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We numerically investigate the "topography" of the multidimensional potential energy landscape of Lennard-Jones model glasses of small size. We first determine the statistical features of local minima and saddle points, relationships betwenn them and cross-correlations among the measured quatities. From these informations we approximate the partition function of the glass restricting the sum over potential energy minima and taking into account harmonic vibrations around them. The approximation is validated by the comparison with Molecular Dynamics computation up to a temperature in the liquid phase, evidencing the reliability of simple local-vibrations/collective-jumps model in describing glass-forming systems.

The diffusion of peritoneal dialysis (PD) at home is somewhat restricted by the difficulty of transport and storage of a large amount of dialytic solutions. This problem is exacerbated in the case of hemodialysis. With the aim of producing pure water to be used in preparing the solution for peritoneal dialysis, or for hemodialysis in general, as one example, we purified the spent dialysate solution from PD. Experiments were carried out with 24 dialysate solutions taken from 8 patients. Pure water was obtained by means of a thermodialysis process in a hollow fiber reactor operating under nonisothermal conditions. Results show that the yield of the nonisothermal process is dependent on the temperature difference applied across the hydrophobic membranes. The production of pure water per square meter of membrane and per hour was equal to 0.55 or 1.2 or 2.0 liters, with a temperature difference of 11°C or 21°C or 28°C, respectively. These results encourage the use of the thermodialysis process in the production of pure water for clinical uses

The phase diagram of a charged colloidal system (Laponite) has been investigated by dynamic light scattering in a previously unexplored range of salt and clay concentrations. Specifically, the clay weight and salt molar concentrations have been varied in the ranges Cw = 0.004 ÷ 0.025 and Cs = (1 × 10-3 ÷ 5 × 10-3) M, respectively. As in the case of free salt water samples (Cs ≃ 1 × 10-4 M), an aging dynamics toward two different arrested phases is found in the whole examined Cw and Cs range. Moreover a transition between these two different regimes is found. It is clear from these measurements that a revision of the phase diagram is necessary and a new “transition” line between two different arrested states is drawn.

The recently developed inelastic X-ray scattering technique opens a new kinematic region at the observation of molecular liquids vibrational dynamics over the lengthscales of the interparticle separation. We illustrate the capabilities of this powerful technique through the results obtained from liquid glycerol. A detailed analysis of the high-frequency vibrational dynamics of this system at ambient temperature is reported. New results in the study of structural relaxational dynamics in the high-temperature range (up to T= 560 K) are also discussed.

The static structure factors S(Q) of liquid normal H2and D2have been measured in the wave-vector region 5 nm−1

In this paper, the soil temperature distribution under a plastic cover is determined, by devising a transient, one-dimensional model to describe the different heat transfer interaction between soil and environment. The inherent radiative heat exchange along a spectral range has been considered, including the variability of incidence angle of solar radiation. Conduction through the soil layers, their volumetric heat capacity, convection within the air gap and radiation through the cover has been taken into account, considering weather data, at the considered site, as boundary conditions. The simulation is carried out by using a numerical method, and results have been favourably validated by experimental observation from field tests. The reported study confirms that, for the employed materials, the thermal regime within the soil depends on their long-wave radiative behaviour.

Raman depolarization ratio has been measured in superionic AgI as a function of temperature. The depolarization ratio shows a change from the value ∼ 1 to about 0.7. We propose a model to explain experimental results of ϱ(T) and IR(T) in which the situation of Ag+ions can be described by an antiferromagnetic-like model: the Ag+ions pass from non stochiometric local configuration (low temperature α-phase), to stochiometric configuration (high temperature α-phase).

Rovibrational Raman spectra of low density H2S gas have been measured with the aim of extracting the components of the polarizability tensor derivatives with respect to the normal modes of the molecule. Absolute values are obtained by comparison with the intensity of the symmetric stretching polarized Q-branch available in the literature.A fit to the free rovibrational spectra is employed in order to separate overlapping bands and to determine the anisotropy ratio for the totally symmetric A1 bands.The results are compared with those obtained with a bond polarizability model and with SCF calculation performed by Martin, Davidson and Eggers [5].

The effects of centrifugal distortions on polarizability anisotropies are taken into account to explain the experimental Rayleigh spectrum of H2S. Centrifugal corrections are calculated following a first-order perturbation theory due to Toyama et al. The simulated spectrum agrees with the experimental one qualitatively, but the calculated corrections to the rotational transitions are not large enough to reproduce the experimental findings. Possible origins of that discrepancy and consequences of a significant variation of the optical anisotropy are briefly discussed.

The rigorous treatment of light scattering effects in dense dielectric media can be achieved only by accounting fully for the dipolar induction appearing in the microscopic Maxwell equations. The starting point, namely the expression for the local microscopic electric field, is here cast in a new form which allows us to deduce, rigorously, for a system of point polarizable atoms, a tractable self-consistent equation for the effective atomic polarizability. The main implications of this equation, which have already been used successfully in evaluating the Brillouin scattering intensity in rare gas crystals, are briefly discussed.

The reaction field method has been extended to include polarization effects. This has been the basis for developing a consistent and fast scheme to be used in molecular dynamics simulations for dealing with long-range dipolar forces and many-body polarization effects. The proposed scheme is convenient for large size samples. The computation time is relatively short and increases only proportionally to the number of molecules. The excellent energy conservation is a major advantage and gives confidence for extracting accurate time correlation functions even at long times.As an application we have included the normal polarizability together with the first and second hyperpolarizabilities in a three-point-charge model for water, of the TIP4P type. If we take as standard the CPU time per step (of a vector computer) for the TIP4P water model with a sample of 500 molecules and Ewald sums, the non-polarizable model with reaction field takes from 25 to 50% depending on the cut-off radius and the polarizable model from 50 to 100%.

Polarized and depolarized Raman spectra in the translational and librational region of liquid water and heavy water have been measured as a function of temperature. A detailed analysis of the isotropic spectrum is performed. This component, which cannot arise from any 'allowed' molecular contribution in this frequency region, shows two distinct spectral features which can be obtained from an analysis of temperature dependent lineshapes. The first one, which dominates the spectrum up to 500 cm-1, shows on the basis of a H2O-D2O comparison a translational behaviour at very low frequency and a librational one at higher frequencies. It is assigned on the basis of its frequency profile, of its absolute intensity and of its temperature dependence to rototranslational spectra due to long range induction mechanisms already found in many molecular liquids.The second one, which is peaked at roughly 800 cm-1 in water and extends up to the bending mode region suggests the existence of a short range interaction induced polarizability.

The general scattering equation is derived and discussed from a microscopical point of view for both ordered and disordered harmonic solids.In particular in the framework of a pure dipole-induced dipole theory the disorder-induced light scattering spectra are discussed and some applications to model systems are shown.

We report a numerical study concerning the vibrational dynamics and the Raman coupling coefficient of two- and three-dimensional site-percolating structures, as well as an analysis of how to characterize the fracton wavefunctions. We discuss the difficulty of finding a scaling law for the Raman coupling coefficient in terms of the macroscopic parameters which characterize the fractal structure and dynamics; the oscillatory nature of the vibrational wavefunctions is examined.

A molecular dynamics simulation of the Raman spectra of water in the translational and librational region is presented. Both depolarized and isotropic spectra are calculated at five temperatures in the 250-380 K range and compared with the experimental data. The relevance of 'collision-induced' contributions is stressed and in particular the dipole-induced-dipole is shown to dominate the depolarized spectra, whereas contributions to the effective molecular polarizability involving higher order terms in the multipolar expansion account for the low frequency isotropic spectrum. Present results strongly support previous analysis of the experimental data.

Corrections to the dipole-induced-dipole theory coming from both electronic overlaps and dispersion-force effects are introduced into the self-consistent equation for the effective atomic polarizability and applied to the case of rare-gas crystals. We show that the one-phonon expansion for Brillouin-scattered intensities can be rigorously solved, with the difference from a pure dipole-induced-dipole theory that Brillouin intensities now contain three microscopic quantities of the system. In the case of krypton crystals these quantities, which are related to the corrections to elasto-optic coefficients, are estimated by using experimental data. A comparison with theoretical predictions and experimental results is discussed. In the case of neon, argon and xenon available experimental data are not sufficient to estimate the three quantities, so just the rates of the elasto-optic coefficients are discussed. A slight discrepancy might be due to an overestimate of the anisotropic short-range contribution coming from the self-consistent-field calculations.

A pure dipole induced dipole (DID) theory, which properly takes into account long range contributions to the effective atomic polarizability renormalization, is developed to evaluate the Brillouin scattering intensities for rare gas crystals (RGC). The DID effect is considered at all the orders by rigorously solving the self consistent equation for the effective atomic polarizability. To evaluate the contribution of distant atoms, which is significant in a cubic structure, the dipole propagator and the driving field phase factor have been both used without short-range approximations. The results obtained for the elastooptic coefficients are discussed in relation to other theoretical predictions. A comparison is made with the experimental data of Stoicheff and coworkers, directly calculating the measured quantities in all the reported scattering configurations. We conclude that pure DID effects will reproduce the experimental results in the case of neon and argon, while the discrepancies increase for krypton and xenon. This suggests that the overlap contributions to the atomic polarizability fluctuations, which has been already included in previous theories, cannot be neglected in heavy rare gas crystals.

Polarized and depolarized Raman spectra of room temperature liquid H2O and D2O have been measured up to the bending region. Both spectral shapes and depolarization ratios are analysed in the translational and librational regions. An isotropic spectral component extending over all the investigated frequency range is derived and interpreted in terms of interaction induced mechanisms involving the polarizabilities of the isolated molecule.

Rotational and interaction induced contributions in the light scattering spectrum of gaseous H2S are identified and discussed as a function of density. The intensity of the latter is shown to obey a density squared dependence and to be in agreement with that predicted by the first order dipoled induced dipole (DID) model for point polarizable scatterers.

Polarization ratio measurements in liquid H2S as a function of frequency are reported from 0 to 1350 cm-1. An isotropic induced contribution to the Rayleigh wing is derived. Absolute intensities, obtained from a comparison with the polarized vibrational stretching, are also discussed.

A comparison between neutron scattering data in single crystals and polycrystals and light scattering data suggest an overall picture of the dynamics of silver and iodine ions. On this basis an interpretation of the Raman spectral shape between 2 and 200 cm−1is given in terms of transverse and longitudinal acoustic phonons as well as optic phonons. The diffusive motion of silver ions is predicted, on the basis of Funke et al. neutron data, in a much lower frequency region, while the correlation between Ag+ions is mainly responsible for the Raman spectral shape and its small variation with temperature.

The interpretation of light scattering data in homogeneous disordered solids, as far as the intensities and positions of the Brillouin peaks are concerned, is reviewed on the basis of the existing phenomenological theories. A microscopic, fully electrodynamic theory is presented, which allows the calculation of Brillouin intensities. The theory, when expanded in terms of fluctuations from the average reference structure, yields zero-order expressions for the elasto-optical coefficients entirely in terms of the refractive index of the medium.A comparison is made with recent data obtained with a new high-resolution high-luminosity high-contrast monochromator and with already published data on a number of glasses. The discrepancies encountered and the role played by higher-order terms in the fluctuations are discussed. It is suggested that the intensity of the depolarized longitudinal and transverse components contains relevant dynamic and structural information on these systems.

In a previous paper the reaction field method has been extended to include polarization effects [1]. This has been the basis for developing a consistent and fast scheme to be used in molecular dynamics simulations for dealing with long-range dipolar forces and many-body polarization effects. The iterative procedure has been found to be very convenient method to solve the electrostatic problem with a large number of induced dipoles and charge interactions. Here we analize the stability and the precision of the iterative solution in molecular dynamics runs, i.e. we study the capability of the algorithm to keep finite the errors on the evaluation of the induced dipoles during the run, as well as we evaluate the mean standard error themself as a function of the relevant free parameters of stable iterative procedures. The validity of the derived expressions has been tested numerically by performing molecular dynamics runs with a plausible polarizable model for water.

We investigate the dynamics of a 10 fs light pulse propagating in a random medium by the direct solution of the three-dimensional Maxwell equations. Our approach employs molecular dynamics to generate a distribution of spherical scatterers and a parallel finite-difference time-domain code for the vectorial wave propagation. We calculate the disorder-averaged energy velocity and the decay time of the transmitted pulse versus the localization length for an increasing refractive index.

A possible autoimmune aggression to pituitary somatotrophs has been suggested by the occurrence of antipituitary antibodies (APA) directed against GH-secreting cells in some cases of GH deficiency (GHD) both in adults and in children and in some patients with autoimmune poliendocrine syndrome. We also detected APA in some patients with idiopathic short stature (ISS) and suggested that the presence of these antibodies could identify those of them prone to develop GHD. In fact, patients with ISS, resulted positive for APA at the first observation, during a longitudinal follow-up showed an impaired GH response to the stimuli in subsequent years suggestive of acquired GHD. Also in such patients we demonstrated that the target of APA were the somatotrophs and that an autoimmune attack to these cells may be the underlying cause of hormonal impairment in several children with GHD positive for APA. In this connection we suggested that in these patients an early iso-hormonal therapy with recombinant GH may be useful to interrupt or delay the progression towards a clinical GHD.

Nei pazienti con deficit idiopatico di GH dell’adulto (GHDI), il rilievo di anticorpi anti-ipofisi (Ab-I) diretti contro le cellule GH-secernenti può indicare la presenza di una patologia ipofisaria autoimmmune. Scopo dello studio è stato quello di 1) valutare la presenza di Ab-I in bambini prepuberi con deficit idiopatico di GH e in bambini con bassa statura idiopatica (BSI), identificando le cellule ipofisarie verso cui erano diretti gli anticorpi anti-ipofisi; 2) verificare se la presenza di Ab-I in bambini con BSI possa essere predittiva dello sviluppo di un deficit di GH (GHD). È stato pertanto eseguito uno studio cross-sectional e in parte longitudinale presso le Unità di Endocrinologia e Pediatria dell’Università di Napoli. Nello studio sono stati arruolati 26 bambini con GHDI (Gruppo 1), 60 bambini con BSI (Gruppo 2), 33 bambini con GHD dovuto a lesioni o anomalie ipotalamo-ipofisarie (Gruppo 3) e infine 40 soggetti di controllo. Diciannove bambini del Gruppo 2 sono stati rivalutati dopo 2 anni. Tutti i pazienti sono stati sottoposti a valutazione della secrezione del GH, alla determinazione dell’IGF-I sierico e degli Ab-I mediante immunofluorescenza indiretta. Al momento dell’arruolamento, Ab-I diretti contro le cellule GH-secernenti sono stati riscontrati in 7 bambini su 26 del Gruppo 1 e in 14 su 60 del Gruppo 2. Diciannove bambini, 8 con Ab-I positiv i e11 con Ab-I negativi, rivalutati 2 anni dopo l’arruolamento nello studio, mostravano lo stesso pattern anticorpale. La rivalutazione della secrezione del GH eseguita 2 anni dopo mostrava lo sviluppo di un GHD in tutti i pazienti con Ab-I positivi tranne uno, mentre nessuno dei pazienti con Ab-I negativi sviluppava GHD. In conclusione, il GHDI nei bambini può essere frequentemente associato con gli Ab-I diretti controllo le cellule GH-secernenti. Il riscontro di Ab-I in bambini con BSI potrebbe identificare coloro che sono predisposti a sviluppare il GHD.