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Sample records for nonradiative rate constants

  1. Gray-Tone Lithography Implementation of Drexhage's Method for Calibrating Radiative and Nonradiative Decay Constants of Fluorophores

    CERN Document Server

    Kwadrin, Andrej; 10.1021/jp3048423

    2013-01-01

    We present a straightforward method to realize non-planar dielectric structures with a controlled height profile for use in calibration of fluorophores. Calibration of fluorescence quantum efficiency and intrinsic radiative and nonradiative decay rates of emitters is possible by using changes in the local density of optical states, provided one can control the emitter-surface distance with nanometer accuracy. We realize a method that is accurate yet fast to implement. We fabricate PMMA wedges (4 mm x 4 mm x 2 \\mu m) by gray-tone UV-lithography of Shipley S1813G2. Its applicability as dielectric spacer is demonstrated in Drexhage experiments for three different emitters in the visible and near-infrared wavelength regime. The decay-rate dependence of the fluorescent state of emitters on the distance to a silver mirror is observed and compared to calculations based on the local density of states. Quantitative values for (non)radiative decay rates and quantum efficiencies are extracted. Furthermore, we discuss ho...

  2. Damping rates of surface plasmons for particles of size from nano- to micrometers; reduction of the nonradiative decay

    CERN Document Server

    Kolwas, Krystyna

    2012-01-01

    Damping rates of multipolar, localized surface plasmons (SP) of gold and silver nanospheres of radii up to $1000nm$ were found with the tools of classical electrodynamics. The significant increase in damping rates followed by noteworthy decrease for larger particles takes place along with substantial red-shift of plasmon resonance frequencies as a function of particle size. We also introduced interface damping into our modeling, which substantially modifies the plasmon damping rates of smaller particles. We demonstrate unexpected reduction of the multipolar SP damping rates in certain size ranges. This effect can be explained by the suppression of the nonradiative decay channel as a result of the lost competition with the radiative channel. We show that experimental dipole damping rates [H. Baida, et al., Nano Lett. 9(10) (2009) 3463, and C. S\\"onnichsen, et al., Phys. Rev. Lett. 88 (2002) 077402], and the resulting resonance quality factors can be described in a consistent and straightforward way within our ...

  3. Nonradiative Electron--Hole Recombination Rate Is Greatly Reduced by Defects in Monolayer Black Phosphorus: Ab Initio Time Domain Study.

    Science.gov (United States)

    Long, Run; Fang, Weihai; Akimov, Alexey V

    2016-02-18

    We report ab initio time-domain simulations of nonradiative electron-hole recombination and electronic dephasing in ideal and defect-containing monolayer black phosphorus (MBP). Our calculations predict that the presence of phosphorus divacancy in MBP (MBP-DV) substantially reduces the nonradiative recombination rate, with time scales on the order of 1.57 ns. The luminescence line width in ideal MBP of 150 meV is 2.5 times larger than MBP-DV at room temperature, and is in excellent agreement with experiment. We find that the electron-hole recombination in ideal MBP is driven by the 450 cm(-1) vibrational mode, whereas the recombination in the MBP-DV system is driven by a broad range of vibrational modes. The reduced electron-phonon coupling and increased bandgap in MBP-DV rationalize slower recombination in this material, suggesting that electron-phonon energy losses in MBP can be minimized by creating suitable defects in semiconductor device material.

  4. Inflation with a constant rate of roll

    Science.gov (United States)

    Motohashi, Hayato; Starobinsky, Alexei A.; Yokoyama, Jun'ichi

    2015-09-01

    We consider an inflationary scenario where the rate of inflaton roll defined by ̈phi/H dot phi remains constant. The rate of roll is small for slow-roll inflation, while a generic rate of roll leads to the interesting case of 'constant-roll' inflation. We find a general exact solution for the inflaton potential required for such inflaton behaviour. In this model, due to non-slow evolution of background, the would-be decaying mode of linear scalar (curvature) perturbations may not be neglected. It can even grow for some values of the model parameter, while the other mode always remains constant. However, this always occurs for unstable solutions which are not attractors for the given potential. The most interesting particular cases of constant-roll inflation remaining viable with the most recent observational data are quadratic hilltop inflation (with cutoff) and natural inflation (with an additional negative cosmological constant). In these cases even-order slow-roll parameters approach non-negligible constants while the odd ones are asymptotically vanishing in the quasi-de Sitter regime.

  5. Nanoantenna enhanced emission of light-harvesting complex 2: the role of resonance, polarization, and radiative and non-radiative rates.

    Science.gov (United States)

    Wientjes, Emilie; Renger, Jan; Curto, Alberto G; Cogdell, Richard; van Hulst, Niek F

    2014-12-01

    Nanoantennae show potential for photosynthesis research for two reasons; first by spatially confining light for experiments which require high spatial resolution, and second by enhancing the photon emission of single light-harvesting complexes. For effective use of nanoantennae a detailed understanding of the interaction between the nanoantenna and the light-harvesting complex is required. Here we report how the excitation and emission of multiple purple bacterial LH2s (light-harvesting complex 2) are controlled by single gold nanorod antennae. LH2 complexes were chemically attached to such antennae, and the antenna length was systematically varied to tune the resonance with respect to the LH2 absorption and emission. There are three main findings. (i) The polarization of the LH2 emission is fully controlled by the resonant nanoantenna. (ii) The largest fluorescence enhancement, of 23 times, is reached for excitation with light at λ = 850 nm, polarized along the long antenna-axis of the resonant antenna. The excitation enhancement is found to be 6 times, while the emission efficiency is increased 3.6 times. (iii) The fluorescence lifetime of LH2 depends strongly on the antenna length, with shortest lifetimes of ∼40 ps for the resonant antenna. The lifetime shortening arises from an 11 times resonant enhancement of the radiative rate, together with a 2-3 times increase of the non-radiative rate, compared to the off-resonant antenna. The observed length dependence of radiative and non-radiative rate enhancement is in good agreement with simulations. Overall this work gives a complete picture of how the excitation and emission of multi-pigment light-harvesting complexes are influenced by a dipole nanoantenna.

  6. Dependence of Reaction Rate Constants on Density in Supercritical Fluids

    Institute of Scientific and Technical Information of China (English)

    WANGTao; SHENZhongyao

    2002-01-01

    A new method,which correlates rate constants of chemical reactions and density or pressure in supercritical fluids,was developed.Based on the transition state theory and thermodynamic principles, the rate constant can be reasonably correlated with the density of the supercritical fluid,and a correlation equation was obtained. Coupled with the equation of state (EOS) of a supercritical solvent,the effect of pressure on reaction rate constant could be represented.Two typical systems were used to test this method.The result indicates that this method is suitable for dilute supercritical fluid solutions.

  7. Kinetic performance limits of constant pressure versus constant flow rate gradient elution separations. Part I: theory.

    Science.gov (United States)

    Broeckhoven, K; Verstraeten, M; Choikhet, K; Dittmann, M; Witt, K; Desmet, G

    2011-02-25

    We report on a general theoretical assessment of the potential kinetic advantages of running LC gradient elution separations in the constant-pressure mode instead of in the customarily used constant-flow rate mode. Analytical calculations as well as numerical simulation results are presented. It is shown that, provided both modes are run with the same volume-based gradient program, the constant-pressure mode can potentially offer an identical separation selectivity (except from some small differences induced by the difference in pressure and viscous heating trajectory), but in a significantly shorter time. For a gradient running between 5 and 95% of organic modifier, the decrease in analysis time can be expected to be of the order of some 20% for both water-methanol and water-acetonitrile gradients, and only weakly depending on the value of V(G)/V₀ (or equivalently t(G)/t₀). Obviously, the gain will be smaller when the start and end composition lie closer to the viscosity maximum of the considered water-organic modifier system. The assumptions underlying the obtained results (no effects of pressure and temperature on the viscosity or retention coefficient) are critically reviewed, and can be inferred to only have a small effect on the general conclusions. It is also shown that, under the adopted assumptions, the kinetic plot theory also holds for operations where the flow rate varies with the time, as is the case for constant-pressure operation. Comparing both operation modes in a kinetic plot representing the maximal peak capacity versus time, it is theoretically predicted here that both modes can be expected to perform equally well in the fully C-term dominated regime (where H varies linearly with the flow rate), while the constant pressure mode is advantageous for all lower flow rates. Near the optimal flow rate, and for linear gradients running from 5 to 95% organic modifier, time gains of the order of some 20% can be expected (or 25-30% when accounting for

  8. Spectroscopy of cyanine dyes in fluid solution at atmospheric and high pressure: The effect of viscosity on nonradiative processes

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, S.; Sauerwein, B.; Drickamer, H.G.; Schuster, G.B. (Univ. of Illinois, Urbana, IL (United States))

    1994-12-22

    The spectroscopy of cyanine dyes was examined at atmospheric pressure and at high pressure in a series of alcohols and other solvents. Variation of external pressure provides the means to control viscosity over a wide range in one solvent at constant temperature. The findings reveal that the nonradiative relaxation of cyanines in fluid solution can occur when the motion leading to the formation of the cis isomer is stopped completely. Analysis of the viscosity dependence of the nonradiative relaxation rate constant reveals consistent deviation from the Kramers-DSE relation. 33 refs., 5 figs., 2 tabs.

  9. Dependence of rate constants on vibrational temperatures - An Arrhenius description

    Science.gov (United States)

    Ford, D. I.; Johnson, R. E.

    1988-01-01

    An interpretation of the variation of rate constants with vibrational temperature is proposed which introduces parameters analogous to those of the classical Arrhenius expression. The constancy of vibrational activation energy is studied for the dissociaton of NO, the ion-molecular reaction of O(+) with N2, and the atom exchange reaction of I with H2. It is found that when a Boltzmann distribution for vibrational states is applicable, the variation of the rate constant with the vibrational temperature can be used to define a vibrational activation energy. The method has application to exchange reactions where a vibrational energy threshold exists.

  10. Evaluation of antioxidants using oxidation reaction rate constants

    Institute of Scientific and Technical Information of China (English)

    SHI Yan; ZHAN Xiancheng; MA Lie; LI Linli; LI Chengrong

    2007-01-01

    An evaluation method for the capacity of antioxidants to protect drugs against oxidation is presented.As a new viewpoint,to determine the priority of the competitive oxidations between the antioxidant and the protected drug,and to compare the drug-protection capacity of antioxidants,it is important to determine their oxidation rate constants using chemical kinetics instead of standard oxidation (or reduction) potentials.Sodium sulfite,sodium bisulfite and sodium pyrosulfite were used as models for the determination of oxidation reaction rate constants in aqueous solutions.In the experiments,sufficient air was continually infused into the solution to keep the concentration of dissolved oxygen constant.The residual concentrations of the antioxidants were determined by iodimetry,and the concentration of dissolved oxygen by oxygen electrode.The data were fitted by linear regressions to obtain the reaction rate constants.It was found that the degradation of sodium sulfite,sodium bisulfite or sodium pyrosulfite obeyed pseudo zero-order kinetics in the buffer solutions.Because of the ionization equilibrium,these three antioxidants have the same ion form in solutions at a definite pH value and therefore their apparent rate constants were essentially the same.The average apparent rate constants of the three antioxidants at 25~C are (1.34±0.03)×10-3 at pH 6.8,(1.20±0.02) x 10-3 at pH 4.0 and (6.58±0.02)×10-3 mol.L-1.h-1 at pH 9.2,respectively.

  11. Prediction of Rate Constants for Catalytic Reactions with Chemical Accuracy.

    Science.gov (United States)

    Catlow, C Richard A

    2016-08-01

    Ex machina: A computational method for predicting rate constants for reactions within microporous zeolite catalysts with chemical accuracy has recently been reported. A key feature of this method is a stepwise QM/MM approach that allows accuracy to be achieved while using realistic models with accessible computer resources.

  12. VMATc: VMAT with constant gantry speed and dose rate

    Science.gov (United States)

    Peng, Fei; Jiang, Steve B.; Romeijn, H. Edwin; Epelman, Marina A.

    2015-04-01

    This article considers the treatment plan optimization problem for Volumetric Modulated Arc Therapy (VMAT) with constant gantry speed and dose rate (VMATc). In particular, we consider the simultaneous optimization of multi-leaf collimator leaf positions and a constant gantry speed and dose rate. We propose a heuristic framework for (approximately) solving this optimization problem that is based on hierarchical decomposition. Specifically, an iterative algorithm is used to heuristically optimize dose rate and gantry speed selection, where at every iteration a leaf position optimization subproblem is solved, also heuristically, to find a high-quality plan corresponding to a given dose rate and gantry speed. We apply our framework to clinical patient cases, and compare the resulting VMATc plans to idealized IMRT, as well as full VMAT plans. Our results suggest that VMATc is capable of producing treatment plans of comparable quality to VMAT, albeit at the expense of long computation time and generally higher total monitor units.

  13. High-temperature rate constant measurements for OH+xylenes

    KAUST Repository

    Elwardani, Ahmed Elsaid

    2015-06-01

    The overall rate constants for the reactions of hydroxyl (OH) radicals with o-xylene (k 1), m-xylene (k 2), and p-xylene (k 3) were measured behind reflected shock waves over 890-1406K at pressures of 1.3-1.8atm using OH laser absorption near 306.7nm. Measurements were performed under pseudo-first-order conditions. The measured rate constants, inferred using a mechanism-fitting approach, can be expressed in Arrhenius form as:k1=2.93×1013exp(-1350.3/T)cm3mol-1s-1(890-1406K)k2=3.49×1013exp(-1449.3/T)cm3mol-1s-1(906-1391K)k3=3.5×1013exp(-1407.5/T)cm3mol-1s-1(908-1383K)This paper presents, to our knowledge, first high-temperature measurements of the rate constants of the reactions of xylene isomers with OH radicals. Low-temperature rate-constant measurements by Nicovich et al. (1981) were combined with the measurements in this study to obtain the following Arrhenius expressions, which are applicable over a wider temperature range:k1=2.64×1013exp(-1181.5/T)cm3mol-1s-1(508-1406K)k2=3.05×109exp(-400/T)cm3mol-1s-1(508-1391K)k3=3.0×109exp(-440/T)cm3mol-1s-1(526-1383K) © 2015 The Combustion Institute.

  14. Reaction rate constant for radiative association of CF{sup +}

    Energy Technology Data Exchange (ETDEWEB)

    Öström, Jonatan, E-mail: jonatan.ostrom@gmail.com; Gustafsson, Magnus, E-mail: magnus.gustafsson@ltu.se [Applied Physics, Division of Materials Science, Department of Engineering Science and Mathematics, Luleå University of Technology, 97187 Luleå (Sweden); Bezrukov, Dmitry S. [Department of Chemistry, M. V. Lomonosov Moscow State University, Moscow, 119991 (Russian Federation); Nyman, Gunnar [Department of Chemistry and Molecular Biology, University of Gothenburg, 41296 Gothenburg (Sweden)

    2016-01-28

    Reaction rate constants and cross sections are computed for the radiative association of carbon cations (C{sup +}) and fluorine atoms (F) in their ground states. We consider reactions through the electronic transition 1{sup 1}Π → X{sup 1}Σ{sup +} and rovibrational transitions on the X{sup 1}Σ{sup +} and a{sup 3}Π potentials. Semiclassical and classical methods are used for the direct contribution and Breit–Wigner theory for the resonance contribution. Quantum mechanical perturbation theory is used for comparison. A modified formulation of the classical method applicable to permanent dipoles of unequally charged reactants is implemented. The total rate constant is fitted to the Arrhenius–Kooij formula in five temperature intervals with a relative difference of <3%. The fit parameters will be added to the online database KIDA. For a temperature of 10–250 K, the rate constant is about 10{sup −21} cm{sup 3} s{sup −1}, rising toward 10{sup −16} cm{sup 3} s{sup −1} for a temperature of 30 000 K.

  15. Reaction Rate Constant for Radiative Association of CF$^+$

    CERN Document Server

    Öström, Jonatan; Nyman, Gunnar; Gustafsson, Magnus

    2015-01-01

    Reaction rate constants and cross sections are computed for the radiative association of carbon cations ($\\text{C}^+$) and fluorine atoms ($\\text{F}$) in their ground states. We consider reactions through the electronic transition $1^1\\Pi \\rightarrow X^1\\Sigma^+$ and rovibrational transitions on the $X^1\\Sigma^+$ and $a^3\\Pi$ potentials. Semiclassical and classical methods are used for the direct contribution and Breit--Wigner theory for the resonance contribution. Quantum mechanical perturbation theory is used for comparison. A modified formulation of the classical method applicable to permanent dipoles of unequally charged reactants is implemented. The total rate constant is fitted to the Arrhenius--Kooij formula in five temperature intervals with a relative difference of $<3\\:\\%$. The fit parameters will be added to the online database KIDA. For a temperature of $10$ to $250\\:\\text{K}$, the rate constant is about $10^{-21}\\:\\text{cm}^3\\text{s}^{-1}$, rising toward $10^{-16}\\:\\text{cm}^3\\text{s}^{-1}$ fo...

  16. Uniaxial tension test on Rubber at constant true strain rate

    Directory of Open Access Journals (Sweden)

    Sourne H.L.

    2012-08-01

    Full Text Available Elastomers are widely used for damping parts in different industrial contexts because of their remarkable dissipation properties. Indeed, they can undergo severe mechanical loading conditions, i.e., high strain rates and large strains. Nevertheless, the mechanical response of these materials can vary from purely rubber-like to glassy depending on the strain rate undergone. Classically, uniaxial tension tests are made in order to find a relation between the stress and the strain in the material at various strain rates. However, even if the strain rate is searched to be constant, it is the nominal strain rate that is considered. Here we develop a test at constant true strain rate, i.e. the strain rate that is experienced by the material. In order to do such a test, the displacement imposed by the machine is an exponential function of time. This test has been performed with a high speed hydraulic machine for strain rates between 0.01/s and 100/s. A specific specimen has been designed, yielding a uniform strain field (and so a uniform stress field. Furthermore, an instrumented aluminum bar has been used to take into account dynamic effects in the measurement of the applied force. A high speed camera enables the determination of strain in the sample using point tracking technique. Using this method, the stress-strain curve of a rubber-like material during a loading-unloading cycle has been determined, up to a stretch ratio λ = 2.5. The influence of the true strain rate both on stiffness and on dissipation of the material is then discussed.

  17. Rate Constant Calculation for Thermal Reactions Methods and Applications

    CERN Document Server

    DaCosta, Herbert

    2011-01-01

    Providing an overview of the latest computational approaches to estimate rate constants for thermal reactions, this book addresses the theories behind various first-principle and approximation methods that have emerged in the last twenty years with validation examples. It presents in-depth applications of those theories to a wide range of basic and applied research areas. When doing modeling and simulation of chemical reactions (as in many other cases), one often has to compromise between higher-accuracy/higher-precision approaches (which are usually time-consuming) and approximate/lower-preci

  18. Quantum Mechanics Rate Constant for the N+ND Reaction

    Institute of Scientific and Technical Information of China (English)

    Ai-jie Zhang; Guo-zhong He

    2011-01-01

    We present nonadiabatic quantum dynamical calculations on the two coupled potential energy surfaces (12A' and 22A') [J.Theor.Comput.Chem.8,849 (2009)] for the reaction.Initial state-resolved reaction probabilities and cross sections for the N+ND→N2+D reaction and N'+ND→N+N'D reaction for collision energies of 5 meV to 1.0 eV are determined,respectively.It is found that the N+ND→N2+D reaction is dominated in the N+ND reaction.In addition,we obtained the rate constants for the N+ND→N2+D reaction which demand further experimental investigations.

  19. Efficient calculation of rate constants: Downhill versus uphill sampling

    Science.gov (United States)

    Klenin, Konstantin V.

    2014-08-01

    The classical transition state theory (TST), together with the notion of transmission coefficient, provides a useful tool for calculation of rate constants for rare events. However, in complex biomolecular reactions, such as protein folding, it is difficult to find a good reaction coordinate, so the transition state is ill-defined. In this case, other approaches are more popular, such as the transition interface sampling (TIS) and the forward flux sampling (FFS). Here, we show that the algorithms developed in the frames of TIS and FFS can be successfully applied, after a modification, for calculation of the transmission coefficient. The new procedure (which we call "downhill sampling") is more efficient in comparison with the traditional TIS and FFS ("uphill sampling") even if the reaction coordinate is bad. We also propose a new computational scheme that combines the advantages of TST, TIS, and FFS.

  20. DILATANCY BEHAVIOR IN CONSTANT STRAIN RATE CONSOLIDATION TEST

    Directory of Open Access Journals (Sweden)

    Berty Sompie

    2006-01-01

    Full Text Available Subjected to remolded young clay, this paper shows that a lot of time dependent behavior in the standard consolidation (SC and constant strain rate consolidation (CSRC tests is represented systematically by a simple assumption concerning the time dependency of dilatancy. In the SC test, at the first stage of each loading step little dilatancy takes place and dilatancy begins to occur several minutes after step loading. In CSRC test, some time period after the stress state has entered the normally consolidated region, dilatancy tends to occur rapidly with the increase in stress ratio. Since most of dilatancy has taken place at the earlier stage of consolidation, little dilatancy occurs at the latter stage of CSRC process. This tendency makes the specimen stiffer with the passage of time, and makes the vertical pressure and pore pressure increase substantially at the last stage of CSRC process. Consideration to such behavior may be effective to correctly interpret the result of CSRC test.

  1. Empirical correlation for prediction of the elutriation rate constant

    Directory of Open Access Journals (Sweden)

    Stojkovski Valentino

    2003-01-01

    Full Text Available In vessels containing fluidized solids, the gas leaving carries some suspended particles. This flux of solids is called entrainment, E or carryover and the bulk density of solids on this leaving gas stream is called the holdup. For design we need to know the rate of this entrainment and the size distribution of these entrained particles Rim in relation to the size distribution in the bed, Rib, as well as the variation of both these quantities with gas and solids properties, gas flow rate, bed geometry and location of the leaving gas stream. Steady-state elutriation experiments have been done in a fluidized bed 0,2 m diameter by 2,94 m high freeboard with superficial gas velocities up to 1 m/s using solids ranging in mean size from 0,15 to 0,58 mm and with particle density 2660 kg/m3. When the fine and coarse particles were mixed, the total entrainment flux above the freeboard was increased. None of the published correlations for estimating the elutriation rate constant were useful. A new simple equation, which is developed on the base of experimental results and theory of dimensional analyses, is presented.

  2. Hemoglobin glycation rate constant in non-diabetic Individuals.

    Science.gov (United States)

    Ladyżyński, Piotr; Wójcicki, Jan M; Bąk, Marianna I; Sabalińska, Stanisława; Kawiak, Jerzy; Foltyński, Piotr; Krzymień, Janusz; Karnafel, Waldemar

    2011-11-01

    The objectives were as follows: (1) estimating mean value of the overall hemoglobin glycation rate constant (k); (2) analyzing inter-individual variability of k; (3) verifying ability of the hemoglobin A1c (HbA1c) formation model to predict changes of HbA1c during red blood cells cultivation in vitro and to reproduce the clinical data. The mean k estimated in a group of 10 non-diabetic subjects was equal to 1.257 ± 0.114 × 10(-9) L mmol(-1) s(-1). The mean k was not affected by a way of estimation of glycemia. The mean k differed less than 20% from values reported earlier and it was almost identical to the mean values calculated on basis of the selected published data. Analysis of variability of k suggests that inter-individual heterogeneity of HbA1c formation is limited or rare. The HbA1c mathematical model was able to predict changes of HbA1c in vitro resulting from different glucose levels and to reproduce a linear relationship of HbA1c and average glucose obtained in the A1C-Derived Average Glucose Study. This study demonstrates that the glycation model with the same k value might be used in majority of individuals as a tool supporting interpretation of HbA1c in different clinical situations.

  3. Biodegradation testing of chemicals with high Henry’s constants – separating mass and effective concentration reveals higher rate constants

    DEFF Research Database (Denmark)

    Birch, Heidi; Andersen, Henrik Rasmus; Comber, Mike

    During simulation-type biodegradation tests, volatile chemicals will continuously partition between water phase and headspace. This study addressed how (1) this partitioning affects biodegradation test results and (2) it can be accounted for by combining mass balance and dynamic biodegradation...... Microextraction (HS-SPME) was applied directly on the test systems to measure substrate depletion by biodegradation relative to abiotic controls. HS-SPME was also applied to determine air to water partitioning ratios. Water phase biodegradation rate constants, kwater, were up to 72 times higher than test system...... biodegradation rate constants, ksystem. True water phase degradation rate constants facilitate extrapolation to other air-water systems and are more suitable input parameters for aquatic exposure and fate models. As such, they should be considered more appropriate for risk assessments than test system rate...

  4. Low-pressure effective fluorescence lifetimes and photo-physical rate constants of one- and two-ring aromatics

    Science.gov (United States)

    Benzler, Thorsten; Faust, Stephan; Dreier, Thomas; Schulz, Christof

    2015-12-01

    One- and two-ring aromatics such as toluene and naphthalene are frequently used molecular tracer species in laser-induced fluorescence (LIF) imaging diagnostics. Quantifying LIF signal intensities requires knowledge of the photo-physical processes that determine the fluorescence quantum yield. Collision-induced and intramolecular energy transfer processes in the excited electronic state closely interact under practical conditions. They can be separated through experiments at variable low pressures. Effective fluorescence lifetimes of gaseous toluene, 1,2,4-trimethylbenzene, anisole, naphthalene, and 1-methylnaphthalene diluted in CO2 were measured after picosecond laser excitation at 266 nm and time-resolved detection of fluorescence intensities. Measurements in an optically accessible externally heated cell between 296 and 475 K and 0.010-1 bar showed that effective fluorescence lifetimes generally decrease with temperature, while the influence of the bath-gas pressure depends on the respective target species and temperature. The results provide non-radiative and fluorescence rate constants and experimentally validate the effect of photo-induced cooling.

  5. Exergy analysis of integrated photovoltaic thermal solar water heater under constant flow rate and constant collection temperature modes

    NARCIS (Netherlands)

    Tiwari, Arvind; Dubey, Swapnil; Sandhu, G.S.; Sodha, M.S.; Anwar, S.I.

    2009-01-01

    In this communication, an analytical expression for the water temperature of an integrated photovoltaic thermal solar (IPVTS) water heater under constant flow rate hot water withdrawal has been obtained. Analysis is based on basic energy balance for hybrid flat plate collector and storage tank, resp

  6. Exergy analysis of integrated photovoltaic thermal solar water heater under constant flow rate and constant collection temperature modes

    NARCIS (Netherlands)

    Tiwari, A.; Dubey, Swapnil; Sandhu, G.S.; Sodha, M.S.; Anwar, S.I.

    2009-01-01

    In this communication, an analytical expression for the water temperature of an integrated photovoltaic thermal solar (IPVTS) water heater under constant flow rate hot water withdrawal has been obtained. Analysis is based on basic energy balance for hybrid flat plate collector and storage tank, resp

  7. Exergy analysis of integrated photovoltaic thermal solar water heater under constant flow rate and constant collection temperature modes

    NARCIS (Netherlands)

    Tiwari, A.; Dubey, Swapnil; Sandhu, G.S.; Sodha, M.S.; Anwar, S.I.

    2009-01-01

    In this communication, an analytical expression for the water temperature of an integrated photovoltaic thermal solar (IPVTS) water heater under constant flow rate hot water withdrawal has been obtained. Analysis is based on basic energy balance for hybrid flat plate collector and storage tank,

  8. Biodegradation testing of chemicals with high Henry's constants - Separating mass and effective concentration reveals higher rate constants.

    Science.gov (United States)

    Birch, Heidi; Andersen, Henrik R; Comber, Mike; Mayer, Philipp

    2017-05-01

    During simulation-type biodegradation tests, volatile chemicals will continuously partition between water phase and headspace. This study addressed how (1) this partitioning affects test results and (2) can be accounted for by combining equilibrium partition and dynamic biodegradation models. An aqueous mixture of 9 (semi)volatile chemicals was first generated using passive dosing and then diluted with environmental surface water producing concentrations in the ng/L to μg/L range. After incubation for 2 h to 4 weeks, automated Headspace Solid Phase Microextraction (HS-SPME) was applied directly on the test systems to measure substrate depletion by biodegradation relatively to abiotic controls. HS-SPME was also applied to determine air to water partitioning ratios. Biodegradation rate constants relating to the chemical in the water phase, kwater, were generally a factor 1 to 11 times higher than biodegradation rate constants relating to the total mass of chemical in the test system, ksystem, with one exceptional factor of 72 times for a long chain alkane. True water phase degradation rate constants were found (i) more appropriate for risk assessment than test system rate constants, (ii) to facilitate extrapolation to other air-water systems and (iii) to be better defined input parameters for aquatic exposure and fate models.

  9. Universality of thermodynamic constants governing biological growth rates.

    Directory of Open Access Journals (Sweden)

    Ross Corkrey

    Full Text Available BACKGROUND: Mathematical models exist that quantify the effect of temperature on poikilotherm growth rate. One family of such models assumes a single rate-limiting 'master reaction' using terms describing the temperature-dependent denaturation of the reaction's enzyme. We consider whether such a model can describe growth in each domain of life. METHODOLOGY/PRINCIPAL FINDINGS: A new model based on this assumption and using a hierarchical Bayesian approach fits simultaneously 95 data sets for temperature-related growth rates of diverse microorganisms from all three domains of life, Bacteria, Archaea and Eukarya. Remarkably, the model produces credible estimates of fundamental thermodynamic parameters describing protein thermal stability predicted over 20 years ago. CONCLUSIONS/SIGNIFICANCE: The analysis lends support to the concept of universal thermodynamic limits to microbial growth rate dictated by protein thermal stability that in turn govern biological rates. This suggests that the thermal stability of proteins is a unifying property in the evolution and adaptation of life on earth. The fundamental nature of this conclusion has importance for many fields of study including microbiology, protein chemistry, thermal biology, and ecological theory including, for example, the influence of the vast microbial biomass and activity in the biosphere that is poorly described in current climate models.

  10. Exergy analysis of integrated photovoltaic thermal solar water heater under constant flow rate and constant collection temperature modes

    Energy Technology Data Exchange (ETDEWEB)

    Tiwari, Arvind [Department of Design, Production and Management, University of Twente, Enschede (Netherlands); Dubey, Swapnil; Sandhu, G.S. [Centre for Energy Studies, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016 (India); Sodha, M.S. [Department of Education and Physics, Lucknow University, Lucknow 226007 (India); Anwar, S.I. [Indian Institute of Sugar-cane Research, Lucknow, U.P. (India)

    2009-12-15

    In this communication, an analytical expression for the water temperature of an integrated photovoltaic thermal solar (IPVTS) water heater under constant flow rate hot water withdrawal has been obtained. Analysis is based on basic energy balance for hybrid flat plate collector and storage tank, respectively, in the terms of design and climatic parameters. Further, an analysis has also been extended for hot water withdrawal at constant collection temperature. Numerical computations have been carried out for the design and climatic parameters of the system used by Huang et al. [Huang BJ, Lin TH, Hung WC, Sun FS. Performance evaluation of solar photovoltaic/thermal systems. Sol Energy 2001; 70(5): 443-8]. It is observed that the daily overall thermal efficiency of IPVTS system increases with increase constant flow rate and decrease with increase of constant collection temperature. The exergy analysis of IPVTS system has also been carried out. It is further to be noted that the overall exergy and thermal efficiency of an integrated photovoltaic thermal solar system (IPVTS) is maximum at the hot water withdrawal flow rate of 0.006 kg/s. The hourly net electrical power available from the system has also been evaluated. (author)

  11. Characteristic thermal constant and dimensionless heating rate. The links to optimum heating rate in GC

    Science.gov (United States)

    Blumberg; Klee

    2000-09-01

    An initial step in the quest of deriving a generalized approach to optimization of a temperature program in gas chromatography is presented. Central to this is the introduction of a dimensionless heating rate, r. As a first step to defining r, a characteristic thermal constant, thetachar, defined as thetachar = -dT/dk at k = 1, where T and k are, respectively, column temperature and solute retention factor, is introduced and evaluated for our own experimental data and for thermodynamic data from the literature. It was determined that, for silicone stationary phases with a phase ratio of 250, thetachar ranged from about 23 degrees C for low molecular weight hydrocarbons such as dimethylpropane to about 45 degrees C for high molecular weight pesticides such as mirex. It was also found that, for a particular solute and a stationary phase type, a 2 orders of magnitude increase in the film thickness caused only about a 2-fold increase in the characteristic thermal constant. Using thetachar as a fundamental temperature unit in GC and void time as a fundamental time unit, a dimensionless heating rate is introduced and its potential utility for the evaluation of the separation-speed tradeoffs in a temperature-programmed GC is demonstrated.

  12. Rate constants of reactions of {kappa}-carrageenan with hydrated electron and hydroxyl radical

    Energy Technology Data Exchange (ETDEWEB)

    Abad, L.V. [Nuclear Professional School, School of Engineering Laboratory, University of Tokyo, 2-22 Shirakata-Shirane, Tokai, Naka, Ibaraki 319-1188 (Japan); Philippine Nuclear Research Institute, Commonwealth Avenue, Diliman, Quezon City (Philippines)], E-mail: lvabad@pnri.dost.gov.ph; Saiki, S.; Kudo, H.; Muroya, Y.; Katsumura, Y. [Nuclear Professional School, School of Engineering Laboratory, University of Tokyo, 2-22 Shirakata-Shirane, Tokai, Naka, Ibaraki 319-1188 (Japan); Rosa, A.M. de la [Philippine Nuclear Research Institute, Commonwealth Avenue, Diliman, Quezon City (Philippines)

    2007-12-15

    The rate constants for the reactions of {kappa}-carrageenan with hydrated electron and hydroxyl radical was investigated by pulse radiolysis and laser photolysis. The kinetics of the reaction of hydrated electron indicates no seeming reaction with {kappa}-carrageenan. On the other hand, hydroxyl radical reacts very rapidly with {kappa}-carrageenan at a rate constant of approximately 1.2 x 10{sup 9} M{sup -1} s{sup -1}. This rate constant varies with pH.

  13. Neural estimation of kinetic rate constants from dynamic PET-scans

    DEFF Research Database (Denmark)

    Fog, Torben L.; Nielsen, Lars Hupfeldt; Hansen, Lars Kai;

    1994-01-01

    A feedforward neural net is trained to invert a simple three compartment model describing the tracer kinetics involved in the metabolism of [18F]fluorodeoxyglucose in the human brain. The network can estimate rate constants from positron emission tomography sequences and is about 50 times faster ...... than direct fitting of rate constants using the parametrized transients of the compartment model...

  14. Apparent Rate Constant for Diffusion-Controlled Three molecular (catalytic) reaction

    OpenAIRE

    Burlatsky, S. F.; Moreau, M

    1996-01-01

    We present simple explicit estimates for the apparent reaction rate constant for three molecular reactions, which are important in catalysis. For small concentrations and $d> 1$, the apparent reaction rate constant depends only on the diffusion coefficients and sizes of the particles. For small concentrations and $d\\le 1$, it is also time -- dependent. For large concentrations, it gains the dependence on concentrations.

  15. Competitive kinetics as a tool to determine rate constants for reduction of ferrylmyoglobin by food components

    DEFF Research Database (Denmark)

    Jongberg, Sisse; Lund, Marianne Nissen; Pattison, David I.

    2016-01-01

    . This approach allows determination of apparent rate constants for the oxidation of proteins by haem proteins of relevance to food oxidation and should be applicable to other systems. A similar approach has provided approximate apparent rate constants for the reduction of MbFe(IV)=O by catechin and green tea...

  16. Nonradiative charge transfer in collisions of protons with rubidium atoms

    Institute of Scientific and Technical Information of China (English)

    Yan Ling-Ling; Qu Yi-Zhi; Liu Chun-Hua; Zhang Yu; Wang Jian-Guo; Buenker Robert J

    2012-01-01

    The nonradiative charge-transfer cross sections for protons colliding with Rb(5s) atoms are calculated by using the quantum-mechanical molecularorbital close-coupling method in an energy range of 10-3 keV 10 keV.The total and state-selective charge-transfer cross sections are in good agreement with the experimental data in the relatively low energy region.The importance of rotational coupling for chargetransfer process is stressed.Compared with the radiative charge-transfer process,nonradiative charge transfer is a dominant mechanism at energies above 15 eV.The resonance structures of state-selective charge-transfer cross sections arising from the competition among channels are analysed in detail.The radiative and nonradiative charge-transfer rate coefficients from low to high temperature are presented.

  17. Nonradial Pulsations in ɛ Persei

    Science.gov (United States)

    Saio, Hideyuki; Kambe, Eiji; Lee, Umin

    2000-11-01

    We consider the question of whether all the modes detected in the line profile variations of ɛ Persei are consistent with nonradial pulsations excited by the kappa mechanism at the opacity Z-bump. We have computed massive (12.5-14 Msolar) main-sequence models, adjusting the parameters such that the evolutionary tracks pass around the approximate position of ɛ Per on the H-R diagram. A linear nonadiabatic, nonradial pulsation analysis is applied to these models. The periods in the frame corotating with the stellar surface for the observed 2.3-4.5 hr modes are found to be consistent with the Z-bump kappa mechanism. We have found, however, that the longest-period mode (8.48 hr in the observer's frame) cannot be explained by the kappa mechanism. We have examined the effect of rotation on the stability of oscillations and found that the stabilizing effect is weak, so that only a few of the shortest-period modes are stabilized for the rotation speed of ɛ Per. No significant difference is found between prograde and retrograde modes in the stability. It is a puzzle why no retrograde mode has been detected in ɛ Per, which should equally be excited by the kappa mechanism. We also discuss the observed and theoretical line profile variations of ɛ Per in the Appendix.

  18. Rate constants for the reaction of CF3O radicals with hydrocarbons at 298 K

    DEFF Research Database (Denmark)

    Kelly, C.; Treacy, J.; Sidebottom, H.W.;

    1993-01-01

    Rate constant ratios of the reactions of CF3O radicals with a number of hydrocarbons have been determined at 298 +/- 2 K and atmospheric pressure using a relative rate method. Using a previously determined value k(CF30 + C2H6) = 1.2 x 10(-12) cm3 molecule-1 s-1 these rate constant ratios provide......-1. The importance of the reactions of CF3O radicals with hydrocarbons under atmospheric conditions is discussed....

  19. Asymptotic solution of nonlinear moment equations for constant-rate aerosol reactors

    Directory of Open Access Journals (Sweden)

    B. D. Shaw

    1998-01-01

    Full Text Available Nonlinear evolution equations based upon moments of the aerosol size distribution function are solved asymptotically for constant-rate aerosol reactors (i.e., where condensible monomer is added at a constant rate operating in the free-molecular limit. The governing equations are nondimensionalized and a large parameter that controls nucleation behavior is identified. Asymptotic analyses are developed in terms of this parameter. Comparison of the asymptotic results with direct numerical integration of the governing equations is favorable. The asymptotic results provide a simplified analytical approach to estimating average particle sizes, particle number densities, and peak supersaturation values for constant-rate aerosol reactors.

  20. Development of a group contribution method to predict aqueous phase hydroxyl radical (HO*) reaction rate constants.

    Science.gov (United States)

    Minakata, Daisuke; Li, Ke; Westerhoff, Paul; Crittenden, John

    2009-08-15

    The hydroxyl radical (HO*) is a strong oxidant that reacts with electron-rich sites of organic compounds and initiates complex chain mechanisms. In order to help understand the reaction mechanisms, a rule-based model was previously developed to predict the reaction pathways. For a kinetic model, there is a need to develop a rate constant estimator that predicts the rate constants for a variety of organic compounds. In this study, a group contribution method (GCM) is developed to predict the aqueous phase HO* rate constants for the following reaction mechanisms: (1) H-atom abstraction, (2) HO* addition to alkenes, (3) HO* addition to aromatic compounds, and (4) HO* interaction with sulfur (S)-, nitrogen (N)-, or phosphorus (P)-atom-containing compounds. The GCM hypothesizes that an observed experimental rate constant for a given organic compound is the combined rate of all elementary reactions involving HO*, which can be estimated using the Arrhenius activation energy, E(a), and temperature. Each E(a) for those elementary reactions can be comprised of two parts: (1) a base part that includes a reactive bond in each reaction mechanism and (2) contributions from its neighboring functional groups. The GCM includes 66 group rate constants and 80 group contribution factors, which characterize each HO* reaction mechanism with steric effects of the chemical structure groups and impacts of the neighboring functional groups, respectively. Literature-reported experimental HO* rate constants for 310 and 124 compounds were used for calibration and prediction, respectively. The genetic algorithms were used to determine the group rate constants and group contribution factors. The group contribution factors for H-atom abstraction and HO* addition to the aromatic compounds were found to linearly correlate with the Taft constants, sigma*, and electrophilic substituent parameters, sigma+, respectively. The best calibrations for 83% (257 rate constants) and predictions for 62% (77

  1. Electron-ion dissociative recombination rate constants relevant to the Titan atmosphere and the Interstellar Medium

    Energy Technology Data Exchange (ETDEWEB)

    Osborne, David; Lawson, Patrick; Adams, Nigel, E-mail: ngadams@uga.edu [University of Georgia, Department of Chemistry, 101 Cedar St., Athens, Georgia 30602 (United States)

    2014-01-21

    Following the arrival of Cassini at Titan in 2004, the Titan atmosphere has been shown to contain large complex polycyclic-aromatic hydrocarbons. Since Cassini has provided a great deal of data, there exists a need for kinetic rate data to help with modeling this atmosphere. One type of kinetic data needed is electron-ion dissociative recombination (e-IDR) rate constants. These data are not readily available for larger compounds, such as naphthalene, or oxygen containing compounds, such as 1,4 dioxane or furan. Here, the rate constants for naphthalene, 1,4 dioxane, and furan have been measured and their temperature dependencies are determined when possible, using the University of Georgia's Variable Temperature Flowing Afterglow. The rate constants are compared with those previously published for other compounds; these show trends which illustrate the effects which multi-rings and oxygen heteroatoms substitutions have upon e-IDR rate constants.

  2. Using the pseudophase kinetic model to interpret chemical reactivity in ionic emulsions: determining antioxidant partition constants and interfacial rate constants.

    Science.gov (United States)

    Gu, Qing; Bravo-Díaz, Carlos; Romsted, Laurence S

    2013-06-15

    Kinetic results obtained in cationic and anionic emulsions show for the first time that pseudophase kinetic models give reasonable estimates of the partition constants of reactants, here t-butylhydroquinone (TBHQ) between the oil and interfacial region, P(O)(I), and the water and interfacial region, P(W)(I), and of the interfacial rate constant, k(I), for the reaction with an arenediazonium ion in emulsions containing a 1:1 volume ratio of a medium chain length triglyceride, MCT, and aqueous acid or buffer. The results provide: (a) an explanation for the large difference in pH, >4 pH units, required to run the reaction in CTAB (pH 1.54, added HBr) and SDS (pH 5.71, acetate buffer) emulsions; (b) reasonable estimates of PO(I) and k(I) in the CTAB emulsions; (c) a sensible interpretation of added counterion effects based on ion exchange in SDS emulsions (Na(+)/H3O(+) ion exchange in the interfacial region) and Donnan equilibrium in CTAB emulsions (Br(-) increasing the interfacial H3O(+)); and (d) the significance of the effect of the much greater solubility of TBHQ in MCT versus octane, 1000/1, as the oil. These results should aid in interpreting the effects of ionic surfactants on chemical reactivity in emulsions in general and in selecting the most efficient antioxidant for particular food applications.

  3. Absolute level-resolved reactive and inelastic rate constants in Li+Li2*

    Science.gov (United States)

    Coppage, Steven; Matei, Paula; Stewart, Brian

    2008-06-01

    We have used nuclear parity-changing collisions to obtain absolute level-to-level rate constants for reactive scattering in a triatomic system with identical nuclei. We have determined rate constants for the system 7Li2*(A 1Σu+)(vi=2,ji=19)+7Li-->7Li+7Li2*(A 1Σu+)(vf,jf), from laser-induced fluorescence spectra of lithium vapor in a heat pipe oven. Parity-preserving collisions yielded measurements of absolute rotationally and vibrationally inelastic rate constants as well. We compare the reactive rate constants with statistical prior distributions and the inelastic results with previously measured results on the Ne+7Li2* system.

  4. DETERMINATION OF HETEROGENEOUS ELECTRON TRANSFER RATE CONSTANTS AT MICROFABRICATED IRIDIUM ELECTRODES. (R825511C022)

    Science.gov (United States)

    There has been an increasing use of both solid metal and microfabricated iridium electrodes as substrates for various types of electroanalysis. However, investigations to determine heterogeneous electron transfer rate constants on iridium, especially at an electron beam evapor...

  5. DETERMINATION OF HETEROGENEOUS ELECTRON TRANSFER RATE CONSTANTS AT MICROFABRICATED IRIDIUM ELECTRODES. (R825511C022)

    Science.gov (United States)

    There has been an increasing use of both solid metal and microfabricated iridium electrodes as substrates for various types of electroanalysis. However, investigations to determine heterogeneous electron transfer rate constants on iridium, especially at an electron beam evapor...

  6. Determination of rapid chlorination rate constants by a stopped-flow spectrophotometric competition kinetics method.

    Science.gov (United States)

    Song, Dean; Liu, Huijuan; Qiang, Zhimin; Qu, Jiuhui

    2014-05-15

    Free chlorine is extensively used for water and wastewater disinfection nowadays. However, it still remains a big challenge to determine the rate constants of rapid chlorination reactions although competition kinetics and stopped-flow spectrophotometric (SFS) methods have been employed individually to investigate fast reaction kinetics. In this work, we proposed an SFS competition kinetics method to determine the rapid chlorination rate constants by using a common colorimetric reagent, N,N-diethyl-p-phenylenediamine (DPD), as a reference probe. A kinetic equation was first derived to estimate the reaction rate constant of DPD towards chlorine under a given pH and temperature condition. Then, on that basis, an SFS competition kinetics method was proposed to determine directly the chlorination rate constants of several representative compounds including tetracycline, ammonia, and four α-amino acids. Although Cl2O is more reactive than HOCl, its contribution to the overall chlorination kinetics of the test compounds could be neglected in this study. Finally, the developed method was validated through comparing the experimentally measured chlorination rate constants of the selected compounds with those obtained or calculated from literature and analyzing with Taft's correlation as well. This study demonstrates that the SFS competition kinetics method can measure the chlorination rate constants of a test compound rapidly and accurately.

  7. Systematic Angle Random Walk Estimation of the Constant Rate Biased Ring Laser Gyro

    Directory of Open Access Journals (Sweden)

    Guohu Feng

    2013-02-01

    Full Text Available An actual account of the angle random walk (ARW coefficients of gyros in the constant rate biased rate ring laser gyro (RLG inertial navigation system (INS is very important in practical engineering applications. However, no reported experimental work has dealt with the issue of characterizing the ARW of the constant rate biased RLG in the INS. To avoid the need for high cost precise calibration tables and complex measuring set-ups, the objective of this study is to present a cost-effective experimental approach to characterize the ARW of the gyros in the constant rate biased RLG INS. In the system, turntable dynamics and other external noises would inevitably contaminate the measured RLG data, leading to the question of isolation of such disturbances. A practical observation model of the gyros in the constant rate biased RLG INS was discussed, and an experimental method based on the fast orthogonal search (FOS for the practical observation model to separate ARW error from the RLG measured data was proposed. Validity of the FOS-based method was checked by estimating the ARW coefficients of the mechanically dithered RLG under stationary and turntable rotation conditions. By utilizing the FOS-based method, the average ARW coefficient of the constant rate biased RLG in the postulate system is estimated. The experimental results show that the FOS-based method can achieve high denoising ability. This method estimate the ARW coefficients of the constant rate biased RLG in the postulate system accurately. The FOS-based method does not need precise calibration table with high cost and complex measuring set-up, and Statistical results of the tests will provide us references in engineering application of the constant rate biased RLG INS.

  8. Reaction mechanisms and rate constants of waste degradation in landfill bioreactor systems with enzymatic-enhancement.

    Science.gov (United States)

    Jayasinghe, P A; Hettiaratchi, J P A; Mehrotra, A K; Kumar, S

    2014-06-01

    Augmenting leachate before recirculation with peroxidase enzymes is a novel method to increase the available carbon, and therefore the food supply to microorganisms at the declining phase of the anaerobic landfill bioreactor operation. In order to optimize the enzyme-catalyzed leachate recirculation process, it is necessary to identify the reaction mechanisms and determine rate constants. This paper presents a kinetic model developed to ascertain the reaction mechanisms and determine the rate constants for enzyme catalyzed anaerobic waste degradation. The maximum rate of reaction (Vmax) for MnP enzyme-catalyzed reactors was 0.076 g(TOC)/g(DS).day. The catalytic turnover number (k(cat)) of the MnP enzyme-catalyzed was 506.7 per day while the rate constant (k) of the un-catalyzed reaction was 0.012 per day.

  9. In vivo Target Residence Time and Kinetic Selectivity: The Association Rate Constant as Determinant.

    Science.gov (United States)

    de Witte, Wilhelmus E A; Danhof, Meindert; van der Graaf, Piet H; de Lange, Elizabeth C M

    2016-10-01

    It is generally accepted that, in conjunction with pharmacokinetics, the first-order rate constant of target dissociation is a major determinant of the time course and duration of in vivo target occupancy. Here we show that the second-order rate constant of target association can be equally important. On the basis of the commonly used mathematical models for drug-target binding, it is shown that a high target association rate constant can increase the (local) concentration of the drug, which decreases the rate of decline of target occupancy. The increased drug concentration can also lead to increased off-target binding and decreased selectivity. Therefore, the kinetics of both target association and dissociation need to be taken into account in the selection of drug candidates with optimal pharmacodynamic properties. Copyright © 2016 Elsevier Ltd. All rights reserved.

  10. Rate constant and reaction coordinate of Trp-cage folding in explicit water

    NARCIS (Netherlands)

    Juraszek, J.; Bolhuis, P.G.

    2008-01-01

    We report rate constant calculations and a reaction coordinate analysis of the rate-limiting folding and unfolding process of the Trp-cage mini-protein in explicit solvent using transition interface sampling. Previous transition path sampling simulations revealed that in this (un)folding process the

  11. ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS. II. ACID AND GENERAL BASE CATALYZED HYDROLYSIS

    Science.gov (United States)

    SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to calculate acid and neutral hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition states of a ...

  12. Microscopic Rate Constants of Crystal Growth from Molecular Dynamic Simulations Combined with Metadynamics

    Directory of Open Access Journals (Sweden)

    Dániel Kozma

    2012-01-01

    Full Text Available Atomistic simulation of crystal growth can be decomposed into two steps: the determination of the microscopic rate constants and a mesoscopic kinetic Monte Carlo simulation. We proposed a method to determine kinetic rate constants of crystal growth. We performed classical molecular dynamics on the equilibrium liquid/crystal interface of argon. Metadynamics was used to explore the free energy surface of crystal growth. A crystalline atom was selected at the interface, and it was displaced to the liquid phase by adding repulsive Gaussian potentials. The activation free energy of this process was calculated as the maximal potential energy density of the Gaussian potentials. We calculated the rate constants at different interfacial structures using the transition state theory. In order to mimic real crystallization, we applied a temperature difference in the calculations of the two opposite rate constants, and they were applied in kinetic Monte Carlo simulation. The novelty of our technique is that it can be used for slow crystallization processes, while the simple following of trajectories can be applied only for fast reactions. Our method is a possibility for determination of elementary rate constants of crystal growth that seems to be necessary for the long-time goal of computer-aided crystal design.

  13. Nonradiative limitations to plasmon propagation in chains of metallic nanoparticles

    CERN Document Server

    Brandstetter-Kunc, Adam; Downing, Charles A; Weinmann, Dietmar; Jalabert, Rodolfo A

    2016-01-01

    We investigate the collective plasmonic modes in a chain of metallic nanoparticles that are coupled by near-field interactions. The size- and momentum-dependent nonradiative Landau damping and radiative decay rates are calculated analytically within an open quantum system approach. These decay rates determine the excitation propagation along the chain. In particular, the behavior of the radiative decay rate as a function of the plasmon wavelength leads to a transition from an exponential decay of the collective excitation for short distances to an algebraic decay for large distances. Importantly, we show that the exponential decay is of a purely nonradiative origin. Our transparent model enables us to provide analytical expressions for the polarization-dependent plasmon excitation profile along the chain and for the associated propagation length. Our theoretical analysis constitutes an important step in the quest for the optimal conditions for plasmonic propagation in nanoparticle chains.

  14. A finite horizon production model with variable production rates and constant demand rate

    OpenAIRE

    2002-01-01

    In this paper we present a finite horizon single product single machine production problem. Demand rate and all the cost patterns do not change over time. However, end of horizon effects may require production rate adjustments at the beginning of each cycle. It is found that no such adjustments are required. The machine should be operated either at minimum speed (i.e. production rate = demand rate; shortage is not allowed), avoiding the buildup of any inventory, or at maximum s...

  15. Extraction of elementary rate constants from global network analysis of E. coli central metabolism

    Directory of Open Access Journals (Sweden)

    Broderick Gordon

    2008-05-01

    Full Text Available Abstract Background As computational performance steadily increases, so does interest in extending one-particle-per-molecule models to larger physiological problems. Such models however require elementary rate constants to calculate time-dependent rate coefficients under physiological conditions. Unfortunately, even when in vivo kinetic data is available, it is often in the form of aggregated rate laws (ARL that do not specify the required elementary rate constants corresponding to mass-action rate laws (MRL. There is therefore a need to develop a method which is capable of automatically transforming ARL kinetic information into more detailed MRL rate constants. Results By incorporating proteomic data related to enzyme abundance into an MRL modelling framework, here we present an efficient method operating at a global network level for extracting elementary rate constants from experiment-based aggregated rate law (ARL models. The method combines two techniques that can be used to overcome the difficult properties in parameterization. The first, a hybrid MRL/ARL modelling technique, is used to divide the parameter estimation problem into sub-problems, so that the parameters of the mass action rate laws for each enzyme are estimated in separate steps. This reduces the number of parameters that have to be optimized simultaneously. The second, a hybrid algebraic-numerical simulation and optimization approach, is used to render some rate constants identifiable, as well as to greatly narrow the bounds of the other rate constants that remain unidentifiable. This is done by incorporating equality constraints derived from the King-Altman and Cleland method into the simulated annealing algorithm. We apply these two techniques to estimate the rate constants of a model of E. coli glycolytic pathways. The simulation and statistical results show that our innovative method performs well in dealing with the issues of high computation cost, stiffness, local

  16. Implementation of a microcanonical variational transition state theory for direct dynamics calculations of rate constants

    Institute of Scientific and Technical Information of China (English)

    王艳; 钱英; 冯文林; 刘若庄

    2003-01-01

    An implementation of the variational quantum RRKM program is presented to utilize the direct ab initio dynamics approach for calculating k(E, J), k(E) and k(T) within the framework of the microcanonical transition state (μTST) and microcanonical variational TST (μVT) theories. An algorithm including tunneling contributions in Beyer-Swinehart method for calculating microcanonical rate constants is also proposed. An efficient piece-wise interpolation method is developed to evaluate the Boltzmann integral in calculation of thermal rate constants. Calculations on several test reactions, namely the H(D)2CO→H(D)2 + CO, CH2CO→CH2 + CO and CH4 + H→CH3 + H2 reactions, show that the results are in good agreement with the previous rate constants calculations. This approach would require much less computational resource.

  17. Feasibility of constant dose rate VMAT in the treatment of nasopharyngeal cancer patients

    OpenAIRE

    Yu, Wenliang; Shang, Haijiao; Xie, Congying; Han, CE; Yi, Jinling; Zhou, Yongqiang; Jin, Xiance

    2014-01-01

    Purpose To investigate the feasibility of constant dose rate volumetric modulated arc therapy (CDR-VMAT) in the treatment of nasopharyngeal cancer (NPC) patients and to introduce rotational arc radiotherapy for linacs incapable of dose rate variation. Materials and methods Twelve NPC patients with various stages treated previously using variable dose rate (VDR) VMAT were enrolled in this study. CDR-VMAT, VDR-VMAT and mutlicriteria optimization (MCO) VMAT plans were generated for each patient ...

  18. Accurate quantum thermal rate constants for the three-dimensional H+H2 reaction

    Science.gov (United States)

    Park, Tae Jun; Light, J. C.

    1989-07-01

    The rate constants for the three-dimensional H+H2 reaction on the Liu-Siegbahn-Truhlar-Horowitz (LSTH) surface are calculated using Pack-Parker hyperspherical (APH) coordinates and a C2v symmetry adapted direct product discrete variable representation (DVR). The C2v symmetry decomposition and the parity decoupling on the basis are performed for the internal coordinate χ. The symmetry decomposition results in a block diagonal representation of the flux and Hamiltonian operators. The multisurface flux is introduced to represent the multichannel reactive flux. The eigenvalues and eigenvectors of the J=0 internal Hamiltonian are obtained by sequential diagonalization and truncation. The individual symmetry blocks of the flux operator are propagated by the corresponding blocks of the Hamiltonian, and the J=0 rate constant k0(T) is obtained as a sum of the rate constants calculated for each block. k0(T) is compared with the exact k0(T) obtained from thermal averaging of the J=0 reaction probabilities; the errors are within 5%-20% up to T=1500 K. The sequential diagonalization-truncation method reduces the size of the Hamiltonian greatly, but the resulting Hamiltonian matrix still describes the time evolution very accurately. For the J≠0 rate constant calculations, the truncated internal Hamiltonian eigenvector basis is used to construct reduced (JKJ) blocks of the Hamiltonian. The individual (JKJ) blocks are diagonalized neglecting Coriolis coupling and treating the off-diagonal KJ±2 couplings by second order perturbation theory. The full wave function is parity decoupled. The rate constant is obtained as a sum over J of (2J+1)kJ(T). The time evolution of the flux for J≠0 is again very accurately described to give a well converged rate constant.

  19. Prediction and dissection of widely-varying association rate constants of actin-binding proteins.

    Directory of Open Access Journals (Sweden)

    Xiaodong Pang

    Full Text Available Actin is an abundant protein that constitutes a main component of the eukaryotic cytoskeleton. Its polymerization and depolymerization are regulated by a variety of actin-binding proteins. Their functions range from nucleation of actin polymerization to sequestering G-actin in 1∶1 complexes. The kinetics of forming these complexes, with rate constants varying at least three orders of magnitude, is critical to the distinct regulatory functions. Previously we have developed a transient-complex theory for computing protein association mechanisms and association rate constants. The transient complex refers to an intermediate in which the two associating proteins have near-native separation and relative orientation but have yet to form short-range specific interactions of the native complex. The association rate constant is predicted as k(a = k(a0 e(-ΔG(el*/k(BT, where k(a0 is the basal rate constant for reaching the transient complex by free diffusion, and the Boltzmann factor captures the bias of long-range electrostatic interactions. Here we applied the transient-complex theory to study the association kinetics of seven actin-binding proteins with G-actin. These proteins exhibit three classes of association mechanisms, due to their different molecular shapes and flexibility. The 1000-fold k(a variations among them can mostly be attributed to disparate electrostatic contributions. The basal rate constants also showed variations, resulting from the different shapes and sizes of the interfaces formed by the seven actin-binding proteins with G-actin. This study demonstrates the various ways that actin-binding proteins use physical properties to tune their association mechanisms and rate constants to suit distinct regulatory functions.

  20. Separating the effect of respiration from the heart rate variability for cases of constant harmonic breathing

    Directory of Open Access Journals (Sweden)

    Kircher Michael

    2015-09-01

    Full Text Available Heart Rate Variability studies are a known measure for the autonomous control of the heart rate. In special situations, its interpretation can be ambiguous, since the respiration has a major influence on the heart rate variability. For this reason it has often been proposed to measure Heart Rate Variability, while the subjects are breathing at a constant respiration rate. That way the spectral influence of the respiration is known. In this work we propose to remove this constant respiratory influence from the heart rate and the Heart Rate Variability parameters to gain respiration free autonomous controlled heart rate signal. The spectral respiratory component in the heart rate signal is detected and characterized. Subsequently the respiratory effect on Heart Rate Variability is removed using spectral filtering approaches, such as the Notch filter or the Raised Cosine filter. As a result new decoupled Heart Variability parameters are gained, which could lead to new additional interpretations of the autonomous control of the heart rate.

  1. Power consumption analysis of constant bit rate data transmission over 3G mobile wireless networks

    DEFF Research Database (Denmark)

    Wang, Le; Ukhanova, Ann; Belyaev, Evgeny

    2011-01-01

    This paper presents the analysis of the power consumption of data transmission with constant bit rate over 3G mobile wireless networks. Our work includes the description of the transition state machine in 3G networks, followed by the detailed energy consumption analysis and measurement results...

  2. On the Temperature Dependence of the Rate Constant of the Bimolecular Reaction of two Hydrated Electrons

    Directory of Open Access Journals (Sweden)

    S.L. Butarbutar

    2013-08-01

    Full Text Available It has been a longstanding issue in the radiation chemistry of water that, even though H2 is a molecular product, its “escape” yield g(H2 increases with increasing temperature. A main source of H2 is the bimolecular reaction of two hydrated electrons (eaq. The temperature dependence of the rate constant of this reaction (k1, measured under alkaline conditions, reveals that the rate constant drops abruptly above ~150°C. Recently, it has been suggested that this temperature dependence should be regarded as being independent of pH and used in high-temperature modeling of near-neutral water radiolysis. However, when this drop in the eaq self-reaction rate constant is included in low (isolated spurs and high (cylindrical tracks linear energy transfer (LET modeling calculations, g(H2 shows a marked downward discontinuity at ~150°C which is not observed experimentally. The consequences of the presence of this discontinuity in g(H2 for both low and high LET radiation are briefly discussed in this communication. It is concluded that the applicability of the sudden drop in k1 observed at ~150°C in alkaline water to near-neutral water is questionable and that further measurements of the rate constant in pure water are highly desirable.

  3. Estimate Of The Decay Rate Constant of Hydrogen Sulfide Generation From Landfilled Drywall

    Science.gov (United States)

    Research was conducted to investigate the impact of particle size on H2S gas emissions and estimate a decay rate constant for H2S gas generation from the anaerobic decomposition of drywall. Three different particle sizes of regular drywall and one particle size of paperless drywa...

  4. Stress relaxation of entangled polystyrene solution after constant-rate, uniaxial elongation

    DEFF Research Database (Denmark)

    Matsumiya, Yumi; Masubuchi, Yuichi; Watanabe, Hiroshi

    For an entangled solution of linear polystyrene (PS 545k; M = 545k) in dibutyl phthalate (DBP), the stress relaxation after constant-rate uniaxial elongation was examined with an extensional viscosity fixture mounted on ARES (TA Instruments). The PS concentration, c = 52 wt%, was chosen in a way...

  5. The Reaction Mechanism and Rate Constants in the Radiolysis of Fe2+-Cu2+ Solutions

    DEFF Research Database (Denmark)

    Bjergbakke, Erling; Sehested, Knud; Rasmussen, O. Lang

    1976-01-01

    Pulse radiolysis and gamma radiolysis have been used to study the reaction mechanism in the radiolysis of aqueous solutions of Fe2+ and Cu2+. A reaction scheme has been developed and confirmed by computation of the corresponding complete set of differential equations. The rate constants for some...

  6. Measurements of Creep Internal Stress Based on Constant Strain Rate and Its Application to Engineering

    Institute of Scientific and Technical Information of China (English)

    TAO Wen-liang; WEI Tao

    2006-01-01

    This research is carried out on the basis of Constant Strain Rate(CSR) to measure creep internal stress. Measurements of creep internal stress are conducted on the material test machine by using the CSR method. A mathematical model of creep internal stress is also proposed and its application is presented in this paper.

  7. Formulation of a universal first-order rate constant for enzymatic reactions.

    Science.gov (United States)

    Imoto, Taiji

    2013-01-01

    It is a common practice to employ k(cat)[E]₀/K(m) as a first-order rate constant for the analysis of an enzymatic reaction, where [E]₀ is the total enzyme concentration. I describe in this report a serious shortcoming in analyzing enzymatic reactions when kcat[E]₀/K(m) is employed and show that k(cat)[E]₀/K(m) can only be applied under very limited conditions. I consequently propose the use of a more universal first-order rate constant, k(cat)[ES](K)/[S]₀, where [ES](K) is the initial equilibrium concentration of the ES-complex derived from [E]₀, [S]₀ and K(m). Employing k(cat)[ES](K)/[S]₀ as the first-order rate constant enables all enzymatic reactions to be reasonably simulated under a wide range of conditions, and the catalytic and binding contributions to the rate constant of any enzyme can be determined under any and all conditions.

  8. Theoretical and Shock Tube Study of the Rate Constants for Hydrogen Abstraction Reactions of Ethyl Formate

    KAUST Repository

    Wu, Junjun

    2017-08-03

    We report a systematic chemical kinetics study of the H-atom abstractions from ethyl formate (EF) by H, O(3P), CH3, OH, and HO2 radicals. The geometry optimization and frequency calculation of all the species were conducted using the M06 method and the cc-pVTZ basis set. The one-dimensional hindered rotor treatment of the reactants and transition states and the intrinsic reaction coordinate analysis were also performed at the M06/cc-pVTZ level of theory. The relative electronic energies were calculated at the CCSD(T)/cc-pVXZ (where X = D, T) level of theory and further extrapolated to the complete basis set limit. Rate constants for the tittle reactions were calculated over the temperature range of 500‒2500 K by the transition state theory (TST) in conjunction with asymmetric Eckart tunneling effect. In addition, the rate constants of H-abstraction by hydroxyl radical were measured in shock tube experiments at 900‒1321 K and 1.4‒2.0 atm. Our theoretical rate constants of OH + EF → Products agree well with the experimental results within 15% over the experimental temperature range of 900‒1321 K. Branching ratios for the five types of H-abstraction reactions were also determined from their individual site-specific rate constants.

  9. USE OF ROUGH SETS AND SPECTRAL DATA FOR BUILDING PREDICTIVE MODELS OF REACTION RATE CONSTANTS

    Science.gov (United States)

    A model for predicting the log of the rate constants for alkaline hydrolysis of organic esters has been developed with the use of gas-phase min-infrared library spectra and a rule-building software system based on the mathematical theory of rough sets. A diverse set of 41 esters ...

  10. The ruin probability of a discrete time risk model under constant interest rate with heavy tails

    NARCIS (Netherlands)

    Tang, Q.

    2004-01-01

    This paper investigates the ultimate ruin probability of a discrete time risk model with a positive constant interest rate. Under the assumption that the gross loss of the company within one year is subexponentially distributed, a simple asymptotic relation for the ruin probability is derived and co

  11. Stress relaxation of entangled polystyrene solution after constant-rate, uniaxial elongation

    DEFF Research Database (Denmark)

    Matsumiya, Yumi; Masubuchi, Yuichi; Watanabe, Hiroshi;

    For an entangled solution of linear polystyrene (PS 545k; M = 545k) in dibutyl phthalate (DBP), the stress relaxation after constant-rate uniaxial elongation was examined with an extensional viscosity fixture mounted on ARES (TA Instruments). The PS concentration, c = 52 wt%, was chosen in a way...

  12. Unimolecular reaction rate constants of NO{sub 2} just above D{sub 0}

    Energy Technology Data Exchange (ETDEWEB)

    Bezel, I.; Stolyarov, D.; Wittig, C.

    1999-12-09

    Photoinitiated unimolecular decomposition on a barrierless potential energy surface (PES) has been studied for the reaction NO{sub 2} {yields} O({sup 3}P{sub 2}) + NO(X{sup 2}{Pi}{sub 1/2}, {nu} = 0) for excess energies up to approximately 17 cm{sup {minus}1} above the dissociation threshold (i.e., D{sub 0} for nonrotating molecules) by using expansion-cooled samples and the time-resolved pump-probe technique. To examine the threshold region with enough energy resolution to discern abrupt changes in the rate constant, should they occur, a pump-probe cross-correlation temporal width of {approximately}25 ps and a pump line width {le}2 cm{sup {minus}1} has been used. These are the first direct observations of the reaction rate constants in this energy regime. The rate constant was found to increase by an order of magnitude, varying from {approximately}2 x 10{sup 10} s{sup {minus}1} to {ge}10{sup 11} s{sup {minus}1}, the latter being a rough lower bound imposed by the experimental arrangement. The rate constant does not display the energy dependence predicted by using phase space theory, at least in detail. Rather, it appears to reflect the highly complex nature of the levels and the multiple PESs that are believed to be responsible for the anomalously high vibronic level density which has been observed just below D{sub 0}. These results bridge the gap between spectroscopic studies which have been carried out at energies just above D{sub 0} and ultrafast experiments which have measured rate constants in this energy region with pump laser spectral widths of {approximately}30 cm{sup {minus}1}.

  13. Structural model for the dynamic buckling of a column under constant rate compression

    CERN Document Server

    Kuzkin, Vitaly A

    2015-01-01

    Dynamic buckling behavior of a column (rod, beam) under constant rate compression is considered. The buckling is caused by prescribed motion of column ends toward each other with constant velocity. Simple model with one degree of freedom simulating static and dynamic buckling of a column is derived. In the case of small initial disturbances the model yields simple analytical dependencies between the main parameters of the problem: critical force, compression rate, and initial disturbance. It is shown that the time required for buckling is inversely proportional to cubic root of compression velocity and logarithmically depends on the initial disturbance. Analytical expression for critical buckling force as a function of compression velocity is derived. It is shown that in a range of compression rates typical for laboratory experiments the dependence is accurately approximated by a power law with exponent equal to $2/3$. Theoretical findings are supported by available results of laboratory experiments. Keywords...

  14. Efficient quantum-classical method for computing thermal rate constant of recombination: application to ozone formation.

    Science.gov (United States)

    Ivanov, Mikhail V; Babikov, Dmitri

    2012-05-14

    Efficient method is proposed for computing thermal rate constant of recombination reaction that proceeds according to the energy transfer mechanism, when an energized molecule is formed from reactants first, and is stabilized later by collision with quencher. The mixed quantum-classical theory for the collisional energy transfer and the ro-vibrational energy flow [M. Ivanov and D. Babikov, J. Chem. Phys. 134, 144107 (2011)] is employed to treat the dynamics of molecule + quencher collision. Efficiency is achieved by sampling simultaneously (i) the thermal collision energy, (ii) the impact parameter, and (iii) the incident direction of quencher, as well as (iv) the rotational state of energized molecule. This approach is applied to calculate third-order rate constant of the recombination reaction that forms the (16)O(18)O(16)O isotopomer of ozone. Comparison of the predicted rate vs. experimental result is presented.

  15. Effect of Molecular Packing and Charge Delocalization on the Nonradiative Recombination of Charge-Transfer States in Organic Solar Cells

    KAUST Repository

    Chen, Xian Kai

    2016-09-05

    In organic solar cells, a major source of energy loss is attributed to nonradiative recombination from the interfacial charge transfer states to the ground state. By taking pentacene–C60 complexes as model donor–acceptor systems, a comprehensive theoretical understanding of how molecular packing and charge delocalization impact these nonradiative recombination rates at donor–acceptor interfaces is provided.

  16. Rate constants for H abstraction from benzo(a)pyrene and chrysene: a theoretical study.

    Science.gov (United States)

    Semenikhin, A S; Savchenkova, A S; Chechet, I V; Matveev, S G; Liu, Z; Frenklach, M; Mebel, A M

    2017-09-12

    Density functional B3LYP/6-31G(d) and ab initio G3(MP2,CC) calculations have been carried out to determine thermal rate constants of direct H abstraction reactions from four- and five-ring polycyclic aromatic hydrocarbons (PAH) chrysene and benzo[a]pyrene by various radicals abundant in combustion flames, such as H, CH3, C3H3, and OH, using transition state theory. The results show that the H abstraction reactions with OH have the lowest barriers of ∼4 kcal mol(-1), followed by those with H and CH3 with barriers of 16-17 kcal mol(-1), and then with propargyl radicals with barriers of 24-26 kcal mol(-1). Thus, the OH radical is predicted to be the fastest H abstractor from PAH. Even at 2500 K, the rate constant for H abstraction by H is still 34% lower than the rate constant for H abstraction by OH. The reaction with H is calculated to have rate constants 35-19 times higher than those for the reaction with CH3 due to a more favorable entropic factor. The reactions of H abstraction by C3H3 are predicted to be orders of magnitude slower than the other reactions considered and their equilibrium is strongly shifted toward the reactants, making propargyl an inefficient H abstractor from the aromatics. The calculations showed strong similarity of the reaction energetics in different H abstraction positions of benzo[a]pyrene and chrysene within armchair and zigzag edges in these molecules, but clear distinction between the armchair and zigzag sites. The zigzag sites appear to be more reactive, with H abstraction rate constants by H, CH3, and OH being respectively 37-42%, a factor of 2.1, and factors of 8-9 higher than the corresponding rate constants for the H abstraction reactions from armchair sites. Although the barrier heights for the two types of edges are similar, the entropic factor makes zigzag sites more favorable for H abstraction. Rate expressions have been generated for all studied reactions with the goal to rectify current combustion kinetics mechanisms.

  17. Determination of the kinetic rate constant of cyclodextrin supramolecular systems by high performance affinity chromatography.

    Science.gov (United States)

    Li, Haiyan; Ge, Jingwen; Guo, Tao; Yang, Shuo; He, Zhonggui; York, Peter; Sun, Lixin; Xu, Xu; Zhang, Jiwen

    2013-08-30

    It is challenging and extremely difficult to measure the kinetics of supramolecular systems with extensive, weak binding (Kahigh performance affinity chromatography (HPAC) was established to determine the dissociation rate constant of cyclodextrin supramolecular systems. The interactions of β-cyclodextrin with acetaminophen and sertraline were used to exemplify the method. The retention times, variances and the plate heights of the peaks for acetaminophen or sertraline, conventional non-retained substance (H2O) on the β-cyclodextrin bonded column and a control column were determined at four flow rates under linear elution conditions. Then, plate heights for the theoretical non-retained substance were estimated by the modified HPAC method, in consideration of the diffusion and stagnant mobile phase mass transfer. As a result, apparent dissociation rate constants of 1.82 (±0.01)s(-1) and 3.55 (±0.37)s(-1) were estimated for acetaminophen and sertraline respectively at pH 6.8 and 25°C with multiple flow rates. Following subtraction of the non-specific binding with the support, dissociation rate constants were estimated as 1.78 (±0.00) and 1.91 (±0.02)s(-1) for acetaminophen and sertraline, respectively. These results for acetaminophen and sertraline were in good agreement with the magnitude of the rate constants for other drugs determined by capillary electrophoresis reported in the literature and the peak fitting method we performed. The method described in this work is thought to be suitable for other supramolecules, with relatively weak, fast and extensive interactions.

  18. Monte Carlo-based revised values of dose rate constants at discrete photon energies

    Directory of Open Access Journals (Sweden)

    T Palani Selvam

    2014-01-01

    Full Text Available Absorbed dose rate to water at 0.2 cm and 1 cm due to a point isotropic photon source as a function of photon energy is calculated using the EDKnrc user-code of the EGSnrc Monte Carlo system. This code system utilized widely used XCOM photon cross-section dataset for the calculation of absorbed dose to water. Using the above dose rates, dose rate constants are calculated. Air-kerma strength S k needed for deriving dose rate constant is based on the mass-energy absorption coefficient compilations of Hubbell and Seltzer published in the year 1995. A comparison of absorbed dose rates in water at the above distances to the published values reflects the differences in photon cross-section dataset in the low-energy region (difference is up to 2% in dose rate values at 1 cm in the energy range 30-50 keV and up to 4% at 0.2 cm at 30 keV. A maximum difference of about 8% is observed in the dose rate value at 0.2 cm at 1.75 MeV when compared to the published value. S k calculations based on the compilation of Hubbell and Seltzer show a difference of up to 2.5% in the low-energy region (20-50 keV when compared to the published values. The deviations observed in the values of dose rate and S k affect the values of dose rate constants up to 3%.

  19. A model for turbulent dissipation rate in a constant pressure boundary layer

    Indian Academy of Sciences (India)

    J DEY; P PHANI KUMAR

    2016-04-01

    Estimation of the turbulent dissipation rate in a boundary layer is a very involved process.Experimental determination of either the dissipation rate or the Taylor microscale, even in isotropic turbulence,which may occur in a portion of the turbulent boundary layer, is known to be a difficult task. For constant pressure boundary layers, a model for the turbulent dissipation rate is proposed here in terms of the local mean flow quantities. Comparable agreement between the estimated Taylor microscale and Kolmogorov length scale with other data in the logarithmic region suggests usefulness of this model in obtaining these quantitiesexperimentally

  20. Constant-load versus heart rate-targeted exercise - Responses of systolic intervals

    Science.gov (United States)

    Lance, V. Q.; Spodick, D. H.

    1975-01-01

    Various systolic intervals were measured prior to and during heart rate-targeted bicycle ergometer exercise. There were striking similarities within each matched exercise set for Q-Im, isovolumetric contraction time, preejection period (PEP), and PEP/left ventricular ejection time (LVET). LVET was significantly shorter for rate-targeted exercise. It is concluded that either constant-load or rate-targeted bicycle ergometry may be used with the choice of method determined by the purpose of the protocol, and that systolic intervals (except LVET) should not be much altered owing to the method chosen.

  1. Rate constant for the reaction SO + BrO yields SO2 + Br

    Science.gov (United States)

    Brunning, J.; Stief, L.

    1986-01-01

    The rate of the radical-radical reaction SO + BrO yields SO2 + Br has been determined at 298 K in a discharge flow system near 1 torr pressure with detection of SO and BrO via collision-free sampling mass spectrometry. The rate constant was determined using two different methods: measuring the decay of SO radicals in the presence of an excess of BrO and measuring the decay of BrO radicals in excess SO. The results from the two methods are in reasonable agreement and the simple mean of the two values gives the recommended rate constant at 298 K, k = (5.7 + or - 2.0) x 10 to the -11th cu cm/s. This represents the first determination of this rate constant and it is consistent with a previously derived lower limit based on SO2 formation. Comparison is made with other radical-radical reactions involving SO or BrO. The reaction SO + BrO yields SO2 + Br is of interest for models of the upper atmosphere of the earth and provides a potential coupling between atmospheric sulfur and bromine chemistry.

  2. Degradation of bisphenol A by ozonation: rate constants, influence of inorganic anions, and by-products

    Directory of Open Access Journals (Sweden)

    Kheng Soo Tay

    2012-02-01

    Full Text Available The second-order rate constants for the reaction between bisphenol A (BPA and ozonewere evaluated over the pH range of 2-12. The rate constants showed minimum values (×104 M-1s-1under acidic condition (pH 10. From pH 4 to 7, the second-order rate constants were found to increase by a magnitudeof almost 102 and this was due to the increase in anionic BPA species in the solution. The rateconstants increased almost twofold when pH increased from 9.6 to 10.2. The presence of commoninorganic anions at levels commonly found in the environment did not affect the rate of degradationof BPA.The degradation by-products from the ozonation of BPA were identified as 4-(prop-1-en-2-ylphenol, hydroquinone, 4-hydroxyacetophenone, 2-(2-(4-hydroxyphenylpropan-2-ylsuccinaldehyde,2-(1-(4-hydroxyphenylvinylpent-2-enal, 3-formyl-4-(4-hydroxyphenyl-4-methylpent-2-enoic acid, monohydroxy-BPA and dihydroxy-BPA. In conclusion, ozonation was found to be aneffective method for the removal of BPA even in the presence of common inorganic anions atenvironmental concentrations. However, incomplete treatment of BPA might produce a variety ofdegradation by-products.

  3. Ab-Initio Based Computation of Rate Constants for Spin Forbidden Metalloprotein-Substrate Reactions

    Science.gov (United States)

    Ozkanlar, Abdullah; Rodriguez, Jorge H.

    2007-03-01

    Some chemical and biochemical reactions are non-adiabatic processes whereby the total spin angular momentum, before and after the reaction, is not conserved. These are named spin- forbidden reactions. The application of ab-initio methods, such as spin density functional theory (SDFT), to the prediction of rate constants is a challenging task of fundamental and practical importance. We apply non-adiabatic transition state theory (NA-TST) in conjuntion with SDFT to predict the rate constant of the spin- forbidden recombination of carbon monoxide with iron tetracarbonyl. To model the surface hopping probability between singlet and triplet states, the Landau-Zener formalism is used. The lowest energy point for singlet-triplet crossing, known as minimum energy crossing point (MECP), was located and used to compute, in a semi-quantum approach, reaction rate constants at 300 K. The predicted rates are in very good agreement with experiment. In addition, we present results for the spin- forbidden ligand binding reactions of iron-containing heme proteins such as myoglobin.

  4. Determination of Methane and Carbon Dioxide Formation Rate Constants for Semi-Continuously Fed Anaerobic Digesters

    Directory of Open Access Journals (Sweden)

    Jan Moestedt

    2015-01-01

    Full Text Available To optimize commercial-scale biogas production, it is important to evaluate the performance of each microbial step in the anaerobic process. Hydrolysis and methanogenesis are usually the rate-limiting steps during digestion of organic waste and by-products. By measuring biogas production and methane concentrations on-line in a semi-continuously fed reactor, gas kinetics can be evaluated. In this study, the rate constants of the fermentative hydrolysis step (kc and the methanogenesis step (km were determined and evaluated in a continuously stirred tank laboratory-scale reactor treating food and slaughterhouse waste and glycerin. A process additive containing Fe2+, Co2+ and Ni2+ was supplied until day 89, after which Ni2+ was omitted. The omission resulted in a rapid decline in the methanogenesis rate constant (km to 70% of the level observed when Ni2+ was present, while kc remained unaffected. This suggests that Ni2+ mainly affects the methanogenic rather than the hydrolytic microorganisms in the system. However, no effect was initially observed when using conventional process monitoring parameters such as biogas yield and volatile fatty acid concentration. Hence, formation rate constants can reveal additional information on process performance and km can be used as a complement to conventional process monitoring tools for semi-continuously fed anaerobic digesters.

  5. Properties of human motor units after prolonged activity at a constant firing rate.

    Science.gov (United States)

    Johnson, K V B; Edwards, S C; Van Tongeren, C; Bawa, P

    2004-02-01

    The primary purpose of this study was to examine if there are changes in the intrinsic properties of spinal motoneurons after prolonged submaximal contractions. To do this, we assessed whether or not the synaptic drive to motoneurons needs to increase in order to maintain a constant firing rate of a motor unit. Recruitment of new units and an increase in total electromyographic (EMG) activity of the muscle of interest were taken as estimates of an increase in synaptic drive. Subjects were asked to maintain a constant firing rate of a clearly identifiable (targeted) motor unit from the first dorsal interosseous muscle for approximately 10 min, while surface EMG and force were recorded simultaneously. For the 60 units studied, the duration of the constant-firing-rate period ranged from 73 to 1,140 s (448 +/- 227 s; mean +/- SD). There was a significant increase ( t-test, prate suggesting an increase in the net excitatory input to the motoneuron pool. Changes occurring simultaneously in other parameters, namely, variability in interspike interval, magnitude of force fluctuations, the duration of motor unit action potentials, and the median power frequency of surface EMG were also computed. The firing rates of 16 concurrently firing motoneurons, not controlled by the subject, remained constant. The key finding of this study is that after prolonged activity, a motoneuron requires a stronger excitatory input to maintain its firing rate. Additional results are indicative of significant changes in the characteristics of the synaptic inputs, changes at the neuromuscular junction (both pre- and postsynaptic regions) and the sarcolemma.

  6. Likelihood inference of non-constant diversification rates with incomplete taxon sampling.

    Directory of Open Access Journals (Sweden)

    Sebastian Höhna

    Full Text Available Large-scale phylogenies provide a valuable source to study background diversification rates and investigate if the rates have changed over time. Unfortunately most large-scale, dated phylogenies are sparsely sampled (fewer than 5% of the described species and taxon sampling is not uniform. Instead, taxa are frequently sampled to obtain at least one representative per subgroup (e.g. family and thus to maximize diversity (diversified sampling. So far, such complications have been ignored, potentially biasing the conclusions that have been reached. In this study I derive the likelihood of a birth-death process with non-constant (time-dependent diversification rates and diversified taxon sampling. Using simulations I test if the true parameters and the sampling method can be recovered when the trees are small or medium sized (fewer than 200 taxa. The results show that the diversification rates can be inferred and the estimates are unbiased for large trees but are biased for small trees (fewer than 50 taxa. Furthermore, model selection by means of Akaike's Information Criterion favors the true model if the true rates differ sufficiently from alternative models (e.g. the birth-death model is recovered if the extinction rate is large and compared to a pure-birth model. Finally, I applied six different diversification rate models--ranging from a constant-rate pure birth process to a decreasing speciation rate birth-death process but excluding any rate shift models--on three large-scale empirical phylogenies (ants, mammals and snakes with respectively 149, 164 and 41 sampled species. All three phylogenies were constructed by diversified taxon sampling, as stated by the authors. However only the snake phylogeny supported diversified taxon sampling. Moreover, a parametric bootstrap test revealed that none of the tested models provided a good fit to the observed data. The model assumptions, such as homogeneous rates across species or no rate shifts, appear

  7. Calculated third order rate constants for interpreting the mechanisms of hydrolyses of chloroformates, carboxylic Acid halides, sulfonyl chlorides and phosphorochloridates

    National Research Council Canada - National Science Library

    Bentley, T William

    2015-01-01

    .... Third order rate constants (k3) are calculated for solvolytic reactions in a wide range of compositions of acetone-water mixtures, and are shown to be either approximately constant or correlated with the Grunwald-Winstein Y parameter...

  8. Ab Initio Calculation of Rate Constants for Molecule–Surface Reactions with Chemical Accuracy

    Science.gov (United States)

    Piccini, GiovanniMaria; Alessio, Maristella

    2016-01-01

    Abstract The ab initio prediction of reaction rate constants for systems with hundreds of atoms with an accuracy that is comparable to experiment is a challenge for computational quantum chemistry. We present a divide‐and‐conquer strategy that departs from the potential energy surfaces obtained by standard density functional theory with inclusion of dispersion. The energies of the reactant and transition structures are refined by wavefunction‐type calculations for the reaction site. Thermal effects and entropies are calculated from vibrational partition functions, and the anharmonic frequencies are calculated separately for each vibrational mode. This method is applied to a key reaction of an industrially relevant catalytic process, the methylation of small alkenes over zeolites. The calculated reaction rate constants (free energies), pre‐exponential factors (entropies), and enthalpy barriers show that our computational strategy yields results that agree with experiment within chemical accuracy limits (less than one order of magnitude). PMID:27008460

  9. I. Determination of chemical reaction rate constants by numerical nonlinear analysis: differential methods

    CERN Document Server

    Jesudason, Christopher G

    2011-01-01

    The primary emphasis of this work on kinetics is to illustrate the a posteriori approach to applications, where focus on data leads to novel outcomes, rather than the a priori tendencies of applied analysis which imposes constructs on the nature of the observable. The secondary intention is the development of appropriate methods consonant with experimental definitions. By focusing on gradients, it is possible to determine both the average and instantaneous rate constants that can monitor changes in the rate constant with concentration changes as suggested by this theory. Here, methods are developed and discussed utilizing nonlinear analysis which does not require exact knowledge of initial concentrations. These methods are compared with those derived from standard methodology. These gradient methods are shown to be consistent with the ones from standard methods and could readily serve as alternatives for studies where there are limits or unknowns in the initial conditions, such as in the burgeoning fields of ...

  10. Absolute rate constants for the reaction of hypochlorous acid with protein side chains and peptide bonds

    DEFF Research Database (Denmark)

    Pattison, D I; Davies, Michael Jonathan

    2001-01-01

    , absolute second-order rate constants for the reactions of HOCl with protein side chains, model compounds, and backbone amide (peptide) bonds have been determined at physiological pH values. The reactivity of HOCl with potential reactive sites in proteins is summarized by the series: Met (3.8 x 10(7) M(-1......) x s(-1)) > backbone amides (10-10(-3) M(-1) x s(-1)) > Gln(0.03 M(-1) x s(-1)) approximately Asn (0.03 M(-1) x s(-1)). The rate constants for reaction of HOCl with backbone amides (peptide bonds) vary by 4 orders of magnitude with uncharged peptide bonds reacting more readily with HOCl than those...

  11. The rate constant for the CO + H2O2 reaction

    DEFF Research Database (Denmark)

    Glarborg, Peter; Marshall, Paul

    2009-01-01

    The rate constant for the reaction CO + H2O2 -> HOCO + OH (R1) at 713 K is determined based on the batch reactor experiments of Baldwin et al. [ R. R. Baldwin, R. W. Walker, S. J. Webster, Combust. Flame 15 (1970) 167] on decomposition of H2O2 sensitized by CO. The value, k(1) (713 K) = 8.1 x 10...... in combustion. The present analysis reconciles the batch reactor data of Baldwin et al. with recent high-level theoretical work on the CO + HO2 reaction.......(2) cm(3) mol(-1) s(-1), is consistent with spin-unrestricted density functional theory. Extrapolation to a wider temperature range through ab initio calculations yields the rate constant k(1) = 3.6 x 10(4)T(2.5) exp(-14425[K]/T) cm(3) mol(-1) s(-1). The reaction is probably of minor importance...

  12. Reaction rate constants of H-abstraction by OH from large ketones: Measurements and site-specific rate rules

    KAUST Repository

    Badra, Jihad

    2014-01-01

    Reaction rate constants of the reaction of four large ketones with hydroxyl (OH) are investigated behind reflected shock waves using OH laser absorption. The studied ketones are isomers of hexanone and include 2-hexanone, 3-hexanone, 3-methyl-2-pentanone, and 4-methl-2-pentanone. Rate constants are measured under pseudo-first-order kinetics at temperatures ranging from 866 K to 1375 K and pressures near 1.5 atm. The reported high-temperature rate constant measurements are the first direct measurements for these ketones under combustion-relevant conditions. The effects of the position of the carbonyl group (CO) and methyl (CH3) branching on the overall rate constant with OH are examined. Using previously published data, rate constant expressions covering, low-to-high temperatures, are developed for acetone, 2-butanone, 3-pentanone, and the hexanone isomers studied here. These Arrhenius expressions are used to devise rate rules for H-abstraction from various sites. Specifically, the current scheme is applied with good success to H-abstraction by OH from a series of n-ketones. Finally, general expressions for primary and secondary site-specific H-abstraction by OH from ketones are proposed as follows (the subscript numbers indicate the number of carbon atoms bonded to the next-nearest-neighbor carbon atom, the subscript CO indicates that the abstraction is from a site next to the carbonyl group (CO), and the prime is used to differentiate different neighboring environments of a methylene group):P1,CO = 7.38 × 10-14 exp(-274 K/T) + 9.17 × 10-12 exp(-2499 K/T) (285-1355 K)S10,CO = 1.20 × 10-11 exp(-2046 K/T) + 2.20 × 10-13 exp(160 K/T) (222-1464 K)S11,CO = 4.50 × 10-11 exp(-3000 K/T) + 8.50 × 10-15 exp(1440 K/T) (248-1302 K)S11′,CO = 3.80 × 10-11 exp(-2500 K/T) + 8.50 × 10-15 exp(1550 K/T) (263-1370 K)S 21,CO = 5.00 × 10-11 exp(-2500 K/T) + 4.00 × 10-13 exp(775 K/T) (297-1376 K) © 2014 the Partner Organisations.

  13. Biotransformation of trace organic chemicals during groundwater recharge: How useful are first-order rate constants?

    KAUST Repository

    Regnery, J.

    2015-05-29

    This study developed relationships between the attenuation of emerging trace organic chemicals (TOrC) during managed aquifer recharge (MAR) as a function of retention time, system characteristics, and operating conditions using controlled laboratory-scale soil column experiments simulating MAR. The results revealed that MAR performance in terms of TOrC attenuation is primarily determined by key environmental parameters (i.e. redox, primary substrate). Soil columns with suboxic and anoxic conditions performed poorly (i.e. less than 30% attenuation of moderately degradable TOrC) in comparison to oxic conditions (on average between 70-100% attenuation for the same compounds) within a residence time of three days. Given this dependency on redox conditions, it was investigated if key parameter-dependent rate constants are more suitable for contaminant transport modeling to properly capture the dynamic TOrC attenuation under field-scale conditions. Laboratory-derived first-order removal kinetics were determined for 19 TOrC under three different redox conditions and rate constants were applied to MAR field data. Our findings suggest that simplified first-order rate constants will most likely not provide any meaningful results if the target compounds exhibit redox dependent biotransformation behavior or if the intention is to exactly capture the decline in concentration over time and distance at field-scale MAR. However, if the intention is to calculate the percent removal after an extended time period and subsurface travel distance, simplified first-order rate constants seem to be sufficient to provide a first estimate on TOrC attenuation during MAR.

  14. Study on improving the turbidity measurement of the absolute coagulation rate constant.

    Science.gov (United States)

    Sun, Zhiwei; Liu, Jie; Xu, Shenghua

    2006-05-23

    The existing theories dealing with the evaluation of the absolute coagulation rate constant by turbidity measurement were experimentally tested for different particle-sized (radius = a) suspensions at incident wavelengths (lambda) ranging from near-infrared to ultraviolet light. When the size parameter alpha = 2pi a/lambda > 3, the rate constant data from previous theories for fixed-sized particles show significant inconsistencies at different light wavelengths. We attribute this problem to the imperfection of these theories in describing the light scattering from doublets through their evaluation of the extinction cross section. The evaluations of the rate constants by all previous theories become untenable as the size parameter increases and therefore hampers the applicable range of the turbidity measurement. By using the T-matrix method, we present a robust solution for evaluating the extinction cross section of doublets formed in the aggregation. Our experiments show that this new approach is effective in extending the applicability range of the turbidity methodology and increasing measurement accuracy.

  15. Shock Tube Measurement for the Dissociation Rate Constant of Acetaldehyde Using Sensitive CO Diagnostics.

    Science.gov (United States)

    Wang, Shengkai; Davidson, David F; Hanson, Ronald K

    2016-09-08

    The rate constant of acetaldehyde thermal dissociation, CH3CHO = CH3 + HCO, was measured behind reflected shock waves at temperatures of 1273-1618 K and pressures near 1.6 and 0.34 atm. The current measurement utilized sensitive CO diagnostics to track the dissociation of CH3CHO via oxygen atom balance and inferred the title rate constant (k1) from CO time histories obtained in pyrolysis experiments of 1000 and 50 ppm of CH3CHO/Ar mixtures. By using dilute test mixtures, the current study successfully suppressed the interferences from secondary reactions and directly determined the title rate constant as k1(1.6 atm) = 1.1 × 10(14) exp(-36 700 K/T) s(-1) over 1273-1618 K and k1(0.34 atm) = 5.5 × 10(12) exp(-32 900 K/T) s(-1) over 1377-1571 K, with 2σ uncertainties of approximately ±30% for both expressions. Example simulations of existing reaction mechanisms updated with the current values of k1 demonstrated substantial improvements with regards to the acetaldehyde pyrolysis chemistry.

  16. Shock Tube Measurement of the High-Temperature Rate Constant for OH + CH3 → Products.

    Science.gov (United States)

    Wang, Shengkai; Li, Sijie; Davidson, David F; Hanson, Ronald K

    2015-08-20

    The reaction between hydroxyl (OH) and methyl radicals (CH3) is critical to hydrocarbon oxidation. Motivated by the sparseness of its high-temperature rate constant data and the large uncertainties in the existing literature values, the current study has remeasured the overall rate constant of the OH + CH3 reaction and extended the measurement temperature range to 1214-1933 K, using simultaneous laser absorption diagnostics for OH and CH3 radicals behind incident and reflected shock waves. tert-Butyl hydroperoxide and azomethane were used as pyrolytic sources for the OH and CH3 radicals, respectively. The current study bridged the temperature ranges of existing experimental data, and good agreement is seen between the current measurement and some previous experimental and theoretical high-temperature studies. A recommendation for the rate constant expression of the title reaction, based on the weighted average of the high-temperature data from selected studies, is given by k1 = 4.19 × 10(1)(T/K)(3.15) exp(5270 K/T) cm(3) mol(-1) s(-1) ±30%, which is valid over 1000-2500 K.

  17. Mechanism of tension generation in muscle: an analysis of the forward and reverse rate constants.

    Science.gov (United States)

    Davis, Julien S; Epstein, Neal D

    2007-04-15

    Tension generation in muscle occurs during the attached phase of the ATP-powered cyclic interaction of myosin heads with thin filaments. The transient nature of tension-generating intermediates and the complexity of the mechanochemical cross-bridge cycle have impeded a quantitative description of tension generation. Recent experiments performed under special conditions yielded a sigmoidal dependence of fiber tension on temperature--a unique case that simplifies the system to a two-state transition. We have applied this two-state analysis to kinetic data obtained from biexponential laser temperature-jump tension transients. Here we present the forward and reverse rate constants for de novo tension generation derived from analysis of the kinetics of the fast laser temperature-jump phase tau(2) (equivalent of the length-jump phase 2(slow)). The slow phase tau(3) is temperature-independent indicating coupling to rather than a direct role in, de novo tension generation. Increasing temperature accelerates the forward, and slows the reverse, rate constant for the creation of the tension-generating state. Arrhenius behavior of the forward and anti-Arrhenius behavior of the reverse rate constant is a kinetic signature of multistate multipathway protein-folding reactions. We conclude that locally unfolded tertiary and/or secondary structure of the actomyosin cross-bridge mediates the power stroke.

  18. Rate constants for the formation of SiO by radiative association

    Science.gov (United States)

    Cairnie, M.; Forrey, R. C.; Babb, J. F.; Stancil, P. C.; McLaughlin, B. M.

    2017-10-01

    Accurate molecular data for the low-lying states of SiO are computed and used to calculate rate constants for radiative association (RA) of Si and O. Einstein A-coefficients are also calculated for transitions between all of the bound and quasi-bound levels for each molecular state. The radiative widths are used together with elastic tunnelling widths to define effective RA rate constants which include both direct and indirect (inverse pre-dissociation) formation processes. The indirect process is evaluated for two kinetic models which represent limiting cases for astrophysical environments. The first case scenario assumes an equilibrium distribution of quasi-bound states and would be applicable whenever collisional and/or radiative excitation mechanisms are able to maintain the population. The second case scenario assumes that no excitation mechanisms are available which corresponds to the limit of zero radiation temperature and zero atomic density. Rate constants for SiO formation in realistic astrophysical environments would presumably lie between these two limiting cases.

  19. Calculating rate constants with updated Hessians using variational transition state theory with multidimensional tunneling.

    Science.gov (United States)

    Chuang, Yao-Yuan

    2007-08-01

    Variational transition state theory with multidimensional tunneling (VTST/MT) has been used for calculating the rate constants of reactions. The updated Hessians have been used to reduce the computational costs for both geometry optimization and trajectory following procedures. In this paper, updated Hessians are used to reduce the computational costs while calculating the rate constants applying VTST/MT. Although we found that directly applying the updated Hessians will not generate good vibrational frequencies along the minimum energy path (MEP), however, we can either re-compute the full Hessian matrices at fixed intervals or calculate the Block Hessians, which is constructed by numerical one-side difference for the Hessian elements in the "critical" region and Bofill updating scheme for the rest of the Hessian elements. Due to the numerical instability of the Bofill update method near the saddle point region, we have suggested a simple strategy in which we follow the MEP until certain percentage of the classical barrier height from the barrier top with full Hessians computed and then performing rate constant calculation with the extended MEP using Block Hessians. This strategy results a mean unsigned percentage deviation (MUPD) around 10% with full Hessians computed till the point with 80% classical barrier height for four studied reactions. This proposed strategy is attractive not only it can be implemented as an automatic procedure but also speeds up the VTST/MT calculation via embarrassingly parallelization to a personal computer cluster.

  20. Constant diversification rates of endemic gastropods in ancient Lake Ohrid: ecosystem resilience likely buffers environmental fluctuations

    Science.gov (United States)

    Föller, K.; Stelbrink, B.; Hauffe, T.; Albrecht, C.; Wilke, T.

    2015-12-01

    Ancient lakes represent key ecosystems for endemic freshwater species. This high endemic biodiversity has been shown to be mainly the result of intra-lacustrine diversification. Whereas the principle role of this mode of diversification is generally acknowledged, actual diversification rates in ancient lakes remain little understood. At least four types are conceivable. Diversification rates may be constant over time, they may fluctuate, rates may be higher in the initial phase of diversification, or there may be a pronounced lag phase between colonization and subsequent diversification. As understanding the tempo of diversification in ancient lake environments may help reveal the underlying processes that drive speciation and extinction, we here use the Balkan Lake Ohrid as a model system and the largest species flock in the lake, the non-pyrgulinid Hydrobiidae, as a model taxon to study changes in diversification rates over time together with the respective drivers. Based on phylogenetic, molecular-clock, lineage-through-time plot, and diversification-rate analyses we found that this potentially monophyletic group is comparatively old and that it most likely evolved with a constant diversification rate. Preliminary data of the SCOPSCO (Scientific Collaboration On Past Speciation Conditions in Lake Ohrid) deep-drilling program do indicate signatures of severe environmental/climatic perturbations in Lake Ohrid. However, so far there is no evidence for the occurrence of catastrophic environmental events. We therefore propose that the constant diversification rate observed in endemic gastropods has been caused by two factors: (i) a potential lack of catastrophic environmental events in Lake Ohrid and/or (ii) a probably high ecosystem resilience, buffering environmental changes. Parameters potentially contributing to the lake's high ecosystem resilience are its distinct bathymetry, ongoing tectonic activities, and karst hydrology. The current study not only

  1. A constant air flow rate control of blower for residential applications

    Energy Technology Data Exchange (ETDEWEB)

    Yang, S.M. [Tamkang Univ., Taipei (Taiwan, Province of China). Dept. of Mechanical Engineering

    1998-03-01

    This paper presents a technique to control a blower for residential applications at constant air flow rate using an induction motor drive. The control scheme combines a variable volt/hertz ratio inverter drive and an average motor current regulation loop to achieve control of the motor torque-speed characteristics, consequently controlling the air flow rate of the blower which the motor is driving. The controller is simple to implement and practical for commercialization. It is also reliable, since no external pressure or air flow sensor is required. Both a theoretical derivation and an experimental verification for the control scheme are presented in this paper.

  2. Application of the compensated Arrhenius formalism to explain the dielectric constant dependence of rates for Menschutkin reactions.

    Science.gov (United States)

    Petrowsky, Matt; Glatzhofer, Daniel T; Frech, Roger

    2013-11-21

    The dependence of the reaction rate on solvent dielectric constant is examined for the reaction of trihexylamine with 1-bromohexane in a series of 2-ketones over the temperature range 25-80 °C. The rate constant data are analyzed using the compensated Arrhenius formalism (CAF), where the rate constant assumes an Arrhenius-like equation that also contains a dielectric constant dependence in the exponential prefactor. The CAF activation energies are substantially higher than those obtained using the simple Arrhenius equation. A master curve of the data is observed by plotting the prefactors against the solvent dielectric constant. The master curve shows that the reaction rate has a weak dependence on dielectric constant for values approximately less than 10 and increases more rapidly for dielectric constant values greater than 10.

  3. Determination of the alpha-tocopherol inhibition rate constant for peroxidation in low-density lipoprotein.

    Science.gov (United States)

    Culbertson, Sean M; Antunes, Fernando; Havrilla, Christine M; Milne, Ginger L; Porter, Ned A

    2002-06-01

    This work reports an estimate of the inhibition rate constant (k(inh)) for alpha-tocopherol (alpha-TOH) in low-density lipoproteins (LDL) based on cholesteryl linoleate hydroperoxide products formed during autoxidation of intact lipoproteins. The ratio of cis,trans/trans,trans product hydroperoxides was determined during the consumption of the antioxidant. For a reasonable determination of k(inh) in LDL, the pro-oxidant behavior of alpha-TOH was minimized by oxidizing LDL with an unsymmetrical amphiphilic azo initiator which significantly reduces phase-transfer mediated pro-oxidant effects of alpha-TOH. This initiator delivers a more constant flux of initiator radicals into LDL lipid regions and permits determination of alpha-TOH k(inh) in LDL. Development of a tocopherol-mediated peroxidation (TMP) model and analysis of cholesteryl linoleate hydroperoxide cis,trans/trans,trans product ratios provided an estimated value for the inhibition rate constant of alpha-TOH in a lipoprotein of k(inh) = 5.9 +/- 0.5 x 10(5) M(-)(1) s(-)(1)

  4. In situ and laboratory determined first-order degradation rate constants of specific organic compounds in an aerobic aquifer

    DEFF Research Database (Denmark)

    Nielsen, P.H.; Bjerg, P.L.; Nielsen, P.;

    1996-01-01

    experiments. First-order degradation rate constants for aromatic and phenolic hydrocarbons ranged between 0.01 and 0.9 day(-1). Local variations in first-order degradation rates and variations between rate constants determined by ISM and LBM were generally with in a factor of 5, but no systematic differences...

  5. Shock tube measurements of the rate constants for seven large alkanes+OH

    KAUST Repository

    Badra, Jihad

    2015-01-01

    Reaction rate constants for seven large alkanes + hydroxyl (OH) radicals were measured behind reflected shock waves using OH laser absorption. The alkanes, n-hexane, 2-methyl-pentane, 3-methyl-pentane, 2,2-dimethyl-butane, 2,3-dimethyl-butane, 2-methyl-heptane, and 4-methyl-heptane, were selected to investigate the rates of site-specific H-abstraction by OH at secondary and tertiary carbons. Hydroxyl radicals were monitored using narrow-line-width ring-dye laser absorption of the R1(5) transition of the OH spectrum near 306.7 nm. The high sensitivity of the diagnostic enabled the use of low reactant concentrations and pseudo-first-order kinetics. Rate constants were measured at temperatures ranging from 880 K to 1440 K and pressures near 1.5 atm. High-temperature measurements of the rate constants for OH + n-hexane and OH + 2,2-dimethyl-butane are in agreement with earlier studies, and the rate constants of the five other alkanes with OH, we believe, are the first direct measurements at combustion temperatures. Using these measurements and the site-specific H-abstraction measurements of Sivaramakrishnan and Michael (2009) [1,2], general expressions for three secondary and two tertiary abstraction rates were determined as follows (the subscripts indicate the number of carbon atoms bonded to the next-nearest-neighbor carbon): S20=1.58×10-11exp(-1550K/T)cm3molecule-1s-1(887-1327K)S30=2.37×10-11exp(-1850K/T)cm3molecule-1s-1(887-1327K)S21=4.5×10-12exp(-793.7K/T)cm3molecule-1s-1(833-1440K)T100=2.85×10-11exp(-1138.3K/T)cm3molecule-1s-1(878-1375K)T101=7.16×10-12exp(-993K/T)cm3molecule-1s-1(883-1362K) © 2014 The Combustion Institute.

  6. Size dependence of surface thermodynamic properties of nanoparticles and its determination method by reaction rate constant

    Energy Technology Data Exchange (ETDEWEB)

    Li, Wenjiao; Xue, Yongqiang, E-mail: xyqlw@126.com; Cui, Zixiang

    2016-08-15

    Surface thermodynamic properties are the fundamental properties of nanomaterials, and these properties depend on the size of nanoparticles. In this paper, relations of molar surface thermodynamic properties and surface heat capacity at constant pressure of nanoparticles with particle size were derived theoretically, and the method of obtaining the surface thermodynamic properties by reaction rate constant was put forward. The reaction of nano-MgO with sodium bisulfate solution was taken as a research system. The influence regularities of the particle size on the surface thermodynamic properties were discussed theoretically and experimentally, which show that the experimental regularities are in accordance with the corresponding theoretical relations. With the decreasing of nanoparticle size, the molar surface thermodynamic properties increase, while the surface heat capacity decreases (the absolute value increases). In addition, the surface thermodynamic properties are linearly related to the reciprocal of nanoparticle diameter, respectively.

  7. Acclimation to constant and variable temperatures in plethodontid salamanders--I. Rates of oxygen consumption.

    Science.gov (United States)

    Feder, M E

    1985-01-01

    In preliminary experiments, salamanders of three species (Desmognathus ochrophaeus, Plethodon cinereus and Plethodon jordani) required 5-11 days to complete metabolic acclimation to a constant warm temperature; the rate of oxygen consumption (VO2) decreased 16-28% during acclimation. Unfed animals of each species underwent cyclic exposure to 5 and 21 degrees C at three different cycle periods (12 hr, 4-5 days, 51 days), or constant exposure to 14 degrees C for 102 days. The experimental treatments significantly affected the VO2 measured at 5, 14, 17.5 and 21 degrees C. The direction and magnitude of the acclimatory effects upon VO2 were inconsistent among species and among experimental temperatures, and resulted in little energy saving. The VO2 during exposure to cyclic temperatures averaged only 83% of that during preliminary experiments, perhaps as a response to starvation.

  8. Laser Measurements of the H Atom + Ozone Rate Constant at Atmospheric Temperatures

    Science.gov (United States)

    Liu, Y.; Smith, G. P.; Peng, J.; Reppert, K. J.; Callahan, S. L.

    2015-12-01

    The exothermic H + O3 reaction produces OH(v) Meinel band emissions, used to derive mesospheric H concentrations and chemical heating rates. We have remeasured its rate constant to reduce resulting uncertainties and the measurement extend to lower mesospheric temperatures using modern laser techniques. H atoms are produced by pulsed ultraviolet laser trace photolysis of O3, followed by reaction of O(D) with added H2. A second, delayed, frequency-mixed dye laser measures the reaction decay rate with the remaining ozone by laser induced fluorescence. We monitor either the H atom decay by 2 photon excitation at 205 nm and detection of red fluorescence, or the OH(v=9) product time evolution with excitation of the B-X (0,9) band at 237 nm and emission in blue B-A bands. By cooling the enclosed low pressure flow cell we obtained measurements from 146-305 K. Small kinetic modeling corrections are made for secondary regeneration of H atoms. The results fully confirm the current NASA JPL recommendation for this rate constant, and establish its extrapolation down to the lower temperatures of the mesosphere. This work was supported by the NSF Aeronomy Program and an NSF Physics summer REU student grant.

  9. A Method for Achieving Constant Rotation Rates in a Micro-Orthogonal Linkage System

    Energy Technology Data Exchange (ETDEWEB)

    Dickey, F.M.; Holswade, S.C.; Romero, L.A.

    1999-05-12

    Silicon micromachine designs include engines that consist of orthog- onally oriented linear comb drive actuators mechanically connected to a rotating gear. These gears are as small as 50 {micro}m in diameter and can be driven at rotation rates exceeding 300,000 rpm. Generally, these en- gines will run with non-uniform rotation rates if the drive signals are not properly designed and maintained over a range of system parameters. We present a method for producing constant rotation rates in a micro-engine driven by an orthogonal linkage system. We show that provided the val- ues of certain masses, springs, damping factors, and lever arms are in the right proportions, the system behaves as though it were symmetrical. We will refer to systems built in this way as being quasi-symmetrical. We show that if a system is built quasi-symmetrically , then it is possible to achieve constant rotation rates even if one does not know the form of the friction function, or the value of the friction. We analyze this case in some detail.

  10. Measured dose rate constant from oncology patients administered 18F for positron emission tomography

    Energy Technology Data Exchange (ETDEWEB)

    Quinn, Brian; Holahan, Brian; Aime, Jean; Humm, John; St Germain, Jean; Dauer, Lawrence T. [Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065 (United States); Department of Radiology, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065 (United States); Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065 (United States) and Department of Radiology, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065 (United States); Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065 (United States); Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065 (United States) and Department of Radiology, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065 (United States)

    2012-10-15

    Purpose: Patient exposure rate measurements verify published patient dose rate data and characterize dose rates near 2-18-fluorodeoxyglucose ({sup 18}F-FDG) patients. A specific dose rate constant based on patient exposure rate measurements is a convenient quantity that can be applied to the desired distance, injection activity, and time postinjection to obtain an accurate calculation of cumulative external radiation dose. This study reports exposure rates measured at various locations near positron emission tomography (PET) {sup 18}F-FDG patients prior to PET scanning. These measurements are normalized for the amount of administered activity, measurement distance, and time postinjection and are compared with other published data. Methods: Exposure rates were measured using a calibrated ionization chamber at various body locations from 152 adult oncology patients postvoid after a mean uptake time of 76 min following injection with a mean activity of 490 MBq {sup 18}F-FDG. Data were obtained at nine measurement locations for each patient: three near the head, four near the chest, and two near the feet. Results: On contact with, 30 cm superior to and 30 cm lateral to the head, the mean (75th percentile) dose rates per unit injected activity at 60 min postinjection were 0.482 (0.511), 0.135 (0.155), and 0.193 (0.223) {mu}Sv/MBq h, respectively. On contact with, 30 cm anterior to, 30 cm lateral to and 1 m anterior to the chest, the mean (75th percentile) dose rates per unit injected activity at 60 min postinjection were 0.623 (0.709), 0.254 (0.283), 0.190 (0.218), and 0.067 (0.081) {mu}Sv/MBq h respectively. 30 cm inferior and 30 cm lateral to the feet, the mean (75th percentile) dose rates per unit injected activity at 60 min postinjection were 0.024 (0.022) and 0.039 (0.044) {mu}Sv/MBq h, respectively. Conclusions: The measurements for this study support the use of 0.092 {mu}Sv m{sup 2}/MBq h as a reasonable representation of the dose rate anterior from the chest of

  11. Non-radiative excitation fluorescence microscopy

    Science.gov (United States)

    Riachy, Lina; Vézy, Cyrille; Jaffiol, Rodolphe

    2016-03-01

    Non-radiative Excitation Fluorescence Microscopy (NEFM) constitutes a new way to observe biological samples beyond the diffraction limit. Non-radiative excitation of the samples is achieved by coating the substrate with donor species, such as quantum dots (QDs). Thus the dyes are not excited directly by the laser source, as in common fluorescence microscopy, but through a non-radiative energy transfer. To prevent dewetting of the donor film, we have recently implemented a silanization process to covalently bond the QDs on the substrate. An homogeneous monolayer of QDs was then deposited on only one side of the coverslips. Atomic force microscopy was then used to characterize the QD layer. We highlight the potential of our method through the study of Giant Unilamellar Vesicles (GUVs) labeled with DiD as acceptor, in interaction with surface functionalized with poly-L-lysine. In the presence of GUVs, we observed a quenching of QDs emission, together with an emission of DiD located in the membrane, which clearly indicated that non-radiative energy transfer from QDs to DiD occurs.

  12. Constant diversification rates of endemic gastropods in ancient Lake Ohrid: ecosystem resilience likely buffers environmental fluctuations

    Directory of Open Access Journals (Sweden)

    K. Föller

    2015-08-01

    Full Text Available Ancient lakes represent key ecosystems for endemic freshwater species. This high endemic biodiversity has been shown to be mainly the result of intra-lacustrine diversification. Whereas the principle role of this mode of diversification is generally acknowledged, actual diversification rates in ancient lakes remain little understood. At least four modes are conceivable. Diversification rates may be constant over time, they may fluctuate, rates may be higher in the initial phase of diversification, or there may be a pronounced lag phase between colonization and subsequent diversification. As understanding the tempo of diversification in ancient lake environments may help unrevealing the underlying processes that drive speciation and extinction, we here use the Balkan Lake Ohrid as a model system and the largest species flock in the lake, the non-pyrgulinid Hydrobiidae, as a model taxon to study changes in diversification rates over time together with the respective drivers. Based on phylogenetic, molecular-clock, lineage-through-time plot and diversification-rate analyses we found that this monophyletic group is comparatively old and that it most likely evolved with a constant diversification rate. Preliminary data of the SCOPSCO deep-drilling program do indicate signatures of severe environmental/climatic perturbations in Lake Ohrid. However, so far there is no evidence for the occurrence of catastrophic environmental events. We therefore propose that the rate homogeneity observed in endemic gastropods has been caused by two factors: (i a potential lack of catastrophic environmental events in Lake Ohrid and/or (ii a high ecosystem resilience, buffering environmental changes. Parameters potentially contributing to the lake's high ecosystem resilience are its distinct bathymetry, ongoing tectonic activities, and karst hydrology. The current study not only contributes to one of the overall goals of the SCOPSCO deep-drilling program – inferring

  13. Calorimetric determination of rate constants and enthalpy changes for zero-order reactions.

    Science.gov (United States)

    Almeida e Sousa, Luis; Beezer, Anthony E; Hansen, Lee D; Clapham, David; Connor, Joseph A; Gaisford, Simon

    2012-06-07

    Calorimetry is a general method for determination of the rates of zero-order processes, but analysis of the data for the rate constant and reaction enthalpy is difficult because these occur as a product in the rate equation so evaluation of one requires knowledge of the other. Three methods for evaluation of both parameters, without prior knowledge, are illustrated with examples and compared with literature data. Method 1 requires the reaction to be studied in two buffers with different enthalpies of ionization. Method 2 is based on calculation of reaction enthalpy from group additivity functions. Method 3 applies when reaction progresses to completion. The methods are applied to the enzymatic hydrolysis of urea, the hydrolysis of acetylsalicylic acid, and the photodegradation of nifedipine, respectively.

  14. Evaluation and comparison of diffusion MR methods for measuring apparent transcytolemmal water exchange rate constant

    Science.gov (United States)

    Tian, Xin; Li, Hua; Jiang, Xiaoyu; Xie, Jingping; Gore, John C.; Xu, Junzhong

    2017-02-01

    Two diffusion-based approaches, CG (constant gradient) and FEXI (filtered exchange imaging) methods, have been previously proposed for measuring transcytolemmal water exchange rate constant kin, but their accuracy and feasibility have not been comprehensively evaluated and compared. In this work, both computer simulations and cell experiments in vitro were performed to evaluate these two methods. Simulations were done with different cell diameters (5, 10, 20 μm), a broad range of kin values (0.02-30 s-1) and different SNR's, and simulated kin's were directly compared with the ground truth values. Human leukemia K562 cells were cultured and treated with saponin to selectively change cell transmembrane permeability. The agreement between measured kin's of both methods was also evaluated. The results suggest that, without noise, the CG method provides reasonably accurate estimation of kin especially when it is smaller than 10 s-1, which is in the typical physiological range of many biological tissues. However, although the FEXI method overestimates kin even with corrections for the effects of extracellular water fraction, it provides reasonable estimates with practical SNR's and more importantly, the fitted apparent exchange rate AXR showed approximately linear dependence on the ground truth kin. In conclusion, either CG or FEXI method provides a sensitive means to characterize the variations in transcytolemmal water exchange rate constant kin, although the accuracy and specificity is usually compromised. The non-imaging CG method provides more accurate estimation of kin, but limited to large volume-of-interest. Although the accuracy of FEXI is compromised with extracellular volume fraction, it is capable of spatially mapping kin in practice.

  15. Shock tube measurements of the rate constant for the reaction ethanol + OH.

    Science.gov (United States)

    Stranic, Ivo; Pang, Genny A; Hanson, Ronald K; Golden, David M; Bowman, Craig T

    2014-02-06

    The overall rate constant for the reaction ethanol + OH → products was determined experimentally from 900 to 1270 K behind reflected shock waves. Ethan(18)ol was utilized for these measurements in order to avoid the recycling of OH radicals following H-atom abstraction at the β-site of ethanol. Similar experiments were also performed with unlabeled ethan(16)ol in order to infer the rate constant that excludes reactivity at the β-site. The two data sets were used to directly infer the branching ratio for the reaction at the β-site. Experimental data in the current study and in previous low-temperature studies for the overall rate constant are best fit by the expression koverall = 5.07 × 10(5) T[K](2.31) exp(608/T[K]) cm(3) mol(-1) s(-1), valid from 300 to 1300 K. Measurements indicate that the branching ratio of the β-site is between 20 and 25% at the conditions studied. Pseudo-first-order reaction conditions were generated using tert-butylhydroperoxide (TBHP) as a fast source of (16)OH with ethanol in excess. (16)OH mole fraction time-histories were measured using narrow-line width laser absorption near 307 nm. Measurements were performed at the linecenter of the R22(5.5) transition in the A-X(0,0) band of (16)OH that does not overlap with any absorption features of (18)OH, thus producing a measurement of the (16)OH mole fraction that is insensitive to the presence of (18)OH.

  16. The constant work rate critical power protocol overestimates ramp incremental exercise performance.

    Science.gov (United States)

    Black, Matthew I; Jones, Andrew M; Kelly, James A; Bailey, Stephen J; Vanhatalo, Anni

    2016-12-01

    The parameters of the power-duration relationship (i.e., the critical power, CP, and the curvature constant, W') may theoretically predict maximal performance capability for exercise above the CP. The CP and W' are associated with the parameters of oxygen uptake ([Formula: see text]O2) kinetics, which can be altered by manipulation of the work-rate forcing function. We tested the hypothesis that the CP and W' derived from constant work-rate (CWR) prediction trials would overestimate ramp incremental exercise performance. Thirty subjects (males, n = 28; females, n = 2) performed a ramp incremental test, and 3-5 CWR prediction trials for the determination of the CP and W'. Multiple ramp incremental tests and corresponding CP and W' estimates were available for some subjects such that in total 51 ramp test performances were predicted. The ramp incremental test performance (729 ± 113 s) was overestimated by the CP and W' estimates derived from the best (751 ± 114 s, P incremental performance suggests that the CP and W' derived from different work-rate forcing functions, thus resulting in different [Formula: see text]O2 kinetics, cannot be used interchangeably. The present findings highlight a potential source of error in performance prediction that is of importance to both researchers and applied practitioners.

  17. Subcritical crack growth in oxide and non-oxide ceramics using the Constant Stress Rate Test

    Directory of Open Access Journals (Sweden)

    Agnieszka Wojteczko

    2015-12-01

    Full Text Available Fracture toughness is one of the most important parameters for ceramics description. In some cases, material failure occurs at lower stresses than described by KIc parameter. In these terms, determination of fracture toughness only, proves to be insufficient. This may be due to environmental factors, such as humidity, which might cause subcritical crack propagation in a material. Therefore, it is very important to estimate crack growth velocities to predict lifetime of ceramics used under specific conditions. Constant Stress Rate Test is an indirect method of subcritical crack growth parameters estimation. Calculations are made by using strength data, thus avoiding crack measurement. The expansion of flaws causes reduction of material strength. If subcritical crack growth phenomenon occurs, critical value of crack lengths increases with decreasing stress rate due to longer time for flaw to grow before the critical crack propagation at KIc takes place. Subcritical crack growth phenomenon is particularly dangerous for oxide ceramics due to chemical interactions occurring as a result of exposure to humidity. This paper presents results of Constant Stress Rate Test performed for alumina, zirconia, silicon carbide and silicon nitride in order to demonstrate the differences in subcritical crack propagation phenomenon course.

  18. Perturbation theory in the catalytic rate constant of the Henri-Michaelis-Menten enzymatic reaction.

    Science.gov (United States)

    Bakalis, Evangelos; Kosmas, Marios; Papamichael, Emmanouel M

    2012-11-01

    The Henry-Michaelis-Menten (HMM) mechanism of enzymatic reaction is studied by means of perturbation theory in the reaction rate constant k (2) of product formation. We present analytical solutions that provide the concentrations of the enzyme (E), the substrate (S), as well as those of the enzyme-substrate complex (C), and the product (P) as functions of time. For k (2) small compared to k (-1), we properly describe the entire enzymatic activity from the beginning of the reaction up to longer times without imposing extra conditions on the initial concentrations E ( o ) and S ( o ), which can be comparable or much different.

  19. Methane combustion kinetic rate constants determination: an ill-posed inverse problem analysis

    Directory of Open Access Journals (Sweden)

    Bárbara D. L. Ferreira

    2013-01-01

    Full Text Available Methane combustion was studied by the Westbrook and Dryer model. This well-established simplified mechanism is very useful in combustion science, for computational effort can be notably reduced. In the inversion procedure to be studied, rate constants are obtained from [CO] concentration data. However, when inherent experimental errors in chemical concentrations are considered, an ill-conditioned inverse problem must be solved for which appropriate mathematical algorithms are needed. A recurrent neural network was chosen due to its numerical stability and robustness. The proposed methodology was compared against Simplex and Levenberg-Marquardt, the most used methods for optimization problems.

  20. Application guide for source PM10 measurement with constant sampling rate

    Energy Technology Data Exchange (ETDEWEB)

    Farthing, W.E.; Dawes, S.S.

    1989-05-01

    The manual presents a method, Constant Sampling Rate (CSR), which allows determination of stationary source PM-10 emissions with hardware similar to that used for Methods 5 or 17. The operating principle of the method is to extract a multipoint sample so that errors due to spatial variation of particle size and anisokinetic sampling are kept within predetermined limits. The manual specifically addresses the use of the CSR methodology for determination of stationary source PM-10 emissions. Material presented in the manual includes calibration of sampling train components, pretest setup calculations, sample recovery, test data reduction, and routine equipment maintenance.

  1. Power consumption analysis of constant bit rate video transmission over 3G networks

    DEFF Research Database (Denmark)

    Ukhanova, Ann; Belyaev, Evgeny; Wang, Le

    2012-01-01

    for the 3GPP transition state machine that allows to decrease power consumption on a mobile device taking signaling traffic, buffer size and latency restrictions into account. Furthermore, we discuss the gain in power consumption vs. PSNR for transmitted video and show the possibility of performing power......This paper presents an analysis of the power consumption of video data transmission with constant bit rate over 3G mobile wireless networks. The work includes the description of the radio resource control transition state machine in 3G networks, followed by a detailed power consumption analysis...... consumption management based on the requirements for the video quality....

  2. Electron attachment rate constant measurement by photoemission electron attachment ion mobility spectrometry (PE-EA-IMS)

    Science.gov (United States)

    Su, Desheng; Niu, Wenqi; Liu, Sheng; Shen, Chengyin; Huang, Chaoqun; Wang, Hongmei; Jiang, Haihe; Chu, Yannan

    2012-12-01

    Photoemission electron attachment ion mobility spectrometry (PE-EA-IMS), with a source of photoelectrons induced by vacuum ultraviolet radiation on a metal surface, has been developed to study electron attachment reaction at atmospheric pressure using nitrogen as the buffer gas. Based on the negative ion mobility spectra, the rate constants for electron attachment to tetrachloromethane and chloroform were measured at ambient temperature as a function of the average electron energy in the range from 0.29 to 0.96 eV. The experimental results are in good agreement with the data reported in the literature.

  3. Rate constants for chemical reactions in high-temperature nonequilibrium air

    Science.gov (United States)

    Jaffe, R. L.

    1986-01-01

    In the nonequilibrium atmospheric chemistry regime that will be encountered by the proposed Aeroassisted Orbital Transfer Vehicle in the upper atmosphere, where air density is too low for thermal and chemical equilibrium to be maintained, the detailed high temperature air chemistry plays a critical role in defining radiative and convective heating loads. Although vibrational and electronic temperatures remain low (less than 15,000 K), rotational and translational temperatures may reach 50,000 K. Attention is presently given to the effects of multiple temperatures on the magnitudes of various chemical reaction rate constants, for the cases of both bimolecular exchange reactions and collisional excitation and dissociation reactions.

  4. Feature analysis of the scale factor variation on a constant rate biased ring laser gyro

    Institute of Scientific and Technical Information of China (English)

    Shiqiao Qin; Zongsheng Huang; Xingshu Wang

    2007-01-01

    Scale factor of a constant rate biased ring laser gyro (RLG) is studied both theoretically and experimentally.By analyzing experimental data, we find that there are three main terms contributing to the scale factor deviation. One of them is independent of time, the second varies linearly with time and the third varies exponentially with time. Theoretical analyses show that the first term is caused by experimental setup,the second and the third are caused by un-uniform thermal expension and cavity loss variation of the RLG.

  5. Rapid estimation of glucosinolate thermal degradation rate constants in leaves of Chinese kale and broccoli (Brassica oleracea) in two seasons.

    Science.gov (United States)

    Hennig, Kristin; Verkerk, Ruud; Bonnema, Guusje; Dekker, Matthijs

    2012-08-15

    Kinetic modeling was used as a tool to quantitatively estimate glucosinolate thermal degradation rate constants. Literature shows that thermal degradation rates differ in different vegetables. Well-characterized plant material, leaves of broccoli and Chinese kale plants grown in two seasons, was used in the study. It was shown that a first-order reaction is appropriate to model glucosinolate degradation independent from the season. No difference in degradation rate constants of structurally identical glucosinolates was found between broccoli and Chinese kale leaves when grown in the same season. However, glucosinolate degradation rate constants were highly affected by the season (20-80% increase in spring compared to autumn). These results suggest that differences in glucosinolate degradation rate constants can be due to variation in environmental as well as genetic factors. Furthermore, a methodology to estimate rate constants rapidly is provided to enable the analysis of high sample numbers for future studies.

  6. Comments to "Analysis of constant rate period of spray drying of slurry" by Liang et al., 2001

    DEFF Research Database (Denmark)

    Jørgensen, Kåre; Jensen, Anker Degn; Sloth, Jakob;

    2006-01-01

    In the study by Liang et al. [2001. Analysis of constant rate period of spray drying of slurry. Chemical Engineering Science 56, 2205-2213] the Darcy flow of liquid through a pore system of primary particles to the surface of a slurry droplet was applied for the constant rate period. Steep primary...

  7. Comments to ”Analysis of constant rate period of spray drying of slurry” by Liang et al

    DEFF Research Database (Denmark)

    Jørgensen, Kåre; Jensen, Anker; Sloth, Jakob;

    2006-01-01

    In the study by Liang et al. [2001. Analysis of constant rate period of spray drying of slurry. Chemical Engineering Science 56, 2205-2213] the Darcy flow of liquid through a pore system of primary particles to the surface of a slurry droplet was applied for the constant rate period. Steep primary...

  8. Computational study of the rate constants and free energies of intramolecular radical addition to substituted anilines

    Directory of Open Access Journals (Sweden)

    Andreas Gansäuer

    2013-08-01

    Full Text Available The intramolecular radical addition to aniline derivatives was investigated by DFT calculations. The computational methods were benchmarked by comparing the calculated values of the rate constant for the 5-exo cyclization of the hexenyl radical with the experimental values. The dispersion-corrected PW6B95-D3 functional provided very good results with deviations for the free activation barrier compared to the experimental values of only about 0.5 kcal mol−1 and was therefore employed in further calculations. Corrections for intramolecular London dispersion and solvation effects in the quantum chemical treatment are essential to obtain consistent and accurate theoretical data. For the investigated radical addition reaction it turned out that the polarity of the molecules is important and that a combination of electrophilic radicals with preferably nucleophilic arenes results in the highest rate constants. This is opposite to the Minisci reaction where the radical acts as nucleophile and the arene as electrophile. The substitution at the N-atom of the aniline is crucial. Methyl substitution leads to slower addition than phenyl substitution. Carbamates as substituents are suitable only when the radical center is not too electrophilic. No correlations between free reaction barriers and energies (ΔG‡ and ΔGR are found. Addition reactions leading to indanes or dihydrobenzofurans are too slow to be useful synthetically.

  9. A generalized Forchheimer radial flow model for constant-rate tests

    Science.gov (United States)

    Liu, Ming-Ming; Chen, Yi-Feng; Zhan, Hongbin; Hu, Ran; Zhou, Chuang-Bing

    2017-09-01

    Models used for data interpretation of constant-rate tests (CRTs) are commonly derived with the assumption of Darcian flow in an idealized integer flow dimension, where the non-Darcian nature of fluid flow and the complexity of flow geometry are disregarded. In this study, a Forchheimer's law-based analytical model is proposed with the assumption of buildup (or drawdown) decomposition for characterizing the non-Darcian flow in a generalized radial formation where the flow dimension n may become non-integer. The proposed model immediately reduces to Barker's (1988) model for Darcian flow in the generalized radial formation and to Mathias et al.'s (2008) model for non-Darcian flow in a two-dimensional confined aquifer. A comparison with numerical simulations shows that the proposed model behaves well at late times for flow dimension n > 1.5. The proposed model is finally applied for data interpretation of the constant-rate pumping tests performed at Ploemeur (Le Borgne et al., 2004), showing that the intrinsic hydraulic conductivity of formations will be underestimated and the specific storage will be overestimated if the non-Darcian effect is ignored. The proposed model is an extension of the generalized radial flow (GRF) model based on Forchheimer's law, which would be of significance for data interpretation of CRTs in aquifers of complex flow geometry in which non-Darcian flow occurs.

  10. Computational study of the rate constants and free energies of intramolecular radical addition to substituted anilines

    Science.gov (United States)

    Seddiqzai, Meriam; Dahmen, Tobias; Sure, Rebecca

    2013-01-01

    Summary The intramolecular radical addition to aniline derivatives was investigated by DFT calculations. The computational methods were benchmarked by comparing the calculated values of the rate constant for the 5-exo cyclization of the hexenyl radical with the experimental values. The dispersion-corrected PW6B95-D3 functional provided very good results with deviations for the free activation barrier compared to the experimental values of only about 0.5 kcal mol−1 and was therefore employed in further calculations. Corrections for intramolecular London dispersion and solvation effects in the quantum chemical treatment are essential to obtain consistent and accurate theoretical data. For the investigated radical addition reaction it turned out that the polarity of the molecules is important and that a combination of electrophilic radicals with preferably nucleophilic arenes results in the highest rate constants. This is opposite to the Minisci reaction where the radical acts as nucleophile and the arene as electrophile. The substitution at the N-atom of the aniline is crucial. Methyl substitution leads to slower addition than phenyl substitution. Carbamates as substituents are suitable only when the radical center is not too electrophilic. No correlations between free reaction barriers and energies (ΔG ‡ and ΔG R) are found. Addition reactions leading to indanes or dihydrobenzofurans are too slow to be useful synthetically. PMID:24062821

  11. Constant rate solutions for a fractured well with an asymmetric fracture

    Energy Technology Data Exchange (ETDEWEB)

    Berumen, S.; Rodriguez, F. [PEMEX E and P and UNAM, Ciudad Universitaria, Postal 70-256, 04510 Coyoacan (Mexico); Tiab, D. [School of Petroleum and Geological Engineering, The University of Oklahoma, 100 East Boyd Street, T301 SEC Norman, OK (United States)

    2000-01-01

    This paper presents solutions for the pressure response on hydraulically fractured wells flowing at constant flow rate through an asymmetric vertical fracture. The pressure behavior of wells intercepting asymmetric fractures of both infinite and finite conductivity was investigated by solving numerically and analytically the mathematical model. The new solutions developed for the dimensionless wellbore pressure under production at constant flow rate are presented in terms of an asymmetry factor {xi}. New curves for these systems were generated and the deviation from the classical solution was readily detected. Some qualitative criteria to interpret the intensity of this effect are provided. Results of our investigation indicated that at early times for fractures of moderate conductivity (C{sub D}<5) the characteristic slope of one fourth is present, except for cases of strong asymmetry (0.85<{xi}{<=}1) where no evidence of straight line having one fourth slope was observed. However, it was also detected that at intermediate fracture conductivities (5

  12. Quantum-instanton evaluation of the isotopic effects on the rate constants

    Science.gov (United States)

    Vanicek, Jiri; Miller, William H.

    2004-03-01

    We present a general quantum-mechanical method suitable for numerical evaluation of the isotopic effects on the rate constants of chemical reactions. Our method is based on the quantum instanton approximation [1-3] and on the path-integral Metropolis Monte-Carlo evaluation of the Boltzmann operator matrix elements. The method is more accurate than existing transition-state theory or semiclassical instanton method since we do not assume a single reaction path and do not use a semiclassical approximation of the Boltzmann operator. In order to calculate the isotopic effect we use a "charging algoritm," whereby the mass of the isotope is continuously changed from the initial to the final value. Direct calculation of the isotopic ratio turns out to be much more efficient than finding the absolute rate constants first and then calculating their ratio. While the Monte-Carlo implementation should make the method accessible to systems with a larger number of atoms, we present numerical results for the Eckart barrier and for the reactions H + H2 arrow H2 + H and H + DH arrow HD + H. [1] W.H. Miller, Y. Zhao, M. Ceotto, and Sandy Yang, J. Chem. Phys. 119, 1329 (2003). [2] T. Yamamoto and W.H. Miller, J. Chem. Phys. (in press). [3] Y. Zhao, T. Yamamoto, and W.H. Miller, J. Chem. Phys. (in press).

  13. Rate constants of chemical reactions from semiclassical transition state theory in full and one dimension.

    Science.gov (United States)

    Greene, Samuel M; Shan, Xiao; Clary, David C

    2016-06-28

    Semiclassical Transition State Theory (SCTST), a method for calculating rate constants of chemical reactions, offers gains in computational efficiency relative to more accurate quantum scattering methods. In full-dimensional (FD) SCTST, reaction probabilities are calculated from third and fourth potential derivatives along all vibrational degrees of freedom. However, the computational cost of FD SCTST scales unfavorably with system size, which prohibits its application to larger systems. In this study, the accuracy and efficiency of 1-D SCTST, in which only third and fourth derivatives along the reaction mode are used, are investigated in comparison to those of FD SCTST. Potential derivatives are obtained from numerical ab initio Hessian matrix calculations at the MP2/cc-pVTZ level of theory, and Richardson extrapolation is applied to improve the accuracy of these derivatives. Reaction barriers are calculated at the CCSD(T)/cc-pVTZ level. Results from FD SCTST agree with results from previous theoretical and experimental studies when Richardson extrapolation is applied. Results from our implementation of 1-D SCTST, which uses only 4 single-point MP2/cc-pVTZ energy calculations in addition to those for conventional TST, agree with FD results to within a factor of 5 at 250 K. This degree of agreement and the efficiency of the 1-D method suggest its potential as a means of approximating rate constants for systems too large for existing quantum scattering methods.

  14. Direct evaluation of the temperature dependence of the rate constant based on the quantum instanton approximation

    CERN Document Server

    Buchowiecki, Marcin

    2010-01-01

    A general method for the direct evaluation of the temperature dependence of the quantum-mechanical reaction rate constant in many-dimensional systems is described. The method is based on the quantum instanton approximation for the rate constant, thermodynamic integration with respect to the inverse temperature, and the path integral Monte Carlo evaluation. It can describe deviations from the Arrhenius law due to the coupling of rotations and vibrations, zero-point energy, tunneling, corner-cutting, and other nuclear quantum effects. The method is tested on the Eckart barrier and the full-dimensional H + H_2 -> H_2 + H reaction. In the temperature range from 300K to 1500K, the error of the present method remains within 13% despite the very large deviations from the Arrhenius law. The direct approach makes the calculations much more efficient, and the efficiency is increased even further (by up to two orders of magnitude in the studied reactions) by using optimal estimators for reactant and transition state the...

  15. Stability Analysis of GI/G/c/K Retrial Queue with Constant Retrial Rate

    CERN Document Server

    Avrachenkov, Konstantin

    2010-01-01

    We consider a GI/G/c/K-type retrial queueing system with constant retrial rate. The system consists of a primary queue and an orbit queue. The primary queue has $c$ identical servers and can accommodate the maximal number of $K$ jobs. If a newly arriving job finds the full primary queue, it joins the orbit. The original primary jobs arrive to the system according to a renewal process. The jobs have general i.i.d. service times. A job in front of the orbit queue retries to enter the primary queue after an exponentially distributed time independent of the orbit queue length. Telephone exchange systems, Medium Access Protocols and short TCP transfers are just some applications of the proposed queueing system. For this system we establish minimal sufficient stability conditions. Our model is very general. In addition, to the known particular cases (e.g., M/G/1/1 or M/M/c/c systems), the proposed model covers as particular cases the deterministic service model and the Erlang model with constant retrial rate. The l...

  16. Determination of the epimerization rate constant of amygdalin by microemulsion electrokinetic chromatography.

    Science.gov (United States)

    Yu, Lishuang; Ye, Hongzhi; Zheng, Lili; Chen, Lidian; Chu, Kedan; Liu, Xianxiang; Xu, Xueqin; Chen, Guonan

    2011-01-01

    A new method for separation and determination of amygdalin and its epimer (neoamygdalin) in the epimerization of amygdalin by MEEKC is proposed. For the chiral separation of amygdalin and neoamygdalin, a running buffer composed of 80 mM sodium cholate, 5.0% v/v butan-1-ol, 0.5% v/v heptane and 94.5% v/v 30 mM Na(2) B(4) O(7) buffer (pH 9.00) is proposed. Under optimum conditions, the basic separation of amygdalin and neoamygdalin can be achieved within 7 min. The calibration curve for amygdalin showed excellent linearity in the concentration range of 20-1000 μg/mL with a detection limit of 5.0 μg/mL (S/N=3). The epimerization rate constant of amygdalin in basic microemulsion was first determined by monitoring the concentration changes of amygdalin, and the epimerization rate constant of amygdalin was found to be 2×10(-3) min(-1) at 25°C under the above optimum microemulsion conditions. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Rate constant for the reaction of atomic oxygen with phosphine at 298 K

    Science.gov (United States)

    Stief, L. J.; Payne, W. A.; Nava, D. F.

    1987-01-01

    The rate constant for the reaction of atomic oxygen with phosphine has been measured at 298 K using flash photolysis combined with time-resolved detection of O(3P) via resonance fluorescence. Atomic oxygen was produced by flash photolysis of N2O or NO highly diluted in argon. The results were shown to be independent of (PH3), (O), total pressure and the source of O(3P). The mean value of all the experiments is k1 = (3.6 + or -0.8) x 10 to the -11th cu cm/s (1 sigma). Two previous measurements of k1 differed by more than an order of magnitude, and the results support the higher value obtained in a discharge flow-mass spectrometry study. A comparison with rate data for other atomic and free radical reactions with phosphine is presented, and the role of these reactions in the aeronomy or photochemistry of Jupiter and Saturn is briefly considered.

  18. Rate Constant and Branching Fraction for the NH2 + NO2 Reaction

    DEFF Research Database (Denmark)

    Klippenstein, Stephen J.; Harding, Lawrence B.; Glarborg, Peter

    2013-01-01

    The NH2 + NO2 reaction has been studied experimentally and theoretically. On the basis of laser photolysis/LIF experiments, the total rate constant was determined over the temperature range 295–625 K as k1,exp(T) = 9.5 × 10–7(T/K)−2.05 exp(−404 K/T) cm3 molecule–1 s–1. This value is in the upper...... may facilitate a small flux between the adducts. High- and low-pressure limit rate coefficients for the various product channels of NH2 + NO2 are determined from the ab initio TST-based master equation calculations for the temperature range 300–2000 K. The theoretical predictions are in good agreement...

  19. Protein balance and evaluation of velocity constant k (drained rate on syneresis of milk

    Directory of Open Access Journals (Sweden)

    Migena Hoxha

    2013-12-01

    Full Text Available The syneresis process is influenced by various factors such as milk pH, curd incubation temperature, fat content, heat treatment of milk, acidity, salt, curd dimension and gel firmness at cutting time. The aim of this study was to investigate balance of protein, the syneresis kinetic of whey drainage and evaluation of velocity constant k (drained rate on curd incubation temperature (25 and 30oC and heat treatment (at 70oC for 5 minutes. Milk was sampled from cow, sheep and goat breeds. The milk samples were analyzed for physical and chemical properties (pH, acidity, protein, casein, fat and lactose, coagulation parameters (R coagulation time in minutes, curd firmness measured in volt after 20 minutes (A20 or 30 minutes (A30 and the rate of firming K20 in minutes as well as for whey volume drained after 30, 50, 70, 90, 110, 130 and 150 minutes. During this study it was observed that the curd incubation temperature is the major factor affecting syneresis. Velocity constant k value (drained rate is increased with higher temperature, but can be decrease significantly at low temperature. The syneresis rate differs between breed’s milk and is influenced by their coagulation properties. Regarding balance of protein, protein recovery and curd yield results to be higher at incubation temperature of 25oC, in spite of breed. Whey protein loss result to be higher for goat’s milk on two incubation temperature (41.05–58.35%, while the whey loss on sheep’s milk result to be lower (14.01–37.61%.

  20. Endo- and exocytic rate constants for spontaneous and protein kinase C-activated T cell receptor cycling

    DEFF Research Database (Denmark)

    Menné, Charlotte; Møller Sørensen, Tine; Siersma, Volkert

    2002-01-01

    To determine the rate constants of spontaneous and activated TCR cycling, we examined TCR endo- and exocytosis in the human T cell line Jurkat by three different methods. Using a simple kinetic model for TCR cycling and non-linear regression analyses, we found that the spontaneous endocytic rate......)) whereas the exocytic rate constant was unaffected. Thus, the TCR becomes a rapidly cycling receptor with kinetics similar to classical cycling receptors subsequent to PKC activation. This results in a reduction of the half-life of cell surface expressed TCR from approximately 58 to 6 min and allows rapid...... constant of the TCR was low (approximately 0.012 min(-1)) whereas the spontaneous exocytic rate constant was similar to that of other cycling receptors (approximately 0.055 min(-1)). Following protein kinase C activation (PKC) the endocytic rate constant was increased tenfold (to approximately 0.128 min(-1...

  1. Periods of constant and falling-rate for infrared drying of carrot slices Períodos de secagem constante e decrescente de fatias de cenoura por infravermelho

    Directory of Open Access Journals (Sweden)

    Fernando M. Botelho

    2011-08-01

    Full Text Available The aim of this work was to study the infrared drying process of carrot slices and to determine coefficients related to the heat and mass transfer of the process. Fresh carrots were used, dried until constant weight in a dryer with infrared heating source. Different models were utilized to fit the experimental data of constant and falling drying rate periods. It was verified that the coefficients of heat and mass transfer, during the constant drying rate, significantly increased with temperature on rise. The Diffusion Approximation, Two Terms, Midili and Verna models satisfactory represented the falling period of drying rate of carrot slices. The effective diffusion coefficient increased with temperature and this relationship can be represented by the Arrhenius equation, obtaining activation energy to the drying process of 29.092 kJ mol-1.Com este trabalho objetivou-se estudar o processo de secagem por infravermelho das fatias de cenoura e determinar alguns coeficientes referentes à transferência de calor e massa do processo. Utilizaram-se cenouras frescas, secadas até massa constante em um secador com fonte de aquecimento por infravermelho. Aos dados experimentais se ajustaram diferentes modelos para os períodos de taxa de secagem constante e decrescentes. Verificou-se que os coeficientes transferência de calor e massa, referentes ao período de secagem constante, aumentaram significativamente com o aumento da temperatura e que os modelos Aproximação da Difusão, Dois Termos, Midili e Verna representaram satisfatoriamente o período de secagem decrescente das fatias de cenoura. O coeficiente de difusão efetivo aumentou com a temperatura e esta relação pode ser representada pela Equação de Arrhenius, obtendo-se uma energia de ativação para o processo de secagem de 29,092 kJ mol-1.

  2. Extension of the master sintering curve for constant heating rate modeling

    Science.gov (United States)

    McCoy, Tammy Michelle

    The purpose of this work is to extend the functionality of the Master Sintering Curve (MSC) such that it can be used as a practical tool for predicting sintering schemes that combine both a constant heating rate and an isothermal hold. Rather than just being able to predict a final density for the object of interest, the extension to the MSC will actually be able to model a sintering run from start to finish. Because the Johnson model does not incorporate this capability, the work presented is an extension of what has already been shown in literature to be a valuable resource in many sintering situations. A predicted sintering curve that incorporates a combination of constant heating rate and an isothermal hold is more indicative of what is found in real-life sintering operations. This research offers the possibility of predicting the sintering schedule for a material, thereby having advanced information about the extent of sintering, the time schedule for sintering, and the sintering temperature with a high degree of accuracy and repeatability. The research conducted in this thesis focuses on the development of a working model for predicting the sintering schedules of several stabilized zirconia powders having the compositions YSZ (HSY8), 10Sc1CeSZ, 10Sc1YSZ, and 11ScSZ1A. The compositions of the four powders are first verified using x-ray diffraction (XRD) and the particle size and surface area are verified using a particle size analyzer and BET analysis, respectively. The sintering studies were conducted on powder compacts using a double pushrod dilatometer. Density measurements are obtained both geometrically and using the Archimedes method. Each of the four powders is pressed into ¼" diameter pellets using a manual press with no additives, such as a binder or lubricant. Using a double push-rod dilatometer, shrinkage data for the pellets is obtained over several different heating rates. The shrinkage data is then converted to reflect the change in relative

  3. The Influence of Photolysis Rate Constants in Ozone Production for the Paso del Norte Region

    Science.gov (United States)

    Becerra, Fernando; Fitzgerald, Rosa

    2012-03-01

    In this research work we are focusing on understanding the relationship between photolysis rates and the photochemical ozone changes observed in the Paso del Norte region. The city of El Paso, Texas together with Ciudad Juarez, Mexico, forms the largest contiguous bi-national metropolitan area. This region suffers year-round ozone pollution events, and a better understanding is needed to mitigate them. Previous studies have found that ambient ozone concentrations tend to be higher on weekends rather than on weekdays, this phenomenon being referred to, as the ``weekend effect.'' If the ozone standard is exceeded more frequently on weekends, then this phenomenon must be considered in the design of ozone control strategies. In this work we investigate some of the most representative weekend ozone episodes at El Paso, TX, during the years 2009, 2010 and 2011 using the ozone photolysis rates. In this research the TUV radiative-transfer model is used to calculate the local photolysis rates and a UV MFRSR instrument is used to obtain experimental parameters. Seasonal variations and the weekday-weekend effect is studied. The results of this research will help to understand the underlying behavior of the photolysis rate constants when different atmospheric conditions are present.

  4. Fast proton exchange in histidine: measurement of rate constants through indirect detection by NMR spectroscopy.

    Science.gov (United States)

    Sehgal, Akansha Ashvani; Duma, Luminita; Bodenhausen, Geoffrey; Pelupessy, Philippe

    2014-05-19

    Owing to its imidazole side chain, histidine participates in various processes such as enzyme catalysis, pH regulation, metal binding, and phosphorylation. The determination of exchange rates of labile protons for such a system is important for understanding its functions. However, these rates are too fast to be measured directly in an aqueous solution by using NMR spectroscopy. We have obtained the exchange rates of the NH3(+) amino protons and the labile NH(ε2) and NH(δ1) protons of the imidazole ring by indirect detection through nitrogen-15 as a function of temperature (272 KExchange rates up to 8.5×10(4) s(-1) could be determined (i.e., lifetimes as short as 12 μs). The three chemical shifts δH(i) of the invisible exchanging protons H(i) and the three one-bond scalar coupling constants (1)J(N,H(i)) could also be determined accurately.

  5. Deuterium recycling rate constants derived from plasma implantation/desorption shots in a martensitic steel surface

    Energy Technology Data Exchange (ETDEWEB)

    Sedano, L.A. [CIEMAT/DIAE, Madrid (Spain); European Commission/JRC, H-Materials Interaction Sector, Ispra (Italy); Esteban, G.A. [UPV-EHU/ETSIIT, D. Nuc. Eng. and Fluid Mec., Bilbao (Spain); Perujo, A. [European Commission/JRC, H-Materials Interaction Sector, Ispra (Italy)

    2001-12-04

    The recombination (K{sub 2}) and dissociation rate constants (K{sub 1}) are essential magnitudes for the tracking of tritium at the first wall (FW) of fusion reactors (FR). This paper presents our plasma implantation/recycling test, the modelling of the experiment and the results obtained for K{sub 2} and K{sub 1} in the case of a deuterium (D{sub 3}{sup +}/D{sub 2}{sup +}) plasma in the martensitic steel DIN 1.4914 (MANET). Once parasitic contributions were accounted, the D{sub 2} release from the target was seen to be surface limited. The values obtained for K{sub 1} and K{sub 2} show low dispersion on impinging flux and ion energies. For K{sub 1} a roughly constant value of 7 x 10{sup -6} mol Pa{sup -1} m{sup -2} s{sup -1} is derived. The obtained K{sub 2} is written as: K{sub 2} = 2.414 exp (-1571/RT) (m{sup 4} mol{sup -1} s{sup -1}), with R = 8.314 J mol{sup -1} K{sup -1}. Our activation energies agree with those existing in the literature derived from permeation experiments. High reflection coefficients are derived, which are in good agreement with the classical theory of ion scattering at low energy. (orig.)

  6. Uptake rate constants and partition coefficients for vapor phase organic chemicals using semipermeable membrane devices (SPMDs)

    Science.gov (United States)

    Cranor, W.L.; Alvarez, D.A.; Huckins, J.N.; Petty, J.D.

    2009-01-01

    To fully utilize semipermeable membrane devices (SPMDs) as passive samplers in air monitoring, data are required to accurately estimate airborne concentrations of environmental contaminants. Limited uptake rate constants (kua) and no SPMD air partitioning coefficient (Ksa) existed for vapor-phase contaminants. This research was conducted to expand the existing body of kinetic data for SPMD air sampling by determining kua and Ksa for a number of airborne contaminants including the chemical classes: polycyclic aromatic hydrocarbons, organochlorine pesticides, brominated diphenyl ethers, phthalate esters, synthetic pyrethroids, and organophosphate/organosulfur pesticides. The kuas were obtained for 48 of 50 chemicals investigated and ranged from 0.03 to 3.07??m3??g-1??d-1. In cases where uptake was approaching equilibrium, Ksas were approximated. Ksa values (no units) were determined or estimated for 48 of the chemicals investigated and ranging from 3.84E+5 to 7.34E+7. This research utilized a test system (United States Patent 6,877,724 B1) which afforded the capability to generate and maintain constant concentrations of vapor-phase chemical mixtures. The test system and experimental design employed gave reproducible results during experimental runs spanning more than two years. This reproducibility was shown by obtaining mean kua values (n??=??3) of anthracene and p,p???-DDE at 0.96 and 1.57??m3??g-1??d-1 with relative standard deviations of 8.4% and 8.6% respectively.

  7. The Constant Growth Rate of the Bound-Zone Peculiar Velocity Profile

    CERN Document Server

    Lee, Jounghun

    2016-01-01

    We present a numerical evidence that the amplitude and slope of the bound-zone peculiar velocity profile grow at the constant rates in a LambdaCDM universe. Analyzing the friends-of-friends halo catalogs from the Millennium-II simulations at various redshifts, we measure the average peculiar velocity profile of the objects located in the bound zone around massive group-size halos and compare it to an analytic formula characterized by the amplitude and slope parameters. It is shown that the amplitude and slope of the bound-zone peculiar velocity profile remain constant in the dark matter dominated epoch but begin to grow linearly with redshift after the onset of the Lambda-domination. Our explanation for this phenomenon is that as the balance between the gravitational attraction of the massive groups and the repulsive force of the Hubble expansion cracks up in the Lambda-dominated epoch, the gravitational influence on the bound-zone halos diminishes more rapidly with the increment of the radial distances. Spec...

  8. Rate constant and thermochemistry for K + O2 + N2 = KO2 + N2

    DEFF Research Database (Denmark)

    Sorvajärvi, Tapio; Viljanen, Jan; Toivonen, Juha;

    2015-01-01

    The addition reaction of potassium atoms with oxygen has been studied using the collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) method. KCl vapor was photolyzed with 266 nm pulses and the absorbance by K atoms at 766.5 nm was measured at various delay times with a narrow...... line width diode laser. Experiments were carried out with O2/N2 mixtures at a total pressure of 1 bar, over 748-1323 K. At the lower temperatures single exponential decays of [K] yielded the third-order rate constant for addition, kR1, whereas at higher temperatures equilibration was observed...... in the form of double exponential decays of [K], which yielded both kR1 and the equilibrium constant for KO2 formation. kR1 can be summarized as 1.07 × 10-30(T/1000 K)-0.733 cm6 molecule-2 s-1. Combination with literature values leads to a recommended kR1 of 5.5 × 10-26T-1.55 exp(-10/T) cm6 molecule-2 s-1...

  9. Critical evaluation and rate constants of chemoselective ligation reactions for stoichiometric conjugations in water.

    Science.gov (United States)

    Saito, Fumito; Noda, Hidetoshi; Bode, Jeffrey W

    2015-04-17

    Chemoselective ligation reactions have contributed immensely to the development of organic synthesis and chemical biology. However, the ligation of stoichiometric amounts of large molecules for applications such as protein-protein conjugates is still challenging. Conjugation reactions need to be fast enough to proceed under dilute conditions and chemoselective in the presence of unprotected functional groups; the starting materials and products must be stable under the reaction conditions. To compare known ligation reactions for their suitability under these conditions, we determined the second-order rate constants of ligation reactions using peptide substrates with unprotected functional groups. The reaction conditions, the chemoselectivity of the reactions, and the stability of the starting materials and products were carefully evaluated. In some cases, the stability could be improved by modifying the substrate structure. These data obtained under the ligation conditions provide a useful guide to choose an appropriate ligation reaction for synthesis of large molecules by covalent ligation reactions of unprotected substrates in water.

  10. Low-energy electron impact cross-sections and rate constants of $NH_2$

    Indian Academy of Sciences (India)

    ANAND BHARADVAJA; SAVINDER KAUR; K L BALUJA

    2017-08-01

    This systematic study reports various electron impact cross-sections, rate constants and transport properties of $NH_2$ radical in the low-energy limit. The collision study is based on $R$-matrix formalism and involves the use of various scattering models employing different active spaces. Both electron excited inelasticcross-sections and resonances are found influenced by correlation and polarization effects. The non-relativistic molecular bremsstrahlung radiation cross-section for soft photons, binary encounter Bethe model-based ionization cross-sections and a few molecular properties of the target radical are also reported. The present calculations are found to be in agreement with the available results. This theoretical study provides a pathway to understand collision dynamics and generates data required in various fields of applied physics.

  11. Temperature dependence of the absolute rate constant for the reaction of ozone with dimethyl sulfide

    Institute of Scientific and Technical Information of China (English)

    WANG Hai-tao; ZHANG Yu-jie; MU Yu-jing

    2007-01-01

    Absolute rate constants for the reaction of ozone with dimethyl sulfide (DMS) were measured in a 200-L Teflon chamber over the temperature range of 283-353 K. Measurements were carried out using DMS in large excess over ozone of 10 to 1 or greater. Over the indicated temperature range,the data could be fit to the simple Arrhenius expression as KDMS = (9.96±3.61)×10-11exp(-(7309.7±1098.2)/T)cm3/(molecule·s). A compared investigation of the reaction between ozone and ethene had a kc2H4 value of(1.35±0.11)×10-18 cm3/(molecule·s) at room temperature.

  12. Determination of ultimate carbonaceous BOD and the specific rate constant (K1)

    Science.gov (United States)

    Stamer, J.K.; Bennett, J.P.; McKenzie, Stuart W.

    1982-01-01

    Ultimate carbonaceous biochemical oxygen demand (BODu) and the specific rate constant (K1) at which the demand is exerted are important parameters in designing biological wastewater treatment plants and in assessing the impact of wastewater on receiving streams. An analytical method is presented which uses time-series concentrations of BOD, defined as the calculated sum of dissolved oxygen (DO) losses at each time of measurement, for determining BODu and K1. Time-series DO measurements are obtained from a water sample that is incubated in darkness at 20 degrees Celsius in the presence of nitrapyrin, a chemical nitrification inhibitor. Time-series concentrations of BOD that approximate first order kinetics can be analyzed graphically or mathematically to compute BODu and K1.

  13. CORAL: QSPR modeling of rate constants of reactions between organic aromatic pollutants and hydroxyl radical.

    Science.gov (United States)

    Toropov, A A; Toropova, A P; Rasulev, B F; Benfenati, E; Gini, G; Leszczynska, D; Leszczynski, J

    2012-09-05

    The rate constants (K(OH)) of reactions between 78 organic aromatic pollutants and hydroxyl radical were examined. Simplified molecular input line entry system was used as representation of the molecular structure of the pollutants. Quantitative structure-property relationships was developed using CORAL software (http://www.insilico.eu/CORAL) for four random splits of the data into the subtraining, calibration, and test sets. The obtained results reveal good predictive potential of the applied approach: correlation coefficients (r(2)) for the test sets of the four random splits are 0.75, 0.91, 0.84, and 0.80. Using the Monte Carlo method CORAL software generated the optimal descriptors for one-variable models. The reproducibility of each model was tested performing three runs of the Monte Carlo optimization. The current data were compared to previous results and discussed. Copyright © 2012 Wiley Periodicals, Inc.

  14. Consideration of demand rate in overall equipment effetiveness (OEE on equipment with constant process time

    Directory of Open Access Journals (Sweden)

    Tay C.C.

    2013-06-01

    research should be conducted to test the possibility and to verify the definition of such performance ratio including Takt time on those processes of which its operating time is possibly to be reduced, especially those are not constant and fixed. This piece of research is temporarily done on the process where its operating time is constant from time to time and there is no ideal cycle time possible.Practical implications: The awareness of the overproduction should be emphasized and raised in the intention of pursuing higher OEE value. As the definition proposed such, the process with constant cycle time could even be defined in different performance ratio from time to time regarding to the customer demands and corresponding production rate. These two variables can be adjusted and balanced to increase the OEE value through optimization of average cycle time. Over this, optimization of average cycle time on equipment with constant operating time can be achieved through the optimization of loading number per each processing.Originality/value: The novelty of the paper is the inclusion of customer demand in obtaining OEE value of any particular equipment. Besides that, the equipment without ideal cycle time, which means those processes carried out in constant cycle time are possibly to be evaluated with performance ratio. As consequence of that, the machine utilization and capability used could be quantified and visualized using the performance ratio data of the OEE proposed.

  15. Quantification of in Situ Biodegradation Rate Constants Using a Novel Combined Isotope Approach

    Science.gov (United States)

    Blum, P.; Sültenfuß, J.; Martus, P.

    2014-12-01

    Numerous studies have shown the enormous potential of the compound-specific isotope analysis (CSIA) for studying the biodegradation of organic compounds such as monoaromatic hydrocarbons (BTEX), polyaromatic hydrocarbons (PAH), chlorinated solvents and other organic contaminants and environmental transformation mechanisms in groundwater. In addition, two-dimensional isotope analysis such as carbon and hydrogen have been successfully studied indicating the potential to also investigate site-specific reaction mechanisms. The main objective of the current study however is to quantify real effective in situ biodegradation rate constants in a coal-tar contaminated aquifer by combining compound-specific isotope analysis (CSIA) and tracer-based (3H-3He) ground-water dating (TGD). Hence, groundwater samples are used to determine groundwater residence times, and carbon and hydrogen stable isotopes are analyzed for selected BTEX and PAH. The results of the hydrogen stable isotopes surprisingly indicate no isotope fractionation and therefore no biodegradation. In contrast, for stable carbon isotopes of selected BTEX such as o-xylene and toluene, isotope shifts are detected indicating active biodegradation under sulfate-reducing conditions. These and previous results of stable carbon isotopes show that only for o-xylene a clear evidence for biodegradation is possible for the studied site. Nevertheless, in combining these results with the groundwater residence times, which range between 1 year for the shallow wells (20 m below surface) and 41 years for the deeper wells (40 m below surface), it is feasible to effectively determine in situ biodegradation rate constants for o-xylene. Conversely, the outcome also evidently demonstrate the major limitations of the novel combined isotope approach for a successful implementation of monitored natural attenuation (MNA) at such field sites.

  16. Feasibility study of volumetric modulated arc therapy with constant dose rate for endometrial cancer

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ruijie [Department of Radiation Oncology, Peking University Third Hospital, Beijing (China); Wang, Junjie, E-mail: junjiewang47@yahoo.com [Department of Radiation Oncology, Peking University Third Hospital, Beijing (China); Xu, Feng [Department of Biomedical Engineering, Peking University Third Hospital, Beijing (China); Li, Hua [Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing (China); Zhang, Xile [Department of Radiation Oncology, Peking University Third Hospital, Beijing (China)

    2013-10-01

    To investigate the feasibility, efficiency, and delivery accuracy of volumetric modulated arc therapy with constant dose rate (VMAT-CDR) for whole-pelvic radiotherapy (WPRT) of endometrial cancer. The nine-field intensity-modulated radiotherapy (IMRT), VMAT with variable dose-rate (VMAT-VDR), and VMAT-CDR plans were created for 9 patients with endometrial cancer undergoing WPRT. The dose distribution of planning target volume (PTV), organs at risk (OARs), and normal tissue (NT) were compared. The monitor units (MUs) and treatment delivery time were also evaluated. For each VMAT-CDR plan, a dry run was performed to assess the dosimetric accuracy with MatriXX from IBA. Compared with IMRT, the VMAT-CDR plans delivered a slightly greater V{sub 20} of the bowel, bladder, pelvis bone, and NT, but significantly decreased the dose to the high-dose region of the rectum and pelvis bone. The MUs decreased from 1105 with IMRT to 628 with VMAT-CDR. The delivery time also decreased from 9.5 to 3.2 minutes. The average gamma pass rate was 95.6% at the 3%/3 mm criteria with MatriXX pretreatment verification for 9 patients. VMAT-CDR can achieve comparable plan quality with significant shorter delivery time and smaller number of MUs compared with IMRT for patients with endometrial cancer undergoing WPRT. It can be accurately delivered and be an alternative to IMRT on the linear accelerator without VDR capability.

  17. A sequence-specific threading tetra-intercalator with an extremely slow dissociation rate constant

    Science.gov (United States)

    Holman, Garen G.; Zewail-Foote, Maha; Smith, Amy Rhoden; Johnson, Kenneth A.; Iverson, Brent L.

    2011-11-01

    A long-lived and sequence-specific ligand-DNA complex would make possible the modulation of biological processes for extended periods. For this purpose, we are investigating a polyintercalation approach to DNA recognition in which flexible chains of aromatic units thread back and forth repeatedly through the double helix. Here we describe the DNA-binding behaviour of a threading tetra-intercalator. Specific binding was observed on a relatively long DNA strand that strongly favoured a predicted 14 base-pair sequence. Kinetic studies revealed a multistep association process, with sequence specificity that primarily derives from large differences in dissociation rates. The rate-limiting dissociation rate constant of the tetra-intercalator complex dissociating from its preferred binding site was extremely slow, corresponding to a half-life of 16 days. This is one of the longest non-covalent complex half-lives yet reported and, to the best of our knowledge, the longest for a DNA-binding molecule.

  18. An Analytical Formula for Potential Water Vapor in an Atmosphere of Constant Lapse Rate

    Directory of Open Access Journals (Sweden)

    Ali Varmaghani

    2012-01-01

    Full Text Available Accurate calculation of precipitable water vapor (PWV in the atmosphere has always been a matter of importance for meteorologists. Potential water vapor (POWV or maximum precipitable water vapor can be an appropriate base for estimation of probable maximum precipitation (PMP in an area, leading to probable maximum flood (PMF and flash flood management systems. PWV and POWV have miscellaneously been estimated by means of either discrete solutions such as tables, diagrams or empirical methods; however, there is no analytical formula for POWV even in a particular atmospherical condition. In this article, fundamental governing equations required for analytical calculation of POWV are first introduced. Then, it will be shown that this POWV calculation relies on a Riemann integral solution over a range of altitude whose integrand is merely a function of altitude. The solution of the integral gives rise to a series function which is bypassed by approximation of saturation vapor pressure in the range of -55 to 55 degrees Celsius, and an analytical formula for POWV in an atmosphere of constant lapse rate is proposed. In order to evaluate the accuracy of the suggested equation, exact calculations of saturated adiabatic lapse rate (SALR at different surface temperatures were performed. The formula was compared with both the diagrams from the US Weather Bureau and SALR. The results demonstrated unquestionable capability of analytical solutions and also equivalent functions.

  19. An Analytical Formula for Potential Water Vapor in an Atmosphere of Constant Lapse Rate

    Directory of Open Access Journals (Sweden)

    Ali Varmaghani

    2012-01-01

    Full Text Available Accurate calculation of precipitable water vapor (PWV in the atmosphere has always been a matter of importance for meteorologists. Potential water vapor (POWV or maximum precipitable water vapor can be an appropriate base for estimation of probable maximum precipitation (PMP in an area, leading to probable maximum flood (PMF and flash flood management systems. PWV and POWV have miscellaneously been estimated by means of either discrete solutions such as tables, diagrams or empirical methods; however, there is no analytical formula for POWV even in a particular atmospherical condition. In this article, fundamental governing equations required for analytical calculation of POWV are first introduced. Then, it will be shown that this POWV calculation relies on a Riemann integral solution over a range of altitude whose integrand is merely a function of altitude. The solution of the integral gives rise to a series function which is bypassed by approximation of saturation vapor pressure in the range of -55 to 55 degrees Celsius, and an analytical formula for POWV in an atmosphere of constant lapse rate is proposed. In order to evaluate the accuracy of the suggested equation, exact calculations of saturated adiabatic lapse rate (SALR at different surface temperatures were performed. The formula was compared with both the diagrams from the US Weather Bureau and SALR. The results demonstrated unquestionable capability of analytical solutions and also equivalent functions.

  20. Stress corrosion cracking of alloy 600 using the constant strain rate test

    Energy Technology Data Exchange (ETDEWEB)

    Bulischeck, T. S.; van Rooyen, D.

    1980-01-01

    The most recent corrosion problems experienced in nuclear steam generators tubed with Inconel alloy 600 is a phenomenon labeled ''denting''. Denting has been found in various degrees of severity in many operating pressurized water reactors. Laboratory investigations have shown that Inconel 600 exhibits intergranular SCC when subjected to high stresses and exposed to deoxygenated water at elevated temperatures. A research project was initiated at Brookhaven National Laboratory in an attempt to improve the qualitative and quantitative understanding of factors influencing SCC in high temperature service-related environments. An effort is also being made to develop an accelerated test method which could be used to predict the service life of tubes which have been deformed or are actively denting. Several heats of commercial Inconel 600 tubing were procured for testing in deaerated pure and primary water at temperatures from 290 to 365/sup 0/C. U-bend type specimens were used to determine crack initiation times which may be expected for tubes where denting has occurred but is arrested and provide baseline data for judging the accelerating effects of the slow strain rate method. Constant extension rate tests were employed to determine the crack velocities experienced in the crack propagation stage and predict failure times of tubes which are actively denting. 8 refs., 17 figs., 5 tabs.

  1. Kinetic mechanism of phenylalanine hydroxylase: intrinsic binding and rate constants from single-turnover experiments.

    Science.gov (United States)

    Roberts, Kenneth M; Pavon, Jorge Alex; Fitzpatrick, Paul F

    2013-02-12

    Phenylalanine hydroxylase (PheH) catalyzes the key step in the catabolism of dietary phenylalanine, its hydroxylation to tyrosine using tetrahydrobiopterin (BH(4)) and O(2). A complete kinetic mechanism for PheH was determined by global analysis of single-turnover data in the reaction of PheHΔ117, a truncated form of the enzyme lacking the N-terminal regulatory domain. Formation of the productive PheHΔ117-BH(4)-phenylalanine complex begins with the rapid binding of BH(4) (K(d) = 65 μM). Subsequent addition of phenylalanine to the binary complex to form the productive ternary complex (K(d) = 130 μM) is approximately 10-fold slower. Both substrates can also bind to the free enzyme to form inhibitory binary complexes. O(2) rapidly binds to the productive ternary complex; this is followed by formation of an unidentified intermediate, which can be detected as a decrease in absorbance at 340 nm, with a rate constant of 140 s(-1). Formation of the 4a-hydroxypterin and Fe(IV)O intermediates is 10-fold slower and is followed by the rapid hydroxylation of the amino acid. Product release is the rate-determining step and largely determines k(cat). Similar reactions using 6-methyltetrahydropterin indicate a preference for the physiological pterin during hydroxylation.

  2. A new method for measuring the oxygen diffusion constant and oxygen consumption rate of arteriolar walls.

    Science.gov (United States)

    Sasaki, Nobuhiko; Horinouchi, Hirohisa; Ushiyama, Akira; Minamitani, Haruyuki

    2012-01-01

    Oxygen transport is believed to primarily occur via capillaries and depends on the oxygen tension gradient between the vessels and tissues. As blood flows along branching arterioles, the O(2) saturation drops, indicating either consumption or diffusion. The blood flow rate, the O(2) concentration gradient, and Krogh's O(2) diffusion constant (K) of the vessel wall are parameters affecting O(2)delivery. We devised a method for evaluating K of arteriolar wall in vivo using phosphorescence quenching microscopy to measure the partial pressure of oxygen in two areas almost simultaneously. The K value of arteriolar wall (inner diameter, 63.5 ± 11.9 μm; wall thickness, 18.0 ± 1.2 μm) was found to be 6.0 ± 1.2 × 10(-11) (cm(2)/s)(ml O(2)·cm(-3) tissue·mmHg(-1)). The arteriolar wall O(2) consumption rate (M) was 1.5 ± 0.1 (ml O(2)·100 cm(-3) tissue·min(-1)), as calculated using Krogh's diffusion equation. These results suggest that the arteriolar wall consumes a considerable proportion of the O(2) that diffuses through it.

  3. Activated barrier crossing dynamics in the non-radiative decay of NADH and NADPH

    Energy Technology Data Exchange (ETDEWEB)

    Blacker, Thomas S., E-mail: t.blacker@ucl.ac.uk [Centre for Mathematics and Physics in the Life Sciences and Experimental Biology (CoMPLEX), University College London, London WC1E 6BT (United Kingdom); Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom); Research Department of Cell and Developmental Biology, University College London, London WC1E 6BT (United Kingdom); Marsh, Richard J., E-mail: richard.marsh@ucl.ac.uk [Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom); Duchen, Michael R., E-mail: m.duchen@ucl.ac.uk [Research Department of Cell and Developmental Biology, University College London, London WC1E 6BT (United Kingdom); Bain, Angus J., E-mail: a.bain@ucl.ac.uk [Centre for Mathematics and Physics in the Life Sciences and Experimental Biology (CoMPLEX), University College London, London WC1E 6BT (United Kingdom); Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)

    2013-08-30

    Highlights: ► NADH and NADPH have a high rate of non-radiative excited state decay. ► Conformational relaxation is shown to be a significant non-radiative pathway. ► The Kramers equation describes the barrier crossing dynamics of the relaxation. ► Conformational restriction upon enzyme binding will alter NAD(P)H lifetimes. - Abstract: In live tissue, alterations in metabolism induce changes in the fluorescence decay of the biological coenzyme NAD(P)H, the mechanism of which is not well understood. In this work, the fluorescence and anisotropy decay dynamics of NADH and NADPH were investigated as a function of viscosity in a range of water–glycerol solutions. The viscosity dependence of the non-radiative decay is well described by Kramers and Kramers–Hubbard models of activated barrier crossing over a wide viscosity range. Our combined lifetime and anisotropy analysis indicates common mechanisms of non-radiative relaxation in the two emitting states (conformations) of both molecules. The low frequencies associated with barrier crossing suggest that non-radiative decay is mediated by small scale motion (e.g. puckering) of the nicotinamide ring. Variations in the fluorescence lifetimes of NADH and NADPH when bound to different enzymes may therefore be attributed to differing levels of conformational restriction upon binding.

  4. KABAM Version 1.0 User's Guide and Technical Documentation - Appendix H - Methods for Estimating Metabolism Rate Constant

    Science.gov (United States)

    Appendix H of KABAM Version 1.0 documentation related to estimating the metabolism rate constant. KABAM is a simulation model used to predict pesticide concentrations in aquatic regions for use in exposure assessments.

  5. [On true and apparent Michaelis constants in enzymology. III. Is it linear dependence between apparent michaelis constant and limiting rate and is it possible to determine the substrate constant value using this dependence?].

    Science.gov (United States)

    Karakhim, S A

    2012-01-01

    The Slater-Bonner method which is used for graphic determination of substrate constant (Ks) by linear dependence of apparent Michaelis constant (Km(app)) on the limiting rate (V(app)) of enzyme-catalysed reactions with activator participation has been critically analysed. It has been shown that although it is possible to record the mechanisms of such reactions as a scheme similar to Michaelis-Menten model which allow to find correlation Km(app) and V(app) as equation Km(app) = Ks + V(app)/k1[E]0 ([E]0 is a total enzyme concentration, k1 is a rate constant of enzyme-substrate complex formation from free enzyme and substrate) in order to calculate Ks and individual rate constants (k1, k(-1)), but this approach for investigation of all reactions with activator participation ought not to be used. The above equation is not obeyed in general, it may be true for some mechanisms only or under certain ratios of kinetic parameters of enzyme-catalysed reactions.

  6. Regularized learning of linear ordered-statistic constant false alarm rate filters (Conference Presentation)

    Science.gov (United States)

    Havens, Timothy C.; Cummings, Ian; Botts, Jonathan; Summers, Jason E.

    2017-05-01

    The linear ordered statistic (LOS) is a parameterized ordered statistic (OS) that is a weighted average of a rank-ordered sample. LOS operators are useful generalizations of aggregation as they can represent any linear aggregation, from minimum to maximum, including conventional aggregations, such as mean and median. In the fuzzy logic field, these aggregations are called ordered weighted averages (OWAs). Here, we present a method for learning LOS operators from training data, viz., data for which you know the output of the desired LOS. We then extend the learning process with regularization, such that a lower complexity or sparse LOS can be learned. Hence, we discuss what 'lower complexity' means in this context and how to represent that in the optimization procedure. Finally, we apply our learning methods to the well-known constant-false-alarm-rate (CFAR) detection problem, specifically for the case of background levels modeled by long-tailed distributions, such as the K-distribution. These backgrounds arise in several pertinent imaging problems, including the modeling of clutter in synthetic aperture radar and sonar (SAR and SAS) and in wireless communications.

  7. Predicting reaction rate constants of ozone with organic compounds from radical structures

    Science.gov (United States)

    Yu, Xinliang; Yi, Bing; Wang, Xueye; Chen, Jianfang

    2012-05-01

    The reaction rate constants of ozone with organic compounds in the atmosphere were predicted by a quantitative structure-activity relationship (QSAR) model. Density functional theory (DFT) calculations, for the first time, were carried out on the radicals from organic compounds, at the UB3LYP level of theory with 6-31G(d) basis set. A set of quantum chemical descriptors calculated from the radicals, the energy of the highest occupied molecular orbital of beta spin states (EβHOMO), the molecular average polarizability (α), and the total energy (ET), were used to build the general QSAR model for aliphatic compounds, applying the genetic algorithm (GA) technique and support vector machine (SVM) regression. The root mean square errors (RMSE) are 0.680 for the training set (68 compounds), 0.777 for the validation set (36 compounds) and 0.709 for the test set (35 compounds). Investigated results indicate that the SVM model given here has good predictivity for aliphatic compounds.

  8. α-Terpineol reactions with the nitrate radical: Rate constant and gas-phase products

    Science.gov (United States)

    Jones, Brian T.; Ham, Jason E.

    The bimolecular rate constant of k rad +α-terpineol (16 ± 4) × 10 -12 cm 3 molecule -1 s -1 was measured using the relative rate technique for the reaction of the nitrate radical (NO 3rad ) with α-terpineol (2-(4-methyl-1-cyclohex-3-enyl)propan-2-ol) at 297 ± 3 K and 1 atmosphere total pressure. To more clearly define part of α-terpineol's indoor environment degradation mechanism, the products of α-terpineol + NO 3rad reaction were investigated. The identified reaction products were: acetone, glyoxal (HC( dbnd O)C( dbnd O)H), and methylglyoxal (CH 3C( dbnd O)C( dbnd O)H). The use of derivatizing agents O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and N, O-bis(trimethylsilyl) trifluoroacetamide (BSTFA) were used to propose the other major reaction products: 6-hydroxyhept-5-en-2-one, 4-(1-hydroxy-1-methylethyl)-1-methyl-2-oxocyclohexyl nitrate, 5-(1-hydroxy-1-methylethyl)-2-oxocyclohexyl nitrate, 1-formyl-5-hydroxy-4-(hydroxymethyl)-1,5-dimethylhexyl nitrate, and 1,4-diformyl-5-hydroxy-1,5-dimethylhexyl nitrate. The elucidation of these products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible α-terpineol + NO 3rad reaction mechanisms based on previously published volatile organic compound + NO 3rad gas-phase mechanisms. The additional gas-phase products (2,6,6-trimethyltetrahydro-2 H-pyran-2,5-dicarbaldehyde and 2,2-dimethylcyclohexane-1,4-dicarbaldehyde) are proposed to be the result of cyclization through a reaction intermediate.

  9. Photolysis of ketene at 193 nm and the rate constant for H + HCCO at 297 K.

    Energy Technology Data Exchange (ETDEWEB)

    Glass, G. P.; Kumaran, S. S.; Michael, J. V.; Chemistry

    2000-01-01

    The 193 nm photolysis of ketene was studied by measuring the amount of atomic hydrogen produced when very dilute ketene/Ar and ketene/H{sub 2} mixtures were irradiated by a single pulse from an ArF excimer laser. Absolute concentrations of atomic hydrogen were monitored over a time interval of 0-2.5 ms by using Lyman-{alpha} atomic resonance absorption spectroscopy (ARAS). Four different photodissociation channels of ketene were identified: H{sub 2}CCO + hv gives (a) CH{sub 2}({sup 3}B1) + CO; (b) CH{sub 2}({sup 1}A{sub 1}) + CO; (c) HCCO + H; and (d) C{sub 2}O(b{sup -1}{Sigma}{sup +}) + H{sub 2}. The quantum yields for each channel were measured as {phi}{sub a} = 0.628, {phi}{sub b} = 0.193, {phi}{sub 3}= 0.107, and {phi}{sub d} = 0.072, respectively. To explore the secondary chemistry that occurred when using higher pressure H{sub 2}CCO/Ar mixtures, a mechanism was constructed that used well-documented reactions and, for most processes, rate constants that had already been accurately determined. Modeling studies using this mechanism showed the [H] profile to be determined largely by the rate of the reaction H + HCCO {yields} CH{sub 2} + CO. An excellent fit to all of the experimental data was obtained when k{sub 2} = (1.7 {+-} 0.3) x 10{sup -10} cm{sup 3} molecule{sup -1} s{sup -1}.

  10. Variable dose rate single-arc IMAT delivered with a constant dose rate and variable angular spacing.

    Science.gov (United States)

    Tang, Grace; Earl, Matthew A; Yu, Cedric X

    2009-11-07

    Single-arc intensity-modulated arc therapy (IMAT) has gained worldwide interest in both research and clinical implementation due to its superior plan quality and delivery efficiency. Single-arc IMAT techniques such as the Varian RapidArc deliver conformal dose distributions to the target in one single gantry rotation, resulting in a delivery time in the order of 2 min. The segments in these techniques are evenly distributed within an arc and are allowed to have different monitor unit (MU) weightings. Therefore, a variable dose-rate (VDR) is required for delivery. Because the VDR requirement complicates the control hardware and software of the linear accelerators (linacs) and prevents most existing linacs from delivering IMAT, we propose an alternative planning approach for IMAT using constant dose-rate (CDR) delivery with variable angular spacing. We prove the equivalence by converting VDR-optimized RapidArc plans to CDR plans, where the evenly spaced beams in the VDR plan are redistributed to uneven spacing such that the segments with larger MU weighting occupy a greater angular interval. To minimize perturbation in the optimized dose distribution, the angular deviation of the segments was restricted to single gantry sweep as in the VDR plans but each sector was delivered with a different value of CDR. For four patient cases, including two head-and-neck, one brain and one prostate, all CDR plans developed with the variable spacing scheme produced similar dose distributions to the original VDR plans. For plans with complex angular MU distributions, the number of sectors increased up to four in the CDR plans in order to maintain the original plan quality. Since each sector was delivered with a different dose rate, extra mode-up time (xMOT) was needed between the transitions of the successive sectors during delivery. On average, the delivery times of the CDR plans were approximately less than 1 min longer than the treatment times of the VDR plans, with an average of

  11. Three-minute constant rate step test for detecting exertional dyspnea relief after bronchodilation in COPD

    Directory of Open Access Journals (Sweden)

    Borel B

    2016-11-01

    Full Text Available Benoit Borel,1,2 Courtney A Wilkinson-Maitland,3 Alan Hamilton,4 Jean Bourbeau,5 Hélène Perrault,6 Dennis Jensen,3,5,7 François Maltais2 1Laboratoire HAVAE, Université de Limoges, Limoges, France; 2Centre de Recherche, Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, 3Clinical Exercise and Respiratory Physiology Laboratory, Department of Kinesiology and Physical Education, McGill University, Montréal, QC, 4Boehringer Ingelheim (Canada Limited, Burlington, ON, 5Respiratory Epidemiology and Clinical Research Unit, Montreal Chest Institute, McGill University Health Center, Montreal, QC, 6Faculty of Health Sciences, University of Ottawa, Ottawa, ON, 7Translational Research in Respiratory Diseases Program, Research Institute of the McGill University Health Centre, Montreal, QC, Canada Background: The aim of this study was to evaluate the responsiveness of the 3-minute constant rate step test (3-MST to detect the relief of exertional dyspnea (respiratory discomfort after acute bronchodilation in COPD patients. Patients and methods: A total of 40 patients with moderate-to-severe COPD (mean forced expiratory volume in 1 second: 45.7 (±14.7, % predicted performed four 3-MSTs at randomly assigned stepping rates of 14, 16, 20 and 24 steps/min after inhalation of nebulized ipratropium bromide (500 µg/salbutamol (2.5 mg and saline placebo, which were randomized to order. Patients rated their intensity of perceived dyspnea at the end of each 3-MST using Borg 0–10 category ratio scale. Results: A total of 37 (92.5%, 36 (90%, 34 (85% and 27 (67.5% patients completed all 3 minutes of exercise at 14, 16, 20 and 24 steps/min under both treatment conditions, respectively. Compared with placebo, ipratropium bromide/salbutamol significantly decreased dyspnea at the end of the third minute of exercise at 14 steps/min (by 0.6±1.0 Borg 0–10 scale units, P<0.01 and 16 steps/min (by 0.7±1.3 Borg 0–10 scale

  12. Application of an Artificial Neural Network to the Prediction of OH Radical Reaction Rate Constants for Evaluating Global Warming Potential.

    Science.gov (United States)

    Allison, Thomas C

    2016-03-03

    Rate constants for reactions of chemical compounds with hydroxyl radical are a key quantity used in evaluating the global warming potential of a substance. Experimental determination of these rate constants is essential, but it can also be difficult and time-consuming to produce. High-level quantum chemistry predictions of the rate constant can suffer from the same issues. Therefore, it is valuable to devise estimation schemes that can give reasonable results on a variety of chemical compounds. In this article, the construction and training of an artificial neural network (ANN) for the prediction of rate constants at 298 K for reactions of hydroxyl radical with a diverse set of molecules is described. Input to the ANN consists of counts of the chemical bonds and bends present in the target molecule. The ANN is trained using 792 (•)OH reaction rate constants taken from the NIST Chemical Kinetics Database. The mean unsigned percent error (MUPE) for the training set is 12%, and the MUPE of the testing set is 51%. It is shown that the present methodology yields rate constants of reasonable accuracy for a diverse set of inputs. The results are compared to high-quality literature values and to another estimation scheme. This ANN methodology is expected to be of use in a wide range of applications for which (•)OH reaction rate constants are required. The model uses only information that can be gathered from a 2D representation of the molecule, making the present approach particularly appealing, especially for screening applications.

  13. On the ambiguity of the reaction rate constants in multivariate curve resolution for reversible first-order reaction systems.

    Science.gov (United States)

    Schröder, Henning; Sawall, Mathias; Kubis, Christoph; Selent, Detlef; Hess, Dieter; Franke, Robert; Börner, Armin; Neymeyr, Klaus

    2016-07-13

    If for a chemical reaction with a known reaction mechanism the concentration profiles are accessible only for certain species, e.g. only for the main product, then often the reaction rate constants cannot uniquely be determined from the concentration data. This is a well-known fact which includes the so-called slow-fast ambiguity. This work combines the question of unique or non-unique reaction rate constants with factor analytic methods of chemometrics. The idea is to reduce the rotational ambiguity of pure component factorizations by considering only those concentration factors which are possible solutions of the kinetic equations for a properly adapted set of reaction rate constants. The resulting set of reaction rate constants corresponds to those solutions of the rate equations which appear as feasible factors in a pure component factorization. The new analysis of the ambiguity of reaction rate constants extends recent research activities on the Area of Feasible Solutions (AFS). The consistency with a given chemical reaction scheme is shown to be a valuable tool in order to reduce the AFS. The new methods are applied to model and experimental data.

  14. Relationship between phenol-induced cytotoxicity and experimental inhibition rate constant or a theoretical parameter.

    Science.gov (United States)

    Fujisawa, S; Kadoma, Y

    2012-06-01

    We synthesized various dimer forms of 2-methoxyphenols and 2-tert-butylphenols, as dimers such as curcumin exhibit potent antioxidant and anti-inflammatory activity. We investigated the QSARs between the cytotoxicity and independent variables; kinetic parameters (inhibition rate constant (kinh/kp), stoichiometric factor (n)) or DFT-based theoretical parameters (i.e. phenolic O-H bond dissociation enthalpy (BDE), ionization potential according to Koopman's theorem (IP), LUMO, absolute hardness (η), electronegativity (χ) and electrophilicity (ω)) for 2-methoxyphenols and 2- tert- or 2,6-di-tert-butylphenols. The cytotoxicity of these phenols against human tumor cells (HSG, HL60) and/or human gingival fibroblasts (HGF) showed a marked negative linear relationship to kinh/kp, suggesting that the cytotoxicity of phenols may be related to radical reactions. By contrast, a linear relationship between the cytotoxicity and η-term was demonstrated; 2-methoxyphenols showed a negative slope, whereas 2-tert- or 2,6-di-tert-butylphenols showed a positive slope. Also, the cytotoxicity of tert-butylphenols was linearly dependent on the LUMO-term, showing a positive slope. The cytotoxicity of methoxy-substituted monophenols toward both HSG and HGF cells was related to both log P and η- terms. Also, that of X-phenols toward murine L-1210 cells was related to both log P and η or IP-terms, determined from a dataset reported by Zhang et al., 1998. It was concluded that the phenol-induced cytotoxicity was attributable to radical reactions resulting from the terms (kinh/kp, IP, η, and LUMO) in QSAR. The LUMO-dependent cytotoxicity of 2-tert- or 2,6-di-tert-butylphenols may be related to their quinone oxidation products. Experimental and theoretical parameters provide a useful approach for analysis of the cytotoxicity for phenolic compounds.

  15. Theoretical study of the mechanism and rate constant of the B + CO2 reaction.

    Science.gov (United States)

    Poully, Benjamin; Bergeat, Astrid; Hannachi, Yacine

    2008-09-04

    The different stationary points on the potential energy surface relative to the title reaction have been reinvestigated at the B3LYP/aug-cc-pVDZ level with relative energies computed at the CCSD(T)/aug-cc-pVTZ level with B3LYP/aug-cc-pVDZ optimized geometries and by using the G3B3 composite method. Two entrance channels have been identified. The first one corresponds to boron addition at one of the oxygen atoms of the CO 2 molecule leading to trans-BOCO, which is found to be about 27 kcal/mol exothermic with a potential energy barrier of 16.4 kcal/mol (G3B3). The second channel, which has not been identified in previous theoretical works, corresponds to a direct insertion of the boron atom into a CO bond and leads to OBCO. The B + CO 2 --> OBCO step is found to be about 84 kcal/mol exothermic and needs to overcome a potential energy barrier of only 3.6 kcal/mol (G3B3). The rate constant at 300 K of the insertion step, calculated by using TST theory with G3B3 calculated activation energy value, is 5.4 10 (-14) cm (3) molecule (-1) s (-1), in very good agreement with the experimental data ((7.0 +/- 2.8) 10 (-14) cm (3) molecule (-1) s (-1), DiGiuseppe, T. G.; Davidovits, P. J. Chem. Phys. 1981, 74, 3287). The one corresponding to the addition process is found to be several orders of magnitude smaller because of a much higher potential energy barrier. The addition channel would not contribute to the title reaction even at high temperature. A modified Arrhenius equation has been fitted in the 300-1000 K temperature range, which might be useful for chemical models.

  16. 100 kV/2A three-phase constant-current repetitive-rate charging equipment

    CERN Document Server

    Tan Yu Gang; Chen Li Dong; Guo Zhi Gang; Zou Xiao Bing; Luo Min; Cao Shao Yun; Chang An Bi

    2002-01-01

    A 100 kV/2A three-phase constant-current repetitive-rate charging equipment was designed and constructed. A three-phase L-C converter is adopted as constant-current power source. Six Insulated Gate Bipolar Transistors (IGBTs) are connected in parallel to control the stop of charge. A Programmable Logical Controller (PLC) is the central element of the control unit. The equipment is used in the repetitive-rate discharge features test of the switch. It works stably under the conditions of 2A charging current, 10 Hz operating voltage, 100 kV repetitive rate and 1 mu F capacitor

  17. Selecting Constant Work Rates for Endurance Testing in COPD : The Role of the Power-Duration Relationship

    NARCIS (Netherlands)

    van der Vaart, Hester; Murgatroyd, Scott R.; Rossiter, Harry B.; Chen, Carey; Casaburi, Richard; Porszasz, Janos

    2014-01-01

    Constant work rate (CWR) exercise testing is highly responsive to therapeutic interventions and reveals physiological and functional benefits. No consensus exists, however, regarding optimal methods for selecting the pre-intervention work rate. We postulate that a CWR whose tolerated duration (t(lim

  18. Kinetics analysis for development of a rate constant estimation model for ultrasonic degradation reaction of methylene blue.

    Science.gov (United States)

    Kobayashi, Daisuke; Honma, Chiemi; Matsumoto, Hideyuki; Takahashi, Tomoki; Kuroda, Chiaki; Otake, Katsuto; Shono, Atsushi

    2014-07-01

    Ultrasound has been used as an advanced oxidation method for wastewater treatment. Sonochemical degradation of organic compounds in aqueous solution occurs by pyrolysis and/or reaction with hydroxyl radicals. Moreover, kinetics of sonochemical degradation has been proposed. However, the effect of ultrasonic frequency on degradation rate has not been investigated. In our previous study, a simple model for estimating the apparent degradation rate of methylene blue was proposed. In this study, sonochemical degradation of methylene blue was performed at various frequencies. Apparent degradation rate constant was evaluated assuming that sonochemical degradation of methylene blue was a first-order reaction. Specifically, we focused on effects of ultrasonic frequency and power on rate constant, and the applicability of our proposed model was demonstrated. Using this approach, maximum sonochemical degradation rate was observed at 490 kHz, which agrees with a previous investigation into the effect of frequency on the sonochemical efficiency value evaluated by KI oxidation dosimetry. Degradation rate increased with ultrasonic power at every frequency. It was also observed that threshold power must be reached for the degradation reaction to progress. The initial methylene blue concentration and the apparent degradation rate constant have a relation of an inverse proportion. Our proposed model for estimating the apparent degradation rate constant using ultrasonic power and sonochemical efficiency value can apply to this study which extended the frequency and initial concentration range.

  19. Toward an understanding of the turbidity measurement of heterocoagulation rate constants of dispersions containing particles of different sizes.

    Science.gov (United States)

    Liu, Jie; Xu, Shenghua; Sun, Zhiwei

    2007-11-01

    Our previous studies have shown that the determination of coagulation rate constants by turbidity measurement becomes impossible for a certain operating wavelength (that is, its blind point) because at this wavelength the change in the turbidity of a dispersion completely loses its response to the coagulation process. Therefore, performing the turbidity measurement in the wavelength range near the blind point should be avoided. In this article, we demonstrate that the turbidity measurement of the rate constant for coagulation of a binary dispersion containing particles of two different sizes (heterocoagulation) presents special difficulties because the blind point shifts with not only particle size but also with the component fraction. Some important aspects of the turbidity measurement for the heterocoagulation rate constant are discussed and experimentally tested. It is emphasized that the T-matrix method can be used to correctly evaluate extinction cross sections of doublets formed during the heterocoagulation process, which is the key data determining the rate constant from the turbidity measurement, and choosing the appropriate operating wavelength and component fraction are important to achieving a more accurate rate constant. Finally, a simple scheme in experimentally determining the sensitivity of the turbidity changes with coagulation over a wavelength range is proposed.

  20. Two Optimization Methods to Determine the Rate Constants of a Complex Chemical Reaction Using FORTRAN and MATLAB

    Directory of Open Access Journals (Sweden)

    Abdel-Latif A. Seoud

    2010-01-01

    Full Text Available Problem statement: For chemical reactions, the determination of the rate constants is both very difficult and a time consuming process. The aim of this research was to develop computer programs for determining the rate constants for the general form of any complex reaction at a certain temperature. The development of such program can be very helpful in the control of industrial processes as well as in the study of the reaction mechanisms. Determination of the accurate values of the rate constants would help in establishing the optimum conditions of reactor design including pressure, temperature and other parameters of the chemical reaction. Approach: From the experimental concentration-time data, initial values of rate constants were calculated. Experimental data encountered several types of errors, including temperature variation, impurities in the reactants and human errors. Simulations of a second order consecutive irreversible chemical reaction of the saponification of diethyl ester were presented as an example of the complex reactions. The rate equations (system of simultaneous differential equations of the reaction were solved to get the analytical concentration versus time profiles. The simulation results were compared with experimental results at each measured point. All deviations between experimental and calculated values were squared and summed up to form a new function. This function was fed into a minimizer routine that gave the optimal rate constants. Two optimization techniques were developed using FORTRAN and MATLAB for accurately determining the rate constants of the reaction at certain temperature from the experimental data. Results: Results showed that the two proposed programs were very efficient, fast and accurate tools to determine the true rate constants of the reaction with less 1% error. The use of the MATLAB embedded subroutines for simultaneously solving the differential equations and minimization of the error function

  1. Rate Constants for Fine-structure Excitations in O-H Collisions with Error Bars Obtained by Machine Learning

    Science.gov (United States)

    Vieira, Daniel; Krems, Roman V.

    2017-02-01

    We present an approach using a combination of coupled channel scattering calculations with a machine-learning technique based on Gaussian Process regression to determine the sensitivity of the rate constants for non-adiabatic transitions in inelastic atomic collisions to variations of the underlying adiabatic interaction potentials. Using this approach, we improve the previous computations of the rate constants for the fine-structure transitions in collisions of O({}3{P}j) with atomic H. We compute the error bars of the rate constants corresponding to 20% variations of the ab initio potentials and show that this method can be used to determine which of the individual adiabatic potentials are more or less important for the outcome of different fine-structure changing collisions.

  2. Kinetics of nonstationary chemiluminescence during the inhibited oxidation of hydrocarbons and determination of the rate constants for peroxy radical decay

    Energy Technology Data Exchange (ETDEWEB)

    Rusina, I.F.; Emanuel, N.M.; Gagarina, A.B.

    1986-05-01

    This paper presents the results of a theoretical analysis of the kinetics of the nonstationary inhibited chemiluminescence and suggests a method for determining the absolute value of the rate constants for the recombination of peroxy radicals and for their removal by reaction with an inhibitor. From the rate curve for the chemiluminescence in the nonstationary regime following the introduction of an inhibitor it is possible simultaneously and independently to determine the absolute values of the rate constants for recombination of the peroxy radicals and their destruction by the inhibitor. Equations are obtained for calculating the time to establish the quasistationary concentration of peroxy radicals and of radicals formed from the inhibitor, using known values of the constants.

  3. Temperature dependence of the rate constant of hydrogen isotope interactions with a lithium capillary-porous system under reactor irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Tazhibayeva, Irina, E-mail: tazhibayeva@ntsc.kz [Institute of Atomic Energy NNC RK, Kurchatov (Kazakhstan); Kulsartov, Timur; Gordienko, Yuri [Institute of Atomic Energy NNC RK, Kurchatov (Kazakhstan); Mukanova, Aliya [Al’ Farabi Kazakh National University, Almaty (Kazakhstan); Ponkratov, Yuri; Barsukov, Nikolay; Tulubaev, Evgeniy [Institute of Atomic Energy NNC RK, Kurchatov (Kazakhstan); Platacis, Erik [University of Latvia (IPUL), Riga (Latvia); Kenzhin, Ergazy [Shakarim Semey State University, Semey (Kazakhstan)

    2013-10-15

    Highlights: • The experiments with Li CPS sample were carried out at reactor IVG-1.M. • The gas absorption technique was used to study hydrogen isotope interaction with lithium CPS. • The temperature dependence of constants of interaction rate was obtained for various power rates of the reactor. • Determination of the activation energies, and pre-exponents of Arrhenius dependence. • The effect of increase of the rate constant under reaction irradiation. -- Abstract: Experiments with a sample of a lithium capillary-porous system (CPS) were performed at the reactor IVG-1.M of the Institute of Atomic Energy NNC RK to study the effects of neutron irradiation on the parameters of hydrogen isotope interactions with a lithium CPS. The absorption technique was used during the experiments, and this technique allowed the temperature dependences of the hydrogen isotope interaction rate constants with the lithium CPS to be obtained under various reactor powers. The obtained dependencies were used to determine the main interaction parameters: the activation energies and the pre-exponents of the Arrhenius dependence of the hydrogen interaction rate constants with lithium and the lithium CPS. An increase of the hydrogen isotope interaction rate with the lithium CPS was observed under reactor irradiation.

  4. High-level theoretical study of the reaction between hydroxyl and ammonia: Accurate rate constants from 200 to 2500 K

    Science.gov (United States)

    Nguyen, Thanh Lam; Stanton, John F.

    2017-10-01

    Hydrogen abstraction from NH3 by OH to produce H2O and NH2—an important reaction in combustion of NH3 fuel—was studied with a theoretical approach that combines high level quantum chemistry and advanced chemical kinetics methods. Thermal rate constants calculated from first principles agree well (within 5%-20%) with available experimental data over a temperature range that extends from 200 to 2500 K. Quantum mechanical tunneling effects were found to be important; they lead to a decided curvature and non-Arrhenius behavior for the rate constant.

  5. Classical reaction probabilities, cross sections and rate constants for the O( 1D) + H2 → OH + H reaction

    Science.gov (United States)

    Alexander, A. J.; Aoiz, F. J.; Bañares, L.; Brouard, M.; Herrero, V. J.; Simons, J. P.

    1997-10-01

    Reaction probabilitiers total reaction cross sections as a function of collision energy, and rate constants have been calculated using the quasi-classical trajectory (QCT) method for the O( 1D) + H 2 reaction on several ab initio potential energy surfaces (PES), including the recent one by Ho, Hollebeck, Rabitz, Harding and Schatz. Detailed QCT results on the Schinke and Lester PES are compared with recent time-dependent wavepacket calculations on the same PES, showing good agreement. The QCT thermal rate constants calculated on the PES of Ho et al. are in better accord with the experimental determinations than those calculated on the Schinke-Lester PES.

  6. The Influence of Uncompensated Solution Resistance on the Determination and Standard Electrochemical Rate Constants Using Cyclic Voltammetry, and Some Comparisons with AC Voltammetry.

    Science.gov (United States)

    1987-09-25

    rate constants, k2r using cyclic voltametry . The res tss are expressed in terms of systematic deviations oP sapparent measured" rate constants, k~b(app...Classification) The Influence of Uncompensated Solution Resistance on the Determination and Standard Electro- - . chemical Rate Constants Using Cyclic ...Year MonhOy SAGE COUNT FIELD GROUP Sue-GROUP digital simulation analysis, uncompensated solution resis- I A tance, electrochemical rate constants, cyclic

  7. Exponential Bounds for Ruin Probability in Two Moving Average Risk Models with Constant Interest Rate

    Institute of Scientific and Technical Information of China (English)

    Ding Jun YAO; Rong Ming WANG

    2008-01-01

    The authors consider two discrete-time insurance risk models. Two moving average risk models are introduced to model the surplus process, and the probabilities of ruin are examined in models with a constant interest force. Exponential bounds for ruin probabilities of an infinite time horizon are derived by the martingale method.

  8. EFRT M-12 Issue Resolution: Caustic Leach Rate Constants from PEP and Laboratory-Scale Tests

    Energy Technology Data Exchange (ETDEWEB)

    Mahoney, Lenna A.; Rassat, Scot D.; Eslinger, Paul W.; Aaberg, Rosanne L.; Aker, Pamela M.; Golovich, Elizabeth C.; Hanson, Brady D.; Hausmann, Tom S.; Huckaby, James L.; Kurath, Dean E.; Minette, Michael J.; Sundaram, S. K.; Yokuda, Satoru T.

    2009-08-14

    concentrated to nominally 20 wt% solids using cross-flow ultrafiltration before adding caustic. The work described in this report addresses the kinetics of caustic leach under WTP conditions, based on tests performed with a Hanford waste simulant. The tests were completed at the lab-scale and in the PEP, which is a 1/4.5-scale mock-up of key PTF process equipment. The purpose of this report is to summarize the results from both scales that are related to caustic leach chemistry to support a scale-up factor for the submodels to be used in the G2 model, which predicts WTP operating performance. The scale-up factor will take the form of an adjustment factor for the rate constant in the boehmite leach kinetic equation in the G2 model.

  9. An economic order quantity model with ramp type demand rate, constant deterioration rate and unit production cost

    Directory of Open Access Journals (Sweden)

    Manna Prasenjit

    2016-01-01

    Full Text Available We have developed an order level inventory system for deteriorating items with demand rate as a ramp type function of time. The finite production rate is proportional to the demand rate and the deterioration rate is independent of time. The unit production cost is inversely proportional to the demand rate. The model with no shortages case is discussed considering that: (a the demand rate is stabilized after the production stopping time and (b the demand is stabilized before the production stopping time. Optimal costs are determined for two different cases.

  10. The form of the rate constant for elementary reactions at equilibrium from MD: framework and proposals for thermokinetics

    CERN Document Server

    Jesudason, C G

    2006-01-01

    The rates or formation and concentration distributions of a dimer reaction showing hysteresis behavior are examined in an ab initio chemical reaction designed as elementary and where the hysteresis structure precludes the formation of transition states (TS) with pre-equilibrium and internal sub-reactions. It was discovered that the the reactivity coefficients, defined as a measure of departure from the zero density rate constant for the forward and backward steps had a ratio that was equal to the activity coefficient ratio for the product and reactant species. From the above observations, a theory is developed with the aid of some proven elementary theorems in thermodynamics, and expressions are derived whereby a feasible experimental and computational method for determining the activity coefficients from the rate constants may be obtained The theory developed is applied to ionic reactions where the standard Bronsted-Bjerrum rate equation and exceptions to this are rationalized, and by viewing ion association...

  11. Dose equivalent rate constants and barrier transmission data for nuclear medicine facility dose calculations and shielding design.

    Science.gov (United States)

    Kusano, Maggie; Caldwell, Curtis B

    2014-07-01

    A primary goal of nuclear medicine facility design is to keep public and worker radiation doses As Low As Reasonably Achievable (ALARA). To estimate dose and shielding requirements, one needs to know both the dose equivalent rate constants for soft tissue and barrier transmission factors (TFs) for all radionuclides of interest. Dose equivalent rate constants are most commonly calculated using published air kerma or exposure rate constants, while transmission factors are most commonly calculated using published tenth-value layers (TVLs). Values can be calculated more accurately using the radionuclide's photon emission spectrum and the physical properties of lead, concrete, and/or tissue at these energies. These calculations may be non-trivial due to the polyenergetic nature of the radionuclides used in nuclear medicine. In this paper, the effects of dose equivalent rate constant and transmission factor on nuclear medicine dose and shielding calculations are investigated, and new values based on up-to-date nuclear data and thresholds specific to nuclear medicine are proposed. To facilitate practical use, transmission curves were fitted to the three-parameter Archer equation. Finally, the results of this work were applied to the design of a sample nuclear medicine facility and compared to doses calculated using common methods to investigate the effects of these values on dose estimates and shielding decisions. Dose equivalent rate constants generally agreed well with those derived from the literature with the exception of those from NCRP 124. Depending on the situation, Archer fit TFs could be significantly more accurate than TVL-based TFs. These results were reflected in the sample shielding problem, with unshielded dose estimates agreeing well, with the exception of those based on NCRP 124, and Archer fit TFs providing a more accurate alternative to TVL TFs and a simpler alternative to full spectral-based calculations. The data provided by this paper should assist

  12. Online rate control in digital cameras for near-constant distortion based on minimum/maximum criterion

    Science.gov (United States)

    Lee, Sang-Yong; Ortega, Antonio

    2000-04-01

    We address the problem of online rate control in digital cameras, where the goal is to achieve near-constant distortion for each image. Digital cameras usually have a pre-determined number of images that can be stored for the given memory size and require limited time delay and constant quality for each image. Due to time delay restrictions, each image should be stored before the next image is received. Therefore, we need to define an online rate control that is based on the amount of memory used by previously stored images, the current image, and the estimated rate of future images. In this paper, we propose an algorithm for online rate control, in which an adaptive reference, a 'buffer-like' constraint, and a minimax criterion (as a distortion metric to achieve near-constant quality) are used. The adaptive reference is used to estimate future images and the 'buffer-like' constraint is required to keep enough memory for future images. We show that using our algorithm to select online bit allocation for each image in a randomly given set of images provides near constant quality. Also, we show that our result is near optimal when a minimax criterion is used, i.e., it achieves a performance close to that obtained by applying an off-line rate control that assumes exact knowledge of the images. Suboptimal behavior is only observed in situations where the distribution of images is not truly random (e.g., if most of the 'complex' images are captured at the end of the sequence.) Finally, we propose a T- step delay rate control algorithm and using the result of 1- step delay rate control algorithm, we show that this algorithm removes the suboptimal behavior.

  13. Site-specific reaction rate constant measurements for various secondary and tertiary H-abstraction by OH radicals

    KAUST Repository

    Badra, Jihad

    2015-02-01

    Reaction rate constants for nine site-specific hydrogen atom (H) abstraction by hydroxyl radicals (OH) have been determined using experimental measurements of the rate constants of Alkane+OH→Products reactions. Seven secondary (S 20, S 21, S 22, S 30, S 31, S 32, and S 33) and two tertiary (T 100 and T 101) site-specific rate constants, where the subscripts refer to the number of carbon atoms (C) connected to the next-nearest-neighbor (N-N-N) C atom, were obtained for a wide temperature range (250-1450K). This was done by measuring the reaction rate constants for H abstraction by OH from a series of carefully selected large branched alkanes. The rate constant of OH with four different alkanes, namely 2,2-dimethyl-pentane, 2,4-dimethyl-pentane, 2,2,4-trimethyl-pentane (iso-octane), and 2,2,4,4-tetramethyl-pentane were measured at high temperatures (822-1367K) using a shock tube and OH absorption diagnostic. Hydroxyl radicals were detected using the narrow-line-width ring-dye laser absorption of the R1(5) transition of OH spectrum near 306.69nm.Previous low-temperature rate constant measurements are added to the current data to generate three-parameter rate expressions that successfully represent the available direct measurements over a wide temperature range (250-1450. K). Similarly, literature values of the low-temperature rate constants for the reaction of OH with seven normal and branched alkanes are combined with the recently measured high-temperature rate constants from our group [1]. Subsequent to that, site-specific rate constants for abstractions from various types of secondary and tertiary H atoms by OH radicals are derived and have the following modified Arrhenius expressions:. S20=8.49×10-17T1.52exp(73.4K/T)cm3molecule-1s-1(250-1450K) S21=1.07×10-15T1.07exp(208.3K/T)cm3molecule-1s-1(296-1440K) S22=2.88×10-13T0.41exp(-291.5K/T)cm3molecule-1s-1(272-1311K) S30=3.35×10-18T1.97exp(323.1K/T)cm3molecule-1s-1(250-1366K) S31=1.60×10-18T2.0exp(500.0K/T)cm3

  14. Tuning nonradiative lifetimes via molecular aggregation

    CERN Document Server

    Celestino, A

    2016-01-01

    We show that molecular aggregation can strongly influence the nonradiative decay (NRD) lifetime of an electronic excitation. As a demonstrative example, we consider a transition-dipole-dipole-interacting dimer whose monomers have harmonic potential energy surfaces (PESs). Depending on the position of the NRD channel ($q_{\\rm nr}$), we find that the NRD lifetime ($\\tau_{\\rm nr}^{\\rm dim}$) can exhibit a completely different dependence on the intermolecular-interaction strength. We observe that (i) for $q_{\\rm nr}$ near the Franck-Condon region, $\\tau_{\\rm nr}^{\\rm dim}$ increases with the interaction strength; (ii) for $q_{\\rm nr}$ near the minimum of the monomer excited PES, the intermolecular interaction has little influence on $\\tau_{\\rm nr}^{\\rm dim}$; (iii) for $q_{\\rm nr}$ near the classical turning point of the monomer nuclear dynamics, on the other side of the minimum, $\\tau_{\\rm nr}^{\\rm dim}$ decreases with the interaction strength. Our findings suggest design principles for molecular systems where a...

  15. Theory and Experiment on the Measurement of Kinetic Rate Constants for Surfactant Exchange at an Air/Water Interface.

    Science.gov (United States)

    Pan; Green; Maldarelli

    1998-09-15

    The paper focuses on the measurement of the rate constants for the kinetic steps of adsorption and desorption of surfactant between an air/water surface and the aqueous bulk sublayer adjacent to the surface. Kinetic constants are determined in nonequilibrium experiments in which either a clean surface is contacted with a bulk solution and surfactant diffuses toward and adsorbs onto the interface, or the area of an established monolayer in equilibrium with an underlying solution is changed, and surfactant exchanges between the surface and bulk. The dynamic tension change due to the surfactant exchange is measured, and compared to predictions of kinetic-diffusive transport models in order to infer the kinetic coefficients as well the diffusion coefficients. Model comparisons for highly surface active surfactants have resolved only the diffusion coefficient as the transport was found to be diffusion controlled; kinetic constants have only been established for less active materials such as alcohols or bolaform surfactants. In this study, we demonstrate that kinetics can be differentiated from diffusion in clean interface adsorption and re-equilibration if high bulk concentrations of the surfactant are used, or in re-equilibration, if the surface is compressed sufficiently. We first establish theoretically that mass transfer shifts from diffusion-limited to mixed as the bulk concentration increases in clean interface adsorption, or the surface compression is increased in re-equilibration. We then experimentally verify this idea by using the polyethoxylated surfactant C12E6 (C12H25 (OCH2CH2)6-OH) and by measuring dynamic surface tensions in clean interface adsorption and re-equilibration, respectively by the shape analysis of pendant bubbles. We find values of 6 x 10(-10) m2/s for the diffusion coefficient, and 1.4 x 10(-5) m/sec and 1.4 x 10(-4) s-1 for the adsorption and desorption rate constants, respectively, in a Frumkin kinetic formulation. While the adsorption

  16. Dynamics of a Ivlev-type predator-prey system with constant rate harvesting

    Energy Technology Data Exchange (ETDEWEB)

    Ling Li [Institute of Nonlinear Analysis, College of Mathematics and Information Science, Wenzhou University, Wenzhou 325035 (China); Wang Weiming [Institute of Nonlinear Analysis, College of Mathematics and Information Science, Wenzhou University, Wenzhou 325035 (China)], E-mail: weimingwang2003@163.com

    2009-08-30

    In this paper, by using the analysis of qualitative method and bifurcation theory, we investigate the dynamical properties of the Ivlev-type predator-prey model with nonzero constant prey harvesting and with or without time delay, respectively. It is shown that the system we considered can exhibit the subcritical and supercritical Hopf bifurcation. We also study the effect of the time delay on the dynamics of the system. By choosing the delay {tau} as a bifurcation parameter, we show that Hopf bifurcation can occur as the delay {tau} crosses some critical values. The direction and stability of the Hopf bifurcation are investigated by following the procedure of deriving normal form given by Faria and Magalhaes. Finally, numerical simulations are performed to illustrate the obtained results.

  17. The saddle-node-transcritical bifurcation in a population model with constant rate harvesting

    CERN Document Server

    Saputra, K V I; Quispel, G R W

    2010-01-01

    We study the interaction of saddle-node and transcritical bifurcations in a Lotka-Volterra model with a constant term representing harvesting or migration. Because some of the equilibria of the model lie on an invariant coordinate axis, both the saddle-node and the transcritical bifurcations are of codimension one. Their interaction can be associated with either a single or a double zero eigenvalue. We show that in the former case, the local bifurcation diagram is given by a nonversal unfolding of the cusp bifurcation whereas in the latter case it is a nonversal unfolding of a degenerate Bogdanov-Takens bifurcation. We present a simple model for each of the two cases to illustrate the possible unfoldings. We analyse the consequences of the generic phase portraits for the Lotka-Volterra system.

  18. Theoretical Prediction of Rate Constants for Hydrogen Abstraction by OH, H, O, CH3, and HO2 Radicals from Toluene.

    Science.gov (United States)

    Li, Shu-Hao; Guo, Jun-Jiang; Li, Rui; Wang, Fan; Li, Xiang-Yuan

    2016-05-26

    Hydrogen abstraction from toluene by OH, H, O, CH3, and HO2 radicals are important reactions in oxidation process of toluene. Geometries and corresponding harmonic frequencies of the reactants, transition states as well as products involved in these reactions are determined at the B3LYP/6-31G(2df,p) level. To achieve highly accurate thermochemical data for these stationary points on the potential energy surfaces, the Gaussian-4(G4) composite method was employed. Torsional motions are treated either as free rotors or hindered rotors in calculating partion functions to determine thermodynamic properties. The obtained standard enthalpies of formation for reactants and some prodcuts are shown to be in excellent agreement with experimental data with the largest error of 0.5 kcal mol(-1). The conventional transition state theory (TST) with tunneling effects was adopted to determine rate constants of these hydrogen abstraction reactions based on results from quantum chemistry calculations. To faciliate its application in kinetic modeling, the obtained rate constants are given in Arrhenius expression: k(T) = AT(n) exp(-EaR/T). The obtained reaction rate constants also agree reasonably well with available expermiental data and previous theoretical values. Branching ratios of these reactions have been determined. The present reaction rates for these reactions have been used in a toluene combustion mechanism, and their effects on some combustion properties are demonstrated.

  19. Ab-Initio Based Computation of Rate Constants of Spin Forbidden Transitions in (Bio)inorganic Complexes and Metalloproteins

    Science.gov (United States)

    Ozkanlar, Abdullah; Rodriguez, Jorge H.

    2009-03-01

    Some (bio)chemical reactions are non-adiabatic processes whereby the total spin angular momentum, before and after the reaction, is not conserved. These are named spin- forbidden reactions. The application of spin density functional theory (SDFT) to the prediction of rate constants is a challenging task of fundamental and practical importance. We apply non-adiabatic transition state theory in conjunction with SDFT to predict the rate constant of the spin- forbidden dihydrogen binding to iron tetracarbonyl. To model the surface hopping probability between singlet and triplet states, the Landau-Zener formalism is used. The lowest energy point for singlet-triplet crossing, known as minimum energy crossing point (MECP), was located and used to compute, in a semi-quantum approach, reaction rate constants at 300 K. The predicted rates are in good agreement with experiment. In addition, we present results which are relevant to the ligand binding reactions of metalloproteins. This work is supported in part by NSF via CAREER award CHE-0349189 (JHR).

  20. Constant growth rate can be supported by decreasing energy flux and increasing aerobic glycolysis

    NARCIS (Netherlands)

    Slavov, Nikolai; Budnik, Bogdan A; Schwab, David; Airoldi, Edoardo M; van Oudenaarden, Alexander

    2014-01-01

    Fermenting glucose in the presence of enough oxygen to support respiration, known as aerobic glycolysis, is believed to maximize growth rate. We observed increasing aerobic glycolysis during exponential growth, suggesting additional physiological roles for aerobic glycolysis. We investigated such ro

  1. Constant growth rate can be supported by decreasing energy flux and increasing aerobic glycolysis

    NARCIS (Netherlands)

    Slavov, Nikolai; Budnik, Bogdan A; Schwab, David; Airoldi, Edoardo M; van Oudenaarden, Alexander

    2014-01-01

    Fermenting glucose in the presence of enough oxygen to support respiration, known as aerobic glycolysis, is believed to maximize growth rate. We observed increasing aerobic glycolysis during exponential growth, suggesting additional physiological roles for aerobic glycolysis. We investigated such

  2. Evaluation of the reaction rate constants for the gas-phase Al-CH4-air combustion chemistry

    Science.gov (United States)

    Sharipov, A. S.; Titova, N. S.; Starik, A. M.

    2012-10-01

    The most likely reaction pathways and reaction products in the Al-CH4-O2-N2 system are investigated using density functional theory and ab initio calculations. The B3LYP functional with extended 6-311+G(3df,2p) basis set as well as the CBS-QB3 composite method are mainly utilised. Theoretical analysis of corresponding reaction rate constants is also performed with the use of simple theoretical models. A critical overview of current knowledge on combustion-relevant reactions with aluminium compounds is given. On the basis of critical comparison of available experimental kinetic data with theoretical calculations, the approximations for rate constants for 44 reversible elementary reactions involving Al-containing species are recommended for use in combustion issues.

  3. Use of Closed Vessel as a Constant Pressure Apparatus for the Measurement of the Rate of Burning of Propellants

    Directory of Open Access Journals (Sweden)

    D. Vittal

    1980-04-01

    Full Text Available A method for the determination of burning rates of propellants whose from function is unknown is introduced. The method consists of burning in the closed vessel, a known charge weight of the test propellant alongwith a known pressure which remains nearly constant during the burning of the test propellant whose web size is the only quantity required for the evaluation of its rate of burning. The test propellants burns at near constant pressure conditions just as in the strand burner technique. This method can be applied to any unknown propellant of any shape whose web size can be measured and very large webs also can be used. In addition, the measurement of the records and the computation are very simple.

  4. Absolute rate constants for the reaction of NO with a series of peroxy radicals in the gas at 295 K

    DEFF Research Database (Denmark)

    Sehested, J.; Nielsen, O.J.; Wallington, T.J.

    1993-01-01

    The rate constants for the reaction of NO with a series of peroxy radicals: CH3O2, C2H5O2, (CH3)3CCH2O2, (CH3)3CC(CH3)2CH2O2, CH2FO2, CH2ClO2, CH2BrO2, CHF2O2, CF2ClO2, CHF2CF2O2, CF3CF2O2, CFCl2CH2O2 and CF2ClCH2O2 were measured at 298 K and a total pressure of 1 atm. The rate constants were obt...... obtained using the absolute technique of pulse radiolysis combined with time-resolved UV-VIS spectroscopy. The results are discussed in terms of reactivity trends and the atmospheric chemistry of peroxy radicals....

  5. Nonradial Pulsations in Classical Cepheids of the Magellanic Clouds

    CERN Document Server

    Moskalik, P; Moskalik, Pawel; Mizerski, Zbigniew Kolaczkowski & Tomasz

    2003-01-01

    We have performed systematic frequency analysis of the LMC Cepheids observed by OGLE project. Several new types of pulsation behaviour are identified, including triple-mode and amplitude-modulated double-mode pulsations. In ~10% of the first overtone Cepheids we find low amplitude secondary periodicities corresponding to nonradial modes. This is the first evidence for excitation of nonradial oscillations in Classical Cepheid variables.

  6. Unified equation for access to rate constants of first-order reactions in dynamic and on-column reaction chromatography.

    Science.gov (United States)

    Trapp, O

    2006-01-01

    A unified equation to evaluate elution profiles of reversible as well as irreversible (pseudo-) first-order reactions in dynamic chromatography and on-column reaction chromatography has been derived. Rate constants k1 and k(-1) and Gibbs activation energies are directly obtained from the chromatographic parameters (retention times tR(A) and tR(B) of the interconverting or reacting species A and B, the peak widths at half-height wA and wB, and the relative plateau height h(p)), the initial amounts A0 and B0 of the reacting species, and the equilibrium constant K(A/B). The calculation of rate constants requires only a few iterative steps without the need of performing a computationally extensive simulation of elution profiles. The unified equation was validated by comparison with a data set of 125,000 simulated elution profiles to confirm the quality of this equation by statistical means and to predict the minimal experimental requirements. Surprisingly, the recovery rate from a defined data set is on average 35% higher using the unified equation compared to the evaluation by iterative computer simulation.

  7. The H2 + CO ↔ H2CO Reaction: Rate Constants and Relevance to Hot and Dense Astrophysical Media

    Science.gov (United States)

    Vichietti, R. M.; Spada, R. F. K.; da Silva, A. B. F.; Machado, F. B. C.; Haiduke, R. L. A.

    2016-07-01

    A theoretical thermochemical and kinetic investigation of the thermal H2 + CO ↔ H2CO reaction was performed for a temperature range from 200 to 4000 K. Geometries and vibrational frequencies of reactants, product, and transition state (TS) were obtained at CCSD/cc-pVxZ (x = T and Q) levels and scaling factors were employed to consider anharmonicity effects on vibrational frequencies, zero-point energies, and thermal corrections provided by these methodologies. Enthalpies Gibbs energies, and rate constants for this reaction were determined by including a complete basis set extrapolation correction for the electronic properties calculated at CCSD(T)/cc-pVyZ (y = Q and 5) levels. Our study indicates that enthalpy changes for this reaction are highly dependent on temperature. Moreover, forward and reverse (high-pressure limit) rate constants were obtained from variational TS theory with quantum tunneling corrections. Thus, modified Arrhenius’ equations were fitted by means of the best forward and reverse rate constant values, which provide very reliable estimates for these quantities within the temperature range between 700 and 4000 K. To our knowledge, this is the first kinetic study done for the forward H2 + CO \\to H2CO process in a wide temperature range. Finally, these results can be used to explain the formaldehyde abundance in hot and dense interstellar media, possibly providing data about the physical conditions associated with H2CO masers close to massive star-forming regions.

  8. Computational study on the mechanisms and rate constants of the OH-initiated oxidation of ethyl vinyl ether in atmosphere.

    Science.gov (United States)

    Han, Dandan; Cao, Haijie; Li, Jing; Li, Mingyue; He, Maoxia; Hu, Jingtian

    2014-09-01

    The hydroxylation reactions of ethyl vinyl ether (EVE) in the present of O2 and NO are analyzed by using MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) level of theory. According to the calculated thermodynamic data, the detailed reaction mechanisms of EVE and OH are proposed. All of the ten possible reaction pathways are discussed. The major products of the title reaction are ethyl formate and formaldehyde, which is in accordance with experimental detection. The rate constants of the primary reactions over the temperature of 250-400K and the pressure range of 100-2000Torr are computed by employing MESMER program. At 298K and 760Torr, OH-addition channels are predominate and the total rate constant is ktot=4.53×10(-11)cm(3)molecule(-1)s(-1). The Arrhenius equation is obtained as ktot=6.27×10(-12)exp(611.5/T), according to the rate constants given at different temperatures. Finally, the atmospheric half life of EVE with respect to OH is estimated to be 2.13h.

  9. APPROXIMATION OF BIODEGRADATION RATE CONSTANTS FOR MONOAROMATIC HYDROCARBONS (BTEX) IN GROUND WATER

    Science.gov (United States)

    Two methods were used to approximate site-specific biodegradation rates of monoaromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylenes [BTEX]) dissolved in ground water. Both use data from monitoring wells and the hydrologic properties of the quifer to estimate a biode...

  10. The effect of solvation on the radiation damage rate constants for adenine

    DEFF Research Database (Denmark)

    Milhøj, Birgitte Olai; Sauer, Stephan P. A.

    2016-01-01

    in calculations of Gibbs free energies and reaction rates for the reaction between the OH radical and the DNA nucleobase adenine using Density Functional Theory at the ωB97X-D/6-311++G(2df,2pd) level with the Eckart tunneling correction. The solvent, water, has been included through either the implicit...

  11. Rate Constants and Activation Energies for Gas‐Phase Reactions of Three Cyclic Volatile Methyl Siloxanes with the Hydroxyl Radical

    Science.gov (United States)

    Safron, Andreas; Strandell, Michael; Kierkegaard, Amelie

    2015-01-01

    ABSTRACT Reaction with hydroxyl radicals (OH) is the major pathway for removal of cyclic volatile methyl siloxanes (cVMS) from air. We present new measurements of second‐order rate constants for reactions of the cVMS octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) with OH determined at temperatures between 313 and 353 K. Our measurements were made using the method of relative rates with cyclohexane as a reference substance and were conducted in a 140‐mL gas‐phase reaction chamber with online mass spectrometry analysis. When extrapolated to 298 K, our measured reaction rate constants of D4 and D5 with the OH radical are 1.9 × 10−12 (95% confidence interval (CI): (1.7–2.2) × 10−12) and 2.6 × 10−12 (CI: (2.3–2.9) × 10−12) cm3 molecule−1 s−1, respectively, which are 1.9× and 1.7× faster than previous measurements. Our measured rate constant for D6 is 2.8 × 10−12 (CI: (2.5–3.2) × 10−12) cm3 molecule−1 s−1 and to our knowledge there are no comparable laboratory measurements in the literature. Reaction rates for D5 were 33% higher than for D4 (CI: 30–37%), whereas the rates for D6 were only 8% higher than for D5 (CI: 5–10%). The activation energies of the reactions of D4, D5, and D6 with OH were not statistically different and had a value of 4300 ± 2800 J/mol. PMID:27708500

  12. Rate Constants and Activation Energies for Gas-Phase Reactions of Three Cyclic Volatile Methyl Siloxanes with the Hydroxyl Radical.

    Science.gov (United States)

    Safron, Andreas; Strandell, Michael; Kierkegaard, Amelie; Macleod, Matthew

    2015-07-01

    Reaction with hydroxyl radicals (OH) is the major pathway for removal of cyclic volatile methyl siloxanes (cVMS) from air. We present new measurements of second-order rate constants for reactions of the cVMS octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) with OH determined at temperatures between 313 and 353 K. Our measurements were made using the method of relative rates with cyclohexane as a reference substance and were conducted in a 140-mL gas-phase reaction chamber with online mass spectrometry analysis. When extrapolated to 298 K, our measured reaction rate constants of D4 and D5 with the OH radical are 1.9 × 10(-12) (95% confidence interval (CI): (1.7-2.2) × 10(-12)) and 2.6 × 10(-12) (CI: (2.3-2.9) × 10(-12)) cm(3) molecule(-1) s(-1), respectively, which are 1.9× and 1.7× faster than previous measurements. Our measured rate constant for D6 is 2.8 × 10(-12) (CI: (2.5-3.2) × 10(-12)) cm(3) molecule(-1) s(-1) and to our knowledge there are no comparable laboratory measurements in the literature. Reaction rates for D5 were 33% higher than for D4 (CI: 30-37%), whereas the rates for D6 were only 8% higher than for D5 (CI: 5-10%). The activation energies of the reactions of D4, D5, and D6 with OH were not statistically different and had a value of 4300 ± 2800 J/mol.

  13. Non-Constant Learning Rates in Retrospective Experience Curve Analyses and their Correlation to Deployment Programs

    Energy Technology Data Exchange (ETDEWEB)

    Wei, Max [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Smith, Sarah J. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Sohn, Michael D. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2015-07-16

    A key challenge for policy-makers and technology market forecasters is to estimate future technology costs and in particular the rate of cost reduction versus production volume. A related, critical question is what role should state and federal governments have in advancing energy efficient and renewable energy technologies? This work provides retrospective experience curves and learning rates for several energy-related technologies, each of which have a known history of federal and state deployment programs. We derive learning rates for eight technologies including energy efficient lighting technologies, stationary fuel cell systems, and residential solar photovoltaics, and provide an overview and timeline of historical deployment programs such as state and federal standards and state and national incentive programs for each technology. Piecewise linear regimes are observed in a range of technology experience curves, and public investments or deployment programs are found to be strongly correlated to an increase in learning rate across multiple technologies. A downward bend in the experience curve is found in 5 out of the 8 energy-related technologies presented here (electronic ballasts, magnetic ballasts, compact fluorescent lighting, general service fluorescent lighting, and the installed cost of solar PV). In each of the five downward-bending experience curves, we believe that an increase in the learning rate can be linked to deployment programs to some degree. This work sheds light on the endogenous versus exogenous contributions to technological innovation and highlights the impact of exogenous government sponsored deployment programs. This work can inform future policy investment direction and can shed light on market transformation and technology learning behavior.

  14. The WiggleZ Dark Energy Survey: constraining the evolution of Newton's constant using the growth rate of structure

    CERN Document Server

    Nesseris, Savvas; Davis, Tamara; Parkinson, David

    2011-01-01

    We constrain the evolution of Newton's constant using the growth rate of large-scale structure measured by the WiggleZ Dark Energy Survey in the redshift range $0.1 < z < 0.9$. We use this data in two ways. Firstly we constrain the matter density of the Universe, $\\Omega_m$ (assuming General Relativity), and use this to construct a diagnostic to detect the presence of an evolving Newton's constant. Secondly we directly measure the evolution of Newton's constant, $G_{eff}$, that appears in Modified Gravity theories, without assuming General Relativity to be true. The novelty of these approaches are that, contrary to other methods, they do not require knowledge of the expansion history of the Universe, $H(z)$, making them model independent tests. Our constraints for the second derivative of Newton's constant at the present day, assuming it is slowly evolving as suggested by Big Bang Nucleosynthesis constraints, using the WiggleZ data is $\\ddotGeff(t_0)=-1.19\\pm 0.95\\cdot 10^{-20}h^2 yr^{-2}$, where $h$ is...

  15. A methodology to study cyclic debond growth at constant mode-mixity and energy release rate

    DEFF Research Database (Denmark)

    Quispitupa, Amilcar; Berggreen, Christian; Carlsson, Leif A.

    2010-01-01

    It is well known that face/core debond crack propagation is governed by the critical energy release rate (fracture toughness) and mode-mixity at the crack tip. Thus, the current study focuses on the developing of a methodology to perform fatigue crack growth experiments of debonded sandwich...... and better control of loading conditions at the crack tip will be the most relevant outcomes of using the proposed fatigue test method....

  16. Flowing afterglow: construction of an apparatus, measurement of rate constants, and consideration of the diffusive behavior of charges

    Energy Technology Data Exchange (ETDEWEB)

    Matsuoka, Shingo; Nakamura, Hirone; Tamura, Takaaki (Tokyo Univ., Tokai, Ibaraki (Japan). Nuclear Engineering Research Lab.); Fujii, Toshihiro

    1984-06-01

    A flowing afterglow apparatus was constructed and the operation of the afterglow system including data analysis was tested by measuring the rate constants for the reactions N/sup +/ + NO, N/sub 2//sup +/ + NO, He/sup +/ + N/sub 2/, and SF/sub 6/ + e; the results were 5.8 x 10/sup -10/, 3.9 x 10/sup -10/, 1.20 x 10/sup -9/, and 2.1 x 10/sup -7/ cm/sup 3/s/sup -1/ respectively. In the measurements an extraction voltage for ion sampling was not applied to the nose cone in order not to introduce an electric field into the reaction region. A ''non-ambipolar'' model developed by us was used for the data analysis of the ion/molecule reactions. For the data analysis of the electron attachment, a typical curve fit mehtod to the product ion signal was used. However, no theoretical curves fit the experimental points. This disagreement is attributed to a change of the ion-sampling efficiency through the nose-cone aperture arising from a change of the electron-dominated plasma to a negative-ion-dominated plasma with an increasing flow rate of SF/sub 6/. Nevertheless, the attachment rate could be determined by fitting the theoretical and experimantal curves in the limited region of the SF/sub 6/ flow rate where the negative-ion-dominated plasma is established at the sampling aperture. All the rate constants obtained here agree reasonably well with literature values. Next, errors in the positive ion/molecule reaction rate constants, which would occur if the diffusion coefficients of the ions and neutrals each have a + 10 % error were calculated for the flow model to be -0.4 and +1.2 % respectively, demonstrating that these parameters are not important in the analysis of data. This insensitivity explains why the nose-cone voltage applied in a typical flowing afterglow operation has not caused a significant error in the published rate constants although it disturbs the ion diffusive behavior.

  17. Implementation of Constant Dose Rate and Constant Angular Spacing Intensity-modulated Arc Therapy for Cervical Cancer by Using a Conventional Linear Accelerator

    Institute of Scientific and Technical Information of China (English)

    Ruo-Hui Zhang; Xiao-Mei Fan; Wen-Wen Bai; Yan-Kun Cao

    2016-01-01

    Background: Volumetric-modulated arc therapy (VMAT) can only be implemented on the new generation linacs such as the Varian Trilogy(R) and Elekta Synergy(R).This prevents most existing linacs from delivering VMAT.The purpose of this study was to investigate the feasibility of using a conventional linear accelerator delivering constant dose rate and constant angular spacing intensity-modulated arc therapy (CDR-CAS-IMAT) for treating cervical cancer.Methods: Twenty patients with cervical cancer previously treated with intensity-modulated radiation therapy (IMRT) using Varian Clinical 23EX were retreated using CDR-CAS-IMAT.The planning target volume (PTV) was set as 50.4 Gy in 28 fractions.Plans were evaluated based on the ability to meet the dose volume histogram.The homogeneity index (HI), target volume conformity index (CI), the dose to organs at risk, radiation delivery time, and monitor units (MUs) were also compared.The paired t-test was used to analyze the two data sets.All statistical analyses were performed using SPSS 19.0 software.Results: Compared to the IMRT group, the CDR-CAS-IMAT group showed better PTV CI (0.85 ± 0.03 vs.0.81 ± 0.03, P =0.001), clinical target volume CI (0.46 ± 0.05 vs.0.43 ± 0.05, P =0.001), HI (0.09±0.02 vs.0.11 ± 0.02, P =0.005) and D95 (5196.33 ± 28.24 cGy vs.5162.63 ± 31.12 cGy, P =0.000), and cord D2 (3743.8 ± 118.7 cGy vs.3806.2 ± 98.7 cGy, P =0.017) and rectum V40 (41.9 ± 6.1% vs.44.2 ± 4.8%, P =0.026).Treatment time (422.7 ± 46.7 s vs.84.6 ± 7.8 s, P =0.000) and the total plan Mus (927.4 ± 79.1 vs.787.5 ± 78.5, P =0.000) decreased by a factor of 0.8 and 0.15, respectively.The IMRT group plans were superior to the CDR-CAS-IMAT group plans considering decreasing bladder V50 (17.4 ± 4.5% vs.16.6 ± 4.2%, P =0.049), bowel V30 (39.6 ± 6.5% vs.36.6 ± 7.5%, P =0.008), and low-dose irradiation volume;there were no significant differences in other statistical indexes.Conclusions: Patients with cervical

  18. Implementation of Constant Dose Rate and Constant Angular Spacing Intensity-modulated Arc Therapy for Cervical Cancer by Using a Conventional Linear Accelerator

    Science.gov (United States)

    Zhang, Ruo-Hui; Fan, Xiao-Mei; Bai, Wen-Wen; Cao, Yan-Kun

    2016-01-01

    Background: Volumetric-modulated arc therapy (VMAT) can only be implemented on the new generation linacs such as the Varian Trilogy® and Elekta Synergy®. This prevents most existing linacs from delivering VMAT. The purpose of this study was to investigate the feasibility of using a conventional linear accelerator delivering constant dose rate and constant angular spacing intensity-modulated arc therapy (CDR-CAS-IMAT) for treating cervical cancer. Methods: Twenty patients with cervical cancer previously treated with intensity-modulated radiation therapy (IMRT) using Varian Clinical 23EX were retreated using CDR-CAS-IMAT. The planning target volume (PTV) was set as 50.4 Gy in 28 fractions. Plans were evaluated based on the ability to meet the dose volume histogram. The homogeneity index (HI), target volume conformity index (CI), the dose to organs at risk, radiation delivery time, and monitor units (MUs) were also compared. The paired t-test was used to analyze the two data sets. All statistical analyses were performed using SPSS 19.0 software. Results: Compared to the IMRT group, the CDR-CAS-IMAT group showed better PTV CI (0.85 ± 0.03 vs. 0.81 ± 0.03, P = 0.001), clinical target volume CI (0.46 ± 0.05 vs. 0.43 ± 0.05, P = 0.001), HI (0.09±0.02 vs. 0.11 ± 0.02, P = 0.005) and D95 (5196.33 ± 28.24 cGy vs. 5162.63 ± 31.12 cGy, P = 0.000), and cord D2 (3743.8 ± 118.7 cGy vs. 3806.2 ± 98.7 cGy, P = 0.017) and rectum V40 (41.9 ± 6.1% vs. 44.2 ± 4.8%, P = 0.026). Treatment time (422.7 ± 46.7 s vs. 84.6 ± 7.8 s, P = 0.000) and the total plan Mus (927.4 ± 79.1 vs. 787.5 ± 78.5, P = 0.000) decreased by a factor of 0.8 and 0.15, respectively. The IMRT group plans were superior to the CDR-CAS-IMAT group plans considering decreasing bladder V50 (17.4 ± 4.5% vs. 16.6 ± 4.2%, P = 0.049), bowel V30 (39.6 ± 6.5% vs. 36.6 ± 7.5%, P = 0.008), and low-dose irradiation volume; there were no significant differences in other statistical indexes. Conclusions

  19. Tempo of Diversification of Global Amphibians: One-Constant Rate, One-Continuous Shift or Multiple-Discrete Shifts?

    Directory of Open Access Journals (Sweden)

    Youhua Chen

    2014-01-01

    Full Text Available In this brief report, alternative time-varying diversification rate models were fitted onto the phylogeny of global amphibians by considering one-constant-rate (OCR, one-continuous-shift (OCS and multiplediscrete- shifts (MDS situations. The OCS diversification model was rejected by γ statistic (γ=-5.556, p⁄ 0.001, implying the existence of shifting diversification rates for global amphibian phylogeny. Through model selection, MDS diversification model outperformed OCS and OCR models using “laser” package under R environment. Moreover, MDS models, implemented using another R package “MEDUSA”, indicated that there were sixteen shifts over the internal nodes for amphibian phylogeny. Conclusively, both OCS and MDS models are recommended to compare so as to better quantify rate-shifting trends of species diversification. MDS diversification models should be preferential for large phylogenies using “MEDUSA” package in which any arbitrary numbers of shifts are allowed to model.

  20. Preference and resistance to change with constant- and variable-duration terminal links: independence of reinforcement rate and magnitude.

    Science.gov (United States)

    Grace, Randolph C; Bedell, Melissa A; Nevin, John A

    2002-05-01

    Pigeons responded in a three-component multiple concurrent-chains procedure in which the variable-interval reinforcement schedules were the same across components but magnitudes differed across components. The terminal links were arranged either as a variable delay followed by presentation of a reinforcer ("variable duration") or as a fixed period of access to the schedule during which a variable number of reinforcers could be earned ("constant duration"). Relative reinforcement rate was varied parametrically across both types of conditions. After baseline training in each condition, resistance to change of terminal-link responding was assessed by delivering food during the initial links according to a variable-time schedule. Both preference and resistance to change were more sensitive to reinforcement-rate differences in the constant-duration conditions. Sensitivities of preference and resistance to change to relative reinforcement rate did not change depending on relative reinforcement magnitude. Taken together, these results confirm and extend those of prior studies, and suggest that reinforcement rate and magnitude combine additively to determine preference and resistance to change. A single structural relation linking preference and resistance to change describes all the data from this and several related studies.

  1. Theoretical determination of chemical rate constants using novel time-dependent methods

    Science.gov (United States)

    Dateo, Christopher E.

    1994-01-01

    The work completed within the grant period 10/1/91 through 12/31/93 falls primarily in the area of reaction dynamics using both quantum and classical mechanical methodologies. Essentially four projects have been completed and have been or are in preparation of being published. The majority of time was spent in the determination of reaction rate coefficients in the area of hydrocarbon fuel combustion reactions which are relevant to NASA's High Speed Research Program (HSRP). These reaction coefficients are important in the design of novel jet engines with low NOx emissions, which through a series of catalytic reactions contribute to the deterioration of the earth's ozone layer. A second area of research studied concerned the control of chemical reactivity using ultrashort (femtosecond) laser pulses. Recent advances in pulsed-laser technologies have opened up a vast new field to be investigated both experimentally and theoretically. The photodissociation of molecules adsorbed on surfaces using novel time-independent quantum mechanical methods was a third project. And finally, using state-of-the-art, high level ab initio electronic structure methods in conjunction with accurate quantum dynamical methods, the rovibrational energy levels of a triatomic molecule with two nonhydrogen atoms (HCN) were calculated to unprecedented levels of agreement between theory and experiment.

  2. Variational RRKM calculation of thermal rate constant for C–H bond fission reaction of nitro methane

    Directory of Open Access Journals (Sweden)

    Afshin Taghva Manesh

    2017-02-01

    Full Text Available The present work provides quantitative results for the rate constants of unimolecular C–H bond fission reactions in the nitro methane at elevated temperatures up to 2000 K. In fact, there are three different hydrogen atoms in the nitro methane. The potential energy surface for each C–H bond fission reaction of nitro methane was investigated by ab initio calculations. The geometry and vibrational frequencies of the species involved in this process were optimized at the MP2 level of theory, using the cc-pvdz basis set. Since C–H bond fission channel is a barrierless reaction, we have used variational RRKM theory to predict rate coefficients. By means of calculated rate coefficients at different temperatures, the Arrhenius expression of the channel over the temperature range of 100–2000 K is k(T = 5.9E19∗exp(−56274.6/T.

  3. An optimal policy for deteriorating items with time-proportional deterioration rate and constant and time-dependent linear demand rate

    Science.gov (United States)

    Singh, Trailokyanath; Mishra, Pandit Jagatananda; Pattanayak, Hadibandhu

    2017-04-01

    In this paper, an economic order quantity (EOQ) inventory model for a deteriorating item is developed with the following characteristics: (i) The demand rate is deterministic and two-staged, i.e., it is constant in first part of the cycle and linear function of time in the second part. (ii) Deterioration rate is time-proportional. (iii) Shortages are not allowed to occur. The optimal cycle time and the optimal order quantity have been derived by minimizing the total average cost. A simple solution procedure is provided to illustrate the proposed model. The article concludes with a numerical example and sensitivity analysis of various parameters as illustrations of the theoretical results.

  4. [Determination of rate constants of gas-phase reactions of alpha-pinene and beta-pinene with ozone].

    Science.gov (United States)

    Liu, Z R; Hu, D

    2001-10-01

    alpha-pinene and beta-pinene are the most dominating species among natural terpenes. Terpenes are mainly emitted from forest trees, flowers and grass. In the lower troposphere terpenes can react fast with OH radical, ozone, NO3 radical and ground state oxygen atom. These reactions may contribute to the occurring of aerosols, peroxides (hydrogen peroxide and organic peroxide), carbon cycle (mainly CO), acid rain (organic acids, NO3- and SO4(2-), ozone and active radicals such as OH radical. Reactions with ozone occur both in the daytime and in the night. The study in this field in China began in the late 1980. The main work focus on the source emission and the experimental simulation has just started. It is most of our group's work. In this paper preliminary experimental simulation of the gas-phase reactions of alpha-pinene and beta-pinene with ozone were carried out in the quartz chamber. The rate constants of these reactions were measured using long-path Fourier transform infra-red combined with relative rate constant method. And the rate constants for the gas-phase reactions of alpha-pinene, beta-pinene with ozone were determined as 2.83 x 10(17) cm3.molecule-1.s-1 and 1.48 x 10(17) cm3.molecule-1.s-1 at 1.0 x 10(5) Pa and 296 +/- 3 K. The results are quite similar to the data from Atkinson group. No cyclohexane was added to the reaction system during the measurement to restrain the formation of OH radical. The formation of OH radical could not be quantified, so that the effect of subsidiary reactions induced by OH radical has not been calculated. In the later simulation study and model this effect should be considered.

  5. Creatine kinase rate constant in the human heart measured with 3D‐localization at 7 tesla

    Science.gov (United States)

    Robson, Matthew D.; Neubauer, Stefan; Rodgers, Christopher T.

    2016-01-01

    Purpose We present a new Bloch‐Siegert four Angle Saturation Transfer (BOAST) method for measuring the creatine kinase (CK) first‐order effective rate constant kf in human myocardium at 7 tesla (T). BOAST combines a variant of the four‐angle saturation transfer (FAST) method using amplitude‐modulated radiofrequency pulses, phosphorus Bloch‐Siegert B1+‐mapping to determine the per‐voxel flip angles, and nonlinear fitting to Bloch simulations for postprocessing. Methods Optimal flip angles and repetition time parameters were determined from Monte Carlo simulations. BOAST was validated in the calf muscle of two volunteers at 3T and 7T. The myocardial CK forward rate constant was then measured in 10 volunteers at 7T in 82 min (after 1H localization). Results BOAST kfCK values were 0.281 ± 0.002 s−1 in the calf and 0.35 ± 0.05 s−1 in myocardium. These are consistent with literature values from lower fields. Using a literature values for adenosine triphosphate concentration, we computed CK flux values of 4.55 ± 1.52 mmol kg−1 s−1. The sensitive volume for BOAST depends on the B1 inhomogeneity of the transmit coil. Conclusion BOAST enables measurement of the CK rate constant in the human heart at 7T, with spatial localization in three dimensions to 5.6 mL voxels, using a 10‐cm loop coil. Magn Reson Med 78:20–32, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. PMID:27579566

  6. Non-steady state mass action dynamics without rate constants: dynamics of coupled reactions using chemical potentials

    Science.gov (United States)

    Cannon, William R.; Baker, Scott E.

    2017-10-01

    Comprehensive and predictive simulation of coupled reaction networks has long been a goal of biology and other fields. Currently, metabolic network models that utilize enzyme mass action kinetics have predictive power but are limited in scope and application by the fact that the determination of enzyme rate constants is laborious and low throughput. We present a statistical thermodynamic formulation of the law of mass action for coupled reactions at both steady states and non-stationary states. The formulation uses chemical potentials instead of rate constants. When used to model deterministic systems, the method corresponds to a rescaling of the time dependent reactions in such a way that steady states can be reached on the same time scale but with significantly fewer computational steps. The relationships between reaction affinities, free energy changes and generalized detailed balance are central to the discussion. The significance for applications in systems biology are discussed as is the concept and assumption of maximum entropy production rate as a biological principle that links thermodynamics to natural selection.

  7. An independent constraint on the secular rate of variation of the gravitational constant from pulsating white dwarfs

    CERN Document Server

    Córsico, Alejandro H; García-Berro, Enrique; Romero, Alejandra D

    2013-01-01

    A secular variation of the gravitational constant modifies the structure and evolutionary time scales of white dwarfs. Using an state-of-the-art stellar evolutionary code and an up-to-date pulsational code we compute the effects of a secularly varying $G$ on the pulsational properties of variable white dwarfs. Comparing the the theoretical results obtained taking into account the effects of a running $G$ with the observed periods and measured rates of change of the periods of two well studied pulsating white dwarfs, G117--B15A and R548, we place constraints on the rate of variation of Newton's constant. We derive an upper bound $\\dot G/G\\sim -1.8\\times 10^{-10}$ yr$^{-1}$ using the variable white dwarf G117--B15A, and $\\dot G/G\\sim -1.3\\times 10^{-10}$ yr$^{-1}$ using R548. Although these upper limits are currently less restrictive than those obtained using other techniques, they can be improved in a future measuring the rate of change of the period of massive white dwarfs.

  8. An independent constraint on the secular rate of variation of the gravitational constant from pulsating white dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Córsico, Alejandro H.; Althaus, Leandro G. [Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, (1900) La Plata (Argentina); García-Berro, Enrique [Departament de Física Aplicada, Universitat Politècnica de Catalunya, c/Esteve Terrades, 5, 08860 Castelldefels (Spain); Romero, Alejandra D., E-mail: acorsico@fcaglp.unlp.edu.ar, E-mail: althaus@fcaglp.unlp.edu.ar, E-mail: enrique.garcia-berro@upc.edu, E-mail: alejandra.romero@ufrgs.br [Departamento de Astronomia, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, Porto Alegre 91501-970, RS (Brazil)

    2013-06-01

    A secular variation of the gravitational constant modifies the structure and evolutionary time scales of white dwarfs. Using an state-of-the-art stellar evolutionary code and an up-to-date pulsational code we compute the effects of a secularly varying G on the pulsational properties of variable white dwarfs. Comparing the the theoretical results obtained taking into account the effects of a running G with the observed periods and measured rates of change of the periods of two well studied pulsating white dwarfs, G117-B15A and R548, we place constraints on the rate of variation of Newton's constant. We derive an upper bound Ġ/G ∼ −1.8 × 10{sup −10} yr{sup −1} using the variable white dwarf G117-B15A, and Ġ/G ∼ −1.3 × 10{sup −10} yr{sup −1} using R548. Although these upper limits are currently less restrictive than those obtained using other techniques, they can be improved in a future measuring the rate of change of the period of massive white dwarfs.

  9. Rate constants and isotope effects for the reaction of H-atom abstraction from RH substrates by PINO radicals

    Science.gov (United States)

    Opeida, I. A.; Litvinov, Yu. E.; Kushch, O. V.; Kompanets, M. A.; Shendrik, A. N.; Matvienko, A. G.; Novokhatko, A. A.

    2016-11-01

    The kinetics of the reactions of hydrogen atom abstraction from the C-H bonds of substrates of different structures by phthalimide- N-oxyl radicals is studied. The rate constants of this reaction are measured and the kinetic isotope effects are determined. It is shown that in addition to the thermodynamic factor, Coulomb forces and donor-acceptor interactions affect the reaction between phthalimide- N-oxyl radicals and substrate molecules, altering the shape of the transition state. This favors the tunneling of hydrogen atoms and leads to a substantial reduction in the activation energy of the process.

  10. Measurement of rate constant for gas-phase reaction of DDVP with OH radical by using LP-FTIR

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Pollution caused by organic pesticides has received increasing attention. Until now, studies on organic pesticides pollution are mainly focused on soil and water. For reactions of organic pesticides in gas-phase, there are very little research results reported. Using a long path quartz reactor to simulate the atmospheric reaction of dimethyl_dichloro_vinyl_phosphate(DDVP) with OH radicals, the rate constant for the reaction at room temperature is measured at (3.06±0.46)×10-11 cm3 s-1 with Fourier transform infrared spectrograph.The result indicates that DDVP degrades relatively fast in the atmosphere and is unlikely to cause persistent pollution.

  11. Non-radiative decay of a dipole emitter close to a metallic nanoparticle: Importance of higher-order multipole contributions

    CERN Document Server

    Moroz, Alexander

    2009-01-01

    The contribution of higher-order multipoles to radiative and non-radiative decay of a single dipole emitter close to a spherical metallic nanoparticle is re-examined. Taking a Ag spherical nanoparticle (AgNP) with the radius of 5 nm as an example, a significant contribution (between 50% and 101% of the total value) of higher-order multipoles to non-radiative rates is found even at the emitter distance of 5 nm from the AgNP surface. On the other hand, the higher-order multipole contribution to radiative rates is negligible. Consequently, a dipole-dipole approximation can yield only an upper bound on the apparent quantum yield. In contrast, the non-radiative rates calculated with the quasistatic Gersten and Nitzan method are found to be in much better agreement with exact electrodynamic results. Finally, the size corrected metal dielectric function is shown to decrease the non-radiative rates near the dipolar surface plasmon resonance.

  12. The Effect of Trailing Vortices on the Production of Lift on an Airfoil Undergoing a Constant Rate of Change of Angle of Attack.

    Science.gov (United States)

    1983-12-01

    The purpose of this study was to investigate the effect a trailing vortex wake has on an airfoil undergoing a constant rate of change of angle of...When applied to the constant rate - of - change of angle-of-attack problem, the results showed that a trailing vortex wake has a measurable and

  13. Rate Constants and Deuterium Kinetic Isotope Effects for Methoxy Radical Reacting with NO_2 and O_2

    Science.gov (United States)

    Chai, J.; Hu, H.; Dibble, T. S.; Tyndall, G. S.; Orlando, J. J.

    2013-06-01

    Alkoxy radicals (RO) are important intermediates in the photooxidation of volatile organic compounds due to their great impacts on ozone formation and gas-particle partitioning of stable oxidation products. Methoxy radical (CH_3O) is the prototype for all alkoxy radicals. The absolute rate constants k_N_O_2(T) for reaction of CH_3O and CD_3O with NO_2 have been measured using laser flash photolysis to generate radicals and laser-induced fluorescence for time-resolved detection. The pressure and temperature dependence for k_N_O_2 have been observed over the range 30-700 Torr and 250-335 K. This will be the first direct measurement of k_N_O_2 for CH_3O near ambient pressure and the first ever for CD_3O.The relative rate constants k_N_O_2/k_O_2(T) have been measured in an environmental chamber with FTIR detection. This combination enables the first determination of k_O_2 (T) for CH_3O and CD_3O for T < 298 K. The results will also help validate theoretical methods for studying alkoxy + O_2 reactions, which are challenging for quantum chemistry.

  14. Optical factors determined by the T-matrix method in turbidity measurement of absolute coagulation rate constants.

    Science.gov (United States)

    Xu, Shenghua; Liu, Jie; Sun, Zhiwei

    2006-12-01

    Turbidity measurement for the absolute coagulation rate constants of suspensions has been extensively adopted because of its simplicity and easy implementation. A key factor in deriving the rate constant from experimental data is how to theoretically evaluate the so-called optical factor involved in calculating the extinction cross section of doublets formed during aggregation. In a previous paper, we have shown that compared with other theoretical approaches, the T-matrix method provides a robust solution to this problem and is effective in extending the applicability range of the turbidity methodology, as well as increasing measurement accuracy. This paper will provide a more comprehensive discussion of the physical insight for using the T-matrix method in turbidity measurement and associated technical details. In particular, the importance of ensuring the correct value for the refractive indices for colloidal particles and the surrounding medium used in the calculation is addressed, because the indices generally vary with the wavelength of the incident light. The comparison of calculated results with experiments shows that the T-matrix method can correctly calculate optical factors even for large particles, whereas other existing theories cannot. In addition, the data of the optical factor calculated by the T-matrix method for a range of particle radii and incident light wavelengths are listed.

  15. Hydroxyl-radical-induced degradative oxidation of beta-lactam antibiotics in water: absolute rate constant measurements.

    Science.gov (United States)

    Dail, Michelle K; Mezyk, Stephen P

    2010-08-19

    The beta-lactam antibiotics are some of the most prevalent pharmaceutical contaminants currently being detected in aquatic environments. Because the presence of any trace level of antibiotic in water may adversely affect aquatic ecosystems and contribute to the production of antibiotic-resistant bacteria, active removal by additional water treatments, such as using advanced oxidation and reduction processes (AO/RPs), may be required. However, to ensure that any AOP treatment process occurs efficiently and quantitatively, a full understanding of the kinetics and mechanisms of all of the chemical reactions involved under the conditions of use is necessary. In this study, we report on our kinetic measurements for the hydroxyl-radical-induced oxidation of 11 beta-lactam antibiotics obtained using electron pulse radiolysis techniques. For the 5-member ring species, an average reaction rate constant of (7.9 +/- 0.8) x 10(9) M(-1) s(-1) was obtained, slightly faster than for the analogous 6-member ring containing antibiotics, (6.6 +/- 1.2) x 10(9) M(-1) s(-1). The consistency of these rate constants for each group infers a common reaction mechanism, consisting of the partitioning of the hydroxyl radical between addition to peripheral aromatic rings and reaction with the central double-ring core of these antibiotics.

  16. KiSThelP: a program to predict thermodynamic properties and rate constants from quantum chemistry results.

    Science.gov (United States)

    Canneaux, Sébastien; Bohr, Frédéric; Henon, Eric

    2014-01-05

    Kinetic and Statistical Thermodynamical Package (KiSThelP) is a cross-platform free open-source program developed to estimate molecular and reaction properties from electronic structure data. To date, three computational chemistry software formats are supported (Gaussian, GAMESS, and NWChem). Some key features are: gas-phase molecular thermodynamic properties (offering hindered rotor treatment), thermal equilibrium constants, transition state theory rate coefficients (transition state theory (TST), variational transition state theory (VTST)) including one-dimensional (1D) tunnelling effects (Wigner, and Eckart) and Rice-Ramsperger-Kassel-Marcus (RRKM) rate constants, for elementary reactions with well-defined barriers. KiSThelP is intended as a working tool both for the general public and also for more expert users. It provides graphical front-end capabilities designed to facilitate calculations and interpreting results. KiSThelP enables to change input data and simulation parameters directly through the graphical user interface and to visually probe how it affects results. Users can access results in the form of graphs and tables. The graphical tool offers customizing of 2D plots, exporting images and data files. These features make this program also well-suited to support and enhance students learning and can serve as a very attractive courseware, taking the teaching content directly from results in molecular and kinetic modelling. © 2013 Wiley Periodicals, Inc.

  17. Tissue vitamin concentrations are maintained constant by changing the urinary excretion rate of vitamins in rats' restricted food intake.

    Science.gov (United States)

    Shibata, Katsumi; Fukuwatari, Tsutomu

    2014-01-01

    We previously reported that mild food restriction induces a reduction in tryptophan-nicotinamide conversion, which helps to explain why death secondary to pellagra is pandemic during the hungry season. In this study, we investigated the levels of B-group vitamins in the liver, kidney, blood, and urine in rats that underwent gradual restriction of food intake (80, 60, 40, and 20% restriction vs. ad libitum food intake). No significant differences in the B-group vitamin concentrations (mol/g tissue) in the liver and kidney were observed at any level of food restriction. However, the urine excretion rates exhibited some characteristic phenomena that differed by vitamin. These results show that the tissue concentrations of B-group vitamins were kept constant by changing the urinary elimination rates of vitamins under various levels of food restriction. Only vitamin B12 was the only (exception).

  18. Apparent activation energy for densification of -Al2O3 powder at constant heating-rate sintering

    Indian Academy of Sciences (India)

    W Q Shao; S O Chen; D Li; H S Cao; Y C Zhang; S S Zhang

    2008-11-01

    The apparent activation energy for densification is a characteristic quantity that elucidates the fundamental diffusion mechanisms during the sintering process. Based on the Arrhenius theory, the activation energy for densification of -Al2O3 at constant heating-rates sintering has been estimated. Sintering of -Al2O3 powder has been executed by the way of a push rod type dilatometer. It is shown that the apparent activation energy does not have a single value but depends directly on the relative density. The apparent activation energy corresponding to lower relative density was higher than that corresponding to higher relative density. In addition, the value of the evaluated activation energy is different at the same density level when the Arrhenius plot involves different heating rates.

  19. Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 2; Constant Stress Rate Experiments

    Science.gov (United States)

    Choi, Sung R.; Nemeth, Noel N.; Gyekenyesi, John P.

    2002-01-01

    The previously determined life prediction analysis based on an exponential crack-velocity formulation was examined using a variety of experimental data on glass and advanced structural ceramics in constant stress rate and preload testing at ambient and elevated temperatures. The data fit to the relation of strength versus the log of the stress rate was very reasonable for most of the materials. Also, the preloading technique was determined equally applicable to the case of slow-crack-growth (SCG) parameter n greater than 30 for both the power-law and exponential formulations. The major limitation in the exponential crack-velocity formulation, however, was that the inert strength of a material must be known a priori to evaluate the important SCG parameter n, a significant drawback as compared with the conventional power-law crack-velocity formulation.

  20. Carbofuran removal in continuous-photocatalytic reactor: Reactor optimization, rate-constant determination and carbofuran degradation pathway analysis.

    Science.gov (United States)

    Vishnuganth, M A; Remya, Neelancherry; Kumar, Mathava; Selvaraju, N

    2017-02-22

    Carbofuran (CBF) removal in a continuous-flow photocatalytic reactor with granular activated carbon supported titanium dioxide (GAC-TiO2) catalyst was investigated. The effects of feed flow rate, TiO2 concentration and addition of supplementary oxidants on CBF removal were investigated. The central composite design (CCD) was used to design the experiments and to estimate the effects of feed flow rate and TiO2 concentration on CBF removal. The outcome of CCD experiments demonstrated that reactor performance was influenced mainly by feed flow rate compared to TiO2 concentration. A second-order polynomial model developed based on CCD experiments fitted the experimental data with good correlation (R(2) ∼ 0.964). The addition of 1 mL min(-1) hydrogen peroxide has shown complete CBF degradation and 76% chemical oxygen demand removal under the following operating conditions of CBF ∼50 mg L(-1), TiO2 ∼5 mg L(-1) and feed flow rate ∼82.5 mL min(-1). Rate constant of the photodegradation process was also calculated by applying the kinetic data in pseudo-first-order kinetics. Four major degradation intermediates of CBF were identified using GC-MS analysis. As a whole, the reactor system and GAC-TiO2 catalyst used could be constructive in cost-effective CBF removal with no impact to receiving environment through getaway of photocatalyst.

  1. Kinetics of the transformation of phenyl-urea herbicides during ozonation of natural waters: rate constants and model predictions.

    Science.gov (United States)

    Benitez, F Javier; Real, Francisco J; Acero, Juan L; Garcia, Carolina

    2007-10-01

    Oxidation of four phenyl-urea herbicides (isoproturon, chlortoluron, diuron, and linuron) was studied by ozone at pH=2, and by a combination of O3/H2O2 at pH=9. These experiments allowed the determination of the rate constants for their reactions with ozone and OH radicals. For reactions with ozone, the following rate constants were obtained: 1.9 +/- 0.2, 16.5 +/- 0.6, 393.5 +/- 8.4, and 2191 +/- 259 M(-1) s(-1) for linuron, diuron, chlortoluron, and isoproturon, respectively. The rate constants for the reaction with OH radicals were (7.9 +/- 0.1) x 10(9) M(-1) s(-1) for isoproturon, (6.9 +/- 0.2) x 10(9) M(-1) s(-1) for chlortoluron, (6.6 +/- 0.1) x 10(5) M(-1) s(-1) for diuron, and (5.9 +/- 0.1) x 10(9) M(-1) s(-1) for linuron. Furthermore, the simultaneous ozonation of these selected herbicides in some natural water systems (a commercial mineral water, a groundwater, and surface water from a reservoir) was studied. The influence of operating conditions (initial ozone dose, nature of herbicides, and type of water systems) on herbicide removal efficiency was established, and the parameter Rct (proposed by Elovitz, M.S., von Gunten, U., 1999. Hydroxyl radical/ozone ratios during ozonation processes. I. The Rct concept. Ozone Sci. Eng. 21, 239-260) was evaluated from simultaneous measurement of ozone and OH radicals. A kinetic model was proposed for the prediction of the elimination rate of herbicides in these natural waters, and application of this model revealed that experimental results and predicted values agreed fairly well. Finally, the partial contributions of direct ozone and radical pathways were evaluated, and the results showed that reaction with OH radicals was the major pathway for the oxidative transformation of diuron and linuron, even when conventional ozonation was applied, while for chlortoluron and isoproturon, direct ozonation was the major pathway.

  2. Latitude distribution of nonradial pulsations in rapidly rotating B stars

    Science.gov (United States)

    Jankov, S.; Mathias, P.; Domiciano de Souza, A., Jr.; Uytterhoeven, K.; Aerts, C.

    2004-05-01

    We present a method for the analysis of latitude distribution associated with temperature and/or velocity perturbations of the stellar surface due to non-radial pulsation (NRP) modes in rapidly rotating B stars. The technique is applied together with Fourier Doppler Imaging (FDI) to high resolution and high signal-to-noise ratio spectroscopic observations of ɛ Per. The main advantage of this approach is that it decomposed complex multi-periodic line profile variations into single components, allowing the detailed analysis of each mode seperately. We study the 10.6-d-1 frequency that is particularly important for modal analysis of non-radial pulsations in the star.

  3. Two-level renegotiated constant bit rate algorithm (2RCBR) for scalable MPEG2 video over QoS networks

    Science.gov (United States)

    Pegueroles, Josep R.; Alins, Juan J.; de la Cruz, Luis J.; Mata, Jorge

    2001-07-01

    MPEG family codecs generate variable-bit-rate (VBR) compressed video with significant multiple-time-scale bit rate variability. Smoothing techniques remove the periodic fluctuations generated by the codification modes. However, global efficiency concerning network resource allocation remains low due to scene-time-scale variability. RCBR techniques provide suitable means to achieving higher efficiency. Among all RCBR techniques described in literature, 2RCBR mechanism seems to be especially suitable for video-on demand. The method takes advantage of the knowledge of the stored video to calculate the renegotiation intervals and of the client buffer memory to perform work-ahead buffering techniques. 2RCBR achieves 100% bandwidth global efficiency with only two renegotiation levels. The algorithm is based on the study of the second derivative of the cumulative video sequence to find out sharp-sloped inflection points that point out changes in the scene complexity. Due to its nature, 2RCBR becomes very adequate to deliver MPEG2 scalable sequences into the network cause it can assure a constant bit rate to the base MPEG2 layer and use the higher rate intervals to deliver the enhanced MPEG2 layer. However, slight changes in the algorithm parameters must be introduced to attain an optimal behavior. This is verified by means of simulations on MPEG2 video patterns.

  4. Creatine kinase rate constant in the human heart measured with 3D-localization at 7 tesla.

    Science.gov (United States)

    Clarke, William T; Robson, Matthew D; Neubauer, Stefan; Rodgers, Christopher T

    2017-07-01

    We present a new Bloch-Siegert four Angle Saturation Transfer (BOAST) method for measuring the creatine kinase (CK) first-order effective rate constant kf in human myocardium at 7 tesla (T). BOAST combines a variant of the four-angle saturation transfer (FAST) method using amplitude-modulated radiofrequency pulses, phosphorus Bloch-Siegert B1+-mapping to determine the per-voxel flip angles, and nonlinear fitting to Bloch simulations for postprocessing. Optimal flip angles and repetition time parameters were determined from Monte Carlo simulations. BOAST was validated in the calf muscle of two volunteers at 3T and 7T. The myocardial CK forward rate constant was then measured in 10 volunteers at 7T in 82 min (after (1) H localization). BOAST kfCK values were 0.281 ± 0.002 s(-1) in the calf and 0.35 ± 0.05 s(-1) in myocardium. These are consistent with literature values from lower fields. Using a literature values for adenosine triphosphate concentration, we computed CK flux values of 4.55 ± 1.52 mmol kg(-1) s(-1) . The sensitive volume for BOAST depends on the B1 inhomogeneity of the transmit coil. BOAST enables measurement of the CK rate constant in the human heart at 7T, with spatial localization in three dimensions to 5.6 mL voxels, using a 10-cm loop coil. Magn Reson Med 78:20-32, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

  5. Estimation of the plasma effect site equilibration rate constant of sufentanil in children using the time to peak effect of heart rate and blood pressure.

    Science.gov (United States)

    Song, In-Kyung; Lee, Ji-Hyun; Jung, SungAe; Kim, Jin-Tae; Kim, Hee-Soo

    2015-01-01

    Although targeting the effect site concentration may offer advantages over the traditional forms of administering intravenous anesthetics, it is not applicable for sufentanil in children because its plasma effect site equilibration rate constant (ke0) is not known yet. We estimated ke0 of sufentanil in children using the time to peak effect (t peak) method. Under general anesthesia, sufentanil t peak was measured after administration of a submaximal bolus dose by means of the decrease in heart rate, blood pressure and calculated approximate entropy (ApEn) of electroencephalogram in 105 children (age range: 3-11 years). ke0 was estimated using t peak and known sufentanil pharmacokinetic parameters in normal children. The mean t peaks were measured as 44 ± 22 s and 227 ± 91 s by heart rate and by mean blood pressure respectively. The estimated ke0 were 5.16/min and 0.49/min by heart rate and blood pressure respectively. t peak could not be measured using the ApEn, thus ke0 could not be calculated by ApEn in children. Shorter measured sufentanil t peak by heart rate compared to blood pressure indicate that the heart rate decrease faster than decreasing of blood pressure. Moreover, the calculated sufentanil ke0 in children depends on the pharmacodynamics parameters.

  6. Calculated Third Order Rate Constants for Interpreting the Mechanisms of Hydrolyses of Chloroformates, Carboxylic Acid Halides, Sulfonyl Chlorides and Phosphorochloridates

    Directory of Open Access Journals (Sweden)

    T. William Bentley

    2015-05-01

    Full Text Available Hydrolyses of acid derivatives (e.g., carboxylic acid chlorides and fluorides, fluoro- and chloroformates, sulfonyl chlorides, phosphorochloridates, anhydrides exhibit pseudo-first order kinetics. Reaction mechanisms vary from those involving a cationic intermediate (SN1 to concerted SN2 processes, and further to third order reactions, in which one solvent molecule acts as the attacking nucleophile and a second molecule acts as a general base catalyst. A unified framework is discussed, in which there are two reaction channels—an SN1-SN2 spectrum and an SN2-SN3 spectrum. Third order rate constants (k3 are calculated for solvolytic reactions in a wide range of compositions of acetone-water mixtures, and are shown to be either approximately constant or correlated with the Grunwald-Winstein Y parameter. These data and kinetic solvent isotope effects, provide the experimental evidence for the SN2-SN3 spectrum (e.g., for chloro- and fluoroformates, chloroacetyl chloride, p-nitrobenzoyl p-toluenesulfonate, sulfonyl chlorides. Deviations from linearity lead to U- or V-shaped plots, which assist in the identification of the point at which the reaction channel changes from SN2-SN3 to SN1-SN2 (e.g., for benzoyl chloride.

  7. A molecular copper catalyst for electrochemical water reduction with a large hydrogen-generation rate constant in aqueous solution.

    Science.gov (United States)

    Zhang, Peili; Wang, Mei; Yang, Yong; Yao, Tianyi; Sun, Licheng

    2014-12-08

    The copper complex [(bztpen)Cu](BF4)2 (bztpen=N-benzyl-N,N',N'-tris(pyridin-2-ylmethyl)ethylenediamine) displays high catalytic activity for electrochemical proton reduction in acidic aqueous solutions, with a calculated hydrogen-generation rate constant (k(obs)) of over 10000 s(-1). A turnover frequency (TOF) of 7000 h(-1) cm(-2) and a Faradaic efficiency of 96% were obtained from a controlled potential electrolysis (CPE) experiment with [(bztpen)Cu](2+) in pH 2.5 buffer solution at -0.90 V versus the standard hydrogen electrode (SHE) over two hours using a glassy carbon electrode. A mechanism involving two proton-coupled reduction steps was proposed for the dihydrogen generation reaction catalyzed by [(bztpen)Cu](2+).

  8. Comparison of ultrasonic degradation rates constants of methylene blue at 22.8 kHz, 127 kHz, and 490 kHz.

    Science.gov (United States)

    Kobayashi, Daisuke; Honma, Chiemi; Suzuki, Atsushi; Takahashi, Tomoki; Matsumoto, Hideyuki; Kuroda, Chiaki; Otake, Katsuto; Shono, Atsushi

    2012-07-01

    Techniques such as solvent extraction, incineration, chemical dehalogenation, and biodegradation have been investigated for the degradation of hazardous organic compounds. We found ultrasound to be an attractive technology for the degradation of hazardous organic compounds in water. However, the effects of ultrasonic frequency on degradation rate constants were not investigated quantitatively. In this study, the degradation process of a model for hazardous organic compound methylene blue was investigated using ultrasonic irradiation. The study focused on the effects of ultrasonic frequency and ultrasonic power on the degradation rate constant. The apparent degradation rate constants were estimated based on time dependence of methylene blue concentration assuming pseudo-first-order kinetics for the decomposition. A linear relationship between the apparent degradation rate constant and ultrasonic power was identified. In addition, the apparent degradation rate constants at frequencies of 127 and 490 kHz were much larger than those at 22.8 kHz. A relationship between the apparent degradation rate constant and the sonochemical efficiency value (SE value) was also found. Based on these results, a simple model for estimating the apparent degradation rate constant of methylene blue based on the ultrasonic power and the SE value is proposed in this study.

  9. Combination of poroelasticity theory and constant strain rate test in modelling land subsidence due to groundwater extraction

    Science.gov (United States)

    Pham, Tien Hung; Rühaak, Wolfram; Sass, Ingo

    2017-04-01

    Extensive groundwater extraction leads to a drawdown of the ground water table. Consequently, soil effective stress increases and can cause land subsidence. Analysis of land subsidence generally requires a numerical model based on poroelasticity theory, which was first proposed by Biot (1941). In the review of regional land subsidence accompanying groundwater extraction, Galloway and Burbey (2011) stated that more research and application is needed in coupling of stress-dependent land subsidence process. In geotechnical field, the constant rate of strain tests (CRS) was first introduced in 1969 (Smith and Wahls 1969) and was standardized in 1982 through the designation D4186-82 by American Society for Testing and Materials. From the reading values of CRS tests, the stress-dependent parameters of poroelasticity model can be calculated. So far, there is no research to link poroelasticity theory with CRS tests in modelling land subsidence due to groundwater extraction. One dimensional CRS tests using conventional compression cell and three dimension CRS tests using Rowe cell were performed. The tests were also modelled by using finite element method with mixed elements. Back analysis technique is used to find the suitable values of hydraulic conductivity and bulk modulus that depend on the stress or void ratio. Finally, the obtained results are used in land subsidence models. Biot, M. A. (1941). "General theory of three-dimensional consolidation." Journal of applied physics 12(2): 155-164. Galloway, D. L. and T. J. Burbey (2011). "Review: Regional land subsidence accompanying groundwater extraction." Hydrogeology Journal 19(8): 1459-1486. Smith, R. E. and H. E. Wahls (1969). "Consolidation under constant rates of strain." Journal of Soil Mechanics & Foundations Div.

  10. Model system-bath Hamiltonian and nonadiabatic rate constants for proton-coupled electron transfer at electrode-solution interfaces.

    Science.gov (United States)

    Navrotskaya, Irina; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2008-06-28

    An extension of the Anderson-Newns-Schmickler model for electrochemical proton-coupled electron transfer (PCET) is presented. This model describes reactions in which electron transfer between a solute complex in solution and an electrode is coupled to proton transfer within the solute complex. The model Hamiltonian is derived in a basis of electron-proton vibronic states defined within a double adiabatic approximation for the electrons, transferring proton, and bath modes. The interaction term responsible for electronic transitions between the solute complex and the electrode depends on the proton donor-acceptor vibrational mode within the solute complex. This model Hamiltonian is used to derive the anodic and cathodic rate constants for nonadiabatic electrochemical PCET. The derivation is based on the master equations for the reduced density matrix of the electron-proton subsystem, which includes the electrons of the solute complex and the electrode, as well as the transferring proton. The rate constant expressions differ from analogous expressions for electrochemical electron transfer because of the summation over electron-proton vibronic states and the dependence of the couplings on the proton donor-acceptor vibrational motion. These differences lead to additional contributions to the total reorganization energy, an additional exponential temperature-dependent prefactor, and a temperature-dependent term in the effective activation energy that has different signs for the anodic and cathodic processes. This model can be generalized to describe both nonadiabatic and adiabatic electrochemical PCET reactions and provides the framework for the inclusion of additional effects, such as the breaking and forming of other chemical bonds.

  11. Effects of a constant rate infusion of detomidine on cardiovascular function, isoflurane requirements and recovery quality in horses.

    Science.gov (United States)

    Schauvliege, Stijn; Marcilla, Miguel Gozalo; Verryken, Kirsten; Duchateau, Luc; Devisscher, Lindsey; Gasthuys, Frank

    2011-11-01

    To examine the influence of a detomidine constant rate infusion (CRI) on cardiovascular function, isoflurane requirements and recovery quality in horses undergoing elective surgery. Prospective, randomized, blinded, clinical trial. Twenty adult healthy horses. After sedation (detomidine, 10 μg kg(-1) intravenously [IV]) and induction of anaesthesia (midazolam 0.06 mg kg(-1) , ketamine 2.2 mg kg(-1) IV), anaesthesia was maintained with isoflurane in oxygen/air (inspiratory oxygen fraction 55%). When indicated, the lungs were mechanically ventilated. Dobutamine was administered when MAPquality and duration were recorded in each horse. For statistical analysis, anova, Pearson chi-square and Wilcoxon rank sum tests were used as relevant. Heart rate (p=0.0176) and ḊO(2) I (p= 0.0084) were lower and SVR higher (p=0.0126) in group D, compared to group S. Heart rate (p=0.0011) and pH (p=0.0187) increased over time. Significant differences in isoflurane requirements were not detected. Recovery quality and duration were comparable between treatments. A detomidine CRI produced cardiovascular effects typical for α(2) -agonists, without affecting isoflurane requirements, recovery duration or recovery quality. © 2011 The Authors. Veterinary Anaesthesia and Analgesia. © 2011 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists.

  12. Energy landscape analysis of native folding of the prion protein yields the diffusion constant, transition path time, and rates.

    Science.gov (United States)

    Yu, Hao; Gupta, Amar Nath; Liu, Xia; Neupane, Krishna; Brigley, Angela M; Sosova, Iveta; Woodside, Michael T

    2012-09-04

    Protein folding is described conceptually in terms of diffusion over a configurational free-energy landscape, typically reduced to a one-dimensional profile along a reaction coordinate. In principle, kinetic properties can be predicted directly from the landscape profile using Kramers theory for diffusive barrier crossing, including the folding rates and the transition time for crossing the barrier. Landscape theory has been widely applied to interpret the time scales for protein conformational dynamics, but protein folding rates and transition times have not been calculated directly from experimentally measured free-energy profiles. We characterized the energy landscape for native folding of the prion protein using force spectroscopy, measuring the change in extension of a single protein molecule at high resolution as it unfolded/refolded under tension. Key parameters describing the landscape profile were first recovered from the distributions of unfolding and refolding forces, allowing the diffusion constant for barrier crossing and the transition path time across the barrier to be calculated. The full landscape profile was then reconstructed from force-extension curves, revealing a double-well potential with an extended, partially unfolded transition state. The barrier height and position were consistent with the previous results. Finally, Kramers theory was used to predict the folding rates from the landscape profile, recovering the values observed experimentally both under tension and at zero force in ensemble experiments. These results demonstrate how advances in single-molecule theory and experiment are harnessing the power of landscape formalisms to describe quantitatively the mechanics of folding.

  13. Aging mathematical model of InGaN/GaN LEDs based on non-radiative recombination

    Science.gov (United States)

    Xu, Linwang; Qian, Keyuan

    2017-08-01

    This paper proposes a new aging mathematical model for InGaN/GaN-based light-emitting diodes (LEDs) based on non-radiative recombination. Light attenuation is an important index of the performance of LEDs, Arrhenius model as the main aging mathematical model of light attenuation is poorly targeted and cannot reflect the physical significance. Based on the physical theory of deep level defects and non-radiation recombination centers, we analyze the aging mechanism of LED chips and then establish the aging mathematical model. Meanwhile, a batch of GaN-based blue LED chips are selected to conduct accelerated life tests with constant current stresses, and the experimental data is obtained to verify the new model. The result shows that compared with the traditional Arrhenius model, the new model has many advantages such as more accurate, strong pertinence and obvious physical meaning.

  14. Oxygen consumption and heart rate responses during and after constant load and alternating intensity exercise at 105% of lactate threshold.

    Science.gov (United States)

    Spanoudaki, S; Karatzanos, E; Baltopoulos, P; Maridaki, M

    2015-12-01

    The purpose of this study was a secondary-analysis of previously published data, in order to compare the acute VO2 responses, the time spent at high percentage of VO2max and total VO2 consumed (TVO2) between constant and alternating intensity exercise of the same intensity and duration. This study also aimed to examine VO2 and heart rate (HR) responses one hour after both exercises. Ten recreationally trained men (24.7±4.7 years) completed the following two exercise tests lasting an hour each and having the same mean intensity at 105% of lactate threshold (70% VO2max): 1) constant load cycling (CON), and 2) alternating intensity exercise (ALT), during which 40 seconds of light exercise (47% VO2max) were alternated with 20 seconds of supramaximal intensity at 120% of VO2max. TVO2 (69.89±7.02 vs. 58.22±9.13 mL/kg/min, P=0.03) and HR (142±16, 128±12, P=0.04) was higher in CON exercise compared to ALT. All participants reached 70% and 80% of VO2max irrespective of the exercise protocol. In ALT exercise the time spent at 90% was higher compared to CON exercise (70.81±21.37 vs. 36.88±11.88 seconds). Also, TVO2 recovery values after ALT exercise was higher compared to CON (11.1 ±2.93 vs. 9.94±3.54 mL/kg/min). ALT exercise allowed participants to spend longer time at 90% of VO2max, even if TVO2 in CON exercise was higher, suggesting that in ALT exercise greater aerobic stress (as based on exercise intensity) is imposed on the athletes. While VO2 recovery values were higher in ALT compared to CON, indicating different substrate utilization during and after exercise.

  15. ESTIMATION OF HYDROLYSIS RATE CONSTANTS OF CARBOXYLIC ACID ESTER AND PHOSPHATE ESTER COMPOUNDS IN AQUEOUS SYSTEMS FROM MOLECULAR STRUCTURE BY SPARC

    Science.gov (United States)

    SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to calculate hydrolysis rate constants for carboxylic acid ester and phosphate ester compounds in aqueous non- aqueous and systems strictly from molecular structure. The energy diffe...

  16. SU-E-T-421: Feasibility Study of Volumetric Modulated Arc Therapy with Constant Dose Rate for Endometrial Cancer

    Energy Technology Data Exchange (ETDEWEB)

    Yang, R; Wang, J [Peking University Third Hospital, Beijing, Beijing (China)

    2014-06-01

    Purpose: To investigate the feasibility, efficiency, and delivery accuracy of volumetric modulated arc therapy with constant dose rate (VMAT-CDR) for whole-pelvic radiotherapy (WPRT) of endometrial cancer. Methods: The nine-Field intensity-modulated radiotherapy (IMRT), VMAT with variable dose-rate (VMAT-VDR), and VMAT-CDR plans were created for 9 patients with endometrial cancer undergoing WPRT. The dose distribution of planning target volume (PTV), organs at risk (OARs), and normal tissue (NT) were compared. The monitor units (MUs) and treatment delivery time were also evaluated. For each VMAT-CDR plan, a dry Run was performed to assess the dosimetric accuracy with MatriXX from IBA. Results: Compared with IMRT, the VMAT-CDR plans delivered a slightly greater V20 of the bowel, bladder, pelvis bone, and NT, but significantly decreased the dose to the high-dose region of the rectum and pelvis bone. The MUs Decreased from 1105 with IMRT to 628 with VMAT-CDR. The delivery time also decreased from 9.5 to 3.2 minutes. The average gamma pass rate was 95.6% at the 3%/3 mm criteria with MatriXX pretreatment verification for 9 patients. Conclusion: VMAT-CDR can achieve comparable plan quality with significant shorter delivery time and smaller number of MUs compared with IMRT for patients with endometrial cancer undergoing WPRT. It can be accurately delivered and be an alternative to IMRT on the linear accelerator without VDR capability. This work is supported by the grant project, National Natural; Science Foundation of China (No. 81071237)

  17. Dynamics of chest wall volume regulation during constant work rate exercise in patients with chronic obstructive pulmonary disease

    Energy Technology Data Exchange (ETDEWEB)

    Takara, L.S.; Cunha, T.M.; Barbosa, P.; Rodrigues, M.K.; Oliveira, M.F.; Nery, L.E. [Setor de Função Pulmonar e Fisiologia Clínica do Exercício, Disciplina de Pneumologia, Departamento de Medicina, Universidade Federal de São Paulo, São Paulo, SP (Brazil); Neder, J.A. [Setor de Função Pulmonar e Fisiologia Clínica do Exercício, Disciplina de Pneumologia, Departamento de Medicina, Universidade Federal de São Paulo, São Paulo, SP (Brazil); Division of Respiratory and Critical Care Medicine, Department of Medicine, Queen' s University, Kingston, ON (Canada)

    2012-10-15

    This study evaluated the dynamic behavior of total and compartmental chest wall volumes [(V{sub CW}) = rib cage (V{sub RC}) + abdomen (V{sub AB})] as measured breath-by-breath by optoelectronic plethysmography during constant-load exercise in patients with stable chronic obstructive pulmonary disease. Thirty males (GOLD stages II-III) underwent a cardiopulmonary exercise test to the limit of tolerance (Tlim) at 75% of peak work rate on an electronically braked cycle ergometer. Exercise-induced dynamic hyperinflation was considered to be present when end-expiratory (EE) V{sub CW} increased in relation to resting values. There was a noticeable heterogeneity in the patterns of V{sub CW} regulation as EEV{sub CW} increased non-linearly in 17/30 “hyperinflators” and decreased in 13/30 “non-hyperinflators” (P < 0.05). EEV{sub AB} decreased slightly in 8 of the “hyperinflators”, thereby reducing and slowing the rate of increase in end-inspiratory (EI) V{sub CW} (P < 0.05). In contrast, decreases in EEV{sub CW} in the “non-hyperinflators” were due to the combination of stable EEV{sub RC} with marked reductions in EEV{sub AB}. These patients showed lower EIV{sub CW} and end-exercise dyspnea scores but longer Tlim than their counterparts (P < 0.05). Dyspnea increased and Tlim decreased non-linearly with a faster rate of increase in EIV{sub CW} regardless of the presence or absence of dynamic hyperinflation (P < 0.001). However, no significant between-group differences were observed in metabolic, pulmonary gas exchange and cardiovascular responses to exercise. Chest wall volumes are continuously regulated during exercise in order to postpone (or even avoid) their migration to higher operating volumes in patients with COPD, a dynamic process that is strongly dependent on the behavior of the abdominal compartment.

  18. Voltage gating by molecular subunits of Na+ and K+ ion channels: higher-dimensional cubic kinetics, rate constants, and temperature.

    Science.gov (United States)

    Fohlmeister, Jürgen F

    2015-06-01

    The structural similarity between the primary molecules of voltage-gated Na and K channels (alpha subunits) and activation gating in the Hodgkin-Huxley model is brought into full agreement by increasing the model's sodium kinetics to fourth order (m(3) → m(4)). Both structures then virtually imply activation gating by four independent subprocesses acting in parallel. The kinetics coalesce in four-dimensional (4D) cubic diagrams (16 states, 32 reversible transitions) that show the structure to be highly failure resistant against significant partial loss of gating function. Rate constants, as fitted in phase plot data of retinal ganglion cell excitation, reflect the molecular nature of the gating transitions. Additional dimensions (6D cubic diagrams) accommodate kinetically coupled sodium inactivation and gating processes associated with beta subunits. The gating transitions of coupled sodium inactivation appear to be thermodynamically irreversible; response to dielectric surface charges (capacitive displacement) provides a potential energy source for those transitions and yields highly energy-efficient excitation. A comparison of temperature responses of the squid giant axon (apparently Arrhenius) and mammalian channel gating yields kinetic Q10 = 2.2 for alpha unit gating, whose transitions are rate-limiting at mammalian temperatures; beta unit kinetic Q10 = 14 reproduces the observed non-Arrhenius deviation of mammalian gating at low temperatures; the Q10 of sodium inactivation gating matches the rate-limiting component of activation gating at all temperatures. The model kinetics reproduce the physiologically large frequency range for repetitive firing in ganglion cells and the physiologically observed strong temperature dependence of recovery from inactivation. Copyright © 2015 the American Physiological Society.

  19. Dynamics of chest wall volume regulation during constant work rate exercise in patients with chronic obstructive pulmonary disease

    Directory of Open Access Journals (Sweden)

    L.S. Takara

    2012-12-01

    Full Text Available This study evaluated the dynamic behavior of total and compartmental chest wall volumes [(V CW = rib cage (V RC + abdomen (V AB] as measured breath-by-breath by optoelectronic plethysmography during constant-load exercise in patients with stable chronic obstructive pulmonary disease. Thirty males (GOLD stages II-III underwent a cardiopulmonary exercise test to the limit of tolerance (Tlim at 75% of peak work rate on an electronically braked cycle ergometer. Exercise-induced dynamic hyperinflation was considered to be present when end-expiratory (EE V CW increased in relation to resting values. There was a noticeable heterogeneity in the patterns of V CW regulation as EEV CW increased non-linearly in 17/30 "hyperinflators" and decreased in 13/30 "non-hyperinflators" (P < 0.05. EEV AB decreased slightly in 8 of the "hyperinflators", thereby reducing and slowing the rate of increase in end-inspiratory (EI V CW (P < 0.05. In contrast, decreases in EEV CW in the "non-hyperinflators" were due to the combination of stable EEV RC with marked reductions in EEV AB. These patients showed lower EIV CW and end-exercise dyspnea scores but longer Tlim than their counterparts (P < 0.05. Dyspnea increased and Tlim decreased non-linearly with a faster rate of increase in EIV CW regardless of the presence or absence of dynamic hyperinflation (P < 0.001. However, no significant between-group differences were observed in metabolic, pulmonary gas exchange and cardiovascular responses to exercise. Chest wall volumes are continuously regulated during exercise in order to postpone (or even avoid their migration to higher operating volumes in patients with COPD, a dynamic process that is strongly dependent on the behavior of the abdominal compartment.

  20. Ion-neutral gas reactions in a collision/reaction cell in inductively coupled plasma mass spectrometry: Correlation of ion signal decrease to kinetic rate constants

    Energy Technology Data Exchange (ETDEWEB)

    Gray, Patrick J. [Trace Element Research Laboratory, School of Earth Sciences, The Ohio State University, 125 S. Oval Mall, Columbus, OH 43210 (United States); Department of Chemistry, The Ohio State University, 120 18th Avenue, Columbus, OH 43210 (United States); Olesik, John W., E-mail: olesik.2@osu.edu [Trace Element Research Laboratory, School of Earth Sciences, The Ohio State University, 125 S. Oval Mall, Columbus, OH 43210 (United States)

    2015-03-01

    Reaction gas flow rate dependent Ar{sub 2}{sup +} and Ar{sup +} signals are correlated to fundamental kinetic rate coefficients. A simple calculation, assuming that gas exits the reaction cell due only to effusion, is described to estimate the gas pressure in the reaction cell. The value of the product of the kinetic rate constant and the ion residence time in the reaction cell can be determined from experimental measurement of the decrease in an ion signal as a function of reaction gas flow rate. New kinetic rate constants are determined for the reaction of CH{sub 3}F with Ar{sup +} and Ar{sub 2}{sup +}. - Highlights: • How to determine pressure and the product of the kinetic rate constant times the ion residence time in reaction cell • Relate measured ICP-DRC-MS signals versus gas flow rate to kinetic rate constants measured previously using SIFT-MS • Describe how to determine previously unmeasured kinetic rate constants using ICP-DRC-MS.

  1. Dose rate constants for the quantity H{sub p}(3) for frequently used radionuclides in nuclear medicine

    Energy Technology Data Exchange (ETDEWEB)

    Szermerski, Bastian; Bruchmann, Iris; Geworski, Lilli [Medical School Hannover (Germany). Dept. for Radiation Protection and Medical Physics; Behrens, Rolf [Physikalisch-Technische Bundesanstalt (PTB), Braunschweig (Germany)

    2016-07-01

    According to recent studies, the human eye lens is more sensitive to ionising radiation than previously assumed. Therefore, the dose limit for personnel occupationally exposed to ionising radiation will be lowered from currently 150 mSv to 20 mSv per year. Currently, no data base for a reliable estimation of the dose to the lens of the eye is available for nuclear medicine. Furthermore, the dose is usually not monitored. The aim of this work was to determine dose rate constants for the quantity H{sub p}(3), which is supposed to estimate the dose to the lens of the eye. For this, H{sub p}(3)-dosemeters were fixed to an Alderson Phantom at different positions. The dosemeters were exposed to radiation from nuclides typically used in nuclear medicine in their geometries analog to their application in nuclear medicine, e.g. syringe or vial. The results show that the handling of high-energy beta (i.e. electron or positron) emitters may lead to a relevant dose to the lens of the eye. For low-energy beta emitters and gamma emitters, an exceeding of the lowered dose limit seems to be unlikely.

  2. Pressure dependence of the absolute rate constant for the reaction Cl + C2H2 from 210-361 K

    Science.gov (United States)

    Brunning, J.; Stief, L. J.

    1985-01-01

    In recent years, considerable attention has been given to the role of chlorine compounds in the catalytic destruction of stratospheric ozone. However, while some reactions have been studied extensively, the kinetic data for the reaction of Cl with C2H2 is sparse with only three known determinations of the rate constant k3. The reactions involved are Cl + C2H2 yields reversibly ClC2H2(asterisk) (3a) and ClC2H2(asterisk) + M yields ClC2H2 + M (3b). In the present study, flash photolysis coupled with chlorine atomic resonance fluorescence have been employed to determine the pressure and temperature dependence of k3 with the third body M = Ar. Room temperature values are also reported for M = N2. The pressure dependence observed in the experiments confirms the expectation that the reaction involves addition of Cl to the unsaturated C2H2 molecule followed by collisional stabilization of the resulting adduct radical.

  3. Catalytic antibody light chain capable of cleaving a chemokine receptor CCR-5 peptide with a high reaction rate constant.

    Science.gov (United States)

    Mitsuda, Yukie; Hifumi, Emi; Tsuruhata, Kumi; Fujinami, Hiroko; Yamamoto, Naoki; Uda, Taizo

    2004-04-20

    A monoclonal antibody (MAb), ECL2B-2, was obtained by immunizing a peptide possessing a part of a sequence of a chemokine receptor, CCR-5, which is present as a membrane protein on the macrophage surface, and which plays an important role in human immunodeficiency virus (HIV) infection. From the DNA and the deduced amino acid sequences of the light and heavy chains of ECL2B-2 MAb, molecular modeling was conducted to calculate the steric conformation of the antibody. Modeling suggested that the structure of ECL2B-2 could possess one or two catalytic triad(s), composed of Asp(1), Ser(27a) (or Ser(27e)), and His(93) (or His(27d)), in the light chain of ECL2B-2. The three amino acid residues, Asp(1), Ser(27a), and His(93), are identical to those of catalytic antibody light chains such as VIPase and i41SL1-2. The light chain of ECL2B-2 MAb degraded the antigenic peptide CCR-5 within about 100 h. Surprisingly, the light chain had a very high catalytic reaction rate constant (k(cat)) of 2.23 min(-1), which is greater by factors of tens to hundreds than those of natural catalytic antibodies obtained previously. The heavy chain of ECL2B-2 MAb, which has no catalytic triad because of a lack of His residue, did not degrade the CCR-5 peptide.

  4. Using a Family of Dividing Surfaces Normal to the Minimum EnergyPath for Quantum Instanton Rate Constants

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yimin; Miller, Wlliam H.

    2006-02-22

    One of the outstanding issues in the quantum instanton (QI) theory (or any transition state-type theory) for thermal rate constants of chemical reactions is the choice of an appropriate ''dividing surface'' (DS) that separates reactants and products. (In the general version of the QI theory, there are actually two dividing surfaces involved.) This paper shows one simple and general way for choosing DS's for use in QI Theory, namely using the family of (hyper) planes normal to the minimum energy path (MEP) on the potential energy surface at various distances s along it. Here the reaction coordinate is not one of the dynamical coordinates of the system (which will in general be the Cartesian coordinates of the atoms), but rather simply a parameter which specifies the DS. It is also shown how this idea can be implemented for an N-atom system in 3d space in a way that preserves overall translational and rotational invariance. Numerical application to a simple system (the colliner H + H{sub 2} reaction) is presented to illustrate the procedure.

  5. Absolute rate constants for hydrogen atom transfer from tertiary amides to the cumyloxyl radical: evaluating the role of stereoelectronic effects.

    Science.gov (United States)

    Salamone, Michela; Milan, Michela; DiLabio, Gino A; Bietti, Massimo

    2014-08-01

    A time-resolved kinetic study of the hydrogen atom transfer (HAT) reactions from a series of alkanamides to the cumyloxyl radical (CumO(•)) was carried out. With N,N-dialkylformamides HAT preferentially occurs from the formyl C-H bond, while in N-formylpyrrolidine HAT mostly occurs from the ring α-C-H bonds. With the acetamides and the alkanamides almost exclusive HAT from the C-H bonds that are α to nitrogen was observed. The results obtained show that alignment between the C-H bond being broken and the amide π-system can lead to significant increases in the HAT rate constant (kH). This finding points toward the important role of stereoelectronic effects on the HAT reactivity and selectivity. The highest kH values were measured for the reactions of CumO(•) with N-acylpyrrolidines. These substrates have ring α-C-H bonds that are held in a conformation that is optimally aligned with the amide π-system, thus allowing for the relatively facile HAT reaction. The lowest kH value was measured for the reaction of N,N-diisobutylacetamide, wherein the steric bulk associated with the N-isobutyl groups increases the energy barrier required to reach the most suitable conformation for HAT. The experimental results are well supported by the computed BDEs for the C-H bonds of the most representative substrates.

  6. A quasi-QSPR modelling for the photocatalytic decolourization rate constants and cellular viability (CV%) of nanoparticles by CORAL.

    Science.gov (United States)

    Toropova, A P; Toropov, A A; Benfenati, E

    2015-01-01

    Most quantitative structure-property/activity relationships (QSPRs/QSARs) predict various endpoints related to organic compounds. Gradually, the variety of organic compounds has been extended to inorganic, organometallic compounds and polymers. However, the so-called molecular descriptors cannot be defined for super-complex substances such as different nanomaterials and peptides, since there is no simple and clear representation of their molecular structure. Some possible ways to define approaches for a predictive model in the case of super-complex substances are discussed. The basic idea of the approach is to change the traditionally used paradigm 'the endpoint is a mathematical function of the molecular structure' with another paradigm 'the endpoint is a mathematical function of available eclectic information'. The eclectic data can be (i) conditions of a synthesis, (ii) technological attributes, (iii) size of nanoparticles, (iv) concentration, (v) attributes related to cell membranes, and so on. Two examples of quasi-QSPR/QSAR analyses are presented and discussed. These are (i) photocatalytic decolourization rate constants (DRC) (10(-5)/s) of different nanopowders; and (ii) the cellular viability under the effect of nano-SiO(2).

  7. Resonant vibrational-excitation cross sections and rate constants for low-energy electron scattering by molecular oxygen

    CERN Document Server

    Laporta, V; Tennyson, J

    2016-01-01

    Resonant vibrational-excitation cross sections and rate constants for electron scattering by molecular oxygen are presented. Transitions between all 42 vibrational levels of O$_2(\\textrm{X}\\ ^3\\Sigma_g^- $) are considered. Molecular rotations are parameterized by the rotational quantum number $J$ which is considered in the range 1 to 151. The lowest four resonant states of O$_2^-$, $^2\\Pi_g$, $^2\\Pi_u$, $^4\\Sigma_u^-$ and $^2\\Sigma_u^-$, are taken into account. The calculations are performed using the fixed-nuclei R-matrix approach to determine the resonance positions and widths, and the boomerang model to characterize the nuclei motion. Two energy regions below and above 4~eV are investigated: the first one is characterized by sharp structures in the cross section, and the second by a broad resonance peaked at 10~eV. The computed cross sections are compared with theoretical and experimental results available in literature for both the energy regions, and are made available for use by modelers. The effect of ...

  8. Atmospheric reaction of Cl + methacrolein: a theoretical study on the mechanism, and pressure- and temperature-dependent rate constants.

    Science.gov (United States)

    Sun, Cuihong; Xu, Baoen; Zhang, Shaowen

    2014-05-22

    Methacrolein is a major degradation product of isoprene, the reaction of methacrolein with Cl atoms may play some roles in the degradation of isoprene where these species are relatively abundant. However, the energetics and kinetics of this reaction, which govern the reaction branching, are still not well understood so far. In the present study, two-dimensional potential energy surfaces were constructed to analyze the minimum energy path of the barrierless addition process between Cl and the C═C double bond of methacrolein, which reveals that the terminal addition intermediate is directly formed from the addition reaction. The terminal addition intermediate can further yield different products among which the reaction paths abstracting the aldehyde hydrogen atom and the methyl hydrogen atom are dominant reaction exits. The minimum reaction path for the direct aldehydic hydrogen atom abstraction is also obtained. The reaction kinetics was calculated by the variational transition state theory in conjunction with the master equation method. From the theoretical model we predicted that the overall rate constant of the Cl + methacrolein reaction at 297 K and atmospheric pressure is koverall = 2.3× 10(-10) cm(3) molecule(-1) s(-1), and the branching ratio of the aldehydic hydrogen abstraction is about 12%. The reaction is pressure dependent at P pressure limit at about 100 Torr. The calculated results could well account for the experimental observations.

  9. Non-Radial Oscillations in an Axisymmetric MHD Incompressible Fluid

    Indian Academy of Sciences (India)

    A. Satya Narayanan

    2000-09-01

    It is well known from Helioseismology that the Sun exhibits oscillations on a global scale, most of which are non-radial in nature. These oscillations help us to get a clear picture of the internal structure of the Sun as has been demonstrated by the theoretical and observational (such as GONG) studies. In this study we formulate the linearised equations of motion for non-radial oscillations by perturbing the MHD equilibrium solution for an axisymmetric incompressible fluid. The fluid motion and the magnetic field are expressed as scalars , , and , respectively. In deriving the exact solution for the equilibrium state, we neglect the contribution due to meridional circulation. The perturbed quantities *, *, *, * are written in terms of orthogonal polynomials. A special case of the above formulation and its stability is discussed.

  10. Superoxide dismutase versus ferricytochrome C: determining rate constants for the spin trapping of superoxide by cyclic nitrones.

    Science.gov (United States)

    Weaver, John; Tsai, Pei; Pou, Sovitj; Rosen, Gerald M

    2004-11-26

    Given that spin trapping/electron paramagnetic resonance (EPR) spectroscopy has become the primary technique to identify important biologically generated free radicals, such as superoxide (O(2)(*-)), in vitro and in vivo models, evaluation of the efficiency of specific spin traps to identify this free radical is paramount. Recently, a family of ester-containing nitrones has been prepared, which appears to have distinct advantages for spin trapping O(2)(*-) compared to the well-studied spin traps 5,5-dimethyl-1-pyrroline N-oxide 1 and 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide 2. An important determinant in the selection of a spin trap is the rate constant (k(app)) for its reaction with O(2)(*-), and several different methods have been employed in estimating this k(app). In this paper, the two most frequently used scavengers of O(2)(*-), ferricytochrome c and Cu/Zn-SOD, were evaluated as competitive inhibitors for spin trapping this free radical. Data presented herein demonstrate that SOD is the preferred compound when determining the k(app) for the reaction of O(2)(*-) with spin traps. Using this model, the k(app) for the reaction of nitrone 1, 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide 3, and 5-methoxycarbonyl-5-methyl-1-pyrroline N-oxide 4 with O(2)(*)(-) was estimated to be 24.6 +/- 3.1, 73.0 +/- 12, and 89.4 +/- 1.0 M(-1) s(-1) at pH 7.0, respectively. Several other comparative studies between known spin traps were also undertaken.

  11. Spiral growth and dissolution models with rate constants related to the frequency of partial dehydration of cations and to the surface tension

    Science.gov (United States)

    Christoffersen, J.; Christoffersen, M. R.

    1988-01-01

    A rate expression is developed for spiral dissolution, similar to the Nielsen expression for spiral growth, with the rate constant expressed in terms of frequencies related to dehydration frequencies. These models for spiral growth and dissolution are applied to growth and dissolution of brushite, DCPD.

  12. Method for determining effective nonradiative lifetime and leakage losses in double-heterostructure lasers

    Energy Technology Data Exchange (ETDEWEB)

    van Opdorp, C.; ' t Hooft, G.W.

    1981-06-01

    Carrier losses in double-heterostructure lasers are twofold: (i) nonradiative recombination through killers in the bulk of the active region and at all its boundaries (interfaces and surfaces), and (ii) leakage out of the active region. A simple theory shows the following. In the high-injection regime (papprox. =n) all processes under (i) are directly proportional to n. Consequently their contributions can be lumped together in a single effective nonradiative carrier lifetime tau/sub nr/ ; this tau/sub nr/ is constant (i.e., independent of n) owing to the constant degree of occupation of all killers in the mentioned regime. On the other hand, the leakage losses (ii) are superlinear in n. This provides a well-grounded basis for disentangling the contributions of (i) and (ii) in a given sample. Further, a simple method is presented for accurately determining tau/sub nr/ from data of the external quantum efficiency eta/sub ext/ measured as a function of current I in the spontaneous high-injection regime below the laser threshold. Knowledge of the light-extraction factor (i.e., the ratio of external and internal quantum efficiencies) is essentially unnecessary with this method. However, optionally it can be determined easily from a slight extension of the method. For illustration the method of determining tau/sub nr/, which is also applicable to double-hetero LED's, has been applied to some thirty LPE and metal-organic VPE GaAs-(Ga,Al)As lasers of widely varying qualities. The values found vary between 0.8 and 55 ns. From the measured values of tau/sub nr/ it follows that the upper limit for the interface recombination velocity in the best samples is 270 cm/s. For most samples tau/sub nr/ cannot account for all electrical losses at laser threshold. The superlinear excess losses are ascribable to leakage.

  13. PENENTUAN KONSTANTA LAJU PENURUNAN KADAR IODAT DALAM GARAM BERIODIUM [Determination of the Rate Constant on the Decrease of Iodate Content in Iodized Salt

    Directory of Open Access Journals (Sweden)

    Wisnu Cahyadi

    2006-04-01

    Full Text Available Potassium iodate used as the source of iodine can be decomposed to become the other species i.e. iodide and iodine during processing and storage. The objective of this research was determination of the rate constant on the decrease of iodate content in iodized salt. The method was used to determine the temperature and the length of storage effects on iodate stability in iodized salt. The research was obtained the rate constant on the decrease of iodate content in iodized salt (K 2.55 x 10-8 ppm day-1 and energy of activation (Ea 12.002 kcal mol-1 K-1.

  14. PENENTUAN KONSTANTA LAJU PENURUNAN KADAR IODAT DALAM GARAM BERIODIUM [Determination of the Rate Constant on the Decrease of Iodate Content in Iodized Salt

    OpenAIRE

    Wisnu Cahyadi

    2006-01-01

    Potassium iodate used as the source of iodine can be decomposed to become the other species i.e. iodide and iodine during processing and storage. The objective of this research was determination of the rate constant on the decrease of iodate content in iodized salt. The method was used to determine the temperature and the length of storage effects on iodate stability in iodized salt. The research was obtained the rate constant on the decrease of iodate content in iodized salt (K) 2.55 x 10-8 ...

  15. Absolute rate constant determinations for the deactivation of O/1D/ by time resolved decay of O/1D/ yields O/3P/ emission

    Science.gov (United States)

    Davidson, J. A.; Sadowski, C. M.; Schiff, H. I.; Howard, C. J.; Schmeltekopf, A. L.; Jennings, D. A.; Streit, G. E.

    1976-01-01

    Absolute rate constants for the deactivation of O(1D) atoms by some atmospheric gases have been determined by observing the time-resolved emission of O(1D) at 630 nm. O(1D) atoms were produced by the dissociation of ozone via repetitive laser pulses at 266 nm. Absolute rate constants for the relaxation of O(1D) at 298 K are reported for N2, O2, CO2, O3, H2, D2, CH4, HCl, NH3, H2O, N2O, and Ne. The results obtained are compared with previous relative and absolute measurements reported in the literature.

  16. Enhanced non-radiative energy transfer in hybrid III-nitride structures

    Energy Technology Data Exchange (ETDEWEB)

    Smith, R. M.; Athanasiou, M.; Bai, J.; Liu, B.; Wang, T., E-mail: t.wang@sheffield.ac.uk [Department of Electrical and Electronic Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD (United Kingdom)

    2015-09-21

    The effect of surface states has been investigated in hybrid organic/inorganic white light emitting structures that employ high efficiency, nearfield non-radiative energy transfer (NRET) coupling. The structures utilize blue emitting InGaN/GaN multiple quantum well (MQW) nanorod arrays to minimize the separation with a yellow emitting F8BT coating. Surface states due to the exposed III-nitride surfaces of the nanostructures are found to reduce the NRET coupling rate. The surface states are passivated by deposition of a silicon nitride layer on the III-nitride nanorod surface leading to reduced surface recombination. A low thickness surface passivation is shown to increase the NRET coupling rate by 4 times compared to an un-passivated hybrid structure. A model is proposed to explain the increased NRET rate for the passivated hybrid structures based on the reduction in surface electron depletion of the passivated InGaN/GaN MQW nanorods surfaces.

  17. Enhanced non-radiative energy transfer in hybrid III-nitride structures

    Science.gov (United States)

    Smith, R. M.; Athanasiou, M.; Bai, J.; Liu, B.; Wang, T.

    2015-09-01

    The effect of surface states has been investigated in hybrid organic/inorganic white light emitting structures that employ high efficiency, nearfield non-radiative energy transfer (NRET) coupling. The structures utilize blue emitting InGaN/GaN multiple quantum well (MQW) nanorod arrays to minimize the separation with a yellow emitting F8BT coating. Surface states due to the exposed III-nitride surfaces of the nanostructures are found to reduce the NRET coupling rate. The surface states are passivated by deposition of a silicon nitride layer on the III-nitride nanorod surface leading to reduced surface recombination. A low thickness surface passivation is shown to increase the NRET coupling rate by 4 times compared to an un-passivated hybrid structure. A model is proposed to explain the increased NRET rate for the passivated hybrid structures based on the reduction in surface electron depletion of the passivated InGaN/GaN MQW nanorods surfaces.

  18. Procedures for Static and Constant-Rate Tests on a Single-Degree-of-Freedom (SDF) Strapdown Gyroscope.

    Science.gov (United States)

    1983-10-01

    permettant de tester des gyroscopes auto correcteurs A centrale lige et . 1° de libert6. Les tests sont limitgs aux modes statistiques et A taux constants...conventionnels utilisEs sont aussi presentfs, de Seme que les considfrations concernant la r6gulation thermique . iii 5 TABLE OF CONTENTS Page Abstract

  19. Full-band structure modeling of the radiative and non-radiative properties of semiconductor materials and devices (Presentation Recording)

    Science.gov (United States)

    Bellotti, Enrico; Wen, Hanqing; Pinkie, Benjamin; Matsubara, Masahiko; Bertazzi, Francesco

    2015-08-01

    Understanding the radiative and non-radiative properties of semiconductor materials is a prerequisite for optimizing the performance of existing light emitters and detectors and for developing new device architectures based on novel materials. Due to the ever increasing complexity of novel semiconductor systems and their relative technological immaturity, it is essential to have design tools and simulation strategies that include the details of the microscopic physics and their dependence on the macroscopic (continuum) variables in the macroscopic device models. Towards this end, we have developed a robust full-band structure based approach that can be used to study the intrinsic material radiative and non-radiative properties and evaluate the same characteristics of low-dimensional device structures. A parallel effort is being carried out to model the effect of substrate driven stress/strain and material quality (dislocations and defects) on microscopic quantities such as non-radiative recombination rate. Using this modeling approach, we have extensively studied the radiative and non-radiative properties of both elemental (Si and Ge) and compound semiconductors (HgCdTe, InGaAs, InAsSb and InGaN). In this work we outline the details of the modelling approach, specifically the challenges and advantages related to the use of the full-band description of the material electronic structure. We will present a detailed comparison of the radiative and Auger recombination rates as a function of temperature and doping for HgCdTe and InAsSb that are two important materials for infrared detectors and emitters. Furthermore we will discuss the role of non-radiatiave Auger recombination processes in explaining the performance of light emitter diodes. Finally we will present the extension of the model to low dimensional structures employed in a number of light emitter and detector structures.

  20. Improved Shock Tube Measurement of the CH4 + Ar = CH3 + H + Ar Rate Constant using UV Cavity-Enhanced Absorption Spectroscopy of CH3.

    Science.gov (United States)

    Wang, Shengkai; Davidson, David F; Hanson, Ronald K

    2016-07-21

    We report an improved measurement for the rate constant of methane dissociation in argon (CH4 + Ar = CH3 + H + Ar) behind reflected shock waves. The experiment was conducted using a sub-parts per million sensitivity CH3 diagnostic recently developed in our laboratory based on ultraviolet cavity-enhanced absorption spectroscopy. The high sensitivity of this diagnostic allowed for measurements of quantitatively resolved CH3 time histories during the initial stage of CH4 pyrolysis, where the reaction system is clean and free from influences of secondary reactions and temperature change. This high sensitivity also allowed extension of our measurement range to much lower temperatures (shock measurements were performed at temperatures between 1487 and 1866 K and pressures near 1.7 atm, resulting in the following Arrhenius rate constant expression for the title reaction: k(1.7 atm) = 3.7 × 10(16) exp(-42 200 K/T) cm(3)/mol·s, with a 2σ uncertainty factor of 1.25. The current data are in good consensus with various theoretical and review studies, but at the low temperature end they suggest a slightly higher (up to 35%) rate constant compared to these previous results. A re-evaluation of previous and current experimental data in the falloff region was also performed, yielding updated expressions for both the low-pressure limit and the high-pressure limit rate constants and improved agreement with all existing data.

  1. Determination of first order rate constants by natural logarithm of the slope plot exemplified by analysis of Aspergillus niger in batch culture

    NARCIS (Netherlands)

    Poulsen, B.R.; Ruiter, G.; Visser, J.; Iversen, J.J.L.

    2003-01-01

    Finding rate constants from experimental data is often difficult because of offset and noise. A computer program was developed to average experimental data points, reducing the effect of noise, and to produce a loge of slope plot - a plot of the natural logarithm of the slope of a curve -

  2. Non-Radiative Energy Transfer Mediated by Hybrid Light-Matter States.

    Science.gov (United States)

    Zhong, Xiaolan; Chervy, Thibault; Wang, Shaojun; George, Jino; Thomas, Anoop; Hutchison, James A; Devaux, Eloise; Genet, Cyriaque; Ebbesen, Thomas W

    2016-05-17

    We present direct evidence of enhanced non-radiative energy transfer between two J-aggregated cyanine dyes strongly coupled to the vacuum field of a cavity. Excitation spectroscopy and femtosecond pump-probe measurements show that the energy transfer is highly efficient when both the donor and acceptor form light-matter hybrid states with the vacuum field. The rate of energy transfer is increased by a factor of seven under those conditions as compared to the normal situation outside the cavity, with a corresponding effect on the energy transfer efficiency. The delocalized hybrid states connect the donor and acceptor molecules and clearly play the role of a bridge to enhance the rate of energy transfer. This finding has fundamental implications for coherent energy transport and light-energy harvesting.

  3. Fitting the elementary rate constants of the P-gp transporter network in the hMDR1-MDCK confluent cell monolayer using a particle swarm algorithm.

    Directory of Open Access Journals (Sweden)

    Deep Agnani

    Full Text Available P-glycoprotein, a human multidrug resistance transporter, has been extensively studied due to its importance to human health and disease. In order to understand transport kinetics via P-gp, confluent cell monolayers overexpressing P-gp are widely used. The purpose of this study is to obtain the mass action elementary rate constants for P-gp's transport and to functionally characterize members of P-gp's network, i.e., other transporters that transport P-gp substrates in hMDR1-MDCKII confluent cell monolayers and are essential to the net substrate flux. Transport of a range of concentrations of amprenavir, loperamide, quinidine and digoxin across the confluent monolayer of cells was measured in both directions, apical to basolateral and basolateral to apical. We developed a global optimization algorithm using the Particle Swarm method that can simultaneously fit all datasets to yield accurate and exhaustive fits of these elementary rate constants. The statistical sensitivity of the fitted values was determined by using 24 identical replicate fits, yielding simple averages and standard deviations for all of the kinetic parameters, including the efflux active P-gp surface density. Digoxin required additional basolateral and apical transporters, while loperamide required just a basolateral tranporter. The data were better fit by assuming bidirectional transporters, rather than active importers, suggesting that they are not MRP or active OATP transporters. The P-gp efflux rate constants for quinidine and digoxin were about 3-fold smaller than reported ATP hydrolysis rate constants from P-gp proteoliposomes. This suggests a roughly 3∶1 stoichiometry between ATP hydrolysis and P-gp transport for these two drugs. The fitted values of the elementary rate constants for these P-gp substrates support the hypotheses that the selective pressures on P-gp are to maintain a broad substrate range and to keep xenobiotics out of the cytosol, but not out of the

  4. Ratiometric analysis in hyperpolarized NMR (I): test of the two-site exchange model and the quantification of reaction rate constants.

    Science.gov (United States)

    Li, Lin Z; Kadlececk, Stephen; Xu, He N; Daye, Dania; Pullinger, Benjamin; Profka, Harrilla; Chodosh, Lewis; Rizi, Rahim

    2013-10-01

    Conventional methods for the analysis of in vivo hyperpolarized (13) C NMR data from the lactate dehydrogenase (LDH) reaction usually make assumptions on the stability of rate constants and/or the validity of the two-site exchange model. In this study, we developed a framework to test the validity of the assumption of stable reaction rate constants and the two-site exchange model in vivo via ratiometric fitting of the time courses of the signal ratio L(t)/P(t). Our analysis provided evidence that the LDH enzymatic kinetics observed by hyperpolarized NMR are in near-equilibrium and satisfy the two-site exchange model for only a specific time window. In addition, we quantified both the forward and reverse exchange rate constants of the LDH reaction for the transgenic and mouse xenograft models of breast cancer using the ratio fitting method developed, which includes only two modeling parameters and is less sensitive to the influence of instrument settings/protocols, such as flip angles, degree of polarization and tracer dosage. We further compared the ratio fitting method with a conventional two-site exchange modeling method, i.e. the differential equation fitting method, using both the experimental and simulated hyperpolarized NMR data. The ratio fitting method appeared to fit better than the differential equation fitting method for the reverse rate constant on the mouse tumor data, with less relative errors on average, whereas the differential equation fitting method also resulted in a negative reverse rate constant for one tumor. The simulation results indicated that the accuracy of both methods depends on the width of the transport function, noise level and rate constant ratio; one method may be more accurate than the other based on the experimental/biological conditions aforementioned. We were able to categorize our tumor models into specific conditions of the computer simulation and to estimate the errors of rate quantification. We also discussed possible

  5. Determination of rate constants and branching ratios for TCE degradation by zero-valent iron using a chain decay multispecies model

    Science.gov (United States)

    Hwang, Hyoun-Tae; Jeen, Sung-Wook; Sudicky, Edward A.; Illman, Walter A.

    2015-06-01

    The applicability of a newly-developed chain-decay multispecies model (CMM) was validated by obtaining kinetic rate constants and branching ratios along the reaction pathways of trichloroethene (TCE) reduction by zero-valent iron (ZVI) from column experiments. Changes in rate constants and branching ratios for individual reactions for degradation products over time for two columns under different geochemical conditions were examined to provide ranges of those parameters expected over the long-term. As compared to the column receiving deionized water, the column receiving dissolved CaCO3 showed higher mean degradation rates for TCE and all of its degradation products. However, the column experienced faster reactivity loss toward TCE degradation due to precipitation of secondary carbonate minerals, as indicated by a higher value for the ratio of maximum to minimum TCE degradation rate observed over time. From the calculated branching ratios, it was found that TCE and cis-dichloroethene (cis-DCE) were dominantly dechlorinated to chloroacetylene and acetylene, respectively, through reductive elimination for both columns. The CMM model, validated by the column test data in this study, provides a convenient tool to determine simultaneously the critical design parameters for permeable reactive barriers and natural attenuation such as rate constants and branching ratios.

  6. Radiative and non-radiative recombinations in tensile strained Ge microstrips: Photoluminescence experiments and modeling

    Energy Technology Data Exchange (ETDEWEB)

    Virgilio, M., E-mail: virgilio@df.unipi.it [Dip. di Fisica “E. Fermi,” Università di Pisa, Largo Pontecorvo 3, 56127 Pisa (Italy); NEST, Istituto Nanoscienze-CNR, P.za San Silvestro 12, 56127 Pisa (Italy); Schroeder, T.; Yamamoto, Y. [IHP, Im Technologiepark 25, 15236 Frankfurt (Oder) (Germany); Capellini, G. [IHP, Im Technologiepark 25, 15236 Frankfurt (Oder) (Germany); Dip. di scienze, Università Roma Tre, viale G. Marconi 446, 00146 Roma (Italy)

    2015-12-21

    Tensile germanium microstrips are candidate as gain material in Si-based light emitting devices due to the beneficial effect of the strain field on the radiative recombination rate. In this work, we thoroughly investigate their radiative recombination spectra by means of micro-photoluminescence experiments at different temperatures and excitation powers carried out on samples featuring different tensile strain values. For sake of comparison, bulk Ge(001) photoluminescence is also discussed. The experimental findings are interpreted in light of a numerical modeling based on a multi-valley effective mass approach, taking in to account the depth dependence of the photo-induced carrier density and of the self-absorption effect. The theoretical modeling allowed us to quantitatively describe the observed increase of the photoluminescence intensity for increasing values of strain, excitation power, and temperature. The temperature dependence of the non-radiative recombination time in this material has been inferred thanks to the model calibration procedure.

  7. Lasing in organic semiconductors - time-resolved studies of non-radiative decay processes

    CERN Document Server

    Zenz, C R

    2000-01-01

    Based on the demonstration of optical gain in an organic single crystal of a soluble oligo-phenylene-vinylene with gain values higher than 60 cm-1 and optically pumped lasing in a longitudinal adjustable microcavity based on laddertype polyparaphenylene, the realization of an organic laserdiode is discussed. The output characteristics of the microcavity can be modeled using classical rate equations, however the obtained threshold values are limited by the short excited state lifetime. A comparison with the lifetime measured on isolated molecules shows, that non-radiative decay processes in the solid state are determining the excited state lifetime. Using conventional and a novel field-assisted differential transmission spectroscopy with femtosecond time resolution, two main decay mechanism could be identified. (i) Triplet exciton in para-hexaphenyl is formed by non-geminate recombination of photo-generated polarons. (ii) Dissociation of the luminescent singlet excitons into polarons is important for two reaso...

  8. Non-Radiative Step Facets in Semiconductor Nanowires.

    Science.gov (United States)

    Sanchez, Ana M; Zhang, Yunyan; Tait, Edward W; Hine, Nicholas D M; Liu, Huiyun; Beanland, Richard

    2017-03-24

    One of the main advantages of nanowires for functional applications is their high perfection, which results from surface image forces that act on line defects such as dislocations, rendering them unstable and driving them out of the crystal. Here we show that there is a class of linear defects that are stable in nanowires, with no long-range strain field or dislocation character. In zinc-blende semiconductors, they take the form of Ʃ3 (112) facets with heights constrained to be a multiple of three {111} monolayers. Density functional theory calculations show that they act as non-radiative recombination centres and have deleterious effects on nanowire properties. We present experimental observations of these defects on twin boundaries and twins that terminate inside GaAsP nanowires and find that they are indeed always multiples of three monolayers in height. Strategies to use the three-monolayer rule during growth to prevent their formation are discussed.

  9. Non-radial Pulsations in the Open Cluster NGC 3766

    CERN Document Server

    Roettenbacher, Rachael M; McSwain, M Virginia

    2009-01-01

    Non-radial pulsations (NRPs) are a proposed mechanism for the formation of decretion disks around Be stars and are important tools to study the internal structure of stars. NGC 3766 has an unusually large fraction of transient Be stars, so it is an excellent location to study the formation mechanism of Be star disks. High resolution spectroscopy can reveal line profile variations from NRPs, allowing measurements of both the degree, l, and azimuthal order, m. However, spectroscopic studies require large amounts of time with large telescopes to achieve the necessary high S/N and time domain coverage. On the other hand, multi-color photometry can be performed more easily with small telescopes to measure l only. Here, we present representative light curves of Be stars and non-emitting B stars in NGC 3766 from the CTIO 0.9m telescope in an effort to study NRPs in this cluster.

  10. General Relativistic Non-radial Oscillations of Compact Stars

    Science.gov (United States)

    Hall, Zack, II; Jaikumar, Prashanth

    2017-01-01

    Currently, we lack a means of identifying the type of matter at the core of compact stars, but in the future, we may be able to use gravitational wave signals produced by fluid oscillations inside compact stars to discover new phases of dense matter. To this end, we study the fluid perturbations inside compact stars such as Neutron Stars and Strange Quark Stars, focusing on modes that couple to gravitational waves. Using a modern equation of state for quark matter that incorporates interactions at moderately high densities, we implement an efficient computational scheme to solve the oscillation equations in the framework of General Relativity, and determine the complex eigenfrequencies that describe the oscillation and damping of the non-radial fluid modes. We discuss the significance of our results for future detection of these modes through gravitational waves. This work is supported in part by the CSULB Graduate Research Fellowship and by the National Science Foundation NSF PHY-1608959.

  11. The chemistry of bromine in the stratosphere: Influence of a new rate constant for the reaction BrO + HO2

    Science.gov (United States)

    Pirre, Michel; Marceau, Francois J.; Lebras, Georges; Maguin, Francoise; Poulet, Gille; Ramaroson, Radiela

    1994-01-01

    The impact of new laboratory data for the reaction BrO + HO2 yields HOBr + O2 in the depletion of global stratospheric ozone has been estimated using a one-dimensional photochemical model taking into account the heterogeneous reaction on sulphate aerosols which converts N2O5 into HNO3. Assuring an aerosol loading 2 times as large as the 'background' and a reaction probability of 0.1 for the above heterogeneous reaction, the 6 fold increase in the measured rate constant for the reaction of BrO with HO2 increases the computed depletion of global ozone produced by 20 ppt of total bromine from 2.01 percent to 2.36 percent. The use of the higher rate constant increases the HOBr mixing ratio and makes the bromine partitioning and the ozone depletion very sensitive to the branching ratio of the potential channel forming HBr in the BrO + HO2 reaction.

  12. Upper limits for the rate constants of the reactions of CF3O2 and CF3O radicals with ozone at 295 K

    DEFF Research Database (Denmark)

    Nielsen, O.J.; Sehested, J.

    1993-01-01

    Using the pulse radiolysis UV absorption technique and subsequent simulations of experimental absorption transients at 254 and 276 nm, upper limits of the rate constants for the reactions of CF3O2 and CF3O radicals with ozone were determined at 295 K, CF3O2+O3-->CF3O+2O2 (4), CF3O+O3-->CF3O2+O2 (......). The upper limits were derived as k4 ozone depletion by hydrofluorocarbons.......Using the pulse radiolysis UV absorption technique and subsequent simulations of experimental absorption transients at 254 and 276 nm, upper limits of the rate constants for the reactions of CF3O2 and CF3O radicals with ozone were determined at 295 K, CF3O2+O3-->CF3O+2O2 (4), CF3O+O3-->CF3O2+O2 (5...

  13. Photochemistry of UV-excited trifluoroacetylacetone and hexafluoroacetylacetone II: Quantum yield and rate constants of hydrogen fluoride photoelimination forming fluorinated methylfuranones

    Science.gov (United States)

    Disselkoen, Kyle R.; Alsum, Joel R.; Thielke, Timothy A.; Muyskens, Mark A.

    2017-03-01

    The photochemistry of gas-phase 1,1,1-trifluoroacetylacetone (TFAA) and 1,1,1,5,5,5-hexafluoroacetylacetone (HFAA) excited with ultraviolet light involves a significant photoelimination channel producing HF and difluoromethylfuranone or pentafluoromethylfuranone, respectively. We report collisional self-quenching of the experimentally-determined relative quantum yield, and determine rate constants of 0.27 ± 0.03 and 0.33 ± 0.04 μs-1, for HFAA and TFAA respectively. A strong collision model is consistent with the observed quenching. The data suggest that this elimination is the primary photochemical fate at low pressure in both cases. The TFAA rate constant is larger than that for HFAA, in spite of TFAA having half as many fluorine atoms as HFAA.

  14. Constant harvest rate for the Pacific sardine (Sardinops caeruleus) fishery in the Gulf of California based on catchability-at-length estimations

    OpenAIRE

    2009-01-01

    Constant harvest rate as a management strategy for the Pacific sardine (Sardinops caeruleus) fishery in the Gulf of California is supported by an analysis of variations in the catchability coefficient (q), stock abundance and commercial catch. Catchability was analyzed based on population length-structured data standard length (SL), expressed as CPUE, for 26 fishing seasons (1972-1973 to 1997-1998). We used a deterministic model of catchability to estimate the catchability-at-length assuming ...

  15. Upper limit on the rate constant for isotope exchange between molecular oxygen and ozone at 298 K

    Science.gov (United States)

    Anderson, S. M.; Morton, J.; Mauersberger, K.

    1987-01-01

    The gas phase bimolecular isotope exchange reaction between molecular oxygen and ozone has been investigated directly for the first time. Its rate coefficient is found to be less than 2 x 10 to the -25th cu cm/sec at 298 K, over six orders of magnitude below recent estimates. Much faster exchange was observed over condensed ozone at 77 K, suggesting isotopic scrambling is catalyzed under these conditions. The low rate coefficient implies that homogeneous exchange between ground state oxygen and ozone molecules cannot play a significant role in heavy ozone chemistry.

  16. QSAR models for oxidation of organic micropollutants in water based on ozone and hydroxyl radical rate constants and their chemical classification

    KAUST Repository

    Sudhakaran, Sairam

    2013-03-01

    Ozonation is an oxidation process for the removal of organic micropollutants (OMPs) from water and the chemical reaction is governed by second-order kinetics. An advanced oxidation process (AOP), wherein the hydroxyl radicals (OH radicals) are generated, is more effective in removing a wider range of OMPs from water than direct ozonation. Second-order rate constants (kOH and kO3) are good indices to estimate the oxidation efficiency, where higher rate constants indicate more rapid oxidation. In this study, quantitative structure activity relationships (QSAR) models for O3 and AOP processes were developed, and rate constants, kOH and kO3, were predicted based on target compound properties. The kO3 and kOH values ranged from 5 * 10-4 to 105 M-1s-1 and 0.04 to 18 * (109) M-1 s-1, respectively. Several molecular descriptors which potentially influence O3 and OH radical oxidation were identified and studied. The QSAR-defining descriptors were double bond equivalence (DBE), ionisation potential (IP), electron-affinity (EA) and weakly-polar component of solvent accessible surface area (WPSA), and the chemical and statistical significance of these descriptors was discussed. Multiple linear regression was used to build the QSAR models, resulting in high goodness-of-fit, r2 (>0.75). The models were validated by internal and external validation along with residual plots. © 2012 Elsevier Ltd.

  17. Learning Rates and Known-to-Unknown Flash-Card Ratios: Comparing Effectiveness While Holding Instructional Time Constant

    Science.gov (United States)

    Forbes, Bethany E.; Skinner, Christopher H.; Black, Michelle P.; Yaw, Jared; Booher, Joshua; Delisle, Jean

    2013-01-01

    Using alternating treatments designs, we compared learning rates across 2 computer-based flash-card interventions (3?min each): a traditional drill intervention with 15 unknown words and an interspersal intervention with 12 known words and 3 unknown words. Each student acquired more words under the traditional drill intervention. Discussion…

  18. Absolute rate constants for the reaction of NO3 radicals with a series of dienes at 295 K

    DEFF Research Database (Denmark)

    Ellermann, T.; Nielsen, O.J.; Skov, H.

    1992-01-01

    The rate constants for the reaction of NO3 radicals with a series of 7 dienes, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, trans-1,3-pentadiene, cis-1,3-pentadiene, trans,trans-2,4-hexadiene, and 1,3-cyclohexadiene, were measured at 295 K and at a total pressure of 1 atm. The rate consta...... were obtained using the absolute technique of pulse radiolysis combined with kinetic UV-VIS spectroscopy. The results are discussed in terms of reactivity trends and previous literature data....

  19. Direct determination of rate constants for coupling between aromatic radical anions and alkyl and benzyl radicals by laser-flash photolysis

    DEFF Research Database (Denmark)

    Lund, T.; Christensen, P.; Wilbrandt, Robert Walter

    2003-01-01

    Coupling rates between the radicals methyl, n-, sec-, tert-butyl and benzyl (R-.) and the aromatic radical anions of 1,4-dicyanonaphthalene, 9,10-dicyanoanthracene and fluorenone (A(-.)) have been obtained using a new laser-flash photolysis method. The radicals R-. and the radical anions A(-.) were...... generated by a photoinduced electron transfer reaction between the aromatic compound A and the alkyl or benzyl triphenylborate anion RB(Ph)(3)(-). For the first time the rate constants of the coupling reaction between methyl and benzyl radicals with aromatic radical anions have been obtained. For all...... of the radicals and the structure and standard potentials of the aromatic radical anions....

  20. The Transfer of Atoms, Ions and Molecular Groups in Solution. Part 3. Monte Carlo Methods for the Evaluation of Rate Constants.

    Science.gov (United States)

    1983-10-31

    tranal. Sykes and Bell) pp. 342-51 12. J. M. McKinley and P. P. Schmidt, Che. Phys. Letters, submitted. and ref. (4) 13. G. Arfken . Mathematical Methods ...Transfer of Atoms, Ions and Molecular Groups Nf in Solution.III. Monte Carlo methods for the evaluation of rate constants I by P. P. Schmidt Prepared...technical Groups in Solution.poilI. Monte Carlo methods for the evaluation of rate a. PERFORMING ORG. REPORT NUMBER congtant 7, AUTHOR(e) B. CONTRACT Oft

  1. Structural effects on the beta-scission reaction of alkoxyl radicals. Direct measurement of the absolute rate constants for ring opening of benzocycloalken-1-oxyl radicals.

    Science.gov (United States)

    Bietti, Massimo; Lanzalunga, Osvaldo; Salamone, Michela

    2005-02-18

    [reaction: see text] The absolute rate constants for beta-scission of a series of benzocycloalken-1-oxyl radicals and of the 2-(4-methylphenyl)-2-butoxyl radical have been measured directly by laser flash photolysis. The benzocycloalken-1-oxyl radicals undergo ring opening with rates which parallel the ring strain of the corresponding cycloalkanes. In the 1-X-indan-1-oxyl radical series, ring opening is observed when X = H, Me, whereas exclusive C-X bond cleavage occurs when X = Et. The factors governing the fragmentation regioselectivity are discussed.

  2. Investigation of the Flow Rate Effect Upstream of the Constant-Geometry Throttle on the Gas Mass Flow

    Directory of Open Access Journals (Sweden)

    Yu. M. Timofeev

    2016-01-01

    Full Text Available The turbulent-flow throttles are used in pneumatic systems and gas-supply ones to restrict or measure gas mass flow. It is customary to install the throttles in joints of pipelines (in teejoints and cross tees or in joints of pipelines with pneumatic automation devices Presently, in designing the pneumatic systems and gas-supply ones a gas mass flow through a throttle is calculated by a known equation derived from the Saint-Venant-Vantсel formula for the adiabatic flow of ideal gas through a nozzle from an unrestrictedly high capacity tank. Neglect of gas velocity at the throttle inlet is one of the assumptions taken in the development of the above equation. As may be seen in practice, in actual systems the diameters of the throttle and the pipe wherein it is mounted can be commensurable. Neglect of the inlet velocity therewith can result in an error when determining the required throttle diameter in design calculation and a flow rate in checking calculation, as well as when measuring a flow rate in the course of the test. The theoretical study has revealed that the flow velocity at the throttle inlet is responsible for two parameter values: the outlet flow velocity and the critical pressure ratio, which in turn determine the gas mass flow value. To calculate the gas mass flow, the dependencies are given in the paper, which allow taking into account the flow rate at the throttle inlet. The analysis of obtained dependencies has revealed that the degree of influence of inlet flow rate upon the mass flow is defined by two parameters: pressure ratio at the throttle and open area ratio of the throttle and the pipe wherein it is mounted. An analytical investigation has been pursued to evaluate the extent to which the gas mass flow through the throttle is affected by the inlet flow rate. The findings of the investigation and the indications for using the present dependencies are given in this paper. By and large the investigation allowed the

  3. Fracture in Westerly granite under AE feedback and constant strain rate loading: Nucleation, quasi-static propagation, and the transition to unstable fracture propagation

    Science.gov (United States)

    Thompson, B.D.; Young, R.P.; Lockner, D.A.

    2006-01-01

    New observations of fracture nucleation are presented from three triaxial compression experiments on intact samples of Westerly granite, using Acoustic Emission (AE) monitoring. By conducting the tests under different loading conditions, the fracture process is demonstrated for quasi-static fracture (under AE Feedback load), a slowly developing unstable fracture (loaded at a 'slow' constant strain rate of 2.5 ?? 10-6/s) and an unstable fracture that develops near instantaneously (loaded at a 'fast' constant strain rate of 5 ?? 10-5/s). By recording a continuous ultrasonic waveform during the critical period of fracture, the entire AE catalogue can be captured and the exact time of fracture defined. Under constant strain loading, three stages are observed: (1) An initial nucleation or stable growth phase at a rate of ??? 1.3 mm/s, (2) a sudden increase to a constant or slowly accelerating propagation speed of ??? 18 mm/s, and (3) unstable, accelerating propagation. In the ??? 100 ms before rupture, the high level of AE activity (as seen on the continuous record) prevented the location of discrete AE events. A lower bound estimate of the average propagation velocity (using the time-to-rupture and the existing fracture length) suggests values of a few m/s. However from a low gain acoustic record, we infer that in the final few ms, the fracture propagation speed increased to 175 m/s. These results demonstrate similarities between fracture nucleation in intact rock and the nucleation of dynamic instabilities in stick slip experiments. It is suggested that the ability to constrain the size of an evolving fracture provides a crucial tool in further understanding the controls on fracture nucleation. ?? Birkha??user Verlag, Basel, 2006.

  4. Reaction rate constant of CH2O + H = HCO + H2 revisited: a combined study of direct shock tube measurement and transition state theory calculation.

    Science.gov (United States)

    Wang, Shengkai; Dames, Enoch E; Davidson, David F; Hanson, Ronald K

    2014-11-06

    The rate constant of the H-abstraction reaction of formaldehyde (CH2O) by hydrogen atoms (H), CH2O + H = H2 + HCO, has been studied behind reflected shock waves with use of a sensitive mid-IR laser absorption diagnostic for CO, over temperatures of 1304-2006 K and at pressures near 1 atm. C2H5I was used as an H atom precursor and 1,3,5-trioxane as the CH2O precursor, to generate a well-controlled CH2O/H reacting system. By designing the experiments to maintain relatively constant H atom concentrations, the current study significantly boosted the measurement sensitivity of the target reaction and suppressed the influence of interfering reactions. The measured CH2O + H rate constant can be expressed in modified Arrhenius from as kCH2O+H(1304-2006 K, 1 atm) = 1.97 × 10(11)(T/K)(1.06) exp(-3818 K/T) cm(3) mol(-1)s(-1), with uncertainty limits estimated to be +18%/-26%. A transition-state-theory (TST) calculation, using the CCSD(T)-F12/VTZ-F12 level of theory, is in good agreement with the shock tube measurement and extended the temperature range of the current study to 200-3000 K, over which a modified Arrhenius fit of the rate constant can be expressed as kCH2O+H(200-3000 K) = 5.86 × 10(3)(T/K)(3.13) exp(-762 K/T) cm(3) mol(-1)s(-1).

  5. Do Insect Populations Die at Constant Rates as They Become Older? Contrasting Demographic Failure Kinetics with Respect to Temperature According to the Weibull Model.

    Directory of Open Access Journals (Sweden)

    Petros Damos

    Full Text Available Temperature implies contrasting biological causes of demographic aging in poikilotherms. In this work, we used the reliability theory to describe the consistency of mortality with age in moth populations and to show that differentiation in hazard rates is related to extrinsic environmental causes such as temperature. Moreover, experiments that manipulate extrinsic mortality were used to distinguish temperature-related death rates and the pertinence of the Weibull aging model. The Newton-Raphson optimization method was applied to calculate parameters for small samples of ages at death by estimating the maximum likelihoods surfaces using scored gradient vectors and the Hessian matrix. The study reveals for the first time that the Weibull function is able to describe contrasting biological causes of demographic aging for moth populations maintained at different temperature regimes. We demonstrate that at favourable conditions the insect death rate accelerates as age advances, in contrast to the extreme temperatures in which each individual drifts toward death in a linear fashion and has a constant chance of passing away. Moreover, slope of hazard rates shifts towards a constant initial rate which is a pattern demonstrated by systems which are not wearing out (e.g. non-aging since the failure, or death, is a random event independent of time. This finding may appear surprising, because, traditionally, it was mostly thought as rule that in aging population force of mortality increases exponentially until all individuals have died. Moreover, in relation to other studies, we have not observed any typical decelerating aging patterns at late life (mortality leveling-off, but rather, accelerated hazard rates at optimum temperatures and a stabilized increase at the extremes.In most cases, the increase in aging-related mortality was simulated reasonably well according to the Weibull survivorship model that is applied. Moreover, semi log- probability hazard

  6. Review of Rate Constants and Exploration of Correlations of the Halogen Transfer Reaction of Tri-substituted Carbon-centered Radicals with Molecular Halogens

    Energy Technology Data Exchange (ETDEWEB)

    Poutsma, Marvin L [ORNL

    2012-01-01

    Rate constants for the reaction (R 3C + X2 R 3CX + X ; X = F, Cl, Br, and I) are reviewed. Because of curved Arrhenius plots and negative EX values, empirical structure-reactivity correlations are sought for log kX,298 rather than EX. The well-known poor correlation with measures of reaction enthalpy is demonstrated. The best quantitative predictor for R 3C is p, the sum of the Hammett p constants for the three substituents, R . Electronegative substituents with lone pairs, such as halogen or oxygen, thus appear to destabilize the formation of a polarized pre-reaction complex and/or TS ( +R---X---X -) by -inductive/field electron withdrawal while simultaneously stabilizing them by -resonance electron donation. The best quantitative predictor of the reactivity order of the halogens, I2 > Br2 >> Cl2 F2, is the polarizability of the halogen, (X-X). For the data set of 60 rate constants which span 6.5 orders of magnitude, a modestly successful correlation of log kX,298 is achieved with only two parameters, p and (X-X), with a mean unsigned deviation of 0.59 log units. How much of this residual variance is the result of inaccuracies in the data compared with over-simplification of the correlation approach remains to be seen.

  7. Correction of dead-time and pile-up in a detector array for constant and rapidly varying counting rates

    Energy Technology Data Exchange (ETDEWEB)

    Guerrero, C. [Centro de Investigaciones Medioambientales, Energéticas y Tecnológicas (CIEMAT), Madrid (Spain); Departamento de Física Atómica, Molecular y Nuclear, Universidad de Sevilla (Spain); Cano-Ott, D.; Mendoza, E. [Centro de Investigaciones Medioambientales, Energéticas y Tecnológicas (CIEMAT), Madrid (Spain); Wright, T. [University of Manchester, Manchester (United Kingdom)

    2015-03-21

    The effect of dead-time and pile-up in counting experiments may become a significant source of uncertainty if not properly taken into account. Although analytical solutions to this problem have been proposed for simple set-ups with one or two detectors, these are limited when it comes to arrays where time correlation between the detector modules is used, and also in situations of variable counting rates. In this paper we describe the dead-time and pile-up corrections applied to the n-TOF Total Absorption Calorimeter (TAC), a 4π γ-ray detector made of 40 BaF{sub 2} modules operating at the CERN n-TOF facility. Our method is based on the simulation of the complete signal detection and event reconstruction processes and can be applied as well in the case of rapidly varying counting rates. The method is discussed in detail and then we present its successful application to the particular case of the measurement of {sup 238}U(n, γ) reactions with the TAC detector.

  8. Binding of hairpin pyrrole and imidazole polyamides to DNA: relationship between torsion angle and association rate constants.

    Science.gov (United States)

    Han, Yong-Woon; Matsumoto, Tomoko; Yokota, Hiroaki; Kashiwazaki, Gengo; Morinaga, Hironobu; Hashiya, Kaori; Bando, Toshikazu; Harada, Yoshie; Sugiyama, Hiroshi

    2012-12-01

    N-methylpyrrole (Py)-N-methylimidazole (Im) polyamides are small organic molecules that bind to DNA with sequence specificity and can be used as synthetic DNA-binding ligands. In this study, five hairpin eight-ring Py-Im polyamides 1-5 with different number of Im rings were synthesized, and their binding behaviour was investigated with surface plasmon resonance assay. It was found that association rate (k(a)) of the Py-Im polyamides with their target DNA decreased with the number of Im in the Py-Im polyamides. The structures of four-ring Py-Im polyamides derived from density functional theory revealed that the dihedral angle of the Py amide carbonyl is 14∼18°, whereas that of the Im is significantly smaller. As the minor groove of DNA has a helical structure, planar Py-Im polyamides need to change their conformation to fit it upon binding to the minor groove. The data explain that an increase in planarity of Py-Im polyamide induced by the incorporation of Im reduces the association rate of Py-Im polyamides. This fundamental knowledge of the binding of Py-Im polyamides to DNA will facilitate the design of hairpin Py-Im polyamides as synthetic DNA-binding modules.

  9. Effect of a constant rate infusion of cytosine arabinoside on mortality in dogs with meningoencephalitis of unknown origin.

    Science.gov (United States)

    Lowrie, M; Thomson, S; Smith, P; Garosi, L

    2016-07-01

    Administration of cytosine arabinoside (CA) by continuous rate infusion (CRI) has pharmacokinetic and pharmacodynamic advantages over traditional intermittent dosing. Whether these advantages translate into clinical efficacy remains unknown. The aim of this study was to assess the efficacy and safety of CRI of CA in dogs with meningoencephalitis of unknown origin (MUO) and to compare outcomes with a group of historical control dogs treated with conventional intermittent subcutaneous (SC) administration of CA; both groups received adjunctive prednisolone. It was hypothesised that a CRI of CA for 24 h at 100 mg/m(2) would improve survival and lesion resolution compared with conventional SC delivery of 50 mg/m(2) every 12 h for 48 h. Eighty dogs with suspected MUO were recruited from consecutive dogs presenting with suspected MUO from 2006 to 2015. All dogs underwent routine clinical evaluation, magnetic resonance imaging of the brain and cerebrospinal fluid analysis. There were 39 dogs in the SC group and 41 dogs in the CRI group; baseline characteristics were similar in both groups. Survival at 3 months was 22/39 (44%) with SC delivery versus 37/41 (90%) with CRI. No dose-limiting toxicities were noted for either group. The resolution rate of magnetic resonance imaging and cerebrospinal fluid abnormalities at the 3 month re-examination were substantially improved in the CRI group versus the SC group. The CRI regimen produced a survival advantage over the SC route of administration without clinically significant toxicity. These data supports the routine use of CRI at first presentation for the treatment of MUO in dogs. Crown Copyright © 2016. Published by Elsevier Ltd. All rights reserved.

  10. Comparison of the effects of xylazine bolus versus medetomidine constant rate infusion on cardiopulmonary function and depth of anesthesia in horses anesthetized with isoflurane.

    Science.gov (United States)

    Creighton, Catherine M; Lemke, Kip A; Lamont, Leigh A; Horney, Barbara S; Riley, Christopher B

    2012-04-15

    To compare the effects of xylazine bolus versus medetomidine constant rate infusion (MCRI) on cardiopulmonary function and depth of anesthesia in dorsally recumbent, spontaneously breathing, isoflurane-anesthetized horses. Prospective, randomized crossover study. 10 healthy adult Standardbreds. Horses were premedicated with xylazine or medetomidine IV. Anesthesia was induced with diazepam and ketamine and maintained with isoflurane for 150 minutes. For the xylazine treatment, end-tidal isoflurane concentration was maintained at 1.7%, and xylazine (0.2 mg/kg [0.09 mg/lb], IV) was administered as a bolus at the end of anesthesia. For the MCRI treatment, end-tidal isoflurane concentration was maintained at 1.4%, and medetomidine (0.005 mg/kg/h [0.0023 mg/lb/h], IV) was infused throughout anesthesia. Physiologic data (ie, heart rate, respiratory rate, rectal temperature, bispectral index, and electromyographic values) were compared between treatments with xylazine bolus versus MCRI. Heart rate was lower, but mean arterial blood pressure was higher from 20 to 40 minutes with MCRI treatment, compared with conventional treatment with xylazine. Respiratory rate and rectal temperature were greater with MCRI treatment. Bispectral index was lower with MCRI treatment from 80 to 150 minutes, and electromyographic values were lower with MCRI treatment from 30 to 150 minutes. In isoflurane-anesthetized horses, premedication with medetomidine followed by administration of medetomidine as a constant rate infusion resulted in decreased heart rate, higher arterial blood pressure from 20 through 40 minutes after induction of anesthesia, and better preserved body temperature, compared with conventional treatment with xylazine. Greater depth of anesthesia and muscle relaxation were seen with MCRI treatment, despite the lower isoflurane concentration.

  11. Evaluation of a balloon constant rate infusion system for treatment of septic arthritis, septic tenosynovitis, and contaminated synovial wounds: 23 cases (2002-2005).

    Science.gov (United States)

    Meagher, Daniel T; Latimer, Federico G; Sutter, W Wes; Saville, William J A

    2006-06-15

    OBJECTIVE-To determine clinical findings and outcome in horses treated by means of a balloon constant rate infusion system. DESIGN-Retrospective case series. ANIMALS-23 horses. PROCEDURES-Medical records of horses examined at The Ohio State University veterinary teaching hospital from 2002 to 2005 that had septic arthritis, septic tenosynovitis, or penetration of a synovial structure and in which treatment involved a balloon constant rate infusion system were searched. Information pertaining to signalment, history, physical examination findings, clinicopathologic data, treatment, and duration of hospitalization was recorded. RESULTS-Mean+/- SD duration of hospitalization was 11.5+/-5.26 days. No correlation between duration of clinical signs and duration of hospitalization or duration of infusion pump use was detected, but correlations between WBC count and duration of hospitalization and WBC and duration of infusion-pump use were observed. All horses survived to discharge. Follow-up information was obtained on 17 horses, 16 of which were alive at the time of follow-up. Twelve of 13 horses for which followup information was available for at least 5 months were alive 5 months or longer after discharge. Thirteen of the 16 horses alive at follow-up were reported by owners as not lame, whereas the remaining 3 were mildly lame or intermittently moderately lame or had developed angular limb deformity in the contralateral limb. CONCLUSIONS AND CLINICAL RELEVANCE-Balloon constant rate infusion systems may be used effectively in treatment of septic arthritis, septic tenosynovitis, and contaminated synovial wounds. Clinical response and long-term outcome appeared to be comparable to results obtained with other techniques.

  12. Time-Dependent Quantum Wave Packet Study of the Si + OH → SiO + H Reaction: Cross Sections and Rate Constants.

    Science.gov (United States)

    Rivero Santamaría, Alejandro; Dayou, Fabrice; Rubayo-Soneira, Jesus; Monnerville, Maurice

    2017-02-15

    The dynamics of the Si((3)P) + OH(X(2)Π) → SiO(X(1)Σ(+)) + H((2)S) reaction is investigated by means of the time-dependent wave packet (TDWP) approach using an ab initio potential energy surface recently developed by Dayou et al. ( J. Chem. Phys. 2013 , 139 , 204305 ) for the ground X(2)A' electronic state. Total reaction probabilities have been calculated for the first 15 rotational states j = 0-14 of OH(v=0,j) at a total angular momentum J = 0 up to a collision energy of 1 eV. Integral cross sections and state-selected rate constants for the temperature range 10-500 K were obtained within the J-shifting approximation. The reaction probabilities display highly oscillatory structures indicating the contribution of long-lived quasibound states supported by the deep SiOH/HSiO wells. The cross sections behave with collision energies as expected for a barrierless reaction and are slightly sensitive to the initial rotational excitation of OH. The thermal rate constants show a marked temperature dependence below 200 K with a maximum value around 15 K. The TDWP results globally agree with the results of earlier quasi-classical trajectory (QCT) calculations carried out by Rivero-Santamaria et al. ( Chem. Phys. Lett. 2014 , 610-611 , 335 - 340 ) with the same potential energy surface. In particular, the thermal rate constants display a similar temperature dependence, with TDWP values smaller than the QCT ones over the whole temperature range.

  13. Influence of pH and ionic strength on electrostatic properties of ferredoxin, FNR, and hydrogenase and the rate constants of their interaction

    Science.gov (United States)

    Diakonova, A. N.; Khrushchev, S. S.; Kovalenko, I. B.; Riznichenko, G. Yu; Rubin, A. B.

    2016-10-01

    Ferredoxin (Fd) protein transfers electrons from photosystem I (PSI) to ferredoxin:NADP+-reductase (FNR) in the photosynthetic electron transport chain, as well as other metabolic pathways. In some photosynthetic organisms including cyanobacteria and green unicellular algae under anaerobic conditions Fd transfers electrons not only to FNR but also to hydrogenase—an enzyme which catalyzes reduction of atomic hydrogen to H2. One of the questions posed by this competitive relationship between proteins is which characteristics of thylakoid stroma media allow switching of the electron flow between the linear path PSI-Fd-FNR-NADP+ and the path PSI-Fd-hydrogenase-H2. The study was conducted using direct multiparticle simulation approach. In this method protein molecules are considered as individual objects that experience Brownian motion and electrostatic interaction with the surrounding media and each other. Using the model we studied the effects of pH and ionic strength (I) upon complex formation between ferredoxin and FNR and ferredoxin and hydrogenase. We showed that the rate constant of Fd-FNR complex formation is constant in a wide range of physiologically significant pH values. Therefore it can be argued that regulation of FNR activity doesn’t involve pH changes in stroma. On the other hand, in the model rate constant of Fd-hydrogenase interaction dramatically depends upon pH: in the range 7-9 it increases threefold. It may seem that because hydrogenase reduces protons it should be more active when pH is acidic. Apparently, regulation of hydrogenase’s affinity to both her reaction partners (H+ and Fd) is carried out by changes in its electrostatic properties. In the dark, the protein is inactive and in the light it is activated and starts to interact with both Fd and H+. Therefore, we can conclude that in chloroplasts the rate of hydrogen production is regulated by pH through the changes in the affinity between hydrogenase and ferredoxin.

  14. Varying Constants

    CERN Document Server

    Damour, Thibault Marie Alban Guillaume

    2003-01-01

    We review some string-inspired theoretical models which incorporate a correlated spacetime variation of coupling constants while remaining naturally compatible both with phenomenological constraints coming from geochemical data (Oklo; Rhenium decay) and with present equivalence principle tests. Barring unnatural fine-tunings of parameters, a variation of the fine-structure constant as large as that recently ``observed'' by Webb et al. in quasar absorption spectra appears to be incompatible with these phenomenological constraints. Independently of any model, it is emphasized that the best experimental probe of varying constants are high-precision tests of the universality of free fall, such as MICROSCOPE and STEP. Recent claims by Bekenstein that fine-structure-constant variability does not imply detectable violations of the equivalence principle are shown to be untenable.

  15. Beyond transition state theory: accurate description of nuclear quantum effects on the rate and equilibrium constants of chemical reactions using Feynman path integrals.

    Science.gov (United States)

    Vanícek, Jirí

    2011-01-01

    Nuclear tunneling and other nuclear quantum effects have been shown to play a significant role in molecules as large as enzymes even at physiological temperatures. I discuss how these quantum phenomena can be accounted for rigorously using Feynman path integrals in calculations of the equilibrium and kinetic isotope effects as well as of the temperature dependence of the rate constant. Because these calculations are extremely computationally demanding, special attention is devoted to increasing the computational efficiency by orders of magnitude by employing efficient path integral estimators.

  16. Site-Specific Rate Constant Measurements for Primary and Secondary H- and D-Abstraction by OH Radicals: Propane and n -Butane

    KAUST Repository

    Badra, Jihad

    2014-07-03

    Site-specific rate constants for hydrogen (H) and deuterium (D) abstraction by hydroxyl (OH) radicals were determined experimentally by monitoring the reaction of OH with two normal and six deuterated alkanes. The studied alkanes include propane (C3H8), propane 2,2 D2 (CH 3CD2CH3), propane 1,1,1-3,3,3 D6 (CD 3CH2CD3), propane D8 (C3D 8), n-butane (n-C4H10), butane 2,2-3,3 D4 (CH3CD2CD2CH3), butane 1,1,1-4,4,4 D6 (CD3CH2CH2CD3), and butane D10 (C4D10). Rate constant measurements were carried out over 840-1470 K and 1.2-2.1 atm using a shock tube and OH laser absorption. Previous low-temperature data were combined with the current high-temperature measurements to generate three-parameter fits which were then used to determine the site-specific rate constants. Two primary (P1,H and P 1,D) and four secondary (S00,H, S00,D, S 01,H, and S01,D) H- and D-abstraction rate constants, in which the subscripts refer to the number of C atoms connected to the next-nearest-neighbor C atom, are obtained. The modified Arrhenius expressions for the six site-specific abstractions by OH radicals are P1,H = 1.90 × 10-18T2.00 exp(-340.87 K/T) cm 3molecule-1s-1 (210-1294 K); P1,D= 2.72 × 10-17 T1.60 exp(-895.57 K/T) cm 3molecule-1s-1 (295-1317 K); S00,H = 4.40 × 10-18 T1.93 exp(121.50 K/T) cm 3molecule-1s-1 (210-1294 K); S00,D = 1.45 × 10-20 T2.69 exp(282.36 K/T) cm 3molecule-1s-1 (295-1341 K); S01,H = 4.65 × 10-17 T1.60 exp(-236.98 K/T) cm 3molecule-1s-1 (235-1407 K); S01,D = 1.26 × 10-18 T2.07 exp(-77.00 K/T) cm 3molecule-1s-1 (294-1412 K). © 2014 American Chemical Society.

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

    Science.gov (United States)

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

    2009-01-01

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

  18. Excited-state structure, vibrations, and nonradiative relaxation of jet-cooled 5-fluorocytosine.

    Science.gov (United States)

    Lobsiger, Simon; Trachsel, Maria A; Den, Takuya; Leutwyler, Samuel

    2014-03-20

    The S0 → S1 vibronic spectrum and S1 state nonradiative relaxation of jet-cooled keto-amino 5-fluorocytosine (5FCyt) are investigated by two-color resonant two-photon ionization spectroscopy at 0.3 and 0.05 cm(–1) resolution. The 0(0)(0) rotational band contour is polarized in-plane, implying that the electronic transition is (1)ππ*. The electronic transition dipole moment orientation and the changes of rotational constants agree closely with the SCS-CC2 calculated values for the (1)ππ* (S1) transition of 5FCyt. The spectral region from 0 to 300 cm(–1) is dominated by overtone and combination bands of the out-of-plane ν1′ (boat), ν2′ (butterfly), and ν3′ (HN–C6H twist) vibrations, implying that the pyrimidinone frame is distorted out-of-plane by the (1)ππ* excitation, in agreement with SCS-CC2 calculations. The number of vibronic bands rises strongly around +350 cm(–1); this is attributed to the (1)ππ* state barrier to planarity that corresponds to the central maximum of the double-minimum out-of-plane vibrational potentials along the ν1′, ν2′, and ν3′ coordinates, which gives rise to a high density of vibronic excitations. At +1200 cm(–1), rapid nonradiative relaxation (k(nr) ≥ 10(12) s(–1)) sets in, which we interpret as the height of the (1)ππ* state barrier in front of the lowest S1/S0 conical intersection. This barrier in 5FCyt is 3 times higher than that in cytosine. The lifetimes of the ν′ = 0, 2ν1′, 2ν2′, 2ν1′ + 2ν2′, 4ν2′, and 2ν1′ + 4ν2′ levels are determined from Lorentzian widths fitted to the rotational band contours and are τ ≥ 75 ps for ν′ = 0, decreasing to τ ≥ 55 ps at the 2ν1′ + 4ν2′ level at +234 cm(–1). These gas-phase lifetimes are twice those of S1 state cytosine and 10–100 times those of the other canonical nucleobases in the gas phase. On the other hand, the 5FCyt gas-phase lifetime is close to the 73 ps lifetime in room-temperature solvents. This lack of

  19. Rate constants for the thermal decomposition of ethanol and its bimolecular reactions with OH and D: reflected shock tube and theoretical studies.

    Science.gov (United States)

    Sivaramakrishnan, R; Su, M-C; Michael, J V; Klippenstein, S J; Harding, L B; Ruscic, B

    2010-09-09

    The thermal decomposition of ethanol and its reactions with OH and D have been studied with both shock tube experiments and ab initio transition state theory-based master equation calculations. Dissociation rate constants for ethanol have been measured at high T in reflected shock waves using OH optical absorption and high-sensitivity H-atom ARAS detection. The three dissociation processes that are dominant at high T are C2H5OH--> C2H4+H2O (A) -->CH3+CH2OH (B) -->C2H5+OH (C).The rate coefficient for reaction C was measured directly with high sensitivity at 308 nm using a multipass optical White cell. Meanwhile, H-atom ARAS measurements yield the overall rate coefficient and that for the sum of reactions B and C , since H-atoms are instantaneously formed from the decompositions of CH(2)OH and C(2)H(5) into CH(2)O + H and C(2)H(4) + H, respectively. By difference, rate constants for reaction 1 could be obtained. One potential complication is the scavenging of OH by unreacted ethanol in the OH experiments, and therefore, rate constants for OH+C2H5OH-->products (D)were measured using tert-butyl hydroperoxide (tBH) as the thermal source for OH. The present experiments can be represented by the Arrhenius expression k=(2.5+/-0.43) x 10(-11) exp(-911+/-191 K/T) cm3 molecule(-1) s(-1) over the T range 857-1297 K. For completeness, we have also measured the rate coefficient for the reaction of D atoms with ethanol D+C2H5OH-->products (E) whose H analogue is another key reaction in the combustion of ethanol. Over the T range 1054-1359 K, the rate constants from the present experiments can be represented by the Arrhenius expression, k=(3.98+/-0.76) x10(-10) exp(-4494+/-235 K/T) cm3 molecule(-1) s(-1). The high-pressure rate coefficients for reactions B and C were studied with variable reaction coordinate transition state theory employing directly determined CASPT2/cc-pvdz interaction energies. Reactions A , D , and E were studied with conventional transition state theory

  20. Calculated rate constants of the chemical reactions involving the main byproducts SO2F, SOF2, SO2F2 of SF6 decomposition in power equipment

    Science.gov (United States)

    Fu, Yuwei; Rong, Mingzhe; Yang, Kang; Yang, Aijun; Wang, Xiaohua; Gao, Qingqing; Liu, Dingxin; Murphy, Anthony B.

    2016-04-01

    SF6 is widely used in electrical equipment as an insulating gas. In the presence of an electric arc, partial discharge (PD) or spark, SF6 dissociation products (such as SF2, SF3 and SF4) react with the unavoidable gas impurities (such as water vapor and oxygen), electrodes and surrounding solid insulation materials, forming several toxic and corrosive byproducts. The main stable decomposition products are SO2F, SO2F2 and SOF2, which have been confirmed experimentally to have a direct relationship with discharge faults, and are thus expected to be useful in the fault diagnosis of power equipment. Various studies have been performed of the main SF6 decomposition species and their concentrations under different types of faults. However, most of the experiments focused on the qualitative analysis of the relationship between the stable products and discharge faults. Although some theoretical research on the formation of main SF6 derivatives have been carried out using chemical kinetics models, the basic data (chemical reactions and their rate constants) adopted in the model are inaccurate and incomplete. The complex chemical reactions of SF6 with the impurities are ignored in most cases. The rate constants of some reactions obtained at ambient temperature or in a narrow temperature range are adopted in the models over a far greater range, for example up to 12 000 K, due to the difficulty in the experimental measurement and theoretical estimation of rate coefficients, particularly at high temperatures. Therefore, improved theoretical models require not only the consideration of additional SF6 decomposition reactions in the presence of impurities but also on improved values of rate constants. This paper is devoted to determining the rate constants of the chemical reactions relating to the main byproducts of SF6 decomposition in SF6 gas-insulated power equipment: SO2F, SOF2 and SO2F2. Quantum chemistry calculations with density functional theory, conventional

  1. Predicted Chemical Activation Rate Constants for HO2 + CH2NH: The Dominant Role of a Hydrogen-Bonded Pre-reactive Complex.

    Science.gov (United States)

    Ali, Mohamad Akbar; Sonk, Jason A; Barker, John R

    2016-09-15

    The reaction of methanimine (CH2NH) with the hydroperoxy (HO2) radical has been investigated by using a combination of ab initio and density functional theory (CCSD(T)/CBSB7//B3LYP+Dispersion/CBSB7) and master equation calculations based on transition state theory (TST). Variational TST was used to compute both canonical (CVTST) and microcanonical (μVTST) rate constants for barrierless reactions. The title reaction starts with the reversible formation of a cyclic prereactive complex (PRC) that is bound by ∼11 kcal/mol and contains hydrogen bonds to both nitrogen and oxygen. The reaction path for the entrance channel was investigated by a series of constrained optimizations, which showed that the reaction is barrierless (i.e., no intrinsic energy barrier along the path). However, the variations in the potential energy, vibrational frequencies, and rotational constants reveal that the two hydrogen bonds are formed sequentially, producing two reaction flux bottlenecks (i.e., two transition states) along the reaction path, which were modeled using W. H. Miller's unified TST approach. The rate constant computed for the formation of the PRC is pressure-dependent and increases at lower temperatures. Under atmospheric conditions, the PRC dissociates rapidly and its lifetime is too short for it to undergo significant bimolecular reaction with other species. A small fraction isomerizes via a cyclic transition state and subsequent reactions lead to products normally expected from hydrogen abstraction reactions. The kinetics of the HO2 + CH2NH reaction system differs substantially from the analogous isoelectronic reaction systems involving C2H4 and CH2O, which have been the subjects of previous experimental and theoretical studies.

  2. Picosecond nonradiative processes in neodymium-doped crystals and glasses: mechansim for the energy gap law

    Energy Technology Data Exchange (ETDEWEB)

    Bibeau, C.; Payne, S.A.

    1997-09-29

    We present measurements of the 4G7/2 emission lifetime for 26 Nd-doped materials. A model of nonradiative decay based on dipole-dipole energy transfer is developed and found to be supported by our data.

  3. Accessing reaction rate constants in on-column reaction chromatography: an extended unified equation for reaction educts and products with different response factors.

    Science.gov (United States)

    Trapp, Oliver; Bremer, Sabrina; Weber, Sven K

    2009-11-01

    An extension of the unified equation of chromatography to directly access reaction rate constants k(1) of first-order reaction in on-column chromatography is presented. This extended equation reflects different response factors in the detection of the reaction educt and product which arise from structural changes by elimination or addition, e.g., under pseudo-first-order reaction conditions. The reaction rate constants k(1) and Gibbs activation energies DeltaG(double dagger) of first-order reactions taking place in a chromatographic system can be directly calculated from the chromatographic parameters, i.e., retention times of the educt E and product P (t(R)(A) and t(R)(B)), peak widths at half height (w(A) and w(B)), the relative plateau height (h(p)) of the conversion profile, and the individual response factors f(A) and f(B). The evaluation of on-column reaction gas chromatographic experiments is exemplified by the evaluation of elution profiles obtained by ring-closing metathesis reaction of N,N-diallytrifluoroacetamide in presence of Grubbs second-generation catalyst, dissolved in polydimethylsiloxane (GE SE 30).

  4. Quantum mechanical calculations of state-to-state cross sections and rate constants for the F + DCl → Cl + DF reaction.

    Science.gov (United States)

    Bulut, Niyazi; Kłos, Jacek; Roncero, Octavio

    2015-06-07

    We present accurate state-to-state quantum wave packet calculations of integral cross sections and rate constants for the title reaction. Calculations are carried out on the best available ground 1(2)A' global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged state-to-state reaction cross sections have been calculated for collision energies up to 0.5 eV and different initial rotational and vibrational excitations, DCl(v = 0, j = 0 - 1; v = 1, j = 0). Also, initial-state resolved rate constants of the title reaction have been calculated in a temperature range of 100-400 K. It is found that the initial rotational excitation of the DCl molecule does not enhance reactivity, in contract to the reaction with the isotopologue HCl in which initial rotational excitation produces an important enhancement. These differences between the isotopologue reactions are analyzed in detail and attributed to the presence of resonances for HCl(v = 0, j), absent in the case of DCl(v = 0, j). For vibrational excited DCl(v = 1, j), however, the reaction cross section increases noticeably, what is also explained by another resonance.

  5. Direct measurements of the total rate constant of the reaction NCN + H and implications for the product branching ratio and the enthalpy of formation of NCN.

    Science.gov (United States)

    Fassheber, Nancy; Dammeier, Johannes; Friedrichs, Gernot

    2014-06-21

    The overall rate constant of the reaction (2), NCN + H, which plays a key role in prompt-NO formation in flames, has been directly measured at temperatures 962 K reaction channel (2a) yielding CH + N2 and channel (2b) yielding HCN + N as the products. A more refined analysis taking into account experimental and theoretical literature data provided a consistent rate constant set for k2a, its reverse reaction k1a (CH + N2 → NCN + H), k2b as well as a value for the controversial enthalpy of formation of NCN, ΔfH = 450 kJ mol(-1). The analysis verifies the expected strong temperature dependence of the branching fraction ϕ = k2b/k2 with reaction channel (2b) dominating at the experimental high-temperature limit. In contrast, reaction (2a) dominates at the low-temperature limit with a possible minor contribution of the HNCN forming recombination channel (2d) at T < 1150 K.

  6. Theoretical study on rate constants for the reactions of CF3CH 2NH 2 (TFEA) with the hydroxyl radical at 298 K and atmospheric pressure.

    Science.gov (United States)

    Mishra, Bhupesh Kumar; Chakrabartty, Arup Kumar; Deka, Ramesh Chandra

    2013-06-01

    Theoretical investigations are carried out on reaction mechanism of the reactions of CF3CH2NH2 (TFEA) with the OH radical by means of ab initio and DFT methods. The electronic structure information on the potential energy surface for each reaction is obtained at MPWB1K/6-31+G(d,p) level and energetic information is further refined by calculating the energy of the species with a Gaussian-2 method, G2(MP2). The existence of transition states on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation. Our calculation indicates that the H abstraction from -NH2 group is the dominant reaction channel because of lower energy barrier. The rate constants of the reaction calculated using canonical transition state theory (CTST) utilizing the ab initio data. The agreement between the theoretical and experimental rate constants is good at the measured temperature. From the comparison with CH3CH2NH2, it is shown that the fluorine substution decreases the reactivity of the C-H bond.

  7. Reaction dynamics with the multi-layer multi-configurational time-dependent Hartree approach: H + CH4 → H2 + CH3 rate constants for different potentials.

    Science.gov (United States)

    Welsch, Ralph; Manthe, Uwe

    2012-12-28

    The multi-layer extension of the multi-configurational time-dependent Hartree (MCTDH) approach is applied to the investigation of elementary bimolecular chemical reactions. Cumulative reaction probabilities and thermal rate constants of the H + CH(4) → H(2) + CH(3) reaction are calculated using flux correlation functions and the quantum transition state concept. Different coordinate systems and potential energy surfaces (PESs) are studied. The convergence properties of different layerings are investigated and the efficiency of multi-layer MCTDH approach is compared to the standard MCTDH approach. It is found that the multi-layer approach can decrease the numerical effort by more than an order of magnitude. The increased efficiency resulting from the multi-layer MCTDH approach is crucial for quantum dynamical calculations on recent global H + CH(4) → H(2) + CH(3) PESs, e.g., the ZBB3-PES [Z. Xie, J. M. Bowman, and X. Zhang, J. Chem. Phys. 125, 133120 (2006)] based on permutational invariant polynomials, which are numerically more demanding than earlier PESs. The results indicate that an accurate description of all transition state frequencies is important to obtain accurate thermal rate constants.

  8. On the Theory of Oxidation-Reduction Reactions Involving Electron Transfer. V. Comparison and Properties of Electrochemical and Chemical Rate Constants

    Science.gov (United States)

    Marcus, R. A.

    1962-01-01

    Using a theory of electron transfers which takes cognizance of reorganization of the medium outside the inner coordination shell and of changes of bond lengths inside it, relations between electrochemical and related chemical rate constants are deduced and compared with the experimental data. A correlation is found, without the use of arbitrary parameters. Effects of weak complexes with added electrolytes are included under specified conditions. The deductions offer a way of coordinating a variety of data in the two fields, internally as well as with each those in another. For example, the rate of oxidation or reduction of a series of related reactants by one reagent is correlated with that of another and with that of the corresponding electrochemical oxidation-reduction reaction, under certain specified conditions. These correlations may also provide a test for distinguishing an electron from an atom transfer mechanism. (auth)

  9. Penetrômetro de cone com taxa constante de penetração no solo: desenvolvimento e teste de funcionalidade Constant-rate cone penetrometer: development and functionality

    Directory of Open Access Journals (Sweden)

    Dalvan J. Reinert

    2007-04-01

    Full Text Available Penetrômetros auxiliam na determinação da capacidade de suporte do solo na engenharia civil e na avaliação da resistência mecânica de solos agrícolas, relacionando-a com compactação do solo e crescimento do sistema radicular das plantas. Este trabalho relata o desenvolvimento de um penetrômetro de cone com taxa constante de penetração, suas partes e funcionalidade, bem como resultados do uso na avaliação comparativa da compactação em experimentos e em lavoura. A quantificação da resistência é realizada com célula de carga, a distância de penetração no solo com potenciômetro, e a aquisição e o armazenamento de dados com placas eletrônicas. A concepção do equipamento, que emprega velocidade constante de penetração da haste no perfil do solo, possibilitou a aquisição de grande coleção de dados relativos com pequena variação de profundidade (5 mm, atingindo a profundidade máxima de 0,80 m. O equipamento é eficaz na aquisição e no tratamento de dados de resistência mecânica do solo à penetração em profundidade do perfil. A variação entre os pontos permite inferir sobre parâmetros e características do solo, bem como sobre o comportamento desses sob condições externas impostas, quer seja imediata, quer seja residual.Penetrometers are used to quantify soil bearing capacity in civil engineering and to evaluate mechanical resistance of agricultural soils, which is an indicator of soil compaction and of root growth. This paper reports the development, components and functionality of a constant-rate cone penetrometer, as well as its application to measure soil compaction. The force is measured by a load cell, the distance is measured by a potentiometer, and data acquisition and storage are performed by an electronic board. The equipment was tested in agricultural field transects with profile variability and experimental plots with compaction variability, generating soil penetration resistance information

  10. Rate Constants of PSII Photoinhibition and its Repair, and PSII Fluorescence Parameters in Field Plants in Relation to their Growth Light Environments.

    Science.gov (United States)

    Miyata, Kazunori; Ikeda, Hiroshi; Nakaji, Masayoshi; Kanel, Dhana Raj; Terashima, Ichiro

    2015-09-01

    The extent of photoinhibition of PSII is determined by a balance between the rate of photodamage to PSII and that of repair of the damaged PSII. It has already been indicated that the rate constants of photodamage (kpi) and repair (krec) of the leaves differ depending on their growth light environment. However, there are no studies using plants in the field. We examined these rate constants and fluorescence parameters of several field-grown plants to determine inter-relationships between these values and the growth environment. The kpi values were strongly related to the excess energy, EY, of the puddle model and non-regulated energy dissipation, Y(NO), of the lake model, both multiplied by the photosynthetically active photon flux density (PPFD) level during the photoinhibitory treatment. In contrast, the krec values corrected against in situ air temperature were very strongly related to the daily PPFD level. The plants from the fields showed higher NPQ than the chamber-grown plants, probably because these field plants acclimated to stronger lightflecks than the averaged growth PPFD. Comparing chamber-grown plants and the field plants, we showed that kpi is determined by the incident light level and the photosynthetic capacities such as in situ rate of PSII electron transport and non-photochemical quenching (NPQ) [e.g. Y(NO)×PPFD] and that krec is mostly determined by the growth light and temperature levels. © The Author 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.

  11. Monte Carlo模拟在聚合反应速率常数估算中的运用%Estimation of rate constants for polymerization based on Monte Carlo simulation

    Institute of Scientific and Technical Information of China (English)

    罗正鸿; 詹晓力; 阳永荣

    2006-01-01

    The application of Monte Carlo method in estimating rate constants for polymerization was described.A general program for Monte Carlo simulation was determined first according to the elementary reactions, after which the rate constants could be automatically adjusted and optimized through comparing of experimental and simulated data with an error expression that meeted a given minimum criterion.Such a process made the rate constants to be estimated without kinetic model in advance.The technique was applied to estimate the rate constants of the bulk polymerization of styrene catalyzed by the rare earth catalyst.The estimated results showed the Monte Carlo method was feasible and effective for estimating rate constants in polymerization engineering.

  12. Model of two-stream non-radial accretion for binary X-ray pulsars

    Energy Technology Data Exchange (ETDEWEB)

    Lipunov, V.M. (Sternberg Astronomical Inst., Moscow (USSR))

    1982-03-01

    The general case of non-radial accretion is assumed to occur in real binary systems containing X-ray pulsars. The structure and the stability of the magnetosphere, the interaction between the magnetosphere and accreted matter, as well as evolution of neutron star in close binary system are examined within the framework of the two-stream model of nonradial accretion onto a magnetized neutron star. Observable parameters of X-ray pulsars are explained in terms of the model considered.

  13. Non-radiation endoscopic retrograde cholangiopancreatography in the management of choledocholithiasis during pregnancy.

    Science.gov (United States)

    Wu, Wenming; Faigel, Douglas O; Sun, Gang; Yang, Yunsheng

    2014-11-01

    Gallstone diseases are common during pregnancy. In most cases, patients are asymptomatic and do not require any treatment. However, choledocholithiasis, cholangitis, and gallstone pancreatitis may potentially become life-threatening for both mother and fetus and often require urgent intervention. Although endoscopic retrograde cholangiopancreatography (ERCP) has become the standard technique for removing common bile duct stones, it is associated with ionizing radiation that could carry teratogenic risk. Non-radiation ERCP (NR-ERCP) is reported to be effective without incurring this risk. Two techniques have been described to confirm bile duct cannulation: bile aspiration and image guidance. With bile aspiration, biliary cannulation is confirmed by applying suction to the cannula to yield bile, thus confirming an intrabiliary position. Image guidance involves using ultrasound or direct visualization (choledochoscopy) to confirm selective biliary cannulation or duct clearance. Once cannulation is achieved, the stones are removed using standard ERCP techniques and tools. Case series and retrospective studies have reported success rates of up to 90% for NR-ERCP with complication rates similar to standard ERCP. Pregnancy outcomes are not adversely affected by NR-ERCP, but whether the avoidance of radiation carries benefit for the baby is unknown. Prospective comparative trials are lacking. NR-ERCP is technically demanding and should be attempted only by skilled biliary endoscopists in properly equipped and staffed health-care institutions, in a multidisciplinary setting. © 2014 The Authors. Digestive Endoscopy © 2014 Japan Gastroenterological Endoscopy Society.

  14. Modeling the downward transport of {sup 210}Pb in Peatlands: Initial Penetration‐Constant Rate of Supply (IP-CRS) model

    Energy Technology Data Exchange (ETDEWEB)

    Olid, Carolina, E-mail: olid.carolina@gmail.com [Department of Ecology and Environmental Science, Umeå University, SE-90187, Umeå (Sweden); Diego, David [Department of Earth Science, University of Bergen, NO-5020 Bergen (Norway); Garcia-Orellana, Jordi [Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra (Spain); Institut de Ciència i Tecnologia Ambientals (ICTA), Universitat Autònoma de Barcelona, E-08193 Bellaterra (Spain); Cortizas, Antonio Martínez [Departamento de Edafoloxía e Química Agrícola, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela (Spain); Klaminder, Jonatan [Department of Ecology and Environmental Science, Umeå University, SE-90187, Umeå (Sweden)

    2016-01-15

    The vertical distribution of {sup 210}Pb is commonly used to date peat deposits accumulated over the last 100–150 years. However, several studies have questioned this method because of an apparent post-depositional mobility of {sup 210}Pb within some peat profiles. In this study, we introduce the Initial Penetration–Constant Rate of Supply (IP-CRS) model for calculating ages derived from {sup 210}Pb profiles that are altered by an initial migration of the radionuclide. This new, two-phased, model describes the distribution of atmospheric-derived {sup 210}Pb ({sup 210}Pb{sub xs}) in peat taking into account both incorporation of {sup 210}Pb into the accumulating peat matrix as well as an initial flushing of {sup 210}Pb through the uppermost peat layers. The validity of the IP-CRS model is tested in four anomalous {sup 210}Pb peat records that showed some deviations from the typical exponential decay profile not explained by variations in peat accumulation rates. Unlike the most commonly used {sup 210}Pb-dating model (Constant Rate of Supply (CRS)), the IP-CRS model estimates peat accumulation rates consistent with typical growth rates for peatlands from the same areas. Confidence in the IP-CRS chronology is also provided by the good agreement with independent chronological markers (i.e. {sup 241}Am and {sup 137}Cs). Our results showed that the IP-CRS can provide chronologies from peat records where {sup 210}Pb mobility is evident, being a valuable tool for studies reconstructing past environmental changes using peat archives during the Anthropocene. - Highlights: • Accurate age dating of peat and sediment cores is critical for evaluating change. • A new {sup 210}Pb dating model that includes vertical transport of {sup 210}Pb was developed. • The IP-CRS model provided consistent peat accumulation rates. • The IP-CRS ages were consistent with independent chronological markers. • The IP-CRS model derives peat ages where downward {sup 210}Pb transport is

  15. Magnetic core test stand for energy loss and permeability measurements at a high constant magnetization rate and test results for nanocrystalline and ferrite materials.

    Science.gov (United States)

    Burdt, Russell; Curry, Randy D

    2008-09-01

    A test stand was developed to measure the energy losses and unsaturated permeability of toroidal magnetic cores, relevant to applications of magnetic switching requiring a constant magnetization rate of the order of 1-10 T/micros. These applications in pulsed power include linear induction accelerators, pulse transformers, and discharge switches. The test stand consists of a coaxial transmission line pulse charged up to 100 kV that is discharged into a magnetic core load. Suitable diagnostics measure the voltage across and the current through a winding on the magnetic core load, from which the energy losses and unsaturated permeability are calculated. The development of the test stand is discussed, and test results for ferrite CN20 and the nanocrystalline material Finemet FT-1HS are compared to demonstrate the unique properties of a nanocrystalline material. The experimental data are compared with published data in a similar parameter space to demonstrate the efficacy of the experimental methods.

  16. Temperature dependence of the rate constant for reactions of hydrated electrons with H, OH and H2O2

    DEFF Research Database (Denmark)

    Christensen, H.; Sehested, K.; Løgager, T.

    1994-01-01

    (A) = 14.0 kJ mol-1 (3.3 kcal mol-1). For reaction with OH radicals the corresponding values are, k(20-degrees-C) = 3.1 x 10(10) M-1 s-1 and E(A) = 14.7 kJ mol-1 (3.5 kcal mol-1) determined in the temperature range 5-175-degrees-C. For reaction with H2O2 the values are, k(20-degrees-C) = 1.2 x 10(10) M-1 s......-1 and E(A) = 15.6 kJ mol-1 (3.7 kcal mol-1) measured from 5-150-degrees-C. Thus, the activation energy for all three fast reactions is close to that expected for diffusion controlled reactions. As phosphates were used as buffer system, the rate constant and activation energy for the reaction...

  17. Rate constants of quenching and vibrational relaxation in the OH({{A}^{2}}{{ \\Sigma }^{+}},v=0,1 ), manifold with various colliders

    Science.gov (United States)

    Martini, L. M.; Gatti, N.; Dilecce, G.; Scotoni, M.; Tosi, P.

    2017-03-01

    Laser induced fluorescence is intensively used for the detection of OH in many atmospheric pressure discharge devices. At this pressure, a quantitative knowledge of the collision phenomena in the upper excited state is critical. Here we report the measurement at T  =  300 K of a set of rate constants of electronic quenching and vibrational relaxation of the OH≤ft({{A}2}{{ Σ }+},{{v}\\prime}=0,1\\right) electronic state, by collision with N2, O2, H2O, CO2, CO, H2, D2, CH4, C2H2, C2H4, C2H6. These are the main gases in applications like plasma medicine, hydrocarbons reforming and CO2 conversion. Available literature data are revisited, and new data are added, mostly relevant to {{v}\\prime}=1 quenching and vibrational relaxation.

  18. Reduction of the hydraulic retention time at constant high organic loading rate to reach the microbial limits of anaerobic digestion in various reactor systems.

    Science.gov (United States)

    Ziganshin, Ayrat M; Schmidt, Thomas; Lv, Zuopeng; Liebetrau, Jan; Richnow, Hans Hermann; Kleinsteuber, Sabine; Nikolausz, Marcell

    2016-10-01

    The effects of hydraulic retention time (HRT) reduction at constant high organic loading rate on the activity of hydrogen-producing bacteria and methanogens were investigated in reactors digesting thin stillage. Stable isotope fingerprinting was additionally applied to assess methanogenic pathways. Based on hydA gene transcripts, Clostridiales was the most active hydrogen-producing order in continuous stirred tank reactor (CSTR), fixed-bed reactor (FBR) and anaerobic sequencing batch reactor (ASBR), but shorter HRT stimulated the activity of Spirochaetales. Further decreasing HRT diminished Spirochaetales activity in systems with biomass retention. Based on mcrA gene transcripts, Methanoculleus and Methanosarcina were the predominantly active in CSTR and ASBR, whereas Methanosaeta and Methanospirillum activity was more significant in stably performing FBR. Isotope values indicated the predominance of aceticlastic pathway in FBR. Interestingly, an increased activity of Methanosaeta was observed during shortening HRT in CSTR and ASBR despite high organic acids concentrations, what was supported by stable isotope data.

  19. Analysis of the tensile stress-strain behavior of elastomers at constant strain rates. I - Criteria for separability of the time and strain effects

    Science.gov (United States)

    Hong, S. D.; Fedors, R. F.; Schwarzl, F.; Moacanin, J.; Landel, R. F.

    1981-01-01

    A theoretical analysis of the tensile stress-strain relation of elastomers at constant strain rate is presented which shows that the time and the stress effect are separable if the experimental time scale coincides with a segment of the relaxation modulus that can be described by a single power law. It is also shown that time-strain separability is valid if the strain function is linearly proportional to the Cauchy strain, and that when time-strain separability holds, two strain-dependent quantities can be obtained experimentally. In the case where time and strain effect are not separable, superposition can be achieved only by using temperature and strain-dependent shift factors.

  20. MATHEMATICAL CONSTANTS.

    Energy Technology Data Exchange (ETDEWEB)

    Robinson, H.P.; Potter, Elinor

    1971-03-01

    This collection of mathematical data consists of two tables of decimal constants arranged according to size rather than function, a third table of integers from 1 to 1000, giving some of their properties, and a fourth table listing some infinite series arranged according to increasing size of the coefficients of the terms. The decimal values of Tables I and II are given to 20 D.

  1. Hemaka's constant

    CERN Document Server

    Sparavigna, Amelia Carolina

    2012-01-01

    As proposed in a previous paper, the decorations of ancient objects can provide some information on the approximate evaluations of constant {\\pi}, the ratio of circumference to diameter. Here we discuss some disks found in the tomb of Hemaka, the chancellor of a king of the First Dynasty of Egypt, about 3000 BC. The discussion is based on measurements of the dimensionless ratio of lengths.

  2. Time since death and decay rate constants of Norway spruce and European larch deadwood in subalpine forests determined using dendrochronology and radiocarbon dating

    Directory of Open Access Journals (Sweden)

    M. Petrillo

    2015-09-01

    Full Text Available Due to the large size and highly heterogeneous spatial distribution of deadwood, the time scales involved in the coarse woody debris (CWD decay of Picea abies (L. Karst. and Larix decidua Mill. in Alpine forests have been poorly investigated and are largely unknown. We investigated the CWD decay dynamics in an Alpine valley in Italy using the five-decay class system commonly employed for forest surveys, based on a macromorphological and visual assessment. For the decay classes 1 to 3, most of the dendrochronological samples were cross-dated to assess the time that had elapsed since tree death, but for decay classes 4 and 5 (poorly preserved tree rings and some others not having enough tree rings, radiocarbon dating was used. In addition, density, cellulose and lignin data were measured for the dated CWD. The decay rate constants for spruce and larch were estimated on the basis of the density loss using a single negative exponential model. In the decay classes 1 to 3, the ages of the CWD were similar varying between 1 and 54 years for spruce and 3 and 40 years for larch with no significant differences between the classes; classes 1–3 are therefore not indicative for deadwood age. We found, however, distinct tree species-specific differences in decay classes 4 and 5, with larch CWD reaching an average age of 210 years in class 5 and spruce only 77 years. The mean CWD rate constants were 0.012 to 0.018 yr−1 for spruce and 0.005 to 0.012 yr−1 for larch. Cellulose and lignin time trends half-lives (using a multiple-exponential model could be derived on the basis of the ages of the CWD. The half-lives for cellulose were 21 yr for spruce and 50 yr for larch. The half-life of lignin is considerably higher and may be more than 100 years in larch CWD.

  3. Comparison of the effects of xylazine bolus versus medetomidine constant rate infusion on the stress response, urine production, and anesthetic recovery characteristics in horses anesthetized with isoflurane.

    Science.gov (United States)

    Creighton, Catherine M; Lemke, Kip A; Lamont, Leigh A; Horney, Barbara S; Doyle, Aimie J

    2012-04-15

    To compare the effect of xylazine bolus versus medetomidine constant rate infusion (MCRI) on serum cortisol and glucose concentrations, urine production, and anesthetic recovery characteristics in dorsally recumbent, spontaneously breathing, isoflurane-anesthetized horses. Prospective, randomized crossover study. 10 healthy Standardbreds. Horses were premedicated with xylazine or medetomidine IV. Anesthesia was induced with diazepam and ketamine and maintained with isoflurane for 150 minutes. For the xylazine treatment, end-tidal isoflurane concentration was maintained at 1.7% and xylazine (0.2 mg/kg [0.09 mg/lb]), IV) was administered as a bolus at the end of anesthesia. For the MCRI treatment, end-tidal isoflurane concentration was maintained at 1.4% and medetomidine (0.005 mg/kg/h [0.0023 mg/lb/h], IV) was infused throughout anesthesia. Serum cortisol and glucose concentrations were measured before, during, and after anesthesia. Urine specific gravity and volume were measured during anesthesia. Unassisted anesthetic recoveries were recorded by a digital video camera for later evaluation by 2 observers who were blinded to treatment. Serum cortisol concentration was lower and serum glucose concentration was higher with MCRI treatment, compared with xylazine treatment. Time to sternal recumbency was longer with MCRI treatment, but no difference was seen between treatments for times to extubation, first movement, or standing. Objective (mean attempt interval) and subjective (visual analog score) recovery scores were significantly better with MCRI treatment, compared with xylazine treatment. In isoflurane-anesthetized horses, premedication and administration of medetomidine as a constant rate infusion resulted in decreased serum cortisol concentration, increased serum glucose concentration, and superior anesthetic recovery characteristics, compared with conventional treatment with xylazine.

  4. Tunable Yb-doped fiber laser based on a FBG array and a theta ring resonator ensuring a constant repetition rate (Conference Presentation)

    Science.gov (United States)

    Tiess, Tobias; Becker, Martin; Rothhardt, Manfred; Bartelt, Hartmut; Jäger, Matthias L.

    2017-03-01

    Fiber lasers provide the perfect basis to develop broadly tunable lasers with high efficiency, excellent beam quality and user-friendly operation as they are increasingly demanded by applications in biophotonics and spectroscopy. Recently, a novel tuning scheme has been presented using fiber Bragg grating (FBG) arrays as fiber-integrated spectral filters containing many standard FBGs with different feedback wavelengths. Based on the discrete spectral sampling, these reflective filters uniquely enable tailored tuning ranges and broad bandwidths to be implemented into fiber lasers. Even though the first implementation of FBG arrays in pulsed tunable lasers based on a sigma ring resonators works with good emission properties, the laser wavelength is tuned by a changing repetition rate, which causes problems with applications in synchronized environments. In this work, we present a modified resonator scheme to maintain a constant repetition rate over the tuning range and still benefit from the advantages of FBG arrays as filters. With a theta ring cavity and two counter propagating filter passes, the distributed feedback of the FBG array is compensated resulting in a constant pulse round trip time for each filter wavelength. Together with an adapted gating scheme controlling the emission wavelength with a modulator, the tuning principle has been realized based on a Ytterbium-doped fiber laser. We present first experimental results demonstrating a tuning range of 25nm, high signal contrast and pulse durations of about 10ns. With the prospect of tailored tuning ranges, this pulsed fiber-integrated laser may be the basis to tackle challenging applications in spectroscopy.

  5. Heart rate and metabolic responses to moderate-intensity aerobic exercise: a comparison of graded walking and ungraded jogging at a constant perceived exertion.

    Science.gov (United States)

    Kilpatrick, Marcus W; Kraemer, Robert R; Quigley, Edward J; Mears, Jennifer L; Powers, Jeremy M; Dedea, Anthony J; Ferrer, Nicholas F

    2009-03-01

    In this study, we assessed how ungraded jogging and graded walking at the same rating of perceived exertion (RPE) affect heart rate and oxygen consumption ([Vdot]O(2)). Twenty untrained participants completed a treadmill test to determine peak [Vdot]O(2) (mean = 40.3 +/- 6.3 ml . kg(-1) . min(-1)). Participants completed separate 30-min trials of moderate exercise (RPE of 13 on the Borg 6-20 scale) in random order on the treadmill: graded walking and ungraded jogging. Treadmill speed or grade was adjusted throughout the trial by the experimenter based on participant responses to maintain an RPE of 13. The jogging trial produced a significantly higher heart rate (161 +/- 18 vs. 142 +/- 24 beats . min(-1)) and [Vdot]O(2) (7.4 +/- 1.8 vs. 5.8 +/- 1.5 METs) (P jogging trial (5.2 +/- 1.0 miles . h(-1) to 5.0 +/- 0.9 miles . h(-1)) (P > 0.05), in an effort to maintain constant RPE. These findings provide evidence that similar perceptions of effort during graded walking and ungraded jogging do not produce similar cardiovascular and metabolic responses. The results indicate that, for a given prescribed perceived effort, jogging provides a greater stimulus for fitness benefits and caloric expenditure.

  6. Scale-up of naringinase production process based on the constant oxygen transfer rate for a novel strain of Bacillus methylotrophicus.

    Science.gov (United States)

    Raval, Keyur; Gehlot, Kartik; B D, Prasanna

    2017-02-07

    Naringinase bioprocess based on Bacillus methylotrophicus was successfully scaled up based on constant oxygen transfer rate (OTR) as the scale-up criterion from 5-L bioreactor to 20-L bioreactor. OTR was measured in 5 and 20-L bioreactor under various operating conditions using dynamic method. The operating conditions, where complete dispersion was observed were identified. The highest OTR of 0.035 and 0.04 mMol/L/s was observed in 5 and 20-L bioreactor, respectively. Critical dissolved oxygen concentration of novel isolated strain B. methylotrophicus was found to be 20% of oxygen saturation in optimized medium. The B. methylotrophicus cells grown on sucrose had maximum oxygen uptake rate of 0.14 mMol/L/s in optimized growth medium. The cells produced the maximum naringinase activity of 751 and 778 U/L at 34 hr in 5 and 20-L bioreactors, respectively. The maximum specific growth rate of about 0.178/hr was observed at both the scales of operations. The maximum naringinase yield of 160 and 164 U/g biomass was observed in 5 and 20-L bioreactors, respectively. The growth and production profiles at both scales were similar indicating successful scale-up strategy for B. methylotrophicus culture.

  7. Dependence of Reaction Rate Constants on Density in Supercritical Fluids%超临界流体中反应速率常数与密度的相互关系

    Institute of Scientific and Technical Information of China (English)

    王涛; 沈忠耀

    2002-01-01

    A new method, which correlates rate constants of chemical reactions and density or pressure in supercritical fluids, was developed. Based on the transition state theory and thermodynamic principles, the rate constant can be reasonably correlated with the density of the supercritical fluid, and a correlation equation was obtained.Coupled with the equation of state (EOS) of a supercritical solvent, the effect of pressure on reaction rate constant could be represented. Two typical systems were used to test this method. The result indicates that this method is suitable for dilute supercritical fluid solutions.

  8. Discrete-state representation of ion permeation coupled to fast gating in a model of CLC-chloride channels: analytic estimation of the state-to-state rate constants.

    Science.gov (United States)

    Coalson, Rob D; Cheng, Mary Hongying

    2011-09-01

    Analytical estimation of state-to-state rate constants is carried out for a recently developed discrete state model of chloride ion motion in a CLC chloride channel (Coalson and Cheng, J. Phys. Chem. B 2010, 114, 1424). In the original presentation of this model, the same rate constants were evaluated via three-dimensional Brownian dynamics simulations. The underlying dynamical theory is an appropriate single- or multiparticle three-dimensional Smoluchowski equation. Taking advantage of approximate geometric symmetries (based on the details of the model channel geometry), well-known formulas for state-to-state transition rates are appealed to herein and adapted as necessary to the problem at hand. Rates of ionic influx from a bulk electrolyte reservoir to the nearest binding site within the channel pore are particularly challenging to compute analytically because they reflect multi-ion interactions (as opposed to single-ion dynamics). A simple empirical correction factor is added to the single-ion rate constant formula in this case to account for the saturation of influx rate constants with increasing bulk Cl(-) concentration. Overall, the agreement between all analytically estimated rate constants is within a factor of 2 of those computed via three-dimensional Brownian dynamics simulations, and often better than this. Current-concentration curves obtained using rate constants derived from these two different computational approaches agree to within 25%.

  9. Time since death and decay rate constants of Norway spruce and European larch deadwood in subalpine forests determined using dendrochronology and radiocarbon dating

    Science.gov (United States)

    Petrillo, Marta; Cherubini, Paolo; Fravolini, Giulia; Marchetti, Marco; Ascher-Jenull, Judith; Schärer, Michael; Synal, Hans-Arno; Bertoldi, Daniela; Camin, Federica; Larcher, Roberto; Egli, Markus

    2016-03-01

    Due to the large size (e.g. sections of tree trunks) and highly heterogeneous spatial distribution of deadwood, the timescales involved in the coarse woody debris (CWD) decay of Picea abies (L.) Karst. and Larix decidua Mill. in Alpine forests are largely unknown. We investigated the CWD decay dynamics in an Alpine valley in Italy using the chronosequence approach and the five-decay class system that is based on a macromorphological assessment. For the decay classes 1-3, most of the dendrochronological samples were cross-dated to assess the time that had elapsed since tree death, but for decay classes 4 and 5 (poorly preserved tree rings) radiocarbon dating was used. In addition, density, cellulose, and lignin data were measured for the dated CWD. The decay rate constants for spruce and larch were estimated on the basis of the density loss using a single negative exponential model, a regression approach, and the stage-based matrix model. In the decay classes 1-3, the ages of the CWD were similar and varied between 1 and 54 years for spruce and 3 and 40 years for larch, with no significant differences between the classes; classes 1-3 are therefore not indicative of deadwood age. This seems to be due to a time lag between the death of a standing tree and its contact with the soil. We found distinct tree-species-specific differences in decay classes 4 and 5, with larch CWD reaching an average age of 210 years in class 5 and spruce only 77 years. The mean CWD rate constants were estimated to be in the range 0.018 to 0.022 y-1 for spruce and to about 0.012 y-1 for larch. Snapshot sampling (chronosequences) may overestimate the age and mean residence time of CWD. No sampling bias was, however, detectable using the stage-based matrix model. Cellulose and lignin time trends could be derived on the basis of the ages of the CWD. The half-lives for cellulose were 21 years for spruce and 50 years for larch. The half-life of lignin is considerably higher and may be more than

  10. Radical scavenging ability of gallic acid toward OH and OOH radicals. Reaction mechanism and rate constants from the density functional theory.

    Science.gov (United States)

    Marino, Tiziana; Galano, Annia; Russo, Nino

    2014-09-04

    Gallic acid is a ubiquitous compound, widely distributed in the vegetal kingdom and frequently found in the human diet. In the present work, its primary antioxidant activity has been investigated using the density functional theory (DFT), and the quantum mechanics-based test for overall free radical scavenging activity (QM-ORSA) protocol. It was found that gallic acid is a better antioxidant than the reference compound, Trolox, regardless of the polarity of the environment. In addition, gallic acid is predicted to be among the best peroxyl radical scavengers identified so far in nonpolar (lipid) media. This compound is capable of scavenging hydroxyl radicals at diffusion-limited rates, and hydroperoxyl radicals with rate constants in the order of 10(5) M(-1) s(-1). The deprotonation of gallic acid, in aqueous solution, is predicted to increase the protective action of this compound against oxidative stress. Gallic acid was also identified as a versatile scavenger, capable of rapidly deactivating a wide variety of reactive oxygen species (ROS) and reactive nitrogen species (RNS) via electron transfer at physiological pH.

  11. Effect of temperature on segmental mobility is reduced, but not eliminated during constant strain rate deformation of poly(methyl methacrylate) glasses

    Science.gov (United States)

    Hebert, Kelly; Bending, Benjamin; Ricci, Josh; Ediger, M. D.

    2015-03-01

    Deformation of polymer glasses is typically nonlinear and not understood at a molecular level. During deformation, segmental motion in polymer glasses can be accelerated by over a factor of 1000. While temperature has a big impact on the segmental motion of polymer glasses in the absence of deformation, some workers suggest that segmental mobility in polymer glasses undergoing deformation should be independent of temperature. We have measured segmental mobility in poly(methyl methacrylate) glasses during constant strain rate deformation at four different temperatures using a probe reorientation method. We find that during deformation, the dependence of segmental mobility on temperature is significantly reduced, though not eliminated. This is in qualitative agreement with the work of Chen and Schweizer. We also find that the KWW β parameter increases during deformation, indicating a narrower distribution of segmental relaxation times. At a given strain rate, this increase of the KWW β parameter is larger at lower temperature. We thank the National Science Foundation (DMR-1404614) for support of this research.

  12. Determination of rate constants for the uptake process involving SO{sub 2} and an aerosol particle. A quantum mechanics/molecular mechanics and quantum statistical investigation

    Energy Technology Data Exchange (ETDEWEB)

    Madsen, Marianne Sloth [Department of Chemistry, H.C. Orsted Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen O (Denmark); Danish Meteorological Institute, Lyngbyvej 100, DK-2100 Copenhagen O (Denmark)], E-mail: msm@dmi.dk; Gross, Allan [Department of Chemistry, H.C. Orsted Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen O (Denmark); Danish Meteorological Institute, Lyngbyvej 100, DK-2100 Copenhagen O (Denmark); Falsig, Hanne [Department of Chemistry, H.C. Orsted Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen O (Denmark); Kongsted, Jacob [Department of Theoretical Chemistry, Chemical Center, University of Lund, P.O. Box 124, S-22100 Lund (Sweden); Osted, Anders; Mikkelsen, Kurt V. [Department of Chemistry, H.C. Orsted Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen O (Denmark); Christiansen, Ove [Department of Chemistry, University of Aarhus, Langelandsgade 140, DK-8000 Aarhus C (Denmark)

    2008-06-02

    We present a combined quantum mechanics/molecular mechanics and quantum statistical investigation of the interactions between a molecule (SO{sub 2}) and an aerosol particle including rate constants for the uptake process. A coupled cluster/molecular mechanics method including explicit polarization is used along with a quantum statistical method for calculating sticking coefficients. The importance of the polarization of the classical subsystem (the aerosol particle), the size of the classical subsystem and the size of one-electron basis sets are studied. The interaction energy is divided into van der Waals, electrostatic and polarization contributions. Relevant binding sites for the evaluation of the sticking coefficient are identified. These are classified into three groups according to the strength of the molecule-aerosol particle interaction energy. The identification of binding sites provides relevant information used in the quantum statistical method and thereby knowledge of the magnitude of the sticking coefficients for the different binding sites along with the total rates for the uptake processes between the aerosol particle and the SO{sub 2} molecule.

  13. Intrinsic non-radiative voltage losses in fullerene-based organic solar cells

    Science.gov (United States)

    Benduhn, Johannes; Tvingstedt, Kristofer; Piersimoni, Fortunato; Ullbrich, Sascha; Fan, Yeli; Tropiano, Manuel; McGarry, Kathryn A.; Zeika, Olaf; Riede, Moritz K.; Douglas, Christopher J.; Barlow, Stephen; Marder, Seth R.; Neher, Dieter; Spoltore, Donato; Vandewal, Koen

    2017-06-01

    Organic solar cells demonstrate external quantum efficiencies and fill factors approaching those of conventional photovoltaic technologies. However, as compared with the optical gap of the absorber materials, their open-circuit voltage is much lower, largely due to the presence of significant non-radiative recombination. Here, we study a large data set of published and new material combinations and find that non-radiative voltage losses decrease with increasing charge-transfer-state energies. This observation is explained by considering non-radiative charge-transfer-state decay as electron transfer in the Marcus inverted regime, being facilitated by a common skeletal molecular vibrational mode. Our results suggest an intrinsic link between non-radiative voltage losses and electron-vibration coupling, indicating that these losses are unavoidable. Accordingly, the theoretical upper limit for the power conversion efficiency of single-junction organic solar cells would be reduced to about 25.5% and the optimal optical gap increases to 1.45-1.65 eV, that is, 0.2-0.3 eV higher than for technologies with minimized non-radiative voltage losses.

  14. The use of digital simulation to improve the cyclic voltammetric determination of rate constants for homogeneous chemical reactions following charge transfers

    Energy Technology Data Exchange (ETDEWEB)

    Mozo, J.D.; Carbajo, J. [Applied Electrochemistry Laboratory, Dep. of Chemical Enginery, Physical Chemistry and Organic Chemistry, Experimental Sciences Faculty, University of Huelva, Av. 3 de Marzo, s/n (Campus El Carmen), ES-21071 Huelva (Spain); Sturm, J.C.; Nunez-Vergara, L.J.; Moscoso, R. [Bioelectrochemistry Laboratory, Chemical and Pharmaceutical Sciences Faculty, University of Chile, 838492 Santiago (Chile); Squella, J.A., E-mail: asquella@ciq.uchile.cl [Bioelectrochemistry Laboratory, Chemical and Pharmaceutical Sciences Faculty, University of Chile, 838492 Santiago (Chile)

    2011-08-05

    Cyclic voltammetry (CV) is a very useful electrochemical tool used to study reaction systems that include chemical steps that are coupled to electron transfers. This type of system generally involves the chemical reaction of an electrochemically generated free radical. Published methods exist that are used to determine the kinetics of electrochemically initiated chemical reactions from the measurements of the peak current ratio (i{sub pa}/i{sub pc}) of a cyclic voltammogram. The published method requires working curves to relate a kinetic parameter to the peak current ratio. In the presented work, a digital simulation package was used to obtain improved working curves for specific working conditions. The curves were compared with the published results for the first- and second-order chemical reactions following the charge transfer step mechanisms. According to the presented results, the previously published working curve is reliable for a mechanism with a first-order chemical reaction; however, a change in the switching potential requires a recalculation of the curve. In the case of mechanisms with a second-order step (dimerisation and disproportionation), several different views exist on how the second-order chemical term should be expressed so that different values of the constant are obtained. Parameters such as electrode type, electrode area, electroactive species concentration, switching potential, scan rate and method for peak current ratio calculation modify the working curves and must always be specified. We propose a standardised method to obtain the most reliable kinetic constant values. The results of this work will permit researchers who handle simulation software to construct their own working curves. Additionally, those who do not have the simulation software could use the working curves described here. The revelations of the presented experiments may be useful to a broad chemistry audience because this study presents a simple and low-cost procedure

  15. Cinética de sinterização para sistemas à base de SnO2 por taxa de aquecimento constante Sintering kinetics for SnO2-based systems by constant heating rate

    Directory of Open Access Journals (Sweden)

    S. M. Tebcheran

    2003-04-01

    in small concentrations as densifying aids for this oxide. In the present study the sintering kinetics of tin oxide was studied considering the effect of sintering atmosphere and of the MnO2 concentration. SnO2-MnO2 systems were prepared from the polymeric precursors method and the obtained powders were characterized by surface area by the BET method. SnO2 powders with varied MnO2 concentrations were pressed in cylindrical shape, and sintered in a dilatometer furnace with constant heating rate and controlled atmospheres. Sintered samples were characterized by scanning electron microscopy. The influence of atmosphere (argon, air or CO2 as well as of the MnO2 concentrations on the sintering kinetics was determined. The kinetics data of linear shrinkage were analyzed in terms of kinetic models for the initial stage of sintering (Woolfrey and Bannister as well as for the global sintering (Su e Johnson allowing the determination of the apparent activation energy. Following the determination of the master sintering curve the apparent activation energy of all sintering process were determined as well as its dependence with the atmosphere and manganese concentrations. Based on these values and on the n exponent, determined by the classical grain growth equation, it was concluded that the most probable sintering mechanism is grain boundary diffusion with surface redistribution controlling the kinetics.

  16. Fully Coriolis-coupled quantum studies of the H + O2 (upsilon i = 0-2, j i = 0,1) --> OH + O reaction on an accurate potential energy surface: integral cross sections and rate constants.

    Science.gov (United States)

    Lin, Shi Ying; Sun, Zhigang; Guo, Hua; Zhang, Dong Hui; Honvault, Pascal; Xie, Daiqian; Lee, Soo-Y

    2008-01-31

    We present accurate quantum calculations of the integral cross section and rate constant for the H + O2 --> OH + O combustion reaction on a recently developed ab initio potential energy surface using parallelized time-dependent and Chebyshev wavepacket methods. Partial wave contributions up to J = 70 were computed with full Coriolis coupling, which enabled us to obtain the initial state-specified integral cross sections up to 2.0 eV of the collision energy and thermal rate constants up to 3000 K. The integral cross sections show a large reaction threshold due to the quantum endothermicity of the reaction, and they monotonically increase with the collision energy. As a result, the temperature dependence of the rate constant is of the Arrhenius type. In addition, it was found that reactivity is enhanced by reactant vibrational excitation. The calculated thermal rate constant shows a significant improvement over that obtained on the DMBE IV potential, but it still underestimates the experimental consensus.

  17. High-accuracy measurements of OH(•) reaction rate constants and IR and UV absorption spectra: ethanol and partially fluorinated ethyl alcohols.

    Science.gov (United States)

    Orkin, Vladimir L; Khamaganov, Victor G; Martynova, Larissa E; Kurylo, Michael J

    2011-08-11

    Rate constants for the gas phase reactions of OH(•) radicals with ethanol and three fluorinated ethyl alcohols, CH(3)CH(2)OH (k(0)), CH(2)FCH(2)OH (k(1)), CHF(2)CH(2)OH (k(2)), and CF(3)CH(2)OH (k(3)) were measured using a flash photolysis resonance-fluorescence technique over the temperature range 220 to 370 K. The Arrhenius plots were found to exhibit noticeable curvature for all four reactions. The temperature dependences of the rate constants can be represented by the following expressions over the indicated temperature intervals: k(0)(220-370 K) = 5.98 × 10(-13)(T/298)(1.99) exp(+515/T) cm(3) molecule(-1) s(-1), k(0)(220-298 K) = (3.35 ± 0.06) × 10(-12) cm(3) molecule(-1) s(-1) [for atmospheric modeling purposes, k(0)(T) is essentially temperature-independent below room temperature, k(0)(220-298 K) = (3.35 ± 0.06) × 10(-12) cm(3) molecule(-1) s(-1)], k(1)(230-370 K) = 3.47 × 10(-14)(T/298)(4.49) exp(+977/T) cm(3) molecule(-1) s(-1), k(2)(220-370 K) = 3.87 × 10(-14)(T/298)(4.25) exp(+578/T) cm(3) molecule(-1) s(-1), and k(3)(220-370 K) = 2.48 × 10(-14)(T/298)(4.03) exp(+418/T) cm(3) molecule(-1) s(-1). The atmospheric lifetimes due to reactions with tropospheric OH(•) were estimated to be 4, 16, 62, and 171 days, respectively, under the assumption of a well-mixed atmosphere. UV absorption cross sections of all four ethanols were measured between 160 and 215 nm. The IR absorption cross sections of the three fluorinated ethanols were measured between 400 and 1900 cm(-1), and their global warming potentials were estimated.

  18. Observation of a nonradiative flat band for spoof surface plasmons in a metallic Lieb lattice

    CERN Document Server

    Kajiwara, Sho; Nakata, Yosuke; Nakanishi, Toshihiro; Kitano, Masao

    2016-01-01

    We demonstrate a nonradiative flat band for spoof surface plasmon polaritons bounded on a structured surface with Lieb lattice symmetry in the terahertz regime. First, we theoretically derive the dispersion relation of spoof plasmons in a metallic Lieb lattice based on the electrical circuit model. We obtain three bands, one of which is independent of wave vector. To confirm the theoretical result, we numerically and experimentally observe the flat band in transmission and attenuated total reflection configurations. We reveal that the quality factor of the nonradiative flat-band mode decoupled from the propagating wave is higher than that of the radiative flat-band mode. This indicates that the nonradiative flat-band mode is three-dimensionally confined in the lattice.

  19. Photoacoustic Determination of Non-radiative Relaxation Time of Absorbing Centers in Maize Seeds

    Science.gov (United States)

    Domínguez-Pacheco, A.; Hernández-Aguilar, C.; Cruz-Orea, A.

    2017-07-01

    Using non-destructive photothermal techniques, it is possible to characterize non-homogenous materials to obtain its optical and thermal properties through photoacoustic spectroscopy (PAS). In photoacoustic (PA) phenomena, there are transient states of thermal excitation, when samples absorb the incident light; these states manifest an excitation process that generates the PA signal, being in direct relation with the non-radiative relaxation times with the sample absorbent centers. The objective of this study was to determine the non-radiative relaxation times associated with different absorbent centers of corn seeds ( Zea mays L.), by using PAS. A frequency scan was done at different wavelengths (350 nm, 470 nm and 650 nm) in order to obtain the non-radiative relaxation times with different types of maize seeds.

  20. Coupling of radial and nonradial oscillations of relativistic stars: Gauge-invariant formalism

    Science.gov (United States)

    Passamonti, Andrea; Bruni, Marco; Gualtieri, Leonardo; Sopuerta, Carlos F.

    2005-01-01

    Linear perturbation theory is appropriate to describe small oscillations of stars, while a mild nonlinearity is still tractable perturbatively but requires one to consider mode coupling, i.e., to take into account second order effects. It is natural to start to look at this problem by considering the coupling between linear radial and nonradial modes. A radial pulsation may be thought of as an important component of an overall mildly nonlinear oscillation, e.g., of a protoneutron star. Radial pulsations of spherical compact objects do not per se emit gravitational waves but, if the coupling between the existing first order radial and nonradial modes is efficient in driving and possibly amplifying the nonradial oscillations, one may expect the appearance of nonlinear harmonics, and gravitational radiation could then be produced to a significant level. More in general, mode coupling typically leads to an interesting phenomenology, thus it is worth investigating in the context of star perturbations. In this paper we develop the relativistic formalism to study the coupling of radial and nonradial first order perturbations of a compact spherical star. From a mathematical point of view, it is convenient to treat the two sets of perturbations as separately parametrized, using a 2-parameter perturbative expansion of the metric, the energy-momentum tensor and Einstein equations in which λ is associated with the radial modes, ɛ with the nonradial perturbations, and the λɛ terms describe the coupling. This approach provides a well-defined framework to consider the gauge dependence of perturbations, allowing us to use ɛ order gauge-invariant nonradial variables on the static background and to define new second order λɛ gauge-invariant variables representing the result of the nonlinear coupling. We present the evolution and constraint equations for our variables outlining the setup for numerical computations, and briefly discuss the surface boundary conditions in terms

  1. Ventilatory expired gas at constant-rate low-intensity exercise predicts adverse events and is related to neurohormonal markers in patients with heart failure.

    Science.gov (United States)

    Arena, Ross; MacCarter, Dean; Olson, Thomas P; Lalande, Sophie; Ceridon, Maile L; Olson, Lyle J; Johnson, Bruce

    2009-08-01

    Ventilatory efficiency (VE/VCO(2) ratio) and the partial pressure of end-tidal carbon dioxide (P(ET)CO(2)), obtained during moderate to high levels of physical exertion demonstrate prognostic value in heart failure (HF). The present investigation assesses the clinical utility of these variables during low-intensity exercise. One hundred and thirty subjects diagnosed with HF underwent a 2-minute, constant-rate treadmill session at 2 miles per hour. Both the VE/VCO(2) ratio and P(ET)CO(2) were recorded during exercise (30-second average) and their change (Delta) from rest. B-type and atrial natriuretic peptide (BNP and ANP) were also determined. Only P(ET)CO(2) and DeltaP(ET)CO(2) emerged from the multivariate Cox regression. Receiver operating characteristic curve analysis revealed the prognostic classification schemes were significant with thresholds of or=34 mm Hg (hazard ratio: 4.2, 95% CI: 2.2-8.0, P or=1 mm Hg (hazard ratio: 3.5, 95% CI: 1.9-6.6, P or=34 mm Hg had a significantly lower BNP (214.1 +/- 431.9 vs. 1110.5 +/- 1854.0 pg/mL, P=.005) and ANP (108.2 +/- 103.6 vs. 246.2 +/- 200.4 pg/mL, P exercise may provide insight into prognosis and cardiac stability.

  2. Calculations with spectroscopic accuracy for energies, transition rates, hyperfine interaction constants, and Landé gJ-factors in nitrogen-like Kr XXX

    Science.gov (United States)

    Wang, K.; Li, S.; Jönsson, P.; Fu, N.; Dang, W.; Guo, X. L.; Chen, C. Y.; Yan, J.; Chen, Z. B.; Si, R.

    2017-01-01

    Extensive self-consistent multi-configuration Dirac-Fock (MCDF) calculations and second-order many-body perturbation theory (MBPT) calculations are performed for the lowest 272 states belonging to the 2s22p3, 2s2p4, 2p5, 2s22p23l, and 2s2p33l (l=s, p, d) configurations of N-like Kr XXX. Complete and consistent data sets of level energies, wavelengths, line strengths, oscillator strengths, lifetimes, AJ, BJ hyperfine interaction constants, Landé gJ-factors, and electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), magnetic quadrupole (M2) transition rates among all these levels are given. The present MCDF and MBPT results are compared with each other and with other available experimental and theoretical results. The mean relative difference between our two sets of level energies is only about 0.003% for these 272 levels. The accuracy of the present calculations are high enough to facilitate identification of many observed spectral lines. These accurate data can be served as benchmark for other calculations and can be useful for fusion plasma research and astrophysical applications.

  3. Application of a Genetic Algorithm to the Optimization of Rate Constants in Chemical Kinetic Models for Combustion Simulation of HCCI Engines

    Science.gov (United States)

    Kim, Sang-Kyu; Ito, Kazuma; Yoshihara, Daisuke; Wakisaka, Tomoyuki

    For numerically predicting the combustion processes in homogeneous charge compression ignition (HCCI) engines, practical chemical kinetic models have been explored. A genetic algorithm (GA) has been applied to the optimization of the rate constants in detailed chemical kinetic models, and a detailed kinetic model (592 reactions) for gasoline reference fuels with arbitrary octane number between 60 and 100 has been obtained from the detailed reaction schemes for iso-octane and n-heptane proposed by Golovitchev. The ignition timing in a gasoline HCCI engine has been predicted reasonably well by zero-dimensional simulation using the CHEMKIN code with this detailed kinetic model. An original reduced reaction scheme (45 reactions) for dimethyl ether (DME) has been derived from Curran’s detailed scheme, and the combustion process in a DME HCCI engine has been predicted reasonably well in a practical computation time by three-dimensional simulation using the authors’ GTT code, which has been linked to the CHEMKIN subroutines with the proposed reaction scheme and also has adopted a modified eddy dissipation combustion model.

  4. Anesthetic management with sevoflurane combined with alfaxalone-medetomidine constant rate infusion in a Thoroughbred racehorse undergoing a long-time orthopedic surgery

    Science.gov (United States)

    WAKUNO, Ai; MAEDA, Tatsuya; KODAIRA, Kazumichi; KIKUCHI, Takuya; OHTA, Minoru

    2017-01-01

    ABSTRACT A three-year old Thoroughbred racehorse was anesthetized with sevoflurane and oxygen inhalation anesthesia combined with constant rate infusion (CRI) of alfaxalone-medetomidine for internal fixation of a third metacarpal bone fracture. After premedication with intravenous (IV) injections of medetomidine (6.0 µg/kg IV), butorphanol (25 µg/kg IV), and midazolam (20 µg/kg IV), anesthesia was induced with 5% guaifenesin (500 ml/head IV) followed immediately by alfaxalone (1.0 mg/kg IV). Anesthesia was maintained with sevoflurane and CRIs of alfaxalone (1.0 mg/kg/hr) and medetomidine (3.0 µg/kg/hr). The total surgical time was 180 min, and the total inhalation anesthesia time was 230 min. The average end-tidal sevoflurane concentration during surgery was 1.8%. The mean arterial blood pressure was maintained above 70 mmHg throughout anesthesia, and the recovery time was 65 min. In conclusion, this anesthetic technique may be clinically applicable for Thoroughbred racehorses undergoing a long-time orthopedic surgery. PMID:28955163

  5. Reduction of the minimum alveolar concentration of isoflurane in dogs using a constant rate of infusion of lidocaine-ketamine in combination with either morphine or fentanyl.

    Science.gov (United States)

    Aguado, Delia; Benito, Javier; Gómez de Segura, Ignacio A

    2011-07-01

    The objective of this study was to determine the effects of a constant rate of infusion of lidocaine and ketamine in combination with either morphine or fentanyl on the minimum alveolar concentration of isoflurane (MAC(ISO)) during ovariohysterectomy in dogs. Female dogs (n=44) were premedicated with acepromazine and midazolam. Anaesthesia was induced with propofol and maintained with isoflurane. Dogs received ketamine (0.6 mg/kg/h) and lidocaine (3 mg/kg/h) together with morphine (0.24 mg/kg/h; MLK) or fentanyl (0.0036 mg/kg/h; FLK). The control group received Ringer's lactate solution. A skin incision was used as the noxious stimulus. The MAC(ISO) value was obtained with Dixon's up-and-down method. MAC(ISO) was 0.7±0.0 vol.% in the control group, 0.3±0.0 vol.% in the MLK group (45% MAC reduction) and 0.0±0.0 vol.% in the FLK group (97% MAC reduction). A combination of fentanyl with lidocaine and ketamine decreased the MAC(ISO) in dogs; this decrease was more pronounced than that produced by morphine, lidocaine and ketamine.

  6. Plasma and interstitial fluid pharmacokinetics of enrofloxacin, its metabolite ciprofloxacin, and marbofloxacin after oral administration and a constant rate intravenous infusion in dogs.

    Science.gov (United States)

    Bidgood, T L; Papich, M G

    2005-08-01

    Enrofloxacin and marbofloxacin were administered to six healthy dogs in separate crossover experiments as a single oral dose (5 mg/kg) and as a constant rate IV infusion (1.24 and 0.12 mg/h.kg, respectively) following a loading dose (4.47 and 2 mg/kg, respectively) to achieve a steady-state concentration of approximately 1 microg/mL for 8 h. Interstitial fluid (ISF) was collected with an in vivo ultrafiltration device at the same time period as plasma to measure protein unbound drug concentrations at the tissue site and assess the dynamics of drug distribution. Plasma and ISF were analyzed for enrofloxacin, its active metabolite ciprofloxacin, and for marbofloxacin by high performance liquid chromatography (HPLC). Lipophilicity and protein binding of enrofloxacin were higher than for marbofloxacin and ciprofloxacin. Compared to enrofloxacin, marbofloxacin had a longer half-life, higher Cmax, and larger AUC(0-infinity) in plasma and ISF after oral administration. Establishing steady state allowed an assessment of the dynamics of drug concentrations between plasma and ISF. The ISF and plasma-unbound concentrations were similar during the steady-state period despite differences in lipophilicity and pharmacokinetic parameters of the drugs.

  7. Direct estimation of the rate constant of the reaction ClO + HO2 → HOCl + O2 from SMILES atmospheric observations

    Directory of Open Access Journals (Sweden)

    K. Kuribayashi

    2013-05-01

    Full Text Available Diurnal variations of ClO, HO2, and HOCl were simultaneously observed by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES between 12 October 2009 and 21 April 2010. These were the first global observations of the diurnal variation of HOCl in the upper atmosphere. A major reaction to produce HOCl is ClO + HO2 → HOCl + O2 (R1 in extra polar region. A model study suggested that in the mesosphere during night this is the only reaction influencing the amount of HOCl and ClO. The evaluation of the pure reaction period, where only reaction (R1 occurred in Cly chemical system, was performed by the consistency between two reaction rates, HOCl production and ClO loss, from SMILES observation data. It turned out that the SMILES data at the pressure level of 0.28 hPa (about 58 km during night (between local time 18:30 and 04:00 in the autumn mid-latitude region (20–40° February–April 2010 were suitable for the estimation of k1. The rate constant was obtained to be k1(245 K = 7.73 ± 0.26 (1σ [× 10–12 cm3/molecule s] from SMILES atmospheric observations. This result was consistent with that from both the laboratory experiment and the ab initio calculations for similar low-pressure conditions. The 1σ precision of k1 obtained was 2–10 times better than those of previous laboratory measurements.

  8. Estimation of autotrophic maximum specific growth rate constant--experience from the long-term operation of a laboratory-scale sequencing batch reactor system.

    Science.gov (United States)

    Su, Yu-min; Makinia, Jacek; Pagilla, Krishna R

    2008-04-01

    The autotrophic maximum specific growth rate constant, muA,max, is the critical parameter for design and performance of nitrifying activated sludge systems. In literature reviews (i.e., Henze et al., 1987; Metcalf and Eddy, 1991), a wide range of muA,max values have been reported (0.25 to 3.0 days(-1)); however, recent data from several wastewater treatment plants across North America revealed that the estimated muA,max values remained in the narrow range 0.85 to 1.05 days(-1). In this study, long-term operation of a laboratory-scale sequencing batch reactor system was investigated for estimating this coefficient according to the low food-to-microorganism ratio bioassay and simulation methods, as recommended in the Water Environment Research Foundation (Alexandria, Virginia) report (Melcer et al., 2003). The estimated muA,max values using steady-state model calculations for four operating periods ranged from 0.83 to 0.99 day(-1). The International Water Association (London, United Kingdom) Activated Sludge Model No. 1 (ASM1) dynamic model simulations revealed that a single value of muA,max (1.2 days(-1)) could be used, despite variations in the measured specific nitrification rates. However, the average muA,max was gradually decreasing during the activated sludge chlorination tests, until it reached the value of 0.48 day(-1) at the dose of 5 mg chlorine/(g mixed liquor suspended solids x d). Significant discrepancies between the predicted XA/YA ratios were observed. In some cases, the ASM1 predictions were approximately two times higher than the steady-state model predictions. This implies that estimating this ratio from a complex activated sludge model and using it in simple steady-state model calculations should be accepted with great caution and requires further investigation.

  9. The use of digital simulation to improve the cyclic voltammetric determination of rate constants for homogeneous chemical reactions following charge transfers.

    Science.gov (United States)

    Mozo, J D; Carbajo, J; Sturm, J C; Núñez-Vergara, L J; Moscoso, R; Squella, J A

    2011-08-05

    Cyclic voltammetry (CV) is a very useful electrochemical tool used to study reaction systems that include chemical steps that are coupled to electron transfers. This type of system generally involves the chemical reaction of an electrochemically generated free radical. Published methods exist that are used to determine the kinetics of electrochemically initiated chemical reactions from the measurements of the peak current ratio (i(pa)/i(pc)) of a cyclic voltammogram. The published method requires working curves to relate a kinetic parameter to the peak current ratio. In the presented work, a digital simulation package was used to obtain improved working curves for specific working conditions. The curves were compared with the published results for the first- and second-order chemical reactions following the charge transfer step mechanisms. According to the presented results, the previously published working curve is reliable for a mechanism with a first-order chemical reaction; however, a change in the switching potential requires a recalculation of the curve. In the case of mechanisms with a second-order step (dimerisation and disproportionation), several different views exist on how the second-order chemical term should be expressed so that different values of the constant are obtained. Parameters such as electrode type, electrode area, electroactive species concentration, switching potential, scan rate and method for peak current ratio calculation modify the working curves and must always be specified. We propose a standardised method to obtain the most reliable kinetic constant values. The results of this work will permit researchers who handle simulation software to construct their own working curves. Additionally, those who do not have the simulation software could use the working curves described here. The revelations of the presented experiments may be useful to a broad chemistry audience because this study presents a simple and low-cost procedure for the

  10. Research on Non-radial Oscillations of the Sun and Stars in the Early 1970s

    Science.gov (United States)

    Osaki, Y.

    2013-12-01

    I describe some historical background of helio- and astero-seismology research in the early 1970s from my personal recollection, particularly on how our Tokyo research group on non-radial oscillations of stars got started. I also describe my recent research on the super-outburst mechanism of SU UMa-type dwarf novae.

  11. A micro-scale hot-surface device based on non-radiative carrier recombination

    NARCIS (Netherlands)

    Kovalgin, Alexeij Y.; Holleman, J.; Iordache, G.

    2004-01-01

    This work employs the idea of making micro-scale hot-surface devices (e.g. sensors, flow meters, micro reactors, etc) based on generation of heat due to nonradiative recombination of carriers in a thin (13 nm) poly silicon surface layer. An important part of the device is a nano-scale (10-100 nm)

  12. Direct spectroscopic observation of singlet oxygen quenching and kinetic studies of physical and chemical singlet oxygen quenching rate constants of synthetic antioxidants (BHA, BHT, and TBHQ) in methanol.

    Science.gov (United States)

    Lee, Jun Hyun; Jung, Mun Yhung

    2010-08-01

    Singlet oxygen quenching by synthetic antioxidants (BHA, BHT, and TBHQ) was directly observed by spectroscopic monitoring of luminescence at 1268 nm. The luminescence data showed unambiguous evidence of singlet oxygen quenching by synthetic phenolic antioxidants with the highest activity for TBHQ, followed by BHA and BHT. The protective activities of these synthetic antioxidants on alpha-terpinene oxidation with chemically-induced singlet oxygen under dark further confirmed their singlet oxygen quenching abilities. Total singlet oxygen quenching rate constants (k(r) + k(q)) of BHA, BHT, and TBHQ were determined in a system containing alpha-terpinene (as a singlet oxygen trap) and methylene blue (as a sensitizer) during light irradiation, and the values were 5.14 x 10(7), 3.41 x 10(6), and 1.99 x 10(8) M(-1)s(-1), respectively. After the k(r) value of alpha-terpinene was first determined, the k(r) values of the synthetic antioxidants were calculated by measuring their relative reaction rates with singlet oxygen to that of alpha-terpinene under the identical conditions. The k(r) values of the BHA, BHT, and TBHQ were 3.90 x 10(5), 1.23 x 10(5), and 2.93 x 10(6), M(-1)s(-1). The percent partition of chemical quenching over total singlet oxygen quenching (k(r) x 100)/(k(r) + k(q)) for BHA, BHT, and TBHQ were 0.76%, 3.61%, and 1.47%, respectively. The results showed that the synthetic antioxidants quench singlet oxygen almost exclusively through the mechanism of physical quenching. This represents the first report on the singlet oxygen quenching mechanism of these synthetic antioxidants. Practical Application: The synthetic antioxidants, especially TBHQ, have been found to have a strong singlet oxygen quenching ability. This article also clearly showed that singlet oxygen quenching by synthetic antioxidants was mainly by the physical quenching mechanism. The results suggested that these synthetic antioxidants, especially TBHQ, could be used practically for the protection

  13. Non-radiative and radiative decays in nanogap emitting devices

    CERN Document Server

    Faggiani, Remi; Lalanne, Philippe

    2015-01-01

    By placing a quantum emitter in the mouths of nanogaps consisting of two metal nanoparticles nearly into contact, significant increases in emission rate are obtained. This mechanism is central in the design of modern plasmonic nanoantennas. However, due to the lack of general knowledge on the balance between the different decay rates in nanogaps (emission, quenching, and metal absorption), nanoantenna design is performed in a rather haphazard fashion and relies on repeated numerical calculations; general intuitive design recipes do not presently exist. With accurate and simple closed-form expressions for the quenching rate and the decay rate into gap plasmons, we provide a comprehensive analysis of nanogap light emitting devices in the limit of small gap thickness. We disclose that the total spontaneous emission rate of quantum emitters in nanometer-thin gaps can largely overcome quenching, for specifically selected metallic and insulator materials, regardless of the gap size. Furthermore, to help further des...

  14. Evidence for the TICT mediated nonradiative deexcitation process for the excited coumarin-1 dye in high polarity protic solvents

    Energy Technology Data Exchange (ETDEWEB)

    Barik, Atanu [Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085 (India); Kumbhakar, Manoj [Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085 (India); Nath, Sukhendu [Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085 (India); Pal, Haridas [Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085 (India)], E-mail: hpal@apsara.barc.ernet.in

    2005-08-29

    Photophysical properties of coumarin-1 (C1) dye in different protic solvents have been investigated using steady-state and time-resolved fluorescence measurements. Correlation of the Stokes' shifts ({delta}{nu}-bar ) with the solvent polarity ({delta}f) suggests the intramolecular charge transfer (ICT) character for the dye fluorescent state. Fluorescence quantum yields ({phi}{sub f}) and lifetimes ({tau}{sub f}) of the dye show an abrupt reduction in high polarity solvents having {delta}f >{approx}0.28. In these solvents {tau}{sub f} is seen to be strongly temperature dependent, though it is temperature independent in solvents with {delta}f <{approx}0.28. It is inferred that in high polarity protic solvents there is a participation of an additional nonradiative decay process via the involvement of twisted intramolecular charge transfer (TICT) state. Unlike present results, no involvement of TICT state was observed even in strongly polar aprotic solvent like acetonitrile. It is indicated that the intermolecular hydrogen bonding of the dye with protic solvents in addition with the solvent polarity helps in the stabilization of the TICT state for C1 dye. Unlike most TICT molecules, the activation barrier ({delta}E{sub a}) for the TICT mediated nonradiative process for C1 dye is seen to increase with solvent polarity. This is rationalized on the basis of the assumption that the TICT to ground state conversion is the activation-controlled rate-determining step for the present system than the usual ICT to TICT conversion as encountered for most other TICT molecules.

  15. Comparison of the rate constants for energy transfer in the light-harvesting protein, C-phycocyanin, calculated from Foerster`s theory and experimentally measured by time-resolved fluorescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Debreczeny, M.P.

    1994-05-01

    We have measured and assigned rate constants for energy transfer between chromophores in the light-harvesting protein C-phycocyanin (PC), in the monomeric and trimeric aggregation states, isolated from Synechococcus sp. PCC 7002. In order to compare the measured rate constants with those predicted by Fdrster`s theory of inductive resonance in the weak coupling limit, we have experimentally resolved several properties of the three chromophore types ({beta}{sub 155} {alpha}{sub 84}, {beta}{sub 84}) found in PC monomers, including absorption and fluorescence spectra, extinction coefficients, fluorescence quantum yields, and fluorescence lifetimes. The cpcB/C155S mutant, whose PC is missing the {beta}{sub 155} chromophore, was, useful in effecting the resolution of the chromophore properties and in assigning the experimentally observed rate constants for energy transfer to specific pathways.

  16. Multivariate curve resolution-alternating least squares and kinetic modeling applied to near-infrared data from curing reactions of epoxy resins: mechanistic approach and estimation of kinetic rate constants.

    Science.gov (United States)

    Garrido, M; Larrechi, M S; Rius, F X

    2006-02-01

    This study describes the combination of multivariate curve resolution-alternating least squares with a kinetic modeling strategy for obtaining the kinetic rate constants of a curing reaction of epoxy resins. The reaction between phenyl glycidyl ether and aniline is monitored by near-infrared spectroscopy under isothermal conditions for several initial molar ratios of the reagents. The data for all experiments, arranged in a column-wise augmented data matrix, are analyzed using multivariate curve resolution-alternating least squares. The concentration profiles recovered are fitted to a chemical model proposed for the reaction. The selection of the kinetic model is assisted by the information contained in the recovered concentration profiles. The nonlinear fitting provides the kinetic rate constants. The optimized rate constants are in agreement with values reported in the literature.

  17. Rate constants for the gas-phase reactions of OH radicals with CH3CHF2 and CHCl2CF3 over the temperature range 295-388 K

    DEFF Research Database (Denmark)

    Nielsen, O.J.

    1991-01-01

    Rate constants for the reactions of OH radicals with CH3CHF2 and CHCl2CF3 have been determined over the temperature range 295-388 K and a total pressure of 1 atm. The OH rate data were obtained using the absolute rate technique of pulse radiolysis combined with kinetic spectroscopy. The data can...... and in the light of the important role CH3CHF2 and CHCl2CF3 play as alternatives to the fully halogenated chlorofluorocarbons....

  18. SU-E-P-55: The Reaserch of Cervical Cancer Delivered with Constant Dose Rate and Gantry Speed Arc Therapy(CDR-CAS-IMAT) On Conventional Linac

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, R; Bai, W; Chi, Z; Gao, C; Xiaomei, F [The Fourth Hospital of Hebei Medical University, Shijiazhuang, Hebei (China); Gao, Y [Hebei General Hospital, Shijiazhuang, Hebei (China)

    2015-06-15

    Purpose: Postoperative cervical cancer patients with large target volume and the target shape is concave, treatmented with static intensity-modulated radiotherapy (IMRT) is time consuming. The purpose of this study is to investigate using constant dose rate and gantry speed arc therapy(CDR-CAS-IMAT) on conventional linear accelrator, by comparing with the IMRT technology to evaluate the performance of CDR-CAS-IMAT on postoperative cervical cancer patients. Methods: 18 cervical cancer patients treated with IMRT on Varian 23IX were replanted using CDR-CAS-IMAT. The plans were generated on Oncentra v4.1 planning system, PTV was prescribed to 50.4 Gy in 28 fractions. Plans were evaluated based on the ability to meet the dose volume histogram. The homogeneity index (HI), conformity index (CI) of target volume, the dose of organs at risk, radiation delivery time and monitor units were also compared. SPSS 19.0 software paired T-test analysis was carried out on the two sets of data. Results: Compared with the IMRT plans PTV’s CI (t= 3.85, P =0.001), CTV’s CI, HI, D90, D95, D98, V95, V98, V100 (t=4.21, −3.18, 2.13, 4.65, 7.79, 2.29, 6.00, 2.13, p=0.001, 0.005, 0.049, 0.000, 0.000, 0.035, 0.000, 0.049), and cord D2 and rectum V40 (t=−2.65, −2.47, p= P =0.017, 0.025), and treatment time and MU (t=−36.0, −6.26, P =0.000, 0.000) were better than that of IMRT group. But the IMRT plans in terms of decreasing bladder V50, bowel V30 (t=2.14, 3.00, P =0.048, 0.008) and low dose irradiation volume were superior to that of CDR-CAS-IMAT plans. There were no significant differences in other statistical index. Conclusion: Cervical cancer patients with CDR-CAS-IMAT on Varian Clinical 23IX can get equivalent or superior dose distribution compared with the IMRT technology. IMAT have much less treatment time and MU can reduce the uncertainty factor and patient discomfort in treatment. This work was supported by the Medical Science Foundation of the health department of Hebei

  19. 饱和冻结粉土在常应变速率下的单轴抗压强度%Uniaxial Compressive Strength of the Saturated Frozen Silt at Constant Strain Rates

    Institute of Scientific and Technical Information of China (English)

    李海鹏; 朱元林; 潘卫东

    2002-01-01

    Uniaxial compressive strength tests were conducted on the saturated frozen Lanzhou silt (loess) at various constant strain rates and at various constant temperatures. It is concluded from the test results that: the compressive strength (σ f) is very sensitive to temperature (θ) and increases with the temperature decreasing as a power law. Compressive strength is sensitive to strain rate () and increases with strain rates increasing within a certain range of strain rates as a power law. Compressive strength decreases when time to failure (tf) increases, also following a power law. Finally, Compressive strength of frozen silt with higher dry density (γd) is higher than that of frozen silt with lower dry density. The difference between them is mainly influenced by strain rate.

  20. Effect of improved TLD dosimetry on the determination of dose rate constants for {sup 125}I and {sup 103}Pd brachytherapy seeds

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, M., E-mail: manuel.rodriguez@rmp.uhn.ca [Carleton Laboratory for Radiotherapy Physics, Carleton University, Ottawa, Ontario K1S 5B6, Canada and Princess Margaret Hospital, Toronto, Ontario M5G 2M9 (Canada); Rogers, D. W. O. [Carleton Laboratory for Radiotherapy Physics, Carleton University, Ottawa, Ontario K1S 5B6 (Canada)

    2014-11-01

    Purpose: To more accurately account for the relative intrinsic energy dependence and relative absorbed-dose energy dependence of TLDs when used to measure dose rate constants (DRCs) for {sup 125}I and {sup 103}Pd brachytherapy seeds, to thereby establish revised “measured values” for all seeds and compare the revised values with Monte Carlo and consensus values. Methods: The relative absorbed-dose energy dependence, f{sup rel}, for TLDs and the phantom correction, P{sub phant}, are calculated for {sup 125}I and {sup 103}Pd seeds using the EGSnrc BrachyDose and DOSXYZnrc codes. The original energy dependence and phantom corrections applied to DRC measurements are replaced by calculated (f{sup rel}){sup −1} and P{sub phant} values for 24 different seed models. By comparing the modified measured DRCs to the MC values, an appropriate relative intrinsic energy dependence, k{sub bq}{sup rel}, is determined. The new P{sub phant} values and relative absorbed-dose sensitivities, S{sub AD}{sup rel}, calculated as the product of (f{sup rel}){sup −1} and (k{sub bq}{sup rel}){sup −1}, are used to individually revise the measured DRCs for comparison with Monte Carlo calculated values and TG-43U1 or TG-43U1S1 consensus values. Results: In general, f{sup rel} is sensitive to the energy spectra and models of the brachytherapy seeds. Values may vary up to 8.4% among {sup 125}I and {sup 103}Pd seed models and common TLD shapes. P{sub phant} values depend primarily on the isotope used. Deduced (k{sub bq}{sup rel}){sup −1} values are 1.074 ± 0.015 and 1.084 ± 0.026 for {sup 125}I and {sup 103}Pd seeds, respectively. For (1 mm){sup 3} chips, this implies an overall absorbed-dose sensitivity relative to {sup 60}Co or 6 MV calibrations of 1.51 ± 1% and 1.47 ± 2% for {sup 125}I and {sup 103}Pd seeds, respectively, as opposed to the widely used value of 1.41. Values of P{sub phant} calculated here have much lower statistical uncertainties than literature values, but

  1. Nonradiating and radiating modes excited by quantum emitters in open epsilon-near-zero cavities

    CERN Document Server

    Liberal, Iñigo

    2015-01-01

    Controlling the emission and interaction properties of quantum emitters (QEs) embedded within an optical cavity is a key technique in engineering light-matter interactions at the nanoscale, as well as in the development of quantum information processing. State-of-the-art optical cavities are based on high Q photonics crystals and dielectric resonators. However, wealthier responses might be attainable with cavities carved in more exotic materials. Here, we theoretically investigate the emission and interaction properties of QEs embedded in open epsilon-near-zero (ENZ) cavities. Using analytical methods and numerical simulations, it is demonstrated that open ENZ cavities present the unique property of supporting nonradiating modes independently of the geometry of the external boundary of the cavity (shape, size, topology...). Moreover, the possibility of switching between radiating and nonradiating modes enables a dynamic control of both the emission by, and the interaction between, QEs. These phenomena provide...

  2. Non-Radial Instabilities and Progenitor Asphericities in Core-Collapse Supernovae

    CERN Document Server

    Mueller, B

    2014-01-01

    Since core-collapse supernova simulations still struggle to produce robust neutrino-driven explosions in 3D, it has been proposed that asphericities caused by convection in the progenitor might facilitate shock revival by boosting the activity of non-radial hydrodynamic instabilities in the post-shock region. We investigate this scenario in depth using 42 relativistic 2D simulations with multi-group neutrino transport to examine the effects of velocity and density perturbations in the progenitor for different perturbation geometries that obey fundamental physical constraints (like the anelastic condition). As a framework for analysing our results, we introduce semi-empirical scaling laws relating neutrino heating, average turbulent velocities in the gain region, and the shock deformation in the saturation limit of non-radial instabilities. The squared turbulent Mach number, , reflects the violence of aspherical motions in the gain layer, and explosive runaway occurs for ~0.3, corresponding to a reduction of t...

  3. nIFTy galaxy cluster simulations I: dark matter & non-radiative models

    CERN Document Server

    Sembolini, Federico; Pearce, Frazer R; Knebe, Alexander; Kay, Scott T; Power, Chris; Cui, Weiguang; Beck, Alexander M; Borgani, Stefano; Vecchia, Claudio Dalla; Davé, Romeel; Elahi, Pascal Jahan; February, Sean; Huang, Shuiyao; Hobbs, Alex; Katz, Neal; Lau, Erwin; McCarthy, Ian G; Murante, Giuseppe; Nagai, Daisuke; Nelson, Kaylea; Newton, Richard D A; Puchwein, Ewald; Read, Justin I; Saro, Alexandro; Schaye, Joop; Thacker, Robert J

    2015-01-01

    We have simulated the formation of a galaxy cluster in a $\\Lambda$CDM universe using twelve different codes modeling only gravity and non-radiative hydrodynamics (\\art, \\arepo, \\hydra\\ and 9 incarnations of GADGET). This range of codes includes particle based, moving and fixed mesh codes as well as both Eulerian and Lagrangian fluid schemes. The various GADGET implementations span traditional and advanced smoothed-particle hydrodynamics (SPH) schemes. The goal of this comparison is to assess the reliability of cosmological hydrodynamical simulations of clusters in the simplest astrophysically relevant case, that in which the gas is assumed to be non-radiative. We compare images of the cluster at $z=0$, global properties such as mass, and radial profiles of various dynamical and thermodynamical quantities. The underlying gravitational framework can be aligned very accurately for all the codes allowing a detailed investigation of the differences that develop due to the various gas physics implementations employ...

  4. Radiative and nonradiative pathways in multiexciton recombination in giant nanocrystal quantum dots

    Science.gov (United States)

    Malko, Anton; Sampat, Siddharth; Htoon, Han; Vela-Becerra, Javier; Chen, Yongfen; Hollingsworth, Jennifer; Klimov, Victor

    2010-03-01

    Recently,footnotetextY. Chen et al., JACS 130, 5026 (2008) we developed ``giant'' nanocrystal quantum dots (g-NQDs), in which a small emitting core of CdSe is overcoated with a thick shell of a wider-gap CdS. We conduct room-temp measurements of photoluminescence (PL) lifetimes in such g-NQDs as a function of excitation power and a number of shell monolayers. At low pump levels, corresponding to excitation of less than 1 exciton per dot on average (>1, fast (˜1ns) PL component appeared, accompanied by a transition to a sub-linear scaling of PL intensity with . Our findings indicate that while g-NQDs indeed produce suppression of nonradiative Auger recombination,footnotetextF. Garcia-Santamaria et al., Nanoletters 9, 3482 (2009) this suppression is incomplete. We conduct systematic studies of relative efficiencies of nonradiative and radiative processes in these nanostructures.

  5. Nonradial modes in RR Lyrae stars from the OGLE Collection of Variable Stars

    CERN Document Server

    Netzel, Henryka; Moskalik, Pawel

    2016-01-01

    The Optical Gravitational Lensing Experiment (OGLE) is a great source of top-quality photometry of classical pulsators. Collection of variable stars from the fourth part of the project contains more than 38 000 RR Lyrae stars. These stars pulsate mostly in the radial fundamental mode (RRab), in radial first overtone (RRc) or in both modes simultaneously (RRd). Analysis of the OGLE data allowed to detect additional non-radial modes in RRc and in RRd stars. We have found more than 260 double-mode stars with characteristic period ratio of the additional (shorter) period to first overtone period around 0.61, increasing the number of known stars of this type by factor of 10. Stars from the OGLE sample form three nearly parallel sequences in the Petersen diagram. Some stars show more than one non-radial mode simultaneously. These modes belong to different sequences.

  6. Observation of non-radiative de-excitation processes in silicon nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Milgram, J.N.; Wojcik, J.; Mascher, P. [Department of Engineering Physics, Centre for Emerging Device Technologies, McMaster University, Hamilton, Ontario (Canada); Crowe, I.; Sherliker, B.; Halsall, M.P. [School of Electrical and Electronic Engineering, University of Manchester (United Kingdom); Gwilliam, R.M. [Surrey Ion Beam Centre, Advanced Technology Institute, University of Surrey, Guildford (United Kingdom); Knights, A.P.

    2009-05-15

    We describe the impact of non-radiative de-excitation mechanisms on the optical emission from silicon nanocrystals formed in SiO{sub 2}. Auger excitation via free carriers deliberately introduced through phosphorus ion implantation, shows a monotonic increase with increasing phosphorus concentration which can be modelled adequately using a simple statistical approach. We also report a reduction in nanocrystal luminescence intensity with increasing exposure to UV radiation and suggest this phenomenon results from the introduction of non-radiative defects in the Si/SiO{sub 2} network. The effect of UV radiation varies significantly depending on the sample preparation. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Non-radial, non-adiabatic solar-like oscillations in RGB and HB stars

    CERN Document Server

    Grosjean, M; Belkacem, K; Montalban, J; Noels, A; Samadi, R

    2013-01-01

    CoRoT and Kepler observations of red giants reveal rich spectra of non-radial solar-like oscillations allowing to probe their internal structure. We compare the theoretical spectrum of two red giants in the same region of the HR diagram but in different evolutionary phases. We present here our first results on the inertia, lifetimes and amplitudes of the oscillations and discuss the differences between the two stars.

  8. The effect of non-radial motions on the CDM model predictions

    CERN Document Server

    Popolo, A D

    1998-01-01

    In this paper we show how non-radial motions, originating from the tidal interaction of the irregular mass distribution within and around protoclusters, can solve some of the problems of the CDM model. Firstly the discrepancy between the CDM predicted two-points correlation function of clusters and the observed one. We compare the two-points correlation function, that we obtain taking account of non-radial motions, with that obtained by Sutherland & Efstathiou (1991) from the analysis of Geller & Hucra's (1988) deep redshift survey and with the data points for the APM clusters obtained by Efstathiou et al. (1992). Secondly the problem of the X-ray clusters abundance over-production predicted by the CDM model. In this case we compare the X-ray temperature distribution function, calculated using Press-Schechter theory and Evrard's (1990) prescriptions for the mass-temperature relation, taking also account of the non-radial motions, with Henry & Arnaud (1991) and Edge et al. (1990) X-ray temperature ...

  9. Non-radial solar wind flows induced by the motion of interplanetary coronal mass ejections

    Directory of Open Access Journals (Sweden)

    M. Owens

    2004-12-01

    Full Text Available A survey of the non-radial flows (NRFs during nearly five years of interplanetary observations revealed the average non-radial speed of the solar wind flows to be ~30km/s, with approximately one-half of the large (>100km/s NRFs associated with ICMEs. Conversely, the average non-radial flow speed upstream of all ICMEs is ~100km/s, with just over one-third preceded by large NRFs. These upstream flow deflections are analysed in the context of the large-scale structure of the driving ICME. We chose 5 magnetic clouds with relatively uncomplicated upstream flow deflections. Using variance analysis it was possible to infer the local axis orientation, and to qualitatively estimate the point of interception of the spacecraft with the ICME. For all 5 events the observed upstream flows were in agreement with the point of interception predicted by variance analysis. Thus we conclude that the upstream flow deflections in these events are in accord with the current concept of the large-scale structure of an ICME: a curved axial loop connected to the Sun, bounded by a curved (though not necessarily circular cross section.

    Key words. Interplanetary physics (flare and stream dynamics; interplanetary magnetic fields; interplanetary shocks

  10. Effects of the impurity-host interactions on the nonradiative processes in ZnS:Cr

    Science.gov (United States)

    Tablero, C.

    2010-11-01

    There is a great deal of controversy about whether the behavior of an intermediate band in the gap of semiconductors is similar or not to the deep-gap levels. It can have significant consequences, for example, on the nonradiative recombination. In order to analyze the behavior of an intermediate band, we have considered the effect of the inward and outward displacements corresponding to breathing and longitudinal modes of Cr-doped ZnS and on the charge density for different processes involved in the nonradiative recombination using first-principles. This metal-doped zinc chalcogenide has a partially filled band within the host semiconductor gap. In contrast to the properties exhibited by deep-gap levels in other systems, we find small variations in the equilibrium configurations, forces, and electronic density around the Cr when the nonradiative recombination mechanisms modify the intermediate band charge. The charge density around the impurity is equilibrated in response to the perturbations in the equilibrium nuclear configuration and the charge of the intermediate band. The equilibration follows a Le Chatelier principle through the modification of the contribution from the impurity to the intermediate band and to the valence band. The intermediate band introduced by Cr in ZnS for the concentrations analyzed makes the electronic capture difficult and later multiphonon emission in the charge-transfer processes, in accordance with experimental results.

  11. Moving nonradiating kinks in nonlocal φ4 and φ4-φ6 models.

    Science.gov (United States)

    Alfimov, G L; Medvedeva, E V

    2011-11-01

    We explore the existence of moving nonradiating kinks in nonlocal generalizations of φ(4) and φ(4)-φ(6) models. These models are described by nonlocal nonlinear Klein-Gordon equation, u(tt)-Lu+F(u)=0, where L is a Fourier multiplier operator of a specific form and F(u) includes either just a cubic term (φ(4) case) or cubic and quintic (φ(4)-φ(6) case) terms. The general mechanism responsible for the discretization of kink velocities in the nonlocal model is discussed. We report numerical results obtained for these models. It is shown that, contrary to the traditional φ(4) model, the nonlocal φ(4) model does not admit moving nonradiating kinks but admits solitary waves that do not exist in the local model. At the same time the nonlocal φ(4)-φ(6) model describes moving nonradiating kinks. The set of velocities allowed for these kinks is discrete with the highest possible velocity c(1). This set of velocities is unambiguously determined by the parameters of the model. Numerical simulations show that a kink launched at the velocity c higher than c(1) starts to decelerate, and its velocity settles down to the highest value of the discrete spectrum c(1).

  12. Non-radiation related osteonecrosis of the jaws in dogs: 14 cases (1996 - 2014

    Directory of Open Access Journals (Sweden)

    Santiago ePeralta

    2015-05-01

    Full Text Available Osteonecrosis of the jaws is an entity of major clinical impact characterized by chronically exposed necrotic mandibular or maxillary bone. Its clinicopathological characteristics and possible inciting or risk factors are well described in humans but only anecdotally reported in dogs. Treatment modalities and outcome vary depending on the inciting factors involved and the extent and severity of the lesions. The objectives of this study were to retrospectively describe the clinicopathological features of non-radiation related osteonecrosis of the jaws in a series of 14 dogs, identify possible inciting or risk factors, and report on the surgical treatment and outcome. For all patients, the medical records were used to collect information regarding signalment, clinical signs, characteristics of the oral, jaw and dental lesions, diagnostic imaging findings, histopathological and microbiological analysis, treatment performed and outcome. The data collected showed that non-radiation related osteonecrosis of the jaws appears to be an infrequent clinical entity but of significant impact in dogs; that a history of systemic antibiotics and dental disease is common among affected dogs; that previous dental extractions are commonly associated with ONJ sites; that using a systematic diagnostic approach is essential for diagnosis; and that thorough surgical débridement combined with a course of oral antibiotics was effective in the described dogs affected by advanced non-radiation related osteonecrosis of the jaws.

  13. Photochemical properties of trans-1-chloro-3,3,3-trifluoropropene (trans-CHCl═CHCF3): OH reaction rate constant, UV and IR absorption spectra, global warming potential, and ozone depletion potential.

    Science.gov (United States)

    Orkin, Vladimir L; Martynova, Larissa E; Kurylo, Michael J

    2014-07-17

    Measurements of the rate constant for the gas-phase reactions of OH radicals with trans-1-chloro-3,3,3-trifluoropropene (trans-CHCl═CHCF3) were performed using a flash photolysis resonance-fluorescence technique over the temperature range 220-370 K. The reaction rate constant exhibits a noticeable curvature of the temperature dependence in the Arrhenius plot, which can be represented by the following expression: kt-CFP (220-370 K) = 1.025 × 10(-13) × (T/298)(2.29) exp(+384/T) cm(3 )molecule(-1) s(-1). The room-temperature rate constant was determined to be kt-CFP (298 K) = (3.29 ± 0.10) × 10(-13) cm(3) molecule(-1) s(-1), where the uncertainty includes both two standard errors (statistical) and the estimated systematic error. For atmospheric modeling purposes, the rate constant below room temperature can be represented by the following expression: kt-CFP (220-298 K) = (7.20 ± 0.46) × 10(-13) exp[-(237 ± 16)/T] cm(3) molecule(-1) s(-1). There was no difference observed between the rate constants determined at 4 kPa (30 Torr) and 40 kPa (300 Torr) at both 298 and 370 K. The UV and IR absorption cross sections of this compound were measured at room temperature. The atmospheric lifetime, global warming potential, and ozone depletion potential of trans-CHCl═CHCF3 were estimated.

  14. Computational studies on the excited states of luminescent platinum(II) alkynyl systems of tridentate pincer ligands in radiative and nonradiative processes.

    Science.gov (United States)

    Lam, Wai Han; Lam, Elizabeth Suk-Hang; Yam, Vivian Wing-Wah

    2013-10-09

    Platinum(II) alkynyl complexes of various tridentate pincer ligands, [Pt(trpy)(C≡CR)](+) (trpy = 2,2':6',2″-terpyridine), [Pt(R'-bzimpy)(C≡CR)](+) (R'-bzimpy = 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine and R' = alkyl), [Pt(R'-bzimb)(C≡CR)] (R'-bzimb = 1,3-bis(N-alkylbenzimidazol-2'-yl)benzene and R' = C4H9), have been found to possess rich photophysical properties. The emission in dilute solutions of [Pt(trpy)(C≡CR)](+) originated from a triplet alkynyl-to-tridentate pincer ligand-to-ligand charge transfer (LLCT) excited state, with mixing of a platinum-to-tridentate pincer ligand metal-to-ligand charge transfer (MLCT) excited state, while that of [Pt(R'-bzimb)(C≡CR)] originated from a triplet excited state of intraligand (IL) character of the tridentate ligand mixed with a platinum-to-tridentate ligand MLCT character. Interestingly, both emissions were observed in [Pt(R'-bzimpy)(C≡CR)](+) in some cases. In addition, [Pt(R'-bzimb)(C≡CR)] displayed a photoluminescence quantum yield higher than that of [Pt(R'-bzimpy)(C≡CR)](+). Computational studies have been performed on the representative complexes [Pt(trpy)(C≡CPh)](+) (1), [Pt(R'-bzimpy)(C≡CPh)](+) (2), and [Pt(R'-bzimb)(C≡CPh)] (3), where R' = CH3 and Ph = C6H5, to provide an in-depth understanding of the nature of their emissive origin as well as the radiative and nonradiative processes. In particular, the factors governing the ordering of the triplet excited states and radiative decay rate constants of the emissive state ((3)ES) have been examined. The potential energy profiles for the deactivation process from the (3)ES via triplet metal-centered ((3)MC) states have also been explored. This work reveals for the first time the potential energy profiles for the thermal deactivation pathway of square planar platinum(II) complexes.

  15. Effect of number of stack on the thermal escape and non-radiative and radiative recombinations of photoexcited carriers in strain-balanced InGaAs/GaAsP multiple quantum-well-inserted solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Aihara, Taketo; Fukuyama, Atsuhiko; Ikari, Tetsuo [Faculty of Engineering, University of Miyazaki, 1-1 Gakuen-Kibanadai-Nishi, Miyazaki 889-2192 (Japan); Suzuki, Hidetoshi [Interdisciplinary Research Organization, University of Miyazaki, 1-1 Gakuen-Kibanadai-Nishi, Miyazaki 889-2192 (Japan); Fujii, Hiromasa; Nakano, Yoshiaki [Research Center for Advanced Science and Technology, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032 (Japan); Sugiyama, Masakazu [School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032 (Japan)

    2015-02-28

    Three non-destructive methodologies, namely, surface photovoltage (SPV), photoluminescence, and piezoelectric photothermal (PPT) spectroscopies, were adopted to detect the thermal carrier escape from quantum well (QW) and radiative and non-radiative carrier recombinations, respectively, in strain-balanced InGaAs/GaAsP multiple-quantum-well (MQW)-inserted GaAs p-i-n solar cell structure samples. Although the optical absorbance signal intensity was proportional to the number of QW stack, the signal intensities of the SPV and PPT methods decreased at high number of stack. To explain the temperature dependency of these signal intensities, we proposed a model that considers the three carrier dynamics: the thermal escape from the QW, and the non-radiative and radiative carrier recombinations within the QW. From the fitting procedures, it was estimated that the activation energies of the thermal escape ΔE{sub barr} and non-radiative recombination ΔE{sub NR} were 68 and 29 meV, respectively, for a 30-stacked MQW sample. The estimated ΔE{sub barr} value agreed well with the difference between the first electron subband and the top of the potential barrier in the conduction band. We found that ΔE{sub barr} remained constant at approximately 70 meV even with increasing QW stack number. However, the ΔE{sub NR} value monotonically increased with the increase in the number of stack. Since this implies that non-radiative recombination becomes improbable as the number of stack increases, we found that the radiative recombination probability for electrons photoexcited within the QW increased at a large number of QW stack. Additional processes of escaping and recapturing of carriers at neighboring QW were discussed. As a result, the combination of the three non-destructive methodologies provided us new insights for optimizing the MQW components to further improve the cell performance.

  16. Nonradiative recombination due to Ar implantation induced point defects in GaInN/GaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Langer, Torsten; Pietscher, Hans-Georg; Joenen, Holger; Rossow, Uwe; Bremers, Heiko; Hangleiter, Andreas [Institut fuer Angewandte Physik, Technische Universitaet Braunschweig (Germany); Menzel, Dirk [Institut fuer Physik der Kondensierten Materie, Technische Universitaet Braunschweig (Germany)

    2013-07-01

    We quantitatively investigate nonradiative recombination at point defects via temperature dependent time-resolved photoluminescence spectroscopy on argon implanted MOVPE-grown GaInN/GaN single quantum wells (QW). An implantation dose dependent (doses: 10{sup 11} cm{sup -2}-10{sup 13} cm{sup -2}) reduction of nonradiative lifetimes from several nanoseconds (unimplanted sample) to less than 100 ps at room temperature is observed. This shortening of nonradiative lifetimes is attributed to nonradiative recombination due to increased implantation induced defect densities. An effective hole capture coefficient can be estimated to about 10{sup 9} cm{sup 3}s{sup -1} via the measured nonradiative lifetimes and simulated (SRIM) defect densities. The thermal stability of the defects is analyzed using rapid thermal annealing at 800 {sup circle} C in order to recover the crystal from implantation damage. At high temperatures, nonradiative recombination in the barriers becomes dominant: defect density dependent losses with an activation energy equal to half the difference between the GaN band gap and the peak position of the QW luminescence are observed.

  17. Fluorescence quenching and photobleaching in Au/Rh6G nanoassemblies: impact of competition between radiative and non-radiative decay

    Science.gov (United States)

    Dong, L.; Ye, F.; Hu, J.; Popov, S.; Friberg, A. T.; Muhammed, M.

    2011-04-01

    Fluorescence quenching from nanoassemblies formed by Rhodamine 6G and gold nanoparticles (Au NPs) of 2.6 nm radius has been investigated. The presence of Au NPs also induces long-term degradation of the photostability (photobleaching) of Rhodamine 6G used as gain medium in a Fabry-Perot laser cavity. We found that the degradation gets profound when the Au NPs concentration is significantly increased. Calculation of the radiative rate and direct time-resolved measurement of the fluorescence decay indicates that both the decrease of radiative decay rate and increase of non-radiative decay rate are responsible for the fluorescence quenching and photostability degradation. An energy transfer from the dye molecules to gold nanoparticles is dominating within the small distance between them and suppresses the quantum efficiency of Rhodamine 6G drastically. In long time scale, the photobleaching rate was slowing down, and laser output intensity reached a stabilized level which depends on the gold nanoparticles concentration.

  18. Nature of Electronically Excited States of Organic Compounds and Processes of Nonradiative Conversion

    Science.gov (United States)

    Mayer, G. V.; Plotnikov, V. G.; Artyukhov, V. Ya.

    2016-08-01

    Models of quantum-chemical calculation of rate constants for internal processes and intersystem crossing in polyatomic molecules are considered. The influence of the nature of electronically excited states in organic compounds is investigated. It is shown that the explicit allowance for the nature of wave functions of electronic states for estimation of electronic matrix elements of nonadiabaticity operators and spin-orbit interaction allows photophysical processes in organic compounds to be considered in detail.

  19. Research the Factor Affecting the Apparent Rate Constant in the Decomposition of Carbendazim by Oozone Oxidation%臭氧氧化多菌灵表观速率常数影响因素的研究

    Institute of Scientific and Technical Information of China (English)

    黄曦; 张雁秋; 刘伟京; 涂勇; 徐军

    2011-01-01

    [目的]考察多菌灵初始浓度、臭氧投加量和温度对臭氧氧化降解多茼灵反应表观速率常数的影响.[方法]采用臭氧氧化降解水体中的多菌灵,考察多菌灵降解过程中表现反应速率常数与反应剂量因素的关系.[结果]在不同臭氧投加量和不同初始浓度条件下,多菌灵降解均符合假一级反应动力学.表现速率常数与臭氧投加量呈正相关性,与多菌灵初始浓度呈负相关性.表观速率常数随多菌灵初始浓度的增加而减小,但是反应物的绝对去除量增加,表明增加多菌灵初始浓度有利于提高臭氧的利用效率.表观速率常数随温度的升高而增加,与一般化学反应规律相符合.[结论]为安全有效地降解多菌灵提供了参考.%[ Objective] The effect of the initial concentration of carbenclazim, the adding amount of ozone and temperature on the apparent rate constant in the degradation of carbendazim was researched. [ Method ] The relationship between the apparent rate constant and reaction dose in the process of the carbendazim degradation in water was experimented. [ Results] The results indicated that under the condition of different doses of ozone-adding and initial concentrations the process of carbendazim degradation was matched with the pseudo-first-order kinetic model. The apparent rate constants had the positive relativity with applied ozone dose and negative correlation with initial concentration. The apparent rate constant was decreased with increment of initial concentration. However, the absolute removal rate of the reactants was increased, which indicated that the increment of initial concentration would be beneficial to the improvement of the utilization rate of ozone. The apparent rate constant was increased with the increment of temperature, which was consistent with the general law of chemical reaction. [ Conclusion] The reference for the safety and efficiency degradation of carbendazim was provided

  20. Title: Elucidation of Environmental Fate of Artificial Sweeteners (Aspartame, Acesulfame K and Saccharin) by Determining Bimolecular Rate Constants with Hydroxyl Radical at Various pH and Temperature Conditions and Possible Reaction By-Products

    Science.gov (United States)

    Teraji, T.; Arakaki, T.; Suzuka, T.

    2012-12-01

    Use of artificial sweeteners in beverages and food has been rapidly increasing because of their non-calorie nature. In Japan, aspartame, acesulfame K and sucralose are among the most widely used artificial sweeteners. Because the artificial sweeteners are not metabolized in human bodies, they are directly excreted into the environment without chemical transformations. We initiated a study to better understand the fate of artificial sweeteners in the marine environment. The hydroxyl radical (OH), the most potent reactive oxygen species, reacts with various compounds and determines the environmental oxidation capacity and the life-time of many compounds. The steady-state OH concentration and the reaction rate constants between the compound and OH are used to estimate the life-time of the compound. In this study, we determine the bimolecular rate constants between aspartame, acefulfame K and saccharin and OH at various pH and temperature conditions using a competition kinetics technique. We use hydrogen peroxide as a photochemical source of OH. Bimolecular rate constant we obtained so far for aspartame was (2.6±1.2)×109 M-1 s-1 at pH = 3.0 and (4.9±2.3)×109 M-1 s-1 at pH = 5.5. Little effect was seen by changing the temperatures between 15 and 40 oC. Activation energy (Ea) was calculated to be -1.0 kJ mol-1 at pH = 3.0, +8.5 kJ mol-1 at pH = 5.5, which could be regarded as zero. We will report bimolecular rate constants at different pHs and temperatures for acesulfame K and saccharin, as well. Possible reaction by-products for aspartame will be also reported. We will further discuss the fate of aspartame in the coastal environment.

  1. Oxygenation, local muscle oxygen consumption and joint specific power in cycling: the effect of cadence at a constant external work rate.

    Science.gov (United States)

    Skovereng, Knut; Ettema, Gertjan; van Beekvelt, Mireille C P

    2016-06-01

    The present study investigates the effect of cadence on joint specific power and oxygenation and local muscle oxygen consumption in the vastus lateralis and vastus medialis in addition to the relationship between joint specific power and local muscle oxygen consumption (mVO2). Seventeen recreationally active cyclists performed 6 stages of constant load cycling using cadences of 60, 70, 80, 90, 100 and 110 rpm. Joint specific power was calculated using inverse dynamics and mVO2 and oxygenation were measured using near-infrared spectroscopy. Increasing cadence led to increased knee joint power and decreased hip joint power while the ankle joint was unaffected. Increasing cadence also led to an increased deoxygenation in both the vastus lateralis and vastus medialis. Vastus lateralis mVO2 increased when cadence was increased. No effect of cadence was found for vastus medialis mVO2. This study demonstrates a different effect of cadence on the mVO2 of the vastus lateralis and vastus medialis. The combined mVO2 of the vastus lateralis and medialis showed a linear increase with increasing knee joint specific power, demonstrating that the muscles combined related to power generated over the joint.

  2. Predicting pressure-dependent unimolecular rate constants using variational transition state theory with multidimensional tunneling combined with system-specific quantum RRK theory: a definitive test for fluoroform dissociation.

    Science.gov (United States)

    Bao, Junwei Lucas; Zhang, Xin; Truhlar, Donald G

    2016-06-22

    Understanding the falloff in rate constants of gas-phase unimolecular reaction rate constants as the pressure is lowered is a fundamental problem in chemical kinetics, with practical importance for combustion, atmospheric chemistry, and essentially all gas-phase reaction mechanisms. In the present work, we use our recently developed system-specific quantum RRK theory, calibrated by canonical variational transition state theory with small-curvature tunneling, combined with the Lindemann-Hinshelwood mechanism, to model the dissociation reaction of fluoroform (CHF3), which provides a definitive test for falloff modeling. Our predicted pressure-dependent thermal rate constants are in excellent agreement with experimental values over a wide range of pressures and temperatures. The present validation of our methodology, which is able to include variational transition state effects, multidimensional tunneling based on the directly calculated potential energy surface along the tunneling path, and torsional and other vibrational anharmonicity, together with state-of-the-art reaction-path-based direct dynamics calculations, is important because the method is less empirical than models routinely used for generating full mechanisms, while also being simpler in key respects than full master equation treatments and the full reduced falloff curve and modified strong collision methods of Troe.

  3. Overlapping $B^{3}_{0u}← X^{1}^{+}_{g}$ and $^{1}_{1u} ← X^{1}^{+}_{g}$ non-radiative characteristic of Br2 vapour in the wavelength region 505–541 nm

    Indian Academy of Sciences (India)

    Ramesh C Sharma; S N Thakur

    2001-01-01

    The vibronic vapour phase photoacoustic spectrum of Br2 in the wavelength region 505–541 nm (19796–18480 cm-1) has been recorded using microphone as well as pump-probe method. Discrete vibronic bands superimposed on a monotonically increasing continuum background towards the dissociation limit results from the overlapping $B^{3}^{+}_{0u}← X^{1}^{+}_{g}$ and $^{1}_{1u}← X^{1}^{+}_{g}$ electronic transitions. Vibronic bands originating from '' = 0 have been used to estimate the relative rate of non-radiative relaxation as a function of the excited state $^{3}_{0u}$ vibrational quantum number '. A comparison with the optical absorption spectroscopy of Br2 leads to the identification of three broad spectral regions between 505 and 541 nm (19796 and 18480 cm-1) on the basis of different non-radiative relaxation processes.

  4. Analysis of initial chlorophyll fluorescence induction kinetics in chloroplasts in terms of rate constants of donor side quenching release and electron trapping in photosystem II

    NARCIS (Netherlands)

    Vredenberg, W.J.

    2008-01-01

    The fluorescence induction F(t) of dark-adapted chloroplasts has been studied in multi-turnover 1 s light flashes (MTFs). A theoretical expression for the initial fluorescence rise is derived from a set of rate equations that describes the sequence of transfer steps associated with the reduction of

  5. Hydrolysis rate constants at 10–25 °C can be more than doubled by a short anaerobic pre-hydrolysis at 35 °C

    NARCIS (Netherlands)

    Zhang, L.; Gao, R.; Naka, A.; Hendrickx, T.L.G.; Rijnaarts, H.H.M.; Zeeman, G.

    2016-01-01

    Hydrolysis is the first step of the anaerobic digestion of complex wastewater and considered as the rate limiting step especially at low temperature. Low temperature (10–25 °C) hydrolysis was investigated with and without application of a short pre-hydrolysis at 35 °C. Batch experiments were

  6. Nonradiative transfer of excitation in coherent decay from a Gaussian atomic distribution

    Energy Technology Data Exchange (ETDEWEB)

    Friedberg, Richard, E-mail: rfriedberg1@nyc.rr.com [Physics Department, Columbia University, NY (United States)

    2011-09-14

    Coherent decay of a spherically symmetric ensemble of initially resonantly phased two-level atoms is studied in the scalar photon model, in the continuum and Markov approximations. Emphasis is on the Gaussian distribution, where nonradiative transfer of excitation to excited states orthogonal to the initial one is found to be nonzero even in the limit of short wavelength, whether or not the scalar kernel exp(ik{sub 0}R)/ik{sub 0}R is replaced by its real part. Numerical results are compared to known values for the uniform distribution.

  7. Nonradiative resonant energy transfer between PbS QDs in porous matrix

    Science.gov (United States)

    Ushakova, Elena V.; Litvin, Aleksandr P.; Parfenov, Peter S.; Fedorov, Anatoly V.; Cherevkov, Sergei A.; Baranov, Alexander V.

    2013-09-01

    Nonradiative fluorescence resonance energy transfer (FRET) between lead sulfide quantum dots (QDs) of two different sizes embedded in porous matrix is observed by a fluorescence spectroscopy. Analysis of decays of photoluminescence from QD mixture shows that energy transfer in studied systems is determined by static quenching, specific for direct contact between QD-donor and QD-acceptor in the QDs close-packed ensembles. From steady-state spectral analysis it was found that efficiency of energy transfer depends on the molar ratio QD-donor/QD-acceptor and energy transfer from the donor to the acceptor passes by several channels.

  8. Correlation of Electrical Noise with Non-radiative Current for High Power QWLs

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The characteristics of low-frequency electrical noise, voltage-current (V-I) and electrical derivation for 980nm InGaAsP/InGaAs/GaAs high power double quantum well lasers(DQWLs) are measured under different conditions. The correlation of the low-frequency electrical noise with surface non-radiative current of devices is discussed. The results indicate the low-frequency electrical noise of 980nm DQWLs with high power is mainly 1/f noise and has good relation with the device surface current at low injection.

  9. Ag colloids and arrays for plasmonic non-radiative energy transfer from quantum dots to a quantum well

    Science.gov (United States)

    Murphy, Graham P.; Gough, John J.; Higgins, Luke J.; Karanikolas, Vasilios D.; Wilson, Keith M.; Garcia Coindreau, Jorge A.; Zubialevich, Vitaly Z.; Parbrook, Peter J.; Bradley, A. Louise

    2017-03-01

    Non-radiative energy transfer (NRET) can be an efficient process of benefit to many applications including photovoltaics, sensors, light emitting diodes and photodetectors. Combining the remarkable optical properties of quantum dots (QDs) with the electrical properties of quantum wells (QWs) allows for the formation of hybrid devices which can utilize NRET as a means of transferring absorbed optical energy from the QDs to the QW. Here we report on plasmon-enhanced NRET from semiconductor nanocrystal QDs to a QW. Ag nanoparticles in the form of colloids and ordered arrays are used to demonstrate plasmon-mediated NRET from QDs to QWs with varying top barrier thicknesses. Plasmon-mediated energy transfer (ET) efficiencies of up to ∼25% are observed with the Ag colloids. The distance dependence of the plasmon-mediated ET is found to follow the same d ‑4 dependence as the direct QD to QW ET. There is also evidence for an increase in the characteristic distance of the interaction, thus indicating that it follows a Förster-like model with the Ag nanoparticle-QD acting as an enhanced donor dipole. Ordered Ag nanoparticle arrays display plasmon-mediated ET efficiencies up to ∼21%. To explore the tunability of the array system, two arrays with different geometries are presented. It is demonstrated that changing the geometry of the array allows a transition from overall quenching of the acceptor QW emission to enhancement, as well as control of the competition between the QD donor quenching and ET rates.

  10. Non-Radiative Energy Transfer for Photovoltaic Solar Energy Conversion: Lead Sulfide Quantum Dots on Silicon Nanopillars

    Science.gov (United States)

    Lingley, Zachary R.

    as QD-solids. These QD solids of controlled and experimentally determined average inter-QD separation enabled the first systematic study of exciton decay dynamics involving competition between separation-dependent QD to QD NRET and QD to QD charge transfer as a function of temperature and quantum dot size. Our principal findings are : (1) the NRET rate from smaller to larger QDs increases with decreasing QD-QD average separation as the inverse sixth power, as expected; (2) reduction in temperature enhances the inter-QD NRET rate (3) exciton decay in the largest QDs is dominated by thermally activated tunneling of charge and (4) a consistent understanding of both inter QD energy and charge transfer is obtained by accounting for the ligand-length dependent effective medium nature of QD solid dielectric constant and postulating the presence of gap states. As transfer of energy from the QDs adjacent to the acceptor channels is an integral step in the NRET-based photovoltaic solar cell paradigm we under took examination of the structural nature of the PbS QD- crystalline Si interface as formed upon deposition of PbS QDs on Si. To directly image the QD-substrate interface in a transmission electron microscope (TEM) we introduced a new approach to TEM specimen preparation that enabled the first simultaneous high resolution imaging of a silicon nanopillar with thickness less than 100 nm and PbS QDs adsorbed on it, and thus the interfacial region as well. The separation between the crystalline core of the PbS QD and the crystalline silicon was found to be substantially less than the length of the ligands that coat the PbS QD. The dissertation concludes with a report on progress towards fabricating and characterizing PbS QD - silicon nanowall solar cell devices. Prototype devices were made by etching high aspect ratio and high density of trenches in silicon having an existing p-n junction. The walls of silicon between the trenches thus act as the charge transport channels for

  11. Rate constants of the Br-initiated gas-phase oxidation of a series of alcohols, furans and benzenes at 300±2 K

    Science.gov (United States)

    Bierbach, A.; Barnes, I.; Becker, K. H.

    Using the relative kinetic technique, rate coefficients have been determined for the gas-phase reaction of Br atoms with a selection of organic compounds, including alcohols, furan derivatives and aromatic hydrocarbons, at 300±2 K in 1000 mbar of synthetic air. Rate coefficients have been obtained for the following compounds (in units of cm 3 molecule -1 s -1): methanol (≤5×10 -16); ethanol (9.2±1.8)×10 -15; propan-1-ol (8.3±1.6)×10 -15; propan-2-ol (4.6±0.9)×10 -14; 2-methylpropan-2-ol (≤5×10 -16); 3-bromobutan-2-ol (2.2±0.4)×10 -13; furan (1.6±0.3)×10 -15; 2-methylfuran (2.2±0.4)×10 -13; 2,5-dimethylfuran (1.9±0.4)×10 -12; furan-2-aldehyde (2.2±0.4)×10 -13; 5-methylfurfural (4.0±0.8)×10 -13; benzene (≤5×10 -16); toluene (1.3±0.2)×10 -14; o-xylene (8.9±1.8)×10 -14; m-xylene (6.6±1.3)×10 -14; p-xylene (9.0±1.8)×10 -14, and 1,2,3-trimethylbenzene (4.8±1.0)×10 -13. Apart from methanol, this study represents the first determination of the rate coefficients for these compounds.

  12. Non-radiation hardened microprocessors in space-based remote sensing systems

    Science.gov (United States)

    DeCoursey, R.; Melton, Ryan; Estes, Robert R., Jr.

    2006-09-01

    The CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) mission is a comprehensive suite of active and passive sensors including a 20Hz 230mj Nd:YAG lidar, a visible wavelength Earth-looking camera and an imaging infrared radiometer. CALIPSO flies in formation with the Earth Observing System Post-Meridian (EOS PM) train, provides continuous, near-simultaneous measurements and is a planned 3 year mission. CALIPSO was launched into a 98 degree sun synchronous Earth orbit in April of 2006 to study clouds and aerosols and acquires over 5 gigabytes of data every 24 hours. Figure 1 shows the ground track of one CALIPSO orbit as well as high and low intensity South Atlantic Anomaly outlines. CALIPSO passes through the SAA several times each day. Spaced based remote sensing systems that include multiple instruments and/or instruments such as lidar generate large volumes of data and require robust real-time hardware and software mechanisms and high throughput processors. Due to onboard storage restrictions and telemetry downlink limitations these systems must pre-process and reduce the data before sending it to the ground. This onboard processing and realtime requirement load may mean that newer more powerful processors are needed even though acceptable radiation-hardened versions have not yet been released. CALIPSO's single board computer payload controller processor is actually a set of four (4) voting non-radiation hardened COTS Power PC 603r's built on a single width VME card by General Dynamics Advanced Information Systems (GDAIS). Significant radiation concerns for CALIPSO and other Low Earth Orbit (LEO) satellites include the South Atlantic Anomaly (SAA), the north and south poles and strong solar events. Over much of South America and extending into the South Atlantic Ocean (see figure 1) the Van Allen radiation belts dip to just 200-800km and spacecraft entering this area are subjected to high energy protons and experience higher than

  13. A Non-radial Eruption in a Quadrupolar Magnetic Configuration with a Coronal Null

    Science.gov (United States)

    Sun, Xudong; Hoeksema, J. Todd; Liu, Yang; Chen, Qingrong; Hayashi, Keiji

    2012-10-01

    We report one of the several homologous non-radial eruptions from NOAA active region (AR) 11158 that are strongly modulated by the local magnetic field as observed with the Solar Dynamic Observatory. A small bipole emerged in the sunspot complex and subsequently created a quadrupolar flux system. Nonlinear force-free field extrapolation from vector magnetograms reveals its energetic nature: the fast-shearing bipole accumulated ~2 × 1031 erg free energy (10% of AR total) over just one day despite its relatively small magnetic flux (5% of AR total). During the eruption, the ejected plasma followed a highly inclined trajectory, over 60° with respect to the radial direction, forming a jet-like, inverted-Y-shaped structure in its wake. Field extrapolation suggests complicated magnetic connectivity with a coronal null point, which is favorable of reconnection between different flux components in the quadrupolar system. Indeed, multiple pairs of flare ribbons brightened simultaneously, and coronal reconnection signatures appeared near the inferred null. Part of the magnetic setting resembles that of a blowout-type jet; the observed inverted-Y structure likely outlines the open field lines along the separatrix surface. Owing to the asymmetrical photospheric flux distribution, the confining magnetic pressure decreases much faster horizontally than upward. This special field geometry likely guided the non-radial eruption during its initial stage.

  14. A NON-RADIAL ERUPTION IN A QUADRUPOLAR MAGNETIC CONFIGURATION WITH A CORONAL NULL

    Energy Technology Data Exchange (ETDEWEB)

    Sun Xudong; Hoeksema, J. Todd; Liu Yang; Hayashi, Keiji [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States); Chen Qingrong, E-mail: xudong@sun.stanford.edu [Department of Physics, Stanford University, Stanford, CA 94305 (United States)

    2012-10-01

    We report one of the several homologous non-radial eruptions from NOAA active region (AR) 11158 that are strongly modulated by the local magnetic field as observed with the Solar Dynamic Observatory. A small bipole emerged in the sunspot complex and subsequently created a quadrupolar flux system. Nonlinear force-free field extrapolation from vector magnetograms reveals its energetic nature: the fast-shearing bipole accumulated {approx}2 Multiplication-Sign 10{sup 31} erg free energy (10% of AR total) over just one day despite its relatively small magnetic flux (5% of AR total). During the eruption, the ejected plasma followed a highly inclined trajectory, over 60 Degree-Sign with respect to the radial direction, forming a jet-like, inverted-Y-shaped structure in its wake. Field extrapolation suggests complicated magnetic connectivity with a coronal null point, which is favorable of reconnection between different flux components in the quadrupolar system. Indeed, multiple pairs of flare ribbons brightened simultaneously, and coronal reconnection signatures appeared near the inferred null. Part of the magnetic setting resembles that of a blowout-type jet; the observed inverted-Y structure likely outlines the open field lines along the separatrix surface. Owing to the asymmetrical photospheric flux distribution, the confining magnetic pressure decreases much faster horizontally than upward. This special field geometry likely guided the non-radial eruption during its initial stage.

  15. Fluorescence and Nonradiative Properties of Nd3+ in Novel Heavy Metal Contained Fluorophosphate Glass

    Directory of Open Access Journals (Sweden)

    Ju H. Choi

    2007-01-01

    Full Text Available We demonstrate new series of heavy metal containing fluorophosphate glass system. The fluorescence and nonradiative properties of Nd3+ ions are investigated as a function of Nd2O3 concentration. The variation of intensity parameters Ω2, Ω4, and Ω6 is determined from absorption spectra. The spontaneous probability (A and branching ratio (β are determined using intensity parameters. The emission cross sections for the 4F3/2→4I13/2 transition, which is calculated by Fuchtbabauer-Ladenburg method, decrease from 6.1×10−21 to 3.0×10−21(pm2 and those for the 4F3/2→4I11/2 transition decrease from 3.51×10−20 to 1.7×10−20 as Nd2O3 concentration increase up to 3 wt%. The nonradiative relaxation is analyzed in terms of multiphonon relaxation and concentration quenching due to energy transfer among Nd3+ ions. Finally, the above results obtained at 1 wt %Nd2O3 are compared with some of reported laser host glasses which indicated the potentials for broadband-amplifiers and high-power laser applications.

  16. nIFTy galaxy cluster simulations - I. Dark matter and non-radiative models

    Science.gov (United States)

    Sembolini, Federico; Yepes, Gustavo; Pearce, Frazer R.; Knebe, Alexander; Kay, Scott T.; Power, Chris; Cui, Weiguang; Beck, Alexander M.; Borgani, Stefano; Dalla Vecchia, Claudio; Davé, Romeel; Elahi, Pascal Jahan; February, Sean; Huang, Shuiyao; Hobbs, Alex; Katz, Neal; Lau, Erwin; McCarthy, Ian G.; Murante, Guiseppe; Nagai, Daisuke; Nelson, Kaylea; Newton, Richard D. A.; Perret, Valentin; Puchwein, Ewald; Read, Justin I.; Saro, Alexandro; Schaye, Joop; Teyssier, Romain; Thacker, Robert J.

    2016-04-01

    We have simulated the formation of a galaxy cluster in a Λ cold dark matter universe using 13 different codes modelling only gravity and non-radiative hydrodynamics (RAMSES, ART, AREPO, HYDRA and nine incarnations of GADGET). This range of codes includes particle-based, moving and fixed mesh codes as well as both Eulerian and Lagrangian fluid schemes. The various GADGET implementations span classic and modern smoothed particle hydrodynamics (SPH) schemes. The goal of this comparison is to assess the reliability of cosmological hydrodynamical simulations of clusters in the simplest astrophysically relevant case, that in which the gas is assumed to be non-radiative. We compare images of the cluster at z = 0, global properties such as mass and radial profiles of various dynamical and thermodynamical quantities. The underlying gravitational framework can be aligned very accurately for all the codes allowing a detailed investigation of the differences that develop due to the various gas physics implementations employed. As expected, the mesh-based codes RAMSES, ART and AREPO form extended entropy cores in the gas with rising central gas temperatures. Those codes employing classic SPH schemes show falling entropy profiles all the way into the very centre with correspondingly rising density profiles and central temperature inversions. We show that methods with modern SPH schemes that allow entropy mixing span the range between these two extremes and the latest SPH variants produce gas entropy profiles that are essentially indistinguishable from those obtained with grid-based methods.

  17. Nonradiating and radiating modes excited by quantum emitters in open epsilon-near-zero cavities.

    Science.gov (United States)

    Liberal, Iñigo; Engheta, Nader

    2016-10-01

    Controlling the emission and interaction properties of quantum emitters (QEs) embedded within an optical cavity is a key technique in engineering light-matter interactions at the nanoscale, as well as in the development of quantum information processing. State-of-the-art optical cavities are based on high quality factor photonic crystals and dielectric resonators. However, wealthier responses might be attainable with cavities carved in more exotic materials. We theoretically investigate the emission and interaction properties of QEs embedded in open epsilon-near-zero (ENZ) cavities. Using analytical methods and numerical simulations, we demonstrate that open ENZ cavities present the unique property of supporting nonradiating modes independently of the geometry of the external boundary of the cavity (shape, size, topology, etc.). Moreover, the possibility of switching between radiating and nonradiating modes enables a dynamic control of the emission by, and the interaction between, QEs. These phenomena provide unprecedented degrees of freedom in controlling and trapping fields within optical cavities, as well as in the design of cavity opto- and acoustomechanical systems.

  18. Nonradial g-mode oscillations in X-ray bursting neutron stars

    Science.gov (United States)

    Mcdermott, P. N.; Taam, Ronald E.

    1987-01-01

    The oscillation spectrum of nonradial g-modes in X-ray bursting neutron stars has been studied. The pulsation periods are found to be sensitive to the envelope temperature and range from about 15 ms to about 50 ms for the l = 1 g(1) mode during the X-ray burst. From a quasi-adiabatic stability analysis it is likely that a spectrum of l-pole g-modes is unstable due to the epsilon-mechanism associated with rapid alpha captures. As the thermal structure of the envelope of the neutron star changes on time scales less than 0.2 s during the rise of the X-ray burst, the oscillations are expected to be quasi-coherent during this phase. The calculated period derivatives are large during the burst and are about 1 ms/s. The pulsations are short-lived and are most likely to be seen in the immediate vicinity of the burst peak. Finally, the possible relevance of nonradial g-mode pulsations to the recently discovered quasi-periodic oscillations observed in a number of X-ray sources is discussed.

  19. Green Development Performance in China: A Metafrontier Non-Radial Approach

    Directory of Open Access Journals (Sweden)

    Ke Li

    2016-03-01

    Full Text Available This paper proposes a green development growth index (GDGI for measuring the changes in sustainable development over time. This index considers a wide range of pollutants, and allows for the incorporation of group heterogeneity and non-radial slack in the conventional green development index. The GDGI is calculated based on a non-radial directional distance function derived by several data envelopment analysis (DEA models, and was decomposed into an efficiency change (EC index, a best-practice gap change (BPC index and a technology gap change (TGC index. The proposed indices are employed to measure green development performance in 30 provinces in China from 2000 to 2012. The empirical results show that China has a low level of green development, with a 2.58% increase per year driven by an innovation effect. China’s green development is mainly led by the eastern region, and the technology gaps between the eastern region and the other two regions (the central and western regions have become wider over the years. The group innovative provinces have set a target for resource utilization of non-innovative provinces in order to catch-up with the corresponding groups, while the metafrontier innovative provinces provide targets for the technology levels of other provinces to improve their green development performance.

  20. Comparative analysis of the heat transfer rates in constant (CAV) and variable (VAV) volumes type multi zone acclimation system operating in hot and humid climate; Analise comparativa das taxas transferencia de calor em sistemas de climatizacao do tipo volume de ar constante (CAV) e volume de ar variavel (VAV) multizona operando em clima quente e umido

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Cesar A.G.; Correa, Jorge E. [Para Univ., Belem (Brazil). Centro Tecnologico. Dept. de Engenharia Mecanica]. E-mails: gsantos@ufpa.br; jecorrea@amazon.com.br

    2000-07-01

    This work performs a comparative analysis among the constant and variable air volume multi zones acclimation systems, used for provide the thermal comfort in buildings. The work used the simulation HVAC2KIT computer program. The results of sensible and latent heats transfer rates on the cooling and dehumidification, inflating fan capacity, and heat transfer on the final heating condenser were obtained and analysed for the climate conditions of the Brazilian city of Belem from Para State, presenting hot and humid climate during all the year.

  1. Rate constants for 1,5- and 1,6-hydrogen atom transfer reactions of mono-, di-, and tri-aryl-substituted donors, models for hydrogen atom transfers in polyunsaturated fatty acid radicals.

    Science.gov (United States)

    DeZutter, Christopher B; Horner, John H; Newcomb, Martin

    2008-03-06

    Rate constants for 1,5- and 1,6-hydrogen atom transfer reactions in models of polyunsaturated fatty acid radicals were measured via laser flash photolysis methods. Photolyses of PTOC (pyridine-2-thioneoxycarbonyl) ester derivatives of carboxylic acids gave primary alkyl radicals that reacted by 1,5-hydrogen transfer from mono-, di-, and tri-aryl-substituted positions or 1,6-hydrogen transfer from di- and tri-aryl-substituted positions to give UV-detectable products. Rate constants for reactions in acetonitrile at room temperature ranged from 1 x 10(4) to 4 x 10(6) s(-1). The activation energies for a matched pair of 1,5- and 1,6-hydrogen atom transfers giving tri-aryl-substituted radicals were approximately equal, as were the primary kinetic isotope effects, but the 1,5-hydrogen atom transfer reaction was 1 order of magnitude faster at room temperature than the 1,6-hydrogen atom transfer reaction due to a less favorable entropy of activation for the 1,6-transfer reaction. Solvent effects on the rate constants for the 1,5-hydrogen atom transfer reaction of the 2-[2-(diphenylmethyl)phenyl]ethyl radical at ambient temperature were as large as a factor of 2 with the reaction increasing in rate in lower polarity solvents. Hybrid density functional theory computations for the 1,5- and 1,6-hydrogen atom transfers of the tri-aryl-substituted donors were in qualitative agreement with the experimental results.

  2. Carrier density dependence of plasmon-enhanced nonradiative energy transfer in a hybrid quantum well-quantum dot structure.

    Science.gov (United States)

    Higgins, L J; Karanikolas, V D; Marocico, C A; Bell, A P; Sadler, T C; Parbrook, P J; Bradley, A L

    2015-01-26

    An array of Ag nanoboxes fabricated by helium-ion lithography is used to demonstrate plasmon-enhanced nonradiative energy transfer in a hybrid quantum well-quantum dot structure. The nonradiative energy transfer, from an InGaN/GaN quantum well to CdSe/ZnS nanocrystal quantum dots embedded in an ~80 nm layer of PMMA, is investigated over a range of carrier densities within the quantum well. The plasmon-enhanced energy transfer efficiency is found to be independent of the carrier density, with an efficiency of 25% reported. The dependence on carrier density is observed to be the same as for conventional nonradiative energy transfer. The plasmon-coupled energy transfer enhances the QD emission by 58%. However, due to photoluminescence quenching effects an overall increase in the QD emission of 16% is observed.

  3. Rate constants for H{sub 2}CO + O{sub 2} {yields} HCO + HO{sub 2} at high temperature

    Energy Technology Data Exchange (ETDEWEB)

    Michael, J. V.; Su, M.-C.; Sutherland, J. W.; Fang, D.-C.; Harding, L. B.; Wagner, A. F.

    2000-01-05

    The reaction between H{sub 2}CO and O{sub 2} has been studied in a reflected shock tube apparatus between 1633--2027 K using trioxane, (H{sub 2}CO){sub 3}, as the source of H{sub 2}CO. O-atom atomic resonance absorption spectrometry (ARAS) was used to observe absolute [O]{sub t} under conditions of low [H{sub 2}CO]{sub 0} so that most secondary reactions were negligible. Hence, the observed [O]{sub t} was the direct result of the rate controlling reaction between H{sub 2}CO and O{sub 2}. Ab initio theoretical results indicated that the process, H{sub 2}CO + O{sub 2} {yields} HCO + HO{sub 2}, is the only possible reaction. After rapid HCO and HO{sub 2} dissociations, O-atoms are then instantaneously produced from H + O{sub 2} {yields} O + OH. Using the ab initio result, variational transition state theoretical calculations (CTST) give k{sub 1} = 4.4929 x 10{sup {minus}20} T{sup 2.9116} exp{minus}18692/T cm{sup 3} molecule{sup {minus}1} S{sup {minus}1}. This theoretical result is consistent with the present experimental determinations and those at lower temperatures.

  4. Development of a chemical kinetic measurement apparatus and the determination of the reaction rate constants for lithium-lead/water interaction

    Energy Technology Data Exchange (ETDEWEB)

    Biney, P.O.

    1993-04-01

    An experimental set-up for accurate measurement of hydrogen generation rate in Lithium-Lead (Li[sub 17]Pb[sub 83]) Steam or water interactions has been designed. The most important features of the design include a pneumatic actuated quick opening and closing high temperature all stainless steel valve used to control the reaction time and the placement of most measuring devices below a water line to minimize leakage of the hydrogen collected. A PC based data acquisition and control system provides remote process sequencing, acquisition and control of all major components of the set-up. Initial tests indicate that the first design objective of maintaining leakproof gas collection chamber has been achieved. Initial pressure tests indicated that the pressure drop over a time span of 30 minutes was within the tolerance of the pressure transducer used to measure the pressure (within 0.690 kPa) at a nominal system pressure of 685 kPa. The experimental system hardware, data acquisition and control programs and data analysis program have been completed, tested and are currently functional.

  5. Applying Stable Isotope Labeled Amino Acids in Micropatterned Hepatocyte Co-Culture to Directly Determine the Degradation Rate Constant for CYP3A4.

    Science.gov (United States)

    Takahashi, Ryan H; Shahidi-Latham, Sheerin; Wong, Susan; Chang, Jae H

    2017-03-13

    The rate of enzyme degradation (kdeg) is an important input parameter for the prediction of clinical drug-drug-interactions (DDI) that result from mechanism-based inactivation or induction of cytochrome P450s. Currently, a large range of reported estimates for CYP3A4 enzyme degradation exists, and consequently, large uncertainty exists in steady-state predictions for DDI. In the current investigations, stable isotope labeled amino acids in culture (SILAC) was applied to a long-lived primary human hepatocyte culture, HepatoPac, to directly monitor the degradation of CYP3A4. This approach allowed selective isotope labeling of a population of de novo synthesized CYP3A4, and specific quantification of proteins with mass spectrometry to determine the CYP3A4 degradation within the hepatocytes. The kdeg estimate was 0.026 ± 0.005 h- 1. This value was reproduced by cultures derived across four individual donors. For these cultures, data indicated that CYP3A4 mRNA and total protein expression (i.e. labeled and not labeled P450s), and activity were stable over the period where degradation had been determined. This kdeg value for CYP3A4 was in good agreement with recently reported values that used alternate analytical approaches, but also employed micropatterned primary human hepatocytes as the in vitro model.

  6. Effects of uncertainty in SAPRC90 rate constants and selected product yields on reactivity adjustment factors for alternative fuel vehicle emissions. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Bergin, M.S.; Russell, A.G.; Yang, Y.J.; Milford, J.B.; Kirchner, F.; Stockwell, W.R.

    1996-07-01

    Tropospheric ozone is formed in the atmosphere by a series of reactions involving volatile organic compounds (VOCs) and nitrogen oxides (NO{sub x}). While NOx emissions are primarily composed of only two compounds, nitrogen oxide (NO) and nitrogen dioxide (NO{sub 2}), there are hundreds of different VOCs being emitted. In general, VOCs promote ozone formation, however, the rate and extent of ozone produced by the individual VOCs varies considerably. For example, it is widely acknowledged that formaldehyde (HCHO) is a very reactive VOC, and produces ozone rapidly and efficiently under most conditions. On the other hand, VOCs such as methane, ethane, propane, and methanol do not react as quickly, and are likely to form less urban ozone than a comparable mass of HCHO. The difference in ozone forming potential is one of the bases for the use of alternative fuels. The fuels considered in this study included compressed natural gas, LPG, mixtures of methanol and gasoline, ethanol and gasoline, and a reformulated gasoline.

  7. Global well-posedness and scattering for the focusing nonlinear Schrödinger equation in the nonradial case

    Directory of Open Access Journals (Sweden)

    Pigong Han

    2012-01-01

    Full Text Available The energy-critical, focusing nonlinear Schrödinger equation in the nonradial case reads as follows: \\[i\\partial_t u = -\\Delta u -|u|^{\\frac{4}{N-2}}u,\\quad (x,0=u_0 \\in H^1 (\\mathbb{R}^N,\\quad N\\geq 3.\\] Under a suitable assumption on the maximal strong solution, using a compactness argument and a virial identity, we establish the global well-posedness and scattering in the nonradial case, which gives a positive answer to one open problem proposed by Kenig and Merle [Invent. Math. 166 (2006, 645–675].

  8. Insurance Calculation of Bankruptcy Probability of Constant Interest Rate Model under Dependent Negative%负相依下带常数利率模型的破产概率的保险计算

    Institute of Scientific and Technical Information of China (English)

    李明倩

    2014-01-01

    本文研究了负相依索赔条件下带常数利率的风险模型在随机区间上的破产问题,最终得到了该模型破产概率的渐进表达式。%This paper studies the risk model under conditions of constant interest rates negatively correlated claims in the bankruptcy issue random intervals, and finally get the asymptotic expression of the model the probability of bankruptcy.

  9. Ion exchange equilibrium constants

    CERN Document Server

    Marcus, Y

    2013-01-01

    Ion Exchange Equilibrium Constants focuses on the test-compilation of equilibrium constants for ion exchange reactions. The book first underscores the scope of the compilation, equilibrium constants, symbols used, and arrangement of the table. The manuscript then presents the table of equilibrium constants, including polystyrene sulfonate cation exchanger, polyacrylate cation exchanger, polymethacrylate cation exchanger, polysterene phosphate cation exchanger, and zirconium phosphate cation exchanger. The text highlights zirconium oxide anion exchanger, zeolite type 13Y cation exchanger, and

  10. A Non-radial Eruption in a Quadrupolar Magnetic Configuration with a Coronal Null

    CERN Document Server

    Sun, Xudong; Liu, Yang; Chen, Qingrong; Hayashi, Keiji

    2012-01-01

    We report one of several homologous non-radial eruptions from NOAA active region (AR) 11158 that are strongly modulated by the local magnetic field as observed with the Solar Dynamic Observatory (SDO). A small bipole emerged in the sunspot complex and subsequently created a quadrupolar flux system. Non-linear force-free field (NLFFF) extrapolation from vector magnetograms reveals its energetic nature: the fast-shearing bipole accumulated ~2e31 erg free energy (10% of AR total) over just one day despite its relatively small magnetic flux (5% of AR total). During the eruption, the ejected plasma followed a highly inclined trajectory, over 60 degrees with respect to the radial direction, forming a jet-like, inverted-Y shaped structure in its wake. Field extrapolation suggests complicated magnetic connectivity with a coronal null point, which is favorable of reconnection between different flux components in the quadrupolar system. Indeed, multiple pairs of flare ribbons brightened simultaneously, and coronal reco...

  11. Disentangling nonradiative recombination processes in Ge micro-crystals on Si substrates

    Science.gov (United States)

    Pezzoli, Fabio; Giorgioni, Anna; Gallacher, Kevin; Isa, Fabio; Biagioni, Paolo; Millar, Ross W.; Gatti, Eleonora; Grilli, Emanuele; Bonera, Emiliano; Isella, Giovanni; Paul, Douglas J.; Miglio, Leo

    2016-06-01

    We address nonradiative recombination pathways by leveraging surface passivation and dislocation management in μm-scale arrays of Ge crystals grown on deeply patterned Si substrates. The time decay photoluminescence (PL) at cryogenic temperatures discloses carrier lifetimes approaching 45 ns in band-gap engineered Ge micro-crystals. This investigation provides compelling information about the competitive interplay between the radiative band-edge transitions and the trapping of carriers by dislocations and free surfaces. Furthermore, an in-depth analysis of the temperature dependence of the PL, combined with capacitance data and finite difference time domain modeling, demonstrates the effectiveness of GeO2 in passivating the surface of Ge and thus in enhancing the room temperature PL emission.

  12. The formation of entropy cores in non-radiative galaxy cluster simulations: SPH versus AMR

    CERN Document Server

    Power, C; Hobbs, A

    2013-01-01

    Abridged: We simulate a massive galaxy cluster in a LCDM Universe using three different approaches to solving the equations of non-radiative hydrodynamics: `classic' Smoothed Particle Hydrodynamics (SPH); a novel SPH with a higher order dissipation switch (SPHS); and adaptive mesh refinement (AMR). We find that SPHS and AMR are in excellent agreement, with both forming a well-defined entropy core that rapidly converges with increasing mass and force resolution. By contrast, SPH exhibits rather different behaviour. At low redshift, entropy decreases systematically with decreasing cluster-centric radius, converging on ever lower central values with increasing resolution. At higher redshift, SPH is in better agreement with SPHS and AMR but shows much poorer numerical convergence. We trace these discrepancies to artificial surface tension in SPH at phase boundaries. At early times, the passage of massive substructures close to the cluster centre stirs and shocks gas to build an entropy core. At later times, artif...

  13. Disentangling nonradiative recombination processes in Ge micro-crystals on Si substrates

    Energy Technology Data Exchange (ETDEWEB)

    Pezzoli, Fabio, E-mail: fabio.pezzoli@unimib.it; Giorgioni, Anna; Gatti, Eleonora; Grilli, Emanuele; Bonera, Emiliano; Miglio, Leo [LNESS and Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, via Cozzi 55, I-20125 Milano (Italy); Gallacher, Kevin; Millar, Ross W.; Paul, Douglas J. [School of Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow G12 8LT (United Kingdom); Isa, Fabio [LNESS, Dipartimento di Fisica del Politecnico di Milano and IFN-CNR, Polo Territoriale di Como, Via Anzani 42, I-22100 Como (Italy); Laboratory for Solid State Physics, ETH Zurich, Otto-Stern-Weg 1, CH-8093 Zürich (Switzerland); Biagioni, Paolo [LNESS, Dipartimento di Fisica del Politecnico di Milano and IFN-CNR, Piazza Leonardo da Vinci 32, I-20133 Milano (Italy); Isella, Giovanni [LNESS, Dipartimento di Fisica del Politecnico di Milano and IFN-CNR, Polo Territoriale di Como, Via Anzani 42, I-22100 Como (Italy)

    2016-06-27

    We address nonradiative recombination pathways by leveraging surface passivation and dislocation management in μm-scale arrays of Ge crystals grown on deeply patterned Si substrates. The time decay photoluminescence (PL) at cryogenic temperatures discloses carrier lifetimes approaching 45 ns in band-gap engineered Ge micro-crystals. This investigation provides compelling information about the competitive interplay between the radiative band-edge transitions and the trapping of carriers by dislocations and free surfaces. Furthermore, an in-depth analysis of the temperature dependence of the PL, combined with capacitance data and finite difference time domain modeling, demonstrates the effectiveness of GeO{sub 2} in passivating the surface of Ge and thus in enhancing the room temperature PL emission.

  14. Discovery of non-radial pulsations in the spectroscopic binary Herbig Ae star RS Cha

    CERN Document Server

    Böhm, T; Catala, C; Alecian, E; Pollard, K; Wright, D

    2008-01-01

    In this article we present a first discovery of non radial pulsations in both components of the Herbig Ae spectroscopic binary star RS Cha. The binary was monitored in quasi-continuous observations during 14 observing nights (Jan 2006) at the 1m Mt John (New Zealand) telescope with the Hercules high-resolution echelle spectrograph. The cumulated exposure time on the star was 44 hrs, corresponding to 255 individual high-resolution echelle spectra with $R = 45000$. Least square deconvolved spectra (LSD) were obtained for each spectrum representing the effective photospheric absorption profile modified by pulsations. Difference spectra were calculated by subtracting rotationally broadened artificial profiles; these residual spectra were analysed and non-radial pulsations were detected. A subsequent analysis with two complementary methods, namely Fourier Parameter Fit (FPF) and Fourier 2D (F2D) has been performed and first constraints on the pulsation modes have been derived. In fact, both components of the spect...

  15. Indirect imaging of nonradial pulsations in a rapidly oscillating Ap star

    CERN Document Server

    Kochukhov, O P

    2004-01-01

    Many types of stars show periodic variations of radius and brightness, which are commonly referred to as `stellar pulsations'. Observed pulsational characteristics are determined by fundamental stellar parameters. Consequently, investigations of stellar pulsations provide a unique opportunity to verify and refine our understanding of the evolution and internal structure of stars. However, a key boundary condition for this analysis -- precise information about the geometry of pulsations in the outer stellar envelopes -- has been notoriously difficult to secure. Here we demonstrate that it is possible to solve this problem by constructing an `image' of the pulsation velocity field from time series observations of stellar spectra. This technique is applied to study the geometry of nonradial pulsations in a prototype magnetic oscillating (roAp) star HR 3831. Our velocity map directly demonstrates an alignment of pulsations with the axis of the global magnetic field and reveals a significant magnetically induced d...

  16. Understanding of the Effects of Ionic Strength on the Bimolecular Rate Constant between Structurally Identified Redox Enzymes and Charged Substrates Using Numerical Simulations on the Basis of the Poisson-Boltzmann Equation.

    Science.gov (United States)

    Sugimoto, Yu; Kitazumi, Yuki; Shirai, Osamu; Yamamoto, Masahiro; Kano, Kenji

    2016-03-31

    To understand electrostatic interactions in biomolecules, the bimolecular rate constants (k) between redox enzymes and charged substrates (in this study, redox mediators in the electrode reaction) were evaluated at various ionic strengths (I) for the mediated bioelectrocatalytic reaction. The k value between bilirubin oxidase (BOD) and positively charged mediators increased with I, while that between BOD and negatively charged mediators decreased with I. The opposite trend was observed for the reaction of glucose oxidase (GOD). In the case of noncharged mediators, the k value was independent of I for both BOD and GOD. These results reflect the electrostatic interactions between the enzymes and the mediators. Furthermore, we estimated k/k° (k° being the thermodynamic rate constant) by numerical simulation (finite element method) based on the Poisson-Boltzmann (PB) equation. By considering the charges of individual atoms involved in the amino acids around the substrate binding sites in the enzymes, the simulated k/k° values well reproduced the experimental data. In conclusion, k/k° can be predicted by PB-based simulation as long as the crystal structure of the enzyme and the substrate binding site are known.

  17. Determination of reaction rate constants for phenol oxidation using SnO2/Ti anodes coupled with activated carbon adsorption in the presence of TiO2 as catalyst.

    Science.gov (United States)

    Zhao, Yuemin; Ding, Yi; Wang, Lizhang; Wang, Xiao

    2011-01-01

    Series of experiments for phenol degradation with assistance of TiO2 catalyst at pH of 6.5 and temperature of 25 degrees C were conducted using a lab-scale electrochemical reactor constructed in our laboratory. According to the results, at the presence of the TiO2 catalyst the removal of phenol was increased and first-order kinetics could describe the evolution of phenol concentration. For inspecting the relationship between rate constants and dosage of TiO2, two possible kinetics were proposed in this study. Contrasted to the abundant experimental data, a reasonable kinetics was obtained for the estimation of phenol concentration effluent during continuous flow of raw wastewater, especially when the TiO2 dosage was less than 0.5g L(-1). The model obtained from these experiments could employed for the calculation of rate constants at different TiO2 dosage and the necessary dosage of catalyst when a discharge standard was designed.

  18. Requirement of Working Stably of Compound Negative Binomial Risk Model with Constant Interest rate%常利率复合负二项风险模型下稳定经营的必要条件

    Institute of Scientific and Technical Information of China (English)

    乔克林; 高渊; 张宁

    2015-01-01

    Assume that insurance companies began to hold capital to u,with constane δ is accumulation of interest rates,and policy number always obey hegative binomia process,manage compensate total number follows poisson process. we give the compound negative binomial risk model with constant interest rate and the requirement of insur-ance company working stably.%假设保险公司刚开始持有的资本为u,以常数δ为利率积累,并且保单总份数服从负二项过程,理赔总次数服从Poisson过程,给出常利率复合负二项风险模型以及稳定经营的必要条件。

  19. Understanding and eliminating non-radiative decay in organic-inorganic perovskites (Conference Presentation)

    Science.gov (United States)

    Stranks, Samuel D.; de Quilettes, Dane

    2016-09-01

    Organic-inorganic perovskites such as CH3NH3PbI3 are highly promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21% and promising applications in light-emitting diodes, lasers and photodetectors also emerging. A key enabling property of the perovskites is their high photoluminescence quantum efficiency, suggesting that these materials could in principle approach the thermodynamic device efficiency limits in which all recombination is radiative. However, non-radiative recombination sites are present which vary heterogeneously from grain to grain and limit device performance. Here, I will present results where we probe the local photophysics of neat CH3NH3PbI3 perovskite films using confocal photoluminescence (PL) measurements and correlate the observations with the local chemistry of the grains using energy-dispersive X-ray spectroscopy (EDX) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). We investigate the connection between grains that are bright or dark in emission and the local Pb:I ratios at the surface and through the grains. We also examine how the photophysics, local chemistry and non-radiative decay pathways change slowly over time under illumination. Our results reveal a "photo-induced cleaning" arising from a redistribution of iodide content in the films, giving strong evidence for photo-induced ion migration. These slow transient effects appear to be related to anomalous hysteresis phenomena observed in full solar cells. I will discuss how immobilizing ions, reducing trap densities and achieving homogenous stoichiometries could suppress hysteresis effects and lead to devices approaching the efficiency limits.

  20. Non-radial pulsations in the γ Doradus star HD 195068

    Science.gov (United States)

    Jankov, S.; Mathias, P.; Chapellier, E.; Le Contel, J.-M.; Sareyan, J.-P.

    2006-07-01

    We present high resolution spectroscopic observations of the γ Doradus star HD 195068. About 230 spectra were collected over 2 years. Time series analysis performed on radial velocity data shows a main peak at 1.61 d-1 , a frequency not yet detected in photometry. The Hipparcos photometric 1.25 d-1 frequency is easily recovered as is 1.30 d-1 while the third photometric frequency, 0.97 d-1 , is only marginally present. The good quality of our data, which includes 196 spectra collected over seven consecutive nights, shows that both the 1.61 d-1 and intermediate 1.27 d-1 (mixture of 1.25 and 1.30 d-1 ) frequencies are present in the line profile variations. Using the Fourier-Doppler Imaging (FDI) method, the variability associated with 1.61 d-1 can be successfully modeled by a non-radial pulsation mode ℓ=5± 1, |m|=4± 1. For the intermediate frequency 1.27 d-1 we deduce ℓ=4± 1, |m|=3± 1. Evidence that the star is not pulsating in the radial mode (ℓ=0) rules out a previous classification as an RR Lyrae type star. We investigate the time variability of FDI power spectra concluding that the observed temporal variability of modes can be explained by a beating phenomenon between closely spaced frequencies of two non-radial modes. The distribution of the oscillation power within the line profile indicates that there is a significant tangential velocity component of oscillations characteristic of high radial order gravity modes which are predicted to be observed in γ Doradus type stars.

  1. Computational Prediction of Kinetic Rate Constants

    Science.gov (United States)

    2009-02-01

    Scotland , 2000 (unpublished). 7. R. S. Zhu and M. C. Lin, J. Chem. Phys. 119 (20), 10667 (2003). 8. J. F. Stanton, J. Gauss, W. J. Lauderdale, and R...Miller and C. T. Bowman, Prog. Energy. Combust. Sci. 15, 287 (1989); D. Lindackers, M. Burmeister and P. Roth , in: 23rd Symp. (Int.) Combust. Proc...Proc. 25, 801 - 808 (1994) F. Kaufman,and F.P. Del Greco, Symp. Int. Combust. Proc. 9 (1963); K. Natarajan, and P. Roth , Combust. Flame 70, 267 - 279

  2. Excitation of a nonradial mode in a millisecond X-ray pulsar XTE J1751-305

    CERN Document Server

    Lee, Umin

    2014-01-01

    We discuss candidates for non-radial modes excited in a mass accreting and rapidly rotating neutron star to explain the coherent frequency identified in the light curves of a millisecond X-ray pulsar XTE J1751-305. The spin frequency of the pulsar is $\

  3. Cosmological Constant, Fine Structure Constant and Beyond

    CERN Document Server

    Wei, Hao; Li, Hong-Yu; Xue, Dong-Ze

    2016-01-01

    In this work, we consider the cosmological constant model $\\Lambda\\propto\\alpha^{-6}$, which is well motivated from three independent approaches. As is well known, the evidence of varying fine structure constant $\\alpha$ was found in 1998. If $\\Lambda\\propto\\alpha^{-6}$ is right, it means that the cosmological constant $\\Lambda$ should be also varying. In this work, we try to develop a suitable framework to model this varying cosmological constant $\\Lambda\\propto\\alpha^{-6}$, in which we view it from an interacting vacuum energy perspective. We propose two types of models to describe the evolutions of $\\Lambda$ and $\\alpha$. Then, we consider the observational constraints on these models, by using the 293 $\\Delta\\alpha/\\alpha$ data from the absorption systems in the spectra of distant quasars, and the data of type Ia supernovae (SNIa), cosmic microwave background (CMB), baryon acoustic oscillation (BAO). We find that the model parameters can be tightly constrained to the narrow ranges of ${\\cal O}(10^{-5})$ t...

  4. The C(3P) + NH3 reaction in interstellar chemistry: II. Low temperature rate constants and modeling of NH, NH2 and NH3 abundances in dense interstellar clouds

    CERN Document Server

    Hickson, Kevin M; Bourgalais, Jérémy; Capron, Michael; Picard, Sebastien D Le; Goulay, Fabien; Wakelam, Valentine

    2016-01-01

    A continuous supersonic flow reactor has been used to measure rate constants for the C + NH3 reaction over the temperature range 50 to 296 K. C atoms were created by the pulsed laser photolysis of CBr4. The kinetics of the title reaction were followed directly by vacuum ultra-violet laser induced fluorescence (VUV LIF) of C loss and through H formation. The experiments show unambiguously that the reaction is rapid at 296 K, becoming faster at lower temperatures, reaching a value of 1.8 10-10 cm3 molecule-1 s-1 at 50 K. As this reaction is not currently included in astrochemical networks, its influence on interstellar nitrogen hydride abundances is tested through a dense cloud model including gas-grain interactions. In particular, the effect of the ortho-to-para ratio of H2 which plays a crucial role in interstellar NH3 synthesis is examined.

  5. Transition state theory thermal rate constants and RRKM-based branching ratios for the N((2)D) + CH(4) reaction based on multi-state and multi-reference ab initio calculations of interest for the Titan's chemistry.

    Science.gov (United States)

    Ouk, Chanda-Malis; Zvereva-Loëte, Natalia; Scribano, Yohann; Bussery-Honvault, Béatrice

    2012-10-30

    Multireference single and double configuration interaction (MRCI) calculations including Davidson (+Q) or Pople (+P) corrections have been conducted in this work for the reactants, products, and extrema of the doublet ground state potential energy surface involved in the N((2)D) + CH(4) reaction. Such highly correlated ab initio calculations are then compared with previous PMP4, CCSD(T), W1, and DFT/B3LYP studies. Large relative differences are observed in particular for the transition state in the entrance channel resolving the disagreement between previous ab initio calculations. We confirm the existence of a small but positive potential barrier (3.86 ± 0.84 kJ mol(-1) (MR-AQCC) and 3.89 kJ mol(-1) (MRCI+P)) in the entrance channel of the title reaction. The correlation is seen to change significantly the energetic position of the two minima and five saddle points of this system together with the dissociation channels but not their relative order. The influence of the electronic correlation into the energetic of the system is clearly demonstrated by the thermal rate constant evaluation and it temperature dependance by means of the transition state theory. Indeed, only MRCI values are able to reproduce the experimental rate constant of the title reaction and its behavior with temperature. Similarly, product branching ratios, evaluated by means of unimolecular RRKM theory, confirm the NH production of Umemoto et al., whereas previous works based on less accurate ab initio calculations failed. We confirm the previous findings that the N((2)D) + CH(4) reaction proceeds via an insertion-dissociation mechanism and that the dominant product channels are CH(2)NH + H and CH(3) + NH.

  6. Generalized Pickands constants

    NARCIS (Netherlands)

    Debicki, K.G.

    2001-01-01

    Pickands constants play an important role in the exact asymptotic of extreme values for Gaussian stochastic processes. By the {it generalized Pickands constant ${cal H_{eta$ we mean the limit begin{eqnarray* {cal H_{eta= lim_{T to inftyfrac{ {cal H_{eta(T){T, end{eqnarray* where ${cal H_{eta(T)= Exp

  7. Non-radiative relaxation of photoexcited chlorophylls: theoretical and experimental study

    Science.gov (United States)

    Bricker, William P.; Shenai, Prathamesh M.; Ghosh, Avishek; Liu, Zhengtang; Enriquez, Miriam Grace M.; Lambrev, Petar H.; Tan, Howe-Siang; Lo, Cynthia S.; Tretiak, Sergei; Fernandez-Alberti, Sebastian; Zhao, Yang

    2015-09-01

    Nonradiative relaxation of high-energy excited states to the lowest excited state in chlorophylls marks the first step in the process of photosynthesis. We perform ultrafast transient absorption spectroscopy measurements, that reveal this internal conversion dynamics to be slightly slower in chlorophyll B than in chlorophyll A. Modeling this process with non-adiabatic excited state molecular dynamics simulations uncovers a critical role played by the different side groups in the two molecules in governing the intramolecular redistribution of excited state wavefunction, leading, in turn, to different time-scales. Even given smaller electron-vibrational couplings compared to common organic conjugated chromophores, these molecules are able to efficiently dissipate about 1 eV of electronic energy into heat on the timescale of around 200 fs. This is achieved via selective participation of specific atomic groups and complex global migration of the wavefunction from the outer to inner ring, which may have important implications for biological light-harvesting function.

  8. Resonant Transparency and Non-Trivial Non-Radiating Excitations in Toroidal Metamaterials

    Science.gov (United States)

    Fedotov, V. A.; Rogacheva, A. V.; Savinov, V.; Tsai, D. P.; Zheludev, N. I.

    2013-01-01

    Engaging strongly resonant interactions allows dramatic enhancement of functionalities of many electromagnetic devices. However, resonances can be dampened by Joule and radiation losses. While in many cases Joule losses may be minimized by the choice of constituting materials, controlling radiation losses is often a bigger problem. Recent solutions include the use of coupled radiant and sub-radiant modes yielding narrow asymmetric Fano resonances in a wide range of systems, from defect states in photonic crystals and optical waveguides with mesoscopic ring resonators to nanoscale plasmonic and metamaterial systems exhibiting interference effects akin to electromagnetically-induced transparency. Here we demonstrate theoretically and confirm experimentally a new mechanism of resonant electromagnetic transparency, which yields very narrow isolated symmetric Lorentzian transmission lines in toroidal metamaterials. It exploits the long sought non-trivial non-radiating charge-current excitation based on interfering electric and toroidal dipoles that was first proposed by Afanasiev and Stepanovsky in [J. Phys. A Math. Gen. 28, 4565 (1995)]. PMID:24132231

  9. FUSE Observations of the Cygnus Loop OVI Emission from a Nonradiative Shock

    CERN Document Server

    Sankrit, R; Sankrit, Ravi; Blair, William P.

    2001-01-01

    We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of a Balmer filament in the northeast region of the Cygnus Loop supernova remnant. The data consist of one spectrum obtained through the 30"x30" (LWRS) aperture and three spectra at adjacent positions obtained through the 4"x20" (MDRS) aperture. The nonradiative shocks in the region giving rise to these faint optical filaments produce strong OVI 1032,1038 emission, which is detected in all the spectra. The OVI emission is resolved by FUSE into a strong component centered at 0 km/s, and weaker components centered at +/- 140 km/s. The MDRS spectra allow us to study the variation of OVI emission in the post-shock structure. We find that the zero velocity emission is associated directly with the Balmer filament shock, while the high velocity emission comes from a more uniformly distributed component elsewhere along the line of sight. We also find that the shocks producing the emission at +/- 140 km/s have velocities between 180 km/s and 220 km/...

  10. Non-radiative relaxation of photoexcited chlorophylls: theoretical and experimental study.

    Science.gov (United States)

    Bricker, William P; Shenai, Prathamesh M; Ghosh, Avishek; Liu, Zhengtang; Enriquez, Miriam Grace M; Lambrev, Petar H; Tan, Howe-Siang; Lo, Cynthia S; Tretiak, Sergei; Fernandez-Alberti, Sebastian; Zhao, Yang

    2015-09-08

    Nonradiative relaxation of high-energy excited states to the lowest excited state in chlorophylls marks the first step in the process of photosynthesis. We perform ultrafast transient absorption spectroscopy measurements, that reveal this internal conversion dynamics to be slightly slower in chlorophyll B than in chlorophyll A. Modeling this process with non-adiabatic excited state molecular dynamics simulations uncovers a critical role played by the different side groups in the two molecules in governing the intramolecular redistribution of excited state wavefunction, leading, in turn, to different time-scales. Even given smaller electron-vibrational couplings compared to common organic conjugated chromophores, these molecules are able to efficiently dissipate about 1 eV of electronic energy into heat on the timescale of around 200 fs. This is achieved via selective participation of specific atomic groups and complex global migration of the wavefunction from the outer to inner ring, which may have important implications for biological light-harvesting function.

  11. Energy efficiency in Spanish wastewater treatment plants: a non-radial DEA approach.

    Science.gov (United States)

    Hernández-Sancho, F; Molinos-Senante, M; Sala-Garrido, R

    2011-06-15

    Wastewater treatment plants (WWTPs) are energy-intensive facilities. Thus, reducing their carbon footprint is particularly important, both economically and environmentally. Knowing the real operating energy efficiency of WWTPs is the starting point for any energy-saving initiative. In this article, we applied a non-radial Data Envelopment Analysis (DEA) methodology to calculate energy efficiency indices for sampling of WWTPs located in Spain. In a second stage analysis, we examined the operating variables contributing to differences in energy efficiency among plants. It is verified that energy efficiencies of the analyzed WWTPs were quite low, with only 10% of them being efficient. We found that plant size, quantity of organic matter removed, and type of bioreactor aeration were significant variables in explaining energy efficiency differences. In contrast, age of the plant was not a determining factor in energy consumption. Lastly, we quantified the potential savings, both in economic terms and in terms of CO(2) emissions, that could be expected from an improvement in energy efficiency of WWTPs.

  12. A New Code for Nonradial Stellar Pulsations and its Application to Low - Mass, Helium White Dwarfs

    CERN Document Server

    Corsico, A H

    2002-01-01

    We present a finite difference code intended for computing linear, adiabatic, nonradial pulsations of spherical stars. This code is based on a general Newton - Raphson technique in order to handle the relaxation of the eigenvalue (square of the eigenfrequency) of the modes and their corresponding eigenfunctions. This code has been tested computing the pulsation spectra of polytropic spheres finding a good agreement with previous work. Then, we have coupled this code to our evolutionary code and applied it to the computation of the pulsation spectrum of a low mass, pure - helium white dwarf of 0.3 M_{sun} for a wide range of effective temperatures. In making this calculation we have taken an evolutionary time step short enough such that eigenmodes corresponding to a given model are used as initial approximation to those of the next one. Specifically, we have computed periods, period spacing, eigenfunctions, weight functions, kinetic energies and variational periods for a wide range of modes. To our notice this...

  13. Origin and implications of non-radial Imbrium Sculpture on the Moon

    Science.gov (United States)

    Schultz, Peter H.; Crawford, David A.

    2016-07-01

    Rimmed grooves, lineations and elongate craters around Mare Imbrium shape much of the nearside Moon. This pattern was coined the Imbrium Sculpture, and it was originally argued that it must have been formed by a giant oblique (~30°) impact, a conclusion echoed by later studies. Some investigators, however, noticed that many elements of the Imbrium Sculpture are not radial to Imbrium, thereby implicating an endogenic or structural origin. Here we use these non-radial trends to conclude that the Imbrium impactor was a proto-planet (half the diameter of Vesta), once part of a population of large proto-planets in the asteroid belt. Such independent constraints on the sizes of the Imbrium and other basin-forming impactors markedly increase estimates for the mass in the asteroid belt before depletion caused by the orbital migration of Jupiter and Saturn. Moreover, laboratory impact experiments, shock physics codes and the groove widths indicate that multiple fragments (up to 2% of the initial diameter) from each oblique basin-forming impactor, such as the one that formed Imbrium, should have survived planetary collisions and contributed to the heavy impact bombardment between 4.3 and 3.8 billion years ago.

  14. Full wave analysis of non-radiative dielectric waveguide modulator for the determination of electrical equivalent circuit

    Indian Academy of Sciences (India)

    N P Pathak; A Basu; S K Koul

    2008-07-01

    This paper reports the determination of electrical equivalent circuit of ON/OFF modulator in non-radiative dielectric (NRD) guide configurations at Ka-band. Schottky barrier mixer diode is used to realize this modulator and its characteristics are determined experimentally using vector network analyzer. Full wave FEM simulator HFSS is used to determine an equivalent circuit for the mounted diode and modulator in ON and OFF states. This equivalent circuit is used to qualitatively explain the experimental characteristics of modulator.

  15. Coupling of Radial and Axial non-Radial Oscillations of Compact Stars: Gravitational Waves from first-order Differential Rotation

    CERN Document Server

    Passamonti, A; Gualtieri, L; Nagar, A; Sopuerta, C F

    2006-01-01

    We investigate the non-linear coupling between radial and non-radial oscillations of static spherically symmetric neutron stars as a possible mechanism for the generation of gravitational waves that may lead to observable signatures. In this paper we concentrate on the axial sector of the non-radial perturbations. By using a multi-parameter perturbative framework we introduce a complete description of the non-linear coupling between radial and axial non-radial oscillations; we study the gauge invariant character of the associated perturbative variables and develop a computational scheme to evolve the non-linear coupling perturbations in the time domain. We present results of simulations corresponding to different physical situations and discuss the dynamical behaviour of this non-linear coupling. Of particular interest is the occurrence of signal amplifications in the form of resonance phenomena when a frequency associated with the radial pulsations is close to a frequency associated with one of the axial w-m...

  16. Constant Proportion Debt Obligations (CPDOs)

    DEFF Research Database (Denmark)

    Cont, Rama; Jessen, Cathrine

    2012-01-01

    be made arbitrarily small—and thus the credit rating arbitrarily high—by increasing leverage, but the ratings obtained strongly depend on assumptions on the credit environment (high spread or low spread). More importantly, CPDO loss distributions are found to exhibit a wide range of tail risk measures......Constant Proportion Debt Obligations (CPDOs) are structured credit derivatives that generate high coupon payments by dynamically leveraging a position in an underlying portfolio of investment-grade index default swaps. CPDO coupons and principal notes received high initial credit ratings from...... the major rating agencies, based on complex models for the joint transition of ratings and spreads for all names in the underlying portfolio. We propose a parsimonious model for analysing the performance of CPDO strategies using a top-down approach that captures the essential risk factors of the CPDO. Our...

  17. Unimolecular decomposition of heptane radicals:a mechanism and rate constant investigation%C7 H15自由基裂解反应机理及速率常数的理论研究

    Institute of Scientific and Technical Information of China (English)

    张田雷; 张鹏; 杨晨

    2015-01-01

    采用CBS-QB3方法构建了C7 H15自由基裂解反应势能剖面。计算结果表明,4种不同构型的C7 H15自由基(1-C7 H15,2-C7 H15,3-C7 H15,4-C7 H15)发生多种不同类型的β位断裂,裂解成C2—C6烯烃和新的自由基。新的自由基继续发生β位断裂,形成诸如CH3自由基以及CH2眫CH2、CH3 CH眫CH2等烯烃。此外,利用VKLab程序包及Wigner 校正模型在200~3000 K温度范围内计算了4种C7 H15自由基各类β位断裂反应速率常数。其中1-C3 H7→C2 H4+CH3反应速率常数的结果与试验结果非常吻合。%The potential energy surfaces of theβ-scission of heptane radicals were performed using the CBS-QB3 method.The results show that the β-scission of 1-C7 H15 , 2-C7 H15 , 3-C7 H15 and 4-C7 H15 radicals involves many different kinds of β-scission reactions to produce olefins and other radicals.Compared to the small n-alkanes, larger n-alkanes can produce more alkyl radicals, which may generate more intermediates and have more possible pathways.Main products were C2~C6 olefins, methyl raticals and hydrogen radicals. The rate constants of all reactions with Eckart correction were calculated by the VKLab program package.The rate constant of 1-C3 H7→C2 H4 +CH3 reaction within the temperature range of 200~3 000 K is in good agree-ment with available experimental values.

  18. Reduction in the rates of protein and amino acid catabolism to slow down the accumulation of endogenous ammonia: a strategy potentially adopted by mudskippers (Periophthalmodon schlosseri snd Boleophthalmus boddaerti) during aerial exposure in constant darkness.

    Science.gov (United States)

    Lim, C B; Chew, S F; Anderson, P M; Ip, Y K

    2001-05-01

    This study was designed to elucidate the strategies adopted by mudskippers to handle endogenous ammonia during aerial exposure in constant darkness. Under these conditions, specimens exhibited minimal locomotory activity, and the ammonia and urea excretion rates in both Periophthalmodon schlosseri and Boleophthalmus boddaerti decreased significantly. As a consequence, ammonia accumulation occurred in the tissues of both species of mudskipper. A significant increase in urea levels was found in the liver of P. schlosseri after 24h of aerial exposure, but no similar increase was seen in the tissues of B. boddaerti. It is unlikely that these two species of mudskipper detoxified ammonia to urea during aerial exposure since B. boddaerti does not possess a complete ornithine-urea cycle (OUC) and, although all the OUC enzymes were present in P. schlosseri, the activity of carbamoyl phosphate synthetase present in the liver mitochondria was too low to render the OUC functional for ammonia detoxification. Peritoneal injection of 15NH4Cl into P. schlosseri showed that this mudskipper was capable of incorporating some of the labelled ammonia into urea in its liver. However, aerial exposure did not affect this capability and did not induce detoxification of the accumulated ammonia to urea. Mudskippers exposed to terrestrial conditions and constant darkness did, however, show significant decreases in the total free amino acid content in the liver and blood, in the case of P. schlosseri and in the muscle of B. boddaerti. No changes in the alanine or glutamine content of the muscle were found in either species. Analyses of the balance between the reduction in nitrogenous excretion and the increase in nitrogenous accumulation further revealed that these two species of mudskipper were capable of reducing their protein and amino acid catabolic rates. Such adaptations constitute the most efficient way to avoid the build-up of internal ammonia, and would render unnecessary the

  19. Variation of Fundamental Constants

    Science.gov (United States)

    Flambaum, V. V.

    2006-11-01

    Theories unifying gravity with other interactions suggest temporal and spatial variation of the fundamental ``constants'' in expanding Universe. The spatial variation can explain a fine tuning of the fundamental constants which allows humans (and any life) to appear. We appeared in the area of the Universe where the values of the fundamental constants are consistent with our existence. We present a review of recent works devoted to the variation of the fine structure constant α, strong interaction and fundamental masses. There are some hints for the variation in quasar absorption spectra. Big Bang nucleosynthesis, and Oklo natural nuclear reactor data. A very promising method to search for the variation of the fundamental constants consists in comparison of different atomic clocks. Huge enhancement of the variation effects happens in transition between accidentally degenerate atomic and molecular energy levels. A new idea is to build a ``nuclear'' clock based on the ultraviolet transition between very low excited state and ground state in Thorium nucleus. This may allow to improve sensitivity to the variation up to 10 orders of magnitude! Huge enhancement of the variation effects is also possible in cold atomic and molecular collisions near Feshbach resonance.

  20. High-level direct-dynamics variational transition state theory calculations including multidimensional tunneling of the thermal rate constants, branching ratios, and kinetic isotope effects of the hydrogen abstraction reactions from methanol by atomic hydrogen.

    Science.gov (United States)

    Meana-Pañeda, Rubén; Truhlar, Donald G; Fernández-Ramos, Antonio

    2011-03-07

    We report a detailed theoretical study of the hydrogen abstraction reaction from methanol by atomic hydrogen. The study includes the analysis of thermal rate constants, branching ratios, and kinetic isotope effects. Specifically, we have performed high-level computations at the MC3BB level together with direct dynamics calculations by canonical variational transition state theory (CVT) with the microcanonically optimized multidimensional tunneling (μOMT) transmission coefficient (CVT/μOMT) to study both the CH(3)OH+H→CH(2)OH+H(2) (R1) reaction and the CH(3)OH+H→CH(3)O+H(2) (R2) reaction. The CVT/μOMT calculations show that reaction R1 dominates in the whole range 298≤T (K)≤2500 and that anharmonic effects on the torsional mode about the C-O bond are important, mainly at high temperatures. The activation energy for the total reaction sum of R1 and R2 reactions changes substantially with temperature and, therefore, the use of straight-line Arrhenius plots is not valid. We recommend the use of new expressions for the total R1 + R2 reaction and for the R1 and R2 individual reactions.

  1. EOQ Model for Deteriorating Items with non-constant Deteriorating Rate under Inflation%通货膨胀下非常数变质率的易变质商品的EOQ模型

    Institute of Scientific and Technical Information of China (English)

    文晓巍

    2011-01-01

    Inventory of deteriorating items has been one of the optimal EOQ model problems challenged by many researchers for several decades.An EOQ model with non-constant deteriorating rate under inflation and permissible delay payments is constructed,and the total cost of the inventory of deteriorating items is analyzed.Then an optimal inventory replenishment policy and algorithms are proposed.Numerical examples are provided to illustrate the theory.%易变质商品的库存问题成为最近几十年中备受学者们关注的EOQ模型优化问题。本文构建了通货膨胀下允许延期支付的非常数变质率的易变质商品的EOQ模型,并分析了对应的总成本函数,同时,给出了总库存成本最小的最优库存补充决策和算法。最后给出了算例进行说明。

  2. THE C({sup 3}P) + NH{sub 3} REACTION IN INTERSTELLAR CHEMISTRY. II. LOW TEMPERATURE RATE CONSTANTS AND MODELING OF NH, NH{sub 2}, AND NH{sub 3} ABUNDANCES IN DENSE INTERSTELLAR CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Hickson, Kevin M.; Loison, Jean-Christophe [Université de Bordeaux, Institut des Sciences Moléculaires, UMR 5255, F-33400 Talence (France); Bourgalais, Jérémy; Capron, Michael; Picard, Sébastien D. Le [Institut de Physique de Rennes, Astrophysique de Laboratoire, UMR CNRS 6251, Université de Rennes 1, Campus de Beaulieu, F-35042 Rennes Cedex (France); Goulay, Fabien [Department of Chemistry, West Virginia University, Morgantown, WV 26506 (United States); Wakelam, Valentine, E-mail: kevin.hickson@u-bordeaux.fr [Université de Bordeaux, Laboratoire d’Astrophysique de Bordeaux, UMR 5804, F-33270 Floirac (France)

    2015-10-20

    A continuous supersonic flow reactor has been used to measure rate constants for the C({sup 3}P) + NH{sub 3} reaction over the temperature range 50–296 K. C({sup 3}P) atoms were created by the pulsed laser photolysis of CBr{sub 4}. The kinetics of the title reaction were followed directly by vacuum ultra-violet laser induced fluorescence of C({sup 3}P) loss and through H({sup 2}S) formation. The experiments show unambiguously that the reaction is rapid at 296 K, becoming faster at lower temperatures, reaching a value of (1.8 ± 0.2) × 10{sup −10} cm{sup 3} molecule{sup −1} s{sup −1} at 50 K. As this reaction is not currently included in astrochemical networks, its influence on interstellar nitrogen hydride abundances is tested through a dense cloud model including gas–grain interactions. In particular, the effect of the ortho-to-para ratio of H{sub 2}, which plays a crucial role in interstellar NH{sub 3} synthesis, is examined.

  3. On the multi-compound Poisson-Geometric risk model of multi-type-insurance with a constant interest rate%多险种多复合Poisson-Geometric过程的常利率风险模型

    Institute of Scientific and Technical Information of China (English)

    李碧云; 余国胜

    2015-01-01

    A multi-compound Poisson-Geometric risk model of multi-type-insurance with a constant interest rate was constructed,and the integral-differential equation of the survival probability under this model was derived.Using the integral-differential equation we established,we got the explicit expression about the Laplace transforms of the survival probability and the exact solution was given when the initial surplus was zero and there were no premium incomes. Finally,we gave a numerical example to illustrate our results.%建立多险种多复合Poisson-Geometric过程的常利率风险模型,得到该模型的生存概率所满足的积分-微分方程.当无保费收入时,由所得到的积分-微分方程推出生存概率的Laplace变换的表达式,对于初始盈余为0时,得到生存概率的精确解.并给出具体的数值计算的实例以解释我们的结果.①

  4. Hybrid Quantum Mechanical and Molecular Mechanics Study of the SN2 Reaction of CCl4 + OH- in Aqueous Solution: The Potential of Mean Force, Reaction Energetics, and Rate Constants

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Ting; Yin, Hongyun; Wang, Dunyou; Valiev, Marat

    2012-02-16

    The bimolecular nucleophilic substitution reaction of CCl{sub 4} and OH{sup -} in aqueous solution was investigated on the basis of a combined quantum mechanical and molecular mechanics method. A multilayered representation approach is employed to achieve high accuracy results at the CCSD(T) level of theory. The potential of mean force calculations at the DFT level and CCSD(T) level of theory yield reaction barrier heights of 22.7 and 27.9 kcal/mol, respectively. Both the solvation effects and the solvent-induced polarization effect have significant contributions to the reaction energetics, for example, the solvation effect raises the saddle point by 10.6 kcal/mol. The calculated rate constant coefficient is 8.6 x 10{sup -28} cm{sup 3} molecule{sup -1} s{sup -1} at the standard state condition, which is about 17 orders magnitude smaller than that in the gas phase. Among the four chloromethanes (CH{sub 3}Cl, CH{sub 2}Cl{sub 2}, CHCl{sub 3}, and CCl{sub 4}), CCl{sub 4} has the lowest free energy activation barrier for the reaction with OH{sup -1} in aqueous solution, confirming the trend that substitution of Cl by H in chloromethanes diminishes the reactivity.

  5. Elastic constants of calcite

    Science.gov (United States)

    Peselnick, L.; Robie, R.A.

    1962-01-01

    The recent measurements of the elastic constants of calcite by Reddy and Subrahmanyam (1960) disagree with the values obtained independently by Voigt (1910) and Bhimasenachar (1945). The present authors, using an ultrasonic pulse technique at 3 Mc and 25??C, determined the elastic constants of calcite using the exact equations governing the wave velocities in the single crystal. The results are C11=13.7, C33=8.11, C44=3.50, C12=4.82, C13=5.68, and C14=-2.00, in units of 1011 dyncm2. Independent checks of several of the elastic constants were made employing other directions and polarizations of the wave velocities. With the exception of C13, these values substantially agree with the data of Voigt and Bhimasenachar. ?? 1962 The American Institute of Physics.

  6. Algorithm for structure constants

    CERN Document Server

    Paiva, F M

    2011-01-01

    In a $n$-dimensional Lie algebra, random numerical values are assigned by computer to $n(n-1)$ especially selected structure constants. An algorithm is then created, which calculates without ambiguity the remaining constants, obeying the Jacobi conditions. Differently from others, this algorithm is suitable even for poor personal computer. ------------- En $n$-dimensia algebro de Lie, hazardaj numeraj valoroj estas asignitaj per komputilo al $n(n-1)$ speciale elektitaj konstantoj de strukturo. Tiam algoritmo estas kreita, kalkulante senambigue la ceterajn konstantojn, obeante kondicxojn de Jacobi. Malsimile al aliaj algoritmoj, tiu cxi tauxgas ecx por malpotenca komputilo.

  7. Radiographic constant exposure technique

    DEFF Research Database (Denmark)

    Domanus, Joseph Czeslaw

    1985-01-01

    The constant exposure technique has been applied to assess various industrial radiographic systems. Different X-ray films and radiographic papers of two producers were compared. Special attention was given to fast film and paper used with fluorometallic screens. Radiographic image quality...... was tested by the use of ISO wire IQI's and ASTM penetrameters used on Al and Fe test plates. Relative speed and reduction of kilovoltage obtained with the constant exposure technique were calculated. The advantages of fast radiographic systems are pointed out...

  8. The aliquot constant

    CERN Document Server

    Bosma, Wieb

    2009-01-01

    The average value of log s(n)/n taken over the first N even integers is shown to converge to a constant lambda when N tends to infinity; moreover, the value of this constant is approximated and proven to be less than 0. Here s(n) sums the divisors of n less than n. Thus the geometric mean of s(n)/n, the growth factor of the function s, in the long run tends to be less than 1. This could be interpreted as probabilistic evidence that aliquot sequences tend to remain bounded.

  9. Time-dependent polymer rheology under constant stress and under constant shear conditions.

    Science.gov (United States)

    Lee, K. H.; Brodkey, R. S.

    1971-01-01

    A kinetic rate theory previously presented for describing non-Newtonian phenomena has been further modified to predict the flow behavior of viscoelastic materials under constant stress conditions. The thixotropic shear stress or shear rate is predicted by the kinetic theory, and the experimental stress or shear rate is obtained by modifying the thixotropic value by a stress or shear rate retardation term. The retardation term stems from a Maxwellian approach for stress retardation. In order to test the validity of this approach, transient and steady-state data were obtained for two solutions of polymethylmethacrylate in diethylphthalate. Both constant stress measurements and constant shear rate data were taken over a broad range.

  10. The 1% concordance Hubble constant

    Energy Technology Data Exchange (ETDEWEB)

    Bennett, C. L.; Larson, D.; Weiland, J. L. [Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Hinshaw, G., E-mail: cbennett@jhu.edu [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1 (Canada)

    2014-10-20

    The determination of the Hubble constant has been a central goal in observational astrophysics for nearly a hundred years. Extraordinary progress has occurred in recent years on two fronts: the cosmic distance ladder measurements at low redshift and cosmic microwave background (CMB) measurements at high redshift. The CMB is used to predict the current expansion rate through a best-fit cosmological model. Complementary progress has been made with baryon acoustic oscillation (BAO) measurements at relatively low redshifts. While BAO data do not independently determine a Hubble constant, they are important for constraints on possible solutions and checks on cosmic consistency. A precise determination of the Hubble constant is of great value, but it is more important to compare the high and low redshift measurements to test our cosmological model. Significant tension would suggest either uncertainties not accounted for in the experimental estimates or the discovery of new physics beyond the standard model of cosmology. In this paper we examine in detail the tension between the CMB, BAO, and cosmic distance ladder data sets. We find that these measurements are consistent within reasonable statistical expectations and we combine them to determine a best-fit Hubble constant of 69.6 ± 0.7 km s{sup –1} Mpc{sup –1}. This value is based upon WMAP9+SPT+ACT+6dFGS+BOSS/DR11+H {sub 0}/Riess; we explore alternate data combinations in the text. The combined data constrain the Hubble constant to 1%, with no compelling evidence for new physics.

  11. Compassion is a constant.

    Science.gov (United States)

    Scott, Tricia

    2015-11-01

    Compassion is a powerful word that describes an intense feeling of commiseration and a desire to help those struck by misfortune. Most people know intuitively how and when to offer compassion to relieve another person's suffering. In health care, compassion is a constant; it cannot be rationed because emergency nurses have limited time or resources to manage increasing demands.

  12. The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine

    Science.gov (United States)

    Trachsel, Maria A.; Wiedmer, Timo; Blaser, Susan; Frey, Hans-Martin; Li, Quansong; Ruiz-Barragan, Sergi; Blancafort, Lluís; Leutwyler, Samuel

    2016-10-01

    We have investigated the S0 → S1 UV vibronic spectrum and time-resolved S1 state dynamics of jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization, UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond time-resolved pump/delayed ionization measurements. The experimental study is complemented with spin-component-scaled second-order coupled-cluster and multistate complete active space second order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cm-1 about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation and out-of-plane distortions upon 1ππ∗ excitation predicted by the calculations. The methyl torsion and ν1 ' (butterfly) vibrations are strongly coupled, in the S1 state. The S0 → S1 vibronic spectrum breaks off at a vibrational excess energy Eexc ˜ 500 cm-1, indicating that a barrier in front of the ethylene-type S1⇝S0 conical intersection is exceeded, which is calculated to lie at Eexc = 366 cm-1. The S1⇝S0 internal conversion rate constant increases from kIC = 2 ṡ 109 s-1 near the S1(v = 0) level to 1 ṡ 1011 s-1 at Eexc = 516 cm-1. The 1ππ∗ state of 1MCyt also relaxes into the lower-lying triplet T1 (3ππ∗) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value is 2.4 cm-1. The ISC rate constant is 10-100 times lower than kIC; it increases from kISC = 2 ṡ 108 s-1 near S1(v = 0) to kISC = 2 ṡ 109 s-1 at Eexc = 516 cm-1. The T1 state energy is determined from the onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cm-1. The T2 (3nπ∗) state lies >1500 cm-1 above S1(v = 0), so S1⇝T2 ISC cannot occur, despite the large SOC parameter of 10.6 cm-1. An upper limit to the adiabatic ionization energy of 1MCyt is determined as 8.41 ± 0.02 e

  13. An Amendment to the Assumption of Constant Risk-Free Interest Rate in Black-Scholes Formula%Black—Scholes公式中无风险利率常数假设的二种改进

    Institute of Scientific and Technical Information of China (English)

    杜玉林

    2012-01-01

    The assumption of constant risk-free interest rate in Black-Scholes formula cannot be satisfied in market. In this paper , we find the option price interval assuming the risk-free lies within a given interval. First we transform this financia/ problem to a stochastic optimal control problem, then obtain options" maximum and minimum price models through dynamic programming principle. We then discuss how to solve the nonlinear PDE model and how to narrow the price interval through optima/static hedging. We conclude this paper by giving its applieations in U. S. A option market through BaiDu options,comparing with Black-scholes, and giving a method how to identify arbitrage opportunity in option markets.%Black—Scholes公式中无风险利率的常数假设与现实不符。本文假设无风险利率在一个区间中变动,讨论求期权价格区间问题。首先将此问题归结为一个随机最优控制问题,然后利用动态规划原理得到期权价格区间上下限满足的模型以及模型解法,并利用最优静态对冲缩小此价格区间,最后以BaiDu股票期权为例给出了模型在期权市场上的应用,提供了一种期权市场上的套利识别方法并与Black—Scholes公式的结果做了比较。

  14. Conformational unfolding in the N-terminal region of ribonuclease A detected by nonradiative energy transfer.

    Science.gov (United States)

    McWherter, C A; Haas, E; Leed, A R; Scheraga, H A

    1986-04-22

    Unfolding in the N-terminal region of RNase A was studied by the nonradiative energy-transfer technique. RNase A was labeled with a nonfluorescent acceptor (2,4-dinitrophenyl) on the alpha-amino group and a fluorescent donor (ethylenediamine monoamide of 2-naphthoxyacetic acid) on a carboxyl group in the vicinity of residue 50 (75% at Glu-49 and 25% at Asp-53). The distribution of donor labeling sites does not affect the results of this study since they are close in both the sequence and the three-dimensional structure. The sites of labeling were determined by peptide mapping. The derivatives possessed full enzymatic activity and underwent reversible thermal transitions. However, there were some quantitative differences in the thermodynamic parameters. When the carboxyl groups were masked, there was a 5 degrees C lowering of the melting temperature at pH 2 and 4, and no significant change in delta H(Tm). Labeling of the alpha-amino group had no effect on the melting temperature or delta H(Tm) at pH 2 but did result in a dramatic decrease in delta H(Tm) of the unfolding reaction at pH 4. The melting temperature did not change appreciably at pH 4, indicating that an enthalpy/entropy compensation had occurred. The efficiencies of energy transfer determined with both fluorescence intensity and lifetime measurements were in reasonably good agreement. The transfer efficiency dropped from about 60% under folding conditions to roughly 20% when the derivatives were unfolded with disulfide bonds intact and was further reduced to 5% when the disulfide bonds were reduced. The interprobe separation distance was estimated to be 35 +/- 2 A under folding conditions. The contribution to the interprobe distance resulting from the finite size of the probes was treated by using simple geometric considerations and a rotational isomeric state model of the donor probe linkage. With this model, the estimated average interprobe distance of 36 A is in excellent agreement with the

  15. White light generation by resonant nonradiative energy transfer from epitaxial InGaN/GaN quantum wells to colloidal CdSe/ZnS core/shell quantum dots

    Science.gov (United States)

    Nizamoglu, Sedat; Sari, Emre; Baek, Jong-Hyeob; Lee, In-Hwan; Demir, Hilmi Volkan

    2008-12-01

    We propose and demonstrate white-light-generating nonradiative energy transfer (ET) from epitaxial quantum wells (QWs) to colloidal quantum dots (QDs) in their close proximity. This proof-of-concept hybrid color-converting system consists of chemically synthesized red-emitting CdSe/ZnS core/shell heteronanocrystals intimately integrated on epitaxially grown cyan-emitting InGaN/GaN QWs. The white light is generated by the collective luminescence of QWs and QDs, for which the dot emission is further increased by 63% with nonradiative ET, setting the operating point in the white region of CIE chromaticity diagram. Using cyan emission at 490 nm from the QWs and red emission at 650 nm from the nanocrystal (NC) luminophors, we obtain warm white light generation with a correlated color temperature of Tc = 3135 K and tristimulus coordinates of (x,y) = (0.42, 0.39) in the white region. By analyzing the time-resolved radiative decay of these NC emitters in our hybrid system with a 16 ps time resolution, the luminescence kinetics reveals a fast ET with a rate of (2 ns)-1 using a multiexponential fit with χ 2 = 1.0171.

  16. The lowest-lying electronic singlet and triplet potential energy surfaces for the HNO-NOH system: energetics, unimolecular rate constants, tunneling and kinetic isotope effects for the isomerization and dissociation reactions.

    Science.gov (United States)

    Bozkaya, Uğur; Turney, Justin M; Yamaguchi, Yukio; Schaefer, Henry F

    2012-04-28

    The lowest-lying electronic singlet and triplet potential energy surfaces (PES) for the HNO-NOH system have been investigated employing high level ab initio quantum chemical methods. The reaction energies and barriers have been predicted for two isomerization and four dissociation reactions. Total energies are extrapolated to the complete basis set limit applying focal point analyses. Anharmonic zero-point vibrational energies, diagonal Born-Oppenheimer corrections, relativistic effects, and core correlation corrections are also taken into account. On the singlet PES, the (1)HNO → (1)NOH endothermicity including all corrections is predicted to be 42.23 ± 0.2 kcal mol(-1). For the barrierless decomposition of (1)HNO to H + NO, the dissociation energy is estimated to be 47.48 ± 0.2 kcal mol(-1). For (1)NOH → H + NO, the reaction endothermicity and barrier are 5.25 ± 0.2 and 7.88 ± 0.2 kcal mol(-1). On the triplet PES the reaction energy and barrier including all corrections are predicted to be 7.73 ± 0.2 and 39.31 ± 0.2 kcal mol(-1) for the isomerization reaction (3)HNO → (3)NOH. For the triplet dissociation reaction (to H + NO) the corresponding results are 29.03 ± 0.2 and 32.41 ± 0.2 kcal mol(-1). Analogous results are 21.30 ± 0.2 and 33.67 ± 0.2 kcal mol(-1) for the dissociation reaction of (3)NOH (to H + NO). Unimolecular rate constants for the isomerization and dissociation reactions were obtained utilizing kinetic modeling methods. The tunneling and kinetic isotope effects are also investigated for these reactions. The adiabatic singlet-triplet energy splittings are predicted to be 18.45 ± 0.2 and 16.05 ± 0.2 kcal mol(-1) for HNO and NOH, respectively. Kinetic analyses based on solution of simultaneous first-order ordinary-differential rate equations demonstrate that the singlet NOH molecule will be difficult to prepare at room temperature, while the triplet NOH molecule is viable with respect to isomerization and dissociation reactions up to

  17. Variation of fundamental constants

    CERN Document Server

    Flambaum, V V

    2006-01-01

    We present a review of recent works devoted to the variation of the fine structure constant alpha, strong interaction and fundamental masses. There are some hints for the variation in quasar absorption spectra, Big Bang nucleosynthesis, and Oklo natural nuclear reactor data. A very promising method to search for the variation of the fundamental constants consists in comparison of different atomic clocks. Huge enhancement of the variation effects happens in transition between accidentally degenerate atomic and molecular energy levels. A new idea is to build a ``nuclear'' clock based on the ultraviolet transition between very low excited state and ground state in Thorium nucleus. This may allow to improve sensitivity to the variation up to 10 orders of magnitude! Huge enhancement of the variation effects is also possible in cold atomic and molecular collisions near Feschbach resonance.

  18. Constant-pressure Blowers

    Science.gov (United States)

    Sorensen, E

    1940-01-01

    The conventional axial blowers operate on the high-pressure principle. One drawback of this type of blower is the relatively low pressure head, which one attempts to overcome with axial blowers producing very high pressure at a given circumferential speed. The Schicht constant-pressure blower affords pressure ratios considerably higher than those of axial blowers of conventional design with approximately the same efficiency.

  19. String Scale Cosmological Constant

    OpenAIRE

    Chalmers, Gordon

    2006-01-01

    The cosmological constant is an unexplained until now phenomena of nature that requires an explanation through string effects. The apparent discrepancy between theory and experiment is enourmous and has already been explained several times by the author including mechanisms. In this work the string theory theory of abolished string modes is documented and given perturbatively to all loop orders. The holographic underpinning is also exposed. The matching with the data of the LIGO and D0 experi...

  20. The Hubble Constant.

    Science.gov (United States)

    Jackson, Neal

    2015-01-01

    I review the current state of determinations of the Hubble constant, which gives the length scale of the Universe by relating the expansion velocity of objects to their distance. There are two broad categories of measurements. The first uses individual astrophysical objects which have some property that allows their intrinsic luminosity or size to be determined, or allows the determination of their distance by geometric means. The second category comprises the use of all-sky cosmic microwave background, or correlations between large samples of galaxies, to determine information about the geometry of the Universe and hence the Hubble constant, typically in a combination with other cosmological parameters. Many, but not all, object-based measurements give H0 values of around 72-74 km s(-1) Mpc(-1), with typical errors of 2-3 km s(-1) Mpc(-1). This is in mild discrepancy with CMB-based measurements, in particular those from the Planck satellite, which give values of 67-68 km s(-1) Mpc(-1) and typical errors of 1-2 km s(-1) Mpc(-1). The size of the remaining systematics indicate that accuracy rather than precision is the remaining problem in a good determination of the Hubble constant. Whether a discrepancy exists, and whether new physics is needed to resolve it, depends on details of the systematics of the object-based methods, and also on the assumptions about other cosmological parameters and which datasets are combined in the case of the all-sky methods.

  1. Universe of constant

    Science.gov (United States)

    Yongquan, Han

    2016-10-01

    The ideal gas state equation is not applicable to ordinary gas, it should be applied to the Electromagnetic ``gas'' that is applied to the radiation, the radiation should be the ultimate state of matter changes or initial state, the universe is filled with radiation. That is, the ideal gas equation of state is suitable for the Singular point and the universe. Maybe someone consider that, there is no vessel can accommodate radiation, it is because the Ordinary container is too small to accommodate, if the radius of your container is the distance that Light through an hour, would you still think it can't accommodates radiation? Modern scientific determinate that the radius of the universe now is about 1027 m, assuming that the universe is a sphere whose volume is approximately: V = 4.19 × 1081 cubic meters, the temperature radiation of the universe (cosmic microwave background radiation temperature of the universe, should be the closest the average temperature of the universe) T = 3.15k, radiation pressure P = 5 × 10-6 N / m 2, according to the law of ideal gas state equation, PV / T = constant = 6 × 1075, the value of this constant is the universe, The singular point should also equal to the constant Author: hanyongquan

  2. Fine-structure constant: Is it really a constant?

    Science.gov (United States)

    Bekenstein, Jacob D.

    1982-03-01

    It is often claimed that the fine-structure "constant" α is shown to be strictly constant in time by a variety of astronomical and geophysical results. These constrain its fractional rate of change α˙α to at least some orders of magnitude below the Hubble rate H0. We argue that the conclusion is not as straightforward as claimed since there are good physical reasons to expect α˙α<

  3. The Hubble Constant

    Directory of Open Access Journals (Sweden)

    Neal Jackson

    2015-09-01

    Full Text Available I review the current state of determinations of the Hubble constant, which gives the length scale of the Universe by relating the expansion velocity of objects to their distance. There are two broad categories of measurements. The first uses individual astrophysical objects which have some property that allows their intrinsic luminosity or size to be determined, or allows the determination of their distance by geometric means. The second category comprises the use of all-sky cosmic microwave background, or correlations between large samples of galaxies, to determine information about the geometry of the Universe and hence the Hubble constant, typically in a combination with other cosmological parameters. Many, but not all, object-based measurements give H_0 values of around 72–74 km s^–1 Mpc^–1, with typical errors of 2–3 km s^–1 Mpc^–1. This is in mild discrepancy with CMB-based measurements, in particular those from the Planck satellite, which give values of 67–68 km s^–1 Mpc^–1 and typical errors of 1–2 km s^–1 Mpc^–1. The size of the remaining systematics indicate that accuracy rather than precision is the remaining problem in a good determination of the Hubble constant. Whether a discrepancy exists, and whether new physics is needed to resolve it, depends on details of the systematics of the object-based methods, and also on the assumptions about other cosmological parameters and which datasets are combined in the case of the all-sky methods.

  4. Spaces of constant curvature

    CERN Document Server

    Wolf, Joseph A

    2010-01-01

    This book is the sixth edition of the classic Spaces of Constant Curvature, first published in 1967, with the previous (fifth) edition published in 1984. It illustrates the high degree of interplay between group theory and geometry. The reader will benefit from the very concise treatments of riemannian and pseudo-riemannian manifolds and their curvatures, of the representation theory of finite groups, and of indications of recent progress in discrete subgroups of Lie groups. Part I is a brief introduction to differentiable manifolds, covering spaces, and riemannian and pseudo-riemannian geomet

  5. Messung der Geschwindigkeitskonstanten der Reaktion NH2+CH4→NH3+CH3 hinter einfallenden Stoßwellen / Measurements of the Rate Constant of the Reaction NH2+CH4→NH3+CH3 behind Incident Shock Waves

    Science.gov (United States)

    Möller, W.; Wagner, H. Gg.

    1984-09-01

    The rate constant of the reaction NH2+CH4→NH3+CH3 was measured at temperatures of about 1800 K by time-resolved UV-spectroscopy of the products behind incident shock waves. NH2 was produced by the presence and thermal decomposition of hydrazine. The data were evaluated by fitting simulated concentration-time-profiles to the measured ones. A mean rate constant k = (4±2) 1011 cm3 mol-1 s-1 1730

  6. Experimental and Theoretical Studies of Radiative and Nonradiative Processes in Semiconductors.

    Science.gov (United States)

    1984-01-01

    lattice constant. This period tions.’ A variety of explanations have been proposed will be theoretically justified below. for this undulatory behavior. 2...pairs. The undulatory behavior of the one atom per unit cell. The acceptor sites are then spectra results from the properties of N( r), the dis

  7. 过氧烷基自由基分子内氢迁移反应类速率常数的计算%Calculation of Rate Constants for Intramolecular Hydrogen Migration Reactions of Alkylperoxy Radicals

    Institute of Scientific and Technical Information of China (English)

    李尚俊; 谈宁馨; 姚倩; 李泽荣; 李象远

    2015-01-01

    Intramolecular hydrogen migration in alkylperoxy reactions is one of the most important reaction classes in hydrocarbon combustion at low temperatures. In this study, the kinetic parameters for reactions in this class were calculated using the isodesmic reaction method. The geometries for al the reactants, transition states, and products were optimized at the B3LYP/6-311+G(d,p) level. A criterion based on conservation of the reaction-center geometry of the transition state was proposed for the reaction class, and the intramolecular hydrogen migration reactions studied were divided into four classes, i.e., (1,3), (1,4), (1,5), and (1,n) (n=6, 7, 8) hydrogen migration. The simplest reaction system for each reaction class was defined as the principal reaction;the approximate single-point energies were obtained at the low level of B3LYP/6-311+G(d,p) and accurate single-point energies were obtained at the high level of CBS-QB3. The other reactions in this class were chosen as the target reactions and the approximate single-point energies were obtained at the B3LYP/6-311+G(d,p) level. The energy barriers and rate constants of these target reactions were corrected using the isodesmic reaction method. The results showed that accurate energy barriers and rate constants for the reactions of large molecules can be obtained by a relatively low level method using the isodesmic reaction method. In this study, classification of the basic isodesmic reaction showed the essential features of the reaction classes. The present work provides accurate kinetic parameters for modeling intramolecular hydrogen migration reactions of hydrocarbons at low temperatures.%过氧烷基自由基分子内氢迁移是低温燃烧反应中的一类重要基元反应。本文用等键反应方法计算了该类反应的动力学参数。所有反应物、过渡态、产物的几何结构均在B3LYP/6-311+G(d,p)水平下优化得到。本文提出了用过渡态反应中心几何结构守恒作为反

  8. The Hubble Constant

    Directory of Open Access Journals (Sweden)

    Jackson Neal

    2007-09-01

    Full Text Available I review the current state of determinations of the Hubble constant, which gives the length scale of the Universe by relating the expansion velocity of objects to their distance. In the last 20 years, much progress has been made and estimates now range between 60 and 75 km s^-1 Mpc^-1, with most now between 70 and 75 km s^-1 Mpc^-1, a huge improvement over the factor-of-2 uncertainty which used to prevail. Further improvements which gave a generally agreed margin of error of a few percent rather than the current 10% would be vital input to much other interesting cosmology. There are several programmes which are likely to lead us to this point in the next 10 years.

  9. When constants are important

    Energy Technology Data Exchange (ETDEWEB)

    Beiu, V.

    1997-04-01

    In this paper the authors discuss several complexity aspects pertaining to neural networks, commonly known as the curse of dimensionality. The focus will be on: (1) size complexity and depth-size tradeoffs; (2) complexity of learning; and (3) precision and limited interconnectivity. Results have been obtained for each of these problems when dealt with separately, but few things are known as to the links among them. They start by presenting known results and try to establish connections between them. These show that they are facing very difficult problems--exponential growth in either space (i.e. precision and size) and/or time (i.e., learning and depth)--when resorting to neural networks for solving general problems. The paper will present a solution for lowering some constants, by playing on the depth-size tradeoff.

  10. Constant Proportion Portfolio Insurance

    DEFF Research Database (Denmark)

    Jessen, Cathrine

    2014-01-01

    Portfolio insurance, as practiced in 1987, consisted of trading between an underlying stock portfolio and cash, using option theory to place a floor on the value of the position, as if it included a protective put. Constant Proportion Portfolio Insurance (CPPI) is an option-free variation...... on the theme, originally proposed by Fischer Black. In CPPI, a financial institution guarantees a floor value for the “insured” portfolio and adjusts the stock/bond mix to produce a leveraged exposure to the risky assets, which depends on how far the portfolio value is above the floor. Plain-vanilla portfolio...... insurance largely died with the crash of 1987, but CPPI is still going strong. In the frictionless markets of finance theory, the issuer’s strategy to hedge its liability under the contract is clear, but in the real world with transactions costs and stochastic jump risk, the optimal strategy is less obvious...

  11. Decay constants in geochronology

    Institute of Scientific and Technical Information of China (English)

    IgorM.Villa; PaulR.Renne

    2005-01-01

    Geologic time is fundamental to the Earth Sciences, and progress in many disciplines depends critically on our ability to measure time with increasing accuracy and precision. Isotopic geochronology makes use of the decay of radioactive nuclides as a help to quantify the histories of rock, minerals, and other materials. Both accuracy and precision of radioisotopic ages are, at present, limited by those of radioactive decay constants. Modem mass spectrometers can measure isotope ratios with a precision of 10-4 or better. On the other hand, the uncertainties associated with direct half-life determinations are, in most cases, still at the percent level. The present short note briefly summarizes progress and problems that have been encountered during the Working Group's activity.

  12. Application of vibrational correlation formalism to internal conversion rate: case study of Cu(n) (n = 3, 6, and 9) and H2/Cu3.

    Science.gov (United States)

    Chiodo, Sandro Giuseppe; Mineva, Tzonka

    2015-03-21

    This work reports non-radiative internal conversion (IC) rate constants obtained for Cun with n = 3, 6, and 9 and H2 on Cu3. The Time-Dependent Density Functional Theory (TDDFT) method was employed with three different functionals in order to investigate the electronic structures and the absorption spectra. The performance of the generalized gradient approximation of Perdew, Burke and Ernzerhof (PBE) and the hybrid B3LYP and PBE0 exchange correlation functionals in combination with the SVP and the def2-TZVP basis sets was examined. TDDFT results were used as input data to compute internal conversion rate constants. For this purpose, we have developed a program package. A description of the theoretical background used in our numerical implementation and the program input file is presented. In view of future applications of this program package in photoinduced catalysis, we present the analysis of the IC rate processes for the photodissociation of H2 on Cu3. These results showed the applicability of the method and the computational program to identify the vibrational modes in transition metal clusters giving rise to the largest IC rate constant due to their interactions with the excited electronic states occurring in the hot-electron induced dissociation phenomena.

  13. Transient behavior of flare-associated solar wind. II - Gas dynamics in a nonradial open field region

    Science.gov (United States)

    Nagai, F.

    1984-01-01

    Transient behavior of flare-associated solar wind in the nonradial open field region is numerically investigated, taking into account the thermal and dynamical coupling between the chromosphere and the corona. A realistic steady solar wind is constructed which passes through the inner X-type critical point in the rapidly diverging region. The wind speed shows a local maximum at the middle, O-type, critical point. The wind's density and pressure distributions decrease abruptly in the rapidly diverging region of the flow tube. The transient behavior of the wind following flare energy deposition includes ascending and descending conduction fronts. Thermal instability occurs in the lower corona, and ascending material flows out through the throat after the flare energy input ceases. A local density distribution peak is generated at the shock front due to the pressure deficit just behind the shock front.

  14. Non-radiative relaxation dynamics of pyrrole following excitation in the range 249.5-200 nm

    Science.gov (United States)

    Kirkby, Oliver M.; Parkes, Michael A.; Neville, Simon P.; Worth, Graham A.; Fielding, Helen H.

    2017-09-01

    The non-radiative relaxation dynamics of pyrrole have been investigated using time-resolved photoelectron spectroscopy and quantum dynamics simulations. Following excitation of the A2 (11 πσ∗) state, we observe population flow out of the Franck-Condon region on a ≲ 50 fs timescale. Following excitation of the B2 (21 ππ∗) state, we observe population being transferred to the A2 (11 πσ∗) state on a <50 fs timescale and subsequently out of the Franck-Condon region, also on a <50 fs timescale. Quantum dynamics calculations suggest that population is transferred from the B2 (21 ππ∗) state through the A2 (1 π 3pz) state to the B1 (21 πσ∗) state before being transferred to the A2 (11 πσ∗) state.

  15. The Interacting and Non-constant Cosmological Constant

    CERN Document Server

    Verma, Murli Manohar

    2009-01-01

    We propose a time-varying cosmological constant with a fixed equation of state, which evolves mainly through its interaction with the background during most of the long history of the universe. However, such interaction does not exist in the very early and the late-time universe and produces the acceleration during these eras when it becomes very nearly a constant. It is found that after the initial inflationary phase, the cosmological constant, that we call as lambda parameter, rolls down from a large constant value to another but very small constant value and further dominates the present epoch showing up in form of the dark energy driving the acceleration.

  16. Quantum Theory without Planck's Constant

    CERN Document Server

    Ralston, John P

    2012-01-01

    Planck's constant was introduced as a fundamental scale in the early history of quantum mechanics. We find a modern approach where Planck's constant is absent: it is unobservable except as a constant of human convention. Despite long reference to experiment, review shows that Planck's constant cannot be obtained from the data of Ryberg, Davisson and Germer, Compton, or that used by Planck himself. In the new approach Planck's constant is tied to macroscopic conventions of Newtonian origin, which are dispensable. The precision of other fundamental constants is substantially improved by eliminating Planck's constant. The electron mass is determined about 67 times more precisely, and the unit of electric charge determined 139 times more precisely. Improvement in the experimental value of the fine structure constant allows new types of experiment to be compared towards finding "new physics." The long-standing goal of eliminating reliance on the artifact known as the International Prototype Kilogram can be accompl...

  17. Non-radial oscillations of the magnetized rotating stars with purely toroidal magnetic fields

    CERN Document Server

    Asai, Hidetaka; Yoshida, Shijun

    2015-01-01

    We calculate non-axisymmetric oscillations of uniformly rotating polytropes magnetized with a purely toroidal magnetic field, taking account of the effects of the deformation due to the magnetic field. As for rotation, we consider only the effects of Coriolis force on the oscillation modes, ignoring those of the centrifugal force, that is, of the rotational deformation of the star. Since separation of variables is not possible for the oscillation of rotating magnetized stars, we employ finite series expansions for the perturbations using spherical harmonic functions. We calculate magnetically modified normal modes such as $g$-, $f$-, $p$-, $r$-, and inertial modes. In the lowest order, the frequency shifts produced by the magnetic field scale with the square of the characteristic Alfv\\'en frequency. As a measure of the effects of the magnetic field, we calculate the proportionality constant for the frequency shifts for various oscillation modes. We find that the effects of the deformation are significant for ...

  18. 一类具有常数存放率的三次kolmogorov系统的定性分析%Qualitative Analysis of a Cubic Kolmogorov System with Constant-Rate Prey Stocking

    Institute of Scientific and Technical Information of China (English)

    黄燕玲

    2012-01-01

    Abstract: In this paper, we study a cubic kolmogorov system with constant-rata prey stocking(dx)/(dt)=x(a0+a1x-a2x2-a3y-a4y2-a5xy)+k,(dy)/(dt)=y(bx2-d)The sufficient conditions of the existence and nonexistence of limit cycles areobtained.%对一类食饵种群具有常数存放率的三次kolmogorov系统:(dx)/(dt)=x(a0+a1x-a2x2-a3y-a4y2-a5xy)+k,(dy)/(dt)=y(bx2-d),进行定性分析,得到该系统不存在极限环和存在极限环的充分条件.

  19. Constant force extensional rheometry of polymer solutions

    DEFF Research Database (Denmark)

    Szabo, Peter; McKinley, Gareth H.; Clasen, Christian

    2012-01-01

    We revisit the rapid stretching of a liquid filament under the action of a constant imposed tensile force, a problem which was first considered by Matta and Tytus [J. Non-Newton. Fluid Mech. 35 (1990) 215–229]. A liquid bridge formed from a viscous Newtonian fluid or from a dilute polymer solution...... filament can be probed. In particular, we show that with this constant force pull (CFP) technique it is possible to readily impose very large material strains and strain rates so that the maximum extensibility of the polymer molecules may be quantified. This unique characteristic of the experiment...

  20. Non-radial oscillations of the rapidly rotating Be star HD 163868

    NARCIS (Netherlands)

    Savonije, G.J.

    2007-01-01

    Context: Oscillations in rotating stars with frequency barsigma of the same order or smaller than the rotation rate Omega cannot be described by a single spherical harmonic due to the effect of the Coriolis force. This is a serious complication which is usually treated by writing the eigenfunctions