Mechanical properties of SBR-networks: I. Determination of crosslink densities by stress-strain-measurements

The tube model is applied for the treatment of stress-strain measurements on SBR networks. It is shown that this theory allows the separation of crosslink and constraint contributions to the stress-strain behavior and, also, a reliable determination of crosslink densities. The consideration of dynamical contributions is discussed and a special numerical method is developed.     

Towards a European Research Area

Research in Europe is not coordinated enough and is too reticent about knowledge transfer. EU Research and Development Commissioner Philippe Busquin aims to change this. His “Communication” on European research, presented in January, has been widely discussed over the past few months. A detailed statement of the CDCh will be presented in our next issue.     

Ba3WFe2O9 (P63mmc and Ba3WFe2O8.42(5) (Fm3m): Comparative study of the crystallographical and magnetic properties

Ba₃WFe₂O₉ has a hexagonal structure which belongs to space group $\text{P6}{}_3\text{mmc}$. Heated at 1350°C under a stream of helium, this compound gives an oxygen-deficient phase, the structure of which is ordered cubic (space group Fm3m). This passage from a hexagonal structure to a cubic structure is consistent with the decrease of the Goldschmidt tolerance factor resulting from the Fe³⁺ partial reduction. Ba₃WFe₂O_8.42(5) (cubic) was compared with Ba₃WFe₂O₉ (hexagonal) and Sr₃WFe₂O_8.85(3) (cubic) as to the crystallographical and magnetic properties. The study of the thermal stability in air for Ba₃WFe₂O_8.42(5) revealed a reoxidation in several steps and the existence of a new cubic compound, stable in air over a broad range of temperature, the formula of which may be written as Ba₃WFe₂O_8.71(5).     

A synthetic acceleration scheme for radiative diffusion calculations

A synthetic method has been developed to accelerate the iterative convergence of the multigroup radiative diffusion equations with temporally implicit material-radiation coupling. The performance of the method is characterized by means of a Fourier analysis. Computational results are given and are found to be consistent with the analysis. Overall, the method appears to be quite effective.