Zur Genauigkeit der Vanadiumbestimmung durch volumetrische und coulometrische Titration

Zusammenfassung Für die Vanadiumbestimmung in supraleitenden Verbindungen, z.B. V₃Si, sind relative Standardabweichungen < 0,001 erforderlich, wobei die Richtigkeit innerhalb dieser Grenzen garantiert werden muß. Es wird untersucht, unter welchen Bedingungen die volumetrische Titration mit Eisen(II) und die coulometrische Titration mit Eisen(II) und Kupfer(I) mit potentiometrischer Äquivalenzpunktsindikation diese Anforderungen erfüllen. Dafür werden Titrationskurven zur Ermittlung der Lage des Äquivalenzpunktes und der Potentialänderungen in dessen Nähe berechnet. Daraus und aus Untersuchungen zur Stromausbeute bei der coulometrischen Titration lassen sich optimale Analysenbedingungen ableiten. Ein Verfahren zur Vanadiumbestimmung in V₃Si wird beschrieben.

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Accuracy of the determination of vanadium by volumetric and coulometric titration in silicovanadium

Summary For the determination of vanadium in superconducting compounds, e.g. V₃Si, relative standard deviations < 0.001 are required and any systematic error must not exceed this limit. Conditions are investigated, on which the volumetric titration with iron(II) and the coulometric titration with iron(II) and copper(I) using potentiometric detection of the equivalent point fulfill these requirements. Titration curves are calculated to identify the position of the equivalent point and the changes of potential in its vicinity. From these calculations and from investigations of current efficiency in the case of coulometric titration optimum conditions for analysis are deduced. A method for the determination of vanadium in V₃Si with high accuracy is described.

Gleichermaßen gilt unser Dank Herrn Dr. R. Stahlberg für die Förderung dieser Arbeit.     

On decomposition theory for unitary representations of locally compact groups

The main purpose of this note is to give a simple example of a unitary representation of a (discrete) group, which cannot be decomposed as a topological direct integral of factor representations. But it is shown that the regular representation of any discrete group is a direct integral (on a compact space) of factor representations.     

Deformation von Gorenstein-Singularitäten der Kodimension 3

Ohne Zusammenfassung     

Spiroconjugation

Spiro compounds having mutually perpendicular π-electron systems (“spiro-polyenes”) exhibit a new kind of homoconjugation, which is designated as spiroconjugation. Spiro-polyenes are readily accessible, e.g. by cycloaddition, by elimination of dinitrogen from 1,2-diazaspiro-polyenes, and by cyclization of carbenium ions or carbanions. The magnitude of the effect exerted by spiroconjugation is estimated by model calculations. It can be detected, for instance, by comparison of the electronic and photoelectron spectra of spiro-polyenes and analogous compounds which are unable to undergo such interaction.     

Experimental investigations on a toroidal screw pinch

High-β Deuterium plasmas in a temperature range of 0.1–1 keV were produced in the fast toroidal screw pinch experiment ISAR IV (B _max≈33 kG,I _{z max}≈100–150 kA, coil diameter 12 cm, aspect ratio 5). The experimentally determined growth rates of the appearing instabilities—especially them=1 mode—are compared with two simple models and a more exact numerical calculation. This comparison and direct measurements of the magnetic field distribution show that the constant pitch model of Bobeldijk¹ is a suitable first approximation for the normal screw pinch. Using a delay of thez and θ-bank as a first simple method of field programming this constant pitch profil could be varied in different directions. The results are discussed in more detail and confirm the theoretical picture of stability behaviour of the high-β screw pinch.