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We report a compared analysis of inelastic X ray scattering (IXS) and of low frequency Raman data of glassy 3-methylpentane. The IXS spectra have been analysed allowing for the existence of two distinct excitations at each scattering wavevector obtaining a consistent interpretation of the spectra. In particular, this procedure allows us to interpret the linewidth of the modes in terms of a simple model which relates them to the width of the first sharp diffraction peak in the static structure factor. In this model, the width of the modes arises from the blurring of the dispersion curves which increases approaching the boundary of the first pseudo-Brillouin zone. The position of the boson peak contribution to the density of vibrational states derived from the Raman scattering measurements is in agreement with the interpretation of the two excitations in terms of a longitudinal mode and a transverse mode, the latter being a result of the mixed character of the transverse modes away from the center of the pseudo-Brillouin zone.

Cyclodextrin nanosponges (CDNS) are a very promising class of cross-linked polymers, made up of cyclodextrins. CDNS swollen in aqueous solution give rise to cyclodextrin-based hydrogel in different states—gel or liquid suspension—depending on the hydration level of the system. Here we present a thorough inspection of the vibrational dynamics of these hydrogel by Raman scattering experiments, with the aim of clarifying the role played by the hydrogen-bond dynamics of water molecules confined into the nano-sized pores of nanosponges in determining the rigidity of the hydrogel network and their maximum water-holding capacity. Changes occurring in the spectral shape of the OH stretching band of water were interpreted by accounting the connectivity pattern of water molecules concurring to the gelation process. Spectral deconvolution analysis gives evidence of the existence of a characteristic cross-over hydration level associated to the rearrangement of water molecules in more cooperative, bulk-like networks as a consequence of saturation sites of water confinement of nanosponges. This interpretation is further confirmed by the inspection of the estimated collective intensities. These findings also support the existence of a specific phase diagram of the cyclodextrin nanosponges hydrogel, where the molecular structure of the cross-linking agent used during the synthesis of nanosponge plays a fundamental role in defining the nano- and microscopic properties of the system.

ed spectra, and assigned to the carbonyl stretching modes of the polymeric network, is performedby using band deconvolution procedures.At the same time, a detailed inspectionof the low-wavenumber vibrational dynamics of these polymers iscarried out, focusing on the modifications occurring on the so-called boson peak. The simultaneous analysis of different wavenumber ranges in Raman and infrared spectra of cyclodextrin nanosponges allows us to develop a reliable strategy for exploring both the cross-linking degree and the elastic properties of these innovative materials. The overall results give a complete characterization of the structural and dynamical properties of the system, in turn strictly connected to the entrapment/transport ability of these polymeric matrices. Copyright © 2013 John Wiley & Sons, Ltd.

The physical properties of disordered systems are in the focus of a large research effort. In particular, one of the open problems related to glasses is their excess of modes in the THz frequency range over the vibrational contribution predicted by the Debye model. In fact, one could expect the continuum approximation underlying the Debye model to hold in glasses at long wavelengths at least as well as in crystalline solids. Experiments, instead, seem to indicate that the specific heat at low temperature (a few Kelvin) and the density of vibrational states at low frequency (a few terahertz) are very different from the Debye prediction. We present here a detailed analysis of specific heat measurements of vitreous GeO2, a prototype of strong glasses, and of permanently densified vitreous GeO2. Our data give experimental evidence that glasses do not show any excess of vibrational modes when compared to their crystalline counterparts of similar mass density.

An integrated experimental approach, based on inelastic light-scattering techniques, has been here employed for a multilength scale characterization of networking properties of cyclodextrin nanosponges, a new class of cross-linked polymeric materials built up from natural oligosaccharides cyclodextrins. By using Raman and Brillouin scattering experiments, we performed a detailed inspection of the vibrational dynamics of these polymers over a wide frequency window ranging from gigahertz to terahertz, with the aim of providing physical descriptors correlated to the cross-linking degree and elastic properties of the material. The results seem to suggest that the stiffness of cross-linked polymers can be successfully tuned by acting on the type and the relative amount of the cross-linker during the synthesis of a polymer matrix, predicting and controlling their swelling and entrapment properties. The proposed experimental approach is a useful tool for investigating the structural and physicochemical properties of polymeric network systems.

International audience; Raman scattering is used to investigate the vibrational spectrum of a sodium silicate glass around the boson peak frequency range at temperatures between 10 and 450 K. The comparison with the density of states measured with coherent neutron scattering allows one to determine the Raman coupling function. This quantity presents a linear frequency dependence in the boson peak region and a negligible temperature dependence, confirming similar observations in other glasses. The Raman spectra at different temperatures scale according to the Debye frequency determined from the sound velocity measured at terahertz frequency with inelastic x-ray scattering. This result confirms previous neutron scattering data and the importance of measuring the elastic properties of the glass in the proper frequency range.

We report on a Raman and inelastic neutron scattering investigation of the vibrational dynamics of permanently densified v-GeO2 glasses. The comparison between the two techniques allows us to derive the Raman coupling function C(omega). This quantity shows a linear frequency dependence in the boson peak range and is not affected by the sample densification. We thus show that Raman spectroscopy can be used as a complementary technique to neutron scattering as a probe of the density of vibrational states in glasses. The evolution of the Raman spectra with the density of the studied samples compares well with the neutron results, confirming the existence of a master curve associated to a single scaling parameter.

We report Raman scattering spectra for the network glass former vitreous germania (v-GeO2) measured in the 10–1200 K temperature range. The results show an interesting temperature dependence of the quasi-elastic scattering. Comparing this study with acoustical attenuation measured by ultrasonic absorption and Brillouin light scattering, we found that the mechanism giving rise to quasi-elastic scattering in this system seems to be the same as the one causing the acoustic attenuation.

Three different samples of β cyclodextrin nanosponges (CDNS) are prepared from β cyclodextrin (βCD) and pyromellitic dianhydride (PMA). CDNS are cross-linked, nanoporous materials whose pore size can be modulated by suitable choice of the CD/PMA molar ratio. In the presence of aqueous solutions they can swell giving rise to gel-like behavior. The Raman spectra of dry and water treated CDNS are described, with emphasis on the group vibration modes in the low frequency part of spectrum, sensitive to molecular environment and cross-linking degree, and on O–H/C–H vibration modes of dry/swollen CDNS, in turn providing information on the hydration dynamics. Powder X-ray diffraction data indicate low crystallinity and the presence of bulk water within the 3D polymer network. High resolution magic angle spinning (HR MAS) NMR spectroscopy is successfully used for investigation of swollen CDNS. The NMR signals of bulk and “bound” water indicate two different states of water molecules inside the gel. Probe solute fluorescein is used to spot on the diffusion properties inside the gel. In one case the diffusion coefficient of fluorescein measured in CDNS results one order of magnitude higher than that in D2O. The acceleration effect uncovered indicates that the motion of fluorescein inside the porous gel is driven by both hydrodynamic and electrostatic factors.

New inelastic Raman scattering experiments on the superionic glasses (AgI)(x)(AgPO3)((1-x)) were performed from room temperature up to the melting temperature. The results are compared with the acoustic attenuation measured in the frequency range between 8 and 9 GHz by Brillouin light scattering. This comparison shows that the quasielastic scattering intensity can be associated with the same mechanisms that cause sound attenuation, thereby demonstrating the same physical origin of these phenomena, in good agreement with suggested models.

We present a detailed investigation of the terahertz vibrational dynamics of 3-methylpentane performed by means of high-resolution inelastic x-ray scattering (IXS). We probe the dynamics in a large temperature range, which includes the glass, the supercooled liquid, and the liquid phases. The characteristic frequency of the excitations follows a well-defined dispersion curve extending beyond 8 nm(-1) at all the investigated temperatures, indicating the persistence of a solidlike behavior also in the liquid phase. This implies the existence of a pseudo-Brillouin zone whose size compares surprisingly well with the periodicity inferred from the first sharp diffraction peak in the static structure factor. We show that, in the investigated temperature range, both sizes undergo a variation of about 15%-20%, comparable to that of the average intermolecular distance. We finally show that the IXS sound velocity coincides with the infinite frequency sound velocity previously inferred from visible and ultraviolet Brillouin spectroscopy data. This analysis confirms the role of the shear relaxation processes in determining the variation with frequency of the apparent sound velocity.

In order to elucidate the effects of the nature of the cross-linker, of the hydration level and of the hydrophobic/ hydrophilic balance on the macro- and microscopic properties of a paradigmatic model of polysaccharide hydrogel, an integrated approach based on the combined use of low-frequency Raman scattering and FTIR-ATR absorption has been developed. The proposed methodology aims to explore the stability range of the liquid and gel phase diagram of the system. This approach was applied to cyclodextrin based nanosponges (CDNS), prepared by polymerization of α-, β-, and γ-cylcodextrins (CDNS) with an activated derivative of ethylenediamine tetra acetic acid. It revealed successful, on one side, for a comparative analysis of the elasticity, as mesoscopic parameter, of the dry polymeric network, measured by Raman spectroscopy in the low frequency (0 ÷ 150 cm–1) range, and, on the other side, for the investigation of the water holding capacity, as macroscopic parameter, through the analysis of the vibrational dynamics of water molecules in the swollen polymers, monitored by FTIR-ATR spectroscopy in two selected wavenumber regions, i.e. 2800 ÷ 3800 cm–1 and 1500 ÷ 1800 cm–1, where the O-H stretching and H-O-H bending vibrations respectively occur. As main result, the same evolution as a function of the molar ratio n, has been observed for the elasticity on mesoscopic scale, as described by the Boson Peak (ωBP) and the swelling ability on macroscopic scale, expressed by the mass ratio m describing the gel-to-sol transition in these systems. From the results, the way for a rational development of stimuli-responsive systems with specific performances, by modulating the stability range of the liquid suspension and gel phases properly changing the molar ratio n during the synthesis, is opened.

Measurements of Raman scattering from vitreous silica (spectrosil) in the temperature range 12–1200 K are analyzed and compared with inelastic neutron scattering measurements done on the same sample. The results show a temperature dependence of the quasi-elastic scattering. Comparing this study with acoustical attenuation measured at 30 GHz by Brillouin light scattering, we found that the mechanism giving rise to quasi-elastic scattering in vitreous silica seems to be the same as the one causing the acoustic attenuation.

New experimental data on vitreous silica, collected in a previously unexplored frequency region between 60 and 120 GHz, are reported. The Brillouin ultraviolet light scattering technique has been used to measure the dynamic structure factor for two exchanged momenta, Q = 0.078 and 0.11 nm−1. The experiment has been performed using the IUVS beam line at the Elettra Synchrotron radiation facility in Trieste. An evidence of a transition between two different dynamical regimes is discussed.

Raman and Brillouin spectroscopies have been used for characterizing hybrid inorganic–organic macromolecular materials obtained from the polymerization of 2-hydroxy ethyl methacrylate (HEMA) or methyl methacrylate (MMA), modified by silicon tetraethoxide (TEOS). Different molar ratios r = [TEOS]/[HEMA], with r varying from 0.5 to 5, and [TEOS]/[MMA] = 0.05 have been considered. The Raman data have provided a qualitative evaluation of the interaction between inorganic and organic components. The data of Brillouin scattering suggest that pure polymers are stiffer than the hybrids, almost irrespective of the inorganic compounds amount. The refractive index of the hybrids is lower than the pure polymer, even in case of small amounts of inorganic compound. The results are tentatively explained on the basis of the structural change in the polymeric network, due to the presence of the inorganic domains.

Inelastic neutron scattering experiments have been performed in melt-quenched vitreous Germania, v-GeO 2 , at room temperature. Coherence effects have been observed in the dynamical structure factor over the collective excitations energy range. Indeed, because of the relatively low velocity of sound of this system (3600 m/s), the linear low- q region of the ( q , ω ) dispersion relationship was accessible to the neutron experiment. The observed effects are consistent with the acoustic-phonon dispersion curves of the corresponding crystal, thus supporting the hypothesis that, also in glassy systems, longitudinal and transverse acoustic branches can be still defined, even if they are broader than in crystals, due to topological disorder.

The mechanisms responsible for phonon attenuation in glasses and in porous systems have been investigated. The acoustic attenuation has been measured by Brillouin light scattering using a Fabry-Perot apparatus and a new ultraviolet spectrometer. In particular, melt-quenched vitreous silica (ρ = 2200 kg m−3), silica xerogels with different densities (ρ = 510 ± 50, 770 ± 80, 1380 ± 140 and 2190 ± 200 kg m−3), and silica aerogel (ρ = 670 ± 80 kg m−3) have been studied. The porosities of the samples have been measured by nitrogen adsorption–desorption techniques. The Brillouin linewidth is found to increase with increasing pore size, being related to the effect of the growing structural disorder. Comparison between the acoustic attenuation obtained by the two wavelengths shows the existence of a crossover length a* which identifies the wave-vector values above which the disorder induced by the pore size starts to be the dominant cause of absorption. The position of the crossover is found to be frequency depen...

Brillouin spectroscopy was used for measuring the sound velocity through hybrid inorganic–organic polymeric materials obtained from the polymerization of 2-hydroxyethylmethacrylate (HEMA) modified by zirconium and aluminum alkoxides. Youngs modulus E, shear modulus G, bulk modulus B and Poissons ratio m were calculated for the pure poly-HEMA, in a good agreement with the elastic constants measured by four point flexural experiments. The sound velocity measurements on the hybrid materials indicate that the elastic modulus of pure poly-HEMA is higher than those of the hybrids, almost irrespective of the concentration of inorganic compounds. This trend is confirmed by the results of the four points flexural tests performed on the same samples. The findings have been tentatively explained on the basis of the structural change in the polymeric network, due to the presence of the inorganic domains. 2003 Elsevier B.V. All rights reserved.

The mechanisms responsible for phonon attenuation in glasses and in porous systems have been investigated. The acoustic attenuation has been measured by Brillouin light scattering using a Fabry–Perot apparatus. Melt-quenched vitreous SiO2 (ρ=2200 kg/m3), silica xerogels with different densities (ρ=510±50, 770 ± 80, 1380 ± 140 and 2190 ± 200 kg/m3), and silica aerogel (ρ=760±80 kg/m3) have been investigated. The porosity of the samples was measured by N2 adsorption/desorption techniques. For pores sizes smaller than ∼8 nm the acoustical attenuation, at the Brillouin frequency, at room temperature, is the same as in v-SiO2 and consequently is attributed to dynamical processes. For larger pore sizes, the Brillouin line width increases and its variation is related to the effect of phonons scattering from the growing structural disorder. On the basis of the present experiment, in porous systems, static and dynamical attenuation mechanisms have been found.

The vibrational dynamic of vitreous germania (v-GeO2) with respect to that of vitreous silica (v-SiO2) has been investigated by means of several inelastic and elastic scattering experiments. These amorphous systems belong to the large family of continuous random network forming glasses. In spite of their topological similarity, some dynamical differences have been singled out. We present experimental data on light Raman scattering at room temperature as well as new elastic and inelastic neutron scattering. Transversal-acoustic character of the vibrations responsible for the density of states excess in the Boson peak energy range is found. 2003 Elsevier B.V. All rights reserved.

The dynamics and the structure of silica xerogels at different degrees of densification have been studied by small angle X-ray scattering and Raman scattering, with the aim to investigate the effects of the inhomogeneous structure on the excitations that give rise to the excess in the density of states (Boson peak). The results are compared with those of specific heat measurements on the same samples. The present results show that the existence of the pores, whose medium size is in the 30–60 A range, does not appreciably affect the density of states in the Boson peak frequency range. On the contrary, at lower frequencies ( ω −1 ), a strong pore-size dependence is observed in the Raman spectra.

New Raman and neutron scattering data on (AgI)x(AgPO3)1-x at various temperatures and Agi concentrations (0.0 < x < 0.55) are compared to obtain the Raman coupling function C(ω) and, in particular, its low-frequency limit. This study indicates a strong variation in the dynamics with increasing AgI content. Moreover the direct comparison of the Raman and neutron scattering data indicates that, in the ω ↪ 0 limit, C(ω) extrapolates to a non-vanishing value, giving interesting indications on the nature of the vibrational modes in disordered systems.

In this work we have studied the dynamics of the silver phosphate glass AgPO3 by Raman and Brillouin light scattering experiments. This system is of interest because it is easy to study the dynamic changes in a wide range of temperatures having a glass transition temperature at about 170°C. This allows us to study the system below and above T g and in the melt (500°C). This study seems to indicate that the low-frequency scattering has a common origin below and above T g

We report X-ray and neutron scattering results in vitreous silica. As in earlier data, clear evidence is found for sound wave modes at the energies of the boson peak. We have observed by X-ray experiments a clear dispersion of Brillouin peaks and we have detected experimental evidence of inelastic scattering in the second Brillouin zone. By neutron scattering experiments we have found coherence eŒects in S…Q;E†. These eŒects are consistent with average acoustic phonon dispersion curves, which are similar in character to the dispersion curves found in crystals but, obviously, broadened by the topological disorder.

Positron annihilation lifetime spectroscopy is employed to measure the size of the interstitial void spaces characterizing the structure of a set of permanently densified ${\mathrm{SiO}}_{2}$ glasses. The average volume of the voids is markedly affected by the densification process and linearly shrinks by almost an order of magnitude after a relative density variation of 22%. In addition, x-ray diffraction shows that this change of density does not modify appreciably the short range order, which remains organized in ${\mathrm{SiO}}_{4}$ tetrahedra. These results strongly suggest a porous medium description for $v\text{\ensuremath{-}}{\mathrm{SiO}}_{2}$ glasses where the compressibility and the medium range order are dominated by the density variation of the voids volume up to densities close to that of $\ensuremath{\alpha}$-quartz.

The vibrational dynamics of a new class of cross-linked polymers made up of cyclodextrins is here investigated in the microscopic range by the joint use of light and inelastic neutron scattering experiments. The effect of increasing the connectivity of the polymeric network on the vibrational dynamics of the system is studied by exploiting the complementarity of these two different probes. The derived densities of vibrational states of the polymers evidence the presence of the characteristic anomalous excess of vibrational modes with respect to the Debye level, already observed in the low-frequency Raman spectra and referred to as boson peak (BP). The overall analysis of the spectra suggests an emerging picture in which the motions of hydrogen atoms of the polymers are progressively hampered when the cross-linking degree of the covalent network increases. At the same time, the frequency and intensity of the BP are found to significantly change by increasing the cross-linking degree of the polymeric network, as clearly suggested by the existence of a scaling-law for the BP evolution. These findings support the conclusion that the growing of the covalent connectivity of the system induces a general modifications of the elastic properties of these cyclodextrin-based polymers, which are, once again, modulated by the cross-linking agent/cyclodextrin molar ratio.

New coherent inelastic neutron scattering measurements on silica xerogels in the 300–1000 K temperature range are presented and compared with those obtained in vitreous silica (heralux). The spectra show the presence of the Boson peak, at temperatures, where the quasi-elastic contribution due to absorbed water is negligible. The Boson peak in silica xerogels is at a frequency of around 5 meV (40 cm−1) and has a shape similar to that of melted silica, even in the smaller density xerogels. This important result seems to indicate that the disorder introduced by the presence of pores does not affect the density of states in frequency region. This evidence is also confirmed by changes in the inelastic structure factor S(Q,ω), measured at the frequencies of the Boson peak as a function of the exchanged Q.

The dynamical structure factor, S(Q,E), of a model system, based on a percolator and using the harmonic approximation, has been calculated using the moments method especially in the smaller Q region. With this particular growth algorithm we calculate systems with densities as small as few percent of the complete lattice. The variation of the width of the Brillouin peak with density and its dependence on the exchanged wavevector are compared with the experimental data available for amorphous silica at different densities. The results show that the dynamical properties of sparse materials, such as aerogels and xerogels, can be reproduced considering only the dynamic of their network neglecting the contribution of the elemental units forming the network.

A comparative study of specific-heat and low-frequency Raman scattering at low temperatures of lanthanide metaphosphate glasses and pentaphosphate single crystals has revealed the presence of low-energy magnetic excitations. In an analogous manner to that found for vibrational modes, topological disorder softens the crystal field magnetic excitations, producing a broad band of low-energy states with a low-energy tail. A self-consistent data analysis using a broad Gaussian distribution of singlet-singlet excitations allows a complete interpretation in Pr glass, which exhibits strong magnetic effects in the temperature range explored. This distribution is used to evaluate the magnetic contribution to the specific heat; about one-fifth of the magnetic ions are characterised by singlet-singlet states with very low energies and contribute to the magnetic entropy.

Brillouin and Raman scattering measurements on (AgI) x (AgPO3) 1-x glasses are compared with low-temperature specific heat measurements. The direct comparison of the Brillouin shift and the freauency of the boson peak maximum shows that these features have the same qualitative behaviours. In fact, a shift towards Iow freauency is observed with increasing Agi content from x = 0 to x = 0.55, indicating a close relationship between Brillouin scattering (acoustic modes) and the boson peak. Correspondingly we have observed a shift to a lower temperature of the maximum Cp/T3 .

A comparative study of low temperature specific heat (1.5–25 K) and low frequency Raman scattering (

New Brillouin and Raman scattering measurements on silica xerogels in a wide range of densities are compared among each other and with data in melt quenched vitreous silica, in the 10-750 K temperature region. In the low frequency part of the Raman spectra, the boson peak characteristic of glasses is observed for all studied densities at low and high temperature when the quasielastic contribution is negligible. The results provide strong evidence of the presence of water in the pores of the silica skeleton.

The structure and the dynamics of silica sol—gel samples have been studied by means of Brillouin and Raman scattering, and specific heat experiments. The results are compared with those of xerogel glasses and amorphous silica, obtained by thermal treatment and by melt quenching respectively. Increasing the treatment temperatures produces progressive densification of the xerogel systems, whose dynamics and calorimetric properties are analysed for a wide range of temperatures.

Large magnetic contributions to the low-temperature specific heats of rare-earth metaphosphate (R2O3)0.25(P2O5)0.75 glasses have been observed. These effects result from electronic transitions between 4f levels multiply split due to local disorder, which also give rise to a strong electronic contribution to the low-frequency Raman scattering at low temperatures in the Pr metaphosphate glass. By contrast Sm and Gd metaphosphate glasses show the usual spectral features for a glass: the quasielastic scattering and the boson peak. Both the thermal and optical characteristics in the Pr glass are associated with a very large density of low-lying magnetic excitations, induced by the topological disorder. Using the electronic low-frequency Raman scattering at 1.5 K, which reflects this high density of low-energy states, it has proved possible to fit the magnetic contribution to the low-temperature specific heat in the Pr glass.

Structure and dynamics of silica xerogel samples are compared with melt quenched amorphous silica by means of infrared, Raman and Brillouin spectroscopes. In particular the attention was concentrated on a family of hydrogenated sol-gel systems whose nominal stoichiometric formula is Si 2 O 3 H 2 , Si 8 O 13 H 6 , Si 4 O 7 H 2 , and Si 8 O 15 H 2 . Thermal treatment of the samples were made at 500°C and at 800°C for 24 h. Samples were cooled at a rate of 0.3°C/min. Densities were measured by pycnometer technique. The densification of the sol-gel network occurs at about 500°C depending on the samples. At about 800°C the structure and the dynamics together with physical properties, such as sound velocities and elastic constants, become indistinguishable from those of glasses derived from melting.

The effect of the inclusion into cyclodextrins (CD) cavity on the low-frequency vibrational dynamics of the anti-inflammatory drug ibuprofen (IBP) is here investigated by using Raman and inelastic neutron scattering (INS) experiments. The differences observed in the frequency regime 0-100 cm(-1) between the vibrational modes of uncomplexed racemic and enantiomeric IBP are discussed on the basis of comparison with the quantum chemical computation results, taking into account the distinct symmetry properties of the molecules involved in the formation of the host-guest complex. Subsequently, the inspection of the same frequency range in the spectra of pure host methyl-β-CD and its IBP-inclusion complexes allows one to identify significant modifications in the vibrational dynamics of the guest molecule after their confinement into CD cavity. The experimental Raman and neutron spectra and the derived Raman coupling function C(R)(ω) show that the complexation process gives rise to a complete amorphization of the drug, as well as to a partial hindering, in the vibrational dynamics of complexes, of the modes between 50 and 150 cm(-1) attributed to CD molecule. The comparison between the Raman and neutron spectra of free and complexed IBP in the energy range of the Boson peak (BP) gives evidence that the dynamics related to this specific vibrational feature is sensitive to complexation phenomena.

Brillouin and Raman experiments have been performed in hydrogenated silica sol - gel and vitreous silica samples made by sol - gel processes (xerogels) and by the melting powder method. The aim of this work has been the study of the low-frequency dynamics of sol - gel systems in comparison with that of amorphous silica. By thermal treatment of the gel a progressive densification of the system was obtained: at we obtained densification (temperature well below the usual temperatures); at higher temperature () the pores were eliminated and the dynamics (Brillouin shifts, quasielastic scattering, and Boson peaks) became equivalent to that of fused silica.

Low frequency Raman and Brillouin scattering experiments in yttrium and lanthanide metaphosphate glasses have been carried out over a wide range of temperature from liquid helium to the glass transition temperature (Tg≅ 900 K). Analysis of the Raman data together with complementary low temperature specific heat and ultrasonic velocity results reveals that the temperature and frequency dependences of the quasi-elastic scattering and Boson peak and in addition the anomalous low temperature specific heat, are in qualitative agreement with the predictions of the soft potential model.

Theoretical models relative to Raman scattering in disordered solids are discussed and compared with the available experimental evidence. In particular, experimental data relative to the Boson peak integrated intensity and computer simulations on three-dimensional site percolators, allow us to infer that the relevant mechanism that produces the peak is disorder-induced light scattering from acoustic modes of a disordered structure.

The Raman spectra of metaphosphate glasses, which contain very high concentrations of either Eu3+ or Gd3+ ions, have been measured over a wide range of temperatures (10–300 K). The high-frequency part of the spectrum (above 200 cm−1) is similar to that found for other phosphate glasses, indicating that these glasses share the common structural feature of a skeleton built up from (PO4)2 tetrahedral units. The low-frequency region is determined by two spectral contributions which are characteristic of the disordered topology of vitreous materials: the light-scattering excess and the ‘boson peak’. The former contribution, clearly observed for frequencies below 10cm−1, becomes larger with increasing temperature, while the latter does not change appreciably as the temperature is increased to room temperature. Interpretation of the light scattering excess and the boson peak in terms of the predictions of the soft potential model can account for their frequency and temperature dependences.

We have obtained low-frequency Raman spectra of samarium phosphate glasses (Sm2O3) x (P2O5)]1-x in a wide temperature range from 11 K up to the glass transition temperature (T g ≈ 910 K) and measured their low-temperature specific heat, in an attempt to test the predictions of some recent models, the soft-potential (SP) model and the mode-coupling (MC) model, addressing low-energy modes in glasses. The temperature and frequency dependence of the boson peak (BP) and the quasielastic scattering (QS), both features characteristic of glasses in the low-frequency range, were determined. In addition, at high temperatures (above 600 K) we have detected a strong structureless background, which is attributed to higher-order Raman scattering. Taking the background into account, the BP changes with temperature in accordance with the Bose-Einstein population factor over the investigated temperature range. The temperature dependence of the QS is found to be consistent with the suggestions of the SP and MC mod...

Some models and experimental results relative to light scattering from disordered solids are reviewed with particular attention to the low-frequency part of the spectrum. Measurements of the low-frequency Raman scattering of superionic glasses (AgI borate glasses and AgI phosphate glasses at several AgI concentrations) and non-superionic glasses (samarium phosphate glasses containing 5 or 25% of Sm 2 O 3 ) are presented. By comparing spectra at different temperatures, a low-frequency extra-scattering (ES) has been separated from the usual disorder-induced scattering, which, at low frequencies, is due to acoustic modes. We found that the ES is approximately Lorentzian in shape and its intensity strongly increases with rising temperature. Because these spectral features are found in both classes of samples (i.e. superionic and non-superionic glasses), it indicates that the origin of quasi-elastic scattering is not related to high ionic conductivity of the superionic systems as has been suggested but seems to be a general characteristic of disordered structures.

Polarized room-temperature Raman scattering spectra measured on heat-treated GeO 2 -based glasses show features resembling particle peaks. They are related to the discrete particle-like structure of thermally treated samples. We have also found that our light scattering spectra have characteristic polarization properties

Alcohol dependence is a chronic relapsing disorder characterized by repetitive alcohol drinking patterns and a loss of control over alcohol consumption. Recent studies have hypothesized that dysregulations in brain neurotrophic support regulated by neurotrophins may be involved in the vulnerability to dependence and in the brain damage caused by chronic alcohol consumption. The neurotrophin brain-derived neurotrophic factor (BDNF) plays a pivotal role in neurodevelopment and in the maintenance of adult brain homeostasis through the regulation of neurogenesis and neuronal plasticity. The role of BDNF and its signaling in the mechanisms of alcohol dependence has been well documented in studies of animal models, but a few studies have been conducted in human peripheral tissues. On the basis of this rationale, we compared BDNF levels in both serum and plasma in alcohol-dependent patients and healthy volunteers.Thirty-seven patients with a principal diagnosis of alcohol dependence were recruited. In parallel, a control group of 37 unrelated volunteers matched for gender and age was enrolled. Serum and plasma BDNF levels were measured by ELISA.A significant reduction in BDNF serum levels was observed in the patient group compared to healthy subjects (p = 0.028). On the contrary, no difference in BDNF plasma levels was evident between patients and controls.In conclusion, our data show an alteration of BDNF peripheral content in patients with alcohol dependence, suggesting the involvement of this neurotrophin in this psychopathology.

Background: Alcohol dependence is a chronic relapsing disorder characterized by repetitive alcohol drinking patterns and a loss of control over alcohol consumption. Recent studies have hypothesized that dysregulations in brain neurotrophic support regulated by neurotrophins may be involved in the vulnerability to dependence and in the brain damage caused by chronic alcohol consumption. The neurotrophin brain-derived neurotrophic factor (BDNF) plays a pivotal role in neurodevelopment and in the maintenance of adult brain homeostasis through the regulation of neurogenesis and neuronal plasticity. The role of BDNF and its signaling in the mechanisms of alcohol dependence has been well documented in studies of animal models, but a few studies have been conducted in human peripheral tissues. On the basis of this rationale, we compared BDNF levels in both serum and plasma in alcohol-dependent patients and healthy volunteers. Methods: Thirty-seven patients with a principal diagnosis of alcohol dependence were recruited. In parallel, a control group of 37 unrelated volunteers matched for gender and age was enrolled. Serum and plasma BDNF levels were measured by ELISA. Results: A significant reduction in BDNF serum levels was observed in the patient group compared to healthy subjects (p = 0.028). On the contrary, no difference in BDNF plasma levels was evident between patients and controls. Conclusions: In conclusion, our data show an alteration of BDNF peripheral content in patients with alcohol dependence, suggesting the involvement of this neurotrophin in this psychopathology. Language: en