1,721,042 research outputs found
Disturbi alimentari e neuroscienze: la rappresentazione del corpo
No full textLa società odierna rivolge sempre maggiore attenzione al corpo e alla sua rappresentazione e tale fenomeno viene indubbiamente enfatizzato dalla realtà mediatica dell’immagine nella quale siamo immersi. Ciò rende il corpo un’icona che si impone fortemente su tutte le altre caratteristiche psicologiche e di personalità dell’individuo, spesso con risultati negativi. Non a caso diversi studi hanno messo in luce come le sensazioni negative riguardanti l’inadeguatezza del proprio corpo siano correlate allo sviluppo dei disturbi della nutrizione e dell’alimentazione (Stice, Shaw, 2002), a loro volta associati a problemi fisici e psicologici a lungo termine (Wagner et al., 2006; Mascolo et al., 2012) nonché al più alto tasso di mortalità tra i disturbi psichiatrici (Smink, van Hoeken, Hoek, 2012). È ormai evidente che l’origine e il decorso dei disturbi alimentari (DA) abbiano un’eziologia multifattoriale e che, accanto ai più noti fattori psicologici, evolutivi, biologici e socioculturali, debbano essere presi in considerazione alcuni aspetti più prettamente cognitivi, tra
i quali la rappresentazione del corpo
Abundance gradients along the Galactic disc from chemical evolution models
Full text linkIn this paper, we study the formation and chemical evolution of the Milky Way disc with particular focus on the abundance patterns ([α/Fe] versus [Fe/H]) at different Galactocentric distances, the present-time abundance gradients along the disc, and the time evolution of abundance gradients. We consider the chemical evolution models for the Galactic disc developed by Grisoni et al. for the solar neighbourhood, both the two-infall and the one-infall ones, and we extend our analysis to the other Galactocentric distances. In particular, we examine the processes that mainly influence the formation of the abundance gradients: the inside-out scenario, a variable star formation efficiency, and radial gas flows. We compare our model results with recent abundance patterns obtained along the Galactic disc from the APOGEE survey and with abundance gradients observed from Cepheids, open clusters, H II regions, and PNe. We conclude that the inside-out scenario is a key ingredient but cannot be the only one to explain abundance patterns at different Galactocentric distances and abundance gradients. Further ingredients, such as radial gas flows and variable star formation efficiency, are needed to reproduce the observed features in the thin disc. The evolution of abundance gradients with time is also shown, although firm conclusions cannot still be drawn
Chemical evolution of Al and Fe in the Milky Way
Full text linkWe present theoretical mass estimates of Al and Fe throughout
the Galaxy, performed with a numerical chemical evolution model including
detailed nucleosynthesis prescriptions for stable and radioactive nuclides. We
compared the results for several sets of stellar yields taken from the
literature, for massive, low and intermediate mass stars, nova systems (only
for Al) and supernovae Type Ia.We then computed the total masses of
Al and Fe in the Galaxy. We studied the bulge and the disc of the
Galaxy in a galactocentric radius range 0-22 kpc. We assumed that the bulge
region (within 2 kpc) evolved quickly suffering a strong star formation burst,
while the disc formed more slowly and inside-out. We compared our results with
the Al mass observed by the -ray surveys COMPTEL and INTEGRAL to
select the best model. Concerning Fe, we do not have any observed mass
value so we just performed a theoretical prediction for future observations. In
conclusion, low, intermediate mass stars and Type Ia supernovae contribute
negligibly to the two isotopes, while massive stars are the dominant source.
The nova contribution is, however, necessary to reproduce the observations of
Al. Our best model predicts M of Al, in
agreement with observations, while for Fe our best mass estimate is
M. We also predicted the present injection rate of
Al and Fe in the Galaxy and compared it with previous results,
and we found a larger present time injection rate along the disc.Comment: accepted,10 pages, 6 figure
The effect of stellar migration on Galactic chemical evolution: an heuristic approach
No full textStellar migration in Galactic disks has been the subject of several investigations in the past years. However, its
impact on the chemical evolution of the Milky Way still needs to be fully quantified. In this paper, we aim to
impose some constraints on the significance of this phenomenon by considering its influence on the chemical
evolution of the Milky Way thin disk. We do not investigate the physical mechanisms underlying the migration of
stars. Rather, we introduce a simple, heuristic treatment of stellar migration in a detailed chemical evolution model
for the thin disk of the Milky Way, which already includes radial gas flows and reproduces several observational
constraints for the solar vicinity and the whole Galactic disk. When stellar migration is implemented according to
the results of chemo-dynamical simulations by Minchev et al. and finite stellar velocities of 1 km s−1 are taken into
account, the high-metallicity tail of the metallicity distribution function of long-lived, thin-disk stars is well
reproduced. By exploring the velocity space, we find that the migrating stars must travel with velocities in the
range of 0.5–2 km s−1 to properly reproduce the high-metallicity tail of the metallicity distribution. We confirm
previous findings by other authors that the observed spread in the age–metallicity relation of solar neighborhood
stars can be explained by the presence of stars that originated at different Galactocentric distances, and we
conclude that the chemical properties of stars currently observed in the solar vicinity do suggest that stellar
migration is present to some extent
Chemical evolution of the Milky Way: constraints on the formation of the thick and thin discs
Full text linkWe study the evolution of Milky Way thick and thin discs in the light of the most recent observational data. In particular, we analyse abundance gradients of O, N, Fe, and Mg along the thin disc as well as the [Mg/Fe] versus [Fe/H] relations and the metallicity distribution functions at different Galactocentric distances. We run several models starting from the two-infall paradigm, assuming that the thick and thin discs formed by means of two different infall episodes, and we explore several physical parameters, such as radial gas flows, variable efficiency of star formation, different times for the maximum infall on to the disc, different distributions of the total surface mass density of the thick disc, and enriched gas infall. Our best model suggests that radial gas flows and variable efficiency of star formation should be acting together with the inside-out mechanism for the thin disc formation. The time-scale for maximum infall on to the thin disc, which determines the gap between the formation of the two discs, should be tmax ≃ 3.25 Gyr. The thick disc should have an exponential, small-scale length density profile and gas infall on the inner thin disc should be enriched. We also compute the evolution of Gaia-Enceladus system and study the effects of possible interactions with the thick and thin discs. We conclude that the gas lost by Enceladus or even part of it could have been responsible for the formation of the thick disc but not the thin disc
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Fluorine in the solar neighborhood : Chemical evolution models
Full text linkContext. In light of new observational data related to fluorine abundances in solar neighborhood stars, we present chemical evolution models testing various fluorine nucleosynthesis prescriptions with the aim to best fit those new data. Aim. We consider chemical evolution models in the solar neighborhood testing various nucleosynthesis prescriptions for fluorine production with the aim of reproducing the observed abundance ratios [F/O] versus [O/H] and [F/Fe] versus [Fe/H]. We study in detail the effects of various stellar yields on fluorine production. Methods. We adopted two chemical evolution models: the classical two-infall model, which follows the chemical evolution of halo-thick disk and thin disk phases; and the one-infall model, which is designed only for thin disk evolution. We tested the effects on the predicted fluorine abundance ratios of various nucleosynthesis yield sources, that is, asymptotic giant branch (AGB) stars, Wolf-Rayet (W-R) stars, Type II and Type Ia supernovae, and novae. Results. The fluorine production is dominated by AGB stars but the W-R stars are required to reproduce the trend of the observed data in the solar neighborhood with our chemical evolution models. In particular, the best model both for the two-infall and one-infall cases requires an increase by a factor of 2 of the W-R yields. We also show that the novae, even if their yields are still uncertain, could help to better reproduce the secondary behavior of F in the [F/O] versus [O/H] relation. Conclusions. The inclusion of the fluorine production by W-R stars seems to be essential to reproduce the new observed ratio [F/O] versus [O/H] in the solar neighborhood. Moreover, the inclusion of novae helps to reproduce the observed fluorine secondary behavior substantially
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