1,138 research outputs found
Single grain (LRE)-Ba-Cu-O superconductors fabricated by top seeded melt growth in air
We have recently reported a practical processing method for the fabrication in air of large, single grain (LRE)-Ba-Cu-O [where LRE Nd, Sm, Eu and Gd] bulk superconductors that exhibit high Tc and high Jc. The process is based initially on the development of a new type of generic seed crystal that can promote effectively the epitaxial nucleation of any (RE)-Ba-Cu-O system and, secondly, by suppressing the formation of (LRE)/Ba solid solution in a controlled manner within large LRE-Ba-Cu-O grains processed in air. In this paper we investigate the degree of homogeneity of large grain Sm-Ba-Cu-O superconductors fabricated by this novel process. The technique offers a significant degree of freedom in terms of processing parameters and reproducibility in the growth of oriented single grains in air and yields bulk samples with significantly improved superconducting and field-trapping properties compared to those processed by conventional top seeded melt growth (TSMG)
Automatic detection of end QRS notching or slurring
The purpose of this study was to define criteria suited to automated detection of end QRS notching and slurring and to evaluate their accuracy. One hundred resting 12 lead ECGs from young adult men, split randomly into equal training and test sets, were examined independently by two reviewers for the presence of such notching or slurring. Consensus was reached by re-examination. Logic was added to the Glasgow resting ECG program to automate the detection of the phenomenon. After training, the automated detection had a sensitivity (SE) of 92.1% and a specificity (SP) of 96.6%. For the test set, SE was 90.5%, SP 96.5%. Two populations of healthy subjects – one Caucasian, one Nigerian – were analysed using the automated method. The prevalence of notching/slurring with peak/onset amplitude respectively ≥ 0.1 mV in two contiguous inferolateral leads was 23% and 29% respectively. In conclusion, the detection of end QRS notching or slurring can be automated with a high degree of accuracy
Anisotropic Superconducting Properties of MgB2 Single Crystals
In-plane electrical transport properties of MgB2 single crystals grown under
high pressure of 4-6 GPa and temperature of 1400-1700oC in Mg-B-N system have
been measured. For all specimens we found sharp superconducting transition
around 38.1-38.3K with transition width within 0.2-0.3K. Estimated resistivity
value at 40K is about 1 mkOhmcm and resistivity ratio R(273K)/R(40K) of about
4.9. Results of measurements in magnetic field up to 5.5T perpendicular to Mg
and B planes and up to 9T in parallel orientation show temperature dependent
anisotropy of the upper critical field with anisotropy ratio increasing from
2.2 close to Tc up to about 3 below 30K. Strong deviation of the angular
dependence of Hc2 from anisotropic mass model has been also found.Comment: 10pages, including 5 figures,submitted to Physica C (in press
Effect of La Doping on Microstructure and Critical Current Density of MgB2
In the present study, La-doped MgB_2 superconductors with different doping
level (Mg1-xLaxB2; x=0.00, 0.01, 0.03 & 0.05) have been synthesized by
solid-state reaction route at ambient pressure. Effect of La doping have been
investigated in relation to microstructural characteristics and superconducting
properties, particularly intragrain critical current density (Jc). The
microstructural characteristics of the as synthesized Mg(La)B2 compounds were
studied employing transmission electron microscopic (TEM) technique. The TEM
investigations reveal inclusion of LaB6 nanoparticles within the MgB2 grains
which provide effective flux pinning centres. The evaluation of intragrain Jc
through magnetic measurements on the fine powdered version of the as
synthesized samples reveal that Jc of the samples change significantly with the
doping level. The optimum result on Jc is obtained for Mg0.97La0.03B2 at 5K,
the Jc reaches ~1.4x107A/cm2 in self field, ~2.1 x 106A/cm2 at 1T, ~2.5 x
105A/cm2 at 2.5T and ~1.8 x 104 A/cm2 at 4.5T. The highest value of intragrain
Jc in Mg0.97La0.03B2 superconductor has been attributed to the inclusion of
LaB6 nanoparticles which are capable of providing effective flux pinning
centres
Evidence for high inter-granular current flow in single-phase polycrystalline MgB2 superconductor
The distribution of magnetic field in single-phase polycrystalline bulk MgB2
has been measured using a Magneto-Optical (MO) technique for an external
magnetic field applied perpendicular to the sample surface. The MO studies
indicate that an inter-granular current network is readily established in this
material and the current is not limited by weak-linked grain boundaries. The
grain boundaries are observed to resist preferential magnetic field
penetration, with the inter-grain mechanism dominating the current flow in the
sample at temperatures up to 30K. The results provide clear evidence that the
intra-granular current flow is isotropic. A critical current density of ~10^4
Acm-2 was estimated at 30K in a field of 150mT from the MO measurements. These
results provide further evidence of the considerable potential for MgB2 for
engineering applications.Comment: 3 pages, 3 figure
Keldysh study of point-contact tunneling between superconductors
We revisit the problem of point-contact tunnel junctions involving
one-dimensional superconductors and present a simple scheme for computing the
full current-voltage characteristics within the framework of the
non-equilibrium Keldysh Green function formalism. We address the effects of
different pairing symmetries combined with magnetic fields and finite
temperatures at arbitrary bias voltages. We discuss extensively the importance
of these results for present-day experiments. In particular, we propose ways of
measuring the effects found when the two sides of the junction have dissimilar
superconducting gaps and when the symmetry of the superconducting states is not
the one of spin-singlet pairing. This last point is of relevance for the study
of the superconducting state of certain organic materials like the Bechgaard
salts and, to some extent, for ruthenium compounds.Comment: 10 pages, 4 figure
Microstructure and superconducting properties of hot isostatically pressed MgB2
Bulk samples of MgB2 have been formed by hot isostatic pressing (HIPping) of
commercial powder at 100MPa and 950=B0C. The resulting material is 100% dense
with a sharp superconducting transition at 37.5K. Microstructural studies have
indicated the presence of small amounts of second phases within the material,
namely MgO and B rich compositions, probably MgB4. Magnetisation measurements
performed at 20K have revealed values of Jc=1.3 x 106A/cm2 at zero field, and
9.3 x 105A/cm2 at 1T. Magneto optical (MO) studies have shown direct evidence
for the superconducting homogeneity and strong intergranular current flow in
the material.Comment: 3 pages, 6 figures, text updated, new references included and
discussed. Submitted to Superconductor Science and Technolog
High critical current densities in superconducting MgB2 thin films
Superconducting MgB2 thin films were prepared on Al2O3(0001) and MgO(100)
substrates. Boron thin films were deposited by the electron-beam evaporation
followed by post-annealing process with magnesium. Proper post annealing
conditions were investigated to grow good superconducting MgB2 thin films. The
X-ray diffraction patterns showed randomly orientated growth of MgB2 phase in
our thin films. The surface morphology was examined by scanning electron
microscope (SEM) and atomic force microscope (AFM). Critical current density
(Jc) measured by transport method was about 10^7 A/cm^2 at 15 K, and
superconducting transition temperature (Tc) was ~ 39 K in the MgB2 thin films
on Al2O3.Comment: 13 pages, 4 figures, submitted on Apr. 4, 2001, only one pdf fil
Renminbi Internationalisation: Precedents and Implications
While it is commonly assumed that there are no known precedents against which to benchmark the internationalisation of the Renminbi (RMB), this paper argues that the PRCs own development experience provides a useful perspective on the internationalisation debate. In particular it indicates that lessons can be learnt from both the successes and the shortcomings of efforts to internationalise the RMB in the 1970s. During this period state-owned banks in Hong Kong played a central role in mobilising finance for foreign trade. Access to Hong Kong’s developed financial institutions allowed the PRC to maximise receipts from foreign trade as well as minimise the risks of undue swings in capital flows. The paper shows that although China no longer faces foreign exchange scarcity, economic reforms have not yet resolved vulnerabilities in China’s financial institutions and as such Hong Kong’s role in mitigating the risk of undue capital swings remains
Association of MUTYH and colorectal cancer
Mutations in the MUTYH gene have been reported to be associated with increased risk of developing colorectal cancer. In this study, we confirmed this association using original data on 928 colorectal cancer cases and 845 healthy controls from Scotland. We then conducted a meta-analysis from published data on the association between mutations at MUTYH and colorectal cancer risk. We show for the first time a small but significant mono-allelic effect with a genotype relative risk (GRR) of 1.27 (95% confidence interval (CI): 1.01–1.61), and confirm and give a more precise estimate of the strong bi-allelic effect with an estimated GRR of 117 (95% CI: 74–184). This study underscores the need for large sample sizes in order to identify small gene effects when the disease allele frequency is low
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