553 research outputs found
Sol-gel synthesis of spherical monodispersed bioactive glass nanoparticles co-doped with boron and copper
In this work, an optimized sol-gel process for the synthesis of spherical and monodispersed bioactive glass nanoparticles doped with boron and copper was developed, by investigating different synthesis parameters. The obtained glasses were characterized in terms of morphology, composition, dispersibility, structure and in vitro reactivity. The performed characterizations demonstrated that shape, dimension and dispersion can be tailored by acting on the timing of the addition of the catalyst and on the synthesis process, in particular the centrifugation step. The optimized glass particles showed a spherical shape, good ions incorporation and good dispersion. In vitro bioactivity test demonstrated that the boron and copper addition did not interfere with the glass ability to induce the precipitation of hydroxyapatite. The shape, dispersion, bioactive behavior and content of boron and copper of these novel bioactive glass particles make them very promising for both hard and soft tissue engineering applications
Sol-gel synthesis of spherical monodispersed bioactive glass nanoparticles co-doped with boron and copper
In this work, an optimized sol-gel process for the synthesis of spherical and monodispersed bioactive glass nanoparticles doped with boron and copper was developed, by investigating different synthesis parameters. The obtained glasses were characterized in terms of morphology, composition, dispersibility, structure and in vitro reactivity. The performed characterizations demonstrated that shape, dimension and dispersion can be tailored by acting on the timing of the addition of the catalyst and on the synthesis process, in particular the centrifugation step. The optimized glass particles showed a spherical shape, good ions incorporation and good dispersion. In vitro bioactivity test demonstrated that the boron and copper addition did not interfere with the glass ability to induce the precipitation of hydroxyapatite. The shape, dispersion, bioactive behavior and content of boron and copper of these novel bioactive glass particles make them very promising for both hard and soft tissue engineering applications
Herpetofauna, municipality of Porto Murtinho, Chaco region, state of Mato Grosso do Sul, Brazil
Among the physiographic regions included in the central South American diagonal of open formations,the Chaco, with some endemic species, represents the southernmost dry area. In Brazil, the Chaco is foundin southwestern corner of Mato Grosso do Sul state, mostly in the municipality of Porto Murtinho along theParaguay and Apa rivers. From February 2008 to December 2009, we carried out an inventory of amphibiansand reptiles in Porto Murtinho, using pitfall traps, time-limited searches, and occasional encounters. A total of34 amphibian and 39 reptile species were registered. Although some typical Chacoan species were found, mostof the species are open area dwellers that also occur in other open biomes, such as the Cerrado and Caatinga
Fluorimetric methods for the measurement of intermediate metabolites (lactate, pyruvate, alanine, β-hydroxybutyrate, glycerol) using a COBAS FARA centrifugal analyser
Intermediate products of the metabolism of glucose, fat and amino-acid are important in the evaluation of such metabolic disorders as diabetes mellitus, liver disease and metabolic acidosis. In the present study, methods for the measurement of intermediate metabolites (lactate, pyruvate, alanine, β-hydroxybutyrate and glycerol) have been adapted to a fast centrifugal analyzer: the COBAS FARA. Correlation coeffcients rangedfrom 0.90 to 0.99, compared to established manual spectrophotometric methods. Within-run coeffcients of variation (CVs) ranged between 2.9 and 8.8% at low levels, between 1.5 and 5.7% at medium levels and between 1.2 and 5.6% at high levels. Between-run CVs were between 4.0 and 15.0% at low levels, between 1.7 and 7.0% at medium levels and between 1.3 and 2.7% at high levels. These fluorimetric assays for the determination of intermediate metabolites on COBAS FARA (Roche) have a good sensitivity and precision, are less costly than manual methods and can be used on a routine basis
Optical Light Curve of the Type Ia Supernova 1998bu in M96 and the Supernova Calibration of the Hubble Constant
We present the UBVRI light curves of the Type Ia supernova SN 1998bu which
appeared in the nearby galaxy M96 (NGC 3368). M96 is a spiral galaxy in the Leo
I group which has a Cepheid-based distance. Our photometry allows us to
calculate the absolute magnitude and reddening of this supernova. These data,
when combined with measurements of the four other well-observed supernovae with
Cepheid based distances, allow us to calculate the Hubble constant with respect
to the Hubble flow defined by the distant Calan/Tololo Type Ia sample. We find
a Hubble constant of 64.0 +/- 2.2(internal) +/- 3.5(external) km/s/Mpc,
consistent with most previous estimates based on Type Ia supernovae. We note
that the two well-observed Type Ia supernovae in Fornax, if placed at the
Cepheid distance to the possible Fornax spiral NGC 1365, are apparently too
faint with respect to the Calan/Tololo sample calibrated with the five Type Ia
supernovae with Cepheid distances to the host galaxies.Comment: AAS LaTeX, 20 pages, 4 figures, 6 tables, accepted for publication in
the Astronomical Journal. Figure 1 (finding chart) not include
The VMC survey - XIV : First results on the look-back time star formation rate tomography of the Small Magellanic Cloud
Date of Acceptance: 20/01/2015We analyse deep images from the VISTA survey of the Magellanic Clouds in the YJKs filters, covering 14 deg2 (10 tiles), split into 120 subregions, and comprising the main body and Wing of the Small Magellanic Cloud (SMC). We apply a colour-magnitude diagram reconstruction method that returns their best-fitting star formation rate SFR(t), age-metallicity relation (AMR), distance and mean reddening, together with 68 per cent confidence intervals. The distance data can be approximated by a plane tilted in the East-West direction with a mean inclination of 39°, although deviations of up to ±3 kpc suggest a distorted and warped disc. After assigning to every observed star a probability of belonging to a given age-metallicity interval, we build high-resolution population maps. These dramatically reveal the flocculent nature of the young star-forming regions and the nearly smooth features traced by older stellar generations. They document the formation of the SMC Wing at ages <0.2 Gyr and the peak of star formation in the SMC Bar at ~40 Myr. We clearly detect periods of enhanced star formation at 1.5 and 5 Gyr. The former is possibly related to a new feature found in the AMR, which suggests ingestion of metal-poor gas at ages slightly larger than 1 Gyr. The latter constitutes a major period of stellar mass formation. We confirm that the SFR(t) was moderately low at even older ages.Peer reviewe
THE VMC SURVEY. XIX. CLASSICAL CEPHEIDS in the SMALL MAGELLANIC CLOUD
The final, definitive version of this paper, V. Ripepi, M. Marconi, M. I. Moretti, G. Clementini, M.-R. L. Cioni, R. de Grijs, J. P. Emerson, M. A. T. Groenewegen1, V. D. Ivanov, and A. E. Piatti. 'THE VMC SURVEY. XIX. CLASSICAL CEPHEIDS IN THE SMALL MAGELLANIC CLOUD' The Astrophysical Journal - Supplement Series, Vol 224(21) June 2016, is available on line at doi:10.3847/0067-0049/224/2/21 © 2016. The American Astronomical Society. All rights reservedThe VISTA near-infrared YJK s survey of the Magellanic Clouds System (VMC) is collecting deep K s-band time-series photometry of pulsating variable stars hosted by the two Magellanic Clouds and their connecting Bridge. In this paper, we present Y, J, K s light curves for a sample of 4172 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with literature V values, allowed us to construct a variety of period-luminosity (PL), period-luminosity-color (PLC), and period-Wesenheit (PW) relationships, which are valid for Fundamental (F), First Overtone (FO), and Second Overtone (SO) pulsators. The relations involving the V, J, K s bands are in agreement with their counterparts in the literature. As for the Y band, to our knowledge, we present the first CC PL, PW, and PLC relations ever derived using this filter. We also present the first near-infrared PL, PW, and PLC relations for SO pulsators to date. We used PW(V, K s) to estimate the relative SMC-LMC distance and, in turn, the absolute distance to the SMC. For the former quantity, we find a value of Δμ = 0.55 -0.04 mag, which is in rather good agreement with other evaluations based on CCs, but significantly larger than the results obtained from older population II distance indicators. This discrepancy might be due to the different geometric distributions of young and old tracers in both Clouds. As for the absolute distance to the SMC, our best estimates are μ SMC = 19.01 -0.05 mag and μ SMC = 19.04 -0.06 mag, based on two distance measurements to the LMC which rely on accurate CC and eclipsing Cepheid binary data, respectively.Peer reviewe
22Ne and 23Na ejecta from intermediate-mass stars: The impact of the new LUNA rate for 22Ne(p,gamma)23Na
We investigate the impact of the new LUNA rate for the nuclear reaction NeNa on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally-pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim we use the PARSEC and COLIBRI codes to compute the complete evolution, from the pre-main sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range , and metallicities , , and . We find that the new LUNA measures have much reduced the nuclear uncertainties of the Ne and Na AGB ejecta, which drop from factors of to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of Na, the uncertainties that still affect the Ne and Na AGB ejecta are mainly dominated by evolutionary aspects (efficiency of mass-loss, third dredge-up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O-Na anti-correlation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anti-correlation, and the observational constraints on the CNO abundance. Results for the corresponding chemical ejecta are made publicly available
Metallicities and ages for 35 star clusters and their surrounding fields in the Small Magellanic Cloud
In this work we study 35 stellar clusters in the Small Magellanic Cloud (SMC)
in order to provide their mean metallicities and ages. We also provide mean
metallicities of the fields surrounding the clusters. We used Str\"omgren
photometry obtained with the 4.1 m SOAR telescope and take advantage of and colors for which there is a metallicity calibration presented in
the literature. The spatial metallicity and age distributions of clusters
across the SMC are investigated using the results obtained by Str\"omgren
photometry. We confirm earlier observations that younger, more metal-rich star
clusters are concentrated in the central regions of the galaxy, while older,
more metal-poor clusters are located farther from the SMC center. We construct
the age-metallicity relation for the studied clusters and find good agreement
with theoretical models of chemical enrichment, and with other literature age
and metallicity values for those clusters. We also provide the mean
metallicities for old and young populations of the field stars surrounding the
clusters, and find the latter to be in good agreement with recent studies of
the SMC Cepheid population. Finally, the Str\"omgren photometry obtained for
this study is made publicly available.Comment: 22 pages, 12 figures, 6 tables, Accepted for publication in A&
Ages and Metallicities of Star Clusters and Surrounding Fields in the Outer Disk of the Large Magellanic Cloud
We present Washington system C,T_1 CMDs of 13 star clusters and their
surrounding fields which lie in the outer parts of the LMC disk. Ages are
determined by means of the magnitude difference between the giant branch clump
and the turnoff, while metallicities are derived from the location of the giant
and subgiant branches as compared to fiducial star clusters. We find that in
most cases the stellar population of each star cluster is quite similar to that
of the field where it is embedded. Three particular fields present remarkable
properties: (i) The so far unique cluster ESO121-SC03 at ~9 Gyr has a
surrounding field which shares the same properties. (ii) The field surrounding
the far eastern intermediate age cluster OHSC37 is noteworthy in the sense that
we do not detect any evidence of LMC stars. (iii) The fields of SL388 and SL509
present CMDs with a secondary clump ~0.45 mag fainter than the dominant
intermediate age clump, suggesting a stellar population component located
behind the LMC disk at a distance comparable to that of the SMC. The mean
metallicity derived for the intermediate age outer disk clusters is
=-0.7 and for their surrounding fields =-0.6. These values are
significantly lower than found by Olszewski et al. (1991, AJ, 101, 515) for a
sample of clusters of similar age, but are in good agreement with several
recent studies. A few clusters stand out in the age--metallicity relation in
the sense that they are intermediate age clusters at relatively low metallicity
([Fe/H]~-1).Comment: LaTeX, to be published in July, 1998 Astronomical Journa
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