Influence of the SiO Underlayer on the Superconductor-Insulator Transition in Amorphous Bi Films

We have measured the temperature (T) dependence of the resistance per square R for a series of ultrathin Bi films quench-condensed onto different SiO underlayers ranging in thickness from zero to 20Å. The R-T characteristics of Bi films on a 4.3Å-thick layer of SiO are different from those on the layers thicker than 10Å, possibly because of the inhomogeneity in Bi films. The results suggest that insufficient thickness of an underlayer causes a larger value of the critical resistance for the superconductor-insulator transition in quench-condensed Bi films.     

High-T c superconducting Nb-Ga wires prepared by heating and quenching in liquid helium

High-T _c Nb-Ga wires were prepared by a diffusion process. The Nb wires dip-coated with Ga were Joule-heated to high temperatures in a liquid He bath and then quenched by switching the current off. The highest onset transition temperature was 17.4 K. It was increased to 20.1 K by annealing for 24 h at 700°C. The midpoint temperature of the resistive transition was 19.8 K.     

Excess electrical conductivity due to fluctuations of quench-condensed superconducting Nb films

The resistive transition of superconducting Nb films evaporated onto a liquid-He-cooled substrate has been investigated, and shows a rounding characteristic of the thermal fluctuations. Transition curves have been measured above and below the superconducting transition temperatureT _c in the absence of a magnetic field. The excess electrical conductivity due to fluctuations aboveT _c of quench-condensed Nb films is well described in terms of the sum of the contributions from the Aslamazov-Larkin term and from the Maki-Thompson term, in contradistinction to the case of quench-condensed Bi, Ga, and Pb films. This suggests that thermal phonons play an important role in the contribution of the Maki term.     

Nanostructure and properties of proton‐conducting sulfonated poly(ether ether ketone) (SPEEK) and zirconia–SPEEK hybrid membranes for direct alcohol fuel cells: effect of the nature of swelling solvent and incorporation of heteropolyacid

The influence, on membrane nanostructure and properties, of water or ethanol as swelling solvent of sulfonated poly(ether ether ketone) (SPEEK) and zirconia–SPEEK hybrid membranes prepared using the sol–gel process has been investigated. Independent of the solvent, small‐angle X‐ray scattering measurements reveal the existence of a two‐level hierarchical structure in SPEEK of greater sulfonation level, consisting of solvent‐swelled spatially correlated primary SO₃H‐rich ionic clusters of around 15 Å in size, forming larger secondary aggregates well dispersed in the PEEK matrix. The size of the primary nanodomains and the connectivity between domains are determining parameters for protonic conductivity, solvent swelling ability and permeability of the membranes. For both SPEEK and zirconia–SPEEK membranes containing ethanol, the pronounced affinity of ethanol molecules with SPEEK leads to an increase in the size of ionic clusters and of the number of connecting channels between clusters compared to membranes containing water. This promotes solvent swelling and proton conductivity. The increase in permeability to water induced by incorporation of ethanol in place of water in both polymeric and hybrid membranes is less in the hybrid membranes. This result suggests that the potential use of zirconia–SPEEK hybrid membranes in direct alcohol fuel cells is more promising than that of pure SPEEK, due not only to the less probable alcohol and water penetration in the membranes associated with their lower permeability, but also to the fact that an eventual penetration of alcohol in hybrid membranes should reduce the risk of cathode flooding compared to zirconia‐free SPEEK membranes. Copyright © 2011 Society of Chemical Industry     

Isomaltulose production by free cells of Serratia plymuthica in a batch process

Free cells of Serratia plymuthica were used to convert sucrose into isomaltulose and trehalulose reducing sugars. The effects of substrate concentration and temperature were observed in a batch process with flasks shaken at 150 rpm. The experimental design and response surface methodology analysis indicated that the conversion parameters had significant influence (p < 0.05) on sucrose conversion, and that a valid model was obtained after an analysis of variance (F_model = 10.48 > F_charted = 5.79) to obtain a response surface and isocurve. Conversion was favoured when a 30% sucrose solution and temperature of 25 °C were used, which resulted in a high conversion into isomaltulose – over 70% – and 7–8% trehalulose. Small amounts of glucose (5–7%) and fructose (5–8%) were formed in the reaction medium.     

A hydrodynamic study of vascular lesion

In order to search for the origin of vascular lesion from the hydrodynamic point of view, the viscous flows in a constricted channel and in a channel with a branch are studied numerically. The results obtained show the importance of the temporal variation of shearing stress on the wall.