Science.gov

Sample records for absorption rate constants

  1. 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.

  2. Determination of the magnetocrystalline anisotropy constant from the frequency dependence of the specific absorption rate in a frozen ferrofluid

    NASA Astrophysics Data System (ADS)

    Mosher, Nathaniel; Perkins-Harbin, Emily; Aho, Brandon; Wang, Lihua; Kumon, Ronald; Rablau, Corneliu; Vaishnava, Prem; Tackett, Ronald; Therapeutic Biomaterials Group Team

    2015-03-01

    Colloidal suspensions of superparamagnetic nanoparticles, known as ferrofluids, are promising candidates for the mediation of magnetic fluid hyperthermia (MFH). In such materials, the dissipation of heat occurs as a result of the relaxation of the particles in an applied ac magnetic field via the Brownian and Neel mechanisms. In order to isolate and study the role of the Neel mechanism in this process, the sample can be frozen, using liquid nitrogen, in order to suppress the Brownian relaxation. In this experiment, dextran-coated Fe3O4 nanoparticles synthesized via co-precipitation and characterized via transmission electron microscopy and dc magnetization are used as MFH mediators over the temperature range between -70 °C to -10 °C (Brownian-suppressed state). Heating the nanoparticles using ac magnetic field (amplitude ~300 Oe), the frequency dependence of the specific absorption rate (SAR) is calculated between 150 kHz and 350 kHz and used to determine the magnetocrystalline anisotropy of the sample. We would like to thank Fluxtrol, Inc. for their help with this project

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

    PubMed

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

    2016-07-21

    We report an improved measurement for the rate constant of methane dissociation in argon (CH4 + Ar = CH3 + H + Ar) behind reflected shock waves. The experiment was conducted using a sub-parts per million sensitivity CH3 diagnostic recently developed in our laboratory based on ultraviolet cavity-enhanced absorption spectroscopy. The high sensitivity of this diagnostic allowed for measurements of quantitatively resolved CH3 time histories during the initial stage of CH4 pyrolysis, where the reaction system is clean and free from influences of secondary reactions and temperature change. This high sensitivity also allowed extension of our measurement range to much lower temperatures (<1500 K). The current-reflected shock measurements were performed at temperatures between 1487 and 1866 K and pressures near 1.7 atm, resulting in the following Arrhenius rate constant expression for the title reaction: k(1.7 atm) = 3.7 × 10(16) exp(-42 200 K/T) cm(3)/mol·s, with a 2σ uncertainty factor of 1.25. The current data are in good consensus with various theoretical and review studies, but at the low temperature end they suggest a slightly higher (up to 35%) rate constant compared to these previous results. A re-evaluation of previous and current experimental data in the falloff region was also performed, yielding updated expressions for both the low-pressure limit and the high-pressure limit rate constants and improved agreement with all existing data. PMID:27380878

  4. Photochemical parameters of atmospheric source gases: accurate determination of OH reaction rate constants over atmospheric temperatures, UV and IR absorption spectra

    NASA Astrophysics Data System (ADS)

    Orkin, V. L.; Khamaganov, V. G.; Martynova, L. E.; Kurylo, M. J.

    2012-12-01

    instrumental uncertainties related to our FP-RF experiment proves a total uncertainty of the OH reaction rate constant to be as small as ca. 2-3%. The high precision of kinetic measurements allows reliable determination of weak temperature dependences of the rate constants and clear resolution of the curvature of the Arrhenius plots for the OH reaction rate constants of various compounds. The results of OH reaction rate constant determinations between 220 K and 370 K will be presented. Similarly, the accuracy of UV and IR absorption measurements will be highlighted to provide an improved basis for atmospheric modeling.

  5. Population Pharmacokinetics of Oral Topotecan in Infants and Very Young Children with Brain Tumors Demonstrates a Role of ABCG2 rs4148157 on the Absorption Rate Constant.

    PubMed

    Roberts, Jessica K; Birg, Anna V; Lin, Tong; Daryani, Vinay M; Panetta, John C; Broniscer, Alberto; Robinson, Giles W; Gajjar, Amar J; Stewart, Clinton F

    2016-07-01

    For infants and very young children with brain tumors, chemotherapy after surgical resection is the main treatment due to neurologic and neuroendocrine adverse effects from whole brain irradiation. Topotecan, an anticancer drug with antitumor activity against pediatric brain tumors, can be given intravenous or orally. However, high interpatient variability in oral drug bioavailability is common in children less than 3 years old. Therefore, this study aimed to determine the population pharmacokinetics of oral topotecan in infants and very young children, specifically evaluating the effects of age and ABCG2 and ABCB1 on the absorption rate constant (Ka), as well as other covariate effects on all pharmacokinetic parameters. A nonlinear mixed effects model was implemented in Monolix 4.3.2 (Lixoft, Orsay, France). A one-compartment model with first-order input and first-order elimination was found to adequately characterize topotecan lactone concentrations with population estimates as [mean (S.E.)]; Ka = 0.61 (0.11) h(-1), apparent volume of distribution (V/F) = 40.2 (7.0) l, and apparent clearance (CL/F) = 40.0 (2.9) l/h. After including the body surface area in the V/F and CL/F as a power model centered on the population median, the ABCG2 rs4148157 allele was found to play a significant role in the value of Ka Patients homozygous or heterozygous for G>A demonstrated a Ka value 2-fold higher than their GG counterparts, complemented with a 2-fold higher maximal concentration as well. These results demonstrate a possible role for the ABCG2 rs4148157 allele in the pharmacokinetics of oral topotecan in infants and very young children, and warrants further investigation. PMID:27052877

  6. Monomeric C-phycocyanin at room temperature and 77 K. Resolution of the absorption and fluorescence spectra of the individual chromophores and the energy-transfer rate constants

    SciTech Connect

    Debreczeny, M.P.; Sauer, K. Univ. of California, Berkeley, CA ); Zhou, J.; Bryant, D.A. )

    1993-09-23

    At both room temperature (RT) and 77 K, the absorption and fluorescence spectra of the three individual chromophore types ([alpha][sub 84], [beta][sub 84], and [beta][sub 155]) found in monomeric C-phycocyanin ([alpha][sup PC][beta][sup PC]), isolated from the cyanobacterium Synechococcus sp. PCC 7002, were resolved along with the rates of energy transfer between the chromophores. The cpcB/C155S mutant, whose PC is missing the [beta][sub 155] chromophore, was useful in effecting this resolution. At RT, the single broad peak in the visible region of the absorption spectrum of ([alpha][sup PC][beta][sup PC]) was resolved into its three-component spectra by comparing the steady-state absorption spectra of the isolated wild-type [alpha] subunit of PC ([alpha][sup PC]) (containing only the [alpha][sub 84] chromophore) with those of the monomeric PCs isolated from the mutant strain ([alpha][sup PC][beta]*) and the wild-type strain ([alpha][sup PC][beta][sup PC]). At 77 K, the visible region of the absorption spectrum of ([alpha][sup PC][beta][sup PC]) splits into two peaks. This partial resolution at 77 K of the chromophore spectra of ([alpha][sup PC][beta][sup PC]) when compared with the 77 K absorption spectra of [alpha][sup PC], [beta][sup PC], and ([alpha][sup PC][beta]*) provided a confirmation of our RT assignments of the chromophore absorption spectra. 38 refs., 9 figs., 6 tabs.

  7. Air kerma rate constants for radionuclides.

    PubMed

    Wasserman, H; Groenewald, W

    1988-01-01

    Conversion to SI units requires that the exposure rate constant which was usually quoted in R.h-1.mCi-1.cm2 be replaced by the air kerma rate constant with units m2.Gy.Bq-1.s-1. The conversion factor is derived and air kerma rate constants for 30 radionuclides used in nuclear medicine and brachytherapy are listed. A table for calculation of air kerma rates for other radionuclides is also given. To calculate absorbed dose to tissue, the air kerma rate has to be multiplied by approximately 1.1. A dose equivalent rate constant is thus listed which allows direct calculation of dose equivalent rate to soft tissue without resorting to exposure rate constants tabulated in the special units R.m2.mCi-1.h-1 which should no longer be used. PMID:3208786

  8. Photochemical properties of trans-1-chloro-3,3,3-trifluoropropene (trans-CHCl═CHCF3): OH reaction rate constant, UV and IR absorption spectra, global warming potential, and ozone depletion potential.

    PubMed

    Orkin, Vladimir L; Martynova, Larissa E; Kurylo, Michael J

    2014-07-17

    Measurements of the rate constant for the gas-phase reactions of OH radicals with trans-1-chloro-3,3,3-trifluoropropene (trans-CHCl═CHCF3) were performed using a flash photolysis resonance-fluorescence technique over the temperature range 220-370 K. The reaction rate constant exhibits a noticeable curvature of the temperature dependence in the Arrhenius plot, which can be represented by the following expression: kt-CFP (220-370 K) = 1.025 × 10(-13) × (T/298)(2.29) exp(+384/T) cm(3 )molecule(-1) s(-1). The room-temperature rate constant was determined to be kt-CFP (298 K) = (3.29 ± 0.10) × 10(-13) cm(3) molecule(-1) s(-1), where the uncertainty includes both two standard errors (statistical) and the estimated systematic error. For atmospheric modeling purposes, the rate constant below room temperature can be represented by the following expression: kt-CFP (220-298 K) = (7.20 ± 0.46) × 10(-13) exp[-(237 ± 16)/T] cm(3) molecule(-1) s(-1). There was no difference observed between the rate constants determined at 4 kPa (30 Torr) and 40 kPa (300 Torr) at both 298 and 370 K. The UV and IR absorption cross sections of this compound were measured at room temperature. The atmospheric lifetime, global warming potential, and ozone depletion potential of trans-CHCl═CHCF3 were estimated. PMID:24955760

  9. Determination of the rate constants of molecular processes regulating the level of induced absorption in a laser based on an aqueous-micellar solution of rhodamine 6G with lamp pumping

    SciTech Connect

    Levin, M.B.; Snegov, M.I.; Cherkasov, A.S.

    1987-03-01

    A method of determining the average lifetime tau of the products responsible for inverse induced absorption in aqueous--micellar solutions of rhodamine 6G (R6G) on lamp pumping based on a comparison of threshold intensities of excitation (W/sub th/) in the resonators of a laser with a different Q is proposed. Using the value of tau found (0.2 ..mu..sec) and experimental data on the change in W/sub th/ with the concentration of cyclooctatetraene (COT) added to the solution the rate constant of quenching of the absorbing products by COT molecules (K/sub q/ = 2.6 x 10/sup 7/ M/sup -1/sec/sup -1/) was determined. In the assumption that the absorbing products are triplet dye molecules, the value of the rate constant of interconversion (K/sub 32/) of R6G into an aqueous--micellar solution (K/sub 32/ = 1.3 x 10/sup 7/ sec/sup -1/) was determined. A comparison was made of the values of the constants found with the corresponding values known from the literature.

  10. 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)

  11. 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.

  12. Double well isomerization rate constants in solution

    NASA Astrophysics Data System (ADS)

    Zawadzki, Anthony G.; Hynes, James T.

    1985-02-01

    The rate constant k for a double well isomerization in solution is calculated over the entire friction range. The importance of frequency-dependent friction for both the vibrational energy transfer (VET) and barrier passage components of k is described. Rapid suppression of the VET transfer component with increasing degrees of freedom is discussed.

  13. 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

  14. Fluorodeoxyglucose rate constants, lumped constant, and glucose metabolic rate in rabbit heart

    SciTech Connect

    Krivokapich, J.; Huang, S.C.; Selin, C.E.; Phelps, M.E.

    1987-04-01

    The isolated arterial perfused rabbit interventricular septum was used to measure myocardial metabolic rate for glucose (MMRGlc) and rate constants and lumped constant (LC) for the glucose analogue (/sup 18/F)fluorodeoxyglucose (FDG) using a tracer kinetic model. FDG was delivered by constant infusion during coincidence counting of tissue /sup 18/F radioactivity. The MMRGlc was measured by the Fick method. Control septa were paced at 72 beats/min and perfused at 1.5 ml/min with oxygenated perfusate containing 5.6 mM glucose and 5 mU/ml insulin. The following conditions were tested: 3.0 and 4.5 ml/min; insulin increased to 25 mU/ml; insulin omitted; 2.8 mM and 11.2 mM glucose; 144 beats/min and 96 paired stimuli/min; and anoxia. Under all conditions studied the phosphorylation (hexokinase) reaction was rate limiting relative to transport. Compared with control conditions, the phosphorylation rate constant was significantly increased with 2.8 mM glucose as well as in anoxia. With 4.5 ml/min and 11.2 mM glucose, conditions that should increase glucose flux into tissue without increasing demand, the phosphorylation rate constant decreased significantly. With 11.2 mM glucose, 96 paired stimuli/min, and anoxia without insulin, a significant increase in the hydrolysis rate of FDG 6-phosphate was observed and suggests that hydrolysis is also an important mechanism for regulating the MMRGlc. Increased transport rate constants were observed with increased flow rates, 96 paired stimuli/min, and anoxia at 96 beats/min. The LC was not significantly different from control in 11 of 14 conditions studied. Therefore, under most conditions in average LC can be used to calculate MMRGlc estimates.

  15. Theophylline: constant-rate infusion predictions.

    PubMed

    Mesquita, C A; Sahebjami, H; Imhoff, T; Thomas, J P; Myre, S A

    1984-01-01

    This study was undertaken to evaluate a method of prospectively estimating appropriate aminophylline infusion rates in acutely ill, hospitalized patients with bronchospasm. Steady-state serum theophylline concentrations (Css), clearances (Cl), and half-lives (t1/2) were estimated by the Chiou method using serum concetrantions obtained 1 and 6 h after the start of a constant-rate intravenous aminophylline infusion in 10 male patients averaging 57 years of age. Using an enzyme-multiplied immunoassay (EMIT) system for theophylline analysis, pharmacokinetic estimations were excellent for Css (r = 0.9103, p less than 0.01) and Cl (r = 0.9750, p less than 0.01). The mean estimation errors were 9.4% (range 0.8-21.5) for Css and 12.3% (range 1.3-28.0) for Cl. There was no correlation between patient age and Cl. This method is useful for rapidly individualizing aminophylline therapy in patients with acute bronchospasm. PMID:6740734

  16. Constant optimization of oral drug absorption kinetics in the compartment absorption and transit models using particle swarm optimization algorithm

    NASA Astrophysics Data System (ADS)

    Prabowo, K.; Sumaryada, T.; Kartono, A.

    2016-01-01

    Simulation of predictive modeling oral drug namely Compartment Absorption and Transit (CAT) using Particle Swarm Optimization (PSO) algorithm has been performed. This research will be carried out optimization of kinetic constant value oral drug use PSO algorithm to obtain the best global transport constant values for CAT equation that can predict drug concentration in plasma. The value of drug absorption rate constant for drug atenolol 25 mg is k10, k12, k21, k13 and k31 with each value is 0.8562, 0.3736, 0.2191, 0.4334 and 1.000 have been obtained thus raising the value of the coefficient of determination of a model CAT. From the experimental data plasma drug concentrations used are Atenolol, the coefficient of determination (R2) obtained from simulations atenolol 25 mg (PSO) was 81.72% and 99.46%. Better correlation between the dependent variable as the drug concentration and explanatory variables such as mass medication, plasma volume, and rate of absorption of the drug has increased in CAT models using PSO algorithm. Based on the results of CAT models fit charts can predict drug concentration in plasma.

  17. Influences of brain tissue poroelastic constants on intracranial pressure (ICP) during constant-rate infusion.

    PubMed

    Li, Xiaogai; von Holst, Hans; Kleiven, Svein

    2013-01-01

    A 3D finite element (FE) model has been developed to study the mean intracranial pressure (ICP) response during constant-rate infusion using linear poroelasticity. Due to the uncertainties in the poroelastic constants for brain tissue, the influence of each of the main parameters on the transient ICP infusion curve was studied. As a prerequisite for transient analysis, steady-state simulations were performed first. The simulated steady-state pressure distribution in the brain tissue for a normal cerebrospinal fluid (CSF) circulation system showed good correlation with experiments from the literature. Furthermore, steady-state ICP closely followed the infusion experiments at different infusion rates. The verified steady-state models then served as a baseline for the subsequent transient models. For transient analysis, the simulated ICP shows a similar tendency to that found in the experiments, however, different values of the poroelastic constants have a significant effect on the infusion curve. The influence of the main poroelastic parameters including the Biot coefficient α, Skempton coefficient B, drained Young's modulus E, Poisson's ratio ν, permeability κ, CSF absorption conductance C(b) and external venous pressure p(b) was studied to investigate the influence on the pressure response. It was found that the value of the specific storage term S(ε) is the dominant factor that influences the infusion curve, and the drained Young's modulus E was identified as the dominant parameter second to S(ε). Based on the simulated infusion curves from the FE model, artificial neural network (ANN) was used to find an optimised parameter set that best fit the experimental curve. The infusion curves from both the FE simulation and using ANN confirmed the limitation of linear poroelasticity in modelling the transient constant-rate infusion. PMID:22452461

  18. 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.

  19. Quenching rate constants of excited halogen atoms in quartet states

    NASA Astrophysics Data System (ADS)

    Mizuta, K.; Kuramasu, T.; Ishikawa, Y.; Arai, S.

    1994-04-01

    Excited halogen atoms in quartet spin states F*(2p43s, 4P5/2), Cl*(3p44s, 4P5/2), and Br*(4p45s, 4P5/2) were produced from helium sensitized radiation chemical decomposition of SF6, CF3Cl, CF3Br, and CF2Br2. Quenching rate constants of these excited halogen atoms by simple gas molecules such as O2, N2, H2, CO, CO2, NO, NO2, N2O, CH4, C2H6, and Xe including parent molecules were determined from absorption decay curves at 685.8 nm for F*, 837.5 nm for Cl*, and 827.4 nm for Br*. The optical densities were assumed to be proportional to (number of excited atoms per one cubic centimeter)0.9. The quenching rate constants obtained here were compared to those reported of metastable rare-gas atoms and an excited oxygen atom O*(2p33s, 5S2), and further discussed in terms of several theoretical kinetic models.

  20. 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.

  1. Biased Brownian dynamics for rate constant calculation.

    PubMed

    Zou, G; Skeel, R D; Subramaniam, S

    2000-08-01

    An enhanced sampling method-biased Brownian dynamics-is developed for the calculation of diffusion-limited biomolecular association reaction rates with high energy or entropy barriers. Biased Brownian dynamics introduces a biasing force in addition to the electrostatic force between the reactants, and it associates a probability weight with each trajectory. A simulation loses weight when movement is along the biasing force and gains weight when movement is against the biasing force. The sampling of trajectories is then biased, but the sampling is unbiased when the trajectory outcomes are multiplied by their weights. With a suitable choice of the biasing force, more reacted trajectories are sampled. As a consequence, the variance of the estimate is reduced. In our test case, biased Brownian dynamics gives a sevenfold improvement in central processing unit (CPU) time with the choice of a simple centripetal biasing force. PMID:10919998

  2. 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...

  3. 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...

  4. Dose rate constant and energy spectrum of interstitial brachytherapy sources.

    PubMed

    Chen, Z; Nath, R

    2001-01-01

    In the past two years, several new manufacturers have begun to market low-energy interstitial brachytherapy seeds containing 125I and 103Pd. Parallel to this development, the National Institute of Standards and Technology (NIST) has implemented a modification to the air-kerma strength (S(K)) standard for 125I seeds and has also established an S(K) standard for 103Pd seeds. These events have generated a considerable number of investigations on the determination of the dose rate constants (inverted V) of interstitial brachytherapy seeds. The aim of this work is to study the general properties underlying the determination of dose rate constant and to develop a simple method for a quick and accurate estimation of dose rate constant. As the dose rate constant of clinical seeds is defined at a fixed reference point, we postulated that dose rate constant may be calculated by treating the seed as an effective point source when the seed's source strength is specified in S(K) and its source characteristics are specified by the photon energy spectrum measured in air at the reference point. Using a semi-analytic approach, an analytic expression for dose rate constant was derived for point sources with known photon energy spectra. This approach enabled a systematic study of dose rate constant as a function of energy. Using the measured energy spectra, the calculated dose rate constant for 125I model 6711 and 6702 seeds and for 192Ir seed agreed with the AAPM recommended values within +/-1%. For the 103Pd model 200 seed, the agreement was 5% with a recently measured value (within the +/-7% experimental uncertainty) and was within 1% with the Monte Carlo simulations. The analytic expression for dose rate constant proposed here can be evaluated using a programmable calculator or a simple spreadsheet and it provides an efficient method for checking the measured dose rate constant for any interstitial brachytherapy seed once the energy spectrum of the seed is known. PMID:11213926

  5. 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...

  6. Subcutaneous insulin infusion: change in basal infusion rate has no immediate effect on insulin absorption rate

    SciTech Connect

    Hildebrandt, P.; Birch, K.; Jensen, B.M.; Kuehl, C.

    1986-11-01

    Eight insulin-dependent diabetic patients were simultaneously given subcutaneous infusions (1.12 IU/h each) of /sup 125/I-labeled Actrapid insulin in each side of the abdominal wall. After 24 h of infusion, the size of the infused insulin depots was measured by external counting for 5 h. The basal infusion rate was then doubled in one side and halved in the other for the next 4 h. Finally, 1.12 IU/h of insulin was given in both sides of the abdominal wall for an additional 3 h. The changes in the size of the depots were measured, and the absorption rates for each hour were calculated. During the first 5 h of infusion, the depot size was almost constant (approximately 5 IU) with an absorption rate that equaled the infusion rate. Doubling the infusion rate led to a significant increase in depot size, but the absorption rate remained unchanged for the first 3 h, and only thereafter was a significant increase seen. When the infusion rate was reduced to the initial 1.12 IU/h, the absorption rate remained elevated during the next 3 h. Correspondingly, when the infusion rate was decreased, the depot size also decreased, but the absorption rate remained unchanged for the first 3 h. The results show that a change in the basal insulin infusion rate does not lead to any immediate change in the insulin absorption rate. This should be considered when planning an insulin-infusion program that includes alteration(s) in the basal-rate setting.

  7. Rate constant for the reaction of atomic chlorine with methane

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

    The rate constant and temperature dependence of the Cl + CH4 reaction have been investigated by the techniques of competitive chlorination of CH4/C2H6 mixtures and by discharge-flow/mass spectroscopy. The objectives were to determine an accurate value for the rate constant for use in stratospheric modeling, and to clarify discrepancies in results previously obtained by different techniques. The results deduced from the competitive chlorination study are in good agreement with the absolute values measured by the mass spectrometric method, and at temperatures above 300 K are in good agreement with measurements by other techniques based on resonance fluorescence detection of atomic chlorine. However, in the 220-300 K region, the competitive experiments indicate lower rate constants than those obtained by resonance fluorescence methods, and do not reproduce the curved Arrhenius plots seen in some of those studies.

  8. Dissociation rate constant of the biotin-streptavidin complex.

    PubMed

    Piran, U; Riordan, W J

    1990-10-01

    We measured the dissociation rate constants of the biotin/streptavidin and biotin/egg avidin complexes by following the release of radiolabeled biotin from the preformed complexes in the presence of excess unlabeled biotin. For separation of bound and free labeled biotin we employed ultrafiltration with disposable microconcentrators. The dissociation rate constant for underivatized streptavidin was 2.4 x 10(-6) s-1, or approximately 30-fold higher than that observed for egg avidin 7.5 x 10(-8) s-1). The value for streptavidin was further increased after derivatization with an acridinium ester label. Both biotin binding proteins exhibited a faster initial phase, suggesting binding site heterogeneity due to partial subunit dissociation or denaturation. The convenience of the method and the relatively fast dissociation of biotin from streptavidin render the dissociation rate constant a practical experimental criterion for monitoring the integrity of the binding site during purification and derivatization procedures. PMID:2212686

  9. Measurements of the rate constant of HOsub2 + NOsub2 + Nsub2 --> HOsub2NOsub2 + Nsub2 using near-infrared wavelength-modulation spectroscopy and UV-visible absorption spectroscopy

    NASA Technical Reports Server (NTRS)

    Christensen, L. E.; Okumura, M.; Sander, S. P.; Friedl, R. R.; Miller, C. E.; Sloan, J. J.

    2004-01-01

    Rate coefficients for the reaction HO(sub 2)+ NO(sub 2) + N(sub 2) --> HO(sub 2)NO(sub 2) + N(sub 2) (reaction 1) were measured using simultaneous near-IR and UV spectroscopy from 220 to 298 K and from 45 to 200 Torr.

  10. 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.

  11. 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.

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

    PubMed

    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. PMID:25789937

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

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... groundwater availability analysis to determine the availability of water during a 1-in-10-year recurrence... 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...

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

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... groundwater availability analysis to determine the availability of water during a 1-in-10-year recurrence... 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...

  15. 18 CFR 806.12 - Constant-rate aquifer testing.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... groundwater availability analysis to determine the availability of water during a 1-in-10-year recurrence... 18 Conservation of Power and Water Resources 2 2010-04-01 2010-04-01 false Constant-rate aquifer testing. 806.12 Section 806.12 Conservation of Power and Water Resources SUSQUEHANNA RIVER...

  16. 18 CFR 806.12 - Constant-rate aquifer testing.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... groundwater availability analysis to determine the availability of water during a 1-in-10-year recurrence... 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...

  17. 18 CFR 806.12 - Constant-rate aquifer testing.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... groundwater availability analysis to determine the availability of water during a 1-in-10-year recurrence... 18 Conservation of Power and Water Resources 2 2011-04-01 2011-04-01 false Constant-rate aquifer testing. 806.12 Section 806.12 Conservation of Power and Water Resources SUSQUEHANNA RIVER...

  18. 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. PMID:27329206

  19. 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…

  20. 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.

  1. 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.

  2. 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.

  3. Iodine induced SCC of Zr alloys at constant strain rate

    NASA Astrophysics Data System (ADS)

    Goryachev, S. B.; Gritsuk, A. R.; Prasolov, F. F.; Snegirev, M. G.; Shestak, V. E.; Novikov, V. V.; Bibilashvili, Yu. K.

    1992-12-01

    Stress corrosion cracking of Zr and its alloys Zry-4, Zry-2 and Zr-1% Nb has been studied in flowing iodine vapour at a constant strain rate. The tests were performed using flat samples of Zr and its alloy claddings as well as Zr coated Zr-1% Nb claddings. Zr-1% Nb is shown to be more resistant to SCC as compared to Zry-4 and Zry-2. No corrosion induced failure of Zr or Zr-coated Zr-1% Nb claddings has been actually observed. The influence of strain rate, temperature and iodine partial pressure on SCC has been studied for Zr-1% Nb.

  4. Towards a spatially and temporally constant Karakorum fault slip rate

    NASA Astrophysics Data System (ADS)

    Chevalier, M.; van der Woerd, J.; Tapponnier, P.; Li, H.; Ryerson, F. J.; Finkel, R. C.

    2012-12-01

    Constraining the Karakorum fault (KF) slip-rate is essential to understand the present-day kinematic role of large strike-slip faults in the deformation of Tibet. The range of geodetic and geologic slip-rates is ~0 - 11 mm/yr. Cumulative offsets of alluvial fans and terrace risers ranging from 38 to 220 m add new quantitative information on its late Quaternary slip-rate. Their ages were determined using 10Be surface-exposure dating of 74 samples collected at 3 alluvial sites along the Bangong - Chaxikang and Gar basin segments, southeast of Bangong Lake. The slip-rate during the 0 - 60 ka period is 2.9(+1.0/-0.6) mm/yr at GUN, >5.3(+4.3/-1.7) mm/yr at CK and >5.3(+3.1/-2.3) mm/yr at GF. These rates are in agreement with those determined to the southeast (>5.5±0.5 mm/yr at Manikala on one strand for the same period, Chevalier et al., 2005a,b; 7.1(+3.2/-1.7) mm/yr at Menshi and 7.9(+3.2/-2.5) mm/yr near Kailas across two strands, Chevalier et al., 2012) and to the northwest (4±1 mm/yr at Tangste, Brown et al., 2002; >5 mm/yr at Muji, Chevalier et al., 2011b, both on one strand, during the Holocene). We suggest that the minimum late Quaternary slip-rate along the entire length of the KF may be relatively constant along-strike at >5 mm/yr on one fault branch or >7 mm/yr across two branches. In addition to being spatially constant, this late Quaternary rate appears to be, within error, in agreement with most studies at various timescales and suggests that at first approximation, no major discrepancy exists between geodetic and geologic rates.

  5. Why Not a Constant Early Lunar Impact Rate?

    NASA Technical Reports Server (NTRS)

    Wilhelms, D. E.

    1985-01-01

    Two distinct episodes of impacting are recorded on the Moon's surface. An early episode marked by an intense barrage that included basin-forming projectiles ended about 3.8 aeons ago when the Orientale basin was created. The second episode, after 3.2 or 3.3 aeons ago, was marked by a much lower impact rate. These very different rates are separated by a short transition period during the Late Imbrian Epoch. It is found that a constant preImbrian impact rate is consistent with all the relevant observations and with the following lunar historical scenario: (1) crustal solidification between about 4.3 and 4.25 aeons ago; (2) formation of Procellarum, South Pole-Aitken, about 22 now-obliterated basins, and about 2,850 now-obliterated 30 to 300 km craters between 4.25 and 4.1 aeons ago; and (3) formation of 39 still-preserved basins, 1,200 still-perserved craters, and 2,200 now-obliterated craters between 4.1 and 3.85 aeons ago. At the constant rate, the amount of mass that impacted the Moon since crustal solidification would not greatly exceed the amount that has left a permanent visible record.

  6. 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.

  7. 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. PMID:26580187

  8. Phototransformation Rate Constants of PAHs Associated with Soot Particles

    PubMed Central

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

    2013-01-01

    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 (k0p), the effective diffusion coefficients (Deff), and the light penetration depths (z0.5) 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 z0.5 is more sensitive to the soot layer thickness than the k0p value. As the thickness of the soot layer increases, the z0.5 values increase, but the k0p 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 k0p and z0.5 in thinner layers, Deff 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. PMID:23247292

  9. Balanced anesthesia and constant-rate infusions in horses.

    PubMed

    Valverde, Alexander

    2013-04-01

    Balanced anesthetic techniques are commonly used in equine patients, and include the combination of a volatile anesthetic with at least one injectable anesthetic throughout the maintenance period. Injectable anesthetics used in balanced anesthesia include the α2-agonists, lidocaine, ketamine, and opioids, and those with muscle-relaxant properties such as benzodiazepines and guaifenesin. Administration of these injectable anesthetics is best using constant-rate infusions based on the pharmacokinetics of the drug, which allows steady-state concentrations and predictable pharmacodynamic actions. This review summarizes the different drug combinations used in horses, and provides calculated recommended doses based on the pharmacokinetics of individual drugs. PMID:23498047

  10. 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. PMID:16897812

  11. 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): PMID:24817270

  12. Influence of Circulation System on Estimation of Absorption and Elimination Constant after per oral Drug Administration: A Reanalysis.

    PubMed

    Rausova, Z; Chrenova, J; Dedik, L

    2013-03-01

    This study aimed to identify the cause of atypical shape of measured concentration-time profile in the peak area by one compartment open model with a lag time (Bateman function with a lag) after single dose oral administration of drug published in "Pharmacokinetic and Pharmacodynamic Data Analysis: Concepts and Application" by Gabrielsson and Weiner (1997) and two concentration profiles after frequent sampling oral glucose tolerance test. Following the oral administration of 100 μg of substance A to human volunteer, frequent sampling was carried out and concentration-time profiles were obtained. Our hemodynamic circulatory structural model capable of parameters estimation of circulation and gastrointestinal subsystem to explain the plateau within the interval 40-100 min (substance A) and 15-30 min (glucose) of the measured concentration-time profile was developed. The mean residence time, the rate constants of absorption and elimination parameters of our model were calculated. Comparing to the Bateman function, our results demonstrate better approximation of the substance A and glucose concentration-time profile and estimation of absorption rate constant by our structural model. Obtained model results indicate that the atypical shape of measured concentration-time profile of single dose oral administration of drug was probably caused by the gastrointestinal and circulation system with deep compartment. This applies to the substances with high coefficient of absorption. PMID:24019565

  13. The air-kerma rate constant of 192Ir.

    PubMed

    Ninković, M M; Raiĉevìć, J J

    1993-01-01

    The air-kerma rate constant gamma delta (and its precursors), as one of the basic radiation characteristics of 192Ir, was determined by many authors. Analysis of accessible data on this quantity led us to the conclusion that published data strongly disagree. That is the reason we calculated this quantity on the basis of our and many other authors' gamma-ray spectral data and the latest data for mass energy-transfer coefficients for air. In this way, a value was obtained for gamma delta of 30.0 +/- 0.9 a Gy m2 s-1 Bq-1 for an unshielded 192Ir source and 27.8 +/- 0.9 a Gy m2s -1Bq-1 for a standard packaged radioactive source taking into account attenuation of gamma rays in the platinum source wall. PMID:8416220

  14. Prediction of Rate Constant for Supramolecular Systems with Multiconfigurations.

    PubMed

    Guo, Tao; Li, Haiyan; Wu, Li; Guo, Zhen; Yin, Xianzhen; Wang, Caifen; Sun, Lixin; Shao, Qun; Gu, Jingkai; York, Peter; Zhang, Jiwen

    2016-02-25

    The control of supramolecular systems requires a thorough understanding of their dynamics, especially on a molecular level. It is extremely difficult to determine the thermokinetic parameters of supramolecular systems, such as drug-cyclodextrin complexes with fast association/dissociation processes by experimental techniques. In this paper, molecular modeling combined with novel mathematical relationships integrating the thermodynamic/thermokinetic parameters of a series of isomeric multiconfigurations to predict the overall parameters in a range of pH values have been employed to study supramolecular dynamics at the molecular level. A suitable form of Eyring's equation was derived and a two-stage model was introduced. The new approach enabled accurate prediction of the apparent dissociation/association (koff/kon) and unbinding/binding (k-r/kr) rate constants of the ubiquitous multiconfiguration complexes of the supramolecular system. The pyronine Y (PY) was used as a model system for the validation of the presented method. Interestingly, the predicted koff value ((40 ± 1) × 10(5) s(-1), 298 K) of PY is largely in agreement with that previously determined by fluorescence correlation spectroscopy ((5 ± 3) × 10(5) s(-1), 298 K). Moreover, the koff/kon and k-r/kr for flurbiprofen-β-cylcodextrin and ibuprofen-β-cyclodextrin systems were also predicted and suggested that the association processes are diffusion-controlled. The methodology is considered to be especially useful in the design and selection of excipients for a supramolecular system with preferred association and dissociation rate constants and understanding their mechanisms. It is believed that this new approach could be applicable to a wide range of ligand-receptor supramolecular systems and will surely help in understanding their complex mechanism. PMID:26840799

  15. A new analysis of fine-structure constant measurements and modelling errors from quasar absorption lines

    NASA Astrophysics Data System (ADS)

    Wilczynska, Michael R.; Webb, John K.; King, Julian A.; Murphy, Michael T.; Bainbridge, Matthew B.; Flambaum, Victor V.

    2015-12-01

    We present an analysis of 23 absorption systems along the lines of sight towards 18 quasars in the redshift range of 0.4 ≤ zabs ≤ 2.3 observed on the Very Large Telescope (VLT) using the Ultraviolet and Visual Echelle Spectrograph (UVES). Considering both statistical and systematic error contributions we find a robust estimate of the weighted mean deviation of the fine-structure constant from its current, laboratory value of Δα/α = (0.22 ± 0.23) × 10-5, consistent with the dipole variation reported in Webb et al. and King et al. This paper also examines modelling methodologies and systematic effects. In particular, we focus on the consequences of fitting quasar absorption systems with too few absorbing components and of selectively fitting only the stronger components in an absorption complex. We show that using insufficient continuum regions around an absorption complex causes a significant increase in the scatter of a sample of Δα/α measurements, thus unnecessarily reducing the overall precision. We further show that fitting absorption systems with too few velocity components also results in a significant increase in the scatter of Δα/α measurements, and in addition causes Δα/α error estimates to be systematically underestimated. These results thus identify some of the potential pitfalls in analysis techniques and provide a guide for future analyses.

  16. Optical constants and transient absorption of solution-deposited RuO2 thin films

    NASA Astrophysics Data System (ADS)

    Owrutsky, Jeffrey; Compton, Ryan; Long, James; Chrevin, Christopher; Bussmann, Konrad; Dunkelberger, Adam; Spann, Bryan; Palin, Irina; Rolison, Debra; Cunningham, Paul; Melinger, Joseph; Desario, Paul; Weidinger, Dan; Heilweil, Edwin

    2015-03-01

    Optical and electrical conductivity properties are determined for the promising, broadband transparent conductor material, solution-deposited RuO2 nanostructured films. The 10-30 nm thick films or nanoskins are less conductive but more optically transmissive than polycrystalline, sputtered RuO2 films which are inherently metallic. The optical constants (0.6 to 4.5 eV) determined by ellipsometry show that ɛ1 is positive for the nanoskins in the spectral region investigated so they are not plasmonic. Transient picosecond absorption with visible (400 nm) pump and various probe wavelengths (visible and THz) are performed for nanoskins calcined to different temperatures. When heated to 200°C the absorption increases in the visible and THz. After heating to 300°C, the films become more polycrystalline and there is evidence for the appearance of a new absorption. Deceased absorptions or bleaches are observed in the THz and for longer visible wavelengths (> 750 nm). The absorption is ascribed to a damped plasmon band of the crystalline nanoparticles formed in the film upon heating.

  17. 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. PMID:26305192

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

    PubMed Central

    Selvam, T. Palani; Shrivastava, Vandana; Chourasiya, Ghanashyam; Babu, D. Appala Raju

    2014-01-01

    Absorbed dose rate to water at 0.2 cm and 1 cm due to a point isotropic photon source as a function of photon energy is calculated using the EDKnrc user-code of the EGSnrc Monte Carlo system. This code system utilized widely used XCOM photon cross-section dataset for the calculation of absorbed dose to water. Using the above dose rates, dose rate constants are calculated. Air-kerma strength Sk needed for deriving dose rate constant is based on the mass-energy absorption coefficient compilations of Hubbell and Seltzer published in the year 1995. A comparison of absorbed dose rates in water at the above distances to the published values reflects the differences in photon cross-section dataset in the low-energy region (difference is up to 2% in dose rate values at 1 cm in the energy range 30–50 keV and up to 4% at 0.2 cm at 30 keV). A maximum difference of about 8% is observed in the dose rate value at 0.2 cm at 1.75 MeV when compared to the published value. Sk calculations based on the compilation of Hubbell and Seltzer show a difference of up to 2.5% in the low-energy region (20–50 keV) when compared to the published values. The deviations observed in the values of dose rate and Sk affect the values of dose rate constants up to 3%. PMID:24600166

  19. Emulsification in turbulent flow 2. Breakage rate constants.

    PubMed

    Vankova, Nina; Tcholakova, Slavka; Denkov, Nikolai D; Vulchev, Vassil D; Danner, Thomas

    2007-09-15

    Systematic experimental study of the effects of several factors on the breakage rate constant, k(BR), during emulsification in turbulent flow is performed. These factors are the drop size, interfacial tension, viscosity of the oil phase, and rate of energy dissipation in the flow. As starting oil-water premixes we use emulsions containing monodisperse oil drops, which have been generated by the method of membrane emulsification. By passing these premixes through a narrow-gap homogenizer, working in turbulent regime of emulsification, we study the evolution of the number concentration of the drops with given diameter, as a function of the emulsification time. The experimental data are analyzed by a kinetic scheme, which takes into account the generation of drops of a given size (as a result of breakage of larger drops) and their disappearance (as a result of their own breakage process). The experimental results for k(BR) are compared with theoretical expressions from the literature and their modifications. The results for all systems could be described reasonably well by an explicit expression, which is a product of: (a) the frequency of collisions between drops and turbulent eddies of similar size, and (b) the efficiency of drop breakage, which depends on the energy required for drop deformation. The drop deformation energy contains two contributions, originating from the drop surface extension and from the viscous dissipation inside the breaking drop. In the related subsequent paper, the size distribution of the daughter drops formed in the process of drop breakage is analyzed for the same experimental systems. PMID:17553511

  20. Primary Gas Thermometry by Means of Laser-Absorption Spectroscopy: Determination of the Boltzmann Constant

    SciTech Connect

    Casa, G.; Castrillo, A.; Galzerano, G.; Wehr, R.; Merlone, A.; Di Serafino, D.; Laporta, P.; Gianfrani, L.

    2008-05-23

    We report on a new optical implementation of primary gas thermometry based on laser-absorption spectrometry in the near infrared. The method consists in retrieving the Doppler broadening from highly accurate observations of the line shape of the R(12) {nu}{sub 1}+2{nu}{sub 2}{sup 0}+{nu}{sub 3} transition in CO{sub 2} gas at thermodynamic equilibrium. Doppler width measurements as a function of gas temperature, ranging between the triple point of water and the gallium melting point, allowed for a spectroscopic determination of the Boltzmann constant with a relative accuracy of {approx}1.6x10{sup -4}.

  1. Atomic calculations and search for variation of the fine-structure constant in quasar absorption spectra

    NASA Astrophysics Data System (ADS)

    Dzuba, V. A.; Flambaum, V. V.

    A brief review of the search for variation of the fine structure constant in quasar absorption spectra is presented. Special consideration is given to the role of atomic calculations in the analysis of the observed data. A range of methods which allow to perform calculations for atoms or ions with different electron structure and which cover practically all periodic table of elements is discussed. Critical compilation of the results of the calculations as well as a review of the most recent results of the analysis are presented.

  2. 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

  3. 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

  4. Rate Constant and Temperature Dependence for the Reaction of Hydroxyl Radicals with 2-Flouropropane (FC-281ea) and Comparison with an Estimated Rate Constant

    NASA Technical Reports Server (NTRS)

    DeMore, W.; Wilson, E., Jr.

    1998-01-01

    Relative rate experiments were used to measure the rate constant and temperature dependence of the reaction of OH radicals with 2-fluoropropane (HFC-281ea), using ethane, propane, ethyl chloride as reference standards.

  5. 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.

  6. 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.

  7. 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.

  8. Constraining the variation of the fine-structure constant with observations of narrow quasar absorption lines

    SciTech Connect

    Songaila, A.; Cowie, L. L.

    2014-10-01

    The unequivocal demonstration of temporal or spatial variability in a fundamental constant of nature would be of enormous significance. Recent attempts to measure the variability of the fine-structure constant α over cosmological time, using high-resolution spectra of high-redshift quasars observed with 10 m class telescopes, have produced conflicting results. We use the many multiplet (MM) method with Mg II and Fe II lines on very high signal-to-noise, high-resolution (R = 72, 000) Keck HIRES spectra of eight narrow quasar absorption systems. We consider both systematic uncertainties in spectrograph wavelength calibration and also velocity offsets introduced by complex velocity structure in even apparently simple and weak narrow lines and analyze their effect on claimed variations in α. We find no significant change in α, Δα/α = (0.43 ± 0.34) × 10{sup –5}, in the redshift range z = 0.7-1.5, where this includes both statistical and systematic errors. We also show that the scatter in measurements of Δα/α arising from absorption line structure can be considerably larger than assigned statistical errors even for apparently simple and narrow absorption systems. We find a null result of Δα/α = (– 0.59 ± 0.55) × 10{sup –5} in a system at z = 1.7382 using lines of Cr II, Zn II, and Mn II, whereas using Cr II and Zn II lines in a system at z = 1.6614 we find a systematic velocity trend that, if interpreted as a shift in α, would correspond to Δα/α = (1.88 ± 0.47) × 10{sup –5}, where both results include both statistical and systematic errors. This latter result is almost certainly caused by varying ionic abundances in subcomponents of the line: using Mn II, Ni II, and Cr II in the analysis changes the result to Δα/α = (– 0.47 ± 0.53) × 10{sup –5}. Combining the Mg II and Fe II results with estimates based on Mn II, Ni II, and Cr II gives Δα/α = (– 0.01 ± 0.26) × 10{sup –5}. We conclude that spectroscopic measurements of

  9. Constraining the Variation of the Fine-structure Constant with Observations of Narrow Quasar Absorption Lines

    NASA Astrophysics Data System (ADS)

    Songaila, A.; Cowie, L. L.

    2014-10-01

    The unequivocal demonstration of temporal or spatial variability in a fundamental constant of nature would be of enormous significance. Recent attempts to measure the variability of the fine-structure constant α over cosmological time, using high-resolution spectra of high-redshift quasars observed with 10 m class telescopes, have produced conflicting results. We use the many multiplet (MM) method with Mg II and Fe II lines on very high signal-to-noise, high-resolution (R = 72, 000) Keck HIRES spectra of eight narrow quasar absorption systems. We consider both systematic uncertainties in spectrograph wavelength calibration and also velocity offsets introduced by complex velocity structure in even apparently simple and weak narrow lines and analyze their effect on claimed variations in α. We find no significant change in α, Δα/α = (0.43 ± 0.34) × 10-5, in the redshift range z = 0.7-1.5, where this includes both statistical and systematic errors. We also show that the scatter in measurements of Δα/α arising from absorption line structure can be considerably larger than assigned statistical errors even for apparently simple and narrow absorption systems. We find a null result of Δα/α = (- 0.59 ± 0.55) × 10-5 in a system at z = 1.7382 using lines of Cr II, Zn II, and Mn II, whereas using Cr II and Zn II lines in a system at z = 1.6614 we find a systematic velocity trend that, if interpreted as a shift in α, would correspond to Δα/α = (1.88 ± 0.47) × 10-5, where both results include both statistical and systematic errors. This latter result is almost certainly caused by varying ionic abundances in subcomponents of the line: using Mn II, Ni II, and Cr II in the analysis changes the result to Δα/α = (- 0.47 ± 0.53) × 10-5. Combining the Mg II and Fe II results with estimates based on Mn II, Ni II, and Cr II gives Δα/α = (- 0.01 ± 0.26) × 10-5. We conclude that spectroscopic measurements of quasar absorption lines are not yet capable of

  10. Atomic Transition Frequencies, Isotope Shifts, and Sensitivity to Variation of the Fine Structure Constant for Studies of Quasar Absorption Spectra

    NASA Astrophysics Data System (ADS)

    Berengut, J. C.; Dzuba, V. A.; Flambaum, V. V.; King, J. A.; Kozlov, M. G.; Murphy, M. T.; Webb, J. K.

    Theories unifying gravity with other interactions suggest spatial and temporal variation of fundamental "constants" in the Universe. A change in the fine structure constant, α = {e}2/hslash c , could be detected via shifts in the frequencies of atomic transitions in quasar absorption systems. Recent studies using 140 absorption systems from the Keck telescope and 153 from the Very Large Telescope, suggest that α varies spatially (61). That is, in one direction on the sky α seems to have been smaller at the time of absorption, while in the opposite direction it seems to have been larger.

  11. 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.

  12. 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

  13. 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.

  14. EFFECTS OF RING STRAIN ON GAS-PHASE RATE CONSTANTS. 2. OH RADICAL REACTIONS WITH CYCLOALKENES

    EPA Science Inventory

    Relative rate constants for the gas phase reactions of OH radicals with a series of cycloalkenes have been determined at 298 + or - 2 K, using methyl nitrite photolysis in air as a source of OH radicals. The data show that the rate constants for the nonconjugated cycloalkenes stu...

  15. RATE CONSTANTS FOR SOME OXIDATIONS OF S(IV) BY RADICALS IN AQUEOUS SOLUTIONS

    EPA Science Inventory

    Rate constants were measured for several radical reactions important in the autoxidation of Sulfite(IV) in atmospheric droplets. In some cases, the rate constants are significantly different than those used previously in atmospheric models. The results suggest that secondary radi...

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

    PubMed

    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. PMID:25669383

  17. 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.

  18. 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.

  19. Experimental and Estimated Rate Constants for the Reactions of Hydroxyl Radicals with Several Halocarbons

    NASA Technical Reports Server (NTRS)

    DeMore, W.B.

    1996-01-01

    Relative rate experiments are used to measure rate constants and temperature dependencies of the reactions of OH with CH3F (41), CH2FCl (31), CH2BrCl (30B1), CH2Br2 (3OB2), CHBr3 (2OB3), CF2BrCHFCl (123aBl(alpha)), and CF2ClCHCl2 (122). Rate constants for additional compounds of these types are estimated using an empirical rate constant estimation method which is based on measured rate constants for a wide range of halocarbons. The experimental data are combined with the estimated and previously reported rate constants to illustrate the effects of F, Cl, and Br substitution on OH rate constants for a series of 19 halomethanes and 25 haloethanes. Application of the estimation technique is further illustrated for some higher hydrofluorocarbons (HFCs), including CHF2CF2CF2CF2H (338pcc), CF3CHFCHFCF2CF3 (43-10mee), CF3CH2CH2CF3 (356ffa), CF3CH2CF2CH2CF3 (458mfcf), CF3CH2CHF2 (245fa), and CF3CH2CF2CH3 (365mfc). The predictions are compared with literature data for these compounds.

  20. 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...

  1. QSARS FOR PREDICTING REDUCTIVE TRANSFORMATION RATE CONSTANTS OF HALOGENATED AROMATIC HYDROCARBONS IN ANOXIC SEDIMENT SYSTEMS

    EPA Science Inventory

    Quantitative structure-activity relationships (QSARs) are developed relating initial and final pseudo-first-order disappearance rate constants of 45 halogenated aromatic hydrocarbons in anoxic sediments to four readily available molecular descriptors: the carbon-halogen bond stre...

  2. Rate constant and mechanism of the reaction between Cl and CH{sub 3}OCl at 295 K

    SciTech Connect

    Carl, S.A.; Roehl, C.M.; Moortgat, G.K.; Crowley, J.N.; Mueller, C.M. |

    1996-10-24

    The reaction between Cl atoms and CH{sub 3}OCl was investigated at 295 K in both air and N{sub 2} bath gases at total pressures between 100 and 850 Torr by the relative rate method. The rate constant of the title reaction was found to be a factor 1.07{+-}0.02 (2{sigma}) greater than that of Cl+C{sub 2}H{sub 6} at room temperature and independent of pressure between 100 and 750 Torr. This yields a rate constant of (6.1{+-}0.6)x10{sup -11} cm{sup 3} molecule{sup -1} s{sup -1}. The products of the reaction were detected by FTIR and UV absorption spectroscopy. Analysis of Cl{sub 2} and HCl products allowed branching ratios of 0.2{+-}0.1 for HCl+CH{sub 2}OCl formation and 0.8{+-}0.2 for Cl{sub 2}+CH{sub 3}O formation to be determined. The high rate constant implies that reaction with Cl atoms is an important loss process for CH{sub 3}OCl in the polar stratosphere. 37 refs., 9 figs., 3 tabs.

  3. Predicting both passive intestinal absorption and the dissociation constant toward albumin using the PAMPA technique.

    PubMed

    Bujard, Alban; Sol, Marine; Carrupt, Pierre-Alain; Martel, Sophie

    2014-10-15

    The parallel artificial membrane permeability assay (PAMPA) is a high-throughput screening (HTS) method that is widely used to predict in vivo passive permeability through biological barriers, such as the skin, the blood brain barrier (BBB) and the gastrointestinal tract (GIT). The PAMPA technique has also been used to predict the dissociation constant (Kd) between a compound and human serum albumin (HSA) while disregarding passive permeability. Furthermore, the assay is based on the use of two separate 5-point kinetic experiments, which increases the analysis time. In the present study, we adapted the hexadecane membrane (HDM)-PAMPA assay to both predict passive gastrointestinal absorption via the permeability coefficient logPe value and determine the Kd. Two assays were performed: one in the presence and one in the absence of HSA in the acceptor compartment. In the absence of HSA, logPe values were determined after a 4-h incubation time, as originally described, but the dimethylsulfoxide (DMSO) percentage and pH were altered to be compatible with the protein. In parallel, a second PAMPA assay was performed in the presence of HSA during a 16-h incubation period. By adding HSA, a variation in the amount of compound crossing the membrane was observed compared to the permeability measured in the absence of HSA. The concentration of compound reaching the acceptor compartment in each case was used to determine both parameters (logPe and logKd) using numerical simulations, which highlighted the originality of this method because these calculations required only two endpoint measurements instead of a complete kinetic study. It should be noted that the amount of compound that reaches the acceptor compartment in the presence of HSA is modulated by complex dissociation in the receptor compartment. Only compounds that are moderately bound to albumin (-3

  4. Selected hydraulic test analysis techniques for constant-rate discharge tests

    SciTech Connect

    Spane, F.A. Jr.

    1993-03-01

    The constant-rate discharge test is the principal field method used in hydrogeologic investigations for characterizing the hydraulic properties of aquifers. To implement this test, the aquifer is stressed by withdrawing ground water from a well, by using a downhole pump. Discharge during the withdrawal period is regulated and maintained at a constant rate. Water-level response within the well is monitored during the active pumping phase (i.e., drawdown) and during the subsequent recovery phase following termination of pumping. The analysis of drawdown and recovery response within the stress well (and any monitored, nearby observation wells) provides a means for estimating the hydraulic properties of the tested aquifer, as well as discerning formational and nonformational flow conditions (e.g., wellbore storage, wellbore damage, presence of boundaries, etc.). Standard analytical methods that are used for constant-rate pumping tests include both log-log type-curve matching and semi-log straight-line methods. This report presents a current state of the art'' review of selected transient analysis procedures for constant-rate discharge tests. Specific topics examined include: analytical methods for constant-rate discharge tests conducted within confined and unconfined aquifers; effects of various nonideal formation factors (e.g., anisotropy, hydrologic boundaries) and well construction conditions (e.g., partial penetration, wellbore storage) on constant-rate test response; and the use of pressure derivatives in diagnostic analysis for the identification of specific formation, well construction, and boundary conditions.

  5. Selected hydraulic test analysis techniques for constant-rate discharge tests

    SciTech Connect

    Spane, F.A. Jr.

    1993-03-01

    The constant-rate discharge test is the principal field method used in hydrogeologic investigations for characterizing the hydraulic properties of aquifers. To implement this test, the aquifer is stressed by withdrawing ground water from a well, by using a downhole pump. Discharge during the withdrawal period is regulated and maintained at a constant rate. Water-level response within the well is monitored during the active pumping phase (i.e., drawdown) and during the subsequent recovery phase following termination of pumping. The analysis of drawdown and recovery response within the stress well (and any monitored, nearby observation wells) provides a means for estimating the hydraulic properties of the tested aquifer, as well as discerning formational and nonformational flow conditions (e.g., wellbore storage, wellbore damage, presence of boundaries, etc.). Standard analytical methods that are used for constant-rate pumping tests include both log-log type-curve matching and semi-log straight-line methods. This report presents a current ``state of the art`` review of selected transient analysis procedures for constant-rate discharge tests. Specific topics examined include: analytical methods for constant-rate discharge tests conducted within confined and unconfined aquifers; effects of various nonideal formation factors (e.g., anisotropy, hydrologic boundaries) and well construction conditions (e.g., partial penetration, wellbore storage) on constant-rate test response; and the use of pressure derivatives in diagnostic analysis for the identification of specific formation, well construction, and boundary conditions.

  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. PMID:24602867

  7. Optical constants of ammonium sulfate in the infrared. [stratospheric aerosol refractive and absorption indices

    NASA Technical Reports Server (NTRS)

    Downing, H. D.; Pinkley, L. W.; Sethna, P. P.; Williams, D.

    1977-01-01

    The infrared spectral reflectance at near normal incidence has been measured for 3.2 M, 2.4 M, and 1.6 M solutions of ammonium sulfate, an aerosol abundant in the stratosphere and also present in the troposphere. Kramers-Kronig analysis was used to determine values of the refractive and absorption indices from the measured spectral reflectance. A synthetic spectrum of crystalline ammonium sulfate was obtained by extrapolation of the absorption index obtained for the solution to the absorber number densities of the NH4 and SO4 ions characteristic of the crystal.

  8. Correlation between nasal membrane permeability and nasal absorption rate.

    PubMed

    Zhang, Hefei; Lin, Chih-Wei; Donovan, Maureen D

    2013-03-01

    The objective of this study was to investigate the relationship between in vitro permeability (Papp) values obtained from isolated nasal tissues and the absorption rates (ka) of the same compounds following nasal administration in animals and humans. The Papp of a set of 11 drug compounds was measured using animal nasal explants and plasma time-concentration profiles for each of the same compounds following intravenous (IV) and intranasal (IN) administration were experimentally determined or obtained from literature reports. The plasma clearance was estimated from the IV plasma time-concentration profiles, and ka was determined from the IN plasma time-concentration profiles using a deconvolution approach. The level of correlation between Papp and ka was established using Pearson correlation analysis. A good correlation (r=0.77) representing a point-to-point relationship for each of the compounds was observed. This result indicates that the nasal absorption for many drug candidates can be estimated from a readily measured in vitro Papp value. PMID:23225081

  9. 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.

  10. Imaging Breathing Rate in the CO2Absorption Band.

    PubMed

    Fei, Jin; Zhu, Zhen; Pavlidis, Ioannis

    2005-01-01

    Following up on our previous work, we have developed one more non-contact method to measure human breathing rate. We have retrofitted our Mid-Wave Infra-Red (MWIR) imaging system with a narrow band-pass filter in the CO2absorption band (4.3 µm). This improves the contrast between the foreground (i.e., expired air) and background (e.g., wall). Based on the radiation information within the breath flow region, we get the mean dynamic thermal signal. This signal is quasi-periodic due to the interleaving of high and low intensities corresponding to expirations and inspirations respectively. We sample the signal at a constant rate and then determine the breathing frequency through Fourier analysis. We have performed experiments on 9 subjects at distances ranging from 6-8 ft. We compared the breathing rate computed by our novel method with ground-truth measurements obtained via a traditional contact device (PowerLab/4SP from ADInstruments with an abdominal transducer). The results show high correlation between the two modalities. For the first time, we report a Fourier based breathing rate computation method on a MWIR signal in the CO2absorption band. The method opens the way for desktop, unobtrusive monitoring of an important vital sign, that is, breathing rate. It may find widespread applications in preventive medicine as well as sustained physiological monitoring of subjects suffering from chronic ailments. PMID:17282279

  11. 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.

  12. 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. PMID:24759644

  13. 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 ...

  14. 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.

  15. 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.

  16. 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.

  17. Constant strain rate compression of bovine cortical bone on the Split-Hopkinson Pressure Bar.

    PubMed

    Bekker, A; Cloete, T J; Chinsamy-Turan, A; Nurick, G N; Kok, S

    2015-01-01

    Cortical bone is a visco-elastic material which implies that strain rate will affect its response. Although the Split-Hopkinson Pressure Bar is an accepted technique for determining the dynamic compressive properties of cortical bone it has been shown that the strain rate of compression does not remain constant throughout the duration of a classical experiment with a uniform striker. This raises concerns as to the measurement of smeared responses. This paper presents a shaped striker technique whereby the incident pulse can be shaped to attain a constant strain rate experiment for bovine bone. Shaped strikers offer benefits such as re-usability and increased test repeatability. A comparison of the stress-strain-strain rate responses attained through classical and constant strain rate experiments shows that the shape of the stress-strain curves from conventional experiments is adversely affected in the portion where the strain rate varies. The dynamic response corridors for the two tests are similar, however the ultimate properties are affected. It is concluded that the strain rate history should be presented with dynamic stress-strain responses since the instantaneous strain rate is a likely contributor to potential constitutive models. PMID:25492009

  18. Impact of transverse and longitudinal dispersion on first-order degradation rate constant estimation

    NASA Astrophysics Data System (ADS)

    Stenback, Greg A.; Ong, Say Kee; Rogers, Shane W.; Kjartanson, Bruce H.

    2004-09-01

    A two-dimensional analytical model is employed for estimating the first-order degradation rate constant of hydrophobic organic compounds (HOCs) in contaminated groundwater under steady-state conditions. The model may utilize all aqueous concentration data collected downgradient of a source area, but does not require that any data be collected along the plume centerline. Using a least squares fit of the model to aqueous concentrations measured in monitoring wells, degradation rate constants were estimated at a former manufactured gas plant (FMGP) site in the Midwest U.S. The estimated degradation rate constants are 0.0014, 0.0034, 0.0031, 0.0019, and 0.0053 day -1 for acenaphthene, naphthalene, benzene, ethylbenzene, and toluene, respectively. These estimated rate constants were as low as one-half those estimated with the one-dimensional (centerline) approach of Buscheck and Alcantar [Buscheck, T.E., Alcantar, C.M., 1995. Regression techniques and analytical solutions to demonstrate intrinsic bioremediation. In: Hinchee, R.E., Wilson, J.T., Downey, D.C. (Eds.), Intrinsic Bioremediation, Battelle Press, Columbus, OH, pp. 109-116] which does not account for transverse dispersivity. Varying the transverse and longitudinal dispersivity values over one order of magnitude for toluene data obtained from the FMGP site resulted in nearly a threefold variation in the estimated degradation rate constant—highlighting the importance of reliable estimates of the dispersion coefficients for obtaining reasonable estimates of the degradation rate constants. These results have significant implications for decision making and site management where overestimation of a degradation rate may result in remediation times and bioconversion factors that exceed expectations. For a complex source area or non-steady-state plume, a superposition of analytical models that incorporate longitudinal and transverse dispersion and time may be used at sites where the centerline method would not be

  19. A specific absorption rate prediction concept for parallel transmission MR.

    PubMed

    Graesslin, Ingmar; Homann, Hanno; Biederer, Sven; Börnert, Peter; Nehrke, Kay; Vernickel, Peter; Mens, Giel; Harvey, Paul; Katscher, Ulrich

    2012-11-01

    The specific absorption rate (SAR) is a limiting factor in high-field MR. SAR estimation is typically performed by numerical simulations using generic human body models. However, SAR concepts for single-channel radiofrequency transmission cannot be directly applied to multichannel systems. In this study, a novel and comprehensive SAR prediction concept for parallel radiofrequency transmission MRI is presented, based on precalculated magnetic and electric fields obtained from electromagnetic simulations of numerical body models. The application of so-called Q-matrices and further computational optimizations allow for a real-time estimation of the SAR prior to scanning. This SAR estimation method was fully integrated into an eight-channel whole body MRI system, and it facilitated the selection of different body models and body positions. Experimental validation of the global SAR in phantoms demonstrated a good qualitative and quantitative agreement with the predictions. An initial in vivo validation showed good qualitative agreement between simulated and measured amplitude of (excitation) radiofrequency field. The feasibility and practicability of this SAR prediction concept was shown paving the way for safe parallel radiofrequency transmission in high-field MR. PMID:22231647

  20. 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.

  1. Phenyl radical thermolysis and rate constants for phenyl + O{sub 2}

    SciTech Connect

    Kumaran, S.S.; Michael, J.V.

    1997-08-01

    The thermal decomposition of C{sub 6}H{sub 5}I has been used to prepare in-situ known initial concentrations of phenyl radicals at high temperatures. These can be degraded by direct decomposition at T > 1350 K giving H + C{sub 6}H{sub 4}. Using H-atom ARAS, rate constants for C{sub 6}H{sub 5} dissociation have been measured. Using the same ARAS technique, constants for C{sub 6}H{sub 5} dissociation have been measured. Using the same ARAS technique, the H- and O-atoms formed from the reaction, C{sub 6}H{sub 5} + O{sub 2}, have both been measured. The rate constant results are discussed along with lower T measurements in terms of RRKM calculations using published ab initio electronic structure determinations of transition states.

  2. Estimation of the reaction rate constant of HOCl by SMILES observation

    NASA Astrophysics Data System (ADS)

    Kuribayashi, Kouta; Kasai, Yasuko; Sato, Tomohiro; Sagawa, Hideo

    2012-07-01

    Hypochlorous acid, HOCl plays an important role to link the odd ClOx and the odd HOx in the atmospheric chemistry with the reaction: {ClO} + {HO_{2}} \\longrightarrow {HOCl} + {O_{2}} Quantitative understanding of the rate constant of the reaction (1.1) is essential for understanding the ozone loss in the mid-latitude region because of a view point of its rate controlling role in the ozone depletion chemistry. Reassessment of the reaction rate constant was pointed out from MIPAS/Envisat observations (von Clarmann et al., 2011) and balloon-borne observations (Kovalenko et al., 2007). Several laboratory studies had been reported, although the reaction rate constants have large uncertainties, as k{_{HOCl}} = (1.75 ± 0.52) × 10^{-12} exp[(368 ± 78)/T] (Hickson et al., 2007), and large discrepancies (Hickson et al., 2007;Stimpfle et al., 1979). Moreover, theoretical ab initio studies pointed out the pressure dependence of the reaction (1.1) (Xu et al., 2003). A new high-sensitive remote sensing technology named Superconducting SubMillimeter-wave Limb-Emission Sounder (SMILES) on the International Space Station (ISS) had observed diurnal variations of HOCl in the upper stratosphere/lower mesosphere (US/LM) region for the first time. ClO and HO_{2} were slso observed simultaneously with HOCl. SMILES performed the observations between 12^{{th}} October 2009 and 21^{{th}} April 2010. The latitude coverage of SMILES observation is normally 38°S-65°N. The altitude region of HOCl observation is about 28-70 km. We estimated the time period in which the reaction (1.1) becomes dominant in the ClO_{y} diurnal chemistry in US/LM. The reaction rate constant was directly estimated by decay of [ClO] and [HO_{2}] amounts in that period. The derived reaction rate constant represented well the increase of [HOCl] amount.

  3. 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.

  4. 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. PMID:27497172

  5. Actuarial aging rate is not constant within the human life span.

    PubMed

    Ekonomov, A L; Rudd, C L; Lomakin, A J

    1989-01-01

    It is often believed that the mortality intensity in the modern human population undergoes an exponential growth after 40 years, i.e. the actuarial aging rate is regarded to be constant after 40 years. To check this assumption we have calculated local aging rate values for 13 age ranges (within the interval of 30-92 years) for the male and female population of 48 states of the US (1969-1971). It was found that generally the male aging rate is not constant but lowers monotonically with time, while for females the aging rate has a pronounced approximately-shaped character with a minimum in the range of 45-60 years and a maximum within the range of 70-80 years. The results obtained are a warning to those who boldly use Gompertz or Gompertz-Makeham formulas when describing human aging on the population level. PMID:2792778

  6. 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 ...

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

    PubMed

    Jongberg, Sisse; Lund, Marianne N; Pattison, David I; Skibsted, Leif H; Davies, Michael J

    2016-05-15

    Competitive kinetics were applied as a tool to determine apparent rate constants for the reduction of hypervalent haem pigment ferrylmyoglobin (MbFe(IV)O) by proteins and phenols in aqueous solution of pH 7.4 and I=1.0 at 25°C. Reduction of MbFe(IV)O by a myofibrillar protein isolate (MPI) from pork resulted in kMPI=2.2 ± 0.1 × 10(4)M(-1)s(-1). Blocking of the protein thiol groups on the MPI by N-ethylmaleimide (NEM) markedly reduced this rate constant to kMPI-NEM=1.3 ± 0.4 × 10(3)M(-1)s(-1) consistent with a key role for the Cys residues on MPI as targets for haem protein-mediated oxidation. This approach allows determination of apparent rate constants for the oxidation of proteins by haem proteins of relevance to food oxidation and should be applicable to other systems. A similar approach has provided approximate apparent rate constants for the reduction of MbFe(IV)O by catechin and green tea extracts, though possible confounding reactions need to be considered. These kinetic data suggest that small molar excesses of some plant extracts relative to the MPI thiol concentration should afford significant protection against MbFe(IV)O-mediated oxidation. PMID:26775941

  8. EFFECTS OF PHENOL MOLECULAR STRUCTURE ON BACTERIAL TRANSFORMATION RATE CONSTANTS IN POND AND RIVER SAMPLES

    EPA Science Inventory

    Microbial transformation rate constants for a series of phenols were correlated with a property of the substituents, van der Waal's radius. Transformation products were the corresponding catecols, with the exception of p-hydroxybenzoic acid, the product of p-acetylphenol. A diffe...

  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. 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

  11. 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 ...

  12. HOMOGENEOUS HYDROLYSIS RATE CONSTANTS FOR SELECTED CHLORINATED METHANES, ETHANES, ETHENES, AND PROPANES

    EPA Science Inventory

    Hydrolysis rate constants of 18 chlorinated methanes, ethanes, ethenes, and propanes have been measured in dilute aqueous solutions within the temperature range of 0 to 180 oC and at pH values of 3 to l4. rrhenius parapmeters were determined for both neutral and alkaline hydrolys...

  13. 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

  14. 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...

  15. Bounds on the fine structure constant variability from Fe ii absorption lines in QSO spectra

    NASA Astrophysics Data System (ADS)

    Molaro, P.; Reimers, D.; Agafonova, I. I.; Levshakov, S. A.

    2008-10-01

    The Single Ion Differential α Measurement (SIDAM)method for measuring Δα/α and its figures of merit are illustrated together withthe results produced by means of Fe ii absorption linesof QSO intervening systems. The method providesΔα/α = -0.12 ±1.79 ppm (parts-per-million) at zabs = 1.15towards HE 0515-4414 and Δα/α = 5.66±2.67 ppm at zabs = 1.84towards Q 1101-264, which are so far the most accurate measurementsfor single systems. SIDAM analysis for 3 systems from the Chand et al. [1]sample provides inconsistent results which we interpret as due tocalibration errors of the Chand et al. data at the level ≈10 ppm.In one system evidence for photo-ionization Dopplershift between Mg ii and Fe ii lines is found.This evidence has important bearings on the Many Multipletmethod where the signal for Δα/αvariabilityis carried mainly by systems involving Mg ii absorbers.Some correlations are also found in the Murphy et al. [10] sample which suggestlarger errors than previously reported.Thus, we consider unlikely that both the Chand et al.and Murphy et al. datasets could providean estimate of Δα/α with an accuracy at the level of 1 ppm.A new spectrograph like the ESPRESSO projectwill be crucial to make progress in the astronomical determination of Δα/α.

  16. Product distributions, rate constants, and mechanisms of LiH +H reactions

    NASA Astrophysics Data System (ADS)

    Defazio, Paolo; Petrongolo, Carlo; Gamallo, Pablo; González, Miguel

    2005-06-01

    We present a quantum-mechanical investigation of the LiH depletion reaction LiH +H→Li+H2 and of the H exchange reaction LiH +H'→LiH'+H. We report product distributions, rate constant, and mechanism of the former, and rate constant and mechanism of the latter reaction. We use the potential-energy surface by Dunne et al. [Chem. Phys. Lett. 336, 1 (2001)], the real-wave-packet method by Gray and Balint-Kurti [J. Chem. Phys. 108, 950 (1998)], and the J-shifting approximation. The H21 nuclear-spin statistics and progressions of vib-rotational states (v',j') rule both initial-state-resolved and thermal product distributions, which have saw-toothed shapes with odd j' preferred with respect to even j'. At high collision energies and temperatures, we obtain a regular 3-to-1 intensity alternation of rotational states. At low collision energies and temperatures, the degeneracy and density of many H2 levels can, however, give more irregular distributions. During the collision, the energy flows from the reactant translational mode to the product vibration and recoil ones. The rate constants of both reactions are not Arrhenius type because the reactions are barrier-less. The low-temperature, LiH depletion rate constant is larger than the H exchange one, whereas the contrary holds at high temperature. The real-time mechanisms show the nuclear rearrangements of the nonreactive channel and of the reactive ones, and point out that the LiH depletion is preferred over the H exchange at short times. This confirms the rate-constant results.

  17. 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. PMID:27232936

  18. 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.

  19. 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.

  20. Constants in estimates for the rates of convergence in von Neumann's and Birkhoff's ergodic theorems

    SciTech Connect

    Kachurovskii, Alexander G; Sedalishchev, Vladimir V

    2011-08-31

    The paper investigates estimates which relate two equivalent phenomena: the power-type rate of convergence in von Neumann's ergodic theorem and the power-type singularity at zero (with the same exponent) exhibited by the spectral measure of the function being averaged with respect to the corresponding dynamical system. The same rate of convergence is also estimated in terms of the rate of decrease of the correlation coefficients. Also, constants are found in analogous estimates for the power-type convergence in Birkhoff's ergodic theorem. All the results have exact analogues for wide-sense stationary stochastic processes. Bibliography: 15 titles.

  1. 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.

  2. 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.

  3. 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.

  4. Mechanism and rate constants of the Cdc42 GTPase binding with intrinsically disordered effectors.

    PubMed

    Pang, Xiaodong; Zhou, Huan-Xiang

    2016-05-01

    Intrinsically disordered proteins (IDPs) are often involved in signaling and regulatory functions, through binding to cellular targets. Many IDPs undergo disorder-to-order transitions upon binding. Both the binding mechanisms and the magnitudes of the binding rate constants can have functional importance. Previously we have found that the coupled binding and folding of any IDP generally follows a sequential mechanism that we term dock-and-coalesce, whereby one segment of the IDP first docks to its subsite on the target surface and the remaining segments subsequently coalesce around their respective subsites. Here we applied our TransComp method within the framework of the dock-and-coalesce mechanism to dissect the binding kinetics of two Rho-family GTPases, Cdc42 and TC10, with two intrinsically disordered effectors, WASP and Pak1. TransComp calculations identified the basic regions preceding the GTPase binding domains (GBDs) of the effectors as the docking segment. For Cdc42 binding with both WASP and Pak1, the calculated docking rate constants are close to the observed overall binding rate constants, suggesting that basic-region docking is the rate-limiting step and subsequent conformational coalescence of the GBDs on the Cdc42 surface is fast. The possibility that conformational coalescence of the WASP GBD on the TC10 surface is slow warrants further experimental investigation. The account for the differences in binding rate constants among the three GTPase-effector systems and mutational effects therein yields deep physical and mechanistic insight into the binding processes. Our approach may guide the selection of mutations that lead to redesigned binding pathways. Proteins 2016; 84:674-685. © 2016 Wiley Periodicals, Inc. PMID:26879470

  5. Extremely asymmetric diffraction as a method of determining magneto-optical constants for X-rays near absorption edges

    SciTech Connect

    Andreeva, M. A.; Repchenko, Yu. L.; Smekhova, A. G.; Dumesnil, K.; Wilhelm, F.; Rogalev, A.

    2015-06-15

    The spectral dependence of the Bragg peak position under conditions of extremely asymmetric diffraction has been analyzed in the kinematical and dynamical approximations of the diffraction theory. Simulations have been performed for the L{sub 3} absorption edge of yttrium in a single-crystal YFe{sub 2} film; they have shown that the magneto-optical constants (or, equivalently, the dispersion corrections to the atomic scattering factor) for hard X-rays can be determined from this dependence. Comparison with the experimental data obtained for a Nb(4 nm)/YFe{sub 2}(40 nm〈110〉)/Fe(1.5 nm)/Nb(50 nm)/sapphire sample at the European Synchrotron Radiation Facility has been made.

  6. Extremely asymmetric diffraction as a method of determining magneto-optical constants for X-rays near absorption edges

    NASA Astrophysics Data System (ADS)

    Andreeva, M. A.; Repchenko, Yu. L.; Smekhova, A. G.; Dumesnil, K.; Wilhelm, F.; Rogalev, A.

    2015-06-01

    The spectral dependence of the Bragg peak position under conditions of extremely asymmetric diffraction has been analyzed in the kinematical and dynamical approximations of the diffraction theory. Simulations have been performed for the L 3 absorption edge of yttrium in a single-crystal YFe2 film; they have shown that the magneto-optical constants (or, equivalently, the dispersion corrections to the atomic scattering factor) for hard X-rays can be determined from this dependence. Comparison with the experimental data obtained for a Nb(4 nm)/YFe2(40 nm<110>)/Fe(1.5 nm)/Nb(50 nm)/sapphire sample at the European Synchrotron Radiation Facility has been made.

  7. 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.

  8. 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.

  9. Thermal rate constants of multi-mode systems for the price of one: aziridine

    NASA Astrophysics Data System (ADS)

    Rom, Naomi; Ryaboy, Victor; Moiseyev, Nimrod

    1993-03-01

    An accurate and highly efficient method for calculating thermal rate constants in the automerization reaction of aziridine is presented. Theoretical results are in good agreement with available experimental data obtained by Borchardt and Bauer. The kinetics of aziridine inversion involve strong coupling of the reaction coordinate with other internal modes. Therefore, it is expected that in order to account for the energy redistribution processes in aziridine, the multi-mode Schrödinger equation should be solved. We show, however, that accurate rate constants for this system can be obtained by performing only one- (or two-) dimensional calculations. The key point in our approach is the insertion of absorbing boundary conditions in the products region of the potential surface, which prevent reflections from the products well to the reactants well, and thereby replace the role of the "neglected" internal modes in the dynamics.

  10. Ab Initio Calculation of Rate Constants for Molecule-Surface Reactions with Chemical Accuracy.

    PubMed

    Piccini, GiovanniMaria; Alessio, Maristella; Sauer, Joachim

    2016-04-18

    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

  11. Solvent effects on the rate constants for reaction of trichloromethylperoxyl radicals with organic reductants

    SciTech Connect

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

    1993-07-15

    Absolute rate constants for the reactions of trichloromethylperoxyl radicals with chloropromazine and trolox have been determined by pulse radiolysis in 16 different solvents. The rate constants were found to vary over two orders of magnitude (10[sup 7]-10[sup 9] L mol[sup [minus]1] s[sup [minus]1]) and to correlate with the Hildebrand solubility parameter (cohesive energy density) of the solvent better than with any other single solvent parameter. The correlation was satisfactory for ClPz and did not improve significantly by including additional parameters. For trolox, however, the correlation was relatively poor but was improved considerably by taking into account the basicity of the solvent. This effect is due to the transfer of a proton upon the oxidation of trolox. 21 refs., 3 figs., 2 tabs.

  12. 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.

  13. 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

  14. 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. PMID:26056765

  15. Mechanism of Tension Generation in Muscle: An Analysis of the Forward and Reverse Rate Constants

    PubMed Central

    Davis, Julien S.; Epstein, Neal D.

    2007-01-01

    Tension generation in muscle occurs during the attached phase of the ATP-powered cyclic interaction of myosin heads with thin filaments. The transient nature of tension-generating intermediates and the complexity of the mechanochemical cross-bridge cycle have impeded a quantitative description of tension generation. Recent experiments performed under special conditions yielded a sigmoidal dependence of fiber tension on temperature—a unique case that simplifies the system to a two-state transition. We have applied this two-state analysis to kinetic data obtained from biexponential laser temperature-jump tension transients. Here we present the forward and reverse rate constants for de novo tension generation derived from analysis of the kinetics of the fast laser temperature-jump phase τ2 (equivalent of the length-jump phase 2slow). The slow phase τ3 is temperature-independent indicating coupling to rather than a direct role in, de novo tension generation. Increasing temperature accelerates the forward, and slows the reverse, rate constant for the creation of the tension-generating state. Arrhenius behavior of the forward and anti-Arrhenius behavior of the reverse rate constant is a kinetic signature of multistate multipathway protein-folding reactions. We conclude that locally unfolded tertiary and/or secondary structure of the actomyosin cross-bridge mediates the power stroke. PMID:17259275

  16. 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. PMID:24483837

  17. 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. PMID:27124124

  18. Solvation effect on kinetic rate constant of reactions in supercritical solvents

    SciTech Connect

    Chialvo, A.A.; Cummings, P.T. |; Kalyuzhnyi, Yu.V.

    1998-03-01

    A statistical mechanical analysis of the solvation effects on the kinetic rate constants of reactions in near and supercritical solvents is presented to understand the experimental findings regarding the thermodynamic pressure effects. This is an extension of the solvation formalism of Chialvo and Cummings to the analysis of the microscopic basis for the macroscopic pressure and temperature effects on the kinetic rate constants of reactions conducted in the compressible region of the solvent phase diagram. This analysis is illustrated with integral equations calculations involving Lennard-Jones infinitely dilute quaternary systems to describe the species in solution during the reaction of triplet benzophenone ({sup 3}BP) with a cosolvent (either O{sub 2} or 1,4-cyclohexadiene) in supercritical CO{sub 2} along the supercritical isotherms T{sub r} = 1.01 and 1.06. The role of the species molecular asymmetries and consequently their solvation behavior in determining the thermodynamic pressure and temperature effects on the kinetic rate constant of reactions at near-critical conditions are discussed.

  19. The responses of primary spindle afferents to fusimotor stimulation at constant and abruptly changing rates.

    PubMed Central

    Hulliger, M

    1979-01-01

    1. Single fusimotor fibres to de-efferented soleus of the cat were stimulated to investigate the size and time course of the responses elicited in single primary spindle afferents. The muscle was kept at constant length close to the physiological maximum. Constant and alternating rates of fusimotor stimulation were used: (a) repetitive stimulation at constant rate (maintained stimulation); (b) modulated stimulation with the rate of activation alternating between two constant levels at repeat frequencies between 0.09 and 2 Hz (rectangular stimulation). The responses were averaged and displayed as post-stimulus time (pst) histograms (a) or as cycle histograms (b). 2. During static fusimotor stimulation the pst histograms could be clearly modulated over a range of rates of stimulation. However, histogram modulation was not a prerequisite of static action since with different fibres the degree of modulation could range from deeply modulated to completely non-modulated to completely non-modulated. 3. Dynamic fusimotor stimulation was almost always accompanied by non-modulated pst histograms. 4. Primary spindle afferents responded to rectangular stimulation of either kind of fusimotor fibre with an approximately rectangular modulation of the rate of discharge. At the repeat frequencies studied the size of the responses was appreciably larger with static than with dynamic activation. It was assessed as 'fusimotor rate-sensitivity during alternating stimulation' by the response/stimulus ratio which is defined as change in firing/change in alternating rate of stimulation, in impulses/stimuli. The mean values of rate-sensitivity were 1.35 impulses/stimuli (statics) and 0.29 (dynamics), with a static/dynamic ratio of 4.7. 5. The afferents' 'fusimotor rate-sensitivity during steady stimulation' (change in firing/change in maintained rate of stimulation( was also determined. The mean values were 0.78 (static) and 0.37 (dynamics), with a static/dynamic ratio of 2.1. 6. The time

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  1. Relative rate constants for the reactions of OH with methane and methyl chloroform

    NASA Technical Reports Server (NTRS)

    Demore, W. B.

    1992-01-01

    Atmospheric lifetimes of methane and methyl chloroform are largely determined by the rates of their reactions with hydroxyl radical. The relative lifetimes for this loss path are inversely proportional to the ratio of the corresponding rate coefficients. The relative rate constants were measured in a slow-flow, temperature-controlled photochemical reactor, and were based on rates of disappearance of the parent compounds as measured by FTIR spectroscopy. The temperature range was 277-356 K. Hydroxyl radicals were generated by 254 nm photolysis of O3 in the presence of water vapor. The preferred Arrhenius expression for the results is k(CH3CCl3)/k(CH4) = 0.62 exp (291/T), corresponding to a value of 1.65 at 298 K and 1.77 at 277 K. The respective uncertainties are 5 and 7 percent.

  2. 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. PMID:24156502

  3. Linear free energy relationship rate constants and basicities of N-substituted phenyl glycines in positronium-glycine complex formation

    NASA Astrophysics Data System (ADS)

    Chen, Rongti; Liang, Jiachang; Du, Youming; Cao, Chun; Yin, Dinzhen; Wang, Shuying; Zhang, Tianbao

    1987-06-01

    Complex formation between positronium and glycine derivatives in solution is discussed and the complex reaction rate constants obtained by means of a positron annihilation lifetime spectrometer with BaF 2 detectors. Rate constants mainly depend on the conjugation effect at the benzene ring and the induction effect of the substituents at the phenyl. There is a linear free energy relationship between rate constants and basicities of N-substituted phenyl glycines in orthopositronium-glycine complex formation.

  4. SPECIFIC ABSORPTION RATE DISTRIBUTIONS IN A HETEROGENEOUS MODEL OF THE HUMAN BODY AT RADIOFREQUENCIES

    EPA Science Inventory

    The electric field distribution of the rate of energy absorption referred to as the specific absorption rate (SAR) in a biological body is a complex function of several exposure parameters such as frequency, intensity of the incident field, polarization, source to object configur...

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

    SciTech Connect

    Quinn, Brian; Holahan, Brian; Aime, Jean; Humm, John; St Germain, Jean; Dauer, Lawrence T.

    2012-10-15

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

  6. 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.

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

    PubMed

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

    2016-06-01

    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. PMID:27193050

  8. Constant-quality constrained-rate allocation for FGS video coded bitstreams

    NASA Astrophysics Data System (ADS)

    Zhang, Xi Min; Vetro, Anthony; Shi, Yun-Qing; Sun, Huifang

    2002-01-01

    This paper proposes an optimal rate allocation scheme for Fine-Granular Scalability (FGS) coded bitstreams that can achieve constant quality reconstruction of frames under a dynamic rate budget constraint. In doing so, we also aim to minimize the overall distortion at the same time. To achieve this, we propose a novel R-D labeling scheme to characterize the R-D relationship of the source coding process. Specifically, sets of R-D points are extracted during the encoding process and linear interpolation is used to estimate the actual R-D curve of the enhancement layer signal. The extracted R-D information is then used by an enhancement layer transcoder to determine the bits that should be allocated per frame. A sliding window based rate allocation method is proposed to realize constant quality among frames. This scheme is first considered for a single FGS coded source, then extended to operate on multiple sources. With the proposed scheme, the rate allocation can be performed in a single pass, hence the complexity is quite low. Experimental results confirm the effectiveness of the proposed scheme under static and dynamic bandwidth conditions.

  9. The Multicenter Aerobic Iron Respiratory Chain of Acidithiobacillus ferrooxidans Functions as an Ensemble with a Single Macroscopic Rate Constant.

    PubMed

    Li, Ting-Feng; Painter, Richard G; Ban, Bhupal; Blake, Robert C

    2015-07-24

    Electron transfer reactions among three prominent colored proteins in intact cells of Acidithiobacillus ferrooxidans were monitored using an integrating cavity absorption meter that permitted the acquisition of accurate absorbance data in suspensions of cells that scattered light. The concentrations of proteins in the periplasmic space were estimated to be 350 and 25 mg/ml for rusticyanin and cytochrome c, respectively; cytochrome a was present as one molecule for every 91 nm(2) in the cytoplasmic membrane. All three proteins were rapidly reduced to the same relative extent when suspensions of live bacteria were mixed with different concentrations of ferrous ions at pH 1.5. The subsequent molecular oxygen-dependent oxidation of the multicenter respiratory chain occurred with a single macroscopic rate constant, regardless of the proteins' in vitro redox potentials or their putative positions in the aerobic iron respiratory chain. The crowded electron transport proteins in the periplasm of the organism constituted an electron conductive medium where the network of protein interactions functioned in a concerted fashion as a single ensemble with a standard reduction potential of 650 mV. The appearance of product ferric ions was correlated with the reduction levels of the periplasmic electron transfer proteins; the limiting first-order catalytic rate constant for aerobic respiration on iron was 7,400 s(-1). The ability to conduct direct spectrophotometric studies under noninvasive physiological conditions represents a new and powerful approach to examine the extent and rates of biological events in situ without disrupting the complexity of the live cellular environment. PMID:26041781

  10. The Multicenter Aerobic Iron Respiratory Chain of Acidithiobacillus ferrooxidans Functions as an Ensemble with a Single Macroscopic Rate Constant*

    PubMed Central

    Li, Ting-Feng; Painter, Richard G.; Ban, Bhupal; Blake, Robert C.

    2015-01-01

    Electron transfer reactions among three prominent colored proteins in intact cells of Acidithiobacillus ferrooxidans were monitored using an integrating cavity absorption meter that permitted the acquisition of accurate absorbance data in suspensions of cells that scattered light. The concentrations of proteins in the periplasmic space were estimated to be 350 and 25 mg/ml for rusticyanin and cytochrome c, respectively; cytochrome a was present as one molecule for every 91 nm2 in the cytoplasmic membrane. All three proteins were rapidly reduced to the same relative extent when suspensions of live bacteria were mixed with different concentrations of ferrous ions at pH 1.5. The subsequent molecular oxygen-dependent oxidation of the multicenter respiratory chain occurred with a single macroscopic rate constant, regardless of the proteins' in vitro redox potentials or their putative positions in the aerobic iron respiratory chain. The crowded electron transport proteins in the periplasm of the organism constituted an electron conductive medium where the network of protein interactions functioned in a concerted fashion as a single ensemble with a standard reduction potential of 650 mV. The appearance of product ferric ions was correlated with the reduction levels of the periplasmic electron transfer proteins; the limiting first-order catalytic rate constant for aerobic respiration on iron was 7,400 s−1. The ability to conduct direct spectrophotometric studies under noninvasive physiological conditions represents a new and powerful approach to examine the extent and rates of biological events in situ without disrupting the complexity of the live cellular environment. PMID:26041781

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

    NASA Astrophysics Data System (ADS)

    Li, Wenjiao; Xue, Yongqiang; Cui, Zixiang

    2016-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  13. Determination of the rate constant of hydroperoxyl radical reaction with phenol

    NASA Astrophysics Data System (ADS)

    Kozmér, Zsuzsanna; Arany, Eszter; Alapi, Tünde; Takács, Erzsébet; Wojnárovits, László; Dombi, András

    2014-09-01

    The rate constant of HO2rad reaction with phenol (kHO2rad +phenol) was investigated. The primary radical set produced in water γ radiolysis (rad OH, eaq- and Hrad ) was transformed to HO2rad /O2rad - by using dissolved oxygen and formate anion (in the form of either formic acid or sodium formate). The concentration ratio of HO2rad /O2rad - was affected by the pH value of the solution: under acidic conditions (using HCOOH) almost all radicals were converted to HO2rad , while under alkaline conditions (using HCOONa) to O2rad -. The degradation rate of phenol was significantly higher using HCOOH. From the ratio of reaction rates under the two reaction conditions kHO2rad +phenol was estimated to be (2.7±1.2)×103 L mol-1 s-1.

  14. Finite Element Solution of the Steady-State Smoluchowski Equation for Rate Constant Calculations

    PubMed Central

    Song, Yuhua; Zhang, Yongjie; Shen, Tongye; Bajaj, Chandrajit L.; McCammon, J. Andrew; Baker, Nathan A.

    2004-01-01

    This article describes the development and implementation of algorithms to study diffusion in biomolecular systems using continuum mechanics equations. Specifically, finite element methods have been developed to solve the steady-state Smoluchowski equation to calculate ligand binding rate constants for large biomolecules. The resulting software has been validated and applied to mouse acetylcholinesterase. Rates for inhibitor binding to mAChE were calculated at various ionic strengths with several different reaction criteria. The calculated rates were compared with experimental data and show very good agreement when the correct reaction criterion is used. Additionally, these finite element methods require significantly less computational resources than existing particle-based Brownian dynamics methods. PMID:15041644

  15. The effect of film thickness on the optical absorption edge and optical constants of the Cr(III) organic thin films

    NASA Astrophysics Data System (ADS)

    Yakuphanoglu, F.; Sekerci, M.; Balaban, A.

    2005-05-01

    The effect of film thickness on optical properties of the Cr(III) complex having 2-pyridincarbaldehye thiosemicarbazone thin films was investigated. The analyses of the optical absorption data revealed existence of direct and indirect transitions in the optical band gap. The optical constants (refractive index and dielectric constant) of the thin films were determined. The thickness of the films causes important changes in refractive index and real part-imaginary parts of the dielectric constant. The most significant result of the present study is to indicate that thickness of the film can be used to modify in the optical band gaps and optical constant of the thin films.

  16. Method for estimating S(N)1 rate constants: solvolytic reactivity of benzoates.

    PubMed

    Matić, Mirela; Denegri, Bernard; Kronja, Olga

    2012-10-19

    Nucleofugalities of pentafluorobenzoate (PFB) and 2,4,6-trifluorobenzoate (TFB) leaving groups have been derived from the solvolysis rate constants of X,Y-substituted benzhydryl PFBs and TFBs measured in a series of aqueous solvents, by applying the LFER equation: log k = s(f)(E(f) + N(f)). The heterolysis rate constants of dianisylmethyl PFB and TFB, and those determined for 10 more dianisylmethyl benzoates in aqueous ethanol, constitute a set of reference benzoates whose experimental ΔG(‡) have been correlated with the ΔH(‡) (calculated by PCM quantum-chemical method) of the model epoxy ring formation. Because of the excellent correlation (r = 0.997), the method for calculating the nucleofugalities of substituted benzoate LGs have been established, ultimately providing a method for determination of the S(N)1 reactivity for any benzoate in a given solvent. Using the ΔG(‡) vs ΔH(‡) correlation, and taking s(f) based on similarity, the nucleofugality parameters for about 70 benzoates have been determined in 90%, 80%, and 70% aqueous ethanol. The calculated intrinsic barriers for substituted benzoate leaving groups show that substrates producing more stabilized LGs proceed over lower intrinsic barriers. Substituents on the phenyl ring affect the solvolysis rate of benzhydryl benzoates by both field and inductive effects. PMID:22973993

  17. An analytical quantification of mass fluxes and natural attenuation rate constants at a former gasworks site

    NASA Astrophysics Data System (ADS)

    Bockelmann, Alexander; Ptak, Thomas; Teutsch, Georg

    2001-12-01

    A new integral groundwater investigation approach was used for the first time to quantify natural attenuation rates at field scale. In this approach, pumping wells positioned along two control planes were operated at distances of 140 and 280 m downstream of a contaminant source zone at a former gasworks site polluted with BTEX- (benzene, toluene, ethyl-benzene, o-, p-xylene) and PAH- (polycyclic aromatic hydrocarbons) compounds. Based on the quantified changes in total contaminant mass fluxes between the control planes, first-order natural attenuation rate constants could be estimated. For BTEX-compounds, these ranged from 1.4e-02 to 1.3e-01 day -1, whereas for PAH-compounds natural attenuation rate constants of 3.7e-04 to 3.1e-02 day -1 were observed. Microbial degradation activity at the site was indicated by an increase in dissolved iron mass flux and a reduction in sulphate mass flux between the two investigated control planes. In addition to information about total contaminant mass fluxes and average concentrations, an analysis of the concentration-time series measured at the control planes also allowed to semi-quantitatively delineate the aquifer regions most likely contaminated by the BTEX- and PAH-compounds.

  18. An analytical quantification of mass fluxes and natural attenuation rate constants at a former gasworks site.

    PubMed

    Bockelmann, A; Ptak, T; Teutsch, G

    2001-12-15

    A new integral groundwater investigation approach was used for the first time to quantify natural attenuation rates at field scale. In this approach, pumping wells positioned along two control planes were operated at distances of 140 and 280 m downstream of a contaminant source zone at a former gasworks site polluted with BTEX- (benzene, toluene, ethyl-benzene, o-, p-xylene) and PAH- (polycyclic aromatic hydrocarbons) compounds. Based on the quantified changes in total contaminant mass fluxes between the control planes, first-order natural attenuation rate constants could be estimated. For BTEX-compounds, these ranged from 1.4e-02 to 1.3e-01 day(-1) whereas for PAH-compounds natural attenuation rate constants of 3.7e-04 to 3.1e-02 day(-1) were observed. Microbial degradation activity at the site was indicated by an increase in dissolved iron mass flux and a reduction in sulphate mass flux between the two investigated control planes. In addition to information about total contaminant mass fluxes and average concentrations, an analysis of the concentration-time series measured at the control planes also allowed to semi-quantitatively delineate the aquifer regions most likely contaminated by the BTEX- and PAH-compounds. PMID:11820481

  19. On the efficient path integral evaluation of thermal rate constants within the quantum instanton approximation

    NASA Astrophysics Data System (ADS)

    Yamamoto, Takeshi; Miller, William H.

    2004-02-01

    We present an efficient path integral approach for evaluating thermal rate constants within the quantum instanton (QI) approximation that was recently introduced to overcome the quantitative deficiencies of the earlier semiclassical instanton approach [Miller, Zhao, Ceotto, and Yang, J. Chem. Phys. 119, 1329 (2003)]. Since the QI rate constant is determined solely by properties of the (quantum) Boltzmann operator (specifically, by the zero time properties of the flux-flux and delta-delta correlation functions), it can be evaluated by well-established techniques of imaginary time path integrals even for quite complex chemical reactions. Here we present a series of statistical estimators for relevant quantities which can be evaluated straightforwardly with any nonlinear reaction coordinates and general Hamiltonians in Cartesian space. To facilitate the search for the optimal dividing surfaces required by the QI approximation, we introduce a two-dimensional quantum free energy surface associated with the delta-delta correlation function and describe how an adaptive umbrella sampling can be used effectively to construct such a free energy surface. The overall computational procedure is illustrated by the application to a hydrogen exchange reaction in gas phase, which shows excellent agreement of the QI rates with those obtained from quantum scattering calculations.

  20. On the efficient path integral evaluation of thermal rate constants within the quantum instanton approximation.

    PubMed

    Yamamoto, Takeshi; Miller, William H

    2004-02-15

    We present an efficient path integral approach for evaluating thermal rate constants within the quantum instanton (QI) approximation that was recently introduced to overcome the quantitative deficiencies of the earlier semiclassical instanton approach [Miller, Zhao, Ceotto, and Yang, J. Chem. Phys. 119, 1329 (2003)]. Since the QI rate constant is determined solely by properties of the (quantum) Boltzmann operator (specifically, by the zero time properties of the flux-flux and delta-delta correlation functions), it can be evaluated by well-established techniques of imaginary time path integrals even for quite complex chemical reactions. Here we present a series of statistical estimators for relevant quantities which can be evaluated straightforwardly with any nonlinear reaction coordinates and general Hamiltonians in Cartesian space. To facilitate the search for the optimal dividing surfaces required by the QI approximation, we introduce a two-dimensional quantum free energy surface associated with the delta-delta correlation function and describe how an adaptive umbrella sampling can be used effectively to construct such a free energy surface. The overall computational procedure is illustrated by the application to a hydrogen exchange reaction in gas phase, which shows excellent agreement of the QI rates with those obtained from quantum scattering calculations. PMID:15268461

  1. Precise limits on cosmological variability of the fine-structure constant with zinc and chromium quasar absorption lines

    NASA Astrophysics Data System (ADS)

    Murphy, Michael T.; Malec, Adrian L.; Prochaska, J. Xavier

    2016-09-01

    The strongest transitions of Zn and Cr II are the most sensitive to relative variations in the fine-structure constant (Δα/α) among the transitions commonly observed in quasar absorption spectra. They also lie within just 40 Å of each other (rest frame), so they are resistant to the main systematic error affecting most previous measurements of Δα/α: long-range distortions of the wavelength calibration. While Zn and Cr II absorption is normally very weak in quasar spectra, we obtained high signal-to-noise, high-resolution echelle spectra from the Keck and Very Large Telescopes of nine rare systems where it is strong enough to constrain Δα/α from these species alone. These provide 12 independent measurements (three quasars were observed with both telescopes) at redshifts 1.0-2.4, 11 of which pass stringent reliability criteria. These 11 are all consistent with Δα/α = 0 within their individual uncertainties of 3.5-13 parts per million (ppm), with a weighted mean Δα/α = 0.4 ± 1.4stat ± 0.9sys ppm (1σ statistical and systematic uncertainties), indicating no significant cosmological variations in α. This is the first statistical sample of absorbers that is resistant to long-range calibration distortions (at the <1 ppm level), with a precision comparable to previous large samples of ˜150 (distortion-affected) absorbers. Our systematic error budget is instead dominated by much shorter range distortions repeated across echelle orders of individual spectra.

  2. 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.

  3. Stress corrosion cracking of Alloy 600 using the constant strain rate test

    SciTech Connect

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

    1981-10-01

    Nuclear grade production tubing of Alloy 600 was evaluated for stress corrosion cracking (SCC) susceptibility in high purity water at 365, 345, 325, and 290 C. Reverse tube U-bend specimens provided crack initiation data and constant extension rate tests were employed to determine the crack velocities experienced in th crack propagation stage. Initial results indicate that a linear extrapolation of data received from high temperature tests can be used to predict the service life of steam generator tubing that has been plastically deformed or is continually deforming by ''denting.''

  4. MEASUREMENT OF HYDROLYSIS RATE CONSTANTS FOR EVALUATION OF HAZARDOUS WASTE LAND DISPOSAL. VOLUME 1. DATA ON 32 CHEMICALS

    EPA Science Inventory

    To provide input data for a mathematical model to estimate potential groundwater contamination from chemicals in land disposal sites, hydrolysis rate constants were determined for 26 regulated chemicals under carefully controlled conditions. Hydrolysis rates were measured under s...

  5. MEASUREMENT OF HYDROLYSIS RATE CONSTANTS FOR EVALUATION OF HAZARDOUS WASTE LAND DISPOSAL. VOLUME 2. DATA ON 54 CHEMICALS

    EPA Science Inventory

    To provide input data for a mathematical model to estimate potential groundwater contamination from chemicals in land disposal sites, hydrolysis rate constants were determined for 31 regulated chemicals under carefully controlled conditions. Hydrolysis rates were measured under s...

  6. MEASUREMENT OF HYDROLYSIS RATE CONSTANTS FOR EVALUATION OF HAZARDOUS WASTE LAND DISPOSAL. VOLUME 3. DATA ON 70 CHEMICALS

    EPA Science Inventory

    To provide input data for a mathematical model to estimate potential groundwater contamination from chemicals in land disposal sites, hydrolysis rate constants were measured for 70 regulated chemicals under carefully controlled conditions. Hydrolysis rates were measured under ste...

  7. Application of chemometrics methods with kinetic constraints for estimation of rate constants of second order consecutive reactions.

    PubMed

    Kompany-Zareh, Mohsen; Khoshkam, Maryam

    2008-05-01

    To determine the rate constants for the second order consecutive reactions of the form U + V -(k1)--> W -(k2)--> P, a number of chemometrics and hard modeling-based methods are described. The absorption spectroscopic data from the reaction were utilized for performing the analysis. Concentrations and extinctions of components were comparable, and all of them were absorbing species. The number of steps in the reaction was less than the number of absorbing species, which resulted in a rank-deficient response matrix. This can cause difficulties for some of the methods described in the literature. The standard MATLAB functions were used for determining the solutions of the differential equations as well as for finding the optimal rate constants to describe the kinetic profiles. The available knowledge about the system determines the approaches described in this paper. The knowledge includes the spectra of reactants and products, the initial concentrations, and the exact kinetics. Some of this information is sometimes not available or is hard to estimate. Multiple linear regression for fitting the kinetic parameters to the obtained concentration profiles, rank augmentation using multiple batch runs, a mixed spectral approach which treats the reaction using a pseudo species concept, and principal components regression are the four groups of methods discussed in this study. In one of the simulated datasets the spectra are quite different, and in the other one the spectra of one reactant and of the product share a high degree of overlap. Instrumental noise, sampling error are the sources of error considered. Our aim was the investigation of the relative merits of each method. PMID:18469471

  8. 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...

  9. Rate constant for the reaction Cl + HO2NO2 yielding products. [in stratospheric chemistry

    NASA Technical Reports Server (NTRS)

    Simonaitis, R.; Leu, M. T.

    1985-01-01

    The rates for the reaction of Cl atoms iwth HO2NO2 were calculated from data obtained by the use of the discharge flow/resonance fluorescence (DF/RF) and the discharge flow/mass spectrometric (DF/MS) techniques. The total rate constant, k1, for the overall reaction: 1a (Cl + HO2NO2 yielding HCl + NO2 +O2), 1b (yielding HO2 + ClNO2), and the two possible additional channels was found to be less than 1.0 x 10 to the -13th cu cm/s at 296 K. The value of (k1a + k1b) was found to be 3.4 + or - 1.4) x 10 to the -14th cu cm/s. Thus, the reaction of Cl with peroxynitric acid is too slow, by a factor of 100, to contribute significantly to the hydrogen abstraction by Cl in the stratosphere.

  10. Scaling of the rupture dynamics of polymer chains pulled at one end at a constant rate.

    PubMed

    Fugmann, S; Sokolov, I M

    2009-02-01

    We consider the rupture dynamics of a homopolymer chain pulled at one end at a constant loading rate r . Compared to single bond breaking, the existence of the chain introduces two aspects into rupture dynamics: The non-Markovian aspect in the barrier crossing and the slow down of the force propagation to the breakable bond. The relative impact of both these processes is investigated, and the second one was found to be the most important at moderate loading rates. The most probable rupture force is found to decrease with the number of bonds as f{max} proportional, variant-[ln(const N/r)]2/3 and finally to approach a saturation value independent on N . All of our analytical findings are confirmed by extensive numerical simulations. PMID:19391768

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  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. PMID:27451646

  16. Mechanism and thermal rate constant for the gas-phase ozonolysis of acenaphthylene in the atmosphere.

    PubMed

    Dang, Juan; Shi, Xiangli; Zhang, Qingzhu; Hu, Jingtian; Wang, Wenxing

    2015-05-01

    Due to its prevalent presence, it is critical to clarify the atmospheric fate of acenaphthylene (Ary). In this paper, the reaction mechanism of the gas-phase ozonolysis of Ary was investigated by using quantum chemistry methods. Possible reaction pathways were discussed, and the theoretical results were compared with the available experimental data. The rate constants of the crucial elementary reactions were determined by the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The main products include secondary ozonide, naphthalene-1,8-dicarbaldehyde, 1,8-naphthalic anhydride, oxaacenaphthylene-2-one, 1-naphthaldehyde, 2-hydroxy-1-naphthaldehyde, and α-hydroxyhydroperoxide. The reaction of the unsaturated cyclo-pentafused ring with O₃ is the dominant pathway. The overall rate constant of the O₃ addition reaction is 5.31×10(-16)cm(3)molecule(-1)s(-1) at 298 K and 1 atm. The atmospheric lifetime of Ary determined by O₃ is about 0.75 h. This work provides a comprehensive investigation of the ozonolysis of Ary and should help to understand its atmospheric fate. PMID:25679814

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

  18. 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. PMID:27369506

  19. 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. PMID:24824504

  20. 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

  1. 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

    2016-07-01

    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. PMID:27253726

  2. 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.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

    Vanicek, Jiri; Miller, William H.

    2004-03-01

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

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

    PubMed

    Gansäuer, Andreas; Seddiqzai, Meriam; Dahmen, Tobias; Sure, Rebecca; Grimme, Stefan

    2013-01-01

    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

  6. Rate Constant and Reaction Coordinate of Trp-Cage Folding in Explicit Water

    PubMed Central

    Juraszek, Jarek; Bolhuis, Peter G.

    2008-01-01

    We report rate constant calculations and a reaction coordinate analysis of the rate-limiting folding and unfolding process of the Trp-cage mini-protein in explicit solvent using transition interface sampling. Previous transition path sampling simulations revealed that in this (un)folding process the protein maintains its compact configuration, while a (de)increase of secondary structure is observed. The calculated folding rate agrees reasonably with experiment, while the unfolding rate is 10 times higher. We discuss possible origins for this mismatch. We recomputed the rates with the forward flux sampling method, and found a discrepancy of four orders of magnitude, probably caused by the method's higher sensitivity to the choice of order parameter with respect to transition interface sampling. Finally, we used the previously computed transition path-sampling ensemble to screen combinations of many order parameters for the best model of the reaction coordinate by employing likelihood maximization. We found that a combination of the root mean-square deviation of the helix and of the entire protein was, of the set of tried order parameters, the one that best describes the reaction coordination. PMID:18676648

  7. 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.

  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. Pharmacokinetics of cyclosporin: influence of rate of constant intravenous infusion in renal transplant patients.

    PubMed

    Gupta, S K; Legg, B; Solomon, L R; Johnson, R W; Rowland, M

    1987-10-01

    1 The pharmacokinetics of cyclosporin were studied in 12 renal transplant patients. Five patients received a constant rate (7 mg kg-1 day-1) intravenous infusion over 72 h and the remainder received rates of 7, 4 and 10 mg kg-1 day-1, consecutively each for at least 24 h. 2 Plasma, separated at 37 degrees C, was analysed by h.p.l.c. 3 The data were best described by a biexponential model. 4 Following the 72 h infusion, a plateau was reached by 24 h and clearance was 0.60 l h-1 kg-1. 5 Clearance associated with the 10 mg kg-1 day-1 infusion rate (0.43 l h-1 kg-1) was estimated to be lower than that following the 4 and 7 mg kg-1 day-1 rates (0.52 and 0.54 l h-1 kg-1 respectively) but the difference is unlikely to be of clinical significance. PMID:3318898

  10. 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.

  11. Toward Improving Atmospheric Models and Ozone Projections: Laboratory UV Absorption Cross Sections and Equilibrium Constant of ClOOCl

    NASA Astrophysics Data System (ADS)

    Wilmouth, D. M.; Klobas, J. E.; Anderson, J. G.

    2015-12-01

    Thirty years have now passed since the discovery of the Antarctic ozone hole, and despite comprehensive international agreements being in place to phase out CFCs and halons, polar ozone losses generally remain severe. The relevant halogen compounds have very long atmospheric lifetimes, which ensures that seasonal polar ozone depletion will likely continue for decades to come. Changes in the climate system can further impact stratospheric ozone abundance through changes in the temperature and water vapor structure of the atmosphere and through the potential initiation of solar radiation management efforts. In many ways, the rate at which climate is changing must now be considered fast relative to the slow removal of halogens from the atmosphere. Photochemical models of Earth's atmosphere play a critical role in understanding and projecting ozone levels, but in order for these models to be accurate, they must be built on a foundation of accurate laboratory data. ClOOCl is the centerpiece of the catalytic cycle that accounts for more than 50% of the chlorine-catalyzed ozone loss in the Arctic and Antarctic stratosphere every spring, and so uncertainties in the ultraviolet cross sections of ClOOCl are particularly important. Additionally, the equilibrium constant of the dimerization reaction of ClO merits further study, as there are important discrepancies between in situ measurements and lab-based models, and the JPL-11 recommended equilibrium constant includes high error bars at atmospherically relevant temperatures (~75% at 200 K). Here we analyze available data for the ClOOCl ultraviolet cross sections and equilibrium constant and present new laboratory spectroscopic results.

  12. Rate constant measurement of the recombination reaction C[sub 3]H[sub 3] + C[sub 3]H[sub 3

    SciTech Connect

    Morter, C.L.; Farhat, S.K.; Adamson, J.D.; Glass, G.P.; Curl, R.F. )

    1994-07-14

    Using the technique of infrared kinetic absorption spectroscopy, the second-order rate constant for the recombination reaction of the propargyl radical (C[sub 3]H[sub 3] + C[sub 3]H[sub 3]) has been measured and found to have the value (1.2 [+-] 0.2) x 10[sup [minus]10] cm[sup 3] molecule[sup [minus]1] s[sup [minus]1] at 295 K. The radical was produced in a flow cell by excimer laser flash photolysis ([lambda] = 193 nm) of the precursors C[sub 3]H[sub 3]Cl or C[sub 3]H[sub 3]Br and detected using time-resolved IR absorption. Absolute concentrations of C[sub 3]H[sub 3] were determined by comparing the C[sub 3]H[sub 3] absorption intensity with that of the Br atom. This calibration scheme was checked by producing methyl radicals by photolysis of methyl bromide and comparing the rate constant for methyl recombination thus obtained with literature values. The quantum yield for HCl production from the photodissociation of C[sub 3]H[sub 3]Cl at 193 nm was determined to be 0.07 [+-] 0.01. 47 refs., 10 figs., 1 tab.

  13. Rate constants and mechanisms for the crystallization of Al nano-goethite under environmentally relevant conditions

    NASA Astrophysics Data System (ADS)

    Bazilevskaya, Ekaterina; Archibald, Douglas D.; Martínez, Carmen Enid

    2012-07-01

    Mobile inorganic and organic nanocolloidal particles originate-from and interact-with bulk solid phases in soil and sediment environments, and as such, they contribute to the dynamic properties of environmental systems. In particular, ferrihydrite and (nano)goethite are the most abundant of nanocolloidal Fe oxy(hydr)oxides in these environments. We therefore investigated the ferrihydrite to goethite phase transformation using experimental reaction conditions that mimicked environmental conditions where the formation of nanocolloidal Fe oxy(hydr)oxides may occur: slow titration of dilute solutions to pH 5 at 25 °C with and without 2 mol% Al. Subsequently, the rate constants from 54-d nano-goethite aging/crystallization experiments at 50 °C were determined using aliquots pulled for vibrational spectroscopy (including multivariate curve resolution, MCR, analyses of infrared spectra) and synchrotron-based X-ray diffraction (XRD). We also present a mechanistic model that accounts for the nano-goethite crystallization observed by the aforementioned techniques, and particle structural characteristics observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). In contrast to the common assumption that metastable ferrihydrite precipitates first, before it transforms to goethite, the presence of characteristic infrared bands in freshly synthesized nanoparticle suspensions indicate goethite can precipitate directly from solution under environmentally relevant conditions: low Fe concentration, ambient temperature, and pH maintained at 5. However, the presence of 2 mol% Al prevented direct goethite precipitation. Rate constants obtained by fitting the contributions from the MCR-derived goethite-like component to the OH-stretching region were (7.4 ± 1.1) × 10-7 s-1 for 0% Al and (4.2 ± 0.4) × 10-7 s-1 for 2 mol% Al suspensions. Rate constants derived from intensities of OH-bending infrared vibrations (795 and 895 cm-1) showed similar values

  14. 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

  15. Channel specific rate constants relevant to the thermal decomposition of disilane.

    SciTech Connect

    Matsumoto, Keiji; Klippenstein, Stephen J.; Koshi, Mitsuo; Tonokura, Kenichi

    2005-01-01

    Rate constants for the thermal dissociation of Si{sub 2}H{sub 6} are predicted with a novel transition state model. The saddle points for dissociation on the Si{sub 2}H{sub 6} potential energy surface are lower in energy than the corresponding separated products, as confirmed by high level ab initio quantum mechanical calculations. Thus, the dissociations of Si{sub 2}H{sub 6} to produce SiH{sub 2} + SiH{sub 4} (R1) and H{sub 3}SiSiH + H{sub 2} (R2) both proceed through tight inner transition states followed by loose outer transition states. The present 'dual' transition state model couples variational phase space theory treatments of the outer transition states with ab initio based fixed harmonic vibrator treatments of the inner transition states to obtain effective numbers of states for the two transition states acting in series. It is found that, at least near room temperature, such a dual transition state model is generally required for the proper description of each of the dissociations. Only at quite high temperatures, i.e., above 2000 K for (R1) and 600 K for (R2), does a single fixed inner transition state provide an adequate description. Similarly, only at quite low temperatures (below 100 and 10 K for (R1) and (R2), respectively) does a single outer transition state provide an adequate description. Pressure dependent rate constants are obtained from solutions to the multichannel master equation. These calculations confirm that dissociation channel (R2) is negligible under conditions relevant to the thermal chemical vapor deposition (CVD) processes. Rate constants for the chemical activation reactions, SiH{sub 2} + SiH{sub 4} {yields} Si{sub 2}H{sub 6} (R-1) and SiH{sub 2} + SiH{sub 4} {yields} H{sub 3}SiSiH + H{sub 2} (R3), are also evaluated within the dual transition state model. It is found that reaction R3 is the dominant channel for low pressures and high temperatures, i.e., below 100 Torr for temperatures above 1100 K.

  16. Channel specific rate constants relevant to the thermal decomposition of disilane.

    PubMed

    Matsumoto, Keiji; Klippenstein, Stephen J; Tonokura, Kenichi; Koshi, Mitsuo

    2005-06-01

    Rate constants for the thermal dissociation of Si2H6 are predicted with a novel transition state model. The saddle points for dissociation on the Si2H6 potential energy surface are lower in energy than the corresponding separated products, as confirmed by high level ab initio quantum mechanical calculations. Thus, the dissociations of Si2H6 to produce SiH2 + SiH4 (R1) and H3SiSiH + H2 (R2) both proceed through tight inner transition states followed by loose outer transition states. The present "dual" transition state model couples variational phase space theory treatments of the outer transition states with ab initio based fixed harmonic vibrator treatments of the inner transition states to obtain effective numbers of states for the two transition states acting in series. It is found that, at least near room temperature, such a dual transition state model is generally required for the proper description of each of the dissociations. Only at quite high temperatures, i.e., above 2000 K for (R1) and 600 K for (R2), does a single fixed inner transition state provide an adequate description. Similarly, only at quite low temperatures (below 100 and 10 K for (R1) and (R2), respectively) does a single outer transition state provide an adequate description. Pressure dependent rate constants are obtained from solutions to the multichannel master equation. These calculations confirm that dissociation channel (R2) is negligible under conditions relevant to the thermal chemical vapor deposition (CVD) processes. Rate constants for the chemical activation reactions, SiH2 + SiH4 --> Si2H6 (R-1) and SiH2 + SiH4 --> H3SiSiH + H2 (R3), are also evaluated within the dual transition state model. It is found that reaction R3 is the dominant channel for low pressures and high temperatures, i.e., below 100 Torr for temperatures above 1100 K. PMID:16833838

  17. 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. PMID:26165545

  18. Probing the protein-folding mechanism using denaturant and temperature effects on rate constants

    PubMed Central

    Guinn, Emily J.; Kontur, Wayne S.; Tsodikov, Oleg V.; Shkel, Irina; Record, M. Thomas

    2013-01-01

    Protein folding has been extensively studied, but many questions remain regarding the mechanism. Characterizing early unstable intermediates and the high–free-energy transition state (TS) will help answer some of these. Here, we use effects of denaturants (urea, guanidinium chloride) and temperature on folding and unfolding rate constants and the overall equilibrium constant as probes of surface area changes in protein folding. We interpret denaturant kinetic m-values and activation heat capacity changes for 13 proteins to determine amounts of hydrocarbon and amide surface buried in folding to and from TS, and for complete folding. Predicted accessible surface area changes for complete folding agree in most cases with structurally determined values. We find that TS is advanced (50–90% of overall surface burial) and that the surface buried is disproportionately amide, demonstrating extensive formation of secondary structure in early intermediates. Models of possible pre-TS intermediates with all elements of the native secondary structure, created for several of these proteins, bury less amide and hydrocarbon surface than predicted for TS. Therefore, we propose that TS generally has both the native secondary structure and sufficient organization of other regions of the backbone to nucleate subsequent (post-TS) formation of tertiary interactions. The approach developed here provides proof of concept for the use of denaturants and other solutes as probes of amount and composition of the surface buried in coupled folding and other large conformational changes in TS and intermediates in protein processes. PMID:24043778

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    Cranor, Walter L.; Alvarez, David A.; Huckins, James N.; Petty, Jimmie D.

    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 m 3 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 m 3 g -1 d -1 with relative standard deviations of 8.4% and 8.6% respectively.

  1. 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

  2. Table 5.1. Exchange current densities and rate constants in aqueous systems

    NASA Astrophysics Data System (ADS)

    Holze, R.

    This document is part of Volume 9 `Electrochemistry', Subvolume A, of Landolt-Börnstein - Group IV `Physical Chemistry'. This document lists the exchange current densities and the electrode reaction rate constants of the following metallic electrodes in aqueous systems for various electrolyte reactions: silver (Ag), aluminium (Al), gold (Au), bismuth (Bi), carbon (C), cadmium (Cd), cobalt (Co), chromium (Cr), cesium (Cs), copper (Cu), iron (Fe), gallium (Ga), mercury (Hg), indium (In), iridium (Ir), potassium (K), lithium (Li), molybdenum (Mo), natrium (Na), niobium (Nb), nickel (Ni), lead (Pb), palladium (Pd), platinum (Pt), rubidium (Rb), rhodium (Rh), ruthenium (Ru), antimony (Sb), tin (Sn), tantalum (Ta), titanium (Ti), thallium (Tl), vanadium (V), tungsten (W), zinc (Zn). For each electrolyte reaction the electrolyte solution, the educt, product and concentration are specified along with the temperature of determination of the given values.

  3. 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.

  4. 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.

  5. Improved quasiclassical trajectory method for state to state reactive scattering cross sections and rate constants

    SciTech Connect

    Ashton, C.J.; Muckerman, J.T.; Schubert, F.E.

    1984-12-15

    A systematic scheme is developed for the incorporation into quasiclassical trajectory (QCT) methodology of recent advances in the understanding of vibrationally adiabatic barriers in collinear atom + diatom reactions. The resulting hybrid QCT method centers on a definite set of rules for optimally combining the results of forward and reverse trajectory calculations. It is argued, and demonstrated by practical examples, that the hybrid method will give a more consistently reliable account of the threshold behavior of collinear reaction cross sections than the conventional QCT method. Extension of the method to the three dimensional F+H/sub 2/ reaction gives similarly encouraging results, both for state to state reaction cross sections and for rate constants.

  6. Improved quasiclassical trajectory method for state to state reactive scattering cross sections and rate constants

    SciTech Connect

    Ashton, C.J.; Muckerman, J.T.; Schubert, F.E.

    1984-12-15

    A systematic scheme is developed for the incorporation into quasiclassical trajectory (QCT) methodology of recent advances in the understanding of vibrationally adiabatic barriers in collinear atom + diatom reactions. The resulting hybrid QCT method centers on a definite set of rules for optimally combining the results of forward and reverse trajectory calculations. It is argued, and demonstrated by practical examples, that the hybrid method will give a more consistently reliable account of the threshold behavior of collinear reaction cross sections than the conventional QCT method. Extension of the method to the three dimensional F + H/sub 2/ reaction gives similarly encouraging results, both for state to state reaction cross sections and for rate constants. 43 references, 15 figures, 4 tables.

  7. Bioaccessibility of metal cations in soil is linearly related to its water exchange rate constant.

    PubMed

    Laird, Brian D; Peak, Derek; Siciliano, Steven D

    2011-05-01

    Site-specific risk assessments often incorporate the concepts of bioaccessibility (i.e., contaminant fraction released into gastrointestinal fluids) or bioavailability (i.e., contaminant fraction absorbed into systemic circulation) into the calculation of ingestion exposure. We evaluated total and bioaccessible metal concentrations for 19 soil samples under simulated stomach and duodenal conditions using an in vitro gastrointestinal model. We demonstrated that the median bioaccessibility of 23 metals ranged between <1 and 41% under simulated stomach conditions and < 1 and 63% under simulated duodenal conditions. Notably, these large differences in metal bioaccessibility were independent of equilibrium solubility and stability constants. Instead, the relationship (stomach phase R = 0.927; duodenum phase R = 0.891) between bioaccessibility and water exchange rates of metal cations (k(H₂O)) indicated that desorption kinetics may influence if not control metal bioaccessibility. PMID:21466150

  8. 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.

  9. 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.

  10. Rate constants of reactions of bromine with phenols in aqueous solution.

    PubMed

    Gallard, Hervé; Pellizzari, Fabien; Croué, Jean Philippe; Legube, B

    2003-07-01

    The kinetics of bromination of six ortho- and para-substituted phenols was investigated between pH 5 and pH 12 in aqueous solution. Kinetics was followed with a continuous-flow reactor previously validated by studying the fast reaction between chlorine and ammonia. The overall reaction rate between bromine and phenols is controlled by the reaction of HOBr with the phenoxide ion between pH 6 and pH 10. The reaction of HOBr with the undissociated phenols and the reaction of BrO(-) with the phenoxide ions become only significant for pH<6 and pH>10, respectively. The second-order rate constants for the reaction of HOBr with phenoxide ions vary between 1.4(+/-0.1)x10(3) and 2.1(+/-0.5)x10(8)M(-1)s(-1) for 2,4,6-trichlorophenol and 4-methylphenol, respectively. Hammett-type correlation was obtained for the reaction of HOBr with the phenoxide ions (log(k)=8.0-3.33 x Sigmasigma) and was compared with Hammett-type correlations of HOCl and HOI. The reaction rate of bromine with phenol-like organic compounds was estimated to be about 10(3)-fold higher than with chlorine and 10(3)-fold lower than with ozone in drinking water treatment conditions. PMID:12767291

  11. Test of the quantum instanton approximation for thermal rate constants for some collinear reactions.

    PubMed

    Ceotto, Michele; Miller, William H

    2004-04-01

    Two variants of the recently developed quantum instanton (QI) model for calculating thermal rate constants of chemical reactions are applied to several collinear atom-diatom reactions with various skew angles. The results show that the original QI version of the model is consistently more accurate than the "simplest" quantum instanton version (both being applied here with one "dividing surface") and thus to be preferred. Also, for these examples (as with other earlier applications) the QI results agree well with the correct quantum rates (to within approximately 20% or better) for all temperatures >200 K, except for situations where dynamical corrections to transition state theory (i.e., "re-crossing" dynamics) are evident. (Since re-crossing effects are substantially reduced in higher dimensionality, this is not a cause for serious concern.) A procedure is also described which facilitates use of the METROPOLIS algorithm for evaluating all quantities that appear in the QI rate expression by Monte Carlo path integral methods. PMID:15267524

  12. 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. PMID:27423150

  13. 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.

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

    PubMed

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

    2013-01-01

    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 V20 of the bowel, bladder, pelvis bone, and NT, but significantly decreased the dose to the high-dose region of the rectum and pelvis bone. The MUs decreased from 1105 with IMRT to 628 with VMAT-CDR. The delivery time also decreased from 9.5 to 3.2 minutes. The average gamma pass rate was 95.6% at the 3%/3mm 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. PMID:23669454

  15. Efficacy and safety of constant-rate intravenous cyclosporine infusion immediately after heart transplantation.

    PubMed

    Schroeder, T J; Myre, S A; Melvin, D B; Van der Bel-Kahn, J; Stephens, G W; Collins, J A; Wolf, R K; Brown, L L; Pesce, A J; First, M R

    1989-01-01

    Oral cyclosporine therapy immediately after heart transplantation is erratic and difficult to predict. The purpose of this study was to evaluate the relative efficacy and safety of cyclosporine when administered by constant-rate infusion immediately after transplantation. Nineteen patients (17 men and two women) aged 50 years (range 25 to 61 years) who weighed 71 +/- 9 kg, participated in the study and received cyclosporine, 7 to 10 mg/hr (117 +/- 15 micrograms/kg/hr). The infusions were initially maintained for 26 +/- 5 hours (range 18 to 42 hours) without adjustments in dosage. Whole blood samples were obtained at hourly intervals for the first 8 to 12 hours and then daily throughout the 7-day study period and were analyzed by high-performance liquid chromatography. Constant-rate cyclosporine infusion resulted in therapeutic blood levels (350 to 450 ng/ml) at 6 hours. These levels remained relatively steady throughout the 7-day infusion, requiring only minimal dosage adjustments. Kidney function was not altered significantly after 7 days of intravenous cyclosporine therapy as evidenced by a mean serum creatinine level of 1.3 mg/dl before therapy and 1.4 mg/dl after therapy. There, however, was a transient rise in serum creatinine level in most patients on the second or third day after transplantation that resolved without a reduction in cyclosporine dosage. The mean endomyocardial biopsy score at 1 week after transplantation was 0.1, and only four of the patients required additional immunosuppressive therapy to treat rejection during the first 6 weeks after transplantation.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2647932

  16. 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.

  17. 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.

  18. 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. PMID:19545885

  19. 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. PMID:18703281

  20. 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.

  1. Estimated rate constants for hydrogen abstraction from N-heterocyclic carbene-borane complexes by an alkyl radical.

    PubMed

    Solovyev, Andrey; Ueng, Shau-Hua; Monot, Julien; Fensterbank, Louis; Malacria, Max; Lacôte, Emmanuel; Curran, Dennis P

    2010-07-01

    Rate constants for hydrogen abstraction by a nonyl radical from 20 complexes of N-heterocyclic carbenes and boranes (NHC-boranes) have been determined by the pyridine-2-thioneoxycarbonyl (PTOC) competition kinetic method at a single concentration point. The rate constants range from <1 x 10(4) to 8 x 10(4) M(-1) s(-1). They show little dependence on the electronic properties of the carbene core, but there is a trend for increasing rate constants with decreasing size of the carbene N-substituents. Two promising new reagents with small N-substituents (R = Me) have been identified. PMID:20536158

  2. Rate constants 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

    2009-04-30

    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. The experimental results can be expressed in Arrhenius form in units of cm{sup 3} molecule{sup -1} s{sup -1} as follows: K{sub OH+n-heptane} = (2.48 {+-} 0.17) x 10{sup -10} exp[(-1927 {+-} 69 K)/T] (838-1287 K); k{sub OH+2,2,3,3-TMB} = (8.26 {+-} 0.89) x 10{sup -11} exp[(-1337 {+-} 94 K)/T] (789-1061 K); K{sub OH+n-pentane} = (1.60 {+-} 0.25) x 10{sup -10} exp[(-1903 {+-} 146 K)/T] (823-1308 K); K{sub OH+n-hexane} = (2.79 {+-} 0.39) x 10{sup -10} exp[(-2301 {+-} 134 K)/T] (798-1299 K); and k{sub OH+2,3-DMB} = (1.27 {+-} 0.16) x 10{sup -10} exp[(-1617 {+-} 118 K)/T] (843-1292 K). The available experimental data, along with lower-T determinations, were used to obtain evaluations of the experimental rate constants over the temperature range from {approx}230 to 1300 K for most of the title reactions. These extended-temperature-range evaluations, given as three-parameter fits, are as follows: k{sub OH+n-heptane} = 2.059 x 10{sup -5}T{sup 1.401} exp(33 K/T) cm{sup 3

  3. Impairment of jejunal absorption rate of carnosine by glycylglycine in man in vivo.

    PubMed Central

    Cook, G C

    1976-01-01

    Using a double-lumen tube jejunal perfusion system in vivo, the mutual effects of carnosine (beta-alanyl-L-histidine) and glycylglycine on their respective absorption rates have been studied in six Zambian African adults. Data on the effect of the constituent amino-acids of carnosine on glycylglycine absorption rate have similarly been obtained. The solutions infused in each subject contained (A) carnosine (50 mmol l.-1), (B) carnosine (50 mmol l.-1) and glycylglycine (50 mmol l.-1), (C) glycylglycine (50 mmol l.-1), and (D) glycylglycine (50 mmol l.-1), L-histidine (50 mmol l.-1) and beta-alanine (50 mmol l.-1). Glycylglycine produced a significant impairment in the mean rate of histidine absorption from carnosine (P less than 0-01). However, carnosine did not have a significant effect on the mean rate of glycine absorption from glycylglycine. Mean rate of histidine absorption from solution D was significantly higher than that from solution A (P less than 0-01). Mean rate of glycine absorption from glycylglycine was not significantly different during infusion of solutions B, C, and D. The results are consistent with the concept that carnosine on glycylglycine is probably because the affinity of mechanism; the lack of influence of carnosine on glycylglycine is probably because the affinity of carnosine for the dipeptide uptake mechanism is relatively low. A gross difference has been shown between mean absorption rate of histidine from free L-histidine (solution D) (25-8 mmol h-1) and when it is given in the form of carnosine in the presence of another dipeptide (solution B) (8-7 mmol h-1); that emphasizes the complexity of amino acid and peptide interaction during absorption, which must be important in nutrition. PMID:773786

  4. Detecting Randomness: the Sensitivity of Statistical Tests to Deviations from a Constant Rate Poisson Process

    NASA Astrophysics Data System (ADS)

    Michael, A. J.

    2012-12-01

    Detecting trends in the rate of sporadic events is a problem for earthquakes and other natural hazards such as storms, floods, or landslides. I use synthetic events to judge the tests used to address this problem in seismology and consider their application to other hazards. Recent papers have analyzed the record of magnitude ≥7 earthquakes since 1900 and concluded that the events are consistent with a constant rate Poisson process plus localized aftershocks (Michael, GRL, 2011; Shearer and Stark, PNAS, 2012; Daub et al., GRL, 2012; Parsons and Geist, BSSA, 2012). Each paper removed localized aftershocks and then used a different suite of statistical tests to test the null hypothesis that the remaining data could be drawn from a constant rate Poisson process. The methods include KS tests between event times or inter-event times and predictions from a Poisson process, the autocorrelation function on inter-event times, and two tests on the number of events in time bins: the Poisson dispersion test and the multinomial chi-square test. The range of statistical tests gives us confidence in the conclusions; which are robust with respect to the choice of tests and parameters. But which tests are optimal and how sensitive are they to deviations from the null hypothesis? The latter point was raised by Dimer (arXiv, 2012), who suggested that the lack of consideration of Type 2 errors prevents these papers from being able to place limits on the degree of clustering and rate changes that could be present in the global seismogenic process. I produce synthetic sets of events that deviate from a constant rate Poisson process using a variety of statistical simulation methods including Gamma distributed inter-event times and random walks. The sets of synthetic events are examined with the statistical tests described above. Preliminary results suggest that with 100 to 1000 events, a data set that does not reject the Poisson null hypothesis could have a variability that is 30% to

  5. 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…

  6. 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.

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

    PubMed Central

    RIENKS, JORDYN N.; VANDERWOUDE, ANDREA A.; MAAS, ELIZABETH; BLEA, ZACHARY M.; SUBUDHI, ANDREW W.

    2015-01-01

    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. PMID:27182417

  8. Partial reactions of the Na,K-ATPase: determination of rate constants

    PubMed Central

    1994-01-01

    Experiments were designed to characterize several partial reactions of the Na,K-ATPase and to demonstrate that a model can be defined that reproduces most of the transport features of the pump with a single set of kientic parameters. We used the fluorescence label 5- iodoacetamidofluorescein, which is thought to be sensitive to conformational changes, and the styryl dye RH 421, which can be applied to detect ion-binding and -release reactions. In addition transient electric currents were measured, which are associated mainly with the E1-->E2 conformational transition. Numerical simulations were performed on the basis of a reaction model, that has been developed from the Post- Albers cycle. Analysis of the experimental data allows the determination of several rate constants of the pump cycle. Our conclusions may be summarized as follows: (a) binding of one Na+ ion at the cytoplasmic face is electrogenic. This Na+ ion is specifically bound to a neutral binding site with an affinity of 8 mM in the presence of 10 mM Mg2+. In the absence of divalent cations, the intrinsic binding affinity was found to be 0.7 mM. (b) The analysis of fluorescence experiments with the cardiotonic steroid strophanthidin indicates that the 5-iodoacetamidofluorescein label monitors the conformational transition (Na3)E1-P-->P-E2(Na2), which is accompanied by the release of one Na+ ion. 5-IAF does not respond to the release of the subsequent two Na+ ions, which can be monitored by the RH 421 dye. These experiments indicate further that the conformational transition E1P-->P-E2 is the rate limiting process of the Na+ translocation. The corresponding rate constant was determined to be 22 s-1 at 20 degrees C. From competition experiments with cardiotonic steroids, we estimated that the remaining 2 Na+ ions are released subsequently with a rate constant of at least 5,000 s-1 from their negatively charged binding sites. (c) Comparing the fluorescence experiments with electric current transients

  9. 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.

  10. Selective determination of rate constants of reactions of atomic hydrogen with various functional groups of a complex molecule

    NASA Astrophysics Data System (ADS)

    Brauer, G. B.; Pugachev, D. V.; Azatyan, V. V.

    2016-05-01

    The possibility of determining absolute values of the rate constants of reactions of active intermediate species with different functional groups of molecules is demonstrated by measuring macrokinetic combustion characteristics. The Arrhenius parameters of the rate constant of the reaction between atomic hydrogen with the methylene group of ethanol and molecular oxygen within the temperature range of 830-970 K are determined. The reasons for the differences between the rate constants of reactions with the methylene and methyl groups of an ethanol molecule are discussed using thermochemical data. It is found that the obtained values of activation energies and preexponential factors of rate constants are in good agreement with the literature data on the region of lower temperatures.

  11. QSARS FOR PREDICTING BIOTIC AND ABIOTIC REDUCTIVE TRANSFORMATION RATE CONSTANTS OF HALOGENATED HYDROCARBONS IN ANOXIC SEDIMENT SYSTEMS

    EPA Science Inventory

    Quantitative structure-activity relationships (QSARs) are developed relating biotic and abiotic pseudo-first-order disappearance rate constants of halogenated hydrocarbons in anoxic sediments to a number of readily available molecular descriptors. ased upon knowledge of the under...

  12. Frequency offset dependence of adiabatic rotating frame relaxation rate constants: relevance to MRS investigations of metabolite dynamics in vivo.

    PubMed

    Mangia, Silvia; Liimatainen, Timo; Garwood, Michael; Tkac, Ivan; Henry, Pierre-Gilles; Deelchand, Dinesh; Michaeli, Shalom

    2011-08-01

    In this work, we investigated the frequency-offset dependence of the rotating frame longitudinal (R(1ρ)) and transverse (R(2ρ)) relaxation rate constants when using hyperbolic-secant adiabatic full passage pulses or continuous-wave spin-lock irradiation. Phantom and in vivo measurements were performed to validate theoretical predictions of the dominant relaxation mechanisms existing during adiabatic full passage pulses when using different settings of the frequency offset relative to the carrier. In addition, adiabatic R(1ρ) and R(2ρ) values of total creatine and N-acetylaspartate were measured in vivo from the human brain at 4 T. When the continuous-wave pulse power was limited to safe specific absorption rates for humans, simulations revealed a strong dependence of R(1ρ) and R(2ρ) values on the frequency offset for both dipolar interactions and anisochronous exchange mechanisms. By contrast, theoretical and experimental results showed adiabatic R(1ρ) and R(2ρ) values to be practically invariant within the large subregion of the bandwidth of the hyperbolic-secant pulse where complete inversion was achieved. However, adiabatic R(1ρ) and R(2ρ) values of the methyl protons of total creatine (at 3.03 ppm) were almost doubled when compared with those of the methyl protons of N-acetylaspartate (at 2.01 ppm) in spite of the fact that these resonances were in the flat region of the inversion band of the adiabatic full passage pulses. We conclude that differences in adiabatic R(1ρ) and R(2ρ) values of human brain metabolites are not a result of their chemical shifts, but instead reflect differences in dynamics. PMID:21264976

  13. Frequency offset dependence of adiabatic rotating frame relaxation rate constants: relevance to MRS investigations of metabolite dynamics in vivo

    PubMed Central

    Mangia, Silvia; Liimatainen, Timo; Garwood, Michael; Tkac, Ivan; Henry, Pierre-Gilles; Deelchand, Dinesh; Michaeli, Shalom

    2011-01-01

    In this work, we investigated the frequency-offset dependence of the rotating frame longitudinal (R1ρ) and transverse (R2ρ) relaxation rate constants when using hyperbolic-secant adiabatic full passage pulses or continuous-wave spin-lock irradiation. Phantom and in vivo measurements were performed to validate theoretical predictions of the dominant relaxation mechanisms existing during adiabatic full passage pulses when using different settings of the frequency offset relative to the carrier. In addition, adiabatic R1ρ and R2ρ values of total creatine and N-acetylaspartate were measured in vivo from the human brain at 4 T. When the continuous-wave pulse power was limited to safe specific absorption rates for humans, simulations revealed a strong dependence of R1ρ and R2ρ values on the frequency offset for both dipolar interactions and anisochronous exchange mechanisms. By contrast, theoretical and experimental results showed adiabatic R1ρ and R2ρ values to be practically invariant within the large subregion of the bandwidth of the hyperbolic-secant pulse where complete inversion was achieved. However, adiabatic R1ρ and R2ρ values of the methyl protons of total creatine (at 3.03 ppm) were almost doubled when compared with those of the methyl protons of N-acetylaspartate (at 2.01 ppm) in spite of the fact that these resonances were in the flat region of the inversion band of the adiabatic full passage pulses. We conclude that differences in adiabatic R1ρ and R2ρ values of human brain metabolites are not a result of their chemical shifts, but instead reflect differences in dynamics. PMID:21264976

  14. Correlation analysis of optical absorption cross section and rate coefficient measurements in reacting systems

    SciTech Connect

    Hessler, J.P.; Ogren, P.J.

    1992-08-31

    A technique was developed for determining relative importance and correlation between reactions making up a complex kinetic system. This technique was used to investigate measurements of optical absorption cross sections and the correlation between cross sections and measured rate coefficients. It is concluded that (1) species, initial conditions, and temporal regions may be identified where cross sections may be measured without interference from the kinetic behavior of the observed species and (2) experiments designed to measure rate coefficients will always be correlated with the absorption cross section of the observed species. This correlation may reduce the accuracy of rate coefficient measurements.

  15. Subpicosecond IR transient absorption spectroscopy: measurement of internal conversion rates in DABCO vapor

    NASA Astrophysics Data System (ADS)

    Glownia, J. H.; Misewich, J.; Sorokin, P. P.

    1987-09-01

    An apparatus combining subpicosecond 248.5 nm pump pulses with a time-resolved subpicosecond broadband infrared absorption spectroscopy probe has been utilized to measure an internal conversion rate in 1,4-diazabicyclo[2.2.2]octane vapor. A subpicosecond (⪅ 500 fs) internal conversion rate has been determined.

  16. Theory of absorption rate of carriers in fused silica under intense laser irradiation

    SciTech Connect

    Deng, Hongxiang; Xiang, Xia; Zheng, WG; Yuan, XD; Wu, SY; Jiang, XD; Gao, Fei; Zu, Xiaotao T.; Sun, Kai

    2010-11-15

    A quantum non-perturbation theory for phonon-assisted photon absorption of conduction band electron in intense laser was developed. By carrying out the calculation in fused silica at wavelengths from ultraviolet to infrared in terawatt intensity laser, we show that the Non-perturbation approach can make a uniform description of energy absorption rate at both short wavelengths and long wavelengths on TW / cm2 intensity laser.

  17. 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. PMID:27478722

  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. Measuring OH Reaction Rate Constants and Estimating the Atmospheric Lifetimes of Trace Gases.

    NASA Astrophysics Data System (ADS)

    Orkin, Vladimir; Kurylo, Michael

    2015-04-01

    Reactions with hydroxyl radicals and photolysis are the main processes dictating a compound's residence time in the atmosphere for a majority of trace gases. In case of very short-lived halocarbons their reaction with OH dictates both the atmospheric lifetime and active halogen release. Therefore, the accuracy of OH kinetic data is of primary importance for the comprehensive modeling of a compound's impact on the atmosphere, such as in ozone depletion (i.e., the Ozone Depletion Potential, ODP) and climate change (i.e., the Global Warming Potential, GWP), each of which are dependent on the atmospheric lifetime of the compound. We have demonstrated the ability to conduct very high accuracy determinations of OH reaction rate constants over the temperature range of atmospheric interest, thereby decreasing the uncertainty of kinetic data to 2-3%. The atmospheric lifetime of a well-mixed compound due to its reaction with tropospheric hydroxyl radicals can be estimated by using a simple scaling procedure that is based on the results of field observations of methyl chloroform concentrations and detailed modeling of the OH distribution in the atmosphere. The currently available modeling results of the atmospheric fate of various trace gases allow for an improved understanding of the ability and accuracy of simplified semi-empirical estimations of atmospheric lifetimes. These aspects will be illustrated in this presentation for a variety of atmospheric trace gases.

  20. Measuring OH Reaction Rate Constants and Estimating the Atmospheric Lifetimes of Trace Gases.

    NASA Astrophysics Data System (ADS)

    Orkin, V. L.; Kurylo, M. J., III

    2014-12-01

    Reactions with hydroxyl radicals and photolysis are the main processes dictating a compound's residence time in the atmosphere for a majority of trace gases. In case of very short-lived halocarbons their reaction with OH dictates both the atmospheric lifetime and active halogen release. Therefore, the accuracy of OH kinetic data is of primary importance for the comprehensive modeling of a compound's impact on the atmosphere, such as in ozone depletion (i.e., the Ozone Depletion Potential, ODP) and climate change (i.e., the Global Warming Potential, GWP), each of which are dependent on the atmospheric lifetime of the compound. We have demonstrated the ability to conduct very high accuracy determinations of OH reaction rate constants over the temperature range of atmospheric interest, thereby decreasing the uncertainty of kinetic data to 2-3%. The atmospheric lifetime of a tropospherically well-mixed compound due to its reaction with tropospheric hydroxyl radicals can be estimated by using a simple scaling procedure that is based on the results of field observations of methyl chloroform concentrations and detailed modeling of the OH distribution in the atmosphere. The currently available modeling results of the atmospheric fate of various trace gases allow for an improved understanding of the ability and accuracy of simplified semi-empirical estimations of atmospheric lifetimes. These aspects will be illustrated in this presentation for a variety of atmospheric trace gases.

  1. Theoretical investigation on H abstraction reaction mechanisms and rate constants of Isoflurane with the OH radical

    NASA Astrophysics Data System (ADS)

    Ren, Hongjiang; Li, Xiaojun

    2015-12-01

    The mechanism of H abstraction reactions for Isoflurane with the OH radical was investigated using density functional theory and G3(MP2) duel theory methods. The geometrical structures of all the species were fully optimised at B3LYP/6-311++G** level of theory. Thermochemistry data were obtained by utilising the high accurate model chemistry method G3(MP2) combined with the standard statistical thermodynamic calculations. Gibbs free energies were used for the reaction channels analysis. All the reaction channels were confirmed throughout the intrinsic reaction coordinate analysis. The results show that two channels were obtained, which correspond to P(1) and P(2) with the respective activation barriers of 63.03 and 54.82 kJ/mol. The rate constants for the two channels over a wide temperature range of 298.15-2000 K were predicted and the calculated data are in agreement with the experimental one. The results show that P(2) is the dominant reaction channel under 800 K and above 800 K, it can be found that P(1) will be more preferable reaction channel.

  2. Predicting the reaction rate constants of micropollutants with hydroxyl radicals in water using QSPR modeling.

    PubMed

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

    2015-11-01

    Quantitative structure-property relationship (QSPR) models which predict hydroxyl radical rate constants (kOH) for a wide range of emerging micropollutants are a cost effective approach to assess the susceptibility of these contaminants to advanced oxidation processes (AOPs). A QSPR model for the prediction of kOH of emerging micropollutants from their physico-chemical properties was developed with special attention to model validation, applicability domain and mechanistic interpretation. In this study, 118 emerging micropollutants including those experimentally determined by the author and data collected from the literature, were randomly divided into the training set (n=89) and validation set (n=29). 951 DRAGON molecular descriptors were calculated for model development. The QSPR model was calibrated by applying forward multiple linear regression to the training set. As a result, 7 DRAGON descriptors were found to be important in predicting the kOH values which related to the electronegativity, polarizability, and double bonds, etc. of the compounds. With outliers identified and removed, the final model fits the training set very well and shows good robustness and internal predictivity. The model was then externally validated with the validation set showing good predictive power. The applicability domain of the model was also assessed using the Williams plot approach. Overall, the developed QSPR model provides a valuable tool for an initial assessment of the susceptibility of micropollutants to AOPs. PMID:26005810

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

    SciTech Connect

    Saito, Keisuke; Sumi, Hitoshi

    2009-10-07

    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.

  4. A QSAR for the prediction of rate constants for the reaction of VOCs with nitrate radicals.

    PubMed

    Schindler, Michael

    2016-07-01

    A QSAR for the prediction of rate constants for the degradation of volatile organic compounds by nitrate radicals is developed using the Partial Least Squares technique. The QSAR is based on experimental data published in the literature for 260 compounds. They are modeled by a set of calculated descriptors from standard descriptor generation tools and from quantum chemistry. Out of several diversity-based partitionings of the data set a diverse set of 99 compounds turned out to be the optimum choice with regard to simplicity and performance. The final QSAR model is characterized by r(2) = 0.831 (fit) and q(2) = 0.823 (prediction), and by an r(2)pred = 0.862 for the n = 155 external validation set. The QSAR needs 3 latent variables. The most important descriptors for the QSAR are the ionization potential, obtained from density functional theory, and the energy of the highest occupied molecular orbital, which are modulated by fingerprints indicating the presence of specific molecular fragments like functional groups or ring systems. The applicability domain of the new QSAR was studied for some compound classes which are important for the crop protection industry, including (di)hydroxbenzenes and heterocyclic compounds. PMID:27037771

  5. Determination of the rate constant for neuronal and extra-neuronal monoamine oxidase

    SciTech Connect

    Cassis, L.; Ludwig, J.; Trendelenburg, U.

    1986-03-01

    In the rat vas deferens, neuronal deamination of /sup 3/H-(-) noradrenaline (/sup 3/H-NA) to /sup 3/H-dihydroxyphenethylglycol (/sup 3/HDOPEG) cannot be inhibited by pretreatment with a monoamine oxidase (MAO) inhibitor. However, in the extraneuronal compartment of the rat heart, inhibition of MAO abolishes the formation of /sup 3/HDOPEG. To clarify this discrepancy, the authors determined the rate constant for MAO (/sup k/mao/) neuronally (rat vas deferens) and extraneuronally (rat heart). For neuronal /sup k/mao, vasa deferentia were incubated with /sup 3/HNA for 300 minutes, and the cumulative formation of /sup 3/HDOPEG measured. The delay in time before /sup 3/HDOPEG achieves steady state (/sup tau/system), is inversely proportional to /sup k/mao. Because /sup tau/system is very short for neuronal MAO, an appreciable delay was only achieved after partial inhibition of MAO with various parglyline concentrations. To relate to the uninhibited enzyme, the percentage inhibition by pargyline was then determined in homogenate preparations. For extraneuronal MAO, a similar procedure was performed in perfused rat hearts. Results show a significantly greater /sup k/mao of neuronal origin, (/sup k/mao = .57min/sup -/1) which when related to the fractional size of the neuronal compartment suggests a very high activity of neuronal MAO.

  6. 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.

  7. Temperature dependence of the rate constants for reactions of O/1D/ atoms with a number of halocarbons

    NASA Technical Reports Server (NTRS)

    Davidson, J. A.; Schiff, H. I.; Brown, T. J.; Howard, C. J.

    1978-01-01

    Results are reported for an experimental study of the reactions of O(1D) with CCl4, CFCl3, CF2Cl2, CHFCl2, CHF2Cl, and CF2ClCFCl2 over the temperature range from 173 to 343 K, based on the time-resolved emission of O(1D) at 630 nm. The experiments involved photolysis of O3 by Nd-YAG laser pulses and measurements of 630-nm emission intensity in mixtures with He and the various halocarbons. Pseudo-first-order rate constants are derived from plots of the logarithms of the 630-nm emission intensities as a function of time for particular He/O3/halocarbon mixtures, and second-order rate constants are then obtained from plots of these pseudo-first-order rate constants as a function of halocarbon concentration at constant He and O3 concentrations. No temperature dependence of the second-order rate constants is observed over the range studied, within the precision of the measurements. It is found that the rate constants decrease as H is substituted for Cl in a halocarbon molecule and as F is substituted for H or Cl.

  8. 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

  9. 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. PMID:27237834

  10. 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.

  11. 3D finite element simulation of effects of deflection rate on energy absorption for TRIP steel

    NASA Astrophysics Data System (ADS)

    Hayashi, Asuka; Pham, Hang; Iwamoto, Takeshi

    2015-09-01

    Recently, with the requirement of lighter weight and more safety for a design of automobile, energy absorption capability of structural materials has become important. TRIP (Transformation-induced Plasticity) steel is expected to apply to safety members because of excellent energy absorption capability and ductility. Past studies proved that such excellent characteristics in TRIP steel are dominated by strain-induced martensitic transformation (SIMT) during plastic deformation. Because SIMT strongly depends on deformation rate and temperature, an investigation of the effects of deformation rate and temperature on energy absorption in TRIP is essential. Although energy absorption capability of material can be estimated by J-integral experimentally by using pre-cracked specimen, it is difficult to determine volume fraction of martensite and temperature rise during the crack extension. In addition, their effects on J-integral, especially at high deformation rate in experiment might be quite hard. Thus, a computational prediction needs to be performed. In this study, bending deformation behavior of pre-cracked specimen until the onset point of crack extension are predicted by 3D finite element simulation based on the transformation kinetics model proposed by Iwamoto et al. (1998). It is challenged to take effects of temperature, volume fraction of martensite and deformation rate into account. Then, the mechanism for higher energy absorption characteristic will be discussed.

  12. Evaluation of different indirect measures of rate of drug absorption in comparative pharmacokinetic studies.

    PubMed

    Lacey, L F; Keene, O N; Duquesnoy, C; Bye, A

    1994-02-01

    As indirect measures of rate of drug absorption (metrics), maximum plasma concentration (Cmax) is confounded by extent of drug absorption and the time to reach Cmax (tmax) is a discrete variable, dependent on blood sampling frequency. Building on the work of Endrenyi et al., we have compared different metrics, including Cmax/area under the curve of concentration versus time from time zero to infinity (AUC infinity), partial AUC from zero to tmax (AUCp), and Cmax.tmax with simulated experiments. Importantly, the performance of these metrics was assessed with the results of actual pharmacokinetic studies involving Glaxo drugs. The results of the simulated and real experiments were consistent and produced the following unambiguous findings: (1) Cmax/AUC infinity is a more powerful metric than Cmax in establishing bioequivalence when the formulations are truly bioequivalent; (2) Cmax/AUC infinity is more sensitive than Cmax at detecting differences in rate of absorption when they exist; and (3) the treatment ratios for AUCp, AUCp/AUC infinity, and Cmax.tmax are very imprecisely estimated and are of no practical value as measures of rate of absorption. Of the metrics examined, Cmax/AUC infinity is the most sensitive and powerful indirect measure of rate of drug absorption in comparative pharmacokinetic studies involving immediate-release dosage forms and should be used instead of Cmax in bioequivalence testing. PMID:8169791

  13. Procedures for static and constant-rate tests on a Single-Degree-of-Freedom (SDF) strapdown gyroscope

    NASA Astrophysics Data System (ADS)

    Apps, R.; Vinnins, M.

    1983-10-01

    Test procedures for testing a rate-integrating, Single-Degree-of-Freedom strapdown gyroscope are presented. Tests are restricted to static and constant-rate modes in both inertial reference servo and analog-torque-to-balance configurations. Alignment procedures and adopted sign conventions are discussed. Temperature control considerations are described.

  14. Energy absorption at high strain rate of glass fiber reinforced mortars

    NASA Astrophysics Data System (ADS)

    Fenu, Luigi; Forni, Daniele; Cadoni, Ezio

    2015-09-01

    In this paper, the dynamic behaviour of cement mortars reinforced with glass fibers was studied. The influence of the addition of glass fibers on energy absorption and tensile strength at high strain-rate was investigated. Static tests in compression, in tension and in bending were first performed. Dynamic tests by means of a Modified Hopkinson Bar were then carried out in order to investigate how glass fibers affected energy absorption and tensile strength at high strain-rate of the fiber reinforced mortar. The Dynamic Increase Factor (DIF) was finally evaluated.

  15. 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. PMID:25453319

  16. 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. PMID:27369495

  17. 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.

  18. 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.

  19. A Marcus Treatment of Rate Constants for Protonation of Ring-Substituted α-Methoxystyrenes

    PubMed Central

    Richard, John P.; Williams, Kathleen B.

    2008-01-01

    Rate and equilibrium constants were determined for protonation of ring-substituted α-methoxystyrenes by hydronium ion and by carboxylic acids to form the corresponding ring-substituted α-methyl α-methoxybenzyl carbocations at 25 ° C and I = 1.0 (KCl). The thermodynamic barrier to carbocation formation increases by14.5 kcal/mol as the phenyl ring substituent(s) is changed from 4-MeO- to 3,5-di-NO2-, and as the carboxylic acid is changed from dichloroacetic to acetic acid. The Brønsted coefficient α for protonation by carboxylic acids increases from 0.67 to 0.77 over this range of phenyl ring substituents and the Brønsted coefficient β for proton transfer increases from 0.63 to 0.69 as the carboxylic acid is changed from dichloroacetic to acetic acid. The change in these Brønsted coefficients with changing reaction driving force, ∂α∕∂ΔGavo=∂β∕∂ΔGavo=1∕8Λ=0.011 is used to calculate a Marcus intrinsic reaction barrier of Λ = 11 kcal/mol which is close to the barrier of 13 kcal/mol for thermoneutral proton transfer between this series of acids and bases. The value of α = 0.66 for thermoneutral proton transfer is greater than α = 0.50 required by a reaction that follows the Marcus equation. This elevated value of β may be due to an asymmetry in the reaction coordinate that arises from the difference in the intrinsic barriers for proton transfer at the oxygen acid reactant and resonance stabilized carbon acid product. PMID:17488079

  20. A "parallel plate" electrostatic model for bimolecular rate constants applied to electron transfer proteins.

    PubMed Central

    Watkins, J. A.; Cusanovich, M. A.; Meyer, T. E.; Tollin, G.

    1994-01-01

    A "parallel plate" model describing the electrostatic potential energy of protein-protein interactions is presented that provides an analytical representation of the effect of ionic strength on a biomolecular rate constant. The model takes into account the asymmetric distribution of charge on the surface of the protein and localized charges at the site of electron transfer that are modeled as elements of a parallel plate condenser. Both monopolar and dipolar interactions are included. Examples of simple (monophasic) and complex (biphasic) ionic strength dependencies obtained from experiments with several electron transfer protein systems are presented, all of which can be accommodated by the model. The simple cases do not require the use of both monopolar and dipolar terms (i.e., they can be fit well by either alone). The biphasic dependencies can be fit only by using dipolar and monopolar terms of opposite sign, which is physically unreasonable for the molecules considered. Alternatively, the high ionic strength portion of the complex dependencies can be fit using either the monopolar term alone or the complete equation; this assumes a model in which such behavior is a consequence of electron transfer mechanisms involving changes in orientation or site of reaction as the ionic strength is varied. Based on these analyses, we conclude that the principal applications of the model presented here are to provide information about the structural properties of intermediate electron transfer complexes and to quantify comparisons between related proteins or site-specific mutants. We also conclude that the relative contributions of monopolar and dipolar effects to protein electron transfer kinetics cannot be evaluated from experimental data by present approximations. PMID:7703857

  1. 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.

  2. Transfer and quenching rate constants for XeF(B) and XeF(C) state in low vibrational levels

    NASA Astrophysics Data System (ADS)

    Brashears, H. C., Jr.; Setser, D. W.

    1982-05-01

    The relative XeF(B-X) and XeF(C-A) emission intensities from the steady-state vacuum ultraviolet photolysis of XeF2 have been used to measure the B-C transfer and quenching rate constants of XeF molecules in low vibrational levels. The rare gases N2, CF4, SF6, F2, NF3, CF3H, CF3Cl, HF, CO2, and XeF2 were investigated as buffer gases at room temperature. The transfer rate constants are much larger than the quenching rate constants for He, Ne, Ar, Kr, N2, CF4, and SF6. For Xe, NF3, CHF3, and CClF3 transfer is only 2-4 times faster than quenching and for F2, HF, and CO2 quenching is faster than B-C state transfer. Quenching for XeF(D) was studied for rare gases and for N2. No convincing evidence was found for three-body quenching by the rare gases and their quenching of the XeF(B, C) and XeF(D) states are reported as two-body processes for pressures below ˜5 atm. The XeF(D) quenching rate constants are of the same magnitude as the B-C state transfer rate constants. The photochemical and collisional (metastable rare gas atom) dissociative excitation of XeF2 and KrF2 are summarized in the Appendix.

  3. Linear free energy relationships between aqueous phase hydroxyl radical reaction rate constants and free energy of activation.

    PubMed

    Minakata, Daisuke; Crittenden, John

    2011-04-15

    The hydroxyl radical (HO(•)) is a strong oxidant that reacts with electron-rich sites on organic compounds and initiates complex radical chain reactions in aqueous phase advanced oxidation processes (AOPs). Computer based kinetic modeling requires a reaction pathway generator and predictions of associated reaction rate constants. Previously, we reported a reaction pathway generator that can enumerate the most important elementary reactions for aliphatic compounds. For the reaction rate constant predictor, we develop linear free energy relationships (LFERs) between aqueous phase literature-reported HO(•) reaction rate constants and theoretically calculated free energies of activation for H-atom abstraction from a C-H bond and HO(•) addition to alkenes. The theoretical method uses ab initio quantum mechanical calculations, Gaussian 1-3, for gas phase reactions and a solvation method, COSMO-RS theory, to estimate the impact of water. Theoretically calculated free energies of activation are found to be within approximately ±3 kcal/mol of experimental values. Considering errors that arise from quantum mechanical calculations and experiments, this should be within the acceptable errors. The established LFERs are used to predict the HO(•) reaction rate constants within a factor of 5 from the experimental values. This approach may be applied to other reaction mechanisms to establish a library of rate constant predictions for kinetic modeling of AOPs. PMID:21410278

  4. 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

  5. Rate constants for reactions between atmospheric reservoir species. 2. H sub 2 O

    SciTech Connect

    Hatakeyama, Shiro; Leu, Mingtaun )

    1989-07-27

    The kinetics of the reactions of H{sub 2}O with ClONO{sub 2}, N{sub 2}O{sub 5}, O{sub 3}, and COCl{sub 2} have been investigated by using a large-volume static cell and a Fourier transform infrared spectrometer at 296 K. Upper limits for the homogeneous gas-phase reaction rate constants of the ClONO{sub 2} + H{sub 2}O, N{sub 2}O{sub 5} + H{sub 2}O, O{sub 3} + H{sub 2}O, and COCl{sub 2} + H{sub 2}O reactions were found to be 3.4 {times} 10{sup {minus}21}, 2.8 {times} 10{sup {minus}21}, 1.1 {times} 10{sup {minus}22}, and 1.2 {times} 10{sup {minus}23}, respectively (all in units of cm{sup 3} s{sup {minus}1}), based on the observed decay rates of ClONO{sub 2}, N{sub 2}O{sub 5}, O{sub 3}, and COCl{sub 2}. Product analyses gave 0.82 {plus minus} 0.07 for the yield of HNO{sub 3} in the ClONO{sub 2} + H{sub 2}O {yields} HOCl + HNO{sub 3} reaction and 1.1 {plus minus} 0.3 for the yield of HNO{sub 3} from the N{sub 2}O{sub 5} + H{sub 2}O {yields} 2HNO{sub 3} reaction. The quoted error represents one standard deviation of the measurement. An attempt was also made to monitor possible reaction products such as H{sub 2}O{sub 2} for the O{sub 3} + H{sub 2}O reaction, and CO{sub 2} or HCl for the COCl{sub 2} + H{sub 2}O reaction. These results may be important in the elucidation of the springtime Antarctic ozone depletion over the past decade. The implication for NO{sub x} chemistry in the nighttime troposphere based on their results of the N{sub 2}O{sub 5} + H{sub 2}O reaction will be discussed.

  6. A review of lung-to-blood absorption rates for radon progeny.

    PubMed

    Marsh, J W; Bailey, M R

    2013-12-01

    The International Commission on Radiological Protection (ICRP) Publication 66 Human Respiratory Tract Model (HRTM) treats clearance of materials from the respiratory tract as a competitive process between absorption into blood and particle transport to the alimentary tract and lymphatics. The ICRP recommended default absorption rates for lead and polonium (Type M) in ICRP Publication 71 but stated that the values were not appropriate for short-lived radon progeny. This paper reviews and evaluates published data from volunteer and laboratory animal experiments to estimate the HRTM absorption parameter values for short-lived radon progeny. Animal studies showed that lead ions have two phases of absorption: ∼10 % absorbed with a half-time of ∼15 min, the rest with a half-time of ∼10 h. The studies also indicated that some of the lead ions were bound to respiratory tract components. Bound fractions, f(b), for lead were estimated from volunteer and animal studies and ranged from 0.2 to 0.8. Based on the evaluations of published data, the following HRTM absorption parameter values were derived for lead as a decay product of radon: f(r) = 0.1, s(r) = 100 d(-1), s(s) = 1.7 d(-1), f(b) = 0.5 and s(b) = 1.7 d(-1). Effective doses calculated assuming these absorption parameter values instead of a single absorption half-time of 10 h with no binding (as has generally been assumed) are only a few per cent higher. However, as there is some conflicting evidence on the absorption kinetics for radon progeny, dose calculations have been carried out for different sets of absorption parameter values derived from different studies. The results of these calculations are discussed. PMID:23887272

  7. 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.

  8. NuSTAR and XMM-Newton observations of NGC 1365: Extreme absorption variability and a constant inner accretion disk

    SciTech Connect

    Walton, D. J.; Harrison, F. A.; Fuerst, F.; Grefenstette, B. W.; Madsen, K. K.; Risaliti, G.; Fabian, A. C.; Kara, E.; Miller, J. M.; Arevalo, P.; Ballantyne, D. R.; Boggs, S. E.; Craig, W. W.; Brenneman, L. W.; Elvis, M.; Christensen, F. E.; Gandhi, P.; Hailey, C. J.; Luo, B.; Marinucci, A.; and others

    2014-06-10

    We present a spectral analysis of four coordinated NuSTAR+XMM-Newton observations of the Seyfert galaxy NGC 1365. These exhibit an extreme level of spectral variability, which is primarily due to variable line-of-sight absorption, revealing relatively unobscured states in this source for the first time. Despite the diverse range of absorption states, each of the observations displays the same characteristic signatures of relativistic reflection from the inner accretion disk. Through time-resolved spectroscopy, we find that the strength of the relativistic iron line and the Compton reflection hump relative to the intrinsic continuum are well correlated, which is expected if they are two aspects of the same broadband reflection spectrum. We apply self-consistent disk reflection models to these time-resolved spectra in order to constrain the inner disk parameters, allowing for variable, partially covering absorption to account for the vastly different absorption states that were observed. Each of the four observations is treated independently to test the consistency of the results obtained for the black hole spin and the disk inclination, which should not vary on observable timescales. We find both the spin and the inclination determined from the reflection spectrum to be consistent, confirming that NGC 1365 hosts a rapidly rotating black hole; in all cases the dimensionless spin parameter is constrained to be a* > 0.97 (at 90% statistical confidence or better).

  9. Differing rates of cholesterol absorption among inbred mouse strains yield differing levels of HDL-cholesterol.

    PubMed

    Sontag, Timothy J; Chellan, Bijoy; Getz, Godfrey S; Reardon, Catherine A

    2013-09-01

    Inbred strains of mice with differing susceptibilities to atherosclerosis possess widely varying plasma HDL levels. Cholesterol absorption and lipoprotein formation were compared between atherosclerosis-susceptible, low-HDL C57BL6/J mice and atherosclerosis-resistant, high-HDL FVBN/J mice. [(3)H]cholesterol and triglyceride appeared in the plasma of FVB mice gavaged with cholesterol in olive oil at a much higher rate than in C57 mice. The plasma cholesterol was found almost entirely as HDL-cholesterol in both strains. Inhibition of lipoprotein catabolism with Tyloxapol revealed that the difference in the rate of [(3)H]cholesterol appearance in the plasma was due entirely to a greater rate of chylomicron secretion from the intestine of the FVB mice. Lipid absorption into the 2nd quarter of the small intestine is greater in the FVB mice and indicates that this region may contain the factors that give rise to the differences in absorption observed between the two mouse strains. Additionally, ad libitum feeding prior to cholesterol gavage accentuates the absorption rate differences compared with fasting. The resultant remodeling of the increased levels of chylomicron in the plasma may contribute to increased plasma HDL. Intestinal gene expression analysis reveals several genes that may play a role in these differences, including microsomal triglyceride transfer protein and ABCG8. PMID:23812556

  10. 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.

  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. A new limit on the variation of the fine-structure constant using absorption line multiplets in the early universe

    NASA Astrophysics Data System (ADS)

    Thong, Le Duc

    2015-08-01

    One of the key questions of modern physics concerns the possibility that physical constants vary over space and time during the history of the universe. The Standard Model of physics is built on these constants, but it does not provide any explanation for their values, nor requires their constancy over space and time. Here we set a new limit on possible spatial and temporal variations of the fine-structure constant , by comparing transitions line multiplets in an ensemble of Fe II 1608, 2344, 2374, 2383, 2587 and 2600 observed in the early universe with those measured in the laboratory. Based on the optical spectra observations of QSO HE 0515-4414, we deduced a constraint of at redshift z = 1.15. This is at present the tightest limit on at early cosmological epochs compared to the published results in the literature.

  13. Mechanism and rate of glucose absorption differ between an Australian honeyeater (Meliphagidae) and a lorikeet (Loriidae).

    PubMed

    Napier, Kathryn R; McWhorter, Todd J; Fleming, Patricia A

    2008-11-01

    Efficient mechanisms of glucose absorption are necessary for volant animals as a means of reducing mass during flight: they speed up gut transit time and require smaller volume and mass of gut tissue. One mechanism that may be important is absorption via paracellular (non-mediated) pathways. This may be particularly true for nectarivorous species which encounter large quantities of sugar in their natural diet. We investigated the extent of mediated and non-mediated glucose absorption in red wattlebirds Anthochaera carunculata (Meliphagidae) and rainbow lorikeets Trichoglossus haematodus (Loriidae) to test the hypothesis that paracellular uptake accounts for a significant proportion of total glucose uptake in these species. We found that routes of glucose absorption are highly dynamic in both species. In lorikeets, absorption of L-glucose (non-mediated uptake) is slower than that of D-glucose (mediated and non-mediated uptake), with as little as 10% of total glucose absorbed by the paracellular pathway initially (contrasting previous indirect estimates of approximately 80%). Over time, however, more glucose may be absorbed via the paracellular route. Glucose absorption by both mediated and non-mediated mechanisms in wattlebirds occurred at a faster rate than in lorikeets, and wattlebirds also rely substantially on paracellular uptake. In wattlebirds, we recorded higher bioavailability of L-glucose (96+/-3%) compared with D-glucose (57+/-2%), suggesting problems with the in vivo use of radiolabeled d-glucose. Further trials with 3-O-methyl-D-glucose revealed high bioavailability in wattlebirds (90+/-5%). This non-metabolisable glucose analogue remains the probe of choice for measuring uptake rates in vivo, especially in birds in which absorption and metabolism occur extremely rapidly. PMID:18978218

  14. Increased absorption rate of diclofenac from fast acting formulations containing its potassium salt.

    PubMed

    Reiner, V; Reiner, A; Reiner, G; Conti, M

    2001-11-01

    Diclofenac (CAS 15307-86-5) is a non-steroidal anti-inflammatory drug largely used, mainly to relief pain of various origin. Diclofenac is present on the market as free acid, as sodium salt (CAS 15307-79-6) and as potassium salt (CAS 15307-81-0). The last salification form has shown a prompter absorption rate and a faster onset of analgesic activity than the acid form and sodium salt. This paper extensively reviews three trials carried out on healthy volunteers, where potassium salt of diclofenac present in three fast-acting formulations, namely sachets (Trial 1), tablets (Trial 2) and oral drops (Trial 3), were compared to reference tablet formulations from the market. A very fast absorption rate was encountered with the three test formulations, with the peak reached in one case 5 min and in most cases within 10-15 min after dosing. The quick absorption rate of test formulations was attributed to the special combination of the salt of diclofenac with a dynamic buffering agent, namely bicarbonate, present in the test formulations and covered by an international patent. The prompt absorption of diclofenac from the new fast-acting formulations was accompanied by the presence of only one peak, whereas the reference formulations produced in most cases two peaks, as widely described in literature. This finding suggested the hypothesis that the absorption of test formulations should occur in a shorter tract of the gut. The faster absorption of diclofenac from the three fast-acting formulations is expected to produce a faster onset of analgesic action, which highlights these new formulations as particularly indicated to relief pain of any origin. PMID:11765589

  15. The gaseous explosive reaction at constant pressure : the reaction order and reaction rate

    NASA Technical Reports Server (NTRS)

    Stevens, F W

    1931-01-01

    The data given in this report covers the explosive limits of hydrocarbon fuels. Incidental to the purpose of the investigation here reported, the explosive limits will be found to be expressed for the condition of constant pressure, in the fundamental terms of concentrations (partial pressures) of fuel and oxygen.

  16. Dose rate constant of a Cesium-131 interstitial brachytherapy seed measured by thermoluminescent dosimetry and gamma-ray spectrometry

    SciTech Connect

    Chen, Z.; Bongiorni, P.; Nath, R.

    2005-11-15

    The aim of this work was to conduct an independent determination of the dose rate constant of the newly introduced Model CS-1 {sup 131}Cs seed. A total of eight {sup 131}Cs seeds were obtained from the seed manufacturer. The air-kerma strength of each seed was measured by the manufacturer whose calibration is traceable to the air-kerma strength standard established for the {sup 131}Cs seeds at the National Institute of Standards and Technology (1{sigma} uncertainty <1%). The dose rate constant of each seed was measured by two independent methods: One based on the actual photon energy spectrum emitted by the seed using gamma-ray spectrometry and the other based on the dose-rate measured by thermoluminescent dosimeter (TLD) in a Solid Water{sup TM} phantom. The dose rate constant in water determined by the gamma-ray spectrometry technique and by the TLD dosimetry are 1.066{+-}0.064 cGyh{sup -1}U{sup -1} and 1.058{+-}0.106 cGyh{sup -1}U{sup -1}, respectively, showing excellent agreement with each other. These values, however, are approximately 15% greater than a previously reported value of 0.915 cGyh{sup -1}U{sup -1} [Med. Phys. 31, 1529-1538 (2004)]. Although low-energy fluorescent x rays at 16.6 and 18.7 keV, originating from niobium present in the seed construction, were measured in the energy spectrum of the {sup 131}Cs seeds, their yields were not sufficient to lower the dose rate constant to the value of 0.915 cGyh{sup -1}U{sup -1}. Additional determinations of the dose rate constant may be needed to establish an AAPM recommended consensus value for routine clinical use of the {sup 131}Cs seed.

  17. Measurement of erosion rate by absorption spectroscopy in a Hall thruster

    SciTech Connect

    Yamamoto, Naoji; Yokota, Shigeru; Matsui, Makoto; Komurasaki, Kimiya; Arakawa, Yoshihiro

    2005-08-15

    The erosion rate of a Hall thruster was estimated with the objective of building a real-time erosion rate monitoring system using a 1 kW class anode layer type Hall thruster. This system aids the understanding of the tradeoff between lifetime and performance. To estimate the flux of the sputtered wall material, the number density of the sputtered iron was measured by laser absorption spectroscopy using an absorption line from ground atomic iron at 371.9935 nm. An ultravioletAl{sub x}In{sub y}Ga{sub (1-x-y)}N diode laser was used as the probe. The estimated number density of iron was 1.1x10{sup 16} m{sup -3}, which is reasonable when compared with that measured by duration erosion tests. The relation between estimated erosion rate and magnetic flux density also agreed with that measured by duration erosion tests.

  18. 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.

  19. TECHNIQUES AFFECTING PRECISION AND ACCURACY IN HYDROLYSIS RATE CONSTANT DETERMINATIONS OF VOLATILE ORGANIC COMPOUNDS USING JEFFERS' ZERO HEADSPACE REACTION BULBS

    EPA Science Inventory

    A recently published method for measurement of hydrolysis rate constants for volatile organic compounds in aqueous samples was adapted for use in our laboratory. n applying the method, we developed the capability to make the zero-headspace reaction bulbs and used them to measure ...

  20. 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.

  1. Quantitative Structure-Activity Relationships Study on the Rate Constants of Polychlorinated Dibenzo-p-Dioxins with OH Radical

    PubMed Central

    Qi, Chuansong; Zhang, Chenxi; Sun, Xiaomin

    2015-01-01

    The OH-initiated reaction rate constants (kOH) are of great importance to measure atmospheric behaviors of polychlorinated dibenzo-p-dioxins (PCDDs) in the environment. The rate constants of 75 PCDDs with the OH radical at 298.15 K have been calculated using high level molecular orbital theory, and the rate constants (kα, kβ, kγ and kOH) were further analyzed by the quantitative structure-activity relationships (QSAR) study. According to the QSAR models, the relations between rate constants and the numbers and positions of Cl atoms, the energy of the highest occupied molecular orbital (EHOMO), the energy of the lowest unoccupied molecular orbital (ELUMO), the difference ΔEHOMO-LUMO between EHOMO and ELUMO, and the dipole of oxidizing agents (D) were discussed. It was found that EHOMO is the main factor in the kOH. The number of Cl atoms is more effective than the number of relative position of these Cl atoms in the kOH. The kOH decreases with the increase of the substitute number of Cl atoms. PMID:26274950

  2. Rate- and Extent-Limiting Factors of Oral Drug Absorption: Theory and Applications.

    PubMed

    Sugano, Kiyohiko; Terada, Katsuhide

    2015-09-01

    The oral absorption of drugs has been represented by various concepts such as the absorption potential, the maximum absorbable dose, the biopharmaceutics classification system, and in vitro-in vivo correlation. The aim of this article is to provide an overview of the theoretical relationships between these concepts. It shows how a simple analytical solution for the fraction of a dose absorbed (Fa equation) can offer a theoretical base to tie together the various concepts, and discusses how this solution relates to the rate-limiting cases of oral drug absorption. The article introduces the Fa classification system as a framework in which all the above concepts were included, and discusses its applications for food effect prediction, active pharmaceutical ingredient form selection, formulation design, and biowaiver strategy. PMID:25712830

  3. Rate constant and secondary organic aerosol yields for the gas-phase reaction of hydroxyl radicals with syringol (2,6-dimethoxyphenol)

    NASA Astrophysics Data System (ADS)

    Lauraguais, Amélie; Coeur-Tourneur, Cécile; Cassez, Andy; Seydi, Abdoulaie

    2012-08-01

    Syringol (2,6-dimethoxyphenol) is a potential marker compound for wood smoke emissions in the atmosphere. To investigate the atmospheric reactivity of this compound, the rate constant for its reaction with hydroxyl radicals (OH) has been determined in a simulation chamber (8 m3) at 294 ± 2 K, atmospheric pressure and low relative humidity (2-4%) using the relative rate method. The syringol and reference compound concentrations were followed by GC/FID (Gas chromatography/Flame Ionization Detection). The determined rate constant (in units of cm3 molecule-1 s-1) is ksyringol = (9.66 ± 1.11) × 10-11. The calculated atmospheric lifetime for syringol is 1.8 h, indicating that it is too reactive to be used as a tracer for wood smoke emissions. Secondary Organic Aerosol (SOA) formation from the OH reaction with syringol was also investigated. The initial mixing ratios for syringol were in the range 495-3557 μg m-3. The aerosol production was monitored using a SMPS (Scanning Mobility Particle Sizer). The SOA yields (Y) were determined as the ratio of the suspended aerosol mass corrected for wall losses (M0) to the total reacted syringol concentration assuming a particle density of 1.4 g cm-3. The aerosol formation yield increases as the initial syringol concentration increases, and leads to aerosol yields ranging from 0.10 to 0.36. Y is a strong function of M0 and the organic aerosol formation can be expressed by a one-product gas/particle partitioning absorption model. To our knowledge, this work represents the first investigation of the rate constant and SOA formation for the reaction of syringol with OH radicals. The atmospheric implications of this reaction are also discussed.

  4. Dissociation and rate constants of some human liver alcohol dehydrogenase isoenzymes.

    PubMed

    Pietruszko, R; de Zalenski, C; Theorell, H

    1976-01-01

    ADH from human liver forms binary complexes with NADH, associated with a blue shift of the peak of the fluorescence emission of NADH. The wavelength shift is the same for all isoenzymes but the accompanying intensification of the fluorescence is different. The fluorescence is further increased by the formation of the very tight ternary enzyme-NADH-isobutyramide complexes. These properties are similar to those for the horse liver ADH, as well as the molecular weight of E=40 000 per active site of the dimer molecule (EE). "Stopped-flow" determined velocity constants (ER in equilibrium E+R) were found to be in good agreement with ethanol activity constants previously determined by activity measurement, confirming the validity of the ordered ternary complex mechanism also for the human ADH. No single isoenzyme activity as high as that reported by Mourad and Woronick or Drum has been found. PMID:184631

  5. A Stringent Limit on Variation of the Fine-Structure Constant Using Absorption Line Multiplets in the Early Universe

    NASA Astrophysics Data System (ADS)

    Le, T. D.

    2016-06-01

    One of the key questions of modern physics concerns the possibility that physical constants have varied throughout the history of the Universe. The standard model of physics is built on these constants, but it does not provide any explanation for their values, nor does it require their constancy over space and time. Here, we set a new limit on possible spatial and temporal variations of the fine-structure constant α = e 2/4πɛ0 ħc by comparing transitions and line multiplets in an ensemble of Fe II λ 1608, λ 2344, λ 2374, λ 2383, λ 2587, and λ 2600 observed in the early Universe with those measured in the laboratory. Based on the optical spectrum observations of QSO HE 0515-4414, we deduce a constraint of Δα/α = (-0.157± 0.300)×10-6 at redshift z = 1.15. At present, this represents the tightest limit on Δα/α in early cosmological epochs compared to the published results in the literature.

  6. Flow variability of an aerial variable-rate nozzle at constant pressures

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  7. Accurate measurements of OH reaction rate constants over atmospheric temperatures and the atmospheric lifetime of trace gases

    NASA Astrophysics Data System (ADS)

    Orkin, V. L.; Khamaganov, V. G.; Martynova, L. E.; Kurylo, M. J.

    2013-12-01

    Reactions with hydroxyl radicals and photolysis are the main processes dictating the compound residence time in the atmosphere for a majority of trace gases. In case of very short lived compounds their reaction with OH dictates both the atmospheric lifetime and active halogen release. Therefore, the accuracy of OH kinetic data is of primary importance for the purpose of comprehensive atmospheric modeling of compound's impact on the atmosphere, such as in ozone depletion (ODP) and climate change (GWP). The currently recommended uncertainties of OH reaction rate constants (NASA/JPL Publications and IUPAC Publications) exceed 10% at room temperature for the majority of compounds to be larger at lower temperatures of atmospheric interest. Thus, uncertainties in the photochemical properties of potential and current atmospheric trace gases obtained under controlled laboratory conditions may constitute a major source of uncertainty in estimating the compound's environmental impact. We will present the higher accuracy results of OH reaction rate constant determinations between 220 K and 370 K. A statistical analysis of the data will be discussed. The high precision of kinetic measurements performed at low temperatures allows reliable determination of temperature dependences of the rate constants. This is especially important because we found that many OH reactions exhibit the curvature of the Arrhenius plots. A detailed inventory of sources of instrumental uncertainties related to our experiment proves a total uncertainty of the OH reaction rate constant to be as small as ~2-3%. The estimation of the atmospheric lifetime of a compound based on its OH reaction rate constant will be discussed.

  8. Mass Loss Rates for Solar-like Stars Measured from Lyα Absorption

    NASA Astrophysics Data System (ADS)

    Wood, B. E.; Müller, H.-R.; Linsky, J. L.

    2003-10-01

    We present a number of mass loss rate measurements for solar-like stars with coronal winds, computed using a Lyα absorption technique. The collision between the solar wind and the interstellar wind seen by the Sun defines the large scale structure of our heliosphere. Similar structures, ``astrospheres,'' exist around other solar-like stars. The deceleration of the interstellar wind at the solar or stellar bow shock heats the interstellar material. Heated neutral hydrogen in the outer astrosphere (and/or heliosphere) produces a broad Lyα absorption profile that is often detectable in high resolution Hubble Space Telescope spectra. The amount of absorption is dependent upon the strength of the stellar wind. With guidance from hydrodynamic models of astrospheres, we use detected astrospheric Lyα absorption to estimate the stellar mass loss rates. For the solar-like GK stars in our sample, mass loss appears to increase with stellar activity, suggesting that young, active stars have stronger winds than old, inactive stars. However, Proxima Cen (M5.5 Ve) and λ And (G8 IV-III+M V) appear to be inconsistent with this relation.

  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. The muscle force component in pedaling retains constant direction across pedaling rates.

    PubMed

    Loras, Havardn; Ettema, Gertjan; Leirdal, Stig

    2009-02-01

    Changes in pedaling rate during cycling have been found to alter the pedal forces. Especially, the force effectiveness is reduced when pedaling rate is elevated. However, previous findings related to the muscular force component indicate strong preferences for certain force directions. Furthermore, inertial forces (due to limb inertia) generated at the pedal increase with elevated pedaling rate. It is not known how pedaling rate alters the inertia component and subsequently force effectiveness. With this in mind, we studied the effect of pedal rate on the direction of the muscle component, quantified with force effectiveness. Cycle kinetics were recorded for ten male competitive cyclists at five cadences (60-100 rpm) during unloaded cycling (to measure inertia) and at a submaximal load (~260 W). The force effectiveness decreased as a response to increased pedaling rate, but subtracting inertia eliminated this effect. This indicates consistent direction of the muscle component of the foot force. PMID:19299833

  11. Comparison of the rate constants for energy transfer in the light-harvesting protein, C-phycocyanin, calculated from Foerster`s theory and experimentally measured by time-resolved fluorescence spectroscopy

    SciTech Connect

    Debreczeny, M.P.

    1994-05-01

    We have measured and assigned rate constants for energy transfer between chromophores in the light-harvesting protein C-phycocyanin (PC), in the monomeric and trimeric aggregation states, isolated from Synechococcus sp. PCC 7002. In order to compare the measured rate constants with those predicted by Fdrster`s theory of inductive resonance in the weak coupling limit, we have experimentally resolved several properties of the three chromophore types ({beta}{sub 155} {alpha}{sub 84}, {beta}{sub 84}) found in PC monomers, including absorption and fluorescence spectra, extinction coefficients, fluorescence quantum yields, and fluorescence lifetimes. The cpcB/C155S mutant, whose PC is missing the {beta}{sub 155} chromophore, was, useful in effecting the resolution of the chromophore properties and in assigning the experimentally observed rate constants for energy transfer to specific pathways.

  12. Specific absorption rate analysis of broadband mobile antenna with negative index metamaterial

    NASA Astrophysics Data System (ADS)

    Alam, Touhidul; Faruque, Mohammad Rashed Iqbal; Islam, Mohammad Tariqul

    2016-03-01

    This paper presents a negative index metamaterial-inspired printed mobile wireless antenna that can support most mobile applications such as GSM, UMTS, Bluetooth and WLAN frequency bands. The antenna consists of a semi-circular patch, a 50Ω microstrip feed line and metamaterial ground plane. The antenna occupies a very small space of 37 × 47 × 0.508 mm3, making it suitable for mobile wireless application. The perceptible novelty shown in this proposed antenna is that reduction of specific absorption rate using the negative index metamaterial ground plane. The proposed antenna reduced 72.11 and 75.53 % of specific absorption rate at 1.8 and 2.4 GHz, respectively.

  13. Absorption cross-section and decay rate of rotating linear dilaton black holes

    NASA Astrophysics Data System (ADS)

    Sakalli, I.; Aslan, O. A.

    2016-02-01

    We analytically study the scalar perturbation of non-asymptotically flat (NAF) rotating linear dilaton black holes (RLDBHs) in 4-dimensions. We show that both radial and angular wave equations can be solved in terms of the hypergeometric functions. The exact greybody factor (GF), the absorption cross-section (ACS), and the decay rate (DR) for the massless scalar waves are computed for these black holes (BHs). The results obtained for ACS and DR are discussed through graphs.

  14. Strain Rate Effects on the Energy Absorption of Rapidly Manufactured Composite Tubes

    SciTech Connect

    Brighton, Aaron M; Forrest, Mark; Starbuck, J Michael; ERDMAN III, DONALD L; Fox, Bronwyn

    2009-01-01

    Quasi-static and intermediate rate axial crush tests were conducted on tubular specimens of Carbon/Epoxy (Toray T700/G83C) and Glass/Polypropylene (Twintex). The quasi-static tests were conducted at 10 mm/min (1.67x10-4 m/s); five different crush initiators were used. Tests at intermediate rates were performed at speeds of 0.25 m/s, 0.5 m/s, 0.75 m/s 1m/s, 2 m/s and 4 m/s. Quasi-static tests of tubular specimens showed high specific energy absorption (SEA) values with 86 kJ/kg for Carbon/Epoxy specimens. The specific energy absorption of the Glass/Polypropylene specimens was measured to be 29 kJ/kg. Results from the intermediate test rates showed that while a decrease in specific energy absorbed was observed as speeds increased, values did not fall below 55kj/kg for carbon specimens or 35 kJ/kg for the Glass/Polypropylene specimens. When compared with steel and aluminium, specific energy absorption values of 15 kJ/kg and 30 kJ/kg respectively, the benefits of using composite materials in crash structures are apparent.

  15. 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. PMID:27164019

  16. Theory for rates, equilibrium constants, and Brønsted slopes in F1-ATPase single molecule imaging experiments

    PubMed Central

    Volkán-Kacsó, Sándor; Marcus, Rudolph A.

    2015-01-01

    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. PMID:26483483

  17. 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. PMID:26483483

  18. Towards universal wavelength-specific photodegradation rate constants for methyl mercury in humic waters, exemplified by a Boreal lake-wetland gradient.

    PubMed

    Fernández-Gómez, Cristal; Drott, Andreas; Björn, Erik; Díez, Sergi; Bayona, Josep M; Tesfalidet, Solomon; Lindfors, Anders; Skyllberg, Ulf

    2013-06-18

    We report experimentally determined first-order rate constants of MeHg photolysis in three waters along a Boreal lake-wetland gradient covering a range of pH (3.8-6.6), concentrations of total organic carbon (TOC 17.5-81 mg L(-1)), total Fe (0.8-2.1 mg L(-1)), specific UV254 nm absorption (3.3-4.2 L mg(-1) m(-1)) and TOC/TON ratios (24-67 g g(-1)). Rate constants determined as a function of incident sunlight (measured as cumulative photon flux of photosynthetically active radiation, PAR) decreased in the order dystrophic lake > dystrophic lake/wetland > riparian wetland. After correction for light attenuation by dissolved natural organic matter (DOM), wavelength-specific (PAR: 400-700 nm, UVA: 320-400 nm and UVB: 280-320 nm) first-order photodegradation rate constants (kpd) determined at the three sites were indistinguishable, with average values (± SE) of 0.0023 ± 0.0002, 0.10 ± 0.024 and 7.2 ± 1.3 m(2) E(-1) for kpdPAR, kpdUVA, and kpdUVB, respectively. The relative ratio of kpdPAR, kpdUVA, and kpdUVB was 1:43:3100. Experiments conducted at varying MeHg/TOC ratios confirm previous suggestions that complex formation with organic thiol groups enhances the rate of MeHg photodegradation, as compared to when O and N functional groups are involved in the speciation of MeHg. We suggest that if the photon fluxes of PAR, UVA, and UVB radiation are separately determined and the wavelength-specific light attenuation is corrected for, the first-order rate constants kpdPAR, kpdUVA, and kpdUVB will be universal to waters in which DOM (possibly in concert with Fe) controls the formation of ROS, and the chemical speciation of MeHg is controlled by the complexation with DOM associated thiols. PMID:23647363

  19. 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...

  20. Reaction rate constant for dry air oxidation of K Basin fuel

    SciTech Connect

    Trimble, D.J.

    1998-04-29

    The rate of oxidation of spent nuclear fuel stored in the K Basin water is an important parameter when assessing the processes and accident scenarios for preparing the fuel for dry storage. The literature provides data and rate laws for the oxidation of unirradiated uranium in various environments. Measurement data for the dry air oxidation of K Basin fuel is compared to the literature data for linear oxidation in dry air. Equations for the correlations and statistical bounds to the K Basin fuel data and the literature data are selected for predicting nominal and bounding rates for the dry air oxidation of the K Basin fuel. These rate equations are intended for use in the Spent Nuclear Fuel Project Technical Data book.

  1. Optimization of high-throughput sequencing kinetics for determining enzymatic rate constants of thousands of RNA substrates.

    PubMed

    Niland, Courtney N; Jankowsky, Eckhard; Harris, Michael E

    2016-10-01

    Quantification of the specificity of RNA binding proteins and RNA processing enzymes is essential to understanding their fundamental roles in biological processes. High-throughput sequencing kinetics (HTS-Kin) uses high-throughput sequencing and internal competition kinetics to simultaneously monitor the processing rate constants of thousands of substrates by RNA processing enzymes. This technique has provided unprecedented insight into the substrate specificity of the tRNA processing endonuclease ribonuclease P. Here, we investigated the accuracy and robustness of measurements associated with each step of the HTS-Kin procedure. We examine the effect of substrate concentration on the observed rate constant, determine the optimal kinetic parameters, and provide guidelines for reducing error in amplification of the substrate population. Importantly, we found that high-throughput sequencing and experimental reproducibility contribute to error, and these are the main sources of imprecision in the quantified results when otherwise optimized guidelines are followed. PMID:27296633

  2. 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.

  3. 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.

  4. Temperature, pressure and deuterium effects on the phosphorescence decay-rate constant of naphthalene in a single crystal of durene

    NASA Astrophysics Data System (ADS)

    Hoshi, Nagahiro; Yamauchi, Seigo; Hirota, Noboru

    1990-06-01

    It is suggested that the hitherto unexplained drastic temperature, pressure and external deuterium isotope effects on the phosphorescence decay-rate constant ( kT) of naphthalene in a single crystal of durene can be consistently explained in terms of the photoinduced hydrogen-abstraction reaction of triplet naphthalene from durene in which tunneling plays an essential role. This suggestion is supported by calculations based on the "golden rule" approach to tunneling developed by Siebrand, Wildman and Zgierski.

  5. 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.

  6. 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.

  7. Theoretical study of the rate constants for the hydrogen atom abstraction reactions of esters with (•)OH radicals.

    PubMed

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

    2014-07-10

    A systematic investigation of the rate constants for hydrogen atom abstraction reactions by hydroxyl radicals on esters has been performed. The geometry optimizations and frequency calculations were obtained using the second-order Møller-Plesset method with the 6-311G(d,p) basis set. The same method was also used in order to determine the dihedral angle potential for each individual hindered rotor in each reactant and transition state. Intrinsic reaction coordinate calculations were used in order to connect each transition state to the corresponding local minimum. For the reactions of methyl ethanoate with an (•)OH radical, the relative electronic energies were calculated using the G3 and the CCSD(T)/cc-pVXZ (where X = D, T, and Q) methods, which were extrapolated to the complete basis set (CBS) limit. The electronic energies obtained using the G3 method were then benchmarked against the CBS results and were found to be within 1 kcal mol(-1) of one another. The high-pressure limit rate constants for every reaction channel were calculated by conventional transition-state theory, with an asymmetric Eckart tunneling correction, using the energies obtained with the G3 method. We report the individual, average, and total rate constants in the temperature range from 500 to 2200 K. Our calculated results are within a factor of 2 for methyl ethanoate and between 40% to 50% for methyl propanoate and methyl butanoate when compared to previously reported experimental data. PMID:24878337

  8. Applying constraints on model-based methods: estimation of rate constants in a second order consecutive reaction.

    PubMed

    Kompany-Zareh, Mohsen; Khoshkam, Maryam

    2013-02-01

    This paper describes estimation of reaction rate constants and pure ultraviolet/visible (UV-vis) spectra of the component involved in a second order consecutive reaction between Ortho-Amino benzoeic acid (o-ABA) and Diazoniom ions (DIAZO), with one intermediate. In the described system, o-ABA was not absorbing in the visible region of interest and thus, closure rank deficiency problem did not exist. Concentration profiles were determined by solving differential equations of the corresponding kinetic model. In that sense, three types of model-based procedures were applied to estimate the rate constants of the kinetic system, according to Levenberg/Marquardt (NGL/M) algorithm. Original data-based, Score-based and concentration-based objective functions were included in these nonlinear fitting procedures. Results showed that when there is error in initial concentrations, accuracy of estimated rate constants strongly depends on the type of applied objective function in fitting procedure. Moreover, flexibility in application of different constraints and optimization of the initial concentrations estimation during the fitting procedure were investigated. Results showed a considerable decrease in ambiguity of obtained parameters by applying appropriate constraints and adjustable initial concentrations of reagents. PMID:23220674

  9. Rate constants for the reactions OH + HOCl. -->. H/sub 2/O + ClO and H + HOCl. -->. products

    SciTech Connect

    Ennis, C.A.; Birks, J.W.

    1988-03-10

    A new laboratory source of gaseous hypochlorous acid (HOCl) has been used in two kinetics investigations in a mass spectrometry-resonance fluorescence discharge flow system. Two potential removal reactions of stratospheric HOCl were studied. The rate constant for the reaction OH + HOCl ..-->.. H/sub 2/O + ClO (1) at 298 K was found to be lower than the NASA estimate by a factor of about 2-12; a value in the range (1.7-9.5) x 10/sup -13/ cm/sup 3/ molecule/sup -1/ s/sup -1/ for k/sub 1/ is reported here. The reaction of Cl/sub 2/O + OH interfered in the study of k/sub 1/ and was the subject of a preliminary investigation. Its rate constant was determined to be (9.4 +/- 1.0) x 10/sup -12/ cm/sup 3/ molecule/sup -1/ s/sup -1/ at 298 K. The rate constant for the reaction H + HOCl ..-->.. products (2) was determined to be (5.0 +/- 1.4) x 298 K. Although branching ratios for three possible products channels could not be determined, OH was identified as a product. The results of this work imply that reactions 1 and 2 are not competitive with direct photolysis in the removal of HOCl from the stratosphere.

  10. 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. PMID:24997901

  11. 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.

  12. 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.

  13. Determination of methane emission rates on a biogas plant using data from laser absorption spectrometry.

    PubMed

    Groth, Angela; Maurer, Claudia; Reiser, Martin; Kranert, Martin

    2015-02-01

    The aim of the work was to establish a method for emission control of biogas plants especially the observation of fugitive methane emissions. The used method is in a developmental stage but the topic is crucial to environmental and economic issues. A remote sensing measurement method was adopted to determine methane emission rates of a biogas plant in Rhineland-Palatinate, Germany. An inverse dispersion model was used to deduce emission rates. This technique required one concentration measurement with an open path tunable diode laser absorption spectrometer (TDLAS) downwind and upwind the source and basic wind information, like wind speed and direction. Different operating conditions of the biogas plant occurring on the measuring day (December 2013) could be represented roughly in the results. During undisturbed operational modes the methane emission rate averaged 2.8 g/s, which corresponds to 4% of the methane gas production rate of the biogas plant. PMID:25446786

  14. Effective absorption cross sections and photolysis rates of anthropogenic and biogenic secondary organic aerosols

    NASA Astrophysics Data System (ADS)

    Romonosky, Dian E.; Ali, Nujhat N.; Saiduddin, Mariyah N.; Wu, Michael; Lee, Hyun Ji (Julie); Aiona, Paige K.; Nizkorodov, Sergey A.

    2016-04-01

    Mass absorption coefficient (MAC) values were measured for secondary organic aerosol (SOA) samples produced by flow tube ozonolysis and smog chamber photooxidation of a wide range of volatile organic compounds (VOC), specifically: α-pinene, β-pinene, β-myrcene, d-limonene, farnesene, guaiacol, imidazole, isoprene, linalool, ocimene, p-xylene, 1-methylpyrrole, and 2-methylpyrrole. Both low-NOx and high-NOx conditions were employed during the chamber photooxidation experiments. MAC values were converted into effective molecular absorption cross sections assuming an average molecular weight of 300 g/mol for SOA compounds. The upper limits for the effective photolysis rates of SOA compounds were calculated by assuming unity photolysis quantum yields and convoluting the absorption cross sections with a time-dependent solar spectral flux. A more realistic estimate for the photolysis rates relying on the quantum yield of acetone was also obtained. The results show that condensed-phase photolysis of SOA compounds can potentially occur with effective lifetimes ranging from minutes to days, suggesting that photolysis is an efficient and largely overlooked mechanism of SOA aging.

  15. Experimental and computational results on exciton/free-carrier ratio, hot/thermalized carrier diffusion, and linear/nonlinear rate constants affecting scintillator proportionality

    SciTech Connect

    Williams, Richard; Grim, Joel; Li, Qi; Ucer, K. B.; Bizarri, G. A.; Kerisit, Sebastien N.; Gao, Fei; Bhattacharya, Pijush; Tupitsyn, Eugene; Rowe, Emmanuel; Buliga, Vladimir M.; Burger, Arnold

    2013-10-01

    Models of nonproportional response in scintillators have highlighted the importance of parameters such as branching ratios, carrier thermalization times, diffusion, kinetic order of quenching, associated rate constants, and radius of the electron track. For example, the fraction ηeh of excitations that are free carriers versus excitons was shown by Payne and coworkers to have strong correlation with the shape of electron energy response curves from Compton-coincidence studies. Rate constants for nonlinear quenching are implicit in almost all models of nonproportionality, and some assumption about track radius must invariably be made if one is to relate linear energy deposition dE/dx to volume-based excitation density n (eh/cm3) in terms of which the rates are defined. Diffusion, affecting time-dependent track radius and thus density of excitations, has been implicated as an important factor in nonlinear light yield. Several groups have recently highlighted diffusion of hot electrons in addition to thermalized carriers and excitons in scintillators. However, experimental determination of many of these parameters in the insulating crystals used as scintillators has seemed difficult. Subpicosecond laser techniques including interband z scan light yield, fluence-dependent decay time, and transient optical absorption are now yielding experimental values for some of the missing rates and ratios needed for modeling scintillator response. First principles calculations and Monte Carlo simulations can fill in additional parameters still unavailable from experiment. As a result, quantitative modeling of scintillator electron energy response from independently determined material parameters is becoming possible on an increasingly firmer data base. This paper describes recent laser experiments, calculations, and numerical modeling of scintillator response.

  16. Experimental and theoretical rate constants for CH{sub 4} + O{sub 2} {yields} CH{sub 3} + HO{sub 2}

    SciTech Connect

    Srinivasan, N.K.; Michael, J.V.; Harding, L.B.; Klippenstein, S.J.

    2007-04-15

    In this study, rate constants for the primary initiation process in low to moderate temperature CH{sub 4} oxidation CH{sub 4} + O{sub 2} {yields} CH{sub 3} + HO{sub 2} have been measured in a reflected shock tube apparatus between 1655 and 1822 K using multipass absorption spectrometric detection of OH radicals at 308 nm. After rapid dissociation of HO{sub 2} yielding H atoms, which are instantaneously converted to OH by H + O{sub 2} {yields} OH + O, the temporal concentration of OH radicals was observed as the final product from the rate-controlling title reaction. The present work utilizes 18 optical passes corresponding to a total path length of 1.6 m. This configuration gives a signal to noise ratio of unity at {proportional_to}3 x 10{sup 12} radicals cm{sup -3}. Hence, kinetics experiments could be performed at conditions of low [CH{sub 4}]{sub 0} (60-70 ppm), thereby substantially reducing secondary chemistry. Possible implications of CH{sub 4} dissociation contributing to the OH formation rates were considered. The present experimental results agree with a priori variational transition state theoretical (VTST) calculations, k{sub th}=3.37 x 10{sup -19}T{sup 2.745} exp (-26,041K/T)cm{sup 3}molecule{sup -1} s{sup -1}, clearly showing overlap of experiment and theory, within experimental error. The new rate constant values obtained in this study are 8-10 times higher than the values used in the popular mechanisms GRI-Mech 3.0 and Leeds Methane Mechanism, version 1.5. (author)

  17. Experimental and computational results on exciton/free-carrier ratio, hot/thermalized carrier diffusion, and linear/nonlinear rate constants affecting scintillator proportionality

    NASA Astrophysics Data System (ADS)

    Williams, R. T.; Grim, Joel Q.; Li, Qi; Ucer, K. B.; Bizarri, G. A.; Kerisit, S.; Gao, Fei; Bhattacharya, P.; Tupitsyn, E.; Rowe, E.; Buliga, V. M.; Burger, A.

    2013-09-01

    Models of nonproportional response in scintillators have highlighted the importance of parameters such as branching ratios, carrier thermalization times, diffusion, kinetic order of quenching, associated rate constants, and radius of the electron track. For example, the fraction ηeh of excitations that are free carriers versus excitons was shown by Payne and coworkers to have strong correlation with the shape of electron energy response curves from Compton-coincidence studies. Rate constants for nonlinear quenching are implicit in almost all models of nonproportionality, and some assumption about track radius must invariably be made if one is to relate linear energy deposition dE/dx to volume-based excitation density n (eh/cm3) in terms of which the rates are defined. Diffusion, affecting time-dependent track radius and thus density of excitations, has been implicated as an important factor in nonlinear light yield. Several groups have recently highlighted diffusion of hot electrons in addition to thermalized carriers and excitons in scintillators. However, experimental determination of many of these parameters in the insulating crystals used as scintillators has seemed difficult. Subpicosecond laser techniques including interband z scan light yield, fluence-dependent decay time, and transient optical absorption are now yielding experimental values for some of the missing rates and ratios needed for modeling scintillator response. First principles calculations and Monte Carlo simulations can fill in additional parameters still unavailable from experiment. As a result, quantitative modeling of scintillator electron energy response from independently determined material parameters is becoming possible on an increasingly firmer data base. This paper describes recent laser experiments, calculations, and numerical modeling of scintillator response.

  18. 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...

  19. Estimation of uptake rate constants for PCB congeners accumulated by semipermeable membrane devices and brown treat (Salmo trutta)

    USGS Publications Warehouse

    Meadows, J.C.; Echols, K.R.; Huckins, J.N.; Borsuk, F.A.; Carline, R.F.; Tillitt, D.E.

    1998-01-01

    The triolein-filled semipermeable membrane device (SPMD) is a simple and effective method of assessing the presence of waterborne hydrophobic chemicals. Uptake rate constants for individual chemicals are needed to accurately relate the amounts of chemicals accumulated by the SPMD to dissolved water concentrations. Brown trout and SPMDs were exposed to PCB- contaminated groundwater in a spring for 28 days to calculate and compare uptake rates of specific PCB congeners by the two matrixes. Total PCB congener concentrations in water samples from the spring were assessed and corrected for estimated total organic carbon (TOC) sorption to estimate total dissolved concentrations. Whole and dissolved concentrations averaged 4.9 and 3.7 ??g/L, respectively, during the exposure. Total concentrations of PCBs in fish rose from 0.06 to 118.3 ??g/g during the 28-day exposure, while concentrations in the SPMD rose from 0.03 to 203.4 ??g/ g. Uptake rate constants (k1) estimated for SPMDs and brown trout were very similar, with k1 values for SPMDs ranging from one to two times those of the fish. The pattern of congener uptake by the fish and SPMDs was also similar. The rates of uptake generally increased or decreased with increasing K(ow), depending on the assumption of presence or absence of TOC.The triolein-filled semipermeable membrane device (SPMD) is a simple and effective method of assessing the presence of waterborne hydrophobic chemicals. Uptake rate constants for individual chemicals are needed to accurately relate the amounts of chemicals accumulated by the SPMB to dissolved water concentrations. Brown trout and SPMDs were exposed to PCB-contaminated groundwater in a spring for 28 days to calculate and compare uptake rates of specific PCB congeners by the two matrixes. Total PCB congener concentrations in water samples from the spring were assessed and corrected for estimated total organic carbon (TOC) sorption to estimate total dissolved concentrations. Whole and

  20. 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.

  1. New constraints in absorptive capacity and the optimum rate of petroleum output

    SciTech Connect

    El Mallakh, R

    1980-01-01

    Economic policy in four oil-producing countries is analyzed within a framework that combines a qualitative assessment of the policy-making process with an empirical formulation based on historical and current trends in these countries. The concept of absorptive capacity is used to analyze the optimum rates of petroleum production in Iran, Iraq, Saudi Arabia, and Kuwait. A control solution with an econometric model is developed which is then modified for alternative development strategies based on analysis of factors influencing production decisions. The study shows the consistencies and inconsistencies between the goals of economic growth, oil production, and exports, and the constraints on economic development. Simulation experiments incorporated a number of the constraints on absorptive capacity. Impact of other constraints such as income distribution and political stability is considered qualitatively. (DLC)

  2. Heating rates in furnace atomic absorption using the L'vov platform

    USGS Publications Warehouse

    Koirtyohann, S.R.; Giddings, R.C.; Taylor, H.E.

    1984-01-01

    Heating rate profiles for the furnace tube wall, the furnace atmosphere, and a L'vov platform were established for a range of conditions in a cyclically heated graphite atomizer. The tube wall profile was made by direct observation with a recording optical pyrometer. The sodium line reversal method was used to establish the heating rate of the furnace atmosphere, and appearance temperatures for a series metals of differing volatility was used to establish platform profiles. The tube wall heating rate was nearly linear at 2240??C s- until the desired temperature was reached after which the temperature remained constant. The furnace atmosphere reached a given temperature 0.2-0.4 s later than the tube wall through most of the atomize cycle. The platform lagged the tube wall 0.5-0.8 s. Under typical operating conditions the furnace atmosphere was 100-200??C cooler than the tube wall and at nearly constant temperature when the analyte vaporized from the platform. The L'vov platform causes the cyclically heated commercial furnace to approximate the behavior of a constant temperature furnace during atomization. ?? 1984.

  3. Specific absorption rate calculations of magnetite, using a modified linear response model for applications in magnetic hyperthermia

    SciTech Connect

    Hernández S, A. E-mail: meduardo2001@hotmail.com; Cano, M. E. E-mail: meduardo2001@hotmail.com; Torres-Arenas, J.

    2014-11-07

    Currently the absorption of electromagnetic radiation by magnetic nanoparticles is studied for biomedical applications of cancer thermotherapy. Several experiments are conduced following the framework of the Rosensweig model, in order to estimate their specific absorption rate. Nevertheless, this linear approximation involves strong simplifications which constrain their accuracy and validity range. The main aim of this work is to incorporate the deviation of the sphericity assumption in particles shapes, to improve the determination of their specific absorption rate. The correction to the effective particles volume is computed as a measure of the apparent amount of magnetic material, interacting with the external AC magnetic field. Preliminary results using the physical properties of Fe3O4 nanoparticles, exhibit an important correction in their estimated specific absorption rate, as a function of the apparent mean particles radius. Indeed, we have observed using a small deviation (6% of the apparent radius), up to 40% of the predicted specific absorption rate by the Rosensweig linear approximation.

  4. 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.

  5. Individual fitness and phenotypic selection in age-structured populations with constant growth rates

    PubMed Central

    Moorad, Jacob A.

    2013-01-01

    Powerful multiple regression-based approaches are commonly used to measure the strength of phenotypic selection, which is the statistical association between individual fitness and trait values. Age structure and overlapping generations complicate determinations of individual fitness, contributing to the popularity of alternative methods for measuring natural selection that do not depend upon such measures. The application of regression-based techniques for measuring selection in these situations requires a demographically appropriate, conceptually sound, and observable measure of individual fitness. It has been suggested that Fisher’s reproductive value applied to an individual at its birth is such a definition. Here I offer support for this assertion by showing that multiple regression applied to this measure and vital rates (age-specific survival and fertility rates) yields the same selection gradients for vital rates as those inferred from Hamilton’s classical results. I discuss how multiple regressions, applied to individual reproductive value at birth, can be used efficiently to estimate measures of phenotypic selection that are problematic for sensitivity analyses. These include nonlinear selection, components of the opportunity for selection, and multi-level selection. PMID:24933826

  6. Rate constants for the reactions of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    Rate constants for the reactions of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br have been measured by a relative rate technique in which the reaction rate of each compound was compared to that of HFC-152a (CH3CHF2) and (for CH2Cl2) HFC-161 (CH3CH2F). Using absolute rate constants for HFC-152a and HFC-161, which we have determined relative to those for CH4, CH3CCl3, and C2H6, temperature dependent rate constants of both compounds were derived. The derived rate constant for CH3Br is in good agreement with recent absolute measurements. However, for the chloromethanes all the rate constants are lower at atmospheric temperatures than previously reported, especially for CH2Cl2 where the present rate constant is about a factor of 1.6 below the JPL 92-20 value. The new rate constant appears to resolve a discrepancy between the observed atmospheric concentrations and those calculated from the previous rate constant and estimated release rates.

  7. 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

  8. 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.

  9. Rate Constant in Far-from-Equilibrium States of a Replicating System with Mutually Catalyzing Chemicals

    NASA Astrophysics Data System (ADS)

    Kamimura, Atsushi; Yukawa, Satoshi; Ito, Nobuyasu

    2006-02-01

    As a first step to study reaction dynamics in far-from-equilibrium open systems, we propose a stochastic protocell model in which two mutually catalyzing chemicals are replicating depending on the external flow of energy resources J. This model exhibits an Arrhenius type reaction; furthermore, it produces a non-Arrhenius reaction that exhibits a power-law reaction rate with regard to the activation energy. These dependences are explained using the dynamics of J; the asymmetric random walk of J results in the Arrhenius equation and conservation of J results in a power-law dependence. Further, we find that the discreteness of molecules results in the power change. Effects of cell divisions are also discussed in our model.

  10. Present knowledge about specific absorption rates inside a human body exposed to radiofrequency electromagnetic fields

    SciTech Connect

    Garn, J.; Gabriel, C.

    1995-02-01

    We have compiled results of scientific investigations about the relationship between external field-strengths and specific absorption rates inside the human body. The data were normalized to SAR-values that form the basis for current safety standards. Results were compared to exposure limits given in these standard. This comparison should serve as a reference for the selection of reliable reference levels for personal protection against thermal effects in radiofrequency electromagnetic fields. The need to measure and monitor ankle/wrist currents to protect some exposed workers is explained. The study has also highlighted a scarcity of dosimetric data at frequencies below 3 MHz. 20 refs., 7 figs.

  11. Direct measurement of Urbach tail and gap state absorption in CuGaSe2 thin films by photothermal deflection spectroscopy and the constant photocurrent method

    NASA Astrophysics Data System (ADS)

    Meeder, A.; Marron, D. Fuertes; Rumberg, A.; Lux-Steiner, M. Ch.; Chu, V.; Conde, J. P.

    2002-09-01

    The applicability of photothermal deflection spectroscopy (PDS) and the constant photocurrent method (CPM) to chemical vapor deposited and physical vapor deposited CuGaSe2 (CGSe) thin films is investigated. Process dependent variations in direct band-gap energies, Urbach tail widths, bulk and surface defect densities of the films are given as a function of composition. Differences in the PDS and CPM absorption spectra of more than one order of magnitude are found. Using the standard a-Si theory of PDS and CPM analysis, a two-layer system consisting of a defect-rich near-surface layer and a less defective bulk layer is found in device-quality films. Optical improvements due to the Ga+Se annealing step as a second stage of the growth process result in a reduced bulk defect density while the near-surface defect density remains unchanged.

  12. 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.

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

    PubMed

    Zhang, Jiwen; Li, Haiyan; Sun, Lixin; Wang, Caifen

    2015-01-01

    The kinetics of the association and dissociation are fundamental kinetic processes for the host-guest interactions (such as the drug-target and drug-excipient interactions) and the in vivo performance of supramolecules. With advantages of rapid speed, high precision and ease of automation, the high-performance affinity chromatography (HPAC) is one of the best techniques to measure the interaction kinetics of weak to moderate affinities, such as the typical host-guest interactions of drug and cyclodextrins by using a cyclodextrin-immobilized column. The measurement involves the equilibration of the cyclodextrin column, the upload and elution of the samples (non-retained substances and retained solutes) at different flow rates on the cyclodextrin and control column, and data analysis. It has been indicated that cyclodextrin-immobilized chromatography is a cost-efficient high-throughput tool for the measurement of (small molecule) drug-cyclodextrin interactions as well as the dissociation of other supramolecules with relatively weak, fast, and extensive interactions. PMID:25749964

  14. 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.

  15. The absorption efficiency and respiration rate of the Florida lancelet, Branchiostoma floridae.

    PubMed

    Nash, Troy R; Ruppert, Edward E; Colacino, James M

    2009-12-01

    The present study investigates some aspects of the digestive biology and physiological energetics of the Florida lancelet, Branchiostoma floridae. Florida lancelets are able to remove 47.2-56.9% of the energy from a diet of mixed algae. The respiration rate is 0.100mL O(2) (STPD) h(-1) g(-1) (wet), which estimates a metabolic rate of 0.248 J h(-1), at an average body mass of 0.125 g (wet). Published values of the chlorophyll a concentration in its natural habitat indicate that a 125 mg lancelet would need to filter 0.018-0.031 L h(-1) to remove sufficient food to support its resting metabolism. The filtration rate of lancelets has been reported as 0.138 L h(-1), indicating that the actual filtration rate is 4-7 times greater than the filtration rate needed to meet resting metabolic demands. It appears that lancelets have the potential to be raised in aquaculture, because their absorption efficiency and respiration rate are comparable to suspension-feeding invertebrates that have been successfully aquacultured. PMID:19758577

  16. 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.

  17. Landfill gas generation after mechanical biological treatment of municipal solid waste. Estimation of gas generation rate constants.

    PubMed

    Gioannis, G De; Muntoni, A; Cappai, G; Milia, S

    2009-03-01

    Mechanical biological treatment (MBT) of residual municipal solid waste (RMSW) was investigated with respect to landfill gas generation. Mechanically treated RMSW was sampled at a full-scale plant and aerobically stabilized for 8 and 15 weeks. Anaerobic tests were performed on the aerobically treated waste (MBTW) in order to estimate the gas generation rate constants (k,y(-1)), the potential gas generation capacity (L(o), Nl/kg) and the amount of gasifiable organic carbon. Experimental results show how MBT allowed for a reduction of the non-methanogenic phase and of the landfill gas generation potential by, respectively, 67% and 83% (8 weeks treatment), 82% and 91% (15 weeks treatment), compared to the raw waste. The amount of gasified organic carbon after 8 weeks and 15 weeks of treatment was equal to 11.01+/-1.25kgC/t(MBTW) and 4.54+/-0.87kgC/t(MBTW), respectively, that is 81% and 93% less than the amount gasified from the raw waste. The values of gas generation rate constants obtained for MBTW anaerobic degradation (0.0347-0.0803y(-1)) resemble those usually reported for the slowly and moderately degradable fractions of raw MSW. Simulations performed using a prediction model support the hypothesis that due to the low production rate, gas production from MBTW landfills is well-suited to a passive management strategy. PMID:18954969

  18. 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.

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

    PubMed

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

    2010-09-01

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

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

    SciTech Connect

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

    2010-09-09

    The thermal decomposition of ethanol and its reactions with OH and D have been studied with both shock tube experiments and ab initio transition state theory-based master equation calculations. Dissociation rate constants for ethanol have been measured at high T in reflected shock waves using OH optical absorption and high-sensitivity H-atom ARAS detection. The three dissociation processes that are dominant at high T are: C{sub 2}H{sub 5}OH {yields} C{sub 2}H{sub 4} + H{sub 2}O; C{sub 2}H{sub 5}OH {yields} CH{sub 3} + CH{sub 2}OH; C{sub 2}H{sub 5}OH {yields} C{sub 2}H{sub 5} + OH. The rate coefficient for reaction C was measured directly with high sensitivity at 308 nm using a multipass optical White cell. Meanwhile, H-atom ARAS measurements yield the overall rate coefficient and that for the sum of reactions B and C, since H-atoms are instantaneously formed from the decompositions of CH{sub 2}OH and C{sub 2}H{sub 5} into CH{sub 2}O + H and C{sub 2}H{sub 4} + H, respectively. By difference, rate constants for reaction 1 could be obtained. One potential complication is the scavenging of OH by unreacted ethanol in the OH experiments, and therefore, rate constants for OH + C{sub 2}H{sub 5}OH {yields} products were measured using tert-butyl hydroperoxide (tBH) as the thermal source for OH. The present experiments can be represented by the Arrhenius expression k = (2.5 {+-} 0.43) x 10{sup -11} exp(- 911 {+-} 191 K/T) cm{sup 3} molecule{sup -1} s{sup -1} over the T range 857-1297 K. For completeness, we have also measured the rate coefficient for the reaction of D atoms with ethanol D + C{sub 2}H{sub 5}OH {yields} products whose H analogue is another key reaction in the combustion of ethanol. Over the T range 1054-1359 K, the rate constants from the present experiments can be represented by the Arrhenius expression, k = (3.98 {+-} 0.76) x 10{sup -10} exp(- 4494 {+-} 235 K/T) cm{sup 3} molecule{sup -1} s{sup -1}. The high-pressure rate coefficients for reactions B and C

  1. Upper limits for the rate constant for the reaction Br + H2O2 yields HB2 + HO2

    NASA Technical Reports Server (NTRS)

    Leu, M.-T.

    1980-01-01

    Upper limits for the rate constant for the reaction Br + H2O2 yields HBr + HO2 have been measured over the temperature range 298 to 417 K in a discharge flow system using a mass spectrometer as a detector. Results are k sub 1 less than 1.5 x 10 to the -15th power cu cm/s at 298 K and k sub 1 less than 3.0 x 10 to the -15th power cu cm/s at 417 K, respectively. The implication to stratospheric chemistry is discussed.

  2. 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.

  3. A simple parameterization of ozone infrared absorption for atmospheric heating rate calculations

    NASA Technical Reports Server (NTRS)

    Rosenfield, Joan E.

    1991-01-01

    A simple parameterization of ozone absorption in the 9.6-micron region which is suitable for two- and three-dimensional stratospheric and tropospheric models is presented. The band is divided into two parts, a brand center region and a band wing region, grouping together regions for which the temperature dependence of absorption is similar. Each of the two regions is modeled with a function having the form of the Goody random model, with pressure and temperature dependent band parameters chosen by empirically fitting line-by-line equivalent widths for pressures between 0.25 and 1000 mbar and ozone absorber amounts between 1.0 x 10 to the -7th and 1.0 cm atm. The model has been applied to calculations of atmospheric heating rates using an absorber amount weighted mean pressure and temperature along the inhomogeneous paths necessary for flux computations. In the stratosphere, maximum errors in the heating rates relative to line-by-line calculations are 0.1 K/d, or 5 percent of the peak cooling at the stratopause. In the troposphere the errors are at most 0.005 K/d.

  4. Elementary reaction rate measurements at high temperatures by tunable-laser flash-absorption

    SciTech Connect

    Hessler, J.P.

    1993-12-01

    The major objective of this program is to measure thermal rate coefficients and branching ratios of elementary reactions. To perform these measurements, the authors constructed an ultrahigh-purity shock tube to generate temperatures between 1000 and 5500 K. The tunable-laser flash-absorption technique is used to measure the rate of change of the concentration of species which absorb below 50,000 cm{sup {minus}1} e.g.: OH, CH, and CH{sub 3}. This technique is being extended into the vacuum-ultraviolet spectral region where one can measure atomic species e.g.: H, D, C, O, and N; and diatomic species e.g.: O{sub 2}, CO, and OH.

  5. 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. PMID:26476062

  6. 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.

  7. Calculations of rate constants for the three-body recombination of H2 in the presence of H2

    NASA Technical Reports Server (NTRS)

    Schwenke, David W.

    1988-01-01

    A new global potential energy hypersurface for H2 + H2 is constructed and quasiclassical trajectory calculations performed using the resonance complex theory and energy transfer mechanism to estimate the rate of three body recombination over the temperature range 100 to 5000 K. The new potential is a faithful representation of ab initio electron structure calculations, is unchanged under the operation of exchanging H atoms, and reproduces the accurate H3 potential as one H atom is pulled away. Included in the fitting procedure are geometries expected to be important when one H2 is near or above the dissociation limit. The dynamics calculations explicitly include the motion of all four atoms and are performed efficiently using a vectorized variable-stepsize integrator. The predicted rate constants are approximately a factor of two smaller than experimental estimates over a broad temperature range.

  8. 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.

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

    PubMed Central

    2016-01-01

    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

  10. Calculation of rate constants for dissociative attachment of low-energy electrons to hydrogen halides HCl, HBr, and HI and their deuterated analogs

    SciTech Connect

    Houfek, Karel; Cizek, Martin; Horacek, Jiri

    2002-12-01

    Calculations of rate constants for the process of dissociative attachment of low-energy electrons to hydrogen halides HCl, HBr, and HI and for the reverse process of associative detachment based on the nonlocal resonance model are reported. The calculated data are of importance for the modeling of plasma processes, environmental chemistry, etc. The calculated dissociative attachment rate constants are found to be in good agreement with existing experimental data. It is shown that at low temperatures the rate constants are very sensitive to small changes of the parameters of the nonlocal resonance model used for the calculation of the rate constants and represent a severe test of the theory. The isotopic effect and its dependence on the temperature is also discussed. The calculations of rate constants for the reverse process of associative detachment are also reported and discussed.

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

    PubMed

    Canneaux, Sébastien; Bohr, Frédéric; Henon, Eric

    2014-01-01

    Kinetic and Statistical Thermodynamical Package (KiSThelP) is a cross-platform free open-source program developed to estimate molecular and reaction properties from electronic structure data. To date, three computational chemistry software formats are supported (Gaussian, GAMESS, and NWChem). Some key features are: gas-phase molecular thermodynamic properties (offering hindered rotor treatment), thermal equilibrium constants, transition state theory rate coefficients (transition state theory (TST), variational transition state theory (VTST)) including one-dimensional (1D) tunnelling effects (Wigner, and Eckart) and Rice-Ramsperger-Kassel-Marcus (RRKM) rate constants, for elementary reactions with well-defined barriers. KiSThelP is intended as a working tool both for the general public and also for more expert users. It provides graphical front-end capabilities designed to facilitate calculations and interpreting results. KiSThelP enables to change input data and simulation parameters directly through the graphical user interface and to visually probe how it affects results. Users can access results in the form of graphs and tables. The graphical tool offers customizing of 2D plots, exporting images and data files. These features make this program also well-suited to support and enhance students learning and can serve as a very attractive courseware, taking the teaching content directly from results in molecular and kinetic modelling. PMID:24190715

  12. Absolute rate constants for O + NO + M /= He, Ne, Ar, Kr/ yields NO2 + M from 217-500 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Payne, W. A.; Whytock, D. A.

    1976-01-01

    Rate constants for the reaction O + NO + M yields NO2 + M have been obtained at temperatures from 217-500 K in four different rare gases by a method combining flash photolysis with time resolved detection of O(3-P) by resonance fluorescence. The measured rate constants in Arrhenius form are (10.8 plus or minus 1.2) x 10 to the -33rd exp(1040 plus or minus 60/1.987 T) for helium; (9.01 plus or minus 1.16) x 10 to the -33rd exp(1180 plus or minus 70/1.987 T) for argon; (9.33 plus or minus 1.10) x 10 to the -33rd exp(1030 plus or minus 60/1.987 T) for neon; and (9.52 plus or minus 1.10) x 10 to the -33rd exp(1140 plus or minus 70/1.987 T) for krypton in units of cm to the 6th/sq molecule/s.

  13. Hydrogen Abstraction Reactions from Phenolic Compounds by Peroxyl Radicals: Multireference Character and Density Functional Theory Rate Constants.

    PubMed

    Galano, Annia; Muñoz-Rugeles, Leonardo; Alvarez-Idaboy, Juan Raul; Bao, Junwei Lucas; Truhlar, Donald G

    2016-07-14

    An assessment of multireference character in transition states is considered to be an important component in establishing the expected reliability of various electronic structure methods. In the present work, the multireference characters of the transition states and the forming and breaking of bonds for a large set of hydrogen abstraction reactions from phenolic compounds by peroxyl radicals have been analyzed using the T1, M, B1, and GB1 diagnostics. The extent of multireference character depends on the system and on the conditions under which the reaction takes place, and some systematic trends are observed. In particular, the multireference character is found to be reduced by solvation, the size of the phenolic compound, and deprotonation in aqueous solution. However, the deviations of calculated rate constants from experimental ones are not correlated with the extent of multireference character. The performance of single-determinant density functional theory was investigated for the kinetics of these reactions by comparing calculated rate constants to experimental data; the results from these analyses showed that the M05 functional performs well for the task at hand. PMID:26378461

  14. Direct rate constant measurements for the reaction of ground-state atomic oxygen with ethylene, 244-1052 K

    SciTech Connect

    Klemm, R.B.; Nesbitt, F.L.; Skolnik, E.G.; Lee, J.H.; Smalley, J.F.

    1987-03-12

    The rate constant for the reaction of ground-state atomic oxygen with ethylene was determined by using two techniques: flash photolysis-resonance fluorescence (FP-RF, 244-1052 K) and discharge flow-resonance fluorescence (DF-RF, 298-1017 K). Kinetic complications due to the presence of molecular oxygen in the FP-RF experiments at high temperatures (T > 800 K) were overcome by using NO as the photolytic source of the O atoms. The rate constant, k/sub 1/ (T), derived in this study exhibits extreme non-Arrhenius behavior, but it can be successfully fit to the sum of exponentials expression, 244-1052 K, k/sub 1/(T) = (1.02 +/- 0.06) x 10/sup -11/ exp(-753 +/- 17 K/T) + (2.75 +/- 0.26) x 10/sup -10/ exp(-4220 +/- 550 K/T), in units of cm/sup 3/ molecule/sup -1/ s/sup -1/. Additionally, a fit of the results of this work to a simple transition-state theory expression and the comparison of these results with those of other workers are discussed.

  15. Silver fluorescent x-ray yield and its influence on the dose rate constant for nine low-energy brachytherapy source models

    SciTech Connect

    Nath, Ravinder; Chen, Zhe Jay

    2007-10-15

    The physical characteristics of the photons emitted by a low-energy brachytherapy source are strongly dependent on the source's construction. Aside from absorption and scattering caused by the internal structures and the source encapsulation, the photoelectric interactions occurred in certain type of source-construction materials can generate additional energetic characteristic x rays with energies different from those emitted by the bare radionuclide. As a result, the same radionuclide encapsulated in different source models can result in dose rate constants and other dosimetric parameters that are strikingly different from each other. The aim of this work was to perform a systematic study on the yield of silver fluorescent x rays produced in nine {sup 125}I sources that are known to contain silver and its impact on the dose-rate constant. Using a high-resolution germanium spectrometer, the relative {sup 125}I spectra emitted by the nine sources on its bisector were measured and found to be similar to each other (the maximum variation in the {sup 125}I-K{sub {beta}} relative intensity was less than 4%). On the other hand, the measured silver fluorescent x-ray spectra exhibited much greater variations from model to model; the maximum change in the measured Ag-K{sub {alpha}} relative intensity was over 95%. This larger variation in the measured silver fluorescent x-ray yield was caused by (1) the different amount of silver that was directly exposed to the {sup 125}I radionuclide in different source models and (2) the stronger influence of the source's internal geometry on the silver fluorescent x rays. Because the addition of silver fluorescent x rays can significantly alter the photon characteristics emitted by the radioactive sources, a precise knowledge on the silver fluorescent x-ray yield is needed in theoretical calculations of the sources' intrinsic dosimetric properties. This study concludes that the differences in silver fluorescent yield are the primary

  16. Aquaporins in ovine amnion: responses to altered amniotic fluid volumes and intramembranous absorption rates.

    PubMed

    Cheung, Cecilia Y; Anderson, Debra F; Brace, Robert A

    2016-07-01

    Aquaporins (AQPs) are transmembrane channel proteins that facilitate rapid water movement across cell membranes. In amniotic membrane, the AQP-facilitated transfer of water across amnion cells has been proposed as a mechanism for amniotic fluid volume (AFV) regulation. To investigate whether AQPs modulate AFV by altering intramembranous absorption (IMA) rate, we tested the hypothesis that AQP gene expression in the amnion is positively correlated with IMA rate during experimental conditions when IMA rate and AFV are modified over a wide range. The relative abundances of AQP1, AQP3, AQP8, AQP9, and AQP11 mRNA and protein were determined in the amnion of 16 late-gestation ovine fetuses subjected to 2 days of control conditions, urine drainage, urine replacement, or intraamniotic fluid infusion. AQP mRNA levels were determined by RT-qPCR and proteins by western immunoblot. Under control conditions, mRNA levels among the five AQPs differed more than 20-fold. During experimental treatments, mean IMA rate in the experimental groups ranged from 100 ± 120 mL/day to 1370 ± 270 mL/day. The mRNA levels of the five AQPs did not change from control and were not correlated with IMA rates. The protein levels of AQP1 were positively correlated with IMA rates (r(2) = 38%, P = 0.01) while the remaining four AQPs were not. These findings demonstrate that five AQPs are differentially expressed in ovine amnion. Our study supports the hypothesis that AQP1 may play a positive role in regulating the rate of fluid transfer across the amnion, thereby participating in the dynamic regulation of AFV. PMID:27440743

  17. Effective light absorption and absolute electron transport rates in the coral Pocillopora damicornis.

    PubMed

    Szabó, Milán; Wangpraseurt, Daniel; Tamburic, Bojan; Larkum, Anthony W D; Schreiber, Ulrich; Suggett, David J; Kühl, Michael; Ralph, Peter J

    2014-10-01

    Pulse Amplitude Modulation (PAM) fluorometry has been widely used to estimate the relative photosynthetic efficiency of corals. However, both the optical properties of intact corals as well as past technical constrains to PAM fluorometers have prevented calculations of the electron turnover rate of PSII. We used a new Multi-colour PAM (MC-PAM) in parallel with light microsensors to determine for the first time the wavelength-specific effective absorption cross-section of PSII photochemistry, σII(λ), and thus PAM-based absolute electron transport rates of the coral photosymbiont Symbiodinium both in culture and in hospite in the coral Pocillopora damicornis. In both cases, σII of Symbiodinium was highest in the blue spectral region and showed a progressive decrease towards red wavelengths. Absolute values for σII at 440 nm were up to 1.5-times higher in culture than in hospite. Scalar irradiance within the living coral tissue was reduced by 20% in the blue when compared to the incident downwelling irradiance. Absolute electron transport rates of P. damicornis at 440 nm revealed a maximum PSII turnover rate of ca. 250 electrons PSII(-1) s(-1), consistent with one PSII turnover for every 4 photons absorbed by PSII; this likely reflects the limiting steps in electron transfer between PSII and PSI. Our results show that optical properties of the coral host strongly affect light use efficiency of Symbiodinium. Therefore, relative electron transport rates do not reflect the productivity rates (or indeed how the photosynthesis-light response is parameterised). Here we provide a non-invasive approach to estimate absolute electron transport rates in corals. PMID:25146689

  18. Specific absorption rate dependence on temperature in magnetic field hyperthermia measured by dynamic hysteresis losses (ac magnetometry)

    NASA Astrophysics Data System (ADS)

    Garaio, Eneko; Sandre, Olivier; Collantes, Juan-Mari; Garcia, Jose Angel; Mornet, Stéphane; Plazaola, Fernando

    2015-01-01

    Magnetic nanoparticles (NPs) are intensively studied for their potential use for magnetic hyperthermia, a treatment that has passed a phase II clinical trial against severe brain cancer (glioblastoma) at the end of 2011. Their heating power, characterized by the ‘specific absorption rate (SAR)’, is often considered temperature independent in the literature, mainly because of the difficulties that arise from the measurement methodology. Using a dynamic magnetometer presented in a recent paper, we measure here the thermal dependence of SAR for superparamagnetic iron oxide (maghemite) NPs of four different size-ranges corresponding to mean diameters around 12 nm, 14 nm, 15 nm and 16 nm. The article reports a parametrical study extending from 10 to 60 {}^\\circ C in temperature, from 75 to 1031 kHz in frequency, and from 2 to 24 kA m-1 in magnetic field strength. It was observed that SAR values of smaller NPs decrease with temperature whereas for the larger sample (16 nm) SAR values increase with temperature. The measured variation of SAR with temperature is frequency dependent. This behaviour is fully explained within the scope of linear response theory based on Néel and Brown relaxation processes, using independent magnetic measurements of the specific magnetization and the magnetic anisotropy constant. A good quantitative agreement between experimental values and theoretical values is confirmed in a tri-dimensional space that uses as coordinates the field strength, the frequency and the temperature.

  19. Determination of the Temperature Dependence of the Rate Constants for HO2/Acetonylperoxy Reaction and Acetonylperoxy Self-Reaction

    NASA Astrophysics Data System (ADS)

    Darby, E. C.; Grieman, F. J.; Hui, A. O.; Okumura, M.; Sander, S. P.

    2014-12-01

    Reactions of hydroperoxy radical, HO2, with carbonyl containing RO2 can play an important role in the oxidation chemistry of the troposphere. Discovered radical product channels in addition to radical termination channels have resulted in increased study of these important reactions. In our continued study of HO2 reactions with acetonylperoxy and acetylperoxy radicals, we report here our first results on the kinetics of the acetonylperoxy system. Previous studies have resulted in conflicting results and no temperature dependence of the rate constants. Using the Infrared Kinetic Spectroscopy (IRKS) method in which a temperature-controlled slow-flow tube apparatus and laser flash photolysis of Cl2 are used to produce HO2 and CH3C(O)CH2O2 from methanol and acetone, respectively, we studied the chemical kinetics involved over the temperature range of 295 to 240 K. Rates of chemical reaction were determined by monitoring the HO2 concentration as a function of time by sensitive near-IR diode laser wavelength modulation spectroscopy while simultaneously measuring the disappearance of [CH3C(O)CH2O2] in the ultraviolet at 300 nm. The simultaneous fits resulted in the determination of the temperature dependence of the rate constants for the HO2/acetonylperoxy reaction and the acetonylperoxy self-reaction. At the lower temperatures, the reactions of HO2 and CH3C(O)CH2O2 with the adducts HO2•CH3OH and HO2•CH3C(O)CH3 formed in significant concentrations needed to be included in the fitting models.

  20. Muonium Addition Reactions and Kinetic Isotope Effects in the Gas Phase: k∞ Rate Constants for Mu + C2H2.

    PubMed

    Arseneau, Donald J; Garner, David M; Reid, Ivan D; Fleming, Donald G

    2015-07-16

    The kinetics of the addition reaction of muonium (Mu) to acetylene have been studied in the gas phase at N2 moderator pressures mainly from ∼800 to 1000 Torr and over the temperature range from 168 to 446 K, but also down to 200 Torr at 168 K and over a much higher range of pressures, from 10 to 44 bar at 295 K, demonstrating pressure-independent rate constants, kMu(T). Even at 200 Torr moderator pressure, the kinetics for Mu + C2H2 addition behave as if effectively in the high-pressure limit, giving k∞ = kMu due to depolarization of the muon spin in the MuC2H2 radical formed in the addition step. The rate constants kMu(T) exhibit modest Arrhenius curvature over the range of measured temperatures. Comparisons with data and with calculations for the corresponding H(D) + C2H2 addition reactions reveal a much faster rate for the Mu reaction at the lowest temperatures, by 2 orders of magnitude, in accord with the propensity of Mu to undergo quantum tunneling. Moreover, isotopic atom exchange, which contributes in a major way to the analogous D atom reaction, forming C2HD + H, is expected to be unimportant in the case of Mu addition, a consequence of the much higher zero-point energy and hence weaker C-Mu bond that would form, meaning that the present report of the Mu + C2H2 reaction is effectively the only experimental study of kinetic isotope effects in the high-pressure limit for H-atom addition to acetylene. PMID:25664674

  1. Fe /Fe oxide nanocomposite particles with large specific absorption rate for hyperthermia

    NASA Astrophysics Data System (ADS)

    Zeng, Q.; Baker, I.; Loudis, J. A.; Liao, Y.; Hoopes, P. J.; Weaver, J. B.

    2007-06-01

    Using a water-in-oil microemulsion with cetyl trimethyl ammonium bromide as the surfactant, iron was reduced to form a metallic core on which a passivating oxide shell was grown. Transmission electron microscopy, vibrating sample magnetometry, and heating measurements were used to characterize these monodispersed magnetic Fe /Fe3O4 composite nanoparticles with respect to the possible application for magnetic hyperthermia treatments of cancer. The aim is to utilize the fact that an iron core (high saturation magnetization) will give a greater heating effect than iron oxide, while the iron oxide coating will allow the nanoparticles to be observed using magnetic resonance imaging so that therapy can be effectively monitored and targeted. The largest specific absorption rate obtained was 345W/g under an alternating magnetic field of 150Oe at 250kHz.

  2. Specific absorption rate in models of man and monkey at 225 and 2000 MHz

    SciTech Connect

    Olsen, R.G.; Griner, T.A.

    1987-01-01

    Full-size models of a man and a rhesus monkey were exposed to radiofrequency (RF) radiation at 225 MHz. The model of man was also exposed to 2000 MHz. Specific absorption rates (SARs) were measured in partial-body sections, such as the arms, legs, etc., using gradient-layer calorimeters. Also, front-surface thermographic images were obtained to qualitatively show the heating patterns. For all of the configurations used, the SAR in the limbs was much higher than in the torso. Agreement (whole-body SARs) with spheroidal models was better for both models at 225 MHz than at 2000 MHz. These results indicate that in the frequency range two orders of magnitude above whole-body resonance, SAR in the limbs significantly contributes to the whole-body average SAR.

  3. Design of Miniaturized Double-Negative Material for Specific Absorption Rate Reduction in Human Head

    PubMed Central

    Faruque, Mohammad Rashed Iqbal; Islam, Mohammad Tariqul

    2014-01-01

    In this study, a double-negative triangular metamaterial (TMM) structure, which exhibits a resounding electric response at microwave frequency, was developed by etching two concentric triangular rings of conducting materials. A finite-difference time-domain method in conjunction with the lossy-Drude model was used in this study. Simulations were performed using the CST Microwave Studio. The specific absorption rate (SAR) reduction technique is discussed, and the effects of the position of attachment, the distance, and the size of the metamaterials on the SAR reduction are explored. The performance of the double-negative TMMs in cellular phones was also measured in the cheek and the tilted positions using the COMOSAR system. The TMMs achieved a 52.28% reduction for the 10 g SAR. These results provide a guideline to determine the triangular design of metamaterials with the maximum SAR reducing effect for a mobile phone. PMID:25350398

  4. Magnetic Nanoparticles with High Specific Absorption Rate at Low Alternating Magnetic Field

    PubMed Central

    Kekalo, K.; Baker, I.; Meyers, R.; Shyong, J.

    2015-01-01

    This paper describes the synthesis and properties of a new type of magnetic nanoparticle (MNP) for use in the hyperthermia treatment of tumors. These particles consist of 2–4 nm crystals of gamma-Fe2O3 gathered in 20–40 nm aggregates with a coating of carboxymethyl-dextran, producing a zetasize of 110–120 nm. Despite their very low saturation magnetization (1.5–6.5 emu/g), the specific absorption rate (SAR) of the nanoparticles is 22–200 W/g at applied alternating magnetic field (AMF) with strengths of 100–500 Oe at a frequency of 160 kHz. PMID:26884816

  5. Quasi-static magnetic measurements to predict specific absorption rates in magnetic fluid hyperthermia experiments

    NASA Astrophysics Data System (ADS)

    Coral, D. F.; Mendoza Zélis, P.; de Sousa, M. E.; Muraca, D.; Lassalle, V.; Nicolás, P.; Ferreira, M. L.; Fernández van Raap, M. B.

    2014-01-01

    In this work, the issue on whether dynamic magnetic properties of polydispersed magnetic colloids modeled using physical magnitudes derived from quasi-static magnetic measurement can be extrapolated to analyze specific absorption rate data acquired at high amplitudes and frequencies of excitation fields is addressed. To this end, we have analyzed two colloids of magnetite nanoparticles coated with oleic acid and chitosan in water displaying, under a radiofrequency field, high and low specific heat power release. Both colloids are alike in terms of liquid carrier, surfactant and magnetic phase composition but differ on the nanoparticle structuring. The colloid displaying low specific dissipation consists of spaced magnetic nanoparticles of mean size around 4.8 nm inside a large chitosan particle of 52.5 nm. The one displaying high specific dissipation consists of clusters of magnetic nanoparticles of mean size around 9.7 nm inside a chitosan particle of 48.6 nm. The experimental evaluation of Néel and Brown relaxation times (˜10-10 s and 10-4 s, respectively) indicate that the nanoparticles in both colloids magnetically relax by Néel mechanism. The isothermal magnetization curves analysis for this mechanism show that the magnetic nanoparticles behave in the interacting superparamagnetic regime. The specific absorption rates were determined calorimetrically at 260 kHz and up to 52 kA/m and were well modeled within linear response theory using the anisotropy density energy retrieved from quasi-static magnetic measurement, validating their use to predict heating ability of a given polydispersed particle suspension. Our findings provide new insight in the validity of quasi-static magnetic characterization to analyze the high frequency behavior of polydispersed colloids within the framework of the linear response and Wohlfarth theories and indicate that dipolar interactions play a key role being their strength larger for the colloid displaying higher dissipation, i

  6. Measurement of OH(X 2Πi υ = 2, 3, 4) Collisional Removal Rate Constants by Oxygen Atoms

    NASA Astrophysics Data System (ADS)

    Boulter, J. E.; Marschall, J.; Copeland, R. A.

    2002-05-01

    The fluorescence of vibrationally excited, ground electronic state hydroxyl radical (OH) in the airglow originates in the mesosphere-lower thermosphere (MLT) region of Earth's atmosphere. Spectroscopic measurements of this infrared emission are being made by the TIMED satellite to characterize the dynamics, temperature profiles, and HOy chemistry in the region 80-100 km. In the atmosphere, hydroxyl radicals in υ = 6-9 are formed in the reaction of hydrogen atoms with ozone; lower vibrational levels are populated through subsequent collisional deactivation by molecular oxygen. The lifetimes of the lower levels (υ <= 4) are significantly affected by collisions with atomic oxygen, as collisions with molecular oxygen are less efficient at relaxation than at higher levels. Given the importance of O-atom collisions in the atmosphere, we have developed an experimental approach and performed experiments on the collisional removal of OH(υ = 2, 3, 4) by atomic oxygen. In this work, the reaction of OH with atomic oxygen is studied using a two-laser method. Ozone is photolyzed in nitrogen with a pulsed excimer laser to generate O(1D), a portion of which reacts with either hydrogen to form OH(υ <= 4) or with water vapor to form OH(υ <= 3); the remainder is rapidly deactivated by collisions with N2 to produce ground state O(3P). A second, tunable dye laser pulse probes the OH population in a specific rovibrational state as a function of reaction time, using fluorescence from the A 2}Σ {+ - X 2Π { i} system. By adjusting the composition of the reactant gas mixture and by varying the photolysis laser fluence to control the ozone dissociation fraction, the dominant relaxation partner can be varied systematically from ozone and water or hydrogen to atomic oxygen. Experimentally determined rate constants for the removal of OH(υ = 2, 3, 4) by O(3P) are obtained at room temperature, with values of 6 x 10-11, 1.0 x 10-10 and 1.6 x 10-10 for υ = 2, 3 and 4, respectively, and 2-

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

    PubMed Central

    Bentley, T. William

    2015-01-01

    Hydrolyses of acid derivatives (e.g., carboxylic acid chlorides and fluorides, fluoro- and chloroformates, sulfonyl chlorides, phosphorochloridates, anhydrides) exhibit pseudo-first order kinetics. Reaction mechanisms vary from those involving a cationic intermediate (SN1) to concerted SN2 processes, and further to third order reactions, in which one solvent molecule acts as the attacking nucleophile and a second molecule acts as a general base catalyst. A unified framework is discussed, in which there are two reaction channels—an SN1-SN2 spectrum and an SN2-SN3 spectrum. Third order rate constants (k3) are calculated for solvolytic reactions in a wide range of compositions of acetone-water mixtures, and are shown to be either approximately constant or correlated with the Grunwald-Winstein Y parameter. These data and kinetic solvent isotope effects, provide the experimental evidence for the SN2-SN3 spectrum (e.g., for chloro- and fluoroformates, chloroacetyl chloride, p-nitrobenzoyl p-toluenesulfonate, sulfonyl chlorides). Deviations from linearity lead to U- or V-shaped plots, which assist in the identification of the point at which the reaction channel changes from SN2-SN3 to SN1-SN2 (e.g., for benzoyl chloride). PMID:26006228

  8. Rate constant of exciton quenching of Ir(ppy)3 with hole measured by time-resolved luminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Oyama, Shiho; Sakai, Heisuke; Murata, Hideyuki

    2016-03-01

    We observed the quenching of tris(2-phenylpyridinato)iridium(III) [Ir(ppy)3] excitons by polarons (holes or electrons) by time-resolved photoluminescence (PL) spectroscopy to clarify the dynamics of the triplet-polaron quenching of excitons. We employed a hole-only device (HOD) and an electron-only device (EOD), where the emitting layer consists of Ir(ppy)3 doped in 4,4‧-bis(carbazol-9-yl)biphenyl. Time-resolved PL spectroscopy of the EOD and HOD were measured under a constant current density. The results showed that the excitons of Ir(ppy)3 were significantly quenched only by holes. The PL decay curves of HOD were well fitted by the biexponential function, where lifetimes (τ1 and τ2) remain unchanged but the coefficient of each exponential term depends on hole current density. From the results, we proposed a model of exciton quenching where the exciton-hole quenching area expands with increasing hole current density. On the basis of the model, the triplet-polaron quenching rate constant Kq was determined.

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

    PubMed

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

    2014-12-01

    The copper complex [(bztpen)Cu](BF4)2 (bztpen=N-benzyl-N,N',N'-tris(pyridin-2-ylmethyl)ethylenediamine) displays high catalytic activity for electrochemical proton reduction in acidic aqueous solutions, with a calculated hydrogen-generation rate constant (k(obs)) of over 10000 s(-1). A turnover frequency (TOF) of 7000 h(-1) cm(-2) and a Faradaic efficiency of 96% were obtained from a controlled potential electrolysis (CPE) experiment with [(bztpen)Cu](2+) in pH 2.5 buffer solution at -0.90 V versus the standard hydrogen electrode (SHE) over two hours using a glassy carbon electrode. A mechanism involving two proton-coupled reduction steps was proposed for the dihydrogen generation reaction catalyzed by [(bztpen)Cu](2+). PMID:25314646

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

    SciTech Connect

    Nesseris, Savvas; Blake, Chris; Davis, Tamara; Parkinson, David E-mail: cblake@astro.swin.edu.au E-mail: d.parkinson@uq.edu.au

    2011-07-01

    We constrain the evolution of Newton's constant using the growth rate of large-scale structure measured by the WiggleZ Dark Energy Survey in the redshift range 0.1 < z < 0.9. We use this data in two ways. Firstly we constrain the matter density of the Universe, Ω{sub m} (assuming General Relativity), and use this to construct a diagnostic to detect the presence of an evolving Newton's constant. Secondly we directly measure the evolution of Newton's constant, G{sub eff}, that appears in Modified Gravity theories, without assuming General Relativity to be true. The novelty of these approaches are that, contrary to other methods, they do not require knowledge of the expansion history of the Universe, H(z), making them model independent tests. Our constraints for the second derivative of Newton's constant at the present day, assuming it is slowly evolving as suggested by Big Bang Nucleosynthesis constraints, using the WiggleZ data is G double-dot{sub eff}(t{sub 0}) = −1.19 ± 0.95·10{sup −20} h{sup 2} yr{sup −2}, where h is defined via H{sub 0} = 100 h km s{sup −1} Mpc{sup −1}, while using both the WiggleZ and the Sloan Digital Sky Survey Luminous Red Galaxy (SDSS LRG) data is G double-dot{sub eff}(t{sub 0}) = −3.6 ± 6.8·10{sup −21} h{sup 2} yr{sup −2}, both being consistent with General Relativity. Finally, our constraint for the rms mass fluctuation σ{sub 8} using the WiggleZ data is σ{sub 8} = 0.75 ± 0.08, while using both the WiggleZ and the SDSS LRG data σ{sub 8} = 0.77 ± 0.07, both in good agreement with the latest measurements from the Cosmic Microwave Background radiation.

  11. Measurement of diffusion coefficients important in modeling the absorption rate of carbon dioxide into aqueous N-methyldiethanolamine

    SciTech Connect

    Rowley, R.L.; Adams, M.E.; Marshall, T.L.; Oscarson, J.L.; Wilding, W.V.; Anderson, D.J.

    1997-03-01

    Natural gas processors use amine treating processes to remove the acid gases H{sub 2}S and CO{sub 2} from gas streams. Absorption rates of gaseous CO{sub 2} into aqueous N-methyldiethanolamine (MDEA) solutions were measured in a quiescent, inverted-tube diffusiometer by monitoring the rate of pressure drop. The absorption rate was found to be insensitive to the diffusion coefficient of CO{sub 2} in solution but very sensitive to the diffusion rate of bicarbonate and protonated MDEA ions. Evidence also suggested that chemical reaction equilibrium is rapid relative to diffusion. A numerical model was developed on the basis of these observations. The model was used to regress diffusion coefficients of bicarbonate and protonated amine, which must be equivalent by electroneutrality arguments, from measured absorption rates. Complete modeling of the absorption process also required data for the diffusion coefficient of MDEA in water. These were measured using a Taylor dispersion apparatus. CO{sub 2} absorption rates and diffusion coefficients of bicarbonate and protonated MDEA were obtained at 298.2 K and 318.2 K in solutions containing 20, 35, and 50 mass % MDEA in water.

  12. Nucleation-dependent tau filament formation: the importance of dimerization and an estimation of elementary rate constants.

    PubMed

    Congdon, Erin E; Kim, Sohee; Bonchak, Jonathan; Songrug, Tanakorn; Matzavinos, Anastasios; Kuret, Jeff

    2008-05-16

    Filamentous inclusions composed of the microtubule-associated protein tau are found in Alzheimer disease and other tauopathic neurodegenerative diseases, but the mechanisms underlying their formation from full-length protein monomer under physiological conditions are unclear. To address this issue, the fibrillization of recombinant full-length four-repeat human tau was examined in vitro as a function of time and submicromolar tau concentrations using electron microscopy assay methods and a small-molecule inducer of aggregation, thiazine red. Data were then fit to a simple homogeneous nucleation model with rate constant constraints established from filament dissociation rate, critical concentration, and mass-per-unit length measurements. The model was then tested by comparing the predicted time-dependent evolution of length distributions to experimental data. Results indicated that once assembly-competent conformations were attained, the rate-limiting step in the fibrillization pathway was tau dimer formation. Filament elongation then proceeded by addition of tau monomers to nascent filament ends. Filaments isolated at reaction plateau contained approximately 2 tau protomers/beta-strand spacing on the basis of mass-per-unit length measurements. The model suggests four key steps in the aggregation pathway that must be surmounted for tau filaments to form in disease. PMID:18359772

  13. Absolute Rate Constants for the Reaction of OH with [|#11#|]Cyclopentane and Cycloheptane from 230-350 K

    NASA Astrophysics Data System (ADS)

    Dransfield, T. J.; Gennaco, M. M.; Huang, Y.; Hannun, R. A.

    2011-12-01

    We report absolute measurements of the rate constants of the reaction of hydroxyl radical (OH) with cyclopentane and cycloheptane in 6-8 Torr of nitrogen from 230-350 K using Harvard's High Pressure Flow System. Ethane's reactivity was simultaneously measured as a test of experimental performance. Hydroxyl concentrations were measured using Laser-Induced Fluorescence, and alkane concentrations were measured using Fourier-Transform Infrared Spectroscopy. Recent work on this flow system has suggested that cyclohexane has a significantly higher activation energy to reaction with OH than does cyclo-octane, a result which is not suggested by our understanding of hydrocarbon reactivity nor predicted by structure-activity relationships. This work examines the temperature dependent rates for two other similarly-sized cycloalkanes to determine whether they behave as cyclohexane or as cyclooctane. While several previous experiments have studied the reaction with cyclopentane, there is significant scatter in the room temperature rates, and only four absolute rate measurements are available at non-ambient temperatures. There are only two absolute rate measurements available for the reaction with cycloheptane; only one of these reports a temperature dependence, and that study is limited to temperatures above 298 K. Thus, this work significantly expands the available data set for both reactions. The data for the reactions of OH with ethane, cyclopentane, cyclohexane, and cycloheptane are all modeled using a simple Arrhenius fit, and also with a modified Arrhenius equation based on transition state theory, ignoring tunneling. Results from the latter fit indicate that the activation barriers for both title reactions are greater than that of OH + cyclo-octane. The measured activation energy for OH + cyclopentane actually exceeds that of OH + cyclohexane.

  14. Selecting constant work rates for endurance testing in COPD: the role of the power-duration relationship.

    PubMed

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

    2014-06-01

    Constant work rate (CWR) exercise testing is highly responsive to therapeutic interventions and reveals physiological and functional benefits. No consensus exists, however, regarding optimal methods for selecting the pre-intervention work rate. We postulate that a CWR whose tolerated duration (tlim) is 6 minutes (WR6) may provide a useful interventional study baseline. WR6 can be extracted from the power-duration relationship, but requires 4 CWR tests. We sought to develop prediction algorithms for easier WR6 identification using backward stepwise linear regression, one in 69 COPD patients (FEV1 45 ± 15% pred) and another in 30 healthy subjects (HLTH), in whom cycle ergometer ramp incremental (RI) and CWR tests with tlim of ∼6 minutes had been performed. Demographics, pulmonary function, and RI responses were used as predictors. We validated these algorithms against power-duration measurements in 27 COPD and 30 HLTH (critical power 43 ± 18W and 231 ± 43W; curvature constant 5.1 ± 2.7 kJ and 18.5 ± 3.1 kJ, respectively). This analysis revealed that, on average, only corrected peak work rate ( = WRpeak-1 min × WRslope) in RI was required to predict WR6 (COPD SEE = 5.0W; HLTH SEE = 5.6W; R(2) > 0.96; p < 0.001). In the validation set, predicted and actual WR6 were strongly correlated (COPD R(2) = 0.937; HLTH 0.978; p < 0.001). However, in COPD, unlike in HLTH, there was a wide range of tlim values at predicted WR6: COPD 8.3 ± 4.1 min (range 3.6 to 22.2 min), and HLTH 5.5 ± 0.7 min (range 3.9 to 7.0 min). This analysis indicates that corrected WRpeak in an incremental test can yield an acceptable basis for calculating endurance testing work rate in HLTH, but not in COPD patients. PMID:24182350

  15. A simple approach to evaluate the kinetic rate constant for ATP synthesis in resting human skeletal muscle at 7 T.

    PubMed

    Ren, Jimin; Sherry, A Dean; Malloy, Craig R

    2016-09-01

    Inversion transfer (IT) is a well-established technique with multiple attractive features for analysis of kinetics. However, its application in measurement of ATP synthesis rate in vivo has lagged behind the more common saturation transfer (ST) techniques. One well-recognized issue with IT is the complexity of data analysis in comparison with much simpler analysis by ST. This complexity arises, in part, because the γ-ATP spin is involved in multiple chemical reactions and magnetization exchanges, whereas Pi is involved in a single reaction, Pi → γ-ATP. By considering the reactions involving γ-ATP only as a lumped constant, the rate constant for the reaction of physiological interest, kPi→γATP , can be determined. Here, we present a new IT data analysis method to evaluate kPi→γATP using data collected from resting human skeletal muscle at 7 T. The method is based on the basic Bloch-McConnell equation, which relates kPi→γATP to m˙Pi, the rate of Pi magnetization change. The kPi→γATP value is accessed from m˙Pi data by more familiar linear correlation approaches. For a group of human subjects (n = 15), the kPi→γATP value derived for resting calf muscle was 0.066 ± 0.017 s(-1) , in agreement with literature-reported values. In this study we also explored possible time-saving strategies to speed up data acquisition for kPi→γATP evaluation using simulations. The analysis indicates that it is feasible to carry out a (31) P IT experiment in about 10 min or less at 7 T with reasonable outcome in kPi→γATP variance for measurement of ATP synthesis in resting human skeletal muscle. We believe that this new IT data analysis approach will facilitate the wide acceptance of IT to evaluate ATP synthesis rate in vivo. Copyright © 2015 John Wiley & Sons, Ltd. PMID:25943328

  16. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

    SciTech Connect

    Soudackov, Alexander V.; Hammes-Schiffer, Sharon

    2015-11-21

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton

  17. Cigarette smoking and rate of gastric emptying: effect on alcohol absorption.

    PubMed Central

    Johnson, R D; Horowitz, M; Maddox, A F; Wishart, J M; Shearman, D J

    1991-01-01

    OBJECTIVE--To examine the effects of cigarette smoking on alcohol absorption and gastric emptying. DESIGN--Randomised crossover study. SETTING--Research project in departments of medicine and nuclear medicine. SUBJECTS--Eight healthy volunteers aged 19-43 who regularly smoked 20-35 cigarettes a day and drank small amounts of alcohol on social occasions. INTERVENTIONS--Subjects drank 400 ml of a radiolabelled nutrient test meal containing alcohol (0.5 g/kg), then had their rates of gastric emptying measured. Test were carried out (a) with the subjects smoking four cigarettes an hour and (b) with the subjects not smoking, having abstained for seven days or more. The order of the tests was randomised and the tests were conducted two weeks apart. MAIN OUTCOME MEASURES--Peak blood alcohol concentrations, absorption of alcohol at 30 minutes, amount of test meal emptied from the stomach at 30 minutes, and times taken for 50% of the meal to leave the proximal stomach and total stomach. RESULTS--Smoking was associated with reductions in (a) peak blood alcohol concentrations (median values in non-smoking versus smoking periods 13.5 (range 8.7-22.6) mmol/l v 11.1 (4.3-13.5) mmol/l), (b) area under the blood alcohol concentration-time curve at 30 minutes (264 x 10(3) (0-509 x 10(3)) mmol/l/min v 140 x 10(3)) (0-217 x 10(3) mmol/l/min), and (c) amount of test meal emptied from the stomach at 30 minutes (39% (5-86%) v 23% (0-35%)). In addition, smoking slowed both the 50% gastric emptying time (37 (9-83) minutes v 56 (40-280) minutes) and the intragastric distribution of the meal. There was a close correlation between the amount of test meal emptied from the stomach at 30 minutes and the area under the blood alcohol concentration-time curve at 30 minutes (r = 0.91; p less than 0.0001). CONCLUSION--Cigarette smoking slows gastric emptying and as a consequence delays alcohol absorption. PMID:1991182

  18. Low Temperature Rate Constants for the Reactions of O((1)D) with N2, O2, and Ar.

    PubMed

    Grondin, Romain; Loison, Jean-Christophe; Hickson, Kevin M

    2016-07-14

    The kinetics of the gas-phase quenching reactions O((1)D) + N2, O((1)D) + O2, and O((1)D) + Ar have been studied over the 50-296 K temperature range using the Laval nozzle method. O((1)D) atoms were created in situ by the pulsed photolysis of O3 precursor molecules at 266 nm. Rate constants for these processes were measured directly, following the decay of O((1)D) atoms through vacuum ultraviolet laser-induced fluorescence at 115.215 nm. For the O((1)D) + N2 and O((1)D) + O2 reactions, the quenching efficiencies are seen to increase as the temperature falls. For the O((1)D) + N2 system, this indicates the likely influence of the intermediate complex lifetime on the quenching rate through nonadiabatic processes. For the O((1)D) + O2 system, which is considerably more complex, this behavior could result from the interactions between several potential energy surfaces. PMID:26814664

  19. State-to-state vibration-translation and vibration-vibration rate constants in H{sub 2}-H{sub 2} and HD-HD collisions

    SciTech Connect

    Cacciatore, M.; Billing G.D.

    1992-01-09

    The authors present calculations of vibration-vibration and vibration-translation energy transfer rate constants in diatom-diatom collisions. The results are compared to recent experimental measurements.

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

    EPA Science Inventory

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

  1. BRIEF COMMUNICATIONS: Dynamic method for measurement of rate constants of heterogeneous chemical reactions taking place under the action of laser radiation

    NASA Astrophysics Data System (ADS)

    Kirichenko, N. A.; Luk'yanchuk, B. S.; Sapetskiĭ, A. N.

    1981-10-01

    A new dynamic method is proposed for determination of the rate constants of heterogeneous reactions. This involves measuring the temperature and its derivative during laser heating of solid targets, and also the finite thickness of the layer of the chemical compound being formed. The method can be used to find the rate constants obeying an arbitrary kinetic law and differs from traditional methods of measurement in being more accurate and less laborious.

  2. Hydrogen atom transfer reactions of ferrate(VI) with phenols and hydroquinone. Correlation of rate constants with bond strengths and application of the Marcus cross relation.

    PubMed

    Xie, Jianhui; Ma, Li; Lam, William W Y; Lau, Kai-Chung; Lau, Tai-Chu

    2016-01-01

    The oxidation of phenols by HFeO4(-) proceeds via a hydrogen atom transfer (HAT) mechanism, as evidenced by a large deuterium isotope effect and a linear correlation between the log(rate constant) and bond dissociation free energy (BDFE) of phenols. The Marcus cross relation has been applied to predict the rate constant of HAT from hydroquinone to HFeO4(-). PMID:26610053

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

    PubMed Central

    2015-01-01

    The structural similarity between the primary molecules of voltage-gated Na and K channels (alpha subunits) and activation gating in the Hodgkin-Huxley model is brought into full agreement by increasing the model's sodium kinetics to fourth order (m3 → m4). Both structures then virtually imply activation gating by four independent subprocesses acting in parallel. The kinetics coalesce in four-dimensional (4D) cubic diagrams (16 states, 32 reversible transitions) that show the structure to be highly failure resistant against significant partial loss of gating function. Rate constants, as fitted in phase plot data of retinal ganglion cell excitation, reflect the molecular nature of the gating transitions. Additional dimensions (6D cubic diagrams) accommodate kinetically coupled sodium inactivation and gating processes associated with beta subunits. The gating transitions of coupled sodium inactivation appear to be thermodynamically irreversible; response to dielectric surface charges (capacitive displacement) provides a potential energy source for those transitions and yields highly energy-efficient excitation. A comparison of temperature responses of the squid giant axon (apparently Arrhenius) and mammalian channel gating yields kinetic Q10 = 2.2 for alpha unit gating, whose transitions are rate-limiting at mammalian temperatures; beta unit kinetic Q10 = 14 reproduces the observed non-Arrhenius deviation of mammalian gating at low temperatures; the Q10 of sodium inactivation gating matches the rate-limiting component of activation gating at all temperatures. The model kinetics reproduce the physiologically large frequency range for repetitive firing in ganglion cells and the physiologically observed strong temperature dependence of recovery from inactivation. PMID:25867741

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

    PubMed Central

    Takara, L.S.; Cunha, T.M.; Barbosa, P.; Rodrigues, M.K.; Oliveira, M.F.; Nery, L.E.; Neder, J.A.

    2012-01-01

    This study evaluated the dynamic behavior of total and compartmental chest wall volumes [(VCW) = rib cage (VRC) + abdomen (VAB)] as measured breath-by-breath by optoelectronic plethysmography during constant-load exercise in patients with stable chronic obstructive pulmonary disease. Thirty males (GOLD stages II-III) underwent a cardiopulmonary exercise test to the limit of tolerance (Tlim) at 75% of peak work rate on an electronically braked cycle ergometer. Exercise-induced dynamic hyperinflation was considered to be present when end-expiratory (EE) VCW increased in relation to resting values. There was a noticeable heterogeneity in the patterns of VCW regulation as EEVCW increased non-linearly in 17/30 “hyperinflators” and decreased in 13/30 “non-hyperinflators” (P < 0.05). EEVAB decreased slightly in 8 of the “hyperinflators”, thereby reducing and slowing the rate of increase in end-inspiratory (EI) VCW (P < 0.05). In contrast, decreases in EEVCW in the “non-hyperinflators” were due to the combination of stable EEVRC with marked reductions in EEVAB. These patients showed lower EIVCW and end-exercise dyspnea scores but longer Tlim than their counterparts (P < 0.05). Dyspnea increased and Tlim decreased non-linearly with a faster rate of increase in EIVCW regardless of the presence or absence of dynamic hyperinflation (P < 0.001). However, no significant between-group differences were observed in metabolic, pulmonary gas exchange and cardiovascular responses to exercise. Chest wall volumes are continuously regulated during exercise in order to postpone (or even avoid) their migration to higher operating volumes in patients with COPD, a dynamic process that is strongly dependent on the behavior of the abdominal compartment. PMID:23250012

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

    SciTech Connect

    Yang, R; Wang, J

    2014-06-01

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

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

    PubMed

    Fohlmeister, Jürgen F

    2015-06-01

    The structural similarity between the primary molecules of voltage-gated Na and K channels (alpha subunits) and activation gating in the Hodgkin-Huxley model is brought into full agreement by increasing the model's sodium kinetics to fourth order (m(3) → m(4)). Both structures then virtually imply activation gating by four independent subprocesses acting in parallel. The kinetics coalesce in four-dimensional (4D) cubic diagrams (16 states, 32 reversible transitions) that show the structure to be highly failure resistant against significant partial loss of gating function. Rate constants, as fitted in phase plot data of retinal ganglion cell excitation, reflect the molecular nature of the gating transitions. Additional dimensions (6D cubic diagrams) accommodate kinetically coupled sodium inactivation and gating processes associated with beta subunits. The gating transitions of coupled sodium inactivation appear to be thermodynamically irreversible; response to dielectric surface charges (capacitive displacement) provides a potential energy source for those transitions and yields highly energy-efficient excitation. A comparison of temperature responses of the squid giant axon (apparently Arrhenius) and mammalian channel gating yields kinetic Q10 = 2.2 for alpha unit gating, whose transitions are rate-limiting at mammalian temperatures; beta unit kinetic Q10 = 14 reproduces the observed non-Arrhenius deviation of mammalian gating at low temperatures; the Q10 of sodium inactivation gating matches the rate-limiting component of activation gating at all temperatures. The model kinetics reproduce the physiologically large frequency range for repetitive firing in ganglion cells and the physiologically observed strong temperature dependence of recovery from inactivation. PMID:25867741

  7. Searching for variations in the fine-structure constant and the proton-to-electron mass ratio using quasar absorption lines

    NASA Astrophysics Data System (ADS)

    King, Julian A.

    2012-02-01

    (abridged) Quasar absorption lines provide a precise test of the assumed constancy of the fundamental constants of physics. We have investigated potential changes in the fine-structure constant, alpha, and the proton-to-electron mass ratio, mu. The many-multiplet method allows one to use optical fine-structure transitions to constrain (Delta alpha)/alpha at better than the 10^(-5) level. We present a new analysis of 154 quasar absorbers with 0.2 < z <3.7 in VLT/UVES spectra. From these absorbers we find 2.2 sigma evidence for angular variations in alpha under a dipole+monopole model. Combined with previous Keck/HIRES observations, we find 4.1 sigma evidence for angular (and therefore spatial) variations in alpha, with maximal increase of alpha occurring in the direction RA=(17.3 +/- 1.0) hr, dec=(-61 +/- 10) deg. Under a model where the observed effect is proportional to the lookback-time distance the significance increases to 4.2 sigma. Dipole models fitted to the VLT and Keck samples and models fitted to z<1.6 and z>1.6 sub-samples independently yield consistent estimates of the dipole direction, which suggests that the effect is not caused by telescope systematics. We consider a number of systematic effects and show that they are unable to explain the observed dipole effect. We have used spectra of the quasars Q0405-443, Q0347-383 and Q0528-250 from VLT/UVES to investigate the absorbers at z=2.595, 3.025 and 2.811 in these spectra respectively. We find that (Delta mu)/mu=(10.1 +/- 6.6) x 10^(-6), (8.2 +/- 7.5) x 10^(-6) and (-1.4 +/- 3.9) x 10^(-6) in these absorbers respectively. A second spectrum of Q0528-250 provides an additional constraint of (Delta mu)/mu=(0.2 +/- 3.2_stat +/- 1.9_sys) x 10^(-6). The weighted mean of these values yields (Delta mu)/mu=(1.7 +/- 2.4) x 10^(-6), the most precise constraint on evolution in mu at z>1.

  8. Stability constants and molar absorptivities for complexes of copper(II) with N-methyldiethanolamine, 1,4-bis(2-hydroxypropyl)-2-methylpiperazine, and 2-amino-2-methyl-1-propanol.

    PubMed

    Siefker, J R; Aroc, R V

    1986-09-01

    The stability constants and molar absorptivities of complexes of Cu(2+) with N-methyldiethanolamine, 1,4-bis(2-hydroxypropyl)-2-methylpiperazine, and 2-amino-2-methyl-1-propanol have been determined from spectrophotometric data for very dilute aqueous solutions. PMID:18964197

  9. Specific absorption rate in electrically coupled biological samples between metal plates.

    PubMed

    Joines, W T; Blackman, C F; Spiegel, R J

    1986-01-01

    The specific absorption rate (SAR) in a biological sample irradiated by electromagnetic fields between the metal plates of a transmission line can be altered significantly by the spacing of the metal plates and the distance between neighboring samples. The SAR in spherical biological samples is calculated for a number of neighboring sample arrangements and metal-plate spacings by using the method of images and induced dipole coupling. For a decrease in metal-plate spacing, the derived equations predict an increase in SAR within a sample and a decrease in SAR with a decrease in neighboring-sample spacing. The calculations are compared with measurements made with the aid of an array of 1-in radius metal hemispheres on the lower plate of two parallel plates (thus forming an image system). The hemisphere on which measurements are taken is insulated from the metal plate and is connected via a coaxial center conductor to an HP 3582A spectrum analyzer that measures the voltage and hence the electric field intensity at the hemisphere. Measurements made at a frequency where wavelength is large compared with sample size (48 Hz) are in good agreement with calculations. PMID:3741491

  10. On the reliable measurement of specific absorption rates and intrinsic loss parameters in magnetic hyperthermia materials

    NASA Astrophysics Data System (ADS)

    Wildeboer, R. R.; Southern, P.; Pankhurst, Q. A.

    2014-12-01

    In the clinical application of magnetic hyperthermia, the heat generated by magnetic nanoparticles in an alternating magnetic field is used as a cancer treatment. The heating ability of the particles is quantified by the specific absorption rate (SAR), an extrinsic parameter based on the clinical response characteristic of power delivered per unit mass, and by the intrinsic loss parameter (ILP), an intrinsic parameter based on the heating capacity of the material. Even though both the SAR and ILP are widely used as comparative design parameters, they are almost always measured in non-adiabatic systems that make accurate measurements difficult. We present here the results of a systematic review of measurement methods for both SAR and ILP, leading to recommendations for a standardised, simple and reliable method for measurements using non-adiabatic systems. In a representative survey of 50 retrieved datasets taken from published papers, the derived SAR or ILP was found to be more than 5% overestimated in 24% of cases and more than 5% underestimated in 52% of cases.

  11. Assessment of specific energy absorption rate (SAR) in the head from a TETRA handset.

    PubMed

    Dimbylow, Peter; Khalid, Mohammed; Mann, Simon

    2003-12-01

    Finite-difference time-domain (FDTD) calculations of the specific energy absorption rate (SAR) from a representative TETRA handset have been performed in an anatomically realistic model of the head. TETRA (Terrestrial Trunked Radio) is a modern digital private mobile radio system designed to meet the requirements of professional users, such as the police and fire brigade. The current frequency allocations in the UK are 380-385 MHz and 390-395 MHz for the public sector network. A comprehensive set of calculations of SAR in the head was performed for positions of the handset in front of the face and at both sides of the head. The representative TETRA handset considered. operating at 1 W in normal use, will show compliance with both the ICNIRP occupational and public exposure restrictions. The handset with a monopole antenna operating at 3 W in normal use will show compliance with both the ICNIRP occupational and public exposure restrictions. The handset with a helical antenna operating at 3 W in normal use will show compliance with the ICNIRP occupational exposure restriction but will be over the public exposure restriction by up to approximately 50% if kept in the position of maximum SAR for 6 min continuously. PMID:14703166

  12. A Prototype RF Dosimeter for Independent Measurement of the Average Specific Absorption Rate (SAR) During MRI

    PubMed Central

    Stralka, John P; Bottomley, Paul A

    2008-01-01

    Purpose To develop a scanner-independent dosimeter for measuring the average radio frequency (RF) power deposition and specific absorption rates (SAR) for human MRI exposure. Materials and Methods A prototype dosimeter has a transducer with orthogonal conducting loops surrounding a small signal-generating MRI sample. The loops contain resistors whose values are adjusted to load the scanner’s MRI coils equivalent to an average head or body during MRI. The scanner adjusts its power output to normal levels during setup, using the MRI sample. Following calibration, the total power and average SAR deposited in the transducer are measured from the root-mean-square (rms) power induced in the transducer during MRI. Results A 1.5 Tesla head transducer was adjusted to elicit the same load as the average of nine adult volunteers. Once adjusted, the transducer loads other head coils the same as the head does. The dosimeter is calibrated at up to 20 W total deposited power and 4.5 W/kg SAR in the average head, with about 5% accuracy. Conclusion This dosimeter provides a simple portable means of measuring the power deposited in a body-equivalent sample load, independent of the scanner. Further work will develop SAR dosimetry for the torso and for higher fields. PMID:17969145

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Technical Reports Server (NTRS)

    Brunning, J.; Stief, L. J.

    1985-01-01

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

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

    SciTech Connect

    Li, Yimin; Miller, Wlliam H.

    2006-02-22

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

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

    PubMed

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

    2015-01-01

    Most quantitative structure-property/activity relationships (QSPRs/QSARs) predict various endpoints related to organic compounds. Gradually, the variety of organic compounds has been extended to inorganic, organometallic compounds and polymers. However, the so-called molecular descriptors cannot be defined for super-complex substances such as different nanomaterials and peptides, since there is no simple and clear representation of their molecular structure. Some possible ways to define approaches for a predictive model in the case of super-complex substances are discussed. The basic idea of the approach is to change the traditionally used paradigm 'the endpoint is a mathematical function of the molecular structure' with another paradigm 'the endpoint is a mathematical function of available eclectic information'. The eclectic data can be (i) conditions of a synthesis, (ii) technological attributes, (iii) size of nanoparticles, (iv) concentration, (v) attributes related to cell membranes, and so on. Two examples of quasi-QSPR/QSAR analyses are presented and discussed. These are (i) photocatalytic decolourization rate constants (DRC) (10(-5)/s) of different nanopowders; and (ii) the cellular viability under the effect of nano-SiO(2). PMID:25608955

  17. Determination of rate constants and half-lives for the simultaneous biodegradation of several cyanobacterial metabolites in Australian source waters.

    PubMed

    Ho, Lionel; Tang, Tim; Hoefel, Daniel; Vigneswaran, Bala

    2012-11-01

    The fate of five cyanobacterial metabolites was assessed in water sourced from Lake Burragorang (Warragamba Dam) in New South Wales, Australia. All of the studied metabolites were shown to be biodegradable in this water source. For some metabolites, biodegradation was influenced by factors, including temperature, location (within the water body) and seasonal variations. The biodegradation of the metabolites was shown to follow pseudo-first-order kinetics with rate constants ranging from 8.0 × 10(-4) to 1.3 × 10(-2) h(-1). Half-lives of the metabolites were also estimated and ranged from 2.2 to 36.1 d. The order of ease of biodegradability in this water source followed the trend: microcystin-LR ≥ cylindrospermopsin > saxitoxins > geosmin ≥ 2-methylisoborneol. The lack of detection of the mlrA gene during microcystin biodegradation suggests that these toxins may be degraded via a different pathway. While no metabolite-degrading organisms were isolated in this study, the inoculation of previously isolated geosmin- and microcystin-degrading bacteria into Lake Burragorang water resulted in efficient biodegradation of the respective metabolites. For example, microcystin-degrading isolate TT25 was able to degrade three microcystin variants to concentrations below analytical detection within 24 h, suggesting that inoculation of such bacteria has the potential to enhance biodegradation in Lake Burragorang. PMID:22921397

  18. Temperature dependence of the rate constant and product channels for the BrO + ClO reaction

    SciTech Connect

    Hills, A.J.; Cicerone, R.J.; Calvert, J.G.; Birks, J.W.

    1988-04-07

    The authors have measured the rate constant for the reactions BrO + ClO ..-->.. Br + OClO (6a), BrO + ClO ..-->.. Br + Cl + O/sub 2/ (6b), and BrO + ClO ..-->.. BrCl + O/sub 2/ (6c) over the temperature range 241-408 K and found k/sub 6/ = (8.2 +/- 1.0) x 10/sup -12/ cm/sup 3/ molecule/sup -1/ s/sup -1/ independent of temperature. Measurement of the individual product branching ratios yielded values for channels 6a, 6b, and 6c equal to 0.55 +/- 0.10, 0.45 +/- 0.10, and < 0.02, respectively. Measurements of ozone in the stratosphere over Antarctica have shown that the springtime ozone column has fallen 40% from 1960 to 1985. The reaction above could account for a large fraction of the springtime ozone hole reported recently, provided that at least 20 ppt of total inorganic bromine is present, and it may provide a source of chlorine dioxide of sufficient magnitude to explain the recent measurements of this species in the Antarctica stratosphere.

  19. Absolute level-to-level rate constants for inelastic collisions and exchange reactions in lithium + gaseous lithium(v,j) going to gaseous lithium(v',j') + lithium

    NASA Astrophysics Data System (ADS)

    Coppage, Steven Danforth

    We report 644 absolute level-to-level inelastic and reactive constants for the L7i*2 A1S+u (nui, ji) + 7Li → L7i*2 A1S+u (nu', j') + 7Li system with initial molecular quantum numbers nui = 2 and ji = 3, 11, and 19. We collected 87 rate constants for rotationally inelastic and vibrationally elastic collisions, 281 rate constants for vibrationally inelastic collisions, and 276 constants for exchange reactions with final vibrational levels from nu f = 0 to nuf = 3. Inelastic collisions are characterized by even changes in rotational quantum number, j , and exchange reactions are identified by odd Deltaj. Level-to-level rate constants for even Deltaj inelastic collisions show distributions similar to those in rare gas collisions with the excited Li2 molecule. The ECS (energy corrected sudden) scaling law of DePristo, et al., fit the vibrationally elastic data well. Reactive rate constant results are characterized by a statistical distribution for Deltanu of 0, -1, and -2 at a substantially reduced effective temperature consistent with a kinematic model proposed by Picconatto et al. Fitting quasiclassical trajectory studies to the data using a modified LEPS potential surface provide first insights into the parameters of the excited-state Li3* three-body potential.

  20. The formation of linear aggregates in magnetic hyperthermia: implications on specific absorption rate and magnetic anisotropy.

    PubMed

    Saville, Steven L; Qi, Bin; Baker, Jonathon; Stone, Roland; Camley, Robert E; Livesey, Karen L; Ye, Longfei; Crawford, Thomas M; Mefford, O Thompson

    2014-06-15

    The design and application of magnetic nanoparticles for use as magnetic hyperthermia agents has garnered increasing interest over the past several years. When designing these systems, the fundamentals of particle design play a key role in the observed specific absorption rate (SAR). This includes the particle's core size, polymer brush length, and colloidal arrangement. While the role of particle core size on the observed SAR has been significantly reported, the role of the polymer brush length has not attracted as much attention. It has recently been reported that for some suspensions linear aggregates form in the presence of an applied external magnetic field, i.e. chains of magnetic particles. The formation of these chains may have the potential for a dramatic impact on the biomedical application of these materials, specifically the efficiency of the particles to transfer magnetic energy to the surrounding cells. In this study we demonstrate the dependence of SAR on magnetite nanoparticle core size and brush length as well as observe the formation of magnetically induced colloidal arrangements. Colloidally stable magnetic nanoparticles were demonstrated to form linear aggregates in an alternating magnetic field. The length and distribution of the aggregates were dependent upon the stabilizing polymer molecular weight. As the molecular weight of the stabilizing layer increased, the magnetic interparticle interactions decreased therefore limiting chain formation. In addition, theoretical calculations demonstrated that interparticle spacing has a significant impact on the magnetic behavior of these materials. This work has several implications for the design of nanoparticle and magnetic hyperthermia systems, while improving understanding of how colloidal arrangement affects SAR. PMID:24767510

  1. Quantifying intra- and extracellular aggregation of iron oxide nanoparticles and its influence on specific absorption rate.

    PubMed

    Jeon, Seongho; Hurley, Katie R; Bischof, John C; Haynes, Christy L; Hogan, Christopher J

    2016-09-21

    A promising route to cancer treatment is hyperthermia, facilitated by superparamagnetic iron oxide nanoparticles (SPIONs). After exposure to an alternating external magnetic field, SPIONs generate heat, quantified by their specific absorption rate (SAR, in W g(-1) Fe). However, without surface functionalization, commercially available, high SAR SPIONs (EMG 308, Ferrotec, USA) aggregate in aqueous suspensions; this has been shown to reduce SAR. Further reduction in SAR has been observed for SPIONs in suspensions containing cells, but the origin of this further reduction has not been made clear. Here, we use image analysis methods to quantify the structures of SPION aggregates in the extra- and intracellular milieu of LNCaP cell suspensions. We couple image characterization with nanoparticle tracking analysis and SAR measurements of SPION aggregates in cell-free suspensions, to better quantify the influence of cellular uptake on SPION aggregates and ultimately its influence on SAR. We find that in both the intra- and extracellular milieu, SPION aggregates are well-described by a quasifractal model, with most aggregates having fractal dimensions in the 1.6-2.2 range. Intracellular aggregates are found to be significantly larger than extracellular aggregates and are commonly composed of more than 10(3) primary SPION particles (hence they are "superaggregates"). By using high salt concentrations to generate such superaggregates and measuring the SAR of suspensions, we confirm that it is the formation of superaggregates in the intracellular milieu that negatively impacts SAR, reducing it from above 200 W g(-1) Fe for aggregates composed of fewer than 50 primary particles to below 50 W g(-1) for superaggregates. While the underlying physical mechanism by which aggregation leads to reduction in SAR remains to be determined, the methods developed in this study provide insight into how cellular uptake influences the extent of SPION aggregation, and enable estimation of the

  2. RATE CONSTANTS FOR THE GAS-PHASE REACTIONS OF A SERIES OF C3-C6 ALDEHYDES WITH OH AND NO3 RADICALS. (R825252)

    EPA Science Inventory

    By using relative rate methods, rate constants for the gas-phase reactions of OH and NO3 radicals with propanal, butanal, pentanal, and hexanal have been measured at 296 ? 2 K and atmospheric pressure of air. By using methyl vinyl ketone as the reference compound, the ...

  3. 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

  4. Protein isotope effects in dihydrofolate reductase from Geobacillus stearothermophilus show entropic-enthalpic compensatory effects on the rate constant.

    PubMed

    Luk, Louis Y P; Ruiz-Pernía, J Javier; Dawson, William M; Loveridge, E Joel; Tuñón, Iñaki; Moliner, Vicent; Allemann, Rudolf K

    2014-12-10

    Catalysis by dihydrofolate reductase from the moderately thermophilic bacterium Geobacillus stearothermophilus (BsDHFR) was investigated by isotope substitution of the enzyme. The enzyme kinetic isotope effect for hydride transfer was close to unity at physiological temperatures but increased with decreasing temperatures to a value of 1.65 at 5 °C. This behavior is opposite to that observed for DHFR from Escherichia coli (EcDHFR), where the enzyme kinetic isotope effect increased slightly with increasing temperature. These experimental results were reproduced in the framework of variational transition-state theory that includes a dynamical recrossing coefficient that varies with the mass of the protein. Our simulations indicate that BsDHFR has greater flexibility than EcDHFR on the ps-ns time scale, which affects the coupling of the environmental motions of the protein to the chemical coordinate and consequently to the recrossing trajectories on the reaction barrier. The intensity of the dynamic coupling in DHFRs is influenced by compensatory temperature-dependent factors, namely the enthalpic barrier needed to achieve an ideal transition-state configuration with minimal nonproductive trajectories and the protein disorder that disrupts the electrostatic preorganization required to stabilize the transition state. Together with our previous studies of other DHFRs, the results presented here provide a general explanation why protein dynamic effects vary between enzymes. Our theoretical treatment demonstrates that these effects can be satisfactorily reproduced by including a transmission coefficient in the rate constant calculation, whose dependence on temperature is affected by the protein flexibility. PMID:25396728

  5. Determination of Bimolecular Rate Constants for Reactions of Hydroxyl Radical with Pharmaceutical and Cosmetics Chemicals - Implications to the Fate in the Aquatic Environment

    NASA Astrophysics Data System (ADS)

    Nakajima, H.; Arakaki, T.; Anastasio, C.

    2008-12-01

    Large organic compounds such as hyaluronic acid and chondroitin sulfate are often used in pharmaceutical and cosmetics products, but their chemical degradation pathways are not well understood. To better elucidate their fate in the aquatic environment, we initiated a study to determine bimolecular rate constants between these organic compounds and hydroxyl radical (OH), which is a potent oxidant in the environment. The lifetimes of many organic compounds are determined by reactions with OH radicals, and the lifetime of OH is often controlled by reactions with organic compounds. To determine these bimolecular rate constants we used a competition kinetics technique with either hydrogen peroxide or nitrate as a source of OH and benzoate as the competing sink. Since the molecular weights of some of the large organic compounds we studied were not known, we used dissolved organic carbon (DOC) concentrations to determine mole-carbon based bimolecular rate constants, instead of the commonly used molar-based bimolecular rate constants. We will report the mole-carbon based bimolecular rate constants of OH, determined at room temperature, with hyaluronic acid, chondroitin sulfate and some other large organic compounds.

  6. Quantum mechanical reaction rate constants by vibrational configuration interaction: the OH + H2->H2O + H reaction as a function of temperature.

    PubMed

    Chakraborty, Arindam; Truhlar, Donald G

    2005-05-10

    The thermal rate constant of the 3D OH + H(2)-->H(2)O + H reaction was computed by using the flux autocorrelation function, with a time-independent square-integrable basis set. Two modes that actively participate in bond making and bond breaking were treated by using 2D distributed Gaussian functions, and the remaining (nonreactive) modes were treated by using harmonic oscillator functions. The finite-basis eigenvalues and eigenvectors of the Hamiltonian were obtained by solving the resulting generalized eigenvalue equation, and the flux autocorrelation function for a dividing surface optimized in reduced-dimensionality calculations was represented in the basis formed by the eigenvectors of the Hamiltonian. The rate constant was obtained by integrating the flux autocorrelation function. The choice of the final time to which the integration is carried was determined by a plateau criterion. The potential energy surface was from Wu, Schatz, Lendvay, Fang, and Harding (WSLFH). We also studied the collinear H + H(2) reaction by using the Liu-Siegbahn-Truhlar-Horowitz (LSTH) potential energy surface. The calculated thermal rate constant results were compared with reported values on the same surfaces. The success of these calculations demonstrates that time-independent vibrational configuration interaction can be a very convenient way to calculate converged quantum mechanical rate constants, and it opens the possibility of calculating converged rate constants for much larger reactions than have been treated until now. PMID:15774583

  7. Estimation of the rate constants associated with the inhibitory effect of okadaic acid on type 2A protein phosphatase by time-course analysis.

    PubMed Central

    Takai, A; Ohno, Y; Yasumoto, T; Mieskes, G

    1992-01-01

    As is often the case with tightly binding inhibitors, okadaic acid produces its inhibitory effect on type 2A protein phosphatase (PP2A) in a time-dependent manner. We measured the rate constants associated with the binding of okadaic acid to PP2A by analysing the time-course of the reduction of the p-nitrophenyl phosphate (pNPP) phosphatase activity of the enzyme after application of okadaic acid. The rate constants for dissociation of okadaic acid from PP2A were also estimated from the time-course of the recovery of the activity from inhibition by okadaic acid after addition of a mouse IgG1 monoclonal antibody raised against the inhibitor. Our results show that the rate constants for the binding of okadaic acid and PP2A are of the order of 10(7) M-1.s-1, a typical value for reactions involving relatively large molecules, whereas those for their dissociation are in the range 10(-4)-10(-3) s-1. The very low values of the latter seems to be the determining factor for the exceedingly high affinity of okadaic acid for PP2A. The dissociation constants for the interaction of okadaic acid with the free enzyme and the enzyme-substrate complex, estimated as the ratio of the rate constants, are both in the range 30-40 pM, in agreement with the results of previous dose-inhibition analyses. PMID:1329723

  8. Combined Acquisition Technique (CAT) for Neuroimaging of Multiple Sclerosis at Low Specific Absorption Rates (SAR)

    PubMed Central

    Biller, Armin; Choli, Morwan; Blaimer, Martin; Breuer, Felix A.; Jakob, Peter M.; Bartsch, Andreas J.

    2014-01-01

    Purpose To compare a novel combined acquisition technique (CAT) of turbo-spin-echo (TSE) and echo-planar-imaging (EPI) with conventional TSE. CAT reduces the electromagnetic energy load transmitted for spin excitation. This radiofrequency (RF) burden is limited by the specific absorption rate (SAR) for patient safety. SAR limits restrict high-field MRI applications, in particular. Material and Methods The study was approved by the local Medical Ethics Committee. Written informed consent was obtained from all participants. T2- and PD-weighted brain images of n = 40 Multiple Sclerosis (MS) patients were acquired by CAT and TSE at 3 Tesla. Lesions were recorded by two blinded, board-certificated neuroradiologists. Diagnostic equivalence of CAT and TSE to detect MS lesions was evaluated along with their SAR, sound pressure level (SPL) and sensations of acoustic noise, heating, vibration and peripheral nerve stimulation. Results Every MS lesion revealed on TSE was detected by CAT according to both raters (Cohen’s kappa of within-rater/across-CAT/TSE lesion detection κCAT = 1.00, at an inter-rater lesion detection agreement of κLES = 0.82). CAT reduced the SAR burden significantly compared to TSE (p<0.001). Mean SAR differences between TSE and CAT were 29.0 (±5.7) % for the T2-contrast and 32.7 (±21.9) % for the PD-contrast (expressed as percentages of the effective SAR limit of 3.2 W/kg for head examinations). Average SPL of CAT was no louder than during TSE. Sensations of CAT- vs. TSE-induced heating, noise and scanning vibrations did not differ. Conclusion T2−/PD-CAT is diagnostically equivalent to TSE for MS lesion detection yet substantially reduces the RF exposure. Such SAR reduction facilitates high-field MRI applications at 3 Tesla or above and corresponding protocol standardizations but CAT can also be used to scan faster, at higher resolution or with more slices. According to our data, CAT is no more uncomfortable than TSE scanning. PMID

  9. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

    SciTech Connect

    Soudackov, Alexander; Hammes-Schiffer, Sharon

    2015-11-17

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency regimes for the proton donor-acceptor vibrational mode. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term does not significantly impact the rate constants derived using the cumulant expansion approach in any of the regimes studied. The effects of the quadratic term may become significant when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant, however, particularly at high temperatures and for proton transfer interfaces with extremely soft proton donor-acceptor modes that are associated with extraordinarily weak hydrogen bonds. Even with the thermal averaging procedure, the effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances, and the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes. We are grateful for support from National Institutes of Health Grant GM056207 (applications to enzymes) and the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy

  10. HIGH CONSTANT INCIDENCE RATES OF SECOND PRIMARY CANCERS OF THE HEAD AND NECK: A POOLED ANALYSIS OF 13 CANCER REGISTRIES

    PubMed Central

    Bosetti, Cristina; Scelo, Ghislaine; Chuang, Shu-Chun; Tonita, Jon M.; Tamaro, Sharon; Jonasson, Jon G.; Kliewer, Erich V.; Hemminki, Kari; Weiderpass, Elisabete; Pukkala, Eero; Tracey, Elizabeth; Olsen, Jorgen H.; Pompe-Kirn, Vera; Brewster, David H.; Martos, Carmen; Chia, Kee-Seng; Brennan, Paul; Hashibe, Mia; Levi, Fabio; La Vecchia, Carlo; Boffetta, Paolo

    2010-01-01

    Scanty data are available on the incidence (i.e., the absolute risk) of second cancers of the head and neck (HN) and its pattern with age. We investigated this issue using data from a multicentric study of 13 population-based cancer registries from Europe, Canada, Australia and Singapore for the years 1943-2000. A total of 99,257 patients had a first primary HN cancer (15,985 tongue, 22,378 mouth, 20,758 pharyngeal, and 40,190 laryngeal cancer), contributing to 489,855 person-years of follow-up. 1294 of the patients (1.3%) were diagnosed with second HN cancers (342 tongue, 345 mouth, 418 pharynx, and 189 larynx). Male incidence rates of first HN cancer steeply increased from 0.68/100,000 at age 30-34 to 46.2/100,000 at age 70-74, and leveled off at higher age; female incidence increased from 0.50/100,000 at age 30-34 to 16.5/100,000 at age 80-84. However, age-specific incidence of second HN cancers after a first HN cancer in men was around 200-300/100,000 between age 40-44 and age 70-74, and tended to decline at subsequent ages (150/100,000 at age 80-84); in women, incidence of second HN cancers was around 200-300/100,000 between age 45-49 and 80-84. The patterns of age-specific incidence were consistent for different subsites of second HN cancer and sexes; moreover, they were similar for age-specific incidence of first primary HN cancer in patients who subsequently developed a second HN cancer. The incidence of second HN cancers does not increase with age, but remains constant, or if anything, decreases with advancing age. Impact statement While the incidence of first primary cancers of the head and neck increases with advancing age that of second primary cancers is stable between age 40 and 70 and, if anything, declines thereafter. PMID:20824702

  11. Survey on Different Samsung with Nokia Smart Mobile Phones in the Specific Absorption Rate Electrical Field of Head.

    PubMed

    Fakhri, Yadolah; Alinejad, Azim; Keramati, Hassan; Bay, Abotaleb; Avazpour, Moayed; Zandsalimi, Yahya; Moradi, Bigard; Rasouli Amirhajeloo, Leila; Mirzaei, Maryam

    2016-01-01

    The use of smart phones is increasing in the world. This excessive use, especially in the last two decades, has created too much concern on the effects of emitted electromagnetic fields and specific absorption rate on human health. In this descriptive-analytical study of the electric field resulting from smart phones of Samsung and Nokia by portable measuring device, electromagnetic field, Model HI-3603-VDT/VLF, were measured. Then, head absorption rate was calculated in these two mobiles by ICNIRP equation. Finally, the comparison of specific absorption rate, especially between Samsung and Nokia smart phones, was conducted by T-Test statistics analysis. The mean of electric field for Samsung and Nokia smart mobile phones was obtained 1.8 ±0.19 v/m  and 2.23±0.39 v/m , respectively, while the range of the electric field was obtained as 1.56-2.21 v/m and 1.69-2.89 v/m for them, respectively. The mean of specific absorption rate in Samsung and Nokia was obtained 0.002 ± 0.0005 W/Kg and 0.0041±0.0013 W/Kg at the frequency of 900 MHz and 0.004±0.001 W/Kg and 0.0062±0.0002 W/Kg at the frequency of 1800 MHz respectively. The ratio of mean electronic field to guidance in the Samsung mobile phone at the frequency of 900 MHz and 1800 MHz was 4.36% and 3.34%, while was 5.62% and 4.31% in the Nokia mobile phone, respectively. The ratio of mean head specific absorption rate in smart mobile phones of Samsung and Nokia in the guidance level at the frequency of 900 was 0.15% and 0.25%, respectively, while was 0.23 %and 0.38% at the frequency of 1800 MHz, respectively. The rate of specific absorption of Nokia smart  mobile phones at the frequencies of 900 and 1800 MHz  was significantly higher than Samsung (p value <0.05). Hence, we can say that in a fixed period, health risks of Nokia smart phones is higher than Samsung smart mobile phone. PMID:27157169

  12. Skin dose rate conversion factors after contamination with radiopharmaceuticals: influence of contamination area, epidermal thickness and percutaneous absorption.

    PubMed

    Covens, P; Berus, D; Caveliers, V; Struelens, L; Vanhavere, F; Verellen, D

    2013-06-01

    Skin contamination with radiopharmaceuticals can occur during biomedical research and daily nuclear medicine practice as a result of accidental spills, after contact with bodily fluids of patients or by inattentively touching contaminated materials. Skin dose assessment should be carried out by repeated quantification to map the course of the contamination together with the use of appropriate skin dose rate conversion factors. Contamination is generally characterised by local spots on the palmar surface of the hand and complete decontamination is difficult as a result of percutaneous absorption. This specific issue requires special consideration as to the skin dose rate conversion factors as a measure for the absorbed dose rate to the basal layer of the epidermis. In this work we used Monte Carlo simulations to study the influence of the contamination area, the epidermal thickness and the percutaneous absorption on the absorbed skin dose rate conversion factors for a set of 39 medical radionuclides. The results show that the absorbed dose to the basal layer of the epidermis can differ by up to two orders of magnitude from the operational quantity Hp(0.07) when using an appropriate epidermal thickness in combination with the effect of percutaneous absorption. PMID:23519114

  13. Abnormal oral glucose tolerance and glucose malabsorption after vagotomy and pyloroplasty. A tracer method for measuring glucose absorption rates

    SciTech Connect

    Radziuk, J.; Bondy, D.C.

    1982-11-01

    The mechanisms underlying the abnormal glucose tolerance in patients who had undergone vagotomy and pyloroplasty were investigated by measuring the rates of absorption of ingested glucose and the clearance rate of glucose using tracer methods. These methods are based on labeling a 100-g oral glucose load with (1-/sup 14/C)glucose and measuring glucose clearance using plasma levels of infused (3-/sup 3/H)glucose. The rate of appearance of both ingested and total glucose is then calculated continuously using a two-compartment model of glucose kinetics. It was found that about 30% of the ingested glucose (100 g) failed to appear in the systemic circulation. That this was due to malabsorption was confirmed using breath-hydrogen analysis. The absorption period is short (101 +/- 11 min) compared with normal values but the clearance of glucose is identical to that in control subjects, and it peaks 132 +/- 7 min after glucose loading. The peak plasma insulin values were more than four times higher in patients than in normal subjects, and this may afford an explanation of rates of glucose clearance that are inappropriate for the short absorption period. The combination of glucose malabsorption and this clearance pattern could yield the hypoglycemia that may be observed in patients after gastric surgery.

  14. Heating from free-free absorption and the mass-loss rate of the progenitor stars to supernovae

    SciTech Connect

    Björnsson, C.-I.; Lundqvist, P. E-mail: peter@astro.su.se

    2014-06-01

    An accurate determination of the mass-loss rate of the progenitor stars to core-collapse supernovae is often limited by uncertainties pertaining to various model assumptions. It is shown that under conditions when the temperature of the circumstellar medium is set by heating due to free-free absorption, observations of the accompanying free-free optical depth allow a direct determination of the mass-loss rate from observed quantities in a rather model-independent way. The temperature is determined self-consistently, which results in a characteristic time dependence of the free-free optical depth. This can be used to distinguish free-free heating from other heating mechanisms. Since the importance of free-free heating is quite model dependent, this also makes possible several consistency checks of the deduced mass-loss rate. It is argued that the free-free absorption observed in SN 1993J is consistent with heating from free-free absorption. The deduced mass-loss rate of the progenitor star is, approximately, 10{sup –5} M {sub ☉} yr{sup –1} for a wind velocity of 10 km s{sup –1}.

  15. AUGMENTATION OF SULFATE ION ABSORPTION FROM THE RATE LUNG BY HEAVY METALS

    EPA Science Inventory

    The effect of heavy metal cations in enhancing the absorption of sulfate ions from the airways of the rat lung was studied. The cations investigated included Cd(2+), Co(2+), Hg(2+), Ni(2+), Fe(3+), Mn(2+), and Zn(2+). The cations exhibited differing efficacies. Co(2+), Hg(2+), Cd...

  16. Calculations of Solar Shortwave Heating Rates due to Black Carbon and Ozone Absorption Using in Situ Measurements

    NASA Technical Reports Server (NTRS)

    Gao, R. S.; Hall, S. R.; Swartz, W. H.; Spackman, J. R.; Watts, L. A.; Fahey, D. W.; Aikin, K. C.; Shetter, R. E.; Bui, T. P.

    2008-01-01

    Results for the solar heating rates in ambient air due to absorption by black-carbon (BC) containing particles and ozone are presented as calculated from airborne observations made in the tropical tropopause layer (TTL) in January-February 2006. The method uses airborne in situ observations of BC particles, ozone and actinic flux. Total BC mass is obtained along the flight track by summing the masses of individually detected BC particles in the range 90 to 600-nm volume-equivalent diameter, which includes most of the BC mass. Ozone mixing ratios and upwelling and partial downwelling solar actinic fluxes were measured concurrently with BC mass. Two estimates used for the BC wavelength-dependent absorption cross section yielded similar heating rates. For mean altitudes of 16.5, 17.5, and 18.5 km (0.5 km) in the tropics, average BC heating rates were near 0.0002 K/d. Observed BC coatings on individual particles approximately double derived BC heating rates. Ozone heating rates exceeded BC heating rates by approximately a factor of 100 on average and at least a factor of 4, suggesting that BC heating rates in this region are negligible in comparison.

  17. 133Xenon absorption into rubber-protected portable cadmium telluride (CdTe(Cl)) detectors invalidating the 133Xenon washout method for measurement of cutaneous and subcutaneous blood flow rates in man.

    PubMed

    Sørensen, J L

    1991-01-01

    The importance of 133Xenon absorption into rubber detector caps during cutaneous and subcutaneous blood flow measurement was investigated in 46 experiments involving 38 persons. 133Xenon was administered atraumatically. Cutaneous and subcutaneous washout rates were registered by portable Cadmium Telluride detectors without rubber caps, with rubber caps, and with rubber caps with Mylar membranes interposed between the rubber and the tissue investigated. No difference in rate constants obtained by means of various detector types was detected. The accumulation of 133Xenon in the rubber caps was found to take place within the first few minutes after the detectors had been brought into position. The 133Xenon then diffused back into the tissue exhibiting a great variation regarding rate constants. The 133Xenon diffused form rubber into air and perfused tissue tracing a monoexponential course; and again the rate constants would vary considerably. No correlation was found between elimination rates obtained with detectors with and without 133Xenon polluted caps, and no way of correcting for the 133Xenon content in the rubber caps was found. Relative changes in rate constants could still be recognized, but absolute values were not obtainable. PMID:1789123

  18. Evaluation of different partial AUCs as indirect measures of rate of drug absorption in comparative pharmacokinetic studies.

    PubMed

    Duquesnoy, C; Lacey, L F; Keene, O N; Bye, A

    1998-10-01

    The performance of different partial AUCs, including partial AUC from zero to t(max) of the reference formulation (AUC(r)) and partial AUC from zero to tmax of test or reference formulation, whichever occurs earliest (AUC(e), as indirect measures of rate of absorption have been evaluated using simulated experiments. The performance of these metrics relative to C(max), t(max) and C(max)/AUC(infinity) was further assessed using the results of actual studies involving a Glaxo drug. The normalised metrics AUC(r)/AUC(infinity) and AUC(e)/AUC(infinity) have also been evaluated. Our provisional conclusions were: (1) AUC(r)/AUC(infinity) and AUC(e)/AUC(infinity) had greater statistical power than C(max) and the non-normalised partial AUCs at detecting true differences in rate of absorption. Using real data, the performance of AUC(e)/AUC(infinity) was poor, however, the performance of AUC(r)/AUC(infinity) was good; (2) C(max)/AUC(infinity) was more precisely estimated than AUC(r)/AUC(infinity) or AUC(e)/AUC(infinity) and may be a superior metric for assessing absorption rates of highly variable drugs. PMID:9795077

  19. First-principles calculation of photo-induced electron transfer rate constants in phthalocyanine-C60 organic photovoltaic materials: Beyond Marcus theory

    NASA Astrophysics Data System (ADS)

    Lee, Myeong H.; Dunietz, Barry D.; Geva, Eitan

    2014-03-01

    Classical Marcus theory is commonly adopted in solvent-mediated charge transfer (CT) process to obtain the CT rate constant, but it can become questionable when the intramolecular vibrational modes dominate the CT process as in OPV devices because Marcus theory treats these modes classically and therefore nuclear tunneling is not accounted for. We present a computational scheme to obtain the electron transfer rate constant beyond classical Marcus theory. Within this approach, the nuclear vibrational modes are treated quantum-mechanically and a short-time approximation is avoided. Ab initio calculations are used to obtain the basic parameters needed for calculating the electron transfer rate constant. We apply our methodology to phthalocyanine(H2PC)-C60 organic photovoltaic system where one C60 acceptor and one or two H2PC donors are included to model the donor-acceptor interface configuration. We obtain the electron transfer and recombination rate constants for all accessible charge transfer (CT) states, from which the CT exciton dynamics is determined by employing a master equation. The role of higher lying excited states in CT exciton dynamics is discussed. This work is pursued as part of the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the US Department of Energy Office of Science, Office of Basic Energy Sciences under 390 Award No. DE-SC0000957.

  20. USING IN VIVO GAS UPDATE STUDIES TO ESTIMATE METABOLIC RATE CONSTANTS FOR CCL CHEMICALS: 1,1-DICHLOROPROPANE AND 2,2-DICHLOROPROPANE

    EPA Science Inventory

    USING IN VIVO GAS UPTAKE STUDIES TO ESTIMATE METABOLIC RATE CONSTANTS FOR CCL CHEMICALS: 1,1-DICHLOROPROPENE AND 2,2-DICHLOROPROPANE.
    Mitchell, C T, Evans, M V, Kenyon, E M. NHEERL, U.S. EPA, ORD, ETD, RTP, NC

    The Safe Drinking Water Act Amendments of 1996 required ...

  1. Smoluchowski Equations for Agglomeration in Conditions of Variable Temperature and Pressure and a New Scaling of Rate Constants: Application to Nozzle-Beam Expansion.

    PubMed

    Chaiken, J; Goodisman, J; Kornilov, O

    2015-07-01

    The Smoluchowski equations provide a rigorous and efficient means for including multiple kinetic pathways when modeling coalescence growth systems. Originally written for a constant temperature and volume system, the equations must be modified if temperature and pressure vary during the coalescence time. In this paper, the equations are generalized, and adaptations appropriate to the situation presented by supersonic nozzle beam expansions are described. Given rate constants for all the cluster-cluster reactions, solution of the Smoluchowski equations would yield the abundances of clusters of all sizes at all times. This is unlikely, but we show that if these rate constants scale with the sizes of the reacting partners, the asymptotic (large size and large time) form of the cluster size distribution can be predicted. Experimentally determined distributions for He fit the predicted asymptotic distribution very well. Deviations between predicted and observed distributions allow identification of special cluster sizes that is, magic numbers. Furthermore, fitting an observed distribution to the theoretical form yields the base agglomeration cross section, from which all cluster-cluster rate constants may be obtained by scaling. Comparing the base cross section to measures of size and reactivity gives information about the coalescence process. PMID:26067086

  2. A simplified method for calculating the atmospheric heating rate by absorption of solar radiation in the stratosphere and mesosphere

    NASA Technical Reports Server (NTRS)

    Shimazaki, T.; Helmle, L. C.

    1979-01-01

    Calculations of the atmospheric heating rate by absorption of solar radiation by O3, H2O, and CO2 are reported. The method needs only seven parameters for each molecule and is particularly useful for heating calculations in three-dimensional global circulation models below 80 km. Applying the formula to the observed distributions of O3, H2O, and CO2 produces reasonable latitudinal and seasonal variations in the heating rate. The calculated heating rate, however, is sensitive to the global distributions of the absorbing gases, and uncertainties in the O3 distribution above approximately 50 km and the H2O distribution below approximately 20 km may seriously affect the global distributions of the heating rate in these regions.

  3. Modifying the high rate algal pond light environment and its effects on light absorption and photosynthesis.

    PubMed

    Sutherland, Donna L; Montemezzani, Valerio; Howard-Williams, Clive; Turnbull, Matthew H; Broady, Paul A; Craggs, Rupert J

    2015-03-01

    The combined use of high rate algal ponds (HRAPs) for wastewater treatment and commercial algal production is considered to be an economically viable option. However, microalgal photosynthesis and biomass productivity is constrained in HRAPs due to light limitation. This paper investigates how the light climate in the HRAP can be modified through changes in pond depth, hydraulic retention time (HRT) and light/dark turnover rate and how this impacts light absorption and utilisation by the microalgae. Wastewater treatment HRAPs were operated at three different pond depth and HRT during autumn. Light absorption by the microalgae was most affected by HRT, significantly decreasing with increasing HRT, due to increased internal self-shading. Photosynthetic performance (as defined by Pmax, Ek and α), significantly increased with increasing pond depth and decreasing HRT. Despite this, increasing pond depth and/or HRT, resulted in decreased pond light climate and overall integrated water column net oxygen production. However, increased light/dark turnover was able to compensate for this decrease, bringing the net oxygen production in line with shallower ponds operated at shorter HRT. On overcast days, modelled daily net photosynthesis significantly increased with increased light/dark turnover, however, on clear days such increased turnover did not enhance photosynthesis. This study has showed that light absorption and photosynthetic performance of wastewater microalgae can be modified through changes to pond depth, HRT and light/dark turnover. PMID:25514661

  4. Operation of a low temperature absorption chiller at rating point and at reduced evaporator temperature

    NASA Astrophysics Data System (ADS)

    Best, R.; Biermann, W.; Reimann, R. C.

    1985-01-01

    The returned fifteen ton Solar Absorption Machine (SAM) 015 chiller was given a cursory visual inspection, some obvious problems were remedied, and then it was placed on a test stand to get a measure of dirty performance. It was then given a standard acid clean, the water side of the tubes was brushed clean, and then the machine was retested. The before and after cleaning data were compared to equivalent data taken before the machine was shipped. The second part of the work statement was to experimentally demonstrate the technical feasibility of operating the chiller at evaporator temperatures below 0(0)C (32(0)F) and identify any operational problems.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  6. FDTD chiral brain tissue model for specific absorption rate determination under radiation from mobile phones at 900 and 1800 MHz

    NASA Astrophysics Data System (ADS)

    Zamorano, M.; Torres-Silva, H.

    2006-04-01

    A new electrodynamics model formed by chiral bioplasma, which represents the human head inner structure and makes it possible to analyse its behaviour when it is irradiated by a microwave electromagnetic field from cellular phones, is presented. The finite-difference time-domain (FDTD) numeric technique is used, which allows simulation of the electromagnetic fields, deduced with Maxwell's equations, and allows us to simulate the specific absorption rate (SAR). The results show the SAR behaviour as a function of the input power and the chirality factor. In considering the chiral brain tissue in the proposed human head model, the two more important conclusions of our work are the following: (a) the absorption of the electromagnetic fields from cellular phones is stronger, so the SAR coefficient is higher than that using the classical model, when values of the chiral factor are of order of 1; (b) 'inverse skin effect' shows up at 1800 MHz, with respect to a 900 MHz source.

  7. FDTD chiral brain tissue model for specific absorption rate determination under radiation from mobile phones at 900 and 1800 MHz.

    PubMed

    Zamorano, M; Torres-Silva, H

    2006-04-01

    A new electrodynamics model formed by chiral bioplasma, which represents the human head inner structure and makes it possible to analyse its behaviour when it is irradiated by a microwave electromagnetic field from cellular phones, is presented. The finite-difference time-domain (FDTD) numeric technique is used, which allows simulation of the electromagnetic fields, deduced with Maxwell's equations, and allows us to simulate the specific absorption rate (SAR). The results show the SAR behaviour as a function of the input power and the chirality factor. In considering the chiral brain tissue in the proposed human head model, the two more important conclusions of our work are the following: (a) the absorption of the electromagnetic fields from cellular phones is stronger, so the SAR coefficient is higher than that using the classical model, when values of the chiral factor are of order of 1; (b) "inverse skin effect" shows up at 1800 MHz, with respect to a 900 MHz source. PMID:16552096

  8. Variable food absorption by Antarctic krill: Relationships between diet, egestion rate and the composition and sinking rates of their fecal pellets

    NASA Astrophysics Data System (ADS)

    Atkinson, A.; Schmidt, K.; Fielding, S.; Kawaguchi, S.; Geissler, P. A.

    2012-01-01

    The kinetics of food processing by zooplankton affects both their energy budgets and the biogeochemical fate of their fecal pellets. We sampled 40 schools of krill across the Scotia Sea during spring, summer and autumn and found that in all 3 seasons, every aspect of their absorption and defecation varied greatly. The C content of fecal pellets varied from 0.85% to 29% of their dry mass (median 9.8%) and C egestion rates varied 75-fold. C:N mass ratios of pellets ranged from 4.9 to 13.2 (median 7.8), higher than values of 3.9 in the krill and 5.4 in their food, pointing to enhanced uptake of N. Pellet sinking rates equated to 27-1218 m d -1 (median 304 m d -1), being governed mainly by pellet diameter (80-600 μm, mean 183 μm) and density (1.038-1.391 g cm -3, mean 1.121 g cm -3). Pellets showed little loss of C or N in filtered seawater over the first 2 days and were physically robust. When feeding rates were low, slow gut passage time and high absorption efficiency resulted in low egestion rates of pellets that were low in C and N content. These pellets were compact, dense and fast-sinking. Conversely, in good feeding conditions much food tended to pass quickly through the gut and was not efficiently absorbed, producing C and N-rich, slow-sinking pellets. Such "superfluous feeding" probably maximises the absolute rates of nutrient absorption. Food composition was also important: diatom-rich diets depressed the C content of the pellets but increased their sinking rates, likely due to silica ballasting. So depending on how krill process food, their pellets could represent both vehicles for rapid export and slow sinking, C and N-rich food sources for pelagic scavengers. C egestion rates by krill averaged 3.4% of summer primary production (and ingestion rates would be 2-10-fold higher than this) so whatever the fate of the pellets, krill are an important re-packager within the food web. While salp pellets tend to sink faster than those of krill, it is the latter

  9. COMPARISON OF IN VIVO DERIVED AND SCALED IN VITRO METABOLIC RATE CONSTANTS FOR SOME VOLATILE ORGANIC COMPOUNDS (VOCS)

    EPA Science Inventory

    The reliability of physiologically based pharmacokinetic (PBPK) models is directly related to the accuracy of the metabolic rate parameters used as model inputs. When metabolic rate parameters derived from in vivo experiments are unavailable, they can be estimated from in vitro d...

  10. A new, fast and accurate spectrophotometric method for the determination of the optical constants of arbitrary absorptance thin films from a single transmittance curve: application to dielectric materials

    NASA Astrophysics Data System (ADS)

    Desforges, Jean; Deschamps, Clément; Gauvin, Serge

    2015-08-01

    The determination of the complex refractive index of thin films usually requires the highest accuracy. In this paper, we report on a new and accurate method based on a spectral rectifying process of a single transmittance curve. The agreements with simulated and real experimental data show the helpfulness of the method. The case of materials having arbitrary absorption bands at midpoint in spectral range, such as pigments in guest-host polymers, is also encompassed by this method.

  11. Temperature-dependent versus constant-rate blood perfusion modelling in ferromagnetic thermoseed hyperthermia: results with a model of the human prostate.

    PubMed

    Tompkins, D T; Vanderby, R; Klein, S A; Beckman, W A; Steeves, R A; Frye, D M; Paliwal, B R

    1994-01-01

    Finite-element solutions to the Pennes bioheat equation are obtained with a model of a tumour-containing, human prostate and surrounding normal tissues. Simulations of ferromagnetic hyperthermia treatments are conducted on the tissue model in which the prostate is implanted with an irregularly spaced array of thermoseeds. Several combinations of thermoseed temperatures with different Curie points are investigated. Non-uniform, constant-rate blood perfusion models are studied and compared with temperature-dependent descriptions of blood perfusion. Blood perfusions in the temperature-dependent models initially increase with tissue temperature and then decrease at higher temperatures. Simulations with temperature-dependent versus constant-rate blood perfusion models reveal significant differences in temperature distributions in and surrounding the tumour-containing prostate. Results from the simulations include differences (between temperature-dependent and constant-rate models) in (1) the percentage of normal tissue volume and tumour volume at temperatures > 42 degrees C, and (2) temperature descriptors in the tumour (subscript t) and normal (subscript n) tissues including Tmax.t, Tmin.t and Tmax.n. Isotherms and grey-scale contours in the tumour and surrounding normal tissues are presented for four simulations that model a combination of high-temperature thermoseeds. Several simulations show that Tmin.t is between 1.7 and 2.6 degrees C higher and Tmax.n is between 2.1 and 3.3 degrees C higher with a temperature-dependent versus a comparable constant-rate blood perfusion model. The same simulations reveal that the percentages of tumour volume at temperatures > 42 degrees C are between 0 and 68% higher with the temperature-dependent versus the constant-rate perfusion model over all seed combinations studied. In summary, a numerical method is presented which makes it possible to investigate temperature-dependent, continuous functions of blood perfusion in simulations

  12. New model for assessing dose, dose rate, and temperature sensitivity of radiation-induced absorption in glasses

    SciTech Connect

    Gilard, Olivier; Quadri, Gianandrea; Caussanel, Matthieu; Duval, Herve; Reynaud, Francois

    2010-11-15

    A new theoretical approach is proposed to explain the dose, dose rate and temperature sensitivity of the radiation-induced absorption (RIA) in glasses. In this paper, a {beta}{sup th}-order dispersive kinetic model is used to simulate the growth of the density of color centers in irradiated glasses. This model yields an explanation for the power-law dependence on dose and dose rate usually observed for the RIA in optical fibers. It also leads to an Arrhenius-like relationship between the RIA and the glass temperature during irradiation. With a very limited number of adjustable parameters, the model succeeds in explaining, with a good agreement, the RIA growth of two different optical fiber references over wide ranges of dose, dose rate and temperature.

  13. Rate-equation model for quantitative concentration measurements in flames with picosecond pump-probe absorption spectroscopy.

    PubMed

    Fiechtner, G J; King, G B; Laurendeau, N M

    1995-02-20

    Measurement of radical concentrations is important in understanding the chemical kinetics involved in combustion. Application of optical techniques allows for the nonintrusive determination of specific radical concentrations. One of the most challenging problems for investigators is to obtain flame data that are independent of the collisional environment. We seek to obviate this difficulty by the use of picosecond pump-probe absorption spectroscopy. A picosecond pump-probe absorption model is developed by rate-equation analysis. Implications are discussed for a laser-pulse width that is much smaller than the excited-state lifetime of the absorbing atom or molecule. The possibility of quantitative, quenching-independent concentration measurements is discussed, and detection limits for atomic sodium and the hydroxyl radical are estimated. For a three-level absorber-emitter, the model leads to a novel pump-probe strategy, called dual-beam asynchronous optical sampling, that can be used to obtain both the electronic quenching-rate coefficient and the doublet mixing-rate coefficient during a single measurement. We discuss the successful demonstration of the technique in a companion paper [Appl. Opt. 34, XXX (1995)]. PMID:21037640

  14. Absolute rate constant of the reaction OH + H2O2 yields HO2 + H2O from 245 to 423 K

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1980-01-01

    The absolute rate constant of the reaction between the hydroxyl radical and hydrogen peroxide was measured by using the discharge-flow resonance fluorescence technique at total pressure between 1 and 4 torr. At 298 K the result is (1.64 + or - 0.32) x 10 to the -12th cu cm/molecule s. The observed rate constant is independent of pressure, surface-to-volume ratio, the addition of vibrational quenchers, and the source of OH. The temperature dependence has also been determined between 245 and 423 K; the resulting Arrhenius expression is k cu cm/molecule s is equal to (2.51 + or - 0.6) x 10 to the -12th exp(-126 + or - 76/T).

  15. Absolute rate constant for the reaction of atomic chlorine with hydrogen peroxide vapor over the temperature range 265-400 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Whytock, D. A.; Lee, J. H.; Payne, W. A.; Stief, L. J.

    1977-01-01

    Rate constants for the reaction of atomic chlorine with hydrogen peroxide were measured from 265-400 K using the flash photolysis-resonance fluorescence technique. Analytical techniques were developed to measure H2O2 under reaction conditions. Due to ambiguity in the interpretation of the analytical results, the data combine to give two equally acceptable representations of the temperature dependence. The results are compared to previous work at 298 K and are theoretically discussed in terms of the mechanism of the reaction. Additional experiments on the H + H2O2 reaction at 298 and 359 K are compared with earlier results from this laboratory and give a slightly revised bimolecular rate constant.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  17. Efficient and reliable calculation of Rice-Ramsperger-Kassel-Marcus unimolecular reaction rate constants for biopolymers: modification of Beyer-Swinehart algorithm for degenerate vibrations.

    PubMed

    Moon, Jeong Hee; Sun, Meiling; Kim, Myung Soo

    2007-06-01

    The Beyer-Swinehart (BS) algorithm, which calculates vibrational state density and sum, was modified for simultaneous treatment of degenerate vibrations. The modified algorithm was used in the grouped-frequency mode of the Rice-Ramsperger-Kassel-Marcus (RRKM) unimolecular reaction rate constant calculation for proteins with relative molecular mass as large as 100,000. Compared to the original BS method, reduction in computation time by a factor of around 3000 was achieved. Even though large systematic errors arising from frequency grouping were observed for state densities and sums, they more or less canceled each other, thus enabling reliable rate constant calculation. The present method is thought to be adequate for efficient and reliable RRKM calculations for any macromolecule in the gas phase such as the molecular ions of proteins, nucleic acids, and carbohydrates generated inside a mass spectrometer. The algorithm can also be used to calculate the internal energy distribution of a macromolecule at thermal equilibrium. PMID:17448674

  18. Effect of solvent on the rate constant for the radiative deactivation of singlet molecular oxygen (/sup 1/. delta. /sub g/O/sub 2/)

    SciTech Connect

    Scurlock, R.D.; Ogilby, P.R.

    1987-08-13

    Relative rate constants for the radiative deactivation (k/sub r/) of singlet molecular oxygen (/sup 3/Sigma/sub g//sup -/O/sub 2/ reverse arrow /sup 1/..delta../sub g/O/sub 2/) have been determined in 15 solvents. A substantial solvent effect is observed. Changes in the value of k/sub r/ can exceed a factor of 20. A reasonably good correlation exists between the solvent polarizability, defined as a function of the solvent refractive index, and the radiative rate constant. We suggest that our data support a model in which /sup 1/..delta../sub g/O/sub 2/ is perturbed through the formation of a discrete oxygen-solvent collision complex.

  19. Morphotectonic and geodetic evidence for a constant slip-rate over the last 45 kyr along the Tabriz fault (Iran)

    NASA Astrophysics Data System (ADS)

    Rizza, M.; Vernant, P.; Ritz, J. F.; Peyret, M.; Nankali, H.; Nazari, H.; Djamour, Y.; Salamati, R.; Tavakoli, F.; Chéry, J.; Mahan, S. A.; Masson, F.

    2013-06-01

    Iran is an active continental domain accommodating the convergence between the Arabia and Eurasia plates. In northwestern Iran, deformation between the Central Iranian block and the Caucasus domain is mainly accommodated by right lateral strike-slip on the Tabriz fault. Cities and villages, including the city of Tabriz, have been destroyed by several strong historical earthquakes (M ˜ 7). In this study, we compare the slip-rates estimated from geodetic measurements (radar interferometry and GPS) with those determined by dating a geomorphological offset of an alluvial fan along the Tabriz fault. The GPS measurements along two profiles normal to the Tabriz fault suggest a slip-rate of 7.3 ± 1.3 mm yr-1. The persistent scatterer radar interferometry analysis of Envisat satellite archives from 2003 to 2010 shows a velocity gradient (6 ± 3 mm yr-1) across the Tabriz fault in agreement with GPS results. Moreover, it reveals that most of the area located south of the Tabriz fault is affected by subsidence, and that some sections of the fault probably act as barriers to fluid migration which may have an impact on its mechanical behaviour. West of Tabriz morphotectonic investigations on an alluvial fan surface show a right-lateral cumulative offset of 320 ± 40 m. Luminescence analyses of the coarse matrix alluvial fan deposits provide an age of 46 ± 3 ka. This yields a slip-rate comprised between 6.5 and 7.3 mm yr-1 along this segment. These results suggest that the Late Quaternary slip-rate is in agreement with the present-day slip-rate estimated by geodetic measurements, showing no slip-rate changes during the past 45 000 yr. Short-term variations within the 45 000 yr related to temporal earthquake clustering over few seismic cycles cannot be ruled out, but if they exist, they do not affect the geodetic and the geomorphological estimates. This study is in agreement with previous ones suggesting that long-term slip-rates (i.e. averaged over several tens of seismic

  20. Experimental and theoretical determination of cross sections and rate constants for charge transfer population of some excited Ag+, I+, and Cu+ levels

    NASA Astrophysics Data System (ADS)

    Temelkov, K. A.; Vuchkov, N. K.; Sabotinov, N. V.

    2007-04-01

    Cross-sections and rate constants for thermal energy charge transfer into some Ag+, I+, and Cu+ excited states are theoretically and experimentally obtained for a gas discharge in the He-CuBr, Ne-CuBr, He-AgI, and Ne-AgI mixtures. Besides the pumping process the formation of the inversion population is determined by the radiative transitions, which populate or depopulate the upper and lower laser levels.

  1. Modelling the fate of nonylphenolic compounds in the Seine River--part 1: determination of in-situ attenuation rate constants.

    PubMed

    Cladière, Mathieu; Bonhomme, Céline; Vilmin, Lauriane; Gasperi, Johnny; Flipo, Nicolas; Tassin, Bruno

    2014-01-15

    Assessing the fate of endocrine disrupting compounds (EDCs) in the environment is currently a key issue for determining their impacts on aquatic ecosystems. The 4-nonylphenol (4-NP) is a well known EDC and results from the biodegradation of surfactant nonylphenol ethoxylates (NPnEOs). Fate mechanisms of NPnEO are well documented but their rate constants have been mainly determined through laboratory experiments. This study aims at evaluating the in-situ fate of 4-NP, nonylphenol monoethoxylate (NP1EO) and nonylphenolic acetic acid (NP1EC). Two sampling campaigns were carried out on the Seine River in July and September 2011, along a 28km-transect downstream Paris City. The field measurements are used for the calibration of a sub-model of NPnEO fate, included into a hydro-ecological model of the Seine River (ProSe). The timing of the sampling is based on the Seine River velocity in order to follow a volume of water. Based on our results, in-situ attenuation rate constants of 4-NP, NP1EO and NP1EC for both campaigns are evaluated. These rate constants vary greatly. Although the attenuation rate constants in July are especially high (higher than 1d(-1)), those obtained in September are lower and consistent with the literature. This is probably due to the biogeochemical conditions in the Seine River. Indeed, the July sampling campaign took place at the end of an algal bloom leading to an unusual bacterial biomass while the September campaign was carried out during common biogeochemical status. Finally, the uncertainties on measurements and on the calibration parameters are estimated through a sensitivity analysis. This study provides relevant information regarding the fate of biodegradable pollutants in an aquatic environment by coupling field measurements and a biogeochemical model. Such data may be very helpful in the future to better understand the fate of nonylphenolic compounds or any other pollutants at the basin scale. PMID:24100207

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

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

    PubMed

    Sudhakaran, Sairam; Amy, Gary L

    2013-03-01

    Ozonation is an oxidation process for the removal of organic micropollutants (OMPs) from water and the chemical reaction is governed by second-order kinetics. An advanced oxidation process (AOP), wherein the hydroxyl radicals (OH radicals) are generated, is more effective in removing a wider range of OMPs from water than direct ozonation. Second-order rate constants (k(OH) and k(O3) are good indices to estimate the oxidation efficiency, where higher rate constants indicate more rapid oxidation. In this study, quantitative structure activity relationships (QSAR) models for O(3) and AOP processes were developed, and rate constants, k(OH) and [Formula: see text] , were predicted based on target compound properties. The k(O3) and k(OH) values ranged from 5 * 10(-4) to 10(5) M(-1)s(-1) and 0.04 to 18 * (10(9)) M(-1) s(-1), respectively. Several molecular descriptors which potentially influence O(3) and OH radical oxidation were identified and studied. The QSAR-defining descriptors were double bond equivalence (DBE), ionisation potential (IP), electron-affinity (EA) and weakly-polar component of solvent accessible surface area (WPSA), and the chemical and statistical significance of these descriptors was discussed. Multiple linear regression was used to build the QSAR models, resulting in high goodness-of-fit, r(2) (>0.75). The models were validated by internal and external validation along with residual plots. PMID:23260175

  4. Hydroxyl Radical Rate Constants: Comparing UV/H2O2 and Pulse Radiolysis for Environmental Pollutants

    EPA Science Inventory

    The objective of this study was to measure OH radical rates using both UV/H2O2 and pulse radiolysis techniques for 13 US EPA Contaminant Candidate List compounds (2,6- and 2,4-DNT, EPTC, prometon, linuron, diuron, dyfonate, diazinon, RDX, molinate, nitrobenz...

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

    ERIC Educational Resources Information Center

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

    2013-01-01

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

  6. Inter-comparison of radar rainfall rate using Constant Altitude Plan Position Indicator and hybrid surface rainfall maps

    NASA Astrophysics Data System (ADS)

    Kwon, Soohyun; Jung, Sung-Hwa; Lee, GyuWon

    2015-12-01

    Ground clutter and beam blockage caused by complex terrain deteriorates the accuracy of radar quantitative precipitation estimations (QPE). To improve radar QPE, we have developed a technique for radar rainfall estimation, the Kyungpook National University Hybrid Surface Rainfall (KHSR), based on a two-dimensional hybrid surface consisting of the lowest radar bins that are immune to ground clutter, beam blockage, and non-meteorological echoes. The KHSR map is a composite of a ground echo mask, a beam blockage mask, and a rain echo mask, and it was applied to an operational S-band dual-polarimetric radar that scans six PPIs at a low elevation angle every 2.5 min. By using three rainfall estimators, R(ZH), R(ZH, ZDR), and R(ZH, ξDR), this technique was compared with an operational Constant Altitude Plan Position Indicator (CAPPI) QPE of the Korea Meteorological Administration during a summer season from June-August 2012. In comparison with CAPPI, KHSR shows improved rainfall estimates for three algorithms, and it was more effective with dual-polarimetric rainfall algorithms than with single polarimetric rainfall algorithms. Error increased with increasing range from radar, but this increase was more rapid using CAPPI than using KHSR. KHSR using the R(ZH, ZDR) algorithm was the most accurate long range (>100 km from the radar) estimator.

  7. Laboratory Measurement of the Gas-Phase Rate Constant for Formation of Nitric Acid from the Reaction of OH and NO2

    NASA Astrophysics Data System (ADS)

    Mollner, A. K.; Feng, L.; Sprague, M. K.; Okumura, M.; Vallavudasan, S.; Sander, S. P.; Martien, P. T.; Harley, R. A.; McCoy, A. B.

    2007-12-01

    The rate constant for the reaction OH + NO2 + M → HONO2 + M is among the most influential parameters affecting air pollution levels. There remains significant uncertainty about this rate, due to lack of laboratory data at 1 atm and to the unknown yield of a secondary channel forming peroxynitrous acid (HOONO). New experimental measurements of both the kinetics and HOONO/HONO2 branching ratios at 760 Torr are presented. The results are compared with current recommendations; when incorporated in models, the new parameters lead to significantly higher modeled ozone levels and reduced formation of nitric acid.

  8. 47 W, 6 ns constant pulse duration, high-repetition-rate cavity-dumped Q-switched TEM(00) Nd:YVO(4) oscillator.

    PubMed

    McDonagh, Louis; Wallenstein, Richard; Knappe, Ralf

    2006-11-15

    We report on a cavity-dumped Q-switched TEM(00) Nd:YVO(4) oscillator offering a unique combination of high power, constant short pulse duration, and high repetition rate, suppressing the gain dependence of pulse duration in classical Q-switched oscillators. Its performance is compared with that of the same oscillator operated in a classical Q-switched regime, demonstrating the much higher peak powers achievable with this technique, especially at high repetition rates. Up to 31 W of 532 nm green light was generated by frequency doubling in a noncritical phase matched LBO crystal, corresponding to 70% conversion efficiency. PMID:17072404

  9. Two-dimensional analytical solutions for chemical transport in aquifers. Part 1. Simplified solutions for sources with constant concentration. Part 2. Exact solutions for sources with constant flux rate

    SciTech Connect

    Shan, C.; Javandel, I.

    1996-05-01

    Analytical solutions are developed for modeling solute transport in a vertical section of a homogeneous aquifer. Part 1 of the series presents a simplified analytical solution for cases in which a constant-concentration source is located at the top (or the bottom) of the aquifer. The following transport mechanisms have been considered: advection (in the horizontal direction), transverse dispersion (in the vertical direction), adsorption, and biodegradation. In the simplified solution, however, longitudinal dispersion is assumed to be relatively insignificant with respect to advection, and has been neglected. Example calculations are given to show the movement of the contamination front, the development of concentration profiles, the mass transfer rate, and an application to determine the vertical dispersivity. The analytical solution developed in this study can be a useful tool in designing an appropriate monitoring system and an effective groundwater remediation method.

  10. High Repetition Rate and Frequency Stabilized Ho:YLF Laser for CO2 Differential Absorption Lidar

    NASA Technical Reports Server (NTRS)

    Bai, Yingxin; Yu, Jirong; Petros, M.; Petzar, Pau; Trieu, Bo; Lee, Hyung; Singh, U.

    2009-01-01

    High repetition rate operation of an injection seeded Ho:YLF laser has been demonstrated. For 1 kHz operation, the output pulse energy reaches 5.8mJ and the optical-to-optical efficiency is 39% when the pump power is 14.5W.

  11. Absorbed Dose Rates in Tissue from Prompt Gamma Emissions from Near-thermal Neutron Absorption.

    PubMed

    Schwahn, Scott O

    2015-10-01

    Prompt gamma emission data from the International Atomic Energy Agency's Prompt Gamma-ray Neutron Activation Analysis database are analyzed to determine the absorbed dose rates in tissue to be expected when natural elements are exposed in a near-thermal neutron environment. PMID:26313590

  12. Absorbed dose rates in tissue from prompt gamma emissions from near-thermal neutron absorption

    DOE PAGESBeta

    Schwahn, Scott O.

    2015-10-01

    Prompt gamma emission data from the International Atomic Energy Agency s Prompt Gamma-ray Neutron Activation Analysis database are analyzed to determine the absorbed dose rates in tissue to be expected when natural elements are exposed in a near-thermal neutron environment.

  13. The ignition temperature of solid explosives with the boundary temperature increasing at a constant rate. Revision 1

    SciTech Connect

    Creighton, J.R.

    1994-03-01

    Goal was to determine variation of ignition temperature with heating rate for some common explosives. Numerical calculations for HMX and TATB are in agreement with experiment. Numerical results also fit a simple curve (single Arrhenius reaction). A simple modification to the One-Dimensional Time to Explosion (ODTE) method would provide data matching the boundary conditions of this paper. A mathematical model is derived to explain this fitting function.

  14. Constraints for the photolysis rate and the equilibrium constant of ClO-dimer from airborne and balloon-borne measurements of chlorine compounds

    NASA Astrophysics Data System (ADS)

    Kleinböhl, Armin; Khosravi, Maryam; Urban, Joachim; Canty, Timothy; Salawitch, Ross J.; Toon, Geoffrey C.; Küllmann, Harry; Notholt, Justus

    2014-06-01

    We analyze measurements of ClO across the terminator taken by the Airborne Submillimeter Radiometer (ASUR) in the activated vortices of the Arctic winters of 1995/1996, 1996/1997, and 1999/2000 to evaluate the plausibility of various determinations of the ClO-dimer photolysis cross section and the rate constant controlling the thermal equilibrium between ClO-dimer and ClO. We use measured ClO during sunlit conditions to estimate total active chlorine (ClOx). As the measurements suggest nearly full chlorine activation in winter 1999/2000, we compare ClOx estimates based on various photolysis frequencies of ClO-dimer with total available inorganic chlorine (Cly), estimated from an N2O-Cly correlation established by a balloon-borne MkIV interferometer measurement. Only ClO-dimer cross sections leading to the fastest photolysis frequencies in the literature (including the latest evaluation by the Jet Propulsion Laboratory) give ClOx mixing ratios that overlap with the estimated range of available Cly. Slower photolysis rates lead to ClOx values that are higher than available Cly. We use the ClOx calculated from sunlit ClO measurements to estimate ClO in darkness based on different equilibrium constants, and compare it with ASUR ClO measurements before sunrise at high solar zenith angles. Calculations with equilibrium constants published in recent evaluations of the Jet Propulsion Laboratory give good agreement with observed ClO mixing ratios. Equilibrium constants leading to a higher ClO/ClOx ratio in darkness yield ClO values that tend to exceed observed abundances. Perturbing the rates for the ClO + BrO reaction in a manner that increases OClO formation and decreases BrCl formation leads to lower ClO values calculated for twilight conditions after sunset, resulting in better agreement with ASUR measurements.

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

    USGS Publications Warehouse

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

    2006-01-01

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

  16. Enhancement of specific absorption rate by exchange coupling of the core-shell structure of magnetic nanoparticles for magnetic hyperthermia

    NASA Astrophysics Data System (ADS)

    Phadatare, M. R.; Meshram, J. V.; Gurav, K. V.; Hyeok Kim, Jin; Pawar, S. H.

    2016-03-01

    Conversion of electromagnetic energy into heat by nanoparticles (NPs) has the potential to be a powerful, non-invasive technique for biomedical applications such as magnetic fluid hyperthermia, drug release, disease treatment and remote control of single cell functions, but poor conversion efficiencies have hindered practical applications so far. In this paper, an attempt has been made to increase the efficiency of magnetic thermal induction by NPs. To increase the efficiency of magnetic thermal induction by NPs, one can take advantage of the exchange coupling between a magnetically hard core and magnetically soft shell to tune the magnetic properties of the NP and maximize the specific absorption rate, which is the gauge of conversion efficiency. In order to examine the tunability of magnetocrystalline anisotropy and its magnetic heating power, a representative magnetically hard material (CoFe2O4) has been coupled to a soft material (Ni0.5Zn0.5Fe2O4). The synthesized NPs show specific absorption rates that are of an order of magnitude larger than the conventional one.

  17. Quantum instanton calculation of rate constant for CH4 + OH → CH3 + H2O reaction: Torsional anharmonicity and kinetic isotope effect

    NASA Astrophysics Data System (ADS)

    Wang, Wenji; Zhao, Yi

    2012-12-01

    Thermal rate constants for the title reaction are calculated by using the quantum instanton approximation within the full dimensional Cartesian coordinates. The results reveal that the quantum effect is remarkable for the reaction at both low and high temperatures, and the obtained rates are in good agreement with experimental measurements at high temperatures. Compared to the harmonic approximation, the torsional anharmonic effect of the internal rotation has a little influence on the rates at low temperatures, however, it enhances the rate by about 20% at 1000 K. In addition, the free energy barriers for the isotopic reactions and the temperature dependence of kinetic isotope effects are also investigated. Generally speaking, for the title reaction, the replacement of OH with OD will reduce the free energy barrier, while substituting D for H (connected to C) will increase the free energy barrier.

  18. Rate and composition control by atomic absorption spectroscopy for the coevaporation of high T sub c superconducting films

    SciTech Connect

    Lu, C. ); Missert, N.; Mooij, J.E.; Rosenthal, P.; Matijasevic, V.; Beasley, M.R.; Hammond, R.H. )

    1989-02-01

    Atomic absorption spectroscopy has been used to control the deposition rates during coevaporation processes with multiple electron-beam sources. This technique is material specific and thus allows the deposition rate of each component to be controlled independently. Because only a light beam is needed to interact with the vapor stream, the sampling region can be selected to be very close to the substrate for precise control of the film composition. With its high sensitivity and no limitations on operation pressure, this technique offers some unique advantages for the preparation of high Tc superconducting films by coevaporation in a high oxygen partial pressure environment. The performance of a multi-source deposition controller and the resultant film properties are presented.

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

    PubMed

    Damos, Petros; Soulopoulou, Polyxeni

    2015-01-01

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

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

    PubMed Central

    Damos, Petros; Soulopoulou, Polyxeni

    2015-01-01

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

  1. Differentiating inflamed and normal lungs by the apparent reaction rate constants of lactate dehydrogenase probed by hyperpolarized 13C labeled pyruvate

    PubMed Central

    Xu, He N.; Kadlececk, Stephen; Shaghaghi, Hoora; Zhao, Huaqing; Profka, Harilla; Pourfathi, Mehrdad; Rizi, Rahim

    2016-01-01

    Background Clinically translatable hyperpolarized (HP) 13C-NMR can probe in vivo enzymatic reactions, e.g., lactate dehydrogenase (LDH)-catalyzed reaction by injecting HP 13C-pyruvate into the subject, which is converted to 13C labeled lactate by the enzyme. Parameters such as 13C-lactate signals and lactate-to-pyruvate signal ratio are commonly used for analyzing the HP 13C-NMR data. However, the biochemical/biological meaning of these parameters remains either unclear or dependent on experimental settings. It is preferable to quantify the reaction rate constants with a clearer physical meaning. Here we report the extraction of the kinetic parameters of the LDH reaction from HP 13C-NMR data and investigate if they can be potential predictors of lung inflammation. Methods Male Sprague-Dawley rats (12 controls, 14 treated) were used. One dose of bleomycin (2.5 U/kg) was administered intratracheally to the treatment group. The lungs were removed, perfused, and observed by the HP-NMR technique, where a HyperSense dynamic nuclear polarization system was used to generate the HP 13C-pyruvate for injecting into the lungs. A 20 mm 1H/13C dual-tuned coil in a 9.4-T Varian vertical bore NMR spectrometer was employed to acquire the 13C spectral data every 1 s over a time period of 300 s using a non-selective, 15-degree radiofrequency pulse. The apparent rate constants of the LDH reaction and their ratio were quantified by applying ratiometric fitting analysis to the time series data of 13C labeled pyruvate and lactate. Results The apparent forward rate constant kp=(3.67±3.31)×10−4 s−1, reverse rate constant kl=(4.95±2.90)×10−2 s−1, rate constant ratio kp/kl=(7.53±5.75)×10−3 for the control lungs; kp=(11.71±4.35)×10−4 s−1, kl=(9.89±3.89)×10−2 s−1, and kp/kl=(12.39±4.18)×10−3 for the inflamed lungs at the 7th day post treatment. Wilcoxon rank-sum test showed that the medians of these kinetic parameters of the 7-day cohort were significantly

  2. Optical Constants of Silicon Carbide for Astrophysical Applications. II. Extending Optical Functions from Infrared to Ultraviolet Using Single-Crystal Absorption Spectra

    NASA Astrophysics Data System (ADS)

    Hofmeister, A. M.; Pitman, K. M.; Goncharov, A. F.; Speck, A. K.

    2009-05-01

    Laboratory measurements of unpolarized and polarized absorption spectra of various samples and crystal structures of silicon carbide (SiC) are presented from 1200-35000 cm-1 (λ ~ 8-0.28 μm) and used to improve the accuracy of optical functions (n and k) from the infrared (IR) to the ultraviolet (UV). Comparison with previous λ ~ 6-20 μm thin-film spectra constrains the thickness of the films and verifies that recent IR reflectivity data provide correct values for k in the IR region. We extract n and k needed for radiative transfer models using a new "difference method," which utilizes transmission spectra measured from two SiC single-crystals with different thicknesses. This method is ideal for near-IR to visible regions where absorbance and reflectance are low and can be applied to any material. Comparing our results with previous UV measurements of SiC, we distinguish between chemical and structural effects at high frequency. We find that for all spectral regions, 3C (β-SiC) and the \\vec{E}\\bot \\vec{c} polarization of 6H (a type of α-SiC) have almost identical optical functions that can be substituted for each other in modeling astronomical environments. Optical functions for \\vec{E} \\Vert \\vec{c} of 6H SiC have peaks shifted to lower frequency, permitting identification of this structure below λ ~ 4 μm. The onset of strong UV absorption for pure SiC occurs near 0.2 μm, but the presence of impurities redshifts the rise to 0.33 μm. Optical functions are similarly impacted. Such large differences in spectral characteristics due to structural and chemical effects should be observable and provide a means to distinguish chemical variation of SiC dust in space.

  3. Similar metabolic rate-temperature relationships after acclimation at constant and fluctuating temperatures in caterpillars of a sub-Antarctic moth.

    PubMed

    Chown, Steven L; Haupt, Tanya M; Sinclair, Brent J

    2016-02-01

    Temperature compensation in whole-animal metabolic rate is one of the responses thought, controversially, to characterize insects from low temperature environments. Temperature compensation may either involve a change in absolute values of metabolic rates or a change in the slope of the metabolic rate - temperature relationship. Moreover, assessments of compensation may be complicated by animal responses to fluctuating temperatures. Here we examined whole animal metabolic rates, at 0 °C, 5 °C, 10 °C and 15 °C, in caterpillars of the sub-Antarctic moth, Pringleophaga marioni Viette (Tineidae), following one week acclimations to 5 °C, 10 °C and 15 °C, and fluctuating temperatures of 0-10 °C, 5-15 °C, and 10-20 °C. Over the short term, temperature compensation was found following acclimation to 5 °C, but the effect size was small (3-14%). By comparison with caterpillars of 13 other lepidopteran species, no effect of temperature compensation was present, with the relationship between metabolic rate and temperature having a Q10 of 2 among species, and no effect of latitude on temperature-corrected metabolic rate. Fluctuating temperature acclimations for the most part had little effect compared with constant temperatures of the same mean value. Nonetheless, fluctuating temperatures of 5-15 °C resulted in lower metabolic rates at all test temperatures compared with constant 10 °C acclimation, in keeping with expectations from the literature. Absence of significant responses, or those of large effect, in metabolic rates in response to acclimation, may be a consequence of the unpredictable temperature variation over the short-term on sub-Antarctic Marion Island, to which P. marioni is endemic. PMID:26592773

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

    SciTech Connect

    Poutsma, Marvin L

    2012-01-01

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

  5. Aqueous suspensions of polymer coated magnetite nanoparticles: Colloidal stability, specific absorption rate, and transverse relaxivity

    NASA Astrophysics Data System (ADS)

    Saville, Steven Lee

    The design, functionalization, characterization, and applications of magnetic nanoparticles have garnered significant interest over the past several decades. While this area has garnered increasing attention, several questions remain unanswered about the stability of these systems and it's influence on their biomedical applications. To help answer these questions about the stability of these, a novel tri(nitroDOPA) terminated polymer based ligand has been developed for the stabilization of magnetite nanoparticles. The synthesis involves a process in which ethylene oxide is polymerized using a trivinyl initiator, modified with carboxylic acid using a free radical addition of mercaptoundecanoic acid, and then functionalized with nitroDOPA using N,N-dicyclohexylcarbodiimide (DCC) and N-hydroxysuccinimide (NHS) chemistry. This polymer has displayed robust adhesion even in harsh chemical environments, out performing many polymers used today for the stabilization of magnetite. Along these same lines, the effects of instability of these systems were analyzed in both MRI and magnetic hyperthermia applications. It is widely known that formation of linear aggregates (i.e. chains) occurs in more concentrated ferrofluids systems and that this has an affect on the ferrofluid properties. It has been recently reported that for some suspensions of magnetic nanoparticles the transverse proton relaxation rate, R2, is dependent on the time that the sample is exposed to an applied magnetic field. This time dependence has been linked to the formation of linear aggregates or chains in an applied magnetic field via numerical modeling. In this work the relationships between colloidal stability, the formation of these linear structures, and changes observed in the proton transverse relaxation rate and heating rate in magnetic hyperthermia of aqueous suspensions of magnetic particles are examined. The results indicate that varying the ligand length has a direct effect on the colloidal

  6. A self-consistent evaluation of the rate constants for the production of the OI 6300 A airglow

    NASA Astrophysics Data System (ADS)

    Link, R.; McConnell, J. C.; Shepherd, G. G.

    1981-06-01

    The considered evaluation shows that the revised quenching rate of O(1D) by N2 in the thermosphere derived from the data of Hays et al. (1978) is k(N2) = 2.3 x 10 to the -11th cc/s, in excellent agreement with the laboratory results of Streit et al. (1976). The laboratory measurements of the O(1D) and O(1S) transition coefficients by Kernahan and Pang (1975) are consistent with the aeronomic results of Frederick et al. (1976), Kopp et al. (1977), Hays et al. (1978), and Rusch et al. (1978) and are in agreement with the theoretical calculations. The revised value of J(O2) = 1.5 x 10 to the -6th per s is in agreement with the observations of Heroux and Swirbalus (1976). The specific recombination rate of O2(+) leading to the production of O(1D) is alpha(1D) = 2.1 x 10 to the -7th cc/s at ionospheric electron temperatures, in good agreement with the laboratory measurement by Zipf (1970).

  7. Reaction Rate Constants of CH4(ads) ⇌ CH3(ads) + H(ads) on Ni(111): The Effect of Lattice Motion.

    PubMed

    Wang, Wenji; Zhao, Yi

    2015-12-31

    Methane dissociation on metal surfaces is of great commercial importance. The dissociation and recombination rate constants of CH4 on Ni(111) are calculated using the quantum instanton approach with the path integral Monte Carlo method. The Ni(111) lattice is treated rigidly, classically, and quantum mechanically to reveal the effects of lattice motion and quantum tunneling. For the dissociation of CH4, the rates have the smallest value on the rigid lattice, while they possess the largest value on the quantum lattice. For instance, at 300 K, the rates on the classical and quantum lattices are 5 and 12 times larger than that on the rigid lattice, respectively. The curve of the Arrhenius plot for the dissociation rates on the rigid lattice demonstrates that the quantum tunneling effect of the ruptured H atom is remarkable, while the nearly invariable dissociation rates at low temperatures on the quantum lattice confirm that the thermally assisted tunneling should be dominant at low temperatures. For the recombination of CH4, the quantum lattice still has rates that are much larger than that of the rigid lattice. For instance, the ratio of the recombination rates on the quantum and rigid lattices is 12 at 300 K. The quantum tunneling effect seems to play a minor role in the recombination rates on the rigid lattice; however, the thermally assisted tunneling is still very significant for the recombination process. PMID:26650500

  8. Exact vs. asymptotic spectral densities in the Garg-Onuchic-Ambegaokar charge transfer model and its effect on Fermi's golden rule rate constants

    NASA Astrophysics Data System (ADS)

    Sun, Xiang; Geva, Eitan

    2016-01-01

    The Garg-Onuchic-Ambegaokar model [J. Chem. Phys. 83, 4491 (1985)] has been used extensively for benchmarking methods aimed at calculating charge transfer rates. Within this model, the donor and acceptor diabats are described as shifted parabolas along a single primary mode, which is bilinearly coupled to a harmonic bath consisting of secondary modes, characterized by an Ohmic spectral density with exponential cutoff. Rate calculations for this model are often performed in the normal mode representation, with the corresponding effective spectral density given by an asymptotic expression derived at the limit where the Ohmic bath cutoff frequency is much larger than the primary mode frequency. We compare Fermi's golden rule rate constants obtained with the asymptotic and exact effective spectral densities. We find significant deviations between rate constants obtained from the asymptotic spectral density and those obtained from the exact one in the deep inverted region. Within the range of primary mode frequencies commonly employed, we find that the discrepancies increase with decreasing temperature and with decreasing primary mode frequency.

  9. Direct estimation of the rate constant of the reaction ClO + HO2 → HOCl + O2 from SMILES atmospheric observations

    NASA Astrophysics Data System (ADS)

    Kuribayashi, K.; Sagawa, H.; Lehmann, R.; Sato, T. O.; Kasai, Y.

    2014-01-01

    Diurnal variations of ClO, HO2, and HOCl were simultaneously observed by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) between 12 October 2009 and 21 April 2010. These were the first global observations of the diurnal variation of HOCl in the upper atmosphere. A major reaction for the production of HOCl is ClO + HO2 → HOCl + O2 (Reaction (R1)) in extra-polar regions. A model study suggested that in the mesosphere, this is the only reaction influencing the amount of HOCl during the night. The evaluation of the pure reaction period, when only Reaction (R1) occurred in the Cly chemical system, was performed by checking the consistency of the HOCl production rate with the ClO loss rate from SMILES observation data. It turned out that the SMILES data at the pressure level of 0.28 hPa (about 58 km) in the autumn mid-latitude region (20-40°, February-April 2010) during night (between modified local time 18:30 and 04:00) were suitable for the estimation of the rate constant, k1. The rate constant obtained from SMILES observations was k1(245 K) = (7.75 ± 0.25) × 10-12 cm3 molecule-1 s-1. This result is consistent with results from a laboratory experiment and ab initio calculations for similar low-pressure conditions.

  10. Rate Constants of PSII Photoinhibition and its Repair, and PSII Fluorescence Parameters in Field Plants in Relation to their Growth Light Environments.

    PubMed

    Miyata, Kazunori; Ikeda, Hiroshi; Nakaji, Masayoshi; Kanel, Dhana Raj; Terashima, Ichiro

    2015-09-01

    The extent of photoinhibition of PSII is determined by a balance between the rate of photodamage to PSII and that of repair of the damaged PSII. It has already been indicated that the rate constants of photodamage (kpi) and repair (krec) of the leaves differ depending on their growth light environment. However, there are no studies using plants in the field. We examined these rate constants and fluorescence parameters of several field-grown plants to determine inter-relationships between these values and the growth environment. The kpi values were strongly related to the excess energy, EY, of the puddle model and non-regulated energy dissipation, Y(NO), of the lake model, both multiplied by the photosynthetically active photon flux density (PPFD) level during the photoinhibitory treatment. In contrast, the krec values corrected against in situ air temperature were very strongly related to the daily PPFD level. The plants from the fields showed higher NPQ than the chamber-grown plants, probably because these field plants acclimated to stronger lightflecks than the averaged growth PPFD. Comparing chamber-grown plants and the field plants, we showed that kpi is determined by the incident light level and the photosynthetic capacities such as in situ rate of PSII electron transport and non-photochemical quenching (NPQ) [e.g. Y(NO)×PPFD] and that krec is mostly determined by the growth light and temperature levels. PMID:26203120

  11. Study of kinetic desorption rate constant in fish muscle and agarose gel model using solid phase microextraction coupled with liquid chromatography with tandem mass spectrometry.

    PubMed

    Togunde, Oluranti Paul; Oakes, Ken; Servos, Mark; Pawliszyn, Janusz

    2012-09-12

    This study aims to use solid phase microextraction (SPME), a simple tool to investigate diffusion rate (time) constant of selected pharmaceuticals in gel and fish muscle by comparing desorption rate of diffusion of the drugs in both agarose gel prepared with phosphate-buffered saline (PBS; pH 7.4) and fish muscle. The gel concentration (agarose gel model) that could be used to simulate tissue matrix (fish muscle) for free diffusion of drugs under in vitro and in vivo conditions was determined to model mass transfer phenomena between fibre polymer coating and environmental matrix such that partition coefficients and desorption time constant (diffusion coefficient) can be determined. SPME procedure involves preloading the extraction phase (fibre) with the standards from spiked PBS for 1h via direct extraction. Subsequently, the preloaded fibre is introduced to the sample such fish or agarose gel for specified time ranging from 0.5 to 60 h. Then, fibre is removed at specified time and desorbed in 100 μL of desorption solution (acetonitrile: water 1:1) for 90 min under agitation speed of 1000 rpm. The samples extract were immediately injected to the instrument and analysed using liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS). The limit of detection of the method in gel and fish muscle was 0.01-0.07 ng mL(-1) and 0.07-0.34 ng g(-1), respectively, while the limit quantification was 0.10-0.20 ng mL(-1) in gel samples and 0.40-0.97 ng g(-1) in fish sample. The reproducibility of the method was good (5-15% RSD). The results suggest that kinetics of desorption of the compounds in fish tissue and different viscosity of gel can be determined using desorption time constant. In this study, desorption time constant which is directly related to desorption rate (diffusion kinetics) of selected drugs from the fibre to the gel matrix is faster as the viscosity of the gel matrix reduces from 2% (w/v) to 0.8% (w/v). As the concentration of gel reduces

  12. Using Optical Oxygen Sensors and Injection Experiments to Determine in situ Microbial Rate Constants for Methane Oxidation and Heterotrophic Respiration in a Boreal Bog and Fen

    NASA Astrophysics Data System (ADS)

    Waldo, N.; Moorberg, C.; Waldrop, M. P.; Turetsky, M. R.; Neumann, R. B.

    2015-12-01

    Wetlands are the largest natural source of methane to the atmosphere, and play a key role in feedback cycles to climate change. In recognition of this, many researchers are developing process-based models of wetland methane emissions at various scales. In these models, the three key biogeochemical reactions are methane production, methane oxidation, and heterotrophic respiration, and they are modeled using Michaelis-Menten kinetics. The majority of Michaelis-Menten rate constants used in models are based on experiments involving slurries of peat incubated in vials. While these slurries provide a highly controlled setting, they are different from in situ conditions in multiple ways; notably they lack live plants and the centimeter-scale heterogeneities that exist in the field. To determine rate constants in a system more representative of in situ conditions, we extracted peat cores intact from a bog and fen located in the Bonanza Creek Experimental Forest near Fairbanks, Alaska and part of the Alaska Peatland Experiment (APEX) research program. Into those cores we injected water with varying concentrations of methane and oxygen at multiple depths. We used planar oxygen sensors installed on the peat cores to collect high resolution, two dimensional oxygen concentration data during the injections and used oxygen consumption rates under various conditions to calculate rate constants. Results were compared to a similar but smaller set of injection experiments conducted against planar oxygen sensors installed in the bog. Results will inform parametrization of microbial processes in wetland models, improving estimates of methane emissions both under current climate conditions and in the future.

  13. Inhibition of ionotropic neurotransmitter receptors by antagonists: strategy to estimate the association and the dissociation rate constant of antagonists with very strong affinity to the receptors.

    PubMed

    Aoshima, H; Inoue, Y; Hori, K

    1992-10-01

    Since binding of an agonist to an ionotropic neurotransmitter receptor causes not only channel opening, but also desensitization of the receptor, inhibition of the receptor by the antagonist sometimes becomes very complicated. The transient state kinetics of ligand association and dissociation, and desensitization of the receptor were considered on the basis of the minimal model proposed by Hess' group, and the following possibilities were proposed. 1) When an agonist is simultaneously applied to the receptor with an antagonist whose affinity to the receptor is extremely strong and different from that of the agonist, it is usually impossible to estimate the real inhibition constant exactly from the responses because desensitization of the receptor proceeds before the equilibrium of the ligand binding. Simultaneous addition of the antagonist with strong affinity to the receptor may apparently accelerate inactivation (desensitization) of the receptor. The association rate constant of the antagonist can be estimated by analyses of the rate of the inactivation in the presence and the absence of the antagonist. 2) A preincubated antagonist with a slow dissociation rate constant, i.e., a very effective inhibitor, may cause apparent noncompetitive inhibition of the receptor, since the receptor is desensitized by an agonist as soon as the antagonist dissociates from the receptor and the dissociation of the antagonist from the receptor becomes the rate-determining step. A nicotinic acetylcholine receptor (nAChR) was expressed in Xenopus oocytes by injecting mRNA prepared from Electrophorus electricus electroplax and used for the experiments on inhibition by an antagonist.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1337082

  14. The effect of shock loading on the performance of a thermophilic anaerobic contact reactor at constant organic loading rate

    PubMed Central

    2014-01-01

    The influences of organic loading disturbances on the process performance of a thermophilic anaerobic contact reactor treating potato-processing wastewater were investigated. For this purpose, while the reactor was operated at steady state conditions with organic loading rate of 5.5 kg COD/m3 · day, an instant acetate concentration increase (1 g/L) was introduced to the reactor. During the shock loading test of acetate, it was observed that the overall process performance was adversely affected by all the shock loading, however, the system reached steady state conditions less than 24 hours of operation indicating that thermophilic anaerobic contact reactor is resistant to shock loading and be capable of returning its normal conditions within a short time period. PMID:24872886

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

    PubMed

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

    2016-07-01

    Administration of cytosine arabinoside (CA) by continuous rate infusion (CRI) has pharmacokinetic and pharmacodynamic advantages over traditional intermittent dosing. Whether these advantages translate into clinical efficacy remains unknown. The aim of this study was to assess the efficacy and safety of CRI of CA in dogs with meningoencephalitis of unknown origin (MUO) and to compare outcomes with a group of historical control dogs treated with conventional intermittent subcutaneous (SC) administration of CA; both groups received adjunctive prednisolone. It was hypothesised that a CRI of CA for 24 h at 100 mg/m(2) would improve survival and lesion resolution compared with conventional SC delivery of 50 mg/m(2) every 12 h for 48 h. Eighty dogs with suspected MUO were recruited from consecutive dogs presenting with suspected MUO from 2006 to 2015. All dogs underwent routine clinical evaluation, magnetic resonance imaging of the brain and cerebrospinal fluid analysis. There were 39 dogs in the SC group and 41 dogs in the CRI group; baseline characteristics were similar in both groups. Survival at 3 months was 22/39 (44%) with SC delivery versus 37/41 (90%) with CRI. No dose-limiting toxicities were noted for either group. The resolution rate of magnetic resonance imaging and cerebrospinal fluid abnormalities at the 3 month re-examination were substantially improved in the CRI group versus the SC group. The CRI regimen produced a survival advantage over the SC route of administration without clinically significant toxicity. These data supports the routine use of CRI at first presentation for the treatment of MUO in dogs. PMID:27240905

  16. XrayOpticsConstants

    2005-06-20

    This application (XrayOpticsConstants) is a tool for displaying X-ray and Optical properties for a given material, x-ray photon energy, and in the case of a gas, pressure. The display includes fields such as the photo-electric absorption attenuation length, density, material composition, index of refraction, and emission properties (for scintillator materials).

  17. Energy transfer among CP29 chlorophylls: calculated Förster rates and experimental transient absorption at room temperature.

    PubMed

    Cinque, G; Croce, R; Holzwarth, A; Bassi, R

    2000-10-01

    The energy transfer rates between chlorophylls in the light harvesting complex CP29 of higher plants at room temperature were calculated ab initio according to the Förster mechanism (Förster T. 1948, Ann. Physik. 2:55-67). Recently, the transition moment orientation of CP29 chlorophylls was determined by differential linear dichroism and absorption spectroscopy of wild-type versus mutant proteins in which single chromophores were missing (Simonetto R., Crimi M., Sandonà D., Croce R., Cinque G., Breton J., and Bassi R. 1999. Biochemistry. 38:12974-12983). In this way the Q(y) transition energy and chlorophyll a/b affinity of each binding site was obtained and their characteristics supported by reconstruction of steady-state linear dichroism and absorption spectra at room temperature. In this study, the spectral form of individual chlorophyll a and b ligands within the protein environment was experimentally determined, and their extinction coefficients were also used to evaluate the absolute overlap integral between donors and acceptors employing the Stepanov relation for both the emission spectrum and the Stokes shift. This information was used to calculate the time-dependent excitation redistribution among CP29 chlorophylls on solving numerically the Pauli master equation of the complex: transient absorption measurements in the (sub)picosecond time scale were simulated and compared to pump-and-probe experimental data in the Q(y) region on the native CP29 at room temperature upon selective excitation of chlorophylls b at 640 or 650 nm. The kinetic model indicates a bidirectional excitation transfer over all CP29 chlorophylls a species, which is particularly rapid between the pure sites A1-A2 and A4-A5. Chlorophylls b in mixed sites act mostly as energy donors for chlorophylls a, whereas site B5 shows high and bidirectional coupling independent of the pigment hosted. PMID:11023879

  18. The absorption and metabolism of a single L-menthol oral versus skin administration: Effects on thermogenesis and metabolic rate.

    PubMed

    Valente, Angelica; Carrillo, Andres E; Tzatzarakis, Manolis N; Vakonaki, Elena; Tsatsakis, Aristidis M; Kenny, Glen P; Koutedakis, Yiannis; Jamurtas, Athanasios Z; Flouris, Andreas D

    2015-12-01

    We investigated the absorption and metabolism pharmacokinetics of a single L-menthol oral versus skin administration and the effects on human thermogenesis and metabolic rate. Twenty healthy adults were randomly distributed into oral (capsule) and skin (gel) groups and treated with 10 mg kg(-1) L-menthol (ORALMENT; SKINMENT) or control (lactose capsule: ORALCON; water application: SKINCON) in a random order on two different days. Levels of serum L-menthol increased similarly in ORALMENT and SKINMENT (p > 0.05). L-menthol glucuronidation was greater in ORALMENT than SKINMENT (p < 0.05). Cutaneous vasoconstriction, rectal temperature and body heat storage showed greater increase following SKINMENT compared to ORALMENT and control conditions (p < 0.05). Metabolic rate increased from baseline by 18% in SKINMENT and 10% in ORALMENT and respiratory exchange ratio decreased more in ORALMENT (5.4%) than SKINMENT (4.8%) compared to control conditions (p < 0.05). Levels of plasma adiponectin and leptin as well as heart rate variability were similar to control following either treatment (p > 0.05). Participants reported no cold, shivering, discomfort, stress or skin irritation. We conclude that a single L-menthol skin administration increased thermogenesis and metabolic rate in humans. These effects are minor following L-menthol oral administration probably due to faster glucuronidation and greater blood menthol glucuronide levels. PMID:26429629

  19. Direct measurements of rate constants for the reactions of CH3 radicals with C2H6, C2H4, and C2H2 at high temperatures.

    PubMed

    Peukert, S L; Labbe, N J; Sivaramakrishnan, R; Michael, J V

    2013-10-10

    The shock tube technique has been used to study the reactions CH3 + C2H6 → C2H4 + CH4 + H (1), CH3 + C2H4 → Products + H (2), and CH3 + C2H2 → Products + H (3). Biacetyl, (CH3CO)2, was used as a clean high temperature thermal source for CH3-radicals for all the three reactions studied in this work. For reaction 1, the experiments span a T-range of 1153 K ≤ T ≤ 1297 K, at P ~ 0.4 bar. The experiments on reaction 2 cover a T-range of 1176 K ≤ T ≤ 1366 K, at P ~ 1.0 bar, and those on reaction 3 a T-range of 1127 K ≤ T ≤ 1346 K, at P ~ 1.0 bar. Reflected shock tube experiments performed on reactions 1-3, monitored the formation of H-atoms with H-atom Atomic Resonance Absorption Spectrometric (ARAS). Fits to the H-atom temporal profiles using an assembled kinetics model were used to make determinations for k1, k2, and k3. In the case of C2H6, the measurements of [H]-atoms were used to derive direct high-temperature rate constants, k1, that can be represented by the Arrhenius equation k1(T) = 5.41 × 10(-12) exp(-6043 K/T) cm(3) molecules(-1) s(-1) (1153 K ≤ T ≤ 1297 K) for the only bimolecular process that occurs, H-atom abstraction. TST calculations based on ab initio properties calculated at the CCSD(T)/CBS//M06-2X/cc-pVTZ level of theory show excellent agreement, within ±20%, of the measured rate constants. For the reaction of CH3 with C2H4, the present rate constant results, k2', refer to the sum of rate constants, k(2b) + k(2c), from two competing processes, addition-elimination, and the direct abstraction CH3 + C2H4 → C3H6 + H (2b) and CH3 + C2H4 → C2H2 + H + CH4 (2c). Experimental rate constants for k2' can be represented by the Arrhenius equation k2'(T) = 2.18 × 10(-10) exp(-11830 K/T) cm(3) molecules(-1) s(-1) (1176 K ≤ T ≤ 1366 K). The present results are in excellent agreement with recent theoretical predictions. The present study provides the only direct measurement for the high-temperature rate constants for these channels

  20. Label-Free Kinetics: Exploiting Functional Hemi-Equilibrium to Derive Rate Constants for Muscarinic Receptor Antagonists.

    PubMed

    Riddy, Darren M; Valant, Celine; Rueda, Patricia; Charman, William N; Sexton, Patrick M; Summers, Roger J; Christopoulos, Arthur; Langmead, Christopher J

    2015-10-01

    Drug receptor kinetics is as a key component in drug discovery, development, and efficacy; however, determining kinetic parameters has historically required direct radiolabeling or competition with a labeled tracer. Here we present a simple approach to determining the kinetics of competitive antagonists of G protein-coupled receptors by exploiting the phenomenon of hemi-equilibrium, the state of partial re-equilibration of agonist, antagonist, and receptor in some functional assays. Using functional [Ca(2+)]i-flux and extracellular kinases 1 and 2 phosphorylation assays that have short incubation times and therefore are prone to hemi-equilibrium "behaviors," we investigated a wide range of structurally and physicochemically distinct muscarinic acetylcholine receptor antagonists. Using a combined operational and hemi-equilibrium model of antagonism to both simulate and analyze data, we derived estimates of association and dissociation rates for the test set of antagonists, identifying both rapidly dissociating (4-DAMP, himbacine) and slowly dissociating (tiotropium, glycopyrrolate) ligands. The results demonstrate the importance of assay incubation time and the degree of receptor reserve in applying the analytical model. There was an excellent correlation between estimates of antagonist pK(B), k(on), and k(off) from functional assays and those determined by competition kinetics using whole-cell [(3)H]N-methylscopolamine binding, validating this approach as a rapid and simple method to functionally profile receptor kinetics of competitive antagonists in the absence of a labeled tracer. PMID:26243731

  1. Temperature Dependence of the Rate Constant for the CH3 Recombination Reaction: A Loss Process in Outer Planet Atmospheres

    NASA Technical Reports Server (NTRS)

    Cody, R. J.; Payne, W. A.; Thorn, R. P., Jr.; Romani, P. N.; Stief, L. J.; Nesbitt, F. L.; Iannone, M. A.; Tardy, D. C.

    2002-01-01

    The methyl free radical (CH3) has been observed in the atmospheres of Saturn and Neptune by the ISO satellite. There are discrepancies between the column densities for the CH3 radical derived from the ISO observations and the column densities derived from atmospheric photochemical models. For Neptune the model column density is 1.5 times that derived from ISO. For Saturn the model is 6 times that from ISO. The recombination of methyl radicals is the major loss process for methyl in these atmospheres. The serious disagreement between observed and calculated levels of CH3 has led to suggestions that the atmospheric models greatly underestimated the loss of CH3 due to poor knowledge of the rate of the reaction (1) CH3 + CH3 + M goes to C2H6 + M at the low temperatures and pressures of these atmospheric systems. Although the reaction CH3 + CH3 + M goes to C2H6 + M has been extensively studied both theoretically and experimentally, the laboratory conditions have been, with only a few exceptions, higher temperatures (T greater than 298K), higher pressures (P greater than or equal to 10 Torr - 13.3 mbar) or M=Ar rather than H2 or He as the bath gas.

  2. Modeling the Effects of Constant and Variable Temperatures on the Vital Rates of an Age-, Stage-, and Sex-Structured Population by Means of the SANDY Approach.

    PubMed

    Nachman, G; Gotoh, T

    2015-06-01

    We present a general and flexible mathematical model (called SANDY) that can be used to describe many biological phenomena, including the phenology of arthropods. In this paper, we demonstrate how the model can be fitted to vital rates (i.e., rates associated with development, survival, hatching, and oviposition) of the two-spotted spider mite (Tetranychus urticae (Koch)) exposed to different constant temperatures ranging from 15°C to 37.5°C. SANDY was incorporated into an age-, stage- and sex-structured dynamic model, which was fitted to cohort life-tables of T. urticae conducted at five constant temperatures (15, 20, 25, 30, and 35°C). Age- and temperature-dependent vital rates for the three main stages (eggs, immatures, and adults) constituting the life-cycle of mites were adequately described by the SANDY model. The modeling approach allows for simulating the growth of a population in a variable environment. We compared the predicted net reproductive rate (R0) and intrinsic rate of natural increase (rm) at fluctuating temperatures with empirical values obtained from life-table experiments conducted at temperatures that changed with a daily amplitude (±0, ±3, ±6, ±9, and ±12°C) around an average of 22°C. Results show that R0 decreases with increasing amplitude, while rm is more robust to variable temperatures. An advantage of SANDY is that the same simple mathematical expression can be applied to describe all the vital rates. Besides, the approach is not confined to modeling the influence of a single factor on population growth but allows for incorporating the combined effect of several limiting factors, provided that the combined effect of the factors is multiplicative. PMID:26313989

  3. Decay of H (D) atoms in solid hydrogen at 4. 2 K. Rate constant for tunneling reaction H sub 2 (D sub 2 , HD) + H (D)

    SciTech Connect

    Miyazaki, Tetsuo; Iwata, Nobuchika; Lee, Kwangpill; Fueki, Kenji )

    1989-04-20

    Decay of H (or D) atoms at 4.2 K, produced by {gamma}-radiolysis of solid hydrogen, has been studied by ESR spectroscopy. The decay is caused by quantum mechanical tunneling. The decay rate of H atoms in H{sub 2} depends upon the initial concentration of the H atoms, and their decay is represented by second-order kinetics. D atoms decay very slowly in the D{sub 2} solid and disappear by reaction with HD, which exists as an impurity. In the HD solid, D atoms decay fast, while H atoms increase complementarily. Since the decay of these atoms is associated with hydrogen atom-molecule tunneling reactions the rate constants for the reactions are obtained from the decay rates. The rate constants for the tunneling reactions H{sub 2} + H {yields} H + H{sub 2}, D{sub 2} + D {yields} D + D{sub 2}, and HD + D {yields} H + D{sub 2} were 1.8 {times} 10, 1.8 {times} 10{sup {minus}3}, and 1.9 {times} 10{sup {minus}3} cm{sup 3} mol{sup {minus}1} s{sup {minus}1}, respectively, at 4.2 K. Room light and desk light promote remarkably the decay rate of H atoms in the H{sub 2} solid and slightly the decay rate of D atoms in the D{sub 2} solid. The decay of D atoms in the HD solid is not, however, affected by the light illumination.

  4. Feeding rates affect growth, intestinal digestive and absorptive capabilities and endocrine functions of juvenile blunt snout bream Megalobrama amblycephala.

    PubMed

    Xu, Chao; Li, Xiang-Fei; Tian, Hong-Yan; Jiang, Guang-Zhen; Liu, Wen-Bin

    2016-04-01

    This study aimed to investigate the optimal feeding rate for juvenile blunt snout bream (average initial weight 23.74 ± 0.09 g) based on the results on growth performance, intestinal digestive and absorptive capabilities and endocrine functions. A total of 840 fish were randomly distributed into 24 cages and fed a commercial feed at six feeding rates ranging from 2.0 to 7.0 % body weight (BW)/day. The results indicated that weight gain rate increased significantly (P < 0.05) as feeding rates increased from 2.0 to 5.0 % BW/day, but decreased with the further increasing feeding rates (P > 0.05). Protein efficiency ratio and nitrogen and energy retention all showed a similar trend. However, feed conversion ratio increased significantly (P < 0.05) with increasing feeding rates. Feeding rates have little effects (P > 0.05) on whole-body moisture, ash and protein contents, but significantly (P < 0.05) affect both lipid and energy contents with the highest values both observed in fish fed 4.0 % BW/day. In addition, moderate ration sizes (2.0-4.0 % BW/day) resulted in the enhanced activities of intestinal enzymes, including lipase, protease, Na(+), K(+)-ATPase, alkaline phosphatase and creatine kinase. Furthermore, the mRNA levels of growth hormone, insulin-like growth factors-I, growth hormone receptor and neuropeptide all increased significantly (P < 0.05) as feeding rates increased from 2.0 to 5.0 % and 6.0 % BW/day, but decreased significantly (P < 0.05) with the further increase in feeding rates, whereas both leptin and cholecystokinin expressions showed an opposite trend. Based on the broken-line regression analysis of SGR against feeding rates, the optimal feeding rate for juvenile blunt snout bream was estimated to be 4.57 % BW/day. PMID:26597852

  5. Comparison of specific absorption rate induced in brain tissues of a child and an adult using mobile phone

    NASA Astrophysics Data System (ADS)

    Lu, Mai; Ueno, Shoogo

    2012-04-01

    The steady increase of mobile phone usage, especially mobile phones by children, has led to a rising concern about the possible adverse health effects of radio frequency electromagnetic field exposure. The objective of this work is to study whether there is a larger radio frequency energy absorption in the brain of a child compared to that of an adult. For this reason, three high-resolution models, two child head models (6 - and 11-year old) and one adult head model (34-year old) have been used in the study. A finite-difference time-domain method was employed to calculate the specific absorption rate (SAR) in the models from exposure to a generic handset at 1750 MHz. The results show that the SAR distributions in the human brain are age-dependent, and there is a deeper penetration of the absorbed SAR in the child's brain. The induced SAR can be significantly higher in subregions of the child's brain. In all of the examined cases, the SAR values in the brains of a child and an adult are well below the IEEE safety standard.

  6. HCFC-133a (CF3CH2Cl): OH rate coefficient, UV and infrared absorption spectra, and atmospheric implications

    NASA Astrophysics Data System (ADS)

    McGillen, Max R.; Bernard, François; Fleming, Eric L.; Burkholder, James B.

    2015-07-01

    HCFC-133a (CF3CH2Cl), an ozone-depleting substance, is primarily removed from the atmosphere by gas-phase reaction with OH radicals and by UV photolysis. The rate coefficient, k, for the OH + HCFC-133a reaction was measured between 233 and 379 K and is given by k(T) = (9.32 ± 0.8) × 10-13 exp(-(1296 ± 28)/T), where k(296 K) was measured to be (1.10 ± 0.02) × 10-14 (cm3 molecule-1 s-1) (2σ precision uncertainty). The HCFC-133a UV absorption spectrum was measured between 184.95 and 240 nm at 213-323 K, and a spectrum parameterization is presented. The HCFC-133a atmospheric loss processes, lifetime, ozone depletion potential, and uncertainties were evaluated using a 2-D atmospheric model. The global annually averaged steady state lifetime and ozone depletion potential (ODP) were determined to be 4.45 (4.04-4.90) years and 0.017 (±0.001), respectively, where the ranges are based solely on the 2σ uncertainty in the kinetic and photochemical parameters. The infrared absorption spectrum of HCFC-133a was measured, and its global warming potential was determined to be 380 on the 100 year time horizon.

  7. Computational study on the mechanisms and rate constants of the Cl-initiated oxidation of methyl vinyl ether in the atmosphere.

    PubMed

    Han, Dandan; Cao, Haijie; Li, Mingyue; Li, Xin; Zhang, Shiqing; He, Maoxia; Hu, Jingtian

    2015-01-29

    The Cl-initiated oxidation reactions of methyl vinyl ether (MVE) are analyzed by using the high-level composite method CBS-QB3. Detailed chemistry for the reactions of MVE with chlorine atoms is proposed according to the calculated thermodynamic data. The primary eight channels, including two Cl-addition reactions and six H-abstraction reactions, are discussed. In accordance with the further investigation of the two dominant additional routes, formyl chloride and formaldehyde are the major products. Over the temperature range of 200-400 K and the pressure range of 100-2000 Torr, the rate constants of primary reactions are calculated by employing the MESMER program. H-abstraction channels are negligible according to the value of rate constants. During the studied temperature range, the Arrhenius equation is obtained as ktot = 5.64 × 10(-11) exp(215.1/T). The total rate coefficient is ktot = 1.25 × 10(-10) cm(3) molecule(-1) s(-1) at 298 K and 760 Torr. Finally, the atmospheric lifetime of MVE with respect to Cl is estimated to be 2.23 h. PMID:25565072

  8. Ab initio and RRKM calculations for multichannel rate constants of the C{sub 2}H{sub 3}+O{sub 2} reaction

    SciTech Connect

    Mebel, A.M.; Diau, E.W.G.; Lin, M.C.; Morokuma, K.

    1996-10-09

    A potential energy surface for the reaction of vinyl radical with molecular oxygen has been studied using the ab initio G2M(RCC, MP2) method. The most favorable reaction pathway leading to the major CHO+CH{sub 2}O products is described. The C{sub 2}H{sub 3}O+O products can be formed by elimination of the oxygen atom from C{sub 2}H{sub 3}OO via TS 23, which is by 7.8 kcal/mol lower in energy than the reactants, but by 6.5 kcal/mol higher than TS 9`. The hydrogen migration in 1` gives rise to another significant product channel: C{sub 2}H{sub 3}+O{sub 2} {yields} 1` {yields} TS 25` {yields} C{sub 2}H{sub 2}+O{sub 2}H, with TS 25` lying below C{sub 2}H{sub 3}+O{sub 2} by 3.5 kcal/mol. Multichannel RRKM calculations have been carried out for the total and individual rate constants for various channels using the G2M(RCC, MP2) energetics and molecular parameters of the intermediates and transition states. The computed low pressure reaction rate constant is in quantitative agreement with experiment. At atmospheric pressure, the title reaction is dominated by the stabilization of vinylperoxy radical C{sub 2}H{sub 3}OO at room temperature. In the 500-900 K temperature range, the CHO+CH{sub 2}O channel has the highest rate constant, and at T >= 900 K, C{sub 2}H{sub 3}O+O are the major products. At very high temperatures, the channel producing C{sub 2}H{sub 2} + O{sub 2}H becomes competitive. 15 refs., 3 figs., 4 tabs.

  9. An Effective Continuum Model for the Liquid-to-Gas Phase Change in a Porous Medium Driven by Solute Diffusion: II. Constant Liquid Withdrawal Rates

    SciTech Connect

    Tsimpanogiannis, Ioannis N.; Yortsos, Yanis C.

    2001-08-15

    This report describes the development of an effective continuum model to describe the nucleation and subsequent growth of a gas phase from a supersaturated, slightly compressible binary liquid in a porous medium, driven by solute diffusion.This report also focuses on the processes resulting from the withdrawal of the liquid at a constant rate. As before, the model addresses two stages before the onset of bulk gas flow, nucleation and gas phase growth. Because of negligible gradients due to gravity or viscous forces, the critical gas saturation, is only a function of the nucleation fraction.

  10. Estimation of rate constant for VE excitation of the С2(D1Σ) state in Не-СО-О2 discharge plasma

    NASA Astrophysics Data System (ADS)

    Grigorian, G.; Cenian, Adam

    2013-01-01

    The paper discusses the experimental results pointing to the efficient channel of the CO vibrational to the C2 electronic energy-transfer. The radiation spectra D1Σu - X1Σg , known as Mulliken bands, are investigated and the relation of their kinetics to a vibrational excitation of CO molecules in the He-CO-O2 plasma is discussed. The rate constant for VE process ( CO(v >= 25) + C2 → CO(v - 25) + C2(D1Σu) ) is estimated, kVE ~ 10-14 см3/с.

  11. A wide-frequency range AC magnetometer to measure the specific absorption rate in nanoparticles for magnetic hyperthermia

    NASA Astrophysics Data System (ADS)

    Garaio, E.; Collantes, J. M.; Garcia, J. A.; Plazaola, F.; Mornet, S.; Couillaud, F.; Sandre, O.

    2014-11-01

    Measurement of specific absorption rate (SAR) of magnetic nanoparticles is crucial to assert their potential for magnetic hyperthermia. To perform this task, calorimetric methods are widely used. However, those methods are not very accurate and are difficult to standardize. In this paper, we present AC magnetometry results performed with a lab-made magnetometer that is able to obtain dynamic hysteresis-loops in the AC magnetic field frequency range from 50 kHz to 1 MHz and intensities up to 24 kA m-1. In this work, SAR values of maghemite nanoparticles dispersed in water are measured by AC magnetometry. The so-obtained values are compared with the SAR measured by calorimetric methods. Both measurements, by calorimetry and magnetometry, are in good agreement. Therefore, the presented AC magnetometer is a suitable way to obtain SAR values of magnetic nanoparticles.

  12. Hydrogen capacity and absorption rate of the SAES St707 non-evaporable getter at various temperatures.

    SciTech Connect

    Hsu, Irving; Mills, Bernice E.

    2010-08-01

    A prototype of a tritium thermoelectric generator (TTG) is currently being developed at Sandia. In the TTG, a vacuum jacket reduces the amount of heat lost from the high temperature source via convection. However, outgassing presents challenges to maintaining a vacuum for many years. Getters are chemically active substances that scavenge residual gases in a vacuum system. In order to maintain the vacuum jacket at approximately 1.0 x 10{sup -4} torr for decades, nonevaporable getters that can operate from -55 C to 60 C are going to be used. This paper focuses on the hydrogen capacity and absorption rate of the St707{trademark} non-evaporable getter by SAES. Using a getter testing manifold, we have carried out experiments to test these characteristics of the getter over the temperature range of -77 C to 60 C. The results from this study can be used to size the getter appropriately.

  13. Determination of direct photolysis rate constants and OH radical reactivity of representative odour compounds in brewery broth using a continuous flow-stirred photoreactor

    NASA Astrophysics Data System (ADS)

    Jürgens, Marion; Jacob, Fritz; Ekici, Perihan; Friess, Albrecht; Parlar, Harun

    A method based on photolysis was developed for the appropriate treatment of organic pollutants in air exhausting from breweries upon wort decoction, and thereby causing smell nuisance. A continuous flow stirred photoreactor was built-up exclusively, allowing OH radicals to react with selected odorous compounds contained in exhaust vapours, such as: 2-methylpropanal, 3-methylbutanal, 2-methylbutanal, 3-methyl-1-butanol, n-hexanal, 2-methylbutyl isobutyrate, 2-undecanone, phenyl acetaldehyde, myrcene, limonene, linalool, humulene, dimethylsulphide, and dimethyltrisulphide. These substances were quantified in brewery broth before and after UV irradiation using high-resolution gas chromatography-mass spectrometry (HRGC-MS). For odour analysis, high-resolution gas chromatography-flame ionisation detection (HRGC-FID) coupled with sensory methods was used. Determined quantum yields of about 10 -3 for phenyl acetaldehyde, myrcene, and humulene pointed out that direct photolysis contributed to their decay. Quantum yields of below 10 -4 for the other substances indicated that UV irradiation did not contribute significantly to their degradation processes. Hydroxyl radical reaction rate constants and Henry constants of organic compounds were also measured. Substances accompanied with low Henry constants converted rapidly, whereas those with higher ones, relatively slowly. Determined aroma values concluded that after UV-H 2O 2 treatment, only dimethylsulphide and myrcene remained as important odorous compounds, but in significantly reduced concentrations. The UV-H 2O 2 treatment of brewery broth has been proved effective to reduce smell-irritating substances formed upon wort decoction.

  14. Development of a carbonate absorption-based process for post-combustion CO2 capture: The role of biocatalyst to promote CO2 absorption rate

    USGS Publications Warehouse

    Lu, Y.; Ye, X.; Zhang, Z.; Khodayari, A.; Djukadi, T.

    2011-01-01

    An Integrated Vacuum Carbonate Absorption Process (IVCAP) for post-combustion carbon dioxide (CO2) capture is described. IVCAP employs potassium carbonate (PC) as a solvent, uses waste or low quality steam from the power plant for CO2 stripping, and employs a biocatalyst, carbonic anhydrase (CA) enzyme, for promoting the CO2 absorption into PC solution. A series of experiments were performed to evaluate the activity of CA enzyme mixed in PC solutions in a stirred tank reactor system under various temperatures, CA dosages, CO2 loadings, CO2 partial pressures, and the presence of major flue gas contaminants. It was demonstrated that CA enzyme is an effective biocatalyst for CO2 absorption under IVCAP conditions. ?? 2011 Published by Elsevier Ltd.

  15. Ingestion of insoluble dietary fibre increased zinc and iron absorption and restored growth rate and zinc absorption suppressed by dietary phytate in rats.

    PubMed

    Hayashi, K; Hara, H; Asvarujanon, P; Aoyama, Y; Luangpituksa, P

    2001-10-01

    We examined the effects of ingestion of five types of insoluble fibre on growth and Zn absorption in rats fed a marginally Zn-deficient diet (6.75 mg (0.103 mmol) Zn/kg diet) with or without added sodium phytate (12.6 mmol/kg diet). The types of insoluble fibre tested were corn husks, watermelon skin, yam-bean root (Pachyrhizus erosus) and pineapple core, and cellulose was used as a control (100 g/kg diet). Body-weight gain in the cellulose groups was suppressed by 57 % by feeding phytate. Body-weight gain in phytate-fed rats was 80 % greater in the watermelon skin fibre and yam-bean root fibre group than that in the cellulose group. Zn absorption ratio in the cellulose groups was lowered by 46 and 70 % in the first (days 7-10) and second (days 16-19) measurement periods with feeding phytate. In the rats fed the phytate-containing diets, Zn absorption ratio in the watermelon skin, yam-bean root and pineapple core fibre groups was 140, 80 and 54 % higher respectively than that in the cellulose group, in the second period. Fe absorption was not suppressed by phytate, however, feeding of these three types of fibre promoted Fe absorption in rats fed phytate-free diets. The concentration of soluble Zn in the caecal contents in the watermelon skin fibre or yam-bean root fibre groups was identical to that in the control group in spite of a higher short-chain fatty acid concentration and lower pH in the caecum. These findings indicate that ingestion of these types of insoluble fibre recovered the growth and Zn absorption suppressed by feeding a high level of phytate, and factors other than caecal fermentation may also be involved in this effect of insoluble fibre. PMID:11591231

  16. A study in normal human volunteers to compare the rate and extent of levothyroxine absorption from Synthroid and Levoxine.

    PubMed

    Berg, J A; Mayor, G H

    1992-12-01

    Numerous branded and generic formulations of levothyroxine (LT4) sodium tablets are currently available. Results from previous studies attempting to examine the comparative bioavailability of these formulations are difficult to interpret because of subject heterogeneity, single time-point blood sampling, varying degrees of hypothyroidism, and other factors. This study was devised to compare the rate and extent of absorption of LT4 from different LT4 sodium tablet formulations, in a simple model using a single-dose two-way single-blind, randomized cross-over design in 30 normal, healthy, nonpregnant, female subjects. This design controlled for many factors that limited previous LT4 bioavailability studies. Subjects were given a single 600 micrograms dose of LT4 as either Synthroid (Boots Pharmaceuticals, Inc., Lincolnshire, IL) tablets (formulation A) or Levoxine tablets (Daniels Pharmaceuticals, St. Petersburg, FL; formulation B). Measurements of baseline-corrected total T4 serum concentrations determined at multiple time points demonstrated statistically significant differences between the two formulations at the 1.00, 3.00, 5.00, and 18.00 hour sampling times. Statistically significant differences for area under the curve (AUC) (0 to 48 hours) (formulation A, 159.9 +/- 9.4 micrograms-hour/dL; formulation B, 193.4 +/- 10.1 micrograms-hour/dL) and maximum peak plasma concentration (Cmax) (formulation A, 5.91 +/- .34; formulation B, 7.12 +/- .32) also were demonstrated. Furthermore, the ratio of the baseline-corrected total T4 concentrations (B/A x 100) were 120.9% for AUC and 120.5% for Cmax. These data demonstrate that the administration of Synthroid and Levoxine result in a significantly different rate and extent of absorption of LT4, and therefore these two formulations cannot be considered bioequivalent.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1487553

  17. Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy

    NASA Astrophysics Data System (ADS)

    Shubitidze, Fridon; Kekalo, Katsiaryna; Stigliano, Robert; Baker, Ian

    2015-03-01

    Magnetic nanoparticles (MNPs), referred to as the Dartmouth MNPs, which exhibit high specific absorption rate at low applied field strength have been developed for hyperthermia therapy applications. The MNPs consist of small (2-5 nm) single crystals of gamma-Fe2O3 with saccharide chains implanted in their crystalline structure, forming 20-40 nm flower-like aggregates with a hydrodynamic diameter of 110-120 nm. The MNPs form stable (>12 months) colloidal solutions in water and exhibit no hysteresis under an applied quasistatic magnetic field, and produce a significant amount of heat at field strengths as low as 100 Oe at 99-164 kHz. The MNP heating mechanisms under an alternating magnetic field (AMF) are discussed and analyzed quantitatively based on (a) the calculated multi-scale MNP interactions obtained using a three dimensional numerical model called the method of auxiliary sources, (b) measured MNP frequency spectra, and (c) quantified MNP friction losses based on magneto-viscous theory. The frequency responses and hysteresis curves of the Dartmouth MNPs are measured and compared to the modeled data. The specific absorption rate of the particles is measured at various AMF strengths and frequencies, and compared to commercially available MNPs. The comparisons demonstrate the superior heating properties of the Dartmouth MNPs at low field strengths (<250 Oe). This may extend MNP hyperthermia therapy to deeper tumors that were previously non-viable targets, potentially enabling the treatment of some of the most difficult cancers, such as pancreatic and rectal cancers, without damaging normal tissue.

  18. Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy

    PubMed Central

    Stigliano, Robert; Baker, Ian

    2015-01-01

    Magnetic nanoparticles (MNPs), referred to as the Dartmouth MNPs, which exhibit high specific absorption rate at low applied field strength have been developed for hyperthermia therapy applications. The MNPs consist of small (2–5 nm) single crystals of gamma-Fe2O3 with saccharide chains implanted in their crystalline structure, forming 20–40 nm flower-like aggregates with a hydrodynamic diameter of 110–120 nm. The MNPs form stable (>12 months) colloidal solutions in water and exhibit no hysteresis under an applied quasistatic magnetic field, and produce a significant amount of heat at field strengths as low as 100 Oe at 99–164 kHz. The MNP heating mechanisms under an alternating magnetic field (AMF) are discussed and analyzed quantitatively based on (a) the calculated multi-scale MNP interactions obtained using a three dimensional numerical model called the method of auxiliary sources, (b) measured MNP frequency spectra, and (c) quantified MNP friction losses based on magneto-viscous theory. The frequency responses and hysteresis curves of the Dartmouth MNPs are measured and compared to the modeled data. The specific absorption rate of the particles is measured at various AMF strengths and frequencies, and compared to commercially available MNPs. The comparisons demonstrate the superior heating properties of the Dartmouth MNPs at low field strengths (<250 Oe). This may extend MNP hyperthermia therapy to deeper tumors that were previously non-viable targets, potentially enabling the treatment of some of the most difficult cancers, such as pancreatic and rectal cancers, without damaging normal tissue. PMID:25825545

  19. Unimolecular Decomposition Rate of the Criegee Intermediate (CH3)2COO Measured Directly with UV Absorption Spectroscopy.

    PubMed

    Smith, Mica C; Chao, Wen; Takahashi, Kaito; Boering, Kristie A; Lin, Jim Jr-Min

    2016-07-14

    The unimolecular decomposition of (CH3)2COO and (CD3)2COO was measured by direct detection of the Criegee intermediate at temperatures from 283 to 323 K using time-resolved UV absorption spectroscopy. The unimolecular rate coefficient kd for (CH3)2COO shows a strong temperature dependence, increasing from 269 ± 82 s(-1) at 283 K to 916 ± 56 s(-1) at 323 K with an Arrhenius activation energy of ∼6 kcal mol(-1). The bimolecular rate coefficient for the reaction of (CH3)2COO with SO2, kSO2, was also determined in the temperature range 283 to 303 K. Our temperature-dependent values for kd and kSO2 are consistent with previously reported relative rate coefficients kd/kSO2 of (CH3)2COO formed from ozonolysis of tetramethyl ethylene. Quantum chemical calculations of kd for (CH3)2COO are consistent with the experiment, and the combination of experiment and theory for (CD3)2COO indicates that tunneling plays a significant role in (CH3)2COO unimolecular decomposition. The fast rates of unimolecular decomposition for (CH3)2COO measured here, in light of the relatively slow rate for the reaction of (CH3)2COO with water previously reported, suggest that thermal decomposition may compete with the reactions with water and with SO2 for atmospheric removal of the dimethyl-substituted Criegee intermediate. PMID:26985985

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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