35,942 research outputs found
Gamow Shell-Model Description of Weakly Bound and Unbound Nuclear States
Recently, the shell model in the complex k-plane (the so-called Gamow Shell
Model) has been formulated using a complex Berggren ensemble representing bound
single-particle states, single-particle resonances, and non-resonant continuum
states. In this framework, we shall discuss binding energies and energy spectra
of neutron-rich helium and lithium isotopes. The single-particle basis used is
that of the Hartree-Fock potential generated self-consistently by the
finite-range residual interaction.Comment: 13 pages, 2 figures, presented by N. Michel at the XXVII Symposium On
Nuclear Physics, Taxco, Guerrero, Mexico, January 5-8 200
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
Density matrix renormalization group approach for many-body open quantum systems
The density matrix renormalization group (DMRG) approach is extended to
complex-symmetric density matrices characteristic of many-body open quantum
systems. Within the continuum shell model, we investigate the interplay between
many-body configuration interaction and coupling to open channels. It is shown
that the DMRG technique applied to broad resonances in the unbound neutron-rich
nucleus 7He provides a highly accurate treatment of the coupling to the
non-resonant scattering continuum.Comment: 4 pages, 3 figure
Density matrix renormalization group approach to two-fluid open many-fermion systems
We have extended the density matrix renormalization group (DMRG) approach to
two-fluid open many-fermion systems governed by complex-symmetric Hamiltonians.
The applications are carried out for three- and four-nucleon (proton-neutron)
systems within the Gamow Shell Model (GSM) in the complex-energy plane. We
study necessary and sufficient conditions for the GSM+DMRG method to yield the
correct ground state eigenvalue and discuss different truncation schemes within
DMRG. The proposed approach will enable configuration interaction studies of
weakly-bound and unbound strongly interacting complex systems which, because of
a prohibitively large size of Fock space, cannot be treated by means of the
direct diagonalization.Comment: 13 pages, 15 figure
Electronic structure and magnetism in two-dimensional hexagonal 5d transition metal carbides, Tan+1Cn (n=1,2,3)
Density functional calculations are used to investigate the electronic
structure of two-dimensional 5d tantalum carbides with honeycomb-like lattice
structures. We focus on changes in the low-energy bands near the Fermi level
with dimensionality. We find that the Ta 5d states dominate, but the extended
nature of the wavefunctions makes them weakly correlated. The carbide sheets
are prone to long range magnetic order. We evaluate the stability of these
states to enhanced electron--electron interactions through a Hubbard U
correction. Lastly, we find spin orbit interactions strongly renormalize the
band structure for n=2, but play a minor role in n=1 and 3.Comment: 4 pages, 4 figure
Structure of Exotic Nuclei
The progress in the modeling of exotic nuclei with an extreme
neutron-to-proton ratio is discussed. Two topics are emphasized: (i) the quest
for the universal microscopic nuclear energy density functional and (ii) the
progress in the continuum shell model.Comment: 10 pages, 2 figures, presented by W. Nazarewicz at the International
Symposium on "A New Era of Nuclear Structure Physics", Kurokawa Village
(Niigata Pref.), Japan, Nov. 19-22, 200
Mobility and asymmetry effects in one-dimensional rock-paper-scissors games
As the behavior of a system composed of cyclically competing species is
strongly influenced by the presence of fluctuations, it is of interest to study
cyclic dominance in low dimensions where these effects are the most prominent.
We here discuss rock-paper-scissors games on a one-dimensional lattice where
the interaction rates and the mobility can be species dependent. Allowing only
single site occupation, we realize mobility by exchanging individuals of
different species. When the interaction and swapping rates are symmetric, a
strongly enhanced swapping rate yields an increased mixing of the species,
leading to a mean-field like coexistence even in one-dimensional systems. This
coexistence is transient when the rates are asymmetric, and eventually only one
species will survive. Interestingly, in our spatial games the dominating
species can differ from the species that would dominate in the corresponding
nonspatial model. We identify different regimes in the parameter space and
construct the corresponding dynamical phase diagram.Comment: 6 pages, 5 figures, to appear in Physical Review
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