Optimal characteristic polynomials for digital multistep pseudorandom numbers

The digital multistep method generates uniform pseudorandom numbers by transforming sequences of integers obtained by multistep recursions. The statistical independence properties of these pseudorandom numbers depend on the characteristic polynomial of the recursion. We describe a method of calculating characteristic polynomials that are optimal with respect to statistical independence of pairs of successive pseudorandom numbers. Tables of such optimal characteristic polynomials for degrees ≤64 are included.     

Referenzprozesse für elektronische Ausschreibungen aus Sicht des industriellen Einkaufs

Many companies and purchasing departments only possess a limited knowledge about the modelling of inter-company business processes for electronic procurement. In the past the discussion about electronic procurement was mostly focused on technical aspects. This article introduces a reference process model for procurement auctions. The process model is made up of a basic process, which describes a minimal process for procurement auctions, and a number of process alternatives, which allow for the adoption of the basic process to changing parameters and individual company requirements.     

Simulationsmodell zur Bestimmung der magnetischen Eigenschaften von Transformatorkernen bei nichtharmonischer Erregung

Übersicht Ausgehend von der modellmäßigen Domänenstruktur ferromagnetischer Werkstoffe werden für den Bereich einer 180°-Blochwand die Kräfte zwischen magnetischen Elementardipolen untereinander und gegenüber einem äußeren Magnetfeld berechnet und so die Blochwanddynamik erfaßt. Da nicht alle benötigten Parameter aus der atomaren Struktur des Werkstoffs ableitbar sind, werden die freien Parameter durch Anpassung der Simulation an eine z.B. B-H-Messung 50 Hz festgelegt. Ziel dieses so kalibrierten Modells ist es, Aussagen zum Werkstoffverhalten in Betriebsbereichen zu liefern, die durch normgerechte Werkstoffbewertung nicht abgedeckt und für den praktischen Einsatz von Interesse sind. Als Anwendungsbeispiel wird die B-H-Charakteristik eines Transformatorkerns bei Impulserregung simuliert. Obwohl die Übereinstimmung mit Messungen gut ist, weisen detailliertere Betrachtungen auf eine verbesserungsfähige Verlustmodellierung hin.

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Simulation model to determine the magnetic properties of transformer cores for non-harmonic excitation

Contents Employing the modelled domain structure in ferromagnetic material, for the area of a 180° blochline the forces between the atomic magnetic dipoles and by an outer magnetic field are calculated and so the dynamic properties of the blochline are considered. Because not all required parameters can be derived from the atomic structure of the material, the remaining parameters are set by adapting the simulation to measured values e.g. for 50 Hz. The aim of the so calibrated model is to determine the behaviour of the material for working conditions, which cannot be investigated by standardized measurings but are of special interest. As an example of application the hysteresis loop of a pulse stressed transformer core is simulated. Although the correspondence with the measured values is quite good, on closer inspection an improvable loss modelling is indicated.

     

Radiale Wärmeleitung in durchströmten Schüttungsrohren

Heat Transport to the Wall of Packed Tubes. Radial conduction of heat in packed tubes has a crucial influence on yield and selectivity of many heterogeneously catalyzed reactions. In spite of many years of intensive research in the field, there are still tremendous discrepancies between correlations of different origin. Even the standard model using two constant heat transport parameters, which was introduced in the fifties and has since become most widely accepted, has been controversially discussed and called into question. The unsatisfactory state of the art has been an incentive for several groups of researchers to take up this old topic once again. Three parallel experimental investigations on heat transport with air flowing in packed tubes of similar dimensions, electrically heated, steam-heated, or water-cooled, were completed in 1991. Comparative evaluation of the results of these three investigations, together with other data from the relevant literature, now provides the first clear answers to some of the questions so controversially discussed in the past.