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 $0.3 \le x \le 0.5$, 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