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220 results on '"Ulivi, L."'

66. Né roccia né palude

Author

Urbani Ulivi, L., Corvi, Roberta, Corvi, Roberta (ORCID:0000-0003-0159-3971), Urbani Ulivi, L., Corvi, Roberta, and Corvi, Roberta (ORCID:0000-0003-0159-3971)

Abstract

Questo contributo ricostruisce il passaggio da una concezione “forte” della conoscenza al modello “debole”, assai più variegato, che ha messo in luce i limiti della precedente impostazione. Il modello “forte”, sostenuto in età con-temporanea dal neopositivismo, vanta una lunga tradizione a partire dall’età moderna, in quanto intende la conoscenza come episteme. Da Popper in poi l’epistemologia ha preso atto che il modello fondazionalista è insostenibile, ma non ha saputo costruire un modello alternativo, che evitasse tanto il relativismo quanto lo scetticismo. Questo saggio suggerisce una direzione in cui l’epistemologia può muoversi al fine di ripensare e, in qualche caso dissolvere, i principali problemi sollevati dalla crisi del modello “forte”, adottanto una prospettiva sistemica, secondo cui la conoscenza non è un mero aggregato di elementi, ma è tale grazie alle relazioni e alle interazioni che si realizzano fra soggetto e oggetto e fra i diversi soggetti conoscenti.

Published
2013

94. Evidence of Phase Separation in the P-T Phase Diagram of the La0.75Ca0.25MnO3 Manganite by Infrared Measurements.

Author

Dore, P., Sacchetti, A., Postorino, P., Congeduti, A., Gorelli, F., and Ulivi, L.

Abstract

Recent infrared absorption measurements performed at different pressures and temperatures on the La0.75Ca0.25MnO3 manganite provided an estimate of the insulator-to-metal transition temperature T IM( P), i.e., the P- T phase diagram of a pseudocubic manganite. Here we consider in detail the P- and T-dependence of the absorption spectral weights n *. The n *( T, P) behavior gives evidence of phase-separation between conducting and insulating domains in the P-T phase diagram, and allows to establish the occurrence of a characteristic temperature T * ≅ 0.6 T IM. For T > T *, when insulating domains decrease on decreasing temperature or on increasing pressure, it is possible to distinguish a metallic region (connected metallic domains) for T * < T < T IM, and an insulating region (disconnected metallic domains) for T > T IM. Below T *, no reduction of the insulating domains, that may still exist, occurs. [ABSTRACT FROM AUTHOR]

Published
2005
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95. Pressure Dependence of Intersubband Transitions in HgTe/Hg0.3Cd0.7Te Superlattices.

Author

Becker, C. R., Latussek, V., Landwehr, G., Bini, R., and Ulivi, L.

Subjects
ABSORPTION, MERCURY, TELLURIUM, CADMIUM, SUPERLATTICES, PHOTOLUMINESCENCE
Abstract

The optical absorption coefficient of HgTe/Hg0.3Cd0.7Te superlattices (SLs) and its pressure dependence has been investigated at hydrostatic pressures up to 30 kbar at room temperature. The corresponding intersubband transition energies result from a comparison of experimental and theoretical absorption coefficients. The latter is based on the band structure, which is calculated using Kane's four-band (8 x 8 k · p) model together with the envelope function approximation. The experimental linear pressure coefficients of the H1 - E1 and H1 - L1 intersubband transitions are in good agreement with the theoretical values, e.g., 7.15 ± 0.3 meV/kbar and 6.2 ± 0.3 meV/kbar compared to 7.4 and 6.4 meV/kbar, respectively. This is in stark contrast to the pressure dependence of ≤1 meV/kbar of the photoluminescence (PL) peaks of a similar SL reported in the literature. Consequently, we conclude that the reported PL peaks are not due to intersubband transitions and that the k · p model correctly reproduces the electronic band structure and its pressure dependence of HgTe/Hg1-xCdxTe SLs. [ABSTRACT FROM AUTHOR]

Published
2005
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96. Infrared Studies of Ar(H2)2 at Low Temperature and High Pressure.

Author

Ulivi, L., Bini, R., Jodl, H., Loubeyre, P., LeToullec, R., and Datchi, F.

Abstract

An extensive infrared absorption study of the compound Ar(H2)2 in the range of pressure from 5 to 30 GPa, and between 30 K and room temperature is presented. This study has permitted the identification and assignment of high–frequency and low frequency vibron–phonon combination bands, as well as of the roto–vibrational bands. Spectra changes lowering temperature, with the appearance of the Q1(0) vibrational peak, are interpreted as arising from conversion of ortho–hydrogen into para–hydrogen in the solid. [ABSTRACT FROM AUTHOR]

Published
1998
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100. Far UV radiation transfer and H2CO lifetime in dense interstellar clouds

Author

Aiello, S., Morbidelli, L., and Ulivi, L.

Abstract

The UV radiation transfer within spherical interstellar dust clouds is analyzed using the method of successive scatterings. The results are used to determine the lifetime of interstellar H2CO against photo-destruction. The effectiveness of this process is compared with those of chemical mechanisms.

Published
1981
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