Nonaxisymmetric electroelastic vibrations of a hollow sphere made of functionally gradient piezoelectric material

The nonaxisymmetric problem of natural vibrations of a hollow sphere made of functionally gradient piezoelectric material is solved based on 3D electroelasticity. The properties of the material change continuously along a radial coordinate according to an exponential law. The external surface of the sphere is free of tractions and either insulated or short-circuited by electrodes. After separation of variables and representation of the components of the displacements and of the stress tensor in terms of spherical functions, the initially three-dimensional problem is reduced to a boundary-value problem for the eigenvalues expressed by ordinary differential equations. This problem is solved by a stable discrete-orthogonalization technique in combination with a step-by-step search method with respect to the radial coordinate. Moreover, a numerical investigation is performed based on the algorithm used for solving the problem. In particular, we investigate the influence of the geometric and electric parameters on the frequency spectrum at the nonaxisymmetry of natural vibrations of an inhomogeneous piezoceramic thick-walled sphere.     

A Raman study of the structural properties of YBa2(Cu1 − xFex)3Oy

The effects of Fe-substitution of YBa₂Cu₃O_y have been investigated by means of Raman scattering, X-ray diffraction, resistivity and susceptibility measurements. A series of samples of YBa₂(Cu_{1 − x}Fe_x)₃O_y with different dopant concentration (0 x 0.15) has been prepared in two batches, the second set having undergone twice the heat and mechanical treatment used to produce the first batch. Considerable improvement in the superconducting transition temperature, T_c, is obtained upon reprocessing. A phase transformation from orthorhombic to tetragonal symmetry is observed for x=0.05 from the X-ray measurements in agreement with previous work. Using a micro-Raman technique, all five A_g vibrational modes have been measured and their dependence on Fe-concentration is analyzed. There are indications that iron substitutes for copper at both sites and that the structure is a mixture of orthorhombic and tetragonal microdomains for all x.     

Monotone Operatoren mit Störungen

Ohne Zusammenfassung Vorgelegt von J. C. C. Nitsche     

Photometrische Aluminiumbestimmung in Stahl mit Eriochromcyanin ohne Abtrennung des Eisens

Zusammenfassung Das beschriebene Verfahren zur Aluminiumbestimmung in Stahl eignet sich in erster Linie als Betriebsverfahren, da es im Vergleich zu den bisher gebräuchlichen Methoden eine relativ kurze Arbeitszeit und einen geringen betrieblichen Aufwand benötigt.Die Schwierigkeit liegt im Grunde nur bei der vollständigen Erfassung des Fe³⁺ durch die Thioglykolsäure. Die ermittelten Ergebnisse sind in ihrer Reproduzierbarkeit und Genauigkeit, bei den hier vorgeschlagenen Mengenbereichen, den durch andere Verfahren erzielten Werten gleichzusetzen und zum Teil sogar überlegen. Die Standardabweichung beträgt ±0,004% für Gehalte bis 1,4% Al.

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Photometric determination of aluminium in steel using Eriochrome cyanine without separation of iron

Reference It could be shown, that the photometric Eriochromecyanine method is advantageous because of its accuracy and simple handling in the scope of factory analysis. In this technique aluminium is bound as colour lake and photometrically measured in the presence of iron, which is masked by thioglycollic acid. The reproducability of the results is comparable and in some parts even better than that of other methods. The standard deviation is ±0.004% for up to 1.4% Al.

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An dieser Stelle sei dem Direktor des Instituts für Eisenhüttenkunde an der Technischen Universität Berlin, Herrn o. Prof. Dr. phil. Franz Oeters, für das der Arbeit entgegengebrachte Interesse gedankt.     

Topological characterizations of linearly uniformizable spaces

The spaces having uniformities with a totally ordered base are characterized in bigger classes of non-archimedean spaces and suborderable spaces. Consequently, several new metrization results are obtained. By examples, we show that the conditions used in our main theorem cannot be weakened essentially. Our examples may be interesting elsewhere, too.