共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
《Physics letters. A》1998,249(4):307-314
3.
We present a normal form for traveling waves in one-dimensional excitable media in the form of a differential delay equation. The normal form is built around the well-known saddle-node bifurcation generically present in excitable media. Finite wavelength effects are captured by a delay. The normal form describes the behavior of single pulses in a periodic domain and also the richer behavior of wave trains. The normal form exhibits a symmetry preserving Hopf bifurcation which may coalesce with the saddle node in a Bogdanov-Takens point, and a symmetry-breaking spatially inhomogeneous pitchfork bifurcation. We verify the existence of these bifurcations in numerical simulations. The parameters of the normal form are determined and its predictions are tested against numerical simulations of partial differential equation models of excitable media with good agreement. 相似文献
4.
5.
We propose a new cellular automaton (CA) model, which reproduces isotropic time-evolution patterns observed in the Belousov-Zhabotinsky reaction. Although several CA models have been proposed exhibiting isotropic patterns of the reaction, most of them need complicated rules and a large number of neighboring cells. Our model can produce isotropic patterns from a simple probabilistic rule among a few (4 or 8) neighboring cells. 相似文献
6.
7.
8.
9.
《Physica D: Nonlinear Phenomena》1988,32(3):437-450
Wave propagation in an inhomogeneous excitable medium is modeled by a two-dimensional, multi-state cellular automaton with absorbing boundary conditions. The inhomogeneity of the meduim affects the normal pattern of wave propagation and various phenomena like delayed propagation and circular wave formation are observed. The different types of wave propagation observed in our computer simulations are summarized in a phase diagram and the predictions of the stochastic models for two of the wave propagation phenomena are presented. This system has been suggested as a simple model of the atrioventricular (AV) node. 相似文献
10.
Z. Knittl 《Czechoslovak Journal of Physics》1968,18(6):763-770
The inhomogeneous layer of an arbitrary index profile is replaced by the conventional multilayer of homogeneous elements. When the number of layers converges to infinity, the solution is performed exactly using the method of rational functions previously described by the author. As a result the reflection coefficient is expressed as the ratio of two infinite power series in (2/)j, the coefficients being defined as multiple integrals of increasing order. The Drude formulae follow as a first approximation.
The paper is dedicated to the memory of Dr. A. Vaíek, Professor of the J. E. Purkyn University in Brno, who died on November 16, 1966. 相似文献
11.
12.
13.
Novel devices for converting a linear polarization state to radial or azimuthal polarization states are realized by use of space-variant inhomogeneous media on a subwavelength scale. The two designs presented use form birefringence to locally transform the polarization state. The devices are fabricated in a GaAs substrate for operation in the far-infrared wavelength range. The experimental characterization is in good agreement with the designs, demonstrating high conversion efficiency. 相似文献
14.
N. G. van Kampen 《Journal of statistical physics》1991,63(5-6):1019-1033
The nonlinear equations that describe transport in inhomogeneous media cannot be obtained by a straightforward extension of the known phenomenological equations for homogeneous media. One cannot therefore asserta priori that the Onsager reciprocity relations remain valid. Previously the correct equations have been obtained for three special models using kinetic theory. It is here shown that in these models the Onsager relations do indeed hold, provided that they are formulated with care. 相似文献
15.
16.
V. P. Yakubov E. D. Telpukhovskiy G. M. Tsepelev V. V. Belov A. V. Klokov N. A. Moiseenko S. N. Novik D. Ya. Sukhanov O. V. Yakubova 《Russian Physics Journal》2006,49(9):923-928
Results of experimental investigations on radar sensing of inhomogeneous media and objects with the use of both superbroadband
(from 0.5 to 17 GHz) multifrequency scanning and supershort nanosecond and subnanosecond radar pulses are considered. It is
demonstrated that addition of angular and spatial scanning and subsequent synthesis of a large aperture allow a three-dimensional
tomography of low-contrast inhomogeneities to be realized with a spatial resolution of about 1 cm. Examples are presented
that confirm a high efficiency of the method for contactless tomography of the forest structure and detection and visualization
of infantry mines below a rough sand surface.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 20–25, September, 2006. 相似文献
17.
A theory is presented for the optical properties of inhomogeneous media consisting of small particles in a continuous dielectric host. In contrast to the commonly used Maxwell-Garnett approach, our theory includes the dipole-dipole coupling between the randomly distributed particles. The pronounced disorder-induced broadening explains the large width of typical experimental absorption lines and thus resolved the long-standing discrepancy between measured spectra and the predictions of the Maxwell-Garnett model. 相似文献
18.
We study spiral wave breakup using a Fitzhugh-Nagumo-type system. We find that spiral wave breakup can occur near the core or far from it in both excitable and oscillatory regimes. There is a faraway breakup scenario in both excitable and oscillatory media that depends on long wavelength modulation modes. We observed three distinct scenarios, including one that involves breakup that does not develop into turbulence. However, we find that the mechanisms behind these three scenarios are the same: they are caused by the interaction between the dispersion relation and the asymptotic behavior of the modulation mode. The difference in phenomenology is due to the asymptotic behavior of the modulation mode. 相似文献
19.
20.
Algebraic formulas predicting the frequencies and shapes of waves in a reaction-diffusion model of excitable media are presented in the form of four recipes. The formulas themselves are based on a detailed asymptotic analysis (published elsewhere) of the model equations at leading order and first order in the asymptotic parameter. The importance of the first order contribution is stressed throughout, beginning with a discussion of the Fife limit, Fife scaling, and Fife regime. Recipes are given for spiral waves and detailed comparisons are presented between the asymptotic predictions and the solutions of the full reaction-diffusion equations. Recipes for twisted scroll waves with straight filaments are given and again comparisons are shown. The connection between the asymptotic results and filament dynamics is discussed, and one of the previously unknown coefficients in the theory of filament dynamics is evaluated in terms of its asymptotic expansion. (c) 2002 American Institute of Physics. 相似文献