10 research outputs found
Reply to 'Comment on 'Heavy element production in inhomogeneous big bang nucleosynthesis''
This is a reply report to astro-ph/0604264. We studied heavy element
production in high baryon density region in early universe astro-ph/0507439.
However it is claimed in astro-ph/0604264 that small scale but high baryon
density region contradicts observations for the light element abundance or in
order not to contradict to observations high density region must be so small
that it cannot affect the present heavy element abundance.
In this paper we study big bang nucleosynthesis in high baryon density region
and show that in certain parameter spaces it is possible to produce enough
amount of heavy element without contradiction to CMB and light element
observations.Comment: 7 pages, 4 figures, References added, one more reference adde
Magnetohydrodynamic Simulations of A Rotating Massive Star Collapsing to A Black Hole
We perform two-dimensional, axisymmetric, magnetohydrodynamic simulations of
the collapse of a rotating star of 40 Msun and in the light of the collapsar
model of gamma-ray burst. Considering two distributions of angular momentum, up
to \sim 10^{17} cm^2/s, and the uniform vertical magnetic field, we investigate
the formation of an accretion disk around a black hole and the jet production
near the hole. After material reaches to the black hole with the high angular
momentum, the disk is formed inside a surface of weak shock. The disk becomes
in a quasi-steady state for stars whose magnetic field is less than 10^{10} G
before the collapse. We find that the jet can be driven by the magnetic fields
even if the central core does not rotate as rapidly as previously assumed and
outer layers of the star has sufficiently high angular momentum. The magnetic
fields are chiefly amplified inside the disk due to the compression and the
wrapping of the field. The fields inside the disk propagate to the polar region
along the inner boundary near the black hole through the Alfv{\'e}n wave, and
eventually drive the jet. The quasi-steady disk is not an advection-dominated
disk but a neutrino cooling-dominated one. Mass accretion rates in the disks
are greater than 0.01 Msun/sec with large fluctuations. The disk is transparent
for neutrinos. The dense part of the disk, which locates near the hole, emits
neutrino efficiently at a constant rate of < 8 \times 10^{51} erg/s. The
neutrino luminosity is much smaller than those from supernovae after the
neutrino burst.Comment: 42 pages, accepted for publication in the Astrophysical Journal. A
paper with higher-resolution figures available at
http://www.ec.knct.ac.jp/~fujimoto/collapsar/mhd-color.pd
Heavy Element Production in Inhomogeneous Big Bang Nucleosynthesis
We present a new astrophysical site of the big bang nucleosynthesis (BBN)
that are very peculiar compared with the standard BBN. Some models of the
baryogenesis suggest that very high baryon density regions were formed in the
early universe. On the other hand, recent observations suggest that heavy
elements already exist in high red-shifts and the origin of these elements
become a big puzzle. Motivated by these, we investigate BBN in very high baryon
density regions. BBN proceeds in proton-rich environment, which is known to be
like the p-process. However, by taking very heavy nuclei into account, we find
that BBN proceeds through both the p-process and the r-process simultaneously.
P-nuclei such as 92Mo, 94Mo, 96Ru, 98Ru whose origin is not well known are also
synthesized.Comment: 6 pages, 7 figure
P-Process Nucleosynthesis inside Supernova-Driven Supercritical Accretion Disks
We investigate p-process nucleosynthesis in a supercritical accretion disk
around a compact object of 1.4 M_solar, using the self-similar solution of an
optically thick advection dominated flow. Supercritical accretion is expected
to occur in a supernova with fallback material accreting onto a new-born
compact object. It is found that appreciable amounts of p-nuclei are
synthesized via the p-process in supernova-driven supercritical accretion disks
(SSADs) when the accretion rate m_dot = M_dot c^2/(16 L_Edd) >10^5, where L_Edd
is the Eddington luminosity. Abundance profiles of p-nuclei ejected from SSADs
have similar feature to those of the oxygen/neon layers in Type II supernovae
when the abundance of the fallback gas far from the compact object is that of
the oxygen/neon layers in the progenitor. The overall abundance profile is in
agreement with that of the solar system. Some p-nuclei, such as Mo, Ru, Sn, and
La, are underproduced in the SSADs as in Type II supernovae. If the fallback
gas is mixed with a small fraction of proton through Rayleigh-Taylor
instability during the explosion, significant amounts of Mo92 are produced
inside the SSADs. Ru96 and La138 are also produced when the fallback gas
contains abundant proton though the overall abundance profile of p-nuclei is
rather different from that of the solar system. The p-process nucleosynthesis
in SSADs contributes to chemical evolution of p-nuclei, in particular Mo92, if
several percents of fallback matter are ejected via jets and/or winds.Comment: 15 pages, 7 figures included, 3 tables, LaTeX emulateapj5.sty,
accepted for publication by the Astronomical Journal (March, 2003
Heavy element nucleosynthesis in a collapsar
We investigate synthesis of heavy elements in a collapsar. We have calculated detailed composition of magnetically driven jets ejected from a collapsar, which is based on long-term, magnetohydrodynamic simulations of a rapidly rotating massive star of 40M â during core collapse. We follow evolution of abundances of about 4000 nuclides from the collapse phase to the ejection phase through the jet generation phase with use of two large nuclear reaction networks. We find that the r-process successfully operates in the jets, so that U and Th are synthesized abundantly when the progenitor has large magnetic field of 10 12 G and rapidly rotating core. Abundance pattern inside the jets is similar compared to that of r-elements in the solar system. Heavy neutron-rich nuclei ⌠0.01M â can be ejected from the collapsar. The detailed abundances depend on nuclear properties of mass model, ÎČ-decay rate, and fission, for nuclei near the neutron drip line. Furthermore, we find that p-nuclei are produced without seed nuclei: not only light p
Different distribution of c-myc and MIB-1 positive cells in malignant meningiomas with reference to TGFs, PDGF, and PgR expression
Massive stars and their supernovae
Stars more massive than about 8-10 solar masses evolve differently from their lower-mass counterparts: nuclear energy liberation is possible at higher temperatures and densities, due to gravitational contraction caused by such high masses, until forming an iron core that ends this stellar evolution. The star collapses thereafter, as insufficient pressure support exists when energy release stops due to Fe/Ni possessing the highest nuclear binding per nucleon, and this implosion turns into either a supernova explosion or a compact black hole remnant object. Neutron stars are the likely compact-star remnants after supernova explosions for a certain stellar mass range. In this chapter, we discuss this late-phase evolution of massive stars and their core collapse, including the nuclear reactions and nucleosynthesis products. We also include in this discussion more exotic outcomes, such as magnetic jet supernovae, hypernovae, gamma-ray bursts and neutron star mergers. In all cases we emphasize the viewpoint with respect to the role of radioactivities
National trends in the outcomes of subarachnoid haemorrhage and the prognostic influence of stroke centre capability in Japan: retrospective cohort study
Objectives To examine the national, 6-year trends in in-hospital clinical outcomes of patients with subarachnoid haemorrhage (SAH) who underwent clipping or coiling and the prognostic influence of temporal trends in the Comprehensive Stroke Center (CSC) capabilities on patient outcomes in Japan.Design Retrospective study.Setting Six hundred and thirty-one primary care institutions in Japan.Participants Forty-five thousand and eleven patients with SAH who were urgently hospitalised, identified using the J-ASPECT Diagnosis Procedure Combination database.Primary and secondary outcome measures Annual number of patients with SAH who remained untreated, or who received clipping or coiling, in-hospital mortality and poor functional outcomes (modified Rankin Scale: 3â6) at discharge. Each CSC was assessed using a validated scoring system (CSC score: 1â25 points).Results In the overall cohort, in-hospital mortality decreased (year for trend, OR (95% CI): 0.97 (0.96 to 0.99)), while the proportion of poor functional outcomes remained unchanged (1.00 (0.98 to 1.02)). The proportion of patients who underwent clipping gradually decreased from 46.6% to 38.5%, while that of those who received coiling and those left untreated gradually increased from 16.9% to 22.6% and 35.4% to 38%, respectively. In-hospital mortality of coiled (0.94 (0.89 to 0.98)) and untreated (0.93 (0.90 to 0.96)) patients decreased, whereas that of clipped patients remained stable. CSC score improvement was associated with increased use of coiling (per 1-point increase, 1.14 (1.08 to 1.20)) but not with short-term patient outcomes regardless of treatment modality.Conclusions The 6-year trends indicated lower in-hospital mortality for patients with SAH (attributable to better outcomes), increased use of coiling and multidisciplinary care for untreated patients. Further increasing CSC capabilities may improve overall outcomes, mainly by increasing the use of coiling. Additional studies are necessary to determine the effect of confounders such as aneurysm complexity on outcomes of clipped patients in the modern endovascular era