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Sample records for constant stressing rate

  1. High-Temperature Slow Crack Growth of Silicon Carbide Determined by Constant-Stress-Rate and Constant-Stress Testing

    NASA Technical Reports Server (NTRS)

    Choi, Sung H.; Salem, J. A.; Nemeth, N. N.

    1998-01-01

    High-temperature slow-crack-growth behaviour of hot-pressed silicon carbide was determined using both constant-stress-rate ("dynamic fatigue") and constant-stress ("static fatigue") testing in flexure at 1300 C in air. Slow crack growth was found to be a governing mechanism associated with failure of the material. Four estimation methods such as the individual data, the Weibull median, the arithmetic mean and the median deviation methods were used to determine the slow crack growth parameters. The four estimation methods were in good agreement for the constant-stress-rate testing with a small variation in the slow-crack-growth parameter, n, ranging from 28 to 36. By contrast, the variation in n between the four estimation methods was significant in the constant-stress testing with a somewhat wide range of n= 16 to 32.

  2. Accelerated Testing Methodology in Constant Stress-Rate Testing for Advanced Structural Ceramics: A Preloading Technique

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Gyekenyesi, John P.; Huebert, Dean; Bartlett, Allen; Choi, Han-Ho

    2001-01-01

    Preloading technique was used as a means of an accelerated testing methodology in constant stress-rate ('dynamic fatigue') testing for two different brittle materials. The theory developed previously for fatigue strength as a function of preload was further verified through extensive constant stress-rate testing for glass-ceramic and CRT glass in room temperature distilled water. The preloading technique was also used in this study to identify the prevailing failure mechanisms at elevated temperatures, particularly at lower test rate in which a series of mechanisms would be associated simultaneously with material failure, resulting in significant strength increase or decrease. Two different advanced ceramics including SiC whisker-reinforced composite silicon nitride and 96 wt% alumina were used at elevated temperatures. It was found that the preloading technique can be used as an additional tool to pinpoint the dominant failure mechanism that is associated with such a phenomenon of considerable strength increase or decrease.

  3. Accelerated Testing Methodology in Constant Stress-Rate Testing for Advanced Structural Ceramics: A Preloading Technique

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Gyekenyesi, John P.; Huebert, Dean; Bartlett, Allen; Choi, Han-Ho

    2001-01-01

    Preloading technique was used as a means of an accelerated testing methodology in constant stress-rate ('dynamic fatigue') testing for two different brittle materials. The theory developed previously for fatigue strength as a function of preload was further verified through extensive constant stress-rate testing for glass-ceramic and CRT glass in room temperature distilled water. The preloading technique was also used in this study to identify the prevailing failure mechanisms at elevated temperatures, particularly at lower test rate in which a series of mechanisms would be associated simultaneously with material failure, resulting in significant strength increase or decrease. Two different advanced ceramics including SiC whisker-reinforced composite silicon nitride and 96 wt% alumina were used at elevated temperatures. It was found that the preloading technique can be used as an additional tool to pinpoint the dominant failure mechanism that is associated with such a phenomenon of considerable strength increase or decrease.

  4. Accelerated Testing Methodology in Constant Stress-Rate Testing for Advanced Structural Ceramics: A Preloading Technique

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Gyekenyesi, John P.; Huebert, Dean; Bartlett, Allen; Choi, Han-Ho

    2001-01-01

    Preloading technique was used as a means of an accelerated testing methodology in constant stress-rate (dynamic fatigue) testing for two different brittle materials. The theory developed previously for fatigue strength as a function of preload was further verified through extensive constant stress-rate testing for glass-ceramic and CRT glass in room temperature distilled water. The preloading technique was also used in this study to identify the prevailing failure mechanisms at elevated temperatures, particularly at lower test rates in which a series of mechanisms would be associated simultaneously with material failure, resulting in significant strength increase or decrease. Two different advanced ceramics including SiC whisker-reinforced composite silicon nitride and 96 wt% alumina were used at elevated temperatures. It was found that the preloading technique can be used as an additional tool to pinpoint the dominant failure mechanism that is associated with such a phenomenon of considerable strength increase or decrease.

  5. Equivalent formulae of stress Green's functions for a constant slip rate on a triangular fault

    NASA Astrophysics Data System (ADS)

    Feng, Xi; Zhang, Haiming

    2017-07-01

    We present an equivalent form of the expressions first obtained by Tada (Geophys J Int 164:653-669, 2006. doi: 10.1111/j.1365-246X.2006.03868.x), which represents the transient stress response of an infinite, homogeneous and isotropic medium to a constant slip rate on a triangular fault that continues perpetually after the slip onset. Our results are simpler than Tada's, and the corresponding codes have a higher running speed.

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

    SciTech Connect

    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.

  7. Estimation and Simulation of Slow Crack Growth Parameters from Constant Stress Rate Data

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.; Weaver, Aaron S.

    2003-01-01

    Closed form, approximate functions for estimating the variances and degrees-of-freedom associated with the slow crack growth parameters n, D, B, and A(sup *) as measured using constant stress rate ('dynamic fatigue') testing were derived by using propagation of errors. Estimates made with the resulting functions and slow crack growth data for a sapphire window were compared to the results of Monte Carlo simulations. The functions for estimation of the variances of the parameters were derived both with and without logarithmic transformation of the initial slow crack growth equations. The transformation was performed to make the functions both more linear and more normal. Comparison of the Monte Carlo results and the closed form expressions derived with propagation of errors indicated that linearization is not required for good estimates of the variances of parameters n and D by the propagation of errors method. However, good estimates variances of the parameters B and A(sup *) could only be made when the starting slow crack growth equation was transformed and the coefficients of variation of the input parameters were not too large. This was partially a result of the skewered distributions of B and A(sup *). Parametric variation of the input parameters was used to determine an acceptable range for using closed form approximate equations derived from propagation of errors.

  8. Slow Crack Growth Analysis of Brittle Materials with Finite Thickness Subjected to Constant Stress-Rate Flexural Loading

    NASA Technical Reports Server (NTRS)

    Chio, S. R.; Gyekenyesi, J. P.

    1999-01-01

    A two-dimensional, numerical analysis of slow crack growth (SCG) was performed for brittle materials with finite thickness subjected to constant stress-rate ("dynamic fatigue") loading in flexure. The numerical solution showed that the conventional, simple, one-dimensional analytical solution can be used with a maximum error of about 5% in determining the SCG parameters of a brittle material with the conditions of a normalized thickness (a ratio of specimen thickness to initial crack size) T > 3.3 and of a SCG parameter n > 10. The change in crack shape from semicircular to elliptical configurations was significant particularly at both low stress rate and low T, attributed to predominant difference in stress intensity factor along the crack front. The numerical solution of SCG parameters was supported within the experimental range by the data obtained from constant stress-rate flexural testing for soda-lime glass microslides at ambient temperature.

  9. Slow Crack Growth Analysis of Brittle Materials with Finite Thickness Subjected to Constant Stress-Rate Flexural Loading

    NASA Technical Reports Server (NTRS)

    Chio, S. R.; Gyekenyesi, J. P.

    1999-01-01

    A two-dimensional, numerical analysis of slow crack growth (SCG) was performed for brittle materials with finite thickness subjected to constant stress-rate ("dynamic fatigue") loading in flexure. The numerical solution showed that the conventional, simple, one-dimensional analytical solution can be used with a maximum error of about 5% in determining the SCG parameters of a brittle material with the conditions of a normalized thickness (a ratio of specimen thickness to initial crack size) T > 3.3 and of a SCG parameter n > 10. The change in crack shape from semicircular to elliptical configurations was significant particularly at both low stress rate and low T, attributed to predominant difference in stress intensity factor along the crack front. The numerical solution of SCG parameters was supported within the experimental range by the data obtained from constant stress-rate flexural testing for soda-lime glass microslides at ambient temperature.

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

    NASA Technical Reports Server (NTRS)

    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.

  11. Time-dependent polymer rheology under constant stress and under constant shear conditions.

    NASA Technical Reports Server (NTRS)

    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.

  12. Analysis of the tensile stress-strain behavior of elastomers at constant strain rates. I - Criteria for separability of the time and strain effects

    NASA Technical Reports Server (NTRS)

    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.

  13. Analysis of the tensile stress-strain behavior of elastomers at constant strain rates. I - Criteria for separability of the time and strain effects

    NASA Technical Reports Server (NTRS)

    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.

  14. Estimation of Slow Crack Growth Parameters for Constant Stress-Rate Test Data of Advanced Ceramics and Glass by the Individual Data and Arithmetic Mean Methods

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Salem, Jonathan A.; Holland, Frederic A.

    1997-01-01

    The two estimation methods, individual data and arithmetic mean methods, were used to determine the slow crack growth (SCG) parameters (n and D) of advanced ceramics and glass from a large number of room- and elevated-temperature constant stress-rate ('dynamic fatigue') test data. For ceramic materials with Weibull modulus greater than 10, the difference in the SCG parameters between the two estimation methods was negligible; whereas, for glass specimens exhibiting Weibull modulus of about 3, the difference was amplified, resulting in a maximum difference of 16 and 13 %, respectively, in n and D. Of the two SCG parameters, the parameter n was more sensitive to the estimation method than the other. The coefficient of variation in n was found to be somewhat greater in the individual data method than in the arithmetic mean method.

  15. Molecular dynamics at constant Cauchy stress.

    PubMed

    Miller, Ronald E; Tadmor, Ellad B; Gibson, Joshua S; Bernstein, Noam; Pavia, Fabio

    2016-05-14

    The Parrinello-Rahman algorithm for imposing a general state of stress in periodic molecular dynamics simulations is widely used in the literature and has been implemented in many readily available molecular dynamics codes. However, what is often overlooked is that this algorithm controls the second Piola-Kirchhoff stress as opposed to the true (Cauchy) stress. This can lead to misinterpretation of simulation results because (1) the true stress that is imposed during the simulation depends on the deformation of the periodic cell, (2) the true stress is potentially very different from the imposed second Piola-Kirchhoff stress, and (3) the true stress can vary significantly during the simulation even if the imposed second Piola-Kirchhoff is constant. We propose a simple modification to the algorithm that allows the true Cauchy stress to be controlled directly. We then demonstrate the efficacy of the new algorithm with the example of martensitic phase transformations under applied stress.

  16. The Rate Constant for Fluorescence Quenching

    ERIC Educational Resources Information Center

    Legenza, Michael W.; Marzzacco, Charles J.

    1977-01-01

    Describes an experiment that utilizes fluorescence intensity measurements from a Spectronic 20 to determine the rate constant for the fluorescence quenching of various aromatic hydrocarbons by carbon tetrachloride in an ethanol solvent. (MLH)

  17. The Rate Constant for Fluorescence Quenching

    ERIC Educational Resources Information Center

    Legenza, Michael W.; Marzzacco, Charles J.

    1977-01-01

    Describes an experiment that utilizes fluorescence intensity measurements from a Spectronic 20 to determine the rate constant for the fluorescence quenching of various aromatic hydrocarbons by carbon tetrachloride in an ethanol solvent. (MLH)

  18. Inflation with a constant rate of roll

    SciTech Connect

    Motohashi, Hayato; Starobinsky, Alexei A.; Yokoyama, Jun'ichi E-mail: alstar@landau.ac.ru

    2015-09-01

    We consider an inflationary scenario where the rate of inflaton roll defined by {sup ··}φ/H φ-dot 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.

  19. Inflation with a constant rate of roll

    NASA Astrophysics Data System (ADS)

    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.

  20. Rate constant for the Cl + Chloroform reaction

    SciTech Connect

    Brahan, K.M.; Hewitt, A.D.; Boone, G.D.

    1995-12-01

    The rate constant for the reaction of Cl with chloroform has been measured relative to the reaction of Cl with methane, methyl chloride, and carbon monoxide using long path FTIR spectroscopy. Our measured rate constant at 298 K and 1 atm of (1.2{plus_minus}0.1)x10{sup -13} cm{sup 3}molecule{sup -1}sec{sup -1} is 50% higher than that recommended for stratospheric modeling; however, it is within experimental error of the values measured by Clyne and Walker and by Watson. The implications of this reaction on the budgets of chloroform and phosgene in the troposphere will be discussed.

  1. On determining dose rate constants spectroscopically

    SciTech Connect

    Rodriguez, M.; Rogers, D. W. O.

    2013-01-15

    Purpose: To investigate several aspects of the Chen and Nath spectroscopic method of determining the dose rate constants of {sup 125}I and {sup 103}Pd seeds [Z. Chen and R. Nath, Phys. Med. Biol. 55, 6089-6104 (2010)] including the accuracy of using a line or dual-point source approximation as done in their method, and the accuracy of ignoring the effects of the scattered photons in the spectra. Additionally, the authors investigate the accuracy of the literature's many different spectra for bare, i.e., unencapsulated {sup 125}I and {sup 103}Pd sources. Methods: Spectra generated by 14 {sup 125}I and 6 {sup 103}Pd seeds were calculated in vacuo at 10 cm from the source in a 2.7 Multiplication-Sign 2.7 Multiplication-Sign 0.05 cm{sup 3} voxel using the EGSnrc BrachyDose Monte Carlo code. Calculated spectra used the initial photon spectra recommended by AAPM's TG-43U1 and NCRP (National Council of Radiation Protection and Measurements) Report 58 for the {sup 125}I seeds, or TG-43U1 and NNDC(2000) (National Nuclear Data Center, 2000) for {sup 103}Pd seeds. The emitted spectra were treated as coming from a line or dual-point source in a Monte Carlo simulation to calculate the dose rate constant. The TG-43U1 definition of the dose rate constant was used. These calculations were performed using the full spectrum including scattered photons or using only the main peaks in the spectrum as done experimentally. Statistical uncertainties on the air kerma/history and the dose rate/history were Less-Than-Or-Slanted-Equal-To 0.2%. The dose rate constants were also calculated using Monte Carlo simulations of the full seed model. Results: The ratio of the intensity of the 31 keV line relative to that of the main peak in {sup 125}I spectra is, on average, 6.8% higher when calculated with the NCRP Report 58 initial spectrum vs that calculated with TG-43U1 initial spectrum. The {sup 103}Pd spectra exhibit an average 6.2% decrease in the 22.9 keV line relative to the main peak when

  2. Estimation of hydrolysis rate constants for carbamates ...

    EPA Pesticide Factsheets

    Cheminformatics based tools, such as the Chemical Transformation Simulator under development in EPA’s Office of Research and Development, are being increasingly used to evaluate chemicals for their potential to degrade in the environment or be transformed through metabolism. Hydrolysis represents a major environmental degradation pathway; unfortunately, only a small fraction of hydrolysis rates for about 85,000 chemicals on the Toxic Substances Control Act (TSCA) inventory are in public domain, making it critical to develop in silico approaches to estimate hydrolysis rate constants. In this presentation, we compare three complementary approaches to estimate hydrolysis rates for carbamates, an important chemical class widely used in agriculture as pesticides, herbicides and fungicides. Fragment-based Quantitative Structure Activity Relationships (QSARs) using Hammett-Taft sigma constants are widely published and implemented for relatively simple functional groups such as carboxylic acid esters, phthalate esters, and organophosphate esters, and we extend these to carbamates. We also develop a pKa based model and a quantitative structure property relationship (QSPR) model, and evaluate them against measured rate constants using R square and root mean square (RMS) error. Our work shows that for our relatively small sample size of carbamates, a Hammett-Taft based fragment model performs best, followed by a pKa and a QSPR model. This presentation compares three comp

  3. The load dependence of rate constants.

    PubMed

    Walcott, Sam

    2008-06-07

    As experimental techniques in biophysics have progressed at the single molecule level, there has been considerable interest in understanding how external mechanical influences (such as load) affect chemical reactions. The majority of biophysical studies investigating load-dependent kinetics use an equation where the rate constant exponentially depends on force, which is sometimes called Bell's equation. This equation requires the determination of two parameters that describe the potential energy-strain function: k(0), which is the reaction rate in the absence of load, and x(c), which is the difference in strain between the reactant and transition states. However, there have been theoretical studies based on Kramers' theory suggesting that the rate constant should have load-dependent pre-exponential terms and nonlinear load-dependent terms in the exponential. Kramers' theory requires an exact knowledge of the potential energy-strain function, which is in general not known for an experimental system. Here, we derive a general approximation of Kramers' theory where the potential energy-strain function is described by five parameters, which can, for small loads, be reduced to four-, three-, and finally to two parameters (Bell's equation). We then use an idealized physical system to validate our approximations to Kramers' theory and show how they can predict parameters of interest (such as k(0) and x(c)) better than Bell's equation. Finally, we show previously published experimental data that are not well fitted by Bell's equation but are adequately fitted by these more exact equations.

  4. Textbook Deficiencies: Ambiguities in Chemical Kinetics Rates and Rate Constants

    NASA Astrophysics Data System (ADS)

    Quisenberry, Keith T.; Tellinghuisen, Joel

    2006-03-01

    Balanced chemical reactions often have at least some stoichiometry coefficients that are not unity. To avoid ambiguity in defining the kinetics rate for a reaction, the IUPAC has established the convention, rate = (1/ν i )/(d[A i ]/d t ) relating the reaction rate to the rate of change of concentration of any reactant or product A i and its stoichiometry number ν i (negative for reactants, positive for products). The rate is a product of the rate constant k and some function of the concentrations of reactants and products that must be determined experimentally. While most general chemistry textbooks correctly state this convention, most also proceed to ignore it in subsequent development, particularly in the use of integrated rate laws and the definition of the reaction half-life. We recommend that in future editions, authors make it clear that (i) the reaction rate and rate constant cannot be defined unambiguously without explicitly stating the reaction for which they apply and therefore (ii) the relation between the half-life, which is a physical property of the reaction system, and the rate constant depends upon how the reaction is written. The errors have arisen in part because most texts simply state the integrated rate expressions for first- and second-order reactions without deriving them. It is both appropriate and easy to include such derivations in texts oriented toward students intending careers in science, engineering, and medicine.

  5. 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.

    PubMed

    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.

  6. When Rate Constants Are Not Enough.

    PubMed

    Barker, John R; Frenklach, Michael; Golden, David M

    2015-07-16

    Real-world chemical systems consisting of multiple isomers and multiple reaction channels often react significantly prior to attaining a steady state energy distribution (SED). Detailed elementary reaction models, which implicitly require SED conditions, may be invalid when non-steady-state energy distributions (NSED) exist. NSED conditions may result in reaction rates and product yields that are different from those expected for SED conditions, although this problem is to some extent reduced by using phenomenological models and rate constants. The present study defines pragmatic diagnostics useful for identifying NSED conditions in stochastic master equation simulations. A representative example is presented for each of four classes of common combustion species: RO2 radicals, aliphatic hydrocarbons, alkyl radicals, and polyaromatic radicals. An example selected from the seminal work of Tsang et al. demonstrates that stochastic simulations and eigenvalue methods for solving the master equation predict the same NSED effects. NSED effects are common under relatively moderate combustion conditions, and accurate simulations may require a master equation analysis.

  7. Microfabricated microengine with constant rotation rate

    DOEpatents

    Romero, Louis A.; Dickey, Fred M.

    1999-01-01

    A microengine uses two synchronized linear actuators as a power source and converts oscillatory motion from the actuators into constant rotational motion via direct linkage connection to an output gear or wheel. The microengine provides output in the form of a continuously rotating output gear that is capable of delivering drive torque at a constant rotation to a micromechanism. The output gear can have gear teeth on its outer perimeter for directly contacting a micromechanism requiring mechanical power. The gear is retained by a retaining means which allows said gear to rotate freely. The microengine is microfabricated of polysilicon on one wafer using surface micromachining batch fabrication.

  8. Microfabricated microengine with constant rotation rate

    SciTech Connect

    Romero, L.A.; Dickey, F.M.

    1999-09-21

    A microengine uses two synchronized linear actuators as a power source and converts oscillatory motion from the actuators into constant rotational motion via direct linkage connection to an output gear or wheel. The microengine provides output in the form of a continuously rotating output gear that is capable of delivering drive torque at a constant rotation to a micromechanism. The output gear can have gear teeth on its outer perimeter for directly contacting a micromechanism requiring mechanical power. The gear is retained by a retaining means which allows said gear to rotate freely. The microengine is microfabricated of polysilicon on one wafer using surface micromachining batch fabrication.

  9. 18 CFR 806.12 - Constant-rate aquifer testing.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 18 Conservation of Power and Water Resources 2 2011-04-01 2011-04-01 false Constant-rate aquifer... COMMISSION REVIEW AND APPROVAL OF PROJECTS Application Procedure § 806.12 Constant-rate aquifer testing. (a... withdraw or increase a withdrawal of groundwater shall perform a constant-rate aquifer test in...

  10. A loading system for creep testing under constant compressive stress

    NASA Technical Reports Server (NTRS)

    Dobes, F.; Zverina, O.; Cadek, J.

    1987-01-01

    A critical analysis is made of layouts assuring constant stress under creep, pointing out the difficulties of using these layouts for compressive testing. A new mechanical system to maintain stress during creep testing is proposed. Constant stress is achieved by a definite motion of the load. The proposed system can be used in tensile or compressive testing. Practical measurements reveal that the stress constancy error is not greater than plus or minus 1.5 percent up to relative deformation of 30 percent.

  11. Calculation of kinetic rate constants from thermodynamic data

    NASA Technical Reports Server (NTRS)

    Marek, C. John

    1995-01-01

    A new scheme for relating the absolute value for the kinetic rate constant k to the thermodynamic constant Kp is developed for gases. In this report the forward and reverse rate constants are individually related to the thermodynamic data. The kinetic rate constants computed from thermodynamics compare well with the current kinetic rate constants. This method is self consistent and does not have extensive rules. It is first demonstrated and calibrated by computing the HBr reaction from H2 and Br2. This method then is used on other reactions.

  12. 18 CFR 806.12 - Constant-rate aquifer testing.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 18 Conservation of Power and Water Resources 2 2014-04-01 2014-04-01 false Constant-rate aquifer testing. 806.12 Section 806.12 Conservation of Power and Water Resources SUSQUEHANNA RIVER BASIN COMMISSION REVIEW AND APPROVAL OF PROJECTS Application Procedure § 806.12 Constant-rate aquifer testing. (a...

  13. 18 CFR 806.12 - Constant-rate aquifer testing.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 18 Conservation of Power and Water Resources 2 2012-04-01 2012-04-01 false Constant-rate aquifer testing. 806.12 Section 806.12 Conservation of Power and Water Resources SUSQUEHANNA RIVER BASIN COMMISSION REVIEW AND APPROVAL OF PROJECTS Application Procedure § 806.12 Constant-rate aquifer testing. (a...

  14. 18 CFR 806.12 - Constant-rate aquifer testing.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 18 Conservation of Power and Water Resources 2 2013-04-01 2012-04-01 true Constant-rate aquifer testing. 806.12 Section 806.12 Conservation of Power and Water Resources SUSQUEHANNA RIVER BASIN COMMISSION REVIEW AND APPROVAL OF PROJECTS Application Procedure § 806.12 Constant-rate aquifer testing. (a...

  15. ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS - ALKALINE HYDROLYSIS

    EPA Science Inventory

    SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to allow the calculation of alkaline hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition state...

  16. ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS - ALKALINE HYDROLYSIS

    EPA Science Inventory

    SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to allow the calculation of alkaline hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition state...

  17. ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS. I. ALKALINE HYDROLYSIS

    EPA Science Inventory

    SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to allow the calculation of alkaline hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition state...

  18. ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS. I. ALKALINE HYDROLYSIS

    EPA Science Inventory

    SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to allow the calculation of alkaline hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition state...

  19. A Priori Estimation of Rate Constants for Unimolecular Decomposition Reactions

    DTIC Science & Technology

    1979-02-01

    priori theoretical predictions for the decomposition rate of the formyl and the methoxy radicals have been made by application of the Rice-Ramsperger...Kassel-Marcus Theory. An ArrheniLus rate coefficient expression is derived for the formyl radical decomposition, and a modified Arrhenius type rate...9 IV. A PREDICTED RATE CONSTANT FOR FORMYL RADICAL DECOMPOSITION. .. .... .................... ........19 V. SUMMtARY

  20. Stress drop with constant, scale independent seismic efficiency and overshoot

    USGS Publications Warehouse

    Beeler, N.M.

    2001-01-01

    To model dissipated and radiated energy during earthquake stress drop, I calculate dynamic fault slip using a single degree of freedom spring-slider block and a laboratory-based static/kinetic fault strength relation with a dynamic stress drop proportional to effective normal stress. The model is scaled to earthquake size assuming a circular rupture; stiffness varies inversely with rupture radius, and rupture duration is proportional to radius. Calculated seismic efficiency, the ratio of radiated to total energy expended during stress drop, is in good agreement with laboratory and field observations. Predicted overshoot, a measure of how much the static stress drop exceeds the dynamic stress drop, is higher than previously published laboratory and seismic observations and fully elasto-dynamic calculations. Seismic efficiency and overshoot are constant, independent of normal stress and scale. Calculated variation of apparent stress with seismic moment resembles the observational constraints of McGarr [1999].

  1. An Introduction to Collision Theory Rate Constants via Distribution Functions.

    ERIC Educational Resources Information Center

    McAlduff, E. J.

    1980-01-01

    Described is an introduction to the collision theory by arriving at the many degrees of freedom rote constant and showing that the (-Ea/RT) is a special case and corresponds to activation in 2 squared terms on the line of center rate constant, which is found through the use of distributed functions. (Author/DS)

  2. ESTIMATION OF CARBOXYLIC ACID ESTER HYDROLYSIS RATE CONSTANTS

    EPA Science Inventory

    SPARC chemical reactivity models were extended to calculate hydrolysis rate constants for carboxylic acid esters from molecular structure. The energy differences between the initial state and the transition state for a molecule of interest are factored into internal and external...

  3. 18 CFR 806.12 - Constant-rate aquifer testing.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... withdraw or increase a withdrawal of groundwater shall perform a constant-rate aquifer test in accordance... groundwater availability analysis to determine the availability of water during a 1-in-10-year recurrence...

  4. ESTIMATION OF CARBOXYLIC ACID ESTER HYDROLYSIS RATE CONSTANTS

    EPA Science Inventory

    SPARC chemical reactivity models were extended to calculate hydrolysis rate constants for carboxylic acid esters from molecular structure. The energy differences between the initial state and the transition state for a molecule of interest are factored into internal and external...

  5. Rate constant for reaction of atomic hydrogen with germane

    NASA Technical Reports Server (NTRS)

    Nava, David F.; Payne, Walter A.; Marston, George; Stief, Louis J.

    1990-01-01

    Due to the interest in the chemistry of germane in the atmospheres of Jupiter and Saturn, and because previously reported kinetic reaction rate studies at 298 K gave results differing by a factor of 200, laboratory measurements were performed to determine the reaction rate constant for H + GeH4. Results of the study at 298 K, obtained via the direct technique of flash photolysis-resonance fluorescence, yield the reaction rate constant, k = (4.08 + or - 0.22) x 10(exp -12) cu cm/s.

  6. Charring rate of wood exposed to a constant heat flux

    Treesearch

    R. H. White; H. C. Tran

    1996-01-01

    A critical factor in the fire endurance of a wood member is its rate of charring. Most available charring rate data have been obtained using the time-temperature curves of the standard fire resistance tests (ASTM E 119 and ISO 834) to define the fire exposure. The increased use of heat release calorimeters using exposures of constant heat flux levels has broadened the...

  7. Reaction rate constant for radiative association of CF+

    NASA Astrophysics Data System (ADS)

    Ã-ström, Jonatan; Bezrukov, Dmitry S.; Nyman, Gunnar; Gustafsson, Magnus

    2016-01-01

    Reaction rate constants and cross sections are computed for the radiative association of carbon cations (C+) and fluorine atoms (F) in their ground states. We consider reactions through the electronic transition 11Π → X1Σ+ and rovibrational transitions on the X1Σ+ and a3Π 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 10-21 cm3 s-1, rising toward 10-16 cm3 s-1 for a temperature of 30 000 K.

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

    PubMed

    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

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

    NASA Technical Reports Server (NTRS)

    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. Flame Chemiluminescence Rate Constants for Quantitative Microgravity Combustion Diagnostics

    NASA Technical Reports Server (NTRS)

    Luque, Jorge; Smith, Gregory P.; Jeffries, Jay B.; Crosley, David R.; Weiland, Karen (Technical Monitor)

    2001-01-01

    Absolute excited state concentrations of OH(A), CH(A), and C2(d) were determined in three low pressure premixed methane-air flames. Two dimensional images of chemiluminescence from these states were recorded by a filtered CCD camera, processed by Abel inversion, and calibrated against Rayleigh scattering, Using a previously validated 1-D flame model with known chemistry and excited state quenching rate constants, rate constants are extracted for the reactions CH + O2 (goes to) OH(A) + CO and C2H + O (goes to) CH(A) + CO at flame temperatures. Variations of flame emission intensities with stoichiometry agree well with model predictions.

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

    NASA Technical Reports Server (NTRS)

    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.

  12. Rate constants for reactions of perhaloalkylperoxyl radicals with alkenes

    SciTech Connect

    Alfassi, Z.B.; Huie, R.E.; Neta, P. )

    1993-07-01

    Trichloro- and tribromomethylperoxyl radicals were produced by radiolytic reduction of CCl[sub 4] and CBr[sub 4] in various aerated solvents. Rate constants for the reactions of these radicals with unsaturated organic compounds were determined in methanol solutions by competition kinetics, using mainly chloropromazine as a reference. The rate constants were in the range k = 10[sup 4]-10[sup 7] L mol[sup [minus]1] s[sup [minus]1], and a good correlation was obtained between log k and the Taft substituent constants [sigma]*. Steric effects were also noticeable in some cases. The reactivities of the radicals were in the order CBr[sub 3]O[sub 2][center dot] < CCl[sub 3]O[sub 2][center dot] < C[sub 4]F[sub 9]O[sub 2][center dot], which is in contrast with the order observed in electron-transfer reactions. The rate constants for reaction of CCl[sub 3]O[sub 2][center dot] with 2,3-dimethyl-2-butene (DMB) and cyclohexene (CH) were studied in 12 solvents. In all cases DMB is considerably more reactive than CH, indicating that at least in the case of DMB the reaction is predominantly via addition. The rate constant for addition of CCl[sub 3]O[sub 2][center dot] to DMB varies by a factor of 7 in the different solvents. No correlation was found between these rate constants and thermodynamic or polarity parameters of the solvents, although viscosity appears to have an effect. 19 refs., 2 figs., 2 tabs.

  13. Theoretical Evaluation of the Transient Response of Constant Head and Constant Flow-Rate Permeability Tests

    USGS Publications Warehouse

    Zhang, M.; Takahashi, M.; Morin, R.H.; Esaki, T.

    1998-01-01

    A theoretical analysis is presented that compares the response characteristics of the constant head and the constant flowrate (flow pump) laboratory techniques for quantifying the hydraulic properties of geologic materials having permeabilities less than 10-10 m/s. Rigorous analytical solutions that describe the transient distributions of hydraulic gradient within a specimen are developed, and equations are derived for each method. Expressions simulating the inflow and outflow rates across the specimen boundaries during a constant-head permeability test are also presented. These solutions illustrate the advantages and disadvantages of each method, including insights into measurement accuracy and the validity of using Darcy's law under certain conditions. The resulting observations offer practical considerations in the selection of an appropriate laboratory test method for the reliable measurement of permeability in low-permeability geologic materials.

  14. Computer Calculation of First-Order Rate Constants

    ERIC Educational Resources Information Center

    Williams, Robert C.; Taylor, James W.

    1970-01-01

    Discusses the computer program used to calculate first-order rate constants. Discussion includes data preparation, weighting options, comparison techniques, infinity point adjustment, least-square fit, Guggenheim calculation, and printed outputs. Exemplifies the utility of the computer program by two experiments: (1) the thermal decomposition of…

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

    PubMed

    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.

  16. Oxygen uptake in maximal effort constant rate and interval running.

    PubMed

    Pratt, Daniel; O'Brien, Brendan J; Clark, Bradley

    2013-01-01

    This study investigated differences in average VO2 of maximal effort interval running to maximal effort constant rate running at lactate threshold matched for time. The average VO2 and distance covered of 10 recreational male runners (VO2max: 4158 ± 390 mL · min(-1)) were compared between a maximal effort constant-rate run at lactate threshold (CRLT), a maximal effort interval run (INT) consisting of 2 min at VO2max speed with 2 minutes at 50% of VO2 repeated 5 times, and a run at the average speed sustained during the interval run (CR submax). Data are presented as mean and 95% confidence intervals. The average VO2 for INT, 3451 (3269-3633) mL · min(-1), 83% VO2max, was not significantly different to CRLT, 3464 (3285-3643) mL · min(-1), 84% VO2max, but both were significantly higher than CR sub-max, 3464 (3285-3643) mL · min(-1), 76% VO2max. The distance covered was significantly greater in CLRT, 4431 (4202-3731) metres, compared to INT and CR sub-max, 4070 (3831-4309) metres. The novel finding was that a 20-minute maximal effort constant rate run uses similar amounts of oxygen as a 20-minute maximal effort interval run despite the greater distance covered in the maximal effort constant-rate run.

  17. Computer Calculation of First-Order Rate Constants

    ERIC Educational Resources Information Center

    Williams, Robert C.; Taylor, James W.

    1970-01-01

    Discusses the computer program used to calculate first-order rate constants. Discussion includes data preparation, weighting options, comparison techniques, infinity point adjustment, least-square fit, Guggenheim calculation, and printed outputs. Exemplifies the utility of the computer program by two experiments: (1) the thermal decomposition of…

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

    NASA Astrophysics Data System (ADS)

    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.

  19. Semiclassical Calculation of Reaction Rate Constants for Homolytical Dissociations

    NASA Technical Reports Server (NTRS)

    Cardelino, Beatriz H.

    2002-01-01

    There is growing interest in extending organometallic chemical vapor deposition (OMCVD) to III-V materials that exhibit large thermal decomposition at their optimum growth temperature, such as indium nitride. The group III nitrides are candidate materials for light-emitting diodes and semiconductor lasers operating into the blue and ultraviolet regions. To overcome decomposition of the deposited compound, the reaction must be conducted at high pressures, which causes problems of uniformity. Microgravity may provide the venue for maintaining conditions of laminar flow under high pressure. Since the selection of optimized parameters becomes crucial when performing experiments in microgravity, efforts are presently geared to the development of computational OMCVD models that will couple the reactor fluid dynamics with its chemical kinetics. In the present study, we developed a method to calculate reaction rate constants for the homolytic dissociation of III-V compounds for modeling OMCVD. The method is validated by comparing calculations with experimental reaction rate constants.

  20. Semiclassical Calculation of Reaction Rate Constants for Homolytical Dissociations

    NASA Technical Reports Server (NTRS)

    Cardelino, Beatriz H.

    2002-01-01

    There is growing interest in extending organometallic chemical vapor deposition (OMCVD) to III-V materials that exhibit large thermal decomposition at their optimum growth temperature, such as indium nitride. The group III nitrides are candidate materials for light-emitting diodes and semiconductor lasers operating into the blue and ultraviolet regions. To overcome decomposition of the deposited compound, the reaction must be conducted at high pressures, which causes problems of uniformity. Microgravity may provide the venue for maintaining conditions of laminar flow under high pressure. Since the selection of optimized parameters becomes crucial when performing experiments in microgravity, efforts are presently geared to the development of computational OMCVD models that will couple the reactor fluid dynamics with its chemical kinetics. In the present study, we developed a method to calculate reaction rate constants for the homolytic dissociation of III-V compounds for modeling OMCVD. The method is validated by comparing calculations with experimental reaction rate constants.

  1. Kinetic performance limits of constant pressure versus constant flow rate gradient elution separations. Part II: experimental.

    PubMed

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

    2011-02-25

    We report on a first series of experiments comparing the selectivity and the kinetic performance of constant flow rate and constant pressure mode gradient elution separations. Both water-methanol and water-acetonitrile mobile phase mixtures have been considered, as well as different samples and gradient programs. Instrument pressures up to 1200 bar have been used. Neglecting some small possible deviations caused by viscous heating effects, the experiments could confirm the theoretical expectation that both operation modes should lead to identical separation selectivities provided the same mobile phase gradient program is run in reduced volumetric coordinates. Also in agreement with the theoretical expectations, the cP-mode led to a gain in analysis time amounting up to some 17% for linear gradients running from 5 to 95% of organic modifier at ultra-high pressures. Gains of over 25% were obtained for segmented gradients, at least when the flat portions of the gradient program were situated in regions where the gradient composition was the least viscous. Detailed plate height measurements showed that the single difference between the constant flow rate and the constant pressure mode is a (small) difference in efficiency caused by the difference in average flow rate, in turn leading to a different intrinsic band broadening. Separating a phenone sample with a 20-95% water-acetonitrile gradient, the cP-mode leads to gradient plate heights that are some 20-40% smaller than in the cF-mode in the B-term dominated regime, while they are some 5-10% larger in the C-term dominated regime. Considering a separation with sub 2-μm particles on a 350 mm long coupled column, switching to the constant pressure mode allowed to finish the run in 29 instead of in 35 min, while also a larger peak capacity is obtained (going from 334 in the cF-mode to 339 in the cP-mode) and the mutual selectivity between the different peaks is fully retained. Copyright © 2010 Elsevier B.V. All rights

  2. The rate constant for formation of HCl through radiative association

    NASA Astrophysics Data System (ADS)

    Kathir, R. K.; Nyman, Gunnar; Gustafsson, Magnus

    2017-09-01

    Formation of HCl in its electronic ground state through radiative association is studied. We ignore spin-orbit couplings and then the formation can happen through two dipole-allowed reactions, one involving an electronic transition and one where the H and Cl atoms approach and remain in the ground electronic molecular state. The radiative association rate constant is computed, through a combination of classical and quantum methods, for use in modelling of interstellar chemistry.

  3. Observational evidence for constant gas accretion rate since z = 5

    NASA Astrophysics Data System (ADS)

    Spring, Eleanor F.; Michałowski, Michał J.

    2017-10-01

    Star formation rate density (SFRD) has not been constant throughout the history of the Universe. The rate at which stars form greatly affects the evolution of the Universe, but the factors which drive SFRD evolution remain uncertain. There must be sufficient amount of gas to fuel the star formation, either as a reservoir within a galaxy, or as inflow from the intergalactic medium (IGM). This work explores how the gas accretion rate onto galaxies over time has affected star formation rate. We propose a novel method of measuring cosmic gas accretion rate. This involves comparing the comoving densities of available Hi and H2 gas and the densities of existing stars at different redshifts. We constrained gas accretion until z = 5, and we found that the gas accretion rate density (GARD) is relatively constant in the range from z = 5 to z = 0. This constancy in the GARD is not reflected by the SFRD, which declines significantly between z = 1.0 and z = 0. This work suggests that the decline is not due to a reduction in GARD.

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

    SciTech Connect

    Öström, Jonatan Gustafsson, Magnus; Bezrukov, Dmitry S.; Nyman, Gunnar

    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.

  5. Reaction rate constant for radiative association of CF(.).

    PubMed

    Öström, Jonatan; Bezrukov, Dmitry S; Nyman, Gunnar; Gustafsson, Magnus

    2016-01-28

    Reaction rate constants and cross sections are computed for the radiative association of carbon cations (C(+)) and fluorine atoms (F) in their ground states. We consider reactions through the electronic transition 1(1)Π → X(1)Σ(+) and rovibrational transitions on the X(1)Σ(+) and a(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(-21) cm(3) s(-1), rising toward 10(-16) cm(3) s(-1) for a temperature of 30,000 K.

  6. Comparison of TID Effects in Space-Like Variable Dose Rates and Constant Dose Rates

    NASA Technical Reports Server (NTRS)

    Harris, Richard D.; McClure, Steven S.; Rax, Bernard G.; Evans, Robin W.; Jun, Insoo

    2008-01-01

    The degradation of the LM193 dual voltage comparator has been studied at different TID dose rate profiles, including several different constant dose rates and a variable dose rate that simulates the behavior of a solar flare. A comparison of results following constant dose rate vs. variable dose rates is made to explore how well the constant dose rates used for typical part testing predict the performance during a simulated space-like mission. Testing at a constant dose rate equal to the lowest dose rate seen during the simulated flare provides an extremely conservative estimate of the overall amount of degradation. A constant dose rate equal to the average dose rate is also more conservative than the variable rate. It appears that, for this part, weighting the dose rates by the amount of total dose received at each rate (rather than the amount of time at each dose rate) results in an average rate that produces an amount of degradation that is a reasonable approximation to that received by the variable rate.

  7. Tensile stress acoustic constants of unidirectional graphite/epoxy composites

    NASA Technical Reports Server (NTRS)

    Prosser, W. H.

    1990-01-01

    Previously, the stress acoustic constants (SACs) of unidirectional graphite/epoxy composites were measured to determine the nonlinear moduli of this material. These measurements were made under compressive loading in order to obtain the sufficient number of values needed to calculate these moduli. However, because their strength in tension along fiber directions can be several times greater, most composites are used under tensile loading. Thus, it is important to characterize the nonlinear properties of these materials in tension as well. The SACs which are defined as the slope of the normalized change in ultrasonic 'natural' velocity as a function of stress were measured in a unidirectional laminate of T300/5208 graphite/epoxy. Tensile load was applied along the fiber axis with the ultrasonic waves propagating perpendicular to the fiber direction. Changes in velocity were measured using a pulsed phase locked loop ultrasonic interferometer with the nominal frequency of the ultrasonic waves being 2.25 MHz.

  8. Tensile Stress Acoustic Constants of Unidirectional Graphite/Epoxy Composites

    NASA Technical Reports Server (NTRS)

    Prosser, W. H.

    1990-01-01

    Previously, the stress acoustic constants (SAC's) of unidirectional graphite/epoxy composites were measured to determine the nonlinear moduli of this material. These measurements were made under compressive loading in order to obtain the sufficient number of values needed to calculate these moduli. However, because their strength in tension along fiber directions can be several times greater, most composites are used under tensile loading. Thus, it is important to characterize the nonlinear properties of these materials in tension as well. The SAC's which are defined as the slope of the normalized change in ultrasonic "natural" velocity as a function of stress were measured in a unidirectional laminate of T300/5208 graphite/epoxy. Tensile load was applied along the fiber axis with the ultrasonic waves propagating perpendicular to the fiber direction. Changes in velocity were measured using a pulsed phase locked loop ultrasonic interferometer with the nominal frequency of the ultrasonic waves being 2.25 MHz.

  9. Constant stress of XD trademark TiAl containing nitrogen

    SciTech Connect

    Robertson, E.; Martin, P.L.

    1990-01-01

    Ti-47at%Al+7vol%(TiN+TiB{sub 2}) alloys, produced by the Martin Marietta XD{trademark} process, were subjected to tensile constant stress creep deformation in the range 760--850{degree}C temperature and 138--276 MPa (20--40 ksi) stress. These alloys have a matrix of TiAl and Ti{sub 3}Al initially containing 1 to 10 {mu}m diameter equiaxed particles of TiB{sub 2} and Ti{sub 2}AlN. Microstructures were examined using optical, SEM and TEM methods in an attempt to correlate the substructures with the property data. In particular, fine coherent particles have been observed to decorate dislocations and the interior of TiAl grains. The presence of these particles is thought to explain the creep resistance of this alloy. 14 refs., 5 figs.

  10. Reaction sintering of zinc ferrite during constant rates of heating

    SciTech Connect

    Rahaman, M.N. . Ceramic Engineering Dept.); De Jonghe, L.C. . Lawrence Berkeley Lab.)

    1993-07-01

    The reaction sintering of equimolar quantities of zinc oxide and ferric oxide was investigated under conditions of constant rates of heating and the data were compared with those for a calcined, single-phase zinc ferrite powder. For the heating rate of 1C/min, the densifications of the reaction-sintered sample and the calcined sample were approximately the same. However, as the heating rate increased, the density at any temperature increased slightly for the reaction-sintered sample but decreased slightly for the calcined powder. The factors responsible for this slight difference in sintering between the reaction-sintered sample and the calcined sample are discussed. For the constant heating rates used, the reaction was completed prior to any significant densification. Relative densities of >95% were obtained for both the reaction-sintered sample and the calcined sample under identical sintering conditions (1-10C/min to 1350C). Reaction sintering in a steep temperature gradient produced a nearly fully dense body prior to complete reaction; a composite microstructure consisting of fine zinc oxide grains in matrix of zinc ferrite was obtained.

  11. Stresses and elastic constants of crystalline sodium, from molecular dynamics

    SciTech Connect

    Schiferl, S.K.

    1985-02-01

    The stresses and the elastic constants of bcc sodium are calculated by molecular dynamics (MD) for temperatures to T = 340K. The total adiabatic potential of a system of sodium atoms is represented by pseudopotential model. The resulting expression has two terms: a large, strictly volume-dependent potential, plus a sum over ion pairs of a small, volume-dependent two-body potential. The stresses and the elastic constants are given as strain derivatives of the Helmholtz free energy. The resulting expressions involve canonical ensemble averages (and fluctuation averages) of the position and volume derivatives of the potential. An ensemble correction relates the results to MD equilibrium averages. Evaluation of the potential and its derivatives requires the calculation of integrals with infinite upper limits of integration, and integrand singularities. Methods for calculating these integrals and estimating the effects of integration errors are developed. A method is given for choosing initial conditions that relax quickly to a desired equilibrium state. Statistical methods developed earlier for MD data are extended to evaluate uncertainties in fluctuation averages, and to test for symmetry. 45 refs., 10 figs., 4 tabs.

  12. Divided Saddle Theory: A New Idea for Rate Constant Calculation.

    PubMed

    Daru, János; Stirling, András

    2014-03-11

    We present a theory of rare events and derive an algorithm to obtain rates from postprocessing the numerical data of a free energy calculation and the corresponding committor analysis. The formalism is based on the division of the saddle region of the free energy profile of the rare event into two adjacent segments called saddle domains. The method is built on sampling the dynamics within these regions: auxiliary rate constants are defined for the saddle domains and the absolute forward and backward rates are obtained by proper reweighting. We call our approach divided saddle theory (DST). An important advantage of our approach is that it requires only standard computational techniques which are available in most molecular dynamics codes. We demonstrate the potential of DST numerically on two examples: rearrangement of alanine-dipeptide (CH3CO-Ala-NHCH3) conformers and the intramolecular Cope reaction of the fluxional barbaralane molecule.

  13. Creep and aging of hard-sphere glasses under constant stress.

    PubMed

    Ballesta, P; Petekidis, G

    2016-04-01

    We investigate the aging behavior of glassy suspensions of nearly hard-sphere colloids submitted to a constant shear stress. For low stresses, below the yield stress, the system is subject to creep motion. As the sample ages, the shear rate exhibits a power-law decrease with time with exponents that depend on the sample age. We use a combination of rheological experiments with time-resolved photon correlation spectroscopy to investigate the time evolution of the sample dynamics under shear on various time and length scales. Long-time light-scattering experiments reveal the occurrence of microscopic rearrangement events that are linked with the macroscopic strain deformation of the sample. Dynamic time sweep experiments indicate that while the internal microscopic dynamics slow down continuously with waiting time, the storage and loss moduli are almost constant after a fast, weak decrease, resembling the behavior of quenched systems with partially frozen-in stresses.

  14. Creep and aging of hard-sphere glasses under constant stress

    NASA Astrophysics Data System (ADS)

    Ballesta, P.; Petekidis, G.

    2016-04-01

    We investigate the aging behavior of glassy suspensions of nearly hard-sphere colloids submitted to a constant shear stress. For low stresses, below the yield stress, the system is subject to creep motion. As the sample ages, the shear rate exhibits a power-law decrease with time with exponents that depend on the sample age. We use a combination of rheological experiments with time-resolved photon correlation spectroscopy to investigate the time evolution of the sample dynamics under shear on various time and length scales. Long-time light-scattering experiments reveal the occurrence of microscopic rearrangement events that are linked with the macroscopic strain deformation of the sample. Dynamic time sweep experiments indicate that while the internal microscopic dynamics slow down continuously with waiting time, the storage and loss moduli are almost constant after a fast, weak decrease, resembling the behavior of quenched systems with partially frozen-in stresses.

  15. Phototransformation rate constants of PAHs associated with soot particles.

    PubMed

    Kim, Daekyun; Young, Thomas M; Anastasio, Cort

    2013-01-15

    Photodegradation is a key process governing the residence time and fate of polycyclic aromatic hydrocarbons (PAHs) in particles, both in the atmosphere and after deposition. We have measured photodegradation rate constants of PAHs in bulk deposits of soot particles illuminated with simulated sunlight. The photodegradation rate constants at the surface (k(p)(0)), the effective diffusion coefficients (D(eff)), and the light penetration depths (z(0.5)) for PAHs on soot layers of variable thickness were determined by fitting experimental data with a model of coupled photolysis and diffusion. The overall disappearance rates of irradiated low molecular weight PAHs (with 2-3 rings) on soot particles were influenced by fast photodegradation and fast diffusion kinetics, while those of high molecular weight PAHs (with 4 or more rings) were apparently controlled by either the combination of slow photodegradation and slow diffusion kinetics or by very slow diffusion kinetics alone. The value of z(0.5) is more sensitive to the soot layer thickness than the k(p)(0) value. As the thickness of the soot layer increases, the z(0.5) values increase, but the k(p)(0) values are almost constant. The effective diffusion coefficients calculated from dark experiments are generally higher than those from the model fitting method for illumination experiments. Due to the correlation between k(p)(0) and z(0.5) in thinner layers, D(eff) should be estimated by an independent method for better accuracy. Despite some limitations of the model used in this study, the fitted parameters were useful for describing empirical results of photodegradation of soot-associated PAHs.

  16. Rate constants for diffusive processes by partial path sampling

    NASA Astrophysics Data System (ADS)

    Moroni, Daniele; Bolhuis, Peter G.; van Erp, Titus S.

    2004-03-01

    We introduce a path sampling method for the computation of rate constants for complex systems with a highly diffusive character. Based on the recently developed transition interface sampling (TIS) algorithm this procedure increases the efficiency by sampling only parts of complete transition trajectories. The algorithm assumes the loss of memory for diffusive progression along the reaction coordinate. We compare the new partial path technique to the TIS method for a simple diatomic system and show that the computational effort of the new method scales linearly, instead of quadratically, with the width of the diffusive barrier. The validity of the memory loss assumption is also discussed.

  17. Determination of acidity constants of curcumin in aqueous solution and apparent rate constant of its decomposition.

    PubMed

    Bernabé-Pineda, Margarita; Ramírez-Silva, María Teresa; Romero-Romo, Mario; González-Vergara, Enrique; Rojas-Hernández, Alberto

    2004-04-01

    The stability of curcumin (H3Cur) in aqueous media is improved when the systems in which it is present are at high pH values (higher than 11.7), fitting a model describable by a pseudo-zero order with a rate constant k' for the disappearance of the Cur3- species of 1.39 (10(-9)) Mmin(-1). There were three acidity constants measured for the curcumin as follows: pKA3 = 10.51 +/- 0.01 corresponding to the equilibrium HCur2- = Cur3- + H+, a pKA2 = 9.88 +/- 0.02 corresponding to the equilibrium H2Cur- = HCur-(2) + H+. These pKA values were attributed to the hydrogen of the phenol part of the curcumin, while the pKA1 = 8.38 +/- 0.04 corresponds to the equilibrium H3Cur = H2Cur- + H+ and is attributed the acetylacetone type group. Formation of quinoid structures play an important role in the tautomeric forms of the curcumin in aqueous media, which makes the experimental values differ from the theoretically calculated ones, depending on the conditions adopted in the study.

  18. Interpretation of the temperature dependence of equilibrium and rate constants.

    PubMed

    Winzor, Donald J; Jackson, Craig M

    2006-01-01

    The objective of this review is to draw attention to potential pitfalls in attempts to glean mechanistic information from the magnitudes of standard enthalpies and entropies derived from the temperature dependence of equilibrium and rate constants for protein interactions. Problems arise because the minimalist model that suffices to describe the energy differences between initial and final states usually comprises a set of linked equilibria, each of which is characterized by its own energetics. For example, because the overall standard enthalpy is a composite of those individual values, a positive magnitude for DeltaH(o) can still arise despite all reactions within the subset being characterized by negative enthalpy changes: designation of the reaction as being entropy driven is thus equivocal. An experimenter must always bear in mind the fact that any mechanistic interpretation of the magnitudes of thermodynamic parameters refers to the reaction model rather than the experimental system. For the same reason there is little point in subjecting the temperature dependence of rate constants for protein interactions to transition-state analysis. If comparisons with reported values of standard enthalpy and entropy of activation are needed, they are readily calculated from the empirical Arrhenius parameters.

  19. Rate constants from instanton theory via a microcanonical approach

    NASA Astrophysics Data System (ADS)

    McConnell, Sean R.; Löhle, Andreas; Kästner, Johannes

    2017-02-01

    Microcanonical instanton theory offers the promise of providing rate constants for chemical reactions including quantum tunneling of atoms over the whole temperature range. We discuss different rate expressions, which require the calculation of stability parameters of the instantons. The traditional way of obtaining these stability parameters is shown to be numerically unstable in practical applications. We provide three alternative algorithms to obtain such stability parameters for non-separable systems, i.e., systems in which the vibrational modes perpendicular to the instanton path couple to movement along the path. We show the applicability of our algorithms on two molecular systems: H2 + OH → H2O + H using a fitted potential energy surface and HNCO + H → NH2CO using a potential obtained on-the-fly from density functional calculations.

  20. Unsteady flow past an airfoil pitched at constant rate

    NASA Technical Reports Server (NTRS)

    Lourenco, L.; Vandommelen, L.; Shib, C.; Krothapalli, A.

    1992-01-01

    The unsteady flow past a NACA 0012 airfoil that is undertaking a constant-rate pitching up motion is investigated experimentally by the PIDV technique in a water towing tank. The Reynolds number is 5000, based upon the airfoil's chord and the free-stream velocity. The airfoil is pitching impulsively from 0 to 30 deg. with a dimensionless pitch rate alpha of 0.131. Instantaneous velocity and associated vorticity data have been acquired over the entire flow field. The primary vortex dominates the flow behavior after it separates from the leading edge of the airfoil. Complete stall emerges after this vortex detaches from the airfoil and triggers the shedding of a counter-rotating vortex near the trailing edge. A parallel computational study using the discrete vortex, random walk approximation has also been conducted. In general, the computational results agree very well with the experiment.

  1. Oxidation kinetics of zinc sulfide: determination of intrinsic rate constant

    SciTech Connect

    Prabhu, G.M.

    1983-06-01

    An initial reaction rate study was done with the help of a thermogravimetric technique. Energy dispersive x-ray analyses on partially oxidized zinc sulfide pellets with a sintered porosity of 72.4% indicated flat sulfur intensity profiles within pellets reacted below 560/sup 0/C, which suggested a homogeneous reaction mechanism. Therefore, reaction temperatures below 600/sup 0/C were chosen for the reaction rate studies. Initial reaction rate studies on 72.4, 58.2, and 34.0% porous, cylindrical zinc sulfide pellets and the corresponding Arrhenius plot suggested chemical control in the temperature range from 480 to 565/sup 0/C. The corresponding intrinsic rate constant is correlated as k = 3.45 x 10/sup 17/ exp (- 86051/RT) cm/s. The variation in sulfur intensity within sintered pellets having a porosity of 72.4% that were reacted at temperatures above 560/sup 0/C indicated that the pore diffusion resistance gradually became comparable to the chemical reaction resistance leading to a mixed control mechanism above 570/sup 0/C. The critical temperature at which this shift occurred, increased with pellet porosity.

  2. Analysis of constant false alarm rate sidelobe canceller criterion

    NASA Astrophysics Data System (ADS)

    Reed, I. S.; Brennan, L. E.

    1985-05-01

    In this final report, the constant false alarm rate (CFAR) detection criterion for a sidelobe canceller (SLC) system, introduced in the last quarterly progress report, is found completely and analyzed. This new detection test for radar exhibits the desirable CFAR property that its probability of a false alarm (PFA) is functionally independent of the covariance of the actual noise field encountered. As a consequence, such a CFAR SLC system is ideally suited to cope with the newly evolving smart jammer threat to radar. An important objective, set in the last quarterly progress report, was to find both the false alarm and signal detection probabilities of this test. The first and most important of these two goals has been met. The probability of a false alarm (or PFA) of this CFAR SLC detection criterion is derived in closed form in this report. The success in finding the PFA is due primarily to the use of a generalization of Cochran's theorem.

  3. On reaction rate constants IO+NO, IO+CO

    NASA Astrophysics Data System (ADS)

    Larin, Igor; Spasskiy, Alexandr; Trofimova, Elen

    2013-04-01

    A method, allowing to define, whether an investigated chemical reaction in a gas phase or on a surface of a reactor for those cases when dependence of the reaction rate on concentration of reagents for heterogeneous and for homogeneous reaction are identical, has been suggested. The method has been used for investigation of reactions of IO with nitric oxide and carbon monoxide. Experiments have been run in the flow reactor with using a method of resonance fluorescence to record atoms of iodine. It has been proved that the reaction of radical IO with nitric oxide proceeds in the gas phase, whereas the reaction of radical IO with carbon monoxide proceeds on the surface of the reactor. It has been obtained that reaction rate constant of IO with nitrogen monoxide in the temperature range 298-353 K is kNO(T)=(1,01±0,2)•10^-11•exp((210±80)/T) cm3*molecule*s-1 and the same for reaction of IO with carbon monoxide is kCO(T)=(1,14±0,64)•10^-14•exp((612±41)/T) cm3*molecule*s-1.

  4. Rate Constant for the OH + CO Reaction at Low Temperatures.

    PubMed

    Liu, Yingdi; Sander, Stanley P

    2015-10-01

    Rate constants for the reaction of OH + CO → products (1) have been measured using laser photolysis/laser-induced fluorescence (LP/LIF) over the temperature range 193–296 K and at pressures of 50–700 Torr of Ar and N2. The reaction was studied under pseudo-first-order conditions, monitoring the decay of OH in the presence of a large excess of CO. The rate constants can be expressed as a combination of bimolecular and termolecular components. The bimolecular component was found to be temperature-independent with an expression given by kbi(T) = (1.54 ± 0.14) × 10(–13)[e(–(13±17)/T)] cm(3) molecule(–1) s(–1), with an error of one standard deviation. The termolecular component was fitted to the expression, kter = k0(T)[M]/[1 + (k0(T)[M]/k∞(T)] × 0.6({1+[log10(k0(T)[M]/k∞(T))]2}−1) where k0(T) = k0(300)(T/300)(−n) and k∞(T) = k∞(300)(T/300)(−m). The parameters for k0(T) were determined to be k0(300) = (6.0±0.5) × 10(−33) cm(6) molecule(–2) s(–1) in N2 and k0(300) = (3.4 ± 0.3) × 10(–33) cm(6) molecule(–2) s(–1) in Ar, with n = 1.9±0.5 and 2.0±0.4 in N2 and Ar, respectively. These parameters were determined using k0(T) and m from the NASA kinetics data evaluation (JPL Publication No. 10-6) since the experimental pressure range was far from the high-pressure limit. Addition of low concentrations of O2 had no discernible effect on the mechanism of the OH + CO reaction but resulted in secondary reactions which regenerated OH.

  5. [Comparison of propofol and propanidid administered at a constant rate].

    PubMed

    Deschodt, J; Lubrano, J F; Peschaud, J L; Eledjam, J J; du Cailar, J

    1988-01-01

    So as to compare the anaesthesia obtained using propofol with that obtained using propanidid, 40 ASA I patients, aged between 18 and 50 years, who were to undergo elective orthopaedic or plastic surgery lasting more than 60 min, were randomly divided into two equal groups, one receiving propofol (PF) and the other propanidid (PD). All the patients received 0.5 mg atropine, 100 mg pethidine and 7.5 mg droperidol (10 mg if weight greater than 60 kg) intramuscularly 45 min before induction. Patients in group PF were then given 2 mg.kg-1 propofol over 1 min and 0.9 microgram.kg-1 fentanyl over 3 min, followed by a constant rate infusion of 5 mg.kg-1.h-1 propofol and 3 micrograms.kg-1.h-1 fentanyl. For PD patients, the doses of fentanyl were identical; they were given 10.6 mg.kg-1 propanidid over 3 min for induction, and 37 mg.kg-1.h-1 for maintenance. All the patients were intubated and ventilated mechanically. The usual anaesthetic parameters were monitored at induction, during surgery, and during recovery. Consciousness was lost more quickly with propofol (p less than 0.05), but the corneal reflex returned more rapidly in group PD (p less than 0.02). The time required for a full return to normal consciousness was identical in both groups. The fall, during induction, and the increase, during recovery, of Pasys were greater in group PD (p less than 0.05 and less than 0.001 respectively). Padia and heart rate were lower in group PF after the 30th min (p less than 0.05 and less than 0.01 respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

  6. Measurement of both the equilibrium constant and rate constant for electronic energy transfer by control of the limiting kinetic regimes.

    PubMed

    Vagnini, Michael T; Rutledge, W Caleb; Wagenknecht, Paul S

    2010-02-01

    Electronic energy transfer can fall into two limiting cases. When the rate of the energy transfer back reaction is much faster than relaxation of the acceptor excited state, equilibrium between the donor and acceptor excited states is achieved and only the equilibrium constant for the energy transfer can be measured. When the rate of the back reaction is much slower than relaxation of the acceptor, the energy transfer is irreversible and only the forward rate constant can be measured. Herein, we demonstrate that with trans-[Cr(d(4)-cyclam)(CN)(2)](+) as the donor and either trans-[Cr([15]ane-ane-N(4))(CN)(2)](+) or trans-[Cr(cyclam)(CN)(2)](+) as the acceptor, both limits can be obtained by control of the donor concentration. The equilibrium constant and rate constant for the case in which trans-[Cr([15]ane-ane-N(4))(CN)(2)](+) is the acceptor are 0.66 and 1.7 x 10(7) M(-1) s(-1), respectively. The equilibrium constant is in good agreement with the value of 0.60 determined using the excited state energy gap between the donor and acceptor species. For the thermoneutral case in which trans-[Cr(cyclam)(CN)(2)](+) is the acceptor, an experimental equilibrium constant of 0.99 was reported previously, and the rate constant has now been measured as 4.0 x 10(7) M(-1) s(-1).

  7. Robust Biased Brownian Dynamics for Rate Constant Calculation

    PubMed Central

    Zou, Gang; Skeel, Robert D.

    2003-01-01

    A reaction probability is required to calculate the rate constant of a diffusion-dominated reaction. Due to the complicated geometry and potentially high dimension of the reaction probability problem, it is usually solved by a Brownian dynamics simulation, also known as a random walk or path integral method, instead of solving the equivalent partial differential equation by a discretization method. Building on earlier work, this article completes the development of a robust importance sampling algorithm for Brownian dynamics—i.e., biased Brownian dynamics with weight control—to overcome the high energy and entropy barriers in biomolecular association reactions. The biased Brownian dynamics steers sampling by a bias force, and the weight control algorithm controls sampling by a target weight. This algorithm is optimal if the bias force and the target weight are constructed from the solution of the reaction probability problem. In reality, an approximate reaction probability has to be used to construct the bias force and the target weight. Thus, the performance of the algorithm depends on the quality of the approximation. Given here is a method to calculate a good approximation, which is based on the selection of a reaction coordinate and the variational formulation of the reaction probability problem. The numerically approximated reaction probability is shown by computer experiments to give a factor-of-two speedup over the use of a purely heuristic approximation. Also, the fully developed method is compared to unbiased Brownian dynamics. The tests for human superoxide dismutase, Escherichia coli superoxide dismutase, and antisweetener antibody NC6.8, show speedups of 17, 35, and 39, respectively. The test for reactions between two model proteins with orientations shows speedups of 2578 for one set of configurations and 3341 for another set of configurations. PMID:14507681

  8. Diurnal rhythm of the pituitary-adrenocortical response to stress: effect of constant light and constant darkness

    NASA Technical Reports Server (NTRS)

    Vernikos-Danellis, J.; Winget, C. M.; Hetherington, N. W.

    1970-01-01

    The existence of a biological rhythm in the response of animals to noxious stimuli and drugs is well known. However, the mechanism of this response is not well understood. This study was undertaken to describe the existence of a diurnal rhythm in the hypothalamic-pituitary-adrenocortical system before and after stress in female rats kept in controlled environmental conditions in 12L:12D, 24L:OD, or OL:24D. Plasma ACTH and plasma corticosterone concentrations were compared in unstressed animals. The time pattern in the response to stress was determined at four hourly intervals during a 24 hr period in which plasma ACTH and plasma corticosterone were measured at different time intervals. The stress response varied considerably with time of day in both magnitude and duration. The adrenals of rats exposed to constant light for 45 days atrophied, whereas the adrenals of animals kept in constant dark for the same period did not differ significantly from those of controls kept in 12L:12D. The increase in plasma ACTH in response to stress was greater both in the animals maintained in constant light and in constant dark than in the 12L:12D controls. Homeostatic mechanisms involved in these changes are discussed.

  9. Diurnal rhythm of the pituitary-adrenocortical response to stress: effect of constant light and constant darkness

    NASA Technical Reports Server (NTRS)

    Vernikos-Danellis, J.; Winget, C. M.; Hetherington, N. W.

    1970-01-01

    The existence of a biological rhythm in the response of animals to noxious stimuli and drugs is well known. However, the mechanism of this response is not well understood. This study was undertaken to describe the existence of a diurnal rhythm in the hypothalamic-pituitary-adrenocortical system before and after stress in female rats kept in controlled environmental conditions in 12L:12D, 24L:OD, or OL:24D. Plasma ACTH and plasma corticosterone concentrations were compared in unstressed animals. The time pattern in the response to stress was determined at four hourly intervals during a 24 hr period in which plasma ACTH and plasma corticosterone were measured at different time intervals. The stress response varied considerably with time of day in both magnitude and duration. The adrenals of rats exposed to constant light for 45 days atrophied, whereas the adrenals of animals kept in constant dark for the same period did not differ significantly from those of controls kept in 12L:12D. The increase in plasma ACTH in response to stress was greater both in the animals maintained in constant light and in constant dark than in the 12L:12D controls. Homeostatic mechanisms involved in these changes are discussed.

  10. Rate constants measured for hydrated electron reactions with peptides and proteins

    NASA Technical Reports Server (NTRS)

    Braams, R.

    1968-01-01

    Effects of ionizing radiation on the amino acids of proteins and the reactivity of the protonated amino group depends upon the pK subscript a of the group. Estimates of the rate constants for reactions involving the amino acid side chains are presented. These rate constants gave an approximate rate constant for three different protein molecules.

  11. Estimating hydraulic properties of volcanic aquifers using constant-rate and variable-rate aquifer tests

    USGS Publications Warehouse

    Rotzoll, K.; El-Kadi, A. I.; Gingerich, S.B.

    2007-01-01

    In recent years the ground-water demand of the population of the island of Maui, Hawaii, has significantly increased. To ensure prudent management of the ground-water resources, an improved understanding of ground-water flow systems is needed. At present, large-scale estimations of aquifer properties are lacking for Maui. Seven analytical methods using constant-rate and variable-rate withdrawals for single wells provide an estimate of hydraulic conductivity and transmissivity for 103 wells in central Maui. Methods based on constant-rate tests, although not widely used on Maui, offer reasonable estimates. Step-drawdown tests, which are more abundantly used than other tests, provide similar estimates as constant-rate tests. A numerical model validates the suitability of analytical solutions for step-drawdown tests and additionally provides an estimate of storage parameters. The results show that hydraulic conductivity is log-normally distributed and that for dike-free volcanic rocks it ranges over several orders of magnitude from 1 to 2,500 m/d. The arithmetic mean, geometric mean, and median values of hydraulic conductivity are respectively 520, 280, and 370 m/d for basalt and 80, 50, and 30 m/d for sediment. A geostatistical approach using ordinary kriging yields a prediction of hydraulic conductivity on a larger scale. Overall, the results are in agreement with values published for other Hawaiian islands. ?? 2007 American Water Resources Association.

  12. Comparison of the quantitative performance of constant pressure versus constant flow rate gradient elution separations using concentration-sensitive detectors.

    PubMed

    Verstraeten, M; Broeckhoven, K; Lynen, F; Choikhet, K; Dittmann, M; Witt, K; Sandra, P; Desmet, G

    2012-04-06

    This contribution discusses the difference in chromatographic performance when switching from the customary employed constant flow rate gradient elution mode to the recently re-introduced constant pressure gradient elution mode. In this mode, the inlet pressure is maintained at a set value even when the mobile phase viscosity becomes lower than the maximum mobile phase viscosity encountered during the gradient program. This leads to a higher average flow rate compared to the constant flow rate mode and results in a shorter analysis time. When both modes carry out the same mobile phase gradient program in volumetric units, normally identical selectivities are obtained. However, small deviations in selectivity are found due to the differences in pressure and viscous heating effects. These selectivity differences are of the same type as those observed when switching from HPLC to UHPLC and are inevitable when speeding up the analysis by applying a higher pressure. It was also found that, when using concentration-sensitive detectors, the constant pressure elution mode leads to identical peak areas as the constant flow rate mode. Also the linearity is maintained. In addition, the repeatability of the peak area and retention time remains the same when switching between both elution modes.

  13. The temperature dependence of the rate constant for the reaction of hydroxyl radicals with nitric acid

    NASA Technical Reports Server (NTRS)

    Kurylo, M. J.; Cornett, K. D.; Murphy, J. L.

    1982-01-01

    The rate constant for the reaction of hydroxyl radicals with nitric acid in the 225-443 K temperature range has been measured by means of the flash photolysis resonance fluorescence technique. Above 300 K, the rate constant levels off in a way that can only be explained by the occurrence of two reaction channels, of which one, operative at low temperatures, proceeds through the formation of an adduct intermediate. The implications of these rate constant values for stratospheric reaction constants is discussed.

  14. The temperature dependence of the rate constant for the reaction of hydroxyl radicals with nitric acid

    NASA Technical Reports Server (NTRS)

    Kurylo, M. J.; Cornett, K. D.; Murphy, J. L.

    1982-01-01

    The rate constant for the reaction of hydroxyl radicals with nitric acid in the 225-443 K temperature range has been measured by means of the flash photolysis resonance fluorescence technique. Above 300 K, the rate constant levels off in a way that can only be explained by the occurrence of two reaction channels, of which one, operative at low temperatures, proceeds through the formation of an adduct intermediate. The implications of these rate constant values for stratospheric reaction constants is discussed.

  15. Determination of Rate Constants and Equilibrium Constants for Solution-Phase Drug–Protein Interactions by Ultrafast Affinity Extraction

    PubMed Central

    2015-01-01

    A method was created on the basis of ultrafast affinity extraction to determine both the dissociation rate constants and equilibrium constants for drug–protein interactions in solution. Human serum albumin (HSA), an important binding agent for many drugs in blood, was used as both a model soluble protein and as an immobilized binding agent in affinity microcolumns for the analysis of free drug fractions. Several drugs were examined that are known to bind to HSA. Various conditions to optimize in the use of ultrafast affinity extraction for equilibrium and kinetic studies were considered, and several approaches for these measurements were examined. The dissociation rate constants obtained for soluble HSA with each drug gave good agreement with previous rate constants reported for the same drugs or other solutes with comparable affinities for HSA. The equilibrium constants that were determined also showed good agreement with the literature. The results demonstrated that ultrafast affinity extraction could be used as a rapid approach to provide information on both the kinetics and thermodynamics of a drug–protein interaction in solution. This approach could be extended to other systems and should be valuable for high-throughput drug screening or biointeraction studies. PMID:24911267

  16. Determination of rate constants and equilibrium constants for solution-phase drug-protein interactions by ultrafast affinity extraction.

    PubMed

    Zheng, Xiwei; Li, Zhao; Podariu, Maria I; Hage, David S

    2014-07-01

    A method was created on the basis of ultrafast affinity extraction to determine both the dissociation rate constants and equilibrium constants for drug-protein interactions in solution. Human serum albumin (HSA), an important binding agent for many drugs in blood, was used as both a model soluble protein and as an immobilized binding agent in affinity microcolumns for the analysis of free drug fractions. Several drugs were examined that are known to bind to HSA. Various conditions to optimize in the use of ultrafast affinity extraction for equilibrium and kinetic studies were considered, and several approaches for these measurements were examined. The dissociation rate constants obtained for soluble HSA with each drug gave good agreement with previous rate constants reported for the same drugs or other solutes with comparable affinities for HSA. The equilibrium constants that were determined also showed good agreement with the literature. The results demonstrated that ultrafast affinity extraction could be used as a rapid approach to provide information on both the kinetics and thermodynamics of a drug-protein interaction in solution. This approach could be extended to other systems and should be valuable for high-throughput drug screening or biointeraction studies.

  17. Constant rate control algorithm for Wyner-Ziv video codec

    NASA Astrophysics Data System (ADS)

    Jakubowski, Mariusz

    2009-06-01

    In a distributed video coding (DVC) system, the total bit-rate depends on bit-rate of the key frames (Intra frames) and the Wyner-Ziv (WZ) frames. The key frames bit-rate is relatively easy to control since they are encoded with an Intra coding scheme (e.g. H.264/AVC Intra), and there are many proposed solutions in literature which address this issue1, 2. On the other hand, rate control (RC) of the WZ frames at the encoder is more difficult since the bit-rate of WZ frames is difficult to predict and control due to the absence of the side information at the decoder side. In this work, an RC algorithm developed within the VISNET II, the European Network of Excellence, is presented as an efficient solution to achieve and maintain the target bit-rate for the overall Intra frames and WZ bitstream, mainly by changing the degree of compression of the Intra frames which is controlled by quantization parameter (QP). In order to maintain a similar quality for the Intra and WZ frames, the WZ quantization index (QIndex) follows the QP changes. A statistical model is used to describe the relationship between QIndex and the WZ frames bit-rate. Additionally, an analysis of influence of the key frames residuum complexity on WZ frames bitrate was conducted. The proposed algorithm adapted to the VISNET2 WZ video codec3 confirms its efficiency in terms of achieving and maintaining the target bit-rate.

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

    PubMed

    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.

  19. Iterative rate-distortion optimization of H.264 with constant bit rate constraint.

    PubMed

    An, Cheolhong; Nguyen, Truong Q

    2008-09-01

    In this paper, we apply the primal-dual decomposition and subgradient projection methods to solve the rate-distortion optimization problem with the constant bit rate constraint. The primal decomposition method enables spatial or temporal prediction dependency within a group of picture (GOP) to be processed in the master primal problem. As a result, we can apply the dual decomposition to minimize independently the Lagrangian cost of all the MBs using the reference software model of H.264. Furthermore, the optimal Lagrange multiplier lambda* is iteratively derived from the solution of the dual problem. As an example, we derive the optimal bit allocation condition with the consideration of temporal prediction dependency among the pictures. Experimental results show that the proposed method achieves better performance than the reference software model of H.264 with rate control.

  20. The vibrational dependence of dissociative recombination: Rate constants for N{sub 2}{sup +}

    SciTech Connect

    Guberman, Steven L.

    2014-11-28

    Dissociative recombination rate constants are reported with electron temperature dependent uncertainties for the lowest 5 vibrational levels of the N{sub 2}{sup +} ground state. The rate constants are determined from ab initio calculations of potential curves, electronic widths, quantum defects, and cross sections. At 100 K electron temperature, the rate constants overlap with the exception of the third vibrational level. At and above 300 K, the rate constants for excited vibrational levels are significantly smaller than that for the ground level. It is shown that any experimentally determined total rate constant at 300 K electron temperature that is smaller than 2.0 × 10{sup −7} cm{sup 3}/s is likely to be for ions that have a substantially excited vibrational population. Using the vibrational level specific rate constants, the total rate constant is in very good agreement with that for an excited vibrational distribution found in a storage ring experiment. It is also shown that a prior analysis of a laser induced fluorescence experiment is quantitatively flawed due to the need to account for reactions with unknown rate constants. Two prior calculations of the dissociative recombination rate constant are shown to be inconsistent with the cross sections upon which they are based. The rate constants calculated here contribute to the resolution of a 30 year old disagreement between modeled and observed N{sub 2}{sup +} ionospheric densities.

  1. Universality of Thermodynamic Constants Governing Biological Growth Rates

    PubMed Central

    Corkrey, Ross; Olley, June; Ratkowsky, David; McMeekin, Tom; Ross, Tom

    2012-01-01

    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. PMID:22348140

  2. Inversion of Spectral Lineshapes to Yield Collision Rate Constants.

    DTIC Science & Technology

    1981-07-15

    Rates for Highly Vibrationally Excited Molecules", J. Chem. Phys. 74, 5031 (1981). 4. E. Wilczek, J. BelBruno and J. Gelfand, " Voigt Profiles of Spectral ... Lines : Accuracy of Line Parameters as a Function of Peak Transmittance", Applied Spectroscopy , in press (1981). 5. J. BelBruno, M. Zughul, J. Gelfand...and H.Rabitz, "Analysis of Collision- Broadened and Overlapping Spectral Lines to Obtain Individual Line Param- eters", J. Mol. Spec., in press (1981

  3. The effect of temperature fluctuations of reaction rate constants in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Chinitz, W.; Antaki, P. J.; Kassar, G. M.

    1981-01-01

    Current models of turbulent reacting flows frequently use Arrhenius reaction rate constants obtained from static or laminar flow theory and/or experiments, or from best fits of static, laminar, and turbulent data. By treating the reaction rate constant as a continuous random variable which is temperature-dependent, the present study assesses the effect of turbulent temperature fluctuations on the reaction rate constant. This model requires that a probability density function (PDF) describing the nature of the fluctuations be specified. Three PDFs are examined: the clipped Gaussian, the beta PDF, and the ramp model. All the models indicate that the reaction rate constant is greater in a turbulent flow field than in an equivalent laminar flow. In addition, an amplification ratio, which is the ratio of the turbulent rate constant to the laminar rate constant, is defined and its behavior as a function of the mean temperature fluctuations is described

  4. The effect of temperature fluctuations of reaction rate constants in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Chinitz, W.; Antaki, P. J.; Kassar, G. M.

    1981-01-01

    Current models of turbulent reacting flows frequently use Arrhenius reaction rate constants obtained from static or laminar flow theory and/or experiments, or from best fits of static, laminar, and turbulent data. By treating the reaction rate constant as a continuous random variable which is temperature-dependent, the present study assesses the effect of turbulent temperature fluctuations on the reaction rate constant. This model requires that a probability density function (PDF) describing the nature of the fluctuations be specified. Three PDFs are examined: the clipped Gaussian, the beta PDF, and the ramp model. All the models indicate that the reaction rate constant is greater in a turbulent flow field than in an equivalent laminar flow. In addition, an amplification ratio, which is the ratio of the turbulent rate constant to the laminar rate constant, is defined and its behavior as a function of the mean temperature fluctuations is described

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

    PubMed

    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.

  6. Measuring kinetic rate constants of multiple-component reactions with optical biosensors.

    PubMed

    Edwards, David A; Evans, Ryan M; Li, Wenbin

    2017-09-15

    One may measure the kinetic rate constants associated with biochemical reactions using an optical biosensor: an instrument in which ligand molecules are convected through a flow cell over a surface to which receptors are immobilized. If there are multiple reactants, one is faced with the problem of fitting multiple kinetic rate constants to one signal, since data from all of the reacting species is lumped together. Even in the presence of ambiguous data, one may use a series of experiments to accurately determine the rate constants. Moreover, the true set of rate constants may be identified by either postprocessing the signals or adjusting the ligand inflow concentrations. Published by Elsevier Inc.

  7. Algebraic methods for deriving steady-state rate equations. Practical difficulties with mechanisms that contain repeated rate constants.

    PubMed Central

    Cornish-Bowden, A

    1976-01-01

    Methods of deriving rate equations that rely on repetition of terms for identification of redundant or invalid terms give incorrect results if used with mechanisms in which some rate constants appear more than once. PMID:999635

  8. Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes, Cycloalkanes, and Dimethyl Ether

    NASA Technical Reports Server (NTRS)

    DeMore, W.; Bayes, K.

    1998-01-01

    Relative rate experiements were used to measure rate constants and temperature denpendencies of the reactions of OH with propane, n-butane, n-pentane, n-hexane, cyclopropane, cyclobutane, cyclopentane, and dimethyl ether.

  9. Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes, Cycloalkanes, and Dimethyl Ether

    NASA Technical Reports Server (NTRS)

    DeMore, W.; Bayes, K.

    1998-01-01

    Relative rate experiements were used to measure rate constants and temperature denpendencies of the reactions of OH with propane, n-butane, n-pentane, n-hexane, cyclopropane, cyclobutane, cyclopentane, and dimethyl ether.

  10. Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 3; Constant Stress and Cyclic Stress Experiments

    NASA Technical Reports Server (NTRS)

    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 advanced structural ceramics tested under constant stress and cyclic stress loading at ambient and elevated temperatures. The data fit to the relation between the time to failure and applied stress (or maximum applied stress in cyclic loading) was very reasonable for most of the materials studied. It was also found that life prediction for cyclic stress loading from data of constant stress loading in the exponential formulation was in good agreement with the experimental data, resulting in a similar degree of accuracy as compared with the power-law formulation. 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 slow-crack-growth (SCG) parameter n, a significant drawback as compared with the conventional power-law crack-velocity formulation.

  11. STATUS OF IN-REACTOR TENSILE STRAINING OF PURE COPPER AT A CONSTANT STRAIN RATE

    SciTech Connect

    Edwards, Danny J.; Singh, Bachu N.; Tahtinen, S.; Moilanen, P.; Jacquet, P.; Dekeyser, J.

    2003-09-03

    Annealed tensile samples of pure copper were irradiated in the fission reactor BR-2 in Mol, Belgium at 90 degrees C with a damage rate of 0.00000006 dpa/sec. The tensile specimens were a sheet-type specimen with a 3-mm gage width and a gage length of 7 mm. The first experiment involved two specimens, one of which was irradiated with no load to provide a comparative specimen to the other specimen, which was loaded at a constant strain rate of 0.00000013 1/s. The uniaxial tensile load was applied 4 hrs after the irradiation rig was inserted into the reactor core. This corresponded to a total displacement damage of 0.00086 dpa accumulated before the tensile test was started. The tensile test was considered complete once the load began rapidly falling and reached 100 MPa, at which level the test was stopped and the load quickly reduced to zero to leave the specimen intact. For these test conditions the specimen reached a total plastic strain of approximately 13 percent when the test was stopped, considerably less than that of unirradiated pure copper tested under the same strain rate, which was on the order of 50 percent total elongation. The second experiment involved two samples irradiated under identical irradiation and test conditions, but in this case the tensile load was not applied until a total dose of 0.01 dpa (approximately 50 hours after insertion into the reactor core) was reached. Once the load was applied, the stress immediately climbed to approximately 150 MPa with little plastic strain, followed by a small yield drop and work hardening up to a maximum stress of approximately 200 MPa. As in the first experiment, the tensile test was stopped when the load began decreasing and reached a level of 100 MPa.

  12. Delay discounting of hypothetical and real money: the effect of holding reinforcement rate constant.

    PubMed

    Dixon, Mark R; Lik, Nicholas Mui Ker; Green, Leonard; Myerson, Joel

    2013-01-01

    We examined the effect of holding reinforcement rate constant on delay discounting of hypothetical and real money when delays were actually experienced. In some conditions, participants were required to wait for the delayed rewards, and in some conditions, reinforcement rate was held constant by adding blackout periods after immediate rewards. Typical discounting occurred with the standard procedure and when there were no blackouts, but not when we held rate of reinforcement constant. Real and hypothetical money produced the same outcomes. © Society for the Experimental Analysis of Behavior.

  13. Rate constant for the fraction of atomic chlorine with formaldehyde from 200 to 500K

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

    A flash photolysis - resonance fluorescence technique was used to measure rate constant. The results were independent of substantial variations in H2CO, total pressure (Ar), and flash intensity (i.e., initial Cl). The rate constant was shown to be invariant with temperature, the best representation for this temperature range being K = (7.48 + or - 0.50) x 10 to the minus 11 power cu cm molecule-1 s-1 where the error is one standard deviation. The rate constant is theoretically discussed and the potential importance of the reaction in stratospheric chemistry is considered.

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

    PubMed

    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

  15. Rate constants of the reaction of C2-C4 peroxy radicals with OH radicals

    NASA Astrophysics Data System (ADS)

    Assaf, Emmanuel; Tanaka, Shisei; Kajii, Yoshizumi; Schoemaecker, Coralie; Fittschen, Christa

    2017-09-01

    The rate constants for the reaction of three peroxy radicals with OH have been measured using different precursors. Peroxy radicals have been prepared by either the reaction of Cl-atoms with C2H6, C3H8 and n-C4H10 or through photolysis of the corresponding alkyliodide. Using Cl-atoms, the following rate constants have been measured: Experiments using 248 nm photolysis of the corresponding alkyliodides as precursor enhances the rate constants by a factor of two, bringing up the suspicion of a fast reaction between I-atoms and OH radicals.

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

    SciTech Connect

    Osborne, David; Lawson, Patrick; Adams, Nigel

    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.

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

    NASA Astrophysics Data System (ADS)

    Osborne, David; Lawson, Patrick; Adams, Nigel

    2014-01-01

    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.

  18. The effects of molecular weight on the single lap shear creep and constant strain rate behavior of thermoplastic polyimidesulfone adhesive

    NASA Technical Reports Server (NTRS)

    Dembosky, Stanley K.; Sancaktar, Erol

    1985-01-01

    The bonded shear creep and constant strain rate behaviors of zero, one, and three percent endcapped thermoplastic polyimidesulfone adhesive were examined at room and elevated temperatures. Endcapping was accomplished by the addition of phthalic anhydrides. The primary objective was to determine the effects of molecular weight on the mechanical properties of the adhesive. Viscoelastic and nonlinear elastic constitutive equations were utilized to model the adhesive. Ludwik's and Crochet's relations were used to describe the experimental failure data. The effects of molecular weight changes on the above mentioned mechanical behavior were assessed. The viscoelastic Chase-Goldsmith and elastic nonlinear relations gave a good fit to the experimental stress strain behavior. Crochet's relations based on Maxwell and Chase-Goldsmith models were fit to delayed failure data. Ludwik's equations revealed negligible rate dependence. Ultimate stress levels and the safe levels for creep stresses were found to decrease as molecular weight was reduced.

  19. Strain rate effects in stress corrosion cracking

    SciTech Connect

    Parkins, R.N. . Dept. of Metallurgy and Engineering Materials)

    1990-03-01

    Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals an environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependence of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this may be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crack growth kinetics.

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

    PubMed

    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.

  1. Absolute rate constant for the reaction of Cl(/sup 2/P) with CINO

    SciTech Connect

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

    1987-09-24

    The room temperature rate constant for the reaction Cl + CINO yields Cl/sub 2/ + NO has been measured by the method of discharge flow mass spectrometry. The rate constant was determined from the decay of CINO in the presence of an excess of Cl atoms at a total pressure of 1 Torr. The rate constant obtained was (7.6 +/- 0.8) X 10/sup -11/ cm/sup 3/ s/sup -1/. This result is compared with previous determinations, the values of which ranged by more than an order of magnitude and all of which depended on knowledge of the absolute concentration of CINO. The authors suggest that the lack of agreement is attributable principally to uncertainties in (CINO) resulting from absorption of this reactive species on glass and metal surfaces. Our result does not depend directly on (CINO) and supports the highest values published for this rate constant.

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

    EPA Science Inventory

    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...

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

    EPA Science Inventory

    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...

  4. The Hydroxyl Radical Reaction Rate Constant and Products of Dimethyl Succinate

    DTIC Science & Technology

    2008-03-01

    AFRL-RX-TY-TR-2008-4522 THE HYDROXYL RADICAL REACTION RATE CONSTANT AND PRODUCTS OF DIMETHYL SUCCINATE Sheryl E. Calidonna and...the gas-phase hydroxyl radical reaction with dimethyl succinate. Additional reports and publications resulting from this work unit are not described...herein but are listed below for reference. Baxley, J.Steven and J.R. Wells, “The Hydroxyl Radical Rate Constant and Atmospheric Transforamtion

  5. Characterization of Iodine Quenching and Energy Transfer Rate Constants for Supersonic Flow Visualization Applications

    DTIC Science & Technology

    2007-09-28

    SUBTITLE Sm. CONTRACTNUBER Characterization of iodine quenching and energy transfer rate FA9550-41-- o3G Sb. GRANT NUMBER constants for supersonic flow...in the nozzle from a chemical oxygen iodine laser (COIL). PLIF images are recorded using laser excitation of the I= B-X transition. Data for the...Preacolbed byANSI Sad Z30.16 20071015188 Final report for the project, "Characterization of iodine quenching and energy transfer rate constants for

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

    PubMed

    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.

    PubMed

    Yu, Huapeng; Wu, Wenqi; Wu, Meiping; Feng, Guohu; Hao, Ming

    2013-02-27

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

    PubMed Central

    Yu, Huapeng; Wu, Wenqi; Wu, Meiping; Feng, Guohu; Hao, Ming

    2013-01-01

    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. PMID:23447008

  9. Higher success rate with transcranial electrical stimulation of motor-evoked potentials using constant-voltage stimulation compared with constant-current stimulation in patients undergoing spinal surgery.

    PubMed

    Shigematsu, Hideki; Kawaguchi, Masahiko; Hayashi, Hironobu; Takatani, Tsunenori; Iwata, Eiichiro; Tanaka, Masato; Okuda, Akinori; Morimoto, Yasuhiko; Masuda, Keisuke; Tanaka, Yuu; Tanaka, Yasuhito

    2017-05-05

    During spine surgery, the spinal cord is electrophysiologically monitored via transcranial electrical stimulation of motor-evoked potentials (TES-MEPs) to prevent injury. Transcranial electrical stimulation of motor-evoked potential involves the use of either constant-current or constant-voltage stimulation; however, there are few comparative data available regarding their ability to adequately elicit compound motor action potentials. We hypothesized that the success rates of TES-MEP recordings would be similar between constant-current and constant-voltage stimulations in patients undergoing spine surgery. The objective of this study was to compare the success rates of TES-MEP recordings between constant-current and constant-voltage stimulation. This is a prospective, within-subject study. Data from 100 patients undergoing spinal surgery at the cervical, thoracic, or lumbar level were analyzed. The success rates of the TES-MEP recordings from each muscle were examined. Transcranial electrical stimulation with constant-current and constant-voltage stimulations at the C3 and C4 electrode positions (international "10-20" system) was applied to each patient. Compound muscle action potentials were bilaterally recorded from the abductor pollicis brevis (APB), deltoid (Del), abductor hallucis (AH), tibialis anterior (TA), gastrocnemius (GC), and quadriceps (Quad) muscles. The success rates of the TES-MEP recordings from the right Del, right APB, bilateral Quad, right TA, right GC, and bilateral AH muscles were significantly higher using constant-voltage stimulation than those using constant-current stimulation. The overall success rates with constant-voltage and constant-current stimulations were 86.3% and 68.8%, respectively (risk ratio 1.25 [95% confidence interval: 1.20-1.31]). The success rates of TES-MEP recordings were higher using constant-voltage stimulation compared with constant-current stimulation in patients undergoing spinal surgery. Copyright © 2017

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

    PubMed

    Badra, Jihad; Elwardany, Ahmed E; Farooq, Aamir

    2014-06-28

    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 (C=O) 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 (C=O), and the prime is used to differentiate different neighboring environments of a methylene group):

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

    PubMed

    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. Copyright © 2014 Elsevier Ltd. All rights reserved.

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

    PubMed

    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.

  13. K{sub Air} and H*(10) Rate Constants for Gamma Emitters

    SciTech Connect

    Vega-Carrillo, H. R.; Juarez, R. Rodriguez; Manzanares-Acuna, E.; Davila, V. M. Hernandez; Mercado, G. A.

    2008-08-11

    Monte Carlo calculations have been carried out to estimate the Air Kerma rate constant and the Ambient dose equivalent rate constant for 139 monoenergetic photon sources. The factor that relates activity to air kerma rate or to ambient dose equivalent is useful to estimate the dose from a photon emitter source. Here 139 point-like and monoenergetic gamma-ray sources, ranging from 0.01 to 10 MeV were utilized in Monte Carlo calculations to estimate both gamma factors. These factors were utilized to calculate the air kerma-and-ambient dose equivalent rate constants for {sup 137}Cs-{sup 137m}Ba, {sup 198}Au, {sup 60}Co, and {sup 131}I, whose values were compared with those published in the literature.

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

    EPA Science Inventory

    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 ...

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

    EPA Science Inventory

    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 ...

  16. Theoretical rate constants of super-exchange hole transfer and thermally induced hopping in DNA.

    PubMed

    Shimazaki, Tomomi; Asai, Yoshihiro; Yamashita, Koichi

    2005-01-27

    Recently, the electronic properties of DNA have been extensively studied, because its conductivity is important not only to the study of fundamental biological problems, but also in the development of molecular-sized electronics and biosensors. We have studied theoretically the reorganization energies, the activation energies, the electronic coupling matrix elements, and the rate constants of hole transfer in B-form double-helix DNA in water. To accommodate the effects of DNA nuclear motions, a subset of reaction coordinates for hole transfer was extracted from classical molecular dynamics (MD) trajectories of DNA in water and then used for ab initio quantum chemical calculations of electron coupling constants based on the generalized Mulliken-Hush model. A molecular mechanics (MM) method was used to determine the nuclear Franck-Condon factor. The rate constants for two types of mechanisms of hole transfer-the thermally induced hopping (TIH) and the super-exchange mechanisms-were determined based on Marcus theory. We found that the calculated matrix elements are strongly dependent on the conformations of the nucleobase pairs of hole-transferable DNA and extend over a wide range of values for the "rise" base-step parameter but cluster around a particular value for the "twist" parameter. The calculated activation energies are in good agreement with experimental results. Whereas the rate constant for the TIH mechanism is not dependent on the number of A-T nucleobase pairs that act as a bridge, the rate constant for the super-exchange process rapidly decreases when the length of the bridge increases. These characteristic trends in the calculated rate constants effectively reproduce those in the experimental data of Giese et al. [Nature 2001, 412, 318]. The calculated rate constants were also compared with the experimental results of Lewis et al. [Nature 2000, 406, 51].

  17. Limit case analysis of the "stable indenter velocity" method for obtaining creep stress exponents from constant load indentation creep tests

    NASA Astrophysics Data System (ADS)

    Campbell, J.; Dean, J.; Clyne, T. W.

    2017-02-01

    This study concerns a commonly-used procedure for evaluating the steady state creep stress exponent, n, from indentation data. The procedure involves monitoring the indenter displacement history under constant load and making the assumption that, once its velocity has stabilised, the system is in a quasi-steady state, with stage II creep dominating the behaviour. The stress and strain fields under the indenter are represented by "equivalent stress" and "equivalent strain rate" values. The estimate of n is then obtained as the gradient of a plot of the logarithm of the equivalent strain rate against the logarithm of the equivalent stress. Concerns have, however, been expressed about the reliability of this procedure, and indeed it has already been shown to be fundamentally flawed. In the present paper, it is demonstrated, using a very simple analysis, that, for a genuinely stable velocity, the procedure always leads to the same, constant value for n (either 1.0 or 0.5, depending on whether the tip shape is spherical or self-similar). This occurs irrespective of the value of the measured velocity, or indeed of any creep characteristic of the material. It is now clear that previously-measured values of n, obtained using this procedure, have varied in a more or less random fashion, depending on the functional form chosen to represent the displacement-time history and the experimental variables (tip shape and size, penetration depth, etc.), with little or no sensitivity to the true value of n.

  18. On the Values at Equilibrium and Rate Constants in Inter - Conversion Processes.

    PubMed

    Olteanu, Octav

    2016-01-01

    Inter - conversion processes of labile molecules obey similar rules to those of reversible chemical reactions. Solving the corresponding linear differential systems is used along this work, as well as in the preceding version. The main purpose of the present mini revue paper is to recall, improve and correct some mathematical methods in determining the optimal values at equilibrium, and remarkable particular rate constants. This part was not proved correctly in my previous work. In my previous work, the proof of the equality of the concentrations of the main species at equilibrium was not correct. In the current manuscript, we use increasing velocity in order to obtain this first important result. To this aim, one applies Schwarz inequality and the case when equality occurs. In order to determine significant rate constants, we characterize these special values in terms of the norm of the linear operator defined by the matrix of the differential system. In my previous work, the normal probability density function was used. The latter method was not realistic. Increasing the velocity, one obtains equal optimal values of the concentrations at equilibrium. This method represents a patent in the field. Secondly, characterization of remarkable rate constants (which are also equal) is deduced. The optimal solutions are written explicitly. Under suitable conditions, the values at equilibrium and the rate constants are equal. The common value at equilibrium equals the common value of the rate constants.

  19. A new approach using coagulation rate constant for evaluation of turbidity removal

    NASA Astrophysics Data System (ADS)

    Al-Sameraiy, Mukheled

    2017-06-01

    Coagulation-flocculation-sedimentation processes for treating three levels of bentonite synthetic turbid water using date seeds (DS) and alum (A) coagulants were investigated in the previous research work. In the current research, the same experimental results were used to adopt a new approach on a basis of using coagulation rate constant as an investigating parameter to identify optimum doses of these coagulants. Moreover, the performance of these coagulants to meet (WHO) turbidity standard was assessed by introducing a new evaluating criterion in terms of critical coagulation rate constant (kc). Coagulation rate constants (k2) were mathematically calculated in second order form of coagulation process for each coagulant. The maximum (k2) values corresponded to doses, which were obviously to be considered as optimum doses. The proposed criterion to assess the performance of coagulation process of these coagulants was based on the mathematical representation of (WHO) turbidity guidelines in second order form of coagulation process stated that (k2) for each coagulant should be ≥ (kc) for each level of synthetic turbid water. For all tested turbid water, DS coagulant could not satisfy it. While, A coagulant could satisfy it. The results obtained in the present research are exactly in agreement with the previous published results in terms of finding optimum doses for each coagulant and assessing their performances. On the whole, it is recommended considering coagulation rate constant to be a new approach as an indicator for investigating optimum doses and critical coagulation rate constant to be a new evaluating criterion to assess coagulants' performance.

  20. A new approach using coagulation rate constant for evaluation of turbidity removal

    NASA Astrophysics Data System (ADS)

    Al-Sameraiy, Mukheled

    2015-09-01

    Coagulation-flocculation-sedimentation processes for treating three levels of bentonite synthetic turbid water using date seeds (DS) and alum (A) coagulants were investigated in the previous research work. In the current research, the same experimental results were used to adopt a new approach on a basis of using coagulation rate constant as an investigating parameter to identify optimum doses of these coagulants. Moreover, the performance of these coagulants to meet (WHO) turbidity standard was assessed by introducing a new evaluating criterion in terms of critical coagulation rate constant (kc). Coagulation rate constants (k2) were mathematically calculated in second order form of coagulation process for each coagulant. The maximum (k2) values corresponded to doses, which were obviously to be considered as optimum doses. The proposed criterion to assess the performance of coagulation process of these coagulants was based on the mathematical representation of (WHO) turbidity guidelines in second order form of coagulation process stated that (k2) for each coagulant should be ≥ (kc) for each level of synthetic turbid water. For all tested turbid water, DS coagulant could not satisfy it. While, A coagulant could satisfy it. The results obtained in the present research are exactly in agreement with the previous published results in terms of finding optimum doses for each coagulant and assessing their performances. On the whole, it is recommended considering coagulation rate constant to be a new approach as an indicator for investigating optimum doses and critical coagulation rate constant to be a new evaluating criterion to assess coagulants' performance.

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

    PubMed Central

    Zhao, Jiao; Ridgway, Douglas; Broderick, Gordon; Kovalenko, Andriy; Ellison, Michael

    2008-01-01

    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 minima and uncertainty

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

    PubMed

    Zhao, Jiao; Ridgway, Douglas; Broderick, Gordon; Kovalenko, Andriy; Ellison, Michael

    2008-05-07

    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. 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 minima and uncertainty inherent with large

  3. Rate constant for the reaction of atomic chlorine with acetaldehyde from 210 to 343 K

    SciTech Connect

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

    1990-09-06

    The absolute rate constant for the reaction of atomic chlorine with acetaldehyde has been measured from 210 to 343 K by use of the flash photolysis-resonance fluorescence technique. The rate constant is shown to be independent of variations in (CH{sub 3}CHO), total pressure (Ar), and, to a lesser extent, flash intensity (initial (Cl)). The rate constant is also independent of temperature over the range studied. The average of all experiments yields k{sub 1} = (6.6 {plus minus} 1.4) {times} 10{sup {minus}11} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, where the error limit is two standard deviations. This result is compared with previous measurements of k{sub 1}, all of which were relative measurements at 298 K.

  4. Rate constant for the reaction of atomic chlorine with formaldehyde from 200 to 500 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Nava, D. F.; Payne, W. A.

    1979-01-01

    The absolute rate constant for the reaction of atomic chlorine with formaldehyde has been measured from 200 to 500 K using the flash photolysis-resonance fluorescence technique. The results were independent of substantial variations in (H2CO), total pressure (Ar), and flash intensity (i.e., initial (Cl)). The rate constant was shown to be invariant with temperature, the best representation for this temperature range being k-sub-1 = (7.48 + or - 0.50) times 10 to the -11 cu cm/molecule sec, where the error is one standard deviation. This result is compared with the only previous determination of k-sub-1, which was a relative value obtained at 298 K. The rate constant is theoretically discussed, and the potential importance of the reaction in stratospheric chemistry is considered.

  5. Rate constant for the reaction of atomic chlorine with formaldehyde from 200 to 500 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Nava, D. F.; Payne, W. A.

    1979-01-01

    The absolute rate constant for the reaction of atomic chlorine with formaldehyde has been measured from 200 to 500 K using the flash photolysis-resonance fluorescence technique. The results were independent of substantial variations in (H2CO), total pressure (Ar), and flash intensity (i.e., initial (Cl)). The rate constant was shown to be invariant with temperature, the best representation for this temperature range being k-sub-1 = (7.48 + or - 0.50) times 10 to the -11 cu cm/molecule sec, where the error is one standard deviation. This result is compared with the only previous determination of k-sub-1, which was a relative value obtained at 298 K. The rate constant is theoretically discussed, and the potential importance of the reaction in stratospheric chemistry is considered.

  6. The rate constant for the reaction of oxygen /3P/ atoms with dichlorine monoxide

    NASA Technical Reports Server (NTRS)

    Miziolek, A. W.; Molina, M. J.

    1978-01-01

    A fast flow discharge apparatus was used to measure the rate constant for the reaction of ground state oxygen atoms with dichlorine monoxide in the temperature range 236-295 K. The air afterflow technique (NO2 chemiluminescence) was used for detection of oxygen atoms. The Arrhenius expression for the rate constant was found to be 2.7 plus or minus 0.3 times 10 to the -11th power exp(-560 plus or minus 80/T) cu cm per molecule per sec. At 295 K the rate constant is 4.1 plus or minus 0.5 times 10 to the -12th power cu cm per molecule per sec.

  7. Elastomeric composites with high dielectric constant for use in Maxwell stress actuators

    NASA Astrophysics Data System (ADS)

    Szabo, Jeffrey P.; Hiltz, Johnathan A.; Cameron, Colin G.; Underhill, Royale S.; Massey, Jason; White, Brian; Leidner, Jacob

    2003-07-01

    Electroactive polymer actuators that utilize the Maxwell stress effect have generated considerable interest in recent years for use in applications such as artificial muscles, sensors, and parasitic energy capture. In order to maximize performance, the dielectric layer in Maxwell stress actuators should ideally have a high dielectric constant and high dielectric breakdown strength. In this study, the effect of high dielectric constant fillers on the electrical and mechanical properties of thin elastomeric films was examined. The fillers studied included the inorganic compounds titanium dioxide (TiO2), barium titanate (BaTiO3), and lead magnesium niobate-lead titanate (Pb(Mg1/3Nb2/3)O3-PbTiO). A high dielectric constant filler based on a polymeric conjugated ligand-metal complex, poly(copper phthalocyanine), was also synthesized and studied. Maxwell stress actuators fabricated with BaTiO3 dispersed in a silicone elastomer matrix were evaluated and compared with unfilled systems. A model was presented which relates filler volume fraction to actuation stress, strain, and elastic energy density at fields below dielectric breakdown. The model and experimental results suggest that for the case of strong filler particle-elastomer matrix interaction, actuation strain decreases with increasing filler content.

  8. A novel path sampling method for the calculation of rate constants

    NASA Astrophysics Data System (ADS)

    van Erp, Titus S.; Moroni, Daniele; Bolhuis, Peter G.

    2003-05-01

    We derive a novel efficient scheme to measure the rate constant of transitions between stable states separated by high free energy barriers in a complex environment within the framework of transition path sampling. The method is based on directly and simultaneously measuring the fluxes through many phase space interfaces and increases the efficiency with at least a factor of 2 with respect to existing transition path sampling rate constant algorithms. The new algorithm is illustrated on the isomerization of a diatomic molecule immersed in a simple fluid.

  9. The constant threat of terrorism: stress levels and coping strategies amongst university students of Karachi.

    PubMed

    Ahmed, Ayesha Ejaz; Masood, Komal; Dean, Sohni Vicky; Shakir, Tanzila; Kardar, Ahmed Abdul Hafeez; Barlass, Usman; Imam, Syed Haider; Mohmand, Mohammad Ghawar Khan; Ibrahim, Hussain; Khan, Imad Saeed; Akram, Usman; Hasnain, Farid

    2011-04-01

    To assess the levels of stress in the face of terrorism and the adopted coping strategies, amongst the student population of universities in Karachi. A descriptive, cross sectional study was conducted on undergraduate students from four universities of Karachi. Self-administered questionnaires were filled out by 291 students. Pearson Chi-Square test was used to assess associations between stress levels and different variables at a level of significance of 0.05%. A total of 65.8% of the students had mild stress levels, 91.5% of university students were exposed to terrorism through television, while only 26.5% students reported personal exposure to terrorism. 67.4% students were forbidden by their parents to go out (p = 0.002). Most of those who had self exposure to an attack were the ones whose parents forbade them from going out (p = 0.00). Most commonly used coping strategy was increased faith in religion. Irritability was the most common stress symptom. A majority of students studying in universities of Karachi had mild stress levels due to the constant threat of terrorism whereas a minority had severe stress levels. Possible reasons for resilience and only mild stress levels could be the history of Karachi's internal conflicts and its prolonged duration of being exposed to terrorism. These students who are positive for stress need to be targeted for counseling either through the media or through their universities. More extensive research is needed in this area.

  10. Rough-to-smooth transition of an equilibrium neutral constant stress layer

    NASA Technical Reports Server (NTRS)

    Logan, E., Jr.; Fichtl, G. H.

    1975-01-01

    Purpose of research on rough-to-smooth transition of an equilibrium neutral constant stress layer is to develop a model for low-level atmospheric flow over terrains of abruptly changing roughness, such as those occurring near the windward end of a landing strip, and to use the model to derive functions which define the extent of the region affected by the roughness change and allow adequate prediction of wind and shear stress profiles at all points within the region. A model consisting of two bounding logarithmic layers and an intermediate velocity defect layer is assumed, and dimensionless velocity and stress distribution functions which meet all boundary and matching conditions are hypothesized. The functions are used in an asymptotic form of the equation of motion to derive a relation which governs the growth of the internal boundary layer. The growth relation is used to predict variation of surface shear stress.

  11. Effects of various process parameters on struvite precipitation kinetics and subsequent determination of rate constants.

    PubMed

    Rahaman, M S; Ellis, N; Mavinic, D S

    2008-01-01

    In this paper, struvite (MgNH(4)PO(4).6H(2)O) precipitation kinetics were studied with different operating conditions (varying supersaturation, pH, Mg:P ratio, degree of mixing and seeding conditions) and relevant rate constants were determined by fitting a slightly modified first-order kinetic model to the experimental data obtained. The rate of change of ortho-P concentration in the bulk solutions increases with increasing supersaturation ratio. The estimated rate constants are 2.034, 1.716 and 0.690 hr(-1) for the supersaturation ratio of 9.64, 4.83, and 2.44, respectively. Kinetic parameters were also evaluated for the Mg:P ratio between the ranges of 1.0 and 1.6, indicating higher phosphorus removal efficiency with increasing Mg:P ratio. The rate constants were found to be 0.942, 2.034 and 2.712 hr(-1) for Mg:P ratios of 1.0, 1.3 and 1.6, respectively. The experimental observations for kinetic study of struvite precipitation with different stirrer speeds clearly show that the mixing intensity used had little effect on the intrinsic rate constants. K values found to be 2.034 and 1.902 h(-1) for 100 and 70 rpm, respectively. Seeding, with 250-500 microm of seed crystals during the struvite precipitation kinetics test, was found to have very little effect on the ortho-P removal.

  12. Robust reconstruction of the rate constant distribution using the phase function method.

    PubMed

    Zhou, Yajun; Zhuang, Xiaowei

    2006-12-01

    Many biological processes exhibit complex kinetic behavior that involves a nontrivial distribution of rate constants. Characterization of the rate constant distribution is often critical for mechanistic understandings of these processes. However, it is difficult to extract a rate constant distribution from data measured in the time domain. This is due to the numerical instability of the inverse Laplace transform, a long-standing mathematical challenge that has hampered data analysis in many disciplines. Here, we present a method that allows us to reconstruct the probability distribution of rate constants from decay data in the time domain, without fitting to specific trial functions or requiring any prior knowledge of the rate distribution. The robustness (numerical stability) of this reconstruction method is numerically illustrated by analyzing data with realistic noise and theoretically proved by the continuity of the transformations connecting the relevant function spaces. This development enhances our ability to characterize kinetics and dynamics of biological processes. We expect this method to be useful in a broad range of disciplines considering the prevalence of complex exponential decays in many experimental systems.

  13. Determination of reaction rate constants for alkylation of 4-(p-nitrobenzyl) pyridine by different alkylating agents.

    PubMed

    Walles, S A

    1980-02-01

    The rate constants have been determined for the reaction between some different alkylating agents and 4-(p-nitrobenzyl) pyridine (NBP) in methanol. These constants have been compared with those for alkylation of aniline in water. All the constants were lower in methanol than in water but in different degrees. The rate constants of the different alkylating agents have been calculated at a nucleophilic strength n=2. The genetic risk defined as the degree of alkylation of a nucleophile (n=2) is equivalent to the rate constant kn=2 and the target dose. The dependence of the genetic risk on the rate constant (kn=2) is discussed.

  14. THEORETICAL ANALYSIS OF THE TRANSIENT PRESSURE RESPONSE FROM A CONSTANT FLOW RATE HYDRAULIC CONDUCTIVITY TEST.

    USGS Publications Warehouse

    Morin, Roger H.; Olsen, Harold W.

    1987-01-01

    Incorporating a flow pump into a conventional triaxial laboratory system allows fluid to be supplied to or withdrawn from the base of a sediment sample at small and constant rates. An initial transient record of hydraulic head versus time is observed which eventually stabilizes to a constant steady state gradient across the sample; values of hydraulic conductivity can subsequently be determined from Darcy's law. In this paper, analytical methods are presented for determining values of specific storage and hydraulic conductivity from the initial transient phase of such a constant flow rate test. These methods are based on a diffusion equation involving pore pressure and are analogous to those used to describe the soil consolidation process and also to interpret aquifer properties from pumping tests.

  15. The air-kerma rate constant: application to air-kerma measurements for homeland security.

    PubMed

    Pibida, L; Minniti, R; Lucas, L; Seltzer, S M

    2008-02-01

    Air-kerma rate measurements from 57Co, 60Co, and 137Cs radioactive sources were performed. These measurements were motivated by the development of new sources at the National Institute of Standards and Technology (NIST) for radiological testing of equipment for homeland security applications. The testing of radiation detection equipment relies on knowing the values of the air-kerma rate for the radioactive sources at a fixed distance from the source. The air-kerma rate can be measured or alternatively estimated by using published values of the air-kerma rate constant. Although there are a large number of published values of the air-kerma rate constant for radionuclide sources based on theoretical calculations, strong disagreement is observed throughout the literature. Furthermore, most of the published values have no uncertainties assigned, and therefore their use for testing radiological equipment is limited. In this work we report experimentally-measured values of the air-kerma rate for three radionuclides with well defined source geometries and activities. The results are compared to estimates based on published values of the air-kerma rate constant. Such values are easily found in the literature from the last three decades and are used commonly by the scientific community.

  16. The rate constant for radiative association of HF: Comparing quantum and classical dynamics

    SciTech Connect

    Gustafsson, Magnus Monge-Palacios, M.; Nyman, Gunnar

    2014-05-14

    Radiative association for the formation of hydrogen fluoride through the A{sup 1}Π → X{sup 1}Σ{sup +} and X{sup 1}Σ{sup +} → X{sup 1}Σ{sup +} transitions is studied using quantum and classical dynamics. The total thermal rate constant is obtained for temperatures from 10 K to 20 000 K. Agreement between semiclassical and quantum approaches is observed for the A{sup 1}Π → X{sup 1}Σ{sup +} rate constant above 2000 K. The agreement is explained by the fact that the corresponding cross section is free of resonances for this system. At temperatures below 2000 K we improve the agreement by implementing a simplified semiclassical expression for the rate constant, which includes a quantum corrected pair distribution. The rate coefficient for the X{sup 1}Σ{sup +} → X{sup 1}Σ{sup +} transition is calculated using Breit–Wigner theory and a classical formula for the resonance and direct contributions, respectively. In comparison with quantum calculations the classical formula appears to overestimate the direct contribution to the rate constant by about 12% for this transition. Below about 450 K the resonance contribution is larger than the direct, and above that temperature the opposite holds. The biggest contribution from resonances is at the lowest temperature in the study, 10 K, where it is more than four times larger than the direct. Below 1800 K the radiative association rate constant due to X{sup 1}Σ{sup +} → X{sup 1}Σ{sup +} transitions dominates over A{sup 1}Π → X{sup 1}Σ{sup +}, while above that temperature the situation is the opposite.

  17. Proximal femur elastic behaviour is the same in impact and constant displacement rate fall simulation.

    PubMed

    Gilchrist, S; Nishiyama, K K; de Bakker, P; Guy, P; Boyd, S K; Oxland, T; Cripton, P A

    2014-11-28

    Understanding proximal femur fracture may yield new targets for fracture prevention screening and treatment. The goal of this study was to characterize force-displacement and failure behaviours in the proximal femur between displacement control and impact loading fall simulations. Twenty-one human proximal femurs were tested in two ways, first to a sub-failure load at a constant displacement rate, then to fracture in an impact fall simulator. Comparisons of sub-failure energy and stiffness were made between the tests at the same compressive force. Additionally, the impact failure tests were compared with previous, constant displacement rate failure tests (at 2 and 100mm/s) in terms of energy, yield force, and stiffness. Loading and displacement rates were characterized and related to specimen stiffness in the impact tests. No differences were observed between the sub-failure constant displacement and impact tests in the aforementioned metrics. Comparisons between failure tests showed that the impact group had the lowest absorbed energy, 24% lower maximum force and 160% higher stiffness than the 100mm/s group (p<0.01 for all), but suffered from low statistical power to differentiate the donor age and specimen BMD. Loading and displacement rates for the specimens tested using impact varied during each test and between specimens and did not show appreciable viscoelasticity. These results indicate that constant displacement rate testing may help understand sub-failure mechanical behaviour, but may not elucidate failure behaviours. The differences between the impact and constant displacement rate fall simulations have important ramifications for interpreting the results of previous experiments.

  18. Residual stress evolution in multilayer ceramic capacitors corresponding to layer increase and its correlation to the dielectric constant

    NASA Astrophysics Data System (ADS)

    Park, Jong-Sung; Kim, Sujin; Shin, Hyunho; Jung, Hyun Suk; Hong, Kug Sun

    2005-05-01

    The residual thermal stress in multilayer ceramic capacitors (MLCCs) with varying number of layers was analyzed using finite element analysis, in order to find the links among the dielectric constant, the number of layers, and the stress state. In the active region of the MLCC, the in-plane stresses in a ceramic layer, σ11 and σ22, were compressive while the out-of-plane stress, σ33, was mostly tensile. Changes in the dielectric constant were related to the reinforcement of the compressive in-plane stress components for small numbers of layers, while out-of-plane tensile stress was attributed to the increased dielectric constant when the number of layers was large. In the intermediate regime, in-plane stress components and out-of-plane components both affected the dielectric constant.

  19. A Modified Constant-Stress Coupon for Enhanced Natural Crack Start during Fatigue Testing

    DTIC Science & Technology

    2016-05-01

    stress is constant within a specified small range). This led McDonald (1999b) to establish the design of an aluminium coupon that maximised the...Chang and Mear 1995; Newman et al. 2006). The assumed linear- elastic material properties for these aluminium coupons are a Young’s Modulus of E...the previously specified linear elastic material properties for aluminium (see Appendix A for a listing of the input deck, which is also located in

  20. Determination of relative rate constants for in vitro RNA processing reactions by internal competition.

    PubMed

    Lin, Hsuan-Chun; Yandek, Lindsay E; Gjermeni, Ino; Harris, Michael E

    2014-12-15

    Studies of RNA recognition and catalysis typically involve measurement of rate constants for reactions of individual RNA sequence variants by fitting changes in substrate or product concentration to exponential or linear functions. A complementary approach is determination of relative rate constants by internal competition, which involves quantifying the time-dependent changes in substrate or product ratios in reactions containing multiple substrates. Here, we review approaches for determining relative rate constants by analysis of both substrate and product ratios and illustrate their application using the in vitro processing of precursor transfer RNA (tRNA) by ribonuclease P as a model system. The presence of inactive substrate populations is a common complicating factor in analysis of reactions involving RNA substrates, and approaches for quantitative correction of observed rate constants for these effects are illustrated. These results, together with recent applications in the literature, indicate that internal competition offers an alternate method for analyzing RNA processing kinetics using standard molecular biology methods that directly quantifies substrate specificity and may be extended to a range of applications. Copyright © 2014 Elsevier Inc. All rights reserved.

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

    PubMed

    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.

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

    EPA Science Inventory

    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 ...

  3. A model to estimate the methane generation rate constant in sanitary landfills using fuzzy synthetic evaluation.

    PubMed

    Garg, Anurag; Achari, Gopal; Joshi, Ramesh C

    2006-08-01

    This paper presents a model using fuzzy synthetic evaluation to estimate the methane generation rate constant, k, for landfills. Four major parameters, precipitation, temperature, waste composition and landfill depth were used as inputs to the model. Whereas, these parameters are known to impact the methane generation, mathematical relationships between them and the methane generation rate constant required to estimate methane generation in landfills, are not known. In addition, the spatial variations of k within a landfill combined with the necessity of site-specific information to estimate its value, makes k one of the most elusive parameters in the accurate prediction of methane generation within a landfill. In this paper, a fuzzy technique was used to develop a model to predict the methane generation rate constant. The model was calibrated and verified using k values from 42 locations. Data from 10 sites were used to calibrate the model and the rest were used to verify it. The model predictions are reasonably accurate. A sensitivity analysis was also conducted to investigate the effect of uncertainty in the input parameters on the generation rate constant.

  4. DISSOCIATION OF ARSENITE-PEPTIDE COMPLEXES: TRIPHASIC NATURE, RATE CONSTANTS, HALF LIVES AND BIOLOGICAL IMPORTANCE

    EPA Science Inventory

    We determined the number and the dissociation rate constants of different complexes formed from arsenite and two peptides containing either one (RV AVGNDYASGYHYGV for peptide 20) or three cysteines (LE AWQGK VEGTEHLYSMK K for peptide 10) via radioactive 73As labeled arsenite and ...

  5. Design of an Excel Spreadsheet to Estimate Rate Constants, Determine Associated Errors, and Choose Curve's Extent

    ERIC Educational Resources Information Center

    Moreira, Luis; Martins, Filomena; Elvas-Leitao, Ruben

    2006-01-01

    A new Microsoft Excel spreadsheet design that enables a prompt calculation of rate constant, k values and associated errors and also addresses less common features such as the choice of an experimental curve's extent is presented. To complete the spreadsheet design, several highlights and squared colored boxes were included to assist the user and…

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

    PubMed

    Wu, Junjun; Khaled, Fethi; Ning, Hongbo; Ma, Liuhao; Farooq, Aamir; Ren, Wei

    2017-08-24

    We report a systematic chemical kinetics study of the H atom abstractions from ethyl formate (EF) by H, O((3)P), 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 500-2500 K by the transition state theory (TST) in conjunction with the 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.

  7. The effect of receptor clustering on diffusion-limited forward rate constants.

    PubMed Central

    Goldstein, B; Wiegel, F W

    1983-01-01

    The effect of receptor clustering on the diffusion-limited forward rate constant (k+) is studied theoretically by modeling cell surface receptors by hemispheres distributed on a plane. We give both exact results and bounds. The exact results are obtained using an electrostatic analogue and applying the method of the images. Accurate upper bounds on k+ are found from a variational principle. PMID:6309261

  8. RELATIVE RATE CONSTANTS OF CONTAMINANT CANDIDATE LIST PESTICIDES WITH HYDROXYL RADICALS

    EPA Science Inventory

    The objective of this study was to establish the rate constants for the reactions of selected pesticides listed on the US EPA Contaminant Candidate List, with UV and hydroxyl radicals (·OH). Batch experiments were conducted in phosphate buffered solution at pH 7. All pestici...

  9. RELATIVE RATE CONSTANTS OF CONTAMINANT CANDIDATE LIST PESTICIDES WITH HYDROXYL RADICALS

    EPA Science Inventory

    The objective of this study was to establish the rate constants for the reactions of selected pesticides listed on the US EPA Contaminant Candidate List, with UV and hydroxyl radicals (·OH). Batch experiments were conducted in phosphate buffered solution at pH 7. All pestici...

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

    EPA Science Inventory

    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...

  11. Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation

    PubMed Central

    Warren, Jeffrey J.; Mayer, James M.

    2010-01-01

    Chemical reactions that involve net hydrogen atom transfer (HAT) are ubiquitous in chemistry and biology, from the action of antioxidants to industrial and metalloenzyme catalysis. This report develops and validates a procedure to predict rate constants for HAT reactions of oxyl radicals (RO•) in various media. Our procedure uses the Marcus cross relation (CR) and includes adjustments for solvent hydrogen-bonding effects on both the kinetics and thermodynamics of the reactions. Kinetic solvent effects (KSEs) are included by using Ingold’s model, and thermodynamic solvent effects are accounted for by using an empirical model developed by Abraham. These adjustments are shown to be critical to the success of our combined model, referred to as the CR/KSE model. As an initial test of the CR/KSE model we measured self-exchange and cross rate constants in different solvents for reactions of the 2,4,6-tri-tert-butylphenoxyl radical and the hydroxylamine 2,2′-6,6′-tetramethyl-piperidin-1-ol. Excellent agreement is observed between the calculated and directly determined cross rate constants. We then extend the model to over 30 known HAT reactions of oxyl radicals with OH or CH bonds, including biologically relevant reactions of ascorbate, peroxyl radicals, and α-tocopherol. The CR/KSE model shows remarkable predictive power, predicting rate constants to within a factor of 5 for almost all of the surveyed HAT reactions. PMID:20215463

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

    EPA Science Inventory

    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 ...

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

    EPA Science Inventory

    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...

  14. DISSOCIATION OF ARSENITE-PEPTIDE COMPLEXES: TRIPHASIC NATURE, RATE CONSTANTS, HALF LIVES AND BIOLOGICAL IMPORTANCE

    EPA Science Inventory

    We determined the number and the dissociation rate constants of different complexes formed from arsenite and two peptides containing either one (RV AVGNDYASGYHYGV for peptide 20) or three cysteines (LE AWQGK VEGTEHLYSMK K for peptide 10) via radioactive 73As labeled arsenite and ...

  15. Computation of Rate Constants for Diffusion of Small Ligands to and from Buried Protein Active Sites.

    PubMed

    Wang, P-H; De Sancho, D; Best, R B; Blumberger, J

    2016-01-01

    The diffusion of ligands to actives sites of proteins is essential to enzyme catalysis and many cellular signaling processes. In this contribution we review our recently developed methodology for calculation of rate constants for diffusion and binding of small molecules to buried protein active sites. The diffusive dynamics of the ligand obtained from molecular dynamics simulation is coarse grained and described by a Markov state model. Diffusion and binding rate constants are then obtained either from the reactive flux formalism or by fitting the time-dependent population of the Markov state model to a phenomenological rate law. The method is illustrated by applications to diffusion of substrate and inhibitors in [NiFe] hydrogenase, CO-dehydrogenase, and myoglobin. We also discuss a recently developed sensitivity analysis that allows one to identify hot spots in proteins, where mutations are expected to have the strongest effects on ligand diffusion rates.

  16. A pumpless perfusion cell culture cap with two parallel channel layers keeping the flow rate constant.

    PubMed

    Lee, Dong Woo; Yi, Sang Hyun; Ku, Bosung; Kim, Jhingook

    2012-01-01

    This article presents a novel pumpless perfusion cell culture cap, the gravity-driven flow rate of which is kept constant by the height difference of two parallel channel layers. Previous pumpless perfusion cell culture systems create a gravity-driven flow by means of the hydraulic head difference (Δh) between the source reservoir and the drain reservoir. As more media passes from the source reservoir to the drain reservoir, the source media level decreases and the drain media level increases. Thus, previous works based on a gravity-driven flow were unable to supply a constant flow rate for the perfusion cell culture. However, the proposed perfusion cell culture cap can supply a constant flow rate, because the media level remains unchanged as the media moves laterally through each channel having same media level. In experiments, using the different fluidic resistances, the perfusion cap generated constant flow rates of 871 ± 27 μL h(-1) and 446 ± 11 μL h(-1) . The 871 and 446 μL h(-1) flow rates replace the whole 20 mL medium in the petri dish with a fresh medium for days 1 and 2, respectively. In the perfusion cell (A549 cell line) culture with the 871 μL h(-1) flow rate, the proposed cap can maintain a lactate concentration of about 2200 nmol mL(-1) and an ammonia concentration of about 3200 nmol mL(-1) . Moreover, although the static cell culture maintains cell viability for 5 days, the perfusion cell culture with the 871 μL h(-1) flow rate can maintain cell viability for 9 days. Copyright © 2012 American Institute of Chemical Engineers (AIChE).

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

    NASA Astrophysics Data System (ADS)

    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.

  18. Shock tube measurements of high temperature rate constants for OH with cycloalkanes and methylcycloalkanes.

    SciTech Connect

    Sivaramakrishnan, R.; Michael, J. V.; Chemical Sciences and Engineering Division

    2009-05-01

    High temperature experiments were performed with the reflected shock tube technique using multi-pass absorption spectrometric detection of OH radicals at 308 nm. The present experiments span a wide T-range, 801-1347 K, and represent the first direct measurements of the title rate constants at T>500 K for cyclopentane and cyclohexane and the only high temperature measurements for the corresponding methyl derivatives. The present work utilized 48 optical passes corresponding to a total path length 4.2 m. As a result of this increased path length, the high [OH] detection sensitivity permitted unambiguous analyses for measuring the title rate constants. The experimental rate constants in units, cm3 molecule-1 s-1, can be expressed in Arrhenius form as k{sub OH+Cyclopentane} = (1.90 {+-} 0.30) x 10{sup -10} exp(-1705 {+-} 156 K/T) (813-1341 K), k{sub OH+Cyclohexane} = (1.86 {+-} 0.24) x 10{sup -10} exp(-1513 {+-} 123 K/T) (801-1347 K), k{sub OH+Methylcyclopentane} = (2.02 {+-} 0.19) x 10{sup -10} exp(-1799 {+-} 96 K/T) (859-1344 K), k{sub OH+Methylcyclohexane} = (2.55 {+-} 0.30) x 10{sup -10} exp(-1824 {+-} 114 K/T) (836-1273 K). These results and lower-T experimental data were used to obtain three parameter evaluations of the experimental rate constants for the title reactions over an even wider T-range. These experimental three parameter fits to the rate constants in units, cm{sup 3} molecule{sup -1} s{sup -1}, are k{sub OH+Cyclopentane} = 1.390 x 10{sup -16}T{sup 1.779} exp(97 K/T) cm{sup 3} molecule{sup -1} s{sup -1} (209-1341 K), k{sub OH+Cyclohexane} = 3.169 x 10{sup -16} T{sup 1.679} exp(119 K/T) cm{sup 3} molecule{sup -1} s{sup -1} (225-1347 K), k{sub OH+Methylcyclopentane} = 6.903 x 10{sup -18}T{sup 2.148} exp(536 K/T) cm{sup 3} molecule{sup -1} s{sup -1} (296-1344 K), k{sub OH+Methylcyclohexane} = 2.341 x 10{sup -18}T{sup 2.325} exp(602 K/T) cm{sup 3} molecule{sup -1} s{sup -1} (296-1273 K). High level electronic structure methods were used to characterize the

  19. Shock tube measurements of high temperature rate constants for OH with cycloalkanes and methylcycloalkanes

    SciTech Connect

    Sivaramakrishnan, R.; Michael, J.V.

    2009-05-15

    High temperature experiments were performed with the reflected shock tube technique using multi-pass absorption spectrometric detection of OH radicals at 308 nm. The present experiments span a wide T-range, 801-1347 K, and represent the first direct measurements of the title rate constants at T>500 K for cyclopentane and cyclohexane and the only high temperature measurements for the corresponding methyl derivatives. The present work utilized 48 optical passes corresponding to a total path length {proportional_to}4.2 m. As a result of this increased path length, the high [OH] detection sensitivity permitted unambiguous analyses for measuring the title rate constants. The experimental rate constants in units, cm{sup 3} molecule{sup -1} s{sup -1}, can be expressed in Arrhenius form as k{sub OH+Cyclopentane}=(1.90{+-}0.30) x 10{sup -10}exp(-1705{+-}56 K/T) (813-1341 K), k{sub OH+Cyclohexane}=(1.86{+-}0.24) x 10{sup -10}exp(-1513{+-}123 K/T) (801-1347 K), k{sub OH+Methylcyclopentane}=(2.02{+-}0.19) x 10{sup -10}exp(-1799{+-}96 K/T) (859-1344 K), k{sub OH+Methylcyclohexane}=(2.55{+-}0.30) x 10{sup -10}exp(-1824{+-}114 K/T) (836-1273 K). These results and lower-T experimental data were used to obtain three parameter evaluations of the experimental rate constants for the title reactions over an even wider T-range. These experimental three parameter fits to the rate constants in units, cm{sup 3} molecule{sup -1} s{sup -1}, are k{sub OH+Cyclopentane}=1.390 x 10{sup -16}T{sup 1.779}exp(97 K/T)cm{sup 3} molecule{sup -1}s{sup -1} (209-1341 K), k{sub OH+Cyclohexane}=3.169 x 10{sup -16}T{sup 1.679}exp(119 K/T)cm{sup 3}molecule{sup -1}s{sup -1} (225-1347 K), k{sub OH+Methylcyclopentane}=6.903 x 10{sup -18}T{sup 2.148}exp(536 K/T)cm{sup 3}molecule{sup -1}s{sup -1} (296-1344 K), k{sub OH+Methylcyclohexane}=2.341 x 10{sup -18}T{sup 2.325}exp(602 K/T)cm{sup 3}molecule{sup -1}s{sup -1} (296-1273 K). High level electronic structure methods were used to characterize the first three

  20. Comparison of radiative-convective models with constant and pressure-dependent lapse rates

    NASA Technical Reports Server (NTRS)

    Hummel, J. R.; Kuhn, W. R.

    1981-01-01

    One of the most commonly used models for studying climatic processes is the convective adjustment radiation model. In current radiation models, stable temperature profiles are maintained with a convective adjustment in which the temperature lapse rate is set equal to a critical lapse rate whenever the computed lapse rates exceed the critical value. First introduced by Manabe and Strickler (1964), a variety of convective adjustment models are now in use. It is pointed out that on a global scale, moist adiabatic processes, and thus moist adiabatic lapse rates, approximate the atmospheric temperature profile. Comparisons of profiles from a one-dimensional-radiative-convective model have been made using the conventional 6.5 K/km as the critical lapse rate and the pressure-dependent moist adiabatic lapse rates. For a clear sky and a single effective cloud the surface temperatures are 1 to 3 K higher with the constant 6.5 K/km critical lapse rate.

  1. Mixed Quantum-Classical Liouville Approach for Calculating Proton-Coupled Electron-Transfer Rate Constants.

    PubMed

    Shakib, Farnaz; Hanna, Gabriel

    2016-07-12

    In this work, we derive a general mixed quantum-classical formula for calculating thermal proton-coupled electron-transfer (PCET) rate constants, starting from the time integral of the quantum flux-flux correlation function. This formula allows for the direct simulation of PCET reaction dynamics via the mixed quantum-classical Liouville approach. Owing to the general nature of the derivation, this formula does not rely on any prior mechanistic assumptions and can be applied across a wide range of electronic and protonic coupling regimes. To test the validity of this formula, we applied it to a reduced model of a condensed-phase PCET reaction. Good agreement with the numerically exact rate constant is obtained, demonstrating the accuracy of our formalism. We believe that this approach constitutes a solid foundation for future investigations of the rates and mechanisms of a wide range of PCET reactions.

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

    PubMed

    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.

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

    PubMed

    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.

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

    PubMed

    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 (Ka<10(5)M(-1)), and fast dissociation, such as those composed of cyclodextrins and drugs. In this study, a modified peak profiling method based on high 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.

  5. Factors underlying the perception of effort during constant heart rate running above and below the critical heart rate.

    PubMed

    Bergstrom, Haley C; Housh, Terry J; Cochrane, Kristen C; Jenkins, Nathaniel D M; Zuniga, Jorge M; Buckner, Samuel L; Goldsmith, Jacob A; Schmidt, Richard J; Johnson, Glen O; Cramer, Joel T

    2015-10-01

    This study examined: (1) the sustainability of the critical heart rate (CHR) minus 5 b min(-1) (CHR - 5) and CHR plus 5 b min(-1) (CHR + 5); (2) the ratings of perceived exertion (RPE), velocity, [Formula: see text], minute ventilation ([Formula: see text]), breathing frequency (f b ), and electromyographic amplitude (EMG AMP) and EMG mean power frequency (MPF) responses during treadmill running at CHR - 5 and CHR + 5 to determine what factors underlie the perception of effort when heart rate (HR) is held constant; and (3) the relationships among RPE, [Formula: see text], and HR, to determine which variable(s) reflect exhaustion during exercise performed at a constant HR. The CHR was determined in eight runners (mean ± SD; age = 24 ± 3 years) from a series of four exhaustive, constant velocity runs. The RPE, velocity, [Formula: see text], [Formula: see text], f b , EMG AMP, and EMG MPF responses were recorded during runs at the CHR - 5 and CHR + 5. At CHR - 5, RPE, f b, and EMG MPF increased, while velocity, [Formula: see text], [Formula: see text], and EMG AMP decreased. At CHR + 5, RPE and f b increased, velocity, [Formula: see text], [Formula: see text], and EMG AMP decreased, and EMG MPF remained constant. The close association between f b and RPE throughout the run at CHR - 5 and during the last 50 % of the run at CHR + 5 indicated that muscle afferents may have provided feedback from metabolic and mechanical stimuli that contributed to the perceptual responses. In addition, only RPE consistently indicated exhaustion and the current findings supported its use to monitor exercise performed at a constant HR.

  6. Constant Rate or Stepwise Injection of Cold Fluid into a Geologic Formation: A Hydro-Thermo-Mechanical Analysis

    NASA Astrophysics Data System (ADS)

    Kim, S.; Hosseini, S. A.

    2015-12-01

    Operations such as CO2 geologic storage, enhanced geothermal systems, and wastewater injection are rendering fluid injection as important as fluid extraction. In particular, injecting fluid colder than the original fluid causes thermal contraction and ensuing decreases in stresses, which yield an effect opposite of what volume expansion driven by the fluid injection imposes. In this study, we conduct numerical simulations to investigate pore-pressure buildup, thermal diffusion, and stress changes for two conditions: (1) constant rate, and (2) stepwise injection of cold fluid. The numerical-simulation method—which combines fluid flow, poroelasticity, thermal diffusion, and thermal stress—is based on the single-phase flow condition to simplify a computation model and thus facilitate a focus on mechanical responses. We also examine temporal evolutions of stress states and mobilized friction angles across base, injection-zone, and caprock layers for two different stress regimes: normal-faulting and reverse-faulting. Under the normal-faulting stress regime, the maximum mobilized friction angle occurs inside of the injection zone, which may act to improve the stability of the caprock. Special attention is required, however, because the location of the maximum mobilized friction angle is close to interfaces with the caprock and base layers. The hypothetical stepwise injection of cold fluid is shown to improve the stability of the injection zone to some extent. Under the reverse-faulting stress regime, the maximum mobilized friction angle occurs near the middle of the injection zone; stability in the injection zone is enhanced while that in the caprock/base is aggravated with time. The hypothetical stepwise injection not only helps improve the stability of the injection zone but also delays the moment when the maximum friction angle is mobilized. Finally, we suggest using dimensionless parameters to determine a prevalence of the thermal-stress effect in the injection

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

    NASA Technical Reports Server (NTRS)

    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.

  8. The Rate Constant for the Reaction H + C2H5 at T = 295 - 150K

    NASA Technical Reports Server (NTRS)

    Pimentel, Andre S.; Payne, Walter A.; Nesbitt, Fred L.; Cody, Regina J.; Stief, Louis J.

    2004-01-01

    The reaction between the hydrogen atom and the ethyl (C2H3) radical is predicted by photochemical modeling to be the most important loss process for C2H5 radicals in the atmospheres of Jupiter and Saturn. This reaction is also one of the major sources for the methyl radicals in these atmospheres. These two simplest hydrocarbon radicals are the initial species for the synthesis of larger hydrocarbons. Previous measurements of the rate constant for the H + C2H5 reaction varied by a factor of five at room temperature, and some studies showed a dependence upon temperature while others showed no such dependence. In addition, the previous studies were at higher temperatures and generally higher pressures than that needed for use in planetary atmospheric models. The rate constant for the reaction H + C2H5 has been measured directly at T = 150, 202 and 295 K and at P = 1.0 Torr He for all temperatures and additionally at P = 0.5 and 2.0 Torr He at T = 202 K. The measurements were performed in a discharge - fast flow system. The decay of the C2H5 radical in the presence of excess hydrogen was monitored by low-energy electron impact mass spectrometry under pseudo-first order conditions. H atoms and C2H5 radicals were generated rapidly and simultaneously by the reaction of fluorine atoms with H2 and C2H6, respectively. The total rate constant was found to be temperature and pressure independent. The measured total rate constant at each temperature are: k(sub 1)(295K) = (1.02+/-0.24)x10(exp -10), k(sub 1)(202K) = (1.02+/-0.22)x10(exp -10) and k(sub 1)(150K) = (0.93+/-0.21)x10(exp -10), all in units of cu cm/molecule/s. The total rate constant derived from all the combined measurements is k(sub 1) = (l.03+/-0.17)x10(exp -10) cu cm/molecule/s. At room temperature our results are about a factor of two higher than the recommended rate constant and a factor of three lower than the most recently published study.

  9. Spectral analysis of heart rate variability during constant and pseudorandom exercise.

    PubMed

    Nakamura, Y; Tamaki, K; Kimura, Y

    1990-04-01

    The purpose of this study was to investigate the limitation for applying a linear model to the cardiorespiratory control system. Four subjects performed the two types of exercise bouts, constant (CONST) and pseudorandom (PRBS) exercise, on an electrically braked cycle ergometer at three different work rates. The target work rate of CONST were set to 80, 100, 120% of the individual anaerobic threshold (AT). In PRBS, the work rates were varied between +/- 10% of the individual AT around the respective target work rates of CONST. Although the spectral density of beat-to-beat heart rate fluctuations showed the conventional patterns for most cases, there was no obvious difference between CONST and PRBS. These results indicated that the variation of +/- 10% of AT did not affect the heart rate variation as the output response, suggesting a dilemma inevitable to apply a linear model based on the transfer function.

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

    NASA Technical Reports Server (NTRS)

    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.

  11. Estimating the rate constant of cyclic GMP hydrolysis by activated phosphodiesterase in photoreceptors

    NASA Astrophysics Data System (ADS)

    Reingruber, Jürgen; Holcman, David

    2008-10-01

    The early steps of light response occur in the outer segment of rod and cone photoreceptor. They involve the hydrolysis of cGMP, a soluble cyclic nucleotide, that gates ionic channels located in the outer segment membrane. We shall study here the rate by which cGMP is hydrolyzed by activated phosphodiesterase (PDE). This process has been characterized experimentally by two different rate constants βd and βsub: βd accounts for the effect of all spontaneously active PDE in the outer segment, and βsub characterizes cGMP hydrolysis induced by a single light-activated PDE. So far, no attempt has been made to derive the experimental values of βd and βsub from a theoretical model, which is the goal of this work. Using a model of diffusion in the confined rod geometry, we derive analytical expressions for βd and βsub by calculating the flux of cGMP molecules to an activated PDE site. We obtain the dependency of these rate constants as a function of the outer segment geometry, the PDE activation and deactivation rates and the aqueous cGMP diffusion constant. Our formulas show good agreement with experimental measurements. Finally, we use our derivation to model the time course of the cGMP concentration in a transversally well-stirred outer segment.

  12. Steady-State Computation of Constant Rotational Rate Dynamic Stability Derivatives

    NASA Technical Reports Server (NTRS)

    Park, Michael A.; Green, Lawrence L.

    2000-01-01

    Dynamic stability derivatives are essential to predicting the open and closed loop performance, stability, and controllability of aircraft. Computational determination of constant-rate dynamic stability derivatives (derivatives of aircraft forces and moments with respect to constant rotational rates) is currently performed indirectly with finite differencing of multiple time-accurate computational fluid dynamics solutions. Typical time-accurate solutions require excessive amounts of computational time to complete. Formulating Navier-Stokes (N-S) equations in a rotating noninertial reference frame and applying an automatic differentiation tool to the modified code has the potential for directly computing these derivatives with a single, much faster steady-state calculation. The ability to rapidly determine static and dynamic stability derivatives by computational methods can benefit multidisciplinary design methodologies and reduce dependency on wind tunnel measurements. The CFL3D thin-layer N-S computational fluid dynamics code was modified for this study to allow calculations on complex three-dimensional configurations with constant rotation rate components in all three axes. These CFL3D modifications also have direct application to rotorcraft and turbomachinery analyses. The modified CFL3D steady-state calculation is a new capability that showed excellent agreement with results calculated by a similar formulation. The application of automatic differentiation to CFL3D allows the static stability and body-axis rate derivatives to be calculated quickly and exactly.

  13. Effects of the anion salt nature on the rate constants of the aqueous proton exchange reactions.

    PubMed

    Paredes, Jose M; Garzon, Andres; Crovetto, Luis; Orte, Angel; Lopez, Sergio G; Alvarez-Pez, Jose M

    2012-04-28

    The proton-transfer ground-state rate constants of the xanthenic dye 9-[1-(2-methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (TG-II), recovered by Fluorescence Lifetime Correlation Spectroscopy (FLCS), have proven to be useful to quantitatively reflect specific cation effects in aqueous solutions (J. M. Paredes, L. Crovetto, A. Orte, J. M. Alvarez-Pez and E. M. Talavera, Phys. Chem. Chem. Phys., 2011, 13, 1685-1694). Since these phenomena are more sensitive to anions than to cations, in this paper we have accounted for the influence of salts with the sodium cation in common, and the anion classified according to the empirical Hofmeister series, on the proton transfer rate constants of TG-II. We demonstrate that the presence of ions accelerates the rate of the ground-state proton-exchange reaction in the same order than ions that affect ion solvation in water. The combination of FLCS with a fluorophore undergoing proton transfer reactions in the ground state, along with the desirable feature of a pseudo-dark state when the dye is protonated, allows one unique direct determination of kinetic rate constants of the proton exchange chemical reaction.

  14. Kinetic rate constant prediction supports the conformational selection mechanism of protein binding.

    PubMed

    Moal, Iain H; Bates, Paul A

    2012-01-01

    The prediction of protein-protein kinetic rate constants provides a fundamental test of our understanding of molecular recognition, and will play an important role in the modeling of complex biological systems. In this paper, a feature selection and regression algorithm is applied to mine a large set of molecular descriptors and construct simple models for association and dissociation rate constants using empirical data. Using separate test data for validation, the predicted rate constants can be combined to calculate binding affinity with accuracy matching that of state of the art empirical free energy functions. The models show that the rate of association is linearly related to the proportion of unbound proteins in the bound conformational ensemble relative to the unbound conformational ensemble, indicating that the binding partners must adopt a geometry near to that of the bound prior to binding. Mirroring the conformational selection and population shift mechanism of protein binding, the models provide a strong separate line of evidence for the preponderance of this mechanism in protein-protein binding, complementing structural and theoretical studies.

  15. Extended geometric method: a simple approach to derive adsorption rate constants of Langmuir-Freundlich kinetics.

    PubMed

    Azizian, Saeid; Haerifar, Monireh; Basiri-Parsa, Jalal

    2007-08-01

    A new and simple equation has been presented here for calculation of adsorption and desorption rate constants of Langmuir-Freundlich kinetic equation. The derivation of new equation is on the basis of extension and correction to the geometric method which has been presented by Kuan et al. [Kuan, W.-H., Lo, S.-L., Chang, C.M., Wang, M.K., 2000. A geometric approach to determine adsorption and desorption kinetic constants. Chemosphere 41, 1741-1747] for the kinetics of adsorption/desorption in aqueous solutions. The correction is to consider that the concentration of solute is not constant and changes as adsorption proceeds. The extension is that we applied Langmuir-Freundlich kinetic model instead of Langmuir kinetic model to consider the heterogeneity and therefore it is more applicable to the real systems. For solving Langmuir-Freundlich kinetic model, some geometric methods and also Taylor expansion were used and finally a simple and novel equation was derived (Eq. (20)) for calculation of adsorption rate constant. This new method was named "extended geometric method". The input data of the obtained equation can be simply derived from initial data of adsorption kinetics. Finally the adsorption of methyl orange onto granular activated carbon was carried out at dynamic and equilibrium conditions and the capabilities of extended geometric method were examined by the experimental data.

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

    PubMed

    Höhna, Sebastian

    2014-01-01

    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 to be

  17. Likelihood Inference of Non-Constant Diversification Rates with Incomplete Taxon Sampling

    PubMed Central

    Höhna, Sebastian

    2014-01-01

    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 to be

  18. Effect of Solvent Dielectric Properties on the Spontaneous-Emission Rate Constant of Molecular Singlet Oxygen

    NASA Astrophysics Data System (ADS)

    Jarnikova, E. S.; Parkhats, M. V.; Stasheuski, A. S.; Dzhagarov, B. M.

    2017-01-01

    Quantum yields and luminescence lifetimes of singlet oxygen in 18 different solvents and binary mixtures were measured using laser fluorometry. The results allowed a direct effect of the refractive index on the radiative rate constant kr of the singlet-oxygen a 1 Δ g → X 3 Σ g - transition caused by a change of photon state density in addition to an indirect effect through a local-field factor to be determined. The experimentally observed rise of kr with increasing medium refractive index could not be explained by the influence of only these two factors. The discrepancy was overcome by taking into account changes of the singlet-oxygen transition dipole moment. Consideration of all three factors explained the influence of the medium on rate constant kr

  19. Absolute rate constant for the O plus NO chemiluminescence in the near infrared

    NASA Technical Reports Server (NTRS)

    Golde, M. F.; Roche, A. E.; Kaufman, F.

    1973-01-01

    Infrared chemiluminescence from the process O + NO (+M) NO2 + hv (+M) has been studied between 1.3 and 4.1 micrometer. The wavelength dependence of the continuum between 1.3 and 3.3 micrometer is in fair agreement with previous studies and the measured radiative rate constant at 1.51 micrometer establishes the NO-O glow in this spectral range as a secondary emission standard. Comparison with previous studies of the visible region of the glow implies that the overall radiative rate constant lies in the range (9.4 to 11.2) x 10 to the minus 17 power cu cm sec/1. In the region 3.3 to 4.1 micrometer, the previously observed broad band, peaking at 3.7 micrometer, shows a complex kinetic dependence on O and M.

  20. Direct rate constant measurement of radical disulphide anion formation for cysteine and cysteamine in aqueous solution

    NASA Astrophysics Data System (ADS)

    Mezyk, Stephen P.

    1995-03-01

    The techniques of pulse radiolysis, laser photolysis and absorption spectroscopy have been used to directly determine rate constants for radical disulphide anion formation for cysteine and cysteamine in aqueous solution. The measured values for cysteine, over the pH range 7-12, allowed calculation of individual rate constants for the constituent reactions RS . + RSH → RSSR -. + H + and RS . + RS - → RSSR -. as (3.39 ± 0.31) × 10 8 and (1.21 ± 0.04) × 10 9 dm 3 mol -1 s -1, respectively. Analogous values for cysteamine were also determined by this technique as (3.06 ± 0.16) × 10 8 and (3.65 ± 0.07) × 10 9 dm 3 mol -1 s -1.

  1. Quantitative rate constants for radical reactions in the nanopores of cotton.

    PubMed

    Hunt, Paula; Worrall, David R; Wilkinson, Frank; Batchelor, Stephen N

    2002-07-24

    The understanding of radical reactions in nanostructured materials is important for developing new synthetic procedures and controlling degradation reactions. To develop this area, an easy method for measuring quantitative rate constants of some radical reactions in nanostructures is required. A simple method for measuring the rate constant of dye bleaching, kdye, by organic radicals in such materials is introduced, involving the measurement of microsecond bleaching kinetics by diffuse reflectance spectroscopy, following laser flash creation of the radicals. Using wet and dry cotton as model substrates, we obtained kdye of 2-hydroxy-2-propyl and 1-hydroxy-1-cyclohexyl radicals with reactive red 3 and reactive orange 4 and compared them to solution-phase values. Surprisingly, the reactions in cotton follow simple liquid-phase kinetics and are diffusion-controlled. A cage effect in cotton is also found.

  2. Evaluation of canonical and microcanonical nonadiabatic reaction rate constants by using the Zhu-Nakamura formulas.

    PubMed

    Zhao, Yi; Mil'nikov, Gennady; Nakamura, Hiroki

    2004-11-08

    We consider a problem of calculating both thermal and microcanonical rate constants for nonadiabatic chemical reactions. Instead of using the conventional transition state theory, we use a generalized seam surface and introduce a concept of a coordinate dependent effective nonadiabatic transition probability based on the Zhu-Nakamura theory which can treat the nonadiabatic tunneling properly. The present approach can be combined with Monte Carlo method so as to be applicable to chemical reactions in complicated systems. The method is demonstrated to work well in wide energy and temperature range. Numerical tests also show that it is very essential for accurate evaluation of the thermal rate constant to use the generalized seam surface and take into account the nonadiabatic tunneling effect.

  3. Rate constants of the reactions of ozone with nitriles, acrylates and terpenes in gas phase

    NASA Astrophysics Data System (ADS)

    Munshi, Hushider B.; Rao, K. V. S. Rama; Iyer, R. Mahadeva

    Rate constants for the reactions of acrylonitrile, methacrylonitrile, methyl and ethyl acrylate with O 3 have been determined with the help of a flow system coupled to an u.v. spectrophotometer. The rate constants obtained have enabled an estimation of the tropospheric lifetimes with respect to O 3 and have also offered a clue to the nature of the initial ozone attack on the unsaturates. Non-stoichiometry observed in the case of acrylonitrile and ethyl acrylate has been rationalized by secondary free radical reactions. Absorptivities of the four unsaturates in vapour as well as in the solution phase have been reported. A brief attempt to study ozone-terpene reactions is also described.

  4. Rate constant for the reaction of O(3P) with diacetylene from 210 to 423 K

    NASA Technical Reports Server (NTRS)

    Mitchell, M. B.; Nava, D. F.; Stief, L. J.

    1986-01-01

    The absolute rate constant for the reaction of O(3P) with diacetylene (C4H2) has been measured as a function of pressure and temperature by the flash-photolysis/resonance-fluorescence method. At 298 K and below, no pressure dependence of the rate constant was observed, but at 423 K a moderate (factor-of-2) increase was detected in the range 3 to 75 torr Ar.Results at or near the high-pressure limit are represented by an Arrhenius expression over the temperature range 210 to 423 K. The results are compared with previous determinations, all of which employed the discharge-flow/mass-spectrometry technique. The mechanism of the reaction is considered, including both primary and secondary processes. The heats of formation of the reactants, adducts, and products for the O(3P) + C4H2 reaction are discussed and contrasted with those for O(3P) + C2H2.

  5. Rate constant for formation of chlorine nitrate by the reaction ClO + NO2 + M

    NASA Technical Reports Server (NTRS)

    Leu, M. T.; Lin, C. L.; Demore, W. B.

    1977-01-01

    The pseudo-first-order decay of ClO in a large excess of NO2 was monitored in a discharge flow/mass-spectrometer apparatus in order to measure the rate constant of the reaction ClO + NO2 + M yields ClONO2 + M for M = He, Ar, and N2 over the temperature range from 248 to 417 K. Numerical results are given for He at 248, 299, 360, and 417 K (1 to 9 torr); for Ar at 298 K (1 to 4 torr); and for N2 at 299, 360, and 417 K (1 to 6 torr). Systematic errors are estimated, and identification of the reaction product is discussed. The results obtained are shown to be in excellent agreement with other recent measurements of the same rate constant.

  6. Estimation of Anaerobic Debromination Rate Constants of PBDE Pathways Using an Anaerobic Dehalogenation Model.

    PubMed

    Karakas, Filiz; Imamoglu, Ipek

    2017-04-01

    This study aims to estimate anaerobic debromination rate constants (km) of PBDE pathways using previously reported laboratory soil data. km values of pathways are estimated by modifying a previously developed model as Anaerobic Dehalogenation Model. Debromination activities published in the literature in terms of bromine substitutions as well as specific microorganisms and their combinations are used for identification of pathways. The range of estimated km values is between 0.0003 and 0.0241 d(-1). The median and maximum of km values are found to be comparable to the few available biologically confirmed rate constants published in the literature. The estimated km values can be used as input to numerical fate and transport models for a better and more detailed investigation of the fate of individual PBDEs in contaminated sediments. Various remediation scenarios such as monitored natural attenuation or bioremediation with bioaugmentation can be handled in a more quantitative manner with the help of km estimated in this study.

  7. Absolute rate constants for the reaction of atomic hydrogen with ketene from 298 to 500 K

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    Rate constants for the reaction of atomic hydrogen with ketene have been measured at room temperature by two techniques, flash photolysis-resonance fluorescence and discharge flow-resonance fluorescence. The measured values are (6.19 + or - 1.68) x 10 to the -14th and (7.3 + or - 1.3) x 10 to the -14th cu cm/molecule/s, respectively. In addition, rate constants as a function of temperature have been measured over the range 298-500 K using the FP-RF technique. The results are best represented by the Arrhenius expression k = (1.88 + or - 1.12) x 10 to the -11th exp(-1725 + or - 190/T) cu cm/molecule/s, where the indicated errors are at the two standard deviation level.

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

    PubMed Central

    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. Rate constants of agonist binding to muscarinic receptors in rat brain medulla. Evaluation by competition kinetics

    SciTech Connect

    Schreiber, G.; Henis, Y.I.; Sokolovsky, M.

    1985-07-25

    The method of competition kinetics, which measures the binding kinetics of an unlabeled ligand through its effect on the binding kinetics of a labeled ligand, was employed to investigate the kinetics of muscarinic agonist binding to rat brain medulla pons homogenates. The agonists studied were acetylcholine, carbamylcholine, and oxotremorine, with N-methyl-4-(TH)piperidyl benzilate employed as the radiolabeled ligand. Our results suggested that the binding of muscarinic agonists to the high affinity sites is characterized by dissociation rate constants higher by 2 orders of magnitude than those of antagonists, with rather similar association rate constants. Our findings also suggest that isomerization of the muscarinic receptors following ligand binding is significant in the case of antagonists, but not of agonists. Moreover, it is demonstrated that in the medulla pons preparation, agonist-induced interconversion between high and low affinity bindings sites does not occur to an appreciable extent.

  10. Estimating average annual percent change for disease rates without assuming constant change.

    PubMed

    Fay, Michael P; Tiwari, Ram C; Feuer, Eric J; Zou, Zhaohui

    2006-09-01

    The annual percent change (APC) is often used to measure trends in disease and mortality rates, and a common estimator of this parameter uses a linear model on the log of the age-standardized rates. Under the assumption of linearity on the log scale, which is equivalent to a constant change assumption, APC can be equivalently defined in three ways as transformations of either (1) the slope of the line that runs through the log of each rate, (2) the ratio of the last rate to the first rate in the series, or (3) the geometric mean of the proportional changes in the rates over the series. When the constant change assumption fails then the first definition cannot be applied as is, while the second and third definitions unambiguously define the same parameter regardless of whether the assumption holds. We call this parameter the percent change annualized (PCA) and propose two new estimators of it. The first, the two-point estimator, uses only the first and last rates, assuming nothing about the rates in between. This estimator requires fewer assumptions and is asymptotically unbiased as the size of the population gets large, but has more variability since it uses no information from the middle rates. The second estimator is an adaptive one and equals the linear model estimator with a high probability when the rates are not significantly different from linear on the log scale, but includes fewer points if there are significant departures from that linearity. For the two-point estimator we can use confidence intervals previously developed for ratios of directly standardized rates. For the adaptive estimator, we show through simulation that the bootstrap confidence intervals give appropriate coverage.

  11. Rate constants for reactions of ClO/x/ of atmospheric interest

    NASA Technical Reports Server (NTRS)

    Watson, R. T.

    1977-01-01

    Chemical kinetics measurements on 82 gas phase reactions of chlorine containing species are reviewed. Recommended rate constants are given. The principal species of interest are Cl, Cl2, ClO, Cl2O, ClOO, OClO, CINO, HCl and halo derivatives of methane and ethane. Absorption spectra are given for 21 species. In addition the chemical kinetics methods used to obtain these data are discussed with regard to their applicability and reliability.

  12. Optimal decay rate for the wave equation on a square with constant damping on a strip

    NASA Astrophysics Data System (ADS)

    Stahn, Reinhard

    2017-04-01

    We consider the damped wave equation with Dirichlet boundary conditions on the unit square parametrized by Cartesian coordinates x and y. We assume the damping a to be strictly positive and constant for x<σ and zero for x>σ . We prove the exact t^{-4/3}-decay rate for the energy of classical solutions. Our main result (Theorem 1) answers question (1) of Anantharaman and Léautaud (Anal PDE 7(1):159-214, 2014, Section 2C).

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

    PubMed

    Regnery, J; Wing, A D; Alidina, M; Drewes, J E

    2015-08-01

    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. A method for computing association rate constants of atomistically represented proteins under macromolecular crowding

    NASA Astrophysics Data System (ADS)

    Qin, Sanbo; Cai, Lu; Zhou, Huan-Xiang

    2012-12-01

    In cellular environments, two protein molecules on their way to form a specific complex encounter many bystander macromolecules. The latter molecules, or crowders, affect both the energetics of the interaction between the test molecules and the dynamics of their relative motion. In earlier work (Zhou and Szabo 1991 J. Chem. Phys. 95 5948-52), it has been shown that, in modeling the association kinetics of the test molecules, the presence of crowders can be accounted for by their energetic and dynamic effects. The recent development of the transient-complex theory for protein association in dilute solutions makes it possible to easily incorporate the energetic and dynamic effects of crowders. The transient complex refers to a late on-pathway intermediate, in which the two protein molecules have near-native relative separation and orientation, but have yet to form the many short-range specific interactions of the native complex. The transient-complex theory predicts the association rate constant as ka = ka0exp( - ΔG*el/kBT), where ka0 is the ‘basal’ rate constant for reaching the transient complex by unbiased diffusion, and the Boltzmann factors captures the influence of long-range electrostatic interactions between the protein molecules. Crowders slow down the diffusion, therefore reducing the basal rate constant (to kac0), and induce an effective interaction energy ΔGc. We show that the latter interaction energy for atomistic proteins in the presence of spherical crowders is ‘long’-ranged, allowing the association rate constant under crowding to be computed as kac = kac0exp[ - (ΔG*el + ΔG*c)/kBT]. Applications demonstrate that this computational method allows for realistic modeling of protein association kinetics under crowding.

  15. Revealing equilibrium and rate constants of weak and fast noncovalent interactions.

    PubMed

    Mironov, Gleb G; Okhonin, Victor; Gorelsky, Serge I; Berezovski, Maxim V

    2011-03-15

    Rate and equilibrium constants of weak noncovalent molecular interactions are extremely difficult to measure. Here, we introduced a homogeneous approach called equilibrium capillary electrophoresis of equilibrium mixtures (ECEEM) to determine k(on), k(off), and K(d) of weak (K(d) > 1 μM) and fast kinetics (relaxation time, τ < 0.1 s) in quasi-equilibrium for multiple unlabeled ligands simultaneously in one microreactor. Conceptually, an equilibrium mixture (EM) of a ligand (L), target (T), and a complex (C) is prepared. The mixture is introduced into the beginning of a capillary reactor with aspect ratio >1000 filled with T. Afterward, differential mobility of L, T, and C along the reactor is induced by an electric field. The combination of differential mobility of reactants and their interactions leads to a change of the EM peak shape. This change is a function of rate constants, so the rate and equilibrium constants can be directly determined from the analysis of the EM peak shape (width and symmetry) and propagation pattern along the reactor. We proved experimentally the use of ECEEM for multiplex determination of kinetic parameters describing weak (3 mM > K(d) > 80 μM) and fast (0.25 s ≥ τ ≥ 0.9 ms) noncovalent interactions between four small molecule drugs (ibuprofen, S-flurbiprofen, salicylic acid and phenylbutazone) and α- and β-cyclodextrins. The affinity of the drugs was significantly higher for β-cyclodextrin than α-cyclodextrin and mostly determined by the rate constant of complex formation.

  16. A comparison of constant-load and constant-deflection stress-corrosion tests on precracked DCB specimens. [Double Cantilever Beam

    NASA Technical Reports Server (NTRS)

    Dorward, R. C.; Hasse, K. R.

    1978-01-01

    A comparison is made between measurements of stress-corrosion crack propagation made by a constant-load procedure and by a constant-deflection procedure. Precracked double cantilever beam specimens from 7075 aluminum alloy plate were used. The specimens were oriented in such a way that cracking would begin in the short-transverse plane and would propagate in the rolling direction. The specimens were subjected to a buffered salt-chromate solution and a 3.6% synthetic sea salt solution. The measurements were made optically with a binocular microscope. Stress intensities and crack lengths were calculated and crack velocities were obtained. Velocity was plotted against the average calculated stress intensity. Good agreement between the two methods was found for the salt-chromate solution, although some descrepancies were noted for the artificial sea salt solution.

  17. A comparison of constant-load and constant-deflection stress-corrosion tests on precracked DCB specimens. [Double Cantilever Beam

    NASA Technical Reports Server (NTRS)

    Dorward, R. C.; Hasse, K. R.

    1978-01-01

    A comparison is made between measurements of stress-corrosion crack propagation made by a constant-load procedure and by a constant-deflection procedure. Precracked double cantilever beam specimens from 7075 aluminum alloy plate were used. The specimens were oriented in such a way that cracking would begin in the short-transverse plane and would propagate in the rolling direction. The specimens were subjected to a buffered salt-chromate solution and a 3.6% synthetic sea salt solution. The measurements were made optically with a binocular microscope. Stress intensities and crack lengths were calculated and crack velocities were obtained. Velocity was plotted against the average calculated stress intensity. Good agreement between the two methods was found for the salt-chromate solution, although some descrepancies were noted for the artificial sea salt solution.

  18. Comparisons of measured rate constants with spectroscopically determined electron-transfer parameters.

    PubMed

    Nelsen, Stephen F; Konradsson, Asgeir E; Weaver, Michael N; Stephenson, Rachel M; Lockard, Jenny V; Zink, Jeffrey I; Zhao, Yi

    2007-06-21

    This work involves comparison of rate constants measured for an intervalence (IV) compound with electron-transfer parameters derived from its optical absorption spectrum. The temperature-dependent rate constants for the radical cation having 3-tert-butyl-2,3-diazabicyclo[2.2.2]oct-2-yl (hydrazine) charge-bearing units attached para to a tetramethylbenzene bridge (1+) were previously measured. In this study, resonance Raman is used to calculate the magnitudes of the distortions of normal modes of vibration caused by excitation into the intervalence absorption band. These data produce a vibrational reorganization energy lambdavsym of 9250 cm(-1), and averaged single-mode omegav for use in the Golden Rule equation of 697 cm(-1). Zhu-Nakamura theory has been used to calculate preexponential factors for analysis of the previously measured variable temperature optical spectra using quartic-enhanced intervalence bands to extract the total reorganization energy and the intramolecular electron-transfer rate constants for intramolecular electron transfer using electron spin resonance. In contrast to using the Golden Rule equation, separation of lambda into solvent and vibrational components is not significant for these data. The Zhu-Nakamura theory calculations produce ln(k/T) versus 1/T slopes that are consistent with the experimental data for electronic couplings that are somewhat larger than the values obtained from the optical spectra using Hush's method.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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.

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

    PubMed

    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.

  2. Rate constant calculations of H-atom abstraction reactions from ethers by HȮ2 radicals.

    PubMed

    Mendes, Jorge; Zhou, Chong-Wen; Curran, Henry J

    2014-02-27

    In this work, we detail hydrogen atom abstraction reactions from six ethers by the hydroperoxyl radical, including dimethyl ether, ethyl methyl ether, propyl methyl ether, isopropyl methyl ether, butyl methyl ether, and isobutyl methyl ether, in order to test the effect of the functional group on the rate constant calculations. The Møller-Plesset (MP2) method with the 6-311G(d,p) basis set has been employed in the geometry optimizations and frequency calculations of all of the species involved in the above reaction systems. The connections between each transition state and the corresponding local minima have been determined by intrinsic reaction coordinate calculations. Energies are reported at the CCSD(T)/cc-pVTZ level of theory and include the zero-point energy corrections. As a benchmark in the electronic energy calculations, the CCSD(T)/CBS extrapolation was used for the reactions of dimethyl ether + HȮ2 radicals. A systematic calculation of the high-pressure limit rate constants has been performed using conventional transition-state theory, including asymmetric Eckart tunneling corrections, in the temperature range of 500-2000 K. The one dimensional hindrance potentials obtained at MP2/6-311G(d,p) for the reactants and transition states have been used to describe the low frequency torsional modes. Herein, we report the calculated individual, average, and total rate constants. A branching ratio analysis for every reaction site has also been performed.

  3. QSPR prediction of the hydroxyl radical rate constant of water contaminants.

    PubMed

    Borhani, Tohid Nejad Ghaffar; Saniedanesh, Mohammadhossein; Bagheri, Mehdi; Lim, Jeng Shiun

    2016-07-01

    In advanced oxidation processes (AOPs), the aqueous hydroxyl radical (HO) acts as a strong oxidant to react with organic contaminants. The hydroxyl radical rate constant (kHO) is important for evaluating and modelling of the AOPs. In this study, quantitative structure-property relationship (QSPR) method is applied to model the hydroxyl radical rate constant for a diverse dataset of 457 water contaminants from 27 various chemical classes. The constricted binary particle swarm optimization and multiple-linear regression (BPSO-MLR) are used to obtain the best model with eight theoretical descriptors. An optimized feed forward neural network (FFNN) is developed to investigate the complex performance of the selected molecular parameters with kHO. Although the FFNN prediction results are more accurate than those obtained using BPSO-MLR, the application of the latter is much more convenient. Various internal and external validation techniques indicate that the obtained models could predict the logarithmic hydroxyl radical rate constants of a large number of water contaminants with less than 4% absolute relative error. Finally, the above-mentioned proposed models are compared to those reported earlier and the structural factors contributing to the AOP degradation efficiency are discussed. Copyright © 2016 Elsevier Ltd. All rights reserved.

  4. Identifiability and interval identifiability of mammillary and catenary compartmental models with some known rate constants.

    PubMed

    Vicini, P; Su, H; DiStefano, J J

    2000-10-01

    The identifiability problem is addressed for n-compartment linear mammillary and catenary models, for the common case of input and output in the first compartment and prior information about one or more model rate constants. We first define the concept of independent constraints and show that n-compartment linear mammillary or catenary models are uniquely identifiable under n-1 independent constraints. Closed-form algorithms for bounding the constrained parameter space are then developed algebraically, and their validity is confirmed using an independent approach, namely joint estimation of the parameters of all uniquely identifiable submodels of the original multicompartmental model. For the noise-free (deterministic) case, the major effects of additional parameter knowledge are to narrow the bounds of rate constants that remain unidentifiable, as well as to possibly render others identifiable. When noisy data are considered, the means of the bounds of rate constants that remain unidentifiable are also narrowed, but the variances of some of these bound estimates increase. This unexpected result was verified by Monte Carlo simulation of several different models, using both normally and lognormally distributed data assumptions. Extensions and some consequences of this analysis useful for model discrimination and experiment design applications are also noted.

  5. Quantitative structure-reactivity relationships of hydroxyl radical rate constants for linear and cyclic volatile methylsiloxanes.

    PubMed

    Kim, Jaeshin; Xu, Shihe

    2017-07-18

    An accurate understanding of the fate of volatile methylsiloxanes (VMS) in air is crucial for determining their persistence and concentrations in the environment. Although oxidation by atmospheric hydroxyl radicals (•OH) is considered as a major degradation mechanism for airborne VMS, the existing bimolecular rate constants with •OH measured and modeled for any given VMS compound varied greatly, depending on the approaches used to generate the data. The objectives of the present study were to measure •OH reaction rate constants for 4 cyclic and 4 linear VMS based on a relative rate method using a newly designed atmospheric chamber and to establish structure-reactivity relationships for the kinetics. In the past, the reaction rate constants for VMS were generally recognized to increase with the number of the methyl groups per molecule, the only differential factor in the existing models. However, the new measurements indicated that molecular structure should also be considered in the prediction of the reaction rates. Better empirical models were developed by simple and multiple linear regressions of the measured values from the present study and the literature. A high correlation existed for the reaction rates with the number of the methyl group attached at 2 distinct siloxane structures (i.e., linear and cyclic VMS). Even better correlations were obtained with one or 2 molecular descriptors that are directly related to the size of VMS, which, in turn, not only depend on the number of methyl groups, but the linear/cyclic structures as well for permethylsiloxanes. Environ Toxicol Chem 2017;9999:1-6. © 2017 SETAC. © 2017 SETAC.

  6. Analytical results for the pulsed operation of high field constant stress coils

    NASA Astrophysics Data System (ADS)

    Vanbockstal, Luc; Askenazy, Salomon; Herlach, Fritz; Schneider-Muntau, Hans-Jorg

    1994-07-01

    Based on the analytical expressions for the radial current density in coils optimized for constant stress, the implications for pulsed operation are discussed; the pulse duration, peak power and energy are determined. A cut-off on the current density, which peaks at the inside of the coil, limits the localized heating and increases the pulse duration at the expense of center field or materials requirements. From the relation between strength, conductivity and cut-off level, optimal properties of construction materials are determined.

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

    PubMed

    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.

  8. Theoretical growth rates, periods, and pulsation constants for long-period variables

    NASA Astrophysics Data System (ADS)

    Fox, M. W.; Wood, P. R.

    1982-08-01

    An extensive set of linear, nonadiabatic pulsation models for red giant and supergiant stars is computed, in order that the dependence of pulsation periods (P), pulsation constants (Q), and growth rate on physical input parameters can be determined from the systematic behavior seen in the models. Also investigated is the extent of the dependence of P, Q, and growth rate on uncertain quantities such as atmospheric molecular opacity, surface boundary conditions, and effective temperature. The growth rate for the fundamental mode is found to increase with luminosity on the giant branch while the growth rate for the first overtone decreases. Dynamical instabilities found in previous adiabatic models of extreme red giants do not occur when nonadiabatic effects are included in the models.

  9. Effects of insulin on glucose turnover rates in vivo: isotope dilution versus constant specific activity technique.

    PubMed

    Hother-Nielsen, O; Henriksen, J E; Holst, J J; Beck-Nielsen, H

    1996-01-01

    The conventional isotope dilution technique was compared with the more accurate constant specific activity (SA) method at six different insulin levels. Paired euglycemic clamp studies were performed in 30 normal subjects (4-hour insulin infusion: 5, 10, 20, 40, 80, and 160 mU . m-2 . min-1) using primed-constant 3-3H-glucose infusion and either conventional unlabeled glucose infusates (Cold-GINF) or labeled glucose infusates (Hot-GINF) to maintain constant SA. At all insulin levels, both glucose disappearance (Rd) and hepatic glucose production (HGP) were underestimated by the conventional technique, and errors during the first 2 hours correlated with glucose infusion rates (GIRs) (r = .93, P < .00001). During the second hour, mean underestimation of HGP varied from 20% +/- 9% to 84% +/- 16% of basal rates from low-dose to high-dose insulin infusion studies. During prolonged equilibration (3 to 4 hours), errors decreased but were still significant in the two low-dose insulin infusion protocols during the fourth hour. In conclusion, using the conventional isotope dilution technique, suppression of glucose production was overestimated and stimulation of glucose Rd was underestimated, and these errors were greater the higher the GIR. Thus, artifactually greater hepatic and smaller peripheral effects may have been assumed for factors or therapies that influence insulin sensitivity in previous studies using a conventional isotope dilution technique, and therefore, reevaluation of these issues may be relevant in future studies.

  10. Direct Shear Tests of Sandstone Under Constant Normal Tensile Stress Condition Using a Simple Auxiliary Device

    NASA Astrophysics Data System (ADS)

    Cen, Duofeng; Huang, Da

    2017-06-01

    Tension-shear failure is a typical failure mode in the rock masses in unloading zones induced by excavation or river incision, etc., such as in excavation-disturbed zone of deep underground caverns and superficial rocks of high steep slopes. However, almost all the current shear failure criteria for rock are usually derived on the basis of compression-shear failure. This paper proposes a simple device for use with a servo-controlled compression-shear testing machine to conduct the tension-shear tests of cuboid rock specimens, to test the direct shear behavior of sandstone under different constant normal tensile stress conditions ( σ = -1, -1.5, -2, -2.5 and -3 MPa) as well as the uniaxial tension behavior. Generally, the fracture surface roughness decreases and the proportion of comminution areas in fracture surface increases as the change of stress state from tension to tension-shear and to compression-shear. Stepped fracture is a primary fracture pattern in the tension-shear tests. The shear stiffness, shear deformation and normal deformation (except the normal deformation for σ = -1 MPa) decrease during shearing, while the total normal deformation containing the pre-shearing portion increases as the normal tensile stress level (| σ|) goes up. Shear strength is more sensitive to the normal tensile stress than to the normal compressive stress, and the power function failure criterion (or Mohr envelope form of Hoek-Brown criterion) is examined to be the optimal criterion for the tested sandstone in the full region of tested normal stress in this study.

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

    PubMed

    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.

  12. Laser Measurements of the H Atom + Ozone Rate Constant at Mesospheric Temperatures.

    PubMed

    Liu, Yingdi; Peng, Jian; Reppert, Kelsey; Callahan, Sara; Smith, Gregory P

    2016-06-09

    The exothermic H + O3 reaction produces OH(v) Meinel band emissions, used to derive mesospheric H concentrations and chemical heating rates. We remeasured its rate constant to reduce its uncertainty and extended the measurements to lower mesospheric temperatures using modern laser-induced fluorescence (LIF) techniques. H atoms were produced by pulsed ultraviolet laser trace photolysis of O3, followed by reaction of O((1)D) with added H2. A second, delayed, frequency-mixed dye laser measured the reaction decay rate with the remaining ozone using LIF. We monitored either the H atom decay by two photon excitation at 205 nm and detection of red fluorescence, or the OH (v = 9) product time evolution with excitation of the B(2)Σ(+)-X(2)Π (0,9) band at 237 nm and emission in the blue B(2)Σ(+)-A(2)Σ(+) (0,7) band. By cooling the enclosed low pressure flow cell we obtained measurements from 140 to 305 K at 20 to 200 Torr in Ar. Small kinetic modeling corrections were made for secondary regeneration of H atoms. The results are consistent with the current NASA JPL recommendation for this rate constant and establish its extrapolation down to the lower temperatures of the mesosphere.

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

    NASA Astrophysics Data System (ADS)

    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.

  14. Isothermal titration calorimetry determination of individual rate constants of trypsin catalytic activity.

    PubMed

    Aguirre, César; Condado-Morales, Itzel; Olguin, Luis F; Costas, Miguel

    2015-06-15

    Determination of individual rate constants for enzyme-catalyzed reactions is central to the understanding of their mechanism of action and is commonly obtained by stopped-flow kinetic experiments. However, most natural substrates either do not fluoresce/absorb or lack a significant change in their spectra while reacting and, therefore, are frequently chemically modified to render adequate molecules for their spectroscopic detection. Here, isothermal titration calorimetry (ITC) was used to obtain Michaelis-Menten plots for the trypsin-catalyzed hydrolysis of several substrates at different temperatures (278-318K): four spectrophotometrically blind lysine and arginine N-free esters, one N-substituted arginine ester, and one amide. A global fitting of these data provided the individual rate constants and activation energies for the acylation and deacylation reactions, and the ratio of the formation and dissociation rates of the enzyme-substrate complex, leading also to the corresponding free energies of activation. The results indicate that for lysine and arginine N-free esters deacylation is the rate-limiting step, but for the N-substituted ester and the amide acylation is the slowest step. It is shown that ITC is able to produce quality kinetic data and is particularly well suited for those enzymatic reactions that cannot be measured by absorption or fluorescence spectroscopy.

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

    SciTech Connect

    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.

  16. Atmospheric fate of a series of carbonyl nitrates: photolysis frequencies and OH-oxidation rate constants.

    PubMed

    Suarez-Bertoa, R; Picquet-Varrault, B; Tamas, W; Pangui, E; Doussin, J-F

    2012-11-20

    Multifunctional organic nitrates are potential NO(x) reservoirs whose atmospheric chemistry is somewhat little known. They could play an important role in the spatial distribution of reactive nitrogen species and consequently in ozone formation and distribution in remote areas. In this work, the rate constants for the reaction with OH radical and the photolysis frequencies of α-nitrooxyacetone, 3-nitrooxy-2-butanone, and 3-methyl-3-nitrooxy-2-butanone have been determined at room temperature at 1000 mbar total pressure of synthetic air. The rate constants for the OH oxidation were measured using the relative rate technique, with methanol as reference compound. The following rate constants were obtained for the reaction with OH: k(OH) = (6.7 ± 2.5) × 10(-13) cm(3) molecule(-1) s(-1) for α-nitrooxyacetone, (10.6 ± 4.1) × 10(-13) cm(3) molecule(-1) s(-1) for 3-nitrooxy-2-butanone, and (2.6 ± 0.9) × 10(-13) cm(3) molecule(-1) s(-1) for 3-methyl-3-nitrooxy-2-butanone. The corresponding photolysis frequencies extrapolated to typical atmospheric conditions for July first at noon at 40° latitude North were (4.8 ± 0.3) × 10(-5) s(-1), (5.7 ± 0.3) × 10(-5) s(-1), and (7.4 ± 0.2) × 10(-5) s(-1), respectively. The data show that photolysis is a major atmospheric sink for these organic nitrates.

  17. Determination of first-order degradation rate constants from monitoring networks.

    PubMed

    Beyer, Christof; Chen, Cui; Gronewold, Jan; Kolditz, Olaf; Bauer, Sebastian

    2007-01-01

    In this article, different strategies for estimating first-order degradation rate constants from measured field data are compared by application to multiple, synthetic, contaminant plumes. The plumes were generated by numerical simulation of contaminant transport and degradation in virtual heterogeneous aquifers. These sites were then individually and independently investigated on the computer by installation of extensive networks of observation wells. From the data measured at the wells, that is, contaminant concentrations, hydraulic conductivities, and heads, first-order degradation rates were estimated by three 1D centerline methods, which use only measurements located on the plume axis, and a two-dimensional method, which uses all concentration measurements available downgradient from the contaminant source. Results for both strategies show that the true rate constant used for the numerical simulation of the plumes in general tends to be overestimated. Overestimation is stronger for narrow plumes from small source zones, with an average overestimation factor of about 5 and single values ranging from 0.5 to 20, decreasing for wider plumes, with an average overestimation factor of about 2 and similar spread. Reasons for this overestimation are identified in the velocity calculation, the dispersivity parameterization, and off-centerline measurements. For narrow plumes, the one- and the two-dimensional strategies show approximately the same amount of overestimation. For wider plumes, however, incorporation of all measurements in the two-dimensional approach reduces the estimation error. No significant relation between the number of observation wells in the monitoring network and the quality of the estimated rate constant is found for the two-dimensional approach.

  18. Osmosis-induced swelling of Eurobitum bituminized radioactive waste in constant total stress conditions

    NASA Astrophysics Data System (ADS)

    Valcke, E.; Marien, A.; Smets, S.; Li, X.; Mokni, N.; Olivella, S.; Sillen, X.

    2010-11-01

    In geological disposal conditions, contact of Eurobitum bituminized radioactive waste, which contains high amounts of the hygroscopic and highly soluble NaNO 3, with groundwater will result in water uptake and swelling of the waste, and in subsequent leaching of the embedded NaNO 3 and radionuclides. The swelling of and the NaNO 3 leaching from non-radioactive Eurobitum samples, comprised between two stainless steel filters and in contact with 0.1 M KOH, was studied in restricted (semi-confined) swelling conditions, i.e. under a constant total stress, or counterpressure, of 2.2, 3.3, or 4.4 MPa ( i.e. oedometer conditions). Four tests were stopped after hydration times between 800 and 1500 days, and the samples were analyzed by micro-focus X-ray Computer Tomography (μCT) and by Environmental Scanning Electron Microscopy (ESEM). The complete set of data enabled a consistent interpretation of the observations and lead to an improved understanding of the phenomenology of the water uptake, swelling, and NaNO 3 leaching in restricted swelling conditions. Under the studied conditions, the bituminous matrix surrounding the NaNO 3 crystals and pores with NaNO 3 solution behaved as a highly efficient semi-permeable membrane, i.e. osmotic processes occurred. In the main part of the leached layers, a high average NaNO 3 concentration and related to this a high osmotic pressure prevailed, explaining why in the studied range the swelling was not measurably affected by the counterpressure. At the interface with the stainless steel filters, a low permeable re-compressed bitumen layer was formed, contributing to the slow release of NaNO 3 compared to the water uptake rate. A fully coupled Chemo-Hydro-Mechanical (CHM) constitutive model has been developed that integrates the key processes involved and that reproduces satisfactorily the results; this is presented in another work. Combination of the experimental and the modelling study allow to conclude that under semi

  19. Laboratory evaluation of mechanical properties of rock using an automated triaxial compression test with a constant mean stress criterion

    SciTech Connect

    Mellegard, K.D.; Pfeifle, T.W.

    1999-07-01

    A computerized, servohydraulic test system has been used in the laboratory to perform axisymmetric, triaxial compression tests on natural rock salt using a load path that maintains constant mean stress. The constant mean stress test protocol illustrates that modern test systems allow a nonstandard load path which can focus on a particular aspect of rock characterization; namely, the onset of dilation. Included are discussions of how the constant mean stress test could be used to investigate material anisotropy and determine elastic moduli. The results from the constant mean stress tests are compared to test results from a traditional test method. The paper also addresses system calibration concerns and the effects of pressure changes on the direct-contact extensometers used to measure strain.

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

    PubMed

    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.

  1. Mn2O3 Slurry Reuse by Circulation Achieving High Constant Removal Rate

    NASA Astrophysics Data System (ADS)

    Kishii, Sadahiro; Nakamura, Ko; Hanawa, Kenzo; Watanabe, Satoru; Arimoto, Yoshihiro; Kurokawa, Syuhei; Doi, Toshiro K.

    2012-04-01

    Fumed silica is widely used in SiO2 chemical mechanical polishing (CMP). In semiconductor processes, only fresh slurry is used, and used slurry is disposed. Sustainable development demands a reduction in waste. Since reuse of slurry is effective for reducing the amount of used slurry generated, we investigated the reuse of Mn2O3 slurry and conventional fumed silica slurry. In both cases, abrasive concentration decreases as reuse time increases. The removal rate for Mn2O3 slurry maintains a value 4 times that of the conventional fumed silica slurry during slurry reuse, because the removal rate for Mn2O3 slurry is almost constant for solid concentrations between 1.0 and 10 wt %. Pad conditioning was not performed for Mn2O3 slurry. The removal rate for conventional slurry decreases as the number of times of reuse increases, even when pad conditioning is appropriately performed.

  2. Strain rate and stress field in Switzerland

    NASA Astrophysics Data System (ADS)

    Houlié, Nicolas; Woessner, Jochen; Giardini, Domenico; Rothacher, Markus

    2016-04-01

    In this study we test whether the surface deformation and the seismic activity are in agreement in terms of seismic moment release and stress/strain orientations within the territory of Switzerland. We find that for most of the country, the stress released (~2.0 10E11 N·m/yr) is consistent with the lithosphere deformation (<5 10E-8 /yr) constrained using the Global Positioning System (GPS). South of the Alpine front, we note that surface strain rates displays few agreement with long-term (and deep) deformation of the upper mantle. In this area, we propose that shear strain is being distributed in the upper crust as a result of the clockwise rotation of the Adria plate. For three regions (Basel, Swiss Jura and Ticino), we find that seismic current activity and surface deformation not to be in agreement. In the Basel area, deep seismicity exists while surface deformation is absent. This situation contrasts to what is found in the Ticino and the Swiss Jura, where seismic activity is close to absent but surface deformation is detected (~2 10E-8 /yr). While the surface deformation and seismic activity is inconsistent for the Ticino, we find them to comply in the Valais region where MW≥6 events are historically documented. Our comparison implies that the Ticino faces the potential of damaging earthquakes every hundred to few hundred years.

  3. The Proline Enamine Formation Pathway Revisited in Dimethyl Sulfoxide: Rate Constants Determined via NMR.

    PubMed

    Haindl, Michael H; Hioe, Johnny; Gschwind, Ruth M

    2015-10-14

    Enamine catalysis is a fundamental activation mode in organocatalysis and can be successfully combined with other catalytic methods, e.g., photocatalysis. Recently, the elusive enamine intermediates were detected, and their stabilization modes were revealed. However, the formation pathway of this central organocatalytic intermediate is still a matter of dispute, and several mechanisms involving iminium and/or oxazolidinone are proposed. Here, the first experimentally determined rate constants and rates of enamine formation are presented using 1D selective exchange spectroscopy (EXSY) buildup curves and initial rate approximation. The trends of the enamine formation rates from exo-oxazolidinones and endo-oxazolidinones upon variation of the proline and water concentrations as well as the nucelophilic/basic properties of additives are investigated together with isomerization rates of the oxazolidinones. These first kinetic data of enamine formations in combination with theoretical calculations reveal the deprotonation of iminium intermediates as the dominant pathway in dimethyl sulfoxide (DMSO). The dominant enamine formation pathway varies according to the experimental conditions, e.g., the presence and strength of basic additives. The enamine formation is zero-order in proline and oxazolidinones, which excludes the direct deprotonation of oxazolidinones via E2 mechanism. The nucleophilicity of the additives influences only the isomerization rates of the oxazolidinones and not the enamine formation rates, which excludes a nucleophile-assisted anti elimination of oxazolidinones as a major enamine formation pathway.

  4. Neuromechanical response to spinal manipulation therapy: effects of a constant rate of force application.

    PubMed

    Nougarou, François; Pagé, Isabelle; Loranger, Michel; Dugas, Claude; Descarreaux, Martin

    2016-06-02

    Neuromechanical responses to spinal manipulation therapy (SMT) have been shown to be modulated through the variation of SMT biomechanical parameters: peak force, time to peak force, and preload force. Although rate of force application was modulated by the variation of these parameters, the assumption that neuromuscular responses are modulated by the rate of force application remains to be confirmed. Therefore, the purpose of the present study was to evaluate the effect of a constant rate of force application in neuromechanical responses to SMT in healthy adults. Four SMT force-time profiles presenting different time to peak force and peak force, but with a constant rate of force application were applied on 25 healthy participants' T7 transverse processes. Muscular responses were recorded through surface electromyography electrodes (T6 and T8 levels), while vertebral displacements were assessed through pasted kinematic markers on T6 to T8 spinous processes. Effects of SMT force-time profiles on neuromechanical responses were assessed using repeated-measures ANOVAs. There was no main effect of SMT force-time profile modulation on muscular responses (ps > .05) except for the left T8 (F (3, 72) = 3.23, p = .03) and left T6 (F (3, 72) = 2.94, p = .04). Muscular responses were significantly lower for the lowest peak force condition than the highest (for T8) or second highest (for T6). Analysis showed that increasing the SMT peak force (and concomitantly time to peak force) led to a significant vertebral displacement increase for the contacted vertebra (F T7 (1, 17) = 354.80, p < .001) and both adjacent vertebras (F T6 (1, 12) = 104.71, p < .001 and F T8 (1, 19) = 468.68, p < .001). This study showed that peak force modulation using constant rate of force application leads to similar neuromuscular responses. Coupled with previous investigations of SMT peak force and duration effects, the results suggest that neuromuscular

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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, 20μm), a broad range of kin values (0.02-30s(-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 10s(-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.

  7. Rate Constants of Hydroperoxyl Radical Addition to Cyclic Nitrones: A DFT Study

    PubMed Central

    Villamena, Frederick A.; Merle, John K.; Hadad, Christopher M.; Zweier*, Jay L.

    2008-01-01

    Nitrones are potential synthetic antioxidants against the reduction of radical-mediated oxidative damage in cells, and as analytical reagent for the identification of HO2• and other such transient species. In this work, the PCM/B3LYP/6−31+G(d,p)//B3LYP/6−31G(d) and PCM/mPW1K/6−31+G(d,p) density functional theory (DFT) methods were employed to predict the reactivity of HO2• with various functionalized nitrones as spin traps. The calculated second-order rate constants and free energies of reaction at both levels of theory were in the range of 100−103 M−1 s−1 and 1 to −12 kcal mol−1, respectively, and the rate constants for some nitrones are on the same order of magnitude as those observed experimentally. The trend in HO2• reactivity to nitrones could not be explained solely on the basis of the relationship of the theoretical positive charge densities on the nitronyl-C, with their respective ionization potentials, electron affinities, rate constants, or free energies of reaction. However, various modes of intramolecular H-bonding interaction were observed at the transition state (TS) structures of HO2• addition to nitrones. The presence of intramolecular H-bonding interactions in the transition states were predicted and may play a significant role towards a facile addition of HO2• to nitrones. In general, HO2• addition to ethoxycarbonyl- and spirolactam- substituted nitrones, as well as those nitrones without electron-withdrawing substituents, such as 5,5-dimethyl-pyrroline N-oxide (DMPO) and 5-spirocyclopentyl-pyrroline N-oxide (CPPO), are most preferred compared to the methylcarbamoyl-substituted nitrones. This study suggests that the use of specific spin traps for efficient trapping of HO2• could pave the way toward improved radical detection and antioxidant protection. PMID:17845014

  8. Theoretical study and rate constant calculation of the CH2O+CH3 reaction

    NASA Astrophysics Data System (ADS)

    Liu, Jing-yao; Li, Ze-sheng; Wu, Jia-yan; Wei, Zhi-gang; Zhang, Gang; Sun, Chia-chung

    2003-10-01

    The potential energy surface of the CH2O+CH3 reaction is explored at the MP2/6-311++G(d,p), MP4SDQ/6-311G(d,p), and QCISD(T)/6-311+G(3df,2p) (single point) levels of theory. Theoretical calculations suggest that the major product channel (R1) is the hydrogen abstraction leading to the product P1 CHO+CH4 (R1), while the addition process leading to P2H+CH3CHO (R2) appears to be negligibly small. The calculated enthalpies and dissociation activation energies for CH3CH2O and CH3OCH2 radicals involved in the reaction are in line with the experimental values. Dual-level dynamics calculation is carried out for the direct hydrogen abstraction channel. The energy profile of (R1) is refined with the interpolated single-point energies (ISPE) method at the QCISD(T)//MP2 level. The rate constants, which are evaluated by canonical variational transition-state theory (CVT) including small-curvature tunneling (SCT) correction, are in good agreement with the available experimental data. It is shown that tunneling effect plays a significant role in the rate constant calculation; and as a result, the CVT/SCT rate constants exhibit typical non-Arrhenius behavior over a wide temperature range 300-2000 K. The three parameter expression is k=6.35×10-26 T4.4 exp(-2450/T) cm3 molecule-1 s-1.

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

    PubMed

    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.

  10. Muscle oxygenation trends during constant work rate cycle exercise in men and women.

    PubMed

    Bhambhani, Y; Buckley, S; Susaki, T

    1999-01-01

    To examine the relationship between muscle oxygenation and arteriovenous oxygen difference [(a - v)O2diff)] at four constant rate workloads in healthy men and women and to compare these responses between the genders. Nineteen men and 14 women consented to perform an incremental test to identify the lactic acidosis threshold (LAT) and maximal aerobic power (VO2max) and an intermittent constant work rate test at an oxygen uptake corresponding to 40% LAT, 80% LAT, 25% LAT-VO2max, and 50% LAT-VO2max. Each exercise interval was 5 min long followed by 2 min of recovery. Cardiac output was measured by CO2 rebreathing at each workload from which (a - v)O2diff was computed. Tissue absorbency was measured from the vastus lateralis in both the test sessions using near infrared spectroscopy (NIRS). Muscle oxygenation during constant work rate exercise and recovery was expressed as a percentage (%Mox) of the maximum range observed during incremental exercise and recovery. A systematic decrease was observed in %Mox with increasing intensity, followed by a proportional increase during recovery from each exercise bout. Significant inverse relationships were observed between %Mox and (a - v)O2diff in men (r = -0.34) and women (r = -0.31) across the four intensities. Mean %Mox was significantly higher (P < 0.05) in women compared with men, suggesting lesser deoxygenation at the same relative exercise intensity. %Mox was not an accurate predictor of mixed (a - v)O2diff during exercise because of the low common variance between these two variables, and it is unclear whether the gender difference in %Mox is a true physiological phenomenon or whether it is an artifact of the NIRS technique.

  11. Constant rate of p53 tetramerization in response to DNA damage controls the p53 response

    PubMed Central

    Gaglia, Giorgio; Lahav, Galit

    2014-01-01

    The dynamics of the tumor suppressor protein p53 have been previously investigated in single cells using fluorescently tagged p53. Such approach reports on the total abundance of p53 but does not provide a measure for functional p53. We used fluorescent protein-fragment complementation assay (PCA) to quantify in single cells the dynamics of p53 tetramers, the functional units of p53. We found that while total p53 increases proportionally to the input strength, p53 tetramers are formed in cells at a constant rate. This breaks the linear input–output relation and dampens the p53 response. Disruption of the p53-binding protein ARC led to a dose-dependent rate of tetramers formation, resulting in enhanced tetramerization and induction of p53 target genes. Our work suggests that constraining the p53 response in face of variable inputs may protect cells from committing to terminal outcomes and highlights the importance of quantifying the active form of signaling molecules in single cells. Quantification of the dynamics of p53 tetramers in single cells using a fluorescent protein-fragment complementation assay reveals that, while total p53 increases proportionally to the DNA damage strength, p53 tetramers are formed at a constant rate. PMID:25344068

  12. Rate constant and reaction channels for the reaction of atomic nitrogen with the ethyl radical

    SciTech Connect

    Stief, L.J.; Nesbitt, F.L.; Payne, W.A. ); Kuo, S.C.; Tao, W.; Klemm, R.B. )

    1995-04-01

    The absolute rate constant and primary reaction products have been determined at [ital T]=298 K for the atom--radical reaction N([sup 4][ital S])+C[sub 2]H[sub 5] in a discharge flow system with collision-free sampling to a mass spectrometer. The rate constant measurements employed low energy electron impact ionization while the product study used dispersed synchrotron radiation as the photoionization source. The rate constant was determined under pseudo-first-order conditions by monitoring the decay of C[sub 2]H[sub 5] or C[sub 2]D[sub 5] as a function of time in the presence of excess N atoms. The result is [ital k]=(1.1[plus minus]0.3)[times]10[sup [minus]10] cm[sup 3] molecule[sup [minus]1] s[sup [minus]1]. For the reaction product experiments using photoionization mass spectrometry, products observed at 114 nm (10.9 eV) were CD[sub 3], D[sub 2]CN and C[sub 2]D[sub 4] for the N+C[sub 2]D[sub 5] reaction. The product identification is based on the unambiguous combination of product [ital m]/[ital z] values, the shift of the [ital m]/[ital z] peaks observed for the N+C[sub 2]D[sub 5] reaction products with respect to the N+C[sub 2]H[sub 5] reaction products and the photoionization threshold measured for the major products. The observed products are consistent with the occurrence of the reaction channels D[sub 2]CN+CD[sub 3](2a) and C[sub 2]D[sub 4]+ND(2c). Formation of C[sub 2]D[sub 4] product via channel (2c) accounts for approximately 65% of the C[sub 2]D[sub 5] reacted. Most, if not all, of the remaining 35% is probably accounted for by channel (2a). These rate constant and product results are compared with those for the N+CH[sub 3] reaction as well as other atom+C[sub 2]H[sub 5] reactions. The role of the N+C[sub 2]H[sub 5] reaction in the formation of HCN in the atmospheres of Titan and Neptune is briefly considered. (Abstract Truncated)

  13. Rate constant for the reaction NH2 + NO from 216 to 480 K

    NASA Technical Reports Server (NTRS)

    Stief, L. J.; Brobst, W. D.; Nava, D. F.; Borkowski, R. P.; Michael, J. V.

    1982-01-01

    The absolute rate constant was measured by the technique of flash photolysis-laser induced fluorescence (FP-LIF). NH2 radicals were produced by the flash photolysis of ammonia and the fluorescent NH2 photons were measured by multiscaling techniques. At each temperature, the results were independent of variations in total pressure, and flash intensity. The results are compared with previous determinations using the techniques of mass spectrometry, absorption spectroscopy, laser absorption spectroscopy, and laser induced fluorescence. The implications of the results are discussed with regard to combustion, post combustion, and atmospheric chemistry. The results are also discussed theoretically.

  14. Determination of the strong coupling constant from jet rates in deep inelastic scattering

    NASA Astrophysics Data System (ADS)

    Ahmed, T.; Aid, S.; Andreev, V.; Andrieu, B.; Appuhn, R.-D.; Arpagaus, M.; Babaev, A.; Baehr, J.; Bán, J.; Baranov, P.; Barrelet, E.; Bartel, W.; Barth, M.; Bassler, U.; Beck, H. P.; Behrend, H.-J.; Belousov, A.; Berger, Ch.; Bergstein, H.; Bernardi, G.; Bernet, R.; Bertrand-Coremans, G.; Besançon, M.; Beyer, R.; Biddulph, P.; Bizot, J. C.; Blobel, V.; Borras, K.; Botterweck, F.; Boudry, V.; Braemer, A.; Brasse, F.; Braunschweig, W.; Brisson, V.; Bruncko, D.; Brune, C.; Buchholz, R.; Büngener, L.; Bürger, J.; Büsser, F. W.; Buniatian, A.; Burke, S.; Buschhorn, G.; Campbell, A. J.; Carli, T.; Charles, F.; Clarke, D.; Clegg, A. B.; Clerbaux, B.; Colombo, M.; Contreras, J. G.; Cormack, C.; Coughlan, J. A.; Courau, A.; Coutures, Ch.; Cozzika, G.; Criegee, L.; Cussans, D. G.; Cvach, J.; Dagoret, S.; Dainton, J. B.; Danilov, M.; Dau, W. D.; Daum, K.; David, M.; Deffur, E.; Delcourt, B.; Del Buono, L.; De Roeck, A.; De Wolf, E. A.; Di Nezza, P.; Dollfus, C.; Dowell, J. D.; Dreis, H. B.; Droutskoi, A.; Duboc, J.; Düllmann, D.; Dünger, O.; Duhm, H.; Ebert, J.; Ebert, T. R.; Eckerlin, G.; Efremenko, V.; Egli, S.; Ehrlichmann, H.; Eichenberger, S.; Eichler, R.; Eisele, F.; Eisenhandler, E.; Ellison, R. J.; Elsen, E.; Erdmann, M.; Erdmann, W.; Evrard, E.; Favart, L.; Fedotov, A.; Feeken, D.; Felst, R.; Feltesse, J.; Ferencei, J.; Ferrarotto, F.; Flamm, K.; Fleischer, M.; Flieser, M.; Flügge, G.; Fomenko, A.; Fominykh, B.; Forbush, M.; Formánek, J.; Foster, J. M.; Franke, G.; Fretwurst, E.; Gabathuler, E.; Gabathuler, K.; Gamerdinger, K.; Garvey, J.; Gayler, J.; Gebauer, M.; Gellrich, A.; Genzel, H.; Gerhards, R.; Goerlach, U.; Goerlich, L.; Gogitidze, N.; Goldberg, M.; Goldner, D.; Gonzalez-Pineiro, B.; Gorelov, I.; Goritchev, P.; Grab, C.; Grässler, H.; Grässler, R.; Greenshaw, T.; Grindhammer, G.; Gruber, A.; Gruber, C.; Haack, J.; Haidt, D.; Hajduk, L.; Hamon, O.; Hampel, M.; Hanlon, E. M.; Hapke, M.; Haynes, W. J.; Heatherington, J.; Heinzelmann, G.; Henderson, R. C. W.; Henschel, H.; Herma, R.; Herynek, I.; Hess, M. F.; Hildesheim, W.; Hill, P.; Hill, K. H.; Hilton, C. D.; Hladký, J.; Hoeger, K. C.; Höppner, M.; Horisberger, R.; Huet, Ph.; Hufnagel, H.; Ibbotson, M.; Itterbeck, H.; Jabiol, M.-A.; Jacholkowska, A.; Jacobsson, C.; Jaffre, M.; Janoth, J.; Jansen, T.; Jönsson, L.; Johannsen, K.; Johnson, D. P.; Johnson, L.; Jung, H.; Kalmus, P. I. P.; Kant, D.; Kaschowitz, R.; Kasselmann, P.; Kathage, U.; Kaufmann, H. H.; Kazarian, S.; Kenyon, I. R.; Kermiche, S.; Keuler, C.; Kiesling, C.; Klein, M.; Kleinwort, C.; Knies, G.; Ko, W.; Köhler, T.; Köhne, J. H.; Kolanoski, H.; Kole, F.; Kolya, S. D.; Korbel, V.; Korn, M.; Kostka, P.; Kotelnikov, S. K.; Krämerkämper, T.; Krasny, M. W.; Krehbiel, H.; Krücker, D.; Krüger, U.; Krüner-Marquis, U.; Kubenka, J. P.; Küster, H.; Kuhlen, M.; Kurča, T.; Kurzhöfer, J.; Kuznik, B.; Lacour, D.; Lamarche, F.; Lander, R.; Landon, M. P. J.; Lange, W.; Lanius, P.; Laporte, J.-F.; Lebedev, A.; Leverenz, C.; Levonian, S.; Ley, Ch.; Lindner, A.; Lindström, G.; Linsel, F.; Lipinski, J.; List, B.; Loch, P.; Lohmander, H.; Lopez, G. C.; Lubimov, V.; Lüke, D.; Magnussen, N.; Malinovski, E.; Mani, S.; Maraček, R.; Marage, P.; Marks, J.; Marshall, R.; Martens, J.; Martin, R.; Martyn, H.-U.; Martyniak, J.; Masson, S.; Mavroidis, T.; Maxfield, S. J.; McMahon, S. J.; Mehta, A.; Meier, K.; Mercer, D.; Merz, T.; Meyer, C. A.; Meyer, H.; Meyer, J.; Mikocki, S.; Milstead, D.; Moreau, F.; Morris, J. V.; Müller, G.; Müller, K.; Murín, P.; Nagovizin, V.; Nahnhauer, R.; Naroska, B.; Naumann, Th.; Newman, P. R.; Newton, D.; Neyret, D.; Nguyen, H. K.; Niebergall, F.; Niebuhr, C.; Nisius, R.; Nowak, G.; Noyes, G. W.; Nyberg-Werther, M.; Oakden, M.; Oberlack, H.; Obrock, U.; Olsson, J. E.; Panaro, E.; Panitch, A.; Pascaud, C.; Patel, G. D.; Peppel, E.; Perez, E.; Phillips, J. P.; Pichler, Ch.; Pitzl, D.; Pope, G.; Prell, S.; Prosi, R.; Rädel, G.; Raupach, F.; Reimer, P.; Reinshagen, S.; Ribarics, P.; Rick, H.; Riech, V.; Riedlberger, J.; Riess, S.; Rietz, M.; Robertson, S. M.; Robmann, P.; Roloff, H. E.; Roosen, R.; Rosenbauer, K.; Rostovtsev, A.; Rouse, F.; Royon, C.; Rüter, K.; Rusakov, S.; Rybicki, K.; Rylko, R.; Sahlmann, N.; Sanchez, E.; Sankey, D. P. C.; Savitsky, M.; Schacht, P.; Schiek, S.; Schleper, P.; von Schlippe, W.; Schmidt, C.; Schmidt, D.; Schmidt, G.; Schöning, A.; Schröder, V.; Schuhmann, E.; Schwab, B.; Schwind, A.; Seehausen, U.; Sefkow, F.; Seidel, M.; Sell, R.; Semenov, A.; Shekelyan, V.; Sheviakov, I.; Shooshtari, H.; Shtarkov, L. N.; Siegmon, G.; Siewert, U.; Sirois, Y.; Skillicorn, I. O.; Smirnov, P.; Smith, J. R.; Soloviev, Y.; Spitzer, H.; Starosta, R.; Steenbock, M.; Steffen, P.; Steinberg, R.; Stella, B.; Stephens, K.; Stier, J.; Stiewe, J.; Stösslein, U.; Strachota, J.; Straumann, U.; Struczinski, W.; Sutton, J. P.; Tapprogge, S.; Taylor, R. E.; Tchernyshov, V.; Thiebaux, C.; Thompson, G.; Truöl, P.; Turnau, J.; Tutas, J.; Uelkes, P.; Usik, A.; Valkár, S.; Valkárová, A.; Vallée, C.; Van Esch, P.; Van Mechelen, P.; Vartapetian, A.; Vazdik, Y.; Vecko, M.; Verrecchia, P.; Villet, G.; Wacker, K.; Wagener, A.; Wagener, M.; Walker, I. W.; Walther, A.; Weber, G.; Weber, M.; Wegener, D.; Wegner, A.; Wellisch, H. P.; West, L. R.; Willard, S.; Winde, M.; Winter, G.-G.; Wright, A. E.; Wünsch, E.; Wulff, N.; Yiou, T. P.; Žáček, J.; Zarbock, D.; Zhang, Z.; Zhokin, A.; Zimmer, M.; Zimmermann, W.; Zomer, F.; Zuber, K.; H1 Collaboration

    1995-02-01

    Jet rates in deep inelastic electron proton scattering are studied with the H1 detector at HERA for momentum transfers squared between 10 and 4000 GeV 2. It is shown that they can be quantitatively described by perturbative QCD in next to leading order making use of the parton densities of the proton and with the strong coupling constant αs as a free parameter. The measured value, αs( MZ2) = 0.123 ± 0.018, is in agreement both with determinations from e+e- annihilation at LEP using the same observable and with the world average.

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

    PubMed

    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.

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

    NASA Technical Reports Server (NTRS)

    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.

  17. Experimental measurements and influence of overload-induced residual stress field on constant amplitude fatigue crack growth in aluminum alloy

    NASA Astrophysics Data System (ADS)

    Wahab, M. A.; Rohrsheim, G. R.; Brown, I. H.

    1997-03-01

    The aim of this research is to investigate current methods in Linear Elastic Fracture Mechanics for their suitability to predict crack growth in Aluminum alloy 7050 - T7451, when a compressive residual stress field is introduced by an overload. A comparative study has been made on the effect of various levels of tensile overload on the crack growth rate in Aluminum alloy. Experiments were performed on center-cracked tension specimens at various values of range of stress- intensity-factor ((Delta) K). Crack growth measurements are performed using crack propagation gauges and a travelling microscope. The average crack growth rate is used to determine an effective (Delta) K value for each interval using the fatigue crack propagation curve. After the application of overloads, the propagation gauges revealed a period of significant retardation before the crack growth rates returned to their baseline levels. The results from the numerical predictions are compared with the experimental results. The prediction model produces conservative results for both constant amplitude crack growth and overload induced retarded growth.

  18. Direct Measurement of the Effective Rate Constant for Primary Charge Separation in Isolated Photosystem II Reaction Centers

    SciTech Connect

    Greenfield, S. R.; Seibert, M.; Govindjee; Wasielewski, M. R.

    1997-03-27

    Transient absorption measurements of the pheophytin a anion band and Qx band bleach region using preferential excitation of P680 are performed on isolated photosystem II reaction centers to determine the effective rate constant for charge separtion. A novel analysis of the Qx band bleach region explicity takes the changing background into account in order to directly measure the rate of growth of the bleach. Both spectral regions reveal biphasic kinetics, with a ca. (8 ps)-1 rate constant for the faster component, and a ca. (50 ps)-1 rate constant for the slower component. We propose that the fster component corresponds to the effective rate constant for charge separation from within the equilibrated reaction center core and provides a lower limit for the intrinsic rate constant for charge separation. The slower component corresponds to charge separation that is limited by slow energy transfer from a long-wavelength accessory chlorophyll a.

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

    PubMed

    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.

  20. Derivation of a valid momentary first-order rate constant for kinetic and energetic analyses of enzymatic reactions.

    PubMed

    Imoto, Taiji

    2016-12-01

    To analyze enzymatic reactions energetically for comparison with non-enzymatic reactions (first order) under the same dimension, a method to derive valid momentary first-order rate constants for enzymatic reactions was developed. The momentary first-order rate constant, k enz0 = k cat[E'S']e,0/[S]0, was derived for an enzymatic reaction under a certain condition. It was shown that this rate constant is applicable for a wide range of enzymatic reactions. Utilizing this constant, one can conduct reliable kinetic and energetic analyses of enzymatic reactions.

  1. Path integral evaluation of the quantum instanton rate constant for proton transfer in a polar solvent

    NASA Astrophysics Data System (ADS)

    Yamamoto, Takeshi; Miller, William H.

    2005-01-01

    The quantum instanton approximation for thermal rate constants, a type of quantum transition state theory (QTST), is applied to a model proton transfer reaction in liquid methyl chloride developed by Azzouz and Borgis. Monte Carlo path integral methods are used to carry out the calculations, and two other closely related QTST's, namely, the centroid-density and Hansen-Andersen QTST, are also evaluated for comparison using the present path integral approach. A technique is then introduced that calculates the kinetic isotope effect directly via thermodynamic integration of the rate with respect to hydrogen mass, which has the practical advantage of avoiding costly evaluation of the activation free energy. The present application to the Azzouz-Borgis problem shows that the above three types of QTST provide very similar results for the rate, within 30% of each other, which is nontrivial considering the totally different derivations of these QTSTs; the latter rates are also in reasonable agreement with some other previous results (e.g., obtained via molecular dynamics with quantum transitions), within a factor of ˜2(7) for the H(D) transfer, thus significantly diminishing the possible range of the exact rates. In addition, it is revealed that a small but nonnegligible inconsistency exists in the parametrization of the Azzouz-Borgis model employed in previous studies, which resulted in the large apparent discrepancy in the calculated rates.

  2. [The catalytic rate constant. Effect of acetone on acidic hydrolysis of ester cyclohexyl acidacetylomethyl (AmMC)].

    PubMed

    Barańczyk, A; Zajac, M

    1992-01-01

    The catalytic rate constants k(HCl) were established for hydrolysis of beta-lactam moiety in AmMC using equation k(obs) = k(H2O) + k(HCl)[HCl]. The estimate the effect of aceton the relation log k(HCl) = log kD + k Z(mu)/D was applied. The rate constant increases with the decrease of dielectric constant of the solvent.

  3. Calibration of the Cenozoic Polarity Time Scale Based on Intervals of Constant Sea Floor Spreading Rates

    NASA Astrophysics Data System (ADS)

    Wilson, D. S.

    2004-12-01

    Astronomical calibration of the polarity time scale is now nearly complete for 0-12 Ma and recent work is making rapid progress on calibrating 12-40 Ma. Integration of radiometric dating and sea floor spreading histories allows calibration of the Middle and Early Miocene to an accuracy arguably 0.1 Myr, supporting an Oligocene-Miocene boundary near 23.0 Ma. Spreading rate histories for the Neogene show that all plate pairs have sudden rate changes, that sudden (<0.5 Myr) rate changes are more common than gradual (>2 Myr) rate changes, and that rate changes usually correlate with recognizable changes in fracture zone trends and location of the pole of relative motion. These relations suggest a calibration strategy of identifying intervals of stable relative plate motion and assuming constant, rather than smoothly changing, spreading rates in these intervals. For Oligocene and Late Eocene (C6C-C17), Australia-Antarctica and Pacific-Nazca (Farallon) spreading distances provide excellent constraints when calibrated against Southwest U.S. ignimbrite polarity stratigraphy [McIntosh et al, 1992] with revisions for the FC 40/39 monitor at 28.21 Ma [Kuiper et al 2004]. Calibration of this interval differs subtly from published alternatives, with the Late-Early Oligocene boundary in C10N at about 28.2 Ma, the Eocene-Oligocene boundary in C13R at about 33.7 Ma, and the Middle-Late Eocene boundary in C17N at about 36.9 Ma, all with accuracy arguably 0.2 Myr or better. Calibration of Paleocene through Middle Eocene is much more speculative due to lack of ideal spreading records, lack of consensus calibration points, and apparently global plate-motion reorganization at or near C21. A strategy assuming constant rate for Pacific-Juan de Fuca (Vancouver) for C13-C21 and minimizing rate changes for Pacific-Farallon for C21-C32 appears to be at least as viable as other, published time scales. This alternative strategy brings ages for much of the Middle Eocene younger than on all

  4. GROUND WATER ISSUE - CALCULATION AND USE OF FIRST-ORDER RATE CONSTANTS FOR MONITORED NATURAL ATTENUATION STUDIES

    EPA Science Inventory

    This issue paper explains when and how to apply first-order attenuation rate constant calculations in monitored natural attenuation (MNA) studies. First-order attenuation rate constant calculations can be an important tool for evaluating natural attenuation processes at ground-wa...

  5. Reduction of iron-oxide-carbon composites: part I. Estimation of the rate constants

    SciTech Connect

    Halder, S.; Fruehan, R.J.

    2008-12-15

    A new ironmaking concept using iron-oxide-carbon composite pellets has been proposed, which involves the combination of a rotary hearth furnace (RHF) and an iron bath smelter. This part of the research focuses on studying the two primary chemical kinetic steps. Efforts have been made to experimentally measure the kinetics of the carbon gasification by CO{sub 2} and wustite reduction by CO by isolating them from the influence of heat- and mass-transport steps. A combined reaction model was used to interpret the experimental data and determine the rate constants. Results showed that the reduction is likely to be influenced by the chemical kinetics of both carbon oxidation and wustite reduction at the temperatures of interest. Devolatilized wood-charcoal was observed to be a far more reactive form of carbon in comparison to coal-char. Sintering of the iron-oxide at the high temperatures of interest was found to exert a considerable influence on the reactivity of wustite by virtue of altering the internal pore surface area available for the reaction. Sintering was found to be predominant for highly porous oxides and less of an influence on the denser ores. It was found using an indirect measurement technique that the rate constants for wustite reduction were higher for the porous iron-oxide than dense hematite ore at higher temperatures (> 1423 K). Such an indirect mode of measurement was used to minimize the influence of sintering of the porous oxide at these temperatures.

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

    NASA Astrophysics Data System (ADS)

    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.

  7. Quantification of rate constants for successive enzymatic reactions with DNP hyperpolarized MR.

    PubMed

    Allouche-Arnon, Hyla; Hovav, Yonatan; Friesen-Waldner, Lanette; Sosna, Jacob; Moshe Gomori, J; Vega, Shimon; Katz-Brull, Rachel

    2014-06-01

    A kinetic model is provided to obtain reaction rate constants in successive enzymatic reactions that are monitored using NMR spectroscopy and hyperpolarized substrates. The model was applied for simulation and analysis of the successive oxidation of choline to betaine aldehyde, and further to betaine, by the enzyme choline oxidase. This enzymatic reaction was investigated under two different sets of conditions: two different choline molecular probes were used, [1,1,2,2-D4 , 1-(13) C]choline chloride and [1,1,2,2-D4 , 2-(13) C]choline chloride, in different MR systems (clinical scanner and high-resolution spectrometer), as well as in different reactors and reaction volumes (4.8 and 0.7 mL). The kinetic analysis according to the model yielded similar results in both set-ups, supporting the robustness of the model. This was achieved despite the complex and negating influences of reaction kinetics and polarization decay, and in the presence of uncontrolled mixing characteristics, which may introduce uncertainties in both effective timing and effective pulses. The ability to quantify rate constants using hyperpolarized MR in the first seconds of consecutive enzyme activity is important for further development of the utilization of dynamic nuclear polarization-MR for biological determinations.

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

    PubMed

    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.

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

    PubMed Central

    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

  10. Decomposition of phenylarsonic acid by AOP processes: degradation rate constants and by-products.

    PubMed

    Jaworek, K; Czaplicka, M; Bratek, Ł

    2014-10-01

    The paper presents results of the studies photodegradation, photooxidation, and oxidation of phenylarsonic acid (PAA) in aquatic solution. The water solutions, which consist of 2.7 g dm(-3) phenylarsonic acid, were subjected to advance oxidation process (AOP) in UV, UV/H2O2, UV/O3, H2O2, and O3 systems under two pH conditions. Kinetic rate constants and half-life of phenylarsonic acid decomposition reaction are presented. The results from the study indicate that at pH 2 and 7, PAA degradation processes takes place in accordance with the pseudo first order kinetic reaction. The highest rate constants (10.45 × 10(-3) and 20.12 × 10(-3)) and degradation efficiencies at pH 2 and 7 were obtained at UV/O3 processes. In solution, after processes, benzene, phenol, acetophenone, o-hydroxybiphenyl, p-hydroxybiphenyl, benzoic acid, benzaldehyde, and biphenyl were identified.

  11. Estimation of rate constants of PCB dechlorination reactions using an anaerobic dehalogenation model.

    PubMed

    Karakas, Filiz; Imamoglu, Ipek

    2017-02-15

    This study aims to estimate anaerobic dechlorination rate constants (km) of reactions of individual PCB congeners using data from four laboratory microcosms set up using sediment from Baltimore Harbor. Pathway km values are estimated by modifying a previously developed model as Anaerobic Dehalogenation Model (ADM) which can be applied to any halogenated hydrophobic organic (HOC). Improvements such as handling multiple dechlorination activities (DAs) and co-elution of congeners, incorporating constraints, using new goodness of fit evaluation led to an increase in accuracy, speed and flexibility of ADM. DAs published in the literature in terms of chlorine substitutions as well as specific microorganisms and their combinations are used for identification of pathways. The best fit explaining the congener pattern changes was found for pathways of Phylotype DEH10, which has the ability to remove doubly flanked chlorines in meta and para positions, para flanked chlorines in meta position. The range of estimated km values is between 0.0001-0.133d(-1), the median of which is found to be comparable to the few available published biologically confirmed rate constants. Compound specific modelling studies such as that performed by ADM can enable monitoring and prediction of concentration changes as well as toxicity during bioremediation.

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

    PubMed

    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.

  13. Determination of Interfacial Charge-Transfer Rate Constants in Perovskite Solar Cells.

    PubMed

    Pydzińska, Katarzyna; Karolczak, Jerzy; Kosta, Ivet; Tena-Zaera, Ramon; Todinova, Anna; Idígoras, Jesus; Anta, Juan A; Ziółek, Marcin

    2016-07-07

    A simple protocol to study the dynamics of charge transfer to selective contacts in perovskite solar cells, based on time-resolved laser spectroscopy studies, in which the effect of bimolecular electron-hole recombination has been eliminated, is proposed. Through the proposed procedure, the interfacial charge-transfer rate constants from methylammonium lead iodide perovskite to different contact materials can be determined. Hole transfer is faster for CuSCN (rate constant 0.20 ns(-1) ) than that for 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD; 0.06 ns(-1) ), and electron transfer is faster for mesoporous (0.11 ns(-1) ) than that for compact (0.02 ns(-1) ) TiO2 layers. Despite more rapid charge separation, the photovoltaic performance of CuSCN cells is worse than that of spiro-OMeTAD cells; this is explained by faster charge recombination in CuSCN cells, as revealed by impedance spectroscopy. The proposed direction of studies should be one of the key strategies to explore efficient hole-selective contacts as an alternative to spiro-OMeTAD. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Bimolecular Rate Constants for FAD-Dependent Glucose Dehydrogenase from Aspergillus terreus and Organic Electron Acceptors

    PubMed Central

    Tsuruoka, Nozomu; Sadakane, Takuya; Hayashi, Rika; Tsujimura, Seiya

    2017-01-01

    The flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) from Aspergillus species require suitable redox mediators to transfer electrons from the enzyme to the electrode surface for the application of bioelectrical devices. Although several mediators for FAD-GDH are already in use, they are still far from optimum in view of potential, kinetics, sustainability, and cost-effectiveness. Herein, we investigated the efficiency of various phenothiazines and quinones in the electrochemical oxidation of FAD-GDH from Aspergillus terreus. At pH 7.0, the logarithm of the bimolecular oxidation rate constants appeared to depend on the redox potentials of all the mediators tested. Notably, the rate constant of each molecule for FAD-GDH was approximately 2.5 orders of magnitude higher than that for glucose oxidase from Aspergillus sp. The results suggest that the electron transfer kinetics is mainly determined by the formal potential of the mediator, the driving force of electron transfer, and the electron transfer distance between the redox active site of the mediator and the FAD, affected by the steric or chemical interactions. Higher k2 values were found for ortho-quinones than for para-quinones in the reactions with FAD-GDH and glucose oxidase, which was likely due to less steric hindrance in the active site in the case of the ortho-quinones. PMID:28287419

  15. Theoretically predicted rate constants for mercury oxidation by hydrogen chloride in coal combustion flue gases.

    PubMed

    Wilcox, Jennifer; Robles, Joe; Marsden, David C J; Blowers, Paul

    2003-09-15

    In this work, theoretical rate constants are estimated for mercury oxidation reactions by hydrogen chloride that may occur in the flue gases of coal combustion. Rate constants are calculated using transition state theory at the quadratic configuration interaction (QCI) level of theory with single and double excitations, and are compared to results obtained from density functional theory, both including high level pseudopotentials for mercury. Thermodynamic and kinetic data from the literature are used to assess the accuracy of the theoretical calculations when possible. Validation of the chosen methods and basis sets is based upon previous and current research on mercury reactions involving chlorine. The present research shows that the QCISD method with the 1992 Stevens et al. basis set leads to the most accurate kinetic and thermodynamic results for the oxidation of mercury via chlorine containing molecules. Also, a comparison of the heats of reaction data for a series of mercury oxidation reactions reveals that the density functional method, B3LYP, with the 1997 Stuttgart basis set provides reasonably accurate results for these large systems.

  16. Absolute rate constants of alkoxyl radical reactions in aqueous solution. [Tert-butyl hydroperoxide

    SciTech Connect

    Erben-Russ, M.; Michel, C.; Bors, W.; Saran, M.

    1987-04-23

    The pulse radiolysis technique was used to generate the alkoxyl radical derived from tert-butyl hydroperoxide (/sup t/BuOOH) in aqueous solution. The reactions of this radical with 2,2'-azinobis(3-ethyl-6-benzothiazolinesulfonate) (ABTS) and promethazine were monitored by kinetic spectroscopy. The unimolecular decay rate constant of the tert-butoxyl radical (/sup t/BuO) was determined to be 1.4 x 10/sup 6/ s/sup -1/. On the basis of this value, the rate constants for /sup t/BuO attack on quercetin, crocin, crocetin, ascorbate, isoascorbate, trolox c, glutathione, thymidine, adenosine, guanosine, and unsaturated fatty acids were determined. In addition, the reaction of /sup t/BuO with the polyunsaturated fatty acids (PUFA) was observed by directly monitoring the formation of the fatty acid pentadienyl radicals. Interestingly, the attack of /sup t/BuO on PUFA was found to be faster by about one order of magnitude as compared to the same reaction in a nonpolar solvent.

  17. Airfoil stall penetration at constant pitch rate and high Reynolds number

    NASA Technical Reports Server (NTRS)

    Lorber, Peter F.; Carta, Franklin O.

    1989-01-01

    The model wing consists of a set of fiberglass panels mounted on a steel spar that spans the 8 ft test section of the UTRC Large Subsonic Wind Tunnel. The first use of this system was to measure surface pressures and flow conditions for a series of constant pitch rate ramps and sinusoidal oscillations a Mach number range, a Reynolds number range, and a pitch angle range. It is concluded that an increased pitch rate causes stall events to be delayed, strengthening of the stall vortex, increase in vortex propagation, and increase in unsteady airloads. The Mach number range causes a supersonic zone near the leading edge, stall vortex to be weaker, and a reduction of unsteady airloads.

  18. Dynamic Monte Carlo rate constants for magnetic Hamiltonians coupled to a phonon bath

    NASA Astrophysics Data System (ADS)

    Solomon, Lazarus; Novotny, Mark

    2007-03-01

    For quantitative comparisons between experimental time- dependent measurements and dynamic Monte Carlo simulations, a relation between the time constant in the simulation and real time is necessary. We calculate the transition rate for spin S system using the lattice frame method for a rigid spin cluster in an elastic medium [1]. We compare this with the transition rate for an Ising spin 12 system using the quantum- mechanical density-matrix method [2] with the results of ref [1,3]. These transition probabilities are different from those of either the Glauber or the Metropolis dynamics, and reflect the properties of the bosonic bath. Comparison with recent experiments [4] will be discussed. [1] E. M. Chudnovsky, D. A. Garanin, and R. Schilling (PRB 72, 2006) [2] K. Park, M. A. Novotny, and P. A. Rikvold (PRE 66, 2002) [3] K Saito, S. Takesue, and S. Miyashita, (PRE 61, 2002) [4] T. Meunier et al (Condensed Matter, 2006)

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

    NASA Technical Reports Server (NTRS)

    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.

  20. Exposure rate constants and lead shielding values for over 1,100 radionuclides.

    PubMed

    Smith, David S; Stabin, Michael G

    2012-03-01

    The authors have assembled a compilation of exposure rate constants, ƒ-factors, and lead shielding thicknesses for more than 1,100 radionuclides described in ICRP Publication 107. Physical data were taken from well established reference sources for mass-energy absorption coefficients in air, attenuation coefficients, and buildup factors in lead and other variables.The data agreed favorably for the most part with those of other investigators; thus this compilation provides an up-to-date and sizeable database of these data, which are of interest to many for routine calculations. Emissions were also segregated by emitting nuclide, and decay product emissions were emitted from the calculated coefficients, thus for the first time providing for the calculation of exposure rates from arbitrary mixtures of nuclides in arbitrary equilibrium states.

  1. Evaluated rate constants for selected HCFC's and HFC's with OH and O((sup)1D)

    NASA Technical Reports Server (NTRS)

    Hampson, Robert F.; Kurylo, Michael J.; Sander, Stanley P.

    1990-01-01

    The chemistry of HCFC's and HFC's in the troposphere is controlled by reactions with OH in which a hydrogen atom is abstracted from the halocarbon to form water and a halo-alkyl radical. The halo-alkyl radical subsequently reacts with molecular oxygen to form a peroxy radical. The reactions of HCFC's and HFC's with O(exp1D) atoms are unimportant in the troposphere, but may be important in producing active chlorine of OH in the stratosphere. Here, the rate constants for the reactions of OH and O(exp1D) with many HFC's and HCFC's are evaluated. Recommendations are given for the five HCFC's and three HFC's specified by AFEAS as primary alternatives as well as for all other isomers of C1 and C2 HCFC's and HFC's where rate data exist. In addition, recommendations are included for CH3CCl3, CH2Cl2, and CH4.

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

    NASA Technical Reports Server (NTRS)

    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.

  3. Rate constants for the quenching of metastable O2 (1Sigma g +) molecules

    NASA Technical Reports Server (NTRS)

    Kwang, Y. C.; Leu, M.-T.

    1985-01-01

    The O2 (1Sigma g +) rates for CO2, H2, N2, Cl2, CO, O3, and 2,3 DMB-2 are determined by monitoring the 762-nm emission in a fast-flow-discharge chemiluminescence detection system (Leu, 1984; Leu and Smith, 1981). The results are presented in tables and graphs and briefly characterized. The rate constants (in cu cm/s x 10 to the -16th) are 4600 + or - 500 for CO2, 7000 + or - 300 for H2, 17 + or - 1 for N2, 4.5 + or - 0.8 for Cl2, 45 + or - 5 for CO, 220,000 + or - 30,000 for O3, and 6000 + or - 100 for 2,3 DMB-2. The temperature dependence of the CO2 and O3 quenching reactions at 245-362 K is found to be negligible.

  4. Tensile Properties of 7075-T6 and 2024-T3 Aluminum-alloy Sheet Heated at Uniform Temperature Rates Under Constant Load

    NASA Technical Reports Server (NTRS)

    Heimerl, George J; Inge, John E

    1955-01-01

    Results are presented of tests to determine the effect of heating at uniform temperature rates from 0.2 degrees to 100 degrees F. per second on the tensile properties of 7075-T6 d(75s-T6) and 2024-T3 (24s-T3) aluminum-alloy sheet under constant-load conditions. Yield and rupture stresses, obtained under rapid-heating conditions, are compared with results of elevated-temperature stress-strain tests for 1/2-hour exposure. Master yield-and-rupture-stress curves based on linear temperature-rate parameter are presented. Yield and rupture stresses and temperatures may be predicted by means of master curves and the parameter.

  5. Solvent dynamics effects on heterogeneous electron transfer rate constants of cobalt tris(bipyridine)

    SciTech Connect

    Pyati, R.; Murray, R.W.

    1996-02-21

    This paper presents microelectrode voltammetry-derived heterogeneous electron transfer kinetic rates k{sub ET} for the redox couple [Co(bpy){sub 3}]{sup 2+/3+} in a series of solvents for which ({tau}{sub L}) longitudinal relaxation values are known (four polar monomeric solvents and four oligomeric polyether solvents, CH{sub 3}O-(CH{sub 2}CH{sub 2}O){sub n}-CH{sub 3} where n=1, 2, 3, and 4) and one, a higher oligomer (n=8, MPEG-400), for which {tau}{sub L} is estimated. {tau}{sub L} ranges from 0.2 to 38 ps. The results show that k{sub ET} varies inversely with {tau}{sub L}, and according to other modes of analysis, as predicted for control of the energy barrier-crossing rate by the dynamics of solvent dipolar relaxation. Additionally, the observed k{sub ET} is proportional to the diffusion coefficient D{sub Co} of [Co(bpy){sub 3}]{sup 2+}, which is rationalized by the mutual connection of D{sub Co} and k{sub ET} to the solvent viscosity. D{sub Co}, k{sub ET}, and viscosity were also measured as a function of electrolyte concentration in MPEG-400 which allowed extension of the overall solvent viscosity range. The [Co(bpy){sub 3}]{sup 2+/3+} rate constant in these media was also proportional to D{sub Co}, indicating solvent dynamics control over a time scale range of ca. 500-fold, larger than any previously reported. Experiments at constant viscosity but varied electrolyte concentration demonstrated the absence of strong double layer or ion pairing influences on the reaction rate. 32 refs., 6 figs., 3 tabs.

  6. Rate and Equilibrium Constants for an Enzyme Conformational Change during Catalysis by Orotidine 5'-Monophosphate Decarboxylase.

    PubMed

    Goryanova, Bogdana; Goldman, Lawrence M; Ming, Shonoi; Amyes, Tina L; Gerlt, John A; Richard, John P

    2015-07-28

    The caged complex between orotidine 5'-monophosphate decarboxylase (ScOMPDC) and 5-fluoroorotidine 5'-monophosphate (FOMP) undergoes decarboxylation ∼300 times faster than the caged complex between ScOMPDC and the physiological substrate, orotidine 5'-monophosphate (OMP). Consequently, the enzyme conformational changes required to lock FOMP at a protein cage and release product 5-fluorouridine 5'-monophosphate (FUMP) are kinetically significant steps. The caged form of ScOMPDC is stabilized by interactions between the side chains from Gln215, Tyr217, and Arg235 and the substrate phosphodianion. The control of these interactions over the barrier to the binding of FOMP and the release of FUMP was probed by determining the effect of all combinations of single, double, and triple Q215A, Y217F, and R235A mutations on kcat/Km and kcat for turnover of FOMP by wild-type ScOMPDC; its values are limited by the rates of substrate binding and product release, respectively. The Q215A and Y217F mutations each result in an increase in kcat and a decrease in kcat/Km, due to a weakening of the protein-phosphodianion interactions that favor fast product release and slow substrate binding. The Q215A/R235A mutation causes a large decrease in the kinetic parameters for ScOMPDC-catalyzed decarboxylation of OMP, which are limited by the rate of the decarboxylation step, but much smaller decreases in the kinetic parameters for ScOMPDC-catalyzed decarboxylation of FOMP, which are limited by the rate of enzyme conformational changes. By contrast, the Y217A mutation results in large decreases in kcat/Km for ScOMPDC-catalyzed decarboxylation of both OMP and FOMP, because of the comparable effects of this mutation on rate-determining decarboxylation of enzyme-bound OMP and on the rate-determining enzyme conformational change for decarboxylation of FOMP. We propose that kcat = 8.2 s(-1) for decarboxylation of FOMP by the Y217A mutant is equal to the rate constant for cage formation from the

  7. Study on constant-step stress accelerated life tests in white organic light-emitting diodes.

    PubMed

    Zhang, J P; Liu, C; Chen, X; Cheng, G L; Zhou, A X

    2014-11-01

    In order to obtain reliability information for a white organic light-emitting diode (OLED), two constant and one step stress tests were conducted with its working current increased. The Weibull function was applied to describe the OLED life distribution, and the maximum likelihood estimation (MLE) and its iterative flow chart were used to calculate shape and scale parameters. Furthermore, the accelerated life equation was determined using the least squares method, a Kolmogorov-Smirnov test was performed to assess if the white OLED life follows a Weibull distribution, and self-developed software was used to predict the average and the median lifetimes of the OLED. The numerical results indicate that white OLED life conforms to a Weibull distribution, and that the accelerated life equation completely satisfies the inverse power law. The estimated life of a white OLED may provide significant guidelines for its manufacturers and customers.

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

    NASA Astrophysics Data System (ADS)

    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

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

    PubMed

    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 < 0.05) and worst (749 ± 111 s, P < 0.05) individual fits of CWR prediction trial data. The error in the prediction was inversely correlated with the magnitude of the W' for the best (r = -0.56, P < 0.05) and worst individual fits (r = -0.36, P < 0.05). The overestimation of ramp 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.

  10. Evaluation of rate constants for enzyme-catalysed reactions by the jackknife technique. Application to liver alcohol dehydrogenase.

    PubMed Central

    Cornish-Bowden, A; Wong, J T

    1978-01-01

    Steady-state measurements of enzyme-catalysed reactions are capable of providing more information about the rate constants of the individual steps than is commonly obtained. We have applied a combination of the jackknife and non-linear regression techniques to measurements of the rate of oxidation of ethanol by NAD+, catalysed by alcohol dehydrogenase from horse liver. This has permitted values and confidence intervals to be assigned to the eight rate constants that characterize the binding of ethanol and NAD+ in random order to the enzyme, and to the net rate constant kcat. for the breakdown of the ternary complex. PMID:743242

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

    PubMed

    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 Krates 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.

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

    NASA Astrophysics Data System (ADS)

    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.

  13. Universally distributed single-copy genes indicate a constant rate of horizontal transfer.

    PubMed

    Creevey, Christopher J; Doerks, Tobias; Fitzpatrick, David A; Raes, Jeroen; Bork, Peer

    2011-01-01

    Single copy genes, universally distributed across the three domains of life and encoding mostly ancient parts of the translation machinery, are thought to be only rarely subjected to horizontal gene transfer (HGT). Indeed it has been proposed to have occurred in only a few genes and implies a rare, probably not advantageous event in which an ortholog displaces the original gene and has to function in a foreign context (orthologous gene displacement, OGD). Here, we have utilised an automatic method to identify HGT based on a conservative statistical approach capable of robustly assigning both donors and acceptors. Applied to 40 universally single copy genes we found that as many as 68 HGTs (implying OGDs) have occurred in these genes with a rate of 1.7 per family since the last universal common ancestor (LUCA). We examined a number of factors that have been claimed to be fundamental to HGT in general and tested their validity in the subset of universally distributed single copy genes. We found that differing functional constraints impact rates of OGD and the more evolutionarily distant the donor and acceptor, the less likely an OGD is to occur. Furthermore, species with larger genomes are more likely to be subjected to OGD. Most importantly, regardless of the trends above, the number of OGDs increases linearly with time, indicating a neutral, constant rate. This suggests that levels of HGT above this rate may be indicative of positively selected transfers that may allow niche adaptation or bestow other benefits to the recipient organism.

  14. Stress focusing and collapse of a thin film under constant pressure

    NASA Astrophysics Data System (ADS)

    Hamm, Eugenio; Cabezas, Nicolas

    2012-02-01

    Thin elastic sheets and shells are prone to focus stress when forced, due to their near inextensibility. Singular structures such as ridges, vertices, and folds arising from wrinkles, are characteristic of the deformation of such systems. Usually the forcing is exerted at the boundaries or at specific points of the surface, in displacement controlled experiments. On the other hand, much of the phenomenology of stress focusing can be found at micro and nanoscales, in physics and biology, making it universal. We will consider the post-buckling regime of a thin elastic sheet that is subjected to a constant normal distributed force. Specifically, we will present experiments made on thin elastoplastic sheets that collapse under atmospheric pressure. For instance, in vacuum-sealing technology, when a flat plastic bag is forced to wrap a solid volume, a series of self-contacts and folds develop. The unfolded bag shows a pattern of scars whose structure is determined by the geometry of the volume and by the exact way it stuck to its surface, by friction. Inspired by this everyday example we study the geometry of folds that result from collapsing a hermetic bag on regular rigid bodies.

  15. A photon spectrometric dose-rate constant determination for the Advantage Pd-103 brachytherapy source

    SciTech Connect

    Chen, Zhe Jay; Bongiorni, Paul; Nath, Ravinder

    2010-02-15

    Purpose: Although several dosimetric characterizations using Monte Carlo simulation and thermoluminescent dosimetry (TLD) have been reported for the new Advantage Pd-103 source (IsoAid, LLC, Port Richey, FL), no AAPM consensus value has been established for the dosimetric parameters of the source. The aim of this work was to perform an additional dose-rate constant ({Lambda}) determination using a recently established photon spectrometry technique (PST) that is independent of the published TLD and Monte Carlo techniques. Methods: Three Model IAPD-103A Advantage Pd-103 sources were used in this study. The relative photon energy spectrum emitted by each source along the transverse axis was measured using a high-resolution germanium spectrometer designed for low-energy photons. For each source, the dose-rate constant was determined from its emitted energy spectrum. The PST-determined dose-rate constant ({sub PST}{Lambda}) was then compared to those determined by TLD ({sub TLD}{Lambda}) and Monte Carlo ({sub MC}{Lambda}) techniques. A likely consensus {Lambda} value was estimated as the arithmetic mean of the average {Lambda} values determined by each of three different techniques. Results: The average {sub PST}{Lambda} value for the three Advantage sources was found to be (0.676{+-}0.026) cGyh{sup -1} U{sup -1}. Intersource variation in {sub PST}{Lambda} was less than 0.01%. The {sub PST}{Lambda} was within 2% of the reported {sub MC}{Lambda} values determined by PTRAN, EGSnrc, and MCNP5 codes. It was 3.4% lower than the reported {sub TLD}{Lambda}. A likely consensus {Lambda} value was estimated to be (0.688{+-}0.026) cGyh{sup -1} U{sup -1}, similar to the AAPM consensus values recommended currently for the Theragenics (Buford, GA) Model 200 (0.686{+-}0.033) cGyh{sup -1} U{sup -1}, the NASI (Chatsworth, CA) Model MED3633 (0.688{+-}0.033) cGyh{sup -1} U{sup -1}, and the Best Medical (Springfield, VA) Model 2335 (0.685{+-}0.033) cGyh{sup -1} U{sup -1} {sup 103}Pd

  16. Rate Constants for Peroxidation of Polyunsaturated Fatty Acids and Sterols in Solution and in Liposomes

    PubMed Central

    Xu, Libin; Davis, Todd A.; Porter, Ned A.

    2013-01-01

    Rate constants for autoxidation propagation of several unsaturated lipids in benzene solution at 37°C and in phosphatidylcholine liposomes were determined by a linoleate radical clock. This radical clock is based on competition between hydrogen atom abstraction by an intermediate peroxyl radical derived from linoleic acid that leads to a trans,cis-conjugated hydroxyoctadecadienoic product and β–fragmentation of the same peroxyl that gives the trans,trans-product hydroxyoctadecadienoic acid. Rate constants determined by this approach in solution relative to linoleic acid (kp = 62 M−1s−1) were: arachidonic acid (kp = 197 ± 13 M−1s−1), eicosapentaenoic acid (kp = 249 ± 16 M−1s−1), docosahexaenoic acid (kp = 334 ± 37 M−1s−1), cholesterol (kp = 11 ± 2 M−1s−1), and 7-dehydrocholesterol (kp = 2,260 ± 40 M−1s−1). Free radical oxidations of multilamellar and unilamellar liposomes of various mixtures of glycerophosphatidylcholine molecular species were also carried out. In some experiments, cholesterol or 7-dehydrocholesterol was incorporated into the lipid mixture undergoing oxidation. A phosphatidylcholine bearing a linoleate ester at sn-2 was a component of each liposome peroxidation reaction and the ratio of trans,cis/trans,trans (t,c/t,t)-conjugated diene oxidation products formed from this phospholipid was determined for each oxidation reaction. This t,c/t,t-product ratio from linoleate was used to “clock” liposome constituents as hydrogen atom donors in the lipid bilayer. Application of this lipid bilayer radical clock gives relative autoxidation propagation rate constants of arachidonate (20:4), eicosapentaenoate (20:5), docosahexaenoate (22:6), and 7-dehydrocholesterol to be 115 ± 7, 145 ± 8, 172 ± 13, and 832 ± 86, respectively, a reactivity trend that parallels the one in solution. We also conclude from the liposome oxidations that linoleate peroxyl radicals at different positions on the eighteen-carbon chain (at C-9 and C

  17. Quantum Yields and Rate Constants of Photochemical and Nonphotochemical Excitation Quenching (Experiment and Model).

    PubMed Central

    Laisk, A.; Oja, V.; Rasulov, B.; Eichelmann, H.; Sumberg, A.

    1997-01-01

    Sunflower (Helianthus annuus L.), cotton (Gossypium hirsutum L.), tobacco (Nicotiana tabacum L.), sorghum (Sorghum bicolor Moench.), amaranth (Amaranthus cruentus L.), and cytochrome b6f complex-deficient transgenic tobacco leaves were used to test the response of plants exposed to differnt light intensities and CO2 concentrations before and after photoinhibition at 4000 [mu]mol photons m-2 s-1 and to thermoinhibition up to 45[deg]C. Quantum yields of photochemical and nonphotochemical excitation quenching (YP and YN) and the corresponding relative rate constants for excitation capture from the antenna-primary radical pair equilibrium system (k[prime]P and k[prime]N) were calculated from measured fluorescence parameters. The above treatments resulted in decreases in YP and K[prime]P and in approximately complementary increases in YN and K[prime]N under normal and inhibitory conditions. The results were reproduced by a mathematical model of electron/proton transport and O2 evolution/CO2 assimilation in photosynthesis based on budget equations for the intermediates of photosynthesis. Quantitative differences between model predictions and experiments are explainable, assuming that electron transport is organized into domains that contain relatively complete electron and proton transport chains (e.g. thylakoids). With the complementation that occurs between the photochemical and nonphotochemical excitation quenching, the regulatory system can constantly maintain the shortest lifetime of excitation necessary to avoid the formation of chlorophyll triplet states and singlet oxygen. PMID:12223845

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

    USGS Publications Warehouse

    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.

  19. Lipase-catalyzed transesterification in organic media: solvent effects on equilibrium and individual rate constants.

    PubMed

    García-Alles, L F; Gotor, V

    1998-09-20

    The kinetics of the immobilized lipase B from Candida antarctica have been studied in organic solvents. This enzyme has been shown to be slightly affected by the water content of the organic media, and it does not seem to be subject to mass transfer limitations. On the other hand, some evidence indicates that the catalytic mechanism of reactions catalyzed by this lipase proceeds through the acyl-enzyme intermediate. Moreover, despite the fact that the immobilization support dramatically enhances the catalytic power of the enzyme, it does not interfere with the intrinsic solvent effect. Consequently, this enzyme preparation becomes optimum for studying the role played by the organic solvent in catalysis. To this end, we have measured the acylation and deacylation individual rate constants, and the binding equilibrium constant for the ester, in several organic environments. Data obtained show that the major effect of the organic solvent is on substrate binding, and that the catalytic steps are almost unaffected by the solvent, indicating the desolvation of the transition state. However, the strong decrease in binding for hydrophilic solvents such as THF and dioxane, compared to the rest of solvents, cannot be easily explained by means of thermodynamic arguments (desolvation of the ester substrate). For this reason, data have been considered as an indication of the existence of an unknown step in the catalytic pathway occurring prior to formation of the acyl-enzyme intermediate.

  20. Crystallization of isotactic polypropylene from mesomorphic phase: a constant heating rate study

    NASA Astrophysics Data System (ADS)

    Asakawa, H.; Nishida, K.; Matsuba, G.; Kanaya, T.; Ogawa, H.

    2011-01-01

    We have studied crystallization behaviour of isotactic polypropylene (iPP) from mesomorphic phase in structural point of view. Time-resolved wide-angle X-ray diffraction (WAXD) measurements during a heating process have been performed using a synchrotron radiation (SR) X-ray beam line at SPring-8, Japan. The heating process was so programmed to reproduce a thermal trace of differential scanning calorimetry (DSC) with a constant heating rate (10 °C/min) in order to compare the structural change with thermal behaviour. SR-WAXD sensitively detected the crystallization behaviour and we have obtained fractions of alpha-crystal, mesomorphic phase and amorphous phase as a function of temperature by analysing the data. The results showed that the crystallization from mesomorphic phase proceeds in between 60 and 120 °C (meso-alpha transition). During this process, the crystallization from amorphous hardly takes place. The crystalline fraction shows almost constant in between 120 and 140 °C meanwhile, the mesomorphic fraction still decreases above 120 °C. The crystalline fraction starts to decrease above 140 °C and the most extensively decreases at around 165 °C (melting point). We have also determined the energy level of the mesomorphic phase (meta-stable state) relative to that of alpha-crystal (stable state), considering the balance among the fractions of alpha-crystal, mesomorphic phase and amorphous.

  1. Rate constants for the slow Mu + propane abstraction reaction at 300 K by diamagnetic RF resonance.

    PubMed

    Fleming, Donald G; Cottrell, Stephen P; McKenzie, Iain; Ghandi, Khashayar

    2015-08-14

    The study of kinetic isotope effects for H-atom abstraction rates by incident H-atoms from the homologous series of lower mass alkanes (CH4, C2H6 and, here, C3H8) provides important tests of reaction rate theory on polyatomic systems. With a mass of only 0.114 amu, the most sensitive test is provided by the rates of the Mu atom. Abstraction of H by Mu can be highly endoergic, due to the large zero-point energy shift in the MuH bond formed, which also gives rise to high activation energies from similar zero-point energy corrections at the transition state. Rates are then far too slow near 300 K to be measured by conventional TF-μSR techniques that follow the disappearance of the spin-polarised Mu atom with time. Reported here is the first measurement of a slow Mu reaction rate in the gas phase by the technique of diamagnetic radio frequency (RF) resonance, where the amplitude of the MuH product formed in the Mu + C3H8 reaction is followed with time. The measured rate constant, kMu = (6.8 ± 0.5) × 10(-16) cm(3) s(-1) at 300 K, is surprisingly only about a factor of three slower than that expected for H + C3H8, indicating a dominant contribution from quantum tunneling in the Mu reaction, consistent with elementary transition state theory calculations of the kMu/kH kinetic isotope effect.

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

    DTIC Science & Technology

    1987-09-25

    constants, k2ob, using cyclic voltammetry . The results are expressed in terms of systematic deviations of ’apparent measured’ rate constants, k2ob...Keywords: Digital simulation analysis, Uncompensated solution resistance, Electrochemical rate constants, Cyclic voltammetry .

  3. The Br+HO 2 reaction revisited: Absolute determination of the rate constant at 298 K

    NASA Astrophysics Data System (ADS)

    Laverdet, G.; Le Bras, G.; Mellouki, A.; Poulet, G.

    1990-09-01

    The absolute determination of the rate constant for the reaction Br+HO 2→HBr+O 2 has been done at 298 K using the discharge-flor EPR method. The value k1 = (1.5±0.2) × 10 -12 cm 3 molecule -1 s -1 was obtained. Previous indirect measurements of k1 from a discharge-flow, LIF/mass spectrometric study of the Br/H 2CO/O 2 system have been reinterpreted, leading to values for k1 ranging from 1.0 × 10 -12 to 2.2 × 10 -12 cm 3 molecule -1 s -1 at 298 K. These results are discussed and compared with other literature values.

  4. Relative rate constants for the reactions of atomic oxygen with HO2 anad OH radicals

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1983-01-01

    Relative rate constants for the reactions O + HO2 - OH + O2 (1) and O + OH - H + O2 (2) were obtained by using the discharge-flow resonance fluorescence technique at 2 torr total pressure and 299 K. HO2 radicals were generated by reacting atomic hydrogen with an excess of O2. Quasi-steady-state concentrations of OH and HO2 were established in the presence of excess atomic oxygen. Observed concentration ratios, namely the ratio of the OH concentration to the HO2 concentration, resulted in a value of 1.7 + or 0.2 for k1/k2. The error limits are twice the standard deviation obtained from the data analysis. Overall experimental error is estimated to be + or - 25 percent. This result confirms earlier direct measurements of k1 and k2 which required knowledge of absolute radical or atomic oxygen concentrations.

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

    PubMed

    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.

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

    USGS Publications Warehouse

    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.

  7. Second order rate constants for intramolecular conversions: Application to gas-phase NMR relaxation times

    NASA Astrophysics Data System (ADS)

    Bauer, S. H.; Lazaar, K. I.

    1983-09-01

    The usually quoted expression for the second order rate constant, for a unimolecular reaction at the low pressure limit, is valid only for strictly irreversible processes. Its application to isomerization reactions (which are to some extent reversible) is demonstrably in error; corrected expressions have been published. Attention is directed to intramolecular conversions over low barriers, for which the inappropriateness of the unidirectional expression becomes obvious. For such isomerizations we propose a model which incorporates only operationally observable states, so that an essential conceptual ambiguity is avoided. Use of this model is illustrated for the syn⇄anti conversions of methyl nitrite, derived from a gas phase NMR coalescence curve (Mc:Tc). The present data suggest that during isomerization the alkyl nitrites may not be completely ergodic on a time scale of 10-9 s. A regional phase-space model is proposed which has the appropriate formalism to account for this behavior.

  8. Negative ion formation by Rydberg electron transfer: Isotope-dependent rate constants

    SciTech Connect

    Carman, H.S. Jr.; Klots, C.E.; Compton, R.N.

    1991-01-01

    The formation of negative ions during collisions of rubidium atoms in selected ns and nd Rydberg states with carbon disulfide molecules has been studied for a range of effective principal quantum numbers (10 {le} n* {le} 25). For a narrow range of n* near n* = 17, rate constants for CS{sub 2}{sup {minus}} formation are found to depend upon the isotopic composition of the molecule, producing a negative ion isotope ratio (mass 78 to mass 76, amu) up to 10.5 times larger than the natural abundance ratio of CS{sub 2} isotopes in the reagent. The isotope ratio is found to depend strongly upon the initial quantum state of the Rydberg atom and perhaps upon the collision energy and CS{sub 2} temperature. 32 refs., 5 figs., 1 tab.

  9. Impact of the differential fluence distribution of brachytherapy sources on the spectroscopic dose-rate constant

    SciTech Connect

    Malin, Martha J.; Bartol, Laura J.; DeWerd, Larry A. E-mail: ladewerd@wisc.edu

    2015-05-15

    Purpose: To investigate why dose-rate constants for {sup 125}I and {sup 103}Pd seeds computed using the spectroscopic technique, Λ{sub spec}, differ from those computed with standard Monte Carlo (MC) techniques. A potential cause of these discrepancies is the spectroscopic technique’s use of approximations of the true fluence distribution leaving the source, φ{sub full}. In particular, the fluence distribution used in the spectroscopic technique, φ{sub spec}, approximates the spatial, angular, and energy distributions of φ{sub full}. This work quantified the extent to which each of these approximations affects the accuracy of Λ{sub spec}. Additionally, this study investigated how the simplified water-only model used in the spectroscopic technique impacts the accuracy of Λ{sub spec}. Methods: Dose-rate constants as described in the AAPM TG-43U1 report, Λ{sub full}, were computed with MC simulations using the full source geometry for each of 14 different {sup 125}I and 6 different {sup 103}Pd source models. In addition, the spectrum emitted along the perpendicular bisector of each source was simulated in vacuum using the full source model and used to compute Λ{sub spec}. Λ{sub spec} was compared to Λ{sub full} to verify the discrepancy reported by Rodriguez and Rogers. Using MC simulations, a phase space of the fluence leaving the encapsulation of each full source model was created. The spatial and angular distributions of φ{sub full} were extracted from the phase spaces and were qualitatively compared to those used by φ{sub spec}. Additionally, each phase space was modified to reflect one of the approximated distributions (spatial, angular, or energy) used by φ{sub spec}. The dose-rate constant resulting from using approximated distribution i, Λ{sub approx,i}, was computed using the modified phase space and compared to Λ{sub full}. For each source, this process was repeated for each approximation in order to determine which approximations used in

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

    NASA Astrophysics Data System (ADS)

    Bharadvaja, Anand; Kaur, Savinder; Baluja, K. L.

    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 inelastic cross-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. Determination of rate constants of N-alkylation of primary amines by 1H NMR spectroscopy.

    PubMed

    Li, Chenghong

    2013-09-05

    Macromolecules containing N-diazeniumdiolates of secondary amines are proposed scaffolds for controlled nitrogen oxide (NO) release medical applications. Preparation of these compounds often involves converting primary amine groups to secondary amine groups through N-alkylation. However, N-alkylation results in not only secondary amines but tertiary amines as well. Only N-diazeniumdiolates of secondary amines are suitable for controlled NO release; therefore, the yield of secondary amines is crucial to the total NO load of the carrier. In this paper, (1)H NMR spectroscopy was used to estimate the rate constants for formation of secondary amine (k1) and tertiary amine (k2) for alkylation reagents such as propylene oxide (PO), methyl acrylate (MA), and acrylonitrile (ACN). At room temperature, the ratio of k2/k1 for the three reactions was found to be around 0.50, 0.026, and 0.0072.

  12. Relative rate constants for the reactions of atomic oxygen with HO2 anad OH radicals

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1983-01-01

    Relative rate constants for the reactions O + HO2 - OH + O2 (1) and O + OH - H + O2 (2) were obtained by using the discharge-flow resonance fluorescence technique at 2 torr total pressure and 299 K. HO2 radicals were generated by reacting atomic hydrogen with an excess of O2. Quasi-steady-state concentrations of OH and HO2 were established in the presence of excess atomic oxygen. Observed concentration ratios, namely the ratio of the OH concentration to the HO2 concentration, resulted in a value of 1.7 + or 0.2 for k1/k2. The error limits are twice the standard deviation obtained from the data analysis. Overall experimental error is estimated to be + or - 25 percent. This result confirms earlier direct measurements of k1 and k2 which required knowledge of absolute radical or atomic oxygen concentrations.

  13. Micro-mechanism and rate constants for OH-initiated degradation of methomyl in atmosphere.

    PubMed

    Wu, Xiuchao; Sun, Xiaomin; Zhang, Chenxi; Gong, Chen; Hu, Jingtian

    2014-07-01

    The atmospheric degradation reactions of the two isomers of methomyl (MTL) initiated by OH radical in the presence of O2, NO and H2O have been investigated by density functional theory (DFT). The calculations were all carried out at MPWB1K level. The geometrical parameters and vibrational frequencies of stationary points were calculated with 6-31+G (d, p) basis sets. Single-point energy calculations were performed with 6-311+G (3df, 2p) basis sets. Profiles of the potential energy surface were constructed and all possible channels involved in the reactions were discussed. The rate constants of main elementary reactions were calculated over a temperature range of 200-400 K and mostly fitted to Arrhenius formulas. The atmospheric lifetimes of reaction species were discussed for the first time, which can be applied to the study on model simulation and management of hazardous materials.

  14. Estimation of rate constants of elementary processes - A review of the state of the art.

    NASA Technical Reports Server (NTRS)

    Golden, D. M.

    1973-01-01

    'Thermochemical kinetics,' the codification and extrapolation of empirical observations, as applied to certain elementary reactions of importance to combustion studies, is described. This approach allows the critical scrutiny of experimental data in areas where sufficient previous data exist, while, at the same time, illuminating those key areas where more experimentation is crucial. It is shown that combination of transition-state theory with an understanding of the molecular basis of entropy puts fairly rigid constraints on the values of the Arrhenius A-factor for most reactions. This, in turn, means that the activation energy is often the key datum that is missing, and that such data can be obtained with some degree of confidence, even from measurements of rate constants at only one temperature. In complex mechanisms, it is often possible to distinguish among alternate pathways and pinpoint key processes.

  15. The conformation-independent QSPR approach for predicting the oxidation rate constant of water micropollutants.

    PubMed

    Ortiz, Erlinda V; Bennardi, Daniel O; Bacelo, Daniel E; Fioressi, Silvina E; Duchowicz, Pablo R

    2017-10-03

    In advanced water treatment processes, the degradation efficiency of contaminants depends on the reactivity of the hydroxyl radical toward a target micropollutant. The present study predicts the hydroxyl radical rate constant in water (k OH) for 118 emerging micropollutants, by means of quantitative structure-property relationships (QSPR). The conformation-independent QSPR approach is employed, together with a large number of 15,251 molecular descriptors derived with the PaDEL, Epi Suite, and Mold2 freewares. The best multivariable linear regression (MLR) models are found with the replacement method variable subset selection technique. The proposed five-descriptor model has the following statistics for the training set: [Formula: see text], RMS train = 0.21, while for the test set is [Formula: see text], RMS test = 0.11. This QSPR serves as a rational guide for predicting oxidation processes of micropollutants.

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

    PubMed

    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.

  17. Surface hopping, transition state theory, and decoherence. II. Thermal rate constants and detailed balance

    SciTech Connect

    Jain, Amber; Subotnik, Joseph E.

    2015-10-07

    We investigate a simple approach to compute a non-adiabatic thermal rate constant using the fewest switches surface hopping (FSSH) dynamics. We study the effects of both decoherence (using our augmented-FSSH (A-FSSH) algorithm) and forbidden hops over a large range of parameters, including high and low friction regimes, and weak and strong electronic coupling regimes. Furthermore, when possible, we benchmark our results against exact hierarchy equations of motion results, where we usually find a maximum error of roughly a factor of two (at reasonably large temperatures). In agreement with Hammes-Schiffer and Tully, we find that a merger of transition state theory and surface hopping can be both accurate and efficient when performed correctly. We further show that detailed balance is followed approximately by A-FSSH dynamics.

  18. Prediction of Chain Propagation Rate Constants of Polymerization Reactions in Aqueous NIPAM/BIS and VCL/BIS Systems.

    PubMed

    Kröger, Leif C; Kopp, Wassja A; Leonhard, Kai

    2017-04-06

    Microgels have a wide range of possible applications and are therefore studied with increasing interest. Nonetheless, the microgel synthesis process and some of the resulting properties of the microgels, such as the cross-linker distribution within the microgels, are not yet fully understood. An in-depth understanding of the synthesis process is crucial for designing tailored microgels with desired properties. In this work, rate constants and reaction enthalpies of chain propagation reactions in aqueous N-isopropylacrylamide/N,N'-methylenebisacrylamide and aqueous N-vinylcaprolactam/N,N'-methylenebisacrylamide systems are calculated to identify the possible sources of an inhomogeneous cross-linker distribution in the resulting microgels. Gas-phase reaction rate constants are calculated from B2PLYPD3/aug-cc-pVTZ energies and B3LYPD3/tzvp geometries and frequencies. Then, solvation effects based on COSMO-RS are incorporated into the rate constants to obtain the desired liquid-phase reaction rate constants. The rate constants agree with experiments within a factor of 2-10, and the reaction enthalpies deviate less than 5 kJ/mol. Further, the effect of rate constants on the microgel growth process is analyzed, and it is shown that differences in the magnitude of the reaction rate constants are a source of an inhomogeneous cross-linker distribution within the resulting microgel.

  19. Reduction of Iron-Oxide-Carbon Composites: Part I. Estimation of the Rate Constants

    NASA Astrophysics Data System (ADS)

    Halder, S.; Fruehan, R. J.

    2008-12-01

    A new ironmaking concept using iron-oxide-carbon composite pellets has been proposed, which involves the combination of a rotary hearth furnace (RHF) and an iron bath smelter. This part of the research focuses on studying the two primary chemical kinetic steps. Efforts have been made to experimentally measure the kinetics of the carbon gasification by CO2 and wüstite reduction by CO by isolating them from the influence of heat- and mass-transport steps. A combined reaction model was used to interpret the experimental data and determine the rate constants. Results showed that the reduction is likely to be influenced by the chemical kinetics of both carbon oxidation and wüstite reduction at the temperatures of interest. Devolatilized wood-charcoal was observed to be a far more reactive form of carbon in comparison to coal-char. Sintering of the iron-oxide at the high temperatures of interest was found to exert a considerable influence on the reactivity of wüstite by virtue of altering the internal pore surface area available for the reaction. Sintering was found to be predominant for highly porous oxides and less of an influence on the denser ores. It was found using an indirect measurement technique that the rate constants for wüstite reduction were higher for the porous iron-oxide than dense hematite ore at higher temperatures (>1423 K). Such an indirect mode of measurement was used to minimize the influence of sintering of the porous oxide at these temperatures.

  20. Ozonation of pharmaceutical compounds: Rate constants and elimination in various water matrices.

    PubMed

    Javier Benitez, F; Acero, Juan L; Real, Francisco J; Roldán, Gloria

    2009-09-01

    The ozonation of four pharmaceuticals (metoprolol, naproxen, amoxicillin, and phenacetin) in ultra-pure (UP) water was studied in the pH range between 2.5 and 9. The experiments allowed the determination of the apparent rate constants for the reactions between ozone and the selected compounds. The values obtained varied depending on the pH, and ranged between 239 and 1.27x10(4)M(-1) s(-1) for metoprolol; 2.62x10(4) and 2.97x10(5)M(-1)s(-1) for naproxen; 2.31x10(3) and 1.21x10(7)M(-1)s(-1) for amoxicillin; and 215 and 1.57x10(3)M(-1)s(-1) for phenacetin. Due to the acidic nature of these substances, the degree of dissociation of each pharmaceutical was determined at every pH of work, and the specific rate constants of the neutral and ionic species formed were evaluated. Additionally, the simultaneous ozonation of the pharmaceuticals in different water matrices was carried out by considering a groundwater, a surface water from a public reservoir, and three secondary effluents from municipal wastewater treatment plants. The influence of the operating conditions (initial ozone dose, nature of pharmaceuticals and type of water) on the pharmaceuticals elimination efficiency was established, and a kinetic model was proposed for the evaluation of the partial contribution to the global oxidation of both, the direct ozonation reaction and the radical pathway.

  1. Bayesian meta-analysis to synthesize decay rate constant estimates for common fecal indicator bacteria.

    PubMed

    Brooks, Lauren E; Field, Katharine G

    2016-11-01

    For decades, fecal indicator bacteria have been used as proxies to quantitatively estimate fecal loading into water bodies. Widely used cultured indicators (e.g. Escherichia coli and Enterococcus spp.) and more recently developed genetic markers are well studied, but their decay in the environment is still poorly understood. We used Hierarchical Bayesian Linear Modeling to conduct a series of meta-analyses using published decay rate constant estimates, to synthesize findings into pooled estimates and identify gaps in the data preventing reliable estimates. In addition to the meta-analysis assuming all estimates come from the same population, meta-regressions including covariates believed to contribute to decay were fit and used to provided synthesized estimates for specific combinations of significant variables. Additionally, statements regarding the significance of variables across studies were made using the 95% confidence interval for meta-regression coefficients. These models were used to construct a mean decay rate constant estimate as well as credible intervals for the mean and the distribution of all likely data points. While synthesized estimates for each targeted indicator bacteria were developed, the amount of data available varied widely for each target, as did the predictive power of the models as determined by testing with additional data not included in the modeling. Temperature was found to be significant for all selected indicators, while light was found to be significant only for culturable indicators. Results from the models must be interpreted with caution, as they are based only on the data available, which may not be representative of decay in other scenarios. Copyright © 2016 Elsevier Ltd. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    Yang, Ruijie; Wang, Junjie; Xu, Feng; Li, Hua; Zhang, Xile

    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.

  4. Cardiopulmonary Effects of Constant-Rate Infusion of Lidocaine for Anesthesia during Abdominal Surgery in Goats

    PubMed Central

    Malavasi, Lais M; Greene, Stephen A; Gay, John M; Grubb, Tammy L

    2016-01-01

    Lidocaine is commonly used in ruminants but has an anecdotal history of being toxic to goats. To evaluate lidocaine's effects on selected cardiopulmonary parameters. Isoflurane-anesthetized adult goats (n = 24) undergoing abdominal surgery received a loading dose of lidocaine (2.5 mg/kg) over 20 min followed by constant-rate infusion of lidocaine (100 μg/kg/min); control animals received saline instead of lidocaine. Data collected at predetermined time points during the 60-min surgery included heart rate, mean arterial blood pressure, pO2, and pCO2. According to Welch 2-sample t tests, cardiopulmonary variables did not differ between groups. For example, after administration of the loading dose, goats in the lidocaine group had a mean heart rate of 88 ± 28 bpm, mean arterial blood pressure of 70 ± 19 mm Hg, pCO2 of 65 ± 13 mm Hg, and pO2 of 212 ± 99 mm Hg; in the saline group, these values were 90 ± 16 bpm, 76 ± 12 mm Hg, 61 ± 9 mm Hg, and 209 ± 83 mm Hg, respectively. One goat in the saline group required an additional dose of butorphanol. Overall our findings indicate that, at the dose provided, intravenous lidocaine did not cause adverse cardiopulmonary effects in adult goats undergoing abdominal surgery. Adding lidocaine infusion during general anesthesia is an option for enhancing transoperative analgesia in goats. PMID:27423150

  5. Cardiopulmonary Effects of Constant-Rate Infusion of Lidocaine for Anesthesia during Abdominal Surgery in Goats.

    PubMed

    Malavasi, Lais M; Greene, Stephen A; Gay, John M; Grubb, Tammy L

    2016-01-01

    Lidocaine is commonly used in ruminants but has an anecdotal history of being toxic to goats. To evaluate lidocaine's effects on selected cardiopulmonary parameters. Isoflurane-anesthetized adult goats (n = 24) undergoing abdominal surgery received a loading dose of lidocaine (2.5 mg/kg) over 20 min followed by constant-rate infusion of lidocaine (100 μg/kg/min); control animals received saline instead of lidocaine. Data collected at predetermined time points during the 60-min surgery included heart rate, mean arterial blood pressure, pO2, and pCO2. According to Welch 2-sample t tests, cardiopulmonary variables did not differ between groups. For example, after administration of the loading dose, goats in the lidocaine group had a mean heart rate of 88 ± 28 bpm, mean arterial blood pressure of 70 ± 19 mm Hg, pCO2 of 65 ± 13 mm Hg, and pO2 of 212 ± 99 mm Hg; in the saline group, these values were 90 ± 16 bpm, 76 ± 12 mm Hg, 61 ± 9 mm Hg, and 209 ± 83 mm Hg, respectively. One goat in the saline group required an additional dose of butorphanol. Overall our findings indicate that, at the dose provided, intravenous lidocaine did not cause adverse cardiopulmonary effects in adult goats undergoing abdominal surgery. Adding lidocaine infusion during general anesthesia is an option for enhancing transoperative analgesia in goats.

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

    PubMed

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

    2011-09-25

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  8. Product distributions and rate constants for ion-molecule reactions in water, hydrogen sulfide, ammonia, and methane

    NASA Technical Reports Server (NTRS)

    Huntress, W. T., Jr.; Pinizzotto, R. F., Jr.

    1973-01-01

    The thermal energy, bimolecular ion-molecule reactions occurring in gaseous water, hydrogen sulfide, ammonia, and methane have been identified and their rate constants determined using ion cyclotron resonance methods. Absolute rate constants were determined for the disappearance of the primary ions by using the trapped ion method, and product distributions were determined for these reactions by using the cyclotron ejection method. Previous measurements are reviewed and compared with the results using the present methods. The relative rate constants for hydrogen-atom abstraction, proton transfer, and charge transfer are also determined for reactions of the parent ions.

  9. Rate constant for the termolecular reaction of OH+toluene+helium in the fall-off range below 10 Torr

    NASA Astrophysics Data System (ADS)

    Bourmada, N.; Devolder, P.; Sochet, L.-R.

    1988-08-01

    We have measured the title rate constant by the discharge flow technique associated with detection of OH by resonance fluorescence and photon counting. The experimental conditions are as follows: pressure range 0.4 to 9.8 Tort; temperature range 297 to 353 K. From room temperature results, the Troe parameters k0 (low-pressure limiting rate constant) and k∞ (high-pressure limiting rate constant) are derived: k0 = (4.0 ± 0.5 ) × 10 -28 cm 6 molecule -2 s -1 ; k∞ = (6.0±0.7) × 10 -12 cm 3 molecule -1 s -1.

  10. Product distributions and rate constants for ion-molecule reactions in water, hydrogen sulfide, ammonia, and methane

    NASA Technical Reports Server (NTRS)

    Huntress, W. T., Jr.; Pinizzotto, R. F., Jr.

    1973-01-01

    The thermal energy, bimolecular ion-molecule reactions occurring in gaseous water, hydrogen sulfide, ammonia, and methane have been identified and their rate constants determined using ion cyclotron resonance methods. Absolute rate constants were determined for the disappearance of the primary ions by using the trapped ion method, and product distributions were determined for these reactions by using the cyclotron ejection method. Previous measurements are reviewed and compared with the results using the present methods. The relative rate constants for hydrogen-atom abstraction, proton transfer, and charge transfer are also determined for reactions of the parent ions.

  11. A Unified Kinetics and Equilibrium Experiment: Rate Law, Activation Energy, and Equilibrium Constant for the Dissociation of Ferroin

    ERIC Educational Resources Information Center

    Sattar, Simeen

    2011-01-01

    Tris(1,10-phenanthroline)iron(II) is the basis of a suite of four experiments spanning 5 weeks. Students determine the rate law, activation energy, and equilibrium constant for the dissociation of the complex ion in acid solution and base dissociation constant for phenanthroline. The focus on one chemical system simplifies a daunting set of…

  12. A Unified Kinetics and Equilibrium Experiment: Rate Law, Activation Energy, and Equilibrium Constant for the Dissociation of Ferroin

    ERIC Educational Resources Information Center

    Sattar, Simeen

    2011-01-01

    Tris(1,10-phenanthroline)iron(II) is the basis of a suite of four experiments spanning 5 weeks. Students determine the rate law, activation energy, and equilibrium constant for the dissociation of the complex ion in acid solution and base dissociation constant for phenanthroline. The focus on one chemical system simplifies a daunting set of…

  13. Spatial variability of time-constant slip rates on the San Jacinto fault zone, southern California

    NASA Astrophysics Data System (ADS)

    Blisniuk, K.; Oskin, M. E.; Sharp, W. D.; Meriaux, A. B.; Rockwell, T. K.; Fletcher, K.; Owen, L. A.

    2011-12-01

    In southern California, the San Andreas (SAF) and San Jacinto fault (SJF) zones account for 70-80% of the relative dextral motion between the Pacific and North American plates, with some studies suggesting that the SJF zone may be the dominant structure. However, few slip rate measurements are available for the SJF zone, making it difficult to evaluate the partitioning of deformation across the plate boundary. To more reliably constrain the late Quaternary slip history of the SJF zone, we measured the displacement of well-preserved alluvial fans along the Clark and Coyote Creek fault strands of the SJF zone using field mapping and high-resolution LiDAR topographic data, and dated the fans using U-series on pedogenic carbonate clast-coatings and in situ cosmogenic 10Be. Our results from four sites along the Clark fault strand and two sites along the Coyote Creek fault strand indicate that late Quaternary slip rates have fluctuated along their length but have remained constant since the late Pleistocene. Slip rates along the Clark fault strand over the past 50-30 kyr decrease southward over a distance of ~60 km from ~13 mm/yr at Anza, to 8.9 ± 2.0 mm/yr at Rockhouse Canyon, and 1.5 ± 0.4 mm/yr near the SE end of the Santa Rosa Mountains, probably due to transfer of slip from the Clark fault strand to the Coyote Creek fault strand and nearby zones of distributed deformation. Slip rates of up to ~14 to 18 mm/yr summed across the southern SJF zone suggest that since the latest Pleistocene, the SJF zone may rival the southern SAF zone in accommodating deformation across the Pacific-North America Plate boundary.

  14. Effect of Beetroot Juice on Moderate-Intensity Exercise at a Constant Rating of Perceived Exertion.

    PubMed

    Rienks, Jordyn N; Vanderwoude, Andrea A; Maas, Elizabeth; Blea, Zachary M; Subudhi, Andrew W

    Dietary nitrate supplementation has been shown to reduce oxygen consumption at a fixed work rate. We questioned whether a similar effect would be observed during variable work rate exercise at a specific rating of perceived exertion (RPE), as is commonly prescribed for aerobic training sessions. Using a double-blind, placebo controlled, crossover design, ten females (25 ± 3 years; VO2peak 37.1 ± 5.3 ml/kg/min) performed two 20-min cycle ergometer trials at a constant RPE of 13 (somewhat hard) 2.5 hours following ingestion of 140 ml of concentrated beetroot juice (12.9 mmol nitrate), or nitrate-depleted placebo. Performance was measured in terms of total VO2 (L) consumed and total mechanical work (kJ) accomplished across each trial. Following each experimental trial, subjects rode at 75W for an additional 5 min to determine the effect of beetroot juice on fixed work rate exercise. Coefficients of variation in total VO2 (L) and work performed (kJ) during the RPE 13 clamp trials were 8.2 and 9.5%, respectively. Consumption of beetroot juice did not affect total VO2 or work performed during RPE 13 exercise, but lowered resting systolic blood pressure by ~5 mmHg (P=0.041) and oxygen consumption at 75W by ~4% (P=0.048), relative to placebo. Since the effect of beetroot juice on oxygen consumption is small and may be masked by daily variability during self-regulated exercise, it is unlikely to have a notable effect on daily training.

  15. Potential chlorofluorocarbon replacements: OH reaction rate constants between 250 and 315 K and infrared absorption spectra

    SciTech Connect

    Garland, N.L.; Medhurst, L.J.; Nelson, H.H.

    1993-12-20

    The authors measured the rate constant for reactions of the OH radical with several potential chlorofluorocarbon replacements over the temperature range 251-314 K using laser photolysis laser-induced fluorescence techniques. The compounds studied and Arrhenius parameters determined from fits to the measured rate constants are as follows: CHF{sub 2}OCHF{sub 2} (E 134), k(T) = (5.4 {+-} 3.5) x 10{sup {minus}13} cm{sup 3} s{sup {minus}1} exp [({minus}3.1 {+-} 0.4 kcal mol{sup {minus}1})/RT]; CF{sub 3}CH{sub 2}CF{sub 3} (FC 236fa), k(T) = (2.0 {+-} 1.0) x 10{sup {minus}14} cm{sup 3} s{sup {minus}1} exp [({minus}1.8 {+-} 0.3 kcal mol{sup {minus}1})/RT]; CF{sub 3}CHFCHF{sub 2} (FC 236ea), k(T) = (2.0 {+-} 0.9) x 10{sup {minus}13} cm{sup 3} s{sup {minus}1} exp [({minus}2.0 {+-} 0.3 kcal mol{sup {minus}1})/RT]; and CF{sub 3}CF{sub 2}CH{sub 2}F (FC 236cb), k(T) = (2.6 {+-} 1.6) x 10{sup {minus}13} cm{sup 3} s{sup {minus}1} exp [({minus}2.2 {+-} 0.4 kcal mol{sup {minus}1})/RT]. The measured activation energies (2-3 kcal mol{sup {minus}1}) are consistent with a mechanism of H atom abstraction. The tropospheric lifetimes, estimated from the measured OH reaction rates, and measured integrated infrared absorption cross sections over the range 770 to 1430 cm{sup {minus}1} suggest that E 134 and FC 236fa may have significant global warming potential, while FC 236ea and FC 236cb do not. 17 refs., 4 figs., 3 tabs.

  16. Adiabatic decohesion in a thermoplastic craze thickening at constant or increasing rate

    NASA Astrophysics Data System (ADS)

    Leevers, Patrick S.; Godart, Marie-Aude

    When a crack in a thermally non-diffusive material is impact loaded—or propagates at high speed—a cohesive process which resists slow crack extension may itself cause decohesion by adiabatic heating. By assuming that decohesion ultimately occurs by low-energy disentanglement within a melt layer of critical thickness, the fracture resistance of craze-forming crystalline polymers can be estimated quantitatively. Previous estimates used a simple, thermomechanically linear representation of craze fibril drawing. This paper presents a more physically realistic, numerical formulation, and demonstrates it for constant craze thickening rate (as imposed by an ideal full-notch tension test) and for linearly increasing thickening rate (as at the tip of an impact-loaded or rapidly propagating crack). For a linear material, the numerical formulation gives results which asymptotically approach those from analytical solutions, as craze density approaches zero. In more realistic model polymers, the enthalpy of fusion increasingly delays decohesion as impact speed increases, although the temperature distribution of an endotherm appears to have little effect. Increasing molecular weight, heuristically associated with decreasing craze density and increasing structural dimension, increases the predicted impact fracture resistance. In every case, fracture resistance passes through a minimum as impact speed increases. The conclusions encourage the use of impact fracture tests, and discourage the use of the full-notch tension test, to assess the dynamic fracture resistance of a craze-forming polymer.

  17. An intercomparison technique for measuring thermal attachment cross sections and rate constants in distinct final channels

    NASA Technical Reports Server (NTRS)

    Alajajian, S. H.; Chutjian, A.

    1987-01-01

    A new technique is introduced for comparing negative-ion signal rates in which a common ion is produced by dissociative attachment in a series of molecules. Measurements are carried out at electron energies less than 100 MeV and at resolutions of 6-8 MeV (FWHM). The technique is demonstrated by detection of the Cl(-) signal in CFCl3, CCl4, CF2Cl2, 1,1,2-C2Cl3F3, 1,1,1-C2Cl3F3 and C2Cl4. Measurements for 1,1,1-C2Cl3F3 show that there is a significant open channel, other than Cl(-) formation, which accounts for about 60 percent of negative-ion formation in thermal-multiple-collision (swarm) experiments. Channel cross sections and rate constants are given for the process Cl(-)/1,1,1-Cl2Cl3F3, as well as in C2Cl4, for the separate channels Cl(-)/C2Cl4 and C2Cl4(-)/C2Cl4.

  18. Constant rate exposure of pregnant hamsters to arsenate during early gestation

    SciTech Connect

    Ferm, V.H.; Hanlon, D.P.

    1985-08-01

    The teratogenic and embryotoxic effects of constant-rate exposure of pregnant hamsters to arsenate have been examined by means of subcutaneous implants of osmotic minipumps. Different total exposure regimes were established by varying the duration of minipump implants and by varying the concentration of arsenate in the minipumps. Dams were killed on Day 13 pregnancy, 5 days after the critical stage of organogenesis. Numbers of resorptions, dead fetuses, and living fetuses were obtained. Fetal weights, crown-rump lengths, and the incidence of malformations were recorded. Control animals were treated identically with minipumps containing demineralized water. The percentage of malformations per litter, a direct measure of teratogenesis, was dependent only upon the concentration of arsenate in the minipumps. The minimum teratogenic response was achieved with a dose of 70 ..mu..mol/kg dam/24 hr during the critical stages of organogenesis. The embryotoxic (fetotoxic) indicators, fetal weight and crown-rump length, decreased with increases in exposure time and with increased concentrations of arsenate. The resorption rate also depended directly upon duration of exposure and concentration of arsenate in the mini-pump.

  19. Evaluation of a constant rate infusion of lidocaine for balanced anesthesia in dogs undergoing surgery.

    PubMed

    Ortega, Maria; Cruz, Ignacio

    2011-08-01

    This study assessed the intraoperative analgesic effects of intravenous lidocaine administered by a constant rate infusion (CRI) in surgical canine patients. A prospective, blinded, randomized study was designed with 2 treatment groups: A (lidocaine) and B (placebo), involving 41 dogs. All patients were premedicated with acepromazine and buprenorphine, induced with propofol and midazolam; anesthesia was maintained with isoflurane in oxygen. Group A received 2 mg/kg IV lidocaine immediately after induction, followed within 5 min by a CRI at 50 μg/kg/min. Group B received an equivalent volume of saline instead of lidocaine. Changes in heart rate and blood pressure during maintenance were treated by increasing CRI. Fentanyl was used as a supplemental analgesic when intraoperative nociceptive response was not controlled with the maximum dose of lidocaine infusion. There was a significantly lower use of supplemental intraoperative analgesia in the lidocaine than in the placebo group. Group B dogs had almost twice as high a risk of intraoperative nociceptive response as group A dogs.

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

    PubMed

    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.

  1. Evaluation of a constant rate infusion of lidocaine for balanced anesthesia in dogs undergoing surgery

    PubMed Central

    Ortega, Maria; Cruz, Ignacio

    2011-01-01

    This study assessed the intraoperative analgesic effects of intravenous lidocaine administered by a constant rate infusion (CRI) in surgical canine patients. A prospective, blinded, randomized study was designed with 2 treatment groups: A (lidocaine) and B (placebo), involving 41 dogs. All patients were premedicated with acepromazine and buprenorphine, induced with propofol and midazolam; anesthesia was maintained with isoflurane in oxygen. Group A received 2 mg/kg IV lidocaine immediately after induction, followed within 5 min by a CRI at 50 μg/kg/min. Group B received an equivalent volume of saline instead of lidocaine. Changes in heart rate and blood pressure during maintenance were treated by increasing CRI. Fentanyl was used as a supplemental analgesic when intraoperative nociceptive response was not controlled with the maximum dose of lidocaine infusion. There was a significantly lower use of supplemental intraoperative analgesia in the lidocaine than in the placebo group. Group B dogs had almost twice as high a risk of intraoperative nociceptive response as group A dogs. PMID:22294791

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

    PubMed

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

    PubMed

    Sorvajärvi, Tapio; Viljanen, Jan; Toivonen, Juha; Marshall, Paul; Glarborg, Peter

    2015-04-09

    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) cm(6) molecule(-2) s(-1). Combination with literature values leads to a recommended kR1 of 5.5 × 10(-26)T(-1.55) exp(-10/T) cm(6) molecule(-2) s(-1) over 250-1320 K, with an error limit of a factor of 1.5. A van't Hoff analysis constrained to fit the computed ΔS298 yields a K-O2 bond dissociation enthalpy of 184.2 ± 4.0 kJ mol(-1) at 298 K and ΔfH298(KO2) = -95.2 ± 4.1 kJ mol(-1). The corresponding D0 is 181.5 ± 4.0 kJ mol(-1). This value compares well with a CCSD(T) extrapolation to the complete basis set limit, with all electrons correlated, of 177.9 kJ mol(-1).

  4. Determination of calibration constants for the hole-drilling residual stress measurement technique applied to orthotropic composites. II - Experimental evaluations

    NASA Technical Reports Server (NTRS)

    Prasad, C. B.; Prabhakaran, R.; Tompkins, S.

    1987-01-01

    The first step in the extension of the semidestructive hole-drilling technique for residual stress measurement to orthotropic composite materials is the determination of the three calibration constants. Attention is presently given to an experimental determination of these calibration constants for a highly orthotropic, unidirectionally-reinforced graphite fiber-reinforced polyimide composite. A comparison of the measured values with theoretically obtained ones shows agreement to be good, in view of the many possible sources of experimental variation.

  5. Determination of calibration constants for the hole-drilling residual stress measurement technique applied to orthotropic composites. II - Experimental evaluations

    NASA Technical Reports Server (NTRS)

    Prasad, C. B.; Prabhakaran, R.; Tompkins, S.

    1987-01-01

    The first step in the extension of the semidestructive hole-drilling technique for residual stress measurement to orthotropic composite materials is the determination of the three calibration constants. Attention is presently given to an experimental determination of these calibration constants for a highly orthotropic, unidirectionally-reinforced graphite fiber-reinforced polyimide composite. A comparison of the measured values with theoretically obtained ones shows agreement to be good, in view of the many possible sources of experimental variation.

  6. Beta-lactamases as fully efficient enzymes. Determination of all the rate constants in the acyl-enzyme mechanism.

    PubMed

    Christensen, H; Martin, M T; Waley, S G

    1990-03-15

    The rate constants for both acylation and deacylation of beta-lactamase PC1 from Staphylococcus aureus and the RTEM beta-lactamase from Escherichia coli were determined by the acid-quench method [Martin & Waley (1988) Biochem. J. 254, 923-925] with several good substrates, and, for a wider range of substrates, of beta-lactamase I from Bacillus cereus. The values of the acylation and deacylation rate constants for benzylpenicillin were approximately the same (i.e. differing by no more than 2-fold) for each enzyme. The variation of kcat./Km for benzylpenicillin with the viscosity of the medium was used to obtain values for all four rate constants in the acyl-enzyme mechanism for all three enzymes. The reaction is partly diffusion-controlled, and the rate constant for the dissociation of the enzyme-substrate complex has approximately the same value as the rate constants for acylation and deacylation. Thus all three first-order rate constants have comparable values. Here there is no single rate-determining step for beta-lactamase action. This is taken to be a sign of a fully efficient enzyme.

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

    EPA Pesticide Factsheets

    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.

  8. Determination of calibration constants for the hole-drilling residual stress measurement technique applied to orthotropic composites. I - Theoretical considerations

    NASA Technical Reports Server (NTRS)

    Prasad, C. B.; Prabhakaran, R.; Tompkins, S.

    1987-01-01

    The hole-drilling technique for the measurement of residual stresses using electrical resistance strain gages has been widely used for isotropic materials and has been adopted by the ASTM as a standard method. For thin isotropic plates, with a hole drilled through the thickness, the idealized hole-drilling calibration constants are obtained by making use of the well-known Kirsch's solution. In this paper, an analogous attempt is made to theoretically determine the three idealized hole-drilling calibration constants for thin orthotropic materials by employing Savin's (1961) complex stress function approach.

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

    PubMed Central

    Borel, Benoit; Wilkinson-Maitland, Courtney A; Hamilton, Alan; Bourbeau, Jean; Perrault, Hélène; Jensen, Dennis; Maltais, François

    2016-01-01

    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 units, P<0.01); however, no statically significant differences were observed between treatments at 20 and 24 steps/min (both P>0.05). Conclusion The 3-MST, when performed at 14 and 16 steps/min, was responsive to detect the relief of exertional dyspnea after acute bronchodilation in patients with moderate-to-severe COPD. PMID:27942208

  10. Estimation of dispersion curves by combining Effective Elastic Constants and SAFE Method: A case study in a plate under stress

    NASA Astrophysics Data System (ADS)

    Quiroga, J. E.; Mujica, L.; Villamizar, R.; Ruiz, M.; Camacho, J.

    2017-05-01

    This paper presents an approach to calculate dispersion curves for homogeneous and isotropic plates subject to stress, via Semi-Analytical Finite Element and the Effective Elastic Constants, since stresses in the waveguide modify the phase and group velocities of the lamb waves. In the proposed methodology an isotropic specimen subjected to anisotropic loading is emulated by proposing an equivalent stress-free anisotropic specimen. This approximation facilitates determining the dispersion curves by using the well-studied numerical solution for the stress-free cases. The lamb wave in anisotropic materials can be studied by means of the Effective Elastic Constants, which reduces the complexity of the numerical implementation. Finally, numerical data available in literature were used to validate the proposed methodology, where it could be demonstrated its effectiveness as approximated method.

  11. U-shaped temperature dependence of rate constant of intramolecular photoinduced charge separation in zinc-porphyrin-bridge-quinone compounds.

    PubMed

    Kichigina, Anna O; Ionkin, Vladimir N; Ivanov, Anatoly I

    2013-06-20

    The multichannel stochastic point transition model of photoinduced electron transfer from both a vibrationally unrelaxed and a relaxed states involving the vibrational relaxation in donor-acceptor pairs has been elaborated. The U-shaped temperature dependencies of the rate constants of the intramolecular photoinduced charge separation from both the vibrationally unrelaxed and the relaxed states observed in Zn-porphyrin-bridge-quinone compounds in 2-methyltetrahydrofuran solvent have been reproduced in the framework of the proposed model that accounts for the temperature dependencies of the charge separation free energy gap and the medium reorganization energy. This modeling has allowed uncovering the mechanism of such a variation of the rate constant with the temperature. In the high temperature region, 310-125 K, the charge separation proceeds in the solvent controlled regime and its rate constant decreases with decreasing the temperature mirroring the temperature dependence of the medium relaxation rate. Further lowering the temperature leads to a rise of the reaction free energy gap so that it becomes larger than the medium reorganization energy. In this region the dynamic solvent effect is strongly suppressed and the charge separation rate constant becomes independent from the solvent relaxation rate. Although the medium relaxation rate continues to decrease with decreasing the temperature, the charge separation rate constant starts to rise because the reaction proceeds in the barrierless region.

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

    PubMed

    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.

  13. Competitive kinetics versus stopped flow method for determining the degradation rate constants of steroids by ozonation.

    PubMed

    López-López, Alberto; Flores-Payán, Valentín; León-Becerril, Elizabeth; Hernández-Mena, Leonel; Vallejo-Rodríguez, Ramiro

    2016-01-01

    Steroids are classified as endocrine disrupting chemicals; they are persistent with low biodegradability and are hardly degraded by conventional methods. Ozonation process has been effective for steroids degradation and the determination of the kinetics is a fundamental aspect for the design and operation of the reactor. This study assessed two methods: competitive kinetics and stopped flow, for determining the degradation kinetics of two steroids, estradiol (E2) and ethinylestradiol (EE2) in spiked water. Experiments were performed at pH 6, 21 °C, and using tertbutyl alcohol as scavenger of hydroxyl radicals; competitive kinetics method used sodium phenolate as reference compound. For the stopped flow, the experiments were performed in a BioLogic SFM-3000/S equipment. For both methods, the second order rate constants were in the order of 10(6) and 10(5) M(-1) s(-1) for E2 and EE2 respectively. The competitive kinetics can be applied with assurance and reliability but needing an additional analysis method to measure the residual concentrations. Stopped flow method allows the evaluation of the degradation kinetics in milliseconds and avoids the use of additional analytical methodologies; this method allows determining the reaction times on line. The methods are applicable for degradation of other emerging contaminants or other steroids and could be applied in water treatment at industrial level. Finally, it is important to consider the resources available to implement the most appropriate method, either competitive kinetics or the stopped-flow method.

  14. Estimating spatially-variable first-order rate constants in groundwater reactive transport systems.

    PubMed

    Bailey, R T; Baù, D

    2011-03-25

    Numerical reactive transport models are often used as tools to assess aquifers contaminated with reactive groundwater solutes as well as investigating mitigation scenarios. The ability to accurately simulate the fate and transport of solutes, however, is often impeded by a lack of information regarding the parameters that define chemical reactions. In this study, we employ a steady-state Ensemble Kalman Filter (EnKF), a data assimilation algorithm, to provide improved estimates of a spatially-variable first-order rate constant λ through assimilation of solute concentration measurement data into reactive transport simulation results. The methodology is applied in a steady-state, synthetic aquifer system in which a contaminant is leached to the saturated zone and undergoes first-order decay. Multiple sources of uncertainty are investigated, including hydraulic conductivity of the aquifer and the statistical parameters that define the spatial structure of the parameter field. For the latter scenario, an iterative method is employed to identify the statistical mean of λ of the reference system. Results from all simulations show that the filter scheme is successful in conditioning the λ ensemble to the reference λ field. Sensitivity analyses demonstrate that the estimation of the λ values is dependent on the number of concentration measurements assimilated, the locations from which the measurement data are collected, the error assigned to the measurement values, and the correlation length of the λ fields.

  15. Unified expression for the rate constant of the bridged electron transfer derived by renormalization

    NASA Astrophysics Data System (ADS)

    Saito, Keisuke; Sumi, Hitoshi

    2009-10-01

    Electron transfer (ET) from a donor to an acceptor through an energetically close intermediary state on a midway molecule is a process found often in natural and artificial solar-energy capturing systems such as photosynthesis. This process has often been thought of in terms of opposing "superexchange" and "sequential or hopping" mechanisms, and the recent theory of Sumi and Kakitani (SK) [J. Phys. Chem. B 105, 9603 (2001)] has shown an interpolation between these mechanisms. In their theory, however, dynamics governing the most interesting intermediary region between them has artificially been introduced by phenomenologies. The dynamics is played by decoherence among electronic states, their decay, and thermalization of phonons in the medium. The present work clarifies the dynamics on a microscopic basis by means of renormalization in electronic coupling among the states, and gives a complete unified expression of the rate constant of the ET. It merges to that given by the SK theory in the semiclassical approximation for phonons interacting with an electron transferred.

  16. Dose rate constants for the quantity Hp(3) for frequently used radionuclides in nuclear medicine.

    PubMed

    Szermerski, Bastian; Bruchmann, Iris; Behrens, Rolf; Geworski, Lilli

    2016-12-01

    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 Hp(3), which is supposed to estimate the dose to the lens of the eye. For this, Hp(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. Copyright © 2015. Published by Elsevier GmbH.

  17. Rate constant for the reaction C2H5 + HBr → C2H6 + Br.

    PubMed

    Golden, David M; Peng, Jingping; Goumri, A; Yuan, J; Marshall, Paul

    2012-06-21

    RRKM theory has been employed to analyze the kinetics of the title reaction, in particular, the once-controversial negative activation energy. Stationary points along the reaction coordinate were characterized with coupled cluster theory combined with basis set extrapolation to the complete basis set limit. A shallow minimum, bound by 9.7 kJ mol(-1) relative to C(2)H(5) + HBr, was located, with a very small energy barrier to dissociation to Br + C(2)H(6). The transition state is tight compared to the adduct. The influence of vibrational anharmonicity on the kinetics and thermochemistry of the title reaction were explored quantitatively. With adjustment of the adduct binding energy by ∼4 kJ mol(-1), the computed rate constants may be brought into agreement with most experimental data in the literature, including new room-temperature results described here. There are indications that at temperatures above those studied experimentally, the activation energy may switch from negative to positive.

  18. Detection of exudates in fundus imagery using a constant false-alarm rate (CFAR) detector

    NASA Astrophysics Data System (ADS)

    Khanna, Manish; Kapoor, Elina

    2014-05-01

    Diabetic retinopathy is the leading cause of blindness in adults in the United States. The presence of exudates in fundus imagery is the early sign of diabetic retinopathy so detection of these lesions is essential in preventing further ocular damage. In this paper we present a novel technique to automatically detect exudates in fundus imagery that is robust against spatial and temporal variations of background noise. The detection threshold is adjusted dynamically, based on the local noise statics around the pixel under test in order to maintain a pre-determined, constant false alarm rate (CFAR). The CFAR detector is often used to detect bright targets in radar imagery where the background clutter can vary considerably from scene to scene and with angle to the scene. Similarly, the CFAR detector addresses the challenge of detecting exudate lesions in RGB and multispectral fundus imagery where the background clutter often exhibits variations in brightness and texture. These variations present a challenge to common, global thresholding detection algorithms and other methods. Performance of the CFAR algorithm is tested against a publicly available, annotated, diabetic retinopathy database and preliminary testing suggests that performance of the CFAR detector proves to be superior to techniques such as Otsu thresholding.

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

    NASA Astrophysics Data System (ADS)

    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.

  20. Three stages of bubble formation on submerged orifice under constant gas flow rate

    NASA Astrophysics Data System (ADS)

    Yu, Xianxian; Wang, Yiwei; Huang, Chenguang; Du, Tezhuan

    2015-12-01

    Bubble formation is involved in many engineering applications. It is important to understand the dynamics of bubble formation. This work reports experimental and numerical results of bubble formation on submerged orifice under constant gas flow rate. Compressible large eddy simulation combined volume of fluid (VOF) was adopted in simulation and results was validated by experiment. Bubble formation is divided into three stages in this paper, expansion stage, elongation stage and pinch-off stage. In expansion stage, The bubble grows radially due to the incoming gas flux, but the bubble base remains attached to the orifice. But as gas injected, the spherical bubble will go into the elongation stage when the downward resultant force is lager than upward resultant force. And when bubble neck's length is bigger than √2Ro the bubble will go into pinch-off stage. Cylindrical Rayleigh-Plesset equation can be used to describe the pinch-off stage. Uncertain parameter r in it is given reference value in this paper.

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Constant false alarm rate algorithm for the dim-small target detection based on the distribution characteristics of target coordinates

    NASA Astrophysics Data System (ADS)

    Fei, Xiao-Liang; Ren, Kan; Qian, Wei-xian; Wang, Peng-cheng

    2015-10-01

    CFAR (Constant False Alarm Rate) is a key technology in Infrared dim-small target detection system. Because the traditional constant false alarm rate detection algorithm gets the probability density distribution which is based on the pixel information of each area in the whole image and calculates the target segmentation threshold of each area by formula of Constant false alarm rate, the problems including the difficulty of probability distribution statistics and large amount of algorithm calculation and long delay time are existing. In order to solve the above problems effectively, a formula of Constant false alarm rate based on target coordinates distribution is presented. Firstly, this paper proposes a new formula of Constant false alarm rate by improving the traditional formula of Constant false alarm rate based on the single grayscale distribution which objective statistical distribution features are introduced. So the control of false alarm according to the target distribution information is implemented more accurately and the problem of high false alarm that is caused of the complex background in local area as the cloud reflection and the ground clutter interference is solved. At the same time, in order to reduce the amount of algorithm calculation and improve the real-time characteristics of algorithm, this paper divides the constant false-alarm statistical area through two-dimensional probability density distribution of target number adaptively which is different from the general identifying methods of constant false-alarm statistical area. Finally, the target segmentation threshold of next frame is calculated by iteration based on the function of target distribution probability density in image sequence which can achieve the purpose of controlling the false alarm until the false alarm is down to the upper limit. The experiment results show that the proposed method can significantly improve the operation time and meet the real-time requirements on

  3. Rate constant measurements for the overall reaction of OH + 1-butanol → products from 900 to 1200 K.

    PubMed

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

    2012-03-15

    The rate constant for the overall reaction OH + 1-butanol → products was determined in the temperature range 900 to 1200 K from measurements of OH concentration time histories in reflected shock wave experiments of tert-butyl hydroperoxide (TBHP) as a fast source of OH radicals with 1-butanol in excess. Narrow-linewidth laser absorption was employed for the quantitative OH concentration measurement. A detailed kinetic mechanism was constructed that includes updated rate constants for 1-butanol and TBHP kinetics that influence the near-first-order OH concentration decay under the present experimental conditions, and this mechanism was used to facilitate the rate constant determination. The current work improves upon previous experimental studies of the title rate constant by utilizing a rigorously generated kinetic model to describe secondary reactions. Additionally, the current work extends the temperature range of experimental data in the literature for the title reaction under combustion-relevant conditions, presenting the first measurements from 900 to 1000 K. Over the entire temperature range studied, the overall rate constant can be expressed in Arrhenius form as 3.24 × 10(-10) exp(-2505/T [K]) cm(3) molecule(-1) s(-1). The influence of secondary reactions on the overall OH decay rate is discussed, and a detailed uncertainty analysis is performed yielding an overall uncertainty in the measured rate constant of ±20% at 1197 K and ±23% at 925 K. The results are compared with previous experimental and theoretical studies on the rate constant for the title reaction and reasonable agreement is found when the earlier experimental data were reinterpreted.

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

    PubMed

    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.

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

    PubMed

    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. Copyright © 2016 Elsevier B.V. All rights reserved.

  6. Temperature-Dependent Rate Constants and Substituent Effects for the Reactions of Hydroxyl Radicals With Three Partially Fluorinated Ethers

    NASA Technical Reports Server (NTRS)

    Hsu, K.-J.; DeMore, W. B.

    1995-01-01

    Rate constants and temperature dependencies for the reactions of OH with CF3OCH3 (HFOC-143a), CF2HOCF2H (HFOC-134), and CF3OCF2H (HFOC-125) were studied using a relative rate technique in the temperature range 298-393 K. The following absolute rate constants were derived: HFOC-143a, 1.9E-12 exp(-1555/T); HFOC-134, 1.9E-12 exp(-2006/T); HFOC-125, 4.7E-13 exp(-2095/T). Units are cm(exp 3)molecule(exp -1) s(exp -1). Substituent effects on OH abstraction rate constants are discussed, and it is shown that the CF3O group has an effect on the OH rate constants similar to that of a fluorine atom. The effects are related to changes in the C-H bond energies of the reactants (and thereby the activation energies) rather than changes in the preexponential factors. On the basis of a correlation of rate constants with bond energies, the respective D(C-H) bond strengths in the three ethers are found to be 102, 104, and 106 kcal/mol, with an uncertainty of about 1 kcal/mol.

  7. Using deformation rates in Northern Cascadia to constrain time-dependent stress- and slip-rate on the megathrust

    NASA Astrophysics Data System (ADS)

    Bruhat, L.; Segall, P.

    2016-12-01

    In northern Cascadia, estimates of interseismic slip deficit on the megathrust are complicated by the poorly understood "gap" between the down-dip limit of the locked region and the top of the Episodic Tremor and Slip (ETS) zone, as revealed by kinematic inversions of deformation rates. Physics-based models of slow slip events (SSE) match the average ETS displacements, and predict nearly constant shear stress when averaged over many SSEs. Yet, when the fault is locked to the top of the ETS zone, such models predict too much locking when compared to observed decadal-scale velocities, especially uplift rates. Minimum norm inversions of GPS and tide gauge/leveling rates show that larger slip rates are necessary within both the gap and the ETS zone relative to the model with constant shear stress, requiring non-stationary shear stress rates. We invert for the distribution of shear stress rate on the fault below a locked zone that best fits the data. We find that negative shear stress rates within both the gap and the ETS region, reaching -3kPa/yr at a depth of 25km, and locking depths around 21km are required by the data. To explain the negative shear stress rates, we investigate models where both the size of the creeping region and the slip profile evolve with time. We explore whether the gap and ETS region act a quasi-static crack, potentially driven up-dip by plate motion at the down dip limit of the ETS region. Stress reaches a peak at the crack tip, and then decreases over a cohesive region. Using MCMC we solve for the locking depth, the crack friction parameters, and the up dip propagation velocity. Best fitting models reveal that a very slow up dip propagation is needed to fit the data and that the gap seems to act as a region of fault weakening. Possible explanations for this include a slow decrease in normal stress within the gap, possibly due to an increase in pore pressure, or a long-term reduction in fault friction.

  8. Reaction mechanism and rate constants of the CH+CH4 reaction: a theoretical study

    NASA Astrophysics Data System (ADS)

    Ribeiro, Joao Marcelo; Mebel, Alexander M.

    2015-07-01

    Ab initio and density functional calculations have been performed to elucidate the mechanism of CH radical insertion into methane. The results show that the reaction can be viewed to occur via two stages. On the first stage, the CH radical approaches methane without large structural changes to acquire proper positioning for the subsequent stage, where H-migration occurs from CH4 to CH, along with a C-C bond formation. Where the first stage ends and the second begins, a tight transition state was located using the B3LYP/6-311G(d,p) and MP4(SDQ)/6-311++G(d,p) methods. Using a rigid rotor - harmonic oscillator approach within transition state theory, we show that at the MP5/6-311++G(d,p)//MP4(SDQ)/6-311++G(d,p) level the calculated rate constants are in a reasonably good agreement with experiment in a broad temperature range of 145-581 K. Even at low temperatures, the insertion reaction bottleneck is found about the location of the tight transition state, rather than at long separations between the CH and CH4 reactants. In addition, high level CCSD(T)-F12/CBS calculations of the remainder of the C2H5 potential energy surface predict the CH+CH4 reaction to proceed via the initial insertion step to the ethyl radical which then can emit a hydrogen atom to form highly exothermic C2H4+H products.

  9. Non-Condon equilibrium Fermi's golden rule electronic transition rate constants via the linearized semiclassical method.

    PubMed

    Sun, Xiang; Geva, Eitan

    2016-06-28

    In this paper, we test the accuracy of the linearized semiclassical (LSC) expression for the equilibrium Fermi's golden rule rate constant for electronic transitions in the presence of non-Condon effects. We do so by performing a comparison with the exact quantum-mechanical result for a model where the donor and acceptor potential energy surfaces are parabolic and identical except for shifts in the equilibrium energy and geometry, and the coupling between them is linear in the nuclear coordinates. Since non-Condon effects may or may not give rise to conical intersections, both possibilities are examined by considering: (1) A modified Garg-Onuchic-Ambegaokar model for charge transfer in the condensed phase, where the donor-acceptor coupling is linear in the primary mode coordinate, and for which non-Condon effects do not give rise to a conical intersection; (2) the linear vibronic coupling model for electronic transitions in gas phase molecules, where non-Condon effects give rise to conical intersections. We also present a comprehensive comparison between the linearized semiclassical expression and a progression of more approximate expressions. The comparison is performed over a wide range of frictions and temperatures for model (1) and over a wide range of temperatures for model (2). The linearized semiclassical method is found to reproduce the exact quantum-mechanical result remarkably well for both models over the entire range of parameters under consideration. In contrast, more approximate expressions are observed to deviate considerably from the exact result in some regions of parameter space.

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

    PubMed

    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.

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

    PubMed

    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.

  12. Non-Condon equilibrium Fermi's golden rule electronic transition rate constants via the linearized semiclassical method

    NASA Astrophysics Data System (ADS)

    Sun, Xiang; Geva, Eitan

    2016-06-01

    In this paper, we test the accuracy of the linearized semiclassical (LSC) expression for the equilibrium Fermi's golden rule rate constant for electronic transitions in the presence of non-Condon effects. We do so by performing a comparison with the exact quantum-mechanical result for a model where the donor and acceptor potential energy surfaces are parabolic and identical except for shifts in the equilibrium energy and geometry, and the coupling between them is linear in the nuclear coordinates. Since non-Condon effects may or may not give rise to conical intersections, both possibilities are examined by considering: (1) A modified Garg-Onuchic-Ambegaokar model for charge transfer in the condensed phase, where the donor-acceptor coupling is linear in the primary mode coordinate, and for which non-Condon effects do not give rise to a conical intersection; (2) the linear vibronic coupling model for electronic transitions in gas phase molecules, where non-Condon effects give rise to conical intersections. We also present a comprehensive comparison between the linearized semiclassical expression and a progression of more approximate expressions. The comparison is performed over a wide range of frictions and temperatures for model (1) and over a wide range of temperatures for model (2). The linearized semiclassical method is found to reproduce the exact quantum-mechanical result remarkably well for both models over the entire range of parameters under consideration. In contrast, more approximate expressions are observed to deviate considerably from the exact result in some regions of parameter space.

  13. Evaluating the methane generation rate constant (k value) of low-organic waste at Danish landfills.

    PubMed

    Mou, Zishen; Scheutz, Charlotte; Kjeldsen, Peter

    2015-01-01

    The methane (CH4) generation rate constant (k value, yr(-1)) is an essential parameter when using first-order decay (FOD) landfill gas (LFG) generation models to estimate CH4 generation from landfills. Four categories of waste (street cleansing, mixed bulky, shredder, and sludge waste) with a low-organic content, as well as temporarily stored combustible waste, were sampled from four Danish landfills. Anaerobic degradation experiments were set up in duplicate for all waste samples and incubated for 405 days, while the cumulative CH4 generation was continuously monitored. Applying FOD equations to the experimental results, half-life time values (t½, yr) and k values of various waste categories were determined. In general, similar waste categories obtained from different Danish landfills showed similar results. Sludge waste had the highest k values, which were in the range 0.156-0.189 yr(-1). The combustible and street cleansing waste showed k values of 0.023-0.027 yr(-1) and 0.073-0.083 yr(-1), respectively. The lowest k values were obtained for mixed bulky and shredder wastes ranging from 0.013 to 0.017 yr(-1). Most low-organic waste samples showed lower k values in comparison to the default numeric values in current FOD models (e.g., IPCC, LandGEM, and Afvalzorg). Compared with the k values reported in the literature, this research determined low-organic waste for the first time via reliable large-scale and long-term experiments. The degradation parameters provided in this study are valuable when using FOD LFG generation models to estimate CH4 generation from modern landfills that receive only low-organic waste. Copyright © 2014 Elsevier Ltd. All rights reserved.

  14. Stress Ratio Effects on Crack Opening Loads and Crack Growth Rates in Aluminum Alloy 2024

    NASA Technical Reports Server (NTRS)

    Riddell, William T.; Piascik, Robert S.

    1998-01-01

    The effects of stress ratio (R) and crack opening behavior on fatigue crack growth rates (da/dN) for aluminum alloy (AA) 2024-T3 were investigated using constant-delta K testing, closure measurements, and fractography. Fatigue crack growth rates were obtained for a range of delta K and stress ratios. Results show that constant delta K fatigue crack growth for R ranging from near 0 to 1 is divided into three regions. In Region 1, at low R, da/dN increases with increasing R. In Region 2, at intermediate R, fatigue crack growth rates are relatively independent of R. In Region 3, at high R, further increases in da/dN are observed with increasing R.

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

    PubMed

    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. Copyright © 2013 Elsevier B.V. All rights reserved.

  16. Mercury chemistry in the MBL: Modeling results including Hg + halogen atom reaction rate constants

    NASA Astrophysics Data System (ADS)

    Hedgecock, I. M.; Pirrone, N.

    2003-04-01

    The inclusion, of recently published kinetic data for the reactions between gas phase elemental Hg and halogen atoms and molecules, in a photochemical box model including aerosols of the Marine Boundary Layer (MBL), suggests that the cycling of Hg over the world's oceans may be much more dynamic than was once thought, as a direct result of halogen activation from marine aerosols. The rate of gas phase oxidation of Hg(0) in the model leads to high concentrations of gas phase oxidised Hg (Hg(II)), which is deposited to the sea surface either directly from the gas phase or indirectly via scavenging by sea salt and non-sea-salt sulphate aerosol particles and subsequent deposition. The model base run predicts Hg(II) concentrations higher than those measured in the marine atmosphere, and a lifetime for Hg(0) of a matter of days, rather than months as has been generally assumed. In light of previous measurements and the known stability of the hemispherical background concentration of Hg(0) the influence of liquid water content (the number of deliquescent aerosol droplets), cloud optical depth at the top of the boundary layer, and the Henry's Law constants for HgCl2 and HgBr2 have been investigated. In order to maintain a stable background concentration of Hg(0) a source strength (for emission from the sea, or entrainment from the free troposphere) of at least 15 ng m-2 hr-1 is required, which seems most unlikely considering results from flux chamber experiments. The model therefore either overestimates the rate of gas phase oxidation or lacks a fundamental reduction process. The evidence from studies of mercury depletion events in the Arctic troposphere lend support to the fast reaction between Hg(0) and Br containing radicals which have been included in the model, it is necessary therefore to investigate homogeneous and heterogeneous mechanisms for the reduction of Hg(II) to Hg(0) in order to explain the measured Hg(II) concentrations in the MBL and the stable

  17. Temperature and pressure dependence of the absolute rate constant for the reactions of NH2 radicals with acetylene and ethylene

    NASA Technical Reports Server (NTRS)

    Bosco, S. R.; Nava, D. F.; Brobst, W. D.; Stief, L. J.

    1984-01-01

    The absolute rate constants for the reaction between the NH2 free radical and acetylene and ethylene is measured experimentally using a flash photolysis technique. The constant is considered to be a function of temperature and pressure. At each temperature level of the experiment, the observed pseudo-first-order rate constants were assumed to be independent of flash intensity. The results of the experiment indicate that the bimolecular rate constant for the NH2 + C2H2 reaction increases with pressure at 373 K and 459 K but not at lower temperatures. Results near the pressure limit conform to an Arrhenius expression of 1.11 (+ or -) 0.36 x 10 to the -13th over the temperature range from 241 to 459 K. For the reaction NH2 + C2H4, a smaller rate of increase in the bimolecular rate constant was observed over the temperature range 250-465 K. The implications of these results for current theoretical models of NH2 + C2H2 (or H4) reactions in the atmospheres of Jupiter and Saturn are discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

    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 <=± 5°. This restriction requires the treatment arc to be broken into multiple sectors such that the local MU fluctuation within each sector is reduced, thereby lowering the angular deviation of the segments during redistribution. The converted CDR plans were delivered with a 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

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

    PubMed

    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

  20. Principals Responding to Constant Pressure: Finding a Source of Stress Management

    ERIC Educational Resources Information Center

    Wells, Caryn M.

    2013-01-01

    This conceptual article presents a review of the research concerning the stress level of principals over the past three decades, with emphasis on the occupational stress that principals encounter because of heightened accountability and expectations for student achievement. Mindfulness meditation, as a stress management intervention, provides the…

  1. Principals Responding to Constant Pressure: Finding a Source of Stress Management

    ERIC Educational Resources Information Center

    Wells, Caryn M.

    2013-01-01

    This conceptual article presents a review of the research concerning the stress level of principals over the past three decades, with emphasis on the occupational stress that principals encounter because of heightened accountability and expectations for student achievement. Mindfulness meditation, as a stress management intervention, provides the…

  2. Pressure dependence of the absolute rate constant for the reaction OH + C2H2 from 228 to 413 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Nava, D. F.; Payne, W. A.; Stief, L. J.; Borkowski, R. P.

    1980-01-01

    The pressure dependence of the absolute rate constant for the reaction of the hydroxyl radical with acetylene, important in both atmospheric and combustion chemistry, is determined for temperatures between 228 and 413 K. The flash photolysis-resonance fluorescence technique was employed at five temperatures over wide ranges of pressure and acetylene concentrations, with the OH produced by water photolysis and hydroxyl resonance fluorescent photons measured by multiscaling techniques. Results indicate that, except at the lowest temperature, the bimolecular rate constant for the reaction depends strongly on total pressure, with the pressure effect becoming more pronounced with increasing temperature. At limiting high pressures, the rate constant is found to be equal to 6.83 + or - 1.19 x 10 to the -12th exp (-646 + or - 47/T) cu cm/molecule per sec, where T is the temperature. Results thus demonstrate the importance of environmental conditions in theoretical studies of atmospheric and combustion product compositions

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Determination of rate and equilibrium constants for the reactions between electron transfer mediators and proteins by linear sweep voltammetry.

    PubMed

    Parker, V D; Roddick, A; Seefeldt, L C; Wang, H; Zheng, G

    1997-07-01

    Redox proteins undergo measurable charge transfer at electrodes only under special circumstances, while they readily take part in electron transfer reactions with mediators in solution. Advantage was taken of the latter fact to develop a new method to study the kinetics and equilibria of protein-mediator electron transfer reactions. It was shown that rate and equilibrium constants for the electron exchange between electron transfer mediator and the protein can be obtained from the analysis of the perturbation of the linear sweep voltammetry (LSV) response of the mediator due to the presence of the protein. The experiments were carried out under conditions where the protein does not interact with the electrode. Theoretical data obtained by digital simulation are presented to show the conditions under which rate and equilibrium constants are accessible by the LSV technique. The electron transfer reactions between ferri- and ferrocytochrome c and N,N,N',N'-tetramethylphenylenediamine and the corresponding radical cation in phosphate-buffered saline (0.04 M phosphate, pH 7.4, 0.1 M NaCl) buffer were selected to demonstrate the technique. These studies resulted in an equilibrium constant equal to 1.0 and forward and reverse rate constants equal to 1.6 x 10(4) M-1 s-1. The data available from this method include forward and reverse rate constants for electron transfer and the formal potential for the protein redox couple.

  5. Effect of initial acceleration on the development of the flow field of an airfoil pitching at constant rate

    NASA Technical Reports Server (NTRS)

    Koochesfahani, M. M.; Smiljanovski, V.; Brown, T. A.

    1992-01-01

    We present results from a series of experiments where an airfoil is pitched at constant rate from 0 to 60 degrees angle of attack. It is well documented that the dynamic stall behavior of such an airfoil strongly depends on the nondimensional pitch rate K = dot-alpha C/(2U(sub infinity)), where C is the chord, dot-alpha the constant pitch rate, and U(sub infinity) the free stream speed. In reality, the actual motion of the airfoil deviates from the ideal ramp due to the finite acceleration and deceleration periods imposed by the damping of drive system and response characteristics of the airfoil. It is possible that the pitch rate alone may not suffice in describing the flow and that the details of the motion trajectory before achieving a desired constant pitch rate may also affect the processes involved in the dynamic stall phenomenon. The effects of acceleration and deceleration periods are investigated by systematically varing the acceleration magnitude and its duration through the initial acceleration phase to constant pitch rate. The magnitude and duration of deceleration needed to bring the airfoil motion to rest is similarly controlled.

  6. Is the dissociative recombination of H3(+) really slow. A new spectroscopic measurement of the rate constant

    SciTech Connect

    Amano, T.

    1988-06-01

    The dissociative rate constant for H3(+) occupies a key role in model calculations of the interstellar chemical evolution. The decay of an infrared absorption signal of H3(+) was measured as a function of time, and the decay curve was analyzed and found to fit very well to the form expected for a recombination decay. The signal decay is attributed to the dissociative recombination with electrons, and the rate constant was determined to be (1./8 + or - 0.2) x 10 to the -7th cu cm/s, which disagrees with the recent value obtained with the flowing afterglow/Langmuir probe technique. 22 references.

  7. Nonequilibrium thermodynamics formalism for Marcus theory of heterogeneous and self-exchange electron-transfer rate constants.

    PubMed

    Sethi, Richa; Sangaranarayanan, M V

    2008-05-08

    The cross-exchange electron-transfer rate constant expression of Marcus is derived from the Flux-force formalism of non-equilibrium thermodynamics. The relationship governing the Onsager's phenomenological coefficients for cross-exchange and self-exchange electron-transfer processes is deduced. Onsager's phenomenological coefficient pertaining to the Butler-Volmer equation is derived and estimated from the experimental exchange current densities. The correlation between the heterogeneous and the homogeneous electron-transfer rate constants derived by Marcus is analyzed in terms of the corresponding phenomenological coefficients.

  8. Novel method of determination of the internal enzyme distribution within porous solid supports and the deactivation rate constant

    SciTech Connect

    Do, D.D.; Hossain, M.M.

    1986-04-01

    This article presents a method for determining the rate constant for deactivation and the internal distribution of immobilized enzyme. This method makes use of the parallel deactivation process in a diffusion-controlled regime, in which the internal activity profile behaves like a penetration front. This front basically traces through the initial active enzymatic profile, and one can determine the internal profile and the rate constant for deactivation from the experimentally observable bulk concentration versus time. This method is applied to the experimental data of the system of hydrogen peroxide-immobilized catalase on controlled pore glas and Si-Al particles. 26 references.

  9. Rate constant measurements for the reaction Cl + CH2O yields HCl + CHO Implications regarding the removal of stratospheric chlorine

    NASA Technical Reports Server (NTRS)

    Anderson, P. C.; Kurylo, M. J.

    1979-01-01

    The flash photolysis resonance fluorescence technique was employed to investigate the rate constant for the reaction Cl + CH2O yields HCl + CHO from 223 to 323 K. An Arrhenius fit of the data gives a rate constant equal to (1.09 + or - 0.40) x 10 to the -10th exp/-(131 + or - 98)/T/ in units of cu cm/molecule per sec. The results are compared to two very recent kinetic studies and are assessed in view of the reaction's role in disrupting the Cl-ClO stratospheric ozone depletion chain.

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

    DOE PAGES

    Nguyen, Thanh Lam; Stanton, John F.

    2017-06-02

    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 to 20%) with available experimental data over a temperature range that extends from 200 to 2500 K. Here, quantum mechanical tunneling effects were found to be important; they lead to a decided curvature and non-Arrhenius behavior for the rate constant.

  11. Absolute rate constant of the reaction between chlorine /2P/ atoms and hydrogen peroxide from 298 to 424 K

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1980-01-01

    The absolute rate constant of the reaction between chlorine (2P) atoms and hydrogen peroxide was determined from 298 to 424 K, using the discharge flow resonance fluorescence technique. Pseudo-first-order conditions were used with hydrogen peroxide in large excess. A fast flow-sampling procedure limited hydrogen peroxide decomposition to less than 5% over the temperature range studied. At 298 K, the rate constant is (4.1 plus or minus 0.2) x 10 to the minus 13th cu cm/molecule-sec.

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

    NASA Astrophysics Data System (ADS)

    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.

  13. Rate constant measurements for the reaction Cl + CH2O yields HCl + CHO Implications regarding the removal of stratospheric chlorine

    NASA Technical Reports Server (NTRS)

    Anderson, P. C.; Kurylo, M. J.

    1979-01-01

    The flash photolysis resonance fluorescence technique was employed to investigate the rate constant for the reaction Cl + CH2O yields HCl + CHO from 223 to 323 K. An Arrhenius fit of the data gives a rate constant equal to (1.09 + or - 0.40) x 10 to the -10th exp/-(131 + or - 98)/T/ in units of cu cm/molecule per sec. The results are compared to two very recent kinetic studies and are assessed in view of the reaction's role in disrupting the Cl-ClO stratospheric ozone depletion chain.

  14. Heart Rate and Stress in a College Setting

    ERIC Educational Resources Information Center

    Elwess, Nancy L.; Vogt, F. Daniel

    2005-01-01

    Conditions producing stress are present in all colleges and universities. In this paper we report on an investigation utilizing heart rate as an indicator of stress in students when participating in activities encountered in a college classroom or laboratory. The activities included presenting an oral report, taking an exam, and participating in a…

  15. Monte Carlo simulations of growth/decay rate constant ratios for small methanol clusters: Application to nucleation data analysis

    NASA Astrophysics Data System (ADS)

    Hale, Barbara; Wilemski, Gerald; Viets, Aaron

    2013-05-01

    The Bennett Monte Carlo technique and the potential of van Leeuwen and Smit are used to calculate growth/decay rate constant ratios for small model methanol clusters at 220K, 240K and 260K. Temperature scaling properties of the rate constant ratios are demonstrated at these temperatures. The Monte Carlo results are used to study heat release from subcritical cluster formation in adiabatic nucleation rate measurements and to determine corrected final temperatures and supersaturation ratios for the methanol data of Strey, Wagner, and Schmeling. The corrected T and S values provide experimental rates with improved scaling properties. Nucleation rates are also calculated from the Monte Carlo free energy differences for the model methanol clusters and demonstrate the same scaling.

  16. Stress, strain rate and anisotropy in Kyushu, Japan

    NASA Astrophysics Data System (ADS)

    Savage, M. K.; Aoki, Y.; Unglert, K.; Ohkura, T.; Umakoshi, K.; Shimizu, H.; Iguchi, M.; Tameguri, T.; Ohminato, T.; Mori, J.

    2016-04-01

    Seismic anisotropy, the directional dependence of wave speeds, may be caused by stress-oriented cracks or by strain-oriented minerals, yet few studies have quantitatively compared anisotropy to stress and strain over large regions. Here we compare crustal stress and strain rates on the Island of Kyushu, Japan, as measured from inversions of focal mechanisms, GPS and shear wave splitting. Over 85,000 shear wave splitting measurements from local and regional earthquakes are obtained from the NIED network between 2004 and 2012, and on Aso, Sakurajima, Kirishima and Unzen volcano networks. Strain rate measurements are made from the Japanese Geonet stations. JMA-determined S arrival times processed with the MFAST shear wave splitting code measure fast polarisations (Φ), related to the orientation of the anisotropic medium and time delays (dt), related to the path length and the percent anisotropy. We apply the TESSA 2-D delay time tomography and spatial averaging code to the highest quality events, which have nearly vertical incidence angles, separating the 3455 shallow (depth < 40 km) from the 4957 deep (> = 40 km) earthquakes. Using square grids with 30 km sides for all the inversions, the best correlations are observed between splitting from shallow earthquakes and stress. Axes of maximum horizontal stress (SHmax) and Φ correlate with a coefficient c of 0.56, significant at the 99% confidence level. Their mean difference is 31.9°. Axes of maximum compressional strain rate and SHmax are also well aligned, with an average difference of 28°, but they do not correlate with each other, meaning that where they differ, the difference is not systematic. Anisotropy strength is negatively correlated with the stress ratio parameter determined from focal mechanism inversion (c = - 0.64; significant at the 99% confidence level). The anisotropy and stress results are consistent with stress-aligned microcracks in the crust in a dominantly strike-slip regime. Eigenvalues of

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

    SciTech Connect

    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.

  18. Effects of a constant rate infusion of magnesium sulphate in healthy dogs anaesthetized with isoflurane and undergoing ovariohysterectomy.

    PubMed

    Rioja, Eva; Dzikiti, Brighton T; Fosgate, Geoffrey; Goddard, Amelia; Stegmann, Frik G; Schoeman, Johan P

    2012-11-01

    To determine the effects of intravenous (IV) magnesium sulphate (MgSO(4) ) as a bolus followed by a constant rate infusion (CRI) on anaesthetic requirements, neuroendocrine stress response to surgery, haemostasis and postoperative analgesia in healthy dogs undergoing ovariohysterectomy. Blinded randomized clinical trial. Sixteen female dogs. After intramuscular premedication with acepromazine (0.05 mg kg(-1) ) and morphine (0.3 mg kg(-1) ), anaesthesia was induced with diazepam (0.2 mg kg(-1) ) and propofol (2 mg kg(-1) ) intravenously and maintained with isoflurane in oxygen in all dogs. Dogs were randomly assigned to two groups, M and C. Group M received MgSO(4) (50 mg kg(-1) over 15 minutes, followed by a 15 mg kg(-1) hour(-1) CRI). Group C received an equivalent bolus and CRI of lactated Ringer's solution. In addition, all dogs received lactated Ringer's solution (10 mL kg(-1) over 15 minutes followed by 10 mL kg(-1) hour(-1) ). End-tidal isoflurane and carbon dioxide tensions, cardio-respiratory variables, arterial blood gases, electrolytes, ACTH and cortisol concentrations were measured at different time points. Thromboelastography (TEG) was performed pre- and post-anaesthesia. Postoperative pain was evaluated using the short form of the Glasgow Composite Pain Scale. Data were analysed with repeated measures anova and Mann-Whitney U tests (p < 0.05). No statistically significant differences between groups were found in any of the measured variables. However, the alpha angle and maximal amplitude recorded by TEG in group M were significantly increased post-anaesthesia, but remained within the reference interval. One dog in Group M and two in Group C received rescue analgesia during recovery. As used in this study, MgSO(4) failed to decrease isoflurane requirements, postoperative pain and stress hormone concentrations; however, it did not produce any cardio-respiratory or major haemostatic side effects. Administration of intravenous MgSO(4) together with an

  19. The excretion rates of stress hormones under mental work.

    PubMed

    Vangelova, K

    2005-03-01

    The aim of the study was to assess stress on the basis of the excretion rates of stress hormones in occupational groups under mental stress. The investigation includes 293 persons, working in power engineering, education, public health and information sector. The stress hormones adrenaline, noradrenaline and 11-oxycorticosteroids (11-OCS) were followed during the working day using spectrofluorimetric methods. Very high excretion rates of adrenaline, noradrenaline and/or 11-OCS were found with leading radio editors, responsible engineers and operators in nuclear power station (NPS), teachers in secondary schools, designing engineers. In conclusion our data indicate high stress in occupational groups working under high psychological demands, high responsibility, making important managing decisions, low job control and are discussed with regard to the health risk.

  20. The ClpXP protease unfolds substrates using a constant rate of pulling but different gears.

    PubMed

    Sen, Maya; Maillard, Rodrigo A; Nyquist, Kristofor; Rodriguez-Aliaga, Piere; Pressé, Steve; Martin, Andreas; Bustamante, Carlos

    2013-10-24

    ATP-dependent proteases are vital to maintain cellular protein homeostasis. Here, we study the mechanisms of force generation and intersubunit coordination in the ClpXP protease from E. coli to understand how these machines couple ATP hydrolysis to mechanical protein unfolding. Single-molecule analyses reveal that phosphate release is the force-generating step in the ATP-hydrolysis cycle and that ClpXP translocates substrate polypeptides in bursts resulting from highly coordinated conformational changes in two to four ATPase subunits. ClpXP must use its maximum successive firing capacity of four subunits to unfold stable substrates like GFP. The average dwell duration between individual bursts of translocation is constant, regardless of the number of translocating subunits, implying that ClpXP operates with constant "rpm" but uses different "gears."

  1. Multiple-estimate Monte Carlo calculation of the dose rate constant for a cesium-131 interstitial brachytherapy seed

    SciTech Connect

    Wittman, Richard S.; Fisher, Darrell R.

    2007-01-03

    The purpose of this study was to calculate a more accurate dose rate constant for the Cs-131 (model CS-1, IsoRay Medical, Inc., Richland, Washington) interstitial brachytherapy seed. Previous measurements of the dose rate constant for this seed have been reported by others with incongruity. Recent direct measurements by thermoluminescence dosimetry and by gamma-ray spectroscopy were about 15 percent greater than earlier thermoluminescence dosimetry measurements. Therefore, we set about to calculate independent values by a Monte Carlo approach that combined three estimates as a consistency check, and to quantify the computational uncertainty. The calculated dose rate constant for the Cs-131 seed was 1.040 cGy h^{-1} U^{-1} for an ionization chamber model and 1.032 cGy h^{-1} U^{-1} for a circular ring model. A formal value of 2.2% uncertainty was calculated for both values. The range of our multi-estimate values were from 1.032 cGy h^{-1} U^{-1} to 1.061 cGy h^{-1} U^{-1}. We also modeled three I-125 seeds with known dose rate constants to test the accuracy of this study's approach.

  2. Temperature dependence of the rate constants for oxidation of organic compounds by peroxyl radicals in aqueous alcohol solutions

    SciTech Connect

    Alfassi, Z.B.; Huie, R.E.; Kumar, M.; Neta, P.

    1992-01-23

    Rate constants for reactions of chlorinated methylperoxyl radicals with chlorpromazine (2-chloro-10-[3-(dimethylamino)-propyl]phenothiazine), trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), and ascorbate in aqueous alcohol solutions have been measured by pulse radiolysis as a function of temperature, generally between 5 and 75{degrees}C. The rate constants varied between 10{sup 6} and 10{sup 9} M{sup {minus}1} s{sup {minus}1}, the calculated Arrhenius activation energies ranged from 1 to 30 kJ mol{sup {minus}1}, and the preexponential factors also varied considerably, with log A ranging from 7 to 14. In general, room temperature rate constants increase with an increase in the number of chlorine atoms on the radical (increasing its electron affinity and thus the driving force for the reaction) and with an increase in the solvent polarity. The Arrhenius preexponential factor and the activation energy both increased as the proportion of water in the solvent mixture increased; i.e., the increase in rate constant with solvent polarity is a result of two compensating effects. Electron transfer from the organic reductants to the chlorinated methylperoxyl radicals is suggested to take place via an inner-sphere mechanism involving a transient adduct of the peroxyl radical to the reductant. 15 refs., 2 figs., 3 tabs.

  3. Reaction rate constant for OH + HOONO/sub 2/. -->. products over the temperature range 246 to 324 K

    SciTech Connect

    Trevor, P.L.; Black, G.; Barker, J.R.

    1982-04-29

    Absolute bimolecular reaction rate constants for the title reaction have been determined for temperatures ranging from 246 to 324 K. The laser flash-photolysis resonance-fluorescence (LFPRF) technique was used to generate O(/sup 1/D) which reacted with H/sub 2/ and/or H/sub 2/O to produce OH radicals. The bimolecular rate constants for the title reaction showed no dependence on total (He) pressure over the range approx. 3 to 15 torr, and they did not depend upon initial (OH) or upon its mode of formation. The H/sub 2/O/sub 2/ impurity was explicitly measured in all experiments, and the rate constants were corrected for its contribution. A weighted least-squares analysis of the data obtained at nine temperatures (226 data points) gave the Arrhenius expression (k +- 1sigma) = (8.05 +- 5.69) x 10/sup -12/ exp (-193 +- 194/T) cm/sup 3/ s/sup -1/ with covariance 1.098 x 10/sup -9/. A simple weighted average (temperature independent) fits the data just as well, and when the effects of systematic errors are taken into account, our recommended rate constant is (k +- 2sigma) = (4.0 +- 1.6) x 10/sup -12/ cm/sup 3/ s/sup -1/.

  4. Fluorescence anisotropy-based measurement of Pseudomonas aeruginosa penicillin-binding protein 2 transpeptidase inhibitor acylation rate constants.

    PubMed

    Shapiro, Adam B; Gao, Ning; Gu, Rong-Fang; Thresher, Jason

    2014-10-15

    High-molecular-weight penicillin-binding proteins (PBPs) are essential integral membrane proteins of the bacterial cytoplasmic membrane responsible for biosynthesis of peptidoglycan. They are the targets of antibacterial β-lactam drugs, including penicillins, cephalosporins, and carbapenems. β-Lactams covalently acylate the active sites of the PBP transpeptidase domains. Because β-lactams are time-dependent inhibitors, quantitative assessment of the inhibitory activity of these compounds ideally involves measurement of their second-order acylation rate constants. We previously described a fluorescence anisotropy-based assay to measure these rate constants for soluble constructs of PBP3 (Anal. Biochem. 439 (2013) 37-43). Here we report the expression and purification of a soluble construct of Pseudomonas aeruginosa PBP2 as a fusion protein with NusA. This soluble PBP2 was used to measure second-order acylation rate constants with the fluorescence anisotropy assay. Measurements were obtained for mecillinam, which reacts specifically with PBP2, and for several carbapenems. The assay also revealed that PBP2 slowly hydrolyzed mecillinam and was used to measure the rate constant for this deacylation reaction. Copyright © 2014 Elsevier Inc. All rights reserved.

  5. Gum chewing modulates heart rate variability under noise stress.

    PubMed

    Ekuni, Daisuke; Tomofuji, Takaaki; Takeuchi, Noriko; Morita, Manabu

    2012-12-01

    Gum chewing may relieve stress, although this hypothesis has not been proven. Heart-rate variability (HRV) is commonly used to measure stress levels. However, it is not known if gum chewing modulates HRV under acute stress. The aim of this study was to investigate the effects of gum chewing on HRV under acute stress. A cross-over study involving 47 non-smoking healthy subjects, aged 22-27 years, was carried out. The subjects received a stress procedure with gum chewing (GS group) and without gum chewing (S group). Additionally, the other 20 subjects were allocated to the gum chewing without stress group (G group). The GS and S groups were exposed to noise for 5 min (75 dBA) as stress. Before and after stress exposure/gum chewing, participants completed the state portion of the State-Trait Anxiety Inventory (STAI-s) and a single Stress Visual Analogue Scale (VAS) measurement. HRV measurement was performed before and during stress/gum chewing for 5 min. After the stress procedure, VAS score significantly increased in the GS and S groups. During the stress procedure, the GS group showed a significantly lower level of high frequency (HF) and higher levels of low frequency (LF) and LF/HF than the S group. However, there were no significant differences in the scores of the state portion of the State-Trait Anxiety Inventory (STAI-s) and VAS between the two stress groups. These findings suggest that gum chewing modulates HRV, but may not relieve acute stress caused by noise.

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

    PubMed

    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

  7. High Accuracy OH Reaction Rate Constant Measurements: Studies of Pressure Dependencies and of the Reactivities of Stereoisomers.

    NASA Astrophysics Data System (ADS)

    Orkin, V. L.; Khamaganov, V. G.; Kurylo, M. J., III

    2016-12-01

    The accuracy of OH kinetic data is of primary importance for the comprehensive modeling of any compound's atmospheric behavior and of its environmental impacts, such as its atmospheric residence time and its potential roles in stratospheric ozone depletion, global warming, and local pollution. Rate constants of OH reactions with hydrocarbons and halogenated hydrocarbons can now be determined with an accuracy of 2-3% over the temperature range 220 K to 370 K. This has been demonstrated in studies of OH reactions with various halogenated and non-substituted organics including alkanes, alkenes, alcohols, and ethers. Lower data scattering and higher measurement accuracy allow for rigorous statistical analysis of the results and can reveal often-missing details about the reactivity, such as the (small) dependencies of the rate constant on the temperature, pressure, and reactant molecular structure. Such details include the temperature dependence of both H-abstraction and OH-addition reactions exhibiting a noticeable curvature in the Arrhenius plot that cannot be attributed to experimental artifacts, determinations of the temperature dependencies of OH-addition rate constants that are approaching the collision frequency, determination of both low-pressure and high-pressure limiting rate constants from data obtained over a limited pressure range, observations of unexpected pressure dependencies for OH-addition reaction rate constants (such as in case of C4 alkenes), and determinations of substantially different reactivities and their temperature dependencies as well as IR absorption spectra for the stereoisomers of unsaturated compounds. This presentation will provide examples of several of these measurement results that were recently obtained in our laboratory.

  8. Flow variability of an aerial variable-rate nozzle at constant pressures

    USDA-ARS?s Scientific Manuscript database

    Variable-rate ground application systems have been in use for the past 15 years, but due to high application speeds, flow requirements, and aerodynamic considerations, variable-rate aerial nozzles have not been available until now. In 2006, Spray Target, Inc. released the VeriRate™ variable-rate aer...

  9. Determination of blade stresses under constant speed and transient conditions with nonlinear damping

    SciTech Connect

    Rao, J.S.; Vyas, N.S.

    1996-04-01

    Determination of resonant stresses is an important step in the life estimation of turbomachine blades. Resonance may occur either at a steady operating speed or under transient conditions of operation when the blade passes through a critical speed. Damping plays a significant role in limiting the amplitudes of vibration and stress values. The blade damping mechanism is very complex in nature, because of interfacial slip, material hysteresis, and gas dynamic damping occurring simultaneously. In this paper, a numerical technique to compute the stress response of a turbine blade with nonlinear damping characteristics, during steady and transient operations of the rotor, is presented. Damping is defined as a function of vibratory mode, rotor speed, and strain amplitude. The technique is illustrated by computing the stress levels at resonant rotor speeds for typical operation of a turbomachine.

  10. Photon spectrometry for the determination of the dose-rate constant of low-energy photon-emitting brachytherapy sources.

    PubMed

    Chen, Zhe Jay; Nath, Ravinder

    2007-04-01

    Accurate determination of dose-rate constant (lambda) for interstitial brachytherapy sources emitting low-energy photons (< 50 keV) has remained a challenge in radiation dosimetry because of the lack of a suitable absolute dosimeter for accurate measurement of the dose rates near these sources. Indeed, a consensus value of lambda taken as the arithmetic mean of the dose-rate constants determined by different research groups and dosimetry techniques has to be used at present for each source model in order to minimize the uncertainties associated with individual determinations of lambda. Because the dosimetric properties of a source are fundamentally determined by the characteristics of the photons emitted by the source, a new technique based on photon spectrometry was developed in this work for the determination of dose-rate constant. The photon spectrometry technique utilized a high-resolution gamma-ray spectrometer to measure source-specific photon characteristics emitted by the low-energy sources and determine their dose-rate constants based on the measured photon-energy spectra and known dose-deposition properties of mono-energetic photons in water. This technique eliminates many of the difficulties arising from detector size, the energy dependence of detector sensitivity, and the use of non-water-equivalent solid phantoms in absolute dose rate measurements. It also circumvents the uncertainties that might be associated with the source modeling in Monte Carlo simulation techniques. It was shown that the estimated overall uncertainty of the photon spectrometry technique was less than 4%, which is significantly smaller than the reported 8-10% uncertainty associated with the current thermo-luminescent dosimetry technique. In addition, the photon spectrometry technique was found to be stable and quick in lambda determination after initial setup and calibration. A dose-rate constant can be determined in less than two hours for each source. These features make it

  11. Does the diversification rate of endemic birds of mainland China follow abrupt, gradual shifting or constant patterns?

    PubMed

    Chen, Youhua

    2017-03-01

    In this brief report, time-varying (including both gradual and abrupt change) and time-constant diversification models are fitted on a phylogeny of endemic birds of mainland China to test the diversification patterns of endemic birds in the region. The results show that phylogeny of endemic birds is best quantified by a constant-rate diversification model through model comparison. Limitations of the study are discussed. In particular, ignorance of non-endemic taxa and the limited sampling of endemic taxa could influence the conclusions of the study. © 2016 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.

  12. Time Dependent Dielectric Breakdown of Silicon Dioxide under Constant Tunneling Current Stress

    DTIC Science & Technology

    1989-03-01

    Two Factor Example Showing Interaction Effects ........ .................... 61 4.22 Example of Curvature .............. 64 3.1 Sianal Current Circuit ...system to yield data for evaluation of the effects of the several stress factors used in this experiment on the integrity of the thin oxides in the...the integrity of the oxides under test and the stress factors. The fabrication and structure of the test vehicles will be more fully covered in the

  13. Real-time association rate constant measurement using combination tapered fiber-optic biosensor (CTFOB) dip-probes

    NASA Astrophysics Data System (ADS)

    Simmonds, Boris; Wang, Chun-Wei; Kapoor, Rakesh

    2010-02-01

    This document reports a novel method of measuring association rate constant (ka) for antibody-antigen interaction using evanescent wave-based combination tapered fiber-optic biosensor (CTFOB) dip-probes. The method was demonstrated by measuring association rate constant for bovine serum albumin (BSA) and anti-BSA antibody interaction. "Direct method" was used for detection; goat anti-BSA "capture" antibodies were immobilized on the probe surfaces while the antigen (BSA) was directly labeled with Alexa 488 dye. The probes were subsequently submerged in 3nM Labeled BSA in egg albumin (1 mg/ml). The fluorescence signal recorded was proportional to BSA anti-BSA conjugates and continuous signal was acquired suing a fiber optic spectrometer (Ocean Optics, Inc.). A 476 nm diode laser was use as an excitation source. Association constant was estimated from a plot of signal as a function of time. Measured association rate constant ka for the binding of BSA with anti-BSA at room temperature is (8.33 +/- 0.01) x 104 M-1s-1.

  14. Rate constant calculations of the C2 + HCN → CCCN+H addition via the Master Equation.

    PubMed

    da Silva, Washington Barbosa; Albernaz, Alessandra F; Barreto, Patricia R P; Correa, Eberth

    2017-04-01

    The addition of C2 to HCN is of relevant interest in astrochemistry. We studied the pathways of this addition to produce CCCN and estimated its reaction rate using the Master Equation in the circumstellar environment. From the results of this study, it was possible to show that a different pathway in the Surface Potential Energy-PES can also be investigated. In a circumstellar envelop environment, with temperatures varying between 1000 K and 2000 K, the abundances of these species are favorable to this kind of addition, and our branching ratio for the rate constant showed that the new pathway is more favorable in comparison with other possibilities for this range of temperatures in this environment, and must be taken into account in any computation of the rate constant. Graphical Abstract Branching ratios of pathways involved in the C2 + HCN → CCCN+H addition, at a temperature range of 1000-2000 K.

  15. Transcriptome analysis reveals that constant heat stress modifies the metabolism and structure of the porcine longissimus dorsi skeletal muscle.

    PubMed

    Hao, Yue; Feng, Yuejin; Yang, Peige; Cui, Yanjun; Liu, Jiru; Yang, Chunhe; Gu, Xianhong

    2016-12-01

    Exposure to high ambient temperatures is detrimental to pig rearing and porcine meat quality. Deep molecular sequencing allows for genomic characterization of porcine skeletal muscles and helps understand how the genomic landscape may impact meat quality. To this end, we performed mRNA-seq to molecularly dissect the impact of heat stress on porcine skeletal muscles, longissimus dorsi. Sixteen castrated, male DLY pigs [which are crossbreeds between Duroc (D) boars and Landrace (L) × Yorkshire (Y) sows, 79.0 ± 1.5 kg BW] were evenly split into two groups that were subjected to either control (CON) (22 °C; 55 % humidity) or constant heat stress (H30; 30 °C; 55 % humidity) conditions for 21 days. Seventy-eight genes were found to be differentially expressed, of which 37 were up-regulated and 41 were down-regulated owing to constant heat stress. We predicted 5247 unknown genes and 6108 novel transcribed units attributed to alternative splicing (AS) events in the skeletal muscle. Furthermore, 30,761 and 31,360 AS events were observed in the CON and H30 RNA-seq libraries, respectively. The differentially expressed genes in the porcine skeletal muscles were involved in glycolysis, lactate metabolism, lipid metabolism, cellular defense, and stress responses. Additionally, the expression levels of these genes were associated with variations in meat quality between the CON and H30 groups, indicating that heat stress modulated genes crucial to skeletal muscle development and metabolism. Our transcriptomic analysis provides valuable information for understanding the molecular mechanisms governing porcine skeletal muscle development. Such insights may lead to innovative strategies to improve meat quality of pigs under heat stress.

  16. Stress corrosion-controlled rates of mode I fracture propagation in calcareous bedrock

    NASA Astrophysics Data System (ADS)

    Voigtlaender, Anne; Leith, Kerry; Krautblatter, Michael

    2014-05-01

    Surface bedrock on natural rock slopes is subject to constant and cyclic environmental stresses (wind, water, wave, ice, seismic or gravitational). Studies indicate that these stresses range up to several hundred kPa, generally too low to cause macroscopic changes in intact rock, although clear evidence of fracture generation, crack propagation and weathering of bedrock illustrates the effect of environmental stresses at the Earth's surface. We suggest that material degradation and its extent, is likely to be controlled by the rate of stress corrosion cracking (SCC). Stress corrosion is a fluid-material reaction, where fluids preferentially react with strained atomic bonds at the tip of developing fractures. Stress corrosion in ferrous and siliceous materials is often accepted as the fracture propagation and degradation rate-controlling process where materials are subject to stresses and fluids. Although evidence for chemical weathering in propagating bedrock fractures is clear in natural environments, the physical system and quantification of stress corrosion in natural rocks is yet to be addressed. Here, we present preliminary data on the relationship between stresses at levels commonly present on natural rock slopes, and material damage resulting from stress corrosion under constant or cyclic tensile loading. We undertake single notch three-point bending tests (SNBT) on fresh calcareous bedrock specimens (1100x100x100mm) over a two-month period. Two beams containing an artificial notch are stressed to 75% of their ultimate strength, and a constant supply of weak acid is applied at the notch tip to enhance chemical reactions. A third, unloaded, beam is also exposed to weak acid in order to elucidate the contribution of stress corrosion cracking to the material degradation. Stresses at the tip of propagating cracks affect the kinetics of the chemical reaction in the specimen exposed to both loading and corrosion, leading to an increase in degradation, and greater

  17. Aftershock decay, productivity, and stress rates in Hawaii: Indicators of temperature and stress from magma sources

    USGS Publications Warehouse

    Klein, Fred W.; Wright, Tom; Nakata, Jennifer

    2006-01-01

    We examined dozens of aftershock sequences in Hawaii in terms of Gutenberg-Richter and modified Omori law parameters. We studied p, the rate of aftershock decay; Ap, the aftershock productivity, defined as the observed divided by the expected number of aftershocks; and c, the time delay when aftershock rates begin to fall. We found that for earthquakes shallower than 20 km, p values >1.2 are near active magma centers. We associate this high decay rate with higher temperatures and faster stress relaxation near magma reservoirs. Deep earthquakes near Kilauea's inferred magma transport path show a range of p values, suggesting the absence of a large, deep magma reservoir. Aftershock productivity is >4.0 for flank earthquakes known to be triggered by intrusions but is normal (0.25 to 4.0) for isolated main shocks. We infer that continuing, post-main shock stress from the intrusion adds to the main shock's stress step and causes higher Ap. High Ap in other zones suggests less obvious intrusions and pulsing magma pressure near Kilauea's feeding conduit. We calculate stress rates and stress rate changes from pre-main shock and aftershock rates. Stress rate increased after many intrusions but decreased after large M7–8 earthquakes. Stress rates are highest in the seismically active volcano flanks and lowest in areas far from volcanic centers. We found sequences triggered by intrusions tend to have high Ap, high (>0.10 day) c values, a stress rate increase, and sometimes a peak in aftershock rate hours after the main shock. We interpret these values as indicating continuing intrusive stress after the main shock.

  18. A Constant Rate of Spontaneous Mutation in DNA-Based Microbes

    NASA Astrophysics Data System (ADS)

    Drake, John W.

    1991-08-01

    In terms of evolution and fitness, the most significant spontaneous mutation rate is likely to be that for the entire genome (or its nonfrivolous fraction). Information is now available to calculate this rate for several DNA-based haploid microbes, including bacteriophages with single- or double-stranded DNA, a bacterium, a yeast, and a filamentous fungus. Their genome sizes vary by ≈6500-fold. Their average mutation rates per base pair vary by ≈16,000-fold, whereas their mutation rates per genome vary by only ≈2.5-fold, apparently randomly, around a mean value of 0.0033 per DNA replication. The average mutation rate per base pair is inversely proportional to genome size. Therefore, a nearly invariant microbial mutation rate appears to have evolved. Because this rate is uniform in such diverse organisms, it is likely to be determined by deep general forces, perhaps by a balance between the usually deleterious effects of mutation and the physiological costs of further reducing mutation rates.

  19. Oxidative turnover increases the rate constant and extent of intramolecular electron transfer in the multicopper enzymes, ascorbate oxidase and laccase.

    PubMed

    Tollin, G; Meyer, T E; Cusanovich, M A; Curir, P; Marchesini, A

    1993-12-07

    Using laser flash photolysis of lumiflavin/EDTA solutions containing ascorbate oxidase, we find that the rate constant for intramolecular electron transfer varies from one enzyme preparation to another and is generally a more sensitive measure of the state of the active site than are steady-state assays. Thus, type I copper is initially reduced in a second-order reaction followed by first-order reoxidation by the type II-III trinuclear copper center. The observed rate constant for this intramolecular process in presumably native enzyme is 160 s-1 at pH 7, whereas an enzyme preparation which had less than 20% activity had a rate constant of 2.6 s-1. Other samples of relatively active enzyme showed biphasic intramolecular kinetics intermediate between the above values. The inactive enzyme sample could be reactivated by dialysis against ascorbate or by treatment with ferricyanide, resulting in a corresponding increase in the intramolecular rate constant for type I copper reoxidation to a value comparable to that of native enzyme. Using this same methodology, we have determined that the type I copper in Japanese lacquer tree laccase is reoxidized by the type II-III trinuclear copper center in a first-order (intramolecular) process with rate constants of 1 s-1 at pH 7.0 and 4.9 s-1 at pH 6.0, values which are approximately two orders of magnitude smaller than for ascorbate oxidase. The intramolecular rate constant and enzyme activity for laccase also increased, but only by a factor of 2-6, when the enzyme was treated with ascorbate or ferricyanide, respectively. We further found that intramolecular electron transfer in laccase was completely inhibited by fluoride ion, in contrast to ascorbate oxidase which is unaffected by this ion. These differences in behavior for these two very similar enzymes are rather remarkable, when it is considered that the distance between copper atoms is constrained by the location of the protein-derived copper ligands in the three

  20. Dynamic shear-stress-enhanced rates of nutrient consumption in gas-liquid semi-continuous-flow suspensions

    NASA Astrophysics Data System (ADS)

    Belfiore, Laurence A.; Volpato, Fabio Z.; Paulino, Alexandre T.; Belfiore, Carol J.

    2011-12-01

    The primary objective of this investigation is to establish guidelines for generating significant mammalian cell density in suspension bioreactors when stress-sensitive kinetics enhance the rate of nutrient consumption. Ultra-low-frequency dynamic modulations of the impeller (i.e., 35104 Hz) introduce time-dependent oscillatory shear into this transient analysis of cell proliferation under semi-continuous creeping flow conditions. Greater nutrient consumption is predicted when the amplitude A of modulated impeller rotation increases, and stress-kinetic contributions to nutrient consumption rates increase linearly at higher modulation frequency via an application of fluctuation-dissipation response. Interphase mass transfer is required to replace dissolved oxygen as it is consumed by aerobic nutrient consumption in the liquid phase. The theory and predictions described herein could be important at small length scales in the creeping flow regime where viscous shear is significant at the interface between the nutrient medium and isolated cells in suspension. Two-dimensional flow around spherically shaped mammalian cells, suspended in a Newtonian culture medium, is analyzed to calculate the surface-averaged magnitude of the velocity gradient tensor and modify homogeneous rates of nutrient consumption that are stimulated by viscous shear, via the formalism of stress-kinetic reciprocal relations that obey Curie's theorem in non-equilibrium thermodynamics. Time constants for stress-free free and stress-sensitive stress nutrient consumption are defined and quantified to identify the threshold (i.e., stress,threshold) below which the effect of stress cannot be neglected in accurate predictions of bioreactor performance. Parametric studies reveal that the threshold time constant for stress-sensitive nutrient consumption stress,threshold decreases when the time constant for stress

  1. Effect of constant, predictable, and unpredictable motor tasks on motor performance and blood markers of stress.

    PubMed

    Kyguoliene, Laura; Skurvydas, Albertas; Eimantas, Nerijus; Baranauskienė, Neringa; Mickeviciene, Dalia; Urboniene, Daiva; Cernych, Margarita; Brazaitis, Marius

    2017-05-01

    An unfamiliar or novel physical stimulus induces activation of dopaminergic neurons within the brain and greater activity in areas involved in emotion; considering this, we aimed to establish whether unpredictable prolonged (fatiguing) motor task (vs. constant vs. predictable) evokes greater dopaminergic activity, enhances neuromuscular performance, motor accuracy, and perception of effort, and delays overall central fatigue. Fifteen healthy male volunteers (aged 22 ± 4 years) were required to perform 1 of 3 exercise trials (at least 1 week apart) of 100 intermittent isometric contraction (IIC) tasks involving knee extensions at 60° flexion. Trials were structured differently by simulated contraction intensity. A fatigue task involved 5-s contractions and 20-s rest. Variables measured before, during, and after IIC were electrically induced force, maximal voluntary contraction, central activation ratio, intramuscular temperature, and blood levels of dopamine, cortisol, and prolactin, and intraindividual motor variability and accuracy (constant and absolute error). We found that IIC increased central and peripheral fatigue, force sensation, and T mu, and decreased absolute and constant error without visual feedback, but did not affect motor variability. There were no significant differences between the three IIC tasks. However, only unpredictable tasks increased dopaminergic activity, which was insufficient to affect central motivation to perform isometric exercise and alter centrally mediated components of fatigue.

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

    PubMed

    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.

  3. Theory for rates, equilibrium constants, and Brønsted slopes in F1-ATPase single molecule imaging experiments.

    PubMed

    Volkán-Kacsó, Sándor; Marcus, Rudolph A

    2015-11-17

    A theoretical model of elastically coupled reactions is proposed for single molecule imaging and rotor manipulation experiments on F1-ATPase. Stalling experiments are considered in which rates of individual ligand binding, ligand release, and chemical reaction steps have an exponential dependence on rotor angle. These data are treated in terms of the effect of thermodynamic driving forces on reaction rates, and lead to equations relating rate constants and free energies to the stalling angle. These relations, in turn, are modeled using a formalism originally developed to treat electron and other transfer reactions. During stalling the free energy profile of the enzymatic steps is altered by a work term due to elastic structural twisting. Using biochemical and single molecule data, the dependence of the rate constant and equilibrium constant on the stall angle, as well as the Børnsted slope are predicted and compared with experiment. Reasonable agreement is found with stalling experiments for ATP and GTP binding. The model can be applied to other torque-generating steps of reversible ligand binding, such as ADP and Pi release, when sufficient data become available.

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

    NASA Astrophysics Data System (ADS)

    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).

  5. Strain rate, temperature and representative length scale influence on plasticity and yield stress in copper

    SciTech Connect

    Dupont, Virginie; Germann, Timothy C

    2011-01-18

    Shock compression of materials constitutes a complex process involving high strain rates, elevated temperatures and compression of the lattice. Materials properties are greatly affected by temperature, the representative length scale and the strain rate of the deformation. Experimentally, it is difficult to study the dynamic microscopic mechanisms that affect materials properties following high intensity shock loading, but they can be investigated using molecular dynamics (MD) simulations. Moreover, MD allows a better control over some parameters. We are using MD simulations to study the effect of the strain rate, representative length scale and temperature on the properties of metals during compression. A half-million-atom Cu sample is subjected to strain rates ranging from 10{sup 7} s{sup -1} to 10{sup 12} s{sup -1} at different temperatures ranging from 50K to 1500K. Single crystals as well as polycrystals are investigated. Plasticity mechanisms as well as the evolution of the micro- and macro-yield stress are observed. Our results show that the yield stress increases with increasing strain rate and decreasing temperature. We also show that the strain rate at which the transition between constant and increasing yield stress as a function of the temperature occurs increases with increasing temperature. Calculations at different grain sizes will give an insight into the grain size effect on the plasticity mechanisms and the yield stress.

  6. QSAR ANALYSIS OF SORPTION-CORRECTED RATE CONSTANTS FOR REDUCTIVE BIOTRANSFORMATION OF HALOGENATED AROMATICS

    EPA Science Inventory

    The inherent coupling among geochemical and microbial reactions may have significant effects on the environmental fate of a containinant. For example, sorption processes may decrease the concentration of an organic compound in solution, thereby reducing the biodegradation rate of...

  7. Unwinding and rewinding the nucleosome inner turn: Force dependence of the kinetic rate constants

    NASA Astrophysics Data System (ADS)

    Mochrie, S. G. J.; Mack, A. H.; Schlingman, D. J.; Collins, R.; Kamenetska, M.; Regan, L.

    2013-01-01

    A simple model for the force-dependent unwinding and rewinding rates of the nucleosome inner turn is constructed and quantitatively compared to the results of recent measurements [A. H. Mack , J. Mol. Biol.JMOBAK0022-283610.1016/j.jmb.2012.08.021 423, 687 (2012)]. First, a coarse-grained model for the histone-DNA free-energy landscape that incorporates both an elastic free-energy barrier and specific histone-DNA bonds is developed. Next, a theoretical expression for the rate of transitions across a piecewise linear free-energy landscape with multiple minima and maxima is presented. Then, the model free-energy landscape, approximated as a piecewise linear function, and the theoretical expression for the transition rates are combined to construct a model for the force-dependent unwinding and rewinding rates of the nucleosome inner turn. Least-mean-squares fitting of the model rates to the rates observed in recent experiments rates demonstrates that this model is able to well describe the force-dependent unwinding and rewinding rates of the nucleosome inner turn, observed in the recent experiments, except at the highest forces studied, where an additional ad hoc term is required to describe the data, which may be interpreted as an indication of an alternate high-force nucleosome disassembly pathway, that bypasses simple unwinding. The good agreement between the measurements and the model at lower forces demonstrates that both specific histone-DNA contacts and an elastic free-energy barrier play essential roles for nucleosome winding and unwinding, and quantifies their relative contributions.

  8. Unwinding and rewinding the nucleosome inner turn: force dependence of the kinetic rate constants.

    PubMed

    Mochrie, S G J; Mack, A H; Schlingman, D J; Collins, R; Kamenetska, M; Regan, L

    2013-01-01

    A simple model for the force-dependent unwinding and rewinding rates of the nucleosome inner turn is constructed and quantitatively compared to the results of recent measurements [A. H. Mack et al., J. Mol. Biol. 423, 687 (2012)]. First, a coarse-grained model for the histone-DNA free-energy landscape that incorporates both an elastic free-energy barrier and specific histone-DNA bonds is developed. Next, a theoretical expression for the rate of transitions across a piecewise linear free-energy landscape with multiple minima and maxima is presented. Then, the model free-energy landscape, approximated as a piecewise linear function, and the theoretical expression for the transition rates are combined to construct a model for the force-dependent unwinding and rewinding rates of the nucleosome inner turn. Least-mean-squares fitting of the model rates to the rates observed in recent experiments rates demonstrates that this model is able to well describe the force-dependent unwinding and rewinding rates of the nucleosome inner turn, observed in the recent experiments, except at the highest forces studied, where an additional ad hoc term is required to describe the data, which may be interpreted as an indication of an alternate high-force nucleosome disassembly pathway, that bypasses simple unwinding. The good agreement between the measurements and the model at lower forces demonstrates that both specific histone-DNA contacts and an elastic free-energy barrier play essential roles for nucleosome winding and unwinding, and quantifies their relative contributions.

  9. Heart rate variability (HRV): an indicator of stress

    NASA Astrophysics Data System (ADS)

    Kaur, Balvinder; Durek, Joseph J.; O'Kane, Barbara L.; Tran, Nhien; Moses, Sophia; Luthra, Megha; Ikonomidou, Vasiliki N.

    2014-05-01

    Heart rate variability (HRV) can be an important indicator of several conditions that affect the autonomic nervous system, including traumatic brain injury, post-traumatic stress disorder and peripheral neuropathy [3], [4], [10] & [11]. Recent work has shown that some of the HRV features can potentially be used for distinguishing a subject's normal mental state from a stressed one [4], [13] & [14]. In all of these past works, although processing is done in both frequency and time domains, few classification algorithms have been explored for classifying normal from stressed RRintervals. In this paper we used 30 s intervals from the Electrocardiogram (ECG) time series collected during normal and stressed conditions, produced by means of a modified version of the Trier social stress test, to compute HRV-driven features and subsequently applied a set of classification algorithms to distinguish stressed from normal conditions. To classify RR-intervals, we explored classification algorithms that are commonly used for medical applications, namely 1) logistic regression (LR) [16] and 2) linear discriminant analysis (LDA) [6]. Classification performance for various levels of stress over the entire test was quantified using precision, accuracy, sensitivity and specificity measures. Results from both classifiers were then compared to find an optimal classifier and HRV features for stress detection. This work, performed under an IRB-approved protocol, not only provides a method for developing models and classifiers based on human data, but also provides a foundation for a stress indicator tool based on HRV. Further, these classification tools will not only benefit many civilian applications for detecting stress, but also security and military applications for screening such as: border patrol, stress detection for deception [3],[17], and wounded-warrior triage [12].

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

    NASA Astrophysics Data System (ADS)

    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.

  11. Rate constants for the reactions of benzyl and methyl-substituted benzyl radicals with O 2 and NO

    NASA Astrophysics Data System (ADS)

    Ebata, Takayuki; Obi, Kin-ichi; Tanaka, Ikuzo

    1981-02-01

    Rate constants for reactions of benzyl, o-niethylbenzyl and p-meihylbenzyl radicals with O 2 and NO have been measured at room temperature. The radicals were generated by UV flash photolysis and the time decay measured by absorption at ≈ 300 nm. The rate constants are: benzyl (0.99 ± 0.07 and 9.5 ± 1.2), o-methylbenzyl (1.2 ± 0.07 and 8.6 ± 0.8) and p-mithyl-benzyl (1.1= 0.10 and 8.9 = 0.9) for O 2 and NO respectively in units of 10 -12 cm 3 molecule -1 s -1.

  12. Rate constant for the reaction of hydroxyl radical with formaldehyde over the temperature range 228-362 K

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

    Absolute rate constants for the reaction OH + H2CO have been measured over the temperature range 228-362 K using the flash photolysis-resonance fluorescence technique. The results were independent of variations in forbidden H2CO, total pressure of forbidden Ar and flash intensity (i.e., initial forbidden OH). The rate constant was found to be invariant with temperature in this range, the best representation being k1 = (1.05 + or - 0.11) x 10 to the -11th cu cm/molecule sec where the error is two standard deviations. This result is compared with previous absolute and relative determinations of k1. The reaction is also discussed from a theoretical point of view.

  13. Equilibrium Fermi's Golden Rule Charge Transfer Rate Constants in the Condensed Phase: The Linearized Semiclassical Method vs Classical Marcus Theory.

    PubMed

    Sun, Xiang; Geva, Eitan

    2016-05-19

    In this article, we present a comprehensive comparison between the linearized semiclassical expression for the equilibrium Fermi's golden rule rate constant and the progression of more approximate expressions that lead to the classical Marcus expression. We do so within the context of the canonical Marcus model, where the donor and acceptor potential energy surface are parabolic and identical except for a shift in both the free energies and equilibrium geometries, and within the Condon region. The comparison is performed for two different spectral densities and over a wide range of frictions and temperatures, thereby providing a clear test for the validity, or lack thereof, of the more approximate expressions. We also comment on the computational cost and scaling associated with numerically calculating the linearized semiclassical expression for the rate constant and its dependence on the spectral density, temperature, and friction.

  14. Comparison of calculated and experimentally resolved rate constants for excitation energy transfer in C-phycocyanin. 2. Trimers

    SciTech Connect

    Debreczeny, M.F.; Sauer, K.; Zhou, J.; Bryant, D.A.

    1995-05-18

    Resolution of the absorption spectrum of the {beta}{sub 155} chromophore in C-phycocyanin (PC) trimers is achieved by comparison of the steady state absorption spectra of ({alpha}{sup PC}{beta}{sup PC}){sub 3} and ({alpha}{sup PC}{beta}{sup *}){sub 3}. Comparison of the anisotropy decays of ({alpha}{sup PC}{beta}{sup PC}){sub 3} and ({alpha}{sup PC}{beta}{sup *}){sub 3} also greatly aids in the assignment of the dominant kinetic processes in PC trimers. A comparison is made of calculated Foerster rate constants for energy transfer with those rate constants resolved experimentally in the PC trimers. 35 refs.., 10 figs., 2 tabs.

  15. Comparison of calculated and experimentally resolved rate constants for excitation energy transfer in C-phycocyanin. 1. Monomers

    SciTech Connect

    Debreczeny, M.P.; Sauer, K.; Zhou, J.; Bryant, D.A.

    1995-05-18

    Rate constants for excitation energy transfer in light-harvesting protein, C-phycocyanin (PC), in the monomeric aggregation state, isolated from the cyanobacterium cynechococcus sp. PCC 7002, are calculated, using Foerster theory and compared with the results of time-resolved fluorescence measurements. The assignments of the energy-transfer rate constants in PC monomers are confirmed here by time-resolved fluorescence anisotropy measurements of the PC monomers isolated from both the wild-type and a mutant strain (cpcB/C155S) whose PC is missing the {beta}{sub 155} chromophore. It is concluded that the Foerster model of resonant energy transfer in the weak coupling limit successfully describes the dominant energy-transfer processes in this protein in the monomeric state. 31 refs., 3 figs., 4 tabs.

  16. Rate constant for the reaction of hydroxyl radical with formaldehyde over the temperature range 228-362 K

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

    Absolute rate constants for the reaction OH ? H2CO measured over the temperature range 228-362 K using the flash photolysis-resonance fluorescence technique are given. The results are independent of variations in H2CO concentration, total pressure Ar concentration, and flash intensity (i.e., initial OH concentration). The rate constant is found to be invariant with temperature in this range, the best representation being k sub 1 = (1.05 ? or - 0.11) x 10 to the 11th power cu cm molecule(-1) s(-1) where the error is two standard deviations. This result is compared with previous absolute and relative determinations of k sub 1. The reaction is also discussed from a theoretical point of view.

  17. Rate constant for the reaction of hydroxyl radical with formaldehyde over the temperature range 228-362 K

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

    Absolute rate constants for the reaction OH + H2CO have been measured over the temperature range 228-362 K using the flash photolysis-resonance fluorescence technique. The results were independent of variations in forbidden H2CO, total pressure of forbidden Ar and flash intensity (i.e., initial forbidden OH). The rate constant was found to be invariant with temperature in this range, the best representation being k1 = (1.05 + or - 0.11) x 10 to the -11th cu cm/molecule sec where the error is two standard deviations. This result is compared with previous absolute and relative determinations of k1. The reaction is also discussed from a theoretical point of view.

  18. Temperature dependence of the rate constant for the bimolecular recombination of Cl-2 in water—A pulse radiolysis study

    NASA Astrophysics Data System (ADS)

    Szala-Bilnik, J.; Pierscieniewska, P.; Wolszczak, M.; Swiatla-Wojcik, D.

    2014-04-01

    The rate constant for the disproportionation of Cl-2 in water has been determined for the temperature range 22-87 °C using pulse radiolysis of 0.1 M NaCl+1 mM HClO4 aqueous solution. The rate constant for the decay of Cl-2 has been found to be 2×(7.35±0.53)×108 M-1 s-1 at 22 °C (at zero ionic strength). The determined activation energy, Ea=10.89±0.37 kJ mol-1, is less than expected for diffusion-controlled reactions. A good fit to the Noyes equation (1/kobs=1/kdiff+1/kreact) has been obtained assuming the reaction step is activationless with kreact=A‧T.

  19. Socioeconomic status and stress rate during pregnancy in Iran.

    PubMed

    Shishehgar, Sara; Dolatian, Mahrokh; Majd, Hamid Alavi; Bakhtiary, Maryam

    2014-04-22

    Stress during pregnancy can have serious adverse outcomes on the mother, the fetus, newborn, children and even adolescents. Socioeconomic status has been recognized as a predictor of stress amongst pregnant women. The first aim of this study was to investigate the role of socioeconomic status in pregnancy stress rates. The second aim was to examine the most important items of socioeconomic status including monthly family income, husband occupational status as well as mother's educational level and their influence on the rate of maternal stress. This study was cross-sectional research and was conducted on 210 pregnant women in three trimesters of pregnancy who attended Shahryar hospital for prenatal care between August-October 2012. They completed two questionnaires of Socioeconomic Status and Specific Pregnancy Stress. Collected data were analyzed by SPSS version 19 including T-test, one-way ANOVA and Spearman correlation. In this study, we considered family income, education and husbands' occupations as the most important variables which may influence perceived stress during pregnancy. The mean age of women was 27±4.8 years. The final result showed that there is no significant relationship between SES and pregnancy stress level (P > 0.05), while we found a significant relationship, as well as indirect correlation between husbands' occupational status and pregnancy stress (P < 0.05, r= -0.364). Further investigations may be considered for extending the results to all pregnant women. Thus, health officials and universities should finance other studies to investigate this fact and whether other dimensions of SES influence pregnancy stress levels or not.

  20. Socioeconomic Status and Stress Rate during Pregnancy in Iran

    PubMed Central

    Shishehgar, Sara; Dolatian, Mahrokh; Majd, Hamid Alavi; Bakhtiary, Maryam

    2014-01-01

    Background: Stress during pregnancy can have serious adverse outcomes on the mother, the fetus, newborn, children and even adolescents. Socioeconomic status has been recognized as a predictor of stress amongst pregnant women. Objectives: The first aim of this study was to investigate the role of socioeconomic status in pregnancy stress rates. The second aim was to examine the most important items of socioeconomic status including monthly family income, husband occupational status as well as mother’s educational level and their influence on the rate of maternal stress. Methods: This study was cross-sectional research and was conducted on 210 pregnant women in three trimesters of pregnancy who attended Shahryar hospital for prenatal care between August-October 2012. They completed two questionnaires of Socioeconomic Status and Specific Pregnancy Stress. Collected data were analyzed by SPSS version 19 including T-test, one-way ANOVA and Spearman correlation. Results: In this study, we considered family income, education and husbands’ occupations as the most important variables which may influence perceived stress during pregnancy. The mean age of women was 27±4.8 years. The final result showed that there is no significant relationship between SES and pregnancy stress level (P>0.05), while we found a significant relationship, as well as indirect correlation between husbands’ occupational status and pregnancy stress (P<0.05, r= -0.364). Conclusion: Further investigations may be considered for extending the results to all pregnant women. Thus, health officials and universities should finance other studies to investigate this fact and whether other dimensions of SES influence pregnancy stress levels or not. PMID:24999123

  1. Hydrolysis rate constants and activation parameters for phosphate- and phosphonate-bridged phthalonitrile monomers under acid, neutral and alkali conditions.

    PubMed

    Belsky, Kirill S; Sulimov, Artem V; Bulgakov, Boris A; Babkin, Alexandr V; Kepman, Alexey V

    2017-08-01

    Hydrolysis data for Bis(3-(3,4-dicyanophenoxy)phenyl) phenyl phosphate and Bis(3-(3,4-dicyanophenoxy)phenyl) phenylphosphonate under pH 4, 7 and 10 are presented. Conversion/time plots collected by HPLC analysis, typical chromatograms and NMR spectra of the reactions products are given. Pseudo-first order rate constants are determined for both substrates at 25, 50 and 80 °C. Activation parameters were calculated from Arrhenius equation.

  2. Rate constants for a mechanism including intermediates in the interconversion of ternary complexes by horse liver alcohol dehydrogenase

    SciTech Connect

    Sekhar, V.C.; Plapp, B.V. )

    1990-05-08

    Transient kinetic data for partial reactions of alcohol dehydrogenase and simulations of progress curves have led to estimates of rate constants for the following mechanism, at pH 8.0 and 25{degrees}C: E in equilibrium E-NAD+ in equilibrium *E-NAD+ in equilibrium E-NAD(+)-RCH2OH in equilibrium E-NAD+-RCH2O- in equilibrium *E-NADH-RCHO in equilibrium E-NADH-RCHO in equilibrium E-NADH in equilibrium E. Previous results show that the E-NAD+ complex isomerizes with a forward rate constant of 620 s-1. The enzyme-NAD(+)-alcohol complex has a pK value of 7.2 and loses a proton rapidly (greater than 1000 s-1). The transient oxidation of ethanol is 2-fold faster in D{sub 2}O, and proton inventory results suggest that the transition state has a charge of -0.3 on the substrate oxygen. Rate constants for hydride ion transfer in the forward or reverse reactions were similar for short-chain aliphatic substrates (400-600 s-1). A small deuterium isotope effect for transient oxidation of longer chain alcohols is apparently due to the isomerization of the E-NAD+ complex. The transient reduction of aliphatic aldehydes showed no primary deuterium isotope effect; thus, an isomerization of the E-NADH-aldehyde complex is postulated, as isomerization of the E-NADH complex was too fast to be detected. The estimated microscopic rate constants show that the observed transient reactions are controlled by multiple steps.

  3. Rate and equilibrium constants for the addition of N-heterocyclic carbenes into benzaldehydes: a remarkable 2-substituent effect.

    PubMed

    Collett, Christopher J; Massey, Richard S; Taylor, James E; Maguire, Oliver R; O'Donoghue, AnnMarie C; Smith, Andrew D

    2015-06-01

    Rate and equilibrium constants for the reaction between N-aryl triazolium N-heterocyclic carbene (NHC) precatalysts and substituted benzaldehyde derivatives to form 3-(hydroxybenzyl)azolium adducts under both catalytic and stoichiometric conditions have been measured. Kinetic analysis and reaction profile fitting of both the forward and reverse reactions, plus onwards reaction to the Breslow intermediate, demonstrate the remarkable effect of the benzaldehyde 2-substituent in these reactions and provide insight into the chemoselectivity of cross-benzoin reactions.

  4. Stability analysis of 4-species Aβ aggregation model: A novel approach to obtaining physically meaningful rate constants.

    PubMed

    Ghag, G; Ghosh, P; Mauro, A; Rangachari, V; Vaidya, A

    2013-11-01

    Protein misfolding and concomitant aggregation towards amyloid formation is the underlying biochemical commonality among a wide range of human pathologies. Amyloid formation involves the conversion of proteins from their native monomeric states (intrinsically disordered or globular) to well-organized, fibrillar aggregates in a nucleation-dependent manner. Understanding the mechanism of aggregation is important not only to gain better insight into amyloid pathology but also to simulate and predict molecular pathways. One of the main impediments in doing so is the stochastic nature of interactions that impedes thorough experimental characterization and the development of meaningful insights. In this study, we have utilized a well-known intermediate state along the amyloid-β peptide aggregation pathway called protofibrils as a model system to investigate the molecular mechanisms by which they form fibrils using stability and perturbation analysis. Investigation of protofibril aggregation mechanism limits both the number of species to be modeled (monomers, and protofibrils), as well as the reactions to two (elongation by monomer addition, and protofibril-protofibril lateral association). Our new model is a reduced order four species model grounded in mass action kinetics. Our prior study required 3200 reactions, which makes determining the reaction parameters prohibitively difficult. Using this model, along with a linear perturbation argument, we rigorously determine stable ranges of rate constants for the reactions and ensure they are physically meaningful. This was accomplished by finding the ranges in which the perturbations dieout in a five-parameter sweep, which includes the monomer and protofibril equilibrium concentrations and three of the rate constants. The results presented are a proof-of-concept method in determining meaningful rate constants that can be used as a bonafide way for determining accurate rate constants for other models involving complex

  5. Rate and Equilibrium Constants for the Addition of N-Heterocyclic Carbenes into Benzaldehydes: A Remarkable 2-Substituent Effect.

    PubMed

    Collett, Christopher J; Massey, Richard S; Taylor, James E; Maguire, Oliver R; O'Donoghue, AnnMarie C; Smith, Andrew D

    2015-06-01

    Rate and equilibrium constants for the reaction between N-aryl triazolium N-heterocyclic carbene (NHC) precatalysts and substituted benzaldehyde derivatives to form 3-(hydroxybenzyl)azolium adducts under both catalytic and stoichiometric conditions have been measured. Kinetic analysis and reaction profile fitting of both the forward and reverse reactions, plus onwards reaction to the Breslow intermediate, demonstrate the remarkable effect of the benzaldehyde 2-substituent in these reactions and provide insight into the chemoselectivity of cross-benzoin reactions.

  6. Rate constants for aqueous-phase reactions of hydroxyl radical ({center_dot}OH) with aldehydes and ketones

    SciTech Connect

    Allen, J.M.; Allen, S.K.

    1995-12-31

    A wide variety of aldehydes and ketones are formed in the troposphere by the gas-phase oxidation of hydrocarbons. These compounds are expected to readily partition into cloud, fog, and aquated aerosol drops where they can participate in a variety of aqueous-phase reactions. It has been previously demonstrated by other researchers that aqueous-phase photochemical reactions involving aromatic aldehydes and ketones may lead to the formation of hydrogen peroxide. Hydrogen peroxide is an important oxidant for S(IV) and is also an {center_dot}OH precursor. Aldehydes and ketones may also participate in other aqueous-phase reactions within atmospheric water drops including reactions with {center_dot}OH. Rate constants for reactions involving {center_dot}OH in aqueous solutions have been reported for only a limited number of tropospheric aldehydes and ketones. The authors have measured the rate constants for aqueous-phase reactions of {center_dot}OH with several tropospheric aldehydes and ketones by the technique of competition kinetics. Hydroxyl radicals were generated by continuous illumination at 313 nm of an aqueous acidified solution containing Fe(ClO{sub 4}){sub 3}, an {center_dot}OH scavenger, the aldehyde or ketone whose rate constant was to be measured, and a standard for which the rate constant for reaction with {center_dot}OH is well known. Nitrobenzene was used as the standard in all experiments. Loss of the aldehyde or ketone and the standard were monitored by HPLC. Losses attributable to direct photolysis and dark reactions were minimal.

  7. Channel specific rate constants for reactions of O(1D) with HCl and HBr

    NASA Technical Reports Server (NTRS)

    Wine, P. H.; Wells, J. R.; Ravishankara, A. R.

    1986-01-01

    The absolute rate coefficients and product yields for reactions of O(1D) with HCl(1) and HBr(2) at 287 K are presently determined by means of the time-resolved resonance fluorescence detection of O(3P) and H(2S) in conjunction with pulsed laser photolysis of O3/HX/He mixtures. Total rate coefficients for O(1D) removal are found to be, in units of 10 to the -10th cu cm/molecule per sec, k(1) = 1.50 + or - 0.18 and k(2) 1.48 + or - 0.16; the absolute accuracy of these rate coefficients is estimated to be + or - 20 percent.

  8. Determination of proton transfer rate constants using Ab initio, molecular dynamics and density matrix evolution calculations.

    PubMed

    van der Spoel, D; Berendsen, H J

    1996-01-01

    In this work we give an overview of the methodologies required to compute the rate of proton transfer in hydrogen bonded systems in solution. Using ab initio or density functional methods we determine proton potentials of a truncated system as a function of proton-donor proton-acceptor distance as well as nonbonding parameters. By classical molecular dynamics we evaluate a swarm of proton potentials with the proton fixed in the reactant well. The rate of proton transfer is calculated perturbatively using the Density Matrix Evolution (DME) method, going beyond the Born Oppenheimer approximation. The method is illustrated by two examples: hydrogen malonate and the active center of HIV-1 protease.

  9. Gas exchange responses to constant work-rate exercise in patients with glycogenosis type V and VII.

    PubMed

    Ong, Hean-Yee; O'Dochartaigh, Conor S; Lovell, Sharon; Patterson, Victor H; Wasserman, Karlman; Nicholls, D Paul; Riley, Marshall S

    2004-06-01

    During constant work-rate exercise above the lactic acidosis threshold, oxygen consumption fails to plateau by 3 minutes, but continues to rise slowly. This slow component correlates closely with the rise in lactate in normal subjects. We investigated if oxygen consumption during constant work-rate exercise could rise after 3 minutes in the absence of a rise in lactate. We studied five patients with McArdle's disease, one patient with phosphofructokinase deficiency and six normal subjects. Subjects performed two 6-minute duration constant work-rate exercise tests at 40 and 70% of peak oxygen consumption. During low-intensity exercise, oxygen consumption reached steady state by 3 minutes in both groups. Lactate rose slightly in control subjects but not in patients. During high-intensity exercise, oxygen consumption rose from the third to the sixth minute by 144 (21-607) ml/minute (median and range) in control subjects and by 142 (73-306) ml/minute in patients (p = not significant, Mann-Whitney U test). Over the same period, lactate (geometric mean and range) rose from 2.68 (1.10-5.00) to 5.39 (2.70-10.00) mmol/L in control subjects, but did not rise in patients (1.20 [0.64-1.60] to 0.70 [0.57-1.20] mmol/L). We conclude that the slow component of oxygen consumption during heavy exercise is not dependent on lactic acidosis.

  10. Pressure dependence of the absolute rate constant for the reaction OH + C2H2 from 228 to 413K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Nava, D. F.; Borokowski, R. P.; Payne, W. A.; Stief, L. J.

    1980-01-01

    The pressure dependence of absolute rate constants for the reaction of OH + C2H2 yields products has been examined at five temperatures ranging from 228 to 413 K. The experimental techniques which was used is flash photolysis-resonance fluoresence. OH was produced by water photolysis and hydroxyl resonance fluorescent photons were measured by multiscaling techniques. The results indicate that the low pressure bimolecular rate constant is 4 x 10 the the minus 13th power cu cm molecule (-1) s(-1) over the temperature range studied. A substantial increase in the bimolecular rate constant with an increase in pressure was observed at all temperatures except 228 K. This indicates the importance of initial adduct formation and subsequent stablization. The high pressure results are well represented by the Arrhenius expression (k sub bi) sub infinity = (6.83 + or - 1.19) x 10 to the minus 12th power exp(-646 + or - 47/T)cu cm molecule (-1) s(-1). The results are compared to previous investigated and are theoretically discussed. The implications of these results on modeling of terrestrial and planetary atmospheres and also in combustion chemistry are discussed.

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

    PubMed

    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.

  12. Rate constant for OH with selected large alkanes : shock-tube measurements and an improved group scheme.

    SciTech Connect

    Sivaramakrishnan, R.; Michael, J. V.; Chemical Sciences and Engineering Division

    2009-04-06

    High-temperature rate constant experiments on OH with the five large (C{sub 5}-C{sub 8}) saturated hydrocarbons n-heptane, 2,2,3,3-tetramethylbutane (2,2,3,3-TMB), n-pentane, n-hexane, and 2,3-dimethylbutane (2,3-DMB) were performed with the reflected-shock-tube technique using multipass absorption spectrometric detection of OH radicals at 308 nm. Single-point determinations at {approx}1200 K on n-heptane, 2,2,3,3-TMB, n-hexane, and 2,3-DMB were previously reported by Cohen and co-workers; however, the present work substantially extends the database to both lower and higher temperature. The present experiments span a wide temperature range, 789-1308 K, and represent the first direct measurements of rate constants at T > 800 K for n-pentane. The present work utilized 48 optical passes corresponding to a total path length of {approx}4.2 m. As a result of this increased path length, the high OH concentration detection sensitivity permitted pseudo-first-order analyses for unambiguously measuring rate constants.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    EPA Science Inventory

    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...

  15. Rate Constant Change of Photo Reaction of Bacteriorhodopsin Observed in Trimeric Molecular System.

    PubMed

    Tsujiuchi, Yutaka; Masumoto, Hiroshi; Goto, Takashi

    2016-04-01

    To elucidate the time evolution of photo reaction of bacteriorhodopsin in glycerol mixed purple membrane at around 196 K under irradiation by red light, a kinetic model was constructed. The change of absorption with irradiation at times of 560 nm and 412 nm was analyzed for the purpose of determining reaction rates of photo reaction of bacteriorhodopsin and its product M intermediate. In this study it is shown that reaction rates of conversion from bacteriorhodopsin to the M intermediate can be explained by a set of linear differential equations. This model analysis concludes that bacteriorhodopsin in which constitutes a trimer unit with other two bacteriorhodopsin molecules changes into M intermediates in the 1.73 of reaction rate, in the initial step, and according to the number of M intermediate in a trimer unit, from three to one, the reaction rate of bacteriorhodopsin into M intermediates smaller as 1.73, 0.80, 0.19 which caused by influence of inter-molecular interaction between bacteriorhodopsin.

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

    EPA Science Inventory

    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...

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

    PubMed Central

    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

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

    PubMed

    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.

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

    SciTech Connect

    Wei, Max; Smith, Sarah J.; Sohn, Michael D.

    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.

  20. Rate constants and temperature dependences for the reactions of hydroxyl radical with several halogenated methanes, ethanes, and propanes by relative rate measurements

    NASA Technical Reports Server (NTRS)

    Hsu, K.-J.; DeMore, W. B.

    1995-01-01

    Rate constants of 15 OH reactions with halogen-substituted alkanes, C1 to C3, were studied using a relative rate technique in the temperature range 283-403 K. Compounds studied were CHF2Cl (22), CHF2Br (22B), CH3F (41), CH2F2 (32), CHF3 (23), CHClFCCl2F (122a), CHCl2CF3 (123), CHClFCF3 (124), CH3CF3 (143a), CH3CH2F (161), CF3CHFCF3 (227ea), CF3CH2CF3 (236fa), CF3CHFCHF2 (236ea), and CHF2CF2CH2F (245ca). Using CH4, CH3CCl3, CF3CF2H, and C2H6 as primary reference standards (JPL 92-20 rate constants), absolute rate constants are derived. Results are in good agreement with previous experimental results for six of the compounds studied, including CHF2Cl, CHF2Br, CH2F2, CH3CF3, CHFClCFCl2, and CF3CHFCF3. For the remainder the relative rate constants are lower than those derived from experiments in which OH loss was used to measure the reaction rate. Comparisons of the derived Arrhenius A factors with previous literature transition-state calculations show order of magnitude agreement in most cases. However, the experimental A factors show a much closer proportionality to the number of H atoms in the molecule than is evident from the transition state calculations. For most of the compounds studied, an A factor of (8 +/- 3)E-13 cm(exp 3)/(molecule s) per C-H bond is observed. A new measurement of the ratio k(CH3CCl3)/k(CH4) is reported that is in good agreement with previous data.

  1. Constant Flux Proxies and Pleistocene Sediment Accumulation Rates on the Juan de Fuca Ridge in the Northeast Pacific

    NASA Astrophysics Data System (ADS)

    Middleton, J. L.; Mukhopadhyay, S.; Langmuir, C. H.; Costa, K.; McManus, J. F.; d'Almeida, M.; Huybers, P. J.; Winckler, G.

    2016-12-01

    Mass accumulation rates of marine sediments are often employed to constrain deposition rates of important proxies such as terrigenous dust, carbonate, and biogenic opal to quantitatively examine variations in continental aridity, atmospheric transport, and biologic productivity across changing climatic conditions. However, deposition rates that are estimated using traditional mass accumulation rates calculated from sediment core age models can be subject to bias from lateral sediment transport and limited age model resolution. Constant flux proxies, such as extraterrestrial helium-3 (3HeET) and excess thorium-230 (230ThXS), can be used to calculate vertical sediment accumulation rates that are independent of age model uncertainties and the effects of lateral sediment transport. While a short half-life limits analyses of 230ThXS to the past 500 ka, 3HeET is stable and could be used to constrain sedimentary fluxes during much of the Cenozoic. Despite the vast paleoceanographic potential of constant flux proxies, few studies have directly compared the behavior of 230ThXS and 3HeET using measurements from the same samples. Sediment grain size fractionation and local scavenging effects may differentially bias one or both proxy systems and complicate the interpretation of 230ThXS or 3HeET data. We will present a new record of vertical sediment accumulation rates spanning the past 600 ka in the Northeast Pacific constrained using analyses of both 3HeET and 230ThXS in two sediment cores from cruise AT26-19 on the Juan de Fuca Ridge. Such a record allows for intercomparison of both constant flux proxies in the mid-ocean ridge environment and examination of sedimentary behavior across multiple glacial cycles. The 230ThXS-derived accumulation rates typically range from 0.5 to 2 g cm-2 ka-1 over the past 450 ka, with periods of maximum deposition coinciding with glacial maxima. Preliminary results of samples analyzed with both 3HeET and 230ThXS indicate relative consistency

  2. Temperature Dependence of the Rate Constants of Charge Recombination Reactions in Bacterial Reaction Centers

    NASA Astrophysics Data System (ADS)

    Thuy, T. T.; Yen, V. T. H.; Thao, T. T.; Viet, Nguyen Ai

    The bacterial reaction center couples light-induced electron transfer via a tightly bound ubiquinone (QA) to a mobile ubiquinone (QB). Based on the electron transfer theory by Marcus, we have investigated the rate of charge recombination reactions from Rhodopseudomonas viridis and Rhodobacter sphaeroides, by mean of finding an approximation formula. The results obtained are verified for not only at high and low temperature as the previous works but also at the medium temperature range.

  3. Slopes, nearly constant loss, universality, and hopping rates for dispersive ionic conduction

    NASA Astrophysics Data System (ADS)

    Macdonald, J. Ross; Ahmad, Mohamad M.

    2007-01-01

    The title topics are investigated, discussed, and new insights provided by considering isothermal frequency response data for seven different materials having quite different conductivity spans and involving different electrode polarization effects and temperatures. These data sets were fitted using several different models, including the Kohlrausch-related K0 and K1 ones derived from stretched-exponential response in the temporal domain. The quasi-universal UN model, the K1 with its shape parameter, β1, fixed at 1/3, fitted most of the data very well, and its fits of such data were used to compare its predictions for hopping rate with those derived from fitting with the conventional 'universal dynamic response' Almond-West real-part-of-conductivity model. The K1-model theoretical hopping rate, involving the mean waiting time for a hop and derived from microscopic stochastic analysis, was roughly twice as large as the empirical Almond-West rate for most of the materials considered and should be used in place of it. Its use in a generalized Nernst-Einstein equation led to comparison of estimates of the concentration of fully dissociated mobile charge carriers in superionic PbSnF4 with earlier estimates of Ahmad using an Almond-West hopping rate value. Agreement with an independent structure-derived value was relatively poor. Fitting results obtained using the K0 model, for Na2SO4 data sets for two different polycrystalline material phases, and involving severely limited conductivity variation, were far superior to those obtained using the K1 model. The estimated values of the K0 shape parameter, β0, were close to 1/3 for both phases, strongly suggesting that the charge motion was one dimensional for each phase, even though they involved different crystalline structures.

  4. Modeling the downward transport of (210)Pb in Peatlands: Initial Penetration-Constant Rate of Supply (IP-CRS) model.

    PubMed

    Olid, Carolina; Diego, David; Garcia-Orellana, Jordi; Cortizas, Antonio Martínez; Klaminder, Jonatan

    2016-01-15

    The vertical distribution of (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 (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 210Pb profiles that are altered by an initial migration of the radionuclide. This new, two-phased, model describes the distribution of atmospheric-derived (210)Pb ((210)Pbxs) in peat taking into account both incorporation of (210)Pb into the accumulating peat matrix as well as an initial flushing of (210)Pb through the uppermost peat layers. The validity of the IP-CRS model is tested in four anomalous (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 (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. (241)Am and (137)Cs). Our results showed that the IP-CRS can provide chronologies from peat records where (210)Pb mobility is evident, being a valuable tool for studies reconstructing past environmental changes using peat archives during the Anthropocene.

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

    PubMed Central

    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

  6. On the thermodynamics of stress rate in the evolution of back stress in viscoplasticity

    NASA Technical Reports Server (NTRS)

    Freed, Alan D.; Chaboche, J.-L.; Walker, K. P.

    1991-01-01

    A thermodynamic foundation using the concept of internal state variables is presented for the kinematic description of a viscoplastic material. Three different evolution equations for the back stress are considered. The first is that of classical, nonlinear, kinematic hardening. The other two include a contribution that is linear in stress rate. Choosing an appropriate change in variables can remove this stress rate dependence. As a result, one of these two models is shown to be equivalent to the classical, kinematic hardening model; while the other is a new model, one which seems to have favorable characteristics for representing ratchetting behavior. All three models are thermodynamically admissible.

  7. Experimental determination of the dose rate constant for selected 125I- and 192Ir-brachytherapy sources

    NASA Astrophysics Data System (ADS)

    Selbach, Hans-Joachim; Bambynek, Markus; Aubineau-Lanièce, Isabelle; Gabris, Frantisek; Stefano Guerra, Antonio; Toni, Maria Pia; de Pooter, Jacco; Sander, Thorsten; Schneider, Thorsten

    2012-10-01

    In 2008, the European project ‘T2.J06, Increasing cancer treatment efficacy using 3D brachytherapy’ was launched. One of the main goals of the Joint Research Project was the experimental determination of the dose rate constant Λ to allow the linkage between the air kerma strength or reference air kerma rate currently used for the source characterization and the ‘new’ absorbed dose rate to water with an uncertainty of <3% (k = 1) for some selected brachytherapy sources. The results obtained by five National Metrology Institutes (NMI) for four different types of brachytherapy sources are presented and compared with consensus data published in the literature. A further goal of the project was to develop a calibration chain for the transfer of the new reference quantity to the end user, minimizing the uncertainty. A first direct calibration in terms of absorbed dose rate to water of a secondary standard and the dissemination to the hospitals is presented.

  8. Volitional Control of Heart Rate During Exercise Stress.

    ERIC Educational Resources Information Center

    LeFevers, Victoria A.

    Thirty five volunteer college women were divided into three groups to determine if heart rate could be conditioned instrumentally and lowered during exercise stress on the treadmill. The three groups were a) experimental group I, 15 subjects who received instrumental conditioning with visual feedback; b) instrumental group II, 9 subjects who…

  9. Volitional Control of Heart Rate During Exercise Stress.

    ERIC Educational Resources Information Center

    LeFevers, Victoria A.

    Thirty five volunteer college women were divided into three groups to determine if heart rate could be conditioned instrumentally and lowered during exercise stress on the treadmill. The three groups were a) experimental group I, 15 subjects who received instrumental conditioning with visual feedback; b) instrumental group II, 9 subjects who…

  10. Unimolecular dissociation rate constants: Chlorobenzene cations revisited by using a new method

    SciTech Connect

    Stanley, R.J.; Cook, M.; Castleman, A.W. Jr. )

    1990-05-03

    Unimolecular dissociation rates of metastable molecular ions formed at the laser focus of a time-of-flight mass spectrometer (TOFMS) have been determined by measuring the relative concentrations of parent metastable ions and the daughter fragment ions as a function of their retained kinetic energies upon dissociation. This is accomplished by the use of a simple one-stage ion mirror/energy analyzer. For a given reflection potential on the ion mirror, only those ions with a kinetic energy equal to or less than the reflection potential are detected. In this way, the relative concentrations of the parent and daughter ions as a function of their position of dissociation in the time-of-flight (TOF) lens can be measured, and consequently the dissociation lifetime can be derived. This technique has been applied to measuring the unimolecular dissociation rate of chlorobenzene ion (C{sub 6}H{sub 5}Cl{sup +}) in the three-photon energy range of 13.64-13.92 eV through resonance-enhanced two-photon state-selected ionization of chlorobenzene in a supersonic molecular jet.

  11. Dissolution rate of South African calcium-based materials at constant pH.

    PubMed

    Siagi, Z O; Mbarawa, M

    2009-04-30

    One of the most important steps in the wet limestone-gypsum flue gas desulphurization (WFGD) process is limestone dissolution, which provides the dissolved alkalinity necessary for SO(2) absorption. Accurately evaluating the limestone dissolution rate is important in the design and efficient operation of WFGD plants. In the present work, the dissolution of limestone from different sources in South Africa has been studied in a pH-Stat apparatus under conditions similar to those encountered in wet FGD processes. The influence of various parameters such as the reaction temperature (30rate increased with a decrease in particle size, decrease in pH and an increase in temperature. Kinetic analysis of the results indicates that the dissolution of limestone is according to the shrinking core model with surface control, i.e. 1-(1-3)(1/3)=kt.

  12. Long-term prediction of creep strains of mineral wool slabs under constant compressive stress

    NASA Astrophysics Data System (ADS)

    Gnip, Ivan; Vaitkus, Saulius; Keršulis, Vladislovas; Vėjelis, Sigitas

    2012-02-01

    The results obtained in determining the creep strain of mineral wool slabs under compressive stress, used for insulating flat roofs and facades, cast-in-place floors, curtain and external basement walls, as well as for sound insulation of floors, are presented. The creep strain tests were conducted under a compressive stress of σ c =0.35 σ 10%. Interval forecasting of creep strain was made by extrapolating the creep behaviour and approximated in accordance with EN 1606 by a power equation and reduced to a linear form using logarithms. This was performed for a lead time of 10 years. The extension of the range of the confidence interval due to discount of the prediction data, i.e. a decrease in their informativity was allowed for by an additional coefficient. Analysis of the experimental data obtained from the tests having 65 and 122 days duration showed that the prediction of creep strains for 10 years can be made based on data obtained in experiments with durations shorter than the 122 days as specified by EN 13162. Interval prediction of creep strains (with a confidence probability of 90%) was based on using the mean square deviation of the actual direct observations of creep strains in logarithmic form to have the linear trend in a retrospective area.

  13. Oxime effects on the rate constants of carbamylation and decarbamylation of acetylcholinesterase for pyridostigmine, physostigmine and insecticidal carbamates.

    PubMed

    Dawson, R M

    1995-06-01

    The effects of the oximes 2-pyridine aldoxime methiodide (PAM), HI-6, HS-6, toxogonin and TMB-4 on the rate of carbamylation of membrane-bound bovine erythrocyte acetylcholinesterase were studied. The second-order rate constant of carbamylation (ki) and the first-order rate constant of decarbamylation (k3) were calculated from the proportion of free acetylcholinesterase at equilibrium and the rate of approach to equilibrium. Twenty insecticidal carbamates plus physostigmine and pyridostigmine were studied. The oximes increased ki for several carbamates, with HI-6 causing an increase in the most number of cases (12) and PAM the least (3). HI-6 was also a potent accelerator of decarbamylation (increase in k3) in all cases, whereas PAM caused a significant decrease in k3 in 15 cases and a nonsignificant decrease in the other 7. Toxogonin and TMB-4 increased k3 or had no significant effect. The results were generally consistent with a proposal in the literature that there is a correlation between increased ki and increased toxicity of the carbamate in the presence of an oxime.

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

    PubMed Central

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

    2002-01-01

    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. PMID:12083678

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

    PubMed

    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.

  16. Theoretical determination of the rate constant for OH hydrogen abstraction from toluene.

    PubMed

    Uc, Víctor H; Alvarez-Idaboy, J Raúl; Galano, Annia; García-Cruz, Isidoro; Vivier-Bunge, Annik

    2006-08-24

    The OH abstraction of a hydrogen atom from both the side chain and the ring of toluene has been studied in the range 275-1000 K using quantum chemistry methods. It is found that the best method of calculation is to perform geometry optimization and frequency calculations at the BHandHLYP/6-311++G(d,p) level, followed by CCSD(T) calculations of the optimized structures with the same basis set. Four different reaction paths are considered, corresponding to the side chain and three possible ring hydrogen abstractions, and the branching ratio is determined as a function of temperature. Although negligible at low temperatures, at 1000 K ring-H abstraction is found to contribute 11% to the total abstraction reaction. The calculated rate coefficients agree very well with experimental results. Side chain abstraction is shown to occur through a complex mechanism that includes the reversible formation of a collisionally stabilized reactant complex.

  17. Metabolic Rate Constants for Hydroquinone in F344 Rat and Human Liver Isolated Hepatocytes: Application to a PBPK model.

    SciTech Connect

    Poet, Torka S.; Wu, Hong; English, J C.; Corley, Rick A.

    2004-11-15

    Hydroquinone (HQ) is an important industrial chemical that also occurs naturally in foods and in the leaves and bark of a number of plant species. Exposure of laboratory animals to HQ may result in a species-, sex-, and strain-specific nephrotoxicity. The sensitivity of male F344 vs. female F344 and Sprague-Dawley rats or B6C3F1 mice appears to be related to differences in the rates of formation and further metabolism of key nephrotoxic metabolites. Metabolic rate constants for the conversion of HQ through several metabolic steps to the mono-glutathione conjugate and subsequent detoxification via mercapturic acid were measured in suspension cultures of hepatocytes isolated from male F344 rats and humans. An in vitro mathematic kinetic model was used to analyze each metabolic step by simultaneously fitting the disappearance of each substrate and the appearance of subsequent metabolites. An iterative, nested approach was used whereby downstream metabolites were considered first and the model was constrained by the requirement that rate constants determined during analysis of individual metabolic steps must also satisfy the complete, integrated metabolism scheme, including competitive pathways. The results from this study indicated that the overall capacity for metabolism of HQ and its mono-glutathione conjugate is greater in hepatocytes from humans than those isolated from rats, suggesting a greater capacity for detoxification of the glutathione conjugates. Metabolic rate constants were applied to an existing physiologically based pharmacokinetic model and the model was used to predict total glutathione metabolites produced in the liver. The results showed that body burdens of these metabolites will be much higher in rats than humans.

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

    NASA Technical Reports Server (NTRS)

    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.

  19. The role of relative rate constants in determining surface state phenomena at semiconductor-liquid interfaces.

    PubMed

    Iqbal, Asif; Hossain, Md Sazzad; Bevan, Kirk H

    2016-10-26

    In this work, we present a theoretical study of surface state occupation statistics at semiconductor-liquid interfaces, as it pertains to the evolution of H2 and O2 through water splitting. Our approach combines semiclassical charge transport and electrostatics at the semiconductor-liquid junction, with a master rate equation describing surface state mediated electron/hole transfer. As a model system we have studied the TiO2-water junction in the absence of illumination, where it is shown that surface states might not always equilibrate with the semiconductor. Non-trivial electrostatics, for example including a shifting of the Mott-Schottky plateau in capacitive measurements, are explored when deep-level surface states partially equilibrate with the liquid. We also endeavor to explain observations of non-linearity present in Mott-Schottky plots, as they pertain to surface state occupation statistics. In general, it is intended that the results of this work will serve to further the use and development of quantitative device modeling techniques in the description of H2 evolution at semiconductor-liquid junctions.

  20. Stress Detection Using Low Cost Heart Rate Sensors.

    PubMed

    Salai, Mario; Vassányi, István; Kósa, István

    2016-01-01

    The automated detection of stress is a central problem for ambient assisted living solutions. The paper presents the concepts and results of two studies targeted at stress detection with a low cost heart rate sensor, a chest belt. In the device validation study ( n = 5), we compared heart rate data and other features from the belt to those measured by a gold standard device to assess the reliability of the sensor. With simple synchronization and data cleaning algorithm, we were able to select highly (>97%) correlated, low average error (2.2%) data segments of considerable length from the chest data for further processing. The protocol for the clinical study ( n = 46) included a relax phase followed by a phase with provoked mental stress, 10 minutes each. We developed a simple method for the detection of the stress using only three time-domain features of the heart rate signal. The method produced accuracy of 74.6%, sensitivity of 75.0%, and specificity of 74.2%, which is impressive compared to the performance of two state-of-the-art methods run on the same data. Since the proposed method uses only time-domain features, it can be efficiently implemented on mobile devices.

  1. Stress Detection Using Low Cost Heart Rate Sensors

    PubMed Central

    Salai, Mario; Kósa, István

    2016-01-01

    The automated detection of stress is a central problem for ambient assisted living solutions. The paper presents the concepts and results of two studies targeted at stress detection with a low cost heart rate sensor, a chest belt. In the device validation study (n = 5), we compared heart rate data and other features from the belt to those measured by a gold standard device to assess the reliability of the sensor. With simple synchronization and data cleaning algorithm, we were able to select highly (>97%) correlated, low average error (2.2%) data segments of considerable length from the chest data for further processing. The protocol for the clinical study (n = 46) included a relax phase followed by a phase with provoked mental stress, 10 minutes each. We developed a simple method for the detection of the stress using only three time-domain features of the heart rate signal. The method produced accuracy of 74.6%, sensitivity of 75.0%, and specificity of 74.2%, which is impressive compared to the performance of two state-of-the-art methods run on the same data. Since the proposed method uses only time-domain features, it can be efficiently implemented on mobile devices. PMID:27372071

  2. Rate of drying and stresses in the first period of drying

    SciTech Connect

    Kowalski, S.J.; Rybicki, A.

    2000-03-01

    The paper presents a computer simulated processes and illustrate how the drying induced stresses are influenced by the rate of drying. It is shown that the moisture transport coefficient, and thus the rate of drying, depends on the thermal state of the drying material, defined by the wet-bulb temperature. Through these simulated processes one can observe the evolution of the moisture content and stress distributions during drying at constant, but in each process different, wet-bulb temperatures. A convective drying process of a bar with rectangular cross-section is considered as example, and a two-dimensional initial-boundary value problem is solved numerically with the use of the finite element method. The numerical results are visualized in spatial diagrams.

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

    NASA Astrophysics Data System (ADS)

    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. Inverting for Shear Stress Rate on the Northern Cascadia Megathrust Using Geodetic Data

    NASA Astrophysics Data System (ADS)

    Bruhat, L.; Segall, P.; Bradley, A. M.

    2014-12-01

    Past physics-based models of slow slip events (SSE) have shown that, when averaged over many SSE cycles, the shear stress within the SSE zone remains roughly constant. Stress accumulates between SSE, and then is released during slow slip events. However, the predicted long-term deformation rates from such models, assuming the plate boundary is locked to the top of the ETS zone, do not fit well GPS velocities and uplift rates determined from leveling and tide-gauge data. These physics-based models particularly misfit the vertical rates. At the same time, previous kinematic inversions display a gap between the down-dip limit of the locked region and the top of the ETS zone. Our inversions of geodetic data for fault slip rates exhibit a steeper slip-rate profile at the top of the ETS zone, relative to the constant shear stress model, as well as creep up dip of the ETS zone. We explore physics-based models with velocity-strengthening regions of different length up dip the ETS zone, i.e. within the "gap" identified in kinematic inversions. However, this still does not match the observations well. We therefore try a new approach: we invert for shear stress rates on the megathrust that best fit the data. We show that a small decrease in shear stress within the top of the ETS zone, reaching 5 kPa/year at a depth of ~ 30 km, is required to fit the data. Possible explanations for this include a slow decrease in normal stress with time, possibly due to an increase in pore pressure, or a reduction in fault friction. We explore these hypotheses, using 2D quasi-dynamic simulations with rate-and-state friction and isothermal v-cutoff models for generating slow slip events. The potential for creep above the top of the ETS zone has important implications for the mechanical relationship between deep slow slip and dynamic events in the locked region.

  5. Determination of Chemical Kinetic Rate Constants of a Model for Carbothermal Processing of Lunar Regolith Simulant Using Methane

    NASA Technical Reports Server (NTRS)

    Balasubramaniam, R; Gokoglu, S.; Hegde, U.

    2009-01-01

    We have previously developed a chemical conversion model of the carbothermal processing of lunar regolith using methane to predict the rate of production of carbon monoxide. In this carbothermal process, gaseous methane is pyrolyzed as it flows over the hot surface of a molten zone of lunar regolith and is converted to carbon and hydrogen. Hydrogen is carried away by the exiting stream of gases and carbon is deposited on the melt surface. The deposited carbon mixes with the melt and reacts with the metal oxides in it to produce carbon monoxide that bubbles out of the melt. In our model, we assume that the flux of carbon deposited is equal to the product of the surface reaction rate constant gamma and the concentration of methane adjacent to the melt surface. Similarly, the rate of consumption of carbon per unit volume in the melt is equal to the product of the melt reaction rate constant k and the concentrations of carbon and metal oxide in the melt. In this paper, we describe our effort to determine gamma and k by comparison of the predictions from our model with test data obtained by ORBITEC (Orbital Technologies Corporation). The concentration of methane adjacent to the melt surface is a necessary input to the model. It is inferred from the test data by a mass balance of methane, adopting the usual assumptions of the continuously-stirred-tank-reactor model, whereby the average concentration of a given gaseous species equals its exit concentration. The reaction rates gamma and k have been determined by a non-linear least-squares fit to the test data for the production of carbon monoxide and the fraction of the incoming methane that is converted. The comparison of test data with our model predictions using the determined chemical kinetic rate constants provides a consistent interpretation of the process over the full range of temperatures, pressures, and methane flow rates used in the tests, thereby increasing our confidence to use the model for scale-up purposes.

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

    PubMed

    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.

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

    PubMed Central

    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

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    Cannon, William R; Baker, Scott E

    2017-08-16

    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.

  10. The reaction H + C4H2 - Absolute rate constant measurement and implication for atmospheric modeling of Titan

    NASA Technical Reports Server (NTRS)

    Nava, D. F.; Mitchell, M. B.; Stief, L. J.

    1986-01-01

    The absolute rate constant for the reaction H + C4H2 has been measured over the temperature (T) interval 210-423 K, using the technique of flash photolysis-resonance fluorescence. At each of the five temperatures employed, the results were independent of variations in C4H2 concentration, total pressure of Ar or N2, and flash intensity (i.e., the initial H concentration). The rate constant, k, was found to be equal to 1.39 x 10 to the -10th exp (-1184/T) cu cm/s, with an error of one standard deviation. The Arrhenius parameters at the high pressure limit determined here for the H + C4H2 reaction are consistent with those for the corresponding reactions of H with C2H2 and C3H4. Implications of the kinetic carbon chemistry results, particularly those at low temperature, are considered for models of the atmospheric carbon chemistry of Titan. The rate of this reaction, relative to that of the analogous, but slower, reaction of H + C2H2, appears to make H + C4H2 a very feasible reaction pathway for effective conversion of H atoms to molecular hydrogen in the stratosphere of Titan.

  11. Measuring Rate Constants for Reactions of the Simplest Criegee Intermediate CH_2OO by Monitoring the OH Radical

    NASA Astrophysics Data System (ADS)

    Liu, Yingdi; Bayes, Kyle D.; Sander, Stanley P.

    2014-06-01

    Criegee radicals are important atmospheric intermediates formed from ozonolysis of alkenes. It potentially contributes to the atmospheric oxidation cycle mainly by generating OH radicals through unimolecular decomposition. In this work, we focus on studying the unimolecular decomposition reaction of the smallest Criegee intermediate (CH2OO), which was generated by reacting CH2I with O2. While generating the CH2OO molecule by reacting CH2I with O2, significant amounts of the OH radical were observed by laser-induced fluorescence. The addition of molecules known to react with CH2OO increased the observed decay rates of the OH signal. Using the OH signals as a proxy for the CH2OO concentration, the rate constant for the reaction of hexafluoroacetone with CH2OO was determined. The rate constant for the reaction of SO2 with CH2OO showed no pressure dependence over the range of 50 to 200 Torr. This work provides the direct experimental evidence for the unimolecular decomposition of CH2OO, and possible mechanisms of CH2OO have been investigated by this multidimensional study.

  12. Measuring rate constants for reactions of the simplest Criegee intermediate (CH2OO) by monitoring the OH radical.

    PubMed

    Liu, Yingdi; Bayes, Kyle D; Sander, Stanley P

    2014-01-30

    While generating the CH2OO molecule by reacting CH2I with O2, significant amounts of the OH radical were observed by laser-induced fluorescence. At least two different processes formed OH. A fast process was probably initiated by a reaction of vibrationally hot CH2I radicals. The second process appeared to be associated with the decay of the CH2OO molecule. The addition of molecules known to react with CH2OO increased the observed decay rates of the OH signal. Using the OH signals as a proxy for the CH2OO concentration, the rate constant for the reaction of hexafluoroacetone with CH2OO was determined to be (3.33 ± 0.27) × 10(-11) cm(3) molecule(-1) s(-1), in good agreement with the value measured by Taatjes et al.1 The rate constant for the reaction of SO2 with CH2OO, (3.53 ± 0.29) × 10(-11) cm(3) molecule(-1) s(-1), showed no pressure dependence over the range of 50-200 Torr and was in agreement with the value at 4 Torr reported by Welz et al.

  13. Effect-compartment equilibrium rate constant (keo) for propofol during induction of anesthesia with a target-controlled infusion device.

    PubMed

    Lim, Thiam Aun; Wong, Wai Hong; Lim, Kin Yuee

    2006-01-01

    The effect-compartment concentration (C(e)) of a drug at a specific pharmacodynamic endpoint should be independent of the rate of drug injection. We used this assumption to derive an effect-compartment equilibrium rate constant (k(eo)) for propofol during induction of anesthesia, using a target controlled infusion device (Diprifusor). Eighteen unpremedicated patients were induced with a target blood propofol concentration of 5 microg x ml(-1) (group 1), while another 18 were induced with a target concentration of 6 microg x ml(-1) (group 2). The time at loss of the eyelash reflex was recorded. Computer simulation was used to derive the rate constant (k(eo)) that resulted in the mean C(e) at loss of the eyelash reflex in group 1 being equal to that in group 2. Using this population technique, we found the k(eo) to be 0.57 min(-1). The mean (SD) effect compartment concentration at loss of the eyelash reflex was 2.39 (0.70) microg x ml(-1). This means that to achieve a desired C(e) within 3 min of induction, the initial target blood concentration should be set at 1.67 times that of the desired C(e) for 1 min, after which it should revert to the desired concentration.

  14. The reaction H + C4H2 - Absolute rate constant measurement and implication for atmospheric modeling of Titan

    NASA Astrophysics Data System (ADS)

    Nava, D. F.; Mitchell, M. B.; Stief, L. J.

    1986-04-01

    The absolute rate constant for the reaction H + C4H2 has been measured over the temperature (T) interval 210-423 K, using the technique of flash photolysis-resonance fluorescence. At each of the five temperatures employed, the results were independent of variations in C4H2 concentration, total pressure of Ar or N2, and flash intensity (i.e., the initial H concentration). The rate constant, k, was found to be equal to 1.39 x 10 to the -10th exp (-1184/T) cu cm/s, with an error of one standard deviation. The Arrhenius parameters at the high pressure limit determined here for the H + C4H2 reaction are consistent with those for the corresponding reactions of H with C2H2 and C3H4. Implications of the kinetic carbon chemistry results, particularly those at low temperature, are considered for models of the atmospheric carbon chemistry of Titan. The rate of this reaction, relative to that of the analogous, but slower, reaction of H + C2H2, appears to make H + C4H2 a very feasible reaction pathway for effective conversion of H atoms to molecular hydrogen in the stratosphere of Titan.

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

    SciTech Connect

    Córsico, Alejandro H.; Althaus, Leandro G.

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  17. Comparison of calculated and experimental thermal attachment rate constants for SF6 in the temperature range 200-600 K

    NASA Technical Reports Server (NTRS)

    Orient, O. J.; Chutjian, A.

    1986-01-01

    Electron-attachment cross sections are calcualted for the process e(-) + SF6 yields SF6(-) in the energy range 1-200 meV. An electron scattering approximation is used in which diatomiclike potential energy curves near the equilibrium SF6 ground state are constructed from recent spectroscopic data. Excellent agreement is found over the entire energy range with experimental attachment cross sections at a temperature of 300 K for s-wave (l = 0) scattering. The same calculation, with appropriate adjustment of the thermal populations, is used to calculate attachment rate constants in the range 50-600 K for both s- and p-wave scattering.

  18. Rate constants calculation with a simple mixed quantum/classical implementation of the flux-flux correlation function method.

    PubMed

    Palma, Juliana

    2009-03-28

    A simple mixed quantum/classical (mixed-Q/C) implementation of the flux-flux correlation function method has been applied to evaluate rate constants for a two-dimensional model system. The model consists of an Eckart barrier resembling the collinear H + H(2) reaction, linearly coupled to a harmonic oscillator. Results are presented for a broad range of parameters for temperatures between 140 and 300 K. It is found that the mixed-Q/C method gives fairly accurate results as long as the reaction does not involve too many recrossings. This suggests that the methodology could be extended to treat direct polyatomic reactions in gas phase.

  19. Stress Distributions and Calving Rates at Antarctic Ice Shelves

    NASA Astrophysics Data System (ADS)

    Christmann, Julia; Müller, Ralf; Humbert, Angelika; Rückamp, Martin

    2014-05-01

    Ice shelves are the floating ice masses from which icebergs are calving off. The calving of large tabular icebergs are singular events and occur on timescales of years to decades. However small scale calving happens on more continuous periods and contribute to the mass balance of an ice shelf. For a better understanding of the influence of environmental parameters on calving mechanisms, a fracture mechanical approach examines the nature and frequency of calving events. The ice shelf is modeled as a two, respectively three, dimensional rectangular body loaded by gravity and water pressure. There are two responses of ice to load: on long time scales ice reacts like a viscous fluid, and on short time scale like an elastic solid. In this study only the small scale calving events are analyzed, which usually occur on a rather short time scale. The finite element software COMSOL is used to compute the deformations and stresses, where in a first approach a linear elastic analysis is performed. The stresses in the vicinity of the calving front are evaluated to estimate the position of a calving event. This leads to a bell shaped distribution of stresses on the surface and the location of the maximum tensile stress, which denotes the most likely position for a calving event, is located at the surface. The distance of the maximum stress at the surface is verified with a model of an elastically supported beam, loaded by a bending moment instead of the water pressure at the ice front. Directly after a calving event the ice front is nearly vertical. After a certain time interval the exposure, due to waves and water flow, leads to an ice front, which is shaped like an under-water "nose". Therefore, the geometry is slightly modified and the added belly at the ice shelf front is modelled as half of an ellipse, where bouyancy forces affect this boundary. A crack originates, if the tensile stress at some point exceeds a critical stress bound. The analysis of calving with a rate

  20. Collagen proteins in electrorefining: Rate constants for glue hydrolysis and effects of molar mass on glue activity

    NASA Astrophysics Data System (ADS)

    Saban, M. D.; Scott, J. D.; Cassidy, R. M.

    1992-03-01

    Animal glue (collagen proteins) degradation was studied in water and in a simulated copper electrolyte (150 g/L H2SO4, 46 g/L Cu2+ as CuSO4) by size-exclusion chromatography. The rate of degradation was relatively slow in pure aqueous solutions, and depending on the temperature and glue concentration, some association to larger molar mass species was observed. For simulated electrolyte in a temperature range of 42 °C to 70 °C and a glue concentration range of 100 to 3000 mg/L, the degradation rate constant was described with the following relation: k' = 1.5· 107exp (-9951 /T), min-1 The degradation rate was zero order with respect to initial concentration of the protein and first order with respect to acid concentration. The results show that glue degradation under normal tankhouse operation should be rapid, with degradation to number-average molar mass (M n ) < 10,000 units occurring in about 40 to 80 minutes depending on the mass transfer rate (or mixing) of the electrolyte solution. Samples of glue from three different sources showed almost no difference in degradation rates. Results calculated from the rate equation for glue degradation have been correlated with cathode polarization data from the literature, and the results suggest that critical glue M n below which the glue loses most of its activity is 3700.