2,075 research outputs found
Quantitative chemical tagging, stellar ages and the chemo-dynamical evolution of the Galactic disc
The early science results from the new generation of high-resolution stellar
spectroscopic surveys, such as GALAH and the Gaia-ESO survey, will represent
major milestones in the quest to chemically tag the Galaxy. Yet this technique
to reconstruct dispersed coeval stellar groups has remained largely untested
until recently. We build on previous work that developed an empirical chemical
tagging probability function, which describes the likelihood that two field
stars are conatal, that is, they were formed in the same cluster environment.
In this work we perform the first ever blind chemical tagging experiment, i.e.,
tagging stars with no known or otherwise discernable associations, on a sample
of 714 disc field stars with a number of high quality high resolution
homogeneous metal abundance measurements. We present evidence that chemical
tagging of field stars does identify coeval groups of stars, yet these groups
may not represent distinct formation sites, e.g. as in dissolved open clusters,
as previously thought. Our results point to several important conclusions,
among them that group finding will be limited strictly to chemical abundance
space, e.g. stellar ages, kinematics, colors, temperature and surface gravity
do not enhance the detectability of groups. We also demonstrate that in
addition to its role in probing the chemical enrichment and kinematic history
of the Galactic disc, chemical tagging represents a powerful new stellar age
determination technique.Comment: 12 pages, 9 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society (MNRAS
Proton emission induced by polarized photons
The proton emission induced by polarized photons is studied in the energy
range above the giant resonance region and below the pion emission threshold.
Results for the 12C, 16O and 40Ca nuclei are presented. The sensitivity of
various observables to final state interaction, meson exchange currents and
short range correlations is analyzed. We found relevant effects due to the
virtual excitation of the resonance.Comment: 12 pages, 11 figures, 1 tabl
Magnetic excitations in nuclei with neutron excess
The excitation of the , and modes in O, O,
O, O, Ca, Ca, Ca and Ca nuclei is
studied with self-consistent random phase approximation calculations.
Finite-range interactions of Gogny type, containing also tensor-isospin terms,
are used. We analyze the evolution of the magnetic resonances with the
increasing number of neutrons, the relevance of collective effects, the need of
a correct treatment of the continuum and the role of the tensor force.Comment: 18 pages, 12 figures, 2 tables, accepted for publication in Physical
Review
Policitemia vera en un perro : su diagnóstico y su tratamiento
En este artÃculo presentamos un caso clÃnico de policitemia vera (eritrocitosis) canina con un nivel de eritropoyetina en suero normal. Fue diagnosticado y tratado mediante flebotomÃas repetidas, en un primer momento y con hidroxyurea posteriormente
Cavity Optomechanics with a Laser Engineered Optical Trap
Laser engineered exciton-polariton networks could lead to dynamically
configurable integrated optical circuitry and quantum devices. Combining cavity
optomechanics with electrodynamics in laser configurable hybrid designs
constitutes a platform for the vibrational control, conversion, and transport
of signals. With this aim we investigate 3D optical traps laser-induced in
quantum-well embedded semiconductor planar microcavities. We show that the
laser generated and controlled discrete states of the traps dramatically modify
the interaction between photons and phonons confined in the resonators,
accessing through coupling of photoelastic origin
MHz an optomechanical cooperativity for mW excitation. The quenching of
Stokes processes and double-resonant enhancement of anti-Stokes ones involving
pairs of discrete optical states in the side-band resolved regime, allows the
optomechanical cooling of 180 GHz bulk acoustic waves, starting from room
temperature down to K. These results pave the way for dynamical
tailoring of optomechanical actuation in the extremely-high-frequency range
(30-300 GHz) for future network and quantum technologies.Comment: 22 pages, 14 figure
A model for two-proton emission induced by electron scattering
A model to study two-proton emission processes induced by electron scattering
is developed. The process is induced by one-body electromagnetic operators
acting together with short-range correlations, and by two-body
currents. The model includes all the diagrams containing a single correlation
function. A test of the sensitivity of the model to the various theoretical
inputs is done. An investigation of the relevance of the currents is
done by changing the final state angular momentum, excitation energy and
momentum transfer. The sensitivity of the cross section to the details of the
correlation function is studied by using realistic and schematic correlations.
Results for C, O and Ca nuclei are presented.Comment: 30 pages, 18 figures, 3 table
Superscaling in electroweak excitation of nuclei
Superscaling properties of 12C, 16O and 40Ca nuclear responses, induced by
electron and neutrino scattering, are studied for momentum transfer values
between 300 and 700 MeV/c. We have defined two indexes to have quantitative
estimates of the scaling quality. We have analyzed experimental responses to
get the empirical values of the two indexes. We have then investigated the
effects of finite dimensions, collective excitations, meson exchange currents,
short-range correlations and final state interactions. These effects strongly
modify the relativistic Fermi gas scaling functions, but they conserve the
scaling properties. We used the scaling functions to predict electron and
neutrino cross sections and we tested their validity by comparing them with the
cross sections obtained with a full calculation. For electron scattering we
also made a comparison with data. We have calculated the total charge-exchange
neutrino cross sections for neutrino energies up to 300 MeV.Comment: 19 pages, 12 figures, 1 table; to be published in Physical Review
Correlations and charge distributions of medium heavy nuclei
The effects of long- and short-range correlations on the charge distributions
of some medium and heavy nuclei are investigated. The long-range correlations
are treated within the Random Phase Approximation framework and the short-range
correlations with a model inspired to the Correlation Basis Function theory.
The two type of correlations produce effects of the same order of magnitude. A
comparison with the empirical charge distribution difference between 206Pb and
205Tl shows the need of including both correlations to obtain a good
description of the data.Comment: 20 pages, Latex, accepted for publication in Jour. Phys.
Low-lying magnetic excitations of doubly-closed-shell nuclei and nucleon-nucleon effective interactions
We have studied the low lying magnetic spectra of 12C, 16O, 40Ca, 48Ca and
208Pb nuclei within the Random Phase Approximation (RPA) theory, finding that
the description of low-lying magnetic states of doubly-closed-shell nuclei
imposes severe constraints on the spin and tensor terms of the nucleon-nucleon
effective interaction. We have first made an investigation by using four
phenomenological effective interactions and we have obtained good agreement
with the experimental magnetic spectra, and, to a lesser extent, with the
electron scattering responses. Then we have made self-consistent RPA
calculations to test the validity of the finite-range D1 Gogny interaction. For
all the nuclei under study we have found that this interaction inverts the
energies of all the magnetic states forming isospin doublets.Comment: 19 pages, 13 figures, 7 tables, accepted for publication in Phys.
Rev.
Mirizzi syndrome-differential diagnosis with cholangiocarcinoma: case report
Mirizzi syndrome is a rare complication of gallstone disease and poses a diagnostic challenge for general surgeons due to its clinical presentation, which resembles other pathological entities such as cholangiocarcinoma. We present a clinical case of a 68-year-old female patient with symptoms of jaundice and right upper quadrant pain. During the patient's diagnostic workup, altered liver function tests were documented, highlighting obstructive pattern hyperbilirubinemia, elevated tumor marker CA 19.9, and suspicion of biliary tract tumor based on imaging studies. However, surgical and pathological confirmation revealed Mirizzi syndrome. This case emphasizes the importance of considering differential diagnoses in patients presenting with obstructive jaundice to provide timely and appropriate treatment
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