6,170 research outputs found
Two- and three-dimensional simulations of core-collapse supernovae with CHIMERA
Ascertaining the core-collapse supernova mechanism is a complex, and yet
unsolved, problem dependent on the interaction of general relativity,
hydrodynamics, neutrino transport, neutrino-matter interactions, and nuclear
equations of state and reaction kinetics. Ab initio modeling of core-collapse
supernovae and their nucleosynthetic outcomes requires care in the coupling and
approximations of the physical components. We have built our multi-physics
CHIMERA code for supernova modeling in 1-, 2-, and 3-D, using ray-by-ray
neutrino transport, approximate general relativity, and detailed neutrino and
nuclear physics. We discuss some early results from our current series of
exploding 2D simulations and our work to perform computationally tractable
simulations in 3D using the "Yin-Yang" grid.Comment: Proceedings of the 12th Symposium on Nuclei in the Cosmos. 5-12
August 2012. Cairns, Australia. Published online at
http://pos.sissa.it/archive/conferences/146/208/NIC%20XII_208.pdf Corrected
typ
Advancing Nucleosynthesis in Self-consistent, Multidimensional Models of Core-Collapse Supernovae
We investigate core-collapse supernova (CCSN) nucleosynthesis in polar
axisymmetric simulations using the multidimensional radiation hydrodynamics
code CHIMERA. Computational costs have traditionally constrained the evolution
of the nuclear composition in CCSN models to, at best, a 14-species
-network. Such a simplified network limits the ability to accurately
evolve detailed composition, neutronization and the nuclear energy generation
rate. Lagrangian tracer particles are commonly used to extend the nuclear
network evolution by incorporating more realistic networks in post-processing
nucleosynthesis calculations. Limitations such as poor spatial resolution of
the tracer particles, estimation of the expansion timescales, and determination
of the "mass-cut" at the end of the simulation impose uncertainties inherent to
this approach. We present a detailed analysis of the impact of these
uncertainties on post-processing nucleosynthesis calculations and implications
for future models.Comment: Proceedings of the 13th Symposium on Nuclei in the Cosmos. 7-11 July
2014. Debrecen, Hungar
Magnetic Dipole Absorption of Radiation in Small Conducting Particles
We give a theoretical treatment of magnetic dipole absorption of
electromagnetic radiation in small conducting particles, at photon energies
which are large compared to the single particle level spacing, and small
compared to the plasma frequency. We discuss both diffusive and ballistic
electron dynamics for particles of arbitrary shape.
The conductivity becomes non-local when the frequency is smaller than the
frequency \omega_c characterising the transit of electrons from one side of the
particle to the other, but in the diffusive case \omega_c plays no role in
determining the absorption coefficient. In the ballistic case, the absorption
coefficient is proportional to \omega^2 for \omega << \omega_c, but is a
decreasing function of \omega for \omega >> \omega_c.Comment: 25 pages of plain TeX, 2 postscipt figure
Distribution of the Absorption by Chaotic States in Quantum Dots
The mesoscopic fluctuations of the absorption at optical transitions from a
low energy regular state to high energy chaotic states in an aggregate of
semiconductor quantum dots is studied. We provide a universal dependence of the
distribution of the absorption coefficient on the total number of dots and the
ratio of the level broadening to the level spacing. The distribution remain
broad even at large broadening, and the absorption spectrum should demonstrate
a strong sensitivity to weak magnetic field in the region of large and weak
absorption. The results can also apply to the absorption of Rydberg atoms in
strong magnetic field at the pre-threshold ionization.Comment: 4 pages, 2 eps figures, REVTeX3 + multicol.sty + epsf.te
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