318 research outputs found
Representative galaxy age-metallicity relationships
The ongoing surveys of galaxies and those for the next generation of
telescopes will demand the execution of high-CPU consuming machine codes for
recovering detailed star formation histories (SFHs) and hence age-metallicity
relationships (AMRs). We present here an expeditive method which provides
quick-look AMRs on the basis of representative ages and metallicities obtained
from colour-magnitude diagram (CMD) analyses. We have tested its perfomance by
generating synthetic CMDs for a wide variety of galaxy SFHs. The representative
AMRs turn out to be reliable down to a magnitude limit with a photometric
completeness factor higher than 85 per cent, and trace the chemical
evolution history for any stellar population (represented by a mean age and an
intrinsic age spread) with a total mass within ~ 40 per cent of the more
massive stellar population in the galaxy.Comment: 12 pages, 11 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
The age-metallicity relationship in the Fornax spheroidal dwarf galaxy
We produce a comprehensive field star age-metallicity relationship (AMR) from
the earliest epoch until ~ 1 Gyr ago for three fields in the Fornax dSph galaxy
by using VI photometric data obtained with FORS1 at the VLT. We find that the
innermost one does not contains dominant very old stars (age > 12 Gyr), whereas
the relatively outer field does not account for representative star field
populations younger than ~ 3 Gyr. When focusing on the most prominent stellar
populations, we find that the derived AMRs are engraved by the evidence of a
outside-in star formation process. The studied fields show bimodal metallicity
distributions peaked at [Fe/H] = (-0.95 +- 0.15) dex and (-1.15 or -1.25 +-
0.05) dex, respectively, but only during the first half of the entire galaxy
lifetime. Furthermore, the more metal-rich population appears to be more
numerous in the outer fields, while in the innermost Fornax field the
contribution of both metallicity populations seems to be similar. We also find
that the metallicity spread ~ 6 Gyr ago is remarkable large, while the
intrinsic metallicity dispersion at ~ 1-2 Gyr results smaller than that for the
relatively older generations of stars. We interpret these outcomes as a result
of a possible merger of two galaxies that would have triggered a star formation
bursting process that peaked between ~ 6 and 9 Gyr ago, depending on the
position of the field in the galaxy.Comment: 7 pages, 5 figures, MNRAS, in pres
Understanding workers’ adoption of productivity mobile applications: a fuzzy set qualitative comparative analysis (fsQCA)
Mobile devices such as smartphones and tablets become more present
in our lives every day. Most of these devices use the Android operating
system (O.S.), becoming the most popular O.S. for mobile devices.
For these devices, there is a huge offer of application software that
provides answers to users’ different needs. This study aims to analyse
how combinations of personality factors, sociodemographic variables
and Internet use influence the adoption of productivity mobile apps by
workers. To achieve this, a combination of these variables is analysed
using fuzzy set Qualitative Comparative Analysis (fsQCA.) that allows us to
analyse complex complementarities among factors. The results show the
importance of distinct personality traits – extraversion and agreeableness
– to understand the adoption of these services. Our study also provides
relevant insight for software developers to target segments interested in
the use of productivity software in their mobile devices
The Star Formation History in a SMC field: IAC-star/IAC-pop at work
We present a progress report of a project to study the quantitative star
formation history (SFH) in different parts of the Small Magellanic Cloud (SMC).
We use the information in [(B-R), R] color-magnitude diagrams (CMDs), which
reach down to the oldest main-sequence turnoffs and allow us to retrieve the
SFH in detail. We show the first results of the SFH in a SMC field located in
the Southern direction (at 1 kpc from the SMC center). This field is
particularly interesting because in spite of being located in a place in which
the HI column density is very low, it still presents a recent enhancement of
star formation.Comment: Poster presented at: Stellar Populations as Building Blocks of
Galaxies, Proceedings IAU Symposium No. 241, 200
Old main-sequence turnoff photometry in the SMC: Star Formation History and Chemical Enrichment Law
We present deep ground-based {\it B} and {\it R} observations of 12 fields in
the Small Magellanic Cloud (SMC). The resulting color-magnitude diagrams (CMDs)
reach the oldest main-sequence (MS) turnoff at M3.5 and reveal
the stellar population differences between the part of the galaxy facing the
Large Magellanic Cloud (LMC) and an area on the opposite side. In the Southern
part of the galaxy, we found that there are still intermediate-age stars as far
as 4 kpc from the SMC center.
The Chemical Enrichment History (CEH) in one of our SMC fields is also
presented.Comment: Contributed talk presented at: Stellar Populations as Building Blocks
of Galaxies, Proceedings IAU Symposium No. 241, 200
How well is Patella vulgata Linnaeus 1758 reflecting changes in sea surface temperatures (SST)? First results using living and archaeological samples from Northern Spain
Human populations have been exploiting coastal regions in different parts of the planet, at least since the Middle Palaeolithic. In Cantabrian Spain, the study of the exploitation of molluscs and shell middens formation during the late Pleistocene and early Holocene has shown the importance of these resources in human diets, being one of the most commonly collected species the limpet Patella vulgata which is present from the upper Palaeolithic to the Neolithic (ca. 40,000-5700 cal BP)
The ISLANDS project I: Andromeda XVI, An Extremely Low Mass Galaxy not Quenched by Reionization
Based on data aquired in 13 orbits of HST time, we present a detailed
evolutionary history of the M31 dSph satellite Andromeda XVI, including its
life-time star formation history, the spatial distribution of its stellar
populations, and the properties of its variable stars. And XVI is characterized
by prolonged star formation activity from the oldest epochs until star
formation was quenched ~6 Gyr ago, and, notably, only half of the mass in stars
of And XVI was in place 10 Gyr ago. And XVI appears to be a low mass galaxy for
which the early quenching by either reionization or starburst feedback seems
highly unlikely, and thus, is most likely due to an environmental effect (e.g.,
an interaction), possibly connected to a late infall in the densest regions of
the Local Group. Studying the star formation history as a function of
galactocentric radius, we detect a mild gradient in the star formation history:
the star formation activity between 6 and 8 Gyr ago is significantly stronger
in the central regions than in the external regions, although the quenching age
appears to be the same, within 1 Gyr. We also report the discovery of 9 RR
Lyrae stars, 8 of which belong to And XVI. The RR Lyrae stars allow a new
estimate of the distance, (m-M)0= 23.72+/-0.09 mag, which is marginally larger
than previous estimates based on the tip of the red giant branch.Comment: Accepted for publication on Ap
Randomized study of aprotinin and DDAVP to reduce postoperative bleeding after cardiopulmonary bypass surgery
BACKGROUND: Patients on cardiopulmonary bypass (CPB) have an increased susceptibility to postoperative bleeding. Previous reports using desmopressin acetate (DDAVP) for the prevention of postoperative bleeding have given contradictory results, whereas the protease inhibitor aprotinin has been shown to reduce blood loss after this type of surgery. This randomized study was performed to assess the efficacy of DDAVP versus aprotinin in the prevention of bleeding after CPB.
METHODS AND RESULTS: One hundred nine of 122 eligible patients were randomized to four different groups: Group A (n = 28) received aprotinin starting with a bolus of 2 x 10(6) KIU followed by a continuous infusion of 0.5 x 10(6) KIU/h until the end of surgery; group B (n = 25) received of DDAVP 0.3 micrograms/kg i.v. on completion of CPB; group C (n = 28) received two doses of DDAVP, the first as in group B and an additional dose 6 hours after surgery; group D (n = 28) received no treatment. There was a marked reduction of postoperative blood loss either at 12 hours (P < .01) or 72 hours (P < .02) in the aprotinin group compared with all other groups, whereas no significant effect was observed in either of the two DDAVP regimens. A significant reduction in the amount of blood used was observed only in the aprotinin group (P < .01). Of the plasma fibrinolytic components assayed, there was a significant reduction of the fibrin degradation product generation in the aprotinin group (P < .001), whereas a significant systemic hyperfibrinolysis was observed in both DDAVP-treated groups and the control group. No side effects related to the study drugs were observed in any patient.
CONCLUSIONS: Aprotinin inhibited fibrinolysis; this correlated with a significant reduction of postoperative blood loss and need for blood replacement after CPB. Neither one nor two doses of DDAVP had a beneficial effect. Aprotinin offers a better alternative than DDAVP in the prevention of bleeding after CPB
Significado y concepciones de conceptos matemáticos escolares
Este estudio ejemplifica un análisis de contenido según varias componentes de significado de un concepto matemático escolar, desarrollado para tres tópicos diferentes del currículo escolar de matemáticas. El trabajo muestra diversas concepciones inferidas de las respuestas obtenidas a través de la aplicación de cuestionarios semánticos y con tres grupos diferentes de estudiantes y de futuros maestros. Tres conceptos se han elegido: la fracción, como relación parte-todo, las razones trigonométricas, así como los números positivos y negativos. En el trabajo se ejemplifica cada componente semántica diferente con solo uno de ellos. Los resultados muestran el dominio de tales nociones, sus diferentes interpretaciones, cómo han sido expresadas y los modos en que han sido usadas. Dichos resultados también muestran una variabilidad y riqueza de respuestas acerca de cada concepto, que se identifican y describen en términos de los componentes semánticos
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