24,061 research outputs found
Nuclear binding energies: Global collective structure and local shell-model correlations
Nuclear binding energies and two-neutron separation energies are analyzed
starting from the liquid-drop model and the nuclear shell model in order to
describe the global trends of the above observables. We subsequently
concentrate on the Interacting Boson Model (IBM) and discuss a new method in
order to provide a consistent description of both, ground-state and
excited-state properties. We address the artefacts that appear when crossing
mid-shell using the IBM formulation and perform detailed numerical calculations
for nuclei situated in the 50-82 shell. We also concentrate on local deviations
from the above global trends in binding energy and two-neutron separation
energies that appear in the neutron-deficient Pb region. We address possible
effects on the binding energy, caused by mixing of low-lying intruder
states into the ground state, using configuration mixing in the IBM framework.
We also study ground-state properties using a deformed mean-field approach.
Detailed comparisons with recent experimental data in the Pb region are amply
discussed.Comment: 69 pages, TeX (ReVTeX). 23 eps figures. 1 table. Modified version.
Accepted in Nucl. Phys.
Comparison of coherence times in three dc SQUID phase qubits
We report measurements of spectroscopic linewidth and Rabi oscillations in
three thin-film dc SQUID phase qubits. One device had a single-turn Al loop,
the second had a 6-turn Nb loop, and the third was a first order gradiometer
formed from 6-turn wound and counter-wound Nb coils to provide isolation from
spatially uniform flux noise. In the 6 - 7.2 GHz range, the spectroscopic
coherence times for the gradiometer varied from 4 ns to 8 ns, about the same as
for the other devices (4 to 10 ns). The time constant for decay of Rabi
oscillations was significantly longer in the single-turn Al device (20 to 30
ns) than either of the Nb devices (10 to 15 ns). These results imply that
spatially uniform flux noise is not the main source of decoherence or
inhomogenous broadening in these devices.Comment: 4 pages, 5 figures, accepted for publication in IEEE Trans. Appl.
Supercon
Dynamical transitions and sliding friction of the phase-field-crystal model with pinning
We study the nonlinear driven response and sliding friction behavior of the
phase-field-crystal (PFC) model with pinning including both thermal
fluctuations and inertial effects. The model provides a continuous description
of adsorbed layers on a substrate under the action of an external driving force
at finite temperatures, allowing for both elastic and plastic deformations. We
derive general stochastic dynamical equations for the particle and momentum
densities including both thermal fluctuations and inertial effects. The
resulting coupled equations for the PFC model are studied numerically. At
sufficiently low temperatures we find that the velocity response of an
initially pinned commensurate layer shows hysteresis with dynamical melting and
freezing transitions for increasing and decreasing applied forces at different
critical values. The main features of the nonlinear response in the PFC model
are similar to the results obtained previously with molecular dynamics
simulations of particle models for adsorbed layers.Comment: 7 pages, 8 figures, to appear in Physcial Review
A CF3I-based SDD Prototype for Spin-independent Dark Matter Searches
The application of Superheated Droplet Detectors (SDDs) to dark matter
searches has so far been confined to the light nuclei refrigerants C2ClF5 and
C4F10 (SIMPLE and PICASSO, respectively), with a principle sensitivity to
spin-dependent interactions. Given the competitive results of these devices, as
a result of their intrinsic insensitivity to backgrounds, we have developed a
prototype trifluoroiodomethane (CF3I)-loaded SDD with increased sensitivity to
spin-independent interactions as well. A low (0.102 kgd) exposure test
operation of two high concentration, 1 liter devices is described, and the
results compared with leading experiments in both spin-dependent and
-independent sectors. Although competitive in both sectors when the difference
in exposures is accounted for, a problem with fracturing of the detector gel
must be addressed before significantly larger exposures can be envisioned.Comment: revised and updated; accepted Astrop. Phy
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