Erholungsvorgänge in UV-bestrahltem Silberchlorid

The formation of defects in AgCl single crystals under UV and X-ray exposure and their thermal annealing are studied by measuring the optical density, the lattice parameter change, the X-ray Ag-reflection and by electronmicroscopical observations. Specks of crystalline silver are found to be produced at the surface of the crystals as well as in the interior. According to surface and volume darkening the isochronal annealing curves exhibit two stages. The activation energy for stage I, (0,59±0,08) eV, is suggested to be the energy for the thermal formation of electrons and Ag ₀ ⁺ -ions from Ag-aggregates. Stage II appears when the crystal is annealed in chlorine at above 523 °K. It is due to the regeneration of silver at the surface, where chlorine was able to leave the crystal during exposure.     

Dimensionslose Theorie der isentropischen Gasströmung durch Kreiselräder unter der Voraussetzung kleiner Breite und unendlicher Schaufelzahl (Stromfadentheorie)

Summary A diagramm is developed by means of which any flow through axisymmetric spaces with and without exchange of energy can be followed up. The flow, too, is assumed to be axisymmetric which, in the case of turbomachines, means that an infinite number of blades is assumed and the average values of the meridian components of the velocities are introduced. In all cases the absolute flow is discussed.      

A generalized companion matrix of a polynomial and some applications

A generalized companion matrix of a polynomial is introduced; the concept is applied to estimates of polynomial roots and to the explicit determination of the characteristic equation of matrix.     

Wirkung von Actinomycin D auf die RNS-Synthese und die synchrone Mitosetätigkeit in Physarum polycephalum

Zusammenfassung Actinomycin D (250 /ml) hemmt in Suspensionskulturen vonPhysarum polycephalum spezifisch die RNS-Synthese, während die DNS- und Proteinsynthese innerhalb der ersten drei Stunden nur wenig beeinträchtigt werden. Die Auslösung einer synchronen Kernteilung in Makroplasmodien kann durch 250 /ml Actinomycin D verhindert oder stark verzögert werden, sofern der Hemmstoff spätestens zu Beginn des letzten Drittels der Interphase ( 2 Stdn. vor Prophase) dem Medium zugesetzt wird. Die Mitosehemmung ist durch Auswaschen des Hemmstoffes reversibel. Die Ergebnisse sprechen dafür, daß zur Vorbereitung einer Mitose während des größten Teiles der Interphase DNS-abhängige RNS neu gebildet werden muß, die möglicherweise als Informationsüberträger die Synthese mitosespezifischer Proteine kontrolliert. Es wird eine Arbeitshypothese diskutiert, nach der die Mitose als ein durch Genregulation gesteuerter Vorgang aufzufassen wäre.

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Actinomycin D (250 /ml) specifically inhibits RNA synthesis in suspension cultures ofPhysarum polycephalum whereas DNA and protein synthesis are less affected within the first three hours. Onset of synchronous mitoses in macroplasmodia is prohibited or largely delayed by 250 /ml actinomycin D if the inhibitor is added to the medium at or prior to the beginning of the last third of interphase ( 2 hrs. prior to prophase). Removal of the inhibitor from the medium reverses the inhibitory effect on mitosis. The results indicate that preparation of mitosis requires synthesis of DNA dependent RNA during the major part of interphase. These RNA molecules possibly carry information for the synthesis of proteins specifically involved with mitosis. A working hypothesis is discussed suggesting that mitotic activities may by controlled by gene regulation.

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Mit 4 Abbildungen

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Herrn Prof. Dr.Hermann Bretschneider zum 60. Geburtstag gewidmet.     

Book Review

Book Review

Book Review     

X-ray detected magnetic resonance at the Fe K-edge in YIG: Forced precession of magnetically polarized orbital components

X-ray detected magnetic resonance (XDMR) has been measured for the first time on exciting the Fe K-edge in a high-quality yttrium iron garnet film epitaxially grown on a gadolinium gallium garnet substrate. This challenging experiment required resonant pumping of yttrium iron garnet at high microwave power, i.e., in the foldover regime. X-ray magnetic circular dichroism (XMCD) was used to probe the change in the longitudinal component of the magnetization M _Z induced by the precession of magnetic moments located at the iron sites. Since XMCD at the Fe K-edge refers mostly to the equilibrium contribution of magnetically polarized 4p orbital components, XDMR at the Fe K-edge should reflect the precessional dynamics of the latter orbital moments. From the measured precession angle, we show that there is no dynamical quenching of the polarized orbital components at the iron sites in yttrium iron garnet.