Coherence resonance

The two species of 202 amu are taken to be the initially formed Franck-Condon structure and the parent species giving coherent resonance motion loss of a bromine atom gives BrCH2CH2CH2, which is detected after ionization by the probe pulse as C3H5, at 41 amu. The decay of BrCH2CH2CH2 leads to cyclopropane, a product not ionized by the probe pulse, and hence not seen through mass spectrometry. 

Zhou, C., and Kurths, J. Noise-induced synchronization and coherence resonance of a Hodgkin-Huxley model of thermally sensitive neurons. Chaos 2003,13 401— 409. 

More convenient approaches for the elimination of undesired coherences are possible in the case of frequency-selective irradiation schemes. If the spins that are involved in zero-quantum coherences resonate in well-separated spectral regions, the spins can be manipulated separately by selective (or semiselective) pulses (Vincent et al., 1992,1993). For example, a selective 90°(7) pulse transforms the antiphase combination (lyS — I Sy), which corresponds to zero-quantum coherence in the tilted frame, into (I S -t- lySy), whereas (—I S - lySy) is obtained if a 90° (7) pulse is used instead. Hence, a two-step phase cycle eliminates the antiphase terms... 

Fig. 1. (a) Capture and loss Auger processes for an ion moving in an electron gas (b) coherent resonant processes (c) capture shell process. 

Figure 8.5 Coherence resonance. Dynamics of an excitable system perturbed by stochastic fluctuations for different values of the noise amplitude increasing from top to bottom. At intermediate noise levels, nearly periodic spikes occur (from Pikovsky and Kurths (1997)).

A.S. Pikovsky and J. Kurths. Coherence resonance in a noise-driven excitable system. Phys. Rev. Lett., 78 775, 1997. 

To characterize the level of coherence of noise-induced excitations we analyze the time evolution of the activator concentration x in the FitzHugh-Nagumo model, see Fig. 1.6. In this representation the excitation loops shown previously in Fig. 1.4 become spikes spaced out by intervals during which the system performs noisy relaxation oscillations aroimd its stable state. The phenomenon of coherence resonance manifests itself in the three realizations of x t) for different noise intensities given in Fig. 1.6. For very low noise intensity (upper panel) an excitation is a rare event which happens at random times. In the panel at the bottom, for high noise intensity, the systems fires more easily but still rather randomly. In the panel in the center instead, at an optimal noise intensity, the system fires almost periodically. 

Coherence resonance with respect to the correlation time... 

Fig. 1.13. Coherence resonance in tlie Oregonator model (Eqs. 1.37) with respect to the correlation lengtlr for different values of the correlation time r gray curve r = 0.3. red curve T = 2, blue curve r = 5, yellow curve t = 20. Excitability j>arauieter — 0.01, system size L 45, noise intensity <7 = 0.25 [5].

V. Beato and H. Engel. Coherence resonance phenomena in an excitable system driven by colored noise. Fluct. Noise Lett., 6 L85-L94, 2006. 

O. Carrillo, M. A. Santos, J. GarciarOjalvo, and J. M. Sancho. Spatial coherence resonance near pattern-forming instabilities. Europhys. Lett, 65 452, 2004. 

A. Neiman, P. I. Saparin, and L. Sone. Coherence resonance at noisy precursors of bifurcations in non linear dynamical systems. Phys. Rev. E, 56 270, 1997. 

R. Toral, C. Mirasso, and J. D. Gunton. System size coherence resonance in coupled FitzHugh-Nagumo models. Europhys. Lett., 61 162, 2003. 

O. V. Ushakov, H.-J. Wnsche, F. Henneberger, I. A. Khovanov, L. Schimansky-Geier, and M. A. Zaks. Coherence resonance near a hopf bifurcation. Physical Review Letters, 95 123903, 2005. 

Noise is an inevitable feature of physical models. Theoretical and experimental research has recently shown that noise can have surprisingly constructive effects in many nonlinear systems. In particular, an optimal noise level may give rise to ordered behavior and even produce new dynamical states [11]. Well-known examples are provided by stochastic resonance [75, 76] in periodically driven systems, and by coherence resonance [10, 77, 78] in autonomous systems. In spite of considerable progress on a fundamental level, useful applications of noise-induced phenomena in technologically relevant devices are still scarce. Here we will demonstrate... 

This quantity, as seen in Fig. 5.11(b) (bottom), is a non-monotonic function of D, exhibiting a minimum at moderate noise intensity. This is the well phenomenon of coherence resonance and is strongly connected to excitability. 

To conclude, noise-induced front motion and oscillations have been observed in a spatially extended system. The former are induced in the vicinity of a global saddle-node bifurcation on a limit cycle where noise uncovers a mechanism of excitability responsible also for coherence resonance. In another dynamical regime, namely below a Hopf bifurcation, noise induces oscillations of decreasing regularity but with almost constant basic time scales. Applying time-delayed feedback enhances the regularity of those oscillations and allows to manipulate the time scales of the system by varying the time delay t. 

Interactions with mesons Photomeson production Coherent resonant ... 

In this contribution we present two laser spectroscopic methods that use coherent resonance Raman scattering to detect rf-or laser -induced Hertzian coherence phenomena in the gas phase these novel coherent double resonance techniques for optical heterodyne detection of sublevel coherence clearly extend the above mentioned previous methods using incoherent light sources. In the case of Doppler broadened optical transitions new signal features appear as a result of velocity-selective optical excitation caused by the narrow-bandwidth laser. We especially analyze the potential and the limitations of the new detection schemes for the study of collision effects in double resonance spectroscopy. In particular, the effect of collisional velocity changes on the Hertzian resonances will be investigated. 

Ramsey s method for the observation of narrow radiofre-guency (rf) resonances is well known from atomic and molecular beam experiments . In this contribution, we demonstrate the occurence of similar Ramsey resonances in an atomic vapor due to collisional velocity diffusion of sublevel coherence within an optical Doppler distribution. This new phenomenon is observed using coherent resonance Raman processes to optically induce and detect Zeeman coherence in the Sm A=570.7 nm J=1-J =0 transition. 

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