Browsing by Issue Date, starting with "2011-05"
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- Bassin versant urbaine Ribeira do Poço das PatasPublication . Pereira, Ana Paula Teixeira; Santos, Renata
- Processamento tecnológico dos minérios de lítio : alguns casos de estudo em PortugalPublication . Amarante, Maria Manuela; Noronha, J. A.; Sousa, A. M. Botelho de; Machado Leite, Mário
- Modelling, control and Pontryagin Maximum Principle for a two-body wave energy devicePublication . Justino, Paulo Alexandre; Cândido, J.Frequency domain analysis is applied to a wave energy device composed by two coaxial axisymmetric bodies. For each frequency optimal damping coefficient values which maximize absorbed power are obtained. Several displacement amplitude restriction scenarios are considered. A stochastic model to describe the device’s behaviour in irregular waves is developed. Optimal mechanical damping and spring coefficients are computed. Considering different sea state conditions, probability density functions are defined for relevant parameters and time averaged absorbed power values are obtained.A time domain model is also developed for the device. A non-linear power take-off mechanism configuration, consisting in a hydraulic circuit with low-pressure and high-pressure gas accumulators, is devised. Time averaged absorbed power is maximized in terms of characteristic mechanism parameter. A sub-optimal method of phase control by latching is applied to the device in order to improve its performance. Analytical development of Pontryagin Maximum Principle is used to establish an algorithm for device’s control.
- Alguns aplito-pegmatitos graníticos com minerais de Li das regiões centro e norte de PortugalPublication . Neiva, A.M.R.; Ramos, João Farinha; Silva, Paulo Bravo
- Quartz from granite pegmatites : a raw-material for high-technologyPublication . Figueiredo, M. Ondina
- Slurry preparation methods affect dental porcelain reliabilityPublication . Pelaez-Vargas, Alejandro; Dussán, Jaime A.; Restrepo, Luís F.; Paucar, Carlos; Ferreira, Jorge Amaral; Monteiro, Fernando J.One-step and incremental mixing procedures are currently used to produce dental ceramic pastes. In the ceramic industry, high quality is obtained using one-step mixing, but in dentistry, the best method has not been yet determined. The purpose of this study is to evaluate the effects of 2 mixing techniques on the biaxial flexural strength and microstructure of dental porcelain. Feldspathic porcelain discs (2 × 15 mm in diameter) were produced and divided according to the ceramic paste preparation method, powder-liquid incremental mixing group (n=50) or one-step mixing, as a control group (n=50). Specimens were tested for biaxial flexural strength and characterized using porosimetry, relative humidity, SEM/EDS, XRD, and FT-IR analyses. Statistical analysis was conducted using Weibull statistics. The Weibull modulus, characteristic strength and relative humidity were compared between groups, using Student's t-test and Mann-Whitney U test (a=.05). The powder-liquid incremental mixing group showed significantly higher values (SD) of Weibull modulus (6.74 (0.70), P<.001) and characteristic strength (79.87 (2.01) MPa, P<.001) when compared to the one-step mixing group (4.94 (0.94) and 75.95 (2.61) MPa). Significantly lower mean (SD) relative humidity values (P=.009) were found for powder-liquid incremental mixing group (20% (0.5%)) compared to one-step mixing group (22% (1%)). XRD spectra showed that the one-step mixing group produced higher amounts of the amorphous phase. Specimens produced by the incremental mixing technique showed higher biaxial flexural strength than one-step mixing.
- Bacia Hidrográfica Urbana da Ribeira do Poço das Patas, PortoPublication . Pereira, Ana Paula Teixeira; Santos, Renata
- Quartzo de pegmatitos graníticos : uma matéria-prima para alta tecnologiaPublication . Figueiredo, M. Ondina
- Contribution to EPMA to airbone pollen analysisPublication . Guimarães, Fernanda; Duque, L.; Ribeiro, H.; Sousa, R.; Abreu, I.As a component of aerosol, pollen is found in suspension with other mineralogical and anthropogenic particles that can adhere to the pollen wall. The aim of this study was to determine possible alterations that pollen grains suffer under different meteorological conditions in the coastal city of Porto, Portugal. For this study, 2 airborne pollen types were taken into account: Poaceae and Alnus spp sampled in July 2010 and February 2011, respectively. Quantitative analysis and X-ray map analysis were performed with a Field Emission Electron Probe Microanalyser (EPMA). Samples were mounted over adhesive carbon tape and carbon coated. Control pollen showed mainly the presence of C, O, N, P, K, Mg, S, Cl and Ca in different quantities, depending on the considered species. Airborne pollen consistently revealed a higher content of Mg and Cl than control pollen, while Si, Ca, K and P contents varied differently according to the samples. Our results show that during their “flight”, pollen grains acquire an external coating, become heavier and change significantly their composition.
- Pegmatitos litiníferos em Portugal : potencial, passado, presente e futuroPublication . de Oliveira, Daniel Pipa Soares; Santana, Helena