22,401 research outputs found
Sensitivity of -decay rates to the radial dependence of the nucleon effective mass
We analyze the sensitivity of -decay rates in 78 Ni and 100,132 Sn to
a correction term in Skyrme energy-density functionals (EDF) which modifies the
radial shape of the nucleon effective mass. This correction is added on top of
several Skyrme parametrizations which are selected from their effective mass
properties and predictions about the stability properties of 132 Sn. The impact
of the correction on high-energy collective modes is shown to be moderate. From
the comparison of the effects induced by the surface-peaked effective mass in
the three doubly magic nuclei, it is found that 132 Sn is largely impacted by
the correction, while 78 Ni and 100 Sn are only moderately affected. We
conclude that -decay rates in these nuclei can be used as a test of
different parts of the nuclear EDF: 78 Ni and 100 Sn are mostly sensitive to
the particle-hole interaction through the B(GT) values, while 132 Sn is
sensitive to the radial shape of the effective mass. Possible improvements of
these different parts could therefore be better constrained in the future
Influence of complex configurations on properties of pygmy dipole resonance in neutron-rich Ca isotopes
Starting from the quasiparticle random phase approximation based on the
Skyrme interaction SLy5, we study the effects of phonon-phonon coupling~(PPC)
on the low-energy electric dipole response in Ca. Using the same set
of parameters we describe available experimental data for Ca and
give prediction for Ca. The inclusion of the PPC results in the
formation of low-energy states. There is an impact of the PPC effect on
low-energy ~strength of Ca. The PPC effect on the electric
dipole polarizability is discussed. We predict a strong increase of the summed
~strength below 10MeV, with increasing neutron number from Ca till
Ca.Comment: 11 pages, 10 figure
Collective excitations in the inner crust of neutron stars : supergiant resonances
We investigate the nuclear collective excitations of Wigner-Seitz cells
containing nuclear clusters immersed in a gas of neutrons. This baryonic
non-uniform system is specific to the structure of inner crust matter of
neutron stars. The collective excitations are studied in the framework of a
spherical Hartree-Fock-Bogoliubov + Quasiparticle Random Phase Approximation,
formulated in coordinate representation. The calculations are done for two
representative Wigner-Seitz cells with baryonic density equal to 0.02 fm
and 0.08 fm. It is shown that the excitations with low multipolarities
are concentrated almost entirely in one strongly collective mode which exhausts
a very large fraction of the energy-weighted sum rule. Since these collective
modes are located at very low energies compared to the giant resonances in
standard nuclei, they may affect significantly the specific heat of baryonic
inner crust matter of neutron stars.Comment: 6 pages, 4 figure
Structure of low-lying quadrupole states in nuclei near 132Sn
The properties of the low-lying 2^+ states in the even-even nuclei around
132Sn are studied within the quasiparticle random phase approximation. Starting
from a Skyrme interaction in the particle-hole channel and a density-dependent
zero-range interaction in the particle-particle channel, we use the finite rank
separable approach in our investigation. It is found that the fourth 2^+ state
in 132Te could be a good candidate for a mixed-symmetry state.Comment: 6 pages, 2 figures, proceedings of International Conference on
Nuclear Structure and Related Topics (NSRT09), June 2009, JINR, Dubna, Russi
Continued fraction approximation for the nuclear matter response function
We use a continued fraction approximation to calculate the RPA response
function of nuclear matter. The convergence of the approximation is assessed by
comparing with the numerically exact response function obtained with a typical
effective finite-range interaction used in nuclear physics. It is shown that
just the first order term of the expansion can give reliable results at
densities up to the saturation density value
Finite-Size Scaling in Two-dimensional Continuum Percolation Models
We test the universal finite-size scaling of the cluster mass order parameter
in two-dimensional (2D) isotropic and directed continuum percolation models
below the percolation threshold by computer simulations. We found that the
simulation data in the 2D continuum models obey the same scaling expression of
mass M to sample size L as generally accepted for isotropic lattice problems,
but with a positive sign of the slope in the ln-ln plot of M versus L. Another
interesting aspect of the finite-size 2D models is also suggested by plotting
the normalized mass in 2D continuum and lattice bond percolation models, versus
an effective percolation parameter, independently of the system structure (i.e.
lattice or continuum) and of the possible directions allowed for percolation
(i.e. isotropic or directed) in regions close to the percolation thresholds.
Our study is the first attempt to map the scaling behaviour of the mass for
both lattice and continuum model systems into one curve.Comment: 9 pages, Revtex, 2 PostScript figure
Modeling predictors of risky drug use behavior among male street laborers in urban Vietnam
BACKGROUND: The application of theoretical frameworks for modeling predictors of drug risk among male street laborers remains limited. The objective of this study was to test a modified version of the IMB (Information-Motivation-Behavioral Skills Model), which includes psychosocial stress, and compare this modified version with the original IMB model in terms of goodness-of-fit to predict risky drug use behavior among this population. METHODS: In a cross-sectional study, social mapping technique was conducted to recruit 450 male street laborers from 135 street venues across 13 districts of Hanoi city, Vietnam, for face-to-face interviews. Structural equation modeling (SEM) was used to analyze data from interviews. RESULTS: Overall measures of fit via SEM indicated that the original IMB model provided a better fit to the data than the modified version. Although the former model was able to predict a lesser variance than the latter (55% vs. 62%), it was of better fit. The findings suggest that men who are better informed and motivated for HIV prevention are more likely to report higher behavioral skills, which, in turn, are less likely to be engaged in risky drug use behavior. CONCLUSIONS: This was the first application of the modified IMB model for drug use in men who were unskilled, unregistered laborers in urban settings. An AIDS prevention program for these men should not only distribute information and enhance motivations for HIV prevention, but consider interventions that could improve self-efficacy for preventing HIV infection. Future public health research and action may also consider broader factors such as structural social capital and social policy to alter the conditions that drive risky drug use among these men
Quasiparticle RPA with finite rank approximation for Skyrme interactions
A finite rank separable approximation for the particle-hole RPA calculations
with Skyrme interactions is extended to take into account the pairing. As an
illustration of the method energies and transition probabilities for the
quadrupole and octupole excitations in some O, Ar, Sn and Pb isotopes are
calculated. The values obtained within our approach are very close to those
that were calculated within QRPA with the full Skyrme interaction. They are in
reasonable agreement with experimental data.Comment: 20 pages, 1 figure, submitted to Phys.Rev.
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