1,585 research outputs found
The population of planetary nebulae and HII regions in M81. A study of radial metallicity gradients and chemical evolution
We analyze the chemical abundances of planetary nebulae and HII regions in
the M81 disk for insight on galactic evolution, and compare it with that of
other galaxies, including the Milky Way. We acquired Hectospec/MMT spectra of
39 PNe and 20 HII regions, with 33 spectra viable for temperature and abundance
analysis. Our PN observations represent the first PN spectra in M81 ever
published, while several HII region spectra have been published before,
although without a direct electron temperature determination. We determine
elemental abundances of helium, nitrogen, oxygen, neon, sulfur, and argon in
PNe and HII regions, and determine their averages and radial gradients. The
average O/H ratio of PNe compared to that of the HII regions indicates a
general oxygen enrichment in M81 in the last ~10 Gyr. The PN metallicity
gradient in the disk of M81 is -0.055+-0.02 dex/kpc. Neon and sulfur in PNe
have a radial distribution similar to that of oxygen, with similar gradient
slopes. If we combine our HII sample with the one in the literature we find a
possible mild evolution of the gradient slope, with results consistent with
gradient steepening with time. Additional spectroscopy is needed to confirm
this trend. There are no Type I PNe in our M81 sample, consistently with the
observation of only the brightest bins of the PNLF, the galaxy metallicity, and
the evolution of post-AGB shells. Both the young and the old populations of M81
disclose shallow but detectable negative radial metallicity gradient, which
could be slightly steeper for the young population, thus not excluding a mild
gradients steepening with the time since galaxy formation. During its evolution
M81 has been producing oxygen; its total oxygen enrichment exceeds that of
other nearby galaxies.Comment: A&A, in pres
Measuring antibiotic availability and use in 20 low- and middle-income countries
Objective To assess antibiotic availability and use in health facilities in low- and middle-income countries, using the service provision assessment and service availability and readiness assessment surveys.
Methods We obtained data on antibiotic availability at 13 561 health facilities in 13 service provision assessment and 8 service availability and readiness assessment surveys. In 10 service provision assessment surveys, child consultations with health-care providers were observed, giving data on antibiotic use in 22 699 children. Antibiotics were classified as access, watch or reserve, according to the World Health Organization’s AWaRe categories. The percentage of health-care facilities across countries with specific antibiotics available and the proportion of children receiving antibiotics for key clinical syndromes were estimated.
Findings The surveys assessed the availability of 27 antibiotics (19 access, 7 watch, 1 unclassified). Co-trimoxazole and metronidazole were most widely available, being in stock at 89.5% (interquartile range, IQR: 11.6%) and 87.1% (IQR: 15.9%) of health facilities, respectively. In contrast, 17 other access and watch antibiotics were stocked, by fewer than a median of 50% of facilities. Of the 22 699 children observed, 60.1% (13 638) were prescribed antibiotics (mostly co-trimoxazole or amoxicillin). Children with respiratory conditions were most often prescribed antibiotics (76.1%; 8972/11 796) followed by undifferentiated fever (50.1%; 760/1518), diarrhoea (45.7%; 1293/2832) and malaria (30.3%; 352/1160).
Conclusion Routine health facility surveys provided a valuable data source on the availability and use of antibiotics in low- and middle-income countries. Many access antibiotics were unavailable in a majority of most health-care facilities
A gas-rich AGN near the centre of a galaxy cluster at z ~ 1.4
The formation of the first virialized structures in overdensities dates back
to ~9 Gyr ago, i.e. in the redshift range z ~ 1.4 - 1.6. Some models of
structure formation predict that the star formation activity in clusters was
high at that epoch, implying large reservoirs of cold molecular gas. Aiming at
finding a trace of this expected high molecular gas content in primeval
clusters, we searched for the 12CO(2-1) line emission in the most luminous
active galactic nucleus (AGN) of the cluster around the radio galaxy 7C
1756+6520 at z ~ 1.4, one of the farthest spectroscopic confirmed clusters.
This AGN, called AGN.1317, is located in the neighbourhood of the central radio
galaxy at a projected distance of ~780 kpc. The IRAM Plateau de Bure
Interferometer was used to investigate the molecular gas quantity in AGN.1317,
observing the 12CO(2-1) emission line. We detect CO emission in an AGN
belonging to a galaxy cluster at z ~ 1.4. We measured a molecular gas mass of
1.1 x 10^10 Msun, comparable to that found in submillimeter galaxies. In
optical images, AGN.1317 does not seem to be part of a galaxy interaction or
merger.We also derived the nearly instantaneous star formation rate (SFR) from
Halpha flux obtaining a SFR ~65 Msun/yr. This suggests that AGN.1317 is
actively forming stars and will exhaust its reservoir of cold gas in ~0.2-1.0
Gyr.Comment: 5 pages, 3 figures, accepted for publication in Astronomy &
Astrophysic
Weathering Effects on Engineering Geological Properties of Trachydacitic Volcanic Rocks from the Monte Amiata (Southern Tuscany, Italy)
Variability in lithology and weathering degree affects physical and mechanical properties
of rocks. In this study, we investigated the relationships between weathering degree and engineering
geological properties of trachydacitic volcanic rocks from Monte Amiata (central Italy) by coupling
field and laboratory analyses. We collected in situ Schmidt hammer tests in the field. We evaluated
weathering quantifying the percentage of secondary minerals through thermal analysis in the
laboratory. We also determined dry density (rd), specific gravity of solids (Gs), porosity (n) and
two-dimensional (2D) porosity as resulted from scanning electron microscopy investigations. The
results of our study indicate a negative linear correlation between Schmidt hammer rebound values
and secondary mineral percentage. This correlation provides a tool to quantitatively estimate the
deterioration of rock uniaxial compressive strength (UCS) as weathering increases. Moreover, thermal
analysis turned out to be a quantitative and reproducible method to evaluate weathering degree of
magmatic rocks
Conceptual-level evaluation of a variable stiffness skin for a morphing wing leading edge
A morphing leading edge produces a continuous aerodynamic surface that has no gaps between the moving and fixed parts. The continuous seamless shape has the potential to reduce drag, compared to conventional devices, such as slats that produce a discrete aerofoil shape change. However, the morphing leading edge has to achieve the required target shape by deforming from the baseline shape under the aerodynamic loads. In this paper, a conceptual-level method is proposed to evaluate the morphing leading edge structure. The feasibility of the skin design is validated by checking the failure index of the composite when the morphing leading edge undergoes the shape change. The stiffness of the morphing leading edge skin is spatially varied using variable lamina angles, and comparisons to the skin with constant stiffness are made to highlight its potential to reduce the actuation forces. The structural analysis is performed using a two-level structural optimisation scheme. The first level optimisation is applied to find the optimised structural proper- ties of the leading edge skin and the associated actuation forces. The structural properties of the skin are given as a stiffness distribution, which is controlled by a B spline interpolation function. In the second level, the design solution of the skin is investigated. The skin is assumed to be made of variable stiffness composite. The stack sequence of the composite is optimised element-by-element to match the target stiffness. A failure criterion is employed to obtain the failure index when the leading edge is actuated from the baseline shape to the target shape. Test cases are given to demonstrate that the optimisation scheme is able to provide the stiffness distribution of the leading edge skin and the actuation forces can be reduced by using a spatially variable stiffness skin
Metal production in M33: space and time variations
Nearby galaxies are ideal places to study in detail metallicity gradients and
their time evolution. We consider chemical abundances of a new sample of \hii\
regions complemented with previous literature data-sets. We compare \hii\
region and PN abundances obtained with a common set of observations taken at
MMT. With an updated theoretical model, we follow the time evolution of the
baryonic components and chemical abundances in the disk of M33, assuming that
the galaxy is accreting gas from an external reservoir. Supported by a uniform
sample of nebular spectroscopic observations, we conclude that: {\em i}) the
metallicity distribution in M33 is very complex, showing a central depression
in metallicity probably due to observational bias; {\em ii}) the metallicity
gradient in the disk of M33 has a slope of -0.037 0.009 dex kpc in
the whole radial range up to 8 kpc, and -0.044 0.009 dex kpc
excluding the central kpc; {\em iii}) there is a small evolution of the slope
with time from the epoch of PN progenitor formation to the present-time.}Comment: A&A accepted, 15 Pags, 13 Figs, language correctio
Serotonin-mediated tuning of human helper T cell responsiveness to the chemokine CXCL12
In addition to its role as neurotransmitter, serotonin (5-HT) is an important modulator of inflammation and immunity. Here, we report novel findings suggesting a 5-HT involvement in T cell migration. In particular, we show that 5-HT tunes the responsiveness of human T lymphocytes to the broadly expressed chemokine CXCL12 in transwell migration assays. By real-time PCR, western blot analysis and electrophysiological patch clamp experiments, we demonstrate that the type 3 5-HT receptor (5-HT 3) is functionally expressed in human primary T cells. In addition, specific 5-HT 3 receptor agonists selectively decrease T cell migration towards gradients of CXCL12 but not of inflammatory chemokines, such as CCL2 and CCL5. In transmigration experiments, 5-HT 3 receptor stimulation reverts the inhibitory effect of endothelial-bound CXCL12 on T cell migration. Our data suggest that the reduced T cell responsiveness to CXCL12 induced by 5-HT may occur to facilitate T cell extravasation and migration into inflamed tissues
Young stellar clusters and associations in M33
We analyse multi-wavelength observations of 32 young star clusters and
associations in M33 with known oxygen abundance (8 < 12 + log(O/H) < 8.7),
using ultraviolet (UV), optical, mid-infrared (MIR), CO (1-0) and 21-cm line
(HI) observations. We derive their spectral energy distribution, and we
determine age, bolometric luminosities, masses and the extinction, by comparing
the multi-band integrated photometry to single-age stellar population models.
The stellar system ages range between 2 and 15 Myr, masses are between 3 x 10^2
and 4 x 10^4 M_sun, and the intrinsic extinction, A_V, varies from 0.3 to 1
mag. We find a correlation between age and extinction, and between the cluster
mass and size. The MIR emission shows the presence of a dust component around
the clusters whose fractional luminosity at 24 um, L_{24}/L_{Bol}, decreases
with the galactocentric distance. However, the total IR luminosity inferred
from L_{24} is smaller than what we derive from the extinction corrections. The
Halpha luminosity predicted by population synthesis models is larger than the
observed one, especially for low-mass systems (M < 10^4 M_sun). Such a
difference is reduced, but not erased, when the incomplete sampling of the
initial mass function (IMF) at the high-mass end is taken into account. Our
results suggest that a non-negligible fraction of UV ionising and non-ionising
radiation is leaking into the ISM outside the HII regions. This would be in
agreement with the large UV and Halpha diffuse fractions observed in M33, but
it implies that stellar systems younger than 3 Myr retain, on average, only 30%
of their Lyman continuum photons. However, the uncertainties on cluster ages
and the stochastic fluctuations of the IMF do not allow to accurately quantify
this issue. We also consider the possibility that this discrepancy is the
consequence of a suppressed or delayed formation of the most massive stars.Comment: 17 pages, 13 figures. Accepted for publications in A&A; v2 --> Table
2 corrected because of a misprint in the FUV magnitude
Planetary nebulae in M33: probes of AGB nucleosynthesis and ISM abundances
We have obtained deep optical spectrophotometry of 16 planetary nebulae in
M33, mostly located in the central two kpc of the galaxy, with the Subaru and
Keck telescopes. We have derived electron temperatures and chemical abundances
from the detection of the [OIII]4363 line for the whole sample. We have found
one object with an extreme nitrogen abundance, 12+log(N/H)=9.20, accompanied by
a large helium content. After combining our data with those available in the
literature for PNe and HII regions, we have examined the behavior of nitrogen,
neon, oxygen and argon in relation to each other, and as a function of
galactocentric distance. We confirm the good correlation between Ne/H and O/H
for PNe in M33. Ar/H is also found to correlate with O/H. This strengthens the
idea that at the metallicity of the bright PNe analyzed in M33, which is
similar to that found in the LMC, these elements have not been significantly
modified during the dredge-up processes that take place during the AGB phase of
their progenitor stars. We find no significant oxygen abundance offset between
PNe and HII regions at any given galactocentric distance, despite the fact that
these objects represent different age groups in the evolution of the galaxy.
Combining the results from PNe and HII regions, we obtain a representative
slope of the ISM alpha-element (O, Ar, Ne) abundance gradient in M33 of -0.025
+/- 0.006 dex/kpc. Both PNe and HII regions display a large abundance
dispersion at any given distance from the galactic center. We find that the N/O
ratio in PNe is enhanced, relative to the HII regions, by approximately 0.8
dex.Comment: 21 pages, 20 figures. Accepted for publication in MNRA
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