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Sample records for fusion reaction rates

  1. Method of controlling fusion reaction rates

    DOEpatents

    Kulsrud, Russell M.; Furth, Harold P.; Valeo, Ernest J.; Goldhaber, Maurice

    1988-01-01

    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.

  2. Method of controlling fusion reaction rates

    DOEpatents

    Kulsrud, Russell M.; Furth, Harold P.; Valeo, Ernest J.; Goldhaber, Maurice

    1988-03-01

    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.

  3. Neutron detector for fusion reaction-rate measurements

    SciTech Connect

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

    1993-09-03

    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.

  4. Nuclear fusion reaction rates for strongly coupled ionic mixtures

    SciTech Connect

    Chugunov, A. I.; DeWitt, H. E.

    2009-07-15

    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.

  5. Fusion reactions at low energy

    SciTech Connect

    Beckerman, M.

    1985-01-01

    Fusion measurement methods at low energies are briefly described, and experimental and theoretical fusion cross sections for /sup 58/Ni + /sup 58/Ni, /sup 58/Ni + /sup 64/Ni and /sup 64/Ni + /sup 64/Ni reactions are discussed. It is shown that quantal tunneling calculations do not describe the near- and sub-barrier behavior of the fusion data. Instead, the WKB predictions fall progressively further blow the experimental results as the energy is lowered. At far subbarrier energies the measured cross sections exceed the WKB predictions by more than three orders of magnitude. The unexpectedly strong dependence of the fusion probability upon the nuclear valence structure is illustrated and discussed. The relationship of channel coupling and quantal tunneling is discussed. In conclusion, it was established that atomic nuclei fuse far more readily at low energies that would be expected from quantal tunneling considerations alone. It was found that the behavior of the cross sections for fusion depends strongly upon the valence structure of the collision partners. This structural dependence extends from light 1p-shell systems to systems involving nearly 200 nucleons. These new phenomena may be viewed as characterizing the tunneling of a quantal system with many degrees of freedom. The failure of standard tunneling models may be understood as resulting from the ability of the dinuclear system to tunnel into the classically forbidden region by means of couplings to intrinsic degrees of freedom. 38 refs. (WHK)

  6. Radiation reaction in fusion plasmas.

    PubMed

    Hazeltine, R D; Mahajan, S M

    2004-10-01

    The effects of a radiation reaction on thermal electrons in a magnetically confined plasma, with parameters typical of planned burning plasma experiments, are studied. A fully relativistic kinetic equation that includes the radiation reaction is derived. The associated rate of phase-space contraction is computed and the relative importance of the radiation reaction in phase space is estimated. A consideration of the moments of the radiation reaction force show that its effects are typically small in reactor-grade confined plasmas, but not necessarily insignificant.

  7. Penetration Factor for Nuclear Fusion Reaction in Nonthermal Astrophysical Plasmas

    NASA Astrophysics Data System (ADS)

    Ki, Dai-Han; Jung, Young-Dae

    2011-02-01

    The nonthermal effects on the nuclear fusion reaction process are investigated in Lorentzian astrophysical plasmas. The closed expression of the classical turning point in Lorentzian plasmas is obtained by the Lambert W-function. Using the WKB analysis with the effective screening length, the closed expressions of the fusion penetration factor and the cross section for the nuclear fusion reaction in Lorentzian plasmas are obtained as functions of the spectral index, relative kinetic energy, and plasma parameters. It is shown that the nonthermal character of the Lorentzian plasma enhances the fusion penetration factor. In addition, the nonthermal effect on the penetration factor is found to be more significant in plasmas with higher densities. It would be expected that the fusion reaction rates of the p-p chain and the CNO cycle in nonthermal plasmas are always greater than those in thermal Maxwellian plasmas.

  8. Applications of Reaction Rate

    ERIC Educational Resources Information Center

    Cunningham, Kevin

    2007-01-01

    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…

  9. Results of an attempt to measure increased rates of the reaction D-2 + D-2 yields He-3 + n in a nonelectrochemical cold fusion experiment

    NASA Technical Reports Server (NTRS)

    Fralick, Gustave C.; Decker, Arthur J.; Blue, James W.

    1989-01-01

    An experiment was performed to look for evidence of deuterium fusion in palladium. The experiment, which involved introducing deuterium into the palladium filter of a hydrogen purifier, was designed to detect neutrons produced in the reaction D-2 + D-2 yields He-3 + n as well as heat production. The neutron counts for deuterium did not differ significantly from background or from the counts for a hydrogen control. Heat production was detected when deuterium, but not hydrogen, was pumped from the purifier.

  10. Cherenkov neutron detector for fusion reaction and runaway electron diagnostics.

    PubMed

    Cheon, MunSeong; Kim, Junghee

    2015-08-01

    A Cherenkov-type neutron detector was newly developed and neutron measurement experiments were performed at Korea Superconducting Tokamak Advanced Research. It was shown that the Cherenkov neutron detector can monitor the time-resolved neutron flux from deuterium-fueled fusion plasmas. Owing to the high temporal resolution of the detector, fast behaviors of runaway electrons, such as the neutron spikes, could be observed clearly. It is expected that the Cherenkov neutron detector could be utilized to provide useful information on runaway electrons as well as fusion reaction rate in fusion plasmas.

  11. Cherenkov neutron detector for fusion reaction and runaway electron diagnostics

    NASA Astrophysics Data System (ADS)

    Cheon, MunSeong; Kim, Junghee

    2015-08-01

    A Cherenkov-type neutron detector was newly developed and neutron measurement experiments were performed at Korea Superconducting Tokamak Advanced Research. It was shown that the Cherenkov neutron detector can monitor the time-resolved neutron flux from deuterium-fueled fusion plasmas. Owing to the high temporal resolution of the detector, fast behaviors of runaway electrons, such as the neutron spikes, could be observed clearly. It is expected that the Cherenkov neutron detector could be utilized to provide useful information on runaway electrons as well as fusion reaction rate in fusion plasmas.

  12. Cherenkov neutron detector for fusion reaction and runaway electron diagnostics

    SciTech Connect

    Cheon, MunSeong Kim, Junghee

    2015-08-15

    A Cherenkov-type neutron detector was newly developed and neutron measurement experiments were performed at Korea Superconducting Tokamak Advanced Research. It was shown that the Cherenkov neutron detector can monitor the time-resolved neutron flux from deuterium-fueled fusion plasmas. Owing to the high temporal resolution of the detector, fast behaviors of runaway electrons, such as the neutron spikes, could be observed clearly. It is expected that the Cherenkov neutron detector could be utilized to provide useful information on runaway electrons as well as fusion reaction rate in fusion plasmas.

  13. From nucleons to nuclei to fusion reactions

    NASA Astrophysics Data System (ADS)

    Quaglioni, S.; Navrátil, P.; Roth, R.; Horiuchi, W.

    2012-12-01

    Nuclei are prototypes of many-body open quantum systems. Complex aggregates of protons and neutrons that interact through forces arising from quantum chromo-dynamics, nuclei exhibit both bound and unbound states, which can be strongly coupled. In this respect, one of the major challenges for computational nuclear physics, is to provide a unified description of structural and reaction properties of nuclei that is based on the fundamental underlying physics: the constituent nucleons and the realistic interactions among them. This requires a combination of innovative theoretical approaches and high-performance computing. In this contribution, we present one of such promising techniques, the ab initio no-core shell model/resonating-group method, and discuss applications to light nuclei scattering and fusion reactions that power stars and Earth-base fusion facilities.

  14. From Nucleons To Nuclei To Fusion Reactions

    SciTech Connect

    Quaglioni, S; Navratil, P; Roth, R; Horiuchi, W

    2012-02-15

    Nuclei are prototypes of many-body open quantum systems. Complex aggregates of protons and neutrons that interact through forces arising from quantum chromo-dynamics, nuclei exhibit both bound and unbound states, which can be strongly coupled. In this respect, one of the major challenges for computational nuclear physics, is to provide a unified description of structural and reaction properties of nuclei that is based on the fundamental underlying physics: the constituent nucleons and the realistic interactions among them. This requires a combination of innovative theoretical approaches and high-performance computing. In this contribution, we present one of such promising techniques, the ab initio no-core shell model/resonating-group method, and discuss applications to light nuclei scattering and fusion reactions that power stars and Earth-base fusion facilities.

  15. Microdroplet fusion mass spectrometry for fast reaction kinetics

    PubMed Central

    Lee, Jae Kyoo; Kim, Samuel; Nam, Hong Gil; Zare, Richard N.

    2015-01-01

    We investigated the fusion of high-speed liquid droplets as a way to record the kinetics of liquid-phase chemical reactions on the order of microseconds. Two streams of micrometer-size droplets collide with one another. The droplets that fused (13 μm in diameter) at the intersection of the two streams entered the heated capillary inlet of a mass spectrometer. The mass spectrum was recorded as a function of the distance x between the mass spectrometer inlet and the droplet fusion center. Fused droplet trajectories were imaged with a high-speed camera, revealing that the droplet fusion occurred approximately within a 500-μm radius from the droplet fusion center and both the size and the speed of the fused droplets remained relatively constant as they traveled from the droplet fusion center to the mass spectrometer inlet. Evidence is presented that the reaction effectively stops upon entering the heated inlet of the mass spectrometer. Thus, the reaction time was proportional to x and could be measured and manipulated by controlling the distance x. Kinetic studies were carried out in fused water droplets for acid-induced unfolding of cytochrome c and hydrogen–deuterium exchange in bradykinin. The kinetics of the former revealed the slowing of the unfolding rates at the early stage of the reaction within 50 μs. The hydrogen–deuterium exchange revealed the existence of two distinct populations with fast and slow exchange rates. These studies demonstrated the power of this technique to detect reaction intermediates in fused liquid droplets with microsecond temporal resolution. PMID:25775573

  16. What Is a Reaction Rate?

    ERIC Educational Resources Information Center

    Schmitz, Guy

    2005-01-01

    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.

  17. Measuring time of flight of fusion products in an inertial electrostatic confinement fusion device for spatial profiling of fusion reactions

    SciTech Connect

    Donovan, D. C.; Boris, D. R.; Kulcinski, G. L.; Santarius, J. F.; Piefer, G. R.

    2013-03-15

    A new diagnostic has been developed that uses the time of flight (TOF) of the products from a nuclear fusion reaction to determine the location where the fusion reaction occurred. The TOF diagnostic uses charged particle detectors on opposing sides of the inertial electrostatic confinement (IEC) device that are coupled to high resolution timing electronics to measure the spatial profile of fusion reactions occurring between the two charged particle detectors. This diagnostic was constructed and tested by the University of Wisconsin-Madison Inertial Electrostatic Confinement Fusion Group in the IEC device, HOMER, which accelerates deuterium ions to fusion relevant energies in a high voltage ({approx}100 kV), spherically symmetric, electrostatic potential well [J. F. Santarius, G. L. Kulcinski, R. P. Ashley, D. R. Boris, B. B. Cipiti, S. K. Murali, G. R. Piefer, R. F. Radel, T. E. Radel, and A. L. Wehmeyer, Fusion Sci. Technol. 47, 1238 (2005)]. The TOF diagnostic detects the products of D(d,p)T reactions and determines where along a chord through the device the fusion event occurred. The diagnostic is also capable of using charged particle spectroscopy to determine the Doppler shift imparted to the fusion products by the center of mass energy of the fusion reactants. The TOF diagnostic is thus able to collect spatial profiles of the fusion reaction density along a chord through the device, coupled with the center of mass energy of the reactions occurring at each location. This provides levels of diagnostic detail never before achieved on an IEC device.

  18. Synthesis of the heaviest nuclei in cold fusion reactions

    NASA Astrophysics Data System (ADS)

    Münzenberg, G.; Morita, K.

    2015-12-01

    Cold fusion of heavy ions paved the way to superheavy elements. It was proposed by Yu.Ts. Oganessian more than forty years ago in 1974 [1,2]. First experiments were carried out at JINR Dubna, starting with the reaction 40Ar + 208Pb → 248Fm* where several hundreds to thousand atoms were produced on one day. The large production rate indicating an enhancement of the fusion cross section, especially for the evaporation of two or three neutrons, proved the concept of cold-fusion with the use of the doubly magic nucleus 208Pb as a target. The Dubna experiments were extended to the transactinide region beyond rutherfordium. The breakthrough came with the separation in-flight. Two different approaches were used: kinematic separation with the velocity filter SHIP [3] at GSI Darmstadt, and with the gasfilled separator GARIS [4,5] at RIKEN. With SHIP the concept of cold fusion of massive nuclear systems was convincingly confirmed by the observation of the one-neutron evaporation channel in the production of 247Rf in an irradiation of 208Pb with 50Ti [6] in 1981 which opened the way to the transactinide region. At SHIP the elements bohrium (107) to copernicium (112) were discovered [7]. A new closed shell region around hassium was found. The RIKEN experiments started in 2002. They confirmed the GSI results and in addition improved the data on structure and production of elements hassium to copernicium significantly. The heaviest element ever created in a cold fusion reaction, Z = 113, was observed at GARIS [8,9].

  19. Additive effects on the energy barrier for synaptic vesicle fusion cause supralinear effects on the vesicle fusion rate.

    PubMed

    Schotten, Sebastiaan; Meijer, Marieke; Walter, Alexander Matthias; Huson, Vincent; Mamer, Lauren; Kalogreades, Lawrence; ter Veer, Mirelle; Ruiter, Marvin; Brose, Nils; Rosenmund, Christian; Sørensen, Jakob Balslev; Verhage, Matthijs; Cornelisse, Lennart Niels

    2015-04-14

    The energy required to fuse synaptic vesicles with the plasma membrane ('activation energy') is considered a major determinant in synaptic efficacy. From reaction rate theory, we predict that a class of modulations exists, which utilize linear modulation of the energy barrier for fusion to achieve supralinear effects on the fusion rate. To test this prediction experimentally, we developed a method to assess the number of releasable vesicles, rate constants for vesicle priming, unpriming, and fusion, and the activation energy for fusion by fitting a vesicle state model to synaptic responses induced by hypertonic solutions. We show that complexinI/II deficiency or phorbol ester stimulation indeed affects responses to hypertonic solution in a supralinear manner. An additive vs multiplicative relationship between activation energy and fusion rate provides a novel explanation for previously observed non-linear effects of genetic/pharmacological perturbations on synaptic transmission and a novel interpretation of the cooperative nature of Ca(2+)-dependent release.

  20. Fusion reactions of Ni,6458+124Sn

    NASA Astrophysics Data System (ADS)

    Jiang, C. L.; Stefanini, A. M.; Esbensen, H.; Rehm, K. E.; Almaraz-Calderon, S.; Avila, M. L.; Back, B. B.; Bourgin, D.; Corradi, L.; Courtin, S.; Fioretto, E.; Galtarossa, F.; Goasduff, A.; Haas, F.; Mazzocco, M. M.; Montanari, D.; Montagnoli, G.; Mijatovic, T.; Sagaidak, R.; Santiago-Gonzalez, D.; Scarlassara, F.; Strano, E. E.; Szilner, S.

    2015-04-01

    Measurements of fusion excitation functions of 58Ni+124Sn and 64Ni+124Sn are extended towards lower energy to cross sections of 1 μ b and are compared to detailed coupled-channels calculations. The calculations clearly show the importance of including transfer reactions in a coupled-channels treatment for such heavy systems. This result is different from the conclusion made in a previous article which claimed that the influence of transfer on fusion is not important for fusion reactions of Ni +Sn . In the energy region studied in this experiment no indication of fusion hindrance has been observed, which is consistent with a systematic study of this behavior.

  1. Transfer-type products accompanying cold fusion reactions

    SciTech Connect

    Adamian, G.G.; Antonenko, N.V.

    2005-12-15

    Production of nuclei heavier than the target is treated for projectile-target combinations used in cold fusion reactions leading to superheavy nuclei. These products are related to transfer-type or to asymmetry-exit-channel quasifission reactions. The production of isotopes in the transfer-type reactions emitting of {alpha} particles with large energies is discussed.

  2. The effect of proton halo on fusion reactions

    NASA Astrophysics Data System (ADS)

    Lay, J. A.; Kumar, Raj; Vitturi, A.

    2015-04-01

    In a recent brief report [Kumar et al., Phys. Rev. C 89, 027601 (2014)] we proposed a method to include the effect of a large break up in fusion reactions with neutron and proton halo nuclei. A stronger enhancement on the total fusion cross section was found for the proton case. However, neither complete nor incomplete fusion was studied and only one target was considered. Here, we revisit the problem in order to address the importance of complete and incomplete fusion. The sensitivity of the cross section to the target is also explored.

  3. Evaluation of charged-particle reactions for fusion applications

    SciTech Connect

    White, R.M.; Resler, D.A.; Warshaw, S.I.

    1991-01-01

    New evaluations of the total reaction cross sections for {sup 2}H(d,n){sup 3}He, {sup 2}H(d,p){sup 3}H, {sup 3}H(t,2n){sup 4}He,{sup 3}H(d,n){sup 4}He, and {sup 3}He(d,p){sup 4}He have been completed. These evaluations are based on all known published data from 1946 to 1990 and include over 1150 measured data points from 67 references. The purpose of this work is to provide a consistent and well-documented set of cross sections for use in calculations relating to fusion energy research. A new thermonuclear data file, TDF, and a library of FORTRAN subprograms to read the file have been developed. Calculated from the new evaluations, the TDF file contains information on the Maxwellian-averaged reaction rates as a function of reaction and plasma temperature and the Maxwellian-averaged average energy of the interacting particles and reaction products. Routines are included that provide thermally-broadened spectral information for the secondary reaction products. 67 refs., 18 figs.

  4. Charge-exchange and fusion reaction measurements during compression experiments with neutral beam heating in the Tokamak Fusion Test Reactor

    SciTech Connect

    Kaita, R.; Heidbrink, W.W.; Hammett, G.W.; Chan, A.A.; England, A.C.; Hendel, H.W.; Medley, S.S.; Nieschmidt, E.; Roquemore, A.L.; Scott, S.D.

    1986-04-01

    Adiabatic toroidal compression experiments were performed in conjunction with high power neutral beam injection in the Tokamak Fusion Test Reactor (TFTR). Acceleration of beam ions to energies nearly twice the injection energy was measured with a charge-exchange neutral particle analyzer. Measurements were also made of 2.5 MeV neutrons and 15 MeV protons produced in fusion reactions between the deuterium beam ions and the thermal deuterium and /sup 3/He ions, respectively. When the plasma was compressed, the d(d,n)/sup 3/He fusion reaction rate increased a factor of five, and the /sup 3/He(d,p)/sup 4/He rate by a factor of twenty. These data were simulated with a bounce-averaged Fokker-Planck program, which assumed conservation of angular momentum and magnetic moment during compression. The results indicate that the beam ion acceleration was consistent with adiabatic scaling.

  5. Fusion reactions initiated by laser-accelerated particle beams in a laser-produced plasma.

    PubMed

    Labaune, C; Baccou, C; Depierreux, S; Goyon, C; Loisel, G; Yahia, V; Rafelski, J

    2013-01-01

    The advent of high-intensity-pulsed laser technology enables the generation of extreme states of matter under conditions that are far from thermal equilibrium. This in turn could enable different approaches to generating energy from nuclear fusion. Relaxing the equilibrium requirement could widen the range of isotopes used in fusion fuels permitting cleaner and less hazardous reactions that do not produce high-energy neutrons. Here we propose and implement a means to drive fusion reactions between protons and boron-11 nuclei by colliding a laser-accelerated proton beam with a laser-generated boron plasma. We report proton-boron reaction rates that are orders of magnitude higher than those reported previously. Beyond fusion, our approach demonstrates a new means for exploring low-energy nuclear reactions such as those that occur in astrophysical plasmas and related environments.

  6. /sup 18/O + /sup 12/C fusion-evaporation reaction

    SciTech Connect

    Heusch, B; Beck, C; Coffin, J P; Freeman, R M; Gallmann, A; Haas, F; Rami, F; Wagner, P; Alburger, D E

    1980-01-01

    A study of the /sup 18/O + /sup 12/C fusion evaporation reaction has been undertaken for 2 reasons: to make a systematic study of the formation cross section for each individual evaporation residue over a broad excitation energy region in the compound nucleus /sup 30/Si:30 to 62 MeV; and to compare all results to fusion-evaporation calculations done in the framework of the Hauser-Feschbach statistical model.

  7. Observed Multi-Decade DD and DT Z-Pinch Fusion Rate Scaling in 5 Dense Plasma Focus Fusion Machines

    SciTech Connect

    Hagen, E. C.; Lowe, D. R.; O'Brien, R.; Meehan, B. T.

    2013-06-18

    Dense Plasma Focus (DPF) machines are in use worldwide or a wide variety of applications; one of these is to produce intense, short bursts of fusion via r-Z pinch heating and compression of a working gas. We have designed and constructed a series of these, ranging from portable to a maximum energy storage capacity of 2 MJ. Fusion rates from 5 DPF pulsed fusion generators have been measured in a single laboratory using calibrated activation detectors. Measured rates range from ~ 1015 to more than 1019 fusions per second have been measured. Fusion rates from the intense short (20 – 50 ns) periods of production were inferred from measurement of neutron production using both calibrated activation detectors and scintillator-PMT neutron time of flight (NTOF) detectors. The NTOF detectors are arranged to measure neutrons versus time over flight paths of 30 Meters. Fusion rate scaling versus energy and current will be discussed. Data showing observed fusion cutoff at D-D fusion yield levels of approximately 1*1012, and corresponding tube currents of ~ 3 MA will be shown. Energy asymmetry of product neutrons will also be discussed. Data from the NTOF lines of sight have been used to measure energy asymmetries of the fusion neutrons. From this, center of mass energies for the D(d,n)3He reaction are inferred. A novel re-entrant chamber that allows extremely high single pulse neutron doses (> 109 neutrons/cm2 in 50 ns) to be supplied to samples will be described. Machine characteristics and detector types will be discussed.

  8. Effects of entrance channel on fusion probability in hot fusion reactions

    NASA Astrophysics Data System (ADS)

    Zhu, Long; Su, Jun; Huang, Ching-Yuan; Zhang, Feng-Shou

    2016-12-01

    Within the framework of the dinuclear system (DNS) model, the fusion reactions leading to the compound nuclei 274Hs* and 286Cn* are investigated. The fusion probability as a function of DNS excitation energy is studied. The calculated results are in good agreement with the available experimental data. The obtained results show that the fusion probabilities are obviously enhanced for the reactions located at high place in potential energy surface, although these reactions may have small values of mass asymmetry. It is found that the enhancement is due to the large potential energy of the initial DNS. Supported by Natural Science Foundation of Guangdong Province China (2016A030310208). National Natural Science Foundation of China (11605296, 11405278, 11505150, 11635003), Fundamental Research Funds for the Central Universities (15 lgpy 30) and China Postdoctoral Science Foundation (2015M582730)

  9. Analysis of quasifission competition in fusion reactions forming heavy nuclei

    NASA Astrophysics Data System (ADS)

    Hammerton, Kalee; Kohley, Zachary; Morrissey, Dave; Wakhle, Aditya; Stiefel, Krystin; Hinde, David; Dasgupta, Mahananda; Williams, Elizabeth; Simenel, Cedric; Carter, Ian; Cook, Kaitlin; Jeung, Dongyun; Luong, Duc Huy; McNeil, Steven; Palshetkar, Chandani; Rafferty, Dominic

    2015-10-01

    Heavy-ion fusion reactions have provided a mechanism for the production of superheavy elements allowing for the extension of both the periodic table and chart of the nuclides. However, fusion of the projectile and target, forming a compound nucleus, is hindered by orders of magnitude by the quasifission process in heavy systems. In order to fully understand this mechanism, and make accurate predictions for superheavy element production cross sections, a clear description of the interplay between the fusion-fission and quasifission reaction channels is necessary. The mass-angle distributions of fragments formed in 8 different Cr + W reactions were measured at the Australia National University in order to explore the N/Z dependence of the quasifission process. Two sets of data were measured: one at a constant energy relative to the fusion barrier and one at a constant compound nucleus excitation energy. The results of this analysis will provide insight into the effect of using more neutron-rich beams in superheavy element production reactions.

  10. Additive effects on the energy barrier for synaptic vesicle fusion cause supralinear effects on the vesicle fusion rate

    PubMed Central

    Schotten, Sebastiaan; Meijer, Marieke; Walter, Alexander Matthias; Huson, Vincent; Mamer, Lauren; Kalogreades, Lawrence; ter Veer, Mirelle; Ruiter, Marvin; Brose, Nils; Rosenmund, Christian

    2015-01-01

    The energy required to fuse synaptic vesicles with the plasma membrane (‘activation energy’) is considered a major determinant in synaptic efficacy. From reaction rate theory, we predict that a class of modulations exists, which utilize linear modulation of the energy barrier for fusion to achieve supralinear effects on the fusion rate. To test this prediction experimentally, we developed a method to assess the number of releasable vesicles, rate constants for vesicle priming, unpriming, and fusion, and the activation energy for fusion by fitting a vesicle state model to synaptic responses induced by hypertonic solutions. We show that complexinI/II deficiency or phorbol ester stimulation indeed affects responses to hypertonic solution in a supralinear manner. An additive vs multiplicative relationship between activation energy and fusion rate provides a novel explanation for previously observed non-linear effects of genetic/pharmacological perturbations on synaptic transmission and a novel interpretation of the cooperative nature of Ca2+-dependent release. DOI: http://dx.doi.org/10.7554/eLife.05531.001 PMID:25871846

  11. Nucleus-nucleus cold fusion reactions analyzed with the l-dependent 'fusion by diffusion' model

    SciTech Connect

    Cap, T.; Siwek-Wilczynska, K.; Wilczynski, J.

    2011-05-15

    We present a modified version of the Fusion by Diffusion (FBD) model aimed at describing the synthesis of superheavy nuclei in cold fusion reactions, in which a low excited compound nucleus emits only one neutron. The modified FBD model accounts for the angular momentum dependence of three basic factors determining the evaporation residue cross section: the capture cross section {sigma}{sub cap}(l), the fusion probability P{sub fus}(l), and the survival probability P{sub surv}(l). The fusion hindrance factor, the inverse of P{sub fus}(l), is treated in terms of thermal fluctuations in the shape degrees of freedom and is expressed as a solution of the Smoluchowski diffusion equation. The l dependence of P{sub fus}(l) results from the l-dependent potential energy surface of the colliding system. A new parametrization of the distance of starting point of the diffusion process is introduced. An analysis of a complete set of 27 excitation functions for production of superheavy nuclei in cold fusion reactions, studied in experiments at GSI Darmstadt, RIKEN Tokyo, and LBNL Berkeley, is presented. The FBD model satisfactorily reproduces shapes and absolute cross sections of all the cold fusion excitation functions. It is shown that the peak position of the excitation function for a given 1n reaction is determined by the Q value of the reaction and the height of the fission barrier of the final nucleus. This fact could possibly be used in future experiments (with well-defined beam energy) for experimental determination of the fission barrier heights.

  12. The Rate Laws for Reversible Reactions.

    ERIC Educational Resources Information Center

    King, Edward L.

    1986-01-01

    Provides background information for teachers on the rate laws for reversible reactions. Indicates that although prediction of the form of the rate law for a reverse reaction given the rate law for the forward reaction is not certain, the number of possibilities is limited because of relationships described. (JN)

  13. Fusion rates for hydrogen isotopic molecules of relevance for 'cold fusion'

    NASA Astrophysics Data System (ADS)

    Szalewicz, K.; Morgan, J. D., III; Monkhorst, H. J.

    1989-09-01

    In response to the recent announcements of evidence for room-temperature fusion in the electrolysis of D2O, an analysis is presented of how the fusion rate depends on the reduced mass of the fusing nuclei, the effective mass of a 'heavy' electron, and the degree of vibrational excitation. The results have been obtained both by accurately solving the Schroedinger equation for the hydrogen molecule and by using the WKB approximation. It is found that in light of the reported d-d fusion rate, the excess heat in the experiment by Fleischmann, Pons, and Hawkins is difficult to explain in terms of conventional nuclear processes.

  14. A New Look at Reaction Rates

    NASA Astrophysics Data System (ADS)

    Cvitas, Tomislav

    1999-11-01

    Both rates of radioactive decays and rates of chemical reactions can be thought of as numbers of transformations per time. The rate of reaction, as an intensive quantity characteristic of the process, is obtained by dividing the amount of chemical transformations per time by the volume of the reaction system. The practical definition of the reaction rate found in the literature can then be derived by defining the stoichiometric numbers as changes in the number of specific molecules taking part in the reaction per chemical transformation. The name concentration of chemical transformations is introduced for what was previously called reaction variable. It is suggested that the conceptual definition of the advancement of reaction and reaction rate be introduced in general chemistry courses.

  15. Secondary Nuclear Reactions in Magneto-Inertial Fusion Plasmas

    NASA Astrophysics Data System (ADS)

    Knapp, Patrick

    2014-10-01

    The goal of Magneto-Inertial Fusion (MIF) is to relax the extreme pressure requirements of inertial confinement fusion by magnetizing the fuel. Understanding the level of magnetization at stagnation is critical for charting the performance of any MIF concept. We show here that the secondary nuclear reactions in magnetized deuterium plasma can be used to infer the magnetic field-radius product (BR), the critical confinement parameter for MIF. The secondary neutron yields and spectra are examined and shown to be extremely sensitive to BR. In particular, embedded magnetic fields are shown to affect profoundly the isotropy of the secondary neutron spectra. Detailed modeling of these spectra along with the ratio of overall secondary to primary neutron yields is used to form the basis of a diagnostic technique used to infer BR at stagnation. Effects of gradients in density, temperature and magnetic field strength are examined, as well as other possible non-uniform fuel configurations. Computational results employing a fully kinetic treatment of charged reaction product transport and Monte Carlo treatment of secondary reactions are compared to results from recent experiments at Sandia National Laboratories' Z machine testing the MAGnetized Liner Inertial Fusion (MagLIF) concept. The technique reveals that the charged reaction products were highly magnetized in these experiments. Implications for eventual ignition-relevant experiments with deuterium-tritium fuel are discussed. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  16. Formation of superheavy elements in cold fusion reactions

    NASA Astrophysics Data System (ADS)

    Smolańczuk, Robert

    2001-04-01

    We calculate the formation cross sections of transactinides (superheavy elements), as well as heavy actinides (No and Lr), which have been or might be obtained in fusion reactions with the evaporation of only one neutron. We use both more realistic fusion barrier and survival probability of the compound nucleus in comparison with the original phenomenological model [Phys. Rev. C 59, 2634 (1999)] that prompted the Berkeley experiment on the synthesis of a new superheavy element 118 [Phys. Rev. Lett. 83, 1104 (1999)]. Calculations are performed for asymmetric and symmetric target-projectile combinations and for reactions with stable and radioactive-ion beams. The formation cross sections measured at GSI-Darmstadt for transactinides and heavy actinides, as well as that for superheavy element 118 reported by the LBNL-Berkeley group, are reproduced within a factor of 2.4, on average. Based on the obtained relatively large cross sections, we predict that optimal reactions with stable beams for the synthesis of so far unobserved superheavy elements 119, 120, and 121 are 209Bi(86Kr, 1n)294119, 208Pb(88Sr, 1n)295120, and 209Bi(88Sr, 1n)296121, respectively. This is because of the magic of both the target and the projectile that leads to larger Q value and, consequently, lower effective fusion barrier with larger transmission probability. The same effect is responsible for relatively large cross sections predicted for the symmetric reactions 136Xe(124Sn, 1n)259Rf, 136Xe(136Xe, 1n)271Hs,138Ba(136Xe, 1n)273110, and 140Ce(136Xe, 1n)275112. Although shell effects in the magic nuclei 124Sn, 136Xe, 138Ba, and 140Ce are not as strong as in 208Pb and 209Bi, they act on both the target and the projectile and lead to the prediction of measurable cross sections.

  17. Sparking fusion: A step toward laser-initiated nuclear fusion reactions

    SciTech Connect

    Peterson, I.

    1996-10-19

    The fusion furnace at the sun`s core burns hydrogen to make helium. Each time two hydrogen nuclei, or protons, merge to create a deuterium nucleus, the process releases energy. A chain of additional energy-producing nuclear reactions then converts deuterium into helium. Because protons, with their like electric charges, naturally repel each other, high temperatures and tremendous pressures are needed to force them together closely enough to initiate and sustain the reactions. These mergers cost energy initially, but the return on that investment proves prodigious. On Earth, such an energy payoff has been achieved only in the uncontrolled fury of a detonated hydrogen bomb. The vision of harnessing and controlling nuclear fusion as a terrestrial energy source has yet to be fulfilled. The proposed National Ignition Facility (NIF) represents an ambitious effort to use powerful lasers to deposit sufficient energy in a small capsule of nuclear fuel to trigger fusion. The main justification for the project is to ensure that a core group of physicists and engineers maintains its expertise in the physics of nuclear weapons. This article presents both the scientific and political sides of the NIF facility.

  18. Impact of Reaction Cross Section on the Unified Description of Fusion Excitation Function

    NASA Astrophysics Data System (ADS)

    Basrak, Z.; Eudes, P.; de la Mota, V.; Sébille, F.; Royer, G.

    A systematics of over 300 complete and incomplete fusion cross section data points covering energies beyond the barrier for fusion is presented. Owing to a usual reduction of the fusion cross sections by the total reaction cross sections and an original scaling of energy, a fusion excitation function common to all the data points is established. A universal description of the fusion exci- tation function relying on basic nuclear concepts is proposed and its dependence on the reaction cross section used for the cross section normalization is discussed. The pioneering empirical model proposed by Bass in 1974 to describe the complete fusion cross sections is rather successful for the incomplete fusion too and provides cross section predictions in satisfactory agreement with the observed universality of the fusion excitation function. The sophisticated microscopic transport DYWAN model not only reproduces the data but also predicts that fusion reaction mechanism disappears due to weakened nuclear stopping power around the Fermi energy.

  19. Reaction Order Ambiguity in Integrated Rate Plots

    ERIC Educational Resources Information Center

    Lee, Joe

    2008-01-01

    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…

  20. Redox reaction rates using potentiostatic coulometry

    SciTech Connect

    Ramette, R.W.; Harris, R.Z.; Bengali, A.A.; Noll, R.J.

    1987-01-01

    A new method based on potentiostatic coulometry was used to study the kinetics of the aqueous redox reactions between the ions chlorate/iodide, bromate/iodide, and bromate/bromide. The halogen product was continuously and rapidly reduced back to halide at a large platinum gauze cathode, the current being a direct measure of reaction rate and the accumulated charge serving to measure the extent of reaction. The reactions were studied at several temperatures, and activation entropies and enthalpies were calculated.

  1. pH & Rate of Enzymatic Reactions.

    ERIC Educational Resources Information Center

    Clariana, Roy B.

    1991-01-01

    A quantitative and inexpensive way to measure the rate of enzymatic reaction is provided. The effects of different pH levels on the reaction rate of an enzyme from yeast are investigated and the results graphed. Background information, a list of needed materials, directions for preparing solutions, procedure, and results and discussion are…

  2. Reaction rates for reaction-diffusion kinetics on unstructured meshes

    NASA Astrophysics Data System (ADS)

    Hellander, Stefan; Petzold, Linda

    2017-02-01

    The reaction-diffusion master equation is a stochastic model often utilized in the study of biochemical reaction networks in living cells. It is applied when the spatial distribution of molecules is important to the dynamics of the system. A viable approach to resolve the complex geometry of cells accurately is to discretize space with an unstructured mesh. Diffusion is modeled as discrete jumps between nodes on the mesh, and the diffusion jump rates can be obtained through a discretization of the diffusion equation on the mesh. Reactions can occur when molecules occupy the same voxel. In this paper, we develop a method for computing accurate reaction rates between molecules occupying the same voxel in an unstructured mesh. For large voxels, these rates are known to be well approximated by the reaction rates derived by Collins and Kimball, but as the mesh is refined, no analytical expression for the rates exists. We reduce the problem of computing accurate reaction rates to a pure preprocessing step, depending only on the mesh and not on the model parameters, and we devise an efficient numerical scheme to estimate them to high accuracy. We show in several numerical examples that as we refine the mesh, the results obtained with the reaction-diffusion master equation approach those of a more fine-grained Smoluchowski particle-tracking model.

  3. Reaction Rate Data Number 59.

    DTIC Science & Technology

    1977-02-01

    18 9. Naval Research Laboratory — Parameterization of the Atmospheric Heating Rate from 15 to 120 km due to 02 and 03 A bsorption of Solar Radiation...Photodissociation Spectroscopy of (‘03 19 12. United Technologies Research Center — Calculatiomi of Energe tics of Selected Atmospheric Systems 19 AUTHOR...the (354) and (52’) ions. 11. Photodissociation Spectroscopy of (‘03 — J. T. Moseley, PC’, Cosbv . and J R. Peterson, Stan- ford Research Institute

  4. Astrophysical S factors for fusion reactions involving C, O, Ne, and Mg isotopes

    SciTech Connect

    Beard, M.; Afanasjev, A.V.; Chamon, L.C.; Gasques, L.R.; Wiescher, M.; Yakovlev, D.G.

    2010-09-15

    Using the Sao Paulo potential and the barrier penetration formalism we have calculated the astrophysical factor S(E) for 946 fusion reactions involving stable and neutron-rich isotopes of C, O, Ne, and Mg for center-of-mass energies E varying from 2 to {approx}18-30 MeV (covering the range below and above the Coulomb barrier). We have parameterized the energy dependence, S(E), by an accurate universal 9-parameter analytic expression and present tables of fit parameters for all the reactions. We also discuss the reduced 3-parameter version of our fit which is highly accurate at energies below the Coulomb barrier, and outline the procedure for calculating the reaction rates. The results can be easily converted to thermonuclear or pycnonuclear reaction rates to simulate various nuclear burning phenomena, in particular, stellar burning at high temperatures and nucleosynthesis in high density environments.

  5. Spin polarization effects in the /sup 3/H(d,n)/sup 4/He fusion reaction

    SciTech Connect

    Conzett, H.E.; Rioux, C.

    1985-06-01

    A recent investigation has shown that the /sup 3/H(d,n)/sup 4/He fusion reaction rate could be enhanced by a factor of 3/2 if the fusion plasma consisted of both polarized deuterons and tritons, forming exclusively the channel-spin S = 3/2, J = 3/2/sup +/ state. This result follows simply from the statistical weights of the quartet S = 3/2 and doublet S = 1/2 initial states, with the assumption of the single J = 3/2/sup +/ reaction amplitude. Since, with a small but nonzero J = 1/2/sup +/ amplitude, the maximum enhancement of the reaction occurs at the peak of the J = 3/2/sup +/ resonance, corresponding to a deuteron lab energy of 107 keV, it is of obvious interest to know what the enhancement would be at the lower energies that are typical of fusion plasmas. We are able to address this question by extending earlier calculations which gave the values of all of the spin-polarization observables at this J = 3/2/sup +/ resonance in both the /sup 3/H(d,n)/sup 4/He and the /sup 3/He(d,p)/sup 4/He reactions.

  6. Effective reaction rates for diffusion-limited reaction cycles

    NASA Astrophysics Data System (ADS)

    Nałecz-Jawecki, Paweł; Szymańska, Paulina; Kochańczyk, Marek; Miekisz, Jacek; Lipniacki, Tomasz

    2015-12-01

    Biological signals in cells are transmitted with the use of reaction cycles, such as the phosphorylation-dephosphorylation cycle, in which substrate is modified by antagonistic enzymes. An appreciable share of such reactions takes place in crowded environments of two-dimensional structures, such as plasma membrane or intracellular membranes, and is expected to be diffusion-controlled. In this work, starting from the microscopic bimolecular reaction rate constants and using estimates of the mean first-passage time for an enzyme-substrate encounter, we derive diffusion-dependent effective macroscopic reaction rate coefficients (EMRRC) for a generic reaction cycle. Each EMRRC was found to be half of the harmonic average of the microscopic rate constant (phosphorylation c or dephosphorylation d), and the effective (crowding-dependent) motility divided by a slowly decreasing logarithmic function of the sum of the enzyme concentrations. This implies that when c and d differ, the two EMRRCs scale differently with the motility, rendering the steady-state fraction of phosphorylated substrate molecules diffusion-dependent. Analytical predictions are verified using kinetic Monte Carlo simulations on the two-dimensional triangular lattice at the single-molecule resolution. It is demonstrated that the proposed formulas estimate the steady-state concentrations and effective reaction rates for different sets of microscopic reaction rates and concentrations of reactants, including a non-trivial example where with increasing diffusivity the fraction of phosphorylated substrate molecules changes from 10% to 90%.

  7. Effective reaction rates for diffusion-limited reaction cycles.

    PubMed

    Nałęcz-Jawecki, Paweł; Szymańska, Paulina; Kochańczyk, Marek; Miękisz, Jacek; Lipniacki, Tomasz

    2015-12-07

    Biological signals in cells are transmitted with the use of reaction cycles, such as the phosphorylation-dephosphorylation cycle, in which substrate is modified by antagonistic enzymes. An appreciable share of such reactions takes place in crowded environments of two-dimensional structures, such as plasma membrane or intracellular membranes, and is expected to be diffusion-controlled. In this work, starting from the microscopic bimolecular reaction rate constants and using estimates of the mean first-passage time for an enzyme-substrate encounter, we derive diffusion-dependent effective macroscopic reaction rate coefficients (EMRRC) for a generic reaction cycle. Each EMRRC was found to be half of the harmonic average of the microscopic rate constant (phosphorylation c or dephosphorylation d), and the effective (crowding-dependent) motility divided by a slowly decreasing logarithmic function of the sum of the enzyme concentrations. This implies that when c and d differ, the two EMRRCs scale differently with the motility, rendering the steady-state fraction of phosphorylated substrate molecules diffusion-dependent. Analytical predictions are verified using kinetic Monte Carlo simulations on the two-dimensional triangular lattice at the single-molecule resolution. It is demonstrated that the proposed formulas estimate the steady-state concentrations and effective reaction rates for different sets of microscopic reaction rates and concentrations of reactants, including a non-trivial example where with increasing diffusivity the fraction of phosphorylated substrate molecules changes from 10% to 90%.

  8. Enhancement of Fusion Rate by Superthermal Tritium Ions

    NASA Astrophysics Data System (ADS)

    Castaldo, Carmine; Cardinali, Alessandro; Marinucci, Massimo

    2011-10-01

    We propose a new concept of a nuclear fusion reactor. It is based on the enhancement of the DT fusion rate in tokamak plasmas by a superthermal population of Tritium ions heated by ICRH. It was already shown that break-even conditions might be reached [C. Castaldo and A. Cardinali, Phys. Plasmas 17, 072513 (2010)]. Here we show that Q ~20, suitable for nuclear fusion power station, can be achieved in a compact tokamak configuration (major radius R=160cm, minor radius a=55cm, elongation k=1.9, triangularity δ=0.4, q95=3.5), operating with IP=8MA plasma current, BT=11.3T toroidal field, line averaged plasma density n=5X1020m-3, and 40% D, 35% H, 25% T concentrations of the Hydrogen isotopes. The burning plasma is obtained by the injection of 15 MW ICRF power, coupled by six antennas, with radiating areas of 0.25m2, at the operating frequency f=125 MHz and toroidal wave number n//=4. The heating scenario has been analyzed by the code TORIC, and approximated analytical equilibria are considered. As a result the total fusion power expected for the proposed scenario is about 350MW, with Q ~20, assuming that at least 70% of the fusion power carried by the α particles is absorbed by the electrons in the plasma core so that the expected central plasma temperature is about 10keV.

  9. Astrophysical Reaction Rates Obtained By Indirect Techniques

    SciTech Connect

    Tribble, R. E.; Al-Abdullah, T.; Alharbi, A.; Banu, A.; Chen, X.; Clark, H. L.; Fu, C.; Gagliardi, C. A.; Hardy, J. C.; Iacob, V. E.; Lui, Y.-W.; McCleskey, M.; Mukhamedzhanov, A.; Nica, N.; Park, H. I.; Roeder, B.; Simmons, E.; Tabacaru, G.; Tokimoto, Y.; Trache, L.

    2010-08-12

    Indirect techniques have been used to obtain information about reaction rates for several proton capture reactions that occur on short-lived nuclei. The techniques used to carry out the measurements are reviewed and the results obtained are presented. Also future prospects for further measurements with a new facility, T-REX are discussed.

  10. Calibrating reaction rates for the CREST model

    NASA Astrophysics Data System (ADS)

    Handley, Caroline A.; Christie, Michael A.

    2017-01-01

    The CREST reactive-burn model uses entropy-dependent reaction rates that, until now, have been manually tuned to fit shock-initiation and detonation data in hydrocode simulations. This paper describes the initial development of an automatic method for calibrating CREST reaction-rate coefficients, using particle swarm optimisation. The automatic method is applied to EDC32, to help develop the first CREST model for this conventional high explosive.

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

    SciTech Connect

    Judd, J.L.

    1981-12-01

    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.

  12. Selected component failure rate values from fusion safety assessment tasks

    SciTech Connect

    Cadwallader, L.C.

    1998-09-01

    This report is a compilation of component failure rate and repair rate values that can be used in magnetic fusion safety assessment tasks. Several safety systems are examined, such as gas cleanup systems and plasma shutdown systems. Vacuum system component reliability values, including large vacuum chambers, have been reviewed. Values for water cooling system components have also been reported here. The report concludes with the examination of some equipment important to personnel safety, atmospheres, combustible gases, and airborne releases of radioactivity. These data should be useful to system designers to calculate scoping values for the availability and repair intervals for their systems, and for probabilistic safety or risk analysts to assess fusion systems for safety of the public and the workers.

  13. Selected Component Failure Rate Values from Fusion Safety Assessment Tasks

    SciTech Connect

    Cadwallader, Lee Charles

    1998-09-01

    This report is a compilation of component failure rate and repair rate values that can be used in magnetic fusion safety assessment tasks. Several safety systems are examined, such as gas cleanup systems and plasma shutdown systems. Vacuum system component reliability values, including large vacuum chambers, have been reviewed. Values for water cooling system components have also been reported here. The report concludes with the examination of some equipment important to personnel safety, atmospheres, combustible gases, and airborne releases of radioactivity. These data should be useful to system designers to calculate scoping values for the availability and repair intervals for their systems, and for probabilistic safety or risk analysts to assess fusion systems for safety of the public and the workers.

  14. Enhanced aqueous photochemical reaction rates after freezing.

    PubMed

    Grannas, Amanda M; Bausch, Alexandra R; Mahanna, Kendell M

    2007-11-01

    Sunlit snow/ice is known to play an important role in the processing of atmospheric species, including photochemical production of NO(x), HONO, molecular halogens, alkyl halides, and carbonyl compounds, among others. It has been shown that a liquid-like (quasi-liquid or disordered) layer exists on the surface of pure ice and that this quasi-liquid layer is also found on the surface of ambient snow crystals and ice at temperatures similar to polar conditions. However, it is unclear what role the liquid-like fractions present in and on frozen water play in potential photochemical reactions, particularly with regard to organic substrates. Here, we report a detailed study of enhanced rates of photochemical nucleophilic substitution of p-nitroanisole (PNA) with pyridine, a well-characterized and commonly used actinometer system. Reaction rates were enhanced by a factor of up to approximately 40 when frozen at temperatures between 236 and 272 K. Reaction rates were dependent on temperature and solute concentration, both variables that control the nature of the liquid-like fraction in frozen water. The results obtained indicate that a major portion of the organic solutes is excluded to the liquid-like layer, significantly impacting the rate of the photochemical nucleophilic substitution reaction studied here. Also, the direct comparison of liquid-phase kinetics to reactions occurring in frozen water systems is drawn into question, indicating that a simple extrapolation of liquid-phase mechanisms to snow/ice may not be valid for certain reactions.

  15. Reaction rates for mesoscopic reaction-diffusion kinetics

    DOE PAGES

    Hellander, Stefan; Hellander, Andreas; Petzold, Linda

    2015-02-23

    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 thismore » 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. Finally, 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.« less

  16. Reaction rates for mesoscopic reaction-diffusion kinetics

    SciTech Connect

    Hellander, Stefan; Hellander, Andreas; Petzold, Linda

    2015-02-23

    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. Finally, 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.

  17. The cytoplasmic domain of the gamete membrane fusion protein HAP2 targets the protein to the fusion site in Chlamydomonas and regulates the fusion reaction

    PubMed Central

    Liu, Yanjie; Pei, Jimin; Grishin, Nick; Snell, William J.

    2015-01-01

    Cell-cell fusion between gametes is a defining step during development of eukaryotes, yet we know little about the cellular and molecular mechanisms of the gamete membrane fusion reaction. HAP2 is the sole gamete-specific protein in any system that is broadly conserved and shown by gene disruption to be essential for gamete fusion. The wide evolutionary distribution of HAP2 (also known as GCS1) indicates it was present in the last eukaryotic common ancestor and, therefore, dissecting its molecular properties should provide new insights into fundamental features of fertilization. HAP2 acts at a step after membrane adhesion, presumably directly in the merger of the lipid bilayers. Here, we use the unicellular alga Chlamydomonas to characterize contributions of key regions of HAP2 to protein location and function. We report that mutation of three strongly conserved residues in the ectodomain has no effect on targeting or fusion, although short deletions that include those residues block surface expression and fusion. Furthermore, HAP2 lacking a 237-residue segment of the cytoplasmic region is expressed at the cell surface, but fails to localize at the apical membrane patch specialized for fusion and fails to rescue fusion. Finally, we provide evidence that the ancient HAP2 contained a juxta-membrane, multi-cysteine motif in its cytoplasmic region, and that mutation of a cysteine dyad in this motif preserves protein localization, but substantially impairs HAP2 fusion activity. Thus, the ectodomain of HAP2 is essential for its surface expression, and the cytoplasmic region targets HAP2 to the site of fusion and regulates the fusion reaction. PMID:25655701

  18. The cytoplasmic domain of the gamete membrane fusion protein HAP2 targets the protein to the fusion site in Chlamydomonas and regulates the fusion reaction.

    PubMed

    Liu, Yanjie; Pei, Jimin; Grishin, Nick; Snell, William J

    2015-03-01

    Cell-cell fusion between gametes is a defining step during development of eukaryotes, yet we know little about the cellular and molecular mechanisms of the gamete membrane fusion reaction. HAP2 is the sole gamete-specific protein in any system that is broadly conserved and shown by gene disruption to be essential for gamete fusion. The wide evolutionary distribution of HAP2 (also known as GCS1) indicates it was present in the last eukaryotic common ancestor and, therefore, dissecting its molecular properties should provide new insights into fundamental features of fertilization. HAP2 acts at a step after membrane adhesion, presumably directly in the merger of the lipid bilayers. Here, we use the unicellular alga Chlamydomonas to characterize contributions of key regions of HAP2 to protein location and function. We report that mutation of three strongly conserved residues in the ectodomain has no effect on targeting or fusion, although short deletions that include those residues block surface expression and fusion. Furthermore, HAP2 lacking a 237-residue segment of the cytoplasmic region is expressed at the cell surface, but fails to localize at the apical membrane patch specialized for fusion and fails to rescue fusion. Finally, we provide evidence that the ancient HAP2 contained a juxta-membrane, multi-cysteine motif in its cytoplasmic region, and that mutation of a cysteine dyad in this motif preserves protein localization, but substantially impairs HAP2 fusion activity. Thus, the ectodomain of HAP2 is essential for its surface expression, and the cytoplasmic region targets HAP2 to the site of fusion and regulates the fusion reaction.

  19. Reaction rates for a generalized reaction-diffusion master equation

    SciTech Connect

    Hellander, Stefan; Petzold, Linda

    2016-01-19

    It has been established that there is an inherent limit to the accuracy of the reaction-diffusion master equation. Specifically, there exists a fundamental lower bound on the mesh size, below which the accuracy deteriorates as the mesh is refined further. In this paper we extend the standard reaction-diffusion master equation to allow molecules occupying neighboring voxels to react, in contrast to the traditional approach in which molecules react only when occupying the same voxel. We derive reaction rates, in two dimensions as well as three dimensions, to obtain an optimal match to the more fine-grained Smoluchowski model, and show in two numerical examples that the extended algorithm is accurate for a wide range of mesh sizes, allowing us to simulate systems that are intractable with the standard reaction-diffusion master equation. In addition, we show that for mesh sizes above the fundamental lower limit of the standard algorithm, the generalized algorithm reduces to the standard algorithm. We derive a lower limit for the generalized algorithm which, in both two dimensions and three dimensions, is on the order of the reaction radius of a reacting pair of molecules.

  20. Reaction rates for a generalized reaction-diffusion master equation.

    PubMed

    Hellander, Stefan; Petzold, Linda

    2016-01-01

    It has been established that there is an inherent limit to the accuracy of the reaction-diffusion master equation. Specifically, there exists a fundamental lower bound on the mesh size, below which the accuracy deteriorates as the mesh is refined further. In this paper we extend the standard reaction-diffusion master equation to allow molecules occupying neighboring voxels to react, in contrast to the traditional approach, in which molecules react only when occupying the same voxel. We derive reaction rates, in two dimensions as well as three dimensions, to obtain an optimal match to the more fine-grained Smoluchowski model and show in two numerical examples that the extended algorithm is accurate for a wide range of mesh sizes, allowing us to simulate systems that are intractable with the standard reaction-diffusion master equation. In addition, we show that for mesh sizes above the fundamental lower limit of the standard algorithm, the generalized algorithm reduces to the standard algorithm. We derive a lower limit for the generalized algorithm which, in both two dimensions and three dimensions, is of the order of the reaction radius of a reacting pair of molecules.

  1. Reaction rates for a generalized reaction-diffusion master equation

    DOE PAGES

    Hellander, Stefan; Petzold, Linda

    2016-01-19

    It has been established that there is an inherent limit to the accuracy of the reaction-diffusion master equation. Specifically, there exists a fundamental lower bound on the mesh size, below which the accuracy deteriorates as the mesh is refined further. In this paper we extend the standard reaction-diffusion master equation to allow molecules occupying neighboring voxels to react, in contrast to the traditional approach in which molecules react only when occupying the same voxel. We derive reaction rates, in two dimensions as well as three dimensions, to obtain an optimal match to the more fine-grained Smoluchowski model, and show inmore » two numerical examples that the extended algorithm is accurate for a wide range of mesh sizes, allowing us to simulate systems that are intractable with the standard reaction-diffusion master equation. In addition, we show that for mesh sizes above the fundamental lower limit of the standard algorithm, the generalized algorithm reduces to the standard algorithm. We derive a lower limit for the generalized algorithm which, in both two dimensions and three dimensions, is on the order of the reaction radius of a reacting pair of molecules.« less

  2. Applications of Skyrme energy-density functional to fusion reactions for synthesis of superheavy nuclei

    SciTech Connect

    Wang Ning; Scheid, Werner; Wu Xizhen; Liu Min; Li Zhuxia

    2006-10-15

    The Skyrme energy-density functional approach has been extended to study massive heavy-ion fusion reactions. Based on the potential barrier obtained and the parametrized barrier distribution the fusion (capture) excitation functions of a lot of heavy-ion fusion reactions are studied systematically. The average deviations of fusion cross sections at energies near and above the barriers from experimental data are less than 0.05 for 92% of 76 fusion reactions with Z{sub 1}Z{sub 2}<1200. For the massive fusion reactions, for example, the {sup 238}U-induced reactions and {sup 48}Ca+{sup 208}Pb, the capture excitation functions have been reproduced remarkably well. The influence of structure effects in the reaction partners on the capture cross sections is studied with our parametrized barrier distribution. By comparing the reactions induced by double-magic nucleus {sup 48}Ca and by {sup 32}S and {sup 35}Cl, the ''threshold-like'' behavior in the capture excitation function for {sup 48}Ca-induced reactions is explored and an optimal balance between the capture cross section and the excitation energy of the compound nucleus is studied. Finally, the fusion reactions with {sup 36}S, {sup 37}Cl, {sup 48}Ca, and {sup 50}Ti bombarding {sup 248}Cm, {sup 247,249}Bk, {sup 250,252,254}Cf, and {sup 252,254}Es, as well as the reactions leading to the same compound nucleus with Z=120 and N=182, are studied further. The calculation results for these reactions are useful for searching for the optimal fusion configuration and suitable incident energy in the synthesis of superheavy nuclei.

  3. Possibilities for synthesis of new isotopes of superheavy nuclei in cold fusion reactions

    NASA Astrophysics Data System (ADS)

    Bao, X. J.; Gao, Y.; Li, J. Q.; Zhang, H. F.

    2016-04-01

    In order to find a way to produce superheavy nuclei (SHN), which appear in the gap between the SHN synthesized by cold fusion and those by hot fusion, or those so far not yet been produced in the laboratory, we tried to make use of a set of projectile isotopic chains, to use a radioactive beam projectile, and to test symmetric fusion reactions for gaining more neutrons to synthesize neutron-richer SHN based on the dinuclear system (DNS) model via cold fusion reactions. It is found that the nuclei 265Mt,Ds,272268,273Rg, and 274,275,276Cn may be produced with the detectable evaporation residual cross sections. The intensities of radioactive beams are significantly less than those of the stable beams, therefore using a stable beam is predicted to be the most favorable method for producing SHN. From the symmetric reaction system 136Xe+136Xe , no fusion event was found.

  4. Fusion and quasifission studies in reactions forming Rn via evaporation residue measurements

    NASA Astrophysics Data System (ADS)

    Shamlath, A.; Prasad, E.; Madhavan, N.; Laveen, P. V.; Gehlot, J.; Nasirov, A. K.; Giardina, G.; Mandaglio, G.; Nath, S.; Banerjee, Tathagata; Vinodkumar, A. M.; Shareef, M.; Jhingan, A.; Varughese, T.; Kumar, Dvgrks; Devi, P. Sandya; Khushboo, Jisha, P.; Kumar, Neeraj; Hosamani, M. M.; Kailas, S.

    2017-03-01

    Background: Formation of the compound nucleus (CN) is highly suppressed by quasifission in heavy-ion collisions involving massive nuclei. Though considerable progress has been made in the understanding of fusion-fission and quasifission, the exact dependence of fusion probability on various entrance channel variables is not completely clear, which is very important for the synthesis of new heavy and superheavy elements. Purpose: To study the interplay between fusion and quasifission in reactions forming CN in the boundary region where the fusion probability starts to deviate from unity. Methods: Fusion evaporation residue cross sections were measured for the Si,3028+180Hf reactions using the Hybrid Recoil Mass Analyser at IUAC, New Delhi. Experimental data were compared with data from other reactions forming the same CN or isotopes of the CN. Theoretical calculations were performed using the dinuclear system and statistical models. Results: Reduced evaporation residue cross sections were observed for the reactions studied compared with the asymmetric reaction forming the same CN, indicating fusion suppression in more symmetric systems. The observations are consistent with fission fragment measurements performed in the same or similar systems. Larger ER cross sections are observed with increase in mass in the isotopic chain of the CN. Conclusions: Fusion probability varies significantly with the entrance channels in reactions forming the same CN. While complete fusion occurs for the 16O+194Pt reaction, the fusion probability drops to approximately 60 -70 % for the 30Si+180Hf and less than 20 % for the 50Ti+160Gd reactions, respectively, forming the same CN at similar excitation energies.

  5. Analysis of the radial potential structure and neutron production rate in the spherical inertial electrostatic confinement fusion devices

    NASA Astrophysics Data System (ADS)

    Ramzanpour, M. A.; Pahlavani, M. R.

    2017-01-01

    The radial dependent potential and neutron production rate in spherical inertial electrostatic confinement fusion (IECF) devices is investigated. The electrostatic potential is determined by solving the Poisson equation for various deuteron and electron distribution functions. The fusion reaction rates are determined using energy distribution function. Also, dependence of potential structure and neutron production rate on some important parameters as the ion and electron convergence, working pressure, kinetic energy of the secondary electrons emitted from the cathode and the fraction of secondary electrons drawn inside the cathode are studied. Total produced neutrons as a function of input power at different working conditions are also obtained.

  6. Thermonuclear Reaction Rate Parameterization for Nuclear Astrophysics

    NASA Astrophysics Data System (ADS)

    Sharp, Jacob; Kozub, Raymond L.; Smith, Michael S.; Scott, Jason; Lingerfelt, Eric

    2004-10-01

    The knowledge of thermonuclear reaction rates is vital to simulate novae, supernovae, X-ray bursts, and other astrophysical events. To facilitate dissemination of this knowledge, a set of tools has been created for managing reaction rates, located at www.nucastrodata.org. One tool is a rate parameterizer, which provides a parameterization for nuclear reaction rate vs. temperature values in the most widely used functional form. Currently, the parameterizer uses the Levenberg-Marquardt method (LMM), which requires an initial estimate of the best-fit parameters. The initial estimate is currently provided randomly from a preselected pool. To improve the quality of fits, a new, active method of selecting parameters has been developed. The parameters of each set in the pool are altered for a few iterations to replicate the input data as closely as possible. Then, the set which most nearly matches the input data (based on chi squared) is used in the LMM as the initial estimate for the final fitting procedure. A description of the new, active algorithm and its performance will be presented. Supported by the U. S. Department of Energy.

  7. Microscopic dynamics simulations of heavy-ion fusion reactions induced by neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Wang, Ning; Ou, Li; Zhang, Yingxun; Li, Zhuxia

    2014-06-01

    The heavy-ion fusion reactions induced by neutron-rich nuclei are investigated with the improved quantum molecular dynamics (ImQMD) model. With a subtle consideration of the neutron skin thickness of nuclei and the symmetry potential, the stability of nuclei and the fusion excitation functions of heavy-ion fusion reactions O16 + Ge76, O16 + Sm154, Ca40 + Zr96, and Sn132 + Ca40 are systematically studied. The fusion cross sections of these reactions at energies around the Coulomb barrier can be well reproduced by using the ImQMD model. The corresponding slope parameter of the symmetry energy adopted in the calculations is L ≈78 MeV and the surface energy coefficient is gsur=18±1.5 MeV fm2. In addition, it is found that the surface-symmetry term significantly influences the fusion cross sections of neutron-rich fusion systems. For sub-barrier fusion, the dynamical fluctuations in the densities of the reaction partners and the enhanced surface diffuseness at neck side result in the lowering of the fusion barrier.

  8. Fusion, reaction, and breakup cross sections of {sup 9}Be on a light mass target

    SciTech Connect

    Marti, G.V.; Capurro, O.A.; Pacheco, A.J.; Testoni, J.E.; Ramirez, M.; Arazi, A.; Gomes, P.R.S.; Padron, I.; Anjos, R.M.; Lubian, J.; Crema, E.

    2005-02-01

    The total fusion cross section for the {sup 9}Be+{sup 27}Al system has been measured at energies close and above the Coulomb barrier. Reaction cross sections for this system were derived from elastic scattering data, and the breakup-plus-transfer-channel cross sections were estimated from the difference between these data and measured cross-section fusion.

  9. Quantum theory of chemical reaction rates

    SciTech Connect

    Miller, W.H. |

    1994-10-01

    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.

  10. Thermodynamic limitations on microbially catalyzed reaction rates

    NASA Astrophysics Data System (ADS)

    LaRowe, Douglas E.; Dale, Andrew W.; Amend, Jan P.; Van Cappellen, Philippe

    2012-08-01

    Quantification of global biogeochemical cycles requires knowledge of the rates at which microorganisms catalyze chemical reactions. In order for models that describe these processes to capture global patterns of change, the underlying formulations in them must account for biogeochemical transformations over seasonal and millennial time scales in environments characterized by different energy levels. Building on existing models, a new thermodynamic limiting function is introduced. With only one adjustable parameter, this function that can be used to model microbial metabolism throughout the range of conditions in which organisms are known to be active. The formulation is based on a comparison of the amount of energy available from any redox reaction to the energy required to maintain a membrane potential, a proxy for the minimum amount of energy required by an active microorganism. This function does not require species- or metabolism-specific parameters, and can be used to model metabolisms that capture any amount of energy. The utility of this new thermodynamic rate limiting term is illustrated by applying it to three low-energy processes: fermentation, methanogenesis and sulfate reduction. The model predicts that the rate of fermentation will be reduced by half once the Gibbs energy of the catalyzed reaction reaches -12 kJ (mol e-)-1, and then slowing exponentially until the energy yield approaches zero. Similarly, the new model predicts that the low energy yield of methanogenesis, -4 to -0.5 kJ (mol e-)-1, for a partial pressure of H2 between 11 and 0.6 Pa decreases the reaction rate by 95-99%. Finally, the new function's utility is illustrated through its ability to accurately model sulfate concentration data in an anoxic marine sediment.

  11. Pycnonuclear reaction rates for binary ionic mixtures

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    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.

  12. Reaction Rate Parameterization for Nuclear Astrophysics Research

    NASA Astrophysics Data System (ADS)

    Scott, J. P.; Lingerfelt, E. J.; Smith, M. S.; Hix, W. R.; Bardayan, D. W.; Sharp, J. E.; Kozub, R. L.; Meyer, R. A.

    2004-11-01

    Libraries of thermonuclear reaction rates are used in element synthesis models of a wide variety of astrophysical phenomena, such as exploding stars and the inner workings of our sun. These computationally demanding models are more efficient when libraries, which may contain over 60000 rates and vary by 20 orders of magnitude, have a uniform parameterization for all rates. We have developed an on-line tool, hosted at www.nucastrodata.org, to obtain REACLIB parameters (F.-K. Thielemann et al., Adv. Nucl. Astrophysics 525, 1 (1987)) that represent reaction rates as a function of temperature. This helps to rapidly incorporate the latest nuclear physics results in astrophysics models. The tool uses numerous techniques and algorithms in a modular fashion to improve the quality of the fits to the rates. Features, modules, and additional applications of this tool will be discussed. * Managed by UT-Battelle, LLC, for the U.S. D.O.E. under contract DE-AC05-00OR22725 + Supported by U.S. D.O.E. under Grant No. DE-FG02-96ER40955

  13. Spectral photoplethysmographic imaging sensor fusion for enhanced heart rate detection

    NASA Astrophysics Data System (ADS)

    Amelard, Robert; Clausi, David A.; Wong, Alexander

    2016-03-01

    Continuous heart rate monitoring can provide important context for quantitative clinical assessment in scenarios such as long-term health monitoring and disability prevention. Photoplethysmographic imaging (PPGI) systems are particularly useful for such monitoring scenarios as contact-based devices pose problems related to comfort and mobility. Each pixel can be regarded as a virtual PPG sensor, thus enabling simultaneous measurements of multiple skin sites. Existing PPGI systems analyze temporal PPGI sensor uctuations related to hemodynamic pulsations across a region of interest to extract the blood pulse signal. However, due to spatially varying optical properties of the skin, the blood pulse signal may not be consistent across all PPGI sensors, leading to inaccurate heart rate monitoring. To increase the hemodynamic signal-to-noise ratio (SNR), we propose a novel spectral PPGI sensor fusion method for enhanced estimation of the true blood pulse signal. Motivated by the observation that PPGI sensors with high hemodynamic SNR exhibit a spectral energy peak at the heart rate frequency, an entropy-based fusion model was formulated to combine PPGI sensors based on the sensors' spectral energy distribution. The optical PPGI device comprised a near infrared (NIR) sensitive camera and an 850 nm LED. Spatially uniform irradiance was achieved by placing optical elements along the LED beam, providing consistent illumination across the skin area. Dual-mode temporally coded illumination was used to negate the temporal effect of ambient illumination. Experimental results show that the spectrally weighted PPGI method can accurately and consistently extract heart rate information where traditional region-based averaging fails.

  14. An approximate classical unimolecular reaction rate theory

    NASA Astrophysics Data System (ADS)

    Zhao, Meishan; Rice, Stuart A.

    1992-05-01

    We describe a classical theory of unimolecular reaction rate which is derived from the analysis of Davis and Gray by use of simplifying approximations. These approximations concern the calculation of the locations of, and the fluxes of phase points across, the bottlenecks to fragmentation and to intramolecular energy transfer. The bottleneck to fragment separation is represented as a vibration-rotation state dependent separatrix, which approximation is similar to but extends and improves the approximations for the separatrix introduced by Gray, Rice, and Davis and by Zhao and Rice. The novel feature in our analysis is the representation of the bottlenecks to intramolecular energy transfer as dividing surfaces in phase space; the locations of these dividing surfaces are determined by the same conditions as locate the remnants of robust tori with frequency ratios related to the golden mean (in a two degree of freedom system these are the cantori). The flux of phase points across each dividing surface is calculated with an analytic representation instead of a stroboscopic mapping. The rate of unimolecular reaction is identified with the net rate at which phase points escape from the region of quasiperiodic bounded motion to the region of free fragment motion by consecutively crossing the dividing surfaces for intramolecular energy exchange and the separatrix. This new theory generates predictions of the rates of predissociation of the van der Waals molecules HeI2, NeI2 and ArI2 which are in very good agreement with available experimental data.

  15. Bayesian Estimation of Thermonuclear Reaction Rates

    NASA Astrophysics Data System (ADS)

    Iliadis, C.; Anderson, K. S.; Coc, A.; Timmes, F. X.; Starrfield, S.

    2016-11-01

    The problem of estimating non-resonant astrophysical S-factors and thermonuclear reaction rates, based on measured nuclear cross sections, is of major interest for nuclear energy generation, neutrino physics, and element synthesis. Many different methods have been applied to this problem in the past, almost all of them based on traditional statistics. Bayesian methods, on the other hand, are now in widespread use in the physical sciences. In astronomy, for example, Bayesian statistics is applied to the observation of extrasolar planets, gravitational waves, and Type Ia supernovae. However, nuclear physics, in particular, has been slow to adopt Bayesian methods. We present astrophysical S-factors and reaction rates based on Bayesian statistics. We develop a framework that incorporates robust parameter estimation, systematic effects, and non-Gaussian uncertainties in a consistent manner. The method is applied to the reactions d(p,γ)3He, 3He(3He,2p)4He, and 3He(α,γ)7Be, important for deuterium burning, solar neutrinos, and Big Bang nucleosynthesis.

  16. The effects of vacuum polarization on thermonuclear reaction rates

    NASA Technical Reports Server (NTRS)

    Gould, Robert J.

    1990-01-01

    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.

  17. Impact of iliac crest bone graft harvesting on fusion rates and postoperative pain during instrumented posterolateral lumbar fusion

    PubMed Central

    Triantafyllopoulos, Dimitrios; Kosmopoulos, Victor; Stafylas, Kosmas

    2007-01-01

    This study aims to evaluate the influence of bone harvesting on postoperative pain and fusion rates. Group 1 patients received iliac crest bone graft (ICBG) either alone or augmented with local bone. Group 2 received only local bone. No statistical significance was found in radiological union or in the Oswestry Disability Index scores. Visual Analogue Scale scores showed less pain in group 2. Logistic regression showed no correlation between residual pain and occurrence of fusion. Harvesting ICBG did not appear to increase fusion rates and no relation was found between radiological non-union and pain. PMID:17724591

  18. CHLORINATION OF AMINO ACIDS: REACTION PATHWAYS AND REACTION RATES.

    PubMed

    How, Zuo Tong; Linge, Kathryn; Busetti, Francesco; Joll, Cynthia A

    2017-03-15

    Chlorination of amino acids can result in the formation of organic monochloramines or organic dichloramines, depending on the chlorine to amino acid ratio (Cl:AA). After formation, organic chloramines degrade into aldehydes, nitriles and N-chloraldimines. In this paper, the formation of organic chloramines from chlorination of lysine, tyrosine and valine were investigated. Chlorination of tyrosine and lysine demonstrated that the presence of a reactive secondary group can increase the Cl:AA ratio required for the formation of N,N-dichloramines, and potentially alter the reaction pathways between chlorine and amino acids, resulting in the formation of unexpected by-products. In a detailed investigation, we report rate constants for all reactions in the chlorination of valine, for the first time, using experimental results and modelling. At Cl:AA = 2.8, the chlorine was found to first react quickly with valine (5.4x104 M-1 s-1) to form N-monochlorovaline, with a slower subsequent reaction with N-monochlorovaline to form N,N-dichlorovaline (4.9x102 M-1 s-1), although some N-monochlorovaline degraded into isobutyraldehyde (1.0x10-4 s-1). The N,N-dichlorovaline then competitively degraded into isobutyronitrile (1.3x10-4 s-1) and N-chloroisobutyraldimine (1.2x10-4 s-1). In conventional drinking water disinfection, N-chloroisobutyraldimine can potentially be formed in concentrations higher than its odour threshold concentration, resulting in aesthetic challenges and an unknown health risk.

  19. Development of an inertial confinement fusion platform to study charged-particle-producing nuclear reactions relevant to nuclear astrophysics

    DOE PAGES

    Gatu Johnson, M.; Zylstra, A. B.; Bacher, A.; ...

    2017-03-28

    Here, this paper describes the development of a platform to study astrophysically relevant nuclear reactions using inertial-confinement fusion implosions on the OMEGA and National Ignition Facility laser facilities, with a particular focus on optimizing the implosions to study charged-particle- producing reactions. Primary requirements on the platform are high yield, for high statistics in the fusion product measurements, combined with low areal density, to allow the charged fusion products to escape. This is optimally achieved with direct-drive exploding pusher implosions using thin-glass-shell capsules. Mitigation strategies to eliminate a possible target sheath potential which would accelerate the emitted ions are discussed. Themore » potential impact of kinetic effects on the implosions is also considered. The platform is initially employed to study the complementary T(t,2n)α, T(3He,np)α and 3He(3He,2p)α reactions. Proof-of-principle results from the first experiments demonstrating the ability to accurately measure the energy and yields of charged particles are presented. Lessons learned from these experiments will be used in studies of other reactions. Ultimately, the goals are to explore thermonuclear reaction rates and fundamental nuclear physics in stellarlike plasma environments, and to push this new frontier of nuclear astrophysics into unique regimes not reachable through existing platforms, with thermal ion velocity distributions, plasma screening, and low reactant energies.« less

  20. Recent developments in heavy-ion fusion reactions around the Coulomb barrier

    NASA Astrophysics Data System (ADS)

    Hagino, K.; Rowley, N.; Yao, J. M.

    2016-06-01

    The nuclear fusion is a reaction to form a compound nucleus. It plays an important role in several circumstances in nuclear physics as well as in nuclear astrophysics, such as synthesis of superheavy elements and nucleosynthesis in stars. Here we discuss two recent theoretical developments in heavy-ion fusion reactions at energies around the Coulomb barrier. The first topic is a generalization of the Wong formula for fusion cross sections in a single-channel problem. By introducing an energy dependence to the barrier parameters, we show that the generalized formula leads to results practically indistinguishable from a full quantal calculation, even for light symmetric systems such as 12C+12C, for which fusion cross sections show an oscillatory behavior. We then discuss a semi-microscopic modeling of heavy-ion fusion reactions, which combine the coupled-channels approach to the state-of-the-art nuclear structure calculations for low-lying collective motions. We apply this method to subbarrier fusion reactions of 58Ni+58Ni and 40Ca+58Ni systems, and discuss the role of anharmonicity of the low-lying vibrational motions.

  1. Quasifission and fusion-fission in reactions with massive nuclei: Comparison of reactions leading to the Z=120 element

    SciTech Connect

    Nasirov, A. K.; Giardina, G.; Mandaglio, G.; Manganaro, M.; Hanappe, F.; Heinz, S.; Hofmann, S.; Muminov, A. I.; Scheid, W.

    2009-02-15

    The yields of evaporation residues, fusion-fission, and quasifission fragments in the {sup 48}Ca+{sup 144,154}Sm and {sup 16}O+{sup 186}W reactions are analyzed in the framework of the combined theoretical method based on the dinuclear system concept and advanced statistical model. The measured yields of evaporation residues for the {sup 48}Ca+{sup 154}Sm reaction can be well reproduced. The measured yields of fission fragments are decomposed into contributions coming from fusion-fission, quasifission, and fast-fission. The decrease in the measured yield of quasifission fragments in {sup 48}Ca+{sup 154}Sm at the large collision energies and the lack of quasifission fragments in the {sup 48}Ca+{sup 144}Sm reaction are explained by the overlap in mass angle distributions of the quasifission and fusion-fission fragments. The investigation of the optimal conditions for the synthesis of the new element Z=120 (A=302) show that the {sup 54}Cr+{sup 248}Cm reaction is preferable in comparison with the {sup 58}Fe+{sup 244}Pu and {sup 64}Ni+{sup 238}U reactions because the excitation function of the evaporation residues of the former reaction is some orders of magnitude larger than that for the last two reactions.

  2. Does the sun shine by pp or CNO fusion reactions?

    PubMed

    Bahcall, John N; Gonzalez-Garcia, M C; Peña-Garay, Carlos

    2003-04-04

    We show that solar neutrino experiments set an upper limit of 7.8% (7.3% including the recent KamLAND measurements) to the fraction of energy that the Sun produces via the CNO fusion cycle, which is an order of magnitude improvement upon the previous limit. New experiments are required to detect CNO neutrinos corresponding to the 1.5% of the solar luminosity that the standard solar model predicts is generated by the CNO cycle.

  3. Role of the neck degree of freedom in cold fusion reactions

    NASA Astrophysics Data System (ADS)

    Adamian, G. G.; Antonenko, N. V.; Lenske, H.

    2015-05-01

    Mass parameters for collective variables of dinuclear systems formed in cold fusion reactions are microscopically calculated with the linear response theory making use of the width of single-particle states and the fluctuation-dissipation theorem. The single-particle spectrum and potential energy surface of the adiabatic two-center shell model are used. The microscopical mass parameter in the neck is found to be much larger than one obtained with the hydrodynamical model. Therefore, the dinuclear system lives a rather long time, comparable to the characteristic time of fusion and, correspondingly, the fusion can be considered at fixed neck parameter. With an adiabatic melting of the dinuclear system along the internuclear distance into a compound system one cannot explain the experimental trends in cold fusion reactions.

  4. Reaction weakening and emplacement of crystalline thrusts: Diffusion control on reaction rate and strain rate

    NASA Astrophysics Data System (ADS)

    O'Hara, Kieran

    2007-08-01

    In the southern Appalachians, the Blue Ridge-Piedmont crystalline thrust sheet was emplaced onto low-grade Late Precambrian and Paleozoic sedimentary rocks in the footwall along a basal detachment consisting of phyllosilicate-rich mylonites (phyllonites). The phyllonites developed first by mechanical breakdown of feldspar followed by chemical breakdown to white mica in the presence of a pore fluid. Diffusion of solute in the pore fluid is the rate limiting step in controlling reaction rate and also the strain rate. Assuming solute diffusion follows the Stokes-Einstein equation, the shear strain rate is given by ⅆγ/ⅆt=2ωkT/5ηrx for shear stress ≥20 MPa, where n is a constant, ω is a geometric factor, k is Boltzmann's constant, T is absolute temperature, η is water viscosity, r is the atomic radius of the diffusing species, and x is the diffusion distance. A bulk diffusion coefficient in the range of ˜10 -10 to 10 -12 m 2/s over distances of 10-100 m results in strain rates of 10 -14 to 10 -13 s -1 in the temperature range 200-400 °C. It is concluded that greenschist grade crystalline thrust sheets develop on pre-existing basement faults that become weak during reaction softening and localize into high strain phyllonite zones in which pore fluid diffusion controls reaction rate and strain rate.

  5. A simple reaction-rate model for turbulent diffusion flames

    NASA Technical Reports Server (NTRS)

    Bangert, L. H.

    1975-01-01

    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.

  6. Probing systematic model dependence of complete fusion for reactions with the weakly bound projectiles Li,76

    NASA Astrophysics Data System (ADS)

    Kundu, A.; Santra, S.; Pal, A.; Chattopadhyay, D.; Nayak, B. K.; Saxena, A.; Kailas, S.

    2016-07-01

    Background: Complete fusion cross section measurements involving weakly bound projectiles show suppression at above-barrier energies compared to coupled-channels (CC) calculations, but no definite conclusion could be drawn for sub-barrier energies. Different CC models often lead to contrasting results. Purpose: We aim to investigate the differences in the fusion cross sections predicted by commonly used CC calculations, using codes such as fresco and ccfull, when compared to experimental data. Methods: The fusion cross sections are normalized to a dimensionless form by isolating the effect of only dynamic channel couplings calculated by both fresco and ccfull, by the method of fusion functions, and compared to a universal fusion function. This acts as a probe for obtaining the model dependence of fusion. Results: A difference is observed between the predictions of fresco and ccfull for all the reactions involving Li,76 as projectiles, and it is noticeably more for systems involving 7Li. Conclusions: With the theoretical foundations of the two CC models being different, their calculation of fusion is different even for the same system. The conclusion about the enhancement or suppression of fusion cross sections is model dependent.

  7. Fusion and quasi-fission dynamics in nearly-symmetric reactions

    NASA Astrophysics Data System (ADS)

    Wang, Ning; Zhao, Kai; Li, ZhuXia

    2015-11-01

    Some nearly-symmetric fusion reactions are systematically investigated with the improved quantum molecular dynamics (ImQMD) model. By introducing two-body inelastic scattering in the Fermi constraint procedure, the stability of an individual nucleus and the description of fusion cross sections at energies near the Coulomb barrier can be further improved. Simultaneously, the quasifission process in 154Sm+160Gd is also investigated with the microscopic dynamics model for the first time. We find that at energies above the Bass barrier, the fusion probability is smaller than 10-5 for this reaction, and the nuclear contact time is generally smaller than 1500 fm/ c. From the central collisions of Sm+Gd, the neutron-rich fragments such as 164,165Gd, 192W can be produced in the ImQMD simulations, which implies that the quasi-fission reaction could be an alternative way to synthesize new neutron-rich heavy nuclei.

  8. Analysis of the role of neutron transfer in asymmetric fusion reactions at subbarrier energies

    SciTech Connect

    Ogloblin, A. A.; Zhang, H. Q.; Lin, C. J.; Jia, H. M.; Khlebnikov, S. V.; Kuzmin, E. A.; Danilov, A. N.; Demyanova, A. S.; Trzaska, W. H.; Xu, X. X.; Yang, F.; Sargsyan, V. V. Adamian, G. G.; Antonenko, N. V.; Scheid, W.

    2015-12-15

    The excitation functions were measured for the {sup 28}Si + {sup 208}Pb complete-fusion (capture) reaction at deep subbarrier energies. The results were compared with the cross sections predicted within the quantum diffusion approach. The role of neutron transfer in the case of positive Q values in the {sup 28}Si + {sup 124}Sn, {sup 208}Pb; {sup 30}Si + {sup 124}Sn, {sup 208}Pb; {sup 20}Ne + {sup 208}Pb; {sup 40}Ca + {sup 96}Zr; and {sup 134}Te + {sup 40}Ca complete-fusion (capture) reactions is discussed.

  9. Representing Rate Equations for Enzyme-Catalyzed Reactions

    ERIC Educational Resources Information Center

    Ault, Addison

    2011-01-01

    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…

  10. Fusion reactions and experimental approaches to the synthesis of superheavy nuclei

    SciTech Connect

    Yeremin, A. V.; Utyonkov, V. K.; Oganessian, Yu. Ts.

    1998-02-15

    The question whether the asymmetric actinide based heavy ion reactions could be used for the synthesis of heavy (Z{>=}106) nuclides is essential from the point of view of the study of limitation on fusion, it is also important in such reactions new nuclides close to the magic number N=162 can be produced. Thus as the problem of a hindrance to fusion still remains unsolved the high excitation energy of the compound nucleus looks to be an obvious obstacle to using these reactions. Using the gas-filled recoil separator and electrostatic recoil separator VAS-SILISSA installed at the beam lines of the U-400 heavy ion cyclotron of the FLNR JINR we investigated the fusion reactions leading to 102, 103, 104, 105 and heaviest isotopes of the 106, 108 and 110 elements. The analysis of the measured cross-sections did not reveal any evidence of a hindrance to fusion at the ion bombarding energy close to the Coulomb barrier. {sup 48}Ca+{sup 232}Th{yields}{sup 280}110*, {sup 48}Ca+{sup 238}U{yields}{sup 286}112*, {sup 48}Ca+{sup 244}Pu{yields}{sup 292}114* appear to be the best reactions from the point of view of their cross-sections.

  11. Calculation of evaporation residue cross sections for the synthesis of superheavy nuclei in hot fusion reactions

    NASA Astrophysics Data System (ADS)

    Zhang, Jinjuan; Wang, Chengbin; Ren, Zhongzhou

    2013-07-01

    A systematic calculation of the production cross sections of superheavy elements (SHEs) in hot fusion reactions is performed. First, we analyze the reactions of 48Ca + 238U, 244Pu, and 248Cm, from which the parameter values in the model for each process are determined by comparing the calculated capture, fusion, and evaporation residue (ER) cross sections, respectively, with the measured data. Then, we calculate the ER cross sections of other hot fusion reactions with the derived parameter values. The calculated results are in good agreement with the available data. Furthermore, the possible isotope production cross sections of elements 118 and 117 in the reactions of 48Ca + ACf and ABk are computed. We find that with the increase of the neutron number of the target, the production cross sections of the SHEs increase, primarily caused by the smaller neutron separation energies of the corresponding neutron-rich compound nucleus (CN). Finally, the production cross sections of elements 120 and 119 are evaluated in fusion-evaporation reactions with 50Ti as a projectile.

  12. Hydrogen generation arising from the {sup 59}Ni(n,p) reaction and its impact on fission-fusion correlations

    SciTech Connect

    Greenwood, L.R.; Garner, A.F.

    1996-04-01

    Whilte the influence of transmutant helium on radiation-induced microstructural evolution has often been studied, there is a tendency to overlook the influence of concurrently-generated hydrogen. There have been some recent speculation and studies, however, that suggest that the influence of hydrogen may be enhanced in the presence of large amounts of helium, especially at lower irradiation temperatures typical of projected ITER operation. The impact of the (n,p) reaction on both hydrogen generation rates and displacement rates are evaluated in this paper for a variety of neutron spectra employed in fission-fusion correlation.

  13. Inertial confinement fusion reaction chamber and power conversion system study

    SciTech Connect

    Maya, I.; Schultz, K.R.; Battaglia, J.M.; Buksa, J.J.; Creedson, R.L.; Erlandson, O.D.; Levine, H.E.; Roelant, D.F.; Sanchez, H.W.; Schrader, S.A.

    1984-09-01

    GA Technologies has developed a conceptual ICF reactor system based on the Cascade rotating-bed reaction chamber concept. Unique features of the system design include the use of low activation SiC in a reaction chamber constructed of box-shaped tiles held together in compression by prestressing tendons to the vacuum chamber. Circulating Li/sub 2/O granules serve as the tritium breeding and energy transport material, cascading down the sides of the reaction chamber to the power conversion system. The total tritium inventory of the system is 6 kg; tritium recovery is accomplished directly from the granules via the vacuum system. A system for centrifugal throw transport of the hot Li/sub 2/O granules from the reaction chamber to the power conversion system has been developed. A number of issues were evaluated during the course of this study. These include the response of first-layer granules to the intense microexplosion surface heat flux, cost effective fabrication of Li/sub 2/O granules, tritium inventory and recovery issues, the thermodynamics of solids-flow options, vacuum versus helium-medium heat transfer, and the tradeoffs of capital cost versus efficiency for alternate heat exchange and power conversion system option. The resultant design options appear to be economically competitive, safe, and environmentally attractive.

  14. Dynamical Dipole mode in heavy-ion fusion reactions in the 192Pb mass region

    NASA Astrophysics Data System (ADS)

    Parascandolo, C.; Pierroutsakou, D.; Alba, R.; Del Zoppo, A.; Maiolino, C.; Santonocito, D.; Agodi, C.; Baran, V.; Boiano, A.; Colonna, M.; Coniglione, R.; De Filippo, E.; Di Toro, M.; Emanuele, U.; Farinon, F.; Guglielmetti, A.; La Commara, M.; Martin, B.; Mazzocchi, C.; Mazzocco, M.; Rizzo, C.; Romoli, M.; Signorini, C.; Silvestri, R.; Soramel, F.; Strano, E.; Torresi, D.; Trifiró, A.; Trimarchi, M.

    2015-04-01

    The dynamical dipole mode was investigated in the mass region of the 192Pb compound nucleus, by using the 40Ca + 152Sm and 48Ca + 144Sm reactions at Elab=11 and 10.1 MeV/nucleon, respectively. Both fusion-evaporation and fission events were studied simultaneously for the first time. Our results for evaporation and fission events (preliminary) show that the dynamical dipole mode survives in reactions involving heavier nuclei than those studied previously.

  15. Variables Affecting Fusion Rates in the Rat Posterolateral Spinal Fusion Model with Autogenic/Allogenic Bone Grafts: A Meta-analysis.

    PubMed

    Ishida, Wataru; Elder, Benjamin D; Holmes, Christina; Lo, Sheng-Fu L; Witham, Timothy F

    2016-11-01

    The rat posterolateral spinal fusion model with autogenic/allogenic bone graft (rat PFABG) has been increasingly utilized as an experimental model to assess the efficacy of novel fusion treatments. The objective of this study was to investigate the reliability of the rat PFABG model and examine the effects of different variables on spinal fusion. A web-based literature search from January, 1970 to September, 2015, yielded 26 studies, which included 40 rat PFABG control groups and 449 rats. Data regarding age, weight, sex, and strain of rats, graft volume, graft type, decorticated levels, surgical approach, institution, the number of control rats, fusion rate, methods of fusion assessment, and timing of fusion assessment were collected and analyzed. The primary outcome variable of interest was fusion rate, as evaluated by manual palpation. Fusion rates varied widely, from 0 to 96%. The calculated overall fusion rate was 46.1% with an I (2) value of 62.4, which indicated moderate heterogeneity. Weight >300 g, age >14 weeks, male rat, Sprague-Dawley strain, and autogenic coccyx grafts increased fusion rates with statistical significance. Additionally, an assessment time-point ≥8 weeks had a trend towards statistical significance (p = 0.070). Multi-regression analysis demonstrated that timing of assessment and age as continuous variables, as well as sex as a categorical variable, can predict the fusion rate with R (2) = 0.82. In an inter-institution reliability analysis, the pooled overall fusion rate was 50.0% [44.8, 55.3%], with statistically significant differences among fusion outcomes at different institutions (p < 0.001 and I (2) of 72.2). Due to the heterogeneity of fusion outcomes, the reliability of the rat PFABG model was relatively limited. However, selection of adequate variables can optimize its use as a control group in studies evaluating the efficacy of novel fusion therapies.

  16. In-cell reaction rate distributions and cell-average reaction rates in fast critical assemblies

    SciTech Connect

    Brumbach, S.B.; Gasidlo, J.M.

    1985-08-01

    Measurements are described for determining average values of fission rates in /sup 235/U, /sup 238/U and /sup 239/Pu and capture rates in /sup 238/U for heterogeneous cells used to construct fast critical assemblies. The measurements are based on irradiations of foils of /sup 238/U, /sup 235/U and /sup 239/Pu with counting of fission and capture products using gamma-ray spectroscopy. Both plate and pin cells are considered. Procedures are described for inferring cell-average reaction rate values from a single foil location based on a cell using a quantity called a cell factor. Cell factors are determined from special measurements in which several foils are irradiated within a cell. Comparisons are presented between cell factors determined by measurements and by Monte Carlo calculations which lend credibility to the measurement procedures.

  17. Fusion of artificial membranes with mammalian spermatozoa. Specific involvement of the equatorial segment after acrosome reaction.

    PubMed

    Arts, E G; Kuiken, J; Jager, S; Hoekstra, D

    1993-11-01

    The fusogenic properties of bovine and human spermatozoa membranes were investigated, using phospholipid bilayers (liposomes) as target membranes. Fusion was monitored by following lipid mixing, as revealed by an assay based on resonance-energy transfer. In addition, fusion was visualized by fluorescence microscopy, using fluorescent lipid vesicles. Cryopreserved bovine sperm fused with liposomes before induction of the acrosome reaction, fluorescence being located in essentially all spermatozoa membrane domains. Fresh bovine and human spermatozoa fused with liposomes only after the induction of the acrosome reaction, as triggered by calcium ionophore A23187 or zonae pellucidae (proteins), while the fluorescence distribution was mainly restricted to the equatorial segment (ES). However, with spermatozoa that had undergone a freeze/thawing cycle, domains other than ES also became labeled. Hence, the redistribution of the lipid probes over the entire membrane occurring during lipid mixing with cryopreserved bovine sperm is probably related to membrane perturbations caused by long-term cryopreservation. Fusion with liposomes was governed by spermatozoa factors and required the presence of acidic phospholipids like cardiolipin and phosphatidylserine in the liposomal bilayer. Incorporation of the zwitterionic lipid phosphatidylcholine in the vesicles inhibited the fusion reaction. Fusion was pH dependent. The results indicate that the ES is the primary domain of spermatozoa membranes that harbours the fusogenic capacity of sperm. Liposomes appear a valuable tool in further characterizing the properties of this domain, which has been claimed [Yanagimachi, R. (1988) in The physiology of reproduction (Knobil, E. & Neill, J., eds) pp. 135-185, Raven Press, New York] to represent the putative, initial fusion site for the oocyte.

  18. Understanding Fuel Magnetization and Mix Using Secondary Nuclear Reactions in Magneto-Inertial Fusion

    NASA Astrophysics Data System (ADS)

    Schmit, P. F.; Knapp, P. F.; Hansen, S. B.; Gomez, M. R.; Hahn, K. D.; Sinars, D. B.; Peterson, K. J.; Slutz, S. A.; Sefkow, A. B.; Awe, T. J.; Harding, E.; Jennings, C. A.; Chandler, G. A.; Cooper, G. W.; Cuneo, M. E.; Geissel, M.; Harvey-Thompson, A. J.; Herrmann, M. C.; Hess, M. H.; Johns, O.; Lamppa, D. C.; Martin, M. R.; McBride, R. D.; Porter, J. L.; Robertson, G. K.; Rochau, G. A.; Rovang, D. C.; Ruiz, C. L.; Savage, M. E.; Smith, I. C.; Stygar, W. A.; Vesey, R. A.

    2014-10-01

    Magnetizing the fuel in inertial confinement fusion relaxes ignition requirements by reducing thermal conductivity and changing the physics of burn product confinement. Diagnosing the level of fuel magnetization during burn is critical to understanding target performance in magneto-inertial fusion (MIF) implosions. In pure deuterium fusion plasma, 1.01 MeV tritons are emitted during deuterium-deuterium fusion and can undergo secondary deuterium-tritium reactions before exiting the fuel. Increasing the fuel magnetization elongates the path lengths through the fuel of some of the tritons, enhancing their probability of reaction. Based on this feature, a method to diagnose fuel magnetization using the ratio of overall deuterium-tritium to deuterium-deuterium neutron yields is developed. Analysis of anisotropies in the secondary neutron energy spectra further constrain the measurement. Secondary reactions also are shown to provide an upper bound for the volumetric fuel-pusher mix in MIF. The analysis is applied to recent MIF experiments [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014), 10.1103/PhysRevLett.113.155003] on the Z Pulsed Power Facility, indicating that significant magnetic confinement of charged burn products was achieved and suggesting a relatively low-mix environment. Both of these are essential features of future ignition-scale MIF designs.

  19. SU-D-304-07: Application of Proton Boron Fusion Reaction to Radiation Therapy

    SciTech Connect

    Jung, J; Yoon, D; Shin, H; Kim, M; Suh, T

    2015-06-15

    Purpose: we present the introduction of a therapy method using the proton boron fusion reaction. The purpose of this study is to verify the theoretical validity of proton boron fusion therapy using Monte Carlo simulations. Methods: After boron is accumulated in the tumor region, the emitted from outside the body proton can react with the boron in the tumor region. An increase of the proton’s maximum dose level is caused by the boron and only the tumor cell is damaged more critically. In addition, a prompt gamma ray is emitted from the proton boron reaction point. Here we show that the effectiveness of the proton boron fusion therapy (PBFT) was verified using Monte Carlo simulations. Results: We found that a dramatic increase by more than half of the proton’s maximum dose level was induced by the boron in the tumor region. This increase occurred only when the proton’s maximum dose point was located within the boron uptake region (BUR). In addition, the 719 keV prompt gamma ray peak produced by the proton boron fusion reaction was positively detected. Conclusion: This therapy method features the advantages such as the application of Bragg-peak to the therapy, the accurate targeting of tumor, improved therapy effects, and the monitoring of the therapy region during treatment.

  20. Understanding fuel magnetization and mix using secondary nuclear reactions in magneto-inertial fusion.

    PubMed

    Schmit, P F; Knapp, P F; Hansen, S B; Gomez, M R; Hahn, K D; Sinars, D B; Peterson, K J; Slutz, S A; Sefkow, A B; Awe, T J; Harding, E; Jennings, C A; Chandler, G A; Cooper, G W; Cuneo, M E; Geissel, M; Harvey-Thompson, A J; Herrmann, M C; Hess, M H; Johns, O; Lamppa, D C; Martin, M R; McBride, R D; Porter, J L; Robertson, G K; Rochau, G A; Rovang, D C; Ruiz, C L; Savage, M E; Smith, I C; Stygar, W A; Vesey, R A

    2014-10-10

    Magnetizing the fuel in inertial confinement fusion relaxes ignition requirements by reducing thermal conductivity and changing the physics of burn product confinement. Diagnosing the level of fuel magnetization during burn is critical to understanding target performance in magneto-inertial fusion (MIF) implosions. In pure deuterium fusion plasma, 1.01 MeV tritons are emitted during deuterium-deuterium fusion and can undergo secondary deuterium-tritium reactions before exiting the fuel. Increasing the fuel magnetization elongates the path lengths through the fuel of some of the tritons, enhancing their probability of reaction. Based on this feature, a method to diagnose fuel magnetization using the ratio of overall deuterium-tritium to deuterium-deuterium neutron yields is developed. Analysis of anisotropies in the secondary neutron energy spectra further constrain the measurement. Secondary reactions also are shown to provide an upper bound for the volumetric fuel-pusher mix in MIF. The analysis is applied to recent MIF experiments [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] on the Z Pulsed Power Facility, indicating that significant magnetic confinement of charged burn products was achieved and suggesting a relatively low-mix environment. Both of these are essential features of future ignition-scale MIF designs.

  1. Study of the mechanism of muon-catalyzed t + t fusion reaction

    SciTech Connect

    Bogdanova, L. N.; Demin, D. L.; Filchenkov, V. V.

    2015-01-15

    The mechanism for the muon catalyzed fusion reaction t + t → {sup 4}He + 2n + 11.33 MeV is investigated. The model of the cascade reaction with {sup 5}He as an intermediate state is considered, both the ground and the first exited states being taken into account. The neutron energy spectrum measured in the recent experiment is compared with the Monte-Carlo-simulated one. Varying reaction parameters, we obtain optimum values for the relative weights of the {sup 5}He ground and excited states and for the excitation energy and width of the excited state.

  2. Near threshold two meson production in hardonic fusion reactions

    NASA Astrophysics Data System (ADS)

    Jahn, Rainer

    1991-04-01

    An approved and funded exclusive COSY experiment is presented, which focuses on near threshold two meson production via the reactions p+d→3 He+π+π- and p+d→3 He+K+K-. It takes advantage of the high quality of the cooled external COSY beam and the existing spectrometer BIG KARL. The setup consists of a vertex wall and a scintillator cylinder and endcap covering a 4π solid angle. The large efficiency and high resolution of this detection method will yield precision data on the low energy (T<50 MeV) meson-meson interaction and probe into questions like the ABC-effect and KḲ molecule. The detector further allows a measurement of possible radiative φ (1020) decay, which will directly probe the strange quark content of the f0(975). Existing inclusive data as well as first results of a very recent `semi-exclusive' experiment performed at SATURNE will be also be presented.

  3. NACRE: A European Compilation of Reaction Rates for Astrophysics

    SciTech Connect

    Carmen Angulo

    1999-12-31

    We report on the program and results of the NACRE network (Nuclear Astrophysics Compilation of Reaction rates). We have compiled low-energy cross section data for 86 charged-particle induced reactions involving light (1 {<=} Z {<=} 14) nuclei. The corresponding Maxwellian-averaged thermonuclear reactions rates are calculated in the temperature range from 10{sup 6} K to 10{sup 10} K. The web site, http://pntpm.ulb.ac.be/nacre.htm, including the cross section data base and the reaction rates, allows users to browse electronically all the information on the reactions studied in this compilation.

  4. NACRE: A European Compilation of Reaction rates for Astrophysics

    SciTech Connect

    Angulo, Carmen

    1999-11-16

    We report on the program and results of the NACRE network (Nuclear Astrophysics Compilation of REaction rates). We have compiled low-energy cross section data for 86 charged-particle induced reactions involving light (1{<=}Z{<=}14) nuclei. The corresponding Maxwellian-averaged thermonuclear reactions rates are calculated in the temperature range from 10{sup 6} K to 10{sup 10} K. The web site http://pntpm.ulb.ac.be/nacre.htm, including the cross section data base and the reaction rates, allows users to browse electronically all the information on the reactions studied in this compilation.

  5. Deep Sub-Barrier Fusion Enhancement in the {sup 6}He+{sup 206}Pb Reaction

    SciTech Connect

    Penionzhkevich, Yu.E.; Zagrebaev, V.I.; Lukyanov, S.M.; Kalpakchieva, R.

    2006-04-28

    The fusion of {sup 6}He with {sup 206}Pb has been studied at energies close to and below the Coulomb barrier. The experiment was carried out at the Dubna Radioactive Ion Beams complex of FLNR, JINR. The {sup 6}He beam intensity was about 5x10{sup 6} pps, the maximum energy being 60.3{+-}0.4 MeV. The yield of the {sup 210}Po isotope, produced in the 2n-evaporation channel, demonstrates an extremely large enhancement of the sub-barrier fusion cross section as compared with the {sup 4}He+{sup 208}Pb reaction. This enhancement is most likely due to the mechanism of 'sequential fusion' with an intermediate neutron transfer from {sup 6}He to the Pb nucleus with positive Q values.

  6. Universal damping mechanism of quantum vibrations in deep sub-barrier fusion reactions

    NASA Astrophysics Data System (ADS)

    Ichikawa, Takatoshi; Matsuyanagi, Kenichi

    2015-08-01

    We demonstrate the damping of quantum octupole vibrations near the touching point when two colliding nuclei approach each other in the mass-asymmetric 16 O + 208 Pb system, for which the strong fusion hindrance was clearly observed. We, for the first time, apply the random-phase approximation method to the heavy-mass asymmetric dinuclear system to calculate the transition strength B (E 3 ) as a function of the center-of-mass distance. The obtained B (E 3 ) strengths are substantially damped near the touching point, because the single-particle wave functions of the two nuclei strongly mix with each other and a neck is formed. The energy-weighted sums of B (E 3 ) are also strongly correlated with the damping factor, which is phenomenologically introduced in the standard coupled-channel calculations to reproduce the fusion hindrance. This strongly indicates that the damping of the quantum vibrations universally occurs in the deep sub-barrier fusion reactions.

  7. Ankle arthrodesis fusion rates for mesenchymal stem cell bone allograft versus proximal tibia autograft.

    PubMed

    Anderson, John J; Boone, Joshua J; Hansen, Myron; Brady, Chad; Gough, Adam; Swayzee, Zflan

    2014-01-01

    Ankle arthrodesis is commonly used in the treatment of ankle arthritis. The present study compared mesenchymal stem cell (MSC) bone allografts and proximal tibia autografts as adjuncts in performing ankle arthrodesis. A total of 109 consecutive ankle fusions performed from 2002 to 2008 were evaluated retrospectively. Of the 109 fusions, 24 were excluded from the present study, leaving 85 patients who had undergone ankle arthrodesis. Of the 85 patients, 41 had received a proximal tibia autograft and 44, an MSC bone allograft. These 2 groups were reviewed and compared retrospectively at least 2 years postoperatively for the overall fusion rate, interval to radiographic fusion, and interval to clinical fusion. A modified and adjusted American College of Foot and Ankle Surgeons ankle scale was used to measure patient satisfaction. The overall fusion rate was 84.1% in the MSC bone allograft group and 95.1% in the proximal tibia autograft group (p = .158). The corresponding mean intervals to radiographic fusion were 13.0 ± 2.5 weeks and 11.3 ± 2.8 weeks (p ≤ .001). The interval to clinical fusion was 13.1 ± 2.1 weeks and 11.0 ± 1.5 weeks (p ≤ .001) in the MSC bone allograft and proximal tibia autograft group, respectively. No statistically significant difference was found in the fusion rates between the MSC bone allograft and proximal tibia autograft groups. Also, no statistically significant difference was found between the preoperative and postoperative scores using a modified and adjusted American College of Foot and Ankle Surgeons ankle scale between the 2 groups (p = .41 and p = .44, respectively). A statistically significant delay to radiographic and clinical fusion was present in the MSC bone allograft group compared with the proximal tibia autograft group; however, no difference was found in patient satisfaction.

  8. Multidimensional reaction rate theory with anisotropic diffusion.

    PubMed

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

    2014-11-28

    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.

  9. Heavy-ion inertial fusion: influence of target gain on accelerator parameters for vacuum-propagation regimes in reaction chambers

    SciTech Connect

    Mark, J.W.K.; Bangerter, R.O.; Barletta, W.A.; Fawley, W.M.; Judd, D.L.

    1982-03-04

    Target physics imposes requirements on the design of inertial fusion drivers. The influence of beam propagation in near vacuum fusion reaction chambers is evaluated for the relation between target gain and the phase-space requirements of heavy-ion accelerators. Initial results suggest that neutralization of the ion beam has a much greater positive effect than the deleterious one of beam stripping provided that the fusion chamber pressure is < 10/sup -3/ torr (of Li vapor or equivalent).

  10. Parameterization of fusion barriers for light-projectiles-induced reactions using the proximity approach

    NASA Astrophysics Data System (ADS)

    Gharaei, R.; Sheibani, J.

    2016-05-01

    In this article we propose a pocket formula for fusion barriers calculated by three versions of the proximity formalism, namely AW 95, Bass 80 and Prox. 2010 potentials, for fusion reactions involving the collisions of the proton and helium projectiles with different targets in mass ranges 51≤ AT ≤ 130 and 40≤ AT ≤ 233 , respectively. For the first type of the colliding systems, it is shown that the proposed pocket formulas are able to predict the actual values of RB and VB within accuracies of ±0.4% and ±0.45% , respectively. Moreover, for the second type of the selected reactions, these accuracies are obtained ±0.24% and ±0.36% , respectively. In this study, the ability of the present pocket formulas is also demonstrated to predict the exact values of the fusion cross sections for our selected mass ranges. A comparison with the results of the previous pocket formulas reveals that our parameterized forms are more successful to reproduce the empirical data of the barrier height and position in the proton- and helium-induced reactions.

  11. Analysis of the energy transport and deposition within the reaction chamber of the prometheus inertial fusion energy reactor

    SciTech Connect

    Eggleston, J.E.; Abdou, M.A.; Tillack, M.S.

    1994-12-31

    One of the parameters affecting the feasibility of Inertial Fusion Energy (IFE) devices is the number of shots per unit time, i.e. the repetition rate. The repetition rate limits the achievable power that can be obtained from the reactor. To obtain an estimate of the allowable time between shots, a code named RECON was developed to model the response of the reaction chamber to the pellet explosion. This paper discusses how the code treats the thermodynamic response of the cavity gas and models the condensation/evaporation of this vapor to and from the first wall. A large amount of energy from the pellet microexplosion is carried by the pellet debris and the x-rays generated in the fusion reaction. Models of x-ray attenuation and ion slowing down are used to estimate the fraction of the pellet energy that is absorbed in the vapor. A large amount of energy is absorbed into the cavity gas, which causes it to become partially ionized. The ionization complicates the calculation of the temperature, pressure, and the radiative heat transfer from the gas to the first wall. To treat this problem, methods developed by Zel`dovich and Raizer are used in modeling the internal energy and the radiative heat flux. RECON was developed to run with a relatively short computational time, yet accurate enough for conceptual reactor design calculations.

  12. Fusion

    NASA Astrophysics Data System (ADS)

    Herman, Robin

    1990-10-01

    The book abounds with fascinating anecdotes about fusion's rocky path: the spurious claim by Argentine dictator Juan Peron in 1951 that his country had built a working fusion reactor, the rush by the United States to drop secrecy and publicize its fusion work as a propaganda offensive after the Russian success with Sputnik; the fortune Penthouse magazine publisher Bob Guccione sank into an unconventional fusion device, the skepticism that met an assertion by two University of Utah chemists in 1989 that they had created "cold fusion" in a bottle. Aimed at a general audience, the book describes the scientific basis of controlled fusion--the fusing of atomic nuclei, under conditions hotter than the sun, to release energy. Using personal recollections of scientists involved, it traces the history of this little-known international race that began during the Cold War in secret laboratories in the United States, Great Britain and the Soviet Union, and evolved into an astonishingly open collaboration between East and West.

  13. Multi-intelligence critical rating assessment of fusion techniques (MiCRAFT)

    NASA Astrophysics Data System (ADS)

    Blasch, Erik

    2015-06-01

    Assessment of multi-intelligence fusion techniques includes credibility of algorithm performance, quality of results against mission needs, and usability in a work-domain context. Situation awareness (SAW) brings together low-level information fusion (tracking and identification), high-level information fusion (threat and scenario-based assessment), and information fusion level 5 user refinement (physical, cognitive, and information tasks). To measure SAW, we discuss the SAGAT (Situational Awareness Global Assessment Technique) technique for a multi-intelligence fusion (MIF) system assessment that focuses on the advantages of MIF against single intelligence sources. Building on the NASA TLX (Task Load Index), SAGAT probes, SART (Situational Awareness Rating Technique) questionnaires, and CDM (Critical Decision Method) decision points; we highlight these tools for use in a Multi-Intelligence Critical Rating Assessment of Fusion Techniques (MiCRAFT). The focus is to measure user refinement of a situation over the information fusion quality of service (QoS) metrics: timeliness, accuracy, confidence, workload (cost), and attention (throughput). A key component of any user analysis includes correlation, association, and summarization of data; so we also seek measures of product quality and QuEST of information. Building a notion of product quality from multi-intelligence tools is typically subjective which needs to be aligned with objective machine metrics.

  14. Imaginary-time formalism for triple-α reaction rates

    NASA Astrophysics Data System (ADS)

    Akahori, T.; Funaki, Y.; Yabana, K.

    2015-08-01

    Using imaginary-time formalism, it is shown that the triple-α 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 a coupled-channel approach.

  15. Non-resonant Triple- α Reaction Rate at Low Temperature

    NASA Astrophysics Data System (ADS)

    Tamii, A.; Aoi, N.; Fujita, H.; Fujita, Y.; Hatanaka, K.; Hashimoto, T.; Kawabata, T.; Miki, K.; Itoh, M.; Itoh, T.; Kamimura, M.; Ogata, K.; Ong, H. J.; Sakaguchi, H.; Shima, T.; Suzuki, T.; Yamamoto, T.

    2013-08-01

    The triple α reaction rate in stars is quite important in many astrophysical scenarios including the stellar evolution and carbon synthesis in stars. Recently the non-resonant triple α reaction rate has been reevaluated using a calculation with the continuum-discretized coupled-channels (CDCC) method, which dramatically increased the rate at low temperature compared to the widely-used NACRE compilation. Since the enhancement influences strongly on astrophysical model simulations, we have planned an experiment for drawing conclusion on the non-resonant triple α reaction rate at low temperature by measuring the three- α continuum state in 12C. We report the present situation of the experiment.

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

    NASA Technical Reports Server (NTRS)

    Rizvi, Farheen

    2013-01-01

    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.

  17. Cross Section Measurements of 12C+16O Fusion Reaction at Stellar Energies

    NASA Astrophysics Data System (ADS)

    Tan, Wanpeng; Fang, X.; Beard, M.; Gilardy, G.; Jung, H.; Liu, Q.; Lyons, S.; Robertson, D.; Setoodehnia, K.; Seymour, C.; Stech, E.; Vande Kolk, B.; Wiescher, M.; de Souza, R.; Hudan, S.; Singh, V.; Tang, X.; Uberseder, E.

    2016-09-01

    12C+16O is one of the three fusion reactions (12C+12C, 12C+16O, and 16O+16O) that play an important role at the late stage of stellar evolution in massive stars. The previous meassurements of its cross section at low energies rely on the singles measurements of either gamma rays or charged particles. New measurement was conducted for the 12C+16O reaction at Ecm = 3.64 - 4.93 MeV with the detection of both gammas and charged particles using the high intensity St ANA accelerator at the University of Notre Dame. The protons and alphas from the fusion evaporation were measured by a large area silicon strip detector array (SAND) while the gamma rays were detected by one large volume HPGe detector right after the target. Statistical model calculation were employed to interpret the experimental results. This provided a more reliable extrapolation for the 12C+16O fusion cross section, reducing substantially the uncertainty for stellar model simulations. This work was supported by the National Science Foundation through Grant Numbers PHY-1068192 and PHY-1419765 and the Joint Institute for Nuclear Astrophysics under Grant No. PHY-0822648.

  18. Refined Calculations of Secondary Nuclear Reactions in Magneto-Inertial Fusion Plasmas

    NASA Astrophysics Data System (ADS)

    Schmit, Paul; Knapp, Patrick; Hansen, Stephanie; Gomez, Matthew; Hahn, Kelly; Sinars, Daniel; Peterson, Kyle; Slutz, Stephen; Sefkow, Adam; Awe, Thomas; Harding, Eric; Jennings, Christopher

    2014-10-01

    Diagnosing the degree of magnetic flux compression at stagnation in magneto-inertial fusion (MIF) is critical for charting the performance of any MIF concept. In pure deuterium plasma, the transport of high-energy tritons produced by the aneutronic DD fusion reaction depends strongly on the magnetic field. The tritons probe and occasionally react with the fuel, emitting secondary DT neutrons. We show that the DT/DD neutron yield ratio and the secondary DT neutron spectra can be used to infer the magnetic field-radius product (BR), the critical confinement parameter for MIF. The amount of fuel-pusher mix also can be constrained by secondary reactions. We discuss the sensitivity to plasma inhomogeneities of the calculations and outline methods to relate secondary yields to alpha particle energy deposition in ignition-relevant experiments employing DT fuel. We compare our calculations to recent tests of the Magnetized Liner Inertial Fusion (MagLIF) concept on the Z Pulsed Power Facility. Supported in part by the SNL Truman Fellowship, which is part of the LDRD Program, and sponsored by Sandia Corporation (a wholly owned subsidiary of Lockheed Martin Corporation) as Operator of SNL under its U.S. DoE Contract No. DE-AC04-94AL85000.

  19. The fusion-fission process in the reaction 34S +186W near the interaction barrier

    NASA Astrophysics Data System (ADS)

    Harca, I. M.; Dmitriev, S.; Itkis, J.; Kozulin, E. M.; Knyazheva, G.; Loktev, T.; Novikov, K.; Azaiez, F.; Gottardo, A.; Matea, I.; Verney, D.; Chubarian, G.; Hanappe, F.; Piot, J.; Schmitt, C.; Trzaska, W. H.; Vardaci, E.

    2015-02-01

    The reaction 34S +186W at Elab=160 MeV was investigated with the aim of diving into the features of the fusion-fission process. Gamma rays in coincidence with binary reaction fragments were measured using the high efficiency gamma-ray spectrometer ORGAM at the TANDEM Accelerator facility of I.P.N., Orsay, and the time-of-flight spectrometer for fission fragments (FF) registration CORSET of the Flerov Laboratory of Nuclear Reactions (FLNR), Dubna. The coupling of the ORGAM and CORSET setups offers the unique opportunity of extracting details for characterizing the fusion-fission process and gives information regarding production of neutron-rich heavy nuclei. The FF-γ coincidence method is of better use then the γ - γ coincidence method when dealing with low statistic measurements and also offers the opportunity to precisely correct the Dopler shift for in-flight emitted gamma rays. Evidence of symmetric and asymmetric fission modes were observed in the mass and TKE distributions, occurring due to shell effects in the fragments. Coincident measurements allow for discrimination between the gamma rays by accepting a specific range within the mass distribution of the reaction products. Details regarding the experimental setup, methods of processing the acquisitioned data and preliminary results are presented.

  20. Rate constant for reaction of atomic hydrogen with germane

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  1. On the Initial Rate of Fluid-Solid Reactions

    NASA Astrophysics Data System (ADS)

    Sohn, Hong Yong; Fan, De-Qiu

    2017-02-01

    It is argued in this paper that the initial rate should not be used for the measurement or analysis the kinetics of a fluid-solid reaction, especially for a reaction in which the effect of pore diffusion starts appearing even moderately as the reaction proceeds. Even in the absence of external mass transfer effects, it is shown in this work by rigorous mathematical analysis that the range of conditions where the initial rate represents the intrinsic kinetics is very narrow. For an initially non-porous solid in the absence of external mass transfer effects, the very initial rate should mathematically be the intrinsic rate even when pore diffusion becomes important as the reaction proceeds. However, even in this case, the range of conditions for this statement is very limited. For the reaction of an initially porous solid, the rate at time zero is already affected by pore diffusion unless its effect is negligible over the entire range of conversion. Furthermore, the initial reaction rates of porous solids reacting under large values of k/D e ratio (chemical reactivity is much greater than the capacity for pore diffusion) have an apparent rate constant of √ {k \\cdot D_{e} } and thus pore diffusion alone does not control the initial rate no matter how large the effect of pore diffusion is overall.

  2. Evidence of complete fusion in the subbarrier {sup 16}O+{sup 238}U reaction

    SciTech Connect

    Nishio, K. Ikezoe, H.; Asai, M.; Tsukada, K.; Mitsuoka, S.; Tsuruta, K.; Satou, K.; Lin, C. J.; Ohsawa, T.

    2006-08-15

    Evaporation residue cross sections in the {sup 16}O+{sup 238}U reaction were measured for the energy range from above-to extreme subbarrier. We used a He-gas-jet system to transport the fusion products, and the {alpha} decay of the evaporation residues was measured by using a rotating wheel system. The measured cross sections for {sup 248,249,250}Fm are reproduced by a statistical model calculation, for which partial cross sections are calculated by a coupled-channel model taking into account the prolate deformation of {sup 238}U. We conclude that complete fusion is the main process in the subbarrier energy region, and quasifission is not an important channel.

  3. Application of proton boron fusion reaction to radiation therapy: A Monte Carlo simulation study

    NASA Astrophysics Data System (ADS)

    Yoon, Do-Kun; Jung, Joo-Young; Suh, Tae Suk

    2014-12-01

    Three alpha particles are emitted from the point of reaction between a proton and boron. The alpha particles are effective in inducing the death of a tumor cell. After boron is accumulated in the tumor region, the emitted from outside the body proton can react with the boron in the tumor region. An increase of the proton's maximum dose level is caused by the boron and only the tumor cell is damaged more critically. In addition, a prompt gamma ray is emitted from the proton boron reaction point. Here, we show that the effectiveness of the proton boron fusion therapy was verified using Monte Carlo simulations. We found that a dramatic increase by more than half of the proton's maximum dose level was induced by the boron in the tumor region. This increase occurred only when the proton's maximum dose point was located within the boron uptake region. In addition, the 719 keV prompt gamma ray peak produced by the proton boron fusion reaction was positively detected. This therapy method features the advantages such as the application of Bragg-peak to the therapy, the accurate targeting of tumor, improved therapy effects, and the monitoring of the therapy region during treatment.

  4. Application of proton boron fusion reaction to radiation therapy: A Monte Carlo simulation study

    SciTech Connect

    Yoon, Do-Kun; Jung, Joo-Young; Suh, Tae Suk

    2014-12-01

    Three alpha particles are emitted from the point of reaction between a proton and boron. The alpha particles are effective in inducing the death of a tumor cell. After boron is accumulated in the tumor region, the emitted from outside the body proton can react with the boron in the tumor region. An increase of the proton's maximum dose level is caused by the boron and only the tumor cell is damaged more critically. In addition, a prompt gamma ray is emitted from the proton boron reaction point. Here, we show that the effectiveness of the proton boron fusion therapy was verified using Monte Carlo simulations. We found that a dramatic increase by more than half of the proton's maximum dose level was induced by the boron in the tumor region. This increase occurred only when the proton's maximum dose point was located within the boron uptake region. In addition, the 719 keV prompt gamma ray peak produced by the proton boron fusion reaction was positively detected. This therapy method features the advantages such as the application of Bragg-peak to the therapy, the accurate targeting of tumor, improved therapy effects, and the monitoring of the therapy region during treatment.

  5. Experimental study of proton rate density in a spherical inertial electrostatic confinement fusion device

    NASA Astrophysics Data System (ADS)

    Gu, Yibin

    The concept of spherical inertial-electrostatic confinement (SIEC) is to focus and accelerate ions and electrons radially inward into the center of a negatively biased, highly transparent spherical grid to create a space-charge double-potential well (a negative-potential well nested inside a positive-potential well) which confines the high-energy ions in the dense central core region such that appreciable nuclear fusion reactions are obtained. This experimental work has focused on creating the double-potential well at high perveance (I/V3/2) where there is a significant charge build-up in the center, and on proving the existence of the well from its characteristic radial proton rate density profile. Based on the spatial measurement of the D-D fusion protons by using a capillary proton collimator and the unfolding of this data, this work has been directed to evaluate the radial proton rate density profiles to explore the evolution of potential-well structure in the current and voltage (perveance) range where the double well is expected. Under the optimized operating conditions admitted by using the Star mode to improve focusing to 1.6× ballistic limit and double-grid setup to reduce the ion radial energy spread to <10%, the experiment has successfully created and, through identification of a distinct two-peak proton rate density profile, demonstrated the existence of the double- potential well. Experimental measurements of the two-peak proton rate density profiles have uniquely shown the emergence of the double potential well for perveances >0.34 mA/kV3/2. As the perveance increases, the feature of the double well becomes prominent. At 1.38 mA/kV3/2 (80 mA and 15 kV), the maximum negative potential well depth obtained from the measured proton rate density was calculated, using a beam-background fusion and charge-exchange model, to be ~22-27% of the applied voltage. Also, during the progress of this dissertation, two valuable SIEC derivatives-an SIEC wavelength

  6. Fission barriers for Po nuclei produced in complete fusion reactions with heavy ions

    SciTech Connect

    Sagaidak, R. N.; Andreyev, A. N.

    2009-05-15

    Evaporation residues and fission excitation functions obtained in complete fusion reactions leading to Po compound nuclei have been analyzed in the framework of the standard statistical model. Macroscopic fission barriers deduced from the cross-section data analysis are compared with the predictions of various theoretical models and available data. A drop in the Po barriers with the decrease in a neutron number was found, which is stronger than predicted by any theory. The presence of entrance channel effects and collective excitations in the compound nucleus decay is considered as a possible reason for the barrier reduction.

  7. Non-resonant triple alpha reaction rate at low temperature

    SciTech Connect

    Itoh, T.; Tamii, A.; Aoi, N.; Fujita, H.; Hashimoto, T.; Miki, K.; Ogata, K.; Carter, J.; Donaldson, L.; Sideras-Haddad, E.; Furuno, T.; Kawabata, T.; Kamimura, M.; Nemulodi, F.; Neveling, R.; Smit, F. D.; Swarts, C.

    2014-05-02

    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.

  8. Analysis of reaction schemes using maximum rates of constituent steps

    PubMed Central

    Motagamwala, Ali Hussain; Dumesic, James A.

    2016-01-01

    We show that the steady-state kinetics of a chemical reaction can be analyzed analytically in terms of proposed reaction schemes composed of series of steps with stoichiometric numbers equal to unity by calculating the maximum rates of the constituent steps, rmax,i, assuming that all of the remaining steps are quasi-equilibrated. Analytical expressions can be derived in terms of rmax,i to calculate degrees of rate control for each step to determine the extent to which each step controls the rate of the overall stoichiometric reaction. The values of rmax,i can be used to predict the rate of the overall stoichiometric reaction, making it possible to estimate the observed reaction kinetics. This approach can be used for catalytic reactions to identify transition states and adsorbed species that are important in controlling catalyst performance, such that detailed calculations using electronic structure calculations (e.g., density functional theory) can be carried out for these species, whereas more approximate methods (e.g., scaling relations) are used for the remaining species. This approach to assess the feasibility of proposed reaction schemes is exact for reaction schemes where the stoichiometric coefficients of the constituent steps are equal to unity and the most abundant adsorbed species are in quasi-equilibrium with the gas phase and can be used in an approximate manner to probe the performance of more general reaction schemes, followed by more detailed analyses using full microkinetic models to determine the surface coverages by adsorbed species and the degrees of rate control of the elementary steps. PMID:27162366

  9. Analysis of reaction schemes using maximum rates of constituent steps.

    PubMed

    Motagamwala, Ali Hussain; Dumesic, James A

    2016-05-24

    We show that the steady-state kinetics of a chemical reaction can be analyzed analytically in terms of proposed reaction schemes composed of series of steps with stoichiometric numbers equal to unity by calculating the maximum rates of the constituent steps, rmax,i, assuming that all of the remaining steps are quasi-equilibrated. Analytical expressions can be derived in terms of rmax,i to calculate degrees of rate control for each step to determine the extent to which each step controls the rate of the overall stoichiometric reaction. The values of rmax,i can be used to predict the rate of the overall stoichiometric reaction, making it possible to estimate the observed reaction kinetics. This approach can be used for catalytic reactions to identify transition states and adsorbed species that are important in controlling catalyst performance, such that detailed calculations using electronic structure calculations (e.g., density functional theory) can be carried out for these species, whereas more approximate methods (e.g., scaling relations) are used for the remaining species. This approach to assess the feasibility of proposed reaction schemes is exact for reaction schemes where the stoichiometric coefficients of the constituent steps are equal to unity and the most abundant adsorbed species are in quasi-equilibrium with the gas phase and can be used in an approximate manner to probe the performance of more general reaction schemes, followed by more detailed analyses using full microkinetic models to determine the surface coverages by adsorbed species and the degrees of rate control of the elementary steps.

  10. Analysis of reaction schemes using maximum rates of constituent steps

    NASA Astrophysics Data System (ADS)

    Hussain Motagamwala, Ali; Dumesic, James A.

    2016-05-01

    We show that the steady-state kinetics of a chemical reaction can be analyzed analytically in terms of proposed reaction schemes composed of series of steps with stoichiometric numbers equal to unity by calculating the maximum rates of the constituent steps, rmax,i, assuming that all of the remaining steps are quasi-equilibrated. Analytical expressions can be derived in terms of rmax,i to calculate degrees of rate control for each step to determine the extent to which each step controls the rate of the overall stoichiometric reaction. The values of rmax,i can be used to predict the rate of the overall stoichiometric reaction, making it possible to estimate the observed reaction kinetics. This approach can be used for catalytic reactions to identify transition states and adsorbed species that are important in controlling catalyst performance, such that detailed calculations using electronic structure calculations (e.g., density functional theory) can be carried out for these species, whereas more approximate methods (e.g., scaling relations) are used for the remaining species. This approach to assess the feasibility of proposed reaction schemes is exact for reaction schemes where the stoichiometric coefficients of the constituent steps are equal to unity and the most abundant adsorbed species are in quasi-equilibrium with the gas phase and can be used in an approximate manner to probe the performance of more general reaction schemes, followed by more detailed analyses using full microkinetic models to determine the surface coverages by adsorbed species and the degrees of rate control of the elementary steps.

  11. Product PCNPsurv or the "reduced" evaporation residue cross section σER/σfusion for "hot" fusion reactions studied with the dynamical cluster-decay model

    NASA Astrophysics Data System (ADS)

    Chopra, Sahila; Kaur, Arshdeep; Hemdeep, Gupta, Raj K.

    2016-04-01

    The product PCNPsurv of compound nucleus (CN) fusion probability PCN and survival probability Psurv is calculated to determine the reduced evaporation residue cross section σER/σfusion , denoted σERreduced, with (total) fusion cross section σfusion given as a sum of CN-formation cross section σCN and non-CN cross section σnCN for each reaction, where σCN is the sum of evaporation residue cross section σER and fusion-fission cross section σff and σnCN, if not measured, is estimated empirically as the difference between measured and calculated σfusion. Our calculations of PCN and Psurv, based on the dynamical cluster-decay model, were successfully made for some 17 "hot" fusion reactions, forming different CN of mass numbers ACN˜100 -300 , with deformations of nuclei up to hexadecapole deformations and "compact" orientations for both coplanar (Φc=0∘ ) and noncoplanar (Φc≠0∘ ) configurations, using various different nuclear interaction potentials. Interesting variations of σERreduced with CN excitation energy E*, fissility parameter χ , CN mass ACN, and Coulomb parameter Z1Z2 show that, independent of entrance channel, different isotopes of CN, and nuclear interaction potentials used, the dominant quantity in the product is Psurv, which classifies all the studied CN into three groups of weakly fissioning, radioactive, and strongly fissioning superheavy nuclei, with relative magnitudes of σERreduced˜1 , ˜10-6 , and ˜10-11 , which, like for PCN, get further grouped in two dependencies of (i) weakly fissioning and strongly fissioning superheavy nuclei decreasing with increasing E* and (ii) radioactive nuclei increasing with increasing E*.

  12. Advanced scheme for high-yield laser driven proton-boron fusion reaction

    NASA Astrophysics Data System (ADS)

    Margarone, D.; Picciotto, A.; Velyhan, A.; Krasa, J.; Kucharik, M.; Morrissey, M.; Mangione, A.; Szydlowsky, A.; Malinowska, A.; Bertuccio, G.; Shi, Y.; Crivellari, M.; Ullschmied, J.; Bellutti, P.; Korn, G.

    2015-02-01

    A low contrast nanosecond laser pulse with relatively low intensity (3 × 1016 W cm-2) was used to enhance the yield of induced nuclear reactions in advanced solid targets. In particular the "ultraclean" proton-boron fusion reaction, producing energetic alpha-particles without neutron generation, was chosen. A spatially well-defined layer of boron dopants in a hydrogen-enriched silicon substrate was used as target. The combination of the specific target geometry and the laser pulse temporal shape allowed enhancing the yield of alpha-particles up to 109 per steradian, i.e 100 times higher than previous experimental achievements. Moreover the alpha particle stream presented a clearly peaked angular and energy distribution, which make this secondary source attractive for potential applications. This result can be ascribed to the interaction of the long laser pre-pulse with the target and to the optimal target geometry and composition.

  13. Role of angular momentum in the production of complex fragments in fusion and quasifission reactions

    SciTech Connect

    Kalandarov, Sh. A.; Adamian, G. G.; Antonenko, N. V.; Scheid, W.

    2011-05-15

    The influence of angular momentum on the competition between complete fusion followed by the decay of compound nucleus and quasifission channels is treated within the dinuclear system model. The charge distributions of the products in the reactions {sup 28}Si+{sup 96}Zr, {sup 4}He+{sup 130}Te, and {sup 40}Ca+{sup 82}Kr are predicted at bombarding energies above the Coulomb barrier. The results of calculations for the reactions {sup 93}Nb+{sup 9}Be,{sup 12}C,{sup 27}Al; {sup 84}Kr+{sup 27}Al; {sup 86}Kr+{sup 63}Cu; {sup 139}La+{sup 12}C,{sup 27}Al; and {sup 45}Sc+{sup 65}Cu are compared with the available experimental data.

  14. Reaction rate of beryllium with fluorine ion for Flibe redox control

    NASA Astrophysics Data System (ADS)

    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

    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.

  15. An accurate analytic representation of the temperature dependence of nonresonant nuclear reaction rate coefficients

    NASA Astrophysics Data System (ADS)

    Shizgal, Bernie D.

    2016-12-01

    There has been intense interest for several decades by different research groups to accurately model the temperature dependence of a large number of nuclear reaction rate coefficients for both light and heavy nuclides. The rate coefficient, k(T) , is given by the Maxwellian average of the reactive cross section expressed in terms of the astrophysical factor, S(E) , which for nonresonant reactions is generally written as a power series in the relative energy E. A computationally efficient algorithm for the temperature dependence of nuclear reaction rate coefficients is required for fusion reactor research and for models of nucleosynthesis and stellar evolution. In this paper, an accurate analytical expression for the temperature dependence of nuclear reaction rate coefficients is provided in terms of τ = 3(b / 2) 2/3 or equivalently, T - 1/3 , where b = B /√{kB T }, B is the Gamow factor and kB is the Boltzmann constant. The methodology is appropriate for all nonresonant nuclear reactions for which S(E) can be represented as a power series in E. The explicit expression for the rate coefficient versus temperature is derived with the asymptotic expansions of the moments of w(E) = exp(- E /kB T - B /√{ E }) in terms of τ. The zeroth order moment is the familiar Gaussian approximation to the rate coefficient. Results are reported for the representative reactions D(d, p)T, D(d, n)3He and 7Li(p, α) α and compared with several different fitting procedures reported in the literature.

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

    NASA Technical Reports Server (NTRS)

    Liechty, Derek S.; Lewis, Mark J.

    2010-01-01

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

  17. Complete and incomplete fusion dynamics of 6,7Li + 159Tb reactions near the Coulomb barrier

    NASA Astrophysics Data System (ADS)

    Gautam, Manjeet Singh; Grover, Neha; Sharma, Manoj K.

    2017-01-01

    The complete fusion (CF) and incomplete fusion (ICF) cross-sections are estimated for 6, 7Li + 159Tb reactions using the energy-dependent Woods-Saxon potential model (EDWSP model) and dynamical cluster-decay model (DCM). The CF data of the 6Li + 159Tb(7Li + 159Tb) reaction at above barrier energies is suppressed with reference to expectations of the EDWSP model by 25% (20%) which is smaller than the reported data by ˜ 9% (6%). This suppression is correlated with the projectile breakup effect. The projectiles 6,7Li are loosely bound systems, which may break up into charged fragments prior to reaching the fusion barrier and subsequently one of the fragment is captured by the target leading to the suppression of fusion data at above barrier energies. The sum of CF and ICF, which is termed as total fusion cross-section (TF), removes the discrepancies between theoretical predictions and the above barrier complete fusion data and hence is adequately explained via the EDWSP model over a wide range of energy spread across the Coulomb barrier. In addition to fusion, the decay mechanism of 6Li + 159Tb reaction is studied within the framework of the dynamical cluster-decay model (DCM). The breakup of the projectile (6Li) in the entrance channel indicates the presence of ICF, which is investigated further using the collective clusterization approach of DCM. The present theoretical analysis suggests that a larger barrier modification is needed to address the fusion data of chosen reactions in the below barrier energy region.

  18. Increased D-D Fusion Reaction Boosted by Electron Screening at the Inner Shell of Metal Atoms

    NASA Astrophysics Data System (ADS)

    Luo, Nie; Miley, George

    2004-10-01

    Recent experiments indicate an abnormally high electron screening effect on the D-D fusion cross-section during low energy (< 10 keV) bombardment of select deuterated metals [1]. The authors attribute this effect to a contribution from core electrons ignored in normal screening calculations [2]. This research studies the contribution of the atomic potential distribution on the classical dynamics of keV deuterons in a host metal, taken here as Pd. A standard atomic code is used to obtain the atomic electron charge density and the potential profile in the metal atom. Using these results, the deuterons are found to spend most of their penetration time near the Pd M shell. This effect drastically increases the probability of a rendezvous between two deuterons in a rather confined area roughly 0.1 angstrom from the Pd nucleus. This mechanism, combined with the increased tunneling rate due to screening from the high electron density at M-shell, enhances the low energy D-D fusion cross-section for metal hydrides. Results from these calculations and comparisons with experimental data will be presented. [1] F. Strieder, C. Rolfs, C. Spitaleri, and P.Corvisiero, Naturwissenschaften, 88 (2001) 461. [2] G. H. Miley, H. Hora, N. Luo, ¡°Screening in Low Energy Nuclear Reactions of Importance to Nuclear Astrophysics¡±, APS April Mtg. (2004), Denver, CO.

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    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.

  20. Analysis of complete, incomplete and total fusion data of 9Be +169Tm, 187Re, 209Bi reactions

    NASA Astrophysics Data System (ADS)

    Kharab, Rajesh; Chahal, Rajiv; Kumar, Rajiv

    2016-11-01

    We have analyzed the incomplete fusion (ICF), complete fusion (CF) and total fusion (TF) excitation functions for reactions induced by 9Be on 169Tm, 187Re and 209Bi targets at near barrier energies using Wong’s formula in conjunction with the energy dependent Woods-Saxon potential. A phenomenological selection function is proposed to separate out the contribution of ICF and CF cross-sections in TF cross-section. The variation of relative contribution of ICF and CF in TF with respect to incident beam energy is very well reproduced through this approach.

  1. Recording system and data fusion algorithm for enhancing the estimation of the respiratory rate from photoplethysmogram.

    PubMed

    Cernat, Roxana A; Ciorecan, Silvia I; Ungureanu, Constantin; Arends, Johan; Strungaru, Rodica; Ungureanu, G Mihaela

    2015-01-01

    The respiratory rate is a vital parameter that can provide valuable information about the health condition of a patient. The extraction of respiratory information from photoplethysmographic signal (PPG) was actually encouraged by the reported results, our main goal being to obtain accurate respiratory rate estimation from the PPG signal. We developed a fusion algorithm that identifies the best derived respiratory signals, from which is possible to extract the respiratory rate; based on these, a global respiratory rate is computed using the proposed fusion algorithm. The algorithm is qualitatively tested on real PPG signals recorded by an acquisition system we implemented, using a reflection pulse oximeter sensor. Its performance is also statistically evaluated using benchmark dataset publically available from CapnoBase.Org.

  2. Reaction rates between water and the Karl Fischer reagent.

    PubMed

    Cedergren, A

    1974-04-01

    Reaction rates between water and the Karl Fischer reagent have been determined by potentiometric measurement for various compositions of the Karl Fischer reagent. The study has been made with an iodine complex concentration of 0.3-1.2 mM and sulphur dioxide complex at 0.01-0.5M. The concentration of excess of pyridine had no measurable effect on the rate of the main reaction. The reaction was found to be first-order with respect to iodine complex, to sulphur dioxide complex, and to water. The rate constant was (1.2+/-0.2) x 10(3) 1(2). mole(-2). sec(-1). In an ordinary titration it is therefore essential to keep the sulphur dioxide concentration high for the reaction to go to completion within a reasonable time. The extent of side-reactions was found to be independent of the iodine concentration at low concentrations. The side-reactions increased somewhat with increasing sulphur dioxide pyridine concentrations and decreased to about 60% when the temperature was lowered from 24 degrees to 7 degrees.

  3. Bone Union Rate Following Instrumented Posterolateral Lumbar Fusion: Comparison between Demineralized Bone Matrix versus Hydroxyapatite

    PubMed Central

    Nam, Woo Dong

    2016-01-01

    Study Design Retrospective study. Purpose To compare the union rate of posterolateral lumbar fusion (PLF) using demineralized bone matrix (DBM) versus hydroxyapatite (HA) as bone graft extender. Overview of Literature To our knowledge, there has been no clinical trial to compare the outcomes of DBM versus HA as a graft material for PLF. Methods We analyzed prospectively collected data from consecutive 79 patients who underwent instrumented PLF. Patients who received DBM were assigned to group B (n=38), and patients who received HA were assigned into group C (n=41). The primary study outcome was fusion rate assessed with radiographs. The secondary outcomes included pain intensity using a visual analogue scale, functional outcome using Oswestry disability index score, laboratory tests of inflammatory profiles and infection rate. Results One year postoperatively, bone fusion was achieved in 73% in group B and 58% in group C without significant difference between the groups (p=0.15). There were no differences between the groups with respect to secondary outcomes. Conclusions DBM would provide noninferior outcomes compared to the HA as a fusion material for PLF, and could be a notable alternative. PMID:27994793

  4. Charge-exchange reaction by Reggeon exchange and W{sup +}W{sup −}-fusion

    SciTech Connect

    Schicker, R.

    2015-04-10

    Charge-exchange reactions at high energies are examined. The existing cross section data on the Reggeon induced reaction pp → n + Δ{sup ++} taken at the ZGS and ISR accelerators are extrapolated to the energies of the RHIC and LHC colliders. The interest in the charge-exchange reaction induced by W{sup ±}-fusion is presented, and the corresponding QCD-background is examined.

  5. Do Trunk Muscles Affect the Lumbar Interbody Fusion Rate?: Correlation of Trunk Muscle Cross Sectional Area and Fusion Rates after Posterior Lumbar Interbody Fusion Using Stand-Alone Cage

    PubMed Central

    Choi, Man Kyu; Park, Bong Jin; Park, Chang Kyu; Kim, Sung Min

    2016-01-01

    Objective Although trunk muscles in the lumbar spine preserve spinal stability and motility, little is known about the relationship between trunk muscles and spinal fusion rate. The aim of the present study is to evaluate the correlation between trunk muscles cross sectional area (MCSA) and fusion rate after posterior lumbar interbody fusion (PLIF) using stand-alone cages. Methods A total of 89 adult patients with degenerative lumbar disease who were performed PLIF using stand-alone cages at L4–5 were included in this study. The cross-sectional area of the psoas major (PS), erector spinae (ES), and multifidus (MF) muscles were quantitatively evaluated by preoperative lumbar magnetic resonance imaging at the L3–4, L4–5, and L5–S1 segments, and bone union was evaluated by dynamic lumbar X-rays. Results Of the 89 patients, 68 had bone union and 21 did not. The MCSAs at all segments in both groups were significantly different (p<0.05) for the PS muscle, those at L3–4 and L4–5 segments between groups were significantly different (p=0.048, 0.021) for the ES and MF muscles. In the multivariate analysis, differences in the PS MCSA at the L4–5 and L5–S1 segments remained significant (p=0.048, 0.043 and odds ratio=1.098, 1.169). In comparison analysis between male and female patients, most MCSAs of male patients were larger than female's. Fusion rates of male patients (80.7%) were higher than female's (68.8%), too. Conclusion For PLIF surgery, PS muscle function appears to be an important factor for bone union and preventing back muscle injury is essential for better fusion rate. PMID:27226860

  6. Capture and Fusion-Fission Processes in Heavy Ion Induced Reactions

    NASA Astrophysics Data System (ADS)

    Itkis, M. G.; Beghini, S.; Behera, B. R.; Bogatchev, A. A.; Bouchat, V.; Corradi, L.; Dorvaux, O.; Fioretto, E.; Gadea, A.; Hanappe, F.; Itkis, I. M.; Jandel, M.; Kliman, J.; Knyazheva, G. N.; Kondratiev, N. A.; Kozulin, E. M.; Krupa, L.; Latina, A.; Lyapin, V. G.; Materna, T.; Montagnoli, G.; Oganessian, Yu. Ts.; Pokrovsky, I. V.; Prokhorova, E. V.; Rowley, N.; Rubchenya, V. A.; Rusanov, A. Ya.; Sagaidak, R. N.; Scarlassara, F.; Schmitt, C.; Stefanini, A. M.; Stuttge, L.; Szilner, S.; Trotta, M.; Trzaska, W. H.; Voskresenski, V. M.

    2005-11-01

    Results of the experiments aimed at the study of fission and quasi-fission processes in the reactions 12C+204Pb, 48Ca+144,154Sm, 168Er, 208Pb, 238U, 244Pu, 248Cm; 58Fe+208Pb, 244Pu, 248Cm, and 64Ni+186W, 242Pu are presented. The choice of the above-mentioned reactions was inspired by the experiments on the production of the isotopes 283112, 289114 and 283116 at Dubna using the same reactions. The 58Fe and 64Ni projectiles were chosen since the corresponding projectile-target combinations lead to the synthesis of even heavier elements. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR, Russia), the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL, Italy) and the Accelerator of the Laboratory of University of Jyvaskyla (JYFL, Finland) using the time-of-flight spectrometer of fission fragments CORSET and the neutron multi-detector DEMON. The role of shell effects and the influence of the entrance channel asymmetry and the deformations of colliding nucleus on the mechanism of the fusion-fission and the competitive process of quasi-fission are discussed.

  7. A D-D/D-T fusion reaction based neutron generator system for liver tumor BNCT

    SciTech Connect

    Koivunoro, H.; Lou, T.P.; Leung, K. N.; Reijonen, J.

    2003-04-02

    Boron-neutron capture therapy (BNCT) is an experimental radiation treatment modality used for highly malignant tumor treatments. Prior to irradiation with low energetic neutrons, a 10B compound is located selectively in the tumor cells. The effect of the treatment is based on the high LET radiation released in the {sup 10}B(n,{alpha}){sup 7}Li reaction with thermal neutrons. BNCT has been used experimentally for brain tumor and melanoma treatments. Lately applications of other severe tumor type treatments have been introduced. Results have shown that liver tumors can also be treated by BNCT. At Lawrence Berkeley National Laboratory, various compact neutron generators based on D-D or D-T fusion reactions are being developed. The earlier theoretical studies of the D-D or D-T fusion reaction based neutron generators have shown that the optimal moderator and reflector configuration for brain tumor BNCT can be created. In this work, the applicability of 2.5 MeV neutrons for liver tumor BNCT application was studied. The optimal neutron energy for external liver treatments is not known. Neutron beams of different energies (1eV < E < 100 keV) were simulated and the dose distribution in the liver was calculated with the MCNP simulation code. In order to obtain the optimal neutron energy spectrum with the D-D neutrons, various moderator designs were performed using MCNP simulations. In this article the neutron spectrum and the optimized beam shaping assembly for liver tumor treatments is presented.

  8. Semiclassical Calculation of Reaction Rate Constants for Homolytical Dissociations

    NASA Technical Reports Server (NTRS)

    Cardelino, Beatriz H.

    2002-01-01

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

  9. Reaction rate uncertainties and the {nu}p-process

    SciTech Connect

    Froehlich, C.; Rauscher, T.

    2012-11-12

    Current hydrodynamical simulations of core collapse supernovae find proton-rich early ejecta. At the same time, the models fail to eject neutron-rich matter, thus leaving the origin of the main r-process elements unsolved. However, the proton-rich neutrino-driven winds from supernovae have been identified as a possible production site for light n-capture elements beyond iron (such as Ge, Sr, Y, Zr) through the {nu}p-process. The detailed nucleosynthesis patterns of the {nu}p-process depend on the hydrodynamic conditions and the nuclear reaction rates of key reactions. We investigate the impact of reaction rate uncertainties on the {nu}p-process nucleosynthesis.

  10. Quantum and semiclassical theories of chemical reaction rates

    SciTech Connect

    Miller, W.H. |

    1995-09-01

    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.

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

    PubMed

    Catlow, C Richard A

    2016-08-01

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

  12. Reaction-Based SiC Materials for Joining Silicon Carbide Composites for Fusion Energy

    SciTech Connect

    Lewinsohn, Charles A.; Jones, Russell H.; Singh, M.; Serizawa, H.; Katoh, Y.; Kohyama, A.

    2000-09-01

    The fabrication of large or complex silicon carbide-fiber-reinforced silicon carbide (SiC/SiC) components for fusion energy systems requires a method to assemble smaller components that are limited in size by manufacturing constraints. Previous analysis indicates that silicon carbide should be considered as candidate joint materials. Two methods to obtain SiC joints rely on a reaction between silicon and carbon to produce silicon carbide. This report summarizes preliminary mechanical properties of joints formed by these two methods. The methods appear to provide similar mechanical properties. Both the test methods and materials are preliminary in design and require further optimization. In an effort to determine how the mechanical test data is influenced by the test methodology and specimen size, plans for detailed finite element modeling (FEM) are presented.

  13. Rate of reaction of OH with HNO3

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

    Measurements of the kinetics of the reaction of OH with HNO3, and mechanisms of HNO3 removal from the stratosphere, are reported. Bimolecular rate constants were determined at temperatures between 224 and 366 K by monitoring the concentrations of OH radicals produced by HNO3 photolysis and HNO3 according to their resonance fluorescence and 184.9-nm absorption, respectively. The rate constant measured at 298 K is found to be somewhat faster than previously accepted values, with a negative temperature dependence. Calculations of a one-dimensional transport-kinetic atmospheric model on the basis of the new rate constant indicate reductions in O3 depletion due to chlorofluoromethane release and NOx injection, of magnitudes dependent on the nature of the reaction products.

  14. Reaction rate constant for radiative association of CF+

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    Reaction rate constants and cross sections are computed for the radiative association of carbon cations (C+) and fluorine atoms (F) in their ground states. We consider reactions through the electronic transition 11Π → X1Σ+ and rovibrational transitions on the X1Σ+ and a3Π potentials. Semiclassical and classical methods are used for the direct contribution and Breit-Wigner theory for the resonance contribution. Quantum mechanical perturbation theory is used for comparison. A modified formulation of the classical method applicable to permanent dipoles of unequally charged reactants is implemented. The total rate constant is fitted to the Arrhenius-Kooij formula in five temperature intervals with a relative difference of <3%. The fit parameters will be added to the online database KIDA. For a temperature of 10-250 K, the rate constant is about 10-21 cm3 s-1, rising toward 10-16 cm3 s-1 for a temperature of 30 000 K.

  15. The temperature-dependence of elementary reaction rates: beyond Arrhenius.

    PubMed

    Smith, Ian W M

    2008-04-01

    The rates of chemical reactions and the dependence of their rate constants on temperature are of central importance in chemistry. Advances in the temperature-range and accuracy of kinetic measurements, principally inspired by the need to provide data for models of combustion, atmospheric, and astrophysical chemistry, show up the inadequacy of the venerable Arrhenius equation--at least, over wide ranges of temperature. This critical review will address the question of how to reach an understanding of the factors that control the rates of 'non-Arrhenius' reactions. It makes use of a number of recent kinetic measurements and shows how developments in advanced forms of transition state theory provide satisfactory explanations of complex kinetic behaviour (72 references).

  16. Abundances in Astrophysical Environments: Reaction Network Simulations with Reaction Rates from Many-nucleon Modeling

    NASA Astrophysics Data System (ADS)

    Amason, Charlee; Dreyfuss, Alison; Launey, Kristina; Draayer, Jerry

    2017-01-01

    We use the ab initio (first-principle) symmetry-adapted no-core shell model (SA-NCSM) to calculate reaction rates of significance to type I X-ray burst nucleosynthesis. We consider the 18O(p,γ)19F reaction, which may influence the production of fluorine, as well as the 16O(α,γ)20Ne reaction, which is key to understanding the production of heavier elements in the universe. Results are compared to those obtained in the no-core sympletic shell model (NCSpM) with a schematic interaction. We discuss how these reaction rates affect the relevant elemental abundances. We thank the NSF for supporting this work through the REU Site in Physics & Astronomy (NSF grant #1560212) at Louisiana State University. This work was also supported by the U.S. NSF (OCI-0904874, ACI -1516338) and the U.S. DOE (DE-SC0005248).

  17. Quasifission and fission rates and their lifetimes in asymmetric reactions forming 216Ra within a dinuclear system approach

    NASA Astrophysics Data System (ADS)

    Khanlari, M. Varasteh; Soheyli, S.

    2017-02-01

    Background: The study of evolution of asymmetric dinuclear systems (DNSs) formed in heavy ion collisions is a topic of intense research. The DNS evolution leads to a variety of reaction channels such as deep inelastic, complete fusion, quasifission, fast fission, fusion-fission, and evaporation of particles. The time evolution of the DNS in the quasifission process and the role of relevant parameters are still not fully understood. Purpose: The influence of the entrance channel mass asymmetry on the time evolution of an excited and rotating DNS, populated via four reactions with different entrance channel mass asymmetry parameters which all lead to the compound nucleus 216Ra, is explored. Method: The driving potential, emission barriers for the binary decay (namely the quasifission and intrinsic fusion barriers), rate of the quasifission channel, and the lifetime of an excited DNS, as well as the fission rate and fission lifetime of the compound nucleus 216Ra formed in the 12C+204Pb,19F+197Au,30Si+186W , and 48Ca+168Er reactions, are calculated by the dinuclear system approach. Results: Our results show that the intrinsic fusion barrier values are equal to zero for the 12C+204Pb and 19F+197Au reactions. Therefore, the quasifission signature is extremely hindered for these reactions, while the 30Si+186W and 48Ca+168Er calculated results contain quasifission contributions. Provided the quasifission rate is nonzero, the quasifission rate increases with increasing orbital angular momentum ℓ of the composite system for a given excitation energy ECN * of the compound nucleus. On the other hand, the quasifission lifetime decreases moderately with increasing ℓ . Furthermore, both quasifission and fission rates increase with increasing excitation energy ECN *, while the quasifission and fission lifetimes decrease with increasing ECN * for a given ℓ . Conclusions: Although these reactions with different entrance channels populate the same compound nucleus 216Ra at

  18. Scaling of geochemical reaction rates via advective solute transport

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    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.

  19. Code System to Calculate Integral Parameters with Reaction Rates from WIMS Output.

    SciTech Connect

    LESZCZYNSKI, FRANCISCO

    1994-10-25

    Version 00 REACTION calculates different integral parameters related to neutron reactions on reactor lattices, from reaction rates calculated with WIMSD4 code, and comparisons with experimental values.

  20. STELLAR EVOLUTION CONSTRAINTS ON THE TRIPLE-{alpha} REACTION RATE

    SciTech Connect

    Suda, Takuma; Fujimoto, Masayuki Y.; Hirschi, Raphael

    2011-11-01

    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 sun} {<=} 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 {approx}> 10 M{sub sun}) is minimal. We find that employing the revised rate suppresses helium shell flashes on asymptotic giant branch phase for stars in the initial mass range 0.8 {<=} M/M{sub sun} {<=} 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. 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 red giant branch tip luminosity even if all the reaction rates related to CNO cycles are enhanced by more than 10 orders of magnitude.

  1. Temperature Dependence of the Rate Constants of Charge Recombination Reactions in Bacterial Reaction Centers

    NASA Astrophysics Data System (ADS)

    Thuy, T. T.; Yen, V. T. H.; Thao, T. T.; Viet, Nguyen Ai

    The bacterial reaction center couples light-induced electron transfer via a tightly bound ubiquinone (QA) to a mobile ubiquinone (QB). Based on the electron transfer theory by Marcus, we have investigated the rate of charge recombination reactions from Rhodopseudomonas viridis and Rhodobacter sphaeroides, by mean of finding an approximation formula. The results obtained are verified for not only at high and low temperature as the previous works but also at the medium temperature range.

  2. Particle emission in the light heavy-ion fusion reactions: 14N, 16,18O+ 12C

    NASA Astrophysics Data System (ADS)

    Carlin Filho, N.; Coimbra, M. M.; Acquadro, J. C.; Liguori Neto, R.; Szanto, E. M.; Farrelly-Pessoa, E.; Szanto de Toledo, A.

    1985-01-01

    From the energy spectra of light particles produced in light-heavy-ion-induced reactions, level densities of the final nuclei as well as the critical angular momenta for fusion may be obtained. The 14N, 16,18O+ 12C reactions were investigated in the energy range 30 MeVfusion critical angular momentum (Jcr), offering an alternative method for the total fusion cross-section determination.

  3. Indirect Study of the 16O+16O Fusion Reaction Toward Stellar Energies by the Trojan Horse Method

    NASA Astrophysics Data System (ADS)

    Hayakawa, S.; Spitaleri, C.; Burtebayev, N.; Aimaganbetov, A.; Figuera, P.; Fisichella, M.; Guardo, G. L.; Igamov, S.; Indelicato, I.; Kiss, G.; Kliczewski, S.; La Cognata, M.; Lamia, L.; Lattuada, M.; Piasecki, E.; Rapisarda, G. G.; Romano, S.; Sakuta, S. B.; Siudak, R.; Trzcińska, A.; Tumino, A.; Urkinbayev, A.

    2016-05-01

    The 16O+16O fusion reaction is important in terms of the explosive oxygen burning process during late evolution stage of massive stars as well as understanding of the mechanism of low-energy heavy-ion fusion reactions. We aim to determine the excitation function for the most major exit channels, α+28Si and p+31P, toward stellar energies indirectly by the Trojan Horse Method via the 16O(20Ne, α28Si)α and 16O(20Ne, p31P)α three-body reactions. We report preliminary results involving reaction identification, and determination of the momentum distribution of α-16O intercluster motion in the projectile 20Ne nucleus.

  4. Rate of reaction of OH with CS/sub 2/

    SciTech Connect

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

    1980-10-02

    The flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction OH + CS/sub 2/ ..-->.. products (k/sub 1/) over the temperature range 251-363 K. Complicating secondary reactions involving CS/sub 2/ photofragments were eliminated only when the photoflash was filtered by 10 torr cm of CS/sub 2/ and SF/sub 6/ was used as the buffer gas. The rate constant was found to be much slower than previous measurements indicated. Based on our experiments, upper limits for k/sub 1/ (in units of 10/sup -15/ cm/sup 3/ molecule/sup -1/s/sup -1/) are 9.9 at 251 K, 1.5 at 297 K, and 1.6 at 363 K. Our results suggest that the title reaction is unimportant as a source for COS in the atmosphere.

  5. Comparison of DSMC reaction models with QCT reaction rates for nitrogen

    NASA Astrophysics Data System (ADS)

    Wysong, Ingrid J.; Gimelshein, Sergey F.

    2016-11-01

    Four empirical models of chemical reactions extensively used in the direct simulation Monte Carlo method in the past are analyzed via comparison of temperature and vibrational level dependent equilibrium and non-equilibrium reaction rates with available classical trajectory and direct molecular simulations for nitrogen dissociation. The considered models are total collision energy, quantum kinetic, vibration-dissociation favoring, and weak vibrational bias. The weak vibrational bias model was found to provide good agreement with benchmark vibrationally-specific dissociation rates, while significant differences were observed for the others.

  6. Fusion hindrance and quasi-fission in heavy-ion induced reactions: disentangling the effect of different parameters

    SciTech Connect

    Fioretto, E.; Stefanini, A. M.; Behera, B. R.; Corradi, L.; Gadea, A.; Latina, A.; Trotta, M.; Beghini, S.; Montagnoli, G.; Scarlassara, F.; Chizhov, A. Yu.; Itkis, I. M.; Itkis, M. G.; Kniajeva, G. N.; Kondratiev, N. A.; Kozulin, E. M.; Pokrovsky, I. V.; Sagaidak, R. N.; Voskressensky, V. M.; Courtin, S.

    2006-04-26

    Experimental results on the fusion inhibition effect near the Coulomb barrier due to the onset of the quasi-fission mechanism are presented. The investigation was focused on reactions induced by 48Ca projectiles on different heavy targets and comparing them to reactions induced by light ions such as 12C and 16O leading to the same compound nuclei. Cross sections and angular distributions of evaporation residues and fission fragments have been measured.

  7. Measurement of the dmud quartet-to-doublet molecular formation rate ratio (lambdaq : lambdad) and the mu d hyperfine rate (lambdaqd) using the fusion neutrons from mu- stops in D2 gas

    NASA Astrophysics Data System (ADS)

    Raha, Nandita

    The MuSun experiment will determine the microd capture rate (micro - + d → n + n + nue) from the doublet hyperfine state Lambdad, of the muonic deuterium atom in the 1S ground state to a precision of 1.5%. Modern effective field theories (EFT) predict that an accurate measurement of Lambdad would determine the two-nucleon weak axial current. This will help in understanding all weak nuclear interactions such as the stellar thermonuclear proton-proton fusion reactions, the neutrino reaction nu + d (which explores the solar neutrino oscillation problem). It will also help us understand weak nuclear interactions involving more than two nucleons---double beta decay---as they do involve a two-nucleon weak axial current term. The experiment took place in the piE3 beam-line of Paul Scherrer Institute (PSI) using a muon beam generated from 2.2 mA proton beam---which is the highest intensity beam in the world. The muons first passed through entrance scintillator and multiwire proportional chamber for determining thier entrance timing and position respectively. Then they were stopped in a cryogenic time projection chamber (cryo-TPC) filled with D2 gas. This was surrounded by plastic scintillators and multiwire proportional chambers for detecting the decay electrons and an array of eight liquid scintillators for detecting neutrons. Muons in deuterium get captured to form microd atoms in the quartet and doublet spin states. These atoms undergo nuclear capture from these hyperfine states respectively. There is a hyperfine transition rate from quartet-to-doublet state---lambdaqd along with dmicrod molecular formation which further undergoes a fusion reaction with the muon acting as a catalyst (MCF). The goal of this dissertation is to measure the dmicro d quartet-to-doublet rate ratio (lambdaq : lambdad) and microd hyperfine rate (lambda qd) using the fusion neutrons from micro. stops in D2 gas. The dmicrod molecules undergo MCF reactions from the doublet and the quartet state

  8. Characterization of Discontinuous Coarsening Reaction Products in INCONEL® Alloy 740H® Fusion Welds

    NASA Astrophysics Data System (ADS)

    Bechetti, Daniel H.; Dupont, John N.; Watanabe, Masashi; de Barbadillo, John J.

    2017-04-01

    Characterization of γ' coarsened zones (CZs) in alloy 740H fusion welds via a variety of electron microscopy techniques was conducted. The effects of solute partitioning during nonequilibrium solidification on the amount of strengthening precipitates along the grain boundaries were evaluated via electron-probe microanalysis and scanning electron microscopy. Electron backscatter diffraction was used to present evidence for the preferential growth of CZs toward regions of lower γ' content, even if growth in that direction increases grain boundary area. Scanning electron microscopy and image analysis were used to quantify the propensity for CZs to develop along certain segments of the grain boundaries, as governed by the local variations in γ' content. Scanning transmission electron microscopy with X-ray energy-dispersive spectrometry (XEDS) was used to assess the compositions of the matrix and precipitate phases within the CZs and to quantify the segregation of alloying components to the reaction front. Thermodynamic and kinetic modeling were used to compare calculated and experimental compositions. The work presented here provides new insight into the progression of the discontinuous coarsening (DC) reaction in a complex engineering alloy.

  9. Characterization of Discontinuous Coarsening Reaction Products in INCONEL® Alloy 740H® Fusion Welds

    NASA Astrophysics Data System (ADS)

    Bechetti, Daniel H.; Dupont, John N.; Watanabe, Masashi; de Barbadillo, John J.

    2017-02-01

    Characterization of γ' coarsened zones (CZs) in alloy 740H fusion welds via a variety of electron microscopy techniques was conducted. The effects of solute partitioning during nonequilibrium solidification on the amount of strengthening precipitates along the grain boundaries were evaluated via electron-probe microanalysis and scanning electron microscopy. Electron backscatter diffraction was used to present evidence for the preferential growth of CZs toward regions of lower γ' content, even if growth in that direction increases grain boundary area. Scanning electron microscopy and image analysis were used to quantify the propensity for CZs to develop along certain segments of the grain boundaries, as governed by the local variations in γ' content. Scanning transmission electron microscopy with X-ray energy-dispersive spectrometry (XEDS) was used to assess the compositions of the matrix and precipitate phases within the CZs and to quantify the segregation of alloying components to the reaction front. Thermodynamic and kinetic modeling were used to compare calculated and experimental compositions. The work presented here provides new insight into the progression of the discontinuous coarsening (DC) reaction in a complex engineering alloy.

  10. Importance of lifetime effects in breakup and suppression of complete fusion in reactions of weakly bound nuclei

    NASA Astrophysics Data System (ADS)

    Cook, K. J.; Simpson, E. C.; Luong, D. H.; Kalkal, Sunil; Dasgupta, M.; Hinde, D. J.

    2016-06-01

    Background: Complete fusion cross sections in collisions of light weakly bound nuclei and high-Z targets show suppression of complete fusion at above-barrier energies. This has been interpreted as resulting from the breakup of the weakly bound nucleus prior to reaching the fusion barrier, reducing the probability of complete charge capture. Below-barrier studies of reactions of 9Be have found that the breakup of 8Be formed by neutron stripping dominates over direct breakup and that transfer-triggered breakup may account for the observed suppression of complete fusion. Purpose: This paper investigates how the above conclusions are affected by lifetimes of the resonant states that are populated prior to breakup. If the mean life of a populated resonance (above the breakup threshold) is much longer than the fusion time scale, then its breakup (decay) cannot suppress complete fusion. For short-lived resonances, the situation is more complex. This work explicitly includes the mean life of the short-lived 2+ resonance in 8Be in classical dynamical model calculations to determine its effect on energy and angular correlations of the breakup fragments and on model predictions of suppression of cross sections for complete fusion at above-barrier energies. Method: Previously performed coincidence measurements of breakup fragments produced in reactions of 9Be with 144Sm, 168Er, 186W, 196Pt, 208Pb, and 209Bi at energies below the barrier have been reanalyzed using an improved efficiency determination of the BALiN detector array. Predictions of breakup observables and of complete and incomplete fusion at energies above the fusion barrier are then made using the classical dynamical simulation code platypus, modified to include the effect of lifetimes of resonant states. Results: The agreement of the breakup observables is much improved when lifetime effects are included explicitly. Sensitivity to subzeptosecond lifetime is observed. The predicted suppression of complete fusion

  11. A model for reaction rates in turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Chinitz, W.; Evans, J. S.

    1984-01-01

    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.

  12. Sensor fusion methods for reducing false alarms in heart rate monitoring.

    PubMed

    Borges, Gabriel; Brusamarello, Valner

    2016-12-01

    Automatic patient monitoring is an essential resource in hospitals for good health care management. While alarms caused by abnormal physiological conditions are important for the delivery of fast treatment, they can be also a source of unnecessary noise because of false alarms caused by electromagnetic interference or motion artifacts. One significant source of false alarms is related to heart rate, which is triggered when the heart rhythm of the patient is too fast or too slow. In this work, the fusion of different physiological sensors is explored in order to create a robust heart rate estimation. A set of algorithms using heart rate variability index, Bayesian inference, neural networks, fuzzy logic and majority voting is proposed to fuse the information from the electrocardiogram, arterial blood pressure and photoplethysmogram. Three kinds of information are extracted from each source, namely, heart rate variability, the heart rate difference between sensors and the spectral analysis of low and high noise of each sensor. This information is used as input to the algorithms. Twenty recordings selected from the MIMIC database were used to validate the system. The results showed that neural networks fusion had the best false alarm reduction of 92.5 %, while the Bayesian technique had a reduction of 84.3 %, fuzzy logic 80.6 %, majority voter 72.5 % and the heart rate variability index 67.5 %. Therefore, the proposed algorithms showed good performance and could be useful in bedside monitors.

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

    SciTech Connect

    Suda, Takuma; Hirschi, Raphael; Fujimoto, Masayuki Y.

    2012-11-12

    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.

  14. Reaction Rate Measurements at the National Criticality Experiments Research Center

    NASA Astrophysics Data System (ADS)

    Bredeweg, T. A.; Bounds, J. A.; Brooks, G. H., Jr.; Favorite, J. A.; Goda, J. M.; Hayes, D. K.; Jackman, K. R.; Little, R. C.; Macinnes, M. R.; Myers, W. L.; Oldham, W. J.; Rundberg, R. S.; Sanchez, R. G.; Schake, A. R.; White, M. C.; Wilkerson, C. W., Jr.

    2014-09-01

    With the resumption of regular operations of the Los Alamos Critical Assemblies at the National Criticality Experiments Research Center (NCERC), located at the Nevada National Security Site, we have embarked upon a series of campaigns to restore the capability to perform integral reaction rate and fission product yield measurements using historical radiochemical methods. This talk will present an overview of the current and future experimental plans, including results from our experimental campaigns on the Comet/Zeus and Flattop assemblies.

  15. Fusion-fission and quasifission in the reactions with heavy ions leading to the formation of Hs

    SciTech Connect

    Itkis, I. M.; Itkis, M. G.; Knyazheva, G. N.; Kozulin, E. M.

    2012-10-20

    Mass and energy distributions of binary reaction products obtained in the reactions {sup 22}Ne+{sup 249}Cf,{sup 26}Mg+{sup 248}Cm,{sup 36}S+{sup 238}U and {sup 58}Fe+{sup 208}Pb leading to Hs isotopes have been measured. At energies below the Coulomb barrier the bimodal fission of Hs*, formed in the reaction {sup 26}Mg+{sup 248}Cm, is observed. In the reaction {sup 36}S+{sup 238}U the considerable part of the symmetric fragments arises from the quasifission process. At energies above the Coulomb barrier the symmetric fragments originate mainly from fusion-fission process for both reactions with Mg and S ions. In the case of the {sup 58}Fe+{sup 208}Pb reaction the quasifission process dominates at all measured energies. The pre- and post-scission neutron multiplicities as a function of the fragment mass have been obtained for the reactions studied.

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

    SciTech Connect

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

    1995-04-01

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

  17. Calculations of Excitation Functions of Some Structural Fusion Materials for ( n, t) Reactions up to 50 MeV Energy

    NASA Astrophysics Data System (ADS)

    Tel, E.; Durgu, C.; Aktı, N. N.; Okuducu, Ş.

    2010-06-01

    Fusion serves an inexhaustible energy for humankind. Although there have been significant research and development studies on the inertial and magnetic fusion reactor technology, there is still a long way to go to penetrate commercial fusion reactors to the energy market. Tritium self-sufficiency must be maintained for a commercial power plant. For self-sustaining (D-T) fusion driver tritium breeding ratio should be greater than 1.05. So, the working out the systematics of ( n, t) reaction cross sections is of great importance for the definition of the excitation function character for the given reaction taking place on various nuclei at different energies. In this study, ( n, t) reactions for some structural fusion materials such as 27Al, 51V, 52Cr, 55Mn, and 56Fe have been investigated. The new calculations on the excitation functions of 27Al( n, t)25Mg, 51V( n, t)49Ti, 52Cr( n, t)50V, 55Mn( n, t)53Cr and 56Fe( n, t)54Mn reactions have been carried out up to 50 MeV incident neutron energy. In these calculations, the pre-equilibrium and equilibrium effects have been investigated. The pre-equilibrium calculations involve the new evaluated the geometry dependent hybrid model, hybrid model and the cascade exciton model. Equilibrium effects are calculated according to the Weisskopf-Ewing model. Also in the present work, we have calculated ( n, t) reaction cross-sections by using new evaluated semi-empirical formulas developed by Tel et al. at 14-15 MeV energy. The calculated results are discussed and compared with the experimental data taken from the literature.

  18. Synthesis of superheavy element 120 via {sup 50}Ti+{sup A}Cf hot fusion reactions

    SciTech Connect

    Liu, Z. H.; Bao Jingdong

    2009-11-15

    Synthesis of superheavy element 120 in terms of the {sup 50}Ti+{sup 249-252}Cf fusion-evaporation reactions is evaluated and discussed. It is found that the reactions of {sup 250,251}Cf({sup 50}Ti,3n){sup 297,298}120 and {sup 251,252}Cf({sup 50}Ti,4n){sup 297,298}120 are relatively favorable with the maximum evaporation-residue cross sections of 0.12, 0.09, 0.11, and 0.25 pb, respectively. However, {sup 252}Cf may be difficult to be target because its spontaneous fission will bring about serious background in the experiment. Fusion probabilities for different target-projectile combinations leading to the formation of surperheavy nucleus {sup 302}120 are estimated with the ''fusion-by-diffusion'' model and presented as a function of the Coulomb parameter Z{sub 1}Z{sub 2}/(A{sub 1}{sup 1/3}+A{sub 2}{sup 1/3}). Among the reactions {sup 50}Ti+{sup 252}Cf, {sup 54}Cr+{sup 248}Cm, {sup 58}Fe+{sup 244}Pu, and {sup 64}Ni+{sup 238}U, the reaction {sup 50}Ti+{sup 252}Cf has the largest fusion probability. Synthesis of superheavy element 120 is of essential importance for determining whether the magic proton shell should be at Z=114 or at higher proton numbers Z=120-126. Therefore, the experiment to produce isotopes with Z=120 in the fusion reactions {sup 50}Ti+{sup 250,251}Cf is of great interest.

  19. Influence of laser induced hot electrons on the threshold for shock ignition of fusion reactions

    NASA Astrophysics Data System (ADS)

    Colaïtis, A.; Ribeyre, X.; Le Bel, E.; Duchateau, G.; Nicolaï, Ph.; Tikhonchuk, V.

    2016-07-01

    The effects of Hot Electrons (HEs) generated by the nonlinear Laser-Plasma Interaction (LPI) on the dynamics of Shock Ignition Inertial Confinement Fusion targets are investigated. The coupling between the laser beam, plasma dynamics and hot electron generation and propagation is described with a radiative hydrodynamics code using an inline model based on Paraxial Complex Geometrical Optics [Colaïtis et al., Phys. Rev. E 92, 041101 (2015)]. Two targets are considered: the pure-DT HiPER target and a CH-DT design with baseline spike powers of the order of 200-300 TW. In both cases, accounting for the LPI-generated HEs leads to non-igniting targets when using the baseline spike powers. While HEs are found to increase the ignitor shock pressure, they also preheat the bulk of the imploding shell, notably causing its expansion and contamination of the hotspot with the dense shell material before the time of shock convergence. The associated increase in hotspot mass (i) increases the ignitor shock pressure required to ignite the fusion reactions and (ii) significantly increases the power losses through Bremsstrahlung X-ray radiation, thus rapidly cooling the hotspot. These effects are less prominent for the CH-DT target where the plastic ablator shields the lower energy LPI-HE spectrum. Simulations using higher laser spike powers of 500 TW suggest that the CH-DT capsule marginally ignites, with an ignition window width significantly smaller than without LPI-HEs, and with three quarters of the baseline target yield. The latter effect arises from the relation between the shock launching time and the shell areal density, which becomes relevant in presence of a LPI-HE preheating.

  20. Application of semiclassical methods to reaction rate theory

    SciTech Connect

    Hernandez, Rigoberto

    1993-11-01

    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.

  1. Temperature Dependent Rate Coefficients for the OH + Pinonaldehyde Reaction

    NASA Astrophysics Data System (ADS)

    Davis, M. E.; Talukdar, R.; Notte, G.; Ellison, G. B.; Ravishankara, A. R.; Burkholder, J. B.

    2005-12-01

    The biogenic emission of monoterpenes is an important source of volatile organic compounds (VOCs) to the atmosphere, approximately 10% of the biogenic hydrocarbons emitted yearly. The oxidation of alpha-pinene, the most abundant monoterpene in the atmosphere, by OH leads to the formation of pinonaldehyde (3-acetyl-2,2-dimethyl-cyclobutyl-ethanal) as a major oxidation product formed in yields > 50%. The atmospheric oxidation of pinonaldehyde will impact radical cycling, ozone formation and air quality on a regional scale. Previous laboratory studies of the OH + pinonaldehyde rate coefficient have used relative rate methods and were limited to room temperature. The reported rate coefficients are in poor agreement with values ranging from 4.0 to 9.1 × 10-11 cm#3 molecule-1 s-1. In this study we have measured absolute rate coefficients to resolve these discrepancies and have extended the measurements to include the temperature dependence. The rate coefficient for the gas phase reaction of OH with pinonaldehyde was measured over the temperature range 297 to 374 K and between 55 and 96 Torr under pseudo first order conditions in OH. Laser-induced fluorescence (LIF) was used to monitor the OH radical which was produced by pulsed laser photolysis. The pinonaldehyde concentration was determined in situ using Fourier transform infrared (FTIR) and UV (185 nm) absorption spectroscopy. The rate coefficient for the OH + pinonaldehyde reaction will be presented. Our results will be compared with previous rate coefficient measurements and the discrepancies and the atmospheric implications of these measurements will be discussed.

  2. Possibilities of production of neutron-deficient isotopes of U, Np, Pu, Am, Cm, and Cf in complete fusion reactions

    SciTech Connect

    Adamian, G. G.; Antonenko, N. V.; Zubov, A. S.; Scheid, W.

    2008-10-15

    Within the dinuclear system model we analyze the production of yet unknown neutron-deficient isotopes of U, Np, Pu, Am, Cm, and Cf in various complete fusion reactions. Different deexcitation channels of the excited compound nucleus are treated. The results are obtained without special adjustment to the selected evaporation channel. The fusion probability is an important ingredient of the excitation function. The results are in good agreement with the available experimental data. The alpha decay half-life times in the neutron-deficient actinides are discussed.

  3. A classical approach in simple nuclear fusion reaction {sub 1}H{sup 2}+{sub 1}H{sup 3} using two-dimension granular molecular dynamics model

    SciTech Connect

    Viridi, S.; Kurniadi, R.; Waris, A.; Perkasa, Y. S.

    2012-06-06

    Molecular dynamics in 2-D accompanied by granular model provides an opportunity to investigate binding between nuclei particles and its properties that arises during collision in a fusion reaction. A fully classical approach is used to observe the influence of initial angle of nucleus orientation to the product yielded by the reaction. As an example, a simplest fusion reaction between {sub 1}H{sup 2} and {sub 1}H{sup 3} is observed. Several products of the fusion reaction have been obtained, even the unreported ones, including temporary {sub 2}He{sup 4} nucleus.

  4. Complication rate during multilevel lumbar fusion in patients above 60 years

    PubMed Central

    Mahesh, Bijjawara; Upendra, Bidre; Vijay, S; Kumar, GC Arun; Reddy, Srinivas

    2017-01-01

    Background: Spine surgery in elderly with comorbidities is reported to have higher complication rates and increased cost. However, the surgical outcome is good irrespective of the complications. Hence, it is essential to identify the factors affecting the complication rates in such patients and the measures to reduce them. This retrospective observational study determines the perioperative complications, their incidence and the measures to reduce complications in the elderly with comorbidities, operated by instrumented multilevel lumbar fusion. Materials and Methods: Patients aged 60 years and above with one or more comorbidities operated by multilevel instrumented lumbar fusion in our center between January 2012 and December 2013 were included in the study. Perioperative complications and their incidence were calculated. Age, number of levels fused, operative time, blood loss, and complication rates were correlated with the duration of stay and the incidence of perioperative complications using SPSS software. Measures to reduce complications are determined by these results and by review of literature. Results: Fifty two patients were included in the study (28 females and 24 males) with an average age of 69 years (range 60-84 years). Hypertension was the most common comorbidity followed by diabetes. Spondylolisthesis was the most common indication. Eleven complications were noted with an incidence of 21%. Three were systemic complications which required transfer to Intensive Care Unit. Local complications were incidental durotomy (three), transient root deficits (two), wound infections (one), and persistent radicular pain (two). Operative time and blood loss were significantly higher in patients with complications. Conclusion: Complication rates strongly correlate with the blood loss and operative time. Reducing the operative time and blood loss by intraoperative tranexamic acid, laminectomy using osteotome, simultaneous bilateral exposure and instrumentation and

  5. Attempt to produce the isotopes of element 108 in the fusion reaction {sup 136}Xe+{sup 136}Xe

    SciTech Connect

    Oganessian, Yu. Ts.; Dmitriev, S. N.; Yeremin, A. V.; Aksenov, N. V.; Bozhikov, G. A.; Chepigin, V. I.; Chelnokov, M. L.; Lebedev, V. Ya.; Malyshev, O. N.; Petrushkin, O. V.; Shishkin, S. V.; Svirikhin, A. I.; Tereshatov, E. E.; Vostokin, G. K.

    2009-02-15

    A setup of the experiment on the production of the isotopes with Z=108 in the fusion reaction {sup 136}Xe+{sup 136}Xe and the obtained results are presented. At the excitation energy 0{<=}E{sub x}{<=}30 MeV of the {sup 272}Hs* compound nucleus the upper limit of the cross section for evaporation residues {sigma}{sub (1-3)n}{<=}4 pb has been measured. The experimental results together with the data from asymmetric reactions point to a strong limitation of the Hs compound nucleus formation with increasing Coulomb forces in the entrance channel of the reaction.

  6. Petawatt laser pulses for proton-boron high gain fusion with avalanche reactions excluding problems of nuclear radiation

    NASA Astrophysics Data System (ADS)

    Hora, Heinrich; Lalousis, Paraskevas; Giuffrida, Lorenzo; Margarone, Daniele; Korn, Georg; Eliezer, Shalom; Miley, George H.; Moustaizis, Stavros; Mourou, Gérard

    2015-05-01

    An alternative way may be possible for igniting solid density hydrogen-11B (HB11) fuel. The use of >petawatt-ps laser pulses from the non-thermal ignition based on ultrahigh acceleration of plasma blocks by the nonlinear (ponderomotive) force, has to be combined with the measured ultrahigh magnetic fields in the 10 kilotesla range for cylindrical trapping. The evaluation of measured alpha particles from HB11 reactions arrives at the conclusion that apart from the usual binary nuclear reactions, secondary reactions by an avalanche multiplication may cause the high gains, even much higher than from deuterium tritium fusion. This may be leading to a concept of clean economic power generation.

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

    PubMed

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

    2016-01-28

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

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

    SciTech Connect

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

    2016-01-28

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

  9. Primordial lithium: New reaction rates, new abundances, new constraints

    SciTech Connect

    Kawano, L.; Schramm, D.; Steigman, G.

    1986-12-01

    Newly measured nuclear reaction rates for /sup 3/H(..cap alpha..,..gamma..)/sup 7/Li (higher than previous values) and /sup 7/Li(p,..cap alpha..)/sup 4/He (lower than previous values) are shown to increase the /sup 7/Li yield from big bang nucleosynthesis for lower baryon to photon ratio (eta less than or equal to 4 x 10/sup -10/); the yield for higher eta is not affected. New, independent determinations of Li abundances in extreme Pop II stars are in excellent agreement with the earlier work of the Spites and give continued confidence in the use of /sup 7/Li in big bang baryon density determinations. The new /sup 7/Li constraints imply a lower limit on eta of 2 x 10/sup -10/ and an upper limit of 5 x 10/sup -10/. This lower limit to eta is concordant with that obtained from considerations of D + /sup 3/He. The upper limit is consistent with, but even more restrictive than, the D bound. With the new rates, any observed primordial Li/H ratio below 10/sup -10/ would be inexplicable by the standard big bang nucleosynthesis. A review is made of the strengths and possible weaknesses of utilizing conclusions drawn from big bang lithium considerations. An appendix discusses the null effect of a factor of 32 increase in the experimental rate for the D(d,..gamma..)/sup 4/He reaction. 28 refs., 1 fig.

  10. Constraining the equation of state of nuclear matter from fusion hindrance in reactions leading to the production of superheavy elements

    NASA Astrophysics Data System (ADS)

    Veselsky, M.; Klimo, J.; Ma, Yu-Gang; Souliotis, G. A.

    2016-12-01

    The mechanism of fusion hindrance, an effect preventing the synthesis of superheavy elements in the reactions of cold and hot fusion, is investigated using the Boltzmann-Uehling-Uhlenbeck equation, where Coulomb interaction is introduced. A strong sensitivity is observed both to the modulus of incompressibility of symmetric nuclear matter, controlling the competition of surface tension and Coulomb repulsion, and to the stiffness of the density-dependence of symmetry energy, influencing the formation of the neck prior to scission. The experimental fusion probabilities were for the first time used to derive constraints on the nuclear equation of state. A strict constraint on the modulus of incompressibility of nuclear matter K0=240 -260 MeV is obtained while the stiff density-dependences of the symmetry energy (γ >1 ) are rejected.

  11. Effects of nuclear orientation on fusion and fission process for reactions using actinide target nuclei

    SciTech Connect

    Nishio, K.; Ikezoe, H.; Mitsuoka, S.; Nishinaka, I.; Makii, H.; Nagame, Y.; Watanabe, Y.; Ohtsuki, T.; Hirose, K.; Hofmann, S.

    2010-04-30

    Fission fragment mass distributions in the reaction of {sup 30}Si+{sup 238}U were measured at the energies around the Coulomb barrier. At the above-barrier energies, the mass distribution showed Gaussian shape. At the sub-barrier energies, triple-humped distribution was observed, which consists of symmetric fission and asymmetric fission peaked at A{sub L}/A{sub H}approx =90/178. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER) cross-sections produced by {sup 30}Si+{sup 238}U. The cross-section for {sup 263}Sg at the above-barrier energy agree with the statistical model calculation which assumes that the measured fission cross-sections are equal to the fusion cross-sections, whereas the one for {sup 264}Sg measured at the sub-barrier energy is smaller than the calculation, indicating the presence for quasifission. We also report the results on the fragment mass distributions for {sup 36,34}S+{sup 238}U and {sup 40}Ar+{sup 238}U.

  12. Tumor Growth Prediction with Reaction-Diffusion and Hyperelastic Biomechanical Model by Physiological Data Fusion

    PubMed Central

    Wong, Ken C. L.; Summers, Ronald M.; Kebebew, Electron; Yao, Jianhua

    2015-01-01

    The goal of tumor growth prediction is to model the tumor growth process, which can be achieved by physiological modeling and model personalization from clinical measurements. Although image-driven frameworks have been proposed with promising results, several issues such as infinitesimal strain assumptions, complicated personalization procedures, and the lack of functional information, may limit their prediction accuracy. In view of these issues, we propose a framework for pancreatic neuroendocrine tumor growth prediction, which comprises a FEM-based tumor growth model with coupled reaction-diffusion equation and nonlinear biomechanics. Physiological data fusion of structural and functional images is used to improve the subject-specificity of model personalization, and a derivative-free global optimization algorithm is adopted to facilitate the complicated model and accommodate flexible choices of objective functions. With this flexibility, we propose an objective function accounting for both the tumor volume difference and the root-mean-squared error of intracellular volume fractions. Experiments were performed on synthetic and clinical data to verify the parameter estimation capability and the prediction performance. Comparisons of using different biomechanical models and objective functions were also performed. From the experimental results of eight patient data sets, the average recall, precision, Dice coefficient, and relative volume difference between predicted and measured tumor volumes were 84.5±6.9%, 85.8±8.2%, 84.6±1.7%, and 14.2±8.4%, respectively. PMID:25962846

  13. On the implementation of a chain nuclear reaction of thermonuclear fusion on the basis of the p+11B process

    NASA Astrophysics Data System (ADS)

    Belyaev, V. S.; Krainov, V. P.; Zagreev, B. V.; Matafonov, A. P.

    2015-07-01

    Various theoretical and experimental schemes for implementing a thermonuclear reactor on the basis of the p+11B reaction are considered. They include beam collisions, fusion in degenerate plasmas, ignition upon plasma acceleration by ponderomotive forces, and the irradiation of a solid-state target from 11B with a proton beam under conditions of a Coulomb explosion of hydrogen microdrops. The possibility of employing ultra-short high-intensity laser pulses to initiate the p+11B reaction under conditions far from thermodynamic equilibrium is discussed. This and some other weakly radioactive thermonuclear reactions are promising owing to their ecological cleanness—there are virtually no neutrons among fusion products. Nuclear reactions that follow the p+11B reaction may generate high-energy protons, sustaining a chain reaction, and this is an advantage of the p+11B option. The approach used also makes it possible to study nuclear reactions under conditions close to those in the early Universe or in the interior of stars.

  14. RPMDRATE: Bimolecular chemical reaction rates from ring polymer molecular dynamics

    NASA Astrophysics Data System (ADS)

    Suleimanov, Yu. V.; Allen, J. W.; Green, W. H.

    2013-03-01

    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 Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH4, OH+CH4 and H+C2H6 reactions. Catalogue identifier: AENW_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AENW_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: MIT license No. of lines in distributed program, including test data, etc.: 94512 No. of bytes in distributed program, including test data, etc.: 1395674 Distribution format: tar.gz Programming language: Fortran 90/95, Python (version 2.6.x or later, including any version of Python 3, is recommended). Computer: Not computer specific. Operating system: Any for which Python, Fortran 90/95 compiler and the required external routines are available. Has the code been vectorized or parallelized?: The program can efficiently utilize 4096+ processors, depending on problem and available computer. At low temperatures, 110 processors are reasonable for a typical umbrella integration run with an analytic potential energy function and gradients on the latest x86-64 machines.

  15. ZGB surface reaction model with high diffusion rates

    NASA Astrophysics Data System (ADS)

    Evans, J. W.

    1993-02-01

    The diffusionless ZGB (monomer-dimer) surface reaction model exhibits a discontinuous transition to a monomer-poisoned state when the fraction of monomer adsorption attempts exceeds 0.525. It has been claimed that this transition shifts to 2/3 with introduction of rapid diffusion of the monomer species, or of both species. We show this is not the case, 2/3 representing the spinodal rather than the transition point. For equal diffusion rates of both species, we find that the transition only shifts to 0.5951±0.0002.

  16. ZGB surface reaction model with high diffusion rates

    SciTech Connect

    Evans, J.W. )

    1993-02-01

    The diffusionless ZGB (monomer--dimer) surface reaction model exhibits a discontinuous transition to a monomer-poisoned state when the fraction of monomer adsorption attempts exceeds 0.525. It has been claimed that this transition shifts to 2/3 with introduction of rapid diffusion of the monomer species, or of both species. We show this is not the case, 2/3 representing the spinodal rather than the transition point. For equal diffusion rates of both species, we find that the transition only shifts to 0.5951[plus minus]0.0002.

  17. Nuclear Fusion Rate Study of a Muonic Molecule via Nuclear Threshold Resonances

    NASA Astrophysics Data System (ADS)

    Faghihi, F.; Eskandari, M. R.

    This work follows our previous calculations of the ground state binding energy, size, and the effective nuclear charge of the muonic T3 molecule, using the Born-Oppenheimer adiabatic approximation. In our past articles, we showed that the system possesses two minimum positions, the first one at the muonic distance and the second at the atomic distance. Also, the symmetric planner vibrational model assumed between the two minima and the approximated potential were calculated. Following from the previous studies, we now calculate the fusion rate of the T3 muonic molecule according to the overlap integral of the resonance nuclear compound nucleus and the molecular wave functions.

  18. Compound nucleus formation probability PCN determined within the dynamical cluster-decay model for various "hot" fusion reactions

    NASA Astrophysics Data System (ADS)

    Kaur, Arshdeep; Chopra, Sahila; Gupta, Raj K.

    2014-08-01

    The compound nucleus (CN) fusion/formation probability PCN is defined and its detailed variations with the CN excitation energy E*, center-of-mass energy Ec .m., fissility parameter χ, CN mass number ACN, and Coulomb interaction parameter Z1Z2 are studied for the first time within the dynamical cluster-decay model (DCM). The model is a nonstatistical description of the decay of a CN to all possible processes. The (total) fusion cross section σfusion is the sum of the CN and noncompound nucleus (nCN) decay cross sections, each calculated as the dynamical fragmentation process. The CN cross section σCN is constituted of evaporation residues and fusion-fission, including intermediate-mass fragments, each calculated for all contributing decay fragments (A1, A2) in terms of their formation and barrier penetration probabilities P0 and P. The nCN cross section σnCN is determined as the quasi-fission (qf) process, where P0=1 and P is calculated for the entrance-channel nuclei. The DCM, with effects of deformations and orientations of nuclei included in it, is used to study the PCN for about a dozen "hot" fusion reactions forming a CN of mass number A ˜100 to superheavy nuclei and for various different nuclear interaction potentials. Interesting results are that PCN=1 for complete fusion, but PCN<1 or PCN≪1 due to the nCN contribution, depending strongly on different parameters of the entrance-channel reaction but found to be independent of the nuclear interaction potentials used.

  19. Possibilities of synthesis of unknown isotopes of superheavy nuclei with charge numbers Z > 108 in asymmetric actinide-based complete fusion reactions

    NASA Astrophysics Data System (ADS)

    Hong, Juhee; Adamian, G. G.; Antonenko, N. V.

    2016-10-01

    The possibilities of production of new isotopes of superheavy nuclei with charge numbers Z = 109-114 in various asymmetric hot fusion reactions are studied for the first time. The excitation functions of the formation of these isotopes in the xn evaporation channels are predicted and the optimal conditions for the synthesis are proposed. The products of the suggested reactions can fill a gap of unknown isotopes between the isotopes of the heaviest nuclei obtained in cold and hot complete fusion reactions.

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

    ERIC Educational Resources Information Center

    Lombardo, Anthony

    1982-01-01

    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)

  1. Investigation of the reaction rates between uranium and liquid aluminum

    SciTech Connect

    Strum, M.J.; Sedillo, E.; Smugeresky, J.

    1995-05-05

    A limited study consisting of scoping experiments was carried out to determine if a uranium-niobium alloy was weakly or strongly resistant to penetration by liquid aluminum alloy 6061. Our investigation was limited to temperatures between 700{degrees}and 900{degrees}C and carried out using small cylindrical coupons of U-6wt.%Nb and unalloyed U in unsaturated molten aluminum and aluminum alloy 6061 baths. The results indicate that indeed, significant dissolution of uranium into molten aluminum occurs and in relatively short times. The diameters of U-6wt.%Nb test cylinders immersed in unsaturated Al-6061 decreased linearly with time at 700{degrees}C, 800{degrees}C, and 900{degrees}C at rates of 1.14 mm/h, 3.0 mm/h, and 3.5 mm/h, respectively. However, we have found that the reaction rates were significantly reduced by the alloying elements niobium and magnesium. These results suggest that a more detailed investigation could lead to a predictive capability for control of these reaction rates. In unalloyed U, the rate of U dissolution increased by up to a factor of ten relative to that in U- 6wt.%Nb. In both materials, the dissolution of the U core was found to occur by advance of a continuous intermetallic layer, which redissolves into the unsaturated liquid Al bath. The Nb additions resulted in the formation of a thick transition layer composed of intermetallic and U-saturated liquid. In unalloyed U, however, the transition layer was largely reduced in thickness, allowing unsaturated liquid adjacent to the continuous intermetallic layer. Another important variable identified was the influence of surface condition on interface reactivity. At 900{degrees}C, liquid attack was completely absent over large regions of U-6wt.% Nb samples immersed in Al-6061. Surface analysis by EDX identified the presence of up to 24 at.% Mg in unattacked areas.

  2. Electron transfer properties and catalytic competence of cytochrome b5 in the fusion protein Hmwb5-EGFP in reactions catalyzed by cytochrome P450 3A4.

    PubMed

    Yantsevich, A V; Gilep, A A; Usanov, S A

    2009-08-01

    In the present paper we describe studies on molecular mechanisms of protein-protein interactions between cytochrome P450 3A4 (CYP3A4) and cytochrome b(5), the latter being incorporated into the artificial recombinant protein Hmwb(5)-EGFP containing full-length cytochrome b(5) (functional module) and a mutant form of the green fluorescent protein EGFP (signal module) fused into a single polypeptide chain. It is shown that cytochrome b(5) within the fusion protein Hmwb(5)-EGFP can be reduced by NADPH-cytochrome P450 reductase in the presence of NADPH, the rate of reduction being dependent on solution ionic strength, indicating that the signal module does not prevent the interaction of the flavo- and hemeproteins. Interaction of cytochrome P450 3A4 and Hmwb(5)-EGFP was estimated based on spin equilibrium shift of cytochrome P450 3A4 to high-spin state in the presence of Hmwb(5)-EGFP, as well as based on steady-state fluorescence anisotropy of the EGFP component of the fusion protein in the presence of CYP3A4. The engineering of chimeric protein Hmwb(5)-EGFP gives an independent method to determine dissociation constant for the complex of cytochrome P450 and cytochrome b(5) that is less sensitive to environmental factors compared to spectrophotometric titration used before. Reconstitution of catalytic activity of cytochrome P450 3A4 in the reaction of testosterone 6beta-hydroxylation in the presence of Hmwb(5)-EGFP indicates that cytochrome b(5) in the fusion protein is able to stimulate the hydroxylation reaction. Using other fusion proteins containing either cytochrome b(5) or its hydrophilic domain to reconstitute catalytic activity of cytochrome P450 3A4 showed that the hydrophobic domain of cytochrome b(5) participates not only in hemeprotein interaction, but also in electron transfer from cytochrome b(5) to cytochrome P450.

  3. Effect of Viscosity on Growth Rates of Interchange Modes in Magnetic Inertial Fusion Plasmas

    NASA Astrophysics Data System (ADS)

    Morse, R. L.; Nachtrieb, R.

    1999-11-01

    Thermal insulating B fields in imploding MIF/MTF confinement systems, as in predecessor static wall confinement systems, must close in the confined plasma and, therefore, have unfavorable curvature for MHD interchange mode stability. Analytic inviscid estimates with typical compressed z-pinch fields Bth=1MG, plasma density n=3.e20 and radius a=1cm give max. m=0 mode growth rates, Gm, of order 1.e8s-1 with wavelengths Lz of .1a to .5a. Thermal conduction to the confining wall increases B there and Gm significantly, as Vekstein discusses in concluding in effect that such confinement would not be useful for fusion. These growth rates and mode forms are confirmed by two supporting compressible models(Freidberg/McCrory). Happily when viscosity(Braginskii) is included; G is reduced, esp. at longer wavelengths, Lz, with scaling Lz**-1, and viscosities of 1e2 to 1e4 poise for the example plasmas give Gm's of order 1.e7s-1 and less with realistic time dependent profiles. We conclude that these Gm's are consistent with significant fusion yields. This work was presented at the UCLA/DoE ICC conference, 3/3-6/97.

  4. Excitation functions for {sup 208-211}Fr produced in the {sup 18}O+{sup 197}Au fusion reaction

    SciTech Connect

    Corradi, L.; Behera, B.R.; Fioretto, E.; Gadea, A.; Latina, A.; Stefanini, A.M.; Szilner, S.; Trotta, M.; Wu, Y.; Beghini, S.; Montagnoli, G.; Scarlassara, F.; Sagaidak, R.N.; Atutov, S.N.; Mai, B.; Stancari, G.; Tomassetti, L.; Mariotti, E.; Khanbekyan, A.; Veronesi, S.

    2005-01-01

    Excitation functions for {sup 208-211}Fr isotopes produced in the {sup 18}O+{sup 197}Au fusion-evaporation reaction have been measured at E{sub lab}=75-130 MeV via characteristic {alpha} decays by means of an electrostatic deflector and a semiconductor detector. Data have been compared with calculations giving barrier-passing (capture) cross sections and probabilities of the compound nucleus decay into different channels according to the standard statistical model.

  5. X-ray ablation rates in inertial confinement fusion capsule materials

    SciTech Connect

    Olson, R. E.; Rochau, G. A.; Leeper, R. J.; Landen, O. L.

    2011-03-15

    X-ray ablation rates have been measured in beryllium, copper-doped beryllium, germanium-doped plastic (Ge-doped CH), and diamondlike high density carbon (HDC) for radiation temperatures T in the range of 160-260 eV. In beryllium, the measured ablation rates range from 3 to 12 mg/cm{sup 2}/ns; in Ge-doped CH, the ablation rates range from 2 to 6 mg/cm{sup 2}/ns; and for HDC, the rates range from 2 to 9 mg/cm{sup 2}/ns. The ablation rates follow an approximate T{sup 3} dependence and, for T below 230 eV, the beryllium ablation rates are significantly higher than HDC and Ge-doped CH. The corresponding implied ablation pressures are in the range of 20-160 Mbar, scaling as T{sup 3.5}. The results are found to be well predicted by computational simulations using the physics packages and computational techniques employed in the design of indirect-drive inertial confinement fusion capsules. An iterative rocket model has been developed and used to compare the ablation rate data set to spherical indirect-drive capsule implosion experiments and to confirm the validity of some aspects of proposed full-scale National Ignition Facility ignition capsule designs.

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

    PubMed

    Liu, Yingdi; Sander, Stanley P

    2015-10-01

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

  7. Manual choice reaction times in the rate-domain.

    PubMed

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

    2014-01-01

    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.

  8. Moderator design studies for a new neutron reference source based on the D-T fusion reaction

    NASA Astrophysics Data System (ADS)

    Mozhayev, Andrey V.; Piper, Roman K.; Rathbone, Bruce A.; McDonald, Joseph C.

    2016-06-01

    The radioactive isotope Californium-252 (252Cf) is relied upon internationally as a neutron calibration source for ionizing radiation dosimetry because of its high specific activity. The source may be placed within a heavy-water (D2O) moderating sphere to produce a softened spectrum representative of neutron fields common to commercial nuclear power plant environments, among others. Due to termination of the U.S. Department of Energy loan/lease program in 2012, the expense of obtaining 252Cf sources has undergone a significant increase, rendering high output sources largely unattainable. On the other hand, the use of neutron generators in research and industry applications has increased dramatically in recent years. Neutron generators based on deuteriumtritium (D-T) fusion reaction provide high neutron fluence rates and, therefore, could possibly be used as a replacement for 252Cf. To be viable, the 14 MeV D-T output spectrum must be significantly moderated to approximate common workplace environments. This paper presents the results of an effort to select appropriate moderating materials and design a configuration to reshape the primary neutron field toward a spectrum approaching that from a nuclear power plant workplace. A series of Monte-Carlo (MCNP) simulations of single layer high- and low-Z materials are used to identify initial candidate moderators. Candidates are refined through a similar series of simulations involving combinations of 2-5 different materials. The simulated energy distribution using these candidate moderators are rated in comparison to a target spectrum. Other properties, such as fluence preservation and/or enhancement, prompt gamma production and other characteristics are also considered.

  9. Moderator design studies for a new neutron reference source based on the D–T fusion reaction

    SciTech Connect

    Mozhayev, Andrey V.; Piper, Roman K.; Rathbone, Bruce A.; McDonald, Joseph C.

    2016-06-01

    The radioactive isotope Californium-252 (252Cf) is relied upon internationally as a neutron calibration source for ionizing radiation dosimetry because of its high specific activity. The source may be placed within a heavy-water (D2O) moderating sphere to produce a softened spectrum representative of neutron fields common to commercial nuclear power plant environments, among others. Due to termination of the U.S. Department of Energy loan/lease program in 2012, the expense of obtaining 252Cf sources has undergone a significant increase, rendering high output sources largely unattainable. On the other hand, the use of neutron generators in research and industry applications has increased dramatically in recent years. Neutron generators based on deuterium-tritium (D-T) fusion reaction provide high neutron fluence rates and, therefore, could possibly be used as a replacement for 252Cf. To be viable, the 14.6 MeV D-T output spectrum must be significantly moderated to approximate common workplace environments. This paper presents the results of an effort to select appropriate moderating materials and design a configuration to reshape the primary neutron field toward a spectrum approaching that from a nuclear power plant workplace. A series of Monte-Carlo (MCNP) simulations of single layer high- and low-Z materials are used to identify initial candidate moderators. Candidates are refined through a similar series of simulations involving combinations of 2 to 5 different materials. The simulated energy distribution using these candidate moderators are rated in comparison to a target spectrum. Other properties, such as fluence preservation and/or enhancement, prompt gamma production and other characteristics are also considered.

  10. Transcriptional dynamics with time-dependent reaction rates

    NASA Astrophysics Data System (ADS)

    Nandi, Shubhendu; Ghosh, Anandamohan

    2015-02-01

    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.

  11. Exploring contributions from incomplete fusion in Li,76+209Bi and Li,76+198Pt reactions

    NASA Astrophysics Data System (ADS)

    Parkar, V. V.; Jha, V.; Kailas, S.

    2016-08-01

    We use the breakup absorption model to simultaneously describe the measured cross sections of complete fusion (CF), incomplete fusion (ICF), and total fusion (TF) in nuclear reactions induced by weakly bound nuclei Li,76 on 209Bi and 198Pt targets. The absorption cross sections are calculated using the continuum discretized coupled channels (CDCC) method with different choices of short-range imaginary potentials to get the ICF, CF, and TF cross sections. It is observed that the cross sections for deuteron ICF / deuteron capture and α ICF / α capture are of similar magnitude, in the case of the 6Li projectile, while the cross sections for the triton ICF / triton capture is more dominant than that of α ICF / α capture in the case of the 7Li projectile. Both these observations are also corroborated by the experimental data. The ratio of ICF to TF cross sections, which defines the value of fusion suppression factor, is found to be in agreement with the data available from the literature. The cross-section ratios of CF/TF and ICF/TF show opposite behavior at below-barrier energies the former decreases while the latter increases as the energy is lowered, which shows the dominance of ICF at below-barrier energies. We have also studied the correlation of the ICF cross sections with the noncapture breakup (NCBU) cross sections as a function of energy, which shows that the NCBU is more significant than ICF at below-barrier energies.

  12. The TDF System for Thermonuclear Plasma Reaction Rates, Mean Energies and Two-Body Final State Particle Spectra

    SciTech Connect

    Warshaw, S I

    2001-07-11

    The rate of thermonuclear reactions in hot plasmas as a function of local plasma temperature determines the way in which thermonuclear ignition and burning proceeds in the plasma. The conventional model approach to calculating these rates is to assume that the reacting nuclei in the plasma are in Maxwellian equilibrium at some well-defined plasma temperature, over which the statistical average of the reaction rate quantity {sigma}v is calculated, where {sigma} is the cross-section for the reaction to proceed at the relative velocity v between the reacting particles. This approach is well-understood and is the basis for much nuclear fusion and astrophysical nuclear reaction rate data. The Thermonuclear Data File (TDF) system developed at the Lawrence Livermore National Laboratory (Warshaw 1991), which is the topic of this report, contains data on the Maxwellian-averaged thermonuclear reaction rates for various light nuclear reactions and the correspondingly Maxwellian-averaged energy spectra of the particles in the final state of those reactions as well. This spectral information closely models the output particle and energy distributions in a burning plasma, and therefore leads to more accurate computational treatments of thermonuclear burn, output particle energy deposition and diagnostics, in various contexts. In this report we review and derive the theoretical basis for calculating Maxwellian-averaged thermonuclear reaction rates, mean particle energies, and output particle spectral energy distributions for these reactions in the TDF system. The treatment of the kinematics is non-relativistic. The current version of the TDF system provides exit particle energy spectrum distributions for two-body final state reactions only. In a future report we will discuss and describe how output particle energy spectra for three- and four-body final states can be developed for the TDF system. We also include in this report a description of the algorithmic implementation of the

  13. The fusion-fission process in the reaction {sup 34}S+{sup 186}W near the interaction barrier

    SciTech Connect

    Harca, I. M.; Dmitriev, S.; Itkis, J.; Kozulin, E. M.; Knyazheva, G.; Loktev, T.; Novikov, K.; Azaiez, F.; Gottardo, A.; Matea, I.; Verney, D.; Hanappe, F.; Piot, J.; Schmitt, C.; Vardaci, E.

    2015-02-24

    The reaction {sup 34}S+{sup 186}W at E{sub lab}=160 MeV was investigated with the aim of diving into the features of the fusion-fission process. Gamma rays in coincidence with binary reaction fragments were measured using the high efficiency gamma-ray spectrometer ORGAM at the TANDEM Accelerator facility of I.P.N., Orsay, and the time-of-flight spectrometer for fission fragments (FF) registration CORSET of the Flerov Laboratory of Nuclear Reactions (FLNR), Dubna. The coupling of the ORGAM and CORSET setups offers the unique opportunity of extracting details for characterizing the fusion-fission process and gives information regarding production of neutron-rich heavy nuclei. The FF–γ coincidence method is of better use then the γ – γ coincidence method when dealing with low statistic measurements and also offers the opportunity to precisely correct the Dopler shift for in-flight emitted gamma rays. Evidence of symmetric and asymmetric fission modes were observed in the mass and TKE distributions, occurring due to shell effects in the fragments. Coincident measurements allow for discrimination between the gamma rays by accepting a specific range within the mass distribution of the reaction products. Details regarding the experimental setup, methods of processing the acquisitioned data and preliminary results are presented.

  14. Reaction rate theory of radiation exposure:Effects of dose rate on mutation frequency

    NASA Astrophysics Data System (ADS)

    Bando, Masako; Nakamura, Issei; Manabe, Yuichiro

    2014-03-01

    We revisit the linear no threshold (LNT) hypothesis deduced from the prominent works done by H. J. Muller for the DNA mutation induced by the artificial radiation and by W. L. Russell and E. M. Kelly for that of mega-mouse experiments, developing a new kinetic reaction theory. While the existing theoretical models primarily rely on the dependence of the total dose D on the mutation frequency, the key ingredient in our theory is the dose rate d(t) that accounts for decrease in the mutation rate during the time course of the cellular reactions. The general form for the mutation frequency with the constant dose rate d is simply expressed as, dFm(t)/dt = A - BFm(t) , with A =a0 +a1(d +deff) and B =b0 +b1(d +deff) . We discuss the solution for a most likely case with B > 0 ; Fm(t) = [A/B -Fm(0) ] (1 -e-Bt) +Fm(0) with the control value Fm(0) . We show that all the data of mega-mouse experiments by Russel with different dose rates fall on the universal scaling function Φ(τ) ≡ [Fm(τ) -Fm(0) ]/[ A / B -Fm(0) ] = 1 - exp(- τ) with scaled time τ = Bt . The concept of such a scaling rule provides us with a strong tool to study different species in a unified manner.

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

    ERIC Educational Resources Information Center

    Copper, Christine L.; Koubeck, Edward

    1999-01-01

    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)

  16. Angular momentum effects and barrier modification in sub-barrier fusion reactions using the proximity potential in the Wong formula

    SciTech Connect

    Kumar, Raj; Bansal, Manie; Arun, Sham K.; Gupta, Raj K.

    2009-09-15

    Using the capture cross-section data from {sup 48}Ca+{sup 238}U, {sup 48}Ca+{sup 244}Pu, and {sup 48}Ca+{sup 248}Cm reactions in the superheavy mass region, and fusion-evaporation cross sections from {sup 58}Ni+{sup 58}Ni, {sup 64}Ni+{sup 64}Ni, and {sup 64}Ni+{sup 100}Mo reactions known for fusion hindrance phenomenon in coupled-channels calculations, the Wong formula is assessed for its angular momentum and barrier-modification effects at sub-barrier energies. The simple, l=0 barrier-based Wong formula is shown to ignore the modifications of the barrier due to its inbuilt l dependence via l summation, which is found to be adequate enough to explain the capture cross sections for all the three above-mentioned {sup 48}Ca-based reactions forming superheavy systems. For the capture (equivalently, quasifission) reactions, the complete l-summed Wong formula is shown to be the same as the dynamical cluster-decay model expression, of one of us (R.K.G.) and collaborators, with the condition of fragment preformation probability P{sub 0}{sup l}=1 for all the angular momentum l values. In the case of fusion-evaporation cross sections, however, a further modification of barriers is required for below-barrier energies, affected in terms of either the barrier 'lowering' or barrier 'narrowing' via the curvature constant. Calculations are made for use of nuclear proximity potential, with effects of multipole deformations included up to hexadecapole, and orientation degrees of freedom integrated for both the coplanar and noncoplanar configurations.

  17. Pressure Dependence of Gas-Phase Reaction Rates

    ERIC Educational Resources Information Center

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

    2004-01-01

    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.

  18. How the projectile neutron number influences the evaporation cross section in complete fusion reactions with heavy ions

    SciTech Connect

    Wang Chengbin; Zhang Jinjuan; Ren, Z. Z.; Shen, C. W.

    2010-11-15

    The influence of the projectile neutron number on the evaporation residue cross sections for the reactions {sup 208}Pb({sup 52,54}Cr,n,2n){sup 258-261}Sg and {sup 208}Pb({sup 48,50}Ti,n,2n){sup 254-257}Rf has been studied within the framework of a fusion-fission statistical model. The results obtained with the kewpie2 code are compared with recent experimental data. The excitation functions represent the experimental results well both in the maximum value and the lactation of the peak. The calculations show that the projectile neutron number greatly influences both the capture cross section and the fusion probability.

  19. Measurements of fusion reactions of low-intensity radioactive carbon beams on 12C and their implications for the understanding of X-ray bursts.

    PubMed

    Carnelli, P F F; Almaraz-Calderon, S; Rehm, K E; Albers, M; Alcorta, M; Bertone, P F; Digiovine, B; Esbensen, H; Niello, J O Fernández; Henderson, D; Jiang, C L; Lai, J; Marley, S T; Nusair, O; Palchan-Hazan, T; Pardo, R C; Paul, M; Ugalde, C

    2014-05-16

    The interaction between neutron-rich nuclei plays an important role for understanding the reaction mechanism of the fusion process as well as for the energy production through pycnonuclear reactions in the crust of neutron stars. We have performed the first measurements of the total fusion cross sections in the systems (10,14,15)C+(12)C using a new active target-detector system. In the energy region accessible with existing radioactive beams, a good agreement between the experimental and theoretical cross sections is observed. This gives confidence in our ability to calculate fusion cross sections for systems which are outside the range of today's radioactive beam facilities.

  20. Measurements of Fusion Reactions of Low-Intensity Radioactive Carbon Beams on C12 and their Implications for the Understanding of X-Ray Bursts

    NASA Astrophysics Data System (ADS)

    Carnelli, P. F. F.; Almaraz-Calderon, S.; Rehm, K. E.; Albers, M.; Alcorta, M.; Bertone, P. F.; Digiovine, B.; Esbensen, H.; Niello, J. O. Fernández; Henderson, D.; Jiang, C. L.; Lai, J.; Marley, S. T.; Nusair, O.; Palchan-Hazan, T.; Pardo, R. C.; Paul, M.; Ugalde, C.

    2014-05-01

    The interaction between neutron-rich nuclei plays an important role for understanding the reaction mechanism of the fusion process as well as for the energy production through pycnonuclear reactions in the crust of neutron stars. We have performed the first measurements of the total fusion cross sections in the systems C10,14,15+C12 using a new active target-detector system. In the energy region accessible with existing radioactive beams, a good agreement between the experimental and theoretical cross sections is observed. This gives confidence in our ability to calculate fusion cross sections for systems which are outside the range of today's radioactive beam facilities.

  1. Atomic data for fusion

    SciTech Connect

    Hunter, H.T.; Kirkpatrick, M.I.; Alvarez, I.; Cisneros, C.; Phaneuf, R.A.; Barnett, C.F.

    1990-07-01

    This report provides a handbook of recommended cross-section and rate-coefficient data for inelastic collisions between hydrogen, helium and lithium atoms, molecules and ions, and encompasses more than 400 different reactions of primary interest in fusion research. Published experimental and theoretical data have been collected and evaluated, and the recommended data are presented in tabular, graphical and parametrized form. Processes include excitation and spectral line emission, charge exchange, ionization, stripping, dissociation and particle interchange reactions. The range of collision energies is appropriate to applications in fusion-energy research.

  2. Photo-fusion reactions in a new compact device for ELI

    SciTech Connect

    Moustaizis, S. D.; Auvray, P.; Hora, H.; Lalousis, P.; Larour, J.; Mourou, G.

    2012-07-09

    In the last few years significant progress on technological, experimental and numerical studies on fusion process in high density and high temperature plasmas produced by a high intensity laser pulse interaction with clusters in a high external applied magnetic field, enable us to propose a compact photo-fusion magnetic device for high neutron production. For the purpose of the project a pulsed magnetic field driver with values up to 110 Tesla has been developed which allows increasing the trapping time of the high density plasma in the device and improving the neutron yield. Numerical simulations show that the proposed device is capable of producing up to 10{sup 9}-10{sup 10} neutrons per laser shot with an external magnetic field of 150 Tesla. The proposed device can be used for experiments and numerical code validation concerning different conventional and (or) exotic fusion fuels.

  3. Enhanced reaction rates in NDP analysis with neutron scattering

    SciTech Connect

    Downing, R. Gregory

    2014-04-15

    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.

  4. Enhanced reaction rates in NDP analysis with neutron scattering

    NASA Astrophysics Data System (ADS)

    Downing, R. Gregory

    2014-04-01

    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.

  5. Enhanced reaction rates in NDP analysis with neutron scattering.

    PubMed

    Downing, R Gregory

    2014-04-01

    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.

  6. Fusion reactions in collisions induced by Li isotopes on Sn targets

    SciTech Connect

    Fisichella, M.; Shotter, A. C.; Di Pietro, A.; Figuera, P.; Lattuada, M.; Marchetta, C.; Musumarra, A.; Pellegriti, M. G.; Ruiz, C.; Scuderi, V.; Strano, E.; Torresi, D.; Zadro, M.

    2012-10-20

    Fusion cross sections for the {sup 6}Li+{sup 120}Sn and {sup 7}Li+{sup 119}Sn systems have been measured. We aim to search for possible effects due to the different neutron transfer Q-values, by comparing the fusion cross sections for the two systems below the barrier. This experiment is the first step of a wider systematic aiming to study the above problems in collisions induced by stable and unstable Li isotopes on tin all forming the same compound nucleus.

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

    NASA Astrophysics Data System (ADS)

    Ribeiro, Joao Marcelo; Mebel, Alexander M.

    2015-07-01

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

  8. Comparison of allograft and polyetheretherketone (PEEK) cage subsidence rates in anterior cervical discectomy and fusion (ACDF).

    PubMed

    Yson, Sharon C; Sembrano, Jonathan N; Santos, Edward Rainier G

    2017-04-01

    Structural allografts and PEEK cages are commonly used interbody fusion devices in ACDF. The subsidence rates of these two spacers have not yet been directly compared. The primary aim of this study was to compare the subsidence rate of allograft and PEEK cage in ACDF. The secondary aim was to determine if the presence of subsidence affects the clinical outcome. We reviewed 67 cases (117 levels) of ACDF with either structural allograft or PEEK cages. There were 85 levels (48 cases) with PEEK and 32 levels (19 cases) with allograft spacers. Anterior and posterior disc heights at each operative level were measured at immediate and 6months post-op. Subsidence was defined as a decrease in anterior or posterior disc heights >2mm. NDI of the subsidence (SG) and non-subsidence group (NSG) were recorded. Chi-square test was used to analyze subsidence rates. T-test was used to analyze clinical outcomes (α=0.05). There was no statistically significant difference between subsidence rates of the PEEK (29%; 25/85) and allograft group (28%; 9/32) (p=0.69). Overall mean subsidence was 2.3±1.7mm anteriorly and 2.6±1.2mm posteriorly. Mean NDI improvement was 11.7 (from 47.1 to 35.4; average follow-up: 12mos) for the SG and 14.0 (from 45.8 to 31.8; average follow-up: 13mos) for the NSG (p=0.74). Subsidence rate does not seem to be affected by the use of either PEEK or allograft as spacers in ACDF. Furthermore, subsidence alone does not seem to be predictive of clinical outcomes of ACDF.

  9. Description of nucleon-transfer and fusion reactions within time-dependent approaches and coupled-channel method

    SciTech Connect

    Samarin, V. V.

    2015-01-15

    The time-dependent Schrödinger equation and the method of perturbed stationary states that is based on the expansion of the total wave function for the system of two nuclear cores and a nucleon in a set of nucleon two-center functions are used to describe nucleon transfers and fusion in low-energy nuclear reactions. A set of multichannel equations that couple the relative motion of nuclei to the motion of the nucleon is obtained. The kinetic-energy coupling matrix is similar to the coupling matrix for collective excitations of nuclei.

  10. On the mechanism of effective chemical reactions with turbulent mixing of reactants and finite rate of molecular reactions

    NASA Astrophysics Data System (ADS)

    Vorotilin, V. P.

    2017-01-01

    A generalization of the theory of chemical transformation processes under turbulent mixing of reactants and arbitrary values of the rate of molecular reactions is presented that was previously developed for the variant of an instantaneous reaction [13]. The use of the features of instantaneous reactions when considering the general case, namely, the introduction of the concept of effective reaction for the reactant volumes and writing a closing conservation equation for these volumes, became possible due to the partition of the whole amount of reactants into "active" and "passive" classes; the reactants of the first class are not mixed and react by the mechanism of instantaneous reactions, while the reactants of the second class approach each other only through molecular diffusion, and therefore their contribution to the reaction process can be neglected. The physical mechanism of reaction for the limit regime of an ideal mixing reactor (IMR) is revealed and described. Although formally the reaction rate in this regime depends on the concentration of passive fractions of the reactants, according to the theory presented, the true (hidden) mechanism of the reaction is associated only with the reaction of the active fractions of the reactants with vanishingly small concentration in the volume of the reactor. It is shown that the rate constant of fast chemical reactions can be evaluated when the mixing intensity of reactants is much less than that needed to reach the mixing conditions in an IMR.

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

    SciTech Connect

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

    2009-08-01

    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.

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

    PubMed

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

    2016-07-13

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

  13. Reaction and fusion cross sections for the near-symmetric system 129Xe+natSn from 8 A to 35 A MeV

    NASA Astrophysics Data System (ADS)

    Manduci, L.; Lopez, O.; Chbihi, A.; Rivet, M. F.; Bougault, R.; Frankland, J. D.; Borderie, B.; Galichet, E.; La Commara, M.; Le Neindre, N.; Lombardo, I.; Pârlog, M.; Rosato, E.; Roy, R.; Verde, G.; Vient, E.; Indra Collaboration

    2016-10-01

    Background: We study heavy-ion reactions from barrier up to Fermi energy. The data were acquired with the INDRA detector at the GANIL (Caen, France) facility. Purpose: We aim to determine the reaction and fusion cross sections for the reactions induced by 129Xe projectiles on natSn targets for incident energies ranging from 8 A to 35 A MeV. In particular, the evaluation of the fusion and incomplete fusion cross sections is the main purpose, altogether with the comparison with the systematics of Eudes et al. [Europhys. Lett. 104, 22001 (2013), 10.1209/0295-5075/104/22001]. Method: The reaction cross sections are evaluated at each beam energy with data acquired thanks to the INDRA 4 π array. The events are sorted with the help of the observable Eiso,max. We focus therefore our study on a selected sample of events, in such a way that the fusion and incomplete fusion cross sections can be estimated. Results: We present the excitation function of reaction and fusion cross sections for the heavy and nearly symmetric system 129Xe+natSn from 8 A to 35 A MeV. For the fusion excitation function the comparison with the systematics of Eudes et al. seems to be in a fair agreement starting from the beam energy 20 A MeV. For the lower beam energies (8 A and 12 A MeV) discrepancies are observed. Conclusions: The evaluated fusionlike cross sections show a good agrement with a recent systematics for beam energies greater than 20 A MeV. For low beam energies the cross-sectional values are lower than the expected ones. A probable reason for these low values is in the fusion hindrance at energies above or close to the barrier.

  14. Cross sections and reaction rates of relevance to aeronomy

    SciTech Connect

    Fox, J.L. )

    1991-01-01

    Experimental and theoretical data relevant to models and measurements of the chemical and thermal structures and luminosity of the thermospheres of the earth and planets published during the last four years are surveyed. Among chemical processes, attention is given to ion-molecule reactions, dissociative recombination of molecular ions, and reactions between neutral species. Both reactions between ground state species and species in excited states are considered, including energy transfer and quenching. Measured and calculated cross sections for interactions of solar radiation with atmospheric species, such as photoabsorption, photoionization, and photodissociation and related processes are surveyed.

  15. Multinucleon transfer in O,1816,19F+208Pb reactions at energies near the fusion barrier

    NASA Astrophysics Data System (ADS)

    Rafferty, D. C.; Dasgupta, M.; Hinde, D. J.; Simenel, C.; Simpson, E. C.; Williams, E.; Carter, I. P.; Cook, K. J.; Luong, D. H.; McNeil, S. D.; Ramachandran, K.; Vo-Phuoc, K.; Wakhle, A.

    2016-08-01

    Background: Nuclear reactions are complex, involving collisions between composite systems where many-body dynamics determines outcomes. Successful models have been developed to explain particular reaction outcomes in distinct energy and mass regimes, but a unifying picture remains elusive. The irreversible transfer of kinetic energy from the relative motion of the collision partners to their internal states, as is known to occur in deep inelastic collisions, has yet to be successfully incorporated explicitly into fully quantal reaction models. The influence of these processes on fusion is not yet quantitatively understood. Purpose: To investigate the population of high excitation energies in transfer reactions at sub-barrier energies, which are precursors to deep inelastic processes, and their dependence on the internuclear separation. Methods: Transfer probabilities and excitation energy spectra have been measured in collisions of O,1816,19F+208Pb , at various energies below and around the fusion barrier, by detecting the backscattered projectile-like fragments in a Δ E -E telescope. Results: The relative yields of different transfer outcomes are strongly driven by Q values, but change with the internuclear separation. In 16O+208Pb , single nucleon transfer dominates, with a strong contribution from -2 p transfer close to the Coulomb barrier, though this channel becomes less significant in relation to the -2 p 2 n transfer channel at larger separations. For 18O+208Pb , the -2 p 2 n channel is the dominant charge transfer mode at all separations. In the reactions with 19F,-3 p 2 n transfer is significant close to the barrier, but falls off rapidly with energy. Multinucleon transfer processes are shown to lead to high excitation energies (up to ˜15 MeV), which is distinct from single nucleon transfer modes which predominantly populate states at low excitation energy. Conclusions: Kinetic energy is transferred into internal excitations following transfer, with this

  16. First measurements of deuterium-tritium and deuterium-deuterium fusion reaction yields in ignition-scalable direct-drive implosions

    DOE PAGES

    Forrest, C. J.; Radha, P. B.; Knauer, J. P.; ...

    2017-03-03

    In this study, the deuterium-tritium (D-T) and deuterium-deuterium neutron yield ratio in cryogenic inertial confinement fusion (ICF) experiments is used to examine multifluid effects, traditionally not included in ICF modeling. This ratio has been measured for ignition-scalable direct-drive cryogenic DT implosions at the Omega Laser Facility using a high-dynamic-range neutron time-of-flight spectrometer. The experimentally inferred yield ratio is consistent with both the calculated values of the nuclear reaction rates and the measured preshot target-fuel composition. These observations indicate that the physical mechanisms that have been proposed to alter the fuel composition, such as species separation of the hydrogen isotopes, aremore » not significant during the period of peak neutron production in ignition-scalable cryogenic direct-drive DT implosions.« less

  17. Rates of primary electron transfer reactions in the photosystem I reaction center reconstituted with different quinones as the secondary acceptor

    SciTech Connect

    Kumazaki, Shigeichi; Kandori, Hideki; Yoshihara, Keitaro ); Iwaki, Masayo; Itoh, Shigeru ); Ikegamu, Isamu )

    1994-10-27

    Rates of sequential electron transfer reactions from the primary electron donor chlorophyll dimer (P700) to the electron acceptor chlorophyll a-686 (A[sub 0]) and to the secondary acceptor quinone (Q[sub [phi

  18. Reaction rate oscillations during catalytic CO oxidation: A brief overview

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    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.

  19. Reaction rate oscillations during catalytic CO oxidation: A brief overview

    NASA Astrophysics Data System (ADS)

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

    1987-04-01

    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.

  20. Fusion Method for Solubility and Dissolution Rate Enhancement of Ibuprofen Using Block Copolymer Poloxamer 407.

    PubMed

    Dugar, Rohit P; Gajera, Bhavin Y; Dave, Rutesh H

    2016-12-01

    Aim of current research was to prepare ibuprofen-poloxamer 407 binary mixtures using fusion method and characterize them for their physicochemical and performance properties. Binary mixtures of ibuprofen and poloxamer were prepared in three different ratios (1:0.25, 1:0.5, and 1:0.75, respectively) using a water-jacketed high shear mixer. In vitro dissolution and saturation solubility studies were carried out for the drug, physical mixtures, and formulations for all ratios in de-ionized water, 0.1 N HCl (pH = 1.2), and phosphate buffer (pH = 7.2). Thermal and physical characterization of samples was done using modulated differential scanning calorimetry (mDSC), X-ray powder diffraction (XRD), and infrared spectroscopy (FTIR). Flow properties were evaluated using a powder rheometer. Maximum solubility enhancement was seen in acidic media for fused formulations where the ratio 1:0.75 had 18-fold increase. In vitro dissolution studies showed dissolution rate enhancement for physical mixtures and the formulations in all three media. The most pronounced effect was seen for formulation (1:0.75) in acidic media where the cumulative drug release was 58.27% while for drug, it was 3.67%. Model independent statistical methods and ANOVA based methods were used to check the significance of difference in the dissolution profiles. Thermograms from mDSC showed a characteristic peak for all formulations with Tpeak of around 45°C which suggested formation of a eutectic mixture. XRD data displayed that crystalline nature of ibuprofen was intact in the formulations. This work shows the effect of eutectic formation and micellar solubilization between ibuprofen and poloxamer at the given ratios on its solubility and dissolution rate enhancement.

  1. Quick and Easy Rate Equations for Multistep Reactions

    ERIC Educational Resources Information Center

    Savage, Phillip E.

    2008-01-01

    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…

  2. Radioscapholunate Fusions

    PubMed Central

    McGuire, Duncan Thomas; Bain, Gregory Ian

    2012-01-01

    Radiocarpal fusions are performed for a variety of indications, most commonly for debilitating painful arthritis. The goal of a wrist fusion is to fuse the painful, diseased joints and to preserve motion through the healthy joints. Depending on the extent of the disease process, radiocarpal fusions may take the form of radiolunate, radioscapholunate, or total wrist fusions. Surgical techniques and instrumentation have advanced over the last few decades, and consequently the functional outcomes have improved and complications decreased. Techniques for partial carpal fusions have improved and now include distal scaphoid and triquetrum excision, which improves range of motion and fusion rates. In this article we discuss the various surgical techniques and fixation methods available and review the corresponding evidence in the literature. The authors' preferred surgical technique of radioscapholunate fusion with distal scaphoid and triquetrum excision is outlined. New implants and new concepts are also discussed. PMID:24179717

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

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

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

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

    PubMed

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

    2005-03-15

    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).

  5. Doc2b promotes GLUT4 exocytosis by activating the SNARE-mediated fusion reaction in a calcium- and membrane bending-dependent manner.

    PubMed

    Yu, Haijia; Rathore, Shailendra S; Davis, Eric M; Ouyang, Yan; Shen, Jingshi

    2013-04-01

    The glucose transporter GLUT4 plays a central role in maintaining body glucose homeostasis. On insulin stimulation, GLUT4-containing vesicles fuse with the plasma membrane, relocating GLUT4 from intracellular reservoirs to the cell surface to uptake excess blood glucose. The GLUT4 vesicle fusion reaction requires soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) as the core fusion engine and a group of regulatory proteins. In particular, the soluble C2-domain factor Doc2b plays a key role in GLUT4 vesicle fusion, but its molecular mechanism has been unclear. Here we reconstituted the SNARE-dependent GLUT4 vesicle fusion in a defined proteoliposome fusion system. We observed that Doc2b binds to GLUT4 exocytic SNAREs and potently accelerates the fusion kinetics in the presence of Ca(2+). The stimulatory activity of Doc2b requires intact Ca(2+)-binding sites on both the C2A and C2B domains. Using electron microscopy, we observed that Doc2b strongly bends the membrane bilayer, and this membrane-bending activity is essential to the stimulatory function of Doc2b in fusion. These results demonstrate that Doc2b promotes GLUT4 exocytosis by accelerating the SNARE-dependent fusion reaction by a Ca(2+)- and membrane bending-dependent mechanism. Of importance, certain features of Doc2b function appear to be distinct from how synaptotagmin-1 promotes synaptic neurotransmitter release, suggesting that exocytic Ca(2+) sensors may possess divergent mechanisms in regulating vesicle fusion.

  6. Fluctuation enhanced electrochemical reaction rates at the nanoscale

    PubMed Central

    García-Morales, Vladimir; Krischer, Katharina

    2010-01-01

    The electrode potential constitutes a dynamical variable whenever an electrode is resistively coupled to the electric circuit. We show that at the nanoscale, the discreteness and stochasticity of an electron transfer event causes fluctuations of the electrode potential that render all elementary electrochemical reactions to be faster on a nanoelectrode than predicted by the macroscopic (Butler–Volmer) electrochemical kinetics. This phenomenon is substantiated by means of a generalized (electro)chemical master equation. PMID:20176966

  7. Isospin Dependence of Incomplete Fusion Reactions at 25 MeV/Nucleon

    SciTech Connect

    Amorini, F.; Agodi, C.; Alba, R.; Anzalone, A.; Coniglione, R.; Di Pietro, A.; Figuera, P.; Maiolino, C.; Santonocito, D.; Sapienza, P.; Cardella, G.; Papa, M.; De Filippo, E.; Pagano, A.; Pirrone, S.; Verde, G.; Giuliani, G.; Berceanu, I.; Pop, A.; Cavallaro, S.

    2009-03-20

    {sup 40}Ca+{sup 40,48}Ca,{sup 46}Ti reactions at 25 MeV/nucleon have been studied using the 4{pi} CHIMERA detector. An isospin effect on the competition between fusionlike and binarylike reaction mechanisms has been observed. The probability of producing a heavy residue is lower in the case of N{approx_equal}Z colliding systems as compared to the case of reactions induced on the neutron rich {sup 48}Ca target. Predictions based on constrained molecular dynamics II calculations show that the competition between fusionlike and binary reactions in the selected centrality bins can constrain the parametrization of the symmetry energy and its density dependence in the nuclear equation of state.

  8. Dynamical Dipole mode in the 40,48 Ca +152,144Sm fusion reactions at 11 MeV/nucleon

    NASA Astrophysics Data System (ADS)

    Parascandolo, C.; Pierroutsakou, D.; Alba, R.; Del Zoppo, A.; Maiolino, C.; Santonocito, D.; Agodi, C.; Baran, V.; Boiano, A.; Colonna, M.; Coniglione, R.; De Filippo, E.; Di Toro, M.; Emanuele, U.; Farinon, F.; Guglielmetti, A.; La Commara, M.; Martin, B.; Mazzocchi, C.; Mazzocco, M.; Rizzo, C.; Romoli, M.; Signorini, C.; Silvestri, R.; Soramel, F.; Strano, E.; Torresi, D.; Trifirò, A.; Trimarchi, M.

    2016-05-01

    The excitation of the dynamical dipole mode along the fusion path was investigated in the formation of a heavy compound nucleus in the A=190 mass region. To form the compound nucleus, the 40Ca + 152Sm and 48Ca + 144Sm reactions were employed at Elab=11 and 10.1 MeV/nucleon, respectively. Both fusion-evaporation and fission events were studied simultaneously for the first time. Our results for evaporation and fission events (preliminary) show that the dynamical dipole mode survives in reactions involving heavier nuclei than those studied previously.

  9. Study of the 20,22Ne+20,22Ne and 10,12,13,14,15C+12C Fusion Reactions with MUSIC

    NASA Astrophysics Data System (ADS)

    Avila, M. L.; Rehm, K. E.; Almaraz-Calderon, S.; Carnelli, P. F. F.; DiGiovine, B.; Esbensen, H.; Hoffman, C. R.; Jiang, C. L.; Kay, B. P.; Lai, J.; Nusair, O.; Pardo, R. C.; Santiago-Gonzalez, D.; Talwar, R.; Ugalde, C.

    2016-05-01

    A highly efficient MUlti-Sampling Ionization Chamber (MUSIC) detector has been developed for measurements of fusion reactions. A study of fusion cross sections in the 10,12,13,14,15C+12C and 20,22Ne+20,22Ne systems has been performed at ATLAS. Experimental results and comparison with theoretical predictions are presented. Furthermore, results of direct measurements of the 17O(α, n)20Ne, 23Ne(α, p)26Mg and 23Ne(α, n)26Al reactions will be discussed.

  10. Error Rate Comparison during Polymerase Chain Reaction by DNA Polymerase

    DOE PAGES

    McInerney, Peter; Adams, Paul; Hadi, Masood Z.

    2014-01-01

    As larger-scale cloning projects become more prevalent, there is an increasing need for comparisons among high fidelity DNA polymerases used for PCR amplification. All polymerases marketed for PCR applications are tested for fidelity properties (i.e., error rate determination) by vendors, and numerous literature reports have addressed PCR enzyme fidelity. Nonetheless, it is often difficult to make direct comparisons among different enzymes due to numerous methodological and analytical differences from study to study. We have measured the error rates for 6 DNA polymerases commonly used in PCR applications, including 3 polymerases typically used for cloning applications requiring high fidelity. Errormore » rate measurement values reported here were obtained by direct sequencing of cloned PCR products. The strategy employed here allows interrogation of error rate across a very large DNA sequence space, since 94 unique DNA targets were used as templates for PCR cloning. The six enzymes included in the study, Taq polymerase, AccuPrime-Taq High Fidelity, KOD Hot Start, cloned Pfu polymerase, Phusion Hot Start, and Pwo polymerase, we find the lowest error rates with Pfu , Phusion, and Pwo polymerases. Error rates are comparable for these 3 enzymes and are >10x lower than the error rate observed with Taq polymerase. Mutation spectra are reported, with the 3 high fidelity enzymes displaying broadly similar types of mutations. For these enzymes, transition mutations predominate, with little bias observed for type of transition.« less

  11. PRODUCTION OF {sup 9}Be THROUGH THE {alpha}-FUSION REACTION OF METAL-POOR COSMIC RAYS AND STELLAR FLARES

    SciTech Connect

    Kusakabe, Motohiko; Kawasaki, Masahiro E-mail: kawasaki@icrr.u-tokyo.ac.jp

    2013-04-10

    Spectroscopic observations of metal-poor stars have indicated possible {sup 6}Li abundances that are much larger than the primordial abundance predicted in the standard big bang nucleosynthesis model. Possible mechanisms of {sup 6}Li production in metal-poor stars include pregalactic and cosmological cosmic-ray (CR) nucleosynthesis and nucleosynthesis by flare-accelerated nuclides. We study {sup 9}Be production via two-step {alpha}-fusion reactions of CR or flare-accelerated {sup 3,4}He through {sup 6}He and {sup 6,7}Li, in pregalactic structure, intergalactic medium, and stellar surfaces. We solve transfer equations of CR or flare particles and calculate nuclear yields of {sup 6}He, {sup 6,7}Li, and {sup 9}Be taking account of probabilities of processing {sup 6}He and {sup 6,7}Li into {sup 9}Be via fusions with {alpha} particles. Yield ratios, i.e., {sup 9}Be/{sup 6}Li, are then calculated for the CR and flare nucleosynthesis models. We suggest that the future observations of {sup 9}Be in metal-poor stars may find enhanced abundances originating from metal-poor CR or flare activities.

  12. Rate of adverse reactions to more than 1 series of viscosupplementation.

    PubMed

    Webber, Tracy A; Webber, Anthony E; Matzkin, Elizabeth

    2012-04-01

    Viscosupplementation, hyaluronic acid treatment, is an ancillary method for treating patients with symptomatic stage I or II osteoarthritis. Previous studies reported that local reactions occurred more frequently in patients receiving >1 course of treatment compared with patients receiving their first course of treatment. One (2%) of 42 first series patients and 4 (21%) of 19 of repeated series patients had adverse reactions severe enough to seek unscheduled care.This study was performed to determine whether patients receiving >1 series of viscosupplementation had an increased adverse reaction rate. A retrospective chart review was performed on all patients who received >1 series of viscosupplementation during the study. A local adverse reaction was defined as acute swelling and pain in the knee, with no injury or trauma within 72 hours after hyaluronic acid injection.Twenty-eight knees received >1 series of viscosupplementation. The adverse reaction rate to second series injections was 1.28% (3.57% of knees). The adverse reaction rate to ≥3 series was 0.9% (6.67% of knees). This adverse reaction rate was significantly less than the 21% reported in previous studies for multiple series injections (z=-1.90; P<.05) and is not significantly different than the 2% rate of adverse reactions reported for first series injections. No significant difference existed in the adverse reaction rates between 2 series and ≥3 series of viscosupplementation.The current study suggests that the rate of adverse reaction was low at 1.28% of second series viscosupplementation.

  13. Cross section systematics for the lightest Bi and Po nuclei produced in complete fusion reactions with heavy ions

    SciTech Connect

    Andreyev, A.N.; Ackermann, D.; Muenzenberg, G.; Antalic, S.; Saro, S.; Streicher, B.; Darby, I.G.; Page, R.D.; Wiseman, D.R.; Franchoo, S.; Hessberger, F.P.; Kuusiniemi, P.; Lommel, B.; Kindler, B.; Mann, R.; Sulignano, B.; Hofmann, S.; Huyse, M.; Vel, K. van de; Duppen, P. van

    2005-07-01

    The production of the very neutron-deficient nuclides {sup 184-192}Bi and {sup 186-192}Po in the vicinity of the neutron midshell at N = 104 has been studied by using heavy-ion-induced complete fusion reactions in a series of experiments at the velocity filter SHIP. The cross sections for the xn and pxn evaporation channels of the {sup 46}Ti+{sup 144}Sm{yields}{sup 190}Po*,{sup 98}Mo+{sup 92}Mo{yields}{sup 190}Po*,{sup 50,52}Cr+{sup 142}Nd{yields}{sup 192,194}Po*, and {sup 94,95}Mo+{sup 93}Nb{yields}{sup 187,188}Bi* reactions were measured. The results obtained, together with the previously known cross section data for the heavier Bi and Po nuclides, are compared with the results of statistical model calculations carried out with the HIVAP code. It is shown that a satisfactory description of the experimental data requires a significant (up to 35%) reduction of the theoretical fission barriers. The optimal reactions for production of the lightest Bi and Po isotopes are discussed.

  14. Effect of delivery condition on desorption rate of ZrCo metal hydride bed for fusion fuel cycle

    SciTech Connect

    Kang, H.G.; Yun, S.H.; Chung, D.; Oh, Y.H.; Chang, M.H.; Cho, S.; Chung, H.; Song, K.M.

    2015-03-15

    For the safety of fusion fuel cycle, hydrogen isotope gases including tritium are stored as metal hydride form. To satisfy fueling requirement of fusion machine, rapid delivery from metal hydride bed is one of major factors for the development of tritium storage and delivery system. Desorption from metal hydride depends on the operation scenario by pressure and temperature control of the bed. The effect of operation scenario and pump performance on desorption rate of metal hydride bed was experimentally investigated using ZrCo bed. The results showed that the condition of pre-heating scenario before actual delivery of gas affected the delivery performance. Different pumps were connected to desorption line from bed and the effect of pump capacity on desorption rate were also found to be significant. (authors)

  15. Upper atmosphere research: Reaction rate and optical measurements

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    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.

  16. Effect of temperature oscillation on chemical reaction rates in the atmosphere

    NASA Technical Reports Server (NTRS)

    Eberstein, I. J.

    1974-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    DeMore, W.; Bayes, K.

    1998-01-01

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

  18. Determination of photochemical reaction rates using thermal lens spectrometry

    NASA Astrophysics Data System (ADS)

    Astrath, N. G. C.; Astrath, F. B. G.; Shen, J.; Zhou, J.; Michaelian, K. H.; Fairbridge, C.; Malacarne, L. C.; Pedreira, P. R. B.; Baesso, M. L.

    2010-03-01

    Considering the time dependence of the absorption coefficient due to the photo-induced chemical reaction (PCR) and species diffusion, we calculate the temperature rise in the thermal lens (TL) effect and the TL signal at the detector plane. This theoretical approach removes the restriction that the PCR time constant is much greater than the characteristic TL time constant, which was assumed in a previously published model. Aqueous Cr(VI)-diphenylcarbazide solution is investigated, and quantitative experimental results for the thermal, optical and PCR properties of the sample are obtained. The relative difference between the parameters extracted from the same experimental data of the Cr(VI) solution using the previous and present models is found to be less than 5%, showing the present model can be used to study the PCR. Moreover the present model is more general than the previous one.

  19. Comparison of complication rates of minimally invasive transforaminal lumbar interbody fusion and lateral lumbar interbody fusion: a systematic review of the literature.

    PubMed

    Joseph, Jacob R; Smith, Brandon W; La Marca, Frank; Park, Paul

    2015-10-01

    OBJECT Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) and lateral lumbar interbody fusion (LLIF) are 2 currently popular techniques for lumbar arthrodesis. The authors compare the total risk of each procedure, along with other important complication outcomes. METHODS This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Relevant studies (up to May 2015) that reported complications of either MI-TLIF or LLIF were identified from a search in the PubMed database. The primary outcome was overall risk of complication per patient. Secondary outcomes included risks of sensory deficits, temporary neurological deficit, permanent neurological deficit, intraoperative complications, medical complications, wound complications, hardware failure, subsidence, and reoperation. RESULTS Fifty-four studies were included for analysis of MI-TLIF, and 42 studies were included for analysis of LLIF. Overall, there were 9714 patients (5454 in the MI-TLIF group and 4260 in the LLIF group) with 13,230 levels fused (6040 in the MI-TLIF group and 7190 in the LLIF group). A total of 1045 complications in the MI-TLIF group and 1339 complications in the LLIF group were reported. The total complication rate per patient was 19.2% in the MI-TLIF group and 31.4% in the LLIF group (p < 0.0001). The rate of sensory deficits and temporary neurological deficits, and permanent neurological deficits was 20.16%, 2.22%, and 1.01% for MI-TLIF versus 27.08%, 9.40%, and 2.46% for LLIF, respectively (p < 0.0001, p < 0.0001, p = 0.002, respectively). Rates of intraoperative and wound complications were 3.57% and 1.63% for MI-TLIF compared with 1.93% and 0.80% for LLIF, respectively (p = 0.0003 and p = 0.034, respectively). No significant differences were noted for medical complications or reoperation. CONCLUSIONS While there was a higher overall complication rate with LLIF, MI-TLIF and LLIF both have

  20. The Trojan Horse Method as a tool for investigating astrophysically relevant fusion reactions

    NASA Astrophysics Data System (ADS)

    Lamia, L.; Spitaleri, C.; Tognelli, E.; Degl'Innocenti, S.; Pizzone, R. G.; Prada Moroni, P. G.

    2016-05-01

    The Trojan Horse Method (THM) has been largely adopted for investigating astrophysically relevant charged-particle induced reactions at Gamow energies. Indeed, THM allows one to by pass extrapolation procedures, thus overcoming this source of uncertainty. Here, the recent THM results and their impact in astrophysics are going to be discussed.

  1. Reaction rates between water and some modified rapidly-reacting Karl Fischer reagents.

    PubMed

    Cedergren, A

    1978-04-01

    Rate constants were determined for the reaction between water and various modified Karl Fischer reagents containing formamide, dimethylformamide or N-methylformamide. It was shown that the reaction rate can be increased by a factor of 100 by using a reagent containing 40% v/v formamide in pyridine compared to that obtained by use of the conventional methanolic reagent.

  2. Communication: rate coefficients from quasiclassical trajectory calculations from the reverse reaction: The Mu + H2 reaction re-visited.

    PubMed

    Homayoon, Zahra; Jambrina, Pablo G; Aoiz, F Javier; Bowman, Joel M

    2012-07-14

    In a previous paper [P. G. Jambrina et al., J. Chem. Phys. 135, 034310 (2011)] various calculations of the rate coefficient for the Mu + H(2) → MuH + H reaction were presented and compared to experiment. The widely used standard quasiclassical trajectory (QCT) method was shown to overestimate the rate coefficients by several orders of magnitude over the temperature range 200-1000 K. This was attributed to a major failure of that method to describe the correct threshold for the reaction owing to the large difference in zero-point energies (ZPE) of the reactant H(2) and product MuH (∼0.32 eV). In this Communication we show that by performing standard QCT calculations for the reverse reaction and then applying detailed balance, the resulting rate coefficient is in very good agreement with the other computational results that respect the ZPE, (as well as with the experiment) but which are more demanding computationally.

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

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    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.

  4. 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)

    Stevens, F W

    1932-01-01

    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.

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

    PubMed

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

    2015-04-17

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

  6. Controlling the emotional heart: heart rate biofeedback improves cardiac control during emotional reactions.

    PubMed

    Peira, Nathalie; Fredrikson, Mats; Pourtois, Gilles

    2014-03-01

    When regulating negative emotional reactions, one goal is to reduce physiological reactions. However, not all regulation strategies succeed in doing that. We tested whether heart rate biofeedback helped participants reduce physiological reactions in response to negative and neutral pictures. When viewing neutral pictures, participants could regulate their heart rate whether the heart rate feedback was real or not. In contrast, when viewing negative pictures, participants could regulate heart rate only when feedback was real. Ratings of task success paralleled heart rate. Participants' general level of anxiety, emotion awareness, or cognitive emotion regulation strategies did not influence the results. Our findings show that accurate online heart rate biofeedback provides an efficient way to down-regulate autonomic physiological reactions when encountering negative stimuli.

  7. Reaction Rates in Deformation and Hydrostatic Experiments in the Anhydrous System Anorthite - Forsterite

    NASA Astrophysics Data System (ADS)

    Stunitz, H.; de Ronde, A.; Tullis, J.

    2004-12-01

    The reaction anorthite + forsterite --> cpx + opx + spinel ± gnt proceeds at high temperatures and elevated pressures in the lower crust and upper mantle. This solid-solid reaction was studied experimentally at 900° C in the pressure range of 1000 to 1600 MPa in both shearing deformation and hydrostatic experiments. Powder mixtures (1:1 by vol) of anorthite (An92) and forsterite (Fo93) are hot pressed at 970° C, 750 MPa for 48 hrs in a Griggs apparatus and deformed (˙ γ = 5 × 105 sec-1) after adjustment of P and T to run conditions. H2O content of the samples has been measured by FTIR and is < 30 ppm. At small pressure overstepping (ca. 200 to 300 MPa) undeformed samples show only 10 % reaction progress after 168 hrs, whereas reaction progress in deformed samples after 72 hrs is 60 %. At greater pressure overstepping (700 to 800 MPa) the difference between deformed and undeformed samples is less pronounced (95 % after 60 hrs deformed, 75 % after 168 hrs undeformed) but still present. At greater pressure overstepping, undeformed samples show an exponential reaction rate, whereas that of deformed samples is always linear. Samples initially deformed and then kept hydrostatically show a fast initial reaction rate (85 % of total reaction progress after 0.25 of total run time), followed by a slower reaction progress (15 % reaction after 0.75 of total time) under hydrostatic conditions. The difference in reaction progress is mainly attributed to different nucleation rates. In all experiments, enstatite rims form around olivine grains separating those from other reaction products. Such coronas are indicative of diffusion-controlled reactions. Plots of rim thickness vs time indicate a relative increase of the bulk diffusion coefficient by a factor 5 in the deformed samples compared to undeformed. However, as the grain size of reaction products of deformed samples is 10 times smaller than in undeformed ones, the nucleation rate in deformed samples is ˜ 5000 times

  8. An overview on incomplete fusion reaction dynamics at energy range ∼ 3-8 MeV/A

    SciTech Connect

    Ali, Rahbar; Singh, D.; Ansari, M. Afzal; Kumar, Rakesh; Muralithar, S.; Golda, K. S.; Singh, R. P.; Bhowmik, R. K.; Rashid, M. H.; Guin, R.; Das, S. K.

    2014-08-14

    The information of ICF reaction has been obtained from the measurement of excitation function (EF) of ERs populated in the interaction of {sup 20}Ne and {sup 16}O on {sup 55}Mn, {sup 159}Tb and {sup 156}Gd targets. Sizable enhancement in the measured cross-sections has been observed in α-emitting channels over theoretical predictions, which has been attributed to ICF of the projectile. In order to confirm the findings of the measurements and analysis of EFs, the forward recoil range distributions of ERs populated in {sup 20}Ne+{sup 159}Tb (E ∼165MeV) and {sup 16}O+{sup 156}Gd (E ∼ 72, 82 and 93MeV) systems, have been measured. It has been observed that peaks appearing at different cumulative thicknesses in the stopping medium are related with different degree of linear momentum transfer from projectile to target nucleus by adopting the break-up fusion model consideration. In order to deduce the angular momentum involved in various CF and / or ICF reaction products, spin distribution and side-feeding intensity profiles of radio-nuclides populated via CF and ICF channels in {sup 16}O+{sup 160}Gd system at energy, E ∼ 5.6 MeV/A, have been studied. Spin distribution of ICF products are found to be distinctly different than that observed from CF products.

  9. Simulation of biochemical reactions with time-dependent rates by the rejection-based algorithm

    SciTech Connect

    Thanh, Vo Hong; Priami, Corrado

    2015-08-07

    We address the problem of simulating biochemical reaction networks with time-dependent rates and propose a new algorithm based on our rejection-based stochastic simulation algorithm (RSSA) [Thanh et al., J. Chem. Phys. 141(13), 134116 (2014)]. The computation for selecting next reaction firings by our time-dependent RSSA (tRSSA) is computationally efficient. Furthermore, the generated trajectory is exact by exploiting the rejection-based mechanism. We benchmark tRSSA on different biological systems with varying forms of reaction rates to demonstrate its applicability and efficiency. We reveal that for nontrivial cases, the selection of reaction firings in existing algorithms introduces approximations because the integration of reaction rates is very computationally demanding and simplifying assumptions are introduced. The selection of the next reaction firing by our approach is easier while preserving the exactness.

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

    NASA Astrophysics Data System (ADS)

    Copper, Christine L.; Koubek, Edward

    1999-12-01

    By performing this experiment, students in general and introductory physical chemistry can learn more about the effect of a catalyst on a chemical reaction. This experiment, which is a modified version of the traditional iodine clock reaction, allows students to calculate rates of reaction, orders of reactants, and activation energies. It also lets students discover that to increase a reaction's rate, a catalyst need only provide any additional pathway for the reaction, not necessarily a pathway having a lower activation energy. This experiment is designed so that students will notice that the amount of catalyst used is important. Furthermore, the slight amount (~10-5 M MoO42-) of catalyst needed to increase the overall reaction rate and the abrupt color change that occurs seem to pique the interest of our students.

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

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

  12. Reaction of singlet oxygen with tryptophan in proteins: a pronounced effect of the local environment on the reaction rate.

    PubMed

    Jensen, Rasmus Lybech; Arnbjerg, Jacob; Ogilby, Peter R

    2012-06-13

    Singlet molecular oxygen, O(2)(a(1)Δ(g)), can influence many processes pertinent to the function of biological systems, including events that result in cell death. Many of these processes involve a reaction between singlet oxygen and a given amino acid in a protein. As a result, the behavior of that protein can change, either because of a structural alteration and/or a direct modification of an active site. Surprisingly, however, little is known about rate constants for reactions between singlet oxygen and amino acids when the latter are in a protein. In this report, we demonstrate using five separate proteins, each containing only a single tryptophan residue, that the rate constant for singlet oxygen reaction with tryptophan depends significantly on the position of this amino acid in the protein. Most importantly, the reaction rate constant depends not only on the accessibility of the tryptophan residue to oxygen, but also on factors that characterize the local molecular environment of the tryptophan in the protein. The fact that the local protein environment can either appreciably inhibit or accelerate the reaction of singlet oxygen with a given amino acid can have significant ramifications for singlet-oxygen-mediated events that perturb cell function.

  13. Chiral Polymerization in Open Systems From Chiral-Selective Reaction Rates

    NASA Astrophysics Data System (ADS)

    Gleiser, Marcelo; Nelson, Bradley J.; Walker, Sara Imari

    2012-08-01

    We investigate the possibility that prebiotic homochirality can be achieved exclusively through chiral-selective reaction rate parameters without any other explicit mechanism for chiral bias. Specifically, we examine an open network of polymerization reactions, where the reaction rates can have chiral-selective values. The reactions are neither autocatalytic nor do they contain explicit enantiomeric cross-inhibition terms. We are thus investigating how rare a set of chiral-selective reaction rates needs to be in order to generate a reasonable amount of chiral bias. We quantify our results adopting a statistical approach: varying both the mean value and the rms dispersion of the relevant reaction rates, we show that moderate to high levels of chiral excess can be achieved with fairly small chiral bias, below 10%. Considering the various unknowns related to prebiotic chemical networks in early Earth and the dependence of reaction rates to environmental properties such as temperature and pressure variations, we argue that homochirality could have been achieved from moderate amounts of chiral selectivity in the reaction rates.

  14. Chiral polymerization in open systems from chiral-selective reaction rates.

    PubMed

    Gleiser, Marcelo; Nelson, Bradley J; Walker, Sara Imari

    2012-08-01

    We investigate the possibility that prebiotic homochirality can be achieved exclusively through chiral-selective reaction rate parameters without any other explicit mechanism for chiral bias. Specifically, we examine an open network of polymerization reactions, where the reaction rates can have chiral-selective values. The reactions are neither autocatalytic nor do they contain explicit enantiomeric cross-inhibition terms. We are thus investigating how rare a set of chiral-selective reaction rates needs to be in order to generate a reasonable amount of chiral bias. We quantify our results adopting a statistical approach: varying both the mean value and the rms dispersion of the relevant reaction rates, we show that moderate to high levels of chiral excess can be achieved with fairly small chiral bias, below 10%. Considering the various unknowns related to prebiotic chemical networks in early Earth and the dependence of reaction rates to environmental properties such as temperature and pressure variations, we argue that homochirality could have been achieved from moderate amounts of chiral selectivity in the reaction rates.

  15. A simple expression for the apparent reaction rate of large wood char gasification with steam.

    PubMed

    Umeki, Kentaro; Roh, Seon-Ah; Min, Tai-Jin; Namioka, Tomoaki; Yoshikawa, Kunio

    2010-06-01

    A simple expression for the apparent reaction rate of large wood char gasification with steam is proposed. Large char samples were gasified under steam atmosphere using a thermo-balance reactor. The apparent reaction rate was expressed as the product of the intrinsic rate and the effective factor. The effective factor was modified to include the effect of change in char diameter and intrinsic reaction rate during the reaction. Assuming uniform conversion ratio throughout a particle, the simplified reaction scheme was divided into three stages. In the initial stage, the local conversion ratio increases without particle shrinkage. In the middle stage, the particle shrinks following the shrinking core model without change in the local conversion ratio. In the final stage, the local conversion ratio increases without particle shrinkage. The validity of the modified effective value was confirmed by comparison with experimental results.

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

    PubMed

    Kim, Yeong Woo; Baird, James K

    2005-06-02

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  18. Mathematical model of reaction rate oscillations on a chain of nm-sized catalyst particles

    NASA Astrophysics Data System (ADS)

    Peskov, N. V.; Slinko, M. M.; Jaeger, N. I.

    2003-05-01

    The model of reaction rate oscillations over the surface of nanoparticles embedded into zeolite matrix is numerically investigated. The reaction rate oscillations on each particle are described by a lumped model. The reactions on separate particles interact via the gas diffusion through the pores, which is modeled in the frame of the Maxwell-Stefan approach. The reaction reveals a complex dynamical behavior if a nonhomogeneous distribution of reagent concentrations exists along the chain of particles with a sufficiently large gradient near the ends of the chain.

  19. Association of EWS-FLI1 Type 1 Fusion with Lower Proliferative Rate in Ewing’s Sarcoma

    PubMed Central

    de Alava, Enrique; Panizo, Angel; Antonescu, Cristina R.; Huvos, Andrew G.; Pardo-Mindán, F. Javier; Barr, Frederic G.; Ladanyi, Marc

    2000-01-01

    The Ewing’s sarcoma (ES) family of tumors, including peripheral neuroectodermal tumor (PNET), is defined genetically by specific chromosomal translocations resulting in fusion of the EWS gene with a member of the ETS family of transcription factors, either FLI1 (90–95%) or ERG (5–10%). A second level of molecular genetic heterogeneity stems from the variation in the location of the translocation breakpoints, resulting in the inclusion of different combinations of exons from EWS and FLI1 (or ERG) in the fusion products. The most common type of EWS-FLI1 fusion transcript, type 1, is associated with a favorable prognosis and appears to encode a functionally weaker transactivator, compared to other fusion types. We sought to determine whether the observed covariation of structure, function, and clinical course correlates with tumor cell kinetic parameters such as proliferative rate and apoptosis, and with expression of the receptor for insulin-like growth factor I (IGF-1R). In a group of 86 ES/PNET with defined EWS-ETS fusions (45 EWS-FLI1 type 1, 27 EWS-FLI1 non-type 1, 14 EWS-ERG), we assessed proliferation rate by immunostaining for Ki-67 using MIB1 antibody (n = 85), apoptosis by TUNEL assay (n = 66), and IGF-1R expression by immunostaining with antibody 1H7 (n = 78). Ki-67 proliferative index was lower in tumors with EWS-FLI1 type 1 than those with non-type 1 EWS-FLI1, whether analyzed as a continuous (P = 0.049) or categorical (P = 0.047) variable. Logistic regression analysis suggests that this association was secondary to the association of type 1 EWS-FLI1 and lower IGF-1R expression (P = 0.04). Comparing EWS-FLI1 to EWS-ERG cases, Ki-67 proliferative index was higher in the latter (P = 0.01, Mann-Whitney test; P = 0.02, Fisher’s exact test), but there was no significant difference in IGF-1R. TUNEL results showed no significant differences between groups. Our results suggest that clinical and functional differences between alternative forms of EWS-FLI1

  20. Stochastic behavior and stirring rate effects in the chlorite-iodide reaction

    NASA Astrophysics Data System (ADS)

    Nagypál, István; Epstein, Irving R.

    1988-12-01

    The autocatalytic reaction between chlorite and iodide ions in a closed system is a clock reaction, showing a sudden appearance of brown I2 followed by a rapid disappearance of the color. Under certain conditions, the reaction time displays a striking irreproducibility. This stochastic behavior is studied potentiometrically and spectrophotometrically as a function of initial [I- ], stirring rate and solution volume. The results imply that the irreproducibility is an inherent feature of the reaction generated by fluctuations in the solution after it is ``well mixed.'' The key contributors to the stochasticity are local concentration inhomogeneities resulting from imperfect stirring and the ``supercatalytic'' reaction kinetics. A qualitative explanation is given that incorporates these aspects.

  1. Thermal properties of light nuclei from 12C + 12C fusion-evaporation reactions

    NASA Astrophysics Data System (ADS)

    Morelli, L.; Baiocco, G.; D'Agostino, M.; Gulminelli, F.; Bruno, M.; Abbondanno, U.; Appannababu, S.; Barlini, S.; Bini, M.; Casini, G.; Cinausero, M.; Degerlier, M.; Fabris, D.; Gelli, N.; Gramegna, F.; Kravchuk, V. L.; Marchi, T.; Olmi, A.; Pasquali, G.; Piantelli, S.; Valdré, S.; Raduta, Ad R.

    2014-07-01

    The 12C + 12C reaction at 95 MeV has been studied through the complete charge identification of its products by means of the GARFIELD+RCo experimental set-up at INFN Laboratori Nazionali di Legnaro (LNL). In this paper, the first of a series of two, a comparison to a dedicated Hauser-Feshbach calculation allows selecting a set of dissipative events which corresponds, to a large extent, to the statistical evaporation of highly excited 24Mg. Information on the isotopic distribution of the evaporation residues in coincidence with their complete evaporation chain is also extracted. The set of data puts strong constraints on the behaviour of the level density (LD) of light nuclei above the threshold for particle emission. In particular, a fast increase of the LD parameter with excitation energy is supported by the data. Residual deviations from a statistical behaviour are seen in two specific channels, and tentatively associated with a contamination from direct reactions and/or α-clustering effects. These channels are studied in further details in the second paper of the series.

  2. Temperature trends for reaction rates, hydrogen generation, and partitioning of iron during experimental serpentinization of olivine

    NASA Astrophysics Data System (ADS)

    McCollom, Thomas M.; Klein, Frieder; Robbins, Mark; Moskowitz, Bruce; Berquó, Thelma S.; Jöns, Niels; Bach, Wolfgang; Templeton, Alexis

    2016-05-01

    A series of laboratory experiments were conducted to examine how partitioning of Fe among solid reaction products and rates of H2 generation vary as a function of temperature during serpentinization of olivine. Individual experiments were conducted at temperatures ranging from 200 to 320 °C, with reaction times spanning a few days to over a year. The extent of reaction ranged from <1% to ∼23%. Inferred rates for serpentinization of olivine during the experiments were 50-80 times slower than older studies had reported but are consistent with more recent results, indicating that serpentinization may proceed more slowly than previously thought. Reaction products were dominated by chrysotile, brucite, and magnetite, with minor amounts of magnesite, dolomite, and iowaite. The chrysotile contained only small amounts of Fe (XFe = 0.03-0.05, with ∼25% present as ferric Fe in octahedral sites), and displayed little variation in composition with reaction temperature. Conversely, the Fe contents of brucite (XFe = 0.01-0.09) increased steadily with decreasing reaction temperature. Analysis of the reaction products indicated that the stoichiometry of the serpentinization reactions varied with temperature, but remained constant with increasing reaction progress at a given temperature. The observed distribution of Fe among the reaction products does not appear to be entirely consistent with existing equilibrium models of Fe partitioning during serpentinization, suggesting improved models that include kinetic factors or multiple reaction steps need to be developed. Rates of H2 generation increased steeply from 200 to 300 °C, but dropped off at higher temperatures. This trend in H2 generation rates is attributable to a combination of the overall rate of serpentinization reactions and increased partitioning of Fe into brucite rather than magnetite at lower temperatures. The results suggest that millimolal concentration of H2 could be attained in moderately hot hydrothermal

  3. Viscosity Dependence of Some Protein and Enzyme Reaction Rates: Seventy-Five Years after Kramers.

    PubMed

    Sashi, Pulikallu; Bhuyan, Abani K

    2015-07-28

    Kramers rate theory is a milestone in chemical reaction research, but concerns regarding the basic understanding of condensed phase reaction rates of large molecules in viscous milieu persist. Experimental studies of Kramers theory rely on scaling reaction rates with inverse solvent viscosity, which is often equated with the bulk friction coefficient based on simple hydrodynamic relations. Apart from the difficulty of abstraction of the prefactor details from experimental data, it is not clear why the linearity of rate versus inverse viscosity, k ∝ η(-1), deviates widely for many reactions studied. In most cases, the deviation simulates a power law k ∝ η(-n), where the exponent n assumes fractional values. In rate-viscosity studies presented here, results for two reactions, unfolding of cytochrome c and cysteine protease activity of human ribosomal protein S4, show an exceedingly overdamped rate over a wide viscosity range, registering n values up to 2.4. Although the origin of this extraordinary reaction friction is not known at present, the results indicate that the viscosity exponent need not be bound by the 0-1 limit as generally suggested. For the third reaction studied here, thermal dissociation of CO from nativelike cytochrome c, the rate-viscosity behavior can be explained using Grote-Hynes theory of time-dependent friction in conjunction with correlated motions intrinsic to the protein. Analysis of the glycerol viscosity-dependent rate for the CO dissociation reaction in the presence of urea as the second variable shows that the protein stabilizing effect of subdenaturing amounts of urea is not affected by the bulk viscosity. It appears that a myriad of factors as diverse as parameter uncertainty due to the difficulty of knowing the exact reaction friction and both mode and consequences of protein-solvent interaction work in a complex manner to convey as though Kramers rate equation is not absolute.

  4. Temperature-Dependent Rate Coefficients for the Reaction of CH2OO with Hydrogen Sulfide.

    PubMed

    Smith, Mica C; Chao, Wen; Kumar, Manoj; Francisco, Joseph S; Takahashi, Kaito; Lin, Jim Jr-Min

    2017-02-09

    The reaction of the simplest Criegee intermediate CH2OO with hydrogen sulfide was measured with transient UV absorption spectroscopy in a temperature-controlled flow reactor, and bimolecular rate coefficients were obtained from 278 to 318 K and from 100 to 500 Torr. The average rate coefficient at 298 K and 100 Torr was (1.7 ± 0.2) × 10(-13) cm(3) s(-1). The reaction was found to be independent of pressure and exhibited a weak negative temperature dependence. Ab initio quantum chemistry calculations of the temperature-dependent reaction rate coefficient at the QCISD(T)/CBS level are in reasonable agreement with the experiment. The reaction of CH2OO with H2S is 2-3 orders of magnitude faster than the reaction with H2O monomer. Though rates of CH2OO scavenging by water vapor under atmospheric conditions are primarily controlled by the reaction with water dimer, the H2S loss pathway will be dominated by the reaction with monomer. The agreement between experiment and theory for the CH2OO + H2S reaction lends credence to theoretical descriptions of other Criegee intermediate reactions that cannot easily be probed experimentally.

  5. Characterization of shock-dependent reaction rates in an aluminum/perfluoropolyether pyrolant

    NASA Astrophysics Data System (ADS)

    Wilson, Dennis; Granier, John; Johnson, Richard; Littrell, Donald

    2017-01-01

    Energetic formulations of perfluoropolyether (PFPE) and aluminum are highly non-ideal. They release energy via a fast self-oxidized combustion wave rather than a true self-sustaining detonation. Unlike high explosives, the reactions are shock dependent and can be overdriven to control energy release rate. Reaction rate experiments show that the velocity can vary from 1.25 to 3 km/s. This paper examines the effect of the initial shock conditions upon the reaction rate of the explosive. The following conditions were varied in a series of reaction rate experiments: the high explosive booster mass and geometry; shock attenuation; confinement; and rate stick diameter and length. Several experiments designed to isolate and quantify these dependencies are described and summarized.

  6. Nuclear reaction rate uncertainties and the 22Ne( p,gamma)23Na reaction: Classical novae and globular clusters

    NASA Astrophysics Data System (ADS)

    Kelly, Keegan John

    The overall theme of this thesis is the advancement of nuclear astrophysics via the analysis of stellar processes in the presence of varying levels of precision in the available nuclear data. With regard to classical novae, the level of mixing that occurs between the outer layers of the white dwarf core and the solar accreted material in oxygen-neon novae is presently undetermined by stellar models, but the nuclear data relevant to these explosive phenomena are fairly precise. This precision allowed for the identification of a series of elemental ratios indicative of the level of mixing occurring in novae. Direct comparisons of the modelled elemental ratios to observations showed that there is likely to be much less of this mixing than was previously assumed. Thus, our understanding of classical novae was altered via the investigation of the nuclear reactions relevant to this phenomenon. However, this level of experimental precision is rare and large nuclear reaction uncertainties can hinder our understanding of certain astrophysical phenomena. For example, it is commonly believed that uncertainties in the 22Ne(p,g)23Na reaction rate at temperatures relevant to thermally-pulsing asymptotic giant branch stars are largely responsible for our inability to explain the observed sodium-oxygen anti-correlation in globular clusters. With this motivation, resonances in the 22Ne(p,g) 23Na reaction at E_{c.m.} = 458, 417, 178, and 151 keV were measured. The direct-capture contribution was also measured at E_{lab} = 425 keV. It was determined that the 22Ne(p,g)23Na reaction rate in the astrophysically relevant temperature range is dominated by the resonances at 178 and 151 keV and that the total reaction rate is greater than the previously assumed rate by a factor of approximately ˜40 at 0.15 GK. This increased reaction rate impacts the expected nucleosynthesis that occurs in these stars and will shed light onto the origin of this anti-correlation as it is incorporated into

  7. A mesoscopic reaction rate model for shock initiation of multi-component PBX explosives.

    PubMed

    Liu, Y R; Duan, Z P; Zhang, Z Y; Ou, Z C; Huang, F L

    2016-11-05

    The primary goal of this research is to develop a three-term mesoscopic reaction rate model that consists of a hot-spot ignition, a low-pressure slow burning and a high-pressure fast reaction terms for shock initiation of multi-component Plastic Bonded Explosives (PBX). Thereinto, based on the DZK hot-spot model for a single-component PBX explosive, the hot-spot ignition term as well as its reaction rate is obtained through a "mixing rule" of the explosive components; new expressions for both the low-pressure slow burning term and the high-pressure fast reaction term are also obtained by establishing the relationships between the reaction rate of the multi-component PBX explosive and that of its explosive components, based on the low-pressure slow burning term and the high-pressure fast reaction term of a mesoscopic reaction rate model. Furthermore, for verification, the new reaction rate model is incorporated into the DYNA2D code to simulate numerically the shock initiation process of the PBXC03 and the PBXC10 multi-component PBX explosives, and the numerical results of the pressure histories at different Lagrange locations in explosive are found to be in good agreements with previous experimental data.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The 18Ne(α ,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.

  9. Imaginary time approach for reaction rate of triple-alpha process

    NASA Astrophysics Data System (ADS)

    Yabana, Kazuhiro; Akahori, Takahiko; Funaki, Yasuro

    2014-09-01

    We propose a new theoretical approach for the radiative capture reaction rate, which we call the imaginary-time theory. In the theory, inverse temperature is identified with the temperature. Since reaction rates can be calculated without solving any scattering problem in the theory, it is ideally suited for the triple-alpha process in which scattering problem of three charged particles has caused difficulties. Using the imaginary-time theory, we obtain the triple-alpha reaction rate in the quantum three-body model treating alpha particles as structureless point particles. The calculated rate is almost identical to the standard NACRE rate. We have also found that the reaction mechanism of the triple-alpha process changes at exactly the same temperatures as those in empirical theories. We may show that it is possible to derive an analytical formula close to that of the NACRE rate, if we introduce some assumptions in the three-body model. We demonstrate that, if we introduce a coupled-channel expansion with a truncation, reaction rate is substantially overestimated. This finding may help to explain the very different reaction rates obtained so far using different theoretical approaches.

  10. The influence of transfer reactions on the sub-barrier fusion enhancement in the systems {sup 58.64}Ni +, {sup 92,100}Mo

    SciTech Connect

    Rehm, K.E.; Jiang, C.L.; Esbensen, H.

    1995-08-01

    High resolution experiments performed during the past few years demonstrated that the various reaction modes occurring in heavy ion collisions can strongly influence each other. This interrelation of the different reaction modes brings a nuclear structure dependence to the fusion and deep-inelastic channels that were previously described in the framework of pure statistical models. In order to fully understand the interrelation between these reaction channels, a complete set of measurements including elastic and inelastic scattering, few-nucleon transfer and fusion is required. In continuation of our earlier measurements of the fusion cross sections in the system {sup 58,64}Ni + {sup 92,100}Mo we finished the studies of the quasielastic process in these systems. The experiments were done in inverse reaction kinematics using the split-pole spectrograph with its hybrid focal-plane detector for particle identification. The experiments with {sup 100}Mo beams were performed previously. First test runs with {sup 92}Mo showed the possible interference with {sup 98}Mo ions which could be eliminated by using the 13{sup +} charge state from the ECR source. The data from these experiments were completely analyzed. The smallest transfer cross sections are observed for the systems {sup 64}Ni + {sup 100}Mo and {sup 58}Ni + {sup 92}Mo, i.e., the most neutron-rich and neutron-deficient systems, respectively. For the other systems, {sup 64}Ni + {sup 92}Mo and {sup 58}Ni + {sup 100}Mo, the transfer cross sections at energies close to the barrier are about of equal magnitude. This observation does not correlate with the deviation of the experimental fusion cross sections from the coupled-channels predictions. While for {sup 58}Ni + {sup 100}Mo discrepancies between the experimental and theoretical fusion cross sections are observed, the system {sup 64}Ni + {sup 92}Mo which shows about the same transfer yields, is quite well described by the coupled-channels calculations.

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

    NASA Technical Reports Server (NTRS)

    Braams, R.

    1968-01-01

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

  12. Development of Theoretical Methods for Predicting Solvent Effects on Reaction Rates in Supercritical Water Oxidation Processes

    DTIC Science & Technology

    2007-11-02

    Tucker, manuscript in preparation. “Examination of Nonequilibrium Solvent Effects on an SN2 Reaction in Supercritical Water,” R. Behera, B...DATES COVERED Final: 7/1/99 - 12/31/02 4. TITLE AND SUBTITLE Development of theoretical methods for predicting solvent effects on reactions ...computational methods for predicting how reaction rate constants will vary with thermodynamic condition in supercritical water (SCW). Towards this

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    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.

  14. Comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reaction flows

    SciTech Connect

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

    1984-01-01

    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.

  15. Astrophysical S-Factors and Reaction Rates of Threshold (p, n)-Reactions on 99-102Ru

    NASA Astrophysics Data System (ADS)

    Skakun, Ye.; Rauscher, T.

    2010-08-01

    Astrophysical S-factors of (p, n) reactions on 99Ru, 100Ru, 101Ru, and 102Ru 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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-08-01

    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 fundamental shortcomings of the Gamow peak concept for narrow resonances at high stellar temperatures. Our new method defines the effective thermonuclear energy range (ETER) by using the 8th, 50th, and 92nd percentiles of the cumulative distribution of fractional resonant reaction rate contributions. This definition is unambiguous and has a straightforward probability interpretation. The ETER is used to define a temperature at which Hauser-Feshbach rates can be matched to experimental rates. This matching temperature is usually much higher compared to previous estimates that employed the Gamow peak concept. We suggest that an increased matching temperature provides more reliable extrapolated reaction rates since Hauser-Feshbach results are more trustwhorthy the higher the temperature. Our ideas are applied to 21 (p,γ), (p,α), and (α,γ) reactions on A=20-40 target nuclei. For many of the cases studied here, our extrapolated reaction rates at high temperatures differ significantly from those obtained using the Gamow peak concept.

  17. Quantitative rate determination by dynamic nuclear polarization enhanced NMR of a Diels-Alder reaction.

    PubMed

    Zeng, Haifeng; Lee, Youngbok; Hilty, Christian

    2010-11-01

    Emerging techniques for hyperpolarization of nuclear spins, foremost dynamic nuclear polarization (DNP), lend unprecedented sensitivity to nuclear magnetic resonance spectroscopy. Sufficient signal can be obtained from a single scan, and reactions even far from equilibrium can be studied in real-time. When following the progress of a reaction by nuclear magnetic resonance, however, spin relaxation occurs concomitantly with the reaction to alter resonance line intensities. Here, we present a model for accounting for spin-relaxation in such reactions studied by hyperpolarized NMR. The model takes into account auto- and cross-relaxation in dipole-dipole coupled spin systems and is therefore applicable to NMR of hyperpolarized protons, the most abundant NMR-active nuclei. Applied to the Diels-Alder reaction of 1,4-dipheneylbutadiene (DPBD) with 4-phenyl-1,2,4-triazole-3,5-dione (PTD), reaction rates could be obtained accurately and reproducibly. Additional parameters available from the same experiment include relaxation rates of the reaction product, which may yield further information about the molecular properties of the product. The method presented is also compatible with an experiment where a single spin in the reactant is labeled in its spin-state by a selective radio frequency pulse for subsequent tracking through the reaction, allowing the unambiguous identification of its position in the product molecule. In this case, the chemical shift specificity of high-resolution NMR can allow for the simultaneous determination of reaction rates and mechanistic information in one experiment.

  18. Nonequilibrium Contribution to the Rate of Reaction. III. Isothermal Multicomponent Systems

    DOE R&D Accomplishments Database

    Shizgal, B.; Karplus, M.

    1970-10-01

    The nonequilibrium contribution to the reaction rate of an isothermal multicomponent system is obtained by solution of the appropriate Chapman-Enskog equation; the system is composed of reactive species in contact with a heat bath of inert atoms M.

  19. Simulation and Experimental Study on the Efficiency of Traveling Wave Direct Energy Conversion for Application to Aneutronic Fusion Reactions

    NASA Astrophysics Data System (ADS)

    Tarditi, Alfonso; Chap, Andrew; Miley, George; Scott, John

    2013-10-01

    A study based on both Particle-in-cell (PIC) simulation and experiments is being developed to study the physics of the Traveling Wave Direct Energy Converter (TWDEC,) with the perspective of application to aneutronic fusion reaction products and space propulsion. The PIC model is investigating in detail the key TWDEC physics process by simulating the time-dependent transfer of energy from the ion beam to an electric load connected to ring-type electrodes in cylindrical symmetry. An experimental effort is in progress on a TWDEC test article at NASA, Johnson Space Center with the purpose of studying the conditions for improving the efficiency of the direct energy conversion process. Using a scaled-down ion energy source, the experiment is primarily focused on the effect of the (bunched) beam density on the efficiency and on the optimization of the electrode design. The simulation model is guiding the development of the experimental configuration and will provide details of the beam dynamics for direct comparison with experimental diagnostics. Work supported by NASA, Johnson Space Center.

  20. Effects of nuclear orientation on fusion and fission process for reactions using {sup 238}U target nucleus

    SciTech Connect

    Nishio, K.; Ikezoe, H.; Mitsuoka, S.; Nishinaka, I.; Makii, H.; Nagame, Y.; Watanabe, Y.; Ohtsuki, T.; Hirose, K.; Hofmann, S.

    2010-06-01

    Fission fragment mass distributions in the reaction of {sup 30}Si+{sup 238}U were measured at the energies around the Coulomb barrier. At the above-barrier energies, the mass distribution showed Gaussian shape. At the sub-barrier energies, asymmetric fission mode peaked at A{sub L}/A{sub H}approx =90/178 was observed. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER) cross-sections produced by {sup 30}Si+{sup 238}U. The cross-section for {sup 263}Sg at the above-barrier energy agree with the statistical model calculation which assumes that the measured fission cross-sections are equal to the fusion cross-sections, whereas the one for {sup 264}Sg measured at the sub-barrier energy is smaller than the calculation, indicating the presence for quasifission. The fragment mass distributions are compared to those for {sup 36}S+{sup 238}U and {sup 40}Ar+{sup 238}U.

  1. On the implementation of a chain nuclear reaction of thermonuclear fusion on the basis of the p+{sup 11}B process

    SciTech Connect

    Belyaev, V. S.; Krainov, V. P.; Zagreev, B. V.; Matafonov, A. P.

    2015-07-15

    Various theoretical and experimental schemes for implementing a thermonuclear reactor on the basis of the p+{sup 11}B reaction are considered. They include beam collisions, fusion in degenerate plasmas, ignition upon plasma acceleration by ponderomotive forces, and the irradiation of a solid-state target from {sup 11}B with a proton beam under conditions of a Coulomb explosion of hydrogen microdrops. The possibility of employing ultra-short high-intensity laser pulses to initiate the p+{sup 11}B reaction under conditions far from thermodynamic equilibrium is discussed. This and some other weakly radioactive thermonuclear reactions are promising owing to their ecological cleanness—there are virtually no neutrons among fusion products. Nuclear reactions that follow the p+{sup 11}B reaction may generate high-energy protons, sustaining a chain reaction, and this is an advantage of the p+{sup 11}B option. The approach used also makes it possible to study nuclear reactions under conditions close to those in the early Universe or in the interior of stars.

  2. A Unified Equation for the Reaction Rate in Dense Matter Stars

    SciTech Connect

    Gasques, L. R.; Wiescher, M.; Yakovlev, D. G.

    2007-10-26

    We analyze thermonuclear and pycnonuclear reaction rates in multi-component dense stellar plasma. First we describe calculations of the astrophysical S-factor at low energies using the Sao Paulo potential on the basis of the barrier penetration model. Then we present a simple phenomenological expression for a reaction rate. The expression contains several fit parameters which we adjust to reproduce the best microscopic calculations available in the literature.

  3. The Effect of the Triple-α Reaction Rate on Stellar Evolution at Low-Metallicity

    NASA Astrophysics Data System (ADS)

    Suda, Takuma; Hirschi, Raphael; Fujimoto, Masayuki Y.

    2010-06-01

    We investigate the effect of the triple-α reaction rates on the evolution of low-mass stars and massive stars. The former is compared with the observations of metal-poor stars known to date. For the latter, we discuss the impact of recent calculation of triple-α reaction rate by Ogata et al. (2009, PTP, 122, 1055) on the evolution until carbon burning.

  4. Fusion and quasifission dynamics in the reactions 48Ca+249Bk and 50Ti+249Bk using a time-dependent Hartree-Fock approach

    NASA Astrophysics Data System (ADS)

    Umar, A. S.; Oberacker, V. E.; Simenel, C.

    2016-08-01

    Background: Synthesis of superheavy elements (SHEs) with fusion-evaporation reactions is strongly hindered by the quasifission (QF) mechanism which prevents the formation of an equilibrated compound nucleus and which depends on the structure of the reactants. New SHEs have been recently produced with doubly-magic 48Ca beams. However, SHE synthesis experiments with single-magic 50Ti beams have so far been unsuccessful. Purpose: In connection with experimental searches for Z =117 ,119 superheavy elements, we perform a theoretical study of fusion and quasifission mechanisms in 48Ca,50Ti+249Bk reactions in order to investigate possible differences in reaction mechanisms induced by these two projectiles. Methods: The collision dynamics and the outcome of the reactions are studied using unrestricted time-dependent Hartree-Fock (TDHF) calculations as well as the density-constrained TDHF method to extract the nucleus-nucleus potentials and the excitation energy in each fragment. Results: Nucleus-nucleus potentials, nuclear contact times, masses and charges of the fragments, as well as their kinetic and excitation energies strongly depend on the orientation of the prolate 249Bk nucleus. Long contact times associated with fusion are observed in collisions of both projectiles with the side of the 249Bk nucleus, but not on collisions with its tip. The energy and impact parameter dependencies of the fragment properties, as well as their mass-angle and mass-total kinetic energy correlations are investigated. Conclusions: Entrance channel reaction dynamics are similar with both 48Ca and 50Ti projectiles. Both are expected to lead to the formation of a compound nucleus by fusion if they have enough energy to get in contact with the side of the 249Bk target.

  5. First Measurements of Deuterium-Tritium and Deuterium-Deuterium Fusion Reaction Yields in Ignition-Scalable Direct-Drive Implosions

    NASA Astrophysics Data System (ADS)

    Forrest, C. J.; Radha, P. B.; Knauer, J. P.; Glebov, V. Yu.; Goncharov, V. N.; Regan, S. P.; Rosenberg, M. J.; Sangster, T. C.; Shmayda, W. T.; Stoeckl, C.; Gatu Johnson, M.

    2017-03-01

    The deuterium-tritium (D-T) and deuterium-deuterium neutron yield ratio in cryogenic inertial confinement fusion (ICF) experiments is used to examine multifluid effects, traditionally not included in ICF modeling. This ratio has been measured for ignition-scalable direct-drive cryogenic DT implosions at the Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997), 10.1016/S0030-4018(96)00325-2] using a high-dynamic-range neutron time-of-flight spectrometer. The experimentally inferred yield ratio is consistent with both the calculated values of the nuclear reaction rates and the measured preshot target-fuel composition. These observations indicate that the physical mechanisms that have been proposed to alter the fuel composition, such as species separation of the hydrogen isotopes [D. T. Casey et al., Phys. Rev. Lett. 108, 075002 (2012), 10.1103/PhysRevLett.108.075002], are not significant during the period of peak neutron production in ignition-scalable cryogenic direct-drive DT implosions.

  6. High-precision (p,t) reaction to determine {sup 25}Al(p,{gamma}){sup 26}Si reaction rates

    SciTech Connect

    Matic, A.; Berg, A. M. van den; Harakeh, M. N.; Woertche, H. J.; Berg, G. P. A.; Couder, M.; Goerres, J.; LeBlanc, P.; O'Brien, S.; Wiescher, M.; Fujita, K.; Hatanaka, K.; Sakemi, Y.; Shimizu, Y.; Tameshige, Y.; Tamii, A.; Yosoi, M.; Adachi, T.; Fujita, Y.; Shimbara, Y.

    2010-08-15

    Since the identification of ongoing {sup 26}Al production in the universe, the reaction sequence {sup 24}Mg(p,{gamma}){sup 25}Al({beta}{sup +{nu}}){sup 25}Mg(p,{gamma}){sup 26}Al has been studied intensively. At temperatures where the radiative capture on {sup 25}Al (t{sub 1/2}=7.2 s) becomes faster than the {beta}{sup +} decay, the production of {sup 26}Al can be reduced due to the depletion of {sup 25}Al. To determine the resonances relevant for the {sup 25}Al(p,{gamma}){sup 26}Si bypass reaction, we measured the {sup 28}Si(p,t){sup 26}Si reaction with high-energy precision using the Grand Raiden spectrometer at the Research Center for Nuclear Physics, Osaka. Several new energy levels were found above the p threshold and for known states excitation energies were determined with smaller uncertainties. The calculated stellar rates of the bypass reaction agree well with previous results, suggesting that these rates are well established.

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

    PubMed

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

    2012-10-28

    Cumulative reaction probabilities (CRPs) at various total angular momenta have been calculated for the barrierless reaction S((1)D) + H(2) → 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)] as well as on the recent PES developed by Song et al. [J. Phys. Chem. A 113, 9213 (2009)]. 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((1)D).

  8. Effect of vibrational excitation of the reagents on the rates of chemical reactions. The reaction Li + H/sub 2/

    SciTech Connect

    Grigor'eva, T.M.; Levitskii, A.A.; Polak, L.S.

    1986-09-01

    The classical trajectories method was used to calculate the smoothed cross sections and rate constants for the exchange reaction Li(/sub 2/S) + H/sup 2/ (X/sup 2/..sigma../sub g/ /sup +/, v) ..-->.. LiH (X/sup 1/..sigma../sup +/) + H(/sup 2/S) and dissociation reaction Li (/sup 2/S) + H/sub 2/ (X/sup 1/..sigma../sub g/ /sup +/, v) ..-->.. Li(/sup 2/S) + H(/sup 2/S) + H(/sup 2/S) for different vibrational levels v of the hydrogen molecule. The smoothed cross sections were approximated by the expression epsilon about theta(..beta..E/sub +/ + ..gamma..E/sub v/ -epsilon epsilon), where epsilon is the reaction threshold, theta (x) a Heaviside function, and ..beta.. and ..gamma.. represent the degrees of participation of translational (E/sub t/ ) and vibrational (E/sub v/ ) energy in the reaction. For the exchange reaction the values ..beta.. = 0.3, ..gamma.. = 1.0 were obtained; consequently in this case vibrational energy is more efficient than translational energy in overcoming the activation barrier.

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

    SciTech Connect

    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

    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.

  10. Design of experiments for zeroth and first-order reaction rates.

    PubMed

    Amo-Salas, Mariano; Martín-Martín, Raúl; Rodríguez-Aragón, Licesio J

    2014-09-01

    This work presents optimum designs for reaction rates experiments. In these experiments, time at which observations are to be made and temperatures at which reactions are to be run need to be designed. Observations are performed along time under isothermal conditions. Each experiment needs a fixed temperature and so the reaction can be measured at the designed times. For these observations under isothermal conditions over the same reaction a correlation structure has been considered. D-optimum designs are the aim of our work for zeroth and first-order reaction rates. Temperatures for the isothermal experiments and observation times, to obtain the most accurate estimates of the unknown parameters, are provided in these designs. D-optimum designs for a single observation in each isothermal experiment or for several correlated observations have been obtained. Robustness of the optimum designs for ranges of the correlation parameter and comparisons of the information gathered by different designs are also shown.

  11. Sensitivity of p-Nuclei to (n,g) Reaction Rates

    NASA Astrophysics Data System (ADS)

    Scriven, Dustin; Naqvi, Farheen; Spyrou, Artemis; Simon, Anna; Mayer, Brad

    2015-10-01

    The astrophysical p-process, which is responsible for the creation of the proton-rich p-nuclei, is still not well understood. A sensitivity study of p-nuclei abundances to (n, γ) and (γ,n) reaction rates was conducted at the National Superconducting Cyclotron Laboratory using a nuclear reaction network created at Clemson University. This network simulates the explosive shock front of a Type II supernova passing through the oxygen/neon layer of a 25 M⊙ star. Reaction rates of many (n, γ) reactions and their inverses were increased and decreased by a factor of 3 and the effects were observed. Probing the sensitivity of p-nuclei abundances aids in pointing out reactions important to the p-process. In turn, this information can be used as a tool to drive experimental research, helping to decrease uncertainties and increase the robustness of p-process and other stellar models.

  12. Effect of soluble P55 tumour-necrosis factor binding fusion protein on the local Shwartzman and Arthus reactions.

    PubMed Central

    Norman, K. E.; Williams, T. J.; Feldmann, M.; Rossi, A. G.

    1996-01-01

    1. In this study, the effects of a protein synthesis inhibitor, cycloheximide, and a soluble tumour necrosis factor (TNF) binding/IgG fusion protein, p55-sf2, on the priming and challenge stages of the local Shwartzman reaction (LSR) were assessed and compared with their effects on the acute inflammatory response induced by recombinant human tumour necrosis factor-alpha (rhTNF), lipopolysaccharide (LPS) and a reversed passive Arthus (RPA) reaction in rabbit skin. 2. The LSR was induced in skin by giving an intradermal (i.d.) priming injection of LPS followed by two i.v. challenge injections 20 h and 22 h later. Accumulation of 51-Cr-labelled red blood cells and [125I]-albumin were measured at 24 h as markers of haemorrhage and oedema formation, respectively. 3. The RPA reaction was induced in the rabbit by giving i.d. injections of Arthus anti-serum (anti-bovine-gamma-globulin, BGG) followed 5 min later by an i.v. injection of the antigen (BGG). Oedema formation and the accumulation of 111In-labelled neutrophils produced in the RPA reaction and in response to i.d. injection of rhTNF and LPS were measured over the 4 h period after inducing the responses. 4. A single local injection of cycloheximide (10 micrograms/site) did not inhibit neutrophil accumulation or oedema formation produced by 100% Arthus anti-sera. Although LPS injected i.d. induced a marked dose-dependent neutrophil accumulation, there was little associated plasma leakage. Cycloheximide (10 micrograms/site) did not significantly inhibit the neutrophil accumulation induced by LPS (0.1 microgram/site). In the LSR, priming i.d. injections of LPS caused a dose-dependent increase in haemorrhage and plasma leakage at skin sites after challenge with LPS (two injections of 100 micrograms, i.v.). Co-injection of a single dose of cycloheximide (10 micrograms/site) with LPS (30 micrograms/site) caused a marked reduction in the amount of haemorrhage. Local cycloheximide (10 micrograms/site) administered

  13. Pore-Scale Process Coupling and Effective Surface Reaction Rates in Heterogeneous Subsurface Materials

    SciTech Connect

    Liu, Chongxuan; Liu, Yuanyuan; Kerisit, Sebastien N.; Zachara, John M.

    2015-09-01

    This manuscript provides a review of pore-scale researches in literature including experimental and numerical approaches, and scale-dependent behavior of geochemical and biogeochemical reaction rates in heterogeneous porous media. A mathematical equation that can be used to predict the scale-dependent behavior of geochemical reaction rates in heterogeneous porous media has been derived. The derived effective rate expression explicitly links the effective reaction rate constant to the intrinsic rate constant, and to the pore-scale variations in reactant concentrations in porous media. Molecular simulations to calculate the intrinsic rate constants were provided. A few examples of pore-scale simulations were used to demonstrate the application of the equation to calculate effective rate constants in heterogeneous materials. The results indicate that the deviation of effective rate constant from the intrinsic rate in heterogeneous porous media is caused by the pore-scale distributions of reactants and their correlation, which are affected by the pore-scale coupling of reactions and transport.

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

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

    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.

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

    PubMed

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

    2012-06-07

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

  16. New determination of 12C(α,γ)16O reaction rate

    NASA Astrophysics Data System (ADS)

    Oulebsir, N.

    2015-12-01

    The reaction 12C(α,γ)16O was investigated through the direct α-transfer reaction (7Li,t) at 28 and 34 MeV incident energies. We determined the reduced α-widths of the sub-threshold 2+ and 1- states of 16O from the DWBA analysis of the transfer reaction 12C(7Li,t)16O performed at two incident energies. The obtained result for the 2+ and 1- sub-threshold resonances as introduced in the R-matrix fitting of radiative capture and elastic-scattering data to determine the E2 and E1 S-factor from 0.01MeV to 4.2MeV in the center-of-mass energy. After determining the astrophysic factor of 12C(α,γ)16O S(E) with Pierre Descouvement code, I determined numerically the new reaction rate of this reaction at a different stellar temperature (0.06 Gk-2 GK). The 12C(α,γ)16O reaction rate at T9 = 0.2 is [7.21-2.25+2.15] × 10-15 cm3 s-1 mol-1. Some comparisons and discussions about our new 12C(α,γ)16O reaction rate are presented. The agreements of the reaction rate below T9 = 2 between our results and with those proposed by NACRE indicate that our results are reliable, and they could be included in the astrophysical reaction rate network.

  17. STARLIB: A Next-generation Reaction-rate Library for Nuclear Astrophysics

    NASA Astrophysics Data System (ADS)

    Sallaska, A. L.; Iliadis, C.; Champange, A. E.; Goriely, S.; Starrfield, S.; Timmes, F. X.

    2013-07-01

    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, γ), (p, α), (α, 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.

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

    SciTech Connect

    Sallaska, A. L.; Iliadis, C.; Champange, A. E.; Goriely, S.; Starrfield, S.; Timmes, F. X.

    2013-07-15

    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.

  19. Reaction rate and composition dependence of the stability of thermonuclear burning on accreting neutron stars

    SciTech Connect

    Keek, L.; Cyburt, R. H.; Heger, A.

    2014-06-01

    The stability of thermonuclear burning of hydrogen and helium accreted onto neutron stars is strongly dependent on the mass accretion rate. The burning behavior is observed to change from Type I X-ray bursts to stable burning, with oscillatory burning occurring at the transition. Simulations predict the transition at a 10 times higher mass accretion rate than observed. Using numerical models we investigate how the transition depends on the hydrogen, helium, and CNO mass fractions of the accreted material, as well as on the nuclear reaction rates of 3α and the hot-CNO breakout reactions {sup 15}O(α, γ){sup 19}Ne and {sup 18}Ne(α, p){sup 21}Na. For a lower hydrogen content the transition is at higher accretion rates. Furthermore, most experimentally allowed reaction rate variations change the transition accretion rate by at most 10%. A factor 10 decrease of the {sup 15}O(α, γ){sup 19}Ne rate, however, produces an increase of the transition accretion rate of 35%. None of our models reproduce the transition at the observed rate, and depending on the true {sup 15}O(α, γ){sup 19}Ne reaction rate, the actual discrepancy may be substantially larger. We find that the width of the interval of accretion rates with marginally stable burning depends strongly on both composition and reaction rates. Furthermore, close to the stability transition, our models predict that X-ray bursts have extended tails where freshly accreted fuel prolongs nuclear burning.

  20. Fusion measurements in light and medium mass heavy-ion reactions. Progress report, June 1, 1980-May 31, 1981

    SciTech Connect

    Prosser, F.W.

    1981-01-01

    The data obtained for fusion residues from the /sup 16/ /sup 18/O + /sup 24/ /sup 26/Mg systems have been analyzed and are being compared to each other and to predictions from the fusion-evaporation code CASCADE. Analysis of data obtained for a small step excitation curve for the /sup 16/O + /sup 24/Mg system has been started to determine the possible presence of structure in the fusion cross section. Additional data for the fusion cross sections of these systems have been obtained at energies from 100 to 140 MeV at the ATLAS facility and are being analyzed. Initial measurements of the fusion-fission cross sections for /sup 58/Ni beams, at energies up to 320 MeV on targets from /sup 116/Sn to /sup 170/Yb have been made. Analysis is in progress and additional experiments are planned. A collaboration is planned at Notre Dame for experiments to determine the entry line for fusion in the /sup 12/C + /sup 16/O system, both for the interest in this system and for preparation for additional experiments at higher energies at Michigan State when the new facility there becomes available. These experiments should lead to information about the importance of incomplete fusion in this system. Experiments to test the limitation on fusion cross sections predicted by the rotating liquid drop model are planned as higher energies become available at ATLAS and MSU.

  1. Second generation fusion neutron time-of-flight spectrometer at optimized rate for fully digital data acquisition

    SciTech Connect

    Zhang, X. E-mail: jnke1@icloud.com Fan, T.; Yuan, X.; Xie, X.; Chen, Z.; Källne, J.; Gorini, G.; Nocente, M.

    2014-04-15

    The progress on high-rate event recording of data is taken as starting point to revisit the design of fusion neutron spectrometers based on the TOF (time-of-flight) technique. The study performed was aimed at how such instruments for optimized rate (TOFOR) can be further developed to enhance the plasma diagnostic capabilities based on measurement of the 2.5 MeV dd neutron emission from D plasmas, especially the weak spectral components that depend on discrimination of extraneous events. This paper describes a design (TOFOR II) adapted for use with digital wave form recording of all detector pulses providing information on both amplitude (pulse height) and timing. The results of simulations are presented and the performance enhancement is assessed in comparison to the present.

  2. Positively charged amino acids at the SNAP-25 C terminus determine fusion rates, fusion pore properties, and energetics of tight SNARE complex zippering.

    PubMed

    Fang, Qinghua; Zhao, Ying; Herbst, Adam Drew; Kim, Brian N; Lindau, Manfred

    2015-02-18

    SNAP-25 is a Q-SNARE protein mediating exocytosis of neurosecretory vesicles including chromaffin granules. Previous results with a SNAP-25 construct lacking the nine C terminal residues (SNAP-25Δ9) showed changed fusion pore properties (Fang et al., 2008), suggesting a model for fusion pore mechanics that couple C terminal zipping of the SNARE complex to the opening of the fusion pore. The deleted fragment contains the positively charged residues R198 and K201, adjacent to layers 7 and 8 of the SNARE complex. To determine how fusion pore conductance and dynamics depend on these residues, single exocytotic events in bovine chromaffin cells expressing R198Q, R198E, K201Q, or K201E mutants were investigated by carbon fiber amperometry and cell-attached patch capacitance measurements. Coarse grain molecular dynamics simulations revealed spontaneous transitions between a loose and tightly zippered state at the SNARE complex C terminus. The SNAP-25 K201Q mutant showed no changes compared with SNAP-25 wild-type. However, K201E, R198Q, and R198E displayed reduced release frequencies, slower release kinetics, and prolonged fusion pore duration that were correlated with reduced probability to engage in the tightly zippered state. The results show that the positively charged amino acids at the SNAP-25 C terminus promote tight SNARE complex zippering and are required for high release frequency and rapid release in individual fusion events.

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

    DOEpatents

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

    2003-09-09

    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.

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

    DOEpatents

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

    2006-05-16

    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.

  5. Evolutionary implications of the new triple-α nuclear reaction rate for low mass stars

    NASA Astrophysics Data System (ADS)

    Dotter, A.; Paxton, B.

    2009-12-01

    Context: Ogata et al. (2009, Progr. Theor. Phys., 122, 1055) presented a theoretical determination of the ^4He(αα,γ)12C, or triple-α, 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-α reaction rate in low mass stars and compare the results with those obtained using the NACRE rate. Methods: The triple-α reaction rates are compared by following the evolution of stellar models at 1 and 1.5 M⊙ with Z = 0.0002 and Z = 0.02. Results: Results show that the OKK rate has severe consequences for the late stages of stellar evolution in low mass stars. Most notable is the shortening-or disappearance-of the red giant phase. Conclusions: The OKK triple-α reaction rate is incompatible with observations of extended red giant branches and He burning stars in old stellar systems.

  6. Calcium dependence of neurotransmitter release and rate of spontaneous vesicle fusions are altered in Drosophila synaptotagmin mutants.

    PubMed Central

    Littleton, J T; Stern, M; Perin, M; Bellen, H J

    1994-01-01

    Since the demonstration that Ca2+ influx into the presynaptic terminal is essential for neurotransmitter release, there has been much speculation about the Ca2+ receptor responsible for initiating exocytosis. Numerous experiments have shown that the protein, or protein complex, binds multiple Ca2+ ions, resides near the site of Ca2+ influx, and has a relatively low affinity for Ca2+. Synaptotagmin is an integral membrane protein of synaptic vesicles that contains two copies of a domain known to be involved in Ca(2+)-dependent membrane interactions. Synaptotagmin has been shown to bind Ca2+ in vitro with a relatively low affinity. In addition, synaptotagmin has been shown to bind indirectly to Ca2+ channels, positioning the protein close to the site of Ca2+ influx. Recently, a negative regulatory role for synaptotagmin has been proposed, in which it functions as a clamp to prevent fusion of synaptic vesicles with the presynaptic membrane. Release of the clamp would allow exocytosis. Here we present genetic and electrophysiological evidence that synaptotagmin forms a multimeric complex that can function as a clamp in vivo. However, upon nerve stimulation and Ca2+ influx, all synaptotagmin mutations dramatically decrease the ability of Ca2+ to promote release, suggesting that synaptotagmin probably plays a key role in activation of synaptic vesicle fusion. This activity cannot simply be attributed to the removal of a barrier to secretion, as we can electrophysiologically separate the increase in rate of spontaneous vesicle fusion from the decrease in evoked response. We also find that some syt mutations, including those that lack the second Ca(2+)-binding domain, decrease the fourth-order dependence of release on Ca2+ by approximately half, consistent with the hypothesis that a synaptotagmin complex functions as a Ca2+ receptor for initiating exocytosis. Images PMID:7971978

  7. Field measurement of slow metamorphic reaction rates at temperatures of 500 degrees to 600 degrees C

    PubMed

    Baxter; DePaolo

    2000-05-26

    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 degrees +/- 17 degrees C to 505 degrees +/- 15 degrees C at pressures up to 9.1 kilobars, the inferred bulk fluid-rock exchange rate is 1.3(-0.4)(+1.1) x 10(-7) grams of solid reacted per gram of solid per year, several orders of magnitude lower than laboratory-based estimates. The inferred reaction rate suggests that mineral chemistry may lag the evolving conditions in Earth's crust during mountain building.

  8. Simulation of chemical reaction via particle tracking: Diffusion-limited versus thermodynamic rate-limited regimes

    NASA Astrophysics Data System (ADS)

    Benson, David A.; Meerschaert, Mark M.

    2008-12-01

    Chemical reactions may be simulated without regard to local concentrations by applying simple probabilistic rules of particle interaction and combination. The forward reaction A + B→ C is coded by calculating the probability that any A and B particles will occupy the same volume over some time interval. This becomes a convolution of the location densities of the two particles. The backward reaction is a simple exponential decay of C particles into A and B particles. When the mixing of reactants is not a limiting process, the classical thermodynamic reaction rates are reproduced. When low mixing (as by diffusion) limits the reaction probabilities, the reaction rates drop significantly, including the rate of approach to global equilibrium. At long enough times, the law of mass action is reproduced exactly in the mean, with some irreducible deviation in the local equilibrium saturations (the equilibrium constant divided by the mass action expression) away from unity. The saturation variability is not sensitive to numerical parameters but depends strongly on how far from equilibrium the system is initiated. This is simply due to a relative paucity of particles of some species as the reaction moves far to one side or the other.

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

    NASA Technical Reports Server (NTRS)

    Ehlers, K.; Fegley, B., Jr.; Prinn, R. G.

    1989-01-01

    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.

  10. Chemical Reaction Rate Coefficients from Ring Polymer Molecular Dynamics: Theory and Practical Applications.

    PubMed

    Suleimanov, Yury V; Aoiz, F Javier; Guo, Hua

    2016-11-03

    This Feature Article presents an overview of the current status of ring polymer molecular dynamics (RPMD) rate theory. We first analyze the RPMD approach and its connection to quantum transition-state theory. We then focus on its practical applications to prototypical chemical reactions in the gas phase, which demonstrate how accurate and reliable RPMD is for calculating thermal chemical reaction rate coefficients in multifarious cases. This review serves as an important checkpoint in RPMD rate theory development, which shows that RPMD is shifting from being just one of recent novel ideas to a well-established and validated alternative to conventional techniques for calculating thermal chemical rate coefficients. We also hope it will motivate further applications of RPMD to various chemical reactions.

  11. Chemical Reaction Rate Coefficients from Ring Polymer Molecular Dynamics: Theory and Practical Applications

    DOE PAGES

    Suleimanov, Yury V.; Aoiz, F. Javier; Guo, Hua

    2016-11-03

    This Feature Article presents an overview of the current status of ring polymer molecular dynamics (RPMD) rate theory. We first analyze the RPMD approach and its connection to quantum transition-state theory. We then focus on its practical applications to prototypical chemical reactions in the gas phase, which demonstrate how accurate and reliable RPMD is for calculating thermal chemical reaction rate coefficients in multifarious cases. This review serves as an important checkpoint in RPMD rate theory development, which shows that RPMD is shifting from being just one of recent novel ideas to a well-established and validated alternative to conventional techniques formore » calculating thermal chemical rate coefficients. We also hope it will motivate further applications of RPMD to various chemical reactions.« less

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

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    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.

  14. Rate of mixing controls rate and outcome of autocatalytic processes: theory and microfluidic experiments with chemical reactions and blood coagulation.

    PubMed

    Pompano, Rebecca R; Li, Hung-Wing; Ismagilov, Rustem F

    2008-08-01

    This article demonstrates that the rate of mixing can regulate the rate and outcome of both biological and nonbiological autocatalytic reaction systems that display a threshold response to the concentration of an activator. Plug-based microfluidics was used to control the timing of reactions, the rate of mixing, and surface chemistry in blood clotting and its chemical model. Initiation of clotting of human blood plasma required addition of a critical concentration of thrombin. Clotting could be prevented by rapid mixing when thrombin was added near the critical concentration, and mixing also affected the rate of clotting when thrombin was added at concentrations far above the critical concentration in two clinical clotting assays for human plasma. This phenomenon was modeled by a simple mechanism--local and global competition between the clotting reaction, which autocatalytically produces an activator, and mixing, which removes the activator. Numerical simulations showed that the Damköhler number, which describes this competition, predicts the effects of mixing. Many biological systems are controlled by thresholds, and these results shed light on the dynamics of these systems in the presence of spatial heterogeneities and provide simple guidelines for designing and interpreting experiments with such systems.

  15. Role of Barrier Modification and Inelastic Surface Excitations in Sub-Barrier Fusion of 16 32 S + 40 94 Zr Reaction

    NASA Astrophysics Data System (ADS)

    Gautam, Manjeet Singh; Rajni; Sharma, Manoj K.

    2016-04-01

    The fusion dynamics of 16 32 S + 40 94 Zr reaction at near and sub-barrier energies is investigated within the context of different theoretical approaches. The various theoretical models like one-dimensional Wong formula, ℓ-summed extended Wong formula, the energy-dependent Woods-Saxon potential model (EDWSP model), and coupled channel formulation have been used to address the impacts of nuclear structure degrees of freedom of the colliding pairs. The roles of different Skyrme forces along with Wong formalism are also tested in the analysis of the sub-barrier fusion dynamics of the 16 32 S + 40 94 Zr reaction. The influence of the low-lying surface vibrational states of the collision partners is investigated within the framework of coupled channel calculations performed by the code CCFULL. In the present work, it has been observed that the EDWSP model introduces barrier modification effects somewhat similar to those of the coupled channel approach, as well as those of using different Skyrme forces and hence it reasonably addresses the observed fusion data of 16 32 S + 40 94 Zr reaction in the close vicinity of the Coulomb barrier.

  16. Enhancement of fusion rates due to quantum effects in the particles momentum distribution in nonideal plasma media

    NASA Astrophysics Data System (ADS)

    Fisch, N. J.; Gladush, M. G.; Petrushevich, Y. V.; Quarati, P.; Starostin, A. N.

    2012-06-01

    This study concerns a situation when measurements of the nonresonant cross-section of nuclear reactions appear highly dependent on the environment in which the particles interact. An appealing example discussed in the paper is the interaction of a deuteron beam with a target of deuterated metal Ta. In these experiments, the reaction cross section for d(d, p)t was shown to be orders of magnitude greater than what the conventional model predicts for the low-energy particles. In this paper we take into account the influence of quantum effects due to the Heisenberg uncertainty principle for particles in a non-ideal plasma medium elastically interacting with the medium particles. In order to calculate the nuclear reaction rate in the non-ideal environment we apply both the Monte Carlo technique and approximate analytical calculation of the Feynman diagram using nonrelativistic kinetic Green's functions in the medium which correspond to the generalized energy and momentum distribution functions of interacting particles. We show a possibility to reduce the 12-fold integral corresponding to this diagram to a fivefold integral. This can significantly speed up the computation and control accuracy. Our calculations show that quantum effects significantly influence reaction rates such as p +7Be, 3He +4He, p +7Li, and 12C +12C. The new reaction rates may be much higher than the classical ones for the interior of the Sun and supernova stars. The possibility to observe the theoretical predictions under laboratory conditions is discussed.

  17. A study of 239Pu production rate in a water cooled natural uranium blanket mock-up of a fusion-fission hybrid reactor

    NASA Astrophysics Data System (ADS)

    Feng, Song; Liu, Rong; Lu, Xinxin; Yang, Yiwei; Xu, Kun; Wang, Mei; Zhu, Tonghua; Jiang, Li; Qin, Jianguo; Jiang, Jieqiong; Han, Zijie; Lai, Caifeng; Wen, Zhongwei

    2016-03-01

    The 239Pu production rate is important data in neutronics design for a natural uranium blanket of a fusion-fission hybrid reactor, and the accuracy and reliability should be validated by integral experiments. The distribution of 239Pu production rates in a subcritical natural uranium blanket mock-up was obtained for the first time with a D-T neutron generator by using an activation technique. Natural uranium foils were placed in different spatial locations of the mock-up, the counts of 277.6 keV γ-rays emitted from 239Np generated by 238U capture reaction were measured by an HPGe γ spectrometer, and the self-absorption of natural uranium foils was corrected. The experiment was analyzed using the Super Monte Carlo neutron transport code SuperMC2.0 with recent nuclear data of 238U from the ENDF/B-VII.0, ENDF/B-VII.1, JENDL-4.0u2, JEFF-3.2 and CENDL-3.1 libraries. Calculation results with the JEFF-3.2 library agree with the experimental ones best, and they agree within the experimental uncertainty in general with the average ratios of calculation results to experimental results (C/E) in the range of 0.93 to 1.01.

  18. Site-Specific Polymer Attachment to HR2 Peptide Fusion Inhibitors against HIV-1 Decreases Binding Association Rates and Dissociation Rates Rather Than Binding Affinity.

    PubMed

    Danial, Maarten; Stauffer, Angela N; Wurm, Frederik R; Root, Michael J; Klok, Harm-Anton

    2017-03-15

    A popular strategy for overcoming the limited plasma half-life of peptide heptad repeat 2 (HR2) fusion inhibitors against HIV-1 is conjugation with biocompatible polymers such as poly(ethylene glycol) (PEG). However, despite improved resistance to proteolysis and reduced renal elimination, covalent attachment of polymers often causes a loss in therapeutic potency. In this study, we investigated the molecular origins of the loss in potency upon conjugation of linear, midfunctional, and hyperbranched PEG-like polymers to peptides that inhibit HIV-1-host cell membrane fusion. Fluorescence binding assays revealed that polymer conjugation imparted mass transport limitations that manifested as coexistent slower association and dissociation rates from the gp41 target on HIV-1. Furthermore, reduced association kinetics rather than affinity disruption was responsible for the loss in antiviral potency. Finally, the binding assays indicated that the unmodified HR2-derived peptide demonstrated diffusion-limited binding. The observed high potency of the unmodified peptide in HIV-1 inhibition assays was therefore attributed to rapid peptide conformational changes upon binding to the gp41 prehairpin structure. This study emphasizes that the view in which polymer ligation to therapeutic peptides inadvertently leads to loss in potency due to a loss in binding affinity requires scientific verification on a case-by-case basis and that high peptide potency may be due to rapid target-binding events.

  19. Effective reaction rates in diffusion-limited phosphorylation-dephosphorylation cycles

    NASA Astrophysics Data System (ADS)

    Szymańska, Paulina; Kochańczyk, Marek; Miekisz, Jacek; Lipniacki, Tomasz

    2015-02-01

    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.

  20. Effective reaction rates in diffusion-limited phosphorylation-dephosphorylation cycles.

    PubMed

    Szymańska, Paulina; Kochańczyk, Marek; Miękisz, Jacek; Lipniacki, Tomasz

    2015-02-01

    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.

  1. Thelytokous parthenogenesis in unmated queen honeybees (Apis mellifera capensis): central fusion and high recombination rates.

    PubMed

    Oldroyd, Benjamin P; Allsopp, Michael H; Gloag, Rosalyn S; Lim, Julianne; Jordan, Lyndon A; Beekman, Madeleine

    2008-09-01

    The subspecies of honeybee indigenous to the Cape region of South Africa, Apis mellifera capensis, is unique because a high proportion of unmated workers can lay eggs that develop into females via thelytokous parthenogenesis involving central fusion of meiotic products. This ability allows pseudoclonal lineages of workers to establish, which are presently widespread as reproductive parasites within the honeybee populations of South Africa. Successful long-term propagation of a parthenogen requires the maintenance of heterozygosity at the sex locus, which in honeybees must be heterozygous for the expression of female traits. Thus, in successful lineages of parasitic workers, recombination events are reduced by an order of magnitude relative to meiosis in queens of other honeybee subspecies. Here we show that in unmated A. m. capensis queens treated to induce oviposition, no such reduction in recombination occurs, indicating that thelytoky and reduced recombination are not controlled by the same gene. Our virgin queens were able to lay both arrhenotokous male-producing haploid eggs and thelytokous female-producing diploid eggs at the same time, with evidence that they have some voluntary control over which kind of egg was laid. If so, they are able to influence the kind of second-division meiosis that occurs in their eggs post partum.

  2. A variable reaction rate model for chlorine decay in drinking water due to the reaction with dissolved organic matter.

    PubMed

    Hua, Pei; Vasyukova, Ekaterina; Uhl, Wolfgang

    2015-05-15

    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.

  3. Unbound states of (32)Cl andthe (31)S(p,gamma)(32)Cl reaction rate

    SciTech Connect

    Matos, M.; Blackmon, Jeff C; Linhardt, Laura; Bardayan, Daniel W; Nesaraja, Caroline D; Clark, Jason; Diebel, C.; O'Malley, Patrick; Parker, P.D.

    2011-01-01

    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.

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

    PubMed Central

    Piccini, GiovanniMaria; Alessio, Maristella

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Olbris, Donald J.; Herzfeld, Judith

    2002-10-01

    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 allows the player to roll three dice instead of two) or catalysts (which lower the activation barrier). The value of acceleration derives from the increasing price of fresh chemicals as resources are depleted and waste products accumulate. The player who nets the most money wins the game. The details of the game are presented, with a set of follow-up questions suitable for either a quiz or discussion. Student reaction to the game is also described.

  6. Generalization of the Activated Complex Theory of Reaction Rates. I. Quantum Mechanical Treatment

    DOE R&D Accomplishments Database

    Marcus, R. A.

    1964-01-01

    In its usual form activated complex theory assumes a quasi-equilibrium between reactants and activated complex, a separable reaction coordinate, a Cartesian reaction coordinate, and an absence of interaction of rotation with internal motion in the complex. In the present paper a rate expression is derived without introducing the Cartesian assumption. The expression bears a formal resemblance to the usual one and reduces to it when the added assumptions of the latter are introduced.

  7. Systematic analysis of astrophysical S-factors and thermonuclear reaction rates

    SciTech Connect

    Katsuma, M.

    2008-05-12

    The astrophysical S-factors of the {sup 13}C({alpha},n){sup 16}O, {sup 17}O({alpha},n){sup 20}Ne, {sup 21}Ne({alpha},n){sup 24}Mg and {sup 25}Mg({alpha},n){sup 28}Si reactions are analyzed with DWBA. The gross structures of the experimental data are reproduced by the DWBA calculations. The resulting reaction rates are compared with those in the CF88 and NACRE compilations.

  8. Kinetics of the benzyl + O(3P) reaction: a quantum chemical/statistical reaction rate theory study.

    PubMed

    da Silva, Gabriel; Bozzelli, Joseph W

    2012-12-14

    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 β-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

  9. Simulation study of the influence of PEB reaction rates on resist LER

    NASA Astrophysics Data System (ADS)

    Bhattarai, Suchit; Neureuther, Andrew R.; Naulleau, Patrick P.

    2015-03-01

    A stochastic resist simulator has first been calibrated to experimental results performed on a commercially available EUV resist, and subsequently has been used to study the influence of acid/base quenching rate and the polymer deprotection rate on resist LER for 22 nm half-pitch lines/spaces. Results indicate that larger quenching rates and smaller deprotection rates result in improved LER performance by causing an increase in the dose to size. With nominal quenching rate determined from literature, halving the deprotection rate relative to nominal value reduces the LER by 33%, while the dose to size increases by 2x. With nominal deprotection rate determined from literature, results indicate a low sensitivity of LER to quenching rate. Expected noise at the line edge calculated by using a shot noise model accounting for absorbed photons, acid, and base count, provides a good explanation for the LER trends calculated for several reaction rate scenarios.

  10. Correlation analysis of the progesterone-induced sperm acrosome reaction rate and the fertilisation rate in vitro.

    PubMed

    Jiang, T; Qin, Y; Ye, T; Wang, Y; Pan, J; Zhu, Y; Duan, L; Li, K; Teng, X

    2015-10-01

    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 (15.6 ± 5.88% versus 9.66 ± 5.771%, 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.

  11. An investigation of the reaction kinetics of luciferase and the effect of ionizing radiation on the reaction rate.

    PubMed

    Berovic, Nikolas; Parker, David J; Smith, Michael D

    2009-04-01

    The bioluminescence produced by luciferase, a firefly enzyme, requires three substrates: luciferin, ATP and oxygen. We find that ionizing radiation, in the form of a proton beam from a cyclotron, will eliminate dissolved oxygen prior to any damage to other substrates or to the protein. The dose constant for removal of oxygen is 70 +/- 20 Gy, a much smaller dose than required to cause damage to protein. Removal of oxygen, which is initially in excess, leads to a sigmoidal response of bioluminescence to radiation dose, consistent with a Michaelis-Menten relationship to substrate concentration. When excess oxygen is exhausted, the response becomes exponential. Following the irradiation, bioluminescence recovers due to a slow leak of oxygen into the solution. This may also explain previous observations on the response of bioluminescent bacteria to radiation. We have studied the dependence of the reaction rate on enzyme and substrate concentration and propose a model for the reaction pathway consistent with this data. The light output from unirradiated samples decreases significantly with time due to product inhibition. We observe that this inhibition rate changes dramatically immediately after a sample is exposed to the beam. This sudden change of the inhibition rate is unexplained but shows that enzyme regulatory function responds to ionizing radiation at a dose level less than 0.6 Gy.

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

    NASA Technical Reports Server (NTRS)

    Jaffe, R. L.

    1986-01-01

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

  13. A simple recipe for modeling reaction-rate in flows with turbulent-combustion

    NASA Technical Reports Server (NTRS)

    Girimaji, Sharath S.

    1991-01-01

    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.

  14. Considerations Based on Reaction Rate on Char Gasification Behavior in Two-stage Gasifier for Biomass

    NASA Astrophysics Data System (ADS)

    Taniguchi, Miki; Nishiyama, Akio; Sasauchi, Kenichi; Ito, Yusuke; Akamatsu, Fumiteru

    In order to develop a small-scale gasifier in which biomass can be converted to energy with high efficiency, we planned a gasification process that consists of two parts: pyrolysis part (rotary kiln) and gasification part (downdraft gasifier). We performed fundamental experiments on gasification part and discussed the appropriate conditions such as air supply location, air ratio, air temperature and hearth load. We considered the results by calculating reaction rates of representative reactions on char gasification part and found that water gas reaction is dominant in the reduction area and its behavior gives important information to decide the adequate length of the char layer.

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

    PubMed

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

    2012-11-01

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

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

    NASA Astrophysics Data System (ADS)

    Newton, Joseph; Longland, Richard; Iliadis, Christian

    2009-05-01

    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 to be unreliable for narrow resonances at high stellar temperatures [1]. Our new approach defines the effective thermonuclear energy range (ETER) by using the 8^th, 50^th and 92^nd percentiles of the cumulative distribution of fractional resonant reaction contributions. The ETER is then used to define a reliable temperature for matching experimental rates to Hauser-Feshbach rates. The resulting matching temperature is often well above the previous result using the Gamow peak concept. Our new method should provide more accurate extrapolated rates since Hauser-Feshbach rates are more reliable at higher temperatures. These ideas are applied to 21 (p,γ), (p,α) and (α,γ) reactions on a range of A = 20-40 target nuclei and results will be presented. [0pt] [1] J. R. Newton, C. Iliadis, A. E. Champagne, A. Coc, Y. Parpottas and R. Ugalde, Phys. Rev. C 75, 045801 (2007).

  17. Triple-alpha reaction rate studied with the Faddeev three-body formalism

    SciTech Connect

    Ishikawa, Souichi

    2012-11-12

    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.

  18. Exploring the influence of transfer channels on fusion reactions: The case of 40 Ca + 58,64 Ni

    DOE PAGES

    Bourgin, D.; Courtin, S.; Haas, F.; ...

    2015-01-29

    Fusion cross sections have been measured in the 40Ca + 58Ni and 40Ca + 64Ni systems at beam energies ranging from Elab = 104.75 MeV to 153.5 MeV using the Laboratori Nazionali di Legnaro electrostatic deflector. Distributions of barriers have been extracted from the experimental data. Preliminary coupled channel calculations were performed and hints of effects of neutron transfers on the fusion below the barrier in the 40Ca + 64Ni are discussed.

  19. Effect of Superposition Location of Ultrasonic Fields on Sonochemical Reaction Rate

    NASA Astrophysics Data System (ADS)

    Yasuda, Keiji; Matsuura, Kazumasa

    2013-07-01

    The effect of the superposition location of ultrasonic fields on the sonochemical reaction rate was investigated using a sonochemical reactor with four transducers at 486 kHz. The transducers were attached at the bottom, upper side middle side, and lower side of a vessel. The reaction rate of potassium iodide in aqueous solution was measured. In the cases of the upper and bottom transducers, and the lower and bottom transducers, the synergy effect of sonochemical efficiency was observed. The amount of synergy effect for the upper and bottom transducers increased with increasing electric power.

  20. Modeling of atmospheric OH reaction rates using newly developed variable distance weighted zero order connectivity index

    NASA Astrophysics Data System (ADS)

    Markelj, Jernej; Pompe, Matevž

    2016-04-01

    A new variable distance weighted zero order connectivity index was used for development of structure-activity relationship for modeling reactivity of OH radical with alkanes and non-conjugated alkenes in the atmosphere. The proposed model is based on the assumptions that the total reaction rate can be obtained by summing all partial reaction rates and that all reaction sites are interrelated by influencing each other. The results suggest that these assumptions are justified. The model was compared with the EPA implemented model in the studied application domain and showed superior prediction capabilities. Further, optimized values of the weights that were used in our model permit some insight into mechanisms that govern the reaction OH + alkane/alkene. The most important conclusion is that the branching degree of the forming radical seems to play a major role in site specific reaction rates. Relative qualitative structural interpretation is possible, e.g. allylic site is suggested to be much more reactive than even tertiary sp3 carbon. Novel modeling software MACI, which was developed in our lab and is now available for research purposes, was used for calculations. Various variable topological indices that are again starting to be recognized because of their great potentials in simplicity, fast calculations, very good correlations and structural information, were implemented in the program.

  1. Controlling the rate of organic reactions: rational design of allosteric Diels-Alderase ribozymes

    PubMed Central

    Amontov, Sergey; Jäschke, Andres

    2006-01-01

    Allosteric mechanisms are widely used in nature to control the rates of enzymatic reactions, but little is known about RNA catalysts controlled by these principles. The only natural allosteric ribozyme reported to date catalyzes an RNA cleavage reaction, and so do almost all artificial systems. RNA has, however, been shown to accelerate a much wider range of chemical reactions. Here we report that RNA catalysts for organic reactions can be put under the stringent control of effector molecules by straight-forward rational design. This approach uses known RNA sequences with catalytic and ligand-binding properties, and exploits weakly conserved sequence elements and available structural information to induce the formation of alternative, catalytically inactive structures. The potential and general applicability is demonstrated by the design of three different systems in which the rate of a catalytic carbon–carbon bond forming reaction is positively regulated up to 2100-fold by theophylline, tobramycin and a specific mRNA sequence, respectively. Although smaller in size than a tRNA, all three ribozymes show typical features of allosteric metabolic enzymes, namely high rate acceleration and tight allosteric regulation. Not only do these findings demonstrate RNA's power as a catalyst, but also highlight on RNA's capabilities as signaling components in regulatory networks. PMID:16990253

  2. Controlling the rate of organic reactions: rational design of allosteric Diels-Alderase ribozymes.

    PubMed

    Amontov, Sergey; Jäschke, Andres

    2006-01-01

    Allosteric mechanisms are widely used in nature to control the rates of enzymatic reactions, but little is known about RNA catalysts controlled by these principles. The only natural allosteric ribozyme reported to date catalyzes an RNA cleavage reaction, and so do almost all artificial systems. RNA has, however, been shown to accelerate a much wider range of chemical reactions. Here we report that RNA catalysts for organic reactions can be put under the stringent control of effector molecules by straight-forward rational design. This approach uses known RNA sequences with catalytic and ligand-binding properties, and exploits weakly conserved sequence elements and available structural information to induce the formation of alternative, catalytically inactive structures. The potential and general applicability is demonstrated by the design of three different systems in which the rate of a catalytic carbon-carbon bond forming reaction is positively regulated up to 2100-fold by theophylline, tobramycin and a specific mRNA sequence, respectively. Although smaller in size than a tRNA, all three ribozymes show typical features of allosteric metabolic enzymes, namely high rate acceleration and tight allosteric regulation. Not only do these findings demonstrate RNA's power as a catalyst, but also highlight on RNA's capabilities as signaling components in regulatory networks.

  3. Relative rate studies of the reactions of chlorine atoms with simple alkanes and the chlorinated methanes

    SciTech Connect

    Wingen, L.; Lee, J.J.; Neavyn, R.

    1995-12-01

    The reactions of chlorine atoms with organics are of interest because atomic chlorine is a potential tropospheric oxidant. Relative rate constants for the reaction of pairs of simple alkanes (ethane/propane, ethane/n-butane, and isobutane/n-butane) and the chlorinated methanes (chloromethane, dichloromethane, and chloroform relative to methane) were measured, using the photolysis of Cl{sub 2} as the source of chlorine atoms and following the loss of the organics by GC-FID. The ratios of the relative rate constants were in excellent agreement with the literature except for ethane/n-butane, where our results are approximately 20% lower than recently published values, and for chloroform/methane, where our value is approximately 50% higher than the values recommended by JPL and JPCRD. Our results will be compard to previously published relative rate studies as well as to the results of absolute rate constant studies, and the differences will be discussed.

  4. Distortion of bulk-ion distribution function due to nuclear elastic scattering and its effect on T(d,n){sup 4}He reaction rate coefficient in neutral-beam-injected deuterium-tritium plasmas

    SciTech Connect

    Matsuura, H.; Nakao, Y.

    2007-05-15

    An effect of nuclear elastic scattering on the rate coefficient of fusion reaction between field deuteron and triton in the presence of neutral beam injection heating is studied. Without assuming a Maxwellian for bulk-ion distribution function, the Boltzmann-Fokker-Planck (BFP) equations for field (bulk) deuteron, field (bulk) triton, {alpha}-particle, and beam deuteron are simultaneously solved in an ITER-like deuterium-tritium thermonuclear plasma [R. Aymar, Fusion Eng. Des. 55, 107 (2001)]. The BFP calculation shows that enhancement of the reaction rate coefficient due to knock-on tail formation in fuel-ion distribution functions becomes appreciable, especially in the case of low-density operations.

  5. Scale-Dependent Rates of Uranyl Surface Complexation Reaction in Sediments

    SciTech Connect

    Liu, Chongxuan; Shang, Jianying; Kerisit, Sebastien N.; Zachara, John M.; Zhu, Weihuang

    2013-03-15

    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.

  6. The influence of the sequence of nanoparticles injection to solution on the rate of fibrinogen-thrombin reaction

    NASA Astrophysics Data System (ADS)

    Kirichenko, M. N.; Krivokhiza, S. V.; Chaikov, L. L.; Bulychev, N. A.

    2017-01-01

    The influence of Fe2O3 nanoparticles on the rate of fibrinogen-thrombin reaction is studied. The nanoparticles were obtained in acoustoplasma discharge with cavitation. The sequence of nanoparticles injection appeared to change dramatically the rate and result of enzymatic reaction. In case of nanoparticles injection to fibrinogen before thrombin addition, enzymatic reaction practically stopped at the first stage. The mixing of nanoparticles with thrombin before its addition to fibrinogen leads to acceleration of gel formation in comparison with reaction without nanoparticles. We believe that Fe2O3 nanoparticles can modify the rate of enzymatic reaction, in one case acting as inhibitors of the reaction and as activators in other.

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

    PubMed

    Imoto, Taiji

    2016-12-01

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

  8. Pore and Continuum Scale Study of the Effect of Subgrid Transport Heterogeneity on Redox Reaction Rates

    SciTech Connect

    Liu, Yuanyuan; Liu, Chongxuan; Zhang, Changyong; Yang, Xiaofan; Zachara, John M.

    2015-08-01

    A micromodel system with a pore structure for heterogeneous flow and transport was used to investigate the effect of subgrid transport heterogeneity on redox reaction rates. Hematite reductive dissolution by injecting a reduced form of flavin mononucleotide (FMNH2) at variable flow rates was used as an example to probe the variations of redox reaction rates in different subgrid transport domains. Experiments, pore-scale simulations, and macroscopic modeling were performed to measure and simulate in-situ hematite reduction and to evaluate the scaling behavior of the redox reaction rates from the pore to macroscopic scales. The results indicated that the measured pore-scale rates of hematite reduction were consistent with the predictions from a pore scale reactive transport model. A general trend is that hematite reduction followed reductant transport pathways, starting from the advection-dominated pores toward the interior of diffusion-dominated domains. Two types of diffusion domains were considered in the micromodel: a micropore diffusion domain, which locates inside solid grains or aggregates where reactant transport is limited by diffusion; and a macropore diffusion domain, which locates at wedged, dead-end pore spaces created by the grain-grain contacts. The rate of hematite reduction in the advection-dominated domain was faster than those in the diffusion-controlled domains, and the rate in the macropore diffusion domain was faster than that in the micropore domain. The reduction rates in the advection and macropore diffusion domains increased with increasing flow rate, but were affected by different mechanisms. The rate increase in the advection domain was controlled by the mass action effect as a faster flow supplied more reactants, and the rate increase in the macropore domain was more affected by the rate of mass exchange with the advection domain, which increased with increasing flow rate. The hematite reduction rate in the micropore domain was, however

  9. Upper limit of a tunneling reaction rate for D-+H2 →HD+H-

    NASA Astrophysics Data System (ADS)

    Endres, Eric S.; Lakhamanskaya, Olga; Simpson, Malcolm; Spieler, Steffen; Wester, Roland

    2017-02-01

    The exothermic proton transfer reaction D-+H2→ HD+H- is known to proceed over a barrier of about 0.33 eV. Here we investigate whether this reaction may occur at low temperatures via tunneling through this barrier. The experiments were carried out in a cryogenic 22-pole ion trap, which provides a high sensitivity for slow ion-molecule reactions. Our experiments show no sign of the tunneling reaction with an upper limit to the rate coefficient of 2.6 ×10-18 cm3/s obtained from the decrease of the D- signal and 9 ×10-19 cm3/s from the absence of an increase of H-. Background impurities were identified to be the main limitation of the sensitivity.

  10. Estimating the effective rate of fast chemical reactions with turbulent mixing of reactants

    SciTech Connect

    Vorotilin, V. P. Yanovskii, Yu. G.

    2015-07-15

    On the basis of representation of a turbulent fluid as an aggregation of independent turbulent particles (vortexes), we derive relations for the effective rate of chemical reactions and obtain a closed system of equations describing reactions with turbulent mixing of reactants. A variant of instantaneous reactions is considered that explains the proposed approach simply. In particular, the turbulent mixing events according to this approach are uniquely related to the acts of chemical interaction, which makes it possible to exclude from consideration the mixing of inert impurities–the most difficult point of the theory formulated using classical notions. The obtained system of equations is closed without introducing arbitrarily adopted correlations, by naturally introducing the concept of effective reaction and writing the equations of conservation for both the concentrations of reactants and their volumes.

  11. Study of the ammonia (gas)-sulfuric acid (aerosol) reaction rate

    SciTech Connect

    McMurry, P.H.; Takano, H.; Anderson, G.R.

    1983-06-01

    An experimental study of the reaction rate between monodisperse sulfuric acid aerosols and ammonia gas is described. Reactions took place in a laminar flow reactor at 24/sup 0/C and 6% relative humidity, and reaction products were sampled from the core of the flow so that reaction times were well defined. For the data reported here, the reaction time was 5.0 +/- 0.5 s, ammonia concentrations ranged from 13 to 63 ppb, and particle sizes ranged from 0.03 to 0.2 ..mu..m. The extent of reaction was determined by comparing the hygroscopic and deliquescent properties of the product aerosols with known properties of aerosols consisting of internal mixtures of sulfuric acid and ammonium sulfate. It was found that the average fraction of ammonia-aerosol collisions that resulted in chemical reaction during neutralization decreased from 0.40 +/- 0.10 for 0.058-..mu..m particles to 0.18 +/- 0.03 for 0.10-..mu..m particles. Differential mobility analyzers were used for generating the monodisperse aerosols and also for measuring the hygroscopic and deliquescent properties of the product aerosols.

  12. Investigating rare events with nonequilibrium work measurements. II. Transition and reaction rates.

    PubMed

    Moradi, Mahmoud; Sagui, Celeste; Roland, Christopher

    2014-01-21

    We present a formalism for investigating transition pathways and transition probabilities for rare events in biomolecular systems. The formalism is based on combining Transition Path Theory with the results of nonequilibrium work relations, and shows that the equilibrium and nonequilibrium transition rates are in fact related. Aside from its fundamental importance, this allows for the calculation of relative equilibrium reaction rates with driven nonequilibrium simulations such as Steered Molecular Dynamics. The workings of the formalism are illustrated with a few typical numerical examples.

  13. Biochemistry on a leash: Confinement as a regulatory mechanism for bimolecular reaction rates

    NASA Astrophysics Data System (ADS)

    Reeves, Daniel; Cheveralls, Keith; Kondev, Jane

    2009-03-01

    We describe two mechanisms by which confinement regulates diffusion-limited bimolecular reaction rates. The first mechanism, illustrated by the actin capping protein formin, uses a flexible polymer to tether ligand binding sites, which serve as intermediaries, to the reactive site. The second mechanism uses a potential (e.g. hard wall potential), to constrain the motion of a ligand receptor within a confining volume. We analyze both mechanisms theoretically, using a combination of analytic and numerical techniques, to obtain the steady state binding kinetics. We explore how the reaction rates are regulated by parameters of the model such as the length of the polymer tether, and use our findings to explain the key features of the formin system. Finally, we suggest other systems, both synthetic and biological, in which these mechanisms for regulating bimolecular reactions might be at play.

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

  17. SENSMG: First-Order Sensitivities of Neutron Reaction Rates, Reaction-Rate Ratios, Leakage, keff, and α Using PARTISN

    SciTech Connect

    Favorite, Jeffrey A.

    2016-11-21

    SENSMG is a tool for computing first-order sensitivities of neutron reaction rates, reaction-rate ratios, leakage, keff, and α using the PARTISN multigroup discrete-ordinates code. SENSMG computes sensitivities to all of the transport cross sections and data (total, fission, nu, chi, and all scattering moments), two edit cross sections (absorption and capture), and the density for every isotope and energy group. It also computes sensitivities to the mass density for every material and derivatives with respect to all interface locations. The tool can be used for one-dimensional spherical (r) and two-dimensional cylindrical (r-z) geometries. The tool can be used for fixed-source and eigenvalue problems. The tool implements Generalized Perturbation Theory (GPT) as discussed by Williams and Stacey. Section II of this report describes the theory behind adjoint-based sensitivities, gives the equations that SENSMG solves, and defines the sensitivities that are output. Section III describes the user interface, including the input file and command line options. Section IV describes the output. Section V gives some notes about the coding that may be of interest. Section VI discusses verification, which is ongoing. Section VII lists needs and ideas for future work. Appendix A lists all of the input files whose results are presented in Sec. VI.

  18. Laser fusion

    SciTech Connect

    Smit, W.A.; Boskma, P.

    1980-12-01

    Unrestricted laser fusion offers nations an opportunity to circumvent arms control agreements and develop thermonuclear weapons. Early laser weapons research sought a clean radiation-free bomb to replace the fission bomb, but this was deceptive because a fission bomb was needed to trigger the fusion reaction and additional radioactivity was induced by generating fast neutrons. As laser-implosion experiments focused on weapons physics, simulating weapons effects, and applications for new weapons, the military interest shifted from developing a laser-ignited hydrogen bomb to more sophisticated weapons and civilian applications for power generation. Civilian and military research now overlap, making it possible for several countries to continue weapons activities and permitting proliferation of nuclear weapons. These countries are reluctant to include inertial confinement fusion research in the Non-Proliferation Treaty. 16 references. (DCK)

  19. Consistency between kinetics and thermodynamics: general scaling conditions for reaction rates of nonlinear chemical systems without constraints far from equilibrium.

    PubMed

    Vlad, Marcel O; Popa, Vlad T; Ross, John

    2011-02-03

    We examine the problem of consistency between the kinetic and thermodynamic descriptions of reaction networks. We focus on reaction networks with linearly dependent (but generally kinetically independent) reactions for which only some of the stoichiometric vectors attached to the different reactions are linearly independent. We show that for elementary reactions without constraints preventing the system from approaching equilibrium there are general scaling relations for nonequilibrium rates, one for each linearly dependent reaction. These scaling relations express the ratios of the forward and backward rates of the linearly dependent reactions in terms of products of the ratios of the forward and backward rates of the linearly independent reactions raised to different scaling powers; the scaling powers are elements of the transformation matrix, which relates the linearly dependent stoichiometric vectors to the linearly independent stoichiometric vectors. These relations are valid for any network of elementary reactions without constraints, linear or nonlinear kinetics, far from equilibrium or close to equilibrium. We show that similar scaling relations for the reaction routes exist for networks of nonelementary reactions described by the Horiuti-Temkin theory of reaction routes where the linear dependence of the mechanistic (elementary) reactions is transferred to the overall (route) reactions. However, in this case, the scaling conditions are valid only at the steady state. General relationships between reaction rates of the two levels of description are presented. These relationships are illustrated for a specific complex reaction: radical chlorination of ethylene.

  20. Reaction Rate Acceleration and Tg Depression of Polycyanurate Under Nanopore Confinement

    NASA Astrophysics Data System (ADS)

    Lopez, Evelyn; Simon, Sindee L.

    2015-03-01

    Material properties such as Tg and the reaction kinetics are known to deviate from the bulk when subjected to nano-sized confinement. Previous work from our laboratory on the trimerization of cyanate esters found that the reaction kinetics were faster for a monofunctional reactant compared to a difunctional monomer, whereas the Tg depression was greater for the crosslinked product of the latter compared to the low molecular weight trimer of the former. The origin of the changes in nanoconfined reaction rates differs from those that govern changes in the Tg. The research objective is to further explore the effect that confinement has on reaction kinetics and Tg using a mixture consisting of mono- and di- cyanate ester monomers. The product is an uncrosslinked polycyanurate with Mn = 5240 g/mol and PDI = 1.78. The confinement mediums are controlled pore glasses with diameters ranging from 8.1 to 111.1 nm. The nanopore-confined material was synthesized in-situ and the reaction kinetics are followed by DSC; after the reaction, the Tg values of the nanoconfined polymer where also measured by DSC. An acceleration factor of 13 and a Tg depression of 38 °C are observed for the material confined in the smallest 8.1 nm-diameter pores. The Tg depression is between those of the trimer and network previously studied, while the acceleration of the reaction rate is lower. Our results are consistent with the reaction acceleration arising from packing effects at the pore wall and the Tg depression arising from intrinsic size effects.

  1. Measurement of proton transfer reaction rates in a microwave cavity discharge flowing afterglow

    NASA Astrophysics Data System (ADS)

    Brooke, George M., IV

    The reaction rate coefficients between the hydronium ion and the molecules ethene (C2H4), propene (C 3H6), 1-butene (C4H8) and hydrogen sulfide (H2S) were measured at 296 K. The measured reaction rates were compared to collision rates calculated using average dipole orientation (ADO) theory. Reaction efficiency depends primarily upon the proton affinity of the molecules. All the measurements were obtained using the newly developed microwave cavity discharge flowing afterglow (MCD-FA) apparatus. This device uses an Asmussen-type microwave cavity discharge ion source that is spatially separated from the flow tube, eliminating many of the problems inherent with the original FA devices. In addition to measuring reaction rate coefficients, the MCD-FA was shown to be an effective tool for measuring trace compounds in atmospheric air. This method has many advantages over current detection techniques since compounds can be detected in almost real time, large mass ranges can be scanned quickly, and repeated calibration is not required. Preliminary measurements were made of car exhaust and exhaled alveolar air. Car exhaust showed the presence of numerous hydrocarbons, such as butene, benzene and toluene while the exhaled alveolar air showed the presence of various volatile organic compounds such as methanol and acetone.

  2. Relative Reaction Rates of Sulfamic Acid and Hydroxylamine with Nitric Acid

    SciTech Connect

    Karraker, D.G.

    2001-03-28

    This report describes a study of comparative reaction rates where the reductant is in excess, as in the 1B bank in the Purex process. The results of this work apply to planned plant tests to partially substitute HAN for the ferrous sulfamate reductant in the Purex 1B bank.

  3. Probing the Rate-Determining Step of the Claisen-Schmidt Condensation by Competition Reactions

    ERIC Educational Resources Information Center

    Mak, Kendrew K. W.; Chan, Wing-Fat; Lung, Ka-Ying; Lam, Wai-Yee; Ng, Weng-Cheong; Lee, Siu-Fung

    2007-01-01

    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…

  4. Should thermostatted ring polymer molecular dynamics be used to calculate thermal reaction rates?

    SciTech Connect

    Hele, Timothy J. H.; Suleimanov, Yury V.

    2015-08-21

    We apply Thermostatted Ring Polymer Molecular Dynamics (TRPMD), a recently proposed approximate quantum dynamics method, to the computation of thermal reaction rates. Its short-time transition-state theory limit is identical to rigorous quantum transition-state theory, and we find that its long-time limit is independent of the location of the dividing surface. TRPMD rate theory is then applied to one-dimensional model systems, the atom-diatom bimolecular reactions H + H{sub 2}, D + MuH, and F + H{sub 2}, and the prototypical polyatomic reaction H + CH{sub 4}. Above the crossover temperature, the TRPMD rate is virtually invariant to the strength of the friction applied to the internal ring-polymer normal modes, and beneath the crossover temperature the TRPMD rate generally decreases with increasing friction, in agreement with the predictions of Kramers theory. We therefore find that TRPMD is approximately equal to, or less accurate than, ring polymer molecular dynamics for symmetric reactions, and for certain asymmetric systems and friction parameters closer to the quantum result, providing a basis for further assessment of the accuracy of this method.

  5. Generalization of the Activated Complex Theory of Reaction Rates. II. Classical Mechanical Treatment

    DOE R&D Accomplishments Database

    Marcus, R. A.

    1964-01-01

    In its usual classical form activated complex theory assumes a particular expression for the kinetic energy of the reacting system -- one associated with a rectilinear motion along the reaction coordinate. The derivation of the rate expression given in the present paper is based on the general kinetic energy expression.

  6. The Transport and Fate of Helium in Nanostructured Ferritic Alloys at Fusion Relevant He/DPA Ratios and DPA Rates

    SciTech Connect

    Yamamoto, Takuya; Odette, George R.; Miao, Pifeng; Hoelzer, D. T.; Bentley, James; Hashimoto, N.; Tanigawa, Hiroyasu; Kurtz, Richard J.

    2007-08-01

    A novel in-situ 59Ni(n,α) reaction He-implanter technique is described, that was used to characterize the effect of the He/dpa ratio on microstructural evolution and changes in the flow properties of various materials at fusion relevant conditions. Irradiations in the High Flux Isotope reactor (HFIR) resulted in α-implantation from thin 1 to 5 µm NiAl coatings on TEM discs producing a uniform He concentration of 5 to 50 appm He/dpa to a depth of 5 to 8 μm. Initial post-irradiation TEM observations of MA957 irradiated to 9 dpa and 380 appm He at 500 ºC provide strong evidence for the existence of high density of small ≤ 1 nm size bubbles trapped on nano-scale YTiO clusters. In contrast, similar irradiations of Eurofer 97, described in a companion paper, produce a lower number density of larger cavities, which may be a mixture of bubbles and voids.

  7. A QSAR for the hydroxyl radical reaction rate constant: validation, domain of application, and prediction

    NASA Astrophysics Data System (ADS)

    Öberg, Tomas

    A large number of anthropogenic organic chemicals are emitted into the troposphere. Reactions with the hydroxyl radical are a dominant removal pathway for most organic compounds, but experimentally determined gas-phase reaction rate constants are only available for about 750 compounds. The lack of experimental data increases the importance of applying quantitative structure-activity relationships (QSAR) to evaluate and predict reactivities. It is generally acknowledged that these empirical relationships are valid only within the same domain for which they were developed. However, model validation is sometimes neglected and the application domain is not always well defined. The purpose of this paper is to outline how validation and domain definition can facilitate the modeling and prediction of the hydroxyl radical reaction rates for a large database. A substantial number of theoretical descriptors (867) were generated from 2D molecular structures for compounds present in the Syracuse Research Corporation's PhysProp Database. A QSAR model was developed for the hydroxyl radical reaction rate constant using a projection-based regression technique, partial least squares regression (PLSR). The PLSR model was subsequently validated with an external test set. The main factors of variation could be attributed to two reaction pathways, hydrogen atom abstraction and addition to double bonds or aromatic systems. A set of 17 293 compounds, drawn from the PhysProp Database, was projected onto the PLSR model and 74% were inside the applicability domain. The predicted hydroxyl reaction rates for 25% of these compounds were slow or negligible, with atmospheric half-lives in the range from days to years. Finally, the list of persistent organic compounds was matched against the OECD list of high production volume chemicals (HPVC). Together with the experimental data, nearly three hundred compounds were identified as both persistent and in high volume production.

  8. High neurological complication rates for extreme lateral lumbar interbody fusion and related techniques: A review of safety concerns

    PubMed Central

    Epstein, Nancy E.

    2016-01-01

    Background: There are frequent reports of lumbosacral plexus and other neurological injuries occurring with extreme lateral interbody fusions (XLIF) and other related lateral lumbar techniques. Methods: This review focuses on the new neurological deficits (e.g. lumbosacral plexus, root injuries) that occur following minimally invasive surgery (MIS) XLIF and other related lateral lumbar techniques. Results: A review of multiple articles revealed the following ranges of new postoperative neurological complications for XLIF procedures: plexus injuries 13.28%; sensory deficits 0–75% (permanent in 62.5%); motor deficits 0.7–33.6%; anterior thigh pain 12.5–25%. Of interest, in a study by Lykissas et al., the frequency of long-term neural injury following lateral lumber interbody fusion (LLIF) with BMP-2 (72 patients) was much higher than for LLIF performed with autograft/allograft (72 patients). The addition of bone morphogenetic protein led to persistent sensory deficits in 29 vs. 20 without BMP; persistent motor deficits in 35 with vs. 17 without BMP; and persistent anterior thigh/groin pain in 8 with vs. 0 without BMP. They should also have noted the unacceptably high incidence of neural injury occurring with LLIF alone without BMP. Conclusion: This review highlights the high risk of neural injury (up to 75% for sensory, 33.6% for motor, and an overall plexus injury rate of 13.28%) utilizing the XLIF and other similar lateral lumbar approaches. With such extensive neurological injuries, is the XLIF really safe, and should it still be performed? PMID:27843679

  9. Investigation of complete and incomplete fusion dynamics of {sup 20}Ne induced reactions at energies above the Coulomb barrier

    SciTech Connect

    Singh, D.; Ali, R.; Kumar, Harish; Ansari, M. Afzal; Rashid, M. H.; Guin, R.

    2014-08-14

    Experiment has been performed to explore the complete and incomplete fusion dynamics in heavy ion collisions using stacked foil activation technique. The measurement of excitation functions of the evaporation residues produced in the {sup 20}Ne+{sup 165}Ho system at projectile energies ranges ≈ 4-8 MeV/nucleon have been done. Measured cumulative and direct cross-sections have been compared with the theoretical model code PACE-2, which takes into account only the complete fusion process. The analysis indicates the presence of contributions from incomplete fusion processes in some α-emission channels following the break-up of the projectile {sup 20}Ne in the nuclear field of the target nucleus {sup 165}Ho.

  10. Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer

    USGS Publications Warehouse

    Green, C.T.; Böhlke, J.K.; Bekins, B.A.; Phillips, S.P.

    2010-01-01

    Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field-scale (apparent) estimated reaction rates and isotopic fractionations and local-scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and field observations were used to study the effects of physical heterogeneity on reaction parameter estimates. Field measurements included major ions, age tracers, stable isotopes, and dissolved gases. Parameters were estimated for the O2 reduction rate, denitrification rate, O 2 threshold for denitrification, and stable N isotope fractionation during denitrification. For multiple geostatistical realizations of the aquifer, inverse modeling was used to establish reactive transport simulations that were consistent with field observations and served as a basis for numerical experiments to compare sample-based estimates of "apparent" parameters with "true" (intrinsic) values. For this aquifer, non-Gaussian dispersion reduced the magnitudes of apparent reaction rates and isotope fractionations to a greater extent than Gaussian mixing alone. Apparent and true rate constants and fractionation parameters can differ by an order of magnitude or more, especially for samples subject to slow transport, long travel times, or rapid reactions. The effect of mixing on apparent N isotope fractionation potentially explains differences between previous laboratory and field estimates. Similarly, predicted effects on apparent O2 threshold values for denitrification are consistent with previous reports of higher values in aquifers than in the laboratory. These results show that hydrogeological complexity substantially influences the interpretation and prediction of reactive transport. ?? 2010 by the American Geophysical Union.

  11. Automated Prediction of Catalytic Mechanism and Rate Law Using Graph-Based Reaction Path Sampling.

    PubMed

    Habershon, Scott

    2016-04-12

    In a recent article [ J. Chem. Phys. 2015 , 143 , 094106 ], we introduced a novel graph-based sampling scheme which can be used to generate chemical reaction paths in many-atom systems in an efficient and highly automated manner. The main goal of this work is to demonstrate how this approach, when combined with direct kinetic modeling, can be used to determine the mechanism and phenomenological rate law of a complex catalytic cycle, namely cobalt-catalyzed hydroformylation of ethene. Our graph-based sampling scheme generates 31 unique chemical products and 32 unique chemical reaction pathways; these sampled structures and reaction paths enable automated construction of a kinetic network model of the catalytic system when combined with density functional theory (DFT) calculations of free energies and resultant transition-state theory rate constants. Direct simulations of this kinetic network across a range of initial reactant concentrations enables determination of both the reaction mechanism and the associated rate law in an automated fashion, without the need for either presupposing a mechanism or making steady-state approximations in kinetic analysis. Most importantly, we find that the reaction mechanism which emerges from these simulations is exactly that originally proposed by Heck and Breslow; furthermore, the simulated rate law is also consistent with previous experimental and computational studies, exhibiting a complex dependence on carbon monoxide pressure. While the inherent errors of using DFT simulations to model chemical reactivity limit the quantitative accuracy of our calculated rates, this work confirms that our automated simulation strategy enables direct analysis of catalytic mechanisms from first principles.

  12. Ambiguities in the rate of oxygen formation during stellar helium burning in the 12C(α,γ) reaction

    NASA Astrophysics Data System (ADS)

    Gai, Moshe

    2013-12-01

    The rate of oxygen formation determines the C/O ratio during stellar helium burning. It is the single most important nuclear input in stellar evolution theory, including the evolution of type II and type Ia supernova. However, the low-energy cross section of the fusion of 4He +12C, denoted as the 12C(α,γ)16O reaction, still remains uncertain. I analyze and critically review the most recent measurements of complete angular distributions of the outgoing γ rays at very low energies (Ec.m.≥1.0 MeV). My analysis of the angular distributions measured with the EUROGAM/GANDI arrays leads to considerably larger error bars than have been published, which excludes them from the current sample of “world data.” I show that the current sample of “world data” of the measured E2 cross-section factors below 1.7 MeV cluster into two distinct groups that lead to two distinct extrapolations: SE2(300)≈60 or SE2(300)≈154 keVb. There is a discrepancy between the measured E1-E2 phase difference (ϕ12) and unitarity as required by the Watson theorem, which suggests systematic problem(s) in some of the measured γ-ray angular distributions. The ambiguity of the extrapolated SE2(300) together with the previously observed ambiguity of SE1(300) (approximately 80 or 10 keVb) must be resolved by future measurements of complete and detailed angular distributions of the 12C(α,γ) reaction at very low energies (Ec.m.≤1.0 MeV).

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

    SciTech Connect

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

    2011-03-30

    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.

  14. Refinement of the aeronomically determined rate coefficient for the reaction of N2/+/ with O

    NASA Technical Reports Server (NTRS)

    Torr, D. G.

    1979-01-01

    An earlier aeronomic determination of the rate coefficient for the reaction N2(+) + O yields NO(+) + N using Atmosphere Explorer data indicated a small increase in the rate coefficient with ion temperature, contrary to laboratory observations. This was incorrectly attributed to neglect of an increase in the N2(+) recombination rate with vibrational excitation. Recent aeronomical results have shown that the rate coefficient for charge exchange of O(+)(2D) with N2 is about an order of magnitude smaller at thermal temperatures than at energies greater than 0.5 eV (i.e., energies at which laboratory measurements have been made). It is shown that the use of the smaller charge exchange rate coefficient coupled with recent results on N2 quenching of O(+)(2D) yields a temperature dependence in excellent agreement with the laboratory results for the rate coefficient.

  15. Population of isomeric states in fusion and transfer reactions in beams of loosely bound nuclei near the Coulomb barrier

    NASA Astrophysics Data System (ADS)

    Skobelev, N. K.

    2015-07-01

    The influence of the mechanisms of nuclear reactions on the population of 195 m Hg and 197 m Hg(7/2-), 198 m Tl and 196 m Tl(7+), and 196 m Au and 198 m Au(12-) isomeric nuclear states obtained in reactions induced by beams of 3He, 6Li, and 6He weakly bound nuclei is studied. The behavior of excitation functions and high values of isomeric ratios ( δ m/ δ g) for products of nuclear reactions proceeding through a compound nucleus and involving neutron evaporation are explained within statistical models. Reactions in which the emission of charged particles occurs have various isomeric ratios depending on the reaction type. The isomeric ratio is lower in direct transfer reactions involving charged-particle emission than in reactions where the evaporation of charged particles occurs. Reactions accompanied by neutron transfer usually have a lower isomeric ratio, which behaves differently for different direct-reaction types (stripping versus pickup reactions).

  16. Estimating Reaction Rate Coefficients Within a Travel-Time Modeling Framework

    SciTech Connect

    Gong, R; Lu, C; Luo, Jian; Wu, Wei-min; Cheng, H.; Criddle, Craig; Kitanidis, Peter K.; Gu, Baohua; Watson, David B; Jardine, Philip M; Brooks, Scott C

    2011-03-01

    A generalized, efficient, and practical approach based on the travel-time modeling framework is developed to estimate in situ reaction rate coefficients for groundwater remediation in heterogeneous aquifers. The required information for this approach can be obtained by conducting tracer tests with injection of a mixture of conservative and reactive tracers and measurements of both breakthrough curves (BTCs). The conservative BTC is used to infer the travel-time distribution from the injection point to the observation point. For advection-dominant reactive transport with well-mixed reactive species and a constant travel-time distribution, the reactive BTC is obtained by integrating the solutions to advective-reactive transport over the entire travel-time distribution, and then is used in optimization to determine the in situ reaction rate coefficients. By directly working on the conservative and reactive BTCs, this approach avoids costly aquifer characterization and improves the estimation for transport in heterogeneous aquifers which may not be sufficiently described by traditional mechanistic transport models with constant transport parameters. Simplified schemes are proposed for reactive transport with zero-, first-, nth-order, and Michaelis-Menten reactions. The proposed approach is validated by a reactive transport case in a two-dimensional synthetic heterogeneous aquifer and a field-scale bioremediation experiment conducted at Oak Ridge, Tennessee. The field application indicates that ethanol degradation for U(VI)-bioremediation is better approximated by zero-order reaction kinetics than first-order reaction kinetics.

  17. Estimating reaction rate coefficients within a travel-time modeling framework.

    PubMed

    Gong, R; Lu, C; Wu, W-M; Cheng, H; Gu, B; Watson, D; Jardine, P M; Brooks, S C; Criddle, C S; Kitanidis, P K; Luo, J

    2011-01-01

    A generalized, efficient, and practical approach based on the travel-time modeling framework is developed to estimate in situ reaction rate coefficients for groundwater remediation in heterogeneous aquifers. The required information for this approach can be obtained by conducting tracer tests with injection of a mixture of conservative and reactive tracers and measurements of both breakthrough curves (BTCs). The conservative BTC is used to infer the travel-time distribution from the injection point to the observation point. For advection-dominant reactive transport with well-mixed reactive species and a constant travel-time distribution, the reactive BTC is obtained by integrating the solutions to advective-reactive transport over the entire travel-time distribution, and then is used in optimization to determine the in situ reaction rate coefficients. By directly working on the conservative and reactive BTCs, this approach avoids costly aquifer characterization and improves the estimation for transport in heterogeneous aquifers which may not be sufficiently described by traditional mechanistic transport models with constant transport parameters. Simplified schemes are proposed for reactive transport with zero-, first-, nth-order, and Michaelis-Menten reactions. The proposed approach is validated by a reactive transport case in a two-dimensional synthetic heterogeneous aquifer and a field-scale bioremediation experiment conducted at Oak Ridge, Tennessee. The field application indicates that ethanol degradation for U(VI)-bioremediation is better approximated by zero-order reaction kinetics than first-order reaction kinetics.

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

    PubMed

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

    2014-06-01

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

  19. Correcting reaction rates measured by saturation-transfer magnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Gabr, Refaat E.; Weiss, Robert G.; Bottomley, Paul A.

    2008-04-01

    Off-resonance or spillover irradiation and incomplete saturation can introduce significant errors in the estimates of chemical rate constants measured by saturation-transfer magnetic resonance spectroscopy (MRS). Existing methods of correction are effective only over a limited parameter range. Here, a general approach of numerically solving the Bloch-McConnell equations to calculate exchange rates, relaxation times and concentrations for the saturation-transfer experiment is investigated, but found to require more measurements and higher signal-to-noise ratios than in vivo studies can practically afford. As an alternative, correction formulae for the reaction rate are provided which account for the expected parameter ranges and limited measurements available in vivo. The correction term is a quadratic function of experimental measurements. In computer simulations, the new formulae showed negligible bias and reduced the maximum error in the rate constants by about 3-fold compared to traditional formulae, and the error scatter by about 4-fold, over a wide range of parameters for conventional saturation transfer employing progressive saturation, and for the four-angle saturation-transfer method applied to the creatine kinase (CK) reaction in the human heart at 1.5 T. In normal in vivo spectra affected by spillover, the correction increases the mean calculated forward CK reaction rate by 6-16% over traditional and prior correction formulae.

  20. Helium Ignition on Accreting Neutron Stars with a New Triple-α Reaction Rate

    NASA Astrophysics Data System (ADS)

    Peng, Fang; Ott, Christian D.

    2010-12-01

    We investigate the effect of a new triple-α reaction rate from Ogata et al. on helium ignition conditions on accreting neutron stars and on the properties of the subsequent type I X-ray burst. We find that the new rate leads to significantly lower ignition column density for accreting neutron stars at low accretion rates. We compare the results of our ignition models for a pure helium accretor to observations of bursts in ultracompact X-ray binaries (UCXBs), which are believed to have nearly pure helium donors. For \\dot{m}> 0.001 \\dot{m}_{{Edd}}, the new triple-α reaction rate from Ogata et al. predicts a maximum helium ignition column of ~3 × 109 g cm-2, corresponding to a burst energy of ~4 × 1040 erg. For \\dot{m}˜ 0.01 \\dot{m}_{{Edd}} at which intermediate long bursts occur, the predicted burst energies are at least a factor of 10 too low to explain the observed energies of such bursts in UCXBs. This finding adds to the doubts cast on the triple-α reaction rate of Ogata et al. by the low-mass stellar evolution results of Dotter & Paxton.

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

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

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

  2. Quantum three-body calculation of nonresonant triple-{alpha} reaction rate at low temperatures

    SciTech Connect

    Ogata, Kazuyuki; Kan, Masataka; Kamimura, Masayasu

    2010-08-12

    Triple-{alpha} reaction rate is re-evaluated by directly solving the three-body Schroedinger equation. The resonant and nonresonant processes are treated on the same footing using the continuum-discretized coupled-channels method for three-body scattering. An accurate description of the {alpha}-{alpha} nonresonant states significantly quenches the Coulomb barrier between the first two {alpha}-particles and the third {alpha}-particle. Consequently, the{alpha}-{alpha} nonresonant continuum states give a markedly larger contribution at low temperatures than that reported in previous studies. We show that Nomoto's method for three-body nonresonant capture processes, which is adopted in the NACRE compilation and many other studies, is a crude approximation of the accurate quantum three-body model calculation. We find an increase in triple-{alpha} reaction rate by about 20 orders of magnitude around 10{sup 7} K compared with the rate of NACRE.

  3. Quantum three-body calculation of nonresonant triple-alpha reaction rate at low temperatures

    SciTech Connect

    Ogata, Kazuyuki; Kan, Masataka; Kamimura, Masayasu

    2010-06-01

    Triple-alpha reaction rate is re-evaluated by directly solving the three-body Schroedinger equation. The resonant and nonresonant processes are treated on the same footing using the continuum-discretized coupled-channels method for three-body scattering. An accurate description of the alpha-alpha nonresonant states significantly quenches the Coulomb barrier between the first two alpha-particles and the third alpha-particle. Consequently, the alpha-alpha nonresonant continuum states give a markedly larger contribution at low temperatures than that reported in previous studies. We show that Nomoto's method for three-body nonresonant capture processes, which is adopted in the NACRE compilation and many other studies, is a crude approximation of the accurate quantum three-body model calculation. We find an increase in triple-alpha reaction rate by 26 orders of magnitude around 10{sup 7} K compared with the rate of NACRE.

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

    NASA Astrophysics Data System (ADS)

    Jones, Brian T.; Ham, Jason E.

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

  5. Cold nuclear fusion and muon-catalyzed fusion. January 1976-April 1989 (Citations from the INSPEC: Information Services for the Physics and Engineering Communities data base). Report for January 1976-April 1989

    SciTech Connect

    Not Available

    1989-04-01

    This bibliography contains citations concerning experiments and research in a type of nuclear fusion process which occurs at lower temperatures and pressures than conventional fusion reactions. The references describe theoretical and experimental results for a proposed muon-catalyzed fusion reactor, and for studies on muon sticking and reactivation, temperature dependence of fusion rates, and resolution of some engineering challenges. (Contains 82 citations fully indexed and including a title list.)

  6. Rapid heartbeat, but dry palms: reactions of heart rate and skin conductance levels to social rejection

    PubMed Central

    Iffland, Benjamin; Sansen, Lisa M.; Catani, Claudia; Neuner, Frank

    2014-01-01

    Background: Social rejection elicits negative mood, emotional distress, and neural activity in networks that are associated with physical pain. However, studies assessing physiological reactions to social rejection are rare and results of these studies were found to be ambiguous. Therefore, the present study aimed to examine and specify physiological effects of social rejection. Methods: Participants (n = 50) were assigned to either a social exclusion or inclusion condition of a virtual ball-tossing game (Cyberball). Immediate and delayed physiological [skin conductance level (SCL) and heart rate] reactions were recorded. In addition, subjects reported levels of affect, emotional states, and fundamental needs. Results: Subjects who were socially rejected showed increased heart rates. However, social rejection had no effect on subjects' SCLs. Both conditions showed heightened arousal on this measurement. Furthermore, psychological consequences of social rejection indicated the validity of the paradigm. Conclusions: Our results reveal that social rejection evokes an immediate physiological reaction. Accelerated heart rates indicate that behavior activation rather than inhibition is associated with socially threatening events. In addition, results revealed gender-specific response patterns suggesting that sample characteristics such as differences in gender may account for ambiguous findings of physiological reactions to social rejection. PMID:25221535

  7. Reevaluation of thermonuclear reaction rate of 50Fe(p, 𝜸)51Co

    NASA Astrophysics Data System (ADS)

    Zhang, Li-Ping; He, Jian-Jun; Chai, Wan-Dong; Hou, Su-Qing; Zhang, Li-Yong

    2016-11-01

    The thermonuclear rate of the 50Fe(p, 𝜸)51Co reaction in the Type I X-ray bursts (XRBs) temperature range has been reevaluated based on a recent precise mass measurement at CSRe Lanzhou, where the proton separation energy Sp = 142±77 keV has been determined firstly for the 51Co nucleus. Comparing to the previous theoretical predictions, the experimental Sp value has much smaller uncertainty. Based on the nuclear shell model and mirror nuclear structure information, we have calculated two sets of thermonuclear rates for the 50Fe(p, 𝜸)51Co reaction by utilizing the experimental Sp value. It shows that the statistical-model calculations are not ideally applicable for this reaction primarily because of the low density of low-lying excited states in 51Co. In this work, we recommend that a set of new reaction rates based on the mirror structure of 51Cr should be incorporated in future astrophysical network calculations. Supported by Natural Science Foundation of Inner Mongolia Autonomous Region of China (2013MS0916) and National Natural Science Foundation of China (11490562, 11405228)

  8. Reaction rate kinetics for in situ combustion retorting of Michigan Antrim oil shale

    USGS Publications Warehouse

    Rostam-Abadi, M.; Mickelson, R.W.

    1984-01-01

    The intrinsic reaction rate kinetics for the pyrolysis of Michigan Antrim oil shale and the oxidation of the carbonaceous residue of this shale have been determined using a thermogravimetric analysis method. The kinetics of the pyrolysis reaction were evaluated from both isothermal and nonisothermal rate data. The reaction was found to be second-order with an activation energy of 252.2 kJ/mole, and with a frequency factor of 9.25 ?? 1015 sec-1. Pyrolysis kinetics were not affected by heating rates between 0.01 to 0.67??K/s. No evidence of any reactions among the oil shale mineral constituents was observed at temperatures below 1173??K. However, it was found that the presence of pyrite in oil shale reduces the primary devolatilization rate of kerogen and increases the amount of residual char in the spent shale. Carbonaceous residues which were prepared by heating the oil shale at a rate of 0.166??K/s to temperatures between 923??K and 1073??K, had the highest reactivities when oxidized at 0.166??K/s in a gas having 21 volume percent oxygen. Oxygen chemisorption was found to be the initial precursor to the oxidation process. The kinetics governing oxygen chemisorption is (Equation Presented) where X is the fractional coverage. The oxidation of the carbonaceous residue was found also to be second-order. The activation energy and the frequency factor determined from isothermal experiments were 147 kJ/mole and 9.18??107 sec-1 respectively, while the values of these parameters obtained from a nonisothermal experiment were 212 kJ/mole and 1.5??1013 sec-1. The variation in the rate constants is attributed to the fact that isothermal and nonisothermal analyses represent two different aspects of the combustion process.

  9. Inference of reaction rate parameters based on summary statistics from experiments

    DOE PAGES

    Khalil, Mohammad; Chowdhary, Kamaljit Singh; Safta, Cosmin; ...

    2016-10-15

    Here, we present the results of an application of Bayesian inference and maximum entropy methods for the estimation of the joint probability density for the Arrhenius rate para meters of the rate coefficient of the H2/O2-mechanism chain branching reaction H + O2 → OH + O. Available published data is in the form of summary statistics in terms of nominal values and error bars of the rate coefficient of this reaction at a number of temperature values obtained from shock-tube experiments. Our approach relies on generating data, in this case OH concentration profiles, consistent with the given summary statistics, usingmore » Approximate Bayesian Computation methods and a Markov Chain Monte Carlo procedure. The approach permits the forward propagation of parametric uncertainty through the computational model in a manner that is consistent with the published statistics. A consensus joint posterior on the parameters is obtained by pooling the posterior parameter densities given each consistent data set. To expedite this process, we construct efficient surrogates for the OH concentration using a combination of Pad'e and polynomial approximants. These surrogate models adequately represent forward model observables and their dependence on input parameters and are computationally efficient to allow their use in the Bayesian inference procedure. We also utilize Gauss-Hermite quadrature with Gaussian proposal probability density functions for moment computation resulting in orders of magnitude speedup in data likelihood evaluation. Despite the strong non-linearity in the model, the consistent data sets all res ult in nearly Gaussian conditional parameter probability density functions. The technique also accounts for nuisance parameters in the form of Arrhenius parameters of other rate coefficients with prescribed uncertainty. The resulting pooled parameter probability density function is propagated through stoichiometric hydrogen-air auto-ignition computations to illustrate

  10. Inference of reaction rate parameters based on summary statistics from experiments

    SciTech Connect

    Khalil, Mohammad; Chowdhary, Kamaljit Singh; Safta, Cosmin; Sargsyan, Khachik; Najm, Habib N.

    2016-10-15

    Here, we present the results of an application of Bayesian inference and maximum entropy methods for the estimation of the joint probability density for the Arrhenius rate para meters of the rate coefficient of the H2/O2-mechanism chain branching reaction H + O2 → OH + O. Available published data is in the form of summary statistics in terms of nominal values and error bars of the rate coefficient of this reaction at a number of temperature values obtained from shock-tube experiments. Our approach relies on generating data, in this case OH concentration profiles, consistent with the given summary statistics, using Approximate Bayesian Computation methods and a Markov Chain Monte Carlo procedure. The approach permits the forward propagation of parametric uncertainty through the computational model in a manner that is consistent with the published statistics. A consensus joint posterior on the parameters is obtained by pooling the posterior parameter densities given each consistent data set. To expedite this process, we construct efficient surrogates for the OH concentration using a combination of Pad'e and polynomial approximants. These surrogate models adequately represent forward model observables and their dependence on input parameters and are computationally efficient to allow their use in the Bayesian inference procedure. We also utilize Gauss-Hermite quadrature with Gaussian proposal probability density functions for moment computation resulting in orders of magnitude speedup in data likelihood evaluation. Despite the strong non-linearity in the model, the consistent data sets all res ult in nearly Gaussian conditional parameter probability density functions. The technique also accounts for nuisance parameters in the form of Arrhenius parameters of other rate coefficients with prescribed uncertainty. The resulting pooled parameter probability density function is propagated through stoichiometric hydrogen-air auto

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

    PubMed

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

    2015-08-14

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

  12. Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction

    SciTech Connect

    Scott C. Brooks; Wenming Dong; Sue Carroll; Jim Fredrickson; Ken Kemner; Shelly Kelly

    2006-06-01

    The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. ? Elucidate the controls on the rate and extent of contaminant reactivity. (2) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions.

  13. Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction

    SciTech Connect

    Scott C. Brooks; Wenming Dong; Sue Carroll; James K. Fredrickson; Kenneth M. Kemner; Shelly D. Kelly

    2006-06-01

    The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. (2) Elucidate the controls on the rate and extent of contaminant reactivity. (3) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions.

  14. The effect of heat conduction on the rate of chemical reaction in dilute gases

    NASA Astrophysics Data System (ADS)

    Fort, J.; Cukrowski, A. S.

    1997-09-01

    Information statistical theory is used to obtain the second-order terms (similar to those analyzed in the Burnett approximation to the solution of the Boltzmann equation) in the expansion of the nonequilibrium velocity distribution function. These terms are used for the evaluation of the effect of the heat flux on the rate of bimolecular chemical reactions. This effect is shown to be important for reactions characterized by high values of the activation energy. However, very large values of the heat flux would be necessary. The results are compared with those obtained earlier from the square terms calculated from the linearized Boltzmann equation and with recent results due to Nettleton.

  15. Helium Find Thaws the Cold Fusion Trail.

    ERIC Educational Resources Information Center

    Pennisi, E.

    1991-01-01

    Reported is a study of cold fusion in which trace amounts of helium, possible evidence of an actual fusion reaction, were found. Research methodology is detailed. The controversy over the validity of experimental results with cold fusion are reviewed. (CW)

  16. Rates for neutron-capture reactions on tungsten isotopes in iron meteorites. [Abstract only

    NASA Technical Reports Server (NTRS)

    Masarik, J.; Reedy, R. C.

    1994-01-01

    High-precision W isotopic analyses by Harper and Jacobsen indicate the W-182/W-183 ratio in the Toluca iron meteorite is shifted by -(3.0 +/- 0.9) x 10(exp -4) relative to a terrestrial standard. Possible causes of this shift are neutron-capture reactions on W during Toluca's approximately 600-Ma exposure to cosmic ray particles or radiogenic growth of W-182 from 9-Ma Hf-182 in the silicate portion of the Earth after removal of W to the Earth's core. Calculations for the rates of neutron-capture reactions on W isotopes were done to study the first possibility. The LAHET Code System (LCS) which consists of the Los Alamos High Energy Transport (LAHET) code and the Monte Carlo N-Particle(MCNP) transport code was used to numerically simulate the irradiation of the Toluca iron meteorite by galactic-cosmic-ray (GCR) particles and to calculate the rates of W(n, gamma) reactions. Toluca was modeled as a 3.9-m-radius sphere with the composition of a typical IA iron meteorite. The incident GCR protons and their interactions were modeled with LAHET, which also handled the interactions of neutrons with energies above 20 MeV. The rates for the capture of neutrons by W-182, W-183, and W-186 were calculated using the detailed library of (n, gamma) cross sections in MCNP. For this study of the possible effect of W(n, gamma) reactions on W isotope systematics, we consider the peak rates. The calculated maximum change in the normalized W-182/W-183 ratio due to neutron-capture reactions cannot account for more than 25% of the mass 182 deficit observed in Toluca W.

  17. Astrophysical Impact of the Updated 9Be(p,α)6Li and 10B(p,α)7Be Reaction Rates As Deduced By THM

    NASA Astrophysics Data System (ADS)

    Lamia, L.; Spitaleri, C.; Tognelli, E.; Degl'Innocenti, S.; Pizzone, R. G.; Prada Moroni, P. G.

    2015-10-01

    The complete understanding of the stellar abundances of lithium, beryllium, and boron represents one of the most interesting open problems in astrophysics. These elements are largely used to probe stellar structure and mixing phenomena in different astrophysical scenarios, such as pre-main-sequence or main-sequence stars. Their different fragility against (p,α) burning reactions allows one to investigate different depths of the stellar interior. Such fusion mechanisms are triggered at temperatures between T ≈ (2-5) × {10}6 K, thus defining a corresponding Gamow energy between ≈ 3-10 keV, where S(E)-factor measurements need to be performed to get reliable reaction rate evaluations. The Trojan Horse Method is a well defined procedure to measure cross sections at Gamow energies overcoming the uncertainties due to low-energy S(E)-factor extrapolation as well as electron screening effects. Taking advantage of the {\\mathtt{THM}} measure of the 9Be(p,α)6Li and 10B(p,α)7Be cross sections, the corresponding reaction rates have been calculated and compared with the evaluations by the NACRE collaboration, widely used in the literature. The impact on surface abundances of the updated 9Be and 10B (p,α) burning rates is discussed for pre-MS stars.

  18. A Particle X-ray Temporal Diagnostic (PXTD) for studies of kinetic, multi-ion effects, and ion-electron equilibration rates in Inertial Confinement Fusion plasmas at OMEGA (invited)

    NASA Astrophysics Data System (ADS)

    Sio, H.; Frenje, J. A.; Katz, J.; Stoeckl, C.; Weiner, D.; Bedzyk, M.; Glebov, V.; Sorce, C.; Gatu Johnson, M.; Rinderknecht, H. G.; Zylstra, A. B.; Sangster, T. C.; Regan, S. P.; Kwan, T.; Le, A.; Simakov, A. N.; Taitano, W. T.; Chacòn, L.; Keenan, B.; Shah, R.; Sutcliffe, G.; Petrasso, R. D.

    2016-11-01

    A Particle X-ray Temporal Diagnostic (PXTD) has been implemented on OMEGA for simultaneous time-resolved measurements of several nuclear products as well as the x-ray continuum produced in High Energy Density Plasmas and Inertial Confinement Fusion implosions. The PXTD removes systematic timing uncertainties typically introduced by using multiple instruments, and it has been used to measure DD, DT, D3He, and T3He reaction histories and the emission history of the x-ray core continuum with relative timing uncertainties within ±10-20 ps. This enables, for the first time, accurate and simultaneous measurements of the x-ray emission histories, nuclear reaction histories, their time differences, and measurements of Ti(t) and Te(t) from which an assessment of multiple-ion-fluid effects, kinetic effects during the shock-burn phase, and ion-electron equilibration rates can be made.

  19. A Particle X-ray Temporal Diagnostic (PXTD) for studies of kinetic, multi-ion effects, and ion-electron equilibration rates in Inertial Confinement Fusion plasmas at OMEGA (invited)

    DOE PAGES

    Sio, H.; Frenje, J. A.; Katz, J.; ...

    2016-09-14

    Here, a Particle X-ray Temporal Diagnostic (PXTD) has been implemented on OMEGA for simultaneous time-resolved measurements of several nuclear products as well as the x-ray continuum produced in High Energy Density Plasmas and Inertial Confinement Fusion implosions. The PXTD removes systematic timing uncertainties typically introduced by using multiple instruments, and it has been used to measure DD, DT, D3He, and T3He reaction histories and the emission history of the x-ray core continuum with relative timing uncertainties within ±10-20 ps. This enables, for the first time, accurate and simultaneous measurements of the x-ray emission histories, nuclear reaction histories, their time differences,more » and measurements of Ti(t) and Te(t) from which an assessment of multiple-ion-fluid effects, kinetic effects during the shock-burn phase, and ion-electron equilibration rates can be made.« less

  20. A Particle X-ray Temporal Diagnostic (PXTD) for studies of kinetic, multi-ion effects, and ion-electron equilibration rates in Inertial Confinement Fusion plasmas at OMEGA (invited).

    PubMed

    Sio, H; Frenje, J A; Katz, J; Stoeckl, C; Weiner, D; Bedzyk, M; Glebov, V; Sorce, C; Gatu Johnson, M; Rinderknecht, H G; Zylstra, A B; Sangster, T C; Regan, S P; Kwan, T; Le, A; Simakov, A N; Taitano, W T; Chacòn, L; Keenan, B; Shah, R; Sutcliffe, G; Petrasso, R D

    2016-11-01

    A Particle X-ray Temporal Diagnostic (PXTD) has been implemented on OMEGA for simultaneous time-resolved measurements of several nuclear products as well as the x-ray continuum produced in High Energy Density Plasmas and Inertial Confinement Fusion implosions. The PXTD removes systematic timing uncertainties typically introduced by using multiple instruments, and it has been used to measure DD, DT, D(3)He, and T(3)He reaction histories and the emission history of the x-ray core continuum with relative timing uncertainties within ±10-20 ps. This enables, for the first time, accurate and simultaneous measurements of the x-ray emission histories, nuclear reaction histories, their time differences, and measurements of Ti(t) and Te(t) from which an assessment of multiple-ion-fluid effects, kinetic effects during the shock-burn phase, and ion-electron equilibration rates can be made.

  1. Reaction of atomic bromine with acetylene and loss rate of atmospheric acetylene due to reaction with OH, Cl, O, and Br

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

    The first-order, diffusion, and bimolecular rate constants for the reaction Br + C2H2 yields C2H3Br are evaluated. The rate constants are measured at 210, 248, 298, and 393 K and at pressures between 15-100 torr Ar using flash photolysis combined with time-resolved detection of atomic bromine via Br resonance radiation. It is observed that the reaction is not affected by pressure or temperature and the bimolecular constant = (4.0 + or - 0.8) x 10 to the -15th cu cm/sec with an error of two standard deviations. The C2H2 + Br reaction rates are compared with reactions of C2H2 with Cl, OH, NH2, and H. The loss rates for atmospheric C2H2 for reactions with OH, Cl, O, and Br are calculated as a function of altitude.

  2. Learned cardiac control with heart rate biofeedback transfers to emotional reactions.

    PubMed

    Peira, Nathalie; Pourtois, Gilles; Fredrikson, Mats

    2013-01-01

    Emotions involve subjective feelings, action tendencies and physiological reactions. Earlier findings suggest that biofeedback might provide a way to regulate the physiological components of emotions. The present study investigates if learned heart rate regulation with biofeedback transfers to emotional situations without biofeedback. First, participants learned to decrease heart rate using biofeedback. Then, inter-individual differences in the acquired skill predicted how well they could decrease heart rate reactivity when later exposed to negative arousing pictures without biofeedback. These findings suggest that (i) short lasting biofeedback training improves heart rate regulation and (ii) the learned ability transfers to emotion challenging situations without biofeedback. Thus, heart rate biofeedback training may enable regulation of bodily aspects of emotion also when feedback is not available.

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

    PubMed

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

    2012-04-28

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

  4. Accurate label-free reaction kinetics determination using initial rate heat measurements

    PubMed Central

    Ebrahimi, Kourosh Honarmand; Hagedoorn, Peter-Leon; Jacobs, Denise; Hagen, Wilfred R.

    2015-01-01

    Accurate label-free methods or assays to obtain the initial reaction rates have significant importance in fundamental studies of enzymes and in application-oriented high throughput screening of enzyme activity. Here we introduce a label-free approach for obtaining initial rates of enzyme activity from heat measurements, which we name initial rate calorimetry (IrCal). This approach is based on our new finding that the data recorded by isothermal titration calorimetry for the early stages of a reaction, which have been widely ignored, are correlated to the initial rates. Application of the IrCal approach to various enzymes led to accurate enzyme kinetics parameters as compared to spectroscopic methods and enabled enzyme kinetic studies with natural substrate, e.g. proteases with protein substrates. Because heat is a label-free property of almost all reactions, the IrCal approach holds promise in fundamental studies of various enzymes and in use of calorimetry for high throughput screening of enzyme activity. PMID:26574737

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

    PubMed

    Imoto, Taiji

    2013-01-01

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

  6. Unexpected heterogeneity of BCR-ABL fusion mRNA detected by polymerase chain reaction in Philadelphia chromosome-positive acute lymphoblastic leukemia

    SciTech Connect

    Hooberman, A.L.; Carrino, J.J.; Leibowitz, D.; Rowley, J.D.; Le Beau, M.M.; Arlin, Z.A.; Westbrook, C.A. )

    1989-06-01

    The Philadelphia (Ph{sup 1}) chromosome results in a fusion of portions of the BCR gene from chromosome 22 and the ABL gene from chromosome 9, producing a chimeric BCR-ABL mRNA and protein. In lymphoblastic leukemias, there are two molecular subtypes of the Ph{sup 1} chromosome, one with a rearrangement of the breakpoint cluster region (bcr) of the BCR gene, producing the same 8.5-kilobase BCR-ABL fusion mRNA seen in chronic myelogenous leukemia (CML), and the other, without a bcr rearrangement, producing a 7.0-kilobase BCR-ABL fusion mRNA that is seen only in acute lymphoblastic leukemia (ALL). The authors studied the molecular subtype of the Ph{sup 1} chromosome in 11 cases of Ph{sup 1}-positive ALL, including 2 with a previous diagnosis of CML, using a sensitive method to analyze the mRNA species based on the polymerase chain reaction (PCR). They observed unexpected heterogeneity in BCR-ABL mRNA in this population. They conclude that the PCR gives additional information about the Ph{sup 1} chromosome gene products that cannot be obtained by genomic analysis, but that it cannot be used as the sole means of detection of this chromosomal abnormality in ALL because of the high incidence of false negative results.

  7. Mathematical Formalism of Nonequilibrium Thermodynamics for Nonlinear Chemical Reaction Systems with General Rate Law

    NASA Astrophysics Data System (ADS)

    Ge, Hao; Qian, Hong

    2017-01-01

    This paper studies a mathematical formalism of nonequilibrium thermodynamics for chemical reaction models with N species, M reactions, and general rate law. We establish a mathematical basis for J. W. Gibbs' macroscopic chemical thermodynamics under G. N. Lewis' kinetic law of entire equilibrium (detailed balance in nonlinear chemical kinetics). In doing so, the equilibrium thermodynamics is then naturally generalized to nonequilibrium settings without detailed balance. The kinetic models are represented by a Markovian jumping process. A generalized macroscopic chemical free energy function and its associated balance equation with nonnegative source and sink are the major discoveries. The proof is based on the large deviation principle of this type of Markov processes. A general fluctuation dissipation theorem for stochastic reaction kinetics is also proved. The mathematical theory illustrates how a novel macroscopic dynamic law can emerges from the mesoscopic kinetics in a multi-scale system.

  8. Light elements burning reaction rates at stellar temperatures as deduced by the Trojan Horse measurements

    SciTech Connect

    Lamia, L.; Spitaleri, C.; La Cognata, M.; Palmerini, S.; Sergi, M. L.; Puglia, S. M. R.

    2015-02-24

    Experimental nuclear astrophysics aims at determining the reaction rates for astrophysically relevant reactions at their Gamow energies. For charged-particle induced reactions, the access to these energies is usually hindered, in direct measurements, by the presence of the Coulomb barrier between the interacting particles or by electron screening effects, which make hard the determination of the bare-nucleus S(E)-factor of interest for astrophysical codes. The use of the Trojan Horse Method (THM) appears as one of the most suitable tools for investigating nuclear processes of interest for astrophysics. Here, in view of the recent TH measurements, the main destruction channels for deuterium ({sup 2}H), for the two lithium {sup 6,7}Li isotopes, for the {sup 9}Be and the one for the two boron {sup 10,11}B isotopes will be discussed.

  9. Rate coefficients of hydroxyl radical reactions with pesticide molecules and related compounds: A review

    NASA Astrophysics Data System (ADS)

    Wojnárovits, László; Takács, Erzsébet

    2014-03-01

    Rate coefficients published in the literature on hydroxyl radical reactions with pesticides and related compounds are discussed together with the experimental methods and the basic reaction mechanisms. Recommendations are made for the most probable values. Most of the molecules whose rate coefficients are discussed have aromatic ring: their rate coefficients are in the range of 2×109-1×1010 mol-1 dm3 s-1. The rate coefficients show some variation with the electron withdrawing-donating nature of the substituent on the ring. The rate coefficients for triazine pesticides (simazine, atrazine, prometon) are all around 2.5×109 mol-1 dm3 s-1. The values do not show variation with the substituent on the s-triazine ring. The rate coefficients for the non-aromatic molecules which have C=C double bonds or several C-H bonds may also be above 1×109 mol-1 dm3 s-1. However, the values for molecules without C=C double bonds or several C-H bonds are in the 1×107-1×109 mol-1 dm3 s-1 range.

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

    PubMed

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

    2016-06-28

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

  11. Beyond transition state theory: Rigorous quantum approaches for determining chemical reaction rates

    SciTech Connect

    Miller, W.H.

    1995-01-01

    Transition state theory (TST) has historically been the most important and widely used theoretical approach for describing the rates of chemical reactions, and for qualitative pictures and order-of-magnitude estimates one does not expect this situation to change. However a rigorous, quantitative treatment of chemical reaction rates must go beyond TST. A rigorous description, for example, must be based on a quantum mechanical description of the molecular system, but the fundamental assumption on which TST is based - namely that the molecular dynamics is {open_quotes}direct,{close_quotes} i.e., that no trajectories re-cross a dividing surface which separates reactants and products (vide infra) - is couched inherently in the language of classical mechanics. There is no unambiguous way to quantize TST, for the various ways of trying to do so invariably require one to introduce additional assumptions about the reaction dynamics. As one tries to eliminate these {open_quotes}additional assumptions{close_quotes} one is driven ultimately to an exact quantum treatment of the reaction dynamics which is then no longer a transition state theory (i.e., approximation) but simply an exact formulation. It is such exact approaches, those without inherent approximations, that are the subject of this chapter.

  12. Reaction rate modeling in cryoconcentrated solutions: alkaline phosphatase catalyzed DNPP hydrolysis.

    PubMed

    Champion, D; Blond, G; Le Meste, M; Simatos, D

    2000-10-01

    The hydrolysis of disodium p-nitrophenyl phosphate catalyzed by alkaline phosphatase was chosen as a model to study the kinetics of changes in frozen food products. The initial reaction rate was determined in concentrated sucrose solutions down to -24 degrees C, and the enzymatic characteristics K(M) and V(max) were calculated. The experimental data were compared to the kinetics predicted by assuming that the reaction was viscosity dependent. Indeed, an analysis of the enzymatic reaction demonstrated that both the diffusion of the substrate and the flexibility of the enzyme segments were controlled by the high viscosity of the media. When the temperature was too low for the viscosity to be measured simply, the Williams-Landel-Ferry equation was used to predict the viscosity, taking, as reference temperature, the glass transition temperature (T(g)) corresponding to the concentration of the freeze-concentrated phase at the test temperature. Predicted values of the reaction rate were very close to the experimental ones in the studied temperature range.

  13. Transition path sampling with quantum/classical mechanics for reaction rates.

    PubMed

    Gräter, Frauke; Li, Wenjin

    2015-01-01

    Predicting rates of biochemical reactions through molecular simulations poses a particular challenge for two reasons. First, the process involves bond formation and/or cleavage and thus requires a quantum mechanical (QM) treatment of the reaction center, which can be combined with a more efficient molecular mechanical (MM) description for the remainder of the system, resulting in a QM/MM approach. Second, reaction time scales are typically many orders of magnitude larger than the (sub-)nanosecond scale accessible by QM/MM simulations. Transition path sampling (TPS) allows to efficiently sample the space of dynamic trajectories from the reactant to the product state without an additional biasing potential. We outline here the application of TPS and QM/MM to calculate rates for biochemical reactions, by means of a simple toy system. In a step-by-step protocol, we specifically refer to our implementation within the MD suite Gromacs, which we have made available to the research community, and include practical advice on the choice of parameters.

  14. Rate parameters for the reaction of atomic hydrogen with dimethyl ether and dimethyl sulfide

    NASA Astrophysics Data System (ADS)

    Lee, J. H.; Machen, R. C.; Nava, D. F.; Stief, L. J.

    1981-03-01

    Absolute rate constants for the reaction of atomic hydrogen with dimethyl ether (DME) and dimethyl sulfide (DMS) were obtained using the flash photolysis-resonance fluorescence technique. Under conditions where secondary reactions are avoided, rate constants for the H+DME reaction over the temperature range 273-426 K are well represented by the Arrhenius expression k1=(4.38±0.59)×10-12 exp(-1956±43/T) cm3 molecule-1 s-1. The corresponding Arrhenius expression for the H+DMS reaction over the temperature range 212-500 K is k2=(1.30±0.43)×10-11exp(-1118±81/T) cm3 molecule-1 s-1. The Arrhenius plot for k2 shows signs of curvature, however, and separate Arrhenius expressions are derived for the data above and below room temperature. These results are discussed and comparisons are made with previous determinations which employed flow discharge and product analysis techniques.

  15. Up-Scaling Geochemical Reaction Rates for Carbon Dioxide (CO2) in Deep Saline Aquifers

    SciTech Connect

    Peters, Catherine A

    2013-02-28

    Geochemical reactions in deep subsurface environments are complicated by the consolidated nature and mineralogical complexity of sedimentary rocks. Understanding the kinetics of these reactions is critical to our ability to make long-term predictions about subsurface processes such as pH buffering, alteration in rock structure, permeability changes, and formation of secondary precipitates. In this project, we used a combination of experiments and numerical simulation to bridge the gap between our knowledge of these reactions at the lab scale and rates that are meaningful for modeling reactive transport at core scales. The focus is on acid-driven mineral dissolution, which is specifically relevant in the context of CO2-water-rock interactions in geological sequestration of carbon dioxide. The project led to major findings in three areas. First, we modeled reactive transport in pore-network systems to investigate scaling effects in geochemical reaction rates. We found significant scaling effects when CO2 concentrations are high and reaction rates are fast. These findings indicate that the increased acidity associated with geological sequestration can generate conditions for which proper scaling tools are yet to be developed. Second, we used mathematical modeling to investigate the extent to which SO2, if co-injected with CO2, would acidify formation brines. We found that there exist realistic conditions in which the impact on brine acidity will be limited due to diffusion rate-limited SO2 dissolution from the CO2 phase, and the subsequent pH shift may also be limited by the lack of availability of oxidants to produce sulfuric acid. Third, for three Viking sandstones (Alberta sedimentary basin, Canada), we employed backscattered electron microscopy and energy dispersive X-ray spectroscopy to statistically characterize mineral contact with pore space. We determined that for reactive minerals in sedimentary consolidated rocks, abundance alone is not a good predictor of

  16. Membrane events in the acrosomal reaction of Limulus sperm. Membrane fusion, filament-membrane particle attachment, and the source and formation of new membrane surface

    PubMed Central

    1979-01-01

    The membranes of Limulus (horseshoe crab) sperm were examined before and during the acrosomal reaction by using the technique of freeze- fracturing and thin sectioning. We focused on three areas. First, we examined stages in the fusion of the acrosomal vacuole with the cell surface. Fusion takes place in a particle-free zone which is surrounded by a circlet of particles on the P face of the plasma membrane and an underlying circlet of particles on the P face of the acrosomal vauole membrane. These circlets of particles are present before induction. Up to nine focal points of fusion occur within the particle-free zone. Second, we describe a system of fine filaments, each 30 A in diameter, which lies between the acrosomal vacuole and the plasma membrane. These filaments change their orientation as the vacuole opens, a process that takes place in less than 50 ms. Membrane particles seen on the P face of the acrosomal vacuole membrane change their orientation at the same time and in the same way as do the filaments, thus indicating that the membrane particles and filaments are probably connected. Third, we examined the source and the point of fusion of new membrane needed to cover the acrosomal process. This new membrane is almost certainly derived from the outer nuclear envelope and appears to insert into the plasma membrane in a particle-free area adjacent to an area rich in particles. The latter is the region where the particles are probably connected to the cytoplasmic filaments. The relevance of these observations in relation to the process of fertilization of this fantastic sperm is discussed. PMID:582596

  17. The rate of the deoxygenation reaction limits myoglobin- and hemoglobin-facilitated O₂ diffusion in cells.

    PubMed

    Endeward, Volker

    2012-05-01

    A mathematical model describing facilitation of O(2) diffusion by the diffusion of myoglobin and hemoglobin is presented. The equations are solved numerically by a finite-difference method for the conditions as they prevail in cardiac and skeletal muscle and in red cells without major simplifications. It is demonstrated that, in the range of intracellular diffusion distances, the degree of facilitation is limited by the rate of the chemical reaction between myglobin or hemoglobin and O(2). The results are presented in the form of relationships between the degree of facilitation and the length of the diffusion path on the basis of the known kinetics of the oxygenation-deoxygenation reactions. It is concluded that the limitation by reaction kinetics reduces the maximally possible facilitated oxygen diffusion in cardiomyoctes by ∼50% and in skeletal muscle fibers by ∼ 20%. For human red blood cells, a reduction of facilitated O(2) diffusion by 36% is obtained in agreement with previous reports. This indicates that, especially in cardiomyocytes and red cells, chemical equilibrium between myoglobin or hemoglobin and O(2) is far from being established, an assumption that previously has often been made. Although the "O(2) transport function" of myoglobin in cardiac muscle cells thus is severely limited by the chemical reaction kinetics, and to a lesser extent also in skeletal muscle, it is noteworthy that the speed of release of O(2) from MbO(2), the "storage function," is not limited by the reaction kinetics under physiological conditions.

  18. Modelling of silicon oxynitridation by nitrous oxide using the reaction rate approach

    SciTech Connect

    Dominique Krzeminski, Christophe

    2013-12-14

    Large technological progress in oxynitridation processing leads to the introduction of silicon oxynitride as ultra-thin gate oxide. On the theoretical side, few studies have been dedicated to the process modelling of oxynitridation. Such an objective is a considerable challenge regarding the various atomistic mechanisms occurring during this fabrication step. In this article, some progress performed to adapt the reaction rate approach for the modelling of oxynitride growth by a nitrous ambient are reported. The Ellis and Buhrman's approach is used for the gas phase decomposition modelling. Taking into account the mass balance of the species at the interface between the oxynitride and silicon, a minimal kinetic model describing the oxide growth has been calibrated and implemented. The influence of nitrogen on the reaction rate has been introduced in an empirical way. The oxidation kinetics predicted with this minimal model compares well with several experiments.

  19. Oxygen consumption rates in subseafloor basaltic crust derived from a reaction transport model.

    PubMed

    Orcutt, Beth N; Wheat, C Geoffrey; Rouxel, Olivier; Hulme, Samuel; Edwards, Katrina J; Bach, Wolfgang

    2013-01-01

    Oceanic crust is the largest potential habitat for life on Earth and may contain a significant fraction of Earth's total microbial biomass; yet, empirical analysis of reaction rates in basaltic crust is lacking. Here we report the first assessment of oxygen consumption in young (~8 Ma) and cool (<25 °C) basaltic crust, which we calculate from modelling dissolved oxygen and strontium pore water gradients in basal sediments collected during Integrated Ocean Drilling Program Expedition 336 to 'North Pond' on the western flank of the Mid-Atlantic Ridge. Dissolved oxygen is completely consumed within the upper to middle section of the sediment column, with an increase in concentration towards the sediment-basement interface, indicating an upward supply from oxic fluids circulating within the crust. A parametric reaction transport model of oxygen behaviour in upper basement suggests oxygen consumption rates of 1 nmol  cm(-3)ROCK d(-1) or less in young and cool basaltic crust.

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

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

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

    PubMed

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

    2004-11-08

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

  2. Reacting gas mixtures in the state-to-state approach: The chemical reaction rates

    SciTech Connect

    Kustova, Elena V.; Kremer, Gilberto M.

    2014-12-09

    In this work chemically reacting mixtures of viscous flows are analyzed within the framework of Boltzmann equation. By applying a modified Chapman-Enskog method to the system of Boltzmann equations general expressions for the rates of chemical reactions and vibrational energy transitions are determined as functions of two thermodynamic forces: the velocity divergence and the affinity. As an application chemically reacting mixtures of N{sub 2} across a shock wave are studied, where the first lowest vibrational states are taken into account. Here we consider only the contributions from the first four single quantum vibrational-translational energy transitions. It is shown that the contribution to the chemical reaction rate related to the affinity is much larger than that of the velocity divergence.

  3. 23Na (α,p )26Mg Reaction Rate at Astrophysically Relevant Energies

    NASA Astrophysics Data System (ADS)

    Howard, A. M.; Munch, M.; Fynbo, H. O. U.; Kirsebom, O. S.; Laursen, K. L.; Diget, C. Aa.; Hubbard, N. J.

    2015-07-01

    The production of 26Al in massive stars is sensitive to the 23Na (α,p )26Mg cross section. Recent experimental data suggest the currently recommended cross sections are underestimated by a factor of ˜40 . We present here differential cross sections for the 23Na (α,p )26Mg reaction measured in the energy range Ec .m .=1.7 - 2.5 MeV . Concurrent measurements of Rutherford scattering provide absolute normalizations that are independent of variations in target properties. Angular distributions are measured for both p0 and p1 permitting the determination of total cross sections. The results show no significant deviation from the statistical model calculations upon which the recommended rates are based. We therefore retain the previous recommendation without the increase in cross section and resulting stellar reaction rates by a factor of 40, impacting the 26Al yield from massive stars by more than a factor of 3.

  4. Absolute rate of the reaction of bromine atoms with ozone from 200 to 360 K

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

    The rate constant for the reaction Br + O3 yields BrO + O2 has been measured from 200 to 360 K by the technique of flash photolysis coupled to time resolved detection of bromine atoms by resonance fluorescence (FP-RF). Br atoms were produced by the flash photolysis of CH3Br at a wavelength of 165 nm. O3 concentration was monitored continuously under reaction conditions by absorption at 253.7 nm. At each of five temperatures the results were independent of substantial variations in O3 concentration, total pressure (Ar), and limited variations in flash intensity (i.e., initial Br concentration). The measured rate constants obey the Arrhenius expression, k = (7.74 plus or minus 0.50) x 10 to the -12th exp(-603 plus or minus 16/T) cu cm/molecule/sec, where the error quoted is two standard deviations.

  5. Turnover rate, reaction order, and elementary steps for the hydrodechlorination of chlorofluorocarbon compounds on palladium catalysts

    SciTech Connect

    Thompson, C.D.; Rioux, R.M.; Chen, N.; Ribeiro, F.H.

    2000-04-13

    The rates of hydrodechlorination catalyzed by Pd supported on carbon for four chlorofluorocarbons spanned a range of 7 orders of magnitude. The rates scaled up to the bond strength of the carbon-chlorine bond for the gas-phase reactant. This finding demonstrates that the rate-determining step involves the scission of the C-Cl bond and suggests, through Polanyi and linear free-energy relationships, that rates for other compounds can be estimated if the C-Cl bond strength is known. The reaction orders for the most abundant products are approximately first-order for the chlorine-containing compound, half-order in H{sub 2}, and inverse first-order in HCl. The reaction steps consistent with these orders include a rate-determining step involving the adsorption of the chlorofluorocarbon to a single site (which could be a single surface palladium atom) and equilibrated steps between gas-phase H{sub 2}, gas-phase HCl, and adsorbed hydrogen and chlorine atoms. The rates on the supported catalysts are comparable to the ones reported before on a Pd foil, indicating that the support does not play a role in the reaction. The product distribution is independent of conversion, implying that the various products are formed from a single visit of the reactant on the surface and not from readsorption of gas-phase products. The four compounds studied were chloropentafluoroethane (CF{sub 3}-CF{sub 2}Cl), 2-chloro-1,1,1,2-tetrafluoroethane (CF{sub 3}-CFClH), 1,1-dichlorotetrafluoroethane (CF{sub 3}-CFCl{sub 2}), and 1,1,1-trichloro-2,2,2-trifluoroethane (CF{sub 3}-CCl{sub 3}).

  6. Rates and Mechanisms of Complexation Reactions of Cations with Crown Ethers and Related Macrocycles

    DTIC Science & Technology

    1989-01-23

    as stability constants and entropies of solvation t, be of paramount importance. Complexation rate constants alone seldom disclose a great deal more...sample equilibrium to assure detectability of the reaction. Disadvantages include 1) the need for high solute concentrations in order to detect small...ultrasonic techniques. In principle, the stability constants of macrocycles complexing various cations can be deduced from the amplitudes of the experimental

  7. Absolute rate of the reaction of hydrogen atoms with ozone from 219-360 K

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

    Absolute rate constants for the reaction of atomic hydrogen with ozone were obtained over the temperature range 219-360 K by the flash photolysis-resonance fluorescence technique. The results can be expressed in Arrhenius form by K = (1.33 plus or minus 0.32)x10 to the minus 10 power exp (-449 plus or minus 58/T) cu cm/molecule/s (two standard deviations). The present work is compared to two previous determinations and is discussed theoretically.

  8. A Review of the Thermodynamic, Transport, and Chemical Reaction Rate Properties of High-temperature Air

    NASA Technical Reports Server (NTRS)

    Hansen, C Frederick; Heims, Steve P

    1958-01-01

    Thermodynamic and transport properties of high temperature air, and the reaction rates for the important chemical processes which occur in air, are reviewed. Semiempirical, analytic expressions are presented for thermodynamic and transport properties of air. Examples are given illustrating the use of these properties to evaluate (1) equilibrium conditions following shock waves, (2) stagnation region heat flux to a blunt high-speed body, and (3) some chemical relaxation lengths in stagnation region flow.

  9. Study of 16O(12C,α20Ne)α for the investigation of carbon-carbon fusion reaction via the Trojan Horse Method

    NASA Astrophysics Data System (ADS)

    Rapisarda, G. G.; Spitaleri, C.; Bordeanu, C.; Hons, Z.; Kiss, G. G.; La Cognata, M.; Mrazek, J.; Nita, C.; Pantelica, D.; Petrascu, H.; Pizzone, R. G.; Romano, S.; Szücs, T.; Trache, L.; Tumino, A.; Velisa, G.

    2016-04-01

    Carbon-carbon fusion reaction represents a nuclear process of great interest in astrophysics, since the carbon burning is connected with the third phase of massive stars (M > 8 M⊙) evolution. In spite of several experimental works, carbon-carbon cross section has been measured at energy still above the Gamow window moreover data at low energy present big uncertainty. In this paper we report the results about the study of the 16O(12C,α 20Ne)α reaction as a possible three-body process to investigate 12C(12C,α)20Ne at astrophysical energy via Trojan Horse Method (THM). This study represents the first step of a program of experiments aimed to measure the 12C+12C cross section at astrophysical energy using the THM.

  10. Clustering effects in fusion evaporation reactions with light even-even N = Z nuclei. The {sup 24}Mg and {sup 28}Si cases

    SciTech Connect

    Morelli, L. D’Agostino, M.; Bruno, M.; Baiocco, G.; Gulminelli, F.; Cinausero, M.; Gramegna, F.; Marchi, T.; Degerlier, M.; Fabris, D.; Barlini, S.; Bini, M.; Casini, G.; Gelli, N.; Olmi, A.; Pasquali, G.; Piantelli, S.

    2015-10-15

    In the recent years, cluster structures have been evidenced in many ground and excited states of light nuclei [1, 2]. Within the currently ongoing experimental campaign by the NUCL-EX collaboration we have measured the {sup 12}C+{sup 12}C and {sup 14}N+{sup 10}B reactions at 95 MeV and 80 MeV respectively, and compared experimental data corresponding to complete fusion of target and projectile into an excited {sup 24}Mg nucleus to the results of a pure statistical model[3, 4]. We found clear deviations from the statstical model in the decay pattern: emission channels involving multiple α particles are more probable than expected from a purely statistical behavior. To continue the investigation on light systems, we have recentely measured the {sup 16}O+{sup 12}C reaction at three different beam energies, namely E{sub beam} = 90, 110 and 130 MeV.

  11. Calculation of the evaporation residue cross sections for the synthesis of the superheavy element Z=119 via the {sup 50}Ti+{sup 249}Bk hot fusion reaction

    SciTech Connect

    Liu Zuhua; Bao, Jing-Dong

    2011-09-15

    The evaporation residue (ER) cross sections for 3n and 4n evaporation channels in the {sup 50}Ti + {sup 249}Bk reaction leading the formation of {sup 296}119 and {sup 295}119 isotopes are evaluated by means of a modified fusion-by-diffusion model. In the model, the dynamic evolution from dinucleus to mononucleus is taken into account with the two-dimensional coupled Langenvin equations. The calculated maximum ER cross sections in 3n and 4n evaporation channels of the {sup 50}Ti + {sup 249}Bk reaction are 0.17 and 0.57 pb, respectively. The cross section of 0.57 pb is close to the present experimental limit for the registration of the evaporation residual nuclei. Therefore, superheavy element 119 may be the most hopeful new element with Z>118 to be synthesized under somehow improved experimental conditions in the near future.

  12. Role of nuclear dissipation and entrance channel mass asymmetry in pre-scission neutron multiplicity enhancement in fusion-fission reactions

    SciTech Connect

    Singh, Hardev; Sandal, Rohit; Behera, Bivash R.; Singh, Gulzar; Govil, I. M.; Golda, K. S.; Ranjeet,; Jhingan, Akhil; Singh, R. P.; Sugathan, P.; Chatterjee, M. B.; Datta, S. K.; Pal, Santanu; Viesti, G.

    2008-08-15

    Pre-scission neutron multiplicities are measured for {sup 12}C + {sup 204}Pb and {sup 19}F + {sup 197}Au reactions at laboratory energies of 75-95 MeV for the {sup 12}C beam and 98-118 MeV for the {sup 19}F beam. The chosen projectile-target combinations in the present study lie on either side of the Businaro-Gallone mass asymmetry ({alpha}{sub BG}) and populate the {sup 216}Ra compound nucleus. The dissipation strength is deduced after comparing the experimentally measured neutron yield with the statistical model predictions which contains the nuclear viscosity as a free parameter. Present results demonstrate the combined effects of entrance channel mass asymmetry and the dissipative property of nuclear matter on the pre-scission neutron multiplicity in fusion-fission reactions.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  14. The CH + CO reaction: Rate coefficient for carbon atom exchange at 294 K

    SciTech Connect

    Anderson, S.M.; McCurdy, K.E.; Kolb, C.E. )

    1989-02-09

    A fast-flow reactor equipped with isotope-specific laser-excited fluorescence detection of CH radicals has been used to study carbon atom exchange in the reaction between CH and CO at 294 K and 2 Torr of total pressure. The rate coefficient for exchange, k{sub 3} = (2.1 {times} 0.3) {times} 10{sup {minus}12} cm{sup 3} s{sup {minus}1}, is about an order of magnitude larger than the bimolecular rate for the addition reaction, k{sub 2} = (2.7 {plus minus} 0.4) {times} 10{sup {minus}13}. High-pressure limiting bimolecular and low-pressure termolecular recombination rate coefficients of 1.1 {times} 10{sup {minus}10} cm{sup 3} s{sup {minus}1} and 4.9 {times} 10{sup {minus}30} cm{sup 6} s{sup {minus}1} are derived. The results are discussed in the context of previous work on the title reaction and on the chemistry of singlet CH{sub 2}.

  15. Rates and mechanisms of the atomic oxygen reaction with nickel at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Christian, J. D.; Gilbreath, W. P.

    1973-01-01

    The oxidation of nickel by atomic oxygen at pressure from 1 to 45 N/sq m between 1050 and 1250 K was investigated. In these ranges, the oxidation was found to follow the parobolic rate law, viz., K sub p = 0.0000114 exp(-13410/T) g squared/cm4/sec for films of greater than 1 micron thickness and was pressure independent. The activation enthalpy for the oxidation reaction was 112 + or - 11 kj/mole (27 + or - 3 kcal/mole). Of a number of possible mechanisms and defect structures considered, it was shown that the most likely was a saturated surface defect model for atomic oxidation, based on reaction activation enthalpies, impurity effects, pressure independence, and magnitudes of rates. A model judged somewhat less likely was one having doubly ionized cationic defects rate controlling in both atomic and molecular oxygen. From comparisons of the appropriate processes, the following enthalpy values were derived: enthalpy of activation (Ni diffusion in Ni0) = 110 + or - 30 kj/mole and standard enthalpy change for reaction formation (doubly ionized cation vacancies in Ni0 from atomic oxygen)= -9 + or - 25 kj/mole.

  16. Reaction rate and collisional efficiency of the rhodopsin-transducin system in intact retinal rods.

    PubMed Central

    Kahlert, M; Hofmann, K P

    1991-01-01

    A model of transducin activation is constructed from its partial reactions (formation of metarhodopsin II, association, and dissociation of the rhodopsin-transducin complex). The kinetic equations of the model are solved both numerically and, for small photoactivation, analytically. From data on the partial reactions in vitro, rate and activation energy profile of amplified transducin turnover are modeled and compared with measured light-scattering signals of transducin activation in intact retinal rods. The data leave one free parameter, the rate of association between transducin and rhodopsin. Best fit is achieved for an activation energy of 35 kJ/mol, indicating lateral membrane diffusion of the proteins as its main determinant. The absolute value of the association rate is discussed in terms of the success of collisions to form the catalytic complex. It is greater than 30% for the intact retina and 10 times lower after permeabilization with staphylococcus aureus alpha-toxin. Dissociation rates for micromolar guanosinetriphosphale (GTP) (Kohl, B., and K. P. Hofmann, 1987. Biophys. J. 52:271-277) must be extrapolated linearly up to the millimolar range to explain the rapid transducin turnover in situ. This is interpreted by an unstable rhodopsin-transducin-GTP transient state. At the time of maximal turnover after a flash, the rate of activation is determined as 30, 120, 800, 2,500, and 4,000 activated transducins per photoactivated rhodopsin and second at 5, 10, 20, 30, 37 degrees C, respectively. PMID:1901231

  17. Quantum Tunneling Rates of Gas-Phase Reactions from On-the-Fly Instanton Calculations.

    PubMed

    Beyer, Adrian N; Richardson, Jeremy O; Knowles, Peter J; Rommel, Judith; Althorpe, Stuart C

    2016-11-03

    The instanton method obtains approximate tunneling rates from the minimum-action path (known as the instanton) linking reactants to the products at a given temperature. An efficient way to find the instanton is to search for saddle-points on the ring-polymer potential surface, which is obtained by expressing the quantum Boltzmann operator as a discrete path-integral. Here we report a practical implementation of this ring-polymer form of instanton theory into the Molpro electronic-structure package, which allows the rates to be computed on-the-fly, without the need for a fitted analytic potential-energy surface. As a test case, we compute tunneling rates for the benchmark H + CH4 reaction, showing how the efficiency of the instanton method allows the user systematically to converge the tunneling rate with respect to the level of electronic-structure theory.

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

    SciTech Connect

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

    1987-09-24

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

  19. Rates and mechanisms for the reactions of chlorine atoms with iodoethane and 2-iodopropane.

    PubMed

    Orlando, John J; Piety, Charles A; Nicovich, J Michael; McKee, Michael L; Wine, Paul H

    2005-08-04

    The reaction of Cl atoms with iodoethane has been studied via a combination of laser flash photolysis/resonance fluorescence (LFP-RF), environmental chamber/Fourier transform (FT)IR, and quantum chemical techniques. Above 330 K, the flash photolysis data indicate that the reaction proceeds predominantly via hydrogen abstraction. The following Arrhenius expressions (in units of cm3 molecule(-1) s(-1)) apply over the temperature range 334-434 K for reaction of Cl with CH3CH2I (k4(H)) and CD3CD2I (k4(D)): k4(H) = (6.53 +/- 3.40) x 10(-11) exp[-(428 +/- 206)/T] and k4(D) = (2.21 +/- 0.44) x 10(-11) exp[-(317 +/- 76)/T]. At room temperature and below, the reaction proceeds both via hydrogen abstraction and via reversible formation of an iodoethane/Cl adduct. Analysis of the LFP-RF data yields a binding enthalpy (0 K) for CD3CD2I x Cl of 57 +/- 10 kJ mol(-1). Calculations using density functional theory show that the adduct is characterized by a C-I-Cl bond angle of 84.5 degrees; theoretical binding enthalpies of 38.2 kJ/mol, G2'[ECP(S)], and 59.0 kJ mol(-1), B3LYP/ECP, are reasonably consistent with the experimentally derived result. Product studies conducted in the environmental chamber show that hydrogen abstraction from both the -CH2I and -CH3 groups occur to a significant extent and also provide evidence for a reaction of the CH3CH2I x Cl adduct with CH3CH2I, leading to CH3CH2Cl formation. Complementary environmental chamber studies of the reaction of Cl atoms with 2-iodopropane, CH3CHICH3, are also presented. As determined by relative rate methods, the reaction proceeds with an effective rate coefficient, k6, of (5.0 +/- 0.6) x 10(-11) cm3 molecule(-1) s(-1) at 298 K. Product studies indicate that this reaction also occurs via two abstraction channels (from the CH3 groups and from the -CHI- group) and via reversible adduct formation.

  20. Atmospheric degradation of saturated alcohols: Room temperature rate coefficients for NO3 radical reactions

    NASA Astrophysics Data System (ADS)

    Moreno, Alberto; Salgado, Sagrario; Taccone, Raul; Martín, Pilar; Cabañas, Beatriz

    2014-10-01

    Rate coefficients for the reactions of NO3 radicals with a series of saturated alcohols are reported here using the relative rate technique. Experiments were performed using air as bath gas in a 50 L glass-pyrex reaction chamber at room temperature (298 ± 2) K with long-path FTIR spectroscopy used to monitor the reaction at atmospheric pressure (708 ± 8) Torr. The reference compounds used and their rate coefficients are: propanal kNO3 = (6.0 ± 0.6) × 10-15, methyl methacrylate kNO3 = (3.55 ± 0.62) × 10-15, acetaldehyde kNO3 = (2.62 ± 0.29) × 10-15 and propene kNO3 = (9.50 ± 1.9) × 10-15, in cm3 molecule-1 s-1. Rate coefficients obtained were (in units cm3 molecule-1 s-1): (1.87 ± 0.14) × 10-15, (2.39 ± 0.20) × 10-15, (2.28 ± 0.17) × 10-15, (1.80 ± 0.13) × 10-15 and (3.52 ± 0.19) × 10-15 for 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 3,3-dimethyl-1-butanol and 3,3-dimethyl-2-butanol respectively. Reactivity trend can be explained in terms of the different types of hydrogen inside the hydrocarbon chain. The reaction occurs by an initial H-atom abstraction mainly from C-H groups of the alcohols by the NO3 radical being NO3 more reactive towards an H atom attached to a tertiary carbon than that attached to a secondary or primary carbon. Reactivity trend is compared with their similar structural 2-butanol and with the corresponding alkanes. Atmospheric implications are also discussed calculating lifetimes of the saturated alcohols studied here due to the reaction with NO3 radicals in comparison to their reactions with the other major atmospheric oxidants.

  1. An investigation of the relationships between rate and driving force in simple uncatalysed and enzyme-catalysed reactions with applications of the findings to chemiosmotic reactions.

    PubMed Central

    Stoner, C D

    1992-01-01

    Both the rate and the driving force of a reaction can be expressed in terms of the concentrations of the reactants and products. Consequently, rate and driving force can be expressed as a function of each other. This has been done for a single-reactant, single-product, uncatalysed reaction and its enzyme-catalysed equivalent using the van't Hoff reaction isotherm and Haldane's generalized Michaelis-Menten rate equation, the primary objective being explanation of the exponential and sigmoidal relationships between reaction rate and delta mu H+ commonly observed in studies on chemiosmotic reactions. Acquisition of a purely thermodynamic rate vs. driving-force relationship requires recognition of the intensive and extensive variables and maintenance of the extensive variables constant. This relationship is identical for the two reactions and is hyperbolic or sigmoidal, depending on whether the equilibrium constant is smaller or larger than unity. In the case of the catalysed reaction, acquisition of the purely thermodynamic relationship requires the assumption that the enzyme be equally effective in catalysing the forward and backward reactions. If this condition is not met, the relationship is modified by the enzyme in a manner which can be determined from the ratio of the Michaelis constants of the reactant and product. Under conditions of enzyme saturation in respect to reactant+product, the rate vs. driving-force relationship is determined exclusively by the thermodynamics of the reaction and a single kinetic parameter, the magnitude of which is determined by the relative effectiveness of the enzyme in catalysing the forward and backward reactions. In view of this finding, it is pointed out that, since the catalytic components of chemiosmotic reactions appear to be saturated with respect to the reactant-product pair that is varied in experimental rate vs. delta mu H+ determinations, and that, since many complex enzymic reactions conform to the simple Michaelis

  2. Upscaling of reaction rates in reactive transport using pore-scale reactive transport model

    NASA Astrophysics Data System (ADS)

    Yoon, H.; Dewers, T. A.; Arnold, B. W.; Major, J. R.; Eichhubl, P.; Srinivasan, S.

    2013-12-01

    Dissolved CO2 during geological CO2 storage may react with minerals in fractured rocks, confined aquifers, or faults, resulting in mineral precipitation and dissolution. The overall rate of reaction can be affected by coupled processes among hydrodynamics, transport, and reactions at the (sub) pore-scale. In this research pore-scale modeling of coupled fluid flow, reactive transport, and heterogeneous reaction at the mineral surface is applied to account for permeability alterations caused by precipitation-induced pore-blocking. This work is motivated by the observed CO2 seeps from a natural analog to geologic CO2 sequestration at Crystal Geyser, Utah. A key observation is the lateral migration of CO2 seep sites at a scale of ~ 100 meters over time. A pore-scale model provides fundamental mechanistic explanations of how calcite precipitation alters flow paths by pore plugging under different geochemical compositions and pore configurations. In addition, response function of reaction rates will be constructed from pore-scale simulations which account for a range of reaction regimes characterized by the Damkohler and Peclet numbers. Newly developed response functions will be used in a continuum scale model that may account for large-scale phenomena mimicking lateral migration of surface CO2 seeps. Comparison of field observations and simulations results will provide mechanistic explanations of the lateral migration and enhance our understanding of subsurface processes associated with the CO2 injection. This work is supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security

  3. Population of isomeric states in fusion and transfer reactions in beams of loosely bound nuclei near the Coulomb barrier

    SciTech Connect

    Skobelev, N. K.

    2015-07-15

    The influence of the mechanisms of nuclear reactions on the population of {sup 195m}Hg and {sup 197m}Hg(7/2{sup −}), {sup 198m}Tl and {sup 196m}Tl(7{sup +}), and {sup 196m}Au and {sub 198m}Au(12{sup −}) isomeric nuclear states obtained in reactions induced by beams of {sup 3}He, {sup 6}Li, and {sup 6}He weakly bound nuclei is studied. The behavior of excitation functions and high values of isomeric ratios (δ{sub m}/δ{sub g}) for products of nuclear reactions proceeding through a compound nucleus and involving neutron evaporation are explained within statistical models. Reactions in which the emission of charged particles occurs have various isomeric ratios depending on the reaction type. The isomeric ratio is lower in direct transfer reactions involving charged-particle emission than in reactions where the evaporation of charged particles occurs. Reactions accompanied by neutron transfer usually have a lower isomeric ratio, which behaves differently for different direct-reaction types (stripping versus pickup reactions)

  4. Reaction Rate Theory in Coordination Number Space: An Application to Ion Solvation

    SciTech Connect

    Roy, Santanu; Baer, Marcel D.; Mundy, Christopher J.; Schenter, Gregory K.

    2016-04-14

    Understanding reaction mechanisms in many chemical and biological processes require application of rare event theories. In these theories, an effective choice of a reaction coordinate to describe a reaction pathway is essential. To this end, we study ion solvation in water using molecular dynamics simulations and explore the utility of coordination number (n = number of water molecules in the first solvation shell) as the reaction coordinate. Here we compute the potential of mean force (W(n)) using umbrella sampling, predicting multiple metastable n-states for both cations and anions. We find with increasing ionic size, these states become more stable and structured for cations when compared to anions. We have extended transition state theory (TST) to calculate transition rates between n-states. TST overestimates the rate constant due to solvent-induced barrier recrossings that are not accounted for. We correct the TST rates by calculating transmission coefficients using the reactive flux method. This approach enables a new way of understanding rare events involving coordination complexes. We gratefully acknowledge Liem Dang and Panos Stinis for useful discussion. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. SR, CJM, and GKS were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. MDB was supported by MS3 (Materials Synthesis and Simulation Across Scales) Initiative, a Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy.

  5. Assessing the Effects of New Reaction Rates and Convection Theory on Studies of Supernova Progenitors

    NASA Astrophysics Data System (ADS)

    Starrfield, Sumner

    We request funding to carry out a systematic evaluation of nuclear reaction rates and convection on the pre-explosion evolution of core-collapse (SN II) and thermonuclear (SN Ia) supernovae. We will use MESA (Modules for Experiments in Stellar Astrophysics) a new stellar evolution computer code that is co-authored by Co-PI Timmes. One goal of this proposal is to determine the effects of new thermonuclear reaction rates, taken from the next-generation library STARLIB developed by Co-PI Iliadis, on the resulting evolution. Another goal is to test the effects of the latest convection theory, microphysics changes, and numerical techniques on the results. STARLIB is a first-of-its-kind nuclear reaction rate library and, unlike all other libraries, it contains the full reaction rate probability densities at all stellar temperatures. It is publicly available as of June 2013. Consequently, we are now in a unique position to model stellar evolution and nucleosynthesis in a quantitative manner that makes predictions for key observations by NASA ground-based and satellite observatories. We will use two complementary strategies. First, we will take the modern and multiple prescriptions of convection that are implemented in MESA, together with the recommended thermonuclear reaction rates provided by STARLIB, to generate new hydrodynamic simulations of SN Ia and SN II progenitor evolution. Second, we will take the temperature-density-time trajectories from the evolutionary results and do Monte Carlo post-processing nucleosynthesis calculations by sampling over the reaction rate probability densities. This procedure could not be applied previously and has only become feasible with the availability of STARLIB. Calculations of pre-supernova evolution with the STARLIB reaction rates and new convection prescriptions will provide, for the first time, statistically rigorous estimates for both their evolutionary structures and resulting nucleosynthesis. Significant insight into pre

  6. A commercial lunar helium 3 fusion power infrasructure

    NASA Astrophysics Data System (ADS)

    Sved, J.; Kulcinski, G. L.; Miley, G. H.

    1995-01-01

    The potential scenario of a commercial aneutronic fusion power economy based on Helium 3 is reviewed with recent developments in fusion grade plasma containment considered. The Spherical Inertial Electrostatic Confinement (IEC) device is a type of fusion reactor with immediate commercial applications as a small non-power reactor. Further development and growth to power reactor fusion reaction rates using Deuterium and Helium 3 offers the potential practical solution to fusion power. Recovery of the lunar Helium 3 inventory for export to power utility customers will require the build-up of a cis-lunar industrial infrastructure. Space transport capacity will be obliged to grow rapidly to support several thousand tons of cargo delivery to the lunar surface per year. A highly reusable, low operations cost cis-lunar transport infrastructure and lunar surface industrial activity will be made more practical by the availability of IEC fusion power units that are intrinsically low mass and compatible with space transport.

  7. Reaction rate of a composite core-shell nanoreactor with multiple nanocatalysts.

    PubMed

    Galanti, Marta; Fanelli, Duccio; Angioletti-Uberti, Stefano; Ballauff, Matthias; Dzubiella, Joachim; Piazza, Francesco

    2016-07-27

    We present a detailed theory for the total reaction rate constant of a composite core-shell nanoreactor, consisting of a central solid core surrounded by a hydrogel layer of variable thickness, where a given number of small catalytic nanoparticles are embedded at prescribed positions and are endowed with a prescribed surface reaction rate constant. Besides the precise geometry of the assembly, our theory accounts explicitly for the diffusion coefficients of the reactants in the hydrogel and in the bulk as well as for their transfer free energy jump upon entering the hydrogel shell. Moreover, we work out an approximate analytical formula for the overall rate constant, which is valid in the physically relevant range of geometrical and chemical parameters. We discuss in depth how the diffusion-controlled part of the rate depends on the essential variables, including the size of the central core. In particular, we derive some simple rules for estimating the number of nanocatalysts per nanoreactor for an efficient catalytic performance in the case of small to intermediate core sizes. Our theoretical treatment promises to provide a very useful and flexible tool for the design of superior performing nanoreactor geometries with optimized nanoparticle load.

  8. Cluster states and container picture in light nuclei, and triple-alpha reaction rate

    NASA Astrophysics Data System (ADS)

    Funaki, Yasuro

    2015-04-01

    The excited states in 12C are investigated by using an extended version of the so- called Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function, where both the 3α condensate and 8Be + α cluster asymptotic configurations are included. We focus on the structures of the “Hoyle band” states, 2+2, and 4+2 states, which are recently observed above the Hoyle state, and of the 0+3 and 0+4 states, which are also quite recently identified in experiment. We show that the Hoyle band is not simply considered to be the 8Be(0+) + α rotation as suggested by previous cluster model calculations, nor to be a rotation of a rigid-body triangle-shaped object composed of the 3α particles. We also discuss the rate of the triple-alpha radiative capture reaction, applyng the imaginary-time method. Results of the triple-alpha reaction rate are consistent with NACRE rate for both high (≈ 109K) and low (≈ 107 K) temperatures. We show that the rate of the imaginary-time calculation in coupled-channels approach has a large enhancement for low temperatures if we truncate the number of channels.

  9. Reaction rate of a composite core-shell nanoreactor with multiple nanocatalysts

    NASA Astrophysics Data System (ADS)

    Galanti, Marta; Fanelli, Duccio; Angioletti-Uberti, Stefano; Ballauff, Matthias; Dzubiella, Joachim; Piazza, Francesco

    We present a detailed theory for the total reaction rate constant of a composite core-shell nanoreactor, consisting of a central solid core surrounded by a hydrogel layer of variable thickness, where a given number of small catalytic nanoparticles are embedded at prescribed positions and are endowed with a prescribed surface reaction rate constant. Besides the precise geometry of the assembly, our theory accounts explicitly for the diffusion coefficients of the reactants in the hydrogel and in the bulk as well as for their transfer free energy jump upon entering the hydrogel shell. Moreover, we work out an approximate analytical formula for the overall rate constant, which is valid in the physically relevant range of geometrical and chemical parameters. We discuss in depth how the diffusion-controlled part of the rate depends on the essential variables, including the size of the central core. In particular, we derive some simple rules for estimating the number of nanocatalysts per nanoreactor for an efficient catalytic performance in the case of small to intermediate core sizes. Our theoretical treatment promises to provide a very useful and flexible tool for the design of superior performing nanoreactor geometries and with optimized nanoparticle load.

  10. Characterization of the reaction rate coefficient of DNA with the hydroxyl radical

    SciTech Connect

    Milligan, J.R.; Ward, J.F.; Aguilera, J.A.

    1996-11-01

    Using agarose gel electrophoresis, we have measured the yield of single-strand breaks (SSBs) induced by {sup 137}Cs {gamma} irradiation in a variety of plasmid DNA substrates ranging in size from 2.7 kb to 38 kb irradiated in aerobic aqueous solution in the presence of the hydroxyl radical scavenger dimethyl sulfoxide (DMSO). Under these conditions DNA SSBs are caused mainly by the hydroxyl radical. Using the competition between DMSO and DNA for the hydroxyl radical, we have estimated the rate coefficient for the reaction of the hydroxyl radical with DNA. The results cannot be characterized by conventional steady-state competition kinetics. However, it is possible to describe the second-order rate constant for the reaction as a function of the scavenging capacity of the solution. The second-order rate constant increases with increasing scavenging capacity, rising from about 5x10{sup 8} dm{sup 3} mol{sup -1} s{sup -1} at 10{sup 5} s{sup -1} to about 10{sup 10} dm{sup 3} mol{sup -1} s{sup -1} at 10{sup 10} s{sup -1}. This dependence of the second-order rate constant on the scavenging capacity appears to be more pronounced for larger plasmids. 17 refs., 4 figs.

  11. A study of the photocatalytic effects of aqueous suspensions of platinized semiconductor materials on the reaction rates of candidate redox reactions

    NASA Technical Reports Server (NTRS)

    Miles, A. M.

    1982-01-01

    The effectiveness of powdered semiconductor materials in photocatalyzing candidate redox reactions was investigated. The rate of the photocatalyzed oxidation of cyanide at platinized TiO2 was studied. The extent of the cyanide reaction was followed directly using an electroanalytical method (i.e. differential pulse polarography). Experiments were performed in natural or artificial light. A comparison was made of kinetic data obtained for photocatalysis at platinized powders with rate data for nonplatinized powders.

  12. Astrophysical reaction rates from a symmetry-informed first-principles perspective

    NASA Astrophysics Data System (ADS)

    Dreyfuss, Alison; Launey, Kristina; Baker, Robert; Draayer, Jerry; Dytrych, Tomas

    2017-01-01

    With a view toward a new unified formalism for studying bound and continuum states in nuclei, to understand stellar nucleosynthesis from a fully ab initio perspective, we studied the nature of surface α-clustering in 20Ne by considering the overlap of symplectic states with cluster-like states. We compute the spectroscopic amplitudes and factors, α-decay width, and absolute resonance strength - characterizing major contributions to the astrophysical reaction rate through a low-lying 1- resonant state in 20Ne. As a next step, we consider a fully microscopic treatment for the n+4 He system, based on the successful first-principles No-Core Shell Model/Resonating Group Method (NCSM/RGM) for light nuclei, but with the capability to reach intermediate-mass nuclei. The new model takes advantage of the symmetry-based concept central to the Symmetry-Adapted No-Core Shell Model (SA-NCSM) to reduce computational complexity in physically-informed and methodical way, with sights toward first-principles calculations of rates for important astrophysical reactions, such as the 23 Al(p , γ) 24 Si reaction, believed to have a strong influence on X-ray burst light curves. Supported by the U.S. NSF (OCI-0904874, ACI -1516338) and the U.S. DOE (DE-SC0005248), and benefitted from computing resources provided by Blue Waters and the LSU Center for Computation & Technology.

  13. Contribution of 19F resonances on 18O( p, α)15N reaction rate

    NASA Astrophysics Data System (ADS)

    Benmeslem, Meriem; Chafa, Azzedine; Barhoumi, Slimane; Tribeche, Mouloud

    2014-08-01

    The 18O( p, α)15N reaction influences the isotopes production such as 19F, 18O, and 15N which can be used to test the models of stellar evolution. 19F is synthesized in both asymptotic giant branch (AGB) and metal-rich Wolf-Rayet (WR) stars. Using R-matrix theory we allow new values of resonances parameters in 19F. We show that the most important contribution to the differential and total cross section at low energies, comes from the levels in 19F situated at resonances energies E R =151, 680 and 840 keV with spin and parity 1/2+. The total width of the 680 keV resonance is badly known. So, we have focused on this broad resonance corresponding to the 8.65 MeV level in 19F. We delimit the temperature range in which each resonance contribution to the total reaction rate occurs by analyzing the ratio ( N A < σν> i / N A < σν>). This allowed us to show that the 680 and 840 keV broad resonances strongly dominate the reaction rate over the stellar temperature range T 9=0.02-0.06 and T 9=0.5-5. Finally, these results were compared to NACRE and Iliadis astrophysical compilations.

  14. Reaction kinetics, P-T-t paths and rates of tectonic processes

    SciTech Connect

    Bohlen, S.R.; Hankins, W.B.; Eckert, J.O. Jr.; Kirby, S.H.; Liu, J. ); Hacker, B.R.; Mosenfelder, J.L. . Dept. of Geology)

    1992-01-01

    The interpretation of portions of P-T-time (t) paths in metamorphic rocks assumes that continuous and discontinuous reactions record local equilibrium as P-T conditions change, implying that the kinetics of many reactions are rapid relative to dT/dt and dP/dt. Occurrence of eclogite veins in granulites from Bergen, Norway as well as occurrences of coesite and diamond in crustal rocks imply that, under certain conditions, this assumption is wrong. Knowledge of the kinetics of important reactions under appropriate conditions would provide limits on the duration of relatively narrowly defined P-T conditions, allow inference of the rates of exhumation of rocks containing high-pressure phases, and allow the calculation of the time required for the conversion of gabbro to eclogite in the lower crust as a function of P-T-t. The authors are currently assessing the rates of key phase transformations: calcite to aragonite, albite to jadeite + quartz, coesite to quartz, opx[sub Fs[sup 80

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

    SciTech Connect

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

    1987-04-23

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

  16. Phosphatase-coupled universal kinase assay and kinetics for first-order-rate coupling reaction.

    PubMed

    Wu, Zhengliang L

    2011-01-01

    Kinases use adenosine-5'-triphosphate (ATP) as the donor substrate and generate adenosine-5'-diphosphate (ADP) as a product. An ADP-based phosphatase-coupled kinase assay is described here. In this assay, CD39L2, a nucleotidase, is added into a kinase reaction to hydrolyze ADP to AMP and phosphate. The phosphate is subsequently detected using malachite green phosphate-detection reagents. As ADP hydrolysis by CD39L2 displays a first-order rate constant, relatively simple equations are derived to calculate the coupling rate and the lagging time of the coupling reaction, allowing one to obtain kinase kinetic parameters without the completion of the coupling reaction. ATP inhibition of CD39L2-catalyzed ADP hydrolysis is also determined for correction of the kinetic data. As examples, human glucokinase, P. chrysogenum APS kinase and human ERK1, kinases specific for sugar, nucleotide and protein respectively, are assayed. To assess the compatibility of the method for high-throughput assays, Z' factors >0.5 are also obtained for the three kinases.

  17. THE IMPACT OF HELIUM-BURNING REACTION RATES ON MASSIVE STAR EVOLUTION AND NUCLEOSYNTHESIS

    SciTech Connect

    West, Christopher; Heger, Alexander; Austin, Sam M. E-mail: alexander.heger@monash.edu

    2013-05-20

    We study the sensitivity of presupernova evolution and supernova nucleosynthesis yields of massive stars to variations of the helium-burning reaction rates within the range of their uncertainties. The current solar abundances from Lodders are used for the initial stellar composition. We compute a grid of 12 initial stellar masses and 176 models per stellar mass to explore the effects of independently varying the {sup 12}C({alpha}, {gamma}){sup 16}O and 3{alpha} reaction rates, denoted R{sub {alpha},12} and R{sub 3{alpha}}, respectively. The production factors of both the intermediate-mass elements (A = 16-40) and the s-only isotopes along the weak s-process path ({sup 70}Ge, {sup 76}Se, {sup 80}Kr, {sup 82}Kr, {sup 86}Sr, and {sup 87}Sr) were found to be in reasonable agreement with predictions for variations of R{sub 3{alpha}} and R{sub {alpha},12} of {+-}25%; the s-only isotopes, however, tend to favor higher values of R{sub 3{alpha}} than the intermediate-mass isotopes. The experimental uncertainty (one standard deviation) in R{sub 3{alpha}}(R{sub {alpha},12}) is approximately {+-}10%({+-}25%). The results show that a more accurate measurement of one of these rates would decrease the uncertainty in the other as inferred from the present calculations. We also observe sharp changes in production factors and standard deviations for small changes in the reaction rates, due to differences in the convection structure of the star. The compactness parameter was used to assess which models would likely explode as successful supernovae, and hence contribute explosive nucleosynthesis yields. We also provide the approximate remnant masses for each model and the carbon mass fractions at the end of core-helium burning as a key parameter for later evolution stages.

  18. Modeling microbial reaction rates in a submarine hydrothermal vent chimney wall

    NASA Astrophysics Data System (ADS)

    LaRowe, Douglas E.; Dale, Andrew W.; Aguilera, David R.; L'Heureux, Ivan; Amend, Jan P.; Regnier, Pierre

    2014-01-01

    The fluids emanating from active submarine hydrothermal vent chimneys provide a window into subseafloor processes and, through mixing with seawater, are responsible for steep thermal and compositional gradients that provide the energetic basis for diverse biological communities. Although several models have been developed to better understand the dynamic interplay of seawater, hydrothermal fluid, minerals and microorganisms inside chimney walls, none provide a fully integrated approach to quantifying the biogeochemistry of these hydrothermal systems. In an effort to remedy this, a fully coupled biogeochemical reaction-transport model of a hydrothermal vent chimney has been developed that explicitly quantifies the rates of microbial catalysis while taking into account geochemical processes such as fluid flow, solute transport and oxidation-reduction reactions associated with fluid mixing as a function of temperature. The metabolisms included in the reaction network are methanogenesis, aerobic oxidation of hydrogen, sulfide and methane and sulfate reduction by hydrogen and methane. Model results indicate that microbial catalysis is generally fastest in the hottest habitable portion of the vent chimney (77-102 °C), and methane and sulfide oxidation peak near the seawater-side of the chimney. The fastest metabolisms are aerobic oxidation of H2 and sulfide and reduction of sulfate by H2 with maximum rates of 140, 900 and 800 pmol cm-3 d-1, respectively. The maximum rate of hydrogenotrophic methanogenesis is just under 0.03 pmol cm-3 d-1, the slowest of the metabolisms considered. Due to thermodynamic inhibition, there is no anaerobic oxidation of methane by sulfate (AOM). These simulations are consistent with vent chimney metabolic activity inferred from phylogenetic data reported in the literature. The model developed here provides a quantitative approach to describing the rates of biogeochemical transformations in hydrothermal systems and can be used to constrain the

  19. Investigation of Shell Effects in the Fusion-Fission Process in the Reaction 34S + 186W Near the Interaction Barrier

    NASA Astrophysics Data System (ADS)

    Harca, I. M.; Kozulin, E. M.; Bogachev, A.; Dmitriev, S. N.; Itkis, J.; Knyazheva, G.; Loktev, T.; Novikov, K.; Vardaci, E.; Azaiez, F.; Gottardo, A.; Matea, I.; Verney, D.; Chubarian, G.; Hanappe, F.; Piot, J.; Schmitt, C.; Trzaska, W. H.

    2015-06-01

    The reaction 34S + 186W at Elab = 160 MeV was investigated with the aim of diving into the features of the fusion-fission process. Gamma rays coincident with binary reaction fragments were measured using the high efficiency gamma-ray spectrometer ORGAM at the TANDEM Accelerator facility of I.P.N., Orsay, and the time-of-flight spectrometer for fission fragments registration CORSET of the Flerov Laboratory of Nuclear Reactions (FLNR), Dubna. Evidence of symmetric and asymmetric fission modes were observed in the mass and TKE distributions, occurring due to shell effects in the fragments. The coupling of the ORGAM and CORSET setups enables the FF-γ coincident measurement which offers the opportunity to extract the isotopic distribution of the fragments of different masses formed in the aforementioned reaction and to find the exact neutron multiplicity, the average spin and average angular momenta. Details regarding the experimental setup, methods of processing the acquisitioned data and preliminary results are presented.

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

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

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

  1. Channel specific rate constants for reactions of O(1D) with HCl and HBr

    NASA Technical Reports Server (NTRS)

    Wine, P. H.; Wells, J. R.; Ravishankara, A. R.

    1986-01-01

    The absolute rate coefficients and product yields for reactions of O(1D) with HCl(1) and HBr(2) at 287 K are presently determined by means of the time-resolved resonance fluorescence detection of O(3P) and H(2S) in conjunction with pulsed laser photolysis of O3/HX/He mixtures. Total rate coefficients for O(1D) removal are found to be, in units of 10 to the -10th cu cm/molecule per sec, k(1) = 1.50 + or - 0.18 and k(2) 1.48 + or - 0.16; the absolute accuracy of these rate coefficients is estimated to be + or - 20 percent.

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

    SciTech Connect

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

    1990-09-06

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

  3. Temperature-dependent, relative-rate study of the reactions of 1- and 2-butoxyl radicals

    NASA Astrophysics Data System (ADS)

    Johnson, D.; Cassanelli, P.; Cox, R. A.

    2003-04-01

    Alkoxyl radicals (RO\\cdot) are important intermediates in the chains of free radical reactions that constitute the gas-phase oxidation of volatile organic compounds (VOCs). Generally there are a number of different reaction pathways available to alkoxyl radicals and, depending on conditions of temperature and the structure of RO\\cdot, these may be in competition. The major reactions of RO\\cdot are (1) reaction with O_2 to yield a carbonyl product and a hydroperoxy, HO_2, radical, (2) decomposition to yield a carbonyl product and a radical fragment, and (3) isomerisation via a six-membered transition state to yield a d-hydroxylated radical species. Thus the chemistry of alkoxyl radicals determines the atmospheric impact of the oxidation of a given VOC, in terms of the immediate effects of closed-shell products, and as a result of the further chemistry of free radical products. HO_2 can react with NO to yield photolabile NO_2 (and hence contribute to photochemical ozone formation), and organic radical fragments act to propagate the oxidation chain of reactions. As ozone has been identified to be an important greenhouse gas in the upper troposphere/lower stratosphere (UTLS) region it is important to understand how temperature affects the relative rates of reactions (1) to (3), and thus how the presence of VOCs in the UTLS region affects the coupled chemistries of HO_x and O_3. In the present study, we have looked at the reactions of 1- and 2-butoxyl radicals (formed in the reaction of OH with butane) in terms of the relative rates of their bimolecular reactions with O_2 (1) and unimolecular processes (2,3). The two butoxyl radicals were studied separately and were formed directly from the photolysis of 1- or 2-butylnitrite. Experiments were carried out using a metre-long photochemical flow cell made of quartz. The temperature of the cell could be controlled and for the experiments carried out in the present study was operated between about 250 and 340 K. Reactant

  4. Absolute rate of the reaction of Cl(p-2) with molecular hydrogen from 200 - 500 K

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

    Rate constants for the reaction of atomic chlorine with hydrogen are measured from 200 - 500 K using the flash photolysis-resonance fluorescence technique. The results are compared with previous work and are discussed with particular reference to the equilibrium constant for the reaction and to relative rate data for chlorine atom reactions. Theoretical calculations, using the BEBO method with tunneling, give excellent agreement with experiment.

  5. X-ray bang-time and fusion reaction history at picosecond resolution using RadOptic detection

    SciTech Connect

    Vernon, S. P.; Lowry, M. E.; Baker, K. L.; Bennett, C. V.; Celeste, J. R.; Cerjan, C.; Haynes, S.; Hernandez, V. J.; Hsing, W. W.; LaCaille, G. A.; London, R. A.; Moran, B.; Schach von Wittenau, A.; Steele, P. T.; Stewart, R. E.

    2012-10-15

    We report recent progress in the development of RadOptic detectors, radiation to optical converters, that rely upon x-ray absorption induced modulation of the optical refractive index of a semiconductor sensor medium to amplitude modulate an optical probe beam. The sensor temporal response is determined by the dynamics of the electron-hole pair creation and subsequent relaxation in the sensor medium. Response times of a few ps have been demonstrated in a series of experiments conducted at the LLNL Jupiter Laser Facility (JLF). This technology will enable x-ray bang-time and fusion burn-history measurements with {approx} ps resolution.

  6. X-ray bang-time and fusion reaction history at ~ps resolution using RadOptic detection

    SciTech Connect

    Vernon, S P; Lowry, M E; Baker, K L; Bennett, C V; Celeste, J R; Cerjan, C; Haynes, S; Hernandez, V J; Hsing, W W; London, R A; Moran, B; von Wittenau, A S; Steele, P T; Stewart, R E

    2012-05-01

    We report recent progress in the development of RadOptic detectors, radiation to optical converters, that rely upon x-ray absorption induced modulation of the optical refractive index of a semiconductor sensor medium to amplitude modulate an optical probe beam. The sensor temporal response is determined by the dynamics of the electron-hole pair creation and subsequent relaxation in the sensor medium. Response times of a few ps have been demonstrated in a series of experiments conducted at the LLNL Jupiter Laser Facility. This technology will enable x-ray bang-time and fusion burn-history measurements with {approx} ps resolution.

  7. Process for the oxidation of materials in water at supercritical temperatures utilizing reaction rate enhancers

    SciTech Connect

    Swallow, K.C.; Killilea, W.R.; Hong, G.T.; Bourhis, A.L.

    1993-08-03

    A method is described for substantially completely oxidizing combustible materials in which an aqueous stream bearing the combustible materials is reacted in the presence of an oxidant comprising diatomic oxygen and at a temperature greater than the critical temperature of water and at a pressure greater than about 25 bar, within a reactor for a period of less than about 5 minutes to produce a reaction product stream, wherein the reaction is initiated in the presence of a rate enhancer comprising at least one oxidizing agent in addition to said oxidant selected from the group consisting of ozone, hydrogen peroxide, salts containing persulfate, salts containing permanganate, nitric acid, salts containing nitrate, oxyacids of chlorine and their corresponding salts, hypochlorous acid, salts containing hypochlorite, chlorous acid, salts containing chlorite, chloric acid, salts containing chlorate, perchloric acid, and salts containing perchlorate.

  8. Structural and dynamical control of the reaction rate in protein electron transfer

    NASA Astrophysics Data System (ADS)

    Balabin, Ilya A.

    Electron transfer (ET) reactions in proteins are key steps in many vital bioenergetic processes, and the reaction rate is known to be highly sensitive to the protein structure in some cases. For most bioenergetic reactions, as described by the Fermi Golden rule, the rate is proportional to a product of the average square of the effective electronic donor to acceptor coupling and a Franck-Condon factor, which accounts for the nuclear control of the energy gap. The nuclear factor is reasonably well described in Marcus theory and its modifications, and this work is focused on the mechanisms that control the effective coupling. About ten years ago, the Pathways model described for the first time how protein environment may control the effective coupling. In this work, a novel theoretical approach is developed to explore the mechanisms of structural and dynamical control beyond the qualitative level of the Pathways model. In Chapter 1, the assumptions of the Pathways model, its limitations and effects of the structure and the electronic Hamiltonian are investigated for model chain-like bridges using the Dyson's equations. In Chapter II, the framework to explore the sensitivity of the effective coupling to quality of the electronic Hamiltonian, the interference among the dominant pathways and the bridge dynamics is presented. This analysis employs the Green's function technique and includes combined molecular dynamics and electronic structure calculations. Finally, in Chapter III, this framework is tested on the bacterial photosynthetic reaction center, and the mechanisms of the structural and dynamical control for different ET steps are discussed.

  9. Contribution of the photo-Fenton reaction to hydroxyl radical formation rates in river and rain water samples.

    PubMed

    Nakatani, Nobutake; Ueda, Marina; Shindo, Hirotaka; Takeda, Kazuhiko; Sakugawa, Hiroshi

    2007-09-01

    The hydroxyl radical (OH radical) formation rates from the photo-Fenton reaction in river and rain water samples were determined by using deferoxamine mesylate (DFOM), which makes a stable and strong complex with Fe(III), resulting in a suppression of the photo-Fenton reaction. The difference between the OH radical formation rates with and without added DFOM denotes the rate from the photo-Fenton reaction. The photoformation rates from the photo-Fenton reaction were in the range of 0.7 - 45.8 x 10(-12) and 2.7 - 32.3 x 10(-12) M s(-1) in river and rain water samples, respectively. A strong positive correlation between the OH radical formation rate from the photo-Fenton reaction and the amount of fluorescent matter in river water suggests that fluorescent matter, such as humic substances, plays an important role in the photo-Fenton reaction. In rain water, direct photolysis of hydrogen peroxide was an important source of OH radicals as well as the photo-Fenton reaction. The contributions of the photo-Fenton reaction to the OH radical photoformation rates in river and rain water samples were in the ranges of 2 - 29 and 5 - 38%, respectively. Taking into account the photo-Fenton reaction, 33 - 110 (mean: 80) and 42 - 110 (mean: 84)% of OH radical sources in river and rain water samples, respectively, collected in Hiroshima prefecture were elucidated.

  10. New reaction rates for improved primordial D /H calculation and the cosmic evolution of deuterium

    NASA Astrophysics Data System (ADS)

    Coc, Alain; Petitjean, Patrick; Uzan, Jean-Philippe; Vangioni, Elisabeth; Descouvemont, Pierre; Iliadis, Christian; Longland, Richard

    2015-12-01

    Primordial or big bang nucleosynthesis (BBN) is one of the three historically strong evidences for the big bang model. Standard BBN is now a parameter-free theory, since the baryonic density of the Universe has been deduced with an unprecedented precision from observations of the anisotropies of the cosmic microwave background radiation. There is a good agreement between the primordial abundances of 4He, D, 3He, and 7Li deduced from observations and from primordial nucleosynthesis calculations. However, the 7Li calculated abundance is significantly higher than the one deduced from spectroscopic observations and remains an open problem. In addition, recent deuterium observations have drastically reduced the uncertainty on D /H , to reach a value of 1.6%. It needs to be matched by BBN predictions whose precision is now limited by thermonuclear reaction rate uncertainties. This is especially important as many attempts to reconcile Li observations with models lead to an increased D prediction. Here, we reevaluate the d (p ,γ )3He, d (d ,n ) 3H3, and d (d ,p ) 3H reaction rates that govern deuterium destruction, incorporating new experimental data and carefully accounting for systematic uncertainties. Contrary to previous evaluations, we use theoretical ab initio models for the energy dependence of the S factors. As a result, these rates increase at BBN temperatures, leading to a reduced value of D /H =(2.45 ±0.10 )×10-5 (2 σ ), in agreement with observations.

  11. Direct Determination of the Simplest Criegee Intermediate (CH2OO) Self Reaction Rate.

    PubMed

    Buras, Zachary J; Elsamra, Rehab M I; Green, William H

    2014-07-03

    The rate of self-reaction of the simplest Criegee intermediate, CH2OO, is of importance in many current laboratory experiments where CH2OO concentrations are high, such as flash photolysis and alkene ozonolysis. Using laser flash photolysis while simultaneously probing both CH2OO and I atom by direct absorption, we can accurately determine absolute CH2OO concentrations as well as the UV absorption cross section of CH2OO at our probe wavelength (λ = 375 nm), which is in agreement with a recently published value. Knowing absolute concentrations we can accurately measure kself = 6.0 ± 2.1 × 10(-11)cm(3) molecule(-1) s(-1) at 297 K. We are also able to put an upper bound on the rate coefficient for CH2OO + I of 1.0 × 10(-11) cm(3) molecule(-1) s(-1). Both of these rate coefficients are at least a factor of 5 smaller than other recent measurements of the same reactions.

  12. 31Cl beta decay and the 30P31S reaction rate in nova nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Bennett, Michael; Wrede, C.; Brown, B. A.; Liddick, S. N.; Pérez-Loureiro, D.; NSCL e12028 Collaboration

    2016-03-01

    The 30P31S reaction rate is critical for modeling the final isotopic abundances of ONe nova nucleosynthesis, identifying the origin of presolar nova grains, and calibrating proposed nova thermometers. Unfortunately, this rate is essentially experimentally unconstrained because the strengths of key 31S proton capture resonances are not known, due to uncertainties in their spins and parities. Using a 31Cl beam produced at the National Superconducting Cyclotron Laboratory, we have populated several 31S states for study via beta decay and devised a new decay scheme which includes updated beta feedings and gamma branchings as well as multiple states previously unobserved in 31Cl beta decay. Results of this study, including the unambiguous identification due to isospin mixing of a new l = 0 , Jπ = 3 /2+ 31S resonance directly in the middle of the Gamow Window, will be presented, and significance to the evaluation of the 30P31S reaction rate will be discussed. Work supported by U.S. Natl. Sci. Foundation (Grants No. PHY-1102511, PHY-1404442, PHY-1419765, and PHY-1431052); U.S. Dept. of Energy, Natl. Nucl. Security Administration (Award No. DE-NA0000979); Nat. Sci. and Eng. Research Council of Canada.

  13. Controlled Nuclear Fusion.

    ERIC Educational Resources Information Center

    Glasstone, Samuel

    This publication is one of a series of information booklets for the general public published by The United States Atomic Energy Commission. Among the topics discussed are: Importance of Fusion Energy; Conditions for Nuclear Fusion; Thermonuclear Reactions in Plasmas; Plasma Confinement by Magnetic Fields; Experiments With Plasmas; High-Temperature…

  14. Absolute determination of the Na22(p,γ)Mg23 reaction rate in novae

    NASA Astrophysics Data System (ADS)

    Sallaska, A. L.; Wrede, C.; García, A.; Storm, D. W.; Brown, T. A. D.; Ruiz, C.; Snover, K. A.; Ottewell, D. F.; Buchmann, L.; Vockenhuber, C.; Hutcheon, D. A.; Caggiano, J. A.; José, J.

    2011-03-01

    Gamma-ray telescopes in orbit around the earth are searching for evidence of the elusive radionuclide Na22 produced in novae. Previously published uncertainties in the dominant destructive reaction, Na22(p,γ)Mg23, indicated new measurements in the proton energy range of 150 to 300 keV were needed to constrain predictions. We have measured the resonance strengths, energies, and branches directly and absolutely by using protons from the University of Washington accelerator with a specially designed beam line, which included beam rastering and cold vacuum protection of the Na22 implanted targets. The targets, fabricated at TRIUMF-ISAC, displayed minimal degradation over a ~20 C bombardment as a result of protective layers. We avoided the need to know the absolute stopping power, and hence the target composition, by extracting resonance strengths from excitation functions integrated over proton energy. Our measurements revealed that resonance strengths for Ep=213, 288, 454, and 610 keV are stronger by factors of 2.4-3.2 than previously reported. Upper limits have been placed on proposed resonances at 198, 209, and 232 keV. These substantially reduce the uncertainty in the reaction rate. We have re-evaluated the Na22(p,γ) reaction rate, and our measurements indicate the resonance at 213 keV makes the most significant contribution to Na22 destruction in novae. Hydrodynamic simulations including our rate indicate that the expected abundance of Na22 ejecta from a classical nova is reduced by factors between 1.5 and 2, depending on the mass of the white-dwarf star hosting the nova explosion.

  15. Rate coefficients for the OH + CFH2CH2OH reaction between 238 and 355 K.

    PubMed

    Rajakumar, B; Burkholder, James B; Portmann, R W; Ravishankara, A R

    2005-06-21

    The rate coefficient for the reaction OH + CFH2CH2OH --> products (k1) between 238 and 355 K was measured using the pulsed laser photolysis-laser induced fluorescence (PLP-LIF) technique to be (5.15 +/- 0.88)x 10(-12) exp[-(330 +/- 45)/T] cm3 molecule(-1) s(-1); k1(298 K)= 1.70 x 10(-12) cm3 molecule(-1) s(-1). The quoted uncertainties are 2sigma(95% confidence level) and include estimated systematic errors. The present results are discussed in relation to the measured rate coefficients for the reaction of OH with other fluorinated alcohols and those calculated using recently reported structure additivity relationships for fluorinated compounds (K. Tokuhashi, H. Nagai, A. Takahashi, M. Kaise, S. Kondo, A. Sekiya, M. Takahashi, Y. Gotoh and A. Suga, J. Phys. Chem. A, 1999, 103, 2664-2672, ). Infrared absorption cross sections for CFH2CH2OH are reported and they are used to calculate the global warming potentials (GWP) for CFH2CH2OH of approximately 8, approximately 2, and approximately 1, respectively, for the 20, 100 and 500 year horizons. A brief discussion of the atmospheric degradation of CFH2CH2OH is provided. It is concluded that CFH2CH2OH is an acceptable substitute for CFCs in terms of its impact on Earth's climate and the composition of the atmosphere. The room temperature rate coefficient for the reaction OH + CFH2CH2OH --> products (k10) was measured to be 3.26 x 10(-12) cm3 molecule(-1) s(-1), in good agreement with recent measurements from this laboratory.

  16. Shock tube/laser absorption measurements of the reaction rates of OH with ethylene and propene.

    PubMed

    Vasu, Subith S; Hong, Zekai; Davidson, David F; Hanson, Ronald K; Golden, David M

    2010-11-04

    Reaction rates of hydroxyl (OH) radicals with ethylene (C₂H₄) and propene (C₃H₆) were studied behind reflected shock waves. OH + ethylene → products (rxn 1) rate measurements were conducted in the temperature range 973-1438 K, for pressures from 2 to 10 atm, and for initial concentrations of ethylene of 500, 751, and 1000 ppm. OH + propene → products (rxn 2) rate measurements spanned temperatures of 890-1366 K, pressures near 2.3 atm, and initial propene concentrations near 300 ppm. OH radicals were produced by shock-heating tert-butyl hydroperoxide, (CH₃)₃-CO-OH, and monitored by laser absorption near 306.7 nm. Rate constants for the reactions of OH with ethylene and propene were extracted by matching modeled and measured OH concentration time-histories in the reflected shock region. Current data are in excellent agreement with previous studies and extend the temperature range of OH + propene data. Transition state theory calculations using recent ab initio results give excellent agreement with our measurements and other data outside our temperature range. Fits (in units of cm³/mol/s) to the abstraction channels of OH + ethylene and OH + propene are k₁ = 2.23 × 10⁴ (T)(2.745) exp(-1115 K/T) for 600-2000 K and k₂ = 1.94 × 10⁶ (T)(2.229) exp(-540 K/T) for 700-1500 K, respectively. A rate constant determination for the reaction TBHP → products (rxn 3) was also obtained in the range 745-1014 K using OH data from behind both incident and reflected shock waves. These high-temperature measurements were fit with previous low-temperature data, and the following rate expression (0.6-2.6 atm), applicable over the temperature range 400-1050 K, was obtained: k₃ (1/s) = 8.13 × 10⁻¹² (T)(7.83) exp(-14598 K/T).

  17. Redox reaction rates in shallow aquifers: Implications for nitrate transport in groundwater and streams

    USGS Publications Warehouse

    Tesoriero, Anthony J.

    2012-01-01

    Groundwater age and water chemistry data along flow paths from recharge areas to streams were used to evaluate the trends and transformations of agricultural chemicals. Results from this analysis indicate that median nitrate recharge concentrations in these agricultural areas have increased markedly over the last 50 years from 4 mg N/L in samples collected prior to 1983 to 7.5 mg N/L in samples collected since 1983. The effect that nitrate accumulation in shallow aquifers will have on drinking water quality and stream ecosystems is dependent on the rate of redox reactions along flow paths and on the age distribution of nitrate discharging to supply wells and streams.

  18. Solid Propellant Kinetics. V. Fuel-Oxidizer Reaction Rates from Heterogeneous Opposed Flow Diffusion Flame

    DTIC Science & Technology

    1974-12-01

    species i and the V1 and v are i i i stoichiometric ratios. Then w = W (V -V ( 8 where W is the molecular weight of species i and molar reaction rate...where W is a constant molecular weight. Then the conservation equations 0 read L (0) L (Y) W Wi T o where 01 = Y W /W (V" - Vi ) i i oi i i T = C T/Q...Let W be the average molecular weight, IV = I/(Y i/Wi Then X = Y W/W so that the X. can be eliminated. Neglecting the variation in W allows one to

  19. Chemical reaction rates using the semiclassical Van-Vleck initialvalue representation

    SciTech Connect

    Venkataraman, Charulatha; Miller, William H.

    2006-11-29

    A semiclassical IVR formulation using the Van-Vleck propagator has been used to calculate the flux correlation function and thereby reaction rate constants. This Van-Vleck formulation of the flux-flux correlation function is computationally as simple as the classical Wigner model. However unlike the latter, it has the ability to capture quantum interference/coherence effects. Classical trajectories are evolved starting from the dividing surface that separates reactants and products, and are evolved negatively in time. This formulation has been tested on model problems ranging from the Eckart barrier, double well to the collinear H + H{sub 2}.

  20. Rates of reaction and process design data for the Hydrocarb Process

    SciTech Connect

    Steinberg, M.; Kobayashi, Atsushi ); Tung, Yuanki )

    1992-08-01

    In support of studies for developing the coprocessing of fossil fuels with biomass by the Hydrocarb Process, experimental and process design data are reported. The experimental work includes the hydropryolysis of biomass and the thermal decomposition of methane in a tubular reactor. The rates of reaction and conversion were obtained at temperature and pressure conditions pertaining to a Hydrocarb Process design. A Process Simulation Computer Model was used to design the process and obtain complete energy and mass balances. Multiple feedstocks including biomass with natural gas and biomass with coal were evaluated. Additional feedstocks including green waste, sewage sludge and digester gas were also evaluated for a pilot plant unit.