A industrialização das células a combustível de eletrólito polimérico sólido ainda é um desafio, devido principalmente aos elevados preços dos catalisadores, da membrana, cinética lenta da reação de redução do oxigênio e estabilidade da célula. Neste trabalho a eficiência e a estabilidade de catalisadores nanoparticulados bimetálicos de Pt-Cr suportados em carbono de elevada área superficial foram estudadas para serem utilizados como cátodos em células a combustível de eletrólito polimérico sólido. A caracterização física destes materiais foi realizada através de técnicas como difração de raios-X (DRX), energia dispersiva de raios-X (EDX), absorção de raios-X (XAS), espectroscopia de fotoelétrons excitados por raios-X (XPS) e microscopia eletrônica de transmissão (TEM). Para os estudos eletroquímicos dos catalisadores foram realizados levantamentos das curvas de polarização na célula unitária utilizando a membrana de Nafion®115, alimentadas com H2 no ânodo e O2/ar no cátodo em diferentes temperaturas e pressões, também foi utilizado a voltametria cíclica e stripping CO para a determinação da área ativa dos catalisadores e finalmente foram realizados os estudos de estabilidade simulando uma degradação acelerada mediante ciclos voltamétricos. Os resultados das curvas de polarização dos catalisadores comercial e preparados pelo método de poliol indicaram que com o aumento da quantidade de cromo obtem-se um decréscimo do desempenho. O catalisador Pt3Cr preparado pelo método de impregnação apresentou o pior desempenho. Os catalisadores Pt3Cr comercial e preparado pelo método do poliol possuem tamanhos de partícula muito próximos e diferentes quantidades de Cr na forma de liga, sendo que cromo no catalisador sintetizado pelo método de poliol apresenta-se na forma oxidada. Os resultados da degradação acelerada para estes catalisadores mostraram que o catalisador sintetizado pelo método de poliol apresentou melhor desempenho e estabilidade. / The commercialization of fuel cells is still a challenge of this technology, principally due to high price of the catalysts and membrane, slow kinetic of oxygen reduction reaction and stability of the cell. In this work the efficiency and stability of the nanoparticulated bimetallic PtCr supported on carbon of high surface area catalysts were studied to be used in the cathodes of proton exchange membrane fuel cell. The physical characterization of these materials was carried out by various techniques, such as X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The catalysts were characterized electrochemically by measuring the polarization curves, which were recorded in a single cell, using Nafion®115 membrane with anode fed with H2 and cathode fed with O2/air. The gases used were saturated with mili-Q water at different temperatures and pressures. Cyclic voltammetry and CO stripping experiments were used to measure the active surface areas of the catalysts and finally the stability studies were conducted, simulating the accelerated degradation through the cyclic voltammetry. The polarization curves results of the catalysts prepared by poliol method and of commercial catalysts showed that with the increase in the quantity of chromium a decline in performance occurs. The Pt3Cr catalyst prepared by impregnation method presented a poor performance. The catalysts prepared by poliol and commercial catalyst have near the same particle sizes and different amount of alloyed Cr, such that the chromium in poliol catalys is present in oxides form. The accelerated degradation results showed that catalyst prepared by poliol method presented a better performance and stability.

Estudou-se a caracterização de blocos sinterizados à base de Co-Cr-Mo visando a obtenção de próteses odontológicas por fresagem CAD/CAM. O processo de sinterização foi estudado e ocorreu através do transporte difusional de massa e calor no estado sólido, denominado sinterização no estado sólido. Esse fenômeno produz uma forte união entre as partículas devido ao transporte de massa, em escala atômica, sob condições controladas de tempo, temperatura e atmosfera. Foram realizadas sinterizações interrompidas a 800, 1000, 1200 e 1300°C nos tempos de 15 minutos, 1 hora e 4 horas. A liga foi caracterizada nas condições recebida e sinterizadas em termos de composição química, propriedades mecânicas e caracterização microestrutural. Para isto, utilizou-se fluorescência de raios X, dilatometria, ensaios de Arquimedes, ensaios de dureza, ensaios de compressão, microscopia eletrônica de varredura (MEV), microscopia óptica e microanálise eletrônica dispersiva (EDS). Os resultados composicionais indicam que a liga se encontrava dentro da faixa de composição química estabelecida pelo manual do fabricante e pela norma ASTM 1537. As partículas analisadas na condição pré-sinterizada exibiram formato esférico, indicando uma provável utilização de pós atomizados. A estimativa do levantamento da distribuição do tamanho das partículas foi realizado utilizando o programa de computador ImageJ, e a distribuição foi caracterizada como assimétrica positiva. O material no estado recebido se apresentou monofásico. A fase presente encontrada foi ?Co com estrutura cristalina CFC. Em contrapartida, as amostras sinterizadas apresentaram porções de fase ?Co, com estrutura cristalina hexagonal, fase esta formada a partir da transformação ?Co <-> ?Co, na qual, a energia armazenada na forma de defeitos é a força motriz da transformação. E sugere que a transformação ocorreu durante resfriamento. A amostra sinterizada por quatro horas em 1200°C apresentou-se no estágio final de sinterização, dado que os poros encontrados tinham aspecto arredondado e com densificação maior que 90%. Os resultados de compressão indicam tensão média de ruptura de 2523 ± 168 MPa. / This work studied the characterization of Co-Cr-Mo sintered blocks in order to obtain dental prosthesis by prototyping CAD/CAM. The sintering process was studied through diffusional mass transport in solid state, termed solid state sintering. This phenomenon produces a strong bond between the particles due to mass transport, at the atomic scale, under controlled conditions of time, temperature and atmosphere. The interrupted sintering was performed at 800, 1000, 1200 and 1300 ° C in times to 15 minutes, 1 hour and 4 hours. The alloy was characterized in conditions as received and sintered in terms of chemical composition, mechanical properties and microstructural characterization. For this, we used X-ray fluorescence, dilatometry, Archimedes tests, hardness tests, compression tests, scanning electron microscopy (SEM), optical microscopy and dispersive electron microanalysis (EDS). The results indicate that the alloy was within the chemical composition range established by the manufacturer and ASTM 1537. The particles analyzed in the pre-sintered condition showed spherical shape, indicating a likely use of atomized powders. The estimate of the particle size distribution was performed using ImageJ software, and the distribution is characterized as positive asymmetric. The samples in the received state were monophasic. This phase was found ?Co with FCC crystal structure. On the order hand, the sintered samples showed ?Co phase portions with hexagonal crystal structure, phase formed from the transformation ?Co <-> ?Co, in which the energy stored in the form of defects is the driving force of transformation and suggests that transformation occurred during the cooling. Sample sintered during four hours at 1200°C was in the final stages of sintering, since the pores were found aspect rounded and densification above 90%. The compression results indicate rupture stress at 2523 ± 168 MPa.

Thesis (Ph.D. (Physics)) --University of Limpopo, 2011 / Planewave pseudopotential calculations were conducted to predict the energetics and phase stability of Pt-Cr and Ru-Cr binary alloys. Validation of appropriate number of k-points and planewave energy cut-off was carried out for all studied systems. At the composition of A3B and AB3 (where A = Cr and B = Pt or Ru) phases, the heats of formation determined for five different structures, L12, A15, tP16, DOC and DO′ C are almost of the same magnitude and the relaxed structures show no rotation. We observed that the cubic L12 Pt3Cr is the most stable structure in agreement with the experiments. The results for PtCr3 indicate the negative heat of formation for the A15 phase whereas all the remaining studied phases have positive heats of formation. It is clear that the PtCr3 (A15) is the most stable structure. PtCr (L10) was found to be more stable compared with PtCr (B2) phase. The L12 Pt3Cr, A15 PtCr3 and L10 PtCr phases could be considered as possible coatings to cover the engines which are exposed to aggresive environments. The heats of formation of all studied compositions and phases of Ru-Cr systems are positive, these results suggest that, generally, studied Ru-Cr phases are not stable. The effect of pressure and doping were investigated on A15 RuCr3 structure which was reported to exist at a higher temperature. Elastic constants and moduli were investigated to determine the strength of the PtCr systems. The strength of PtCr L10 is greater than that of B2 phase. The ratio of shear to bulk modulus (G/B) has been used to predict the ductility or the brittleness of the material. It was found that Pt3Cr L12 is the most ductile phase among those considered in this study. The density of states were calculated to further analyze the stability of systems. The magnetic properties of Cr were studied using VASP which predicted an anti-ferromagnetic and a non-magnetic ground state for pure Cr. We have investigated the thermal stability at 0 GPa for different phases of Pt3Cr, PtCr3, PtCr and RuCr3 A15 phase, where we detected the soft modes at X, G, M and R points of the Brillouin zone from the phonon spectra of Pt3Cr A15 phase. Pt3Cr L12 and PtCr3 A15 are predicted as dynamically stable structures. RuCr3 A15 phase was found to be dynamically stable but thermodynamically unstable. Phonon DOS were studied to observe the modes of vibration and atoms that contribute to soft modes. Lastly we investigated the thermal expansion of Pt3Cr L12 and A15 phases. / The National Research Foundation,and the South African Gas Turbine Research Program

The USEPA Maximum Contaminant Level (MCL) for Total Chromium in drinking water is 100 μg/L. Total chromium includes both trivalent chromium (Cr(III), a trace nutrient) and hexavalent chromium (Cr(VI), a probable human carcinogen). The State of California set a Cr(VI)-specific MCL of 10 μg/L in 2014, and USEPA is considering a new federal MCL for Cr(VI). This would have a significant impact on drinking water systems across the US, with estimated annual cost of compliance between $0.6 to 5.1 billion per year. While Cr(VI) is the species of concern for health effects, water utilities must also consider Cr(III) since it can be oxidized to Cr(VI) by various chemicals. This oxidation has been documented for commonly used disinfectants. However, past studies were conducted with higher levels of chromium (e.g., 20 to 500 μg/L) and it is unknown if the reactions proceed at the same rate and extent at the lower concentrations relevant to most water treatment plants (< 10 μg/L). This project, funded by the Water Research Foundation, systematically evaluated the extent of oxidation of Cr(III) by drinking water oxidants under conditions relevant to drinking water utilities. Five oxidants (chlorine, monochloramine, chlorine dioxide, potassium permanganate, and ozone) were tested. Two doses were used for each chemical with their respective reaction times reflecting the typical application of the chemical in treatment. Three different water qualities were evaluated, each at pH 5.5, 7, and 9, and at two different temperatures (5 and 16 °C). Chlorine consistently oxidized an average of 80% of the available Cr(III), with the majority of the oxidation happening within the first 7 hours. Monochloramine did not significantly oxidize Cr(III) at any of the conditions tested. Chlorine dioxide was an effective oxidant at pH 7, with complete oxidation occurring in 6 hours, but was less effective at pH 5.5 and 9. Potassium permanganate achieved complete oxidation in 4 hours at each pH, with pH 7 experiencing the fastest oxidation. Ozone oxidized all available Cr(III) within minutes at all pH values. Quantifying the Cr(III) oxidation as a result of using these oxidants provides understanding of potential Cr(VI) addition into drinking water.

Informe de Seminario para optar al grado de Licenciado en Lengua y Literatura Hisp?nica menci?n Literatura / La siguiente investigaci?n se centrar? en el estudio de la denominada literatura de cordel chilena m?s conocida como Lira Popular o poes?a popular impresa. Mostraremos c?mo este tipo de producci?n discursiva ser? el resultado del problem?tico y complejo tr?nsito que, hacia mediados del siglo XIX, experimentar? la tradicional poes?a oral, de fuerte raigambre rural, al entrar en contacto con el convulsionado contexto urbano que la recibe. Este escenario le impondr? una serie de transformaciones que se manifestar?n en variados y significativos aspectos textuales, los cuales, como se?alan algunos expertos, no deben ser considerados aisladamente, puesto que a la larga, modificar?n la estructura misma de la poes?a.

Informe de Seminario para optar al grado de Licenciado en Lengua y Literatura Hisp?nica / Facultad de Filosof?a y Humanidades / El presente ensayo nace desde un imperativo moral, desde el llamado de la herencia. No s? si en mi cuerpo corre de esa sangre, pero basta con verla derramada, como excusa para construir nuestra historia como chilenos para que la sienta viva dentro de m?. Desde all?, posicionado firmemente, intento establecer un recorrido de la relaci?n entre escritura y el mundo mapuche, desde su adquisici?n como t?cnica, para luego vincularlas con el quehacer po?tico y las posibilidades que tienen, como sujetos fuertemente marginados, de establecerse contra-hegem?nicamente desde el discurso, la literatura y la poes?a.

Informe de Seminario para optar al grado de Licenciada en Lengua y Literatura Hisp?nica / En el presente informe, proponemos abordar el uso y sentido del recurso ret?rico del exemplum en la obra David Pecador y David Penitentede autor?a de Fray Antonio de Lorea, mediante la selecci?n y posterior an?lisis, de tres empresas de la obra. Uno de los antecedentes claves para el desarrollo de la emblem?tica, descans?en la vasta producci?n de empresas durante el siglo XV, las cuales representaban un concepto ?nico, expresado figuradamente mediante el uso de im?genes y sentencias, cuyo ejercicio se convirti? en todo un desaf?o para el intelecto. La utilizaci?n recurrente de este nuevo formato que combinaba im?genes y sentencias (escritura), abri? un vasto y abundante terreno para el despliegue de distintos tipos de empresas. Por lo mismo, paulatinamente fueron tomadas como un instrumento apto para la ense?anza. A esa misma finalidad did?ctica respondela obra David Pecador y David Penitente,compuesta por treinta empresas morales de tipo pol?tico-cristianas, y sus respectivos discursos que componen la obra en su totalidad, pretenden inculcar m?ximas morales y pol?ticas en los hombres, y en particular en los pr?ncipes. Para llevar a cabo tal pretensi?n, su autor retom? el relato b?blico del rey David, situ?ndolo como elexemplo m?s integro de rey cristiano.

This study indicate that the chemical inter-diffusion between the Cr-doped glass/glass ceramic and quartz (SiO2) influence the fluorescence properties of glass, mainly because of Cr4+ replacing by tetrahedral of Si4+. Cr4+ fluorescence intensity was reduced and its emission band was shifted to longer wavelength (red shift). We selected the SiO2-based glass composition: Mg2SiO4 glass-ceramic and reduced a ratio of SiO2 sintered into the ceramic powder. This paper used diffusion characteristics of quartz (SiO2) to compensate for reduced SiO2 in the ceramic powder. After diffusing with quartz (SiO2), ceramics powder changed into glasses. The intensity of fluorescence and the crystal field had been improved. The center of Cr4+ fluorescence is about 1100nm belonging to Cr4+:Mg2SiO4 crystal. The ratio of Cr4+ in Mg2SiO4 crystal/Cr4+ in MgO-SiO2 glass increases from 0.33 to 1.74. The goal is to develop a novel glass which is resistant to SiO2 inter-diffusion degradation during fiber fabrication, and provide the new fiber technology to avoid the influence of inter-diffusion This study provides new types of treatment: Laser induced crystallization. Laser heat-treatment can more quickly induce crystals in glass during seconds, than traditional heat-treatment which require several hours. This study also indicate that one step laser heat-treatment induce micro-crystals, but one step laser heat-treatment induce nano-crystals. We successfully produced nano-crystallization during seconds.

La géométrie de Cauchy-Riemann, CR en abrégé, est la géométrie naturelle des hypersurfaces réelles pseudoconvexes de $C^{n+1}$, lorsque $ngeq 1$. Nous considérons le cas générique où les variétés CR considérées sont de contact. La géométrie CR présente de nombreuses similarités avec la géométrie conforme ; les invariants mis au jour et les techniques éprouvées en géométrie conforme peuvent donc être adaptées dans ce contexte. Nous nous intéressons dans cette thèse à deux invariants de ce type. Dans une première partie, en utilisant la géométrie asymptotiquement hyperbolique complexe, nous introduisons un opérateur différentiel CR covariant agissant sur les applications allant d'une variété CR vers une variété riemannienne, égal pour les fonctions à l'opérateur de Paneitz CR. Dans une seconde partie, nous proposons un invariant de Yamabe pour les variétés de contact admettant une structure CR, et nous étudions son comportement sous somme connexe. / Cauchy-Riemann geometry, CR for short, is the natural geometry of real pseudoconvex hypersurfaces of $C^{n+1}$ for $ngeq 1$. We consider the generic case when CR manifolds are contact manifolds. CR geometry presents strong analogies with conformal geometry; hence, known invariants and techniques of conformal geometry can be transported to that context. We focus in this thesis on two such invariants. In a first part, using asymptotically complex hyperbolic geometry, we introduce a CR covariant differential operator on maps from a CR manifold to a Riemannian manifold, which coincides on functions with the CR Paneitz operator. In a second part, we propose a Yamabe invariant for contact manifolds which admit a CR structure, and we study its behaviour under connected sum.

The development and economic growth in Paraguay are highly dependent on agriculture, which in recent years has undergone an expansion. The computerization of operations for managing the crops and the search for improvements based on localized management of inputs and productivity of crops that involve the use of geotechnology and global positioning systems (GPS) applied in the management of agricultural crops, the production of meshes for the realization of georeferenced soil sampling, the structuring of a digital terrain model for mapping of fertility and productivity, variable rate application of inputs, statistical analyzes and interpretation of maps, geostatistics have a promising future in rural management. With this adaptation work to Paraguay of Campeiro CR System, it seeks to meet the need of Paraguay to have software adapted to regional conditions to develop their agriculture projects in their areas of precision agriculture. Therefore, it was translated into Spanish the application of Precision Agriculture and were inserted Departments and Districts of Paraguay, as well as the bands interpretation of various attributes of soil fertility for the generation of maps of fertility according to criteria calibrated with local studies in Paraguay and has been validated tools for Precision Agriculture System through a case study conducted with a plot and a producer of Paraguay, determining spatial variability in soil attributes, and also held a tutorial of the changes affected the operation for use in country with their adaptations to the system to its application in Paraguay agriculture. / O desenvolvimento e o crescimento econômico do Paraguai são altamente dependentes do setor agrícola, o qual nos últimos anos tem passado por uma expansão. A informatização para o gerenciamento das operações nas lavouras e a busca de melhoras baseadas no manejo localizado dos insumos e da produtividade dos cultivos que envolvem o uso de geotecnologias como sistemas de posicionamento global (GPS) aplicadas no manejo de culturas agrícolas, a elaboração de malhas para a realização da amostragem georreferenciada do solo, a estruturação de modelos digitais do terreno para a elaboração de mapas de fertilidade e de produtividade, a aplicação da taxa variável de insumos, as análises estatísticas e a interpretação de mapas, geoestatística, entre outras ferramentas, têm um futuro promissório na gestão rural. Com este trabalho de adaptação para o Paraguai do Sistema CR Campeiro, busca-se satisfazer a necessidade que tem o Paraguai de contar com um software adaptado a suas condições regionais para desenvolver projetos de agricultura de precisão nas suas áreas agrícolas. Para isso, foi traduzido para o espanhol o aplicativo de Agricultura de Precisão e foram inseridos os Departamentos e Distritos do Paraguai, assim como os níveis de fertilidade dos diversos atributos da fertilidade de solo para a geração dos mapas de fertilidade segundo critérios calibrados com pesquisas locais no Paraguai e foram validadas as ferramentas de Agricultura de Precisão do Sistema através de um estudo de caso realizado com um talhão e um produtor do Paraguai, determinando variabilidade espacial em atributos de solos, assim também se realizou um tutorial do funcionamento das mudanças atingidas para uso no país com suas respectivas adaptações no sistema visando a sua aplicação na agricultura paraguaia.