Browsing by Issue Date, starting with "2011-06"
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- Recrystallization of silicon polygonal tubes using an electric closed molten zonePublication . Gamboa, Roberto; Brito, M.C.; Serra, J.M.; Alves, J. Maia; Vallêra, A.M.This article describes a process for generating and controlling a closed molten zone with an induced electrical current, and using it for silicon ribbon tube recrystallization. The silicon tube is the secondary loop of a transformer in which the current is generated by electrical induction. The Joule heat caused by the induced current generates a closed molten line along a cross section of the silicon tube; scanning this molten zone along the tube axis results in material recrystallization, with no contact with foreign materials. From the recrystallized silicon tube faces test solar cells were produced, revealing minority carrier diffusion lengths around 100 mm.
- Drift field limitations to the energy resolution in Time Projection Chambers for 136Xe neutrino-less double beta decay searchPublication . Neves, P.N.B.; Conde, C.A.N.; de Oliveira Pegado de Noronha E Távora, Luís MiguelThe effect of drift electric field in the degradation of the energy resolution of gaseous xenon Time Projection Chambers for the search of neutrino-less double beta decay of 136Xe is calculated with the PENELOPE code. Calculations are presented first for single electron emission with energies from 0.2 to 3 MeV and reduced electric fields in the 0.1–2 V cm−1 Torr−1 range, showing energy resolution degradations by as much as 12% (FWHM). Calculations are also presented for neutrino-less double beta decay of 136Xe assuming two decay mechanisms, the mass mechanism (MM) and the right-handed current due to the λ parameter (RHCλ) mechanism, for reduced drift electric fields in the 0.03–0.8 V cm−1 Torr−1 range. It is shown that the drift field degrades the energy resolution of the two electrons sum peak (2457.8 keV) by an amount that is significant even for reduced fields as low as 0.1 V cm−1 Torr−1. It is concluded that to reach the experimental target of 1% (FWHM) for the energy resolution of TPCs set-ups (like the NEXT collaboration set-up) the drift electric field should be weaker than about 0.1 V cm−1 Torr−1.
- EditorialPublication . Bartolo, Paulo; Chua, C. K.
- Study of the degradation mechanisms of polyethylene during reprocessingPublication . Mendes, Ausenda; Cunha, A.M.; Bernardo, C.A.The present work aims at evaluating the behaviour of various grades of high and low density polyethylene subjected to continuous injection moulding operations. It is based on a wide range of experimental techniques that allowed the establishment of relationships between the observed property changes and the structural modifications developed in the polymers. The study confirmed the coexistence of two distinct degradation mechanisms, crosslinking and chain scission, that occur due to thermo-oxidative reactions arising during the different injection moulding stages. The relative importance of these two mechanisms depends on the material structure and on the processing conditions used. It was also possible to confirm that the polyethylenes with lower molecular mass show low sensitivity to degradation during reprocessing. Furthermore, the more branched polymers (as is the case of LDPE) also proved to be less sensitive to thermo-degradation phenomena. Overall, it was concluded that the primary recycling of polyethylene, if performed under well controlled conditions, will lead to only minor material property losses.
- Improving teaching and learning of computer programming through the use of the Second Life virtual worldPublication . Esteves, Micaela; Fonseca, Benjamim; Morgado, Leonel; Martins, PauloThe emergence of new technologies such as three‐dimensional virtual worlds brings new opportunities for teaching and learning. We conducted an action research approach to the analysis of how teaching and learning of computer programming at the university level could be developed within the Second Life virtual world. Results support the notion that it is possible to use this environment for better effectiveness in the learning of programming. The main results are the identification of problems hampering the teacher's intervention in this virtual world and the detection of solutions for those problems that were found effective to the success in using this environment for teaching/learning computer programming.
- PHEMA-based thin hydrogel films for biomedical applicationsPublication . De Giglio, E.; Cafagna, D.; Giangregorio, MM; Domingos, Marco; Mattioli-Belmonte, M.; Cometa, S.Poly(2-hydroxyethyl methacrylate) based thin coatings were electro-synthesized by cyclic voltammetry on Au-coated quartz crystal surfaces to study different solid—liquid interfacial processes. By varying the electrochemical parameters and the presence or not of a crosslinking agent, films were obtained with thicknesses ranging from 5 to 90 nm. Surface characterization was performed by X-ray photoelectron spectroscopy, atomic force microscopy, and static contact angle measurements. Using quartz crystal microbalance with dissipation monitoring to investigate the relationship between the film thickness and the swelling behavior, it was found that these characteristics can be modulated by varying either the number of voltammetric cycles or the presence of the crosslinker. Cell adhesion and biocompatibility tests indicate that these film coatings were suitable for biomedical applications.