Compression modes in nuclei: microscopic models with Skyrme interactions

The isoscalar giant monopole resonances (ISGMR) and giant dipole resonances (ISGDR) in medium-heavy nuclei are investigated in the framework of HF+RPA and HF-BCS+QRPA with Skyrme effective interactions. It is found that pairing has little effect on these modes. It is also found that the coupling of the RPA states to 2p-2h configurations results in about (or less than) 1 MeV shifts of the resonance energies and at the same time gives the correct total widths. For the ISGMR, comparison with recent data leads to a value of nuclear matter compression modulus close to 215 MeV. However, a discrepancy between calculated and measured energies of the ISGDR in $^{208}$Pb is found and remains an open problem.Comment: To appear in: ``RIKEN Symposium and Workshop on Selected Topics in Nuclear Collective Excitations'', proceedings of the meeting, RIKEN, Wako city (Japan), March 20--24, 199

On dipole compression modes in nuclei

Isoscalar dipole strength distributions in spherical medium- and heavy-mass nuclei are calculated within random phase approximation (RPA) or quasiparticle RPA. Different Skyrme-type interactions corresponding to incompressibilities in the range 200 - 250 MeV are used. The results are discussed in comparison with existing data on isoscalar giant dipole resonances. Two main issues are raised, firstly the calculated giant resonance energies are somewhat higher than the observed ones, and secondly a sizable fraction of strength is predicted below 20 MeV which needs to be experimentally confirmed

PMUTs Arrays for Structural Health Monitoring of Bolted-Joints

Micro-electro-mechanical systems (MEMS) have enabled new techniques for the miniaturization of sensors suitable for Structural Health Monitoring (SHM) applications. In this study, MEMS-based sensors, specifically Piezoelectric Micromachined Ultrasonic Transducers (PMUT), are used to evaluate and monitor the pre-tensioning of a bolted joint structural system. For bolted joints to function properly, it is essential to maintain a suitable level of pre-tensioning. In this work, an array of PMUTs attached to the head and to the end of a bolt, serve as transmitter and receiver, respectively, in a pitch-catch Ultrasonic Testing (UT) scenario. The primary objective is to detect the Change in Time of Flight (CTOF) of the acoustic wave generated by the PMUT array and propagating along the bolt’s axis between a non-loaded bolt and a bolt in service. To model the pre-tensioning of bolted joints and the transmission of the acoustic wave to and from a group of PMUTs through the bolt, a set of numerical models is created. The CTOF is found to be linearly related to the amount of pre-tensioning. The numerical model is validated through comparisons with the results of a preliminary experimental campaign

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.

Grandi e piccole imprese nel Centro-Nord e nel Mezzogiorno: un modello empirico dell’impatto occupazionale nel lungo periodo

Questo lavoro presenta una verifica dell'ipotesi formulata in Florio (1991, 1996) secondo cui le relazioni fra grandi e piccole imprese sono la risultante di due forze opposte. Da un lato le grandi imprese possono agire come propulsori di sviluppo locale secondo modelli di propagazione ben studiati dal punto di vista teorico ed empirico. D'altro canto le stesse grandi imprese, soprattutto in settori e contesti ambientali deboli, possono avere effetti di spiazzamento dell'offerta locale in particolare attraverso il reclutamento come dipendenti di potenziali piccoli imprenditori. Quale delle due forze prevalga non pu\uf2 essere detto in generale, ma va esaminato in diversi periodi, settori, contesti regionali. Il tema ha particolare rilevanza nel caso italiano sotto il profilo delle politiche pubbliche, in particolare del ruolo che le politiche di sviluppo regionale e per l'occupazione dovrebbero assegnare alle grandi imprese, anche in considerazione dei processi di ristrutturazione che le coinvolgono (Giunta, 1997). Fra queste politiche in Italia, ad esempio, vi sono i contratti di programma con i quali lo Stato sussidia grandi progetti industriali in aree depresse (Florio, Giunta, 1998). Il presente testo non intende rispondere in modo definitivo alla questione proposta, ma suggerisce una metodologia che potr\ue0 essere ulteriormente sviluppata. Per lo svolgimento dell'analisi \ue8 stata costruita una base-dati che comprende dati censuari e dati Inps a base provinciale. In particolare i dati dei censimenti sono stati raccolti dal 1951 al 1991, con una copertura quindi pari a mezzo secolo di storia economica nazionale, aggiornando e migliorando un analogo esercizio presentato in Florio (1991). Il lavoro \ue8 strutturato come segue: a) una prima sezione presenta alcune considerazioni suggerite dall'esame dei dati; b) la seconda sezione presenta un modello empirico; c) nella terza sezione sono esposti i risultati. In appendice, sono riportati per esteso i dati provinciali utilizzati. Gli autori saranno lieti di fornire tale base-dati su dischetto ad altri ricercatori che desiderino verificare o estendere l'analisi

Evaluation of a stacked-FET cell for high-frequency applications

This paper presents the design, electromagnetic simulation strategies and experimental characterisation of a two-stage stacked-FET cell in a 100 nm GaN on Si technology around 18.8 GHz, suited for Ka band satellite downlink applications. A good agreement is found between the electromagnetic simulations and the measured performance on the manufactured prototype, thus demonstrating that a successful voltage combining architecture can be obtained in the frequency range of interest with the selected topology, based on a symmetric fork-like connection between the transistors. This proves the effectiveness of an appropriate electromagnetic simulation set-up in correctly predicting the crosstalk, which typically affects this structure, leading to a correct stacking operation