共查询到20条相似文献,搜索用时 62 毫秒
1.
A detailed asymptotic study of the effect of small Gaussian white noise on a relaxation oscillator undergoing a supercritical Hopf bifurcation is presented. The analysis reveals an intricate stochastic bifurcation leading to several kinds of noise-driven mixed-mode oscillations at different levels of amplitude of the noise. In the limit of strong time-scale separation, five different scaling regimes for the noise amplitude are identified. As the noise amplitude is decreased, the dynamics of the system goes from the limit cycle due to self-induced stochastic resonance to the coherence resonance limit cycle, then to bursting relaxation oscillations, followed by rare clusters of several relaxation cycles (spikes), and finally to small-amplitude oscillations (or stable fixed point) with sporadic single spikes. These scenarios are corroborated by numerical simulations. 相似文献
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J. K. Srivastava 《Hyperfine Interactions》1988,42(1-4):1127-1130
Using Kubo-Anderson stochastic model calculation it is shown that a microwave-optical-Mőssbauer triple resonance (MOMTR) experiment,
which is essentially a Mőssbauer resonance study in presence of microwave-optical double resonance (MODR), can measure short
relaxation times of the ion's excited state. This is an improvement over the existing MODR technique. 相似文献
4.
We call attention to the fact that data on spin-lattice relaxation in liqudis can give information about the rate of resonant acoustic transitions in substances where ordinary electron paramagnetic resonance (epr) and nuclear magnetic resonance (nmr) have been studied. Secondly it is shown that sound coherence may be exploited to discriminate between effects of stochastic Brownian motion and sound exitation. Preliminary experimental data are presented on the sound modulation of the proton spin-echoes in water with magnetic dipoles Cu2+. 相似文献
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Artjom Vargunin 《Physics letters. A》2008,372(48):7187-7190
The response of a ferroelectric particle to an applied harmonic field is studied using the Fokker-Planck equation approach. The size effect in dielectric susceptibility is interpreted as the complementarity between stochastic resonance and response anomaly of the second-order phase transition. The borderline between stochastic and deterministic behavior is established. Two universal volume-independent ratios of the damping rates are predicted and may be verified in the relaxation experiments. The approach can be generalized also to other finite condensed systems. 相似文献
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《Physica A》1987,143(3):468-493
A theory of low field resonance and relaxation is formulated on the basis of the time-convolution equation formalism. A fluctuating field is assumed to be stochastic, and in certain cases, exact solutions are obtained in closed analytic form.Relevance to recent μSR experiments on a random magnetic system is discussed. 相似文献
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Electron spin echo (ESE) of nitroxide spin labels allows detecting fast nanosecond stochastic restricted rotations (stochastic molecular librations), which is a common property of molecules in disordered media including biological systems. Under the typical experimental conditions, the anisotropic electron paramagnetic resonance (EPR) spectrum of a nitroxide is only partly excited by microwave pulses, which allows selecting an anisotropic contribution to the transverse spin relaxation by comparing echo decays at different spectral positions. On the other hand, for low-amplitude orientational motion, the excitation bandwidth is large enough to cover the range of spectral diffusion occurring during the echo formation. To verify that the two-pulse echo decay is indeed related to fast motions, the stimulated electron spin echo can be used. In addition, theory predicts an increase of the relaxation rates at higher microwave resonance frequency. To check this prediction, in the present work we performed a comparative study of ESE decays at microwave X- and Q-bands, for spin-labeled lipids in the gel phase of a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer. A good agreement found between experimental data and computer simulation provides additional justification for the model of fast stochastic molecular librations. 相似文献
8.
We investigate oscillation regularity of a noise-driven system modeled with a slow after-hyperpolarizing adaptation current (AHP) composed of multiple-exponential relaxation time scales. Sufficiently separated slow and fast AHP time scales (biphasic decay) cause a peak in oscillation irregularity for intermediate input currents I, with relatively regular oscillations for small and large currents. An analytic formulation of the system as a stochastic escape problem establishes that the phenomena is distinct from standard forms of coherence resonance. Our results explain data on the oscillation regularity of the pre-B?tzinger complex, a neural oscillator responsible for inspiratory breathing rhythm generation in mammals. 相似文献
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A. I. Shushin V. P. Sakun 《Russian Journal of Physical Chemistry B, Focus on Physics》2007,1(1):15-19
A non-Markovian version of the Liouville stochastic equation was used to analyze spin relaxation in a pair of particles with spins 1/2 and the dipole-dipole interaction between the spins. The particles were involved in anomalously slow stochastic relative rotation described by the angular correlation function K(t) ~ 1/t α with α < 1. The Liouville stochastic equation could be used to describe memory effects in the kinetic dependence of rotational relaxation resulting in a very slow descent of K(t). Our analysis showed that the anomalous relative motion of radicals manifested itself in special features of the shape of the magnetic resonance line of the particle pair. 相似文献
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Marc Mangel 《Physica A》1979,97(3):616-642
A generalized critical point can be characterized by non-linear dynamics. We formulate the deterministic and stochastic theory of relaxation at such a point. Canonical problems are used to motivate the general solutions. In the deterministic theory, we show that at the critical point certain modes have polynomial (rather than exponential) growth or decay. The stochastic relaxation rates can be calculated in terms of various incomplete special functions. Three examples are considered. First, a substrate inhibited reaction (marginal type dynamical system) is treated. Second, the relaxation of a mean field ferromagnet is considered. We obtain a result that generalizes the work of Griffiths et al. Third, we study the relaxation of a critical harmonic oscillator. 相似文献
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Yu. P. Kalmykov Yu. L. Raikher W. T. Coffey S. V. Titov 《Physics of the Solid State》2005,47(12):2325-2332
The signal-to-noise ratio for magnetic stochastic resonance in a superparamagnetic particle with cubic anisotropy is shown to be strongly dependent on the Larmor precession damping α. This phenomenon is due to the coupling of the relaxation and precession modes and can be used for measuring α. The dependence of the signal-to-noise ratio on α is characteristic of particles with nonaxial anisotropy; so the effect is absent in uniaxial particles. 相似文献
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G. S. Agarwal 《Zeitschrift für Physik B Condensed Matter》1979,33(1):111-124
The stochastic and quantum dynamics of open quantum systems interacting with stochastic perturbations in considered. The master equations for one time and multi-time correlation functions of such a system are derived to all orders in the interaction with the stochastic perturbations. The importance of the non-markovian character of such equations in the study of various problems in optical resonance is discussed. The simplified form of the non-markovian master equations in Born approximation is also given. It is shown that such non-markovian master equations in Born approximation are exact if there is only one random perturbation, of the telegraphic signal type, acting on the system. The master equations for the linear response functions of an open system interacting with stochastic perturbations are also derived. The non-markovian master equations for multitime correlations are used to study the behaviour of two level atoms interacting with fluctuating laser fields. Both amplitude and phase fluctuations are taken into account. Explicit results are presented for the spectrum of resonance fluorescence, absorption spectrum, photon antibunching effects etc. The calculations are done for arbitrary values of the relaxation parameters and intial conditions. In general the fluorescence spectrum is found to be asymmetric for off resonant fields. 相似文献
15.
A basic model of magnetic resonance is considered. The model takes into account external static and orthogonal to it rotating magnetic fields together with fluctuating (local) field directed along the static field. The local field is considered as smooth normal stochastic process. New solutions for longitudinal relaxation are obtained in the region of adiabatic slow fluctuations and nonadiabatic losses are estimated. 相似文献
16.
We investigate functions that are exact solutions to chaotic dynamical systems. A generalization of these functions can produce truly random numbers. For the first time, we present solutions to random maps. This allows us to check, analytically, some recent results about the complexity of random dynamical systems. We confirm the result that a negative Lyapunov exponent does not imply predictability in random systems. We test the effectiveness of forecasting methods in distinguishing between chaotic and random time series. Using the explicit random functions, we can give explicit analytical formulas for the output signal in some systems with stochastic resonance. We study the influence of chaos on the stochastic resonance. We show, theoretically, the existence of a new type of solitonic stochastic resonance, where the shape of the kink is crucial. Using our models we can predict specific patterns in the output signal of stochastic resonance systems. (c) 2001 American Institute of Physics. 相似文献
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We study different nonlinear systems which possess noise-induced nonequlibrium transitions and shed light on the role of additive noise in these effects. We find that the influence of additive noise can be very nontrivial: it can induce first- and second-order phase transitions, can change properties of on-off intermittency, or stabilize oscillations. For the Swift-Hohenberg coupling, that is a paradigm in the study of pattern formation, we show that additive noise can cause the formation of ordered spatial patterns in distributed systems. We show also the effect of doubly stochastic resonance, which differs from stochastic resonance, because the influence of noise is twofold: multiplicative noise and coupling induce a bistability of a system, and additive noise changes a response of this noise-induced structure to the periodic driving. Despite the close similarity, we point out several important distinctions between conventional stochastic resonance and doubly stochastic resonance. Finally, we discuss open questions and possible experimental implementations. (c) 2001 American Institute of Physics. 相似文献
18.
We present the results of an extensive numerical study on the phenomenon of stochastic resonance in a bimodal cubic map. Both
Gaussian random noise as well as deterministic chaos are used as input to drive the system between the basins. Our main result
is that when two identical systems capable of stochastic resonance are coupled, the SNR of either system is enhanced at an
optimum coupling strength. Our results may be relevant for the study of stochastic resonance in biological systems. 相似文献
19.
Fuhs M Prisner T Möbius K 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,149(1):67-73
Stochastic excitation with a full-width-half-maximum bandwidth of 250 MHz was used to perform Fourier-transform (FT) high-field/high-frequency electron paramagnetic resonance (EPR) at 3.4T/95 GHz (W-band). Thereby, the required microwave peak power is reduced by a factor of tau(p)/T1 as compared to equivalent pulsed FT EPR in which the spin system with spin-lattice relaxation time T1 is excited by a single microwave pulse of length tau(p). Stochastic EPR is particularly interesting under high-field/high-frequency conditions, because the limited output power of mm microwave sources, amplifiers, and mixers makes pulse FT EPR in that frequency domain impossible, at least for the near future. On the other hand, FT spectroscopy offers several advantages compared to field-swept magnetic resonance methods, as is demonstrated by its success in NMR and X-band EPR. In this paper we describe a novel stochastic W-band microwave bridge including a bimodal induction mode transmission resonator that serves for decoupling the microwave excitation and signal detection. We report first EPR measurements and discuss experimental difficulties as well as achieved sensitivity. Moreover, we discuss future improvements and the possibility for an application of stochastic W-band FT EPR to transient signals such as those of photoexcited radical pairs in photosynthetic reaction centers. 相似文献