Browsing by Subject "Erregbare Medien"

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Vergleichende Untersuchungen zur Musterbildung in erregbaren Medien mit Vermerken zum Einfluss schwacher magnetischer Felder - Schwerpunkt: Belousov-Zhabotinsky-Reaktion
(2007) Dolzmann, Kerstin; Hanke, Wolfgang
In this work we did some research on the influence of a weak external magnetic field (MF) on the creation of patterns in excitable media (duration field (DC) and alternating field (AC)). As examples we chose the well known Belousov-Zhabotinsky reaction (BZR) and ferrofluids. If ferrofluids are stimulated mechanically by vertical vibration they show changes of phases in the building of patterns while raising the induced energy (here by different hights of amplitudes). The viscosity of the magnetic fluid is increasing in a DC-field. Because of this the changing of the phase is different from the ones without an external force. A non-stationary stirred BZR shows a periodic change of colour between yellow and colourless ? or red and blue, if ferroin is added as a catalyst. This oscillation is described as a simple curve in literature. We, however, found a much more complex behaviour in the experiment. The intrinsic optical signals (IOS) of a ferroin-catalysed, stirred BZR show a double-peak at the beginning of the reaction, which is fading after a few further oscillations. This behaviour depends on the concentration of ferroin and resembles very much electrical and optical signals known from neuronal processes (e.g. retinal spreading depression). This basic similarity makes the BZR an ideal model for a variety of neurophysiological signals, even if the underlying mechanisms are completely different. If this system is put to the influence of a weak external magnetic DC-field a further inner oscillation is added to the double-peak behaviour of the IOS. Also the double-peak itself looks different from the one without external field. If further components are added to the system it gradually changes to chaotic behaviour. This could be the induced little currents in an AC-field. Each expansion of the system is followed by further bifurcation culminating in a transition from pattern to chaos. BRZ gels show bright propagating concentric rings or spirals as a pattern. With the used materials and methods of measurement we were not able to record changes in the formation of patterns if the system was expanded. But one can assume that the behaviour of the gel is changing in the DC-field: all in all it seems to get faster.