304 research outputs found
Coulomb tunneling for fusion reactions in dense matter: Path integral Monte Carlo versus mean field
We compare Path Integral Monte Carlo calculations by Militzer and Pollock
(Phys. Rev. B 71, 134303, 2005) of Coulomb tunneling in nuclear reactions in
dense matter to semiclassical calculations assuming WKB Coulomb barrier
penetration through the radial mean-field potential. We find a very good
agreement of two approaches at temperatures higher than ~1/5 of the ion plasma
temperature. We obtain a simple parameterization of the mean field potential
and of the respective reaction rates. We analyze Gamow-peak energies of
reacting ions in various reaction regimes and discuss theoretical uncertainties
of nuclear reaction rates taking carbon burning in dense stellar matter as an
example.Comment: 13 pages, 7 figures, to appear in Phys. Rev.
SU(2) Skyrme Vortices
A regular method for constructing vortex-like solutions with cylindrical
symmetry to the equations of the SU(2) Skyrme chiral model is proposed. A
numerical estimate for the length density of mass is given
Large collection of astrophysical S-factors and its compact representation
Numerous nuclear reactions in the crust of accreting neutron stars are
strongly affected by dense plasma environment. Simulations of superbursts, deep
crustal heating and other nuclear burning phenomena in neutron stars require
astrophysical S-factors for these reactions (as a function of center-of-mass
energy E of colliding nuclei). A large database of S-factors is created for
about 5000 non-resonant fusion reactions involving stable and unstable isotopes
of Be, B, C, N, O, F, Ne, Na, Mg, and Si. It extends the previous database of
about 1000 reactions involving isotopes of C, O, Ne, and Mg. The calculations
are performed using the Sao Paulo potential and the barrier penetration
formalism. All calculated S-data are parameterized by an analytic model for
S(E) proposed before [Phys. Rev. C 82, 044609 (2010)] and further elaborated
here. For a given reaction, the present S(E)-model contains three parameters.
These parameters are easily interpolated along reactions involving isotopes of
the same elements with only seven input parameters, giving an ultracompact,
accurate, simple, and uniform database. The S(E) approximation can also be used
to estimate theoretical uncertainties of S(E) and nuclear reaction rates in
dense matter, as illustrated for the case of the 34Ne+34Ne reaction in the
inner crust of an accreting neutron star.Comment: 13 pages, 2 figures, Phys. Rev. C, accepte
A preliminary factor analytic investigation into the first-order factor structure of the Fifteen Factor Plus (15FQ+) on a sample of Black South African managers
The original publication is available at http://www.sajip.co.zaMoyo, S. & Theron, C. 2011. A preliminary factor analytic investigation into the first-order factor structure of the Fifteen Factor Plus (15FQ+) on a sample of Black South African managers. SA Journal of Industrial Psychology, 37(1), 1-22, doi: 10.4102/sajip.v37i1.934.Orientation: The Fifteen Factor Questionnaire Plus (15FQ+) is a prominent personality
questionnaire that organisations frequently use in personnel selection in South Africa.
Research purpose: The primary objective of this study was to undertake a factor analytic
investigation of the first-order factor structure of the 15FQ+.
Motivation for the study: The construct validity of the 15FQ+, as a measure of personality, is
necessary even though it is insufficient to justify its use in personnel selection.
Research design, approach and method: The researchers evaluated the fit of the measurement
model, which the structure and scoring key of the 15FQ+ implies, in a quantitative study that
used an ex post facto correlation design through structural equation modelling. They conducted
a secondary data analysis. They selected a sample of 241 Black South African managers from
a large 15FQ+ database.
Main findings: The researchers found good measurement model fit. The measurement model
parameter estimates were worrying. The magnitude of the estimated model parameters
suggests that the items generally do not reflect the latent personality dimensions the designers
intended them to with a great degree of precision. The items are reasonably noisy measures of
the latent variables they represent.
Practical/managerial implications: Organisations should use the 15FQ+ carefully on Black
South African managers until further local research evidence becomes available.
Contribution/value-add: The study is a catalyst to trigger the necessary additional research
we need to establish convincingly the psychometric credentials of the 15FQ+ as a valuable
assessment tool in South Africa.Publisher's versio
GAMMA-RAY SPECTROMETRY OF HOT PLASMAS
Gamma-ray spectrometry provides diagnostics of fast ion behavior in plasmas of large tokamaks. Information acquiring with the gamma-ray diagnostics gives possibility to identify and distinguish simultaneously presence of fast alpha-particles and other ions He), to obtain its relative densities and also to perform tomographic radial profile reconstruction of the gammaemission sources
Neutron rich matter, neutron stars, and their crusts
Neutron rich matter is at the heart of many fundamental questions in Nuclear
Physics and Astrophysics. What are the high density phases of QCD? Where did
the chemical elements come from? What is the structure of many compact and
energetic objects in the heavens, and what determines their electromagnetic,
neutrino, and gravitational-wave radiations? Moreover, neutron rich matter is
being studied with an extraordinary variety of new tools such as Facility for
Rare Isotope Beams (FRIB) and the Laser Interferometer Gravitational Wave
Observatory (LIGO). We describe the Lead Radius Experiment (PREX) that is using
parity violation to measure the neutron radius in 208Pb. This has important
implications for neutron stars and their crusts. Using large scale molecular
dynamics, we model the formation of solids in both white dwarfs and neutron
stars. We find neutron star crust to be the strongest material known, some 10
billion times stronger than steel. It can support mountains on rotating neutron
stars large enough to generate detectable gravitational waves. Finally, we
describe a new equation of state for supernova and neutron star merger
simulations based on the Virial expansion at low densities, and large scale
relativistic mean field calculations.Comment: 10 pages, 2 figures, Plenary talk International Nuclear Physics
Conference 2010, Vancouver, C
Study of runaway electron dynamics at the ASDEX Upgrade tokamak during impurity injection using fast hard x-ray spectrometry
Exact Self-consistent Particle-like Solutions to the Equations of Nonlinear Scalar Electrodynamics in General Relativity
Exact self-consistent particle-like solutions with spherical and/or
cylindrical symmetry to the equations governing the interacting system of
scalar, electromagnetic and gravitational fields have been obtained. As a
particular case it is shown that the equations of motion admit a special kind
of solutions with sharp boundary known as droplets. For these solutions, the
physical fields vanish and the space-time is flat outside of the critical
sphere or cylinder. Therefore, the mass and the electric charge of these
configurations are zero.Comment: 17 pages, Submitted to the International Journal of Theoretical
Physic
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