Oxygen non-stoichiometry and defect structure of LaMn1-zCuzO3+δ

The quantitative model analysis of the defect structure of copper doped lanthanum manganites LaMn1-zCuzO3+δ (z = 0.05 and 0.1) was performed. In the framework of the model, the independent course of the three reactions of defect formation, including the electronic exchange between manganese and copper, completion of a lattice by the absorption of oxygen and the disproportionation of manganese was considered. It is shown that the increase in the dopant content leads to a change in the dominant electronic process. This is reflected in the lock and disproportionation and leads to the increase in the concentration of holes and decrease the concentration of electrons localized on the manganese atoms

Strategies for L2 lecture comprehension: an intervention study

The study reported in this article set out to investigate the effect o f an intervention into the strategies for second language (L2) lecture comprehension. The research was conducted in a Bulgarian university context and adopted a quasi-experimental pretest-posttest design. The 15-week instructional sequence was based on explicit/ direct teaching o f cognitive and metacognitive strategies for listening to lectures in English. The results indicated that the students in the experimental group (n = 34) significantly outperformed their counterparts in the comparison group (n = 25) in a multiple-choice test used as a measure for L2 lecture comprehension. The findings, therefore, suggest that the strategy-based instruction could facilitate the development o f L2 lecture listening skill

Study and optimization of the synthesis routine of the single phase YBaCo2O6–δ double perovskite

Received: 07.09.2017; accepted: 25.09.2017; published: 20.10.2017.The chemical interaction of YCoO3–δ and BaCoO3-δ with formation of double perovskite was studied depending on temperature and oxygen partial pressure. The stability of YCoO3 was shown to have а crucial influence on the kinetics and mechanism of YBaCo2O6-δ formation. It was found that at 1000 °C in air, i.e. under conditions when YCoO3 is unstable, the double perovskite YBaCo2O6-δ is formed much slower compared to the pure oxygen atmosphere where YCoO3 is stable at the same temperature. Thus controlling YCoO3 stability was shown to be the factor of key importance for optimal preparation of the YBaCo2O6-δ single phase

Investigation of GdBaCo2-xFexO6-δ (x = 0, 0.2) - Ce0.8Sm0.2O2 composite cathodes for intermediate temperature solid oxide fuel cells

The double perovskites GdBaCo2-xFexO 6-δ (x = 0, 0.2) and composites (100 - y) GdBaCo 2-xFexO6-δ (x = 0, 0.2) - y Ce 0.8Sm0.2O2 (y = 10-50 wt.%) were investigated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). Chemical compatibility of GdBaCo2-xFexO 6-δ (x = 0, 0.2) with solid electrolyte Ce0.8Sm 0.2O2, thermal expansion, DC conductivity and electrochemical performance of (100 - y) GdBaCo2-xFe xO6-δ (x = 0, 0.2) - y Ce0.8Sm 0.2O2 (y = 10-50 wt.%) were studied. Partial substitution of Fe for Co was shown to lead to decrease of double perovskite GdBaCo 2-xFexO6-δ reactivity with the solid electrolyte Ce0.8Sm0.2O2. Polarization resistance of cathodes studied was found to depend significantly on firing temperature. Variation of solid electrolyte content in (100 - y) GdBaCo 2-xFexO6-δ (x = 0, 0.2) - y Ce 0.8Sm0.2O2 (y = 10-50 wt.%) composites was shown to allow to optimize their electrochemical performance. Cathode materials of 80 wt.% GdBaCo2O6-δ - 20 wt.% Ce 0.8Sm0.2O2 and 65 wt.% GdBaCo 1.8Fe0.2O6-δ - 35 wt.% Ce 0.8Sm0.2O2 were found to have the lowest polarization resistances and reasonable values of thermal expansion coefficient (TEC) and, therefore, can be considered as promising cathode materials for IT-SOFCs. © 2013 Elsevier B.V. All rights reserved

Observed and Physical Properties of Core-Collapse Supernovae

I use photometry and spectroscopy data for 24 Type II plateau supernovae to examine their observed and physical properties. This dataset shows that these objects encompass a wide range of ~5 mag in their plateau luminosities, their expansion velocities vary by x5, and the nickel masses produced in these explosions go from 0.0016 to 0.26 Mo. From a subset of 16 objects I find that the explosion energies vary between 0.6x and 5.5x10^51 ergs, the ejected masses encompass the range 14-56 Mo, and the progenitors' radii go from 80 to 600 Ro. Despite this great diversity several regularities emerge, which reveal that there is a continuum in the properties of these objects from the faint, low-energy, nickel-poor SNe 1997D and 1999br, to the bright, high-energy, nickel-rich SN 1992am. This study provides evidence that more massive progenitors produce more energetic explosions, thus suggesting that the outcome of the core collapse is somewhat determined by the envelope mass. I find also that supernovae with greater energies produce more nickel. Similar relationships appear to hold for Type Ib/c supernovae, which suggests that both Type II and Type Ib/c supernovae share the same core physics. When the whole sample of core collapse objects is considered, there is a continous distribution of energies below 8x10^51 ergs. Far above in energy scale and nickel production lies the extreme hypernova 1998bw, the only supernova firmly associated to a GRB.Comment: 25 pages, 7 figures, accepted for Part 1 of Astrophysical Journa