Untersuchungen über zeitabhängig selbsterregte,symmetrische Kreisel

Übersicht Es wird eine allgemeine Lösung für den Bewegungszustand eines durch beliebige Momente selbsterregten symmetrischen Kreisels angegeben. Für drei spezielle Formen der Momente werden die Untersuchungen weiter ausgeführt. Bei konstanten Erregermomenten können Polkegel und mögliche permanente Drehungen angegeben werden. Für Erregung durch Momentenstöße oder durch umlaufende Momentenvektoren lassen sich explizite Lösungen ausrechnen, die unmittelbar auf Lageregelungen und Nutationsdämpfung von Raumfahrzeugen angewendet werden können.

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Summary A general solution is given for the rotational motion of a self-excited rigid body, the ellipsoid of inertia of which is an ellipsoid of revolution. The exciting torques may be arbitrary time-depending functions. For three special cases more detaued results are given. Permanent rotations and the cone of rotation (body-cone) can be calculated for time independent torques. Explicit analytic solutions may be found in the case of excitation by series of torque-shocks or by torque-vectors turning with respect to the body. These results can be applied to the problems of attitude-control and nutation-damping of space vehicles.

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Herrn Professor Dr. Henry Görtler zum 60. Geburtstag gewidmet.     

Stationäre Schwingungen in nichtlinearen dynamischen Systemen mit Totzeiten

Ohne ZusammenfassungDiese Untersuchungen wurden im Rahmen eines Forschungsprogrammes durchgeführt, für dessen Unterstützung der Deutschen Forschungsgemeinschaft zu danken ist.     

Silicon in synthesis: use of the highly nucleophilic trimethylsilyallyl anion for the synthesis of steroidal 17-spiro-γ-lactones

Trimethylsilylallylzinc chloride $\text{2}$ (M  ZnCl) reacts with 17-ketosteroids to give adducts $\text{4}$ that can be converted into 17-spirolactones.     

Oxygen-related band gap state in single crystal rubrene

A molecular exciton signature is established and investigated under different ambient conditions in rubrene single crystals. An oxygen-related band gap state is found to form in the ambient atmosphere. This state acts as an acceptor center and assists in the fast dissociation of excitons, resulting in a higher dark and photoconductivity of oxidized rubrene. The band gap state produces a well-defined photoluminescence band at an energy 0.25 eV below the energy of the 0-0 molecular exciton transition. Two-photon excitation spectroscopy shows that the states are concentrated near the surface of naturally oxidized rubrene.     

Double excitations of helium in weak static electric fields

A dramatic electric field dependence has been observed in the fluorescence yield spectrum of the doubly excited states in helium, where a rich phenomenology is encountered below the threshold. Fluorescence yields of certain states can be tuned to zero, while other dipole-forbidden states are significantly enhanced, for fields much weaker than 1 kV/cm. Using an R-matrix multichannel quantum defect theory, spherical-to-parabolic frame transformation method, we are able to reproduce the main features of the observed spectrum, and we discuss the qualitative behavior in terms of weak electric field mixing.     

Electrochemical wettability switches gate aqueous liquids in microfluidic systems

We demonstrate a simple low-voltage technique for gating the flow of aqueous liquids in microfluidic systems employing the electrochemically-controlled surface energy of the conjugated polymer poly(3-hexylthiophene).     

Sign of excited spin state magnetic anisotropy parameters

By using high frequency high field EPR spectroscopy we demonstrate how to extract the sign of magnetic anisotropy parameters pertinent to excited spin multiplets of antiferromagnetically coupled clusters. The method is demonstrated on a manganese(II) dimer.