Surface and Bulk Oxygen Kinetics of BaCo0.4Fe0.4Zr0.2−XYXO3−δ Triple Conducting Electrode Materials

Triple ionic-electronic conductors have received much attention as electrode materials. In this work, the bulk characteristics of oxygen diffusion and surface exchange were determined for the triple-conducting BaCo0.4Fe0.4Zr0.2−XYXO3−δ suite of samples. Y substitution increased the overall size of the lattice due to dopant ionic radius and the concomitant formation of oxygen vacancies. Oxygen permeation measurements exhibited a three-fold decrease in oxygen permeation flux with increasing Y substitution. The DC total conductivity exhibited a similar decrease with increasing Y substitution. These relatively small changes are coupled with an order of magnitude increase in surface exchange rates from Zr-doped to Y-doped samples as observed by conductivity relaxation experiments. The results indicate that Y-doping inhibits bulk O2− conduction while improving the oxygen reduction surface reaction, suggesting better electrode performance for proton-conducting systems with greater Y substitution.

Curie temperature adjustment in the solid solution Gd1–x Y x PtMg

GdPtMg and YPtMg (both crystallize with the ZrNiAl-type structure) form a complete solid solution Gd1–x Y x PtMg. Samples in x = 0.1 steps were synthesized from the elements in sealed tantalum ampoules in an induction furnace and characterized by Guinier powder patterns. The structures of four members of the solid solution were refined from single-crystal X-ray diffractometer data, confirming the mixed occupation of the Gd/Y site; however, without any indication for Gd/Y ordering. Temperature dependent magnetic susceptibility measurements reveal Curie-Weiss behavior for all samples and ferromagnetic ordering in the low-temperature regime. The Curie temperature drops linearly from 97.6 K for GdPtMg to 3.7 K for Gd0.1Y0.9PtMg. All samples are soft ferromagnets. The Gd/Y substitution is a suitable tool for adjusting magnetic ordering temperatures of gadolinium intermetallics over a broad temperature range.

Influence of Y-substitution on phase composition and proton uptake of self-generated Ba(Ce,Fe)O3-δ - Ba(Fe,Ce)O3-δ composites

Self-generated composites from the series BaCe1-(x+z)FexYzO3-ẟ with z=0.2 for 0.1≤x≤0.6 and z=0 for Ce:Fe = 1 were obtained by one-pot synthesis. The composites consist of proton and electron conducting phases...

A short note on determinantal representation of stable polynomials

In this paper we provide some results that replace the condition ”real-zero” by the properties so-called x-substitution and y-substitution. We show that using these properties, we can still write the determinantal representation of a stable polynomial in terms of identity and Hermitian matrices.

Ceftazidime-Avibactam Resistance Mediated by the N346Y Substitution in Various AmpC β-Lactamases

ABSTRACT Chromosomal and plasmid-borne AmpC cephalosporinases are a major resistance mechanism to β-lactams in Enterobacteriaceae and Pseudomonas aeruginosa. The new β-lactamase inhibitor avibactam effectively inhibits class C enzymes and can fully restore ceftazidime susceptibility. The conserved amino acid residue Asn346 of AmpC cephalosporinases directly interacts with the avibactam sulfonate. Disruption of this interaction caused by the N346Y amino acid substitution in Citrobacter freundii AmpC was previously shown to confer resistance to the ceftazidime-avibactam combination (CAZ-AVI). The aim of this study was to phenotypically and biochemically characterize the consequences of the N346Y substitution in various AmpC backgrounds. Introduction of N346Y into Enterobacter cloacae AmpC (AmpCcloacae), plasmid-mediated DHA-1, and P. aeruginosa PDC-5 led to 270-, 12,000-, and 79-fold decreases in the inhibitory efficacy (k2/Ki) of avibactam, respectively. The kinetic parameters of AmpCcloacae and DHA-1 for ceftazidime hydrolysis were moderately affected by the substitution. Accordingly, AmpCcloacae and DHA-1 harboring N346Y conferred CAZ-AVI resistance (MIC of ceftazidime of 16 μg/ml in the presence of 4 μg/ml of avibactam). In contrast, production of PDC-5 N346Y was associated with a lower MIC (4 μg/ml) since this β-lactamase retained a higher inactivation efficacy by avibactam in comparison to AmpCcloacae N346Y. For FOX-3, the I346Y substitution did not reduce the inactivation efficacy of avibactam and the substitution was highly deleterious for β-lactam hydrolysis, including ceftazidime, preventing CAZ-AVI resistance. Since AmpCcloacae and DHA-1 display substantial sequence diversity, our results suggest that loss of hydrogen interaction between Asn346 and avibactam could be a common mechanism of acquisition of CAZ-AVI resistance.