Verbessertes Widerstandsgesetz für Stufendiffusoren

Zusammenfassung Es wird ein allgemeines Widerstandsgesetz für Stufendiffusoren hergeleitet, bei dem die Widerstandszahl den Zusatzverlust gegenüber den Verlusten der bis zum Kontursprung reichenden fiktiven Kanal- bzw. Rohrstr?mungen in der Zu- und Abstr?mung beschreibt. Unter vereinfachenden Annahmen reduziert sich dieses Gesetz auf die bekannte Carnot-Formel. Insbesondere wird dabei der Anteil des Zusatzverlustes, der vom Unterdruck an der Stufe und von der Wandschubspannungs?nderung unmittelbar hinter der Stufe herrührt, vernachl?ssigt. Die Berücksichtigung dieses Anteils führt zu einem gegenüber der Carnot-Formel verbesserten Widerstandsgesetz. Herrn Prof. Dr.-Ing. Martin Fiebig zum 60. Geburtstag     

Production and properties of micro‐porous glas bubble zinc and aluminium composites

Micro‐porous syntactic foams were produced by means of integration of glass bubbles into aluminium and zinc matrices. Preforms of glass bubbles were pressure infiltrated with the alloys AlSi9Cu9 ans ZnAl4Cu using squeeze casting. The preforms were sintered thermically without the use of bonding agents. Using the combination of different sintering steps syntactic foams with locally different densities could be produced. The mechanical properties of the foams were tested indicating a high compression strength of the foams and a very good compression energy absorption. Furthermore, corrosion behaviour and behaviour at higher temperatures were investigated.     

Fast method to compute the scalar product of gradient and given vector

The paper deals with a special problem in Automatic Differentiation. Letf be a rational function ofn variables, let #(f) denote the number of operations to evaluatef(x), letg denote the gradient off. Many algorithms for minimizingf(x) require the scalar productg(u) ^tv. In the standard method for computingg(u) ^tv the amount of work grows withn·#(f). In this note a new method for computingg(u) ^tv is presented. The new method is considerably faster, its amount of work only grows with #(f).     

The possibility of evolving a theory for predicting the service life of reinforced concrete structures

The development in recent years with increasing air pollution, increasing need of energy saving and last not least the growing number of damage in old structures leads to a raising demand to calculate the durability of structures, too. The paper has been prepared by request of the RILEM Technical Committee 45-LTO to show that, in principle, it is possible to evolve a theory for predicting the service life of r.c. structures and to sketch a way how that could be achieved. A lot of necessary basic data can be found scattered in the literature. To collect these data will be the first step to take.     

Embedding universal computer arithmetic in higher programming languages

In numerical computations mainly real and complex numbers, intervals as well as matrices and vectors with such components occur. It is well known that the arithmetic operations with real numbers, complex numbers etc. can be carried over to real floating-point numbers, complex floating-point numbers etc. using roundings. This proceeding results in agreeable arithmetic-, order- and compatibility-properties for an abundance of numerical data types and the accompanying arithmetic operations. Most programming languages however only provide real floating-point numbers; all the other data types and operations have to be simulated, e. g. in the form of arrays and procedure calls, which often causes loss of accuracy and arithmetic properties. Furthermore the complicate notation makes programs difficult to read. Therefore in this article an extension of PASCAL is presented which serves as an example for the way these numerical data types can be embedded into the syntax of a programming language.     

Simple and modified rule of mixtures of deformation parameters in stage III of single ductile fibre-ductile matrix composites

By employing a single thick molybdenum fibre-copper matrix composite with very weak interfacial bonding, it was confirmed that flow stress, internal stress, effective stress and change in flow stress due to change in strain rate of the composite obey the simple rule of mixtures; strain-hardening exponent, stress exponent of strain rate, effective stress exponent of dislocation velocity and activation volume obey the modified rule of mixtures in the whole range of plastic deformation of the composite. This means that the inherent features of the fibre in the present composite were conserved beyond the failure strain of the fibre tested alone, and the above deformation parameters of the composite were, to a first approximation, determined by the inherent parameters of the fibre and the matrix.     

How to avoid logarithms in comparisons with uniform random variables

In many algorithms for sampling from non-uniform distributions the logarithm of a uniform deviate must be compared with some test quantity. It is shown that all these comparisons can be done efficiently without calling a logarithm subprogram: two procedures for this task are presented and compared.