4,854 research outputs found
Renormalized relativistic Hartree-Bogoliubov equations with a zero-range pairing interaction
A recently introduced scheme for the renormalization of the
Hartree-Fock-Bogoliubov equations in the case of zero-range pairing interaction
is extended to the relativistic Hartree-Bogoliubov model. A density-dependent
strength parameter of the zero-range pairing is adjusted in such a way that the
renormalization procedure reproduces the empirical pairing gap in
isospin-symmetric nuclear matter. The model is applied to the calculation of
ground-state pairing properties of finite spherical nuclei.Comment: 13 pages, 8 figures, accepted for publication in Physical Review
Beyond the relativistic Hartree mean-field approximation: energy dependent effective mass
The standard relativistic mean-field model is extended by including dynamical
effects that arise in the coupling of single-nucleon motion to collective
surface vibrations. A phenomenological scheme, based on a linear ansatz for the
energy dependence of the scalar and vector components of the nucleon
self-energy for states close to the Fermi surface, allows a simultaneous
description of binding energies, radii, deformations and single-nucleon spectra
in a self-consistent relativistic framework. The model is applied to the
spherical, doubly closed-shell nuclei 132Sn and 208Pb.Comment: 14 pages, 2 figures; replaced with revised versio
Pairing in the Framework of the Unitary Correlation Operator Method (UCOM): Hartree-Fock-Bogoliubov Calculations
In this first in a series of articles, we apply effective interactions
derived by the Unitary Correlation Operator Method (UCOM) to the description of
open-shell nuclei, using a self-consistent Hartree-Fock-Bogoliubov framework to
account for pairing correlations. To disentangle the particle-hole and
particle-particle channels and assess the pairing properties of \VUCOM, we
consider hybrid calculations using the phenomenological Gogny D1S interaction
to derive the particle-hole mean field. In the main part of this article, we
perform calculations of the tin isotopic chain using \VUCOM in both the
particle-hole and particle-particle channels. We study the interplay of both
channels, and discuss the impact of non-central and non-local terms in
realistic interactions as well as the frequently used restriction of pairing
interactions to the partial wave. The treatment of the center-of-mass
motion and its effect on theoretical pairing gaps is assessed independently of
the used interactions.Comment: 14 pages, 10 figures, to appear in Phys. Rev. C, title modified
accordingl
Random-phase approximation based on relativistic point-coupling models
The matrix equations of the random-phase approximation (RPA) are derived for
the point-coupling Lagrangian of the relativistic mean-field (RMF) model. Fully
consistent RMF plus (quasiparticle) RPA illustrative calculations of the
isoscalar monopole, isovector dipole and isoscalar quadrupole response of
spherical medium-heavy and heavy nuclei, test the phenomenological effective
interactions of the point-coupling RMF model. A comparison with experiment
shows that the best point-coupling effective interactions accurately reproduce
not only ground-state properties, but also data on excitation energies of giant
resonances.Comment: 24 pages, 4 figures, accepted for publication in Physical Review
Relativistic description of exotic collective excitation phenomena in atomic nuclei
The low-lying dipole and quadrupole states in neutron rich nuclei, are
studied within the fully self-consistent relativistic quasiparticle
random-phase approximation (RQRPA), formulated in the canonical basis of the
Relativistic Hartree-Bogoliubov model (RHB), which is extended to include the
density dependent interactions. In heavier nuclei, the low-lying E1 excited
state is identified as a pygmy dipole resonance (PDR), i.e. as a collective
mode of excess neutrons oscillating against a proton-neutron core. Isotopic
dependence of the PDR is characterized by a crossing between the PDR and
one-neutron separation energies. Already at moderate proton-neutron asymmetry
the PDR peak is calculated above the neutron emission threshold, indicating
important implications for the observation of the PDR in (gamma,gamma')
scattering, and on the theoretical predictions of the radiative neutron capture
rates in neutron-rich nuclei. In addition, a novel method is suggested for
determining the neutron skin of nuclei, based on measurement of excitation
energies of the Gamow-Teller resonance relative to the isobaric analog state.Comment: 8 pages, 3 figures, invited talk at the international workshop
"Blueprints for the nucleus: From First Principles to Collective Motion", May
17-22. 2004, Istanbul, Turkey; to appear in Int. J. Mod. Phys.
Drug Distribution and Stent Retention of Drug Eluting Stents
In this paper the examinations of drug eluting coronary stents are shown, such as the morphology of the coatings before expansion, drug distribution, the methodology and the value of stent retention. Surface qualities of drug coatings were examined with stereo-microscope, metallographic microscope and scanning electron microscope. Examinations with confocal microscope show drug distribution in the coatings. Stent retention is a very important property of the stent system. Stent retention is a force, needed to the stent slip down from the balloon. Three drug eluting coronary stents were tested with our method
Toroidal dipole resonances in the relativistic random phase approximation
The isoscalar toroidal dipole strength distributions in spherical nuclei are
calculated in the framework of a fully consistent relativistic random phase
approximation. It is suggested that the recently observed "low-lying component
of the isoscalar dipole mode" might in fact correspond to the toroidal giant
dipole resonance. Although predicted by several theoretical models, the
existence of toroidal resonances has not yet been confirmed in experiment. The
strong mixing between the toroidal resonance and the dipole compression mode
might help to explain the large discrepancy between theory and experiment on
the position of isoscalar giant dipole resonances.Comment: 10 pages, 3 figures; Phys.Rev.C, in prin
Microscopic description of nuclear quantum phase transitions
The relativistic mean-field framework, extended to include correlations
related to restoration of broken symmetries and to fluctuations of the
quadrupole deformation, is applied to a study of shape transitions in Nd
isotopes. It is demonstrated that the microscopic self-consistent approach,
based on global effective interactions, can describe not only general features
of transitions between spherical and deformed nuclei, but also the singular
properties of excitation spectra and transition rates at the critical point of
quantum shape phase transition.Comment: 10 pages, 4 figures, accepted for publication in Physical Review
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