5,627 research outputs found
Relative production rates of He, Be, C in astrophysical environments
We assume an environment of neutrons and -particles of given density
and temperature where nuclear syntheses into He, Be and C
are possible. We investigate the resulting relative abundance as a function of
density and temperature. When the relative abundance of -particles
is between 0.2 and 0.9, or larger than 0.9, the largest production
is Be or C, respectively. When He is mostly
frequently produced for temperatures above about 2 GK whereas the Be
production dominates at smaller temperatures.Comment: 5 pages, 4 figure
Matter--wave emission in optical lattices: Single particle and collective effects
We introduce a simple set--up corresponding to the matter-wave analogue of
impurity atoms embedded in an infinite photonic crystal and interacting with
the radiation field. Atoms in a given internal level are trapped in an optical
lattice, and play the role of the impurities. Atoms in an untrapped level play
the role of the radiation field. The interaction is mediated by means of lasers
that couple those levels. By tuning the lasers parameters, it is possible to
drive the system through different regimes, and observe phenomena like matter
wave superradiance, non-Markovian atom emission, and the appearance of bound
atomic states.Comment: 5 pages, 3 figure
Few-body decay and recombination in nuclear astrophysics
Three-body continuum problems are investigated for light nuclei of
astrophysical relevance. We focus on three-body decays of resonances or
recombination via resonances or the continuum background. The concepts of
widths, decay mechanisms and dynamic evolution are discussed. We also discuss
results for the triple decay in connection with resonances and
density and temperature dependence rates of recombination into light nuclei
from -particles and neutrons.Comment: 9 pages, 8 figures. Proceedings of the 21st European Few Body
Conference held in Salamanca (Spain) in August-September 201
The southernmost range limit for the hidden angelshark Squatina occulta
Background: Angelsharks (Genus Squatina) are distributed in the southern Southwest Atlantic Ocean between southeastern Brazil and central Patagonia. The endangered hidden angelshark Squatina occulta is reported in the literature as ranging from Espírito Santo, Brazil to Southern Uruguay. Its presence in Argentine waters has been suspected but not verified so far. This study describes and analyzes a specimen of S. occulta found in Puerto Quequén 38° 40′S - 58° 50′W, Buenos Aires Province, Argentina. Results: An immature male of 578 mm total length and 1,450 g was collected from commercial landings of the bottom trawl fishery of Puerto Quequén. The specimen exhibited the coloration pattern, dermal denticle distribution, and tooth formula characteristic of S. occulta. Conclusions: Squatina guggenheim and S. argentina are already known to occur off Puerto Quequén. The present finding confirms the presence of a third species of angelshark in Argentina and constitutes the southernmost record of S. occulta.Fil: Estalles, María Lourdes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; ArgentinaFil: Chiaramonte, Gustavo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; ArgentinaFil: Faria, Vicente V.. Universidade Federal do Ceará; BrasilFil: Luzzatto, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin
Cluster sum rules for three-body systems with angular-momentum dependent interactions
We derive general expressions for non-energy weighted and energy-weighted
cluster sum rules for systems of three charged particles. The interferences
between pairs of particles are found to play a substantial role. The
energy-weighted sum rule is usually determined by the kinetic energy operator,
but we demonstrate that it has similar additional contributions from the
angular momentum and parity dependence of two- and three-body potentials
frequently used in three-body calculations. The importance of the different
contributions is illustrated with the dipole excitations in He. The results
are compared with the available experimental data.Comment: 11 pages, 3 figures, 2 table
Genome sequence of Rhizobium sullae HCNT1 isolated from Hedysarum coronarium nodules and featuring peculiar denitrification phenotypes
The genome sequence of Rhizobium sullae strain HCNT1, isolated from root nodules of the legume Hedysarum coronarium growing in wild stands in Tuscany, Italy, is described here. Unlike other R. sullae strains, this isolate features a truncated denitrification pathway lacking NO/N2O reductase activity and displaying high sensitivity to nitrite under anaerobic conditions
Strong field limit analysis of gravitational retro-lensing
We present a complete treatment in the strong field limit of gravitational
retro-lensing by a static spherically symmetric compact object having a photon
sphere. The results are compared with those corresponding to ordinary lensing
in similar strong field situations. As examples of application of the
formalism, a supermassive black hole at the galactic center and a stellar mass
black hole in the galactic halo are studied as retro-lenses, in both cases
using the Schwarzschild and Reissner-Nordstrom geometries.Comment: 11 pages, 1 figure; v2: minor changes. Accepted for publication in
Physical Review
Hamiltonian dynamics and constrained variational calculus: continuous and discrete settings
The aim of this paper is to study the relationship between Hamiltonian
dynamics and constrained variational calculus. We describe both using the
notion of Lagrangian submanifolds of convenient symplectic manifolds and using
the so-called Tulczyjew's triples. The results are also extended to the case of
discrete dynamics and nonholonomic mechanics. Interesting applications to
geometrical integration of Hamiltonian systems are obtained.Comment: 33 page
Nonholonomic constraints in -symplectic Classical Field Theories
A -symplectic framework for classical field theories subject to
nonholonomic constraints is presented. If the constrained problem is regular
one can construct a projection operator such that the solutions of the
constrained problem are obtained by projecting the solutions of the free
problem. Symmetries for the nonholonomic system are introduced and we show that
for every such symmetry, there exist a nonholonomic momentum equation. The
proposed formalism permits to introduce in a simple way many tools of
nonholonomic mechanics to nonholonomic field theories.Comment: 27 page
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