bluuebunny/crossref_metadata_2025 huggingface dataset:
EMPIRICAL FORMALISM FOR PROJECTILE FRAGMENTATION AND PRODUCTION OF NEW NEUTRON-RICH NUCLEI WITH RIBS
Authors: BHOWMICK DEBASIS , CHAKRABARTI ALOK , BASU D. N. , GHOSH PREMOMOY , GOSWAMI RANJANA
Published: September 2003

The projectile fragment separator type radioactive ion beam (RIB) facilities, being developed in different laboratories, provide the scope for producing many new exotic nuclei through fragmentation of high energy radioactive ion (RI) beams. A new empirical parametrization for the estimation of cross-sections of projectile fragments has been prescribed for studying the advantages and limitations of high energy RI beams for the production of new exotic nuclei. The parametrization reproduces the experimental data for the production of fragments from neutron-rich projectiles accurately in contrast to the existing parametrization which tends to overestimate the cross-section of neutron-rich fragments in most cases. The modified formalism has been used to compute the cross-sections of neutron-rich species produced by fragmentation of radioactive projectiles (RIBs). It has been found that, given any limit of production cross-section, the exoticity of the fragment increases rather slowly and shows a saturation tendency as the projectile is made more and more exotic. This essentially limits, to an extent, the utility of very neutron-rich radioactive beams vis-a-vis production of new neutron-rich exotic species.
NEW REPRESENTATION FOR GAUGE-INVARIANT WIGNER OPERATOR OF AN ELECTRON IN A UNIFORM MAGNETIC FIELD
Authors: FAN HONG-YI , YANG ZHEN-SHAN
Published: September 2003

By using the technique of integration within an ordered product (IWOP) of operators, we derive the normal-product form of the gauge-invariant Wigner operator of an electron in a uniform magnetic field and its expression in the newly constructed |λ> representation. The virtue of working in the |λ> representation lies in the fact that it is expressed in terms of the ladder operators Π±, K±(see Eq. (10)), thus the magnetic vector potential can naturally be included. On these bases we can easily obtain Wigner functions of some important electron states.
VIRTUAL MESON CLOUD OF THE NUCLEON AND INTRINSIC STRANGENESS AND CHARM
Authors: PAIVA S. , NIELSEN M. , NAVARRA F. S. , DURÃES F. O. , BARZ L. L.
Published: September 2003

We have used the Meson Cloud Model (MCM) to calculate the charm and strange antiquark distribution in the nucleon. The resulting curve, in the case of charm, is very similar to the intrinsic charm momentum distribution. This allows us to identify the intrinsic quark distribution with the valence quark distribution in the cloud and, at the same time, explains why other MCM calculations fail in reproducing the low x region data. From the intrinsic strange quark distribution in the nucleon, we have extracted information about the relative importance of various intermediate states that should be considered in a loop calculation.
MATRIX THEORY, HILBERT SCHEME AND INTEGRABLE SYSTEM
Authors: MATSUO YUTAKA
Published: September 2003

We give a reinterpretation of the matrix theory discussed by Moore, Nekrasov and Shatashivili (MNS) in terms of the second quantized operators which describes the homology class of the Hilbert scheme of points on surfaces. It naturally relates the contribution from each pole to the inner product of orthogonal basis of free boson Fock space. These bases can be related to the eigenfunctions of Calogero–Sutherland (CS) equation and the deformation parameter of MNS is identified with coupling of CS system. We discuss the structure of Virasoro symmetry in this model.
PROTON-SKIN IN 8B-NUCLEUS
Authors: PATRA S. K. , WU CHENG-LI , PRAHARAJ C. R.
Published: September 2003

Using axially symmetric deformed relativistic mean field model, we calculate the proton, neutron and matter distributions radii, the quadrupole moments, the binding energies and the single particle energies of 7 Be , 8 B , 9 B and 10 B . Analysis of the single particle energies and the calculated density distributions of protons and neutrons of these nuclei show the existence of a thick proton-skin in 8 B . For 7 Be and 9 B the skins are less pronounced; while for 10 B the neutron and proton distributions are almost identical.
THE SUPPRESSION OF πNN(1535) COUPLING IN QCD
Authors: ZHU SHI-LIN
Published: September 2003

The lightcone QCD sum rules are employed to calculate the πNN(1535) coupling gπNN*.We study the two-point correlation function of two nucleon currents sandwiched between the vacuum and the pion state. The contribution from the excited states and the continuum is subtracted from the double Borel transform with respect to the nucleon and N(1535) momenta, [Formula: see text]. Our calculation shows that the πNN(1535) coupling is strongly suppressed.
EVOLUTION OF GRAVITATIONAL WAVES THROUGH THE COSMOLOGICAL QCD TRANSITION
Authors: SCHWARZ DOMINIK J.
Published: September 2003

The spectrum of gravitational waves that have been produced in inflation is modified during cosmological transitions. Significant decrease in the number of relativistic particles, like during the QCD transition or at e+ e- annihilation, leads to steps in the spectrum of gravitational waves. We calculate the transfer function for the differential energy density of gravitational waves for a first-order and for a crossover QCD transition.
DIRAC'S CONTOUR REPRESENTATION FOR PARAPARTICLES
Authors: JING SICONG , NELSON CHARLES A.
Published: September 2003

Dirac's contour representation is extended to para-Bose and para-Fermi systems by use of deformed algebra techniques. In this analytic representation, the action of the para-particle annihilation operator is equivalent to a deformed differentiation which encodes the statistics of the paraparticle. In the para-Fermi case, the derivative's ket-domain is degree p polynomial.
FRACTAL SUBSTRUCTURES OF THE UNIVERSE
Authors: TERAZAWA HIDEZUMI
Published: September 2003

It is pointed out that the universe has fractal substructures such as clusters of galaxies, galaxies, clusters of stellar systems, and stellar systems due to the scaling properties in these gravitational subsystem with respect to the numbers and masses of constituents, and the size-scales and time-scales of substructures. Also suggested is a clue to explain both the "less-large-number hypothetical relations" of NG~NS(~NC~1011) where NG and NS(NC) are the "total number of galaxies" in the universe and the average total number of stars in a galaxy (the average total number of comets in a solar system), respectively, and the "even-less-large-number hypothetical relations" of n1~n2~n3(~103) for n1≡RU/DG, n2≡DG/RG and n3≡RG/DS where RU(RG) is the "radius of the universe" (the average radius of an ordinary galaxy) and DG(DS) is the average distance between two neighboring galaxies (that between two neighboring stars).
FERMION–BOSON DUALITY IN INTEGRABLE QUANTUM FIELD THEORY
Authors: BASEILHAC P. , FATEEV V. A.
Published: September 2003

We introduce and study one-parameter family of integrable quantum field theories. This family has a Lagrangian description in terms of massive Thirring fermions ψ, ψ† and charged bosons χ, [Formula: see text] of complex sinh–Gordon model coupled with BCn affine Toda theory. Perturbative calculations, analysis of the factorized scattering theory and the Bethe ansatz technique are applied to show that under duality transformation, which relates weak and strong coupling regimes of the theory, the fermions ψ, ψ† transform to bosons and χ, [Formula: see text] and vice versa. The scattering amplitudes of neutral particles in this theory coincide exactly with S-matrix of particles in pure BCn Toda theory, i.e. the contribution of charged bosons and fermions to these amplitudes exactly cancel each other. We describe and discuss the symmetry responsible for this compensation property.
ON THE SL(2,Z) COVARIANT WORLDSHEET ACTION WITH SOURCES
Authors: MUKHERJI SUDIPTA
Published: September 2003

We analyze various worldsheet properties of the SL (2,Z) covariant type IIB string action by coupling it with SL (2,Z) covariant source.
J/ψ ELASTICITY DISTRIBUTION IN THE VECTOR DOMINANCE APPROACH
Authors: DURÃES F. O. , NAVARRA F. S. , WILK G.
Published: September 2003

The j/ψ elasticity distribution measured at HERA has recently been understood in terms of QCD models. We suggest that data can also be explained by the vector meson dominance mechanism supplemented by some hadronic description of energy loss, which is assumed to be provided by the Interacting Gluon Model (IGM).
MASSES, MAGNETIC MOMENTS, AND SEMILEPTONIC DECAYS OF SPIN-1/2 BARYONS WITH SEA CONTRIBUTION
Authors: GUPTA V. , RITTO P. , SÁNCHEZ-COLÓN G.
Published: September 2003

The spin-1/2 baryons are pictured as a composite system made out of a "core" of three valence quarks (as in the simple quark model) surrounded by a "sea" (of gluon and [Formula: see text] pairs) which is specified by its total quantum numbers. We assume that the sea is an SU(3) flavor octet with spin 0 or 1 but no color. This model, considered earlier, is used to obtain simultaneous fits for masses, magnetic moments and GA/GV for semileptonic decays. These fits give predictions for nucleon spin distributions in reasonable agreement with experiment.
TWIST-TWO LIGHTCONE PION WAVE FUNCTION
Authors: BELYAEV V. M. , JOHNSON MIKKEL B.
Published: September 2003

We present an analysis of the existing constraints for the twist-two lightcone pion wave function. We find that existing information on the pion wave function does not exclude the possibility that the pion wave function attains its asymptotic form. New bounds on the parameters of the pion wave function are presented.
FACTORIZATION OF THE CHARGE CORRELATION FUNCTION IN $B^0 {\bar B}^0$ OSCILLATIONS
Authors: DASS G. V. , SARMA K. V. L.
Published: September 2003

Extraction of the mass difference Δm from [Formula: see text] oscillations involves tagging of bottom flavor at production and at decay. The charge correlation function is the asymmetry between the unmixed and mixed events. In their data using the lepton-jet-method, the ALEPH collaboration recently verified that this asymmetry factorizes into two parts, one depending on the production tag and the other on the decay tag. Except for this particular "verification", analyses of experiments on the time-dependence of beon oscillations have been assuming this factorization, without statement or explanation of their assumption. We theoretically explain this factorization as arising from the neglect of terms which involve CP-violation in the second order.
NEW STATISTICAL TESTS APPLIED ON THE FOUR-YEAR COBE–DMR MAPS
Authors: PERIVOLAROPOULOS L. , SIMATOS N.
Published: September 2003

We apply new statistical tests on the four-year 53 GHz DMR data and show that there is excessive probability for the existence of coherent temperature discontinuities hidden in the CMB maps around the galactic poles. Such discontinuities could have been produced by long strings in our horizon. Comparing Monte–Carlo simulations with the 53 GHz DMR maps we find that the probability for the existence of a coherent discontinuity with amplitude 0.2×(δT/T) rms superposed on the Gaussian fluctuations is more than double the corresponding probability when no discontinuity is present. This result cannot be used as a detection because the DMR value of the introduced statistical variable MSD is consistent with a pure Gaussian map at a 20% level. However, when combined with the recent findings of Ferreira et al.1 it points out that the confidence by which the COBE maps are assumed to be Gaussian should probably be reduced.
R-CHARGE KILLS MONOPOLES
Authors: BAJC BORUT , RIOTTO ANTONIO , SENJANOVIĆ GORAN
Published: September 2003

Large charge density, unlike high temperature, may lead to nonrestoration of global and gauge symmetries. Supersymmetric GUTs with the appealing scenario of unification scale being generated dynamically naturally contain global continuous R-symmetries. We point out that the presence of a large R-charge in the early universe can lead to GUT symmetry nonrestoration. This provides a simple way out of the monopole problem and, at the same time, solves the well-known cosmological problem of the theory being caught permanently in the wrong vacuum with the GUT gauge group unbroken.
THE LORENTZ FORCE BETWEEN D0 AND D6 BRANES IN STRING AND M(ATRIX) THEORY
Authors: BILLÓ M. , DI VECCHIA P. , FRAU M. , LERDA A. , RUSSO R. , SCIUTO S.
Published: September 2003

We use different techniques to analyze the system formed by a D0-brane and a D6- brane (with background gauge fields) in relative motion. In particular, using the closed string formalism of boosted boundary states, we show the presence of a term linear in the velocity, corresponding to the Lorentz force experienced by the D0-brane moving in the magnetic background produced by the D6-brane. This term, that was missed in previous analyses of this system, comes entirely from the R–R odd spin structure and is also reproduced by a M(atrix) theory calculation.
NONLINEAR SUPERSYMMETRIC EFFECTIVE LAGRANGIAN AND GOLDSTINO INTERACTIONS AT HIGH ENERGIES
Authors: LEE TAEKOON , WU GUO-HONG
Published: September 2003

We show that the nonlinear supersymmetric effective Lagrangian can be used for model-independent parametrization of the light gravitino scattering amplitude at energies up to and above the soft supersymmetry-breaking masses. This provides the most convenient framework for systematic studies of goldstino phenomenology both at low energies and in high energy colliders.
QUANTUM MECHANICALLY INDUCED WESS–ZUMINO TERM IN THE PRINCIPAL CHIRAL MODEL
Authors: MIYAZAKI HITOSHI , TSUTSUI IZUMI
Published: September 2003

It is argued that in the two-dimensional principal chiral model, the Wess–Zumino term may be induced quantum mechanically in a manner analogous to the θ-term in QCD. Our argument is based on the fact that the configuration space of the model has a structure topologically identified as a sphere, and that the Dirac monopole potential, which is induced on the sphere by inequivalent quantizations, appears in the guise of the Wess–Zumino term. Our result suggests that, at the critical value λ2=8π/|k| of the coupling constant, the principal chiral model belongs to the same family of models with the Wess–Zumino–Novikov–Witten model at the quantum level.
ENERGY DEPENDENCE OF THE POMERON SPIN-FLIP
Authors: KOPELIOVICH B. Z. , POVH B.
Published: September 2003

There is no theoretical reason to think that the spin-flip component of the Pomeron is zero. One can measure the spin-flip part using Coulomb-nuclear interference (CNI). Perturbative QCD calculations show that the spin-flip component is sensitive to the smallest quark separation in the proton, while the non-flip part probes the largest separation. According to HERA results on the proton structure function at very low x, the energy dependence of the cross-section correlates with the size of the color dipole. Analyzing the data from HERA we predict that the ratio of the spin-flip to non-flip amplitude grows with energy as r(s)∝(1/x)0.1-0.2, violating Regge factorization of the Pomeron.
HIGH ENERGY PROTONS FROM PKS 1333-33
Authors: ANCHORDOQUI L. A. , ROMERO G. E. , COMBI J. A. , PEREZ BERGLIAFFA S. E.
Published: September 2003

In this letter we give an account of the possible acceleration of protons in the outer radio lobes of the active galaxy PKS 1333-33. We also make estimates of the arrival energy spectrum.
DEVIATIONS FROM LOW-ENERGY THEOREM FOR VLVL SCATTERING DUE TO PSEUDO-GOLDSTONE BOSONS
Authors: BAHNÍK TOMÁS , HOŘEJSÍ JIŘÍ
Published: September 2003

Possible deviations from a low-energy theorem for the scattering of strongly interacting longitudinally polarized W and Z bosons are discussed within a particular scheme of electroweak symmetry breaking. The scheme (suggested earlier by other authors in a slightly different context) is based on spontaneous breakdown of an SU(4) symmetry to custodial SU(2) subgroup. The physical spectrum of such a model contains a set of relatively light pseudo-Goldstone bosons whose interactions with vector bosons modify the low-energy theorem proven for a "minimal" symmetry-breaking sector The Goldstone-boson manifold SU(4)/SU(2) is not a symmetric space. In this context it is observed that, on the other hand, there is a large class of models of electroweak symmetry breaking, involving groups G and H such that the G/H is a symmetric space and the corresponding rich multiplets of pseudo-Goldstone bosons do not influence the canonical low-energy theorem. For the scheme considered here, the relevant interactions are described in terms of an effective chiral Lagrangian and tree-level contributions of the pseudo-Goldstone boson exchanges to the vector boson scattering are computed explicitly. A comparison with the standard model is made.
SCALAR NEUTRINOS AND HIGGS BOSONS PRODUCTION WITH PHOTONS AT LEPTON–ANTILEPTON COLLIDERS
Authors: ALANAKYAN R. A.
Published: September 2003

Scalar and pseudoscalar neutral Higgs bosons production with photons μ+μ-→H0γ is considered in model independent way in the tree approximation. Under some conditions the tree contributions to this process may exceed loop contribution.

Also the related processes of scalar neutrinos production with photons in e+e-, μ+μ-, [Formula: see text] are considered in the framework of supersymmetric models with R-parity violation. Our results are also applicable for flavor changing scalars and pseudoscalars production with photons.
CANCELLATION OF ULTRAVIOLET DIVERGENCES FOR LOCALLY FLAT METRICS
Authors: HORTAÇSU M. , ÖZDEMIR N.
Published: September 2003

We extend the work done for cosmic strings on the perturbative calculation of vacuum polarization of a massless field in the space–time of multiple cosmic strings and show that for a more general class of locally flat metrics, the one-loop calculation does not introduce any new divergences to the vev of the energy of a scalar particle or a spinor particle.
NONLOCALITY AND GRAVITY-INDUCED CP VIOLATION
Authors: AHLUWALIA D. V.
Published: September 2003

We consider a space–time dependent relative phase between the right- and left-handed spinors and show that it results in a violation of locality in the presence of gravity once the demand of parity covariance is dropped. This violation of locality is such that it readily interprets itself as a gravity-induced CP violation, and at the same time confirms an earlier remark by Wigner that a representation space carries more information than a wave equation. This happens, as Kirchbach has noted, because while the dimensionality of an irreducible representation space does not depend upon the concrete realization of the symmetry generators, Noether currents (Dirac, versus Majorana, versus the CP violating construct presented here) do. The gravity-induced CP violation provides a dynamical reason on how a neutron star carrying its baryon and lepton numbers can collapse into a black hole and loose information on the latter characteristics.
D0-BRANE DESCRIPTION OF THE CHARGED BLACK HOLE
Authors: KATO YURIKO , SUGAMOTO AKIO , NOJIRI SHIN'ICHI
Published: September 2003

The charged black hole is considered from the viewpoint of D0-brane in the matrix theory. It can be obtained from the Kaluza–Klein mechanism by boosting the Schwarzschild black hole in a circle, which is the compactified one-dimensional space. In particular, it shows how the extremal limit is realized by the Boltzmann gas of D0-brane. In the course of our discussion, the virial theorem for the statistical average plays an important role.
PADÉ-IMPROVED EXTRACTION OF αs(Mτ) FROM Rτ
Authors: STEELE T. G. , ELIAS V.
Published: September 2003

The perturbative series used to extract αs(Mτ) from the τ hadronic width exhibits slow convergence. Asymptotic Padé-approximant and Padé summation techniques provide an estimate of these unknown higher-order effects, leading to values for αs(Mτ) that are about 10% smaller than current estimates. Such a reduction improves the agreement of αs(Mτ) with the QCD evolution of the strong coupling constant from αs(Mz).
ANISOTROPIC NULL STRING COSMOLOGIES
Authors: GIANNAKIS IOANNIS , KLEIDIS K. , KUIROUKIDIS A. , PAPADOPOULOS D.
Published: September 2003

We study string propagation in an anisotropic, cosmological background. We solve the equations of motion and the constraints by performing a perturbative expansion of the string coordinates in powers if c2 — the worldsheet speed of light. To zeroth order the string is approximated by a tensionless string (since c is proportional to the string tension T). We obtain exact, analytical expressions for the zeroth- and first-order solutions and we discuss some cosmological implications.
KNOT SOLITONS
Authors: GOVINDARAJAN T. R.
Published: September 2003

The existence of ring-like and knotted solitons in O(3) nonlinear σ-model is analyzed. The role of isotopy of knots/links in classifying such solitons is pointed out. Appearance of torus knot solitons is seen.
RSFP CONSTRAINTS ON THE TWISTING PROFILES OF SOLAR MAGNETIC FIELDS FROM THE SOLAR NEUTRINO DATA
Authors: PANDEY UMESH CHANDRA , CHAUHAN B. C. , DEV S.
Published: September 2003

Constraints on the possible twisting profiles of the magnetic fields in the convective zone of the Sun have been derived within the framework of the Resonant Spin Flavor Precession (RSFP) scenario in the light of solar neutrino observations.
DECAY RATE ASYMMETRY OF TOP SQUARK
Authors: AOKI MAYUMI , OSHIMO NORIYUKI
Published: September 2003

We discuss a decay rate asymmetry of the top squark, which is induced by a new source of CP violation intrinsic in the supersymmetric standard model. Although new sources of CP violation in this model are severely constrained from the electric dipole moment of the neutron, an unsuppressed CP violating phase can still coexist with a top squark whose mass is accessible by near-future colliders. Then the dominant decay mode of the top squark has a width different from its CP conjugate process. The magnitude of this CP asymmetry becomes of order 10-3.
NEW PHYSICS DISCOVERY POTENTIAL IN FUTURE EXPERIMENTS
Authors: BITYUKOV S. I. , KRASNIKOV N. V.
Published: September 2003

We propose a method to estimate the probability of new physics discovery in future high energy physics experiments. Physics simulation gives both the average numbers  of background and  of signal events. We find that the proper definition of the significance for ,  ≫ 1 is [Formula: see text] in comparison with often used significances: [Formula: see text] and [Formula: see text]. We propose a method of taking into account the systematical errors related to nonexact knowledge of background and signal cross-sections. An account of such systematics is essential in the search for supersymmetry at LHC. We also propose a method for estimating exclusion limits on new physics in future experiments.
Chaotic Diffusion of Particles with Finite Mass in Oscillating and Turbulent Convections
Authors: Sakaguchi Hidetsugu
Published: October 2003

Deterministic diffusion of a particle with finite mass is numerically studied in oscillating and turbulent convections. For the turbulent convection, we use a coupled Ginzburg-Landau-Swift-Hohenberg equation for the soft-mode turbulence in liquid crystal. The diffusion constants are numerically calculated for convection models with free and rigid boundary conditions.
Thermal Properties of Degenerate Relativistic Quantum Gases
Authors: Homorodean Laurean
Published: September 2003

We present the concentration-temperature phase diagram, characteristic functions, thermal equation of state and heat capacity at constant volume for degenerate ideal gases of relativistic fermions and bosons. The nonrelativistic and ultrarelativistic limits of these laws are also discussed.
Coherent Transport in Nb/δ-Doped-GaAs Hybrid Microstructures
Authors: Giazotto F. , Pingue P. , Beltram F.
Published: September 2003

Coherent transport in Nb/GaAs superconductor-semiconductor microstructures is presented. The structure fabrication procedure is based on δ-doped layers grown by molecular-beam-epitaxy near the GaAs surface, followed by an As cap layer to protect the active semiconductor layers during ex situ transfer. The superconductor is then sputter deposited in situ after thermal desorption of the protective layer. Two types of structures in particular will be discussed, i.e. a reference junction and the engineered one that contains an additional insulating AlGaAs barrier inserted during the growth in the semiconductor. This latter configuration may give rise to controlled interference effects and realizes the model introduced by de Gennes and Saint-James in 1963. While both structures show reflectionless tunneling-dominated transport, only the engineered junction shows additionally a low-temperature single marked resonance peaks superimposed to the characteristic Andreev-dominated subgap conductance. The analysis of coherent magnetotransport in both microstructures is successfully performed within the random matrix theory of Andreev transport and ballistic effects are included by directly solving the Bogoliubov–de Gennes equations. The impact of junction morphology on reflectionless tunneling and the application of the employed fabrication technique to the realization of complex semiconductor-superconductor systems are also discussed.
Green's Function Approach to Global Parameter Estimation in Information Processing
Authors: Wong K. Y. Michael , Li Fuli
Published: September 2003

In information processing systems for classification and regression tasks, global parameters are often introduced to balance the prior expectation about the processed data and the emphasis on reproducing the training data. Since over-emphasizing either of them leads to poor generalization, optimal global parameters are needed. Conventionally, a time-consuming cross-validation procedure is used. Here we introduce a novel approach to this problem, based on the Green's function. All estimations can be made empirically and hence can be easily extended to more complex systems. The method is fast since it does not require the validation step. Its performances on benchmark data sets are very satisfactory.
Effect of a Charged Impurity on a Lithium Quantum Dot
Authors: Liu Yi-Min , Huang Gang-Ming
Published: September 2003

A lithium quantum dot (QD) with a charged impurity is studied, where the charged impurity is located on the z-axis at a distance d from the lithium QD plane (the x–y plane). Using the method of few-body physics, the energy spectra of the low-lying states of the QD are obtained as a function of d. It is found that the energy spectra depend strongly on both the position and charge of the impurity. Furthermore, the impurity affects the electronic configurations of the QD, i.e. the spatial distribution of the electrons of the QD. Our calculations indicate that the change of d induces transitions in the ground states of the QD, which can be explained by dynamics and symmetry.
Performance Analysis in General Cyclic ADCs
Authors: Ren Yong , Lin Hao , Ma Zhengxin , Shan Xiuming
Published: September 2003

The cyclic A/D converting process is equivalent to iterations of a chaotic may using symbolic dynamics. The principle can be extended to construct "general cyclic ADCs" based on chaotic iterations. In this paper, the two necessary conditions of iterated maps are presented, and the new attributes of these converters are also discussed. By establishing a noise model, the analytic expressions of the random and system errors in general cyclic ADCs are derived and verified by simulations. With the same level of additive white noise, the optimal iterative maps for general cyclic ADCs are deduced.
One-Parameter Bifurcations in Planar Filippov Systems
Authors: Kuznetsov Yu. A. , Rinaldi S. , Gragnani A.
Published: September 2003

We give an overview of all codim 1 bifurcations in generic planar discontinuous piecewise smooth autonomous systems, here called Filippov systems. Bifurcations are defined using the classical approach of topological equivalence. This allows the development of a simple geometric criterion for classifying sliding bifurcations, i.e. bifurcations in which some sliding on the discontinuity boundary is critically involved. The full catalog of local and global bifurcations is given, together with explicit topological normal forms for the local ones. Moreover, for each bifurcation, a defining system is proposed that can be used to numerically compute the corresponding bifurcation curve with standard continuation techniques. A problem of exploitation of a predator–prey community is analyzed with the proposed methods.
Baroclinic Flow and the Lorenz-84 Model
Authors: van Veen Lennaert
Published: September 2003

The bifurcation diagram of a truncation to six degrees of freedom of the equations for quasi-geostrophic, baroclinic flow is investigated. Period-doubling cascades and Shil'nikov bifurcations lead to chaos in this model. The low dimension of the chaotic attractor suggests the possibility to reduce the model to three degrees of freedom. In a physically comprehensible limit of the parameters this reduction is done explicitly. The bifurcation diagram of the reduced model in this limit is compared to the diagram of the six degrees of freedom model and agrees well. A numerical implementation of the graph transform is used to approximate the three-dimensional invariant manifold away from the limit case. If the six-dimensional model is reduced to a linearisation of the invariant manifold about the Hadley state, the Lorenz-84 model is found. Its parameters can then be calculated from the physical parameters of the quasi-geostrophic model. Bifurcation diagrams at physical and traditional parameter values are compared and routes to chaos in the Lorenz-84 model are described.
The Nonlinear Dynamics of the Crayfish Mechanoreceptor System
Authors: Bahar Sonya , Moss Frank
Published: September 2003

We review here the nonlinear dynamical properties of the crayfish mechanoreceptor system from the hydrodynamically sensitive hairs on the tailfan through the caudal photoreceptor neurons embedded in the 6th ganglion. Emphasis is on the extraction of low dimensional behavior from the random processes (noise) that dominate this neural system. We begin with stochastic resonance in the sensory root afferents and continue with a discussion of the photoreceptor oscillator and its instabilities. Stochastic synchronization, rectification and the generation of second harmonic responses in the photoreceptors are finally discussed.
Surrogate Testing by Estimating the Local Dispersions in Phase Space
Authors: Nagarajan Radhakrishnan
Published: September 2003

In this report, a clustering approach is presented to detect dynamical nonlinearity in a stationary time series. The one-dimensional time series sampled from a dynamical system is mapped on to the m-dimensional phase space by the method of delays. The vectors in the phase space are partitioned by k-means clustering technique. The local trajectory matrix for the vectors in each of the clusters is determined. The eigenvalues of the local trajectory matrices represent the variation along the principal directions and are obtained by singular value decomposition (SVD). The product of the eigenvalues represents the generalized variance and is a measure of the local dispersion in the phase space. The sum of the local dispersions (gT) is used as the discriminant statistic to classify data sets obtained from deterministic and stochastic settings. The surrogates were generated by the Iterated Amplitude Adjusted Fourier Transform (IAAFT) technique.
Plane Maps with Denominator. Part II: Noninvertible Maps with Simple Focal Points
Authors: Bischi Gian-Italo , Gardini Laura , Mira Christian
Published: September 2003

This paper is the second part of an earlier work devoted to the properties specific to maps of the plane characterized by the presence of a vanishing denominator, which gives rise to the generation of new types of singularities, called set of nondefinition, focal points and prefocal curves. A prefocal curve is a set of points which are mapped (or "focalized") into a single point, called focal point, by the inverse map when it is invertible, or by at least one of the inverses when it is noninvertible. In the case of noninvertible maps, the previous text dealt with the simplest geometrical situation, which is nongeneric. To be more precise this situation occurs when several focal points are associated with a given prefocal curve. The present paper defines the generic case for which only one focal point is associated with a given prefocal curve. This is due to the fact that only one inverse of the map has the property of focalization, but with properties different from those of invertible maps. Then the noninvertible maps of the previous Part I appear as resulting from a bifurcation leading to the merging of two prefocal curves, without merging of two focal points.
Shrubs in the Mandelbrot Set Ordering
Authors: Romera M. , Pastor G. , Álvarez G. , Montoya F.
Published: September 2003

We introduce shrubs in this paper in order to present a first approach to studying the structure of the Mandelbrot set. Primary, secondary… and N-ary shrubs are analyzed. We have experimentally obtained formulae to calculate the periods of the hyperbolic component representatives of the structural branches, and the preperiods and periods of both the nodes — where structural branches emanate — and the tips — where the shrub enters in crisis. A generalization allows us to give in each case one formula to calculate representative periods and preperiods and periods of nodes and tips.
Simultaneous Amplitude and Frequency Noise Analysis in Chua's Circuit
Authors: Friedt J.-M. , Gillet D. , Planat M.
Published: September 2003

A large number of simultaneous frequency and amplitude data from an electronic chaotic circuit (Chua's circuit) have been obtained. These acquisitions are validated by plotting the bifurcation diagrams of the experimental data versus the bifurcation parameter. We introduce a topological parallel between the Colpitts oscillator and Chua's circuit, and look for similar behavior of the frequency fluctuations using the Allan deviation.
Large Noise Level Estimation
Authors: Leontitsis Alexandros , Pange Jenny , Bountis Tassos
Published: September 2003

We generalize a method of noise estimation for chaotic time series due to [Schreiber, 1993] in cases where the noise level is relatively large. The noise estimation is based on the correlation integral, which, for small amounts of noise, is not affected by the attractor's curvature effects. When the noise is large, however, one has to increase the range of the correlation integral and this brings about significant inaccuracies in its evaluation due to both curvature effects and noise. In this Letter, we present a modification of Schreiber's noise level estimation method, which uses a robust error estimator based on L-∞(rather than the usual L2) norm in the computations. Since L-∞was proved less sensitive to curvature effects, it gives a more accurate estimation of the noise standard deviation compared with Schreiber's results. Here, we illustrate our approach on the Hénon map corrupted by Gaussian white noise with zero mean, as well as on real data obtained from the Nasdaq Composite time series of daily returns.
Classical Limit and Chaotic Regime in a Semi-Quantum Hamiltonian
Authors: Kowalski A. M. , Martin M. T. , Plastino A. , Proto A. N.
Published: September 2003

Based on a quantum dynamical invariant of motion, I, we study the classical limit of a semiclassical Hamiltonian composed by a full quantum harmonic oscillator plus a classical particle plus a "semiclassical" coupling quartic term. The motion-invariant is closely related to the uncertainty principle. The classical limit (CL) is determined by the relationship between I and the total energy of the system, defining an adimensional invariant Er. We find that the CL coincides with the results of a purely classical treatment. Both invariants allow to follow the transit between quantum nonchaotic to the classical chaotic regime. Particularly, with Er we define the threshold above which chaos appears, and the interval during which both regimes co-exist.
Crisis-Induced Intermittency Due to Attractor-Widening in a Buoyancy-Driven Solar Dynamo
Authors: Ossendrijver Mathieu , Covas Eurico
Published: September 2003

In a recent paper [Ossendrijver, 2000] numerical simulations of a 2D mean-field model where shown to produce grand minima, typical of the long-term behavior of solar magnetic activity. The model consisted of a dynamo that features an α effect based on the buoyancy instability of magnetic flux tubes, which gives rise to the switching back and forth from grand minima to "regular" solar behavior. In this Letter, we report evidence from a time-series analysis of the model for the presence of crisis-induced intermittency due to attractor-widening. We support this finding by showing that the average duration of the minima, <τ>, follows the theoretically predicted scaling [Formula: see text], where Cδαis the bifurcation parameter of interest, together with other strong statistical evidence. As far as we are aware, this is the first time concrete and detailed evidence has been produced for the occurrence of this type of crisis-induced intermittency — due to attractor widening — for such dynamo models.
A Novel Framework for Synchronizing via Scalar Signal Hyperchaotic Systems with One or Several Nonlinearities
Authors: Cafagna Donato , Grassi Giuseppe
Published: September 2003

In this paper a novel framework for synchronizing hyperchaotic systems with one or several nonlinearities is presented. The proposed technique exploits observer design and time-division multiplexing of the transmitted signal. A remarkable feature of the approach is that only a scalar signal is required for achieving hyperchaos synchronization. Simulation results are carried out for eighth order circuits with one nonlinearity as well as sixth order circuits with two nonlinearities.
Blind Multiuser Receivers for Chaos Based Communications
Authors: Argüello Francisco , Bugallo Manuel , López Juan
Published: September 2003

Recently, there has been a good deal of interest in the use of chaotic signals for direct sequence code division multiple access (DS-CDMA) communication systems. The capacity of DS-CDMA systems is interference-limited, and can therefore be increased by techniques that suppress interference. This letter is devoted to the evaluation of the impact of blind multiuser detection techniques on chaos based DS-CDMA systems. Blind receivers can suppress multiple access interference and do not require knowledge of the code sequences and propagation channels of the interference. We demonstrate that, for chaotic sequence-based communications, blind multiuser receivers significantly improve the BER with respect to single-user receivers, and that their use is practically essential with a high number of users.
Differential Equations with Bifocal Homoclinic Orbits
Authors: Glendinning Paul
Published: September 2003

Global bifurcation theory can be used to understand complicated bifurcation phenomena in families of differential equations. There are many theoretical results relating to systems having a homoclinic orbit biasymptotic to a stationary point at some value of the parameters, and these results depend upon the eigenvalues of the Jacobian matrix of the flow evaluated at the stationary point. Three important cases arise in the theoretical analysis, and there are many examples of systems which illustrate two of these three cases. We describe a construction which can be used to produce examples of the third case (bifocal homoclinic orbits), and use this construction to prove the existence of a bifocal homoclinic orbit in a simple piecewise linear differential equation.
Homoclinic and Heteroclinic Situations Specific to Two-Dimensional Noninvertible Maps
Authors: Millerioux Gilles , Mira Christian
Published: September 2003

These situations are put in evidence from two examples of (Z0 - Z2) maps. It is recalled that such maps (the simplest type of non-invertible ones) are related to the separation of the plane into a region without preimage, and a region each point of which has two rank-one preimages. With respect to diffeomorphisms, non-invertibility introduces more complex structures of the stable and unstable sets defining the homoclinic and heteroclinic situations, and the corresponding bifurcations. Critical curves permit the analysis of this question. More particularly, a basic global contact bifurcation (contact of the map critical curve with a non-connected saddle stable set Ws) plays a fundamental role for explaining the qualitative change of Ws, which occurs between two boundary homoclinic bifurcations limiting a parameter region related to the disappearing of an attracting invariant closed curve.
A Note on the Determination of the Type of Communication Areas
Authors: Jansen Wolfgang
Published: September 2003

The paper presents a method that determines, by standard numerical means, the type of mutual relations of fold and flip bifurcations (configured as a so-called communication area) of a map. Equation systems are developed for the computation of points where a transition between areas of different types occurs.

Furthermore, it is shown that saddle area↔spring area transitions can exist which have not yet been considered in the literature. Analytical conditions of that transition are derived.
Information Flow in Chaotic Symbolic Dynamics for Finite and Infinitesimal Resolution
Authors: Deco Gustavo , Schittenkopf Christian , Schürmann Bernd
Published: September 2003

We introduce an information-theory-based concept for the characterization of the information flow in chaotic systems in the framework of symbolic dynamics for finite and infinitesimal measurement resolutions. The information flow characterizes the loss of information about the initial conditions, i.e. the decay of statistical correlations (i.e. nonlinear and non-Gaussian) between the entire past and a point p steps into the future as a function of p. In the case where the partition generating the symbolic dynamics is finite, the information loss is measured by the mutual information that measures the statistical correlations between the entire past and a point p steps into the future. When the partition used is a generator and only one step ahead is observed (p = 1), our definition includes the Kolmogorov–Sinai entropy concept. The profiles in p of the mutual information describe the short- and long-range forecasting possibilities for the given partition resolution. For chaos it is more relevant to study the information loss for the case of infinitesimal partitions which characterizes the intrinsic behavior of the dynamics on an extremely fine scale. Due to the divergence of the mutual information for infinitesimal partitions, the "intrinsic" information flow is characterized by the conditional entropy which generalizes the Kolmogorov–Sinai entropy for the case of observing the uncertainty more than one step into the future. The intrinsic information flow offers an instrument for characterizing deterministic chaos by the transmission of information from the past to the future.
Constructing Normal Forms from Experimental Observations and Time Series Analysis
Authors: Karantonis Antonis , Pagitsas Michael
Published: September 2003

A method is proposed for the construction of normal forms from experimental observations which describe the dynamics of a system close to the bifurcation points. The method is applied for the bifurcation of the Fe/2 M H2SO4 electrochemical system from a steady state to a chaotic attractor by considering the applied potential and the external ohmic resistance as bifurcation parameters. Steady state and time evolution curves of the response function are recorded. Perturbation experiments, time delay reconstruction of the attractors and calculation of power and Lyapunov spectra are performed. From the above experimental procedure the linear part of the normal form is constructed. The nonlinear part of the normal form is derived only from the knowledge of the linear part. Perturbations of the derived normal form on the bifurcation point are considered through the versal deformation of the normal form and the construction of the versal family of the normal form. The resulting normal form equations reproduce the dynamic characteristics and the bifurcation diagram of the electrochemical system.
Basin Boundary Bifurcations and Boundary Crisis in the Twin-Well Duffing Oscillator: Scenarios Related to the Saddle of the Large Resonant Orbit
Authors: Szemplińska-Stupnicka Wanda , Janicki Krzysztof L.
Published: September 2003

Bifurcation phenomena in the twin-well Duffing system are considered for such regions of the system parameters, where the saddle DL associated with the two-well T-periodic attractor (large orbit) undergoes homoclinic bifurcation. In particular, a co-dimension-two bifurcation, the bifurcation defined by the intersection of the homoclinic bifurcation of the large orbit with the saddle-node bifurcation of the nonresonant single-well orbit in the system parameter plane is the main point of interest. In the four subdomains around the co-dimension-two point, the manifold structure of the saddle DL and the basins of attractions are studied numerically. The analysis reveals new phenomena and new features of the system behavior. A complex bifurcational structure is observed that includes boundary crisis of the cross-well chaotic attractor, intermittency (subduction) phenomena, and explosion of the basin of attraction of the large orbit. The analysis also explains why, in one of the subdomains, the two-well T-periodic attractor (large orbit) becomes the unique attractor of the system.
Symmetry of Generic Bifurcations in Cubic Domains
Authors: Gabriela M. , Gomes M. , Stewart Ian
Published: September 2003

It is now well known that bifurcation problems arising from elliptic PDEs on finite domains may possess translational symmetries, even though translations cannot leave a finite domain invariant. These "hidden symmetries" are well understood when the domain is a multidimensional rectangle, a square, and a hemisphere. Hidden symmetries have two effects: they extend the symmetries of known solutions, and they make it possible to prove the existence of solutions that were not previously known.

We determine the appropriate group action, which depends upon the mode numbers of the bifurcating solution. Throughout we consider only single modes (supported by absolutely irreducible representations). The group theory is considerably richer than for rectangular domains, because a cubic domain is invariant under the group Sn of all permutations of the coordinate axes. We specialize our results to the cases n = 1, 2, 3. When n = 2 we establish a conjecture of Crawford, made in the context of the Faraday experiment, by using hidden symmetries to predict the unexpected branches that he found. We also show that all such branches are pitchforks. The analysis of the case n = 3 is extensive and we find many new branches by using group elements that do not leave the appropriate fixed-point space invariant to define one-dimensional fixed-point spaces and applying the equivariant branching lemma. We illustrate sample planforms for these solutions when the mode numbers are (15, 6, 10), (42, 15, 35) and (21, 15, 35), the smallest numbers for which all pairs have a nontrivial common factor. Finally we observe that generic normal forms must vary wildly with the mode numbers, unlike the situation for rectangles. We briefly describe an algorithm to find normal forms in any specific case.
Modeling Research on Spatiotemporal Dynamics of the Hippocampus
Authors: Sun Haijian , Liu Lin , Feng Chunhua , Guo Aike
Published: September 2003

The spatiotemporal dynamics of the hippocampus is studied. We first propose a fractal algorithm to model the growth of hippocampal CA1 pyramidal cells, together with an avalanche model for information transmission. Then the optical records of an epileptic focus in the hippocampus are analyzed and simulated. These processes indicate that the hippocampus normally stays in self-organized criticality with a harmonious spatiotemporal behavioral pattern, that is, showing 1/f fluctuation and power law distribution. In case of a neurological insult, the hippocampal system may step into supercriticality and initiate epilepsy.