518 research outputs found
Generalization of the Scheme and the Structure of the Valence Space
The scheme, which has been extensively applied to even-even nuclei,
is found to be a very good benchmark for odd-even, even-odd, and doubly-odd
nuclei as well. There are no apparent shifts in the correlations for these four
classes of nuclei. The compact correlations highlight the deviant behavior of
the Z=78 nuclei, are used to deduce effective valence proton numbers near Z=64,
and to study the evolution of the Z=64 subshell gap.Comment: 10 pages, 4 figure
Ground State Bands of the E(5) and X(5) Critical Symmetries Obtained from Davidson Potentials through a Variational Procedure
Davidson potentials of the form , when used in
the original Bohr Hamiltonian for -independent potentials bridge the
U(5) and O(6) symmetries. Using a variational procedure, we determine for each
value of angular momentum the value of at which the derivative of
the energy ratio with respect to has a sharp maximum,
the collection of values at these points forming a band which practically
coincides with the ground state band of the E(5) model, corresponding to the
critical point in the shape phase transition from U(5) to O(6). The same
potentials, when used in the Bohr Hamiltonian after separating variables as in
the X(5) model, bridge the U(5) and SU(3) symmetries, the same variational
procedure leading to a band which practically coincides with the ground state
band of the X(5) model, corresponding to the critical point of the U(5) to
SU(3) shape phase transition. A new derivation of the Holmberg-Lipas formula
for nuclear energy spectra is obtained as a by-product.Comment: LaTeX, 12 pages, 4 postscript figure
Systematics of 2+ states in semi-magic nuclei
We propose a simple systematics of low lying 2+ energy levels and
electromagnetic transitions in semi-magic isotopic chains Z=28,50,82 and
isotonic chains N=28,50,82,126. To this purpose we use a two-level pairing plus
quadrupole Hamiltonian, within the spherical Quasiparticle Random Phase
Approximation (QRPA). We derive a simple relation connecting the 2+ energy with
the pairing gap and quadrupole-quadupole (QQ) interaction strength. It turns
out that the systematics of energy levels and B(E2) values predicted by this
simple model is fulfilled with a reasonable accuracy by all available
experimental data. Both systematics suggest that not only active nucleons but
also those filling closed shells play an important role
Soft triaxial roto-vibrational motion in the vicinity of
A solution of the Bohr collective hamiltonian for the soft,
soft triaxial rotor with is presented making use
of a harmonic potential in and Coulomb-like and Kratzer-like
potentials in . It is shown that, while the angular part in the
present case gives rise to a straightforward extension of the rigid triaxial
rotor energy in which an additive harmonic term appears, the inclusion of the
part results instead in a non-trivial expression for the spectrum. The
negative anharmonicities of the energy levels with respect to a simple rigid
model are in qualitative agreement with general trends in the experimental
data.Comment: 4 pages, 2 figures, accepted in Phys.Rev.
Parameter-Free Solution of the Bohr Hamiltonian for Actinides Critical in the Octupole Mode
An analytic, parameter-free (up to overall scale factors) solution of the
Bohr Hamiltonian involving axially symmetric quadrupole and octupole
deformations, as well as an infinite well potential, is obtained, after
separating variables in a way reminiscent of the Variable Moment of Inertia
(VMI) concept. Normalized spectra and B(EL) ratios are found to agree with
experimental data for 226-Ra and 226-Th, the nuclei known to lie closest to the
border between octupole deformation and octupole vibrations in the light
actinide region.Comment: 11 pages, LaTeX, including 5 .eps figure
Exactly separable version of the Bohr Hamiltonian with the Davidson potential
An exactly separable version of the Bohr Hamiltonian is developed using a
potential of the form u(beta)+u(gamma)/beta^2, with the Davidson potential
u(beta)= beta^2 + beta_0^4/beta^2 (where beta_0 is the position of the minimum)
and a stiff harmonic oscillator for u(gamma) centered at gamma=0. In the
resulting solution, called exactly separable Davidson (ES-D), the ground state
band, gamma band and 0_2^+ band are all treated on an equal footing. The
bandheads, energy spacings within bands, and a number of interband and
intraband B(E2) transition rates are well reproduced for almost all
well-deformed rare earth and actinide nuclei using two parameters (beta_0,
gamma stiffness). Insights regarding the recently found correlation between
gamma stiffness and the gamma-bandhead energy, as well as the long standing
problem of producing a level scheme with Interacting Boson Approximation SU(3)
degeneracies from the Bohr Hamiltonian, are also obtained.Comment: 35 pages, 11 postscript figures, LaTe
Functional Outcomes of the Low Vision Depression Prevention Trial in Age-Related Macular Degeneration.
Purpose: To compare the efficacy of behavioral activation (BA) plus low vision rehabilitation with an occupational therapist (OT-LVR) with supportive therapy (ST) on visual function in patients with age-related macular degeneration (AMD).
Methods: Single-masked, attention-controlled, randomized clinical trial with AMD patients with subsyndromal depressive symptoms (n = 188). All subjects had two outpatient low vision rehabilitation optometry visits, then were randomized to in-home BA + OT-LVR or ST. Behavioral activation is a structured behavioral treatment aiming to increase adaptive behaviors and achieve valued goals. Supportive therapy is a nondirective, psychological treatment that provides emotional support and controls for attention. Functional vision was assessed with the activity inventory (AI) in which participants rate the difficulty level of goals and corresponding tasks. Participants were assessed at baseline and 4 months.
Results: Improvements in functional vision measures were seen in both the BA + OT-LVR and ST groups at the goal level (d = 0.71; d = 0.56 respectively). At the task level, BA + OT-LVR patients showed more improvement in reading, inside-the-home tasks and outside-the-home tasks, when compared to ST patients. The greatest effects were seen in the BA + OT-LVR group in subjects with a visual acuity ≥20/70 (d = 0.360 reading; d = 0.500 inside the home; d = 0.468 outside the home).
Conclusions: Based on the trends of the AI data, we suggest that BA + OT-LVR services, provided by an OT in the patient\u27s home following conventional low vision optometry services, are more effective than conventional optometric low vision services alone for those with mild visual impairment. (ClinicalTrials.gov number, NCT00769015.)
Generalized Pseudo-SU(3) Model and Pairing
The pseudo-SU(3) model is extended to explicitly include the spin and
proton-neutron degrees of freedom. A general formalism for evaluating matrix
elements of one-body and two-body tensor operators within this framework is
presented. The pairing interaction, which couples different irreducible
representations of SU(3), is expressed in terms of pseudo-space tensors and a
general result is given for calculating its matrix elements. The importance of
pairing correlations in pseudo-SU(3) model calculations is demonstrated by
examining the dependence of wavefunctions, low-energy collective excitation
spectra, and moments of inertia on the strength of the pairing interaction.Comment: 21 Pages, 7 Figures (available upon request), Nucl. Phys. A in pres
Phase Transitions in Finite Nuclei and the Integer Nucleon Number Problem
The study of spherical-deformed ground--state phase transitions in finite
nuclei as a function of N and Z is hindered by the discrete values of the
nucleon number. A resolution of the integer nucleon number problem, and
evidence relating to phase transitions in finite nuclei, are discussed from the
experimental point of view and interpreted within the framework of the
interacting boson model.Comment: 8 pages Latex + 8 figs (postscript). In Phys Rev Lett, June 199
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