1,327 research outputs found
Multipopulation aftereffects on the color-magnitude diagram and Cepheid variables of young stellar systems
Context: The evidence of a multipopulation scenario in Galactic globular
clusters raises several questions about the formation and evolution of the two
(or more) generations of stars. These populations show differences in their age
and chemical composition. These differences are found in old- and intermediate-
age stellar clusters in the Local Group. The observations of young stellar
systems are expected to present footprints of multiple stellar populations.
Aims: This theoretical work intends to be a specific step in exploring the
space of the observational indicators of multipopulations, without covering all
the combinations of parameters that may contribute to the formation of multiple
generations of stars in a cluster or in galaxy. The goal is to shed light on
the possible observational features expected by core He-burning stars that
belong to two stellar populations with different original He content and ages.
Methods: The tool adopted was the stellar population synthesis. We used new
stellar and pulsation models to construct a homogeneous and consistent
framework. Synthetic color-magnitude diagrams (CMDs) of young- and
intermediate-age stellar systems (from 20 Myr up to 1 Gyr) were computed in
several photometric bands to derive possible indicators of double populations
both in the observed CMDs and in the pulsation properties of the Cepheids.
Results: We predict that the morphology of the red/blue clump in VIK bands
can be used to photometrically indicate the two stellar populations in a rich
assembly of stars if there is a significant difference in their original He
content. Moreover, the period distribution of the Cepheids appears to be widely
affected by the coeval multiple generations of stars within stellar systems. We
show that the Wesenheit relations may be affected by the helium content of the
Cepheids.Comment: in press on A&
Photometric and spectroscopic study of the intermediate-age open cluster NGC 2355
In this paper we analyse the evolutionary status and properties of the old
open cluster NGC 2355, located in the Galactic anticentre direction, as a part
of the long term programme BOCCE. NGC 2355 was observed with LBC@LBT using the
Bessel , , and filters. The cluster parameters have been obtained
using the synthetic colour-magnitude diagram (CMD) method, as done in other
papers of this series. Additional spectroscopic observations with FIES@NOT of
three giant stars were used to determine the chemical properties of the
cluster. Our analysis shows that NGC 2355 has metallicity slightly less than
solar, with [Fe/H] dex, age between 0.8 and 1 Gyr, reddening
in the range 0.14 and 0.19 mag, and distance modulus of about 11 mag.
We also investigated the abundances of O, Na, Al, , iron-peak, and
neutron capture elements, showing that NGC 2355 falls within the abundance
distribution of similar clusters (same age and metallicity). The Galactocentric
distance of NGC~2355 places it at the border between two regimes of metallicity
distribution; this makes it an important cluster for the study of the chemical
properties and evolution of the disc.Comment: 20 pages, 11 figures, Accepted on MNRA
Avaliação de genótipos de cebolas em sistema de produção de base ecológica.
Resumos do VIII Congresso Brasileiro de Agroecologia - Porto Alegre/RS - 25 a 28/11/2013
Emergence of a confined state in a weakly bent wire
In this paper we use a simple straightforward technique to investigate the
emergence of a bound state in a weakly bent wire. We show that the bend behaves
like an infinitely shallow potential well, and in the limit of small bending
angle and low energy the bend can be presented by a simple 1D delta function
potential.Comment: 4 pages, 3 Postscript figures (uses Revtex); added references and
rewritte
Ethanol potentiates hypoxic liver injury: role of hepatocyte Na+ overload
AbstractCentrilobular hypoxia has been suggested to contribute to hepatic damage caused by alcohol intoxication. However, the mechanisms involved are still poorly understood. We have investigated whether alterations of Na+ homeostasis might account for ethanol-mediated increase in hepatocyte sensitivity to hypoxia. Addition of ethanol (100 mmol/l) to isolated rat hepatocytes incubated under nitrogen atmosphere greatly stimulated cell death. An increase in intracellular Na+ levels preceded cell killing and Na+ levels in hepatocytes exposed to the combination of ethanol and hypoxia were almost twice those in hypoxic cells without ethanol. Na+ increase was also observed in hepatocytes incubated with ethanol in oxygenated buffer. Ethanol addition significantly lowered hepatocyte pH. Inhibiting ethanol and acetaldehyde oxidation with, respectively, 4-methylpyrazole and cyanamide prevented this effect. 4-methylpyrazole, cyanamide as well as hepatocyte incubation in a HCO3−-free buffer or in the presence of Na+/H+ exchanger blocker 5-(N,N-dimethyl)-amiloride also reduced Na+ influx in ethanol-treated hepatocytes. 4-methylpyrazole and cyanamide similarly prevented ethanol-stimulated Na+ accumulation and hepatocyte killing during hypoxia. Moreover, ethanol-induced Na+ influx caused cytotoxicity in hepatocytes pre-treated with Na+,K+-ATPase inhibitor ouabain. Also in this condition 4-methylpyrazole and 5-(N,N-dimethyl)-amiloride decreased cell killing. These results indicate that ethanol can promotes cytotoxicity in hypoxic hepatocytes by enhancing Na+ accumulation
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