3,639 research outputs found
R-Matrix Formulation of the Quantum Inhomogeneous Groups Iso_qr(N) and Isp_qr(N)
The quantum commutations and the orthogonal (symplectic) conditions
for the inhomogeneous multiparametric -groups of the type are
found in terms of the -matrix of . A consistent
Hopf structure on these inhomogeneous -groups is constructed by means of a
projection from . Real forms are discussed: in
particular we obtain the -groups , including the quantum
Poincar\'e group.Comment: 14 pages, latex, no figure
CCD PHOTOMETRY OF RR LYRAE STARS IN M5 AS A TEST FOR THE PULSATIONAL SCENARIO
In this paper we present new CCD investigations of RR Lyrae pulsators in the
Oo.I globular cluster M5. B V curves of light for 15 RR Lyrae are presented.
With the addition of further 11 curves of light by Storm, Carney and Beck
(1991) one is dealing with a sample of 26 well studied cluster pulsators whose
properties have been implemented with similar data for RR Lyrae in clusters M3,
M15, M68 to allow a comparison with the theoretical scenario recently presented
by Bono and Stellingwerf (1994). On this basis, we discuss the distribution of
stars in the period amplitude diagram, disclosing a substantial reduction of
Sandage's period shift. We suggest that theoretical constraints concerning
periods and amplitudes could allow information on masses and luminosity of the
pulsators directly from Bailey's diagram only. Static temperatures have been
derived for all stars in the sample, discussing the dependence on the
temperature of the observed pulsational properties.Comment: postscript file of 17 pages of text plus 7 figures and 2 tables. For
any problem please write to [email protected]
Spectroscopic and thermodynamic properties in a four-band model for pnictides
In this paper we provide a comprehesive analysis of different properties of
pnictides both in the normal and superconducting state, with a particular focus
on the optimally-doped BaKFeAs system. We show that, by
using the band dispersions experimentally measured by ARPES, a four-band
Eliashberg model in the intermediate-coupling regime can account for both the
measured hierarchy of the gaps and for several spectroscopic and thermodynamic
signatures of low-energy renormalization. These include the kinks in the band
dispersion and the effective masses determined via specific-heat and
superfluid-density measurements. We also show that, although an
intermediate-coupling Eliashberg approach is needed to account for the
magnitude of the gaps, the temperature behavior of the thermodynamic quantities
does not show in this regime a significant deviation with respect to
weak-coupling BCS calculations. This can explain the apparent success of
two-band BCS fits of experimental data reported often in the literature.Comment: 12 pages, 6 figures, final versio
Stellar models for very low mass main sequence stars: the role of model atmospheres
We present Very Low Mass stellar models as computed including non-grey model
atmospheres for selected assumptions about the star metallicities. The role of
atmospheres is discussed and the models are compared with models based on the
Eddington approximation and with similar models appeared in the recent
literature. Theoretical predictions concerning both the HR diagram location and
the mass-luminosity relation are presented and discussed in terms of
expectations in selected photometric bands. Comparison with available
observational data concerning both galactic globular clusters and dwarfs in the
solar neighborhood reveals a satisfactory agreement together with the existence
of some residual mismatches.Comment: 10 pages including 13 figures, gzip postscript file, To be published
in MNRA
Predicted HST FOC and broad band colours for young and intermediate Simple Stellar Populations
This paper presents theoretical HST and broad band colours from population
synthesis models based on an homogeneous set of stellar evolutionary tracks as
computed under canonical (no overshooting) assumptions, covering the range of
cluster ages from t=8 Myr to t=5 Gyr for three different metallicities (Z=0.02,
0.006, and 0.001). Statistical fluctuations in the cluster population have been
investigated, assessing the predicted fluctuations of the various colours as a
function of the cluster integrated absolute magnitude. We show that the red
leak in HST UV filters deeply affects the predicted fluxes and colours.
However, we find that for F152M-F307M < 0.5 and for F170M-F278M < 0.5 (which
means ages lower than 1 Gyr) the HST UV colours can still be used to infer
reliable indications on the age of distant clusters. Moreover, one finds that
the age calibration of these colours is scarcely affected by the amount of
original helium or by the assumed IMF. On this basis, we present a calibration
of the HST UV two-colours (F152M-F307M vs F170M-F278M) in terms of cluster ages
for the three above quoted metallicities. We suggest the combined use of HST UV
colours and IR colours (V-K in particular) to disentangle the metallicity-age
effect in integrated colours of young stellar populations (t< 1 Gyr).Comment: Latex 18 pages, 16 encapsulated figures, 6 tables, A&ASS accepte
Synthetic Stellar Clusters for Pop III
We present preliminary results of an incoming theoretical work concerning the
integrated properties of the Population III clusters of stars. On the basis of
synthetic Color-Magnitude Diagrams, we provide a grid of optical and near-IR
colors of Simple Stellar Populations with very low metallicity (Z=10
and Z=10) and age which spans from 10 Myr to 15 Gyr. A comparison with
higher metallicities up to 0.006 is also shown, disclosing sizable differences
in the CMD morphology, integrated colors and Spectral Energy Distribution
(SED).Comment: 2 pages, incl. 2 figures, "The First Stars", Proceedings of the
second MPA/ESO workshop, Eds.: Weiss, Abel, Hill, Springer, Heidelberg, 200
Localized Manifold Harmonics for Spectral Shape Analysis
The use of Laplacian eigenfunctions is ubiquitous in a wide range of computer graphics and geometry processing applications. In particular, Laplacian eigenbases allow generalizing the classical Fourier analysis to manifolds. A key drawback of such bases is their inherently global nature, as the Laplacian eigenfunctions carry geometric and topological structure of the entire manifold. In this paper, we introduce a new framework for local spectral shape analysis. We show how to efficiently construct localized orthogonal bases by solving an optimization problem that in turn can be posed as the eigendecomposition of a new operator obtained by a modification of the standard Laplacian. We study the theoretical and computational aspects of the proposed framework and showcase our new construction on the classical problems of shape approximation and correspondence. We obtain significant improvement compared to classical Laplacian eigenbases as well as other alternatives for constructing localized bases
Screening of Nuclear Reactions in the Sun and Solar Neutrinos
We quantitatively determine the effect and the uncertainty on solar neutrino
production arising from the screening process. We present predictions for the
solar neutrino fluxes and signals obtained with different screening models
available in the literature and by using our stellar evolution code. We explain
these numerical results in terms of simple laws relating the screening factors
with the neutrino fluxes. Futhermore we explore a wider range of models for
screening, obtained from the Mitler model by introducing and varying two
phenomenological parameters, taking into account effects not included in the
Mitler prescription. Screening implies, with respect to a no-screening case, a
central temperat reduction of 0.5%, a 2% (8%) increase of Beryllium
(Boron)-neutrino flux and a 2% (12%) increase of the Gallium (Chlorine) signal.
We also find that uncertainties due to the screening effect ar at the level of
1% for the predicted Beryllium-neutrino flux and Gallium signal, not exceeding
3% for the Boron-neutrino flux and the Chlorine signal.Comment: postscript file 11 pages + 4 figures compressed and uuencoded we have
replaced the previous paper with a uuencoded file (the text is the same) for
any problem please write to [email protected]
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