Surface Chemistry of Oxides and Electrocatalysis

After an introductory description of the moment acquired by some oxide electrodes in the electrochemical technology, the procedure for their preparation and the physicochemical and electrochemical characterizations are described emphasizing the interdisciplinary character of the research in this field. The importance of -separating geometrical from electronic parameters for a proper understanding of the factors governing the electro- catalytic activity is stressed. Arguments along these lines lead to the association of electrocatalysis with surface acid-base dissociation concepts. A parallel analysis of the behaviour of the point of zero charge and of the electrocatalytic activity for the anodic evolution of oxygen shows that the former property can be used as a diagnostic, intensive parameter for a relative evaluation of the electrocatalytic activity of a set of oxide electrodes. Results for RuOx, IrOx, C03O4 and NiCo2C>4 are discussed

THE EFFECTS OF VERBAL OPERANT TRAINING AND RESPONSE INTERRUPTION AND REDIRECTION ON VOCAL STEREOTYPY

Verbal operant training is a typical intervention for individuals with Autism Spectrum Disorder. Response Interruption and Redirection (RIRD) is a highly effective intervention for problem behavior and various forms of stereotypy. In this study verbal operant training was combined with RIRD to see if there was a bigger impact in decreasing vocal stereotypy. The participant was a 9-year old male, and the intervention was done across settings. The results showed that combined with intraverbal training and RIRD, vocal stereotypy decreased significantly in all settings. The results also indicate this is a highly effective treatment for vocal stereotypy when the function is non-social automatic reinforcement (i.e. self-stimulation). Key words: Autism Spectrum Disorder, Intraverbal, Response Interruption and Redirection, RIRD, Verbal Operants, Vocal Stereotyp

Exploring the nature of radio relics and halos in galaxy clusters through GHz radio observations

Clusters of galaxies are the largest gravitationally bound systems in the Universe. A fraction of them hosts diffuse Mpc-scale synchrotron sources (referred to as radio relics and radio halos) not related to any discrete cluster member, but rather to the diffuse medium. The emission from these sources helps in unambiguously prove the presence of weak magnetic fields and non-thermal plasma in the intra-cluster medium (ICM) of galaxy clusters, coexisting with the hot thermal component emitting X-rays. The radio emitting electrons, given their relatively short lifetime respect to the extent of these sources, must have undergone some form of acceleration. It is widely believed that they are connected to the most energetic phenomena in the Universe, mergers between clusters, during which shocks and turbulence may develop in the ICM leading eventually to the acceleration of particles through Fermi mechanisms. Both phenomena are, indeed, mostly observed in galaxy clusters with a disturbed dynamical state. However, the details of the acceleration mechanisms are still greatly debated. According to the proposed models, the currently known radio relics and halos are the most energetic cases, for which relatively high-frequency observations are necessary in order to test the models expectations. However, for most of them the highest studied frequency is 1.4 GHz. In this thesis we studied the properties of this kind of sources at frequencies > 1 GHz. We mainly focused on two clusters, Abell 1656 (best known as the Coma cluster) and Abell 2256, known to possess both a radio relic and a radio halo. We observed a wide field on the Coma cluster, covering both the peripheral relic and the central halo, with the Effelsberg 100-m telescope at 1400 MHz. Moreover, the Coma relic field and the Coma halo field have been covered separately with respectively a 3-pointing and a 9-pointing mosaics performed with the WSRT at 2273 MHz. We have observed the cluster Abell 2256 with the Effelsberg-100m Telescope at 2640 MHz and at 4850 MHz. The same field was observed with a 3-pointing mosaic performed with the WSRT at 2273 MHz. The observations were performed in full polarization mode. The Effelberg observations were carried out during an observational campaign of a small sample of galaxy clusters known to host diffuse non-thermal emission. We include preliminary results from the analysis of Effelsberg C-band data of the galaxy clusters Abell 0115 and Abell 2255. We highlight the importance of high-frequencies observations for the study of both the total intensity and the polarization properties of these sources. The connection of the radio properties observed with the properties of the thermal gas derived from X-ray and S-Z effect observations is also discussed. It is generally assumed that radio relics are observed in stationary conditions. In this case the widely accepted model for radio relics, the diffusive acceleration at merger shocks (DSA), predicts single power-law integrated spectra. However, we observe a departure from a pure power-law integrated spectrum at frequencies > 1.4 GHz for the radio relic in Abell 2256 that puts tension on the commonly assumed conditions for DSA. Moreover, theoretical studies have shown that in the case of strong shocks the DSA model predicts magnetic field compression and alignment with the shock front. At high frequencies, the observed polarized emission is less affected by Faraday effects and it is therefore a better indicator of the intrinsic properties of the sources. Possible alignment of the polarization vectors measured across the extent of radio relics can, therefore, be used to reconstruct the geometry of the shock passage in case of shock acceleration. We show that the polarization properties in the Abell 2256 relic are difficult to be reconciled with a single outgoing shock front, requiring a more complex scenario. We also show how the combination of interferometric and single-dish data in the Fourier domain (applied to the observations of the Coma cluster) allow us to overcome the "missing short spacings problem" suffered by interferometers at these frequencies, that makes them blind to very extended emission. The combination technique is, therefore, a promising tool to study the properties of radio relics and halos at GHz frequencies

The Surface Potential of Water at Metal-Solution Interfaces

Relative values of the surface poitential of water at metal- aqueous solution interfaces at the potential of zero charge are derived by comparing experimental charge-potential curves for various metals. The principle of the method is presented and discussed. Absolute values for all the othe1r mefa~s are obtamed by estimating the absolute value of the surface potential of water on Hg. Three indeipendent routes are suggested. They are described and discussed. Experimental results are presented. The final estima: te sugigests that the surface potential of water on Hg is between 0.07 a1D.d 0.08 V, probably closer to 0.07 V. Water molecules are oriented wUh the oxy,gen atom facing the solid for all the metals investigated. A model is proposed to explaiin the metal-dep\u27endent orientation of water at the 1nterface with electrodes at the potential of ze1ro charge

Gravity changes due to overpressure sources in 3D heterogeneous media: application to Campi Flegrei caldera, Italy

Employing 3D finite element method, we develop an algorithm to calculate gravity changes due to pressurized sources of any shape in elastic and inelastic heterogeneous media. We consider different source models, such as sphere, spheroid and sill, dilating in elastic media (homogeneous and heterogeneous) and in elasto-plastic media. The models are oriented to reproduce the gravity changes and the surface deformation observed at Campi Flegrei caldera (Italy), during the 1982-84 unrest episode. The source shape and the characteristics of the medium have great influence in the calculated gravity changes, leading to very different values for the source densities. Indeed, the gravity residual strongly depends upon the shape of the source. Non negligible contributions also come from density and rigidity heterogeneities within the medium. Furthermore, if the caldera is elasto-plastic, the resulting gravity changes exhibit a pattern similar to that provided by a low effective rigidity. Even if the variation of the source volumes is quite similar for most of the models considered, the density inferred for the source ranges from ∼ 400 kg/m3 (supercritical water) to ∼ 3300 kg/m3 (higher than trachytic basalts), with drastically different implications for risk assessment

Gravity changes due to overpressure sources in 3D heterogeneous media: application to Campi Flegrei caldera, Italy

Employing a 3D finite element method, we develop an algorithm to calculate gravity changes due to pressurized sources of any shape in elastic and inelastic heterogeneous media. We consider different source models, such as sphere, spheroid and sill, dilating in elastic media (homogeneous and heterogeneous) and in elasto-plastic media. The models are oriented to reproduce the gravity changes and the surface deformation observed at Campi Flegrei caldera (Italy), during the 1982-1984 unrest episode. The source shape and the characteristics of the medium have great influence on the calculated gravity changes, leading to very different values for the source densities. Indeed, the gravity residual strongly depends upon the shape of the source. Non negligible contributions also come from density and rigidity heterogeneities within the medium. Furthermore, if the caldera is elasto- plastic, the resulting gravity changes exhibit a pattern similar to that provided by a low effective rigidity. Even if the variation of the source volumes is quite similar for most of the models considered, the density inferred for the source ranges from ∼400 kg/m3 (super critical water) to ∼3300 kg/m3 (higher than trachytic basalts), with drastically different implications for risk assessment

Finite element inversion of DInSAR data from the Mw 6.3 L’Aquila earthquake, 2009 (Italy)

Fault slip distribution is usually retrieved from geodetic data assuming that the local crust is an elastic, homogeneous and isotropic half‐space. In the last decades spatially dense geodetic data (e.g., DInSAR maps) have highlighted complex patterns of coseismic deformation that require new modeling tools, such as numerical methods, able to represent rheological and geometrical complexities of the Earth’s crust. In this work, we develop a procedure to perform inversion of geodetic data based on the finite element method, accounting for a more realistic description of the local crust. The method is applied to the 2009 L’Aquila earthquake (Mw 6.3), using DInSAR images of the coseismic displacement. Results highlight the non‐negligible influence of the medium structure: homogeneous and heterogeneous models show discrepancies up to 20% in the fault slip distribution values. Furthermore, in the heterogeneous models a new area of slip appears above the hypocenter. We also perform a resolution study, showing that the information about fault slip distributions retrieved from geodetic data should be considered as averaged on surrounding patches

EFFETTO DELLA SOLLECITAZIONE MECCANICA A FLESSIONE SUL COMPORTAMENTO A CORROSIONE DI LEGHE DI Al STRUTTURALI

The present work reports on the effect of constant bending load on the electrochemical behavior of structural aluminum alloys AA 2024-T3 (Al-Cu-Mg) and AA 7075-T6 (Al-Zn-Mg-Cu). The single cycle anodic polarization curves in 0.6 M NaCl (pH 6.5) were carried out using four-point bent beam specimens (4PBB). Lower propensity to localized corrosion has been indicated for compressive stresses. The effect of tensile stresses on the electrochemical response is more complex and depends on the alloy nature