arXiv subjects

Lorenzo Fortunato

Publications and source records attributed to Lorenzo Fortunato.

25 records · Page 2Linked to original sources

arXiv2004

Soft triaxial roto-vibrational motion in the vicinity of $γ=π/6$

A solution of the Bohr collective hamiltonian for the $β-$soft, $γ-$soft triaxial rotor with $γ\sim π/6$ is presented making use of a harmonic potential in $γ$ and Coulomb-like and Kratzer-like potentials in $β$. It is shown that, while the $γ-$angular part in the present case gives rise to a straightforward extension of the rigid triaxial rotor energy in which an additive harmonic term appears, the inclusion of the $β$ part results instead in a non-trivial expression for the spectrum. The negative anharmonicities of the energy levels with respect to a simple rigid model are in qualitative agreement with general trends in the experimental data.

nucl-th↗

arXiv2003

New analytic solutions of the collective Bohr hamiltonian for a beta-soft, gamma-soft axial rotor

New analytic solutions of the quadrupole collective Bohr hamiltonian are proposed, exploiting an approximate separation of the beta and gamma variables to describe gamma-soft prolate axial rotors. The model potential is a sum of two terms: a beta-dependent term taken either with a Coulomb-like or a Kratzer-like form, and a gamma-dependent term taken as an harmonic oscillator. In particular it is possible to give a one parameter paradigm for a beta-soft, gamma-soft axial rotor that can be applied, with a considerable agreement, to the spectrum of 234U.

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arXiv2003

Structure studies of conventional and novel excitations to the continuum in reactions with unstable nuclei

The themes covered in the present thesis are: a detailed study of double phonon giant resonances in normal nuclei, the enhancement of the excitation of Giant Pairing Vibrations using weakly-bound nuclei, an extension of the Steinwedel-Jensen model for Giant Dipole Resonances to treat surface effects and presence of neutron skin and, finally, a model on breakup reactions in weakly-bound dicluster nuclei.

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arXiv2003

Analytically solvable potentials for $γ$-unstable nuclei

An analytical solution of the collective Bohr equation with a Coulomb-like and a Kratzer-like $γ-$unstable potential in quadrupole deformation space is presented. Eigenvalues and eigenfunctions are given in closed form and transition rates are calculated for the two cases. The corresponding SO(2,1)$\times$SO(5) algebraic structure is discussed.

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arXiv2002

Break-up and electromagnetic response of light weakly-bound dicluster systems

This study is focused on the break-up and electromagnetic response of light weakly-bound dicluster nuclei. The cluster picture in the case of $ ^7$Li is shown to be a very good approximation and in this framework we calculate nuclear structure observables. We solve the Schrödinger equation for the relative motion both for discrete and continuum states and this automatically takes into a proper account the role of resonances. A concentration of strength in the low energy continuum, solely due to the weakly-bound nature of the bound states is seen and explained as a favourable matching between the wavelengths of the initial and final states. Finally preliminary results on form factors are briefly outlined and their microscopic derivation as well as utilization in reaction studies is discussed.

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arXiv2002

Study of Giant Pairing Vibrations with neutron-rich nuclei

We investigate the possible signature of the presence of giant pairing states at excitation energy of about 10 MeV via two-particle transfer reactions induced by neutron-rich weakly-bound projectiles. Performing particle-particle RPA calculations on $^{208}$Pb and BCS+RPA calculations on $^{116}$Sn, we obtain the pairing strength distribution for two particles addition and removal modes. Estimates of two-particle transfer cross sections can be obtained in the framework of the 'macroscopic model'. The weak-binding nature of the projectile kinematically favours transitions to high-lying states. In the case of $(~^6He, \~^4He)$ reaction we predict a population of the Giant Pairing Vibration with cross sections of the order of a millibarn, dominating over the mismatched transition to the ground state.

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arXiv2001

Realistic modellization for the growth of a yeast colony

An evolving yeast colony is simulated by means of a cellular automaton that takes care of many important features of the system under study. A complete survey of the properties of the colony is done and a set of scaling relations is found, together with the analysis of the critical exponents. The Family-Vicsek relation between them is verified to a good accuracy. A mobility parameter is introduced in order to relate the behaviour of the growth exponent with the temperature and we propose that the brownian motion is a key feature to describe the bacterial and fungi growth process in diluted solutions. The chemical and geometrical correlations are found to play a relevant role in the modellization, so that the need of realism is emphasized. A new phase space built upon the relevant 'thermodinamical' variables is explored.

cond-mat.stat-mech↗