219 research outputs found
Type Ia Supernova: Burning and Detonation in the Distributed Regime
A simple, semi-analytic representation is developed for nuclear burning in
Type Ia supernovae in the special case where turbulent eddies completely
disrupt the flame. The speed and width of the ``distributed'' flame front are
derived. For the conditions considered, the burning front can be considered as
a turbulent flame brush composed of corrugated sheets of well-mixed flames.
These flames are assumed to have a quasi-steady-state structure similar to the
laminar flame structure, but controlled by turbulent diffusion. Detonations
cannot appear in the system as long as distributed flames are still
quasi-steady-state, but this condition is violated when the distributed flame
width becomes comparable to the size of largest turbulent eddies. When this
happens, a transition to detonation may occur. For current best estimates of
the turbulent energy, the most likely density for the transition to detonation
is in the range 0.5 - 1.5 x 10^7 g cm^{-3}.Comment: 12 pages, 4 figure
Cluster virial expansion for nuclear matter within a quasiparticle statistical approach
Correlations in interacting many-particle systems can lead to the formation
of clusters, in particular bound states and resonances. Systematic quantum
statistical approaches allow to combine the nuclear statistical equilibrium
description (law of mass action) with mean-field concepts. A chemical picture,
which treats the clusters as distinct entities, serves as an intuitive concept
to treat the low-density limit. Within a generalized Beth-Uhlenbeck approach,
the quasiparticle virial expansion is extended to include arbitrary clusters,
where special attention must be paid to avoid inconsistencies such as double
counting. Correlations are suppressed with increasing density due to Pauli
blocking. The contribution of the continuum to the virial coefficients can be
reduced by considering clusters explicitly and introducing quasiparticle
energies. The cluster-virial expansion for nuclear matter joins known
benchmarks at low densities with those near saturation density.Comment: 18 pages, 6 figures, 2 table
Neutron and proton drip lines using the modified Bethe-Weizsacker mass formula
Proton and neutron separation energies have been calculated using the
extended Bethe-Weizsacker mass formula. This modified Bethe-Weizsacker mass
formula describes minutely the positions of all the old and the new magic
numbers. It accounts for the disappearance of some traditional magic numbers
for neutrons and provides extra stability for some new neutron numbers. The
neutron and proton drip lines have been predicted using this extended
Bethe-Weizsacker mass formula. The implications of the proton drip line on the
astrophysical rp-process and of the neutron drip line on the astrophysical
r-process have been discussed.Comment: 5 pages, 2 figure
Symmetry energy of dilute warm nuclear matter
The symmetry energy of nuclear matter is a fundamental ingredient in the
investigation of exotic nuclei, heavy-ion collisions and astrophysical
phenomena. New data from heavy-ion collisions can be used to extract the free
symmetry energy and the internal symmetry energy at subsaturation densities and
temperatures below 10 MeV. Conventional theoretical calculations of the
symmetry energy based on mean-field approaches fail to give the correct
low-temperature, low-density limit that is governed by correlations, in
particular by the appearance of bound states. A recently developed quantum
statistical (QS) approach that takes the formation of clusters into account
predicts symmetry energies that are in very good agreement with the
experimental data. A consistent description of the symmetry energy is given
that joins the correct low-density limit with quasiparticle approaches valid
near the saturation density.Comment: 4 pages, 2 figures, 1 tabl
On the small-scale stability of thermonuclear flames in Type Ia supernovae
We present a numerical model which allows us to investigate thermonuclear
flames in Type Ia supernova explosions. The model is based on a finite-volume
explicit hydrodynamics solver employing PPM. Using the level-set technique
combined with in-cell reconstruction and flux-splitting schemes we are able to
describe the flame in the discontinuity approximation. We apply our
implementation to flame propagation in Chandrasekhar-mass Type Ia supernova
models. In particular we concentrate on intermediate scales between the flame
width and the Gibson-scale, where the burning front is subject to the
Landau-Darrieus instability. We are able to reproduce the theoretical
prediction on the growth rates of perturbations in the linear regime and
observe the stabilization of the flame in a cellular shape. The increase of the
mean burning velocity due to the enlarged flame surface is measured. Results of
our simulation are in agreement with semianalytical studies.Comment: 9 pages, 7 figures, Uses AASTEX, emulateapj5.sty, onecolfloat.sty.
Replaced with accepted version (ApJ), Figures 1 and 3 are ne
Constraints on the high-density nuclear equation of state from the phenomenology of compact stars and heavy-ion collisions
A new scheme for testing nuclear matter equations of state (EsoS) at high
densities using constraints from neutron star phenomenology and a flow data
analysis of heavy-ion collisions is suggested. An acceptable EoS shall not
allow the direct Urca process to occur in neutron stars with masses below
, and also shall not contradict flow and kaon production data of
heavy-ion collisions. Compact star constraints include the mass measurements of
2.1 +/- 0.2 M_sun (1 sigma level) for PSR J0751+1807, of 2.0 +/- 0.1 M_sun from
the innermost stable circular orbit for 4U 1636-536, the baryon mass -
gravitational mass relationships from Pulsar B in J0737-3039 and the
mass-radius relationships from quasiperiodic brightness oscillations in 4U
0614+09 and from the thermal emission of RX J1856-3754. This scheme is applied
to a set of relativistic EsoS constrained otherwise from nuclear matter
saturation properties with the result that no EoS can satisfy all constraints
simultaneously, but those with density-dependent masses and coupling constants
appear most promising.Comment: 15 pages, 8 figures, 5 table
Relativistic quantum kinetic equation of the Vlasov type for systems with internal degrees of freedom
We present an approach to derive a relativistic kinetic equation of the
Vlasov type. Our approach is especially reliable for the description of quantum
field systems with many internal degrees of freedom. The method is based on the
Heisenberg picture and leads to a kinetic equation which fulfills the
conservation laws. We apply the approach to the standard Walecka Lagrangian and
an effective chiral Lagrangian.Comment: 11 pages, LaTeX, uses ijmpel.st
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