Institute of Acoustics and Sensors "Orso Mario Corbino"

We performed the statistical analysis of acoustic emission time series in the ultrasonic frequency range, obtained experimentally from laboratory samples subjected to external uniaxial elastic stress. We found a power law scaling behavior in both the acoustic emission amplitude distribution and time correlation function, with exponents very close to those found in fracturing processes occurring at different time and space scales. These facts strongly suggest the existence of a critical dynamics underlying the process, which might be related to the idea of a self-organized critical state based on the energy dissipation through all the length scales.

The electron--optical-phonon scattering rates in GaAs/AlAs quantum wells are calculated on the basis of a fully microscopic description of the phonon spectra. The results indicate the great importance of confined as well as GaAs-like and AlAs-like interface phonons. By comparing our results with those of several macroscopic models, we resolve a long-standing controversy on their ability to describe the relevant vibrations.

We investigate the properties of a model of granular matter consisting of $N$ Brownian particles on a line, subject to inelastic mutual collisions. This model displays a genuine thermodynamic limit for the mean values of the energy, and the energy dissipation. When the typical relaxation time $\ensuremath{\tau}$ associated with the Brownian process is small compared with the mean collision time ${\ensuremath{\tau}}_{c}$ the spatial density is nearly homogeneous and the velocity probability distribution is Gaussian. In the opposite limit $\ensuremath{\tau}\ensuremath{\gg}{\ensuremath{\tau}}_{c}$ one has strong spatial clustering, with a fractal distribution of particles, and the velocity probability distribution strongly deviates from the Gaussian one.

We present a calculation of the electron--LO-phonon scattering rate in quasi-two-dimensional systems, based on a fully microscopic description of the phonon spectra. The results obtained for a GaAs/AlAs quantum-well structure indicate the great importance of interface phonons and allow us to solve a long-standing controversy on the validity of simplified macroscopic models for describing the relevant vibrations.

This article describes the first emotional corpus, named EMOVO, applicable to Italian language,.It is a database built from the voices of up to 6 actors who played 14 sentences simulating 6 emotional states (disgust, fear, anger, joy, surprise, sadness) plus the neutral state.These emotions are the well-known Big Six found in most of the literature related to emotional speech.The recordings were made with professional equipment in the Fondazione Ugo Bordoni laboratories.The paper also describes a subjective validation test of the corpus, based on emotion-discrimination of two sentences carried out by two different groups of 24 listeners.The test was successful because it yielded an overall recognition accuracy of 80%.It is observed that emotions less easy to recognize are joy and disgust, whereas the most easy to detect are anger, sadness and the neutral state.

Vibration frequency and damping have been measured as a function of temperature in the range 4.5°K–300°K, for lead, copper, aluminum, and silver rods. Damping has been found to reach a maximum near 13 of Debye temperature, owing to a new relaxation effect. Near the absolute zero both damping and frequency changes vanish as a high power of temperature.

The piezopotential in floating, homogeneous, quasi-1D piezo-semiconductive nanostructures under axial stress is an anti-symmetric (i.e., odd) function of force. Here, after introducing piezo-nano-devices with floating electrodes for maximum piezo-potential, we show that breaking the anti-symmetric nature of the piezopotential-force relation, for instance by using conical nanowires, can lead to better nanogenerators, piezotronic and piezophototronic devices.

We describe a fast and effective procedure for the preparation of high efficiency hybrid photoanodes for dye-sensitized solar cells (DSCs), based on nanocrystalline TiO 2 with limited addition of multiwall carbon nanotubes (CNTs). The mixing process between CNTs and TiO 2 nanoparticles is almost instantaneous, which makes it feasible for large-scale fabrication. Enhanced electron lifetime and reduced charge recombination lead to highly increased short circuit current density and overall photoconversion efficiency (from 13.6 mA cm –2 to 16.0 mA cm –2 and from 7.0% to 9.0%, respectively, considering the bare TiO 2 and the optimum CNTs concentration, which is 0.010 wt %), while the small reduction in open circuit photovoltage does not significantly affect cell performances. This result is remarkable since a standard dye molecule (N719) was used and no chemical treatments of the photoanodes prior to cell fabrication were applied (i.e., soaking in TiCl 4 to boost open circuit photovoltage).

The elastic properties of ZnO films deposited by rf magnetron sputtering on Al2O3 substrates have been analyzed by means of an acoustic investigation technique. The phase velocities of a spectrum of acoustic modes propagating along the layered structure have been measured and the results exploited for determining the complete set of elastic constants of the film. The effective constants of the film are lower than those of the bulk material by amounts which depend on the elastic constant considered and range from −1.2% for c33 to −24.8% for c11. The values obtained were used for determining the dispersion curves of acoustic modes propagating along ZnO layers deposited on fused quartz and silicon and showed good agreement with experimental results.

The growth, collapse, and rebound of a vapor bubble generated by an underwater spark is studied by means of high-speed cinematography, simultaneously acquiring the emitted acoustic signature. Video recordings show that the growth and collapse phases are nearly symmetrical during the first two or three cycles, the bubble shape being approximately spherical. After 2-3 cycles the bubble behavior changes from a collapsing/rebounding regime with sound-emitting implosions to a pulsating regime with no implosions. The motion of the bubble wall during the first collapses was found to be consistent with the Rayleigh model of a cavity in an incompressible liquid, with the inclusion of a vapor pressure term at constant temperature within each bubble cycle. An estimate of the pressure inside the bubble is obtained measuring the collapse time and maximum radius, and the amount of energy converted into acoustical energy upon each implosion is deduced. The resulting value of acoustic efficiency was found to be in agreement with measurements based on the emitted acoustic pulse.

In this Brief Report we present a version of a network growth model, generalized in order to describe the behavior of social networks. The case of study considered is the preprint archive at cul.arxiv.org. Each node corresponds to a scientist, and a link is present whenever two authors wrote a paper together. This graph is a nice example of degree-assortative network, that is, to say a network where sites with similar degree are connected to each other. The model presented is one of the few able to reproduce such behavior, giving some insight on the microscopic dynamics at the basis of the graph structure.

Phonon spectra of ultrathin (GaAs${)}_{\mathrm{n}}$(AlAs${)}_{\mathrm{n}}$ (001) superlattices are studied theoretically using linear-response density-functional techniques. Results are presented for n=1,2,3 superlattices, along with prototype supercell calculations aimed at simulating a completely disordered (alloy) as well as some partially disordered superlattices. Besides interfacial disorder, which modifies the effective confinement length of low-order longitudinal-optic phonons, we find that---in the ultrathin regime---some degree of cationic mixing must also affect inner planes in order to explain experimental findings.

Electronic noses (ENs) have recently emerged as valuable candidates in various areas of food quality control and traceability, including microbial contamination diagnosis. In this paper, the EN technology for microbiological screening of food products is reviewed. Four paradigmatic and diverse case studies are presented: (a) Alicyclobacillus spp. spoilage of fruit juices, (b) early detection of microbial contamination in processed tomatoes, (c) screening of fungal and fumonisin contamination of maize grains, and (d) fungal contamination on green coffee beans. Despite many successful results, the high intrinsic variability of food samples together with persisting limits of the sensor technology still impairs ENs trustful applications at the industrial scale. Both advantages and drawbacks of sensor technology in food quality control are discussed. Finally, recent trends and future directions are illustrated.

Diamond films are very desirable for application to SAW devices because of their high acoustic wave velocity, which allows the extending of the frequency limit of operation at a given interdigital transducer line-width resolution. Use of high-quality AIN as the piezoelectric layer in conjunction with diamond is also desirable because of its high SAW velocity--the highest among all piezoelectric materials--together with its excellent electrical, mechanical, and chemical properties. The problems arising in the growth of A1N films on diamond have prevented, until now, the use of this combination of materials. In this paper we present recent results on the growth of highly oriented, low-stressed A1N films on diamond. SAW propagation on A1N/diamond has been theoretically investigated together with electromechanical coupling for both the Rayleigh and the Sezawa modes. The theoretical calculations show that high SAW velocities are achievable with good coupling efficiencies. Under proper conditions very large piezoelectric couplings are predicted--k2 = 2.2 and 4% for the Rayleigh and the Sezawa wave, respectively--comparable to those observed in strongly piezoelectric single crystals such as LiNbO3, but with SAW velocities approximately two-fold higher. Experiments performed on A1N/diamond/Si SAW test devices have shown good agreement between experimental results and theoretical predictions and demonstrate the feasibility of SAW devices based on this technology.

The present paper reports a socio-acoustic survey carried out in three large urban parks in Rome, selected on the basis of the outcome of a preliminary online survey. According to the experimental protocol applied in a previous study carried out in Milan and Naples, binaural recordings in 85 sites and interviews with 266 users of the three parks were performed only during the day in summertime. On the basis of selected acoustical descriptors, the sonic environment of the three parks was categorized and, thanks to statistical analysis, three clusters were identified. The results confirm that the sound environment in urban parks is often considered as "good" or "excellent" even if the sound pressure level is nearly always higher than the limits commonly used to define quiet areas. This is due to the influence of other factors, such as the presence of trees, natural features, and the tranquility; all of these components cannot be neglected in the assessment of the soundscape because they directly affect the psychological state of the person.

The phonon spectrum of InAs/GaSb superlattices is calculated with a linear-chain model with interplanar force constants. Apart from confined and extended modes, as found also in GaAs/GaAlAs superlattices, this system shows new modes localized at the interface. These latter modes depend crucially on the nature (InSb or GaAs) of the interface and some of them do not coincide with any other possible superlattice mode. This fact would make them easily experimentally identifiable.

The vibrational properties of GaAs/AlAs (001) superlattices are studied theoretically by means of an ab initio approach---based on interatomic force constants---that allows one to treat the effects of compositional disorder using very large supercells. We find that the experimental Raman spectra in thin samples cannot be explained without taking into account disorder occurring at the interfaces. Moreover, we show that some of the AlAs-like LO modes are extremely sensitive to disorder, and they are therefore suitable for a rather precise characterization of the samples.

The ultrafast generation of acoustic waves in copper films is investigated with a femtosecond optical pump and probe technique. By studying the generation at times before the electrons and the lattice come into equilibrium, the strength of their interaction can be measured and the dynamics of ultrafast electron diffusion can be studied. The acoustic strain pulses observed are bipolar in shape with exponential tails that are much broader than expected from simple thermoelastic stress generation. This can be explained by the supersonic diffusion of electrons over distances larger than the optical skin depth. The nonequilibrium diffusion equations governing stress generation are nonlinear, and are solved numerically. Using a linearized formulation, we also solve them analytically to a good approximation. The acoustic strain profile provides a 'snapshot' of the initial spatial temperature distribution of the lattice, thus allowing a sensitive probe of the nonequilibrium dynamics of the diffusion. The electron-phonon coupling constant can be estimated directly from the acoustic pulse duration, provided that the sound velocity and thermal conductivity are known. In general, the relaxation and diffusion of carriers is specific to the sample in question, whether metal or semiconductor, suggesting the use of this method for thin film characterization.>

Volume contraction in bulk silicon crystals is observed on excitation with femtosecond visible optical pulses. The surface deformation and generated acoustic strain are measured using detection based on both probe beam reflectivity changes and probe beam deflection. The contraction is explained by the dominant electronic contribution to the strain from excitation of electron-hole pairs, which swamps the thermoelastic expansion.

A hydrogen sensitive detection technique utilizing a surface acoustic wave (SAW) delay line coated with a palladium thin film is presented. The hydrogen-palladium interaction produces a change in the velocity of SAW propagating on the coated substrate, which is detected as phase shift at the output of the delay line. Presently, hydrogen concentrations as small as 50 ppm in a flowing H2+N2 mixture have been detected.