11,125 research outputs found
A robust motion estimation and segmentation approach to represent moving images with layers
The paper provides a robust representation of moving images based on layers. To that goal, we have designed efficient motion estimation and segmentation techniques by affine model fitting suitable for the construction of layers. Layered representations, originally introduced by Wang and Adelson (see IEEE Transactions on Image Processing, vol.3, no.5, p.625-38, 1994) are important in several applications. In particular they are very appropriate for object tracking, object manipulation and content-based scalability which are among the main functionalities of the future MPEG-4 standard. In addition a variety of examples are provided that give a deep insight into the performance bounds of the representation of moving images using layers.Peer ReviewedPostprint (published version
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
Numerical precision radiative corrections to the Dalitz plot of baryon semileptonic decays including the spin-momentum correlation of the decaying and emitted baryons
We calculate the radiative corrections to the angular correlation between the
polarization of the decaying and the direction of the emitted spin one-half
baryons in the semileptonic decay mode. The final results are presented, first,
with the triple integration of the bremsstrahlung photon ready to be performed
numerically and, second, in an analytical form. A third presentation of our
results in the form of numerical arrays of coefficients to be multiplied by the
quadratic products of form factors is discussed. This latter may be the most
practical one to use in Monte Carlo simulations. A series of crosschecks is
performed. Previous results to order (alpha/pi)(q/M_1) for the decays of
unpolarized baryons are reviewed, too, where q is the momentum transfer and M_1
is the mass of the decaying baryon. This paper is self-contained and organized
to make it accessible and reliable in the analysis of the Dalitz plot of
precision experiments involving heavy quarks and is not compromised to fixing
the form factors at predetermined values. It is assumed that the real photons
are kinematically discriminated. Otherwise, our results have a general
model-independent applicability.Comment: 34 pages, 4 tables, no figures. Some sections have been shortened.
Conclusions remain unchange
Radiative corrections to all charge assignments of heavy quark baryon semileptonic decays
In semileptonic decays of spin-1/2 baryons containing heavy quarks up to six
charge assignments for the baryons and lepton are possible. We show that the
radiative corrections to four of these possibilities can be directly obtained
from the final results of the two possibilities previously studied. There is no
need to recalculate integrals over virtual or real photon momentum or any
traces.Comment: 15 pages, 2 figures, RevTex. Extended discussion. Final version to
appear in Physical Review
Probing the electron-phonon coupling in ozone-doped graphene by Raman spectroscopy
We have investigated the effects of ozone treatment on graphene by Raman
scattering. Sequential ozone short-exposure cycles resulted in increasing the
doping levels as inferred from the blue shift of the 2 and peak
frequencies, without introducing significant disorder. The two-phonon 2 and
2 Raman peak intensities show a significant decrease, while, on the
contrary, the one-phonon G Raman peak intensity remains constant for the whole
exposure process. The former reflects the dynamics of the photoexcited
electrons (holes) and, specifically, the increase of the electron-electron
scattering rate with doping. From the ratio of 2 to 2 intensities, which
remains constant with doping, we could extract the ratio of electron-phonon
coupling parameters. This ratio is found independent on the number of layers up
to ten layers. Moreover, the rate of decrease of 2 and 2 intensities
with doping was found to slowdown inversely proportional to the number of
graphene layers, revealing the increase of the electron-electron collision
probability
Monte Carlo simulations of post-common-envelope white dwarf + main sequence binaries: The effects of including recombination energy
Detached WD+MS PCEBs are perhaps the most suitable objects for testing
predictions of close-compact binary-star evolution theories, in particular, CE
evolution. The population of WD+MS PCEBs has been simulated by several authors
in the past and compared with observations. However, most of those predictions
did not take the possible contributions to the envelope ejection from
additional sources of energy (mostly recombination energy) into account. Here
we update existing binary population models of WD+MS PCEBs by assuming that a
fraction of the recombination energy available within the envelope contributes
to ejecting the envelope. We performed Monte Carlo simulations of 10^7 MS+MS
binaries for 9 different models using standard assumptions for the initial
primary mass function, binary separations, and initial-mass-ratio distribution
and evolved these systems using the publicly available BSE code. Including a
fraction of recombination energy leads to a clear prediction of a large number
of long orbital period (>~10 days) systems mostly containing high-mass WDs. The
fraction of systems with He-core WD primaries increases with the CE efficiency
and the existence of very low-mass He WDs is only predicted for high values of
the CE efficiency (>~0.5). All models predict on average longer orbital periods
for PCEBs containing C/O-core WDs than for PCEBs containing He WDs. This effect
increases with increasing values of both efficiencies. Longer periods after the
CE phase are also predicted for systems containing more massive secondary
stars. The initial-mass-ratio distribution affects the distribution of orbital
periods, especially the distribution of secondary star masses. Our simulations,
in combination with a large and homogeneous observational sample, can provide
constraints on the values of the CE efficiencies, as well as on the
initial-mass-ratio distribution for MS+MS binary stars.Comment: 11 pages, 10 figures, accepted for publication in A&
Hidden clear cell acanthoma with uncommon dermoscopic findings
Dear Editor, A 73-year-old woman presented with less than a 1-year history of an erythematous, well-delimited and shiny lesion on her left buttock, near the gluteal fold. Dermoscopic examination showed dotted vessels arranged in a linear pattern involving the entire lesion. These vascular findings are also called metaphorically a âstring of pearlsâ pattern. Another vascular pattern observed on the periphery of the lesion is that of branched vessels with rounded endings. Surprisingly, dermoscopy also revealed multiple rosettes (also known as âfour-clod dotsâ). Differential diagnoses included mainly clear cell acanthoma, irritated seborrheic keratosis, BowenÂŽs disease and eccrine poroma. The lesion was completely surgically removed and histopathologic examination revealed an epidermic lesion with marked psoriasiform hyperplasia, in which epidermal cells show clear cytoplasms (Fig. 3). These findings are consistent with the diagnosis of Clear Cell Acanthoma (CCA)..
Monte Carlo simulations of post-common-envelope white dwarf + main sequence binaries: comparison with the SDSS DR7 observed sample
Detached white dwarf + main sequence (WD+MS) systems represent the simplest
population of post-common envelope binaries (PCEBs). Since the ensemble
properties of this population carries important information about the
characteristics of the common-envelope (CE) phase, it deserves close scrutiny.
However, most population synthesis studies do not fully take into account the
effects of the observational selection biases of the samples used to compare
with the theoretical simulations. Here we present the results of a set of
detailed Monte Carlo simulations of the population of WD+MS binaries in the
Sloan Digital Sky Survey (SDSS) Data Release 7. We used up-to-date stellar
evolutionary models, a complete treatment of the Roche lobe overflow episode,
and a full implementation of the orbital evolution of the binary systems.
Moreover, in our treatment we took into account the selection criteria and all
the known observational biases. Our population synthesis study allowed us to
make a meaningful comparison with the available observational data. In
particular, we examined the CE efficiency, the possible contribution of
internal energy, and the initial mass ratio distribution (IMRD) of the binary
systems. We found that our simulations correctly reproduce the properties of
the observed distribution of WD+MS PCEBs. In particular, we found that once the
observational biases are carefully taken into account, the distribution of
orbital periods and of masses of the WD and MS stars can be correctly
reproduced for several choices of the free parameters and different IMRDs,
although models in which a moderate fraction (<=10%) of the internal energy is
used to eject the CE and in which a low value of CE efficiency is used (<=0.3)
seem to fit better the observational data. We also found that systems with
He-core WDs are over-represented in the observed sample, due to selection
effects.Comment: 15 pages, 7 figures, accepted for publication in A&
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