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Analytical and Bioanalytical Chemistry - 相似文献
164.
Doris Heiligmann 《Fresenius' Journal of Analytical Chemistry》1956,149(5):383
Ohne Zusammenfassung 相似文献
165.
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. 相似文献
166.
Wightman F Kistler D Brungart D 《The Journal of the Acoustical Society of America》2006,119(6):3940-3949
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. 相似文献
167.
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. 相似文献
168.
Crnković Dean Danilović Doris Dumičić Egan Ronan Švob Andrea 《Journal of Algebraic Combinatorics》2022,55(1):245-257
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... 相似文献
169.
Doris Chen Elizabeth V. Jones Corey W. Williams Tan-Khang N. Huynh Tristan C. McPhail Prof. Dr. Stefan France 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(52):e202201368
Herein, a SnCl4-catalyzed intramolecular, interrupted homo-Nazarov cascade biscyclization to access angular (hetero)aryl-fused polycycles is reported. Subsequent decarboxylation of the readily enolizable products afforded the angular products in up to 71 % yield over two steps, with the trans-diastereomers as the major products. The cyclopropyl homo-Nazarov cyclization precursors were formed using a scalable and modular synthetic route that, ultimately, offers access to 6,6,6-, 6,6,5-, 6,5,6-, 6,6,5,6-, and 6,6,6,5-fused angular polycyclic products. To showcase the rigor and utility of the method, an 8-step total synthesis of (±)-1-oxoferruginol, an antibacterial aromatic abietane diterpenoid, was disclosed. 相似文献
170.