Energy use efficiency of organic and agroforestry farming systems

Im Versuchsbetrieb Scheyern (Süddeutschland) wurde in Feldexperimenten die Energienutzungseffizienz (EUE) ökologischer Anbausysteme analysiert. Die EUE wurde für verschiedene Systemebenen - die Fruchtarten, die Fruchtfolge sowie Agroforstsysteme (AFS) bestimmt. Die Agroforstsysteme bestehen aus Baumreihen mit schnellwachsenden Gehölzen zur energetischen Nutzung sowie einer Fruchtfolge zur Nahrungserzeugung. Die EUE entspricht dem Verhältnis von Energieoutput zum Energieinput. Der Energieinput umfasst den Einsatz fossiler Energie, der Energieoutput den Brennwert der Ernteprodukte. Die EUE von Weizen wird stark von der Vorfrucht beeinflusst; sie beträgt nach Kartoffeln 10,1, nach Luzerne-Kleegras 19,5, im AFS 9,7 (nach Kartoffeln) und 18,8 (nach Luzerne-Kleegras).Die Energienutzungseffizienz der Fruchtfolge beträgt 10,3, die des Agroforstsystems 12,8

Methylation of DNA by incubation with methylamine and nitrite

DNA was incubated in septum-closed reaction vials with [14C]methylamine and nitrite. The DNA was purified, hydrolysed with hydrochloric acid, and the purines were analysed by h.p.I.c. 7-Methylguanine was detectable as a result of DNA methylation in experiments performed in 100 mM acetate at pH 4. Using different concentrations of amine and nitrite a first order reaction for total amine and a second order for total nitrite could be shown. A study on the pH dependence using 100 mM malonate buffer, pH 2.0-6.0, revealed a maximum rate at pH 3.5, with steep slopes above and below this pH value, in agreement with a mathematical analysis of the reaction equations. The data show that the alkylating agent formed spontaneously by nitrosation and deamination of a primary amine has a long enough lifetime to react with DNA in vitro. Using the reaction orders established here, an extrapolation to lower concentrations found in the stomach can now be performed. Future in vivo experiments on the methylation of gastro-intestinal DNA then would show to what extent DNA in a cell is protected from alkylatio

Investigation of high efficiency GaAs solar cells

Investigations of basic mechanisms which limit the performance of high efficiency GaAs solar cells are discussed. P/N heteroface structures have been fabricated from MOCVD epiwafers. Typical AM1 efficiencies are in the 21 to 22 percent range, with a SERI measurement for one cell being 21.5 percent. The cells are nominally 1.5 x 1.5 cm in size. Studies have involved photoresponse, T-I-V analyses, and interpretation of data in terms of appropriate models to determine key cell parameters. Results of these studies are utilized to determine future approaches for increasing GaAs solar cell efficiencies