452 research outputs found
Modeling non-thermal emission from stellar bow shocks
Runaway O- and early B-type stars passing throughout the interstellar medium
at supersonic velocities and characterized by strong stellar winds may produce
bow shocks that can serve as particle acceleration sites. Previous theoretical
models predict the production of high energy photons by non-thermal radiative
processes, but their efficiency is still debated. We aim to test and explain
the possibility of emission from the bow shocks formed by runaway stars
traveling through the interstellar medium by using previous theoretical models.
We apply our model to AE Aurigae, the first reported star with an X-ray
detected bow shock, to BD+43 3654, in which the observations failed in
detecting high energy emission, and to the transition phase of a supergiant
star in the late stages of its life.From our analysis, we confirm that the
X-ray emission from the bow shock produced by AE Aurigae can be explained by
inverse Compton processes involving the infrared photons of the heated dust. We
also predict low high energy flux emission from the bow shock produced by BD+43
3654, and the possibility of high energy emission from the bow shock formed by
a supergiant star during the transition phase from blue to red supergiant.Bow
shock formed by different type of runaway stars are revealed as a new possible
source of high energy photons in our neighbourhood
Accretion-ejection connection in the young brown dwarf candidate ISO-Cha1 217
As the number of observed brown dwarf outflows is growing it is important to
investigate how these outflows compare to the well studied jets from young
stellar objects. A key point of comparison is the relationship between outflow
and accretion activity and in particular the ratio between the mass outflow and
accretion rates (/). The brown dwarf candidate
ISO-ChaI 217 was discovered by our group, as part of a spectro-astrometric
study of brown dwarfs, to be driving an asymmetric outflow with the
blue-shifted lobe having a position angle of 20. The aim here
is to further investigate the properties of ISO-ChaI 217, the morphology and
kinematics of its outflow, and to better constrain
(/). The outflow is spatially resolved in the
lines and is detected out to 1\farcs6
in the blue-shifted lobe and ~ 1" in the red-shifted lobe. The asymmetry
between the two lobes is confirmed although the velocity asymmetry is less
pronounced with respect to our previous study. Using thirteen different
accretion tracers we measure log() [M/yr]= -10.6
0.4. As it was not possible to measure the effect of extinction on the ISO-ChaI
217 outflow was derived for a range of values of A, up to
a value of A = 2.5 mag estimated for the source extinction. The logarithm
of the mass outflow () was estimated in the range -11.7 to -11.1
for both jets combined. Thus / [\Msun/yr] lies
below the maximum value predicted by magneto-centrifugal jet launching models.
Finally, both model fitting of the Balmer decrements and spectro-astrometric
analysis of the H line show that the bulk of the H I emission comes
from the accretion flow.Comment: accepted by Astronomy & Astrophysic
Quality of board members’ training and bank financial performance : evidence from Portugal
This study examines the impact of the quality of board members’ training on the financial performance of Portuguese banks. The study employs a sample of 276 board members.
Financial ratios such as return on average assets (ROAA) and return on average equity (ROAE) are used as measures for gauging banks’ financial performance. Three indexes are used as proxies for board members’ educational qualifications, specifically: Eduindex, for all academic qualifications obtained in areas such as business or economics; EduindexDP, for all qualifications obtained in prestigious domestic business schools; and EduindexFP, for all qualifications obtained in prestigious foreign business schools.
The study findings have important policy implications, specifically a positive and significant impact on the bank’s financial performance from having board members holding degrees from prestigious foreign business schools. In particular, the findings suggest that the prudential supervision developed by Banco de Portugal in cooperation with the European Central Bank should include a more rigorous process in the selection of board members. The present study is one of the first attempts in the literature emphasizing all these aspects simultaneously, that is, the banking sector, quality of board members’ training, and Eduniversal Rankings, in the context in which all the banks of a specific country are analysed.peer-reviewe
Childhood Obesity Determinants of Childhood Overweight
Introduction
The number of obese children has grown exponentially in the recent decades, which has been the subject of concern byseveral entities, health care and education. Thus we performed a framework, in theoretical terms, the concept of childhood obesity and its relationship with risk factors / protective, eating habits, physical activity and sedentary lifestyle, also recent studies with conclusions that are later confronted.
Method
Considering the issue under study, the participants in this study are children (n = 1424) born in the years 2006, 2007 and 2008, aged between 3 and 6 years enrolled in 2011–2012 school
year in kindergartens districts of Viseu, Leiria, Évora and Vila Real - Portugal
Quality of board members’ training and bank financial performance: evidence from Portugal
This study examines the impact of the quality of board members’ training on the financial performance of Portuguese banks. The study employs a sample of 276 board members. Financial ratios such as return on average assets (ROAA) and return on average equity (ROAE) are used as measures for gauging banks’ financial performance. Three indexes are used as proxies for board members’ educational qualifications, specifically: Eduindex, for all academic qualifications obtained in areas such as business or economics; EduindexDP, for all qualifications obtained in prestigious domestic business schools; and EduindexFP, for all qualifications obtained in prestigious foreign business schools. The study findings have important policy implications, specifically a positive and significant impact on the bank’s financial performance from having board members holding degrees from prestigious foreign business schools. In particular, the findings suggest that the prudential supervision developed by Banco de Portugal in cooperation with the European Central Bank should include a more rigorous process in the selection of board members. The present study is one of the first attempts in the literature emphasizing all these aspects simultaneously, that is, the banking sector, quality of board members’ training, and Eduniversal Rankings, in the context in which all the banks of a specific country are analysed. © 2018 International Strategic Management Association.info:eu-repo/semantics/publishedVersio
AE Aurigae: first detection of non-thermal X-ray emission from a bow shock produced by a runaway star
Runaway stars produce shocks when passing through interstellar medium at
supersonic velocities. Bow shocks have been detected in the mid-infrared for
several high-mass runaway stars and in radio waves for one star. Theoretical
models predict the production of high-energy photons by non-thermal radiative
processes in a number sufficiently large to be detected in X-rays. To date, no
stellar bow shock has been detected at such energies. We present the first
detection of X-ray emission from a bow shock produced by a runaway star. The
star is AE Aur, which was likely expelled from its birthplace by the encounter
of two massive binary systems and now is passing through the dense nebula IC
405. The X-ray emission from the bow shock is detected at 30" to the northeast
of the star, coinciding with an enhancement in the density of the nebula. From
the analysis of the observed X-ray spectrum of the source and our theoretical
emission model, we confirm that the X-ray emission is produced mainly by
inverse Compton upscattering of infrared photons from dust in the shock front.Comment: Accepted for publication in the Astrophysical Journal with number
ApJ, 757, L6. Four figure
Effects of herbivory, nutrients, and reef protection on algal proliferation and coral growth on a tropical reef
Maintaining coral reef resilience against increasing anthropogenic disturbance is critical for effective reef management. Resilience is partially determined by how processes, such as herbivory and nutrient supply, affect coral recovery versus macroalgal proliferation following disturbances. However, the relative effects of herbivory versus nutrient enrichment on algal proliferation remain debated. Here, we manipulated herbivory and nutrients on a coral-dominated reef protected from fishing, and on an adjacent macroalgal-dominated reef subject to fishing and riverine discharge, over 152 days. On both reefs, herbivore exclusion increased total and upright macroalgal cover by 9–46 times, upright macroalgal biomass by 23–84 times, and cyanobacteria cover by 0–27 times, but decreased cover of encrusting coralline algae by 46–100% and short turf algae by 14–39%. In contrast, nutrient enrichment had no effect on algal proliferation, but suppressed cover of total macroalgae (by 33–42%) and cyanobacteria (by 71% on the protected reef) when herbivores were excluded. Herbivore exclusion, but not nutrient enrichment, also increased sediment accumulation, suggesting a strong link between herbivory, macroalgal growth, and sediment retention. Growth rates of the corals Porites cylindrica and Acropora millepora were 30–35% greater on the protected versus fished reef, but nutrient and herbivore manipulations within a site did not affect coral growth. Cumulatively, these data suggest that herbivory rather than eutrophication plays the dominant role in mediating macroalgal proliferation, that macroalgae trap sediments that may further suppress herbivory and enhance macroalgal dominance, and that corals are relatively resistant to damage from some macroalgae but are significantly impacted by ambient reef condition
Long QT syndrome in a neonate
Congenital long QT syndrome (cLQTS) is a channelopathy characterized by ventricular repolarization disturbances. The clinical presentation varies from an asymptomatic patient to a patient with recurrent syncopes, seizures, and even sudden death. This article aims to contribute
to medical knowledge of this relatively new disease in newborns, so that early diagnoses with timely treatments can be made. Genotypically, there are 13 types of cLQTS, which are classified by phenotype into: Romano-Ward, Jervell-Lange-Nielsen, Andersen-Tawil and Timothy.
We present the following case of a newborn who presented clinical sustained bradycardia on her first day of life, who was admitted to the Neonatal Intensive Care, where her assessment and imaging studies guided us to a cLQTS diagnosis. The patient recovered satisfactorily, and
was discharged with outpatient follow-up without complications. All abnormal QT patients should be assessed with an integral clinical report, Holter analyzer, and a stress test. Ideally, a genetic screening, which can have a great impact on the
treatment, should be done. Although it is relatively uncommon, recognition of this entity is important because it can prevent death. We present a case of cLQTS diagnosis, with approach and treatment
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