Browsing by Author "Bär, Markus"

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    Chemical waves in media with state-dependent anisotropy
    (1994) Gottschalk-Mazouz, Niels; Mertens, Franz; Bär, Markus; Eiswirth, Markus; Imbihl, Ronald
    In the reduction of NO with H2 on a Rh(110) surface rectangularly shaped target patterns and spirals with sharp corners have been observed. These patterns can be reproduced with a simple model assuming that the (anisotropic) diffusion is state dependent. Such a dependence is realized in the system Rh(110)/NO + H2 by the presence of different adsorbate-induced reconstructions with varying substrate geometries.
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    Spiral waves in a surface reaction : model calculations
    (1994) Bär, Markus; Gottschalk-Mazouz, Niels; Eiswirth, Markus; Ertl, Gerhard
    A systematic study of spiral waves in a realistic reaction-diffusion model describing the isothermal CO oxidation on Pt(110) is carried out. Spirals exist under oscillatory, excitable, and bistable (doubly metastable) conditions. In the excitable region, two separate meandering transitions occur, both when the time scales become strongly different and when they become comparable. By the assumption of surface defects of the order of 10 µm, to which the spirals can be pinned, the continuous distribution of wavelengths observed experimentally can be explained. An external periodic perturbation generally causes a meandering motion of a free spiral, while a straight drift results, if the period of the perturbation divided by the rotation period is a natural number.