Elbert E. N. Macau

Integrated chaos-based communication

Abstract We characterize a recently proposed new integrated communication scheme fully based on chaos theory (Phys. Rev. E 62 (2000) 4835). We show that this method is very efficient, i.e., it sends large amounts of information with low bit-error rate. This is achieved because we explore the deterministic characteristic of a chaotic system, using it to predict non-transmitted signals.

2009 Special Issue: Chaotic phase synchronization and desynchronization in an oscillator network for object selection

Object selection refers to the mechanism of extracting objects of interest while ignoring other objects and background in a given visual scene. It is a fundamental issue for many computer vision and image analysis techniques and it is still a challenging task to artificial visual systems. Chaotic phase synchronization takes place in cases involving almost identical dynamical systems and it means that the phase difference between the systems is kept bounded over the time, while their amplitudes remain chaotic and may be uncorrelated. Instead of complete synchronization, phase synchronization is believed to be a mechanism for neural integration in brain. In this paper, an object selection model is proposed. Oscillators in the network representing the salient object in a given scene are phase synchronized, while no phase synchronization occurs for background objects. In this way, the salient object can be extracted. In this model, a shift mechanism is also introduced to change attention from one object to another. Computer simulations show that the model produces some results similar to those observed in natural vision systems.

Patrol Mobile Robots and Chaotic Trajectories

This paper presents a study of special trajectories attainment for mobile robots based on the dynamical features of chaotic systems. This method of trajectories construction is envisaged for missions for terrain exploration, with the specific purpose of search or patrol, where fast scanning of the robot workspace is required. We propose the imparting of chaotic motion behavior to the mobile robot by means of a planner of goal positions sequence based on an area-preserving chaotic map. As a consequence, the robot trajectories seem highly opportunistic and unpredictable for external observers, and the trajectoriess characteristics ensure the quick scanning of the patrolling space. The kinematic modeling and the closed-loop control of the robot are described. The results and discussion of numerical simulations close the paper.

Analysis of chaotic saddles in high-dimensional dynamical systems: The Kuramoto–Sivashinsky equation

This paper presents a methodology to study the role played by nonattracting chaotic sets called chaotic saddles in chaotic transitions of high-dimensional dynamical systems. Our methodology is applied to the Kuramoto-Sivashinsky equation, a reaction-diffusion partial differential equation. The paper describes a novel technique that uses the stable manifold of a chaotic saddle to characterize the homoclinic tangency responsible for an interior crisis, a chaotic transition that results in the enlargement of a chaotic attractor. The numerical techniques explained here are important to improve the understanding of the connection between low-dimensional chaotic systems and spatiotemporal systems which exhibit temporal chaos and spatial coherence.

A network of dynamically coupled chaotic maps for scene segmentation

In this paper, a computational model for scene segmentation based on a network of dynamically coupled chaotic maps is proposed. Time evolutions of chaotic maps that correspond to an object in the given scene are synchronized with one another, while this synchronized evolution is desynchronized with respect to time evolution of chaotic maps corresponding to other objects in the scene. In this model, the coupling range of each active element increases dynamically according to predefined rules until a saturated state is achieved, i.e., locally coupled chaotic maps corresponding to an object in the initial state will be coupled globally in the final state. Consequently, the advantage of both global coupling and local coupling are incorporated in a single scheme. In comparison to continuous models, this proposed model is suitable for computational implementation. Another significant benefit is that the good performance and transparent dynamics of the model are obtained by utilizing one-dimensional chaotic map instead of complex neuron as each element.

The Aster Project: Flight to a Near-Earth Asteroid

The information on the project being developed in Brazil for a flight to binary or triple near-Earth asteroid is presented. The project plans to launch a spacecraft into an orbit around the asteroid and to study the asteroid and its satellite within six months. Main attention is concentrated on the analysis of trajectories of flight to asteroids with both impulsive and low thrust in the period 2013-2020. For comparison, the characteristics of flights to the (45) Eugenia triple asteroid of the Main Belt are also given.

SCENE SEGMENTATION OF THE CHAOTIC OSCILLATOR NETWORK

A chaotic oscillatory correlation network for scene segmentation is presented. It is a two-dimensional array with locally coupled chaotic elements. It offers a mechanism to escape from the synchrony–desynchrony dilemma. As a result, this model has unbounded capacity of segmentation. Chaotic dynamics and chaotic synchronization in the model are analyzed. Desynchronization property is guaranteed by the definition of chaos. Computer simulations confirm the theoretical prediction.

Do the recent severe droughts in the Amazonia have the same period of length

We propose a new measure based on drought period length to assess the temporal difference between the recent two severe droughts of 2005 and 2010 in the Amazonia. The sensitivity of the measure is demonstrated by disclosing the distinct spatial responding mechanisms of the Northeastern and Southwestern Amazon (NA, SA) to the surrounding sea surface temperature (SST) variabilities. The Pacific and Atlantic oceans have different roles on the precipitation patterns in Amazonia. More specifically, the very dry periods in the NA are influenced by El Niño events, while the very dry periods in the SA are affected by the anomalously warming of the SST in the North Atlantic. Our analysis discloses convincingly that the drought 2005 hit SA, which is correlated to the North Atlantic only. Furthermore, it suggests that there are two phases in the drought 2010: (1) it was started in the NA in August 2009 co-occurred with the El Niño event, and (2) later shifted the center of action to SA resulted from anomalously high SST in North Atlantic, which further intensifies the impacts on the spatial coverage.

Isochronal synchronization of time delay and delay-coupled chaotic systems

This paper studies the problem of isochronal synchronization of time-delay chaotic systems featuring also coupling delay. Based on the Lyapunov–Krasovskii stability theory, sufficient conditions are derived for the stability of isochronal synchronization between a pair of identical chaotic systems. Such criteria permit the proper design of stable proportional linear feedback controller, more specifically, the design of adequate proportional feedback gain matrices. The proposed criteria are suited to systems with (i) intrinsic delay, (ii) coupling delay or (iii) both. Numerical simulations of the synchronization of delay-coupled systems are presented as examples of the application of the criteria.

Communication with chaos over band-limited channels

Abstract Recently, many works have pointed out the fact that the complexity inhereent in the dynamics of a chaotic systems can be advantageously used to implement digital communication system [1,8–14]. Digital information is encoded in large-scale features of the waveform by using small perturbations to control the symbolic dynamics [1]. Chaotic oscillations cover a wide spectral domain and can efficiently mask an information signal scrambled by the chaotic encoder [1–2]. However, the wide spectrum poses intrinsic difficulties in the decoding process if the codified chaotic signal is transmitted over real communication channels with limited bandwidth [12,13]. We address this problem numerically, and we propose an approach to improve chaotic communication over band-limited and noisy channels. Our results suggest that chaotic communication concept is a convenient approach to be exploited to efficiently transmit large amount of date with a good level of security, which makes this concept as a good option to be used for the next generation communication satellites.