79 research outputs found
The Chromospheric Solar Millimeter-wave Cavity; a Common Property in the Semi-empirical Models
The semi-empirical models of the solar chromosphere are useful in the study
of the solar radio emission at millimeter - infrared wavelengths. However,
current models do not reproduce the observations of the quiet sun. In this work
we present a theoretical study of the radiative transfer equation for four
semi- empirical models at these wavelengths. We found that the Chromospheric
Solar Milimeter-wave Cavity (CSMC), a region where the atmosphere becomes
locally optically thin at millimeter wavelengths, is present in the
semi-empirical models under study. We conclude that the CSMC is a general
property of the solar chromosphere where the semi-empirical models shows
temperature minimum.Comment: Accepted in Geofisica Internaciona
A Grid of Synthetic Stellar UV Fluxes
We present preliminary results of a large project aimed at creating an
extended theoretical and observational database of stellar spectra in the
ultraviolet wavelength range. This library will consist of IUE spectra at low
and high resolution, and a set of LTE and NLTE theoretical fluxes. A first grid
of 50 model fluxes with solar metallicity, in the wavelength interval 1000 -
4400 AA, is reported here. Calculations are based on the Kurucz (1993) SYNTHE
code. The models span effective temperatures between 10,000 K and 50,000 K, and
a surface gravity in the range 2.5 <= log g <= 5.0 dex.Comment: 2 pages, 1 figure, To appear in proceedings, "New Quests in Stellar
Astrophysics: The Link Between Stars and Cosmology ", March 26-30, 2001, Eds.
M. Chavez, A. Bressan, A. Buzzoni & D. Mayy
A determination of the fragmentation functions of pions, kaons, and protons with faithful uncertainties
We present NNFF1.0, a new determination of the fragmentation functions (FFs)
of charged pions, charged kaons, and protons/antiprotons from an analysis of
single-inclusive hadron production data in electron-positron annihilation. This
determination, performed at leading, next-to-leading, and
next-to-next-to-leading order in perturbative QCD, is based on the NNPDF
methodology, a fitting framework designed to provide a statistically sound
representation of FF uncertainties and to minimise any procedural bias. We
discuss novel aspects of the methodology used in this analysis, namely an
optimised parametrisation of FFs and a more efficient minimisation
strategy, and validate the FF fitting procedure by means of closure tests. We
then present the NNFF1.0 sets, and discuss their fit quality, their
perturbative convergence, and their stability upon variations of the kinematic
cuts and the fitted dataset. We find that the systematic inclusion of
higher-order QCD corrections significantly improves the description of the
data, especially in the small- region. We compare the NNFF1.0 sets to other
recent sets of FFs, finding in general a reasonable agreement, but also
important differences. Together with existing sets of unpolarised and polarised
parton distribution functions (PDFs), FFs and PDFs are now available from a
common fitting framework for the first time.Comment: 50 pages, 22 figures, 5 table
Infrared excesses in stars with and without planets using revised photometry
We present an analysis on the potential prevalence of mid infrared excesses
in stars with and without planetary companions. Based on an extended database
of stars detected with the satellite, we studied two stellar
samples: one with 236 planet hosts and another with 986 objects for which
planets have been searched but not found. We determined the presence of an
excess over the photosphere by comparing the observed flux ratio at 22 m
and 12 m () with the corresponding synthetic value, derived
from results of classical model photospheres. We found a detection rate of
0.85 at 22 m (2 excesses) in the sample of stars with planets and
0.1 (1 detection) for the stars without planets. The difference of the
detection rate between the two samples is not statistically significant, a
result that is independent of the different approaches found in the literature
to define an excess in the wavelength range covered by
observations. As an additional result, we found that the fluxes
required a normalisation procedure to make them compatible with synthetic data,
probably pointing out a revision of the data calibration.Comment: 10 pages, 6 figures, 3 tables. Accepted for publication in MNRA
Three Synchronous Head and Neck Cancers: A Multidisciplinary and Surgical Challenge.
Second primary cancer (SPC) is a term used to describe a new primary cancer occurring in patients who had formerly been diagnosed with tumor. Even though SPCs appear to be related to primary cancers, they are actually entities that have arisen independently and not as a result of recurrence. This report is of the first case in literature of a patient hospitalized for the surgical treatment of 3 synchronous Head and Neck Cancers. A 66-year-old male was admitted to our hospital (Ospedale Degli Infermi—Biella, Italy) complaining about pharyngodynia. Three different lesions were identified through endoscopic examination and narrow band imaging: the first one on left tonsil, the second one on epiglottis, and the third one on right aryepiglottic fold. The case was subject to a multidisciplinary team analysis due to its complexity, then the surgery consisted in (1) CO2 laser left tonsillectomy, associated with (2) CO2 laser excision of the lesion on epiglottis free edge, and (3) CO2 laser excision of right aryepiglottic fold lesion. Synchronous tumors are among the most defiant challenges for surgeons since no international guideline specifies differentiated strategies to be adopted in patients affected by synchronous Head and Neck Cancers, therefore surgical planning must be tailored differently from patient to patient, and many unsolved questions still concern clinical treatments to be adopted
Statistical properties of the GALEX spectroscopic stellar sample
The GALEX General Data Release 4/5 includes 174 spectroscopic tiles, obtained
from slitless grism observations, for a total of more than 60,000 ultraviolet
spectra. We have determined statistical properties of the sample of GALEX
stars. We have defined a suitable system of spectroscopic indices, which
measure the main mid-UV features at the GALEX low spectral resolution and we
have employed it to determine the atmospheric parameters of of stars in the
range 4500<Teff<9000 K. Our preliminary results indicate that the sample is
formed by a majority of main sequence F- and G-type stars, with metallicity
[M/H]>-1 dex.Comment: 9 pages, 9 figures, accepted for publication in Astrophysics & Space
Science, UV universe special issu
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