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

Permanent Superhumps in V1974 Cyg

We present results of 32 nights of CCD photometry of V1974 Cygni, from the years 1994 and 1995. We verify the presence of two distinct periodicities in the light curve: 0.0812585 day~1.95 hours and 0.0849767 d~2.04 hr. We establish that the shorter periodicity is the orbital period of the underlying binary system. The longer period oscillates with an average value of |dot(P)| ~ 3x10^(7)--typical to permanent superhumps. The two periods obey the linear relation between the orbital and superhump periods that holds among members of the SU Ursae Majoris class of dwarf novae. A third periodicity of 0.083204 d~2.00 hr appeared in 1994 but not in 1995. It may be related to the recently discovered anti-superhump phenomenon. These results suggest a linkage between the classical nova V1974 Cyg and the SU UMa stars, and indicate the existence of an accretion disk and permanent superhumps in the system no later than 30 months after the nova outburst. From the precessing disk model of the superhump phenomenon we estimate that the mass ratio in the binary system is between 2.2 and 3.6. Combined with previous results this implies a white dwarf mass of 0.75-1.07 M sun.Comment: 11 pages, 10 eps. figures, Latex, accepted for publication in MNRA

Long-term results of cyclosporine-steroid therapy in 131 non-matched cadaveric renal transplants.

One-hundred-and-twenty-eight recipients of 131 consecutive, non-matched cadaver renal allografts were treated with cyclosporine and steroids. They have been followed for 4 to 6 yr. Cumulative patient survival at 1-yr was 92.2% and at 6yr it is 77.8%. Cumulative graft survival at 1-yr was 79.4% and at 6 yr it is 50.0%. After the high-risk 1st yr, the rate of graft loss was even and similar to that reported after the 1st yr for grafts treated with azathioprine and steroids. This indicates that cyclosporine nephrotoxicity has not had an obvious adverse effect on the survival of chronically functioning grafts. The results were better with primary grafting versus retransplantation, but were not significantly influenced by age, diabetes mellitus, or a delayed switch in patients from cyclosporine to azathioprine. We have concluded that cyclosporine-steroid therapy is safe and effective for long-term use after cadaveric renal transplantation

The relationship between the L1 and L2 domains of the insulin and epidermal growth factor receptors and leucine-rich repeat modules

BACKGROUND: Leucine-rich repeats are one of the more common modules found in proteins. The leucine-rich repeat consensus motif is LxxLxLxxNxLxxLxxLxxLxx- where the first 11–12 residues are highly conserved and the remainder of the repeat can vary in size Leucine-rich repeat proteins have been subdivided into seven subfamilies, none of which include members of the epidermal growth factor receptor or insulin receptor families despite the similarity between the 3D structure of the L domains of the type I insulin-like growth factor receptor and some leucine-rich repeat proteins. RESULTS: Here we have used profile searches and multiple sequence alignments to identify the repeat motif Ixx-LxIxx-Nx-Lxx-Lxx-Lxx-Lxx- in the L1 and L2 domains of the insulin receptor and epidermal growth factor receptors. These analyses were aided by reference to the known three dimensional structures of the insulin-like growth factor type I receptor L domains and two members of the leucine rich repeat family, porcine ribonuclease inhibitor and internalin 1B. Pectate lyase, another beta helix protein, can also be seen to contain the sequence motif and much of the structural features characteristic of leucine-rich repeat proteins, despite the existence of major insertions in some of its repeats. CONCLUSION: Multiple sequence alignments and comparisons of the 3D structures has shown that right-handed beta helix proteins such as pectate lyase and the L domains of members of the insulin receptor and epidermal growth factor receptor families, are members of the leucine-rich repeat superfamily

Supernumerary teeth in a sample of South African dental patients

Supernumerary teeth (SNT) are often associated with malocclusions. Data on SNT in the South African population are not well documented. To determine the prevalence, distribution of characteristics and any associated complications of SNT in a South African sample of dental patients. The study was retrospective, cross-sectional and descriptive. Method: Orthopantomographs of 12,005 dental patients were reviewed for the presence of SNT. The number, morphology, location, eruption status and orientation of SNT were assessed. Associated orthodontic problems were noted. The prevalence rate was 2.48%. No sexual dimorphism in the distribution of SNT was noted. Types of SNT tabulated were: supplementary, conical, tuberculate and odontoma. Maxilla demonstrated a higher predilection for SNT. Variation in the distribution of SNT in the anterior, premolar and molar regions in each jaw and across jaws was statistically significant. Relationship of eruption status to the morphology and orientation of SNT was of significance. Malocclusions noted were displacement and impaction of adjacent teeth. From an orthodontic perspective, presence of SNT may compromise tooth movement and space closure in patients. Additionally, as majority of SNT in this population were in the maxillary molar and mandibular premolar regions, caution is advised when planning the placement of orthodontic implants in these regions

Meta-analysis of sex difference in testosterone levels in umbilical cord blood

This meta-analysis reviewed published literature comparing human male and female umbilical cord total testosterone (T) levels. A total of 18 studies using 1,229 samples from 602 male and 627 female newborns were analysed using the RevMan 5 statistical package. Analysis using the inverse variance method based on a random-effects model revealed significantly higher cord T in boys than girls at a moderate effect size (Hedges' g = 0.57). There was significant heterogeneity between the 18 studies, although the five studies using direct assays showed no heterogeneity. For studies using extraction and chromatography, those that combined T from arterial and venous cord blood found a larger sex difference than those using only cord venous samples (Hedges' g = 0.94 vs 0.32); this suggests umbilical cord venous T is of maternal/placental origin and arterial T is of fetal origin. The wide range of T values between studies suggests high cross-reactivity in the assay methods reviewed