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Amorphous silicon carbide films were obtained by plasma enhanced chemical vapor deposition (PECVD) technique using a gas mixture of silane, methane, and hydrogen with a high excitation frequency and a high hydrogen dilution ratio. The high temperature annealing behavior of the amorphous silicon carbide films was studied by annealing at 1373 K for 1 h in nitrogen atmosphere. A very thin Au film was deposited on part of the films to investigate the metal induced crystallization effect. Well aligned nanotubes were found on the silicon carbide films covered by a thin gold layer after the high temperature annealing by atomic force microscopy. Further study is necessary to identify the nature of the nanotubes and elucidate their growth mechanism. © 2006 Elsevier B.V. All rights reserved.

The electrosynthesis of polypyrrole (PPy) has been achieved on aluminium in aqueous medium of malic acid by means of cyclic voltammetry, potentiostatic and galvanostatic techniques. Scanning electron microscopy (SEM) and X-ray microanalysis by dispersion energy spectroscopy (EDS) applying on surfaces show that the PPy coating is developed from the metal surface through the cracks of the initial Al2O3 layer. Moreover, the results reveal that the homogeneity of the film achieved increases with the time of electropolymerization. A mechanism involving the participation of the supporting electrolyte and the pyrrole (Py) in distinct active sites was proposed based on the linear sweep voltammetry. It is observed for all the applied electrochemical techniques that the pyrrole concentration has to be higher than 0.1 M to allow the polypyrrole electrodeposition in acid medium. Scanning electron microscopy, secondary electrons (SE) and backscattering electrons (BE), shows that the PPy coating obtained in galvanostatic and potentiostatic modes starts with small islands at weak applied potentials or current densities. The corrosion results in 3% NaCl medium show that the PPy coating decreases the corrosion behaviour of the aluminium. The bilayer Al2O3/PPy shows a capacitor with future applications. © 2006 Elsevier B.V. All rights reserved.

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A classical theorem of Coifman, Rochberg, and Weiss on commutators of singular integrals is extended to the case of generalized Lp spaces with variable exponent.

Given a complete rewriting system R on X and a subset X0 of X+ satisfying certain conditions, we present a complete rewriting system for the submonoid of M(X;R) generated by X0. The obtained result will be applied to the group of units of a monoid satisfying H1 = D1. On the other hand we prove that all maximal subgroups of a monoid defined by a special rewriting system are isomorphic.

This thesis deals with the analysis of the behaviour of retrofitting reinforced concrete circular columns with FRP materials which were subjected either to axial cyclic compression or axial compression and alternated cyclic horizontal loads. The choice of this topic derived from the need to investigate the behaviour of the strengthening of reinforced concrete columns to seismic actions, especially with new materials such as carbon and glass fibres or polymeric mortars. Another reason for such choice is linked to the strong seismicity of the Portuguese territory.
It has been verified that confined concrete columns with FRP jackets have their resistance and ductility highly increased as these considerably reduce the columns transversal deformation, thus preventing the buckling of longitudinal reinforcement. There has been an increasing use of FRP composites in the strengthening of structures, mainly with GFRP (Glass Fibre Reinforced Plastics) or CFRP (Carbon Fibre Reinforced Plastics). This is due to their attractive characteristics such as high resistance to corrosion, lowratio for weight/strength, moldability, easy application and the fact that there is no need of support structures.
Forty-five experimental tests were carried out, dealing with retrofitting reinforced concrete columns with axial monotonic or cyclic compression reinforced with FRP composites. The column height of 750 mm was maintained in order to evaluate the influence of several parameters in its behaviour: the column geometry (change in its diameter), the type of column (plain or reinforced concrete), transversal reinforcement ratio of concrete columns, the type of external confinement with FRP (C or GFRP), the number of FRP layers and the type of axial loading (monotonic or cyclic).
Twelve additional experimental tests were conducted in order to analyse the behaviour of reinforced concrete columns jacketed with FRP composites and subjected to axial cyclic compression and alternated cyclic horizontal loads. The columns’ dimension was maintained (1500 mm height by 250 mm diameter) and the models were subjected to a series of cyclic and alternated loadings. This enabled the study of the various parameters’ influence in their behaviour such as the type of FRP confinement, the number of FRP layers, the level of axial loading, the jacket’s height or the strengthening of the plastic hinge by replacing the cover concrete with polymeric mortar.
Based on the numerical models presented and experimental analysis carried out, models were proposed and developed to simulate the behaviour of columns jacketed with FRP composites.

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