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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.
- The pathways to higher education: lexical availability in adult candidate students and in young first-year studentsPublication . Barbeiro, Luís; João, Cláudia; Santos, SusanaIn the past few years there has been an increase in the number of adult students in higher education courses, many of whom have returned to school after a break. Most of these students do not intend to continue their studies from the point where they stopped; rather, they want to prepare for specific tests in order to have direct access to higher education courses, which in Portugal is a legal option for students over the age of 23. In response to this new cohort, higher education institutions need to find out what kind of students these are, determining their characteristics, capabilities and major problems, if they are to provide them with successful learning opportunities alongside younger students. This article presents a comparative study of lexical competence, focusing on lexical availability, contrasting those adult applicants to higher education who are attending a course preparatory to higher education with first-year students who have just entered higher education. The results show significant differences between the two groups, the adult group in general showing poorer results. Their withdrawal from schooling is clearly reflected in their vocabulary activation with regard to transversal themes. The most salient contrasts are related to the number of words mentioned and the frequency of words in the group, as well as the greater or lesser proximity to the topic of the terms mentioned.
- Mechanical behaviour of PVC/CaCO3 Particulate Composites – Influence of TemperaturePublication . Costa, J. D. M.; Capela, C.; Ferreira, J. A. M.This paper is concerned with the study of temperature influence on Young’s modulus, ultimate strength and fracture toughness properties of PVC/CaCO3 particulate composites with different volume fractions. The tests were performed in three- and four-point bending. The resonant technique was also used to analyse the influence of both volume fraction and temperature on Young’s modulus. Significant decrease of ultimate strength, fracture toughness and Young’s modulus was observed with the increase of the temperature. Ultimate strength decreases with the increase of particle volume fraction at room temperature. For the other temperatures, this decreasing trend is less clear. PVC/CaCO3 flexural Young’s modulus calculated for a much lower loading segment increases with volume fraction. The same trend was obtained using the resonant technique. However, as the loading segment used to calculate the Young’s modulus was increased a significant decrease of Young’s modulus was obtained as a result of a progressive debonding at the particle-matrix interface. A 2D simplified FE simulation also confirms such trend. The dependence of Young’s modulus relatively to the loading segment increases as the volume fraction is increased, leading to composite Young’s modulus below matrix value for higher volume fractions and higher loading segments. Fracture toughness decreases with volume fraction.
- 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.
- Diapir Mudstone Properties, Leiria, PortugalPublication . Veiga, Anabela; Quinta-Ferreira, MárioThe engineering geology study of the Dagorda Formation outcropping in the core of the Parceiros-Leiria diapir, was based on field reconnaissance, on in situ and laboratory tests. The formation is constituted mainly by clay and silt, sometimes with sand, occasionally with gypsum or marls. The engineering geology properties of the fine materials showed large variability depending on their degree of consolidation and water content, ranging from very poor to fair. The presence of soluble minerals can develop dissolution voids. When exposed, for example in excavation surfaces, they tend to deteriorate because of decompression and exposure to the external environment, easily losing strength when wet, which facilitates the failure on slopes or foundations. The presence of soluble minerals (gypsum and rock salt at greater depth) can develop dissolution voids due to circulating water. In depth the variation of the mechanical properties may lead to difficulties in foundation ground, as well as difficulty of concreting piles, due to the escape of concrete between neighboring piles along fissures and dissolution voids. The occurrence of very low strength seams, may constrain the stability of cuttings. The unusual geotechnical behavior of these terrains due to the presence of both clay and soluble minerals must be taken into account. In all engineering works to be carried out on these materials it is recommended to develop a detailed engineering geology study prior to construction, in order to early identify the problems and to define the suitable solutions and construction techniques to be adapted to each case. The construction works must have geotechnical assistance in order to improve the construction operations.