477 research outputs found
Impedance Spectra of Mixed Conductors: a 2D Study of Ceria
In this paper we develop an analytical framework for the study of
electrochemical impedance of mixed ionic and electronic conductors (MIEC). The
framework is based on first-principles and it features the coupling of
electrochemical reactions, surface transport and bulk transport processes. We
utilize this work to analyze two dimensional systems relevant for fuel cell
science via finite element method (FEM). Alternate current Impedance
Spectroscopy (IS) of a ceria symmetric cell is simulated near equilibrium
condition (zero bias) for a wide array of working conditions including
variations of temperature and partial pressure on a two dimensional fuel
cell sample with patterned metal electrodes. The model shows agreement of IS
curves with the experimental literature with the relative error on the
impedance being consistently below 2%. Important two-dimensional effects such
the effects of thickness decrease and the influence of variable electronic and
ionic diffusivities on the impedance spectra are also explored
Elucidating the role of the TRPM7 alpha-kinase: TRPM7 kinase inactivation leads to magnesium deprivation resistance phenotype in mice
TRPM7 is an unusual bi-functional protein containing an ion channel covalently linked to a protein kinase domain. TRPM7 is implicated in regulating cellular and systemic magnesium homeostasis. While the biophysical properties of TRPM7 ion channel and its function are relatively well characterized, the function of the TRPM7 enzymatically active kinase domain is not understood yet. To investigate the physiological role of TRPM7 kinase activity, we constructed mice carrying an inactive TRPM7 kinase. We found that these mice were resistant to dietary magnesium deprivation, surviving three times longer than wild type mice; also they displayed decreased chemically induced allergic reaction. Interestingly, mutant mice have lower magnesium bone content compared to wild type mice when fed regular diet; unlike wild type mice, mutant mice placed on magnesium-depleted diet did not alter their bone magnesium content. Furthermore, mouse embryonic fibroblasts isolated from TRPM7 kinase-dead animals exhibited increased resistance to magnesium deprivation and oxidative stress. Finally, electrophysiological data revealed that the activity of the kinase-dead TRPM7 channel was not significantly altered. Together, our results suggest that TRPM7 kinase is a sensor of magnesium status and provides coordination of cellular and systemic responses to magnesium deprivation
Elucidating the role of the TRPM7 alpha-kinase: TRPM7 kinase inactivation leads to magnesium deprivation resistance phenotype in mice
TRPM7 is an unusual bi-functional protein containing an ion channel covalently linked to a protein kinase domain. TRPM7 is implicated in regulating cellular and systemic magnesium homeostasis. While the biophysical properties of TRPM7 ion channel and its function are relatively well characterized, the function of the TRPM7 enzymatically active kinase domain is not understood yet. To investigate the physiological role of TRPM7 kinase activity, we constructed mice carrying an inactive TRPM7 kinase. We found that these mice were resistant to dietary magnesium deprivation, surviving three times longer than wild type mice; also they displayed decreased chemically induced allergic reaction. Interestingly, mutant mice have lower magnesium bone content compared to wild type mice when fed regular diet; unlike wild type mice, mutant mice placed on magnesium-depleted diet did not alter their bone magnesium content. Furthermore, mouse embryonic fibroblasts isolated from TRPM7 kinase-dead animals exhibited increased resistance to magnesium deprivation and oxidative stress. Finally, electrophysiological data revealed that the activity of the kinase-dead TRPM7 channel was not significantly altered. Together, our results suggest that TRPM7 kinase is a sensor of magnesium status and provides coordination of cellular and systemic responses to magnesium deprivation
Relações morfométricas para árvores dominantes de Pinus taeda no Estado do Paraná.
Este trabalho objetivou estudar as relações morfomĂ©tricas de árvores dominantes de Pinus taeda no municĂpio de Ponta Grossa, Paraná. Em cada amostra a árvore de maior diâmetro a altura do peito (DAP) foi considerada dominante em relação Ă s suas vizinhas. Destas foram mensuradas dap, altura total, altura da copa e oito raios de copa. As variáveis morfomĂ©tricas analisadas foram: diâmetro de copa, altura da copa, proporção de copa, grau de esbeltez, Ăndice de saliĂŞncia, Ăndice de abrangĂŞncia e formal de copa. Estas foram correlacionadas com o dap e altura atravĂ©s de correlação de Pearson. De acordo com os Ăndices, as árvores analisadas possuem mĂ©dia instabilidade, copas arredondadas e nĂŁo há necessidade de desbaste na área. O diâmetro a altura do peito se correlacionou melhor com as variáveis morfomĂ©tricas estudadas, indicando que estas sofrem alterações conforme as árvores incrementam em diâmetro
Automated detection of bacteria in urine
A method for detecting the presence of bacteria in urine was developed which utilizes the bioluminescent reaction of adenosine triphosphate with luciferin and luciferase derived from the tails of fireflies. The method was derived from work on extraterrestrial life detection. A device was developed which completely automates the assay process
ĂŤndices de sĂtios para Hovenia dulcis Thunberg na regiĂŁo central do estado do Rio Grande do Sul, Brasil.
Este trabalho teve como objetivo construir curvas Ăndice de sĂtios florestais, a partir da altura dominante e idade, de populações localizadas na regiĂŁo central do Estado do Rio Grande do Sul. Para tanto, foram utilizadas informações de trĂŞs povoamentos (sĂtios) com idades de 25 anos, localizados na Fundação de Pesquisa Agropecuária (FEPAGRO). Para classificar os sĂtios florestais, coletaram-se informações de 18 árvores dominantes nos locais, observando a metodologia para análise de tronco. Na construção das curvas de Ăndice de sĂtio, foi o selecionado o modelo de Backman, ficando constatada a necessidade da construção de dois conjuntos de curvas, com intervalo de 2 m, da idade de 5 a 25 anos, com idade Ăndice de 25 anos. Para o SĂtio I-A, foram geradas 3 curvas Ăndices, de 22 a 24 m e, para os SĂtios I-B+II+III, 6 curvas Ăndices de 8 a 18 m
Ambient Pressure XPS Study of Mixed Conducting Perovskite-type SOFC Cathode and Anode Materials under Well-Defined Electrochemical Polarization
The oxygen exchange activity of mixed conducting oxide surfaces has been widely investigated, but a detailed understanding of the corresponding reaction mechanisms and the rate-limiting steps is largely still missing. Combined in situ investigation of electrochemically polarized model electrode surfaces under realistic temperature and pressure conditions by near-ambient pressure (NAP) XPS and impedance spectroscopy enables very surface-sensitive chemical analysis and may detect species that are involved in the rate-limiting step. In the present study, acceptor-doped perovskite-type La0.6Sr0.4CoO3-δ (LSC), La0.6Sr0.4FeO3-δ (LSF), and SrTi0.7Fe0.3O3-δ (STF) thin film model electrodes were investigated under well-defined electrochemical polarization as cathodes in oxidizing (O2) and as anodes in reducing (H2/H2O) atmospheres. In oxidizing atmosphere all materials exhibit additional surface species of strontium and oxygen. The polaron-type electronic conduction mechanism of LSF and STF and the metal-like mechanism of LSC are reflected by distinct differences in the valence band spectra. Switching between oxidizing and reducing atmosphere as well as electrochemical polarization cause reversible shifts in the measured binding energy. This can be correlated to a Fermi level shift due to variations in the chemical potential of oxygen. Changes of oxidation states were detected on Fe, which appears as FeIII in oxidizing atmosphere and as mixed FeII/III in H2/H2O. Cathodic polarization in reducing atmosphere leads to the reversible formation of a catalytically active Fe0 phase
TRPM7 is essential for Mg2+ homeostasis in mammals
Mg2+ is the second-most abundant cation in animal cells and is an essential cofactor in numerous enzymatic reactions. The molecular mechanisms controlling Mg2+ balance in the organism are not well understood. In this study, we report identification of TRPM7, a bifunctional protein containing a protein kinase fused to an ion channel, as a key regulator of whole body Mg2+ homeostasis in mammals. We generated TRPM7-deficient mice with the deletion of the kinase domain. Homozygous TRPM7Δkinase mice demonstrated early embryonic lethality, whereas heterozygous mice were viable, but developed signs of hypomagnesaemia and revealed a defect in intestinal Mg2+ absorption. Cells derived from heterozygous TRPM7Δkinase mice demonstrated reduced TRPM7 currents that had increased sensitivity to the inhibition by Mg2+. Embryonic stem cells lacking TRPM7 kinase domain displayed a proliferation arrest phenotype that can be rescued by Mg2+ supplementation. Our results demonstrate that TRPM7 is essential for the control of cellular and whole body Mg2+ homeostasis
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