6,992 research outputs found
Study of sdO models. Pulsation Analysis
We have explored the possibility of driving pulsation modes in models of sdO
stars in which the effects of element diffusion, gravitational settling and
radiative levitation have been neglected so that the distribution of iron-peak
elements remains uniform throughout the evolution. The stability of these
models was determined using a non-adiabatic oscillations code. We analysed 27
sdO models from 16 different evolutionary sequences and discovered the first
ever sdO models capable of driving high-radial order g-modes. In one model, the
driving is by a classical kappa-mechanism due to the opacity bump from
iron-peak elements at temperature ~200,000 K. In a second model, the driving
result from the combined action of kappa-mechanisms operating in three distinct
regions of the star: (i) a carbon-oxygen partial ionization zone at temperature
~2 10^6 K, (ii) a deeper region at temperature ~2 10^7 K, which we attribute to
ionization of argon, and (iii) at the transition from radiative to conductive
opacity in the core of the star.Comment: 13 pages, 19 figures, accepted for publication in MNRAS, 2009
September 1
Study of sdO models: mode trapping
We present the first description of mode trapping for sdO models. Mode
trapping of gravity modes caused by the He/H chemical transition is found for a
particular model, providing a selection effect for high radial order trapped
modes. Low- and intermediate-radial order {\em p}-modes (mixed modes with a
majority of nodes in the P-mode region) are found to be trapped by the C-O/He
transition, but with no significant effects on the driving. This region seems
to have also a subtle effect on the trapping of low radial order {\em g}-modes
(mixed modes with a majority of nodes in the G-mode region), but again with no
effect on the driving. We found that for mode trapping to have an influence on
the driving of sdO modes (1) the mode should be trapped in a way that the
amplitude of the eigenfunctions is lower in a damping region and (2) in this
damping region significant energy interchange has to be produced.Comment: 10 pages, 13 figures, accepted for publication in MNRAS, 2009
December 1
Estudio de correlación y variabilidad de los métodos de inmersión en mercurio y el método capacitivo resonante para determinar densidad aparente de material cerámico crudo
En el siguiente trabajo, se presentan los resultados del estudio de correlación de las variables y parámetros asociados a la
medición de la Densidad Aparente (DAP) para material cerámico crudo utilizado en la fabricación industrial de baldosas
para piso, frente al método de inmersión en mercurio. Los anteriores resultados se obtuvieron teniendo en cuenta la
aplicación de un modelo matemático al DAP como función no lineal de parámetros como la temperatura, permitividad
eléctrica relativa y variables como la humedad relativa HR, voltaje y frecuencia de resonancia, medidos con un dispositivo
electrónico diseñado en la Universidad Central por el grupo de investigación en Estado Sólido y Optoelectrónica ESSOPTO
y utilizado en el Centro de Investigación en Materiales Cerámicos de la UFPS – CIMAC de la Universidad Francisco de Paula
Santander – Cúcuta Colombia.Peer reviewe
A search for new hot subdwarf stars by means of Virtual Observatory tools
Hot subdwarf stars are faint, blue objects, and are the main contributors to
the far-UV excess observed in elliptical galaxies. They offer an excellent
laboratory to study close and wide binary systems, and to scrutinize their
interiors through asteroseismology, as some of them undergo stellar
oscillations. However, their origins are still uncertain, and increasing the
number of detections is crucial to undertake statistical studies. In this work,
we aim at defining a strategy to find new, uncatalogued hot subdwarfs. Making
use of Virtual Observatory tools we thoroughly search stellar catalogues to
retrieve multi-colour photometry and astrometric information of a known sample
of blue objects, including hot subdwarfs, white dwarfs, cataclysmic variables
and main sequence OB stars. We define a procedure to discriminate among these
spectral classes, particularly designed to obtain a hot subdwarf sample with a
low contamination factor. In order to check the validity of the method, this
procedure is then applied to two test sky regions: the Kepler FoV and to a test
region of around (RA:225, DEC:5) deg. As a result, we obtained 38 hot subdwarf
candidates, 23 of which had already a spectral classification. We have acquired
spectroscopy for three other targets, and four additional ones have an
available SDSS spectrum, which we used to determine their spectral type. A
temperature estimate is provided for the candidates based on their spectral
energy distribution, considering two-atmospheres fit for objects with clear
infrared excess. Eventually, out of 30 candidates with spectral classification,
26 objects were confirmed to be hot subdwarfs, yielding a contamination factor
of only 13%. The high rate of success demonstrates the validity of the proposed
strategy to find new uncatalogued hot subdwarfs. An application of this method
to the entire sky will be presented in a forthcoming work.Comment: 13 pages, 7 figure
Pulsations in M dwarf stars
We present the results of the first theoretical non-radial non-adiabatic
pulsational study of M dwarf stellar models with masses in the range 0.1 to
0.5M_solar. We find the fundamental radial mode to be unstable due to an
\epsilon mechanism caused by deuterium (D-) burning for the young 0.1 and
0.2M_solar models, by non-equilibrium He^3 burning for the 0.2 and 0.25M_solar
models of 10^4Myr, and by a flux blocking mechanism for the partially
convective 0.4 and 0.5M_solar models once they reach the age of 500Myr. The
periods of the overstable modes excited by the D-burning are in the range 4.2
to 5.2h for the 0.1M_solar models and is of order 8.4h for the 0.2M_solar
models. The periods of the modes excited by He^3 burning and flux blocking are
in the range 23 to 40min. The more massive and oldest models are more promising
for the observational detection of pulsations, as their ratio of instability
e-folding time to age is more favourable.Comment: 5 pages, 4 figures, 2 tables. Accepted for publication in MNRAS
Letters on 2011 October 11 Version 2 is the accepted manuscript with changes
in boldfac
noise and integrable systems
An innovative test for detecting quantum chaos based on the analysis of the
spectral fluctuations regarded as a time series has been recently proposed.
According to this test, the fluctuations of a fully chaotic system should
exhibit 1/f noise, whereas for an integrable system this noise should obey the
1/f^2 power law. In this letter, we show that there is a family of well-known
integrable systems, namely spin chains of Haldane-Shastry type, whose spectral
fluctuations decay instead as 1/f^4. We present a simple theoretical
justification of this fact, and propose an alternative characterization of
quantum chaos versus integrability formulated directly in terms of the power
spectrum of the spacings of the unfolded spectrum.Comment: 5 pages, 3 figures, RevTe
The bulbus arteriosus of the holocephalan heart
El resumen aparece en el Program & Abstracts of the 10th International Congress of Vertebrate Morphology, Barcelona 2013.Anatomical Record, Volume 296, Special Feature — 1: P-074.Previous work has shown that the outflow tract of the elasmobranch heart, namely the
cardiac portion intercalated between the ventricle and the ventral aorta, does not consist
of a single component, the conus arteriosus, as has classically been assumed, but two,
the myocardial conus arteriosus and the non-myocardial bulbus arteriosus. From the
evolutionary perspective, knowledge of the anatomy of the cardiac outflow tract of the
holocephali is important, as they are the sister group of elasmobranchs. Our aim is to
describe the cardiac outflow tract of four holocephalan species, two of them, Chimaera
monstrosa and Hydrolagus affinis of the family Chimaeridae, and the other two, Harriotta
raleighana and Rhinochimaera atlantica, of the family Rhinochimaeridae. The cardiac
outflow tract of the four species consisted of a myocardial conus arteriosus, furnished
with valves, and a bulbus arteriosus devoid of cardiac muscle. Both the bulbus and
conus are tubular in shape. The length of the bulbus relative to the total length of the
outflow tract is somewhat smaller in the rhinochimaerids (15%-19%) than in the
chimaerids (19%-23%). The bulbus is covered by epicardium and is crossed by the main
coronary artery trunks. Histologically, the bulbus is mainly composed of elastin and
collagen, and, to a lesser extent, by smooth muscle. This suggests that in
holocephalans, the bulbus actively helps to protect the gill vasculature from exposure to
high-pressure pulses of blood. Our results prove that the bulbus arteriosus is common to
chondrichthyans. In addition, they support the hypothesis that the cardiac outflow tract
consisted of a conus arteriosus and a bulbus arteriosus from the beginning of the jawed
vertebrate radiation, contributing to our understanding of the morphological changes that
have occurred at the arterial pole of the heart in both actinopterygians and
sarcopterygians.Proyecto CGL2010-16417/BOS; Fondos FEDE
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