159 research outputs found
Beryllium abundances in stars hosting giant planets
We have derived beryllium abundances in a wide sample of stars hosting
planets, with spectral types in the range F7V-K0V, aimed at studying in detail
the effects of the presence of planets on the structure and evolution of the
associated stars. Predictions from current models are compared with the derived
abundances and suggestions are provided to explain the observed
inconsistencies. We show that while still not clear, the results suggest that
theoretical models may have to be revised for stars with Teff<5500K. On the
other hand, a comparison between planet host and non-planet host stars shows no
clear difference between both populations. Although preliminary, this result
favors a ``primordial'' origin for the metallicity ``excess'' observed for the
planetary host stars. Under this assumption, i.e. that there would be no
differences between stars with and without giant planets, the light element
depletion pattern of our sample of stars may also be used to further
investigate and constraint Li and Be depletion mechanisms.Comment: A&A in press -- accepted on the 22/02/2002 (11 pages, 6 figures
included
Discontinuous transitions in double exchange materials
It is shown that the double exchange Hamiltonian, with weak antiferromagnetic
interactions, has a rich variety of first order transitions between phases with
different electronic densities and/or magnetizations. For band fillings in the
range , and at finite temperatures, a discontinuous
transition between phases with similar electronic densities but different
magnetizations takes place. This sharp transition, which is not suppressed by
electrostatic effects, and survives in the presence of an applied field, is
consistent with the phenomenology of the doped manganites near the transition
temperature.Comment: three more variational ansatzs considere
Satisfacción de usuarios de servicios deportivos en Orihuela (Alicante)
The aim of this study was to evaluate the perceived quality and user satisfaction of the municipal sports facility "Water Palace" in Orihuela (Alicante). The sample was formed by 36 users of the facility. Questionnaire EPOD (Nuviala, Tamayo, Iranzo and Falcón, 2008) was administered to the sample in order to measure the users satisfaction. The most significant results show that users are satisfied with the sports facility, with the best results in the image of the organization, the activities and technical aspects. The lowest scores appear in sports facilities and material. Therefore, it is concluded that, as future implications in the management of the facility, it is advisable to focus the attention on the dimensions related to sports facilities and material because they obtained the lowest scores.El objetivo del presente estudio ha sido evaluar la calidad percibida y satisfacción de usuarios de la instalación deportiva municipal del "Palacio del Agua" en la localidad alicantina de Orihuela. La muestra estuvo formada por 36 usuarios de dicha instalación. Se aplicó el cuestionario EPOD (Escala de Percepción de Organizaciones Deportivas), de Nuviala, Tamayo, Iranzo y Falcón (2008), el cual mide la satisfacción de usuarios de organizaciones que prestan servicios deportivos. Los resultados más significativos muestran que los usuarios están satisfechos con la instalación deportiva, obteniendo los mejores resultados en los apartados de imagen de la organización, actividades y aspectos técnicos. Sin embargo, se denotan puntuaciones más bajas en el apartado de instalación y material. Por todo ello, se concluye que, como futuras implicaciones en la gestión de la instalación, se debería focalizar la atención en las dimensiones relacionadas con la instalación y el material, ya que obtienen las puntuaciones más bajas
Are beryllium abundances anomalous in stars with giant planets?
In this paper we present beryllium (Be) abundances in a large sample of 41
extra-solar planet host stars, and for 29 stars without any known
planetary-mass companion, spanning a large range of effective temperatures. The
Be abundances were derived through spectral synthesis done in standard Local
Thermodynamic Equilibrium, using spectra obtained with various instruments. The
results seem to confirm that overall, planet-host stars have ``normal'' Be
abundances, although a small, but not significant, difference might be present.
This result is discussed, and we show that this difference is probably not due
to any stellar ``pollution'' events. In other words, our results support the
idea that the high-metal content of planet-host stars has, overall, a
``primordial'' origin. However, we also find a small subset of planet-host
late-F and early-G dwarfs that might have higher than average Be abundances.
The reason for the offset is not clear, and might be related either to the
engulfment of planetary material, to galactic chemical evolution effects, or to
stellar-mass differences for stars of similar temperature.Comment: 15 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
Nitrogen abundances in Planet-harbouring stars
We present a detailed spectroscopic analysis of nitrogen abundances in 91
solar-type stars, 66 with and 25 without known planetary mass companions. All
comparison sample stars and 28 planet hosts were analysed by spectral synthesis
of the near-UV NH band at 3360 \AA observed at high resolution with the
VLT/UVES,while the near-IR NI 7468 \AA was measured in 31 objects. These two
abundance indicators are in good agreement. We found that nitrogen abundance
scales with that of iron in the metallicity range -0.6 <[Fe/H]< +0.4 with the
slope 1.08 \pm 0.05. Our results show that the bulk of nitrogen production at
high metallicities was coupled with iron. We found that the nitrogen abundance
distribution in stars with exoplanets is the high [Fe/H] extension of the curve
traced by the comparison sample of stars with no known planets. A comparison of
our nitrogen abundances with those available in the literature shows a good
agreement.Comment: 15 pages, 7 figures, Accepted for publication in A&
Phase diagram and influence of defects in the double perovskites
The phase diagram of the double perovskites of the type Sr_{2-x} La_x Fe Mo
O_6 is analyzed, with and without disorder due to antisites. In addition to an
homogeneous half metallic ferrimagnetic phase in the absence of doping and
disorder, we find antiferromagnetic phases at large dopings, and other
ferrimagnetic phases with lower saturation magnetization, in the presence of
disorder.Comment: 4 pages, 3 postscript figures, some errata correcte
A Molecular Platinum Cluster Junction: A Single-Molecule Switch
We present a theoretical study of the electronic transport through
single-molecule junctions incorporating a Pt6 metal cluster bound within an
organic framework. We show that the insertion of this molecule between a pair
of electrodes leads to a fully atomically engineered nano-metallic device with
high conductance at the Fermi level and two sequential high on/off switching
states. The origin of this property can be traced back to the existence of a
HOMO which consists of two degenerate and asymmetric orbitals, lying close in
energy to the Fermi level of the metallic leads. Their degeneracy is broken
when the molecule is contacted to the leads, giving rise to two resonances
which become pinned close to the Fermi level and display destructive
interference.Comment: 4 pages, 4 figures. Reprinted (adapted) with permission from J. Am.
Chem. Soc., 2013, 135 (6), 2052. Copyright 2013 American Chemical Societ
Expresión del factor de crecimiento del endotelio vascular en carcinomas renales y su relación con la microdensidad vascular, la embolia tumoral y las metástasis a distancia
Los carcinomas renales de células claras derivan de las células epiteliales renales originadas en los túbulos contorneados proximales de las nefronas y se caracterizan por presentar una profusa vascularización. El funcionamiento aberrante del gen del VHL presente en gran parte de estos tumores, se traduce en la liberación de una serie de factores de crecimiento, entre ellos del factor de crecimiento del endotelio vascular (VEGF), implicado en el crecimiento y proliferación de las células tumorales, así como en el proceso de angiogénesis necesaria para el desarrollo de metástasis por vía hematógena. Varios trabajos han sostenido la hipótesis de que la marcación con VEGF podría ser de importancia como factor pronóstico.
El objetivo del presente trabajo es determinar la distribución e intensidad de la inmunomarcación con VEGF en tumores renales de células calaras y su relación con la microdensidad vascular (MDV), la presencia de embolias tumorales y las metástasis a distancia.Facultad de Ciencias Médica
Chemical abundances of planet-host stars: Results for alpha and Fe-group elements
In this paper, we present a study of the abundances of Si, Ca, Sc, Ti, V, Cr,
Mn, Co, and Ni in a large set of stars known to harbor giant planets, as well
as in a comparison sample of stars not known to have any planet ary-mass
companions. We have checked for possible chemical differences between planet
hosts and field stars without known planets. Our results show that overall, and
for a given value of [Fe/H], the abundance trends for the planet hosts are
nearly indistinguishable from those of the field stars. In general, the trends
show no discontinuities,and the abundance distributions of stars with giant
planets are high [Fe/H] extensions to the curves traced by the field dwarfs
without planets. The only elements that might present slight differences
between the two groups of stars are V, Mn, and to a lesser extent Ti and Co. We
also use the available data to describe galactic chemical evolution trends for
the elements studied. When comparing the results with former studies, a few
differences emerge for the high [Fe/H] tail of the distribution, a region that
is sampled with unprecedented detail in our analysis.Comment: Accepted for publication in Astronomy & Astrophysic
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