Structural and optical properties of europium doped zirconia single crystals fibers grown by laser floating zone

Yttria stabilized zirconia single crystal fibers doped with europium ions were developed envisaging optical applications. The laser floating zone technique was used in order to grow millimetric high quality single crystal fibers. The as-grown fibers are completely transparent and inclusion free, exhibiting a cubic structure. Under ultraviolet (UV) excitation, a broad emission band appears at 551 nm. The europium doped fibers are translucent with a tetragonal structure and exhibit an intense red emission at room temperature under UV excitation. The fingerprint transition lines between the 5D0 and 7FJ(0–4) multiplets of the Eu3+ ions are observed with the main emission line at ∼ 606 nm due to 5D0→7F2 transition. Photoluminescence excitation and wavelength dependent the photoluminescence spectra confirm the existence of different Eu3+ optical centers. © 2011 American Institute of PhysicsFCT-PTDC/CTM/66195/2006FCT-SFRH/BD/45774/200

Influence of Lu content on (LuxGd1-x)2SiO5 oxyorthosilicates grown by Laser Floating Zone: structural studies and transparency

Lutetium gadolinium oxyorthosilicates (LGSO, (LuxGd1-x)2SiO5, x = 0.1, 0.3 and 0.5)) were obtained by the Laser Floating Zone (LFZ) in air at 10 mm/h, much faster than those produced by the standard Czochralski method. The LGSO fibres were structural and optically characterized. Scanning electron microscopy (SEM/EDS) allowed observing homogeneous monophasic crystalline fibres that obey the expected phase transition from P21/c to C2/c monoclinic structures, as revealed by X-Ray diffraction and Raman spectroscopy. Finally, transmission studies in the near UV to visible range allowed to quantify the transmission and to appraise the presence of energy transfer bands that favor their use as host materials in photonic applications.publishe

Tipografia corporativa : codificação e descodificação gráfica

Trata-­‐se de uma investigação que visa compreender como é descodificada a Identidade Visual Corporativa, com o intuito de aumentar a eficácia comunicacional do trabalho dos designers ao nível da codificação, considerando o objectivo da empresa ou marca. Com base em 15 casos de estudo e através de quatro questionários, pretende-­‐se identificar conotações gráficas de logótipos e da tipografia corporativa, atendendo aos interesses estratégicos da empresa, produto ou serviço que representam e ao mercado em que operam. O desígnio dos designers ao nível da Identidade Visual Corporativa é confrontado com a percepção pública, de modo a obter dados sobre significados conotativos e denotativos veiculados pela tipografia corporativa e o modo como têm influência na definição da Imagem Corporativa. É objectivo deste estudo, a obtenção de dados ou método de suporte e avaliação de projectos de Identidade Visual Corporativa

Prediction of diffuse horizontal irradiance using a new climate zone model

Knowledge on the diffuse horizontal irradiance (DHI), and direct normal irradiance (DNI) is crucial for the estimation of the irradiance on tilted surfaces, which in turn is critical for photovoltaic (PV) applications and for designing and simulating concentrated solar power (CSP) plants. Since global horizontal irradiance (GHI) is the most commonly measured solar radiation variable, it is advantageous for establishing a suitable method that uses it to compute DHI and DNI. In this way, a new model for predicting the diffuse fraction (K_d) based on the climate zone is proposed, using only the clearness index (K_t) as the predictor and 1-min resolution GHI data. A review of the literature on models that use hourly and sub-hourly K_t values to compute K_d was also carried out, and an extensive performance assessment of both the proposed model and the models from the literature was conducted using ten statistical indicators and a global performance index (GPI). A set of model parameters was determined for each climate zone considered in this study (arid, high albedo, temperate and tropical) using 48 worldwide radiometric stations. It was found that the best overall performing model was the model proposed in this work

Comparison and assessment of circumsolar ratio models for Évora, Portugal

The sun rays are scattered due to molecules, aerosols and some cloud types, such as cirrus clouds, and a region near to the vicinity of the sun disk, known as circumsolar region, with relatively high diffuse sky radiance is formed [1]. Consequently, this diffuse radiation is called circumsolar normal irradiance (CSNI). Modelling the CSNI is important because pyrheliometers (the instruments that are used to measure direct normal irradiance – DNI), have an aperture angle wider than the circumsolar region, and thus DNI measurements obtained with these instruments cannot resolve the distribution of solar radiance in that region [2]. Moreover, since concentrated solar power (CSP) systems only capture solar radiation from this region but with a narrower aperture angle than that of the pyrheliometers, this leads to an overestimation of the energy reaching the receiver of the CSP systems [1]. This can result in misleading power output estimations, which can harm the bankability of CSP projects. Information on CSNI is also crucial when designing, sizing and operating CSP powerplants

Contribution to the diffuse radiation modelling in Évora, Portugal

Solar radiation data is crucial for the design of energy systems based on the solar resource. Since diffuse radiation measurements are not always available in the archive data series, either due to the inexistence of measuring equipment, shading device misplacement or missing data, models to generate these data are needed. In this work, one year of hourly and daily horizontal solar global and diffuse irradiation measurements in Évora are used to establish a new relation between the diffuse radiation and the clearness index. The proposed model includes a fitting parameter, which was adjusted through a simple optimization procedure to minimize the Least Square Error as compared to measurements. A comparison against several other fitting models presented in the literature was also carried out using the Root Mean Square Error as statistical indicator, and it was found that the present model is more accurate than the previous fitting models for the diffuse radiation data in Évora

Laser assisted flow deposition: a new method to grow ZnO

Zinc oxide (ZnO) has been one of the most studied materials in the last decades. Either as bulk material, epilayers or nanostructures, this direct wide band gap semiconductor is known to possess great potential for fundamental science and modern technology applications

Clinical quiz.

J Pediatr Gastroenterol Nutr. 2005 Oct;41(4):483-4, 484. Clinical quiz. Prior AC, Selores M, Pina R, Dias JA, Costa FM, Vale L, Gomes L. Department of Pediatrics, Hospital Geral de Santo António, Portugal. PMID: 16205521 [PubMed - indexed for MEDLIN

Actividades manipulativas como herramienta didáctica en la educación científico-tecnológica

Las actividades manipulativas son una conocida herramienta del aprendizaje que favorecen la educación científico-tecnológica. Intentando promover su uso generalizado en todos los ámbitos posibles se creó en el año 2003 la red educativa "Hands-on Science" (HSci) dentro del programa Sócrates de la Unión Europea en una asociación de veintiocho instituciones de diez países europeos (BE, CY, DE, ES, GR, MT, PT, RO, SL, UK) y un consorcio transnacional (CoLoS). Acabado el proyecto trianual se estableció una asociación internacional con el mismo propósito y filosofía. Su objetivo es difundir entre profesorado, escuelas y consejos educativos, prácticas bien establecidas del aprendizaje de la Ciencia y de la Tecnología, fomentando el desarrollo y uso de actividades manipulativas en los ámbitos formal e informal del aprendizaje. Se pretende que los estudiantes “hagan” ciencia en vez de estar simplemente “expuestos” a ella, aumentando al mismo tiempo la alfabetización científica de la sociedad. En este trabajo se presentan los principales objetivos, estrategias y propuestas pedagógicas de la red, así como sus logros más destacados.Palabras clave: Actividades Manipulativas; Aprendizaje Informal; Ciencia; Proyecto Educativo.Hands-on activities as a didactical tool in Science and Technology educationManipulative activities are a popular learning tool that promotes the effectiveness on scientific and technological education. Aiming to promote its widespread use in all possible areas, in 2003 it was established the educational network "Hands-on Science” (HSci) in the frame of the Socrates program of the European Commission. It enrolled initially twenty-eight institutions from ten European countries (BE, CY, DE, ES, MO, MT, PT, RO, SL, UK) and a multinational consortium (CoLoS). Once finished the three-year project the network was established as an international association with the same purposes and philosophy. In an open and open-minded and participated way we approach and involve teachers, schools and educational boards, presenting, discussing and implementing well-established practices of the learning of Science and Technology. Its objective is to promote the development and use of manipulative activities in formal and informal learning, so that students "do" science rather than simply being "exposed" to it, while in the same time increasing society’ scientific literacy. In this paper we will briefly present the main objectives, pedagogical strategies and proposals of the network as well as the outstanding achievements so far.Key words: Hands-on Activity; Informal Learning; Science; Educative Project

Stability boundary characterization of nonlinear autonomous dynamical systems in the presence of saddle-node equilibrium points

A dynamical characterization of the stability boundary for a fairly large class of nonlinear autonomous dynamical systems is developed in this paper. This characterization generalizes the existing results by allowing the existence of saddle-node equilibrium points on the stability boundary. The stability boundary of an asymptotically stable equilibrium point is shown to consist of the stable manifolds of the hyperbolic equilibrium points on the stability boundary and the stable, stable center and center manifolds of the saddle-node equilibrium points on the stability boundary