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F. Zardi

Publications and source records attributed to F. Zardi.

9 recordsLinked to original sources
arXiv2021

Minimum-Complexity Failure Correction in Linear Arrays via Compressive Processing

Given an array with defective elements, failure correction (FC) aims at finding a new set of weights for the working elements so that the properties of the original pattern can be recovered. Unlike several FC techniques available in the literature, which update all the working excitations, the Minimum-Complexity Failure Correction (MCFC) problem is addressed in this paper. By properly reformulating the FC problem, the minimum number of corrections of the whole excitations of the array is determined by means of an innovative Compressive Processing (CP) technique in order to afford a pattern as close as possible to the original one (i.e., the array without failures). Selected examples, from a wide set of numerical test cases, are discussed to assess the effectiveness of the proposed approach as well as to compare its performance with other competitive state-of-the-art techniques in terms of both pattern features and number of corrections.

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arXiv2009

Coulomb Excitation of Multi-Phonon Levels of the Giant Dipole Resonance

A closed expression is obtained for the cross-section for Coulomb excitation of levels of the giant dipole resonance of given angular momentum and phonon number. Applications are made to the Goldhaber-Teller and Steinwedel-Jensen descriptions of the resonance, at non-relativistic and relativistic bombarding energies.

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arXiv2006

Relativistic Coulomb excitation at small impact parameters

The semiclassical model of relativistic Coulomb excitation is studied in situations in which the impact parameter is small enough so that projectile and target charge distributions overlap. The electromagnetic effects of this overlap are shown to be small. Realistic nucleon-nucleon reaction cross-sections, and realistic nuclear radial charge and matter distributions are used to determine a formula for the lower impact parameter limit to be used in the calculation of the Coulomb excitation cross-section. A wide selection of projectile-target pairs is explored, in the bombarding energy range of 1 GeV to 5 GeV per nucleon.

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arXiv2005

Quantum derivation of the use of classical electromagnetic potentials in relativistic Coulomb excitation

We prove that a relativistic Coulomb excitation calculation in which the classical electromagnetic field of the projectile is used to induce transitions between target states gives the same target transition amplitudes, to all orders of perturbation theory, as would a calculation in which the interaction between projectile and target is mediated by a quantized electromagnetic field.

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arXiv2004

Gauge dependence of calculations in relativistic Coulomb excitation

Before a quantum-mechanical calculation involving electromagnetic interactions is performed, a choice must be made of the gauge to be used in expressing the potentials. If the calculation is done exactly, the observable results it predicts will be independent of the choice of gauge. However, in most practical calculations approximations are made, which can destroy the gauge invariance of the predictions. We compare here the results of coupled-channel time-dependent relativistic Coulomb excitation calculations, as performed in either Lorentz or Coulomb gauges. We find significant differences when the bombarding energy per nucleon is $\geq$ 2 GeV, which indicates that the common practice of relying completely on the Lorentz gauge can be dangerous.

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arXiv2003

Comparison of exact and approximate cross-sections in relativistic Coulomb excitation

We present a new method of obtaining time-dependent matrix elements of the electromagnetic pulse produced by a highly-relativistic projectile. These matrix elements are used in a coupled-channel calculation to predict the cross-sections for population of 1- and 2-phonon states of the giant dipole resonance. Comparisons are made with the predictions of the long-wavelength and Born approximations.

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arXiv2001

Coulomb excitation at ultra-relativistic energies

In previous studies of the theory of Coulomb excitation, the term in the electromagnetic interaction which is quadratic in the vector potential has been ignored. In this paper, we use qualitative arguments and detailed numerical calculations to show that this quadratic term must be included when the bombarding energy is in excess of about 20 GeV per nucleon.

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