Search

This work reports an optical and photoelectrochemical study on the use of not edible parts of eggplant in a photovoltaic device. In this paper we employ, for the first time, the leaves and the bark of eggplant twigs, as pigment sources for dye-sensitized solar cells (DSSCs). We compared and discussed both the absorption spectra of two natural extracts and photovoltaic performances in DSSCs. We also compared, for a similar natural sensitizer, our electrolyte respect to several electrolytes reported in literature. Solar power conversion (η = 1%) and the short circuit current density (Jsc = 8 mA/cm2) achieved by studied devices are higher of 27% and 110% respectively, than literature data, so far reported. Furthermore, we demonstrated, by a thermodynamic study, thermal stability up to 125 °C of the eggplant extract, when anchored to TiO2 layer, and finally we presented some stability tests, under solar irradiation, of the DSSCs based on this natural extract.

Structural changes of (Ag2O)x(B2O3)1-x glasses, over the range between X = 0.0 and X = 0.14, have been monitored by Raman spectroscopy. Low temperature heat capacity measurements have been also performed between 0.4 K and 25 K to investigate along with low frequency Raman scattering the behavior of the low-energy vibrational dynamics. A progressively decreasing intensity of the main band at 808 cm−1 and the appearance of a band at about 775 cm−1 with increasing Ag2O content have been observed and analyzed in detail. The strongly polarized band at 808 cm−1 is ascribed to the breathing vibration of boroxol rings and the decrease of its intensity indicates the reduction of the number of these units in the network. The band at 775 cm−1 is assigned to vibrations of pentaborate units, formed from two boroxol rings linked by a tetrahedral BO4 group. The rate of formation of BO4 groups appears to increase as X/(1-X). Raman investigation has been extended to very low frequencies, where a broad intense band, the Boson peak (BP), dominates the spectrum of all the samples below 100 cm−1. Addition of Ag2O shifts the BP position from 26 cm−1 up to 33 cm−1 and gives rise to a decrease of its intensity up to X = 0.09 and a sudden increase for X = 0.14, which has been explained as due to rattling motion of silver ions whose contribution is added to that of localized vibrations. The formation of tetrahedral BO4 groups stiffens the network and leads to a decrease of the excess heat capacity over the Debye prediction below 20 K, which is not taken into account by the simple hardening of the elastic continuum but seems to follow the reduction of boroxol rings. This result contrasts the observations on borate glasses with high Ag content and emphasizes the crucial role of the network continuity on the vibrational dynamics of a glass.

Objectives Higher prevalence of psychiatric disorders, such as anxiety and depression, has been found in people with Crohn's disease and Ulcerative Colitis compared to the general population. Nowadays, international guidelines advocate psychotherapy and psycho-pharmacological treatments as playing an important role in IBD care. The main goal of this systematic literature review was summarize the evidence on the utilization and effectiveness of treatments for depression and anxiety in persons with IBD. Methods A systematic literature review was conducted using three different electronic databases: MEDLINE, PsychINFO, and EMBASE to identify studies reporting the prevalence and efficacy of psycho-pharmacological and psychotherapeutic treatments for IBD. A quality appraisal was conducted using several scales as appropriate for each study design. A narrative synthesis was also performed. Results Forty-three studies were included. Although a high rate of psychoactive drug use was found in people with IBD, a low proportion of IBD patients have access to psychiatric referral. 1/3 of the studies found that psychotherapy was effective for improving the quality of life, perception of stress, anxiety and depression as well as disease. Antidepressants proved effective in reducing disease activity, gastrointestinal symptoms, anxiety and depression. Conclusion Our results suggest that psychiatric treatment should be implemented in IBD care. However, further studies are needed to confirm the findings of our systematic review.

The specific role of acetonitrile and methoxypropionitrile, as accelerators of the relaxation dynamics of polyvinyl butyral (PVB), was investigated in polymer/additive mixtures with a saturation liquid content. The aim was to improve the ionic mobility of PVB-based solid electrolytes to be used in solid dye-sensitized solar cells. Mechanical and dielectric relaxation measurements between 120 K and 380 K revealed that the a-relaxation observed above 330 K in dry-PVB is shifted quite below room temperature in PVB/additives. Both the additives cause a growing intermolecular cooperativity, the sub-glass b-relaxation exhibiting a strength enhanced by a factor 3 and a frequency factor which increases from 1015 s21 to 1021 s21. This discloses an activation entropy as high as 165.7 J/K mol in comparison to 40.8 J/K mol in dry-PVB. It is suggested the existence of cooperative transitions, mainly driven by bridges formed through additive molecules, which influence both short- and long-scale segmental motions and also favor the ion dynamics in PVB/additive/electrolyte systems. The room temperature ionic conductivity rrt exhibits large changes from 6.4*10214 S/m in dry PVB, through 1.5*1028 S/m in PVB/LiI, to 2.45*1025 S/m in PVB/MPN/LiI.bject]

This study reports on characterization and photoactivity of nanostructured TiO2 samples, which have been permanently densified under high pressures, up to 2.1 GPa. Commercial Mirkat 211 anatase has been used as a benchmark sample, in order to investigate the effect of unidirectional high pressure on structural, optical and photocatalytic properties of TiO2. Vibrational Raman spectroscopy shows that the treatment does not cause transitions among the different crystalline phases of titanium dioxide. UV-vis diffuse reflectance spectra reveal that increasing pressure gives rise to a shift of the absorption onset towards higher wavelength enhancing the photoactivity under visible radiation. Samples are also photo-electrochemically characterized and tested in the gas phase with partial oxidation of ethanol to acetaldehyde under visible irradiation. Compaction up to 0.8 GPa depresses both the alcohol conversion and the aldehyde yield, while samples treated under higher pressures show enhanced characteristics of conversion compared to the pristine material. Moreover, promising results in the reduction of CO2 are also obtained under UV-visible radiation.

Low-temperature experiments of Raman scattering and heat capacity have been performed in a B2O3 glass, pressure quenched from 1200 degrees C in order to obtain the density as largest as possible (rho=2373kg/m(3)). When compared to those of compacted B2O3 glasses having smaller density, the Raman spectrum of this glass exhibits a strong decrease of the intensities of the Boson peak and the band at 808cm(-1), both the features being determined by the decrease of the boroxol ring population. Moreover, the Boson peak exhibits a large shift to 68cm(-1) (from 26cm(-1) observed in normal vitreous B2O3). The high atomic packing of the glassy network also leads to a marked decrease of the excess heat capacity over the Debye T-3-behaviour characterizing the crystal. The density g(nu) of low-frequency vibrational states has been assessed by using the low-frequency Raman intensity to determine the temperature dependence of the low-temperature heat capacity. The observations performed over a wide range of glass densities are compared to the predictions of theoretical models and computer simulations explaining the nature of the Boson peak. Consistency with the results of a simulation study concerning the vibrations of jammed particles leads to evaluate a nanometre length scale which suggests the existence of poorly packed domains formed from several connected boroxols. These soft regions are believed to be the main source of low-frequency optic-like vibrations giving rise to the Boson peak.

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.

A study of low temperature specific heat capacity (1–30 K) has been performed on samples of vitreous SiO2, which have been compacted under pressures up to 8 GPa to explore different glassy phases having growing density. Increasing densification by more than 21% leads to a progressive reduction of the specific heat capacity Cp and to a shift from 10 K up to about 17 K of the broad hump, the calorimetric Boson peak (BP), observed above 1 K in a Cp(T)/T3 vs. T plot. The revealed changes are not accounted for by the modifications of the elastic continuum, implying a nature of additional vibrations at variance with the extended sound waves. Increasing atomic packing of the glassy network leads to a progressively decreasing excess heat capacity over that of α-quartz, a crystalline polymorph of SiO2. By using the low-frequency Raman intensity measured in these glasses to determine the temperature dependence of the low temperature heat capacity, it has been evaluated the density of low-frequency vibrational state...

Background— The most suitable approach for patients with aspirin hypersensitivity undergoing percutaneous coronary intervention remains to be assessed. Methods and Results— Pubmed, Google Scholar, and Cochrane were systematically searched for papers describing protocols about aspirin hypersensitivity in the percutaneous coronary intervention setting. Discharge from hospital with aspirin was the primary end point, whereas rates of adverse reactions being a secondary outcome. An online international survey was performed to critically analyze rates of aspirin hypersensitivity and its medical and interventional management. Eleven studies with 283 patients were included. An endovenous desensitization protocol was performed on one of them, with high efficacy rate (98%) and a low adverse reaction rate when compared with oral administration. No significant differences were reported among the oral protocols in terms of efficacy (less versus more fractionated [95.8% {95.4%–96.2%} versus 95.9% {95.2–96.5%}]), whereas higher incidence of rash and angioedema were reported for protocols with Conclusions— Available protocols for aspirin hypersensitivity are effective and safe, representing a feasible approach for patients needing dual antiplatelet therapy.

Objectives: Serotonin (5-hydroxytryptamine, 5-HT) metabolism may be altered in gut disorders, including in the irritable bowel syndrome (IBS). We assessed in patients with IBS vs. healthy controls (HCs) the number of colonic 5-HT-positive cells; the amount of mucosal 5-HT release; their correlation with mast cell counts and mediator release, as well as IBS symptoms; and the effects of mucosal 5-HT on electrophysiological responses in vitro. Methods: We enrolled 25 Rome II IBS patients and 12 HCs. IBS symptom severity and frequency were graded 0-4. 5-HT-positive enterochromaffin cells and tryptase-positive mast cells were assessed with quantitative immunohistochemistry on colonic biopsies. Mucosal 5-HT and mast cell mediators were assessed by high-performance liquid chromatography or immunoenzymatic assay, respectively. The impact of mucosal 5-HT on electrophysiological activity of rat mesenteric afferent nerves was evaluated in vitro. Results: Compared with HCs, patients with IBS showed a significant increase in 5-HT-positive cell counts (0.370.16% vs. 0.560.26%; P

Measurements of differential scanning calorimetry, dynamic mechanical analysis, and dilatometry have been performed in heterocyclic polymer networks (HPNs), whose effective network density has been gradually varied keeping the overall chemical structure essentially unchanged. Evidence of a growing intermolecular cooperativity for a local relaxation motion is offered by the investigation of the subglass mechanical ?-relaxation, whose frequency factor and apparent activation energy strongly increase with increasing cross-linking density from about 1015 s-1 and 44.2 kJ/mol to about 1019 s-1 and 69.8 kJ/mol. The analysis of the characteristics of the mechanical ?-relaxation suggests the existence of cooperative transitions of consecutive relaxing units, mainly driven by the crank-shaft motion of the network junctions between the isocyanurate heterocycles building up the structure. Comparison with previous results concerning the dielectric ?-relaxation evidence a less cooperative character and a different microscopic origin for the conformational transitions driving the dielectric process. Moreover, a decrease in the thermodynamic fragility with increasing network density has been revealed, which contrasts with the increasing dynamic fragility, as measured by dielectric and mechanical probes.

Experiments of differential scanning calorimetry and dynamic mechanical spectroscopy on linear and cross-linked heterocyclic polymer networks (HPNs) have been performed over the temperature range between 120 and 400 K. The temperature dependences of the storage modulus E ′ and the internal friction Q −1 of HPNs, investigated by mechanical waves of frequencies ranging between 0.3 and 30 Hz, reveal anelastic behaviors which are mainly governed by the secondary β- and primary α-relaxations. The addition of cross-links in an apparently linear polymer network was accompanied by the shift of the glass transition to higher temperatures. Differently from the α-relaxation whose strength decreases with cross-linking, the β-relaxation strength increases. This observation implies the lack of any dynamical hierarchy between the local and cooperative segmental dynamics in these systems. The β-relaxation follows the Arrhenius law with values of the characteristic frequency ω 0 and the activation energy E act ranging between 10 15 and 10 16 s −1 and 43.7 and 48.7 kJ/mole, respectively. In both the HPNs the β-loss peaks have been quantitatively analyzed by the symmetric double-well potential (SDWP) model.

The infrared absorption spectra of thermoplastic interpenetrating polymer networks based on semi-crystalline polyurethane (CPU) and a styrene/acrylic acid block-copolymer (S-b-AA(K+), salt form) have been measured over the spectral range between 4000 and 600 cm-1 in an attempt to study their structure. The analysis of the spectra of the individual polymers and CPU/S-b-AA(K+) blends has shown the mutual influence of components on the formation of a network of intra- and intermolecular physical bonds between functional groups of the components. In close agreement with these observations, the composition behaviors of experimental results of density, tensile strength, differential scanning calorimetry and dynamic mechanical spectroscopy reveal deviations from a simple additive law which have been associated to a weak affinity of the individual components. It has been suggested that the existence of specific weak interactions (H-bonds) between the functional groups of the two components ensure the formation of a mixed microphase.

Celle solari realizzate con coloranti di origine vegetale

AIMS Contrast-induced nephropathy (CIN) and periprocedural myocardial infarction (PMI) represent frequent complications of percutaneous coronary intervention (PCI) and negatively impact subsequent length of hospitalization, costs of adjunctive diagnostic-therapeutic measures and mid-term cardiovascular events. The aim of the EURO-CRIPS trial is to test whether remote ischemic preconditioning (RIPC) may reduce the incidence of these complications and improve mid-term outcome. METHODS This will be a double-blind, randomized, placebo-controlled multicentre study. Patients will be allocated 1 : 1 to RIPC or standard therapy if they were younger than 85 years old, with a renal clearance in the interval 30-60 ml/min/1.73 m and candidate to PCI for all clinical indications except for primary PCI in ST segment elevation myocardial infarction (STEMI), unstable haemodynamic presentations or ongoing severe arrhythmias. Incidence of CIN will be the primary end point and the amount of periprocedural cardiac enzyme leakage will be the secondary end point. In addition, we will evaluate whether the preconditioned patients will have a reduction of MACCE at 6 months (major adverse cardiac and cerebrovascular event). CONCLUSION The EURO-CRIPS Study will be the first large-scale, multicentre clinical trial to test the role of RIPC in current clinical practice. The results of this randomized trial will provide important insights to optimize management strategy of patients undergoing PCI and to improve their outcome.

Sound propagation has been investigated at megahertz and gigahertz frequencies in ${\mathrm{B}}_{2}{\mathrm{O}}_{3}$ solids which have been pressure quenched to go through different glassy phases having growing density until the crystalline state. Over the temperature range between 10 and 300 K, the attenuation and velocity of sound in glasses are regulated by classical activation over potential barriers of structural defects and vibrational anharmonicity. The defect states are absent in the crystalline phase whose acoustic behavior is determined only by the anharmonic coupling between sound waves and thermal vibrations. Our study leads to identification of the specific superstructural units subjected to thermally activated motions in vitreous ${\mathrm{B}}_{2}{\mathrm{O}}_{3}$. These molecular groups are the boroxol rings which are formed due to the poor atomic packing of glassy networks and are missing in the crystal.

We have measured the elastic moduli and the thermal expansion in permanently compacted B 2 O 3 glasses whose structural transformations have been determined by Raman spectroscopy. Growing glass densification, obtained by melt-quenching under pressures in the GPa range, is mainly associated to the decrease of the population of boroxol rings (B 3 O 6 ), the glassy molecular units formed by connected BO 3 planar triangles. Increasing density gives rise to a substantial hardening of the elastic continuum, while reducing the thermal expansion of these glasses. Evaluation of the average thermal Gruneisen parameter γ th evidences an increase which has been explained in terms of bending vibrations gradually depressed in glassy networks having a growing packing fraction.

A comparative study of Raman scattering and low temperature specific heat capacity has been performed on samples of ${\mathrm{B}}_{2}{\mathrm{O}}_{3}$, which have been high-pressure quenched to go through different glassy phases having growing density to the crystalline state. It has revealed that the excess volume characterizing the glassy networks favors the formation of specific glassy structural units, the boroxol rings, which produce the boson peak, a broad band of low energy vibrational states. The decrease of boroxol rings with increasing pressure of synthesis is associated with the progressive depression of the excess low energy vibrations until their full disappearance in the crystalline phase, where the rings are missing. These observations prove that the additional soft vibrations in glasses arise from specific units whose formation is made possible by the poor atomic packing of the network.

The elastic and anelastic properties of densified B${}_{2}$O${}_{3}$ glasses, melt quenched under pressures of 2 and 4 GPa, were investigated by measuring the sound velocity and the acoustic attenuation of longitudinal and shear ultrasonic waves in the megahertz range over the temperature interval between 8 and 300 K. Densification from 1826 to 2373 kg/m${}^{3}$ leads to an extraordinarily large growth of both bulk and shear moduli but leaves the Poisson's ratio nearly constant. In the glass compacted at 4 GPa, the elastic moduli become larger by a factor of five than those characterizing normal vitreous B${}_{2}$O${}_{3}$ (v-B${}_{2}$O${}_{3}$) as a consequence of modifications of the chemical bonding in the network. The thermally activated relaxations of intrinsic structural defects, which dominate the acoustic behaviors of normal glass below 150 K, giving rise to an intense attenuation peak and a corresponding steep decrease in sound velocity, are increasingly depressed by growing densification. Above 150 K, the ultrasonic velocity is mainly regulated by the vibrational anharmonicity and shows a nearly linear decrease as the temperature is increased, with a substantially smaller slope with increasing densification. Modeling the relaxation losses and the related velocity variations by an asymmetric double-well potential model that has a distribution of both the barrier potential and the asymmetry, it has been possible to separate the relaxation and the anharmonic contributions to the sound velocity. The former has been ascribed to local motions of boroxol rings formed by connected BO${}_{3}$ planar triangles, the basic units building up the network of v-B${}_{2}$O${}_{3}$, while the latter has been interpreted in terms of the Akhiezer mechanism concerning the ``thermal vibration viscosity.''

The elastic and anelastic properties of densified B2O3 glasses, melt quenched under pressures of 2 and 4 GPa, were investigated by measuring the sound velocity and the acoustic attenuation of longitudinal and shear ultrasonic waves in the megahertz range over the temperature interval between 8 and 300 K. Densification from 1826 to 2373 kg/m3 leads to an extraordinarily large growth of both bulk and shear moduli but leaves the Poisson's ratio nearly constant. In the glass compacted at 4 GPa, the elastic moduli become larger by a factor of five than those characterizing normal vitreous B2O3 (v-B2O3) as a consequence of modifications of the chemical bonding in the network. The thermally activated relaxations of intrinsic structural defects, which dominate the acoustic behaviors of normal glass below 150 K, giving rise to an intense attenuation peak and a corresponding steep decrease in sound velocity, are increasingly depressed by growing densification. Above 150 K, the ultrasonic velocity is mainly regulated by the vibrational anharmonicity and shows a nearly linear decrease as the temperature is increased, with a substantially smaller slope with increasing densification. Modeling the relaxation losses and the related velocity variations by an asymmetric double-well potential model that has a distribution of both the barrier potential and the asymmetry, it has been possible to separate the relaxation and the anharmonic contributions to the sound velocity. The former has been ascribed to local motions of boroxol rings formed by connected BO3 planar triangles, the basic units building up the network of v-B2O3, while the latter has been interpreted in terms of the Akhiezer mechanism concerning the "thermal vibration viscosity."

Inelastic light-scattering spectra of normal and permanently densified ${\mathrm{B}}_{2}$O${}_{3}$ glasses were investigated over the frequency range between 6 and 1600 cm${}^{\ensuremath{-}1}$. Densification from 1826 to 2320 kg$/$m${}^{3}$ was obtained by loading ${\mathrm{B}}_{2}$O${}_{3}$ glasses in a multianvil apparatus for synthesis at 2 and 4 GPa; they were fused at temperatures between 1400 and 1500 K and then were quenched at those pressures. It is shown that increasing densification gives rise to (i) a growing decrease of the intensity of the strong band at 808 cm${}^{\ensuremath{-}1}$, ascribed to the breathing vibration of boroxol rings, implying a reduction in the number of rings in the network and (ii) the appearance of a band at 775 cm${}^{\ensuremath{-}1}$ in the glass compacted at 4 GPa, which is assigned to the vibrations of structural units containing tetrahedral BO${}_{4}$ groups. The low-frequency Raman scattering includes the boson peak (BP), which dominates the spectra between 10 and 100 cm${}^{\ensuremath{-}1}$. Densification significantly decreases the intensity of the BP and shifts its position from about 26 cm${}^{\ensuremath{-}1}$, through 39 cm${}^{\ensuremath{-}1}$ (2-GPa glass), up to 68 cm${}^{\ensuremath{-}1}$ (4-GPa glass). These increases are stronger than those expected from the substantial hardening of the elastic continuum: The elastic moduli increase up to about a factor of 5 compared to those of normal glass. These observations imply that densification drives the system toward a structure having a more efficient packing of molecular units, causing substantial variations of the short- and medium-range orders with the formation of boron atoms in the four-fold-coordinated state at a quenching pressure of 4 GPa.

Specific heat was measured over the temperature range 0.4–25 K in GeO2 glasses, compacted at pressures of 2 and 6 GPa to achieve more than 20% densification. Above 1 K, specific heat C was reduced by up to a factor of 2.5 with increasing density; the variation being stronger than that observed below 1 K. The broad peak observed above 1 K in a C/T 3 vs. T plot shifted to higher temperatures with increasing density, exhibiting changes which cannot be explained by the modifications of the elastic continuum. In addition, the peak showed no changes in shape, clearly indicating that the overall distribution of the underlying vibrational modes was independent of density. The temperature dependence of C over the explored range was in qualitative agreement with the predictions of the Soft Potential Model.

The potential relevance of systemic and gastrointestinal immune activation in the pathophysiology and symptom generation in the irritable bowel syndrome (IBS) is supported by a number of observations. Infectious gastroenteritis is the strongest risk factor for the development of IBS and increased rates of IBS-like symptoms have been detected in patients with inflammatory bowel disease in remission or in celiac disease patients on a gluten free diet. The number of T cells and mast cells in the small and large intestine of patients with IBS is increased in a large proportion of patients with IBS over healthy controls. Mediators released by immune cells and likely from other non-immune competent cells impact on the function of enteric and sensory afferent nerves as well as on epithelial tight junctions controlling mucosal barrier of recipient animals, isolated human gut tissues or cell culture systems. Antibodies against microbiota antigens (bacterial flagellin), and increased levels of cytokines have been detected systemically in the peripheral blood advocating the existence of abnormal host-microbial interactions and systemic immune responses. Nonetheless, there is wide overlap of data obtained in healthy controls; in addition, the subsets of patients showing immune activation have yet to be clearly identified. Gender, age, geographic differences, genetic predisposition, diet and differences in the intestinal microbiota likely play a role and further research has to be done to clarify their relevance as potential mechanisms in the described immune system dysregulation. Immune activation has stimulated interest for the potential identification of biomarkers useful for clinical and research purposes and the development of novel therapeutic approaches.

Nella ordinaria magnetofluidodinamica la forza unitaria di volume che interviene nell'equazione indefinita del moto si pensa decom-posta in varie parti, di cui una ha origine elettromagnetica.

Inelastic light-scattering spectra of normal and permanently densified B2O3 glasses were investigated over the frequency range between 6 and 1600 cm-1. Densification from 1826 to 2320 kg/m3 was obtained by loading B2O3 glasses in a multianvil apparatus for synthesis at 2 and 4 GPa; they were fused at temperatures between 1400 and 1500 K and then were quenched at those pressures. It is shown that increasing densification gives rise to (i) a growing decrease of the intensity of the strong band at 808 cm-1, ascribed to the breathing vibration of boroxol rings, implying a reduction in the number of rings in the network and (ii) the appearance of a band at 775 cm-1 in the glass compacted at 4 GPa, which is assigned to the vibrations of structural units containing tetrahedral BO4 groups. The low-frequency Raman scattering includes the boson peak (BP), which dominates the spectra between 10 and 100 cm-1. Densification significantly decreases the intensity of the BP and shifts its position from about 26 cm-1, through 39 cm-1 (2-GPa glass), up to 68 cm-1 (4-GPa glass). These increases are stronger than those expected from the substantial hardening of the elastic continuum: The elastic moduli increase up to about a factor of 5 compared to those of normal glass. These observations imply that densification drives the system toward a structure having a more efficient packing of molecular units, causing substantial variations of the short- and medium-range orders with the formation of boron atoms in the four-fold-coordinated state at a quenching pressure of 4 GPa.

We show that within the relativistic dynamics of a particle the Hamilton's action yields the mechanical contribution of the action which is assumed in the space-time manifold by means of the least action principle. Furthermore, after introducing the four-potential and the skew-symmetric double tensor describing the field, we determine a new four-dimensional differential equation of motion for a particle, where there are involved the aforementioned four-dimensional quantities.

The internal friction and the sound velocity in a cesium borate glass (Cs(2)O)(0.14)(B(2)O(3))(0.86) were measured at ultrasonic and hypersonic frequencies by Brillouin scattering measurements over the temperature range between 15 and 300 K. The analysis of the experimental results show that, in addition to thermally activated local motions of structural defects, the vibrational anharmonicity contributes substantially to the temperatures dependences of both the hypersonic loss and velocity. It has been also proved that above 150 K the vibrational anharmonicity appears to be governed by the Akhiezer mechanism of phonon viscosity.

Measurements of Brillouin light scattering have been performed in (M2O)(0.14)(B2O3)(0.86) alkali-borate glasses, where M=Li and K, as a function of temperature between 15 and 300 K. The temperature behaviors of hypersonic attenuation and velocity have been explained in terms of thermally activated relaxations of intrinsic structural defects and of anharmonic interactions between hypersonic waves and thermal vibrational modes. In the temperature region above 150 K, where the mean free path of thermal modes is shorter than the acoustic wavelength, it has been shown that the sound propagation is mainly regulated by the Akhiezer mechanism of "phonon viscosity." It causes a linear increase in the hypersonic attenuation and a linear decrease in the sound velocity with increasing temperature.

In this study, we present the dependence of the relaxation processes from the size cation and thermal history in complexes of polyethylene oxide (PEO) and alkali metal salts (sodium and potassium thiocyanates). The internal friction behavior as a function of temperature and frequency reveals the presence of local (γ) and cooperative (a a ) molecular relaxations. The region of the γ-relaxation, which shows a single mechanical loss peak in pure PEO and in PEO-NaSCN, is strongly modified by the addition of potassium salt to PEO and two close peaks are present. Samples, prepared by a slow evaporation of the solvent, have a semi-crystalline structure. A “quenching” procedure imposed on them gives rise to the same structure, but enhances the amorphous phase and shifts the glass transition to lower temperatures, probably as an effect of decreasing constraints of the crystalline phases on the amorphous regions. Finally, different thermal histoires also produce changes on the low temperature γ-relaxation, which are discussed accordingly with the revealed phase behavior.

International audience; Comparative measurements of Brillouin light scattering and ultrasounds in (K2O)0.04(B2O3)0.96 and (Ag2O)0.14(B2O3)0.86 borate glasses as a function of temperature between 1.5 and 300 K reveal that distinct mechanisms regulate the temperature behaviours of the acoustic attenuation. In the MHz range the attenuation and the sound velocity are mainly governed by (i) quantum-mechanical tunnelling below 20 K, (ii) thermally activated relaxations between 20 and 200 K and (iii) vibrational anharmonicity at even higher temperatures. In the GHz range and in the temperature interval between 77 and 300 K, additional contributions besides the relaxation process must be taken into consideration to account for the hypersonic attenuation.

The fragility and the anharmonicity of (Ag2O)x(B2O3)1−x borate glasses have been quantified by measuring the change in the specific heat capacity at the glass transition temperature Tg and the room-temperature thermodynamic Gruneisen parameter. Increasing the silver oxide content above X = 0.10 leads to an increase of both the parameters, showing that a growing fragility of a glass-forming liquid is predictive of an increasing overall anharmonicity of its glassy state. The attenuation and velocity of ultrasonic waves of frequencies in the range of 10–70 MHz have also been measured in silver borate glasses as a function of temperature between 1.5 and 300 K. The experimental data reveal anelastic behaviours which are governed by (i) quantum-mechanical tunnelling below 20 K, (ii) thermally activated relaxations between 20 and 200 K and (iii) vibrational anharmonicity at even higher temperatures. Evaluation of tunnelling (C) and relaxation (C*) strengths shows that C is independent of the structural changes affecting the borate network with increasing metal oxide content and is at least one order of magnitude smaller than C*. The latter observation implies that only a small fraction of the locally mobile defects are subjected to tunnelling motions.

The relaxation losses and the corresponding velocity variations, observed at ultrasonic frequencies in (M2O)0.14(B2O3)0.86 alkali borate glasses (M = Li, K, Cs) between 1.5 and 300 K, have been modelled by an asymmetric double-well potential model having a distribution of both the barrier potential and the asymmetry. It is shown that the relaxation strength C* and the spectral density of asymmetries f0 decreases markedly with decreasing cation size. Below 10 K the sound attenuation is regulated by the phonon-assisted relaxation of tunnelling systems and exhibits a tunnelling strength C, ranging between 10−4 and 10−3. At variance with the behaviour observed for C*, C slightly increases with decreasing cation size and is more than one order of magnitude smaller than C*. It is concluded that, differently from classical relaxing states, tunnelling systems are independent of bond strengths and of structural changes characterizing a glassy network, confirming their inherent universality. Above about 120 K the ultrasonic velocity is mainly regulated by vibrational anharmonicity and shows a nearly linear decrease as the temperature is increased, the slope scaling with the cation size. Taken together, the observations point to the existence of a distinct correlation between anharmonicity and local mobility in the glassy network.

The attenuation and velocity of ultrasonic waves of frequencies in the range of $10\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}70\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ have been measured in ${({\mathrm{Li}}_{2}\mathrm{O})}_{x}{({\mathrm{B}}_{2}{\mathrm{O}}_{3})}_{1\ensuremath{-}x}$ borate glasses as a function of temperature between 1.5 and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Two distinct features characterize the attenuation behavior: (i) a plateau at temperatures below $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, (ii) a broad high-temperature peak. The former feature is interpreted in terms of the phonon-assisted relaxation of two level systems and the latter by assuming the existence of a distribution of thermally activated relaxing centers. The spectral density of two-level systems results to be independent on the alkali oxide content, while the density of relaxing particles decreases with increasing lithium ion concentration supporting their association to the triangular $\mathrm{B}{\stackrel{\ensuremath{\llap{\not\;}}}{\mathrm{O}}}_{3}$ units building up the borate skeleton ($\stackrel{\ensuremath{\llap{\not\;}}}{\mathrm{O}}=\text{oxygen}$ atom bridging between two network-forming ions, i.e., boron ions). The comparison between the number densities of two-level systems and of relaxing particles indicates that only a small fraction of the locally mobile defects are subjected to tunneling motions. At temperatures below $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ the sound velocity is mainly governed by the relaxation contribution, while above $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ it is regulated by the vibrational anharmonicity and shows a nearly linear temperature dependence, whose slope strongly depends on the concentration of network modifier ions (${\mathrm{Li}}^{+}$ ions). The determination of the average thermal Gr\"uneisen parameters permits us also to disclose the existence of a distinct correlation between anharmonicity and fragility of lithium borate glasses: a growing fragility is predictive of an increasing anharmonicity.

The attenuation and velocity of ultrasonic waves of frequencies in the range from 10 MHz to 50 MHz have been measured in (M 2 O) 0.14 (B 2 O 3 ) 0.86 borate glasses (M = Li, Cs or Ag) as a function of temperature between 15 K and 300 K. Broad relaxation peaks characterize the acoustic attenuation at temperatures below 100 K and are paralleled by corresponding dispersive behaviors of the sound velocity. The velocity of sound waves decreases with increasing temperature in all the glasses, the decrease as the temperature is increased being larger in glasses containing cesium than in those with lithium or silver. Above 100 K the ultrasonic velocity is regulated by the vibrational anharmonicity and shows a nearly linear temperature dependence, whose slope scales with the size of the network modifier ion. The results suggest that the local motion of structural defects and the anharmonicity in borate glasses are strongly affected by the polarizing power of network modifier ions.

The attenuation and velocity of ultrasonic waves of frequencies in the range from 10MHz to 50MHz have been measured in (M2O)0.14(B2O3)0.86 borate glasses (M = Li, Cs or Ag) as a function of temperature between 15K and 300K. Broad relaxation peaks characterize the acoustic attenuation at temperatures below 100K and are paralleled by corresponding dispersive behaviors of the sound velocity. The velocity of sound waves decreases with increasing temperature in all the glasses, the decrease as the temperature is increased being larger in glasses containing cesium than in those with lithium or silver. Above 100K the ultrasonic velocity is regulated by the vibrational anharmonicity and shows a nearly linear temperature dependence, whose slope scales with the size of the network modifier ion. The results suggest that the local motion of structural defects and the anharmonicity in borate glasses are strongly affected by the polarizing power of network modifier ions.