Synthesis, Characterization, and Electrocatalytic Activity toward Methanol Oxidation of Carbon-Supported Pt(x)-(RuO(2)-M)(1-x) Composite Ternary Catalysts (M = CeO(2), MoO(3), or PbO(x))

Carbon-supported platinum is commonly used as an anode electrocatalyst in low-temperature fuel cells fueled with methanol. The cost of Pt and the limited world supply are significant barriers for the widespread use of this type of fuel cell. Moreover, Pt used as anode material is readily poisoned by carbon monoxide produced as a byproduct of the alcohol oxidation. Although improvements in the catalytic performance for methanol oxidation were attained using Pt-Ru alloys, the state-of-the-art Pt-Ru catalyst needs further improvement because of relatively low catalytic activity and the high cost of noble Pt and Ru. For these reasons, the development of highly efficient ternary platinum-based catalysts is an important challenge. Thus, various compositions of ternary Pt(x)-(RuO(2)-M)(1-x)/C composites (M = CeO(2), MoO(3), or PbO(x)) were developed and further investigated as catalysts for the methanol electro-oxidation reaction. The characterization carried out by X-ray diffraction, energy-dispersive X-ray analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry point out that the different metallic oxides were successfully deposited on the Pt/C, producing small and well-controlled nanoparticles in the range of 2.8-4.2 nm. Electrochemical experiments demonstrated that the Pt(0.50)(RuO(2)-CeO(2))(0.50)/C composite displays the higher catalytic activity toward the methanol oxidation reaction (lowest onset potential of 207 mV and current densities taken at 450 mV, which are 140 times higher than those at commercial Pt/C), followed by the Pt(0.75)(RuO(2)-MoO(3))(0.25)/C composite. In addition, both of these composites produced low quantities of formic acid and formaldehyde when compared to a commercially available Pt(0.75)-Ru(0.25)/C composite (from E-Tek, Inc.), suggesting that the oxidation of methanol occurs mainly by a pathway that produces CO(2) forming the intermediary CO(ads).

Estudo experimental e teórico das propriedades magnéticas e supercondutoras dos compostos borocarbetos da série Y(Ni 1-x Mn x) 2 B2 C com x = 0,0, 0,01, 0,025, 0,05, 0,10 e 0,15

Apresentamos neste trabalho os resultados de um estudo experimental e teórico dos compostos borocarbetos supercondutores da série Y(Ni1-xMnx)2B2C com x = 0; 0,01; 0,025; 0,05; 0,10; 0,15. A principal motivação para este trabalho foi investigar a estrutura eletrônica e a possível formação do momento magnético sobre os átomos de impureza de Mn nos compostos Y(Ni1- xMnx)2B2C. O aparecimento do momento magnético localizado no sítio da impureza possibilitou estudar a influência do Mn sobre o mecanismo de quebra de pares supercondutores e sobre as propriedades magnéticas do composto. Os borocarbetos são compostos de estrutura cristalina tetragonal de corpo centrado e altamente anisotrópicos (c/a~3). São intermetálicos de alta temperatura crítica supercondutora Tc, com forte acoplamento elétron-fonon. Em alguns casos podem apresentar ordem magnética, supercondutividade e também coexistência ou competição energética entre ambos. As medidas de transporte eletrônico, em função da temperatura, foram feitas utilizando-se um detector síncroton baseado na técnica de quatro pontos operando na faixa de 4,2K até 300K. Essas medidas possibilitaram o estudo das propriedades relacionadas ao transporte eletrônico na fase supercondutora. Na fase normal, extraiu-se a dependência em energia da função espectral de fonons α² F (ω) para alguns compostos da série estudada. As medidas magnéticas em função da temperatura e do campo magnético foram feitas utilizando-se um SQUID (Superconducting Quantun Interference Device – Quantun Design Model MPMS XL). Tais medidas permitiram a caracterização das propriedades magnéticas de nossas amostras. Em particular determinou-se o valor, em regime de saturação, do momento magnético associado ao sítio cristalino do Mn. Foram determinadas também as correntes críticas supercondutoras usando o Modelo de estado crítico de Bean e a variação da temperatura crítica supercondutora (Tc) com a mudança do campo externo aplicado. As medidas magnéticas permitiram a obtenção do diagrama que relaciona o campo crítico inferior (HC1) e a temperatura, variando-se a concentração do átomo dopante de manganês. Foi feito um esforço teórico no sentido de interpretar os resultados experimentais. Para isso foram usados três modelos: O modelo de estado crítico de Bean já citado acima e um modelo baseado na fórmula de Ziman usando uma aproximação para a função espectral de fonons para descrever a resistividade no regime de alta temperatura. Além disto, usou-se o modelo de duas sub-redes para a descrição do momento magnético das impurezas de Mn, em função da concentração, na série Y(Ni ) ( 2 ω α F 1-xMnx)2B2C.

Full IFRS x lei 11.638 (1ª fase) x lei 6.404: impacto esperado nos resultados de 2010 a partir das empresas que se anteciparam

Este estudo objetiva estimar o impacto esperado do full IFRS no resultado de 2010 a ser reportado pelas empresas brasileiras, a partir da análise das companhias que voluntariamente anteciparam sua adoção nos relatórios de 2008 ou 2009. É aplicado o inverso do “Índice de Conservadorismo” de Gray (1980), renomeado “Índice de Comparabilidade” por Weetman et al. (1998), para determinar o impacto da transição entre os três conjuntos normativos no processo de convergência: da lei 6.404 para a lei 11.638 (primeira fase da transição), da lei 11.638 para o full IFRS (última fase da transição), bem como do processo total (da lei 6.404 para o full IFRS). Os resultados encontrados são consistentes com a hipótese de conservadorismo da contabilidade brasileira preconizado por Gray (1988), sendo apurados aumentos médios no lucro reportado de 44% no exercício de 2007 e de 64% em 2008 e, no patrimônio líquido, de 8,7% em 2007 e 21% em 2008 (todos significativos a pelo menos 5%, exceto o patrimônio líquido de 2004). O estudo também apurou um aumento incremental médio no lucro de 31% em 2007 e de 38% em 2008 (ambos significativos a pelo menos 10%) e de 6,8% e 51%, respectivamente, no patrimônio líquido de 2007 e de 2008 das empresas analisadas (embora só o de 2008 seja significativo a 5%). Assim, prevê-se um novo aumento no lucro e patrimônio líquido das empresas nos relatórios a serem publicados em 2011 em decorrência da aplicação da fase final da convergência para o full IFRS.

Predicting the chemical composition of the body and the carcass of 3/4Boer x 1/4Saanen kids using body components

The determination of the chemical composition of body and carcass is important in nutritional and growth regulation studies. The purpose of this study was to develop equations to predict the chemical composition of body and carcass using chemical composition of body components. Twenty 3/4Boer x 1/4Saanen crossbred male kids, weighing from 20 to 35 kg, were used in this study. The empty body chemical composition was measured by grinding all body components and sampling for chemical analyses. The body components used to estimate body and carcass composition were: neck, fore leg, ribs, loin, hind leg, 9-11 th rib section, non-carcass components (head plus feet, organs plus blood, and hide), visceral fat, and kidney fat. The chemical composition of organs plus blood and 9-11 th rib section had the highest precision to estimate percentage of fat, protein, and water in the body (r(2) of 0.94, 0.82, and 0.90, respectively). For carcass composition, the chemical composition of ribs was the best component to predict all carcass chemical components; however, the equations to estimate the percentages of protein and ash showed a low precision (r(2) = 0.48, 0.44, respectively). The 9-11 th rib section was accurate and precise to estimate carcass fat percentage. We concluded the chemical composition of the body of 3/4Boer x 1/4Saanen crossbred male kids was highly correlated with the composition of body parts, specifically organs plus blood and 9-11 th rib section. Further studies should focus on evaluating these body parts for different breeds and genders under different production scenarios. (C) 2007 Elsevier B.V. All rights reserved.

Crystallization study of the (1-x)Sb2O3-(x)SbPO4 glass system

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effects of strontium and calcium simultaneous substitution on electrical and structural properties of Pb1-x-y Ca (x) Sr (y) TiO3 thin films

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

Resonant excitation of Mn local vibrational modes in the higher order Raman spectra of nanocrystalline Ga(1-x)Mn(x)N films

The effect of manganese on the vibrational properties of Ga(1-x)Mn(x)N (0 <= x <= 0.18) films has been investigated by Raman scattering using 488.0 and 632.8 nm photon excitations. The first-order transverse and longitudinal optical GaN vibrational bands were observed in the whole composition range using both excitations, while the corresponding overtones, as well as a prominent peak located in 1238 cm(-1) (153.5 meV) were only observed in the Mn-containing films under 488.0 nm excitation. We propose that the peak observed at 1238 cm(-1) is due to resonant Mn local vibrational modes, the excitation process being related to electronic transitions involving the Mn acceptor band.

The optical absorption edge of nanocrystalline Ga(1-x)Mn(x)N films deposited by reactive sputtering

We have focused on the optical absorption edge of nanocrystalline Ga(1-x)Mn(x)N (0.00 <= x <= 0.18) films deposited by reactive RF magnetron sputtering. The films obtained are nanocrystalline with grain sizes of about 25 nm, having wurtzite structure and strong orientation texture in the c-axis direction. The optical characterizations of the absorption edges were obtained in the 190-2600 nm spectral range. The increase of the Mn content causes an increase of the absorption coefficient which can be clearly noticed at low energies, and a quasi-linear decrease of the optical gap. Broad absorption bands observed around similar to 1.3 and similar to 2.2 eV were associated with transitions between the Mn acceptor level and the valence and conduction bands, respectively. The observed changes in the optical properties due to the Mn incorporation observed in these nanocrystalline films are similar to those reported for ferromagnetic GaMnN single-crystal films.

Theoretical study of the structure and stability of NbxOy, and NbxOy+ (x = 1-3; y = 2-5, 7, 8) clusters

Geometric, thermodynamic and electronic properties of cluster neutrals NbxOy and cations NbxOy+ (x = 1-3; y = 2-5, 7, 8) have been characterized theoretically. A DFT calculation using a hybrid combination of B3LYP with contracted Huzinaga basis sets. Numerical results of the relative stabilities, ionization potentials and band gaps of different clusters are in agreement with experiment. Analysis of dissociation channels supports the more stable building blocks as formed by NbO2, NbO2+ NbO3 and NbO3+ stoichiometries. The net atomic charges suggest that oxygen donor molecules can interact more favorably on central niobium atoms of cluster cations, while the interaction with oxygen acceptor molecules is more favorable on the terminal oxygen atoms of neutral clusters. A topological analysis of the electron localization function gradient field indicates that the clusters may be described as having a strong ionic interaction between Nb and O atoms. Published by Elsevier B.V. B.V.

Vacuum effects on massive spinor fields: S-1 x R-3 topology

The aim of this work was to investigate the role played by an external field on the Casimir energy density for massive fermions under S-1 x R-3 topology. Both twisted- and untwisted-spin connections are considered and the calculation in a closed form is performed using an alternative approach based on the combination of the analytic regularization method and the Euler-Maclaurin summation formula. It is shown that no mass scale appears in the final result and, therefore, Casimir effect arises only from the boundary conditions and vacuum fluctuations induced by the coupling with the external field.

Ionized oxygen vacancy-related electrical conductivity in (Pb(1-x)La(x)) (Zr(0.90)Ti(0.10))(1-x/4)O(3) ceramics

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

Crystallization and preliminary X-ray diffraction analysis of an acidic phospholipase A(2) complexed with p-bromophenacyl bromide and alpha-tocopherol inhibitors at 1.9-and 1.45-A resolution

An acidic phospholipase A(2) (PLA(2)) isolated from Bothrops jararacussu snake venom was crystallized with two inhibitors: alpha-tocopherol (vitamin E) and p-bromophenacyl bromide (BPB). The crystals diffracted at 1.45- and 1.85-Angstrom resolution, respectively, for the complexes with alpha-tocopherol and p-bromophenacyl bromide. The crystals are not isomorphous with those of the native protein, suggesting the inhibitors binding was successful and changes in the quaternary structure may have occurred. (C) 2004 Elsevier B.V. All rights reserved.

(1-x)PMN-xPT ceramics prepared by conventional and modified columbite route: Effect on electrical properties

This study aims to demonstrate how the chemical homogeneity of B cations affects the microstructure and electrical responses of (1-x) PMN-xPT ceramics. Two methodologies were employed to synthesize three different compositions, with x assuming the values 0.10, 0.28, and 0.35. If compared to conventional method, the Ti-modified columbite route, which is characterized by higher B cation homogeneity, leads to PMN-PT powders and ceramics with lower content of PNT pyrochlore phase and, for 0.65PMN-0.35PT composition, minor amount of tetragonal phase is found. Conclusively, PMN-PT ceramics obtained by modified route favors B cations homogeneity, enhancing the dielectric, ferroelectric and piezoelectric properties.

Characterization of the columbite precursor and (1-x)PMN-xPT powders prepared by Ti-modified columbite route

This study proposes to synthesize (1-x)PMN-xPT powders, where 0.10 < x < 0.45, using the T-modified columbite route. This methodology consists in the preparation of the MNT columbite precursor via the polymeric precursor method, followed by the solid state reaction with PbO to get the PMN-PT powders. It was verified that from 15 mol% of Ti, the MNT presents the coexistence of two main phases with different crystal symmetry: Rutile and Columbite. However, the synthesis of (1-x)PMN-xPT powders is not affected by this event. A detailed study of structural effects in MNT and PMN-PT powders as function of Ti content was made using the Rietveld method. It was also demonstrated that powders possess high chemical and microstructural homogeneity.

Structural characterization of 0.5PbMg(1/3)Nb(2/3)O(3)-0.5Ba(x)Pb((1-x))TiO(3) powders

The present work reports the effects caused by barium on phase formation, morphology and sintering of lead magnesium niobate-lead titanate (PMN-50PT). Ab initio study of 0.5PbMg(1/3)Nb(2/3)O(3)-0.5Ba(x)Pb((1-x))TiO(3) ceramic powders, with x = 0, 0.20, and 0.40 was proposed, considering that the partial substitution of lead by barium can reestablish the equilibrium of monoclinic-tetragonal phases in the system. It was verified that even for 40 mol% of barium, it was possible to obtain pyrochlore-free PMN-PT powders. The increase of the lattice parameters of PMN-PT doped-powders confirmed dopant incorporation into the perovskite phase. The presence of barium improved the reactivity of the powders, with an average particle size of 120 nm for 40 mol% of barium against 167 mn for the pure sample. Although high barium content (40 mol%) was deleterious for a dense ceramic, contents up to 20 mol% allowed 95% density when sintered at 1100 degrees C for 4 h. (c) 2007 Elsevier Ltd. All rights reserved.