ERIC Educational Resources Information Center
Silvestri, Michael G.; Dills, Charles E.
1989-01-01
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)
NASA Astrophysics Data System (ADS)
Zhang, Lei; Chen, Lingen; Sun, Fengrui
2016-03-01
The finite-time thermodynamic method based on probability analysis can more accurately describe various performance parameters of thermodynamic systems. Based on the relation between optimal efficiency and power output of a generalized Carnot heat engine with a finite high-temperature heat reservoir (heat source) and an infinite low-temperature heat reservoir (heat sink) and with the only irreversibility of heat transfer, this paper studies the problem of power optimization of chemically driven heat engine based on first and second order reaction kinetic theory, puts forward a model of the coupling heat engine which can be run periodically and obtains the effects of the finite-time thermodynamic characteristics of the coupling relation between chemical reaction and heat engine on the power optimization. The results show that the first order reaction kinetics model can use fuel more effectively, and can provide heat engine with higher temperature heat source to increase the power output of the heat engine. Moreover, the power fluctuation bounds of the chemically driven heat engine are obtained by using the probability analysis method. The results may provide some guidelines for the character analysis and power optimization of the chemically driven heat engines.
Kompany-Zareh, Mohsen; Khoshkam, Maryam
2008-05-01
To determine the rate constants for the second order consecutive reactions of the form U + V -(k1)--> W -(k2)--> P, a number of chemometrics and hard modeling-based methods are described. The absorption spectroscopic data from the reaction were utilized for performing the analysis. Concentrations and extinctions of components were comparable, and all of them were absorbing species. The number of steps in the reaction was less than the number of absorbing species, which resulted in a rank-deficient response matrix. This can cause difficulties for some of the methods described in the literature. The standard MATLAB functions were used for determining the solutions of the differential equations as well as for finding the optimal rate constants to describe the kinetic profiles. The available knowledge about the system determines the approaches described in this paper. The knowledge includes the spectra of reactants and products, the initial concentrations, and the exact kinetics. Some of this information is sometimes not available or is hard to estimate. Multiple linear regression for fitting the kinetic parameters to the obtained concentration profiles, rank augmentation using multiple batch runs, a mixed spectral approach which treats the reaction using a pseudo species concept, and principal components regression are the four groups of methods discussed in this study. In one of the simulated datasets the spectra are quite different, and in the other one the spectra of one reactant and of the product share a high degree of overlap. Instrumental noise, sampling error are the sources of error considered. Our aim was the investigation of the relative merits of each method. PMID:18469471
TRANSPORT OF DISSOLVED SUBSTANCES WITH SECOND-ORDER REACTION
A mass transport equation which allows coupled second-order reaction between two chemical components in groundwater systems is described. everal analytical solutions to the system of nonlinear equations for advective flow systems have been found, and the features of the solution ...
An Example of Following Second-Order Kinetics by Simple Laboratory Means
ERIC Educational Resources Information Center
Schreiber, Gisela
1976-01-01
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)
Chen, Jiale; Center for Magnetic Fusion Theory, Chinese Academy of Sciences, Hefei ; Gao, Zhe; Center for Magnetic Fusion Theory, Chinese Academy of Sciences, Hefei
2013-08-15
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.
Mankbadi, Michael R; Barakat, Mohamed A; Ramadan, Mohamed H; Woodcock, H Lee; Kuhn, John N
2011-11-24
This study presents a kinetic model of the chelation of iron ions by generation 4 hydroxyl-terminated polyamidoamine (PAMAM) with ethylenediamine core (G4-OH). The coordination processes of iron ions from ferric chloride, FeCl(3), and ferrous bromide, FeBr(2), to G4-OH dendrimers were analyzed using ultraviolet-visible (UV-vis) spectroscopy, proton nuclear magnetic resonance ((1)H NMR) spectroscopy, and liquid chromatography-mass spectrometry (LC-MS). In the visible region, a charge-transfer was observed when the dendrimer was added to a ferric chloride solution. This phenomenon is a ligand-to-metal charge-transfer (LMCT) between the free electron group of the dendrimer's internal amines and the dehalogenated iron ion that takes 2 h to complete at room temperature. Analysis of potential rate laws and diffusion effects led to a second-order kinetic model for this reaction. By measuring the rate coefficients as a function of temperature (22-37 °C), an apparent activation energy of 41.5 kJ/mol was obtained using the Arrhenius method. The results of this study will fuel research of PAMAM dendrimers for environmental, pharmaceutical, and materials applications. PMID:21995617
First-Order or Second-Order Kinetics? A Monte Carlo Answer
ERIC Educational Resources Information Center
Tellinghuisen, Joel
2005-01-01
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…
Temporal Frequency Modulates Reaction Time Responses to First-Order and Second-Order Motion
ERIC Educational Resources Information Center
Hutchinson, Claire V.; Ledgeway, Tim
2010-01-01
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…
Ashworth, Ian W; Cox, Brian G; Meyrick, Brian
2010-12-01
The kinetics of the HCl-catalyzed deprotection of the Boc-protected amine, thioester 2 to liberate AZD3409 1 have been studied in a mixture of toluene and propan-2-ol. The reaction rate was found to exhibit a second-order dependence upon the HCl concentration. This behavior was found to have a degree of generality as the deprotection of a second Boc-protected amine, tosylate 3 to yield amine 4 using HCl, sulfuric acid, and methane sulfonic acid showed the same kinetic dependence. In contrast the deprotection of tosylate 3 with trifluoroacetic acid required a large excess of acid to obtain a reasonable rate of reaction and showed an inverse kinetic dependence upon the trifluoroacetate concentration. These observations are rationalized mechanistically in terms of a general acid-catalyzed separation of a reversibly formed ion-molecule pair arising from the fragmentation of the protonated tert-butyl carbamate. PMID:21067172
Implementing the Second-Order Fermi Process in a Kinetic Monte-Carlo Simulation
NASA Astrophysics Data System (ADS)
Summerlin, E. J.
2010-12-01
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.
An Activation Energy Experiment for a Second-Order Reaction in a Single Laboratory Period.
ERIC Educational Resources Information Center
Barile, Raymond C.; Michiels, Leo P.
1983-01-01
Describes modification of a chemical reaction to a single 4 1/2-hour laboratory period. Reaction kinetics between 2, 4-initrochlorobenzene and piperidine to form 2, 4-dinitrophenyl-piperidine and piperidinium hydrochloride are followed conductometrically at three temperatures to obtain data to calculate activation parameters. (Author/JN)
Radiation-Reaction Force on a Small Charged Body to Second Order
NASA Astrophysics Data System (ADS)
Moxon, Jordan; Flanagan, Eanna
2015-04-01
In classical electrodynamics, an accelerating charge emits radiation and experiences a corresponding radiation reaction force, or self force. We extend to greater precision (higher order in perturbation theory) a previous rigorous derivation of the electromagnetic self force in flat spacetime by Gralla, Harte, and Wald. The method introduced by Gralla, Harte, and Wald computes the self-force from the Maxwell field equations and conservation of stress-energy, and does not require regularization of a singular point charge, as has been necessary in prior computations. For our higher order compuation, it becomes necessary to adopt an adjusted definition of the mass of the body to avoid including self-energy from the electromagnetic field sourced during the history of the body. We derive the evolution equations for the mass, spin, and center of mass position of an extended body through second order using our adjusted formalism. The final equations give an acceleration dependent evolution of the spin (self-torque), as well as a mixing between the extended body effects and the acceleration dependent effects on the overall body motion.
Poling kinetics and second order NLO properties of DCNP doped PMMA based thin film
NASA Astrophysics Data System (ADS)
Manea, Ana-Maria; Rau, Ileana; Tane, Alexandrina; Kajzar, Francois; Sznitko, Lech; Miniewicz, Andrzej
2013-11-01
Results of DC field poling and second harmonic generation experiments on a thin film of polymethyl methacrylate (PMMA) polymer doped with the dye molecule (3-(1,1-dicyanothenyl)-1-phenyl-4, 5-dihydro-1H-pryazole) (DCNP) are reported. The temporal variation of SHG signal upon application of static (DC) electric field at the temperature close to the glass transition Tg of PMMA establishes rapidly, within 66 s. A large value of second order NLO susceptibility dpp(-2ω;ω,ω) of 52 ± 8 pm/V at 1064.2 nm fundamental wavelength was observed. Its possible origin is proposed and discussed.
Structural changes of small amplitude kinetic Alfvén solitary waves due to second-order corrections
Choi, Cheong R.
2015-10-15
The structural changes of kinetic Alfvén solitary waves (KASWs) due to higher-order terms are investigated. While the first-order differential equation for KASWs provides the dispersion relation for kinetic Alfvén waves, the second-order differential equation describes the structural changes of the solitary waves due to higher-order nonlinearity. The reductive perturbation method is used to obtain the second-order and third-order partial differential equations; then, Kodama and Taniuti's technique [J. Phys. Soc. Jpn. 45, 298 (1978)] is applied in order to remove the secularities in the third-order differential equations and derive a linear second-order inhomogeneous differential equation. The solution to this new second-order equation indicates that, as the amplitude increases, the hump-type Korteweg-de Vries solution is concentrated more around the center position of the soliton and that dip-type structures form near the two edges of the soliton. This result has a close relationship with the interpretation of the complex KASW structures observed in space with satellites.
Structural changes of small amplitude kinetic Alfvén solitary waves due to second-order corrections
NASA Astrophysics Data System (ADS)
Choi, Cheong R.
2015-10-01
The structural changes of kinetic Alfvén solitary waves (KASWs) due to higher-order terms are investigated. While the first-order differential equation for KASWs provides the dispersion relation for kinetic Alfvén waves, the second-order differential equation describes the structural changes of the solitary waves due to higher-order nonlinearity. The reductive perturbation method is used to obtain the second-order and third-order partial differential equations; then, Kodama and Taniuti's technique [J. Phys. Soc. Jpn. 45, 298 (1978)] is applied in order to remove the secularities in the third-order differential equations and derive a linear second-order inhomogeneous differential equation. The solution to this new second-order equation indicates that, as the amplitude increases, the hump-type Korteweg-de Vries solution is concentrated more around the center position of the soliton and that dip-type structures form near the two edges of the soliton. This result has a close relationship with the interpretation of the complex KASW structures observed in space with satellites.
Positronium formation as a three-body reaction. II. The second-order nuclear amplitudes
Shojaei, F.; Bolorizadeh, M. A.; Ghanbari-Adivi, E.; Brunger, M. J.
2009-01-15
We derive an exact analytic form for the second-order nuclear amplitudes, under the Faddeev three-body approach, which is applicable to the nonrelativistic high energy impact interaction where positronium is formed in the collision of a positron with an atom.
A second-order accurate kinetic-theory-based method for inviscid compressible flows
NASA Technical Reports Server (NTRS)
Deshpande, Suresh M.
1986-01-01
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.
Piponnier, Jean-Claude; Forget, Robert; Gagnon, Isabelle; McKerral, Michelle; Giguère, Jean-François; Faubert, Jocelyn
2016-01-15
Mild traumatic brain injury (mTBI) has subtle effects on several brain functions that can be difficult to assess and follow up. We investigated the impact of mTBI on the perception of sine-wave gratings defined by first- and second-order characteristics. Fifteen adults diagnosed with mTBI were assessed at 15 days, 3 months, and 12 months postinjury. Fifteen matched controls followed the same testing schedule. Reaction times (RTs) for flicker detection and motion direction discrimination were measured. Stimulus contrast of first- and second-order patterns was equated to control for visibility, and correct-response RT means, standard deviations (SDs), medians, and interquartile ranges (IQRs) were calculated. The level of symptoms was also evaluated to compare it to RT data. In general in mTBI, RTs were longer, and SDs as well as IQRs larger, than those of controls. In addition, mTBI participants' RTs to first-order stimuli were shorter than those to second-order stimuli, and SDs as well as IQRs larger for first- than for second-order stimuli in the motion condition. All these observations were made over the three sessions. The level of symptoms observed in mTBI was higher than that of control participants, and this difference did also persist up to 1 year after the brain injury, despite an improvement. The combination of RT measures with particular stimulus properties is a highly sensitive method for measuring mTBI-induced visuomotor anomalies and provides a fine probe of the underlying mechanisms when the brain is exposed to mild trauma. PMID:25950948
NASA Astrophysics Data System (ADS)
Hayat, Tasawar; Imtiaz, Maria; Alsaedi, Ahmed
2015-12-01
This paper addresses the steady three-dimensional boundary layer flow of viscous nanofluid. The flow is caused by a permeable stretching surface with second order velocity slip and homogeneous-heterogeneous reactions. Water is treated as base fluid and copper as nanoparticle. An incompressible fluid fills the porous space. The fluid is electrically conducting in the presence of an applied magnetic field. A system of ordinary differential equations is obtained by using suitable transformations. Convergent series solutions are derived. Impact of various pertinent parameters on the velocity, concentration and skin friction coefficient is discussed. Analysis of the obtained results shows that the flow field is influenced appreciably by the presence of velocity slip parameters. Also concentration distribution decreases for larger values of strength of homogeneous reaction parameter while it increases for strength of heterogeneous reaction parameter.
Hbner, U; Keller, S; Jekel, M
2013-11-01
The application of the R(CT)-concept for predicting the removal of trace organic compounds (TrOCs) in organic rich WWTP effluents is often problematic due to the fast ozone depletion with instantaneous ozone demand in the range of typically applied ozone dosages. In this study, the determination of OH-radical and ozone exposure from second order rate kinetics with two internal tracer substances was evaluated as alternative approach for these waters. Results from batch and semi-batch experiments showed a linear correlation of OH-radical exposure with ozone consumption, characterized by its slope indicating the formation efficiency of OH-radicals and a lag ozone consumption without significant formation of OH-radicals. Evaluation of data from the project PILOTOX on ozonation of secondary effluent confirmed reasonable prediction of ozone resistant compound removal from relative residual concentration of an internal tracer substance. In contrast, predicting the reduction of TrOCs by direct reactions with ozone from internal tracers was not feasible. Similar removal efficiencies for fast reacting compounds with different rate constants from k(O3) = 10(4) M(-1) s(-1) to k(O3) = 10(6) M(-1) s(-1) were observed indicating a limitation of the reaction by mass transfer. This effect was observed at low ozone dosages in semi-batch and pilot experiments as well as in batch experiments, where mass transfer from gas to liquid phase is not limiting. It is assumed that consumption of low ozone dosages is faster than sample homogenization in the batch reactors used. Thus, prediction of compound removal by direct reaction with ozone always needs to consider reactor design and geometry. PMID:24050684
Cieslar, J H; Dobson, G P
2000-03-01
The relationship between free cytosolic [ADP] (and [P(i)]) and steady-state aerobic muscle work in rat gastrocnemius muscle in vivo using (31)P NMR was investigated. Anesthetized rats were ventilated and placed in a custom-built cradle fitted with a force transducer that could be placed into a 7-tesla NMR magnet. Muscle work was induced by supramaximal sciatic nerve stimulation that activated all fibers. Muscles were stimulated at 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 1.0, and 2.0 Hz until twitch force, phosphocreatine, and P(i) were unchanged between two consecutive spectra acquired in 4-min blocks (8-12 min). Parallel bench experiments were performed to measure total tissue glycogen, lactate, total creatine, and pyruvate in freeze-clamped muscles after 10 min of stimulation at each frequency. Up to 0.5 Hz, there was no significant change in muscle glycogen, lactate, and the lactate/pyruvate ratios between 8-12 min. At 0.8 Hz, there was a 17% fall in glycogen and a 65% rise in the muscle lactate with a concomitant fall in pH. Above this frequency, glycogen fell rapidly, lactate continued to rise, and ATP and pH declined. On the basis of these force and metabolic measurements, we estimated the maximal mitochondrial capacity (V(max)) to be 0.8 Hz. Free [ADP] was then calculated at each submaximal workload from measuring all the reactants of the creatine kinase equilibrium after adjusting the K'(CK) to the muscle temp (30 degrees C), pH, and pMg. We show that ADP (and P(i)) and tension-time integral follow a Hill relationship with at least a second order function. The K(0.5) values for free [ADP] and [P(i)] were 48 microM and 9 mM, respectively. Our data did not fit any form of the Michaelis-Menten equation. We therefore conclude that free cytosolic [ADP] and [P(i)] could potentially control steady-state oxidative phosphorylation in skeletal muscle in vivo. PMID:10692403
Cuzinatto, R.R. . E-mail: rodrigo@ift.unesp.br; Melo, C.A.M. de . E-mail: cassius.anderson@gmail.com; Pompeia, P.J. . E-mail: pompeia@ift.unesp.br
2007-05-15
A gauge theory of second order in the derivatives of the auxiliary field is constructed following Utiyama's program. A novel field strength G = {partial_derivative}F + fAF arises besides the one of the first order treatment, F = {partial_derivative}A - {partial_derivative}A + fAA. The associated conserved current is obtained. It has a new feature: topological terms are determined from local invariance requirements. Podolsky Generalized Eletrodynamics is derived as a particular case in which the Lagrangian of the gauge field is L {sub P} {proportional_to} G {sup 2}. In this application the photon mass is estimated. The SU (N) infrared regime is analysed by means of Alekseev-Arbuzov-Baikov's Lagrangian.
Kang, Chao; Wu, Hai-Long; Zhou, Chang; Xiang, Shou-Xia; Zhang, Xiao-Hua; Yu, Yong-Jie; Yu, Ru-Qin
2016-03-01
The metabolic coenzymes reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) are the primary electron donor and acceptor respectively, participate in almost all biological metabolic pathways. This study develops a novel method for the quantitative kinetic analysis of the degradation reaction of NADH and the formation reaction of FAD in human plasma containing an uncalibrated interferent, by using three-way calibration based on multi-way fluorescence technique. In the three-way analysis, by using the calibration set in a static manner, we directly predicted the concentrations of both analytes in the mixture at any time after the start of their reactions, even in the presence of an uncalibrated spectral interferent and a varying background interferent. The satisfactory quantitative results indicate that the proposed method allows one to directly monitor the concentration of each analyte in the mixture as the function of time in real-time and nondestructively, instead of determining the concentration after the analytical separation. Thereafter, we fitted the first-order rate law to their concentration data throughout their reactions. Additionally, a four-way calibration procedure is developed as an alternative for highly collinear systems. The results of the four-way analysis confirmed the results of the three-way analysis and revealed that both the degradation reaction of NADH and the formation reaction of FAD in human plasma fit the first-order rate law. The proposed methods could be expected to provide promising tools for simultaneous kinetic analysis of multiple reactions in complex systems in real-time and nondestructively. PMID:26873466
Second-Order Algebraic Theories
NASA Astrophysics Data System (ADS)
Fiore, Marcelo; Mahmoud, Ola
Fiore and Hur [10] recently introduced a conservative extension of universal algebra and equational logic from first to second order. Second-order universal algebra and second-order equational logic respectively provide a model theory and a formal deductive system for languages with variable binding and parameterised metavariables. This work completes the foundations of the subject from the viewpoint of categorical algebra. Specifically, the paper introduces the notion of second-order algebraic theory and develops its basic theory. Two categorical equivalences are established: at the syntactic level, that of second-order equational presentations and second-order algebraic theories; at the semantic level, that of second-order algebras and second-order functorial models. Our development includes a mathematical definition of syntactic translation between second-order equational presentations. This gives the first formalisation of notions such as encodings and transforms in the context of languages with variable binding.
Local reaction kinetics by imaging
NASA Astrophysics Data System (ADS)
Suchorski, Yuri; Rupprechter, Günther
2016-01-01
In the present contribution we present an overview of our recent studies using the "kinetics by imaging" approach for CO oxidation on heterogeneous model systems. The method is based on the correlation of the PEEM image intensity with catalytic activity: scaled down to the μm-sized surface regions, such correlation allows simultaneous local kinetic measurements on differently oriented individual domains of a polycrystalline metal-foil, including the construction of local kinetic phase diagrams. This allows spatially- and component-resolved kinetic studies and, e.g., a direct comparison of inherent catalytic properties of Pt(hkl)- and Pd(hkl)-domains or supported μm-sized Pd-powder agglomerates, studies of the local catalytic ignition and the role of defects and grain boundaries in the local reaction kinetics.
Local reaction kinetics by imaging☆
Suchorski, Yuri; Rupprechter, Günther
2016-01-01
In the present contribution we present an overview of our recent studies using the “kinetics by imaging” approach for CO oxidation on heterogeneous model systems. The method is based on the correlation of the PEEM image intensity with catalytic activity: scaled down to the μm-sized surface regions, such correlation allows simultaneous local kinetic measurements on differently oriented individual domains of a polycrystalline metal-foil, including the construction of local kinetic phase diagrams. This allows spatially- and component-resolved kinetic studies and, e.g., a direct comparison of inherent catalytic properties of Pt(hkl)- and Pd(hkl)-domains or supported μm-sized Pd-powder agglomerates, studies of the local catalytic ignition and the role of defects and grain boundaries in the local reaction kinetics. PMID:26865736
Kinetics and mechanism of the reaction between phenyl isocyanate and alcohols in benzene medium
Sivakamasundari, S.; Ganesan, R.
1984-02-14
The reaction of phenyl isocyanate with various alcohols followed second-order kinetics. The reactions were studied at temperatures of 20, 30, and 40 +/- 1/sup 0/C. Evidence is presented to support a dipole-dipole type of mechanism for the reaction.
Kinetics of actinide complexation reactions
Nash, K.L.; Sullivan, J.C.
1997-09-01
Though the literature records extensive compilations of the thermodynamics of actinide complexation reactions, the kinetics of complex formation and dissociation reactions of actinide ions in aqueous solutions have not been extensively investigated. In light of the central role played by such reactions in actinide process and environmental chemistry, this situation is somewhat surprising. The authors report herein a summary of what is known about actinide complexation kinetics. The systems include actinide ions in the four principal oxidation states (III, IV, V, and VI) and complex formation and dissociation rates with both simple and complex ligands. Most of the work reported was conducted in acidic media, but a few address reactions in neutral and alkaline solutions. Complex formation reactions tend in general to be rapid, accessible only to rapid-scan and equilibrium perturbation techniques. Complex dissociation reactions exhibit a wider range of rates and are generally more accessible using standard analytical methods. Literature results are described and correlated with the known properties of the individual ions.
Combustion kinetics and reaction pathways
Klemm, R.B.; Sutherland, J.W.
1993-12-01
This project is focused on the fundamental chemistry of combustion. The overall objectives are to determine rate constants for elementary reactions and to elucidate the pathways of multichannel reactions. A multitechnique approach that features three independent experiments provides unique capabilities in performing reliable kinetic measurements over an exceptionally wide range in temperature, 300 to 2500 K. Recent kinetic work has focused on experimental studies and theoretical calculations of the methane dissociation system (CH{sub 4} + Ar {yields} CH{sub 3} + H + Ar and H + CH{sub 4} {yields} CH{sub 3} + H{sub 2}). Additionally, a discharge flow-photoionization mass spectrometer (DF-PIMS) experiment is used to determine branching fractions for multichannel reactions and to measure ionization thresholds of free radicals. Thus, these photoionization experiments generate data that are relevant to both reaction pathways studies (reaction dynamics) and fundamental thermochemical research. Two distinct advantages of performing PIMS with high intensity, tunable vacuum ultraviolet light at the National Synchrotron Light Source are high detection sensitivity and exceptional selectivity in monitoring radical species.
NASA Astrophysics Data System (ADS)
Lukes, P.; Dolezalova, E.; Sisrova, I.; Clupek, M.
2014-02-01
The formation of transient species (OH·, NO2·, NO radicals) and long-lived chemical products (O3, H2O2, NO_{3}^{-} , NO_{2}^{-} ) produced by a gas discharge plasma at the gas-liquid interface and directly in the liquid was measured in dependence on the gas atmosphere (20% oxygen mixtures with nitrogen or with argon) and pH of plasma-treated water (controlled by buffers at pH 3.3, 6.9 or 10.1). The aqueous-phase chemistry and specific contributions of these species to the chemical and biocidal effects of air discharge plasma in water were evaluated using phenol as a chemical probe and bacteria Escherichia coli. The nitrated and nitrosylated products of phenol (4-nitrophenol, 2-nitrophenol, 4-nitrocatechol, 4-nitrosophenol) in addition to the hydroxylated products (catechol, hydroquinone, 1,4-benzoquinone, hydroxy-1,4-benzoquinone) evidenced formation of NO2·, NO· and OH· radicals and NO+ ions directly by the air plasma at the gas-liquid interface and through post-discharge processes in plasma-activated water (PAW) mediated by peroxynitrite (ONOOH). Kinetic study of post-discharge evolution of H2O2 and NO_{2}^{-} in PAW has demonstrated excellent fit with the pseudo-second-order reaction between H2O2 and NO_{2}^{-} . The third-order rate constant k = 1.1 × 103 M-2 s-1 for the reaction NO_{2}^{-} +H_{2}O_{2}+H^{+}\\to ONOOH+H_{2}O was determined in PAW at pH 3.3 with the rate of ONOOH formation in the range 10-8-10-9 M s-1. Peroxynitrite chemistry was shown to significantly participate in the antibacterial properties of PAW. Ozone presence in PAW was proved indirectly by pH-dependent degradation of phenol and detection of cis,cis-muconic acid, but contribution of ozone to the inactivation of bacteria by the air plasma was negligible.
Modelling reaction kinetics inside cells
Grima, Ramon; Schnell, Santiago
2009-01-01
In the past decade, advances in molecular biology such as the development of non-invasive single molecule imaging techniques have given us a window into the intricate biochemical activities that occur inside cells. In this article we review four distinct theoretical and simulation frameworks: (1) non-spatial and deterministic, (2) spatial and deterministic, (3) non-spatial and stochastic and (4) spatial and stochastic. Each framework can be suited to modelling and interpreting intracellular reaction kinetics. By estimating the fundamental length scales, one can roughly determine which models are best suited for the particular reaction pathway under study. We discuss differences in prediction between the four modelling methodologies. In particular we show that taking into account noise and space does not simply add quantitative predictive accuracy but may also lead to qualitatively different physiological predictions, unaccounted for by classical deterministic models. PMID:18793122
Isegawa, Miho; Liu, Fengyi; Maeda, Satoshi; Morokuma, Keiji
2014-10-21
We report reaction paths starting from N({sup 2}D) + H{sub 2}O for doublet spin states, D{sub 0} and D{sub 1}. The potential energy surfaces are explored in an automated fashion using the global reaction route mapping strategy. The critical points and reaction paths have been fully optimized at the complete active space second order perturbation theory level taking all valence electrons in the active space. In addition to direct dissociation pathways that would be dominant, three roaming processes, two roaming dissociation, and one roaming isomerization: (1) H{sub 2}ON → H–O(H)N → H–HON → NO({sup 2}Π) + H{sub 2}, (2) cis-HNOH → HNO–H → H–HNO → NO + H{sub 2}, (3) H{sub 2}NO → H–HNO → HNO–H → trans-HNOH, are confirmed on the D{sub 0} surface.
Kinetic studies of elementary chemical reactions
Durant, J.L. Jr.
1993-12-01
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.
Binocular Combination of Second-Order Stimuli
Zhou, Jiawei; Liu, Rong; Zhou, Yifeng; Hess, Robert F.
2014-01-01
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
Rudakov, E.S.; Ignatenko, V.M.
1987-11-01
The kinetics of thiophene oxidation by Pd(II) aqua complexes at (TH) << (Pd/sup II/) have been studied in HClO/sub 4/ solutions (0.4-0.5 M) and H/sub 2/SO/sub 4/ (2.5 M). The kinetics can be described by the equation -(d(TH)dtau) = k/sub 1/k/sub 2/(TH)(Pd/sup II/)/sup 2/(k/sup -1/(H/sup +/) = k/sub 2/(Pd/sup II/)). It has also been found that the order of the reaction with respect to Pd/sup II/ can vary between one and two, depending on the (H/sup +/)(Pd/sup II/) ratio. Participation of the first Pd/sup II/ ion leads to the formation of 2-thienylpalladium (II), while the second ion facilitates its oxidative decomposition to give products, namely Pd/sub 2//sup 2 +/ and, tentatively, 2-thienol. The proposed mechanism is consistent with the data concerning the effects of TH and Pd/sup II/ concentrations on the rate of the reaction, as well as with the effects of acidity, ionic strength, addition of oxidizing and reducing agents, and kinetic isotope effects
An Analysis of Second-Order Autoshaping
ERIC Educational Resources Information Center
Ward-Robinson, Jasper
2004-01-01
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…
Using of "pseudo-second-order model" in adsorption.
Ho, Yuh-Shan
2014-01-01
A research paper's contribution exists not only in its originality and creativity but also in its continuity and development for research that follows. However, the author easily ignores it. Citation error and quotation error occurred very frequently in a scientific paper. Numerous researchers use secondary references without knowing the original idea from authors. Sulaymon et al. (Environ Sci Pollut Res 20:3011-3023, 2013) and Spiridon et al. (Environ Sci Pollut Res 20:6367-6381, 2013) presented wrong pseudo-second-order models in Environmental Science and Pollution Research, vol. 20. This comment pointed the errors of the kinetic models and offered information for citing original idea of pseudo-second-order kinetic expression. In order to stop the proliferation of the mistake, it is suggested to cite the original paper for the kinetic model which provided greater accuracy and more details about the kinetic expression. PMID:24132523
Radioactive iodine exchange reaction of HIPDM: kinetics and mechanism
Lui, B.; Chang, J.; Sun, J.S.; Billings, J.; Steves, A.; Ackerhalt, R.; Molnar, M.; Kung, H.F.
1987-03-01
In conjunction with single photon emission computed tomography (SPECT), iodine-123 (/sup 123/I)-labeled N,N,N'-trimethyl-(2-hydroxy-3-methyl-5-iodobenzyl)-1,3-propanediamine (HIPDM) has been used clinically as a regional cerebral perfusion imaging agent. The (/sup 123/I)HIPDM can be prepared by a simple aqueous exchange reaction in a kit form. We synthesized unlabeled HIPDM by condensation of 2-hydroxy-3-methyl-5-iodobezaldehyde and N,N,N'-trimethyl-1,3-propanediamine, followed by a sodium borohydride reduction reaction. The kinetics of the radioactive iodine exchange reaction for the preparation of (/sup 123/I)HIDM is controlled by the pH, the temperature, and the presence of reductant (sodium bisulfite), and oxidant (sodium iodate). The reaction is a second order iodine-iodine exchange with an activation energy of 30.6 kcal/mole. The mechanism of this reaction probably involves the formation of an active 1+ or iodine free radical, which is sensitive to the presence of a reductant, such as sodium bisulfite.
Radioactive iodine exchange reaction of HIPDM: kinetics and mechanism.
Lui, B; Chang, J; Sun, J S; Billings, J; Steves, A; Ackerhalt, R; Molnar, M; Kung, H F
1987-03-01
In conjunction with single photon emission computed tomography (SPECT), iodine-123 (123I)-labeled N,N,N'-trimethyl-[2-hydroxy-3-methyl-5-iodobenzyl]-1,3-propanediamine (HIPDM) has been used clinically as a regional cerebral perfusion imaging agent. The [123I]HIPDM can be prepared by a simple aqueous exchange reaction in a kit form. We synthesized unlabeled HIPDM by condensation of 2-hydroxy-3-methyl-5-iodobezaldehyde and N,N,N'-trimethyl-1,3-propanediamine, followed by a sodium borohydride reduction reaction. The kinetics of the radioactive iodine exchange reaction for the preparation of [123I]HIDM is controlled by the pH, the temperature, and the presence of reductant (sodium bisulfite), and oxidant (sodium iodate). The reaction is a second order iodine-iodine exchange with an activation energy of 30.6 kcal/mole. The mechanism of this reaction probably involves the formation of an active 1+ or iodine free radical, which is sensitive to the presence of a reductant, such as sodium bisulfite. PMID:3819852
Thermodynamically feasible kinetic models of reaction networks.
Ederer, Michael; Gilles, Ernst Dieter
2007-03-15
The dynamics of biological reaction networks are strongly constrained by thermodynamics. An holistic understanding of their behavior and regulation requires mathematical models that observe these constraints. However, kinetic models may easily violate the constraints imposed by the principle of detailed balance, if no special care is taken. Detailed balance demands that in thermodynamic equilibrium all fluxes vanish. We introduce a thermodynamic-kinetic modeling (TKM) formalism that adapts the concepts of potentials and forces from irreversible thermodynamics to kinetic modeling. In the proposed formalism, the thermokinetic potential of a compound is proportional to its concentration. The proportionality factor is a compound-specific parameter called capacity. The thermokinetic force of a reaction is a function of the potentials. Every reaction has a resistance that is the ratio of thermokinetic force and reaction rate. For mass-action type kinetics, the resistances are constant. Since it relies on the thermodynamic concept of potentials and forces, the TKM formalism structurally observes detailed balance for all values of capacities and resistances. Thus, it provides an easy way to formulate physically feasible, kinetic models of biological reaction networks. The TKM formalism is useful for modeling large biological networks that are subject to many detailed balance relations. PMID:17208985
The second-order gravitational red shift
NASA Technical Reports Server (NTRS)
Jaffe, J.
1973-01-01
The direct measurement of the nonlinear term of the gravitational field equations by using very stable clocks is discussed along with measuring the perhelion advance of a planet or satellite. These are considered measurements of the second-order gravitational red shift. The exact expression for the frequency shift of light in a gravitational field is derived. Other topics discussed include: The Doppler-cancelling technique; the second-order red shift in a spherically symmetric gravitational field; finite signal transit time; and the reality and interpretation of coordinates in the second-order red shift experiment.
Second-order gravitational self-force.
Pound, Adam
2012-08-01
Using a rigorous method of matched asymptotic expansions, I derive the equation of motion of a small, compact body in an external vacuum spacetime through second order in the body's mass (neglecting effects of internal structure). The motion is found to be geodesic in a certain locally defined regular geometry satisfying Einstein's equation at second order. I outline a method of numerically obtaining both the metric of that regular geometry and the complete second-order metric perturbation produced by the body. PMID:23006161
Modeling the enzyme kinetic reaction.
Atangana, Abdon
2015-09-01
The Enzymatic control reactions model was presented within the scope of fractional calculus. In order to accommodate the usual initial conditions, the fractional derivative used is in Caputo sense. The methodologies of the three analytical methods were used to derive approximate solution of the fractional nonlinear system of differential equations. Two methods use integral operator and the other one uses just an integral. Numerical results obtained exhibit biological behavior of real world problem. PMID:25930963
Computational simulation of second order motion perception
NASA Astrophysics Data System (ADS)
Sun, Bin; Sang, Nong
2007-11-01
Physiological studies have provided clear evidence of neurons sensitive to second-order motion, and first-order motion mechanisms are blind to second-order motion. In this paper, we propose a computational simulation of second order motion perception, which bases on energy-based detector with a preceded nonlinear process called texture grabber. Generally, a texture grabber consists of a linear spatial filter, a linear temporal filter and a nonlinear transform, such as full-wave rectification. Here Difference of Gaussians (DoG) functions are used as the spatial filters, and Difference of Gammas (DoGamma) functions are chosen as the temporal filters. A series of experiments are computed and the results confirm that our motion perception system detects second-order motion correctly.
Kinetic study of flavonoid reactions with stable radicals.
Butković, Vjera; Klasinc, Leo; Bors, Wolf
2004-05-19
The antiradical activities of some flavonols (kaempferol, quercetin, robinetin, quercetagetin, and myricetin), flavones (apigenin, baicalein, and luteolin), flavanones (naringenin and dihydroquercetin), and flavanols [(+)-catechin and (-)-epicatechin] were determined by measuring the reaction kinetics with 2,2-diphenyl-1-picrylhydrazyl (DPPH) and alpha,gamma-bisdiphenylene-beta-phenylallyl (BDPA) radicals. The reactions, which follow the mixed second-order rate law, were investigated under pseudo-first-order conditions by use of a large excess of flavonoids, and their stoichiometry was determined by spectrophotometric titration. The results confirm stoichiometric factors of 1, 2, and 3 for flavonoids with one, two, and three hydroxyl groups in the B-ring, respectively, excluding kaempferol, which, despite a single OH group in the B-ring, has a factor of 2, which is explained by the 3-OH group supporting the reaction with free radicals. Structure-activity considerations indicate for the present series of flavonoids the importance of multiple OH substitutions and conjugation. The logarithms of reaction rate constants with the OH, DPPH, and BDPA radicals correlate well with the reduction potential of the flavonoids. PMID:15137819
Selfishness as second-order altruism
Eldakar, Omar Tonsi; Wilson, David Sloan
2008-01-01
Selfishness is seldom considered a group-beneficial strategy. In the typical evolutionary formulation, altruism benefits the group, selfishness undermines altruism, and the purpose of the model is to identify mechanisms, such as kinship or reciprocity, that enable altruism to evolve. Recent models have explored punishment as an important mechanism favoring the evolution of altruism, but punishment can be costly to the punisher, making it a form of second-order altruism. This model identifies a strategy called “selfish punisher” that involves behaving selfishly in first-order interactions and altruistically in second-order interactions by punishing other selfish individuals. Selfish punishers cause selfishness to be a self-limiting strategy, enabling altruists to coexist in a stable equilibrium. This polymorphism can be regarded as a division of labor, or mutualism, in which the benefits obtained by first-order selfishness help to “pay” for second-order altruism. PMID:18448681
Kinetics of the reaction of hypobromous acid and organic matters in water treatment processes.
Echigo, S; Minear, R A
2006-01-01
The fate of bromine species from human activity is affected by the bromination reaction in water treatment processes. In this study, kinetic information of the reaction between hypobromous acid (HOBr) and seven different natural organic matters (NOM) was collected by sequential stopped-flow techniques. Multiple reaction phases were found in the reaction between HOBr and NOM. The number of reaction sites for the faster reaction phase ranged from 0.26 to 0.92 micromole (mg DOC)(-1), and was correlated to both SUVA and specific phenolic content at pH 7.0. The apparent second-order rate constants for the faster reaction phase at pH 7.0 ranged from 5.4 x 10(5) to 1.4 x 10(6) M(-1) x s(-1), indicating that vanillin-like structures are involved in this reaction phase. PMID:16862795
Urban Principals' Second Order Change Leadership
ERIC Educational Resources Information Center
Taylor, Rosemarye T.; La Cava, Gonzalo S.
2011-01-01
Urban school leaders have challenges in continually improving student achievement and making change as quickly as needed. To address this problem 37 non-Title I principals completed an on-line survey, Principal's Actions Survey (PAS), based on the seven responsibilities for second order change identified by Marzano, Waters, and McNulty (2005).…
Second-Order Conditioning in "Drosophila"
ERIC Educational Resources Information Center
Tabone, Christopher J.; de Belle, J. Steven
2011-01-01
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…
Nine Practices of Second Order Schools
ERIC Educational Resources Information Center
Brown, Bill; Tucker, Patrick; Williams, Thomas L.
2012-01-01
Many schools are in some stage of implementing differentiated instruction, with some already in what Carol Tomlinson describes in "The Differentiated School" as "second order change," where the entire school practices differentiation. In high-performing schools, differentiation has proved to be an effective instructional strategy; in classroom…
Calculating Second-Order Effects in MOSFET's
NASA Technical Reports Server (NTRS)
Benumof, Reuben; Zoutendyk, John A.; Coss, James R.
1990-01-01
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.
Visualizing second order tensor fields with hyperstreamlines
NASA Technical Reports Server (NTRS)
Delmarcelle, Thierry; Hesselink, Lambertus
1993-01-01
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.
Second order Horner's syndrome in a cat.
De Risio, Luisa; Fraser McConnell, James
2009-08-01
This case report describes the clinical and magnetic resonance imaging (MRI) findings of a 3.5-year-old, male neutered, domestic shorthair cat with second order Horner's syndrome as the only clinical abnormality. The neuroanatomical pathway of the sympathetic innervation to the eye, differential diagnoses for Horner's syndrome in cats, and the interpretation of pharmacological testing are reviewed. The unusual MRI findings and the value of fat-suppressed MRI sequences are discussed. PMID:19261500
Spacetime encodings. III. Second order Killing tensors
NASA Astrophysics Data System (ADS)
Brink, Jeandrew
2010-01-01
This paper explores the Petrov type D, stationary axisymmetric vacuum (SAV) spacetimes that were found by Carter to have separable Hamilton-Jacobi equations, and thus admit a second-order Killing tensor. The derivation of the spacetimes presented in this paper borrows from ideas about dynamical systems, and illustrates concepts that can be generalized to higher-order Killing tensors. The relationship between the components of the Killing equations and metric functions are given explicitly. The origin of the four separable coordinate systems found by Carter is explained and classified in terms of the analytic structure associated with the Killing equations. A geometric picture of what the orbital invariants may represent is built. Requiring that a SAV spacetime admits a second-order Killing tensor is very restrictive, selecting very few candidates from the group of all possible SAV spacetimes. This restriction arises due to the fact that the consistency conditions associated with the Killing equations require that the field variables obey a second-order differential equation, as opposed to a fourth-order differential equation that imposes the weaker condition that the spacetime be SAV. This paper introduces ideas that could lead to the explicit computation of more general orbital invariants in the form of higher-order Killing tensors.
Spacetime encodings. III. Second order Killing tensors
Brink, Jeandrew
2010-01-15
This paper explores the Petrov type D, stationary axisymmetric vacuum (SAV) spacetimes that were found by Carter to have separable Hamilton-Jacobi equations, and thus admit a second-order Killing tensor. The derivation of the spacetimes presented in this paper borrows from ideas about dynamical systems, and illustrates concepts that can be generalized to higher-order Killing tensors. The relationship between the components of the Killing equations and metric functions are given explicitly. The origin of the four separable coordinate systems found by Carter is explained and classified in terms of the analytic structure associated with the Killing equations. A geometric picture of what the orbital invariants may represent is built. Requiring that a SAV spacetime admits a second-order Killing tensor is very restrictive, selecting very few candidates from the group of all possible SAV spacetimes. This restriction arises due to the fact that the consistency conditions associated with the Killing equations require that the field variables obey a second-order differential equation, as opposed to a fourth-order differential equation that imposes the weaker condition that the spacetime be SAV. This paper introduces ideas that could lead to the explicit computation of more general orbital invariants in the form of higher-order Killing tensors.
Wariishi, Hiroyuki; Gold, M.H. ); Dunford, H.B.; MacDonald, I.D. )
1989-02-25
Stopped-flow techniques were used to investigate the kinetics of the formation of manganese peroxidase compound I (MnPI) and of the reactions of MnPI and manganese peroxidase compound II (MnPII) with p-cresol and Mn{sup II}. All of the rate data were obtained from single turnover experiments under pseudo-first order conditions. In the presence of H{sub 2}O{sub 2} the formation of MnPI is independent of pH over the range 3.12-8.29 with a second-order rate constant of (2.0{+-}0.1) {times} 10{sup 6} M{sup {minus}1} s{sup {minus}1}. The activation energy for MnPI formation is 20 kJ mol{sup {minus}1}. MnPI formation also occurs with organic peroxides such as peracetic acid, m-chloroperoxybenzoic acid, and p-nitroperoxybenzoic acid with second-order rate constants of 9.7 x 10{sup 5}, 9.5 {times} 10{sup 4}, and 5.9 {times} 10{sup 4} M{sup {minus}1} s{sup {minus}1}, respectively. The reactions of MnPI and MnPII with p-cresol strictly obeyed second-order kinetics. The second-order rate constant for the reaction of MnPII with p-cresol is extremely low, (9.5{+-}0.5) m{sup {minus}1} s{sup {minus}1}. Kinetic analysis of the reaction of Mn{sup II} with MnPI and MnPII showed a binding interaction with the oxidized enzymes which led to saturation kinetics. The first-order dissociation rate constants for the reaction of Mn{sup II} with MnPI and MnPII are (0.7{+-}0.1) and (0.14{+-}0.01) s{sup {minus}1}, respectively, when the reaction is conducted in lactate buffer. Rate constants are considerably lower when the reactions are conducted in succinate buffer. Single turnover experiments confirmed that Mn{sup II} serves as an obligatory substrate for MnPII and that both oxidized forms of the enzyme form productive complexes with Mn{sup II}. Finally, these results suggest the {alpha}-hydroxy acids such as lactate facilitate the dissociation of Mn{sup II} from the enzyme.
Unravelling the impact of obstacles in diffusion and kinetics of an enzyme catalysed reaction.
Mourão, Márcio; Kreitman, Doree; Schnell, Santiago
2014-03-14
Lattice gas automata simulations of diffusion-limited reactions in heterogeneous media exhibit fractal-like kinetics, which is a generalised mass action kinetics with time-dependent rate constants. We develop a two dimensional lattice gas automata simulation of the Michaelis-Menten mechanism in diffusion-limited conditions to investigate the effect of density and size of obstacles on reactant diffusion and rate coefficients. In order to simulate more physicochemical realistic conditions, reactants rotate and interact according to their specific orientation. We also model weak interaction forces between reactants and obstacles. Our results show that obstacle density and size affect diffusion, first- and second-order rates. We also find that particle rotations and weak force interactions among particles lead to a significant decay in the fractal-like kinetic exponent h. These results suggest that the effects of fractal-like kinetics disappear under less restricted conditions than previously believed in lattice based simulations. PMID:24141265
Kinetic analysis of complex reactions using FEMLAB
Cao, Chunshe; Wang, Yong
2005-06-07
A finite element method software FEMALB has been implemented to the kinetic analysis of complex reaction systems. The established protocol provides fast solutions to the coupled differential-algebraic equations. It shows significant advantages over the conventional coding process with the standard implicit Runge-Kutta (IRK) method. The accuracy and high efficiency have been demonstrated in the simulation of the reaction processes such as glucose/fructose hydrogenation and catalytic cracking of gasoil. As model validation, the numerical results showed satisfactory agreement with the exact solutions. With the powerful capability of solving large matrixes of differential equations (both ODE and PDE) with nonlinear algebraic constrains, such an algorithm has greatly reduced the coding labor in reaction mechanistic studies and provided a unique tool in reactor design and optimization.
Spectroscopy and reaction kinetics of HCO
Guo, Yili
1989-01-01
The high-resolution infrared spectrum of the C-H stretching fundamental of HCO has been studied by means of infrared flash kinetic spectroscopy. HCO was generated by flash photolysis of acetaldehyde or formaldehyde using a 308 nm (XeCl) excimer laser. The transient absorption was probed with an infrared difference frequency laser system. The high resolution spectra obtained were assigned and fitted with rotational, spin-rotational, and centrifugal distortion constants. The ..nu../sub 1/ band origin is 2434.48 cm/sup /minus/1/. New ground state constants have been derived from a least-squares fit combining the ..nu../sub 1/ data with previous microwave and FIR LMR measurements. A new set of spectroscopic constants for the (1, 0, 0) state, the equilibrium rotational constants, and the orientation of the transition dipole moment are also reported. The kinetics and product branching ratios of the HCO + NO/sub 2/ reaction have been studied using visible and infrared laser flash kinetic spectroscopy. The rate constant for the disappearance of HCO radical at 296 K is (5.7 +- 0.9) /times/ 10/sup /minus/11/ cm/sup 3/ molec/sup /minus/1/ sec/sup /minus/1/, and it is independent of the pressure of SF/sub 6/ buffer gas up to 700 torr. Less than 10% of the reaction goes through the most exothermic product channel, HNO + CO/sub 2/. The product channel, H + CO/sub 2/ + NO, is responsible for 52% of the reaction. HONO has been observed, though not quantitatively, as a reaction product corresponding to the HONO + CO channel. 51 refs., 21 figs., 8 tabs.
Kinetics of rouleau formation. II. Reversible reactions.
Samsel, R W; Perelson, A S
1984-04-01
Red blood cells aggregate face-to-face to form long, cylindrical, straight chains and sometimes branched structures called rouleaux. Here we extend a kinetic model developed by R. W. Samsel and A. S. Perelson (1982, Biophys. J. 37:493-514) to include both the formation and dissociation of rouleaux. We examine thermodynamic constraints on the rate constants of the model imposed by the principle of detailed balance. Incorporation of reverse reactions allows us to compute mean sizes of rouleaux and straight chain segments within rouleaux, as functions of time and at equilibrium. Using the Flory - Stockmayer method from polymer chemistry, we obtain a closed-form solution for the size distribution of straight chain segments within rouleaux at any point in the evolution of the reaction. The predictions of our theory compare favorably with data collected by D. Kernick , A.W.L. Jay , S. Rowlands , and L. Skibo (1973, Can. J. Physiol. Pharmacol. 51:690-699) on the kinetics of rouleau formation. When rouleaux grow large, they may contain rings or loops and take on the appearance of a network. We demonstrate the importance of including the kinetics of ring closure in the development of realistic models of rouleaux formation. PMID:6426540
NASA Astrophysics Data System (ADS)
Medien, H. A. A.
1996-11-01
A new and sensitive spectrophotometric method is described for the determination of p-benzoquinone, p-chloranil and 1.4-naphthoquinone. The method is based on the reaction between quinones and barbituric acid, by which a color is developed with maximum absorption between 485 and 555 nm in 50% methyl alcohol-water mixture. The absorption of the product obeys Beer's law within the concentration range 0.025-05 mM of orginal quinone. The kinetics of the reaction between p-benzoquinone and barbituric acid was studied in a range of methyl alcohol-water mixtures. The reaction follows overall second order kinetics, first order in each of the reactants. The rate increases with increasing dielectric constant. The method was applied for determination of barbituric acid with p-benzoquinone in the concentration range of 0.025-0.345 mM. Other barbiturates do not interfere.
Reactions in microemulsions: Effect of thermal fluctuations on reaction kinetics
NASA Astrophysics Data System (ADS)
Ganesan, Venkat; Fredrickson, Glenn H.
2000-08-01
In this paper we address the generic effects arising from the interplay of thermal fluctuations and reactions. This is accomplished by considering specifically the kinetics of reactions effected in microemulsion media. In the first part of this paper we consider the kinetics of the reaction A+B→O/ in bicontinuous microemulsion media, wherein the solutes A and B are assumed to be preferentially attracted to water and oil, respectively, and O/ constitutes an inert product. We formulate the diffusion and reaction of these solutes in a field-theoretical framework within which the fluctuations of the background microemulsion are embedded. We then employ mean-field arguments and a perturbative Wilson-type renormalization group (RG) approach to discern the relevance, at long length scales, of the background fluctuations. Our analysis indicates that the dynamic fluctuations of the microemulsion prove irrelevant in impacting the asymptotic kinetics of the reaction. In view of the fact that our field-theoretic approach enables us to probe only the long time characteristics, moreover, only in the weak-coupling limit, in the second part of this paper we analyze similar issues in the context of the droplet phase of microemulsions. This enables us to surmount some of the restrictions placed upon the results of the first part of this paper. In the second part, our analysis focuses upon a simpler reaction, viz., A→O/, wherein the solute A which is present only in the water phase is anhiliated upon contact with the fluctuating interfaces of the droplets. We employ a standard diffusion equation framework to formulate the transport and reaction of A. The fluctuations of the microemulsion are manifest in the boundary condition positing the vanishing concentration of A. We then employ a perturbation scheme to the solution of the diffusion equation, and thereby discern the explicit effects of the fluctuations of the sinks. Our formulation enables, in a sequentially improvable asymptotic manner, the explicit computation of the time-dependent and the steady state fluctuation contributions to the reaction rate.
Robust stability of second-order systems
NASA Technical Reports Server (NTRS)
Chuang, C. H.
1993-01-01
This report presents a robust control design using strictly positive realness for second-order dynamic systems. The robust strictly positive real controller allows the system to be stabilized with only acceleration measurements. An important property of this design is that stabilization of the system is independent of the system parameters. The control design connects a virtual system to the given plant. The combined system is positive real regardless of system parameter uncertainty. Then any strictly positive real controllers can be used to achieve robust stability. A spring-mass system example and its computer simulations are presented to demonstrate this controller design.
Second-order coherence of supercontinuum light.
Genty, Goëry; Surakka, Minna; Turunen, Jari; Friberg, Ari T
2010-09-15
We analyze the coherence properties of supercontinuum generated in photonic crystal fibers by applying the second-order coherence theory of nonstationary light. Using an ensemble of simulated realizations, we construct two-frequency cross-spectral density and two-time mutual coherence functions. This allows us to introduce measures of temporal and spectral coherence. We show that, in the long-pulse regime, supercontinuum light can be decomposed into a sum of coherent and quasi-stationary contributions. Our approach and findings are also applicable in the short-pulse regime. PMID:20847777
Second order Kerr-Newman time delay
NASA Astrophysics Data System (ADS)
He, G.; Lin, W.
2016-01-01
The explicit form for the post-Newtonian gravitational time delay of light signals propagating on the equatorial plane of a Kerr-Newman black hole is derived. Based on the null geodesic in Kerr-Newman spacetime, we adopt the iterative method to calculate the time delay. Our result reduces to the previous formulation for the Kerr black hole if we drop the contribution from the electrical charge. Our time-delay formula for the Reissner-Nordström geometry is different from the previous publication [Phys. Rev. D 69, 023002 (2004)], in which the largest second order contribution to the time delay is missing.
Kinetic treatment of radiation reaction effects
NASA Astrophysics Data System (ADS)
Noble, Adam; Gratus, Jonathan; Burton, David; Ersfeld, Bernhard; Islam, M. Ranaul; Kravets, Yevgen; Raj, Gaurav; Jaroszynski, Dino
2011-05-01
Modern accelerators and light sources subject bunches of charged particles to quasiperiodic motion in extremely high electric fields, under which they may emit a substantial fraction of their energy. To properly describe the motion of these particle bunches, we require a kinetic theory of radiation reaction. We develop such a theory based on the notorious Lorentz-Dirac equation, and explore how it reduces to the usual Vlasov theory in the appropriate limit. As a simple illustration of the theory, we explore the radiative damping of Langmuir waves.
First- and second-order Poisson spots
NASA Astrophysics Data System (ADS)
Kelly, William R.; Shirley, Eric L.; Migdall, Alan L.; Polyakov, Sergey V.; Hendrix, Kurt
2009-08-01
Although Thomas Young is generally given credit for being the first to provide evidence against Newton's corpuscular theory of light, it was Augustin Fresnel who first stated the modern theory of diffraction. We review the history surrounding Fresnel's 1818 paper and the role of the Poisson spot in the associated controversy. We next discuss the boundary-diffraction-wave approach to calculating diffraction effects and show how it can reduce the complexity of calculating diffraction patterns. We briefly discuss a generalization of this approach that reduces the dimensionality of integrals needed to calculate the complete diffraction pattern of any order diffraction effect. We repeat earlier demonstrations of the conventional Poisson spot and discuss an experimental setup for demonstrating an analogous phenomenon that we call a "second-order Poisson spot." Several features of the diffraction pattern can be explained simply by considering the path lengths of singly and doubly bent paths and distinguishing between first- and second-order diffraction effects related to such paths, respectively.
Robust stability of second-order systems
NASA Technical Reports Server (NTRS)
Chuang, C.-H.
1995-01-01
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.
Reaction kinetics of dolomite rim growth
NASA Astrophysics Data System (ADS)
Helpa, V.; Rybacki, E.; Abart, R.; Morales, L. F. G.; Rhede, D.; Jeřábek, P.; Dresen, G.
2014-04-01
Reaction rims of dolomite (CaMg[CO3]2) were produced by solid-state reactions at the contacts of oriented calcite (CaCO3) and magnesite (MgCO3) single crystals at 400 MPa pressure, 750-850 °C temperature, and 3-146 h annealing time to determine the reaction kinetics. The dolomite reaction rims show two different microstructural domains. Elongated palisades of dolomite grew perpendicular into the MgCO3 interface with length ranging from about 6 to 41 µm. At the same time, a 5-71 µm wide rim of equiaxed granular dolomite grew at the contact with CaCO3. Platinum markers showed that the original interface is located at the boundary between the granular and palisade-forming dolomite. In addition to dolomite, a 12-80 µm thick magnesio-calcite layer formed between the dolomite reaction rims and the calcite single crystals. All reaction products show at least an axiotactic crystallographic relationship with respect to calcite reactant, while full topotaxy to calcite prevails within the granular dolomite and magnesio-calcite. Dolomite grains frequently exhibit growth twins characterized by a rotation of 180° around one of the equivalent axis. From mass balance considerations, it is inferred that the reaction rim of dolomite grew by counter diffusion of MgO and CaO. Assuming an Arrhenius-type temperature dependence, activation energies for diffusion of CaO and MgO are E a (CaO) = 192 ± 54 kJ/mol and E a (MgO) = 198 ± 44 kJ/mol, respectively.
Slowly rotating scalar field wormholes: The second order approximation
Kashargin, P. E.; Sushkov, S. V.
2008-09-15
We discuss rotating wormholes in general relativity with a scalar field with negative kinetic energy. To solve the problem, we use the assumption about slow rotation. The role of a small dimensionless parameter plays the ratio of the linear velocity of rotation of the wormhole's throat and the velocity of light. We construct the rotating wormhole solution in the second-order approximation with respect to the small parameter. The analysis shows that the asymptotical mass of the rotating wormhole is greater than that of the nonrotating one, and the null energy condition violation in the rotating wormhole spacetime is weaker than that in the nonrotating one.
Second-order (2 +1 ) -dimensional anisotropic hydrodynamics
NASA Astrophysics Data System (ADS)
Bazow, Dennis; Heinz, Ulrich; Strickland, Michael
2014-11-01
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.
Reaction rates for mesoscopic reaction-diffusion kinetics
Hellander, Stefan; Hellander, Andreas; Petzold, Linda
2016-01-01
The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic scale-dependent reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a Robin boundary condition at the reaction radius of two molecules. We also establish fundamental limits on the range of mesh resolutions for which this approach yields accurate results and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics. We show that for mesh sizes below the fundamental lower limit, results are less accurate. Thus, the lower limit determines the mesh size for which we obtain the most accurate results. PMID:25768640
Reaction rates for mesoscopic reaction-diffusion kinetics
NASA Astrophysics Data System (ADS)
Hellander, Stefan; Hellander, Andreas; Petzold, Linda
2015-02-01
The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic scale-dependent reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a Robin boundary condition at the reaction radius of two molecules. We also establish fundamental limits on the range of mesh resolutions for which this approach yields accurate results and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics. We show that for mesh sizes below the fundamental lower limit, results are less accurate. Thus, the lower limit determines the mesh size for which we obtain the most accurate results.
DOE R&D Accomplishments Database
Weinberg, Alvin M.; Noderer, L. C.
1951-05-15
The large scale release of nuclear energy in a uranium fission chain reaction involves two essentially distinct physical phenomena. On the one hand there are the individual nuclear processes such as fission, neutron capture, and neutron scattering. These are essentially quantum mechanical in character, and their theory is non-classical. On the other hand, there is the process of diffusion -- in particular, diffusion of neutrons, which is of fundamental importance in a nuclear chain reaction. This process is classical; insofar as the theory of the nuclear chain reaction depends on the theory of neutron diffusion, the mathematical study of chain reactions is an application of classical, not quantum mechanical, techniques.
Second order non-linear optical polyphosphazenes
NASA Astrophysics Data System (ADS)
Dembek, Alexa A.; Allcock, Harry R.; Kim, Chulhee; Steier, William H.; Spangler, Charles W.; Devine, Robert L. S.; Yongquiang, Shi
1990-03-01
In this contribution, we describe the synthesis and second-order optical properties of a series of mixed-substituent poly(organophosphazenes)that possess covalently attached donor-acceptor substituted, conjugated moieties. The general structure of the polymer is (NP(OCH2CF3)x(OR)(y))(n), where OR = -O(CH2O) (k)C6H4-CH=CH-C6H4NO2; where k = 1-3, and -OCH2CH2N(CH2CH3)C6H4-N=N-C6H4NO2, and x + y = 100 percent. The nonlinear optical properties of thin films of the polymers were investigated by using second harmonic generation, giving second-harmonic coefficients, d(33), in the range 4.1 to 34 pm/V.
A novel approach to modeling the reaction kinetics of tetracycline antibiotics with aqueous ozone.
Hopkins, Zachary R; Blaney, Lee
2014-01-15
Tetracycline antibiotics represent one of the most successful classes of pharmaceuticals and are extensively used around the world for human and veterinary health. Ozone-based processes have emerged as a selective water treatment process for many pharmaceuticals. The primary objective of this study was to determine the reaction kinetics for transformation of five tetracycline antibiotics (i.e., chlortetracycline, doxycycline, oxytetracycline, rolitetracycline, and tetracycline) by ozone across the pH2 to 9 range. The apparent second-order rate constant for tetracycline was on the order of 1-6 × 10(4) M(-1) s(-1) at low pH, and 0.6-2.0 × 10(6) M(-1) s(-1) at near neutral pH. The apparent second-order rate constants did not fit a conventional pKa-based model, presumably due to the complex acid/base speciation of tetracycline antibiotics. A model that considers the net charge on tetracycline molecules in solution provided a nice fit to experimental data for all five tetracyclines. The five tetracycline antibiotics demonstrated similar reaction kinetics with ozone, and a cumulative analysis of all kinetics data provides a baseline model for other tetracycline compounds. The ozone exposure required for complete transformation of tetracycline antibiotics (10(-5) M-s) is well below that achieved during ozone disinfection processes (10(-3) M-s), indicating that ozone is an effective treatment for tetracycline antibiotics. PMID:24041601
Reaction rate kinetics for in situ combustion retorting of Michigan Antrim oil shale
Rostam-Abadi, M.; Mickelson, R.W.
1984-01-01
The intrinsic reaction rate kinetics for the pyrolysis of Michigan Antrim oil shale and the oxidation of the carbonaceous residue of this shale have been determined using a thermogravimetric analysis method. The kinetics of the pyrolysis reaction were evaluated from both isothermal and nonisothermal rate data. The reaction was found to be second-order with an activation energy of 252.2 kJ/mole, and with a frequency factor of 9.25 ?? 1015 sec-1. Pyrolysis kinetics were not affected by heating rates between 0.01 to 0.67??K/s. No evidence of any reactions among the oil shale mineral constituents was observed at temperatures below 1173??K. However, it was found that the presence of pyrite in oil shale reduces the primary devolatilization rate of kerogen and increases the amount of residual char in the spent shale. Carbonaceous residues which were prepared by heating the oil shale at a rate of 0.166??K/s to temperatures between 923??K and 1073??K, had the highest reactivities when oxidized at 0.166??K/s in a gas having 21 volume percent oxygen. Oxygen chemisorption was found to be the initial precursor to the oxidation process. The kinetics governing oxygen chemisorption is (Equation Presented) where X is the fractional coverage. The oxidation of the carbonaceous residue was found also to be second-order. The activation energy and the frequency factor determined from isothermal experiments were 147 kJ/mole and 9.18??107 sec-1 respectively, while the values of these parameters obtained from a nonisothermal experiment were 212 kJ/mole and 1.5??1013 sec-1. The variation in the rate constants is attributed to the fact that isothermal and nonisothermal analyses represent two different aspects of the combustion process.
Reaction kinetic analysis of reactor surveillance data
NASA Astrophysics Data System (ADS)
Yoshiie, T.; Sato, K.; Xu, Q.; Nagai, Y.
2015-06-01
In reactor pressure vessel surveillance data, it was found that the concentration of matrix defects was very low even after nearly 40 years of operation, though a large number of precipitates existed. In this paper, defect structures obtained from surveillance data of A533B (high Cu concentration) were simulated using reaction kinetic analysis with 11 rate equations. The coefficients used in the equations were quite different from those obtained by fitting a Fe-0.6 wt%Cu alloy irradiated by the Kyoto University Reactor. The difference was mainly caused by alloying elements in A533B, and the effect of alloying elements was extracted. The same code was applied to low-Cu A533B irradiated with high irradiation damage rate, and the formation of voids was correctly simulated.
Reaction kinetics of paddy husk thermal decomposition
Jain, A.K.; Sharma, S.K.; Singh, D.
1996-12-31
Paddy husk production in world is estimated to be around 80 million tons. It has a calorific value of 15 MJ/kg and thus has a tremendous potential as a renewable energy source. Its current uses are: cattle feed, raw material for paper and board, furfural production and silica industries. A large quantity of paddy husk is used in husk fired boiler furnaces at a very low efficiency. For efficient design of husk fired furnaces, reliable data on thermal characteristics of rice husk is essential which is lacking in the literature. In the present study, paddy husk was subjected to Thermogravimetric Analysis at heating rates of 10 and 100 C/min. in a thermal analyzer. The analysis was carried out in air and mixture of oxygen and nitrogen (5:95%) atmosphere. Reaction kinetic parameters such as activation energy, frequency factor and order of reaction have been evaluated and reported. These are relevant to the design of paddy husk fired gasifiers, furnaces and other thermochemical conversion equipment. The results of the thermochemical studies and their potential applications are presented in the paper.
[Kinetics modeling and reaction mechanism of ferrate(VI) oxidation of triclosan].
Yang, Bin; Ying, Guang-Guo; Zhao, Jian-Liang
2011-09-01
Triclosan (TCS) is a broad-spectrum antibacterial agent widely used in many personal care products. We investigated oxidation of TCS by aqueous ferrate Fe(VI) to determine reaction kinetics, interpreted the reaction mechanism by a linear free-energy relationship, and evaluated the degradation efficiency. Second-order reaction kinetics was used to model Fe (VI) oxidation of TCS, with the apparent second-order rate constant (k(app)) being 531.9 L x (mol x s)(-1) at pH 8.5 and (24 +/- 1) degrees C. The half life (t1/2) is 25.8 s for an Fe( VI) concentration of 10 mg x L(-1). The rate constants of the reaction decrease with increasing pH values. These pH-dependent variations in k(app) could be distributed by considering species-specific reactions between Fe(VI) species and acid-base species of an ionizable TCS. Species-specific second-order reaction rate constants, k, were determined for reaction of HFeO4(-) with each of TCS's acid-base species. The value of k determined for neutral TCS was (4.1 +/- 3.5) x 10(2) L x (mol x s)(-1), while that measured for anionic TCS was (1.8 +/- 0.1) x 10(4) L x (mol x s)(-1). The reaction between HFeO4(-) and the dissociated TCS controls the overall reaction. A linear free-energy relationship illustrated the electrophilic oxidation mechanism. Fe (VI) reacts initially with TCS by electrophilic attack at the latter's phenol moiety. At a n[Fe(VI)]: n(TCS) > 7: 1, complete removal of TCS was achieved. And lower concentration of the humic acid could enhance the k(app) of Fe( VI) with TCS. In conclusion, Fe(VI) oxidation technology appears to be a promising tool for applications of WWTPs effluents and other decontamination processes. PMID:22165218
Izzo, B.; Harrell, C.; Klein, M.T.; LaMarca, C.
1996-12-31
The reaction chemistry of acetonitrile and benzonitrile in High Temperature Water (HTW) was investigated. The reaction products were the associated amides and carboxylic acids. A kinetic model incorporating two autocatalytic steps captured the kinetics observed. The optimized rate constants highlighted differences in the reaction chemistry of aliphatic and aromatic nitrites at these reaction conditions. 6 refs., 3 figs., 2 tabs.
Kinetic analysis of free-radical reactions in the low-temperature autoxidation of triglycerides
Zhu, Jingmin; Sevilla, M.D. )
1990-02-22
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.
Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks
ERIC Educational Resources Information Center
Cloonan, Carrie A.; Nichol, Carolyn A.; Hutchinson, John S.
2011-01-01
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
Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks
ERIC Educational Resources Information Center
Cloonan, Carrie A.; Nichol, Carolyn A.; Hutchinson, John S.
2011-01-01
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…
A Case Study in Chemical Kinetics: The OH + CO Reaction.
ERIC Educational Resources Information Center
Weston, Ralph E., Jr.
1988-01-01
Reviews some important properties of the bimolecular reaction between the hydroxyl radical and carbon monoxide. Investigates the kinetics of the reaction, the temperature and pressure dependence of the rate constant, the state-to-state dynamics of the reaction, and the reverse reaction. (MVL)
Second-Order Nonlinear Optical Imaging of Chiral Crystals
Kissick, David J.; Wanapun, Debbie; Simpson, Garth J.
2012-01-01
Second-order nonlinear optical imaging of chiral crystals (SONICC) is an emerging technique for crystal imaging and characterization. We provide a brief overview of the origin of second harmonic generation signals in SONICC and discuss recent studies using SONICC for biological applications. Given that they provide near-complete suppression of any background, SONICC images can be used to determine the presence or absence of protein crystals through both manual inspection and automated analysis. Because SONICC creates high-resolution images, nucleation and growth kinetics can also be observed. SONICC can detect metastable, homochiral crystalline forms of amino acids crystallizing from racemic solutions, which confirms Ostwald’s rule of stages for crystal growth. SONICC’s selectivity, based on order, and sensitivity, based on background suppression, make it a promising technique for numerous fields concerned with chiral crystal formation. PMID:21469954
A generalized kinetic model for heterogeneous gas-solid reactions.
Xu, Zhijie; Sun, Xin; Khaleel, Mohammad A
2012-08-21
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
A generalized kinetic model for heterogeneous gas-solid reactions
NASA Astrophysics Data System (ADS)
Xu, Zhijie; Sun, Xin; Khaleel, Mohammad A.
2012-08-01
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.
Sreedhara, S.; Huh, Kang Y.
2005-12-01
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.
Kinetic Study of the Heck Reaction: An Interdisciplinary Experiment
ERIC Educational Resources Information Center
Gozzi, Christel; Bouzidi, Naoual
2008-01-01
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
Kinetic Study of the Heck Reaction: An Interdisciplinary Experiment
ERIC Educational Resources Information Center
Gozzi, Christel; Bouzidi, Naoual
2008-01-01
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…
The surface reaction kinetics of salicylate on alumina
Wang, Z.; Ainsworth, C.C.; Friedrich, D.M.; Joly, A.G.; Gassman, P.L.
1997-12-31
The kinetics of reaction of salicylate with colloidal alumina in aqueous suspension and with Al(III) in homogeneous aqueous solution were studied by stopped-flow laser fluorescence spectroscopy. The emission spectra confirmed the formation of both monodentate complexes and more stable bidentate chelates. Temporal evolution of the spectra indicated that the reaction was fast (within first few minutes) for both the homogeneous and heterogeneous reactions but slowed down afterwards for the latter. Reactions completed within 10 minutes in homogeneous phase at pH 3.3 but took more than 12 hours in alumina suspension. Analysis of the fluorescence intensity within first four minutes showed that in homogeneous phase the reaction followed a single pseudo-first-order kinetics. In alumina suspension log plots were nonlinear and characteristic of multiple heterogeneous reaction paths. The kinetics are interpreted in terms of the simultaneous formation of multiple species as well as subsequent conversion between species.
A relativistic correlationless kinetic equation with radiation reaction fully incorporated
NASA Astrophysics Data System (ADS)
Lai, H. M.
1984-06-01
The Landau-Lifshitz expression for the Lorentz-Dirac equation is used to derive a relativistic correlationless kinetic equation for a system of electrons with radiation reaction fully incorporated. Various situations and possible applications are discussed.
Reaction Kinetics: An Experiment for Biochemistry and Organic Chemistry Laboratories.
ERIC Educational Resources Information Center
Ewing, Sheila
1982-01-01
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)
Simulations of the reaction kinetics on nanometer supported catalyst particles
NASA Astrophysics Data System (ADS)
Zhdanov, V. P.; Kasemo, B.
2000-07-01
Real catalysts frequently consist of nm-sized (1-100 nm) metal particles deposited on the internal surface of a more or less inactive porous support. The complexity of such systems in combination with relatively high (atmospheric) reactant pressures, typical for practical catalysis, hinders the application of surface science methods to their full potential and makes it difficult to interpret the measured reaction kinetics on the basis of kinetic data for single-crystal samples. To bridge these pressure and structure gaps and to form a conceptual basis for the understanding of reactions occurring on supported catalyst, we have performed simulations scrutinizing qualitatively new effects in the reaction kinetics on the nm scale. The attention is focused on the particle size range, where the catalyst particles have reached sufficient size to essentially have the electronic properties of bulk crystals, but where they are still small enough that the kinetic effects connected with the particle size are important. We treat in detail such factors inherent for nm chemistry as reactant supply via the support, interplay of the reaction kinetics on different facets of supported particles due to interfacet diffusion, adsorbate-induced reshaping of catalyst particles, and oscillation and chaos on the nm scale. All these factors are demonstrated to be especially important in the case of rapid catalytic reactions occurring far from the adsorption-desorption equilibrium. The kinetics of chemically induced Ostwald ripening of nm catalyst particles and also the gas-phase diffusion limitations in reactions on model supported nm catalysts, prepared by employing electron beam lithography, are discussed as well. As a general conclusion, we find that kinetic effects alone (i.e., no special kinetic effects or "active sites") can cause large differences in reaction kinetics on nm particles and single crystals. Practical consequences and experimental opportunities to measure these effects are briefly discussed.
Kinetics of Acid Reactions: Making Sense of Associated Concepts
ERIC Educational Resources Information Center
Tan, Kim Chwee Daniel; Treagust, David F.; Chandrasegaran, A. L.; Mocerino, Mauro
2010-01-01
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
Kinetics of Acid Reactions: Making Sense of Associated Concepts
ERIC Educational Resources Information Center
Tan, Kim Chwee Daniel; Treagust, David F.; Chandrasegaran, A. L.; Mocerino, Mauro
2010-01-01
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…
Chemical Kinetics and Reaction Dynamics (by Paul L. Houston)
NASA Astrophysics Data System (ADS)
Krenos, John R.
2001-11-01
Paul Houston is an outstanding scientist working in the areas of chemical reaction and photodissociation dynamics; this book demonstrates that he is a gifted educator as well. As one who has taught a graduate course in chemical kinetics on and off for over 25 years, I am eager to put his text to the test under classroom conditions. For physical chemists everywhere, Chemical Kinetics and Reaction Dynamics merits a prominent spot on your bookshelf.
Karlesa, Anggita; De Vera, Glen Andrew D; Dodd, Michael C; Park, Jihye; Espino, Maria Pythias B; Lee, Yunho
2014-09-01
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
Kumar, K Vasanth
2007-04-01
Kinetic experiments were carried out for the sorption of safranin onto activated carbon particles. The kinetic data were fitted to pseudo-second order model of Ho, Sobkowsk and Czerwinski, Blanchard et al. and Ritchie by linear and non-linear regression methods. Non-linear method was found to be a better way of obtaining the parameters involved in the second order rate kinetic expressions. Both linear and non-linear regression showed that the Sobkowsk and Czerwinski and Ritchie's pseudo-second order models were the same. Non-linear regression analysis showed that both Blanchard et al. and Ho have similar ideas on the pseudo-second order model but with different assumptions. The best fit of experimental data in Ho's pseudo-second order expression by linear and non-linear regression method showed that Ho pseudo-second order model was a better kinetic expression when compared to other pseudo-second order kinetic expressions. PMID:17011122
Reaction kinetics in food extrusion: methods and results.
Zhao, Xuewei; Wei, Yimin; Wang, Zhangcun; Chen, Fengliang; Ojokoh, Anthony Okhonlaye
2011-01-01
Extrusion cooking is a highly efficient food processing technology. During the extrusion process, there are many desirable and undesirable reactions which will determine final product quality. While being heated and sheared simultaneously, food raw materials experience a non-isothermal process and their residence time in the extruder is distributed. All these factors contribute to the difficulties in determining the kinetic parameters for those reactions. Therefore, this paper attempts to review the reaction kinetics in food extrusion. First of all, the kinetic models for the reactions are outlined. After elucidating how to determine reaction time in an extruder, the methodological approaches for determining the reaction order, rate constant, and activation energy of a reaction under isothermal or non-isothermal conditions with or without residence time distribution (RTD) are presented. Then, different models relating the rate constant to its various impact factors, with especially focusing on shear stress, are reviewed. Subsequently, how shear stress is estimated in an extruder, is illustrated. In the last part of this paper, the reported data of rate constant, reaction order, and activation energy for the reactions occurring during food extrusion are summarized, with detailed impacts of temperature, moisture content, shear stress, and determination method on these kinetic parameters. Finally, future research needs are suggested. PMID:21888534
Kinetics of the Fischer-Tropsch reaction.
Markvoort, Albert J; van Santen, Rutger A; Hilbers, Peter A J; Hensen, Emiel J M
2012-09-01
Long carbon chains: Self-assembly of monomeric carbon intermediates into long-chain hydrocarbons on catalytically reactive surface was studied when full reversibility of the chain growth is included in the kinetic model. Using Brønsted-Evans-Polanyi relations, the maximum chain growth as a function of the surface reactivity is predicted. PMID:22829559
A study of the Sabatier-methanation reaction kinetics
NASA Technical Reports Server (NTRS)
Verostko, C. E.; Forsythe, R. K.
1974-01-01
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.
Reaction kinetics of hydrothermal carbonization of loblolly pine.
Reza, M Toufiq; Yan, Wei; Uddin, M Helal; Lynam, Joan G; Hoekman, S Kent; Coronella, Charles J; Vásquez, Victor R
2013-07-01
Hydrothermal carbonization (HTC) is a pretreatment process to convert diverse feedstocks to homogeneous energy-dense solid fuels. Understanding of reaction kinetics is necessary for reactor design and optimization. In this study, the reaction kinetics and effects of particle size on HTC were investigated. Experiments were conducted in a novel two-chamber reactor maintaining isothermal conditions for 15s to 30 min reaction times. Loblolly pine was treated at 200, 230, and 260°C. During the first few minutes of reaction, the solid-product mass yield decreases rapidly while the calorific value increases rapidly. A simple reaction mechanism is proposed and validated, in which both hemicellulose and cellulose degrade in parallel first-order reactions. Activation energy of hemicellulose and cellulose degradation were determined to be 30 and 73 kJ/mol, respectively. For short HTC times, both reaction and diffusion effects were observed. PMID:23651600
Exact analytical solutions of second order conformal hydrodynamics
NASA Astrophysics Data System (ADS)
Hatta, Yoshitaka; Noronha, Jorge; Xiao, Bo-Wen
2014-03-01
We present some exact solutions of relativistic second order hydrodynamic equations in theories with conformal symmetry. Starting from a spherically expanding solution in ideal hydrodynamics, we take into account general conformal second order corrections and construct, for the first time, fully analytical axisymmetric solutions including the case with nonzero vorticity. These solutions are time reversible despite having a nonvanishing shear stress tensor, and provide a useful quantitative measure of the second order effects in relativistic hydrodynamics.
Kinetic and theoretical study of the reaction of Cl atoms with a series of linear thiols
Garzon, Andres; Albaladejo, Jose
2008-11-21
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.
Steady-state kinetics of the catalase reaction in the presence of cyanide.
Ogura, Y; Yamazaki, I
1983-08-01
Under carefully controlled experimental conditions, the Michaelis constant for H2O2 was measured to be 1.39 and 1.29 M in the reactions of beef erythrocyte and liver catalases, respectively. These values remained unchanged at temperatures between 1 and 26 degrees C. The turnover number of the Michaelis complex was about 2.25 X 10(7) s-1 for either enzyme at 26 degrees C. The cyanide inhibition in the catalase reaction has been reported to be noncompetitive in spite of the fact that cyanide and H2O2 compete for the same site on the catalase molecule. At high concentrations of H2O2, however, the inhibition became clearly competitive. The existence of the Michaelis complex and the anomalous features of cyanide inhibition were clearly accounted for on the basis of simple kinetic models. At H2O2 concentrations below 100 mM, the catalase reaction obeyed first order kinetics with respect to H2O2 and its apparent second order rate constant was measured to be 7.6 X 10(6) and 7.9 X 10(6) M-1 . S-1 for erythrocyte and liver catalases, respectively. PMID:6630165
Kinetics of enzymatic reactions in lipid membranes containing domains
NASA Astrophysics Data System (ADS)
Zhdanov, Vladimir P.; Höök, Fredrik
2015-04-01
An appreciable part of enzymes operating in vivo is associated with lipid membranes. The function of such enzymes can be influenced by the presence of domains containing proteins and/or composed of different lipids. The corresponding experimental model-system studies can be performed under well controlled conditions, e.g., on a planar supported lipid bilayer or surface-immobilized vesicles. To clarify what may happen in such systems, we propose general kinetic equations describing the enzyme-catalyzed substrate conversion occurring via the Michaelis-Menten (MM) mechanism on a membrane with domains which do not directly participate in reaction. For two generic situations when a relatively slow reaction takes place primarily in or outside domains, we take substrate saturation and lateral substrate-substrate interactions at domains into account and scrutinize the dependence of the reaction rate on the average substrate coverage. With increasing coverage, depending on the details, the reaction rate reaches saturation via an inflection point or monotonously as in the conventional MM case. In addition, we show analytically the types of reaction kinetics occurring primarily at domain boundaries. In the physically interesting situation when the domain growth is fast on the reaction time scale, the latter kinetics are far from conventional. The opposite situation when the reaction is fast and controlled by diffusion has been studied by using the Monte Carlo technique. The corresponding results indicate that the dependence of the reaction kinetics on the domain size may be weak.
Chemical kinetics computer program for static and flow reactions
NASA Technical Reports Server (NTRS)
Bittker, D. A.; Scullin, V. J.
1972-01-01
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.
Adsorption Isotherms and Surface Reaction Kinetics
ERIC Educational Resources Information Center
Lobo, L. S.; Bernardo, C. A.
1974-01-01
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)
The Kinetic Rate Law for Autocatalytic Reactions.
ERIC Educational Resources Information Center
Mata-Perez, Fernando; Perez-Benito, Joaquin F.
1987-01-01
Presented is a method of obtaining accurate rate constants for autocatalytic reactions. The autocatalytic oxidation of dimethylamine by permanganate ion in aqueous solution is used as an example. (RH)
Kinetic Analysis of Sequential Multi-step Reactions
Zhou, Yajun; Zhuang, Xiaowei
2009-01-01
Many processes in biology and chemistry involve multi-step reactions or transitions. The kinetic data associated with these reactions are manifested by superpositions of exponential decays that are often difficult to dissect. Two major challenges have hampered the kinetic analysis of multi-step chemical reactions: (1) Reliable and unbiased determination of the number of reaction steps, (2) Stable reconstruction of the distribution of kinetic rate constants. Here, we introduce two numerically stable integral transformations to solve these two challenges. The first transformation enables us to deduce the number of rate-limiting steps from kinetic measurements, even when each step has arbitrarily distributed rate constants. The second transformation allows us to reconstruct the distribution of rate constants in the multi-step reaction using the phase function approach, without fitting the data. We demonstrate the stability of the two integral transformations by both analytic proofs and numerical tests. These new methods will help providing robust and unbiased kinetic analysis for many complex chemical and biochemical reactions. PMID:17994718
Kinetics of Chemical Reactions in Flames
NASA Technical Reports Server (NTRS)
Zeldovich, Y.; Semenov, N.
1946-01-01
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.
A second-order BGK scheme for the equations of radiation hydrodynamics
NASA Astrophysics Data System (ADS)
Jiang, Song; Sun, Wenjun
2007-01-01
We present a second-order BGK scheme for the equations of multidimensional radiation hydrodynamics (RHE) in zero diffusion limit by using the generalized Maxwellian (Comput. Fluids 2000; 29:917-933) and the second-order BGK scheme for the Euler equations (J. Comput. Phys. 1993; 109:53-66; Gas Kinetic Scheme for Unsteady Compressible Flow Simulations. Lecture Note Series 1998-03. Von Kárman Institute for Fluid Dynamics, 1998). This extends a (first-order) kinetic flux vector splitting scheme (KFVS) for RHE (Tang and Wu (2000)) to a second-order BGK scheme. Several one- and two-dimensional numerical examples demonstrate improvement of the scheme in accuracy and resolution compared with the KFVS scheme (Tang and Wu (2000)) and the first-order BGK scheme.
Fluid flow and chemical reaction kinetics in metamorphic systems
Lasaga, A.C.; Rye, D.M. )
1993-05-01
The treatment and effects of chemical reaction kinetics during metamorphism are developed along with the incorporation of fluid flow, diffusion, and thermal evolution. The interplay of fluid flow and surface reaction rates, the distinction between steady state and equilibrium, and the possible overstepping of metamorphic reactions are discussed using a simple analytic model. This model serves as an introduction to the second part of the paper, which develops a reaction model that solves the coupled temperature-fluid flow-chemical composition differential equations relevant to metamorphic processes. Consideration of stable isotopic evidence requires that such a kinetic model be considered for the chemical evolution of a metamorphic aureole. A general numerical scheme is discussed to handle the solution of the model. The results of this kinetic model allow us to reach several important conclusions regarding the factors controlling the chemical evolution of mineral assemblages during a metamorphic event. 41 refs., 19 figs., 5 tabs.
Kinetics and mechanisms of some atomic oxygen reactions
NASA Technical Reports Server (NTRS)
Cvetanovic, R. J.
1987-01-01
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.
Second-Order Conditioning during a Compound Extinction Treatment
ERIC Educational Resources Information Center
Pineno, Oskar; Zilski, Jessica M.; Schachtman, Todd R.
2007-01-01
Two conditioned taste aversion experiments with rats were conducted to establish if a target taste that had received a prior pairing with illness could be subject to second-order conditioning during extinction treatment in compound with a flavor that also received prior conditioning. In these experiments, the occurrence of second-order
Reaction kinetics of paddy husk thermal decomposition
Jain, A.K.; Sharma, S.K.; Singh, D.
1999-02-01
The physical characteristics, proximate analysis, elemental analysis and chemical analysis of paddy husk, an important renewable source of energy, are reported in this paper. The kinetic parameters for the thermal degradation of paddy husk at heating rates of 10 and 100 C min{sup {minus}1} and under atmospheres of air and oxygen-nitrogen mixture (5:95) have been evaluated from experimentally obtained TGA data. The limitations of the existing TGA models are discussed, and a modified model has been used for correlation of the data.
Reaction kinetics between fiber and matrix
NASA Technical Reports Server (NTRS)
Kopp, M. W.; Tien, J. K.; Petrasek, D. W.
1988-01-01
Interdiffusion and interdiffusion controlled intermediate phase formation in metal matrix composites can be of interest for the prolonged application of these systems at high temperatures. Methods are discussed that address the kinetics of interdiffusion in systems that exhibit solid solution intermixing or the formation of a third intermediate phase at the fiber/matrix interface, or both. The tungsten fiber reinforced niobium and tungsten fiber reinforced superalloy systems are employed as model systems for experimentation and discussion. In an effort to impede interdiffusion, the concept of ion implanted diffusion barriers have been examined. Preliminary results on the feasibility and effectiveness of ion implanted diffusion barriers are presented.
SECOND-ORDER MODEL TO PREDICT MICROBIAL DEGRADATION OF ORGANIC COMPOUNDS IN NATURAL WATERS
The reliability of second-order rate constants for assessing microbial degradation kinetics in natural waters was examined by using three compounds that undergo hydrolytic degradation. The butoxyethyl ester of 2,4-diclorophenoxyacetic acid was studied in water samples from 31 sit...
Visualization of second order tensor fields and matrix data
NASA Technical Reports Server (NTRS)
Delmarcelle, Thierry; Hesselink, Lambertus
1992-01-01
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.
A TGA study on the chlorination reaction kinetics of Zircaloy-4 cladding hulls
NASA Astrophysics Data System (ADS)
Jeon, Min Ku; Choi, Yong Taek; Kang, Kweon Ho; Park, Geun Il
2015-04-01
The chlorination reaction kinetics of Zircaloy-4 cladding hulls were investigated using a home-made thermogravimetric analysis for a hull chlorination (TGA-HC) system. The reproducibility of the TGA-HC system was verified by repeated measurements at an identical condition, which showed only 6.6% of maximum difference. The effect of total flow rate (Q) was investigated for Q of 120 and 240 mL/min, and it was revealed that the reaction rate is not influenced in this condition. Using the Sharp-Hancock plot, the volumetric contraction model was identified as the most suitable model for the Zircaloy-4 chlorination reaction. The influence of chlorine partial pressure was studied at 9.21, 16.9, and 23.4 kPa of Cl2 partial pressure conditions, and it was identified that the reaction rate is proportional to the chlorine partial pressure on the order of (0.669). The effect of reaction temperature was investigated for 300-450 °C, and it was revealed that the chlorination reaction exhibits an activation energy of 26.2 kJ/mol. Using the experimental and fitting results, the reaction rate equation for the Zircaloy-4 chlorination reaction was achieved, but the equation was valid only until the conversion fraction (α) reaches up to (0.60). When α is higher than 0.60, the volumetric contraction model was not applicable. A second-order reaction rate equation was suggested for the 0.6 < α region, although it needs further investigation.
Reversibly Switching Silver Hierarchical Structures via Reaction Kinetics
Liu, Jianmei; Yang, Tao; Li, Chengxiang; Dai, Jinhui; Han, Yongsheng
2015-01-01
Here we report a study on controllable synthesis of hierarchical silver structures via regulating reaction kinetics. Silver particles with various morphologies are synthesized by a solution-based reduction approach at the addition of amino acids. The amino acid is used to coordinate with silver ions to slow down the reduction of silver ions. With the increase of glycine concentration, the morphologies of silver particles switch from dendrites, to flowers and to compacted spheres, which is attributed to the decrease of reaction rate as a result of the coordination. Three more amino acids are examined and confirms the role of reaction kinetic in shaping silver particles. Furthermore, by increasing the concentration of the reductant, the silver morphologies change from compact spheres to loose flowers as a result of the increase of reaction rate. Therefore the silver hierarchical structure can be reversibly switched by reaction kinetics. The silver particles synthesized are tested for surface enhanced Raman scattering (SERS) property and the dendritic particles present a remarkable SERS activity. This study shows that reaction kinetics is a powerful tool to tune hierarchical structures of silver particles, which is expected to be transferable to other material systems. PMID:26442867
Reversibly Switching Silver Hierarchical Structures via Reaction Kinetics
NASA Astrophysics Data System (ADS)
Liu, Jianmei; Yang, Tao; Li, Chengxiang; Dai, Jinhui; Han, Yongsheng
2015-10-01
Here we report a study on controllable synthesis of hierarchical silver structures via regulating reaction kinetics. Silver particles with various morphologies are synthesized by a solution-based reduction approach at the addition of amino acids. The amino acid is used to coordinate with silver ions to slow down the reduction of silver ions. With the increase of glycine concentration, the morphologies of silver particles switch from dendrites, to flowers and to compacted spheres, which is attributed to the decrease of reaction rate as a result of the coordination. Three more amino acids are examined and confirms the role of reaction kinetic in shaping silver particles. Furthermore, by increasing the concentration of the reductant, the silver morphologies change from compact spheres to loose flowers as a result of the increase of reaction rate. Therefore the silver hierarchical structure can be reversibly switched by reaction kinetics. The silver particles synthesized are tested for surface enhanced Raman scattering (SERS) property and the dendritic particles present a remarkable SERS activity. This study shows that reaction kinetics is a powerful tool to tune hierarchical structures of silver particles, which is expected to be transferable to other material systems.
Periodic perturbation of the kinetics of heterogeneous catalytic reactions
NASA Astrophysics Data System (ADS)
Zhdanov, Vladimir P.
2004-09-01
Periodic forcing of reaction kinetics via, e.g., variation of reactant pressure(s), temperature or flow reversal is one of the useful tools employed in basic and applied studies of heterogeneous catalytic processes. In the case of conventional (stable) kinetics, this strategy is used to clarify the mechanisms of reactions and obtain data on reaction rate constants or to improve the reaction performance, e.g., to increase reaction rate and/or selectivity with respect to desired products. In experiments, that are focused on oscillatory catalytic reactions, periodic perturbations are employed to stabilize period-1 oscillations. This is easily achieved if the external and internal frequencies are equal. In a more general context, periodic perturbation of chemical reactions, that exhibit period-1 oscillations, may result in complex reaction behaviour, including period doubling and irregular kinetics provided that the external and internal frequencies do not coincide. We consider in this review both the relevant data available in the literature and the results of systematic calculations for a few generic models.
NASA Astrophysics Data System (ADS)
Hidayat, Arif; Rochmadi, Wijaya, Karna; Budiman, Arief
2015-12-01
Recently, a new strategy of preparing novel carbon-based solid acids has been developed. In this research, the esterification reactions of Palm Fatty Acid Distillate (PFAD) with methanol, using coconut shell biochar sulfonated catalyst from biomass wastes as catalyst, were studied. In this study, the coconut shell biochar sulfonated catalysts were synthesized by sulfonating the coconut shell biochar using concentrated H2SO4. The kinetics of free fatty acid (FFA) esterification in PFAD using a coconut shell biochar sulfonated catalyst was also studied. The effects of the mass ratio of catalyst to oil (1-10%), the molar ratio of methanol to oil (6:1-12:1), and the reaction temperature (40-60°C) were studied for the conversion of PFAD to optimize the reaction conditions. The results showed that the optimal conditions were an methanol to PFAD molar ratio of 12:1, the amount of catalyst of 10%w, and reaction temperature of 60°C. The proposed kinetic model shows a reversible second order reaction and represents all the experimental data satisfactorily, providing deeper insight into the kinetics of the reaction.
The reaction kinetics of alanine and glycine under hydrothermal conditions
NASA Astrophysics Data System (ADS)
Cox, Jenny S.; Seward, Terry M.
2007-05-01
Experimental data on the hydrothermal reaction kinetics of α-alanine, glycine, and β-alanine were acquired using a custom-built spectrophotometric reaction cell which permits in situ observation under hydrothermal conditions. Quantitative kinetic information, including rate constants, concentration versus time profiles, and calculations of the individual component spectra, was obtained from the data using a self-modeling chemometric approach based on factor analysis which treats the rate expressions simultaneously as a system of differential algebraic equations (DAE) of index 1. Experimental data collected at 120-165 °C and 20 bar indicates that aqueous α-alanine, glycine and β-alanine will preferentially undergo dimerization and subsequent cyclization when heated in an inert reactor. The results presented here lend further support to the roles of temperature, exposed reactive surfaces, and matrix additives in the reaction kinetics of the structurally simple amino acids examined in this study.
Kinetic analysis of protein modification reactions at equilibrium.
Rakitzis, E T
1989-01-01
A kinetic analysis is presented of reactions of protein modification, and/or of modification-induced enzyme inactivation, which can formally be described by a single exponential function, or by a summation of two exponential functions, of reaction time plus a constant term. The reaction schemes compatible with the kinetic formalism of these cases are given, and a simple kinetic criterion is described whereby the identification of one of these cases, strong negative protein modification co-operativity, may be carried out. The treatment outlined in this paper is applied to a case from the literature, the inactivation of glyceraldehyde-3-phosphate dehydrogenase by butane-2,3-dione [Asriyants, Benkevich & Nagradova (1983) Biokhimiya (Engl. Transl.) 48, 164-171]. PMID:2597131
Method to render second order beam optics programs symplectic
Douglas, D.; Servranckx, R.V.
1984-10-01
We present evidence that second order matrix-based beam optics programs violate the symplectic condition. A simple method to avoid this difficulty, based on a generating function approach to evaluating transfer maps, is described. A simple example illustrating the non-symplectricity of second order matrix methods, and the effectiveness of our solution to the problem, is provided. We conclude that it is in fact possible to bring second order matrix optics methods to a canonical form. The procedure for doing so has been implemented in the program DIMAT, and could be implemented in programs such as TRANSPORT and TURTLE, making them useful in multiturn applications. 15 refs.
Second-order state estimation experiments using acceleration measurements
NASA Technical Reports Server (NTRS)
Belvin, W. K.
1992-01-01
The estimation of dynamic states for feedback control of structural systems using second-order differential equations and acceleration measurements is described. The formulation of the observer model, and the design of the observer gains is discussed in detail. It is shown the second-order observer is highly stable because the stability constraints on the observer gains are model independent. The limitation of the proposed observer is the need for 'nearly' collocated actuators and accelerometers. Experimental results using a control-structure interaction testbed are presented that show the second-order observer provided more stability than a Kalman filter estimator without decreasing closed-loop performance.
A study of second-order supersonic flow theory
NASA Technical Reports Server (NTRS)
Van Dyke, Milton D
1952-01-01
Second-order solutions of supersonic-flow problems are sought by iteration, using the linearized solution as the first step. For plane and axially symmetric flows, particular solutions of the iteration equation are discovered which reduce the second-order problem to an equivalent linearized problem. Comparison of second-order solutions with exact and numerical results shows great improvement over linearized theory. For full three-dimensional flow, only a partial particular solution is found. The inclined cone is solved, and the possibility of treating more general problems is considered.
Study of second order upwind differencing in a recirculating flow
NASA Technical Reports Server (NTRS)
Vanka, S. P.
1985-01-01
The accuracy and stability of the second order upwind differencing scheme was investigated. The solution algorithm employed is based on a coupled solution of the nonlinear finite difference equations by the multigrid technique. Calculations have been made of the driven cavity flow for several Reynolds numbers and finite difference grids. In comparison with the hybrid differencing, the second order upwind differencing is somewhat more accurate but it is not monotonically accurate with mesh refinement. Also, the convergence of the solution algorithm deteriorates with the use of the second order upwind differencing.
Second order guiding-center Vlasov-Maxwell equations
Madsen, Jens
2010-08-15
Second order gyrogauge invariant guiding-center coordinates with strong ExB-flow are derived using the Lie transformation method. The corresponding Poisson bracket structure and equations of motion are obtained. From a variational principle the explicit Vlasov-Maxwell equations are derived including second order terms. The second order contributions contain the lowest order finite-Larmor-radius corrections to the electromagnetic field. Therefore, the model is capable of describing situations where strong ExB-flows and finite-Larmor-radius effects are mutually important.
Optimal second order sliding mode control for nonlinear uncertain systems.
Das, Madhulika; Mahanta, Chitralekha
2014-07-01
In this paper, a chattering free optimal second order sliding mode control (OSOSMC) method is proposed to stabilize nonlinear systems affected by uncertainties. The nonlinear optimal control strategy is based on the control Lyapunov function (CLF). For ensuring robustness of the optimal controller in the presence of parametric uncertainty and external disturbances, a sliding mode control scheme is realized by combining an integral and a terminal sliding surface. The resulting second order sliding mode can effectively reduce chattering in the control input. Simulation results confirm the supremacy of the proposed optimal second order sliding mode control over some existing sliding mode controllers in controlling nonlinear systems affected by uncertainty. PMID:24780159
Reaction kinetics of nanostructured silicon carbide
NASA Astrophysics Data System (ADS)
Wallis, K. L.; Patyk, J. K.; Zerda, T. W.
2008-08-01
SiC nanowires were produced from carbon nanotubes and silicon by two different methods at high temperature. X-ray powder diffraction was used to determine SiC concentration. The reaction rate using the Avrami-Erofeev method was determined for samples sintered at temperatures ranging from 1313 to 1823 K. The activation energy was found to be (254 ± 36) kJ mol-1. The limiting factor in SiC formation is diffusion of silicon and carbon atoms through the produced layer of SiC.
NASA Technical Reports Server (NTRS)
Miller, Ronald H.; Winske, Dan; Gary, S. P.
1992-01-01
A second-order theory for electrostatic instabilities driven by counterstreaming ion beams is developed which describes momentum coupling and heating of the plasma via wave-particle interactions. Exchange rates between the waves and particles are derived, which are suitable for the fluid equations simulating microscopic effects on macroscopic scales. Using a fully kinetic simulation, the electrostatic ion cyclotron instability due to counterstreaming H(+) beams has been simulated. A power spectrum from the kinetic simulation is used to evaluate second-order exchange rates. The calculated heating and momentum loss from second-order theory is compared to the numerical simulation.
Francés-Monerris, Antonio; Merchán, Manuela; Roca-Sanjuán, Daniel
2013-08-21
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)(π2) state of the C6OH adducts is determined to be the main responsible in all compounds for the absorption band in the Vis range. PMID:23968062
Chemical kinetic reaction mechanism for the combustion of propane
NASA Technical Reports Server (NTRS)
Jachimowski, C. J.
1984-01-01
A detailed chemical kinetic reaction mechanism for the combustion of propane is presented and discussed. The mechanism consists of 27 chemical species and 83 elementary chemical reactions. Ignition and combustion data as determined in shock tube studies were used to evaluate the mechanism. Numerical simulation of the shock tube experiments showed that the kinetic behavior predicted by the mechanism for stoichiometric mixtures is in good agrement with the experimental results over the entire temperature range examined (1150-2600K). Sensitivity and theoretical studies carried out using the mechanism revealed that hydrocarbon reactions which are involved in the formation of the HO2 radical and the H2O2 molecule are very important in the mechanism and that the observed nonlinear behavior of ignition delay time with decreasing temperature can be interpreted in terms of the increased importance of the HO2 and H2O2 reactions at the lower temperatures.
Quasiequilibrium approximation of fast reaction kinetics in stochastic biochemical systems.
Goutsias, John
2005-05-01
We address the problem of eliminating fast reaction kinetics in stochastic biochemical systems by employing a quasiequilibrium approximation. We build on two previous methodologies developed by [Haseltine and Rawlings, J. Chem. Phys. 117, 6959 (2002)] and by [Rao and Arkin, J. Chem. Phys. 118, 4999 (2003)]. By following Haseltine and Rawlings, we use the numbers of occurrences of the underlying reactions to characterize the state of a biochemical system. We consider systems that can be effectively partitioned into two distinct subsystems, one that comprises "slow" reactions and one that comprises "fast" reactions. We show that when the probabilities of occurrence of the slow reactions depend at most linearly on the states of the fast reactions, we can effectively eliminate the fast reactions by modifying the probabilities of occurrence of the slow reactions. This modification requires computation of the mean states of the fast reactions, conditioned on the states of the slow reactions. By assuming that within consecutive occurrences of slow reactions, the fast reactions rapidly reach equilibrium, we show that the conditional state means of the fast reactions satisfy a system of at most quadratic equations, subject to linear inequality constraints. We present three examples which allow analytical calculations that clearly illustrate the mathematical steps underlying the proposed approximation and demonstrate the accuracy and effectiveness of our method. PMID:15918689
Orthogonal canonical forms for second-order systems
NASA Technical Reports Server (NTRS)
Williams, Trevor; Laub, Alan
1989-01-01
The authors prove that a linear second-order system with arbitrary damping cannot be reduced to Hessenberg-triangular form by means of orthogonal transformations, while this reduction is always possible for the modal damping commonly assumed for models of flexible structures. The type of canonical form obtainable by means of orthogonal transformations acting on a second-order system is heavily dependent on the type of damping considered. If the damping matrix is merely positive semi-definite symmetric, it is generally not possible to obtain a reduction to Hessenberg-triangular form, while this reduction is trivial for zero or Rayleigh damping. If damping is modal, however, as is commonly assumed in structural models, the reduction exists and is nontrivial. Furthermore, reduction to triangular second-order Schur form is always possible for such damping: this canonical form appears likely to have applications to second-order system theory.
Oscillation theorems for second order nonlinear forced differential equations.
Salhin, Ambarka A; Din, Ummul Khair Salma; Ahmad, Rokiah Rozita; Noorani, Mohd Salmi Md
2014-01-01
In this paper, a class of second order forced nonlinear differential equation is considered and several new oscillation theorems are obtained. Our results generalize and improve those known ones in the literature. PMID:25077054
Second-order model selection in mixture experiments
Redgate, P.E.; Piepel, G.F.; Hrma, P.R.
1992-07-01
Full second-order models for q-component mixture experiments contain q(q+l)/2 terms, which increases rapidly as q increases. Fitting full second-order models for larger q may involve problems with ill-conditioning and overfitting. These problems can be remedied by transforming the mixture components and/or fitting reduced forms of the full second-order mixture model. Various component transformation and model reduction approaches are discussed. Data from a 10-component nuclear waste glass study are used to illustrate ill-conditioning and overfitting problems that can be encountered when fitting a full second-order mixture model. Component transformation, model term selection, and model evaluation/validation techniques are discussed and illustrated for the waste glass example.
Fast second-order consensus via predictive mechanisms
NASA Astrophysics Data System (ADS)
Wu, Jie; Zhang, Li-Yi; Bai, Yu
2015-01-01
In this paper, we discuss second-order consensus problems for multi-agent systems with dynamic agents and fixed topologies. A new second-order consensus protocol incorporating the predictive mechanism is proposed and a convergence analysis related to the real and imaginary parts of the eigenvalues of the Laplacian matrix of the corresponding network is provided. We establish a direct connection between the eigenvalues of the Laplacian matrix and parameters of the proposed second-order consensus model, and we compute a lower bound for the sum of parameters. It is proved under general conditions related to the second-order consensus protocol and the network topology that the asymptotic consensus is achieved and the convergence speed is increased via designing a state predictor. Finally, simulation results are provided to verify the effectiveness of the proposed protocol and the analytical claims.
Orthogonal canonical forms for second-order systems
NASA Technical Reports Server (NTRS)
Williams, Trevor; Laub, Alan J.
1992-01-01
It is shown that a linear second-order system with arbitrary damping cannot be reduced to Hessenberg-triangular form by means of orthogonal transformations. However, it is also shown that such an orthogonal reduction is always possible for the modal damping commonly assumed for models of flexible structures. It is shown that modally damped models can be orthogonally reduced to a new triangular second-order Schur form.
Kubo formulas for second-order hydrodynamic coefficients.
Moore, Guy D; Sohrabi, Kiyoumars A
2011-03-25
At second order in gradients, conformal relativistic hydrodynamics depends on the viscosity η and on five additional "second-order" hydrodynamical coefficients τ(Π), κ, λ₁, λ₂, and λ₃. We derive Kubo relations for these coefficients, relating them to equilibrium, fully retarded three-point correlation functions of the stress tensor. We show that the coefficient λ₃ can be evaluated directly by Euclidean means and does not in general vanish. PMID:21517309
Kinetics and Mechanisms of Calcite Reactions with Saline Waters
Chapman, Piers; *Morse, John W.
2010-11-15
1. Objective The general objective of this research was to determine the kinetics and mechanisms of calcite reactions with saline waters over a wide range of saline water composition, carbon dioxide partial pressure (pCO2), and modest ranges of T and P. This would be done by studying both reaction rates and solubility from changes in solution chemistry. Also, nanoscale observations of calcite surface morphology and composition would be made to provide an understanding of rate controlling mechanisms.
Second-order sloshing over an arbitrary bed
NASA Astrophysics Data System (ADS)
Chapman, G. J. D.; Porter, R.
2005-02-01
The two-dimensional problem of the free sloshing of an inviscid fluid in a vertically walled tank with an arbitrary bed shape is solved at both first and second order in the Stokes expansion of the velocity potential. The approach employed at both orders uses Green's functions for a flat bed in conjunction with the Cauchy-Riemann equations to derive integral equations for the tangential flux along the varying bed. The first- and second-order potentials everywhere in the fluid may then be related to these fluxes. Significant analytic progress is made with the calculation of various contributions to the integral equations at second order. The equations at first and second order are ultimately solved using a variational principle equivalent to the Galerkin method, giving efficient and accurate results. In particular, the work involved in determining the second-order solution is no more intensive than in solving the first-order problem. The first-order solution is shown to reproduce known results for specific bed shapes. The method is applied to a range of bed shapes and the second-order correction to the free-surface elevation is illustrated.
SABIO-RK—database for biochemical reaction kinetics
Wittig, Ulrike; Kania, Renate; Golebiewski, Martin; Rey, Maja; Shi, Lei; Jong, Lenneke; Algaa, Enkhjargal; Weidemann, Andreas; Sauer-Danzwith, Heidrun; Mir, Saqib; Krebs, Olga; Bittkowski, Meik; Wetsch, Elina; Rojas, Isabel; Müller, Wolfgang
2012-01-01
SABIO-RK (http://sabio.h-its.org/) is a web-accessible database storing comprehensive information about biochemical reactions and their kinetic properties. SABIO-RK offers standardized data manually extracted from the literature and data directly submitted from lab experiments. The database content includes kinetic parameters in relation to biochemical reactions and their biological sources with no restriction on any particular set of organisms. Additionally, kinetic rate laws and corresponding equations as well as experimental conditions are represented. All the data are manually curated and annotated by biological experts, supported by automated consistency checks. SABIO-RK can be accessed via web-based user interfaces or automatically via web services that allow direct data access by other tools. Both interfaces support the export of the data together with its annotations in SBML (Systems Biology Markup Language), e.g. for import in modelling tools. PMID:22102587
Internal Diffusion-Controlled Enzyme Reaction: The Acetylcholinesterase Kinetics.
Lee, Sangyun; Kim, Ji-Hyun; Lee, Sangyoub
2012-02-14
Acetylcholinesterase is an enzyme with a very high turnover rate; it quenches the neurotransmitter, acetylcholine, at the synapse. We have investigated the kinetics of the enzyme reaction by calculating the diffusion rate of the substrate molecule along an active site channel inside the enzyme from atomic-level molecular dynamics simulations. In contrast to the previous works, we have found that the internal substrate diffusion is the determinant of the acetylcholinesterase kinetics in the low substrate concentration limit. Our estimate of the overall bimolecular reaction rate constant for the enzyme is in good agreement with the experimental data. In addition, the present calculation provides a reasonable explanation for the effects of the ionic strength of solution and the mutation of surface residues of the enzyme. The study suggests that internal diffusion of the substrate could be a key factor in understanding the kinetics of enzymes of similar characteristics. PMID:26596618
Penicillin Hydrolysis: A Kinetic Study of a Multistep, Multiproduct Reaction.
ERIC Educational Resources Information Center
McCarrick, Thomas A.; McLafferty, Fred W.
1984-01-01
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)
REACTION KINETICS OF CA-BASED SORBENTS WITH HC1
The paper gives results of an investigation of the kinetics of the reaction between CaO and HC1 under conditions that minimize bulk mass transfer and pore diffusion limitations. eactivity data from 0.2 to 1 s exposure to 5000 ppm HC1 in a fixed-bed reactor were analyzed by a shri...
REACTION KINETICS OF CA-BASED SORBENTS WITH HC1
The kinetics of the reaction between CaO and HCl were investigated under conditions that minimize bulk mass transfer and pore diffusion limitations. Reactivity data from 0.2- to 1-s exposure to 5000 ppm HCl in a fixed bed reactor were analyzed by a shrinking core model of diffusi...
Palm fatty acid biodiesel: process optimization and study of reaction kinetics.
Yadav, Praveen K S; Singh, Onkar; Singh, R P
2010-01-01
The relatively high cost of refined oils render the resulting fuels unable to compete with petroleum derived fuel. In this study, biodiesel is prepared from palm fatty acid (PFA) which is a by-product of palm oil refinery. The process conditions were optimized for production of palm fatty acid methyl esters. A maximum conversion of 94.4% was obtained using two step trans-esterification with 1:10 molar ratio of oil to methanol at 65°C. Sulfuric acid and Sodium hydroxide were used as acid and base catalyst respectively. The composition of fatty acid methyl esters (FAME) obtained was similar to that of palm oil. The biodiesel produced met the established specifications of biodiesel of American Society for Testing and Materials (ASTM). The kinetics of the trans-esterification reaction was also studied and the data reveals that the reaction is of first order in fatty acid and methanol (MeOH) and over all the reaction is of second order. PMID:20972357
Kinetics and Thermochemistry of the Cl((sup 2)P(sub J)) + C2Cl4 Association Reaction
NASA Technical Reports Server (NTRS)
Nicovich, J. M.; Wang, S.; Mckee, M. L.; Wine, P. H.
1997-01-01
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.
Reaction kinetics of CO2 absorption in to phosphonium based anion-functionalized ionic liquids.
Gurkan, Burcu E; Gohndrone, Thomas R; McCready, Mark J; Brennecke, Joan F
2013-05-28
The reaction kinetics between CO2 and trihexyl(tetradecyl)phosphonium ([P66614])-based ionic liquids (ILs) with prolinate ([Pro]), 2-cyanopyrrolide ([2-CNpyr]), and 3-(trifluoromethyl)pyrazolide ([3-CF3pyra]) anions are studied at temperatures from 22-60 °C. The absorption of CO2 is carried out in a stirred reactor under pseudo first order conditions. ILs are diluted to concentrations of 0.05, 0.1 and 0.15 M with tetraglyme--a nonreactive, low volatility solvent with much lower viscosity than the ILs. Physical solubility of CO2 in the mixtures is calculated using correlations developed from CO2 solubility measurements in tetraglyme and the N2O-analogy for ILs and dilute IL solutions. The diffusivity of CO2 is estimated from viscosity-dependent correlations chosen after a thorough literature review. The results indicate partial first order reaction kinetics with respect to IL with values ranging from 19,500 L mol(-1) s(-1) ([P66614][Pro]) to 3200 L mol(-1) s(-1) ([P66614][3-CF3pyra]) at 22 °C. The second order reaction rate constants follow Arrhenius behavior with the highest activation energy of 43 kJ mol(-1) measured for [P66614][Pro]. ILs with aprotic heterocylic anions (AHA), on the other hand, show small activation energies of 18 and 11 kJ mol(-1) for [P66614][3-CF3pyra] and [P66614][2-CNpyr], respectively. The ILs studied in this work exhibit reactivity comparable to or higher than common aqueous amines. High reaction rates and tunable capacity make ILs, and AHA ILs in particular, attractive solvents for CO2 separations. PMID:23598368
Spatial variances of wind fields and their relation to second-order structure functions and spectra
NASA Astrophysics Data System (ADS)
Vogelzang, Jur; King, Gregory P.; Stoffelen, Ad
2015-02-01
Kinetic energy variance as a function of spatial scale for wind fields is commonly estimated either using second-order structure functions (in the spatial domain) or by spectral analysis (in the frequency domain). Both techniques give an order-of-magnitude estimate. More accurate estimates are given by a statistic called spatial variance. Spatial variances have a clear interpretation and are tolerant for missing data. They can be related to second-order structure functions, both for discrete and continuous data. Spatial variances can also be Fourier transformed to yield a relation with spectra. The flexibility of spatial variances is used to study various sampling strategies, and to compare them with second-order structure functions and spectral variances. It is shown that the spectral sampling strategy is not seriously biased to calm conditions for scatterometer ocean surface vector winds. When the second-order structure function behaves like rp, its ratio with the spatial variance equals >(p+1>)>(p+2>). Ocean surface winds in the tropics have p between 2/3 and 1, so one-sixth to one-fifth of the second-order structure function value is a good proxy for the cumulative variance.
Spatial Variances of Wind Fields and Their Relation to Second-Order Structure Functions and Spectra
NASA Astrophysics Data System (ADS)
King, G. P.; Vogelzang, J.; Stoffelen, A.; Portabella, M.
2014-12-01
Kinetic energy variance as a function of spatial scale for wind fields is commonly estimated either using second-order structure functions (in the spatial domain) or by spectral analysis (in the frequency domain). It will be demonstrated that neither spectra nor second-order structure functions offer a good representation of the variance as a function of scale. These difficulties can be circumvented by using a statistical quantity called spatial variance. It combines the advantages of spectral analysis and spatial statistics. In particular, when applied to observations, spatial variances have a clear interpretation and are tolerant for missing data. They can be related to second-order structure functions, both for discrete and continuous data. For data sets without missing points the relation is statistically exact. Spatial variances can also be Fourier transformed to yield a relation with spectra. The flexibility of spatial variances is used to study various sampling strategies, and to compare them with second-order structure functions and spectral variances. It is shown that the spectral sampling strategy is not seriously biased to calm conditions for scatterometer ocean surface vector winds, and that one-fifth of the second-order structure function value is a good proxy for the cumulative variance.
Alternative nonlinear model for estimating second-order rate coefficients for biodegradation.
Suflita, J M; Smolenski, W J; Robinson, J A
1987-01-01
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 implicit in the use of the second-order rate equation, but still requires the assumption of first-order kinetics over the course of substrate depletion. Violation of the no-growth assumption is particularly important since overestimates of the pseudo-first-order rate coefficient lead to underestimates of the time required for the removal of a xenobiotic chemical from a contaminated environment. Our calculations show that the errors introduced into the pseudo-first-order rate coefficient (and the resulting estimates of the second-order rate coefficient) approach 100% if one doubling occurs in activity over the course of substrate depletion. For an exemplary data set, use of a first-order model resulted in a 100% overestimate of the first-order decay coefficient, which would in turn lead to a corresponding overestimate of the second-order rate coefficient. The modified model we describe is a potential alternative to the pseudo-first-order model for the routine estimation of second-order rate coefficients. PMID:3606091
Pulsed ion beam investigation of the kinetics of surface reactions
NASA Technical Reports Server (NTRS)
Horton, C. C.; Eck, T. G.; Hoffman, R. W.
1989-01-01
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.
Radical scavenging reaction kinetics with multiwalled carbon nanotubes
Tsuruoka, Shuji; Matsumoto, Hidetoshi; Koyama, Kenichi; Akiba, Eiji; Yanagisawa, Takashi; Cassee, Flemming R.; Saito, Naoto; Usui, Yuki; Kobayashi, Shinsuke; Porter, Dale W.; Castranova, Vincent; Endo, Morinobu
2016-01-01
Progress in the development of carbon nanotubes (CNTs) has stimulated great interest among industries providing new applications. Meanwhile, toxicological evaluations on nanomaterials are advancing leading to a predictive exposure limit for CNTs, which implies the possibility of designing safer CNTs. To pursue safety by design, the redox potential in reactions with CNTs has been contemplated recently. However, the chemical reactivity of CNTs has not been explored kinetically, so that there is no scheme to express a redox reaction with CNTs, though it has been investigated and reported. In addition, the reactivity of CNTs is discussed with regard to impurities that consist of transition metals in CNTs, which obfuscates the contribution of CNTs to the reaction. The present work aimed at modeling CNT scavenging in aqueous solution using a kinetic approach and a simple first-order reaction scheme. The results show that CNTs follow the redox reaction assumption in a simple chemical system. As a result, the reaction with multiwalled CNTs is semi-quantitatively denoted as redox potential, which suggests that their biological reactions may also be evaluated using a redox potential scheme. PMID:27030782
Reaction Mechanism Generator: Automatic construction of chemical kinetic mechanisms
NASA Astrophysics Data System (ADS)
Gao, Connie W.; Allen, Joshua W.; Green, William H.; West, Richard H.
2016-06-01
Reaction Mechanism Generator (RMG) constructs kinetic models composed of elementary chemical reaction steps using a general understanding of how molecules react. Species thermochemistry is estimated through Benson group additivity and reaction rate coefficients are estimated using a database of known rate rules and reaction templates. At its core, RMG relies on two fundamental data structures: graphs and trees. Graphs are used to represent chemical structures, and trees are used to represent thermodynamic and kinetic data. Models are generated using a rate-based algorithm which excludes species from the model based on reaction fluxes. RMG can generate reaction mechanisms for species involving carbon, hydrogen, oxygen, sulfur, and nitrogen. It also has capabilities for estimating transport and solvation properties, and it automatically computes pressure-dependent rate coefficients and identifies chemically-activated reaction paths. RMG is an object-oriented program written in Python, which provides a stable, robust programming architecture for developing an extensible and modular code base with a large suite of unit tests. Computationally intensive functions are cythonized for speed improvements.
Second-order quasinormal mode of the Schwarzschild black hole
Nakano, Hiroyuki; Ioka, Kunihito
2007-10-15
We formulate and calculate the second-order quasinormal modes (QNMs) of a Schwarzschild black hole (BH). Gravitational waves (GW) from a distorted BH, the so-called ringdowns, are well understood as QNMs in general relativity. Since QNMs from binary BH mergers will be detected with a high signal-to-noise ratio by GW detectors, it is also possible to detect the second perturbative order of QNMs, generated by nonlinear gravitational interaction near the BH. In the BH perturbation approach, we derive the master Zerilli equation for the metric perturbation to second order and explicitly regularize it at the horizon and spatial infinity. We numerically solve the second-order Zerilli equation by implementing the modified Leaver continued fraction method. The second-order QNM frequencies are found to be twice the first-order ones, and the GW amplitude is up to {approx}10% that of the first order for the binary BH mergers. Since the second-order QNMs always exist, we can use their detections (i) to test the nonlinearity of general relativity, in particular, the no-hair theorem, (ii) to remove fake events in the data analysis of QNM GWs, and (iii) to measure the distance to the BH.
Children's understanding of second-order mental states.
Miller, Scott A
2009-09-01
The most popular topic in theory-of-mind research has been first-order false belief: the realization that it is possible to hold false beliefs about events in the world. A more advanced development is second-order false belief: the realization that it is possible to hold a false belief about someone else's belief. This article reviews research directed to second-order false belief and other forms of higher order, recursive mentalistic reasoning. Three general issues are considered. Research directed to developmental changes indicates that preschoolers typically fail second-order tasks and that success emerges at about age 5 or 6, although results vary some with method of assessment. Research directed to the consequences of second-order competence has revealed positive relations with a number of other aspects of children's development. Finally, measures of both language and executive function relate positively to performance on second-order tasks; the causal bases for the correlations, however, remain to be established. This article concludes with suggestions for future research. PMID:19702381
A kinetics investigation of several reactions involving chlorine containing compounds
NASA Technical Reports Server (NTRS)
Davis, D. D.
1978-01-01
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.
Transient State Kinetic Investigation of 5-Aminolevulinate Synthase Reaction Mechanism*
Zhang, Junshun; Ferreira, Gloria C.
2013-01-01
5-Aminolevulinate synthase (ALAS), a pyridoxal 5′-phosphate-dependent enzyme, catalyzes the first, and regulatory, step of the heme biosynthetic pathway in nonplant eukaryotes and some bacteria. 5-Aminolevulinate synthase is a dimeric protein having an ordered kinetic mechanism with glycine binding before succinyl-CoA and with aminolevulinate release after CoA and carbon dioxide. Rapid scanning stopped-flow absorption spectrophotometry in conjunction with multiple turnover chemical quenched-flow kinetic analyses and a newly developed CoA detection method were used to examine the ALAS catalytic reaction and identify the rate-determining step. The reaction of glycine with ALAS follows a three-step kinetic process, ascribed to the formation of the Michaelis complex and the pyridoxal 5′-phosphate-glycine aldimine, followed by the abstraction of the glycine pro-R proton from the external aldimine. Significantly, the rate associated with this third step (k3 = 0.002 s−1) is consistent with the rate determined for the ALAS-catalyzed removal of tritium from [2-3H2]glycine. Succinyl-CoA and acetoacetyl-CoA increased the rate of glycine proton removal ~250,000-and 10-fold, respectively, supporting our previous proposal that the physiological substrate, succinyl-CoA, promotes a protein conformational change, which accelerates the conversion of the external aldimine into the initial quinonoid intermediate (Hunter, G. A., and Ferreira, G. C. (1999) J. Biol. Chem. 274, 12222–12228). Rapid scanning stopped-flow and quenched-flow kinetic analyses of the ALAS reaction under single turnover conditions lend evidence for two quinonoid reaction intermediates and a model of the ALAS kinetic mechanism in which product release is at least the partially rate-limiting step. Finally, the carbonyl and carboxylate groups of 5-aminolevulinate play a major protein-interacting role by inducing a conformational change in ALAS and, thus, possibly modulating product release. PMID:12191993
A unifying kinetic framework for modeling oxidoreductase-catalyzed reactions
Chang, Ivan; Baldi, Pierre
2013-01-01
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
Reaction kinetics of cellulose hydrolysis in subcritical and supercritical water
NASA Astrophysics Data System (ADS)
Olanrewaju, Kazeem Bode
The uncertainties in the continuous supply of fossil fuels from the crisis-ridden oil-rich region of the world is fast shifting focus on the need to utilize cellulosic biomass and develop more efficient technologies for its conversion to fuels and chemicals. One such technology is the rapid degradation of cellulose in supercritical water without the need for an enzyme or inorganic catalyst such as acid. This project focused on the study of reaction kinetics of cellulose hydrolysis in subcritical and supercritical water. Cellulose reactions at hydrothermal conditions can proceed via the homogeneous route involving dissolution and hydrolysis or the heterogeneous path of surface hydrolysis. The work is divided into three main parts. First, the detailed kinetic analysis of cellulose reactions in micro- and tubular reactors was conducted. Reaction kinetics models were applied, and kinetics parameters at both subcritical and supercritical conditions were evaluated. The second major task was the evaluation of yields of water soluble hydrolysates obtained from the hydrolysis of cellulose and starch in hydrothermal reactors. Lastly, changes in molecular weight distribution due to hydrothermolytic degradation of cellulose were investigated. These changes were also simulated based on different modes of scission, and the pattern generated from simulation was compared with the distribution pattern from experiments. For a better understanding of the reaction kinetics of cellulose in subcritical and supercritical water, a series of reactions was conducted in the microreactor. Hydrolysis of cellulose was performed at subcritical temperatures ranging from 270 to 340 °C (tau = 0.40--0.88 s). For the dissolution of cellulose, the reaction was conducted at supercritical temperatures ranging from 375 to 395 °C (tau = 0.27--0.44 s). The operating pressure for the reactions at both subcritical and supercritical conditions was 5000 psig. The results show that the rate-limiting step in converting cellulose to fermentable sugars in subcritical and supercritical water differs because of the difference in their activation energies. Cellulose and starch were both hydrolyzed in micro- and tubular reactors and at subcritical and supercritical conditions. Due to the difficulty involved in generating an aqueous based dissolved cellulose and having it reacted in subcritical water, dissolved starch was used instead. Better yield of water soluble hydrolysates, especially fermentable sugars, were observed from the hydrolysis of cellulose and dissolved starch in subcritical water than at supercritical conditions. The concluding phase of this project focuses on establishing the mode of scission of cellulose chains in the hydrothermal reactor. This was achieved by using the simulated degradation pattern generated based on different scission modes to fingerprint the degradation pattern obtained from experiment.
Some restrictions on the existence of second order limit language
NASA Astrophysics Data System (ADS)
Ahmad, Muhammad Azrin; Sarmin, Nor Haniza; Yusof, Yuhani; Fong, Wan Heng
2015-10-01
The cut and paste phenomenon on DNA molecules with the presence of restriction enzyme and appropriate ligase has led to the formalism of mathematical modelling of splicing system. A type of splicing system named Yusof-Goode splicing system is used to present the transparent behaviour of the DNA splicing process. The limit language that is defined as the leftover molecules after the system reaches its equilibrium point has been extended to a second order limit language. The non-existence of the second order limit language biologically has lead to this study by using mathematical approach. In this paper, the factors that restrict the formation of the second order limit language are discussed and are presented as lemmas and theorem using Y-G approach. In addition, the discussion focuses on Yusof- Goode splicing system with at most two initial strings and two rules with one cutting site and palindromic crossing site and recognition sites.
Deflection of light to second order in conformal Weyl gravity
Sultana, Joseph
2013-04-01
We reexamine the deflection of light in conformal Weyl gravity obtained in Sultana and Kazanas (2010), by extending the calculation based on the procedure by Rindler and Ishak, for the bending angle by a centrally concentrated spherically symmetric matter distribution, to second order in M/R, where M is the mass of the source and R is the impact parameter. It has recently been reported in Bhattacharya et al. (JCAP 09 (2010) 004; JCAP 02 (2011) 028), that when this calculation is done to second order, the term γr in the Mannheim-Kazanas metric, yields again the paradoxical contribution γR (where the bending angle is proportional to the impact parameter) obtained by standard formalisms appropriate to asymptotically flat spacetimes. We show that no such contribution is obtained for a second order calculation and the effects of the term γr in the metric are again insignificant as reported in our earlier work.
Textural segmentation, second-order statistics, and textural elements.
Beck, J
1983-01-01
Beck (1972, 1973) hypothesized that textural segmentation occurs strongly on the basis of simple properties such as brightness, color, size, and the slopes of contours and lines of the elemental descriptors of a texture or textural elements. The experiment reported supports the hypothesis that specific stimulus features, rather than second-order statistics, account for textural segmentation. The results agree with Julesz (1981a,b) who has reported evidence disproving his original conjecture of the importance of second-order statistics. Julesz (1981a,b) now hypothesizes textural segmentation to be a function of local features which he called textons. Textons are features that give textural segmentation when textures have identical second-order statistics. The two hypotheses are to date in complete agreement on the stimulus features producing textural segmentation, and the experiment reported is consistent with both. PMID:6626590
Second-order axial color of thin lenses in air.
Nobis, Thomas
2015-10-01
In present research, the influence of higher-order aberrations on the correction of secondary axial color is under investigation. Analytical solutions have so far been restricted to special cases and simple optical systems. Common theories require the tracing of rays of different wavelengths. Such numerical approaches do not support the comprehension of the underlying physical effects. In this paper, a formula for second-order axial color contributions is derived which is based on paraxial ray data for the reference wavelength only. Therefore, it allows the determination of second-order axial color in early paraxial design stages without further numerical ray trace. For systems of thin lenses in air, three second-order effects are identified and discussed using simple examples. A quantitative comparison with intrinsic secondary axial color is given. PMID:26479939
Second order perturbations during inflation beyond slow-roll
Huston, Ian; Malik, Karim A. E-mail: k.malik@qmul.ac.uk
2011-10-01
We numerically calculate the evolution of second order cosmological perturbations for an inflationary scalar field without resorting to the slow-roll approximation or assuming large scales. In contrast to previous approaches we therefore use the full non-slow-roll source term for the second order Klein-Gordon equation which is valid on all scales. The numerical results are consistent with the ones obtained previously where slow-roll is a good approximation. We investigate the effect of localised features in the scalar field potential which break slow-roll for some portion of the evolution. The numerical package solving the second order Klein-Gordon equation has been released under an open source license and is available for download.
Weak value amplification via second-order correlated technique
NASA Astrophysics Data System (ADS)
Ting, Cui; Jing-Zheng, Huang; Xiang, Liu; Gui-Hua, Zeng
2016-02-01
We propose a new framework combining weak measurement and second-order correlated technique. The theoretical analysis shows that weak value amplification (WVA) experiment can also be implemented by a second-order correlated system. We then build two-dimensional second-order correlated function patterns for achieving higher amplification factor and discuss the signal-to-noise ratio influence. Several advantages can be obtained by our proposal. For instance, detectors with high resolution are not necessary. Moreover, detectors with low saturation intensity are available in WVA setup. Finally, type-one technical noise can be effectively suppressed. Project supported by the Union Research Centre of Advanced Spaceflight Technology (Grant No. USCAST2013-05), the National Natural Science Foundation of China (Grant Nos. 61170228, 61332019, and 61471239), and the High-Tech Research and Development Program of China (Grant No. 2013AA122901).
Elasto-plastic model with second order defect density tensor
NASA Astrophysics Data System (ADS)
Cleja-Ţigoiu, Sanda
2011-05-01
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.
The Poisson equation at second order in relativistic cosmology
Hidalgo, J.C.; Christopherson, Adam J.; Malik, Karim A. E-mail: Adam.Christopherson@nottingham.ac.uk
2013-08-01
We calculate the relativistic constraint equation which relates the curvature perturbation to the matter density contrast at second order in cosmological perturbation theory. This relativistic ''second order Poisson equation'' is presented in a gauge where the hydrodynamical inhomogeneities coincide with their Newtonian counterparts exactly for a perfect fluid with constant equation of state. We use this constraint to introduce primordial non-Gaussianity in the density contrast in the framework of General Relativity. We then derive expressions that can be used as the initial conditions of N-body codes for structure formation which probe the observable signature of primordial non-Gaussianity in the statistics of the evolved matter density field.
Kubo Formulas for Second-Order Hydrodynamic Coefficients
Moore, Guy D.; Sohrabi, Kiyoumars A.
2011-03-25
At second order in gradients, conformal relativistic hydrodynamics depends on the viscosity {eta} and on five additional ''second-order'' hydrodynamical coefficients {tau}{sub {Pi}}, {kappa}, {lambda}{sub 1}, {lambda}{sub 2}, and {lambda}{sub 3}. We derive Kubo relations for these coefficients, relating them to equilibrium, fully retarded three-point correlation functions of the stress tensor. We show that the coefficient {lambda}{sub 3} can be evaluated directly by Euclidean means and does not in general vanish.
Reactions of allylic radicals that impact molecular weight growth kinetics.
Wang, Kun; Villano, Stephanie M; Dean, Anthony M
2015-03-01
The reactions of allylic radicals have the potential to play a critical role in molecular weight growth (MWG) kinetics during hydrocarbon oxidation and/or pyrolysis. Due to their stability (when compared to alkyl radicals), they can accumulate to relatively high concentrations. Thus, even though the rate coefficients for their various reactions are small, the rates of these reactions may be significant. In this work, we use electronic structure calculations to examine the recombination, addition, and abstraction reactions of allylic radicals. For the recombination reaction of allyl radicals, we assign a high pressure rate rule that is based on experimental data. Once formed, the recombination product can potentially undergo an H-atom abstraction reaction followed by unimolecular cyclization and β-scission reactions. Depending upon the conditions (e.g., higher pressures) these pathways can lead to the formation of stable MWG species. The addition of allylic radicals to olefins can also lead to MWG species formation. Once again, cyclization of the adduct followed by β-scission is an important energy accessible route. Since the recombination and addition reactions produce chemically-activated adducts, we have explored the pressure- and temperature-dependence of the overall rate constants as well as that for the multiple product channels. We describe a strategy for estimating these pressure-dependencies for systems where detailed electronic structure information is not available. We also derive generic rate rules for hydrogen abstraction reactions from olefins and diolefins by methyl and allyl radicals. PMID:25648200
NASA Technical Reports Server (NTRS)
Thron, R. P.; Daykin, E. P.; Wine, P.H.
1997-01-01
A laser flash photolysis-long path absorption technique has been employed to study the kinetics of the reaction BrO + NO2 + M yields (k1) products as a function of temperature (248-346 K), pressure (16-800 torr), and buffer gas identity (N2,CF4) The reaction is found to be in the falloff regime between third and second-order over the entire range of conditions investigated This is the first study where temperature-dependent measurements of k1(P,T) have been reported at pressures greater than 12 torr; hence, our results help constrain choices of k1(P,T) for use in models of lower stratospheric BrO(x) chemistry. Approximate falloff parameters in a convenient form for atmospheric modeling are derived.
Kinetic studies of Np(VI) reduction reactions with kojic acid and tropolone
Kim, W.
1987-01-01
To study the problems of potential migration of radionuclides from a nuclear waste repository, the Np(VI) reduction reactions with kojic acid and with tropolone were investigated at tracer level concentration of Np(VI). From results on the kinetic studies of these reactions, the NpO/sub 2//sup + +/ is reduced to the NpO/sub 2//sup +/ in a one-electron transfer process with no structural change of the dioxo neptunium species. The rates for both reactions are directly proportional to the total concentrations of Np(VI) ion and of oxidizing organic compounds: i.e., kojic acid or tropolone. However, the hydrogen ion dependence on the rate is inverse first-order for kojic acid and inverse second-order for tropolone. The Np(VI) reduction proceeds from the precursor complex via an activated complex and results in oxidation products from radicals formed in the rate-limiting step. The rate for the formation of Np(V) by kojic acid (k/sub 1/ = 6.06 +/- 0.30 sec/sup -1/) is faster than by tropolone (k/sub 1/ = 2.49 +/- 0.10 sec/sup -1/). The rate of reduction increases with the pK/sub a/ values (basicity) of the hydroxyl group in oxidizing organic compounds. The activation parameters for the Np(VI) reduction with kojic acid and tropolone have the same values within the uncertainties: i.e., ..delta..H/sup not equal to/ = 82.7 +/- 3.4 KJ/mol, ..delta..S/sup not equal to/ = 15 +/- 12 J/mol/deg for tropolone. Therefore, the Np(VI) reduction reaction occurs through the same mechanism in both reactions.
Kinetic measurements of hydrocarbon conversion reactions on model metal surfaces.
Wilson, Jarod; Guo, Hansheng; Morales, Ricardo; Podgornov, Egor; Lee, Ilkeun; Zaera, Francisco
2007-08-01
Examples from recent studies in our laboratory are presented to illustrate the main tools available to surface scientists for the determination of the kinetics of surface reactions. Emphasis is given here to hydrocarbon conversions and studies that rely on the use of model systems, typically single crystals and controlled (ultrahigh vacuum) environments. A detailed discussion is provided on the use of temperature-programmed desorption for the determination of activation energies as well as for product identification and yield estimations. Isothermal kinetic measurements are addressed next by focusing on studies under vacuum using molecular beams and surface-sensitive spectroscopies. That is followed by a review of the usefulness of high-pressure cells and other reactor designs for the emulation of realistic catalytic conditions. Finally, an analysis of the power of isotope labeling and chemical substitutions in mechanistic research on surface reactions is presented. PMID:17637975
Portable centrifugal analyzer for the determination of rapid reaction kinetics
Bostick, W.D.; Bauer, M.L.; McCracken, R.; Mrochek, J.E.
1980-02-01
A portable centrifugal analyzer prototype is capable of rapidly initiating reactions and monitoring 17 optical channels as they rotate past a stationary photodetector. An advanced rotor drive permits transfer of discretely loaded sample and reagent into a cuvette within 60 ms. Various rotor designs have been employed to ensure effieicnt mixing concurrent with solution transfer, thus permitting absorbance or luminescence measurements to be made almost immediately after solution contract. Dye-dillution studies have been used to investigate transfer and mixing efficiencies. Rotor designs with parallel access for sample and reagent into the cuvette were found to promote efficient mixing during liquid transfer. The hypochlorite-luminol chemiluminescent reaction served to demonstrate the utility of the system for performing rapid kinetic analyses. Appropriate adjustment of reaction conditions allows first-order reaction half-lives as short as 0.04 s to be measured. 13 figures, 3 tables.
Maximum Probability Reaction Sequences in Stochastic Chemical Kinetic Systems
Salehi, Maryam; Perkins, Theodore J.
2010-01-01
The detailed behavior of many molecular processes in the cell, such as protein folding, protein complex assembly, and gene regulation, transcription and translation, can often be accurately captured by stochastic chemical kinetic models. We investigate a novel computational problem involving these models – that of finding the most-probable sequence of reactions that connects two or more states of the system observed at different times. We describe an efficient method for computing the probability of a given reaction sequence, but argue that computing most-probable reaction sequences is EXPSPACE-hard. We develop exact (exhaustive) and approximate algorithms for finding most-probable reaction sequences. We evaluate these methods on test problems relating to a recently-proposed stochastic model of folding of the Trp-cage peptide. Our results provide new computational tools for analyzing stochastic chemical models, and demonstrate their utility in illuminating the behavior of real-world systems. PMID:21629860
Maximum Probability Reaction Sequences in Stochastic Chemical Kinetic Systems
Salehi, Maryam; Perkins, Theodore J.
2010-01-01
The detailed behavior of many molecular processes in the cell, such as protein folding, protein complex assembly, and gene regulation, transcription and translation, can often be accurately captured by stochastic chemical kinetic models. We investigate a novel computational problem involving these models – that of finding the most-probable sequence of reactions that connects two or more states of the system observed at different times. We describe an efficient method for computing the probability of a given reaction sequence, but argue that computing most-probable reaction sequences is EXPSPACE-hard. We develop exact (exhaustive) and approximate algorithms for finding most-probable reaction sequences. We evaluate these methods on test problems relating to a recently-proposed stochastic model of folding of the Trp-cage peptide. Our results provide new computational tools for analyzing stochastic chemical models, and demonstrate their utility in illuminating the behavior of real-world systems. PMID:21441987
Second-Order Conditioning of Human Causal Learning
ERIC Educational Resources Information Center
Jara, Elvia; Vila, Javier; Maldonado, Antonio
2006-01-01
This article provides the first demonstration of a reliable second-order conditioning (SOC) effect in human causal learning tasks. It demonstrates the human ability to infer relationships between a cause and an effect that were never paired together during training. Experiments 1a and 1b showed a clear and reliable SOC effect, while Experiments 2a…
Second-order phase transition in causal dynamical triangulations.
Ambjørn, Jan; Jordan, S; Jurkiewicz, J; Loll, R
2011-11-18
Causal dynamical triangulations are a concrete attempt to define a nonperturbative path integral for quantum gravity. We present strong evidence that the lattice theory has a second-order phase transition line, which can potentially be used to define a continuum limit in the conventional sense of nongravitational lattice theories. PMID:22181870
Modeling Ability Differentiation in the Second-Order Factor Model
ERIC Educational Resources Information Center
Molenaar, Dylan; Dolan, Conor V.; van der Maas, Han L. J.
2011-01-01
In this article we present factor models to test for ability differentiation. Ability differentiation predicts that the size of IQ subtest correlations decreases as a function of the general intelligence factor. In the Schmid-Leiman decomposition of the second-order factor model, we model differentiation by introducing heteroscedastic residuals,…
PREDICTIONS OF HIGHWAY EMISSIONS BY A SECOND ORDER CLOSURE MODEL
The dispersion of sulfur hexafluoride tracer and sulfate from automobile emissions in the immediate vicinity of a highway were estimated for conditions similar to those existing during the General Motors sulfate dispersion experiment conducted at a GM test track. A second-order c...
Forward and Backward Second-Order Pavlovian Conditioning in Honeybees
ERIC Educational Resources Information Center
Hussaini, Syed Abid; Komischke, Bernhard; Menzel, Randolf; Lachnit, Harald
2007-01-01
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…
Second-order variational equations for N-body simulations
NASA Astrophysics Data System (ADS)
Rein, Hanno; Tamayo, Daniel
2016-03-01
First-order variational equations are widely used in N-body simulations to study how nearby trajectories diverge from one another. These allow for efficient and reliable determinations of chaos indicators such as the Maximal Lyapunov characteristic Exponent (MLE) and the Mean Exponential Growth factor of Nearby Orbits (MEGNO). In this paper we lay out the theoretical framework to extend the idea of variational equations to higher order. We explicitly derive the differential equations that govern the evolution of second-order variations in the N-body problem. Going to second order opens the door to new applications, including optimization algorithms that require the first and second derivatives of the solution, like the classical Newton's method. Typically, these methods have faster convergence rates than derivative-free methods. Derivatives are also required for Riemann manifold Langevin and Hamiltonian Monte Carlo methods which provide significantly shorter correlation times than standard methods. Such improved optimization methods can be applied to anything from radial-velocity/transit-timing-variation fitting to spacecraft trajectory optimization to asteroid deflection. We provide an implementation of first and second-order variational equations for the publicly available REBOUND integrator package. Our implementation allows the simultaneous integration of any number of first and second-order variational equations with the high-accuracy IAS15 integrator. We also provide routines to generate consistent and accurate initial conditions without the need for finite differencing.
Solving Second-Order Differential Equations with Variable Coefficients
ERIC Educational Resources Information Center
Wilmer, A., III; Costa, G. B.
2008-01-01
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
A New Factorisation of a General Second Order Differential Equation
ERIC Educational Resources Information Center
Clegg, Janet
2006-01-01
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
Children's Understanding of Second-Order Mental States
ERIC Educational Resources Information Center
Miller, Scott A.
2009-01-01
The most popular topic in theory-of-mind research has been first-order false belief: the realization that it is possible to hold false beliefs about events in the world. A more advanced development is second-order false belief: the realization that it is possible to hold a false belief about someone else's belief. This article reviews research…
Solving Second-Order Differential Equations with Variable Coefficients
ERIC Educational Resources Information Center
Wilmer, A., III; Costa, G. B.
2008-01-01
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…
A New Factorisation of a General Second Order Differential Equation
ERIC Educational Resources Information Center
Clegg, Janet
2006-01-01
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…
Second-order accurate nonoscillatory schemes for scalar conservation laws
NASA Technical Reports Server (NTRS)
Huynh, Hung T.
1989-01-01
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.
Second-Order Conditioning during a Compound Extinction Treatment
ERIC Educational Resources Information Center
Pineno, Oskar; Zilski, Jessica M.; Schachtman, Todd R.
2007-01-01
Two conditioned taste aversion experiments with rats were conducted to establish if a target taste that had received a prior pairing with illness could be subject to second-order conditioning during extinction treatment in compound with a flavor that also received prior conditioning. In these experiments, the occurrence of second-order…
Generalized Second-Order Partial Derivatives of 1/r
ERIC Educational Resources Information Center
Hnizdo, V.
2011-01-01
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…
A stable second order method for training back propagation networks
NASA Technical Reports Server (NTRS)
Nachtsheim, Philip R.
1993-01-01
A simple method for improving the learning rate of the back-propagation algorithm is described. The basis of the method is that approximate second order corrections can be incorporated in the output units. The extended method leads to significant improvements in the convergence rate.
Second-order nonlinear optical metamaterials: ABC-type nanolaminates
Alloatti, L. Kieninger, C.; Lauermann, M.; Köhnle, K.; Froelich, A.; Wegener, M.; Frenzel, T.; Freude, W.; Leuthold, J.; Koos, C.
2015-09-21
We demonstrate a concept for second-order nonlinear metamaterials that can be obtained from non-metallic centrosymmetric constituents with inherently low optical absorption. The concept is based on iterative atomic-layer deposition of three different materials, A = Al{sub 2}O{sub 3}, B = TiO{sub 2}, and C = HfO{sub 2}. The centrosymmetry of the resulting ABC stack is broken since the ABC and the inverted CBA sequences are not equivalent—a necessary condition for non-zero second-order nonlinearity. In our experiments, we find that the bulk second-order nonlinear susceptibility depends on the density of interfaces, leading to a nonlinear susceptibility of 0.26 pm/V at a wavelength of 800 nm. ABC-type nanolaminates can be deposited on virtually any substrate and offer a promising route towards engineering of second-order optical nonlinearities at both infrared and visible wavelengths.
Modeling Ability Differentiation in the Second-Order Factor Model
ERIC Educational Resources Information Center
Molenaar, Dylan; Dolan, Conor V.; van der Maas, Han L. J.
2011-01-01
In this article we present factor models to test for ability differentiation. Ability differentiation predicts that the size of IQ subtest correlations decreases as a function of the general intelligence factor. In the Schmid-Leiman decomposition of the second-order factor model, we model differentiation by introducing heteroscedastic residuals,
Forward and Backward Second-Order Pavlovian Conditioning in Honeybees
ERIC Educational Resources Information Center
Hussaini, Syed Abid; Komischke, Bernhard; Menzel, Randolf; Lachnit, Harald
2007-01-01
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
High temperature heterogeneous reaction kinetics and mechanisms of tungsten oxidation
NASA Astrophysics Data System (ADS)
Sabourin, Justin L.
Tungsten, which is a material used in many high temperature applications, is limited by its susceptibility to oxidation at elevated temperatures. Although tungsten has the highest melting temperature of any metal, at much lower temperatures volatile oxides are formed during oxidation with oxygen containing species. This differs from many heterogeneous oxidation reactions involving metals since most reactions form very stable oxides that have higher melting or boiling points than the pure metal (e.g., aluminum, iron). Understanding heterogeneous oxidation and vaporization processes may allow for the expansion and improvement of high temperature tungsten applications. In order to increase understanding of the oxidation processes of tungsten, there is a need to develop reaction mechanisms and kinetics for oxidation processes involving oxidizers and environmental conditions of interest. Tungsten oxidation was thoroughly studied in the past, and today there is a good phenomenological understanding of these processes. However, as the design of large scale systems increasingly relies on computer modeling there becomes a need for improved descriptions of chemical reactions. With the increase in computing power over the last several decades, and the development of quantum chemistry and physics theories, heterogeneous systems can be modeled in detail at the molecular level. Thermochemical parameters that may not be measured experimentally may now be determined theoretically, a tool that was previously unavailable to scientists and engineers. Additionally, chemical kinetic modeling software is now available for both homogeneous and heterogeneous reactions. This study takes advantage of these new theoretical tools, as well as a thermogravimetric (TG) flow reactor developed as part of this study to learn about mechanisms and kinetics of tungsten oxidation. Oxidizers of interest are oxygen (O2), carbon dioxide (CO 2), water (H2O), and other oxidizers present in combustion and energy systems. The primary application for this research topic is the migration of erosion processes in solid rocket motor nozzles. Since oxidation is the primary erosion mechanism of tungsten based nozzles, mitigation of this process through improved comprehension of the chemical mechanisms will increase performance of future rocket systems. In this dissertation, results of the high temperature reaction rates of bulk tungsten are studied using TG analysis in oxidizing atmospheres of O2, CO2, and H2O using helium (He) as an inert carrier gas. Isothermal reaction rates were determined at temperatures up to 1970 K, and oxidizing species partial pressures up to 64.6 torr. Kinetic parameters such as activation energies, frequency factors, and pressure exponents were determined for each reactive system. An important contribution of this work was quantifying the effects of carbon monoxide (CO) on the CO2 reaction, and hydrogen (H2) on the H2O reaction. In both cases the non-oxidizing species significantly reduced oxidation rates. Results have led to new interpretations and thought processes for limiting nozzle erosion in rocket motors. Combined with the TG analysis, as well as recent theoretical interpretations of reaction thermodynamics and kinetics, a new mechanism for tungsten and O2 oxidation has been developed using a one-dimensional numerical model of the TG flow reactor. Important chemical processes and species are also identified for reaction systems involving H2O and CO2. In the future, additional studies are needed to improve our understanding of these chemical species and processes so that more advanced kinetic mechanisms may be developed. In addition to a detailed analysis of high temperature tungsten corrosion processes, synthetic graphite corrosion processes are studied in detail as well. Details of these studies are presented in an attached appendix of this dissertation. These studies considered not only oxidation processes, but decomposition of synthetic graphite in the presence of reducing and inert gas environments.
Electrochemically responsive heterogeneous catalysis for controlling reaction kinetics.
Mao, Xianwen; Tian, Wenda; Wu, Jie; Rutledge, Gregory C; Hatton, T Alan
2015-01-28
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
Characterization of hot hydrogen-atom reactions by kinetic spectrography.
NASA Technical Reports Server (NTRS)
Tomalesky, R. E.; Sturm, J. E.
1971-01-01
The flash photolysis of hydrogen iodide in the presence of nitrous oxide, carbon dioxide, and water has been investigated by kinetic spectroscopy. Although the fraction of hydrogen iodide dissociated was very large, the only observable intermediate was imidogen. It was demonstrated that the rapid removal of imidogen and the apparent absence of hydroxyl radicals in each case is a result of the following two reactions, respectively: (1) NH + HI yields NH2 + I; and (2) OH + HI yields H2O + I.
Cheng, Hanyang; Song, Dean; Liu, Huijuan; Qu, Jiuhui
2015-10-01
In this work, the fate of diclofenac (DCF) during permanganate (Mn(VII)) oxidation was investigated at environmentally relevant pH conditions (from 5 to 9). The batch experiments showed that the kinetics of the Mn(VII)/DCF reaction follows a second-order rate law with an apparent rate constant of 1.57±0.02 M(-1) s(-1) at pH 7 and 20 °C. The half-value of DCF was calculated to be 37.5 min, when the concentration of Mn(VII) (0.4 mM) was 20-fold excess of DCF. The pH-dependence of the reaction kinetics was investigated, and the DCF reactivity with Mn(VII) was found to decrease with increasing pH. The second-order rate constants were then quantitatively described by incorporating the species distribution of DCF. A lower reactivity of the anionic DCF (DCF(-)) in comparison with its neutral counterpart (DCF(0)) was most likely attributable to the interaction between the ionized carboxylate group and amine nitrogen position, which can reduce the nucleophilicity of amine nitrogen by inductive and resonance effects. Moreover, a range of degradation products and the corresponding structures were proposed on the basis of the LC-Q-TOF-MS analysis. A detailed ring-opening reaction mechanism was proposed as follows: Mn(VII) acts as an electrophile to attack the amine moiety, leading to the formation of the primary intermediate products 2,6-dichloroaniline and 5-hydroxy-diclofenac, which can be further transformed. The further degradation proceeded through a multistep process including ring-opening, decarboxylation, hydroxylation, and cyclation reactions. PMID:25522850
Kinetics of the reversible reaction of struvite crystallisation.
Crutchik, D; Garrido, J M
2016-07-01
The crystallisation of struvite could be a sustainable and economical alternative for recovering phosphorus from wastewater streams with high phosphate concentrations. Knowledge regarding the kinetics and thermodynamics that are involved in the crystallisation of struvite is the key to determine the optimal conditions for obtaining an efficient process. This study was conducted in a continuous stirred batch reactor. Different sets of experiments were performed in which struvite was either dissolved (undersaturated) or precipitated (oversaturated). These experiments were conducted at different temperatures (25, 30 and 35 °C) and pH values (8.2, 8.5 and 8.8) to determine the kinetics of struvite precipitation and dissolution. Struvite crystallisation was modelled as a reversible reaction. The kinetic rate parameters of struvite precipitation were 1.03·10(-4), 1.25·10(-4) and 1.54·10(-4) mol m(-2) min(-1) at 25, 30 and 35 °C, respectively. Similar kinetic rate parameters were determined for struvite dissolution. Struvite heterogeneous crystallisation can be represented by a first-order kinetic model that fitted well the experimental data. PMID:27085317
Second order optical nonlinearity in silicon by symmetry breaking
NASA Astrophysics Data System (ADS)
Cazzanelli, Massimo; Schilling, Joerg
2016-03-01
Although silicon does not possess a dipolar bulk second order nonlinear susceptibility due to its centro-symmetric crystal structure, in recent years several attempts were undertaken to create such a property in silicon. This review presents the different sources of a second order susceptibility (χ(2)) in silicon and the connected second order nonlinear effects which were investigated up to now. After an introduction, a theoretical overview discusses the second order nonlinearity in general and distinguishes between the dipolar contribution—which is usually dominating in non-centrosymmetric structures—and the quadrupolar contribution, which even exists in centro-symmetric materials. Afterwards, the classic work on second harmonic generation from silicon surfaces in reflection measurements is reviewed. Due to the abrupt symmetry breaking at surfaces and interfaces locally a dipolar second order susceptibility appears, resulting in, e.g., second harmonic generation. Since the bulk contribution is usually small, the study of this second harmonic signal allows a sensitive observation of the surface/interface conditions. The impact of covering films, strain, electric fields, and defect states at the interfaces was already investigated in this way. With the advent of silicon photonics and the search for ever faster electrooptic modulators, the interest turned to the creation of a dipolar bulk χ(2) in silicon. These efforts have been focussing on several experiments applying an inhomogeneous strain to the silicon lattice to break its centro-symmetry. Recent results suggesting the impact of electric fields which are exerted from fixed charges in adjacent covering layers are also included. After a subsequent summary on "competing" concepts using not Si but Si-related materials, the paper will end with some final conclusions, suggesting possible future research direction in this dynamically developing field.
Microdroplet fusion mass spectrometry for fast reaction kinetics
Lee, Jae Kyoo; Kim, Samuel; Nam, Hong Gil; Zare, Richard N.
2015-01-01
We investigated the fusion of high-speed liquid droplets as a way to record the kinetics of liquid-phase chemical reactions on the order of microseconds. Two streams of micrometer-size droplets collide with one another. The droplets that fused (13 μm in diameter) at the intersection of the two streams entered the heated capillary inlet of a mass spectrometer. The mass spectrum was recorded as a function of the distance x between the mass spectrometer inlet and the droplet fusion center. Fused droplet trajectories were imaged with a high-speed camera, revealing that the droplet fusion occurred approximately within a 500-μm radius from the droplet fusion center and both the size and the speed of the fused droplets remained relatively constant as they traveled from the droplet fusion center to the mass spectrometer inlet. Evidence is presented that the reaction effectively stops upon entering the heated inlet of the mass spectrometer. Thus, the reaction time was proportional to x and could be measured and manipulated by controlling the distance x. Kinetic studies were carried out in fused water droplets for acid-induced unfolding of cytochrome c and hydrogen–deuterium exchange in bradykinin. The kinetics of the former revealed the slowing of the unfolding rates at the early stage of the reaction within 50 μs. The hydrogen–deuterium exchange revealed the existence of two distinct populations with fast and slow exchange rates. These studies demonstrated the power of this technique to detect reaction intermediates in fused liquid droplets with microsecond temporal resolution. PMID:25775573
Reaction Path Optimization with Holonomic Constraints and Kinetic Energy Potentials
Brokaw, Jason B.; Haas, Kevin R.; Chu, Jhih-wei
2009-08-11
Two methods are developed to enhance the stability, efficiency, and robustness of reaction path optimization using a chain of replicas. First, distances between replicas are kept equal during path optimization via holonomic constraints. Finding a reaction path is, thus, transformed into a constrained optimization problem. This approach avoids force projections for finding minimum energy paths (MEPs), and fast-converging schemes such as quasi-Newton methods can be readily applied. Second, we define a new objective function - the total Hamiltonian - for reaction path optimization, by combining the kinetic energy potential of each replica with its potential energy function. Minimizing the total Hamiltonian of a chain determines a minimum Hamiltonian path (MHP). If the distances between replicas are kept equal and a consistent force constant is used, then the kinetic energy potentials of all replicas have the same value. The MHP in this case is the most probable isokinetic path. Our results indicate that low-temperature kinetic energy potentials (<5 K) can be used to prevent the development of kinks during path optimization and can significantly reduce the required steps of minimization by 2-3 times without causing noticeable differences between a MHP and MEP. These methods are applied to three test cases, the C₇eq-to-Cax isomerization of an alanine dipeptide, the ⁴C₁- to-¹C₄ transition of an α-D-glucopyranose, and the helix-to-sheet transition of a GNNQQNY heptapeptide. By applying the methods developed in this work, convergence of reaction path optimization can be achieved for these complex transitions, involving full atomic details and a large number of replicas (>100). For the case of helix-to-sheet transition, we identify pathways whose energy barriers are consistent with experimental measurements. Further, we develop a method based on the work energy theorem to quantify the accuracy of reaction paths and to determine whether the atoms used to define a path are enough to provide quantitative estimation of energy barriers.
Gilli, L.; Lathouwers, D.; Kloosterman, J. L.; Van Der Hagen, T. H. J. J.
2012-07-01
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)
Kinetic Studies on the Reaction between Dicyanocobinamide and Hypochlorous Acid
Maitra, Dhiman; Ali, Iyad; Abdulridha, Rasha M.; Shaeib, Faten; Khan, Sana N.; Saed, Ghassan M.; Pennathur, Subramaniam; Abu-Soud, Husam M.
2014-01-01
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
Modeling Large Zinc Isotope Fractionations Associated with Reaction Kinetics
NASA Astrophysics Data System (ADS)
Black, J. R.; John, S.; Kavner, A.
2009-12-01
Often multiple processes govern isotope fractionation during a chemical reaction, such as the mass-transport, equilibrium and reaction kinetics between reactants and products. Here we use experimental electrochemical techniques to control the mass-transport and reaction kinetics of the electrodeposition reaction: Zn2+ + 2e- = Zn(s); and model the isotopic fractionation measured to resolve the underlying mechanisms of fractionation. Zn was plated on a rotating disc electrode at various applied overpotentials, rotation rates and temperatures. Electroplated Zn was recovered in acid for analysis of the stable isotope composition by multi-collector ICP-MS. The isotopic composition (66Zn/64Zn) of plated metal is reported relative to the stock solution. A large range of Δ66Znsample-stock is observed, with increasing fractionation at higher rotation rates (Fig. 1A), and lower overpotentials (Fig. 1B). Models of electrochemical kinetics, show that these variables control the relative rates of precipitation and diffusion, as defined by the Koutecky-Levich equation [Bard and Faulkner (2001), Electrochemical Methods, John Wiley & Sons]. Using this equation to interpret our data shows that all the data fall along a systematic trend (Fig. 1C) with smaller fractionations in the mass-transport limited regime and larger fractionations produced under electrochemical kinetic control. We extend the Koutecky-Levich model to predict isotope fractionation during electrochemical processes as a function of mass-dependent diffusion (Fig. 2A); standard rate constant (Fig. 2B); and transfer coefficient, describing reaction barrier symmetry (Fig. 2C). A comparison of the model and our data shows that diffusive and equilibrium fractionation alone (Fig. 2A-B) cannot reproduce the trends in our data, but a mass-dependence in α can explain our observations. However, the predicted fractionation is very sensitive to the magnitude of k0 (Fig. 2C). This model predicts how isotope fractionation varies over a wide range of reaction rates, showing that the largest fractionations arise in a regime away from equilibrium and yet without mass-transport limitations. Fig 1. Zn isotope fractionation during electrodeposition Fig 2. Modeling Zn isotope fractionation at 25°C. A) diffusive control; B) equilibrium control; C) combined diffusion, equilibrium and electrochemical control.
Kinetics and Mechanisms of Calcite Reactions with Saline Waters
Gorman, Brian P
2015-09-02
Project Description: The general objective of the proposed research is to determine the kinetics and mechanisms of calcite reactions with saline waters over a wide range of saline water composition, pCO_{2}, and modest ranges in T and P. This will be accomplished by studying both reaction rates and solubility from changes in solution chemistry, and making nanoscale observations of calcite precipitate surface morphology and composition at the micro-to-nano-scale to provide an understanding of controlling reaction mechanisms and pathways. The specific objectives necessary to reach the general objective are: a) determination of how pCO_{2}, Ca^{2+}, ionic strength and “foreign” ions influence reaction rates; and b) investigate the influence of these parameters on apparent kinetic solubility from dissolution and precipitation reactions. This information will clearly be central to the construction of reliable reaction-transport models to predict reservoir and formation response to increased CO_{2} in saline waters. This program was initially collaborative with John Morse at Texas A&M, however his passing shortly after the beginning of this program resulted in abbreviated research time and effort. Summary of Results: Early studies using electron microscopy and spectroscopy indicated that carbonate precipitation from natural seawater (NSW) conditions onto aragonite substrates was mediated by a surface amorphous calcium carbonate layer. It was hypothesized that this ACC layer (observed after < 5days reaction time) was responsible for the abnormal reaction kinetics and also served as a metastable seed layer for growth of epitaxial aragonite. Further studies of the ACC formation mechanism indicated a strong dependence on the Mg concentration in solution. Subsequent studies at shorter times (10 hrs) on calcite substrates and in a wide range of supersaturation conditions did not indicate any ACC layer. Instead, an epitaxial layer by layer growth mechanism was confirmed by grazing incidence X-ray diffraction, µ-Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and electron diffraction. Extended time studies out to 45 days confirmed the epitaxial relationship of the overgrowth layer with the substrate. Under NSW conditions, overgrowths were found to have ~0.4 to 0.8 nm / hr growth rates and accommodating 4 at% Mg, resulting in a highly strained overgrowth layer. Following the initial layer by layer growth mechanism, the growth changes to Stranski-Krastanov type after a critical thickness of approximately 100 nm.
Reaction kinetics of the CN radical with methyl bromide
NASA Astrophysics Data System (ADS)
Hodny, Michael; Hershberger, John F.
2016-02-01
The kinetics of the CN + CH3Br reaction were studied using transient infrared laser absorption spectroscopy to detect CN reactants and HCN products. This reaction has a rate constant of k = (2.20 0.6) 10-12 exp (453 98/T) cm3 molecule-1 s-1 over the range 298-523 K. Hydrogen abstraction to produce HCN + CH2Br is only a minor reaction product, with a branching fraction of 0.12 0.02. Other product channels, including BrCN + CH3, CH2CN + HBr, CH3CN + Br are likely. An upper limit of 0.01 was established for the HBr yield. These results are in qualitative agreement with recent ab initio calculations.
Correction for instrument time constant in determination of reaction kinetics.
Chilton, Marie; Clark, Jared; Thomas, Nathan; Nicholson, Allen; Hansen, Lee D.; Hansen, Clifford W.; Hansen, Jaron
2010-02-01
Rates of reactions can be expressed as dn/dt = kcf(n) where n is moles of reaction, k is a rate constant, c is a proportionality constant, and f(n) is a function of the properties of the sample. When the instrument time constant, ?, and k are sufficiently comparable that measured rates are significantly affected by instrument response, correction for instrument response must be done to obtain accurate reaction kinetics. Correction for instrument response has previously been done by truncating early data or by use of the Tian equation. Both methods can lead to significant errors. We describe a method for simultaneous determination of ?, k, and c by fitting equations describing the combined instrument response and rate law to rates observed as a function of time. The method was tested with data on the heat rate from acid-catalyzed hydrolysis of sucrose.
Global stereo reconstruction under second-order smoothness priors.
Woodford, Oliver; Torr, Philip; Reid, Ian; Fitzgibbon, Andrew
2009-12-01
Second-order priors on the smoothness of 3D surfaces are a better model of typical scenes than first-order priors. However, stereo reconstruction using global inference algorithms, such as graph cuts, has not been able to incorporate second-order priors because the triple cliques needed to express them yield intractable (nonsubmodular) optimization problems. This paper shows that inference with triple cliques can be effectively performed. Our optimization strategy is a development of recent extensions to alpha -- expansion, based on the "QPBO" algorithm. The strategy is to repeatedly merge proposal depth maps using a novel extension of QPBO. Proposal depth maps can come from any source, for example, frontoparallel planes as in alpha-expansion, or indeed any existing stereo algorithm, with arbitrary parameter settings. PMID:19834135
Bounded solutions of a second order evolution equation and applications
NASA Astrophysics Data System (ADS)
Leiva, Hugo
2001-02-01
In this paper we study the following abstract second order differential equation with dissipation in a Hilbert space H: u?+cu'+dA u+kG(u)=P(t), u?H, t?R, where c, d and k are positive constants, G:H?H is a Lipschitzian function and P:R?H is a continuous and bounded function. A:D(A)?H?H is an unbounded linear operator which is self-adjoint, positive definite and has compact resolvent. Under these conditions we prove that for some values of d, c and k this system has a bounded solution which is exponentially asymptotically stable. Moreover; if P(t) is almost periodic, then this bounded solution is also almost periodic. These results are applied to a very well known second order system partial differential equations; such as the sine-Gordon equation, The suspension bridge equation proposed by Lazer and McKenna, etc.
First- and second-order charged particle optics
Brown, K.L.; Servranckx, R.V.
1984-07-01
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.
Symmetries of second-order PDEs and conformal Killing vectors
NASA Astrophysics Data System (ADS)
Tsamparlis, Michael; Paliathanasis, Andronikos
2015-06-01
We study the Lie point symmetries of a general class of partial differential equations (PDE) of second order. An equation from this class naturally defines a second-order symmetric tensor (metric). In the case the PDE is linear on the first derivatives we show that the Lie point symmetries are given by the conformal algebra of the metric modulo a constraint involving the linear part of the PDE. Important elements in this class are the Klein-Gordon equation and the Laplace equation. We apply the general results and determine the Lie point symmetries of these equations in various general classes of Riemannian spaces. Finally we study the type II hidden symmetries of the wave equation in a Riemannian space with a Lorenzian metric.
Analysis of the blazing effect in second-order gratings
Matsumoto, Masauki )
1992-10-01
The validity of the blazing effect for improving the output-coupling efficiency of second-order gratings for use in grating-coupled surface-emitting lasers is examined. The Floquet-Bloch expansion method is used for the analysis of finite-length gratings with asymmetric tooth shapes operated in resonance condition. It is shown that for saw-tooth gratings the blazing effect is almost lost around the second-order Bragg wavelength because the reflected guide mode generated in the distributed Bragg reflector radiates preferentially into the substrate. By using a parallelogram grating with equal tooth and groove lengths, however, a high efficiency of radiation into the air is attainable even at the Bragg wavelength while the reflectivity is reduced. 32 refs.
Second order modeling of boundary-free turbulent shear flows
NASA Technical Reports Server (NTRS)
Shih, T.-H.; Chen, Y.-Y.; Lumley, J. L.
1991-01-01
A set of realizable second order models for boundary-free turbulent flows is presented. The constraints on second order models based on the realizability principle are re-examined. The rapid terms in the pressure correlations for both the Reynolds stress and the passive scalar flux equations are constructed to exactly satisfy the joint realizability. All other model terms (return-to-isotropy, third moments, and terms in the dissipation equations) already satisfy realizability. To correct the spreading rate of the axisymmetric jet, an extra term is added to the dissipation equation which accounts for the effect of mean vortex stretching on dissipation. The test flows used in this study are the mixing shear layer, plane jet, axisymmetric jet, and plane wake. The numerical solutions show that the unified model equations predict all these flows reasonably. It is expected that these models would be suitable for more complex and critical flows.
A Second-Order Achromat Design Based on FODO Cell
Sun, Yipeng; /SLAC
2011-08-19
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.
Second-order closure models for supersonic turbulent flows
NASA Technical Reports Server (NTRS)
Speziale, Charles G.; Sarkar, Sutanu
1991-01-01
Recent work on the development of a second-order closure model for high-speed compressible flows is reviewed. This turbulent closure is based on the solution of modeled transport equations for the Favre-averaged Reynolds stress tensor and the solenoidal part of the turbulent dissipation rate. A new model for the compressible dissipation is used along with traditional gradient transport models for the Reynolds heat flux and mass flux terms. Consistent with simple asymptotic analyses, the deviatoric part of the remaining higher-order correlations in the Reynolds stress transport equations are modeled by a variable density extension of the newest incompressible models. The resulting second-order closure model is tested in a variety of compressible turbulent flows which include the decay of isotropic turbulence, homogeneous shear flow, the supersonic mixing layer, and the supersonic flat-plate turbulent boundary layer. Comparisons between the model predictions and the results of physical and numerical experiments are quite encouraging.
On the second order spatiochromatic structure of natural images.
Provenzi, Edoardo; Delon, Julie; Gousseau, Yann; Mazin, Baptiste
2016-03-01
We provide a theoretical analysis of some empirical facts about the second order spatiochromatic structure of natural images in color. In particular, we show that two simple assumptions on the covariance matrices of color images yield eigenvectors made by the Kronecker product of Fourier features times the triad given by luminance plus color opponent channels. The first of these assumptions is second order stationarity while the second one is commutativity between color correlation matrices. The validity of these assumptions and the predicted shape of the PCA components of color images are experimentally observed on two large image databases. As a by-product of this experimental study, we also provide novel data to support an exponential decay law of the spatiochromatic covariance between pairs of pixels as a function of their spatial distance. PMID:26024561
Quantum degradation of a second-order phase transition
NASA Astrophysics Data System (ADS)
Stishov, S. M.; Petrova, A. E.; Gavrilkin, S. Yu.; Klinkova, L. A.
2015-04-01
The specific heat, magnetization, and thermal expansion of single crystals of the antiferromagnetic insulator EuTe, measured at temperatures down to 2 K and in magnetic fields up to 90 kOe, demonstrate nontrivial properties. The Néel temperature, being ˜9.8 at H =0 , decreases with magnetic field and tends to zero at ˜76 kOe , therefore forming a quantum critical point. The heat capacity and thermal expansion coefficient reveal λ -type anomalies at the second order magnetic phase transition at low magnetic fields, evolving into simple jumps at high magnetic fields and low temperatures; these are well described in a fluctuation-free mean-field theory. The experimental data and the corresponding analysis favor the quantum concept of an effective increase in spatial dimensionality at low temperatures that suppresses a fluctuation-driven divergence at a second-order phase transition.
Optimal second order sliding mode control for linear uncertain systems.
Das, Madhulika; Mahanta, Chitralekha
2014-11-01
In this paper an optimal second order sliding mode controller (OSOSMC) is proposed to track a linear uncertain system. The optimal controller based on the linear quadratic regulator method is designed for the nominal system. An integral sliding mode controller is combined with the optimal controller to ensure robustness of the linear system which is affected by parametric uncertainties and external disturbances. To achieve finite time convergence of the sliding mode, a nonsingular terminal sliding surface is added with the integral sliding surface giving rise to a second order sliding mode controller. The main advantage of the proposed OSOSMC is that the control input is substantially reduced and it becomes chattering free. Simulation results confirm superiority of the proposed OSOSMC over some existing. PMID:25249166
Mechanisms and kinetics of reaction-bonded aluminium oxide ceramics
Wu, Suxing; Holz, D.; Claussen, N. . Advanced Ceramics Group)
1993-04-01
Reaction-bonded Al[sub 2]O[sub 3] (RBAO) ceramics were fabricated starting from mechanically alloyed Al[sub 2]O[sub 3]/Al, Al[sub 2]O[sub 3]/Al/ZrO[sub 2], and Al[sub 2]O[sub 3]/Al/ZrO[sub 2]/Zr mixtures. Isopressed compacts were heat-treated in air up to 1,550 C. Reaction-bonding mechanisms, kinetics, and the influence of ZrO[sub 2] and Zr additions are investigated. Independent of additive, oxidation of Al proceeds both as solid/gas and liquid/gas reaction, and the reaction kinetics follow a parabolic rate law. The reaction rate depends strongly on the particle size of Al. The activation energy of the reaction depends essentially on green density. Below the melting temperature of Al, in samples containing 45 vol% Al and 55 vol% Al[sub 2]O[sub 3], it is 112 and 152 kJ/mol at [approximately]64% and [approximately]74% TD, respectively, while above the melting temperature, it lies in the range [approximately]26--33 kJ/mol. Zr additions reduce the activation energy to some extent. Samples with only ZrO[sub 2] additions exhibit nearly the same activation energies as ZrO[sub 2]-free samples, though ZrO[sub 2] has a very positive effect on the microstructural development in RBAO ceramics. Microstructure evolution and some strength data of RBAO bodies are also reported.
Extensions and applications of a second-order landsurface parameterization
NASA Technical Reports Server (NTRS)
Andreou, S. A.; Eagleson, P. S.
1983-01-01
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.
Gravitational waves from global second order phase transitions
Jr, John T. Giblin; Price, Larry R.; Siemens, Xavier; Vlcek, Brian E-mail: larryp@caltech.edu E-mail: bvlcek@uwm.edu
2012-11-01
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.
Asymptotic Dynamics of Second Order Nonautonomous Systems on Infinite Lattices
NASA Astrophysics Data System (ADS)
Abdallah, Ahmed Y.
We have introduced abstract sufficient conditions for the existence of a uniform exponential attractor for a special family of second order nonautonomous lattice dynamical systems with quasiperiodic symbols in a standard space of infinite sequences. Compared with the lattice dynamical system in [Zhou & Zhao, 2014], here a generalized nonlinear part and weaker assumptions have been presented, kindly see Remark Remark 2.1 for more details.
Second order filter response with series coupled silica microresonators
NASA Technical Reports Server (NTRS)
Savchenkov, A.; Iitchenko, V. S.; Handley, T.; Maleki, L.
2002-01-01
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.
NO sub x -char reactions: Kinetics and transport aspects
Calo, J.M.; Suuberg, E.M.
1990-01-01
The present project is motivated by the need to reduce NO{sub x} emissions from combustors, especially coal combustors. Reactions with carbon are known to be effective at reducing No to N{sub 2}, and remain interesting candidates in a wide variety of possible applications. These reactions are known to be important in reducing NO{sub x} emissions from fluidized bed coal combustors, in which the coal char itself serves as the reducing agent. The principal goal of this project is to develop a mechanistic understanding of the processes by which carbons reduce NO to N{sub 2}. The carbon was a char derived from phenol-formaldehyde resin. This material has been noted to be a reasonable model for coal chars in most respects, expect that its gasification behavior is not complicated by catalytic processes due to minerals. In the first phases of the project, the global kinetics of the process were established. In more recent work, attention has been turned to the individual steps in the mechanism. Recent quarterly reports have detailed the role of both chemisorption and desorption processes in determining the course and kinetics of the process. This report continues the reporting of results obtained along these lines, and draws an important new conclusion concerning the number of separate processes involved in determining the kinetics. 40 refs., 3 figs., 2 tabs.
Full-sky lensing shear at second order
Bernardeau, Francis; Bonvin, Camille; Vernizzi, Filippo
2010-04-15
We compute the reduced cosmic shear up to second order in the gravitational potential without relying on the small-angle or thin-lens approximation. This is obtained by solving the Sachs equation which describes the deformation of the infinitesimal cross section of a light bundle in the optical limit, and maps galaxy intrinsic shapes into their angular images. The calculation is done in the Poisson gauge without a specific matter content, including vector and tensor perturbations generated at second order and taking account of the inhomogeneities of a fixed redshift source plane. Our final result is expressed in terms of spin-2 operators on the sphere and is valid on the full sky. Beside the well-known lens-lens and Born corrections that dominate on small angular scales, we find new nonlinear couplings. These are a purely general relativistic intrinsic contribution, a coupling between the gravitational potential at the source with the lens, couplings between the time delay with the lens and between two photon deflections, as well as nonlinear couplings due to the second-order vector and tensor components. The inhomogeneity in the redshift of the source induces a coupling between the photon redshift with the lens. All these corrections become important on large angular scales and should thus be included when computing higher-order observables such as the bispectrum, in full or partially full-sky surveys.
Second-order reconstruction of the inflationary potential
NASA Technical Reports Server (NTRS)
Liddle, Andrew R.; Turner, Michael S.
1994-01-01
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.
NASA Astrophysics Data System (ADS)
Kipriyanov, Alexander A.; Kipriyanov, Alexey A.; Doktorov, Alexander B.
2010-11-01
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.
Local kinetics and thermodynamics of rapid electrochemical reactions
NASA Astrophysics Data System (ADS)
Přibyl, Michal; Šnita, Dalimil
2014-04-01
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.
Kinetics and deuterium kinetic isotope effects in 3,3- and 2,3-sigmatropic reactions
Emrani, J.
1985-01-01
In previous work, Conrad, using ..cap alpha..-2/sup 0/ deuterium kinetic isotope effects (KIE), showed that variable transition states are involved in Cope and Claisen rearrangements, two groups of sigmatropic reactions. The variation could be understood in terms of substituents affecting the relative extents of bond making and bond breaking. The kinetics and KIEs have now been determined for rearrangements of allyl trimethyl silyl ketene actal (TMS-KA), diisopropyl allylamine-oxide (diamo), and 1,3- and 1,4-diphenyl-1,5-hexadienes. Measurements of KIE in the reaction of TMS-KA and diamo, have shown that the transition state of both these reactions involve much more bond breaking than bond making. Solvent and phenyl substituent effects have been measured for TMS-KA, and these verify a non-polar reaction with substantial bond cleavage. The origin of the behavior is discussed. Measurements of the activation free energies for Cope rearrangement of 1,3- and 1,4-diphenyl-1,5-hexadienes reveal parameters similar to that of 3-phenyl-1,5-hexadiene. The values are consistent with a theoretical model developed for substituent effects in these reactions.
A study of switchgrass pyrolysis: Product variability and reaction kinetics
NASA Astrophysics Data System (ADS)
Bovee, Jonathan Matthew
Samples of the same cultivar of cave-in-rock switchgrass were harvested from plots in Frankenmuth, Roger City, Cass County, and Grand Valley, Michigan. It was determined that variation exists, between locations, among the pyrolytic compounds which can lead to variability in bio-oil and increased processing costs at bio-refineries to make hydrocarbon fuels. Washed and extractives-free switchgrass samples, which contain a lower alkali and alkaline earth metals content than untreated samples, were shown to produce lower amounts of acids, esters, furans, ketones, phenolics, and saccharides and also larger amounts of aldehydes upon pyrolysis. Although the minerals catalyzed pyrolytic reactions, there was no evidence indicating their effect on reducing the production of anhydrosugars, specifically levoglucosan. To further link minerals present in the biomass to a catalytic pathway, mathematic models were employed to determine the kinetic parameters of the switchgrass. While the calculated activation energies of switchgrass, using the FWO and KAS methods, were 227.7 and 217.8 kJ/mol, correspondingly, it was concluded that the activation energies for the switchgrass hemicellulose and cellulose peaks were 115.5 and 158.2 kJ/mol, respectively, using a modified model-fitting method. The minerals that effect the production of small molecules and levoglucosan also have an observable catalytic effect on switchgrass reaction rate, which may be quantifiable through the use of reaction kinetics so as to determine activation energy.
Classic reaction kinetics can explain complex patterns of antibiotic action.
Abel Zur Wiesch, Pia; Abel, Sören; Gkotzis, Spyridon; Ocampo, Paolo; Engelstädter, Jan; Hinkley, Trevor; Magnus, Carsten; Waldor, Matthew K; Udekwu, Klas; Cohen, Ted
2015-05-13
Finding optimal dosing strategies for treating bacterial infections is extremely difficult, and improving therapy requires costly and time-intensive experiments. To date, an incomplete mechanistic understanding of drug effects has limited our ability to make accurate quantitative predictions of drug-mediated bacterial killing and impeded the rational design of antibiotic treatment strategies. Three poorly understood phenomena complicate predictions of antibiotic activity: post-antibiotic growth suppression, density-dependent antibiotic effects, and persister cell formation. We show that chemical binding kinetics alone are sufficient to explain these three phenomena, using single-cell data and time-kill curves of Escherichia coli and Vibrio cholerae exposed to a variety of antibiotics in combination with a theoretical model that links chemical reaction kinetics to bacterial population biology. Our model reproduces existing observations, has a high predictive power across different experimental setups (R(2) = 0.86), and makes several testable predictions, which we verified in new experiments and by analyzing published data from a clinical trial on tuberculosis therapy. Although a variety of biological mechanisms have previously been invoked to explain post-antibiotic growth suppression, density-dependent antibiotic effects, and especially persister cell formation, our findings reveal that a simple model that considers only binding kinetics provides a parsimonious and unifying explanation for these three complex, phenotypically distinct behaviours. Current antibiotic and other chemotherapeutic regimens are often based on trial and error or expert opinion. Our "chemical reaction kinetics"-based approach may inform new strategies, which are based on rational design. PMID:25972005
Kinetics and mechanisms of reactions involving small aromatic reactive intermediates
Lin, M.C.
1993-12-01
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.
Kinetics of the reaction of hydroxyl radicals with nitric acid
NASA Technical Reports Server (NTRS)
Margitan, J. J.; Watson, R. T.
1982-01-01
An extensive study was made of the reaction of hydroxyl radicals with nitric acid in a laser photolysis-resonance fluorescence system. A 266 nm laser was used to photolyze HNO3 in the temperature range 225-415 K at pressures of 20-300 torr. A temperature dependence was detected below room temperature, with a leveling off at 298 K and a wide spread in the rate constants. A pressure dependence was observed over the entire range and was more pronounced at lower temperatures. The results are noted to be in agreement with those of previous investigations. However, the wide range of rate constants are suggested to be a problem for stratospheric HO(x) modeling for anthropogenic effects. No explanation could be given of the varying results obtained by other investigators regarding the kinetics of the reactions.
Determination of robust stability margin for second-order systems
NASA Technical Reports Server (NTRS)
Chuang, C.-H.; Kau, C.-T.; Juang, Jer-Nan
1992-01-01
Robust stabilization of uncertain systems has been extensively investigated and the stability test for the whole set of uncertain parameters has been reduced to a finite number of test points, four points for the characteristic polynomial with independent coefficients. As a result the robust stability margin can be determined using a reasonable amount of computation. It is impossible to apply the results of the test to a practical system as the coefficients of the characteristic polynomial for a physical system are usually functions of uncertain parameters. However, many physical systems may be represented by a second-order mass-spring-damper system with a special multilinear form in its characteristic polynomial. This paper investigates second-order mass-spring-damper systems and the reduction of the number of test points. It is shown that such a system with arbritrary compensators always has a multilinear characteristic polynomial. It is also shown that a line in the two-dimensional parameter space forms the boundary after the mapping of a multilinear characteristic polynomial and this interior extreme line forms a conic curve in the complex plane. The boundary of uncertain domain for a multilinear polynomial with two uncertainty parameters can be determined analytically using this curve, and the four sides image of a square of the uncertain parameter. Therefore, the stability margin may be determined by checking the intersections of the boundary with the zero point. A similar procedure can be used for second-order systems with more than two uncertainty parameters when parameter optimization is used in determining the boundary.
P-stable boundary value methods for second order IVPs
NASA Astrophysics Data System (ADS)
Aceto, Lidia; Ghelardoni, Paolo; Magherini, Cecilia
2012-09-01
We introduce a family of Linear Multistep Methods used as Boundary Value Methods for the numerical solution of initial value problems for second order ordinary differential equations of special type. The aim is to obtain P-stable methods with arbitrary order of accuracy. This result allows to overcome the order barrier established by Lambert and Watson which limited to p = 2 the maximum order of a P-stable Linear Multistep Method. In addition, an extension of the methods in the Exponential Fitting framework is also considered.
Time regularity of the solutions to second order hyperbolic equations
NASA Astrophysics Data System (ADS)
Kinoshita, Tamotu; Taglialatela, Giovanni
2011-04-01
We consider the Cauchy problem for a second order weakly hyperbolic equation, with coefficients depending only on the time variable. We prove that if the coefficients of the equation belong to the Gevrey class ?^{s0} and the Cauchy data belong to ?^{s1}, then the Cauchy problem has a solution in ?^{s0}([0,T^{*}];?^{s1}({R})) for some T *>0, provided 1? s 1?2-1/ s 0. If the equation is strictly hyperbolic, we may replace the previous condition by 1? s 1? s 0.
Galaxy number counts to second order and their bispectrum
Dio, Enea Di; Durrer, Ruth; Marozzi, Giovanni; Montanari, Francesco E-mail: Ruth.Durrer@unige.ch E-mail: Francesco.Montanari@unige.ch
2014-12-01
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.
Stochastic systems with delay: Perturbation theory for second order statistics
NASA Astrophysics Data System (ADS)
Frank, T. D.
2016-03-01
Within the framework of delay Fokker-Planck equations, a perturbation theoretical method is developed to determine second-order statistical quantities such as autocorrelation functions for stochastic systems with delay. Two variants of the perturbation theoretical approach are presented. The first variant is based on a non-local Fokker-Planck operator. The second variant requires to solve a Fokker-Planck equation with source term. It is shown that the two variants yield consistent results. The perturbation theoretical approaches are applied to study negative autocorrelations that are induced by feedback delays and mediated by the strength of the fluctuating forces that act on the feedback systems.
Universality in the Dynamics of Second-Order Phase Transitions.
Nikoghosyan, G; Nigmatullin, R; Plenio, M B
2016-02-26
When traversing a symmetry-breaking second-order phase transition at a finite rate, topological defects form whose number dependence on the quench rate is given by simple power laws. We propose a general approach for the derivation of such scaling laws that is based on the analytical transformation of the associated equations of motion to a universal form rather than employing plausible physical arguments. We demonstrate the power of this approach by deriving the scaling of the number of topological defects in both homogeneous and nonhomogeneous settings. The general nature and extensions of this approach are discussed. PMID:26967403
Octonic second-order equations of relativistic quantum mechanics
Mironov, Victor L.; Mironov, Sergey V.
2009-01-15
We demonstrate a generalization of relativistic quantum mechanics using eight-component value ''octons'' that generate an associative noncommutative spatial algebra. It is shown that the octonic second-order equation for the eight-component octonic wave function, obtained from the Einstein relation for energy and momentum, describes particles with spin 1/2. It is established that the octonic wave function of a particle in the state with defined spin projection has a specific spatial structure that takes the form of an octonic oscillator with two spatial polarizations: longitudinal linear and transverse circular.
Supersonic second order analysis and optimization program user's manual
NASA Technical Reports Server (NTRS)
Clever, W. C.
1984-01-01
Approximate nonlinear inviscid theoretical techniques for predicting aerodynamic characteristics and surface pressures for relatively slender vehicles at supersonic and moderate hypersonic speeds were developed. Emphasis was placed on approaches that would be responsive to conceptual configuration design level of effort. Second order small disturbance theory was utilized to meet this objective. Numerical codes were developed for analysis and design of relatively general three dimensional geometries. Results from the computations indicate good agreement with experimental results for a variety of wing, body, and wing-body shapes. Case computational time of one minute on a CDC 176 are typical for practical aircraft arrangement.
Universality in the Dynamics of Second-Order Phase Transitions
NASA Astrophysics Data System (ADS)
Nikoghosyan, G.; Nigmatullin, R.; Plenio, M. B.
2016-02-01
When traversing a symmetry-breaking second-order phase transition at a finite rate, topological defects form whose number dependence on the quench rate is given by simple power laws. We propose a general approach for the derivation of such scaling laws that is based on the analytical transformation of the associated equations of motion to a universal form rather than employing plausible physical arguments. We demonstrate the power of this approach by deriving the scaling of the number of topological defects in both homogeneous and nonhomogeneous settings. The general nature and extensions of this approach are discussed.
Optimal automatic reaction and species elimination in kinetic mechanisms
Mitsos, A.
2008-10-15
A known challenge for the simulation of reacting flow systems is that detailed chemical mechanisms contain hundreds to thousands of species and thousands of reactions, leading to high CPU requirements despite the use of state-of-the-art solvers. For specific conditions of interest (temperature, pressure, and composition), smaller mechanisms can predict the chemistry relatively accurately. One possibility for obtaining such mechanisms is species elimination from a detailed mechanism. Here, an automatic method for kinetic model reduction by simultaneous reaction and species elimination is proposed, based on an integer linear program (ILP) formulation. The solution of the ILP is an optimally reduced kinetic mechanism that reproduces the predictions of a reference mechanism within prespecified tolerances for finitely many reference points in the state space. The method is applied to generate optimally reduced models for isobaric, adiabatic homogeneous combustion. Case studies are presented for the combustion of n-heptane. Comparisons between the full and reduced models are shown and the tradeoff between species and reaction elimination is discussed. Tolerances in the ILP formulation control the error introduced by the model reduction. For increasing acceptable error, more species and/or reactions are eliminated. A method of quantifying this tradeoff between approximation error and reduction achieved is proposed, based on multiobjective optimization, and demonstrated in a case study. The effect of variable initial conditions is investigated. The mechanisms generated achieve significant reduction in the CPU requirement and can accurately predict the trajectories of the state variables (species mass fractions and temperature), as well as other metrics of interest, such as ignition time delay. (author)
Wang, Hongyu; Liu, Yibing; Jiang, Jia-Qian
2016-07-01
This paper investigates the degradation of acetaminophen (AAP) in aqueous solutions by ferrate (VI), aiming to propose the kinetics, pathways and the oxidation products' formation in the AAP degradation. A series of jar tests were undertaken over ferrate (VI) dosages (molar ratios of ferrate (VI):AAP, 5:1 to 25:1) and pH values (4-11). The effects of co-existing ions (0.2-5 mM) and humic acid (10-50 mg l(-1)) on the AAP removal were investigated. Ferrate (VI) can remove 99.6% AAP (from 1000 μg l(-1)) in 60 min under study conditions when majority of the AAP reduction occurred in the first 5 min. The treatment performance depended on the ferrate(VI) dosage, pH and the type and strength of co-existing ions and humic acid. Raising ferrate (VI) dosage with optimal pH 7 improved the AAP degradation. In the presence of humic acid, the AAP degradation by ferrate (VI) was promoted in a short period (<30 min) but then inhibited with increasing in humic acid contents. The presence of Al(3+), CO3(2-) and PO4(3-) ions declined but the existence of K(+), Na(+), Mg(2+) and Ca(2+) ions can improve the AAP removal. The catalytic function of Al(3+) on the decomposition of ferrate (VI) in aqueous solution was found. The kinetics of the reaction between ferrate (VI) and AAP was pseudo first-order for ferrete (VI) and pseudo second-order for AAP. The pseudo rate constant of ferrate (VI) with AAP was 1.4 × 10(-5) L(2) mg(-2) min(-1). Three oxidation products (OPs) were identified and the AAP degradation pathways were proposed. PMID:27155474
NASA Technical Reports Server (NTRS)
Liechty, Derek S.; Lewis, Mark J.
2010-01-01
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.
Dodd, Michael C; Buffle, Marc-Olivier; Von Gunten, Urs
2006-03-15
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
Kinetic studies of the hydroxyl radical reaction with PAHs
NASA Astrophysics Data System (ADS)
Ananthula, Rajeshwar
An existing quartz optical reactor heating system was designed to permit higher temperature kinetic measurements more closely associated with post-combuston conditions (up to 1200 K). A pulsed laser photolysis/pulsed laser-induced fluorescence (PLP/PLIF) technique was then applied with this modified reactor to study the OH radical kinetics with polycyclic aromatic hydrocarbons (PAHs). The kinetics of the reaction of a surrogate three-ring PAH, anthracene (and its deuterated form) with hydroxyl (OH) radicals was investigated over the temperature range of 373 to 1200 K. This study represents the first examination of the OH kinetics for this class of reactions at elevated temperatures (>470 K). The results indicate a complex temperature dependence similar to that observed for simpler aromatic compounds, e.g., benzene. At low temperatures (373-498 K), the rate measurements exhibited Arrhenius behavior (1.82 x 10-11 exp(542.35/T) in units of cm3 molecule -1 s-1) and kinetic isotope effect (KIE) measurements were consistent with an OH addition mechanism. The low temperature results are extrapolated to atmospheric temperatures and compared with previous measurements. Rate measurements between 673 and 923 K exhibited a sharp decrease in the magnitude of the rate coefficients (a factor of 9). KIE measurements under these conditions were still consistent with an OH addition mechanism. The following modified Arrhenius equation is the best fit to our anthracene measurements between 373 and 923 K, 8.17 x 1014 T-8.3 exp(-3171.71/T) (in units of cm3 molecule-1 s-1). For a limited temperature range between 1000 and 1200 K, the rate measurements exhibited an apparent positive temperature dependence with the following Arrhenius equation the best fit to the data, 2.18 x 10-11*exp(-1734.11/T) (in units of cm3molecule-1s -1). KIE measurements above 999 K were slightly larger than unity, but inclusive regarding the mechanism of the reaction. Theoretical calculations of the KIE indicate the mechanism of reaction at these elevated temperatures is dominated by OH addition with H abstraction a minor contributor. The OH kinetic study was extended to the three-ring PAH, phenanthrene, (an isomer of anthracene) and its deuterated form. The rate measurements between 373 and 1000 K were best fit by the modified Arrhenius expression, 1.68 x 10-4 * T-2.46 * exp (-228.31/T) (in units of cm3molecule-1s-1). KIE measurements for phenanthrene indicated that the OH addition pathway dominated at temperature below 1000 K, in agreement with the anthracene results. The rate measurements on three ring PAHs are compared with available one and two ring PAHs to understand the effect of increasing molecule size on PAH reactivity with hydroxyl radicals.
Classic reaction kinetics can explain complex patterns of antibiotic action
zur Wiesch, P. Abel; Abel, S.; Gkotzis, S.; Ocampo, P.; Engelstädter, J.; Hinkley, T.; Magnus, C.; Waldor, M. K.; Udekwu, K.; Cohen, T.
2015-01-01
Finding optimal dosing strategies for treating bacterial infections is extremely difficult, and improving therapy requires costly and time-intensive experiments. To date, an incomplete mechanistic understanding of drug effects has limited our ability to make accurate quantitative predictions of drug-mediated bacterial killing and impeded the rational design of antibiotic treatment strategies. Three poorly understood phenomena complicate predictions of antibiotic activity: post-antibiotic growth suppression, density-dependent antibiotic effects, and persister cell formation. Here, we show that chemical binding kinetics alone are sufficient to explain these three phenomena, using single cell data and time-kill curves of Escherichia coli and Vibrio cholerae exposed to a variety of antibiotics in combination with a theoretical model that links chemical reaction kinetics to bacterial population biology. Our model reproduces existing observations, has a high predictive power across different experimental setups (R2= 0.86), and makes several testable predictions, which we verified in new experiments and by analysing published data from a clinical trial on tuberculosis therapy. While a variety of biological mechanisms have previously been invoked to explain post-antibiotic growth suppression, density-dependent antibiotic effects, and especially persister cell formation, our findings reveal that a simple model which considers only binding kinetics provides a parsimonious and unifying explanation for these three complex, phenotypically distinct behaviours. Current antibiotic and other chemotherapeutic regimens are often based on trial-and-error or expert opinion. Our ‘chemical reaction kinetics’-based approach may inform new strategies, that are based on rational design. PMID:25972005
Second-order analytic solutions for re-entry trajectories
NASA Astrophysics Data System (ADS)
Kim, Eun-Kyou
1993-01-01
With the development of aeroassist technology, either for near-earth orbital transfer with or without a plane change or for planetary aerocapture, it is of interest to have accurate analytic solutions for reentry trajectories in an explicit form. Starting with the equations of motion of a non-thrusting aerodynamic vehicle entering a non-rotating spherical planetary atmosphere, a normalization technique is used to transform the equations into a form suitable for an analytic integration. Then, depending on the type of planar entry modes with a constant angle-of-attack, namely, ballistic fly-through, lifting skip, and equilibrium glide trajectories, the first-order solutions are obtained with the appropriate simplification. By analytic continuation, the second-order solutions for the altitude, speed, and flight path angle are derived. The closed form solutions lead to explicit forms for the physical quantities of interest, such as the deceleration and aerodynamic heating rates. The analytic solutions for the planar case are extended to three-dimensional skip trajectories with a constant bank angle. The approximate solutions for the heading and latitude are developed to the second order. In each type of trajectory examined, explicit relations among the principal variables are in a form suitable for guidance and navigation purposes. The analytic solutions have excellent agreement with the numerical integrations. They also provide some new results which were not reported in the existing classical theory.
A-posteriori error estimation for second order mechanical systems
NASA Astrophysics Data System (ADS)
Ruiner, Thomas; Fehr, Jörg; Haasdonk, Bernard; Eberhard, Peter
2012-06-01
One important issue for the simulation of flexible multibody systems is the reduction of the flexible bodies degrees of freedom. As far as safety questions are concerned knowledge about the error introduced by the reduction of the flexible degrees of freedom is helpful and very important. In this work, an a-posteriori error estimator for linear first order systems is extended for error estimation of mechanical second order systems. Due to the special second order structure of mechanical systems, an improvement of the a-posteriori error estimator is achieved. A major advantage of the a-posteriori error estimator is that the estimator is independent of the used reduction technique. Therefore, it can be used for moment-matching based, Gramian matrices based or modal based model reduction techniques. The capability of the proposed technique is demonstrated by the a-posteriori error estimation of a mechanical system, and a sensitivity analysis of the parameters involved in the error estimation process is conducted.
Transport coefficients in second-order non-conformal viscous hydrodynamics
NASA Astrophysics Data System (ADS)
Ryblewski, Radoslaw
2015-05-01
Based on the exact solution of Boltzmann kinetic equation in the relaxation-time approximation, the precision of the two most recent formulations of relativistic second-order non-conformal viscous hydrodynamics (14-moment approximation and causal Chapman-Enskog method), standard Israel-Stewart theory, and anisotropic hydrodynamics framework, in the simple case of one-dimensional Bjorken expansion, is tested. It is demonstrated that the failure of Israel-Stewart theory in reproducing exact solutions of the Boltzmann kinetic equation occurs due to neglecting and/or choosing wrong forms of some of the second-order transport coefficients. In particular, the importance of shear-bulk couplings in the evolution equations for dissipative quantities is shown. One finds that, in the case of the bulk viscous pressure correction, such coupling terms are as important as the corresponding first-order Navier-Stokes term and must be included in order to obtain, at least qualitative, overall agreement with the kinetic theory.
Constraints on general second-order scalar-tensor models from gravitational Cherenkov radiation
Kimura, Rampei; Yamamoto, Kazuhiro E-mail: kazuhiro@hiroshima-u.ac.jp
2012-07-01
We demonstrate that the general second-order scalar-tensor theories, which have attracted attention as possible modified gravity models to explain the late time cosmic acceleration, could be strongly constrained from the argument of the gravitational Cherenkov radiation. To this end, we consider the purely kinetic coupled gravity and the extended galileon model on a cosmological background. In these models, the propagation speed of tensor mode could be less than the speed of light, which puts very strong constraints from the gravitational Cherenkov radiation.
Magnetic Compensation for Second-Order Doppler Shift in LITS
NASA Technical Reports Server (NTRS)
Burt, Eric; Tjoelker, Robert
2008-01-01
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.
Kinetics and mechanism of OH reactions with organic sulfides
Hynes, A.J.; Wine, P.H.; Semmes, D.H.
1986-08-14
The conventional flash photolysis-resonance fluorescence technique was employed to study reactions of OH with CH/sub 3/SCH/sub 3/ (1), CD/sub 3/SCD/sub 3/ (2), CH/sub 3/SC/sub 2/H/sub 5/ (3), and C/sub 2/H/sub 5/SC/sub 2/H/sub 5/ (4) in argon buffer gas. Reactivity trends, temperature dependencies, and isotope effects suggest that hydrogen abstraction is the dominant observed reaction pathway under these conditions. A pulsed-laser photolysis-pulsed-laser-induced fluorescence technique was employed to study reactions 1 and 2 in N/sub 2/, air, and O/sub 2/ buffer gases. Complex kinetics were observed in the presence of O/sub 2/. A four-step mechanism involving hydrogen abstraction, reversible addition to the sulfur atom, and scavenging of the (thermalized) adduct by O/sub 2/ is required to explain all experimental observations. In 1 atm of air, the effective bimolecular rate constant for reaction 1 decreases monotonically from 1.58 x 10/sup -11/ to 5.2 x 10/sup -12/ cm/sup 3/ molecule/sup -1/s/sup -1/ over the lower tropospheric temperature range 250-310 K. Over the same temperature range the branching ratio for hydrogen abstraction increases monotonically from 0.24 to 0.87. At 261 K, the rate constant for unimolecular decomposition of the CD/sub 3/S(OH)CD/sub 3/ adduct is (3.5 +/- 2.0) x 10/sup 6/ s/sup -1/ and the rate constant for the adduct reaction with O/sub 2/ is (4.2 +/- 2.2) x 10/sup -12/ cm/sup 3/ molecule/sup -1/s/sup -1/.
Kinetics of enol formation from reaction of OH with propene.
Huynh, Lam K; Zhang, Hongzhi R; Zhang, Shaowen; Eddings, Eric; Sarofim, Adel; Law, Matthew E; Westmoreland, Phillip R; Truong, Thanh N
2009-04-01
Kinetics of enol generation from propene has been predicted in an effort to understand the presence of enols in flames. A potential energy surface for reaction of OH with propene was computed by CCSD(T)/cc-pVDZ//B3LYP/cc-pVTZ calculations. Rate constants of different product channels and branching ratios were then calculated using the Master Equation formulation (J. Phys. Chem. A 2006, 110, 10528). Of the two enol products, ethenol is dominant over propenol, and its pathway is also the dominant pathway for the OH + propene addition reactions to form bimolecular products. In the temperature range considered, hydrogen abstraction dominated propene + OH consumption by a branching ratio of more than 90%. Calculated rate constants of enol formation were included in the Utah Surrogate Mechanism to model the enol profile in a cyclohexane premixed flame. The extended model shows consistency with experimental data and gives 5% contribution of ethenol formation from OH + propene reaction, the rest coming from ethene + OH. PMID:19271758
A second-order closure analysis of turbulent diffusion flames. [combustion physics
NASA Technical Reports Server (NTRS)
Varma, A. K.; Fishburne, E. S.; Beddini, R. A.
1977-01-01
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.
Second-order nonlinear optical activity vs. chromophore content in simple organic glass/PMMA system
NASA Astrophysics Data System (ADS)
Lee, Seung Mook; Jahng, Woong Sang; Lee, Jin Hyun; Rhee, Bum Ku; Park, Ki Hong
2005-08-01
A simple organic glass with a connection of two nonlinear optical (NLO) moieties was synthesized by condensation reaction of alkyl-substituted dibenzaldehyde with barbituric acid. This organic glass with Tg of 81 °C was formed to be optically transparent films without any phase separation even at the highest chromophore content (100 wt% loading without host matrix). The second-order NLO properties with various organic glass/PMMA composition systems were systematically studied by Maker fringe method at a wavelength of 1064 nm. We demonstrate that second-order optical nonlinearity of this organic glass/PMMA system can be progressively enlarged with increasing chromophore loading from 0 to 100 wt%.
Dispersion of second-order nonlinear optical coefficient
NASA Astrophysics Data System (ADS)
Seres, J.
A simple, approximate relation between the dispersion of the second-order nonlinear optical (SNLO) coefficient and first-order susceptibility has been derived using the well-known results of density-matrix calculation of quantum-mechanical theory. A new tensor of SNLO coefficient has been defined, which retains symmetries when the input beams are in the spectral range of transparency while the generated beam can also be in the spectral range of absorption. The validity of the relation has been checked for three ferroelectric crystals, KTP, LiNbO3 and KNbO3, which are transparent in the visible and near infrared, and for two semiconductors, GaP and GaAs, which absorb in the visible. Contrary to Miller's law, the presented relation is in good agreement with measurements.
Second-order Boltzmann equation: gauge dependence and gauge invariance
NASA Astrophysics Data System (ADS)
Naruko, Atsushi; Pitrou, Cyril; Koyama, Kazuya; Sasaki, Misao
2013-08-01
In the context of cosmological perturbation theory, we derive the second-order Boltzmann equation describing the evolution of the distribution function of radiation without a specific gauge choice. The essential steps in deriving the Boltzmann equation are revisited and extended given this more general framework: (i) the polarization of light is incorporated in this formalism by using a tensor-valued distribution function; (ii) the importance of a choice of the tetrad field to define the local inertial frame in the description of the distribution function is emphasized; (iii) we perform a separation between temperature and spectral distortion, both for the intensity and polarization for the first time; (iv) the gauge dependence of all perturbed quantities that enter the Boltzmann equation is derived, and this enables us to check the correctness of the perturbed Boltzmann equation by explicitly showing its gauge-invariance for both intensity and polarization. We finally discuss several implications of the gauge dependence for the observed temperature.
Regularized orbital-optimized second-order perturbation theory
Stück, David; Head-Gordon, Martin
2013-12-28
Orbital-optimized second-order perturbation theory (OOMP2) optimizes the zeroth order wave function in the presence of correlations, removing the dependence of the method on Hartree–Fock orbitals. This is particularly important for systems where mean field orbitals spin contaminate to artificially lower the zeroth order energy such as open shell molecules, highly conjugated systems, and organometallic compounds. Unfortunately, the promise of OOMP2 is hampered by the possibility of solutions being drawn into divergences, which can occur during the optimization procedure if HOMO and LUMO energies approach degeneracy. In this work, we regularize these divergences through the simple addition of a level shift parameter to the denominator of the MP2 amplitudes. We find that a large level shift parameter of 400 mE{sub h} removes divergent behavior while also improving the overall accuracy of the method for atomization energies, barrier heights, intermolecular interactions, radical stabilization energies, and metal binding energies.
Absorbing boundary conditions for second-order hyperbolic equations
NASA Technical Reports Server (NTRS)
Jiang, Hong; Wong, Yau Shu
1989-01-01
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.
Invariant classification of second-order conformally flat superintegrable systems
NASA Astrophysics Data System (ADS)
Capel, J. J.; Kress, J. M.
2014-12-01
In this paper we continue the work of Kalnins et al in classifying all second-order conformally-superintegrable (Laplace-type) systems over conformally flat spaces, using tools from algebraic geometry and classical invariant theory. The results obtained show, through Stäckel equivalence, that the list of known nondegenerate superintegrable systems over three-dimensional conformally flat spaces is complete. In particular, a seven-dimensional manifold is determined such that each point corresponds to a conformal class of superintegrable systems. This manifold is foliated by the nonlinear action of the conformal group in three dimensions. Two systems lie in the same conformal class if and only if they lie in the same leaf of the foliation. This foliation is explicitly described using algebraic varieties formed from representations of the conformal group. The proof of these results rely heavily on Gröbner basis calculations using the computer algebra software packages Maple and Singular.
New implicitly solvable potential produced by second order shape invariance
Cannata, F.; Ioffe, M.V.; Kolevatova, E.V.; Nishnianidze, D.N.
2015-05-15
The procedure proposed recently by Bougie et al. (2010) to study the general form of shape invariant potentials in one-dimensional Supersymmetric Quantum Mechanics (SUSY QM) is generalized to the case of Higher Order SUSY QM with supercharges of second order in momentum. A new shape invariant potential is constructed by this method. It is singular at the origin, it grows at infinity, and its spectrum depends on the choice of connection conditions in the singular point. The corresponding Schrödinger equation is solved explicitly: the wave functions are constructed analytically, and the energy spectrum is defined implicitly via the transcendental equation which involves Confluent Hypergeometric functions. - Highlights: • New potential with 2nd order irreducible shape invariance was constructed. • The connection conditions at the singularity of potential were obtained. • The explicit expressions for all wave functions were derived. • The implicit equation for the energy spectrum was obtained.
Absorbing boundary conditions for second-order hyperbolic equations
NASA Technical Reports Server (NTRS)
Jiang, Hong; Wong, Yau Shu
1990-01-01
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.
K-inflationary power spectra at second order
Martin, Jérôme; Vennin, Vincent; Ringeval, Christophe E-mail: christophe.ringeval@uclouvain.be
2013-06-01
Within the class of inflationary models, k-inflation represents the most general single field framework that can be associated with an effective quadratic action for the curvature perturbations and a varying speed of sound. The incoming flow of high-precision cosmological data, such as those from the Planck satellite and small scale Cosmic Microwave Background (CMB) experiments, calls for greater accuracy in the inflationary predictions. In this work, we calculate for the first time the next-to-next-to-leading order scalar and tensor primordial power spectra in k-inflation needed in order to obtain robust constraints on the inflationary theory. The method used is the uniform approximation together with a second order expansion in the Hubble and sound flow functions. Our result is checked in various limits in which it reduces to already known situations.
Nonoscillation for second order sublinear dynamic equations on time scales
NASA Astrophysics Data System (ADS)
Erbe, Lynn; Baoguo, Jia; Peterson, Allan
2009-10-01
Consider the Emden-Fowler sublinear dynamic equation x[Delta][Delta](t)+p(t)f(x([sigma](t)))=0, where , is a time scale, , where ai>0, 0<[beta]i<1, with [beta]i the quotient of odd positive integers, 1<=i<=m. When m=1, and , (0.1) is the usual sublinear Emden-Fowler equation which has attracted the attention of many researchers. In this paper, we allow the coefficient function p(t) to be negative for arbitrarily large values of t. We extend a nonoscillation result of Wong for the second order sublinear Emden-Fowler equation in the continuous case to the dynamic equation (0.1). As applications, we show that the sublinear difference equation has a nonoscillatory solution, for b>0, c>[alpha], and the sublinear q-difference equation has a nonoscillatory solution, for , q>1, b>0, c>1+[alpha].
A new approach for second-order perturbation theory.
Tomlinson, David G; Asadchev, Andrey; Gordon, Mark S
2016-05-30
A new second-order perturbation theory (MP2) approach is presented for closed shell energy evaluations. The new algorithm has a significantly lower memory footprint, a lower FLOP (floating point operations) count, and a lower time to solution compared to previously implemented parallel MP2 methods in the GAMESS software package. Additionally, this algorithm features an adaptive approach for the disk/distributed memory storage of the MP2 amplitudes. The algorithm works well on a single workstation, small cluster, and large Cray cluster, and it allows one to perform large calculations with thousands of basis functions in a matter of hours on a single workstation. The same algorithm has been adapted for graphical processing unit (GPU) architecture. The performance of the new GPU algorithm is also discussed. © 2016 Wiley Periodicals, Inc. PMID:26940648
Digital second-order phase-locked loop
NASA Technical Reports Server (NTRS)
Holes, J. K.; Carl, C.; Tegnelia, C. R. (Inventor)
1973-01-01
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.
WEAK GALERKIN METHODS FOR SECOND ORDER ELLIPTIC INTERFACE PROBLEMS.
Mu, Lin; Wang, Junping; Wei, Guowei; Ye, Xiu; Zhao, Shan
2013-10-01
Weak Galerkin methods refer to general finite element methods for partial differential equations (PDEs) in which differential operators are approximated by their weak forms as distributions. Such weak forms give rise to desirable flexibilities in enforcing boundary and interface conditions. A weak Galerkin finite element method (WG-FEM) is developed in this paper for solving elliptic PDEs with discontinuous coefficients and interfaces. Theoretically, it is proved that high order numerical schemes can be designed by using the WG-FEM with polynomials of high order on each element. Extensive numerical experiments have been carried to validate the WG-FEM for solving second order elliptic interface problems. High order of convergence is numerically confirmed in both L 2 and L ∞ norms for the piecewise linear WG-FEM. Special attention is paid to solve many interface problems, in which the solution possesses a certain singularity due to the nonsmoothness of the interface. A challenge in research is to design nearly second order numerical methods that work well for problems with low regularity in the solution. The best known numerical scheme in the literature is of order [Formula: see text] to [Formula: see text] for the solution itself in L ∞ norm. It is demonstrated that the WG-FEM of the lowest order, i.e., the piecewise constant WG-FEM, is capable of delivering numerical approximations that are of order [Formula: see text] to [Formula: see text] in the L ∞ norm for C (1) or Lipschitz continuous interfaces associated with a C (1) or H (2) continuous solution. PMID:24072935
WEAK GALERKIN METHODS FOR SECOND ORDER ELLIPTIC INTERFACE PROBLEMS
MU, LIN; WANG, JUNPING; WEI, GUOWEI; YE, XIU; ZHAO, SHAN
2013-01-01
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
Second order closure modeling of turbulent buoyant wall plumes
NASA Technical Reports Server (NTRS)
Zhu, Gang; Lai, Ming-Chia; Shih, Tsan-Hsing
1992-01-01
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.
Spectator Ions ARE Important! A Kinetic Study of the Copper-Aluminum Displacement Reaction
ERIC Educational Resources Information Center
Sobel, Sabrina G.; Cohen, Skyler
2010-01-01
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…
Spectator Ions ARE Important! A Kinetic Study of the Copper-Aluminum Displacement Reaction
ERIC Educational Resources Information Center
Sobel, Sabrina G.; Cohen, Skyler
2010-01-01
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
NASA Astrophysics Data System (ADS)
Doktorov, Alexander B.; Kipriyanov, Alexander A.; Kipriyanov, Alexey A.
2010-05-01
Using an modern many-particle method for the derivation of non-Markovian binary kinetic equations, we have treated theoretically the applicability of the encounter theory (ET) (the prototype of the collision theory) concepts to the widely known diffusion assisted irreversible bulk reaction A +A→product (for example, radical reaction) in dilute solutions. The method shows that the agreement with the ET is observed when the familiar integral ET is employed which in this method is just a step in the derivation of kinetic equations. It allows for two-particle correlations only, but fails to take account of correlation of reactant simultaneously with the partner of the encounter and the reactant in the bulk. However, the next step leading to the modified ET under transformation of equations to the regular form both extends the time range of the applicability of ET rate equation (as it was for reactions proceeding with one of the reactants in excess), and gives the equation of the generalized ET. In full agreement with physical considerations, this theory reveals macroscopic correlations induced by the encounters in the reservoir of free walks. This means that the encounters of reactants in solution are correlated on a rather large time interval of the reaction. Though any nonstationary (non-Markovian) effects manifest themselves rather weakly in the kinetics of the bimolecular reaction in question, just the existence of the revealed macroscopic correlations in the binary theory is of primary importance. In particular, it means that the well-known phenomena which are generally considered to be associated solely with correlation of particles on the encounter (for example, chemically induced dynamic nuclear polarization) may be induced by correlation in the reservoir of free random walks of radicals in solution.
Reaction Kinetics of Meteoric Sodium Reservoirs in the Upper Atmosphere.
Gómez Martín, J C; Garraway, S A; Plane, J M C
2016-03-10
The gas-phase reactions of a selection of sodium-containing species with atmospheric constituents, relevant to the chemistry of meteor-ablated Na in the upper atmosphere, were studied in a fast flow tube using multiphoton ionization time-of-flight mass spectrometry. For the first time, unambiguous observations of NaO and NaOH in the gas phase under atmospheric conditions have been achieved. This enabled the direct measurement of the rate constants for the reactions of NaO with H2, H2O, and CO, and of NaOH with CO2, which at 300-310 K were found to be (at 2σ confidence level): k(NaO + H2O) = (2.4 ± 0.6) × 10(-10) cm(3) molecule (-1) s(-1), k(NaO + H2) = (4.9 ± 1.2) × 10(-12) cm(3) molecule (-1) s(-1), k(NaO + CO) = (9 ± 4) × 10(-11) cm(3) molecule (-1) s(-1), and k(NaOH + CO2 + M) = (7.6 ± 1.6) × 10(-29) cm(6) molecule (-2) s(-1) (P = 1-4 Torr). The NaO + H2 reaction was found to make NaOH with a branching ratio ≥99%. A combination of quantum chemistry and statistical rate theory calculations are used to interpret the reaction kinetics and extrapolate the atmospherically relevant experimental results to mesospheric temperatures and pressures. The NaO + H2O and NaOH + CO2 reactions act sequentially to provide the major atmospheric sink of meteoric Na and therefore have a significant impact on the underside of the Na layer in the terrestrial mesosphere: the newly determined rate constants shift the modeled peak to about 93 km, i.e., 2 km higher than observed by ground-based lidars. This highlights further uncertainties in the Na chemistry cycle such as the unknown rate constant of the NaOH + H reaction. The fast Na-recycling reaction between NaO and CO and a re-evaluated rate constant of the NaO + CO2 sink should be now considered in chemical models of the Martian Na layer. PMID:25723735
Kinetic Deuterium Isotope Effects in Cytochrome P450 Oxidation Reactions
Guengerich, F. Peter
2016-01-01
Cytochrome P450 (P450) enzymes account for ~ 75% of the metabolism of drugs. Most of the reactions catalyzed by P450s are mixed-function oxidations, and a C-H bond is (usually) broken. The rate-limiting nature of this step can be analyzed using the kinetic isotope effect (KIE) approach. The most relevant type of KIE is one termed intermolecular non-competitive, indicative of rate-limiting C-H bond breaking. A KIE vs. kcat for several P450s showed a correlation coefficient (r2) of 0.62. Deuterium substitution has been considered as a potential means of slowing drug metabolism or redirecting sites of metabolism in some cases, and several general points can be made regarding the potential for application of deuterium in drug design/development based on what is known about P450 KIEs. PMID:24285515
Adaptive approach for nonlinear sensitivity analysis of reaction kinetics.
Horenko, Illia; Lorenz, Sönke; Schütte, Christof; Huisinga, Wilhelm
2005-07-15
We present a unified approach for linear and nonlinear sensitivity analysis for models of reaction kinetics that are stated in terms of systems of ordinary differential equations (ODEs). The approach is based on the reformulation of the ODE problem as a density transport problem described by a Fokker-Planck equation. The resulting multidimensional partial differential equation is herein solved by extending the TRAIL algorithm originally introduced by Horenko and Weiser in the context of molecular dynamics (J. Comp. Chem. 2003, 24, 1921) and discussed it in comparison with Monte Carlo techniques. The extended TRAIL approach is fully adaptive and easily allows to study the influence of nonlinear dynamical effects. We illustrate the scheme in application to an enzyme-substrate model problem for sensitivity analysis w.r.t. to initial concentrations and parameter values. PMID:15858828
Reaction Kinetics of the Hydrothermal Treatment of Lignin
NASA Astrophysics Data System (ADS)
Zhang, Bo; Huang, Hua-Jiang; Ramaswamy, Shri
Lignins derived from abundant and renewable resources are nontoxic and extremely versatile in performance, qualities that have made them increasingly important in many industrial applications. We have shown recently that liquefaction of lignin extracted from aspen wood resulted in a 90% yield of liquid. In this paper, the hydrothermal treatment of five types of lignin and biomass residues was studied: Kraft pine lignin provided by MeadWestvaco, Kraft pine lignin from Sigma-Aldrich, organosolv lignin extracted from oat hull, the residues of mixed southern hardwoods, and switchgrass after hydrolysis. The yields were found dependent on the composition or structure of the raw materials, which may result from different pretreatment processes. We propose a kinetic model to describe the hydrothermal treatment of Kraft pine lignin and compare it with another model from the literature. The kinetic parameters of the presented model were estimated, including the reaction constants, the pre-exponential factor, and the activation energy of the Arrhenius equations. Results show that the presented model is well in agreement with the experiments.
Nuclear quantum effects and kinetic isotope effects in enzyme reactions.
Vardi-Kilshtain, Alexandra; Nitoker, Neta; Major, Dan Thomas
2015-09-15
Enzymes are extraordinarily effective catalysts evolved to perform well-defined and highly specific chemical transformations. Studying the nature of rate enhancements and the mechanistic strategies in enzymes is very important, both from a basic scientific point of view, as well as in order to improve rational design of biomimetics. Kinetic isotope effect (KIE) is a very important tool in the study of chemical reactions and has been used extensively in the field of enzymology. Theoretically, the prediction of KIEs in condensed phase environments such as enzymes is challenging due to the need to include nuclear quantum effects (NQEs). Herein we describe recent progress in our group in the development of multi-scale simulation methods for the calculation of NQEs and accurate computation of KIEs. We also describe their application to several enzyme systems. In particular we describe the use of combined quantum mechanics/molecular mechanics (QM/MM) methods in classical and quantum simulations. The development of various novel path-integral methods is reviewed. These methods are tailor suited to enzyme systems, where only a few degrees of freedom involved in the chemistry need to be quantized. The application of the hybrid QM/MM quantum-classical simulation approach to three case studies is presented. The first case involves the proton transfer in alanine racemase. The second case presented involves orotidine 5'-monophosphate decarboxylase where multidimensional free energy simulations together with kinetic isotope effects are combined in the study of the reaction mechanism. Finally, we discuss the proton transfer in nitroalkane oxidase, where the enzyme employs tunneling as a catalytic fine-tuning tool. PMID:25769515
Um, Ik-Hwan; Kang, Ji-Sun; Shin, Young-Hee; Buncel, Erwin
2013-01-18
Pseudofirst-order rate constants (k(obsd)) have been measured spectrophotometrically for the nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzenesulfonates 4a-f and Y-substituted phenyl benzenesulfonates 5a-k with EtOK in anhydrous ethanol. Dissection of k(obsd) into k(EtO(-)) and k(EtOK) (i.e., the second-order rate constants for the reactions with the dissociated EtO(-) and ion-paired EtOK, respectively) shows that the ion-paired EtOK is more reactive than the dissociated EtO(-), indicating that K(+) ion catalyzes the reaction. The catalytic effect exerted by K(+) ion (e.g., the k(EtOK)/k(EtO(-)) ratio) decreases linearly as the substituent X in the benzenesulfonyl moiety changes from an electron-donating group (EDG) to an electron-withdrawing group (EWG), but it is independent of the electronic nature of the substituent Y in the leaving group. The reactions have been concluded to proceed through a concerted mechanism from analyses of the kinetic data through linear free energy relationships (e.g., the Brønsted-type, Hammett, and Yukawa-Tsuno plots). K(+) ion catalyzes the reactions by increasing the electrophilicity of the reaction center through a cyclic transition state (TS) rather than by increasing the nucleofugality of the leaving group. Activation parameters (e.g., ΔH(‡) and ΔS(‡)) determined from the reactions performed at five different temperatures further support the proposed mechanism and TS structures. PMID:23215678
da Silva, Gabriel; Chen, Chiung-Chu; Bozzelli, Joseph W
2007-09-01
Aromatic compounds such as toluene and xylene are major components of many fuels. Accurate kinetic mechanisms for the combustion of toluene are, however, incomplete, as they do not accurately model experimental results such as strain rates and ignition times and consistently underpredict conversion. Current kinetic mechanisms for toluene combustion neglect the reactions of the methylphenyl radicals, and we believe that this is responsible, in part, for the shortcomings of these models. We also demonstrate how methylphenyl radical formation is important in the combustion and pyrolysis of other alkyl-substituted aromatic compounds such as xylene and trimethylbenzene. We have studied the oxidation reactions of the methylphenyl radicals with O2 using computational ab initio and density functional theory methods. A detailed reaction submechanism is presented for the 2-methylphenyl radical + O2 system, with 16 intermediates and products. For each species, enthalpies of formation are calculated using the computational methods G3 and G3B3, with isodesmic work reactions used to minimize computational errors. Transition states are calculated at the G3B3 level, yielding high-pressure limit elementary rate constants as a function of temperature. For the barrierless methylphenyl + O2 and methylphenoxy + O association reactions, rate constants are determined from variational transition state theory. Multichannel, multifrequency quantum Rice-Ramsperger-Kassel (qRRK) theory, with master equation analysis for falloff, provides rate constants as a function of temperature and pressure from 800 to 2400 K and 1 x 10(-4) to 1 x 10(3) atm. Analysis of our results shows that the dominant pathways for reaction of the three isomeric methylphenyl radicals is formation of methyloxepinoxy radicals and subsequent ring opening to methyl-dioxo-hexadienyl radicals. The next most important reaction pathway involves formation of methylphenoxy radicals + O in a chain branching process. At lower temperatures, the formation of stabilized methylphenylperoxy radicals becomes significant. A further important reaction channel is available only to the 2-methylphenyl isomer, where 6-methylene-2,4-cyclohexadiene-1-one (ortho-quinone methide, o-QM) is produced via an intramolecular hydrogen transfer from the methyl group to the peroxy radical in 2-methylphenylperoxy, with subsequent loss of OH. The decomposition of o-QM to benzene + CO reveals a potentially important new pathway for the conversion of toluene to benzene during combustion. A number of the important products of toluene combustion proposed in this study are known to be precursors of polyaromatic hydrocarbons that are involved in soot formation. Reactions leading to the important unsaturated oxygenated intermediates identified in this study, and the further reactions of these intermediates, are not included in current aromatic oxidation mechanisms. PMID:17696501
Kinetic analysis of the genome packaging reaction in bacteriophage lambda.
Yang, Qin; Catalano, Carlos E; Maluf, Nasib Karl
2009-11-17
Bacteriophage lambda is a double-stranded DNA virus that infects the Escherichia coli bacterium. lambda genomic DNA is replicated via rolling circle replication, resulting in multiple genomes linked head to tail at the cos site. To insert a single lambda genome into the viral capsid, the lambda terminase enzyme introduces symmetric nicks, 12 bp apart, at the cos site, and then promotes a strand separation reaction, releasing the tail end of the previous genome and leaving a binary complex consisting of lambda terminase bound to the head end of the adjacent genome. Next, the genome is translocated into the interior of the capsid particle, in a process that requires ATP hydrolysis by lambda terminase. Even though DNA packaging has been studied extensively, currently no bulk assays are available that have been optimized to report directly on DNA translocation. Rather, these assays are sensitive to assembly steps reflecting formation of the active, DNA packaging machine. In this work, we have modified the DNase protection assay commonly used to study DNA packaging in several bacteriophage systems, such that it reports directly on the kinetics of the DNA packaging reaction. We have analyzed our DNA packaging data according to an N-step sequential minimal kinetic model and have estimated an overall packaging rate of 119 +/- 8 bp/s, at 4 degrees C and 1 mM ATP. Furthermore, we have measured an apparent step size for the this reaction (m(obs)) of 410 +/- 150 bp. The magnitude of this value indicates that our assay is most likely sensitive to both mechanical steps associated with DNA insertion as well as occasional slow steps that are repeated every >410 bp. These slow steps may be reflective of the pausing events observed in recent single-molecule studies of DNA packaging in bacteriophage lambda [Fuller, D. N., et al. (2007) J. Mol. Biol. 373, 1113-1122]. Finally, we show that either ATP or ADP is required for terminase cutting at cos, to generate the active, DNA packaging complex. PMID:19788336
On computing first and second order derivative spectra
NASA Astrophysics Data System (ADS)
Roy, Indrajit G.
2015-08-01
Enhancing resolution in spectral response and an ability to differentiate spectral mixing in delineating the endmembers from the spectral response are central to the spectral data analysis. First and higher order derivatives analysis of absorbance and reflectance spectral data is commonly used techniques in differentiating the spectral mixing. But high sensitivity of derivative to the noise in data is a major problem in the robust estimation of derivative of spectral data. An algorithm of robust estimation of first and second order derivative spectra from evenly spaced noisy normal spectral data is proposed. The algorithm is formalized in the framework of an inverse problem, where based on the fundamental theorem of calculus a matrix equation is formed using a Volterra type integral equation of first kind. A regularization technique, where the balancing principle is used in selecting a posteriori optimal regularization parameter is designed to solve the inverse problem for robust estimation of first order derivative spectra. The higher order derivative spectra are obtained while using the algorithm in sequel. The algorithm is tested successfully with synthetically generated spectral data contaminated with additive white Gaussian noise, and also with real absorbance and reflectance spectral data for fresh and sea water respectively.
A novel second-order flux splitting for ideal magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Borah, Kalpajyoti; Natarajan, Ganesh; Dass, Anoop K.
2016-05-01
A new flux splitting scheme based on wave-particle behaviour is developed for one-dimensional ideal magnetohydrodynamics. We exploit the idea that while ideal magnetohydrodynamics equations are non-convex with non-homogeneous fluxes as opposed to their hydrodynamic counterparts, they exhibit an overall wave-like structure. The proposed approach splits the flux vector into three distinct parts: the particle-like transport part and the wave-like pressure and magnetic parts, with the latter vanishing for pure hydrodynamics. The pressure part of the fluxes satisfy homogeneity property and the split flux Jacobians are constructed with a provision to regulate the numerical dissipation. The magnetic part of the fluxes however is non-homogeneous and is treated using a central scheme with artificial viscosity. This disparate treatment of the individual components of the total flux vector results in a scheme with a central-upwind character that can be implemented with low computational effort. Referred to as Magneto-acoustic Wave Particle Splitting (MWPS) scheme, it is extended to second-order accuracy by using slope limiters incorporated through the solution-dependent weighted least squares approach for gradient calculations. Several one-dimensional MHD problems are numerically solved to highlight the accuracy, positivity preservation and robustness of the MWPS scheme and comparative studies show that MWPS performs at least as well as the Advection Upstream Splitting Method (AUSM) and even outperforms it for some test cases.
Second-order perturbation theory: Problems on large scales
NASA Astrophysics Data System (ADS)
Pound, Adam
2015-11-01
In general-relativistic perturbation theory, a point mass accelerates away from geodesic motion due to its gravitational self-force. Because the self-force is small, one can often approximate the motion as geodesic. However, it is well known that self-force effects accumulate over time, making the geodesic approximation fail on long time scales. It is less well known that this failure at large times translates to a failure at large distances as well. At second perturbative order, two large-distance pathologies arise: spurious secular growth and infrared-divergent retarded integrals. Both stand in the way of practical computations of second-order self-force effects. Utilizing a simple flat-space scalar toy model, I develop methods to overcome these obstacles. The secular growth is tamed with a multiscale expansion that captures the system's slow evolution. The divergent integrals are eliminated by matching to the correct retarded solution at large distances. I also show how to extract conservative self-force effects by taking local-in-time "snapshots" of the global solution. These methods are readily adaptable to the physically relevant case of a point mass orbiting a black hole.
Correction of the Chromaticity up to Second Order for MEIC
H. K. Sayed, S.A. Bogacz, P. Chevtsov
2010-03-01
The proposed electron collider lattice exhibits low β- functions at the Interaction Point (IP) (βx∗100mm − βy∗ 20 mm) and rather large equilibrium momentum spread of the collider ring (δp/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.
Modal cost analysis for linear matrix-second-order systems
NASA Technical Reports Server (NTRS)
Skelton, R. E.; Hughes, P. C.
1980-01-01
Reduced models and reduced controllers for systems governed by matrix-second-order differential equations are obtained by retaining those modes which make the largest contributions to quadratic control objectives. Such contributions, expressed in terms of modal data, used as mode truncation criteria, allow the statement of the specific control objectives to influence the early model reduction from very high order models which are available, for example, from finite element methods. The relative importance of damping, frequency, and eigenvector in the mode truncation decisions are made explicit for each of these control objectives: attitude control, vibration suppression and figure control. The paper also shows that using modal cost analysis (MCA) on the closed loop modes of the optimally controlled system allows the construction of reduced control policies which feedback only those closed loop modal coordinates which are most critical to the quadratic control performance criterion. In this way, the modes which should be controlled (and hence the modes which must be observable by choice of measurements), are deduced from truncations of the optimal controller.
Second order sliding mode control for a quadrotor UAV.
Zheng, En-Hui; Xiong, Jing-Jing; Luo, Ji-Liang
2014-07-01
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
Second order statistics target-specified virtual dimensionality
NASA Astrophysics Data System (ADS)
Paylor, Drew; Chang, Chein-I.
2013-05-01
Virtual dimensionality (VD) has received considerable interest in its use of specifying the number of spectrally distinct signatures. So far all techniques are decomposition approaches which use eigenvalues, eigenvectors or singular vectors to estimate the virtual dimensionality. However, when eigenvalues are used to estimate VD such as Harsanyi-Farrand- Chang's method or hyperspectral signal subspace identification by minimum error (HySime), there will be no way to find what the spectrally distinct signatures are. On the other hand, if eigenvectors/singular vectors are used to estimate VD such as maximal orthogonal complement algorithm (MOCA), eigenvectors/singular vectors do not represent real signal sources. In this paper we introduce a new concept, referred to as target-specified VD (TSVD), which operates on the signal sources themselves to both determine the number of distinct sources and identify their signature. The underlying idea of TSVD was derived from that used to develop high-order statistics (HOS) VD where its applicability to second order statistics (2OS) was not explored. In this paper we investigate a 2OS-based target finding algorithm, called automatic target generation process (ATGP) to determine VD. Experiments are conducted in comparison with well-known and widely used eigen-based approaches.
Cavity-Enhanced Second-Order Nonlinear Photonic Logic Circuits
NASA Astrophysics Data System (ADS)
Trivedi, Rahul; Khankhoje, Uday K.; Majumdar, Arka
2016-05-01
A large obstacle for realizing photonic logic is the weak optical nonlinearity of available materials, which results in large power consumption. In this paper, we present the theoretical design of all-optical logic with second-order (χ(2 )) nonlinear bimodal cavities and their networks. Using semiclassical models derived from the Wigner quasiprobability distribution function, we analyze the power consumption and signal-to-noise ratio (SNR) of networks implementing an optical and gate and an optical latch. A comparison between the second- and third-order (χ(3 )) optical logic reveals that, while the χ(3 ) design outperforms the χ(2 ) design in terms of the SNR for the same input power, employing the χ(3 ) nonlinearity necessitates the use of cavities with ultrahigh-quality factors (Q ˜106) to achieve a gate power consumption comparable to that of the χ(2 ) design at significantly smaller quality factors (Q ˜104). Using realistic estimates of the χ(2 ) and χ(3 ) nonlinear susceptibilities of available materials, we show that, at achievable quality factors (Q ˜104), the χ(2 ) design is an order of magnitude more energy efficient than the corresponding χ(3 ) design.
Covariance kernel representations of multidimensional second-order stochastic processes
Su, C.H.; Lucor, Didier . E-mail: lucor@lmm.jussieu.fr
2006-09-01
The dynamics of stationary stochastic processes in space is not exactly analogous to that of stationary stochastic processes in the time domain. This is due to the unilateral nature of the time series that is only influenced by past values as opposed to the dependence in all directions of the spatial process. In this work, we unfold the connection that exits between the covariance kernel of a multi-dimensional second-order autoregressive random process and its underlying discrete random dynamical system. Starting from a discrete random dynamical system, we show that the random process satisfying that system is governed by the modified Helmholtz equation in the continuous limit. We establish the dependence of the correlation constant on the grid size of the discretization. We also show that the random forcing term in the continuous case turns out to be a white noise process. A number of covariance functions are worked out for simple and more complex geometrical domains with various boundary conditions in multi-dimensions. We use both the discrete and the continuous systems in our computations.
Becerra, Rosa; Bowes, Sarah-Jane; Ogden, J Steven; Cannady, J Pat; Adamovic, Ivana; Gordon, Mark S; Almond, Matthew J; Walsh, Robin
2005-08-01
Time-resolved kinetic studies of the reaction of silylene, SiH2, generated by laser flash photolysis of phenylsilane, have been carried out to obtain rate constants for its bimolecular reaction with O(2). The reaction was studied in the gas phase over the pressure range 1-100 Torr in SF(6) bath gas, at five temperatures in the range 297-600 K. The second order rate constants at 10 Torr were fitted to the Arrhenius equation: [see text] The decrease in rate constant values with increasing temperature, although systematic is very small. The rate constants showed slight increases in value with pressure at each temperature, but this was scarcely beyond experimental uncertainty. From estimates of Lennard-Jones collision rates, this reaction is occurring at ca. 1 in 20 collisions, almost independent of pressure and temperature. Ab initio calculations at the G3 level backed further by multi-configurational (MC) SCF calculations, augmented by second order perturbation theory (MRMP2), support a mechanism in which the initial adduct, H(2)SiOO, formed in the triplet state (T), undergoes intersystem crossing to the more stable singlet state (S) prior to further low energy isomerisation processes leading, via a sequence of steps, ultimately to dissociation products of which the lowest energy pair are H2O+SiO. The decomposition of the intermediate cyclo-siladioxirane, via O-O bond fission, plays an important role in the overall process. The bottleneck for the overall process appears to be the T-->S process in H2SiOO. This process has a small spin-orbit coupling matrix element, consistent with an estimate of its rate constant of 1x10(9) s-1 obtained with the aid of RRKM theory. This interpretation preserves the idea that, as in its reactions in general, SiH2 initially reacts at the encounter rate with O2. The low values for the secondary reaction barriers on the potential energy surface account for the lack of an observed pressure dependence. Some comparisons are drawn with the reactions of CH2+O2 and SiCl2+O2. PMID:16189609
Kinetics and mechanism of ligand-exchange reactions of Cd(II) chelates
Nivorozhkin, L.E.; Kalabin, G.A.; Nivorozhkin, A.L.; Valeev, R.B.; Minkin, V.I.
1987-03-01
Tetrahedral Cd(II) bis(5-thio(or seleno)pyrazole-4-carboxaldiminates) of types II and III have been synthesized for the first time. The kinetics of the degenerate ligand exchange and enantiomerization of the complexes obtained have been studied by dynamic /sup 111/Cd, /sup 77/Se, and /sup 1/H (s = 1/2) NMR. The rate of intramolecular enantiomerization (k = 1/tau) is more than an order of magnitude greater than the corresponding values for processes of degenerate ligand exchange (a second-order reaction) determined from the dynamics of the averaging of the /sup 111/Cd-/sup 77/Se and /sup 111/Cd-N=CH spin-spin coupling constants. The cleavage and formation processes of the Cd-Se and Cd-N bonds are isoenergetic (..delta.. G/sub 298//sup not equal to/ = 14.4 kcal/mole for chelate II with X = Se and R = CH/sub 2/C/sub 6/H/sub 5/). The free energies of activation of degenerate ligand exchange determined form the dynamics of the averaging of the /sup 111/Cd N=CH spin-spin coupling constant increase from 12.7 to 17.9 kcal/mole along the following series for R: C/sub 2/H/sub 5/ < Ar < CH/sub 2/C/sub 6/H/sub 5/ < t-C/sub 4/H/sub 9/ < cyclo-C/sub 6/H/sub 11/. Replacement of the sulfur atom in the chelate ring by selenium results in increases in the rates of ligand exchange. A mechanism of degenerate ligand exchange has been proposed.
Reaction kinetics of dual setting α-tricalcium phosphate cements.
Hurle, Katrin; Christel, Theresa; Gbureck, Uwe; Moseke, Claus; Neubauer, Juergen; Goetz-Neunhoeffer, Friedlinde
2016-01-01
Addition of ductile polymers to calcium-deficient hydroxyapatite (CDHA)-forming bone cements based on α-tricalcium phosphate (α-TCP) is a promising approach to improve the mechanical performance of α-TCP cements and extend their application to load-bearing defects, which is else impeded by the brittleness of the hardened cement. One suitable polymer is poly-(2-hydroxyethylmethacrylate) (p-HEMA), which forms during cement setting by radical polymerisation of the monomer. In this study the hydration kinetics and the mechanical performance of α-TCP cements modified with addition of different HEMA concentrations (0-50 wt% in the cement liquid) was investigated by quantitative in situ XRD and four-point bending tests. Morphology of CDHA crystals was monitored by scanning electron microscopy. The hydration of α-TCP to CDHA was increasingly impeded and the visible crystal size of CDHA increasingly reduced with increasing HEMA concentration. Modification of the cements by adding 50 wt% HEMA to the cement liquid changed the brittle performance of the hardened cement to a pseudoplastic behaviour, reduced the flexural modulus and increased the work of fracture, while lower HEMA concentrations had no significant effect on these parameters. In such a composite, the extent of CDHA formation was considerably reduced (34.0 ± 1.8 wt% CDHA with 50 % HEMA compared to 54.1 ± 2.4 wt% CDHA in the reference formed after 48 h), while the general reaction kinetics were not changed. In conclusion, while the extent of CDHA formation was decreased, the mechanical properties were noticeably improved by addition of HEMA. Hence, α-TCP/HEMA composites might be suitable for application in some load-bearing defects and have adequate properties for mechanical treatment after implantation, like insertion of screws. PMID:26610924
NASA Technical Reports Server (NTRS)
Bittker, D. A.; Scullin, V. J.
1972-01-01
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.
Second-order spatial correlation in the far-field: Comparing entangled and classical light sources
NASA Astrophysics Data System (ADS)
Zhang, Erfeng; Liu, Weitao; Lin, Huizu; Chen, Pingxing
2016-02-01
We consider second-order spatial correlation with entangled and classical light in the far-field. The quantum theory of second-order spatial correlation is analyzed, and the role of photon statistics and detection mode in the second-order spatial correlation are discussed. Meanwhile, the difference of second-order spatial correlation with entangled and classical light sources is deduced.
Second order multidimensional sign-preserving remapping for ALE methods
Hill, Ryan N; Szmelter, J.
2010-12-15
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.
Constraining kinetic rates of mineral reactions using reactive transport models
NASA Astrophysics Data System (ADS)
Bolton, E. W.; Wang, Z.; Ague, J.; Bercovici, D.; Cai, Z.; Karato, S.; Oristaglio, M. L.; Qiu, L.
2012-12-01
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.
Not Available
1988-01-01
This project provides kinetic data over wide temperature ranges on important combustion reactions. The HTP (high-temperature photochemistry) technique is used for the kinetic measurements. Additionally we have, in the past year, worked on the O + 1,3- butadiene and O + HCl reactions, as well as on the high-temperature photolysis of benzene. 6 refs.
Kinetics and Mechanism of Iodide Oxidation by Iron(III): A Clock Reaction Approach
ERIC Educational Resources Information Center
Bauer, Jurica; Tomisic, Vladislav; Vrkljan, Petar B. A.
2008-01-01
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…
Kinetics and Mechanism of Iodide Oxidation by Iron(III): A Clock Reaction Approach
ERIC Educational Resources Information Center
Bauer, Jurica; Tomisic, Vladislav; Vrkljan, Petar B. A.
2008-01-01
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
Cell population kinetic parameters for acute epidermal reactions in man
Cohen, L.
1986-11-01
Cell population kinetic parameters for acute reactions in squamous epithelium were estimated using available data on skin tolerance doses. Roughly equivalent doses for kilovoltage radiation delivered in equal daily fractions, as reported by F. Ellis (Br. J. Radiol. 15, 348-350 (1942)) and by R. Paterson (The Treatment of Malignant Disease by Radium and X-Rays. Edward Arnold, London, 1948), were combined with data for nonstandard fractionation at longer intervals of 1 or 2 weeks. By analyzing the combined data set, well-determined parameters could be derived. The data show that repopulation, with a potential cell doubling time of about 7 days, must occur in irradiated human skin, though this may possibly be limited to no more than seven doublings. The parameters derived are distinctly different from those associated with late-reacting dose-limiting tissues. The main difference is the steeper initial slope of the computed survival curve, that is a larger J parameter (multitarget model) or a larger alpha component (linear-quadratic model).
Kinetics of the ClO + NO2 + M reaction
NASA Technical Reports Server (NTRS)
Molina, M. J.; Molina, L. T.; Ishiwata, T.
1980-01-01
The ClO + NO2 + M reaction has been studied with two techniques: Fourier transform infrared spectroscopy of the products, and flash photolysis-ultraviolet absorption to monitor the decay of ClO in excess NO2. The measured third-order rate constant is 1.5 x 10 to the -31st cm to the 6th/molecule-squared per sec at 298 K with M = N2, in good agreement with previous literature values, but the rate constant appears to decrease by up to a factor of three in the presence of increasing amounts of OClO. For the infrared studies a stoichiometric mixture of ClO and NO2 was prepared in a flow system by mixing NO with OClO; at least as much NO2 as ClONO2 was produced under a variety of experimental conditions. These two sets of results are incompatible with the assumption made in previous kinetic studies that ClONO2 is the only recombination product; other isomers such as OClONO or ClOONO are likely to be formed three to four times faster. These results imply that potential stratospheric ozone depletion due to chlorofluoromethanes may be even larger than previously thought.
Photoinhibition of Chloroplast Reactions. I. Kinetics and Action Spectra 1
Jones, L. W.; Kok, B.
1966-01-01
A study was made of photoinhibition of spinach chloroplast reactions. The kinetics and spectral characteristics of the photoinhibition over a range between 230 and 700 mμ have been examined. The decline of activity due to preillumination was independent of wavelength, and dependent upon the number of quanta applied, not upon the rate of application. The effectiveness spectra of photoinhibition indicate that active ultraviolet light is absorbed by a pigment which is not a normal light absorber for photosynthesis and acts with a high quantum efficiency (> 0.1) for photoinhibition. Active visible light is absorbed by the pigments which sensitize photosynthesis (chlorophyll, carotenoids). A very low quantum efficiency (about 10−4) was observed for the photoinhibition with visible light. The action spectrum of the photoinhibition of dye reduction by chloroplasts and lyophylized Anacystis cells indicated that the damage caused by visible light is due to quanta absorbed by photosystem II. However, since system I might not be involved in dye reduction, the spectra may reflect only damage to photosystem II. PMID:16656345
Reassessing the dissolution of marine carbonates: II. Reaction kinetics
NASA Astrophysics Data System (ADS)
Gehlen, M.; Bassinot, F. C.; Chou, L.; McCorkle, D.
2005-08-01
We studied dissolution kinetics of the carbonate fraction >150 μm of sediments sampled along two bathymetric transects in the eastern tropical Atlantic: the Sierra Leone Rise (SLR) and the Cape Verde Plateau (CVP). The reaction was followed by monitoring solution pH during freedrift experiments lasting between 46 and 50 h (20 °C, pCO 2≈3100 ppm and 1 atm pressure). The alkalinity reached at the end of the dissolution experiments ranged between 2.444 and 2.798 meq/kg sw. The dissolution time series was extrapolated to equilibrium by fitting an empirical relation to the data. The estimated asymptotic concentration products ([Ca 2+] ∞×[CO 32-] ∞, for t→∞ and dA/dt=0) range from 4.27×10 -7 to 6.77×10 -7 mol 2/kg sw2. These asymptotic concentration products are comparable with the stoichiometric concentration product of aragonite (6.56×10 -7 mol 2/kg sw2) and calcite (4.37 (±0.22)×10 -7 mol 2/kg sw2) derived for the same sediment material during long-term equilibration experiments. They are indicative of the presence of trace amounts of a higher solubility carbonate phase in sediments of the shallow stations (SLR station A, 2637 m; CVP station M, 3104 m). While it is likely that this phase is aragonite, the presence of authigenic carbonate precipitated in contact with supersaturated bottom waters cannot be excluded. Calcite is the main dissolving carbonate mineral in sediments from deeper stations. The order of reaction is always greater than unity. It varies between 1.4 (SLR station C) and 2.8 (CVP station M2), with an average n=2.3±0.4. The higher order reaction is explained in terms of a multiphase system. Specific rate constants range from 0.09 to 0.53 meq/m 2/d.
Second-order truncated functional expansions of energy density functionals
NASA Astrophysics Data System (ADS)
Joubert, Daniel
2001-11-01
Parr and Liu [Chem. Phys. Lett., 276, 164 (1997)], showed that the electron-electron repulsion functional Vee[?] can be expressed in terms of its first and second functional derivatives under certain assumptions. Starting from this expansion it is shown that with the same assumptions, the density-functional exchange energy Ex[?], correlation energy Ec[?], and the kinetic contribution to the correlation energy Tc[?], can each be expressed in terms of their first and second functional derivatives only. It is pointed out that some expansions of density functionals proposed in the literature are not compatible with the expressions derived.
Experimental and theoretical methods in kinetic studies of heterogeneously catalyzed reactions.
Reyniers, Marie-Franoise; Marin, Guy B
2014-01-01
This review aims to illustrate the potential of kinetic analysis in general and microkinetic modeling in particular for rational catalyst design. Both ab initio calculations and experiments providing intrinsic kinetic data allow us to assess the effects of catalytic properties and reaction conditions on the activity and selectivity of the targeted reactions. Three complementary approaches for kinetic analysis of complex reaction networks are illustrated, using select examples of acid zeolite-catalyzed reactions from the authors' recent work. Challenges for future research aimed at defining targets for synthesis strategies that enable us to tune zeolite properties are identified. PMID:24910922
Kinetics of formation and reactions of thiyl radicals in aqueous solution
Huston, P.; Espenson, J.H.; Bakac, A. )
1992-03-04
Very few kinetic data are available that describe reactions of sulfur-centered radicals, despite their importance in biological systems. Thiyl radicals may be produced by generating carbon-centered radicals using visible laser flash photolysis and taking advantage of the repair reaction. Thiyl radicals are difficult to detect directly and require the use of a kinetic probe such as ABTS{sup 2{minus}} or TMPD. Kinetic studies of these reactions as well as reactions of ethanethiyl radicals with hexaaqua complexes of chromium(II), vanadium(II), and iron(II) are described.
Soil solid materials affect the kinetics of extracellular enzymatic reactions
NASA Astrophysics Data System (ADS)
Lammirato, C.; Miltner, A.; Kästner, M.
2009-04-01
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 solid materials tested, only activated charcoal may affect the reaction rate by limiting the substrate bioavailability while all the materials tested may affect the reaction rate by limiting the enzymatic activity. The results from the experiments on the effect of kaolinite on the reaction rate lead to the conclusion that even the degradation of substrates with unrestricted bioavailability can be affected by soil solid materials. The next experiments will show how much activity is lost by beta-glucosidase when adsorbed to bentonite and goethite and how activated carbon affects the reaction by limiting the substrate bioavailability and the enzymatic activity. In this last case beta-glucosidase will also be used in the immobilized form to eliminate the effect of activated carbon on the enzyme.
Pereira, José Clayston Melo; Iretskii, Alexei V; Han, Rui-Min; Ford, Peter C
2015-01-14
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(μ-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
A G-quadruplex based platform for label-free monitoring of DNA reaction kinetics.
Nie, Ji; Cai, Liang-Yuan; Zhang, Fang-Ting; Zhao, Ming-Zhe; Zhou, Ying-Lin; Zhang, Xin-Xiang
2014-12-21
Research on the kinetic characteristics and mechanisms of DNA reactions is crucial for bioengineering and biosensing. A G-quadruplex, which can form a peroxidase-mimicking DNAzyme with hemin, was for the first time used to establish a versatile platform for kinetic investigations on DNA reactions. G-quadruplex sequence EAD2 was incorporated into the corresponding nucleic acid reaction as product. The kinetic curves can be obtained rapidly and simply via the quantification of created DNAzyme. In this paper, the kinetics of isothermal linear strand displacement amplification reactions with different DNA lengths and isothermal exponential amplification reactions were successfully elucidated via the G-quadruplex based monitoring platform. As a safe and accessible alternative to the traditional methods, this robust, label-free, time-saving and high-throughput platform shows great potential for the exploration of more novel DNA reactions or circuits in an ingenious manner. PMID:25349990
Zhang, Fan; Yeh, Gour-Tsyh; Parker, Jack C; Brooks, Scott C; Pace, Molly N; Kim, Young-Jin; Jardine, Philip M; Watson, David B
2007-06-16
This paper presents a reaction-based water quality transport model in subsurface flow systems. Transport of chemical species with a variety of chemical and physical processes is mathematically described by M partial differential equations (PDEs). Decomposition via Gauss-Jordan column reduction of the reaction network transforms M species reactive transport equations into two sets of equations: a set of thermodynamic equilibrium equations representing N(E) equilibrium reactions and a set of reactive transport equations of M-N(E) kinetic-variables involving no equilibrium reactions (a kinetic-variable is a linear combination of species). The elimination of equilibrium reactions from reactive transport equations allows robust and efficient numerical integration. The model solves the PDEs of kinetic-variables rather than individual chemical species, which reduces the number of reactive transport equations and simplifies the reaction terms in the equations. A variety of numerical methods are investigated for solving the coupled transport and reaction equations. Simulation comparisons with exact solutions were performed to verify numerical accuracy and assess the effectiveness of various numerical strategies to deal with different application circumstances. Two validation examples involving simulations of uranium transport in soil columns are presented to evaluate the ability of the model to simulate reactive transport with complex reaction networks involving both kinetic and equilibrium reactions. PMID:17229488
Second-order analytic solutions for re-entry trajectories
NASA Astrophysics Data System (ADS)
Vinh, Nguyen X.; Kim, Eun-Kyou; Greenwood, Donald T.
With the development of aeroassist technology, either for near-earth operations or for planetary aero-capture, it is of interest to have accurate analytic solutions for the speed, flight path angle and altitude during the atmospheric passage. For a future aerospace plane which uses the accumulated kinetic energy to glide for a long range, explicit relations among the main state variables are also useful for guidance purposes. In this paper we have used normalization to put the equations of motion for planar entry around a non-rotating planet into a form which is suitable for an analytic integration. Explicit and accurate solutions are then obtained for ballistic fly-through trajectories, lifting skip trajectories and equilibrium glide trajectories.
Further development and testing of a second-order bulk boundary layer model. Master's thesis
Krasner, R.D.
1993-05-03
A one-layer bulk boundary layer model is developed. The model predicts the mixed layer values of the potential temperature, mixing ratio, and u- and v-momentum. The model also predicts the depth of the boundary layer and the vertically integrated turbulence kinetic energy (TKE). The TKE is determined using a second-order closure that relates the rate of dissipation to the TKE. The fractional area covered by rising motion sigma and the entrainment rate (E) are diagnostically determined. The model is used to study the clear convective boundary layer (CBL) using data from the Wangara, Australia boundary layer experiment. The Wangara data is also used as an observation base to validate model results. A further study is accomplished by simulating the planetary boundary layer (PBL) over an ocean surface. This study is designed to find the steady-state solutions of the prognostic variable.
Ji, Yuefei; Kong, Deyang; Lu, Junhe; Jin, Hao; Kang, Fuxing; Yin, Xiaoming; Zhou, Quansuo
2016-08-01
Degradation of tetrabromobisphenol A (TBBPA), a flame retardant widely spread in the environment, in Co(II) catalyzed peroxymonosulfate (PMS) oxidation process was systematically explored. The second-order-rate constant for reaction of sulfate radical (SO4(-)) with TBBPA was determined to be 5.27×10(10)M(-1)s(-1). Apparently, degradation of TBBPA showed first-order kinetics to the concentrations of both Co(II) and PMS. The presence of humic acid (HA) and bicarbonate inhibited TBBPA degradation, most likely due to their competition for SO4(-). Degradation of TBBPA was initiated by an electron abstraction from one of the phenolic rings. Detailed transformation pathways were proposed, including β-scission of isopropyl bridge, phenolic ring oxidation, debromination and coupling reactions. Further oxidative degradation of intermediates in Co(II)/PMS process yielded brominated disinfection by-products (Br-DBPs) such as bromoform and brominated acetic acids. Evolution profile of Br-DBPs showed an initially increasing and then decreasing pattern with maximum concentrations occurring around 6-10h. The presence of HA enhanced the formation of Br-DBPs significantly. These findings reveal potentially important, but previously unrecognized, formation of Br-DBPs during sulfate radical-based oxidation of bromide-containing organic compounds that may pose toxicological risks to human health. PMID:27107323
Kinetics of exciplex formation/dissipation in reaction following Weller Scheme II
Fedorenko, S. G.; Burshtein, A. I.
2014-09-21
Creation of exciplexes from the charged products of photoionization is considered by means of Integral Encounter Theory. The general kinetic equations of such a reaction following the Weller scheme II are developed. The special attention is given to the particular case of irreversible remote ionization of primary excited electron donor. Kinetics of exciplex formation is considered at fast biexponential geminate transformation of exciplexes in cage that gives way to subsequent bulk reaction of equilibrated reaction products controlled by power law recombination of ions. It is shown that the initial geminate stage of exciplex kinetics is observed only in diffusion controlled regime of the reaction and disappears with increasing mobility of ions in passing to kinetic regime. The quantum yield of exciplexes is studied along with their kinetics.
Ab initio study of the kinetics of hydrogen abstraction reactions on toluene and tetralin
Beste, Ariana; Britt, Phillip F; Buchanan III, A C; Harrison, Robert J; Hathorn, Bryan C
2008-01-01
Hydrogen abstraction reactions play a key role in many thermal and catalytic processes involved in the production of fuels and chemicals. In this paper, the reaction barriers and rate constants for the hydrogen abstraction reactions on toluene and tetralin by the benzyl radical are calculated by ab initio methods. These reactions are representatives of similar reactions occurring in the thermolysis of lignin model compounds containing the phenethyl phenyl ether (PPE) structural moiety. Thermolysis of PPE occurs by a free radical chain mechanism in which the product selectivity arises from competitive hydrogen abstraction at the benzylic and nonbenzylic methylen sites by chain carrying benzyl and phenoxyl radicals. The title reactions serve to calibrate the theoretical methods to be used in the study of PPE through comparison of the rate constants and the reaction enthalpies with reliable experimental values. In this study, we used two different hybrid density functionals (BHandHLYP, B3LYP) and second-order perturbation theory to obtain equilibrium and transition state geometries. Multiple transition states were found for both reactions. BHandHLYP underestimates and second-order perturbation theory overestimates the reaction barriers; B3LYP energy barriers agree well with experiment. Absolute and relative rate constants were calculated using transition state theory. We found that the relative rate constant using the B3LYP functional agrees within a factor of 2.0 with experiment at the experimental temperature of 333 K, indicating that the B3LYP functional will be successful in predicting relative rate constants for hydrogen abstraction reactions participating in the pyrolysis of PPE.
Radical Recombination Kinetics: An Experiment in Physical Organic Chemistry.
ERIC Educational Resources Information Center
Pickering, Miles
1980-01-01
Describes a student kinetic experiment involving second order kinetics as well as displaying photochromism using a wide variety of techniques from both physical and organic chemistry. Describes measurement of (1) the rate of the recombination reaction; (2) the extinction coefficient; and (3) the ESR spectrometer signal. (Author/JN)
NASA Astrophysics Data System (ADS)
Markovic, Bojan; Vladimirov, Sote; Cudina, Olivera; Savic, Vladimir; Karljikovic-Rajic, Katarina
2010-02-01
A novel topical corticosteroid FA-21-PhP, 2-phenoxypropionate ester of fluocinolone acetonide, has been synthesized in order to investigate the possibility of decreasing systemic side effects. In this study model system for in vitro solvolytic reaction of FA-21-PhP has been analyzed in ethanol/water (90:10, v/v) with excess of sodium hydrogen carbonate. The selected conditions have been used as in vitro model for activation of corticosteroid C-21 ester prodrug. The second-order derivative spectrophotometric method (DS) using zero-crossing technique was developed for monitoring ternary mixture of solvolysis. Fluocinolone acetonide (FA) as a solvolyte was determined in the mixture in the concentration range 0.062-0.312 mM using amplitude 2D 274.96. Experimentally determined LOD value was 0.0295 mM. The accuracy of proposed DS method was confirmed with HPLC referent method. Peak area of parent ester FA-21-PhP was used for solvolysis monitoring to ensure the initial stage of changes. Linear relationship in HPLC assay for parent ester was obtained in the concentration range 0.054-0.54 mM, with experimentally determined LOD value of 0.0041 mM. Investigated solvolytic reaction in the presence of excess of NaHCO 3 proceeded via a pseudo-first-order kinetic with significant correlation coefficients 0.9891 and 0.9997 for DS and HPLC, respectively. The values of solvolysis rate constant calculated according to DS and HPLC methods are in good accordance 0.038 and 0.043 h -1, respectively.
A Pore Scale Evaluation of the Kinetics of Mineral Dissolution and Precipitation Reactions (EMSI)
Steefel, Carl I.
2006-06-01
The chief goals for CEKA are to (1) collect and synthesize molecular-level kinetic data into a coherent framework that can be used to predict time evolution of environmental processes over a range of temporal and spatial scales; (2) train a cohort of talented and diverse students to work on kinetic problems at multiple scales; (3) develop and promote the use of new experimental techniques in environmental kinetics; (4) develop and promote the use of new modeling tools to conceptualize reaction kinetics in environmental systems; and (5) communicate our understanding of issues related to environmental kinetics and issues of scale to the broader scientific community and to the public.
Model for reaction kinetics in pyrolysis of wood
Ahuja, P.; Singh, P.C.; Upadhyay, S.N.; Kumar, S.
1996-12-31
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.
Effects of Deception on Children's Understanding of Second-Order False Belief
ERIC Educational Resources Information Center
Miller, Scott A.
2013-01-01
This research examined two questions: effects of deception on children's understanding of second-order false belief, and possible effects of number of siblings on second-order performance. Kindergarten children responded to 3 second-order problems that varied in the presence and the nature of deception. Performance was better on the problems
Exam Question Exchange: A Popular Approach to Reaction Kinetics.
ERIC Educational Resources Information Center
Collins, Michael P. S.; Alexander, John J., Ed.
1979-01-01
Presents an undergraduate physical chemistry question and its acceptable solution. This question, presented to share exam questions with other teachers, shows the analogy between molecular kinetics and population dynamics. (HM)
Bahr, Jean M.; Rubin, Jacob
1987-01-01
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.
Li, Jianhua; Peng, Jianbiao; Zhang, Ya; Ji, Yuefei; Shi, Huanhuan; Mao, Liang; Gao, Shixiang
2016-06-01
This study investigated and compared reaction kinetics, product characterization, and toxicity variation of triclosan (TCS) removal mediated by soybean peroxidase (SBP), a recognized potential peroxidase for removing phenolic pollutants, and the commonly used horseradish peroxidase (HRP) with the goal of assessing the technical feasibility of SBP-catalyzed removal of TCS. Reaction conditions such as pH, H2O2 concentration and enzyme dosage were found to have a strong influence on the removal efficiency of TCS. SBP can retain its catalytic ability to remove TCS over broad ranges of pH and H2O2 concentration, while the optimal pH and H2O2 concentration were 7.0 and 8μM, respectively. 98% TCS was removed with only 0.1UmL(-1) SBP in 30min reaction time, while an HRP dose of 0.3UmL(-1) was required to achieve the similar conversion. The catalytic performance of SBP towards TCS was more efficient than that of HRP, which can be explained by catalytic rate constant (KCAT) and catalytic efficiency (KCAT/KM) for the two enzymes. MS analysis in combination with quantum chemistry computation showed that the polymerization products were generated via CC and CO coupling pathways. The polymers were proved to be nontoxic through growth inhibition of green alga (Scenedesmus obliquus). Taking into consideration of the enzymatic treatment cost, SBP may be a better alternative to HRP upon the removal and detoxification of TCS in water/wastewater treatment. PMID:26921508
Glaude, P A; Melius, C; Pitz, W J; Westbrook, C K
2001-12-13
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.
Kinetics and thermodynamics of chemical reactions in Li/SOCl2 cells
NASA Technical Reports Server (NTRS)
Hansen, Lee D.; Frank, Harvey
1987-01-01
Work is described that was designed to determine the kinetic constants necessary to extrapolate kinetic data on Li/SOCl2 cells over the temperature range from 25 to 75 C. A second objective was to characterize as far as possible the chemical reactions that occur in the cells since these reactions may be important in understanding the potential hazards of these cells. The kinetics of the corrosion processes in undischarged Li/SOCl2 cells were determined and separated according to their occurrence at the anode and cathode; the effects that switching the current on and off has on the corrosion reactions was determined; and the effects of discharge state on the kinetics of the corrosion process were found. A thermodynamic analysis of the current-producing reactions in the cell was done and is included.
Naik, C; Westbrook, C K; Herbinet, O; Pitz, W J; Mehl, M
2010-01-22
New chemical kinetic reaction mechanisms are developed for two of the five major components of biodiesel fuel, methyl stearate and methyl oleate. The mechanisms are produced using existing reaction classes and rules for reaction rates, with additional reaction classes to describe other reactions unique to methyl ester species. Mechanism capabilities were examined by computing fuel/air autoignition delay times and comparing the results with more conventional hydrocarbon fuels for which experimental results are available. Additional comparisons were carried out with measured results taken from jet-stirred reactor experiments for rapeseed methyl ester fuels. In both sets of computational tests, methyl oleate was found to be slightly less reactive than methyl stearate, and an explanation of this observation is made showing that the double bond in methyl oleate inhibits certain low temperature chain branching reaction pathways important in methyl stearate. The resulting detailed chemical kinetic reaction mechanism includes more approximately 3500 chemical species and more than 17,000 chemical reactions.
ERIC Educational Resources Information Center
Koga, Nobuyoshi; Goshi, Yuri; Yoshikawa, Masahiro; Tatsuoka, Tomoyuki
2014-01-01
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
ERIC Educational Resources Information Center
Koga, Nobuyoshi; Goshi, Yuri; Yoshikawa, Masahiro; Tatsuoka, Tomoyuki
2014-01-01
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…
Utilization of the Recycle Reactor in Determining Kinetics of Gas-Solid Catalytic Reactions.
ERIC Educational Resources Information Center
Paspek, Stephen C.; And Others
1980-01-01
Describes a laboratory scale reactor that determines the kinetics of a gas-solid catalytic reaction. The external recycle reactor construction is detailed with accompanying diagrams. Experimental details, application of the reactor to CO oxidation kinetics, interphase gradients, and intraphase gradients are discussed. (CS)
Jašíková, Lucie; Anania, Mariarosa; Hybelbauerová, Simona; Roithová, Jana
2015-10-28
A new method to investigate the reaction kinetics of intermediates in solution by electrospray ionization mass spectrometry is presented. The method, referred to as delayed reactant labeling, allows investigation of a reaction mixture containing isotopically labeled and unlabeled reactants with different reaction times. It is shown that we can extract rate constants for the degradation of reaction intermediates and investigate the effects of various reaction conditions on their half-life. This method directly addresses the problem of the relevance of detected gaseous ions toward the investigated reaction solution. It is demonstrated for geminally diaurated intermediates formed in the gold mediated addition of methanol to alkynes. Delayed reactant labeling allows us to directly link the kinetics of the diaurated intermediates with the overall reaction kinetics determined by NMR spectroscopy. It is shown that the kinetics of protodeauration of these intermediates mirrors the kinetics of the addition of methanol demonstrating they are directly involved in the catalytic cycle. Formation as well as decomposition of diaurated intermediates can be drastically slowed down by employing bulky ancillary ligands at the gold catalyst; the catalytic cycle then proceeds via monoaurated intermediates. The reaction is investigated for 1-phenylpropyne (Ph-CC-CH3) using [AuCl(PPh3)]/AgSbF6 and [AuCl(IPr)]/AgSbF6 as model catalysts. Delayed reactant labeling is achieved by using a combination of CH3OH and CD3OH or Ph-CC-CH3 and Ph-CC-CD3. PMID:26430872
Second Order Catalytic Quasispecies Yields Discontinuous Mean Fitness at Error Threshold
NASA Astrophysics Data System (ADS)
Wagner, Nathaniel; Tannenbaum, Emmanuel; Ashkenasy, Gonen
2010-05-01
The quasispecies model describes processes related to the origin of life and viral evolutionary dynamics. We discuss how the error catastrophe that reflects the transition from localized to delocalized quasispecies population is affected by catalytic replication of different reaction orders. Specifically, we find that second order mechanisms lead to a discontinuity in the mean fitness of the population at the error threshold. This is in contrast to the behavior of the first order, autocatalytic replication mechanism considered in the standard quasispecies model. This suggests that quasispecies models with higher order replication mechanisms produce discontinuities in the mean fitness, and hence the viable population fraction as well, at the error threshold, while lower order replication mechanisms yield a continuous mean fitness function. We discuss potential implications for understanding replication in the RNA world and in virology.
Kinetic measurements on elementary fossil fuel combustion reactions over wide temperature ranges
Fontijn, A.
1991-01-01
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.
SECOND-ORDER SOLUTIONS OF COSMOLOGICAL PERTURBATION IN THE MATTER-DOMINATED ERA
Hwang, Jai-chan; Noh, Hyerim; Gong, Jinn-Ouk
2012-06-10
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.
Incorporation of aqueous reaction and sorption kinetics andbiodegradation into TOUGHREACT
Xu, Tianfu
2006-04-17
The needs for considering aqueous and sorption kinetics and microbiological processes arises in many subsurface problems, such as environmental and acid mine remediation. A general rate expression has been implemented into TOUGHREACT, which considers multiple mechanisms(pathways) and includes multiple product, Monod, and inhibition terms. In this paper, the formulation for incorporating kinetic rates among primary species into the mass balance equations is presented. A batch sulfide oxidation problem is simulated. The resulting concentrations are consistent with simple hand calculations. A 1-D reactive transport problem with kinetic biodegradation and sorption was investigated, which models the processes when a pulse of water containing NTA (nitrylotriacetate) and cobalt is injected into a column. The problem has several interacting chemical processes that are common to many environmental problems: biologically-mediated degradation of an organic substrate, bacterial cell growth and decay, metal sorption and aqueous speciation including metal-ligand complexation. The TOUGHREACT simulation results agree very well with those obtained with other simulators.
Probing Aluminum Reactions in Combustion and Explosion Via the Kinetic Isotope Effect
NASA Astrophysics Data System (ADS)
Tappan, Bryce
2015-06-01
The mechanism that controls the reaction speed of aluminum in explosion and combustion is poorly understood, and experimentally difficult to measure. Recently, work in our laboratory has demonstrated that during the combustion of nanoparticulate aluminum with H2O or D2O, different reaction rates due to the kinetic isotope effect are observed. This result is the first-ever observed kinetic isotope effect in a metal combustion reaction and verifies that chemical reaction kinetics play a major role in determining the global burning rate. During or shortly after a detonation, however, the reaction rates are dramatically faster and the physical mechanism controlling Al reaction is likely different than during combustion events. To utilize the kinetic isotope effect to probe Al reactions in detonation, formulations were produced that contain powdered Al in deuterated high explosives and high-fidelity detonation velocity were determined along with PDV measurements to observe early wall velocity expansion measurements. The JWL equation of state was solved to determine temperature, pressure and energies at specific time periods, in addition of Gurney energies, which enables the elucidation of Al reaction extent. By comparison of the Al oxidation with LiF, data indicate that Al oxidation occurs on an extremely fast time scale and isotope effects in both the HE detonation and post-detonation Al reactions are discussed.
Kinetics of Reactions of Monomeric Nitrosomethane Induced by Flash Photolysis.
ERIC Educational Resources Information Center
Kozubek, H.; And Others
1984-01-01
Describes an experiment in which the kinetics of dimerization of nitrosamine induced by a flash of light is measured. The experiment can be performed with a commercial ultraviolet-VIS spetrophotometer with easy to make modifications. The experiment demonstrates a flash photolysis system not always available in university chemistry laboratories.…
A New Perspective on Kinetic and Thermodynamic Control of Reactions.
ERIC Educational Resources Information Center
Snadden, R. B.
1985-01-01
Kinetic versus thermodynamic control of product formation is discussed in undergraduate textbooks, and journal papers suggest suitable experiments to illustrate this concept. In rationalizing experimental observations, this paper offers a new alternative to that conventionally employed and provides students with an interesting exercise in
Bahr, J.M.
1990-01-01
This paper extends a four-step derivation procedure, previously presented for cases of transport affected by surface reactions, to transport problems involving homogeneous reactions. Derivations for these classes of reactions are used to illustrate the manner in which mathematical differences between reaction classes are reflected in the mathematical derivation procedures required to identify kinetically influenced terms. Simulation results for a case of transport affected by a single solution phase complexation reaction and for a case of transport affected by a precipitation-dissolution reaction are used to demonstrate the nature of departures from equilibrium-controlled transport as well as the use of kinetically influenced terms in determining criteria for the applicability of the local equilibrium assumption. A final derivation for a multireaction problem demonstrates the application of the generalized procedure to a case of transport affected by reactions of several classes. -from Author
High temperature chemical kinetic study of the H2-CO-CO2-NO reaction system
NASA Technical Reports Server (NTRS)
Jachimowski, C. J.
1975-01-01
An experimental study of the kinetics of the H2-CO-CO2-NO reaction system was made behind incident shock waves at temperatures of 2460 and 2950 K. The overall rate of the reaction was measured by monitoring radiation from the CO + O yields CO2 + h upoilon reaction. Correlation of these data with a detailed reaction mechanism showed that the high-temperature rate of the reaction N + OH yields NO + H can be described by the low-temperature (320 K) rate coefficient. Catalytic dissociation of molecular hydrogen was an important reaction under the tests conditions.
Kinetic Studies of the Solvolysis of Two Organic Halides
ERIC Educational Resources Information Center
Duncan, J. A.; Pasto, D. J.
1975-01-01
Describes an undergraduate organic chemistry laboratory experiment which utilizes the solvolysis of organic halides to demonstrate first and second order reaction kinetics. The experiment also investigates the effect of a change of solvent polarity on reaction rate, common-ion and noncommon-ion salt effects, and the activation parameters of a…
Kinetics of Ethyl Acetate Synthesis Catalyzed by Acidic Resins
ERIC Educational Resources Information Center
Antunes, Bruno M.; Cardoso, Simao P.; Silva, Carlos M.; Portugal, Ines
2011-01-01
A low-cost experiment to carry out the second-order reversible reaction of acetic acid esterification with ethanol to produce ethyl acetate is presented to illustrate concepts of kinetics and reactor modeling. The reaction is performed in a batch reactor, and the acetic acid concentration is measured by acid-base titration versus time. The
Kinetics of Ethyl Acetate Synthesis Catalyzed by Acidic Resins
ERIC Educational Resources Information Center
Antunes, Bruno M.; Cardoso, Simao P.; Silva, Carlos M.; Portugal, Ines
2011-01-01
A low-cost experiment to carry out the second-order reversible reaction of acetic acid esterification with ethanol to produce ethyl acetate is presented to illustrate concepts of kinetics and reactor modeling. The reaction is performed in a batch reactor, and the acetic acid concentration is measured by acid-base titration versus time. The…
Atmospheric chemistry: Laboratory studies of kinetics of important reactions
NASA Astrophysics Data System (ADS)
Smith, S. J.
Experiments to measure the rate constants for some reactions of the atmospherically important nitrate radical (NO3) are described using the discharge-flow technique. The nitrate radical was monitored by optical absorption at lambda = 662 nm. The reactions of NO3 with some stable organic and inorganic substrates are reported. The temperature dependences of some of the rate constants were also determined (298 less than T less than 523 K). In most cases, computer simulation was used to extract the rate constant for the primary process because the time-dependent behavior of (NO3) was affected by secondary reactions of NO3 with products of the primary interaction. The Arrhenius parameter for the reactions of NO3 with CH3CH3, CH2CH2, CH3OH, CHCl3, and HCl were determined. The activation energies for the reactions studied between NO3 and some alkynes are presented along with the corresponding pre-exponential factors. Some reactions were studied at room temperature (298 plus or minus 2 K) only and the rate constants found (in units of cubic cm/molecule sec) are: buta-1,3-diene (1.8 x 10 (exp -13), isobutene (2.8 x 10 (exp -13), HBr (1.3 x 10 (exp -15) and hex-2-yne (3.0 x 10 (exp -14). Non-Arrhenius behavior was found in the reactions of NO3 with n-butane, isobutane and propene. The empirical variation of these rate constants with temperature is presented. The curvature of the Arrhenius plots is discussed in terms of (1) a temperature-dependent pre-exponential factor, and (2) the possibility that two competing channels, possessing differing activation energies, exist for each reaction. The atmospheric implications of these reactions are discussed with reference to the nighttime production of nitric acid and the importance of the these reactions as loss processes for NO3.
Kinetics of sunflower oil methanolysis at low temperatures.
Stamenković, Olivera S; Todorović, Zoran B; Lazić, Miodrag L; Veljković, Vlada B; Skala, Dejan U
2008-03-01
The kinetics of the sunflower oil methanolysis process was studied at lower temperatures (10-30 degrees C). The sigmoidal kinetics of the process was explained by the mass transfer controlled region in the initial heterogenous regime, followed by the chemical reaction controlled region in the pseudo-homogenous regime. A simple kinetic model, which did not require complex computation of the kinetic constants, was used for simulation of the TG conversion and the FAME formation in the latter regime: the fast irreversible second-order reaction was followed by the slow reversible second-order reaction close to the completion of the methanolysis reaction. The mass transfer was related to the drop size of the dispersed (methanol) phase, which reduced rapidly with the progress of the methanolysis reaction. This was attributed to the formation of the emulsifying agents stabilizing the emulsion of methanol drops into the oil. PMID:17434728
Implementing the Second-Order Fermi Process in a Kinetic Monte-Carlo Simulation
NASA Technical Reports Server (NTRS)
Summerlin, Errol J.
2010-01-01
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
CHLORINE DEMAND AND TTHM FORMATION KINETICS: A SECOND-ORDER MODEL
Much effort has been expended in attempting to develop mathematical models for chlorine demand in water and wastewater. Most of these efforts have centered around the use of first-order functions or modifications of first-order functions. Recently there has also been interest i...
Kinetic calculations and mechanism definition for reactions in an ammonium perchlorate flame
Ermolin, N.E.; Fomin, V.M.; Korobeinichev, O.P.; Tereshchenko, A.G.
1982-09-01
This article reports on detailed calculations on the reaction kinetics in APC flames on the basis of a wide set of possible reactions and experimental data on the initial composition of the gas mixture (gasification products from APC). The purpose is to select the most important reactions in this system by comparing the calculations on the kinetics with experimental data on the concentration profiles in APC flames. Discusses kinetic equations; rate constants as the reaction mechanism; results from kinetic calculations; and identification of major stages. A laminar flame such as that provided by ammonium perchlorate is described in general form by a system of differential equations that incorporate the transport of heat and matter in the presence of chemical reactions. APC is a system consisting of 4 elements (N,H,Cl and O). Points out that the scheme enables one to determine which reactions are responsible for producing the final products. Suggests that in the future one will be able to analyze experimental data on the reaction-rate profiles for stable components in order to determine either the atom and radical concentrations or the rate constants of the reactions involving them.
Reactions between beta-lactoglobulin and genipin: kinetics and characterization of the products
Technology Transfer Automated Retrieval System (TEKTRAN)
In this paper, we present the first detailed report of the reaction kinetics studies and the characterization of the products from the endothermic reactions between beta-lactoglobulin and genipin. The effects of concentration, temperature, and pH were examined. In the temperature range studied, th...
Brown, L.F.; Robinson, B.A.
1986-01-01
The technique of temperature-programmed reaction (TPR) is shown to be a practical experimental method for determining reaction-rate expressions and kinetics parameters for reactions in dilute aqueous solutions under high ambient pressure. By sampling and measuring the extent of reaction during a rise in temperature, information normally obtained from a series of isothermal batch kinetics experiments can be found in a single TPR test. The use of nonlinear least-squares regression eliminates the need to achieve a constant rate of temperature rise, simplifies the experimental requirements for TPR results, and gives more accurate answers than does a linear analysis of TPR results. Numerical simulations of TPR tests in the presence of random concentration-measurement error is used to assess the accuracy of the technique and to identify the best values of crucial operating parameters. The results of two TPR experiments measuring the alkaline hydrolysis of ethyl acetate demonstrate the applicability of the technique to reactions in dilute aqueous solutions at high pressure. These preliminary experimental results, along with numerical simulations, allow us to chart a course for future TPR kinetics experiments on a large number of similar reactions. 16 refs., 6 figs., 8 tabs.
Surface reactions kinetics between nanocrystalline magnetite and uranyl.
Missana, Tiziana; Maffiotte, César; García-Gutiérrez, Miguel
2003-05-01
Magnetite is the most important end member of iron corrosion products under reducing environment, which is the condition expected in a deep geological high level radioactive waste disposal. Nanocrystalline magnetite was synthesized in the laboratory and its physicochemical properties were analyzed in detail. The kinetics of the adsorption of U(VI) and the kinetics of the actinide reduction to a lower oxidation state, in presence of the oxide, were studied by means of batch sorption techniques and X-ray photoelectron spectroscopy (XPS) analysis. The results showed that the uranium sorption and reduction processes on the magnetite surface have very fast kinetics (hours), the reduction process being triggered by sorption. XPS measurements showed that the speciation of uranium at the surface does not show significant changes with time (from 1 day to 3 months), as well as the quantity of uranium detected at the surface. The surface speciation depended on the initial pH of the contact solution. Considering that the Eh of equilibrium between magnetite and the solution, under our experimental conditions, is slightly positive (50-100 mV), the uranium reduction would also be thermodynamically possible within the liquid phase. However, the kinetics of reduction in the liquid occur at a much slower rate which, in turn, has to depend on the attainment of the magnetite/solution equilibrium. The decrease of uranium in solution, observed after the uranyl adsorption stage, and particularly at acidic pH, is most probably due to the precipitation of U(IV) formed in the solution. PMID:12725835
Mechanistic interpretation of glass reaction: Input to kinetic model development
Bates, J.K.; Ebert, W.L.; Bradley, J.P.; Bourcier, W.L.
1991-05-01
Actinide-doped SRL 165 type glass was reacted in J-13 groundwater at 90{degrees}C for times up to 278 days. The reaction was characterized by both solution and solid analyses. The glass was seen to react nonstoichiometrically with preferred leaching of alkali metals and boron. High resolution electron microscopy revealed the formation of a complex layer structure which became separated from the underlying glass as the reaction progressed. The formation of the layer and its effect on continued glass reaction are discussed with respect to the current model for glass reaction used in the EQ3/6 computer simulation. It is concluded that the layer formed after 278 days is not protective and may eventually become fractured and generate particulates that may be transported by liquid water. 5 refs., 6 figs., 3 tabs.
Mechanistic interpretation of glass reaction: Input to kinetic model development
Bates, J.K.; Ebert, W.L.; Bradley, J.P.; Bourcier, W.L.
1991-05-01
Actinide-doped SRL 165 type glass was reacted in J-13 groundwater at 90{degree}C for times up to 278 days. The reaction was characterized by both solution and solid analyses. The glass was seen to react nonstoichiometrically with preferred leaching of alkali metals and boron. High resolution electron microscopy revealed the formation of a complex layer structure which became separated from the underlying glass as the reaction progressed. The formation of the layer and its effect on continued glass reaction are discussed with respect to the current model for glass reaction used in the EQ3/6 computer simulation. It is concluded that the layer formed after 278 days is not protective and may eventually become fractured and generate particulates that may be transported by liquid water. 5 refs., 5 figs. , 3 tabs.
Comparison of kinetic and equilibrium reaction models insimulating the behavior of porous media
Kowalsky, Michael B.; Moridis, George J.
2006-11-29
In this study we compare the use of kinetic and equilibriumreaction models in the simulation of gas (methane) hydrate behavior inporous media. Our objective is to evaluate through numerical simulationthe importance of employing kinetic versus equilibrium reaction modelsfor predicting the response of hydrate-bearing systems to externalstimuli, such as changes in pressure and temperature. Specifically, we(1) analyze and compare the responses simulated using both reactionmodels for natural gas production from hydrates in various settings andfor the case of depressurization in a hydrate-bearing core duringextraction; and (2) examine the sensitivity to factors such as initialhydrate saturation, hydrate reaction surface area, and numericaldiscretization. We find that for large-scale systems undergoing thermalstimulation and depressurization, the calculated responses for bothreaction models are remarkably similar, though some differences areobserved at early times. However, for modeling short-term processes, suchas the rapid recovery of a hydrate-bearing core, kinetic limitations canbe important, and neglecting them may lead to significantunder-prediction of recoverable hydrate. Assuming validity of the mostaccurate kinetic reaction model that is currently available, the use ofthe equilibrium reaction model often appears to be justified andpreferred for simulating the behavior of gas hydrates, given that thecomputational demands for the kinetic reaction model far exceed those forthe equilibrium reaction model.
Kinetics and mechanism of the IO + IO reaction
NASA Technical Reports Server (NTRS)
Sander, S. P.
1986-01-01
The flash photolysis-absorption technique has been used to measure the rate constant for the reaction IO + IO over the temperature range 250-373 K and pressure range 20-700 torr of N2. The rate constant for the overall reaction was found to be independent of pressure and equal to 1.73 x 10 to the -12th exp (1020 + or - 200)/T cu cm/molecule s. Branching ratios for the reaction channels forming 2I + O2, I2 + O2, and I2O2, were found to be pressure dependent, with the I2 channel accounting for less than 5 percent of the total reaction over the observed pressure range. A stable reaction product was observed between 230 and 300 nm which was formed on a long time scale compared to IO disappearance. The rate constant for the reaction I + O3 + yields to IO + O2 was measured at 298 K and found to be (9.5 + or - 1.5) x 10 to the -13th cu cm/molecule s.
Kinetic and mechanistic studies of free-radical reactions in combustion
Tully, F.P.
1993-12-01
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.
Zhidkov, A.B.; Smirnov, E.P.
1989-02-01
This work is devoted to the study of the kinetics of the reaction of titanium tetrachloride with the hydride functional groups of diamond. The research was performed on submicron powders of ASM 0.7/0.3 grade synthetic diamond with a specific surface area of 8.0 m/sup 2//g as measured from the adsorption of nitrogen. The reaction was carried out in a flow-through quartz reactor in a flow of dry He. The content of the titanium in the samples was determined by a photocolorimetric method. A kinetic equation for the reaction of diamond with titanium tetrachloride was found on the basis of a statistical approach.
Yeh, G.T.; Iskra, G.A.; Szecsody, J.E.; Zachara, J.M.; Streile, G.P.
1995-01-01
This report presents the development of a mixed chemical Kinetic and Equilibrium MODel in which every chemical species can be treated either as a equilibrium-controlled or as a kinetically controlled reaction. The reaction processes include aqueous complexation, adsorption/desorption, ion exchange, precipitation/dissolution, oxidation/reduction, and acid/base reactions. Further development and modification of KEMOD can be made in: (1) inclusion of species switching solution algorithms, (2) incorporation of the effect of temperature and pressure on equilibrium and rate constants, and (3) extension to high ionic strength.
General theory of multistage geminate reactions of isolated pairs of reactants. I. Kinetic equations
Doktorov, Alexander B.; Kipriyanov, Alexey A.
2014-05-14
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
2014-05-14
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. PMID:24832250
General theory of multistage geminate reactions of isolated pairs of reactants. I. Kinetic equations
NASA Astrophysics Data System (ADS)
Doktorov, Alexander B.; Kipriyanov, Alexey A.
2014-05-01
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.
Carrasquillo-Flores, Ronald; Gallo, Jean Marcel R.; Hahn, Konstanze; Dumesic, James A.; Mavrikakis, Manos
2013-11-05
Periodic, self-consistent density functional theory calculations (DFT-GGA-PW91) on Pt(111) and Pt_{3}Re(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.
Barbot, Antoine; Landy, Michael S.; Carrasco, Marisa
2012-01-01
The visual system can use a rich variety of contours to segment visual scenes into distinct perceptually coherent regions. However, successfully segmenting an image is a computationally expensive process. Previously we have shown that exogenous attention—the more automatic, stimulus-driven component of spatial attention—helps extract contours by enhancing contrast sensitivity for second-order, texture-defined patterns at the attended location, while reducing sensitivity at unattended locations, relative to a neutral condition. Interestingly, the effects of exogenous attention depended on the second-order spatial frequency of the stimulus. At parafoveal locations, attention enhanced second-order contrast sensitivity to relatively high, but not to low second-order spatial frequencies. In the present study we investigated whether endogenous attention—the more voluntary, conceptually-driven component of spatial attention—affects second-order contrast sensitivity, and if so, whether its effects are similar to those of exogenous attention. To that end, we compared the effects of exogenous and endogenous attention on the sensitivity to second-order, orientation-defined, texture patterns of either high or low second-order spatial frequencies. The results show that, like exogenous attention, endogenous attention enhances second-order contrast sensitivity at the attended location and reduces it at unattended locations. However, whereas the effects of exogenous attention are a function of the second-order spatial frequency content, endogenous attention affected second-order contrast sensitivity independent of the second-order spatial frequency content. This finding supports the notion that both exogenous and endogenous attention can affect second-order contrast sensitivity, but that endogenous attention is more flexible, benefitting performance under different conditions. PMID:22895879
Manoj, Kelath Murali; Baburaj, Arun; Ephraim, Binoy; Pappachan, Febin; Maviliparambathu, Pravitha Parapurathu; Vijayan, Umesh K; Narayanan, Sivaprasad Valiyaveettil; Periasamy, Kalaiselvi; George, Ebi Ashley; Mathew, Lazar T
2010-01-01
Many heme enzymes show remarkable versatility and atypical kinetics. The fungal extracellular enzyme chloroperoxidase (CPO) characterizes a variety of one and two electron redox reactions in the presence of hydroperoxides. A structural counterpart, found in mammalian microsomal cytochrome P450 (CYP), uses molecular oxygen plus NADPH for the oxidative metabolism (predominantly hydroxylation) of substrate in conjunction with a redox partner enzyme, cytochrome P450 reductase. In this study, we employ the two above-mentioned heme-thiolate proteins to probe the reaction kinetics and mechanism of heme enzymes. Hitherto, a substrate inhibition model based upon non-productive binding of substrate (two-site model) was used to account for the inhibition of reaction at higher substrate concentrations for the CYP reaction systems. Herein, the observation of substrate inhibition is shown for both peroxide and final substrate in CPO catalyzed peroxidations. Further, analogy is drawn in the "steady state kinetics" of CPO and CYP reaction systems. New experimental observations and analyses indicate that a scheme of competing reactions (involving primary product with enzyme or other reaction components/intermediates) is relevant in such complex reaction mixtures. The presence of non-selective reactive intermediate(s) affords alternate reaction routes at various substrate/product concentrations, thereby leading to a lowered detectable concentration of "the product of interest" in the reaction milieu. Occam's razor favors the new hypothesis. With the new hypothesis as foundation, a new biphasic treatment to analyze the kinetics is put forth. We also introduce a key concept of "substrate concentration at maximum observed rate". The new treatment affords a more acceptable fit for observable experimental kinetic data of heme redox enzymes. PMID:20498847
Heterogeneous reaction mechanisms and kinetics relevant to the CVD of semiconductor materials
Creighton, J.R.; Coltrin, M.E.
1994-03-01
This report documents the state of the art in experimental and theoretical techniques for determining reaction mechanisms and chemical kinetics of heterogeneous reactions relevant to the chemical vapor deposition of semiconductor materials. It summarizes the most common ultra-high vacuum experimental techniques that are used and the types of rate information available from each. Several case studies of specific chemical systems relevant to the microelectronics industry are described. Theoretical methods for calculating heterogeneous reaction rate constants are also summarized.
Thermal analysis of paddy husk. Part 2: Order of reaction and other kinetic parameters
Jain, A.K.; Sharma, S.K.; Singh, D.
1997-12-31
This paper presents experimental data on the thermal degradation of paddy husk and cellulose in air, argon and a mixture of nitrogen and oxygen (95:5) at different linear heating rates. The data is used for the determination of kinetic parameters using different orders of reaction and an optimum order of reaction identified. The often used assumption of unity order of reaction under all circumstances is shown to have a limited validity.
Second-order sideband effects mediated by microwave in hybrid electro-optomechanical systems
NASA Astrophysics Data System (ADS)
Chen, Bin; Wang, Lei-Dong; Zhang, Jie; Zhai, Ai-Ping; Xue, Hai-Bin
2016-02-01
We theoretically investigate the second-order sideband effects in a hybrid electro-optomechanical system, and mainly focus on the influence of the microwave signal on the second-order sideband generation. The numerical results show that just by tuning the power and the detuning of the microwave signal, the second-order sideband can be significantly modified. More importantly, while driving this hybrid system by a blue detuned microwave with suitable power, strong second-order sideband effect can be induced. These results can find potential applications in optical frequency converters in the quantum information processing.
Linear matrix inequalities for analysis and control of linear vector second-order systems
Adegas, Fabiano D.; Stoustrup, Jakob
2014-10-06
Many dynamical systems are modeled as vector second-order differential equations. This paper presents analysis and synthesis conditions in terms of LMI with explicit dependence in the coefficient matrices of vector second-order systems. These conditions benefit from the separation between the Lyapunov matrix and the system matrices by introducing matrix multipliers, which potentially reduce conservativeness in hard control problems. Multipliers facilitate the usage of parameter-dependent Lyapunov functions as certificates of stability of uncertain and time-varying vector second-order systems. The conditions introduced in this work have the potential to increase the practice of analyzing and controlling systems directly in vector second-order form.
Snodgrass, Michael; Kalaida, Natasha; Winer, E Samuel
2009-06-01
Access can either be first-order or second-order. First order access concerns whether contents achieve representation in phenomenal consciousness at all; second-order access concerns whether phenomenally conscious contents are selected for metacognitive, higher order processing by reflective consciousness. When the optional and flexible nature of second-order access is kept in mind, there remain strong reasons to believe that exclusion failure can indeed isolate phenomenally conscious stimuli that are not so accessed. Irvine's [Irvine, E. (2009). Signal detection theory, the exclusion failure paradigm and weak consciousness-Evidence for the access/phenomenal distinction? Consciousness and Cognition.] partial access argument fails because exclusion failure is indeed due to lack of second-order access, not insufficient phenomenally conscious information. Further, the enable account conforms with both qualitative differences and subjective report, and is simpler than the endow account. Finally, although first-order access may be a distinct and important process, second-order access arguably reflects the core meaning of access generally. PMID:19243977
Kinetics and Mechanism of the Chlorate-Bromide Reaction.
Sant'Anna, Rafaela T P; Faria, Roberto B
2015-11-01
The chlorate-bromide reaction, ClO3(-) + 6Br(-) + 6H(+) → 3Br2 + Cl(-) + 3H2O, was followed at the Br3(-)/Br2 isosbestic point (446 nm). A fifth-order rate law was found: (1)/3 d[Br2]/dt = k[ClO3(-)][Br(-)][H(+)](3) (k = 5.10 × 10(-6) s(-1) L(4) mol(-4)) at 25 °C and I = 2.4 mol L(-1). At high bromide concentrations, the bromide order becomes close to zero, indicating a saturation profile on bromide concentration, similar to the chloride saturation profile observed in the chlorate-chloride reaction. A mechanism is proposed that considers the formation of the intermediate BrOClO2(2-), similar to the intermediate ClOClO2(2-) proposed in the mechanism of the chlorate-chloride reaction. PMID:26467822
Second-order structure function analysis of scatterometer winds over the Tropical Pacific
NASA Astrophysics Data System (ADS)
King, Gregory P.; Vogelzang, Jur; Stoffelen, Ad
2015-01-01
second-order structure functions are used to quantify and compare the small-scale information contained in near-surface ocean wind products derived from measurements by ASCAT on MetOp-A and SeaWinds on QuikSCAT. Two ASCAT and three SeaWinds products are compared in nine regions (classified as rainy or dry) in the tropical Pacific between 10S and 10N and 140 and 260E for the period November 2008 to October 2009. Monthly and regionally averaged longitudinal and transverse structure functions are calculated using along-track samples. To ease the analysis, the following quantities were estimated for the scale range 50 to 300 km and used to intercompare the wind products: (i) structure function slopes, (ii) turbulent kinetic energies (TKE), and (iii) vorticity-to-divergence ratios. All wind products are in good qualitative agreement, but also have important differences. Structure function slopes and TKE differ per wind product, but also show a common variation over time and space. Independent of wind product, longitudinal slopes decrease when sea surface temperature exceeds the threshold for onset of deep convection (about 28C). In rainy areas and in dry regions during rainy periods, ASCAT has larger divergent TKE than SeaWinds, while SeaWinds has larger vortical TKE than ASCAT. Differences between SeaWinds and ASCAT vortical TKE and vorticity-to-divergence ratios for the convectively active months of each region are large.
An efficient second-order accurate and continuous interpolation for block-adaptive grids
NASA Astrophysics Data System (ADS)
Borovikov, Dmitry; Sokolov, Igor V.; Tóth, Gábor
2015-09-01
In this paper we present a second-order and continuous interpolation algorithm for cell-centered adaptive-mesh-refinement (AMR) grids. Continuity requirement poses a non-trivial problem at resolution changes. We develop a classification of the resolution changes, which allows us to employ efficient and simple linear interpolation in the majority of the computational domain. The algorithm is well suited for massively parallel computations. Our interpolation algorithm allows extracting jump-free interpolated data distribution along lines and surfaces within the computational domain. This capability is important for various applications, including kinetic particles tracking in three dimensional vector fields, visualization (i.e. surface extraction) and extracting variables along one-dimensional curves such as field lines, streamlines and satellite trajectories, etc. Particular examples are models for acceleration of solar energetic particles (SEPs) along magnetic field-lines. As such models are sensitive to sharp gradients and discontinuities the capability to interpolate the data from the AMR grid to be passed to the SEP model without producing false gradients numerically becomes crucial. We provide a complete description of the algorithm and make the code publicly available as a Fortran 90 library.
Atmospheric Chemistry: Laboratory Studies of Kinetics of Important Reactions.
NASA Astrophysics Data System (ADS)
Smith, S. J.
Available from UMI in association with The British Library. Requires signed TDF. This thesis describes the experiments to measure the rate constants for some reactions of the atmospherically important nitrate radical (NO_3) using the discharge-flow technique. The nitrate radical was monitored by optical absorption at lambda = 662 nm. The reactions of NO_3 with some stable organic and inorganic substrates are reported. The temperature dependences of some of the rate constants have also been determined (298 < T < 523 K). In most cases, computer simulation was used to extract the rate constant for the primary process because the time-dependent behaviour of (NO_3) was affected by secondary reactions of NO_3 with products of the primary interaction. The Arrhenius parameter in parentheses (E _{rm a}/kJ mol^ {-1}, A/cm^3 molecule ^{-1}s^ {-1} respectively) for the following reactions have been determined: ethane (37, 6.7 times 10^{-12}), ethylene (25.8, 6.3 times 10^ {-12}), CH_3OH (21.3, 1.2 times 10^ {-12}), CHCiota_3 (23.4, 8.6 times 10 ^{-13}) and HCl (27.7, 4 times 10^{-12}). The activation energies for the reactions studied between NO_3 and some alkynes are represented well by the value 25 +/- 3 kJ mol^{-1} and the corresponding pre-exponential factors (expressed as ln(10 ^{13}A/cm^3 molecule^{-1}s ^{-1}) are as follows: C_2H_2 (1.6 +/- 1.4), C_3H _4 (5.0 +/- 1.4), 1-C_4H_6 (5.8 +/- 1.0), 1-C_5 H_8 (5.7 +/- 0.6) and 1-C_6H _{10} (4.5 +/- 0.4). Some reactions were studied at room temperature _3(298 +/- 2 K) only and the rate constants found (in units of cm ^3 molecule^{ -1}s^{-1}) are: buta-1,3-diene (1.8 times 10 ^{-13}), isobutene (2.8 times 10^{-13 }), HBr (1.3 times 10 ^{-15}) and hex-2-yne (3.0 times 10^{-14 }). Non-Arrhenius behaviour was found in the reactions of NO_3 with n-butane, isobutane and propene. The empirical variation of these rate constants with temperature is well represented by the three parameter expressions:. k(T) = 1.2 times 10 ^{-46}T^{11.4 }exp(-1131/T) for n-butane; k(T) = 1.6 times 10^ {-49}T^{12.3} exp(-1828/T) for isobutane; and for propene, k(T) = 2.4 times 10 ^{-19}T^ {2.25}exp(-700/T). The curvature of the Arrhenius plots is discussed in terms of (a) a temperature-dependent pre-exponential factor and (b) the possibility that two competing channels, possessing differing activation energies, exist for each reaction. The atmospheric implications of these reactions are discussed with reference to the nigh-time production of nitric acid and the importance of the these reactions as loss processes for NO_3.
Yoon, In-Ho; Yoo, Gursong; Hong, Hye-Jin; Kim, Jungmin; Kim, Min Gyu; Choi, Wang-Kyu; Yang, Ji-Won
2016-02-01
In this study, we investigated phenol degradation via zero-valent iron (ZVI)-assisted Fenton reaction through kinetic and spectroscopic analysis. In batch experiments, 100 mg/L of phenol was completely degraded, and 75% of TOC was removed within 3 min under an optimal hydrogen peroxide (H2O2) concentration (50 mM) via the Fenton reaction. In the absence of H2O2, oxygen (O2) was dissolved into the solution and produced H2O2, which resulted in phenol degradation. However, phenol removal efficiency was not very high compared to external H2O2 input. The Fenton reaction rapidly occurred at the surface of ZVI, and then phenol mobility from the solution to the ZVI surface was the rate determining step of the whole reaction. The pseudo-second order adsorption kinetic model well describes phenol removal, and its rate increased according to the H2O2 concentration. X-ray absorption spectroscopic analysis revealed that iron oxide (Fe-O bonding) was formed on ZVI with [H2O2] > 50 mM. A high concentration of H2O2 led to rapid degradation of phenol and caused corrosion on the ZVI surface, indicating that Fe(2+) ions were rapidly oxidized to Fe(3+) ions due to the Fenton reaction and that Fe(3+) was precipitated as iron oxide on the ZVI surface. However, ZVI did not show corroded characteristics in the absence of H2O2 due to the insufficient ZVI-assisted Fenton reaction and oxidation of Fe(2+) to Fe(3+). PMID:26692518
Oxygen Diffusion and Reaction Kinetics in Continuous Fiber Ceramic Matrix Composites
NASA Technical Reports Server (NTRS)
Halbig, Michael C.; Eckel, Andrew J.; Cawley, James D.
1999-01-01
Previous stressed oxidation tests of C/SiC composites at elevated temperatures (350 C to 1500 C) and sustained stresses (69 MPa and 172 MPa) have led to the development of a finite difference cracked matrix model. The times to failure in the samples suggest oxidation occurred in two kinetic regimes defined by the rate controlling mechanisms (i.e. diffusion controlled and reaction controlled kinetics). Microstructural analysis revealed preferential oxidation along as-fabricated, matrix microcracks and also suggested two regimes of oxidation kinetics dependent on the oxidation temperature. Based on experimental results, observation, and theory, a finite difference model was developed. The model simulates the diffusion of oxygen into a matrix crack bridged by carbon fibers. The model facilitates the study of the relative importance of temperature, the reaction rate constant, and the diffusion coefficient on the overall oxidation kinetics.
Gargano, Immacolata; Olivieri, Giuseppe; Spasiano, Danilo; Andreozzi, Roberto; Pollio, Antonino; Marotta, Raffaele; D'Ambrosio, Nicola; Marzocchella, Antonio
2015-10-20
The kinetic characterization of the photosynthetic activity in autotrophic microalgae plays a key role in the design of optimized photobioreactors. This paper presents a procedure to assess kinetic parameters of a three-state photosynthetic reaction centres model. Four kinetic parameters of the model were assessed by processing the time-series measurements of pulse-amplitude modulation fluorimetry. The kinetic parameters were assessed for several microalgal strains (Stichococcus bacillaris, Scenedesmus vacuolatus, Chlamydomonas reinhardtii, Chlorella vulgaris) growth in vertical and inclined bubble columns and irradiated by white-light or red/blue light. The procedure was successfully applied to the investigated strains. The assessed parameters allow identifying the irradiance range under which: the photochemical process is controlled by the photons capture; the photoinhibition competes with the photochemical quenching. The analysis of the time-scale of the photosynthetic reaction centres as a function of the irradiance allows interpreting the performances of photobioreactors characterized by non-homogeneous irradiance. PMID:26216180
The Gaseous Explosive Reaction : A Study of the Kinetics of Composite Fuels
NASA Technical Reports Server (NTRS)
Stevens, F W
1929-01-01
This report deals with the results of a series of studies of the kinetics of gaseous explosive reactions where the fuel under observation, instead of being a simple gas, is a known mixture of simple gases. In the practical application of the gaseous explosive reaction as a source of power in the gas engine, the fuels employed are composite, with characteristics that are apt to be due to the characteristics of their components and hence may be somewhat complex. The simplest problem that could be proposed in an investigation either of the thermodynamics or kinetics of the gaseous explosive reaction of a composite fuel would seem to be a separate study of the reaction characteristics of each component of the fuel and then a study of the reaction characteristics of the various known mixtures of those components forming composite fuels more and more complex. (author)
NASA Technical Reports Server (NTRS)
Radhakrishnan, Krishnan; Bittker, David A.
1993-01-01
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.
Reaction kinetics, molecular action, and mechanisms of cellulolytic proteins.
Mosier, N S; Hall, P; Ladisch, C M; Ladisch, M R
1999-01-01
Cellulolytic proteins form a complex of enzymes that work together to depolymerize cellulose to the soluble products cellobiose and glucose. Fundamental studies on their molecular mechanisms have been facilitated by advances in molecular biology. These studies have shown homology between cellulases from different microorganisms, and common mechanisms between enzymes whose modes of action have sometimes been viewed as being different, as suggested by the distribution of soluble products. A more complete picture of the cellulolytic action of these proteins has emerged and combines the physical and chemical characteristics of solid cellulose substrates with the specialized structure and function of the cellulases that break it down. This chapter combines the fundamentals of cellulose structure with enzyme function in a manner that relates the cellulose binding and biochemical kinetics at the catalytic site of the proteins to the macroscopic behavior of cellulase enzyme systems. PMID:10533433
Hydrodynamic/kinetic reactions in liquid-dominated geothermal systems
NASA Astrophysics Data System (ADS)
Nesewich, J. P.; Gracey, C. M.
1982-04-01
A mobile geothermal well-site test unit at the Mercer 2 well in South Brawley, California (Imperial Valley), was constructed and tested. The equipment controlled, monitored, and recorded all process conditions of single- and dual-flash power cycles. Single and two-phase flashed brine effluents were flowed through piping component test sections to provide hydrodynamic/kinetic data for scale formation. The unit operated at flowrates in excess of 200 gpm and is designed to accommodate flowrates up to 300 gpm. Primary scale formations encountered were those of PbS, Fe2(OH)3Cl (iron hydroxychloride), iron chlorides, and non-crystalline forms of SiO2. The formation of iron hydroxychloride was due to the unusually high concentration of iron in the wellhead brine (5000 mg/l).
Complex Cure Kinetics of the Hydroxyl-Epoxide Reaction in DGEBA Epoxy Hardened with Diethanolamine
NASA Astrophysics Data System (ADS)
Ancipink, Windy; McCoy, John; Kropka, Jamie; Celina, Mathias
The curing of a diglycidyl ether of bisphenol-A Epoxy (Epon 828) with diethanolamine (DEA) involves a fast amine-epoxide reaction followed by a slower hydroxyl-epoxide reaction. At curing temperatures below 100°C, the time scales of these two reactions are well separated, and the hydroxyl addition can be studied as an ''isolated'' reaction. The hydroxyl-epoxide reaction is of great interest due to the complex kinetics involved, which are brought about by competing reactions. The reaction kinetics are believed to be tertiary amine catalyzed and are well fit to a modified form of the Kamal-type equation. Here we study the complex long term reaction kinetics at various temperatures, by using isothermal modulated differential scanning calorimetry, micro calorimetry, and infrared spectroscopy. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
Ab initio studies of the kinetic isotope effect of the CH4 + OH atmospheric reaction
NASA Astrophysics Data System (ADS)
Lasaga, Antonio C.; Gibbs, G. V.
1991-07-01
High level ab initio calculations have been carried out on the C-13 - C-12 kinetic isotope effect of the CH4 + OH reaction in the atmosphere. The results agree quite well with both the absolute value of the isotope effect and the temperature dependence of the effect, based on new experimental data. The calculated kinetic isotope effect supports a bigger effect of biomass burning on the methane global budget.
Reaction kinetics of resveratrol with tert-butoxyl radicals
NASA Astrophysics Data System (ADS)
Džeba, Iva; Pedzinski, Tomasz; Mihaljević, Branka
2012-09-01
The rate constant for the reaction of t-butoxyl radicals with resveratrol was studied under pseudo-first order conditions. The rate constant was determined by measuring the phenoxyl radical formation rate at 390 nm as function of resveratrol concentration in acetonitrile. The rate constant was determined to be 6.5×108 M-1s-1. This high value indicates the high reactivity consistent with the strong antioxidant activity of resveratrol.
Reaction Mechanism and Kinetics of Enargite Oxidation at Roasting Temperatures
NASA Astrophysics Data System (ADS)
Padilla, Rafael; Aracena, Alvaro; Ruiz, Maria C.
2012-10-01
Roasting of enargite (Cu3AsS4) in the temperature range of 648 K to 898 K (375 °C to 625 °C) in atmospheres containing variable amounts of oxygen has been studied by thermogravimetric methods. From the experimental results of weight loss/gain data and X-ray diffraction (XRD) analysis of partially reacted samples, the reaction mechanism of the enargite oxidation was determined, which occurred in three sequential stages:
Kinetics of the reaction of nitric oxide with hydrogen
NASA Technical Reports Server (NTRS)
Flower, W. L.; Hanson, R. K.; Kruger, C. H.
1975-01-01
The reaction of nitric oxide with hydrogen has been studied in the temperature range 2400-4500 K using a shock-tube technique. 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 decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principal result of the study was the determination of the rate constant k1 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 k1 were obtained for each test through comparisons of measured and numerically predicted NO profiles. The data are fit closely by the expression k1 = 1.34 times 10 to the fourteenth power exp(-49 200/RT) cu cm/mole-sec. These data appear to be the first available for this rate constant.
Low temperature kinetics of the CH3OH + OH reaction.
Gmez Martn, J C; Caravan, R L; Blitz, M A; Heard, D E; Plane, J M C
2014-04-17
The rate constant of the reaction between methanol and the hydroxyl radical has been studied in the temperature range 56-202 K by pulsed laser photolysis-laser induced fluorescence in two separate experiments using either a low temperature flow tube coupled to a time-of-flight mass spectrometer or a pulsed Laval nozzle apparatus. The two independent techniques yield rate constants that are in mutual agreement and consistent with the results reported previously below 82 K [Shannon et al. Nat. Chem. 2013, 5, 745-749] and above 210 K [Dillon et al. Phys. Chem. Chem. Phys. 2005, 7, 349-355], showing a very sharp increase with decreasing temperature with an onset around 180 K. This onset is also signaled by strong chemiluminescence tentatively assigned to formaldehyde, which is consistent with the formation of the methoxy radical at low temperature by quantum tunnelling, and its subsequent reaction with H and OH. Our results add confidence to the previous low temperature rate constant measurements and consolidate the experimental reference data set for further theoretical work required to describe quantitatively the tunnelling mechanism operating in this reaction. An additional measurement of the rate constant at 56 K yielded a value of (4.9 0.8) 10(-11) cm(3) molecule(-1) s(-1) (2?), showing that the rate constant is increasing less rapidly at temperatures below 70 K. PMID:24669816
Kinetic of antigent-antibody reactions with scattering method
NASA Astrophysics Data System (ADS)
Bilyi, Olexander I.; Kiselyov, Yevgen M.; Novikov, Volodymyr P.
2001-07-01
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.
Low Temperature Kinetics of the CH3OH + OH Reaction
Martín, J. C. Gómez; Caravan, R. L.; Blitz, M. A.; Heard, D. E.; Plane, J. M. C.
2014-01-01
The rate constant of the reaction between methanol and the hydroxyl radical has been studied in the temperature range 56-202 K by pulsed laser photolysis-laser induced fluorescence in two separate experiments using either a low temperature flow tube coupled to a time of flight mass spectrometer or a pulsed Laval nozzle apparatus. The two independent techniques yield rate constants which are in mutual agreement and consistent with the results reported previously below 82 K [Shannon et al., Nature Chemistry, 2013, 5, 745-749] and above 210 K [Dillon et al., Phys. Chem. Chem. 2005, 7, 349-355], showing a very sharp increase with decreasing temperature with an onset around 180 K. This onset is also signalled by strong chemiluminescence tentatively assigned to formaldehyde, which is consistent with the formation of the methoxy radical at low temperature by quantum tunnelling, and its subsequent reaction with H and OH. Our results add confidence to the previous low temperature rate constant measurements and consolidate the experimental reference dataset for further theoretical work required to describe quantitatively the tunnelling mechanism operating in this reaction. An additional measurement of the rate constant at 56 K yielded a value of (4.9 ± 0.8) × 10−11 cm3 molecule−1 s−1 (2σ), showing that the rate constant is increasing less rapidly at temperatures below 70 K. PMID:24669816
Post processing with first- and second-order hidden Markov models
NASA Astrophysics Data System (ADS)
Taghva, Kazem; Poudel, Srijana; Malreddy, Spandana
2013-01-01
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.
Operator Factorization and the Solution of Second-Order Linear Ordinary Differential Equations
ERIC Educational Resources Information Center
Robin, W.
2007-01-01
The theory and application of second-order linear ordinary differential equations is reviewed from the standpoint of the operator factorization approach to the solution of ordinary differential equations (ODE). Using the operator factorization approach, the general second-order linear ODE is solved, exactly, in quadratures and the resulting…
On group classification of normal systems of linear second-order ordinary differential equations
NASA Astrophysics Data System (ADS)
Meleshko, S. V.; Moyo, S.
2015-05-01
In this paper we study the general group classification of systems of linear second-order ordinary differential equations inspired from earlier works and recent results on the group classification of such systems. Some interesting results and subsequent theorem arising from this particular study are discussed here. This paper considers the study of irreducible systems of second-order ordinary differential equations.
The similarity rules for second-order subsonic and supersonic flow
NASA Technical Reports Server (NTRS)
Van Dyke, Milton D
1958-01-01
The similarity rules for linearized compressible flow theory (Gothert's rule and its supersonic counterpart) are extended to second order. It is shown that any second-order subsonic flow can be related to "nearly incompressible" flow past the same body, which can be calculated by the Janzen-Rayleigh method.
ERIC Educational Resources Information Center
Coull, Greig J.; Leekam, Susan R.; Bennett, Mark
2006-01-01
This study investigated how 4- to 7-year-old children's second-order belief attribution might be facilitated by either reducing information processing or varying the sequence of task questions. In Experiment 1, compared with Perner and Wimmer's (1985) original second-order false-belief task, a new task with reduced information-processing demands…
Having a Second-Order Mind while Doing First-Order Therapy.
ERIC Educational Resources Information Center
Simon, George M.
1992-01-01
Contends that overemphasis in literature on distinguishing first- and second-order therapeutic perspectives has produced schism within field of family therapy. Attempts to bridge that schism, using view of language that informs dialectical psychology to construct both-order, and framing of first- and second-order, perspectives. Such framing…
Optimality Conditions in Differentiable Vector Optimization via Second-Order Tangent Sets
Jimenez, Bienvenido Novo, Vicente
2004-03-15
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.
Tomita, Kenji; Inoue, Kaiki Taro
2008-05-15
We study second order gravitational effects of local inhomogeneities on the cosmic microwave background radiation in flat universes with matter and a cosmological constant {lambda}. We find that the general relativistic correction to the Newtonian approximation is negligible at second order provided that the size of the inhomogeneous region is sufficiently smaller than the horizon scale. For a spherically symmetric top-hat type quasilinear perturbation, the first order temperature fluctuation corresponding to the linear integrated Sachs-Wolfe effect is enhanced (suppressed) by the second order one for a compensated void (lump). As a function of redshift of the local inhomogeneity, the second order temperature fluctuations due to evolution of the gravitational potential have a peak before the matter-{lambda} equality epoch for a fixed comoving size and a density contrast. The second order gravitational effects from local quasilinear inhomogeneities at a redshift z{approx}1 may significantly affect the cosmic microwave background.
The effects of second-order hydrodynamics on a semisubmersible floating offshore wind turbine
NASA Astrophysics Data System (ADS)
Bayati, I.; Jonkman, J.; Robertson, A.; Platt, A.
2014-06-01
The objective of this paper is to assess the second-order hydrodynamic effects on a semisubmersible floating offshore wind turbine. Second-order hydrodynamics induce loads and motions at the sum- and difference-frequencies of the incident waves. These effects have often been ignored in offshore wind analysis, under the assumption that they are significantly smaller than first-order effects. The sum- and difference-frequency loads can, however, excite eigenfrequencies of a floating system, leading to large oscillations that strain the mooring system or vibrations that cause fatigue damage to the structure. Observations of supposed second-order responses in wave-tank tests performed by the DeepCwind consortium at the Maritime Research Institute Netherlands (MARIN) offshore basin suggest that these effects might be more important than originally expected. These observations inspired interest in investigating how second-order excitation affects floating offshore wind turbines and whether second-order hydrodynamics should be included in offshore wind simulation tools like FAST. In this work, the effects of second-order hydrodynamics on a floating semisubmersible offshore wind turbine are investigated. Because FAST is currently unable to account for second-order effects, a method to assess these effects was applied in which linearized properties of the floating wind system derived from FAST (including the 6x6 mass and stiffness matrices) are used by WAMIT to solve the first- and second-order hydrodynamics problems in the frequency domain. The method was applied to the Offshore Code Comparison Collaboration Continuation OC4-DeepCwind semisubmersible platform, supporting the National Renewable Energy Laboratory's 5-MW baseline wind turbine. In this paper, the loads and response of the system caused by the second-order hydrodynamics are analysed and compared to the first-order hydrodynamic loads and induced motions in the frequency domain. Further, the second-order loads and induced response data are compared to the loads and motions induced by aerodynamic loading as solved by FAST.
Effects of Second-Order Hydrodynamics on a Semisubmersible Floating Offshore Wind Turbine: Preprint
Bayati, I.; Jonkman, J.; Robertson, A.; Platt, A.
2014-07-01
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.
Characterization of reaction kinetics in a porous electrode
NASA Technical Reports Server (NTRS)
Fedkiw, Peter S.
1990-01-01
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.
Chang, M. H.; Cho, S.; Lee, E. S.; Ahn, M. Y.; Kim, D. H.; Jung, J. J.; Chung, H.; Shim, M.; Song, K. M.; Kim, D.; Yoshida, H.
2008-07-15
The de-hydriding reaction between ZrCo and hydrogen is the most important role of delivering hydrogen isotopes for fusion energies. Many researchers experimented in various conditions and estimated the relationship between ZrCo and hydrogen. In this study the kinetic approaches are performed using numerical simulations between ZrCo and hydrogen. Two kinds of parameter estimations are performed for the equilibrium pressure and the kinetics modeling and those are validated by the good agreement between predicted and experimental data. Based on the numerical simulation with obtained parameters, more rapid rates of de-hydriding reaction can be achieved with lower pressure and higher temperature. (authors)
New Colorimetric reaction for end-point, continuous-flow, and kinetic measurement of urea.
Jung, D; Biggs, H; Erikson, J; Ledyard, P U
1975-07-01
A reaction of urea, o-phthalaldehyde and N-(1-naphthyl)ethylenediamine is described for measurement of urea by manual, continuous-flow, and kinetic methods. The continuous-flow system requires 25 mu-l of sample; 40 samples can be analyzed per hour. The kinetic method requires no enzymes, has no lag phase, and has good sensitivity. A major advantage of the reaction is that it occurs at a temperature of 37 degrees C or lower. The results obtained by all three methods agree well with those for a continuous-flow procedure in which diacetyl is a reagent. PMID:1137920
Nikerel, I Emrah; van Winden, Wouter A; Verheijen, Peter J T; Heijnen, Joseph J
2009-01-01
In this work, we present a time-scale analysis based model reduction and parameter identifiability analysis method for metabolic reaction networks. The method uses the information obtained from short term chemostat perturbation experiments. We approximate the time constant of each metabolite pool by their turn-over time and classify the pools accordingly into two groups: fast and slow pools. We performed a priori model reduction, neglecting the dynamic term of the fast pools. By making use of the linlog approximative kinetics, we obtained a general explicit solution for the fast pools in terms of the slow pools by elaborating the degenerate algebraic system resulting from model reduction. The obtained relations yielded also analytical relations between a subset of kinetic parameters. These relations also allow to realize an analytical model reduction using lumped reaction kinetics. After solving these theoretical identifiability problems and performing model reduction, we carried out a Monte Carlo approach to study the practical identifiability problems. We illustrated the methodology on model reduction and theoretical/practical identifiability analysis on an example system representing the glycolysis in Saccharomyces cerevisiae cells. PMID:18718548
Semitsoglou-Tsiapou, Sofia; Templeton, Michael R; Graham, Nigel J D; Hernández Leal, Lucía; Martijn, Bram J; Royce, Alan; Kruithof, Joop C
2016-03-15
The degradation kinetics of three pesticides - metaldehyde, clopyralid and mecoprop - by ultraviolet photolysis and hydroxyl radical oxidation by low pressure ultraviolet hydrogen peroxide (LP-UV/H2O2) advanced oxidation was determined. Mecoprop was susceptible to both LP-UV photolysis and hydroxyl radical oxidation, and exhibited the fastest degradation kinetics, achieving 99.6% (2.4-log) degradation with a UV fluence of 800 mJ/cm(2) and 5 mg/L hydrogen peroxide. Metaldehyde was poorly degraded by LP-UV photolysis while 97.7% (1.6-log) degradation was achieved with LP-UV/H2O2 treatment at the maximum tested UV fluence of 1000 mJ/cm(2) and 15 mg/L hydrogen peroxide. Clopyralid was hardly susceptible to LP-UV photolysis and exhibited the lowest degradation by LP-UV/H2O2 among the three pesticides. The second-order reaction rate constants for the reactions between the pesticides and OH-radicals were calculated applying a kinetic model for LP-UV/H2O2 treatment to be 3.6 × 10(8), 2.0 × 10(8) and 1.1 × 10(9) M(-1) s(-1) for metaldehyde, clopyralid and mecoprop, respectively. The main LP-UV photolysis reaction product from mecoprop was 2-(4-hydroxy-2-methylphenoxy) propanoic acid, while photo-oxidation by LP-UV/H2O2 treatment formed several oxidation products. The photo-oxidation of clopyralid involved either hydroxylation or dechlorination of the ring, while metaldehyde underwent hydroxylation and produced acetic acid as a major end product. Based on the findings, degradation pathways for the three pesticides by LP-UV/H2O2 treatment were proposed. PMID:26803264
Kinetics of the reaction Cl + NO2 + M
NASA Technical Reports Server (NTRS)
Leu, M.-T.
1984-01-01
Using atomic chlorine resonance fluorescence at 140 nm to detect the decay of atomic chlorine in the presence of an excess of NO2, the rate constant for the reaction Cl + NO2 + M, where M is the total gas concentration, is measured over the temperature range 264 to 417 K and at a pressure 1 to 7 torr in a discharge flow system. The rate constants for M= He and M= N2 are measured and the results are summarized in a table. The systematic error of the rate constants is estimated to be about 15 percent. A static photolysis system coupled with an FTIR spectrophotometer is used to determine the branching ratio for the formation of two possible isomers. The ratio is concluded to be ClONO (greater than or equal 75 percent) and ClNO2 (less than or equal 25 percent) which is in agreement with the results of Niki et al. (1978).
Theoretical study of the kinetics of reactions of the monohalogenated methanes with atomic chlorine.
Brudnik, Katarzyna; Twarda, Maria; Sarzyński, Dariusz; Jodkowski, Jerzy T
2013-04-01
Ab initio calculations at the G2 level were used in a theoretical description of the kinetics and mechanism of the hydrogen abstraction reactions from fluoro-, chloro- and bromomethane by chlorine atoms. The profiles of the potential energy surfaces show that mechanism of the reactions under investigation is complex and consists of two - in the case of CH3F+Cl - and of three elementary steps for CH3Cl+Cl and CH3Br+Cl. The heights of the energy barrier related to the H-abstraction are of 8-10 kJ mol(-1), the lowest value corresponds to CH3Cl+Cl and the highest one to CH3F+Cl. The rate constants were calculated using the theoretical method based on the RRKM theory and the simplified version of the statistical adiabatic channel model. The kinetic equations derived in this study[Formula: see text]and[Formula: see text]allow a description of the kinetics of the reactions under investigation in the temperature range of 200-3000 K. The kinetics of reactions of the entirely deuterated reactants were also included in the kinetic analysis. Results of ab initio calculations show that D-abstraction process is related with the energy barrier of 5 kJ mol(-1) higher than the H-abstraction from the corresponding non-deuterated reactant molecule. The derived analytical equations for the reactions, CD3X+Cl, CH2X+HCl and CD2X+DCl (X = F, Cl and Br) are a substantial supplement of the kinetic data necessary for the description and modeling of the processes of importance in the atmospheric chemistry. PMID:23239396
Design, synthesis and polymerization of novel second-order nonlinear optical materials
NASA Astrophysics Data System (ADS)
Ghosn, Rima Kamal
1997-10-01
This dissertation focuses on the design, synthesis and nonlinear optical properties of large second-order nonlinearity chromophores. A review of the fundamentals of nonlinear optics and polymeric materials is provided in the first chapter. The second chapter focuses on the optimization of reaction conditions of asymmetric diphenyl diacetylene liquid crystals. The third chapter deals with the design and synthesis of chromophores derived from thiobarbituric acids. Conventional nonlinear optical organic materials employ chromophores possessing a large transition dipole moment between the ground and first excited states. This requirement is fulfilled using conjugated molecules containing optimally balanced electron donor and acceptor moieties. Barbituric acid is a strong electron acceptor that yields molecules with a large first hyperpolarizabilities. There are two classes of chromophores investigated, both capable of covalent polymer incorporation, which include the main chain and double-end crosslinkable chromophores. These chromophores, high in both nonlinearity and thermal stability, are regarded as ideal candidates for electrooptical devices. The fourth chapter investigates polyimides as stable NLO polymeric materials.
Kinetics of Thermochemical Reactions Important in the Venus Atmospheric Sulfur Cycle
NASA Technical Reports Server (NTRS)
Fegley, Bruce, Jr.
1997-01-01
The purpose of this project was to experimentally measure the rates of several thermochemical gas-solid reactions between sulfur gases in the Venus atmosphere and reactive minerals on the hot Venus surface. Despite the great importance of these reactions for the maintenance of significant amounts of sulfur gases (and thus for the maintenance of the global cloud cover) in the atmosphere of Venus, essentially no kinetic data are currently available for them.
Form and motion processing of second-order stimuli in color vision.
Garcia-Suarez, Luis; Mullen, Kathy T
2013-01-01
We investigate whether there are second-order form and motion mechanisms in human color vision. Second-order stimuli are contrast modulations of a noise carrier. The contrast envelopes are static Gabors of different spatial frequencies (0.125-1 cycles/) or drifting Gabors of different temporal frequencies (0.25 cycles/, 0.5-4 Hz). Stimuli are isoluminant red-green or achromatic. Second-order form processing is measured using a simultaneous 2IFC (two-interval forced-choice) detection and orientation identification task, and direction identification is used for second-order motion processing. We find that for simple detection thresholds, chromatic performance is as good or better than achromatic performance, whereas for both motion and form tasks, chromatic performance is poorer than achromatic. Chromatic second-order form perception is very poor across all spatial and temporal frequencies measured and has a lowpass contrast modulation sensitivity function with a spatial cutoff of 1 cycle/ and temporal cutoff of 4 Hz. Chromatic second-order motion sensitivity is even poorer than for form and typically is limited to 1-2 Hz. To determine whether this residual motion processing might be based on feature tracking, we used the pedestal paradigm of Lu and Sperling (1995). We find that adding a static pedestal of the same spatial frequency as the drifting Gabor envelope, with its contrast set to 1-2 times its detection threshold, impairs motion direction performance for the chromatic stimuli but not the achromatic. This suggests that the motion of second-order chromatic stimuli is not processed by a second-order system but by a third-order, feature-tracking system, although a genuine second-order motion system exists for achromatic stimuli. PMID:23766541
Yancey, Benjamin; Vyazovkin, Sergey
2015-04-21
This study highlights the effect of the aggregate state of a reactant on the reaction kinetics under the conditions of nanoconfinement. Our previous work (Phys. Chem. Chem. Phys., 2014, 16, 11409) has demonstrated considerable deceleration of the solid state trimerization of sodium dicyanamide in organically modified silica nanopores. In the present study we use FTIR, NMR, pXRD, TGA and DSC to analyze the kinetics and mechanism of the liquid state trimerization of potassium and rubidium dicyanamide under similar conditions of nanoconfinement. It is found that nanoconfinement accelerates dramatically the kinetics of the liquid state trimerization, whereas it does not appear to affect the reaction mechanism. Kinetic analysis indicates that the acceleration is associated with an increase in the preexponential factor. Although nanoconfinement has the opposite effects on the respective kinetics of solid and liquid state trimerization, both effects are linked to a change in the preexponential factor. The results obtained are consistent with our hypothesis that the effects differ because nanoconfinement may promote disordering of the solid and ordering of the liquid reaction media. PMID:25796991
Kinetics of Single-Enzyme Reactions on Vesicles: Role of Substrate Aggregation
NASA Astrophysics Data System (ADS)
Zhdanov, Vladimir P.
2015-03-01
Enzymatic reactions occurring in vivo on lipid membranes can be influenced by various factors including macromolecular crowding in general and substrate aggregation in particular. In academic studies, the role of these factors can experimentally be clarified by tracking single-enzyme kinetics occurring on individual lipid vesicles. To extend the conceptual basis for such experiments, we analyze herein the corresponding kinetics mathematically with emphasis on the role of substrate aggregation. In general, the aggregation may occur on different length scales. Small aggregates may e.g. contain a few proteins or peptides while large aggregates may be mesoscopic as in the case of lipid domains which can be formed in the membranes composed of different lipids. We present a kinetic model describing comprehensively the effect of aggregation of the former type on the dependence of the reaction rate on substrate membrane concentration. The results obtained with physically reasonable parameters indicate that the aggregation-related deviations from the conventional Michaelis-Menten kinetics may be appreciable. Special Issue Comments: This theoretical article is focused on single-enzyme reactions occurring in parallel with substrate aggregation on individual vesicles. This subject is related to a few Special Issue articles concerning enzyme dynamics6,7 and function8 and mathematical aspects of stochastic kinetics.9
Studies of Reaction Kinetics of Methane Hydrate Dissocation in Porous Media
Moridis, George J.; Seol, Yongkoo; Kneafsey, Timothy J.
2005-03-10
The objective of this study is the description of the kinetic dissociation of CH4-hydrates in porous media, and the determination of the corresponding kinetic parameters. Knowledge of the kinetic dissociation behavior of hydrates can play a critical role in the evaluation of gas production potential of gas hydrate accumulations in geologic media. We analyzed data from a sequence of tests of CH4-hydrate dissociation by means of thermal stimulation. These tests had been conducted on sand cores partially saturated with water, hydrate and CH4 gas, and contained in an x-ray-transparent aluminum pressure vessel. The pressure, volume of released gas, and temperature (at several locations within the cores) were measured. To avoid misinterpreting local changes as global processes, x-ray computed tomography scans provided accurate images of the location and movement of the reaction interface during the course of the experiments. Analysis of the data by means of inverse modeling (history matching ) provided estimates of the thermal properties and of the kinetic parameters of the hydration reaction in porous media. Comparison of the results from the hydrate-bearing porous media cores to those from pure CH4-hydrate samples provided a measure of the effect of the porous medium on the kinetic reaction. A tentative model of composite thermal conductivity of hydrate-bearing media was also developed.
Second-order Born effect in coplanar doubly symmetric (e,2e) collisions for sodium
NASA Astrophysics Data System (ADS)
Wang, Yang; Jiao, Liguang; Zhou, Yajun
2012-06-01
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.
Analytical solution of the problem on thermal slip of second order for molecular gases
NASA Astrophysics Data System (ADS)
Popov, V. N.
2006-05-01
Results obtained using exact analytical methods in the problem on thermal slip of second order for molecular gases with allowance for the rotational degrees of freedom of molecules have been presented. Numerical calculations of the thermal-slip coefficient for a number of molecular gases have been carried out. The dependence of the velocity of thermal slip of second order of a molecular gas on the Prandtl number has been shown. The found value of the coefficient of thermal slip of second order theoretically confirms the existence of negative (in the direction of the temperature gradient) thermophoresis for molecular gases.
First and Second Order Necessary Conditions for Stochastic Optimal Control Problems
Bonnans, J. Frederic; Silva, Francisco J.
2012-06-15
In this work we consider a stochastic optimal control problem with either convex control constraints or finitely many equality and inequality constraints over the final state. Using the variational approach, we are able to obtain first and second order expansions for the state and cost function, around a local minimum. This fact allows us to prove general first order necessary condition and, under a geometrical assumption over the constraint set, second order necessary conditions are also established. We end by giving second order optimality conditions for problems with constraints on expectations of the final state.
First and second order approximations to stage numbers in multicomponent enrichment cascades
Scopatz, A.
2013-07-01
This paper describes closed form, Taylor series approximations to the number product stages in a multicomponent enrichment cascade. Such closed form approximations are required when a symbolic, rather than a numeric, algorithm is used to compute the optimal cascade state. Both first and second order approximations were implemented. The first order solution was found to be grossly incorrect, having the wrong functional form over the entire domain. On the other hand, the second order solution shows excellent agreement with the 'true' solution over the domain of interest. An implementation of the symbolic, second order solver is available in the free and open source PyNE library. (authors)
Orientation-selective adaptation to first- and second-order patterns in human visual cortex
Larsson, Jonas; Landy, Michael S.; Heeger, David J.
2006-01-01
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
NASA Astrophysics Data System (ADS)
Tungatarov, Aliaskar; Rzayeva, Gulnar
2015-09-01
The main purpose of the present paper consists an investigation of an elliptic system in the plane with Laplace operator in differential part. Within the scope of this target, investigation of the continuous solutions of a class of complex partial second order differential equations in the plane in explicit form are constructed. Robin boundary value problem for second order elliptic system in the plane with singular coefficients in unbounded angular domain is solved. In this article, a new method for construction of the general solution of second order ordinary differential equation with variable coefficients developed by A. Tungatarov is used.
NASA Astrophysics Data System (ADS)
Luo, T.; Khursheed, A.
2006-04-01
At present transmission electron energy loss spectrum (EELS) analysis is only carried out in dedicated research instruments such as transmission electron microscopes (TEMs) or scanning transmission electron microscopes. This article presents a new design of second-order geometric aberration corrected EELS spectrometer attachment using split plates, which enables conventional scanning electron microscopes (SEMs) to provide TEM-like EELS spectra. Correction to a third-order dominant geometric aberration pattern has been achieved, which indicates that most of the second-order geometric aberration component is eliminated. This second-order aberration corrected spectrometer attachment design can enable SEMs to provide transmission EELS spectrums.
Ismagilov, Timur Z.
2015-02-01
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.
Excluded volume effects on the intrachain reaction kinetics.
Kim, Ji-Hyun; Lee, Woojin; Sung, Jaeyoung; Lee, Sangyoub
2008-05-15
On the basis of the recently developed optimized Rouse-Zimm theory of chain polymers with excluded volume interactions, we calculate the long-time first-order rate constant k(1) for end-to-end cyclization of linear chain polymers. We first find that the optimized Rouse-Zimm theory provides the longest chain relaxation times tau(1) of excluded volume chains that are in excellent agreement with the available Brownian dynamics simulation results. In the free-draining limit, the cyclization rate is diffusion-controlled and k(1) is inversely proportional to tau(1), and the k(1) values calculated using the Wilemski-Fixman rate theory are in good agreement with Brownian dynamics simulation results. However, when hydrodynamic interactions are included, noticeable deviations are found. The main sources of errors are fluctuating hydrodynamic interaction and correlation hole effects as well as the non-Markovian reaction dynamic effect. The physical natures of these factors are discussed, and estimates for the magnitudes of required corrections are given. When the corrections are included, the present theory allows the prediction of accurate k(1) values for the cyclization of finite-length chains in good solvents as well as the correct scaling exponent in the long-chain limit. PMID:18419166
Thermodynamics and kinetics of reactions in protective coating systems
NASA Technical Reports Server (NTRS)
Gupta, B.; Sarkhel, A.; Sivakumar, R.; Seigle, L.
1974-01-01
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.
Kinetics and mechanism of the rat brain phenol sulphotransferase reaction.
Pennings, E J; Vrielink, R; van Kempen, G M
1978-01-01
Some properties of rat brain phenol sulphotransferase were investigated in in vitro at pH7.4. The enzyme was purified 10-fold by chromatography on DEAE-Sephadex -50. It can be assayed with 4-hydroxy-3-methoxyphenylethylene glycol or 4-methylumbelliferone as the sulphate acceptor. The partially purified enzyme is stable for at least 1 week when stored at 4 degrees C. It is, however, additionally activated (10--20%) and stabilized by 1 mM-dithiothreitol. The activity of the enzyme does not depend on the addition of exogenous Mg2+. The pH optima for the sulphation of 4-hydroxy-3-methoxyphenylethylene glycol and 4-methylumbelliferone are 7.8 and 7.4 respectively. Substrate inhibition by the sulphate acceptor is apparent at concentrations over 0.05mM. Initial-velocity studies in the absence and presence of product and dead-end inhibitors suggested that the mechanism of the rat brain sulphotransferase reaction is sequential ordered Bi Bi with a dead-end complex of enzyme with adenosine 3',5'-biphosphate and sulphate acceptor. The sulphate donor adenosine 3'-phosphate 5'-sulphatophosphate is the first substrate that adds to the enzyme, and the sulphate acceptor is the second substrate. The dissociation constant for the complex of enzyme with sulphate donor is 21 micron. The sulphated substrate is the first product and adenosine 3',5'-biphosphate is the second product that leaves the enzyme. PMID:28735
NASA Astrophysics Data System (ADS)
Wang, Haifeng; Popov, Pavel P.; Pope, Stephen B.
2010-03-01
We study a class of methods for the numerical solution of the system of stochastic differential equations (SDEs) that arises in the modeling of turbulent combustion, specifically in the Monte Carlo particle method for the solution of the model equations for the composition probability density function (PDF) and the filtered density function (FDF). This system consists of an SDE for particle position and a random differential equation for particle composition. The numerical methods considered advance the solution in time with (weak) second-order accuracy with respect to the time step size. The four primary contributions of the paper are: (i) establishing that the coefficients in the particle equations can be frozen at the mid-time (while preserving second-order accuracy), (ii) examining the performance of three existing schemes for integrating the SDEs, (iii) developing and evaluating different splitting schemes (which treat particle motion, reaction and mixing on different sub-steps), and (iv) developing the method of manufactured solutions (MMS) to assess the convergence of Monte Carlo particle methods. Tests using MMS confirm the second-order accuracy of the schemes. In general, the use of frozen coefficients reduces the numerical errors. Otherwise no significant differences are observed in the performance of the different SDE schemes and splitting schemes.
Jarvis, Michael J Y; Blagojevic, Voislav; Koyanagi, Gregory K; Bohme, Diethard K
2013-02-14
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
Marcus Theory: Thermodynamics CAN Control the Kinetics of Electron Transfer Reactions
ERIC Educational Resources Information Center
Silverstein, Todd P.
2012-01-01
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
Kinetics of the reaction of diethylene glycol bis-chloroformate with allyl alcohol
Alekseev, N.N.; Shtoda, N.F.; Dzumedzei, N.V.
1988-10-01
The kinetics of diethylene glycol bis-chloroformate solvolysis by excess allyl alcohol in toluene and carbon tetrachloride has been studied. Under conditions of a pseudofirst order reaction with respect to diethylene glycol bis-chloroformate the activation parameters confirm an addition-detachment mechanism.
Architectural Effects on Reaction-Diffusion Kinetics in Molecular Glass Photoresists
Sha, Jing; Lee, Jin-Kyun; Ober, Christoper K.; Kang, Shuhui; Prabhu, Vivek M.; Soles, Christopher L.; Bonnesen, Peter V
2010-01-01
Understanding acid reaction-diffusion kinetics is crucial for controlling the lithographic performance of chemically amplified photoresists. In this work, we study how the molecular architectures of positive-tone chemically amplified molecular glass resists can affect acid reaction-diffusion kinetics during post exposure bake. We compare the acid reaction-diffusion kinetics of a common photoacid generator in molecular glass resists with chemical structural similarity to poly(4-hydroxystyrene), designed with branched and ring architectures. An in situ FTIR method was used to measure reaction rate, acid trapping behavior, and acid diffusivity as a function of post exposure bake temperature. We have found that the acid kinetics performance in molecular glass resists is correlated to the film molar densities which are affected by the architectures of the resist molecules. These results allow a modeling analysis of latent image formation in molecular glass resists, which is critical for resolution and line edge roughness of pattern features. A comparison between experimentally measured and theoretically predicted diffusion lengths in one molecular glass resist system was made. Since there is little understood about acid diffusion in molecular glass resists, this paper is the first that tackles this process across a variety of materials and provides some insight into the molecular design of photoresists for high resolution lithography.
Employing Magnetic Levitation to Monitor Reaction Kinetics and Measure Activation Energy
ERIC Educational Resources Information Center
Benz, Lauren; Cesafsky, Karen E.; Le, Tran; Park, Aileen; Malicky, David
2012-01-01
This article describes a simple and inexpensive undergraduate-level kinetics experiment that uses magnetic levitation to monitor the progress and determine the activation energy of a condensation reaction on a polymeric solid support. The method employs a cuvette filled with a paramagnetic solution positioned between two strong magnets. The
ERIC Educational Resources Information Center
Abdel-Kader, M. H.; Steiner, U.
1983-01-01
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…
Shaozeng Sun; Juwei Zhang; Xidong Hu; Shaohua Wu; Jiancheng Yang; Yang Wang; Yukun Qin
2009-01-15
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.
An Inexpensive Kinetic Study: The Reaction of FD&C Red #3 (Erythrosin B) with Hypochlorite
ERIC Educational Resources Information Center
Henary, Maher M.; Russell, Arlene A.
2007-01-01
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…
Marcus Theory: Thermodynamics CAN Control the Kinetics of Electron Transfer Reactions
ERIC Educational Resources Information Center
Silverstein, Todd P.
2012-01-01
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…
Employing Magnetic Levitation to Monitor Reaction Kinetics and Measure Activation Energy
ERIC Educational Resources Information Center
Benz, Lauren; Cesafsky, Karen E.; Le, Tran; Park, Aileen; Malicky, David
2012-01-01
This article describes a simple and inexpensive undergraduate-level kinetics experiment that uses magnetic levitation to monitor the progress and determine the activation energy of a condensation reaction on a polymeric solid support. The method employs a cuvette filled with a paramagnetic solution positioned between two strong magnets. The…
Pulsed laser photolysis kinetics study of the O(3P) + ClO reaction
NASA Technical Reports Server (NTRS)
Nicovich, J. M.; Wine, P. H.; Ravishankara, A. R.
1988-01-01
A pulsed laser photolysis technique was used to investigate the kinetics of the important stratospheric reaction O + ClO yields Cl + O2 in buffer gas over the temperature and pressure ranges of 231-367 K and 25-500 torr. The results indicate a lack of pressure dependence at 298 K over the 25-500 torr range.
Interfacial reaction kinetics of coated SiC fibers with various titanium alloys
NASA Technical Reports Server (NTRS)
Gundel, D. B.; Wawner, F. E.
1991-01-01
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.
Young, J.E.; Wong, S.H.; Johnson, J.E.; Sikand, N.; Jonke, A.A.
1980-02-01
This work is directed toward support studies for the national program for the development and demonstration of in situ coal gasification processes. The objective of this work is to determine the reaction-controlling variables and reaction kinetics for the gasification of chars obtained by pyrolyzing coal in simulated underground gasification conditions. The reactions being studied and to be studied include steam-char, CO/sub 2/-char, H/sub 2/-char, the water-gas shift reaction, and the methanation reaction. In this report are presented data regarding the kinetics of the reaction of steam with chars prepared from Pittsburgh seam high-volatile bituminous coal. In addition, a reaction model is described correlating the steam-char reaction rates measured earlier for Hanna subbituminous coal with operating conditions including temperature, partial pressures of steam and hydrogen, and extent of carbon gasification. Partial results are presented and discussed for an investigation of structural parameters of Hanna char as a function of pyrolysis conditions and extent of carbon gasified.
Macroscopic Kinetic Effect of Cell-to-Cell Variation in Biochemical Reactions
NASA Astrophysics Data System (ADS)
Kim, Pan-Jun; Price, Nathan D.
2010-04-01
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.
A Gas-Kinetic Scheme for Multimaterial Flows and Its Application in Chemical Reaction
NASA Technical Reports Server (NTRS)
Lian, Yongsheng; Xu, Kun
1999-01-01
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.
Bench-scale Kinetics Study of Mercury Reactions in FGD Liquors
Gary Blythe; John Currie; David DeBerry
2008-03-31
This document is the final report for Cooperative Agreement DE-FC26-04NT42314, 'Kinetics Study of Mercury Reactions in FGD Liquors'. The project was co-funded by the U.S. DOE National Energy Technology Laboratory and EPRI. The objective of the project has been to determine the mechanisms and kinetics of the aqueous reactions of mercury absorbed by wet flue gas desulfurization (FGD) systems, and develop a kinetics model to predict mercury reactions in wet FGD systems. The model may be used to determine optimum wet FGD design and operating conditions to maximize mercury capture in wet FGD systems. Initially, a series of bench-top, liquid-phase reactor tests were conducted and mercury species concentrations were measured by UV/visible light spectroscopy to determine reactant and byproduct concentrations over time. Other measurement methods, such as atomic absorption, were used to measure concentrations of vapor-phase elemental mercury, that cannot be measured by UV/visible light spectroscopy. Next, a series of bench-scale wet FGD simulation tests were conducted. Because of the significant effects of sulfite concentration on mercury re-emission rates, new methods were developed for operating and controlling the bench-scale FGD experiments. Approximately 140 bench-scale wet FGD tests were conducted and several unusual and pertinent effects of process chemistry on mercury re-emissions were identified and characterized. These data have been used to develop an empirically adjusted, theoretically based kinetics model to predict mercury species reactions in wet FGD systems. The model has been verified in tests conducted with the bench-scale wet FGD system, where both gas-phase and liquid-phase mercury concentrations were measured to determine if the model accurately predicts the tendency for mercury re-emissions. This report presents and discusses results from the initial laboratory kinetics measurements, the bench-scale wet FGD tests, and the kinetics modeling efforts.
Nagaraj, Karuppiah; Senthil Murugan, Krishnan; Thangamuniyandi, Pilavadi; Sakthinathan, Subramanian
2015-05-15
The kinetics of outer sphere electron transfer reaction of surfactant cobalt(III) complex ions, cis-[Co(en)2(C12H25NH2)2](3+) (1), cis-[Co(dp)2(C12H25NH2)2](3+) (2), cis-[Co(trien)(C12H25NH2)2](3+) (3), cis-[Co(bpy)2(C12H25NH2)2](3+) (4) and cis-[Co(phen)2(C12H25NH2)2](3+) (5) (en: ethylenediamine, dp: diaminopropane, trien : triethylenetetramine, bpy: 2,2'-bipyridyl, phen: 1,10-phenanthroline and C12H25NH2 : dodecylamine) have been interrogated by Fe(2+) ion in ionic liquid (1-butyl-3-methylimidazoliumbromide) medium at different temperatures (298, 303, 308, 313, 318 and 323K) by the spectrophotometry method under pseudo first order conditions using an excess of the reductant. Experimentally the reactions were found to be of second order and the electron transfer as outer sphere. The second order rate constant for the electron transfer reaction in ionic liquids was found to increase with increase in the concentration of all these surfactant cobalt(III) complexes. Among these complexes (from en to phen ligand), complex containing the phenanthroline ligand rate is higher compared to other complexes. By assuming the outer sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of ionic liquids formed by the surfactant cobalt(III) complexes in the reaction medium. The activation parameters (enthalpy of activation ΔH(‡) and entropy of activation ΔS(‡)) of the reaction have been calculated which substantiate the kinetics of the reaction. PMID:25721780
NASA Astrophysics Data System (ADS)
Nagaraj, Karuppiah; Senthil Murugan, Krishnan; Thangamuniyandi, Pilavadi; Sakthinathan, Subramanian
2015-05-01
The kinetics of outer sphere electron transfer reaction of surfactant cobalt(III) complex ions, cis-[Co(en)2(C12H25NH2)2]3+ (1), cis-[Co(dp)2(C12H25NH2)2]3+ (2), cis-[Co(trien)(C12H25NH2)2]3+ (3), cis-[Co(bpy)2(C12H25NH2)2]3+ (4) and cis-[Co(phen)2(C12H25NH2)2]3+ (5) (en: ethylenediamine, dp: diaminopropane, trien : triethylenetetramine, bpy: 2,2‧-bipyridyl, phen: 1,10-phenanthroline and C12H25NH2 : dodecylamine) have been interrogated by Fe2+ ion in ionic liquid (1-butyl-3-methylimidazoliumbromide) medium at different temperatures (298, 303, 308, 313, 318 and 323 K) by the spectrophotometry method under pseudo first order conditions using an excess of the reductant. Experimentally the reactions were found to be of second order and the electron transfer as outer sphere. The second order rate constant for the electron transfer reaction in ionic liquids was found to increase with increase in the concentration of all these surfactant cobalt(III) complexes. Among these complexes (from en to phen ligand), complex containing the phenanthroline ligand rate is higher compared to other complexes. By assuming the outer sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of ionic liquids formed by the surfactant cobalt(III) complexes in the reaction medium. The activation parameters (enthalpy of activation ΔH‡ and entropy of activation ΔS‡) of the reaction have been calculated which substantiate the kinetics of the reaction.
Coherent chemical kinetics as quantum walks. I. Reaction operators for radical pairs
NASA Astrophysics Data System (ADS)
Chia, A.; Tan, K. C.; Pawela, Ł.; Kurzyński, P.; Paterek, T.; Kaszlikowski, D.
2016-03-01
Classical chemical kinetics uses rate-equation models to describe how a reaction proceeds in time. Such models are sufficient for describing state transitions in a reaction where coherences between different states do not arise, in other words, a reaction that contains only incoherent transitions. A prominent example of a reaction containing coherent transitions is the radical-pair model. The kinetics of such reactions is defined by the so-called reaction operator that determines the radical-pair state as a function of intermediate transition rates. We argue that the well-known concept of quantum walks from quantum information theory is a natural and apt framework for describing multisite chemical reactions. By composing Kraus maps that act only on two sites at a time, we show how the quantum-walk formalism can be applied to derive a reaction operator for the standard avian radical-pair reaction. Our reaction operator predicts the same recombination dephasing rate as the conventional Haberkorn model, which is consistent with recent experiments [K. Maeda et al., J. Chem. Phys. 139, 234309 (2013), 10.1063/1.4844355], in contrast to previous work by Jones and Hore [J. A. Jones and P. J. Hore, Chem. Phys. Lett. 488, 90 (2010), 10.1016/j.cplett.2010.01.063]. The standard radical-pair reaction has conventionally been described by either a normalized density operator incorporating both the radical pair and reaction products or a trace-decreasing density operator that considers only the radical pair. We demonstrate a density operator that is both normalized and refers only to radical-pair states. Generalizations to include additional dephasing processes and an arbitrary number of sites are also discussed.
Oxygen exchange reaction kinetics for cerium(IV) oxide at 1000 °C
Whiting, Christofer E. Douglas, John M.; Cremeans, Bethany M.; Barklay, Chadwick D.; Kramer, Daniel P.
2014-10-15
Bulk oxygen exchange rate kinetics on CeO{sub 2} at 1000 °C were observed to have a first order dependence on the fraction of reaction remaining and to be independent of oxygen partial pressure, total pressure, particle size, and specific surface area. This suggests that the exchange reaction is dominated by an internal chemical reaction that is occurring throughout the bulk of the material, and not at the material surface. Oxygen exchange rates were limited by this internal chemical reaction for all CeO{sub 2} powders studied (15 nm to −325 mesh), and had a rate constant of 1.19×10{sup −2} s{sup −1} with a time to completion of 617 s. These results are similar to the exchange rates observed previously on PuO{sub 2}, suggesting that oxygen exchange on PuO{sub 2} may also be dominated by an internal chemical reaction under similar conditions. This work will help guide future experiments on {sup 238}PuO{sub 2} oxygen exchange reactions. - Graphical abstract: Oxygen exchange kinetics on CeO{sub 2} at 1000 °C are independent of a wide range of experimental conditions and exhibit first-order chemical reaction kinetics. - Highlights: • Stable oxygen exchange rates obtained on a variety of CeO{sub 2} powders at 1000 °C. • Exchange rates are independent of atmospheric composition and specific surface area. • Exchange rates are limited by an internal chemical reaction, not a surface reaction. • CeO{sub 2} exchange rates appear similar to the rates observed on PuO{sub 2} at 1000 °C.
Multiple Positive Solutions in the Second Order Autonomous Nonlinear Boundary Value Problems
NASA Astrophysics Data System (ADS)
Atslega, Svetlana; Sadyrbaev, Felix
2009-09-01
We construct the second order autonomous equations with arbitrarily large number of positive solutions satisfying homogeneous Dirichlet boundary conditions. Phase plane approach and bifurcation of solutions are the main tools.
On Picard boundary value problem for second order asymptotically homogeneous equations
NASA Astrophysics Data System (ADS)
Dong, Y.
Using the Leray-Schauder continuation principle we give some existence results for the Picard boundary value problem of second order asymptotically homogeneous equations. Some previous results by Tippett, Gaines-Mawhin, Lazer-Leach will be extended.
Comparison of Second-Order Loads on a Tension-Leg Platform for Wind Turbines: Preprint
Gueydon, S.; Wuillaume, P.; Jonkman, J.; Robertson, A.; Platt, A.
2015-03-01
The first objective of this work is to compare the two floating offshore wind turbine simulation packages {DIFFRAC+aNySIM} and {WAMIT+FAST}. The focus is on second-order wave loads, and so first- and second-order wave loads are applied to a structure sequentially for a detailed comparison and a more precise analysis of the effects of the second-order loads. aNySIM does not have the capability to model flexible bodies, and so the simulations performed in this tool are done assuming a rigid body. FAST also assumes that the platform is rigid, but can account for the flexibility of the tower. The second objective is to study the effects of the second-order loads on the response of a TLP floating wind turbine. The flexibility of the tower must be considered for this investigation, and therefore only FAST is used.
NASA Astrophysics Data System (ADS)
Huang, Juntao; Hu, Zexi; Yong, Wen-An
2016-04-01
In this paper, we present a kind of second-order curved boundary treatments for the lattice Boltzmann method solving two-dimensional convection-diffusion equations with general nonlinear Robin boundary conditions. The key idea is to derive approximate boundary values or normal derivatives on computational boundaries, with second-order accuracy, by using the prescribed boundary condition. Once the approximate information is known, the second-order bounce-back schemes can be perfectly adopted. Our boundary treatments are validated with a number of numerical examples. The results show the utility of our boundary treatments and very well support our theoretical predications on the second-order accuracy thereof. The idea is quite universal. It can be directly generalized to 3-dimensional problems, multiple-relaxation-time models, and the Navier-Stokes equations.
NASA Technical Reports Server (NTRS)
Schmidt, K. H.
1970-01-01
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.
Schofield, Andrew J; Ledgeway, Timothy; Hutchinson, Claire V
2007-01-01
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
Comments on the present state of second-order closure models for incompressible flows
NASA Technical Reports Server (NTRS)
Speziale, Charles G.
1992-01-01
Second-order closure models account for history and nonlocal effects of the mean velocity gradients on the Reynolds stress tensor. Turbulent flows involving body forces or curvature, Reynolds stress relaxational effects, and counter-gradient transport are usually better described. The topics are presented in viewgraph form and include: (1) the Reynolds stress transport equation; (2) issues in second-order closure modeling; and (3) near wall models.
Wang, Xu; Ding, Jie; Guo, Wan-Qian; Ren, Nan-Qi
2010-12-01
Investigating how a bioreactor functions is a necessary precursor for successful reactor design and operation. Traditional methods used to investigate flow-field cannot meet this challenge accurately and economically. Hydrodynamics model can solve this problem, but to understand a bioreactor in sufficient depth, it is often insufficient. In this paper, a coupled hydrodynamics-reaction kinetics model was formulated from computational fluid dynamics (CFD) code to simulate a gas-liquid-solid three-phase biotreatment system for the first time. The hydrodynamics model is used to formulate prediction of the flow field and the reaction kinetics model then portrays the reaction conversion process. The coupled model is verified and used to simulate the behavior of an expanded granular sludge bed (EGSB) reactor for biohydrogen production. The flow patterns were visualized and analyzed. The coupled model also demonstrates a qualitative relationship between hydrodynamics and biohydrogen production. The advantages and limitations of applying this coupled model are discussed. PMID:20727741
Kinetics of the Br2-CH3CHO Photochemical Chain Reaction
NASA Technical Reports Server (NTRS)
Nicovich, J. M.; Shackelford, C. J.; Wine, P. H.
1997-01-01
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).
Label-free measurements of reaction kinetics using a droplet-based optofluidic device.
Mao, Zhangming; Guo, Feng; Xie, Yuliang; Zhao, Yanhui; Lapsley, Michael Ian; Wang, Lin; Mai, John D; Costanzo, Francesco; Huang, Tony Jun
2015-02-01
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 β-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
Carbon kinetic isotope effect in the reaction of CH4 with HO
NASA Technical Reports Server (NTRS)
Davidson, J. A.; Cantrell, C. A.; Tyler, S. C.; Shetter, R. E.; Cicerone, R. J.
1987-01-01
The carbon kinetic isotope effect in the CH4 + HO reaction is measured experimentally and the use of carbon isotope ratios to diagnose atmospheric methane is examined. The chemical, photolysis, and analytical experimental conditions and procedures are described. It is determined that the CH4 + HO reaction has a carbon kinetic isotope effect of 1.010 + or 0.007 for k(12)k(13) (rate constants ratio) at 297 + or - 3 K. This value is compared with the data of Rust and Stevens (1980). Causes for the poor correlation between the data at high methane conversions are discussed. It is supposed that the difference between the k(12) and k(13) values is due to a difference in the activation energy of the two reactions.
A stable second-order mass-weighted upwind scheme for unstructured meshes
NASA Astrophysics Data System (ADS)
Dung Tran, Luu; Masson, Christian; Smaïli, Arezki
2006-07-01
In this paper, an original second-order upwind scheme for convection terms is described and implemented in the context of a Control-Volume Finite-Element Method (CVFEM).The proposed scheme is a second-order extension of the first-order MAss-Weighted upwind (MAW) scheme proposed by Saabas and Baliga (Numer. Heat Transfer 1994; 26B:381-407). The proposed second-order scheme inherits the well-known stability characteristics of the MAW scheme, but exhibits less artificial viscosity and ensures much higher accuracy. Consequently, and in contrast with nearly all second-order upwind schemes available in the literature, the proposed second-order MAW scheme does not need limiters.Some test cases including two pure convection problems, the driven cavity and steady and unsteady flows over a circular cylinder, have been undertaken successfully to validate the new scheme.The verification tests show that the proposed scheme exhibits a low level of artificial viscosity in the pure convection problems; exhibits second-order accuracy for the driven cavity; gives accurate reattachment lengths for low-Reynolds steady flow over a circular cylinder; and gives constant-amplitude vortex shedding for the case of high-Reynolds unsteady flow over a circular cylinder.
ERIC Educational Resources Information Center
Lundberg, Dan; Stjerndahl, Maria
2011-01-01
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…
ERIC Educational Resources Information Center
Lundberg, Dan; Stjerndahl, Maria
2011-01-01
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
Kowalsky, Michael B.; Moridis, George J.
2006-11-29
In this study we compare the use of kinetic and equilibriumreaction models in the simulation of gas (methane) hydrate behavior inporous media. Our objective is to evaluate through numerical simulationthe importance of employing kinetic versus equilibrium reaction modelsfor predicting the response of hydrate-bearing systems to externalstimuli, such as changes in pressure and temperature. Specifically, we(1) analyze and compare the responses simulated using both reactionmodels for natural gas production from hydrates in various settings andfor the case of depressurization in a hydrate-bearing core duringextraction; and (2) examine the sensitivity to factors such as initialhydrate saturation, hydrate reaction surface area, and numericaldiscretization. We find that for large-scale systems undergoing thermalstimulation and depressurization, the calculated responses for bothreaction models are remarkably similar, though some differences areobserved at early times. However, for modeling short-term processes, suchas the rapid recovery of a hydrate-bearing core, kinetic limitations canbe important, and neglecting them may lead to significantunder-prediction of recoverable hydrate. The use of the equilibriumreaction model often appears to be justified and preferred for simulatingthe behavior of gas hydrates, given that the computational demands forthe kinetic reaction model far exceed those for the equilibrium reactionmodel.
Determination of reaction kinetics of rice husks in air using thermogravimetric analysis
Mansaray, K.G.; Ghaly, A.E.
1999-12-01
Rice husk is produced in large quantities as a by-product of rice milling in rice-producing countries and has posed disposal problems in these countries. Disposal of or energy recovery from rice husk can be accomplished by thermochemical conversion processes (pyrolysis, combustion, and gasification). However, it appears that the kinetics of rice husk, which can contribute to the accurate modeling and design of thermochemical conversion processes, have not been studied extensively. In this paper the technique of thermogravimetric analysis (TGA) was used to study the thermochemical behavior of four varieties of rice husk (Lemont LG, ROK 14, CP 4, and Pa Potho). The thermal degradation of rice husk was studied in an air atmosphere (21% oxygen and 79% nitrogen) from ambient temperature to 700 C at the heating rate of 20 C/min. The thermograms showed two distinct reaction zones. The kinetic parameters (activation energy, preexponential factor, and order of reaction) were determined for the two reaction zones by applying thermoanalytical techniques to the reaction kinetics. Higher thermal degradation rates were observed in the first reaction zone due to rapid release of volatiles as compared to those in the second reaction zone. In the first reaction zone the activation energies ranged from 37.0 to 54.7 kJ/mol. Relatively lower activation energies (18.0--21.0 kJ/mol) were obtained in the second reaction zone. The preexponential factors were in the range of 4.3 x 10{sup 4} to 6.4 x 10{sup 6} min{sup {minus}1} in the first reaction zone and 4.5 x 10{sup 2} to 1.5 x 10{sup 3} min{sup {minus}1} in the second reaction zone. The orders of reaction were in the range of 1.2--1.6 and 0.4--0.5 for the first and second reaction zones, respectively. The predicted thermal degradations were in good agreement with the experimental data in both the first and second reaction zones.
NASA Astrophysics Data System (ADS)
Salvage, Karen M.; Yeh, Gour-Tsyh
1998-08-01
This paper presents the conceptual and mathematical development of the numerical model titled BIOKEMOD, and verification simulations performed using the model. BIOKEMOD is a general computer model for simulation of geochemical and microbiological reactions in batch aqueous solutions. BIOKEMOD may be coupled with hydrologic transport codes for simulation of chemically and biologically reactive transport. The chemical systems simulated may include any mixture of kinetic and equilibrium reactions. The pH, pe, and ionic strength may be specified or simulated. Chemical processes included are aqueous complexation, adsorption, ion-exchange and precipitation/dissolution. Microbiological reactions address growth of biomass and degradation of chemicals by microbial metabolism of substrates, nutrients, and electron acceptors. Inhibition or facilitation of growth due to the presence of specific chemicals and a lag period for microbial acclimation to new substrates may be simulated if significant in the system of interest. Chemical reactions controlled by equilibrium are solved using the law of mass action relating the thermodynamic equilibrium constant to the activities of the products and reactants. Kinetic chemical reactions are solved using reaction rate equations based on collision theory. Microbiologically mediated reactions for substrate removal and biomass growth are assumed to follow Monod kinetics modified for the potentially limiting effects of substrate, nutrient, and electron acceptor availability. BIOKEMOD solves the ordinary differential and algebraic equations of mixed geochemical and biogeochemical reactions using the Newton-Raphson method with full matrix pivoting. Simulations may be either steady state or transient. Input to the program includes the stoichiometry and parameters describing the relevant chemical and microbiological reactions, initial conditions, and sources/sinks for each chemical species. Output includes the chemical and biomass concentrations at desired times. BIOKEMOD has been coupled with a hydrologic transport code, HYDROGEOCHEM, to allow the simulation of coupled advective-dispersive transport and biogeochemical transformation of pollutants in groundwater. Three verification exercises are compared with analytical solutions to demonstrate the correctness of the code. Two validation simulations of batch laboratory systems are compared with the laboratory data to demonstrate the code's ability to replicate behavior observed in real systems, and two validation exercises simulating reactive transport are presented to demonstrate the code's performance in simulating mixed equilibrium and kinetic biogeochemical reactions coupled with hydrologic transport.
Oxazines: A New Class of Second-Order Nonlinear Optical Switches.
Beaujean, Pierre; Bondu, Flavie; Plaquet, Aurélie; Garcia-Amorós, Jaume; Cusido, Janet; Raymo, Françisco M; Castet, Frédéric; Rodriguez, Vincent; Champagne, Benoît
2016-04-20
A combined experimental-theoretical investigation has revealed that oxazine-based compounds are multiaddressable, multistate, and multifunctional molecular switches exhibiting contrasts of both linear and second-order nonlinear optical properties. The switching properties are particularly large when the substituent is a donor group. In this study, the cleavage of the C-O bond at the junction of the indole and oxazine cycles (of the closed a forms) is acido-triggered, leading to an open form (b(+)) characterized by larger first hyperpolarizabilities (βHRS) and smaller excitation energies than in the closed form. These results are confirmed and interpreted utilizing ab initio calculations that have been carried out on a broad set of compounds to unravel the role of the substituent. With respect to acceptor groups, oxazines bearing donor groups are characterized not only by larger βHRS and βHRS contrast ratios but also by smaller excitation energies, larger opening-induced charge transfer, and reduction of the bond length alternation, as well as smaller Gibbs energies of the opening reaction. Compared to protonated open forms (b(+)), calculations on the zwitterionic open forms (b) have pointed out similarities in the long-wavelength UV/vis absorption spectra, whereas their βHRS values might differ strongly as a function of the substituent. Indeed, the open forms present two NLOphores, the indoleninium-substituent entity and the nitrophenol (present in the protonated open form, b(+)) or nitrophenolate (present in the zwitterionic open form, b) moiety. Then, nitrophenolate displays a larger first hyperpolarizability than nitrophenol and the β tensor of the two entities might reinforce or cancel each other. PMID:26996994
Genome-scale Metabolic Reaction Modeling: a New Approach to Geomicrobial Kinetics
NASA Astrophysics Data System (ADS)
McKernan, S. E.; Shapiro, B.; Jin, Q.
2014-12-01
Geomicrobial rates, rates of microbial metabolism in natural environments, are a key parameter of theoretical and practical problems in geobiology and biogeochemistry. Both laboratory- and field-based approaches have been applied to study rates of geomicrobial processes. Laboratory-based approaches analyze geomicrobial kinetics by incubating environmental samples under controlled laboratory conditions. Field methods quantify geomicrobial rates by observing the progress of geomicrobial processes. To take advantage of recent development in biogeochemical modeling and genome-scale metabolic modeling, we suggest that geomicrobial rates can also be predicted by simulating metabolic reaction networks of microbes. To predict geomicrobial rates, we developed a genome-scale metabolic model that describes enzyme reaction networks of microbial metabolism, and simulated the network model by accounting for the kinetics and thermodynamics of enzyme reactions. The model is simulated numerically to solve cellular enzyme abundance and hence metabolic rates under the constraints of cellular physiology. The new modeling approach differs from flux balance analysis of system biology in that it accounts for the thermodynamics and kinetics of enzymatic reactions. It builds on subcellular metabolic reaction networks, and hence also differs from classical biogeochemical reaction modeling. We applied the new approach to Methanosarcina acetivorans, an anaerobic, marine methanogen capable of disproportionating acetate to carbon dioxide and methane. The input of the new model includes (1) enzyme reaction network of acetoclastic methanogenesis, and (2) representative geochemical conditions of freshwater sedimentary environments. The output of the simulation includes the proteomics, metabolomics, and energy and matter fluxes of M. acetivorans. Our simulation results demonstrate the predictive power of the new modeling approach. Specifically, the results illustrate how methanogenesis rates vary with acetate concentrations and the energy available in the environment, and how M. acetivorans regulate the enzymes of methanogenesis under different biogeochemical conditions.
Thermal decomposition of sugarcane straw, kinetics and heat of reaction in synthetic air.
Rueda-Ordóñez, Yesid Javier; Tannous, Katia
2016-07-01
The aim of this work was to analyze the thermal decomposition, kinetics and heat of reaction of sugarcane straw in synthetic air by thermogravimetry (TG) and differential scanning calorimetry (DSC). The TG and DSC experiments were carried out using heating rates of 2.5°C/min, 5°C/min, and 10°C/min, and particle diameter of 0.250mm. In the study of the smoldering reaction were identified three consecutive stages, drying, oxidative pyrolysis, and combustion. Thus, the kinetic pathway was composed by six independent parallel reactions, three for each stage after drying, in which the activation energies were 176, 313, 150, 80, 150, and 100kJ/mol. The heat of reaction in synthetic air was completely exothermic releasing 8MJ/kg. The modeled curves of thermal decomposition of sugarcane straw presented good agreement with experimental data. Then, the kinetic parameters obtained could be used to analyze different processes involving smoldering. PMID:27019126
Michaelis-Menten kinetics in shear flow: Similarity solutions for multi-step reactions
Ristenpart, W. D.; Stone, H. A.
2012-01-01
Models for chemical reaction kinetics typically assume well-mixed conditions, in which chemical compositions change in time but are uniform in space. In contrast, many biological and microfluidic systems of interest involve non-uniform flows where gradients in flow velocity dynamically alter the effective reaction volume. Here, we present a theoretical framework for characterizing multi-step reactions that occur when an enzyme or enzymatic substrate is released from a flat solid surface into a linear shear flow. Similarity solutions are developed for situations where the reactions are sufficiently slow compared to a convective time scale, allowing a regular perturbation approach to be employed. For the specific case of Michaelis-Menten reactions, we establish that the transversally averaged concentration of product scales with the distance x downstream as x5/3. We generalize the analysis to n-step reactions, and we discuss the implications for designing new microfluidic kinetic assays to probe the effect of flow on biochemical processes. PMID:22662093
Sensitivity of Polar Stratospheric Ozone Loss to Uncertainties in Chemical Reaction Kinetics
NASA Technical Reports Server (NTRS)
Kawa, S. Randolph; Stolarksi, Richard S.; Douglass, Anne R.; Newman, Paul A.
2008-01-01
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.
Chemical kinetic analysis of hydrogen-air ignition and reaction times
NASA Technical Reports Server (NTRS)
Rogers, R. C.; Schexnayder, C. J., Jr.
1981-01-01
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.
Lozano, Valeria A; Escandar, Graciela M
2013-06-11
A photochemically induced fluorescence system combined with second-order chemometric analysis for the determination of the anticonvulsant carbamazepine (CBZ) is presented. CBZ is a widely used drug for the treatment of epilepsy and is included in the group of emerging contaminant present in the aquatic environment. CBZ is not fluorescent in solution but can be converted into a fluorescent compound through a photochemical reaction in a strong acid medium. The determination is carried out by measuring excitation-emission photoinduced fluorescence matrices of the products formed upon ultraviolet light irradiation in a laboratory-constructed reactor constituted by two simple 4 W germicidal tubes. Working conditions related to both the reaction medium and the photoreactor geometry are optimized by an experimental design. The developed approach enabled the determination of CBZ at trace levels without the necessity of applying separation steps, and in the presence of uncalibrated interferences which also display photoinduced fluorescence and may be potentially present in the investigated samples. Different second-order algorithms were tested and successful resolution was achieved using multivariate curve resolution-alternating least-squares (MCR-ALS). The study is employed for the discussion of the scopes and yields of each of the applied second-order chemometric tools. The quality of the proposed method is probed through the determination of the studied emerging pollutant in both environmental and drinking water samples. After a pre-concentration step on a C18 membrane using 50.0 mL of real water samples, a prediction relative error of 2% and limits of detection and quantification of 0.2 and 0.6 ng mL(-1) were respectively obtained. PMID:23708282
Kinetic and thermochemical studies of the ClO + ClO + M ↔ Cl2O2 + M reaction
NASA Astrophysics Data System (ADS)
Ferracci, V.; Rowley, D. M.
2009-12-01
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, ΔrH° and ΔrS°, from the measured equilibrium constants. The values obtained from the Second Law analysis (ΔrH° = - 80.8 ± 2.2 kJ mol-1; ΔrS° = - 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
Rashed, Mohammed Abouelleil
2015-04-01
The centenary of Karl Jaspers' General Psychopathology was recognised in 2013 with the publication of a volume of essays dedicated to his work (edited by Stanghellini and Fuchs). Leading phenomenological-psychopathologists and philosophers of psychiatry examined Jaspers notion of empathic understanding and his declaration that certain schizophrenic phenomena are 'un-understandable'. The consensus reached by the authors was that Jaspers operated with a narrow conception of phenomenology and empathy and that schizophrenic phenomena can be understood through what they variously called second-order and radical empathy. This article offers a critical examination of the second-order empathic stance along phenomenological and ethical lines. It asks: (1) Is second-order empathy (phenomenologically) possible? (2) Is the second-order empathic stance an ethically acceptable attitude towards persons diagnosed with schizophrenia? I argue that second-order empathy is an incoherent method that cannot be realised. Further, the attitude promoted by this method is ethically problematic insofar as the emphasis placed on radical otherness disinvests persons diagnosed with schizophrenia from a fair chance to participate in the public construction of their identity and, hence, to redress traditional symbolic injustices. PMID:25820144
Comparison between fourth and second order DT-MR image segmentations
NASA Astrophysics Data System (ADS)
El-Hilo, Saba; Weldeselassie, Yonas T.; Atkins, M. Stella
2011-03-01
A second order tensor is usually used to describe the diffusion of water for each voxel within Diffusion Tensor Magnetic Resonance (DT-MR) images. However, a second order tensor approximation fails to accurately represent complex local tissue structures such as crossing fibers. Therefore, higher order tensors are used to represent more complex diffusivity profiles. In this work we examine and compare segmentations of both second order and fourth order DT-MR images using the Random Walker segmentation algorithm with the emphasis of pointing-out the shortcomings of second order tensor model in segmenting regions with complex fiber structures. We first adopt the Random Walker algorithm for segmenting diffusion tensor data by using appropriate tensor distance metrics and then demonstrate the advantages of performing segmentation on higher order DT-MR data. The approach proposed takes advantage of all the information provided by the tensors by using suitable tensor distance metrics. The distance metrics used are: the Log-Euclidean for the second order tensors and the normalized L2 distance for the fourth order tensors. The segmentation is carried out on a weighted graph that represents the image, where the tensors are the nodes and the edge weights are computed using the tensor distance metrics. Applying the approach to both synthetic and real DT-MRI data yields segmentations that are both robust and qualitatively accurate.
NASA Astrophysics Data System (ADS)
Reina, Borja; Vera, Raül
2015-08-01
Hartle's model describes the equilibrium configuration of a rotating isolated compact body in perturbation theory up to second order in general relativity. The interior of the body is a perfect fluid with a barotropic equation of state, no convective motions and rigid rotation. That interior is matched across its surface to an asymptotically flat vacuum exterior. Perturbations are taken to second order around a static and spherically symmetric background configuration. Apart from the explicit assumptions, the perturbed configuration is constructed upon some implicit premises, in particular the continuity of the functions describing the perturbation in terms of some background radial coordinate. In this work we revisit the model within a modern general and consistent theory of perturbative matchings to second order, which is independent of the coordinates and gauges used to describe the two regions to be joined. We explore the matching conditions up to second order in full. The main particular result we present is that the radial function m0 (in the setting of the original work) of the second order perturbation tensor, contrary to the original assumption, presents a jump at the surface of the star, which is proportional to the value of the energy density of the background configuration there. As a consequence, the change in mass δ M needed by the perturbed configuration to keep the value of the central energy density unchanged must be amended. We also discuss some subtleties that arise when studying the deformation of the star.
Hilbe, Christian; Traulsen, Arne; Rhl, Torsten; Milinski, Manfred
2014-01-14
Individuals usually punish free riders but refuse to sanction those who cooperate but do not punish. This missing second-order peer punishment is a fundamental problem for the stabilization of cooperation. To solve this problem, most societies today have implemented central authorities that punish free riders and tax evaders alike, such that second-order punishment is fully established. The emergence of such stable authorities from individual decisions, however, creates a new paradox: it seems absurd to expect individuals who do not engage in second-order punishment to strive for an authority that does. Herein, we provide a mathematical model and experimental results from a public goods game where subjects can choose between a community with and without second-order punishment in two different ways. When subjects can migrate continuously to either community, we identify a bias toward institutions that do not punish tax evaders. When subjects have to vote once for all rounds of the game and have to accept the decision of the majority, they prefer a society with second-order punishment. These findings uncover the existence of a democracy premium. The majority-voting rule allows subjects to commit themselves and to implement institutions that eventually lead to a higher welfare for all. PMID:24367116
Hilbe, Christian; Traulsen, Arne; Röhl, Torsten; Milinski, Manfred
2014-01-01
Individuals usually punish free riders but refuse to sanction those who cooperate but do not punish. This missing second-order peer punishment is a fundamental problem for the stabilization of cooperation. To solve this problem, most societies today have implemented central authorities that punish free riders and tax evaders alike, such that second-order punishment is fully established. The emergence of such stable authorities from individual decisions, however, creates a new paradox: it seems absurd to expect individuals who do not engage in second-order punishment to strive for an authority that does. Herein, we provide a mathematical model and experimental results from a public goods game where subjects can choose between a community with and without second-order punishment in two different ways. When subjects can migrate continuously to either community, we identify a bias toward institutions that do not punish tax evaders. When subjects have to vote once for all rounds of the game and have to accept the decision of the majority, they prefer a society with second-order punishment. These findings uncover the existence of a democracy premium. The majority-voting rule allows subjects to commit themselves and to implement institutions that eventually lead to a higher welfare for all. PMID:24367116
A second order operator splitting method for Allen-Cahn type equations with nonlinear source terms
NASA Astrophysics Data System (ADS)
Lee, Hyun Geun; Lee, June-Yub
2015-08-01
Allen-Cahn (AC) type equations with nonlinear source terms have been applied to a wide range of problems, for example, the vector-valued AC equation for phase separation and the phase-field equation for dendritic crystal growth. In contrast to the well developed first and second order methods for the AC equation, not many second order methods are suggested for the AC type equations with nonlinear source terms due to the difficulties in dealing with the nonlinear source term numerically. In this paper, we propose a simple and stable second order operator splitting method. A core idea of the method is to decompose the original equation into three subequations with the free-energy evolution term, the heat evolution term, and a nonlinear source term, respectively. It is important to combine these three subequations in proper order to achieve the second order accuracy and stability. We propose a method with a half-time free-energy evolution solver, a half-time heat evolution solver, a full-time midpoint solver for the nonlinear source term, and a half-time heat evolution solver followed by a final half-time free-energy evolution solver. We numerically demonstrate the second order accuracy of the new numerical method through the simulations of the phase separation and the dendritic crystal growth.
Weese, R K; Burnham, A K; Fontes, A T
2005-03-23
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.
Sahoo, Chittaranjan; Gupta, Ashok K; Pillai, Indu M Sasidharan
2012-01-01
Real textile wastewater collected from the cotton dyeing bath of a fabric dyeing and finishing plant was subjected to heterogeneous photocatalysis using Ag(+) doped TiO(2) under UV irradiation in a batch reactor. The photocatalysts were characterized by FESEM, XRD, EDS, FTIR, DRS and BET analyses. The kinetics of the reaction was also evaluated. Colour removal was more than 88%, 94% and 99%, respectively for undiluted, 2 times diluted and 5 times diluted wastewater with Ag(+) doped TiO(2) (2.5 g/L) after UV irradiation for 360 minutes. The COD removal for undiluted, 2 times diluted and 5 times diluted wastewater was 47%, 70% and 92%, respectively under similar conditions. The reaction followed Langmuir-Hinshelwood pseudo first order kinetic model and the data fitted well to polynomial regression analysis. PMID:22871009
Kinetics of the Reaction of O((sup 3)P) with CF3NO
NASA Technical Reports Server (NTRS)
Thorn, R. P.; Nicovich, J. M.; Cronkhite, J. M.; Wine, P. H.
1997-01-01
A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction of O((sup 3)P) with CF3NO (k(2)) as a function of temperature. Our results are described by the Arrhenius expression k(2)(T) = (4.54 +/- 0.70) x 10(exp -l2)exp[(-560 +/- 46)/T] cu cm/molecule.s (243 K is less than or equal to T is less than or equal to 424 K); errors are 2 sigma and represent precision only. The O((sup 3)P) + CF3NO reaction is sufficiently rapid that CF3NO cannot be employed as a selective quencher for O2(alpha(1) Delta-g) in laboratory systems where O((sup 3)P) and O2(alpha 1 Delta g) coexist, and where O((sup 3)P) kinetics are being investigated.
Samadi, F.R.; Hill, G.A. )
1988-06-01
A heavy crude oil produced using conventional techniques from a Saskatchewan reservoir was subjected to thermal stresses under both closed and opened operating conditions. Measurements were made of the oil's permanent viscosity as a function of time at several different operating temperatures ranging from 220 to 425{degree}C. The experimental results clearly showed that previous crude oill kinetic models for thermal degradation reactions were not valid. As such, several new kinetic models were hypothesized and compared to the experimental data. The results showed that a three product model could closely simulate the experimental data under both closed and opened operating condition. The reaction rate constants varied from extremely large values of 1 hr{sup {minus}1} for the production of viscous products to very low values around 0.01 hr{sup {minus}1} for the production of low viscosity products.
Kinetic modeling of propane aromatization reaction over HZSM-5 and GaHZSM-5
Lukyanov, D.B.; Gnep, N.S.; Guisnet, M.R. . Catalyse en Chimie Organique)
1995-02-01
A detailed kinetic model for a propane aromatization reaction over HZSM-5 and GaHZSM-5 is developed. Kinetic modeling results show that propane transformation over HZSM-5 occurs via protolytic cracking and hydrogen transfer routes. The contributions of both routes in propane conversion are established. Rate constants of propane transformation steps are found to be at least 1,000 times lower than the rate constants of diene formation steps, which, in turn, are the slowest among the acid-catalyzed olefin aromatization steps. Gallium introduced into ZSM-5 catalyst is active in dehydrogenation of propane into propene, of olefins into dienes, and of naphthenes into aromatics. At the same time, gallium species catalyze propane transformation into methane and ethene hydrogenation into ethane. Both latter reactions appear to be the main reasons for the limit to aromatics selectivity over GaHZSM-5 catalysts.
Lockhart, D.J.; Boxer, S.G. ); Kirmaier, C.; Holten, D. )
1990-09-06
The effect of an applied electric field on the kinetics of the initial picosecond electron-transfer reaction in Rb. sphaeroides reaction centers has been measured in isotropic samples at 77 K. The net rate of formation of H{sub L} is reduced upon application of an electric field of 10{sup 6} V/cm, consistent with the previously observed increase in the quantum yield of the competing prompt fluorescence. The observed magnitude of the effect on the initial reaction is compared with the predictions of various models, and the consequences of including indirect electronic coupling between the initial and final states through a third state (superexchange) are investigated. It is found that the treatments of the initial electron-transfer reaction commonly in use greatly overestimate the magnitude of the field effect they are based on a dependence of the rate of electron transfer on the free energy change which is steeper than appears to be appropriate for this process.
Kinetics of the reaction between Pu(III) and Fe(III) in nitric acid solution
Koltunov, V.S.; Zhuravleva, G.I.
1988-01-01
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.
Morphological impact on the reaction kinetics of size-selected cobalt oxide nanoparticles
Bartling, Stephan Meiwes-Broer, Karl-Heinz; Barke, Ingo; Pohl, Marga-Martina
2015-09-21
Apart from large surface areas, low activation energies are essential for efficient reactions, particularly in heterogeneous catalysis. Here, we show that not only the size of nanoparticles but also their detailed morphology can crucially affect reaction kinetics, as demonstrated for mass-selected, soft-landed, and oxidized cobalt clusters in a 6 nm to 18 nm size range. The method of reflection high-energy electron diffraction is extended to the quantitative determination of particle activation energies which is applied for repeated oxidation and reduction cycles at the same particles. We find unexpectedly small activation barriers for the reduction reaction of the largest particles studied, despite generally increasing barriers for growing sizes. We attribute these observations to the interplay of reaction-specific material transport with a size-dependent inner particle morphology.
Hydrolysis reaction of 2,4-dichlorophenoxyacetic acid. A kinetic and computational study
NASA Astrophysics Data System (ADS)
Romero, Jorge Marcelo; Jorge, Nelly Lidia; Grand, André; Hernández-Laguna, Alfonso
2015-10-01
The degradation of the 2,4-dichlorophenoxyacetic acid in aqueous solution is an hydrolysis reaction. Two products are identified: 2,4-dichlorophenol and glycolic acid. Reaction is investigated as a function of pH and temperature, and it is first-order kinetics and pH-dependent. Reaction is modeled in gas phase, where a proton catalyses the reaction. Critical points of PES are calculated at B3LYP/6-311++G(3df,2p), and aug-cc-pvqz//6-311++G(3df,2p) levels plus ZPE at 6-311++G(3df,2p) level. The activation barrier is 21.2 kcal/mol. Theoretical results agree with the experimental results. A second mechanism related with a Cl2Phsbnd Osbnd CH2sbnd COOH⋯H2O complex is found, but with a rate limiting step of 38.4 kcal/mol.
de Anna, Pietro; Dentz, Marco; Tartakovsky, Alexandre M.; Le Borgne, Tanguy
2014-07-08
We investigate the effective kinetics of a reaction front for mixing limited bimolecular reaction $A+B\\rightarrow C$ in a porous medium. While Fickian diffusion predicts a scaling of the cumulative mass produced as $M_C \\propto t^{1/2}$, we observe two time regimes in which the total product mass evolves faster then $t^{1/2}$. At early times the invading solute is organized in fingers of high velocity. Reactions take place only at the fingers boundaries whose surface grows linearly in time. We show that this configuration leads to a mass scaling $M_C \\propto t^2$. When diffusion mixes reactants and destroy these finger structures, the effective reaction rate slows down and we relate it to the longitudinal advective spreading providing $M_C \\propto \\sigma_x$. The transition time between these two regimes is characterized by the diffusion time over the transverse fingers cross section.
Stoichiometry and kinetics of the reaction of nitrite with free chlorine in aqueous solutions
Diyamandoglu, V.; Marinas, B.J.; Selleck, R.E. )
1990-11-01
The reaction of nitrite with free chlorine in dilute aqueous solution (3.4 < pH < 11.5) was studied under continuous-flow mixing conditions. Chlorine, chloride, nitrite, and nitrate were all measured analytically. Stoichiometric balances demonstrated that nitrate was oxidized to nitrate, and chlorine was reduced to chloride, without the significant production of any other chemical species. The kinetic studies demonstrated that the reaction is very fast at neutral or acidic pH with the rate decreasing with increasing pH. The reaction was strictly bimolecular in the pH range of 9.5-11.6, whereas it was sufficiently slow to be followed with time. The reaction appears to proceed between nitrous and hypochlorous acid molecules, or HNO{sub 2} + HOCl {yields} 2H{sup +} + NO{sub 3}{sup {minus}} + Cl{sup {minus}}.
Duan, Hui; Li, Mengyang; Zhang, Guanghui; Gallagher, James R.; Huang, Zhiliang; Sun, Yu; Luo, Zhong; Chen, Hongzhong; Miller, Jeffrey T.; Zou, Ruqiang; Lei, Aiwen; Zhao, Yanli
2015-01-01
ABSTRACT: The development of organometallic single-site catalysts (SSCs) has inspired the designs of new heterogeneous catalysts with high efficiency. Nevertheless, the application of SSCs in certain modern organic reactions, such as C-C bond formation reactions, has still been less investigated. In this study, a single-site Pd(II) catalyst was developed, where 2,2'-bipyridine-grafted periodic mesoporous organosilica (PMO) was employed as the support of a Pd(II) complex. The overall performance of the single-site Pd(II) catalyst in the oxidative Heck reaction was then investigated. The investigation results show that the catalyst displays over 99% selectivity for the product formation with high reaction yield. Kinetic profiles further confirm its high catalytic efficiency, showing that the rate constant is nearly 40 times higher than that for the free Pd(II) salt. X-ray absorption spectroscopy reveals that the catalyst has remarkable lifetime and recyclability.
Sankaran, R.; Grout, R.
2012-01-01
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.
Purification and characterization of Fab fragments with rapid reaction kinetics against myoglobin.
Song, Hyung-Nam; Kim, Dong-Hyung; Park, Sung-Goo; Lee, Myung Kyu; Paek, Se-Hwan; Woo, Eui-Jeon
2015-01-01
Myoglobin is an early biomarker for acute myocardial infarction. Recently, we isolated the antibody IgG-Myo2-7ds, which exhibits unique rapid reaction kinetics toward human myoglobin antigen. Antibodies with rapid dissociation kinetics are thought to be premature IgG forms that are produced during the early stage of in vivo immunization. In the present study, we identified the epitope region of the IgG-Myo2-7ds antibody to be the C-terminal region of myoglobin, which corresponds to 144-154 aa. The Fab fragment was directly purified by papain cleavage and protein G affinity chromatography and demonstrated kinetics of an association constant of 4.02 × 10(4) M(-1) s(-1) and a dissociation constant of 2.28 × 10(-2) s(-1), which retained the unique reaction kinetics of intact IgG-Myo2-7ds antibodies. Because a rapid dissociation antibody can be utilized for antibody recycling, the results from this study would provide a platform for the development of antibody engineering in potential diagnostic areas such as a continuous monitoring system for heart disease. PMID:25561012
Berry, Hugues
2002-01-01
Conventional equations for enzyme kinetics are based on mass-action laws, that may fail in low-dimensional and disordered media such as biological membranes. We present Monte Carlo simulations of an isolated Michaelis-Menten enzyme reaction on two-dimensional lattices with varying obstacle densities, as models of biological membranes. The model predicts that, as a result of anomalous diffusion on these low-dimensional media, the kinetics are of the fractal type. Consequently, the conventional equations for enzyme kinetics fail to describe the reaction. In particular, we show that the quasi-stationary-state assumption can hardly be retained in these conditions. Moreover, the fractal characteristics of the kinetics are increasingly pronounced as obstacle density and initial substrate concentration increase. The simulations indicate that these two influences are mainly additive. Finally, the simulations show pronounced S-P segregation over the lattice at obstacle densities compatible with in vivo conditions. This phenomenon could be a source of spatial self organization in biological membranes. PMID:12324410
Grout, Ray W
2012-01-01
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.