149 research outputs found
Microscopic calculation of neutrino mean free path inside hot neutron matter
We calculate the neutrino mean free path and the Equation of State of pure
neutron matter at finite temperature within a selfconsistent scheme based on
the Brueckner--Hartree--Fock approximation. We employ the nucleon-nucleon part
of the recent realistic baryon-baryon interaction (model NSC97e) constructed by
the Nijmegen group. The temperatures considered range from 10 to 80 MeV. We
report on the calculation of the mean field, the residual interaction and the
neutrino mean free path including short and long range correlations given by
the Brueckner--Hartree--Fock plus Random Phase Approximation (BHF+RPA)
framework. This is the first fully consistent calculation in hot neutron matter
dedicated to neutrino mean free path. We compare systematically our results to
those obtain with the D1P Gogny effective interaction, which is independent of
the temperature. The main differences between the present calculation and those
with nuclear effective interactions come from the RPA corrections to BHF (a
factor of about 8) while the temperature lack of consistency accounts for a
factor of about 2
Histone deacetylase inhibitors induce apoptosis in human eosinophils and neutrophils
BACKGROUND: Granulocytes are important in the pathogenesis of several inflammatory diseases. Apoptosis is pivotal in the resolution of inflammation. Apoptosis in malignant cells is induced by histone deacetylase (HDAC) inhibitors, whereas HDAC inhibitors do not usually induce apoptosis in non-malignant cells. The aim of the present study was to explore the effects of HDAC inhibitors on apoptosis in human eosinophils and neutrophils. METHODS: Apoptosis was assessed by relative DNA fragmentation assay, annexin-V binding, and morphologic analysis. HDAC activity in nuclear extracts was measured with a nonisotopic assay. HDAC expression was measured by real-time PCR. RESULTS: A HDAC inhibitor Trichostatin A (TSA) induced apoptosis in the presence of survival-prolonging cytokines interleukin-5 and granulocyte-macrophage colony stimulating factor (GM-CSF) in eosinophils and neutrophils. TSA enhanced constitutive eosinophil and neutrophil apoptosis. Similar effects were seen with a structurally dissimilar HDAC inhibitor apicidin. TSA showed additive effect on the glucocorticoid-induced eosinophil apoptosis, but antagonized glucocorticoid-induced neutrophil survival. Eosinophils and neutrophils expressed all HDACs at the mRNA level except that HDAC5 and HDAC11 mRNA expression was very low in both cell types, HDAC8 mRNA was very low in neutrophils and HDAC9 mRNA low in eosinophils. TSA reduced eosinophil and neutrophil nuclear HDAC activities by ~50-60%, suggesting a non-histone target. However, TSA did not increase the acetylation of a non-histone target NF-κB p65. c-jun-N-terminal kinase and caspases 3 and 6 may be involved in the mechanism of TSA-induced apoptosis, whereas PI3-kinase and caspase 8 are not. CONCLUSIONS: HDAC inhibitors enhance apoptosis in human eosinophils and neutrophils in the absence and presence of survival-prolonging cytokines and glucocorticoids
Can Neutron Star Mergers Alone Explain the r-process Enrichment of the Milky Way?
© 2023. The Author(s). Published by the American Astronomical Society. This is an open access article under the terms of the Creative Commons Attribution License, https://creativecommons.org/licenses/by/4.0/Comparing Galactic chemical evolution models to the observed elemental abundances in the Milky Way, we show that neutron star mergers can be a leading r-process site only if at low metallicities such mergers have very short delay times and significant ejecta masses that are facilitated by the masses of the compact objects. Namely, black hole–neutron star mergers, depending on the black hole spins, can play an important role in the early chemical enrichment of the Milky Way. We also show that none of the binary population synthesis models used in this Letter, i.e., COMPAS, StarTrack, Brussels, ComBinE, and BPASS, can currently reproduce the elemental abundance observations. The predictions are problematic not only for neutron star mergers, but also for Type Ia supernovae, which may point to shortcomings in binary evolution models.Peer reviewe
Magnetically-driven explosions of rapidly-rotating white dwarfs following Accretion-Induced Collapse
We present 2D multi-group flux-limited diffusion magnetohydrodynamics (MHD)
simulations of the Accretion-Induced Collapse (AIC) of a rapidly-rotating white
dwarf. We focus on the dynamical role of MHD processes after the formation of a
millisecond-period protoneutron star. We find that including magnetic fields
and stresses can lead to a powerful explosion with an energy of a few Bethe,
rather than a weak one of at most 0.1 Bethe, with an associated ejecta mass of
~0.1Msun, instead of a few 0.001Msun. The core is spun down by ~30% within
500ms after bounce, and the rotational energy extracted from the core is
channeled into magnetic energy that generates a strong magnetically-driven
wind, rather than a weak neutrino-driven wind. Baryon loading of the ejecta,
while this wind prevails, precludes it from becoming relativistic. This
suggests that a GRB is not expected to emerge from such AICs during the early
protoneutron star phase, except in the unlikely event that the massive white
dwarf has sufficient mass to lead to black hole formation. In addition, we
predict both negligible 56Ni-production (that should result in an
optically-dark, adiabatically-cooled explosion) and the ejection of 0.1Msun of
material with an electron fraction of 0.1-0.2. Such pollution by neutron-rich
nuclei puts strong constraints on the possible rate of such AICs. Moreover,
being free from ``fallback,'' such highly-magnetized millisecond-period
protoneutron stars may later become magnetars, and the magnetically-driven
winds may later transition to Poynting-flux-dominated, relativistic winds,
eventually detectable as GRBs at cosmological distances. However, the low
expected event rate of AICs will constrain them to be, at best, a small subset
of GRB and/or magnetar progenitors.Comment: 16 pages, 8 figures, paper accepted to ApJ; High resolution version
available at http://hermes.as.arizona.edu/~luc/aic_mhd/aic_mhd.htm
Transport of Magnetic Fields in Convective, Accreting Supernova Cores
We consider the amplification and transport of a magnetic field in the
collapsed core of a massive star, including both the region between the
neutrinosphere and the shock, and the central, opaque core. An analytical
argument explains why rapid convective overturns persist within a newly formed
neutron star for roughly 10 seconds ( overturns), consistent with
recent numerical models. A dynamical balance between turbulent and magnetic
stresses within this convective layer corresponds to flux densities in excess
of G. Material accreting onto the core is heated by neutrinos and also
becomes strongly convective. We compare the expected magnetic stresses in this
convective `gain layer' with those deep inside the neutron core.
Buoyant motions of magnetized fluid are greatly aided by the intense neutrino
flux. We calculate the transport rate through a medium containing free neutrons
protons, and electrons, in the limiting cases of degenerate or non-degenerate
nucleons. Fields stronger than G are able to rise through the
outer degenerate layers of the neutron core during the last stages of
Kelvin-Helmholtz cooling (up to 10 seconds post-collapse), even though these
layers have become stable to convection. We also find the equilibrium shape of
a thin magnetic flux rope in the dense hydrostatic atmosphere of the neutron
star, along with the critical separation of the footpoints above which the rope
undergoes unlimited expansion against gravity. The implications of these
results for pulsar magnetism are summarized, and applied to the case of late
fallback over the first 1,000-10,000 s of the life of a neutron starComment: 45 pages, 3 figures, Astrophysical Journal, in pres
The influence of collective neutrino oscillations on a supernova r-process
Recently, it has been demonstrated that neutrinos in a supernova oscillate
collectively. This process occurs much deeper than the conventional
matter-induced MSW effect and hence may have an impact on nucleosynthesis. In
this paper we explore the effects of collective neutrino oscillations on the
r-process, using representative late-time neutrino spectra and outflow models.
We find that accurate modeling of the collective oscillations is essential for
this analysis. As an illustration, the often-used "single-angle" approximation
makes grossly inaccurate predictions for the yields in our setup. With the
proper multiangle treatment, the effect of the oscillations is found to be less
dramatic, but still significant. Since the oscillation patterns are sensitive
to the details of the emitted fluxes and the sign of the neutrino mass
hierarchy, so are the r-process yields. The magnitude of the effect also
depends sensitively on the astrophysical conditions - in particular on the
interplay between the time when nuclei begin to exist in significant numbers
and the time when the collective oscillation begins. A more definitive
understanding of the astrophysical conditions, and accurate modeling of the
collective oscillations for those conditions, is necessary.Comment: 27 pages, 10 figure
Gravitational Wave Extraction in Simulations of Rotating Stellar Core Collapse
We perform simulations of general relativistic rotating stellar core collapse
and compute the gravitational waves (GWs) emitted in the core bounce phase of
three representative models via multiple techniques. The simplest technique,
the quadrupole formula (QF), estimates the GW content in the spacetime from the
mass quadrupole tensor. It is strictly valid only in the weak-field and
slow-motion approximation. For the first time, we apply GW extraction methods
in core collapse that are fully curvature-based and valid for strongly
radiating and highly relativistic sources. We employ three extraction methods
computing (i) the Newman-Penrose (NP) scalar Psi_4, (ii)
Regge-Wheeler-Zerilli-Moncrief (RWZM) master functions, and (iii)
Cauchy-Characteristic Extraction (CCE) allowing for the extraction of GWs at
future null infinity, where the spacetime is asymptotically flat and the GW
content is unambiguously defined. The latter technique is the only one not
suffering from residual gauge and finite-radius effects. All curvature-based
methods suffer from strong non-linear drifts. We employ the fixed-frequency
integration technique as a high-pass waveform filter. Using the CCE results as
a benchmark, we find that finite-radius NP extraction yields results that agree
nearly perfectly in phase, but differ in amplitude by ~1-7% at core bounce,
depending on the model. RWZM waveforms, while in general agreeing in phase,
contain spurious high-frequency noise of comparable amplitudes to those of the
relatively weak GWs emitted in core collapse. We also find remarkably good
agreement of the waveforms obtained from the QF with those obtained from CCE.
They agree very well in phase but systematically underpredict peak amplitudes
by ~5-11% which is comparable to the NP results and is within the uncertainties
associated with core collapse physics. (abridged)Comment: 26 pages, 10 figures, 5 tables, matches published versio
The Physics of Core-Collapse Supernovae
Supernovae are nature's grandest explosions and an astrophysical laboratory
in which unique conditions exist that are not achievable on Earth. They are
also the furnaces in which most of the elements heavier than carbon have been
forged. Scientists have argued for decades about the physical mechanism
responsible for these explosions. It is clear that the ultimate energy source
is gravity, but the relative roles of neutrinos, fluid instabilities, rotation
and magnetic fields continue to be debated.Comment: Review article; 17 pages, 5 figure
Massive stars as thermonuclear reactors and their explosions following core collapse
Nuclear reactions transform atomic nuclei inside stars. This is the process
of stellar nucleosynthesis. The basic concepts of determining nuclear reaction
rates inside stars are reviewed. How stars manage to burn their fuel so slowly
most of the time are also considered. Stellar thermonuclear reactions involving
protons in hydrostatic burning are discussed first. Then I discuss triple alpha
reactions in the helium burning stage. Carbon and oxygen survive in red giant
stars because of the nuclear structure of oxygen and neon. Further nuclear
burning of carbon, neon, oxygen and silicon in quiescent conditions are
discussed next. In the subsequent core-collapse phase, neutronization due to
electron capture from the top of the Fermi sea in a degenerate core takes
place. The expected signal of neutrinos from a nearby supernova is calculated.
The supernova often explodes inside a dense circumstellar medium, which is
established due to the progenitor star losing its outermost envelope in a
stellar wind or mass transfer in a binary system. The nature of the
circumstellar medium and the ejecta of the supernova and their dynamics are
revealed by observations in the optical, IR, radio, and X-ray bands, and I
discuss some of these observations and their interpretations.Comment: To be published in " Principles and Perspectives in Cosmochemistry"
Lecture Notes on Kodai School on Synthesis of Elements in Stars; ed. by Aruna
Goswami & Eswar Reddy, Springer Verlag, 2009. Contains 21 figure
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