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1

Pseudo-first-order reaction of chemically and biologically formed green rusts with Hg(II) and C15H15N3O2: Effects of pH and stabilizing agents (phosphate, silicate, polyacrylic acid, and bacterial cells).  

PubMed

The kinetics of Hg(II) and methyl red (MR) reduction by hydroxycarbonate green rust (GR1) and by hydroxysulfate green rust (GR2) were studied in the presence of naturally occurring organic and inorganic ligands (phosphate, polyacrylic acid, bacterial cells, silicate). The reducing ability of biogenic hydroxycarbonate green rust (GR1bio), obtained after microbial reduction of lepidocrocite by Shewanella putrefaciens, was also investigated and compared to those of chemically synthesized GR1 and GR2 (GR1ab and GR2ab). Pseudo first-order rate constants (kobs) of Hg(II) reduction (at pH 7.0, 8.2, and 9.5) and MR reduction (at pH 7.0) were determined and were normalized to the structural Fe(II) content of GRs (kFeII) and to the estimated concentration of surface Fe(II) sites (kS). The kS values ranged from 0.3Lmmol(-1) min(-1) to 43Lmmol(-1) min(-1) for the Hg reduction, and from 0.007Lmmol(-1) min(-1) to 3.4Lmmol(-1) min(-1) for the MR reduction. No significant discrepancy between GRab and GRbio was observed in term of reactivity. However, the reduction kinetics of MR was generally slower than the Hg(II) reduction kinetics for all tested GRs. While a slight difference in Hg(II) reduction rate was noted whatever the pH values (7.0, 8.2, or 9.5), the reduction of MR was significantly affected in the presence of ligands. A decrease by a factor of 2-200, depending on the type of ligand used, was observed. These data give new insights into the reactivity of GRs in the presence of co-occurring organic and inorganic ligands, and have major implications in the characterization of contaminated systems as well as water treatment processes. PMID:25543237

Remy, P-Ph; Etique, M; Hazotte, A A; Sergent, A-S; Estrade, N; Cloquet, C; Hanna, K; Jorand, F P A

2015-03-01

2

Increasing PCB Radiolysis Rates in Transformer Oil  

SciTech Connect

The kinetics of Aroclor 1242 radiolysis in transformer oil, using high-energy electrons, was found to be analogous to that previously measured for individual polychlorinated biphenyl (PCB) congeners irradiated with -rays. The plot of the pseudo-first-order rate constant for PCB decomposition versus initial PCB concentration is a power function, with high rate constants for low concentrations. The addition of alkaline isopropanol to transformer oil was found to increase the pseudo-first-order rate constant for PCB decomposition. The rate constant under these conditions is independent of concentration. This may be explained by the establishment of chain reaction dechlorination in the oil.

Mincher, Bruce Jay

2002-11-01

3

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

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

4

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

NASA Technical Reports Server (NTRS)

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.

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

1978-01-01

5

Thermonuclear reaction rates. II  

Microsoft Academic Search

A revision and updating of charged particle reactions involving nuclei ; with A less than or approximately equal to 30, except for the $sup ; 2$H(d,$gamma$)⁴He reaction whose reaction rate is very uncertain, is ; presented. Reactions involving neutrons are treated as neutron-producing ; reactions but factors for calculating the reverse reaction rate are provided for ; all reactions. The

W. A. Fowler; G. R. Caughlan; B. A. Zimmerman

1975-01-01

6

Reaction kinetics of resveratrol with tert-butoxyl radicals  

NASA Astrophysics Data System (ADS)

The rate constant for the reaction of t-butoxyl radicals with resveratrol was studied under pseudo-first order conditions. The rate constant was determined by measuring the phenoxyl radical formation rate at 390 nm as function of resveratrol concentration in acetonitrile. The rate constant was determined to be 6.5108 M-1s-1. This high value indicates the high reactivity consistent with the strong antioxidant activity of resveratrol.

Deba, Iva; Pedzinski, Tomasz; Mihaljevi?, Branka

2012-09-01

7

Faster rates with less catalyst in template-directed reactions  

NASA Technical Reports Server (NTRS)

We have recently shown that the polycytidylic acid-directed polymerization of guanosine 5'-monophosphate 2-methylimidazolide (2-MeImpG) is amenable to kinetic study and that rate determinations as a function of 2-MeImpG concentration can reveal much mechanistic detail (Kanavarioti et al. 1993). Here we report kinetic data which show that, once the reaction has been initiated by the formation of dimers, the elongation of dimers to form longer oligomers is accelerated by decreasing polycytidylate (poly(C)) concentration from 0.05 to 0.002 M. This result is consistent with the previously proposed mechanism. The increase in the observed pseudo-first order rate constant for formation of the trimer, k3', and the corresponding constant for formation of oligomers longer than the trimer, ki' (ki' is independent of oligomer length for i > or = 4), with decreasing template concentration for a given monomer concentration is attributed to an increase in template occupancy as template concentration is reduced.

Kanavarioti, A.; Baird, E. E.

1995-01-01

8

The sonochemical degradation of azobenzene and related azo dyes: Rate enhancements via Fenton's reactions  

SciTech Connect

The sonochemical degradation of aqueous solutions of azobenzene and related azo dyes (methyl orange, o-methyl red, and p-methyl red) was performed at 500 kHz and 50 W, under air, O{sub 2}, or Ar saturation at 288 K. Reaction products and intermediates were identified by HPLC-ES-MS. Total organic carbon (TOC) was also determined as a function of reaction time. The authors propose a reaction mechanism based on the observed species and the extent and rate of TOC depletion. The effects of the dye structures and of the background gas on the sonochemical bleaching rates were also investigated. The reaction rates for o-methyl red were approximately 30--40% faster than those for the other compounds. Saturating with Ar instead of air or O{sub 2} increased the pseudo first-order rate constants for the degradation by 10%. The acceleration of the sonochemical bleaching and the mineralization process upon addition of Fe(II) was also investigated in Ar-saturated methyl orange solutions. A 3-fold increase in the reaction rate was observed at optimal Fe(II) concentrations. This kinetic effect is quantitatively accounted for by a simple kinetic model based on the reaction of Fe(II) with sonochemically produced H{sub 2}O{sub 2} (Fenton's reaction). This latter effect illustrates a simple way of achieving a substantial improvement in the efficiency of sonochemical degradation reactions.

Joseph, J.M.; Destaillats, H.; Hung, H.M.; Hoffmann, M.R.

2000-01-20

9

On Thermonuclear Reaction Rates  

E-print Network

Nuclear reactions govern major aspects of the chemical evolution od galaxies and stars. Analytic study of the reaction rates and reaction probability integrals is attempted here. Exact expressions for the reaction rates and reaction probability integrals for nuclear reactions in the case of nonresonant, modified nonresonant, screened nonresonant and resonant cases are given. These are expressed in terms of H-functions, G-functions and in computable series forms. Computational aspects are also discussed.

H. J. Haubold; A. M. Mathai

1996-12-02

10

HYDROLYSIS REACTIONS OF N-PHOSPHOAMINO ACIDSA MODEL FOR PROTEIN DEPHOSPHORYLATION  

Microsoft Academic Search

Phosphoamino acids are the smallest units of phosphoprotein. In Tris-HCl buffer (pH7.5)\\/DMSO(v\\/v=1:1) mixed solvent at 40C the kinetic rates of N-phosphoamino acid hydrolysis reactions were studied. The reactions were pseudo first-order. and the hydrolysis rates of the N-phosphoamino acids were much faster than those of simple phosphoamidates under the same conditions. The kinetic results suggested that the side chain groups

Yongfang Li; Weihua Zhou; Qian Wang; Hui Liu; Yufen Zhao

1996-01-01

11

Applications of Reaction Rate  

ERIC Educational Resources Information Center

This article presents an assignment in which students are to research and report on a chemical reaction whose increased or decreased rate is of practical importance. Specifically, students are asked to represent the reaction they have chosen with an acceptable chemical equation, identify a factor that influences its rate and explain how and why it

Cunningham, Kevin

2007-01-01

12

Rate coefficients for the reaction of methylglyoxal (CH3COCHO) with OH and NO2 and glyoxal (HCO)2 with NO3  

NASA Astrophysics Data System (ADS)

Rate coefficients, k, for the gas-phase reaction of CH3COCHO (methylglyoxal) with the OH and NO3 radicals and (CHO)2 (glyoxal) with the NO3 radical are reported. Rate coefficients for the OH + CH3COCHO (k1) reaction were measured under pseudo-first-order conditions in OH as a function of temperature (211-373 K) and pressure (100-220 Torr, He and N2 bath gases) using pulsed laser photolysis to produce OH radicals and laser induced fluorescence to measure its temporal profile. k1 was found to be independent of the bath gas pressure with k1(295 K) = (1.29 0.13) 10-11 cm3 molecule-1 s-1 and a temperature dependence that is well represented by the Arrhenius expression k1(T) = (1.74 0.20) 10-12 exp[(590 40)/T] cm3 molecule-1 s-1 where the uncertainties are 2? and include estimated systematic errors. Rate coefficients for the NO3+ (CHO)2 (k3) and NO3+ CH3COCHO (k4) reactions were measured using a relative rate technique to be k3(296 K) = (3.7 1.0) 10-16 cm3 molecule-1 s-1 and k4(296 K) = (4.1 1.2) 10-16 cm3 molecule-1 s-1. k3(T) was also measured using an absolute rate coefficient method under pseudo-first-order conditions at 296 and 353 K to be (4.2 0.8) 10-16 and (7.9 3.6) 10-16 cm3 molecule-1 s-1, respectively, in agreement with the relative rate result obtained at room temperature. The atmospheric implications of the OH and NO3 reaction rate coefficients measured in this work are discussed.

Talukdar, R. K.; Zhu, L.; Feierabend, K. J.; Burkholder, J. B.

2011-06-01

13

Rate coefficients for the reaction of methylglyoxal (CH3COCHO) with OH and NO3 and glyoxal (HCO)2 with NO3  

NASA Astrophysics Data System (ADS)

Rate coefficients, k, for the gas-phase reaction of CH3COCHO (methylglyoxal) with the OH and NO3 radicals and (CHO)2 (glyoxal) with the NO3 radical are reported. Rate coefficients for the OH + CH3COCHO (k1) reaction were measured under pseudo-first-order conditions in OH as a function of temperature (211-373 K) and pressure (100-220 Torr, He and N2 bath gases) using pulsed laser photolysis to produce OH radicals and laser induced fluorescence to measure its temporal profile. k1 was found to be independent of the bath gas pressure with k1(295 K) = (1.29 0.13) 10-11 cm3 molecule-1 s-1 and a temperature dependence that is well represented by the Arrhenius expression k1(T) = (1.74 0.20) 10-12 exp[(590 40)/T] cm3 molecule-1 s-1 where the uncertainties are 2? and include estimated systematic errors. Rate coefficients for the NO3 + (CHO)2 (k3) and NO3 + CH3COCHO (k4) reactions were measured using a relative rate technique to be k3(296 K) = (4.0 1.0) 10-16 cm3 molecule-1 s-1 and k4(296 K) = (5.1 2.1) 10-16 cm3 molecule-1 s-1. k3(T) was also measured using an absolute rate coefficient method under pseudo-first-order conditions at 296 and 353 K to be (4.2 0.8) 10-16 and (7.9 3.6) 10-16 cm3 molecule-1 s-1, respectively, in agreement with the relative rate result obtained at room temperature. The atmospheric implications of the OH and NO3 reaction rate coefficients measured in this work are discussed.

Talukdar, R. K.; Zhu, L.; Feierabend, K. J.; Burkholder, J. B.

2011-11-01

14

Thermonuclear reaction rates V  

Microsoft Academic Search

Analytic expressions are given for the reaction rates of astrophysically important thermonuclear reactions involving low-mass nuclei (1less than or equal toZless than or equal to14). Numerical values of the rates are tabulated for the temperature range 10⁶less than or equal toTless than or equal to10¹° K. This provides a comprehensive update of our previous publications. copyright 1988 Academic Press, Inc.

G. R. Caughlan; W. A. Fowler

1988-01-01

15

Rates of Hydrothermal Reactions  

Microsoft Academic Search

The rates of reactions of silicates and aqueous fluids follow zero-order kinetics controlled by the reacting surface area with the rate constant given by the equation: log k\\/bumpeq -2900\\/T - 6.85, where T is temperature and where k has the unit's gram-atoms of oxygen per square centimeter per second. This expression appears to hold for all silicates and for reactions

Bernard J. Wood; John V. Walther

1983-01-01

16

MONITORING THE RATE OF HYDROLYSIS OF AMINOPHOSPHONIC ACID ESTERS BY UV-VIS AND NMR-SPECTROSCOPY  

Microsoft Academic Search

Two aminophosphonic acid dimethylesters 1 and 3 bearing COOH functions attached to UV-VIS absorbing groups were hydrolysed by aqueous NaOH to yield the corresponding monomethylesters 2 and 4. The rates of hydrolysis were monitored by UV-VIS methods. The type of reaction observed is of pseudo first order with rate constants k1[1 mol s] of 1.92.10 (1, 25C). 4.96.10(1, 50C) and

G. Sievers; G. Hgele; S. Failla; P. Finocchiaro

1999-01-01

17

Temperature and pressure dependence of the absolute rate constant for the reactions of NH2 radicals with acetylene and ethylene  

NASA Technical Reports Server (NTRS)

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.

Bosco, S. R.; Nava, D. F.; Brobst, W. D.; Stief, L. J.

1984-01-01

18

Rate Coefficients for the OH + (CHO)2 (Glyoxal) Reaction Between 240 and 400 K  

NASA Astrophysics Data System (ADS)

Glyoxal (CHO)2, the simplest dialdehyde, is an end product formed in the atmospheric oxidation of biogenic hydrocarbons, for example, isoprene. As such, glyoxal plays a role in regional air quality and ozone production in certain locations. Glyoxal is lost in the atmosphere via UV photolysis and reaction with OH. However, the currently available rate coefficient data for the OH + glyoxal reaction is limited to a single room- temperature measurement made using the relative rate method. A determination of the rate coefficient temperature dependence is therefore needed for a more complete interpretation of the atmospheric processing of glyoxal. This study reports the rate coefficient for the OH + (CHO)2 reaction measured under pseudo- first-order conditions in OH ([(CHO)2] > 1000 [OH]0). OH radicals were produced using 248 nm pulsed laser photolysis of H2O2 or HNO3 and detected by pulsed laser induced fluorescence. The concentration of glyoxal in the reactor was determined using three independent techniques; gas flow rates as well as in situ UV and IR absorption. The total pressure in the reactor was varied from 40 to 300 Torr (He), and the rate coefficient was found to be independent of pressure over the temperature range studied. The rate coefficient exhibits a negative temperature dependence between 240 and 400 K consistent with the dependence previously observed for many other aldehydes. Our room-temperature rate coefficient is smaller than the relative rate value that is currently recommended for use in atmospheric model calculations. Our measured rate coefficients are discussed with respect to those for other aldehydes. The atmospheric implications of our work will also be discussed.

Feierabend, K. J.; Talukdar, R. K.; Zhu, L.; Ravishankara, A. R.; Burkholder, J. B.

2006-12-01

19

What Is a Reaction Rate?  

ERIC Educational Resources Information Center

The definition of reaction rate is derived and demonstrations are made for the care to be taken while using the term. Reaction rate can be in terms of a reaction property, the extent of reaction and thus it is possible to give a definition applicable in open and closed systems.

Schmitz, Guy

2005-01-01

20

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

PubMed

The overall rate constant for the reaction ethanol + OH ? products was determined experimentally from 900 to 1270 K behind reflected shock waves. Ethan(18)ol was utilized for these measurements in order to avoid the recycling of OH radicals following H-atom abstraction at the ?-site of ethanol. Similar experiments were also performed with unlabeled ethan(16)ol in order to infer the rate constant that excludes reactivity at the ?-site. The two data sets were used to directly infer the branching ratio for the reaction at the ?-site. Experimental data in the current study and in previous low-temperature studies for the overall rate constant are best fit by the expression koverall = 5.07 10(5) T[K](2.31) exp(608/T[K]) cm(3) mol(-1) s(-1), valid from 300 to 1300 K. Measurements indicate that the branching ratio of the ?-site is between 20 and 25% at the conditions studied. Pseudo-first-order reaction conditions were generated using tert-butylhydroperoxide (TBHP) as a fast source of (16)OH with ethanol in excess. (16)OH mole fraction time-histories were measured using narrow-line width laser absorption near 307 nm. Measurements were performed at the linecenter of the R22(5.5) transition in the A-X(0,0) band of (16)OH that does not overlap with any absorption features of (18)OH, thus producing a measurement of the (16)OH mole fraction that is insensitive to the presence of (18)OH. PMID:24405356

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

2014-02-01

21

Kinetic and products of the BrO+CH 3SH reaction: temperature and pressure dependence  

Microsoft Academic Search

The kinetics and the mechanism of the reaction BrO+CH3SH?P (1) have been studied using the mass spectrometric discharge-flow method over the temperature range 259333 K and at low total pressure between 0.5 and 3 Torr. The temperature dependence of the reaction rate constant has been determined under pseudo-first-order kinetic conditions in excess of CH3SH over BrO radicals, k=(2.21.9)10?15exp[(827255)\\/T]cm3molecule?1s?1. The reaction

Alfonso Aranda; Yolanda D??az de Mera; Diana Rodr??guez; Sagrario Salgado; Ernesto Mart??nez

2002-01-01

22

Rates of Chemical Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the third of four Science Objects in the Chemical Reactions SciPack. It demonstrates

National Science Teachers Association (NSTA)

1900-01-01

23

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

24

Chemical reaction- and particle diffusion-based kinetic modeling of metal biosorption by a Phormidium sp.-dominated cyanobacterial mat  

Microsoft Academic Search

The present study explores the suitability of chemical reaction-based and diffusion-based kinetic models for defining the biosorption of Cu(II), Cd(II) and Pb(II) by Phormidium sp.-dominated mat. The time-course data of metal sorption by the test mat significantly (r2=0.9320.999) fitted to the chemical reaction-based models namely pseudo-first-order, -second-order, and the general rate law. However, these models fail to accurately describe the

Dhananjay Kumar; J. P. Gaur

2011-01-01

25

Investigating Factors Influencing Rates of Chemical Reactions  

NSDL National Science Digital Library

This activity is a lab investigation in which students observe the rate of generation of hydrogen gas from a reaction, and then modify the procedure to compare another variable affecting the rate of this reaction.

Paula Derickson

26

Atmospheric chemistry of (Z)-CF3CH?CHCF3: OH radical reaction rate coefficient and global warming potential.  

PubMed

Rate coefficients, k, for the gas-phase reaction of the OH radical with (Z)-CF(3)CH?CHCF(3) (cis-1,1,1,4,4,4-hexafluoro-2-butene) were measured under pseudo-first-order conditions in OH using pulsed laser photolysis (PLP) to produce OH and laser-induced fluorescence (LIF) to detect it. Rate coefficients were measured over a range of temperatures (212-374 K) and bath gas pressures (20-200 Torr; He, N(2)) and found to be independent of pressure over this range of conditions. The rate coefficient has a non-Arrhenius behavior that is well-described by the expression k(1)(T) = (5.73 0.60) 10(-19) T(2) exp[(678 10)/T] cm(3) molecule(-1) s(-1) where k(1)(296 K) was measured to be (4.91 0.50) 10(-13) cm(3) molecule(-1) s(-1) and the uncertainties are at the 2? level and include estimated systematic errors. Rate coefficients for the analogous OD radical reaction were determined over a range of temperatures (262-374 K) at 100 Torr (He) to be k(2)(T) = (4.81 0.20) 10(-19) T(2) exp[(776 15)/T], with k(2)(296 K) = (5.73 0.50) 10(-13) cm(3) molecule(-1) s(-1). OH radical rate coefficients were also measured at 296, 345, and 375 K using a relative rate technique and found to be in good agreement with the PLP-LIF results. A room-temperature rate coefficient for the O(3) + (Z)-CF(3)CH?CHCF(3) reaction was measured using an absolute method with O(3) in excess to be <6 10(-21) cm(3) molecule(-1) s(-1). The atmospheric lifetime of (Z)-CF(3)CH?CHCF(3) due to loss by OH reaction was estimated to be ~20 days. Infrared absorption spectra of (Z)-CF(3)CH?CHCF(3) measured in this work were used to determine a (Z)-CF(3)CH?CHCF(3) global warming potential (GWP) of ~9 for the 100 year time horizon. A comparison of the OH reactivity of (Z)-CF(3)CH?CHCF(3) with other unsaturated fluorinated compounds is presented. PMID:21879770

Baasandorj, Munkhbayar; Ravishankara, A R; Burkholder, James B

2011-09-29

27

Rate constant for OH,,2 ... reaction  

E-print Network

Rate constant for OH,,2 ...+O,,3 P...\\H,,2 S...+O2,,3 g - ... reaction on an improved ab initio and the rate constant for the title reaction was obtained using a J-shifting method. The calculated rate lower rate at temperature range below 30 K, offering a possible explanation for the "interstellar oxygen

Honvault, Pascal

28

Method of controlling fusion reaction rates  

DOEpatents

A method of controlling the reaction rates of the fuel atoms in a fusion reactor comprises the step of polarizing the nuclei of the fuel atoms in a particular direction relative to the plasma confining magnetic field. Fusion reaction rates can be increased or decreased, and the direction of emission of the reaction products can be controlled, depending on the choice of polarization direction.

Kulsrud, Russell M. (Princeton, NJ); Furth, Harold P. (Princeton, NJ); Valeo, Ernest J. (Princeton Junction, NJ); Goldhaber, Maurice (Bayport, NY)

1988-01-01

29

Reaction rates of hydrochloric acid with chalks  

Microsoft Academic Search

The reaction rate of hydrochloric acid with carbonate rock at acid-fracturing conditions depends on controllable variables such as injection rate and acid concentration, and variables inherent to the carbonate rock (permeability, mineral composition, etc.). In a previous study, the effects of some controllable variables on reaction rates were investigated and the results correlated with theory. This paper presents the results

Naim A. Mumallah

1998-01-01

30

Nuclear reaction rates and the primordial nucleosynthesis  

Microsoft Academic Search

The theoretical predictions of the primordial abundances of elements in the big-bang nucleosynthesis (BBN) are dominated by uncertainties in the input nuclear reaction rates. We investigate the effect of modifying these reaction rates on light element abundance yields in BBN by replacing the thirty-five reaction rates out of the existing eighty-eight. We have studied these yields as functions of evolution

Abhishek Mishra; D. N. Basu

2011-01-01

31

Reaction Order Ambiguity in Integrated Rate Plots  

ERIC Educational Resources Information Center

Integrated rate plots are frequently used in reaction kinetics to determine orders of reactions. It is often emphasised, when using this methodology in practice, that it is necessary to monitor the reaction to a substantial fraction of completion for these plots to yield unambiguous orders. The present article gives a theoretical and statistical

Lee, Joe

2008-01-01

32

Resonances and the thermonuclear reaction rate  

E-print Network

We present an approximate analytic expression for thermonuclear reaction rate of charged particles when the cross section contains a single narrow or wide resonance described by a Breit-Wigner shape. The resulting expression is uniformly valid as the effective energy and resonance energy coalesce. We use our expressions to calculate the reaction rate for $^{12}$C(p,$\\gamma$)$^{13}$N.

M. S. Hussein; M. Ueda; A. J. Sargeant; M. P. Pato

2003-07-21

33

COMPUTERIZED EXTRAPOLATION OF HYDROLYSIS RATE DATA  

EPA Science Inventory

The program RATE was developed to aid in the extrapolation and interpretation of hydrolysis rate data to a format that is useful for environmental risk assessment. ydrolysis data typically are reported in the literature as pseudo-first-order rate constants at the temperature and ...

34

Control of Reaction Rate in Dust Flames  

Microsoft Academic Search

EVER since Nusselt1 introduced the boundary layer concept, about forty years ago, for calculating rates of heat and mass transfer to a spherical particle, it has been universally accepted (without proof) by subsequent theoretical work (see ref. 2) that the reaction-rate of particles in a dust flame is determined by the rate of supply of oxygen through a diffusional boundary

J. M. Ber; R. H. Essenhigh

1960-01-01

35

(CH3)3COOH (tert-butyl hydroperoxide): OH reaction rate coefficients between 206 and 375 K and the OH photolysis quantum yield at 248 nm.  

PubMed

Rate coefficients, k, for the gas-phase reaction of the OH radical with (CH(3))(3)COOH (tert-butyl hydroperoxide) were measured as a function of temperature (206-375 K) and pressure (25-200 Torr (He, N(2))). Rate coefficients were measured under pseudo-first-order conditions using pulsed laser photolysis to produce OH and laser induced fluorescence (PLP-LIF) to measure the OH temporal profile. Two independent methods were used to determine the gas-phase infrared cross sections of (CH(3))(3)COOH, absolute pressure and chemical titration, that were used to determine the (CH(3))(3)COOH concentration in the LIF reactor. The temperature dependence of the rate coefficients is described, within the measurement precision, by the Arrhenius expression k(1)(T) = (7.0 1.0) 10(-13) exp[(485 20)/T] cm(3) molecule(-1) s(-1) where k(1)(296 K) was measured to be (3.58 0.54) 10(-12) cm(3) molecule(-1) s(-1). The uncertainties are 2? (95% confidence level) and include estimated systematic errors. UV absorption cross sections of (CH(3))(3)COOH were determined at 185, 214, 228, and 254 nm and over the wavelength range 210-300 nm. The OH quantum yield following the 248 nm pulsed laser photolysis of (CH(3))(3)COOH was measured relative to the OH quantum yields of H(2)O(2) and HNO(3) using PLP-LIF and found to be near unity. PMID:20694250

Baasandorj, Munkhbayar; Papanastasiou, Dimitrios K; Talukdar, Ranajit K; Hasson, Alam S; Burkholder, James B

2010-10-14

36

Rate of reaction of OH with CS  

Microsoft Academic Search

The flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction OH + CS ..-->.. products (k) over the temperature range 251-363 K. Complicating secondary reactions involving CS photofragments were eliminated only when the photoflash was filtered by 10 torr cm of CS and SF was used as the buffer gas. The rate constant was found

P. H. Wine; R. C. Shah; A. R. Ravishankara

1980-01-01

37

Solar Models and NACRE thermonuclear reaction rates  

E-print Network

Using the most recent updated physics, calibrated solar models have been computed with the new thermonuclear reaction rates of NACRE, the recently available European compilation. Comparisons with models computed with the reaction rates of Caughlan & Fowler (\\cite{cf88}) and of Adelberger et al. (\\cite{a98}) are made for global structure, expected neutrinos fluxes, chemical composition and sound speed profiles, helioseismological properties of p-modes and g-modes.

P. Morel; B. Pichon; J. Provost; G. Berthomieu

1999-07-27

38

Nuclear Reaction Rates and Carbon Star Formation  

E-print Network

We have studied how the third dredge-up and the carbon star formation in low-mass Asymptotic Giant Branch stars depends on certain key nuclear reaction rates. We find from a set of complete stellar evolution calculations of a 2Msun model with Z=0.01 including mass loss, that varying either the N14(p,g)O15 or the 3-alpha reaction rate within their uncertainties as given in the NACRE compilation results in dredge-up and yields that differ by a factor of 2. Model tracks with a higher rate for the 3-alpha rate and a lower rate for the N14(p,g)O15 reaction both show more efficient third dredge-up. New experimental results for the N14(p,g)O15 reaction rates are surveyed, yielding a rate which is about 40% lower than the tabulated NACRE rate, and smaller than NACRE's lower limit. We discuss the possible implications of the revised nuclear reaction stellar evolution calculations that aim to reproduce the observed carbon star formation at low mass, which requires efficient third dredge-up.

Falk Herwig; Sam M. Austin

2004-08-21

39

New approach for kinetic parameters determination for hydrothermal oxidation reaction  

E-print Network

1 New approach for kinetic parameters determination for hydrothermal oxidation reaction David different methods, namely pseudo first order kinetics, multiple linear regression and Runge-Kutta algorithm for industrial or agricultural applications. In order to scale up reactors for HOT of industrial wastewaters

Paris-Sud XI, Universit de

40

Rate of reaction of OH with HNO  

Microsoft Academic Search

The kinetics of the reaction OH+HNO \\/sup k\\/\\/sub arrow-right\\/ products has been studied over the temperature range 224--366 K. OH radicals were produced by pulsed (laser or flash lamp) photolysis of HNO. The course of the reaction was monitored by detecting OH using the resonance fluorescence technique. A total of 27 bimolecular rate constants (derived from 150 individual experiments) were

P. H. Wine; A. R. Ravishankara; N. M. Kreutter; R. C. Shah; J. M. Nicovich; R. L. Thompson; D. J. Wuebbles

1981-01-01

41

Oxidative Degradation of Decabromodiphenyl Ether (BDE 209) by Potassium Permanganate: Reaction Pathways, Kinetics, and Mechanisms Assisted by Density Functional Theory Calculations.  

PubMed

This study found that decabromodiphenyl ether (BDE 209) could be oxidized effectively by potassium permanganate (KMnO4) in sulfuric acid medium. A total of 15 intermediate oxidative products were detected. The reaction pathways were proposed, which primarily included cleavage of the ether bond to form pentabromophenol. Direct oxidation on the benzene ring also played an important role because hydroxylated polybrominated diphenyl ethers (PBDEs) were produced during the oxidation process. The degradation occurred dramatically in the first few minutes and fitted pseudo-first-order kinetics. Increasing the water content decelerated the reaction rate, whereas increasing the temperature facilitated the reaction. In addition, density functional theory (DFT) was employed to determine the frontier molecular orbital (FMO) and frontier electron density (FED) of BDE 209 and the oxidative products. The theoretical calculation results confirmed the proposed reaction pathways. PMID:25751737

Shi, Jiaqi; Qu, Ruijuan; Feng, Mingbao; Wang, Xinghao; Wang, Liansheng; Yang, Shaogui; Wang, Zunyao

2015-04-01

42

Back Reaction And Local Cosmological Expansion Rate  

E-print Network

We calculate the back reaction of cosmological perturbations on a general relativistic variable which measures the local expansion rate of the Universe. Specifically, we consider a cosmological model in which matter is described by a single field. We analyze back reaction both in a matter dominated Universe and in a phase of scalar field-driven chaotic inflation. In both cases, we find that the leading infrared terms contributing to the back reaction vanish when the local expansion rate is measured at a fixed value of the matter field which is used as a clock, whereas they do not appear to vanish if the expansion rate is evaluated at a fixed value of the background time. We discuss possible implications for more realistic models with a more complicated matter sector.

Ghazal Geshnizjani; Robert Brandenberger

2002-04-23

43

Kinetics study of the Cl/2P/ + Cl2O yields Cl2 + ClO reaction at 298 K  

NASA Technical Reports Server (NTRS)

The kinetics of the Cl + Cl2O reaction, a possible source of ClO(2 Pi) radicals for atmospheric photochemical studies, are investigated at 298 K. The discharge flow/mass spectrometry and discharge flow/resonance fluorescence techniques were used to monitor the decay of C12O in the presence of excess concentrations of atomic chlorine and chlorine monoxide, respectively. The pseudo-first order rate constants obtained from both experiments are found to be in excellent agreement, averaging 9.8 + or - 0.8 x 10 to the -11th cu cm/molecule per sec. Results are consistent with the lower limit obtained by Edgecombe et al. (1957) but differ by a factor of 150 from those of Basco and Dogra (1971). The present value is also noted to be consistent with a lower value for the rate constant of the reaction of oxygen atoms with Cl2O.

Ray, G. W.; Keyser, L. F.; Watson, R. T.

1980-01-01

44

Reaction rates for mesoscopic reaction-diffusion kinetics  

E-print Network

The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework, frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a mixed boundary condition at the reaction radius of two molecules. We also establish fundamental limits for the range of mesh resolutions for which this approach yields accurate results, and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics.

Stefan Hellander; Andreas Hellander; Linda Petzold

2015-01-28

45

Reaction rates for mesoscopic reaction-diffusion kinetics  

NASA Astrophysics Data System (ADS)

The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic scale-dependent reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a Robin boundary condition at the reaction radius of two molecules. We also establish fundamental limits on the range of mesh resolutions for which this approach yields accurate results and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics. We show that for mesh sizes below the fundamental lower limit, results are less accurate. Thus, the lower limit determines the mesh size for which we obtain the most accurate results.

Hellander, Stefan; Hellander, Andreas; Petzold, Linda

2015-02-01

46

The reaction rate in nuclear fusion  

Microsoft Academic Search

SummaryA method to evaluate the reaction rate in nuclear fusion is proposed. This method is obtained in the framework of the elastic\\u000a model for subbarrier fusion. Conditions for the validity of the method are given. Some examples are discussed.

A. Scalia

1988-01-01

47

Reaction rate assessment of multiphonon relaxation  

Microsoft Academic Search

An investigation is made into whether the reaction rate formalism also applies to describing inelastic tunneling vibronic processes associated with the absorption and emission of phonons. We propose that Bardeen-Christov's quantum-mechanical approach to the transition (tunneling) probabilities originally intended for elastic tunneling alone can formally be extended to cover inelastic tunneling as well. Namely, we show that inelastic tunneling through

Mladen Georgiev; Alexander Gochev

2005-01-01

48

Prediction of Astrophysical Reaction Rates: Methods, Data Needs, and  

E-print Network

Prediction of Astrophysical Reaction Rates: Methods, Data Needs, and Consequences sections and reaction rates by theoretical means. The majority of reactions can be treated in the framework with two different sets of reaction rates are compared. Key reactions and required nuclear information

Rauscher, Thomas

49

Rates of elementary reactions - Measurement and applications  

NASA Technical Reports Server (NTRS)

Techniques used for characterizing elementary chemical reaction kinetics are explored. Flash- or laser-photolysis (FP) involves producing reactive species on the psec time scale and monitoring the changes spectroscopically. In the discharge flow (DF) method, reactive species are produced continuously in a flow of an inert gas containing the reactants. FP avoids surface and transport effects, while DF allows several reactions to be studied in different regions of one flow. Transport and surface boundary layer models are defined for DF calculations and sample calculations are carried out to illustrate the difficulties inherent in theoretically defining the rate constants for elementary reactions. Applications of the models thus far derived in atmospheric science and combustion studies are discussed.

Kaufman, F.

1985-01-01

50

Thermonuclear-Reaction Rates at High Temperature  

Microsoft Academic Search

Thermonuclear-reaction rates have been calculated over the temperature range 2<~((T)\\/(109))K<~6 for some cases of particular interest in nucleosynthesis during silicon burning (Michaud and Fowler). We explicitly relate our calculations to the evaporation theory and the optical model for particle channels. For gamma-ray channels we develop an approximate formula fitted to the experimental results of Macklin and Gibbons on radiative capture

Georges Michaud; William A. Fowler

1970-01-01

51

Quantum theory of chemical reaction rates  

SciTech Connect

If one wishes to describe a chemical reaction at the most detailed level possible, i.e., its state-to-state differential scattering cross section, then it is necessary to solve the Schroedinger equation to obtain the S-matrix as a function of total energy E and total angular momentum J, in terms of which the cross sections can be calculated as given by equation (1) in the paper. All other physically observable attributes of the reaction can be derived from the cross sections. Often, in fact, one is primarily interested in the least detailed quantity which characterizes the reaction, namely its thermal rate constant, which is obtained by integrating Eq. (1) over all scattering angles, summing over all product quantum states, and Boltzmann-averaging over all initial quantum states of reactants. With the proper weighting factors, all of these averages are conveniently contained in the cumulative reaction probability (CRP), which is defined by equation (2) and in terms of which the thermal rate constant is given by equation (3). Thus, having carried out a full state-to-state scattering calculation to obtain the S-matrix, one can obtain the CRP from Eq. (2), and then rate constant from Eq. (3), but this seems like ``overkill``; i.e., if one only wants the rate constant, it would clearly be desirable to have a theory that allows one to calculate it, or the CRP, more directly than via Eq. (2), yet also correctly, i.e., without inherent approximations. Such a theory is the subject of this paper.

Miller, W.H. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley Lab., CA (United States). Chemical Sciences Div.

1994-10-01

52

Electric field heating and reaction rate effects  

Microsoft Academic Search

The effects are described of electrical fields upon heating and reaction rates of the reacting gases of methane-air and methane-oxygen in the recirculation zone of a jet-stirred reactor. The effects of thermal and field gas heatings on concentrations of CO and CO were also studied. The experiments included measurements of gas temperature distribution across the reactor, current-voltage characteristics for dc

S. M. A. Ibrahim; D. Bradley

1986-01-01

53

Pycnonuclear reaction rates for binary ionic mixtures  

NASA Technical Reports Server (NTRS)

Through a combination of compositional scaling arguments and examinations of Monte Carlo simulation results for the interparticle separations in binary-ionic mixture (BIM) solids, we have derived parameterized expressions for the BIM pycnonuclear rates as generalizations of those in one-component solids obtained previously by Salpeter and Van Horn and by Ogata et al. We have thereby discovered a catalyzing effect of the heavier elements, which enhances the rates of reactions among the lighter elements when the charge ratio exceeds a critical value of approximately 2.3.

Ichimaru, S.; Ogata, S.; Van Horn, H. M.

1992-01-01

54

Nuclear Reaction Rates in Dense Plasmas  

E-print Network

We solve the quasiclassical problem of tunneling through an external potential barrier in a dense plasma, where the tunneling particles undergo simultaneous collisions with other particles in thermodynamic equilibrium. Under such conditions the spectral density of states available to the particle has a Lorentz shape, rather than the delta function, which leads to a quantum tail in the particle momentum distribution function. We show that, this tail indeed significantly alters the average nuclear reaction rates, which supports earlier suggestions. This rate can be many orders of magnitude higher than would be normally calculated by averaging over the Maxwell distribution of energies.

V. I. Savchenko

1999-04-21

55

Maillard reaction rate in various glassy matrices.  

PubMed

The Maillard Reaction (MR) rate below the glass transition temperature (T(g)) for various model glassy food systems was studied at temperatures between 40 degrees C and 70 degrees C. As a sample, freeze-dried glucose and lysine systems embedded in various glassy matrices (e.g., polyvinylpyrrolodone and trehalose) were used, and the MR rate below the T(g) was compared among the various glassy matrices. The extent of MR was estimated spectrophotometrically from the optical density at 280 nm (OD(280)), and the MR rate (k(280)) was determined as a pseudo zero order reaction rate from the time course of OD(280). Although k(280) was described by the Arrhenius plot, the temperature dependence of k(280) was almost the same and the intercept was different among the matrices. From the comparison of k(280), it was suggested that the MR rate in glassy matrix was affected not only by the T(g), but also by the hydrogen bonding between MR reactants and glassy matrix. PMID:15564666

Kawai, Kiyoshi; Hagiwara, Tomoaki; Takai, Rikuo; Suzuki, Toru

2004-11-01

56

Rate coefficient for the reaction N + NO  

NASA Technical Reports Server (NTRS)

Evidence has been advanced that the rate coefficient for the reaction N + NO right arrow N2 + O has a small positive temperature dependence at the high temperatures (900 to 1500 K) that prevail in the terrestrial middle and upper thermosphere by Siskind and Rusch (1992), and at the low temperatures (100 to 200 K) of the Martian lower thermosphere by Fox (1993). Assuming that the rate coefficient recommended by the Jet Propulsion Laboratory evaluation (DeMore et al., 1992) is accurate at 300 K, we derive here the low temperature value of the activation energy for this reaction and thus the rate coefficient that best fits the Viking 1 measured NO densities. We find that the fit is acceptable for a rate coefficient of about 1.3 x 10(exp -10)(T/300)(exp 0.5)exp(-400/T) and better for a value of about 2.5 x 10(exp -10)(T/300)(exp 0.5)exp(-600/T)cu cm/s.

Fox, J. L.

1994-01-01

57

EFFECT OF REACTION RATE PERIODICITY ON DETONATION PROPAGATION  

E-print Network

EFFECT OF REACTION RATE PERIODICITY ON DETONATION PROPAGATION Eric O. Morano and Joseph E. Shepherd. As an alternative to homogeneous reaction rates, we implement "synthetic" hot- spots through a depletion rate an empirical reaction rate. There is no general agreement on how to construct such a rate. Other key issues

Barr, Al

58

Mechanisms and rates of plagioclase carbonation reactions  

NASA Astrophysics Data System (ADS)

Plagioclase is one of the most abundant sources of calcium in the earths crust, and it may play an important role for CO2 storage. This study address the carbonation of anorthite-rich plagioclase (An67-An73) in a system with fluid transport, and under stagnant conditions. A combined approach of flow-through column and batch experiments has been used. Experimental conditions ranging from 100 to 250 C and 20 to 120 bar and different preparations of the starting material were applied. The overall carbonation reaction consists of plagioclase dissolution coupled to a number of precipitation reactions. The flow-through column experiments at 250 C showed stoichiometric dissolution of the plagioclase. Al-hydroxide (proto Al-hydroxide) nucleated on the plagioclase as the first phase to precipitate. A secondary porosity developed between the shrinking plagioclase and the enclosing proto Al-hydroxide. Calcite, as the second phase to precipitate, filled the primary pore space. A reaction front was developed separating the zone at the inlet where all the plagioclase had dissolved and the less reacted outlet of the column. Redissolution of the calcite and formation of euhedral boehmite crystals occurred when a sufficient amount of plagioclase had dissolved. Clay minerals were not precipitated in the column experiments. Between 11% and 30% of the plagioclase was dissolved within 72-168 h of reaction. A much higher extent of plagioclase dissolution was observed in the high pressure experiments compared to the low pressure. However, a smaller share of the released Ca was trapped as calcite in the high pressure experiments. Both observations are consistent with a more rapid progression of the dissolution front at high pressure. The batch experiments showed conversion of the plagioclase to a mixture of Al-hydroxide, possibly gibbsite, clays and calcite. A range in conversion from below the detection limit to 91% was observed within reaction periods of 24-72 h. Crystallinity of the feldspar was the most important factor contributing to increased reaction rates. A general positive effect of increasing temperature on the conversion is observed for all materials, whereas pressure and the addition of CaCl2 did not have any effect. The carbonation of plagioclase at stagnant conditions is slow compared to olivine at temperatures around 200 C. However, industrial operations involving high fluid flows of CO2-water mixtures induce gradients in pH or solute concentrations, which may lead to increased reaction rates and changes in porosity/permeability.

Munz, I. A.; Brandvoll, .; Haug, T. A.; Iden, K.; Smeets, R.; Kihle, J.; Johansen, H.

2012-01-01

59

Astrophysical reaction rate for the 8 Li,,n, ...9  

E-print Network

Astrophysical reaction rate for the 8 Li,,n, ...9 Li reaction Hiroshi Kobayashi,1, * Kazuo Ieki,1 A, with E in eV, n, 930E 1/2 b. The corre- sponding limit on the astrophysical reaction rate is 790 cm3 mol 1 s 1 . Theoretical predictions of the reaction rate have exceeded our upper limit by factors of 3

Horvth, kos

60

Nuclear reaction rates and the nova outburst  

SciTech Connect

In this paper we examined the consequences of improving the nuclear reaction library on our simulations of TNRs on 1.25M, WD and 1.35M, WDS. We have found that the changes in the rates have affected the nucleosynthesis predictions of our calculations but not, to any great extent, the gross features. In addition, we have used a lower mass accretion rate than in our previous studies in order to accrete (and eject) more material. This has, as expected, caused the peak values of some important parameters to increase over our previous studies at the same WD mass. However, because some important reaction rates have declined in the new compilation this has not increased the abundances for nuclei above aluminum and, in fact, they have declined while the abundances of both {sup 26}Al and {sup 27}Al have increased at both WD masses. In contrast, the abundance of {sup 22}Na has declined at both WD masses over the values predicted in our earlier work. This has important implications with respect to predictions of the observability of novae with INTEGRAL.

Starrfield, S.G.; Iliadis, C. [and others

2000-10-01

61

Fusion Reaction Rate in an Inhomogeneous Plasma  

SciTech Connect

The local fusion rate, obtained from the assumption that the distribution is a local Maxwellian, is inaccurate if mean-free-paths of fusing particles are not sufficiently small compared with the inhomogeneity length of the plasma. We calculate the first order correction of P0 in terms of the small spatial gradient and obtain a non-local modification of P(sub)0 in a shock region when the gradient is not small. Use is made of the fact that the fusion reaction cross section has a relatively sharp peak as a function of energy.

S. Son; N.J. Fisch

2004-09-03

62

A simple reaction-rate model for turbulent diffusion flames  

NASA Technical Reports Server (NTRS)

A simple reaction rate model is proposed for turbulent diffusion flames in which the reaction rate is proportional to the turbulence mixing rate. The reaction rate is also dependent on the mean mass fraction and the mean square fluctuation of mass fraction of each reactant. Calculations are compared with experimental data and are generally successful in predicting the measured quantities.

Bangert, L. H.

1975-01-01

63

November 8, 2004 Quantum mechanical reaction rate constants  

E-print Network

November 8, 2004 Quantum mechanical reaction rate constants by vibrational configuration converged rate constants for much larger reactions than have been treated up to now. The rate constant to the axes. The reaction rate over a wide range of temperature (2901100 K) was calculated by evaluating

Truhlar, Donald G

64

On the Rate Expressions for "Reversible" Gas-Solid Reactions  

NASA Astrophysics Data System (ADS)

It is argued that the term with the negative sign in the rate expression for an equilibrium-limited gas-solid reaction can be viewed as representing a lowering of the concentration driving force for the forward reaction due to equilibrium limitation. While the gas composition favors the forward reaction, the negative term may represent the local rate of the reverse reaction. When the gas composition changes significantly to the opposite side of equilibrium, however, this term as written for the forward reaction does not represent the rate of the reverse reaction. Even the reaction order with respect to the same gaseous species may become different for the reverse reaction.

Sohn, Hong Yong

2014-10-01

65

Stochastic analysis of effective rate constant for heterogeneous reactions  

E-print Network

Stochastic analysis of effective rate constant for heterogeneous reactions P. C. Lichtner, D. M reaction rates for mineral precipitation/ dissolution reactions are related to an average mineral grain reaction involving an aqueous solution reacting with a solid phase in a batch. This system is described

Tartakovsky, Daniel M.

66

Upscaling geochemical reaction rates using pore-scale network modeling  

E-print Network

Upscaling geochemical reaction rates using pore-scale network modeling Li Li, Catherine A. Peters Available online 6 December 2005 Abstract Geochemical reaction rate laws are often measured using crushed. Such rate laws are often used directly in reactive transport models to predict the reaction and transport

Peters, Catherine A.

67

Representing Rate Equations for Enzyme-Catalyzed Reactions  

ERIC Educational Resources Information Center

Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of

Ault, Addison

2011-01-01

68

Energy diffusion controlled reaction rate in dissipative Hamiltonian systems  

Microsoft Academic Search

In this paper the energy diffusion controlled reaction rate in dissipative Hamiltonian systems is investigated by using the stochastic averaging method for quasi Hamiltonian systems. The boundary value problem of mean first-passage time (MFPT) of averaged system is formulated and the energy diffusion controlled reaction rate is obtained as the inverse of MFPT. The energy diffusion controlled reaction rate in

Mao-Lin Deng; Wei-Qiu Zhu

2007-01-01

69

Behaviour of smooth catalysts at high reaction rates  

Microsoft Academic Search

In evaluating effective reaction rates in catalysts subject to heat and mass transport limitations, the size of the catalytic body is best defined by the so-called characteristic length ?, the ratio between catalyst volume and its external surface area, ?=Vp\\/Sp. This result follows from the limiting behaviour at very high reaction rates, when the effective reaction rates are proportional to

Sergio D. Keegan; Nstor J. Mariani; Osvaldo M. Martnez; Guillermo F. Barreto

2005-01-01

70

ESTIMATION OF UPPER BOUNDS FOR THE RATES OF ENZYMATIC REACTIONS  

Microsoft Academic Search

A general methodology that allows the estimation of maximum rates of enzymatic reactions is described. For a typical mechanism of an enzymatic reaction, the rate is a function of kinetic parameters which are unknown but required to obey certain constraints. Specifically, the ratio of forward to backward rate constants must be consistent with the equilibrium constant, and the rate of

MICHAEL L. MAVROVOUNIOTIS; GEORGE STEPHANOPOULOS; GREGORY STEPHANOPOULOS

1990-01-01

71

Reaction rates in accreting neutron stars  

Microsoft Academic Search

Temperature conditions in the deep layers of neutron star crusts can be affected by the occurence of pycnonuclear reaction processes. To simulate the fate of accreted matter in neutron star binary systems, we have calculated pycnonuclear reactions for the ashes of rp-process nucleosynthesis at extreme density conditions. Building on the work of Salpeter and Van Horn, nuclear reactions between very

Mary Beard; Michael Wiescher

2002-01-01

72

Kinetic study of Nafion degradation by Fenton reaction  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

73

Kinetic studies of inverse electron demand DielsAlder reactions (iEDDA) of norbornenes and 3,6-dipyridin-2-yl-1,2,4,5-tetrazine  

PubMed Central

Inverse electron demand DielsAlder additions (iEDDA) between 1,2,4,5-tetrazines and olefins have recently found widespread application as a novel click chemistry scheme and as a mild technique for the modification of materials. Norbornenes are, due to their straightforward synthetic availability, especially interesting in the latter context. Therefore, the reactivity of different norbornene-based compounds was compared with unsubstituted norbornene and other alkenes using UV-vis measurements for the determination of reaction rates under pseudo first order conditions. Thereby, exo,exo-5-norbornene-2,3-dimethanol was found to be almost as reactive as unsubstituted norbornene whereas ()-endo,exo-dimethyl-5-norbornene-2,3-dicarboxylate reacted only insignificanty faster than unstrained alkenes. PMID:25152544

Knall, Astrid-Caroline; Hollauf, Manuel; Slugovc, Christian

2014-01-01

74

Effects of jump diffusion rates on reaction kinetics in solids  

Microsoft Academic Search

Applying Torreys treatment of jump diffusion in solids to the study of reaction kinetics, a method is presented to describe the dynamics of caging processes in solids in which the reactants are confined to the cages. We put our attention to the study of three measures of time-dependent reactivity; namely, the observed reaction rate, cumulative reaction rate, and the fraction

Lian-Pin Hwang

1982-01-01

75

Field Based Constraints on Reaction Rates in the Crust  

Microsoft Academic Search

Modern research in plate boundary processes involving metamorphism frequently employs complex physical models. Such models require some quantification (or assumption) of the rate at which metamorphic reactions, or chemical exchange, proceed in natural systems. Here, a compilation of available quantitative field-based constraints on high temperature reaction rates will be presented. These include quantifications based on isotopic exchange, porphyroblast and reaction

E. F. Baxter

2004-01-01

76

Dependence of Up-scaled Reaction Rate on Flow Rate in Porous Media  

E-print Network

1 Dependence of Up-scaled Reaction Rate on Flow Rate in Porous Media D. Kim · W. B. Lindquist to inherent heterogeneities in structure, mineral placement and fluid velocity in rock, bulk reaction rates conditions commensurate with CO2 sequestration, we compute up-scaled reaction rates at the core scale

New York at Stoney Brook, State University of

77

Nonuniform reaction rate distribution for the generalized Fisher equation: Ignition ahead of the reaction front  

E-print Network

Nonuniform reaction rate distribution for the generalized Fisher equation: Ignition ahead equation involving diffusion transport with a finite velocity and a spatially nonuniform reaction rate. We for a piecewise constant reaction rate. By using a relativistic mechanics technique based on the principle

Fedotov, Sergei

78

Increasing PCB radiolysis rates in transformer oil  

Microsoft Academic Search

The kinetics of Aroclor 1242 radiolysis in transformer oil, using high-energy electrons, was found to be analogous to that previously measured for individual polychlorinated biphenyl (PCB) congeners irradiated with ?-rays. The plot of the pseudo-first-order rate constant for PCB decomposition versus initial PCB concentration is a power function, with high rate constants for low concentrations. The addition of alkaline isopropanol

Bruce J Mincher; Richard R. Brey; Ren G Rodriguez; Scott Pristupa; Aaron Ruhter

2002-01-01

79

Rate Constants for Reactions of Peroxyl Radicals in Fluid Solutions  

Microsoft Academic Search

Absolute rate constants for reactions of alkylperoxyl and substituted alkylperoxyl radicals with inorganic and organic compounds in aqueous and non-aqueous fluid solutions have been compiled. The radicals have been generated by radiolysis or photolysis and their rate constants were determined generally by kinetic spectrophotometry or esr. Rate constants are included also for formation of peroxyl radicals by reaction of alkyl

P. Neta; Rober E. Huie; Alberta B. Ross

1990-01-01

80

Combination of overall reaction rate with Gibbs energy minimization  

Microsoft Academic Search

A method to calculate multi-component chemical reaction mixtures as a sequence of time-dependent, intermediate thermochemical states is presented. The method combines the overall reaction kinetics with thermodynamic Gibbs energy minimization. The overall reaction is assumed to proceed according to the Arrhenius rate law. During the time-course of the reaction, the temperature and composition of the reaction mixture are calculated by

Pertti Koukkari; Ismo Laukkanen; Simo Liukkonen

1997-01-01

81

Reaction of tris(2-chloroethyl)phosphate with reduced sulfur species.  

PubMed

Tris(2-chloroethyl)phosphates (TCEP) is a widely used flame retardant in the US. It has recently been identified as one of the most frequently detected contaminants in US streams. This contaminant is of toxicological concern in sensitive coastal ecosystems such as estuaries and salt marshes. It is likely that reactions with reduced sulfur species such as polysulfides (S(n)(2-)), bisulfide (HS(-)), and thiophenolate (PhS(-)) present in anoxic subregions of coastal water bodies could have a significant impact on rates of removal of such a contaminant. The kinetics of reaction of reduced sulfur species with tris(2-chloroethyl)phosphate have been determined in well-defined aqueous solutions under anoxic conditions. Reactions were monitored at varying concentrations of reduced sulfur species to obtain the second-order rate constants from the observed pseudo-first-order rate constants. The determined second-order rate constant for the reaction of TCEP with polysulfide at 25C is 5.0 (1.4)10(-4) M(-1) s(-1), with thiophenolate at 50C is 34 (2)10(-4) M(-1) s(-1) and with bisulfide at 50C is 0.910(-4) M(-1) s(-1), respectively. In addition, the degradation products of hydrolysis and the reactions with polysulfides, thiophenolate, and bisulfide with TCEP were studied with GC-FID and LC-MS-MS and were quantified. PMID:21419471

Saint-Hilaire, Dickens; Ismail, Kamal Z; Jans, Urs

2011-05-01

82

Reaction of Tris(2-chloroethyl)phosphate with Reduced Sulfur Species  

PubMed Central

Tris(2-chloroethyl)phosphates (TCEP) is a widely used flame retardant in the U.S. It has recently been identified as one of the most frequently detected contaminants in U.S. streams. This contaminant is of toxicological concern in sensitive coastal ecosystems such as estuaries and salt marshes. It is likely that reactions with reduced sulfur species such as polysulfides (Sn2?), bisulfide (HS?), and thiophenolate (PhS?) present in anoxic subregions of coastal water bodies could have a significant impact on rates of removal of such a contaminant. The kinetics of reaction of reduced sulfur species with tris(2-chloroethyl)phosphate have been determined in well-defined aqueous solutions under anoxic conditions. Reactions were monitored at varying concentrations of reduced sulfur species to obtain the second-order rate constants from the observed pseudo-first order rate constants. The determined second-order rate constant for the reaction of TCEP with polysulfide at 25C is 5.0 ( 1.4) 10?4 M?1 s?1, with thiophenolate at 50 C is 34 ( 2) 10?4 M?1 s?1 and with bisulfide at 50 C is 0.9 10?4 M?1 s?1, respectively. In addition, the degradation products of hydrolysis and the reactions with polysulfides, thiophenolate, and bisulfide with TCEP were studied with GC-FID and LC-MS-MS and were quantified. PMID:21419471

Hilaire, Dickens Saint; Ismail, Kamal Z.; Jans, Urs

2014-01-01

83

Kinetic and product studies of the heterogeneous reactions of surface-bound polycyclic aromatic hydrocarbons with selected atmospheric oxidants  

NASA Astrophysics Data System (ADS)

The heterogeneous reaction of surface-bound polycyclic aromatic hydrocarbons (PAHs) and gas-phase ozone was used as a model system to investigate the factors that influence the heterogeneous reactions of organic compounds. The heterogeneous reactions of surface-bound anthracene and benzo[a]pyrene with ozone on different aerosol substrates were determined using an aerosol flow tube apparatus. The kinetics of these reactions displayed pseudo-first order behaviour with respect to ozone. The non-linear dependence of the pseudo-first order rate constant as a function of ozone concentration was consistent with reactions that proceed by the Langmuir---Hinshelwood mechanism for the substrates and PAHs investigated. The variability in the kinetics from substrate to substrate was influenced more by the partitioning of ozone to the aerosol surface than by the surface-phase reaction rate. The product yield of anthraquinone, one of the known products of the reaction between anthracene and ozone, as a function of ozone concentration yielded a non-linear functional dependence that was similar to a Langmuir adsorption profile thus providing the first direct evidence that ozone is involved in the rate-limiting step in the formation of this product. Investigations of the heterogeneous oxidation of anthracene, pyrene and n-hexane soot with the NO3 radical, using a suite of analytical techniques indicated the formation of nitro functional groups on the surface. Carbonyl functionalities were observed in addition to nitro functional groups on the surface of soot surfaces following exposure to a nitrating flow. Absorption experiments indicate that the nitration of PAHs alter the optical properties of the particles to which they are adsorbed, giving rise to absorption intensity in the near UV and visible portions of the spectrum. The experimental results of the kinetic studies were used in a multimedia model that was the first to assess the importance of these heterogeneous reactions in an urban environment. The kinetic, product and modeling studies illustrate that PAHs found on particle surfaces may be lost at a rate greater than by gas-phase loss mechanisms. Further, these studies suggest that the rate of formation of the toxic oxidized PAHs may also be significant in the urban environment.

Kwamena, Nana-Owusua Alecia

84

Statistical methods for thermonuclear reaction rates and nucleosynthesis simulations  

NASA Astrophysics Data System (ADS)

Rigorous statistical methods for estimating thermonuclear reaction rates and nucleosynthesis are becoming increasingly established in nuclear astrophysics. The main challenge being faced is that experimental reaction rates are highly complex quantities derived from a multitude of different measured nuclear parameters (e.g., astrophysical S-factors, resonance energies and strengths, particle and ?-ray partial widths). We discuss the application of the Monte Carlo method to two distinct, but related, questions. First, given a set of measured nuclear parameters, how can one best estimate the resulting thermonuclear reaction rates and associated uncertainties? Second, given a set of appropriate reaction rates, how can one best estimate the abundances from nucleosynthesis (i.e., reaction network) calculations? The techniques described here provide probability density functions that can be used to derive statistically meaningful reaction rates and final abundances for any desired coverage probability. Examples are given for applications to s-process neutron sources, core-collapse supernovae, classical novae, and Big Bang nucleosynthesis.

Iliadis, Christian; Longland, Richard; Coc, Alain; Timmes, F. X.; Champagne, Art E.

2015-03-01

85

RPMDrate: Bimolecular chemical reaction rates from ring polymer molecular dynamics  

E-print Network

We present RPMDrate, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the ...

Suleimanov, Yu.V.

86

DSMC predictions of non-equilibrium reaction rates.  

SciTech Connect

A set of Direct Simulation Monte Carlo (DSMC) chemical-reaction models recently proposed by Bird and based solely on the collision energy and the vibrational energy levels of the species involved is applied to calculate nonequilibrium chemical-reaction rates for atmospheric reactions in hypersonic flows. The DSMC non-equilibrium model predictions are in good agreement with theoretical models and experimental measurements. The observed agreement provides strong evidence that modeling chemical reactions using only the collision energy and the vibrational energy levels provides an accurate method for predicting non-equilibrium chemical-reaction rates.

Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

2010-04-01

87

A review of reaction rates in high temperature air  

NASA Technical Reports Server (NTRS)

The existing experimental data on the rate coefficients for the chemical reactions in nonequilibrium high temperature air are reviewed and collated, and a selected set of such values is recommended for use in hypersonic flow calculations. For the reactions of neutral species, the recommended values are chosen from the experimental data that existed mostly prior to 1970, and are slightly different from those used previously. For the reactions involving ions, the recommended rate coefficients are newly chosen from the experimental data obtained more recently. The reacting environment is assumed to lack thermal equilibrium, and the rate coefficients are expressed as a function of the controlling temperature, incorporating the recent multitemperature reaction concept.

Park, Chul

1989-01-01

88

Temperature averages and rates of stratospheric reactions  

Microsoft Academic Search

Use of zonal average temperatures is common in numerical modeling of stratospheric chemistry. In most cases, this approach is accurate. The exceptions are when a heterogeneous reaction or a thermal process which is highly non-linear in temperature is involved. The differences between use of an average temperature and more realistic temperature are presented for cases where temperature fluctuations are of

D. M. Murphy; A. R. Ravishankara

1994-01-01

89

Upscaling geochemical reaction rates using pore-scale network modeling  

Microsoft Academic Search

Geochemical reaction rate laws are often measured using crushed minerals in well-mixed laboratory systems that are designed to eliminate mass transport limitations. Such rate laws are often used directly in reactive transport models to predict the reaction and transport of chemical species in consolidated porous media found in subsurface environments. Due to the inherent heterogeneities of porous media, such use

Li Li; Catherine A. Peters; Michael A. Celia

2006-01-01

90

Workshop on Thermonuclear Reaction Rates for Astrophysics Applications  

E-print Network

Workshop on Thermonuclear Reaction Rates for Astrophysics Applications 24-25 November 2011, Athens circular for the Workshop on Thermonuclear Reaction Rates for Astrophysics Applications, to be held-of-the-art astrophysics models to the nuclear physics needs with special emphasis on the role and determination

91

Temperature Dependence of Reaction Rate in Crystalline State Racemization  

Microsoft Academic Search

In crystalline state racemization of cobaloxime complexes, the reaction rate and the reaction cavity, a void space around a reactive group, depend linearly on temperature. The change of the unit cell dimensions did not reveal the true rate when the cavity was large enough. The Arrhenius plot indicated that the activation energy for the crystalline state racemization is 59 kJmol.

Yasuyuki Takenaka; Yuko Kojima; Yuji Ohashi; Yoshiaki Ohgo

1992-01-01

92

Introduction Intracellular reaction rates are dependent both on the catalytic  

E-print Network

3505 Introduction Intracellular reaction rates are dependent both on the catalytic properties studies have focused only on reaction kinetics, neglecting potential effects of diffusion. This simplified diffusion distances are short and diffusion of metabolites is therefore very fast relative to the rate

Kinsey, Stephen

93

On the rate of relativistic surface chemical reactions.  

PubMed

On the basis of special relativity and the classical theory of chemical reaction rates it is shown how the surface chemical reaction rates vary as v --> c, where v is the velocity of the object under study and c is the velocity of light. PMID:15178286

Veitsman, E V

2004-07-15

94

Astrophysical reaction rate for ?( ?n, ?) 9Be by photodisintegration  

Microsoft Academic Search

We study the astrophysical reaction rate for the formation of 9Be through the three body reaction ?(?n,?). This reaction is one of the key reactions which could bridge the mass gap at A=8 nuclear systems to produce intermediate-to-heavy mass elements in alpha- and neutron-rich environments such as r-process nucleosynthesis in supernova explosions, s-process nucleosynthesis in asymptotic giant branch (AGB) stars,

K. Sumiyoshi; H. Utsunomiya; S. Goko; T. Kajino

2002-01-01

95

Hydro-Reactive Computations with a Temperature Dependent Reaction Rate  

Microsoft Academic Search

Hydro-reactive computations are usually performed with a reaction model containing a pressure dependent reaction rate (PDRR). A well-known example is the ``Ignition & Growth'' (I&G) reaction model introduced by Lee and Tarver some twenty years ago. Performing such computations it has become evident that in many cases the results obtained seem unreliable. For these cases using a temperature dependent reaction

Y. Partom

2002-01-01

96

Nonequilibrium velocity distribution and reaction rate in ion-molecule reactions  

Microsoft Academic Search

The nonequilibrium velocity distribution and reaction rate in fast ion-molecule reactions with non-Langevin reaction cross sections are studied using the Monte Carlo simulation in steady-state systems where ions are diluted in heat-bath reactant molecules and ion sources compensate the loss of ions due to the reaction. The non-Langevin reaction cross sections are taken as the power and exponential dependences on

Katsuhisa Koura

1981-01-01

97

Charged-Particle Thermonuclear Reaction Rates: II. Tables and Graphs of Reaction Rates and Probability Density Functions  

E-print Network

Numerical values of charged-particle thermonuclear reaction rates for nuclei in the A=14 to 40 region are tabulated. The results are obtained using a method, based on Monte Carlo techniques, that has been described in the preceding paper of this series (Paper I). We present a low rate, median rate and high rate which correspond to the 0.16, 0.50 and 0.84 quantiles, respectively, of the cumulative reaction rate distribution. The meaning of these quantities is in general different from the commonly reported, but statistically meaningless expressions, "lower limit", "nominal value" and "upper limit" of the total reaction rate. In addition, we approximate the Monte Carlo probability density function of the total reaction rate by a lognormal distribution and tabulate the lognormal parameters {\\mu} and {\\sigma} at each temperature. We also provide a quantitative measure (Anderson-Darling test statistic) for the reliability of the lognormal approximation. The user can implement the approximate lognormal reaction rate probability density functions directly in a stellar model code for studies of stellar energy generation and nucleosynthesis. For each reaction, the Monte Carlo reaction rate probability density functions, together with their lognormal approximations, are displayed graphically for selected temperatures in order to provide a visual impression. Our new reaction rates are appropriate for bare nuclei in the laboratory. The nuclear physics input used to derive our reaction rates is presented in the subsequent paper of this series (Paper III). In the fourth paper of this series (Paper IV) we compare our new reaction rates to previous results.

Christian Iliadis; Richard Longland; Art Champagne; Alain Coc; Ryan Fitzgerald

2010-04-23

98

Imaginary-time theory for triple-alpha reaction rate  

E-print Network

Using imaginary-time theory, it is shown that the triple-alpha reaction rate can be reliably calculated without the need to solve scattering problems involving three charged particles. The calculated reaction rate is found to agree well with the empirical NACRE rate, which is widely adopted in stellar evolution calculations. The reason for this is explained using $R$-matrix theory. Extremely slow convergence is found to occur when a coupled-channel expansion is introduced, which helps to explain the very different reaction rates obtained using different theoretical approaches.

T. Akahori; Y. Funaki; K. Yabana

2014-01-17

99

Rate constants from the reaction path Hamiltonian. I. Reactive flux simulations for dynamically correct rates  

E-print Network

ARTICLES Rate constants from the reaction path Hamiltonian. I. Reactive flux simulations for dynamically correct rates Baron Peters and Alexis T. Bell Department of Chemical Engineering, University in calculating rate constants. This paper introduces a general method for diabatically constructing

Bell, Alexis T.

100

Enzyme Reaction Rates at Limited Water Activities  

Microsoft Academic Search

A well-mixed powder consisting of dry urea and urease exposed to air containing discrete amounts of water vapor showed a release of carbon-14 dioxide above 60-percent relative humidity. The relative activity of urease followed the water-vapor adsorption isotherm of urease. The minimum amount of water required for the reaction observed was 1.3 moles per mole of side-chain polar groups of

J. J. Skujins; A. D. McLaren

1967-01-01

101

INFLUENCE OF CHAR PROPERTIES ON REACTION RATES  

Microsoft Academic Search

The reaction of coal char is affected by the char morphology, which is dependent on the temperature and pressure at which the char is prepared. Char properties, such as surface area (by CO2 adsorption) and diffusion coefficients of CO2 in char have been measured for chars prepared at 900-1200C and at pressure to 16 atm at 900C. The diffusion coefficient

J. T. SEARS; S. S. TAMHANKAR; A. RADMAN; C. Y. WEN; T. C. CHEN

1985-01-01

102

Basics of Chemical Kinetics -1 Rate of reaction = rate of disappearance of A =  

E-print Network

Basics of Chemical Kinetics - 1 Rate of reaction = rate of disappearance of A = # of moles/volume) ; 1 mole = 6.023x1023 molecules rA = -k [A] rA = -k [A]2 rA = -k1 [A]/(1+k2[A]) Reaction rate law is an algebraic equation involving concentrations (not a differential equation) For a given reaction, the rate law

Albert, Rka

103

Estimation of the rate of volcanism on Venus from reaction rate measurements  

Microsoft Academic Search

Laboratory rate data for the reaction between SO2 and calcite to form anhydrite are presented. If this reaction rate represents the SO2 reaction rate on Venus, then all SO2 in the Venusian atmosphere will disappear in 1.9 Myr unless volcanism replenishes the lost SO2. The required volcanism rate, which depends on the sulfur content of the erupted material, is in

Bruce Fegley; R. G. Prinn

1989-01-01

104

Multidimensional reaction rate theory with anisotropic diffusion.  

PubMed

An analytical expression is derived for the rate constant that describes diffusive transitions between two deep wells of a multidimensional potential. The expression, in contrast to the Kramers-Langer formula for the rate constant, is valid even when the diffusion is highly anisotropic. Our approach is based on a variational principle for the reactive flux and uses a trial function for the splitting probability or commitor. The theoretical result is validated by Brownian dynamics simulations. PMID:25429932

Berezhkovskii, Alexander M; Szabo, Attila; Greives, Nicholas; Zhou, Huan-Xiang

2014-11-28

105

Heterogeneous reactions between NO 2 and anthracene adsorbed on SiO 2 and MgO  

NASA Astrophysics Data System (ADS)

The heterogeneous reactions of NO 2 with anthracene adsorbed on SiO 2 and MgO were investigated under dark conditions at 298 K using DRIFTS, GCMS, and UV-Vis. The pseudo-first-order rate constants of anthracene on SiO 2 and MgO were obtained by fitting the exponential decay of adsorbed PAH concentrations versus reaction time. The reaction on SiO 2 was almost two times faster than on MgO when the concentration of NO 2 was 3.69 10 12 molecules cm -3. Both 9-nitroanthracene and 9,10-anthraquinone were the products of the nitration of anthracene adsorbed on SiO 2 whereas 9,10-anthraquinone was the only product formed by NO 2 reaction with anthracene adsorbed on MgO. These results suggest that mineral oxides not only control the reaction kinetics of PAHs with NO 2 but also alter the reaction pathway for the heterogeneous reaction of PAHs with NO 2. The difference in the heterogeneous reactivity of NO 2 with anthracene adsorbed on SiO 2 and MgO was ascribed to the formation of HNO 3 on SiO 2, which can catalyze the nitration of PAHs by NO 2. Due to the formation of nitro-anthracene and oxy-anthracene, the heterogeneous reactions of NO 2 with anthracene also altered the optical properties of the mineral oxides on which anthracene were adsorbed.

Ma, Jinzhu; Liu, Yongchun; He, Hong

2011-02-01

106

Estimating the Backup Reaction Wheel Orientation Using Reaction Wheel Spin Rates Flight Telemetry from a Spacecraft  

NASA Technical Reports Server (NTRS)

A report describes a model that estimates the orientation of the backup reaction wheel using the reaction wheel spin rates telemetry from a spacecraft. Attitude control via the reaction wheel assembly (RWA) onboard a spacecraft uses three reaction wheels (one wheel per axis) and a backup to accommodate any wheel degradation throughout the course of the mission. The spacecraft dynamics prediction depends upon the correct knowledge of the reaction wheel orientations. Thus, it is vital to determine the actual orientation of the reaction wheels such that the correct spacecraft dynamics can be predicted. The conservation of angular momentum is used to estimate the orientation of the backup reaction wheel from the prime and backup reaction wheel spin rates data. The method is applied in estimating the orientation of the backup wheel onboard the Cassini spacecraft. The flight telemetry from the March 2011 prime and backup RWA swap activity on Cassini is used to obtain the best estimate for the backup reaction wheel orientation.

Rizvi, Farheen

2013-01-01

107

Reactions of three halogenated organophosphorus flame retardants with reduced sulfur species.  

PubMed

Tris(haloalkyl)phosphates (THAPs) are among the most widely used flame retardants in the U.S. They have been identified as one of the most frequently detected contaminants in U.S. streams. These contaminants are of toxicological concern in sensitive coastal ecosystems such as estuaries and salt marshes. It is likely that reactions with reduced sulfur species such as polysulfides (Sn(2-)) and bisulfide (HS(-)), present in anoxic subregions of coastal water bodies could have a significant impact on rates of removal of such contaminants, especially since no significant degradation reactions in the environment (e.g., hydrolysis, biological degradation) is reported for these compounds. The kinetics of the reaction of reduced sulfur species with three structurally related THAPs have been determined in well-defined aqueous solutions under anoxic conditions. Reactions were monitored at varying concentrations of reduced sulfur species to obtain second-order rate constants from the observed pseudo-first order rate constants. The degradation products were studied with GC-FID and LC-MS. The reactivity of Sn(2-), thiophenolate, and HS(-) were compared and steric, as well as electronic factors are used to explain the relative reactivity of the three THAPs with these three sulfur species. PMID:23948611

Saint-Hilaire, Dickens; Jans, Urs

2013-11-01

108

Reactions of Three Halogenated Organophosphorus Flame Retardants with Reduced Sulfur Species  

PubMed Central

Tris(haloalkyl)phosphates (THAPs) are among the most widely used flame retardants in the U.S. They have been identified as one of the most frequently detected contaminants in U.S. streams. These contaminants are of toxicological concern in sensitive coastal ecosystems such as estuaries and salt marshes. It is likely that reactions with reduced sulfur species such as polysulfides (Sn2?) and bisulfide (HS?), present in anoxic subregions of coastal water bodies could have a significant impact on rates of removal of such contaminants, especially since no significant degradation reactions in the environment (e.g., hydrolysis, biological degradation) is reported for these compounds. The kinetics of the reaction of reduced sulfur species with three structurally related THAPs have been determined in well-defined aqueous solutions under anoxic conditions. Reactions were monitored at varying concentrations of reduced sulfur species to obtain second-order rate constants from the observed pseudo-first order rate constants. The degradation products were studied with GC-FID and LC-MS. The reactivity of Sn2?, thiophenolate, and HS? were compared and steric, as well as electronic factors are used to explain the relative reactivity of the three THAPs with these three sulfur species. PMID:23948611

Saint-Hilaire, Dickens; Jans, Urs

2014-01-01

109

Reaction rates in a heat bath  

Microsoft Academic Search

The presence of a heat bath of photons gives an extra effective mass to charged particles and changes the effective strength of the interaction responsible for a decay. All effects are calculated and it is shown that, in order alphaT2, the decay rate is not modified.

M. Jacob; P. V. Landshoff

1992-01-01

110

Review of Mathematical Techniques Applicable in Astrophysical Reaction Rate Theory  

E-print Network

An overview is presented on statistical techniques for the analytic evaluation of integrals for non-resonant, non-resonant depleted, non-resonant cut-off, non-resonant sccreened, and resonant thermonuclear reaction rates. The techniques are based on statistical distribution theory and the theory of Meijer's G-function and Fox's H-function. The implementation of Meijer's G-function in Mathematica constituts an additional utility for analytic manipulations and numerical computation of thermonuclear reaction rate integrals. Recent results in the astrophysical literature related to the use of analytic thermonuclear reaction rates are incorporated.

A. M. Mathai; H. J. Haubold

2002-06-23

111

Rate constant for reaction of atomic hydrogen with germane  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

112

Calculations of parabolic reaction rate constants  

Microsoft Academic Search

The oxidation kinetics of only a very limited number of pure metals or binary alloys can be described by the simplest parabolic law, ?m2=kpt, Thus for a transient period of faster kinetics, the steady state parabolic law is given by (?m-?mi)2 = kp(t-ti) when the initial weight gain ?mi does not contribute to steady state rate control. In such a

B. Pieraggi

1987-01-01

113

Report on study of oxidation reaction rates  

Microsoft Academic Search

A series of experiments were conducted to determine the rate of oxidation of scintillation cocktail components, vacuum pump oil and trichloroethylene by Delphi Research, Inc.`s patented MEDETOX catalytic wet oxidation process utilizing iron(III) oxidant. The materials were placed in acid digestion bombs with the catalytic solution and heated to temperatures in the range of 150--225°C in the presence of platinum

Dhooge

1991-01-01

114

Report on study of oxidation reaction rates  

Microsoft Academic Search

A series of experiments were conducted to determine the rate of oxidation of scintillation cocktail components, vacuum pump oil and trichloroethylene by Delphi Research, Inc.'s patented MEDETOX catalytic wet oxidation process utilizing iron(III) oxidant. The materials were placed in acid digestion bombs with the catalytic solution and heated to temperatures in the range of 150--225°C in the presence of platinum

Dhooge

1991-01-01

115

An Improved Reaction Rate Equation for Simulating the Ignition and Growth of Reaction in High Explosives  

SciTech Connect

We describe an improved reaction rate equation for simulating ignition and growth of reaction in high explosives. It has been implemented into CALE and ALE3D as an alternate to the baseline the Lee-Tarver reactive flow model. The reactive flow model treats the explosive in two phases (unreacted/reactants and reacted/products) with a reaction rate equation to determine the fraction reacted, F. The improved rate equation has fewer parameters, is continuous with continuous derivative, results in a unique set of reaction rate parameters for each explosive while providing the same functionality as the baseline rate equation. The improved rate equation uses a cosine function in the ignition term and a sine function in the growth and completion terms. The improved rate equation is simpler with fewer parameters.

Murphy, M J

2010-03-08

116

Trajectory studies of the reaction F - +HCl --> HF+Cl - . I. Reaction rate constant  

Microsoft Academic Search

Abinitio calculations at the MP4\\/631G** level in conjunction with experimental data were used to derive an analytical potential energy function for the reaction F?+HCl?HF+Cl?. A Monte Carlo-classical trajectory method was used to estimate the thermal energy reaction rate constants at various temperatures. The results showed that the reaction efficiency decreases sharply as temperature increases. At room temperature, the calculated reaction

Jianmei Wei; Qin Meng; Timothy Su

1995-01-01

117

Nonequilibrium velocity distributions and reaction rates in fast highly exothermic reactions  

Microsoft Academic Search

The nonequilibrium velocity distributions and reaction rates in fast highly exothermic reactions with a low activation energy &egr;*f?k T0 ?slant 5, a high steric factor P ?slant 0.1, and a large heat of reaction Q*?k T0 ? O (10), are investigated by solving the semiclassical Boltzmann equation with a Monte Carlo method. The explicit time-dependent velocity distribution functions and reaction

Katsuhisa Koura

1973-01-01

118

Nuclear Reactions Rates Governing the Nucleosynthesis of Ti44  

E-print Network

Large excesses of Ca44 in certain presolar graphite and silicon carbide grains give strong evidence for Ti44 production in supernovae. Furthermore, recent detection of the Ti44 gamma-line from the Cas A SNR by CGRO/COMPTEL shows that radioactive Ti44 is produced in supernovae. These make the Ti44 abundance an observable diagnostic of supernovae. Through use of a nuclear reaction network, we have systematically varied reaction rates and groups of reaction rates to experimentally identify those that govern Ti44 abundance in core-collapse supernova nucleosynthesis. We survey the nuclear-rate dependence by repeated calculations of the identical adiabatic expansion, with peak temperature and density chosen to be 5.5xE9 K and 1E7 g/cc, respectively, to approximate the conditions in detailed supernova models. We find that, for equal total numbers of neutrons and protons (eta=0), Ti44 production is most sensitive to the following reaction rates: Ti44(alpha,p)V47, alpha(2alpha,gamma)C12, Ti44(alpha,gamma)Cr48, V45(p,gamma)Cr46. We tabulate the most sensitive reactions in order of their importance to the Ti44 production near the standard values of currently accepted cross-sections, at both reduced reaction rate (0.01X) and at increased reaction rate (100X) relative to their standard values. Although most reactions retain their importance for eta > 0, that of V45(p,gamma)Cr46 drops rapidly for eta >= 0.0004. Other reactions assume greater significance at greater neutron excess: C12(alpha,gamma)O16, Ca40(alpha,gamma)Ti44, Al27(alpha,n)P30, Si30(alpha,n)S33. Because many of these rates are unknown experimentally, our results suggest the most important targets for future cross section measurements governing the value of this observable abundance.

L. -S. The; D. D. Clayton; L. Jin; B. S. Meyer

1998-06-15

119

A compilation of charged-particle induced thermonuclear reaction rates  

Microsoft Academic Search

Low-energy cross section data for 86 charged-particle induced reactions involving light (1 ? Z ? 14), mostly stable, nuclei are compiled. The corresponding Maxwellian-averaged thermonuclear reaction rates of relevance in astrophysical plasmas at temperatures in the range from 106 K to 1010 K are calculated. These evaluations assume either that the target nuclei are in their ground state, or that

C. Angulo; M. Arnould; M. Rayet; P. Descouvemont; D. Baye; C. Leclercq-Willain; A. Coc; S. Barhoumi; P. Aguer; C. Rolfs; R. Kunz; J. W. Hammer; A. Mayer; T. Paradellis; S. Kossionides; C. Chronidou; K. Spyrou; S. Degl'Innocenti; G. Fiorentini; B. Ricci; S. Zavatarelli; C. Providencia; H. Wolters; J. Soares; C. Grama; J. Rahighi; A. Shotter; M. Lamehi Rachti

1999-01-01

120

Self-heating of coal: The diminishing reaction rate  

Microsoft Academic Search

Several models for the self-heating of coal resulting from the chemisorption of oxygen are investigated. All of the models investigated include the effect of a diminishing reaction rate. The various mathematical forms used to represent the diminishing part of the reaction are compared and a new formulation in the form of a generic power-law model is introduced. Results from the

Sadiq J. Zarrouk; Michael J. O'Sullivan

2006-01-01

121

Infrared singularities cancellation in reaction rates at finite temperature  

Microsoft Academic Search

Using dispersion relations, we show the cancellation of infrared singularities in reaction rates at finite temperature for topologies involving self-energy insertions at all orders of the perturbation theory. We discuss also other topologies and possible generalizations.

Tanguy Altherr

1991-01-01

122

Gas-solid reaction-rate enhancement by pressure cycling  

NASA Astrophysics Data System (ADS)

An experimental study and mathematical modeling of the effects of external pressure cycling on gas-solid reactions have been conducted using the reduction of nickel oxide pellets by hy-drogen. Experiments were carried out in two phases: In the first phase, the intrinsic kinetic parameters were measured, and in the second phase, the gas-solid reaction was carried out under a constant or cycling external pressure. The effects of the frequency and amplitude of pressure cycling were studied at various reaction conditions. Pressure cycling substantially increases the overall rate of the reaction. A mathematical model was developed from the first principles to establish the extent of the overall reaction-rate enhancement and subsequently to analyze the experimental observations. The calculated values from the mathematical model are in good agreement with the experimental results. The effects are most pronounced when the overall rate under a constant pressure is controlled by diffusion. Depending on the reaction condition, a very large degree of rate enhancement could be achieved. Furthermore, low-amplitude pressure waves, like acoustic waves, could significantly increase the rates of gas-solid reactions.

Sohn, H. Y.; Aboukheshem, M. B.

1992-06-01

123

Urea degradation by electrochemically generated reactive chlorine species: products and reaction pathways.  

PubMed

This study investigated the transformation of urea by electrochemically generated reactive chlorine species (RCS). Solutions of urea with chloride ions were electrolyzed using a bismuth doped TiO2 (BiOx/TiO2) anode coupled with a stainless steel cathode at applied anodic potentials (Ea) of either +2.2 V or +3.0 V versus the normal hydrogen electrode. In NaCl solution, the current efficiency of RCS generation was near 30% at both potentials. In divided cell experiments, the pseudo-first-order rate of total nitrogen decay was an order of magnitude higher at Ea of +3.0 V than at +2.2 V, presumably because dichlorine radical (Cl2(-)) ions facilitate the urea transformation primary driven by free chlorine. Quadrupole mass spectrometer analysis of the reactor headspace revealed that N2 and CO2 are the primary gaseous products of the oxidation of urea, whose urea-N was completely transformed into N2 (91%) and NO3(-) (9%). The higher reaction selectivity with respect to N2 production can be ascribed to a low operational ratio of free available chlorine to N. The mass-balance analysis recovered urea-C as CO2 at 77%, while CO generation most likely accounts for the residual carbon. In light of these results, we propose a reaction mechanism involving chloramines and chloramides as reaction intermediates, where the initial chlorination is the rate-determining step in the overall sequence of reactions. PMID:25219459

Cho, Kangwoo; Hoffmann, Michael R

2014-10-01

124

Photolysis and heterogeneous reaction of coniferyl aldehyde adsorbed on silica particles with ozone.  

PubMed

The pseudo-first-order loss of coniferyl aldehyde, adsorbed on silicon dioxide particles, upon heterogeneous ozonolysis was monitored at various ozone mixing ratios in the absence and presence of simulated sunlight. For the first time we investigated the effect of light on the heterogeneous ozonolysis of coniferyl aldehyde adsorbed on silica particles. We found that UV-VIS light (?>300 nm) does not impact the degradation of coniferyl aldehyde by ozone but induces an additional, slow photolysis of the aldehyde with a photolytic rate constant of ~10(-5) s(-1). In both cases, that is, in presence and/or absence of light, the heterogeneous ozonation kinetics are well described by an immediate gas-surface reaction formalism with light-independent rate constants of k(2nd)=(7.20.9)10(-19) cm(3) molec(-1) s(-1) and (7.61.7)10(-19) cm(3) molec(-1) s(-1) in the absence and presence of light, respectively. Five oxidation products: glycolic acid, oxalic acid, vanillin, vanillic acid and 3,4-dihydroxybenzoic acid were identified and confirmed by their corresponding standards. Vanillin and vanillic acid absorb light in the region ?>300 nm and thus can further participate in the direct and indirect photolysis processes of atmospheric relevance. A reaction mechanism is proposed in order to elucidate the ozonolysis reaction and to explain the reaction products. PMID:21117122

Net, Sopheak; Gomez Alvarez, Elena; Balzer, Natalja; Wortham, Henri; Zetzsch, Cornelius; Gligorovski, Sasho

2010-12-17

125

Reaction rates and apparent toxicity of Houston Ship Channel water  

E-print Network

, the nitrogen test series (for total nitrogen, organic, ammonia, nitrite, and nitrate), and both volatile and fixed solids determinations. I!itrification stud- ies were run on several of the samples to determine the signif- icance of nitrification... 45 VI. Summary of Specific Rates of Reaction VI I. Results of Nitrification Study. Vill. Pesults of General Analysis IX. Summary of Specific Rates of Reaction X. Results of tlitrification Study. Xl. Results of General Analysis Xll. Summary...

Schneider, Peter William

1969-01-01

126

Nuclear reaction rate enhancement in dense stellar matter  

Microsoft Academic Search

The enhancement factor for the rate of thermonuclear reactions in dense stellar matter is calculated in the one-component, strongly coupled plasma model. The nuclear reaction rate is related to the short-range behavior of the quantum-mechanical pair correlation function. Within the range of parameters which is investigated here, the pair correlation function is expressed in terms of classical quantities, which are

A. Alastuey; B. Jancovici

1978-01-01

127

Resonance reaction rate of 21Na(p,?)22Mg  

Microsoft Academic Search

By using the new Coulomb screening model and most recent experimental results, this paper calculates the resonance reaction rates of 21Na(p,?)22Mg. The derived result shows that the effect of electron screening on resonant reaction is prominent in astrophysical interesting temperature range. In conjunction with the experimental results, the recommended rates of21Na(p,?)22Mg would increase at least 10%, which undoubtedly affect the

Liu Hong-Lin; Liu Men-Quan; Liu Jing-Jing; Luo Zhi-Quan

2007-01-01

128

The Reaction Rate Sensitivity of Nucleosynthesis in Type II Supernovae  

E-print Network

We explore the sensitivity of the nucleosynthesis of intermediate mass elements (28 reaction rates employed in the model. Two standard sources of reaction rate data (Woosley et al. 1978; and Thielemann et al. 1987) are employed in pairs of calculations that are otherwise identical. Both include as a common backbone the experimental reactions rates of Caughlan & Fowler (1988). Two stellar models are calculated for each of two main sequence masses: 15 and 25 solar masses. Each star is evolved from core hydrogen burning to a presupernova state carrying an appropriately large reaction network, then exploded using a piston near the edge of the iron core as described by Woosley & Weaver (1995). The final stellar yields from the models calculated with the two rate sets are compared and found to differ in most cases by less than a factor of two over the entire range of nuclei studied. Reasons for the major discrepancies are discussed in detail along with the physics underlying the two reaction rate sets employed. The nucleosynthesis results are relatively robust and less sensitive than might be expected to uncertainties in nuclear reaction rates, though they are sensitive to the stellar model employed.

R. D. Hoffman; S. E. Woosley; T. A. Weaver; T. Rauscher; F. -K. Thielemann; .

1999-04-06

129

Heterogeneous photochemical reaction of ozone with anthracene adsorbed on mineral dust  

NASA Astrophysics Data System (ADS)

The heterogeneous reactions of O3 with anthracene adsorbed on TiO2 and on Asian dust storm particles were investigated in the dark and in the presence of light. The reaction rate constants of the heterogeneous reaction between O3 and anthracene adsorbed on TiO2 were increased by a factor of 1.5 in the presence of light compared to the dark conditions. Anthraquinone, which was identified as the main surface product of anthracene reacted with O3 in the dark, can react with O3 quickly in the presence of light. The reactions on Asian dust storm particles exhibited pseudo-first-order kinetics for anthracene loss, and the reactions between O3 and anthracene adsorbed on Asian dust storm particles proceed by the Langmuir-Hinshelwood mechanism in the dark and in the presence of light. At extremely high ozone concentrations, the degradation of anthracene is enhanced by a factor of 3 in the presence of light compared to the dark conditions.

Ma, Jinzhu; Liu, Yongchun; Ma, Qingxin; Liu, Chang; He, Hong

2013-06-01

130

Reactions and reaction rates in the regional aquifer beneath the Pajarito Plateau, north-central New Mexico, USA  

Microsoft Academic Search

Reactions and reaction rates within aquifers are fundamental components of critical hydrological processes. However, reactions simulated in laboratory experiments typically demonstrate rates that are much faster than those observed in the field. Therefore, it is necessary to conduct more reaction rate analyses in natural settings. This study of geochemical reactions in the regional aquifer in the Pajarito Plateau near Los

Anne G. Hereford; Elizabeth H. Keating; George D. Guthrie; Chen Zhu

2007-01-01

131

A reaction class approach for modeling gas phase reaction rates Thanh N. Truong,* Wendell T. Duncan and Max Tirtowidjojo  

E-print Network

A reaction class approach for modeling gas phase reaction rates Thanh N. Truong,* Wendell T. Duncan the growing number of known elementary reaction rate constants, the current kinetic data- base is far from of polyatomic gas-phase reactions. It is now possible to calculate rate con- stants for reactions of moderate

Truong, Thanh N.

132

Non-resonant triple alpha reaction rate at low temperature  

SciTech Connect

Our experimental goal is to study the non-resonant triple alpha reaction rate at low temperture (T < 10{sup 8} K). The {sup 13}C(p,d) reaction at 66 MeV has been used to probe the alpha-unbound continuum state in {sup 12}C just below the 2{sup nd} 0{sup +} state at 7.65 MeV. The transition strength to the continuum state is predicted to be sensitive to the non-resonant triple alpha reaction rate. The experiment has been performed at iThemba LABS. We report the present status of the experiment.

Itoh, T.; Tamii, A.; Aoi, N.; Fujita, H.; Hashimoto, T.; Miki, K.; Ogata, K. [Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047 (Japan); Carter, J.; Donaldson, L.; Sideras-Haddad, E. [Schools of Physics, University of Witwatersrand, Johannesburg 2050 (South Africa); Furuno, T.; Kawabata, T. [Departments of Physics, Kyoto University, Sakyo, Kyoto, 606-8502 (Japan); Kamimura, M. [RIKEN Nishina Center, Wako, Saitama, 351-0198 (Japan); Nemulodi, F.; Neveling, R.; Smit, F. D.; Swarts, C. [iThemba Laboratory for Accelerator Based Sciences Somerset, West, 7129 (South Africa)

2014-05-02

133

Rate of reaction between molecular hydrogen and molecular oxygen  

NASA Technical Reports Server (NTRS)

The shock tube data of Jachimowski and Houghton were rigorously analyzed to obtain rate constants for the candidate initiation reactions H2 + O2 yields H + HO2, H2 + O2 yields H2O + O, and H2 + O2 yields OH + OH. Reaction (01) is probably not the initiation process because the activation energy obtained is less than the endothermicity and because the derived rates greatly exceed values inferred in the literature from the reverse of reaction (01). Reactions (02) and (03) remain as possibilities, with reaction (02) slightly favored on the basis of steric and statistical considerations. The solution of the differential equations is presented in detail to show how the kinetics of other ignition systems may be solved.

Brokaw, R. S.

1973-01-01

134

Statistical Methods for Thermonuclear Reaction Rates and Nucleosynthesis Simulations  

E-print Network

Rigorous statistical methods for estimating thermonuclear reaction rates and nucleosynthesis are becoming increasingly established in nuclear astrophysics. The main challenge being faced is that experimental reaction rates are highly complex quantities derived from a multitude of different measured nuclear parameters (e.g., astrophysical S-factors, resonance energies and strengths, particle and gamma-ray partial widths). We discuss the application of the Monte Carlo method to two distinct, but related, questions. First, given a set of measured nuclear parameters, how can one best estimate the resulting thermonuclear reaction rates and associated uncertainties? Second, given a set of appropriate reaction rates, how can one best estimate the abundances from nucleosynthesis (i.e., reaction network) calculations? The techniques described here provide probability density functions that can be used to derive statistically meaningful reaction rates and final abundances for any desired coverage probability. Examples are given for applications to s-process neutron sources, core-collapse supernovae, classical novae, and big bang nucleosynthesis.

Christian Iliadis; Richard Longland; Alain Coc; F. X. Timmes; Art E. Champagne

2014-09-19

135

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

NASA Technical Reports Server (NTRS)

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

Liechty, Derek S.; Lewis, Mark J.

2010-01-01

136

Revisiting catalytic model reaction p-nitrophenol/NaBH4 using metallic nanoparticles coated on polymeric spheres  

NASA Astrophysics Data System (ADS)

The early reported pseudo-first-order reaction kinetics of the polymer-supported metallic nanocatalysts for the model reaction of p-nitrophenol (p-NP)/NaBH4 were probably oversimplified. Here a detailed study of p-NP reduction by NaBH4 in the presence of the raspberry-like poly(allylamine hydrochloride)-modified polymer poly(glycidyl methacrylate) composite sub-microspheres with tunable gold nanoparticles (PGMA@PAH@AuNPs) was presented. Effects of polyelectrolyte concentration, the ratio of polymer spheres to gold nanoparticles, and the solution pH value for composite synthesis on the induction period, reaction time, average reaction rate and average turnover frequency were systematically investigated. Experimental results in all cases of our study revealed an nth order (n > 1) of the p-NP/NaBH4 catalytic reaction by the prepared polymer composite particles. The apparent order of reaction, n, is dependent on the total surface area of the coated gold nanoparticles on the polymer spheres, which can be closely correlated with the tunable gold nanoparticle surface coverage. The mechanism of the observed catalytic activity enhancement was proposed based on active epoxy groups of the polymer spheres and a large adsorption of p-nitrophenolate anions onto the positively-charged spheres.

Li, Maolin; Chen, Guofang

2013-11-01

137

Temperature effects on lithium-nitrogen reaction rates  

Microsoft Academic Search

A series of experiments have been run with the aim of measuring the reaction rate of lithium and nitrogen over a wide spectrum of lithium pool temperatures. In these experiments, pure nitrogen was blown at a controlled flow rate over a preheated lithium pool. The pool had a surface area of approximately 4 cm² and a total volume of approximately

W. J. Ijams; M. S. Kazimi

1985-01-01

138

Stellar Evolution Constraints on the Triple-Alpha Reaction Rate  

E-print Network

We investigate the quantitative constraint on the triple-alpha reaction rate based on stellar evolution theory, motivated by the recent significant revision of the rate proposed by nuclear physics calculations. Targeted stellar models were computed in order to investigate the impact of that rate in the mass range of 0.8 evolution of low- and intermediate-mass stars, while its influence on the evolution of massive stars (M >~ 10 Msun) is minimal. We find that employing the revised rate suppresses helium shell flashes on AGB phase for stars in the initial mass range 0.8 10 at T = 1 - 1.2 x 10^8 K where the cross section is proportional to T^{nu}. We also derive the helium ignition curve to estimate the maximum cross section to retain the low-mass first red giants. The semi-analytically derived ignition curves suggest that the reaction rate should be less than ~ 10^{-29} cm^6 s^{-1} mole^{-2} at ~ 10^{7.8} K, which corresponds to about three orders of magnitude larger than that of the NACRE compilation. In an effort to compromise with the revised rates, we calculate and analyze models with enhanced CNO cycle reaction rates to increase the maximum luminosity of the first giant branch. However, it is impossible to reach the typical RGB tip luminosity even if all the reaction rates related to CNO cycles are enhanced by more than ten orders of magnitude.

Takuma Suda; Raphael Hirschi; Masayuki Y. Fujimoto

2011-07-25

139

Charged-particle thermonuclear reaction rates: II. Tables and graphs of reaction rates and probability density functions  

Microsoft Academic Search

Numerical values of charged-particle thermonuclear reaction rates for nuclei in the A=14 to 40 region are tabulated. The results are obtained using a method, based on Monte Carlo techniques, that has been described in the preceding paper of this issue (Paper I). We present a low rate, median rate and high rate which correspond to the 0.16, 0.50 and 0.84

Christian Iliadis; Richard Longland; Art Champagne; Alain Coc; Ryan Fitzgerald

2010-01-01

140

A Statistical Model for Predicting Thermal Chemical Reaction Rate: Application to Bimolecule Reactions  

NASA Astrophysics Data System (ADS)

A model based on the statistics of individual atoms [Europhys. Lett. 94 (2011) 40002], which has been successfully applied to predict the rate constant of unimolecular reactions, was further extended to bimolecular reactions induced by collisions. Compared with the measured rate constants of the reactions S+SO2?SO+SO and NH3+Cl?NH2+HCl, the model is proved to be significantly better than conventional transition state theory. In order to strictly test the model, we perform molecular dynamics simulation of C60+C60?C120, and show that the rate constants are in excellent agreement with our model but far away from the transition state theory.

Li, Wang-Yao; Lin, Zheng-Zhe; Xu, Jian-Jun; Ning, Xi-Jing

2012-08-01

141

Photochemical reactions of 2,4-dinitrotoluene in surfactant solutions  

SciTech Connect

Photochemical reactions ({lambda}=254 nm) of 2,4-dinitrotoluene were investigated in aqueous solutions containing various additives. These additives were a cationic surfactant (cetyltrimethylammonium bromide; CTAB) or a nonionic surfactant (Brij 58), a hydrogen donor (sodium borohydride; NaBH{sub 4}), and base (sodium hydroxide). All photochemical experiments were performed in a Rayonet RPR-100 photoreactor equipped with a merry-go-round apparatus. Light sources were two phosphor-coated low pressure mercury lamps that emit nearly monochromatic light at 253.7 nm. Illumination of a saturated solution of DNT in solutions containing either 1.9 mM Brij 58 and 1.9 mM NaBH{sub 4}, or 1.8 mM CTAB and 2.5 mM NaBH{sub 4} resulted in pseudo-first order half-lives of 77 minutes and 17 minutes, respectfully. In the presence of BH{sub 4}{sup -}, the reaction rate of 2,4-DNT was enhanced tremendously by addition of CTAB at concentrations above the critical micelle concentration (cmc=0.066 mM with 0.1 M NaCl).

Diehl, C.A.; Jafvert, C.T. [Purdue Univ., West Lafayette, IN (United States); Larson, R.A. [Univ. of Illinois, Champaign, IL (United States)

1995-12-31

142

Nonlinear dynamical effects on reaction rates in thermally fluctuating environments.  

PubMed

A framework to calculate the rate constants of condensed phase chemical reactions of manybody systems is presented without relying on the concept of transition state. The theory is based on a framework we developed recently adopting a multidimensional underdamped Langevin equation in the region of a rank-one saddle. The theory provides a reaction coordinate expressed as an analytical nonlinear functional of the position coordinates and velocities of the system (solute), the friction constants, and the random force of the environment (solvent). Up to moderately high temperature, the sign of the reaction coordinate can determine the final destination of the reaction in a thermally fluctuating media, irrespective of what values the other (nonreactive) coordinates may take. In this paper, it is shown that the reaction probability is analytically derived as the probability of the reaction coordinate being positive, and that the integration with the Boltzmann distribution of the initial conditions leads to the exact reaction rate constant when the local equilibrium holds and the quantum effect is negligible. Because of analytical nature of the theory taking into account all nonlinear effects and their combination with fluctuation and dissipation, the theory naturally provides us with the firm mathematical foundation of the origin of the reactivity of the reaction in a fluctuating media. PMID:20544104

Kawai, Shinnosuke; Komatsuzaki, Tamiki

2010-07-21

143

Microphotometric measurement of initial maximum reaction rates in quantitative enzyme histochemistry in situ  

Microsoft Academic Search

SummaryFinal reaction product formation was recorded microphotometrically for succinate dehydrogenase in cross-sectioned muscle fibres at initial rate conditions and during prolonged incubations. Incubations with gel films and aqueous reaction medium both showed a decline of reaction rates. Maximum reaction rates could only be determined at initial rate conditions during the first minute of the incubation. Reaction rates recorded in different

Dirk Pette; Universitfit Konstanz

1981-01-01

144

Reaction diffusion with a time-dependent reaction rate: the single-species diffusion annihilation process  

NASA Astrophysics Data System (ADS)

We study the single-species diffusion-annihilation process with a time-dependent reaction rate, lgr(t) = lgr0 t-ohgr. Scaling arguments show that there is a critical value of the decay exponent ohgrc(d) separating a reaction-limited regime for ohgr > ohgrc from a diffusion-limited regime for ohgr < ohgrc. The particle density displays a mean-field, ohgr-dependent, decay when the process is reaction limited whereas it behaves as for a constant reaction rate when the process is diffusion limited. These results are confirmed by Monte Carlo simulations. They allow us to discuss the scaling behaviour of coupled diffusion-annihilation processes in terms of effective time-dependent reaction rates.

Turban, L.

2004-09-01

145

Rate coefficients, binding probabilities, and related quantities for area reactivity models  

NASA Astrophysics Data System (ADS)

We further develop the general theory of the area reactivity model that describes the diffusion-influenced reaction of an isolated receptor-ligand pair in terms of a generalized Feynman-Kac equation and that provides an alternative to the classical contact reactivity model. Analyzing both the irreversible and reversible reaction, we derive the equation of motion of the survival probability as well as several relationships between single pair quantities and the reactive flux at the encounter distance. Building on these relationships, we derive the equation of motion of the many-particle survival probability for irreversible pseudo-first-order reactions. Moreover, we show that the usual definition of the rate coefficient as the reactive flux is deficient in the area reactivity model. Numerical tests for our findings are provided through Brownian Dynamics simulations. We calculate exact and approximate expressions for the irreversible rate coefficient and show that this quantity behaves differently from its classical counterpart. Furthermore, we derive approximate expressions for the binding probability as well as the average lifetime of the bound state and discuss on- and off-rates in this context. Throughout our approach, we point out similarities and differences between the area reactivity model and its classical counterpart, the contact reactivity model. The presented analysis and obtained results provide a theoretical framework that will facilitate the comparison of experiment and model predictions.

Prstel, Thorsten; Meier-Schellersheim, Martin

2014-11-01

146

Rate coefficients, binding probabilities, and related quantities for area reactivity models.  

PubMed

We further develop the general theory of the area reactivity model that describes the diffusion-influenced reaction of an isolated receptor-ligand pair in terms of a generalized Feynman-Kac equation and that provides an alternative to the classical contact reactivity model. Analyzing both the irreversible and reversible reaction, we derive the equation of motion of the survival probability as well as several relationships between single pair quantities and the reactive flux at the encounter distance. Building on these relationships, we derive the equation of motion of the many-particle survival probability for irreversible pseudo-first-order reactions. Moreover, we show that the usual definition of the rate coefficient as the reactive flux is deficient in the area reactivity model. Numerical tests for our findings are provided through Brownian Dynamics simulations. We calculate exact and approximate expressions for the irreversible rate coefficient and show that this quantity behaves differently from its classical counterpart. Furthermore, we derive approximate expressions for the binding probability as well as the average lifetime of the bound state and discuss on- and off-rates in this context. Throughout our approach, we point out similarities and differences between the area reactivity model and its classical counterpart, the contact reactivity model. The presented analysis and obtained results provide a theoretical framework that will facilitate the comparison of experiment and model predictions. PMID:25416882

Prstel, Thorsten; Meier-Schellersheim, Martin

2014-11-21

147

Updating the Nuclear Reaction Rate Library (REACLIB) I. Experimental Reaction Rates of the Proton-Proton Chain  

Microsoft Academic Search

REACLIB is one of the most comprehensive and popular astrophysical reaction rate libraries. However, its experimentally obtained rates for light isotopes still rely mainly on the Caughlan and Fowler (1988) compilation and have never been updated despite the progress in many relevant nuclear astrophysics experiments. Moreover, due to fitting errors REACLIB is not reliable at temperatures lower than 107K. In

T. Liolios; G. I. Karathanou; T. S. Kosmas; V. Tsikoudi

2009-01-01

148

Updating the nuclear reaction rate library REACLIB. (I. Experimental reaction rates of the proton-proton chain)  

Microsoft Academic Search

REACLIB is one of the most comprehensive and popular astrophysical reaction rate libraries. However, its experimentally obtained rates for light isotopes still rely mainly on the Caughlan & Fowler (1988) compilation and have never been updated despite the progress in many relevant nuclear astrophysics experiments. Moreover, due to fitting errors REACLIB is not reliable at temperatures lower than 10^{7}K. In

Theodore E. Liolios

2005-01-01

149

Reaction rate of 24Mg(p, ?) 25Al  

Microsoft Academic Search

The proton-capture reaction on 24Mg has been investigated in the bombarding energy range of Ep=0.21.7 MeV. Resonance properties (strengths, branching ratios and lifetimes) of low-energy resonances have been measured. From the experimental results, accurate proton partial widths, ?-ray partial widths and total widths (?p, ??, and ?) have been deduced. The present experimental information establishes the 24Mg+p reaction rates over

D. C. Powell; C. Iliadis; A. E. Champagne; C. A. Grossmann; S. E. Hale; V. Y. Hansper; L. K. McLean

1999-01-01

150

Reaction Rate Sensitivity of the gamma-Process Path  

E-print Network

The location of the (gamma,p)/(gamma,n) and (gamma,alpha)/(gamma,n) line at gamma-process temperatures is discussed, using recently published reaction rates based on global Hauser-Feshbach calculations. The results can directly be compared to previously published, classic gamma-process discussions. The nuclei exhibiting the largest sensitivity to uncertainties in nuclear structure and reaction parameters are specified.

T. Rauscher

2004-07-16

151

Benchmark calculations of thermal reaction rates. I - Quantal scattering theory  

NASA Technical Reports Server (NTRS)

The thermal rate coefficient for the prototype reaction H + H2 yields H2 + H with zero total angular momentum is calculated by summing, averaging, and numerically integrating state-to-state reaction probabilities calculated by time-independent quantum-mechanical scattering theory. The results are very carefully converged with respect to all numerical parameters in order to provide high-precision benchmark results for confirming the accuracy of new methods and testing their efficiency.

Chatfield, David C.; Truhlar, Donald G.; Schwenke, David W.

1991-01-01

152

Nonequilibrium velocity distribution and reaction rate in hot-atom reactions  

Microsoft Academic Search

The nonequilibrium velocity distribution and reaction rate in hot-atom reactions are studied by solving the time-dependent Boltzmann equation with the Monte Carlo simulation. The explicit time-dependent velocity distribution, temperature, and rate constant of hot atoms from initial to steady states are obtained for a simple model system where hot atoms are dispersed in the heat bath of surrounding molecules without

Katsuhisa Koura

1976-01-01

153

Glow Fast, Glow Slow: Alter the Rate of a Reaction!  

NSDL National Science Digital Library

Learners investigate one factor affecting reaction rates: temperature. In a darkened room, two identical lightsticks are placed in water -- one in hot water and one in cold water. The lightstick in the hot water glows brighter than the lightstick in the cold water since the light-producing reaction is faster in hot water. This activity, located on page 2 of the PDF, is one of three activities in the Take Home guide for the Chemical Reactions unit in OMSI's Chemistry Lab. Also included on the PDF are two additional activities: Cloudy Globs and Gas Production.

Oregon Museum of Science and Industry

1997-01-01

154

Imaginary-time method for radiative capture reaction rate  

E-print Network

We propose a new computational method for astrophysical reaction rate of radiative capture process. In the method, an evolution of a wave function is calculated along the imaginary-time axis which is identified as the inverse temperature. It enables direct evaluation of reaction rate as a function of temperature without solving any scattering problem. The method is tested for two-body radiative capture reaction, ${^{16}{\\rm O}}(\\alpha,\\gamma){^{20}{\\rm Ne}}$, showing that it gives identical results to that calculated by the ordinary procedure. The new method will be suited for calculation of triple-alpha radiative capture rate for which an explicit construction of the scattering solution is difficult.

Kazuhiro Yabana; Yasuro Funaki

2012-02-15

155

Estimation of the rate of volcanism on Venus from reaction rate measurements  

NASA Technical Reports Server (NTRS)

Laboratory rate data for the reaction between SO2 and calcite to form anhydrite are presented. If this reaction rate represents the SO2 reaction rate on Venus, then all SO2 in the Venusian atmosphere will disappear in 1.9 Myr unless volcanism replenishes the lost SO2. The required volcanism rate, which depends on the sulfur content of the erupted material, is in the range 0.4-11 cu km of magma erupted per year. The Venus surface composition at the Venera 13, 14, and Vega 2 landing sites implies a volcanism rate of about 1 cu km/yr. This geochemically estimated rate can be used to determine if either (or neither) of two discordant geophysically estimated rates is correct. It also suggests that Venus may be less volcanically active than the earth.

Fegley, Bruce, Jr.; Prinn, Ronald G.

1989-01-01

156

Study of Reaction NH3 + H NH2 + H2 by a Simple Program to Determine the Reaction Rate  

E-print Network

Study of Reaction NH3 + H NH2 + H2 by a Simple Program to Determine the Reaction Rate Patricia R developed a simple program to determine the reaction rate by using conventional transition state theory abstraction in the reaction NH3 + H NH2 + H2 is used as a model to demonstrate usage of the program. The rate

157

The Influence of Particle Charge on Heterogeneous Reaction Rate Coefficients  

NASA Technical Reports Server (NTRS)

The effects of particle charge on heterogeneous reaction rates are presented. Many atmospheric particles, whether liquid or solid are charged. This surface charge causes a redistribution of charge within a liquid particle and as a consequence a perturbation in the gaseous uptake coefficient. The amount of perturbation is proportional to the external potential and the square of the ratio of debye length in the liquid to the particle radius. Previous modeling has shown how surface charge affects the uptake coefficient of charged aerosols. This effect is now included in the heterogeneous reaction rate of an aerosol ensemble. Extension of this analysis to ice particles will be discussed and examples presented.

Aikin, A. C.; Pesnell, W. D.

2000-01-01

158

Sonication effect on the reaction of 4-bromo-1-methylbenzene with sodium sulfide in liquid-liquid multi-site phase-transfer catalysis condition - kinetic study.  

PubMed

The synthesis of di-p-tolylsulfane from the reaction of 4-bromo-1-methylbenzene (BMB) with sodium sulfide was carried out using a multi-site phase-transfer catalyst (MPTC) viz., 1,4-dihexyl-1,4-diazoniabicyclo[2.2.2]octanium dibromide and ultrasonic irradiation in a liquid-liquid reaction condition. The overall reaction rate is greatly enhanced when catalyzed by multi-site phase-transfer catalyst (MPTC) combined with sonication (40 kHz, 300 W) in a batch reactor than catalyzed by MPTC without sonication. Effects on the reaction due to various operating conditions, such as agitation speed, different ultrasound frequencies, different phase-transfer catalysts, different organic solvents, the amount of MPTC, temperature, amount of sodium sulfide, effect of sodium hydroxide, volume of n-hexane and the concentration of 4-bromo-1-methylbenzene. The reaction obeys a pseudo first-order rate law and a suitable mechanism was proposed based on the experimental observation. PMID:25199442

Abimannan, Pachaiyappan; Selvaraj, Varathan; Rajendran, Venugopal

2015-03-01

159

Assessment of reaction-rate predictions of a collision-energy approach for chemical reactions in atmospheric flows  

Microsoft Academic Search

A recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates is assessed for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. DSMC non-equilibrium reaction

Michail A. Gallis; Ryan Bomar Bond; John Robert Torczynski

2010-01-01

160

Assessment of reaction-rate predictions of a collision-energy approach for chemical reactions in atmospheric flows.  

SciTech Connect

A recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates is assessed for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological nonequilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, significant differences can be found. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

2010-06-01

161

A logarithmic approximation to initial rates of enzyme reactions.  

PubMed

A straightforward and empirical regression method based on a logarithmic approximation has been developed to accurately estimate initial rates from nonlinear progress curves of enzyme reactions. The principle of this parametric approach is to use a relatively large number of observations, while averaging out random errors, to predict the curvature at time zero, which has the highest rate of change. The usual linear regression of a few initial time points lacks prediction power at time zero and therefore underestimates the true initial rate. Application of this nonlinear regression approach to enzyme reactions demonstrated satisfactory results. This approach is less subjective in choosing initial time points to be used for rate determination, and much more robust to random errors. Moreover, it is relatively easy to realize with commonly available software. PMID:12694727

Lu, Wei-Ping; Fei, Lin

2003-05-01

162

Massive Star Evolution: Nucleosynthesis and Nuclear Reaction Rate Uncertainties  

E-print Network

We present a nucleosynthesis calculation of a 25 solar mass star of solar composition that includes all relevant isotopes up to polonium. In particular, all stable isotopes and necessary nuclear reaction rates are covered. We follow the stellar evolution from hydrogen burning till iron core collapse and simulate the explosion using a ``piston'' approach. We discuss the influence of two key nuclear reaction rates, C12(a,g) and Ne22(a,n), on stellar evolution and nucleosynthesis. The former significantly influences the resulting core sizes (iron, silicon, oxygen) and the overall presupernova structure of the star. It thus has significant consequences for the supernova explosion itself and the compact remnant formed. The later rate considerably affects the s-process in massive stars and we demonstrate the changes that different currently suggested values for this rate cause.

A. Heger; S. E. Woosley; T. Rauscher; R. D. Hoffman; M. M. Boyes

2001-09-30

163

Fusion Reaction Rate Coefficient for Different Beam and Target Scenarios  

NASA Astrophysics Data System (ADS)

Fusion power output is proportional not only to the fuel particle number densities participating in reaction but also to the fusion reaction rate coefficient (or reactivity), which is dependent on reactant velocity distribution functions. They are usually assumed to be dual Maxwellian distribution functions with the same temperature for thermal nuclear fusion circumstances. However, if high power neutral beam injection and minority ion species ICRF plasma heating, or multi-pinched plasma beam head-on collision, in a converging region are required and investigated in future large scale fusion reactors, then the fractions of the injected energetic fast ion tail resulting from ionization or charge exchange will be large enough and their contribution to the non-Maxwellian distribution functions is not negligible, hence to the fusion reaction rate coefficient or calculation of fusion power. In such cases, beam-target, and beam-beam reaction enhancement effect contributions should play very important roles. In this paper, several useful formulae to calculate the fusion reaction rate coefficient for different beam and target combination scenarios are derived in detail.

Ou, Wei; Zeng, Xian-Jun; Deng, Bai-Quan; Gou, Fu-Jun

2015-02-01

164

Dissipation Scale Fluctuations and Chemical Reaction Rates in Turbulent Flows  

E-print Network

Small separation between reactants, not exceeding $10^{-8}-10^{-7}cm$, is the necessary condition for various chemical reactions. It is shown that random advection and stretching by turbulence leads to formation of scalar-enriched sheets of {\\it strongly fluctuating thickness} $\\eta_{c}$. The molecular-level mixing is achieved by diffusion across these sheets (interfaces) separating the reactants. Since diffusion time scale is $\\tau_{d}\\propto \\eta_{c}^{2}$, the knowledge of probability density $Q(\\eta_{c},Re)$ is crucial for evaluation of chemical reaction rates. In this paper we derive the probability density $Q(\\eta_{c},Re,Sc)$ and predict a transition in the reaction rate behavior from ${\\cal R}\\propto \\sqrt{Re}$ ($Re\\leq 10^{4}$) to the high-Re asymptotics ${\\cal R}\\propto Re^{0}$. The theory leads to an approximate universality of transitional Reynolds number $Re_{tr}\\approx 10^{4}$. It is also shown that if chemical reaction involves short-lived reactants, very strong anomalous fluctuations of the length-scale $\\eta_{c}$ may lead to non-negligibly small reaction rates.

Victor Yakhot

2007-06-29

165

Radiant heater assembly for limited reaction-rate processing applications  

Microsoft Academic Search

We discuss the design and performance of a radiant heating assembly for limited reaction-rate processing applications. The heating assembly is fabricated in stainless steel on a 300 mm bore flange for incorporation with an ultrahigh vacuum compatible low-pressure chemical vapor deposition system. The heating source is an array of 18 tungsten-halogen lamps; each lamp is rated at 360 W and

G. J. Parker; J. M. Bonar; C. M. K. Starbuck

1992-01-01

166

Semiclassical Calculation of Reaction Rate Constants for Homolytical Dissociations  

NASA Technical Reports Server (NTRS)

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.

Cardelino, Beatriz H.

2002-01-01

167

Nuclear fusion in dense matter: Reaction rate and carbon burning  

E-print Network

In this paper we analyze the nuclear fusion rate between equal nuclei for all five different nuclear burning regimes in dense matter (two thermonuclear regimes, two pycnonuclear ones, and the intermediate regime). The rate is determined by Coulomb barrier penetration in dense environments and by the astrophysical S-factor at low energies. We evaluate previous studies of the Coulomb barrier problem and propose a simple phenomenological formula for the reaction rate which covers all cases. The parameters of this formula can be varied, taking into account current theoretical uncertainties in the reaction rate. The results are illustrated for the example of the ^{12}C+^{12}C fusion reaction. This reaction is very important for the understanding of nuclear burning in evolved stars, in exploding white dwarfs producing type Ia supernovae, and in accreting neutron stars. The S-factor at stellar energies depends on a reliable fit and extrapolation of the experimental data. We calculate the energy dependence of the S-factor using a recently developed parameter-free model for the nuclear interaction, taking into account the effects of the Pauli nonlocality. For illustration, we analyze the efficiency of carbon burning in a wide range of densities and temperatures of stellar matter with the emphasis on carbon ignition at densities rho > 10^9 g/cc.

L. R. Gasques; A. V. Afanasjev; E. F. Aguilera; M. Beard; L. C. Chamon; P. Ring; M. Wiescher; D. G. Yakovlev

2005-06-16

168

Nuclear fusion in dense matter: Reaction rate and carbon burning  

SciTech Connect

In this paper we analyze the nuclear fusion rates among equal nuclei for all five different nuclear burning regimes in dense matter (two thermonuclear regimes, two pycnonuclear ones, and the intermediate regime). The rate is determined by Coulomb barrier penetration in dense environments and by the astrophysical S factor at low energies. We evaluate previous studies of the Coulomb barrier problem and propose a simple phenomenological formula for the reaction rate that covers all cases. The parameters of this formula can be varied to take into account current theoretical uncertainties in the reaction rate. The results are illustrated for the example of the {sup 12}C+{sup 12}C fusion reaction. This reaction is important for the understanding of nuclear burning in evolved stars, in exploding white dwarfs producing type Ia supernovas, and in accreting neutron stars. The S factor at stellar energies depends on a reliable fit and extrapolation of the experimental data. We calculate the energy dependence of the S factor by using a recently developed parameter-free model for the nuclear interaction, taking into account the effects of the Pauli nonlocality. For illustration, we analyze the efficiency of carbon burning in a wide range of densities and temperatures of stellar matter with the emphasis on carbon ignition at densities {rho} > or approx. 10{sup 9} g cm{sup -3}.

Gasques, L.R.; Afanasjev, A.V.; Beard, M.; Wiescher, M. [Department of Physics and Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Aguilera, E.F. [Departamento del Accelerador, Instituto Nacional de Investigaciones Nucleares, A.P. 18-1027, C.P. 11801, Destrito Federal (Mexico); Chamon, L.C. [Departamento de Fisica Nuclear, Instituto de Fisica da Universidade de Sao Paulo, Caixa Postal 66318, 05315-970, Sao Paulo, SP (Brazil); Ring, P. [Physik-Department, Technische Universitat Muenchen, D-85747, Garching (Germany); Yakovlev, D.G. [Ioffe Physical Technical Institute, Poliekhnicheskaya 26, RU-194021 St. Petersburg (Russian Federation)

2005-08-01

169

Finite temperature amplitudes and reaction rates in Thermofield dynamics  

E-print Network

We propose a method for calculating the reaction rates and transition amplitudes of generic process taking place in a many body system in equilibrium. The relationship of the scattering and decay amplitudes as calculated in Thermo Field Dynamics the conventional techniques is established. It is shown that in many cases the calculations are relatively easy in TFD.

A. Rakhimov; F. C. Khanna

2001-09-28

170

COMMENT: 'Effect of the magnetic field on fusion reaction rates'  

Microsoft Academic Search

Imazu (1986) claims that a magnetic field can halve the nuclear reaction rate in a high temperature plasma. In a comment Jarvis (1987) points out that this must be incorrect because a magnetic field has no effect on the velocity distribution of particles in thermodynamic equilibrium, and assigned the error to a misinterpretation of a geometrical model in equation (7).

M. G. Haines

1987-01-01

171

Quantum and semiclassical theories of chemical reaction rates  

SciTech Connect

A rigorous quantum mechanical theory (and a semiclassical approximation thereto) is described for calculating chemical reaction rates ``directly``, i.e., without having to solve the complete state-to-state reactive scattering problem. The approach has many vestiges of transition state theory, for which it may be thought of as the rigorous generalization.

Miller, W.H. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley National Lab., CA (United States). Chemical Sciences Div.

1995-09-01

172

EXPERIMENTAL PROTOCOL FOR DETERMINING HYDROXYL RADICAL REACTION RATE CONSTANTS  

EPA Science Inventory

An experimental protocol for the determination of rate constants for the reactions of the hydroxyl (OH) radical with chemicals in the gas phase at room temperature has been developed and is described in detail. This protocol will thus provide a basis for evaluating the relative i...

173

Enhancement of the reaction rate by ICRF heating  

Microsoft Academic Search

ICRF heating at the second harmonic of deuterium in a D-T plasma produces an anisotropic tail of the deuterium ions in the direction perpendicular to the magnetic field. The non-Maxwellian distribution function leads to a significant enhancement of the reaction rate, corresponding to that of Maxwellian ions at much higher bulk temperature. The auxiliary power in the presence of ICRF

V. B. Krapchev

1985-01-01

174

A slow reaction rate in detonations due to carbon clustering  

Microsoft Academic Search

Theoretical calculations have been made to estimate the rate of heat release due to the carbon clustering process in detonations where elemental carbon is a reaction product. The process is assumed to be diffusion limited. Diffusion constants are determined using modified Enskog theory and the Stokes-Einstein relation. The carbon cluster energy is treated by a surface correction to the bulk.

M. S. Shaw; J. D. Johnson

1987-01-01

175

Cancellation of infrared singularities in finite-temperature reaction rates  

Microsoft Academic Search

In the framework of finite-temperature perturbative QED (and its scalar counterpart) we examine the problem of cancellation of infrared divergence. Taking up a generic process l incident gamma*'s + heat bath --> n detected gamma*'s + anything (gamma* is virtual photon), we give a rigorous proof that its reaction rate is free of leading infrared singularity in each order of

A. Nigawa; K. Takashiba

1992-01-01

176

Application of the Theory of Absolute Reaction Rates to Overvoltage  

Microsoft Academic Search

It is shown by means of the theory of absolute reaction rates that the current density I at an electrode is related to the overvoltage V by the expression I = I0e?VF\\/RT where I0 is a constant for a given electrode, representing the current passing in each direction at the reversible potential, and ? is the fraction of the added

H. Eyring; S. Glasstone; K. J. Laidler

1939-01-01

177

Direct measurement and theoretical calculation of the rate coefficient for Cl + CH3 from T = 202 - 298 K.  

SciTech Connect

The rate coefficient has been measured under pseudo-first-order conditions for the Cl + CH{sub 3} association reaction at T = 202, 250, and 298 K and P = 0.3-2.0 Torr helium using the technique of discharge-flow mass spectrometry with low-energy (12-eV) electron-impact ionization and collision-free sampling. Cl and CH{sub 3} were generated rapidly and simultaneously by reaction of F with HCl and CH{sub 4}, respectively. Fluorine atoms were produced by microwave discharge in an approximately 1% mixture of F{sub 2} in He. The decay of CH{sub 3} was monitored under pseudo-first-order conditions with the Cl-atom concentration in large excess over the CH{sub 3} concentration ([Cl]{sub 0}/[CH{sub 3}]{sub 0} = 9-67). Small corrections were made for both axial and radial diffusion and minor secondary chemistry. The rate coefficient was found to be in the falloff regime over the range of pressures studied. For example, at T = 202 K, the rate coefficient increases from 8.4 x 10{sup -12} at P = 0.30 Torr He to 1.8 x 10{sup -11} at P = 2.00 Torr He, both in units of cm{sup 3} molecule{sup -1} s{sup -1}. A combination of ab initio quantum chemistry, variational transition-state theory, and master-equation simulations was employed in developing a theoretical model for the temperature and pressure dependence of the rate coefficient. Reasonable empirical representations of energy transfer and of the effect of spin-orbit interactions yield a temperature- and pressure-dependent rate coefficient that is in excellent agreement with the present experimental results. The high-pressure limiting rate coefficient from the RRKM calculations is k{sub 2} = 6.0 x 10{sup -11} cm{sup 3} molecule{sup -1} s{sup -1}, independent of temperature in the range from 200 to 300 K.

Payne, Walter A. (NASA/Goddard Space Flight Center, Greenbelt, MD); Harding, Lawrence B. (Argonne National Laboratory, Argonne, IL); Stief, Louis J. (NASA/Goddard Space Flight Center, Greenbelt, MD); Parker, James F. (James Fletcher), 1925-; Klippenstein, Stephen J.; Nesbitt, Fred L. (NASA/Goddard Space Flight Center, Greenbelt, MD); Cody, Regina J. (NASA/Goddard Space Flight Center, Greenbelt, MD)

2004-10-01

178

Nuclear fusion reaction rates for strongly coupled ionic mixtures  

SciTech Connect

We analyze the effect of plasma screening on nuclear reaction rates in dense matter composed of atomic nuclei of one or two types. We perform semiclassical calculations of the Coulomb barrier penetrability taking into account a radial mean-field potential of plasma ions. The mean-field potential is extracted from the results of extensive Monte Carlo calculations of radial pair distribution functions of ions in binary ionic mixtures. We calculate the reaction rates in a wide range of plasma parameters and approximate these rates by an analytical expression that is expected to be applicable to multicomponent ion mixtures. Also, we analyze Gamow-peak energies of reacting ions in various nuclear burning regimes. For illustration, we study nuclear burning in {sup 12}C-{sup 16}O mixtures.

Chugunov, A. I.; DeWitt, H. E. [Ioffe Physical-Technical Institute, Politekhnicheskaya 26, RU-194021 St. Petersburg (Russian Federation); Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

2009-07-15

179

Reactions and reaction rates in the regional aquifer beneath the Pajarito Plateau, north-central New Mexico, USA  

Microsoft Academic Search

Reactions and reaction rates within aquifers are fundamental components of critical hydrological processes. However, reactions\\u000a simulated in laboratory experiments typically demonstrate rates that are much faster than those observed in the field. Therefore,\\u000a it is necessary to conduct more reaction rate analyses in natural settings. This study of geochemical reactions in the regional\\u000a aquifer in the Pajarito Plateau near Los

Anne G. Hereford; Elizabeth H. Keating; George D. Guthrie; Chen Zhu

2007-01-01

180

Reaction rate and products for the reaction O/3P/ + H2CO  

NASA Technical Reports Server (NTRS)

A study of reaction kinetics of O + H2CO in a discharge-flow system using mass spectrometric detection of reactants and products is presented. It was performed under both oxygen-atom-rich and formaldehyde-rich conditions over the 296 to 437 K range, showing that the global bimolecular rate constant is in agreement with other studies. This study differs from others in that the reaction products can be observed, and a substantial yield of a primary reaction product was measured with a mass spectral peak at m/e=44. This suggests that the global reaction rate probably consists of combination, as well as of simple abstraction. For the combination, one hypothesis is that triplet dioxymethylene is formed which polymerizes to triplet formic acid; the vibrationally excited triplet formic acid may decompose to form several sets of products, including HCO + OH and HCO2 + H.

Chang, J. S.; Barker, J. R.

1979-01-01

181

Scaling of geochemical reaction rates via advective solute transport  

NASA Astrophysics Data System (ADS)

Transport in porous media is quite complex, and still yields occasional surprises. In geological porous media, the rate at which chemical reactions (e.g., weathering and dissolution) occur is found to diminish by orders of magnitude with increasing time or distance. The temporal rates of laboratory experiments and field observations differ, and extrapolating from laboratory experiments (in months) to field rates (in millions of years) can lead to order-of-magnitude errors. The reactions are transport-limited, but characterizing them using standard solute transport expressions can yield results in agreement with experiment only if spurious assumptions and parameters are introduced. We previously developed a theory of non-reactive solute transport based on applying critical path analysis to the cluster statistics of percolation. The fractal structure of the clusters can be used to generate solute distributions in both time and space. Solute velocities calculated from the temporal evolution of that distribution have the same time dependence as reaction-rate scaling in a wide range of field studies and laboratory experiments, covering some 10 decades in time. The present theory thus both explains a wide range of experiments, and also predicts changes in the scaling behavior in individual systems with increasing time and/or length scales. No other theory captures these variations in scaling by invoking a single physical mechanism. Because the successfully predicted chemical reactions include known results for silicate weathering rates, our theory provides a framework for understanding changes in the global carbon cycle, including its effects on extinctions, climate change, soil production, and denudation rates. It further provides a basis for understanding the fundamental time scales of hydrology and shallow geochemistry, as well as the basis of industrial agriculture.

Hunt, A. G.; Ghanbarian, B.; Skinner, T. E.; Ewing, R. P.

2015-07-01

182

Using the Power-Law Rate Expression for Assessment of Rate Data and Detection of Infeasible Mechanisms for Reversible Reactions  

E-print Network

of rate data of reversible, heterogeneous reactions which uses the power-law rate expression is described. Introduction The design of a catalytic reactor involves the need for a correlation relating the reaction rates appropriate rate expression is a lengthy process, involving postulation of reaction mechanisms, isothermal

Brauner, Neima

183

A statistical model for predicting thermal chemical reaction rate  

NASA Astrophysics Data System (ADS)

A simple model based on the statistics of individual atoms [Europhys. Lett. 94 40002 (2011)] or molecules [Chin. Phys. Lett. 29 080504 (2012)] was used to predict chemical reaction rates without empirical parameters, and its physical basis was further investigated both theoretically and via MD simulations. The model was successfully applied to some reactions of extensive experimental data, showing that the model is significantly better than the conventional transition state theory. It is worth noting that the prediction of the model on ab initio level is much easier than the transition state theory or unimolecular RRKM theory.

Lin, Zheng-Zhe; Li, Wang-Yao; Ning, Xi-Jing

2014-05-01

184

Reaction rate for two-neutron capture by 4 He  

Microsoft Academic Search

Recent investigations suggest that the neutrino-heated hot bubble between the nascent neutron star and the overlying stellar\\u000a mantle of a type-II supernova may be the site of the r-process. In the preceding ?-process building up the elements toA?100, the4He(2n,?)6He- and6He(?,n)9Be-reactions bridging the instability gap atA=5 andA=8 could be of relevance. We suggest a mechanism for4He(2n,?)6He and calculate the reaction rate

V. D. Efros; W. Balogh; H. Herndl; R. Hofinger; H. Oberhummer

1996-01-01

185

Photochemical generation of strong one-electron reductants via light-induced electron transfer with reversible donors followed by cross reaction with sacrificial donors.  

PubMed

This work illustrates a modified approach for employing photoinduced electron transfer reactions coupled to secondary irreversible electron transfer processes for the generation of strongly reducing equivalents in solution. Through irradiation of [Ru(LL)3](2+) (LL= diimine ligands) with tritolylamine (TTA) as quencher and various alkyl amines as sacrificial electron donors, yields in excess of 50% can be achieved for generation of reductants with E(0)(2+/1+) values between -1.0 and -1.2 V vs NHE. The key to the system is the fact that the TTA cation radical, formed in high yield in reaction with the photoexcited [Ru(LL)3](2+) complex, reacts irreversibly with various sacrificial electron donating amines that are kinetically unable to directly react with the photoexcited complex. The electron transfer between the TTA(+) and the sacrificial amine is an energetically uphill process. Kinetic analysis of these parallel competing reactions, consisting of bimolecular and pseudo first-order reactions, allows determination of electron transfer rate constants for the cross electron transfer reaction between the sacrificial donor and the TTA(+). A variety of amines were examined as potential sacrificial electron donors, and it was found that tertiary 1,2-diamines are most efficient among these amines for trapping the intermediate TTA(+). This electron-donating combination is capable of supplying a persistent reducing flux of electrons to catalysts used for hydrogen production. PMID:24882233

Shan, Bing; Schmehl, Russell

2014-11-13

186

Theoretical reaction rates of the $^{12}$C($?$,$?$)$^{16}$O reaction from the potential model  

E-print Network

The radiative capture cross sections of $^{12}$C($\\alpha$,$\\gamma$)$^{16}$O and derived reaction rates are calculated from the direct capture potential model. The resulting $S$-factor at low energies is found to be dominated by $E$2 transition to the $^{16}$O ground state. The $E$1 and $E$2 $S$-factors at $E_{c.m.}=0.3$ MeV are $S_{E1}\\approx3$ keV~b and $S_{E2}=150^{+41}_{-17}$ keV~b, respectively. The sum of the cascade transition through the excited state of $^{16}$O is $S_{\\rm casc}= 18\\pm4.5$ keV~b. The derived reaction rates at low temperatures seem to be concordant with those from the previous evaluation. For astrophysical applications, our reaction rates below $T_9=3$ are provided in an analytic expression.

M. Katsuma

2015-01-26

187

Rate-determining cooperative effects of bimolecular reactions in solution.  

PubMed

An expression for the rate constant of condensed-phase bimolecular reactions is derived. The key feature of the proposed model is the formulation of the energy-dependent rate constant in terms of the diffusion rate and the ratio of the volume in phase space that leads to product over the total volume. The dependence of the bimolecular rate constant by the reduced barrier x = E thermod/kT is given in explicit form in terms of the incomplete and the complete gamma functions of Euler. The performance of the proposed model is tested against the experimental rate constants for the Menschutkin reaction by fitting the parameters of the expression for the rate constant to experimental data at various temperatures. The potential energy barrier obtained from the regression (16.75 kcal mol-1) is close to the independently computed value at the CPCM B3LYP/CRENBL.6-311(+)G(d) level of theory (16.84 kcal mol-1). The corresponding fitting to the transition state theory expression affords the lower value of 14.65 kcal mol-1. PMID:17149848

Canepa, Carlo

2006-12-14

188

Screening in Thermonuclear Reaction Rates in the Sun  

E-print Network

We evaluate the effect of electrostatic screening by ions and electrons on low-Z thermonuclear reactions in the sun. We use a mean field formalism and calculate the electron density of the screening cloud using the appropriate density matrix equation of quantum statistical mechanics. Because of well understood physical effects that are included for the first time in our treatment, the calculated enhancement of reaction rates does not agree with the frequently used interpolation formulae. Our result does agree, within small uncertainties, with Salpeter's weak screening formula. If weak screening is used instead of the commonly employed screening prescription of Graboske et al., the predicted $^8$B neutrino flux is increased by 7% and the predicted chlorine rate is increased by 0.4 SNU.

Andrei V. Gruzinov; John N. Bahcall

1998-01-20

189

A model for reaction rates in turbulent reacting flows  

NASA Technical Reports Server (NTRS)

To account for the turbulent temperature and species-concentration fluctuations, a model is presented on the effects of chemical reaction rates in computer analyses of turbulent reacting flows. The model results in two parameters which multiply the terms in the reaction-rate equations. For these two parameters, graphs are presented as functions of the mean values and intensity of the turbulent fluctuations of the temperature and species concentrations. These graphs will facilitate incorporation of the model into existing computer programs which describe turbulent reacting flows. When the model was used in a two-dimensional parabolic-flow computer code to predict the behavior of an experimental, supersonic hydrogen jet burning in air, some improvement in agreement with the experimental data was obtained in the far field in the region near the jet centerline. Recommendations are included for further improvement of the model and for additional comparisons with experimental data.

Chinitz, W.; Evans, J. S.

1984-01-01

190

Triple-{alpha} reaction rate constrained by stellar evolution models  

SciTech Connect

We investigate the quantitative constraint on the triple-{alpha} reaction rate based on stellar evolution theory, motivated by the recent significant revision of the rate proposed by nuclear physics calculations. Targeted stellar models were computed in order to investigate the impact of that rate in the mass range of 0.8{<=}M/M{sub Circled-Dot-Operator }{<=}25 and in the metallicity range between Z= 0 and Z= 0.02. The revised rate has a significant impact on the evolution of low-and intermediate-mass stars, while its influence on the evolution of massive stars (M > 10M{sub Circled-Dot-Operator }) is minimal. We find that employing the revised rate suppresses helium shell flashes on AGB phase for stars in the initial mass range 0.8{<=}M/M{sub Circled-Dot-Operator }{<=}6, which is contradictory to what is observed. The absence of helium shell flashes is due to the weak temperature dependence of the revised triple-{alpha} reaction cross section at the temperature involved. In our models, it is suggested that the temperature dependence of the cross section should have at least {nu} > 10 at T = 1-1.2 Multiplication-Sign 10{sup 8}K where the cross section is proportional to T{sup {nu}}. We also derive the helium ignition curve to estimate the maximum cross section to retain the low-mass first red giants. The semi-analytically derived ignition curves suggest that the reaction rate should be less than {approx} 10{sup -29} cm{sup 6} s{sup -1} mole{sup -2} at Almost-Equal-To 10{sup 7.8} K, which corresponds to about three orders of magnitude larger than that of the NACRE compilation.

Suda, Takuma; Hirschi, Raphael; Fujimoto, Masayuki Y. [National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan); Keele University, Keele, Staffordshire ST5 5BG (United Kingdom) and Institute for the Physics and Mathematics of the Universe, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8583 (Japan); Hokkaido University, Kita 10 Nishi 8, Kita-ku, Sapporo 060-0810 (Japan)

2012-11-12

191

Determination of palladium--aluminum reaction propagation rates and temperatures  

Microsoft Academic Search

Three experimental techniques--thermometry, framing and streaking photography, and dynamic radiography--were employed to determine the reaction propagation rates and temperatures of various mixtures of palladium and aluminum. Pellets of 94\\/6, 90\\/10, and 80\\/20 Pd\\/Al mixtures with an average density of 5 x 10³ kg\\/m³ were prepared and tested in an insulating sleeve. Pretest radiography was used to determine the density in

Birnbaum

1978-01-01

192

SELF-REDUCING PELLETS FOR IRONMAKING: REACTION RATE AND PROCESSING  

Microsoft Academic Search

Self-reducing pellets bearing iron oxides and carbonaceous material are considered as an efficient way of promoting the carbothermic reduction of iron ore or iron-containing wastes, as several processes already employ this technology. This paper discusses the reaction rates obtained when this kind of agglomerate is heated at different temperatures. To take advantage of the kinetic features presented by self-reducing pellets,

MARCELO B. MOURO; CYRO TAKANO

2003-01-01

193

Updating the nuclear reaction rate library REACLIB. (I. Experimental reaction rates of the proton-proton chain)  

E-print Network

REACLIB is one of the most comprehensive and popular astrophysical reaction rate libraries. However, its experimentally obtained rates for light isotopes still rely mainly on the Caughlan & Fowler (1988) compilation and have never been updated despite the progress in many relevant nuclear astrophysics experiments. Moreover, due to fitting errors REACLIB is not reliable at temperatures lower than 10^{7}K. In this work we establish the formalism for updating the obsolete Caughlan-Fowler experimental rates of REACLIB. Then we use the NACRE compilation and results from the LUNA experiments to update some important charged-particle induced rates of REACLIB focusing on the proton-proton chain. The updated rates (available also in digital form) can now be used in the low temperature regime (below 10^{7}K) which was forbidden to the old version of REACLIB.

Theodore E. Liolios

2005-02-03

194

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

PubMed

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

Jaworek, K; Czaplicka, M; Bratek, ?

2014-10-01

195

Application of semiclassical methods to reaction rate theory  

SciTech Connect

This work is concerned with the development of approximate methods to describe relatively large chemical systems. This effort has been divided into two primary directions: First, we have extended and applied a semiclassical transition state theory (SCTST) originally proposed by Miller to obtain microcanonical and canonical (thermal) rates for chemical reactions described by a nonseparable Hamiltonian, i.e. most reactions. Second, we have developed a method to describe the fluctuations of decay rates of individual energy states from the average RRKM rate in systems where the direct calculation of individual rates would be impossible. Combined with the semiclassical theory this latter effort has provided a direct comparison to the experimental results of Moore and coworkers. In SCTST, the Hamiltonian is expanded about the barrier and the ``good`` action-angle variables are obtained perturbatively; a WKB analysis of the effectively one-dimensional reactive direction then provides the transmission probabilities. The advantages of this local approximate treatment are that it includes tunneling effects and anharmonicity, and it systematically provides a multi-dimensional dividing surface in phase space. The SCTST thermal rate expression has been reformulated providing increased numerical efficiency (as compared to a naive Boltzmann average), an appealing link to conventional transition state theory (involving a ``prereactive`` partition function depending on the action of the reactive mode), and the ability to go beyond the perturbative approximation.

Hernandez, R.

1993-11-01

196

Atmospheric photooxidation reactions. Rates, reactivity, and mechanism for reaction of organic compounds with hydroxyl radicals  

Microsoft Academic Search

The photooxidation of a number of organic species, representing several classes of atmospheric pollutants, was studied in the presence of HONO, NO, and NO at parts per million concentrations. The experiments give information on the rate and mechanism of the reaction with organic molecules of HO radicals produced by photolysis of HONO under these conditions. The data allow evaluation of

Richard A. Cox; Richard G. Derwent; Michael R. Williams

1980-01-01

197

Pressure and temperature dependence of the reaction NO2 + NO3 + M yields N2O5 + M  

NASA Technical Reports Server (NTRS)

The pressure and temperature dependences of the reaction NO2 + NO3 + M which yields N2O5 + M are investigated by using the flash photolysis/visible absorption technique in which the pseudo-first-order decay of NO3 is monitored as a function of total pressure (20-700 torr), diluent gas (M = He and N2), and temperature (236-358 K). The reaction is found to be in the falloff region in the 20-700 torr pressure range with collision efficiencies increasing in the order He less than N2. Falloff parameters are obtained by fitting the experimental data to the falloff equation of Troe and co-workers. The expression for k1(N2 concentration, T) is obtained and compared with the evaluations presented in the NASA (DeMore, 1983) and CODATA (Baulch et al., 1982) reviews of kinetic data for atmospheric chemistry. Both evaluations are based on N2O5 thermal decomposition data coupled with estimates of the equilibrium constant. The significance of the reactions for atmospheric chemistry rests not only on their rates but on the extent to which they result in a permanent sink for NOX.

Kircher, C. C.; Margitan, J. J.; Sander, S. P.

1984-01-01

198

An age extended progress variable for conditioning reaction rates  

NASA Astrophysics Data System (ADS)

An aging progress variable (APV) is proposed as a convenient tool for conditioning quantities used to calculate reaction rates in premixed turbulent combustion. The APV is defined to obey an advection-diffusion-reaction equation where the source term is linearly related to the fuel consumption rate when the APV is less than a threshold representative of the trailing edge of the fuel consumption layer. Above this threshold, the APV has a constant source term. To test the proposal, three-dimensional fully compressible direct numerical simulation (DNS) is performed in an inflow-outflow configuration with inlet turbulence forcing using a modified version of the DNS code SENGA. A model chemical mechanism involving two steps and four species is used which has an order of magnitude difference between the time scales associated with the two steps. The inlet Taylor scale Reynolds number is 51 and the Damkhler numbers are 2.0 and 0.29 for the two steps. When conditionally averaged on the proposed APV the scalar fluctuations about the conditional average are negligible. Further, it is shown that the probability density function of the APV can be reasonably approximated based on the first two moments of the APV and the fuel mass fraction. The APV probability density function (PDF) is approximated on rectangular slabs of cells normal to the flow direction using only these moments as a test case. Convolution of the PDF so approximated with conditional mean reaction ratescalculated from conditionally averaged scalar fields where the averaging was carried out over the entire domainleads to an approximation for the unconditional mean reaction rates on each of these slabs typically within 10% of the true value for both steps. That the correlation between the reaction rates and the APV is strong, and that the PDF can be approximated for a situation where approximating the PDF for a product based progress variable is nontrivial, makes the proposed APV a strong alternative to traditional progress variables for both flamelet models and premixed conditional moment closure (CMC) approaches.

Grout, R. W.

2007-10-01

199

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

ERIC Educational Resources Information Center

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

Lombardo, Anthony

1982-01-01

200

Rate of Mixing Controls Rate and Outcome of Autocatalytic Processes: Theory and Microfluidic Experiments with Chemical Reactions and  

E-print Network

to the concentration of an activator. Plug-based microfluidics was used to control the timing of reactions, the rate the total rate of reaction is not sensitive to spatial heterogeneity in reagent distribution (Fig. 1, a and b). However, mixing influences the rate of reaction in systems with nonlinear kinetics, because

Ismagilov, Rustem F.

201

Preparation of stabilized nano zero-valent iron particles via a rheological phase reaction method and their use in dye decolourization.  

PubMed

In this study, sodium carboxymethyl cellulose (NaCMC)-stabilized nano zero-valent iron (C-nZVI) was synthesized using a rheological phase reaction method. The orthogonal method was used to evaluate the factors influencing C-nZVI properties and this showed that the reaction time, solid-liquid ratio (w/v), grinding time and NaCMC concentration were all important factors. Characterization with scanning electron microscopy validated the hypothesis that the introduction of CMC led to a decrease in aggregation of iron nanoparticles. X-ray diffraction confirmed the existence of Fe(0) and the strong antioxidant activity of the iron particles. Batch decolourization experiments exhibited that solution pH, C-nZVI dosage and reaction time have significant effects on dye decolourization. A high decolourization efficiency (94.5%) was obtained within 30 min for 100 mg/L of reactive blue-19 at the optimal pH value of 5 and C-nZVI loading of 6 g/L at room temperature. The decolourization rates followed modified pseudo-first-order kinetic equations with respect to dye concentration. The observed removal rate constant was 0.0447 min(-1) for the C-nZVI loading of 6 g/L. PMID:23530358

Cheng, Yue; Lu, Mang; Jiao, Chuang; Liu, Hai-Jiang

2013-01-01

202

Updating the nuclear reaction rate library REACLIB. (I. Experimental reaction rates of the proton-proton chain)  

Microsoft Academic Search

REACLIB is one of the most comprehensive and popular astrophysical reaction\\u000arate libraries. However, its experimentally obtained rates for light isotopes\\u000astill rely mainly on the Caughlan & Fowler (1988) compilation and have never\\u000abeen updated despite the progress in many relevant nuclear astrophysics\\u000aexperiments. Moreover, due to fitting errors REACLIB is not reliable at\\u000atemperatures lower than 10^{7}K. In

T. E. Liolios; G. I. Karathanou; T. S. Kosmas; V. Tsikoudi

2005-01-01

203

Kinetics of the reaction OH + HO2 yields H2O + O2 from 254 to 382 K  

NASA Technical Reports Server (NTRS)

The discharge-flow resonance fluorescence technique has been used to determine the absolute rate constant for the reaction OH + HO2 yields H2O + O2 from 254 to 382 K at a total pressure of 1 Torr. Pseudo-=first-order conditions were used with HO2 in large excess over OH. The rate constant was obtained directly from observed decays of OH and measured concentrations of HO2. Since the observed rate constant was found to be very sensitive to small background concentrations of O and H atoms, NO2 was used to remove both atom species from the system. With added NO2 the result at 299 K is (1.1 + or - 0.3) x 10 to the -10th cu cm/molecule where the error limits are one standard deviation and include an estimate of overall experimental uncertainty. The temperature dependence expressed in Arrhenius form is (4.8 + or - 0.8) x 10 to the -11th exp (250 + or - 50)/T. The results are independent of the type of reactor surface and the precursor used to produce OH and HO2. The present results agree well with earlier measurements near 1-atm total pressure and suggest that this rate constant exhibits little or no pressure dependence between 1 and 1000 Torr.

Keyser, Leon F.

1988-01-01

204

Effect of confinement on reaction rates within polymer nanotemplates  

NASA Astrophysics Data System (ADS)

The most efficient catalysts have been developed and optimized by living systems. Indeed, in vivo enzyme-catalyzed reactions are several orders of magnitude more efficient than platinum based catalyzed reactions. However, the rate of reaction and equilibrium interactions are considerably reduced when the biological systems are studied in vitro. This phenomenon is largely attributed to the effect of confinement or macromolecular crowding present in the cell. Confinement can also be observed in an aqueous solution containing surfactants (amphiphilic copolymers). For example, copolymers can self-assemble into well defined ordered structures such as micelles, nanotubes, vesicles; and the geometries and shapes of a given copolymer can be controlled by their solvent affinity. The hollow nanoarchitectures obtained by self-assembly can be used as a model template to study confinement within a soft shell system to mimic biosystems. These systems provide a very controlled environment for the study of confinement. In this paper we will present the effect of confinement on polymerisation reactions combining both simulation and experimental characterisation for a comprehensive study of the effect of confinement on the interactions among confined molecules.

Malardier-Jugroot, Cecile; Li, Xia

2012-02-01

205

Scanning electrochemical microscopy for direct imaging of reaction rates.  

PubMed

Not only in electrochemistry but also in biology and in membrane transport, localized processes at solid-liquid or liquid-liquid interfaces play an important role at defect sites, pores, or individual cells, but are difficult to characterize by integral investigation. Scanning electrochemical microscopy is suitable for such investigations. After two decades of development, this method is based on a solid theoretical foundation and a large number of demonstrated applications. It offers the possibility of directly imaging heterogeneous reaction rates and locally modifying substrates by electrochemically generated reagents. The applications range from classical electrochemical problems, such as the investigation of localized corrosion and electrocatalytic reactions in fuel cells, sensor surfaces, biochips, and microstructured analysis systems, to mass transport through synthetic membranes, skin and tissue, as well as intercellular communication processes. Moreover, processes can be studied that occur at liquid surfaces and liquid-liquid interfaces. PMID:17285666

Wittstock, Gunther; Burchardt, Malte; Pust, Sascha E; Shen, Yan; Zhao, Chuan

2007-01-01

206

An Improved Reaction Rate Formulation for Charged-Particle Induced Thermonuclear Reaction of 2H(d,gamma)4He  

Microsoft Academic Search

The reaction rate formula utilized in compilations such as the Nuclear Astrophysics Compilation of Reaction Rates (NACRE) uses low energy approximation due to temperatures in stars are in the region of a few keVs. Most nuclear reaction experiments were done in MeV range and the interior temperatures of massive stars are ~109 K. Hence an improved formulation for calculating the

Azni Abdul Aziz; Norhasliza Yusof; Mahirah Idris; Hasan Abu Kassim

2011-01-01

207

Reaction Rate of Small Diffusing Molecules on a Cylindrical Membrane  

NASA Astrophysics Data System (ADS)

Biomembranes consist of a lipid bi-layer into which proteins are embedded to fulfill numerous tasks in localized regions of the membrane. Often, the proteins have to reach these regions by simple diffusion. Motivated by the observation that IP3 receptor channels (IP3R) form clusters on the surface of the endoplasmic reticulum (ER) during ATP-induced calcium release, the reaction rate of small diffusing molecules on a cylindrical membrane is calculated based on the Smoluchowski approach. In this way, the cylindrical topology of the tubular ER is explicitly taken into account. The problem can be reduced to the solution of the diffusion equation on a finite cylindrical surface containing a small absorbing hole. The solution is constructed by matching appropriate `inner' and `outer' asymptotic expansions. The asymptotic results are compared with those from numerical simulations and excellent agreement is obtained. For realistic parameter sets, we find reaction rates in the range of experimentally measured clustering rates of IP3R. This supports the idea that clusters are formed by a purely diffusion limited process.

Straube, Ronny; Ward, Michael J.; Falcke, Martin

2007-10-01

208

Measurement of Intrinsic Rate Constants in the Tyrosine Hydroxylase Reaction  

PubMed Central

Tyrosine hydroxylase (TyrH) is a pterin-dependent mononuclear nonheme aromatic amino acid hydroxylase that catalyzes the conversion of tyrosine to dihydroxyphenylalanine (DOPA). Chemical quench analyses of the enzymatic reaction show a burst of DOPA formation, followed by a linear rate equal to the kcat value at both 5 C and 30 C. The effects of increasing solvent viscosity confirm that kcat is ~86 % limited by diffusion, most probably due to slow product release, and that tyrosine has a commitment to catalysis of 0.45. The effect of viscosity on the kcat/Km for 6-methyltetrahydropterin is greater than the theoretical limit, consistent with the coupling of pterin binding to the movement of a surface loop. The absorbance changes in the spectrum of the tetrahydropterin during the first turnover, the kinetics of DOPA formation during the first turnover, and the previously described kinetics for formation and decay of the Fe(IV)O intermediate (Eser, B. E., Barr, E. W., Frantom, P. A., Saleh, L., Bollinger, J. M., Jr., Krebs, C., and Fitzpatrick, P. F. (2007) J. Amer. Chem. Soc. 129, 1133411335) were analyzed globally to obtain a single set of rate constants for the TyrH reaction. Reversible binding of oxygen is followed by formation of Fe(IV)O and 4a-hydroxpterin with a rate constant of 13 s?1 at 5 C. Transfer of oxygen from the Fe(IV)O to tyrosine to form DOPA follows with a rate constant of 22 s?1. Release of DOPA and/or the 4a-hydroxypterin with a rate constant of 0.86 s?1 completes turnover. PMID:20025246

Eser, Bekir E.; Fitzpatrick, Paul F.

2010-01-01

209

Metal-silicon reaction rates - The effects of capping  

NASA Technical Reports Server (NTRS)

Evidence is presented showing that the presence of the commonly used anti-reflection coating material Ta2O5 on the free surface of contact metallization can either suppress or enhance, depending on the system, the interaction that takes place at elevated temperatures between the metallization and the underlying Si. The cap layer is shown to suppress both the generation and annihilation of vacancies at the free surface of the metal which are necessary to support metal-Si interactons. Evidence is also presented indicating that the mechanical condition of the free metal surface has a significant effect on the metal-silicon reaction rate.

Weizer, Victor G.; Fatemi, Navid S.

1989-01-01

210

Novel technique for constraining r-process (n,$?$) reaction rates  

E-print Network

A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r-process. As a proof-of-principle, the $\\gamma$-spectra from the $\\beta$-decay of $^{76}$Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and $\\gamma$-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the $^{75}$Ge($n,\\gamma$)$^{76}$Ge cross section and reaction rate.

A. Spyrou; S. N. Liddick; A. C. Larsen; M. Guttormsen; K. Cooper; A. C. Dombos; D. J. Morrissey; F. Naqvi; G. Perdikakis; S. J. Quinn; T. Renstrm; J. A. Rodriguez; A. Simon; C. S. Sumithrarachchi; R. G. T. Zegers

2014-08-27

211

Novel technique for constraining r-process (n, ?) reaction rates.  

PubMed

A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r process. As a proof of principle, the ? spectra from the ? decay of ^{76}Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and ?-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the ^{75}Ge(n,?)^{76}Ge cross section and reaction rate. PMID:25526121

Spyrou, A; Liddick, S N; Larsen, A C; Guttormsen, M; Cooper, K; Dombos, A C; Morrissey, D J; Naqvi, F; Perdikakis, G; Quinn, S J; Renstrm, T; Rodriguez, J A; Simon, A; Sumithrarachchi, C S; Zegers, R G T

2014-12-01

212

Primordial lithium - New reaction rates, new abundances, new constraints  

NASA Technical Reports Server (NTRS)

Newly measured nuclear reaction rates for H-3(alpha, gamma)Li-7 (higher than previous values) and Li-7(p, alpha)He-4 (lower than previous values) are shown to increase the Li-7 yield from big band nucleosynthesis for lower baryon-to-photon ratio (less than about 4 x 10 to the 10th). Recent revisions in the He-3(alpha, gamma)Be-7 and the D(p, gamma)He-3 rates enhance the high (greater than 4 x 10 to the 10th) Li-7(Be) production. New, independent determinations of Li abundances in extreme population II stars are in excellent agreement with the work of Spites and give continued confidence in the use of Li-7 in big bang baryon density determinations.

Kawano, Lawrence; Schramm, David; Steigman, Gary

1988-01-01

213

Pore-scale heterogeneous reaction rates on a dissolving limestone surface Yael Levensona  

E-print Network

Pore-scale heterogeneous reaction rates on a dissolving limestone surface Yael Levensona , Simon. We suggest that the observed heterogeneous reaction rates could instead be due to the elevated-based dissolution rates. Keywords: atomic force microscopy; kinetics; porosity; reaction rates; weathering. 1

Simon, Emmanuel

214

Effects of mineral spatial distribution on reaction rates in porous media  

E-print Network

Effects of mineral spatial distribution on reaction rates in porous media L. Li,1 C. A. Peters,2 on reaction rates in porous media. Pore-scale network models were constructed to represent sandstones-scale heterogeneities, reaction rates from network models were compared to rates from continuum models that use uniform

Peters, Catherine A.

215

Absolute and relative rate constants for the reactions of OH and Cl with Pentanols  

E-print Network

1 Absolute and relative rate constants for the reactions of OH and Cl with Pentanols M. Lendar ABSTRACT The rate constants for the reactions of OH with three pentanols have been determined in the range on these reactions. In addition, using the relative rate method, the rate constants for OH and Cl

Boyer, Edmond

216

Reaction rate prediction for elementary reactions in binary mixed solvents assuming an additive solvation of reactant(s)  

E-print Network

REACTION RATE PREDICTION FOR ELEMENTARY REACTIONS IN BINARY MIXED SOLVENTS ASSUMING AN ADDITIVE SOLVATION OF REACTANT(S) A Thesis by HOWARD CLARK VAN WOERT, JR. Submitted to the Graduate College of Texas AkN University in partial fulfillment... of the requirement for the degree of MASTER OF SCIENCE August 1976 Major Subject: Chemistry REACTION RATE PREDICTION FOR ELEMENTARY REACTIONS IN BINARY MIXED SOLVENTS ASSUMING AN ADDITIVE SOLVATION OF REACTANT(S) A Thesis HOWARD CLARK VAN WOERT, JR. Approved...

Van Woert, Howard Clark

1976-01-01

217

Determination of the stellar reaction rate for 12C(?, ?)16O: using a new expression with the reaction mechanism  

Microsoft Academic Search

The astrophysical reaction rate of 12C(?, ?)16O plays a key role in massive star evolution. However, this reaction rate and its uncertainties have not been well determined yet, especially at T9 = 0.2. The existing results even disagree with each other to a certain extent. In this paper, the E1, E2 and total (E1+E2) 12C(?, ?)16O reaction rates are calculated

Xu Yi; Xu Wang; Ma Yu-Gang; Cai Xiang-Zhou; Chen Jin-Gen; Fan Gong-Tao; Fan Guang-Wei; Guo Wei; Luo Wen; Pan Qiang-Yan; Shen Wen-Qing; Yang Li-Feng

2009-01-01

218

Heterogeneous reactions of ozone with pyrene, 1-hydroxypyrene and 1-nitropyrene adsorbed on particles  

NASA Astrophysics Data System (ADS)

This work deals with the kinetic study of the reactions of ozone with pyrene, 1-hydroxypyrene and 1-nitropyrene, adsorbed on model particles. Experiments were performed at room temperature and atmospheric pressure, using a quasi-static flow reactor in the absence of light. Compounds were extracted from particles using pressurized fluid extraction (PFE) and concentration measurements were performed using gas chromatography/mass spectrometry (GC/MS). The pseudo-first order rate constants were obtained from the fit of the experimental decay of particulate polycyclic compound concentrations versus reaction time. Experiments were performed at three different O 3 concentrations from which second order rate constants were calculated. The following rate constant values were obtained at 293 K: k(O 3 + Pyrene) = (3.2 0.7) 10 -16 cm 3 molecule -1 s -1; k(O 3 + 1OHP) = (7.7 1.4) 10 -16 cm 3 molecule -1 s -1; and k(O 3 + 1NP) = (2.2 0.5) 10 -17 cm 3 molecule -1 s -1, for pyrene, 1-hydroxypyrene and 1-nitropyrene adsorbed on silica particles. The variation in the rate constants demonstrates the strong influence of the substituent (OH or NO 2) on the heterogeneous reactivity of pyrene. The pyrene particulate concentration was also varied in order to check how this parameter may influence the experiments. Finally, oxidation products were investigated for all reactions and some were detected and identified for the first time for ozone heterogeneous reaction with pyrene adsorbed on particles.

Miet, K.; Le Menach, K.; Flaud, P. M.; Budzinski, H.; Villenave, E.

219

An Experiment To Demonstrate How a Catalyst Affects the Rate of a Reaction.  

ERIC Educational Resources Information Center

Describes a chemistry experiment that allows students to calculate rates of reaction, orders of reaction, and activation energies. The activity demonstrates that to increase a reaction's rate, a catalyst need only provide any additional pathway for the reaction, not necessarily a pathway having lower activation energy. (WRM)

Copper, Christine L.; Koubeck, Edward

1999-01-01

220

Reaction-rate formula in out of equilibrium quantum field theory  

E-print Network

A complete derivation, from first principles, of the reaction-rate formula for a generic reaction taking place in an out of equilibrium quantum-field system is given. It is shown that the formula involves no finite-volume correction. Each term of the reaction-rate formula represents a set of physical processes that contribute to the reaction under consideration.

A. Niegawa; K. Okano; H. Ozaki

1999-11-29

221

Manual choice reaction times in the rate-domain  

PubMed Central

Over the last 150 years, human manual reaction times (RTs) have been recorded countless times. Yet, our understanding of them remains remarkably poor. RTs are highly variable with positively skewed frequency distributions, often modeled as an inverse Gaussian distribution reflecting a stochastic rise to threshold (diffusion process). However, latency distributions of saccades are very close to the reciprocal Normal, suggesting that rate (reciprocal RT) may be the more fundamental variable. We explored whether this phenomenon extends to choice manual RTs. We recorded two-alternative choice RTs from 24 subjects, each with 4 blocks of 200 trials with two task difficulties (easy vs. difficult discrimination) and two instruction sets (urgent vs. accurate). We found that rate distributions were, indeed, very close to Normal, shifting to lower rates with increasing difficulty and accuracy, and for some blocks they appeared to become left-truncated, but still close to Normal. Using autoregressive techniques, we found temporal sequential dependencies for lags of at least 3. We identified a transient and steady-state component in each block. Because rates were Normal, we were able to estimate autoregressive weights using the Box-Jenkins technique, and convert to a moving average model using z-transforms to show explicit dependence on stimulus input. We also found a spatial sequential dependence for the previous 3 lags depending on whether the laterality of previous trials was repeated or alternated. This was partially dissociated from temporal dependency as it only occurred in the easy tasks. We conclude that 2-alternative choice manual RT distributions are close to reciprocal Normal and not the inverse Gaussian. This is not consistent with stochastic rise to threshold models, and we propose a simple optimality model in which reward is maximized to yield to an optimal rate, and hence an optimal time to respond. We discuss how it might be implemented. PMID:24959134

Harris, Christopher M.; Waddington, Jonathan; Biscione, Valerio; Manzi, Sean

2014-01-01

222

Reaction rate constant of SO3+NH3 in the gas phase  

Microsoft Academic Search

The reaction rate constant of SO3+NH3 in the gas phase was measured using a photofragment emission flow tube technique. The reaction rate constant at room temperature is (6.9+\\/-1.5)10-11 cm3 molecule-1 s-1 at He pressures of 1-2 torr. This measured reaction rate is new information for studying the formation process of ammounium sulfates in the atmosphere. The reaction rate constant of

Gaunlin Shen; Masako Suto; L. C. Lee

1990-01-01

223

The effects of vacuum polarization on thermonuclear reaction rates  

NASA Astrophysics Data System (ADS)

Added to the pure Coulomb potential, the contribution from vacuum polarization increases the barrier, reducing the wave function (u) for reacting nuclei within the range of nuclear forces. The cross section and reaction rate are then reduced accordingly by a factor proportional to u squared. The effect is treated by evaluating the vacuum polarization potential as a small correction to the Coulomb term, then computing u in a WKB formulation. The calculation is done analytically employing the small r power-series expansion for the Uehling potential to express the final result in terms of convenient parameters. At a temperature of 1.4 x 10 to the 7th K the (negative) correction is 1.3 percent for the fundamental fusion process p + p yields d + e(+) + nu.

Gould, Robert J.

1990-11-01

224

The effects of vacuum polarization on thermonuclear reaction rates  

NASA Technical Reports Server (NTRS)

Added to the pure Coulomb potential, the contribution from vacuum polarization increases the barrier, reducing the wave function (u) for reacting nuclei within the range of nuclear forces. The cross section and reaction rate are then reduced accordingly by a factor proportional to u squared. The effect is treated by evaluating the vacuum polarization potential as a small correction to the Coulomb term, then computing u in a WKB formulation. The calculation is done analytically employing the small r power-series expansion for the Uehling potential to express the final result in terms of convenient parameters. At a temperature of 1.4 x 10 to the 7th K the (negative) correction is 1.3 percent for the fundamental fusion process p + p yields d + e(+) + nu.

Gould, Robert J.

1990-01-01

225

Transcriptional dynamics with time-dependent reaction rates  

NASA Astrophysics Data System (ADS)

Transcription is the first step in the process of gene regulation that controls cell response to varying environmental conditions. Transcription is a stochastic process, involving synthesis and degradation of mRNAs, that can be modeled as a birthdeath process. We consider a generic stochastic model, where the fluctuating environment is encoded in the time-dependent reaction rates. We obtain an exact analytical expression for the mRNA probability distribution and are able to analyze the response for arbitrary time-dependent protocols. Our analytical results and stochastic simulations confirm that the transcriptional machinery primarily act as a low-pass filter. We also show that depending on the system parameters, the mRNA levels in a cell population can show synchronous/asynchronous fluctuations and can deviate from Poisson statistics.

Nandi, Shubhendu; Ghosh, Anandamohan

2015-02-01

226

Transcriptional dynamics with time-dependent reaction rates.  

PubMed

Transcription is the first step in the process of gene regulation that controls cell response to varying environmental conditions. Transcription is a stochastic process, involving synthesis and degradation of mRNAs, that can be modeled as a birth-death process. We consider a generic stochastic model, where the fluctuating environment is encoded in the time-dependent reaction rates. We obtain an exact analytical expression for the mRNA probability distribution and are able to analyze the response for arbitrary time-dependent protocols. Our analytical results and stochastic simulations confirm that the transcriptional machinery primarily act as a low-pass filter. We also show that depending on the system parameters, the mRNA levels in a cell population can show synchronous/asynchronous fluctuations and can deviate from Poisson statistics. PMID:25670682

Nandi, Shubhendu; Ghosh, Anandamohan

2015-02-01

227

Charged-particle thermonuclear reaction rates: I. Monte Carlo method and statistical distributions  

Microsoft Academic Search

A method based on Monte Carlo techniques is presented for evaluating thermonuclear reaction rates. We begin by reviewing commonly applied procedures and point out that reaction rates that have been reported up to now in the literature have no rigorous statistical meaning. Subsequently, we associate each nuclear physics quantity entering in the calculation of reaction rates with a specific probability

Richard Longland; Christian Iliadis; Art Champagne; Joe Newton; Claudio Ugalde; Alain Coc; Ryan Fitzgerald

2010-01-01

228

Atmospheric Environment 38 (2004) 21772185 Proton transfer reaction rate constants between hydronium ion  

E-print Network

Atmospheric Environment 38 (2004) 21772185 Proton transfer reaction rate constants between in revised form 3 December 2003; accepted 14 January 2004 Abstract We report proton transfer reaction rate employing the density function theory-B3LYP. The ionmolecule reaction rates were determined using

2004-01-01

229

Rate Constants for Reactions of Phenoxyl Radicals in Solution Pedatsur Netaa...  

E-print Network

Rate Constants for Reactions of Phenoxyl Radicals in Solution Pedatsur Netaa... National Institute 1 June 2004; published online 7 April 2005 Absolute rate constants for reactions of phenoxyl for which the rate constants of both the forward and the reverse reaction have been measured. The radicals

Magee, Joseph W.

230

An efficient Monte Carlo method for calculating ab initio transition state theory reaction rates in solution  

E-print Network

An efficient Monte Carlo method for calculating ab initio transition state theory reaction rates in liquid environments are still inferred from isotope and solvent medium effects on the reaction rate.6 the calculation of kinetic iso- tope effects and reaction rates in solution are associated with the fact

Schofield, Jeremy

231

Students' Ideas about Reaction Rate and Its Relationship with Concentration or Pressure  

ERIC Educational Resources Information Center

This cross-sectional study identifies key conceptual difficulties experienced by upper secondary school and pre-service chemistry teachers (N = 191) in the area of reaction rates. Students' ideas about reaction rates were elicited through a series of written tasks and individual interviews. In this paper, students' ideas related to reaction rate

Cakmakci, Gultekin; Leach, John; Donnelly, James

2006-01-01

232

Rate of diffusiondimited reactions in dispersions of spherical traps via multipole scattering  

E-print Network

Rate of diffusiondimited reactions in dispersions of spherical traps via multipole scattering R. T, California 91125 (Received 31 May 1990;accepted27 September1990) The elective reaction rate is calculated of two-body interactions has a negligible effect on the effective reaction rates computed, in contrast

233

PHYSICAL REVIEW C 80, 014611 (2009) Nuclear fusion reaction rates for strongly coupled ionic mixtures  

E-print Network

PHYSICAL REVIEW C 80, 014611 (2009) Nuclear fusion reaction rates for strongly coupled ionic April 2009; published 31 July 2009) We analyze the effect of plasma screening on nuclear reaction rates functions of ions in binary ionic mixtures. We calculate the reaction rates in a wide range of plasma

2009-01-01

234

A simple program to determine the reaction rate and thermodynamic properties of reacting system  

E-print Network

A simple program to determine the reaction rate and thermodynamic properties of reacting system program to determine the reaction rate by using conventional transition state theory with the Wigner in the reaction NH3 H ! NH2 H2 is used as a model to demonstrate the program usage. The rate constants have

235

Reaction rate calculation with time-dependent invariant manifolds Thomas Bartsch,1  

E-print Network

Reaction rate calculation with time-dependent invariant manifolds Thomas Bartsch,1 F. Revuelta,2 R 2012) The identification of trajectories that contribute to the reaction rate is the crucial dynamical, and used in a formally exact reaction rate calculation based on perturbation theory for any

236

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

E-print Network

Test of the quantum instanton approximation for thermal rate constants for some collinear reactions of the recently developed quantum instanton QI model for calculating thermal rate constants of chemical reactions. To this end we have recently developed a theory for calculating thermal rate constants of chemical reactions

Miller, William H.

237

Supplementary Material 1: Simulation Results Effective Reaction Rates The `in vitro' numbers (mean and  

E-print Network

Supplementary Material 1: Simulation Results Effective Reaction Rates The `in vitro' numbers (mean number of S molecules is smaller, which means that the in vivo reaction rate (consuming the S molecules) is faster than the in vitro reaction rate. Time step in the simulations: (from top to bottom) t = 2.667x10

Lygeros, John

238

Solutions to a Reduced PoissonNernstPlanck System and Determination of Reaction Rates  

E-print Network

Solutions to a Reduced Poisson­Nernst­Planck System and Determination of Reaction Rates Bo Li to the underlying re- duced PNP system, and calculate the reaction rate for the reactive species. We give a rigorous dependence of the reaction rates of the reactive species on the magnitude of its far field concentration

Li, Bo

239

Eective rate constant of ferriin reduction in the BelousovZhabotinsky reaction  

E-print Network

Eective rate constant of ferriin reduction in the BelousovZhabotinsky reaction J. Ungvarai,a Zsed Oregonator model. The frequently used rate constant for the reaction between ferriin and the organic~5 The mechanism of the BelousovZhabotinsky (BZ) reaction, including a thermodynamically consistent set of rate

Enderlein, Jrg

240

Four-Angle Saturation Transfer (FAST) Method for Measuring Creatine Kinase Reaction Rates In Vivo  

E-print Network

Four-Angle Saturation Transfer (FAST) Method for Measuring Creatine Kinase Reaction Rates In Vivo of measuring kinetic reaction rates for two-site chemical exchange is described. The method employs saturation different flip angles, and the equilibrium magnetization, relaxation times, and reaction rates

Ouwerkerk, Ronald

241

Role of Fitted Reaction Rates in Predicting Thrombin Pro-Wenrui Hao1  

E-print Network

Role of Fitted Reaction Rates in Predicting Thrombin Pro- duction Wenrui Hao1 and Guang Lin2 model. Results: We have used a systematic approach to analyze how simulation fitted reaction rate the significance of the 16 data-fitted reaction rates with respect to the total thrombin production

Sommese, Andrew J.

242

A Method for Estimating In Situ Reaction Rates from Push-Pull Experiments for Arbitrary Solute  

E-print Network

A Method for Estimating In Situ Reaction Rates from Push-Pull Experiments for Arbitrary Solute, IN 47405-1405 Key Terms: Push-Pull Test, Reaction Rates, Numer- ical Modeling, Net Mass Transfer ABSTRACT This paper presents a general method and the mathematical equations for estimating in situ reaction rates

Zhu, Chen

243

Water-Splitting Photoelectrolysis Reaction Rate via Microscopic Imaging of Evolved Oxygen Bubbles  

E-print Network

Water-Splitting Photoelectrolysis Reaction Rate via Microscopic Imaging of Evolved Oxygen Bubbles of the gas-evolving reaction rate. Optical microscopy was used to record the bubble growth on single a focused argon laser. By analyzing the bubble size as a function of time, the water-splitting reaction rate

Atwater, Harry

244

PHYSICAL REVIEW C 72, 025806 (2005) Nuclear fusion in dense matter: Reaction rate and carbon burning  

E-print Network

PHYSICAL REVIEW C 72, 025806 (2005) Nuclear fusion in dense matter: Reaction rate and carbon a simple phenomenological formula for the reaction rate that covers all cases. The parameters of this formula can be varied to take into account current theoretical uncertainties in the reaction rate

2005-01-01

245

Up-Scaling Geochemical Reaction Rates Accompanying Acidic CO2-Saturated Brine Flow in Sandstone Aquifers  

E-print Network

1 Up-Scaling Geochemical Reaction Rates Accompanying Acidic CO2-Saturated Brine Flow in Sandstone modeling of reactive flow requires determination of effective reaction rates applicable to field scale-scaling of anorthite and kaolinite reaction rates from pore to core scales. Unique to our simulations is the use

New York at Stoney Brook, State University of

246

FIELD MEASUREMENT OF HIGH TEMPERATURE BULK REACTION RATES I: THEORY AND TECHNIQUE  

E-print Network

FIELD MEASUREMENT OF HIGH TEMPERATURE BULK REACTION RATES I: THEORY AND TECHNIQUE ETHAN F. BAXTER, California 94720 ABSTRACT. Knowledge of metamorphic reaction rates is crucial to accurately interpret rock, and material flux estimates, requires that local reaction rates among system phases are fast relative to local

Baxter, Ethan F.

247

The Treatment of NonInteger Exponents in Reaction Rate Expressions  

E-print Network

being supplied which give the rate of reaction as a function of local temperature and local. To be precise, the reaction rate depends expo­ nentially on temperature and so when the wall temperatureThe Treatment of Non­Integer Exponents in Reaction Rate Expressions A. Spencey \\Lambda D. J. Worthy

Bath, University of

248

Rate Constants for Reactions of Aliphatic Carbon-Centered Radicals in Aqueous Solution  

Microsoft Academic Search

Absolute rate constants for reactions of aliphatic carbon-centered radicals in aqueous solutions have been compiled and evaluated from the literature. Rate constants are included for reactions of radicals with inorganic and organic compounds and for decay by radicalradical reactions. The radicals were generated by radiolysis, photolysis, or other techniques, and their rate constants were determined generally by kinetic spectrophotometry. The

Pedatsur Neta; Jan Grodkowski; Alberta B. Ross

1996-01-01

249

Thermal and Microcanonical Rates of Unimolecular Reactions from an Energy Diffusion Theory Approach  

E-print Network

Thermal and Microcanonical Rates of Unimolecular Reactions from an Energy Diffusion Theory Approach and microcanonical unimolecular reaction rates by solving the general energy diffusion equation. The solution naturally provides the rates in the diffusion limit for fast reactions and the transition state theory (TST

Miller, William H.

250

Rates of ionic reactions with charged nanoparticles in aqueous media.  

PubMed

A theory is developed to evaluate the electrostatic correction for the rate of reaction between a small ion and a charged ligand nanoparticle. The particle is assumed to generally consist of an impermeable core and a shell permeable to water and ions. A derivation is proposed for the ion diffusion flux that includes the impact of the equilibrium electrostatic field distribution within and around the shell of the particle. The contribution of the extra- and intraparticulate field is rationalized in terms of a conductive diffusion factor, f(el), that includes the details of the particle geometry (core size and shell thickness), the volume charge density in the shell, and the parameters defining the electrostatic state of the particle core surface. The numerical evaluation of f(el), based on the nonlinear Poisson-Boltzmann equation, is successfully complemented with semianalytical expressions valid under the Debye-Hckel condition in the limits of strong and weak electrostatic screening. The latter limit correctly includes the original result obtained by Debye in his 1942 seminal paper about the effect of electrostatics on the rate of collision between two ions. The significant acceleration and/or retardation possibly experienced by a metal ion diffusing across a soft reactive particle/solution interphase is highlighted by exploring the dependence of f(el) on electrolyte concentration, particle size, particle charge, and particle type (i.e., hard, core/shell, and entirely porous particles). PMID:22074411

Duval, Jrme F L; van Leeuwen, Herman P

2012-06-28

251

Reexamination of reaction rates for a key stellar reaction of $^{14}$O($\\\\alpha$,p)$^{17}$F  

Microsoft Academic Search

The reaction rates of the key stellar reaction of $^{14}$O($\\\\alpha$,p)$^{17}$F have been reexamined. The previous conclusion, the 6.15-MeV state ($J^{\\\\pi}$=1$^-$) dominating this reaction rate, has been overthrown by a careful reanalysis of the previous experimental data [J. G\\\\'{o}mez del Campo {\\\\it et al.}, Phys. Rev. Lett. {\\\\bf 86}, 43 (2001)]. According to the present $R$-matrix analysis, the previous 1$^-$ assignment

J. J. He; H. W. Wang; J. Hu; L. Li; L. Y. Zhang; M. L. Liu; S. W. Xu; X. Q. Yu

2010-01-01

252

Kinetics of tetrabromobisphenol A (TBBPA) reactions with H?SO?, HNO? and HCl: implication for hydrometallurgy of electronic wastes.  

PubMed

Hydrometallurgy is an acid leaching based process widely used for recovering precious metals from electronic wastes (e-wastes). The effects of acid leaching on the fate of brominated flame retardants (BFRs) in typical hydrometallurgical processes remain largely unknown. This study was aimed at evaluating the fate of tetrabromobisphenol A (TBBPA), a commonly used BFR, in three acid leaching reagents (i.e. H2SO4, HNO3, and HCl) commonly used in hydrometallurgy. It was found that the reactions of TBBPA with concentrated H2SO4 followed a pseudo-zero-order rate and the reaction rates declined rapidly as the concentrations of H2SO4 decreased. In contrast, TBBPA could be easily transformed in less concentrated HNO3 solutions (<21.7 wt%) and the reactions followed a pseudo-first-order rate. The reaction products identified by GC-MS indicated different transformation pathways of TBBPA in H2SO4 and HNO3. HCl or HCl/H2SO4 mixtures (3:1, v/v) did not appear to react with TBBPA, while aqua regia (3:1 HCl/HNO3, v/v) reacted violently with TBBPA and led to almost complete disappearance of TBBPA within a minute. It suggested that HNO3 significantly affected the fate of TBBPA and the use of HNO3 as leaching reagents in hydrometallurgy of e-wastes should be carefully evaluated. Collectively, our findings of distinct fate of TBBPA in different acid leaching reagents provided fundamental information for design of hydrometallurgical treatment of e-wastes to minimize acid reactions with BFRs within plastics matrix and to maximize acid leaching efficiency for metals recycling processes. PMID:24594840

Zhong, Yin; Li, Dan; Mao, Zhe; Huang, Weilin; Peng, Ping'an; Chen, Pei; Mei, Jun

2014-04-15

253

Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows.  

SciTech Connect

This report summarizes the work completed during FY2009 for the LDRD project 09-1332 'Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows'. The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary nonequilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological non-equilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, the difference between the two models can exceed 10 orders of magnitude. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates. Extensions of the model to reactions typically found in combustion flows and ionizing reactions are also found to be in very good agreement with available measurements, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

2009-08-01

254

Reaction-rate, mixture-fraction, and temperature imaging in turbulent methane\\/air jet flames  

Microsoft Academic Search

Instantaneous two-dimensional measurements of reaction rate, mixture fraction, and temperature are demonstrated in turbulent partially premixed methane\\/air jet flames. The forward reaction rate of the reaction CO OH ? CO2 H is measured by simultaneous OH laser-induced fluorescence (LIF) and two-photon CO LIF. The product of the two LIF signals is shown to be proportional to the reaction rate. Temperature

Jonathan H. Frank; Sebastian A. Kaiser; Marshall B. Long

2002-01-01

255

The influence of steric hindrance on kinetics and isotope effects in the reaction of 2,2-bis(4-dimethylaminophenyl)-1-nitro-1-(4-nitrophenyl)ethane with DBU base in acetonitrile  

NASA Astrophysics Data System (ADS)

The pKa value for 2,2-bis(4-dimethylaminophenyl)-1-nitro-1-(4-nitrophenyl)ethane, (dmap)2 (pKa = 25.11) has been measured spectrophotometrically using buffer solutions of a few strong amine bases: 1,8-diazabicyclo[5.4.0]undec-7-ene, (DBU); 1,1,3,3-tetramethylguanidine, (TMG); 1,5,7-triazabicyclo[4.4.0]dec-5-ene, (TBD); 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, (MTBD) and their salts. The low energy conformers of nitrophenyl nitroalkanes have been determined using the semiempirical PM6 methods, (B3-LYP) density functional theory (DFT) together with the 6-31G(d,p) basis set. The participation of the low energy conformer in the proton transfer reaction to DBU base has been discussed. The kinetic data for proton transfer reactions between (dmap)2 and DBU in acetonitrile (MeCN) at pseudo-first order conditions have been presented. The influence of steric hindrance brought by reacting C-acid and organic base on the stability of the transition state has been discussed. The rates of second-order rate constants for series of nitrophenyl nitroalkanes, NO2PhCHRNO2 (R = Me; Et; iPr; dimethylaminophenyl = (dmap)2) are presented and discussed.

Nowak, Iwona; Jarczewski, Arnold

2014-11-01

256

Reaction kinetics of CO2 absorption in to phosphonium based anion-functionalized ionic liquids.  

PubMed

The reaction kinetics between CO2 and trihexyl(tetradecyl)phosphonium ([P66614])-based ionic liquids (ILs) with prolinate ([Pro]), 2-cyanopyrrolide ([2-CNpyr]), and 3-(trifluoromethyl)pyrazolide ([3-CF3pyra]) anions are studied at temperatures from 22-60 C. The absorption of CO2 is carried out in a stirred reactor under pseudo first order conditions. ILs are diluted to concentrations of 0.05, 0.1 and 0.15 M with tetraglyme--a nonreactive, low volatility solvent with much lower viscosity than the ILs. Physical solubility of CO2 in the mixtures is calculated using correlations developed from CO2 solubility measurements in tetraglyme and the N2O-analogy for ILs and dilute IL solutions. The diffusivity of CO2 is estimated from viscosity-dependent correlations chosen after a thorough literature review. The results indicate partial first order reaction kinetics with respect to IL with values ranging from 19,500 L mol(-1) s(-1) ([P66614][Pro]) to 3200 L mol(-1) s(-1) ([P66614][3-CF3pyra]) at 22 C. The second order reaction rate constants follow Arrhenius behavior with the highest activation energy of 43 kJ mol(-1) measured for [P66614][Pro]. ILs with aprotic heterocylic anions (AHA), on the other hand, show small activation energies of 18 and 11 kJ mol(-1) for [P66614][3-CF3pyra] and [P66614][2-CNpyr], respectively. The ILs studied in this work exhibit reactivity comparable to or higher than common aqueous amines. High reaction rates and tunable capacity make ILs, and AHA ILs in particular, attractive solvents for CO2 separations. PMID:23598368

Gurkan, Burcu E; Gohndrone, Thomas R; McCready, Mark J; Brennecke, Joan F

2013-05-28

257

Direct and Indirect Techniques for Determining Reaction Rates  

Microsoft Academic Search

Astrophysically important reactions have been studied through indirect techniques for many years due to their prohibitively small cross sections at Gamow window energies. Indirect techniques, such as alpha-transfer reactions, constrain the reaction cross section of interest in the astrophysically relevant energy range. Recently, we determined the contribution of the 3^- state at 6.4 MeV in ^18O to the ^14C(,) reaction

Eric Johnson

2009-01-01

258

Determination of reaction rate parameters using heat conduction microcalorimetry  

Microsoft Academic Search

By using the LKB 2277 thermal activity monitor, it is demonstrated that both ampoule and flow-through modes can be used to monitor the reaction parameters for chemical reactions. Theoretical relationships applicable to first-order reactions are proposed and compared with those reported in the literature. Mathematical relationships applicable to second-order reactions are also proposed. The experimental results confirmed the validity of

A. Bakri; L. H. M. Janssen; J. Wilting

1988-01-01

259

Pressure Dependence of Gas-Phase Reaction Rates  

ERIC Educational Resources Information Center

It is presented that only simple concepts, mainly taken from activated-complex or transition-state theory, are required to explain and analytically describe the influence of pressure on gas-phase reaction kinetics. The simplest kind of elementary gas-phase reaction is a unimolecular decomposition reaction.

De Persis, Stephanie; Dollet, Alain; Teyssandier, Francis

2004-01-01

260

Neutron detector for fusion reaction-rate measurements  

SciTech Connect

We have developed a fast, sensitive neutron detector for recording the fusion reaction-rate history of inertial-confinement fusion (ICF) experiments. The detector is based on the fast rise-time of a commercial plastic scintillator (BC-422) and has a response < 25-ps FWHM. A thin piece of scintillator material acts as a neutron-to- light converter. A zoom lens images light from the scintillator surface to a high-speed (15 ps) optical streak camera for recording. The zoom lens allows the scintillator to be positioned between 1 and 50 cm from a target. The camera simulaneously records an optical fiducial pulse which allows the camera time base to be calibrated relative to the incident laser power. Bursts of x rays formed by focusing 20-ps, 2.5-TW laser pulses onto gold disk targets demonstrate the detector resolution to be < 25 ps. We have recorded burn histories for deuterium/tritium-filled targets producing as few as 3 {times} 10{sup 7} neutrons.

Lerche, R.A.; Phillion, D.W.; Tietbohl, G.L.

1993-09-03

261

Enhanced reaction rates in NDP analysis with neutron scattering  

SciTech Connect

Neutron depth profiling (NDP) makes accessible quantitative information on a few isotopic concentration profiles ranging from the surface into the sample a few micrometers. Because the candidate analytes for NDP are few, there is little interference encountered. Furthermore, neutrons have no charge so mixed chemical states in the sample are of no direct concern. There are a few nuclides that exhibit large probabilities for neutron scattering. The effect of neutron scattering on NDP measurements has not previously been evaluated as a basis for either enhancing the reaction rates or as a source of measurement error. Hydrogen is a common element exhibiting large neutron scattering probability found in or around sample volumes being analyzed by NDP. A systematic study was conducted to determine the degree of signal change when neutron scattering occurs during analysis. The relative signal perturbation was evaluated for materials of varied neutron scattering probability, concentration, total mass, and geometry. Signal enhancements up to 50% are observed when the hydrogen density is high and in close proximity to the region of analysis with neutron beams of sub thermal energies. Greater signal enhancements for the same neutron number density are reported for thermal neutron beams. Even adhesive tape used to position the sample produces a measureable signal enhancement. Because of the shallow volume, negligible distortion of the NDP measured profile shape is encountered from neutron scattering.

Downing, R. Gregory, E-mail: gregory.downing@nist.gov [National Institute of Standards and Technology, Chemical Sciences Division, Gaithersburg, Maryland 20899 (United States)

2014-04-15

262

Reevaluation of the 23Mg(p,?) 24 Al reaction rate  

Microsoft Academic Search

Based on a new screening Coulomb model, this paper discusses the effect of electron screening on proton capture reaction of 23Mg. The derived result shows that, in some considerable range of stellar temperatures, the effect of electron screening on resonant reaction is prominent; on the non-resonant reaction the effect is obvious only in the low stellar temperatures. The reaction rates

Liu Hong-Lin; Liu Men-Quan; Lai Xiang-Jun; Luo Zhi-Quan

2007-01-01

263

Rates of hydration reactions in crustal shear zones and their implications for temporal variations in rheology  

Microsoft Academic Search

Crustal shear zones are commonly accompanied by retrograde metamorphism of pre-existing higher grade rocks. The retrograde reactions involve hydration, but the localisation of the retrogression suggests that reaction is limited by either the availability of water or the effect of deformation on reaction kinetics. Depending on the rate of retrograde hydration reactions, shear zones may either be uniformly wet for

B. W. D. Yardley; D. E. Harlov; W. Heinrich

2009-01-01

264

Depletion: A Game with Natural Rules for Teaching Reaction Rate Theory  

Microsoft Academic Search

Depletion is a game that reinforces central concepts of reaction rate theory through simulation. Each player buys chemicals and guides them through a series of reactions, thereby earning money to buy more chemicals. The reactions occur when players roll a high enough value on two dice to overcome an activation barrier. The reactions may be accelerated by buying heat (which

Donald J. Olbris; Judith Herzfeld

2002-01-01

265

Influence of chemical kinetics on postcolumn reaction in a capillary Taylor reactor with catechol analytes and photoluminescence following electron transfer.  

PubMed

Postcolumn derivatization reactions can enhance detector sensitivity and selectivity, but their successful combination with capillary liquid chromatography has been limited because of the small peak volumes in capillary chromatography. A capillary Taylor reactor (CTR), developed in our laboratory, provides simple and effective mixing and reaction in a 25-microm-radius postcolumn capillary. Homogenization of reactant streams occurs by radial diffusion, and a chemical reaction follows. Three characteristic times for a given reaction process can be predicted using simple physical and chemical parameters. Two of these times are the homogenization time, which governs how long it takes the molecules in the analyte and reagent streams to mix, and the reaction time, which governs how long the molecules in a homogeneous solution take to react. The third characteristic time is an adjustment to the reaction time called the start time, which represents an estimate of the average time the analyte stream spends without exposure to reagent. In this study, laser-induced fluorescence monitored the extent of the postcolumn reaction (reduction of Os(bpy)3(3+) by analyte to the photoluminescent Os(bpy)3(2+)) in a CTR. The reaction time depends on the reaction rates. Analysis of product versus time data yielded second-order reaction rate constants between the PFET reagent, tris(2,2'-bipyridine)osmium, and standards ((ferrocenylmethyl)trimethylammonium cation and p-hydroquinone) or catechols (dopamine, epinephrine, norepinephrine, 3, 4-dihydroxyphenylacetic acid. The extent of the reactions in a CTR were then predicted from initial reaction conditions and compared to experimental results. Both the theory and experimental results suggested the reactions of catechols were generally kinetically controlled, while those of the standards were controlled by mixing time (1-2 s). Thus, the extent of homogenization can be monitored in a CTR using the relatively fast reaction of the reagent and p-hydroquinone. Kinetically controlled reactions of catechols, however, could be also completed in a reasonable time at increased reagent concentration. A satisfactory reactor, operating at 1.7 cm/s (2 microL/min) velocity with solutes having diffusion coefficients in the 5 x 10(-6) cm2/s range, can be constructed from 8.0 cm of 25-microm-radius capillary. Slower reactions require longer reaction times, but theoretical calculations expect that a CTR does not broaden a chromatographic peak (N = 14 000) from a 100-microm-capillary chromatography column by 10% if the pseudo-first-order rate constant is larger than 0.1 s(-1). PMID:15858975

Jung, Moon Chul; Weber, Stephen G

2005-02-15

266

Low Temperature Rate Coefficients of the Ethynyl Radical  

NASA Astrophysics Data System (ADS)

The experiments performed for this dissertation involve measuring low temperature rate coefficients for the reactions of the ethynyl radical, C_2 H, with various molecular species important in the chemistry of the outer planets and Titan. The specific experiments entail measuring the reaction rate coefficients of C_2H with the following species: C_2H_2, O_2, CH_4, CD_4, C_2H _4, C_2H_6, and H _2, from 143 to 359 K. All rate coefficients measured in this thesis are obtained with a technique called flash kinetic infrared absorption spectroscopy. The ethynyl radicals are produced in a meter long transverse flow cell by acetylene photolysis with a pulsed excimer laser at 193 nm. The ethynyl radical is probed with a tunable color center laser in absorption as it reacts with various molecular species under pseudo first-order conditions. The decay traces are all fit to single exponential decays to obtain time constants which, when corrected for the reaction of C_2H _2 precursor and C_2H, can be plotted against their respective concentrations of reacting species to obtain a rate constant. This procedure is then repeated at numerous temperatures from 143-359 K to obtain an Arrhenius plot of each separate C _2H reaction. Once an Arrhenius plot is made, the energy of activation, E_{ rm a}, can be found for the reaction if it obeys the Arrhenius expression k(T)=A exp(-E_{rm a}/RT), where k(T) is the rate constant as a function of temperature, A is the pre-exponential factor, R is the molar gas constant equal to 8.314 J mol^{-1}K ^{-1}, and T is the temperature in K. The reactions of C_2H with C_2H_2, C _2H_4, C_2H _6 and O_2 all show evidence of a negative temperature dependence over the experimental conditions and the reaction of C_2 H + C_2H_2 even displays some curvature around 143 K. This is evidence of an addition-elimination mechanism with little or no barrier to complex formation before undergoing unimolecular decomposition. The reactions of C_2H with CH_4, CD_4, and H_2 all show a positive temperature dependence over the experimental conditions.

Opansky, Brian Joseph

267

"Depletion": A Game with Natural Rules for Teaching Reaction Rate Theory.  

ERIC Educational Resources Information Center

Depletion is a game that reinforces central concepts of reaction rate theory through simulation. Presents the game with a set of follow-up questions suitable for either a quiz or discussion. Also describes student reaction to the game. (MM)

Olbris, Donald J.; Herzfeld, Judith

2002-01-01

268

Acidbase chemical reaction model for nucleation rates in the polluted atmospheric boundary layer  

E-print Network

Acidbase chemical reaction model for nucleation rates in the polluted atmospheric boundary layer for modeling nucleation rates, based on a sequence of acidbase reactions. The model uses empirical estimates, therefore, the earth's radiation budget. Measurements worldwide show that nucleation rates in the atmo

269

Acceleration of Key Reactions as a Strategy to Elucidate the Rate-Limiting Chemistry Underlying  

E-print Network

Acceleration of Key Reactions as a Strategy to Elucidate the Rate-Limiting Chemistry Underlying approach for identifying the rate-limiting step in a series of reactions is to evaluate the consequences PURPOSE. A reconstituted system was used to establish a strat- egy to determine the rate

Wensel, Theodore G.

270

Effect of Finite-rate Chemical Reactions on Turbulence in Hypersonic Turbulent Boundary Layers  

E-print Network

Effect of Finite-rate Chemical Reactions on Turbulence in Hypersonic Turbulent Boundary Layers Lian and the reaction rate is typically temperature Ph.D. Student, Department of Mechanical and Aerospace Engineering simulations of reacting turbulent boundary layers to study the effects of finite-rate chemistry on turbulence

Martín, Pino

271

SHEAR LOCALIZATION AND CHEMICAL REACTION IN HIGH-STRAIN, HIGH-STRAIN-RATE DEFORMATION OF  

E-print Network

SHEAR LOCALIZATION AND CHEMICAL REACTION IN HIGH-STRAIN, HIGH-STRAIN-RATE DEFORMATION OF Ti.61 mm. Thermodynamic and kinetic calculations yield the reaction rate outside the shear bands.S.A. (Received 19 June 1997; accepted 19 December 1997) AbstractTiSi mixtures were subjected to high-strain-rate

Meyers, Marc A.

272

Gasification of coal char with steam. Part 1. Analysis of reaction rate  

Microsoft Academic Search

Tests on the steam gasification of activated carbon produced from brown and bituminous coal chars demonstrated that the gasification rate is affected by reaction-generated changes in pore structure. Investigating temperature dependence, steam partial pressure, and char pore structure at atmospheric conditions, researchers concluded that the (1) gasification rate is proportional to the steam partial pressure, (2) reaction rate increases with

G. Chin; S. Kimura; S. Tone; T. Otake

1983-01-01

273

Development of the new approach to the diffusion-limited reaction rate theory  

SciTech Connect

The new approach to the diffusion-limited reaction rate theory, recently proposed by the author, is further developed on the base of a similar approach to Brownian coagulation. The traditional diffusion approach to calculation of the reaction rate is critically analyzed. In particular, it is shown that the traditional approach is applicable only in the special case of reactions with a large reaction radius and the mean inter-particle distances, and become inappropriate in calculating the reaction rate in the case of a relatively small reaction radius. In the latter case, most important for chemical reactions, particle collisions occur not in the diffusion regime but mainly in the kinetic regime characterized by homogeneous (random) spatial distribution of particles on the length scale of the mean inter-particle distance. The calculated reaction rate for a small reaction radius in three dimensions formally (and fortuitously) coincides with the expression derived in the traditional approach for reactions with a large reaction radius, but notably deviates at large times from the traditional result in the planar two-dimensional geometry. In application to reactions on discrete lattice sites, new relations for the reaction rate constants are derived for both three-dimensional and two-dimensional lattices.

Veshchunov, M. S., E-mail: vms@ibrae.ac.ru [Russian Academy of Sciences, Nuclear Safety Institute (IBRAE) (Russian Federation)

2012-04-15

274

A turbulent reaction rate model for premixed turbulent combustion in spark-ignition engines  

Microsoft Academic Search

A new reaction rate model has been developed and validated for premixed turbulent combustion in spark-ignition (SI) engines. The formulation is within the context of the BrayMossLibby (BML) formalism for turbulent transport in premixed flames. The laminar flamelet concept is employed to split the volumetric reaction rate into a reaction rate per unit surface area and a surface area per

G. M. Abu-Orf; R. S. Cant

2000-01-01

275

Reaction rate constant of SO sub 3 + NH sub 3 in the gas phase  

Microsoft Academic Search

The reaction rate constant of SO + NH in the gas phase was measured using a photofragment emission flow tube technique. The reaction rate constant at room temperature is (6.9 {plus minus} 1.5) 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ at He pressures of 1-2 torr. This measured reaction rate is new information for studying the formation process of ammonium sulfates in

Gaunlin Shen; Masako Suto; L. C. Lee

1990-01-01

276

Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows  

Microsoft Academic Search

This report summarizes the work completed during FY2009 for the LDRD project 09-1332 'Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows'. The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates

Michail A. Gallis; Ryan Bomar Bond; John Robert Torczynski

2009-01-01

277

Proton-induced Thermonuclear Reaction Rates for A=20-40 Nuclei  

Microsoft Academic Search

Proton-induced reaction rates on 26 stable and 29 unstable target nuclei in the mass A=20-40 region have been evaluated and compiled. Recommended reaction rates, assuming that all interacting nuclei are in the ground state, are presented in tabular form on a temperature grid in the range T=0.01-10.0 GK. Most reaction rates involving stable targets were normalized to a set of

Christian Iliadis; John M. D'Auria; Sumner Starrfield; William J. Thompson; Michael Wiescher

2001-01-01

278

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

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

279

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

NASA Astrophysics Data System (ADS)

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

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

1997-10-01

280

Effect of macromolecular crowding on reaction rates: a computational and theoretical study.  

PubMed

The effect of macromolecular crowding on the rates of association reactions are investigated using theory and computer simulations. Reactants and crowding agents are both hard spheres, and when two reactants collide they form product with a reaction probability, p(rxn). A value of p(rxn) < 1 crudely mimics the fact that proteins must be oriented properly for an association reaction to occur. The simulations show that the dependence of the reaction rate on the volume fraction of crowding agents varies with the reaction probability. For reaction probabilities close to unity where most of encounters between reactants lead to a reaction, the reaction rate always decreases as the volume fraction of crowding agents is increased due to the reduced diffusion coefficient of reactants. On the other hand, for very small reaction probabilities where, in most of encounters, the reaction does not occur, the reaction rate increases with the volume fraction of crowding agents--in this case, due to the increase probability of a recollision. The Smoluchowski theory refined with the radiation boundary condition and the radial distribution function at contact is in quantitative agreement with simulations for the reaction rate constant and allows the quantitative analysis of both effects separately. PMID:19217851

Kim, Jun Soo; Yethiraj, Arun

2009-02-18

281

Direct ab initio dynamics studies of vibrational-state selected reaction rate of the OH H2~H H2O reaction  

E-print Network

Direct ab initio dynamics studies of vibrational-state selected reaction rate of the OH H2~H H2O of vibrational-state selected reaction rates of the OH H2H H2O reaction. Rate constants for both the OH H2 v 1 on the reaction rate of bimo- lecular reactions have been a focus of many theoretical and experimental studies

Truong, Thanh N.

282

Atmospheric chemistry of hydrazoic acid (HN3): UV absorption spectrum, HO reaction rate, and reactions of the N3 radical.  

PubMed

Processes related to the tropospheric lifetime and fate of hydrazoic acid, HN3, have been studied. The ultraviolet absorption spectrum of HN3 is shown to possess a maximum near 262 nm with a tail extending to at least 360 nm. The photolysis quantum yield for HN3 is shown to be approximately 1 at 351 nm. Using the measured spectrum and assuming unity quantum yield throughout the actinic region, a diurnally averaged photolysis lifetime near the earth's surface of 2-3 days is estimated. Using a relative rate method, the rate coefficient for reaction of HO with HN3 was found to be (3.9 +/-0.8) x 10(-12) cm3 molecule(-1) s(-1), substantially larger than the only previous measurement. The atmospheric HN3 lifetime with respect to HO oxidation is thus about 2-3 days, assuming a diurnally averaged [HO] of 10(6) molecule cm(-3). Reactions of N3, the product of the reaction of HO with HN3, were studied in an environmental chamber using an FTIR spectrometer for end-product analysis. The N3 radical reacts efficiently with NO, producing N2O with 100% yield. Reaction of N3 with NO2 appears to generate both NO and N2O, although the rate coefficient for this reaction is slower than that for reaction with NO. No evidence for reaction of N3 with CO was observed, in contrast to previous literature data. Reaction of N3 with O2 was found to be extremely slow, k < 6 x 10(-20) cm3 molecule(-1) s(-1), although this upper limit does not necessarily rule out its occurrence in the atmosphere. Finally, the rate coefficient for reaction of Cl with HN3 was measured using a relative rate method, k = (1.0+/-0.2) x 10(-12) cm3 molecule(-1) s(-1). PMID:15819219

Orlando, John J; Tyndall, Geoffrey S; Betterton, Eric A; Lowry, Joe; Stegall, Steve T

2005-03-15

283

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

NASA Technical Reports Server (NTRS)

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.

DeMore, W.; Bayes, K.

1998-01-01

284

Effect of temperature oscillation on chemical reaction rates in the atmosphere  

NASA Technical Reports Server (NTRS)

The effect of temperature fluctuations on atmospheric ozone chemistry is examined by considering the Chapman photochemical theory of ozone transport to calculate globally averaged ozone production rates from mean reaction rates, activation energies, and recombination processes.

Eberstein, I. J.

1974-01-01

285

Quick and Easy Rate Equations for Multistep Reactions  

ERIC Educational Resources Information Center

Students rarely see closed-form analytical rate equations derived from underlying chemical mechanisms that contain more than a few steps unless restrictive simplifying assumptions (e.g., existence of a rate-determining step) are made. Yet, work published decades ago allows closed-form analytical rate equations to be written quickly and easily for

Savage, Phillip E.

2008-01-01

286

Reactions and reaction rates in the regional aquifer beneath the Pajarito Plateau, north-central New Mexico, USA  

NASA Astrophysics Data System (ADS)

Reactions and reaction rates within aquifers are fundamental components of critical hydrological processes. However, reactions simulated in laboratory experiments typically demonstrate rates that are much faster than those observed in the field. Therefore, it is necessary to conduct more reaction rate analyses in natural settings. This study of geochemical reactions in the regional aquifer in the Pajarito Plateau near Los Alamos, New Mexico combines modeling with petrographic assessment to further knowledge and understanding of complex natural hydrologic systems. Groundwater geochemistry shows marked evolution along assumed flow paths. The flow path chosen for this study was evaluated using inverse mass balance modeling to calculate the mass transfer. X-ray diffraction and field emission gun scanning electron microscopy were used to identify possible reactants and products. Considering the mineralogy of the aquifer and saturation indices for the regional water refined initial interpretations. Calculations yielded dissolution rates for plagioclase on the order of 10-15 mol s-1 m-2 and for K-feldspar on the order of 10-17 mol s-1 m-2, orders of magnitude slower than laboratory rates. While these rates agree with other aquifer studies, they must be considered in the light of the uncertainty associated with geometric surface area estimates, 14C ages, and aquifer properties.

Hereford, Anne G.; Keating, Elizabeth H.; Guthrie, George D.; Zhu, Chen

2007-05-01

287

HIGH-TEMPERATURE REACTION RATES OF SEVERAL METALS WITH HYDROGEN CHLORIDE AND WATER VAPOR  

Microsoft Academic Search

An experimental study was made of the hightemperature reaction rates of ; various metal filaments with HCl and H0 vapors and mixtures of the two. ; Measurements were made by an electrical method in which the change in resistance ; of the metal filament was related to the loss in pure metal due to the vapor-; metal reaction. Measurable reaction

Milton Farber

1959-01-01

288

The effect of reagent energy on chemical reaction rates: An information theoretic analysis  

Microsoft Academic Search

The effect of changing reagent vibrational and rotational energy on the reaction rate has been analyzed for over 20 chemical reactions. In most cases the selectivity in energy requirements could be characterized by a single (''consumption potential'') parameter, even when the reactivity varied by many orders of magnitude. The reactions analyzed covered atom-diatom and diatom-diatom collisions and included both simple

R. D. Levine; J. Manz

1975-01-01

289

Estimation of the Mutation Rate during Error-prone Polymerase Chain Reaction  

E-print Network

Estimation of the Mutation Rate during Error-prone Polymerase Chain Reaction Dai Wang1 , Cheng-prone polymerase chain reaction (PCR) is widely used to introduce point mutations during in vitro evolution step of in vitro evolution is mutagenesis. Error-prone polymerase chain reaction (PCR) (Leung et al

Sun, Fengzhu - Sun, Fengzhu

290

Isotope effects for formaldehyde plus hydrogen addition and abstraction reactions: rate calculations including tunnelling  

Microsoft Academic Search

Tunnelling plays a crucial role in the low-temperature chemistry in the interstellar medium (ISM), in particular for reactions involving hydrogen atoms. Using harmonic quantum transition state theory we studied reaction rates down to 20 K including tunnelling effects for the gas phase reaction of formaldehyde with hydrogen atoms, paying particular attention to isotope effects. Hydrogen atoms can either add to

T. P. M. Goumans

2011-01-01

291

The Effects of New Nuclear Reaction Rates and Opacities on Hydrodynamic Simulations of the Nova Outburst  

Microsoft Academic Search

We report on the results of new calculations of thermonuclear runaways on 1.25 Msolar oxygen, neon, and magnesium white dwarfs, using our one-dimensional, fully implicit, hydrodynamic stellar evolution code that includes a large nuclear reaction network. We have updated the nuclear reaction network by including both new and improved experimental and theoretical determinations of the nuclear reaction rates. We have

S. Starrfield; W. M. Sparks; J. W. Truran; M. C. Wiescher

2000-01-01

292

Reaction rate oscillations during catalytic CO oxidation: A brief overview  

NASA Technical Reports Server (NTRS)

It is not the intent here to present a comprehensive review of the dynamic behavior of the catalytic oxidation of CO. This reaction is one of the most widely studied in the field of catalysis. A review paper by Engel and Ertl has examined the basic kinetic and mechanistic aspects, and a comprehensive paper by Razon and Schmitz was recently devoted to its dynamic behavior. Those interested in further study of the subject should consult these reviews and a number of general review papers on catalytic reaction dynamics. The goal is to present a brief overview of certain interesting aspects of the dynamic behavior of this reaction and to discuss a few questions and issues, which are still the subject of study and debate.

Tsotsis, T. T.; Sane, R. C.

1987-01-01

293

Evolutionary implications of the new triple-alpha nuclear reaction rate for low mass stars  

Microsoft Academic Search

Context: Ogata et al. (2009, Progr. Theor. Phys., 122, 1055) presented a theoretical determination of the ^4He(alphaalpha,gamma)12C, or triple-alpha, nuclear reaction rate. Their rate differs from the NACRE rate by many orders of magnitude at temperatures relevant for low mass stars. Aims: We explore the evolutionary implications of adopting the OKK triple-alpha reaction rate in low mass stars and compare

Aaron Dotter; Bill Paxton

2009-01-01

294

Modelling Thermal Runaway and Criticality in Systems with Diminishing Reaction Rates: The Uniform Temperature (Semenov) Approximation  

Microsoft Academic Search

Various complex exothermic oxidations of considerable technical importance can be represented by an empirical rate-law in which the isothermal reaction rate diminishes with the elapsed time t according to rate propto t-alpha or, more generally, rate propto (t+tpr)-alpha. Here tpr is a 'prior reaction' time and the exponent alpha lies between 0 and 1. We have computed the generalized behaviour

T. Boddington; P. Gray; S. K. Scott

1982-01-01

295

Interlaboratory reaction rate program. 12th progress report, November 1976-October 1979  

SciTech Connect

The Interlaboratory Reaction Rate UILRR) program is establishing the capability to accurately measure neutron-induced reactions and reaction rates for reactor fuels and materials development programs. The goal for the principal fission reactions, /sup 235/U, /sup 238/U and /sup 239/Pu, is an accuracy to within +- 5% at the 95% confidence level. Accurate measurement of other fission and nonfission reactions is also required, but to a lesser accuracy, between +- 5% and 10% at the 95% confidence level. A secondary program objective is improvement in knowledge of the nuclear parameters involved in the standarization of fuels and materials dosimetry measurements of neutron flux, spectra, fluence and burnup.

Lippincott, E.P.; McElroy, W.N.; Preston, C.C. (comps.)

1980-09-01

296

Fluctuating reaction rate and non-exponential blinking statistics in single-enzyme kinetics  

NASA Astrophysics Data System (ADS)

Extending the Michaelis-Menten kinetic scheme, we consider a three-state diffusion-controlled reaction model to investigate the effects of fluctuating reaction rate on the blinking statistics of single-enzyme catalytic reactions. As a result of conformational changes, the barrier-height and the reaction rate for the bottleneck enzymatic reaction could fluctuate in time, leading to non-exponential blinking statistics. To illustrate model applications, some reported experimental data for single ?-galactosidase molecules were reanalyzed here to extract useful kinetic parameters.

Tang, Jau; Yeh, Yi-Cheun; Tai, Po-Tse

2008-09-01

297

THE {sup 8}Li({alpha}, n){sup 11}B REACTION RATE AT ASTROPHYSICAL TEMPERATURES  

SciTech Connect

At temperatures (0.5-1.2) x 10{sup 9} K, the {sup 8}Li + {sup 4}He {yields} {sup 11}B+n reaction can allow for {sup 12}C and heavier element production in the framework of the inhomogeneous big bang nucleosynthesis. At temperatures (2.5-5) x 10{sup 9} K, it can influence the production of seed nuclei, later burnt to heavier elements by means of rapid neutron capture reactions, during Type II supernova explosions. Previous determinations of the reaction rate show an untenable disagreement. In this work, a new reaction rate calculation is proposed for the intervals of astrophysical interest. This new recommendation turns out to be up to a factor of five larger than the most recent rate in the literature, thus enforcing the role of {sup 8}Li + {sup 4}He {yields} {sup 11}B+n as a candidate for key astrophysical reactions. The analytical expression of the recommended reaction rate is given.

La Cognata, Marco; Del Zoppo, Antonio, E-mail: delzoppo@lns.infn.it [INFN-Laboratori Nazionali del Sud, Via S. Sofia 62, I95123 Catania (Italy)

2011-08-01

298

Influence of the microsilica state on pozzolanic reaction rate  

Microsoft Academic Search

Silica fume is generally supplied as an ultrafine powder in its original state, densified or in suspension. The difference in states should not influence the pozzolanic behaviour of this by-product in a cementitious matrix. In the present work, experimental results relating to pozzolanic reaction have been obtained by different methods: a chemical method, in which lime fixed by pozzolanic material

M. I. Snchez de Rojas; J. Rivera; M. Fr??as

1999-01-01

299

Matching of experimental and statistical-model thermonuclear reaction rates at high temperatures  

Microsoft Academic Search

Reliable reaction rates at high stellar temperatures are necessary for the study of advanced stellar burning stages, supernovae and x-ray bursts. We suggest a new procedure for extrapolating experimental thermonuclear reaction rates to these higher temperatures (T > 1 GK) using statistical model (Hauser-Feshbach) results. Current, generally accepted, procedures involve the use of the Gamow peak, which has been shown

Joseph Newton; Richard Longland; Christian Iliadis

2009-01-01

300

BRUSLIB and NETGEN: the Brussels nuclear reaction rate library and nuclear network generator for astrophysics  

Microsoft Academic Search

Nuclear reaction rates are quantities of fundamental importance in astrophysics. Substantial efforts have been devoted in the last decades to measuring or calculating them. This paper presents a detailed description of the Brussels nuclear reaction rate library BRUSLIB and of the nuclear network generator NETGEN. BRUSLIB is made of two parts. The first one contains the 1999 NACRE compilation based

M. Aikawa; M. Arnould; S. Goriely; A. Jorissen; K. Takahashi

2005-01-01

301

Overall Rate Constant Measurements of the Reaction of Chloroalkylperoxy Radicals with Nitric Oxide  

E-print Network

Overall Rate Constant Measurements of the Reaction of Chloroalkylperoxy Radicals with Nitric Oxide, Oberlin, Ohio 44074 ReceiVed: January 21, 2005; In Final Form: March 22, 2005 The overall rate constants of the NO reaction with chloroalkylperoxy radicals derived from the Cl-initiated oxidation of several atmospherically

Elrod, Matthew J.

302

Putting Reaction Rates and Collision Theory in the Hands of Your Students.  

ERIC Educational Resources Information Center

Describes a simulation that can be used to give concrete analogies of collision theory and the factors that affect reaction rates including temperature, concentration, catalyst, and molecular orientation. The simulation works best if done as an introduction to the concepts to help prevent misconceptions about reaction rates and collision theory.

Evenson, Andy

2002-01-01

303

Compilation and R-matrix analysis of Big Bang nuclear reaction rates  

E-print Network

We use the R-matrix theory to fit low-energy data on nuclear reactions involved in Big Bang nucleosynthesis. A special attention is paid to the rate uncertainties which are evaluated on statistical grounds. We provide S factors and reaction rates in tabular and graphical formats.

Pierre Descouvemont; Abderrahim Adahchour; Carmen Angulo; Alain Coc; Elisabeth Vangioni-Flam

2004-07-06

304

Microscopic theory of protein folding rates. II. Local reaction coordinates and chain dynamics  

E-print Network

Microscopic theory of protein folding rates. II. Local reaction coordinates and chain dynamics John paper. Local reaction coordinates are identified as collective growth modes of the unstable fluctuations of the backbone dihedral angles. We find that the folding rate depends linearly on the solvent friction for high

Takada, Shoji

305

A model to predict the thermal reaction norm for the embryo growth rate from field data  

E-print Network

., 2002) and growth rates (Gillooly et al., 2001), are affected by temperature.1 Egg incubationA model to predict the thermal reaction norm for the embryo growth rate from field data Marc Available online 23 August 2014 Keywords: Temperature Incubation Embryo Growth Norm of reaction Reptile

Girondot, Marc

306

Reexamination of Astrophysical Resonance Reaction Rate Equations for An Isolated, Narrow Resonance  

Microsoft Academic Search

The well-known astrophysical resonant reaction rate equations for an isolated narrow resonance have been reexamined. The validity of those `look reliable' assumptions used in deriving the analytic reaction rate equations has been checked, and the reality is they only hold for certain circumstances. Importantly an integration-range issue hidden in the classical integration equations has been revealed and it hints us

J. J. He; J. Hu; S. W. Xu; X. Q. Yu; L. Li; L. Y. Zhang

2009-01-01

307

RATE CONSTANT FOR THE REACTION OF OH RADICALS WITH DIACETYLENE AT 297 + OR - 2K  

EPA Science Inventory

Using a relative rate technique, the rate constant for the gas phase reaction of OH radicals with diacetylene, a reaction considered to be of importance in fuel-rich acetylene oxidation, has been determined at 297 + or - 2 K and atmospheric pressure....

308

Astrophysical reaction rate for \\/alpha(alphan,gamma)9Be by photodisintegration  

Microsoft Academic Search

We study the astrophysical reaction rate for the formation of 9Be through the three body reaction \\/alpha(alphan,gamma). This reaction is one of the key reactions which could bridge the mass gap at \\/A=8 nuclear systems to produce intermediate-to-heavy mass elements in alpha- and neutron-rich environments such as r-process nucleosynthesis in supernova explosions, s-process nucleosynthesis in asymptotic giant branch (AGB) stars,

K. Sumiyoshi; H. Utsunomiya; S. Goko; T. Kajino

2002-01-01

309

Absolute rate parameters for the reaction of ground state atomic oxygen with carbonyl sulfide  

NASA Technical Reports Server (NTRS)

The rate parameters for the reaction of O(3P) with carbonyl sulfide, O(3P) + OCS yields CO + SO, have been determined directly by monitoring O(3P) using the flash photolysis-resonance fluorescence technique. The value for reaction rate was measured over a temperature range of 263-502 K and the data were fitted to an Arrhenius expression with good linearity. A comparison of the present results with those from previous studies of this reaction is also presented.

Klemm, R. B.; Stief, L. J.

1974-01-01

310

Reaction rate constants of HO2 + O3 in the temperature range 233-400 K  

NASA Technical Reports Server (NTRS)

The reaction rate constants of HO2 + O3 were measured in the temperature range 233-400 K using a discharge flow system with photofragment emission detection. In the range 233-253 K, the constants are approximately a constant value, and then increase with increasing temperature. This result suggests that the reaction may have two different channels. An expression representing the reaction rate constants is presented.

Wang, Xiuyan; Suto, Masako; Lee, L. C.

1988-01-01

311

Screened triple-alpha reaction rate to produce carbon in stellar interiors  

Microsoft Academic Search

Recent experimental data for radiative width and resonance energy are used to find reaction rates and mean lifetimes for triple-alpha reaction affecting screening effect. The reaction rates are found to be drastically altered. Plots of various dimensionless parameters in temperature-density plane are given. The red-giant stage will be of short duration. The mean lifetimes for gravitationally collapsing stars are insignificantly

A. E. M. Khairozzaman

1983-01-01

312

Screened triple-alpha reaction rate to produce carbon in stellar interiors  

Microsoft Academic Search

Recent experimental data for radiative width and resonance energy are used to find reaction rates and mean lives for triple-alpha reaction affecting screening effect. The reaction rates are found to be drastically altered. Plots of various dimensionless parameters in temperature-density plane are given. The red-giant sttage will be of short duration. The mean lives for gravitationally collapsing stars are insignificantly

A. E. M. D. Khairozzaman

1983-01-01

313

Ensemble-averaged thermonuclear reaction rates for turbulent convection in stellar interiors  

NASA Astrophysics Data System (ADS)

It is well known in combustion research that the interaction between turbulence and chemsitry can substantially modify flame speeds and overall fuel consumption rates compared to the laminar values. An analogous effect exists for thermonuclear reaction rates in turbulent convection zones in stellar interions. We describe a parametric study that estimates the modification of ensemble-averaged thermonuclear reaction rates by turbulence. The basic approach is to assume some parametric form for the joint probability density function for the reaction variables, estimate the values of the parameters, and then perform the necessary integration to get the averaged reaction rate. We conclude that the effect is not likely to be important during quiescent core-burning phases. The effect is likely to be important for explosive events such as the core helium flash, novae, and supernovae. However, accurate calculation of the turbulent reaction rates must await a reliable quantitative theory of stellar convection.

Cloutman, Lawrence D.

1994-12-01

314

Electron-transfer reactions of cobalt(III) complexes. 1. The kinetic investigation of the reduction of various surfactant cobalt(III) complexes by iron(II) in surface active ionic liquids.  

PubMed

The kinetics of outer sphere electron transfer reaction of surfactant cobalt(III) complex ions, cis-[Co(en)2(C12H25NH2)2](3+) (1), cis-[Co(dp)2(C12H25NH2)2](3+) (2), cis-[Co(trien)(C12H25NH2)2](3+) (3), cis-[Co(bpy)2(C12H25NH2)2](3+) (4) and cis-[Co(phen)2(C12H25NH2)2](3+) (5) (en: ethylenediamine, dp: diaminopropane, trien : triethylenetetramine, bpy: 2,2'-bipyridyl, phen: 1,10-phenanthroline and C12H25NH2 : dodecylamine) have been interrogated by Fe(2+) ion in ionic liquid (1-butyl-3-methylimidazoliumbromide) medium at different temperatures (298, 303, 308, 313, 318 and 323K) by the spectrophotometry method under pseudo first order conditions using an excess of the reductant. Experimentally the reactions were found to be of second order and the electron transfer as outer sphere. The second order rate constant for the electron transfer reaction in ionic liquids was found to increase with increase in the concentration of all these surfactant cobalt(III) complexes. Among these complexes (from en to phen ligand), complex containing the phenanthroline ligand rate is higher compared to other complexes. By assuming the outer sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of ionic liquids formed by the surfactant cobalt(III) complexes in the reaction medium. The activation parameters (enthalpy of activation ?H() and entropy of activation ?S()) of the reaction have been calculated which substantiate the kinetics of the reaction. PMID:25721780

Nagaraj, Karuppiah; Senthil Murugan, Krishnan; Thangamuniyandi, Pilavadi; Sakthinathan, Subramanian

2015-05-15

315

The Evolution Of Slow Dispersal Rates: A Reaction Diffusion Model  

Microsoft Academic Search

We consider n phenotypes of a species in a continuous but heterogeneous environment. Itis assumed that the phenotypes differ only in their diffusion rates. With haploid genetics and asmall rate of mutation, it is shown that the only nontrivial equilibrium is a population dominatedby the slowest diffusing phenotype. We also prove that if there are only two possible phenotypes,then this

Jack Dockery; Vivian Hutson

1997-01-01

316

Reaction rate of 24Mg(p,gamma)25Al  

Microsoft Academic Search

The proton-capture reaction on 24Mg has been investigated in the bombarding energy range of Ep = 0.2 - 1.7 MeV. Resonance properties (strengths, branching ratios and lifetimes) of low-energy resonances have been measured. From the experimental results, accurate proton partial widths, gamma-ray partial widths and total widths (Gammap, Gammagamma, and Gamma) have been deduced. The present experimental information establishes the

D. C. Powell; C. Iliadis; A. E. Champagne; C. A. Grossmann; S. E. Hale; V. Y. Hansper; L. K. McLean

1999-01-01

317

A Systematic Study of Astrophysical Reaction Rates through 8Li  

Microsoft Academic Search

Excitation functions of 8Li(alpha,n), (d, t) and 12B(alpha,n) reactions were directly measured in the energy region of astrophysical interest using low-energy radioactive nuclear beams of 8Li and 12B. Each measured excitation function is strongly affected by one or more resonances through a compound nucleus. The measured excitation functions are presented. Dominant r-process paths through 8Li at various temperatures are discussed

Hironobu Ishiyama; Takashi Hashimoto; Kanako Yamaguchi; Yutaka Watanabe; Nobuaki Imai; Yoshikazu Hirayama; Hiroari Miyatake; Masa-Hiko Tanaka; Nobuharu Yoshikawa; Sunchan Jeong; Yoshihide Fuchi; Ichiro Katayama; Toru Nomura; Tomoko Ishikawa; Suranjan K. Das; Yutaka Mizoi; Tomokazu Fukuda; Katsuhisa Nishio; Shinichi Mitsuoka; Hiroshi Ikezoe; Makoto Matsuda; Shinichi Ichikawa; Tadashi Shimoda; Kori Otsuki; Toshiki Kajino

2009-01-01

318

Theoretical reaction rates of the $^{12}$C($\\alpha$,$\\gamma$)$^{16}$O reaction from the potential model  

E-print Network

The radiative capture cross sections of $^{12}$C($\\alpha$,$\\gamma$)$^{16}$O and derived reaction rates are calculated from the direct capture potential model. The resulting $S$-factor at low energies is found to be dominated by $E$2 transition to the $^{16}$O ground state. The $E$1 and $E$2 $S$-factors at $E_{c.m.}=0.3$ MeV are $S_{E1}\\approx3$ keV~b and $S_{E2}=150^{+41}_{-17}$ keV~b, respectively. The sum of the cascade transition through the excited state of $^{16}$O is $S_{\\rm casc}= 18\\pm4.5$ keV~b. The derived reaction rates at low temperatures seem to be concordant with those from the previous evaluation. For astrophysical applications, our reaction rates below $T_9=3$ are provided in an analytic expression.

Katsuma, M

2015-01-01

319

The Gaseous Explosive Reaction : the Effect of Pressure on the Rate of Propagation of the Reaction Zone and upon the Rate of Molecular Transformation  

NASA Technical Reports Server (NTRS)

This study of gaseous explosive reaction has brought out a number of important fundamental characteristics of the explosive reaction indicating that the basal processes of the transformation are much simpler and corresponds more closely to the general laws and principles of ordinary transformations than is usually supposed. The report calls attention to the point that the rate of molecular transformation within the zone was found in all cases to be proportional to pressure, that the transformation within the zone is the result of binary impacts. This result is of unusual interest in the case of the reaction of heavy hydrocarbon fuels and the reaction mechanism proposed by the recent kinetic theory of chain reactions.

Stevens, F W

1932-01-01

320

Beyond the mean-potential approximation in the calculation of thermonuclear reaction rates in dense stars  

NASA Astrophysics Data System (ADS)

In dense matter the thermonuclear reaction rate is significantly affected by neighbouring ions to a reacting pair. The rigorous theory of Alastuey & Jancovici shows that, if small quantum-mechanical effects associated with the neighbouring ions are neglected, the correct way to estimate thermonuclear reaction rates in dense matter is first to calculate the rate for a fixed configuration of neighbours to the fusing pair, and then to thermally average over positions of the neighbours. The standard assumption made in most calculations of rates is that the processes of thermodynamic averaging and the evaluation of the tunneling amplitude may be reversed. This is equivalent to assuming that the fusing pair of ions move in the average potential produced by the other ions. We make quantitative estimates of the reaction rate for a simple, physically motivated, three-dimensional model, and show that under some circumstances the standard approximation can give reaction rates that are too high by a factor 2.

Sahrling, M.

1994-03-01

321

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

322

The evolution of slow dispersal rates: a reaction diffusion model  

Microsoft Academic Search

.?We consider n phenotypes of a species in a continuous but heterogeneous environment. It is assumed that the phenotypes differ only in their\\u000a diffusion rates. With haploid genetics and a small rate of mutation, it is shown that the only nontrivial equilibrium is a\\u000a population dominated by the slowest diffusing phenotype. We also prove that if there are only two

Jack Dockery; Vivian Hutson; Konstantin Mischaikow; Mark Pernarowski

1998-01-01

323

Systematic study of (g,n) reaction rates for Z>=78 isotopes  

E-print Network

The (g,n) reaction rates of the isotopes 196,198,204-Hg and 204-Pb have been determined using the photoactivation technique in an energy region relevant for p process nucleosynthesis. The systematic study of the ground-state (g,n) reaction rates on even-even nuclei in the mass region Z>=78 is complemented with these experiments. The data are compared to rates predicted in the framework of two statistical model approaches.

K. Sonnabend; K. Vogt; D. Galaviz; S. Mueller; A. Zilges

2005-01-06

324

Effects of network dissolution changes on pore-to-core up-scaled reaction rates for kaolinite and anorthite reactions under acidic conditions  

E-print Network

1 Effects of network dissolution changes on pore-to-core up-scaled reaction rates for kaolinite present in the solid matrix Geometric and reaction rate law factors exert differential influence the effect of these changes on up-scaled (pore-scale to core-scale)5 reaction rates and compared against

New York at Stoney Brook, State University of

325

Reaction Rate Uncertainties: NeNa and MgAl in AGB Stars  

E-print Network

We study the effect of uncertainties in the proton-capture reaction rates of the NeNa and MgAl chains on nucleosynthesis due to the operation of hot bottom burning (HBB) in intermediate-mass asymptotic giant branch (AGB) stars. HBB nucleosynthesis is associated with the production of sodium, radioactive Al26 and the heavy magnesium isotopes, and it is possibly responsible for the O, Na, Mg and Al abundance anomalies observed in globular cluster stars. We model HBB with an analytic code based on full stellar evolution models so we can quickly cover a large parameter space. The reaction rates are varied first individually, then all together. This creates a knock-on effect, where an increase of one reaction rate affects production of an isotope further down the reaction chain. We find the yields of Ne22, Na23 and Al26 to be the most susceptible to current nuclear reaction rate uncertainties.

Robert Izzard; Maria Lugaro; Christian Iliadis; Amanda Karakas

2006-07-24

326

Improved Whitten-Rabinovitch Approximation for the Rice-Ramsperger-Kassel-Marcus Calculation of Unimolecular Reaction Rate Constants for Proteins  

E-print Network

of Unimolecular Reaction Rate Constants for Proteins Meiling Sun, Jeong Hee Moon, and Myung Soo Kim*, Department) unimolecular reaction rate constant was improved for reliable application to protein reactions. The state sum of the protein mass. I. Introduction In the study of a unimolecular reaction, it is often useful to have a rate

Kim, Myung Soo

327

Proceedings of the Combustion Institute, Volume 29, 2002/pp. 26872694 REACTION-RATE, MIXTURE-FRACTION, AND TEMPERATURE IMAGING IN  

E-print Network

2687 Proceedings of the Combustion Institute, Volume 29, 2002/pp. 26872694 REACTION-RATE, MIXTURE-dimensional measurements of reaction rate, mixture fraction, and temperature are demonstrated in turbulent partially premixed methane/air jet flames. The forward reaction rate of the reaction CO OH CO2 H is measured

Long, Marshall B.

328

Upper atmosphere research: Reaction rate and optical measurements  

NASA Technical Reports Server (NTRS)

The objective is to provide photochemical, kinetic, and spectroscopic information necessary for photochemical models of the Earth's upper atmosphere and to examine reactions or reactants not presently in the models to either confirm the correctness of their exclusion or provide evidence to justify future inclusion in the models. New initiatives are being taken in technique development (many of them laser based) and in the application of established techniques to address gaps in the photochemical/kinetic data base, as well as to provide increasingly reliable information.

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

1990-01-01

329

Simulation of Transport and Reaction Using Random Walks: Reactions Without Concentrations and the Automatic Simulation of Drastically Different Thermodynamic--- Versus Diffusion---Limited Reaction Rates  

NASA Astrophysics Data System (ADS)

We extend the advantages of Lagrangian random walk particle tracking (RWPT) methods that have long been used to simulate advection and dispersion in highly heterogeneous media. By formulating dissolution as a random, independent decay process, the classical continuum rate law is recovered. A novel formulation of the random precipitation process requires a consideration of the probability that two nearby particles will occupy the same differential volume in a given time period. This depends on local mixing (as by diffusion) and the total domain particle number density, which are fixed and therefore easy to calculate. The result is that the effective reaction rate follows two regimes. First, for high thermodynamic reaction probability and/or fast mixing, the classical continuum rate laws are reproduced. These are coded in the Gillespie method. This implies an exponentially fast approach to equilibrium. Second, for diffusion (mixing) limited reaction rates, equilibrium is approached much more slowly, following a power law that differs for 1-, 2-, or 3-d. At long enough times, the classical law of mass action for equilibrium reactions is reproduced, in an ensemble sense, for either rate regime. The same number of parameters for A+B ? C are needed in a probabilistic versus continuum reaction simulation---one each for forward and backward probabilities that correspond to continuum thermodynamic rates. The random nature of the simulations allows for significant disequilibrium in any given region at any time that is independent of the numerical details such as time stepping or particle density. This is exemplified by nearby or intermingled groups of reactants and little or no product---a result that is often noted in the field that is difficult to reconcile with continuum methods or coarse-grained Eulerian models. Our results support both the recent experiments that show mixing-limited reactions and the results of perturbed advection-dispersion-reaction continuum models. We show that many different kinds of reactions can be easily added to existing RWPT codes.

Benson, D. A.; Meerschaert, M. M.

2008-12-01

330

Rate and pathways for the reaction of OH with the biogenic p-cymene, an alkylated aromatic  

NASA Astrophysics Data System (ADS)

Aromatics are known to contribute strongly to tropospheric formation of ozone, and p-cymene (4-isopropyltoluene) is one of only a few biogenic, volatile aromatic hydrocarbons. In spite of its symmetry, this molecule (CH3 - -CH(CH3)2) has a multitude of potential pathways of its reaction with OH radicals. Addition of OH is well-known to be the predominating primary step in the tropospheric transformation of aromatic hydrocarbons. The addition is expected to occur preferably at a non-occupied position, where four positions are available: two equivalent ones ortho to the methyl group and two equivalent ones ortho to the isopropyl group. Furthermore, various C-H bonds (4 aromatic and 10 aliphatic) are available for abstraction, leading to benzyl-type radicals in two cases. The present study combines theoretical calculations with kinetic experiments in the gas phase. The theoretical calculations are based on electronic quantum chemistry DFT method for the investigation of the possible pathways in the potential energy surface of the reaction. The experiments are carried out by the flash photolysis/resonance fluorescence technique. OH radicals are produced by pulsed vacuum-UV photolysis of H2O (> 115 nm) in the presence of p-cymene in a slow flow of He as carrier gas. Their pseudo-first-order decays are monitored by resonance fluorescence, storing the photon counts by multichannel scaling in a PC and accumulating 50 decays each; see Koch et al. (2007) for details of the technique and evaluation of data. The temperature was varied between room temperature (295 K) and 345K, the He pressure was 250 mbar, and the level of p-cymene was increased stepwise, up to 3 x 1013 molecules/cm3. The decays of OH were observed to be exponential at room temperature, becoming clearly biexponential at higher temperatures, thus indicating reversible addition of OH according to the equilibration OH + p-cymene ?? p-cymene-OH (1, -1) These reactions might be accompanied by various abstraction channels, summarized as OH + p-cymene ?? alkylbenzyl + H2O (2) A value of 1.4 x 10-11 cm3 s-1 at 295 K is obtained for the sum k1 + k2, in good agreement with a value of 1.51 x 10-11 cm3 s-1determined by Corchnoy and Atkinson (1990) in a smog chamber at 295 K. The sum k1 + k2 decreases slightly with increasing temperature, falling below 10-11 cm3 s-1 at 345 K. The Arrhenius plot reveals a curved behaviour with a negative activation energy, approximately 1 x 10-12 exp (60 K/T) cm3 s-1. The biexponential behaviour corresponds to an apparent equilibrium constant of k1/k-1 = 8 x 10-25 exp [(-8500 400) K/T] cm3 s-1. On the other hand, the bond energy of OH in the adduct can hardly be obtained from this biexponential behaviour alone since the abstraction of H atoms from the alkyl groups of p-cymene can be estimated to contribute markedly. Extrapolating the respective abstraction channels of toluene and the xylenes to two methyl substituents would yield k2= 1.6 x 10-18 T2exp (-38 K/T) cm3 s-1 (Atkinson, 1989). This amounts to 1.2x10-12 cm3 s-1 at 295 K (about 9% of the observed reactivity) and 1.7x10-12 cm3 s-1 at 345K (>17% of the observed reactivity) and does not even take the possibly largerreactivity of the isopropyl group (as compared to CH3) into account. The abstraction channel has been found to predominate in the analogous reaction of atomic Cl with p-cymene (Finlayson-Pitts et al, 1999), and further experiments by other methods are required to clarify the reaction channels for OH radicals. References Atkinson, R. (1989) Kinetics and Mechanisms of the Gas-Phase Reactions of the Hydroxyl Radical with Organic Compounds. J. Phys. Chem. Ref. Data, Monograph 1, Am. Chem. Soc./Am. Inst. Phys./NIST, p. 229. Corchnoy, S.B., Atkinson, R. (1990) Kinetics of the gas-phase reactions of OH and NO3 radicals with 2-Carene, 1,8-CineoIe, p-Cymene, and Terpinolene. Environ. Sci. Technol. 24, 1497-1502. Finlayson-Pitts, B. J., Keoshian, C.J., Buehler, B., Ezell, A.A. (1999) Kinetics of reaction of chlorine atoms with some biogenic organics. Int

Strekowski, R.; Rayez, M.-T.; Rayez, J.-C.; Zetzsch, C.

2009-04-01

331

Reaction-rate theory: fifty years after Kramers  

Microsoft Academic Search

The calculation of rate coefficients is a discipline of nonlinear science of importance to much of physics, chemistry, engineering, and biology. Fifty years after Kramers' seminal paper on thermally activated barrier crossing, the authors report, extend, and interpret much of our current understanding relating to theories of noise-activated escape, for which many of the notable contributions are originating from the

Peter Hnggi; Peter Talkner; Michal Borkovec

1990-01-01

332

Reaction rate theory perspectives on some problems in materials science  

Microsoft Academic Search

Early applications of rate theory to atomic processes in solids were largely concerned with the postirradiation annealing of native defects or the growth of precipitates from a supersaturated solution. However, the materials problems spawned by the demands of fast reactor and fusion reactor technology necessitated generalizations of the existing formalism to account for the possibilities of both time-dependent point defect

A. D. Brailsford

1989-01-01

333

THE EVOLUTION OF SLOW DISPERSAL RATES: A REACTION DIFFUSION MODEL  

E-print Network

genetics and a small rate of mutation, it is shown that the only nontrivial equilibrium is a population, then this equilibrium is a global attractor and conjecture that this is true in general. Numerical simulations from an ecological and genetic point of view in a variety of situations. These effects have been much

Mischaikow, Konstantin

334

Estimation of the prevalence and rate of acute transfusion reactions occurring in Windhoek, Namibia  

PubMed Central

Background Acute transfusion reactions are probably common in sub-Saharan Africa, but transfusion reaction surveillance systems have not been widely established. In 2008, the Blood Transfusion Service of Namibia implemented a national acute transfusion reaction surveillance system, but substantial under-reporting was suspected. We estimated the actual prevalence and rate of acute transfusion reactions occurring in Windhoek, Namibia. Methods The percentage of transfusion events resulting in a reported acute transfusion reaction was calculated. Actual percentage and rates of acute transfusion reactions per 1,000 transfused units were estimated by reviewing patients records from six hospitals, which transfuse >99% of all blood in Windhoek. Patients records for 1,162 transfusion events occurring between 1st January 31st December 2011 were randomly selected. Clinical and demographic information were abstracted and Centers for Disease Control and Prevention National Healthcare Safety Network criteria were applied to categorize acute transfusion reactions1. Results From January 1 December 31, 2011, there were 3,697 transfusion events (involving 10,338 blood units) in the selected hospitals. Eight (0.2%) acute transfusion reactions were reported to the surveillance system. Of the 1,162 transfusion events selected, medical records for 785 transfusion events were analysed, and 28 acute transfusion reactions were detected, of which only one had also been reported to the surveillance system. An estimated 3.4% (95% confidence interval [CI]: 2.34.4) of transfusion events in Windhoek resulted in an acute transfusion reaction, with an estimated rate of 11.5 (95% CI: 7.614.5) acute transfusion reactions per 1,000 transfused units. Conclusion The estimated actual rate of acute transfusion reactions is higher than the rate reported to the national haemovigilance system. Improved surveillance and interventions to reduce transfusion-related morbidity and mortality are required in Namibia. PMID:24333079

Meza, Benjamin P.L.; Lohrke, Britta; Wilkinson, Robert; Pitman, John P.; Shiraishi, Ray W.; Bock, Naomi; Lowrance, David W.; Kuehnert, Matthew J.; Mataranyika, Mary; Basavaraju, Sridhar V.

2014-01-01

335

Reaction kinetics and critical phenomena: rates of some first order gas evolution reactions in binary solvents with a consolute point.  

PubMed

We have measured the rate of carbon dioxide evolution in the aniline catalyzed decomposition of acetone dicarboxylic acid in a mixture of isobutyric acid + water near its consolute point. Within a temperature interval of 1 degrees C, which included the critical solution temperature, the first-order rate constant oscillated in magnitude by about 10% as it passed through three complete cycles of slowing down followed by speeding up. Whereas we can find no ready explanation for the speeding up, we suggest that, because the mixture contained no inert components, the slowing down should belong to the Griffiths-Wheeler class of strong critical effects [Phys. Rev. A 1970, 2, 1047]. As a check on this conclusion, we have measured the rate of the SN1 decomposition of benzene diazonium tetrafluoroborate in 2-butoxyethanol + water near the lower critical solution temperature and also the rate of the acid-catalyzed decomposition of ethyl diazoacetate in isobutyric acid + water near the upper critical solution temperature. Both of these reactions evolve nitrogen. In the first reaction, 2-butoxyethanol is inert, whereas in the second, isobutyric acid is inert. In both cases, because there was one inert component, we regarded the response of the rate constant to temperature in the critical region to be representative of the Griffiths-Wheeler class of weak critical effects. Within our accuracy of measurement of about 2% in the rate constant and about 1 mK in the temperature, we could detect no effect of the critical point on the rates of either of these reactions, suggesting that a weak effect may be too small to be seen with our experimental apparatus. The successful observation of a critical effect in the rate of decomposition of acetone dicarboxylic acid proves, however, that kinetic critical phenomena are observable in heterogeneous reactions. PMID:16833817

Kim, Yeong Woo; Baird, James K

2005-06-01

336

Thermonuclear reaction rate of $^{18}$Ne($\\alpha$,$p$)$^{21}$Na from Monte-Carlo calculations  

E-print Network

The $^{18}$Ne($\\alpha$,$p$)$^{21}$Na reaction impacts the break-out from the hot CNO-cycles to the $rp$-process in type I X-ray bursts. We present a revised thermonuclear reaction rate, which is based on the latest experimental data. The new rate is derived from Monte-Carlo calculations, taking into account the uncertainties of all nuclear physics input quantities. In addition, we present the reaction rate uncertainty and probability density versus temperature. Our results are also consistent with estimates obtained using different indirect approaches.

Mohr, P; Iliadis, C

2014-01-01

337

Thermonuclear reaction rate of 18Ne(? ,p ) 21Na from Monte Carlo calculations  

NASA Astrophysics Data System (ADS)

The 18Ne(? ,p ) 21Na reaction impacts the break-out from the hot CNO cycles to the r p process in type-I x-ray bursts. We present a revised thermonuclear reaction rate, which is based on the latest experimental data. The new rate is derived from Monte Carlo calculations, taking into account the uncertainties of all nuclear physics input quantities. In addition, we present the reaction rate uncertainty and probability density versus temperature. Our results are also consistent with estimates obtained using different indirect approaches.

Mohr, P.; Longland, R.; Iliadis, C.

2014-12-01

338

Thermonuclear reaction rate of $^{18}$Ne($?$,$p$)$^{21}$Na from Monte-Carlo calculations  

E-print Network

The $^{18}$Ne($\\alpha$,$p$)$^{21}$Na reaction impacts the break-out from the hot CNO-cycles to the $rp$-process in type I X-ray bursts. We present a revised thermonuclear reaction rate, which is based on the latest experimental data. The new rate is derived from Monte-Carlo calculations, taking into account the uncertainties of all nuclear physics input quantities. In addition, we present the reaction rate uncertainty and probability density versus temperature. Our results are also consistent with estimates obtained using different indirect approaches.

P. Mohr; R. Longland; C. Iliadis

2014-12-14

339

ACTIVE: a program to calculate and plot reaction rates from ANISN calculated fluxes  

SciTech Connect

The ACTIVE code calculates spatial heating rates, tritium production rates, neutron reaction rates, and energy spectra from particle fluxes calculated by ANISN. ACTIVE has a variety of input options including the capability to plot all calculated spatial distributions. The code was primarily designed for use with fusion first wall/blanket systems, but could be applied to any one-dimensional problem.

Judd, J.L.

1981-12-01

340

Rate constants measured for hydrated electron reactions with peptides and proteins  

NASA Technical Reports Server (NTRS)

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.

Braams, R.

1968-01-01

341

ACTIVE: a program to calculate and plot reaction rates from ANISN calculated fluxes  

Microsoft Academic Search

The ACTIVE code calculates spatial heating rates, tritium production rates, neutron reaction rates, and energy spectra from particle fluxes calculated by ANISN. ACTIVE has a variety of input options including the capability to plot all calculated spatial distributions. The code was primarily designed for use with fusion first wall\\/blanket systems, but could be applied to any one-dimensional problem.

Judd

1981-01-01

342

Direct use of the mass output of a thermobalance for controlling the reaction rate of solid-state reactions  

Microsoft Academic Search

Sample controlled thermal analysis equipment has been developed constituted by an electrobalance in which the mass output (TG signal) is directly used for monitoring the temperature of thermal decomposition reactions under constant rate thermal analysis (CRTA) or stepwise isothermal analysis (SIA) control. The sample weight is programmed to follow a preset linear decrease as a function of the time by

M. J. Dinez; L. A. Prez Maqueda; J. M. Criado

2004-01-01

343

Evaluation of antioxidants using oxidation reaction rate constants  

Microsoft Academic Search

An evaluation method for the capacity of antioxidants to protect drugs against oxidation is presented. As a new viewpoint,\\u000a to determine the priority of the competitive oxidations between the antioxidant and the protected drug, and to compare the\\u000a drug-protection capacity of antioxidants, it is important to determine their oxidation rate constants using chemical kinetics\\u000a instead of standard oxidation (or reduction)

Yan Shi; Xiancheng Zhan; Lie Ma; Linli Li; Chengrong Li

2007-01-01

344

Time-Resolved O3 Chemical Chain Reaction Kinetics Via High-Resolution IR Laser Absorption Methods  

NASA Technical Reports Server (NTRS)

Excimer laser photolysis in combination with time-resolved IR laser absorption detection of OH radicals has been used to study O3/OH(v = 0)/HO2 chain reaction kinetics at 298 K, (i.e.,(k(sub 1) is OH + 03 yields H02 + 02 and (k(sub 2) is H02 + 03 yields OH + 202). From time-resolved detection of OH radicals with high-resolution near IR laser absorption methods, the chain induction kinetics have been measured at up to an order of magnitude higher ozone concentrations ([03] less than or equal to 10(exp 17) molecules/cu cm) than accessible in previous studies. This greater dynamic range permits the full evolution of the chain induction, propagation, and termination process to be temporally isolated and measured in real time. An exact solution for time-dependent OH evolution under pseudo- first-order chain reaction conditions is presented, which correctly predicts new kinetic signatures not included in previous OH + 03 kinetic analyses. Specifically, the solutions predict an initial exponential loss (chain "induction") of the OH radical to a steady-state level ([OH](sub ss)), with this fast initial decay determined by the sum of both chain rate constants, k(sub ind) = k(sub 1) + k(sub 2). By monitoring the chain induction feature, this sum of the rate constants is determined to be k(sub ind) = 8.4(8) x 10(exp -14) cu cm/molecule/s for room temperature reagents. This is significantly higher than the values currently recommended for use in atmospheric models, but in excellent agreement with previous results from Ravishankara et al.

Kulcke, Axel; Blackmon, Brad; Chapman, William B.; Kim, In Koo; Nesbitt, David J.

1998-01-01

345

Calcite dissolution and Ca/Na ion-exchange reactions in columns with different flow rates through high ESR soil  

E-print Network

of stability was used to calculate rate constants which were then compared for the influence of flow rate on overall reaction rate. The rate constant approximately doubled as the flow rate was doubled, which implied flow rate control of the reactions...

Navarre, Audrey

1999-01-01

346

Thermonuclear reaction rate of 17O(p,gamma)18F  

Microsoft Academic Search

The 17O(p,gamma)18F and 17O(p,alpha)14N reactions have a profound influence on hydrogen-burning nucleosynthesis in a number of stellar sites, including red giants, asymptotic giant branch (AGB) stars, massive stars, and classical novae. Previously evaluated thermonuclear rates for both reactions carry large uncertainties. We investigated the proton-capture reaction on 17O in the bombarding energy range of Elabp=180-540keV. We observed a previously undiscovered

C. Fox; C. Iliadis; A. E. Champagne; R. P. Fitzgerald; R. Longland; J. Newton; J. Pollanen; R. Runkle

2005-01-01

347

Reaction rate of 15O(a,g)19Ne via indirect measurements  

Microsoft Academic Search

15 O(alpha,gamma) is the critical breakout reaction from the hot CNO cycles, which triggers the thermonu- clear runaways or X-ray bursts occurring in accreting neutron stars. Recent studies have shown that this reaction is critical for the burst amplitude and periodicity of X-ray bursters. However, a direct measurement of this reaction rate at astrophysically relevant temperatures is not feasible yet

Wanpeng Tan; J. Gorres; J. Daly; M. Beard; M. Couder; A. Couture; S. Falahat; L. Lamm; P. J. LeBlanc; H. Y. Lee; S. O'Brien; A. Palumbo; E. Stech; E. Strandberg; M. Wiescher

2006-01-01

348

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

Microsoft Academic Search

Some chemical and biochemical reactions are non-adiabatic processes whereby the total spin angular momentum, before and after the reaction, is not conserved. These are named spin- forbidden reactions. The application of ab-initio methods, such as spin density functional theory (SDFT), to the prediction of rate constants is a challenging task of fundamental and practical importance. We apply non-adiabatic transition state

Abdullah Ozkanlar; Jorge H. Rodriguez

2007-01-01

349

Estimation of the Molecular Junction Temperatures in Four-Ball Contacts by Chemical Reaction Rate Studies  

Microsoft Academic Search

A super-refined paraffinic mineral oil has been used to study the chemical reactions under boundary conditions in a four-ball wear tester. By quantatively analyzing the wear debris generated, chemical reaction rate data used to correlate between dynamic wear tests and static, externally controlled temperature runs. The reaction temperature at the wear junction has been estimated to be 351C for 40kg

Stephen M. Hsu; E. Erwin Klaus

1978-01-01

350

HIGH TEMPERATURE X-RAY DIFFRACTION STUDY OF REACTION RATES IN CERAMICS  

Microsoft Academic Search

The reaction rates and formation mechanisms of various n=3 Aurivillius phases were studied. Current research has shown that in order to make phase pure materials via solid-state synthesis, over 100 hours of heat treatment are necessary. A custom high temperature X-ray diffractometer (HTXRD) was utilized to observe in-situ formation reactions. The Bi2Sr2Nb2TiO12 formation reaction could not be followed to completion

M. S. Peterson; S. A. Speakman; S. T. Misture

351

BRUSLIB and NETGEN: the Brussels nuclear reaction rate library and nuclear network generator for astrophysics  

E-print Network

Nuclear reaction rates are quantities of fundamental importance in astrophysics. Substantial efforts have been devoted in the last decades to measure or calculate them. The present paper presents for the first time a detailed description of the Brussels nuclear reaction rate library BRUSLIB and of the nuclear network generator NETGEN so as to make these nuclear data packages easily accessible to astrophysicists for a large variety of applications. BRUSLIB is made of two parts. The first one contains the 1999 NACRE compilation based on experimental data for 86 reactions with (mainly) stable targets up to Si. The second part of BRUSLIB concerns nuclear reaction rate predictions calculated within a statistical Hauser-Feshbach approximation, which limits the reliability of the rates to reactions producing compound nuclei with a high enough level density. These calculations make use of global and coherent microscopic nuclear models for the quantities entering the rate calculations. The use of such models is utterly important, and makes the BRUSLIB rate library unique. A description of the Nuclear Network Generator NETGEN that complements the BRUSLIB package is also presented. NETGEN is a tool to generate nuclear reaction rates for temperature grids specified by the user. The information it provides can be used for a large variety of applications, including Big Bang nucleosynthesis, the energy generation and nucleosynthesis associated with the non-explosive and explosive hydrogen to silicon burning stages, or the synthesis of the heavy nuclides through the s-, alpha- and r-, rp- or p-processes.

M. Aikawa; M. Arnould; S. Goriely; A. Jorissen; K. Takahashi

2005-06-24

352

Chaotic Scattering Theory of Transport and Reaction-Rate Coefficients  

E-print Network

The chaotic scattering theory is here extended to obtain escape-rate expressions for the transport coefficients appropriate for a simple classical fluid, or for a chemically reacting system. This theory allows various transport coefficients such as the coefficients of viscosity, thermal conductivity, etc., to be expressed in terms of the positive Lyapunov exponents and Kolmogorov-Sinai entropy of a set of phase space trajectories that take place on an appropriate fractal repeller. This work generalizes the previous results of Gaspard and Nicolis for the coefficient of diffusion of a particle moving in a fixed array of scatterers.

J. R. Dorfman; P. Gaspard

1994-05-16

353

Reaction rate of O + with O 2 , N 2 , and NO under highly disturbed auroral conditions  

Microsoft Academic Search

There are no published reaction rates of O + ions with 02, N2, and NO for ion temperatures in excess of 6000 K in the ionosphere. Yet, there are now documented cases of very strong perpendicular high-latitude ionospheric electric fields, with resulting ion temperatures well in excess of 10,000 K. We have therefore extended the calculations of O + reaction

J.-P. St.-Maurice; P. J. Laneville

1998-01-01

354

Magnetic-field dependence of chemical reaction rates at high temperatures  

Microsoft Academic Search

The theory of magnetic-field dependence of chemical reaction rates at high temperatures is discussed. It is shown that in the zero-order approximation in the parameter (muH\\/kT)2 this dependence can be significant. It depends crucially on the nature of the reaction and the way particles are created.

B. Spivak; F. Zhou

1994-01-01

355

Alkylation of phosphorus iodides. II. Influence of iodine on the reaction rate  

SciTech Connect

The reaction of phosphorus triiodide with an excess of iodomethane at room temperature results in the formation of a compound with two carbon-phosphorus bonds. The addition of iodine to the reaction mixture accelerates alkylation. The rate of alkylation also depends on the quantity of iodomethane.

Kudryavtseva, L.I.

1987-10-20

356

Effects of arsenic incorporation on jarosite dissolution rates and reaction products  

E-print Network

Effects of arsenic incorporation on jarosite dissolution rates and reaction products Matthew R to hematite with time in ultra-pure water, but increasing arsenic concentrations slow this transition. At pH >3.5, arsenic from the dissolution of arsenojarosite adsorbs onto newly formed reaction products

Hu, Qinhong "Max"

357

Chemical rates in detonation reaction zones: Determination of temperature and pressure dependence  

Microsoft Academic Search

Bardo et al1 have pointed out that at detonalion pressure the volume of activation of a reaction can have an important effect on the reaction rate. It is shown that both the activation energy and activation volume cannot be determine from the experimental data2. (AIP)

John B. Bdzil; Ray Engelke

1982-01-01

358

An upper limit to the rate of the HCl + ClONO2 reaction  

NASA Technical Reports Server (NTRS)

The reaction HCl + ClONO2 yields Cl2 + HNO3 has been studied by Fourier transform infrared spectroscopy and by a static wall-less UV absorption technique. An upper limit to the homogeneous bimolecular rate constant of 10 to the -19th cu cm/molecule per sec was established, making the reaction unimportant in the stratosphere.

Molina, L. T.; Molina, M. J.; Stachnik, R. A.; Tom, R. D.

1985-01-01

359

Thermophysical properties and reaction rate of composite reactant of calcium chloride and expanded graphite  

Microsoft Academic Search

Experimental studies have been conducted in order to obtain information on thermophysical properties and reaction characteristics of composite reactant of calcium chloride and expanded graphite, which has been developed to improve the performance of a reactor bed used for gassolid chemical heat pumps. Effective thermal conductivity, permeability and reaction rate of the composite reactant have been measured. From the results

Keiko Fujioka; Hiroshi Suzuki

360

Combustion of Bimodal Nano\\/Micro Aluminum Suspension with New Reaction Rate Model  

Microsoft Academic Search

In this study a mathematical model for combustion of bimodal particle in lean flow was developed. The difference between structure of flame in this work and previous ones was that, in those flame was divided by five zones and reaction rate was considered to be constant in reaction zones and also zero in post flame zone. In reality it was

M. Bidabadi; N. Moallemi; I. Shafieenejad; M. Jadidi

361

Abstraction and exchange contributions to the rate constant of muonium+hydrogen chloride reaction  

NASA Astrophysics Data System (ADS)

Quantum collinear rate constants for the abstraction and the exchange channels of the Mu+HCl reaction have been calculated in order to have an estimate of the relative efficiency of the two processes in promoting reactivity for this system.

Lagan, A.; Ciccarelli, L.

1987-02-01

362

Method and apparatus for obtaining enhanced production rate of thermal chemical reactions  

DOEpatents

The present invention is a method and apparatus (vessel) for providing a heat transfer rate from a reaction chamber through a wall to a heat transfer chamber substantially matching a local heat transfer rate of a catalytic thermal chemical reaction. The key to the invention is a thermal distance defined on a cross sectional plane through the vessel inclusive of a heat transfer chamber, reaction chamber and a wall between the chambers. The cross sectional plane is perpendicular to a bulk flow direction of the reactant stream, and the thermal distance is a distance between a coolest position and a hottest position on the cross sectional plane. The thermal distance is of a length wherein the heat transfer rate from the reaction chamber to the heat transfer chamber substantially matches the local heat transfer rate.

Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Wegeng, Robert S [Richland, WA; Gao, Yufei [Kennewick, WA

2003-04-01

363

Improving the rate of the triple alpha reaction  

NASA Astrophysics Data System (ADS)

The rate of the triple alpha process, which plays a central role in the production of 12C in stars, is known with an accuracy of about 12%. Variations within the 12% errors in this rate can cause significant changes in the determination of the mass of the iron core in core-collapse supernovae and the composition of the material later ejected in the interstellar medium, as well as a factor of two change in the surface abundance of 12C in light ABG stars. The triple alpha experiment presented here is a collaborative effort between the Western Michigan University (WMU) and the National Superconducting Cyclotron Laboratory (NSCL) and aims at reducing the uncertainty on the knowledge of this rate to about 6% by measuring more accurately than has been done in the past the pair branch for the 7.654 MeV state in 12C. This state is excited by inelastic proton scattering ( 12C(p, p )12C(7.654MeV ) ), taking advantage of a strong resonance at a bombarding energy of about 10.6 MeV and a scattering angle of 135 degrees in the laboratory. The decay pairs are detected in an almost 4? scintillator system surrounding the target. The protons are produced using the Tandem accelerator at Western Michigan University and detected by silicon detectors at 135 degrees in the lab. The pair branch is given by the ratio of the number of electron-positron pairs detected in the plastic scintillators in coincidence with the protons in the 7.654 MeV silicon spectra to the number of those protons. A reduction in the gamma ray background, mainly due to the cascade gamma decay of the 7.654 MeV state through the 4.44 MeV 2+ state, is achieved by a coincidence requirement between a thin scintillator tube and the large block of plastic scintillator surrounding it. The measurement is expected to take place in the summer of 2006.

Tur, Clarisse; Austin, S. M.; Wuosmaa, A.; Lighthall, J.; Marley, S.; Goodman, N.; Bos, J. J.

364

Matching of experimental and statistical-model thermonuclear reaction rates at high temperatures  

Microsoft Academic Search

We address the problem of extrapolating experimental thermonuclear reaction rates toward high stellar temperatures (T>1 GK) by using statistical model (Hauser-Feshbach) results. Reliable reaction rates at such temperatures are required for studies of advanced stellar burning stages, supernovae, and x-ray bursts. Generally accepted methods are based on the concept of a Gamow peak. We follow recent ideas that emphasized the

J. R. Newton; R. Longland; C. Iliadis

2008-01-01

365

THE REACTION RATE OF SODIUM SULFITE WITH DISSOLVED OXYGEN. Technical Report No. 73  

Microsoft Academic Search

The reaction rate of sodium sulfite was studied as a function of oxygen ;\\u000a concentration, NaSO\\/O ratio, temperature, catalyst, pH and ;\\u000a surface\\/volume ratio.The reaction rate of hydrazine with dissolved oxygen was ;\\u000a also studied. Oxygen removal is incomplete when the sulfite to oxygen ratio is ;\\u000a leas than the stoichiometric quantity. With the stoichiometric quantities of ;\\u000a oxygen and

1960-01-01

366

Temperature dependence of modified CNO nuclear reaction rates in dense stellar plasmas  

Microsoft Academic Search

We study the dependence of the CNO nuclear reaction rates on temperature, in the range of 107108K, the typical range of temperature evolution from a Sun-like star towards a white dwarf. We show that the temperature dependence of the CNO nuclear reaction rates is strongly affected by the presence of non-extensive statistical effects in the dense stellar core. A very

F. Ferro; A. Lavagno; P. Quarati

2004-01-01

367

Resonance reaction rate of 21Na(p,gamma)22Mg  

Microsoft Academic Search

By using the new Coulomb screening model and most recent experimental results, this paper calculates the resonance reaction rates of 21Na(p,gamma)22Mg. The derived result shows that the effect of electron screening on resonant reaction is prominent in astrophysical interesting temperature range. In conjunction with the experimental results, the recommended rates of21Na(p,gamma)22Mg would increase at least 10%, which undoubtedly affect the

Hong-Lin Liu; Men-Quan Liu; Jing-Jing Liu; Zhi-Quan Luo

2007-01-01

368

Determination of rate constants for the reaction between methyldiethanolamine and carbon dioxide  

E-print Network

DETERMINATION OF RATE CONSTANTS FOR THE REACTION BETWEEN METHYLDIETHANOLAMINE AND CARBON DIOXIDE A Thesis by CHARLES MEADE BRABSON, JR. Submitted to the Graduate College of Texas A6M University in partial fulfillment of the requirements... for the degree of MASTER OF SCIENCE August 1985 Major Subject: Chemical Engineering DETERMINATION OF RATE CONSTANTS FOR THE REACTION BETWEEN METHYLDIETHANOLAMINE AND CARBON DIOXIDE A Thesis by CHARLES MEADE BRABSONp JR. Approved as to style and content...

Brabson, Charles Meade

1985-01-01

369

Polar organic solvents accelerate the rate of DNA strand replacement reaction.  

PubMed

Herein, we report a novel strategy to accelerate the rate of DNA strand replacement reaction (DSRR) by polar organic solvents. DSRR plays a vital role in DNA nanotechnology but prolonged reaction time limits its further advancement. That is why it is extremely important to speed up the rate of DSRR. In this work, we introduce different polar organic solvents in both simple and complicated DSRR systems and observe that the rate constant is much more than in aqueous buffer. The rate acceleration of DSRR by polar organic solvents is very obvious and we believe that this strategy will extend the application of DNA nanotechnology in future. PMID:25675278

Zhang, Tianchi; Shang, Chunli; Duan, Ruixue; Hakeem, Abdul; Zhang, Zhenyu; Lou, Xiaoding; Xia, Fan

2015-03-01

370

Astrophysical S-Factors and Reaction Rates of Threshold (p, n)-Reactions on {sup 99-102}Ru  

SciTech Connect

Astrophysical S-factors of (p, n) reactions on {sup 99}Ru, {sup 100}Ru, {sup 101}Ru, and {sup 102}Ru were derived from the sum of experimental isomeric and ground states cross sections measured in the incident proton energy range of 5-9 MeV. They were compared with Hauser-Feshbach statistical model predictions of the NON-SMOKER code. Good agreement was found in the majority of cases. Reaction rates were derived up to 8.7 GK stellar temperature by combining experiment and theory.

Skakun, Ye. [Kharkiv Institute of Physics and Technology, Academicheskaja str., 1, 61108 Kharkiv (Ukraine); Rauscher, T. [Department of Physics, University of Basel, Klingelbergstr, 82, CH-4056 Basel (Switzerland)

2010-08-12

371

A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reaction flows  

NASA Technical Reports Server (NTRS)

The use of silane (SiH4) as an effective ignitor and flame stabilizing pilot fuel is well documented. A reliable chemical kinetic mechanism for prediction of its behavior at the conditions encountered in the combustor of a SCRAMJET engine was calculated. The effects of hydrogen addition on hydrocarbon ignition and flame stabilization as a means for reduction of lengthy ignition delays and reaction times were studied. The ranges of applicability of chemical kinetic models of hydrogen-air combustors were also investigated. The CHARNAL computer code was applied to the turbulent reaction rate modeling.

Magnotti, F.; Diskin, G.; Matulaitis, J.; Chinitz, W.

1984-01-01

372

Dynamic Incompressible Navier-Stokes Model of Catalytic Converter in 1-D Including Fundamental Oxidation Reaction Rate Expressions  

E-print Network

of these terms is studied for proper inclusion in the model. Furthermore, it is evident from the history of catalyst modeling that precise reaction rate expressions are needed for accurate predictions. In order to determine the correct reaction rate expression...

Loya, Sudarshan Kedarnath

2011-12-31

373

Thick target measurement of the 40Ca(alpha,gamma)44Ti reaction rate  

SciTech Connect

The thick-target yield for the {sup 40}Ca({alpha},{gamma}){sup 44}Ti reaction has been measured for E{sub beam} = 4.13, 4.54, and 5.36 MeV using both an activation measurement and online {gamma}-ray spectroscopy. The results of the two measurements agree. From the measured yield a reaction rate is deduced that is smaller than statistical model calculations. This implies a smaller {sup 44}Ti production in supernova compared to recently measured {sup 40}Ca({alpha},{gamma}){sup 44}Ti reaction rates.

Sheets, S A; Burke, J T; Scielzo, N D; Phair, L; Bleuel, D; Norman, E B; Grant, P G; Hurst, A M; Tumey, S; Brown, T A; Stoyer, M

2009-02-06

374

Review of rate coefficients of ionic reactions determined from measurements made by the atmosphere explorer satellites  

NASA Technical Reports Server (NTRS)

The large data base of aeronomic parameters measured by the Atmosphere Explorer C, D, and E satellites since December 1973 has been used to determine a number of reaction rate coefficients highly relevant to our understanding of thermospheric chemistry. In this paper the results are reviewed for ionic rate coefficients for recombination of NO(+), O2(+), for reactions of O(+) + N2, N2(+) + O, and O(++) + O, and for various reactions involving O(+)(2D) and O(+)(2P) ions with O and N2.

Torr, D. G.; Torr, M. R.

1978-01-01

375

STARLIB: A NEXT-GENERATION REACTION-RATE LIBRARY FOR NUCLEAR ASTROPHYSICS  

SciTech Connect

STARLIB is a next-generation, all-purpose nuclear reaction-rate library. For the first time, this library provides the rate probability density at all temperature grid points for convenient implementation in models of stellar phenomena. The recommended rate and its associated uncertainties are also included. Currently, uncertainties are absent from all other rate libraries, and, although estimates have been attempted in previous evaluations and compilations, these are generally not based on rigorous statistical definitions. A common standard for deriving uncertainties is clearly warranted. STARLIB represents a first step in addressing this deficiency by providing a tabular, up-to-date database that supplies not only the rate and its uncertainty but also its distribution. Because a majority of rates are lognormally distributed, this allows the construction of rate probability densities from the columns of STARLIB. This structure is based on a recently suggested Monte Carlo method to calculate reaction rates, where uncertainties are rigorously defined. In STARLIB, experimental rates are supplemented with: (1) theoretical TALYS rates for reactions for which no experimental input is available, and (2) laboratory and theoretical weak rates. STARLIB includes all types of reactions of astrophysical interest to Z = 83, such as (p, {gamma}), (p, {alpha}), ({alpha}, n), and corresponding reverse rates. Strong rates account for thermal target excitations. Here, we summarize our Monte Carlo formalism, introduce the library, compare methods of correcting rates for stellar environments, and discuss how to implement our library in Monte Carlo nucleosynthesis studies. We also present a method for accessing STARLIB on the Internet and outline updated Monte Carlo-based rates.

Sallaska, A. L. [National Institute of Standards and Technology, Gaithersburg, MD 20899-8462 (United States); Iliadis, C.; Champange, A. E. [University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255 (United States); Goriely, S. [Institut d'Astronomie et d'Astrophysique, Universite Libre de Bruxelles, C.P. 226, B-1050 Brussels (Belgium); Starrfield, S.; Timmes, F. X., E-mail: anne.sallaska@nist.gov [Arizona State University, Tempe, AZ 85287-1504 (United States)

2013-07-15

376

Acceleration of the reaction of carbon dioxide into aqueous 2-amino-2-hydroxymethyl-1,3-propanediol solutions by piperazine addition  

Microsoft Academic Search

In this work, the kinetics of the reaction between CO2 and piperazine-activated aqueous solutions of a sterically hindered alkanolamine, 2-amino-2-hydroxymethyl-1,3-propanediol (AHPD) was studied in a wetted wall column contactor at 303.15, 313.15 and 323.15K. The AHPD concentration in the aqueous solutions was kept at 1kmolm-3 while the piperazine (PZ) concentration varied in the range 0.10.4kmolm-3. Under pseudo-first-order CO2 absorption conditions,

Francis Bougie; Julien Lauzon-Gauthier; Maria C. Iliuta

2009-01-01

377

Temperature-dependent reaction-rate expression for oxygen recombination at Shuttle entry conditions  

NASA Technical Reports Server (NTRS)

A temperature-dependent oxygen surface reaction-rate coefficient has been determined from experimental STS-2 heating and wall temperature data at altitudes of 77.91 km, 74.98 km, and 71.29 km. The coefficient is presented in an Arrhenius form and is shown to be less temperature dependent than previous results. Finite-rate viscous-shock-layer heating rates based on this present expression have been compared with predicted heating rates using the previous rate coefficients and with experimental heating data obtained over an extensive range of STS-2 and STS-3 entry conditions. A substantial improvement is obtained in comparison of experimental data and predicted heating rates using the present oxygen reaction-rate expression.

Zoby, E. V.; Simmonds, A. L.; Gupta, R. N.

1984-01-01

378

The nuclear fusion reaction rate based on relativistic equilibrium velocity distribution  

E-print Network

The Coulomb barrier is in general much higher than thermal energy. Nuclear fusion reactions occur only among few protons and nuclei with higher relative energies than Coulomb barrier. It is the equilibrium velocity distribution of these high-energy protons and nuclei that participates in determining the rate of nuclear fusion reactions. In the circumstance it is inappropriate to use the Maxwellian velocity distribution for calculating the nuclear fusion reaction rate. We use the relativistic equilibrium velocity distribution for this purpose. The rate based on the relativistic equilibrium velocity distribution has a reduction factor with respect to that based on the Maxwellian distribution, which factor depends on the temperature, reduced mass and atomic numbers of the studied nuclear fusion reactions. This signifies much to the solar neutrino problem.

Jian-Miin Liu

2002-10-20

379

Monte Carlo analysis of uncertainty propagation in a stratospheric model. 2: Uncertainties due to reaction rates  

NASA Technical Reports Server (NTRS)

A concise stratospheric model was used in a Monte-Carlo analysis of the propagation of reaction rate uncertainties through the calculation of an ozone perturbation due to the addition of chlorine. Two thousand Monte-Carlo cases were run with 55 reaction rates being varied. Excellent convergence was obtained in the output distributions because the model is sensitive to the uncertainties in only about 10 reactions. For a 1 ppby chlorine perturbation added to a 1.5 ppby chlorine background, the resultant 1 sigma uncertainty on the ozone perturbation is a factor of 1.69 on the high side and 1.80 on the low side. The corresponding 2 sigma factors are 2.86 and 3.23. Results are also given for the uncertainties, due to reaction rates, in the ambient concentrations of stratospheric species.

Stolarski, R. S.; Butler, D. M.; Rundel, R. D.

1977-01-01

380

The Effects of Thermonuclear Reaction Rate Variations on Nova Nucleosynthesis: A Sensitivity Study  

E-print Network

We investigate the effects of thermonuclear reaction rate uncertainties on nova nucleosynthesis. One-zone nucleosynthesis calculations have been performed by adopting temperature-density-time profiles of the hottest hydrogen-burning zone (i.e., the region in which most of the nucleosynthesis takes place). We obtain our profiles from 7 different, recently published, hydrodynamic nova simulations covering peak temperatures in the range from Tpeak=0.145-0.418 GK. For each of these profiles, we individually varied the rates of 175 reactions within their associated errors and analyzed the resulting abundance changes of 142 isotopes in the mass range below A=40. In total, we performed 7350 nuclear reaction network calculations. We use the most recent thermonuclear reaction rate evaluations for the mass ranges A=1-20 and A=20-40. For the theoretical astrophysicist, our results indicate the extent to which nova nucleosynthesis calculations depend on presently uncertain nuclear physics input, while for the experimental nuclear physicist our results represent at least a qualitative guide for future measurements at stable and radioactive ion beam facilities. We find that present reaction rate estimates are reliable for predictions of Li, Be, C and N abundances in nova nucleosynthesis. However, rate uncertainties of several reactions have to be reduced significantly in order to predict more reliable O, F, Ne, Na, Mg, Al, Si, S, Cl and Ar abundances. Results are presented in tabular form for each adopted nova simulation.

Christian Iliadis; Art Champagne; Jordi Jose; Sumner Starrfield; Paul Tupper

2002-06-03

381

Sensitivity of Type I X-Ray Bursts to rp-Process Reaction Rates  

E-print Network

First steps have been taken in a more comprehensive study of the dependence of observables in Type I X-ray bursts on uncertain (p,gamma) reaction rates along the rp-process path. We use the multizone hydrodynamics code KEPLER which implicitly couples a full nuclear reaction network of more than 1000 isotopes, as needed, to follow structure and evolution of the X-ray burst layer and its ashes. This allows us to incorporate the full rp-process network, including all relevant nuclear reactions, and individually study changes in the X-ray burst light curves when modifying selected key nuclear reaction rates. In this work we considered all possible proton captures to nuclei with 10 reaction rates within a symmetric full width uncertainty of a factor of 10000, early results for some rates show changes in the burst light curve as large as 10 percent of peak luminosity. This is very large compared to the current sensitivity of X-ray observations. More precise reaction rates are therefore needed to test current X-ray burst models, particularly of the burst rise, with observational data and to constrain astrophysical parameters.

A. Matthew Amthor; Daniel Galaviz; Alexander Heger; Alexander Sakharuk; Hendrik Schatz; Karl Smith

2006-08-21

382

The Reaction of Exchange Rates and Interest Rates to News Releases  

Microsoft Academic Search

This paper examines the response of exchange rates and interest rates--US and foreign--to economic news. The news is associated with the surprise component of the monthly release of six US macroeconomic variables. The results suggest that dollar exchange rates systematically react to news about real economic activity--a surprise of 100,000 on non-farm payroll employment leads to a 0.2% appreciation of

Hali J. Edison

1997-01-01

383

The reaction of exchange rates and interest rates to news releases  

Microsoft Academic Search

This paper examines the response of exchange rates and interest rates--U.S. and foreign--to economic news. The news is associated with the surprise component of the monthly release of six U.S. macroeconomic variables. The results suggest that dollar exchange rates systematically react to news about real economic activity--a surprise of 100,000 on nonfarm payroll employment leads to a 0.2 percent appreciation

Hali J. Edison

1996-01-01

384

Measurement of Screening Enhancement to Nuclear Reaction Rates using a Strongly Magnetized and Strongly Correlated Non-neutral Plasma  

E-print Network

Measurement of Screening Enhancement to Nuclear Reaction Rates using a Strongly Magnetized) An analogy is uncovered between the nuclear reaction rate in a dense neutral plasma and the energy. However, the twin requirements of high temperature (for measurable nuclear reaction rates) and high

California at San Diego, University of

385

Stochastic theory of large-scale enzyme-reaction networks: Finite copy number corrections to rate equation models  

E-print Network

Stochastic theory of large-scale enzyme-reaction networks: Finite copy number corrections to rate to the solutions of the rate equations for chemical reaction networks composed of arbitrarily large numbers of the rate equations will always underestimate the actual steady-state substrate concentrations for an enzyme-reaction

Straube, Arthur V.

386

Semi-Classical Theory for Non-separable Systems: Construction of "Good" Action-Angle Variables for Reaction Rate Constants*  

E-print Network

for Reaction Rate Constants* BY WILLIAMH. MILLER-^ Department of Chemistry, and Materials and Molecular A semiclassicalexpressionfor bimolecular rate constants for reactions which have a single activa- tion barrier is obtained as separable saddle points. 1. INTRODUCTION A semiclassical expression for reaction rate constants has recently

Miller, William H.

387

Thermonuclear rates of the 28Si(p, y) reaction M. Kicinska-Habior and T. Matulewicz  

E-print Network

1881 Thermonuclear rates of the 28Si(p, y) reaction M. Kicinska-Habior and T. Matulewicz Institute Thermonuclear reaction rates NA av > are the quan- tities of essential importance for models of stellar in a much more extended energy range. The thermonuclear rates of the 28Si(p, y) reaction, although it does

Paris-Sud XI, Universit de

388

Rate Constants for Reactions between Iodine-and Chlorine-Containing Species: A Detailed Mechanism of the  

E-print Network

Rate Constants for Reactions between Iodine- and Chlorine-Containing Species: A Detailed Mechanism. The final mechanism and rate constants of the overall reaction and of its subsystems were determined experimentally determined rate and equilibrium constants fits both the overall reaction and all of its subsystems

Epstein, Irving R.

389

Quantum Mechanical Pressure-Dependent Reaction and Recombination Rates for O + OH f H + O2, HO2  

E-print Network

ARTICLES Quantum Mechanical Pressure-Dependent Reaction and Recombination Rates for O + OH f H + O2 methods for the direct computation of thermal reaction rate constants and unimolecular recombination rates to the case where both reaction and recombination are possible. Rather than a single transition state dividing

Miller, William H.

390

Variable-Temperature Rate Coefficients of Proton-Transfer Equilibrium Reaction C2H4 + H3O+  

E-print Network

Variable-Temperature Rate Coefficients of Proton-Transfer Equilibrium Reaction C2H4 + H3O+ C2H5 the observed rate coefficients, a new type of reaction temperature was defined in these studies that considered rate coefficients of this reaction, with molecular beam and ion temperatures varied independently from

Sanov, Andrei

391

The reaction of radicals with Absolute rate coefficientC measurements for T = 295800 K, and quantum chemical study of  

E-print Network

be characterised over very broad temperature ranges. The rate constants of the reaction of with species such asC 2 experimental determinations of the rate coef- cient of the reaction over the temperatureC 2 H ] C 2 H 6 range of a wider study of the temperature dependences of the rates of reactions,C 2 H and the development

Nguyen, Minh Tho

392

Rate coefficients from quantum and quasi-classical cumulative reaction probabilities for the S(1D) + H2 reaction  

NASA Astrophysics Data System (ADS)

Cumulative reaction probabilities (CRPs) at various total angular momenta have been calculated for the barrierless reaction S(1D) + H2 ? SH + H at total energies up to 1.2 eV using three different theoretical approaches: time-independent quantum mechanics (QM), quasiclassical trajectories (QCT), and statistical quasiclassical trajectories (SQCT). The calculations have been carried out on the widely used potential energy surface (PES) by Ho et al. [J. Chem. Phys. 116, 4124 (2002), 10.1063/1.1431280] as well as on the recent PES developed by Song et al. [J. Phys. Chem. A 113, 9213 (2009), 10.1021/jp903790h]. The results show that the differences between these two PES are relatively minor and mostly related to the different topologies of the well. In addition, the agreement between the three theoretical methodologies is good, even for the highest total angular momenta and energies. In particular, the good accordance between the CRPs obtained with dynamical methods (QM and QCT) and the statistical model (SQCT) indicates that the reaction can be considered statistical in the whole range of energies in contrast with the findings for other prototypical barrierless reactions. In addition, total CRPs and rate coefficients in the range of 20-1000 K have been calculated using the QCT and SQCT methods and have been found somewhat smaller than the experimental total removal rates of S(1D).

Jambrina, P. G.; Lara, Manuel; Menndez, M.; Launay, J.-M.; Aoiz, F. J.

2012-10-01

393

Path Integral Approach to the Calculation of Reaction Rates for a Reaction Coordinate Coupled to a Dual Harmonic Bath  

E-print Network

We present a new method for the numerical calculation of canonical reaction rate constants in complex molecular systems, which is based on a path integral formulation of the flux-flux correlation function. Central is the partitioning of the total system into a relevant part coupled to a dual bath. The latter consists of two parts: First, a set of strongly coupled harmonic modes, describing, for example, intramolecular degrees of freedom. They are treated on the basis of a reaction surface Hamiltonian approach. Second, a set of bath modes mimicking an unspecific environment modeled by means of a continuous spectral density. After deriving a set of general equations expressing the canonical rate constant in terms of appropriate influence functionals, several approximations are introduced to provide an efficient numerical implementation. Results for an initial application to the H-transfer in 6-Aminofulvene-1-aldimine are discussed.

Yonggang Yang; Oliver Khn

2011-11-13

394

REACLIB: A Reaction Rate Library for the Era of Collaborative Science  

Microsoft Academic Search

Thermonuclear reaction rates and weak decay rates are of great importance to modern nuclear astrophysics. They are critical in the study of many topics such as Big Bang Nucleosynthesis, X-ray bursts, Supernovae, and S-process element formation, among others. The Joint Institute for Nuclear Astrophysics (JINA) has been created to increase connectivity amongst nuclear astrophysicists in our modern age of highly

Zachary Meisel

2008-01-01

395

The Effect of Conceptual Change Pedagogy on Students' Conceptions of Rate of Reaction  

ERIC Educational Resources Information Center

This paper reports on an investigation of the effect of conceptual change pedagogy on students' conceptions of "rate of reaction" concepts. The study used a pre-test/post-test non-equivalent comparison group design approach and the sample consisted of 72 Turkish grade-11 students (aged 16-18 years) selected from two intact classrooms. The "Rate of

Calik, Muammer; Kolomuc, Ali; Karagolge, Zafer

2010-01-01

396

Method and apparatus for obtaining enhanced production rate of thermal chemical reactions  

DOEpatents

Reactors and processes are disclosed that can utilize high heat fluxes to obtain fast, steady-state reaction rates. Porous catalysts used in conjunction with microchannel reactors to obtain high rates of heat transfer are also disclosed. Reactors and processes that utilize short contact times, high heat flux and low pressure drop are described. Improved methods of steam reforming are also provided.

Tonkovich, Anna Lee; Wang, Yong; Wegeng, Robert S.; Gao, Yufei

2003-09-09

397

Method and apparatus for obtaining enhanced production rate of thermal chemical reactions  

DOEpatents

Reactors and processes are disclosed that can utilize high heat fluxes to obtain fast, steady-state reaction rates. Porous catalysts used in conjunction with microchannel reactors to obtain high rates of heat transfer are also disclosed. Reactors and processes that utilize short contact times, high heat flux and low pressure drop are described. Improved methods of steam reforming are also provided.

Tonkovich, Anna Lee Y. (Pasco, WA); Wang, Yong (Richland, WA); Wegeng, Robert S. (Richland, WA); Gao, Yufei (Kennewick, WA)

2006-05-16

398

Interest rate reaction functions and the Taylor rule in the Euro area  

Microsoft Academic Search

Traditional Taylor rules, which are estimated using a level specification linking the short-term interest rate to inflation and the output gap, are unstable when estimated on euro area data and forecast poorly out of sample. We present an alternative reaction function which takes the non-stationarity of the data into account. The estimated interest rate rule is stable and forecasts well.

Petra Gerlach-Kristen

2003-01-01

399

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...

400

On the intrinsic reaction rate of biomass char gasification with carbon dioxide and steam  

Microsoft Academic Search

The gasification of beech wood char and oil palm shell char with carbon dioxide and steam was studied. To avoid heat and mass transport limitations during gasification, the amount of char, particle size and flow rate were varied in isothermal experiments. A rate expression of the LangmuirHinshelwood-type was applied to match the experimental data at different partial pressures and reaction

Wolfgang Klose; Michael Wlki

2005-01-01

401

Exothermic Systems with Diminishing Reaction Rates: Temperature Evolution, Criticality and Spontaneous Ignition in the Sphere  

Microsoft Academic Search

The behaviour of an exothermic, spherical mass, in which reaction rate diminishes with time t according to the law rate ? (t+t{_pr})-alpha, tpr >=slant 0, 0 <=slant alpha < 1, is studied by numerical computation. (Analytical solutions are not attainable.) This law is a useful empirical representation of various complex systems of great practical importance: coal, sawdust, wool, polypropylene and

T. Boddington; P. Gray; I. K. Walker

1980-01-01

402

REACLIB: A Reaction Rate Library for the Era of Collaborative Science  

NASA Astrophysics Data System (ADS)

Thermonuclear reaction rates and weak decay rates are of great importance to modern nuclear astrophysics. They are critical in the study of many topics such as Big Bang Nucleosynthesis, X-ray bursts, Supernovae, and S-process element formation, among others. The Joint Institute for Nuclear Astrophysics (JINA) has been created to increase connectivity amongst nuclear astrophysicists in our modern age of highly collaborative science. Within JINA there has been an effort to create a frequently updated and readily accessible database of thermonuclear reactions and weak decay rates. This database is the REACLIB library, which can be accessed at the web address: http://www.nscl.msu.edu/nero/db/. Here I will discuss the JINA REACLIB Project, including a new procedure to fit reaction rates as a function of temperature that takes full advantage of physicality. With these updated reaction rates, astrophysical modelers will no longer have to worry about the adverse effects of using obsolete reaction rate libraries lacking physical behavior.

Meisel, Zachary

2008-10-01

403

Reevaluation of the O(+)(2P) reaction rate coefficients derived from Atmosphere Explorer C observations  

NASA Technical Reports Server (NTRS)

O(+)(2P) is an important species for studies of the ionosphere and thermosphere: its emission at 7320 A can be used as a diagnostic of the thermospheric atomic oxygen density. Unfortunately, there are no laboratory measurements of the O and N2 reaction rates which are needed to determine the major sinks of (O+)(2p). We have recalculated the O and N2 reaction rates for O(+) (2P) using recent improvements in the solar EUV flux, cross sections, and photoelectron fluxes. For the standard solar EUV flux, the new N2 reaction rate of 3.4 +/- 1.5 x 10 exp -10 cu cm/s is close to the value obtained by Rusch et al. (1977), but the new O reaction rate of 4.0 +/- 1.9 x 10 exp -10 cu cm/sec is about 8 times larger. These new reaction rates are derived using neutral densities, electron density, and solar EUV fluxes measured by Atmosphere Explorer C in 1974 during solar minimum. The new theoretical emission rates are in good agreement with the data for the two orbits studied by Rusch et al.

Chang, T.; Torr, D. G.; Richards, P. G.; Solomon, S. C.

1993-01-01

404

Reaction rate and energy-loss rate for photopair production by relativistic nuclei  

NASA Technical Reports Server (NTRS)

The process of e(+/-) pair production by relativistic nuclei on ambient photons is considered. The process is important for cosmic-ray nuclei in interstellar and intergalactic space as well as in galactic and extragalactic compact objects. The rate of this process is given by an integral of the cross section over the photon angular and energy distribution. In the case of isotropic photons, the angular integration is performed to provide an expression for the rate at given photon energy in the nucleus rest frame. The total rate then becomes a single integral of that rate over the photon energy distribution. Formulas are also given for the fractional energy loss of a relativistic nucleus colliding with a photon of a given energy in the rest frame. The nucleus energy-loss rate is integrated over the photon angular distribution in the case of isotropic photons, and simple fits are provided.

Chodorowski, Michal J.; Zdziarski, Andrzej A.; Sikora, Marek

1992-01-01

405

On the Influence of Uncertainties in Chemical Reaction Rates on Results of the Astrochemical Modelling  

E-print Network

With the chemical reaction rate database UMIST95 (Millar et al. 1997) we analyze how uncertainties in rate constants of gas-phase chemical reactions influence the modelling of molecular abundances in the interstellar medium. Random variations are introduced into the rate constants to estimate the scatter in theoretical abundances. Calculations are performed for dark and translucent molecular clouds where gas phase chemistry is adequate. Similar approach was used by Pineau des Forets & Roueff (2000) for the study of chemical bistability. All the species are divided into 6 sensitivity groups according to the value of the scatter in their model abundances computed with varied rate constants. It is shown that the distribution of species within these groups depends on the number of atoms in a molecule and on the adopted physical conditions. The simple method is suggested which allows to single out reactions that are most important for the evolution of a given species.

A. I. Vasyunin; A. M. Sobolev; D. S. Wiebe; D. A. Semenov

2003-11-19

406

Rate Coefficient Measurements of the Reaction CH3 + O2 = CH3O + O  

NASA Technical Reports Server (NTRS)

Rate coefficients for the reaction CH3 + O2 = CH3O + O were measured behind reflected shock waves in a series of lean CH4-O2-Ar mixtures using hydroxyl and methyl radical diagnostics. The rate coefficients are well represented by an Arrhenius expression given as k = (1.60(sup +0.67, sub -0.47 ) x 10(exp 13) e(-15813 +/- 587 K/T)/cubic cm.mol.s. This expression, which is valid in the temperature range 1575-1822 K, supports the downward trend in the rate coefficients that has been reported in recent determinations. All measurements to date, including the present study, have been to some extent affected by secondary reactions. The complications due to secondary reactions, choice of thermochemical data, and shock-boundary layer interactions that affect the determination of the rate coefficients are examined.

Hwang, S. M.; Ryu, Si-Ok; DeWitt, K. J.; Rabinowitz, M. J.

1999-01-01

407

Rate Coefficient Measurements of the Reaction CH3+O2+CH3O+O  

NASA Technical Reports Server (NTRS)

Rate coefficients for the reaction CH3 + O2 = CH3O + O were measured behind reflected shock waves in a series of lean CH4-O2-Ar mixtures using hydroxyl and methyl radical diagnostics. The rate coefficients are well represented by an Arrhenius expression given as k = (1.60(sup +0.67, -0.47)) X 10(exp 13) exp(- 15813 +/- 587 K/T)cc/mol s. This expression, which is valid in the temperature range 1575-1822 K, supports the downward trend in the rate coefficients that has been reported in recent determinations. All measurements to date, including the present study, have been to some extent affected by secondary reactions. The complications due to secondary reactions, choice of thermochemical data, and shock-boundary layer interactions that affect the determination of the rate coefficients are examined.

Hwang, S. M.; Ryu, Si-Ok; DeWitt, K. J.; Rabinowitz, M. J.

1999-01-01

408

Venus volcanism: Rate estimates from laboratory studies of sulfur gas-solid reactions  

NASA Technical Reports Server (NTRS)

Thermochemical reactions between sulfur-bearing gases in the atmosphere of Venus and calcium-, iron-, magnesium-, and sulfur-bearing minerals on the surface of Venus are an integral part of a hypothesized cycle of thermochemical and photochemical reactions responsible for the maintenance of the global sulfuric acid cloud cover on Venus. SO2 is continually removed from the Venus atmosphere by reaction with calcium bearing minerals on the planet's surface. The rate of volcanism required to balance SO2 depletion by reactions with calcium bearing minerals on the Venus surface can therefore be deduced from a knowledge of the relevant gas-solid reaction rates combined with reasonable assumptions about the sulfur content of the erupted material (gas + magma). A laboratory program was carried out to measure the rates of reaction between SO2 and possible crustal minerals on Venus. The reaction of CaCO3(calcite) + SO2 yields CaSO4 (anhydrite) + CO was studied. Brief results are given.

Ehlers, K.; Fegley, B., Jr.; Prinn, R. G.

1989-01-01

409

NUCLEAR PHYSICS: Determination of the stellar reaction rate for 12C(alpha, gamma)16O: using a new expression with the reaction mechanism  

Microsoft Academic Search

The astrophysical reaction rate of 12C(alpha, gamma)16O plays a key role in massive star evolution. However, this reaction rate and its uncertainties have not been well determined yet, especially at T9 = 0.2. The existing results even disagree with each other to a certain extent. In this paper, the E1, E2 and total (E1+E2) 12C(alpha, gamma)16O reaction rates are calculated

Yi Xu; Wang Xu; Yu-Gang Ma; Xiang-Zhou Cai; Jin-Gen Chen; Gong-Tao Fan; Guang-Wei Fan; Wei Guo; Wen Luo; Qiang-Yan Pan; Wen-Qing Shen; Li-Feng Yang

2009-01-01

410

Predicting gas phase organic molecule reaction rates using linear free-energy correlations. I. O(³P) and OH addition and abstraction reactions  

Microsoft Academic Search

Linear free-energy (LFE) correlations for gas phase O(³P) and OH addition and abstraction reactions with a number of organic compounds have been established using existing room-temperature rate constants evaluated from the literature. Addition reaction rate constant correlations with ionization potential and abstraction reaction rate constant corelations with bond dissociation energies are examined and compared to the LFE approach. Using multiple

J. S. Gaffney; S. Z. Levine

1979-01-01

411

Reaction of the m-THPC triplet state with the antioxidant Trolox and the anesthetic Propofol: modulation of photosensitization mechanisms relevant to photodynamic therapy?  

PubMed

Antioxidants may affect the outcome of photodynamic therapy (PDT) through the inactivation of reactive oxygen species. Their direct interaction with photosensitizers excited at the triplet state is also worthy of interest. This process is investigated by laser flash photolysis of m-THPC (meso-tetra(3-hydroxyphenyl)chlorin, Foscan) hydroalcoholic solutions added with Trolox (TrOH), a standard antioxidant or Propofol (PfOH, Diprivan()), a common anesthetic agent also characterized for its antioxidant properties. Transient UV-visible absorption spectra, kinetics at selected wavelengths and final spectra after extensive laser irradiation show that both compounds react with the m-THPC triplet state, (3)m-THPC, to ultimately restore the photosensitizer in its ground state. For PfOH, this process mainly appears as a single step obeying pseudo-first order kinetics. The bimolecular rate constant for the quenching of (3)m-THPC by PfOH is around 2 10(6) M(-1) s(-1), a value increased to some extent by the water content of the solution. A bimolecular reaction between (3)m-THPC and TrOH is observed with a rate constant of similar magnitude and dependence upon water. However, the reaction leads, at least partly, to intermediate species assigned to the TrO? radical and the m-THPC anion radical. Within a few ms, these species back react to yield m-THPC in its ground state. A general mechanism involving an intermediate activated complex with some charge transfer character is proposed. Depending on the redox potentials for the oxidation of the antioxidant, this complex evolves predominantly either toward the formation of radicals (TrOH) or back to the photosensitizer ground state (PfOH). Notably, the kinetics data suggest that Propofol may quench (3)m-THPC at concentrations relevant of clinical situation in PDT involving anesthesia. PMID:22307091

Friaa, O; Maillard, P; Brault, D

2012-04-01

412

Kinetic study of the proton transfer reaction between 1-nitro-1-(4-nitrophenyl)alkanes and P 1- t-Bu phosphazene base in THF solvent  

NASA Astrophysics Data System (ADS)

The rates of proton transfer reactions between C-acids of the series of nitroalkanes with increasing bulk of R=H, Me, Et, i-Pr substituents as 4-nitro-phenylnitromethane ( 1), 1-(4-nitrophenyl)-1-nitroethane ( 2), 1-(4-nitrophenyl)-1-nitropropane ( 3), 2-methyl-1-(4-nitrophenyl)-1-nitropropane ( 4) and the P 1- t-Bu phosphazene have been measured in THF at pseudo-first-order conditions. The product of the proton transfer reaction with P 1- t-Bu is associated into ion pair. The equilibrium constants decrease along with growing bulk of alkyl substituent in the reacting C-acid: >100 000, 1170, 590, and 11.8 for 1, 2, 3, 4, respectively. The second order rate constants ( k2H) for this very strong base and C-acids are rapidly declining: 9357, 2.31, 0.66, 0.09 dm 3 mol -1 s -1 for 1, 2, 3, 4, respectively, and could not be accounted for the small values of the enthalpies of activation ?HH?=6.1,18.0,20.7 and 11.1 kJ mol. The appropriate values of the entropies of activation were all negative and relatively large ?SH?=-149.7,-176.5,-178.7,-227.8 J mol deg indicating an importance of steric and ordering effects in forming the transition state. The primary deuterium kinetic isotope effects are large showing tendency of reverse relation towards steric hindrance of the reacting C-acids, kH/ kD=15.8, 13.6, 13.2 for 1, 2, and 3, respectively. The explanation of the unusual slow proton transfer abstraction caused by this extremely strong base is undertaken.

Wis?ocka, ?aneta; Nowak, Iwona; Jarczewski, Arnold

2006-05-01

413

Effective reaction rates in diffusion-limited phosphorylation-dephosphorylation cycles  

NASA Astrophysics Data System (ADS)

We investigate the kinetics of the ubiquitous phosphorylation-dephosphorylation cycle on biological membranes by means of kinetic Monte Carlo simulations on the triangular lattice. We establish the dependence of effective macroscopic reaction rate coefficients as well as the steady-state phosphorylated substrate fraction on the diffusion coefficient and concentrations of opposing enzymes: kinases and phosphatases. In the limits of zero and infinite diffusion, the numerical results agree with analytical predictions; these two limits give the lower and the upper bound for the macroscopic rate coefficients, respectively. In the zero-diffusion limit, which is important in the analysis of dense systems, phosphorylation and dephosphorylation reactions can convert only these substrates which remain in contact with opposing enzymes. In the most studied regime of nonzero but small diffusion, a contribution linearly proportional to the diffusion coefficient appears in the reaction rate. In this regime, the presence of opposing enzymes creates inhomogeneities in the (de)phosphorylated substrate distributions: The spatial correlation function shows that enzymes are surrounded by clouds of converted substrates. This effect becomes important at low enzyme concentrations, substantially lowering effective reaction rates. Effective reaction rates decrease with decreasing diffusion and this dependence is more pronounced for the less-abundant enzyme. Consequently, the steady-state fraction of phosphorylated substrates can increase or decrease with diffusion, depending on relative concentrations of both enzymes. Additionally, steady states are controlled by molecular crowders which, mostly by lowering the effective diffusion of reactants, favor the more abundant enzyme.

Szyma?ska, Paulina; Kocha?czyk, Marek; Miekisz, Jacek; Lipniacki, Tomasz

2015-02-01

414

Scale-dependent rates of uranyl surface complexation reaction in sediments  

NASA Astrophysics Data System (ADS)

Scale-dependency of uranyl[U(VI)] surface complexation rates was investigated in stirred flow-cell and column systems using a U(VI)-contaminated sediment from the US Department of Energy, Hanford site, WA. The experimental results were used to estimate the apparent rate of U(VI) surface complexation at the grain-scale and in porous media. Numerical simulations using molecular, pore-scale, and continuum models were performed to provide insights into and to estimate the rate constants of U(VI) surface complexation at the different scales. The results show that the grain-scale rate constant of U(VI) surface complexation was over 3-10 orders of magnitude smaller than the rate constant calculated using the molecular simulations. The largest rate constant at the grain-scale decreased additional 2 orders of magnitude when the rate was scaled to the porous media in the column. The scaling effect from the grain-scale to the porous media became less important for the slower sorption sites. Pore-scale simulations revealed the importance of coupled mass transport and reactions in both intragranular and inter-granular domains, which caused both spatial and temporal dependence of U(VI) surface complexation rates in the sediment. Pore-scale simulations also revealed that the rate of coupled diffusion and molecular surface complexation reaction in the intragranular porous domains was slower than either individual process alone. The results provide important implications for developing models to scale geochemical/biogeochemical reactions.

Liu, Chongxuan; Shang, Jianying; Kerisit, Sebastien; Zachara, John M.; Zhu, Weihuang

2013-03-01

415

The rate of the reaction between CN and C2H2 at interstellar temperatures.  

PubMed

The rate coefficient for the important interstellar reaction between CN and C2H2 has been calculated as a function of temperature between 10 and 300 K. The potential surface for this reaction has been determined through ab initio quantum chemical techniques; the potential exhibits no barrier in the entrance channel but does show a small exit channel barrier, which lies below the energy of reactants. Phase-space calculations for the reaction dynamics, which take the exit channel barrier into account, show the same unusual temperature dependence as determined by experiment, in which the rate coefficient at first increases as the temperature is reduced below room temperature and then starts to decrease as the temperature drops below 50-100 K. The agreement between theory and experiment provides strong confirmation that the reaction occurs appreciably at cool interstellar temperatures. PMID:11541461

Woon, D E; Herbst, E

1997-03-01

416

Nonequilibrium Weak Processes in Kaon Condensation I --- Reaction rate for the thermal kaon process ---  

E-print Network

We investigate the thermal kaon process,in which kaons are thermally produced via nucleon-nucleon collisions.This process is relevant to nonequilibrium dynamics of kaon condensation inside neutron stars.The reaction rates for these processes are calculated, and their temperature and density dependences are compared with those of other reaction rates.It is shown that the thermal kaon process is dominant over other relevant weak reactions throughout the nonequilibrium process, such as the kaon-induced Urca and the modified Urca reactions, and may control the entire evolution of the kaon condensate. The characteristic role of the soft and hard kaons during the evolution is explained, and implications for astrophysical phenomena are briefly discussed.

Takumi Muto; Toshitaka Tatsumi; Naoki Iwamoto

1999-06-09

417

The thermonuclear rate for the 19F(a,p)22Ne reaction at stellar temperatures  

E-print Network

The $^{19}$F($\\alpha$,p)$^{22}$Ne reaction is considered to be one of the main sources of fluorine depletion in AGB and Wolf-Rayet stars. The reaction rate still retains large uncertainties due to the lack of experimental studies available. In this work the yields for both exit channels to the ground state and first excited state of $^{22}$Ne have been measured and several previously unobserved resonances have been found in the energy range E$_{lab}$=792-1993 keV. The level parameters have been determined through a detailed R-matrix analysis of the reaction data and a new reaction rate is provided on the basis of the available experimental information.

Claudio Ugalde; Richard Azuma; Aaron Couture; Joachim Grres; Hye-Young Lee; Edward Stech; Elizabeth Strandberg; Wanpeng Tan; Michael Wiescher

2008-03-04

418

Unbound states of 32Cl and the 31S(p,?)32Cl reaction rate  

E-print Network

The 31S(p,\\gamma)32Cl reaction is expected to provide the dominant break-out path from the SiP cycle in novae and is important for understanding enrichments of sulfur observed in some nova ejecta. We studied the 32S(3He,t)32Cl charge-exchange reaction to determine properties of proton-unbound levels in 32Cl that have previously contributed significant uncertainties to the 31S(p,\\gamma)32Cl reaction rate. Measured triton magnetic rigidities were used to determine excitation energies in 32Cl. Proton-branching ratios were obtained by detecting decay protons from unbound 32Cl states in coincidence with tritons. An improved 31S(p,\\gamma)32Cl reaction rate was calculated including robust statistical and systematic uncertainties.

M. Mato; J. C. Blackmon; L. E. Linhardt; D. W. Bardayan; C. D. Nesaraja; J. A. Clark; C. M. Deibel; P. D. O'Malley; P. D. Parker

2011-11-20

419

Unbound states of (32)Cl andthe (31)S(p,gamma)(32)Cl reaction rate  

SciTech Connect

The {sup 31}S(p,{gamma}){sup 32}Cl reaction is expected to provide the dominant break-out path from the SiP cycle in novae and is important for understanding enrichments of sulfur observed in some nova ejecta. We studied the {sup 32}S(3He,t){sup 32}Cl charge-exchange reaction to determine properties of proton-unbound levels in {sup 32}Cl that have previously contributed significant uncertainties to the {sup 31}S(p,{gamma}){sup 32}Cl reaction rate. Measured triton magnetic rigidities were used to determine excitation energies in {sup 32}Cl. Proton-branching ratios were obtained by detecting decay protons from unbound {sup 32}Cl states in coincidence with tritons. An improved {sup 31}S(p,{gamma}){sup 32}Cl reaction rate was calculated including robust statistical and systematic uncertainties.

Matos, M. [Louisiana State University; Blackmon, Jeff C [ORNL; Linhardt, Laura [Louisiana State University; Bardayan, Daniel W [ORNL; Nesaraja, Caroline D [ORNL; Clark, Jason [Argonne National Laboratory (ANL); Diebel, C. [Yale University; O'Malley, Patrick [Rutgers University; Parker, P.D. [Yale University

2011-01-01

420

The rate of the reaction between CN and C2H2 at interstellar temperatures  

NASA Technical Reports Server (NTRS)

The rate coefficient for the important interstellar reaction between CN and C2H2 has been calculated as a function of temperature between 10 and 300 K. The potential surface for this reaction has been determined through ab initio quantum chemical techniques; the potential exhibits no barrier in the entrance channel but does show a small exit channel barrier, which lies below the energy of reactants. Phase-space calculations for the reaction dynamics, which take the exit channel barrier into account, show the same unusual temperature dependence as determined by experiment, in which the rate coefficient at first increases as the temperature is reduced below room temperature and then starts to decrease as the temperature drops below 50-100 K. The agreement between theory and experiment provides strong confirmation that the reaction occurs appreciably at cool interstellar temperatures.

Woon, D. E.; Herbst, E.

1997-01-01

421

A kinetics study of the O( sup 3 P) + CH sub 3 Cl reaction over the 556-1485 K range by the HTP and LP-ST techniques  

SciTech Connect

The high-temperature photochemistry (HTP) and laser photolysis-shock tube (LP-ST) techniques have been combined to study the kinetics of the reaction between ground-state oxygen atoms with CH{sub 3}Cl over the temperature range, 556--1485 K. In the HTP reactor, used for the 556--1291 K range, O atoms were generated by flash photolysis of O{sub 2}, CO{sub 2} or SO{sub 2}, and the atom concentrations were monitored by resonance fluorescence, while with the LP-ST technique, used for the 916--1485 K range, O atoms were generated by the photolysis of either SO{sub 2} or NO with the 193 nm light from a pulsed ArF excimer laser, and atomic resonance absorption spectroscopy (ARAS) was used to monitor (O){sub t}. In both studies, rate coefficients were derived from the (O) profiles under the pseudo-first-order condition, (O){much lt}(CH{sub 3}Cl). The data obtained by the two techniques are in excellent agreement and are best represented by the expression, k(T) = 2.57 {times} 10{sup {minus}11} (T/K){sup 0.31} exp({minus}5633 K/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} with a 2{sigma} precision varying from {plus minus}6 {plus minus}22% and an estimated 2{sigma} accuracy of {plus minus}21% to {plus minus}30%, depending on temperature. The rate coefficients for the title reaction are essentially identical to those for the O + CH{sub 4} reaction over the observed temperature range, the reasons for which are discussed.

Ko, Taeho; Fontijn, A. (Rensselaer Polytechnic Inst., Troy, NY (United States). High-Temperature Reaction Kinetics Lab.); Lim, K.P.; Michael, J.V. (Argonne National Lab., IL (United States))

1991-12-01

422

A kinetics study of the O({sup 3}P) + CH{sub 3}Cl reaction over the 556-1485 K range by the HTP and LP-ST techniques  

SciTech Connect

The high-temperature photochemistry (HTP) and laser photolysis-shock tube (LP-ST) techniques have been combined to study the kinetics of the reaction between ground-state oxygen atoms with CH{sub 3}Cl over the temperature range, 556--1485 K. In the HTP reactor, used for the 556--1291 K range, O atoms were generated by flash photolysis of O{sub 2}, CO{sub 2} or SO{sub 2}, and the atom concentrations were monitored by resonance fluorescence, while with the LP-ST technique, used for the 916--1485 K range, O atoms were generated by the photolysis of either SO{sub 2} or NO with the 193 nm light from a pulsed ArF excimer laser, and atomic resonance absorption spectroscopy (ARAS) was used to monitor [O]{sub t}. In both studies, rate coefficients were derived from the [O] profiles under the pseudo-first-order condition, [O]{much_lt}[CH{sub 3}Cl]. The data obtained by the two techniques are in excellent agreement and are best represented by the expression, k(T) = 2.57 {times} 10{sup {minus}11} (T/K){sup 0.31} exp({minus}5633 K/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} with a 2{sigma} precision varying from {plus_minus}6 {plus_minus}22% and an estimated 2{sigma} accuracy of {plus_minus}21% to {plus_minus}30%, depending on temperature. The rate coefficients for the title reaction are essentially identical to those for the O + CH{sub 4} reaction over the observed temperature range, the reasons for which are discussed.

Ko, Taeho; Fontijn, A. [Rensselaer Polytechnic Inst., Troy, NY (United States). High-Temperature Reaction Kinetics Lab.; Lim, K.P.; Michael, J.V. [Argonne National Lab., IL (United States)

1991-12-01

423

Correlation analysis of the progesterone-induced sperm acrosome reaction rate and the fertilisation rate in vitro.  

PubMed

In this study, we aimed to investigate whether progesterone-induced acrosome reaction (AR) rate could be an indicator for fertilisation rate in vitro. Twenty-six couples with unexplained infertility and undergoing in vitro fertilisation (IVF) treatment were involved. On the oocytes retrieval day after routine IVF, residual sperm samples were collected to receive progesterone induction (progesterone group) or not (control group). AR rate was calculated and fertilisation rate was recorded. The correlation between progesterone-induced AR and fertilisation rate and between sperm normal morphology and 3PN (tripronuclear) were analysed using the Spearman correlation analysis. The AR rate of progesterone group was statistically higher than that of the control group (15.65.88% versus 9.665.771%, P<0.05), but not significantly correlated with fertilisation rate (r=-0.053, P>0.01) or rate of high-quality embryo development (r=-0.055, P>0.01). Normal sperm morphology also showed no significant correlation with the amount of 3PN zygotes (r=0.029, P>0.01), rate of 3PN zygotes production (r=0.20, P>0.01), rate of 3PN embryo development (r=-0.406, P>0.01), fertilisation rate (r=-0.148, P>0.01) or progesterone-induced AR rate (r=0.214, P>0.01). Progesterone can induce AR in vitro significantly; however, the progesterone-induced AR may not be used to indicate fertilisation rate. PMID:25310969

Jiang, T; Qin, Y; Ye, T; Wang, Y; Pan, J; Zhu, Y; Duan, L; Li, K; Teng, X

2014-10-13

424

A study of rates of reaction of some substituted diphenyldiazomethanes and benzoic acid  

E-print Network

. Log of the Optical Density Versus Time.............. 31 2. Log k Versus reaction for organic molecules... in the field of reaction rates (1). L. P. Hammett, "Physical Organic Chemistry", 1st ed., McGraw-Hill Book Co., Inc., New York, N.Y., 19^0, p. 185. (2). H. Staudinger and A* Gaule, Ber., 1897 (1916). (3). H. Staudinger, Helv. Chim. Acta, 4, 239 (1921...

Gilby, Ralph Fredrick

1954-01-01

425

Nuclear Reaction Rate Uncertainties and their effects on Nova Nucleosynthesis Modeling  

E-print Network

The nucleosynthesis and other observable consequences of a nova outburst depend sensitively on the details of the thermonuclear runaway which initiates the outburst. One important source of uncertainty in our current models is the nuclear reaction data used as input for the evolutionary calculations. We present preliminary results of the first analyses of the impact on nova nucleosynthesis of all reaction rate uncertainties considered simultaneously.

W. Raphael Hix; Michael S. Smith; Anthony Mezzacappa; Sumner Starrfield; Donald L. Smith

2001-01-05

426

Astrophysical Rate for 12N(p,g)13O Direct Capture Reactions  

E-print Network

The proton capture on the unstable nuclei plays a very important role for the nucleonsynthesis. The 12N(p,g)13O reaction rates at the energies of astrophysical interests are estimated with the spectroscopic factor and asymptotic normalization coefficient methods. The present results show that the 12N(p,g)13O reaction may play an important role in x-ray bursts.

Li Zhi-Hong

2009-03-17

427

Computer generated pyrolysis modeling: On-the-fly generation of species, reactions, and rates  

Microsoft Academic Search

The development of an integrated system for the computer generation of kinetic models is described. Required input is the structure of the reactants, the reaction rules, and the parameters of a structure\\/property kinetics correlation. The algorithm transforms this information into reactant\\/product relationships, i.e., the reaction network, species properties, rate constants, and the FORTRAN code corresponding to the governing species' balance

Linda J. Broadbelt; Scott M. Stark; Michael T. Klein

1994-01-01

428

On the enhancement of nuclear reaction rates in high-temperature plasma  

Microsoft Academic Search

We argue that the Maxwellian approximation can essentially underestimate the rates of some nuclear reactions in hot plasma under conditions very close to thermal equilibrium. This phenomenon is demonstrated explicitly on the example of reactions in self-sustained DT fusion plasma with admixture of light elements X=Li,Be,C. A kinetic analysis shows that the reactivity enhancement results from non-Maxwellian knock-on perturbations of

Makoto Nakamura; Victor T. Voronchev; Yasuyuki Nakao

2006-01-01

429

Adsorbed species and reaction rates for NO-CO-O 2 over Rh(111)  

Microsoft Academic Search

We have studied the NO-CO-O2 reaction over a Rh(111) catalyst by monitoring the reaction products (CO2, N2O, and N2) and the infrared (IR) intensity of surface CO and NO at various partial pressures of NO, CO and O2, and sample temperatures. The selectivity for N2O formation, apparent activation energy for product formation, and NO consumption rate during NO-CO-O2 are identical

H. Permana; K. Y. Simon Ng; C. H. F. Peden; S. J. Schmieg; D. K. Lambert; D. N. Belton

1997-01-01

430

The effect of phase transition of methanol on the reaction rate in the alkylation of hydroquinone  

Microsoft Academic Search

An O-alkylation reaction of hydroquinone with excess methanol was carried out by using alkaline metal ion-exchanged zeolite\\u000a catalysts at various phases of methanol in a slurry type reactor. The amount of methanol, used as a methylating agent and\\u000a also a solvent, significantly affected the reaction rate. When the amount of methanol was decreased from 2 mol to 0.6 mol,\\u000a the

Jung Je Park; Soo Chool Lee; Sang Sung Lee; Suk Yong Jung; Soo Jae Lee; Jae Chang Kim

2009-01-01

431

Rate of browning reaction during preparation of coconut and palm sugar  

Microsoft Academic Search

The objective of this research was to analyse the rate of browning reaction during preparation of palm and coconut sugar. Brown colour formation during preparation of coconut sugar at a laboratory scale followed a zero order reaction with a constant of formation (k) equal to 5.1510?3 AU min?1 (AU=Absorbance Unit). The amount of glucose, fructose and sucrose decreased during this

Anton Apriyantono; Astrid Aristyani; Nurhayati; Yeni Lidya; Slamet Budiyanto; Soewarno T Soekarto

2002-01-01

432

Thermonuclear rate for the F(,p)Ne reaction at stellar temperatures  

Microsoft Academic Search

The F(,p)Ne reaction is considered to be one of the main sources of fluorine depletion in AGB and Wolf-Rayet stars. The reaction rate still retains large uncertainties due to the lack of experimental studies available. In this work the yields for both exit channels to the ground state and first excited state of Ne have been measured and several previously

C. Ugalde; R. E. Azuma; A. Couture; J. Goerres; H. Y. Lee; E. Stech; E. Strandberg; W. Tan; M. Wiescher

2008-01-01

433

Capture Gamma Reaction Rates at Stellar Energies by the Asymptotic Normalization Coefficient Method  

NASA Astrophysics Data System (ADS)

Peripheral transfer reactions can be used to determine asymptotic normalization coefficients (ANCs). These coefficients, which provide the normalization of the tail of the overlap function for a proton bound to a nucleus, determine S factors for direct capture reactions at astrophysical energies. A variety of proton transfer reactions have been used to measure ANCs using both stable and radioactive beams. The technique of utilizing ANCs to predict astrophysical S factors has been tested for 9Be(p, ?)10B, 16O(p, ?)17F and recently 13C(p, ?)14N using ANCs from transfer reaction measurements. Recent applications include measurements of ANCs appropriate for determining stellar reaction rates for 7Be(p, ?)8B, 11C(p, ?)12N and 14N(p, ?)15O.

Tribble, R. E.; Azhari, A.; Gagliardi, C. A.; Mukhamedzhanov, A. M.; Pirlepesov, F.; Sattarov, A.; Tang, X.; Trache, L.; Bem, P.; Burjan, V.; Kroha, V.; Novk, J.; Pisko?, .; imeckov, E.; Vincour, J.; Crstoiu, F.

2003-06-01

434

Calculations on the rate of the ion-molecule reaction between NH3(+) and H2  

NASA Technical Reports Server (NTRS)

The rate coefficient for the ion-molecule reaction NH3(+) + H2 yields NH4(+) + H has been calculated as a function of temperature with the use of the statistical phase space approach. The potential surface and reaction complex and transition state parameters used in the calculation have been taken from ab initio quantum chemical calculations. The calculated rate coefficient has been found to mimic the unusual temperature dependence measured in the laboratory, in which the rate coefficient decreases with decreasing temperature until 50-100 K and then increases at still lower temperatures. Quantitative agreement between experimental and theoretical rate coefficients is satisfactory given the uncertainties in the ab initio results and in the dynamics calculations. The rate coefficient for the unusual three-body process NH3(+) + H2 + He yields NH4(+) + H + He has also been calculated as a function of temperature and the result found to agree well with a previous laboratory determination.

Herbst, Eric; Defrees, D. J.; Talbi, D.; Pauzat, F.; Koch, W.

1991-01-01

435

Thermonuclear reaction rate of ¹⁷O(p,γ)¹⁸F  

Microsoft Academic Search

The ¹⁷O(p,γ)¹⁸F and ¹⁷O(p,α)¹⁴N reactions have a profound influence on hydrogen-burning nucleosynthesis in a number of stellar sites, including red giants, asymptotic giant branch (AGB) stars, massive stars, and classical novae. Previously evaluated thermonuclear rates for both reactions carry large uncertainties. We investigated the proton-capture reaction on ¹⁷O in the bombarding energy range of E{sub p}{sup lab} = 180-540 keV.

C. Fox; C. Iliadis; A. E. Champagne; R. P. Fitzgerald; R. Longland; J. Newton; J. Pollanen; R. Runkle

2005-01-01

436

Rate constants for chemical reactions in high-temperature nonequilibrium air  

NASA Technical Reports Server (NTRS)

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.

Jaffe, R. L.

1986-01-01

437

A simple recipe for modeling reaction-rate in flows with turbulent-combustion  

NASA Technical Reports Server (NTRS)

A computationally viable scheme to account for chemical reaction in turbulent flows is presented. The multivariate beta-pdf model for multiple scalar mixing forms the basis of this scheme. Using the model scalar joint pdf and a general form of the instantaneous reaction-rate, the unclosed chemical reaction terms are expressed as simple functions of scalar means and the turbulent scalar energy. The calculation procedure requires that the mean scalar equations and only one other transport equation - for the turbulent scalar energy - be solved.

Girimaji, Sharath S.

1991-01-01

438

Absolute rate parameters for the reaction of ground state atomic oxygen with dimethyl sulfide and episulfide  

NASA Technical Reports Server (NTRS)

It is pointed out that the investigated reaction of oxygen with dimethyl sulfide may play an important role in photochemical smog formation and in the chemical evolution of dense interstellar clouds. Kinetic data were obtained with the aid of the flash photolysis-resonance fluorescence method. The photodecomposition of molecular oxygen provided the oxygen atoms for the experiments. The decay of atomic oxygen was studied on the basis of resonance fluorescence observations. Both reactions investigated were found to be fast processes. A negative temperature dependence of the rate constants for reactions with dimethyl sulfide was observed.

Lee, J. H.; Timmons, R. B.; Stief, L. J.

1976-01-01

439

Determination of the rate constant of hydroperoxyl radical reaction with phenol  

NASA Astrophysics Data System (ADS)

The rate constant of HO2rad reaction with phenol (kHO2rad +phenol) was investigated. The primary radical set produced in water ? 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 (2.71.2)103 L mol-1 s-1.

Kozmr, Zsuzsanna; Arany, Eszter; Alapi, Tnde; Takcs, Erzsbet; Wojnrovits, Lszl; Dombi, Andrs

2014-09-01

440

The Influence of Reaction Rates on the Final p-Abundances  

E-print Network

The astrophysical p-process is responsible for the origin of the proton rich nuclei,which are heavier than iron. A huge network involving thousands of reaction rates is necessary to calculate the final p-abundances. But not all rates included in the network have a strong influence on the p-nuclei abundances. The p-process was investigated using a full nuclear reaction network for a type II supernovae explosion when the shock front passes through the O/Ne layer. Calculations were done with a multi-layer model adopting the seed of a pre-explosion evolution of a 25 mass star. In extensive simulations we investigated the impact of single reaction rates on the final p-abundances. The results are important for the strategy of future experiments in this field.

W. Rapp; M. Wiescher; H. Schatz; F. Kppeler

2004-08-03

441

Direct and sequential radiative three-body reaction rates at low temperatures  

E-print Network

We investigate the low-temperature reaction rates for radiative capture processes of three particles. We compare direct and sequential capture mechanisms and rates using realistic phenomenological parametrizations of the corresponding photodissociation cross sections.Energy conservation prohibits sequential capture for energies smaller than that of the intermediate two-body structure. A finite width or a finite temperature allows this capture mechanism. We study generic effects of positions and widths of two- and three-body resonances for very low temperatures. We focus on nuclear reactions relevant for astrophysics, and we illustrate with realistic estimates for the $\\alpha$-$\\alpha$-$\\alpha$ and $\\alpha$-$\\alpha$-$n$ radiative capture processes. The direct capture mechanism leads to reaction rates which for temperatures smaller than 0.1 GK can be several orders of magnitude larger than those of the NACRE compilation.

E. Garrido; R. de Diego; D. V. Fedorov; A. S. Jensen

2011-08-24

442

Temperature dependence of modified CNO nuclear reaction rates in dense stellar plasmas  

E-print Network

We study the dependence of the CNO nuclear reaction rates on temperature, in the range of $10^7\\div 10^8$ K, the typical range of temperature evolution from a Sun-like star towards a white dwarf. We show that the temperature dependence of the CNO nuclear reaction rates is strongly affected by the presence of non-extensive statistical effects in the dense stellar core. A very small deviation from the Maxwell-Boltzmann particle distribution implies a relevant enhancement of the CNO reaction rate and could explain the presence of heavier elements (e.g. Fe, Mg) in the final composition of a white dwarf core. Such a behavior is consistent with the recent experimental upper limit to the fraction of energy that the Sun produces via the CNO fusion cycle.

F. Ferro; A. Lavagno; P. Quarati

2003-12-24

443

Triple-alpha reaction rate studied with the Faddeev three-body formalism  

SciTech Connect

The triple-alpha (3{alpha}) reaction, {sup 4}He+{sup 4}He+{sup 4}He{yields}{sup 12}C+{gamma}, which plays a significant role in the stellar evolution scenarios, is studied in terms of a three-alpha (3-{alpha}) model. The reaction rate of the process is calculated via an inverse process, 3-{alpha} photodisintegration of a {sup 12}C nucleus. Both of 3-{alpha} bound and-continuum states are calculated by a Faddeev method with accommodating the long range Coulomb interaction. With being adjusted to the empirical E2-strength for {sup 12}C(0{sub 2}{sup +}){yields}{sup 12}C(2{sub 1}{sup +}) transition, results of the 3{alpha} reaction rate <{alpha}{alpha}{alpha}> at higher temperature (T > 10{sup 8} K), where the reaction proceeds mainly through the {sup 8}Be and {sup 12}C(0{sub 2}{sup +}) resonant states, almost agree with those of the Nuclear Astrophysics Compilation of Reaction Rates (NACRE). On the other hand, calculated values of <{alpha}{alpha}{alpha}> are about 10{sup 3} times larger than the NACRE rate at a low temperature (T= 10{sup 7} K), which means our results are remarkably smaller than recent CDCC results.

Ishikawa, Souichi [Hosei University, 2-17-1 Fujimi, Chiyoda, Tokyo 102-8160 (Japan)

2012-11-12

444

Impact of strange quark matter nuggets on pycnonuclear reaction rates in the crusts of neutron stars  

SciTech Connect

This article presents an investigation into the pycnonuclear reaction rates in dense crustal matter of neutron stars contaminated with strange quark matter nuggets. The presence of such nuggets in the crustal matter of neutron stars would be a natural consequence if Witten's strange quark matter hypothesis is correct. The methodology presented in this article is a recreation of a recent representation of nuclear force interactions embedded within pycnonuclear reaction processes. The study then extends the methodology to incorporate distinctive theoretical characteristics of strange quark matter nuggets, like their low charge-per-baryon ratio, and then assesses their effects on the pycnonuclear reaction rates. Particular emphasis is put on the impact of color superconductivity on the reaction rates. Depending on whether quark nuggets are in this novel state of matter, their electric charge properties vary drastically, which turns out to have a dramatic effect on the pycnonuclear reaction rates. Future nuclear fusion network calculations may thus have the potential to shed light on the existence of strange quark matter nuggets and on whether they are in a color superconducting state, as suggested by QCD.

Golf, B.; Hellmers, J.; Weber, F. [Department of Physics, San Diego State University, 5500 Campanile Drive, San Diego, California 92182 (United States)

2009-07-15

445

Kinetic Concepts for Measuring Microbial Rate Constants: Effects of Nutrients on Rate Constants  

PubMed Central

We investigated the effect of preincubation of environmental waters amended with inorganic nutrients (nitrogen, phosphorus, and traces of iron and magnesium) on the kinetics of the microbial transformation of phenol, propanil, propyl ester of (2,4-dichlorophenoxy)acetic acid, methyl parathion, Ronnel, and methoxychlor in pond and river waters. No effect on the second-order rate constants for these compounds was observed, although there was an increase in the bacterial populations and the pseudo-first-order rate constants. The use of nutrient-amended waters could be a useful tool for estimating second-order rate constants for an expanded number of compounds. This technique would provide a larger data base for predicting the behavior of xenobiotic compounds in the environment by using currently available mathematical models. PMID:16346980

Paris, D. F.; Rogers, J. E.

1986-01-01

446

A variable reaction rate model for chlorine decay in drinking water due to the reaction with dissolved organic matter.  

PubMed

A second order kinetic model for simulating chlorine decay in bulk water due to the reaction with dissolved organic matter (DOM) was developed. It takes into account the decreasing reactivity of dissolved organic matter using a variable reaction rate coefficient (VRRC) which decreases with an increasing conversion. The concentration of reducing species is surrogated by the maximum chlorine demand. Temperature dependency, respectively, is described by the Arrhenius-relationship. The accuracy and adequacy of the proposed model to describe chlorine decay in bulk water were evaluated and shown for very different waters and different conditions such as water mixing or rechlorination by applying statistical tests. It is thus very well suited for application in water quality modeling for distribution systems. PMID:25765169

Hua, Pei; Vasyukova, Ekaterina; Uhl, Wolfgang

2015-05-15

447

Conversion of waste cellulose to ethanol. Phase 2: Reaction kinetics with phosphoric acid  

NASA Astrophysics Data System (ADS)

Waste cellulosic material can be hydrolyzed in dilute acid solution to produce fermentable sugars which can then be converted into ethanol. A laboratory investigation was made of the feasibility of using phosphoric acid as the hydrolysis catalyst. The hydrolysis reaction with phosphoric acid solutions was compared with the reaction employing the more conventional dilute sulfuric acid catalyst. The purpose of this research was to examine the hydrolysis step in a proposed process for the conversion of cellulose (from wood, newspapers, municipal solid waste, or other sources) into ethanol - by which a potentially valuable co-product, DICAL (dicalcium phosphate), might be made and sold with or without the lignin content as a fertilizer. The pertinent reaction kinetics for the acid catalyzed production of glucose from cellulose consists of consecutive, pseudo-first order reactions.

Moeller, M. B.; Isbell, R. E.

1982-05-01

448

Reaction rate constant of HO2+O3 measured by detecting HO2 from photofragment fluorescence  

NASA Technical Reports Server (NTRS)

A room-temperature discharge-flow system investigation of the rate constant for the reaction 'HO2 + O3 yields OH + 2O2' has detected HO2 through the OH(A-X) fluorescence produced by photodissociative excitation of HO2 at 147 nm. A reaction rate constant of 1.9 + or - 0.3 x 10 to the -15th cu cm/molecule per sec is obtained from first-order decay of HO2 in excess O3; this agrees well with published data.

Manzanares, E. R.; Suto, Masako; Lee, Long C.; Coffey, Dewitt, Jr.

1986-01-01

449

Effect of macromolecular crowding on the rate of diffusion-limited enzymatic reaction  

E-print Network

The cytoplasm of a living cell is crowded with several macromolecules of different shapes and sizes. Molecular diffusion in such a medium becomes anomalous due to the presence of macromolecules and diffusivity is expected to decrease with increase in macromolecular crowding. Moreover, many cellular processes are dependent on molecular diffusion in the cell cytosol. The enzymatic reaction rate has been shown to be affected by the presence of such macromolecules. A simple numerical model is proposed here based on percolation and diffusion in disordered systems to study the effect of macromolecular crowding on the enzymatic reaction rates. The model explains qualitatively some of the experimental observations.

Manish Agrawal; S. B. Santra; Rajat Anand; Rajaram Swaminathan

2008-07-19

450

Astrophysical reaction rate for $^9$Be formation within a three-body approach  

E-print Network

The structure of the Borromean nucleus $^9$Be ($\\alpha+\\alpha+n$) is addressed within a three-body approach using the analytical transformed harmonic oscillator method. The three-body formalism provides an accurate description of the radiative capture reaction rate for the entire temperature range relevant in Astrophysics. At high temperatures, results match the calculations based on two-step sequential processes. At low temperatures, where the particles have no access to intermediate two-body resonances, the three-body direct capture leads to reaction rates larger than the sequential processes. These results support the reliability of the method for systems with several charged particles.

J. Casal; M. Rodrguez-Gallardo; J. M. Arias; I. J. Thompson

2014-09-19

451

Observation of double pygmy resonances in $^{195,196}$Pt and enhanced astrophysical reaction rates  

E-print Network

Our measurements of $^{195,196}$Pt $\\gamma$-strength functions show a double-humped enhancement in the $E_{\\gamma}= 4-8$ MeV region. For the first time, the detailed shape of these resonances is revealed for excitation energies in the quasicontinuum. We demonstrate that the corresponding neutron-capture cross sections and astrophysical reaction rates are increased by up to a factor of 2 when these newly observed pygmy resonances are included. These results lend credence to theoretical predictions of enhanced reaction rates due to such pygmy resonances and hence are important for a better understanding of r-process nucleosynthesis.

F. Giacoppo; F. L. Bello Garrote; T. K. Eriksen; A. Grgen; M. Guttormsen; T. W. Hagen; A. C. Larsen; B. V. Kheswa; M. Klintefjord; P. E. Koehler; H. T. Nyhus; T. Renstr\\om; E. Sahin; S. Siem; T. G. Tornyi

2014-02-11

452

Kinetics of the benzyl + O(3P) reaction: a quantum chemical/statistical reaction rate theory study.  

PubMed

The resonance stabilized benzyl radical is an important intermediate in the combustion of aromatic hydrocarbons and in polycyclic aromatic hydrocarbon (PAH) formation in flames. Despite being a free radical, benzyl is relatively stable in thermal, oxidizing environments, and is predominantly removed through bimolecular reactions with open-shell species other than O(2). In this study the reaction of benzyl with ground-state atomic oxygen, O((3)P), is examined using quantum chemistry and statistical reaction rate theory. C(7)H(7)O energy surfaces are generated at the G3SX level, and include several novel pathways. Transition state theory is used to describe elementary reaction kinetics, with canonical variational transition state theory applied for barrierless O atom association with benzyl. Apparent rate constants and branching ratios to different product sets are obtained as a function of temperature and pressure from solving the time-dependent master equation, with RRKM theory for microcanonical k(E). These simulations indicate that the benzyl + O reaction predominantly forms the phenyl radical (C(6)H(5)) plus formaldehyde (HCHO), with lesser quantities of the C(7)H(6)O products benzaldehyde, ortho-quinone methide, and para-quinone methide (+H), along with minor amounts of the formyl radical (HCO) + benzene. Addition of O((3)P) to the methylene site in benzyl produces a highly vibrationally excited C(7)H(7)O* adduct, the benzoxyl radical, which can ?-scission to benzaldehyde + H and phenyl + HCHO. In order to account for the experimental observation of benzene as the major reaction product, a roaming radical mechanism is proposed that converts the nascent products phenyl and HCHO to benzene + HCO. Oxygen atom addition at the ortho and para ring sites in benzyl, which has not been previously considered, is shown to lead to the quinone methides + H; these species are less-stable isomers of benzaldehyde that are proposed as important combustion intermediates, but are yet to be identified experimentally. Franck-Condon simulations of the benzaldehyde, o-quinone methide, and p-quinone methide photoelectron spectra suggest that these C(7)H(6)O isomers could be distinguished using tunable VUV photoionization mass spectrometry. PMID:23108328

da Silva, Gabriel; Bozzelli, Joseph W

2012-12-14

453

Reaction Rate Prediction via Group Additivity Part 1: H Abstraction from Alkanes by H and CH 3  

Microsoft Academic Search

Reliable estimates of high-pressure-limit reaction rates as a function of temperature are essential for the development of reaction sets that can be used to model complex chemical processes. As these reaction rates depend primarily on the thermodynamic properties of the reactants and the corresponding transition state, this work attempts to predict these properties within the framework of group additivity. Using

R. Sumathi; H.-H. Carstensen

2001-01-01

454

Vibrational and total energy dependence of the reaction rate of Na with CO2 laser-excited SF6  

Microsoft Academic Search

The rate of reaction between sodium and sulfur hexafluoride has been studied as a function of the vibrational energy and total thermal energy of the SF6 in the temperature range 380440 K. Vibrational energy was increased by absorption of radiation from a pulsed CO2 laser, and total energy was increased by heating the reaction system. The reaction rate was determined

Mark Eyal; Frederick R. Grabiner; Uri Agam; Leonard A. Gamss

1981-01-01

455

Reaction rates as a function of scale within ionic liquids: microscale in droplet microreactors versus macroscale reactions in the case of the Grieco three-component condensation reaction.  

PubMed

Task-specific ionic liquids (TSILs) and more specifically binary task-specific ionic liquids (BTSILs), a unique subclass, have been shown to be excellent supports for solution-phase chemistry. The negligible volatility of ionic liquids enables their use as stable droplet microreactors in atmospheric environments without oil protection or confinement. These droplets can be moved, merged and mixed by electrowetting on a chip. Solution-phase synthesis can be performed on these open digital microfluidic labs-on-a-chip as illustrated by a study of the Grieco three-component reaction in [tmba][NTf(2)]-droplet (tmba=N-trimethyl-N-butylammonium NTf(2)=bis(trifluoromethylsulfonyl)imide) microreactors. A detailed study of matrices and scale effects on conversion and kinetic rates of this three-component condensation is presented in this paper. Reactions have been shown to be slower in droplets than in batches in the absence of additional mixing. Also, a significant influence of the ionic-liquid matrix has been observed. Finally, an increase of droplet's temperature resulted in a kinetics enhancement so as to reach macroscale reaction rates, probably because of a much better mixing of reaction's components involving a Marangoni's effect. PMID:17506052

Dubois, Philippe; Marchand, Gilles; Gmouh, Said; Vaultier, Michel

2007-01-01

456

Scale-Dependent Rates of Uranyl Surface Complexation Reaction in Sediments  

SciTech Connect

Scale-dependency of uranyl[U(VI)] surface complexation rates was investigated in stirred flow-cell and column systems using a U(VI)-contaminated sediment from the US Department of Energy, Hanford site, WA. The experimental results were used to estimate the apparent rate of U(VI) surface complexation at the grain-scale and in porous media. Numerical simulations using molecular, pore-scale, and continuum models were performed to provide insights into and to estimate the rate constants of U(VI) surface complexation at the different scales. The results showed that the grain-scale rate constant of U(VI) surface complexation was over 3 to 10 orders of magnitude smaller, dependent on the temporal scale, than the rate constant calculated using the molecular simulations. The grain-scale rate was faster initially and slower with time, showing the temporal scale-dependency. The largest rate constant at the grain-scale decreased additional 2 orders of magnitude when the rate was scaled to the porous media in the column. The scaling effect from the grain-scale to the porous media became less important for the slower sorption sites. Pore-scale simulations revealed the importance of coupled mass transport and reactions in both intragranular and inter-granular domains, which caused both spatial and temporal dependence of U(VI) surface complexation rates in the sediment. Pore-scale simulations also revealed a new rate-limiting mechanism in the intragranular porous domains that the rate of coupled diffusion and surface complexation reaction was slower than either process alone. The results provided important implications for developing models to scale geochemical/biogeochemical reactions.

Liu, Chongxuan; Shang, Jianying; Kerisit, Sebastien N.; Zachara, John M.; Zhu, Weihuang

2013-03-15

457

Acid-base chemical reaction model for nucleation rates in the polluted atmospheric boundary layer.  

PubMed

Climate models show that particles formed by nucleation can affect cloud cover and, therefore, the earth's radiation budget. Measurements worldwide show that nucleation rates in the atmospheric boundary layer are positively correlated with concentrations of sulfuric acid vapor. However, current nucleation theories do not correctly predict either the observed nucleation rates or their functional dependence on sulfuric acid concentrations. This paper develops an alternative approach for modeling nucleation rates, based on a sequence of acid-base reactions. The model uses empirical estimates of sulfuric acid evaporation rates obtained from new measurements of neutral molecular clusters. The model predicts that nucleation rates equal the sulfuric acid vapor collision rate times a prefactor that is less than unity and that depends on the concentrations of basic gaseous compounds and preexisting particles. Predicted nucleation rates and their dependence on sulfuric acid vapor concentrations are in reasonable agreement with measurements from Mexico City and Atlanta. PMID:23091030

Chen, Modi; Titcombe, Mari; Jiang, Jingkun; Jen, Coty; Kuang, Chongai; Fischer, Marc L; Eisele, Fred L; Siepmann, J Ilja; Hanson, David R; Zhao, Jun; McMurry, Peter H

2012-11-13

458

Acidbase chemical reaction model for nucleation rates in the polluted atmospheric boundary layer  

PubMed Central

Climate models show that particles formed by nucleation can affect cloud cover and, therefore, the earth's radiation budget. Measurements worldwide show that nucleation rates in the atmospheric boundary layer are positively correlated with concentrations of sulfuric acid vapor. However, current nucleation theories do not correctly predict either the observed nucleation rates or their functional dependence on sulfuric acid concentrations. This paper develops an alternative approach for modeling nucleation rates, based on a sequence of acidbase reactions. The model uses empirical estimates of sulfuric acid evaporation rates obtained from new measurements of neutral molecular clusters. The model predicts that nucleation rates equal the sulfuric acid vapor collision rate times a prefactor that is less than unity and that depends on the concentrations of basic gaseous compounds and preexisting particles. Predicted nucleation rates and their dependence on sulfuric acid vapor concentrations are in reasonable agreement with measurements from Mexico City and Atlanta. PMID:23091030

Chen, Modi; Titcombe, Mari; Jiang, Jingkun; Jen, Coty; Kuang, Chongai; Fischer, Marc L.; Eisele, Fred L.; Siepmann, J. Ilja; Hanson, David R.; Zhao, Jun; McMurry, Peter H.

2012-01-01

459

Influence of two updated nuclear reaction rates on the evolution of low and intermediate mass stars  

E-print Network

Two key reactions of hydrostatic nuclear burning in stars have recently been revised by new experimental data - the 14N(p,gamma)15O and triple alpha reaction rates. We investigate how much the new rates influence the evolution of low-mass, metal-poor and metal-free, stars and of an intermediate-mass star of solar-type composition. We concentrate on phases of helium ignition or thermally unstable helium burning. Our global result is that the new triple alpha rate has no significant influence on such stars, but that there is a noticable, though small, effect of the new 14N(p,gamma)15O rate, in particular on the core helium flash and the blue loop during core helium burning in the intermediate-mass star.

A. Weiss; A. Serenelli; A. Kitsikis; H. Schlattl; J. Christensen-Dalsgaard

2005-07-22

460

Reevaluation of the $^{14}$O($?$,p)$^{17}$F Resonant Reaction Rate  

E-print Network

The reaction rates of the key stellar reaction of $^{14}$O($\\alpha$,p)$^{17}$F have been reevaluated. It is thought that the previous 1$^-$ assignment for the 6.15-MeV state is incorrect by a careful reanalysis of the previous experimental data [J. G\\'{o}mez del Campo {\\it et al.}, Phys. Rev. Lett. {\\bf 86}, 43 (2001)]. Most probably, the 6.286-MeV state is the key 1$^-$ state and the 6.15-MeV state is a 2$^-$ one, and hence the resonance at $E_x$=6.286 MeV ($J^{\\pi}$=1$^-$) actually dominates the reaction rates in the temperature region of astrophysical interests. The newly calculated reaction rates for the $^{14}$O($\\alpha$,p)$^{17}$F reaction are quite different from the previous ones, for instance, it's only about 1/6 of the previous value around 0.4 GK, while it's about 2.4 times larger than the previous value around 2 GK. The astrophysical implications have been briefly discussed based on the present conclusions.

J. J. He; H. W. Wang; J. Hu; S. W. Xu

2011-05-30

461

Field Measurement of Slow Metamorphic Reaction Rates at Temperatures of 500 to 600C  

Microsoft Academic Search

High-temperature metamorphic reaction rates were measured using strontium isotopic ratios of garnet and whole rock from a field site near Simplon Pass, Switzerland. For metamorphic conditions of cooling from 612 +\\/- 17C to 505 +\\/- 15C at pressures up to 9.1 kilobars, the inferred bulk fluid-rock exchange rate is 1.3-0.4+1.1 10-7 grams of solid reacted per gram of solid

Ethan F. Baxter; Donald J. DePaolo

2000-01-01

462

Direct and sequential radiative three-body reaction rates at low temperatures  

Microsoft Academic Search

We investigate the low-temperature reaction rates for radiative capture processes of three particles. We compare direct and sequential capture mechanisms and rates using realistic phenomenological parametrizations of the corresponding photodissociation cross-sections. Energy conservation prohibits sequential capture for energies smaller than that of the intermediate two-body structure. A finite width or a finite temperature allows this capture mechanism. We study generic

E. Garrido; R. de Diego; D. V. Fedorov; A. S. Jensen

2011-01-01

463

Rate of reaction of steam and carbon dioxide with chars produced from subbituminous coals  

Microsoft Academic Search

Chars produced by pyrolysis of Roland and Felix seam subbituminous Wyoming coals are very porous and reactive. The rates of reaction of these chars in steam and CO at 1 atm have been measured by means of a differential-flow packed bed reactor. The chars react with steam at an initial rate of 1 percent\\/hr at 530C, and with CO at

R. W. Taylor; D. W. Bowman

1976-01-01

464

Atmospheric fate of hydrofluoroethanes and hydrofluorochloroethanes: 1. Rate coefficients for reactions with OH  

Microsoft Academic Search

The rate coefficients for the reactions of OH with five halocarbons (CFCH (HFC 134a), CFCHClF (HCFC 124), CFCHCl (HCFC 123), CHCHF (HFC 152a), and CHCFCl (HCFC 142b)), which are proposed as alternatives to chlorofluoromethanes, have been measured. A pulsed pholtolysis system and a discharge flow apparatus were used to measure the rate coefficients between approximately 210 and 425 K. Use

Tomasz Gierczak; Ranajit Talukdar; E. R. Lovejoy; A. R. Ravishankara; G. L. Vaghjiani

1991-01-01

465

Influence of new reaction rates on 18F production in novae  

E-print Network

Gamma-ray emission from classical novae is dominated, during the first hours, by positron annihilation resulting from the beta decay of radioactive nuclei. The main contribution comes from the decay of 18F and hence is directly related to 18F formation during the outburst. A good knowledge of the nuclear reaction rates of production and destruction of 18F is required to study 18F synthesis in novae and the resulting gamma-ray emission. The rates relevant for the main mode of 18F destruction (i.e, through proton captures) have been the object of many recent experiments. However, subsequent analyses were focused on providing rates for X-ray burst nucleosynthesis not valid at nova temperatures (lower than 3.5 10^8 K). Accordingly, it is crucial to propose and discuss new reaction rates, incorporating all new experimental results, down to the domain of nova nucleosynthesis. We show that in this temperature regime, the 18F(p,gamma) and (p,alpha) reaction rates remain uncertain and deserve further experimental and theoretical efforts. Our hydrodynamic calculations including the new nuclear rates demonstrate that their impact on 18F synthesis in nova explosions is quite large and, consequently, the early gamma-ray emission from classical novae is also affected.

Alain Coc; Margarita Hernanz; Jordi Jose; Jean-Pierre Thibaud

2000-03-13

466

Thermonuclear Reaction Rate Libraries and Software Tools for Nuclear Astrophysics Research  

NASA Astrophysics Data System (ADS)

Thermonuclear reaction rates are a crucial input for simulating a wide variety of astrophysical environments. A new collaboration has been formed to ensure that astrophysical modelers have access to reaction rates based on the most recent experimental and theoretical nuclear physics information. To reach this goal, a new version of the REACLIB library has been created by the Joint Institute for Nuclear Astrophysics (JINA), now available online at http://www.nscl.msu.edu/~nero/db. A complementary effort is the development of software tools in the Computational Infrastructure for Nuclear Astrophysics, online at nucastrodata.org, to streamline, manage, and access the workflow of the reaction evaluations from their initiation to peer review to incorporation into the library. Details of these new projects will be described.

Smith, Michael S.; Cyburt, Richard; Schatz, Hendrik; Wiescher, Michael; Smith, Karl; Warren, Scott; Ferguson, Ryan; Lingerfelt, Eric; Buckner, Kim; Nesaraja, Caroline D.

2008-05-01

467

Extended Reaction Rate Integral as Solutions of Some General Differential Equations  

E-print Network

Here an extended form of the reaction rate probability integral, in the case of nonresonant thermonuclear reactions with the depleted tail and the right tail cut off, is considered. The reaction rate integral then can be looked upon as the inverse of the convolution of the Mellin transforms of Tsallis type statistics of nonextensive statistical mechanics and stretched exponential as well as that of superstatistics and stretched exponentials. The differential equations satisfied by the extended probability integrals are derived. The idea used is a novel one of evaluating the extended integrals in terms of some special functions and then by invoking the differential equations satisfied by these special functions. Some special cases of limiting situations are also discussed.

D. P. Joseph; H. J. Haubold

2010-01-13

468

The Impact of Nuclear Reaction Rate Uncertainties on Evolutionary Studies of the Nova Outburst  

E-print Network

The observable consequences of a nova outburst depend sensitively on the details of the thermonuclear runaway which initiates the outburst. One of the more important sources of uncertainty is the nuclear reaction data used as input for the evolutionary calculations. A recent paper by Starrfield, Truran, Wiescher, & Sparks (1998) has demonstrated that changes in the reaction rate library used within a nova simulation have significant effects, not just on the production of individual isotopes (which can change by an order of magnitude), but on global observables such as the peak luminosity and the amount of mass ejected. We present preliminary results of systematic analyses of the impact of reaction rate uncertainties on nova nucleosynthesis.

W. Raphael Hix; Michael S. Smith; Anthony Mezzacappa; Sumner Starrfield; Donald L. Smith

2000-01-27

469

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

470

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

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

471

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

NASA Technical Reports Server (NTRS)

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.

Simonaitis, R.; Leu, M. T.

1985-01-01

472

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

PubMed

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

Luo, Zhi-yong; Zheng, Huai-li

2014-06-01

473

An Improved Reaction Rate Formulation for Charged-Particle Induced Thermonuclear Reaction of {sup 2}H(d,{gamma}){sup 4}He  

SciTech Connect

The reaction rate formula utilized in compilations such as the Nuclear Astrophysics Compilation of Reaction Rates (NACRE) uses low energy approximation due to temperatures in stars are in the region of a few keVs. Most nuclear reaction experiments were done in MeV range and the interior temperatures of massive stars are {approx}10{sup 9} K. Hence an improved formulation for calculating the nuclear reaction rate that is applicable to high temperatures is discussed in this work. The exact tunneling probability that is applicable for all energies is obtained by solving the Schroedinger equation. This yields an enhanced expression for the astrophysical S-factor for calculating the thermonuclear reaction rate at high temperature. The thermonuclear reaction rate from this work is applied to the {sup 2}H(d,{gamma}){sup 4}He reaction and is compared with the NACRE compilation. This improved reaction rate can be included in the nuclear reaction network in a Big Bang nucleosynthesis (BBN) code or a stellar nuclear network code.

Aziz, Azni Abdul; Yusof, Norhasliza; Idris, Mahirah; Kassim, Hasan Abu [Department of Physics, University of Malaya, 50603 Kuala Lumpur (Malaysia)

2011-03-30

474

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)

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.

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

1998-01-01

475

Upscaling geochemical reaction rates accompanying acidic CO2-saturated brine flow in sandstone aquifers  

Microsoft Academic Search

Network flow models were used to simulate the flow of CO2-saturated brine in the pore networks corresponding to three different sandstones. The simulations were used to study upscaling of anorthite and kaolinite reaction rates from pore to core scales. Unique to our simulations is the use of computed tomography to capture the mineral distribution in the samples as well as

D. Kim; C. A. Peters; W. B. Lindquist

2011-01-01

476

NON-EQUILIBRIUM REACTION RATES IN THE MACROSCOPIC CHEMISTRY METHOD FOR DSMC CALCULATIONS  

Microsoft Academic Search

The Direct Simulation Monte Carlo (DSMC) method is used to simulate the flow of rarefied gases. In the Macroscopic Chemistry Method (MCM) for DSMC, chemical reaction rates calculated from local macroscopic flow properties are enforced in each cell. Unlike the standard total collision energy (TCE) chemistry model for DSMC, the new method is not restricted to an Arrhenius form of

M. J. GOLDSWORTHY; M. N. MACROSSAN; M. M ABDEL-JAWAD

2007-01-01

477

Nonequilibrium reaction rates in the macroscopic chemistry method for direct simulation Monte Carlo calculations  

Microsoft Academic Search

The direct simulation Monte Carlo (DSMC) method is used to simulate the flow of rarefied gases. In the macroscopic chemistry method (MCM) for DSMC, chemical reaction rates calculated from local macroscopic flow properties are enforced in each cell. Unlike the standard total collision energy (TCE) chemistry model for DSMC, the new method is not restricted to an Arrhenius form of

M. J. Goldsworthy; M. N. Macrossan; M. M. Abdel-jawad

2007-01-01

478

Reaction rate of beryllium with fluorine ion for Flibe redox control  

NASA Astrophysics Data System (ADS)

An experimental effort to apply Flibe (a mixed molten salt of 2LiF + BeF 2) to a self-cooled liquid blanket of a fusion reactor was carried out under a Japan-US collaboration called JUPITER-II. Maintaining Flibe under a reducing atmosphere is a key issue to transform TF to T 2 with a faster reaction rate compared with the residence time in blanket. One of the tasks was to clarify whether or not the redox control of Flibe can be achieved with Be. The dissolution rate of a Be rod and the reaction rate of Be + 2HF = BeF 2 + H 2 in Flibe were experimentally determined. Sufficiently fast rates of the Be dissolution and the reduction reaction of HF to H 2 were clarified by our redox control experiment. Close agreement was obtained between experiments and our simplified complete-mixing model. In particular, the reaction between Be and a F - ion immediately after their contact was found to be limited by diffusion of the F - ion.

Fukada, S.; Simpson, M. F.; Anderl, R. A.; Sharpe, J. P.; Katayama, K.; Smolik, G. R.; Oya, Y.; Terai, T.; Okuno, K.; Hara, M.; Petti, D. A.; Tanaka, S.; Sze, D.-K.; Sagara, A.

2007-08-01

479

Effect of Conceptual Change Approach on Students' Understanding of Reaction Rate Concepts  

ERIC Educational Resources Information Center

The purpose of the present study was to investigate the effect of conceptual change text oriented instruction compared to traditional instruction on 10th grade students' understanding of reaction rate concepts. 45 students from two classes of the same teacher in a public high school participated in this study. Students in the experimental group

Kingir, Sevgi; Geban, Omer

2012-01-01

480

Structural identifiability of the yield coefficients in bioprocess models when the reaction rates are unknown  

Microsoft Academic Search

The identification problem of bioprocesses in a stirred tank reactor essentially concerns the determination of the yield coefficients and the reaction rates involved in a general state-space model. This paper deals with the analysis of structural identifiability of the yield coefficients issuing from a two-step identification procedure. In fact, the identification of the yield coefficients can be completely decoupled from

G. Bastin

1996-01-01

481

The efficient computation of transition state resonances and reaction rates from a quantum normal form  

E-print Network

A quantum version of a recent formulation of transition state theory in {\\em phase space} is presented. The theory developed provides an algorithm to compute quantum reaction rates and the associated Gamov-Siegert resonances with very high accuracy. The algorithm is especially efficient for multi-degree-of-freedom systems where other approaches are no longer feasible.

Roman Schubert; Holger Waalkens; Stephen Wiggins

2005-10-14

482

Probing the Rate-Determining Step of the Claisen-Schmidt Condensation by Competition Reactions  

ERIC Educational Resources Information Center

Competition experiments are a useful tool for preliminary study of the linear free energy relationship of organic reactions. This article describes a physical organic experiment for upper-level undergraduates to identify the rate-determining step of the Claisen-Schmidt condensation of benzaldehyde and acetophenone by studying the linear free

Mak, Kendrew K. W.; Chan, Wing-Fat; Lung, Ka-Ying; Lam, Wai-Yee; Ng, Weng-Cheong; Lee, Siu-Fung

2007-01-01

483

Putting Reaction Rates and Collision Theory in the Hands of Your Students  

Microsoft Academic Search

This article describes a simulation that can be used to give concrete analogies of collision theory and the factors that affect reaction rates, including temperature, concentration, catalyst, and molecular orientation. The simulation is a dry-laboratory exercise and makes use of materials that are easily accessible at most department stores. The students involved in this one-period simulation easily master the abstract

Andy Evenson