36,755 research outputs found
Neutrino-nucleus reactions and their role for supernova dynamics and nucleosynthesis
The description of nuclear reactions induced by supernova neutrinos has
witnessed significant progress during the recent years. At the energies and
momentum transfers relevant for supernova neutrinos neutrino-nucleus cross
sections are dominated by allowed transitions, however, often with
non-negligible contributions from (first) forbidden transitions. For several
nuclei allowed Gamow-Teller strength distributions could be derived from
charge-exchange reactions and from inelastic electron scattering data.
Importantly the diagonalization shell model has been proven to accurately
describe these data and hence became the appropriate tool to calculate the
allowed contributions to neutrino-nucleus cross sections for supernova
neutrinos. Higher multipole contributions are usually calculated within the
framework of the Quasiparticle Random Phase Approximation, which describes the
total strength and the position of the giant resonances quite well.
This manuscript reviews the recent progress achieved in calculating
supernova-relevant neutrino-nucleus cross sections and discusses its
verification by data. Moreover, the review summarizes also the impact which
neutrino-nucleus reactions have on the dynamics of supernovae and on the
associated nucleosynthesis. These include the absorption of neutrinos by nuclei
(the inverse of nuclear electron capture which is the dominating
weak-interaction process during collapse), inelastic neutrino-nucleus
scattering and nuclear de-excitation by neutrino-pair emission. We also discuss
the role of neutrino-induced reactions for the recently discovered
process, for the r-process and for the neutrino process, for which
neutrino-nucleus reactions have the largest impact. Finally, we briefly review
neutrino-nucleus reactions important for the observation of supernova neutrinos
by earthbound detectors. (Abridged)Comment: 77 pages, 29 figures, 4 tables, submitted to Progress in Particle and
Nuclear Physic
Cellular automaton supercolliders
Gliders in one-dimensional cellular automata are compact groups of
non-quiescent and non-ether patterns (ether represents a periodic background)
translating along automaton lattice. They are cellular-automaton analogous of
localizations or quasi-local collective excitations travelling in a spatially
extended non-linear medium. They can be considered as binary strings or symbols
travelling along a one-dimensional ring, interacting with each other and
changing their states, or symbolic values, as a result of interactions. We
analyse what types of interaction occur between gliders travelling on a
cellular automaton `cyclotron' and build a catalog of the most common
reactions. We demonstrate that collisions between gliders emulate the basic
types of interaction that occur between localizations in non-linear media:
fusion, elastic collision, and soliton-like collision. Computational outcomes
of a swarm of gliders circling on a one-dimensional torus are analysed via
implementation of cyclic tag systems
Prediction of jet engine parameters for control design using genetic programming
The simulation of a jet engine behavior is widely used in many different aspects of the engine development and maintenance. Achieving high quality jet engine control systems requires the iterative use of these simulations to virtually test the performance of the engine avoiding any possible damage on the real engine. Jet engine simulations involve the use of mathematical models which are complex and may not always be available. This paper introduces an approach based on Genetic Programming (GP) to model different parameters of a small engine for control design such as the Exhaust Gas Temperature (EGT). The GP approach has no knowledge of the characteristics of the engine. Instead, the model is found by the evolution of models based on past measurements of parameters such as the pump voltage. Once the model is obtained, it is used to predict the behaviour of the jet engine one step ahead. The proposed approach is successfully applied for the simulation of a Behotec j66 jet engine and the results are presented
Supernova neutrinos and nucleosynthesis
Observations of metal-poor stars indicate that at least two different
nucleosynthesis sites contribute to the production of r-process elements. One
site is responsible for the production of light r-process elements Z<~50 while
the other produces the heavy r-process elements. We have analyzed recent
observations of metal-poor stars selecting only stars that are enriched in
light r-process elements and poor in heavy r-process elements. We find a strong
correlation between the observed abundances of the N=50 elements (Sr, Y and Zr)
and Fe. It suggest that neutrino-driven winds from core-collapse supernova are
the main site for the production of these elements. We explore this possibility
by performing nucleosynthesis calculations based on long term Boltzmann
neutrino transport simulations. They are based on an Equation of State that
reproduces recent constrains on the nuclear symmetry energy. We predict that
the early ejecta is neutron-rich with Ye ~ 0.48, it becomes proton rich around
4 s and reaches Ye = 0.586 at 9 s when our simulation stops. The
nucleosynthesis in this model produces elements between Zn and Mo, including
92Mo. The elemental abundances are consistent with the observations of the
metal-poor star HD 12263. For the elements between Ge and Mo, we produce mainly
the neutron-deficient isotopes. This prediction can be confirmed by
observations of isotopic abundances in metal-poor stars. No elements heavier
than Mo (Z=42) and no heavy r-process elements are produced in our
calculations.Comment: 18 pages, 5 figures, submitted to J. Phys. G: Nucl. Part. Phys.
(Focus issue "Nucleosynthesis and the role of neutrinos", ed. Baha Balantekin
and Cristina Volpe
Effects of heat release on triple flames
Heat release effects on laminar flame propagation in partially premixed flows are studied. Data for analysis are obtained from direct numerical simulations of a laminar mixing layer with a uniformly approaching velocity field. The structure that evolves under such conditions is a triple flame, which consists of two premixed wings and a trailing diffusion flame. Heat release increases the flame speed over that of the corresponding planar premixed flame. In agreement with previous analytical work, reductions in the mixture fraction gradient also increase the flame speed. The effects of heat release and mixture fraction gradients on flame speed are not independent, however; heat release modifies the effective mixture fraction gradient in front of the flame. For very small mixture fraction gradients, scaling laws that determine the flame speed in terms of the density change are presented. © 1995 American Institute of Physics
Dalitz plot slope parameters for decays and two particle interference
We study the possible distortion of phase-space in the decays , which may result from final state interference among the decay products.
Such distortion may influence the values of slope parameters extracted from the
Dalitz plot distribution of these decays. We comment on the consequences on the
magnitude of violation of the rule in these decays.Comment: 17 pages, LaTex2e, 6 figures, v2 authors' affiliation modified, to
appear in Mod. Phys. Lett.
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