534 research outputs found
Review of M. Galtarossa. Mandarini veneziani, Aracne editrice, Rome 2009
No full textCR de M. Galtarossa. Mandarini veneziani, Aracne editrice, Rome 2009[à paraître dans la revue "Storicamente" en 2012] Recensione di M. Galtarossa. Mandarini veneziani. La cancelleria ducale nel Settecento, Aracne editrice, Rome 200
Distributed characterization of coupling in multimode and multicore fibers
No full textDistributed characterization of mode coupling is key to understanding the behavior of multimode and multicore fibers. This paper presents a theoretical framework that precisely assess limits and potentialities of mode-selective distributed measurements based on Rayleigh backscattering
Liberali, cattolici e socialisti a Verona dalla fine dell’Ottocento al Fascismo
No full textAtti del convegno “Una città, un’industria, una famiglia: i Galtarossa” (tenutosi il 7.2.1997), organizzato da Associazione industriali e Osservatorio Provinciale del settore Metalmeccanico Fim Fiom Uilm di Veron
Reflectometric measurements of polarization properties in optical-fiber links
No full textPolarization sensitive reflectometric techniques can be effectively used to perform spatially resolved measurements of polarization properties of fiber optic link - such as birefringence, polarization mode dispersion and polarization dependent loss. In particular, this contribution is focused on polarization sensitive OTDR and provides a survey of its theory and main applications. Special emphasis is given to the characterization of fiber birefringence, that allows to inspect the fiber while cabled and, consequently, to test and improve the cabling process. In addition, the analysis of the birefringence also allows to define reliable mathematical models, which are essential for the design of low polarization mode dispersion fibers. Reflectometric measurements of polarization mode dispersion and polarization dependent loss are also discussed
A Preliminary Analysis of Spin in Few-Mode Optical Fibers
No full textThe effect that spin has on modal dispersion of few-mode fibers is qualitatively studied. The analysis shows that spin may indeed reduce modal dispersion within the LP1,1 manifold, although reduction may be not as effective as in single-mode fibers, because spin-induced mode coupling is not always as uniform
Stress distribution in optical-fiber ribbons
No full textPrevious results indicate that fibers in ribbons are sometimes affected by systematic birefringence superimposed on the random one, their relative weights depending on fiber position in the ribbon. We report new theoretical and experimental results on stress distribution in ribbons, which is shown to depend on thermal and mechanical properties of the common coating. Numerical simulations are based on the theory of elasticity and the finite-element method (FEM). Polarization dispersion measurements vs. temperature match very well with numerical results, and indicate that central fibers in the ribbon exhibit significantly larger birefringence than lateral ones
Multinucleon transfer in the 197Au+130Te reaction studied with a high-resolution kinematic coincidence
No full textHeavy ion transfer reactions play an important role for the definition of the reaction mechanism that describes the evolution from the quasi-elastic to the more complex deep-inelastic regime. At energies close to the Coulomb barrier these processes are mainly governed by optimum Q-value considerations and nuclear form factors. As a consequence, for nuclei close to the stability line the dominant channels are the neutron pick-up and the proton stripping. The use of neutron-rich projectiles is expected to open the possibility to populate neutron stripping and proton pick-up paths. This corresponds, for the heavy partner, to the population in the “south-east” direction of the nuclear chart, leading to the neutron-rich heavy region, like that below 208Pb or in the actinides and trans-actinides, which can be hardly accessed by fragmentation or fission reactions. Multinucleon transfer may represent a suitable mechanism to approach these neutron-rich areas.
In this work we studied the multinucleon transfer reaction 197Au+130Te at Elab = 1.07 GeV in inverse kinematics to extract absolute yields for neutron and proton transfer channels in the vicinity of 132Sn and, at the same time, to obtain information on the associated heavy partner. We adopted for the first time a method which makes use of a particle-particle coincidence in which one of the two devices is a high-resolution mass spectrometer, PRISMA, which can completely identify the light partner of the reaction in A, Z and Q value; the coincident detector works as a second arm of PRISMA and is placed at the kinematically correlated angle for the detection of the heavy partner with lower resolution but comparable efficiency. The obtained yields can then be compared with theoretical calculations which predict, for this system, the population of neutron stripping and proton pick-up channels, in turn leading to the production of neutron-rich nuclei approaching the region close to 208Pb.
This thesis presents the results of this experiment. Through an event-by-event trajectory reconstruction in PRISMA we could achieve enough mass resolution to distinguish final isotopes and extract the corresponding yields for neutron transfer channels. For proton ones, with about ten times less cross sections, we could extract the mass-integrated yields corresponding to each nuclear charge. As theoretically predicted, the neutron stripping and proton pick-up channels have been identified and their yields compared with the calculations performed with the GRAZING model for transfer reactions. For neutron transfer the comparison showed a quite good agreement; for proton transfer the model is able to reproduce quite well the stripping channels but largely underestimates the pick-up ones.
After verifying the correct functioning of the kinematic coincidence, we reconstructed the mass of the heavy partner in the second arm by assuming a binary character of the reaction. From the correlation between the mass of the Te isotopes identified in PRISMA and the mass distributions of the Au ions detected in the second arm, we could assess that the reaction maintains its (quasi) binary character up to the transfer of 3-4 neutrons. This result is consistent with the behaviour of the total kinetic energy loss distributions, analyzed and compared, on the same footing, with and without using the information of the coincident second arm. The yields of the Au mass distributions correlated to each Te isotope in PRISMA were compared with GRAZING calculations. The trend of the yields corresponding to the population of neutron-rich isotopes of the heavy partners well agrees with the GRAZING predictions. The limited effect of the evaporation on the final yields when a low bombarding energy is employed has been argued from the comparison between experimental widths of the mass distributions and Monte Carlo calculations.Le reazioni di trasferimento tra ioni pesanti giocano un ruolo importante nel definire i meccanismi di reazione che descrivono l'evoluzione dal regime quasi-elastic al più complesso deep-inelastic. A energie vicine alla barriera Coulombiana questi processi sono governati principalmente da considerazioni di ottimo Q-valore e fattori di forma nucleari. Di conseguenza per nuclei vicini alla stabilità i canali dominanti sono il pick-up di neutroni e lo stripping di protoni. Ci si aspetta che l'uso di proiettili ricchi di neutroni apra la possibilità di popolare i canali di stripping di neutroni e pick-up di protoni. Questo corrisponde, per il partner pesante, alla popolazione in direzione "sud-est" nella carta dei nuclidi, verso la regione pesante ricca di neutroni, come quella sotto il 208Pb o negli attinidi e trans-attinidi, difficilmente raggiungibile tramite reazioni di frammentazione o di fissione. Il trasferimento di molti nucleoni (MNT) può rappresentare un metodo adatto per raggiungere queste regioni.
In questo lavoro abbiamo studiato la reazione di MNT 197Au+130Te a Elab = 1.07 GeV in cinematica inversa per estrarre le yield assolute dei canali di trasferimento di neutroni e protoni nelle vicinanze del 132Sn e, allo stesso tempo, ottenere informazioni sul partner pesante associato. Si è adottato per la prima volta un metodo di coincidenza particella-particella in cui uno dei due rivelatori è uno spettrometro magnetico ad alta risoluzione, PRISMA, che identifica completamente il partner leggero della reazione in A, Z e Q valore; il rivelatore coincidente è usato come secondo braccio di PRISMA posizionato all'angolo cinematicamente correlato per la rivelazione del partner pesante con minore risoluzione ma comparabile efficienza. Si possono confrontare le yield ottenute con calcoli teorici che predicono, per questo sistema, la popolazione di canali di stripping di neutroni e pick-up di protoni, che conducono a loro volta alla produzione di nuclei ricchi di neutroni in prossimità della regione vicina al 208Pb.
Questa tesi presenta i risultati di questo esperimento. In PRISMA si è ottenuta una risoluzione in massa sufficiente per estrarre le correspondenti yield per i canali di trasferimento di neutroni. Per quelli di protoni, con sezioni d'urto circa 10 volte inferiori, abbiamo estratto le yield massa-integrate corrispondenti ad ogni Z. Come predetto teoricamente, si sono identificati i canali di stripping di neutroni e pick-up di protoni e le loro yield confrontate con le predizioni del modello GRAZING per reazioni di trasferimento. Per i neutroni il confronto ha mostrato un buon accordo tra dati sperimentali e calcoli. Per i protoni il modello riesce a riprodurre abbastanza bene i canali di stripping ma sottostima di molto quelli di pick-up.
Dopo aver verificato il corretto funzionamento della coincidenza cinematica, abbiamo ricostruito la massa del partner pesante nel secondo braccio assumendo un carattere binario della reazione. Dalla correlazione tra la massa degli isotopi del Te identificati in PRISMA e le distribuzioni di massa degli ioni Au rivelati nel secondo braccio, si è potuto dimostrare che la reazione mantiene il suo carattere (quasi) binario fino al trasferimento di 3-4 neutroni. Questo risultato è consistente con il comportamento delle distribuzioni di perdita di energia cinetica totale, analizzate e confrontate, allo stesso livello, con e senza l'utilizzo del secondo braccio coincidente. Le yield delle distribuzioni di massa del Au correlate ad ogni isotopo del Te in PRISMA sono state comparate con calcoli di GRAZING. Il trend delle yield corrispondenti alla popolazione di isotopi del partner pesante ricchi di neutroni è in buon accordo con le predizioni di GRAZING. L'effetto limitato dell'evaporazione sulle yield finali quando viene impiegata una bassa energia di bombardamento è stato derivato dal confronto tra le larghezze sperimentali delle distribuzioni di massa e i calcoli Monte Carlo
Optical fibre with reduced polarization mode dispersion and method for obtaining an optical fibre with reduced polarization mode dispersion
No full textThis invention relates to optical fibres, in particular to single mode optical fibres with reduced polarization mode dispersion (PMD). This invention also relates to a method for obtaining an optical fibre with reduced PMD.
The invention may apply to all kinds of optical fibres, as for example dispersion-unshifted fibres, dispersion-shifted fibres, non-zero-dispersion fibres, dispersion-compensating fibres, fibres for optical amplifiers (such as erbium doped fibres), fibres for optical sensors, fibres for gratings
Distributed characterization of few-mode fibers based on optical frequency domain reflectometry
No full textA novel technique to measure differential group delay and modal birefringence along few mode fibers is presented. The method relies on the analysis of the spectral correlation between two properly-selected sections of the fiber's Rayleigh-backscattered trace, acquired with an optical frequency domain reflectometer. Experiments performed on a two-mode-group fiber confirm the viability of the method
Widely time-dispersion-tuned fiber optical oscillator and frequency comb based on multiple nonlinear processes
No full textAn all-fiber optical oscillator based on three nonlinear processes, namely stimulated Raman scattering and broadband
and narrow-band optical parametric amplification, is presented and experimentally characterized. The
wavelength tuning is achieved by means of the time-dispersion technique and spans over 160 nm. Through the same
technique a fast tunable optical frequency comb has been realized exploiting cascaded four-wave mixing
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