bluuebunny/crossref_metadata_2025 huggingface dataset:
TEXT CATEGORIZATION IN AN INTELLIGENT AGENT FOR FILTERING INFORMATION ON THE WEB
Authors: GENTILI G. L. , MARINILLI M. , MICARELLI A. , SCIARRONE F.
Published: April 2003

This paper presents a text categorization system, capable of analyzing HTML/text documents collected from the Web. The system is a component of a more extensive intelligent agent for adaptive information filtering on the Web. It is based on a hybrid case-based architecture, where two multilayer perceptrons are integrated into a case-based reasoner. An empirical evaluation of the system was performed by means of a confidence interval technique. The experimental results obtained are encouraging and support the choice of a hybrid case-based approach to text categorization.
DYNAMIC ADAPTIVE AUTONOMY IN MULTIAGENT SYSTEMS: REPRESENTATION AND JUSTIFICATION
Authors: BARBER K. SUZANNE , MARTIN CHERYL E.
Published: April 2003

Autonomy is an often cited but rarely agreed upon agent characteristic. Although no definition of agent autonomy is universally accepted, the concept of adaptive autonomy promises increasingly flexible and robust agent-based systems. In general, adaptive autonomy gives agents the ability to seek help for problems or take initiative when otherwise they would be constrained by their design to follow some fixed procedures or rules for interacting with other agents. In order to access these benefits, this article provides a core definition and representation of agent autonomy designed to support the implementation of adaptive agent autonomy. This definition identifies "decision-making control" governing the determination of agent goals and tasks as the key dimension of agent autonomy. In order to gain run-time flexibility and any associated performance improvements, agents must be able to dynamically adapt their autonomy during system operation. This article justifies the implementation of dynamic adaptive autonomy through a series of experiments showing that a multiagent system operating under dynamic adaptive autonomy performs better than a multiagent system operating under fixed autonomy for the same changing run-time conditions.
HOW CAN AI SYSTEMS DEAL WITH LARGE AND COMPLEX PROBLEMS?
Authors: OHSUGA SETSUO
Published: April 2003

Problems arising in the near future may grow larger and more complex beyond the human capability for managing them and it is worrying that this can cause trouble for human society. The only possible way to solve this problem is to make computers more intelligent to back up the weak points of human beings. At least, it is necessary to provide a method for capturing and recording all human decisions in problem-solving. This view leads one to an idea of a computer-led interactive system such that the computer becomes able to manage problem-solving process and makes records of individual decisions made by a human being. Autonomy, generality and practicality are the major requirements for such computer-led interactive systems. New information technology to meet this condition is discussed. It is very different from the conventional computer technology in many aspects. The major topics are: a model-based software architecture for future information systems, a modeling scheme to accept and represent a wide area of problems, a method for externalizing human ideas and of representing it as a model, a method for solving problems represented in the form of a model and so on. It outlines a part of the research work being promoted by the author's group under the sponsorship of the Science and Technology Agency of the Japanese Government.
FAST SEARCH ALGORITHMS FOR INDUSTRIAL INSPECTION
Authors: CHANG MING-CHING , FUH CHIOU-SHANN , CHEN HSIEN-YEI
Published: April 2003

This paper presents an efficient general purpose search algorithm for alignment and an applied procedure for IC print mark quality inspection. The search algorithm is based on normalized cross-correlation and enhances it with a hierarchical resolution pyramid, dynamic programming, and pixel over-sampling to achieve subpixel accuracy on one or more targets. The general purpose search procedure is robust with respect to linear change of image intensity and thus can be applied to general industrial visual inspection. Accuracy, speed, reliability, and repeatability are all critical for the industrial use. After proper optimization, the proposed procedure was tested on the IC inspection platforms in the Mechanical Industry Research Laboratories (MIRL), Industrial Technology Research Institute (ITRI), Taiwan. The proposed method meets all these criteria and has worked well in field tests on various IC products.
3D SHAPE RECONSTRUCTION OF HYBRID REFLECTANCE USING THE LMS ALGORITHM
Authors: LEE MAL-REY
Published: April 2003

In this paper, we present a new approach for determining the reflectance properties of surface and recovering 3D shapes from intensity images. We determine reflectance parameters which minimize the sum squared difference of the intensity distribution between the image of a sample sphere and the calculated image. The estimated reflectance parameters provide the range data with intensity distributions. Therefore, we generate three reference images of a range sphere, which has the same diameter as that of the sample, from the same viewpoint but with different light directions. Direct matching of the object images to the references can precisely reconstruct the shape of the object. This paper uses a plate diffuse illumination to alleviate the effects of specular spike and highlights. The simulation results show that the proposed method can estimate reflectance properties of the hybrid surface, and also recover the object shape.
OFFLINE SIGNATURE VERIFICATION BY THE ANALYSIS OF CURSIVE STROKES
Authors: FANG B. , WANG Y. Y. , LEUNG C. H. , TSE K. W. , TANG Y. Y. , KWOK P. C. K. , WONG Y. K.
Published: April 2003

In this paper, a method is proposed for offline signature verification. It is based on a smoothness criterion. It is observed that the cursive segments of forgery signatures are generally less smooth and less natural than the genuine ones, especially for those signatures that consist of cursive graphic patterns. Two approaches are proposed to extract a smoothness feature: a crossing method and a fractal dimension method. When the proposed smoothness feature is combined with other global shape features for signature verification, satisfactory results are obtained.
A NEW STROKE EXTRACTION METHOD OF CHINESE CHARACTERS
Authors: SUN XINGMING , YANG LIHUA , TANG Y. Y. , HU YUNFA
Published: April 2003

Stroke extraction of Chinese characters plays an important role in Chinese character information processing such as character recognition, document analysis, document compression and storage, font automation and so on. By analyzing the structure of Chinese characters deeply, this paper developed a novel method to extract strokes of Chinese characters directly from the original character pattern image. Two theorems, eight rules and an algorithm for stroke extraction of Chinese characters are presented. This method can overcome the difficulties encountered in disposing the intersection or connection of different strokes, and can eliminate noises successfully. Our experiments have shown that this method can extract strokes both accurately and efficiently.
IMAGE SMOOTHING WITH EXPONENTIAL FUNCTIONS
Authors: BASU MITRA , SU MIN
Published: April 2003

Noise reduction in images, also known as image smoothing, is an essential and first step before further processings of the image. The key to image smoothing is to preserve important features while removing noise from the image. Gaussian function is widely used in image smoothing. Recently it has been reported that exponential functions (value of the exponent is not equal to 2) perform substantially better than Gaussian functions in modeling and preserving image features. In this paper we propose a family of exponential functions, that include Gaussian when the value of the exponent is 2, for image smoothing. We experiment with a variety of images, artificial and real, and demonstrate that optimal results are obtained when the value of the exponent is within a certain range.
FORGERY DETECTION BY LOCAL CORRESPONDENCE
Authors: GUO JINHONG KATHERINE , DOERMANN DAVID , ROSENFELD AZRIEL
Published: April 2003

Signatures may be stylish or unconventional and have many personal characteristics that are challenging to reproduce by anyone other than the original author. For this reason, signatures are used and accepted as proof of authorship or consent on personal checks, credit purchases and legal documents. Currently signatures are verified only informally in many environments, but the rapid development of computer technology has stimulated great interest in research on automated signature verification and forgery detection.

In this paper, we focus on forgery detection of offline signatures. Although a great deal of work has been done on offline signature verification over the past two decades, the field is not as mature as online verification. Temporal information used in online verification is not available offline and the subtle details necessary for offline verification are embedded at the stroke level and are hard to recover robustly. We approach the offline problem by establishing a local correspondence between a model and a questioned signature. The questioned signature is segmented into consecutive stroke segments that are matched to the stroke segments of the model. The cost of the match is determined by comparing a set of geometric properties of the corresponding substrokes and computing a weighted sum of the property value differences. The least invariant features of the least invariant substrokes are given the biggest weights, thus emphasizing features that are highly writer-dependent.

Random forgeries are detected when a good correspondence cannot be found, i.e. the process of making the correspondence yields a high cost. Many simple forgeries can also be identified in this way. The threshold for making these decisions is determined by a Gaussian statistical model.

Using the local correspondence between the model and a questioned signature, we perform skilled forgery detection by examining the writer-dependent information embedded at the substroke level and try to capture unballistic motion and tremor information in each stroke segment, rather than as global statistics. Experiments on random, simple and skilled forgery detection are presented.
REGULARIZATION OF GRAPHLIKE SETS IN GRAY-TONE DIGITAL IMAGES
Authors: ARCELLI CARLO , SERINO LUCA
Published: April 2003

The repeated application of topology preserving reduction operations to a gray-tone digital image produces a homotopic image including a set S which has graphlike structure and may be regarded as a stylized version of the foreground, when it is perceived as an elongated subset of the image. To improve the capability of S to represent the foreground in a perceptually appealing way, it is convenient to modify some of the arcs of S by removing part or all of them. This regularization of S is discussed in the paper with respect to different significance measures for arc points, which allow an evaluation of the saliency of each arc. We deal with two types of regularization criteria, which are respectively applied while examining the arcs from end points and from normal points. Specific criteria depend on parameters which are allowed to vary within certain ranges and should be tuned with respect to the application at hand. Both types of criteria are concerned with the closeness of an arc to the part of the background surrounding it, but the former takes also into account the region elongation, while the latter is concerned with the indentations possibly present in the profile of the arc. Experimental work has been carried out on gray-tone images including neurons, and some results are shown.
CHAOS-BASED SIGNAL PROCESSING
Authors: DEDIEU HERVÉ , OGORZAŁEK MACIEJ
Published: April 2003

Given a time series measured (or generated) by a known or an unknown dynamical system we address a series of problems which can be considered as advanced signal processing tasks, namely: (1) section-wise approximation of the measured signal by pieces of trajectories from a chosen nonlinear dynamical system (model); (2) signal restoration when the measured signal has been corrupted e.g. by quantization; (3) signal coding and compression. These tasks can be addressed using a new approach to the shadowing problem based on nonlinear observability problem. Its goal is to reproduce initial conditions for a dynamical system under consideration (approximating waveform generator) giving rise to an orbit which is optimal in the sense of average distance from the measured (or prescribed) transient output waveform. We present the results obtained using the Chua's circuit as approximating waveform generator.
CHAOTIC SYNCHRONIZATION: INFORMATION VIEWPOINT
Authors: DMITRIEV ALEXANDER S. , KASSIAN GENNADY A. , KHILINSKY ALEXANDER D.
Published: April 2003

The phenomenon of chaotic synchronization is investigated from an information viewpoint. The synchronization of a "receiver" of chaos with a chaotic "source" is discussed as an ability of the receiver to recover a copy of the chaotic signal generated by the source. The main idea of the paper is to show that in terms of the information approach the condition for the chaotic synchronization is not due to the physical effect of one system on the other, but the transmission of necessary information about the chaotic process and, hence, the information carrying capacity of the "communication channel" between the source and the receiver.
SYNCHRONIZATION THROUGH FILTERING
Authors: CRUZ C. , NIJMEIJER H.
Published: April 2003

We study the synchronization problem in discrete-time via an extended Kalman filter (EKF). That is, synchronization is obtained of transmitter and receiver dynamics in case the receiver is given via an EKF that is driven by a noisy drive signal from a noisy transmitter dynamics. The convergence of the filter dynamics towards the transmitter dynamics is rigorously shown using recent results in extended Kalman filtering. Two extensive simulation examples show that the filter is indeed suitable for synchronization of (noisy) chaotic transmitter dynamics. An application to private communication is also given.
EXPLOITING SYNCHRONIZATION TO COMBAT CHANNEL DISTORTIONS IN COMMUNICATION WITH CHAOTIC SYSTEMS
Authors: SHARMA NARESH , OTT EDWARD
Published: April 2003

We propose and illustrate a synchronization-based method to combat the channel distortions of a signal transmitted by a chaos-based communication system. In particular, we consider channel distortions like time-varying fading, multipath and time-invariant linear filtering and additive noise. The time-varying parameters are tracked at the receiver to maintain synchronization. The correct noise estimate at the receiver yields synchronization and has minimum norm. A numerical experiment illustrating the method is presented, and shows that successful recovery of the transmitted signal is possible for signal to noise ratios of order unity.
ENCODING DIGITAL INFORMATION USING TRANSIENT CHAOS
Authors: LAI YING-CHENG
Published: April 2003

Recent work has demonstrated that symbolic representations of controlled chaotic orbits can be utilized for encoding digital information. So far, this idea has been demonstrated using systems exhibiting sustained chaotic motion on chaotic attractors. The purpose of this work is to explore digital encoding by using transient chaos naturally arising in nonlinear systems. Dynamically, transient chaos is caused by nonattracting chaotic saddles. We argue that there are two major advantages when trajectories on chaotic saddles are exploited as information source: (1) the channel capacity can in general be large, and (2) the influence of channel noise can be reduced. We present a control scheme and also a practical example of encoding a digital message.
CHAOS SYNCHRONIZATION: A LAGRANGE PROGRAMMING NETWORK APPROACH
Authors: SUYKENS J. A. K. , VANDEWALLE J.
Published: April 2003

In this paper we interpret chaos synchronization schemes within the framework of Lagrange programming networks, which form a class of continuous-time optimization methods for solving constrained nonlinear optimization problems. From this study it follows that standard synchronization schemes can be regarded as a Lagrange programming network with soft constraining, where synchronization between state vectors is defined as a constraint to the dynamical systems. New schemes are proposed then which implement synchronization by hard and soft constraints within Lagrange programming networks. A version is derived which takes into account synchronization errors within the problem formulation. Furthermore Lagrange programming networks for achieving partial and generalized synchronization are given. The methods assume the existence of potential functions for the given systems. The proposed Lagrange programming networks with hard and soft constraining show improved performance on many simulation examples for identical and nonidentical chaotic systems. The schemes are illustrated on Chua's circuit, Lorenz attractor and n-scroll circuits.
ROBUSTNESS OF SYMBOLIC DYNAMICS AND SYNCHRONIZATION PROPERTIES
Authors: GALIAS ZBIGNIEW
Published: April 2003

In this paper we introduce the method for investigation of coupled chaotic systems using topological methods. We show that if the coupling is small then there exists independent symbolic dynamics for every coupled subsystem and in consequence the systems are not synchronized. As an example we consider coupled Hénon maps. Using computer interval arithmetic we find parameter mismatch and perturbation range for which the symbolic dynamics in the Hénon system is sustained. For coupled Hénon maps we compute the value of coupling strength for which the symbolic dynamics in every subsystem survives.
SYNCHRONIZATION IN ARRAYS OF CHAOTIC CIRCUITS COUPLED VIA DYNAMIC COUPLING ELEMENTS
Authors: WU CHAI WAH
Published: April 2003

We study synchronization in arrays of chaotic circuits which are coupled via dynamic coupling elements which can themselves possess chaotic dynamics. We express the synchronization conditions in terms of properties of the underlying hypergraphs and present a result which suggests that under suitable conditions, the more connected the hypergraph is, the easier it is to synchronize the array. The special case of an array of two chaotic circuits is considered. We show that in some cases not all chaotic circuits are synchronized with each other, but clusters are formed in which circuits within a cluster are synchronized to each other.
PHASE CLUSTERING AND COLLECTIVE BEHAVIORS IN GLOBALLY COUPLED MAP LATTICES DUE TO MEAN FIELD EFFECTS
Authors: MAZA D. , BOCCALETTI S. , MANCINI H.
Published: April 2003

We describe the emergence of phase clustering and collective behaviors in an ensemble of chaotic coupled map lattices, due to a mean field interaction. This kind of interaction is responsible for the appearence of a collective state, wherein the mean field evolution of each lattice undergoes a periodic behavior in space. We analyze the transition to such a state in an ensemble of one-dimensional lattices of logistic maps, showing that the resulting behavior cooperatively maximizes the energy of the mean field activity.
ATTRACTOR BUBBLING IN COUPLED HYPERCHAOTIC OSCILLATORS
Authors: BLAKELY JONATHAN N. , GAUTHIER DANIEL J.
Published: April 2003

We investigate experimentally attractor bubbling in a system of two coupled hyperchaotic electronic circuits. The degree of synchronization over a range of coupling strengths for two different coupling schemes is measured to identify bubbling. The circuits display regimes of both attractor bubbling and high-quality synchronization. For the coupling scheme where high-quality synchronization is observed, the transition to bubbling is "soft" and its scaling with coupling strength near the transition point does not fit into the known categories of transition types. We also compare the observed behavior to several proposed criteria for estimating the regime of high-quality synchronization. It is found that none of these methods is completely satisfactory for predicting accurately the regimes of attractor bubbling and high-quality synchronization.
ANTIPHASE SYNCHRONIZATION IN SYMMETRICALLY COUPLED SELF-OSCILLATORS
Authors: ASTAKHOV V. , SHABUNIN A. , ANISHCHENKO V.
Published: April 2003

We consider the antiphase synchronization in symmetrically coupled self-oscillators. As model, two Chua's circuits coupled via a capacity are used. Linear analysis in the vicinity of the symmetric subspace gives the stability conditions for antiphase oscillations. Numerical oscillations demonstrate controlled antiphase synchronization at different values of the parameters of the system.
PRACTICAL STABILITY OF IMPULSIVE SYNCHRONIZATION BETWEEN TWO NONAUTONOMOUS CHAOTIC SYSTEMS
Authors: YANG TAO , CHUA LEON O.
Published: April 2003

The practical stability of impulsive synchronization between two nonautonomous chaotic systems is studied in this paper, and this is equivalent to that of the origin of the synchronization error system, which is modeled by an impulsive differential equation. We develop theoretical methods of choosing the time interval between two successive synchronization impulses and strengths of synchronization impulses for restricting synchronization errors within prescribed regions around the origin. Numerical experimental results are given to demonstrate theoretical results.
SYNCHRONIZATION OF KURAMOTO–SIVASHINSKY EQUATIONS USING SPATIALLY LOCAL COUPLING
Authors: TASEV ZARKO , KOCAREV LJUPCO , JUNGE LUTZ , PARLITZ ULRICH
Published: April 2003

The synchronization properties of a pair of Kuramoto–Sivashinsky equations are examined using only a finite number of coupling signals that are given in terms of local spatial averages. The dependence of the synchronization on the number of coupling signals and the width of the spatial average intervals is examined, including spatiotemporal intermittency of the synchronization error near the onset of synchronization.
DETECTING CHAOTIC DRIVE–RESPONSE GEOMETRY IN GENERALIZED SYNCHRONIZATION
Authors: PECORA LOUIS M. , CARROLL THOMAS L.
Published: April 2003

Dynamical systems which can be decomposed into a drive–response pair sometimes display the phenomenon of generalized synchronization wherein the response state y is a function of the drive state x, y = ϕ (x). The questions of detecting when this is true in experimental data, and what are the properties of the function ϕ, require the development of statistics that are based on concepts and definitions from analysis, rather than the standard statistics literature. We show that these statistics can display when such a generalized synchronization situation exists and characterize the nature of the manifold (given by ϕ) of the response over the drive, including when that manifold is fractal.
EXPLOSION OF STRANGE ATTRACTORS AND CRISIS-INDUCED INTERMITTENCY FROM A FORCED PHASE-LOCKED LOOP CIRCUIT: THEORY AND EXPERIMENTS
Authors: ENDO TETSURO , OHNO WATARU , UEDA YOSHISUKE
Published: April 2003

In this article, we investigate a mechanism of explosion and extinction of strange attractors and their crisis-induced intermittency observed after the explosion in the PLL equation used as an FM-demodulator. Namely, we elucidate that, explosion of the first type P1 (second type P2) chaotic attractor to their marged P1&P2-chaotic attractor occurs due to the heteroclinic tangency between an unstable manifold of the inversely unstable fixed point, and a stable manifold of the associated directly unstable fixed point (I-D chain). We demonstrate this explosion both by computer simulation and electronic circuit experiments.
ABSOLUTELY UNPREDICTABLE CHAOTIC SEQUENCES
Authors: GONZALEZ JORGE A. , MARTIN-LANDROVE MIGUEL , TRUJILLO LEONARDO
Published: April 2003

We study chaotic functions that are exact solutions to nonlinear maps. A generalization of these functions cannot be expressed as a map of type Xn+1 = g(Xn, Xn-1, …, Xn-r+1). The generalized functions can produce truly random sequences. Even if the initial conditions are known exactly, the next values are in principle unpredictable from the previous values. Although the generating law for these random sequences exists, this law cannot be learned from observations.
ON THE BIASING EFFECT OF A BATTERY ON A SELF-EXCITING FARADAY DISK HOMOPOLAR DYNAMO LOADED WITH A LINEAR SERIES MOTOR
Authors: GOLDBRUM PAUL , MOROZ IRENE M. , HIDE RAYMOND
Published: April 2003

We extend the study of Hide et al. [1996] for a self-exciting Faraday disk homopolar dynamo with a linear motor connected in series with the coil to cases when a battery is included in the circuit, using the set of nonlinear equations for biased systems given in [Hide, 1997]. The presence of the battery introduces asymmetry into the model, creating two distinct branches of equilibrium solutions, two distinct branches of oscillatory solutions and two different codimension-two bifurcations.
BIFURCATION ANALYSIS AND CONTROL OF NONLINEAR SYSTEMS WITH A NONSEMISIMPLE ZERO AT CRITICALITY AND APPLICATION
Authors: FU JYUN-HORNG (ALEX)
Published: April 2003

Bifurcation analysis and control of nonlinear systems with defective repetitive zero at criticality is presented. The results are applied to stabilize a flexible, inverted pendulum mounted on a moving cart that is approximated with a coefficient of flexibility.
ANTIMONOTONICITY AND CHAOTIC DYNAMICS IN A FOURTH-ORDER AUTONOMOUS NONLINEAR ELECTRIC CIRCUIT
Authors: KYPRIANIDIS I. M. , STOUBOULOS I. N. , HARALABIDIS P. , BOUNTIS T.
Published: April 2003

In this paper we study the dynamics of a fourth-order autonomous nonlinear electric circuit with two active elements, one linear negative conductance and one nonlinear resistor with a symmetrical piecewise-linear v–i characteristic. Using the capacitances C1 and C2 as the control parameters, we observe the phenomenon of antimonotonicity and the formation of "bubbles" in the development of bifurcations, resulting typically in reverse period-doubling sequences. We also find a crisis-induced intermittency, when the spiral attractor suddenly widens to a double-scroll attractor. We have plotted several bifurcation diagrams of reverse period-doubling sequences and computed the scaling parameter δ versus the control parameter C2 for the different regimes, where bubbles evolve. Thus, besides the usual Feigenbaum constant δ → δF = 4.6692…, we also observe, in some cases, a convergence of δ to [Formula: see text], as expected from theoretical considerations. Finally, by plotting a return map associated with one of the state variables, we demonstrate the strongly one-dimensional character of the dynamics and discuss the dependence of this map on the parameters of the system.
BIFURCATION ANALYSIS OF CHEN'S EQUATION
Authors: UETA TETSUSHI , CHEN GUANRONG
Published: April 2003

Anticontrol of chaos by making a nonchaotic system chaotic has led to the discovery of some new chaotic systems, particularly the continuous-time three-dimensional autonomous Chen's equation with only two quadratic terms. This paper further investigates some basic dynamical properties and various bifurcations of Chen's equation, thereby revealing its different features from some other chaotic models such as its origin, the Lorenz system.
STOCHASTIC RESONANCE IN 2D COUPLED MAP LATTICE MODEL OF FIELD-LIKE NEURAL TISSUE
Authors: SBITNEV VALERY I. , PUSTOVOIT MARK A.
Published: April 2003

An electrical activity of slices of field-type neural tissues, namely the hippocampal slices, simulated by a 2D CML with piecewise-linear sigmoid nonlinearity, is studied. Under the combined action of internal white noise and small external periodic signal the system exhibits stochastic resonance.
DETECTING NONLINEAR DETERMINISM IN VOICED SOUNDS OF JAPANESE VOWEL /a/
Authors: MIYANO TAKAYA , NAGAMI AKIRA , TOKUDA ISAO , AIHARA KAZUYUKI
Published: April 2003

Nonlinear determinism in voiced sounds of the Japanese vowel /a/ is tested by the time series analysis associated with the surrogate method. To capture nonlinear dynamics underlying the speech signal, we apply the generalized radial basis function networks as nonlinear predictors to the time series data. The optimized network parameters may show a trail of the nonlinear dynamics though not conspicuously. This may be due to paucity of data points.
GENERIC RC REALIZATIONS OF CHUA'S CIRCUIT
Authors: ELWAKIL A. S. , KENNEDY M. P.
Published: April 2003

We propose novel generic RC realizations of Chua's circuit. These realizations are based on the simplest possible models for second-order RC sinusoidal oscillators that are used to replace the active tank resonator in the classical Chua's circuit configuration. The sinusoidal oscillators are represented by circuit-independent black-box models. Hence, numerous circuit realizations can be derived.
EVALUATION OF A CONTINUOUS VALUED CHAOTIC SPREADER USED IN A CHAOTIC DIGITAL CODE-DIVISION MULTIPLE ACCESS ((CD)2MA) SYSTEM
Authors: KRAUS JOCHEN , NOSSEK JOSEF A. , YANG TAO , CHUA LEON O.
Published: April 2003

This paper presents a possible realization of a ( CD )2 MA multiuser communication system. The state variables of two synchronized chaotic Chua's circuits are thereby used to generate identical continuous valued spreader sequences in the transmitter and the receiver. To create a higher degree of randomness in the signatures, the state variables are processed by a k-shift cypher. The performance to be expected for such a system as opposed to designs using binary spreaders can be estimated theoretically. For verification, extensive simulations were run that allow for a direct comparison of the chaotic spreader with a traditional binary Gold sequence or a sequence of continuous random numbers, respectively, in terms of the achievable bit error ratio for a given data rate and number of simultaneous users per channel. A brief description of the system and channel models implemented in the simulation program is provided. The simuation results are presented and discussed.
NONLINEAR SIGNAL PROPAGATION ENHANCED BY NOISE VIA STOCHASTIC RESONANCE
Authors: CHAPEAU-BLONDEAU FRANÇOIS , ROJAS-VARELA JULIO
Published: April 2003

A model is developed for a nonlinear line of coupled noisy threshold elements. The propagation on the line of various information-carrying signals, periodic, aperiodic or random, is analyzed. Different measures quantifying the efficacy of the propagation are calculated, including signal-to-noise ratio, cross-correlation measures, information-theoretic measures and propagation length. These measures are shown to be improvable by the addition of noise. These results establish a new instance of the nonlinear phenomenon of stochastic resonance under the form of a noise-enhanced propagation applying to a broad variety of signals and noises. The results also contain significance for the propagation of neuronal signals.
DETECTING UNSTABLE PERIODIC ORBITS IN CHEN'S CHAOTIC ATTRACTOR
Authors: YU XINGHUO , XIA YANG
Published: April 2003

This letter further explores the newly discovered Chen's chaotic attractor by means of detecting its unstable periodic orbits. An effective and simple computational detection algorithm based on the sliding mode concept is proposed and used for finding these orbits.
POPULATION DYNAMICS IN HETEROGENEOUS ENVIRONMENTS: A DISCRETE MODEL
Authors: FERNANDEZ BASTIEN , TERESHKO VALERY
Published: April 2003

We study the dynamics of a multidimensional coordinate-dependent mapping governing the time evolution of a population spread over a one-dimensional lattice. The nonlinearity is of mean-field type and the dependence on coordinates, given by the so-called fitness, allows to take into account the spatial heterogeneities of the habitat. A global picture of the dynamics is given in the case without diffusion and in the case with diffusion when the fitness is homogeneous and leads to a periodic orbit. Moreover it is shown that, periodic fitnesses close to homogeneous ones impose their periodicity on the asymptotic dynamics when the latter is time-periodic.
A METHOD TO CALCULATE BASIN BIFURCATION SETS FOR A TWO-DIMENSIONAL NONINVERTIBLE MAP
Authors: KITAJIMA H. , KAWAKAMI H. , MIRA C.
Published: April 2003

For models in the form of noninvertible maps we propose a numerical method to calculate a class of basin bifurcation sets in a parameter space. It is known that basin bifurcations may result from the contact of a basin boundary with the critical curve (locus of points having two coincident rank-one preimages) segment. Therefore, when the map is smooth, we propose the method to obtain the tangent points of a basin boundary (stable set of saddle type periodic points) and a critical curve. Numerical examples for a two-dimensional quadratic noninvertible map are illustrated and new results of basin bifurcations are shown.
FRACTAL DIMENSION FOR POINCARÉ RECURRENCES AS AN INDICATOR OF SYNCHRONIZED CHAOTIC REGIMES
Authors: AFRAIMOVICH VALENTIN S. , LIN WEN-WEI , RULKOV NIKOLAI F.
Published: April 2003

The studies of the phenomenon of chaos synchronization are usually based upon the analysis of the existence of transversely stable invariant manifold that contains an invariant set of trajectories corresponding to synchronous motions. In this paper we develop a new approach that relies on the notions of topological synchronization and the dimension for Poincaré recurrences. We show that the dimension of Poincaré recurrences may serve as an indicator for the onset of synchronized chaotic oscillations. This indicator is capable of detecting the regimes of chaos synchronization characterized by the frequency ratio p:q.
ENTRAINMENT BETWEEN HEART RATE AND WEAK NONINVASIVE FORCING
Authors: ANISHCHENKO V. S. , BALANOV A. G. , JANSON N. B. , IGOSHEVA N. B. , BORDYUGOV G. V.
Published: April 2003

We demonstrate that the heart rate of a healthy human can be synchronized by means of weak external noninvasive forcing in the form of a sequence of sound and light pulses, being either periodic or aperiodic, the latter forcing given by interbeat intervals of the heart of another subject. The phenomenon of phase locking of n:m type is observed for both situations in about 90% of our experiments. The plot for the ratio of forcing frequency to the average frequency of response versus detuning possesses a plateau and is in agreement with classical synchronization theory.
CHARACTERIZATION OF SYNCHRONIZED SPATIOTEMPORAL STATES IN COUPLED NONIDENTICAL COMPLEX GINZBURG–LANDAU EQUATIONS
Authors: BRAGARD J. , ARECCHI F. T. , BOCCALETTI S.
Published: April 2003

We characterize the synchronization of two nonidentical spatially extended fields ruled by one-dimensional Complex Ginzburg–Landau equations, in the two regimes of phase and amplitude turbulence. If two fields display the same dynamical regime, the coupling induces a transition to a completely synchronized state. When, instead, the two fields are in different dynamical regimes, the transition to complete synchronization is mediated by defect synchronization. In the former case, the synchronized manifold is dynamically equivalent to that of the unsynchronized systems, while in the latter case the synchronized state substantially differs from the unsynchronized one, and it is mainly dictated by the synchronization process of the space-time defects.
DETECTING CARDIORESPIRATORY COORDINATION BY RESPIRATORY PATTERN ANALYSIS OF HEART PERIOD DYNAMICS — THE MUSICAL RHYTHM APPROACH
Authors: BETTERMANN H. , CYSARZ D. , VAN LEEUWEN P.
Published: April 2003

The purpose of this study was to demonstrate that cardiorespiratory coordination can be unveiled by analyzing solely the heart period data from electrocardiogram (ECG). The analysis was done (1) on the basis of symbolic musical pattern analysis to detect intermittent cardiorespiratory phase coordination and (2) on the quantitative evaluation of respiratory sinus arrhythmia (RSA) to examine long-term frequency coordination between heartbeat and respiration. The methods were applied to 196 ECGs of 98 healthy subjects. The results showed that at night (1) intermittent phase coordination occurred reproducibly in individual subjects, and (2) long-term frequency ratios statistically approached 4:1 over all subjects to within an accuracy of 0.02, although individual values ranged from 2.5–6.0 with a high intraindividual reproducibility (r=0.94, day A versus day B). Moreover, intermittent phase coordination ratios and long-term frequency ratios corresponded to each other with a remarkably high correlation (r=0.95). In the light of clinical applications, the coordination analysis presented here has an enormous advantage over those techniques depending on respiratory flow measurements, because the pattern technique requires only ECG recordings, and it is thus applicable over a longer period of time under daily life conditions.
CHAOS AND PHASE SYNCHRONIZATION IN ECOLOGICAL SYSTEMS
Authors: BLASIUS BERND , STONE LEWI
Published: April 2003

An ecological population model is presented for the purposes of exploring complex synchronization phenomena in biological systems. The model describes a three level predator–prey–resource system which oscillates with Uniform Phase evolution, yet has Chaotic Abundance levels or Amplitudes (UPCA). We investigate the phase synchronization of two nonidentical diffusively coupled phase coherent models (i.e. with UPCA dynamics) and extend the analysis to study the models' "funnel" regimes and response to noise forcing. Similar synchronization effects are reported for a two-dimensional lattice of chaotic population models coupled via nearest neighbors. With weak coupling, a collective phase synchronization emerges yet the peak population abundance levels are chaotic and largely uncorrelated. The synchronization patterns and traveling wave structures found in the spatial model correspond to those observed in natural systems — in particular, Ecology's well-known Canadian hare–lynx cycle. We show that phase synchronization has important applications in the study of ecological communities where the spatial coupling of populations can lead to large scale complex synchronization effects.
OBSERVATIONS OF PHASE SYNCHRONIZATION PHENOMENA IN ONE-DIMENSIONAL ARRAYS OF COUPLED CHAOTIC ELECTRONIC CIRCUITS
Authors: DABROWSKI ANDRZEJ , GALIAS ZBIGNIEW , OGORZAŁEK MACIEJ
Published: April 2003

Using numerical experiments we show that the phase synchronization concept enables better insight into the synchronization phenomena encountered in coupled nonlinear chaotic circuits. In some cases when the phase plot inspection does not allow to confirm synchrony such kind of behavior can be distinguished by inspection of the phase calculated using the analytic signal approach.
PHASE SYNCHRONIZATIONS: TRANSITIONS FROM HIGH- TO LOW-DIMENSIONAL TORI THROUGH CHAOS
Authors: HU BAMBI , ZHENG ZHIGANG
Published: April 2003

Phase synchronized entrainment of coupled nonidentical limit cycles and chaotic oscillators is a generic phenomenon in complicated and chaotic dynamics. Recent developments in phase synchronization are reviewed. Two approaches: The statistical approach and the dynamical approach are proposed. From a statistical viewpoint, phase entrainment exhibits a nonequilibrium phase transition from the disordered state to the ordered state. Dynamically, phase synchronization among oscillators shows a tree-like bifurcation and a number of clustered states are experienced. The route from partial to complete phase synchronization for coupled limit cycles is identified as a cascade of transitions from high- to low-dimensional tori (quasiperiodicity) interrupted by intermittent chaos. For coupled periodic oscillators, desynchronization-induced chaos originates from the mixing of intermittent ON–OFF duration time scales. For coupled chaotic cases, the route to phase entrainment is identified as transitions from high- to low-dimensional chaos.
GENERATION, RECOGNITION AND LEARNING OF RECURRENT SIGNALS BY PULSE PROPAGATION NETWORKS
Authors: JUDD KEVIN , AIHARA KAZUYUKI
Published: April 2003

Pulse propagation networks (PPN) are neural networks in which individual action potentials encode information. The dynamics of PPN depend not only on the synaptic weights of connections but also the delay in the propagation of action potentials between neural elements. It is known that PPN can perform complex computations and information processing by encoding information as the time intervals between action potential events. In this paper we approach the practical question of constructing PPN to generate, recognize and learn arbitrary recurrent signals. We present specific examples of networks that generate and recognize signals and also describe a learning algorithm that allows PPN to learn by self-organization. Finally we discuss the possible importance of dynamical fluctuations about the mean-activity field of a neural network.
STUDYING SINGLE-TRIALS OF PHASE SYNCHRONOUS ACTIVITY IN THE BRAIN
Authors: LACHAUX JEAN-PHILIPPE , RODRIGUEZ EUGENIO , LE VAN QUYEN MICHEL , LUTZ ANTOINE , MARTINERIE JACQUES , VARELA FRANCISCO J.
Published: April 2003

This paper introduces a new method, single-trial phase locking statistics (S-PLS) to estimate phase locking in single trials of brain signals between two electrodes. The possibility of studying single trials removes an important limitation in the study of long-range synchrony in brain signals. S-PLS is closely related to our previous method, phase locking statistics (PLS) that estimates phase locking over a set of trials. The S-PLS method is described in detail and applied to human surface recordings during the task of face-recognition. We compare these results with those provided by PLS and show that they are qualitatively very similar, although S-PLS provides better discrimination of synchronic episodes.
PHASE SYNCHRONIZATION OF PERIODIC AND CHAOTIC STATES INDUCED BY EXTERNAL OPTICAL INJECTION IN SEMICONDUCTOR LASERS
Authors: LARIONTSEV E.
Published: April 2003

We present results on a numerical simulation of phase synchronization of the periodic and chaotic states induced by optical injection in a semiconductor laser. Such states occur in an unstable part of the injection locking region. We find two branches of the stable periodic solutions (bistability) which are synchronized by the injected signal. We show that phase synchronization of the periodic states exists in the truncated period-doubling cascade to chaos and is maintained in some region of the chaotic states. We present a mapping of the region of synchronized chaotic states as a function of the amplitude and frequency detuning of the external optical injection.
ENCODING CARRIER AMPLITUDE MODULATIONS VIA STOCHASTIC PHASE SYNCHRONIZATION
Authors: LONGTIN ANDRÉ , ST-HILAIRE MARTIN
Published: April 2003

The firings of excitable systems can phase lock to periodic forcing. In many situations however, the firings are separated by a random number of forcing cycles, even though they occur near a preferred phase of the forcing. Also, the associated interspike interval histograms display peaks over a continuous range of integer multiples of the forcing period, and the peak heights are a unimodal function of increasing multiples of the period. This paper focusses on these patterns of stochastic phase synchronization and their alteration by physiologically relevant stimuli that modulate the amplitude of the periodic forcing. Specifically, two regimes of the FitzHugh–Nagumo system exhibiting stochastic phase locking are considered. We discuss how internal noise, originating from e.g. synaptic or conductance fluctuations, must interact with either suprathreshold or subthreshold dynamics, and in some instances with subthreshold chaos, to produce such firing patterns. These responses to constant amplitude "carriers" are then compared to those from carriers with random band-limited amplitude modulations (AM's). The comparison is based on the mean firing rate, as well as phase synchronization computed using a suitably defined input–output phase difference. Further, using the stimulus reconstruction technique to characterize synchrony between random AM's and spikes, the internal noise is shown to help transmit information about random carrier AM's in the subthreshold and slightly suprathreshold cases. This transmission also depends nonmonotonically on the carrier frequency. Our results provide biophysical insight into the dynamics of neural signal encoding that combines a mean rate code on long time scales and a precise temporal code based on phase locking on the shorter time scale of the carrier period.
SYNCHRONIZATION AND CLUSTERING IN COUPLED SAW-TOOTH MAPS
Authors: MANRUBIA SUSANNA C. , MIKHAILOV ALEXANDER S.
Published: April 2003

We consider ensembles of saw-tooth maps modified by adding a nonlinear term. The dynamics of an individual map is intermittent. Our numerical investigations show that the globally coupled ensemble can display asynchronous chaotic oscillations, coherent two-cluster collective behavior and complete mutual synchronization, depending on the coupling intensity. Circular arrays of these intermittent maps with a finite interaction radius support a variety of complex patterns, including spatial dynamic domains and traveling waves.
A NEW METHOD TO ANALYZE COMPLETE STABILITY OF PWL CELLULAR NEURAL NETWORKS
Authors: FORTI M. , TESI A.
Published: April 2003

In recent years, the standard Cellular Neural Networks (CNN's) introduced by Chua and Yang [1988] have been one of the most investigated paradigms for neural information processing. In a wide range of applications, the CNN's are required to be completely stable, i.e. each trajectory should converge toward some stationary state. However, a rigorous proof of complete stability, even in the simplest original setting of piecewise-linear (PWL) neuron activations and symmetric interconnections [Chua & Yang, 1988], is still lacking. This paper aims primarily at filling this gap, in order to give a sound analytical foundation to the CNN paradigm. To this end, a novel approach for studying complete stability is proposed. This is based on a fundamental limit theorem for the length of the CNN trajectories. The method differs substantially from the classic approach using LaSalle invariance principle, and permits to overcome difficulties encountered when using LaSalle approach to analyze complete stability of PWL CNN's. The main result obtained, is that a symmetric PWL CNN is completely stable for any choice of the network parameters, i.e. it possesses the Absolute Stability property of global pattern formation. This result is really general and shows that complete stability holds under hypotheses weaker than those considered in [Chua & Yang, 1988]. The result does not require, for example, that the CNN has binary stable equilibrium points only. It is valid even in degenerate situations where the CNN has infinite nonisolated equilibrium points. These features significantly extend the potential application fields of the standard CNN's.
DEGENERATE BIFURCATION ANALYSIS ON A PARAMETRICALLY AND EXTERNALLY EXCITED MECHANICAL SYSTEM
Authors: ZHANG WEI , YU PEI
Published: April 2003

A general parametrically and externally excited mechanical system is considered. The main attention is focused on the dynamical properties of local bifurcations as well as global bifurcations including homoclinic and heteroclinic bifurcations. In particular, degenerate bifurcations of codimension 3 are studied in detail. The original mechanical system is first transformed to averaged equations using the method of multiple scales. With the aid of normal form theory, the explicit expressions of the normal form associated with a double-zero eigenvalue and Z2-symmetry for the averaged equations are obtained. Based on the normal form, it has been shown that a parametrically and externally excited mechanical system can exhibit homoclinic and heteroclinic bifurcations, multiple limit cycles, and jumping phenomena in amplitude modulated oscillations. Numerical simulations are also given to verify the good analytical predictions.