http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/8536 Thu, 09 Apr 2026 15:57:20 GMT 2026-04-09T15:57:20Z http://tede2.ufrpe.br:8080/tede/retrieve/13092/pengfis.png http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/8536 http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9043 Título: Distribuição de cátions de Ce3+ e Er3+ na estrutura cristalina do composto Y3Fe5O12 e seu efeito sobre as propriedades estruturais, óticas e magnéticas Autor: FERREIRA, Mirelly Gonçalves Primeiro orientador: GARCIA, Ramón Raudel Peña Abstract: Herein, we have studied the structural, optical, and magnetic properties of Y3-xCexFe5-yEryO12 (0.00 ≤ x ≤ 0.02), (0.00 ≤ y ≤ 0.06) compound synthesized via sol gel process. Structural characterization by X-ray diffraction (XRD) confirmed the YIG single phase formation, belong to the Ia3d-𝑂ℎ10cubic centrosymmetric crystal structure. The lattice constant, lattice strain, dislocation density and average crystallite size variations were calculated and discussed in terms of the rare earth’s dopant concentrations. Fourier Transform Infrared Spectroscopy (FTIR) analysis showed redshift for the Fe–O stretching modes as the dopant content increase, testifying the crystal lattice expansion. Raman spectra inspection corroborated the YIG single phase formation and shifts in the vibrational modes confirmed the Ce3+ and Er3+ rare earths inclusion in the sites occupied by Y3+ and Fe3+ cations, respectively. The coral-like of YIG nanoparticles were confirmed by scanning (SEM) and transmission (TEM) microscopies, whereas the existence of the elements Y, Fe, O, Ce and Er, were verified by Energy Dispersive Spectroscopy analysis (EDS). The optical band gap (Eg) decreases, while Urbach energy (Eu) increases varying the Er content. The result confirms the effect of Ce3+ and Er3+ addition on the optical properties of YIG, contributing to localized oxygen vacancy defects formation. Using a phenomenological model, it was shown that, the highest probability of Er3+ cations occupation corresponds to octahedral sites. For the Y2.98Ce0.02Fe5-yEryO12 (0.00 ≤ y ≤ 0.06) compound, the theoretical saturation magnetization (Ms) was calculated from the cation distribution obtained by the phenomenological model, resulting a slight increase with the Er content. The result agrees with the experimental Ms measurements, although for y = 0.06 a discrepancy was detected, which can be attributed to the breaking of collinear array of magnetic moments due to high lattice distortions. Instituição: Universidade Federal Rural de Pernambuco Tipo do documento: Dissertação Mon, 27 Feb 2023 00:00:00 GMT http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9043 2023-02-27T00:00:00Z http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9041 Título: Estudo comparativo entre os métodos AHP e ANP para classificação de acumuladores de energia elétrica aplicados a recursos energéticos distribuídos Autor: ALBUQUERQUE JÚNIOR, Paulo Pereira de Primeiro orientador: SILVA, Ítalo Roger Ferreira Moreno Pinheiro da Abstract: With the growth in the use of electricity in different sectors of society each year, when analyzing the global and Brazilian situation, this growth is accompanied by different forms of energy generation, whether centralized or distributed. Distributed generation (DG) has become an alternative for the electrical power system not to be overloaded. On the other hand, intermittent sources of DG (such as solar and wind) have restrictions on the generation of electricity due to the availability of primary energy, which reduces the generation potential. In this way, the integration of electric energy accumulators to the DG has been adopted as a solution to increase this potential, for example, storing the surplus of generated energy, in relation to the demand, to supply it to the electric grid during times of peak load or loads close to the center of GD. In this context, aiming to define and classify the most suitable accumulator technologies for DG, this dissertation presents a careful analysis of the operational and constructive characteristics of energy accumulators, in terms of investment cost, efficiency, specific energy, among others. In addition, the application segments of accumulators in DG were considered, which can be highlighted in: very short and short-term application. To this end, hierarchical methods and multicriteria decision making, such as the analytical hierarchy process (AHP), have been extensively explored in the literature for classifying accumulators in various applications. However, the use of the analytical network process (ANP), which is a generalization of the AHP, and which includes the interrelation between the criteria/aspects under analysis, has been little explored. Therefore, the application of the ANP in the characterization and classification of accumulator technologies in the DG context was proposed. As a result, after surveying and defining the criteria and alternatives, building the layers of the ANP and determining the weights of the criteria, the VRB technology obtained the highest global weight for very short-term application, while the Li-Ion technology obtained the highest global weight for short-term application. In addition, the result obtained by the ANP was compared to the result of the AHP under the same analyzed scenario. Instituição: Universidade Federal Rural de Pernambuco Tipo do documento: Dissertação Tue, 28 Feb 2023 00:00:00 GMT http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9041 2023-02-28T00:00:00Z http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/8924 Título: Nanofotocatalisadores de ZnO dopados com cério para tratamento de efluentes da indústria têxtil pernambucana Autor: SANTIAGO, Leonardo Felix Primeiro orientador: ARAÚJO, Vinícius Dantas de Abstract: The state of Pernambuco has one of the largest textile centers in Brazil, and as the entire textile industry uses a large volume of water in the dyeing and finishing stages, the laundries and the textile sector have greatest potential for contamination of effluents due to the amount of organic matter generated, creating various environmental and social problems. In recent decades, photocatalytic processes have stood out as an alternative for the treatment of effluents with high organic load, using semiconductors as photocatalysts, in particular zinc oxide (ZnO). In this sense, the objective of this dissertation was to synthesize Zn(1-x)CexO nanoparticles with x= 0, 0.005, 0.01, 0.02, 0.03, 0.04 and 0.05, by the microwave-assisted hydrothermal method and evaluate their efficiency as photocatalysts. Synthesis was performed at 120°C for a time of 32 minutes in alkaline NaOH 3M solution. The samples were obtained in powder form and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-Visible spectroscopy (UV-VIS) measurements. SEM images showed that the particles are constituted by nanoplates with average thickness between 41 and 87 nm, and width between 329 and 741 nm, forming a three-dimensional cluster with a perimeter between 11 and 46 μm. XRD technique showed that all samples have a hexagonal wurtzite type crystalline structure of ZnO. For samples with Ce content greater than 1%, peaks referring to the cubic phase of CeO2 were identified. UV-VIS spectra showed a reduction in the optical band gap of the samples with the increase in cerium content. In the photocatalytic tests all synthesized samples were able to fully degrade the methylene blue dye after 30 min. An increase in photocatalytic efficiency was verified with increasing Ce content up to 1%, due to the creation of intermediate states in the band gap optimizing the removal power of the photocatalyst. Instituição: Universidade Federal Rural de Pernambuco Tipo do documento: Dissertação Fri, 23 Jul 2021 00:00:00 GMT http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/8924 2021-07-23T00:00:00Z http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/8923 Título: Propagação de feixes incoerentes em meios não lineares dissipativos Autor: PEREIRA, Cícera Carla de Souza Primeiro orientador: OCAS, Albert Stevens Reyna Abstract: Speckle patterns are distributions of light intensity, formed from the interaction between a coherent light source and an irregular surface (or medium), which results in a distribution of wave vectors with random phases. In this way, as randomness plays a relevant role in the formation of spot patterns, their characterization, as well as the analysis of various optical phenomena excited from them are followed by making use of statistical analysis tools. Among the most important tools such as intensity intensity functions and the intensity probability distribution provide indirect information about the manipulation of the transmission source, the degree of scattering (or randomness) of the rough medium, in addition to the optical properties of the medium where the radiation propagates. In this dissertation, the changes that the statistics of speckle patterns suffer when they propagate in self-defocusing non-linear media, with the influence of several non-linear absorption processes, are studied. For this, the dye LDS722 diluted in ethanol was used as a non-linear medium, which, when excited with different intensities, presents the effects of absorption of 1 photon; 2 photon absorption; and absorption of 2 photons. These different effects were characterized using the Z-Scan technique. In order for the non-linear expression of the stain patterns to be influenced by one (or more than one) dissipative effect (simultaneously), three different patterns were generated, with intensity envelopes: (i) Gaussian, (ii) super-Gaussian and (iii) top hat. In this way, it is observed that during the controlled analysis, if the speckles pattern is affected only by a single non-linear absorption process, with top-hat intensity background, its statistical properties follow different behaviors to the patterns influenced by more than one effect simultaneous non-linear absorption with Gaussian and super-Gaussian intensity backgrounds. The studies carried out in this dissertation present, for the first time in the literature, results on the influence of the various non-linear absorption effects on the signaling of speckle patterns. Furthermore, by monitoring the changes in the statistical properties that the speck patterns undergo throughout their defensiveness, it was possible to propose a new methodology to analyze the self-deflection effect induced by the modulation of the non-linear refractive index. Therefore, we propose the use of speckles patterns to characterize the non-linear optical response of different materials. Instituição: Universidade Federal Rural de Pernambuco Tipo do documento: Dissertação Thu, 16 Feb 2023 00:00:00 GMT http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/8923 2023-02-16T00:00:00Z