Evolution of the fractal dimension for simultaneous coagulation and sintering

Simulation results on the evolution of aggregate structure in aerosol processes with coagulation and sintering as the dominant mechanisms are presented. A model for simulation of the three-dimensional morphology of nano-structured aggregates formed by concurrent coagulation and sintering is applied. The model is based on a stochastic diffusion controlled cluster-cluster aggregation algorithm and sintering is modeled as a successive overlapping of spherical primary particles, which are allowed to grow in order to maintain mass conservation. This leads to computer simulated structured aggregates which are then subject to evaluation. Two different methods to determine the fractal dimension are presented which give comparable results. It is shown that even very small particles show the same fractal behavior. Furthermore, equilibrium structures assuming a constant ratio of the characteristic collision time to the characteristic fusion time are considered as well as the kinetics of structural changes due to a change in the ambient conditions.     

Zur Theorie der Trennfestigkeit metallischer Werkstoffe

Begriff der Trennfestigkeit. Aufstellung von Festigkeitsbedingungen für homogene isotrope Stoffe. Darstellung der Festigkeitsgrenzen im Hencky-Schaubild. Vieldeutigkeit der Mehrachsigkeitsziffern. Eindeutige Kennzeichnung der Form eines Spannungszustandes. Ermittlung der Hauptspannungen für reine Zugspannungszustände. Plastizitätsgrenze und kritischer Räumlichkeitsgrad. Zahlenbeispiel für den Baustahl St 42-3. Anwendung auf Kerbspannungen.     

Die Schlackenbildung beim Aufblasen von Sauerstoff mit Feinkalk auf phosphorreiches Roheisen

Gefügeuntersuchungen an Schlackenproben, die während des Blasens einem 18-t-?LD-AC?-Konverter entnommen wurden. Die ?Schlackenbildung? beim Blasen ohne und mit Vorverlegung der Entphosphorung vor die Entkohlung. Hinweise für das Schäumen der Schlacken.     

Microbial production,structure elucidation and bioconversion of sophorose lipids

Cultivation of Torulopsis bombicola ATCC 22214 on a mixture of glucose and oleic acid (A) or oleic acid alone (B) produced large amounts of sophorose lipids. In the case of A, 38 g/1 of crude product were finally isolated; fermentation B led to 77 g/1. After separation by MPLC and TLC, six glycolipids were obtained and identified by NMR and fast atom bombardment-mass spectrometry (FAB-MS). In general, a 17-hydroxyocta-decanoic acid at the C-1’ -position and acetate groups at the C-6’ -and C-6’ -positions of sophorose were found as substituents in the lactone and acidic forms of these lipids. The composition of product from A was as follows: 62% of sophorolipid 1’,4’ -lactone 6’ ,6’ -diacetate (SL-1), 4% of sophorolipid 1’,4’-lactone 6’-monoacetate (SL-2), 4% of sophorolipid 1’,4 ’-lactone (SL-3), 4% of sophorolipid 1’,6’-and l’,6’-lactones (SL-4a,b), 4% of sophorolipid 6’-monoacetate acid (SL-5), 4% of sophorolipid acid (SL-6) and finally 17% of other lipids. In B, the principal lactone (40%) had a double bond in the fatty acid moiety; the other components were identical with the above products. Yields of 13% SL-2 and of 35% lipids containing no carbohydrate were significant. SL-1 was deacetylated to SL-3 (yield: 25-307c) using acetyl-esterase in a two-phase system (cyclohexane/water). To whom correspondence should be addressed.