Biomedical subjects

W von Niessen

Publications and source records attributed to W von Niessen.

3 recordsLinked to original sources

PubMed2002

Internal spatiotemporal stochastic resonance in the presence of weak noise.

We show the existence of internal stochastic resonance in a microscopic stochastic model for the oscillating A+1 / 2B(2) reaction on a square lattice. This stochastic resonance arises directly from the elementary reaction steps of the system without any external input. The lattice gas model is investigated by means of Monte Carlo simulations. It shows oscillation phenomena and mesoscopic pattern formation. Stochastic resonance arises when homogeneous nucleation of the individual lattice site states is considered. This nucleation is modeled as a weak noise process. As a result, synchronization of the kinetic oscillations is obtained. We show that all characteristics known from the research on stochastic resonance are obtained in our model. We also show that the model explains easily several phenomena observed in the experiment. Internal stochastic resonance may thus be an internal regulation mechanism of extreme adaptability.

Journal Article↗

PubMed2002

Kinetic model for surface reconstruction.

A microscopic kinetic model for the alpha <==> beta [e.g., hex <==> 1x1 for Pt(100) and 1x2 <==> 1x1 for Pt(110)] surface reconstruction is investigated by means of the mean field approximation and Monte Carlo simulations. It considers homogeneous phase nucleation that induces small surface phase defects. These defects can grow or decline via phase border propagation in dependence on the chemical coverage by an adsorbate A (CO). An asymmetry in the adsorbate surface diffusion from one surface phase to the other gives rise to two critical coverages that determine the intervals of stability of the homogeneous alpha phase, the dynamically stable heterogeneous state, and the homogeneous beta phase. Both surfaces show a very similar qualitative behavior regarding the phase transitions that are of second order in both cases. As a result the experimentally observed nonlinear island growth rate and the critical coverages can be explained at a quantitative level.

Journal Article↗

PubMed2001

Comment on "surface restructuring, kinetic oscillations, and chaos in heterogeneous catalytic reactions".

In a recent article Zhdanov studied the oscillating NO+H2 reaction on the Pt(100) single-crystal surface [V. P. Zhdanov, Phys. Rev. E 59, 6292 (1999)]. We have scrutinized his model and found fundamental errors in the chemical modeling, in the modeling of the surface reconstruction and in the simulation procedure itself.

Comment↗