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Search Results: 1 - 10 of 325288 matches for " S. Villanova "
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Excluidos o incluidos?: Recuperadores de materiales reciclables en Latinoamérica Excluded or included?: Recyclable material recoverers in Latin America
Nicolás Villanova
Revista mexicana de sociología , 2012,
Abstract: El fenómeno de la recuperación de materiales reciclables se masificó en varios países de Latinoamérica durante las últimas décadas. Este artículo se propone examinar el circuito que recorren esos materiales en ciudades de tres países: Argentina, Brasil y México. El objetivo es analizar este proceso y las condiciones de trabajo de quienes recolectan y clasifican el material de manera independiente o en cooperativas y su vínculo con las empresas que usan esos productos como materia prima, sobre todo las papeleras, a través de fuentes bibliográficas, estadísticas oficiales y artículos periodísticos, y estudios de caso propios en el análisis de la situación en Argentina. The phenomenon of recyclable materials recovery has occurred on a massive scale in several Latin American countries in recent decades. This article seeks to examine the circuit followed by these materials in cities of three countries: Argentina, Brazil and Mexico. The aim is to analyze this process and the labor conditions of those who collect and classify the material independently or in cooperatives and their link with firms that use these products as raw material, particularly paper mills, using bibliographical sources, official statistics and newspaper articles and case studies in the analysis of the situation in Argentina.
VLT multi-epoch radial velocity survey toward NGC 6253. Analysis of three transiting planetary candidates
M. Montalto,S. Villanova,J. Koppenhoefer
Physics , 2010, DOI: 10.1051/0004-6361/200913582
Abstract: We measured the radial velocity of 139 stars in the region of NGC 6253, discussing cluster's membership and binarity in this sample, complementing our analysis with photometric, proper motion, and radial velocity data available from previous studies of this cluster, and analyzing three planetary transiting candidates we found in the field of NGC 6253. Spectra were obtained with the UVES and GIRAFFE spectrographs at the VLT, during three epochs in August 2008. The mean radial velocity of the cluster is -29.11+/-0.85 km/s. Using both radial velocities and proper motions we found 35 cluster's members, among which 12 are likely cluster's close binary systems. One star may have a sub-stellar companion, requiring a more intensive follow-up. Our results are in good agreement with past radial velocity and photometric measurements. Furthermore, using our photometry, astrometry and spectroscopy we identified a new sub-giant branch eclipsing binary system, member of the cluster. The cluster's close binary frequency at 29% +/- 9% (34% +/-10% once including long period binaries), appears higher than the field binary frequency equal to (22% +/- 5%, though these estimates are still consistent within the uncertainties. Among the three transiting planetary candidates the brightest one (V=15.26) is worth to be more intensively investigated with higher percision spectroscopy. We discussed the possibility to detect sub-stellar companions (brown dwarfs and planets) with the radial velocity technique (both with UVES/GIRAFFE and HARPS) around turn-off stars of old open clusters [abridged].
The Origin and Chemical Evolution of the Exotic Globular Cluster NGC3201
C. Mu?oz,D. Geisler,S. Villanova
Physics , 2013, DOI: 10.1093/mnras/stt868
Abstract: NGC3201 is a globular cluster (GC) which shows very peculiar kinematic characteristics including an extreme radial velocity and a highly retrograde orbit, strongly suggesting an extraGalactic origin. Our aims are to study NGC3201 in the context of multiple populations (MPs), hoping to constrain possible candidates for the self-enrichment by studying the chemical abundance pattern, as well as adding insight into the origin of this intriguing cluster. We present a detailed chemical abundance analysis of eight red giant branch (RGB) stars using high resolution spectroscopy. We measured 29 elements and found [Fe/H]=-1.53+/-0.01, we cannot rule out a metallicity spread of ~0.12 dex, and an alpha-enhancement typical of halo GCs. However significant spreads are observed in the abundances of all light elements except for Mg. We confirm the presence of an extended Na-O anticorrelation. n-capture elements generally are dominated by the r-process, in good agreement with the bulk of Galactic GCs. The total (C+N+O) abundance is slightly supersolar and requires a small downward correction to the isochrone age, yielding 11.4 Gyr. Kinematically, NGC3201 appears likely to have had an extraGalactic origin but its chemical evolution is similar to most other, presumably native, Galactic GCs.
The Helium content of Globular Clusters: light element abundance correlations and HB morphology. I. NGC6752
S. Villanova,G. Piotto,R. G. Gratton
Physics , 2009, DOI: 10.1051/0004-6361/200811493
Abstract: Helium has been proposed as the key element to interpret the observed multiple main sequences (MS), subgiant branches (SGB) and red giant branches (RGB), as well as the complex horizontal branch (HB) morphology in Globular Clusters (GC). However, up to now, He was never directly measured in suitable GC stars (8500
The metallicity spread and the age-metallicity relation of Omega Centauri
S. Villanova,D. Geisler,R. G. Gratton,S. Cassisi
Physics , 2014, DOI: 10.1088/0004-637X/791/2/107
Abstract: Omega Centauri is a peculiar Globular Cluster formed by a complex stellar population. To shed light on this, we studied 172 stars belonging to the 5 SGBs that we can identify in our photometry, in order to measure their [Fe/H] content as well as estimate their age dispersion and the age-metallicity relation. The first important result is that all of these SGBs has a distribution in metallicity with a spread that exceeds the observational errors and typically displays several peaks that indicate the presence of several sub-populations. We were able to identified at least 6 of them based on their mean [Fe/H] content. These metallicity-based sub-populations are seen to varying extents in each of the 5 SGBs. Taking advantage of the age-sensitivity of the SGB we showed that, first of all, at least half of the sub-populations have an age spread of at least 2 Gyrs. Then we obtained an age-metallicity relation that is the most complete up to date for this cluster. The interpretation of the age-metallicity relation is not straightforward, but it is possible that the cluster (or what we can call its progenitor) was initially composed of two populations having different metallicities. Because of their age, it is very unlikely that the most metal-rich derives from the most metal-poor by some kind of chemical evolution process, so they must be assumed as two independent primordial objects or perhaps two separate parts of a single larger object, that merged in the past to form the present-day cluster.
Aplica??es farmacêuticas de polímeros
Villanova, Janaina C. O.;Oréfice, Rodrigo L.;Cunha, Armando S.;
Polímeros , 2010, DOI: 10.1590/S0104-14282010005000009
Abstract: polymers are very versatile for a series of applications including pharmaceutical applications. natural polymers, modified natural polymers and synthetic polymers are employed as excipients in the manufacture of cosmetics and systems for conventional and modified delivery of drugs. more recently, polymers have been developed to be able to modulate and deliver drugs to target places. biodegradable polymers, bioadhesives, biomimetic materials and responsive hydrogels have been included in pharmaceutical formulations. the advances in the concept of new drug delivery systems will only be possible with the development of polymers specifically designed for the pharmaceutical field. therefore, this manuscript intends to review and report information regarding the use of polymers in pharmaceutical applications that can be useful in designing new systems with improved performance.
The lithium content of omega Centauri. New clues to the cosmological Li problem from old stars in external galaxies
L. Monaco,P. Bonifacio,L. Sbordone,S. Villanova,E. Pancino
Physics , 2010, DOI: 10.1051/0004-6361/201015162
Abstract: A discrepancy has emerged between the cosmic lithium abundance inferred by the WMAP satellite measurement coupled with the prediction of the standard big-bang nucleosynthesis theory, and the constant Li abundance measured in metal-poor halo dwarf stars (the so-called Spite plateau). Several models are being proposed to explain this discrepancy, involving either new physics, in situ depletion, or the efficient depletion of Li in the pristine Galaxy by a generation of massive first stars. The realm of possibilities may be narrowed considerably by observing stellar populations in different galaxies, which have experienced different evolutionary histories. The WCen stellar system is commonly considered as the remnant of a dwarf galaxy accreted by the Milky Way (MW). We investigate the Li content of a conspicuous sample of unevolved stars in this object. We obtained moderate resolution (R=17000) spectra for 91 main-sequence/early sub-giant branch (MS/SGB) WCen stars using the FLAMES-GIRAFFE/VLT spectrograph. Li abundances were derived by matching the equivalent width of the LiI resonance doublet at 6708A, to the prediction of synthetic spectra computed with different Li abundances. Synthetic spectra were computed using the SYNTHE code along with ATLAS9 model atmospheres. The stars effective temperatures are derived by fitting the wings of the Ha line with synthetic profiles. We obtain a mean content of A(Li)=2.19+-0.14~dex for WCen MS/SGB stars. This is comparable to what is observed in Galactic halo field stars of similar metallicities and temperatures. The Spite plateau seems to be an ubiquitous feature of old, warm metal-poor stars. It exists also in external galaxies, if we accept the current view about the origin of WCen. This implies that the mechanism(s) that causes the "cosmological lithium problem" may be the same in the MW and other galaxies.
Testing Newtonian gravity with distant globular clusters: NGC1851 and NGC1904
R. Scarpa,G. Marconi,G. Carraro,R. Falomo,S. Villanova
Physics , 2010, DOI: 10.1051/0004-6361/201014462
Abstract: Globular clusters are useful to test the validity of Newtonian dynamics in the low acceleration regime typical of galaxies, without the complications of non-baryonic dark matter. Specifically, in absence of disturbing effects, e.g. tidal heating, their velocity dispersion is expected to vanish at large radii. If such behaviour is not observed, and in particular if, as observed in elliptical galaxies, the dispersion is found constant at large radii below a certain threshold acceleration, this might indicate a break down of Newtonian dynamics. To minimise the effects of tidal heating in this paper we study the velocity dispersion profile of two distant globular clusters, NGC 1851 and NGC 1904. The velocity dispersion profile is derived from accurate radial velocities measurements, obtained at the ESO 8m VLT telescope. Reliable data for 184 and 146 bona fide cluster star members, respectively for NGC 1851 and NGC 1904, were obtained. These data allow to trace the velocity dispersion profile up to ~2r0, where r0 is the radius at which the cluster internal acceleration of gravity is a0 = 10e-8 cm/s/s. It is found that in both clusters the velocity dispersion becomes constant beyond ~r0. These new results are fully in agreement with those found for other five globular clusters previously investigated as part of this project. Taken all together, these 7 clusters support the claim that the velocity dispersion is constant beyond r0, irrespectively of the specific physical properties of the clusters: mass, size, dynamical history, and distance from the Milky Way. The strong similarly with the constant velocity dispersion observed in elliptical galaxies beyond r0 is suggestive of a common origin for this phenomenon in the two class of objects, and might indicate a breakdown of Newtonian dynamics below a0.
A lack of close binaries among hot horizontal branch stars in globular clusters. II. NGC\,2808
C. Moni Bidin,S. Villanova,G. Piotto,Y. Momany
Physics , 2011, DOI: 10.1051/0004-6361/201016232
Abstract: Models based on their binary origin have been very successful in reproducing the properties of field subdwarf-B stars, but the observations of their analogues in globular clusters has posed new problems, while the discovery of multiple populations offered an appealing alternative scenario for the formation of these stars. We search for binaries of period P<200 days among a sample of blue horizontal branch stars (Teff=12000-22000 K) in NGC2808, a cluster known to host three distinct stellar populations and a multimodal horizontal branch. The final sample consists of 64 targets. The radial velocity of the targets was measured in fourteen epochs, spanning a temporal interval of about 75 days. We detect no RV variable object among stars cooler than the photometric G1 gap at 17000 K, while two close (P<10 days) and two intermediate-period (P=10-50 days) systems are found among hotter targets. The close and intermediate-period binary fraction for stars cooler than the gap are fc<5% and fip<10%, respectively, with 95% confidence. The most probable values among hotter stars are fc~20% and fip~30%, but the 90%- confidence level intervals are large (6-42% and 11-72%, respectively). The G1 gap appears as a discontinuity in the binary faction, with a higher incidence of binaries among hotter stars, but a constant increase in f with temperature rather than a discontinuity cannot be excluded from our observations. We find that intermediate-period binaries, never investigated before among cluster HB stars, could play an important role, being more than ~15-20% of the hottest stars of our sample. Our results indicate that fc among hot HB stars is most probably higher for younger clusters, confirming the recently proposed age-fc relation. However, the large observed difference in binary fraction between clusters (e.g. NGC2808 and NGC6752) is still not reproduced by binary population synthesis models.
The cosmological Lithium problem outside the Galaxy: the Sagittarius globular cluster M54
A. Mucciarelli,M. Salaris,P. Bonifacio,L. Monaco,S. Villanova
Physics , 2014, DOI: 10.1093/mnras/stu1522
Abstract: The cosmological Li problem is the observed discrepancy between Li abundance, A(Li), measured in Galactic dwarf, old and metal-poor stars (traditionally assumed to be equal to the initial value A(Li)_0), and that predicted by standard Big Bang Nucleosynthesis calculations (A(Li)_{BBN}). Here we attack the Li problem by considering an alternative diagnostic, namely the surface Li abundance of red giant branch stars that in a colour magnitude diagram populate the region between the completion of the first dredge-up and the red giant branch bump. We obtained high-resolution spectra with the FLAMES facility at the Very Large Telescope for a sample of red giants in the globular cluster M54, belonging to the Sagittarius dwarf galaxy. We obtain A(Li)=+0.93+-0.11 dex, translating -- after taking into account the dilution due to the dredge up-- to initial abundances (A(Li)_0) in the range 2.35--2.29 dex, depending on whether or not atomic diffusion is considered. This is the first measurement of Li in the Sagittarius galaxy and the more distant estimate of A(Li)_0 in old stars obtained so far. The A(Li)_0 estimated in M54 is lower by ~0.35 dex than A(Li)_{BBN}, hence incompatible at a level of ~3sigma. Our result shows that this discrepancy is a universal problem concerning both the Milky Way and extra-galactic systems. Either modifications of BBN calculations, or a combination of atomic diffusion plus a suitably tuned additional mixing during the main sequence, need to be invoked to solve the discrepancy.
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