376 research outputs found
Influence of soil moisture, nitrogen fertilization, and temperature on quality and amino acid composition of Thatcher wheat, The
Includes bibliographical references (pages 227-228).The protein content of Thatcher wheat grown in the growth chamber was increased by reduced water supply, nitrogen fertilization, and higher air temperatures. Soil moisture conditions had a greater influence on protein content at higher temperatures, while the largest responses to nitrogen fertilization were obtained at the medium moisture level. Changes in sedimentation value and mixing time were associated with protein content except for plants grown at 62°F. Apparently the low temperature had an adverse effect on gluten quality. The relative distribution of 9 amino acids was significantly correlated with changes in grain protein content. Only 6 amino acids gave similar high correlations with flour protein content and sedimentation value. These differences are explained on the basis of changes in the morphology of the wheat grain and the proportion of flour proteins
Absolute Determination of the 22Na(p,g) Reaction Rate in Novae
Gamma-ray telescopes in orbit around the Earth are searching for evidence of
the elusive radionuclide 22Na produced in novae. Previously published
uncertainties in the dominant destructive reaction, 22Na(p,g)23Mg, 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 beamline, which included beam
rastering and cold vacuum protection of the 22Na 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
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 E_p = 213, 288, 454, and 610
keV are stronger by factors of 2.4 to 3.2 than previously reported. Upper
limits have been placed on proposed resonances at 198-, 209-, and 232-keV. We
have re-evaluated the 22Na(p,g) reaction rate, and our measurements indicate
the resonance at 213 keV makes the most significant contribution to 22Na
destruction in novae. Hydrodynamic simulations including our rate indicate that
the expected abundance of 22Na 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.Comment: 20 pages, 18 figures; shortened paper, accepted in Phys. Rev.
On the close to threshold meson production in neutron-neutron collisions
A method of measuring the close to threshold meson production in
neutron-neutron collisions is described where the momenta of the colliding
neutrons can be determined with the accuracy obtainable for the proton-proton
reaction. The technique is based on the double quasi-free nn --> nn X^0
reaction, where deuterons are used as a source of neutronsComment: 6 pages, 2 figures, to be published in Phys. Lett.
“some kind of thing it aint us but yet its in us”: David Mitchell, Russell Hoban, and metafiction after the millennium
This article appraises the debt that David Mitchell’s Cloud Atlas owes to the novels of Russell Hoban, including, but not limited to, Riddley Walker. After clearly mapping a history of Hoban’s philosophical perspectives and Mitchell’s inter-textual genre-impersonation practice, the article assesses the degree to which Mitchell’s metatextual methods indicate a nostalgia for by-gone radical aesthetics rather than reaching for new modes of its own. The article not only proposes several new backdrops against which Mitchell’s novel can be read but also conducts the first in-depth appraisal of Mitchell’s formal linguistic replication of Riddley Walker
The 21Na(p,gamma)22Mg Reaction and Oxygen-Neon Novae
The 21Na(p,gamma)22Mg reaction is expected to play an important role in the
nucleosynthesis of 22Na in Oxygen-Neon novae. The decay of 22Na leads to the
emission of a characteristic 1.275 MeV gamma-ray line. This report provides the
first direct measurement of the rate of this reaction using a radioactive 21Na
beam, and discusses its astrophysical implications. The energy of the important
state was measured to be E= 205.7 0.5 keV with a resonance
strength meV.Comment: Accepted for publication in Physical Review Letter
The pd <--> pi+ t reaction around the Delta resonance
The pd pi+ t process has been calculated in the energy region around the
Delta-resonance with elementary production/absorption mechanisms involving one
and two nucleons. The isobar degrees of freedom have been explicitly included
in the two-nucleon mechanism via pi-- and rho-exchange diagrams. No free
parameters have been employed in the analysis since all the parameters have
been fixed in previous studies on the simpler pp pi+ d process. The
treatment of the few-nucleon dynamics entailed a Faddeev-based calculation of
the reaction, with continuum calculations for the initial p-d state and
accurate solutions of the three-nucleon bound-state equation. The integral
cross-section was found to be quite sensitive to the NN interaction employed
while the angular dependence showed less sensitivity. Approximately a 4% effect
was found for the one-body mechanism, for the three-nucleon dynamics in the p-d
channel, and for the inclusion of a large, possibly converged, number of
three-body partial states, indicating that these different aspects are of
comparable importance in the calculation of the spin-averaged observables.Comment: 40 Pages, RevTex, plus 5 PostScript figure
Measurement of radiative proton capture on F 18 and implications for oxygen-neon novae reexamined
Background: The rate of the F18(p,Îł)Ne19 reaction affects the final abundance of the radioisotope F18 ejected from novae. This nucleus is important as its abundance is thought to significantly influence the first-stage 511-keV and continuum Îł-ray emission in the aftermath of novae. No successful measurement of this reaction existed prior to this work, and the rate used in stellar models had been calculated based on incomplete information from contributing resonances. Purpose: Of the two resonances thought to provide a significant contribution to the astrophysical reaction rate, located at Ec.m.=330 and 665 keV, the former has a radiative width estimated from the assumed analog state in the mirror nucleus, F19, while the latter resonance does not have an analog state assignment, resulting in an arbitrary radiative width being assumed. As such, a direct measurement was needed to establish what role this resonance plays in the destruction of F18 at nova temperatures. This paper extends and takes the place of a previous Letter which reported the strength of the Ec.m.=665 keV resonance. Method: The DRAGON recoil separator was used to directly measure the strength of the important 665-keV resonance in this reaction, in inverse kinematics, by observing Ne19 reaction products. A radioactive F18 beam was provided by the ISAC facility at TRIUMF. R-matrix calculations were subsequently used to evaluate the significance of the results at astrophysical energies. Results: We report the direct measurement of the F18(p,Îł)Ne19 reaction with the reevaluation of several detector efficiencies and the use of an updated Ne19 level scheme in the reaction rate analysis. The strength of the 665-keV resonance (Ex=7.076 MeV) is found to be an order of magnitude weaker than currently assumed in nova models. An improved analysis of the previously reported data is presented here, resulting in a slightly different value for the resonance strength. These small changes, however, do not alter the primary conclusions. Conclusions: Reaction rate calculations definitively show that the 665-keV resonance plays no significant role in the destruction of F18 at nova temperatures
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