Observations on the regio- and stereoselective trapping of organozinc carbenoids by acetoxybutadienes: a useful route to functionalised vinylcyclopropanes

Regiospecific trapping of organozinc carbenoids generated from carbonyl compounds with Z-1-acetoxybutadiene provides a useful preparative route to functionalised vinyl and divinylcyclopropanes.     

Die Eisenbestimmung im Grundwasser

Ohne Zusammenfassung     

Universal relation between hall conductivity and the damping constant of edge magnetoplasma resonances

The spectra of edge magnetoplasma excitations in two-dimensional (2D) electron disks have been analyzed by the method of optical detection of resonant microwave absorption. The magnetic dispersion of an edge magnetoplasmon in samples with a high 2D electron density is found to be poorly reproduced by existing theoretical models. Analysis of the magnetic-field dependence of the linewidth of resonant microwave absorption for samples with various 2D electron densities shows that the inverse width of the main mode of resonant microwave absorption is universally proportional to the Hall resistance of 2D electrons.     

Self-organized growth of quantum dot-tunnel barrier systems

Surface selective epitaxial growth on patterned substrates is used to fabricate quantum dot-tunnel barrier systems, which can be used as single-electron transistor devices. In the centre of a pre-patterned constriction a self-assembled GaAs quantum dot embedded in barrier material is formed during the molecular beam epitaxial growth of an Al_0.33Ga_0.67As/GaAs heterostructure. The quantum dot is connected via self-aligned tunnelling barriers to source and drain electrodes. In-plane-gate electrodes are also realized within the epitaxial growth process. The paper describes the fabrication process of the device and the characterization of the direct grown quantum dot-tunnel barrier system using scanning-electron microscopy, atomic-force microscopy and transport spectroscopy.     

Multielement analysis of biological reference materials by total-reflection X-ray fluorescence and inductively coupled plasma mass spectrometry in the semiquant mode

Summary Total-reflection X-ray fluorescence (TXRF) and inductively coupled plasma mass spectrometry (ICP-MS) were used for the analysis of two biological reference materials. The quantifications were carried out after addition of one single standard element which serves as an internal standard in both cases. The results of TXRF analysis were good to satisfactory. The method is therefore suitable for fast multielement analysis, because it needs no special calibration specimens. The results of ICP-MS analysis are at least in the order of magnitude of the certified values. In some cases recoveries fit very well. For quantitative analysis, however, the use of the standard addition method or the calibration with external standards is required.