Aluminum doped silicon carbide thin films prepared by hot-wire CVD: Influence of the substrate temperature on material properties

Successful p-type doping of μc-SiC:H with Al introduced from trimethylaluminum has been already demonstrated. In this work we focus on the influence of substrate temperature (T_S = 300-390 °C) on the Al-doping. As T_S is reduced from 390 °C to 300 °C, the crystallinity decreases from 75% to 55% and the dark conductivity σ_D decreases first by about three orders of magnitude before increasing again at T_S = 300 °C. Both microstructure, as determined from Raman spectroscopy, and optical absorption are little affected by the change in T_S. Upon annealing at 450 °C in vacuum, σ_D increases typically by two orders of magnitude up to 10⁻⁴ S/cm, which is explained by dopant activation as a result of hydrogen desorption. It is concluded that a process temperature > 350 °C is needed to obtain effective Al-doping for p-type μc-SiC:H thin films.     

Gaschromatographisch-massenspektrometrische Untersuchungen zur Kinetik der Redoxreaktionen vonl -Ascorbins?ure undl -Dehydroascorbins?ure in Weizenmehlteigen

Summary A gaschromatographic/mass spectrometric method for separation and determination ofl-ascorbic acid (l-AA) and the different isomeric forms ofl-dehydro ascorbic acid (l-DAA) and 2,3-diketogulonic acid (l-DKG) in wheat doughs is described. Doughs with addedl-AA resp.l-DAA were included in the investigation. In all doughs thel-DAA was in its monomeric 3,6-anhydro-2-hydrate form. 2,3-DKG was not detectable.[/p]We confirm recent statements in the literature about the kinetics of the oxidation ofl-AA tol-DAA in doughs with addedl-AA. The loss of total ascorbic acid (l-AA+l-DAA) after dough making was approx. 30%. Only a small quantity ofl-AA was formed in doughs upon addition ofl-DAA. In this case the loss of total ascorbic acid was approx. 70%.[/p]From that and from investigations on doughs with 14C-labeledl-AA and measurements of the available thiol groups in doughs we conclude thatl-AA/l-DAA at least partially doesn't react like a redox system but thatl-DAA forms intermolecular condensation products with amino groups of proteins. These may contribute to improved baking quality.Zusammenfassung Es wird eine gaschromatographisch-massenspektrometrische Methode beschrieben, mit derl-Ascorbinsäure (l-AS) und die verschiedenen isomeren Formen derl-Dehydroascorbinsäure (l-DAS) und der 2,3-Diketogulonsdure (2,3-DKG) in Weizenmehlteigen getrennt und quantitativ bestimmt werden können. Teige mit Zusatz vonl-AS bzw.l-DAS wurden analysiert. Die L-DAS lag in allen Fällen in der monomeren bicyclischen 3,6-Anhydro-2-Hydrat-Form vor; 2,3-DKG war nicht nachweisbar. Bei Teigen mit Zusatz vonl-AS konnten die Angaben der Literatur über die Kinetik der Oxidation derl-AS zurl-DAS bestätigt werden. Der Verlust an Gesamtascorbinsäure (l-AS +l-DAS) lag nach dem Anteigen bei ca. 30%. In Teigen mit Zusatz vonl-DAS wurde nur wenigl-AS gebildet, der Verlust an Gesamtascorbinsäure lag in diesem Fall bei ca. 70%. Hieraus und aus Untersuchungen an Teigen mit 14C-markierterl-AS und Messungen des verfügbaren Thiolgehalts in Teigen schließen wir, dal-AS/l-DAS zumindest teilweise nicht als Redoxsystem reagiert, sondern daß diel-DAS mit Aminogruppen der Proteine intermolekulare Kondensationsprodukte bildet, die zur backverbessernden Wirkung beitragen dürften.[/p]     

Magnetic and other physical properties of X 52, X 60, X 70, and X 80 grade linepipe steels

The following magnetic properties were determined for X 52, X 60, X 70, and X 80 grade linepipe steels: magnetic induction as a function of magnetic field strength in the form of hysteresis loops, coercive force and saturation magnetisation. In addition, the following physical properties were determined: coefficient of thermal expansion between -180 and 400°C, elastic constants between -180 or 20 and 300°C, electrical resistivity, thermal conductivity and thermal diffusivity between -180 and 300°C. The crystallographic textures of the materials were represented by pole figures.     

Tragverhalten von Stahlbetonbalken bei geneigter Querkraft

Bearing Behaviour of RC Beams Subjected to Biaxial Shear Forces The shear bearing behaviour of RC beams is still subject of expert's discussion and intensive research. Most investigations focus on uniaxial loading conditions parallel to one principal axis. More recently, biaxial shear – leading to inclined shear forces – was theoretically considered and integrated into new design concepts. However, its experimental basis is rather limited. Thus, extensive biaxial shear tests are carried out and analysed. Their main findings are presented in the paper. The design concept is elaborated to introduce inclination effects into all partitions of the resistances provided by the tensile and the compressive shear struts. Designs become more precise and more economic.