59 research outputs found
Effect of collective neutrino flavor oscillations on vp-process nucleosynthesis
The vp process is a primary nucleosynthesis process which occurs in core
collapse supernovae. An essential role in this process is being played by
electron antineutrinos. They generate, by absorption on protons, a supply of
neutrons which, by (n,p) reactions, allow to overcome waiting point nuclei with
rather long beta-decay and proton-capture lifetimes. The synthesis of heavy
elements by the vp process depends sensitively on the \bar{\nu}_e luminosity
and spectrum. As has been shown recently, the latter are affected by collective
neutrino flavor oscillations which can swap the \bar{\nu}_e and
\bar{\nu}_{\mu,\tau} spectra above a certain split energy. Assuming such a swap
scenario, we have studied the impact of collective neutrino flavor oscillations
on the vp-process nucleosynthesis. Our results show that the production of
light p-nuclei up to mass number A=108 is very sensitive to collective neutrino
oscillations.Comment: 4 pages, 3 figures, submitted to Physics Letters
r-Process Nucleosynthesis in Hot Accretion Disk Flows from Black Hole - Neutron Star Mergers
We consider hot accretion disk outflows from black hole - neutron star
mergers in the context of the nucleosynthesis they produce. We begin with a
three dimensional numerical model of a black hole - neutron star merger and
calculate the neutrino and antineutrino fluxes emitted from the resulting
accretion disk. We then follow the element synthesis in material outflowing the
disk along parameterized trajectories. We find that at least a weak r-process
is produced, and in some cases a main r-process as well. The neutron-rich
conditions required for this production of r-process nuclei stem directly from
the interactions of the neutrinos emitted by the disk with the free neutrons
and protons in the outflow.Comment: 10 pages, 4 figures, one table and additional references adde
The consequences of nuclear electron capture in core collapse supernovae
The most important weak nuclear interaction to the dynamics of stellar core
collapse is electron capture, primarily on nuclei with masses larger than 60.
In prior simulations of core collapse, electron capture on these nuclei has
been treated in a highly parameterized fashion, if not ignored. With realistic
treatment of electron capture on heavy nuclei come significant changes in the
hydrodynamics of core collapse and bounce. We discuss these as well as the
ramifications for the post-bounce evolution in core collapse supernovae.Comment: Accepted by PRL, 5 pages, 2 figure
Can a Large Neutron Excess Help Solve the Baryon Loading Problem in Gamma-Ray Burst Fireballs?
We point out that the baryon-loading problem in Gamma-Ray Burst (GRB) models
can be amelioriated if a significant fraction of the baryons which inertially
confine the fireball are converted to neutrons. A high neutron fraction in some
circumstances can result in a reduced transfer of energy from relativistic
light particles in the fireball to baryons. The energy needed to produce the
required relativistic flow in the GRB is consequently reduced, in some cases by
orders of magnitude. This could be relevant to GRB models because a high
neutron-to-proton ratio has been calculated in neutron star-merger fireball
environments. Significant neutron excess also could occur near compact objects
with high neutrino fluxes.Comment: 5 pages, 2 figures, to appear in Phys. Rev. Let
A New Connection between Central Engine Weak Physics and the Dynamics of Gamma-Ray Burst Fireballs
We demonstrate a qualitatively new aspect of the dynamics of Gamma-Ray Burst
(GRB) fireballs: the development of a substantial dispersion in the proton
component in fireballs in which neutron decoupling occurs and is sufficiently
pronounced. This effect depends sensitively on the neutron to proton ratio in
the fireball, becoming more dramatic with increasing neutron excess. Simple
physical arguments and transport calculations indicate that the dispersion in
Lorentz factor of the protons can be of order the final mean Lorentz factor of
the fireball. We show how plasma instabilities could play an important role in
the evolution of the fireball and how they might ultimately govern the
development of such a velocity dispersion in the proton component. The role of
these instabilities in setting/diminishing a proton Lorentz factor dispersion
represents a new and potentially important venue for the study of plasma
instabilities. Significant dispersion in the proton velocities translates into
fewer protons attaining the highest Lorentz factors. This is tantamount to a
reduction in the total energy required to attain a given Lorentz factor for the
highest energy protons. As well, a proton component dispersion can have
consequences for the electromagnetic and neutrino signature of GRBs.Comment: Added discussion of plasma instabilities and the requirement of
charge neutrality. 6 pages, 4 figure
Neutrino-driven wind simulations and nucleosynthesis of heavy elements
Neutrino-driven winds, which follow core-collapse supernova explosions,
present a fascinating nuclear astrophysics problem that requires understanding
advanced astrophysics simulations, the properties of matter and neutrino
interactions under extreme conditions, the structure and reactions of exotic
nuclei, and comparisons against forefront astronomical observations. The
neutrino-driven wind has attracted vast attention over the last 20 years as it
was suggested to be a candidate for the astrophysics site where half of the
heavy elements are produced via the r-process. In this review, we summarize our
present understanding of neutrino-driven winds from the dynamical and
nucleosynthesis perspectives. Rapid progress has been made during recent years
in understanding the wind with improved simulations and better micro physics.
The current status of the fields is that hydrodynamical simulations do not
reach the extreme conditions necessary for the r-process and the proton or
neutron richness of the wind remains to be investigated in more detail.
However, nucleosynthesis studies and observations point already to
neutrino-driven winds to explain the origin of lighter heavy elements, such as
Sr, Y, Zr.Comment: Submitted to: J. Phys. G: Nucl. Phy
Explosive Nucleosynthesis: What we learned and what we still do not understand
This review touches on historical aspects, going back to the early days of
nuclear astrophysics, initiated by BFH and Cameron, discusses (i) the
required nuclear input from reaction rates and decay properties up to the
nuclear equation of state, continues (ii) with the tools to perform
nucleosynthesis calculations and (iii) early parametrized nucleosynthesis
studies, before (iv) reliable stellar models became available for the late
stages of stellar evolution. It passes then through (v) explosive environments
from core-collapse supernovae to explosive events in binary systems (including
type Ia supernovae and compact binary mergers), and finally (vi) discusses the
role of all these nucleosynthesis production sites in the evolution of
galaxies. The focus is put on the comparison of early ideas and present, very
recent, understanding.Comment: 11 pages, to appear in Springer Proceedings in Physics (Proc. of
Intl. Conf. "Nuclei in the Cosmos XV", LNGS Assergi, Italy, June 2018
Gravitating discs around black holes
Fluid discs and tori around black holes are discussed within different
approaches and with the emphasis on the role of disc gravity. First reviewed
are the prospects of investigating the gravitational field of a black
hole--disc system by analytical solutions of stationary, axially symmetric
Einstein's equations. Then, more detailed considerations are focused to middle
and outer parts of extended disc-like configurations where relativistic effects
are small and the Newtonian description is adequate.
Within general relativity, only a static case has been analysed in detail.
Results are often very inspiring, however, simplifying assumptions must be
imposed: ad hoc profiles of the disc density are commonly assumed and the
effects of frame-dragging and completely lacking. Astrophysical discs (e.g.
accretion discs in active galactic nuclei) typically extend far beyond the
relativistic domain and are fairly diluted. However, self-gravity is still
essential for their structure and evolution, as well as for their radiation
emission and the impact on the environment around. For example, a nuclear star
cluster in a galactic centre may bear various imprints of mutual star--disc
interactions, which can be recognised in observational properties, such as the
relation between the central mass and stellar velocity dispersion.Comment: Accepted for publication in CQG; high-resolution figures will be
available from http://www.iop.org/EJ/journal/CQ
Role of Core-collapse Supernovae in Explaining Solar System Abundances of p Nuclides
This is an author-created, un-copyedited version of an article accepted for published in The Astrophysical Journal. The Version of Record is available online at: https://doi.org/10.3847/1538-4357/aaa4f7The production of the heavy stable proton-rich isotopes between 74Se and 196Hg - the p nuclides - is due to the contribution from different nucleosynthesis processes, activated in different types of stars. Whereas these processes have been subject to various studies, their relative contributions to Galactic chemical evolution (GCE) are still a matter of debate. Here we investigate for the first time the nucleosynthesis of p nuclides in GCE by including metallicity and progenitor mass-dependent yields of core-collapse supernovae (ccSNe) into a chemical evolution model. We used a grid of metallicities and progenitor masses from two different sets of stellar yields and followed the contribution of ccSNe to the Galactic abundances as a function of time. In combination with previous studies on p-nucleus production in thermonuclear supernovae (SNIa), and using the same GCE description, this allows us to compare the respective roles of SNeIa and ccSNe in the production of p-nuclei in the Galaxy. The γ process in ccSN is very efficient for a wide range of progenitor masses (13 M o-25 M o) at solar metallicity. Since it is a secondary process with its efficiency depending on the initial abundance of heavy elements, its contribution is strongly reduced below solar metallicity. This makes it challenging to explain the inventory of the p nuclides in the solar system by the contribution from ccSNe alone. In particular, we find that ccSNe contribute less than 10% of the solar p nuclide abundances, with only a few exceptions. Due to the uncertain contribution from other nucleosynthesis sites in ccSNe, such as neutrino winds or α-rich freeze out, we conclude that the light p-nuclides 74Se, 78Kr, 84Sr, and 92Mo may either still be completely or only partially produced in ccSNe. The γ-process accounts for up to twice the relative solar abundances for 74Se in one set of stellar models and 196Hg in the other set. The solar abundance of the heaviest p nucleus 196Hg is reproduced within uncertainties in one set of our models due to photodisintegration of the Pb isotopes 208,207,206Pb. For all other p nuclides, abundances as low as 2% of the solar level were obtained.Peer reviewe
Management of upper airway edema caused by hereditary angioedema
Hereditary angioedema is a rare disorder with a genetic background involving mutations in the genes encoding C1-INH and of factor XII. Its etiology is unknown in a proportion of cases. Recurrent edema formation may involve the subcutis and the submucosa - the latter can produce obstruction in the upper airways and thereby lead to life-threatening asphyxia. This is the reason for the high, 30-to 50-per-cent mortality of undiagnosed or improperly managed cases. Airway obstruction can be prevented through early diagnosis, meaningful patient information, timely recognition of initial symptoms, state-of-the-art emergency therapy, and close monitoring of the patient. Prophylaxis can substantially mitigate the risk of upper airway edema and also improve the patients' quality of life. Notwithstanding the foregoing, any form of upper airway edema should be regarded as a potentially life-threatening condition. None of the currently available prophylactic modalities is capable of preventing UAE with absolute certainty
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