Efeito da Gália como aditivo de sinterização em eletrólitos cerâmicos à base de céria sintetizados pelo método de complexação de cátions

Fuel cells are considered one of the most promising ways of converting electrical energy due to its high yield and by using hydrogen (as fuel) which is considered one of the most important source of clean energy for the future. Rare earths doped ceria has been widely investigated as an alternative material for the electrolyte of solid oxide fuel cells (SOFCs) due to its high ionic conductivity at low operating temperatures compared with the traditional electrolytes based on stabilized zirconia. This work investigates the effect of gallium oxide (Gallia) as a sintering aid in Eu doped ceria ceramic electrolytes since this effect has already been investigated for Gd, Sm and Y doped ceria electrolytes. The desired goal with the use of a sintering aid is to reduce the sintering temperature aiming to produce dense ceramics. In this study we investigated the effects on densification, microstructure and ionic conduction caused by different molar fraction of the dopants europium (10, 15 and 20%) and gallium oxide (0.3, 0.6 and 0.9%) in samples sintered at 1300, 1350 and 1450 0 C. Samaria (10 and 20%) doped ceria samples sintered between 1350 and 1450 °C were used as reference. Samples were synthesized using the cation complexation method. The ceramics powders were characterized by XRF, XRD and SEM, while the sintered samples were investigated by its relative density, SEM and impedance spectroscopy. It was showed that gallia contents up to 0.6% act as excellent sintering aids in Eu doped ceria. Above this aid content, gallia addition does not promote significant increase in density of the ceramics. In Ga free samples the larger densification were accomplished with Eu 15% molar, effect expressed in the microstructure with higher grain growth although reduced and surrounded by many open pores. Relative densities greater than 95 % were obtained by sintering between 1300 and 1350 °C against the usual range 1500 - 1600 0 C. Samples containing 10% of Sm and 0.9% of Ga reached 96% of theoretical density by sintering at 1350 0 C for 3h, a gain compared to 97% achieved with 20% of Sm and 1% of Ga co-doped cerias sintered at 1450 0 C for 24 h as described in the literature. It is found that the addition of gallia in the Eu doped ceria has a positive effect on the grain conductivity and a negative one in the grain boundary conductivity resulting in a small decrease in the total conductivity which will not compromise its application as sintering aids in ceria based electrolytes. Typical total conductivity values at 600 and 700 °C, around 10 and 30 mS.cm -1 respectively were reached in this study. Samples with 15% of Eu and 0.9 % of Ga sintered at 1300 and 1350 °C showed relative densities greater than 96% and total conductivity (measured at 700 °C) between 20 and 33 mS.cm -1 . The simultaneous sintering of the electrolyte with the anode is one of the goals of research in materials for SOFCs. The results obtained in this study suggest that dense Eu and Ga co-doped ceria electrolytes with good ionic conductivity can be sintered simultaneously with the anode at temperatures below 1350 °C, the usual temperature for firing porous anode materials

Desempenho de um painel fotovoltaico de baixa tensão, acoplado ao protótipo de um conversor dc/dc topologia Booster

Low voltage solar panels increase the reliability of solar panels due to reduction of in series associations the configurations of photovoltaic cells. The low voltage generation requires DCDC converters devices with high efficiency, enabling raise and regulate the output voltage. This study analyzes the performance of a photovoltaic panel of Solarex, MSX model 77, configured to generate an open circuit voltage of 10.5 V, with load voltage of 8.5 V, with short circuit current of 9 A and a power of 77 W. The solar panel was assembled in the isolated photovoltaic system configuration, with and without energy storage as an interface with a DCDC converter, Booster topology. The converter was designed and fabricated using SMD (Surface Mounted Devices) technology IC (integrated circuit) that regulates its output voltage at 14.2 V, with an efficiency of 87% and providing the load a maximum power of 20.88 W. The system was installed and instrumented for measurement and acquisition of the following data: luminosities, average global radiation (data of INPE Instituto Nacional de Pesquisas Espaciais), solar panel and environment temperatures, solar panel and DC-DC converter output voltages, panel, inverter, and battery charge output currents. The photovoltaic system was initially tested in the laboratory (simulating its functioning in ideal conditions of operation) and then subjected to testing in real field conditions. The panel inclination angle was set at 5.5°, consistent with the latitude of Natal city. Factors such as climatic conditions (simultaneous variations of temperature, solar luminosities and ra diation on the panel), values of load resistance, lower limit of the maximum power required by the load (20.88 W) were predominant factors that panel does not operate with energy efficiency levels greater than 5 to 6%. The average converter efficiency designed in the field test reached 95%

Formação de particulas submicrometricas de pmma por cristalização termica de solução polimérica

Polymer particles in the nanometer range are of fundamental interest today, especially when used as carrier systems in the controlled release of drugs, cosmetics and nutraceuticals, as well as in coating materials with magnetic properties. The main objective of the present study concerns the production of submicron particles of poly (methyl methacrylate) (PMMA) by crystallization of a polymer solution by thermally controlled cooling. In this work, PMMA solutions in ethanol and 1-propanol were prepared at different concentrations (1% to 5% by weight) and crystallized at different cooling rates (0.2 to 0.8 ° C / min) controlled linearly. Analysis of particle size distribution (DLS / CILAS) and scanning electron microscopy (SEM) were performed in order to evaluate the morphological characteristics of the produced particles. The results demonstrated that it is possible to obtain submicron polymer perfectly spherical particles using the technique discussed in this study. It was also observed that, depending on the cooling rate and the concentration of the polymer solution, it is possible to achieve high yield in the formation of submicron particles. In addition, preliminary tests were performed in order to verify the ability of this technique to form particulated carrier material with magnetic properties. The results showed that the developed technique can be an interesting alternative to obtain polymer particles with magnetic properties

Avaliação de uma fração polissacaridica da alga Lobophora variegata (Lamouroux) em modelo de artrite induzida em ratos por Zymosan

Fucans seaweed Lobophora variegata estructures are known for their chemical and biological properties. In this study, we analyzed, the action of fucans L. variegata and the fractions purified with acetone in Zymosan-induced arthritis. After differential fractionation with acetone, six fractions were obtained and named F0.3, F0.5, F0.8, F1, F1.5 and F2. The results showed that the fraction F1 showed high yield (51.9%) and was chosen for studies of antioxidant activity and induced arthritis. Nuclear magnetic resonance (NMR) of 13C showed signals at 103.3 and 15.78 ppm that are assigned to links β13 galactose and of the C6 methyl fucose, respectively. The infrared (IR) showed absorbance at 1238 and 850 cm-1 which are attributed to sulfate. The fraction F1 showed antioxidant activities in vitro. For analysis of inflammatory parameters chosen the polysaccharide was administered in different doses (25, 50 and 75 mg / kg ip, per body weight) and diclofenac sodium (5 mg / kg ip) and L-NAME (25 mg / kg ip) in groups of animals (n = 6). After 6 h, were analyzed for cellular influx and levels of nitrite. In experiment five days, were made analysis of swelling and serum TNF-α. Histopathological analysis were performed for confirmation of results. The fraction F1 (25, 50 and 75 mg / kg ip) reduced the cellular influx (52.1 to 96.7%) and nitric oxide levels (27.2 - 39%) compared to control group. The reduction of edema (63.4 - 100%) and serum TNF-α (p <0.001) were observed when the polysaccharide F1 administered at a dose (50 mg / kg) These results suggest that these heterofucanas of Lobophora variegata have besides the activity antioxidant and potential anti-inflammatory activity in arthritis induced by zymosan

Efeito da Gália como aditivo de sinterização em eletrólitos cerâmicos à base de céria sintetizados pelo método de complexação de cátions

Fuel cells are considered one of the most promising ways of converting electrical energy due to its high yield and by using hydrogen (as fuel) which is considered one of the most important source of clean energy for the future. Rare earths doped ceria has been widely investigated as an alternative material for the electrolyte of solid oxide fuel cells (SOFCs) due to its high ionic conductivity at low operating temperatures compared with the traditional electrolytes based on stabilized zirconia. This work investigates the effect of gallium oxide (Gallia) as a sintering aid in Eu doped ceria ceramic electrolytes since this effect has already been investigated for Gd, Sm and Y doped ceria electrolytes. The desired goal with the use of a sintering aid is to reduce the sintering temperature aiming to produce dense ceramics. In this study we investigated the effects on densification, microstructure and ionic conduction caused by different molar fraction of the dopants europium (10, 15 and 20%) and gallium oxide (0.3, 0.6 and 0.9%) in samples sintered at 1300, 1350 and 1450 0 C. Samaria (10 and 20%) doped ceria samples sintered between 1350 and 1450 °C were used as reference. Samples were synthesized using the cation complexation method. The ceramics powders were characterized by XRF, XRD and SEM, while the sintered samples were investigated by its relative density, SEM and impedance spectroscopy. It was showed that gallia contents up to 0.6% act as excellent sintering aids in Eu doped ceria. Above this aid content, gallia addition does not promote significant increase in density of the ceramics. In Ga free samples the larger densification were accomplished with Eu 15% molar, effect expressed in the microstructure with higher grain growth although reduced and surrounded by many open pores. Relative densities greater than 95 % were obtained by sintering between 1300 and 1350 °C against the usual range 1500 - 1600 0 C. Samples containing 10% of Sm and 0.9% of Ga reached 96% of theoretical density by sintering at 1350 0 C for 3h, a gain compared to 97% achieved with 20% of Sm and 1% of Ga co-doped cerias sintered at 1450 0 C for 24 h as described in the literature. It is found that the addition of gallia in the Eu doped ceria has a positive effect on the grain conductivity and a negative one in the grain boundary conductivity resulting in a small decrease in the total conductivity which will not compromise its application as sintering aids in ceria based electrolytes. Typical total conductivity values at 600 and 700 °C, around 10 and 30 mS.cm -1 respectively were reached in this study. Samples with 15% of Eu and 0.9 % of Ga sintered at 1300 and 1350 °C showed relative densities greater than 96% and total conductivity (measured at 700 °C) between 20 and 33 mS.cm -1 . The simultaneous sintering of the electrolyte with the anode is one of the goals of research in materials for SOFCs. The results obtained in this study suggest that dense Eu and Ga co-doped ceria electrolytes with good ionic conductivity can be sintered simultaneously with the anode at temperatures below 1350 °C, the usual temperature for firing porous anode materials

Ação da cafeína sobre o rendimento esportivo de ciclistas em condições de calor e umidade

Objetivo: Verificar a ação da cafeína no tempo de rendimento, a taxa de esforço percebido (RPE), os níveis plasmáticos de glicose, sódio e potássio, a temperatura timpânica (Tt), o peso corporal (PC), freqüência cardíaca (FC) e concentração urinária da cafeína com a ingestão de doses de 5 e 9 mg/kg de cafeína e placebo, em provas ciclísticas sob condições de alto risco térmico. Métodos: Foram estudados 8 ciclistas treinados e aclimatizados em 3 provas de 45 km utilizando o modelo experimental e duplo-cego com randomização intra-sujeitos. Resultados: Não foram observadas diferenças significativas entre as variáveis avaliadas, entretanto o tempo de rendimento e a RPE foram menores com as doses de 5 e 9 mg/kg de cafeína que com a dose placebo. Conclusões: Estes dados indicam que as condições de calor e umidade podem ser suficientes para mascarar o benefício ergogênico da cafeína, entretanto deve-se considerar que a cafeína pode exercer influencia sobre a percepção subjetiva de esforço podendo levar à redução dos sinais de fadiga durante o exercício e conseqüente melhora do desempenho esportivo

Rendimento acadêmico e sua relação com os estilos de personalidade de estudantes universitários

One of the Psychology challenges, especially among the assessment and educational areas, is to understand and predict individual differences. In this context, this research aimed to verify the personality styles of students with high and low academic performance. The study included 236 university students from Petrolina-PE and Juazeiro-BA campus of the UNIVASF (Universidade Federal do Vale do São Francisco). They were uniformly distributed in four disciplines (medicine, psychology, administration and civil engineering), 10 students from each semester (five highest scores average students and five lowest scores average students) took place of the sample. The Millon Index Personality Styles (MIPS) was applied to analyze the personality/behavioral styles of the students. The MIPS is a 180 dichotomous (true/false) item scale. It was also developed and applied a questionnaire about the students characteristics and their academic information. Descriptive and central tendency statistics analysis (mean, standard deviation, frequency and percentage) were done to provide sample information. Then we performed a Mann-Whitney test in the overall sample and in each course and a factorial ANOVA. The results suggest that the university population is heterogeneous and there are significant differences (p <0.05) between the personality styles of students with high and low academic performance, when analyzing the overall sample and in courses of different areas of knowledge. Students of Medicine who have higher performance as personality styles prevalent the conformism and compliance, while students with lower income in this course, the styles are: innovation and discrepancy. Psychology students with higher income are more systematic and lower income students to score significantly on accommodation. The civil engineering students of the two groups differed only in personality style intuition, being such a style more characteristic of higher income students. Students of Management with higher yield stand out more in the style of the doubt and lower yields in these styles: individual, reflection and discrepancy. This study is correlational, but had an exploratory nature because there are no studies about this relationship in Brazil. Therefore, it provided a better understanding of the action characteristics of students with high and low academic performance. Further studies using the Big Five Personality Factors instruments are required because it is the most used model in understanding the influence of personality on students performance. This way, the relation between personality and academic performance will be better discussed. Otherwise, it will be possible to compare with the existing studies in the area

Novos métodos determinísticos para gerar centros iniciais dos grupos no algoritmo fuzzy C-Means e variantes

Data clustering is applied to various fields such as data mining, image processing and pattern recognition technique. Clustering algorithms splits a data set into clusters such that elements within the same cluster have a high degree of similarity, while elements belonging to different clusters have a high degree of dissimilarity. The Fuzzy C-Means Algorithm (FCM) is a fuzzy clustering algorithm most used and discussed in the literature. The performance of the FCM is strongly affected by the selection of the initial centers of the clusters. Therefore, the choice of a good set of initial cluster centers is very important for the performance of the algorithm. However, in FCM, the choice of initial centers is made randomly, making it difficult to find a good set. This paper proposes three new methods to obtain initial cluster centers, deterministically, the FCM algorithm, and can also be used in variants of the FCM. In this work these initialization methods were applied in variant ckMeans.With the proposed methods, we intend to obtain a set of initial centers which are close to the real cluster centers. With these new approaches startup if you want to reduce the number of iterations to converge these algorithms and processing time without affecting the quality of the cluster or even improve the quality in some cases. Accordingly, cluster validation indices were used to measure the quality of the clusters obtained by the modified FCM and ckMeans algorithms with the proposed initialization methods when applied to various data sets