204,564 research outputs found
Cross sections for pentaquark baryon production from protons in reactions induced by hadrons and photons
Using hadronic Lagrangians that include the interaction of pentaquark
baryon with and , we evaluate the cross sections for its
production from meson-proton, proton-proton, and photon-proton reactions near
threshold. With empirical coupling constants and form factors, the predicted
cross sections are about 1.5 mb in kaon-proton reactions, 0.1 mb in rho-nucleon
reactions, 0.05 mb in pion-nucleon reactions, 20 b in proton-proton
reactions, and 40 nb in photon-proton reactions.Comment: 14 pages, 7 figure
The analysis of fatigue crack growth mechanism and oxidation and fatigue life at elevated temperatures
Two quantitative models based on experimentally observed fatigue damage processes have been made: (1) a model of low cycle fatigue life based on fatigue crack growth under general-yielding cyclic loading; and (2) a model of accelerated fatigue crack growth at elevated temperatures based on grain boundary oxidation. These two quantitative models agree very well with the experimental observations
Oxidation and low cycle fatigue life prediction
When a metallic material is exposed to a high temperature in an ambient atmosphere, oxidation takes place on the metallic surface. The formed oxides (both surface and grain boundary oxides) are mechanically brittle so that if the stress is high enough the oxides will be cracked. The grain boundary oxide formation in TAZ-8A nickel-base superalloy was studied. The effect of oxide crack nucleus on low cycle fatigue life will be analyzed. The TAZ-8A was subjected to high temperature oxidation tests in air under the stress-free condition. The oxidation temperatures were 600, 800, and 1000 C. The oxidation time varies from 10 to 1000 hours
Model Study of Three-Body Forces in the Three-Body Bound State
The Faddeev equations for the three-body bound state with two- and three-body
forces are solved directly as three-dimensional integral equation. The
numerical feasibility and stability of the algorithm, which does not employ
partial wave decomposition is demonstrated. The three-body binding energy and
the full wave function are calculated with Malfliet-Tjon-type two-body
potentials and scalar Fujita-Miyazawa type three-body forces. The influence of
the strength and range of the three-body force on the wave function, single
particle momentum distributions and the two-body correlation functions are
studied in detail. The extreme case of pure three-body forces is investigated
as well.Comment: 25 pages, 15 postscript figure
Three-Body Scattering without Partial Waves
The Faddeev equation for three-body scattering at arbitrary energies is
formulated in momentum space and directly solved in terms of momentum vectors
without employing a partial wave decomposition. In its simplest form the
Faddeev equation for identical bosons is a three-dimensional integral equation
in five variables, magnitudes of relative momenta and angles. The elastic
differential cross section, semi-exclusive d(N,N') cross sections and total
cross sections of both elastic and breakup processes in the intermediate energy
range up to about 1 GeV are calculated based on a Malfliet-Tjon type potential,
and the convergence of the multiple scattering series is investigated in every
case. In general a truncation in the first or second order in the two-body
t-matrix is quite insufficient.Comment: 3 pages, Oral Contribution to the 19th European Few-Body Conference,
Groningen Aug. 23-27, 200
Three-Body Elastic and Inelastic Scattering at Intermediate Energies
The Faddeev equation for three-body scattering at arbitrary energies is
formulated in momentum space and directly solved in terms of momentum vectors
without employing a partial wave decomposition. For identical bosons this
results in a three-dimensional integral equation in five variables, magnitudes
of relative momenta and angles. The cross sections for both elastic and breakup
processes in the intermediate energy range up to about 1 GeV are calculated
based on a Malfliet-Tjon type potential, and the convergence of the multiple
scattering series is investigated.Comment: Talk at the 18th International IUPAP Conference on Few-Body Problems
in Physics, Aug. 21-26, 2006, Santos, Brazi
Grain boundary oxidation and an analysis of the effects of pre-oxidation on subsequent fatigue life
The effects of preoxidation on subsequent fatigue life were studied. Surface oxidation and grain boundary oxidation of a nickel-base superalloy (TAZ-8A) were studied at 600 to 1000 C for 10 to 1000 hours in air. Surface oxides were identified and the kinetics of surface oxidation was discussed. Grain boundary oxide penetration and morphology were studied. Pancake type grain boundary oxide penetrates deeper and its size is larger, therefore, it is more detrimental to fatigue life than cone-type grain boundary oxide. Oxide penetration depth, a (sub m), is related to oxidation temperature, T, and exposure time, t, by an empirical relation of the Arrhenius type. Effects of T and t on statistical variation of a (sub m) were analyzed according to the Weibull distribution function. Once the oxide is cracked, it serves as a fatigue crack nucleus. Statistical variation of the remaining fatigue life, after the formation of an oxide crack of a critical length, is related directly to the statistical variation of grain boundary oxide penetration depth
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