on structural analogy. Furthermore, comparison of chlorine to ozone reactivity towards aromatic compounds (electrophilic attack) shows a good correlation, with chlorine rate constants being about four orders of magnitude smaller than those for ozone. PMID:17915284

Deborde, Marie; von Gunten, Urs

2008-01-01

237

Atmospheric reactions Cl+CH3-(CH2)n-OH (n=0-4): A kinetic and theoretical study  

NASA Astrophysics Data System (ADS)

The reactions of Cl with a series of linear alcohols: methanol (k1), ethanol (k2), 1-propanol (k3), 1-butanol (k4), and 1-pentanol (k5) were investigated as a function of temperature in the range of 264-382 K by laser photolysis-resonance fluorescence. The obtained kinetic data were used to derive the following Arrhenius expressions: k1=(3.55+/-0.22)×10-10 exp[-(559+/-40)/T], k2=(5.25+/-0.52)×10-11 exp[(190+/-68)/T], k3=(2.63+/-0.21)×10-11 exp[(525+/-51)/T], k4=(3.12+/-0.31)×10-11 exp[(548+/-65)/T], and k5=(3.97+/-0.48)×10-11 exp[(533+/-77)/T] (in units of cm3 molecule-1 s-1). To our knowledge, these are the first absolute kinetic data reported for 1-butanol and 1-pentanol and also the first kinetic study as a function of temperature for these two compounds. Results, mechanism, and tropospheric implications are discussed and compared with the reported reactivity with OH radicals. Moreover, a theoretical insight into the mechanisms of these reactions has also been pursued through ab initio Möller-Plesset second-order perturbation treatment calculations with 6-311G** basis sets. Optimized geometries and vibrational frequencies have been obtained for transition states and molecular complexes appearing along the different reaction pathways. Furthermore, molecular energies have been calculated at quadratic configuration interaction with single, double, and triple excitations level in order to get an estimation of the activation energies.

Garzón, Andrés; Cuevas, Carlos A.; Ceacero, Antonio A.; Notario, Alberto; Albaladejo, José; Fernández-Gómez, Manuel

2006-09-01

238

Thermochemistry, reaction paths, and kinetics on the tert-isooctane radical reaction with O2.  

PubMed

Thermochemical properties of tert-isooctane hydroperoxide and its radicals are determined by computational chemistry. Enthalpies are determined using isodesmic reactions with B3LYP density function and CBS QB3 methods. Application of group additivity with comparison to calculated values is illustrated. Entropy and heat capacities are determined using geometric parameters and frequencies from the B3LYP/6-31G(d,p) calculations for the lowest energy conformer. Internal rotor potentials are determined for the tert-isooctane hydroperoxide and its radicals in order to identify isomer energies. Recommended values derived from the most stable conformers of tert-isooctane hydroperoxide of are -77.85 ± 0.44 kcal mol(-1). Isooctane is a highly branched molecule, and its structure has a significant effect on its thermochemistry and reaction barriers. Intramolecular interactions are shown to have a significant effect on the enthalpy of the isooctane parent and its radicals on peroxy/peroxide systems, the R• + O2 well depths and unimolecular reaction barriers. Bond dissociation energies and well depths, for tert-isooctane hydroperoxide ? R• + O2 are 33.5 kcal mol(-1) compared to values of ?38 to 40 kcal mol(-1) for the smaller tert-butyl-O2 ? R• + O2. Transition states and kinetic parameters for intramolecular hydrogen atom transfer and molecular elimination channels are characterized to evaluate reaction paths and kinetics. Kinetic parameters are determined versus pressure and temperature for the chemically activated formation and unimolecular dissociation of the peroxide adducts. Multifrequency quantum RRK (QRRK) analysis is used for k(E) with master equation analysis for falloff. The major reaction paths at 1000 K are formation of isooctane plus HO2 followed by cyclic ether plus OH. Stabilization of the tert-isooctane hydroperoxy radical becomes important at lower temperatures. PMID:24894154

Snitsiriwat, Suarwee; Bozzelli, Joseph W

2014-07-01

239

Kinetic studies of reactions of cobalt clusters with deuterium  

SciTech Connect

The kinetics of chemical reactions of cobalt clusters Co{sub n} with deuterium are described. Absolute rate constants have been measured in the cluster range n = 7--68 at 293 K. The rate constants are found to be a strong function of cluster size, varying by up to three orders of magnitude. This size , dependence is most prominent in the n = 7--25 size range: CO{sub 15} is the most reactive cluster, and CO{sub 7-9} and CO{sub 19--20} are particularly unreactive. Abrupt changes in the rate constants from one cluster size to the next are observed. For the clusters above n = 25, the rate constants show several less prominent maxima and minima superimposed on a slow, nearly monotonic increase with cluster size.

Ho, J.; Zhu, L.; Parks, E.K.; Riley, S.J.

1992-10-01

240

Kinetic studies of reactions of cobalt clusters with deuterium  

SciTech Connect

The kinetics of chemical reactions of cobalt clusters Co{sub n} with deuterium are described. Absolute rate constants have been measured in the cluster range n = 7--68 at 293 K. The rate constants are found to be a strong function of cluster size, varying by up to three orders of magnitude. This size , dependence is most prominent in the n = 7--25 size range: CO{sub 15} is the most reactive cluster, and CO{sub 7-9} and CO{sub 19--20} are particularly unreactive. Abrupt changes in the rate constants from one cluster size to the next are observed. For the clusters above n = 25, the rate constants show several less prominent maxima and minima superimposed on a slow, nearly monotonic increase with cluster size.

Ho, J.; Zhu, L.; Parks, E.K.; Riley, S.J.

1992-01-01

241

Reaction Kinetics of the Hydrothermal Treatment of Lignin  

NASA Astrophysics Data System (ADS)

Lignins derived from abundant and renewable resources are nontoxic and extremely versatile in performance, qualities that have made them increasingly important in many industrial applications. We have shown recently that liquefaction of lignin extracted from aspen wood resulted in a 90% yield of liquid. In this paper, the hydrothermal treatment of five types of lignin and biomass residues was studied: Kraft pine lignin provided by MeadWestvaco, Kraft pine lignin from Sigma-Aldrich, organosolv lignin extracted from oat hull, the residues of mixed southern hardwoods, and switchgrass after hydrolysis. The yields were found dependent on the composition or structure of the raw materials, which may result from different pretreatment processes. We propose a kinetic model to describe the hydrothermal treatment of Kraft pine lignin and compare it with another model from the literature. The kinetic parameters of the presented model were estimated, including the reaction constants, the pre-exponential factor, and the activation energy of the Arrhenius equations. Results show that the presented model is well in agreement with the experiments.

Zhang, Bo; Huang, Hua-Jiang; Ramaswamy, Shri

242

An Efficient Second-Order Accurate and Continuous Interpolation for Block-Adaptive Grids  

E-print Network

In this paper we present a second-order and continuous interpolation algorithm for cell-centered adaptive-mesh-refinement (AMR) grids. Continuity requirement poses a non-trivial problem at resolution changes. We develop a classification of the resolution changes, which allows us to employ efficient and simple linear interpolation in the majority of the computational domain. The benefit of such approach is higher efficiency. The algorithm is well suited for massively parallel computations. Our interpolation algorithm allows extracting jump-free interpolated data distribution along lines and surfaces within the computational domain. This capability is important for various applications, including kinetic particles tracking in three dimensional vector fields, visualization (i.e. surface extraction) and extracting variables along one-dimensional curves such as field lines, streamlines and satellite trajectories, etc. Particular examples of the latter are models for acceleration of solar energetic particles (SEPs)...

Borovikov, Dmitry; Toth, Gabor

2014-01-01

243

Second-order analytic solutions for re-entry trajectories  

NASA Astrophysics Data System (ADS)

With the development of aeroassist technology, either for near-earth operations or for planetary aero-capture, it is of interest to have accurate analytic solutions for the speed, flight path angle and altitude during the atmospheric passage. For a future aerospace plane which uses the accumulated kinetic energy to glide for a long range, explicit relations among the main state variables are also useful for guidance purposes. In this paper we have used normalization to put the equations of motion for planar entry around a non-rotating planet into a form which is suitable for an analytic integration. Explicit and accurate solutions are then obtained for ballistic fly-through trajectories, lifting skip trajectories and equilibrium glide trajectories.

Vinh, Nguyen X.; Kim, Eun-Kyou; Greenwood, Donald T.

244

Stereochemical Lability of Azatitanacyclopropanes: Dynamic Kinetic Resolution in Reductive Cross-Coupling Reactions with Allylic Alcohols‡  

PubMed Central

Azatitanacyclopropanes (titanaziridines) are shown to be stereochemically labile under reaction conditions for reductive cross-coupling. This fundamental property has been employed to realize highly selective asymmetric coupling reactions with allylic alcohols that proceed by dynamic kinetic resolution. PMID:23963189

Yang, Dexi

2014-01-01

245

Hydrogen Oxidation and Evolution Reaction Kinetics on Platinum: Acid vs Alkaline Electrolytes  

E-print Network

The kinetics of the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) on polycrystalline platinum [Pt(pc)] and high surface area carbon-supported platinum nanoparticles (Pt/C) were studied in 0.1 M ...

Sheng, Wenchao

246

Existential Second Order Logic Expression With Horn First Order for Max Clique (Decision Version)  

E-print Network

We will show that the maximum clique problem (decision version) can be expressed in existential second order (ESO) logic, where the first order part is a Horn formula in second-order quantified predicates.

Manyem, Prabhu

2010-01-01

247

Theoretical analysis of kinetic isotope effects on proton transfer reactions between substituted alpha-methoxystyrenes and substituted acetic acids.  

PubMed

Primary kinetic isotope effects (KIEs) on a series of carboxylic acid-catalyzed protonation reactions of aryl-substituted alpha-methoxystyrenes (X-1) to form oxocarbenium ions have been computed using the second-order Kleinert variational 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 relatively 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 alpha-methoxystyrenes by chloroacetic acid, but for the reactions of the parent and 4-NO(2) substituted alpha-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, DeltaG(o) approximately 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, that is, the driving force DeltaG(o), along with a good correlation of Hammond shift in the transition state structure. PMID:19754046

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

2009-10-01

248

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

249

LETTER TO THE EDITOR: Evolution of second-order cosmological perturbations  

NASA Astrophysics Data System (ADS)

We present a method for constructing gauge-invariant cosmological perturbations which are gauge-invariant up to second order. As an example, we give the gauge-invariant definition of the second-order curvature perturbation on uniform density hypersurfaces. Using only the energy conservation equation, we show that this curvature perturbation is conserved at second order on large scales for adiabatic perturbations.

Malik, Karim A.; Wands, David

2004-06-01

250

Reaction kinetics on model catalysts: Molecular beam methods and time-resolved vibrational spectroscopy  

Microsoft Academic Search

Reaction kinetics on nanometer-scale particles are different from perfect single crystal surfaces. In heterogeneous catalysts this fact is empirically made use of in order to maximize the catalytic performance. Molecular beam experiments combined with vibrational spectroscopy on structurally well-defined model catalysts can provide detailed insight into the underlying reaction kinetics at the microscopic level. We critically review the recent developments,

Jörg Libuda

2005-01-01

251

Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels  

E-print Network

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

Paris-Sud XI, Université de

252

Time-dependent kinetic complexities in cholinesterase-catalyzed reactions.  

PubMed

Cholinesterases (ChEs) display a hysteretic behavior with certain substrates and inhibitors. Kinetic cooperativity in hysteresis of ChE-catalyzed reactions is characterized by a lag or burst phase in the approach to steady state. With some substrates damped oscillations are shown to superimpose on hysteretic lags. These time dependent peculiarities are observed for both butyrylcholinesterase and acetylcholinesterase from different sources. Hysteresis in ChE-catalyzed reactions can be interpreted in terms of slow transitions between two enzyme conformers E and E'. Substrate can bind to E and/or E', both Michaelian complexes ES and ?'S can be catalytically competent, or only one of them can make products. The formal reaction pathway depends on both the chemical structure of the substrate and the type of enzyme. In particular, damped oscillations develop when substrate exists in different, slowly interconvertible, conformational, and/or micellar forms, of which only the minor form is capable of binding and reacting with the enzyme. Biphasic pseudo-first-order progressive inhibition of ChEs by certain carbamates and organophosphates also fits with a slow equilibrium between two reactive enzyme forms. Hysteresis can be modulated by medium parameters (pH, chaotropic and kosmotropic salts, organic solvents, temperature, osmotic pressure, and hydrostatic pressure). These studies showed that water structure plays a role in hysteretic behavior of ChEs. Attempts to provide a molecular mechanism for ChE hysteresis from mutagenesis studies or crystallographic studies failed so far. In fact, several lines of evidence suggest that hysteresis is controlled by the conformation of His438, a key residue in the catalytic triad of cholinesterases. Induction time may depend on the probability of His438 to adopt the operative conformation in the catalytic triad. The functional significance of ChE hysteresis is puzzling. However, the accepted view that proteins are in equilibrium between preexisting functional and non-functional conformers, and that binding of a ligand to the functional form shifts equilibrium towards the functional conformation, suggests that slow equilibrium between two conformational states of these enzymes may have a regulatory function in damping out the response to certain ligands and irreversible inhibitors. This is particularly true for immobilized (membrane bound) enzymes where the local substrate and/or inhibitor concentrations depend on influx in crowded organellar systems, e.g. cholinergic synaptic clefts. Therefore, physiological or toxicological relevance of the hysteretic behavior and damped oscillations in ChE-catalyzed reactions and inhibition cannot be ruled out. PMID:23157295

Masson, P

2012-10-01

253

Carbon kinetic isotope effect in the reaction of CH4 with HO  

Microsoft Academic Search

The carbon kinetic isotope effect in the CH4 + HO reaction can enrich atmospheric methane in 13C relative to its sources. In the only previous measurement of the carbon kinetic isotope effect in this reaction, a value of k12\\/k13 of 1.003 was reported. In the present experimental determination we have found a significantly larger kinetic isotope effect of 1.010 +\\/-

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

1987-01-01

254

Experimental and theoretical methods in kinetic studies of heterogeneously catalyzed reactions.  

PubMed

This review aims to illustrate the potential of kinetic analysis in general and microkinetic modeling in particular for rational catalyst design. Both ab initio calculations and experiments providing intrinsic kinetic data allow us to assess the effects of catalytic properties and reaction conditions on the activity and selectivity of the targeted reactions. Three complementary approaches for kinetic analysis of complex reaction networks are illustrated, using select examples of acid zeolite-catalyzed reactions from the authors' recent work. Challenges for future research aimed at defining targets for synthesis strategies that enable us to tune zeolite properties are identified. PMID:24910922

Reyniers, Marie-Françoise; Marin, Guy B

2014-01-01

255

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

256

A cross-linked electro-optic polymer for second order nonlinear optical applications  

NASA Astrophysics Data System (ADS)

Electro-optic properties of a cross-linked second order nonlinear optical polymer were reported. This polymer was synthesized via the crosslinking reaction with cross linker Trimethylolmelamine by doping the chromophores into the cellulose diacetate system. The crosslinking temperature is 144°C. The electro-optic coefficient was measured to be 7.12 pm/v at 1550 nm after poling. The stability characteristic of electro-optic effects was studied by a combination of the electro-optic coefficient and dielectric relaxation measurements. Results show that the cross-linked electro-optic polymer system possesses an excellent long-time stability. The average relaxation time is as large as 5880 days and the relaxation was modeled by KWW equation. The dielectric analyses show that the temperature dependence of the relaxation time follows Arrhenius law.

Hong, Jianxun; Li, Chengjun; Zhou, Jianxin; Zhou, Limin; Chen, Shuiping; Chen, Wei

2008-11-01

257

SECOND-ORDER SOLUTIONS OF COSMOLOGICAL PERTURBATION IN THE MATTER-DOMINATED ERA  

SciTech Connect

We present the growing mode solutions of cosmological perturbations to the second order in the matter-dominated era. We also present several gauge-invariant combinations of perturbation variables to the second order in the most general fluid context. Based on these solutions, we study the Newtonian correspondence of relativistic perturbations to the second order. In addition to the previously known exact relativistic/Newtonian correspondence of density and velocity perturbations to the second order in the comoving gauge, here we show that in the sub-horizon limit we have the correspondences for density, velocity, and potential perturbations in the zero-shear gauge and in the uniform-expansion gauge to the second order. Density perturbation in the uniform-curvature gauge also shows the correspondence to the second order in the sub-horizon scale. We also identify the relativistic gravitational potential that shows exact correspondence to the Newtonian one to the second order.

Hwang, Jai-chan [Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 702-701 (Korea, Republic of); Noh, Hyerim [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Gong, Jinn-Ouk [Theory Division, CERN, CH-1211 Geneve 23 (Switzerland)

2012-06-10

258

A G-quadruplex based platform for label-free monitoring of DNA reaction kinetics.  

PubMed

Research on the kinetic characteristics and mechanisms of DNA reactions is crucial for bioengineering and biosensing. A G-quadruplex, which can form a peroxidase-mimicking DNAzyme with hemin, was for the first time used to establish a versatile platform for kinetic investigations on DNA reactions. G-quadruplex sequence EAD2 was incorporated into the corresponding nucleic acid reaction as product. The kinetic curves can be obtained rapidly and simply via the quantification of created DNAzyme. In this paper, the kinetics of isothermal linear strand displacement amplification reactions with different DNA lengths and isothermal exponential amplification reactions were successfully elucidated via the G-quadruplex based monitoring platform. As a safe and accessible alternative to the traditional methods, this robust, label-free, time-saving and high-throughput platform shows great potential for the exploration of more novel DNA reactions or circuits in an ingenious manner. PMID:25349990

Nie, Ji; Cai, Liang-Yuan; Zhang, Fang-Ting; Zhao, Ming-Zhe; Zhou, Ying-Lin; Zhang, Xin-Xiang

2014-11-10

259

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

E-print Network

Kinetics - 4 Reaction Stoichiometry + Law of Conservation of Mass rA -a rB -b rC c rD d = = = (Irrespective Michaelis-Menten model of enzymatic reactions #12;Michaelis-Menten kinetics Mass conservation: Assumption/volume) ; 1 mole = 6.023x1023 molecules rA = -k [A] rA = -k [A]2 rA = -k1 [A]/(1+k2[A]) Reaction rate law

Albert, Réka

260

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

SciTech Connect

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

261

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

262

Kinetic modelling of GlmU reactions - prioritization of reaction for therapeutic application.  

PubMed

Mycobacterium tuberculosis(Mtu), a successful pathogen, has developed resistance against the existing anti-tubercular drugs necessitating discovery of drugs with novel action. Enzymes involved in peptidoglycan biosynthesis are attractive targets for antibacterial drug discovery. The bifunctional enzyme mycobacterial GlmU (Glucosamine 1-phosphate N-acetyltransferase/ N-acetylglucosamine-1-phosphate uridyltransferase) has been a target enzyme for drug discovery. Its C- and N- terminal domains catalyze acetyltransferase (rxn-1) and uridyltransferase (rxn-2) activities respectively and the final product is involved in peptidoglycan synthesis. However, the bifunctional nature of GlmU poses difficulty in deciding which function to be intervened for therapeutic advantage. Genetic analysis showed this as an essential gene but it is still unclear whether any one or both of the activities are critical for cell survival. Often enzymatic activity with suitable high-throughput assay is chosen for random screening, which may not be the appropriate biological function inhibited for maximal effect. Prediction of rate-limiting function by dynamic network analysis of reactions could be an option to identify the appropriate function. With a view to provide insights into biochemical assays with appropriate activity for inhibitor screening, kinetic modelling studies on GlmU were undertaken. Kinetic model of Mtu GlmU-catalyzed reactions was built based on the available kinetic data on Mtu and deduction from Escherichia coli data. Several model variants were constructed including coupled/decoupled, varying metabolite concentrations and presence/absence of product inhibitions. This study demonstrates that in coupled model at low metabolite concentrations, inhibition of either of the GlmU reactions cause significant decrement in the overall GlmU rate. However at higher metabolite concentrations, rxn-2 showed higher decrement. Moreover, with available intracellular concentration of the metabolites and in vivo variant of model, uncompetitive inhibition of rxn-2 caused highest decrement. Thus, at physiologically relevant metabolite concentrations, targeting uridyltranferase activity of Mtu GlmU would be a better choice for therapeutic intervention. PMID:22952829

Singh, Vivek K; Das, Kaveri; Seshadri, Kothandaraman

2012-01-01

263

A literature review of reactions and kinetics of lithium hydride hydrolysis  

NASA Astrophysics Data System (ADS)

Studies of lithium hydride (LiH) reactions with H 2O are reviewed in this paper. We discuss reaction products that are formed and the reaction kinetics involved. For discussion purposes, the studies are roughly categorized as reactions between LiH and H 2O in low and higher concentration regimes, as well as reactions between LiH hydrolysis products. Both LiH and H 2O can exist in many structural or phase variations and can contain various impurities, all of which may affect products and kinetics.

Haertling, C.; Hanrahan, R. J.; Smith, R.

2006-02-01

264

Laboratory studies of stratospheric bromine chemistry: Kinetics of the reactions of bromine monoxide with nitrogen dioxide and atomic oxygen  

SciTech Connect

A laser flash photolysis - long path absorption - technique has been employed to study the kinetics of the reaction BrO+NO2+M(k[sub 16]) yields products as a function of temperature (248-346 K), pressure (16-800 Torr), and buffer gas identity (N2, CF4). 351 nm photolysis of NO2/Br2/N2 mixtures generated BrO. The BrO decay in the presence of excess NO2 was followed by UV absorption at 338.3 nm. The reaction is 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 k[sub 16](P,T) have been reported at pressures greater than 12 Torr; hence, these results help constrain choices of k[sub 16](P,T) for use in modeling stratospheric BrO(x) chemistry. The kinetics of the important stratospheric reaction BrO+O(P-3)(k[sub 14]) yields Br+O2 in N2 buffer gas have been studied as a function of temperature (233-328 K) and pressure (25-150 Torr) using a novel dual laser flash photolysis/long path absorption/resonance fluorescence technique. 248 nm pulsed laser photolysis of Br2/O3/N2 mixtures produces O atoms in excess over Br2. After a delay sufficient for BrO to be generated, a 532 nm laser pulse photolysis a small fraction of the O3 to generate O(P-3). The decay of O(P-3) in the presence of an excess, known concentration of BrO, as determined by UV absorption at 338.3 nm and by numerical simulation, is then followed by time-resoved atomic resonance fluorescence spectroscopy. The experimental results have shown the reaction kinetics to be independent of pressure, to increase with decreasing temperature, and to be faster than suggested by the only previous (indirect) measurement. The resulting Anhenius expression for k[sub 14](T) is k[sub 14](T) = 1.64 x 10(exp -11) exp(263/T) cm(exp 3) molecule(exp-1)s(exp -1). The absolute accuracy of k[sub 14](T) at any temperature within the range studied is estimated to be +/- 25%.

Thorn, R.P.

1993-01-01

265

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

Microsoft Academic Search

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

CHARLES K. WESTBROOK; WILLIAM J. PITZ

1984-01-01

266

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

NASA Technical Reports Server (NTRS)

Radio JOVE is an education and outreach project intended to give students and other interested individuals hands-on experience in learning radio astronomy. They can do this through building a radio telescope from a relatively inexpensive kit that includes the parts for a receiver and an antenna as well as software for a computer chart recorder emulator (Radio Skypipe) and other reference materials

Summerlin, Errol J.

2010-01-01

267

Inferring Genetic Interactions via a Data-Driven Second Order Model  

PubMed Central

Genetic/transcriptional regulatory interactions are shown to predict partial components of signaling pathways, which have been recognized as vital to complex human diseases. Both activator (A) and repressor (R) are known to coregulate their common target gene (T). Xu et al. (2002) proposed to model this coregulation by a fixed second order response surface (called the RS algorithm), in which T is a function of A, R, and AR. Unfortunately, the RS algorithm did not result in a sufficient number of genetic interactions (GIs) when it was applied to a group of 51 yeast genes in a pilot study. Thus, we propose a data-driven second order model (DDSOM), an approximation to the non-linear transcriptional interactions, to infer genetic and transcriptional regulatory interactions. For each triplet of genes of interest (A, R, and T), we regress the expression of T at time t?+?1 on the expression of A, R, and AR at time t. Next, these well-fitted regression models (viewed as points in R3) are collected, and the center of these points is used to identify triples of genes having the A-R-T relationship or GIs. The DDSOM and RS algorithms are first compared on inferring transcriptional compensation interactions of a group of yeast genes in DNA synthesis and DNA repair using microarray gene expression data; the DDSOM algorithm results in higher modified true positive rate (about 75%) than that of the RS algorithm, checked against quantitative RT-polymerase chain reaction results. These validated GIs are reported, among which some coincide with certain interactions in DNA repair and genome instability pathways in yeast. This suggests that the DDSOM algorithm has potential to predict pathway components. Further, both algorithms are applied to predict transcriptional regulatory interactions of 63 yeast genes. Checked against the known transcriptional regulatory interactions queried from TRANSFAC, the proposed also performs better than the RS algorithm. PMID:22563331

Jiang, Ci-Ren; Hung, Ying-Chao; Chen, Chung-Ming; Shieh, Grace S.

2012-01-01

268

Second-order polarization mode dispersion: impact on analog and digital transmissions  

Microsoft Academic Search

Second-order polarization mode dispersion (PMD) is a major limitation to the transmission capabilities of analog systems and of high bit rate digital systems. Basically, the effect of second-order PMD is the same as that of chromatic dispersion. However, like all polarization effects in standard single-mode fibers, the effects of second-order PMD are stochastic, due to the random polarization mode coupling

Philippe Ciprut; B. Gisin; Nicolas Gisin; Rogerio Passy; P. Von Der Weld; F. Prieto; C. W. Zimmer

1998-01-01

269

Programmable floating-gate second-order sections for GmC filter applications  

Microsoft Academic Search

We present programmable, fully-differential Gm-C second-order sections showing tunability over a wide range of frequencies. The second-order sections use a floating-gate operational transconductance amplifier (FG-OTA) to realize tunability. We present experimental results showing frequency- and Q-tuning for a lowpass (LPSOS) and a bandpass second-order section (BPSOS) designed using these FG-OTAs. Measured 1-dB compression for LPSOS and BPSOS are -15 dBm

Ravi Chawla; Guillermo Serrano; Daniel Allen; Paul Hasler

2005-01-01

270

Second-order sliding mode control for a magnetic levitation system  

Microsoft Academic Search

This paper presents a second-order sliding mode position control design for robust stabilization and disturbance rejection of the magnetic ball suspension system. With respect to conventional sliding mode control, the second-order sliding mode technique shows the same properties of robustness to uncertainties of model and external disturbances. The proposed second-order sliding mode control has the continuous control signal that improves

Huann-Keng Chiang; Chun-Chiang Fang; Wen-Bin Lin; Guan-Wei Chen

2011-01-01

271

Second-order Volterra filtering and its application to nonlinear system identification  

Microsoft Academic Search

Some recent results on the design and implementation of second-order Volterra filters are presented. The (second-order) Volterra filter is a nonlinear filter with the filter structure of (second-order) Volterra series. A simple minimum mean-square error solution for the Volterra filter is derived, based on the assumption that the filter input is Gaussian. Also, we propose an iterative factorization technique to

Taiho Koh; EDWARD J. POWERS

1985-01-01

272

A general approach to specific second order ordinary differential equations using homotopy perturbation method  

Microsoft Academic Search

Homotopy perturbation method is used to solve specific second order ordinary differential equations and tested for different examples. The results obtained demonstrate efficiency of the proposed method.

Arif Rafiq; Munshoor Ahmed; Sifat Hussain

2008-01-01

273

Reaction kinetics of isomerization of n-butenes to isobutylene  

SciTech Connect

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

274

Model for reaction kinetics in pyrolysis of wood  

SciTech Connect

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 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. 6 refs., 3 figs., 2 tabs.

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

1996-12-31

275

Model for reaction kinetics in pyrolysis of wood  

SciTech Connect

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

276

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)] 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

277

Supporting Information for Reaction Kinetics and Transformation of Carbadox and Structurally Related  

E-print Network

of Na2S2O3 quenching agent on the observed CDX kinetics. Text S3. Experimental setup for reaction of CDX with free chlorine in H2 18 O at pH 9. Text S4. Results for CDX loss at low and neutral/high pH without. Figure S1. CDX/DCR competition kinetics. Figure S2. DCDX/CDX competition kinetics. Figure S3. Model kapp

Huang, Ching-Hua

278

Linear free energy relationship and deuterium kinetic isotope effect observed on phospho and thiophosphoryl transfer reactions in some organophosphorous compounds  

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

279

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

SciTech Connect

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

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

2001-12-13

280

Reaction kinetics for the high temperature oxidation of Pu--1wt%Ga in water vapor  

SciTech Connect

Oxidation of plutonium metal is greatly accelerated by the presence of water vapor. The magnitude of the effect of water vapor on oxidation kinetics is determined by temperature, water concentration, and oxygen concentration. Most of the previous work has been directed toward evaluating the effect of moisture on the atmospheric oxidation of plutonium. Work on the isolation and characterization of the water reaction with plutonium has been very limited. The present work was undertaken to determine the kinetics of the plutonium--water reaction over a wide range of temperature and pressure. Reaction kinetics were measured using a vacuum microbalance system. The temperature range investigated was 100--500/degree/C. The effect of water vapor pressure on reaction kinetics was determined at 300/degree/C by varying the water pressure from 0.1 to 15 Torr. 2 figs.

Stakebake, J L; Saba, M A

1988-01-01

281

Physico-Geometrical Kinetics of Solid-State Reactions in an Undergraduate Thermal Analysis Laboratory  

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

282

Determination of reaction kinetic parameters from variable temperature DSC or DTA  

Microsoft Academic Search

An equation is derived for evaluating the kinetic parameters of a transformation from variable temperature DSC or DTA, taking account of the variation in the reaction rate constant with time and temperature. Kinetic parameters for the crystallization of a ZrF4-BaF2-LaF3 glass are calculated using this equation.

N. P. Bansal; R. H. Doremus

1984-01-01

283

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

284

Kinetics for the reaction of hydrogen with uranium powder  

Microsoft Academic Search

The reaction of hydrogen with uranium powder was investigated at 13.3 and 26.6 kPa between 50 and 250°C. The reaction order was independent of temperature but varied from 2\\/3-order at 13.3 kPa to 1st-order at 26.6 kPa. Increasing temperatures resulted in decreasing reaction rates over the temperature range studied. A reaction mechanism with adsorption as the rate controlling step is

J. L. Stakebake

1979-01-01

285

Kinetic studies of isoprene reactions with hydroxyl and chlorine radicals  

E-print Network

, formic acid, methyl-glyoxal, and hydrogen chloride. Other likely products of the isoprene reactions include a, P ? unsaturated carbonyls (methyl vinyl ketone and methacrolein) ' ' In addition, the branching ratio for the reaction of isoprene with Cl..., formic acid, methyl-glyoxal, and hydrogen chloride. Other likely products of the isoprene reactions include a, P ? unsaturated carbonyls (methyl vinyl ketone and methacrolein) ' ' In addition, the branching ratio for the reaction of isoprene with Cl...

Suh, Inseon

2012-06-07

286

Size- and temperature-dependent second-order optical effects in copper-doped cadmium iodide nanocrystals  

NASA Astrophysics Data System (ADS)

Size and temperature dependences of second-order optical effects in Cu-doped cadmium iodide nanocrystals are studied. A large enhancement of photoinduced second harmonic generation (PSHG) with decreasing thickness of the nanocrystals or temperature is observed. The PSHG is also found to be enhanced with increasing Cu doping. However, due to the formation of the metallic agglomerates, the PSHG for the crystals with high Cu contents decreases. The results are presented by discussing photoinduced kinetics of the electron-phonon anharmonic interaction and nanosized quantum confined effect, the crucial roles played in the observed effects.

Miah, M. Idrish

2008-09-01

287

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

288

Reaction kinetics of plutonium with oxygen, water and humid air: moisture enhancement of the corrosion rate  

Microsoft Academic Search

Kinetic measurements for the reactions of unalloyed plutonium with water vapor and oxygen in the 35 to 400°C range show that moisture enhancement of the corrosion rate is confined to a temperature regime below 200°C. In combination with kinetic data from literature sources and measurements with air at 25°C, the data define a rate-temperature envelope in which the corrosion reaction

John M. Haschke; Thomas H. Allen; Jerry L. Stakebake

1996-01-01

289

Recent advances in the fundamentals of the kinetics of steelmaking reactions  

Microsoft Academic Search

G.R. Belton was the leader in developing our understanding of the kinetics of metallurgical reactions. Selected recent kinetic\\u000a studies, based on this understanding and the application of the results to actual processes, are presented in this article.\\u000a In particular, the rates of reaction of carbon and carbon in iron with CO2 and H2O gases and FeO in slag are reviewed

R. J. Fruehan; D. Goldstein; B. Sarma; S. R. Story; P. C. Glaws; H. U. Pasewicz

2000-01-01

290

Kinetic measurements on elementary fossil fuel combustion reactions over wide temperature ranges  

SciTech Connect

The goals of this work are to provide accurate data on the temperature dependence of the kinetics of elementary combustion reactions (i) for use by combustion modelers, and (ii) to gain a better fundamental understanding of, and hence predictive ability for, the chemistry involved. In this reporting period our work on the O + Hcl reaction was published, experimental work on the O + benzene and O + 1-butene reactions was completed, and measurements on the O + isobutene reaction were initiated.

Fontijn, A.

1991-01-01

291

SOERP; second-order error propagation code. [IBM360,370; CDC7600; FORTRAN IV  

Microsoft Academic Search

SOERP computes second-order error propagation equations for the first four moments of a function of independently distributed random variables. SOERP was written for a rigorous second-order error propagation of any function which may be expanded in a multivariable Taylor series, the input variables being independently distributed. The required input consists of numbers directly related to the partial derivatives of the

N. D. Cox; C. F. Miller

2008-01-01

292

Stereotyping, Groups and Cultural Evolution: A Case of "Second Order Emergence"?  

E-print Network

Stereotyping, Groups and Cultural Evolution: A Case of "Second Order Emergence"? David Hales­going project investigating group formation, stereotyping and cultural evolution using an artificial society a form of ``second order emergence'' [11] in which agents come to recognise the cultural groupings

Hales, David

293

The similarity rules for second-order subsonic and supersonic flow  

NASA Technical Reports Server (NTRS)

The similarity rules for linearized compressible flow theory (Gothert's rule and its supersonic counterpart) are extended to second order. It is shown that any second-order subsonic flow can be related to "nearly incompressible" flow past the same body, which can be calculated by the Janzen-Rayleigh method.

Van Dyke, Milton D

1958-01-01

294

GRAVITY ERROR COMPENSATION USING SECOND-ORDER GAUSS-MARKOV PROCESSES  

E-print Network

as a first-order Gauss- Markov process (GMP1) to estimate un-modeled accelerations. In this work, we addressAAS 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

Born, George

295

Second-order accurate particle image velocimetry S. T. Wereley, C. D. Meinhart  

E-print Network

Second-order accurate particle image velocimetry S. T. Wereley, C. D. Meinhart Abstract An adaptive, second-order accurate particle image velocimetry (PIV) technique is presented. The technique uses two of particle image velocimetry (PIV), researchers have realized that PIV algorithms do not generally make

Meinhart, Carl

296

A New Simple Model for Land Mobile Satellite Channels: First-and Second-Order Statistics  

E-print Network

1 A New Simple Model for Land Mobile Satellite Channels: First- and Second-Order Statistics Ali-form and mathematically-tractable expressions for the fundamental channel statistics such as the envelope probability diversity. Comparison of the first- and the second-order statistics of the proposed model with different

Abdi, Ali

297

Unified interpretation for second-order subwavelength interference based on Feynman's path-integral theory  

SciTech Connect

The second-order spatial subwavelength interference pattern is observed in a modified Michelson interferometer with single-mode continuous-wave laser beams. By analyzing our subwavelength interference experiment based on Feynman's path integral theory, a unified interpretation for all the second-order subwavelength interference is suggested.

Liu Jianbin; Zhang Guoquan [MOE Key Laboratory of Weak Light Nonlinear Photonics, Nankai University, Tianjin 300457 (China) and Photonics Center, School of Physics, Nankai University, Tianjin 300071 (China)

2010-07-15

298

Cascaded second-order soliton for high-coherence supercontinuum generation  

E-print Network

Cascaded second-order soliton for high-coherence supercontinuum generation Qian Li1 , J. Nathan@polyu.edu.hk Abstract We propose the use of cascaded second-order soliton for high-coherence supercontinuum generation. 1. Introduction Supercontinuum (SC) generation in optical fibers has attracted widespread interests

Wai, Ping-kong Alexander

299

The kinetics of the uranium-oxygen-water vapour reaction between 40 and 100°c  

NASA Astrophysics Data System (ADS)

The kinetics of the uranium-oxygen-water vapour reaction have been measured between 40 and 100°C and between 11 and 75% relative humidity. This work is the first systematic study of the kinetics of this reaction over this range of temperature and humidity. The reaction rate is given by the equation: k = 7.6 × 10 13 exp(-26.4 kcal/RT) mg weight gain/cm 2·h. This is in good agreement with the rate equation deduced in a previous review of a wide variety of different investigations. There was no systematic dependence of the reaction rate on either humidity or surface treatment over the whole temperature range. The reaction shows linear kinetics.

Ritchie, A. G.; Greenwood, R. C.; Randles, S. J.

1986-06-01

300

Incorporation of aqueous reaction and sorption kinetics andbiodegradation into TOUGHREACT  

SciTech Connect

The needs for considering aqueous and sorption kinetics and microbiological processes arises in many subsurface problems, such as environmental and acid mine remediation. A general rate expression has been implemented into TOUGHREACT, which considers multiple mechanisms(pathways) and includes multiple product, Monod, and inhibition terms. In this paper, the formulation for incorporating kinetic rates among primary species into the mass balance equations is presented. A batch sulfide oxidation problem is simulated. The resulting concentrations are consistent with simple hand calculations. A 1-D reactive transport problem with kinetic biodegradation and sorption was investigated, which models the processes when a pulse of water containing NTA (nitrylotriacetate) and cobalt is injected into a column. The problem has several interacting chemical processes that are common to many environmental problems: biologically-mediated degradation of an organic substrate, bacterial cell growth and decay, metal sorption and aqueous speciation including metal-ligand complexation. The TOUGHREACT simulation results agree very well with those obtained with other simulators.

Xu, Tianfu

2006-04-17

301

High temperature chemical kinetic study of the H2-CO-CO2-NO reaction system  

NASA Technical Reports Server (NTRS)

An experimental study of the kinetics of the H2-CO-CO2-NO reaction system was made behind incident shock waves at temperatures of 2460 and 2950 K. The overall rate of the reaction was measured by monitoring radiation from the CO + O yields CO2 + h upoilon reaction. Correlation of these data with a detailed reaction mechanism showed that the high-temperature rate of the reaction N + OH yields NO + H can be described by the low-temperature (320 K) rate coefficient. Catalytic dissociation of molecular hydrogen was an important reaction under the tests conditions.

Jachimowski, C. J.

1975-01-01

302

Chlorination and oxidation of heparin and hyaluronan by hypochlorous acid and hypochlorite anions: effect of sulfate groups on reaction pathways and kinetics.  

PubMed

Hypochlorous acid (HOCl), produced in inflammatory conditions by the enzyme myeloperoxidase, and its anion hypochlorite (OCl(-)) exist in vivo at almost equal concentrations. Their reactions with hyaluronan and heparin (as a model for sulfated glycosaminoglycans in the extracellular matrix) have been studied as a function of pH. The major product in these reactions is the chloramide derivative of the glycosaminoglycans. Spectral, chloramide yield, and kinetic measurements show sharply contrasting behavior of heparin and hyaluronan and the data allow the calculation of second-order rate constants for the reactions of both HOCl and OCl(-) for all reaction pathways leading to the formation of chloramides and also oxidation products. By comparison with hyaluronan, it can be demonstrated that both N-sulfate and O-sulfate groups in heparin influence the proportions of these pathways in this glycosaminoglycan. Evidence is also given for further oxidation pathways involving a reaction of HOCl with the chloramide product of hyaluronan but not with heparin. The significance of these results for the mechanisms of inflammation, particularly for fragmentation of extracellular matrix glycosaminoglycans, is discussed. PMID:23220380

Akeel, Almabrok; Sibanda, Sambulelwe; Martin, Stephen W; Paterson, Andrew W J; Parsons, Barry J

2013-03-01

303

Kinetics of reactions of derivatives of bischloromethylphosphinic acid with amines  

Microsoft Academic Search

The authors have made a kinetic study of nucleophilic replacement of chlorine by an amino group in derivatives of bischloromethylphosphinic acid. The process takes place by an SN1-mechanism in the case of weak nucleophilic reagents (the aniline type) and by an Sn2-mechanism in the case of strong nucleophilic reagents (benzylamine type).

M. K. Il'ina; I. M. Shermergorn

1969-01-01

304

NO sub x char reactions: Kinetics and transport aspects  

Microsoft Academic Search

The carbon selected for study was derived from a phenol-formaldehyde resin, the oxidation kinetics (with Oâ) of which had been extensively studied previously. This material has been shown to be a reasonable model for coal chars, but without the complexity associated with the heterogeneity of coal and its possibly catalytic mineral components. In the first phases of the project, the

J. M. Calo; E. M. Suuberg; H. Teng; I. D. Milosavljevic

1990-01-01

305

Kinetics of reactions catalyzed by enzymes in solutions of surfactants  

Microsoft Academic Search

The effect of surfactants, both in water-in-oil microemulsions (hydrated reverse micelles) and aqueous solutions upon enzymatic processes is reviewed, with special emphasis on the effect of the surfactant upon the kinetic parameters of the process. Differences and similarities between processes taking place in aqueous and organic solvents are highlighted, and the main models currently employed to interpret the results are

María A. Biasutti; Elsa B. Abuin; Juana J. Silber; N. Mariano Correa; Eduardo A. Lissi

2008-01-01

306

NO sub x char reactions: Kinetics and transport aspects  

Microsoft Academic Search

The principal goal of this project is to develop a mechanistic understanding of the processes by which carbons reduce NO to Nâ. The reaction of interest may be represented by the non-stoichiometric equation: C + NO â CO, COâ, Nâ. The relative yields of CO and COâ depend upon the reaction conditions, as will be described below. The carbon selected

J. M. Calo; E. M. Suuberg; H. Teng; I. D. Milosavljevic

1990-01-01

307

NO sub x char reactions: Kinetics and transport aspects  

Microsoft Academic Search

The present project is motivated by the need to reduce NOâ emissions from combustors, especially coal combustors. Reactions with carbon are known to be effective at reducing No to Nâ, and remain interesting candidates in a wide variety of possible applications. These reactions are known to be important in reducing NOâ emissions from fluidized bed coal combustors, in which the

J. M. Calo; E. M. Suuberg

1990-01-01

308

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

309

New approach to thermal analysis kinetics by considering several first order reactions  

Microsoft Academic Search

An approach to thermal decomposition kinetics is proposed in which it is assumed that the thermal decomposition of a given material is produced by a large, but finite, number of first order reactions. Initially a set of first order reaction “covering” the thermal analysis curves is selected. Usually between 500 and 1500 first order curves are generated. Then, the problem

José A. Caballero; Juan A. Conesa

2011-01-01

310

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

Microsoft Academic Search

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

311

A normative framework for the study of second-order sensitivity in vision.  

PubMed

While the contrast sensitivity approach has been successful in evaluating the processing of first-order stimuli, there is a need to develop comparable ways of assessing second-order vision. Our purpose here is to establish normative data on second-order contrast-, orientation-, and motion-modulation sensitivity in humans. We propose a unified framework, applying the quick contrast sensitivity function (qCSF) method, which was recently developed for the rapid measurement of contrast sensitivity across the full spatial-frequency range (Lesmes, Lu, Baek, & Albright, 2010), to measure both first- and second-order sensitivity functions. We first show that the qCSF methodology can be successfully adapted to different kinds of first- and second-order measurements. We provide a normative dataset for both first- and second-order sensitivity, and we show that the sensitivity to all these stimuli is equal in the two eyes. Our results confirm some strong differences between first- and second-order processing, in accordance with the classical filter-rectify-filter model. They suggest a common contrast detection mechanism but different second-order mechanisms. PMID:25096156

Reynaud, Alexandre; Tang, Yong; Zhou, Yifeng; Hess, Robert F

2014-01-01

312

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

SciTech Connect

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

313

The Locomotor Activity of Fish: An Analogy to the Kinetics of an Opposed First-Order Chemical Reaction  

Microsoft Academic Search

The kinetic behavior of a laboratory population of bluegill (Lepomis macrochirus) under defined laboratory conditions is shown to be analogous to the reaction kinetics described by a population of molecules engaged in an opposed (reversible) first-order reaction. Thus as in chemical kinetics, the locomotor activity of fish can be described quantitatively in the form of rate constants.

Erik G. Ellgaard; Kerry S. Bloom; Anthony A. Malizia JR; Gerald E. Gunning; Richard E. Jensen

1975-01-01

314

A comparison of pedestal effects in first- and second-order patterns.  

PubMed

The human visual system is sensitive to both luminance (first-order) and contrast (second-order) modulations in an image. A linear-nonlinear-linear model is commonly used to explain visual processing of second-order patterns. Here we used a pattern-masking paradigm to compare first-order and second-order visual mechanisms and to characterize the nonlinear properties underlying them. The carriers were either a high-frequency horizontal grating (8 c/°) or a binary random dot pattern; they were either added to a vertical low-frequency (2 c/°) sinusoidal grating (first-order stimuli) or multiplied by it (second-order stimuli). The incremental discrimination threshold of the target was measured with pedestals whose spatial properties matched those of the target, with the exception of contrast (in the first-order pedestal) or modulation depth (in the second-order pedestal). The threshold function showed a typical dipper shape for both first- and second-order stimuli. The results for the first-order stimuli with different types of carrier and the second-order stimuli with a grating carrier were well explained by a divisive inhibition model in which the facilitatory input was divided by the sum of broadband inhibitory inputs. The results for the second-order stimuli with a random-dot carrier were explained by a modified divisive inhibition model that operated on modulation depth. Our results suggest that divisive inhibition is required to explain visual discrimination in both first- and second-order patterns. However, the source and nonlinearity of the divisive inhibition may be different for these two types of patterns and carrier. PMID:24413392

Huang, Pi-Chun; Chen, Chien-Chung

2014-01-01

315

Chlorination of bisphenol A: kinetics and by-products formation  

Microsoft Academic Search

The kinetics of initial chlorination of bisphenol A (BPA) was studied between pH 2 and 11 at room temperature (20±2 °C). pH Profile of the apparent second-order rate constant of the reaction of BPA with chlorine were modeled considering the elementary reactions of HOCl with BPA species and an acid-catalyzed reaction. The predominant reactions at near neutral pH were the

Hervé Gallard; Amélie Leclercq; Jean-Philippe Croué

2004-01-01

316

KEMOD: A mixed chemical kinetic and equilibrium model of aqueous and solid phase geochemical reactions  

SciTech Connect

This report presents the development of a mixed chemical Kinetic and Equilibrium MODel in which every chemical species can be treated either as a equilibrium-controlled or as a kinetically controlled reaction. The reaction processes include aqueous complexation, adsorption/desorption, ion exchange, precipitation/dissolution, oxidation/reduction, and acid/base reactions. Further development and modification of KEMOD can be made in: (1) inclusion of species switching solution algorithms, (2) incorporation of the effect of temperature and pressure on equilibrium and rate constants, and (3) extension to high ionic strength.

Yeh, G.T.; Iskra, G.A. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Civil Engineering; Szecsody, J.E.; Zachara, J.M.; Streile, G.P. [Pacific Northwest Lab., Richland, WA (United States)

1995-01-01

317

Kinetic and mechanistic studies of free-radical reactions in combustion  

SciTech Connect

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

318

Using temperature-programmed reaction for kinetic analysis of reactions in dilute aqueous solutions at high pressure  

SciTech Connect

The technique of temperature-programmed reaction (TPR) is shown to be a practical experimental method for determining reaction-rate expressions and kinetics parameters for reactions in dilute aqueous solutions under high ambient pressure. By sampling and measuring the extent of reaction during a rise in temperature, information normally obtained from a series of isothermal batch kinetics experiments can be found in a single TPR test. The use of nonlinear least-squares regression eliminates the need to achieve a constant rate of temperature rise, simplifies the experimental requirements for TPR results, and gives more accurate answers than does a linear analysis of TPR results. Numerical simulations of TPR tests in the presence of random concentration-measurement error is used to assess the accuracy of the technique and to identify the best values of crucial operating parameters. The results of two TPR experiments measuring the alkaline hydrolysis of ethyl acetate demonstrate the applicability of the technique to reactions in dilute aqueous solutions at high pressure. These preliminary experimental results, along with numerical simulations, allow us to chart a course for future TPR kinetics experiments on a large number of similar reactions. 16 refs., 6 figs., 8 tabs.

Brown, L.F.; Robinson, B.A.

1986-01-01

319

The making of an Alfvenic fluctuation: The resolution of a second-order analysis  

NASA Astrophysics Data System (ADS)

Ulysses observations of the high speed polar streams show that they are largely occupied by very large amplitude Alfvenic fluctuations accompanied by many rotational discontinuities. These fluctuations have a nearly constant magnetic intensity or amplitude, and the magnetic field direction per wave cycle sweeps only through a limited arc, much as a car wiperblade would do. Barnes and Hollweg (JGR, 79, 2302, 1974) suggested that this unusual waveform could arise from an obliquely propagating and linearly polarized Alfven wave of finite amplitude. From a second-order analysis, they showed that the existence of a particular solution with a constant amplitude but could not resolve the outcome of the homogeneous solution which consisted of fast waves. They suggested that Landau damping of these fast waves may be needed to get the observed waveform. We present a 1 1/2 D hybrid simulation which is fully nonlinear and correctly describes the ion kinetics for an initially monochromatic and linearly polarized Alfven wave propagating obliquely to the background magnetic field. The wave has a large amplitude and a wavelength so long that it can be considered dispersionless for simulation times. At early times, the second harmonic in density and in magnetic field transverse to the initial wave magnetic field are generated and have more power than other harmonics. Steepening is observed with a weak fast shock emerging, but no rotational discontinuity is left behind, and instead a constant amplitude and an arc-shaped waveform is made. The compressional component which develops after the shocks have dissipated is to zeroth order better described as a pure acoustic wave than as a fast wave. This might be explained by the relaxing of the Alfven wave to a state where its ponderomotive force vanishes so that the compressional component can travel almost independently of it.

Vasquez, Bernard J.; Hollweg, Joseph V.

1995-06-01

320

Density Functional Theory and Reaction Kinetics Studies of the Water–Gas Shift Reaction on Pt–Re Catalysts  

SciTech Connect

Periodic, self-consistent density functional theory calculations (DFT-GGA-PW91) on Pt(111) and Pt3Re(111) surfaces, reaction kinetics measurements, and microkinetic modeling are employed to study the mechanism of the water–gas shift (WGS) reaction over Pt and Pt–Re catalysts. The values of the reaction rates and reaction orders predicted by the model are in agreement with the ones experimentally determined; the calculated apparent activation energies are matched to within 6% of the experimental values. The primary reaction pathway is predicted to take place through adsorbed carboxyl (COOH) species, whereas formate (HCOO) is predicted to be a spectator species. We conclude that the clean Pt(111) is a good representation of the active site for the WGS reaction on Pt catalysts, whereas the active sites on the Pt–Re alloy catalyst likely contain partially oxidized metal ensembles.

Carrasquillo-Flores, Ronald; Gallo, Jean Marcel R.; Hahn, Konstanze; Dumesic, James A.; Mavrikakis, Manos

2013-12-01

321

Proton-transfer reactions. 5. Observed primary kinetic isotope effect that increases with increasing temperature  

Microsoft Academic Search

The reactions of substituted ..beta.., ..beta..-difluorostyrene with methanolic sodium methoxide to yield carbanions are reported. Product ratios for reaction in pure MeOD and MeOH are used to calculate the primary kinetic isotope effect (PKIE) associated with proton transfer from methanol to neutralize the carbanions. Compounds studied and their relative reaction rates at 25°C are recorded. A noted increase in PKIE

Heinz F. Koch; Andrew S. Koch

1984-01-01

322

An ab initio direct-trajectory study of the kinetic isotope effect on the bifurcating reaction  

Microsoft Academic Search

The isotope effects on the bifurcating reaction path of the isomerization reaction, H3CO-->H2COH (stereoisomers of P and P*), have been investigated recently [J. Chem. Phys. 113, 477 (2000)], and it was found that the valley-ridge inflection point appears in the totally symmetric direction relative to the intrinsic reaction coordinate in the deuterium-substituted system. In the present report, the kinetic isotope

Tetsuya Taketsugu; Yuko Kumeda

2001-01-01

323

Complete gauge-invariant formalism for arbitrary second-order perturbations of a Schwarzschild black hole  

SciTech Connect

Using recently developed efficient symbolic manipulations tools, we present a general gauge-invariant formalism to study arbitrary radiative (l{>=}2) second-order perturbations of a Schwarzschild black hole. In particular, we construct the second-order Zerilli and Regge-Wheeler equations under the presence of any two first-order modes, reconstruct the perturbed metric in terms of the master scalars, and compute the radiated energy at null infinity. The results of this paper enable systematic studies of generic second-order perturbations of the Schwarzschild spacetime, in particular, studies of mode-mode coupling and nonlinear effects in gravitational radiation, the second-order stability of the Schwarzschild spacetime, or the geometry of the black hole horizon.

Brizuela, David; Martin-Garcia, Jose M.; Tiglio, Manuel [Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid (Spain); Laboratoire Univers et Theories, Observatoire de Paris, CNRS, Universite Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France, and Institut d'Astrophysique de Paris, Universite Pierre et Marie Curie, CNRS, 98 bis boulevard Arago, 75014 Paris (France); Center for Scientific Computation and Mathematical Modeling and Center for Fundamental Physics, Department of Physics, University of Maryland, College Park, Maryland, 20742 (United States)

2009-07-15

324

Second-Order Nonlinearity in Triangular Lattice Perforated Gold Film due to Surface Plasmas Resonance  

PubMed Central

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

325

Second-order magneto-optic effects in anisotropic thin films.  

SciTech Connect

For films with in-plane anisotropy, second-order magneto-optic effects proportional to the square of the spin-orbit interaction can manifest themselves. We report typical measurements of the second-order magneto-optic Kerr effect in Fe, Co, and NiFe thin films with in-plane anisotropy and compare to theoretical predictions based on an interband transition model. We conclude that intraband transitions must play a role at 1.96 eV. The second-order magneto-optic effects provide interesting insights into the magnetization reversal process, and also describe the dielectric tensor of a ferromagnetic metal. Furthermore, since the second-order magneto-optic effect is connected with the asymmetry of the magneto-optic hysteresis loop, which arises as a result of the coherent rotation of the magnetization vector, we interpret such asymmetries, which have been previously reported in the literature.

Osgood, R. M., III; Bader, S. D.; Clemens, B. M.; White, R. L.; Matsuyama, H.; Materials Science Division; Stanford Univ.; Hitachi, Ltd.

1998-01-01

326

Blind Separation of Noisy Multivariate Data Using Second-Order Statistics: Remote-Sensing Applications  

E-print Network

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.

327

Estimating Second Order Ionospheric Delays During GPS-LEO Radio Occultation Observations: An Alternative Approach  

NASA Astrophysics Data System (ADS)

The demand for millimeter accuracy in Global Positioning System (GPS) applications (receiver and precise point positioning) has raised a considerable interest in studying second order ionospheric delays. Unlike first order, second order ionospheric delays are functions of both, the Total Electron Content (TEC), and the geomagnetic field along the integrated signal path between the transmitter (GPS) and the receiver. The standard method of computing second order ionospheric delays makes use of ionosphere (IRI-2007) and magnetic field models (IGRF-10). We propose a different approach in estimating second order ionospheric delays, based solely on dual frequency GPS raw ionospheric excess phase delays. Specifically, our goal is twofold: (1) compute TEC free from second order ionospheric errors and (2) calculate geomagnetic field values along the integrated signal path between a GPS transmitter and a receiver. We apply our method to near-real time observational data provided by the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Data Analysis and Archive Centre (CDAAC), from which second order ionospheric delays can be realized. Second order ionospheric delays estimated based on our model attains values between -9 mm and 16 mm, which is larger than the values obtained for ground-based GPS observations. Currently, TEC estimations are based on differencing dual frequency GPS ionospheric excess phase delays, without accounting for second order ionospheric effects. We propose an alternative approach according to which we model the observed carrier-phase observables (L1, L2) taking into account the geomagnetic field that is the source of the second order ionospheric effect. Subsequently, by combining linearly the GPS observables we can solve for the TEC that is free from the second order ionospheric affect. In a second step, we compute geomagnetic field values along the integrated signal path between a GPS transmitter and a receiver based on the Faraday rotation effect, taking advantage of the relation between the rotation angle of the polarization plane of the GPS signal and the Earth's magnetic field. We analyze 30 COSMIC ionospheric radio occultation (RO) events in 2006, 2007 and 2008 and show that our results are in a very good agreement with the IGRF-10 model within 0.2% and 9%. We also demonstrate that the weighted mean geomagnetic field along a GPS-LEO integrated signal path during an RO event is conservative, as it has been assumed by many researchers when estimating second order ionospheric delays, but never proven.

Vergados, P.; Pagiatakis, S. D.

2009-05-01

328

Investigating local network interactions underlying first- and second-order processing  

Microsoft Academic Search

We compared the spatial lateral interactions for first-order cues to those for second-order cues, and investigated spatial inter- actions between these two types of cues. We measured the apparent modulation depth of a target Gabor at fixation, in the presence and the absence of horizontally flanking Gabors. The Gabors' gratings were either added to (first-order) or multiplied with (second- order)

Dave Ellemberg; Harriet A. Allen; Robert F. Hess

2004-01-01

329

Algorithms and design for a second-order automatic differentiation module  

SciTech Connect

This article describes approaches to computing second-order derivatives with automatic differentiation (AD) based on the forward mode and the propagation of univariate Taylor series. Performance results are given that show the speedup possible with these techniques relative to existing approaches. The authors also describe a new source transformation AD module for computing second-order derivatives of C and Fortran codes and the underlying infrastructure used to create a language-independent translation tool.

Abate, J. [Univ. of Texas, Austin, TX (United States). Texas Inst. for Computational and Applied Mathematics; Bischof, C.; Roh, L. [Argonne National Lab., IL (United States). Mathematics and Computer Science Div.; Carle, A. [Rice Univ., Houston, TX (United States). Center for Research on Parallel Computation

1997-07-01

330

A new Lie systems approach to second-order Riccati equations  

E-print Network

This work presents a newly renovated approach to the analysis of second-order Riccati equations from the point of view of the theory of Lie systems. We show that these equations can be mapped into Lie systems through certain Legendre transforms. This result allows us to construct new superposition rules for studying second-order Riccati equations and to reduce their integration to solving (first-order) Riccati equations.

J. F. Cariñena; J. de Lucas; C. Sardón

2011-10-14

331

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

Microsoft Academic Search

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

332

Peripheral sensitivity to biological motion conveyed by first and second order signals  

Microsoft Academic Search

pThere is evidence that human observers are more sensitive to the direction-of-heading of point-light walkers defined by first-order than second-order motions. We addressed this question by measuring the minimum direction difference (azimuth) that observers could discriminate when the dots composing the walkers were conveyed by first or second-order motions. Sensitivity to azimuth differences for four stimulus types (two first-order and

Rick Gurnsey; Nikolaus F. Troje

2010-01-01

333

Dynamical Consensus Algorithm for Second-Order Multi-Agent Systems Subjected to Communication Delay  

NASA Astrophysics Data System (ADS)

To solve the dynamical consensus problem of second-order multi-agent systems with communication delay, delay-dependent compensations are added into the normal asynchronously-coupled consensus algorithm so as to make the agents achieve a dynamical consensus. Based on frequency-domain analysis, sufficient conditions are gained for second-order multi-agent systems with communication delay under leaderless and leader-following consensus algorithms respectively. Simulation illustrates the correctness of the results.

Liu, Cheng-Lin; Liu, Fei

2013-06-01

334

The second-order monostatic HF radar cross section incorporating antenna barge motion  

Microsoft Academic Search

The second-order HF radar ocean cross section is derived for the case of the transmitting and receiving antenna undergoing platform (i.e. barge) motion. The derivation for electromagnetic patch scatter begins with a general expression for the bistatically received second-order electric field. Based on an assumption that the ocean surface can be described as a Fourier series with coefficients being zero-mean

John Walsh; Weimin Huang; Eric Gill

2009-01-01

335

The steadily propagating crack in an elastic\\/power-law material: Second order solutions  

Microsoft Academic Search

We present second-order asymptotic solutions to the near-tip field for a crack propagating under steady-state, antiplane strain conditions in an elastic\\/power-law material. First-order solutions to this problem were originally given by Hui and Riedel. For values of the power-law exponent n < 3, the second-order solution is found to satisfy a linear, inhomogeneous equation. For n > 3, however, an

T. J. Delph; P. A. Blythe

1995-01-01

336

Anomalies and time reversal invariance in relativistic hydrodynamics: The second order and higher dimensional formulations  

Microsoft Academic Search

We present two new results on relativistic hydrodynamics with anomalies and external electromagnetic fields, ``chiral magnetohydrodynamics'' (CMHD). First, we study CMHD in four dimensions at second order in the derivative expansion assuming the conformal\\/Weyl invariance. We classify all possible independent conformal second order viscous corrections to the energy-momentum tensor and to the U(1) current in the presence of external electric

Dmitri E. Kharzeev; Ho-Ung Yee

2011-01-01

337

A stable second-order mass-weighted upwind scheme for unstructured meshes  

NASA Astrophysics Data System (ADS)

In this paper, an original second-order upwind scheme for convection terms is described and implemented in the context of a Control-Volume Finite-Element Method (CVFEM).The proposed scheme is a second-order extension of the first-order MAss-Weighted upwind (MAW) scheme proposed by Saabas and Baliga (Numer. Heat Transfer 1994; 26B:381-407). The proposed second-order scheme inherits the well-known stability characteristics of the MAW scheme, but exhibits less artificial viscosity and ensures much higher accuracy. Consequently, and in contrast with nearly all second-order upwind schemes available in the literature, the proposed second-order MAW scheme does not need limiters.Some test cases including two pure convection problems, the driven cavity and steady and unsteady flows over a circular cylinder, have been undertaken successfully to validate the new scheme.The verification tests show that the proposed scheme exhibits a low level of artificial viscosity in the pure convection problems; exhibits second-order accuracy for the driven cavity; gives accurate reattachment lengths for low-Reynolds steady flow over a circular cylinder; and gives constant-amplitude vortex shedding for the case of high-Reynolds unsteady flow over a circular cylinder.

Dung Tran, Luu; Masson, Christian; Smaïli, Arezki

2006-07-01

338

First-Principles-Based Reaction Kinetics for Decomposition of Hot, Dense Liquid TNT from ReaxFF Multiscale Reactive Dynamics  

E-print Network

. The activation energy of the initial endothermic decomposition rate and the subsequent exothermic reactions wereFirst-Principles-Based Reaction Kinetics for Decomposition of Hot, Dense Liquid TNT from Reax Supporting Information ABSTRACT: The reaction kinetics of the thermal decomposition of hot, dense liquid TNT

Goddard III, William A.

339

Kinetics of and intermediates in a photocycle branching reaction of the photoactive yellow protein from Ectothiorhodospira halophila  

E-print Network

/Vis spectroscopy. As compared to the parallel dark recovery reaction of the presumed blue-shifted signaling state pKinetics of and intermediates in a photocycle branching reaction of the photoactive yellow protein Abstract We have studied the kinetics of the blue light-induced branching reaction in the photocycle

van Stokkum, Ivo

340

Mechanism and kinetics of phase transitions and other reactions in solids  

E-print Network

The work is presented, leading to the universal contact molecular mechanism of phase transitions and other reactions in solid state. The two components of the mechanism - nucleation and interface propagation - are investigated in detail and their role in the kinetics is specified. They were shown to be peculiar: nucleation is "pre-coded", rather than resulted from a successful fluctuation, and the interface propagates by molecular filling of thin layers in the transverse direction. The structure of the nucleation sites is determined. The inherent instability and irreproducibility of the kinetics in question is revealed. A linear kinetics, as opposed to the bulk kinetics, is introduced and shown to be in accord with the contact mechanism. Ferromagnetic phase transition and magnetization are added to the list of solid-state reactions; neither occurs without structural rearrangement.

Yuri Mnyukh

2011-10-07

341

The Gaseous Explosive Reaction : A Study of the Kinetics of Composite Fuels  

NASA Technical Reports Server (NTRS)

This report deals with the results of a series of studies of the kinetics of gaseous explosive reactions where the fuel under observation, instead of being a simple gas, is a known mixture of simple gases. In the practical application of the gaseous explosive reaction as a source of power in the gas engine, the fuels employed are composite, with characteristics that are apt to be due to the characteristics of their components and hence may be somewhat complex. The simplest problem that could be proposed in an investigation either of the thermodynamics or kinetics of the gaseous explosive reaction of a composite fuel would seem to be a separate study of the reaction characteristics of each component of the fuel and then a study of the reaction characteristics of the various known mixtures of those components forming composite fuels more and more complex. (author)

Stevens, F W

1929-01-01

342

Anomalous kinetics in diffusion limited reactions linked to non-Gaussian concentration probability distribution function  

NASA Astrophysics Data System (ADS)

We investigate anomalous reaction kinetics related to segregation in the one-dimensional reaction-diffusion system A + B --> C. It is well known that spatial fluctuations in the species concentrations cause a breakdown of the mean-field behavior at low concentration values. The scaling of the average concentration with time changes from the mean-field t-1 to the anomalous t-1/4 behavior. Using a stochastic modeling approach, the reaction-diffusion system can be fully characterized by the multi-point probability distribution function (PDF) of the species concentrations. Its evolution is governed by a Fokker-Planck equation with moving boundaries, which are determined by the positivity of the species concentrations. The concentration PDF is in general non-Gaussian. As long as the concentration fluctuations are small compared to the mean, the PDF can be approximated by a Gaussian distribution. This behavior breaks down in the fluctuation dominated regime, for which anomalous reaction kinetics are observed. We show that the transition from mean field to anomalous reaction kinetics is intimately linked to the evolution of the concentration PDF from a Gaussian to non-Gaussian shape. This establishes a direct relationship between anomalous reaction kinetics, incomplete mixing and the non-Gaussian nature of the concentration PDF.

de Anna, Pietro; Le Borgne, Tanguy; Dentz, Marco; Bolster, Diogo; Davy, Philippe

2011-11-01

343

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

E-print Network

LIBRARY A A N COLLEGE OF TEXAS A KINETIC INVESTIGATION OI" TIIE RFACTION OF DIBUTYL SODIOITIOSPHONATE II'ITH N BUTYL BROIIllDE A Thesis By James Howard Shaffer Submitted to the Oraduate School of the Agricultural and Mechanical College... 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...

Shaffer, James Howard

2012-06-07

344

Reduction of iron oxide in carbon monoxide atmosphere—reaction controlled kinetics  

Microsoft Academic Search

Thermogravimetric analysis (TGA) of the reduction of Fe2O3 in a continuous stream of 100% CO was conducted at temperatures ranging from 800 to 900 °C. X-ray diffraction analysis of solids identified the presence of iron, graphite and a carbide of iron as the products of reactions. A kinetic model based on the first-order irreversible rate kinetics was developed and fitted

K. Mondal; H. Lorethova; E. Hippo; T. Wiltowski; S. B. Lalvani

2004-01-01

345

A kinetic mechanism inducing oscillations in simple chemical reactions networks  

E-print Network

, for example, cell cycle [1], Ca+ -induced oscillations [8], glycolysis [15, 20, 14], yeast metabolic cycle [19 for this work) is given by ATP in the glycolysis pathway [20]. ATP is a cofactor in some of the reaction steps (e.g. in the step catalyzed by Hexokinase: glucose - glucose-6-phosphate) while a too high

Altafini, Claudio

346

Relative rates and kinetic isotope effects of reactions in solution  

Microsoft Academic Search

Making and breaking chemical bonds is often less important than encounter as a contributor to the overall barrier. Curvature can have an intrinsic component which is associated with changes in rate and equilibrium constants for the proton-transfer step, as well as a coupling component which arises from coupling of proton transfer with other steps in the overall reaction. It is

Joseph R. Murdoch

1980-01-01

347

Reaction of benzophenone UV filters in the presence of aqueous chlorine: kinetics and chloroform formation.  

PubMed

The transformation of two benzophenone UV filters (Oxybenzone and Dioxybenzone) was examined over the pH range 6-11 in the presence of excess aqueous chlorine. Under these conditions, both UV filters were rapidly transformed by aqueous chlorine just above circumneutral pH while transformation rates were significantly lower near the extremes of the pH range investigated. Observed first-order rate coefficients (k(obs)) were obtained at each pH for aqueous chlorine concentrations ranging from 10 to 75 ?M. The k(obs) were used to determine the apparent second-order rate coefficient (k(app)) at each pH investigated as well as determine the reaction order of aqueous chlorine with each UV filter. The reaction of aqueous chlorine with either UV filter was found to be an overall second-order reaction, first-order with respect to each reactant. Assuming elemental stoichiometry described the reaction between aqueous chlorine and each UV filter, models were developed to determine intrinsic rate coefficients (k(int)) from the k(app) as a function of pH for both UV filters. The rate coefficients for the reaction of HOCl with 3-methoxyphenol moieties of oxybenzone (OXY) and dioxybenzone (DiOXY) were k(1,OxY) = 306 ± 81 M?¹s?¹ and k(1,DiOxY) = 154 ± 76 M?¹s?¹, respectively. The k(int) for the reaction of aqueous chlorine with the 3-methoxyphenolate forms were orders of magnitude greater than the un-ionized species, k(2,OxY) = 1.03(±0.52) × 10? M?¹s?¹ and k(2_1,DiOxY) = 4.14(±0.68) × 10? M?¹s?¹. Also, k(int) for the reaction of aqueous chlorine with the DiOXY ortho-substituted phenolate moiety was k(2_2,DiOxY) = 2.17(±0.30) × 10³ M?¹s?¹. Finally, chloroform formation potential for OXY and DiOXY was assessed over the pH range 6-10. While chloroform formation decreased as pH increased for OXY, chloroform formation increased as pH increased from 6 to 10 for DiOXY. Ultimate molar yields of chloroform per mole of UV filter were pH dependent; however, chloroform to UV filter molar yields at pH 8 were 0.221 CHCl?/OXY and 0.212 CHCl?/DiOXY. PMID:23168312

Duirk, Stephen E; Bridenstine, David R; Leslie, Daniel C

2013-02-01

348

An assessment of the role of nonlinear reaction kinetics in parameterization of metamorphic fluid flow  

NASA Astrophysics Data System (ADS)

on inverse modeling of reaction progress data using a numerical framework that considers coupled advection and diffusion, linear and nonlinear reaction kinetics, and with effective diffusivity given by Archie's law, we show that (1) choice of reaction order has little effect (<0.3 orders of magnitude) on estimates of time-integrated and time-averaged metamorphic fluid fluxes and metamorphic fluid flow durations based on reaction progress data, (2) reaction order must be known for robust determination of time-averaged net reaction rates based on reaction progress data and that underestimation of this term by more than 3 orders of magnitude can arise from assuming linear reaction kinetics, (3) differing reaction orders between laboratory experiments and natural metamorphic systems and/or a nonlinear dependence of effective diffusivity on porosity can explain order-of-magnitude discrepancies between field-based and laboratory-based estimates of time-averaged net reaction rates, and (4) parameterization of metamorphic fluid flow is limited to time-averaged values which fail to account for the possibility that metamorphism occurs in short-lived pulses during longer time periods of metamorphic quiescence.

Zhao, Zhihong; Skelton, Alasdair

2014-08-01

349

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

350

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

351

Kinetics of the reaction between oxygen atoms and allyl radicals  

Microsoft Academic Search

The reaction between CâHâ and O(³P) has been studied over the temperature range 300-600 K by using two time-resolved techniques: laser flash photolysis of CâHâBr\\/SOâ\\/He mixtures at 193 nm with detection by photoionization mass spectrometry, and laser flash photolysis of CâHââ\\/NâO\\/Nâ mixtures at 193 nm using absorption spectroscopy and resonance fluorescence to detect CâHâ and O, respectively. A temperature and

I. R. Slagle; J. R. Bernhardt; D. Gutman; M. A. Hanning-Lee; M. J. Pilling

1990-01-01

352

Fundamentals, kinetics and endothermicity of the biomass pyrolysis reaction  

Microsoft Academic Search

The paper reviews the pyrolysis of biomass constituents and possible secondary reactions. Biomass pyrolysis yields mostly liquid and solid fuel, easy to store and transport.Relevant working conditions for experiments and large-scale operation are: (i) biomass particles<200?m, (ii) a particle heating rate of at least about 80Kmin?1 and (iii) a reactor environment where the internal resistance to heat penetration is smaller

Manon Van de Velden; Jan Baeyens; Anke Brems; Bart Janssens; Raf Dewil

2010-01-01

353

Kinetics of the reaction of KO 2 with LiCl  

Microsoft Academic Search

1.The authors have studied the kinetics of the reaction of KO2 with LiCl in mixtures of various compositions at 200–260°.2.In the kinetic range the main product is Li2O2. The apparent activation energy of the process E˜19 kcal\\/M.3.For the reaction period accompanied by a decrease in Li2O2, E˜43 kcal\\/M.4.An excess of LiCl in the initial mixture increases the rate of formation

A. B. Tsentsiper; Z. I. Kuznetsova

1967-01-01

354

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 of the corresponding decay reactions. Using finite heat bath theory we calculate from these data the binding energies of the decaying cluster ions.

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

355

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

356

Low Temperature Kinetics of the CH3OH + OH Reaction  

PubMed Central

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

Martin, J. C. Gomez; Caravan, R. L.; Blitz, M. A.; Heard, D. E.; Plane, J. M. C.

2014-01-01

357

On the complexity of kinetics and the mechanism of the thiosulfate-periodate reaction.  

PubMed

The thiosulfate-periodate reaction has been studied spectrophotometrically in a slightly acidic medium at 25.0 ± 0.1 °C in an acetate/acetic acid buffer by monitoring the absorbance in the 250-600 nm wavelength range at a constant ionic strength adjusted by the buffer component sodium acetate. In agreement with a previous study, we found that the reaction cannot be described by a single stoichiometric equation, tetrathionate and sulfate are simultaneously formed, and its ratio strongly depends on the pH. As expected at certain initial concentration ratios of the reactants, the reaction behaves as a clock reaction, but after its appearance, iodine is slowly consumed mainly because of the moderate tetrathionate-iodine reaction. It is also enlightened that the initial rate of the reaction is completely independent of the pH, which apparently contradicts a previous study, which postulates a "supercatalytic" behavior of the hydrogen ion on the title reaction. Significant buffer assistance that may change the absorbance-time profiles was also observed. On the basis of the kinetic data, a robust 28-step kinetic model with 22 fitted parameters is proposed and discussed to explain adequately all of the important characteristics of the kinetic curves. PMID:21612189

Rauscher, Evelin; Cseko, György; Horváth, Attila K

2011-06-20

358

Kinetics and Equilibria Involving Copper and Oxygen in Germanium  

Microsoft Academic Search

Germanium solutions supersaturated with respect to both oxygen and copper have been investigated in the range 300–500°C by means of conductivity and Hall effect measurements. Kinetics results indicate that the initial rates of disappearance of holes is second order in both the Cu and the O concentrations. The failure of the hole mobility to increase with degree of reaction suggests

C. S. Fuller; K. B. Wolfstrin

1962-01-01

359

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

360

Democratic decisions establish stable authorities that overcome the paradox of second-order punishment.  

PubMed

Individuals usually punish free riders but refuse to sanction those who cooperate but do not punish. This missing second-order peer punishment is a fundamental problem for the stabilization of cooperation. To solve this problem, most societies today have implemented central authorities that punish free riders and tax evaders alike, such that second-order punishment is fully established. The emergence of such stable authorities from individual decisions, however, creates a new paradox: it seems absurd to expect individuals who do not engage in second-order punishment to strive for an authority that does. Herein, we provide a mathematical model and experimental results from a public goods game where subjects can choose between a community with and without second-order punishment in two different ways. When subjects can migrate continuously to either community, we identify a bias toward institutions that do not punish tax evaders. When subjects have to vote once for all rounds of the game and have to accept the decision of the majority, they prefer a society with second-order punishment. These findings uncover the existence of a democracy premium. The majority-voting rule allows subjects to commit themselves and to implement institutions that eventually lead to a higher welfare for all. PMID:24367116

Hilbe, Christian; Traulsen, Arne; Röhl, Torsten; Milinski, Manfred

2014-01-14

361

Nitrogen dioxide reactions with 46 atomic main-group and transition metal cations in the gas phase: room temperature kinetics and periodicities in reactivity.  

PubMed

Experimental results are reported for the gas-phase room-temperature kinetics of chemical reactions between nitrogen dioxide (NO(2)) and 46 atomic main-group and transition metal cations (M(+)). Measurements were taken with an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer in helium buffer gas at a pressure of 0.35 ± 0.01 Torr and at 295 ± 2 K. The atomic cations were produced at ca. 5500 K in an ICP source and allowed to decay radiatively and to thermalize to room temperature by collisions with Ar and He atoms prior to reaction with NO(2). Measured apparent bimolecular rate coefficients and primary reaction product distributions are reported for all 46 atomic metal cations and these provide an overview of trends across and down the periodic table. Three main types of reactions were observed: O-atom transfer to form either MO(+) or NO(+), electron transfer to form NO(2)(+), and addition to form MNO(2)(+). Bimolecular O-atom transfer was observed to predominate. Correlations are presented between reaction efficiency and the O-atom affinity of the metal cation and between the prevalence of NO(+) product formation and the electron recombination energy of the product metal oxide cation. Some second-order reactions are evident with metal cations that react inefficiently. Most interesting of these is the formation of the MNO(+) cation with Rh(+) and Pd(+). The higher-order chemistry with NO(2) is very diverse and includes the formation of numerous NO(2) ion clusters and a number of tri- and tetraoxide metal cations. Group 2 metal dioxide cations (CaO(2)(+), SrO(2)(+), BaO(2)(+)) exhibit a unique reaction with NO(2) to form MO(NO)(+) ions perhaps by NO transfer from NO(2) concurrent with O(2) formation by recombination of a NO(2) and an oxide oxygen. PMID:22894764

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

2013-02-14

362

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

363

Diastereoselectivity and kinetics of hetero diels-alder reactions under high pressure  

Microsoft Academic Search

The Hetero Diels-Alder reaction of enamino ketones and ethyl vinyl ether to give dihydropyrans is studied in different solutions under pressure up to 7 kbar. The kinetics is measured via on-line FT IR spectroscopy. The cycloaddition shows a remarkable pressure dependent increase in diastereo-selectivity. For the difference in activation volumes referring to the reaction to the two diastereomers, values up

L. F. Tietze; Th. Hübsch; M. Buback; W. Tost

1990-01-01

364

Kinetics and products of the reaction of diazo compounds with SO 2  

Microsoft Academic Search

Data were obtained on the composition of products and kinetics of the reaction of SO2 with Ph(R)CN2 (R=Ph, Me) in solutions of isooctane, 1,4-di-oxane, and ethanol at 295 K. A mechanism was proposed for the process in accordance with which the sulfene being formed participates in concurrent reactions with the starting reagents. The relative rate constants for the process stages

A. M. Nazarov; A. I. Nikolaev; S. Yu. Serenko; V. D. Komissarov

1990-01-01

365

The kinetics of the nitrogen reaction with liquid iron-Sulfur alloys  

Microsoft Academic Search

An experimental apparatus was designed and constructed which permits utilization of both the modified Sieverts' technique\\u000a and the isotope exchange technique for study of the kinetics of ni-trogen reaction with liquid iron alloys. Experimental results\\u000a from the two techniques are used in con-junction with the current knowledge in the field to readdress several persisting questions\\u000a dealing with the nitrogen reaction.

P. C. Glaws; R. J. Fruehan

1985-01-01

366

Kinetic reactions of calcium, phosphate, and fluoride ions at the enamel surface-solution interface  

Microsoft Academic Search

Surfaces of tooth enamel were interfaced with recirculating solutions containing calcium and phosphate. The kinetic interfacial reactions of calcium, phosphate, fluoride, and hydrogen ions were determined in solutions of constant fluoride ion concentrations (0.012, 0.025, 0.050, 0.250, or 0.500 mM\\/l) and \\/or constant pH (6.8, 7.0, 7.2, or 7.4). The rates of the calcium, phosphate, fluoride, and hydrogen ion reactions

F. F. Feagin; M. Gonzalez; B. G. Jeansonne

1972-01-01

367

Antenna excited state decay kinetics establish primary electron transfer in reaction centers as heterogeneous.  

PubMed

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

368

Studies of Reaction Kinetics of Methane Hydrate Dissocation in Porous Media  

SciTech Connect

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

369

A Quasi-Lie Schemes Approach to Second-Order Gambier Equations  

NASA Astrophysics Data System (ADS)

A quasi-Lie scheme is a geometric structure that provides t-dependent changes of variables transforming members of an associated family of systems of first-order differential equations into members of the same family. In this note we introduce two quasi-Lie schemes for studying second-order Gambier equations in a geometric way. This allows us to study the transformation of these equations into simpler canonical forms, which solves a gap in the previous literature, and other relevant differential equations, which leads to derive new constants of motion for families of second-order Gambier equations. Additionally, we describe general solutions of certain second-order Gambier equations in terms of particular solutions of Riccati equations, linear systems, and t-dependent frequency harmonic oscillators.

Cariñena, José F.; Guha, Partha; de Lucas, Javier

2013-03-01

370

Spectral methods for the wave equation in second-order form  

SciTech Connect

Current spectral simulations of Einstein's equations require writing the equations in first-order form, potentially introducing instabilities and inefficiencies. We present a new penalty method for pseudospectral evolutions of second order in space wave equations. The penalties are constructed as functions of Legendre polynomials and are added to the equations of motion everywhere, not only on the boundaries. Using energy methods, we prove semidiscrete stability of the new method for the scalar wave equation in flat space and show how it can be applied to the scalar wave on a curved background. Numerical results demonstrating stability and convergence for multidomain second-order scalar wave evolutions are also presented. This work provides a foundation for treating Einstein's equations directly in second-order form by spectral methods.

Taylor, Nicholas W.; Teukolsky, Saul A. [Center for Radiophysics and Space Research, Cornell University, Ithaca, New York 14853 (United States); Theoretical Astrophysics 350-17, California Institute of Technology, Pasadena, California 91125 (United States); Kidder, Lawrence E. [Center for Radiophysics and Space Research, Cornell University, Ithaca, New York 14853 (United States)

2010-07-15

371

First- and Second-Order Full-Differential in Edge Analysis of Images  

PubMed Central

Two concepts of first- and second-order differential of images are presented to deal with the changes of pixels. These are the basic ideas in mathematics. We propose and reformulate them with a uniform definition framework. Based on our observation and analysis with the difference, we propose an algorithm to detect the edge from image. Experiments on Corel5K and PASCAL VOC 2007 are done to show the difference between the first order and the second order. After comparison with Canny operator and the proposed first-order differential, the main result is that the second-order differential has the better performance in analysis of changes of the context of images with good selection of control parameter. PMID:25054162

Pu, Dong-Mei; Yuan, Yu-Bo

2014-01-01

372

The second-order interference of two independent single-mode He-Ne lasers  

E-print Network

The second-order spatial and temporal interference patterns with two independent single-mode He-Ne lasers are observed in a Hong-Ou-Mandel interferometer. Two-photon interference in Feynman's path integral theory is employed to interpret the experimental results. The conditions to observe the second-order interference pattern with two independent single-mode continuous wave lasers are discussed. It is concluded that two-photon interference exists for not only identical photons, but also photons with different spectrums if the detection system can not distinguish them in principle. The second-order temporal beating with two independent lasers can be employed to measure the coherence time and frequency of one laser if the properties of the other laser were known.

Jianbin Liu; Minglan Le; Bin Bai; Wentao Wang; Hui Chen; Yu Zhou; Fu-Li Li; Zhuo Xu

2014-10-08

373

A Damped Gauss-Newton Method for the Second-Order Cone Complementarity Problem  

SciTech Connect

We investigate some properties related to the generalized Newton method for the Fischer-Burmeister (FB) function over second-order cones, which allows us to reformulate the second-order cone complementarity problem (SOCCP) as a semismooth system of equations. Specifically, we characterize the B-subdifferential of the FB function at a general point and study the condition for every element of the B-subdifferential at a solution being nonsingular. In addition, for the induced FB merit function, we establish its coerciveness and provide a weaker condition than Chen and Tseng (Math. Program. 104:293-327, 2005) for each stationary point to be a solution, under suitable Cartesian P-properties of the involved mapping. By this, a damped Gauss-Newton method is proposed, and the global and superlinear convergence results are obtained. Numerical results are reported for the second-order cone programs from the DIMACS library, which verify the good theoretical properties of the method.

Pan Shaohua [South China University of Technology, School of Mathematical Sciences (China)], E-mail: shhpan@scut.edu.cn; Chen, J.-S. [National Taiwan Normal University, Department of Mathematics (China)], E-mail: jschen@math.ntnu.edu.tw

2009-06-15

374

Boltzmann hierarchy for the cosmic microwave background at second order including photon polarization  

SciTech Connect

Non-Gaussianity and B-mode polarization are particularly interesting features of the cosmic microwave background, as--at least in the standard model of cosmology--their only sources to first order in cosmological perturbation theory are primordial, possibly generated during inflation. If the primordial sources are small, the question arises how large is the non-Gaussianity and B-mode background induced in second order from the initially Gaussian and scalar perturbations. In this paper we derive the Boltzmann hierarchy for the microwave background photon phase-space distributions at second order in cosmological perturbation theory including the complete polarization information, providing the basis for further numerical studies. As an aside we note that the second-order collision term contains new sources of B-mode polarization and that no polarization persists in the tight-coupling limit.

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

2010-09-15

375

Use of the particle swarm optimization algorithm for second order design of levelling networks  

NASA Astrophysics Data System (ADS)

The weight problem in geodetic networks can be dealt with as an optimization procedure. This classic problem of geodetic network optimization is also known as second-order design. The basic principles of geodetic network optimization are reviewed. Then the particle swarm optimization (PSO) algorithm is applied to a geodetic levelling network in order to solve the second-order design problem. PSO, which is an iterative-stochastic search algorithm in swarm intelligence, emulates the collective behaviour of bird flocking, fish schooling or bee swarming, to converge probabilistically to the global optimum. Furthermore, it is a powerful method because it is easy to implement and computationally efficient. Second-order design of a geodetic levelling network using PSO yields a practically realizable solution. It is also suitable for non-linear matrix functions that are very often encountered in geodetic network optimization. The fundamentals of the method and a numeric example are given.

Yetkin, Mevlut; Inal, Cevat; Yigit, Cemal Ozer

2009-08-01

376

Sum Frequency Vibrational Spectroscopy: The Molecular Origins of the Optical Second-Order Nonlinearity of Collagen  

PubMed Central

The molecular origins of second-order nonlinear effects in type I collagen fibrils have been identified with sum-frequency generation vibrational spectroscopy. The dominant contributing molecular groups are: 1), the methylene groups associated with a Fermi resonance between the fundamental symmetric stretch and the bending overtone of methylene; and 2), the carbonyl and peptide groups associated with the amide I band. The noncentrosymmetrically aligned methylene groups are characterized by a distinctive tilt relative to the axis perpendicular to the main axis of the collagen fiber, a conformation producing a strong achiral contribution to the second-order nonlinear effect. In contrast, the stretching vibration of the carbonyl groups associated with the amide I band results in a strong chiral contribution to the optical second-order nonlinear effect. The length scale of these chiral effects ranges from the molecular to the supramolecular. PMID:17766339

Rocha-Mendoza, Israel; Yankelevich, Diego R.; Wang, Mingshi; Reiser, Karen M.; Frank, Curt W.; Knoesen, Andre

2007-01-01

377

Second-Order Belief Attribution in Williams Syndrome: Intact or Impaired?  

PubMed Central

Second-order mental state attribution in a group of children with Williams syndrome was investigated. The children were compared to age, IQ, and language-matched groups of children with Prader-Willi syndrome or nonspecific mental retardation. Participants were given two trials of a second-order reasoning task. No significant differences between the Williams syndrome and Prader-WiIli or mentally retarded groups on any of the test questions were found. Results contrast with the view that individuals with Williams syndrome have an intact theory of mind and suggest that in their attributions of second-order mental states, children with Williams syndrome perform no better than do other groups of children with mental retardation. PMID:10587733

Sullivan, Kate; Tager-Flusberg, Helen

2005-01-01

378

Consistency of Equations in the Second-Order Gauge-Invariant Cosmological Perturbation Theory  

NASA Astrophysics Data System (ADS)

Along the general framework of the gauge-invariant perturbation theory developed in the papers [K.~Nakamura, Prog.~Theor.~Phys. 110 (2003), 723; Prog.~Theor.~Phys. 113 (2005), 481], we rederive the second-order Einstein equation on four-dimensional homogeneous isotropic background universe in a gauge-invariant manner without ignoring any mode of perturbations. We consider the perturbations both in the universe dominated by the single perfect fluid and in that dominated by the single scalar field. We also confirmed the consistency of all the equations of the second-order Einstein equation and the equations of motion for matter fields, which are derived in the paper [K.~Nakamura, arXiv:0804.3840]. This confirmation implies that all the derived equations of the second order are self-consistent and these equations are correct in this sense.

Nakamura, K.

2009-06-01

379

First- and second-order full-differential in edge analysis of images.  

PubMed

Two concepts of first- and second-order differential of images are presented to deal with the changes of pixels. These are the basic ideas in mathematics. We propose and reformulate them with a uniform definition framework. Based on our observation and analysis with the difference, we propose an algorithm to detect the edge from image. Experiments on Corel5K and PASCAL VOC 2007 are done to show the difference between the first order and the second order. After comparison with Canny operator and the proposed first-order differential, the main result is that the second-order differential has the better performance in analysis of changes of the context of images with good selection of control parameter. PMID:25054162

Pu, Dong-Mei; Yuan, Yu-Bo

2014-01-01

380

Part A: Nonprincipal-plane scattering from flat plates: Second-order and corner diffractions  

NASA Technical Reports Server (NTRS)

Two models of a flat plate for nonprincipal-plane scattering are explored. The first is a revised version of the Physical Optics/Physical Theory of Diffraction (PO/PTD) model with second-order PTD equivalent currents included to account for second-order interactions among the plate edges. The second model uses a heurisitcally derived corner diffraction coefficient to account for the corner scattering mechanism. The patterns obtained using the newer models were compared to the data of previously reported models, the Moment Method (MM), and experimental results. Near normal incidence, all the models agreed; however, near grazing incidence a need for higher-order and corner diffraction mechanisms was noted. In many instances the second-order and corner-scattered fields which were formulated improved the results.

Balanis, Constantine A.; Polka, Lesley A.

1989-01-01

381

The second-order interference of two independent single-mode He-Ne lasers  

E-print Network

The second-order spatial and temporal interference patterns with two independent single-mode He-Ne lasers are observed in a Hong-Ou-Mandel interferometer. Two-photon interference in Feynman's path integral theory is employed to interpret the experimental results. The conditions to observe the second-order interference pattern with two independent single-mode continuous wave lasers are discussed. It is concluded that two-photon interference exists for not only identical photons, but also photons with different spectrums if the detection system can not distinguish them in principle. The second-order temporal beating with two independent lasers can be employed to measure the coherence time and frequency of one laser if the properties of the other laser were known.

Liu, Jianbin; Bai, Bin; Wang, Wentao; Chen, Hui; Zhou, Yu; Li, Fu-Li; Xu, Zhuo

2014-01-01

382

Time-dependent Second Order Scattering Theory for Weather Radar with a Finite Beam Width  

NASA Technical Reports Server (NTRS)

Multiple scattering effects from spherical water particles of uniform diameter are studied for a W-band pulsed radar. The Gaussian transverse beam-profile and the rectangular pulse-duration are used for calculation. An second-order analytical solution is derived for a single layer structure, based on a time-dependent radiative transfer theory as described in the authors' companion paper. When the range resolution is fixed, increase in footprint radius leads to increase in the second order reflectivity that is defined as the ratio of the second order return to the first order one. This feature becomes more serious as the range increases. Since the spaceborne millimeter-wavelength radar has a large footprint radius that is competitive to the mean free path, the multiple scattering effect must be taken into account for analysis.

Kobayashi, Satoru; Tanelli, Simone; Im, Eastwood; Ito, Shigeo; Oguchi, Tomohiro

2006-01-01

383

Shot-Noise Seeded Microbunching Instability: Second-Order Correction to the Gain Function  

SciTech Connect

We determine the second-order correction to the gain function of the microbunching instability in single-pass systems of interest for the next generation of light sources. The calculation applies to the case where the instability is seeded by shot noise. We examine an analytically treatable model of beam dynamics where collective forces are active only in non-dispersive sections of the linac. We find that the second order term can augment the linear gain significantly while affecting the spectrum of the overall gain only marginally. The weight of the second-order correction relative to the linear gain is found to scale quadratically with respect to R56. The qualitative behavior predicted by the model is consistent with exact numerical solutions of the Vlasov equations for realistic lattices.

Venturini, Marco

2008-06-30

384

Reactions of yeast thioredoxin peroxidases I and II with hydrogen peroxide and peroxynitrite: Rate constants by competitive kinetics  

Microsoft Academic Search

Peroxiredoxins are receiving increasing attention as defenders against oxidative damage and sensors of hydrogen peroxide-mediated signaling events. Likely to be critical for both functions is a rapid reaction with hydrogen peroxide, typically with second-order rate constants higher than 105 M?1 s?1. Until recently, however, the values reported for these rate constants have been in the range of 104?105 M?1 s?1, including those

Renata Ogusucu; Daniel Rettori; Daniela Cristina Munhoz; Luis Eduardo Soares Netto; Ohara Augusto

2007-01-01

385

Kinetics of heterogeneously catalyzed tert-amyl methyl ether reactions in the liquid phase  

SciTech Connect

The kinetics of tert-amyl methyl ether (TAME, 2-methoxy-2-methylbutane) reactions was investigated using a commercial ion exchange resin (Amberlyst 16) as catalyst at temperatures between 324 and 354 K. The rates of reaction were determined experimentally in the liquid phase in a continuous stirred tank reactor at a pressure of 0.8 MPa. Kinetic equations derived for three different mechanisms were compared. In the forward reaction the adsorbed methanol reacted with isoamylene (2-methyl-l-butene or 2-methyl-2-butene) striking from the bulk liquid phase, and in the splitting reaction the adsorbed ether split to alcohol and isoamylene. The kinetic equations were written in terms of activities, and the activity coefficients were calculated by the UNIQUAC method. The activation energy was determined to be 95 kJ/mol for the splitting reaction of TAME to 2-methyl-l-butene and methanol and 100 kJ/mol for the splitting reaction of TAME to 2-methyl-2-butene and methanol.

Rihko, L.K.; Krause, A.O.I. [Helsinki Univ. of Technology, Espoo (Finland). Lab. of Industrial Chemistry

1995-04-01

386

Substitution reactions involving cyclometalated platinum(II) complexes: Kinetic investigations  

Microsoft Academic Search

Substitution reaction of the labile SMe2 ligand in the cyclometalated platinum(II) complexes of general formula [PtAr(ppy)(SMe2)], 1, in which ppy = deprotonated 2-phenylpyridyl and Ar = p-MeC6H4 or p-MeOC6H4, by several N or P donor reagents were studied; the N-donors, N, are pyridine (Py) and substituted pyridines, N = 4-MePy, Py, Py-d5, 2-MePy, 3-PhPy, 3,4-Me2Py, 4-tBuPy or 3-C(O)OMePy, and the P-donors, L, are phosphines or phosphites,

S. Masoud Nabavizadeh; Hamid R. Shahsavari; Masoud Namdar; Mehdi Rashidi

2011-01-01

387

Discrete integration of continuous Kalman filtering equations for time invariant second-order structural systems  

NASA Technical Reports Server (NTRS)

A general form for the first-order representation of the continuous second-order linear structural-dynamics equations is introduced to derive a corresponding form of first-order continuous Kalman filtering equations. Time integration of the resulting equations is carried out via a set of linear multistep integration formulas. It is shown that a judicious combined selection of computational paths and the undetermined matrices introduced in the general form of the first-order linear structural systems leads to a class of second-order discrete Kalman filtering equations involving only symmetric sparse N x N solution matrices.

Park, K. C.; Belvin, W. Keith

1990-01-01

388

Unifying intensity noise and second-order coherence properties of amplified spontaneous emission sources  

NASA Astrophysics Data System (ADS)

We present joint investigations of relative intensity noise (RIN) and second-order coherence properties of amplified spontaneous emission (ASE) generated by a superluminescent diode. We introduce a generalized intensity noise description for ASE sources that contains the shot noise contribution but also accounts for first- and second-order coherence properties reflecting the process of light generation. We find excellent agreement between pump-current-dependent RIN values and this new description, with the perspective of particular interesting consequences for the realization of low-noise broadband emitters.

Blazek, Martin; Hartmann, Sébastien; Molitor, Andreas; Elsaesser, Wolfgang

2011-09-01

389

Imaging in scattering media via the second-order correlation of light field  

E-print Network

Imaging with the second-order correlation of two light fields is a method to image an object by two-photon interference involving a joint detection of two photons at distant space-time points. We demonstrate for the first time that an image with high quality can still be obtained in the scattering media by applying the second-order correlation of illuminating light field. The scattering effect on the visibility of images is analyzed both theoretically and experimentally. Potential applications and the methods to further improve the visibility of the images in scattering media are also discussed.

Wenlin Gong; Pengli Zhang; Xia Shen; Shensheng Han

2009-08-03

390

Qualitative Analysis in a Second-Order Impact Model for Forest Fires  

NASA Astrophysics Data System (ADS)

Natural forest fires are the problems that influence ecosystems, and they have been researched from of old. For solving this problem, a prediction model for forest fires was proposed. The model imitates fires that are seen in mediterranean forests, boreal forests and savannas. In recent years, it was simplified a second-order impact model. Furthermore, the model of mediterranean forests have been analyzed. However, the others are insufficient yet, and the qualitative property of forest fires has not been discussed enough. In this letter, we analyze the second-order impact model that is seen in boreal forests and savannas. Moreover, we consider what bifurcation phenomena essentially influences some periodic solutions.

Tomonaga, Shingo; Kousaka, Takuji

391

Test of the second order asymptotic theory with low degree solar gravity modes  

SciTech Connect

Further testing of first and second order asymptotic theory predictions for solar gravity modes is possible with the work of gu and Hill in which the number of classified low-degree gravity mode multiplets was increased from 31 to 53. In an extension of the work where the properties of 31 multiplets were analyzed in the framework of first order asymptotic theory, a new analysis has been performed using the properties of the 53 classified multiplets. The result of this analysis again shows the inadequacy of first order asymptotic theory for describing the eigenfrequency spectrum and clearly demonstrates the necessity of using second order asymptotic theory. 30 refs.

Barry, C.T.; Rosenwald, R.D.; Gu, Y.; Hill, H.A

1988-01-01

392

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

E-print Network

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

Jenks, Richard Lee

2012-06-07

393

ON STEPFUNCTION REACTION KINETICS MODEL IN THE ABSENCE OF MATERIAL DIFFUSION  

E-print Network

Abstract. We propose a precise definition of the step-function kinetics suitable for approxi- mating Background and Existing Modeling Approaches. In this paper we give a precise definition of the step rate coupled with the exothermicity of the reaction must be sufficient to overcome heat losses

Golovaty, Dmitry

394

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

395

Nonisothermal Thermal Decomposition Reaction Kinetics of Double-base Propellant Catalyzed with Lanthanum Citrate  

Microsoft Academic Search

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

396

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

397

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

398

Racing carbon atoms. Atomic motion reaction coordinates and structural effects on Newtonian kinetic isotope effects.  

PubMed

Intramolecular (13)C kinetic isotope effects were determined for the dimerization of methacrolein. Trajectory studies accurately predict the isotope effects and support an origin in Newton's second law of motion, with no involvement of zero-point energy or transition state recrossing. Atomic motion reaction coordinate diagrams are introduced as a way to qualitatively understand the selectivity. PMID:23025278

Andujar-De Sanctis, Ivonne L; Singleton, Daniel A

2012-10-19

399

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

400

STUDY OF Cr(VI) \\/ TERTIARY AMINE REACTION KINETICS USING A MODIFIED ROTATING DIFFUSION CELL  

Microsoft Academic Search

An investigation of the equilibrium and kinetic behaviour of Radiamine 6366, a tertiary amine dissolved in decane extracting Cr(VI) from acid solution is presented. Equilibrium and interfacial reaction models were used to describe the results obtained from shake tests and a modified Rotating Diffusion Cell. The modified cell allowed on-line measurement of the concentration in the aqueous phase. A second

P. J Harrington; G. W Stevens

2000-01-01

401

KINETICS OF GAS-GRAIN REACTIONS IN THE SOLAR NEBULA BRUCE FEGLEY, JR.  

E-print Network

KINETICS OF GAS-GRAIN REACTIONS IN THE SOLAR NEBULA BRUCE FEGLEY, JR. Planetary Chemistry the local en- vironment cooled significantly or before the gaseous solar nebula was dispersed indicates that troilite formation proceeded to completion in the solar nebula. Magnetite formation was much

Fegley Jr., Bruce

402

Setting Reactions in Dental Amalgam Part 2. the Kinetics of Amalgamation  

Microsoft Academic Search

The literature on the setting mechanisms of dental amalgams made from powders of silver-rich alloys of tin and\\/or copper has been critically reviewed. Part 2 is a review of the kinetics of the reactions that convert the mixture of alloy powder and liquid mercury to hardened amalgam containing the phases and microstructures described in Part I . It is emphasized

T. Okabe; R. J. Mitchell

1996-01-01

403

Reaction kinetics and reactor modeling for fuel processing of liquid hydrocarbons to produce hydrogen: isooctane reforming  

Microsoft Academic Search

A mathematical model was developed in the framework of the process simulator Aspen Plus® in order to describe the reaction kinetics and performance of a fuel processor used for autothermal reforming of liquid hydrocarbons. Experimental results obtained in the facilities of Argonne National Laboratories (ANL) when reforming isooctane using a ceria-oxide catalyst impregnated with platinum were used in order to

Manuel Pacheco; Jorge Sira; John Kopasz

2003-01-01

404

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

E-print Network

believed to cause fuel formation for in-situ combustion have been studied and modeled. A thin, packed bedPaper Number 15736-PA Title Reaction Kinetics of Fuel Formation for In-Situ Combustion Authors Abu-Khamsin, Sidqi A., Stanford U.; Brigham, William E., Stanford U.; Ramey Jr., Henry J., Stanford U. Journal SPE

Abu-Khamsin, Sidqi

405

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

406

A comprehensive detailed chemical kinetic reaction mechanism for combustion of nalkane  

E-print Network

A comprehensive detailed chemical kinetic reaction mechanism for combustion of nalkane 94550, USA b University College of Ireland, Galway, Ireland Abstract Detailed chemical, published in "Combustion and Flame 156 (2008) 181-199" DOI : 10.1016/j.combustflame.2008.07.014 #12

Paris-Sud XI, Université de

407

Racing Carbon Atoms. Atomic Motion Reaction Coordinates and Structural Effects on Newtonian Kinetic Isotope Effects  

PubMed Central

Intramolecular 13C kinetic isotope effects were determined for the dimerization of methacrolein. Trajectory studies accurately predict the isotope effects and support an origin in Newton’s second law of motion, with no involvement of zero-point energy or transition state recrossing. Atomic motion reaction coordinate diagrams are introduced as a way to qualitatively understand the selectivity. PMID:23025278

Andujar-De Sanctis, Ivonne L.

2012-01-01

408

Ab initio study on carbon Kinetic Isotope Effect (KIE) in the reaction of CH4+Cl  

Microsoft Academic Search

Recent studies suggest that the destruction of methane by Cl• in the marine boundary layer could be accounted for as another major sink besides the methane destruction by OH•. High level ab initio molecular orbital calculations have been carried out to study the CH4+Cl• reaction, the carbon Kinetic Isotope Effect (KIE) is calculated using Conventional Transition-State Theory (CTST) plus Wigner

Noriyuki Tanaka; Yitian Xiao; Antonio C. Lasaga

1996-01-01

409

Measurement of Condensed-Phase Reaction Kinetics in the Aerosol Phase Using Single Particle Mass Spectrometry  

E-print Network

-power pulsed laser in the extraction field of the time-of-flight mass spectrometer. The mass spectra thusMeasurement of Condensed-Phase Reaction Kinetics in the Aerosol Phase Using Single Particle Mass mass spectrometer to analyze the elemental composition of individual aerosol particles and applied

Zachariah, Michael R.

410

Studies of NO-char reaction kinetics obtained from drop-tube furnace and thermogravimetric experiments  

SciTech Connect

Four coal chars were prepared in a flat flame flow reactor (FFR), which can simulate the temperature and gas composition of a real pulverized coal combustion environment. The pore structure of chars was measured by mercury porosimetry and nitrogen adsorption, and the Hg and Brunauer-Emmett-Teller (BET) surface areas were obtained. The kinetics of NO-char was studied in a drop-tube furnace (DTF) and thermogravimetric analyzer (TGA). In the TGA experiments, the random pore model (RPM) was applied to describe the NO-char reactions and obtain the intrinsic kinetics. By presenting the data of DTF and TGA experiments on the same Arrhenius plot, it can be concluded that TGA is an available tool to study the kinetics of a high-temperature NO-char reaction. With respect to the DTF experiments, in comparison to the BET surface area, the Hg surface area is a better basis for normalizing the reactivity of different coal chars because of less scatter in the measured values, better agreement with TGA experimental data, and more stable values during the process of reaction. Moreover, by comparing the Hg surface area of chars before and after reactions, it is believed that the Hg surface area basis is more appropriate for high-rank coal chars. The determined kinetic rate constants are in good agreement with other data in the literature, and a new rate constant expression is proposed. 30 refs., 8 figs., 7 tabs.

Shaozeng Sun; Juwei Zhang; Xidong Hu; Shaohua Wu; Jiancheng Yang; Yang Wang; Yukun Qin [Harbin Institute of Technology, Harbin (China). Combustion Engineering Research Institute

2009-01-15

411

Supporting Information A Fast Kinetics Study of the Reactions of Transient Silylenes with Alcohols. Direct  

E-print Network

. The insets show transient decay traces recorded at monitoring wavelengths of 300 and 570 nm. S3 #12;S2 Figure subtracting the second spectrum from the first. The insets show transient decay traces recorded at monitoringSupporting Information A Fast Kinetics Study of the Reactions of Transient Silylenes with Alcohols

Leigh, William J.

412

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

E-print Network

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

Paris-Sud XI, Université de

413

A Molecular Reaction Cycle with a Solvatochromic Merocyanine Dye: An Experiment in Photochemistry, Kinetics, and Catalysis.  

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

414

Nucleophilic activation of carbon monoxide. A kinetics investigation of the reaction of chloride with triruthenium dodecacarbonyl  

SciTech Connect

Kinetics studies of the reaction of the triruthenium cluster Ru[sub 3](CO)[sub 12] with the [open quotes]highly dissociated[close quotes] chloride salt [PPN]Cl to give the Ru[sub 3](CO)[sub 11]Cl[sup [minus

Lillis, J.; Rokicki, A.; Chin, T.; Ford, P.C. (Univ. of California, Santa Barbara, CA (United States))

1993-11-10

415

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

416

Laboratory support for in situ gasification: reaction kinetics. Annual report October 1977-September 1978  

SciTech Connect

This work is directed toward support studies for the national program for the development and demonstration of in situ coal gasification processes. The objective of this work is to determine the reaction-controlling variables and reaction kinetics for the gasification of chars obtained by pyrolyzing coal in simulated underground gasification conditions. The reactions being studied and to be studied include steam-char, CO/sub 2/-char, H/sub 2/-char, the water-gas shift reaction, and the methanation reaction. In this report are presented data regarding the kinetics of the reaction of steam with chars prepared from Pittsburgh seam high-volatile bituminous coal. In addition, a reaction model is described correlating the steam-char reaction rates measured earlier for Hanna subbituminous coal with operating conditions including temperature, partial pressures of steam and hydrogen, and extent of carbon gasification. Partial results are presented and discussed for an investigation of structural parameters of Hanna char as a function of pyrolysis conditions and extent of carbon gasified.

Young, J.E.; Wong, S.H.; Johnson, J.E.; Sikand, N.; Jonke, A.A.

1980-02-01

417

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

PubMed

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

418

Control of Mass Transport and Chemical Reaction Kinetics in Ultrasmall Volumes  

NASA Astrophysics Data System (ADS)

This talk will describe means for triggering chemical reactions for studying reaction kinetics under extreme confinement with sub-millisecond temporal resolution, including on-demand generation and fusion of femtoliter (10-15 L) volume water-in-oil droplets, and triggering reactions in femtoliter chambers microfabricated in poly(dimethylsiloxane) (PDMS). We demonstrated a reversible chemical toggle switch, which lays the groundwork for exploring more complex chemical and biochemical reaction sequences triggered and monitored in real time in discrete ultrasmall reactors, such as sequential and coupled enzymatic reactions. We are also developing methods to vary confinement and macromolecular crowding in ultrasmall, water-in-oil droplets and chambers micromolded in PDMS as biomimetic reaction vessels containing minimal synthetic gene circuits, in order to better understand how confinement, reduced dimensionality and macromolecular crowding affect molecular mechanisms involved in the operation and regulation of genetic circuits in living cells.

Collier, Charles

2012-02-01

419

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

420

Reaction kinetics for the oxygen hydrogenation process on Pt(111) derived from temperature-programmed XPS  

NASA Astrophysics Data System (ADS)

Oxygen hydrogenation under ultra high vacuum conditions at the platinum surface was explored using temperature-programmed X-ray photoelectron spectroscopy. Through modeling of the oxygen consumption, information on the reaction kinetics was obtained indicating that the reaction rate of the oxygen hydrogenation process depends on the hydrogen diffusion and on the lifetime of hydroxyl intermediates. The reaction rate is, however, enhanced when an autocatalytic process stabilizes the hydroxyl intermediates through hydrogen bonding to neighboring water molecules. The overall activation energy for the hydrogenation of atomic oxygen to form water was determined to be 0.20 eV with a frequency factor of only 103 s- 1.

Näslund, Lars-Åke

2013-12-01

421

Kinetics for the reaction of hydrogen with a plutonium-1 weight percent gallium alloy powder  

SciTech Connect

Kinetics for the reaction of hydrogen with plutonium-1 w/o gallium were measured using powder prepared ''in situ.'' The rates obeyed a first-order rate law and were independent of temperature from -29/degree/ to 355/degree/C. A pressure dependence proportional to P/sup //one-half/ was observed at pressures less than 1 kPa. From 1 to 70 kPa the pressure dependence rapidly decreased. Total pressure dependence could be accurately described by a Langmuir equation. Results indicate an adsorption-controlled reaction at low pressures and a reaction-controlled process at high pressure. 19 refs.

Stakebake, J.L.

1981-11-01

422

Kinetics and products of the reactions of NO sub 3 with monoalkenes, dialkenes, and monoterpenes  

SciTech Connect

Rate constants for the reactions of NO{sub 3} with a number of aliphatic mono- and dialkenes and monoterpenes have been determined in a 420 1 reaction chamber at 1-bar total pressure of synthetic air by 298 K with a relative kinetic method. The products of these reactions have been investigated also at 1-bar total pressure of synthetic air with in situ FT-IR spectrometry and gas chromatography. In all cases, the initial formation of thermally unstable nitrooxy-peroxynitrate-type compounds containing the difunctional group -CH(OONO{sub 2})-CH(ONO{sub 2})- has been observed.

Barnes, I.; Bastian, V.; Becker, K.H.; Tong, Zhu (Bergische Universitaet, Wuppertal (West Germany))

1990-03-22

423

A general approach to mechanism in multiproduct reactions: product-specific intermolecular kinetic isotope effects.  

PubMed

Here we report a general method for the measurement of (13)C kinetic isotope effects at natural abundance for reactions that yield two or more products concurrently. We use, as an example, a recently reported Co-catalyzed reaction between cyclopentene and 1-phenyl-1-propyne. High-precision intermolecular (13)C isotope effects are reported for both the formal [2+2] cycloaddition (major) and Alder-ene (minor) reaction products. Mechanistic possibilities that are in accord with observed isotope effect measurements are discussed. PMID:24721128

Xiang, Shuhuai; Meyer, Matthew P

2014-04-23

424

Kinetics of hydrogen peroxide--sulfur(IV) reaction in rainwater collected at a northeastern U. S. Site  

Microsoft Academic Search

The kinetics of the reaction of dissolved S(IV) with HâOâ was studied in freshly collected precipitation samples in order to examine whether there exist any important influences on this reaction from trace constituents present in natural atmospheric liquid water, that is, rainwater and snowmelt. The kinetic study was carried out on over 300 freshly collected precipitation samples obtained at Brookhaven

Y.-N. Lee; J. Shen; P. J. Klotz; S. E. Schwartz; L. Newman

1986-01-01

425

Effects of diffusion boundary layer on reaction kinetics of immunoassay in a biosensor  

NASA Astrophysics Data System (ADS)

Specific binding reaction is a natural characteristic that is applied to design biosensors. This work simulates the binding reaction kinetics of two commonly used proteins, C-reactive protein and immunoglobulin G, in a reaction chamber (microchannel) of a biosensor. For a diffusion-limited protein, the diffusion boundary layer on the reaction surface of the biosensor would hinder the binding reaction from association and dissociation. Several crucial factors, which influence the binding reaction curves in the simulation, are discussed, including the concentration of analyte, the inlet flow velocity, the channel height, and the length of the reaction surface. A higher channel causes the diffusive transport of the analyte to take longer time to reach the reaction surface, which in turn decreases the reaction rate of the protein pairs. The length of the reaction surface plays an important role in the formation of the boundary layer. For longer reaction surface, it takes more time to allow diffusion to overcome the larger zone of the diffusion boundary layer, resulting in a slower binding rate and a longer time to reach saturation. The presented data of simulation are useful in designing the biosensors.

Yang, Chih-Kai; Chang, Jeng-Shian; Chao, Sheng D.; Wu, Kuang-Chong

2008-04-01

426

Enzyme catalysis in microgravity: steady-state kinetic analysis of the isocitrate lyase reaction.  

PubMed

Two decades of research in microgravity have shown that certain biochemical processes can be altered by weightlessness. Approximately 10 years ago, our team, supported by the European Space Agency (ESA) and the Agenzia Spaziale Italiana, started the Effect of Microgravity on Enzyme Catalysis project to test the possibility that the microgravity effect observed at cellular level could be mediated by enzyme reactions. An experiment to study the cleavage reaction catalyzed by isocitrate lyase was flown on the sounding rocket MASER 7, and we found that the kinetic parameters were not altered by microgravity. During the 28th ESA parabolic flight campaign, we had the opportunity to replicate the MASER 7 experiment and to perform a complete steady-state analysis of the isocitrate lyase reaction. This study showed that both in microgravity and in standard g controls the enzyme reaction obeyed the same kinetic mechanism and none of the kinetic parameters, nor the equilibrium constant of the overall reaction were altered. Our results contrast with those of a similar experiment, which was performed during the same parabolic flight campaign, and showed that microgravity increased the affinity of lipoxygenase-1 for linoleic acid. The hypotheses suggested to explain this change effect of the latter were here tested by computer simulation, and appeared to be inconsistent with the experimental outcome. PMID:12568939

Ranaldi, Francesco; Vanni, Paolo; Giachetti, Eugenio

2003-01-21

427

Kinetics of CH3S(-) reaction with in situ ferrate(VI) in aqueous alkaline solution.  

PubMed

This study introduced a new treatment process named "in situ ferrate(VI) oxidation (IFO)" in which odorous compounds such as CH3S(-) can be quickly degraded by in situ freshly generated ferrate(VI) through electrolysis in aqueous alkaline solution. Two kinetic models to describe the in situ ferrate(VI) generation and its reaction with CH3S(-) were established mathematically by considering three main reaction mechanisms of ferrate(VI) electrochemical generation, ferrate(VI) self-decomposition and CH3S(-) degradation in aqueous strong alkaline solution. The effects of three key factors: (i) NaOH concentration, (ii) applied current density, and (iii) initial CH3S(-) concentration on the performance of the IFO process were investigated by conducting three sets of experiments and the kinetic models were validated by fitting the experimental data. The goodness of the fittings demonstrated that the new models could well describe both the kinetics of ferrate(VI) generation reaction and CH3S(-) degradation reaction. The experimental results confirmed that the higher NaOH concentration and current density applied would be beneficial to the electrochemical generation of ferrate(VI) and also elimination of its self-decomposition, but the experiments also demonstrated an optimum NaOH concentration at 10M to achieve the best performance of CH3S(-) degradation reaction in such an IFO system. PMID:23725753

Ding, Ling; Li, Xiang-Zhong; Lee, Shun-Cheng

2013-08-01

428

Kinetics of the ferrous/ferric electrode reaction in the absence of chloride catalysis  

SciTech Connect

The kinetics of the ferrous ferric redox electrode reaction has been investigated by many workers as a simple, uncomplicated charge transfer reaction which seems ideal for testing experimental techniques and charge transfer theories. However, it has only recently been understood that very small traces of chloride can have a considerable effect on the reaction rate. The relation between the chloride content of the solution and the rate constant of the ferrous/ferric reaction on a gold electrode in perchloric acid solutions is confirmed in this work. The chloride effect free apparent standard rate constant is found to be 2.2 x 10/sup -5/ cm s/sup -1/, which is two to three orders of magnitude smaller than the rate constants normally reported for this reaction if the chloride content of the solution is not scrupulously controlled. Measurements were carried out by using two different in situ methods for cleaning the working electrode surface rather than employing extensive solution purification. In the first method the measuring electrode was potentiostated at sufficiently negative potentials to desorb the chloride from the surface followed by a potential step to the equilibrium potential and a pulse measurement of the kinetics. In the second method chloride ions were removed from the surface before and during the kinetic measurement by continuous oxidation of chromous ions added in small concentration to the test solution. Good agreement was found among the rate constants determined by these methods and a reported rate constant determined in ultraclean solution.

Hung, N.C.; Nagy, Z.

1987-09-01

429

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

430

SECURE STEGANOGRAPHY: STATISTICAL RESTORATION OF THE SECOND ORDER DEPENDENCIES FOR IMPROVED SECURITY  

E-print Network

SECURE STEGANOGRAPHY: STATISTICAL RESTORATION OF THE SECOND ORDER DEPENDENCIES FOR IMPROVED practical approaches for steganography that can pro- vide improved security by closely matching the second steganalysis. We establish correspondence between steganography and the earth-mover's distance (EMD), a popular

Madhow, Upamanyu

431

ALTERNATIVE NONLINEAR MODEL FOR ESTIMATING SECOND-ORDER RATE COEFFICIENTS FOR BIODEGRADATION  

EPA Science Inventory

A modification of the second-order model for biodegradation was derived, applied to an example data set and shown to be superior for describing the anaerobic biodegradation of p-cresol by an enriched bacterial consortium. The modified model circumvents the no-growth assumption im...

432

Maximally confined high-speed second-order silicon microdisk switches.  

SciTech Connect

We demonstrate the first high-speed second-order silicon microdisk bandpass switch. The switch, constructed of a pair of 3 {micro}m radii active microdisks possesses {approx}40GHz flat-top passbands, a 4.2THz free-spectral-range, and a 2.4ns switching time.

Young, Ralph Watson; Trotter, Douglas Chandler; Watts, Michael R.

2008-03-01

433

Optimal energy conserving local discontinuous Galerkin methods for second-order wave equation in heterogeneous media  

E-print Network

propagation, local discontinuous Galerkin method, energy conserva- tion, optimal error estimate, heterogeneousOptimal energy conserving local discontinuous Galerkin methods for second-order wave equation in heterogeneous media Ching-Shan Chou1 , Chi-Wang Shu2 and Yulong Xing3 Abstract Solving wave propagation problems

Shu, Chi-Wang

434

Fundamenta Informaticae 88 (2008) 115 1 Second Order Fuzzy Measure and Weighted Co-Occurrence Matrix  

E-print Network

-Occurrence Matrix for Segmentation of Brain MR Images Pradipta Maji and Malay K. Kundu Machine Intelligence Unit images by splitting the image histogram into multiple crisp subsets. The histogram of the given image is thresholded according to the similarity between gray levels. The similarity is assessed through a second order

Kundu, Malay Kumar

435

Particle-particle and particle-wall interactions in a second-order fluid  

Microsoft Academic Search

The motion of a sphere normal to a wall is investigated. The normal stress at the surface of the sphere is calculated and the viscoelastic effects on the normal stress for different separation distances are analyzed. The contribution of the second-order fluid to the overall force applied to the particle is an attractive force towards the wall. Results are obtained

Arezoo M. Ardekani; Roger H. Rangel; Daniel D. Joseph

2007-01-01

436

Spatial control of second-order optical susceptibility induced in thermally poled glasses  

NASA Astrophysics Data System (ADS)

Second-order susceptibility thermally induced in poled glass samples was erased in doped borophosphate, lead silica, and fused silica glasses using an optical method. A simple law describes the temporal evolution and the spatial profile of the erased nonlinear region versus the intensity and profile of the erasure laser beam. A comparison is made between one and two photon absorption induced spatial profiles.

Guillet de Chatellus, H.; Montant, S.; Freysz, E.

2001-05-01

437

Lift on a sphere near a plane wall in a second-order fluid  

Microsoft Academic Search

In this paper, we examine the lift on a sphere moving very close to an infinite plane wall in a shear flow of a second-order fluid. The sphere is allowed to both translate and rotate along the plane. We focus on the limit when the sphere touches the wall. We found that due to the normal stress effect, the flow

Howard H. Hu; Daniel D. Joseph

1999-01-01

438

Why the SU(\\infty) phase transition might be of second order  

E-print Network

Based upon what is known about the phase transition(s) of an SU(3) gauge theory, we argue that in a SU(N_c) gauge theory without quarks, at nonzero temperature the deconfining phase transition is of second order when N_c \\geq 4.

Robert D. Pisarski; Michel Tytgat

1997-02-14

439

Sample Sizes for Two-Group Second-Order Latent Growth Curve Models  

ERIC Educational Resources Information Center

Second-order latent growth curve models (S. C. Duncan & Duncan, 1996; McArdle, 1988) can be used to study group differences in change in latent constructs. We give exact formulas for the covariance matrix of the parameter estimates and an algebraic expression for the estimation of slope differences. Formulas for calculations of the required sample…

Wanstrom, Linda

2009-01-01

440

Collective Electronic Oscillators for Second-Order Polarizabilities of Push-Pull Carotenoids  

E-print Network

Collective Electronic Oscillators for Second-Order Polarizabilities of Push-Pull Carotenoids and analyzed using a quasiparticle, collective electronic oscillators (CEO) representation. The few oscillators for the reduced single electron density matrix. The variations of these oscillators and the relevant

Mukamel, Shaul

441

Keep Your Distance! Using Second-Order Ordinary Differential Equations to Model Traffic Flow  

ERIC Educational Resources Information Center

A simple mathematical model for how vehicles follow each other along a stretch of road is presented. The resulting linear second-order differential equation with constant coefficients is solved and interpreted. The model can be used as an application of solution techniques taught at first-year undergraduate level and as a motivator to encourage…

McCartney, Mark

2004-01-01

442

Second order (F,a,q,d)-convexity and duality in multiobjective programming  

E-print Network

Second order (F,a,q,d)-convexity and duality in multiobjective programming I. Ahmad, Z. Husain.08.003 * Corresponding author. E-mail addresses: iahmad@postmark.net (I. Ahmad), zhusain@math.com (Z. Husain here is the following multiobjective nonlinear programming problem: I. Ahmad, Z. Husain / Information

Ahmad, Izahr

443

Anomalies and time reversal invariance in relativistic hydrodynamics: The second order and higher dimensional formulations  

SciTech Connect

We present two new results on relativistic hydrodynamics with anomalies and external electromagnetic fields, 'chiral magnetohydrodynamics' (CMHD). First, we study CMHD in four dimensions at second order in the derivative expansion assuming the conformal/Weyl invariance. We classify all possible independent conformal second order viscous corrections to the energy-momentum tensor and to the U(1) current in the presence of external electric and/or magnetic fields, and identify 18 terms that originate from the triangle anomaly. We then propose and motivate the following guiding principle to constrain the CMHD: the anomaly-induced terms that are even under the time-reversal invariance should not contribute to the local entropy production rate. This allows us to fix 13 out of the 18 transport coefficients that enter the second order formulation of CMHD. We also relate one of our second order transport coefficients to the chiral shear waves. Our second subject is hydrodynamics with (N+1)-gon anomaly in an arbitrary 2N dimensions. The effects from the (N+1)-gon anomaly appear in hydrodynamics at (N-1)th order in the derivative expansion, and we identify precisely N such corrections to the U(1) current. The time-reversal constraint is powerful enough to allow us to find the analytic expressions for all transport coefficients. We confirm the validity of our results (and of the proposed guiding principle) by an explicit fluid/gravity computation within the AdS/CFT correspondence.

Kharzeev, D.E.; Yee, H.-U.

2011-08-25

444

New Complex-Step Derivative Approximations with Application to Second-Order Kalman Filtering  

E-print Network

New Complex-Step Derivative Approximations with Application to Second-Order Kalman Filtering Kok extensions of the complex-step approximation to compute numerical derivatives. For first derivatives achieve near analytical accuracy. However, for second derivatives straight implementation of the complex

Crassidis, John L.

445

MULTIPLE SYMMETRIC POSITIVE SOLUTIONS FOR A SECOND ORDER BOUNDARY VALUE PROBLEM  

Microsoft Academic Search

For the second order boundary value problem, y00 + f(y )=0 , 0 t 1, y(0) = 0 = y(1), where f : R ! (0;1); growth conditions are imposed on f which yield the existence of at least three symmetric positive solutions.

JOHNNY HENDERSON; H. B. THOMPSON

2000-01-01

446

Second-order autocorrelation of XUV FEL pulses via time resolved two-photon single  

E-print Network

-5198, Japan *moshamme@mpi-hd.mpg.de Abstract: Second-order autocorrelation spectra of XUV free-electron laser of America OCIS codes: (030.1640) Coherence; (140.2600) Free-electron lasers (FELs); (340.7450) X the Free Electron Laser in Hamburg, FLASH," New J. Phys. 12(7), 073035 (2010). 2. N. Rohringer and R

Kling, Matthias

447

For Four Intercorrelated Variables: First- and Second-Order Partial Correlations  

NSDL National Science Digital Library

This page will calculate the first- and second-order partial correlations for four intercorrelated variables, W, X, Y, and Z. If you enter a value of N (providing N>9), the program will also calculate the values of t along with the associated two-tailed probability values.

Lowry, Richard, 1940-

2008-06-25

448

A test for second order stationarity of a time series based on the Discrete Fourier Transform  

E-print Network

A test for second order stationarity of a time series based on the Discrete Fourier Transform property, we construct a Portmanteau type test statistic for testing stationarity of the time series. It is shown that under the null of stationarity, the test statistic is approximately a chi square distribution

Subba Rao, Suhasini

449

Symmetries and invariants of the systems of two linear second-order ordinary differential equations  

NASA Astrophysics Data System (ADS)

For arbitrary systems of two linear second-order ordinary differential equations, the symmetry Lie algebra is described in terms of invariant theory, resulting in eleven non-equivalent symmetry types. The result is compared with the group classification approach recently obtained by different authors.

Bagderina, Yulia Yu.

2014-10-01

450

A SECOND-ORDER GODUNOV ALGORITHM FOR TWO-DIMENSIONAL SOLID MECHANICS  

E-print Network

A SECOND-ORDER GODUNOV ALGORITHM FOR TWO-DIMENSIONAL SOLID MECHANICS* *ation in two- dimensional solids undergoing nonlinear finite deformation. It is shown that th* *is propagation in one-dimensional elastic-plastic solids. * *This has ranged from studying the characteristic

Trangenstein, John A.

451

user's guide to viscosity solutions of second order partial differential equations  

Microsoft Academic Search

The notion of viscosity solutions of scalar fully nonlinear partial differential equations of second order provides a framework in which startling comparison and uniqueness theorems, existence theorems, and theorems about continuous dependence may now be proved by very efficient and striking arguments. The range of important applications of these results is enormous. This article is a self-contained exposition of the

Michael G. Crandall; Hitoshi Ishii; Pierre-Louis Lions

1992-01-01

452

Spatiochromatic statistics of natural scenes: first-and second-order information  

E-print Network

the cosine-windowed images with oriented Gabor functions, whose gains were scaled to give equal amplitude response across spatial fre- quency to random fractal images. Second-order filtering was implemented via a filter­rectify­filter cascade, with Gabor functions for both first- and second-stage filters. Both signed

Kingdom, Frederick A. A.

453

Centrifugal bias for second-order but not first-order motion  

E-print Network

nystagmus. Further evidence for sepa- rate mechanisms is provided by the studies of Mather and West12 in their ability to induce motion aftereffects (MAEs). Second-order motion stimuli produce no MAEs on a static background but may induce MAEs on a flickering background.16­19 Furthermore, ag- ing has been shown to have

Hess, Robert F.

454

Second-Order Sliding Mode Control for DFIG-Based Wind Turbines  

E-print Network

Second-Order Sliding Mode Control for DFIG-Based Wind Turbines Fault Ride-Through Capability, 3 (2014) 827-833" #12;Nomenclature WT = Wind Turbine; DFIG = Doubly-Fed Induction Generator; FRT]. LVRT requires wind turbines to remain connected to the grid in presence of grid voltage sags. The DFIG

Brest, Université de

455

Simulation of boundary condition influence in a second-order ferroelectric phase transition  

E-print Network

method, we have calculated stable domain configurations resulting from a second-order ferroelectric phase surface. The domain wall thickness of a finite system without surface electrodes was found to become structures, such as domains and domain walls. For example, it has been deter- mined experimentally that 70

Cao, Wenwu

456

CONVERGENCE IN VARIANCE OF FIRST-ORDER AND SECOND-ORDER CHEBYSHEV ACCELERATED GIBBS SAMPLERS  

E-print Network

precision. Key words. Chebyshev polynomial acceleration, Gauss Seidel, Gibbs, geometric convergence, samplerCONVERGENCE IN VARIANCE OF FIRST-ORDER AND SECOND-ORDER CHEBYSHEV ACCELERATED GIBBS SAMPLERS COLIN is a stochastic version of the Gauss-Seidel linear solver. The iteration operator that acts on the error in mean

Fox, Colin

457

Fast Curvature Matrix-Vector Products for Second-Order Gradient Descent  

E-print Network

various second-order gradient steps | Newton, Gauss-Newton, Levenberg-Mar- quardt, and natural gradient(n). Two recent acceleration techniques for online learning, matrix momentum and stochastic meta;cation thereof (Gauss-Newton, Levenberg-Marquardt, etc.), or the Fisher information (natural gradient

Schmidhuber, Juergen

458

Evidence of Second-Order Factor Structure in a Diagnostic Problem Space: Implications for Medical Education.  

ERIC Educational Resources Information Center

Chest pain was identified as a specific medical problem space, and disease classes were modeled to define it. Results from a test taken by 628 medical residents indicate a second-order factor structure that suggests that chest pain is a multidimensional problem space. Implications for medical education are discussed. (SLD)

Papa, Frank J.; And Others

1997-01-01

459

Conservation of Autonomy: Toward a Second-Order Perspective on Psychosomatic Symptoms.  

ERIC Educational Resources Information Center

Considers families of people suffering from psychosomatic disorders from perspective of second-order cybernetics in which emphasis is on autonomy of various levels of system. Describes psychosomatic symptoms and illustrates symptoms as expression of ideas aimed at conservation of autonomy, both at individual and family level. Highlights…

Fourie, David P.

1993-01-01

460

Electron-transfer photochromism to switch bulk second-order nonlinear optical properties with high contrast.  

PubMed

The first bulk electron-transfer photochromic compound with intrinsic second-order nonlinear optical (NLO) photoswitching properties has been synthesized. This system employs an electron-transfer photoactive asymmetric viologen ligand coordinated to a zinc(II) center. PMID:25195919

Li, Pei-Xin; Wang, Ming-Sheng; Zhang, Ming-Jian; Lin, Chen-Sheng; Cai, Li-Zhen; Guo, Sheng-Ping; Guo, Guo-Cong

2014-10-20

461

Concurrent Second-Order Schedules: Some Effects of Variations in Response Number and Duration  

ERIC Educational Resources Information Center

To examine the effects on concurrent performance of independent manipulations of response-unit duration and number, 6 hens were exposed to concurrent second- order schedules of reinforcement. Each first-order operant unit required completion of a fixed-ratio schedule within the time specified by a fixed- interval schedule, with one further…

Sealey, Diane M.; Sumpter, Catherine E.; Temple, W.; Foster, T. Mary

2005-01-01

462

Second-Order Schedules of Token Reinforcement with Pigeons: Implications for Unit Price  

ERIC Educational Resources Information Center

Four pigeons were exposed to second-order schedules of token reinforcement, with stimulus lights serving as token reinforcers. Tokens were earned according to a fixed-ratio (token-production) schedule, with the opportunity to exchange tokens for food (exchange period) occurring after a fixed number had been produced (exchange-production ratio).…

Bullock, Christopher E.; Hackenberg, Timothy D.

2006-01-01

463

The effect of second-order couple on the application of torque  

Microsoft Academic Search

Complex combinations of linear forces, moments, and couples are developed by the arch wire during orthodontic treatment. For instance, application of torque to a canine during distal driving may create force interactions if the tooth tips distally toward the extraction site. Th