3,586 research outputs found
Medium modification of the charged current neutrino opacity and its implications
Previous work on neutrino emission from proto-neutron stars which employed
full solutions of the Boltzmann equation showed that the average energies of
emitted electron neutrinos and antineutrinos are closer to one another than
predicted by older, more approximate work. This in turn implied that the
neutrino driven wind is proton rich during its entire life, precluding
-process nucleosynthesis and the synthesis of Sr, Y, and Zr. This work
relied on charged current neutrino interaction rates that are appropriate for a
free nucleon gas. Here, it is shown in detail that the inclusion of the nucleon
potential energies and collisional broadening of the response significantly
alters this conclusion. Iso-vector interactions, which give rise to the nuclear
symmetry energy, produce a difference between the neutron and proton
single-particle energies and alter the kinematics of the
charged current reactions. In neutron-rich matter, and for a given
neutrino/antineutrino energy, the rate for is
enhanced while is suppressed because the
value for these reactions is altered by , respectively. In the
neutrino decoupling region, collisional broadening acts to enhance both
and cross-sections and RPA corrections decrease the
cross-section and increase the cross-section, but mean field
shifts have a larger effect. Therefore, electron neutrinos decouple at lower
temperature than when the nucleons are assumed to be free and have lower
average energies. The change is large enough to allow for a reasonable period
of time when the neutrino driven wind is predicted to be neutron rich. It is
also shown that the electron fraction in the wind is influenced by the nuclear
symmetry energy.Comment: Version submitted to PRC, 10 pages, 6 figures (Additional discussion
of RPA effects added
Shadow Price Guided Genetic Algorithms
The Genetic Algorithm (GA) is a popular global search algorithm. Although it has been used successfully in many fields, there are still performance challenges that prevent GA’s further success. The performance challenges include: difficult to reach optimal solutions for complex problems and take a very long time to solve difficult problems. This dissertation is to research new ways to improve GA’s performance on solution quality and convergence speed. The main focus is to present the concept of shadow price and propose a two-measurement GA. The new algorithm uses the fitness value to measure solutions and shadow price to evaluate components. New shadow price Guided operators are used to achieve good measurable evolutions. Simulation results have shown that the new shadow price Guided genetic algorithm (SGA) is effective in terms of performance and efficient in terms of speed
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