Fabrication of high performance Gd–Ba–Cu–O single grains in air using a practical melt processing technique

A practical processing route for the fabrication of LRE-Ba–Cu–O single grain superconductors has been developed at the University of Cambridge based on a generic, Mg-doped Nd-123 melt textured seed and suppression of the formation of the solid solution phase in air by enriching the precursors with higher Ba concentration. The processing of high performance Gd–Ba–Cu–O single grains using this processing route is described. The Mg-doped generic seed crystal has been used effectively to promote heterogeneous nucleation via a cold-seeding process. The Gd/Ba solid solution has been suppressed by enriching Gd–Ba–Cu–O precursor powders with two different Ba-rich compositions. This involved adding BaO₂ and GdBa₆Cu₃O_y (Gd-163) (a novel Ba-rich second phase) to the precursor powders, respectively. The Gd-163 phase has been observed not only to suppress formation of the solid solution phase, but also to promote increased heterogeneous grain size. A detailed further study has been carried out with an initial aim of optimizing the BaO₂ and Gd-163 phase content of the precursor composition to produce a single grain almost free of solid solution. Based on the optimized parameters, large single grain Gd–Ba–Cu–O superconductors have been fabricated in an air atmosphere and demonstrated to exhibit record trapped magnetic fields for this material melt processed in air in relatively small single grain samples. The trapped fields of samples produced in air atmosphere are at least comparable to those processed under reduced oxygen partial pressure.     

Repetitive spectral subtraction method for the spectrophotometric determination of rare earth elements

Summary A new multiwavelength data-analysis method for the determination of multicomponent mixtures, the repetitive spectral subtraction method (RSSM), is proposed. In RSSM, spectral data are obtained at evenly spaced wavelengths in the range of interest, and the analysis of the spectrum is performed as repetitive determination-subtraction cycle. In the determination step, the series of data in the narrow wavelength range is used, which is specified as to include the most characteristic or the largest peak for each component. Assuming a linear background, the target component, which can be a small group of components, is simultaneously determined together with co-existing components. In the next subtraction step, the calculated contribution of the component is subtracted from the spectral data in the whole measured wavelength range, and the component is assigned as determined and is excluded from the following analysis. This determination-subtraction cycle is repeated until all the components are determined.With RSSM, a mixture of many components can be precisely determined by the use of most information contained in the spectrum. The accuracy of determination can be improved by automatic estimation of the background and the gradual decrease of interferences. In order to demonstrate the usefulness of RSSM, the 8 rare earth elements (Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm) in the model mixtures were determined by spectrophotometry, and the results were compared with those of the usual correction factor method and the derivative method. Furthermore, the 8 rare earth elements were determined in ores, monazite and xenotime.

---

Spektralphotometrische Bestimmung von Seltenen Erden mit Hilfe eines Verfahrens der wiederholten Subtraktion

     

Sensitive determination of tyrosine metabolites, p-hydroxyphenylacetic acid, 4-hydroxy-3-methoxyphenyl-acetic acid and 4-hydroxy-3-methoxymandelic acid, by gas chromatography-negative-ion chemical-ionization mass spectrometry. Application to a stable isotope-labelled tracer experiment to investigate their metabolism in man

A method has been established for studying the dynamic metabolism of tyrosine to its metabolites in humans using a deuterium-labelled amino acid. Phenylalanine-d5 was administered orally to human subjects (5 mg/kg) and the levels of p-hydroxyphenylacetic acid-d4, 4-hydroxy-3-methoxyphenylacetic acid-d3, and 4-hydroxy-3-methoxymandelic acid-d3 excreted into urine every hour were determined by gas chromatography-negative-ion chemical-ionization mass spectrometry. This method was also applied to some patients with depression and it was possible to detect a slight alteration in the excretion of some compounds compared with the control.     

Analysis of red phosphorus in resins using pyrolysis-gas chromatography/mass spectrometry.

Although red phosphorus is used as a flame retardant for polymer materials, no analysis methods for it in resins has been established. Analysis methods for red phosphorus in resins were investigated using pyrolysis-gas chromatograpy/mass spectrometry (Py-GC/MS) by paying attention to the fact that it has a sublimation property. We found that the mass spectrum of red phosphorus shows a series of ions at m/z=62, 93 and 124, and a fragment pattern indicating that red phosphorus (P4=124, P=31) was pyrolytically decomposed. The coefficient of the correlation between the content of red phosphorus in the resin and the peak intensity in Py-GC/MS was 0.9781. The relative standard deviations of this analysis method was 6.29% (n=5). Py-GC/MS was applicable not only to qualitative analysis but also to the quantitative analysis of red phosphorus.     

Enantioselective preparation of C-ring fragment of cotylenin A via catalytic asymmetric intramolecular cyclopropanation of α-diazo β-keto ester

A synthetic pathway to the C-ring fragment of cotylenin A which emerged from our retrosynthetic analysis of cotylenin A is described. The catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of the α-diazo-β-keto ester bearing 2,4,6-trimethylphenyl group as the ester part has been found to afford the crystalline product with high ee, which allowed to establish the approach to the C-ring fragment which required ten-pot operations. The developed approach would be beneficial to a large scale synthesis of the C-ring fragment for the total synthesis of cotylenin A.     

Octave-spanning carrier-envelope phase stabilized visible pulse with sub-3-fs pulse duration

The visible second harmonic of the idler output from a noncollinear optical parametric amplifier was compressed using adaptive dispersion control with a deformable mirror. The amplifier was pumped by and seeded in the signal path by a common 400 nm second-harmonic pulse from a Ti:sapphire regenerative amplifier. Thus, both the idler output and the second harmonic of the idler were passively carrier-envelope phase stabilized. The shortest pulse duration achieved was below 3 fs.     

Singularities of Blaschke normal maps of convex surfaces

We prove that the difference between the numbers of positive swallowtails and negative swallowtails of the Blaschke normal map for a given convex surface in affine space is equal to the Euler number of the subset where the affine shape operator has negative determinant.