Kondensationsreaktionen von α-Aminothionamiden und α-Oxothionamiden

Ohne Zusammenfassung64. Mitt.:F. Asinger, H. Offermanns undP. Krings, Ann. Chem. (im Druck). P. Müller, Teil der Diplomarbeit, Techn. Hochschule Aachen, 1967. H. Andree, Teil der Diplomarbeit, Techn. Hochschule Aachen, 1967.     

Syntheses and Crystal Structures of Novel Ternary Alkali Metal Gold Acetylides MIAuC2 (MI = Li,Na, K,Rb, Cs)

By the reaction of AuI with alkali metal hydrogen acetylides M^IC₂H (M^I = Li–Cs) in liquid ammonia and subsequent heating of the remaining residue in refluxing pyridine (M^I = Li, Na, K) or as a solid phase at about 110 °C in vacuum (M^I = Rb, Cs) ternary alkali metal gold acetylides M^IAuC₂ were obtained. Their crystal structures were investigated by the means of X‐ray powder diffraction. [Au(C₂)_2/2^–] chains are the characteristic structural motif which are packed in a hexagonal (LiAgC₂) and tetragonal arrangement (NaAuC₂–CsAuC₂), respectively. Simple calculations based on the close packing of rods and spheres can explain these different arrangements. The existence of C–C triple bonds in the title compounds is confirmed by Raman spectroscopic investigations.     

Hexagonal high‐temperature form of aluminium phosphate tridymite from X‐ray powder data

Similar to silica tridymite, AlPO₄ tridymite shows a sequence of displacive phase transitions resulting in a dynamically disordered hexagonal high‐temperature modification. Rietveld refinement reveals that the thermal motions of the tetrahedra can be described either by strongly anisotropic displacement parameters for oxy­gen or by split O atoms. Due to the ordered distribution of aluminium and phospho­rus over alternating tetrahedra, the space group symmetry of high‐temperature AlPO₄ tridymite is reduced with respect to SiO₂ tridymite from P6₃/mmc to P6₃mc.     

Pd-katalysierter Deuterium-Austausch am Octa(silsesquioxan)H8Si8O12 zu D8Si8O12

Pd-Catalyzed Deuterium Exchange of Octa(silsesquioxane) H₈Si₈O₁₂ to D₈Si₈O₁₂ Deuterium exchange on octa(silsesquioxane) H₈Si₈O₁₂ to D₈Si₁₈O₁₂ catalyzed by palladium on carbon is reported.     

Biosynthesis of the Purple Membrane of Halobacteria

Halobacteria are extremely specialized organisms. They live exclusively in saturated solutions of common salt. The cell membrane of these bacteria exhibit insular regions which can be isolated by membrane fractionation. These regions consist of a lipid matrix containing bateriorhodopsin molecules in a hexagonal crystalline arrangement. Bacteriorhodopsin is a deep purple retinal-protein complex (“purple membrane”). The purple membrane functions as a light energy converter.—How can such a differentiated membrane region arise? In vivo studies on the biosynthesis of the purple membrane showed another cell membrane fraction, the so-called brown membrane, to be a biosynthetic precursor. Bacterioopsin (the retinal-free protein) is initially incorporated into the brown membrane and can only form the purple membrane by crystallization in an energy-dependent reaction after prior reaction with retinal. This reaction is reversible. Removal of the retinal by formation of retinal oxime causes the purple membrane regions to disappear. Reconstitution of the bacteriorhodopsin by addition of retinal regenerates the purple membrane.     

Crystal growth and transport rates of GeSe and GeTe in micro-gravity environment

Six vapor transport experiments on the systems GeSe-GeI₄ and GeTe-GeI₄ were performed on Skylab to determine the effects of micro-gravity on crystal growth and transport rates. Based on a direct comparison of crystals and transport data obtained on earth and in space, employing X-ray diffraction, microscopic and etching techniques, the results demonstrate a considerable improvement of the space grown crystals in terms of growth morphology and bulk perfection. The observation of greater mass transport rates than expected in micro-gravity for diffusion-controlled transport could indicate the existence of other transport modes in a reactive solid-gas phase system. The combined results show that the interference of gravity-driven convection with the transport process causes negative effects on crystal growth as observed on earth for otherwise identical conditions. This points to the unique environment of weightlessness for the observation of basic transport phenomena.     

Identification of plastic material parameters with error estimation

In recent years, inverse analysis has become a common approach to typical engineering problems such as model identification. In this contribution, the inverse problem is discussed in light of taking experimental uncertainties into account. This involves in particular the propagation of experimental errors and the analysis of the sensitivity of the model response to variations in the model parameters to be determined. The method is applied to an elasto-viscoplastic material model which is used in the context of electromagnetic high-speed forming. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A model-theoretic characterization of constant-depth arithmetic circuits

We study the class ${\mathrm{\#}\text{AC}}^0$ of functions computed by constant-depth polynomial-size arithmetic circuits of unbounded fan-in addition and multiplication gates. No model-theoretic characterization for arithmetic circuit classes is known so far. Inspired by Immerman's characterization of the Boolean circuit class ${\text{AC}}^0$, we remedy this situation and develop such a characterization of ${\mathrm{\#}\text{AC}}^0$. Our characterization can be interpreted as follows: Functions in ${\mathrm{\#}\text{AC}}^0$ are exactly those functions counting winning strategies in first-order model checking games. A consequence of our results is a new model-theoretic characterization of ${\text{TC}}^0$, the class of languages accepted by constant-depth polynomial-size majority circuits.