973 resultados para Z-scan technique


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High energy band gap hosts doped with lanthanide ions are suitable for optical devices applications To study the potential of Ta(2)O(5) as a host compound pure and Eu(2)O(3)-doped Ta(2)O(5) crystal fibers were grown by the laser-heated pedestal growth technique in diameters ranging from 250 to 2600 pm and in lengths of up to 50 mm The axial temperature gradient at the solid/liquid interface of pure Ta(2)O(5) fibers revealed a critical diameter of 2200 gm above which the fiber cracks X-ray diffraction measurements of the pure Ta(2)O(5) single crystals showed a monoclinic symmetry and a growth direction of [1 (1) over bar 0] An analysis of the pulling rate as a function of the fiber diameter for Eu(2)O(3)-doped Ta(2)O(5) fibers indicated a well defined region in which constitutional supercooling is absent Photoluminescence measurements of pure Ta(2)O(5) crystals using excitation above the band gap (3 8 eV) were dominated by a broad unstructured green band that peaked at 500 nm Three Eu(3+)-related optical centers were identified in the doped samples with nominal concentrations exceeding 1 mol% Two of these centers were consistent with the ion in the monoclinic phase with different oxygen coordinations The third one was visible in the presence of the triclinic phase (C) 2010 Elsevier B V All rights reserved

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Aim. The purpose of this study was to provide normal values for maximum phonation time (MPT) and the s/z ratio by examining 1660 children aged 4-12 years and without vocal signs or symptoms.Methods. The technique was based on the sustained emission of the /a/ vowel and fricatives /s/ and /z/.Results. The average of the MPT in children of the different age groups was as follows: 6.09 seconds for the age group 4-6 years (males, 5.97; female, 6.21 seconds), 7.94 seconds for the age group 7-9 years (males, 8.07; females, 7.79 seconds), and 8.98 for the age group 10-12 years (males, 9.05; females, 8.92 seconds). The overall average for males was 7.78 and females 7.64 seconds. The s/z ratio was near 1.0 in most children but above 1.2 in 133 children and below 0.8 in 133 children.Conclusion. These values of MPT and s/z ratio can be used as normative in further pediatric studies.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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For any finite commutative ring B with an identity there is a strict inclusion B[X; Z(0)] subset of B[X; Z(0)] subset of B[X; 1/2(2)Z(0)] of commutative semigroup rings. This work is a continuation of Shah et al. (2011) [8], in which we extend the study of Andrade and Palazzo (2005) [7] for cyclic codes through the semigroup ring B[X; 1/2; Z(0)] In this study we developed a construction technique of cyclic codes through a semigroup ring B[X; 1/2(2)Z(0)] instead of a polynomial ring. However in the second phase we independently considered BCH, alternant, Goppa, Srivastava codes through a semigroup ring B[X; 1/2(2)Z(0)]. Hence we improved several results of Shah et al. (2011) [8] and Andrade and Palazzo (2005) [7] in a broader sense. Published by Elsevier Ltd

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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The Z(4)-linearity is a construction technique of good binary codes. Motivated by this property, we address the problem of extending the Z(4)-linearity to Z(q)n-linearity. In this direction, we consider the n-dimensional Lee space of order q, that is, (Z(q)(n), d(L)), as one of the most interesting spaces for coding applications. We establish the symmetry group of Z(q)(n) for any n and q by determining its isometries. We also show that there is no cyclic subgroup of order q(n) in Gamma(Z(q)(n)) acting transitively in Z(q)(n). Therefore, there exists no Z(q)n-linear code with respect to the cyclic subgroup.

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This work describes an application of a multilayer perceptron neural network technique to correct dome emission effects on longwave atmospheric radiation measurements carried out using an Eppley Precision Infrared Radiometer (PIR) pyrgeometer. It is shown that approximately 7-month-long measurements of dome and case temperatures and meteorological variables available in regular surface stations (global solar radiation, air temperature, and air relative humidity) are enough to train the neural network algorithm and correct the observed longwave radiation for dome temperature effects in surface stations with climates similar to that of the city of São Paulo, Brazil. The network was trained using data from 15 October 2003 to 7 January 2004 and verified using data, not present during the network-training period, from 8 January to 30 April 2004. The longwave radiation values generated by the neural network technique were very similar to the values obtained by Fairall et al., assumed here as the reference approach to correct dome emission effects in PIR pyrgeometers. Compared to the empirical approach the neural network technique is less limited to sensor type and time of day (allows nighttime corrections).

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This paper addresses the problem of allocating the cost of the transmission network to generators and demands. A physically-based network usage procedure is proposed. This procedure exhibits desirable apportioning properties and is easy to implement and understand. A case study based on the IEEE 24-bus system is used to illustrate the working of the proposed technique. Some relevant conclusions are finally drawn.

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We report the preparation and characterization of yttria-stabilized zirconia/nickel oxide composites (YSZ/NiO). This composite is the precursor material of the cermet YSZ/Ni, which is used as solid oxide fuel cell anode material. The performance of the anode is strongly dependent on the microstructural properties of the cermet. Therefore, the control of the microstructure of the YSZ/NiO composite is a key step for the fabrication of high-performance anodes. In this study, the composites were prepared by a modified liquid mixture technique. Scanning electron microscopy analysis evidenced the good dispersion of the phases and that NiO nanoparticles are spread over the YSZ surface. Sintered pellets were studied by X-ray diffraction and impedance spectroscopy. The main results show that the composite is comprised of a well-dispersed mixture of the two phases. The electrical conductivity data show that there is a strong dependence of the transport mechanism on the relative composition of phases. (c) 2005 Elsevier Ltd. All rights reserved.

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dIn this work, a perceptron neural-network technique is applied to estimate hourly values of the diffuse solar-radiation at the surface in São Paulo City, Brazil, using as input the global solar-radiation and other meteorological parameters measured from 1998 to 2001. The neural-network verification was performed using the hourly measurements of diffuse solar-radiation obtained during the year 2002. The neural network was developed based on both feature determination and pattern selection techniques. It was found that the inclusion of the atmospheric long-wave radiation as input improves the neural-network performance. on the other hand traditional meteorological parameters, like air temperature and atmospheric pressure, are not as important as long-wave radiation which acts as a surrogate for cloud-cover information on the regional scale. An objective evaluation has shown that the diffuse solar-radiation is better reproduced by neural network synthetic series than by a correlation model. (C) 2004 Elsevier Ltd. All rights reserved.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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A detailed study of the microstructural and electrical properties of the yttria-stabilized zirconia/nickel oxide (YSZ/NiO) composite was performed. This material is the precursor to the solid oxide fuel cell anode cermet YSZ/Ni. A liquid mixture technique was developed to produce the YSZ/NiO composite to fabricate high-performance SOFC anodes. This technique resulted in fine and homogeneous powders and specimens with high electrical conductivity. The combined results showed that this technique is suitable for the production of the anode cermet.

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Thermogravimetric analysis is one of the most common instrumental techniques used for the characterization of pastes, mortars and concretes based on both calcium hydroxide and Portland cement. Important information about pozzolanic materials can be assessed concerning calcium hydroxide consumption and the formation of new hydrated products. Nevertheless, in some cases, problems associated with the overlapped decomposition processes for hydrates make the analysis of obtained data difficult. In this paper, the use of high-resolution thermogravimetric analysis, a powerful technique that allows separating decomposition processes in analysis of hydrated binders, was performed for spent FCC catalyst-Portland cement pastes. These pastes were monitored for 1, 4, 8 h and 1, 2, 3, 7 and 28 curing days. In order to study the influence of the pozzolanic material (spent FCC catalyst), Portland cement replacements of 5, 15 and 30 % by mass were carried out. The presence of spent FCC catalyst in blended pastes modified the amount and the nature of the formed hydrates, mainly ettringite and stratlingite.

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Aim. The purpose of this study was to provide normal values for maximum phonation time (MPT) and the s/z ratio by examining 1660 children aged 4-12 years and without vocal signs or symptoms. Methods. The technique was based on the sustained emission of the /a/ vowel and fricatives /s/ and /z/. Results. The average of the MPT in children of the different age groups was as follows: 6.09 seconds for the age group 4-6 years (males, 5.97; female, 6.21 seconds), 7.94 seconds for the age group 7-9 years (males, 8.07; females, 7.79 seconds), and 8.98 for the age group 10-12 years (males, 9.05; females, 8.92 seconds). The overall average for males was 7.78 and females 7.64 seconds. The s/z ratio was near 1.0 in most children but above 1.2 in 133 children and below 0.8 in 133 children. Conclusion. These values of MPT and s/z ratio can be used as normative in further pediatric studies.