Hot spot formation in focused-ion-beam-fabricated YBa2Cu3O7-x nanobridges with high critical current densities.

We report on the fabrication and evaluation of nanoscale YBa2Cu3O7-x (YBCO) constrictions using focused-ion-beam techniques for potential application as YBCO bolometers. A gold protective layer was found to be critical for supressing contamination from gallium ions in order to obtain high critical current densities. Further processing using a radio-frequency plasma to remove the gold protective layer has also been studied and was found to be effective in minimizing sample damage resulting from overheating. Current-voltage measurement indicate that the nanobridges go through the transition from superconducting to normal state with different dissipation mechanism including flux creep and hot spot formation.

A nanoscale SQUID operating at high magnetic fields.

A washer-free Nb nanoSQUID has been developed for measuring magnetization changes from nanoscale objects. The SQUID loop is etched into a 250 nm wide Au/Nb bilayer track and the diameter of the SQUID hole is ∼70 nm. In the presence of a magnetic field perpendicular to the plane of the SQUID, vortex penetration into the 250 nm wide track can be observed via the critical current-applied field characteristic and the value at which vortex first penetrates is consistent with the theoretical prediction. Upon removing the applied field, the penetrated vortices escape the track and the critical current at zero field is restored.

Guided Vortex Motion Control in Superconducting Thin Films by Sawtooth Ion Surface Modification.

Design of flux profile and guided motion of magnetic flux quanta (also known as vortices) are central issues for functionality of superconducting devices. Anchoring vortex movement by trapping flux lines through the use of defects and preventing vortex entry by shielding magnetic field have been broadly explored, which can also enable reduction of noise for optimal device operation. Removing vortices entirely via the so-called ratchet effect (employing an asymmetric energy potential) is another alternative. This ratcheting potential is also used in DNA splitting, particle separation, surface atom electromigration, and electrophoresis. Utilizing a superconductor with the ratchet vortex pinning potential induces a dominant motion direction, which can be used to pump flux out from device functional zones. In this work, a varying thickness superconductor with its tailored intrinsic pinning mechanism has been simulated and proven to provide this preferential vortex motion. We demonstrate both theoretically and experimentally that a varying thickness superconducting ratchet is indeed possible. Furthermore, the sawtooth shape of the bridge provides a tunability to the preferred vortex motion direction, dependent on the ramp gradient and intrinsic pinning strength.

Non-covalent surface modification of boron nitride nanotubes for enhanced catalysis.

Boron nitride nanotubes were functionalized with microperoxidase-11 in aqueous media, showing improved catalytic performance due to a strong electron coupling between the active centre of microperoxidase-11 and boron nitride nanotubes.

Combined resynchronisation and implantable defibrillator therapy in left ventricular dysfunction: Bayesian network meta-analysis of randomised controlled trials.

OBJECTIVE: To review the evidence base from randomised controlled trials of combined cardiac resynchronisation therapy and implantable cardioverter defibrillator therapy in left ventricular impairment and symptomatic heart failure. DESIGN: Bayesian network meta-analysis. DATA SOURCES: Medline, Embase, and Cochrane databases up to June 2006. REVIEW METHODS: Two reviewers independently assessed trial eligibility and quality. Included trials compared cardiac resynchronisation therapy, implantable cardioverter defibrillator therapy, combined resynchronisation and implantable defibrillator therapy, and medical therapy alone, in patients with impaired left ventricular systolic function. Bayesian random effects network models were used to examine overall number of deaths. RESULTS: 12 studies including 1636 events in 8307 patients were identified. Combined cardiac resynchronisation and implantable cardioverter defibrillator therapy reduced the number of deaths by one third compared with medical therapy alone (odds ratio 0.57, 95% credible interval 0.40 to 0.80) but did not further improve survival when compared with implantable defibrillator therapy (0.82, 0.57 to 1.18) or resynchronisation (0.85, 0.60 to 1.22) therapy alone. CONCLUSION: Evidence from randomised controlled trials is insufficient to show the superiority of combined cardiac resynchronisation and implantable cardioverter defibrillator therapy over cardiac resynchronisation therapy alone in patients with left ventricular impairment.