bluuebunny/crossref_metadata_2025 huggingface dataset:
THE COLPITTS OSCILLATOR: FAMILIES OF PERIODIC SOLUTIONS AND THEIR BIFURCATIONS
Authors: DE FEO OSCAR , MAGGIO GIAN MARIO , KENNEDY MICHAEL PETER
Published: May 2003

In this work we consider the Colpitts oscillator as a paradigm for sinusoidal oscillation and we investigate its nonlinear dynamics. In particular, we carry out a two-parameter bifurcation analysis of a model of the oscillator. This analysis is conducted by combining numerical continuation techniques and normal form theory. First, we show that the birth of the harmonic cycle is associated with a Hopf bifurcation and we discuss the effects of idealization in the model. Various families of limit cycles are identified and their bifurcations are analyzed in detail. In particular, we demonstrate that the bifurcation diagram in the parameter space is organized by an infinite family of homoclinic bifurcations. Finally, local and global coexistence phenomena are described.
BIFURCATION CURVES OF LIMIT CYCLES IN SOME LIÉNARD SYSTEMS
Authors: LÓPEZ-RUIZ R. , LÓPEZ J. L.
Published: May 2003

Liénard systems of the form [Formula: see text], with f(x) an even continuous function, are considered. The bifurcation curves of limit cycles are calculated exactly in the weak (ε → 0) and in the strongly (ε → ∞) nonlinear regime in some examples. The number of limit cycles does not increase when ε increases from zero to infinity in all the cases analyzed.
LOCAL BIFURCATION ANALYSIS IN THE FURUTA PENDULUM VIA NORMAL FORMS
Authors: PAGANO DANIEL , PIZARRO LUIS , ARACIL JAVIER
Published: May 2003

Inverted pendulums are very suitable to illustrate many ideas in automatic control of nonlinear systems. The rotational inverted pendulum is a novel design that has some interesting dynamics features that are not present in inverted pendulums with linear motion of the pivot. In this paper the dynamics of a rotational inverted pendulum has been studied applying well-known results of bifurcation theory. Two classes of local bifurcations are analyzed by means of the center manifold theorem and the normal form theory — first, a pitchfork bifurcation that appears for the open-loop controlled system; second, a Hopf bifurcation, and its possible degeneracies, of the equilibrium point at the upright pendulum position, that is present for the controlled closed-loop system. Some numerical results are also presented in order to verify the validity of our analysis.
CHAOTIC PROPERTIES OF SUBSHIFTS GENERATED BY A NONPERIODIC RECURRENT ORBIT
Authors: FU XIN-CHU , FU YIBIN , DUAN JINQIAO , MACKAY ROBERT S.
Published: May 2003

The chaotic properties of some subshift maps are investigated. These subshifts are the orbit closures of certain nonperiodic recurrent points of a shift map. We first provide a review of basic concepts for dynamics of continuous maps in metric spaces. These concepts include nonwandering point, recurrent point, eventually periodic point, scrambled set, sensitive dependence on initial conditions, Robinson chaos, and topological entropy. Next we review the notion of shift maps and subshifts. Then we show that the one-sided subshifts generated by a nonperiodic recurrent point are chaotic in the sense of Robinson. Moreover, we show that such a subshift has an infinite scrambled set if it has a periodic point. Finally, we give some examples and discuss the topological entropy of these subshifts, and present two open problems on the dynamics of subshifts.
SOLITON-LIKE WAVES ON DISSIPATIVE TODA LATTICES
Authors: MAKAROV V. A. , EBELING W. , VELARDE M. G.
Published: May 2003

Dissipative soliton-like waves in 1D Toda lattices generated by suitable energy supply from external sources have been studied. Using the general theory of canonical-dissipative systems we have constructed a special canonical-dissipative system whose solution starting from an arbitrarily initial condition decays to a solution of the standard, conservative Toda system. The energy of the final state may be prescribed beforehand. We have also studied the influence of noise and have calculated the distribution of probability density in phase space and the energy distribution. Other noncanonical models of energy input, including nonlinear nearest neighbor coupling and "Rayleigh" friction, have been analyzed. We have shown under what conditions the lattices can sustain the propagation of stable solitary waves and wave trains.
STORAGE OF INFORMATION IN ONE-DIMENSIONAL PIECEWISE-CONTINUOUS MAPS
Authors: ROUABHI SAMIR
Published: May 2003

A method of information storage via unstable cycles of one-dimensional piecewise-continuous maps is presented. This method consists in associating a well-defined cycle of a map with a given information to be stored. A neural network is proposed to emulate the information processing. A procedure of extracting the stored information using control of chaos by feedback loop is proposed. The retrieval of the information stored is done by control of chaos. An associative memory property is obtained.
SLIDING MODE CONTROL OF CHAOTIC SYSTEMS WITH UNCERTAINTIES
Authors: YAU HER-TERNG , CHEN CHA'O-KUANG , CHEN CHIEH-LI
Published: May 2003

A sliding mode hyperplane design for a class of chaotic systems with uncertainties is considered in this paper. The concept of extended systems is used such that continuous control input is obtained using a sliding mode design scheme. It is guaranteed that under the proposed control law, uncertain chaotic systems can asymptotically track target orbits. The converging speed of error states can be arbitrarily set by assigning the corresponding dynamics to the sliding surfaces. Illustrative examples of a controlled uncertain Duffing–Holmes system are presented.
ANALYSIS OF A NONSYNCHRONIZED SINUSOIDALLY DRIVEN DYNAMICAL SYSTEM
Authors: MÉNARD O. , LETELLIER C. , MAQUET J. , LE SCELLER L. , GOUESBET G.
Published: May 2003

A nonautonomous system, i.e. a system driven by an external force, is usually considered as being phase synchronized with this force. In such a case, the dynamical behavior is conveniently studied in an extended phase space which is the product of the phase space ℝm of the undriven system by an extra dimension associated with the external force. The analysis is then performed by taking advantage of the known period of the external force to define a Poincaré section relying on a stroboscopic sampling. Nevertheless, it may so happen that the phase synchronization does not occur. It is then more convenient to consider the nonautonomous system as an autonomous system incorporating the subsystem generating the driving force. In the case of a sinusoidal driving force, the phase space is ℝm+2 instead of the usual extended phase space ℝm × S1. It is also demonstrated that a global model may then be obtained by using m + 2 dynamical variables with two variables associated with the driving force. The obtained model characterizes an autonomous system in contrast with a classical input/output model obtained when the driving force is considered as an input.
AN ALTERNATE PARTITIONING TECHNIQUE TO QUANTIFY THE REGULARITY OF COMPLEX TIME SERIES
Authors: RADHAKRISHNAN N. , WILSON JAMES D. , LOIZOU PHILIPOS C.
Published: May 2003

In this paper we use the concepts of information theory to analyze the time series obtained from complex systems. The procedure discussed here can be applied to quantify the regularity of chaotic time series, although it might not certify chaos. The main idea is to map the time series into a finite sequence of symbols using an efficient partitioning technique, and quantify the regularity of the resulting sequence by a chosen complexity measure. A proper partitioning technique is essential for any meaningful analysis of the resulting sequence. We have used a clustering technique to partition the time series into a finite sequence and the Lempel–Ziv complexity measure to quantify the regularity of this sequence.
RICH VARIETY OF BIFURCATIONS AND CHAOS IN A VARIANT OF MURALI–LAKSHMANAN–CHUA CIRCUIT
Authors: THAMILMARAN K. , LAKSHMANAN M. , MURALI K.
Published: May 2003

A very simple nonlinear parallel nonautonomous LCR circuit with Chua's diode as its only nonlinear element, exhibiting a rich variety of dynamical features, is proposed as a variant of the simplest nonlinear nonautonomous circuit introduced by Murali, Lakshmanan and Chua (MLC). By constructing a two-parameter phase diagram in the (F - ω) plane, corresponding to the forcing amplitude (F) and frequency (ω), we identify, besides the familiar period-doubling scenario to chaos, intermittent and quasiperiodic routes to chaos as well as period-adding sequences, Farey sequences, and so on. The chaotic dynamics is verified by both experimental as well as computer simulation studies including PSPICE.
NONLINEAR TIME-SERIES ANALYSIS OF THE GREEK EXCHANGE-RATE MARKET
Authors: ANDREOU A. S. , PAVLIDES G. , KARYTINOS A.
Published: May 2003

Using concepts from the theory of chaos and nonlinear dynamical systems, a time-series analysis is performed on four major currencies against the Greek Drachma. The R/S analysis provided evidence for fractality due to noisy chaos in only two of the data series, while the BDS test showed that all four systems exhibit nonlinearity. Correlation dimension and related tests, as well as Lyapunov exponents, gave consistent results, which did not rule out the possibility of deterministic chaos for the two possibly fractal series, rejecting though the occurrence of a simple low-dimensional attractor, while the other two series seemed to have followed a behavior close to that of a random signal. SVD analysis, used to filter away noise, strongly supported the above findings and provided reliable evidence for the existence of an underlying system with a limited number of degrees-of-freedom only for those series found to exhibit fractality, while it revealed a noise domination over the remaining two. These results were further confirmed through a forecasting attempt using artificial neural networks.
ELLIPSOIDAL BILLIARDS WITH ISOTROPIC HARMONIC POTENTIALS
Authors: WIERSIG JAN
Published: May 2003

The classical dynamics of the triaxial ellipsoidal billiard with isotropic harmonic potential attracting to the center of the ellipsoid is discussed. The integrability preserving potential introduces an energy dependence to the foliation of energy shells into invariant tori. This foliation and the character of the corresponding motion is described in terms of 13 qualitatively different energy surfaces in the space of the action variables. Frequencies and the location of resonances are calculated. The consequences of the superintegrability of the low-energy case, the isotropic harmonic oscillator, for the energy surfaces in action space are investigated.
RESONANT GLUING BIFURCATIONS
Authors: GHRIST ROBERT W.
Published: May 2003

We consider the codimension-three phenomenon of homoclinic bifurcations of flows containing a pair of orbits homoclinic to a saddle point whose principal eigenvalues are in resonance. We concentrate upon the simplest possible configuration, the so-called "figure-of-eight," and reduce the dynamics near the homoclinic connections to those on a two-dimensional locally invariant centre manifold. The ensuing resonant gluing bifurcations exhibit features of both gluing bifurcations and resonant homoclinic bifurcations. Under certain twist conditions, the bifurcation structure is extremely rich, although describing zero-entropy flows. The analysis carefully exploits the topology of the orbits, the centre manifold and the parameter space.
SMALE HORSESHOE OF CELLULAR NEURAL NETWORKS
Authors: HSU CHENG-HSIUNG
Published: May 2003

The paper shows the spatial disorder of one-dimensional Cellular Neural Networks (CNN) using the iteration map method. Under certain parameters, the map is two-dimensional and the Smale horseshoe is constructed. Moreover, we also illustrate the variant of CNN, closely related to Henón-type and Belykh maps, and discrete Allen–Cahn equations.
THE GLOBAL BIFURCATIONS THAT LEAD TO TRANSIENT TUMBLING CHAOS IN A PARAMETRICALLY DRIVEN PENDULUM
Authors: SZEMPLIŃSKA-STUPNICKA W. , TYRKIEL E. , ZUBRZYCKI A.
Published: May 2003

Criteria for occurrence of transient tumbling chaos in the parametrically driven pendulum are examined by computer aided methods. It is shown that stable manifolds of the saddles associated with the rotating attractors play a crucial role in separating the oscillating and rotating attractors in the phase-plane. A sequence of global bifurcations related to the saddles generates the fractal structure of the basins of attraction of the coexisting attractors. The fractal structure of the basin boundaries implies occurrence of the transient tumbling motion, i.e. the transients that involve rotations with changing directions and oscillatory motion.
EXPERIMENTAL DETERMINATION OF POINT LOCALIZED TIME CORRELATION AND POWER SPECTRUM IN A FARADAY EXPERIMENT
Authors: CABEZA C. , NEGREIRA C. , SICARDI SCHIFINO A. C. , GIBIAT V.
Published: May 2003

Experimental results from a classical Faraday experiment have been obtained using a point-localized measurement of the displacement of the fluid surface. We used a capacitive transducer as probe, and have been able to study the period-doubling bifurcations in time domain through the determination of cross-correlation and power spectrum.
STRANGE NONCHAOTIC ATTRACTOR IN LOW-FREQUENCY QUASIPERIODICALLY DRIVEN SYSTEMS
Authors: SHUAI J. W. , DURAND D. M.
Published: May 2003

To generate strange nonchaotic attractor in quasiperiodically driven systems, there must be an unstable region in its phase-space. In this paper, a theoretical analysis shows that the quasiperiodic force acts as noise to lead the trajectory running into different expanding orbits when the trajectory repeatedly runs into the unstable region. Thus the resulting attractor is strange. The local-phase Lyapunov exponent is introduced for the study of low-frequency quasiperiodically driven systems. It is shown that the local-phase Lyapunov exponents can be approximated by the exponents of autonomous systems. The statistical properties of SNA system driven by low-frequency quasiperiodic force can then be approached by a set of autonomous systems.
ON PHASE SYNCHRONIZATION BY PERIODIC FORCE IN CHAOTIC OSCILLATORS WITH SADDLE EQUILIBRIA
Authors: ZAKS MICHAEL A. , PARK EUN-HYOUNG , KURTHS JÜRGEN
Published: May 2003

A periodic action onto a chaotic system can result in phase synchronization: Although the oscillations remain chaotic, their pace is prescribed by the rhythm of the force. We show how this adjustment of characteristic timescales to the period of the forcing is violated when, due to the presence of a saddle point in the autonomous attractor, the time intervals between returns onto a Poincaré plane are unbounded. In such a situation, the segments of a chaotic trajectory in which its phase follows the phase of the force, can alternate with short segments of phase-locking in ratios different from 1:1. This phenomenon is demonstrated for several nonlinear systems.
CROSS-SPECTRAL ANALYSIS OF TREMOR TIME SERIES
Authors: TIMMER J. , LAUK M. , HÄUßLER S. , RADT V. , KÖSTER B. , HELLWIG B. , GUSCHLBAUER B. , LÜCKING C. H. , EICHLER M. , DEUSCHL G.
Published: May 2003

We discuss cross-spectral analysis and report applications for the investigation of human tremors. For the physiological tremor in healthy subjects, the analysis enables to determine the resonant contribution to the oscillation and allows to test for a contribution of reflexes to this tremor. Comparing the analysis of the relation between the tremor of both hands in normal subjects and subjects with a rare abnormal organization of certain neural pathways proves the involvement of central structures in enhanced physiological tremor. The relation between the left and the right side of the body in pathological tremor shows a specific difference between orthostatic and all other forms of tremor. An investigation of EEG and tremor in patients suffering from Parkinson's disease reveals the tremor-correlated cortical activity. Finally, the general issue of interpreting the results of methods designed for the analysis of bivariate processes when applied to multivariate processes is considered. We discuss and apply partial cross-spectral analysis in the frame of graphical models as an extention of bivariate cross-spectral analysis for the multivariate case.
TRANSITION TO CHAOTIC PHASE SYNCHRONIZATION THROUGH RANDOM PHASE JUMPS
Authors: PAZÓ D. , MARIÑO I. P. , PÉREZ-VILLAR V. , PÉREZ-MUÑUZURI V.
Published: May 2003

Phase synchronization is shown to occur between opposite cells of a ring consisting of chaotic Lorenz oscillators coupled unidirectionally through driving. As the coupling strength is diminished, full phase synchronization cannot be achieved due to random generation of phase jumps. The Brownian dynamics underlying this process is studied in terms of a stochastic diffusion model of a particle in a one-dimensional medium.
STOCHASTIC SYNCHRONIZATION OF COUPLED COHERENCE RESONANCE OSCILLATORS
Authors: POSTNOV D. E. , SOSNOVTSEVA O. V. , HAN S. K. , YIM T. G.
Published: May 2003

The effect of coherence resonance can change the firing process in noise-driven excitable systems towards rather regular dynamics. This effect provides a mechanism of the generation of stochastic oscillations whose characteristics are controlled by noise intensity. Following this, a noisy excitable system can be considered as a corehence resonance oscillator. For such functional units, we investigate the mutual and forced synchronization in terms of locking of the peak frequencies in the power spectrum and also in terms of phase locking. The connection of synchronization phenomenon of noise-induced oscillations and coherence resonance effect is discussed. The examples, studied numerically and experimentally, include Morris–Lecar neuron model and a monovibrator electronic circuit, respectively.
STOCHASTIC SYNCHRONIZATION OF ELECTRORECEPTORS IN PADDLEFISH
Authors: NEIMAN ALEXANDER B. , RUSSELL DAVID F. , PEI XING , WOJTENEK WINFRIED , TWITTY JENNIFER , SIMONOTTO ENRICO , WETTRING BARBARA A. , WAGNER EVA , WILKENS LON A. , MOSS FRANK
Published: May 2003

We studied synchronization of electrosensitive cells of the paddlefish by means of electrophysiological experiments. We found that primary afferents of the paddlefish are represented by noisy nonlinear oscillators. Different types of phase locked regimes are observed. The influence of internal noise is discussed.
SYNCHRONIZATION BASED SIGNAL TRANSMISSION WITH HETEROGENEOUS CHAOTIC SYSTEMS
Authors: MURALI K.
Published: May 2003

By considering cascaded heterogeneous chaotic systems with drive-response configurations, information signal is encoded in the first chaotic system of the drive-module. A small amplitude chaotic signal from this first system is used as new information signal to the second different chaotic system within the drive-module. The chaotic signal from the second system of the drive-module is now transmitted to the response-module. An appropriate feedback loop is constructed in the response-module to achieve synchronization among the variables of the drive- and response-modules. We apply this approach to transmit analog and digital information signals in which the quality of the recovered signal is higher and the encoding is potentially secure.
NUMERICAL COMPUTATION OF CANARDS
Authors: GUCKENHEIMER JOHN , HOFFMAN KATHLEEN , WECKESSER WARREN
Published: May 2003

Singularly perturbed systems of ordinary differential equations arise in many biological, physical and chemical systems. We present an example of a singularly perturbed system of ordinary differential equations that arises as a model of the electrical potential across the cell membrane of a neuron. We describe two periodic solutions of this example that were numerically computed using continuation of solutions of boundary value problems. One of these periodic orbits contains canards, trajectory segments that follow unstable portions of a slow manifold. We identify several mechanisms that lead to the formation of these and other canards in this example.
QUANTITATIVE ANALYSIS OF CARDIORESPIRATORY SYNCHRONIZATION IN INFANTS
Authors: MROWKA RALF , PATZAK ANDREAS , ROSENBLUM MICHAEL
Published: May 2003

We investigate the phase synchronization of heartbeat and respiration in a group of healthy infants. Having presented and compared two quantitative measures of synchronization, we conclude that one of these measures — the conditional probability index — allows reliable detection of synchronous epochs of different order n:m and, thus, makes possible an automatic processing of large data sets. In our analysis of experimental time series, we have found numerous epochs of phase synchronization. It turned out that the average degree of synchronization varies with the age of the newborns.
IS THE SOLAR ACTIVITY CYCLE SYNCHRONIZED WITH THE SOLAR INERTIAL MOTION?
Authors: PALUŠ MILAN , KURTHS JÜRGEN , SCHWARZ UDO , NOVOTNÁ DAGMAR , CHARVÁTOVÁ IVANKA
Published: May 2003

The 300 year record of the yearly sunspot numbers and numerically generated trajectory of the solar inertial motion (SIM) were subjects of a synchronization analysis. Phase synchronization of the sunspot cycle and a fast component of the SIM have been found and confirmed with statistical significance in three epochs (1727–1757, 1802–1832 and 1863–1922) of the entire 1700–1997 record. This result can be considered as a quantitative support for the hypothesis that there is a weak interaction of gravity and solar activity.
MODELING NONLINEAR DETERMINISM IN SHORT TIME SERIES FROM NOISE DRIVEN DISCRETE AND CONTINUOUS SYSTEMS
Authors: CHON K. H. , YIP K. P. , CAMINO B. M. , MARSH D. J. , HOLSTEIN-RATHLOU N.-H.
Published: May 2003

Current methods for detecting deterministic chaos in a time series require long, stationary, and relatively noise-free data records. This limits the utility of these methods in most experimental and clinical settings. Recently we presented a new method for detecting determinism in a time series, and for assessing whether this determinism has chaotic attributes, i.e. sensitivity to initial conditions. The method is based on fitting a deterministic nonlinear autoregressive (NAR) model to the data [Chon et al., 1997]. This approach assumes that the noise in the model can be represented as a series of independent, identically distributed random variables. If this is not the case the accuracy of the algorithm may be compromised. To explicitly deal with the possibility of more complex noise structures, we present a method based on a stochastic NAR model. The method iteratively estimates NAR models for both the deterministic and the stochastic parts of the signal. An additional feature of the algorithm is that it includes only the significant autoregressive terms among the pool of candidate terms searched. As a result the algorithm results in a model with significantly fewer terms than a model obtained by traditional model order search criterions. Subsequently, Lyapunov exponents are calculated for the estimated models to examine if chaotic determinism (i.e. sensitivity to initial conditions) is present in the time series. The major advantages of this algorithm are: (1) it provides accurate parameter estimation with a small number of data points, (2) it is accurate for signal-to-noise ratios as low as -9 dB for discrete and -6 dB for continuous chaotic systems, and (3) it allows characterization of the dynamics of the system, and thus prediction of future states of the system, over short time scales. The stochastic NAR model is applied to renal tubular pressure data from normotensive and hypertensive rats. One form of hypertension was genetic, and the other was induced on normotensive rats by placing a restricting clip on one of their renal arteries. In both types of hypertensive rats, positive Lyapunov exponents were present, indicating that the fluctuations observed in the proximal tubular pressure were due to the operation of a system with chaotic determinism. In contrast, only negative exponents were found in the time series from normotensive rats.
EFFECTS DUE TO INDUCED AZIMUTHAL EDDY CURRENTS IN A SELF-EXCITING FARADAY DISK HOMOPOLAR DYNAMO WITH A NONLINEAR SERIES MOTOR II: THE GENERAL CASE
Authors: MOROZ IRENE M. , HIDE RAYMOND
Published: May 2003

This paper forms the second part of a two-part study into the effects of azimuthal eddy currents in the Faraday disk self-exciting homopolar dynamo, connected in series with the coil when the applied couple driving the disk is steady. The Lorentz couple driving the armature of the motor is a general quadratic function I(1 - ε + εSI) of the current I(t), where 0 ≤ ε ≤ 1. Here we investigate how cases with 0 < ε < 1 relate to the two special cases of ε = 0 and ε = 1, considered in Part I of our study [Hide & Moroz, 1999]. One key difference is that the lack of reflectional symmetry in the general ε problem means that the linear stability curves for the onset of both steady and oscillatory behavior for both the trivial and the nontrivial equilibrium solutions no longer coincide. This results in distinct Takens–Bogdanov double-zero bifurcations for these states, as well as multiple branches to the Hopf bifurcation curves, associated with bifurcations from the nontrivial equilibrium states. Multiple bifurcations involving simultaneous steady and nondegenerate oscillatory solutions are also possible.
SECURE COMPUTER COMMUNICATION USING CHAOTIC ALGORITHMS
Authors: SOBHY MOHAMED I. , SHEHATA ALAA-EL-DIN
Published: May 2003

In this paper the application of chaotic algorithms in sending computer messages is described. The communication is achieved through email. Other transmission media can also be used. The algorithm has a degree of security many orders of magnitude higher than systems based on physical electronic circuitry. Both text, image or recorded voice messages can be transmitted. The algorithm can be used for computer communication and for secure databases.
ADAPTIVE OBSERVER-BASED SYNCHRONIZATION FOR COMMUNICATION
Authors: FRADKOV ALEXANDER , NIJMEIJER HENK , MARKOV ALEXEY
Published: May 2003

The problem of synchronizing two nonlinear systems (transmitter and receiver) is considered. A simple design of an adaptive observer for estimating the unknown parameters of the transmitter is proposed based on the design of quadratic Lyapunov function for the error system. The results are illustrated by an example of signal transmission based on a pair of synchronizing Chua circuits.
STUDY OF A TWO-DIMENSIONAL ENDOMORPHISM BY USE OF THE PARAMETRIC SINGULARITIES
Authors: CARCASSES JEAN-PIERRE , TAHA ABDEL-KADDOUS
Published: May 2003

A two-dimensional cubic endomorphism depending on three parameters is considered. The qualitative changes of the bifurcation curves in a parameter plane are studied when the third parameter varies. More particularly, the crossing through a "saddle-node" singularity of the parameter plane is analytically analyzed.
DETERMINISTIC STRUCTURE IN MULTICHANNEL PHYSIOLOGICAL DATA
Authors: CAO LIANGYUE , MEES ALISTAIR
Published: May 2003

We have found numerical evidence of deterministic properties in a multichannel physiological time series, a segment of the Santa Fe data set B which was recorded from a patient with sleep apnea. We used recently developed methods for finding good time-delay embeddings for multichannel data, together with nonlinear deterministic prediction. We show that determining good embeddings for this multivariate time series gives good short-term predictions, and convincing free-run (simulation) behavior, using only a simple local-linear approximation method. We also discovered relations between the different channels, which are heart-rate, respiration and blood-oxygen saturation.
QUADRANGULAR REFINEMENTS OF CONVEX POLYGONS WITH AN APPLICATION TO FINITE-ELEMENT MESHES
Authors: MÜLLER-HANNEMANN MATTHIAS , WEIHE KARSTEN
Published: May 2003

We present a linear–time algorithm that decomposes a convex polygon conformally into a minimum number of strictly convex quadrilaterals. Moreover, we characterize the polygons that can be decomposed without additional vertices inside the polygon, and we present a linear–time algorithm for such decompositions, too. As an application, we consider the problem of constructing a minimum conformal refinement of a mesh in the three–dimensional space, which approximates the surface of a workpiece. We prove that this problem is strongly [Formula: see text] –hard, and we present a linear-time algorithm with a constant approximation ratio of four.
COMPUTING LARGEST CIRCLES SEPARATING TWO SETS OF SEGMENTS
Authors: BOISSONNAT JEAN-DANIEL , CZYZOWICZ JUREK , DEVILLERS OLIVIER , URRUTIA JORGE , YVINEC MARIETTE
Published: May 2003

A circle C separates two planar sets if it encloses one of the sets and its open interior disk does not meet the other set. A separating circle is a largest one if it cannot be locally increased while still separating the two given sets. An Θ(n log n) optimal algorithm is proposed to find all largest circles separating two given sets of line segments when line segments are allowed to meet only at their endpoints. In the general case, when line segments may intersect Ω(n2) times, our algorithm can be adapted to work in O(nα(n) log n) time and O (nα(n)) space, where α(n) represents the extremely slowly growing inverse of the Ackermann function.
QUADRILATERAL MESHING BY CIRCLE PACKING
Authors: BERN MARSHALL , EPPSTEIN DAVID
Published: May 2003

We use circle-packing methods to generate quadrilateral meshes for polygonal domains, with guaranteed bounds both on the quality and the number of elements. We show that these methods can generate meshes of several types: (1) the elements form the cells of a Voronoï diagram, (2) all elements have two opposite 90° angles, (3) all elements are kites, or (4) all angles are at most 120°. In each case the total number of elements is O(n), where n is the number of input vertices.
A COST/BENEFIT ANALYSIS OF SIMPLICIAL MESH IMPROVEMENT TECHNIQUES AS MEASURED BY SOLUTION EFFICIENCY
Authors: FREITAG LORI A. , OLLIVIER-GOOCH CARL
Published: May 2003

The quality of unstructured meshes has long been known to affect both the efficiency and the accuracy of the numerical solution of application problems. Mesh quality can often be improved through the use of algorithms based on local reconnection schemes, node smoothing, and adaptive refinement or coarsening. These methods typically incur a significant cost, and in this paper, we provide an analysis of the tradeoffs associated with the cost of mesh improvement in terms of solution efficiency. We first consider simple finite element applications and show the effect of increasing the number of poor quality elements in the mesh and decreasing their quality on the solution time of a number of different solvers. These simple application problems are theoretically well-understood, and we show the relationship between the quality of the mesh and the eigenvalue spectrum of the resulting linear system. We then consider realistic finite element and finite volume application problems, and show that the cost of mesh improvement is significantly less than the cost of solving the problem on a poorer quality mesh.
HOMEOMORPHISM OF 2-COMPLEXES IS EQUIVALENT TO GRAPH ISOMORPHISM
Authors: DÚNLAING COLM Ó , WATT COLUM , WILKINS DAVID
Published: May 2003

Whittlesey12,13,14gave a criterion which decides when two finite 2-dimensional complexes are homeomorphic. We show that graph isomorphism can be reduced efficiently to 2-complex homeomorphism, and that Whittlesey's criterion can be reduced efficiently to graph isomorphism. Therefore graph isomorphism and 2-complex homeomorphism are polynomial-time equivalent.
OPTIMAL REPARAMETRIZATION OF POLYNOMIAL ALGEBRAIC CURVES
Authors: SENDRA J. RAFAEL , VILLARINO CARLOS
Published: May 2003

In this paper, we present an algorithm for optimally parametrizing polynomial algebraic curves. Let [Formula: see text] be a polynomial plane algebraic curve given by a polynomial parametrization [Formula: see text] , where [Formula: see text] is a finite field extension of a field [Formula: see text] of characteristic zero. We prove that if [Formula: see text] is polynomial over [Formula: see text] , then Weil's descente variety associated with [Formula: see text] is surprisingly simple; it is, in fact, a line. Applying this result we are able to derive an effective algorithm to algebraically optimal reparametrize polynomial algebraic curves.
EFFICIENT APPROXIMATION ALGORITHMS FOR TWO-LABEL POINT LABELING
Authors: ZHU BINHAI , POON C. K.
Published: May 2003

In this paper we propose and study two practical variations of the map labeling problem: Given a set S of n distinct (point) sites in the plane, label each site with: (1) a pair of non-intersecting squares of maximum possible size, (2) a pair of non-intersecting circles of maximum possible size (all the squares and circles are topologically open and are of uniform size). Almost nothing has been done before in this aspect, i.e., multi-label map labeling. We obtain constant-factor approximation algorithms for these problems. We also study bicriteria approximation schemes for these problems under a mild condition.
QUASINEUTRAL LIMIT OF THE DRIFT-DIFFUSION MODEL FOR SEMICONDUCTORS WITH GENERAL INITIAL DATA
Authors: SCHMEISER CHRISTIAN , WANG SHU
Published: May 2003

The limit for vanishing Debye length (charge neutral limit) in a bipolar drift-diffusion model for semiconductors with general initial data allowing the presence of an initial layer is studied. The quasineutral limit (zero-Debye-length limit) is performed rigorously by using two different entropy functionals which yield appropriate uniform estimates. This investigation extends the results of Refs. 7 and 8 for charge neutral initial data where no initial layer occurs.
EVOLUTIONARY VARIATIONAL INEQUALITIES AND ECONOMIC MODELS FOR DEMAND–SUPPLY MARKETS
Authors: DANIELE PATRIZIA
Published: May 2003

In this paper we aim to present a model of spatially distributed economic markets under the assumptions that each demand market becomes a supply market after the time Δ. This problem is expressed by a time-dependent variational inequality for which we provide existence theorems and an example of computational procedure.
ONE-SIDED ESTIMATES AND UNIQUENESS FOR HYPERBOLIC SYSTEMS OF BALANCE LAWS
Authors: GOATIN PAOLA
Published: May 2003

Uniqueness of solutions of genuinely nonlinear n × n strictly hyperbolic systems of balance laws is established moving from Oleïnik-type decay estimates. As middle step, the result relies on the fulfillment of a condition which controls the local oscillation of the solution in a forward neighborhood of each point in the t–x plane.
ON MORTAR-TYPE TRUNC ELEMENT METHOD FOR A PLATE BENDING PROBLEM
Authors: LIU QING , LI LIKANG , HUANG JIANGUO
Published: May 2003

In this paper, a mortar-type TRUNC element method for the discretization of a plate bending problem is established. All the subdomains are triangulated independently. At the interfaces, three mortar conditions are given to ensure the convergence of the method: the first is a pointwise condition for the solution, while the other two are projection conditions for the normal and tangential derivatives of the solution. An error estimate in the energy norm is obtained under the regularity assumptions that the exact solution [Formula: see text] and f ∈ L2 (Ω). The error order is optimal as for the usual TRUNC element method. Finally, some numerical results are provided in order to show the validness of our theoretical results.
MODELING OF THE INCLUSION OF A REINFORCING SHEET WITHIN A 3D MEDIUM
Authors: CHAPELLE D. , FERENT A.
Published: May 2003

We propose a variational formulation suitable for coupling a shell and a surrounding softer 3D medium. This is intended to model the behavior of a reinforcing sheet as frequently occurs in applications. The crucial issue of the kinematical coupling conditions is addressed by taking into account the rotation degrees of freedom of the shell. We then perform an asymptotic analysis of the coupled model in which the distinction between bending-dominated and membrane-dominated shells arises. For the limit solutions we identify coupling kinematical conditions that do not involve rotations. Finally we present some numerical results that illustrate our discussions.
APPROXIMATE REDUCTION OF MULTI-TYPE GALTON–WATSON PROCESSES WITH TWO TIME SCALES
Authors: SANZ LUIS , BLASCO ÁNGEL , BRAVO DE LA PARRA RAFAEL
Published: May 2003

Approximate aggregation techniques consist of introducing certain approximations that allow one to reduce a complex system involving many coupled variables obtaining a simpler "aggregated system" governed by a few "macrovariables". Moreover, they give results that allow one to extract information about the complex original system in terms of the behavior of the reduced one. Often, the feature that allows one to carry out such a reduction is the presence of different time scales.

In this work we deal with the approximate aggregation of a model for a population subjected to demographic stochasticity and whose dynamics is controlled by two processes with different time scales. There are no restrictions on the slow process while the fast process is supposed to be conservative of the total number of individuals. The incorporation of the effects of demographic stochasticity in the dynamics of the population makes both the fast and the slow processes being modelled by two multi-type Galton–Watson branching processes. We present a multi-type global model that incorporates the combined effect of the fast and slow processes and develop a method that takes advantage of the difference of time scales to reduce the model obtaining an "aggregated" simpler system. We show that, given the separation of time scales between the two processes is high enough, we can obtain relevant information about the behavior of the multi-type global model through the study of this simple aggregated system.
UNIQUE SOLVABILITY FOR ELECTROMAGNETIC BOUNDARY VALUE PROBLEMS IN THE PRESENCE OF PARTLY LOSSY INHOMOGENEOUS ANISOTROPIC MEDIA AND MIXED BOUNDARY CONDITIONS
Authors: ALONSO RODRÍGUEZ ANA , RAFFETTO MIRCO
Published: May 2003

A result on the existence and uniqueness of the solutions of electromagnetic boundary value problems is presented. It is a generalization of the results already available in the open literature which holds true in all cases of practical interest. As a matter of fact, it holds true even in the presence of general inhomogeneous anisotropic media, surfaces of discontinuity, topologically complicated domains and mixed boundary conditions.
PERTURBATIVE ANALYSIS OF GENERALIZED EINSTEIN THEORIES
Authors: FABRIS JÚLIO CÉSAR , KERNER RICHARD , TOSSA JOËL
Published: May 2003

The hypothesis that the energy–momentum tensor of ordinary matter is not conserved separately, leads to a nonadiabatic expansion and, in many cases, to an Universe older than usual. This may provide a solution for the entropy and age problems of the Standard Cosmological Model. We consider two different theories of this type, and we perform a perturbative analysis, yielding analytical expressions for the evolution of gravitational waves, rotational modes and density perturbations. One of these theories exhibits satisfactory properties at this level, while the other one should be discarded.
FINITE FIELD THEORY ON NONCOMMUTATIVE GEOMETRIES
Authors: CHO S. , HINTERDING R. , MADORE J. , STEINACKER H.
Published: May 2003

The propagator is calculated on a noncommutative version of the flat plane and the Lobachevsky plane with and without an extra (Euclidean) time parameter. In agreement with the general idea of noncommutative geometry it is found that the limit when the two "points" coincide is finite and diverges only when the geometry becomes commutative. The flat four-dimensional case is also considered. This is at the moment less interesting since there has been no curved case developed with which it can be compared.
ON GRAVITATIONAL FLUCTUATIONS AND THE SEMICLASSICAL LIMIT IN MINISUPERSPACE MODELS
Authors: CASADIO ROBERTO
Published: May 2003

An attempt is made to go beyond the semiclassical approximation for gravity in the Born–Oppenheimer decomposition of the wave-function in minisuperspace. New terms are included which correspond to quantum gravitational fluctuations on the background metric. They induce a back-reaction on the semiclassical background and can lead to the avoidance of the singularities the classical theory predicts in cosmology and in the gravitational collapse of compact objects.
PRIMORDIAL BLACK HOLE FORMATION FROM INFLATON
Authors: MENG XIN HE , WANG BIN , FENG S.
Published: May 2003

Measurements of the distances to SNe Ia have produced strong evidence that the expansion of the Universe is really accelarating, implying the existence of a nearly uniform component of dark energy with the simplest explanation as a cosmological constant. In this paper a small changing cosmological term is proposed, which is a function of a slow-rolling scalar field, by which the de Sitter primordial black holes' properties, for both charged and uncharged cases, are carefully examined and the relationship between the black hole formation and the energy transfer of the inflaton is eluciated. The criterion for primordial black hole formation is given.
GRAVITATIONAL WAVES EMITTED BY EXTRASOLAR PLANETARY SYSTEMS
Authors: FERRARI VALERIA , BERTI EMANUELE , D'ANDREA MARCO
Published: May 2003

In this paper we consider the Extrasolar Planetary Systems recently discovered in our Galaxy as potential sources of gravitational waves. We estimate the frequency and characteristic amplitude of the radiation they emit due to the orbital motion, using the quadrupole formalism. In addition, we check whether the conditions needed for the resonant excitation of the f- and g-modes of the central star can be fulfilled. By a Roche-lobe analysis, we show that there could exist systems in which the low-order g-modes could be excited, although this does not happen in the systems discovered up to now.
MATCHING CONDITION ON THE EVENT HORIZON AND HOLOGRAPHY PRINCIPLE
Authors: DZHUNUSHALIEV V.
Published: May 2003

It is shown that the event horizon of 4D black hole or ds2=0 surfaces of multidimensional wormhole-like solutions reduce the amount of information necessary for determining the whole spacetime and hence satisfy the Holography principle. This leads to the fact that by matching two metrics on a ds2=0 surface (an event horizon for 4D black holes) we can match only the metric components but not their derivatives. For example, this allows us to obtain a composite wormhole inserting a 5D wormhole-like flux tube between two Reissner–Nordström black holes and matching them on the event horizon. Using the Holography principle, the entropy of a black hole from the algorithm theory is obtained.
BOSON STARS WITH GENERIC SELF-INTERACTIONS
Authors: SCHUNCK FRANZ E. , TORRES DIEGO F.
Published: May 2003

We study boson star configurations with generic, but not nontopological, self-interaction terms. When compared with the usual λ|ψ|4 potential, similar results for masses and number of particles appear. However, changes are noticed in the order of a few percent of the star mass. We explore, using catastrophe theory, the stability properties of the configurations and look for possible observational outputs that may differentiate one model from the other: gravitational redshifts, rotation curves of accreted particles, and lensing phenomena are computed for our new cases.
GEODESICS IN THE γ SPACETIME
Authors: HERRERA L. , PAIVA FILIPE M. , SANTOS N. O.
Published: May 2003

Geodesics are studied in the spacetime described by the γ metric. Their behaviour is compared with the spherically symmetric situation, bringing out the sensitivity of the trajectories to deviations from spherical symmetry.
DISTINGUISHING MARKS OF SIMPLY-CONNECTED UNIVERSES
Authors: REBOUÇAS M. J.
Published: May 2003

A statistical quantity suitable for distinguishing simply-connected Robertson–Walker (RW) universes is introduced, and its explicit expressions for the three possible classes of simply-connected RW universes with an uniform distribution of matter are determined. Graphs of the distinguishing mark for each class of RW universes are presented and analyzed. There sprout from our results an improvement on the procedure to extract the topological signature of multiply-connected RW universes, and a refined understanding of that topological signature of these universes studied in previous works.
NUCLEOSYNTHESIS IN A UNIVERSE WITH A LINEARLY EVOLVING SCALE FACTOR
Authors: BATRA ANNU , LOHIYA DAKSH , MAHAJAN SHOBHIT , MUKHERJEE AMITABHA
Published: May 2003

Primordial nucleosynthesis is regarded as a success story of the standard big bang (SBB) cosmology. In this article nucleosynthesis is explored in models in which the cosmological scale factor R(t) increases linearly with time. This relationship of R(t) and t continues from the period when nucleosynthesis begins until the present time. It turns out that weak interactions remain in thermal equilibrium upto temperatures which are two orders of magnitude lower than the corresponding (weak interaction decoupling) temperatures in SBB. Inverse beta decay of the proton can ensure adequate production of helium while producing primordial metallicity much higher than that produced in SBB. Attractive features of such models are the absence of the horizon, flatness and age problems as well consistency with classical cosmological tests.
DEVELOPMENT OF THE ELECTROWEAK PHASE TRANSITION AND BARYOGENESIS
Authors: MÉGEVAND ARIEL
Published: May 2003

We investigate the evolution of the electroweak phase transition, using a one-Higgs effective potential that can be regarded as an approximation for the Minimal Supersymmetric Standard Model. The phase transition occurs in a small interval around a temperature Tt below the critical one. We calculate this temperature as a function of the parameters of the potential and of a damping coefficient related to the viscosity of the plasma. The parameters that are relevant for baryogenesis, such as the velocity and thickness of the walls of bubbles and the value of the Higgs field inside them, change significantly in the range of temperatures where the first-order phase transition can occur. However, we find that in the likely interval for Tt there is no significant variation of these parameters. Furthermore, the temperature Tt is in general not far below the temperature at which bubbles begin to nucleate.
SIGNATURE FOR THE SHAPE OF THE UNIVERSE
Authors: GOMERO G. I. , REBOUÇAS M. J. , TEIXEIRA A. F. F.
Published: May 2003

If the universe has a nontrivial shape (topology) the sky may show multiple correlated images of cosmic objects. These correlations can be couched in terms of distance correlations. We propose a statistical quantity which can be used to reveal the topological signature of any Robertson–Walker (RW) spacetime with nontrivial topology. We also show through computer-aided simulations how one can extract the topological signatures of flat, elliptic, and hyperbolic RW universes with nontrivial topology.
DILATON GRAVITY WITH A NONMINIMALLY COUPLED SCALAR FIELD
Authors: ALVES M. , BEZERRA V.
Published: May 2003

We discuss the two-dimensional dilaton gravity with a scalar field as the source matter. The coupling between the gravity and the scalar, massless, field is presented in an unusual form. We work out two examples of these couplings, and solutions with black-hole behaviour are discussed and compared with those found in the literature.
GRAVITOELECTROMAGNETISM AND THE INTEGRAL FORMULATION OF MAXWELL'S EQUATIONS
Authors: BINI DONATO , GERMANI CRISTIANO , JANTZEN ROBERT T.
Published: May 2003

The integral formulation of Maxwell's equations expressed in terms of an arbitrary observer family in a curved spacetime is developed and used to clarify the meaning of the lines of force associated with observer-dependent electric and magnetic fields.
CURVATURE INHERITANCE SYMMETRY IN RIEMANNIAN SPACES WITH APPLICATIONS TO STRING CLOUD AND STRING FLUIDS
Authors: YILMAZ İHSAN , TARHAN İSMAIL , YAVUZ İLHAMI , BAYSAL HÜSNÜ , CAMCI UǦUR
Published: May 2003

We study, in this paper, curvature inheritance symmetry (CI), [Formula: see text], where α is a scalar function, for string cloud and string fluid in the context of general relativity. Also, we have obtained some result when a proper CI (i.e., α ≠ 0) is also a conformal Killing vector.