61 research outputs found
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
Upper critical field and irreversibility line in superconducting MgB_2
The upper critical field Hc2(T) of sintered pellets of the recently
discovered MgB_2 superconductor was investigated by transport, ac
susceptibility and dc magnetization measurements in magnetic fields up to 16 T
covering a temperature range between Tc ~ 39 K and T = 3 K ~ 0.1Tc. The
temperature dependence of the upper critical field, Hc2(T), shows a positive
curvature near Tc similar to that found for the borocarbides YNi_2B_2C and
LuNi_2B_2C indicating that MgB_2 is in the clean limit. The irreversibility
line was consistently determined from dc magnetization measurements and from
the imaginary component of ac susceptibility. The irreversibility field was
found to increase up to 8.5 T at 10 K.Comment: 8 pages with 5 figures, submitted to Solid State Communication
Magnetic anomalies in the spin chain system, SrCuZnIrO
We report the results of ac and dc magnetization (M) and heat-capacity (C)
measurements on the solid solution, SrCuZnIrO. While the Zn
end member is known to form in a rhombohedral pseudo one-dimensional
KCdCl structure with an antiferromagnetic ordering temperature of
(T =) 19 K, the Cu end member has been reported to form in a monoclinically
distorted form with a Curie temperature of (T =) 19 K. The magnetism of the
Zn compound is found to be robust to synthetic conditions and is broadly
consistent with the behavior known in the literature. However, we find a lower
magnetic ordering temperature (T) for our Cu compound (~ 13 K), thereby
suggesting that T is sensitive to synthetic conditions. The Cu sample
appears to be in a spin-glass-like state at low temperatures, judged by a
frequency dependence of ac magnetic susceptibility and a broadening of the C
anomaly at the onset of magnetic ordering, in sharp contrast to earlier
proposals. Small applications of magnetic field, however, drive this system to
ferromagnetism as inferred from the M data. Small substitutions for Cu/Zn (x =
0.75 or 0.25) significantly depress magnetic ordering; in other words, T
varies non-monotonically with x (T ~ 6, 3 and 4 K for x = 0.25, 0.5, and
0.67 respectively). The plot of inverse susceptibility versus temperature is
non-linear in the paramagnetic state as if correlations within (or among) the
magnetic chains continuously vary with temperature. The results establishComment: 7 pages, 7 figures, Revte
Evidence for strong electron-phonon coupling in MgCNi_3
The title compound is investigated by specific heat measurements in the
normal and superconducting state supplemented by upper critical field
transport, susceptibility and magnetization measurements. From a detailed
analysis including also full potential electronic structure calculations for
the Fermi surface sheets, Fermi velocities and partial densities of states the
presence of both strong electron-phonon interactions and considerable
pair-breaking has been revealed. The specific heat and the upper critical field
data can be described to first approximation by an effective single band model
close to the clean limit derived from a strongly coupled predominant hole
subsystem with small Fermi velocities. However, in order to account also for
Hall-conductivity and thermopower data in the literature, an effective general
two-band model is proposed. This two-band model provides a flexible enough
frame to describe consistently all available data within a scenario of phonon
mediated s-wave superconductivity somewhat suppressed by sizeable
electron-paramagnon or electron-electron Coulomb interaction. For quantitative
details the relevance of soft phonons and of a van Hove type singularity in the
electronic density of states near the Fermi energy is suggested.Comment: 21 pages, 26 figures (high quality version of figures 2,11 available
at http://www.ifw-dresden.de/imw/21/coworker/waelte.priv/
Overall complication rates of DIEP flap breast reconstructions in Germany – a multi-center analysis based on the DGPRÄC prospective national online registry for microsurgical breast reconstructions
While autologous breast reconstruction has gained momentum over recent years, there is limited data on the structure and quality of care of microsurgical breast reconstruction in Germany. Using the breast reconstruction database established by the German Society of Plastic, Reconstructive and Aesthetic Surgeons (DGPRÄC), the presented study investigated the overall outcomes of deep inferior epigastric perforator (DIEP) flap reconstructions in Germany. Data of 3926 patients and 4577 DIEP flaps performed by 22 centers were included in this study. Demographics, patient characteristics, perioperative details and postoperative outcomes were accounted for. Centers performing < Ø 40 (low-volume (LV)) vs. ≥ Ø 40 (high-volume (HV)) annual DIEP flaps were analyzed separately. Overall, total and partial flap loss rates were as low as 2.0% and 1.1% respectively, and emergent vascular revision surgery was performed in 4.3% of cases. Revision surgery due to wound complications was conducted in 8.3% of all cases. Mean operative time and length of hospital stay was significantly shorter in the HV group (LV: 385.82 min vs. HV: 287.14 min; LV: 9.04 (18.87) days vs. HV: 8.21 (5.04) days; both p < 0.05). The outcome and complication rates deduced from the national registry underline the high standard of microsurgical breast reconstruction on a national level in Germany
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