V. Pérez-Muñuzuri

Autowaves for image processing on a two-dimensional CNN array of excitable nonlinear circuits: flat and wrinkled labyrinths

A two-dimensional (2-D) cellular neural network (CNN) array of resistively coupled Chua circuits which can be designed to implement some elementary aspects of spatial recognition, namely, distinguishing open curves from closed ones and locating the shortest path between two locations, is described. In the latter, two situations are analyzed: flat and wrinkled surfaces. The 2-D CNN array of Chua circuits is shown to be capable of finding the shortest path between two points on a wrinkled labyrinth. The performance of this parallel processing approach was examined using computer simulations, although this method can be implemented in real time via VLSI technology. >

Spiral waves on a 2-D array of nonlinear circuits

Spatio-temporal patterns formed in a 2-D array of Chuas circuits have been studied numerically. It has been found that spiral wave solutions can appear over a large range of parameters and some of their properties have been measured. This demonstrates that spiral wave dynamics can be studied in arrays of discrete electronic circuits, such as a 2-D array of Chuas circuits, where real-time results can be obtained. We also study the influence of small differences in the parameters of the circuits, as is the case in real electronic components, where a 5% device tolerance is typical. >

SPATIOTEMPORAL STRUCTURES IN DISCRETELY-COUPLED ARRAYS OF NONLINEAR CIRCUITS: A REVIEW

Spatiotemporal pattern formation occurring in discretely-coupled nonlinear dynamical systems has been studied numerically. Reaction-diffusion systems can be viewed as an assembly of a large number of identical local subsystems which are coupled to each other by diffusion. Here, the local subsystems are defined by a system of nonlinear ordinary differential equations. While for continuous systems, the characteristic time scale corresponding to the diffusion is slower than that corresponding to the local subsystems, in discretely-coupled systems, both time scales can be of the same order of magnitude. Discrete systems can exhibit behaviors different from those exhibited by their equivalent continuous model: the wave propagation failure phenomenon occurring in nerve-pulse propagation due to transmission blockage is a case in point. In this case, it is found that the wave fails to propagate at or below some critical value of the coupling coefficient. Systems of coupled cells can be found to occur in the trans...

PROPAGATION FAILURE IN LINEAR ARRAYS OF CHUA’S CIRCUITS

Traveling wave fronts are considered for a one-dimensional array of Chua’s circuits. For diffusion coefficients less than some nonzero critical value it has been observed numerically that the traveling fronts fail to propagate. Propagation failure is compared with similar phenomena occurring in pulse propagation in nerves, and in coupled continuously-stirred tank reactors.

Vulnerability in excitable Belousov-Zhabotinsky medium: from 1D to 2D

Abstract Mechanisms for initiating rotating waves in 1D and 2D excitable media were compared and parameters affecting wavefront formation were analyzed. The time delay between two sequentially initiated wavefronts (a conditioning wave followed by a test wave) was varied in order to induce rotating waves, a protocol similar to that utilized in cardiac muscle experiments to reveal vulnerability to rotating wave initiation. We define the vulnerability region, VR, as the range of time delays between conditioning and test waves where the test waves evolves into a rotating wave. The smaller the VR, the more resistant the heart is against origination of dangerous cardiac arrhythmias. Heterogeneity of cardiac muscle is widely recognized as the prerequisite for rotating wave initiation. We have identified the VR in homogeneous 2D excitable media. In the Belousov-Zhabotinsky (BZ) reaction with immobilized catalyst and in the Oregonator model of this reaction, a properly timed test wave gives rise to rotating waves. The VR was increased when the size of the perturbation used for test wave creation was increased or when the threshold for propagation was decreased. Increasing the dimensionality of the medium for 1D to 2D results in diminishing of VR.

Introductory analysis of Bénard–Marangoni convection

We describe experiments on Benard–Marangoni convection which permit a useful understanding of the main concepts involved in this phenomenon such as, for example, Benard cells, aspect ratio, Rayleigh and Marangoni numbers, Crispation number and critical conditions. In spite of the complexity of convection theory, we carry out a simple and introductory analysis which has the additional advantage of providing very suggestive experiments. As a consequence, we recommend our device for use as a laboratory experiment for undergraduate students of the thermodynamics of nonlinear and fluid physics.

Interaction of chaotic rotating waves in coupled rings of chaotic cells

Abstract The interaction of two chaotic rotating waves of the type recently reported by Matias et al. [Europhys. Lett. 37 (1997) 379] is studied experimentally with arrays of non-linear electronic circuits arranged in ring geometries. Unidirectional coupling is assumed for the cell-to-cell coupling within the same ring, but between rings, cells are coupled diffusively. Depending on the relative sense of driving, competition between a rotating chaotic wave and a global synchronized state has been observed. The results are rationalized by means of a linear stability analysis around the uniform synchronized behavior, where the circulant symmetry of the system allows to express the problem as a superposition of a series of Fourier modes.

Forecasting and Diagnostic Analysis of Plume Transport around a Power Plant

A nonreactive Lagrangian atmospheric diffusion model is used for the simulation of SO 2 concentration around the As Pontes 1400-MW power plant located in northwestern Spain. This diffusion model has two kinds of input: 1) diagnostic wind fields from real measurements and 2) forecast wind fields from a 24-h mesoscale prediction. This model-based system is applied for a particular day around the As Pontes 1400-MW power plant, which is a coal-fired power plant. The shape of estimated and forecast plumes are compared, and the meteorological prediction results are analyzed.

Spiral breakup induced by an electric current in a Belousov-Zhabotinsky medium.

Sprial breakup in the Belousov-Zhabotinsky reaction has been observed under the influence of an externally applied alternating electric current. The dynamic mechanism of this breakup is explained in the framework of this reaction. The dependence of the critical electric current amplitude on the period of the wave and on the excitability of the medium is analyzed. Spiral breakup is shown to provide a limit of validity of electric-field-induced drift of vortices in excitable media. Experimental results are complemented with numerical simulations provided by two- and three-variable Oregonator models.

Electric current control of spiral wave dynamics

The control of spiral wave parameters by electric current was investigated in the Belousov-Zhabotinsky (BZ) reaction. It was found that the wavelength and the period of spiral waves increase by a factor of up to 3 with electric current (both dc and ac). Using this procedure spiral waves with a period higher than the period of medium bulk oscillations were observed. It was also found that hysteresis phenomena occur in the system considered.