1,668 research outputs found
A simple model for the microscopic effective pairing interaction
The microscopic effective pairing interaction in the -channel is
investigated for two different values of the chemical potential starting
from the separable form of the Paris NN-potential. It is shown that, within a
high accuracy, this effective interaction can be approximated by the off-shell
free T-matrix taken at the negative energy .Comment: LaTeX, 8 pages, 6 ps-figure
First NACO observations of the Brown Dwarf LHS 2397aB
Observations of the standard late type M8 star LHS 2397aA were obtained at
the ESO-VLT 8m telescope ``Yepun'' using the NAOS/CONICA Adaptive Optics
facility. The observations were taken during the NACO commissioning, and the
infrared standard star LHS 2397aA was observed in the H, and Ks broad band
filters. In both bands the brown dwarf companion LHS2397aB was detected. Using
a program recently developed (Bouy et al., 2003) for the detection of stellar
binaries we calculated the principal astrometric parameters (angular binary
separation and position angle P.A.) and the photometry of LHS 2397aA and LHS
2397aB. Our study largely confirms previous results obtained with the
AO-Hokupa'a facility at Gemini-North (Freed et al., 2003); however a few
discrepancies are observed.Comment: 5 page
Surface behaviour of the pairing gap in semi-infinite nuclear matter
The -pairing gap in semi-infinite nuclear matter is evaluated
microscopically using the effective pairing interaction recently found
explicitly in the coordinate representation starting from the separable form of
the Paris NN-potential. Instead of direct iterative solution of the gap
equation, a new method proposed by V.A.Khodel, V.V.Khodel and J.W.Clark was
used which simplifies the procedure significantly. The gap obtained in
our calculations exibits a strong variation in the surface region with a
pronounced maximum near the surface.Comment: 9 pages, 2 ps figure
Skyrmions and the Nuclear Force
The derivation of the nucleon-nucleon force from the Skyrme model is
reexamined. Starting from previous results for the potential energy of
quasistatic solutions, we show that a calculation using the Born-Oppenheimer
approximation properly taking into account the mixing of nucleon resonances,
leads to substantial central attraction. We obtain a potential that is in
qualitative agreement with phenomenological potentials. We also study the
non-adiabatic corrections, such as the velocity dependent transition
potentials, and discuss their importance.Comment: 24 pages, UPR-0124M
Paris nucleon-antinucleon potential constrained by recent antiprotonic-atom data and antineutron-proton total cross sections
We report on an updated Paris nucleon-antinucleon optical potential. The
long- and intermediate-range real parts are obtained by G-parity transformation
of the Paris nucleon-nucleon potential based on a theoretical
dispersion-relation treatment of the correlated and uncorrelated two-pion
exchange. The short-range imaginary potential parametrization results from the
calculation of the nucleon-antinucleon annihilation box diagram into two mesons
with a nucleon-antinucleon intermediate state in the crossed channel. The
parametrized real and imaginary short range parts are determined by fitting not
only the existing experimental data included in the 1999 version of the Paris
nucleon-antinucleon potential, but also the recent antiprotonic-hydrogen data
and antineutron-proton total cross sections. The description of these new
observables is improved. Only this readjusted potential generates an isospin
zero 1S0, 52 MeV broad quasibound state at 4.8 MeV below the threshold. Recent
BES data on J/psi decays could support the existence of such a state.Comment: 10 pages, 20 figures, expanded version with more detail
Surface behaviour of the pairing gap in a slab of nuclear matter
The surface behaviour of the pairing gap previously studied for semi-infinite
nuclear matter is analyzed in the slab geometry. The gap-shape function is
calculated in two cases: (a) pairing with the Gogny force in a hard-wall
potential and (b) pairing with the separable Paris interaction in a Saxon-Woods
mean-field potential. It is shown that the surface features are preserved in
the case of slab geometry, being almost independent of the width of the slab.
It is also demonstrated that the surface enhancement is strengthened as the
absolute value of chemical potential decreases which simulates the
approach to the nucleon drip line.Comment: 12 pages, 2 figure
Polarization observables of the gamma d --> PiNN reaction in the Delta(1232)-resonance region
Polarization observables of the three charge states of the pion for the
reaction with polarized photon beam and/or oriented
deuteron target are evaluated over the whole (1232)-resonance region
adopting a nonrelativistic model based on time-ordered perturbation theory.
Results for the -meson spectra, linear photon asymmetry, vector and tensor
target asymmetries are presented. Particular attention is given, for the first
time, to double polarization asymmetries for which we present results for
and . We found that all other double
polarization asymmetries of photon and deuteron target are vanished.Comment: 17 Pages, 8 Figures, accepted for publication in Int. J. Mod. Phys.
On the K^+D Interaction at Low Energies
The Kd reactions are considered in the impulse approximation with NN
final-state interactions (NN FSI) taken into account. The realistic parameters
for the KN phase shifts are used. The "quasi-elastic" energy region, in which
the elementary KN interaction is predominantly elastic, is considered. The
theoretical predictions are compared with the data on the K^+d->K^+pn,
K^+d->K^0pp, K^+d->K^+d and K^+d total cross sections. The NN FSI effect in the
reaction K^+d->K^+pn has been found to be large. The predictions for the Kd
cross sections are also given for slow kaons, produced from phi(1020) decays,
as the functions of the isoscalar KN scattering length a_0. These predictions
can be used to extract the value of a_0 from the data.Comment: 22 pages, 5 figure
The Transient Dendritic Solidification Experiment (TDSE)
The study of steady-state dendritic growth has both validated many element of transport phenomena in dendritic growth, and yielded many new insights. Further development in simulation and modeling are needed, as is further understanding of the role of selection or scaling in dendritic growth. The TDSE contributes to the further study of dendritic phenomena by carefully measuring and modeling transient effects on dendritic growth. The major challenge encountered in measuring and analyzing the transient behavior of isothermal dendrites is defining precisely the initial conditions from which or to which the dendrite evolves. Our proposed pressure-mediated TDSE microgravity experiment, obviates this difficulty, because the transient occurs between two well-characterized steady-states, rather than between an ill-defined initial state and the final steady state. The major results expected are unique data on transient behavior that will extend the scientific bounds from the now well-understood thermal effects, and provide insight into interfacial dynamics where open questions remain
Integrated systems research for sustainable smallholder agriculture in the Central Mekong: Achievements and challenges of implementing integrated systems research
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