Gamal M. Mahmoud

ACTIVE CONTROL AND GLOBAL SYNCHRONIZATION OF THE COMPLEX CHEN AND LÜ SYSTEMS

Chaos synchronization is a very important nonlinear phenomenon, which has been studied to date extensively on dynamical systems described by real variables. There also exist, however, interesting cases of dynamical systems, where the main variables participating in the dynamics are complex, for example, when amplitudes of electromagnetic fields are involved. Another example is when chaos synchronization is used for communications, where doubling the number of variables may be used to increase the content and security of the transmitted information. It is also well-known that similar generalization of the Lorenz system to one with complex ODEs has been introduced to describe and simulate the physics of a detuned laser and thermal convection of liquid flows. In this paper, we study chaos synchronization by applying active control and Lyapunov function analysis to two such systems introduced by Chen and Lu. First we show that, written in terms of complex variables, these systems can have chaotic dynamics and...

ANALYSIS OF HYPERCHAOTIC COMPLEX LORENZ SYSTEMS

This paper introduces and analyzes new hyperchaotic complex Lorenz systems. These systems are 6-dimensional systems of real first order autonomous differential equations and their dynamics are very complicated and rich. In this study we extend the idea of adding state feedback control and introduce the complex periodic forces to generate hyperchaotic behaviors. The fractional Lyapunov dimension of the hyperchaotic attractors of these systems is calculated. Bifurcation analysis is used to demonstrate chaotic and hyperchaotic behaviors of our new systems. Dynamical systems where the main variables are complex appear in many important fields of physics and communications.

Basic Properties And Chaotic Synchronization Of Complex Lorenz System

This paper aims at studying the basic properties and chaotic synchronization of complex Lorenz system: where α, γ, β are positive (real or complex) parameters, x and y are complex variables, z is a real variable, an overbar denotes complex conjugate variable and dots represent derivatives with respect to time. This system arises in many important applications in physics, for example, in laser physics and rotating fluids dynamics. Numerically we show that this system is a chaotic system and exhibits chaotic attractors. The necessary conditions for system (⋆) to generate chaos are obtained. Analytical and numerical calculations are presented to achieve synchronization. Active control technique is used to synchronize chaotic attractors of equations (⋆).

Synchronization and control of hyperchaotic complex Lorenz system

The aim of this paper is to investigate the phenomenon of projective synchronization (PS) and modified projective synchronization (MPS) of hyperchaotic attractors of hyperchaotic complex Lorenz system which has been introduced recently in our work. The control problem of these attractors is also studied. Our system is a 6-dimensional continuous real autonomous hyperchaotic system. The active control method based on Lyapunov function is used to study PS and MPS of this system. The problem of hyperchaos control is treated by adding the complex periodic forcing. The control performances are verified by calculating Lyapunov exponents. Numerical simulations are implemented to verify the results of these investigations.

THE DYNAMICS OF SYSTEMS OF COMPLEX NONLINEAR OSCILLATORS: A REVIEW

Dynamical systems in the real domain are currently one of the most popular areas of scientific study. A wealth of new phenomena of bifurcations and chaos has been discovered concerning the dynamics of nonlinear systems in real phase space. There is, however, a wide variety of physical problems, which, from a mathematical point of view, can be more conveniently studied using complex variables. The main advantage of introducing complex variables is the reduction of phase space dimensions by a half. In this survey, we shall focus on such classes of autonomous, parametrically excited and modulated systems of complex nonlinear oscillators. We first describe appropriate perturbation approaches, which have been specially adapted to study periodic solutions, their stability and control. The stability analysis of these fundamental periodic solutions, though local by itself, can yield considerable information about more global properties of the dynamics, since it is in the vicinity of such solutions that the largest regions of regular or chaotic motion are observed, depending on whether the periodic solution is, respectively, stable or unstable. We then summarize some recent studies on fixed points, periodic solutions, strange attractors, chaotic behavior and the problem of chaos control in systems of complex oscillators. Some important applications in physics, mechanics and engineering are mentioned. The connection with a class of complex partial differential equations, which contains such famous examples, as the nonlinear Schrodinger and Ginzburg–Landau equations is also discussed. These complex equations play an important role in many branches of physics, e.g. fluids, superconductors, plasma physics, geophysical fluids, modulated optical waves and electromagnetic fields.

Strange attractors and chaos control in periodically forced complex Duffing's oscillators

An interesting and challenging research subject in the field of nonlinear dynamics is the study of chaotic behavior in systems of more than two degrees of freedom. In this work we study fixed points, strange attractors, chaotic behavior and the problem of chaos control for complex Duffings oscillators which represent periodically forced systems of two degrees of freedom. We produce plots of Poincare map and study the fixed points and strange attractors of our oscillators. The presence of chaotic behavior in these models is verified by the existence of positive maximal Lyapunov exponent. We also calculate the power spectrum and consider its implications regarding the properties of the dynamics. The problem of controlling chaos for these oscillators is studied using a method introduced by Pyragas (Phys. Lett. A 170 (1992) 421), which is based on the construction of a special form of a time-continuous perturbation. The study of coupled periodically forced oscillators is of interest to several fields of physics, mechanics and engineering. The connection of our oscillators to the nonlinear Schrodinger equation is discussed.

On projective synchronization of hyperchaotic complex nonlinear systems based on passive theory for secure communications

In this paper we deal with the projective synchronization (PS) of hyperchaotic complex nonlinear systems and its application in secure communications based on passive theory. The unpredictability of the scaling factor in PS can additionally enhance the security of communications. In this paper, a scheme for secure message transmission is proposed, and we try to transmit more than one large or bounded message from the transmitter to the receiver. The new hyperchaotic complex Lorenz system is employed to encrypt these messages. In the transmitter, the original messages are modulated into its parameter. In the receiver, we assume that the parameter of the receiver system is uncertain. The controllers and corresponding parameter update law are constructed to achieve PS between the transmitter and receiver system with an uncertain parameter, and identify the unknown parameter via passive theory. The original messages can be recovered successfully through some simple operations by the estimated parameter. Numerical results have verified the effectiveness and feasibility of the presented method.

Chaotic and hyperchaotic attractors of a complex nonlinear system

In this paper, we introduce a complex nonlinear hyperchaotic system which is a five-dimensional system of nonlinear autonomous differential equations. This system exhibits both chaotic and hyperchaotic behavior and its dynamics is very rich. Based on the Lyapunov exponents, the parameter values at which this system has chaotic, hyperchaotic attractors, periodic and quasi-periodic solutions and solutions that approach fixed points are calculated. The stability analysis of these fixed points is carried out. The fractional Lyapunov dimension of both chaotic and hyperchaotic attractors is calculated. Some figures are presented to show our results. Hyperchaos synchronization is studied analytically as well as numerically, and excellent agreement is found.

Approximate solutions of a class of complex nonlinear dynamical systems

Nonlinear dynamical systems, being a realistic representation of nature, often exhibit a somewhat complicated behaviour. Their analysis requires a thorough investigation into the solutions of the governing nonlinear differential equations. In this paper, an approximate method is presented for solving complex nonlinear differential equations of the form: z+ω2z+ef(z,z,z,z)=0,where z is a complex function and e is a small parameter. It is based on the generalized averaging method which we have developed recently. Our approach can be viewed as a generalization of the approximate method based on the Krylov–Bogoliubov averaging method. The study of these systems is of interest to several fields of statistical mechanics, physics, electronics and engineering. Application of this method to special cases is performed for the purpose of comparison with numerical computations. Excellent agreement is found for reasonably large values of e, which shows the applicability of this method to this kind of nonlinear dynamical systems. This agreement gives extra confidence that the analytical results are correct. These analytical results can be used as a theoretical guidance for doing further numerical or theoretical studies.

Modified projective synchronization and control of complex Chen and Lü systems

In this paper we present a modified projective synchronization of complex Chen and Lü systems which were introduced recently in our work. These complex systems appear in many important fields of physics and engineering, for example, laser physics, nonlinear circuits and secure communication. The active control technique based on a Lyapunov function is used to synchronize the chaotic attractors of both identical and different systems. Controlling these attractors is investigated by adding a complex periodic forcing. The control performances are verified by calculating Lyapunov exponents. Numerical computations are presented to verify our analytical results for control functions to achieve the modified projective synchronization.