748 research outputs found
Characterization of a defective PbWO4 crystal cut along the a-c crystallographic plane: structural assessment and a novel photoelastic stress analysis
Among scintillators, the PWO is one of the most widely used, for instance in
CMS calorimeter at CERN and PANDA project. Crystallographic structure and
chemical composition as well as residual stress condition, are indicators of
homogeneity and good quality of the crystal. In this paper, structural
characterization of a defective PbWO4 (PWO) crystal has been performed by X-ray
Diffraction (XRD), Energy Dispersive Spectroscopy (EDS) and Photoelasticity in
the unusual a-c crystallographic plane. XRD and EDS analysis have been used to
investigate crystallographic orientation and chemical composition, while stress
distribution, which indicates macroscopic inhomogeneities and defects, has been
obtained by photoelastic approaches, in Conoscopic and Sphenoscopic
configuration. Since the sample is cut along the a-c crystallographic plane, a
new method is proposed for the interpretation of the fringe pattern. The
structural analysis has detected odds from the nominal lattice dimension, which
can be attributed to the strong presence of Pb and W. A strong inhomogeneity
over the crystal sample has been revealed by the photoelastic inspection. The
results give reliability to the proposed procedure which is exploitable in
crystals with other structures.Comment: 18 pages, 10 figures, revised versio
Ruprecht 147: a paradigm of dissolving star cluster
We employed recent Gaia/DR2 data to investigate the dynamical status of the
nearby (300 pc), old (2.5 Gyr) open cluster Ruprecht~147. We found prominent
leading and trailing tails of stars along the cluster orbit, which demonstrates
that Ruprecht~147 is losing stars at fast pace. Star counts indicate the
cluster has a core radius of 33.3 arcmin, and a tidal radius of 137.5 arcmin.
The cluster also possesses an extended corona, which cannot be reproduced by a
simple King model. We computed the present-day cluster mass using its
luminosity and mass function, and derived an estimate of 23452
. We also estimated the cluster original mass using available
recipes extracted from N-body simulations obtaining a mass at birth of
500006500 . Therefore dynamical mass loss, mostly caused by
tidal interaction with the Milky Way, reduced the cluster mass by about 99\%.
We then conclude that Ruprecht~147 is rapidly dissolving into the general
Galactic disc.Comment: 13 pages, 10 figure, in press in the Astronomical Journa
Awareness, values and attitudes of user generated content website users and non-users towards privacy in France : a quantitative study
This document presents the French results of a study undertaken as part of the CONSENT project. Analyses and results are based on an online survey regarding the awareness, values and attitudes of user generated content (UGC) website users towards privacy. The questionnaire consisted of 75 questions and was available online in several European languages, including French, between July and December 2011. The French sample consists of 388 respondents (4.5% of the total sample), of which 53.8% male and 46.2% female, with an average age of 39 and 88% tertiary education. With 78% UGC users (total sample 90%), 11.88 mean years of internet usage (total sample 10.67) and 84.9% using the internet at home every day or almost every day (total sample 93%), it is a considered a sample of predominantly experienced internet users.CONSENT
Consumer Sentiment regarding privacy on user generated content (UGC) services in the digital economy
(G.A. 244643).
The project was co-financed by the European Union within the Seventh Framework Programme (2007-2013).peer-reviewe
VLT multi-epoch radial velocity survey toward NGC 6253. Analysis of three transiting planetary candidates
We measured the radial velocity of 139 stars in the region of NGC 6253,
discussing cluster's membership and binarity in this sample, complementing our
analysis with photometric, proper motion, and radial velocity data available
from previous studies of this cluster, and analyzing three planetary transiting
candidates we found in the field of NGC 6253. Spectra were obtained with the
UVES and GIRAFFE spectrographs at the VLT, during three epochs in August 2008.
The mean radial velocity of the cluster is -29.11+/-0.85 km/s. Using both
radial velocities and proper motions we found 35 cluster's members, among which
12 are likely cluster's close binary systems. One star may have a sub-stellar
companion, requiring a more intensive follow-up. Our results are in good
agreement with past radial velocity and photometric measurements. Furthermore,
using our photometry, astrometry and spectroscopy we identified a new sub-giant
branch eclipsing binary system, member of the cluster. The cluster's close
binary frequency at 29% +/- 9% (34% +/-10% once including long period
binaries), appears higher than the field binary frequency equal to (22% +/- 5%,
though these estimates are still consistent within the uncertainties. Among the
three transiting planetary candidates the brightest one (V=15.26) is worth to
be more intensively investigated with higher percision spectroscopy. We
discussed the possibility to detect sub-stellar companions (brown dwarfs and
planets) with the radial velocity technique (both with UVES/GIRAFFE and HARPS)
around turn-off stars of old open clusters [abridged].Comment: 25 pages, 18 figures, 8 tables. Accepted for publication in A&
Variable stars in the open cluster NGC 6791 and its surrounding field
Aims: This work presents a high--precision variability survey in the field of
the old, super metal-rich open cluster NGC 6791.
Methods: The data sample consists of more than 75,000 high-precision CCD time
series measurements in the V band obtained mainly at the Canada-France-Hawaii
Telescope, with additional data from S. Pedro Martir and Loiano observatories,
over a time span of ten nights. The field covers an area of 42x28 arcmin^2.
Results: We have discovered 260 new variables and re-determined periods and
amplitudes of 70 known variable stars. By means of a photometric evaluation of
the membership in NGC 6791, and a preliminary membership based on the proper
motions, we give a full description of the variable content of the cluster and
surrounding field in the range 16<V<23.5. Accurate periods can be given for the
variables with P<4.0 d, while for ones with longer periods the limited
time-baseline hampered precise determinations. We categorized the entire sample
as follows: 6 pulsating, 3 irregular, 3 cataclysmic, 89 rotational variables
and 61 eclipsing systems; moreover, we detected 168 candidate variables for
which we cannot give a variability class since their periods are much longer
than our time baseline.
Conclusions: On the basis of photometric considerations, and of the positions
of the stars with respect to the center of the cluster, we inferred that 11 new
variable stars are likely members of the cluster, for 22 stars the membership
is doubtful and 137 are likely non-members. We also detected an outburst of
about 3 mag in the light curve of a very faint blue star belonging to the
cluster and we suggest that this star could be a new U Gem (dwarf nova)
cataclysmic variable.Comment: 24 pages, 19 Figures, A&A accepte
A Dynamic Bayesian Network for Mt. Etna Volcano State Assessment
Nowadays, the real-time monitoring of Mt. Etna volcano is mostly delegated to one or more human experts in
volcanology, who interpret the data coming from different kind of monitoring networks. Among their duties, the
evaluation of the volcano state is one of the most critical task for civil protection purposes. Unfortunately, the
coupling of highly non-linear and complex volcanic dynamic processes leads to measurable effects that can show a
large variety of different behaviors. Moreover, due to intrinsic uncertainties and possible failures in some recorded
data the volcano state needs to be expressed in probabilistic terms, thus making the fast volcano state assessment
sometimes impracticable for the personnel on duty at the 24h control room. With the aim of aiding the personnel
on duty in volcano monitoring, here we present an expert system approach based on Bayesian networks to estimate
automatically the ongoing volcano state from all the available different kind of measurements. A Bayesian network
is a static probabilistic graphical model that represents a set of random variables and their conditional dependencies
via a directed acyclic graph. We consider model variables both the measurements and the possible states of the
volcano. In order to include the time in the model, we use a Dynamic Bayesian Network (DBN) which relates
variables to each other over adjacent time steps. The model output consists of an estimation of the probability
distribution of the feasible volcano states. We build the model by considering the long record of data from 2011 to
2014 and we cross-validate it by considering 3 years for parameter estimation and 1 year for testing in simulated real-time mode
A real-time framework for fast data retrieval in an image database of volcano activity scenarios
Explosive Activity at Stromboli Volcano (Aeolian Islands) is continuously monitored by INGV-OE in order to
analyze its eruptive dynamics and specific scenarios. In particular, the images acquired from thermal cameras
represent a big collection of data. In order to extract useful information from thermal image sequences, we need
an efficient way to explore and retrieve information from a huge amount of data. In this work, a novel framework
capable of fast data retrieval, using the "metric space" concept, is shown. In the light of it, we implemented an
indexing algorithm related to similarity laws. The focal point is finding objects of a set that are “close” in relation
to a given query, according to a similarity criterion. In order to perform this task, we performed morphological
image processing techniques to each video frame, in order to map the shape area of each explosion into a closed
curve, representing the explosion contour itself. In order to constitute a metric space, we chose a certain number of
features obtained from parameters related to this closed curve and used them as objects of this metric space where
similarity can be evaluated, using an appropriate “metric” function to calculate the distances. Unfortunately, this
approach has to deal with an intrinsic issue involving the complexity and the number of distance functions to be
calculated on a large amount of data. To overcome this drawback, we used a novel abstract data structure called
"K-Pole Tree", having the property of minimizing the number of distances to be calculated among objects. Our
method allows for fast retrieval of similar objects using an euclidean distance function among the features of the
metric space. Thus, we can cluster explosions related to different kinds of volcanic activity, using "pivot" items.
For example, given a known image sequence related to a particular type of explosion, it is possible to quickly and
easily find all the image sequences that contain only similar explosions. Our framework is able to both classify
each new explosion and dynamically insert the corresponding object into our tree data structure. This approach is
able to cluster the entire data space, ensuring that objects with similar features are grouped and classified together
An Atypical Case of Taravana Syndrome in a Breath-Hold Underwater Fishing Champion: A Case Report
Dysbaric accidents are usually referred to compressed air-supplied diving. Nonetheless, some cases of decompression illness are known to have occurred among breath-hold (BH) divers also, and they are reported in the medical literature. A male BH diver ((à years old), underwater *shing champion, presented neurological disorders as dizziness, sensory numbness, blurred vision, and le+ frontoparietal pain a+er many dives to a ( meters sea water depth with short surface intervals. Symptoms spontaneously regressed and the patient came back home. )e following morning, pain and neurological impairment occurred again and the diver went by himself to the hospital where he had a generalized tonic-clonic seizure and lost consciousness. A magnetic resonance imaging of the brain disclofsed a cortical T -weighted hypointense area in the temporal region corresponding to infarction with partial hemorrhage. An early hyperbaric oxygen therapy led to prompt resolution of neurological *ndings. All clinical and imaging characteristics were referable to the Taravana diving syndrome, induced by repetitive prolonged deep BH dives. )e reappearance of neurological signs a+er an uncommon ! -hour symptom-free interval may suggest an atypical case of Taravana syndrome
A perioperative uncontrollable bleeding in an elderly patient with acquired hemophilia A: a case report
Acquired hemophilia A should be taken into account in the differential diagnosis of perioperative bleeding in patients without any apparent reason for activated partial thromboplastin time prolongation
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