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M Lucchesi

Publications and source records attributed to M Lucchesi.

At least 19 recordsLinked to original sources
PubMed2005

Emergence of a new feature in the high pressure-high temperature relaxation spectrum of tri-propylene glycol.

We investigated dielectric relaxation of a tri-propylene glycol system under high compression. By increasing temperature and pressure we observed that a new relaxation process emerges from the low frequency tail of the structural peak. This new peak starts to be visible at about 0.5 GPa and becomes clearly evident at 1.7 GPa. However, this additional peak merges again with the structural one as the glass transition is approached, since it has a weaker temperature dependence. This finding enriches the relaxation scenario of molecular glass formers confirming that the application of very high hydrostatic pressure can favor the detection of new relaxation or otherwise unresolved processes in supercooled liquid systems.

Journal Article↗
PubMed2004

Adam-Gibbs model for the supercooled dynamics in the ortho-terphenyl ortho-phenylphenol mixture.

Dielectric measurements of the alpha-relaxation time were carried out on a mixture of ortho-terphenyl (OTP) with ortho-phenylphenol, over a range of temperatures at two pressures, 0.1 and 28.8 MPa. These are the same conditions for which heat capacity, thermal expansivity, and compressibility measurements were reported by Takahara et al. [S. Takahara, M. Ishikawa, O. Yamamuro, and T. Matsuo, J. Phys. Chem. B 103, 3288 (1999)] for the same mixture. From the combined dynamic and thermodynamic data, we determine that density and temperature govern to an equivalent degree the variation of the relaxation times with temperature. Over the measured range, the dependence of the relaxation times on configurational entropy is in accord with the Adam-Gibbs model, and this dependence is invariant to pressure. Consistent with the implied connection between relaxation and thermodynamic properties, the kinetic and thermodynamic fragilities are found to have the same pressure independence. In comparing the relaxation properties of the mixture to those of neat OTP, density effects are stronger in the former, perhaps suggestive of less efficient packing.

Journal Article↗
PubMed2004

Dynamics of supercooled and glassy dipropyleneglycol dibenzoate as functions of temperature and aging: Interpretation within the coupling model framework.

Dielectric relaxation measurements of a typical small molecular glassformer, dipropyleneglycol dibenzoate show the presence of two secondary relaxations. Their dynamic properties differ in the equilibrium liquid and glassy states, as well as the changes during structural recovery after rapid quenching the liquid to form a glass. These differences enable us to identify the slower secondary relaxation as the genuine Johari-Goldstein (JG) beta-relaxation, acting as the precursor of the primary alpha-relaxation. Agreement between the JG beta-relaxation time and the independent relaxation time of the coupling model leads to predicted quantitative relations between the JG beta-relaxation and the alpha-relaxation that are supported by the experimental data.

Journal Article↗
PubMed2002

Relaxation processes in an epoxy resin studied by time-resolved optical Kerr effect.

The dynamics of the epoxy resin phenyl glycidyl ether, a fragile glass-forming liquid, is investigated in the liquid and supercooled phases by time-resolved optical Kerr effect experiment with an heterodyne detection technique. We tested the mode-coupling theory and found that the predicted dynamic scenario allows to reproduce properly the measured signal, for t>1 ps, in the whole temperature interval investigated. Furthermore, the values of T(c) and lambda, obtained from the analysis of three different and independent dynamic regimes (alpha regime, von Schweidler, beta regime), are in remarkable agreement. Moreover, relaxation times obtained from optical Kerr effect and dielectric spectroscopy measurements are compared. The two time scales differ only for a constant factor in the whole temperature interval investigated.

Journal Article↗
PubMed2001

Effect of pressure on the dynamics of glass formers.

A description of the pressure dependence of the structural relaxation time has been derived from the Adam-Gibbs theory by writing the configurational entropy in terms of the excess heat capacity and the molar thermal expansion. This new equation was tested successfully on dielectric relaxation data for an epoxy compound over a wide range of temperature and pressure.

Journal Article↗
PubMed2001

Pressure dependence of structural relaxation time in terms of the Adam-Gibbs model.

A new equation describing the behavior of the structural relaxation time, tau(T,P), as a function of both pressure and temperature, is discussed. This equation has been derived from the Adam-Gibbs theory by writing the configurational entropy, S(c), in terms of the excess thermal heat capacity and of the molar thermal expansion. Consequently, the parameters introduced in the expression are directly related to specific physical properties of the material, such as the thermal expansion coefficient alpha and the isothermal bulk modulus K0. At a fixed pressure, for low pressures, the found equation reduces to a Vogel-Fulcher-Tammann equation of tau versus temperature with the fragility parameter independent from pressure. The equation for tau(T,P) was successfully tested directly by fitting the dielectric relaxation time data for two isothermal and one isobaric measurements on diglycidyl ether of bisphenol-A, carried out in previous experiments. The parameters estimated by the best fit were in reasonable agreement with the values determined from the known physical properties of the material. Finally, the expression for the change versus pressure of the temperatures at which the same value of tau(max) is obtained (e.g., the change versus pressure of the glass transition temperature) agrees with several expressions previously proposed in the literature to provide a phenomenological description of the observed phenomena.

Journal Article↗
PubMed2000

Mucormycosis manifesting as proptosis and unilateral blindness.

A 51-year-old woman presented to the emergency department (ED) of another institution with sudden onset of blindness in the left eye. The patient was found to have no light perception in the left eye and a marked chemosis occurring several days after a fall. She was transferred to the hospital for ophthalmologic evaluation. Upon careful history and physical examination, the diagnosis of rhinocerebral mucormycosis was considered and urgent ophthalmology and otolaryngology consults were obtained. The patient underwent extensive surgical debridement and pharmacologic treatment. The diagnosis was confirmed by pathological specimens. In this case report, the clinical presentation, pathogenesis, diagnostic workup, and ED management of mucormycosis are discussed, highlighting the possible diagnostic and therapeutic pitfalls that are most pertinent to the emergency physician.

Accidental Falls↗
PubMed1984

Antimycobacterial activity of rifaximin (L/105) in experimental tuberculosis in the guinea pig.

The antimycobacterial activity of rifaximin was studied in the guinea pig, after oral administration. The experiment confirmed the scanty absorption of rifaximin in the gastrointestinal tract, as the two dosages used (60 and 30 mg/kg) did not modify the tubercular illness after four months of therapy. Furthermore, sensitivity to rifaximin of the callenging Mycobacterium tuberculosis isolated at the end of the study from the spleen, lung, liver and lymph nodes of the guinea pigs that received rifaximin did not change.

Animals↗
PubMed1976

Primary resistence of mycobacteria in tuberculosis patients.

Primary mycobactria resistance especially in some countries may be a serious obstacle to a successful therapy and the number of patients carrier of primary resistant mycobacteria remains almost at the same level in spite of the chemotherapeutic treatments and the usually rapid recover of the newly diagnosed cases. This may probably be attributed to the fact that the number of chronic patients, spitting resistant tubercle bacilli has remained almost the same, because these patients are eliminated little by little. In our country there is a constant regression of the morbidity, but not so rapid as expected, The newly diagnosed patients are generally young and, if well treated, they heal quickly and well; moreover, they are usually not so richly bacillised as they used to be once and the severity of their disease, globally evaluated, appears also reduced. The cultural positivity at the first admission into hospital is also diminishing. From all the above facts it is obvious that in order to eradicate tuberculosis it is necessary: First - to avoid creatin chronic patients; in order to reach this goal the treatment must be the most effective possible from the very beginning: INH and Rifampin. Second - to try to cure the chronic patients and to render them abacillary of, at least, to treat them intensively, with the purpose of inducing in the infecting flora a polyresistance which reners the mycobacteria hypovirulent, especially if it includes a R/AMP resistance over 40-gamma. Third - the role of the primary resistance in the epidemiology and the evolution of tuberculosis in the various countries and in the single patients, may be very different.

Adolescent↗