ABSTRACT
Photoluminescence lineshape properties of quasi-two-dimensional electron systems in setback δ-doped GaAs heterostructures are studied at liquid helium temperature. Contributions from the ground and the first excited two-dimensional subband are clearly observed. A simple fit to the lineshape including broadening demonstrates that there is an exponential low-energy tail associated with the ground subband. No such tail is observed for the first excited subband. The fit precisely reveals the subband bottom energies, the Fermi energy, the electron temperature and the recombination intensities. A self-consistent calculation of subband properties including the potential contribution of the setback δ-doping reproduces well the subband properties and the recombination intensities.
ABSTRACT
We find that the long-wavelength magnetoplasmon, resistively detected by photoconductivity spectroscopy in high-mobility two-dimensional electron systems, deviates from its well-known semiclassical nature as uncovered in conventional absorption experiments. A clear filling-factor dependent plateau-type dispersion is observed that reveals a so far unknown relation between the magnetoplasmon and the quantum Hall effect.
ABSTRACT
The antileukemic and anti-HTLV-III (anti-HIV) agent avarol, a sesquiterpenoid hydroquinone, was determined to be converted into its corresponding quinone derivative avarone via the semiquinone free radical. Its g-value was 2.0047; after hyperfine splitting the energy levels revealed 16 isotropic Hfs. The redox reaction products were identified at the pH values 4.0, 7.0 and 12.0 and the overall reaction pathways were formulated. In vivo experiments with L5178y mouse lymphoma cells in the ascites of mice revealed that the cytostatic potencies of avarol and avarone cannot be augmented by lowering the pH value. Incubation studies with L5178y cells in vitro showed that the intracellular levels of superoxide dismutases (SODases) and of glutathione (GSH) peroxidase activities significantly change after avarol administration. While both the Mn-SODase and the Cu/Zn-SODase activities dropped significantly, the GSH peroxidase activity increased inversely. From these experiments we assume that the anti-tumour and the antiviral effects of avarol/avarone may be due to an increase, induced by the drug, of the intracellular concentrations of superoxide radicals.
