1,721,418 research outputs found
Impact of AGB Stars on the Chemical Evolution of Neutron-Capture Elements
Full text linkIn this review, we discuss the impact of s-process nucleosynthesis in asymptotic giant branch stars on the enrichment of heavy elements. We review the main steps made on this subject in the last 40 years and discuss the importance of modelling the evolution of the abundances of such elements in our Milky Way. From the comparison between model results and observations, we can impose strong constraints on stellar nucleosynthesis, as well as on the evolution of the Milky Way
Importance of pet with 68ga-labeled somatostatin analogs
No full textNeuroendocrine tumors (NETs) still represent a diagnostic challenge because their clinical presentation is often nonspecific and usually occurs late in the disease, when metastases are already present
Zirconium titanate ceramic pigments: Crystal structure, optical spectroscopy and technological properties
Full text linkSrilankite-type zirconium titanate, a promising structure for ceramic pigments, was synthesized at 1400 degrees C following three main doping strategies: (a) ZrTi(1-x)A(x)O(4), (b) ZrTi(1-x-y)A(x)B(y)O(4) and (c) Zr1-xCTiO4 where A = Co, Cr, Fe, Mn. Ni or V (chromophores), B = Sb or W (counterions) and C = Pr (chromophore); x = y = 0.05. Powders were characterized by XRD with Rietveld refinements and DRS in the UV-visible-NIR range; technological properties were appraised in several ceramic matrices (frits, glazes and body). Zirconium titanate can be usefully coloured with first row transition elements, giving green and greenish yellow (Co and Ni); orange-buff (Cr and V); tan-brown hues (Mn and Fe). In industrial-like synthesis conditions, a disordered structure as (Zr,Ti)O-2, with both Zr and Ti randomly distributed in the octahedral site, is achieved. Doping with chromophores and counterions induces unit cell dimensions variation and causes an oversaturation in zirconium oxide. Optical spectroscopy reveals the occurrence of Co2+, Cr3+, Fe3+, Mn2+, Mn3+, Ni2+, V3+ and V4+. The zirconium titanate pigments fulfil current technological requirements for low-temperature applications, but exhibit a limited chemico-physical stability for higher firing temperature and in chemically aggressive media
On the delay times of merging double neutron stars
Full text linkThe merging rate of double neutron stars (DNS) has a great impact on many astrophysical issues, including the interpretation of gravitational waves signals, of the short gamma-ray bursts (GRBs), and of the chemical properties of stars in galaxies. Such rate depends on the distribution of the delay times (DDT) of the merging events. In this paper, we derive a theoretical DDT of merging DNS following from the characteristics of the clock controlling their evolution. We show that the shape of the DDT is governed by a few key parameters, primarily the lower limit and the slope of the distribution of the separation of the DNS systems at birth. With a parametric approach, we investigate on the observational constraints on the DDT from the cosmic rate of short GRBs and the europium-to-iron ratio in Milky Way stars, taken as tracer of the products of the explosion. We find that the local rate of DNS merging requires that ∼ per cent of neutron stars progenitors live in binary systems which end their evolution as merging DNS within a Hubble time. The redshift distribution of short GRBs does not yet provide a strong constraint on the shape of the DDT, although the best-fitting models have a shallow DDT. The chemical pattern in Milky Way stars requires an additional source of europium besides the products from merging DNS, which weakens the related requirement on the DDT. At present both constraints can be matched with the same DDT for merging DNS
The Chemical Evolution in the Solar Vicinity and the Nucleosynthesis of Neutron Capture Elements
No full textAbundance 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 models for local group dwarf spheroidal galaxies: the evolution of Fe-peak elements
No full textIdentificazione delle popolazioni del gr. Ranunculus ficaria L. nei Monti della Tolfa (Lazio)
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