24,147 research outputs found
Roles of proton-neutron interactions in alpha-like four-nucleon correlations
An extended pairing plus QQ force model, which has been shown to successfully
explain the nuclear binding energy and related quantities such as the symmetry
energy, is applied to study the alpha-like four-nucleon correlations in
1f_{7/2} shell nuclei.
The double difference of binding energies, which displays a characteristic
behavior at , is interpreted in terms of the alpha-like
correlations. Important roles of proton-neutron interactions forming the
alpha-like correlated structure are discussed.Comment: 10 pages, 2 figures, RevTex, submitted to Phys. Rev.
Structure and decays of nuclear three-body systems: the Gamow coupled-channel method in Jacobi coordinates
Weakly bound and unbound nuclear states appearing around
particle thresholds are prototypical open quantum systems. Theories of such
states must take into account configuration mixing effects in the presence of
strong coupling to the particle continuum space.
To describe structure and decays of three-body systems, we
developed a Gamow coupled-channel (GCC) approach in Jacobi coordinates by
employing the complex-momentum formalism. We benchmarked the new framework
against the complex-energy Gamow Shell Model (GSM).
The GCC formalism is expressed in Jacobi coordinates, so
that the center-of-mass motion is automatically eliminated. To solve the
coupled-channel equations, we use hyperspherical harmonics to describe the
angular wave functions while the radial wave functions are expanded in the
Berggren ensemble, which includes bound, scattering and Gamow states.
We show that the GCC method is both accurate and robust. Its
results for energies, decay widths, and nucleon-nucleon angular correlations
are in good agreement with the GSM results.
We have demonstrated that a three-body GSM formalism
explicitly constructed in cluster-orbital shell model coordinates provides
similar results to a GCC framework expressed in Jacobi coordinates, provided
that a large configuration space is employed. Our calculations for
systems and O show that nucleon-nucleon angular correlations are
sensitive to the valence-neutron interaction. The new GCC technique has many
attractive features when applied to bound and unbound states of three-body
systems: it is precise, efficient, and can be extended by introducing a
microscopic model of the core.Comment: 10 pages, 8 figure
Induced polarization and electronic properties of carbon doped boron-nitride nanoribbons
The electronic properties of boron-nitride nanoribbons (BNNRs) doped with a
line of carbon atoms are investigated by using density functional calculations.
Three different configurations are possible: the carbon atoms may replace a
line of boron or nitrogen atoms or a line of alternating B and N atoms which
results in very different electronic properties. We found that: i) the NCB
arrangement is strongly polarized with a large dipole moment having an
unexpected direction, ii) the BCB and NCN arrangement are non-polar with zero
dipole moment, iii) the doping by a carbon line reduces the band gap
independent of the local arrangement of boron and nitrogen around the carbon
line, iv) an electric field parallel to the carbon line polarizes the BN sheet
and is found to be sensitive to the presence of carbon dopants, and v) the
energy gap between the highest occupied molecular orbital and the lowest
unoccupied molecular orbital decreases linearly with increasing applied
electric field directed parallel to the carbon line. We show that the
polarization and energy gap of carbon doped BNNRs can be tuned by an electric
field applied parallel along the carbon line.Comment: 11 pages, 6 figure
Corrections to local scale invariance in the non-equilibrium dynamics of critical systems: numerical evidences
Local scale invariance (LSI) has been recently proposed as a possible
extension of the dynamical scaling in systems at the critical point and during
phase ordering. LSI has been applied inter alia to provide predictions for the
scaling properties of the response function of non-equilibrium critical systems
in the aging regime following a quench from the high-temperature phase to the
critical point. These predictions have been confirmed by Monte Carlo
simulations and analytical results for some specific models, but they are in
disagreement with field-theoretical predictions. By means of Monte Carlo
simulations of the critical two- and three-dimensional Ising model with Glauber
dynamics, we study the intermediate integrated response, finding deviations
from the corresponding LSI predictions that are in qualitative agreement with
the field-theoretical computations. This result casts some doubts on the
general applicability of LSI to critical dynamics.Comment: 4 pages, 2 figures, minor changes, version to appear in Phys. Rev. B
as a Rapid Communicatio
Multi-site observations of Delta Scuti stars 7 Aql and 8 Aql (a new Delta Scuti variable): The twelfth STEPHI campaign in 2003
We present an analysis of the pulsation behaviour of the Delta Scuti stars 7
Aql (HD 174532) and 8 Aql (HD 174589) -- a new variable star -- observed in the
framework of STEPHI XII campaign during 2003 June--July. 183 hours of high
precision photometry were acquired by using four-channel photometers at three
sites on three continents during 21 days. The light curves and amplitude
spectra were obtained following a classical scheme of multi-channel photometry.
Observations in different filters were also obtained and analyzed. Six and
three frequencies have been unambiguously detected above a 99% confidence level
in the range 0.090 mHz--0.300 mHz and 0.100 mHz-- 0.145 mHz in 7 Aql and 8 Aql
respectively. A comparison of observed and theoretical frequencies shows that 7
Aql and 8 Aql may oscillate with p modes of low radial orders, typical among
Delta Scuti stars. In terms of radial oscillations the range of 8 Aql goes from
n=1 to n=3 while for 7 Aql the range spans from n=4 to n=7. Non-radial
oscillations have to be present in both stars as well. The expected range of
excited modes according to a non adiabatic analysis goes from n=1 to n=6 in
both stars.Comment: 8 pages, 7 fugures, 5 tables, accepted for publication in
Astronomical Journa
Depolarization volume and correlation length in the homogenization of anisotropic dielectric composites
In conventional approaches to the homogenization of random particulate
composites, both the distribution and size of the component phase particles are
often inadequately taken into account. Commonly, the spatial distributions are
characterized by volume fraction alone, while the electromagnetic response of
each component particle is represented as a vanishingly small depolarization
volume. The strong-permittivity-fluctuation theory (SPFT) provides an
alternative approach to homogenization wherein a comprehensive description of
distributional statistics of the component phases is accommodated. The
bilocally-approximated SPFT is presented here for the anisotropic homogenized
composite which arises from component phases comprising ellipsoidal particles.
The distribution of the component phases is characterized by a two-point
correlation function and its associated correlation length. Each component
phase particle is represented as an ellipsoidal depolarization region of
nonzero volume. The effects of depolarization volume and correlation length are
investigated through considering representative numerical examples. It is
demonstrated that both the spatial extent of the component phase particles and
their spatial distributions are important factors in estimating coherent
scattering losses of the macroscopic field.Comment: Typographical error in eqn. 16 in WRM version is corrected in arxiv
versio
The `bare' strange stars might not be bare
It is proposed that the `bare' strange matter stars might not be bare, and
radio pulsars might be in fact `bare' strange stars. As strange matter stars
being intensely magnetized rotate, the induced unipolar electric fields would
be large enough to construct magnetospheres. This situation is very similar to
that discussed by many authors for rotating neutron stars. Also, the strange
stars with accretion crusts in binaries could act as X-ray pulsars or X-ray
bursters. There are some advantages if radio pulsars are `bare' strange stars.Comment: 11 pages, 1 Postscript figures, LaTeX, Chin. Phys. Lett. 1998,
Vol.15, Nov.12, p.93
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