142 research outputs found
Design e prevenção em saúde : uma parceria em potencial
Este artigo apresenta alguns caminhos possÃveis para a
elaboração de conceitos teóricos que permitam repensar aspectos
problemáticos da comunicação visual na prevenção em saúde ligada a
Aids/HIV e DST´S, por meio da participação do profissional de design na
elaboração de ações de prevenção desde a sua concepção até a arte
finalização.
A partir dessa problematização, é proposta uma reflexão no sentido de
formular alternativas de comunicação para prevenção e controle da
epidemia de HIV/Aids que estejam em melhor consonância com as atuais
demandas de saúde decorrentes das mudanças sociais e das descobertas
cientificas ligadas ao vÃrus, no sentido de promover uma melhor resposta
preventiva por parte da população.ABSTRACT: This article intends to show some possible paths to the
creation of new teorical concepts that leads to the solution of
problematic aspects of the health prevention of Aids/HIV and STD´S,
through the participation of the designer in the prevention advent since it
´s conception until the last graphic retouch.
Once the problematic aspects of health prevention of Aids in Brazil are
exposed, a new path, suggesting new alternatives of prevention and
control for the HIV/Aids epidemics that are more connected with the
recent preventive demands that came with the social and scientific
changes related to the HIVinfo:eu-repo/semantics/publishedVersio
The Cosmic Near Infrared Background: Remnant Light from Early Stars
The redshifted ultraviolet light from early stars at z ~ 10 contributes to
the cosmic near infrared background. We present detailed calculations of its
spectrum with various assumptions about metallicity and mass spectrum of early
stars. We show that if the near infrared background has a stellar origin,
metal-free stars are not the only explanation of the excess near infrared
background; stars with metals (e.g. Z=1/50 Z_sun) can produce the same amount
of background intensity as the metal-free stars. We quantitatively show that
the predicted average intensity at 1-2 microns is essentially determined by the
efficiency of nuclear burning in stars, which is not very sensitive to
metallicity. We predict \nu I_\nu / \dot{\rho}_* ~ 4-8 nW m^-2 sr^-1, where
\dot{\rho_*} is the mean star formation rate at z=7-15 (in units of M_sun yr^-1
Mpc^-3) for stars more massive than 5 M_sun. On the other hand, since we have
very little knowledge about the form of mass spectrum of early stars,
uncertainty in the average intensity due to the mass spectrum could be large.
An accurate determination of the near infrared background allows us to probe
formation history of early stars, which is difficult to constrain by other
means. While the star formation rate at z=7-15 inferred from the current data
is significantly higher than the local rate at z<5, it does not rule out the
stellar origin of the cosmic near infrared background. In addition, we show
that a reasonable initial mass function, coupled with this star formation rate,
does not over-produce metals in the universe in most cases, and may produce as
little as less than 1 % of the metals observed in the universe today.Comment: 37 pages, 7 figures, (v2) Changes to abstract to emphasize that the
excess near infrared background can solely be explained by stars with
significant metals. (Metal-free stars are not necessarily needed.) (v3)
Expanded discussion on the metallicity constraint. Accepted for publication
in Ap
Simulating galaxy clusters -- I. Thermal and chemical properties of the intra-cluster medium
We have performed a series of N-body/hydrodynamical (TreeSPH) simulations of
clusters and groups of galaxies, selected from cosmological N-body simulations
within a CDM framework: these objects have been re-simulated at higher
resolution to =0, in order to follow also the dynamical, thermal and
chemical input on to the ICM from stellar populations within galaxies. The
simulations include metal dependent radiative cooling, star formation according
to different IMFs, energy feedback as strong starburst-driven galactic
super-winds, chemical evolution with non-instantaneous recycling of gas and
heavy elements, effects of a meta-galactic UV field and thermal conduction in
the ICM. In this Paper I of a series of three, we derive results, mainly at
, on the temperature and entropy profiles of the ICM, its X-ray
luminosity, the cluster cold components (cold fraction as well as
mass--to--light ratio) and the metal distribution between ICM and stars.
In general, models with efficient super-winds, along with a top-heavy stellar
IMF, are able to reproduce fairly well the observed relation, the
entropy profiles and the cold fraction. Observed radial ICM temperature
profiles can be matched, except for the gradual decline in temperature inside
of ~0.1. Metal enrichment of the ICM gives rise to
somewhat steep inner iron gradients; yet, the global level of enrichment
compares well to observational estimates after correcting for the stars formed
at late times at the base of the cooling flows; also the metal partition
between stars and ICM gets into good agreement with observations.Comment: 23 pages, 20 colour figures; final version accepte
A Mechanism for the Oxygen and Iron Bimodal Radial Distribution Formation in the Disc of our Galaxy
Recently it has been proposed that there are two types of SN Ia progenitors
-- short-lived and long-lived. On the basis of this idea, we develope a theory
of a unified mechanism for the formation of the bimodal radial distribution of
iron and oxygen in the Galactic disc. The underlying cause for the formation of
the fine structure of the radial abundance pattern is the influence of spiral
arms, specifically, the combined effect of the corotation resonance and
turbulent diffusion. From our modelling we conclude that to explain the bimodal
radial distributions simultaneously for oxygen and iron and to obtain
approximately equal total iron output from different types of supernovae, the
mean ejected iron mass per supernova event should be the same as quoted in
literature if maximum mass of stars, that eject heavy elements, is . For the upper mass limit of the production of iron
by a supernova II explosion should be increased by about 1.5 times.Comment: 7 pages, 6 figures, MNRAS submitte
Are ancient dwarf satellites the building blocks of the Galactic halo?
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2016 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.According to the current cosmological cold dark matter paradigm, the Galactic halo could have been the result of the assemblage of smaller structures. Here we explore the hypothesis that the classical and ultra-faint dwarf spheroidal satellites of the Milky Way have been the building blocks of the Galactic halo by comparing their [α/Fe] and [Ba/Fe] versus [Fe/H] patterns with the ones observed in Galactic halo stars. The α elements deviate substantially from the observed abundances in the Galactic halo stars for [Fe/H] values larger than −2 dex, while they overlap for lower metallicities. On the other hand, for the [Ba/Fe] ratio, the discrepancy is extended at all [Fe/H] values, suggesting that the majority of stars in the halo are likely to have been formed in situ. Therefore, we suggest that [Ba/Fe] ratios are a better diagnostic than [α/Fe] ratios. Moreover, for the first time we consider the effects of an enriched infall of gas with the same chemical abundances as the matter ejected and/or stripped from dwarf satellites of the Milky Way on the chemical evolution of the Galactic halo. We find that the resulting chemical abundances of the halo stars depend on the assumed infall time-scale, and the presence of a threshold in the gas for star formation. In particular, in models with an infall time-scale for the halo around 0.8 Gyr coupled with a threshold in the surface gas density for the star formation (4 M pc−2), and the enriched infall from dwarf spheroidal satellites, the first halo stars formed show [Fe/H]>−2.4 dex. In this case, to explain [α/Fe] data for stars with [Fe/H]<−2.4 dex, we need stars formed in dSph systems.Peer reviewedFinal Published versio
Abundance Gradients and the Formation of the Milky Way
In this paper we adopt a chemical evolution model, which is an improved
version of the Chiappini, Matteucci and Gratton (1997) model, assuming two main
accretion episodes for the formation of the Galaxy. The present model takes
into account in more detail than previously the halo density distribution and
explores the effects of a threshold density in the star formation process,
during both the halo and disk phases. In the comparison between model
predictions and available data, we have focused our attention on abundance
gradients as well as gas, stellar and star formation rate distributions along
the disk. We suggest that the mechanism for the formation of the halo leaves
detectable imprints on the chemical properties of the outer regions of the
disk, whereas the evolution of the halo and the inner disk are almost
completely disentangled. This is due to the fact that the halo and disk
densities are comparable at large Galactocentric distances and therefore the
gas lost from the halo can substantially contribute to building up the outer
disk. We also show that the existence of a threshold density for the star
formation rate, both in the halo and disk phase, is necessary to reproduce the
majority of observational data in the solar vicinity and in the whole disk.
Moreover, we predict that the abundance gradients along the Galactic disk must
have increased with time and that the average [alpha/Fe] ratio in stars (halo
plus disk) slightly decrease going from 4 to 10 Kpcs from the Galactic center.
We also show that the same ratios increase substantially towards the outermost
disk regions and the expected scatter in the stellar ages decreases, because
the outermost regions are dominated by halo stars.Comment: 41 pages (including the figures), To be published in Ap
The mass surface density in the local disk and the chemical evolution of the Galaxy
We have studied the effect of adopting different values of the total baryonic
mass surface density in the local disk at the present time in a model for the
chemical evolution of the Galaxy. We have compared our model results with the
G-dwarf metallicity distribution, the amounts of gas, stars, stellar remnants,
infall rate and SN rate in the solar vicinity, and with the radial abundance
gradients and gas distribution in the disk. This comparison strongly suggests
that the value of the total baryonic mass surface density in the local disk
which best fits the observational properties should lie in the range 50-75 Msun
pc-2, and that values outside this range should be ruled out.Comment: 6 pages, LaTeX, 3 figures, accepted for publication in the
Astrophysical Journal, uses emulateapj.st
The Formation of Fossil Galaxy Groups in the hierarchical Universe
We use a set of twelve high-resolution N-body/hydrodynamical simulations in
the CDM cosmology to investigate the origin and formation rate of
fossil groups (FGs), which are X-ray bright galaxy groups dominated by a large
elliptical galaxy, with the second brightest galaxy being at least two
magnitudes fainter. The simulations invoke star formation, chemical evolution
with non-instantaneous recycling, metal dependent radiative cooling, strong
star burst driven galactic super winds, effects of a meta-galactic UV field and
full stellar population synthesis. We find an interesting correlation between
the magnitude gap between the first and second brightest galaxy and the
formation time of the group. It is found that FGs have assembled half of their
final dark matter mass already at z\ga1, and subsequently typically grow by
minor merging only, wheras non-FGs on average form later. The early assembly of
FGs leaves sufficient time for galaxies of to merge into the
central one by dynamical friction, resulting in the large magnitude gap at
. A fraction of 3316% of the groups simulated are found to be fossil,
whereas the observational estimate is 10-20%. The FGs are found to be
X-ray over-luminous relative to non-FGs of the same optical luminosity, in
qualitative agreement with observations. Finally, from a dynamical friction
analysis is found that only because infall of galaxies happens
along filaments with small impact parameters do FGs exist at all.Comment: 4 pages, 3 figures, one figure removed. Accepted for publication in
ApJ Lette
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