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Inhalt:
- Michael Zeuske: Humboldt, Historismus, Humboldteanisierung. Der „Geschichtsschreiber von Amerika“, die Massensklaverei und die Globalisierungen der Welt
- Christian Suckow: Abenteuer Alexander-von-Humboldt-Bibliographie
- Sandra Rebok: Alexander von Humboldt im Spiegel der spanischen Presse.
Zur Wahrnehmung seiner Person und seiner Ideen während der ersten Hälfte des 19. Jahrhunderts
- Renate Nöller: Jade aus Amerika und weitere Grünsteinobjekte von Alexander von Humboldt aus dem Berliner Mineralienkabinett
- Frank Holl: Humboldt y el Colonialismo
- Ottmar Ette: „… daß einem leid tut, wie er aufgehört hat, deutsch zu sein“. Alexander von Humboldt, Preußen und Amerika
We examine the influence of noise on the propagation of harmonic signals with two frequencies through discrete bistable media. We show that random fluctuations enhance propagation of this kind of signals for low coupling strengths, similarly to what happens with purely monochromatic signals. As a more relevant finding, we observe that the frequency being propagated with better efficiency can be selected by tuning the intensity of the noise, in such a way that for large noises the highest frequency is transmitted better than the lower one, whereas for small noises the reverse holds. Such a noise-induced frequency selection can be expected to exist for general multifrequency harmonic signals.
We report on the effect of vibrational resonance in a spatially extended system of coupled noisy oscillators under the action of two periodic forces, a low-frequency one (signal) and a high-frequency one (carrier). Vibrational resonance manifests itself in the fact that for optimally selected values of high-frequency force amplitude, the response of the system to a low-frequency signal is optimal. This phenomenon is a synthesis of two effects, a noise- induced phase transition leading to bistability, and a conventional vibrational resonance, resulting in the optimization of signal processing. Numerical simulations, which demonstrate this effect for an extended system, can be understood by means of a zero-dimensional "effective" model. The behavior of this "effective" model is also confirmed by an experimental realization of an electronic circuit.
We show that external fluctuations are able to induce propagation of harmonic signals through monostable media. This property is based on the phenomenon of doubly stochastic resonance, where the joint action of multiplicative noise and spatial coupling induces bistability in an otherwise monostable extended medium, and additive noise resonantly enhances the response of the system to a harmonic forcing. Under these conditions, propagation of the harmonic signal through the unforced medium i observed for optimal intensities of the two noises. This noise-induced propagation is studied and quantified in a simple model of coupled nonlinear electronic circuits.