These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

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

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...

3

An Example of Following Second-Order Kinetics by Simple Laboratory Means  

ERIC Educational Resources Information Center

Describes a procedure for studying the kinetics of the second-order hydrolysis of ethylene bromohydrine in alkaline medium by incorporating a substance that changes color as one of the reacting components is depleted. (MLH)

Schreiber, Gisela

1976-01-01

4

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

5

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

Microsoft Academic Search

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 influenced by temporal frequency, especially in the case of second-order motion. At 1 Hz, reaction times were faster for

Claire V. Hutchinson; Tim Ledgeway

2010-01-01

6

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

7

Second-Order Kinetic Analysis of IAsys Biosensor Data: Its Use and Applicability  

E-print Network

-affinity interactions. In this paper we derive analytical solutions of the second-order differential kinetic equations to the integrated first-order rate equation below Rt Rmax A kass kass A kdiss 1 exp kass A kdiss t , [1] where Rmax the conditions un- der which the pseudo-first-order assumption ceases to be valid. It is found that the effect

Leatherbarrow, Robin J.

8

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

E-print Network

Temporal Frequency Modulates Reaction Time Responses to First-Order and Second-Order Motion Claire the effect of temporal frequency and modulation depth on reaction times for discriminating the direction using equal multiples of direction-discrimination threshold. Results showed that reaction times were

Nottingham, University of

9

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

10

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...

11

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

2014-10-26

12

Interference by neutron induced second order nuclear reaction in activation analysis of rare earths  

Microsoft Academic Search

In determining the trace impurities existing in high-purity rare earth samples by the neutron activation analysis, there are\\u000a much interference due to nuclides induced from neutron induced second order nuclear reaction. This paper presents the degree\\u000a of interference calculated over the ranges of irradiation time from 105 to 107 sec and of thermal-neutron flux from 1·1012 to 1·1015 n·cm?2·sec?1. According

M. Kubota

1977-01-01

13

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

14

Choice reaction times for identifying the direction of first-order motion and different varieties of second-order motion  

E-print Network

Choice reaction times for identifying the direction of first-order motion and different varieties of the human visual system by measuring forced-choice reaction times for dis- criminating the drift direction of stimulus modulation depths. In general, reaction times for all types of second-order motion were slower

Nottingham, University of

15

Conjugate mass transfer to a spherical drop accompanied by a second-order chemical reaction inside the drop  

Microsoft Academic Search

Conjugate mass transfer between a drop and a surrounding fluid flow with second-order (inclusive the particular case – pseudo-first-order), irreversible chemical reaction in the dispersed phase has been analyzed. The dispersed phase reactant is insoluble in the continuous phase and its complete depletion is allowed. Two sphere models were considered: the rigid sphere and the fluid sphere with internal circulation.

Gh Juncu

2002-01-01

16

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

17

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

NASA Technical Reports Server (NTRS)

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

Deshpande, Suresh M.

1986-01-01

18

Choice reaction times for identifying the direction of first-order motion and different varieties of second-order motion  

Microsoft Academic Search

This study sought to quantify the temporal properties of the human visual system by measuring forced-choice reaction times for discriminating the drift direction of first-order motion (luminance-modulated noise) and a variety of second-order motion patterns (modulations of either the contrast, polarity, orientation or spatial length of a noise carrier) over a range of stimulus modulation depths. In general, reaction times

Tim Ledgeway; Claire V. Hutchinson

2008-01-01

19

Reaction path determination for quantum mechanical\\/molecular mechanical modeling of enzyme reactions by combining first order and second order ``chain-of-replicas'' methods  

Microsoft Academic Search

A two-step procedure for the determination of reaction paths in enzyme systems is presented. This procedure combines two chain-of-states methods: a quantum mechanical\\/molecular mechanical (QM\\/MM) implementation of the nudged elastic band (NEB) method and a second order parallel path optimizer method both recently developed in our laboratory. In the first step, a reaction path determination is performed with the NEB

G. Andrés Cisneros; Haiyan Liu; Zhenyu Lu; Weitao Yang

2005-01-01

20

Longer VEP latencies and slower reaction times to the onset of second-order motion than to the onset of first-order motion  

Microsoft Academic Search

We compared visual evoked potentials and psychophysical reaction times to the onset of first- and second-order motion. The stimuli consisted of luminance-modulated (first-order) and contrast-modulated (second-order) 1 cpd vertical sine-wave gratings drifting rightward for 140 ms at a velocity of 6 °\\/s. For each condition, we analysed the latencies and peak-to-baseline amplitudes of the P1 and N2 peaks recorded at

D. Ellemberg; K. Lavoie; T. L. Lewis; D. Maurer; F. Lepore; J.-P. Guillemot

2003-01-01

21

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

22

Electrode kinetics: reactions  

Microsoft Academic Search

This is Volume 27 in the Comprehensive Chemical Kinetics series. The contributors are Calvo (Argentina), Hamnett (England), O'Sullivan (United States), and Weaver (United States). The book's chapters cover Redox Reactions at Metal-Solution Interfaces, Semiconductor Electrochemistry, and Reactions at Metal Oxide Electrodes. The references date from the 1960s to the mid-1980s. An index is included.

1987-01-01

23

Reaction kinetics, geospeedometry, and relaxation theory  

NASA Astrophysics Data System (ADS)

This paper explores the application of homogeneous reaction kinetics to geospeedometry and to structural relaxation theory. Numerical simulations of reaction kinetics during cooling for some first- and second-order elementary reactions have been carried out to systematically examine the effects of kinetic parameters and cooling histories on the final speciation. An analytical solution for a special case of first-order reaction A ? B has also been obtained. On the basis of both the analytical solution and the numerical simulation, the cooling rate ( -dT/dt) at the apparent equilibrium temperature ( T ae, obtained by measuring 'quenched' speciation) and the relaxation time scale ( ? r, the time for the departure from equilibrium to decrease to 1/e of the initial departure) at T ae can be approximately related as follows: (-dT/dt)| T=T ae ? 2RT ae/max( E f, E b) where R is the gas constant, and max( E f, E b) is the greater of E f and E b, which are the activation energies of the forward and backward reactions. This approximation works well when the initial temperature ( T 0) is high such that ? r(T 0) is small compared to the cooling time scale. Using the above relation, the cooling rate at T ae can be estimated easily and the cooling history of a natural assemblage can be inferred if enough homogeneous reactions are characterized. Relaxation of homogeneous reactions during the quench of a silicate melt into a glass can be studied quantitatively using the above method if the kinetic parameters are known. Melt-glass transitions probably involve the quenching of many homogeneous reactions that may have different T ae for a given quench rate, and are thus complicated. Authors have previously discussed relaxation of a reaction during cooling using the idea of a melt-glass transition. Because glass relaxation is complicated and the theory is still in its infancy, whereas reaction kinetics can be understood and quantified, it may be more productive to study the relaxation of homogeneous reactions directly and to study glass relaxation using the concept of reaction kinetics instead.

Zhang, Youxue

1994-04-01

24

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

25

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

26

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

27

Factors Affecting Reaction Kinetics of Glucose Oxidase  

NASA Astrophysics Data System (ADS)

Basic principles of enzyme kinetics are demonstrated using the enzyme glucose oxidase. The glucose oxidase enzymatic reaction is coupled to horseradish peroxidase, which in turn catalyzes the oxidation of a dye to a bright blue-green color. The appearance of the blue-green dye is used to monitor the course of the reaction and is quite visible in a classroom setting. A series of reactions are arranged that vary the enzyme concentration, substrate concentration, temperature, and the substrate used in the reaction. By monitoring the rate of the color change in each beaker, the reaction kinetics of glucose oxidase in each series is observed.

Johnson, Kristin A.

2002-01-01

28

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

29

Chemical Kinetics: Rate of Reaction  

NSDL National Science Digital Library

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

Blauch, David N.

30

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

31

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

32

An Analysis of Second-Order Autoshaping  

ERIC Educational Resources Information Center

Three mechanisms can explain second-order conditioning: (1) The second-order conditioned stimulus (CS2) could activate a representation of the first-order conditioned stimulus (CS1), thereby provoking the conditioned response (CR); The CS2 could enter into an excitatory association with either (2) the representation governing the CR, or (3) with a…

Ward-Robinson, Jasper

2004-01-01

33

Hybrid Aligned Nematics and second order elasticity  

NASA Astrophysics Data System (ADS)

The effect of the second order elasticity on the critical thickness of Hybrid Aligned Nematic cells possessing either weak planar or weak homeotropic anchoring has been analysed. It is found that the critical thickness of such cells is strictly dependent on the surface elastic constant K13 and on the second order bulk elastic constant K*. Moreover, an experimental method for an indirect measurement of K13 and K* is proposed.

Sparavigna, A.; Komitov, L.; Strigazzi, A.

1991-02-01

34

Multidimensional reaction kinetic ablation program /REKAP/  

NASA Technical Reports Server (NTRS)

Multidimensional reaction kinetics ablation program provides an improved capability for analyzing thermal performance of partially penetrated charring ablator heat shields. The capability was provided for determining transient temperature histories in an ablating three-dimensional shape consisting of up to five layers of material.

Aston, B.; Binck, E.; Collingswood, B.

1967-01-01

35

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

36

Frenetic aspects of second order response.  

PubMed

Starting from the second order around thermal equilibrium, the response of a statistical mechanical system to an external stimulus is not only governed by dissipation and depends explicitly on dynamical details of the system. The so called frenetic contribution in the second order around equilibrium is illustrated in different physical examples, such as for non-thermodynamic aspects in the coupling between a system and reservoir, for the dependence on disorder in the dielectric response and for the nonlinear correction to the Sutherland-Einstein relation. More generally, the way in which a system's dynamical activity changes by perturbation is visible (only) from the nonlinear response. PMID:25666909

Basu, Urna; Krüger, Matthias; Lazarescu, Alexandre; Maes, Christian

2015-02-18

37

Second Order Symmetries of the Conformal Laplacian  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

38

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

39

Circulant preconditioners for second order hyperbolic equations  

Microsoft Academic Search

Linear systems arising from implicit time discretizations and finite difference space discretizations of second-order hyperbolic equations in two dimensions are considered. We propose and analyze the use of circulant preconditioners for the solution of linear systems via preconditioned iterative methods such as the conjugate gradient method. Our motivation is to exploit the fast inversion of circulant systems with the Fast

Xiao-Qing Jin; Raymond H. Chan

1992-01-01

40

Second order density perturbations for dust cosmologies  

NASA Astrophysics Data System (ADS)

We present simple expressions for the relativistic first and second order fractional density perturbations for Friedmann-Lemaître cosmologies with dust, in four different gauges: the Poisson, uniform curvature, total matter and synchronous-comoving gauges. We include a cosmological constant and arbitrary spatial curvature in the background. A distinctive feature of our approach is our description of the spatial dependence of the perturbations using a canonical set of quadratic differential expressions involving an arbitrary spatial function that arises as a conserved quantity. This enables us to unify, simplify and extend previous seemingly disparate results. We use the primordial matter and metric perturbations that emerge at the end of the inflationary epoch to determine the additional arbitrary spatial function that arises when integrating the second order perturbation equations. This introduces a non-Gaussianity parameter into the expressions for the second order density perturbation. In the special case of zero spatial curvature we show that the time evolution simplifies significantly, and requires the use of only two nonelementary functions, the so-called growth suppression factor at the linear level, and one new function at the second order level. We expect that the results will be useful in applications, for example, studying the effects of primordial non-Gaussianity on the large scale structure of the Universe.

Uggla, Claes; Wainwright, John

2014-08-01

41

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

E-print Network

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

Knyazev, Vadim D.

42

Extracting Biochemical Reaction Kinetics from Time Series Data  

E-print Network

Extracting Biochemical Reaction Kinetics from Time Series Data Edmund J. Crampin1 , Patrick E. Mc consider the problem of inferring kinetic mechanisms for biochemical reactions from time series data. Using systems. In this paper we discuss an approach to inferring reaction kinetics from time series data using

McSharry, Patrick E.

43

Extracting Biochemical Reaction Kinetics from Time Series Data  

E-print Network

Extracting Biochemical Reaction Kinetics from Time Series Data Edmund J. Crampin 1? , Patrick E. Mc consider the problem of inferring kinetic mechanisms for biochemical reactions from time series data. Using systems. In this paper we discuss an approach to inferring reaction kinetics from time series data using

McSharry, Patrick E.

44

The structure of rotating polytropes (Second order)  

NASA Astrophysics Data System (ADS)

The structural equations for the inner and outer regions of a rotating polytrope (as used in stellar-structure models) are reformulated to include second-order terms in the perturbation parameter alpha and solved by extending the method of Monaghan and Roxburgh (1965), as used in the first order by Singh and Singh (1982). A critical configuration at which the centrifugal force balances gravity at the equator is defined, and numerical results for parameter values of interest in astrophysics are presented in tables. Comparison of the results for alpha, xi(e), and xi(p) with those of James (1964) and Singh and Singh (1982) shows that the improvement introduced by the use of the second-order method is small, and continued modeling based on the first-order values is recommended.

Singh, G. R.; Singh, M.

1984-11-01

45

Calculating Second-Order Effects in MOSFET's  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

46

Second-order gravitational self-force  

E-print Network

We derive an expression for the second-order gravitational self-force that acts on a self-gravitating compact-object moving in a curved background spacetime. First we develop a new method of derivation and apply it to the derivation of the first-order gravitational self-force. Here we find that our result conforms with the previously derived expression. Next we generalize our method and derive a new expression for the second-order gravitational self-force. This study also has a practical motivation: The data analysis for the planned gravitational wave detector LISA requires construction of waveforms templates for the expected gravitational waves. Calculation of the two leading orders of the gravitational self-force will enable one to construct highly accurate waveform templates, which are needed for the data analysis of gravitational-waves that are emitted from extreme mass-ratio binaries.

Eran Rosenthal

2006-09-18

47

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

48

Unfolded partial least-squares with residual quadrilinearization: A new multivariate algorithm for processing five-way data achieving the second-order advantage. Application to fourth-order excitation-emission-kinetic-pH fluorescence analytical data  

Microsoft Academic Search

Unfolded partial least-squares in combination with residual quadrilinearization (U-PLS\\/RQL), is developed as a new latent structured algorithm for the processing of fourth-order instrumental data. In order to check its analytical predictive ability, fluorescence excitation-emission-kinetic-pH data were measured and processed. The concentration of the fluorescent pesticide carbaryl was determined in the presence of the pesticides fuberidazole and thiabendazole as uncalibrated interferents,

Rubén M. Maggio; Arsenio Muñoz de la Peña; Alejandro C. Olivieri

2011-01-01

49

Reaction of a bridged frustrated Lewis pair with nitric oxide: a kinetics study.  

PubMed

Described is a kinetics and computational study of the reaction of NO with the intramolecular bridged P/B frustrated Lewis pair (FLP) endo-2-(dimesitylphosphino)-exo-3-bis(pentafluorophenyl)boryl-norbornane to give a persistent FLP-NO aminoxyl radical. This reaction follows a second-order rate law, first-order in [FLP] and first-order in [NO], and is markedly faster in toluene than in dichloromethane. By contrast, the NO oxidation of the phosphine base 2-(dimesitylphosphino)norbornene to the corresponding phosphine oxide follows a third-order rate law, first-order in [phosphine] and second-order in [NO]. Formation of the FLP-NO radical in toluene occurs with a ?H(‡) of 13 kcal mol(-1), a feature that conflicts with the computation-based conclusion that NO addition to a properly oriented B/P pair should be nearly barrierless. Since the calculations show the B/P pair in the most stable solution structure of this FLP to have an unfavorable orientation for concerted reaction, the observed barrier is rationalized in terms of the reversible formation of a [B]-NO complex intermediate followed by a slower isomerization-ring closure step to the cyclic aminoxyl radical. This combined kinetics/theoretical study for the first time provides insight into mechanistic details for the activation of a diatomic molecule by a prototypical FLP. PMID:24328325

Pereira, José Clayston Melo; Sajid, Muhammad; Kehr, Gerald; Wright, Ashley M; Schirmer, Birgitta; Qu, Zheng-Wang; Grimme, Stefan; Erker, Gerhard; Ford, Peter C

2014-01-01

50

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

NASA Astrophysics Data System (ADS)

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

Bazow, Dennis; Heinz, Ulrich; Strickland, Michael

2014-11-01

51

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

52

Synchronization from Second Order Network Connectivity Statistics  

PubMed Central

We investigate how network structure can influence the tendency for a neuronal network to synchronize, or its synchronizability, independent of the dynamical model for each neuron. The synchrony analysis takes advantage of the framework of second order networks, which defines four second order connectivity statistics based on the relative frequency of two-connection network motifs. The analysis identifies two of these statistics, convergent connections, and chain connections, as highly influencing the synchrony. Simulations verify that synchrony decreases with the frequency of convergent connections and increases with the frequency of chain connections. These trends persist with simulations of multiple models for the neuron dynamics and for different types of networks. Surprisingly, divergent connections, which determine the fraction of shared inputs, do not strongly influence the synchrony. The critical role of chains, rather than divergent connections, in influencing synchrony can be explained by their increasing the effective coupling strength. The decrease of synchrony with convergent connections is primarily due to the resulting heterogeneity in firing rates. PMID:21779239

Zhao, Liqiong; Beverlin, Bryce; Netoff, Theoden; Nykamp, Duane Q.

2011-01-01

53

Nonlinear second order current cancellation in HBTs  

NASA Astrophysics Data System (ADS)

Heterojunction Bipolar Transistor (HBT) has very good linear properties when operated at high frequencies and in large signal modes of operation. In this article we examine the fundamental reasons for such good performance of HBTs, compare various models and look into the influence of different parameters. In particular, cancellation of the second harmonic currents in the base-emitter junction, as proposed by Maas et al.[1], is examined. A set of new analytical expressions is developed for equivalent circuits of varying complexity by using the method of nonlinear currents. We found that the emitter resistance Ree linearizes the HBT at low frequencies by providing negative feedback and by bringing the phase difference of the second order currents closer to 180°. At high frequencies the base collector capacitance Cbc dominates the feedback and its inherent nonlinearity degrades the cancellation of second order currents in the base-emitter junction. Numerical tools are used for comparison and will be needed for future investigations. We have also found an equivalence between what at first appeared to be very different models for current gain.

Woywode, Oliver; Pejc?inovi?, Branimir

1997-09-01

54

Robust stability of second-order systems  

NASA Technical Reports Server (NTRS)

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

Chuang, C.-H.

1995-01-01

55

Second-order superintegrable quantum systems  

SciTech Connect

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

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

2007-03-15

56

Challenges for an enzymatic reaction kinetics database.  

PubMed

The scientific literature contains a tremendous amount of kinetic data describing the dynamic behaviour of biochemical reactions over time. These data are needed for computational modelling to create models of biochemical reaction networks and to obtain a better understanding of the processes in living cells. To extract the knowledge from the literature, biocurators are required to understand a paper and interpret the data. For modellers, as well as experimentalists, this process is very time consuming because the information is distributed across the publication and, in most cases, is insufficiently structured and often described without standard terminology. In recent years, biological databases for different data types have been developed. The advantages of these databases lie in their unified structure, searchability and the potential for augmented analysis by software, which supports the modelling process. We have developed the SABIO-RK database for biochemical reaction kinetics. In the present review, we describe the challenges for database developers and curators, beginning with an analysis of relevant publications up to the export of database information in a standardized format. The aim of the present review is to draw the experimentalist's attention to the problem (from a data integration point of view) of incompletely and imprecisely written publications. We describe how to lower the barrier to curators and improve this situation. At the same time, we are aware that curating experimental data takes time. There is a community concerned with making the task of publishing data with the proper structure and annotation to ontologies much easier. In this respect, we highlight some useful initiatives and tools. PMID:24165050

Wittig, Ulrike; Rey, Maja; Kania, Renate; Bittkowski, Meik; Shi, Lei; Golebiewski, Martin; Weidemann, Andreas; Müller, Wolfgang; Rojas, Isabel

2014-01-01

57

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

58

Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks  

ERIC Educational Resources Information Center

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

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

2011-01-01

59

Statistical Thermodynamics and Kinetics of DNA Multiplex Hybridization Reactions  

Microsoft Academic Search

A general analytical description of the equilibrium and reaction kinetics of DNA multiplex hybridization has been developed. In this approach, multiplex hybridization is considered to be a competitive multichannel reaction process: a system wherein many species can react both specifically and nonspecifically with one another. General equations are presented that can consider equilibrium and kinetic models of multiplex hybridization systems

M. T. Horne; D. J. Fish; A. S. Benight

2006-01-01

60

Kinetics and Mechanism of Oxidation Reactions of Porphyrin-Iron(IV)-Oxo Intermediates  

PubMed Central

The kinetics of reactions of three porphyrin-iron(IV)-oxo derivatives with alkenes and benzylic alcohols were measured. The iron-oxo systems studied were 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin-iron(IV)-oxo (2a), 5,10,15,20-tetrakis(2,6-difluorophenyl)porphyrin-iron(IV)-oxo (2b), and 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin-iron(IV)-oxo (2c). Species 2 were stable for hours at room temperature as dilute solutions in acetonitrile and reacted hundreds to thousands of times faster in the presence of high concentrations of substrates. Typical second-order rate constants determined from pseudo-first-order kinetic studies are 1–2 × 10?2 M?1 s?1 for reactions with styrene and 3 × 10?2 M?1 s?1 for reactions with benzyl alcohol. The reactivity order for the iron-oxo species was 2a > 2b > 2c, which is inverted from that expected on the basis of the electron demand of the porphyrin macrocycles, and the oxidation reaction was suppressed when excess porphyrin-iron(III) complex was added to reaction mixtures. These observations indicate that the reactions involve disproportionation of the iron(IV)-oxo species 2 to give an iron(III) species and a more highly oxidized iron species, presumed to be iron(IV)-oxo porphyrin radical cation, that is the true oxidant in the reactions. Analyses of the kinetics of oxidations of a series of para-substituted benzylic alcohols with Hammett ?+ substituent constants and with a dual parameter method developed by Jiang (Jiang, X. K. Acc. Chem. Res. 1997, 30, 283) indicated that considerable positive charge developed on the benzylic carbons in the oxidation reactions, as expected for electrophilic oxidants, and also that substantial radical character developed on the benzyl carbon in the transition states. PMID:17630728

Pan, Zhengzheng; Newcomb, Martin

2010-01-01

61

Current issues in sol-gel reaction kinetics  

SciTech Connect

This paper surveys a few of the current issues in sol-gel reaction kinetics. Many times seemingly modest changes in reactants or reaction conditions can lead to substantial differences in the overall reaction rates and pathways. For example, qualitative features of the reaction kinetics can depend on catalyst concentration. At very high acid-catalyst concentrations, reverse are significant for TMOS sol-gels, while for moderate acid-catalyst concentrations, reverse reactions are substantially reduced. The reaction kinetics are substantially reduced. The reaction kinetics of two similar tetraalkoxysilanes: tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS), can be markedly different under identical reaction conditions. Under acid-catalyzed reaction conditions, a TMOS sol-gel undergoes both water-and alcohol-producing condensation reactions while a TEOS sol-gel undergoes only water-producing condensation. The early time hydrolysis and condensation reactions of a TMOS sol-gel are statistical in nature and can be quantitatively described by a few simple reaction rate constants while the reaction behavior of a TEOS sol-gel is markedly nonstatistical. A comprehensive theory of sol-gel kinetics must address diverse experimental findings. 9 refs., 3 figs., 1 tab.

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

1990-01-01

62

Assessment of closure schemes in second-order conditional moment closure against DNS with extinction and ignition  

SciTech Connect

The performance of second-order conditional moment closure (CMC) depends on models to evaluate conditional variances and covariances of temperature and species mass fractions. In this paper the closure schemes based on the steady laminar flamelet model (SLFM) are validated against direct numerical simulation (DNS) involving extinction and ignition. Scaling is performed to reproduce proper absolute magnitudes, irrespective of the origin of mismatch between local flamelet structures and scalar dissipation rates. DNS based on the pseudospectral method is carried out to study hydrogen-air combustion with a detailed kinetic mechanism, in homogeneous, isotropic, and decaying turbulent media. Lewis numbers are set equal to unity to avoid complication of differential diffusion. The SLFM-based closures for correlations among fluctuations of reaction rate, scalar dissipation rate, and species mass fractions show good comparison with DNS. The variance parameter in lognormal PDF and the constants in the dissipation term have been estimated from DNS results. Comparison is made for the resulting conditional profiles from DNS, first-order CMC, and second-order CMC with correction to the most critical reaction step according to sensitivity analysis. Overall good agreement ensures validity of the SLFM-based closures for modeling conditional variances and covariances in second-order CMC.

Sreedhara, S.; Huh, Kang Y. [Department of Mechanical Engineering, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784 (Korea, Republic of)

2005-12-01

63

A generalized kinetic model for heterogeneous gas-solid reactions.  

PubMed

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

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

2012-08-21

64

Second-Order Accurate Method for Solving Radiation-Hydrodynamics  

E-print Network

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

Edwards, Jarrod Douglas

2013-11-12

65

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

66

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

67

Reaction Kinetics: An Experiment for Biochemistry and Organic Chemistry Laboratories.  

ERIC Educational Resources Information Center

Describes an experiment to examine the kinetics of carbamate decomposition and the effect of buffer catalysis on the reaction. Includes background information, laboratory procedures, evaluation of data, and teaching suggestions. (Author/JN)

Ewing, Sheila

1982-01-01

68

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

69

Kinetics of Acid Reactions: Making Sense of Associated Concepts  

ERIC Educational Resources Information Center

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

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

2010-01-01

70

A study of the Sabatier-methanation reaction kinetics  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

71

Chemical kinetics computer program for static and flow reactions  

NASA Technical Reports Server (NTRS)

General chemical kinetics computer program for complex gas mixtures has been developed. Program can be used for any homogeneous reaction in either one dimensional flow or static system. It is flexible, accurate, and easy to use. It can be used for any chemical system for which species thermodynamic data and reaction rate constant data are known.

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

1972-01-01

72

Supracolloidal Reaction Kinetics of Janus Spheres  

Microsoft Academic Search

Clusters in the form of aggregates of a small number of elemental units display structural, thermodynamic, and dynamic properties different from those of bulk materials. We studied the kinetic pathways of self-assembly of ``Janus spheres'' with hemispherical hydrophobic attraction and found key differences from those characteristic of molecular amphiphiles. Experimental visualization combined with theory and molecular dynamics simulation shows that

Qian Chen; Jonathan K. Whitmer; Shan Jiang; Sung Chul Bae; Erik Luijten; Steve Granick

2011-01-01

73

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

PubMed

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

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

2015-02-15

74

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

75

Direct method for solving second order delay differential equations  

NASA Astrophysics Data System (ADS)

This paper considers the implementation of fourth order direct method in the form of Adams Moulton method for solving directly second order delay differential equations. The proposed method approximates the solutions using constant step size. Numerical results are presented to show that the proposed code is suitable for solving second order delay differential equations.

Seong, Hoo Yann; Abdul Majid, Zanariah

2013-04-01

76

Second-Order Approach to Optimal Semiconductor Design  

Microsoft Academic Search

Second order methods for optimal semiconductor design based on the standard drift diffusion model are developed. Second–order\\u000a necessary and sufficient conditions are established. Local quadratic convergence for the Newton method is proved. Numerical\\u000a results for an unsymmetric (n–p) diode are presented.

Michael Hinze; R. Pinnau

2007-01-01

77

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

78

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

79

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

80

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

81

Foldy-Wouthuysen-type reduction of the second-order Dirac equation  

Microsoft Academic Search

A nonrelativistic reduction of the second-order Dirac equation is investigated. An equation K2+[&Pgr;0; K?&Pgr;ˆ]=m2+&Pgr;ˆ2 is obtained for a ‘‘kinetic Hamiltonian’’ K such that &Fgr; obeys a nonrelativistic Schro¨dinger-type equation &Pgr;0&Fgr;=K&Fgr; in addition to obeying the second-order Dirac equation. Non-self-adjoint terms in K are removed by a change of representation from &Fgr; to &Fgr;T ?P&Fgr;, and a closed expression P?[ 1\\/2

Levere Hostler

1989-01-01

82

Reaction mechanism and kinetics of the traceless Staudinger ligation.  

PubMed

The traceless Staudinger ligation enables the formation of an amide bond between a phosphinothioester (or phosphinoester) and an azide without the incorporation of residual atoms. Here, the coupling of peptides by this reaction was characterized in detail. Experiments with [(18)O]H(2)O indicated that the reaction mediated by (diphenylphosphino)methanethiol proceeded by S-->N acyl transfer of the iminophosphorane intermediate to form an amidophosphonium salt, rather than by an aza-Wittig reaction and subsequent hydrolysis of the resulting thioimidate. A continuous (13)C NMR-based assay revealed that the rate-determining step in the Staudinger ligation of glycyl residues mediated by (diphenylphosphino)methanethiol was the formation of the initial phosphazide intermediate. Less efficacious coupling reagents and reaction conditions led to the accumulation of an amine byproduct (which resulted from a Staudinger reduction) or phosphonamide byproduct (which resulted from an aza-Wittig reaction). The Staudinger ligation mediated by (diphenylphosphino)methanethiol proceeded with a second-order rate constant (7.7 x 10(-3) M(-1) s(-1)) and yield (95%) that was unchanged by the addition of exogenous nucleophiles. Ligations mediated by phosphinoalcohols had lower rate constants or less chemoselectivity. Accordingly, (diphenylphosphino)methanethiol was judged to be the most efficacious known reagent for effecting the traceless Staudinger ligation. PMID:16819875

Soellner, Matthew B; Nilsson, Bradley L; Raines, Ronald T

2006-07-12

83

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

84

Calcite Reaction Kinetics in Saline Waters  

E-print Network

of ~45-50 percent required for dissolution to proceed in undersaturated solutions at 25-55 degrees C and pCO2 = 0.1 – 1 atm. Precipitation rates were modeled using the general and Davies and Jones rate equations yielding similar results. Reaction orders...

Finneran, David

2012-02-14

85

Second-order design sensitivities for linear elastic problems  

NASA Technical Reports Server (NTRS)

The subject of this paper is the efficient and accurate determination of second-order design sensitivities in elastic bodies. The approach being carried out here is the direct differentiation of the governing derivative boundary element method (DBEM) formulation of the problem. Second-order sensitivities of boundary stresses are obtained in an elegant manner. A numerical implementation of the method is carried out with isoparametric quadratic boundary elements and numerical results are presented for several sample problems. Considerable savings in computational effort for an optimization procedure is possible through the use of efficiently determined accurate second-order design sensitivities.

Zhang, Qing; Mukherjee, Subrata

1990-01-01

86

Microwave enhanced reaction kinetics in ceramics  

Microsoft Academic Search

Numerous observations have been reported in the literature of enhanced mass transport and solid-state reaction rates during\\u000a microwave heating or processing of a variety of ceramic, glass, and polymer materials. These empirical observations of microwave\\u000a enhancements have been broadly called the ”microwave effect”. In the past, these claims have been the source of significant\\u000a controversy, due in part to the

J. H. Booske; Reid F. Cooper; Samuel A. Freeman

1997-01-01

87

Oscillation of second-order elliptic equations with damping terms  

NASA Astrophysics Data System (ADS)

Some oscillation criteria are given for the second-order elliptic differential equation with damping terms The results are extensions of modified Riccati technique and include earlier results of Noussair and Swanson, Xu, and Zhang et al.

Xu, Zhi-Ting

2006-05-01

88

QUEST FOR THE CONTROL ON THE SECOND ORDER ...  

E-print Network

Oct 8, 2010 ... on the second order derivatives of the field solution, in addition to zero and .... For example, a negative curvature with large absolute value is signature ..... Consider an orthogonal local curvilinear coordinate system coincides ...

2010-10-08

89

Second-Order Perturbation Theory for Spin-Orbit Resonances  

Microsoft Academic Search

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 such as Mercury and the Moon, first-order perturbation theory is adequate, whereas

Angela E. Flynn; Prasenjit Saha

2005-01-01

90

Second-order type isomorphisms through game semantics  

Microsoft Academic Search

The characterization of second-order type isomorphisms is a purely syntactical problem that we propose to study under the enlightenment of game semantics. We study this question in the case of second-order??-calculus, which can be seen as an extension of system F to classical logic, and for which we define a categorical framework: control hyperdoctrines. Our game model of??-calculus is based

Joachim De Lataillade; Équipe Preuves; Denis Diderot

2008-01-01

91

On the linearization of second-order ordinary differential equations  

Microsoft Academic Search

In this Letter, the problem of characterizing all second-order ordinary differential equations y?=f(x, y, y') which are locally linearizable by a change of dependent and independent variables (x, y)?(X, Y) is considered. Since all second-order linear equations are locally equivalent to y?=0, the problem amounts to finding necessary and sufficient conditions for y?=f(x, y, y') to be locally equivalent to

Artemio González-López

1989-01-01

92

The temporal properties of first- and second-order vision  

Microsoft Academic Search

Vision is sensitive to first-order modulations of luminance and second-order modulations of image contrast. There is now a body of evidence that the two types of modulation are detected by separate mechanisms. Some previous experiments on motion detection have suggested that the second-order system is quite sluggish compared to the first-order system. Here we derive temporal properties of first- and

Andrew J. Schofield; Mark A. Georgeson

2000-01-01

93

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

ERIC Educational Resources Information Center

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

McCarrick, Thomas A.; McLafferty, Fred W.

1984-01-01

94

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...

95

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...

96

Pulsed ion beam investigation of the kinetics of surface reactions  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

97

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

98

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

99

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

100

A comparison of varieties of "second-order" motion.  

PubMed

Bistable apparent-movement displays were created using four different kinds of "second-order" stimuli in which figures were defined by binocular disparity, spatial phase shifts of periodic luminance distributions, relative motion, and texture-element orientation differences. For each display, characteristics of the local structure of the figures, backgrounds, or both were varied. For each experimental condition, the type of apparent movement seen as a function of interstimulus interval was measured, and it was found that the relationship between perceived apparent movement and interstimulus interval differed across the types of displays viewed. The results suggest that the transformations between first-order stimulus properties and second-order motion may be too complex to imply a single uniform class of second-order motion detectors. Alternative physiological accounts of the results are discussed. PMID:7900291

Petersik, J T

1995-02-01

101

On second order shape optimization methods for electrical impedance tomography  

E-print Network

This paper is devoted to the analysis of a second order method for recovering the \\emph{a priori} unknown shape of an inclusion $\\omega$ inside a body $\\Omega$ from boundary measurement. This inverse problem - known as electrical impedance tomography - has many important practical applications and hence has focussed much attention during the last years. However, to our best knowledge, no work has yet considered a second order approach for this problem. This paper aims to fill that void: we investigate the existence of second order derivative of the state $u$ with respect to perturbations of the shape of the interface $\\partial\\omega$, then we choose a cost function in order to recover the geometry of $\\partial \\omega$ and derive the expression of the derivatives needed to implement the corresponding Newton method. We then investigate the stability of the process and explain why this inverse problem is severely ill-posed by proving the compactness of the Hessian at the global minimizer.

Afraites, Lekbir; Kateb, Djalil

2007-01-01

102

The Second-Order Talbot Effect with Entangled Photon Pairs  

E-print Network

The second-order Talbot effect is analyzed for a periodic object illuminated by entangled photon pairs in both the quantum imaging and quantum lithography configurations. The Klyshko picture is applied to describe the quantum imaging scheme, in which self-images of the object that may or may not be magnified can be observed nonlocally in the photon coincidences but not in the singles count rate. In the quantum lithography setup, we find that the second-order Talbot length is half that of the classical first-order case, thus the resolution may be improved by a factor of two.

Luo, Kai-Hong; Chen, Xi-Hao; Liu, Qian; Xiao, Min; Wu, Ling-An

2009-01-01

103

Second-order Talbot effect with entangled photon pairs  

NASA Astrophysics Data System (ADS)

The second-order Talbot effect is analyzed for a periodic object illuminated by entangled photon pairs in both the quantum imaging and quantum lithography configurations. The Klyshko picture is applied to describe the quantum imaging scheme, in which self-images of the object that may or may not be magnified can be observed nonlocally in the photon coincidences but not in the singles count rate. In the quantum lithography setup, we find that the second-order Talbot length is half that of the classical first-order case, thus the resolution may be improved by a factor of 2.

Luo, Kai-Hong; Wen, Jianming; Chen, Xi-Hao; Liu, Qian; Xiao, Min; Wu, Ling-An

2009-10-01

104

The Second-Order Talbot Effect with Entangled Photon Pairs  

E-print Network

The second-order Talbot effect is analyzed for a periodic object illuminated by entangled photon pairs in both the quantum imaging and quantum lithography configurations. The Klyshko picture is applied to describe the quantum imaging scheme, in which self-images of the object that may or may not be magnified can be observed nonlocally in the photon coincidences but not in the singles count rate. In the quantum lithography setup, we find that the second-order Talbot length is half that of the classical first-order case, thus the resolution may be improved by a factor of two.

Kai-Hong Luo; Jianming Wen; Xi-Hao Chen; Qian Liu; Min Xiao; Ling-An Wu

2009-09-24

105

Second-order Talbot effect with entangled photon pairs  

SciTech Connect

The second-order Talbot effect is analyzed for a periodic object illuminated by entangled photon pairs in both the quantum imaging and quantum lithography configurations. The Klyshko picture is applied to describe the quantum imaging scheme, in which self-images of the object that may or may not be magnified can be observed nonlocally in the photon coincidences but not in the singles count rate. In the quantum lithography setup, we find that the second-order Talbot length is half that of the classical first-order case, thus the resolution may be improved by a factor of 2.

Luo Kaihong; Chen Xihao; Liu Qian; Wu Lingan [Laboratory of Optical Physics, Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190 (China); Wen Jianming; Xiao Min [Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701 (United States)

2009-10-15

106

Second-order Talbot self-imaging with pseudothermal light  

NASA Astrophysics Data System (ADS)

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

Song, Xin-Bing; Xiong, Jun; Zhang, Xiangdong; Wang, Kaige

2010-09-01

107

Monadic second-order model-checking on decomposable matroids  

Microsoft Academic Search

A notion of branch-width, which generalizes the one known for graphs, can be\\u000adefined for matroids. We first give a proof of the polynomial time\\u000amodel-checking of monadic second-order formulas on representable matroids of\\u000abounded branch-width, by reduction to monadic second-order formulas on trees.\\u000aThis proof is much simpler than the one previously known. We also provide a\\u000alink between

Yann Strozecki; Denis Diderot

2011-01-01

108

Elasto-plastic model with second order defect density tensor  

NASA Astrophysics Data System (ADS)

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

Cleja-?igoiu, Sanda

2011-05-01

109

Second-order effects in proton solution endor  

NASA Astrophysics Data System (ADS)

The radical cation of 6-hydrodipyrido-[1,2-c:2'.1'-e]-imidazolium iodide (monomethylene diquat) has been investigated using ESR, ENDOR and triple resonance. The bridge methylene protons have a large hyperfine coupling constant (2.46 mT) and show second-order interaction both in the ESR and ENDOR spectra. The relative signs of the coupling constants were obtained using triple resonance. The observed ENDOR second-order splitting (0.009 mT) together with the line positions are in complete agreement with theoretical prediction.

Evans, J. C.; Obaid, A. Y.; Rowlands, C. C.

1984-08-01

110

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

111

DC current induced second order optical nonlinearity in graphene.  

PubMed

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

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

2014-06-30

112

Unexpected second-order nonlinear optical effects in conjugated polymers  

NASA Astrophysics Data System (ADS)

Conjugated polymers do not only attract great attention due to their suitability in organic transistors, light emitting diodes and solar cells, moreover, they posses unexpected record-high second-order nonlinear optical responses. Nonlinear optical polymers have been reported as attractive materials for space applications such as electro-optic modulation and optical power limiting. In this work, we report on a new approach for increased second-order nonlinear properties demonstrated in a series of poly(thiophene) derivatives and poly(phenanthrene)s.

Asselberghs, Inge; Clays, Koen; Verbiest, Thierry; Koeckelberghs, Guy

2011-09-01

113

Second order bibliometric operators in the Astrophysics Data System  

NASA Astrophysics Data System (ADS)

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 systems in the degree to which users are permitted to make use of these concepts. Given a knowledge of how the second order operators work, ADS users can create complex logical algebras which facilitate the discovery of very highly specific information.

Kurtz, Michael J.; Eichhorn, Guenther; Accomazzi, Alberto; Grant, Carolyn S.; Murray, Stephen S.

2002-12-01

114

Second order perturbation theory for nonlinear time-dependent problems: Application to a simplified coupled transient  

SciTech Connect

In this paper a second-order perturbation technique for nonlinear time-dependent problems is presented and applied to a simplified multi-physics model. This method is developed by using the properties of the adjoint problem which allows calculating the set of first and second order coefficients by solving a number of linear systems. As an illustrative example the adjoint procedure is applied to a reference transient problem, represented by a coupled point-kinetic/lumped-parameters model, and used to calculate the sensitivity coefficients of a safety related response with respect to a set of input parameters. The results obtained are compared with the values given by a direct sampling of the forward nonlinear problem. A way to reduce the number of calculations required for the application of second order adjoint techniques is also discussed. Our first results show that the procedure provides good estimations in presence of higher order perturbation components, being able to reconstruct the responses of interest even in presence of non-Gaussian probability density functions. Furthermore, the use of reduced second order information decreases the computational requirements of the method, making it appealing for possible large scale applications. (authors)

Gilli, L.; Lathouwers, D.; Kloosterman, J. L.; Van Der Hagen, T. H. J. J. [Delft Univ. of Technology, Dept. of Radiation, Radionuclides and Reactors, Physics of Nuclear Reactors, Mekelweg 15, 2629 JB Delft (Netherlands)

2012-07-01

115

Electrochemically responsive heterogeneous catalysis for controlling reaction kinetics.  

PubMed

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

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

2015-01-28

116

Why Fundamental Physical Equations Are of Second Order?  

E-print Network

Why Fundamental Physical Equations Are of Second Order? Takeshi Yamakawa1 and Vladik Kreinovich2 1 physical equations, i.e., equations which describe the evolution of fundamental 1 #12;fields and forces describe electrodynamics, Einstein's equations which describe general relativity, Schr¨odinger's and Dirac

Kreinovich, Vladik

117

Why Fundamental Physical Equations Are of Second Order?  

E-print Network

Why Fundamental Physical Equations Are of Second Order? Takeshi Yamakawa 1 and Vladik Kreinovich 2 physical equations, i.e., equations which describe the evolution of fundamental 1 #12; fields and forces describe electrodynamics, Einstein's equations which describe general relativity, Schr¨odinger's and Dirac

Kreinovich, Vladik

118

Exploiting Second-Order Cone Structure for Global Optimization  

E-print Network

Oct 28, 2010 ... harmonic mean of positive affine functions, using second-order cones. ... If A is positive semidefinite, all eigenvalues of A are nonnegative. ...... automatically, without any manual intervention. .... Journal of Global Optimization, 6:215–230, 1995. doi: ... The behavior of eigenvalues and singular values under ...

2010-10-28

119

Second-order Talbot effect with entangled photon pairs  

Microsoft Academic Search

The second-order Talbot effect is analyzed for a periodic object illuminated by entangled photon pairs in both the quantum imaging and quantum lithography configurations. The Klyshko picture is applied to describe the quantum imaging scheme, in which self-images of the object that may or may not be magnified can be observed nonlocally in the photon coincidences but not in the

Kai-Hong Luo; Jianming Wen; Xi-Hao Chen; Qian Liu; Min Xiao; Ling-An Wu

2009-01-01

120

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

121

Second-Order DMOC Using Projection Kristine L. Snyder  

E-print Network

, is a method that uses variational integrators to find the optimal control for a given discretized physicalSecond-Order DMOC Using Projection Kristine L. Snyder Department of Applied Mathematics 526 UCB-murphey@northwestern.edu Abstract-- Discrete mechanics and optimal control (DMOC) is a recent development in optimal control

Hartmann, Mitra J. Z.

122

Implicit second-order immersed boundary methods with boundary mass  

Microsoft Academic Search

The immersed boundary method is a computational framework for problems involving the interaction of a fluid and immersed elastic structures. Immersed boundary computations typically evaluate the elastic forces explicitly in the configuration of the immersed elastic structure. In many applications this results in a severe restriction on the time step. We present a semi-implicit and a fully implicit second-order accurate

Yoichiro Mori; Charles S. Peskin

2008-01-01

123

Second order sliding mode motion control of rigid robot manipulators  

Microsoft Academic Search

This paper presents a control strategy for robot manipulators, based on the coupling of the inverse dynamics method with the so-called second order sliding mode control approach. The motivation for using sliding mode control in robotics mainly relies on its appreciable features, such as design simplicity and robustness. Yet, the chattering effect, typical of the conventional sliding mode control, can

Luca M. Capisani; Antonella Ferrara; Lorenza Magnani

2007-01-01

124

Two-photon pattern in a second-order interference  

Microsoft Academic Search

An interferometric arrangement utilizing a pair of twin photons, generated by parametric down-conversion, is devised to show second-order interferences revealing de Broglie's wavelength of the photon pair as a whole and the Pancharatnam phase depending on the number of photons. This proposed experiment utilizes the phenomenon ``induced coherence without stimulated emission'' to generate a coherent superposition of states distinct from

H. H. Arnaut; G. A. Barbosa

1998-01-01

125

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

126

Generalized Second-Order Partial Derivatives of 1/r  

ERIC Educational Resources Information Center

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

Hnizdo, V.

2011-01-01

127

Second-order accurate nonoscillatory schemes for scalar conservation laws  

NASA Technical Reports Server (NTRS)

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

Huynh, Hung T.

1989-01-01

128

A New Factorisation of a General Second Order Differential Equation  

ERIC Educational Resources Information Center

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

Clegg, Janet

2006-01-01

129

Second-order contribution to the gravitational deflection of light  

SciTech Connect

We calculate the gravitational deflection of light to second order in the Newtonian constant G. For a light ray passing the Sun with impact parameter b, the deflection in general relativity is (4GM/sub sun/ /bc/sup 2/) x (1+(15..pi../16)(GM/sub sun/ /bc/sup 2/)) radians.

Fischbach, E.; Freeman, B.S.

1980-12-15

130

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

131

SECOND ORDER PDES WITH DIRICHLET WHITE NOISE BOUNDARY CONDITIONS  

E-print Network

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

Sydney, University of

132

Missile autopilot design based on second order sliding modes control  

Microsoft Academic Search

The difficulties in designing an effective load control missile autopilot arise from highly nonlinear and non-minimum phase plant characteristics because the missile acceleration is regarded as output. To avoid the instability problem associated with unstable zero dynamics, a modified second order sliding mode controller was proposed through reconstruction of the novel sliding surface, and the suitable commutation logic of control

Anli Shang; Wenjin Gu; Yuman Yuan; Congying Li

2004-01-01

133

SECOND-ORDER ELASTICITY AND FIRST-ORDER FREDERIKS TRANSITIONS  

E-print Network

SECOND-ORDER ELASTICITY AND FIRST-ORDER FREDERIKS TRANSITIONS IN NEMATIC LIQUID CRYSTALS H. P by Deuling and Hel- frich [5] for homeotropic nematic liquid crystal layers with a large anisotropic.aid of the surface anchoring energy. 1. Introduction. -- The static deformations in nematic liquid layers with Rapini

Boyer, Edmond

134

Solving Second-Order Differential Equations with Variable Coefficients  

ERIC Educational Resources Information Center

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

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

2008-01-01

135

Second-order cone programming approach for elliptically distributed ...  

E-print Network

May 21, 2014 ... programming problems based on second-order cone programming, which ... A problem involving probability constraints was first formulated by ..... Law. Characteristic generator ?(t) Radial density gs(t) Normalizing constant cs ...... Dempster, editors, Stochastic Optimization Methods in Finance and Energy, ...

2014-05-21

136

Second-order accurate difference schemes on highly irregular meshes  

SciTech Connect

In this paper compact-as-possible second-order accurate difference schemes will be constructed for boundary-value problems of arbitrary order on highly irregular meshes. It will be shown that for equations of order (K) these schemes will have truncation error of order (3/endash/K). This phenomena is known as supraconvergence. 7 refs.

Manteuffel, T.A.; White, A.B. Jr.

1988-01-01

137

A GENERALIZED SECOND ORDER FRAME BUNDLE FOR FRECHET MANIFOLDS  

E-print Network

A GENERALIZED SECOND ORDER FRAME BUNDLE FOR FR´ECHET MANIFOLDS C.T.J. DODSON, G.N. GALANIS, AND E. VASSILIOU Abstract. Working within the framework of Fr´echet modelled infinite di- mensional manifolds, we characteristics of a frame bundle: It is a principal Fr´echet bun- dle associated (differentially

Dodson, C.T.J.

138

Second order structures for sprays and connections on Frechet manifolds  

E-print Network

Second order structures for sprays and connections on Fr´echet manifolds M. Aghasi1 , A.R. Bahari1 paper all of these results are generalized to a large class of Fr´echet mani- folds. It is proved Fr´echet man- ifolds which can be considered as projective limits of Banach manifolds. These concepts

Dodson, C.T.J.

139

PID Control of Second-Order Systems with Hysteresis  

E-print Network

PID Control of Second-Order Systems with Hysteresis Bayu Jayawardhana, Hartmut Logemann & Eugene P 2007 Abstract. The efficacy of proportional, integral and derivative (PID) control for set point on the PID gains, explicitly formulated in terms of the system data, are determined under which asymptotic

Ryan, E.P.

140

Nonmonotone Impulse Effects in Second Order Periodic Boundary Value Problems  

E-print Network

Nonmonotone Impulse Effects in Second Order Periodic Boundary Value Problems Irena Rach°unkov´a and Milan Tvrd´y September 20, 2002 Summary. This paper deals with the nonlinear impulsive periodic boundary. In contrast to previous papers investigating such problems, the monotonicity of the impulse functions Ji, Mi

Rachùnkova, Irena

141

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

142

Bayesian experts in exploring reaction kinetics of transcription circuits  

PubMed Central

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

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

2010-01-01

143

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

144

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

145

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

146

Oxidation of antibacterial molecules by aqueous ozone: moiety-specific reaction kinetics and application to ozone-based wastewater treatment.  

PubMed

Ozone and hydroxyl radical (*OH) reaction kinetics were measured for 14 antibacterial compounds from nine structural families, to determine whether municipal wastewater ozonation is likely to result in selective oxidation of these compounds' biochemically essential moieties. Each substrate is oxidized by ozone with an apparent second-order rate constant, k''(O3,app) > 1 x 10(3) M(-1) s(-1), at pH 7, with the exception of N(4)-acetylsulfamethoxazole (K''(O3,app) is 2.5 x 102 M(-1) s(-1)). k''(O3,app) values (pH 7) for macrolides, sulfamethoxazole, trimethoprim, tetracycline, vancomycin, and amikacin appear to correspond directly to oxidation of biochemically essential moieties. Initial reactions of ozone with N(4)-acetylsulfamethoxazole, fluoroquinolones, lincomycin, and beta-lactams do not lead to appreciable oxidation of biochemically essential moieties. However, ozone oxidizes these moieties within fluoroquinolones and lincomycin via slower reactions. Measured k''(O3,app) values and second-order *OH rate constants, k''(*OH,app) were utilized to characterize pollutant losses during ozonation of secondary municipal wastewater effluent. These losses were dependent on k''(O3,app), but independent of k''(*OH,app). Ozone doses > or =3 mg/L yielded > or =99% depletion of fast-reacting substrates (K''(O3,app) > 5 x 10(4) M(-1) s(-1)) at pH 7.7. Ten substrates reacted predominantly with ozone; only four were oxidized predominantly by .OH. These results indicate that many antibacterial compounds will be oxidized in wastewater via moiety-specific reactions with ozone. PMID:16570623

Dodd, Michael C; Buffle, Marc-Olivier; Von Gunten, Urs

2006-03-15

147

Manifestation of macroscopic correlations in elementary reaction kinetics. II. Irreversible reaction A +B?C  

NASA Astrophysics Data System (ADS)

The applicability of the Encounter Theory (ET) (the prototype of the Collision Theory) concepts for widely occurring diffusion assisted irreversible bulk reaction A +B?C (for example, radical reaction) in dilute solutions with arbitrary ratio of initial concentrations of reactants has been treated theoretically with modern many-particle method for the derivation of non-Markovian binary kinetic equations. The method shows that, just as in the reaction A +A?C considered earlier, the agreement with the Encounter Theory is observed when the familiar Integral Encounter Theory is used which is just a step in the derivation of kinetic equations in the framework of the method employed. It allows for two-particle correlations only, and fails to consider the correlation of reactant simultaneously with a partner and with a reactant in the bulk. However, the next step leading to the Modified Encounter Theory under reduction of equations to a regular form both extends the time applicability interval of ET homogeneous rate equation (as for reactions proceeding in excess of one of the reactants), and yields the inhomogeneous equation of the Generalized Encounter Theory (GET) that reveals macroscopic correlations induced by the encounters in a reservoir of free walks in full agreement with physical considerations. This means that the encounters of reactants in solution are correlated at rather large time interval of the reaction course. However, unlike the reaction A +A?C of identical reactants, the reaction A +B?C accumulation of the above macroscopic correlations (even with the initial concentrations of reactants being equal) proceeds much slower. Another distinction is that for the reaction A +A?C the long-term behavior of ET and GET kinetics is the same, while in the reaction A +B?C these kinetics behave differently. It is of interest that just taking account of the above macroscopic correlations in the reaction A +B?C (in GET) results in the universal character of the long-term behavior of the kinetics for the case of equal initial concentrations of reactants and that where one of the reactants is in excess. This is more natural from the point of view of the reaction course on the encounters of reactants in solutions.

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

2010-11-01

148

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

149

Periodic orbits from second order perturbation via rational trigonometric integrals  

NASA Astrophysics Data System (ADS)

The second order Poincaré-Pontryagin-Melnikov perturbation theory is used in this paper to study the number of bifurcated periodic orbits from certain centers. This approach also allows us to give the shape and the period up to the first order. We address these problems for some classes of Abel differential equations and quadratic isochronous vector fields in the plane. We prove that two is the maximum number of hyperbolic periodic orbits bifurcating from the isochronous quadratic centers with a birational linearization under quadratic perturbations of second order. In particular the configurations (2,0) and (1,1) are realizable when two centers are perturbed simultaneously. The required computations show that all the considered families share the same iterated rational trigonometric integrals.

Prohens, R.; Torregrosa, J.

2014-07-01

150

On second-order, divergence-free tensors  

NASA Astrophysics Data System (ADS)

The aim of this paper is to describe the vector spaces of those second-order tensors on a pseudo-Riemannian manifold (i.e., tensors whose local expressions only involve second derivatives of the metric) that are divergence-free. The main result establishes isomorphisms between these spaces and certain spaces of tensors (at a point) that are invariant under the action of an orthogonal group. This result is valid for tensors with an arbitrary number of indices and symmetries among them and, in certain cases, it allows to explicitly compute basis, using the classical theory of invariants of the orthogonal group. In the particular case of tensors with two indices, we prove the Lovelock tensors are a basis for the vector space of second-order, divergence-free 2-tensors. This statement generalizes to arbitrary dimension a result established by Lovelock in the case of four-dimensional manifolds.

Navarro, José

2014-06-01

151

Finite differencing second order systems describing black hole spacetimes  

SciTech Connect

Keeping Einstein's equations in second order form can be appealing for computational efficiency, because of the reduced number of variables and constraints. Stability issues emerge, however, which are not present in first order formulations. We show that a standard discretization of the second order 'shifted' wave equation leads to an unstable semidiscrete scheme if the shift parameter is too large. This implies that discretizations obtained using integrators such as Runge-Kutta, Crank-Nicholson, and leapfrog are unstable for any fixed value of the Courant factor. We argue that this situation arises in numerical relativity, particularly in simulations of spacetimes containing black holes, and discuss several ways of circumventing this problem. We find that the first order reduction in time based on Arnowitt-Deser-Misner-type variables is very effective.

Calabrese, Gioel [School of Mathematics, University of Southampton, Southampton, SO17 1BJ (United Kingdom)

2005-01-15

152

First- and second-order charged particle optics  

SciTech Connect

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

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

1984-07-01

153

Smoothing Functions for Second-Order-Cone Complementarity Problems  

Microsoft Academic Search

Smoothing functions have been much studied in the solution of optimization and complementarityproblems with nonnegativity constraints. In this paper, we extend smoothing functions to problemswhere the nonnegative orthant is replaced by the direct product of second-order cones. Thesesmoothing functions include the Chen-Mangasarian class and the smoothed Fischer-Burmeisterfunction. We study the Lipschitzian and dierential properties of these functions and, in particular,we

Masao Fukushima; Zhi-Quan Luo; Paul Tseng

2002-01-01

154

Minimum time control of a second-order system  

Microsoft Academic Search

A new algorithm for determining the switching time and final time for the minimum-time control of a second-order system is described. We show that if there is only one switch in the bang-bang control, then the switching time and final time are related through an affine mapping. This mapping is determined by the system dynamics, the initial and target states,

Zhaolong Shen; Sean B. Andersson

2010-01-01

155

Superquadric Glyphs for Symmetric Second-Order Tensors  

Microsoft Academic Search

Symmetric second-order tensor fields play a central role in scientific and biomedical studies as well as in image analysis and feature-extraction methods. The utility of displaying tensor field samples has driven the development of visualization techniques that encode the tensor shape and orientation into the geometry of a tensor glyph. With some exceptions, these methods work only for positive-definite tensors

Thomas Schultz; Gordon L. Kindlmann

2010-01-01

156

Gravitational waves from global second order phase transitions  

SciTech Connect

Global second-order phase transitions are expected to produce scale-invariant gravitational wave spectra. In this manuscript we explore the dynamics of a symmetry-breaking phase transition using lattice simulations. We explicitly calculate the stochastic gravitational wave background produced during the transition and subsequent self-ordering phase. We comment on this signal as it compares to the scale-invariant spectrum produced during inflation.

Jr, John T. Giblin [Department of Physics, Kenyon College, 201 North College Rd, Gambier, OH 43022 (United States); Price, Larry R.; Siemens, Xavier; Vlcek, Brian, E-mail: giblinj@kenyon.edu, E-mail: larryp@caltech.edu, E-mail: siemens@gravity.phys.uwm.edu, E-mail: bvlcek@uwm.edu [Center for Gravitation and Cosmology, Department of Physics, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201 (United States)

2012-11-01

157

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 temperatures below the electron mass that is $Ttemperatures has explicitly been checked. The electromagnetic properties of such a thermal medium are modified. Parameters like electric permittivity and magnetic permeability of such a medium are no more constant and become functions of temperature.

Samina S. Masood; Mahnaz Q. Haseeb

2006-12-11

158

Second order symmetric duality for nonlinear minimax mixed integer programs  

Microsoft Academic Search

Wolfe type second order minimax mixed integer dual programs are formulated and a symmetric duality theorem is e established under separability and bonvexity\\/boncavity of the kernel function K(x, y). Mond-Weir type symmetric duality is also discussed under weaker bonvexity assumptions. Moreover, self-duality theorems for these pairs are obtained assuming K(x, y) to be skew symmetric.

T. R. Gulati; Izhar Ahmad

1997-01-01

159

Harmonic entanglement with second-order non-linearity  

E-print Network

We investigate the second-order non-linear interaction as a means to generate entanglement between fields of differing wavelengths. And show that perfect entanglement can, in principle, be produced between the fundamental and second harmonic fields in these processes. Neither pure second harmonic generation, nor parametric oscillation optimally produce entanglement, such optimal entanglement is rather produced by an intermediate process. An experimental demonstration of these predictions should be imminently feasible.

Nicolai B. Grosse; Warwick P. Bowen; Kirk McKenzie; Ping Koy Lam

2005-07-08

160

Cosmological perturbations at second order and recombination perturbed  

Microsoft Academic Search

We derive the full set of second-order equations governing the evolution of cosmological perturbations, including the effects of the first-order electron number density perturbations, deltae. We provide a detailed analysis of the perturbations to the recombination history of the universe and show that a perturbed version of the Peebles effective 3-level atom is sufficient for obtaining the evolution of deltae

Leonardo Senatore; Svetlin Tassev; Matias Zaldarriaga

2009-01-01

161

Local conservation laws of second-order evolution equations  

E-print Network

Generalizing results by Bryant and Griffiths [Duke Math. J., 1995, V.78, 531-676], we completely describe local conservation laws of second-order (1+1)-dimensional evolution equations up to contact equivalence. The possible dimensions of spaces of conservation laws prove to be 0, 1, 2 and infinity. The canonical forms of equations with respect to contact equivalence are found for all nonzero dimensions of spaces of conservation laws.

Roman O. Popovych; Anatoly M. Samoilenko

2008-06-17

162

Second order filter response with series coupled silica microresonators  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

163

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

164

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

165

Second order ODEs under area-preserving maps  

NASA Astrophysics Data System (ADS)

We study the geometry of real analytic second order ODEs under the local real analytic diffeomorphism of {R}^2 which are area preserving, through the method of Cartan. We obtain a subdivision into three "parts". The first one is the most symmetric case. It is characterized by the vanishing of an area-preserving relative invariant namely f_y+dfrac{2}{9}f_{y^' }}2-dfrac{1}{3}{D}(f_{y^' }}) . In this situation we associate a local affine normal Cartan connection on the first jet J1({R},{R}) space whose curvature contains all the area-preserving relative differential invariants, to any second order ODE under study. The second case which includes all the Painlevé transcendents is given by the ODEs for which f_y+dfrac{2}{9}f_{y^' }}2-dfrac{1}{3}{D}(f_{y^' }})not ? 0 . In the latter case we give all necessary steps in order to obtain an e -structure on J1({R},{R}) for a generic second order ODE equation of that type. Finally we give the method to reduce to an e -structure on J1 when f_{y^' y^' y^' y^' }not ? 0.

Wone, Oumar

2014-07-01

166

Numerical treatment of interfaces for second-order wave equations  

E-print Network

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

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

2014-06-12

167

Second-order reconstruction of the inflationary potential  

NASA Technical Reports Server (NTRS)

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

Liddle, Andrew R.; Turner, Michael S.

1994-01-01

168

Kinetics and equilibria of the reductive and oxidative half-reactions of human renalase with ?-NADPH.  

PubMed

Renalase is a recently discovered flavoprotein that has been reported to be a hormone produced by the kidney to down-modulate blood pressure and heart rate. The consensus belief has been that renalase oxidizes circulating catecholamine neurotransmitters thereby attenuating vascular tone. However, a convincing in vitro demonstration of this activity has not been made. We have recently discovered that renalase has ?-NAD(P)H oxidase/anomerase activity. Unlike most naturally occurring nucleotides, NAD(P)H can accumulate small amounts of the ?-anomers that once oxidized are configurationally stable and unable to participate in cellular activity. Thus, anomerization of NAD(P)H would result in a continual loss of cellular redox currency. As such, it appears that the root purpose of renalase is to return ?-anomers of nicotinamide dinucleotides to the ?-anomer pool. In this article, we measure the kinetics and equilibria of renalase in turnover with ?-NADPH. Renalase is selective for the ?-anomer, which binds with a dissociation constant of ?20±3 ?M. This association precedes monophasic two-electron reduction of the FAD cofactor with a rate constant of 40.2±1.3 s(-1). The reduced enzyme then delivers both electrons to dioxygen in a second-order reaction with a rate constant of ?2900 M(-1) s(-1). Renalase has modest affinity for its ?-NADP+ product (Kd=2.2 mM), and the FAD cofactor has a reduction potential of -155 mV that is unaltered by saturating ?-NADP+. Together these data suggest that the products are formed and released in a kinetically ordered sequence (?-NADP+ then H2O2), however, the reoxidation of renalase is not contingent on the dissociation of ?-NADP+. Neither the oxidized nor the reduced form of renalase is able to catalyze anomerization, implying that the redox and anomerization chemistries are inextricably linked through a common intermediate. PMID:24266457

Beaupre, Brett A; Hoag, Matthew R; Carmichael, Brenton R; Moran, Graham R

2013-12-10

169

Local kinetics and thermodynamics of rapid electrochemical reactions  

NASA Astrophysics Data System (ADS)

We introduce and discuss a local kinetic mechanism for an n-electron electrochemical reaction at the interface formed by an electrode and diluted electrolyte. We show that the suggested mechanism is in agreement with the Nernst equation in the thermal equilibrium. We also qualitatively characterize the structure of a flat electrode-diluted electrolyte boundary in the meaning of the spatial distribution of electrochemical reactants and electric potential. As the suggested kinetic mechanism is not limited by the duration of relaxation processes in electric double layers, it is suitable for the understanding and simulation of fast transient processes that appear in modern applications such as nanocolloid dielectrophoresis, AC electrospray, AC electroosmosis, or nanopore biosensing.

P?ibyl, Michal; Šnita, Dalimil

2014-04-01

170

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

171

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

172

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

NASA Technical Reports Server (NTRS)

Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

Liechty, Derek S.; Lewis, Mark J.

2010-01-01

173

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

NASA Astrophysics Data System (ADS)

Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

Liechty, Derek S.; Lewis, Mark J.

2011-05-01

174

Kinetic studies of cascade reactions in high-throughput systems.  

PubMed

The application of robotic systems to the study of complex reaction kinetics is considered, using the cascade reaction A --> B --> C as a working example. Practical problems in calculating the rate constants k1 and k2 for the reactions A --> B and B --> C from concentration measurements of CA, CB, or CC are discussed in the light of the symmetry and invertability of the rate equations. A D-optimal analysis is used to determine the points in time and the species that will give the best (i.e., most accurate) results. When exact data are used, the most robust solution results from measuring the pair of concentrations (CA, CC). The system's information function is computed using numeric methods. This function is then used to estimate the amount of information obtainable from a given cascade reaction at any given time. The theoretical findings are compared with experimental results from a set of two-stage cascade experiments monitored using UV-visible spectroscopy. Finally, the pros and cons of using a single reaction sample to estimate both k1 and k2 are discussed. PMID:16465720

Iron, David; Boelens, Hans F M; Westerhuis, Johan A; Rothenberg, Gadi

2003-12-01

175

Kinetic study of Nafion degradation by Fenton reaction  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

176

Modeling Binding Kinetics at the QA Site in Bacterial Reaction Centers†  

PubMed Central

Bacterial reaction centers (RCs) catalyze a series of electron-transfer reactions reducing a neutral quinone to a bound, anionic semiquinone. The dissociation constants and association rates of 13 tailless neutral and anionic benzo- and naphthoquinones for the QA site were measured and compared. The Kd values for these quinones range from 0.08 to 90 ?M. For the eight neutral quinones, including duroquinone (DQ) and 2,3-dimethoxy-5-methyl-1,4-benzoquinone (UQ0), the quinone concentration and solvent viscosity dependence of the association rate indicate a second-order rate-determining step. The association rate constants (kon) range from 105 to 107 M?1 s?1. Association and dissociation rate constants were determined at pH values above the hydroxyl pKa for five hydroxyl naphthoquinones. These negatively charged compounds are competitive inhibitors for the QA site. While the neutral quinones reach equilibrium in milliseconds, anionic hydroxyl quinones with similar Kd values take minutes to bind or dissociate. These slow rates are independent of ionic strength, solvent viscosity, and quinone concentration, indicating a first-order rate-limiting step. The anionic semiquinone, formed by forward electron transfer at the QA site, also dissociates slowly. It is not possible to measure the association rate of the unstable semiquinone. However, as the protein creates kinetic barriers for binding and releasing anionic hydroxyl quinones without greatly increasing the affinity relative to neutral quinones, it is suggested that the QA site may do the same for anionic semiquinone. Thus, the slow semiquinone dissociation may not indicate significant thermodynamic stabilization of the reduced species in the QA site. PMID:16101283

Madeo, Jennifer; Gunner, M. R.

2009-01-01

177

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

178

Anomalous kinetics of attractive A + B-->0 reactions.  

PubMed

We investigate the kinetics of the A + B-->0 reaction with the attractive interaction between opposite species in one spatial dimension. The attractive interaction leads to isotropic diffusions inside segregated single species domains, and accelerates the reactions of opposite species at the domain boundaries. At equal initial densities of and , we analytically and numerically show that the density of particles (rho), the size of domains (l), the distance between the closest neighbor of same species (lAA), and the distance between adjacent opposite species (lAB) scale in time as rho approximately t(-1/3), lAA approximately t(1/3), and l approximately lAB approximately lAB(2/3), respectively. These dynamical exponents define critical behavior distinguished from the class of uniformly driven systems of hard-core particles. PMID:16605379

Kwon, Sungchul; Yoon, S Y; Kim, Yup

2006-02-01

179

Chaotic properties of spin lattices near second-order phase transitions  

E-print Network

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

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

2014-10-21

180

Two-photon pattern in a second-order interference  

NASA Astrophysics Data System (ADS)

An interferometric arrangement utilizing a pair of twin photons, generated by parametric down-conversion, is devised to show second-order interferences revealing de Broglie's wavelength of the photon pair as a whole and the Pancharatnam phase depending on the number of photons. This proposed experiment utilizes the phenomenon ``induced coherence without stimulated emission'' to generate a coherent superposition of states distinct from the usual superposition with beam splitters, where the photons are independently scattered. In this experiment interference occurs due to recombination of photon trajectories on a beam splitter and also through frustration or enhancement of the down-conversion processes.

Arnaut, H. H.; Barbosa, G. A.

1998-11-01

181

Dynamic Uncertainty for Compensated Second-Order Systems  

PubMed Central

The compensation of LTI systems and the evaluation of the according uncertainty is of growing interest in metrology. Uncertainty evaluation in metrology ought to follow specific guidelines, and recently two corresponding uncertainty evaluation schemes have been proposed for FIR and IIR filtering. We employ these schemes to compare an FIR and an IIR approach for compensating a second-order LTI system which has relevance in metrology. Our results suggest that the FIR approach is superior in the sense that it yields significantly smaller uncertainties when real-time evaluation of uncertainties is desired. PMID:22163618

Eichstädt, Sascha; Link, Alfred; Elster, Clemens

2010-01-01

182

Witnessing Entanglement of EPR States With Second-Order Interference  

E-print Network

The separability of the continuous-variable EPR state can be tested with Hanbury-Brown and Twiss type interference. The second-order visibility of such interference can provide an experimental test of entanglement. It is shown that time-resolved interference leads to the Hong, Ou and Mandel deep, that provides a signature of quantum non-separability for pure and mixed EPR states. A Hanbury-Brown and Twiss type witness operator can be constructed to test the quantum nature of the EPR entanglement.

Magdalena Stobi?ska; Krzysztof Wódkiewicz

2006-08-31

183

Combined first and second order Fermi acceleration at comets  

NASA Technical Reports Server (NTRS)

Two-dimensional, time-dependent model calculations indicate that an interplay between velocity and spatial diffusion may be responsible for the acceleration of implanted heavy ions in the cometary preshock region. Velocity diffusion (second order Fermi acceleration) accelerates the pickup ions to moderate energies thus creating a seed population for the more efficient diffusive-compressive shock acceleration. Solar wind convection limits the time available for diffusive-compressive acceleration, therefore the resulting energy spectrum above 100 keV is a power law with a spectral index of 5 - 6, a value which is in reasonably good agreement with observations.

Gombosi, T. I.; Lorencz, K.; Jokipii, J. R.

1989-01-01

184

Galaxy number counts to second order and their bispectrum  

NASA Astrophysics Data System (ADS)

We determine the number counts to second order in cosmological perturbation theory in the Poisson gauge and allowing for anisotropic stress. The calculation is performed using an innovative approach based on the recently proposed ``geodesic light-cone" gauge. This allows us to determine the number counts in a purely geometric way, without using Einstein's equation. The result is valid for general dark energy models and (most) modified gravity models. We then evaluate numerically some relevant contributions to the number counts bispectrum. In particular we consider the terms involving the density, redshift space distortion and lensing.

Di Dio, Enea; Durrer, Ruth; Marozzi, Giovanni; Montanari, Francesco

2014-12-01

185

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

186

UV-induced reaction kinetics of dilinoleoylphosphatidylethanolamine monolayers.  

PubMed Central

The UV-induced reactivity of dilinoleoylphosphatidylethanolamine (DLiPE) Langmuir and Langmuir-Blodgett films has been studied by in situ measurements of the changes in the mean molecular area, UV-vis and Fourier transform infrared spectroscopy, and atomic force microscopy (AFM). Optimum orientation and packing density of the DLiPE molecules in the monolayer were achieved by adding uranyl acetate to the subphase. A first-order reaction kinetic model was successfully fitted to the experimental reaction kinetics data obtained at a surface pressure of 30 mN/m. Topographical studies of LB films by AFM were performed on bilayer structures as a function of subphase composition and UV irradiation time. The orientational effect of the uranyl ions on the monolayer molecules was observed as an enhanced homogeneity of the freshly prepared monomeric LB films. However, the long-term stability of these films proved to be bad; clear reorganization and loss of a true monolayer structure were evidenced by the AFM images. This instability was inhibited for the UV-irradiated films, indicating that the UV irradiation gave rise to a cross-linked structure. PMID:10233096

Viitala, T; Peltonen, J

1999-01-01

187

Second-Order Relational Manipulations Affect Both Humans and Monkeys  

PubMed Central

Recognition and individuation of conspecifics by their face is essential for primate social cognition. This ability is driven by a mechanism that integrates the appearance of facial features with subtle variations in their configuration (i.e., second-order relational properties) into a holistic representation. So far, there is little evidence of whether our evolutionary ancestors show sensitivity to featural spatial relations and hence holistic processing of faces as shown in humans. Here, we directly compared macaques with humans in their sensitivity to configurally altered faces in upright and inverted orientations using a habituation paradigm and eye tracking technologies. In addition, we tested for differences in processing of conspecific faces (human faces for humans, macaque faces for macaques) and non-conspecific faces, addressing aspects of perceptual expertise. In both species, we found sensitivity to second-order relational properties for conspecific (expert) faces, when presented in upright, not in inverted, orientation. This shows that macaques possess the requirements for holistic processing, and thus show similar face processing to that of humans. PMID:21991354

Dahl, Christoph D.; Logothetis, Nikos K.; Bülthoff, Heinrich H.; Wallraven, Christian

2011-01-01

188

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

ERIC Educational Resources Information Center

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

Sobel, Sabrina G.; Cohen, Skyler

2010-01-01

189

Chlorine Transfer Reactions between Chloramine and 1-Piperidine: Kinetic Reactivity and Characterization in a  

E-print Network

1 Chlorine Transfer Reactions between Chloramine and 1- Piperidine: Kinetic Reactivity) 98-111" #12;2 Abstract The kinetics of the chlorine transfer reaction between chloramine and 1H ranging between 8.25 and 12.89. The chlorine transfer reaction resulted in the formation of 1

Boyer, Edmond

190

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

191

Second-order effects in complex rheological flows  

NASA Astrophysics Data System (ADS)

The interfacial shape of two immiscible simple fluids in a vertical cylinder which oscillates about its axis is investigated using the theory of domain perturbations. The perturbation stresses are expressed by integrals over the history of the deformation. At first order the azimuthal velocity field satisfies the requirements of continuity in velocity and shear stresses across the interface. At second order the solution consists of a mean part and a time periodic part varying at twice the frequency of the cylinder. The mean problem is inverted for the mean secondary flow, pressure and interfacial shape. Experimental data for two polymeric oils (TLA227 and STP) show qualitative agreement with theoretical predictions for the mean interfacial shapes.

Tieu, H. A.

192

Simple expressions for second order density perturbations in standard cosmology  

E-print Network

In this paper we present four simple expressions for the relativistic first and second order fractional density perturbations for $\\Lambda$CDM cosmologies in different gauges: the Poisson, uniform curvature, total matter and synchronous gauges. A distinctive feature of our approach is the use of a canonical set of quadratic differential expressions involving an arbitrary spatial function, the so-called comoving curvature perturbation, to describe the spatial dependence, which enables us to unify, simplify and extend previous seemingly disparate results. The simple structure of the expressions makes the evolution of the density perturbations completely transparent and clearly displays the effect of the cosmological constant on the dynamics, namely that it stabilizes the perturbations. We expect that the results will be useful in applications, for example, studying the effects of primordial non-Gaussianity on the large scale structure of the universe.

Claes Uggla; John Wainwright

2014-02-11

193

Digital second-order phase-locked loop  

NASA Technical Reports Server (NTRS)

A digital second-order phase-locked loop is disclosed in which a counter driven by a stable clock pulse source is used to generate a reference waveform of the same frequency as an incoming waveform, and to sample the incoming waveform at zero-crossover points. The samples are converted to digital form and accumulated over M cycles, reversing the sign of every second sample. After every M cycles, the accumulated value of samples is hard limited to a value SGN = + or - 1 and multiplied by a value delta sub 1 equal to a number of n sub 1 of fractions of a cycle. An error signal is used to advance or retard the counter according to the sign of the sum by an amount equal to the sum.

Holes, J. K.; Carl, C.; Tegnelia, C. R. (inventors)

1973-01-01

194

Absorbing boundary conditions for second-order hyperbolic equations  

NASA Technical Reports Server (NTRS)

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

Jiang, Hong; Wong, Yau Shu

1990-01-01

195

A second-order analytic analysis for frozen orbits  

NASA Technical Reports Server (NTRS)

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

Tang, Charles C. H.

1988-01-01

196

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

197

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

198

Second order closure modeling of turbulent buoyant wall plumes  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

199

Kinetic study of the reactions between chloramine disinfectants and hydrogen peroxide: temperature dependence and reaction mechanism.  

PubMed

The temperature-dependent kinetics for the reaction between hydrogen peroxide and chloramine water disinfectants (NH2Cl, NHCl2, and NCl3) have been determined using stopped flow-UV/Vis spectrophotometry. Rate constants for the mono- and dichloramine-peroxide reaction were on the order of 10(-2)M(-1)s(-1) and 10(-5)M(-1)s(-1), respectively. The reaction of trichloramine with peroxide was negligibly slow compared to its thermal and photolytically-induced decomposition. Arrhenius expressions of ln(kH2O2-NH2Cl)=(17.3±1.5)-(51500±3700)/RT and ln(kH2O2-NHCl2)=(18.2±1.9)-(75800±5100)/RT were obtained for the mono- and dichloramine peroxide reaction over the temperature ranges 11.4-37.9 and 35.0-55.0°C, respectively. Both monochloramine and hydrogen peroxide were first-order in the rate-limiting kinetic step and concomitant measurements made using a chloride ion selective electrode showed that the chloride was produced quantitatively. These data will aid water utilities in predicting chloramine concentrations (and thus disinfection potential) throughout the water distribution system. PMID:23601896

McKay, Garrett; Sjelin, Brittney; Chagnon, Matthew; Ishida, Kenneth P; Mezyk, Stephen P

2013-09-01

200

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

201

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

202

Kinetic study of hydrated lime reaction with HCl.  

PubMed

Hydrochloride (HCl) is an acidic pollutant present in the flue gas of most municipal or hazardous waste incinerators. Hydrated lime (Ca(OH)2) is often used as a dry sorbent for injection in a spray reactor to remove HCI. However, due to the short residence time encountered, this control method has generally been found to have low conversion efficiencies which results in the high lime usage and generates large amount of fly ash as solid wastes. A fundamental study was carried outto investigate the kinetics of HCl-lime reaction under simulated flue gas conditions in order to better understand the process thereby providing a basis for an optimized lime usage and reduced fly ash production. The initial reaction rate and conversion of three limes were studied using a thermogravimetric analyzer by varying the gas flow rate, temperature (170-400 degrees C), and HCI concentrations (600-1200 mg/m3) as well as the associated particle size and surface area of the limes. The initial lime conversions were found to rely mostly on the residence time, while the ultimate lime conversions were strongly influenced by temperature and the reaction products. CaOHCI was found to be the primary product in most cases, while for one specific lime, CaCl2 was the ultimate conversion product after an extended time period. The true utilization of lime in flue gas cleanup is thus higher when CaOHCl is considered as the final product than those based on CaCl2 as the final product, which has been commonly used in previous studies. The initial reaction was controlled by diffusion of HCl in gas phase and the subsequent reaction by gaseous diffusion through the developing product layer. Increasing the HCI concentration raised the initial rate as well as conversion. However, overloading the lime with excessive HCI caused clogging at its surface and a drop in the ultimate conversion. Limes with smaller particle diameters and higher surface areas were found to be more reactive. The effect of gas-phase mass transfer was minimized when an optimum flow rate was chosen, and in the absence of internal diffusion the reaction was found to be first order with respect to HCI concentration. PMID:12831043

Yan, Rong; Chin, Terence; Liang, David Tee; Laursen, Karin; Ong, Wan Yean; Yao, Kaiwen; Tay, Joo Hwa

2003-06-01

203

General chemical kinetics computer program for static and flow reactions, with application to combustion and shock-tube kinetics  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

204

Correction of the Chromaticity up to Second Order for MEIC  

SciTech Connect

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

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

2010-03-01

205

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

206

Second-order asymptotics for quantum hypothesis testing  

E-print Network

In the asymptotic theory of quantum hypothesis testing, the minimal error probability of the first kind jumps sharply from zero to one when the error exponent of the second kind passes by the point of the relative entropy of the two states in an increasing way. This is well known as the direct part and strong converse of quantum Stein's lemma. Here we look into the behavior of this sudden change and have make it clear how the error of first kind grows smoothly according to a lower order of the error exponent of the second kind, and hence we obtain the second-order asymptotics for quantum hypothesis testing. This actually implies quantum Stein's lemma as a special case. Meanwhile, our analysis also yields tight bounds for the case of finite sample size. These results have potential applications in quantum information theory. Our method is elementary, based on basic linear algebra and probability theory. It deals with the achievability part and the optimality part in a unified fashion.

Ke Li

2014-02-27

207

Dinitrosyl Iron Complexes with Cysteine. Kinetics Studies of the Formation and Reactions of DNICs in Aqueous Solution.  

PubMed

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

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

2015-01-14

208

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

ERIC Educational Resources Information Center

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

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

2008-01-01

209

Kinetics and Thermodynamics of Atmospherically Relevant Aqueous Phase Reactions of Pinene Oxide  

E-print Network

Kinetics and Thermodynamics of Atmospherically Relevant Aqueous Phase Reactions of Pinene Oxide products, kinetics, and equilibria of the aqueous phase reactions of that epoxide, -pinene oxide. The present results indicate that -pinene oxide will react very quickly with aqueous atmospheric particles

Elrod, Matthew J.

210

Reactions of plutonium and uranium with water: Kinetics and potential hazards  

Microsoft Academic Search

The chemistry and kinetics of reactions between water and the metals and hydrides of plutonium and uranium are described in an effort to consolidate information for assessing potential hazards associated with handling and storage. New experimental results and data from literature sources are presented. Kinetic dependencies on pH, salt concentration, temperature and other parameters are reviewed. Corrosion reactions of the

Haschke

1995-01-01

211

Kinetics and mechanism of electron transfer in intact photosystem II and in the isolated reaction center  

E-print Network

Kinetics and mechanism of electron transfer in intact photosystem II and in the isolated reaction center: Pheophytin is the primary electron acceptor A. R. Holzwarth , M. G. Mu¨ ller , M. Reus , M and kinetics of electron transfer in isolated D1 D2-cytb559 photosystem (PS) II reaction centers (RCs

Roegner, Matthias

212

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

213

Second-Order Self-Organization in Coordination-Driven Self-Assembly: Exploring the Limits of Self-Selection  

PubMed Central

Self-organization during the self-assembly of a series of functionalized bispyridyl organic donors with complementary di-Pt(II) acceptors into supramolecular rhomboids and rectangles is explored. The connectivity and location of functional groups on the organic donors ensures that they do not interfere sterically or electronically with their respective binding sites. Carefully controlled reaction conditions are employed so that the only means of self-organization during self-assembly is through “second-order” effects arising from the distal functional groups themselves. With the selection of functionalized systems studied the extent of second-order self-organization varies from essentially zero to quite pronounced. PMID:18980302

Northrop, Brian H.; Yang, Hai-Bo; Stang, Peter J.

2009-01-01

214

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

215

Second order nonlinear spatial stability analysis of compressible mixing layers  

NASA Astrophysics Data System (ADS)

Second order nonlinear spatial stability to three-dimensional perturbation waves is analyzed for compressible mixing layers by expanding the perturbations into amplitude-dependent harmonic waves and truncating the Landau equation to the second term. This leads to a system of nonlinear ordinary differential equations for the harmonics. The two constants in Landau equation are calculated, wherein the independent variable, time t, is replaced by the streamwise coordinate direction x. The basic procedure in this paper is similar to that by Liu for compressible laminar wakes [Phys. Fluids 12, 1763 (1969)]. However, unlike this reference, which does not provide any results for their analysis, the present paper obtained many interesting results. The linear results from the present work compare very favorably with those reported by Day, Reynolds, and Mansour [Phys. Fluids 10, 993 (1998)], who employed a different procedure and limited their analysis to the linear regime. In the present studies, both the linear and nonlinear problems were analyzed in exactly the same manner, with the implication that the nonlinear results are probably accurate. These results include the convergence of the amplitude to an equilibrium value that depends on the two constants in the amplitude equation from Landau's procedure. The present analysis is restricted to exponentially decaying linear solutions at the boundaries and hence to region one in the phase speed-Mach number diagram. However, we have observed that nonlinear effects could introduce constant, decaying, or outgoing wave solutions at the boundaries, depending on the velocity and density ratios and the Mach number of the fast stream. Other effects of these parameters are reported.

Ladeinde, F.; Wu, J.

2002-09-01

216

Constraining kinetic rates of mineral reactions using reactive transport models  

NASA Astrophysics Data System (ADS)

We use a reactive transport model to better understand results of experiments to obtain kinetic rates of mineral reactions in closed systems. Closed system experiments pose special challenges in that secondary minerals may form that modify the fluid composition evolution and may grow on the dissolving minerals thus armoring the surface. Even so, such closed system experiments provide critical data for what minerals would actually form in field applications and how coupled dissolution and precipitation mineral reactions are strongly linked. Comparing to experimental observations can test the reactive transport model, and the experimental observations can be better understood by comparing the results to the modeling. We apply a 0D end member of the model to understand the dissolution of single crystals of forsterite in a variety of settings (low pH, high pH, or NaHCO3 initial fluids, at 100 C and 1 bar, or 200 C and 150 bar). Depending on the initial conditions, we observe the precipitation of talc, brucite, amorphous silica, chrysotile, or magnesite, in various combinations. We compare simulation results to fluid compositions and the presence of secondary minerals experimentally sampled at various times. Insight from the simulations helped create an inverse model to extract the rates of forsterite dissolution and to create a simple forward model useful for exploring the influence of system size, secondary mineral surface areas, etc. Our reactive transport model allows secondary minerals to armor the forsterite surface, which can strongly decrease the dissolution rate as the system evolves. Tuning our model with experimentally derived rates and assuring relevant processes are included so as to reproduce experimental observations is necessary before upscaling to heterogeneous field conditions. The reactive transport model will be used for field-scale sequestration simulations and coupled with a geomechanical model that includes the influence of deformation.

Bolton, E. W.; Wang, Z.; Ague, J.; Bercovici, D.; Cai, Z.; Karato, S.; Oristaglio, M. L.; Qiu, L.

2012-12-01

217

Soil solid materials affect the kinetics of extracellular enzymatic reactions  

NASA Astrophysics Data System (ADS)

INTRODUCTION Soil solid materials affect the degradation processes of many organic compounds by decreasing the bioavailability of substrates and by interacting with degraders. The magnitude of this effect in the environment is shown by the fact that xenobiotics which are readily metabolized in aquatic environments can have long residence times in soil. Extracellular enzymatic hydrolysis of cellobiose (enzyme: beta-glucosidase from Aspergillus niger) was chosen as model degradation process since it is easier to control and more reproducible than a whole cell processes. Furthermore extracellular enzymes play an important role in the environment since they are responsible for the first steps in the degradation of organic macromolecules; beta-glucosidase is key enzyme in the degradation of cellulose and therefore it is fundamental in the carbon cycle and for soil in general. The aims of the project are: 1) quantification of solid material effect on degradation, 2) separation of the effects of minerals on enzyme (adsorption ?change in activity) and substrate (adsorption ?change in bioavailability). Our hypothesis is that a rate reduction in the enzymatic reaction in the presence of a solid phase results from the sum of decreased bioavailability of the substrate and decreased activity of enzyme molecules. The relative contribution of the two terms to the overall effect can vary widely depending on the chemical nature of the substrate, the properties of the enzyme and on the surface properties of the solid materials. Furthermore we hypothesize that by immobilizing the enzyme in an appropriate carrier the adsorption of enzymes to soil materials can be eliminated and that therefore immobilization can increase the overall reaction rate (activity loss caused by immobilization < activity loss caused by adsorption to soil minerals). MATERIALS AND METHODS Enzymatic kinetic experiments are carried out in homogeneous liquid systems and in heterogeneous systems where solid materials (bentonite, kaolinite, goethite, activated charcoal) are suspended in a mixed liquid (standard experimental conditions: 66 mM phosphate buffer, pH 5, 25°C, 20 mg solid/ml buffer). The enzyme in an immobilized form (covalent bonding to oxirane groups on the surfaces of macroporous Eupergit® C particles) is used to exclude a direct effect of soil solid materials on the enzyme without excluding their effect on the availability of the substrate.The progress of the reactions is determined by measuring the accumulation of the product (i.e. glucose) in the systems at different times (after destroying enzymatic activity by boiling the samples) with a coupled enzymatic assay and an automatic microplate spectrophotometer. A regression analysis on the data points is performed to calculate the initial reaction rates, which is the parameter that allows to compare the different systems. RESULTS AND DISCUSSION The results show that, under the standard experimental conditions, cellobiose is not adsorbed by the clay minerals bentonite and kaolinite and by the iron oxyhydroxide goethite. In the case of activated charcoal a rapid adsorption phase in the first 20' is followed by a much slower process; after 4h 30' approximately 98% of cellobiose was adsorbed. The results from the adsorption experiments of beta-glucosidase to bentonite, kaolinite, goethite and activated charcoal show that, under the standard experimental conditions, the adsorption process is rapid in all cases (more than 80% of the adsorption takes place in the first 20 minutes). After 1h 20min the following fractions of enzyme were adsorbed: 30 % to bentonite, 60% to kaolinite, 67% to goethite, 100% to activated charcoal. The effect of kaolinite on the reaction rate was quantified: under the standard experimental conditions the initial reaction rate in presence of the mineral was 22% less then in the control. The fraction of enzyme molecules which are adsorbed to kaolinite (60%) loses 37% of its activity. CONCLUSIONS The results from the adsorption experiments lead to the conclusion that, among the sol

Lammirato, C.; Miltner, A.; Kästner, M.

2009-04-01

218

Interior Proximal Algorithm with Variable Metric for Second-Order ...  

E-print Network

external forces applied at the nodes) the structures deformates, until the reaction forces caused ..... report the CPU time by using our implementation in MATLAB of this ..... Machine Perception, Department of Cybernetics, Faculty of Electrical ...

2009-06-05

219

A second-order turbulence model for gaseous mixtures induced by Richtmyer—Meshkov instability  

NASA Astrophysics Data System (ADS)

A second order turbulence model for compressible one-dimensional mixing flows is used to calculate the experiment performed by Poggi et al. [18] where mixtures were induced by Richtmyer Meshkov instability. This Rij-? model is supplemented by equations for the turbulent mass flux and the density variance . In Poggi's experiments, beside usual mixing length measurement, the laser Doppler anemometry technique gave temporal evolution of the turbulent kinetic energy. The present study shows that a statistical turbulence model can reproduce these strongly differential experimental data. Indeed, evolution of the radial component of the Reynolds stress tensor as well as that of the anisotropy are satisfactorily calculated. Nevertheless, discrepancies are observed at the very beginning of the process where the turbulence is probably not fully developed. The three-layer Meshkov experiment [16] is also successfully interpreted with the same procedure. In addition, the dependence of the evolution of turbulent quantities on the initial conditions is addressed.

Grégoire Olivier Grégoire, Olivier; Souffland, Denis; Gauthier, Serge

220

Milestones of the development of kinetics of electrode reactions  

Microsoft Academic Search

The birth and the development of the kinetics of electrode processes–mostly focusing on the case of the hindered charge transfer\\u000a step and the early period–are reviewed. It is shown how this important branch of electrochemistry was established and how\\u000a and why the ideas of chemical kinetics have been introduced in electrochemistry. The history of electrode kinetics represents\\u000a a good example

György Inzelt

221

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

E-print Network

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

Sontag, Eduardo

222

A non-isothermal, non-equimolar transient kinetic model for gas-solid reactions  

Microsoft Academic Search

A numerical model is presented, designed to simulate the kinetic and thermal behaviour of a porous pellet in which any gas-solid reaction is taking place. Its novelty consists in the fact that it can deal with reactions whether they are exothermic or endothermic, whether they are equimolar or not, whether they are reversible or irreversible and further reactions in the

Fabrice Patisson; Magda Galant François; Denis Ablitzer

1998-01-01

223

Sensitivity to contrast modulation: the spatial frequency dependence of second-order vision  

Microsoft Academic Search

We consider the overall shape of the second-order modulation sensitivity function (MSF). Because second-order modulations of local contrast or orientation require a carrier signal, it is necessary to evaluate modulation sensitivity against a variety of carriers before reaching a general conclusion about second-order sensitivity. Here we present second-order sensitivity functions for new carrier types (low pass (1\\/f) noise, and high

Andrew J Schofield; Mark A Georgeson

2003-01-01

224

An adjoint method for second-order switching time optimization T. M. Caldwell  

E-print Network

An adjoint method for second-order switching time optimization T. M. Caldwell Department the example in Section III II. FIRST- AND SECOND-ORDER SWITCHING TIME OPTIMIZATION A switched system transition. This paper presents second- order optimization of these switching times and compares its

Hartmann, Mitra J. Z.

225

Oxidation of microcystins by permanganate: reaction kinetics and implications for water treatment.  

PubMed

A few genera of cyanobacteria produce toxins which contaminate drinking water resources. Microcystins (MC), widely reported cyanotoxins, cause acute and chronic toxicity effects in living beings including humans and warrant removal from drinking water. In the present study, unknown second-order rate constants for the reactions of microcystin-LR (MC-LR), -RR and -YR with potassium permanganate were determined at pH 6.2-8.2 and temperature 10-25 degrees C. The reaction of permanganate with MCs is second-order overall and first-order with respect to both permanganate and toxin. The second-order rate constant for the reaction of MC-LR with permanganate at pH 7 and 20 degrees C was 357.2+/-17.5M(-1)s(-1). The influence of pH on the oxidation process was not appreciable and the activation energy was 28.8 kJ mol(-1). Slightly higher reactivity with permanganate was found for MC-RR (418.0M(-1)s(-1)) and MC-YR (405.9M(-1)s(-1)). According to the results obtained, permanganate likely attacks the Adda moiety of the MC molecule. The oxidation of MCs in a natural surface water was also investigated. A permanganate dose of 1-1.25mgL(-1) was enough to reduce MCs concentration below the guideline value of 1microgL(-1). Permanganate oxidation is therefore a feasible option for microcystin removal during preoxidation processes. However, the oxidant dose must be carefully optimized in order to remove extracellular MCs without causing cell lysis (due to chemical stress) and further release of MCs. PMID:17097716

Rodríguez, Eva; Majado, María E; Meriluoto, Jussi; Acero, Juan L

2007-01-01

226

DIRECT COMPARISON OF KINETIC AND LOCAL EQUILIBRIUM FORMULATIONS FOR SOLUTE TRANSPORT AFFECTED BY SURFACE REACTIONS.  

USGS Publications Warehouse

Modeling transport of reacting solutes in porous media often requires a choice between models based on the local equilibrium assumption (LEA) and models involving reaction kinetics. Direct comparison of the mathematical formulations for these two types of transport models can aid in this choice. For cases of transport affected by surface reaction, such a comparison is made possible by a new derivation procedure. This procedure yields a kinetics-based formulation that is the sum of the LEA formulation and one or more kinetically influenced terms. The dimensionless form of the new kinetics-based formulation facilitates identification of critical parameter groupings which control the approach to transport behavior consistent with LEA model predictions. Results of numerical experiments demonstrate that criteria for LEA applicability can be expressed conveniently in terms of these parameter groupings. The derivation procedure is demonstrated for examples of surface reactions including first-order reversible sorption, Langmuir-type kinetics and binary, homovalent ion exchange.

Bahr, Jean M.; Rubin, Jacob

1987-01-01

227

Kinetics  

NSDL National Science Digital Library

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

Nurrenbern, Susan C.; Robinson, William R.

2008-02-27

228

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

229

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

230

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

231

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

232

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

233

Second-order Solutions of Cosmological Perturbation in the Matter-dominated Era  

NASA Astrophysics Data System (ADS)

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; Noh, Hyerim; Gong, Jinn-Ouk

2012-06-01

234

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

235

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

236

Comparison of Biodegradation Kinetics With an Instantaneous Reaction Model for Groundwater  

NASA Astrophysics Data System (ADS)

Biodegradation modeling is gaining more attention as a useful tool for predicting the attenuation of organic contaminants in groundwater. In this paper we compare two conceptual models. The first approximates biodegradation with an instantaneous reaction between the organics and oxygen. The advantage of this model is its simplicity and minimal biotransformation data requirements. Inherent in this model is the assumption that biodegradation in groundwater is oxygen transport limited. The second conceptual model utilizes a dual substrate Monod kinetic relationship to calculate biodegradation. While theoretically more accurate, the model suffers from being numerically more complex to implement. The kinetic model also requires more biotransformation data for each organic contaminant than the instantaneous reaction model. The analysis presented in this paper is intended to determine the requirements that must be placed on a system's Damköhler number to guarantee that reaction mechanisms are not kinetically limited. Results indicate that the instantaneous reaction is an adequate assumption when nondimensionalized reaction rates are large.

Rifai, Hanadi S.; Bedient, Philip B.

1990-04-01

237

The maintenance of the second-order advantage: second-order calibration of excitation-emission matrix fluorescence for quantitative analysis of herbicide napropamide in various environmental samples.  

PubMed

A rapid non-separative spectrofluorometric method based on the second-order calibration of excitation-emission matrix (EEM) fluorescence was proposed for the determination of napropamide (NAP) in soil, river sediment, and wastewater as well as river water samples. With 0.10 mol L(-1) sodium citrate-hydrochloric acid (HCl) buffer solution of pH 2.2, the system of NAP has a large increase in fluorescence intensity. To handle the intrinsic fluorescence interferences of environmental samples, the alternating penalty trilinear decomposition (APTLD) algorithm as an efficient second-order calibration method was employed. Satisfactory results have been achieved for NAP in complex environmental samples. The limit of detection obtained for NAP in soil, river sediment, wastewater and river water samples were 0.80, 0.24, 0.12, 0.071 ng mL(-1), respectively. Furthermore, in order to fully investigate the performance of second-order calibration method, we test the second-order calibration method using different calibration approaches including the single matrix model, the intra-day various matrices model and the global model based on the APTLD algorithm with nature environmental datasets. The results showed the second-order calibration methods also enable one or more analyte(s) of interest to be determined simultaneously in the samples with various types of matrices. The maintenance of second-order advantage has been demonstrated in simultaneous determinations of the analyte of interests in the environmental samples of various matrices. PMID:21645706

Li, Yuan-Na; Wu, Hai-Long; Qing, Xiang-Dong; Nie, Chong-Chong; Li, Shu-Fang; Yu, Yong-Jie; Zhang, Shu-Rong; Yu, Ru-Qin

2011-07-15

238

Synthetic semiconductor diamond electrodes: kinetics of some redox reactions  

Microsoft Academic Search

Linear-sweep voltammograms were recorded on boron-doped diamond thin-film electrodes in K3Fe(CN)6, K4Fe(CN)6, quinone, and hydroquinone solutions; transfer coefficients and rate constants for anodic and cathodic reactions were determined. The reaction rates were compared to the diamond samples' electrical characteristics measured by the impedance spectroscopy techniques. The polarization (faradaic) resistance of a redox reaction at its equilibrium potential was shown to

A. D. Modestov; Yu. E. Evstefeeva; Yu. V. Pleskov; V. M. Mazin; V. P. Varnin; I. G. Teremetskaya

1997-01-01

239

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

NASA Astrophysics Data System (ADS)

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

Shah, Stimit

240

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

241

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

Microsoft Academic Search

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

B. van Leer

1979-01-01

242

Photon-number correlations in waveguide lattices with second order coupling  

NASA Astrophysics Data System (ADS)

We introduce second-order coupling into the transport and coupling of photons in waveguide lattices. Second-order coupling, as well as high-order couplings, can be significant in long, compact or some special lattices, and is important for large-scale quantum circuits. Photon-number correlations with various amounts of second-order couplings are calculated. Some distinctive and interesting effects arise, and these are helpful for our comprehension of quantum walks in waveguide lattices.

Qi, F.; Feng, Z. G.; Wang, Y. F.; Xu, P.; Zhu, S. N.; Zheng, W. H.

2014-12-01

243

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

244

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

SciTech Connect

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

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

2014-05-14

245

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

246

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

247

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

248

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

Microsoft Academic Search

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

François Nicot; Ali Daouadji; Farid Laouafa; Félix Darve

2011-01-01

249

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

250

Second order parameter-uniform convergence for a finite difference method for a singularly perturbed linear parabolic system  

E-print Network

A singularly perturbed linear system of second order partial differential equations of parabolic reaction-diffusion type with given initial and boundary conditions is considered. The leading term of each equation is multiplied by a small positive parameter. These singular perturbation parameters are assumed to be distinct. The components of the solution exhibit overlapping layers. Shishkin piecewise-uniform meshes are introduced, which are used in conjunction with a classical finite difference discretisation, to construct a numerical method for solving this problem. It is proved that the numerical approximations obtained with this method are first order convergent in time and essentially second order convergent in the space variable uniformly with respect to all of the parameters.

V. Franklin; M. Paramasivam; S. Valarmathi; J. J. H. Miller

2010-08-14

251

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.

252

LSENS, a general chemical kinetics and sensitivity analysis code for gas-phase reactions: User's guide  

NASA Technical Reports Server (NTRS)

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

Radhakrishnan, Krishnan; Bittker, David A.

1993-01-01

253

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

ERIC Educational Resources Information Center

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

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

2005-01-01

254

Notes on Second Order Linear Differential Equations Stony Brook University Mathematics Department  

E-print Network

Notes on Second Order Linear Differential Equations Stony Brook University Mathematics Department 1. The general second order homogeneous linear differential equation with constant coefficients looks like Ay +By this becomes a first order linear equation, which we already know how to solve. So we will consider the case

Sutherland, Scott

255

Fundamental notions of analysis in subsystems of second-order arithmetic  

E-print Network

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

Avigad, Jeremy

256

Second-order adjoint state methods for Full Waveform Inversion June 25, 2013  

E-print Network

Second-order adjoint state methods for Full Waveform Inversion June 25, 2013 Author list on efficient first-order optimization schemes, as the steepest descent or the nonlinear conjugate gradient optimization. However, second-order infor- mation provided by the Hessian matrix is proven to give a useful

Boyer, Edmond

257

Second Order Switching Time Optimization for Time-Varying Nonlinear Systems  

E-print Network

Second Order Switching Time Optimization for Time-Varying Nonlinear Systems Elliot R. Johnson and Todd D. Murphey Abstract-- This paper presents second-order switching time optimization techniques Switching time optimization frequently arises in the anal- ysis of hybrid systems­systems that discretely

Hartmann, Mitra J. Z.

258

Beyond second-order statistics for learning: A pairwise interaction model for entropy estimation  

Microsoft Academic Search

Second order statistics have formed the basis of learning and adaptation due to its appeal and analytical simplicity. On the other hand, in many realistic engineering problems requiring adaptive solutions, it is not sufficient to consider only the second order statistics of the underlying distributions. Entropy, being the average information content of a distribution, is a better-suited criterion for adaptation

Deniz Erdogmus; José Carlos Príncipe; Kenneth E. Hild II

2002-01-01

259

Vanishing moment method and moment solutions for second order fully nonlinear partial differential equations  

Microsoft Academic Search

This paper concerns with numerical approximations of solutions of second order fully nonlinear partial differential equations (PDEs). A new notion of weak solutions, called moment solutions, is introduced for second order fully nonlinear PDEs. Unlike viscosity solutions, moment solutions are defined by a constructive method, called vanishing moment method, hence, they can be readily computed by existing numerical methods such

Xiaobing Feng; Michael Neilan

2007-01-01

260

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

261

Increasing stimulus size impairs first- but not second-order motion perception  

PubMed Central

As stimulus size increases, the direction of high-contrast moving stimuli becomes increasingly difficult to perceive. This counterintuitive effect, termed spatial suppression, is believed to reflect antagonistic center-surround mechanisms, which play key roles in tasks requiring sensitivity to relative motion. It is unknown, however, whether second-order motion also exhibits spatial suppression. To test this hypothesis, we measured direction discrimination thresholds for first- and second-order stimuli of varying sizes. The results revealed increasing thresholds with increasing size for first-order stimuli, but demonstrated no spatial suppression of second-order motion. This selective impairment of first-order motion predicts increasing predominance of second-order cues as stimulus size increases. We confirmed this prediction by utilizing compound stimuli that contain first- and second-order information moving in opposite directions. Specifically, we found that for large stimuli, motion perception becomes increasingly determined by the direction of second-order cues. Overall, our findings show a lack of spatial suppression for second-order stimuli, suggesting that the second-order system may have distinct functional roles, roles that do not require high sensitivity to relative motion. PMID:22114314

Glasser, Davis M.; Tadin, Duje

2011-01-01

262

Post processing with first- and second-order hidden Markov models  

NASA Astrophysics Data System (ADS)

In this paper, we present the implementation and evaluation of first order and second order Hidden Markov Models to identify and correct OCR errors in the post processing of books. Our experiments show that the first order model approximately corrects 10% of the errors with 100% precision, while the second order model corrects a higher percentage of errors with much lower precision.

Taghva, Kazem; Poudel, Srijana; Malreddy, Spandana

2013-01-01

263

STABILITY OF SECOND-ORDER ASYMMETRIC LINEAR MECHANICAL SYSTEMS WITH APPLICATION TO ROBOT GRASPING  

E-print Network

STABILITY OF SECOND-ORDER ASYMMETRIC LINEAR MECHANICAL SYSTEMS WITH APPLICATION TO ROBOT GRASPING a surprisingly simple analytical criterion for the stability of general second-order asymmetric linear systems such that the overall linear system is stable. This stability criterion is then applied to robot grasping arrangements

Shapiro, Amir

264

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

265

Uniqueness Results for Second Order Bellman-Isaacs Equations under Quadratic Growth Assumptions and Applications  

E-print Network

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

Paris-Sud XI, Université de

266

Modulation frequency and orientation tuning of second-order texture mechanisms  

E-print Network

Modulation frequency and orientation tuning of second-order texture mechanisms A. Serge Arsenault October 15, 1998 Modulation frequency and orientation tuning of second-order mechanisms underlying was modulated about an aver- age value of 4.7 cycles per degree (cpd) according to a sinusoidal function

Kingdom, Frederick A. A.

267

CONVERGENCE OF ADAPTIVE DISCONTINUOUS GALERKIN APPROXIMATIONS OF SECOND-ORDER ELLIPTIC PROBLEMS  

E-print Network

CONVERGENCE OF ADAPTIVE DISCONTINUOUS GALERKIN APPROXIMATIONS OF SECOND-ORDER ELLIPTIC PROBLEMS is introduced and analyzed for a discontinuous Galerkin formulation of a model second-order elliptic problem with Dirichlet-Neumann type boundary conditions. An adaptive algorithm using this estimator together

Karakashian, Ohannes

268

Second-Order Methods for Distributed Approximate Single-and Multicommodity Flow  

E-print Network

Second-Order Methods for Distributed Approximate Single- and Multicommodity Flow S. Muthukrishnan1 for maximum flow and multicommodity flow problems in distributed networks. We propose a second-order method The multicommodity flow problem is the problem of simultaneously shipping multiple com- modities through

Suel, Torsten

269

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

E-print Network

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

Cerveny, Vlastislav

270

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

E-print Network

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

Cerveny, Vlastislav

271

SECOND{ORDER AND HIGHER{ORDER PERTURBATIONS OF TRAVEL TIME IN ISOTROPIC AND ANISOTROPIC MEDIA  

E-print Network

SECOND{ORDER AND HIGHER{ORDER PERTURBATIONS OF TRAVEL TIME IN ISOTROPIC AND ANISOTROPIC MEDIA Lud derivatives of travel time with respect to model parameters are re- ferred to as perturbations. Explicit equations for the second{order and higher{order perturbations of travel time in both isotropic

Cerveny, Vlastislav

272

Some kinetic aspects of unsteady-state partial oxidation reactions. Dynamic processes on metal oxide surfaces  

Microsoft Academic Search

It is shown that steady-state kinetic data do not allow the discrimination between the redox and associated mechanisms of the partial oxidation reactions. A discrimination between these mechanisms was performed using transient experiments. The obtained rate expressions are in agreement with experimental kinetic data for catalytic partial oxidation of o-xylene.An influence of the conjugate oxidation of a catalyst surface on

Yuri I. Pyatnitsky; Nina I. Ilchenko

1996-01-01

273

Seismic implications of the kinetics of the reaction perovskite + ferropericlase = ringwoodite  

NASA Astrophysics Data System (ADS)

Kinetics of the mantle transition zone phase transitions/mineral reactions may give insights into the density structure and rheology of subducting slabs or mantle plume regions. The effect of kinetics in mantle up- and downwellings on the seismic structure has not been investigated in detail and would add further constraints on mantle dynamics. Here we study whether and how the effects of reaction kinetics can be resolved with PP and SS precursors in mantle upwellings. PP or SS precursors are underside reflections of P- or S-waves off the discontinuities, halfway between the source and the receivers. We use data from kinetic experiments of the reaction of perovskite and ferropericlase to ringwoodite and combine them with thermodynamic calculations of phase assemblages to obtain the seismic structure of kinetically inhibited mineral assemblages. The kinetic data show sensitivity to grain size and upwelling rate. From the profiles of density, P wave and S wave velocity, we calculate 1D synthetic seismograms for a range of dominant frequencies. We analyse the frequency dependence of the amplitudes and traveltime residuals of the reflected waves. The synthetic modelling shows that kinetic inhibition of the backward reaction of ringwoodite, i.e. the recombination of perovskite + ferropericlase to ringwoodite, affects the amplitudes of PP and SS underside reflections, showing larger amplitudes for shorter periods due to the finite depth interval where the kinetic inhibition occurs. Thus the frequency dependency of PP and SS precursor amplitudes can be a probe to investigate regions of mantle upwellings and to further constrain grain size in the mantle.

Lessing, Stephan; Dobson, David P.; Cobden, Laura; Sebastian, Rost; Thomas, Christine

2014-05-01

274

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

275

Second-order diffraction loads on an array of vertical cylinders in bichromatic bidirectional waves  

SciTech Connect

A complete second-order solution is presented for the Hydrodynamic forces due to the action of bichromatic, bidirectional, waves on an array of bottom-mounted, surface-piercing cylinders of arbitrary cross-section in water of uniform finite depth. Based on the constant structural cross-section, the first-order problem is solved utilizing a two-dimensional Green`s function approach while in assisting radiation potential approach is used to obtain the hydrodynamic loads due to the second-order potential. Results are presented which illustrate the influence of wave directionality on the second-order sum- and difference frequency hydrodynamic forces on a two cylinder array. It is found that wave directionality may have a significant influence on the second-order hydrodynamic loads on these arrays and that the assumption of unidirectional waves does not always lead to conservative estimates of the second-order loading.

Vazquez, J.H.; Williams, A.N. [Univ. of Houston, TX (United States). Dept. of Civil and Environmental Engineering

1994-12-31

276

Second-order diffraction forces on an array of vertical cylinders in bichromatic bidirectional waves  

SciTech Connect

A complete second-order solution is presented for the hydrodynamic forces due to the action of bichromatic, bidirectional waves on an array of bottom-mounted, surface-piercing cylinders of arbitrary cross section in water of uniform finite depth. Based on the constant structural cross section, the first-order problem is solved utilizing a two-dimensional Green function approach, while an assisting radiation potential approach is used to obtain the hydrodynamic loads due to the second-order potential. Results are presented which illustrate the influence of wave directionality on the second-order sum and difference frequency hydrodynamic forces on a two-cylinder array. It is found that wave directionality may have a significant influence on the second-order hydrodynamic forces on these arrays and that the assumption of unidirectional waves does not always lead to conservative estimates of the second-order loading.

Vazquez, J.H. [Lamar Univ., Beaumont, TX (United States). Dept. of Civil Engineering; Williams, A.N. [Univ. of Houston, TX (United States). Dept. of Civil and Environmental Engineering

1995-02-01

277

Optimality Conditions in Differentiable Vector Optimization via Second-Order Tangent Sets  

SciTech Connect

We provide second-order necessary and sufficient conditions for a point to be an efficient element of a set with respect to a cone in a normed space, so that there is only a small gap between necessary and sufficient conditions. To this aim, we use the common second-order tangent set and the asymptotic second-order cone utilized by Penot. As an application we establish second-order necessary conditions for a point to be a solution of a vector optimization problem with an arbitrary feasible set and a twice Frechet differentiable objective function between two normed spaces. We also establish second-order sufficient conditions when the initial space is finite-dimensional so that there is no gap with necessary conditions. Lagrange multiplier rules are also given.

Jimenez, Bienvenido [Departamento de Economia e Historia Economica, Facultad de Economia y Empresa, Universidad deSalamanca, Campus Miguel de Unamuno, s/n, 37007 Salamanca (Spain)], E-mail: bjimen1@encina.pntic.mec.es; Novo, Vicente [Departamento de Matematica Aplicada, E.T.S.I. Industriales, UNED, c/ Juan del Rosal 12, Apartado 60149, 28080 Madrid (Spain)], E-mail: vnovo@ind.uned.es

2004-03-15

278

KINETICS, CATALYSIS, AND REACTION ENGINEERING Nonthermal Plasma Reactions of Dilute Nitrogen Oxide Mixtures  

E-print Network

of the charged particles is not significantly different from the kinetic energy of the neutral species. We refer in an otherwise neutral gas is referred to as plasma. If we apply a potential difference to plasma, the electric not move far between the collisions or the electric field is weak or both, the kinetic energy

Yeung, Man-Chung

279

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

280

Kinetics of OCN- formation from the HNCO + NH3 solid-state thermal reaction  

NASA Astrophysics Data System (ADS)

Context. Solid-state features in infrared astronomical spectra can provide useful information on interstellar ices within different astrophysical environments. Solid OCN- has an absorption feature at 4.62 ?m, which is observed in star formation regions only with a large source-to-source abundance variation. Aims: We aim to investigate the thermal formation mechanism of solid OCN- from HNCO on the basis of kinetic arguments. Methods: We experimentally studied the kinetics of the low-temperature OCN- formation from the purely thermal reaction between HNCO and NH3 in interstellar ice analogs using Fourier transform infrared spectroscopy. We used a rate equation approach, a kinetic Monte Carlo approach and a gamma probability distribution approach to derive kinetic parameters from experimental data. Results: The kinetics can de divided into two-processes, a fast process corresponding to the chemical reaction, and a slow process that we interpret as the spatial orientation of the two reactants within the ice. The three approaches give the same results. The HNCO + NH3 ? OCN- + NH4+ reaction rate follows an Arrhenius law with an activation energy of 0.4 ± 0.1 kJ mol-1 (48 ± 12 K) and a pre-exponential factor of 0.0035 ± 0.0015 s-1. Conclusions: The present experiment has the important implication that the HNCO + NH3 reaction can account for the observed abundances of solid OCN- and the HNCO non detection in young stellar objects.

Mispelaer, F.; Theule, P.; Duvernay, F.; Roubin, P.; Chiavassa, T.

2012-04-01

281

Kinetics Of Isomerisation Reaction Of Oriented Polyacetylene Induced By Laser  

Microsoft Academic Search

The impact of a laser's photons (lambda = 514.5 nm) on the surface of polyacetylene films (PA), composed of macromolecules PAcis and PAtrans produces simultaneously thermal and Raman diffusion [1]. The thermal effect initializes the isomerization of macromolecules PAcis to PAtrans [2] this reaction is exothermic. Samples are polyacetylene oriented films synthesized horizontally or vertically in cis configuration and are

S. Mammeri; M. Belloum; V. Tabacik

2008-01-01

282

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

SciTech Connect

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

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

2014-07-01

283

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

284

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

285

Second order temperature jump boundary condition for nano/microscale and hypersonic rarefied gas flow simulations  

NASA Astrophysics Data System (ADS)

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

Le, Nam T. P.; Roohi, Ehsan

2014-12-01

286

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

287

Reaction kinetics and product distributions in photoelectrochemical cells  

SciTech Connect

Hot electron reaction studies at p-InP/CH[sub 3]CN interface revealed essential/desirable features for redox systems used to investigate hot carriers in photoelectrocehmical cells. Reduction of dibromoethylbenzene (DBEB) in presence of metallocene couples is being studied using rotating rink disk electrodes of n-and p-InP disks and Pt rings. At highly doped p-InP electrodes, reduction of DBEB can be very efficient (>30%). A minielectrochemical cell was used to investigate electron transfer at nonilluminated n-WSe[sub 2]/dimethylferrocene[sup +/0] interfaces.

Koval, C.A.

1992-01-01

288

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

289

Second order finite volume scheme for Maxwell's equations with discontinuous electromagnetic properties on unstructured meshes  

NASA Astrophysics Data System (ADS)

This paper presents a second order finite volume scheme for numerical solution of Maxwell's equations with discontinuous dielectric permittivity and magnetic permeability on unstructured meshes. The scheme is based on Godunov scheme and employs approaches of Van Leer and Lax-Wendroff to increase the order of approximation. To keep the second order of approximation near dielectric permittivity and magnetic permeability discontinuities a novel technique for gradient calculation and limitation is applied near discontinuities. Results of test computations for problems with linear and curvilinear discontinuities confirm second order of approximation. The scheme was applied to modelling propagation of electromagnetic waves inside photonic crystal waveguides with a bend.

Ismagilov, Timur Z.

2015-02-01

290

Orientation-selective adaptation to first- and second-order patterns in human visual cortex  

PubMed Central

Second-order textures – patterns that cannot be detected by mechanisms sensitive only to luminance changes – are ubiquitous in visual scenes, but the neuronal mechanisms mediating perception of such stimuli are not well understood. We used an adaptation protocol to measure neural activity in the human brain selective for the orientation of second-order textures. FMRI responses were measured in three subjects to presentations of first- and second-order probe gratings after adapting to a high-contrast first- or second-order grating that was either parallel or orthogonal to the probe gratings. First-order (LM) stimuli were generated by modulating the stimulus luminance. Second-order stimuli were generated by modulating the contrast (CM) or orientation (OM) of a first-order carrier. We used four combinations of adapter and probe stimuli: LM:LM, CM:CM, OM:OM, and LM:OM. The fourth condition tested for cross-modal adaptation with first-order adapter and second-order probe stimuli. Attention was diverted from the stimulus by a demanding task at fixation. Both first- and second-order stimuli elicited orientation-selective adaptation in multiple cortical visual areas, including V1, V2, V3, V3A/B, a newly identified visual area anterior to dorsal V3 which we have termed LO1, hV4, and VO1. For first-order stimuli (condition LM:LM), the adaptation was no larger in extrastriate areas than in V1, implying that the orientation-selective first-order (luminance) adaptation originated in V1. For second-order stimuli (conditions CM:CM and OM:OM), the magnitude of adaptation, relative to the absolute response magnitude, was significantly larger in VO1 (and for condition CM:CM, also in V3A/B and LO1) than in V1, suggesting that second-order stimulus orientation was extracted by additional processing after V1. There was little difference in the amplitude of adaptation between the second-order conditions. No consistent effect of adaptation was found in the cross-modal condition LM:OM, in agreement with psychophysical evidence for weak interactions between first- and second-order stimuli and computational models of separate mechanisms for first- and second-order visual processing. PMID:16221748

Larsson, Jonas; Landy, Michael S.; Heeger, David J.

2006-01-01

291

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

NASA Astrophysics Data System (ADS)

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

Wang, Yang; Jiao, Liguang; Zhou, Yajun

2012-06-01

292

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

293

[Kinetics of reactions in multienzyme systems. I. Steady state processes in bienzyme systems. Lineal multienzyme sequences].  

PubMed

Kinetic aspects of reactions in multienzyme systems are discussed. Detailed formal-kinetic discription of bienzyme system is made for the steady-state conditions. Two important cases--constant and variable concentration of initial substrate are discussed. The criteria for realization of steady-state condition of system are formulated. Equations which describe the steady rates and steady state concentrations of intermediates as functions of initial concentrations and kinetic parameters of individual enzymes were developed. The time range of steady-state conditions was estimated and methods for the determination of kinetic parameters of enzymes in steady-state condition were developed. The regulation aspects of bienzyme system are considered. An analysis of reactions kinetics in lineal multienzyme systems was made and criteria of steady-state condition were formulated. Methods of determination of kinetic parameters Vmax and Kmax for each individual enzyme of multienzyme system were developed. The principle of limiting step was formulated quantitatively, criteria and methods of the finding of limiting step were developed. PMID:752794

Varfolomeev, S D

1977-01-01

294

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

NASA Technical Reports Server (NTRS)

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.

1995-01-01

295

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

296

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

297

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

Microsoft Academic Search

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

Wing Tsang

1992-01-01

298

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

299

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

300

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

301

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

302

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

303

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

304

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

NASA Astrophysics Data System (ADS)

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

Kim, Pan-Jun; Price, Nathan D.

2010-04-01

305

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

E-print Network

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

Pan-Jun Kim; Nathan D. Price

2010-04-08

306

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

E-print Network

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

Kim, Pan-Jun

2009-01-01

307

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

308

A test for second-order stationarity and approximate confidence intervals for localized  

E-print Network

processing: automatically determining pitch-side/studio footage from Rugby Union broadcasts in Davies stationary 1 Introduction Many professionals encounter time series that they suspect are not second- order

Nason, Guy

309

Global Solutions of Certain Second-Order Differential Equations with a High Degree of Apparent Singularity  

NASA Astrophysics Data System (ADS)

Infinitely many explicit solutions of certain second-order differential equations with an apparent singularity of characteristic exponent -2 are constructed by adjusting the parameter of the multi-indexed Laguerre polynomials.

Sasaki, Ryu; Takemura, Kouichi

2012-11-01

310

Sixth order electron and muon (g-2)\\/2 from second order vacuum polarization insertion  

Microsoft Academic Search

We complete the analytic evaluation of sixth order contributions to electron and muon anomalous magnetic moments coming from second order vacuum polarization insertions into all the fourth order graphs. On leave from Istituto di Fisica dell'Università, Bologna.

Riccardo Barbieri; E. Remiddi

1974-01-01

311

Second-Order Global Consensus in Multiagent Networks With Random Directional Link Failure.  

PubMed

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

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

2014-05-16

312

Analytical and numerical Gubser solutions of the second-order hydrodynamics  

E-print Network

Evolution of quark-gluon plasma (QGP) near equilibrium can be described by the second-order relativistic viscous hydrodynamic equations. Consistent and analytically verifiable numerical solutions are critical for phenomenological studies of the collective behavior of QGP in high-energy heavy-ion collisions. A novel analytical solution based on the conformal Gubser flow which is a boost-invariant solution with transverse fluid velocity is presented. It is used to verify with high precision the numerical solution with a newly developed $(3+1)$-dimensional second-order viscous hydro code (CLVisc). The perfect agreement between the analytical and numerical solutions demonstrates the reliability of the numerical simulations with the second-order viscous corrections. This lays the foundation for future phenomenological studies that allow one to gain access to the second-order transport coefficients.

Long-Gang Pang; Yoshitaka Hatta; Xin-Nian Wang; Bo-Wen Xiao

2014-11-28

313

Evaluation of decay curves of a chemical species undergoing simultaneous first- and second-order decay  

NASA Technical Reports Server (NTRS)

IBM 1620 computer prepares tables to enable fast calculation of the first- and second-order rate constants from two half-lives and the corresponding initial concentrations, obtained from either one or two decay curves.

Schmidt, K. H.

1970-01-01

314

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.

315

Coleman - de Luccia instanton of the second order in a brane world  

E-print Network

The second order Coleman - de Luccia instanton and its action in the Randall - Sundrum type II model are investigated and the comparison with the results in Einstein's general relativity is done in the present paper.

Michal Demetrian

2006-06-29

316

Eleven-channel second-order silicon microring-resonator filterbank with tunable channel spacing  

E-print Network

A wide-band, eleven-channel second-order filterbank fabricated on an SOI platform is demonstrated with tunable channel spacing and a 20 GHz single-channel bandwidth. The tuning efficiency is ~28 ?W/GHz/ring.

Dahlem, Marcus Vinicius Sobral

317

Hydrolysis of Surfactants Containing Ester Bonds: Modulation of Reaction Kinetics and Important Aspects of Surfactant Self-Assembly  

ERIC Educational Resources Information Center

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

Lundberg, Dan; Stjerndahl, Maria

2011-01-01

318

Reaction of plutonium with water kinetic and equilibrium behavior of binary and ternary phases in the Pu + O + H system  

Microsoft Academic Search

The kinetic and equilibrium behavior of the Pu + O + H system has been studied by measuring the production of hydrogen gas formed by a sequence of hydrolysis reactions. The kinetic dependence of the Pu + HâO reaction on salt concentration and temperature has been defined. The metal is quantitatively converted to a fine black powder which has been

J. M. Haschke; A. E. Hodges; G. E. Bixby; R. L. Lucas

1983-01-01

319

Laboratory studies of photochemistry and gas phase radical reaction kinetics relevant to planetary atmospheres.  

PubMed

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

Blitz, M A; Seakins, P W

2012-10-01

320

The perceived speed of second-order motion and its dependence on stimulus contrast  

Microsoft Academic Search

Speed matches were obtained, using a spatial two-alternative forced-choice task, between a second-order motion stimulus and a first-order motion stimulus. The second-order motion stimulus was composed of contrast-modulated noise [produced by multiplying two-dimensional (2-d), static noise by a drifting, one-dimensional (1-d) sinusoid]. The first-order motion stimulus was composed of luminance-modulated noise (produced by summing, rather than multiplying, 2-d noise and

Timothy Ledgeway; Andrew T. Smith

1995-01-01

321

Second-order schedules of drug self-administration in animals  

Microsoft Academic Search

.   On a second-order schedule, a subject responds according to one schedule (the unit schedule) for a brief presentation of\\u000a a stimulus such as a light. Responding by the subject on this unit schedule is then reinforced according to another schedule\\u000a of reinforcement. Second-order schedules of drug injection allow the study of more complex behavioral sequences than do simple\\u000a schedules

Charles W. Schindler; Leigh V. Panlilio; Steven R. Goldberg

2002-01-01

322

Second-Order Change in Marriage and Family Therapy: A Web-Based Modified Delphi Study  

Microsoft Academic Search

Second-order change is a central concept in Marriage and Family Therapy, but still remains poorly operationalized. We conducted a web-based modified Delphi study with 31 established faculty members currently teaching in COAMFTE-accredited Master's and Doctoral programs in the United States and in Canada to identify consensus regarding second-order change concepts, clinical operationalization, evaluation, and teaching principles. Numerous exemplars of first

Maureen Davey; Tracey Duncan; Karni Kissil; Adam Davey; Linda Stone Fish

2011-01-01

323

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

324

Superconducting second-order sigma-delta modulators utilizing multi-flux-quantum generators  

Microsoft Academic Search

We have been developing a superconducting second-order sigma-delta analog-to-digital converter with a large bandwidth and a large dynamic range for software radio applications. In a superconducting second-order sigma-delta modulator utilizing a passive integrator and single-flux-quantum (SFQ) feedback, gain to compensate the large attenuation in the passive integrator of the modulator is required to obtain a large dynamic range. In this

Tatsunori Hashimoto; Haruhiro Hasegawa; Shuichi Nagasawa; Hideo Suzuki; Kazunori Miyahara; Youichi Enomoto

2001-01-01

325

Second-order statistical properties of the WSS Jakes' fading channel simulator  

Microsoft Academic Search

An improved Jakes' (1994) fading channel simulator was proposed by Pop and Beaulieu (see ibid., vol.49, p.699-708, Apr. 2001) to eliminate the stationarity problem occurring in Jakes' original design. In this paper, second-order statistical properties of the improved Jakes' simulator are analyzed. Consistent with Pop and Beaulieu's caution about high-order statistics of the simulator, it is proved that some second-order

Chengshan Xiao; Yahong R. Zheng; Norman C. Beaulieu

2002-01-01

326

First and second-order Raman scattering from finite-size crystals of graphite  

Microsoft Academic Search

First- and second-order Raman scattering from graphite has been studied. The second-order spectra of single crystals and of highly oriented pyrolytic graphite are continuous and exhibit several well-defined bands which can be attributed to features in the density of vibrational states as determined from current lattice-dynamics models. The density of states deduced from the lattice-dynamics model of Nicklow, Wakabayashi, and

R. J. Nemanich; S. A. Solin

1979-01-01

327

Three-dimensional direct femtosecond laser writing of second-order nonlinearities in glass.  

PubMed

We demonstrate that direct femtosecond laser writing in silver-containing zinc and gallium phosphate glass enables generation of three-dimensional (3D) optical second-order nonlinear microstructures having an ?(2) value about 2.5 times that of quartz. The proposed physical model involves photo-reduction, photo-dissociation, and migration of silver species within the glass matrix. 3D laser-written second-order nonlinear structures could become a new class of nonlinear optical components. PMID:22446213

Choi, Jiyeon; Bellec, Matthieu; Royon, Arnaud; Bourhis, Kevin; Papon, Gautier; Cardinal, Thierry; Canioni, Lionel; Richardson, Martin

2012-03-15

328

An alternative assessment of second-order closure models in turbulent shear flows  

NASA Technical Reports Server (NTRS)

The performance of three recently proposed second-order closure models is tested in benchmark turbulent shear flows. Both homogeneous shear flow and the log-layer of an equilibrium turbulent boundary layer are considered for this purpose. An objective analysis of the results leads to an assessment of these models that stands in contrast to that recently published by other authors. A variety of pitfalls in the formulation and testing of second-order closure models are uncovered by this analysis.

Speziale, Charles G.; Gatski, Thomas B.

1994-01-01

329

Invariance of Second-Order Modes under Frequency Transformation in 2-D Separable Denominator Digital Filters  

Microsoft Academic Search

This paper discusses the invariance of the second-order modes of 2-D separable denominator digital filters under frequency transformation. This paper first derives a state-space description for 2-D digital filters obtained by 2-D frequency transformation and then represents the controllability Gramians and the observability Gramians of the transformed 2-D digital filters. This description proves that the second-order modes of 2-D separable

Shunsuke Koshita; Masayuki Kawamata

2005-01-01

330

Second-order cone programming with warm start for elastoplastic analysis with von Mises yield criterion  

Microsoft Academic Search

The incremental problem for quasistatic elastoplastic analysis with the von Mises yield criterion is discussed within the\\u000a framework of the second-order cone programming (SOCP). We show that the associated flow rule under the von Mises yield criterion\\u000a with the linear isotropic\\/kinematic hardening is equivalently rewritten as a second-order cone complementarity problem. The\\u000a minimization problems of the potential energy and the complementary energy

Kazuo Yonekura; Yoshihiro Kanno

331

Crowding between first- and second-order letter stimuli in normal foveal and peripheral vision  

PubMed Central

Evidence that the detection of first- and second-order visual stimuli is processed by separate pathways abounds. This study asked whether first- and second-order stimuli remain independent at the stage of processing where crowding occurs. We measured thresholds for identifying a first-order (luminance defined) or second-order (contrast defined) target letter in the presence of two second- or first-order flanking letters. For comparison, we also measured thresholds when the target and flanking letters were all first or second order. Contrast of the flankers was 1.6 times their respective contrast thresholds. Measurements were obtained at the fovea and 10° in the lower visual field of four normally sighted observers. Two observers were also tested at 10° nasal visual field. As expected, in both the fovea and periphery, the magnitude of crowding (threshold elevation) was maximal at the closest letter separation and decreased as letter separation increased. The magnitude of crowding was greater for second- than for first-order target letters, independent of the order type of flankers; however, the critical distance for crowding was similar for first- and second-order letters. Substantial crossover crowding occurred when the target and flanking letters were of different order type. Our finding of substantial interaction between first- and second-order stimuli suggests that the processing of these stimuli is not independent at the stage of processing at which crowding occurs. PMID:18217825

Chung, Susana T. L.; Li, Roger W.; Levi, Dennis M.

2009-01-01

332

What is second-order vision for? Discriminating illumination versus material changes.  

PubMed

The human visual system is sensitive to second-order modulations of the local contrast (CM) or amplitude (AM) of a carrier signal. Second-order cues are detected independently of first-order luminance signals; however, it is not clear why vision should benefit from second-order sensitivity. Analysis of the first- and second-order contents of natural images suggests that these cues tend to occur together, but their phase relationship varies. We have shown that in-phase combinations of LM and AM are perceived as a shaded corrugated surface whereas the anti-phase combination can be seen as corrugated when presented alone or as a flat material change when presented in a plaid containing the in-phase cue. We now extend these findings using new stimulus types and a novel haptic matching task. We also introduce a computational model based on initially separate first- and second-order channels that are combined within orientation and subsequently across orientation to produce a shading signal. Contrast gain control allows the LM + AM cue to suppress responses to the LM - AM when presented in a plaid. Thus, the model sees LM - AM as flat in these circumstances. We conclude that second-order vision plays a key role in disambiguating the origin of luminance changes within an image. PMID:20884600

Schofield, Andrew J; Rock, Paul B; Sun, Peng; Jiang, Xiaoyue; Georgeson, Mark A

2010-01-01

333

The maintenance of the second-order advantage: Second-order calibration of excitation–emission matrix fluorescence for quantitative analysis of herbicide napropamide in various environmental samples  

Microsoft Academic Search

A rapid non-separative spectrofluorometric method based on the second-order calibration of excitation–emission matrix (EEM) fluorescence was proposed for the determination of napropamide (NAP) in soil, river sediment, and wastewater as well as river water samples. With 0.10molL?1 sodium citrate–hydrochloric acid (HCl) buffer solution of pH 2.2, the system of NAP has a large increase in fluorescence intensity. To handle the

Yuan-Na Li; Hai-Long Wu; Xiang-Dong Qing; Chong-Chong Nie; Shu-Fang Li; Yong-Jie Yu; Shu-Rong Zhang; Ru-Qin Yu

2011-01-01

334

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

335

Label-Free Measurements of Reaction Kinetics Using a Droplet-Based Optofluidic Device.  

PubMed

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

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

2014-09-23

336

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

337

Asymmetric transfer of the dynamic motion aftereffect between first- and second-order cues and among different second-order cues.  

PubMed

Recent work on motion processing has suggested a distinction between first-order cues (such as luminance modulation [LM]) and second-order cues (such as local contrast modulation [CM]). We studied interactions between moving LM, CM, and orientation modulation (OM) first comparing their spatial- and temporal-frequency sensitivity. We then tested for the transfer of the dynamic motion aftereffect (dMAE) between the three cues, matched for visibility. Observers adapted to moving, 0.5-c/deg horizontal modulations for 2 min (with 10 s top-ups). Relatively strong dMAEs were found when the adaptation and test patterns were defined by the same cue (i.e., both LM, both CM, or both OM); these effects were tuned for spatial frequency in the case of LM and CM. There was a partial transfer of the dMAE from LM to CM and OM; this transferred effect seemed to lose its tuning. The aftereffect transferred well from CM to OM and retained its tuning. There was little or no transfer from CM to LM or from OM to CM or LM. This asymmetric transfer of the dMAE between first- and second-order cues and between the second-order cues suggests some degree of separation between the mechanisms that process them. PMID:17685808

Schofield, Andrew J; Ledgeway, Timothy; Hutchinson, Claire V

2007-01-01

338

Carbon kinetic isotope effect in the reaction of CH4 with HO  

NASA Astrophysics Data System (ADS)

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±0.007 (95% confidence interval). This report discusses the experimental details of the carbon kinetic isotope effect determination in the CH4 + HO reaction and the possible atmospheric implications in the use of the present result. Tropospheric methane is known to have a 13C/12C ratio of -47‰ (parts per thousand) relative to Peedee belemnite, and most known methane sources for which measurements of the stable carbon isotope ratio have been performed are depleted in 13C relative to the atmosphere. A k12/k13 ratio of 1.010 leads to an expected value for the weighted average of the 13C/12C ratio of the methane sources which is about 10‰ more depleted than the atmosphere (approximately -57‰). This result is fundamentally important to those researchers who use stable carbon isotope ratios to study atmospheric methane.

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

1987-02-01

339

Kinetics of the oxidation of hexacyanoferrate(III) with pyrolusite  

NASA Astrophysics Data System (ADS)

It is established that the oxidation of potassium ferricyanide at pH 7-11 proceeds as a pseudo-second-order reaction with rate constants of 2.93, 4.19, 6.16, 8.66, and 9.22 L/(mol min) at 313, 323, 333, 343, and 353 K, respectively. The activation energy of the reaction is found to be 27.82 kJ/mol. The second order of the reaction, as along with the non-dependence of the rate constant on the liquid-phase volume: solidphase weight ratio, and on the rotation speed of the mixer, allow us to assume that the reaction proceeds in the kinetic region with a transition to the diffusion-kinetic mode at 353 K.

Chirkst, D. E.; Cheremisina, O. V.; Sulimova, M. A.

2013-06-01

340

Kinetic and thermochemical studies of the ClO + ClO + M ? Cl2O2 + M reaction  

NASA Astrophysics Data System (ADS)

Chlorine monoxide (ClO) radicals play a crucial role in polar ozone destruction events and the ClO dimer cycle has been identified as one of the most effective ozone-depleting catalytic cycles operating in the polar winter. A recent paper by von Hobe et al.1 highlighted significant inconsistencies between laboratory results, theoretical calculations and field observations concerning the ClO dimer ozone destruction cycle. This work has investigated the temperature dependence of the equilibrium constant of one of the key reactions in this cycle, ClO + ClO + M ? Cl2O2 + M (1, -1), by means of laser flash photolysis coupled with time-resolved UV absorption spectroscopy. ClO radicals were generated via laser flash photolysis of Cl2/Cl2O mixtures in synthetic air. The concentration of radicals was monitored via UV absorption spectroscopy: the use of a Charge Coupled Device (CCD) detector allowed time resolution over a broad range of wavelengths. The equilibrium constant Keq was determined as the ratio of the rate constants of the forward and reverse reaction (1, -1) over the T range 256 - 312 K. Second Law and Third Law analytical methods were employed to determine the standard enthalpy and entropy changes of reaction 1, ?rH° and ?rS°, from the measured equilibrium constants. The values obtained from the Second Law analysis (?rH° = - 80.8 ± 2.2 kJ mol-1; ?rS° = - 168.4 ± 7.9 J K-1 mol-1) are in good agreement with previous work 2 but greater in magnitude than current NASA recommendations 3. It was also found that, under typical laboratory conditions employed in this work, [ClO] decay exhibits pure second order kinetics at T ? 250 K. A higher rate constant for the ClO recombination reaction (1) was also observed in this work (compared to the NASA evaluation 3), implying a higher Keq and a different partitioning between ClO and Cl2O2, shifting towards the dimer. 1. M. Von Hobe, R. J. Salawitch, T. Canty, H. Keller-Rudek, G. K. Moortgat, J.-U. Grooss, R. Müller, F. Stroh, Atmospheric Chemistry and Physics, 2007, 7, 3055 2. S. L. Nickolaisen, R. R. Friedl, S. P. Sander, Journal of Physical Chemistry, 1994, 98, 155 3. S. P. Sander, R. R. Friedl, D. M. Golden, M. J. Kurylo, R. E. Huie, V. L. Orkin, G. K. Moortgat, A. R. Ravishankara, C. E. Kolb, M. J. Molina, B. J. Finlayson-Pitts, Chemical Kinetics and Photochemical Data for use in Atmospheric Studies, Evaluation No. 14, JPL Publication 02-25, NASA Jet Propulsion Laboratory, Pasadena CA, 2003

Ferracci, V.; Rowley, D. M.

2009-12-01

341

Ability of Sagittal Kinematic Variables to Estimate Ground Reaction Forces and Joint Kinetics in Running  

PubMed Central

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

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

2015-01-01

342

Kinetic studies of dicopper complexes in catechol oxidase model reaction by using an approximationless evaluating method  

Microsoft Academic Search

The oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-o-benzoquinone catalyzed by dinuclear copper(II) complexes {[Cu2(L1)(CF3SO3)2(H2O)4]-(CF3SO3)2 (1) and [Cu2(L2O)](CF3SO3)2 (2)| has been investigated in methanol saturated with O2 at ambient temperature. Detailed kinetic studies were carried out and for the treatment the fitting software ZiTa was applied. On the basis of the results in the kinetic studies a possible mechanism of the catalytic reaction

Katalin Selmeczi; Marius Réglier; Gábor Speier; Gábor Peintler

2004-01-01

343

Study on the kinetics of homogeneous enzyme reactions in a micro/nanofluidics device.  

PubMed

In this paper, a micro/nanofluidic preconcentration device integrated with an electrochemical detector has been used to study the enrichment of enzymes and homogeneous enzyme reaction kinetics. The enzymes are first concentrated in front of a nanochannel via an exclusion-enrichment effect (EEE) mechanism of the nanochannel integrated in a microfluidics device. If a substrate is electrokinetically transported to the concentrated enzymes, homogeneous enzymatic reaction occurs. The enzymatic reaction product can penetrate through the nanochannel to be detected electrochemically. In this device, the enriched enzymes can be well retained and repeatedly used, thus, the enzymatic reaction occurs in a continuous-flow mode. For demonstration, Glucose oxidase (GOx) was chosen as the model enzyme to study the influence of enzyme concentration on its reaction kinetics. The different concentration of GOx in front of the nanochannel was simply achieved by using different enrichment time. When substrate glucose was introduced electrokinetically, a rapid electrochemical steady-state response could be obtained. It was found that the electrochemical response to a constant glucose concentration increased with the increase of enzyme enrichment time, which is expected for homogeneous enzymatic reactions. Under proper conditions, the electrochemical responds linearly to the glucose concentration ranging from 0 to 15 mM, and the Michaelis constants (K(m)) are relatively low, which indicates a more efficient complex formation between enzyme and substrate. These results suggest that the present micro/nanofluidics device is promising for the study of enzymatic reaction kinetics and other bioassays such as cell assays, drug discovery, and clinical diagnosis. PMID:20162240

Wang, Chen; Li, Su-Juan; Wu, Zeng-Qiang; Xu, Jing-Juan; Chen, Hong-Yuan; Xia, Xing-Hua

2010-03-01

344

Chemical kinetic analysis of hydrogen-air ignition and reaction times  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

345

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

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

346

Assessing Stability and Change in a Second-Order Confirmatory Factor Model of Meaning in Life.  

PubMed

Research indicates that meaning in life is an important correlate of health and well-being. However, relatively little is known about the way a sense of meaning may change over time. The purpose of this study is to explore two ways of assessing change in meaning within a second-order confirmatory factor analysis framework. First, tests are conducted to see if the first and second-order factor loadings and measurement error terms are invariant over time. Second, a largely overlooked technique is used to assess change and stability in meaning at the second-order level. Findings from a nationwide survey reveal that the first and second-order factor loadings are invariant of time. Moreover, the second-order measurement error terms, but not the first-order measurement error terms, are invariant, as well. The results further reveal that standard ways of assessing stability mask significant change in meaning that is due largely to regression to the mean. PMID:24778574

Krause, Neal; Hayward, R David

2014-04-01

347

CP: AN INVESTIGATION OF COEFFICIENT OF THERMAL EXPANSION, DECOMPOSITION KINETICS, AND REACTION TO VARIOUS STIMULI  

SciTech Connect

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

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

2005-03-23

348

Reaction kinetics of Cl atoms with limonene: An experimental and theoretical study  

NASA Astrophysics Data System (ADS)

Rate coefficients for the reaction of Cl atoms with limonene (C10H16) were measured between 278-350 K and 800 Torr of N2, using the relative rate technique, with 1,3-butadiene (C4H6), n-nonane (C9H20), and 1-pentene (C5H10) as reference compounds. Cl atoms were generated by UV photolysis of oxalyl chloride ((COCl)2) at 254 nm. A gas chromatograph equipped with a flame ionization detector (GC-FID) was used for quantitative analysis of the organics. The rate coefficient for the reaction of Cl atoms with limonene at 298 K was measured to be (8.65 ± 2.44) × 10-10 cm3 molecule-1 s-1. The rate coefficient is an average value of the measurements, with two standard deviations as the quoted error, including uncertainties in the reference rate coefficients. The kinetic data obtained over the temperature range of 278-350 K were used to derive the following Arrhenius expression: k(T) = (9.75 ± 4.1) × 10-11 exp[(655 ± 133)/T] cm3 molecule-1 s-1. Theoretical kinetic calculations were also performed for the title reaction using conventional transition state theory (CTST) in combination with G3(MP2) theory between 275 and 400 K. The kinetic data obtained over the temperature range of 275-400 K were used to derive an Arrhenius expression: k(T) = (7.92 ± 0.82) × 10-13 exp[(2310 ± 34)/T] cm3 molecule-1 s-1. The addition channels contributes maximum to the total reaction and H-abstraction channels can be neglected in the range of studied pressures. The Atmospheric lifetime (?) of limonene due to its reaction with Cl atoms was estimated and concluded that the reaction with chlorine atoms can be an effective tropospheric loss pathway in the marine boundary layer and in coastal urban areas.

Dash, Manas Ranjan; Rajakumar, B.

2014-12-01

349

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

SciTech Connect

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

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

1988-01-01

350

Shear-induced reaction-limited aggregation kinetics of Brownian particles at arbitrary concentrations  

E-print Network

The aggregation of interacting Brownian particles in sheared concentrated suspensions is an important issue in colloid and soft matter science per se. Also, it serves as a model to understand biochemical reactions occurring in vivo where both crowding and shear play an important role. We present an effective medium approach within the Smoluchowski equation with shear which allows one to calculate the encounter kinetics through a potential barrier under shear at arbitrary colloid concentrations. Experiments on a model colloidal system in simple shear flow support the validity of the model in the range considered. By generalizing Kramers' rate theory to the presence of collective hydrodynamics, our model explains the significant increase in the shear-induced reaction-limited aggregation kinetics upon increasing the colloid concentration.

Alessio Zaccone; Daniele Gentili; Hua Wu; Massimo Morbidelli

2010-04-13

351

Role of reaction kinetics and mass transport in glucose sensing with nanopillar array electrodes  

PubMed Central

The use of nanopillar array electrodes (NAEs) for biosensor applications was explored using a combined experimental and simulation approach to characterize the role of reaction kinetics and mass transport in glucose detection with NAEs. Thin gold electrodes with arrays of vertically standing gold nanopillars were fabricated and their amperometric current responses were measured under bare and functionalized conditions. Results show that the sensing performances of both the bare and functionalized NAEs were affected not only by the presence and variation of the nanoscale structures on the electrodes but also by the reaction kinetics and mass transport of the analyte species involved. These results will shed new light for enhancing the performance of nanostructure based biosensors. PMID:18271981

Anandan, Venkataramani; Yang, Xiaoling; Kim, Euihyeon; Rao, Yeswanth L; Zhang, Guigen

2007-01-01

352

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

353

Accelerating the Computation of Detailed Chemical Reaction Kinetics for Simulating Combustion of Complex Fuels  

SciTech Connect

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

Grout, Ray W [ORNL

2012-01-01

354

Accelerating the Computation of Detailed Chemical Reaction Kinetics for Simulating Combustion of Complex Fuels  

SciTech Connect

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

Sankaran, R.; Grout, R.

2012-01-01

355

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

356

Established pseudo solution of second-order Dirac-Coulomb equation with position-dependent mass  

E-print Network

We show that one of exact solutions of the second-order Dirac-Coulomb equation were pseudo. In the corresponding original literature, it was considered that the mass of the electron with a Coulomb potential was position-dependent, but the obtained eigenvalues set was not the inevitable mathematical deduction of the given second-order Dirac equation, and the second-order Dirac equations were not the inevitable mathematical deduction of the given couplet first-order Dirac equation with the position-dependent mass of the electron. In the present paper, we obtain the correct solution of the introduced first-order differential equations. This new solution would be tenable only when the wave equation is correct, but there is not any experiment date to validate the so-called position-dependent of the electron in the Coulomb field.

Ruida Chen

2007-06-28

357

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

358

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

359

Exact calculation of three-body contact interaction to second order  

E-print Network

For a system of fermions with a three-body contact interaction the second-order contributions to the energy per particle $\\bar E(k_f)$ are calculated exactly. The three-particle scattering amplitude in the medium is derived in closed analytical form from the corresponding two-loop rescattering diagram. We compare the (genuine) second-order three-body contribution to $\\bar E(k_f)\\sim k_f^{10}$ with the second-order term due to the density-dependent effective two-body interaction, and find that the latter term dominates. The results of the present study are of interest for nuclear many-body calculations where chiral three-nucleon forces are treated beyond leading order via a density-dependent effective two-body interaction.

N. Kaiser

2012-03-28

360

Exact calculation of three-body contact interaction to second order  

E-print Network

For a system of fermions with a three-body contact interaction the second-order contributions to the energy per particle $\\bar E(k_f)$ are calculated exactly. The three-particle scattering amplitude in the medium is derived in closed analytical form from the corresponding two-loop rescattering diagram. We compare the (genuine) second-order three-body contribution to $\\bar E(k_f)\\sim k_f^{10}$ with the second-order term due to the density-dependent effective two-body interaction, and find that the latter term dominates. The results of the present study are of interest for nuclear many-body calculations where chiral three-nucleon forces are treated beyond leading order via a density-dependent effective two-body interaction.

Kaiser, N

2012-01-01

361

Second order gauge invariant measure of a tidally deformed black hole  

SciTech Connect

In this paper, a Lagrangian perturbation theory for the second order treatment of small disturbances of the event horizon in Schwarzchild black holes is introduced. The issue of gauge invariance in the context of general relativistic theory is also discussed. The developments of this paper is a logical continuation of the calculations presented in [1], in which the first order coordinate dependance of the intrinsic and exterinsic geometry of the horizon is examined and the first order gauge invariance of the intrinsic geometry of the horizon is shown. In context of second order perturbation theory, It is shown that the rate of the expansion of the congruence of the horizon generators is invariant under a second order reparametrization; so it can be considered as a measure of tidal perturbation. A generally non-vanishing expression for this observable, which accomodates tidal perturbations and implies nonlinear response of the horizon, is also presented.

Ahmadi, Nahid, E-mail: nahmadi@ut.ac.ir [Department of Physics, University of Tehran, Kargar Avenue North, Tehran 14395-547 (Iran, Islamic Republic of)

2012-08-01

362

A second-order algorithm for solving dynamic cell membrane equations.  

PubMed

This paper describes an extension of the so-called Rush-Larsen scheme, which is a widely used numerical method for solving dynamic models of cardiac cell electrophysiology. The proposed method applies a local linearization of nonlinear terms in combination with the analytical solution of linear ordinary differential equations to obtain a second-order accurate numerical scheme. We compare the error and computational load of the second-order scheme to the original Rush-Larsen method and a second-order Runge-Kutta (RK) method. The numerical results indicate that the new method outperforms the original Rush-Larsen scheme for all the test cases. The comparison with the RK solver reveals that the new method is more efficient for stiff problems. PMID:19237339

Sundnes, Joakim; Artebrant, Robert; Skavhaug, Ola; Tveito, Aslak

2009-10-01

363

a Two-Level Second-Order Finite Difference Scheme for the Single Term Structure Equation  

NASA Astrophysics Data System (ADS)

In the paper [6] the classical single factor term structure equation for models that predict non-negative interest rates is numerically studied. For these models the authors proposed a second order accurate three-level finite difference scheme (FDs) using the appropriate boundary conditions at zero. For the same problem we propose a two-level second-order accurate FDs. We also propose an effective algorithm for solving the difference schemes, for which also follows the positivity of the numerical solution. The flexibility of our FDs makes it easy to change the drift and diffusion terms in the model. The numerical experiments confirm the second-order of accuracy of the scheme and the positivity-convexity property.

Chernogorova, T.; Valkov, R.

2011-12-01

364

Feasibility of a second-order gravitational red-shift experiment  

NASA Technical Reports Server (NTRS)

The number of gravitation experiments undertaken since the advent of Einstein's theory of gravitation is quite small, with, so far, only the famous perihelion-advance experiment and a recent lunar-laser-ranging experiment being capable of measuring a nonlinear, second-order effect. It now appears that another distinct test of the second-order term may be feasible through the use of very stable atomic clocks. This experiment, which would measure the second-order gravitational red-shift, is a bona fide test of the field equations of gravity, not just a test of the underlying principle of equivalence. The nature of such an experiment, the basic equations, model-orbit calculations, and some tracking-accuracy requirements are presented. It is concluded that current space-probe tracking capabilities cannot determine all the necessary orbital parameters with sufficient accuracy for this experiment at the present time.

Jaffe, J.; Vessot, R. F. C.

1976-01-01

365

Second-order Born calculation of coplanar symmetric (e, 2e) process on Mg  

NASA Astrophysics Data System (ADS)

The second-order distorted wave Born approximation (DWBA) method is employed to investigate the triple differential cross sections (TDCS) of coplanar doubly symmetric (e, 2e) collisions for magnesium at excess energies of 6 eV-20 eV. Comparing with the standard first-order DWBA calculations, the inclusion of the second-order Born term in the scattering amplitude improves the degree of agreement with experiments, especially for backward scattering region of TDCS. This indicates that the present second-order Born term is capable to give a reasonable correction to DWBA model in studying coplanar symmetric (e, 2e) problems of two-valence-electron target in low energy range.

Zhang, Yong-Zhi; Wang, Yang; Zhou, Ya-Jun

2014-06-01

366

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

367

First- or second-order transition in the melting of repeat sequence DNA.  

PubMed Central

Both theoretical analysis and observation of the continuity of the melted fraction of base pairs indicate that the melting transition in DNA is second order. Analysis of the salt dependence of the transition by polyelectrolyte limiting laws, however, has first-order dynamics imbedded in the analysis. This paper proposes that the observation taken to be a latent heat of melting in the limiting law analysis could instead be a specific heat anomaly associated with a second-order transition. The limiting laws can be reconstructed based on a second-order transition with a specific heat anomaly. The T2M dependence of this excess heat is also consistent with its being a specific heat anomaly of a system displaying classical critical behavior. Classical critical behavior indicates that theoretical mean field approaches such as MSPA should be particularly appropriate to helix melting studies. PMID:8130338

Chen, Y Z; Prohofsky, E W

1994-01-01

368

Mean-value second-order uncertainty analysis method: application to water quality modelling  

NASA Astrophysics Data System (ADS)

Uncertainty analysis in hydrology and water quality modelling is an important issue. Various methods have been proposed to estimate uncertainties on model results based on given uncertainties on model parameters. Among these methods, the mean-value first-order second-moment (MFOSM) method and the advanced mean-value first-order second-moment (AFOSM) method are the most common ones. This paper presents a method based on a second-order approximation of a model output function. The application of this method requires the estimation of first- and second-order derivatives at a mean-value point in the parameter space. Application to a Streeter-Phelps prototype model is presented. Uncertainties on two and six parameters are considered. Exceedance probabilities (EP) of dissolved oxygen concentrations are obtained and compared with EP computed using Monte Carlo, AFOSM and MFOSM methods. These results show that the mean-value second-order method leads to better estimates of EP.

Mailhot, Alain; Villeneuve, Jean-Pierre

369

Second-order nonlinear Schrödinger equation breather solutions in the degenerate and rogue wave limits  

NASA Astrophysics Data System (ADS)

We present an explicit analytic form for the two-breather solution of the nonlinear Schrödinger equation with imaginary eigenvalues. It describes various nonlinear combinations of Akhmediev breathers and Kuznetsov-Ma solitons. The degenerate case, when the two eigenvalues coincide, is quite involved. The standard inverse scattering technique does not generally provide an answer to this scenario. We show here that the solution can still be found as a special limit of the general second-order expression and appears as a mixture of polynomials with trigonometric and hyperbolic functions. A further restriction of this particular case, where the two eigenvalues are equal to i, produces the second-order rogue wave with two free parameters considered as differential shifts. The illustrations reveal a precarious dependence of wave profile on the degenerate eigenvalues and differential shifts. Thus we establish a hierarchy of second-order solutions, revealing the interrelated nature of the general case, the rogue wave, and the degenerate breathers.

Kedziora, David J.; Ankiewicz, Adrian; Akhmediev, Nail

2012-06-01

370

Construction of Hydrazine and NTO Kinetic Reaction Model for Bipropellant Thruster Simulation  

NASA Astrophysics Data System (ADS)

Hydrazine (N2H4) and NTO (dinitrogen tetroxide: N2O4) mixtures are used in spacecraft bipropellant systems, having the advantage, for sampling missions, of having no carbon composition. However, no reasonable hydrazine and NTO combustion model has been developed. To construct a hydrazine and NTO combustion model that is useful for bipropellant thruster CFD simulation, we extracted efficient elementary reactions from detailed kinetic reaction model proposed by Ohminami and Ogawa in 2007. The reduced hydrazine and NTO combustion model was composed of 61 extracted reactions with 23 chemical species and was coincident with the original detailed kinetic reaction model in terms of combustion gas temperatures and ignition delay times over O/F(oxidizer and fuel mass ration) =0.82-1.84. Also the simulated combustion gas temperatures were good agreed with the adiabatic flame temperatures, and the simulated ignition delay time at O/F=1.2 was consistent with the literature value. Chemical reaction paths before and after ignition were showed, and could explain hydrazine and NTO combustion network mechanism change.

Ohminami, Kaori; Ogawa, Hiroyuki; Hayashi, A. Koichi

371

Reactions of plutonium and uranium with water: Kinetics and potential hazards  

SciTech Connect

The chemistry and kinetics of reactions between water and the metals and hydrides of plutonium and uranium are described in an effort to consolidate information for assessing potential hazards associated with handling and storage. New experimental results and data from literature sources are presented. Kinetic dependencies on pH, salt concentration, temperature and other parameters are reviewed. Corrosion reactions of the metals in near-neutral solutions produce a fine hydridic powder plus hydrogen. The corrosion rate for plutonium in sea water is a thousand-fold faster than for the metal in distilled water and more than a thousand-fold faster than for uranium in sea water. Reaction rates for immersed hydrides of plutonium and uranium are comparable and slower than the corrosion rates for the respective metals. However, uranium trihydride is reported to react violently if a quantity greater than twenty-five grams is rapidly immersed in water. The possibility of a similar autothermic reaction for large quantities of plutonium hydride cannot be excluded. In addition to producing hydrogen, corrosion reactions convert the massive metals into material forms that are readily suspended in water and that are aerosolizable and potentially pyrophoric when dry. Potential hazards associated with criticality, environmental dispersal, spontaneous ignition and explosive gas mixtures are outlined.

Haschke, J.M.

1995-12-01

372

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

373

Thermal Behavior, Nonisothermal Decomposition Reaction Kinetics of Mixed Ester Double-base Gun Propellants  

Microsoft Academic Search

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

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

2008-01-01

374

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

DOE Data Explorer

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

375

Reaction kinetic studies of strontium hexaferrite nanoparticles synthesized by co-precipitation method  

Microsoft Academic Search

Nano crystalline strontium hexaferrite, SrFe12O19 powders have been synthesized using co-precipitation method. The ferrite precursors were obtained from aqueous mixtures of\\u000a strontium chloride and ferric chloride by precipitating strontium and iron using 7.5 M sodium hydroxide solution. These precursors\\u000a were heat treated at 800 and 1200°C in nitrogen atmosphere. The decomposition behaviour and reaction kinetics were investigated\\u000a by means of

Sachin Tyagi; R. C. Agarwala; Vijaya Agarwala

2010-01-01

376

Kinetics of Garnet Breakdown Reaction Rims: Experimental Simulations of Natural Xenoliths  

Microsoft Academic Search

Polyphase reaction rims in garnet-bearing systems were experimentally produced to determine the kinetics of garnet corona formation. We used the Piston Cylinder apparatus with noble metal capsules containing polished pyr-alm grt slabs and cpx powder (several compositions were used) and several wt% H2O. The experiments were elevated to temperatures between 800-1150° C and pressures from 0.7-1.2 GPa, simulating the conditions

M. S. Blondes; W. G. Minarik

2002-01-01

377

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

ERIC Educational Resources Information Center

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

Sattsangi, Prem D.

2011-01-01

378

Kinetics of Imidazole Catalyzed Ester Hydrolysis: Use of Buffer Dilutions to Determine Spontaneous Rate, Catalyzed Rate, and Reaction Order.  

ERIC Educational Resources Information Center

Described is an advanced undergraduate kinetics experiment using buffer dilutions to determine spontaneous rate, catalyzed rate, and reaction order. The reaction utilized is hydrolysis of p-nitro-phenyl acetate in presence of imidazole, which has been shown to enhance rate of the reaction. (Author/JN)

Lombardo, Anthony

1982-01-01

379

Reaction kinetics of ethylene glycol reforming over platinum in the vapor versus aqueous phases  

SciTech Connect

First-principles, periodic, density functional theory (DFT) calculations are carried out on Pt(111) to investigate the structure and energetics of dehydrogenated ethylene glycol species and transition states for the cleavage of C-H/O-H and C-C bonds. Additionally, reaction kinetics studies are carried out for the vapor phase reforming of ethylene glycol (C{sub 2}H{sub 6}O{sub 2}) over Pt/Al{sub 2}O{sub 3} at various temperatures, pressures, and feed concentrations. These results are compared to data for aqueous phase reforming of ethylene glycol on this Pt catalyst, as reported in a previous publication (Shabaker, J. W.; et al. J. Catal. 2003, 215, 344). Microkinetic models were developed to describe the reaction kinetics data obtained for both the vapor-phase and aqueous-phase reforming processes. The results suggest that C?C bond scission in ethylene glycol occurs at an intermediate value of x (3 or 4) in C{sub 2}H{sub x}O{sub 2}. It is also found that similar values of kinetic parameters can be used to describe the vapor and aqueous phase reforming data, suggesting that the vapor phase chemistry of this reaction over platinum is similar to that in the aqueous phase over platinum.

Kandoi, S.; Greeley, J.; Simonetti, D.; Shabaker, J.; Dumesic, J. A.; Mavrikakis, M. (Center for Nanoscale Materials); (Univ. of Wisconsin at Madison)

2011-01-01

380

Refolded scFv Antibody Fragment against Myoglobin Shows Rapid Reaction Kinetics  

PubMed Central

Myoglobin is one of the early biomarkers for acute myocardial infarction. Recently, we have screened an antibody with unique rapid reaction kinetics toward human myoglobin antigen. Antibodies with rapid reaction kinetics are thought to be an early IgG form produced during early stage of in vivo immunization. We produced a recombinant scFv fragment for the premature antibody from Escherichia coli using refolding technology. The scFv gene was constructed by connection of the VH–VL sequence with a (Gly4Ser)3 linker. The scFv fragment without the pelB leader sequence was expressed at a high level, but the solubility was extremely low. A high concentration of 8 M urea was used for denaturation. The dilution refolding process in the presence of arginine and the redox reagents GSH and GSSH successfully produced a soluble scFv protein. The resultant refolded scFv protein showed association and dissociation values of 9.32 × 10?4 M?1·s?1 and 6.29 × 10?3 s?1, respectively, with an affinity value exceeding 107 M?1 (kon/koff), maintaining the original rapid reaction kinetics of the premature antibody. The refolded scFv could provide a platform for protein engineering for the clinical application for diagnosis of heart disease and the development of a continuous biosensor. PMID:25530617

Song, Hyung-Nam; Jang, Jun-Hyuck; Kim, Young-Wan; Kim, Dong-Hyung; Park, Sung-Goo; Lee, Myung Kyu; Paek, Se-Hwan; Woo, Eui-Jeon

2014-01-01

381

Thermochemical properties and non-isothermal decomposition reaction kinetics of 3,4-dinitrofurazanfuroxan (DNTF).  

PubMed

The constant-volume combustion energy, DeltacU (DNTF, s, 298.15K) and kinetic behavior of the exothermic decomposition reaction of the title compound (DNTF) are determined by a precise rotating bomb calorimeter and DSC, respectively. Its standard enthalpy of combustion, DeltacHmtheta (DNTF, s, 298.15K), standard enthalpy of formation, DeltacHmtheta (DNTF, s, 298.15K) and kinetic parameters of the major exothermic decomposition reaction in a temperature-programmed mode [the apparent activation energy (Ea) and pre-exponential factor (A)] are calculated. The values of DeltacU (DNTF, s, 298.15K), DeltacHmtheta (DNTF, s, 298.15K), and DeltacHmtheta (DNTF, s, 298.15K) of DNTF are -9733.96 +/- 8.59 Jg(-1), -3018.29 +/- 2.68 kJ mol(-1), and 657.23 +/- 2.70 kJ mol(-1), respectively. The kinetic model function in integral form and the value of E(a) and A of the major exothermic decomposition reaction of DNTF are 1-(1-alpha)1/3, 177.03 kJ mol(-1) and 10(13.68)s(-1), respectively. The critical temperature of thermal explosion of DNTF is 240.6 degrees C. PMID:15363515

Feng-qi, Zhao; Pei, Chen; Rong-zu, Hu; Yang, Luo; Zhi-zhong, Zhang; Yan-shui, Zhou; Xu-wu, Yang; Yin, Gao; Sheng-li, Gao; Qi-zhen, Shi

2004-09-10

382

Kinetics of the bosonic A+B-->0 reaction with on-site attractive interaction.  

PubMed

We investigate kinetics of the uniformly driven bosonic A+B-->0 reaction with on-site attractive interaction in one dimension. In this model, n(i)(lambda) particles from a site with n(i) particles are driven to the right. When particles of opposite species occupy the same site, the reaction takes place instantaneously. Since n(i)(lambda)kinetics of the reaction is independent of lambda as long as lambda<1. The lambda -independent kinetics results from the lambda -independent collective motions of single species domains. PMID:17358328

Kwon, Sungchul; Kim, Yup

2007-02-01

383

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

SciTech Connect

Recent developments by the authors in the field of comprehensive detailed chemical kinetic reaction mechanisms for hydrocarbon fuels are reviewed. Examples are given of how these mechanisms provide fundamental chemical insights into a range of combustion applications. Practical combustion consists primarily of chemical heat release from reactions between a fuel and an oxidizer, and computer simulations of practical combustion systems have become an essential tool of combustion research (Westbrook et al., 2005). At the heart of most combustion simulations, the chemical kinetic submodel frequently is the most detailed, complex and computationally costly part of a system model. Historically, the chemical submodel equations are solved using time-implicit numerical algorithms, due to the extreme stiffness of the coupled rate equations, with a computational cost that varies roughly with the cube of the number of chemical species in the model. While early mechanisms (c. 1980) for apparently simple fuels such as methane (Warnatz, 1980) or methanol (Westbrook and Dryer, 1979) included perhaps 25 species, current detailed mechanisms for much larger, more complex fuels such as hexadecane (Fournet et al., 2001; Ristori et al., 2001; Westbrook et al., 2008) or methyl ester methyl decanoate (Herbinet et al., 2008) have as many as 2000 or even 3000 species. Rapid growth in capabilities of modern computers has been an essential feature in this rapid growth in the size and complexity of chemical kinetic reaction mechanisms.

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

2008-07-16

384

Refolded scFv Antibody Fragment against Myoglobin Shows Rapid Reaction Kinetics.  

PubMed

Myoglobin is one of the early biomarkers for acute myocardial infarction. Recently, we have screened an antibody with unique rapid reaction kinetics toward human myoglobin antigen. Antibodies with rapid reaction kinetics are thought to be an early IgG form produced during early stage of in vivo immunization. We produced a recombinant scFv fragment for the premature antibody from Escherichia coli using refolding technology. The scFv gene was constructed by connection of the VH-VL sequence with a (Gly4Ser)3 linker. The scFv fragment without the pelB leader sequence was expressed at a high level, but the solubility was extremely low. A high concentration of 8 M urea was used for denaturation. The dilution refolding process in the presence of arginine and the redox reagents GSH and GSSH successfully produced a soluble scFv protein. The resultant refolded scFv protein showed association and dissociation values of 9.32 × 10-4 M-1·s-1 and 6.29 × 10-3 s-1, respectively, with an affinity value exceeding 107 M-1 (kon/koff), maintaining the original rapid reaction kinetics of the premature antibody. The refolded scFv could provide a platform for protein engineering for the clinical application for diagnosis of heart disease and the development of a continuous biosensor. PMID:25530617

Song, Hyung-Nam; Jang, Jun-Hyuck; Kim, Young-Wan; Kim, Dong-Hyung; Park, Sung-Goo; Lee, Myung Kyu; Paek, Se-Hwan; Woo, Eui-Jeon

2014-01-01

385

Quadratic Curvature Gravity with Second Order Trace and Massive Gravity Models in Three Dimensions  

E-print Network

The quadratic curvature lagrangians having metric field equations with second order trace are constructed relative to an orthonormal coframe. In $n>4$ dimensions, pure quadratic curvature lagrangian having second order trace constructed contains three free parameters in the most general case. The fourth order field equations of some of these models, in arbitrary dimensions, are cast in a particular form using the Schouten tensor. As a consequence, the field equations for the New massive gravity theory are related to those of the Topologically massive gravity. In particular, the conditions under which the latter is "square root" of the former are presented.

Ahmet Baykal

2012-05-05

386

The Perceived Speed of Second-order Motion and its Dependence on Stimulus Contrast  

Microsoft Academic Search

Speed matches were obtained, using a spatial two-alternative forced-choice task, between a second-order motion stimulus and a first-order motion stimulus. The second-order motion stimulus was composed of contrast-modulated noise (produced by multiplying two-dimensional (2-d), static noise by a drifting, one-dimensional (l-d) sinusoid). The first-order motion stimulus was composed of luminance-modulated noise (produced by summing, rather than multiplying, 2-d noise and

TIMOTHY LEDGEWAY; ANDREW T. SMITH

1995-01-01

387

Semi analytical solution of second order fuzzy Riccati equation by homotopy perturbation method  

NASA Astrophysics Data System (ADS)

In this work, the Homotopy Perturbation Method (HPM) is formulated to find a semi-analytical solution of the Fuzzy Initial Value Problem (FIVP) involving nonlinear second order Riccati equation. This method is based upon homotopy perturbation theory. This method allows for the solution of the differential equation to be calculated in the form of an infinite series in which the components can be easily calculated. The effectiveness of the algorithm is demonstrated by solving nonlinear second order fuzzy Riccati equation. The results indicate that the method is very effective and simple to apply.

Jameel, A. F.; Ismail, Ahmad Izani Md

2014-07-01

388

First- and second-order polarization mode dispersion generated by a two-stage emulator.  

PubMed

A two-stage polarization mode dispersion (PMD) emulator design consisting of two variable delay lines separated by a rotatable half-wave linear retarder is analyzed and shown to generate an adjustable amount of first- and second-order PMD without any higher orders. This two-stage PMD emulator configuration provides a simple easy-to-breadboard solution for second-order PMD emulators. When compared with PMD emulators based on birefringent crystals, this two-stage emulator is simpler to calibrate. PMID:15605546

Chipman, Russell A; Kinnera, Ravinderkumar

2004-11-20

389

Comparatively Large Second-Order Hyperpolarizability of Aromatic Sulfonate Anion with Short Cutoff Wavelength  

NASA Astrophysics Data System (ADS)

The second-order hyperpolarizabilities (?) of ionic species of sodium p-toluenesulfonate ( pTSNa) and its corresponding neutral derivative methyl p-toluenesulfonate ( p TSMe) in methanol were evaluated to be 2.2×10-29 and 1.2×10-29 esu, respectively, using the hyper Rayleigh scattering method at 1064 nm. Since ionic p TSNa has short cutoff wavelength of 280 nm as well as comparatively large |?| value, i.e., about twice that of neutral p TSMe and about two-thirds that of p-nitroaniline, aromatic sulfonate ions are concluded to be worth investigating as potential chromophores for second-order nonlinear optics.

Duan, Xuan-Ming; Okada, Shuji; Oikawa, Hidetoshi; Matsuda, Hiro; Nakanishi, Hachiro

1994-11-01

390

Second-order explicit finite-difference methods for transient-flow analysis  

NASA Technical Reports Server (NTRS)

Three second-order accurate numerical methods - MacCormack's method, Lambda scheme and Gabutti scheme - are introduced to solve the quasi-linear, hyperbolic partial differential equations describing transient flows in closed conduits. The details of these methods and the treatment of boundary conditions are presented and the results computed by using these methods for a typical piping system are compared. It is shown that for the same accuracy, second-order methods require considerably lesser number of computational nodes and computer time as compared to those required by the first-order methods.

Chaudhry, M. H.; Hussaini, M. Y.

1983-01-01

391

Second Order Adjoint-based Optimization of Ordinary and Partial Differential Equations with Application to Air Traffic Flow  

E-print Network

Second Order Adjoint-based Optimization of Ordinary and Partial Differential Equations to implement the second order Newton method on ordinary differential equation (ODE) and partial differential first order algorithms, while not significantly increasing computational time. I. INTRODUCTION Optimal

Tomlin, Claire

392

A kinetic study of the CH2OO Criegee intermediate self-reaction, reaction with SO2 and unimolecular reaction using cavity ring-down spectroscopy.  

PubMed

Criegee intermediates are important species formed during the ozonolysis of alkenes. Reaction of stabilized Criegee intermediates with various species like SO2 and NO2 may contribute significantly to tropospheric chemistry. In the laboratory, self-reaction can be an important loss pathway for Criegee intermediates and thus needs to be characterized to obtain accurate bimolecular reaction rate coefficients. Cavity ring-down spectroscopy was used to perform kinetic measurements for various reactions of CH2OO at 293 K and under low pressure (7 to 30 Torr) conditions. For the reaction CH2OO + CH2OO (8), a rate coefficient k8 = (7.35 ± 0.63) × 10(-11) cm(3) molecule(-1) s(-1) was derived from the measured CH2OO decay rates, using an absorption cross section value reported previously. A rate coefficient of k4 = (3.80 ± 0.04) × 10(-11) cm(3) molecule(-1) s(-1) was obtained for the CH2OO + SO2 (4) reaction. An upper limit for the unimolecular CH2OO loss rate coefficient of 11.6 ± 8.0 s(-1) was deduced from studies of reaction (4). SO2 catalysed CH2OO isomerization or intersystem crossing is proposed to occur with a rate coefficient of (3.53 ± 0.32) × 10(-11) cm(3) molecule(-1) s(-1). PMID:25553776

Chhantyal-Pun, Rabi; Davey, Anthony; Shallcross, Dudley E; Percival, Carl J; Orr-Ewing, Andrew J

2015-02-01

393

Kinetic limitations in gas-particle reactions arising from slow diffusion in secondary organic aerosol.  

PubMed

The potential for aerosol physical properties, such as phase, morphology and viscosity/ diffusivity, to affect particle reactivity remains highly uncertain. We report here a study of the effect of bulk diffusivity of polycyclic aromatic hydrocarbons (PAHs) in secondary organic aerosol (SOA) on the kinetics of the heterogeneous reaction of particle-borne benzo[a]pyrene (BaP) with ozone. The experiments were performed by coating BaP-ammonium sulfate particles with multilayers of SOA formed from ozonolysis of alpha-pinene, and by subsequently investigating the kinetics of BaP loss via reaction with excess ozone using an aerosol flow tube coupled to an Aerodyne Aerosol Mass Spectrometer (AMS). All reactions exhibit pseudo-first order kinetics and are empirically well described by a Langmuir-Hinshelwood (L-H) mechanism. The results show that under dry conditions (RH < 5%) diffusion through the SOA coating can lead to significant mass transfer constraints on the kinetics, with behavior between that previously observed by our group for solid and liquid organic coats. The reactivity of BaP was enhanced at -50% relative humidity (RH) suggesting that water uptake lowers the viscosity of the SOA, hence lifting the mass transfer constraint to some degree. The kinetics for -70% RH were similar to results obtained without SOA coats, indicating that the SOA had sufficiently low viscosity and was sufficiently liquid-like that reactants could rapidly diffuse through the coat. A kinetic multi-layer model for aerosol surface and bulk chemistry was applied to simulate the kinetics, yielding estimates for the diffusion coefficients (in cm2 s(-1)) for BaP in alpha-pinene SOA of 2 x 10(-14), 8 x 10(-14) and > 1 x 10(-12) for dry (RH < 5%), 50% RH and 70% RH conditions, respectively. These results clearly indicate that slow diffusion of reactants through SOA coats under specific conditions can provide shielding from gas-phase oxidants, enabling the long-range atmospheric transport of toxic trace species, such as PAHs and persistent organic pollutants. PMID:24601014

Zhou, Shouming; Shiraiwa, Manabu; McWhinney, Robert D; Pöschl, Ulrich; Abbatt, Jonathan P D

2013-01-01

394

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

395

A Kinetic Study of the Gas-Phase Reaction of OH with Br2  

PubMed Central

An experimental, temperature-dependent kinetic study of the gas-phase reaction of the hydroxyl radical with molecular bromine (reaction 1) has been performed using a pulsed laser photolysis/pulsed-laser-induced fluorescence technique over a wide temperature range of 297 – 766 K, and at pressures between 6.68 and 40.29 kPa of helium. The experimental rate coefficients for reaction 1 demonstrate no correlation with pressure and exhibit a negative temperature dependence with a slight negative curvature in the Arrhenius plot. A non-linear least-squares fit with two floating parameters of the temperature dependent k1(T) data set using an equation of the form k1(T) = ATn yields the recommended expression k1(T) = 1.85×10?9T ? 0.66 cm3 molecule?1 s?1 for the temperature dependence of the reaction 1 rate coefficient. The potential energy surface (PES) of reaction 1 was investigated using quantum chemistry methods. The reaction proceeds through formation of a weakly bound OH···Br2 complex and a PES saddle point with an energy below that of the reactants. Temperature dependence of the reaction rate coefficient was modeled using the RRKM method on the basis of the calculated PES. PMID:16854030

Bryukov, Mikhail G.; Dellinger, Barry; Knyazev, Vadim D.

2011-01-01

396

Kinetics of solid-state reactions between zirconium thin film and silicon carbide at elevated temperatures  

NASA Astrophysics Data System (ADS)

Solid state reactions between a thin film (133 nm) of Zr and bulk single crystalline 6H-SiC substrates have been studied at temperatures between 600 °C and 850 °C for durations of 30, 60 and 120 min under high vacuum conditions. The deposited film and reaction zones were investigated by Rutherford backscattering spectrometry (RBS) and X-ray diffraction. The RBS spectra were simulated in order to obtain the deposited layer thickness, reaction zone compositions and reaction zone thickness. The as-deposited spectra fit well with those annealed at 600 °C, thus showing there were no reactions taking place. At temperatures of 700 °C and above, Zr reacted with the SiC substrate and formed a mixed layer of Zr carbide (ZrCx) and Zr silicides (ZrSi, Zr2Si and Zr5Si3). Annealing at 850 °C for 240 min revealed that all the deposited Zr had completely reacted. The interface reaction follows the parabolic growth law thereby indicating diffusion controlled reaction kinetics. The activation energy for the diffusion process obtained was 1.6 eV in the relatively narrow temperature range 700-850 °C.

Njoroge, E. G.; Theron, C. C.; Malherbe, J. B.; Ndwandwe, O. M.

2014-08-01

397

Generalized Galileons: All scalar models whose curved background extensions maintain second-order field equations and stress tensors  

SciTech Connect

We extend to curved backgrounds all flat-space scalar field models that obey purely second-order equations, while maintaining their second-order dependence on both field and metric. This extension simultaneously restores to second order the, originally higher derivative, stress tensors as well. The process is transparent and uniform for all dimensions.

Deffayet, C.; Deser, S.; Esposito-Farese, G. [AstroParticule and Cosmologie, UMR 7164-CNRS, Universite Denis Diderot-Paris 7, CEA, Observatoire de Paris, 10 rue Alice Domon et Leonie Duquet, F-75205 Paris Cedex 13 (France); Physics Department, Brandeis University, Waltham, Massachusetts 02454, USA, and Lauritsen Laboratory, California Institute of Technology, Pasadena, California 91125 (United States); GReCO, Institut d'Astrophysique de Paris, UMR 7095-CNRS, Universite Pierre et Marie Curie-Paris 6, 98bis boulevard Arago, F-75014 Paris (France)

2009-09-15

398

A constant-time kinetic Monte Carlo algorithm for simulation of large biochemical reaction networks.  

PubMed

The time evolution of species concentrations in biochemical reaction networks is often modeled using the stochastic simulation algorithm (SSA) [Gillespie, J. Phys. Chem. 81, 2340 (1977)]. The computational cost of the original SSA scaled linearly with the number of reactions in the network. Gibson and Bruck developed a logarithmic scaling version of the SSA which uses a priority queue or binary tree for more efficient reaction selection [Gibson and Bruck, J. Phys. Chem. A 104, 1876 (2000)]. More generally, this problem is one of dynamic discrete random variate generation which finds many uses in kinetic Monte Carlo and discrete event simulation. We present here a constant-time algorithm, whose cost is independent of the number of reactions, enabled by a slightly more complex underlying data structure. While applicable to kinetic Monte Carlo simulations in general, we describe the algorithm in the context of biochemical simulations and demonstrate its competitive performance on small- and medium-size networks, as well as its superior constant-time performance on very large networks, which are becoming necessary to represent the increasing complexity of biochemical data for pathways that mediate cell function. PMID:18513044

Slepoy, Alexander; Thompson, Aidan P; Plimpton, Steven J

2008-05-28

399

A First-Passage Kinetic Monte Carlo method for reaction–drift–diffusion processes  

SciTech Connect

Stochastic reaction–diffusion models are now a popular tool for studying physical systems in which both the explicit diffusion of molecules and noise in the chemical reaction process play important roles. The Smoluchowski diffusion-limited reaction model (SDLR) is one of several that have been used to study biological systems. Exact realizations of the underlying stochastic processes described by the SDLR model can be generated by the recently proposed First-Passage Kinetic Monte Carlo (FPKMC) method. This exactness relies on sampling analytical solutions to one and two-body diffusion equations in simplified protective domains. In this work we extend the FPKMC to allow for drift arising from fixed, background potentials. As the corresponding Fokker–Planck equations that describe the motion of each molecule can no longer be solved analytically, we develop a hybrid method that discretizes the protective domains. The discretization is chosen so that the drift–diffusion of each molecule within its protective domain is approximated by a continuous-time random walk on a lattice. New lattices are defined dynamically as the protective domains are updated, hence we will refer to our method as Dynamic Lattice FPKMC or DL-FPKMC. We focus primarily on the one-dimensional case in this manuscript, and demonstrate the numerical convergence and accuracy of our method in this case for both smooth and discontinuous potentials. We also present applications of our method, which illustrate the impact of drift on reaction kinetics.

Mauro, Ava J., E-mail: avamauro@bu.edu [Department of Mathematics and Statistics, Boston University, 111 Cummington Mall, Boston, MA 02215 (United States); Sigurdsson, Jon Karl; Shrake, Justin [Department of Mathematics, University of California, Santa Barbara (United States)] [Department of Mathematics, University of California, Santa Barbara (United States); Atzberger, Paul J., E-mail: atzberg@math.ucsb.edu [6712 South Hall, Department of Mathematics, University of California, Santa Barbara, CA 93106 (United States); Isaacson, Samuel A., E-mail: isaacson@math.bu.edu [Department of Mathematics and Statistics, Boston University, 111 Cummington Mall, Boston, MA 02215 (United States)

2014-02-15

400

The kinetics and mechanisms of the reactions of iron(III) with quercetin and morin.  

PubMed

The kinetics and mechanisms of the reactions of a pseudo-first order excess of iron(III) with the flavonoids quercetin and morin have been investigated in aqueous solution at 25 degrees C and an ionic strength of 0.5M. Mechanisms have been proposed which account satisfactorily for the kinetic data. The data are consistent with a mechanism in which the metal:ligand complex formed initially on reaction of iron(III) with the ligand subsequently decomposes through an electron transfer step. Morin forms a 1:1 metal:ligand complex while quercetin forms a 2:1 metal:ligand complex. Both ligands showed evidence for the involvement of the iron hydroxo dimer Fe2(OH)2(4+) in the complex formation reaction at the hydroxy-carbonyl moiety. The iron(III) assisted decomposition of the initial iron(III) complex formed was also investigated and the rate constants evaluated. Both the complex formation and subsequent electron transfer reactions of iron(III) with these ligands were monitored using UV-visible spectrophotometry. All of the suggested mechanisms and calculated rate constants are supported by calculations carried out using global analysis of time dependant spectra. PMID:17868888

Ryan, Paul; Hynes, Michael J

2008-01-01

401

A First-Passage Kinetic Monte Carlo method for reaction-drift-diffusion processes  

NASA Astrophysics Data System (ADS)

Stochastic reaction-diffusion models are now a popular tool for studying physical systems in which both the explicit diffusion of molecules and noise in the chemical reaction process play important roles. The Smoluchowski diffusion-limited reaction model (SDLR) is one of several that have been used to study biological systems. Exact realizations of the underlying stochastic processes described by the SDLR model can be generated by the recently proposed First-Passage Kinetic Monte Carlo (FPKMC) method. This exactness relies on sampling analytical solutions to one and two-body diffusion equations in simplified protective domains. In this work we extend the FPKMC to allow for drift arising from fixed, background potentials. As the corresponding Fokker-Planck equations that describe the motion of each molecule can no longer be solved analytically, we develop a hybrid method that discretizes the protective domains. The discretization is chosen so that the drift-diffusion of each molecule within its protective domain is approximated by a continuous-time random walk on a lattice. New lattices are defined dynamically as the protective domains are updated, hence we will refer to our method as Dynamic Lattice FPKMC or DL-FPKMC. We focus primarily on the one-dimensional case in this manuscript, and demonstrate the numerical convergence and accuracy of our method in this case for both smooth and discontinuous potentials. We also present applications of our method, which illustrate the impact of drift on reaction kinetics.

Mauro, Ava J.; Sigurdsson, Jon Karl; Shrake, Justin; Atzberger, Paul J.; Isaacson, Samuel A.

2014-02-01

402

Microbial respiration and dissolution precipitation reactions of minerals: thermo-kinetics and reactive transport modelling  

NASA Astrophysics Data System (ADS)

Microbial processes interact closely with abiotic geochemical reactions and mineralogical transformations in several hydrogeochemical systems. Reactive transport models are aimed to analyze these complex mechanisms integrating as well as the degradation of organic matter as the redox reactions involving successive terminal electron acceptors (TEAPs) mediated by microbes through the continuum of unsaturated zone (soil) - saturated zone (aquifer). The involvement of microbial processes in reactive transport in soil and subsurface geologic greatly complicates the mastery of the major mechanisms and the numerical modelling of these systems. The introduction of kinetic constraints of redox reactions in aqueous phase requires the decoupling of equilibrium reactions and the redefinition of mass balance of chemical elements including the concept of basis species and secondary species of thermodynamic databases used in geochemical modelling tools. An integrated methodology for modelling the reactive transport has been developed and implemented to simulate the transfer of arsenic, denitrification processes and the role of metastable aqueous sulfur species with pyrite and organic matter as electron donors entities. A mechanistic rate law of microbial respiration in various geochemical environments was used to simulate reactive transport of arsenic, nitrate and organic matter combined to the generalized rate law of mineral dissolution - precipitation reactions derived from the transition state theory was used for dissolution - precipitation of silica, aluminosilicate, carbonate, oxyhydroxide, and sulphide minerals. The kinetic parameters are compiled from the literature measurements based on laboratory constrained experiments and field observations. Numerical simulations, using the geochemical software PHREEQC, were performed aiming to identify the key reactions mediated by microbes in the framework of in the first hand the concept of the unsaturated - saturated zones of an artificial recharge of deep aquifers system and in a second hand an acid mine drainage system. A large amount of data is available on the old mine site of Cheni (France). This field data on acid mine drainage are compared to a thermokinetic model including biological kinetics, precipitation-dissolution kinetics and surface complexation on ferrihydrite. The kinetic parameters are from literature and from a fitting on batch biological experiments. The integrated approach combining reaction kinetics and biogeochemical thermodynamic constraints is successfully applied to denitrification experiments in the presence of acetate and pyrite conducted in the laboratory for batch and column systems. The powerful of this coupled approach allows a fine description of the different transition species from nitrate to nitrogen. The fitted kinetic parameters established for modelling these laboratory results are thus extended to simulate the denitrification processes in a field case where organic matter and pyrite FeS2 are the electron donors and O2, NO3, Fe(OH)3, SO4 are the electron acceptors in the framework of a continuum UZ - SZ aiming to identify the stabilized redox zones of acid mine drainage. The detailed results obtained on two actual case studies will be presented.

Azaroual, M. M.; Parmentier, M.; Andre, L.; Croiset, N.; Pettenati, M.; Kremer, S.

2010-12-01

403

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

404

Structural characteristics and second order nonlinear optical properties of borate crystals  

E-print Network

Structural characteristics and second order nonlinear optical properties of borate crystals D. Xue optical (NLO) responses of some typical borate crystals with various crystal structures have been the reported inorganic crystal structures there are in total only 15% of noncentrosymmetric structure

Osnabrück, Universität

405

SEMI-LAGRANGIAN DISCONTINUOUS GALERKIN SCHEMES FOR SOME FIRST AND SECOND ORDER PARTIAL  

E-print Network

SEMI-LAGRANGIAN DISCONTINUOUS GALERKIN SCHEMES FOR SOME FIRST AND SECOND ORDER PARTIAL DIFFERENTIAL, Mehrenberger and Vecil (2010) and of Qiu and Shu (2011), for first order equations, based on exact integration when possible. First, in Section 2, we revisit the one-dimensional first order advection equation

Paris-Sud XI, Université de

406

Numerical Properties of Constraint-Preserving Bound-ary Conditions for a Second Order Wave Equation  

E-print Network

- lution of second order vector wave equation and compare the performance of three sets of differential governing evolution equations are coupled to differential constraint equations are common in mathematics to the first order in time form. We compare the performance of three sets of boundary conditions. The first set

Alekseenko, Alexander

407

A Multilevel Algorithm for the Solution of Second Order Elliptic Differential Equations on Sparse Grids  

NASA Technical Reports Server (NTRS)

A multilevel algorithm is presented that solves general second order elliptic partial differential equations on adaptive sparse grids. The multilevel algorithm consists of several V-cycles. Suitable discretizations provide that the discrete equation system can be solved in an efficient way. Numerical experiments show a convergence rate of order Omicron(1) for the multilevel algorithm.

Pflaum, Christoph

1996-01-01

408

A novel unsplit perfectly matched layer for the second-order acoustic wave equation.  

PubMed

When solving acoustic field equations by using numerical approximation technique, absorbing boundary conditions (ABCs) are widely used to truncate the simulation to a finite space. The perfectly matched layer (PML) technique has exhibited excellent absorbing efficiency as an ABC for the acoustic wave equation formulated as a first-order system. However, as the PML was originally designed for the first-order equation system, it cannot be applied to the second-order equation system directly. In this article, we aim to extend the unsplit PML to the second-order equation system. We developed an efficient unsplit implementation of PML for the second-order acoustic wave equation based on an auxiliary-differential-equation (ADE) scheme. The proposed method can benefit to the use of PML in simulations based on second-order equations. Compared with the existing PMLs, it has simpler implementation and requires less extra storage. Numerical results from finite-difference time-domain models are provided to illustrate the validity of the approach. PMID:24794509

Ma, Youneng; Yu, Jinhua; Wang, Yuanyuan

2014-08-01

409

Lie symmetries of systems of second-order linear ordinary differential equations with constant coefficients  

PubMed Central

Lie symmetries of systems of second-order linear ordinary differential equations with constant coefficients are exhaustively described over both the complex and real fields. The exact lower and upper bounds for the dimensions of the maximal Lie invariance algebras possessed by such systems are obtained using an effective algebraic approach. PMID:23564972

Boyko, Vyacheslav M.; Popovych, Roman O.; Shapoval, Nataliya M.

2013-01-01

410

On the oscillation of certain second-order nonlinear differential equations  

Microsoft Academic Search

In this paper, oscillation criteria for the nonlinear second-order ordinary differential equation r(t)?x(t)x?(t)p?2x?(t)?+c(t)fx(t)=0 are given. The results extend the integral averaging technique and include earlier results. Our methodology is somewhat different from that of previous authors.

Aydýn Tiryaki; Devrim Çakmak; Bülent Ayanlar

2003-01-01

411

EXPANDED MIXED FINITE ELEMENT METHODS FOR QUASILINEAR SECOND ORDER ELLIPTIC PROBLEMS, II  

E-print Network

EXPANDED MIXED FINITE ELEMENT METHODS FOR QUASILINEAR SECOND ORDER ELLIPTIC PROBLEMS, II Zhangxin formulation for linear second­order elliptic problems. Optimal order and superconvergent error estimates­ processing scheme proposed here for the first time for nonlinear mixed methods is not a straightforward

412

A parallel second-order adaptive mesh algorithm for incompressible flow in porous media  

Microsoft Academic Search

In this paper we present a second-order accurate adaptive algorithm for solving multiphase, incompressible ow in porous media. We assume a multiphase form of Darcy's law with relative permeabilities given as a function of the phase saturation. The remaining equations express conservation of mass for the uid constituents. In this setting the total velocity, dened to be the sum of

George S. H. Pau; Ann S. Almgren; John B. Bell

2009-01-01

413

Second order cone programming (SOCP) relaxations for large margin HMMs in speech recognition  

Microsoft Academic Search

In this paper, we present a new fast optimization method to solve large margin estimation (LME) of continuous density hidden Markov models (CDHMMs) for speech recognition based on second order cone programming (SOCP). SOCP is a class of nonlinear convex optimization problems which can be solved very efficiently. In this work, we have formulated the LME of CDHMMs as an

Yan Yin; Hui Jiang

2009-01-01

414

EXPANDED MIXED FINITE ELEMENT METHODS FOR QUASILINEAR SECOND ORDER ELLIPTIC PROBLEMS, It (*)  

Microsoft Academic Search

Anew mixed formulation recently proposedfor hnear problems is extended to quasihnear second-order elliptic problems This new formulation expands the standard mixed formulation in the sense that three variables are explicitly treated, ie, the scalar unknown, Us gradient, and itsflux (the coefficient times the gradient) Based on this formulation, mixed finite element approximations of the quasihnear problems are estabhshed Existence and

Zhangxin CHEN

1994-01-01

415

Artifact reduction in magnetoneurography based on time-delayed second-order correlations  

Microsoft Academic Search

Artifacts in magnetoneurography data due to endogenous biological noise sources, like the cardiac signal, can be four orders of magnitude higher than the signal of interest. Therefore, it is important to establish effective artifact reduction methods. We propose a blind source separation algorithm using only second-order temporal correlations for cleaning biomagnetic measurements of evoked responses in the peripheral nervous system.

Andreas Ziehe; Klaus-Robert Müller; Guido Nolte; Bruno-Marcel Mackert; Gabriel Curio

2000-01-01

416

Convergence to second order stationary points of a primal-dual algorithm model for nonlinear programming  

Microsoft Academic Search

We define a primal-dual algorithm model (SOLA) for inequality constrained optimization problems that generates a sequence converging to points satisfying the second order neces- sary conditions for optimality. This property can be enforced by combining the equivalence between the original constrained problem and the unconstrained minimization of an exact augmented Lagrangian function and the use of a curvilinear linesearch technique

Antonio Ruberti

417

Stability Results for Second-Order Evolution Equations with Switching Time-Delay  

NASA Astrophysics Data System (ADS)

We consider second-order evolution equations in an abstract setting with intermittently delayed/ not-delayed damping. We give sufficient conditions for asymptotic and exponential stability, improving and generalising our previous results from [19]. In particular, under suitable conditions, we can consider unbounded damping operators. Some concrete examples are finally presented.

Nicaise, Serge; Pignotti, Cristina

2014-09-01

418

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

419

Strichartz estimates for second order hyperbolic operators with nonsmooth coefficients, II  

Microsoft Academic Search

In an earlier work we have proved some estimates of Strichartz type for second order hyperbolic operators with C s coefficients for 0 s 1. Here we improve these estimates and extend the range of s to 0 s 2. In particular for s = 2 we obtain the full Strichartz estimates. 1. Introduction. The Strichartz estimates are dispersive estimates

Daniel Tataru

2001-01-01

420

Oscillatory behavior of closed isotropic models in second order gravity theory  

E-print Network

Homogeneous and isotropic models are studied in the Jordan frame of the second order gravity theory. The late time evolution of the models is analysed with the methods of the dynamical systems. The normal form of the dynamical system has periodic solutions for a large set of initial conditions. This implies that an initially expanding closed isotropic universe may exhibit oscillatory behaviour.

J. Miritzis

2007-08-10

421

Safe Distributed Motion Coordination for Second-Order Systems with Different Planning Cycles  

E-print Network

(Ferguson et al., 2006). During each cycle, a robot executes a previously computed trajectory while planning. An example simulation is shown in Figure 1. The duration of a planning cycle can vary per robot and is alsoSafe Distributed Motion Coordination for Second-Order Systems with Different Planning Cycles Kostas

Moll, Mark

422

Asynchronous Distributed Motion Planning with Safety Guarantees under Second-Order Dynamics  

E-print Network

Asynchronous Distributed Motion Planning with Safety Guarantees under Second-Order Dynamics Devin K- tory for the next replanning cycle. The planning process must guarantee the robot's safety by ensuring and the robots make planning decisions at different time instants. This paper shows how to guarantee the safe

Kavraki, Lydia E.

423

Parallel R-Point Explicit Block Method for Solving Second Order Ordinary Differential Equations Directly  

Microsoft Academic Search

A new parallel R-point explicit block method for solving second order ordinary differential equations (ODEs) directly is developed. The method computes the numerical solution of the equations at three points simultaneously. Each problem was tested on the shared memory parallel computer Sequent S27 using both the sequential and parallel implementations of the new method and the conventional 1-point method. Numerical

Z. Omar; Mohd Yazid Saman; David J. Evans

2002-01-01

424

Fourth-order explicit hybrid method for solving special second-order ordinary differential equations  

NASA Astrophysics Data System (ADS)

In this paper, a fourth-order explicit hybrid method with constant step-size is developed. The free parameters are chosen so that the error constant is small. Numerical comparisons are carried out to show the advantage of the new method for solving special second order ordinary differential equations.

Samat, Faieza; Ismail, Fudziah

2013-04-01

425

Block Methods based on Newton Interpolations for Solving Special Second Order Ordinary Differential Equations Directly  

Microsoft Academic Search

This study focused mainly on the derivation of the 2 and 3-point block methods with constant coefficients for solving special second order ordinary differential equations directly based on Newton-Gregory backward interpolation formula. The performance of the new methods was compared with the conventional 1-point method using a standard set of test problems. Numerical results were presented to illustrate the effectiveness

Yap Lee Ken; Fudziah Ismail; Mohamed Suleiman

2008-01-01

426

Learning and Extracting Finite State Automata with Second-Order Recurrent Neural Networks  

Microsoft Academic Search

We show that a recurrent, second-order neural network using a real-time, forward training algorithm readily learns to infer small regular grammars from positive and negative string training samples. We present simulations that show the effect of initial conditions, training set size and order, and neural network architecture. All simulations were performed with random initial weight strengths and usually converge after

C. Lee Giles; Clifford B. Miller; D. Chen; H. H. Chen; Guo-zheng Sun; Y. C. Lee

1992-01-01

427

The Development of Perceptual Sensitivity to Second-Order Facial Relations in Children  

ERIC Educational Resources Information Center

This study investigated children's perceptual ability to process second-order facial relations. In total, 78 children in three age groups (7, 9, and 11 years) and 28 adults were asked to say whether the eyes were the same distance apart in two side-by-side faces. The two faces were similar on all points except the space between the eyes, which was…

Baudouin, Jean-Yves; Gallay, Mathieu; Durand, Karine; Robichon, Fabrice

2010-01-01

428

Estimation of second order parameters using Probability Weighted Moments Julien Worms  

E-print Network

Estimation of second order parameters using Probability Weighted Moments Julien Worms Universit Sciences, B^at. Fermat, 45 av. des Etats-Unis, 78035 Versailles Cedex e-mail : worms@math.uvsq.fr Rym Worms av. du Gl de Gaulle, 94010 Cr´eteil cedex e-mail : rym.worms@univ-paris12.fr Version : March 9th

Paris-Sud XI, Université de

429

First- and second-order configural sensitivity for greeble stimuli in baboons.  

PubMed

Previous studies on nonhuman primates have shown inconsistencies in their processing of first- and second-order relational properties of facial stimuli. Using greeble stimuli sharing configural properties with faces, this study assessed configural processing in baboons. Five baboons were trained to recognize a positive stimulus among pairs of greebles in a two-alternative forced choice task. They were then tested with new stimulus pairs involving either a first-order version, with modifications in global qualitative spatial relations, or a second-order version, with modifications of finer spatial relations. Performance remained above chance in all test conditions, including when only second-order cues were available, but it was higher for first-order trials. It is proposed that an extensive training with greebles led to the processing of second-order relational properties. These results demonstrate that configural sensitivity is not restricted to faces in baboons and suggest that a common mechanism may support configural processing for face and nonface stimuli. PMID:21048228

Parron, Carole; Fagot, Joël

2010-11-01

430

Independence of First- and Second-Order Memories in Newborn Rabbits  

ERIC Educational Resources Information Center

The mammary pheromone promotes the acquisition of novel odorants (CS1) in newborn rabbits. Here, experiments pinpoint that CS1 becomes able to support neonatal learning of other odorants (CS2). We therefore evaluated whether these first- and second-order memories remained dependent after reactivation. Amnesia induced after CS2 recall selectively…

Coureaud, Gerard; Languille, Solene; Joly, Virginie; Schaal, Benoist; Hars, Bernard

2011-01-01

431

A second-order accurate parabolized Navier-Stokes algorithm for internal flows  

NASA Technical Reports Server (NTRS)

A parabolized implicit Navier-Stokes algorithm which is of second-order accuracy in both the cross flow and marching directions is presented. The algorithm is used to analyze three model supersonic flow problems (the flow over a 10-degree edge). The results are found to be in good agreement with the results of other techniques available in the literature.

Chitsomboon, T.; Tiwari, S. N.

1984-01-01

432

Computer Simulation for Calculating the Second-Order Correlation Function of Classical and Quantum Light  

ERIC Educational Resources Information Center

We propose an undergraduate numerical project for simulating the results of the second-order correlation function as obtained by an intensity interference experiment for two kinds of light, namely bunched light with Gaussian or Lorentzian power density spectrum and antibunched light obtained from single-photon sources. While the algorithm for…

Facao, M.; Lopes, A.; Silva, A. L.; Silva, P.

2011-01-01

433

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...

434

Determination of the second order doppler shift of iron in myoglobin by Mössbauer spectroscopy  

Microsoft Academic Search

We have performed Mössbauer absorption experiments on a sample of deoxygenated myoglobin crystals from 5 K to 280 K. With two series of measurements, one with the source and sample at the same temperature and the other with the source always at 298 K, we are able to extract information from the second-order Doppler effect in the sample. Simple models

L. Reinisch; J. Heidemeier; F. Parak

1985-01-01

435

Blind source separation and identification of nonlinear multiuser channels using second order statistics and modulation codes  

Microsoft Academic Search

In this paper, a Blind Source Separation (BSS) and channel identification method using second order statistics is proposed for nonlinear multiuser communication channels. It is based on the joint diagonalization of a set of covariance matrices. Modulation codes (constrained codes) are used to ensure the orthogonality of nonlinear combinations of the transmitted signals, allowing the application of a joint diagonalization

C. A. R. Fernandes; G. Favier; J. C. M. Mota

2007-01-01

436

Positive solutions to a system of second-order nonlocal boundary value problems  

Microsoft Academic Search

In this paper we study the existence of positive solutions to a system of second-order nonlocal boundary value problems by using fixed point index theory in a cone. Our hypotheses imposed on nonlinearities are those which characterize systems of nonlocal boundary value problems, and our boundary value conditions are expressed in terms of possibly nonlinear functions of Riemann–Stieltjes integrals, thus

Zhilin Yang

2005-01-01

437

Tolerance synthesis using second-order fuzzy comprehensive evaluation and genetic algorithm  

Microsoft Academic Search

In modern manufacturing engineering, tolerance synthesis is important because it directly eÄ ects product quality and manufacturing cost. This paper introduces a new method for tolerance synthesis of machining parts. The new method consists of three steps. First, machining parts are evaluated using the second-order fuzzy comprehensive evaluation (FCE). Then, a mathematical model for tolerance allo- cation is formed based

SHUPING JI; XIAOLI LI

438

A Second-Order Maximum Principle in Optimal Control under State Constraints  

E-print Network

, Daniel Hoehener and Daniela Tonon Combinatoire & Optimisation Institut de Math´ematiques de Jussieu Universit´e Pierre et Marie Curie 4 place Jussieu, 75252 Paris cedex 05, France October 9, 2013 Abstract the first-order necessary optimality condition (¯c) = 0 (Fermat rule) and the second-order condition (¯c

Boyer, Edmond

439

AIAA-2000-1654 Decoupled Second-Order Equations and Modal Analysis  

E-print Network

AIAA-2000-1654 Decoupled Second-Order Equations and Modal Analysis of a General Nonconservative System Mayuresh J. Patil Abstract The paper presents the theoretical basis for modal analysis of a general nonconservative system. The modal analysis uses only real modes in terms of the dis- placements

Patil, Mayuresh

440

An Immersed Boundary Method with Formal Second-Order Accuracy and Reduced Numerical Viscosity  

Microsoft Academic Search

A formally second-order accurate immersed boundary method is presented and tested in this paper. We apply this new scheme to simulate the flow past a circular cylinder and study the effect of numerical viscosity on the accuracy of the computation by comparing the numerical results with those of a first-order method. The numerical evidence shows that the new scheme has

Ming-Chih Lai; Charles S. Peskin

2000-01-01

441

Estimating the spectral indices of correlated astrophysical foregrounds by a second-order statistical approach  

Microsoft Academic Search

We present the first tests of a new method, the correlated component analysis (CCA) based on second-order statistics, to estimate the mixing matrix, a key ingredient to separate astrophysical foregrounds superimposed to the Cosmic Microwave Background (CMB). In the present application, the mixing matrix is parametrized in terms of the spectral indices of Galactic synchrotron and thermal dust emissions, while

A. Bonaldi; L. Bedini; E. Salerno; C. Baccigalupi; G. de Zotti

2006-01-01

442

Navier-Stokes computation of compressible turbulent flows with a second order closure, part 1  

NASA Technical Reports Server (NTRS)

A second order closure turbulence model for compressible flows is developed and implemented in a 2D Reynolds-averaged Navier-Stokes solver. From the beginning where a kappa-epsilon turbulence model was implemented in the bidiagonal implicit method of MACCORMACK (referred to as the MAC3 code) to the final stage of implementing a full second order closure in the efficient line Gauss-Seidel algorithm, numerous work was done, individually and collectively. Besides the collaboration itself, the final product of this work is a second order closure derived from the Launder, Reece, and Rodi model to account for near wall effects, which has been called FRAME model, which stands for FRench-AMerican-Effort. During the reporting period, two different problems were worked out. The first was to provide Ames researchers with a reliable compressible boundary layer code including a wide collection of turbulence models for quick testing of new terms, both in two equations and in second order closure (LRR and FRAME). The second topic was to complete the implementation of the FRAME model in the MAC5 code. The work related to these two different contributions is reported. dilatation in presence of stron shocks. This work, which has been conducted during a work at the Center for Turbulence Research with Zeman aimed also to cros-check earlier assumptions by Rubesin and Vandromme.

Haminh, Hieu; Kollmann, Wolfgang; Vandromme, Dany

1990-01-01

443

Achievement of Global Second Order Mesh Convergence for Discontinuous Flows with Adapted  

E-print Network

Achievement of Global Second Order Mesh Convergence for Discontinuous Flows with Adapted to govern the adapted mesh generation. As regards steady flow computations with discontinuities, a global discontinuities or sharp gradients in the modelled flow. In order to address this issue, a continuous mesh

Frey, Pascal

444

Can Reflection Be Confined into Roles? First and Second Order Research in Action Research.  

ERIC Educational Resources Information Center

The distinction between first-order and second-order research in action research is explored in the context of work on the Management for Organizational and Human Development (MOHD) project in Italy. Researchers worked with two groups of heads of primary schools in Italy to develop a path of reflection and research on their roles and functions and…

Losito, Bruno; Pozzo, Graziella; Somekh, Bridget

445

Diagonally implicit block backward differentiation formula for solving linear second order ordinary differential equations  

NASA Astrophysics Data System (ADS)

The three point block method for solving second order ordinary differential equations (ODEs) directly using constant step size is derived. The reliability of this new method is verified in the numerical results with the improved performance in terms of computation time while maintaining the accuracy. The comparison is presented between the new method and classical backward differentiation formulas (BDF) of order 3.

Zainuddin, N.; Ibrahim, Z. B.; Othman, K. I.

2014-10-01

446

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

447

Oscillation for a second-order neutral differential equation with impulses  

E-print Network

Oscillation for a second-order neutral differential equation with impulses E. M. Bonotto , L. P controlled abrupt perturbations (called impulses). As a matter of fact, some particular non-impulsive cases of the system are oscillatory already. Thus, we are interested in finding adequate impulse controls under which

Federson, Márcia - Instituto de Ciências Matemáticas e de Computação, Universidade de São Paulo

448

Second order BVPs with state dependent impulses via lower and upper  

E-print Network

Second order BVPs with state dependent impulses via lower and upper functions Irena Rach with p state­dependent impulses (p N) z (t) = f(t, z(t)) for a.e. t [0, T], z(0) = 0, z(T) = 0, z (i: Impulsive differential equation, state­dependent impulses, upper and lower functions method, upper and lower

Rachùnkova, Irena

449

ON THE ARTIFICIAL COMPRESSION METHOD FOR SECOND-ORDER NONOSCILLATORY CENTRAL DIFFERENCE SCHEMES FOR SYSTEMS  

E-print Network

-order central di#11;erence schemes for conservation laws have a tendency of smearing linear discontinuitiesON THE ARTIFICIAL COMPRESSION METHOD FOR SECOND-ORDER NONOSCILLATORY CENTRAL DIFFERENCE SCHEMES central di#11;erence scheme, #12;rst introduced in 1954 by Lax [11], which was extended to second

450

ON THE ARTIFICIAL COMPRESSION METHOD FOR SECOND-ORDER NONOSCILLATORY CENTRAL DIFFERENCE SCHEMES FOR SYSTEMS  

E-print Network

-order central di#11;erence schemes for conservation laws have a tendency of smearing linear discontinuitiesON THE ARTIFICIAL COMPRESSION METHOD FOR SECOND-ORDER NONOSCILLATORY CENTRAL DIFFERENCE SCHEMES in a stable and accurate manner. An alternative to the Godunov-type upwind schemes is the central di#11;erence

Noelle, Sebastian

451

Second-Order Factor Structure of the MBTI: A Construct Validity Assessment.  

ERIC Educational Resources Information Center

Factor adequacy and other results based on data from college students (N=359) provided positive evidence regarding the construct validity of the Myers-Briggs Type Indicator (MBTI). Second order factor analysis supported the appropriateness of the MBTI item weighting procedures. (Author/ABB)

Thompson, Bruce; Borrello, Gloria M.

1986-01-01

452

Kinetics and Thermochemistry of the Br((sup 2)P3/2) + NO2 Association Reaction  

NASA Technical Reports Server (NTRS)

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the Br((sup 2)P3/2) + NO2 association reaction as a function of temperature (259-432 K) pressure (12.5 - 700 Torr), and buffer gas identity (He, Ar, H2, N2, CO2, CF4, SF6). The reaction is found to be in the falloff regime between third and second order over the entire range of conditions investigated. At temperatures below 350 K, the association reaction is found to be irreversible on the time scale of the experiment (approximately 30 ms). At higher temperatures reversible addition is observed, allowing equilibrium constants for BrNO2 formation and dissociation to be determined. Second- and third-law analyses of the equilibrium data are in only fair agreement and lead to the following thermochemical parameters for the association reaction: Delta-H(298) = 19.6 +/- 1.7 kcal/mol, Delta-H(0) = -18.6 +/- 2.0 kcal/mol, Delta-S(298) = 29.3 +/- 4.2 cal/mol/K, Delta-H(sub f)(sub 298)(BrNO2) = 17.0 +/-1.8 kcal/mol(uncertainties are 2 sigma estimates of absolute accuracy). The value for Delta-H(0) determined in this study has been employed to calculate k(sub 0)(sup SC), the low-pressure third-order rate coefficient in the strong collision limit, by using the method of Troe; calculated values of k(sub 0)(sup SC) are inconsistent with experimental results unless Delta-H(0) is assigned a value near the lower limit derived from analysis of the high-temperature approach to equilibrium data, i.e. delta-H(0) approximately equals -16.6 kcal/mol. A potential source of systematic error in the calculation of both k(sub 0)(sup SC) and the absolute entropy of BrNO2 results from the complete lack of knowledge of the energies and degeneracies of the electronic states of BrNO3. The procedure developed by Troe and co-workers has been employed to extrapolate experimental falloff curves to the low- and high-pressure limits. Derived values for k(sub 0)(M,298K) in units of 10(exp -31) cm(exp 6)/sq molecule/s range from 2.75 for M = He to 6.54 for M = CO2; 2 sigma uncertainties are estimated to be +/- 20%. Values for k(sub 0)(N2,T) in units of 10(exp -31) cm(exp 6)/sq molecule/s are 5.73 at 259 K, 4.61 at 298 K, and 3.21 at 346 K; the observed temperature dependence for k(sub 0)(N2,T) is consistent with the theoretical temperature dependence for Beta(sub c)k(sub 0)(sup SC). Values for k(sub infinity)(T) in units of 10(exp -11) cu cm/molecule/s are 2.86 at 259 K, 3.22 at 298 K, and 3.73 at 346 K; 2 sigma uncertainties are estimated to be a factor of 2. Approximate falloff parameters in a convenient format for atmospheric modeling are also derived.

Kreutter, K. D.; Nicovich, J. M.; Wine, P. H.

1997-01-01

453

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

PubMed

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

Luo, Zhi-yong; Zheng, Huai-li

2014-06-01

454

Thickness Dependence of Oxygen Reduction Reaction Kinetics on Strontium-Substituted Lanthanum Manganese Perovskite Thin-Film Microelectrodes  

E-print Network

Oxygen reduction reaction (ORR) kinetics was investigated on dense La?.?Sr?.?MnO? microelectrodes as a function of temperature and microelectrode thickness using electrochemical impedance spectroscopy. The surface oxygen ...

la O’, G. J.

455

Golden rule kinetics of transfer reactions in condensed phase: The microscopic model of electron transfer reactions in disordered solid matrices  

SciTech Connect

The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ?{sub 0}=??{sub 0}/k{sub B}T where ?{sub 0} is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (?{sub 0} < 1 ? 3) and for low (?{sub 0}? 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T? 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local modes immersed in the continuum harmonic medium is formulated for both classical and quantum regimes, and accounts explicitly for the mode/medium interaction. The kinetics of the energy exchange between the local ET subsystem and the surrounding environment essentially determine the total ET rate. The efficient computer code for rate computations is elaborated on. The computations are available for a wide range of system parameters, such as the temperature, external field, local mode frequency, and characteristics of mode/medium interaction. The relation of the present approach to the Marcus ET theory and to the quantum-statistical reaction rate theory [V. G. Levich and R. R. Dogonadze, Dokl. Akad. Nauk SSSR, Ser. Fiz. Khim. 124, 213 (1959); J. Ulstrup, Charge Transfer in Condensed Media (Springer, Berlin, 1979); M. Bixon and J. Jortner, Adv. Chem. Phys. 106, 35 (1999)] underlying it is discussed and illustrated by the results of computations for practically important target systems.

Basilevsky, M. V.; Mitina, E. A. [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation)] [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation); Odinokov, A. V. [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation) [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation); National Research Nuclear University “MEPhI,” 31, Kashirskoye shosse, Moscow (Russian Federation); Titov, S. V. [Karpov Institute of Physical Chemistry, 3-1/12, Building 6, Obuha pereulok, Moscow (Russian Federation)] [Karpov Institute of Physical Chemistry, 3-1/12, Building 6, Obuha pereulok, Moscow (Russian Federation)

2013-12-21

456

Kinetics, mechanism and intermediates of some radiation-induced reactions in aqueous solutions  

NASA Astrophysics Data System (ADS)

The results of pulse radiolysis studies of the kinetics and mechanism of fast one-electron redox reactions of halide ions, metal ions, actinides and other compounds with hydrated electrons, hydroxyl and other radicals and hydrogen atoms and the properties of intermediates formed in these reactions are analysed. The oxidation of a mixture of chloride and bromide ions yields mixed radical anions ClBr-·. Data on the formation of metal atoms and ions in unusual and unstable oxidation states by the reduction of metal ions in aqueous solutions and on the reactions involving such ions are presented. It is shown that the reduction of compounds in aqueous solutions with organic radicals takes place through outer- or inner-sphere electron transfer.

Ershov, Boris G.

2004-01-01

457

Second order distorted born approximation for backscattering from a layer of discrete random medium  

NASA Technical Reports Server (NTRS)

In recent years there has been increasing interest in scattering and depolarization characteristics of the vegetation canopies. Scattering models applied to the microwave remote sensing of vegetation canopies showed that multiple scattering effects can be important in simulating the backscattering coefficients correctly. In particular, in most applications, the cross-polarized backscattering coefficients are often underestimated by single scattering models. Recently, there have been concerted efforts to include the second order terms in the radiative transfer models of vegetation canopies in order to account for multiple scattering within the canopy. The coherent wave theory approach is extended to include multiple scattering effects to predict the coherent and incoherent backscattering contributions from a layer of vegetation canopy. The problem is initially formulated in terms of the exact equation for the correlation function of the field, i.e., the Bethe-Salpeter equation. Using fractional volume as a small parameter, a Foldy type approximation is made to obtain a more manageable correlation equation. This equation is iterated to obtain first and second order solutions. The iteration procedure assumes the variance of the field fluctuations are small compared to the coherent intensity. This assumption proved to be particularly successful in computing backscattering coefficients. First and second order backscattering coefficients are calculated from the iterants of the correlation equation. It is shown that the first order coefficients are the same as the distorted Born results used previously by the authors. These results contained enhancement terms in the direct-reflected contributions. The important contributions to second order backscattering are examined and interpreted in terms of scattering diagrams. Examples of situations in which second order backscattering coefficients are important are given.

Lang, Roger H.; Saatchi, Sasan S.

1993-01-01

458

Kinetic stabilization against the oxidation reaction induced by a silaalkane cage in a thiophene-bridged molecular gyroscope.  

PubMed

Macrocage molecules with a bridged rotor have been synthesized as molecular gyroscopes. The kinetics of the oxidation reaction of the thiophene-bridged molecular gyroscope, whose thiophene ring was bridged inside a silaalkane cage, was investigated. A remarkable kinetic stabilization against the oxidation of the thiophene moiety induced by the molecular cage framework was observed. PMID:24317303

Setaka, Wataru; Ohmizu, Soichiro; Kira, Mitsuo

2014-02-01

459

Analytical potential of the reaction between p -phenylenediamines and peroxodisulfate for kinetic spectrophotometric determination of traces of ascorbic acid  

Microsoft Academic Search

The analytical potential of the redox reactions between N,N-dimethyl- or N,N,N',N'-tetramethyl-p-phenylenediamine (DMPPD or TMPPD, respectively) and peroxodisulfate in acidic media for kinetic spectrophotometric determination of trace amounts of ascorbic acid (AA) has been investigated. The goal was to explore reaction conditions ensuring an excess or a deficit of S2O82-, and to identify some kinetic features of the global process for

Alexandra Rustoiu-Csavdari; Ulrich Nickel

2002-01-01

460

Experimental study of the reactions of limonene with OH and OD radicals: kinetics and products.  

PubMed

The kinetics of the reactions of limonene with OH and OD radicals has been studied using a low-pressure flow tube reactor coupled with a quadrupole mass spectrometer: OH + C10H16 ? products (1), OD + C10H16 ? products (2). The rate constants of the title reactions were determined using four different approaches: either monitoring the kinetics of OH (OD) radicals or limonene consumption in excess of limonene or of the radicals, respectively (absolute method), and by the relative rate method using either the reaction OH (OD) + Br2 or OH (OD) + DMDS (dimethyl disulfide) as the reference one and following HOBr (DOBr) formation or DMDS and limonene consumption, respectively. As a result of the absolute and relative measurements, the overall rate coefficients, k1 = (3.0 ± 0.5) × 10(-11) exp((515 ± 50)/T) and k2 = (2.5 ± 0.6) × 10(-11) exp((575 ± 60)/T) cm(3) molecule(-1) s(-1), were determined at a pressure of 1 Torr of helium over the temperature ranges 220-360 and 233-353 K, respectively. k1 was found to be pressure independent over the range 0.5-5 Torr. There are two possible pathways for the reaction between OH (OD) and limonene: addition of the radical to one of the limonene double bonds (reactions 1a and 2a ) and abstraction of a hydrogen atom (reactions 1b and 2b ), resulting in the formation of H2O (HOD). Measurements of the HOD yield as a function of temperature led to the following branching ratio of the H atom abstraction channel: k2b/k2 = (0.07 ± 0.03) × exp((460 ± 140)/T) for T = (253-355) K. PMID:25211148

Braure, Tristan; Bedjanian, Yuri; Romanias, Manolis N; Morin, Julien; Riffault, Véronique; Tomas, Alexandre; Coddeville, Patrice

2014-10-01

461

Low-temperature Kinetic Studies of OH Radical Reactions Relevant to Planetary Atmospheres  

NASA Astrophysics Data System (ADS)

In the solar system, the temperature (T) of the atmosphere of giant planets or their satellites is only several tens of Kelvin (K). The temperature of the tropopause of Titan (satellite of Saturn) and the surface of Mars is 70 K and 210 K, respectively. In the Earth's atmosphere, T decreases from 298 K (surface) to 210 K close to the T-inversion region (tropopause). The principal oxidants in the Earth's lower atmosphere are ozone, the hydroxyl (OH) radical and hydrogen peroxide. A number of critical atmospheric chemical problems depend on the Earth's oxidising capacity, which is essentially the global burden of these oxidants. In the interstellar clouds and circumstellar envelopes, OH radicals have also been detected. As the chemistry of atmospheres is highly influenced by temperature, the knowledge of the T-dependence of the rate coefficients for OH-reactions (k) is the key to understanding the underlying molecular mechanisms. In general, these reactions take place on a short temporal scale. Therefore, a detection technique with high temporal resolution is required. Measurements of k at low temperatures can be achieved by maintaining a thermalised environment using either cryogenic cooling (T>200 K) or supersonic gas expansion with a Laval nozzle (several tens of K). The pulsed laser photolysis technique coupled with laser induced fluorescence detection has been widely used in our laboratory to determine the rate coefficients of OH-reactions with different volatile organic compounds, such as alcohols (1), saturated and unsaturated aliphatic aldehydes (2), linear ketones (3), as a function of temperature (260 350 K). An experimental system based on the CRESU (Cinetique de Reaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in a Uniform Supersonic Flow) technique is currently under construction. This technique will allow the performance of kinetic studies of OH-reactions of astrophysical interest at temperatures lower than 200 K.

Townsend, T. M.; Antiñolo, M.; Ballesteros, B.; Jimenez, E.; Canosa, A.

2011-05-01

462

Kinetics and intermediates of the reaction of fully reduced Escherichia coli bo? ubiquinol oxidase with O?.  

PubMed

Cytochrome bo? ubiquinol oxidase from Escherichia coli catalyzes the reduction of O? to water by ubiquinol. The reaction mechanism and the role of ubiquinol continue to be a subject of discussion. In this study, we report a detailed kinetic scheme of the reaction of cytochrome bo? with O? with steps specific to ubiquinol. The reaction was investigated using the CO flow-flash method, and time-resolved optical absorption difference spectra were collected from 1 ?s to 20 ms after photolysis. Singular value decomposition-based global exponential fitting resolved five apparent lifetimes, 22 ?s, 30 ?s, 42 ?s, 470 ?s, and 2.0 ms. The reaction mechanism was derived by an algebraic kinetic analysis method using frequency-shifted spectra of known bovine states to identify the bo3 intermediates. It shows 42 ?s O? binding (3.8 × 10(7) M(-1) s(-1)), producing compound A, followed by faster (22 ?s) heme b oxidation, yielding a mixture of PR and F, and rapid heme b rereduction by ubiquinol (30 ?s), producing the F intermediate and semiquinone. In the 470 ?s step, the o? F state is converted into the o?(3+) oxidized state, presumably by semiquinone/ubiquinol, without the concomitant oxidation of heme b. The final 2 ms step shows heme b reoxidation and the partial rereduction of the binuclear center and, following O? binding, the formation of a mixture of P and F during a second turnover cycle. The results show that ubiquinol/semiquinone plays a complex role in the mechanism of O? reduction by bo?, displaying kinetic steps that have no analogy in the CuA-containing heme-copper oxidases. PMID:25076393

Szundi, Istvan; Kittredge, Clive; Choi, Sylvia K; McDonald, William; Ray, Jayashree; Gennis, Robert B; Einarsdóttir, Ólöf

2014-08-26

463

Understanding composite explosive energetics: 3, Reactive flow modeling of aluminum reaction kinetics in PETN and TNT  

SciTech Connect

Using Fabry-Perot interferometry techniques, we have determined that early time rate of energy release from detonating PETN and TNT explosives filled with 5 and 10 wt % of either 5 {mu}m of 18 {mu}m spherical aluminum (Al) particles. From the measured particle velocity data, we are able to infer the reaction rate of aluminum with the detonation products, and calculate the extent of reaction 1--3 {mu}s after the detonation. We observed that a substantional portion of the aluminum metal in all of the PETN and TNE formulations reacted within the timeframe of the one-dimensional experiment. In the PETN formulation filed with 5 wt % of 5 {mu}m aluminum, all of the metal reacted within 1.5 {mu}s, resulting in an increase of 22% in energy compared to pure PETN. A reactive-flow hydrodynamic model based on the Zeldovich-von Neumann-Doring (ZND) description of the reaction zone and subsequent reaction produce expansion (Taylor wave) is used to interpret the reaction rate of the aluminum particles with detonation product gases. The diffusion-controlled reaction mechanism for aluminum and the global kinetic parameters used in the model have been found to be consistent for all the PETN and TNT formulations.

Tao, W.C.; Tarver, C.M.; Ornellas, D.L.

1991-12-06

464

Weathering Reactions in Soils on Peoria Loess Document Mineral Weathering Kinetics as a Function of Climate  

NASA Astrophysics Data System (ADS)

Through physical and chemical weathering, primary minerals are transformed to soil minerals in the Critical Zone. Using a published dataset, we investigated reaction fronts occurring in modern soils developed on Peoria Loess in the Mississippi River Valley over the last 10,000 to 13,000 years. After normalization to Zr, elemental concentrations document several different characteristic reaction fronts. Na, Ca, and Mg are depleted at the surface while Al, Fe, and Si show depletion at the surface and enrichment at depth. In contrast, the macronutrients P and K show reaction fronts that reveal the effect of biogenic uptake. Finally, the elemental profile for Mn is classified as an addition-only profile which reflects a relative increase in concentration from parent to surface. This Mn profile is attributed to contaminated dust input. Using the GENESIS v2 Global Climate Model, we performed climate simulations for three periods (modern, 6kyr BP and 10kyr BP) roughly spanning the time of soil development, and extracted model temperature, precipitation, and soil pore water flux for a north-south transect representing the Mississippi Valley. The extents of mineral reaction and reaction kinetic constants vary as functions of these climate variables along the transect. Reaction rate constants will be summarized as a function of these variables for minerals in the profiles.

Williams, J. Z.; Pollard, D.; Brantley, S. L.

2006-12-01

465

Kinetic sonication effects in aqueous acetonitrile solutions. Reaction rate levelling by ultrasound.  

PubMed

The kinetics of the pH-independent hydrolysis of 4-methoxyphenyl dichloroacetate were investigated with and without ultrasonic irradiation in acetonitrile-water binary mixtures containing 0.008 to 35 wt.% of acetonitrile and the kinetic sonication effects (kson/knon) were calculated. Molecular dynamics (MD) simulations of the structure of the solutions were performed with ethyl acetate as the model ester. The ester is preferentially solvated by acetonitrile. The excess of acetonitrile over water in the solvation shell grows fast with an increase in the co-solvent content in the bulk solution. In parallel, the formation of a second solvation shell rich in acetonitrile takes place. Significant kinetic sonication effects for the hydrolysis were explained with facile destruction of the diffuse second solvation shell followed by a rearrangement of the remaining solvent layer under sonication. The rate levelling effect of ultrasound was discussed. In an aqueous-organic binary solvent, independent of the solvent composition, the ultrasonic irradiation evokes changes in the reaction medium which result in an almost identical solvation state of the reagent thus leading to the reaction rate levelling. PMID:23643415

Piiskop, Sander; Salmar, Siim; Tuulmets, Ants; Kuznetsov, Aleksei; Järv, Jaak

2013-11-01

466

REACTION KINETICS AND X-RAY ABSORPTION SPECTROSCOPY STUDIES OF YTTRIUM CONTAINING METAL HYDRIDE ELECTRODES  

SciTech Connect

This was a study of electrode degradation mechanisms and the reaction kinetics of LaNi{sub 4.7}Sn{sub 0.3}, La{sub (1{minus}x)}, (x = 0.1, 0.2, and 0.3) and La{sub 0.7}Y{sub 0.3}Ni{sub 4.6}Sn{sub 0.3}Co{sub 0.1} metal hydride electrodes. Alloy characterization included x-ray diffraction (XRD), x-ray absorption (XAS), hydrogen absorption in a Sieverts apparatus, and electrochemical cycling of alloy electrodes. The atomic volume of H was determined for two of the alloys. Electrochemical kinetic measurements were made using steady state galvanostatic measurements, galvanodynamic sweep, and electrochemical impedance techniques. XAS was used to examine the degree of corrosion of the alloys with cycling. Alloying with Y decreased the corrosion rate. The results are consistent with corrosion inhibition by a Y containing passive film. The increase in the kinetics of the hydrogen oxidation reaction (HOR) with increasing depth of discharge was much greater on the Y containing alloys. This may be due to the dehydriding of the catalytic species on the surface of the metal hydride particles.

TICIANELLI,E.A.; MUKERJEE,S.; MCBREEN,J.; ADZIC,G.D.; JOHNSON,J.R.; REILLY,J.J.

1998-11-01

467

Serpentine: Finite Difference Methods for Wave Propagation in Second Order Formulation  

SciTech Connect

Wave propagation phenomena are important in many DOE applications such as nuclear explosion monitoring, geophysical exploration, estimating ground motion hazards and damage due to earthquakes, non-destructive testing, underground facilities detection, and acoustic noise propagation. There are also future applications that would benefit from simulating wave propagation, such as geothermal energy applications and monitoring sites for carbon storage via seismic reflection techniques. In acoustics and seismology, it is of great interest to increase the frequency bandwidth in simulations. In seismic exploration, greater frequency resolution enables shorter wave lengths to be included in the simulations, allowing for better resolution in the seismic imaging. In nuclear explosion monitoring, higher frequency seismic waves are essential for accurate discrimination between explosions and earthquakes. When simulating earthquake induced motion of large structures, such as nuclear power plants or dams, increased frequency resolution is essential for realistic damage predictions. Another example is simulations of micro-seismic activity near geothermal energy plants. Here, hydro-fracturing induces many small earthquakes and the time scale of each event is proportional to the square root of the moment magnitude. As a result, the motion is dominated by higher frequencies for smaller seismic events. The above wave propagation problems are all governed by systems of hyperbolic partial differential equations in second order differential form, i.e., they contain second order partial derivatives of the dependent variables. Our general research theme in this project has been to develop numerical methods that directly discretize the wave equations in second order differential form. The obvious advantage of working with hyperbolic systems in second order differential form, as opposed to rewriting them as first order hyperbolic systems, is that the number of differential equations in the second order system is significantly smaller. Another issue with re-writing a second order system into first order form is that compatibility conditions often must be imposed on the first order form. These (Saint-Venant) conditions ensure that the solution of the first order system also satisfies the original second order system. However, such conditions can be difficult to enforce on the discretized equations, without introducing additional modeling errors. This project has previously developed robust and memory efficient algorithms for wave propagation including effects of curved boundaries, heterogeneous isotropic, and viscoelastic materials. Partially supported by internal funding from Lawrence Livermore National Laboratory, many of these methods have been implemented in the open source software WPP, which is geared towards 3-D seismic wave propagation applications. This code has shown excellent scaling on up to 32,768 processors and has enabled seismic wave calculations with up to 26 Billion grid points. TheWPP calculations have resulted in several publications in the field of computational seismology, e.g.. All of our current methods are second order accurate in both space and time. The benefits of higher order accurate schemes for wave propagation have been known for a long time, but have mostly been developed for first order hyperbolic systems. For second order hyperbolic systems, it has not been known how to make finite difference schemes stable with free surface boundary conditions, heterogeneous material properties, and curvilinear coordinates. The importance of higher order accurate methods is not necessarily to make the numerical solution more accurate, but to reduce the computational cost for obtaining a solution within an acceptable error tolerance. This is because the accuracy in the solution can always be improved by reducing the grid size h. However, in practice, the available computational resources might not be large enough to solve the problem with a low order method.

Petersson, N A; Sjogreen, B

2012-03-26

468

Kinetic analysis of subunit oligomerization of the legume lectin soybean agglutinin.  

PubMed

The reconstitution of soybean agglutinin (SBA), a tetrameric GalNAc/Gal-specific legume lectin, after denaturation in urea has been studied using fluorescence, far-UV CD, a hemagglutination assay, and chemical cross-linking with glutaraldehyde as a bifunctional reagent. The reconstituted protein exhibits similar quaternary structure and activity as of native lectin. The kinetics of subunit oligomerization has been determined from the cross-linking reaction of the reconstituting protein followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Monomers and tetramers could be quantitatively analyzed during reconstitution. Dimers are not detectable. The reassociation reaction follows second-order kinetics. The results are described by a kinetic mechanism in which the monomer-to-dimer association (characterized by a second-order rate constant (k(1)) of 1.4 x 10(4) M(-1) s(-1) at 37 degrees C) is involved in the rate-determining step of the oligomerization reaction. PMID:14567683

Chatterjee, Manjeer; Mandal, Dipak K

2003-10-28

469

The effect of Co alloying content on the kinetics of reaction zone growth in tungsten fiber reinforced superalloy composites  

NASA Technical Reports Server (NTRS)

A Co-free modified superalloy similar in composition to Waspaloy is investigated in an effort to understand the effect of Co on reaction zone growth kinetics and verify the chemistry dependence of reaction zone growth in the matrix of tungsten fiber reinforced superalloy composites. The values of the parabolic rate constant, characterizing the kinetics of reaction zone growth, for the Waspaloy matrix and the C-free alloy as well as five other alloys from a previous study confirm the dependence of reaction zone growth kinetics on cobalt content of the matrix. The Co-free alloy composite exhibits the slowest reaction zone growth among all tungsten fiber reinforced composites studied to date.

Rodriguez, A.; Tien, J. K.; Caulfield, T.; Petrasek, D. W.

1988-01-01

470

Numerical modeling of surface reaction kinetics in electrokinetically actuated microfluidic devices.  

PubMed

We outline a comprehensive numerical procedure for modeling of species transport and surface reaction kinetics in electrokinetically actuated microfluidic devices of rectangular cross section. Our results confirm the findings of previous simplified approaches that a concentration wave is created for sufficiently long microreactors. An analytical solution, developed for the wave propagation speed, shows that, when normalizing with the fluid mean velocity, it becomes a function of three parameters comprising the channel aspect ratio, the relative adsorption capacity, and the kinetic equilibrium constant. Our studies also reveal that the reactor geometry idealized as a slit, instead of a rectangular shape, gives rise to the underestimation of the saturation time. The extent of this underestimation increases by increasing the Damkohler number or decreasing the dimensionless Debye-Hückel parameter. Moreover, increasing the values of the Damkohler number, the dimensionless Debye-Hückel parameter, the relative adsorption capacity, and the velocity scale ratio results in lower saturation times. PMID:25064245

Sadeghi, Arman; Amini, Younes; Saidi, Mohammad Hassan; Chakraborty, Suman

2014-08-01

471

HTP kinetics studies on isolated elementary combustion reactions over wide temperature ranges  

SciTech Connect

The goals of this project 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. Experimental measurements are made mainly by using the pseudo-static HTP (high-temperature photochemistry) technique. While continuing rate coefficient measurements, further aspects of kinetics research are being explored. Thus, starting from the data obtained, a method for predicting the temperature dependence of rate coefficients of oxygen-atom olefin experiment and confirms the underlying mechanistic assumptions. Mechanistic information of another sort, i.e. by product analysis, has recently become accessible with the inauguration of our heated flow tube mass spectrometer facility; early results are reported here. HTP experiments designed to lead to measurements of product channels by resonance fluorescence have started.

Fontijn, A.; Adusei, G.Y.; Hranisavlevic, J.; Bajaj, P.N. [Rensselaer Polytechnic Institute, Troy, NY (United States)

1993-12-01

472

Influence of acrylic superplasticizer and cellulose-ether on the kinetics of tricalcium silicate hydration reaction.  

PubMed

This paper reports on the analysis of the hydration kinetics of a tricalcium silicate paste cured in presence of polymers industrially used in the extrusion process of mortars. In particular, we investigated the effect of a rheology-modifying additive (a methyl hydroxy ethyl cellulose) and a superplasticizer (a polyacrylic polymer). These polymers have been added to tricalcium silicate paste, both separately and together, to understand their distinct influence on the tricalcium silicate hydration and their possible synergies. The kinetic curves have been monitored from 10 to 40°C by means of Differential Scanning Calorimetry and fitted using the generalized Boundary Nucleation and Growth Model combined to a diffusion-limited model, to extract: induction times, reaction rates, activation energies and diffusion coefficients. As a main result, this paper contributes to the advancement of the knowledge in the field of the extrusion process of cementitious materials, providing a thermodynamic support to the empirical evaluations of the additives performances. PMID:23352872

Ridi, Francesca; Fratini, Emiliano; Alfani, Roberta; Baglioni, Piero

2013-04-01

473

Second-order ionospheric effects on satellite radio occultation observations and their impact on atmospheric studies  

NASA Astrophysics Data System (ADS)

This dissertation describes the development of first-of-a-kind mathematical models that both quantify higher-order ionospheric effects and their impact on Global Positioning System radio occultation (GPS/RO) data products. We develop new and innovative models to: a) remove the second-order ionospheric effect from Total Electron Content (TEC) estimations; b) quantify the second-order ionospheric delay in GPS/RO signal propagation using the Faraday phenomenon; c) quantify the vertical distribution of the first- and second-order ionospheric residual effects on GPS/RO data products; and d) retrieve improved atmospheric water vapour profiles. For the first time we combine GPS/RO measurements with space-based gravity missions to characterize the response of the GPS/RO-derived atmospheric parameters to the Earth's gravity anomalies. Independently, we implement these mathematical models in a new GPS/RO processing software package to investigate, for the first time, the impact of higher-order ionospheric residual effects on ionospheric and atmospheric products. We observe that under low solar activity, the second-order ionospheric residual effect introduces: a) slowly varying positive systematic biases of ˜1-3 TECU on TEC estimations as function of occultation time; b) maximum negative systematic biases of ˜0.35 N-units on atmospheric refractivity close to the Earth's surface; c) negative systematic biases of ˜0.5 K close to the Earth's surface, which decrease with altitude and above 26 km become positive, peaking at ˜2.0 K at 50 km and d) negative systematic biases of ˜0.08 mbar on the water vapour pressure. Further studies reveal that the second-order ionospheric residual effect increases non-linearly with solar variability, oscillating between +/-3 mm (at Rz12=2) and +/-15 mm (at Rz12=114), whereas its value increases with increasing latitude. The first-order ionospheric residual effect arising from the geometrical splitting of the dual-frequency GPS radiowave signals is ˜2-3 orders of magnitude smaller than the second-order ionospheric residual effect, with the potential of increasing in magnitude at high solar activity. A series of sensitivity studies show that the LEO velocity uncertainties affect the GPS/RO bending angle accuracy more than the Doppler shift uncertainties. Finally, we find that the Earth's gravity anomalies can introduce negative systematic biases on the atmospheric temperature profiles of up to ˜0.5 K close to the Earth's surface. This dissertation demonstrates the simplicity, innovation, effectiveness and importance of our proposed mathematical models on the future of GPS/RO atmospheric remote sensing.

Vergados, Panagiotis

474

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

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

475

Effect of reaction kinetics on predicted concentration profiles during subsurface bioremediation  

NASA Astrophysics Data System (ADS)

The lack of a complete mechanistic description of subsurface interactions between contaminants and microbes has limited the ability to predict the effectiveness of subsurface bioremediation processes. Important microbial processes which must be included in such mechanistic descriptions of bioremediation are microbial growth, death and transport, including microbial attachment to and detachment from the soil surfaces. Recent advances have provided a better understanding of the relationships between contaminant destruction rates and such microbial processes. In this manuscript, contaminant profiles predicted using more realistic descriptions are compared with those obtained using less complete, previously published mathematical models. The more comprehensive model described here includes mathematical descriptions for microbial growth and transport. Contaminant profiles predicted using this model are compared with those obtained when the contaminant destruction processes are described by assuming that (1) no reaction occurs, (2) the contaminant reacts instantaneously with any available oxygen, and (3) dual-substrate Monod kinetics without consideration of microbial growth and transport. This work demonstrates that if reaction kinetics are ignored, the size of the plume wil