9,638 research outputs found
The pairing Hamiltonian for one pair of identical nucleons bound in a potential well
The problem of one pair of identical nucleons sitting in single
particle levels of a potential well and interacting through the pairing force
is treated introducing even Grassmann variables. The eigenvectors are
analytically expressed solely in terms of these with coefficients fixed by the
eigenvalues and the single particle energies. When the latter are those of an
harmonic oscillator well an accurate expression is derived for both the
collective eigenvalue and for those trapped in between the single particle
levels, for any strength of the pairing interaction and for any number of
levels. Notably the trapped solutions are labelled through an index upon which
they depend parabolically.Comment: 5 pages, 1 postscript figur
On the analytic solution of the pairing problem: one pair in many levels
We search for approximate, but analytic solutions of the pairing problem for
one pair of nucleons in many levels of a potential well. For the collective
energy a general formula, independent of the details of the single particle
spectrum, is given in both the strong and weak coupling regimes. Next the
displacements of the solutions trapped in between the single particle levels
with respect to the unperturbed energies are explored: their dependence upon a
suitably defined quantum number is found to undergo a transition between two
different regimes.Comment: 30 pages, AMS Latex, 8 figures. Submitted to Phys. Rev.
Validation of a statistic algorithm applied to LES model - Part I: First and second order statistics
The main objective of this work is to develop a statistical algorithm to process the data generated by the Large-Eddy-Simulation model (LES) in real time. The simulations analyzed here were based on a convective, neutral and stable periods. Mainly the temperature and velocity components were analyzed. The new statistical algorithm generates all the first and second order statistic moments for “u,v,w, ¿ ,q”, and the components of TKE equation budget. All these parameters were developed to the resolved and sub-grid scales and indicate agreement with the expected profile
Nuclear effects in charged-current quasielastic neutrino-nucleus scattering
After a short review of the recent developments in studies of
neutrino-nucleus interactions, the predictions for double-differential and
integrated charged current-induced quasielastic cross sections are presented
within two different relativistic approaches: one is the so-called SuSA method,
based on the superscaling behavior exhibited by electron scattering data; the
other is a microscopic model based on relativistic mean field theory, and
incorporating final-state interactions. The role played by the meson-exchange
currents in the two-particle two-hole sector is explored and the results are
compared with the recent MiniBooNE data.Comment: 12 pages, 9 figures, to appear in the Proceedings of "XIII Convegno
di Cortona su Problemi di Fisica Nucleare Teorica", Cortona (Italy), April
6-8, 201
Quasielastic Charged Current Neutrino-nucleus Scattering
We provide integrated cross sections for quasielastic charged-current
neutrino-nucleus scattering. Results evaluated using the phenomenological
scaling function extracted from the analysis of experimental data are
compared with those obtained within the framework of the relativistic impulse
approximation. We show that very reasonable agreement is reached when a
description of final-state interactions based on the relativistic mean field is
included. This is consistent with previous studies of differential cross
sections which are in accord with the universality property of the superscaling
function.Comment: 5 pages, 3 figures, to be published in Phys. Rev. Let
Relativistic descriptions of final-state interactions in charged-current quasielastic neutrino-nucleus scattering at MiniBooNE kinematics
The results of two relativistic models with different descriptions of the
final-state interactions are compared with the MiniBooNE data of
charged-current quasielastic cross sections. The relativistic mean field model
uses the same potential for the bound and ejected nucleon wave functions. In
the relativistic Green's function (RGF) model the final-state interactions are
described in the inclusive scattering consistently with the exclusive
scattering using the same complex optical potential. The RGF results describe
the experimental data for total cross-sections without the need to modify the
nucleon axial mass.Comment: 5 pages 3 figure
Relativistic Models for Quasi-Elastic Neutrino-Nucleus Scattering
Two relativistic approaches to charged-current quasielastic neutrino-nucleus
scattering are illustrated and compared: one is phenomenological and based on
the superscaling behavior of electron scattering data and the other relies on
the microscopic description of nuclear dynamics in relativistic mean field
theory. The role of meson exchange currents in the two-particle two-hole sector
is explored. The predictions of the models for differential and total cross
sections are presented and compared with the MiniBooNE data.Comment: 3 pages, 3 figures, Proceedings of PANIC 2011, MIT, Cambridge, MA,
July 201
Pionic correlations and meson-exchange currents in two-particle emission induced by electron scattering
Two-particle two-hole contributions to electromagnetic response functions are
computed in a fully relativistic Fermi gas model. All one-pion exchange
diagrams that contribute to the scattering amplitude in perturbation theory are
considered, including terms for pionic correlations and meson-exchange currents
(MEC). The pionic correlation terms diverge in an infinite system and thus are
regularized by modification of the nucleon propagator in the medium to take
into account the finite size of the nucleus. The pionic correlation
contributions are found to be of the same order of magnitude as the MEC.Comment: 14 pages, 15 figure
An Integrated Picture of Star Formation, Metallicity Evolution, and Galactic Stellar Mass Assembly
We present an integrated study of star formation and galactic stellar mass
assembly from z=0.05-1.5 and galactic metallicity evolution from z=0.05-0.9
using a very large and highly spectroscopically complete sample selected by
rest-frame NIR bolometric flux in the GOODS-N. We assume a Salpeter IMF and fit
Bruzual & Charlot (2003) models to compute the galactic stellar masses and
extinctions. We determine the expected formed stellar mass density growth rates
produced by star formation and compare them with the growth rates measured from
the formed stellar mass functions by mass interval. We show that the growth
rates match if the IMF is slightly increased from the Salpeter IMF at
intermediate masses (~10 solar masses). We investigate the evolution of galaxy
color, spectral type, and morphology with mass and redshift and the evolution
of mass with environment. We find that applying extinction corrections is
critical when analyzing galaxy colors; e.g., nearly all of the galaxies in the
green valley are 24um sources, but after correcting for extinction, the bulk of
the 24um sources lie in the blue cloud. We find an evolution of the
metallicity-mass relation corresponding to a decrease of 0.21+/-0.03 dex
between the local value and the value at z=0.77 in the 1e10-1e11 solar mass
range. We use the metallicity evolution to estimate the gas mass of the
galaxies, which we compare with the galactic stellar mass assembly and star
formation histories. Overall, our measurements are consistent with a galaxy
evolution process dominated by episodic bursts of star formation and where star
formation in the most massive galaxies (>1e11 solar masses) ceases at z<1.5
because of gas starvation. (Abstract abridged)Comment: 48 pages, Accepted by the Astrophysical Journa
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