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

Modifying a pyrheliometer to measure direct normal and circumsolar irradiance

Direct normal irradiance (DNI) is key to concentrating solar power (CSP) systems energy generation. However, pyrheliometric measurements of DNI also include a circumsolar normal irradiance (CSNI) component because the aperture angle of the instrument is larger than the sun disk. CSNI is due to the scattering of the sun rays by molecules, aerosols and some cloud types such as cirrus clouds [1]. As a result, energy is transferred from the direct solar beam to the circumsolar region, i.e., the region in the vicinity of the sun disk [2]. Typically, CSP systems have a lower aperture angle than that of pyrheliometers, which means that these systems are not able to absorb the same amount of CSNI as the amount that is present in the DNI measurements, leading to an inaccurate forecast of energy generation of CSP systems if DNI measurements are directly used in its sizing and operation. In this way, measuring CSNI for different aperture angles is important to better size, operate and optimize the energy generation of CSP systems. In this work, a conventional pyrheliometer field-of-view is modified through the variation of its collimator length and diameter in order to gather information on the circumsolar irradiance [3]. The modified pyrheliometer is composed by a revolver with four possible combinations of tube lengths and diameters and a stepper motor, which automatically enable varying the field-of-view of the pyrheliometer

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

ZnGa2O4:Mn2+ phosphors grown by Laser Floating Zone

Cubic zinc gallate (c-ZnGa2O4) has attracted the attention of the scientific community due to its potential phosphor applications, namely in field emission displays (FEDs) and other electroluminescent devices. Among other advantages, this oxide matrix shows superior thermal and chemical stability when compared to ZnS based phosphors. Most of the above mentioned works comprise nanostructures, thin films or pressed pellets while scarce information is found on bulk c-ZnGa2O4 material. In particular, no records were found regarding c-ZnGa2O4 crystal growth by the laser floating zone (LFZ) technique. In this work, crystalline fibres of manganese doped (0.01 mol %) zinc gallate were produced via LFZ in order to investigate its applicability in efficient phosphors. The transition metal ions are suitable activators and show some advantages over the widely used rare earths, namely at environmental and economic levels

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