InAs quantum dot photonic crystal lasers and their temperature dependence

We report on the demonstration of optically pumped photonic crystal lasers with InAs quantum dot active regions operating at room temperature near 1310 nm. Absorbed threshold pump powers as low as 25 /spl mu/W are observed. We also extract a characteristic temperature of 17 K, which is attributed to limitations caused by surface recombination.     

Hilfsmittel zum Auffinden einer ersten Gestalt beim methodischen Konstruieren: Gestaltbeeinflussung durch die Verwendung physikalischer Effekte

Zusammenfassung Ziel des Teilvorhabens, über das hier berichtet wird, was es, für eine Auswahl von physikalischen Effekten eine Zuordnung von gestaltbeeinflussenden Merkmalen auf sehr abstrakter Ebene zu erreichen und damit eine n?here Charakterisierung der Wirkfl?chen und Wirkr?ume zu erreichen die zur Umsetzung eines physikalischen Effektes notwendig sind. Die hieraus resultierenden Ergebnisse sind dem Abschlu?bericht zu entnehmen [1]. Weiterführende Themen, die basierend auf den vorliegenden Erkenntnissen bearbeitet werden, haben zum Ziel, die wesentlichen und entscheidenden Parameter einer Konstruktionsaufgabe zu erkennen und zukünftig zielgerichtet L?sungsvarianten zu erstellen, um somit für eine Neukonstruktion sinnvolle L?sungsfelder sehr frühzeitig abzugrenzen.     

Reproducibility of functional transcranial Doppler sonography in determining hemispheric language lateralization

BACKGROUND AND PURPOSE: Since functional transcranial Doppler ultrasonography (fTCD) allows convenient and fully automated quantification of language lateralization, it seems ideal for longitudinal studies of perfusion changes during deterioration as well as recovery of language functions. However, during serial examinations, the technical, stochastic, and physiological variabilities of cerebral blood flow velocities (CBFV) have to be considered. Therefore, before fTCD is accepted as a tool for evaluation of changes in lateralization in the diseased state, its reliability in healthy subjects needs to be determined. METHODS: We performed fTCD during a word generation task based on a previously validated technique with automated calculation of the averaged CBFV differences in the middle cerebral arteries providing an index of lateralization (LI). RESULTS: (1) The accuracy of the LI as assessed by the confidence interval was better than 1% of the mean hemispheric difference. (2) On repeated examination, LIs obtained from 10 subjects showed a high test-retest reproducibility (Pearson product moment correlation coefficient r = 0.95, P < 0.0001). (3) On 10 repeated assessments of LI in the same subject, no practice effects were detected. CONCLUSIONS: Functional TCD is a suitable and very robust tool for the longitudinal quantitative measurement of cerebral language lateralization.     

Überlegungen zur Erweiterung des Klebstoffangebots im Holzleimbau

The procedure of testing adhesives for glulam production depends in Europe on the kind of resin. For example the testing of phenol-formaldehyde resins (PF-resins) includes the boiling test method, because the curing rate of these resins show a significant correlation between the strength after boiling and the resistance to moisture influence. On the other hand this test method is commonly insufficient for testing other resins. The results of investigations of glulam based on different kinds of resins show that there is a possibility to substitute the boiling test by a short-time accelerated aging method (KZB-Test) which will offer the same differentiation.     

Self-consistent calculation of the lasing eigenmode of thedielectrically apertured Fabry-Perot microcavity with idealized ordistributed Bragg reflectors

Optical confinement in the dielectrically apertured Fabry-Perot microcavity is investigated theoretically. The apertured region is first treated as embedded in an idealized planar waveguide to show that the confined eigenmode's resonant frequency can cut off parasitic waveguide modes existing outside the aperture, and lead to three-dimensional optical confinement. For more realistic cavities with nonunity mirror reflectivities, self-consistent calculations of the eigenmode characteristics are performed for the limit of an optically thin aperture to derive the lowest order confined eigenmode frequency, threshold susceptibility, and mode profile. The analysis is then extended to treat dielectric cavities based on Bragg reflectors     

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Ohne Zusammenfassung     

Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy Characterization of Glass Phase in Sol-Gel-Derived Mullite

Sol-gel-derived mullite ceramics were processed by pressureless sintering at 1600°, 1650°, and 1700°C for 4 h. Microstructural and microchemical characterization of the mullite materials was performed using transmission electron microscopy, in conjunction with energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy (EELS). Apart from mullite grain diameter and triplepocket size, no major microstructural changes were observed with increasing sintering temperature. Residual glass was present at triple pockets and along two-grain junctions. Not all grain boundaries revealed the presence of a continuous amorphous intergranular film. Clean interfaces were observed only at boundaries with one grain parallel to the [001] orientation (low-energy configuration). Quantitative EELS analysis of mullite grains and glass pockets revealed only small changes in composition with increasing sintering temperature; i.e., the alumina:silica ratio slightly increased for mullite and glass. The analysis implied that mullite with this relatively high aluminum content would not be stable adjacent to residual glass. However, a stable glass-mullite system has been proposed, because impurity cations were detected within glass pockets, which suggested a slight shift of the subsolidus line (glass-mullite/ mullite) to a higher amount of alumina. Energy-loss nearedge structure studies of the Si- L _2,3 edge revealed a similar near-edge structure for the mullite, residual glass, and quartz. Thus, SiO₄ tetrahedra were thought to be the main building units of the glass contained in sintered mullite.     

Online Coloring of Bipartite Graphs with and without Advice

In the online version of the well-known graph coloring problem, the vertices appear one after the other together with the edges to the already known vertices and have to be irrevocably colored immediately after their appearance. We consider this problem on bipartite, i.e., two-colorable graphs. We prove that at least ?1.13746?log₂(n)?0.49887? colors are necessary for any deterministic online algorithm to be able to color any given bipartite graph on n vertices, thus improving on the previously known lower bound of ?log₂ n?+1 for sufficiently large n. Recently, the advice complexity was introduced as a method for a fine-grained analysis of the hardness of online problems. We apply this method to the online coloring problem and prove (almost) tight linear upper and lower bounds on the advice complexity of coloring a bipartite graph online optimally or using 3 colors. Moreover, we prove that \(O(\sqrt{n})\) advice bits are sufficient for coloring any bipartite graph on n vertices with at most ?log₂ n? colors.     

Interactions in compatible polymer systems

Summary Dynamic mechanical measurements on polystyrene — poly(vinylmethylether) blends are demonstrating that the relaxation processes in the blends are mainly connected with the motions of the poly(vinylmethylether) chain.Concerning the effect of mixing on topological properties of the blends, an increase of the polydispersity of the relaxation processes is detected in blends with high molecular weight polystyrene while low molecular weight polystyrene exerts an effect of dilution upon the relaxation of the high molecular poly(vinylmethylether) chains.From these measurements as well as from thermoanalytical data it results that the energetic interaction is more pronounced in the blends with oligomeric than with high molecular weight polystyrene. The glass transition temperature shows a larger deviation from additivity for blends with high molecular polystyrene than for those with oligomeric polystyrene.Herrn Prof. Dr. M. Kryszewski zum 60. Geburtstag herzlichst gewidmet     

Grain-Boundary Wetting-Dewetting in z= 1 SiAlON Ceramic

The grain-boundary structure of a model SiAlON polycrystal with nominal composition Si₅AlON₇ was characterized by transmission electron microscopy (TEM) both in an equilibrium (as-processed) state at room temperature and after quenching from elevated temperature. In addition, low-frequency (1–13 Hz) internal friction data were recorded as a function of temperature, showing a pronounced grain-boundary sliding peak positioned at 1030°C. High-resolution transmission electron microscopy (HRTEM) of the equilibrated low-temperature microstructure revealed residual glass only at multigrain junctions, but no amorphous intergranular films were observed. The detection of clean interfaces in the as-processed sample contradicts the internal friction data, which instead suggests the presence of a low-viscosity grain boundary phase, sliding at elevated temperatures. Therefore, a thin section of the as-sintered material was heated to 1380°C and rapidly quenched. HRTEM analysis of this sample showed, apart from residual glass pockets, wetted grain boundaries, which is in line with the internal friction experiment. This wetting-dewetting phenomenon observed in z = 1 SiAlON is expected to have a strong impact not only on high-temperature engineering ceramics but also on geological, temperature-activated processes such as volcanic eruptions.