Quasiparticle tunnelling and field-dependent critical current in 2212-BSCCO

Intrinsic c-axis tunnelling in the superconducting state has been measured in zero and finite fields in small mesa structures fabricated on the surface of 2212-BSCCO single crystals. The temperature dependence of the zero-field critical current and quasi-particle conductance is related to microscopic d-wave models in the presence of impurity scattering. The strong field dependence of the c-axis critical current provides information on the correlation of flux pancakes across adjacent superconducting bi-layers. An instability in the IV characteristics is observed below 20K, which accounts for the apparent drop in critical current at low temperatures previously reported

Intrinsic c-axis transport in 2212-BSCCO

We describe two experimental approaches to circumvent the problem of self-heating in IV measurements on small mesa samples of 2212-BSCCO. Simultaneous dc and temperature measurements have been performed, allowing corrections for heating to be made. Short pulse measurements have also been made, where the IV characteristics and the mesa temperature can be measured on a $\mu$s time-scale enabling intrinsic IV characteristics to be derived, even in the presence of appreciable self-heating. Self-heating leads to an appreciable depression of the apparent energy gap and also accounts, in major part, for the s-shaped characteristics often reported at high currents. By correcting for the temperature rise, we derive the intrinsic temperature dependence of the tunnelling characteristics for crystals with a range of doping. Results are compared with recent theoretical models for c-axis transport in d-wave superconductors

Interlayer tunnelling in Bi2Sr2CaCu2O8+d single crystals

We present measurements of the intrinsic quasi-particle conductivity along the c-axis of 2212-BSCCO single-crystal mesa structures in the superconducting and normal states. Direct measurement of the mesa temperature enables corrections to be made for self-heating and permits the acquisition of reliable I-V characteristics over a wide range of temperatures and voltages. Unlike a conventional superconductor, there is no evidence for any change in the quasiparticle conductivity at Tc, consistent with precursor pairing of electrons in the normal state. At low temperatures the initial low-voltage linear conductivity exhibits a T2 dependence, approaching a limiting value at zero temperature

System for fast time-resolved measurements of c-axis quasiparticle conductivity in intrinsic Josephson junctions of 2212-BSCCO

A wide-band cryogenic ampli¯er measurement system for time-resolved 4-point VI-characteristic measurements on Bi2Sr2CaCu2O8+± mesa structures is described. We present measurements which demonstrate the importance of self-heating on » 50 ns time scales. Such heating is likely to have been very signi¯cant in many previously published measurements, where the reported nonlinear VI characteristics have been used to derive superconducting energy gaps

Explaining coronary heart disease trends in Hong Kong: creation of a model for policy and planning.

1. The largest contribution of coronary heart disease (CHD) mortality reductions was from medical treatment. 2. A smaller contribution was estimated to be due to risk factors changes. 3. Improvement of treatment uptake levels can have a substantial effect in reducing CHD mortality.published_or_final_versio

Shock resilience of structural pillars in naval vessels

Although structural pillars are extensively used in commercial vessels, traditionally their use on board UK warships has been discouraged. This is due to the tendency of pillars to "punch through" the deck when subjected to the high impulse loading of shock from underwater explosions (UNDEX). There are however many spaces within naval ships that would significantly benefit from the wide-open spaces created from the use of pillars as opposed to full bulkheads, such as machinery rooms, mooring decks and accommodation flats. This paper re-addresses the question of a shock capable pillar, looking at how a pillar can be designed or mounted to increase its resilience to shock from underwater explosions. It is proposed that the advice against the use of pillars in warships could be unfounded; this is supported by the fact that not all navies reject their use. The results of this study imply that as long as the pillar is sited properly on primary structural members, then pillar buckling should occur long before "punch though"

Differing lifestyles of Staphylococcus epidermidis as revealed through Bayesian clustering of multilocus sequence types

Staphylococcus epidermidis is part of the normal bacterial flora of human skin and a leading cause of infections associated with indwelling medical devices. Previous phylogenetic analyses of subgenomic data have been unable to distinguish between S. epidermidis strains with nosocomial or commensal lifestyles, despite the identification of specific phenotypes and accessory genes that may contribute to such lifestyles. To attempt to better define the population structure of this species, the international S. epidermidis multilocus sequence typing database was analyzed with the Bayesian clustering programs STRUCTURE and BAPS. A total of six genetic clusters (GCs) were identified. A local population of S. epidermidis from clinical specimens was classified according to these six GCs, and further characterized for antibiotic susceptibilities, biofilm, and various genetic markers. GC5 was abundant and significantly enriched for isolates that were resistant to four classes of antibiotics, high biofilm production, and positive for the virulence markers icaA, IS256, and sesD/bhp, indicating its potential clinical relevance. In contrast, GC2 was rare and contained the only isolates positive for the putative commensal marker, fdh. GC1 and GC6 were abundant but not significantly associated with any of the examined characteristics, except for sesF/aap and GC6. GC3 was rare and identified as a potential genetic sink that received, but did not donate, core genetic material from other GCs. In conclusion, population genetics analyses were essential for identifying clusters of strains that may differ in their adaptation to nosocomial or commensal lifestyles. These results provide a new, population genetics framework for studying S. epidermidis

Shock resilience of structural pillars in naval vessels

Although structural pillars are extensively used in commercial vessels, traditionally their use on board UK warships has been discouraged. This is due to the tendency of pillars to "punch through" the deck when subjected to the high impulse loading of shock from underwater explosions (UNDEX). There are however many spaces within naval ships that would significantly benefit from the wide-open spaces created from the use of pillars as opposed to full bulkheads, such as machinery rooms, mooring decks and accommodation flats. This paper re-addresses the question of a shock capable pillar, looking at how a pillar can be designed or mounted to increase its resilience to shock from underwater explosions. It is proposed that the advice against the use of pillars in warships could be unfounded; this is supported by the fact that not all navies reject their use. The results of this study imply that as long as the pillar is sited properly on primary structural members, then pillar buckling should occur long before "punch though"