Showing papers by "University of Antwerp published in 1970"

Theory of Cyclotron Resonance of Fröhlich Polarons in High Magnetic Fields

Abstract: Cyclotron resonance of polarons in ionic crystals is studied by means of a Born-Oppenheimer type method. The Lee, Low, Pines approximation is made for the electron—phonon interaction and so the translational invariance along the magnetic field direction is exploited. Our approach is therefore valid at weak and intermediate couplings and cyclotron frequencies ωc larger than the L.O. phonon frequency ω, which requires rather intense magnetic fields. For relatively large electron—phonon coupling (α ≧ 4) the results also apply qualitatively for weak magnetic fields. The ground state energy and the energy of two excited levels are obtained. The excited states which are treated here are internal excited states of the polaron system and they are different from the normal Landau levels. The stability of some of these states is enhanced under the action of the magnetic field. This leads us to predict absorption at new cyclotron frequencies in ionic crystals especially relevant for intermediate coupling strengths α ≈ 4. [Russian Text Ignored].

Behaviour of Hela cells grown on young chick blastoderms in vitro.

Abstract: A suspension of Hela cells was applied on young stage 4 chick blastoderms in vitro. Two experimental groups were used, the first consisting of intact embryos, the second of entoblast-free blastoderms. Hela cells did not produce morphological deformations in the intact blastoderms, but, the entoblast-free embryos showed abnormal development. The regeneration of the entoblast was inhibited by the Hela cells and neurulation was absent. A striking feature was the entoblast-like modulation of the Hela cells in several defects of the entoblast in the entoblast-free group. The difference between the groups is discussed in terms of the interaction of the cancer cells and the developing embryos in certain circumstances.