The effect of contamination by Ca2 ions in proton conductive membranes f or polymer electrolyte fuel cells was investigated systematically. Ion and water transport characteristics of Nafion membranes, which were equilibrated with 0.02 to 0.03 kmol m3 of HC1/CaCl2 mixed solutions of various mixing ratios, were studied by electromotive force analysis. Membrane composition analysis, showed that Ca2 has much higher affinity than H to the ion exchange sites in Naf ion membranes. The water content in the membrane, as expressed by the amount of water per cationic site }120/SO;, decreased about 19% from 21 for H-form membrane to 17 for Ca-form membrane. The water transference coefficient was obtained from streaming potential measurements of Nafion 115 membranes of various H/Ca2 cationic compositions. The water transference coefficient increased from 2.5 toward 11 as the Ca2 content in the membrane increased, especially when the equivalent fraction of H in the cationic exchange sites x became less than 0.5. Ionic transference numbers for H in the membrane, determined by a new electromotive force method, showed rapid decrease when the cationic site occupancy by H became less than 0.5. Membrane conductivity changed linearly with H composition in the membrane. In strong contrast to the interaction mode between H and Ca cations during ionic conduction, which appeared almost independent, a certain extent of interference was observed among water molecules as they were carried along by cations in the membrane. It was predicted that if Ca2 ions enter the fuel-cell membrane, they cause serious effects to membrane drying and result in deterioration of fuel-cell performance. The advantage of this methodology in the study of transport characteristics of fuel-cell membranes is stressed due to ease and accuracy of measurements.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2015-02-07 to IP
I consider the quantum electromagnetic field in a coaxial cylindrical waveguide, such that the outer cylindrical surface has a time-dependent radius. The field propagates parallel to the axis, inside the annular region between the two cylindrical surfaces. When the mechanical frequency and the thickness of the annular region are small enough, only transverse electromagnetic photons may be generated by the dynamical Casimir effect. The photon emission rate is calculated in this regime, and compared with the case for parallel plates in the limit of very short distances between the two cylindrical surfaces. The proximity force approximation holds for the transition matrix elements in this limit, but the emission rate scales quadratically with the mechanical frequency, as opposed to the cubic dependence for parallel plates.
An improvement in the distribution of junction properties for YBaCuO/PrBaCuO/YBaCuO trilayer junctions has been demonstrated. In order to ensure a uniform substrate temperature during the deposition of trilayer films, Al/Cu/Al stacked foils are introduced as a backing plate between the substrate and sample holder. Furthermore, the film composition is optimized to reduce the precipitated particles on the surface of the films. All the junctions with a barrier thickness of 35 nm and an area less than 100 µ m2 show RSJ-like current voltage characteristics with some excess current at 4.2 K. The 1-σ spreads of Josephson critical current density J
c and normalized junction resistance R
n
A are obtained to be 34% and 25%, respectively, for 88 junctions on the same substrate. This result is comparable to the 1-σ spreads of ramp-edge type junctions.
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