31,351 research outputs found
R-Process Nucleosynthesis In Neutrino-Driven Winds From A Typical Neutron Star With M = 1.4 Msun
We study the effects of the outer boundary conditions in neutrino-driven
winds on the r-process nucleosynthesis. We perform numerical simulations of
hydrodynamics of neutrino-driven winds and nuclear reaction network
calculations of the r-process. As an outer boundary condition of hydrodynamic
calculations, we set a pressure upon the outermost layer of the wind, which is
approaching toward the shock wall. Varying the boundary pressure, we obtain
various asymptotic thermal temperature of expanding material in the
neutrino-driven winds for resulting nucleosynthesis. We find that the
asymptotic temperature slightly lower than those used in the previous studies
of the neutrino-driven winds can lead to a successful r-process abundance
pattern, which is in a reasonable agreement with the solar system r-process
abundance pattern even for the typical proto-neutron star mass Mns ~ 1.4 Msun.
A slightly lower asymptotic temperature reduces the charged particle reaction
rates and the resulting amount of seed elements and lead to a high
neutron-to-seed ratio for successful r-process. This is a new idea which is
different from the previous models of neutrino-driven winds from very massive
(Mns ~ 2.0 Msun) and compact (Rns ~ 10 km) neutron star to get a short
expansion time and a high entropy for a successful r-process abundance pattern.
Although such a large mass is sometimes criticized from observational facts on
a neutron star mass, we dissolve this criticism by reconsidering the boundary
condition of the wind. We also explore the relation between the boundary
condition and neutron star mass, which is related to the progenitor mass, for
successful r-process.Comment: 14 pages, 2 figure
The Grounds For Time Dependent Market Potentials From Dealers' Dynamics
We apply the potential force estimation method to artificial time series of
market price produced by a deterministic dealer model. We find that dealers'
feedback of linear prediction of market price based on the latest mean price
changes plays the central role in the market's potential force. When markets
are dominated by dealers with positive feedback the resulting potential force
is repulsive, while the effect of negative feedback enhances the attractive
potential force.Comment: 9 pages, 3 figures, proceedings of APFA
An Implicit Lagrangean Code for Spherically Symmetric General Relativistic Hydrodynamics with an Approximate Riemann Solver
An implicit Lagrangian hydrodynamics code for general relativistic spherical
collapse is presented. This scheme is based on an approximate linearized
Riemann solver (Roe type scheme). This code is aimed especially at the
calculation of the late phase of collapse-driven supernovae and the nascent
neutron star, where there is a remarkable contrast between the dynamical time
scale of the proto-neutron star and the diffusion time scale of neutrinos,
without such severe limitation of the Courant condition at the center of the
neutron star. Several standard test calculations have been done. Two other
adiabatic simulations have also been done in order to test the performance of
the code in the context of the collapse-driven supernovae. It is found that the
time step can be extended far beyond the Courant limitation at the center of
the neutron star. The details of the scheme and the results of these test
calculations are discussed.Comment: AASTeX v4.0, 24 pages, 13 figures on request from
[email protected], submitted to Ap
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