Redox stability and high-temperature electrical conductivity of magnesium-and aluminium-substituted magnetite

Spinel-type magnetite-based oxides, possessing relatively high electrical conductivity, are considered as promising consumable anode materials for high temperature pyroelectrolysis, a breakthrough low-CO2 steel technology to overcome the environmental impact of classical extractive metallurgy. The present work was focused on the analysis of phase stability, thermal expansion and high-temperature electrical conductivity in (Fe,Mg,Al)(3)O-4 system under oxidizing and mildly reducing conditions. Metastable, nearly single-phase at room temperature (Fe,Mg,Al)(3)O-4 ceramics was obtained by sintering at 1753-1773 K for 10 h in argon atmosphere. Thermal expansion and redox induced dimensional changes were studied on heating, using TG, XRD and dilatometry. The results revealed that magnesium improves the tolerance against oxidative decomposition and minimizes unfavorable dimensional changes in ceramic samples upon thermal cycling. Co-substitution of iron with aluminium and magnesium was proved to be a promising strategy for improvement of refractoriness and phase stability of Fe3O4-based spinels at elevated temperatures, without significant reduction in the electrical conductivity. (C) 2013 Elsevier Ltd. All rights reserved

In vivo resolution of oligomers with fluorescence photobleaching recovery histograms

Simple independent enzyme-catalyzed reactions distributed homogeneously throughout an aqueous environment cannot adequately explain the regulation of metabolic and other cellular processes in vivo. Such an unstructured system results in unacceptably slow substrate turnover rates and consumes inordinate amounts of cellular energy. Current approaches to resolving compartmentalization in living cells requires the partitioning of the molecular species in question such that its localization can be resolved with fluorescence microscopy. Standard imaging approaches will not resolve localization of protein activity for proteins that are ubiquitously distributed, but whose function requires a change in state of the protein. The small heat shock protein sHSP27 exists as both dimers and large multimers and is distributed homogeneously throughout the cytoplasm. A fusion of the green fluorescent protein variant S65T and sHSP27 is used to assess the ability of diffusion rate histograms to resolve compartmentalization of the 2 dominant oligomeric species of sHSP27. Diffusion rates were measured by multiphoton fluorescence photobleaching recovery. Under physiologic conditions, diffusion rate histograms resolved at least 2 diffusive transport rates within a living cell potentially corresponding to the large and small oligomers of sHSP27. Given that oligomerization is often a means of regulation, compartmentalization of different oligomer species could provide a means for efficient regulation and localization of sHsp27 activity

Mutations in CTNNA1 cause butterfly-shaped pigment dystrophy and perturbed retinal pigment epithelium integrity

Butterfly-shaped pigment dystrophy is an eye disease characterized by lesions in the macula that can resemble the wings of a butterfly. Here we report the identification of heterozygous missense mutations in the CTNNA1 gene (encoding α-catenin 1) in three families with butterfly-shaped pigment dystrophy. In addition, we identified a Ctnna1 missense mutation in a chemically induced mouse mutant, tvrm5. Parallel clinical phenotypes were observed in the retinal pigment epithelium (RPE) of individuals with butterfly-shaped pigment dystrophy and in tvrm5 mice, including pigmentary abnormalities, focal thickening and elevated lesions, and decreased light-activated responses. Morphological studies in tvrm5 mice demonstrated increased cell shedding and the presence of large multinucleated RPE cells, suggesting defects in intercellular adhesion and cytokinesis. This study identifies CTNNA1 gene variants as a cause of macular dystrophy, indicates that CTNNA1 is involved in maintaining RPE integrity and suggests that other components that participate in intercellular adhesion may be implicated in macular disease

Redox stability and electrical conductivity of Fe2.3Mg0.7O4 +/-delta spinel prepared by mechanochemical activation

This paper addresses the potential of mechanochemical activation of MgO and alpha-Fe2O3 precursor powders to obtain Fe2.3Mg0.7O4 ceramics with enhanced redox stability and electrical conductivity. X-ray diffraction (XRD) and Mossbauer spectroscopy suggest the initial formation of the spinel phase after 5 h of high-energy milling in inert gas, but after 10 h of mechanoactivation, the precursor still comprised hematite as a major phase with minor amounts of magnesiowustite as by-product. The activated mixtures can be nearly completely converted to spinel solid solution by heating to 1173 K, whereas single-phase, dense spinel ceramics can be prepared by sintering at 1773 K in inert atmosphere. These ceramics demonstrated redox stability under mildly reducing conditions (p(O-2) similar to 10 Pa), as confirmed by XRD, thermogravimetry and electrical measurements. The electrical conductivity of Fe2.3Mg0.7O4 at this oxygen partial pressure is lower compared to magnetite, but it is still as high as 60 S/cm at 1073 K and 15 S/cm at room temperature. Cooling below 1473 K in air results in a drop of conductivity due to segregation of hematite phase at the grain boundaries. However, the phase separation is kinetically stagnated at 1073 K, and, after slight initial degradation, the retained electrical conductivity is more than 3 orders of magnitude higher compared to hematite and MgFe2O4 spinel. (C) 2013 Elsevier Ltd. All rights reserved

Thermodynamic description of the Pb-O system

The phase relations and thermodynamic properties of the Pb-O system are reviewed and assessed. The transformation temperature between PbO and Pb3O4 was also experimentally reinvestigated. A model description of the Pb-O system is then proposed and thermodynamic parameters are optimized. The values calculated from the resulting consistent set of Gibbs energy functions are compared with experimental data and discussed