Grundlagenforschung zur Entwicklung und Anwendung von Sensoren fuer die Erfassung und Weiterleitung seismischer Aktivitaeten Abschlussbericht

Up to now there are no seismic sensors for long time high temperature applications available because of the failure of electronics by temperatures above 450 Kelvin. The aim of this project is to search for sensor principles suitable for seismic measurements in extreme environments especially in deep boreholes. A first test model of a mechanical oscillator of such a seismic sensor was developed and investigated. The dynamical behaviour of the oscillator is simulated by use of the finite element program ANSYS. A fiber optic Fabry-Perot-Interferometer represents a suitable principle for single transforming. The project was finished untimely because the institute is closed down. (orig.)Gegenwaertig sind keine seismischen Sensoren, die fuer den Einsatz bei hohen Temperaturen ueber lange Zeitraeume geeignet sind, verfuegbar. Der wesentliche Grund dafuer liegt im Versagen der Elektronik bei Temperaturen ueber 450 Grad Kelvin. Das Ziel dieses Projektes ist die Suche nach Prinziploesungen fuer seismische Sensoren fuer den Einsatz unter extremen aeusseren Bedingungen, speziell in tiefen Bohrloechern. Ein erstes Muster des mechanischen Empfaengers eines solchen seismischen Sensors wurde entwickelt und getestet. Das dynamische Verhalten des mechanischen Schwingers wird mit Hilfe des FEM-Programms ANSYS simuliert. Als geeignetes Prinzip fuer die Signalwandlung erweist sich ein faseroptisches Fabry-Perot-Interferometer. Das Projekt musste vorzeitig auf Grund der Schliessung des Instituts beendet werden. (orig.)Available from TIB Hannover: F94B0327+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Left-Handed Dimer of EphA2 Transmembrane Domain: Helix Packing Diversity among Receptor Tyrosine Kinases

The Eph receptor tyrosine kinases and their membrane-bound ephrin ligands control a diverse array of cell-cell interactions in the developing and adult organisms. During signal transduction across plasma membrane, Eph receptors, like other receptor tyrosine kinases, are involved in lateral dimerization and subsequent oligomerization presumably with proper assembly of their single-span transmembrane domains. Spatial structure of dimeric transmembrane domain of EphA2 receptor embedded into lipid bicelle was obtained by solution NMR, showing a left-handed parallel packing of the transmembrane helices (535–559)2. The helices interact through the extended heptad repeat motif L535X3G539X2A542X3V546X2L549 assisted by intermolecular stacking interactions of aromatic rings of (FF557)2, whereas the characteristic tandem GG4-like motif A536X3G540X3G544 is not used, enabling another mode of helix-helix association. Importantly, a similar motif AX3GX3G as was found is responsible for right-handed dimerization of transmembrane domain of the EphA1 receptor. These findings serve as an instructive example of the diversity of transmembrane domain formation within the same family of protein kinases and seem to favor the assumption that the so-called rotation-coupled activation mechanism may take place during the Eph receptor signaling. A possible role of membrane lipid rafts in relation to Eph transmembrane domain oligomerization and Eph signal transduction was also discussed