9,469 research outputs found
The puzzle of metallicity and multiple stellar populations in the Globular Clusters in Fornax
We examine the photometric data for Fornax clusters, focussing our attention
on their horizontal branch color distribution and, when available, on the RR
Lyr variables fraction and period distribution. Based on our understanding of
the HB morphology in terms of varying helium content in the context of multiple
stellar generations, we show that clusters F2, F3 and F5 must contain
substantial fractions of second generation stars (~54-65%). On the basis of a
simple chemical evolution model we show that the helium distribution in these
clusters can be reproduced by models with cluster initial masses ranging from
values equal to ~4 to ~10 times larger than the current masses. Models with a
very short second generation star formation episode can also reproduce the
observed helium distribution but require larger initial masses up to about
twenty times the current mass. While the lower limit of this range of possible
initial GC masses is consistent with those suggested by the observations of the
low metallicity field stars, we also discuss the possibility that the
metallicity scale of field stars (based on CaII triplet spectroscopy) and the
metallicities derived for the clusters in Fornax may not be consistent with
each other. The reproduction of the HB morphology in F2,F3,F5 requires two
interesting hypotheses: 1) the first generation HB stars lie all at "red"
colours. According to this interpretation, the low metallicity stars in the
field of Fornax, populating the HB at colours bluer than the blue side
((V-I)o<=0.3 or (B-V)o<=0.2) of the RR Lyrs, should be second generation stars
born in the clusters;a preliminary analysis of available colour surveys of
Fornax field provides a fraction ~20% of blue HB stars, in the low metallicity
range; 2) the mass loss from individual second generation red giants is a few
percent of a solar mass larger than the mass loss from first generation stars.Comment: 14 pages, 8 figures. Accepted for publication in MNRA
Impact of communicative and informative strategies on influenza vaccination adherence and absenteeism from work of health care professionals working at the university hospital of palermo, Italy: A quasi-experimental field trial on twelve influenza seasons
Every year, about 20% of health care workers (HCWs) acquire influenza, continuing to work and encouraging virus spreading. Influenza vaccination coverage rates and absenteeism from work among HCWs of the University Hospital (UH) of Palermo were analyzed before and after the implementation of several initiatives in order to increase HCWs’ awareness about influenza vaccination. Vaccines administration within hospital units, dedicated web pages on social media and on the UH of Palermo institutional web site, and mandatory compilation of a dissent form for those HCWs who refused vaccination were carried out during the last four influenza seasons. After the introduction of these strategies, influenza vaccination coverage went up from 5.2% (2014/2015 season) to 37.2% (2018/2019 season) (p<0.001), and mean age of vaccinated HCWs significantly decreased from 48.1 years (95% CI: 45.7–50.5) to 35.9 years (95% CI: 35.0–36.8). A reduction of working days lost due to acute sickness among HCWs of the UH of Palermo was observed. Fear of adverse reactions and not considering themselves as a high-risk group for contracting influenza were the main reasons reported by HCWs that refused vaccination. Strategies undertaken at the UH of Palermo allowed a significant increase in vaccination adherence and a significant reduction of absenteeism from work
Topological mass mechanism and exact fields mapping
We present a class of mappings between models with topological mass mechanism
and purely topological models in arbitrary dimensions. These mappings are
established by directly mapping the fields of one model in terms of the fields
of the other model in closed expressions. These expressions provide the
mappings of their actions as well as the mappings of their propagators. For a
general class of models in which the topological model becomes the BF model the
mappings present arbitrary functions which otherwise are absent for
Chern-Simons like actions. This work generalizes the results of [1] for
arbitrary dimensions.Comment: 11 page
Color space distortions in patients with type 2 diabetes mellitus
Color vision impairment was examined in patients with type 2 diabetes mellitus (DM2) without retinopathy. We assessed the type and degree of distortions of individual color spaces. DM2 patients (n = 32), and age-matched controls (n = 20)were tested using the Farnsworth D-15 and the Lanthony D-15d tests. In addition, subsets of caps
from both tests were employed in a triadic procedure (Bimler & Kirkland, 2004). Matrices of inter-cap subjective dissimilarities were estimated from each subject’s “odd-one-out” choices, and processed using non-metric
multidimensional scaling. Two-dimensional color spaces, individual and group (DM2 patients; controls), were reconstructed, with the axes interpreted as the R0G and B0Y perceptual opponent systems. Compared to controls, patient results were not significant for the D-15 and D-15d. In contrast, in the triadic procedure the residual distances were significantly different compared to controls: right eye, P 0.021, and left eye, P 0.022. Color
space configurations for the DM2 patients were compressed along the B0Y and R0G dimensions. The present findings agree with earlier studies demonstrating diffuse losses in early stages of DM2. The proposed method of testing uses color spaces to represent discrimination and provides more differentiated quantitative diagnosis, which
may be interpreted as the perceptual color system affected. In addition, it enables the detection of very mild color vision impairment that is not captured by the D-15d test. Along with fundoscopy, individual color spaces may serve for monitoring early functional changes and thereby to support a treatment strategy
The peculiar supernova remnant CTB 80
Deep CCD exposures of the peculiar supernova remnant CTB 80 in the light of
major optical lines have been obtained. These images reveal significant shock
heated emission in the area of the remnant. The sulfur line image shows
emission in the north along the outer boundary of the IRAS and HI shells. The
comparison between the [OIII] and [OII] line images further suggest the
presence of significant inhomogeneities in the interstellar medium. The flux
calibrated images do not indicate the presence of incomplete recombination
zones, and we estimate that the densities of the preshock clouds should not
exceed a few atoms per cm^3. The area covered by the optical radiation along
with the radio emission at 1410 MHz suggest that CTB 80 occupies a larger
angular extent than was previously known.Comment: 19 pages, 6 png figures. Submitted revised version to A &
Helium variation due to self-pollution among Globular Cluster stars: consequences on the horizontal branch morphology
It is becoming clear that `self--pollution' by the ejecta of massive asymptotic giant branch stars has an important role in the early chemical evolution of globular cluster stars, producing CNO abundance spreads which are observed also at the surface of unevolved stars. Considering that the ejecta which are CNO processed must also be helium enriched, we have modelled stellar evolution of globular cluster stars by taking into account this possible helium enhancement with respect to the primordial value. We show that the differences between the main evolutionary phases (main sequence, turn--off and red giants) are small enough that it would be very difficult to detect them observationally. However, the difference in the evolving mass may play a role in the morphology of the horizontal branch, and in particular in the formation of blue tails, in those globular clusters which show strong CNO abundance variations, such as M13 and NGC 6752
The early evolution of Globular Clusters: the case of NGC 2808
Enhancement and spread of helium among globular cluster stars have been
recently suggested as a way to explain the horizontal branch blue tails, in
those clusters which show a primordial spread in the abundances of CNO and
other elements involved in advanced CNO burning (D'Antona et al. 2002). In this
paper we examine the implications of the hypothesis that, in many globular
clusters, stars were born in two separate events: an initial burst (first
generation), which gives origin to probably all high and intermediate mass
stars and to a fraction of the cluster stars observed today, and a second,
prolonged star formation phase (second generation) in which stars form directly
from the ejecta of the intermediate mass stars of the first generation. In
particular, we consider in detail the morphology of the horizontal branch in
NGC 2808 and argue that it unveils the early cluster evolution, from the birth
of the first star generation to the end of the second phase of star formation.
This framework provides a feasible interpretation for the still unexplained
dichotomy of NGC 2808 horizontal branch, attributing the lack of stars in the
RR Lyr region to the gap in the helium content between the red clump, whose
stars are considered to belong to the first stellar generation and have
primordial helium, and the blue side of the horizontal branch, whose minimum
helium content reflects the helium abundance in the smallest mass
(~4Msun)contributing to the second stellar generation. This scenario provides
constraints on the required Initial Mass Function, in a way that a great deal
of remnant neutron stars and stellar mass black holes might have been produced.Comment: 23 pages, 7 figures, in press on The Astrophysical Journa
Influenza vaccine effectiveness among high-risk groups: a systematic literature review and metaanalysis of case-control and cohort studies
Vaccination represents the most effective intervention to prevent infection, hospitalization and mortality due to influenza. This meta-analysis quantifies data reporting influenza vaccine effectiveness (VE) on influenza visits and hospitalizations of case-control and cohort studies among
high-risk groups.
A systematic literature review including original articles published between 2007 and 2016, using a
protocol registered on Prospero with No. 42017054854, and a meta-analysis were conducted.
For three high-risk groups (subjects with underlying health conditions, pregnant women and health
care workers) only a qualitative evaluation was carried out. The VE quantitative analysis
demonstrated a clear significant overall effect of 39% (95%CI: 32%-46%) for visits and 57%
(95%CI: 30%-74%) for hospitalization among children. Considering the elderly influenza VE had a
clear effect of 25% (95%CI: 6%-40%) for visits and 14% (95%CI: 7%-21%; p<0.001) for
hospitalization.
This study showed the high VE of influenza vaccination among high-risk groups, representing a
tool for public health decision-makers to develop evidence-based preventive interventions to avoid
influenza outcome
The viscosity of shoshonitic melts (Vulcanello Peninsula, Aeolian Islands, Italy): insight on the magma ascent in dikes
The viscosity of shoshonitic melts from Vulcanello Peninsula (Vulcano Island, Italy) is
experimentally determined at temperatures between 733 K and 1673 K. The water content of the
melts varies from 0.03 to 4.75 wt% H2O. The micropenetration technique is employed at ambient
pressure in the high viscosity range (109-1012 Pa·s). Falling sphere(s) experiments are performed
at 500 and 2000 MPa in the low viscosity range (100.5-103 Pa·s). Results show a decrease of about
2 orders of magnitude in viscosity if ~ 3 wt% of water is added to the dry melt at 1300 K. At high
temperature the viscosity of Vulcanello melts is intermediate between that of andesitic and
basaltic melts. In contrast, at low temperatures (≤1050 K), the shoshonitic melt is characterized
by a lower viscosity with respect to the two previous melts. Based on our new data set, a
calculation model is proposed to predict the viscosity of the shoshonitic melts as a function of
temperature and water content. The viscosity data are used to constrain the ascent velocity of
shoshonitic magmas from Vulcanello within dikes. Using petrological data (temperature and
crystal content of the magma) and volcanological information (geometrical parameters of the
eruptive fissure and depth of magma storage), we estimate the time scale for the ascent of magma
from the main reservoir to the surface. Results show time scales in the order of hours to few days.
We conclude that the rapid ascent of poorly evolved melts from Moho depths should be taken
into account for the hazard assessment of Vulcano Island
The near-IR counterpart of IGR J17480-2446 in Terzan 5
Some globular clusters in our Galaxy are noticeably rich in low-mass X-ray
binaries. Terzan 5 has the richest population among globular clusters of X- and
radio-pulsars and low-mass X-ray binaries. The detection and study of
optical/IR counterparts of low-mass X-ray binaries is fundamental to
characterizing both the low-mass donor in the binary system and investigating
the mechanisms of the formation and evolution of this class of objects. We aim
at identifying the near-IR counterpart of the 11 Hz pulsar IGRJ17480-2446
discovered in Terzan 5. Adaptive optics (AO) systems represent the only
possibility for studying the very dense environment of GC cores from the
ground. We carried out observations of the core of Terzan 5 in the near-IR
bands with the ESO-VLT NAOS-CONICA instrument. We present the discovery of the
likely counterpart in the Ks band and discuss its properties both in outburst
and in quiescence. Archival HST observations are used to extend our discussion
to the optical bands. The source is located at the blue edge of the turn-off
area in the color-magnitude diagram of the cluster. Its luminosity increase
from quiescence to outburst, by a factor 2.5, allows us to discuss the nature
of the donor star in the context of the double stellar generation population of
Terzan 5 by using recent stellar evolution models.Comment: 7 pages, 4 figure
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