Vur Nicotinbestimmung in Tabak

Ohne Zusammenfassung     

Zur Bestimmung von Stilboestrol und Hexoestrol in Futtermitteln

Analytical and Bioanalytical Chemistry -     

Bestimmung von Fremdfett in Kakaoerzeugnissen

Ohne Zusammenfassung     

Bonding and ion-ion interactions of Mn ions in fluoride-phosphate and boro-silicate glasses probed by EPR and fluorescence spectroscopy

Electron paramagnetic resonance (EPR) and fluorescence spectroscopy are sensitive and selective methods for probing coordination and bonding of Mn²⁺ ions in glasses. Both methods provide additional information on Mn-Mn ion interactions and cluster formation. Mn²⁺ was found to be tetrahedrally coordinated in boro-silicate glasses of high optical basicity, and octahedrally coordinated in low alkaline boro-silicate glasses (duran-type) as in fluoride-phosphate glasses. Broad emission bands and multicomponent fluorescence decay curves in duran glasses indicate very strong Mn-Mn ion interactions and the presence of multiple Mn²⁺ sites. Site distribution is more homogenous in metaphosphate glasses, though concentration quenching is apparent at high Mn-levels. As the Mn-content increases the EPR spectra show exchange narrowing due to a decrease in the Mn-Mn distances in the duran series, but show extreme linewidth broadening due to increased cluster sizes at constant Mn-Mn distances for metaphosphate glasses. For the fluoride-phosphate and boro-silicate systems investigated, fluorescence lifetimes are found to decrease as the wavelength of the emission maximum increases and with increasing g-values of the sextet at g = 2. For octahedral coordination of Mn²⁺ ions the EPR hyperfine splitting constant decreases linearly with increasing optical basicity, as a result of an increasing covalent character of the Mn²⁺-ligand bond.     

Informational masking of speech in children: auditory-visual integration

The focus of this study was the release from informational masking that could be obtained in a speech task by viewing a video of the target talker. A closed-set speech recognition paradigm was used to measure informational masking in 23 children (ages 6-16 years) and 10 adults. An audio-only condition required attention to a monaural target speech message that was presented to the same ear with a time-synchronized distracter message. In an audiovisual condition, a synchronized video of the target talker was also presented to assess the release from informational masking that could be achieved by speechreading. Children required higher target/distracter ratios than adults to reach comparable performance levels in the audio-only condition, reflecting a greater extent of informational masking in these listeners. There was a monotonic age effect, such that even the children in the oldest age group (12-16.9 years) demonstrated performance somewhat poorer than adults. Older children and adults improved significantly in the audiovisual condition, producing a release from informational masking of 15 dB or more in some adult listeners. Audiovisual presentation produced no informational masking release for the youngest children. Across all ages, the benefit of a synchronized video was strongly associated with speechreading ability.     

Evidence for temperature-dependent electron band dispersion in pentacene

Evidence for temperature-dependent electron band dispersion in a pentacene thin film polymorph on graphite is provided by angle- and energy-dependent ultraviolet photoelectron spectroscopy. The bands derived from the highest occupied molecular orbital exhibit dispersion of approximately 190 meV at room temperature, and approximately 240 meV at 120 K. Intermolecular electronic coupling in pentacene thin films is thus confirmed to be dependent on temperature and possibly crystal structure, as suggested by additional infrared absorption measurements.     

Time-resolved fluorescence measurements on Dy3+ and Sm3+ doped glasses

Various fluoride, phosphate and borosilicate glasses with known properties and global structure have been doped with Dy³⁺ (4f⁹) and Sm³⁺ (4f⁵) between 10¹⁸ and 10²¹ cm^?3 and their time resolved fluorescence in the visible range in combination with characteristic physical properties were studied. Different fit procedures were carried out. Although both ions differ in their intrinsic fluorescence lifetime, with 1.5 ms for Dy³⁺ and 6.5 ms for Sm³⁺, their dependence on glass matrix is remarkable similar. Fluoroaluminate glasses with varying phosphate content between 0 and 20 mol% (FPx), a pure phosphate glass (P100), and two borosilicate glasses with low (DURAN^®-like) and high optical basicity (NBS1) were used for investigations. A strongly ionic surrounding by fluorine ligands, as in fluoroaluminate glass samples, provides the longest fluorescence lifetime. It decreases with increasing phosphate content by increasing oxygen surrounding and with increasing RE³⁺ doping. Large differences were detected in the two borosilicate glasses depending on their optical basicity mainly due to differences in the Na₂O/B₂O₃ ratio. Duran-like samples with low Na₂O content have shown phase separation with higher doping concentration. The RE³⁺ ions are accumulated in the borate-rich droplets. Surprisingly only very low concentration-quenching effects were observed. In the opposite of NBS1 samples with high Na₂O content this generated extremely high quenching effect.     

Periodic Golay pairs and pairwise balanced designs

Journal of Algebraic Combinatorics - In this paper we exploit a relationship between certain pairwise balanced designs with v points and periodic Golay pairs of length v, to classify periodic Golay...