3,173 research outputs found
The EUVE point of view of AD Leo
All the Extreme Ultraviolet Explorer (EUVE) observations of AD Leo, totalling
1.1 Ms of exposure time, have been employed to analyze the corona of this
single M dwarf. The light curves show a well defined quiescent stage, and a
distribution of amplitude of variability following a power law with a ~-2.4
index. The flaring behavior exhibits much similarity with other M active stars
like FK Aqr or YY Gem, and flares behave differently from late type active
giants and subgiants. The Emission Measure Distribution (EMD) of the summed
spectrum, as well as that of quiescent and flaring stages, were obtained using
a line-based method. The average EMD is dominated by material at log T(K)~6.9,
with a second peak around log T(K)~6.3, and a large increase in the amount of
material with log T(K)>~7.1 during flares, material almost absent during
quiescence. The results are interpreted as the combination of three families of
loops with maximum temperatures at log T(K)~6.3, ~6.9 and somewhere beyond log
T(K)>~7.1. A value of the abundance of [Ne/Fe]=1.05+-0.08 was measured at log
T(K)~5.9. No significative increment of Neon abundance was detected between
quiescence and flaring states.Comment: Full PS version can be found also at
http://www.astropa.unipa.it/~jsanz/papers0002.htm
Hybrid rule-based - example-based MT: feeding apertium with sub-sentential translation units
This paper describes a hybrid machine translation (MT) approach that consists of integrating bilingual chunks (sub-sentential translation units) obtained from parallel corpora into an MT system built using the Apertium free/open-source rule-based machine translation platform, which uses a shallow-transfer translation approach. In the integration of bilingual chunks, special care has been
taken so as not to break the application of the existing Apertium structural transfer rules, since this would increase the number of ungrammatical translations. The method consists of (i) the application of a dynamic-programming algorithm to compute the best translation coverage of the input sentence given the collection of bilingual chunks available; (ii) the translation of the input sentence as usual by Apertium; and (iii) the application of a language model to choose one of the possible translations for each of the bilingual chunks detected. Results are reported for the translation from English-to-Spanish, and vice versa, when marker-based bilingual chunks automatically obtained from parallel
corpora are used
Effects of XUV radiation on circumbinary planets
Several circumbinary planets have recently been discovered. The orbit of a
planet around a binary stellar system poses several dynamic constraints. The
effects that radiation from the host stars may have on the planet atmospheres
must be considered. Because of the configuration of a close binary system,
these stars have a high rotation rate, which causes a permanent state of high
stellar activity and copious XUV radiation. The accumulated effects are
stronger than for exoplanets around single stars, and cause a faster
evaporation of their atmospheres. We evaluate the effects that stellar
radiation has on the evaporation of exoplanets around binary systems and on the
survival of these planets. We considered the XUV spectral range to account for
the photons that are easily absorbed by a planet atmosphere that is mainly
composed of hydrogen. A more complex atmospheric composition is expected to
absorb this radiation more efficiently. We used direct X-ray observations to
evaluate the energy in the X-rays range and coronal models to calculate the
(nondetectable) EUV part of the spectrum. The simulations show that exoplanets
in a close orbit will suffer strong photoevaporation that may cause a total
loss of atmosphere in a short time. A binary system of two solar-like stars
will be highly efficient in evaporating the atmosphere of the planet. These
systems will be difficult to find, even if they are dynamically stable. Still,
planets may orbit around binary systems of low mass stars for wider orbits.
Currently known circumbinary planets are not substantially affected by thermal
photoevaporation processes, unless Kepler-47 b has an inflated atmosphere. The
distribution of the orbital periods of circumbinary planets is shifted to much
longer periods than the average of Kepler planets, which supports a scenario of
strong photoevaporation in close-in circumbinary planets.Comment: Accepted by A&A. 8 pages, 5 figure
Estimation of the XUV radiation onto close planets and their evaporation
Context: The current distribution of planet mass vs. incident stellar X-ray
flux supports the idea that photoevaporation of the atmosphere may take place
in close-in planets. Integrated effects have to be accounted for. A proper
calculation of the mass loss rate due to photoevaporation requires to estimate
the total irradiation from the whole XUV range. Aims: The purpose of this paper
is to extend the analysis of the photoevaporation in planetary atmospheres from
the accessible X-rays to the mostly unobserved EUV range by using the coronal
models of stars to calculate the EUV contribution to the stellar spectra. The
mass evolution of planets can be traced assuming that thermal losses dominate
the mass loss of their atmospheres. Methods: We determine coronal models for 82
stars with exoplanets that have X-ray observations available. Then a synthetic
spectrum is produced for the whole XUV range (~1-912 {\AA}). The determination
of the EUV stellar flux, calibrated with real EUV data, allows us to calculate
the accumulated effects of the XUV irradiation on the planet atmosphere with
time, as well as the mass evolution for planets with known density. Results: We
calibrate for the first time a relation of the EUV luminosity with stellar age
valid for late-type stars. In a sample of 109 exoplanets, few planets with
masses larger than ~1.5 Mj receive high XUV flux, suggesting that intense
photoevaporation takes place in a short period of time, as previously found in
X-rays. The scenario is also consistent with the observed distribution of
planet masses with density. The accumulated effects of photoevaporation over
time indicate that HD 209458b may have lost 0.2 Mj since an age of 20 Myr.
Conclusions: Coronal radiation produces rapid photoevaporation of the
atmospheres of planets close to young late-type stars. More complex models are
needed to explain fully the observations.Comment: Accepted by A&A. 10 pages, 8 figures, 7 Tables (2 online). Additional
online material includes 7 pages, 6 figures and 6 tables, all include
Salting Babies. Innovation and Tradition in Premodern Procedures for Neonatal Care
The paper studies two aspects of the procedures of neonatal care explained by ancient and medieval medicine: the application of salt to the newbornâs skin in order to harden it, and the alternative proposed by Ibn Zuhr, anointment with acorn oil. The latter procedure was echoed by several physicians in al-Andalus and was known to the physicians of the
Renaissance, some of whom preferred it to all other methods. Ibn Zuhrâs anointment with acorn oil is analyzed as a case study that broadens our knowledge of the innovative character of this author, one of the outstanding physicians in the history of al-Andalus medicine, and of the doctrinal change and its transmission in Pre-Modern medicine. The paper sketches the history of the application of salt in newborns, a practice still in use at present time, from its early antecedents in the Semitic cultures to Late Middle Ages and Renaissance, studying in particular the main sources of neonatal care in Greek and Arabo-Islamic medicine. Another ancestral procedure for the same purpose, rubbing with henna, and the interaction between learned and folk medicine are also considered within the framework of the discussion of whether salt or acorn oil was better for newborns
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