6,043 research outputs found
Warm inflation and scalar perturbations of the metric
A second-order expansion for the quantum fluctuations of the matter field was
considered in the framework of the warm inflation scenario. The friction and
Hubble parameters were expended by means of a semiclassical approach. The
fluctuations of the Hubble parameter generates fluctuations of the metric.
These metric fluctuations produce an effective term of curvature. The power
spectrum for the metric fluctuations can be calculated on the infrared sector.Comment: 10 pages, no figures, to be published in General Rel. and Gravitatio
Phantom cosmology with a decaying cosmological function induced from five-dimensional (5D) geometrical vacuum
Introducing a variable cosmological function in a geometrical
manner from a 5D Riemann-flat metric, we investigate the possibility of having
a geometrical criterion to choose a suitable cosmological function for every 4D dynamical hypersurface capable of generate phantom
cosmologies.Comment: final versio
Resuming elective surgical activity after the COVID-19 wave: what the patients need to know
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus causing coronavirus disease 2019 (COVID-19), infected more than four million people during the first months of 2021, and Italy was reported to have the highest death toll per million population at the beginning of May2. While there is no consensus on the treatment of the disease yet, understanding how the virus and its transmission will behave in the future is a cardinal priority for planning the re-establishment of routine healthcare services, such as surgery, in view of preventing indirectly COVID-19-related deaths due to undelivered care and lack of adequate treatment. Sadly, elective surgery on patients with perioperative SARS-CoV-2 infection, has shown increased mortality risk, therefore increasing anxiety among the population waiting for surgical interventions, as most of the elective activity was suspended due to COVID-19
outbreak
Ground-based astrometry with wide field imagers. V. Application to near-infrared detectors: HAWK-I@VLT/ESO
High-precision astrometry requires accurate point-spread function modeling
and accurate geometric-distortion corrections. This paper demonstrates that it
is possible to achieve both requirements with data collected at the high acuity
wide-field K-band imager (HAWK-I), a wide-field imager installed at the Nasmyth
focus of UT4/VLT ESO 8m telescope. Our final astrometric precision reaches ~3
mas per coordinate for a well-exposed star in a single image with a systematic
error less than 0.1 mas. We constructed calibrated astro-photometric catalogs
and atlases of seven fields: the Baade's Window, NGC 6656, NGC 6121, NGC 6822,
NGC 6388, NGC 104, and the James Webb Space Telescope calibration field in the
Large Magellanic Cloud. We make these catalogs and images electronically
available to the community. Furthermore, as a demonstration of the efficacy of
our approach, we combined archival material taken with the optical wide-field
imager at the MPI/ESO 2.2m with HAWK-I observations. We showed that we are able
to achieve an excellent separation between cluster members and field objects
for NGC 6656 and NGC 6121 with a time base-line of about 8 years. Using both
HST and HAWK-I data, we also study the radial distribution of the SGB
populations in NGC 6656 and conclude that the radial trend is flat within our
uncertainty. We also provide membership probabilities for most of the stars in
NGC 6656 and NGC 6121 catalogs and estimate membership for the published
variable stars in these two fields.Comment: 36 pages (included appendix), 13 tables, 35 figures (26 in low
resolution), accepted for publication in Astronomy and Astrophysics. Online
materials will be soon available on CDS. Meanwhile, online materials can be
requested directly to the first autho
Measurements of the Cerenkov light emitted by a TeO2 crystal
Bolometers have proven to be good instruments to search for rare processes
because of their excellent energy resolution and their extremely low intrinsic
background. In this kind of detectors, the capability of discriminating alpha
particles from electrons represents an important aspect for the background
reduction. One possibility for obtaining such a discrimination is provided by
the detection of the Cerenkov light which, at the low energies of the natural
radioactivity, is only emitted by electrons. In this paper, the results of the
analysis of the light emitted by a TeO2 crystal at room temperature when
transversed by a cosmic ray are reported. Light is promptly emitted after the
particle crossing and a clear evidence of its directionality is also found.
These results represent a strong indication that Cerenkov light is the main, if
not even the only, component of the light signal in a TeO2 crystal. They open
the possibility to make large improvements in the performance of experiments
based on this kind of material
High-precision astrometry with VVV. I. An independent reduction pipeline for VIRCAM@VISTA
We present a new reduction pipeline for the VIRCAM@VISTA detector and
describe the method developed to obtain high-precision astrometry with the
VISTA Variables in the V\'ia L\'actea (VVV) data set. We derive an accurate
geometric-distortion correction using as calibration field the globular cluster
NGC 5139, and showed that we are able to reach a relative astrometric precision
of about 8 mas per coordinate per exposure for well-measured stars over a field
of view of more than 1 square degree. This geometric-distortion correction is
made available to the community. As a test bed, we chose a field centered
around the globular cluster NGC 6656 from the VVV archive and computed proper
motions for the stars within. With 45 epochs spread over four years, we show
that we are able to achieve a precision of 1.4 mas/yr and to isolate each
population observed in the field (cluster, Bulge and Disk) using proper
motions. We used proper-motion-selected field stars to measure the motion
difference between Galactic disk and bulge stars. Our proper-motion
measurements are consistent with UCAC4 and PPMXL, though our errors are much
smaller. Models have still difficulties in reproducing the observations in this
highly-reddened Galactic regions.Comment: 11 pages, 10 figures (some in low res), 1 table. Accepted for
publication in MNRAS on March 25, 2015. The FORTRAN routine will be soon made
available at http://groups.dfa.unipd.it/ESPG/ , and via email request to the
first autho
Broken-Bond Rule for the Surface Energies of Noble Metals
Using two different full-potential ab-initio techniques we introduce a
simple, universal rule based on the number of broken first-neighbor bonds to
determine the surface energies of the three noble metals Cu, Ag and Au. When a
bond is broken, the rearrangement of the electronic charge for these metals
does not lead to a change of the remaining bonds. Thus the energy needed to
break a bond is independent of the surface orientation. This novel finding can
lead to the development of simple models to describe the energetics of a
surface like step and kink formation, crystal growth, alloy formation,
equilibrium shape of mesoscopic crystallites and surface faceting.Comment: 4 pages, 2 figure
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