2,279 research outputs found
s-Process Nucleosynthesis in Advanced Burning Phases of Massive Stars
We present a detailed study of s-process nucleosynthesis in massive stars of
solar-like initial composition and masses 15, 20,25, and 30 Msun. We update our
previous results of s-process nucleosynthesis during the core He-burning of
these stars and then focus on an analysis of the s-process under the physical
conditions encountered during the shell-carbon burning. We show that the recent
compilation of the Ne22(alpha,n)Mg25 rate leads to a remarkable reduction of
the efficiency of the s-process during core He-burning. In particular, this
rate leads to the lowest overproduction factor of Kr80 found to date during
core He-burning in massive stars. The s-process yields resulting from shell
carbon burning turn out to be very sensitive to the structural evolution of the
carbon shell. This structure is influenced by the mass fraction of C12 attained
at the end of core helium burning, which in turn is mainly determined by the
C12(alpha,gamma)O16 reaction. The still present uncertainty in the rate for
this reaction implies that the s-process in massive stars is also subject to
this uncertainty. We identify some isotopes like Zn70 and Rb87 as the
signatures of the s-process during shell carbon burning in massive stars. In
determining the relative contribution of our s-only stellar yields to the solar
abundances, we find it is important to take into account the neutron exposure
of shell carbon burning. When we analyze our yields with a Salpeter Initial
Mass Function, we find that massive stars contribute at least 40% to s-only
nuclei with mass A 90, massive stars
contribute on average ~7%, except for Gd152, Os187, and Hg198 which are ~14%,
\~13%, and ~11%, respectively.Comment: 52 pages, 16 figures, accepted for publication in Ap
Equation of state for -stable hot nuclear matter
We provide an equation of state for hot nuclear matter in -equilibrium
by applying a momentum-dependent effective interaction. We focus on the study
of the equation of state of high-density and high-temperature nuclear matter,
containing leptons (electrons and muons) under the chemical equilibrium
condition in which neutrinos have left the system. The conditions of charge
neutrality and equilibrium under -decay process lead first to the
evaluation of proton and lepton fractions and afterwards of internal energy,
free energy, pressure and in total to the equation of state of hot nuclear
matter. Thermal effects on the properties and equation of state of nuclear
matter are assesed and analyzed in the framework of the proposed effective
interaction model. Special attention is dedicated to the study of the
contribution of the components of -stable nuclear matter to the entropy
per particle, a quantity of great interest for the study of structure and
collapse of supernova.Comment: 28 pages, 18 figure
The Molecular Hydrogen Deficit in Gamma-Ray Burst Afterglows
Recent analysis of five gamma-ray burst (GRB) afterglow spectra reveal the
absence of molecular hydrogen absorption lines, a surprising result in light of
their large neutral hydrogen column densities and the detection of H in
similar, more local star-forming regions like 30 Doradus in the Large
Magellanic Cloud (LMC). Observational evidence further indicates that the bulk
of the neutral hydrogen column in these sight lines lies 100 pc beyond the
progenitor and that H was absent prior to the burst, suggesting that direct
flux from the star, FUV background fields, or both suppressed its formation. We
present one-dimensional radiation hydrodynamical models of GRB host galaxy
environments, including self-consistent radiative transfer of both ionizing and
Lyman-Werner photons, nine-species primordial chemistry with dust formation of
H, and dust extinction of UV photons. We find that a single GRB progenitor
is sufficient to ionize neutral hydrogen to distances of 50 - 100 pc but that a
galactic Lyman-Werner background is required to dissociate the molecular
hydrogen in the ambient ISM. Intensities of 0.1 - 100 times the Galactic mean
are necessary to destroy H in the cloud, depending on its density and
metallicity. The minimum radii at which neutral hydrogen will be found in
afterglow spectra is insensitive to the mass of the progenitor or the initial
mass function (IMF) of its cluster, if present.Comment: 12 pages, 7 figures, accepted for Ap
Evolution of Massive Stars Up to the End of Central Oxygen Burning
We present a detailed study of the evolution of massive stars of masses 15,
20, 25 and 30 \msun assuming solar-like initial chemical composition. The
stellar sequences were evolved through the advanced burning phases up to the
end of core oxygen burning. We present a careful analysis of the physical
characteristics of the stellar models. In particular, we investigate the effect
of the still unsettled reaction C(,)O on the
advanced evolution by using recent compilations of this rate. We find that this
rate has a significant impact on the evolution not only during the core helium
burning phase, but also during the late burning phases, especially the shell
carbon-burning. We have also considered the effect of different treatment of
convective instability based on the Ledoux criterion in regions of varying
molecular weight gradient during the hydrogen and helium burning phases. We
compare our results with other investigations whenever available. Finally, our
present study constitutes the basis of analyzing the nucleosynthesis processes
in massive stars. In particular we will present a detail analysis of the {\it
s}-process in a forthcoming paper.Comment: 46 pages, 15 figures. To be published in ApJ vol 611, August 10, 200
Equation of state for dense supernova matter
We provide an equation of state for high density supernova matter by applying
a momentum-dependent effective interaction. We focus on the study of the
equation of state of high-density and high-temperature nuclear matter
containing leptons (electrons and neutrinos) under the chemical equilibrium
condition. The conditions of charge neutrality and equilibrium under
-decay process lead first to the evaluation of the lepton fractions and
afterwards the evaluation of internal energy, pressure, entropy and in total to
the equation of state of hot nuclear matter for various isothermal cases.
Thermal effects on the properties and equation of state of nuclear matter are
evaluated and analyzed in the framework of the proposed effective interaction
model. Since supernova matter is characterized by a constant entropy we also
present the thermodynamic properties for isentropic case. Special attention is
dedicated to the study of the contribution of the components of -stable
nuclear matter to the entropy per particle, a quantity of great interest for
the study of structure and collapse of supernova.Comment: 23 pages, 15 figure
Successfully treated necrotizing fasciitis using extracorporeal life support combined with hemoadsorption device and continuous renal replacement therapy
INTRODUCTION: Necrotizing fasciitis represents a life-threatening infectious condition that causes spreading necrotisis of superficial fascia and subcutaneous cellular tissues. We describe the case of a patient diagnosed with septic and toxic shocks leading to multiple organ failure successfully treated with a combination of extracorporeal life support, continuous renal replacement therapy, and a hemoadsorption device.
METHODS: A 41-year-old patient presented with necrotizing fasciitis and multi-organ failure. Initial extracorporeal life support therapy was implanted, compensating for systolic failure. Due to acute renal failure that persisted in time, continuous renal replacement therapy was added. Despite these treatments and as a last attempt to control the septic condition, a CytoSorb hemoadsorption device was installed in parallel to the extracorporeal life support circuit and two sessions were run.
RESULTS: During the days following CytoSorb treatment, hemodynamic stabilization was observed, as well as normalization of lactic acidosis and blood parameters.
CONCLUSION: This case describes the successful use of CytoSorb with continuous renal replacement therapy and extracorporeal life support in a combined way to overcome a critical phase of septic shock in a young adult patient. This combination of treatments turned out to be efficient for this patient in the context of necrotizing fasciitis
Stellar Nucleosynthesis in the Hyades Open Cluster
We report a comprehensive light element (Li, C, N, O, Na, Mg, and Al)
abundance analysis of three solar-type main sequence (MS) dwarfs and three red
giant branch (RGB) clump stars in the Hyades open cluster using high-resolution
and high signal-to-noise spectroscopy. For each group (MS or RGB), the CNO
abundances are found to be in excellent star-to-star agreement. Our results
confirm that the giants have undergone the first dredge-up and that material
processed by the CN cycle has been mixed to the surface layers. The observed
abundances are compared to predictions of a standard stellar model based on the
Clemson-American University of Beirut (CAUB) stellar evolution code. The model
reproduces the observed evolution of the N and O abundances, as well as the
previously derived 12C/13C ratio, but it fails to predict by a factor of 1.5
the observed level of 12C depletion. Li abundances are derived to determine if
non-canonical extra mixing has occurred in the Hyades giants. The Li abundance
of the giant gamma Tau is in good accord with the predicted level of surface Li
dilution, but a ~0.35 dex spread in the giant Li abundances is found and cannot
be explained by the stellar model. Possible sources of the spread are
discussed; however, it is apparent that the differential mechanism responsible
for the Li dispersion must be unrelated to the uniformly low 12C abundances of
the giants. Na, Mg, and Al abundances are derived as an additional test of our
stellar model. All three elements are found to be overabundant by 0.2-0.5 dex
in the giants relative to the dwarfs. Such large enhancements of these elements
are not predicted by the stellar model, and non-LTE effects significantly
larger (and, in some cases, of opposite sign) than those implied by extant
literature calculations are the most likely cause.Comment: 40 pages, 6 figures, 6 tables; accepted by Ap
Simultaneous infection of Ixodes ricinus nymphs by two Borrelia burgdorferi sensu lato species: possible implications for clinical manifestations.
info:eu-repo/semantics/publishe
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