Enhanced critical magnetization currents of hot-pressed YBa2Cu3O6+x through partial melting post-oxygenation

Bulk YBa₂Cu₃O_6+x superconductor was synthesized using the hot-pressing technique combined with various oxygen-annealing cycles. Pressed samples, with theirab-planes perpendicular to the pressing axis, annealed in oxygen at the partial melting point of approximately 1000°C and slowly cooled at different rates in the temperature ranges 975–935 and 935–450°C showed enhanced magnetization hysteresis loops with a weak field dependence. Due to oxygen-deficient regions in these materials, anomalous magnetization hysteresis loops with a butterfly contour were observed at temperatures above 50 K. This indicates that these regions act as effective flux-pinning centres at high temperatures. The critical magnetization current density (J _c) calculated using the Bean model and the average grain dimension was of the order of 10⁴ A cm^–2 at 75 K up to 1 T. Because of a shorter period of oxygenation and a weak field dependence ofJ _c s, the synthesis process reported here is very promising and further optimization of the period in various annealing temperature ranges to limit the weak links caused by excessive grain growth becomes necessary. The observations are also correlated with the morphology and the crystal orientation studied by scanning electron microscopy and X-ray diffractometry, respectively.     

Main challenges to international student mobility in the European arena

Scientometrics - This study analyses international student mobility (ISM) in Europe since the 1999 Bologna Declaration. International mobility of higher education students is both a driver and a...     

Primary total hip reconstruction with a titanium fiber-coated prosthesis inserted without cement

A prospective study was done of the intermediate-term clinical and radiographic results of 121 total hip arthroplasties in which a Harris-Galante porous titanium-fiber-coated prosthesis was inserted without cement in 110 patients. The average age at the time of the operation was forty-nine years (range, twenty to seventy years). The average duration of follow-up was sixty-seven months (range, fifty-five to seventy-nine months). The average preoperative Harris hip score was 55 points, and the average postoperative score was 93 points. One acetabular component was revised due to recurrent dislocation. Eleven femoral implants were unstable, and of these, four were revised. Cortical erosion was present around the distal part of the femoral stem in nine patients (8 per cent) who had stable implants, and one of these femoral implants was revised because the erosion was extensive. Survivorship analysis at five years revealed a 97 per cent chance of survival (95 per cent confidence limit, 0.937 to 1.0) of the Harris-Galante femoral-stem implant inserted without cement.     

ac losses in Nb3Ge composite tape conductors

ac losses of Nb₃Ge tapes prepared by chemical vapour deposition have been measured between 4 and 16 K. Several tapes were observed to exhibit complete shielding of the normal substrate by the Nb₃Ge coating, which is continuous around the tape circumference. These tapes had measured losses that were acceptably low for power transmission up to 14 K. Another class of tapes showed high losses characteristic of ohmic currents flowing through the normal substrates. Microscopic examination revealed continuous longitudinal edge cracks for these samples. A correlation observed between ‘edge cracking’ and Nb³Ge coat thickness is discussed in terms of the differential contraction from coating temperature between the Nb₃Ge and the substrate in a completely enclosed geometry.     

A method for the measurement of the parameters of a two-layer stratified earth

A two-layer stratified model is assumed for the earth. The distances involved are assumed to be sufficiently short that the earth can be considered flat. The measurement of the parameters of the top layer can easily be made from the surface, but the parameters of the lower layer are somewhat more difficult. A method is given for the evaluation of these quantifies in terms of measurements of propagation between two antennas located at the surface of the earth. The theoretical solution for the field of an antenna located at the surface of a flat stratified earth has been given by J. R. Wait. This solution is taken as the starting point; it is put into a form which explicitly shows the influence of the parameters of the lower layer. The method of least squares is then used to evaluate the unknown parameters in terms of the measurements. This process allows the use of a large number of measurements which are essentially subjected to an averaging procedure. This prevents localized irregularities in the earth's surface from unduly affecting the results.     

Strongly enhanced current densities in superconducting coated conductors of YBa2Cu3O7-x + BaZrO3

There are numerous potential applications for superconducting tapes based on YBa(2)Cu(3)O(7-x) (YBCO) films coated onto metallic substrates. A long-established goal of more than 15 years has been to understand the magnetic-flux pinning mechanisms that allow films to maintain high current densities out to high magnetic fields. In fact, films carry one to two orders of magnitude higher current densities than any other form of the material. For this reason, the idea of further improving pinning has received little attention. Now that commercialization of YBCO-tape conductors is much closer, an important goal for both better performance and lower fabrication costs is to achieve enhanced pinning in a practical way. In this work, we demonstrate a simple and industrially scaleable route that yields a 1.5-5-fold improvement in the in-magnetic-field current densities of conductors that are already of high quality.