23,755 research outputs found
Weak decays of medium and heavy Lambda-hypernuclei
We have made a new evaluation of the Lambda decay width in nuclear matter
within the Propagator Method. Through the Local Density Approximation it is
possible to obtain results in finite nuclei. We have also studied the
dependence of the widths on the N-N and Lambda-N short range correlations.
Using reasonable values for the parameters that control these correlations, as
well as realistic nuclear densities and Lambda wave functions, we reproduce,
for the first time, the experimental non-mesonic widths in a wide range of mass
numbers (from medium to heavy hypernuclei).Comment: 22 pages, including 5 figure
Multi- nuclei and kaon condensation
We extend previous relativistic mean-field (RMF) calculations of multi- nuclei, using vector boson fields with SU(3) PPV coupling constants and
scalar boson fields constrained phenomenologically. For a given core nucleus,
the resulting separation energy , as well as the
associated nuclear and -meson densities, saturate with the number
of mesons for . Saturation
appears robust against a wide range of variations, including the RMF nuclear
model used and the type of boson fields mediating the strong interactions.
Because generally does not exceed 200 MeV, it is argued that
multi- nuclei do not compete with multihyperonic nuclei in providing
the ground state of strange hadronic configurations and that kaon condensation
is unlikely to occur in strong-interaction self-bound strange hadronic matter.
Last, we explore possibly self-bound strange systems made of neutrons and
mesons, or protons and mesons, and study their properties.Comment: 21 pages, 8 figures, revised text and reference
Kinetic Ising System in an Oscillating External Field: Stochastic Resonance and Residence-Time Distributions
Experimental, analytical, and numerical results suggest that the mechanism by
which a uniaxial single-domain ferromagnet switches after sudden field reversal
depends on the field magnitude and the system size. Here we report new results
on how these distinct decay mechanisms influence hysteresis in a
two-dimensional nearest-neighbor kinetic Ising model. We present theoretical
predictions supported by numerical simulations for the frequency dependence of
the probability distributions for the hysteresis-loop area and the
period-averaged magnetization, and for the residence-time distributions. The
latter suggest evidence of stochastic resonance for small systems in moderately
weak oscillating fields.Comment: Includes updated results for Fig.2 and minor text revisions to the
abstract and text for clarit
Dynamically generated open charmed baryons beyond the zero range approximation
The interaction of the low lying pseudo-scalar mesons with the ground state
baryons in the charm sector is studied within a coupled channel approach using
a t-channel vector-exchange driving force. The amplitudes describing the
scattering of the pseudo-scalar mesons off the ground-state baryons are
obtained by solving the Lippmann--Schwinger equation. We analyze in detail the
effects of going beyond the approximation. Our model predicts the
dynamical generation of several open charmed baryon resonances in different
isospin and strangeness channels, some of which can be clearly identified with
recently observed states.Comment: 7 figures, 8 table
Space program: Space debris a potential threat to Space Station and shuttle
Experts estimate that more than 3.5 million man-made objects are orbiting the earth. These objects - space debris - include whole and fragmentary parts of rocket bodies and other discarded equipment from space missions. About 24,500 of these objects are 1 centimeter across or larger. A 1-centimeter man-made object travels in orbit at roughly 22,000 miles per hour. If it hit a spacecraft, it would do about the same damage as would a 400-pound safe traveling at 60 miles per hour. The Government Accounting Office (GAO) reviews NASA's plans for protecting the space station from debris, the extent and precision of current NASA and Defense Department (DOD) debris-tracking capabilities, and the extent to which debris has already affected shuttle operations. GAO recommends that the space debris model be updated, and that the findings be incorporated into the plans for protecting the space station from such debris. GAO further recommends that the increased risk from debris to the space shuttle operations be analyzed
Lasso Estimation of an Interval-Valued Multiple Regression Model
A multiple interval-valued linear regression model considering all the
cross-relationships between the mids and spreads of the intervals has been
introduced recently. A least-squares estimation of the regression parameters
has been carried out by transforming a quadratic optimization problem with
inequality constraints into a linear complementary problem and using Lemke's
algorithm to solve it. Due to the irrelevance of certain cross-relationships,
an alternative estimation process, the LASSO (Least Absolut Shrinkage and
Selection Operator), is developed. A comparative study showing the differences
between the proposed estimators is provided
The entropy of a correlated system of nucleons
Realistic nucleon-nucleon interaction induce correlations to the nuclear
many-body system which lead to a fragmentation of the single-particle strength
over a wide range of energies and momenta. We address the question of how this
fragmentation affects the thermodynamical properties of nuclear matter. In
particular, we show that the entropy can be computed with the help of a
spectral function which can be evaluated in terms of the self-energy obtained
in the Self-Consistent Green's Function approach. Results for the density and
temperature dependences of the entropy per particle for symmetric nuclear
matter are presented and compared to the results of lowest order finite
temperature Brueckner--Hartree--Fock calculations. The effects of correlations
on the calculated entropy are small, if the appropriate quasi-particle
approximation is used. The results demonstrate the thermodynamical consistency
of the self-consistent T-matrix approximation for the evaluation of the Green's
functions.Comment: REVTEX4 - 43 pages, 10 figures - Published versio
The entropy of a correlated system of nucleons
Realistic nucleon-nucleon interaction induce correlations to the nuclear
many-body system which lead to a fragmentation of the single-particle strength
over a wide range of energies and momenta. We address the question of how this
fragmentation affects the thermodynamical properties of nuclear matter. In
particular, we show that the entropy can be computed with the help of a
spectral function which can be evaluated in terms of the self-energy obtained
in the Self-Consistent Green's Function approach. Results for the density and
temperature dependences of the entropy per particle for symmetric nuclear
matter are presented and compared to the results of lowest order finite
temperature Brueckner--Hartree--Fock calculations. The effects of correlations
on the calculated entropy are small, if the appropriate quasi-particle
approximation is used. The results demonstrate the thermodynamical consistency
of the self-consistent T-matrix approximation for the evaluation of the Green's
functions.Comment: REVTEX4 - 43 pages, 10 figures - Published versio
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