bluuebunny/crossref_metadata_2025 huggingface dataset:
n-FOLD TIME COINCIDENCES ON IGEC GRAVITATIONAL WAVE EVENTS DATA USING DATA-BASE TECHNOLOGY
Authors: TERENZI ROBERTO
Published: May 2003

Gravitational events on IGEC data are marked with their detection time td. Although td takes into account phase shifts due to hardware and software, it could be statistically retarded or anticipated by noise with respect to the arrival time ta of a gravitational wave. Then we can estimate a time interval Δ for each event so that we can consider the ta of the event equally likely in Δ. Consequently we can define a n-fold coincidence as a n-tuple of events whose associated time intervals have a non-empty intersection. Using this definition and taking into account some time interval properties we show that a n-fold coincidence set can be computed by an appropriate selection of events from the 2-fold coincidence sets. Furthermore, we stress that a data base management system (DBMS) is a very effective tool to store IGEC data (i.e. events) and to implement n-fold coincidence analysis based on the above considerations. Finally we propose to use a DBMS to build a database of both events and n-fold coincidence analysis data in order to have an efficient and powerful tool for data retrieval and further analysis.
HORIZONS AND GEODESICS OF BLACK ELLIPSOIDS
Authors: VACARU SERGIU I.
Published: May 2003

We analyze the horizon and geodesic structure of a class of 4D off–diagonal metrics with deformed spherical symmetries, which are exact solutions of the vacuum Einstein equations with anholonomic variables. The maximal analytic extension of the ellipsoid type metrics are constructed and the Penrose diagrams are analyzed with respect to the adapted frames. We prove that for small deformations (small eccentricities) there are such metrics that the geodesic behaviour is similar to the Schwarzcshild one. We conclude that some vacuum static and stationary ellipsoid configurations1,2 may describe black ellipsoid objects.
PERTURBATIONS AND STABILITY OF BLACK ELLIPSOIDS
Authors: VACARU SERGIU I.
Published: May 2003

We study the perturbations of two classes of static black ellipsoid solutions of four-dimensional vacuum Einstein equations. Such solutions are described by generic off-diagonal metrics which are generated by anholonomic transforms of diagonal metrics. The analysis is performed in the approximation of small eccentricity deformations of the Schwarzschild solution. We conclude that such anisotropic black hole objects may be stable with respect to the perturbations parametrized by the Schrodinger equations in the framework of the one-dimensional inverse scattering theory.
QUARK–DIQUARK EQUATIONS OF STATE MODELS: THE ROLE OF INTERACTIONS
Authors: HORVATH J. E. , LUGONES G. , DE FREITAS PACHECO J. A.
Published: May 2003

Recent observational data suggests a high compacticity (the quotient M/R) of some "neutron" stars. Motivated by these works we revisit models based on quark–diquark degrees of freedom and address the question of whether that matter is stable against diquark disassembling and hadronization within the different models. We find that equations of state modeled as effective λϕ4 theories do not generally produce stable self-bound matter and are not suitable for constructing very compact star models, that is the matter would decay into neutron matter. We also discuss some insights obtained by including hard sphere terms in the equation of state to model repulsive interactions. We finally compare the resulting equations of state with previous models and emphasize the role of the boundary conditions at the surface of compact self-bound stars, features of a possible normal crust of the latter and related topics.
QUARK–DIQUARK MATTER EQUATION OF STATE AND COMPACT STAR STRUCTURE
Authors: LUGONES G. , HORVATH J. E.
Published: May 2003

We present the equation of state (EOS) of quark-diquark matter in the quark mass-density-dependent model. The region of the 2-D parameter space inside which this quark-diquark matter is stable against diquark disassembling and hadronization is determined. Motivated by observational data suggesting a high compactness of some neutron stars (NS) we present models based on the present EOS and compare the results with those obtained with previous works addressing a quark-diquark composition based on the MIT Bag model. We show that very compact self-bound stars (yet having ≥ 1M⊙) are allowed by our EOS even if the diquark itself is unbound.
TESTS FOR COSMOLOGICAL EVOLUTION OF A BRANE UNIVERSE MODEL
Authors: MENG XINHE , HOU JINGMIN , LU KAIYI , ZHAO WENYAO
Published: May 2003

The relativistic Friedmann Lemaitre cosmology model (FLCM) is very sucessful in describing the evolution history of the Universe from the "First three Minutes". Any alternative model should be consistent with the FLCM explanations to the later stage evolutions of the Universe at certain points. A noncompact extra dimension model was recently proposed by Randall and Sundrum. Binetruy et al. obtained the modified Friedmann equation, in which the energy density of the brane appears quadratically in contrast with the linear behavior of the standard Friedmann equation. We investigate various kinds of classical cosmological effects of the new models and get a general solution of the cosmic evolution for this extended model, with more detail discussions of the brane tension parameter on these cosmological tests.
THE GENERAL-COVARIANT AND GAUGE-INVARIANT THEORY OF QUANTUM PARTICLES IN CLASSICAL BACKGROUNDS
Authors: NIKOLIĆ HRVOJE
Published: May 2003

A new approach to the concept of particles and their production in quantum field theory is developed. A local operator describing the current of particle density is constructed for scalar and spinor fields in arbitrary gravitational and electromagnetic backgrounds. This enables one to describe particles in a local, general-covariant and gauge-invariant way. However, the current depends on the choice of a 2-point function. There is a choice that leads to the local non-conservation of the current in a gravitational or an electromagnetic background, which describes local particle production consistent with the usual global description based on the Bogoliubov transformation. The most natural choice based on the Green function calculated using the Schwinger–DeWitt method leads to the local conservation of the current, provided that interactions with quantum fields are absent. Interactions with quantum fields lead to the local non-conservation of the current which describes local particle production consistent with the usual global description based on the interaction picture.
SELF INTERACTING BRANS–DICKE COSMOLOGY AND QUINTESSENCE
Authors: SEN S. , SESHADRI T. R.
Published: May 2003

Recent cosmological observations reveal that we are living in a flat accelerated expanding universe. In this work we have investigated the nature of the potential compatible with the power law expansion of the universe in a self interacting Brans–Dicke cosmology with a perfect fluid background and have analyzed whether this potential supports the accelerated expansion. It is found that positive power law potential is relevant in this scenario and can drive accelerated expansion for negative Brans–Dicke coupling parameter ω. The evolution of the density perturbation is also analyzed in this scenario and is seen that the model allows growing modes for negative ω.
MATCHING TORSION Λ-TERM WITH OBSERVATIONS
Authors: CAPOZZIELLO S. , CARDONE V. F. , PIEDIPALUMBO E. , SERENO M. , TROISI A.
Published: May 2003

Taking into account a torsion field gives rise to a negative pressure contribution in cosmological dynamics and then to an accelerated behaviour of Hubble fluid. The presence of torsion has the same effect as a Λ-term. We obtain a general exact solution which well fits data coming from high redshift supernovae and Sunyaev–Zeldovich/X-ray method for the determination of cosmological parameters. On the other hand, it is possible to obtain observational constraints on the amount of torsion density. A dust dominated Friedmann behaviour is recovered as soon as torsion effects are not relevant.
EINSTEIN–STRAUS PROBLEM IN HIGHER DIMENSIONS
Authors: CHATTERJEE S. , ZHANG Y. Z. , PANIGRAHI D.
Published: May 2003

Years ago Einstein and Straus (ES) showed that it is possible to match a static Schwarzschild region to an external expanding Friedmann universe. This model is extended in this work to a spacetime of arbitrary dimensions. Frequency shift of radiation coming from the boundary of the two spacetimes is calculated. Depending on the relative magnitude of gravitational and doppler effects our model gives both blue shift and red shift. The dynamical behaviour of the boundary is investigated and it is found that like the ES case our model is also unstable against small perturbation.
THE FILAMENTARY NATURE OF PISCES-PERSEUS
Authors: HAQUE-COPILAH S. , ACHONG A.
Published: May 2003

Minimal Spanning Tree (MST) statistics and associated reducing procedures have been used to establish the level of filamentary structure, if any in Pisces-Perseus, a sample containing 4501 galaxies. The procedure has been applied to subsets of galaxies with 247 galaxies that we call the Most Conspicuous sample which contain the larger intrinsic linear diameters and the brighter galaxies, and to the Least Conspicuous samples with 253 galaxies containing the smaller intrinsic linear diameter and the fainter members as well as the entire sample. The results show that there are longer filaments in the Most Conspicuous samples with less coiling as opposed to the Least Conspicuous sample. Pruning and separating also highlight the key structures in this region and not only the filamentary ones. Voids are highlighted, also indicating that MST's can be used to identify voids in the large scale structure of the Universe.
SCALING PROPERTIES OF THE COSMIC BACKGROUND PLASMA AND RADIATION
Authors: BERSHADSKII A.
Published: May 2003

Scaling properties of the cosmic microwave background (CMB) radiation are studied using satellite (COBE-DMR maps), balloon-borne and ground-based (combined QMASK map) data. Quantitative consistency is found between the multiscaling properties of the COBE-DMR and QMASK CMB maps. Surprisingly, it is found that the observed CMB temperature multiscaling quantitatively resembles the multiscaling properties of fluid turbulence, that indicates primordial plasma turbulence as an origin of the CMB temperature space anisotropy.
GRAVITATIONAL COLLAPSE OF SELF-SIMILAR AND SHEAR-FREE FLUID WITH HEAT FLOW
Authors: CHAN R. , DA SILVA M. F. A. , DA ROCHA JAIME F. VILLAS
Published: May 2003

A class of solutions to Einstein field equations is studied, which represents gravitational collapse of thick spherical shells made of self-similar and shear-free fluid with heat flow. It is shown that such shells satisfy all the energy conditions, and the corresponding collapse always forms naked singularities.
STABILITY OF A STRING INSPIRED INFLATIONARY SCENARIO
Authors: BATISTA CARLOS EDUARDO MAGALHÃES , FABRIS JÚLIO CÉSAR
Published: May 2003

We consider an inflationary model inspired in the low energy limit of string theory. In this model, the scale factor grows exponentially with time, while the scalar fields are time independent. A perturbation study is performed, and we establish the conditions for such a model to be stable or not. These stability conditions can have consequences either for the structure formation and for the graceful exit problems.
REMARKS ON A DECRUMPLING MODEL OF THE UNIVERSE
Authors: LIMA J. A. S. , MOHAZZAB M.
Published: May 2003

It is argued that the full set of Einstein's field equations has more information than the spatial components of Einstein's equation plus the energy conservation law. Applying the former approach to the D-dimensional decrumpling FRW cosmology recently proposed, it is shown that the spacetime singularity cannot be avoided and that turning points are absent.
INERTIAL MASS FROM SPIN NONLINEARITY
Authors: COHEN MARCUS
Published: May 2003

The inertial mass of a Fermion shows up as chiral cross-coupling in its Dirac system. No scalar term can invariantly couple left and right chirality fields; the Dirac matrices must be spin tensors of mixed chirality. We show how such tensor couplings could arise from nonlinear mixing of four spinor fields, two representing the local electron fields and two inertial spinor fields sourced in the distant masses. We thus give a model that implements Mach's principle.

Following Mendel Sachs,1 we let the inertial spinors factor the moving spacetime tetrads qα(x) and [Formula: see text] that appear in the Dirac operator. The inertial spinors do more than set the spacetime "stage;" they are players in the chiral dynamics. Specifically, we show how the massive Dirac system arises as the envelope modulation equations coupling left and right chirality electron fields on a Friedmann universe via nonlinear "spin gratings" with the inertial spinor fields. These gratings implement Penrose's "mass-scatterings," which keep the null zig-zags of the bispinor wave function confined to a timelike world tube. Local perturbations to the inertial spinor fields appear in the Dirac system as Abelian and non-Abelian vector potentials.
SUPERSYMMETRIC QUANTUM COSMOLOGY FOR BIANCHI CLASS A MODELS
Authors: MACÍAS ALFREDO , MIELKE ECKEHARD W. , SOCORRO JOSÉ
Published: May 2003

The canonical theory of [Formula: see text] supergravity, with a matrix representation for the gravitino covector–spinor, is applied to the Bianchi class A spatially homogeneous cosmologies. The full Lorentz constraint and its implications for the wave function of the universe are analyzed in detail. We found that in this model no physical states other than the trivial "rest frame" type occur.
FEATURES OF A ROTATING SPACETIME
Authors: RADU E. , AMARIUTEI D.
Published: May 2003

The qualitative properties of the geodesic motion are investigated in a two parameter class of homogeneous Gödel-type spacetimes. The Klein–Gordon and Weyl equations are solved and a preliminary discussion of quantizing a scalar field in the presence of closed timelike curves is given.
HOW DID THE UNIVERSE BEGIN?
Authors: POLLOCK M. D.
Published: May 2003

The question of the initial configuration of the Universe — did the expanding Friedmann space-time ds2 = dt2 - a2(t)dx2 tend to a singularity when extrapolated back in time, or was there a turning point, indicating a previous phase of contraction? — is re-examined in the context of the heterotic superstring theory of Gross et al. If the adiabatic index tends to the value γ = 1, then the higher-derivative terms ℛ2 in the Lagrangian L dominate the Einstein–Hilbert term R/16πG in the time interval t p ≲ t ≲ 4t p , during which the action is S ≈ 25ℏ, guaranteeing the approximate validity of the classical field equations (if the compactification process is ignored), where [Formula: see text] is the Newton gravitational constant and t p is the Planck time. Under these conditions, Ruzmaĭkina and Ruzmaĭkina have shown, for a flat three-space with K = 0, that the initial singularity can only be avoided at all if there is a spin-zero tachyon, a conclusion modified by Barrow and Ottewill if K = ±1. We have previously shown, however, that the theory is tachyon-free, and have argued that K has to vanish for the existence of a well-defined, quantum-mechanical ground state. Also, if there is no inflation, the radius function is always much too large for the terms in K to exert any effect, a(t) ≳ 5 × 1029t p . While if γ = 2, then ℛ2 never dominates R/16πG. Accordingly, we conjecture that the Universe did not bounce, irrespective of the value of γ, the absence of a prior contracting phase thus being an aspect of causality.
KALUZA–KLEIN–GORDON FIELD THEORY
Authors: LIU HONGYA , WESSON PAUL S.
Published: May 2003

We extend the induced-matter interpretation of Kaluza–Klein field theory to obtain the Klein–Gordon equation for a scalar particle. The motion of the particle is correctly recovered, and we give an exact plane-wave solution whose induced energy-momentum tensor depends only on first derivatives of the scalar field, as in flat-space quantum field theory. However, in general the energy and momenta of the particle also include terms in second derivatives, which should repay investigation.
MAXWELL FIELDS IN ANISOTROPIC SPACETIMES
Authors: WOLLENSAK MATTHIAS
Published: May 2003

Maxwell's equations are rewritten with respect to anholonomic orthonormal frames and applied to the case when the background is described by a diagonal Bianchi Type I universe with line element [Formula: see text]. It is generally shown that solutions analogous to plane wave solutions in flat spacetime must obey two transversality conditions when the spacetime is anisotropic i.e., when at least one of the coefficients αj(t) differs from the others.

Analytic solutions are presented for propagation along the respective coordinate axes and a special stiff fluid model. Furthermore, by use of a generally applicable ansatz the long- and short-time behavior of waves traveling in the axisymmetric Kasner universe have been investigated.
ENERGY DISTRIBUTION OF CHARGED DILATON BLACK HOLES
Authors: XULU S. S.
Published: May 2003

Chamorro and Virbhadra studied, using the energy-momentum complex of Einstein, the energy distribution associated with static spherically symmetric charged dilaton black holes for an arbitrary value of the coupling parameter γ which controls the strength of the dilaton to the Maxwell field. We study the same in Tolman's prescription and get the same result as obtained by Chamorro and Virbhadra. The energy distribution of charged dilaton black holes depends on the value of γ and the total energy is independent of this parameter.
VACUUM QUANTUM EFFECTS OF NONCONFORMAL SCALAR FIELD IN A NONSINGULAR COSMOLOGICAL MODEL
Authors: NOVELLO M. , BEZERRA V. B. , MOSTEPANENKO V. M.
Published: May 2003

The total vacuum stress-energy tensor of nonconformal scalar field is calculated in a nonsingular metric determined by some background matter with the effective negative energy density and pressure. The corrections due to the field nonconformity are shown to dominate the conformal contributions for some cases. The back reaction problem of vacuum stress-energy tensor upon the background metric is also discussed.
INFLATIONARY COSMOLOGY OF THE EXTREME COSMIC STRING
Authors: GONZÁLEZ-DÍAZ P. F.
Published: May 2003

Starting with a study of the cosmological solution to the Einstein equations for the internal spacetime of an extreme supermassive cosmic string kink, and by evaluating the probability measure for the formation of such a kink in semiclassical approximation using a minisuperspace with the appropriate symmetry, we have found a set of arguments in favor of the claim that the kinked extreme string can actually be regarded as an unbounded chain of pairs of Planck-sized universes. Once one such universe pairs is created along a primordial phase transition at the Planck scale, it undergoes an endless process of continuous self-regeneration driven by chaotic inflation in each of the universes forming the pair.
MORE ABOUT ELECTROWEAK BARYOGENESIS IN THE MINIMAL SUPERSYMMETRIC STANDARD MODEL
Authors: RIOTTO ANTONIO
Published: May 2003

We compute the baryon asymmetry generated at the electroweak phase transition by the Higgs scalar sector of the minimal supersymmetric standard model. Because of large enhancement effects from low momentum modes, Higgs particles may be responsible for the observed baryon asymmetry even though CP-violation in the Higgs sector only appears at the one-loop level. We also discuss the approximations made in the analysis and suggest possible improvements.
GRAVITATIONAL SIGNALS EMITTED IN CORE COLLAPSES LEADING TO BLACK HOLE FORMATION
Authors: FERRARI VALERIA , PALOMBA CRISTIANO
Published: May 2003

In this paper, we review the results of numerical studies on the gravitational radiation emitted in collapses of compact cores ending in a black hole. We compare the waveforms and the energy spectra obtained by using either perturbative or fully relativistic approaches, and discuss the preminent features that characterize these signals and their detectability by current experiments on gravitational wave detection.
COSMOLOGICAL MODELS IN GENERALIZED SCALAR–TENSOR THEORY WITH CAUSAL VISCOUS FLUID
Authors: SINGH G. P. , GHOSH S. G. , BEESHAM AROONKUMAR
Published: May 2003

We consider generalized Brans–Dicke theory in which the coupling parameter is not constant but a function of the scalar field. Friedmann–Robertson–Walker models with bulk viscous fluid source described by full (i.e., nontruncated) causal nonequilibrium thermodynamics are analyzed. Exact solutions for the flat case have been obtained. Our results are compared with those in the usual Brans–Dicke theory with causal thermodynamics.
DIFFERENTIAL FORMS AND WAVE EQUATIONS FOR GENERAL RELATIVITY
Authors: LAU STEPHEN R.
Published: May 2003

In recent papers, Choquet–Bruhat and York and Abrahams, Anderson, Choquet–Bruhat, and York (we refer to both works jointly as AACY) have cast the 3 + 1 evolution equations of general relativity in gauge-covariant and causal "first-order symmetric hyperbolic form," thereby cleanly separating physical from gauge degrees of freedom in the Cauchy problem for general relativity. A key ingredient in their construction is a certain wave equation which governs the light-speed propagation of the extrinsic curvature tensor. Along a similar line, we construct a related wave equation which, as the key equation in a system, describes vacuum general relativity. Whereas the approach of AACY is based on tensor-index methods, the present formulation is written solely in the language of differential forms. Our approach starts with Sparling's tetrad-dependent differential forms, and our wave equation governs the propagation of Sparling's two-form, which in the "time-gauge" is built linearly from the "extrinsic curvature one-form." The tensor-index version of our wave equation describes the propagation of (what is essentially) the Arnowitt–Deser–Misner gravitational momentum.
QUANTUM FIELDS IN SCHWARZSCHILD–DE SITTER SPACE
Authors: WU ZHONG CHAO
Published: May 2003

In the No-Boundary Universe a primordial black hole is created from a constrained gravitational instanton. The black hole created is immersed in the de Sitter background with a positive cosmological constant. The constrained instanton is characterized not only by the external parameters, the mass parameter, charge and angular momentum, but also by one more internal parameter, the identification period in the imaginary time coordinate. Although the period has no effect on the black hole background, its inverse is the temperature of the no-boundary state of the perturbation modes perceived by an observer. By using the Bogoliubov transformation, we show that the perturbation modes of both scalar and spinor fields are in thermal equilibrium with the black hole background at the arbitrary temperature. However, for the two extreme cases, the de Sitter and the Nariai models, the no-boundary state remains pure.
SPHERICALLY SYMMETRIC SOLUTION FOR TORSION AND THE DIRAC EQUATION IN 5D SPACETIME
Authors: DZHUNUSHALIEV V. D.
Published: May 2003

Torsion in a 5D spacetime is considered. In this case, gravitation is defined by the 5D metric and the torsion. It is conjectured that torsion is connected with a spinor field. In this case, Dirac's equation becomes the nonlinear Heisenberg equation. It is shown that this equation has a discrete spectrum of solutions with each solution being regular on the whole space and having finite energy. Every solution is concentrated on the Planck region and hence we can say that torsion should play an important role in quantum gravity in the formation of bubbles of spacetime foam. On the basis of the algebraic relation between torsion and the classical spinor field in Einstein–Cartan gravity, the geometrical interpretation of the spinor field is considered as "the square root" of torsion.
A QUANTUM MECHANICAL APPROACH FOR A SYSTEM OF SELF-GRAVITATING PARTICLES AS APPLIED TO THE UNIVERSE
Authors: TRIPATHY D. N. , MISHRA SUBODHA
Published: May 2003

A quantum mechanical formulation for the evolution of the present universe is made by considering it as a system of self-gravitating particles, fermionic in nature. Using a model single particle density distribution ρ(r) of its particles, singular at the origin, a compact expression for its radius R0 is obtained. A singular form of ρ(r) may be considered to be consistent with the Big Bang Theory of the universe. Assuming Mach's principle to hold good in the evolution of the universe, and taking the age of the present universe, τ0, to be 20 × 109 yr, we obtain the total mass of the universe M = (1.28 × 1023) M⊙, M⊙ being the solar mass, and the value [Formula: see text], in extremely good agreement with the results obtained by others. Considering neutrinos to be the most possible candidate for the Dark Matter (DM), we find its mass to be ≃ 8 eV/c2, which also nicely agrees with the result as speculated by some recent calculations. Our theory reproduces the ratio of the neutrinos to the number of nucleons and the density of neutrinos in the present universe correctly.
A GENERALIZATION OF THE WAHLQUIST SOLUTION
Authors: PAPAKOSTAS TAXIARCHIS
Published: May 2003

We present a new perfect fluid solution belonging to (1,1) subfamily of Hauser–Mahlist spaces, rigidly rotating, type D in Petrov classification which reduces to the Wahlquist metric for particular values of our constants of integration. Unfortunately it is characterized by the equation of state of the Wahlquist solution: e + 3p = constant .
AN ALGORITHM FOR THE ALGEBRAIC CLASSIFICATION OF THE SYMMETRIC (3,1)-SPINOR
Authors: ANDERSSON F.
Published: May 2003

We present a detailed classification of the symmetric (3,1)-spinor according to its factorization properties, analogously with the Petrov classification of the (4,0)-spinor, and present an efficient algorithm, suitable for implementation on a computer, for performing such a classification. One application would be for the classification of spacetimes with torsion, since the symmetric part of the torsion spinor is a symmetric (3,1)-spinor. This algorithm can also be applied to the Lanczos spinor potential of the Weyl curvature spinor.
GRAVITATIONAL CAPTURE OF COSMIC STRINGS BY A BLACK HOLE
Authors: DE VILLIERS JEAN-PIERRE , FROLOV VALERI
Published: May 2003

The gravitational interaction of an infinitely long cosmic string with a Schwarzschild black hole is studied. We consider a straight string that is initially at a great distance and moving at some initial velocity v (0 < v < c) towards the black hole. The equations of motion of the string are solved numerically to obtain the dependence of the capture impact parameter on the initial velocity.
INTERMITTENT LASER EMISSION OF A SEYFERT GALAXY NUCLEUS
Authors: BERSHADSKII A.
Published: May 2003

Intermittent emission of the Seyfert galaxy NGC 4151 nucleus is described by a new type of statistical distribution — multifractal Bernoulli distribution, that allows to identified this emission with intermittent emission of an optically pumped NH3 ring laser.
PRECARIOUS STARS — A VARIETY OF BOSON STARS
Authors: HAFIZI M.
Published: May 2003

In this paper we study boson stars made up of real scalar λϕ4 self-interacting fields at finite temperature. For the reason of their equation of state, we call these configurations "precarious stars." The equation of state for these stars follows from the Gaussian approximation applied to real scalar λϕ4 self-interacting fields. We numerically calculate these configurations in the frame of general relativity. We obtain masses, radii, surface temperatures and other characteristics. After a numerical analysis of the thermal radiation emitted from their surface, we conclude that these stars radiate rapidly all their energy and mass. Nevertheless, we raise the question of the role these configurations may have played in formation of the large scale structures of the Universe.
FRACTAL CONFORMATION OF POLYMERS
Authors: ADAM M. , LAIREZ D.
Published: May 2003

In this review, our purpose is to apply fractal concept to the description of the conformation of linear polymers, star polymers and branched polymers, in dilute and semi-dilute solutions in good solvent. Experimental evidence to theoretical predictions will be presented.
ON THE EXISTENCE OF WELL DEFINED SINGULARITIES IN MULTIFRACTALS
Authors: CZIRÓK ANDRÁS , SZÉPFALUSY PÉTER , VICSEK TAMÁS
Published: May 2003

The two most commonly used interpretations of multifractals are based on two approaches: (i) constructing a histogram of the corresponding probability distribution, and (ii) the study of the spatial distribution of the local singularities characterizing the fractal measures. In this paper we shall consider these approaches with the purpose of investigating some of the open problems arising from their relationship. In particular, we address the question of whether there exists a well defined exponent α describing the strength of the local singularity of a fractal measure. From theoretical and numerical studies of a multiplicative measure defined on the unit interval, we conclude that an a exists for all points whose decimal digits have an asymptotic distribution, and that α(x) depends only on the asymptotic ratio of these digits. We have also examined the connections between the two different definitions of the f(α) spectra.
SCALING OF THE POINT-POINT CORRELATION FUNCTION OF DLA
Authors: PLATT DANIEL E. , FAMILY FEREYDOON
Published: May 2003

The scaling of the point-point correlation function of DLA has shown itself to be more complex and challenging than had at first been imagined. This paper determines from the results of previous studies that a more general scaling rule must be applied, at least robust enough to allow different moments of the point-point correlation function to scale non-trivially, and for the scale length to scale non-trivially. In this sense, it is seen that the scaling problem is analogous to that of multifractal scaling. The authors present a group-theoretic derivation of the most general scaling transformations possible, and show that it is adequately robust to explain the non-trivial scaling observed in the moments of the point-point correlation function.
STRUCTURE FACTOR OF DETERMINISTIC FRACTALS WITH ROTATIONS
Authors: DETTMANN C.P. , FRANKEL N.E.
Published: May 2003

We derive a recursion relation for the Fourier transform of any self-similar multifractal mass distribution. This is then used to find sufficient conditions under which S(k)↛0 as |k|→∞. Among two-dimensional distributions for which the similarity transformations contain 2π/n rotations, it is found that for values of n equal to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 18 and 30, distributions may be constructed satisfying the above condition. The possible scaling factors in the similarity transformations are strongly constrained by the value of n. In three dimensions, the equivalent condition is that all rotations/reflections are elements of a finite group, together with similar constraints on the scaling factors.
THE KURTOSIS OF REFLECTION COEFFICIENTS IN A FRACTAL SEQUENCE OF SEDIMENTARY LAYERS
Authors: KORVIN G.
Published: May 2003

In the reflection seismic technique of hydrocarbon prospecting, the measured signal is the convolution of an unknown sequence of reflection coefficients by a statistically known source signature. A basic task of seismic processing is to estimate the sequence of reflection coefficients. The aim of this paper is to show that in case of a fractal sedimentation model, the conventional statistical descriptors (variance, skewness, kurtosis) of the reflection coefficient sequence are strongly dependent on, or are even divergent functions of, the resolution.
COMPARISON OF THE SURFACE DIMENSION AND THE MASS DIMENSION OF BLOOD VESSEL SYSTEMS
Authors: JESTCZEMSKI F. , BOLTERAUER H. , SERNETZ M.
Published: May 2003

The arterial blood vessel system of kidneys is known to be fractal with a global mass dimension of 2.2 to 2.3. The global mass dimensions were determined by the mass-radius method.1 We support these results of the mass correlation analysis with an examination of the surface, which is in good approximation with the "true mass" of the border between the tissue (parenchyma) and the blood. We applied the Minkowski cover to the vessel surfaces and determined their scaling behavior, which yielded the surface global dimension. The examinations on kidney arteries1 are supplemented with new data of placentoma arteries2 and a comparison is made between their surface and mass dimensions.
A FRACTAL-LIKE STRUCTURE IN THE SKIN
Authors: HONDA HISAO , IMAYAMA SHUHEI , TANEMURA MASAHARU
Published: May 2003

Objects in a biological body consist of structures which themselves have finer structures, and such a relation repeats several orders. We show that the interface between the dermis and the epidermis in human skin is one of them and is considered as a fractal-like structure. To determine the degree of complexity of the structure, we estimated the fractal dimension. Its fractal dimension was 2.4. Folding of the interface increases the area that occupies a three-dimensional volume, enhancing functionality and promoting strong adhesion between the dermis and the epidermis. The fractal dimension quantifies this space-filling; it was found to increase from 2 to 3 as the surface folds more extensively. We discuss the functional significance of the fractal-like structure of the human skin and the other structures in a biological body.
PATTERN FORMATION IN AN ETCHED RADIAL HELE SHAW CELL
Authors: BATCHELOR M. T. , HENRY B. I.
Published: May 2003

We have introduced numerical schemes for simulating pattern formation at the interface between two imiscible fluids in an etched radial Hele Shaw cell. Our simulations, which have been carried out over a range of two model parameters, are compared with experimental results that have been reported for a range of plate spacings and applied pressures. The simulations reproduce the complete range of morphology transitions in the experiments.
FRACTAL ROUGHNESS CHARACTERIZATION OF SUPER-GROUND Mn-Zn FERRITE SINGLE CRYSTALS
Authors: YU J. , NAMBA Y. , SHIOKAWA M.
Published: May 2003

The surface of superground Mn-Zn ferrite single crystal may be identified as a self-affine fractal in the stochastic sense. The rms roughness increased as a power of the scale from 102 nm to 106 nm with the roughness exponent α=0.17±0.04, and 0.11±0.06, for grinding feed rate of 15 and 10 μm/rev, respectively. The scaling behavior coincided with the theory prediction well used for growing self-affine surfaces in the interested region for magnetic heads performance. The rms roughnesses increased with increase in the feed rate, implying that the feed rate is a crucial grinding parameter affecting the supersmooth surface roughness in the machining process.
TRANSPORT PHENOMENA IN PERCOLATING STRUCTURES: A KEY FOR THE ANALYSIS AND REINTERPRETATION OF SOME PRACTICAL MODELING PROBLEMS
Authors: ANDRADE J. S. , STREET D. A. , SHIBUSA Y. , ITO N.
Published: May 2003

The percolating morphology is adopted as a reference conceptualization to evaluate the “fractality” effect on the transport phenomena in disordered systems. The relevance of this approach is demonstrated using two practical case studies: conducting polymers and porous media. In the first case, a conceptual model for conducting polymers is proposed in terms of a random resistor network subjected to percolation disorder. The effect of topological and morphological disorder on the conducting behavior of an idealized system is investigated and some insights, are given as to the way in which conducting polymers could be designed. In the second case, the examination of effective transport properties in percolation-like porous structures enables us to reinterpret the classical guidelines for the characterization of fluid flow through porous beds.
POWER LAW RELAXATION OF PERIMETER LENGTH OF FRACTAL AGGREGATES
Authors: IRISAWA TOSHIHARU , UWAHA MAKIO , SAITO YUKIO
Published: May 2003

For a realistic aggregate grown under the diffusion control, the fractal scaling holds between two cutoff lengths. These cutoff lengths often control the dynamics of aggregation and relaxation. During thermal annealing, coarsening of the aggregate structure takes place, and the lower cutoff length increases. When the relaxation is limited by kinetics, we show by a simple dimensional argument that the perimeter length (or area) A of the aggregate shrinks in a power law with time t as A(t) ~ t(d–1–D)/2 in a d-dimensional space, where D is the fractal dimension of the aggregate. This prediction is tested by Monte Carlo simulation of the thermal relaxation of a two-dimensional diffusion-limited aggregation.
SCALING THEORY ON GROWING ROUGH SURFACES
Authors: HONDA K.
Published: May 2003

We study the dynamics of growth processes of rough surfaces based on mathematical models such as the Kardar-Parisi-Zhang equation. The white-noise assumption in the KPZ equation is, however, noted to fail for higher dimensional cases. A careful continuum limit leads to a smooth surface solution for the cases. We develop the scaling theory to give an insight into the problem, by means of the intermediate asymptotics of the second kind, which is a very useful notion for the purpose. We find the roughness exponent and the dynamic exponent as functions of the substrate dimensionality for a model equation applicable to quenched disorder systems.
FRACTALS IN THE GLASS TRANSITION
Authors: CONIGLIO ANTONIO
Published: May 2003

The static and fractal properties of the frustrated percolation model are investigated. This model, which contains frustration as an essential ingredient, displays glassy behavior at high density or low temperature and exhibits two transitions: a percolation transition at a temperature Tp with critical exponents of the ferromagnetic s=1/2 state Potts model, and a second transition at a lower temperature Tg in the same universality class of the Ising spin glass model.
DYNAMICAL BEHAVIOR OF ACOUSTICALLY COUPLED CHAOS OSCILLATORS
Authors: HARADA Y. , MASUDA K. , OGAWA A.
Published: May 2003

We have found, for the first time, that Acoustically Coupling Chaos Oscillator (ACCO) also exhibits a chaotic attractor called the “double scroll Chua’s attractor” by using the modified Chua’s circuit. When each ACCO is in an oscillating periodic state, the interaction of sound waves with acoustic coupling of two ACCOs can also result in the appearance of chaotic sound waves.
Wavelet Compression of AVHRR Imagery
Authors: Amato Umberto , Angelini Claudia , Serio Carmine
Published: May 2003

A compression tool for satellite based imagery of the earth's land and atmosphere is presented. Orthogonal wavelet filters are adopted for this purpose. The ability of the technique to compress images has been applied to AVHRR images of cloud fields and the earth's surface. Compression by a factor as large as 50 is possible in clear sky condition without any significant loss of information, whereas for frontal cloud fields, which are the most interesting in terms of meteorological studies, factors of ten are easily achieved.
Neighborhood Volume for Bounded, Locally Self-Similar Fractals
Authors: Semkow Thomas M.
Published: May 2003

We derive the formulas for neighborhood volume (Minkowski volume in d-dimensions) for fractals which have a curvature bias and are thus bounded. Both local surface fractal dimension and local mass fractal dimension are included as well as a radius of the neighborhood volume comparable with the size of the fractal. We consider two types of the neighborhood volumes: simplified and generalized, as well as the volumes below and above the fractal boundary. The formulas derived are generalizations of the equations for isotropic unbounded fractals. Based on the simplified-volume concept, we establish the procedure for calculating a distribution of physical quantities on bounded fractals and apply it to the distribution of trace elements in soil particles. Using the concept of the generalized volume, we show how an expectation value of a physical process can be calculated on bounded fractals, and apply it to the radon emanation from solid particles.
Thermal Fluctuations in Systems with Continuous Symmetry
Authors: Zürcher U.
Published: May 2003

We investigate relaxation and thermal fluctuations in systems with continuous symmetry in arbitrary spatial dimensions. For the scalar order parameter ζ(r, t) with r∈ℛd, the deterministic relaxation is caused by hydrodynamic modes η∂ζ(r, t)/∂t= K∇2ζ(r, t). For a finite volume V, we expand the scalar field in a discrete Fourier series and then we study the behavior in the limit V→∞. We find that the second moment is well defined for dimensions d≥3, while it diverges for d=1, 2. Furthermore, we show that for d<4, the decay of the scalar field does not define an "effective" relaxation time. For dimensions d<4, these two properties suggest scale-invariant properties of the scalar field in the limit V→∞. We show that thermal fluctuations are described by fractional Brownian motion for d ≤ 3 and by ordinary Brownian motion for d ≥ 4. The spectral density of the stochastic force follows 1/f for d=1 and d=2, [Formula: see text] for d=3, and "white noise," f0 for d≥4. We find explicit representation of the equilibrium distribution of the conserved scalar field. For d≥4 it is a Gaussian distribution, while for d=1 and d=2, it is the Cauchy distribution.
The Scaling Behavior of a Self-Affine Fractal Interface in a Paper Tearing Experiment
Authors: Kwon Tai-Hyung
Published: May 2003

The scaling behavior of a self-affine fractal interface is examined in a paper tearing experiment. A sheet of heavy duty construction paper, 30 cm × 23 cm, is torn lengthwise across the grain of the paper, and the tear line is scanned and digitized to obtain the interface height h(x) as a function of position x. From these, the interface width w(L) is determined as a function of system size L. It is found that the interface width scales with system size L as w(L) ~ Lα, with α=0.66±0.02. The result is assessed in comparison with other relevant experimental and theoretical results.
Conditional and Relative Multifractal Spectra
Authors: Riedi Rudolf H. , Scheuring Istvan
Published: May 2003

In the study of the involved geometry of singular distributions, the use of fractal and multifractal analysis has shown results of outstanding significance. So far, the investigation has focussed on structures produced by one single mechanism which were analyzed with respect to the ordinary metric or volume. Most prominent examples include self-similar measures and attractors of dynamical systems. In certain cases, the multifractal spectrum is known explicitly, providing a characterization in terms of the geometrical properties of the singularities of a distribution. Unfortunately, strikingly different measures may possess identical spectra. To overcome this drawback we propose two novel methods, the conditional and the relativemultifractal spectrum, which allow for a direct comparison of two distributions. These notions measure the extent to which the singularities of two distributions 'correlate'. Being based on multifractal concepts, however, they go beyond calculating correlations. As a particularly useful tool, we develop the multifractal formalism and establish some basic properties of the new notions. With the simple example of Binomial multifractals, we demonstrate how in the novel approach a distribution mimics a metric different from the usual one. Finally, the applications to real data show how to interpret the spectra in terms of mutual influence of dense and sparse parts of the distributions.
Structure Characterization of Disordered Porous Media — A Memorial Review Dedicated to Vicente Mayagoitia
Authors: Kornhauser I. , Rojas F. , Faccio R. J. , Riccardo J. L. , Vidales A. M. , Zgrablich G.
Published: May 2003

We present a review of the description of disordered porous media according to the Dual Site-Bond model introduced by Vicente Mayagoitia. The model formulation, percolation properties and applications to problems of practical interest are discussed.
Diffusion on Self-Similar Structures
Authors: Roman H. Eduardo
Published: May 2003

Diffusion on self-similar structures is reviewed within a unified theoretical framework. Much attention is devoted to the asymptotic form of the probability density of random walks on fractals, for which analytical solutions are discussed. New predictions for the structure of percolation clusters at criticality are presented.
Multifractal Cascade Dynamics and Turbulent Intermittency
Authors: Schertzer D. , Lovejoy S. , Schmitt F. , Chigirinskaya Y. , Marsan D.
Published: May 2003

Turbulent intermittency plays a fundamental role in fields ranging from combustion physics and chemical engineering to meteorology. There is a rather general agreement that multifractals are being very successful at quantifying this intermittency. However, we argue that cascade processes are the appropriate and necessary physical models to achieve dynamical modeling of turbulent intermittency. We first review some recent developments and point out new directions which overcome either completely or partially the limitations of current cascade models which are static, discrete in scale, acausal, purely phenomenological and lacking in universal features. We review the debate about universality classes for multifractal processes. Using both turbulent velocity and temperature data, we show that the latter are very well fitted by the (strong) universality, and that the recent (weak, log-Poisson) alternative is untenable for both strong and weak events. Using a continuous, space-time anisotropic framework, we then show how to produce a causal stochastic model of intermittent fields and use it to study the predictability of these fields. Finally, by returning to the origins of the turbulent "shell models" and restoring a large number of degrees of freedom (the Scaling Gyroscope Cascade, SGC models) we partially close the gap between the cascades and the dynamical Navier–Stokes equations. Furthermore, we point out that beyond a close agreement between universal parameters of the different modeling approaches and the empirical estimates in turbulence, there is a rather common structure involving both a "renormalized viscosity" and a "renormalized forcing". We conclude that this gives credence to the possibility of deriving analytical/renormalized models of intermittency built on this structure.
Neural Networks for Prediction and Control of Chaotic Fluidized Bed Hydrodynamics
Authors: Bakker R. , de Korte R. J. , Schouten J. C. , Van Den Bleek C. M. , Takens F.
Published: May 2003

A neural-network-based model that has learnt the chaotic hydrodynamics of a fluidized bed reactor is presented. The network is trained on measured electrical capacitance tomography data. A training algorithm is used that does not only minimize the short-term prediction error but also the information needed to synchronize the model with the real system. This forces the model to focus more on learning the longer term dynamics of the system, expressed in the average multi-step-ahead prediction error and dynamic invariants such as correlation entropy and dimension. The availability of the model is an important step towards control of chaos in gas-solid fluidized beds.