298 research outputs found
Thermalization of Photoexcited Localized Excitons in GaSe Samples with Stacking Disorder
No full textWe have studied the photoluminescence of GaSe at 80 K under energy-selective excitation conditions. For excitation energies on the low-energy side of the n=1 direct free-exciton absorption line we find that the emission line due to the n=1 direct free excitons follows rigidly the excitation energy, whereas for excitation energies on the high-energy side the respective emission spectrum shifts to lower energies and the linewidth increases. Similar behavior is found on exciting into the excited n=2 direct exciton states. At room temperature and for excitation energies larger than the direct gap the emission spectra become independent of the excitation energy. We show that the experimental findings can be understood in terms of an extended version of the multiple-trapping model, which accounts for the localization of excitons in the direction perpendicular to the layers of GaSe. This localization is a consequence of the stacking disorder present in our samples. The resulting physical picture is that at low temperatures and for low excitation energies thermalization effects can be neglected within the recombination lifetime, whereas at high temperatures or high excitation energies the thermalization takes place within the recombination lifetime
-circulant Matrices and the Classical Maschke Theorem
No full textIn this note, we use the isomorphism of the ring of -circulant matrices
over a field with the group ring to derive a very short proof of the
Classical Maschke Theorem
How do Astronaut Candidate Profiles differ from Airline Pilot Profile
No full text Sixteen years after the second Europe-wide astronaut selection campaign, the European Space Agency started the third campaign by putting out a call for new astronauts in 2008. Due to extreme environmental conditions, expensive scientific experiments, and high public interest, not only are the psychological requirements on a high level, but they are also wide in variety: Besides cognitive and psychomotor requirements, greater importance than in comparable campaigns was put on personality and behavioral aspects, especially regarding interpersonal aspects. The psychological selection was conducted in two steps: Phase 1 concentrated mainly on performance tests and Phase 2 focused on personality and interpersonal behavior. Out of the 902 tested candidates, 46 fulfilled the psychological requirements. Significant differences were found between the astronaut candidates and the general population as well as airline pilot candidates. </jats:p
Strategies for improving plasmid stability in genetically modified bacteria in bioreactors
No full textKumar PKR, Maschke H-E, Friehs K, Schügerl K. Strategies for improving plasmid stability in genetically modified bacteria in bioreactors. Trends in biotechnology. 1991;9(1):279-284.Exploitation of recombinant organisms for the large-scale, commercial production of foreign proteins is often hampered by the problem of plasmid instability. A wide range of strategies have been reported for improving the stability of recombinant organisms. A combination of manipulating both the genetic design of recombinants and the conditions of culturing the organisms may be used to achieve stable host-vector associations during culture of recombinant organisms in bioreactors
Conservation laws and open systems on higher-dimensional networks
No full textWe discuss a framework for defining physical open systems on higher-dimensional complexes. We start with the formalization of the dynamics of open electrical circuits and the Kirchhoff behavior of the underlying open graph or 1-complex. It is discussed how the graph can be closed to an ordinary graph, and how this defines a Dirac structure on the extended graph. Then it is shown how this formalism can be extended to arbitrary k-complexes, which is illustrated by a discrete formulation of heat transfer on a two-dimensional spatial domain.
Supplemental_material - A Retrospective Analysis of Nonocclusive Mesenteric Ischemia in Medical and Surgical ICU Patients: Clinical Data on Demography, Clinical Signs, and Survival
No full textSupplemental_material for A Retrospective Analysis of Nonocclusive Mesenteric Ischemia in Medical and Surgical ICU Patients: Clinical Data on Demography, Clinical Signs, and Survival by Klaus Stahl, Markus Busch, Sabine K. Maschke, Andrea Schneider, Michael P. Manns, Jan Fuge, Olaf Wiesner, Bernhard C. Meyer, Marius M. Hoeper, Jan B. Hinrichs, and Sascha David in Journal of Intensive Care Medicine</p
Nächtliches Erwachen durch Fluglärm
No full textDie nächtliche Aufweckschwelle von 60 dB(A), die in Deutschland vielfach zur Festlegung von “Lärmbelastungsgebieten” für den schlafenden Menschen herangezogen wird, ist mit einer fehlerhaften statistischen Datenaufbereitung der 1976 von Griefahn et al. durchgeführten Literaturauswertung [1] belastet. Das ist das Ergebnis einer umfangreichen Revision. Bei einem statistisch korrekten Vorgehen ergibt sich am Ohr des Schläfers ein Maximalpegel von höchstens 48 dB(A) für die Aufweckschwelle und nicht ein Maximalpegel von 60 dB(A), wie in der Arbeit von Griefahn et al. errechnet. Die lineare Dosis-Wirkungs-Beziehung, die im Rahmen der Revision aus den alten Arbeiten abgeleitet werden konnte, stimmt gut mit den Ergebnissen neuerer Literaturauswertungen überein. Im vorliegenden Beitrag wird nicht der Frage nachgegangen, ob es präventivmedizinisch sinnvoll ist, ein nächtliches Schutzkriterium allein auf den Beginn von lärmbedingten Aufwachreaktionen abzustellen. In diesem Zusammenhang ist auf das Mediationsverfahren “Ausbau Flughafen Frankfurt/Main” hinzuweisen. Von den anwesenden Experten (Bullinger, Griefahn, Hecht, Kastka, Maschke, Spreng) wurde übereinstimmend ein nächtlicher Maximalpegel von 52 bis 53 dB(A) als Beginn für vegetative Beeinträchtigungen angesehen ([2], S. 9). Nach heutigem Kenntnisstand ist daher als minimales Schutzziel zu fordern, dass regelmäßige nächtliche Maximalpegel von 52 dB(A) am Ohr des Schläfers vermieden bzw. unterschritten werden sollten.The nightly wakening-noise threshold of 60 dB (A), that is often used in Germany to es-tablish “noise suffering areas”, is distorted by an erroneous statistical data processing. This is the conclusion of an extensive revision of the original literature published by Griefahn et al. in 1976 [1]. When correctly calculated, a maximum indoor sound level of at 48 dB(A) is found to be the disturbance threshold, not the 60dB(A) stated by Griefhahn et al. The linear dose-response-relationship derived from the revision of the literature agrees well with the results from more recently published data. The article does not address the question whether it is advisable to base night-time noise protection criteria on studies of noise-induced awakening alone. In this context, the recommendations of the mediation committee “Airport Frankfurt/Main” should be mentioned. The German experts involved (Bullinger, Griefahn, Hecht, Kastka, Maschke, Spreng) unanimously agree that a threshold of 52–53 dB (A) exists above which vegetative disorders start (see [2], S. 9). Given this knowledge it is appropriate to demand that during the night regular maximum-levels of 52 dB(A) should be avoided
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