95 research outputs found
Explosion mechanism of core-collapse supernovae: role of the Si/O interface
We present a simple criterion to predict the explodability of massive stars
based on the density and entropy profiles before collapse. If a pronounced
density jump is present near the Si/Si-O interface, the star will likely
explode. We develop a quantitative criterion by using 1D
simulations where -driven turbulence is included via time-dependent
mixing-length theory. This criterion correctly identifies the outcome of the
supernova more than of the time. We also find no difference in how this
criterion performs on two different sets of progenitors, evolved using two
different stellar evolution codes: FRANEC and KEPLER. The explodability as a
function of mass of the two sets of progenitors is very different, showing: (i)
that uncertainties in the stellar evolution prescriptions influence the
predictions of supernova explosions; (ii) the most important properties of the
pre-collapse progenitor that influence the explodability are its density and
entropy profiles. We highlight the importance that -driven turbulence
plays in the explosion by comparing our results to previous works.Comment: 20 pages, 12 figures, submitted to Ap
On the origin of the Galactic thin and thick discs, their abundance gradients and the diagnostic potential of their abundance ratios
Using a semi-analytical model of the evolution of the Milky Way, we show how
secular evolution can create distinct overdensities in the phase space of
various properties (e.g. age vs metallicity or abundance ratios vs age)
corresponding to the thin and thick discs. In particular, we show how key
properties of the Solar vicinity can be obtained by secular evolution, with no
need for external or special events, like galaxy mergers or paucity in star
formation. This concerns the long established double-branch behaviour of
[alpha/Fe] vs metallicity and the recently found non-monotonic evolution of the
stellar abundance gradient, evaluated at the birth radii of stars. We extend
the discussion to other abundance ratios and we suggest a classification
scheme, based on the nature of the corresponding yields (primary vs secondary
or odd elements) and on the lifetimes of their sources (short-lived vs
long-lived ones). The latter property is critical in determining the single- or
double- branch behavior of an elementary abundance ratio in the Solar
neighborhood. We underline the high diagnostic potential of this finding, which
can help to separate clearly elements with sources evolving on different
timescales and help determining the site of e.g. the r-process(es). We define
the "abundance distance" between the thin and thick disc sequences as an
important element for such a separation. We also show how the inside-out
evolution of the Milky Way disc leads rather to a single-branch behavior in
other disc regions.Comment: 20 pages, 16 figures, to appear in MNRA
Social cognition in people with schizophrenia: A cluster-analytic approach
Background The study aimed to subtype patients with schizophrenia on the basis of social cognition (SC), and to identify cut-offs that best discriminate among subtypes in 809 out-patients recruited in the context of the Italian Network for Research on Psychoses. Method A two-step cluster analysis of The Awareness of Social Inference Test (TASIT), the Facial Emotion Identification Test and Mayer-Salovey-Caruso Emotional Intelligence Test scores was performed. Classification and regression tree analysis was used to identify the cut-offs of variables that best discriminated among clusters. Results We identified three clusters, characterized by unimpaired (42%), impaired (50.4%) and very impaired (7.5%) SC. Three theory-of-mind domains were more important for the cluster definition as compared with emotion perception and emotional intelligence. Patients more able to understand simple sarcasm (14 for TASIT-SS) were very likely to belong to the unimpaired SC cluster. Compared with patients in the impaired SC cluster, those in the very impaired SC cluster performed significantly worse in lie scenes (TASIT-LI <10), but not in simple sarcasm. Moreover, functioning, neurocognition, disorganization and SC had a linear relationship across the three clusters, while positive symptoms were significantly lower in patients with unimpaired SC as compared with patients with impaired and very impaired SC. On the other hand, negative symptoms were highest in patients with impaired levels of SC. Conclusions If replicated, the identification of such subtypes in clinical practice may help in tailoring rehabilitation efforts to the person's strengths to gain more benefit to the person
Social cognition in people with schizophrenia: A cluster-analytic approach
Background The study aimed to subtype patients with schizophrenia on the basis of social cognition (SC), and to identify cut-offs that best discriminate among subtypes in 809 out-patients recruited in the context of the Italian Network for Research on Psychoses. Method A two-step cluster analysis of The Awareness of Social Inference Test (TASIT), the Facial Emotion Identification Test and Mayer-Salovey-Caruso Emotional Intelligence Test scores was performed. Classification and regression tree analysis was used to identify the cut-offs of variables that best discriminated among clusters. Results We identified three clusters, characterized by unimpaired (42%), impaired (50.4%) and very impaired (7.5%) SC. Three theory-of-mind domains were more important for the cluster definition as compared with emotion perception and emotional intelligence. Patients more able to understand simple sarcasm (14 for TASIT-SS) were very likely to belong to the unimpaired SC cluster. Compared with patients in the impaired SC cluster, those in the very impaired SC cluster performed significantly worse in lie scenes (TASIT-LI <10), but not in simple sarcasm. Moreover, functioning, neurocognition, disorganization and SC had a linear relationship across the three clusters, while positive symptoms were significantly lower in patients with unimpaired SC as compared with patients with impaired and very impaired SC. On the other hand, negative symptoms were highest in patients with impaired levels of SC. Conclusions If replicated, the identification of such subtypes in clinical practice may help in tailoring rehabilitation efforts to the person's strengths to gain more benefit to the person
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