Friedemann Kaiser

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We discuss the influence of additive, spatiotemporally correlated (i.e., colored) noise on pattern formation in a two-dimensional network of excitable systems. The signature of spatiotemporal stochastic resonance (STSR) is analyzed using cross-correlation and information theoretic measures. It is found that the STSR behavior is affected by both the spatial(More)
Starting with a subexcitable net of FitzHugh-Nagumo elements it is shown that parameter variability (diversity) is able to induce pattern formation. These patterns are most coherent for an intermediate variability strength. This effect is similar to the well-known spatiotemporal stochastic resonance generated by additive noise in subexcitable media.(More)
The influence of variability on the response of a net of bistable FitzHugh-Nagumo elements to a weak signal is investigated. The response of the net undergoes a resonancelike behavior due to additive variability. For an intermediate strength of additive variability the external signal is optimally enhanced in the output of the net (diversity-induced(More)
Experiments on the effects of extremely-low-frequency (ELF) electric and magnetic fields on cells of the immune system, T-lymphocytes in particular, suggest that the external field interacts with the cell at the level of intracellular signal transduction pathways. These are directly connected with changes in the calcium-signaling processes of the cell.(More)
Leaves of the Crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perrier de la Bâthie show overt circadian rhythms in net CO2 uptake, leaf conductance to water and intercellular CO2 concentration, which are entrained by periodic temperature cycles. To probe their sensitivity to thermoperiodic perturbations, intact leaves were exposed(More)
The external stimulation of many cells by a hormone, for example, often leads to an oscillating cytosolic calcium concentration. This periodic behavior is now designated the cytosolic calcium oscillator. A theoretical model is presented that describes this behavior on the basis of inositol(1,4,5)trisphosphate-induced calcium oscillations. In contrast to(More)
We demonstrate numerically that partially incoherent light can be trapped in the spectral band gaps of a photonic lattice, creating partially incoherent multi-component spatial optical solitons in a self-defocusing nonlinear periodic medium. We find numerically such incoherent multi-gap optical solitons and discuss how to generate them in experiment by(More)
We report on the experimental observation of stable double-charge discrete vortex solitons generated in hexagonal photonic lattices created optically in self-focusing nonlinear media and show that single-charge vortex solitons are unstable in analogous conditions. Subsequently, we study, both theoretically and experimentally , the existence and stability of(More)
We display rich spatial and temporal dynamics of light fields counterpropagating in a saturable self-focusing medium numerically, and analyze instabilities that counterpropagating solitons experience. An expression for the maximum length that the medium must not exceed for the solitons to be stable is derived and connected to the coupling strength of beam(More)
We study (2+1) -dimensional multicomponent spatial vector solitons with a nontrivial topological structure of their constituents and demonstrate that these solitary waves exhibit a symmetry-breaking instability, provided their total topological charge is nonzero. We describe a novel type of stable multicomponent dipole-mode solitons with intriguing swinging(More)