Vorgänge bei der Bildung primärer Desoxydationsprodukte in Stählen

Desoxydation unlegierter Stahlschmelzen mit Titan; Versuchsdurchführung. Auswertung der Ergebnisse für die verschiedenen Eisenschmelzen mit Vergleichen zur Aluminiumdesoxydation. Deutung der Versuchsergebnisse. Einschlußuntersuchung mittels Rückstandsuntersuchung. Desoxydation nichtrostender Chrom-Nickel-Stähle mit Aluminium. Folgerungen.     

Shear test for thermoplastic polymers

A shear test is proposed as a complement to the tensile test in order to characterize the short time mechanical behavior of thermoplastic polymers. The proposed test geometry makes the test easy to perform and to evaluate and gives relevant information about anisotropy, plastic deformation, crack initiation, and propagation properties. Three different materials have been tested and the results are discussed.     

A Thermodynamic Model of the EAF Process for Stainless Steel

A time‐dependent thermochemical model has been developed for the electric arc furnace (EAF) process for stainless steel production. Time dependency is implemented by a stepwise input of energy and matter into an equilibrium reactor. The equilibrium calculations are performed using data from FACT‐databases and implemented using the programming library ChemApp. The material input for the model was generated by reconciliation of industrial data and the energy input is approximated from the industrial data and scaled through an efficiency factor. The model is used to calculate the evolution of temperature and composition of gas, slag and metal phases with time. Agreement of the end composition in the metal phase with industrial data is good. In the slag phase, however, Cr, Fe, Mn and Si are oxidized significantly less than expected due to excess formation of CO‐gas. The dynamics of the slag composition are examined in more detail. Here a fair agreement is reached for the main slag components. However, for Cr, Fe and Mn the model cannot predict the dynamics, which seem to be strongly kinetically controlled. The results of the equilibrium model can thus provide some insight into the kinetics of the process.     

Kristalline und flüssigkristalline copolyester substituierter und unsubstituierter 4-hydroxybenzoesären

Three synthetic strategies were explored to lower the melting point of poly(4-hydroxybenzoate) below 400°C. Binary copolyesters of 4-hydroxybenzoic acid and 3-substituted 4-hydroxybenzoic acid were highly crystalline, regardless of composition, and did not melt below 400°C. In contrast ternary and quartenary copolyesters containing 3-bromo-4-hydroxybenzoic acid may possess melting points below 360°C. Binary copolyesters of 4-mercaptobenzoic acid and 3-substituted 4-hydroxybenzoic acids melt in the range of 360–400°C. Random copolyesters of 3-(4-hydrophenyl) propionic acid and 4-hydroxybenzoic acid are mainly amorphous with glass-transition temperatures between 50 and 15°C. They contain liquid-crystalline domains, which in the case of the 1:1 copolyester are stable over a range of ca. 400°C. The heat-distortion temperatures are low (60–80°C) due to the predominant influence of the amorphous matrix.     

DNA microarray enhancement using a continuously and discontinuously rotating microchamber

It is demonstrated that the most efficient way to enhance DNA microarray analysis consists of a maximal reduction of the total device volume (to keep the concentration of the available DNA as high as possible), combined with the creation of a strong lateral convective transport of the sample. In the present study, DNA microarray hybridizations are performed in a set of rotating, circular microchambers covering exactly the spotted area of the microarray and with a depth varying between 70 and 1.6 microm. Rotating the microchamber substrate while keeping the microarray stationary, the rotating microchamber bottom wall literally drags the sample past the microarray spots with a velocity which is independent of the fluid layer thickness. Interestingly, it was found that transporting the sample in a discontinuous mode (with stop periods of several minutes) not only yields a more stable and reproducible operation, it also yields significantly larger hybridization intensities (typically a factor of 2-3 larger) than a continuous rotation. This seems to be due to the fact that the velocity field disturbs the binding process at the binding site level. Working under limiting DNA sample mass conditions, the system yielded in a short, 30-min experiment already a 5-fold increase of the hybridization intensity, as compared to a conventional microscope slide/coverslip system operated overnight under diffusion-driven conditions. Compared to a commercial pump-around hybridization system, the gain was even more impressive, precisely due to the fact that the pump-around system requires larger volumes, which with a fixed amount of available genetic material leads to the application of more diluted samples.     

Experimental validation of the tetrahedral skeleton model pressure drop correlation for silica monoliths and the influence of column heterogeneity

This paper describes the use of computational fluid dynamics for the calculation of the flow resistance through computer-generated models resembling silica monoliths. This study was undertaken to determine the effect of skeleton heterogeneity on the flow resistance and, more precisely, to test the hypothesis that increased skeleton heterogeneity decreases the flow resistance. To evaluate the proposed model, 24 real silica monoliths have been prepared using the same method, covering a wide range of skeleton sizes (2.2 microm < d(s) < 8 microm) and porosities (0.47 < epsilon < 0.66). The permeability of these monoliths was determined by pressure drop measurements, and structural information was obtained by image analysis of laser scanning confocal microscopy-generated 3D images of the skeleton structure. The results indicate that the presence of preferential flow paths due to an increased heterogeneity of the flow through pore space reduces the flow resistance of monolithic media. It is also shown that the pore size is hence a much better suited scaling dimension than the skeleton size to reduce the permeability of monolithic columns.     

Kolmogorov-conditions for vectorial approximation problems

A general vectorial best approximation problem in linear and locally convex topological spaces, respectively, is considered. The approximation is based on socalled vectorial norms. For efficient, weakly efficient and strongly efficient solutions sufficient optimality conditions which can be interpreted as generalized Kolmogorov-conditions are obtained in vectorial as well as scalarized form.