bluuebunny/crossref_metadata_2025 huggingface dataset:
DEMONSTRATION OF 1/f FLUCTUATIONS AND WHITE NOISE IN THE HUMAN HEART RATE BY THE VARIANCE-TIME-CURVE: IMPLICATIONS FOR SELF-SIMILARITY
Authors: MEESMANN MALTE , BOESE JAN , CHIALVO DANTE R. , KOWALLIK PETER , BAUER WOLFGANG R. , PETERS WERNER , GRÜNEIS FERDINAND , KNIFFKI KLAUS-DIETRICH
Published: November 2004

Spectral analysis of heart rate variability is usually performed by Fast Fourier Transform. Here we demonstrate the self-affine properties of the human heart rate using a spectral analysis based on counting statistics. Each QRS complex is considered to be a point event and from the number of events N(Δt) in consecutive time windows Δt the variance is calculated. From the finding that the variance of N(Δt) follows a power law proportional to (Δt)1+b in case of 1/fb noise, it is shown that the variance of the heart rate as determined for windows of length Δt, i.e., N(Δt)/Δt, is proportional to (Δt)b−1. From a 12-day Holter recording, the scaling region could be determined to cover 0.16 to 0.000136 Hz.

A function X(t) is self-affine if X(t) and X(rt)/rH have the same distribution functions. From the variance-time-curve, it can be shown that the exponent H is dependent on b with b=2H−1. In young healthy men, the parameter b fluctuates between 0.2 and 1.0 during 24 h and thus determines the self-affine scaling factor H=(b−1)/2 for the amplitude of heart rate, if the time axis is scaled by r. Thus, during periods of 1/f noise, the heart rate scales with H=0, and for periods of almost white noise, with H close to [Formula: see text].
FRACTAL GEOMETRY AND ECOLOGY OF LICHENS
Authors: MARCHI ANGELO DE , CASSI DAVIDE
Published: November 2004

From a morphological point of view lichens are usually classified in three life-forms: foliose, crustose and fruticose. In this paper we consider one lichen for each of them [a foliose (Parmelia tiliacea), a crustose (Rhizocarpon geographicum) and a fruticose (Cladonia mediterranea) lichen], and by direct measurement we show that these samples have fractal geometry and we detemine their fractal dimensions and fractality ranges. On the basis of these results, we then discuss the possible ecological causes that could have selected these geometries and that should be considered in a realistic mathematical model of growth.
MICROBIAL GROWTH PATTERNS: FRACTAL AND KINETIC CHARACTERISTICS OF PATTERNS GENERATED BY A COMPUTER MODEL TO SIMULATE FUNGAL GROWTH
Authors: OBERT MARTIN
Published: November 2004

This investigation is concerned with the description of patterns that are generated by a computer model that mimics fungal colonies. The computer model is based on parameters that can be related to biological processes in a fungus, i.e., branching, tip growth, and next neighborhood behavior (repulsion or attraction between cells). We study the systematic variations of parameter values in the model quantitatively by the fractal dimension D as a function of the diameter (L), the iteration (I), and the mass (M) of the simulated structures. We find a very different increase of D as a function of L, I, or M during the pattern development, which depends on the chosen parameter values. Therefore, the variation of parameter values in the model helps us to understand which biological processes might be affected, leading to different fungal growth patterns: e.g. the model can mimic the concentration dependent griseofulvin influence on the morphology by variation of rather straight or rather zigzag growing tips as it is found experimentally for the strain Sordaria macrospora. Analyzing the model leads to the assumption that especially the study of D as a function of the diameter and the iteration will be very fruitful for a detailed understanding of microbial pattern formation. The correlation between geometrical and kinetic properties of the patterns generated by the model are shown. (The experimental results and parts of the growth model were published previously in a doctoral thesis.)
TEMPORAL FLUCTUATIONS IN BIORHYTHMS: EXPRESSION OF SELF-ORGANIZED CRITICALITY?
Authors: KNIFFKI KLAUS-D. , MANDEL WOLFGANG , TRAN-GIA PHUOC
Published: November 2004

Recently, a general organizing principle has been reported connecting 1/f-noise with the self-similar scale-invariant ‘fractal’ properties in space, hence reflecting two sides of a coin, the so-called self-organized critical state. The basic idea is that dynamical systems with many degrees of freedom operate persistently far from equilibrium at or near a threshold of stability at the border of chaos. Temporal fluctuations which cannot be explained as consequences of statistically independent random events are found in a variety of physical and biological phenomena. The fluctuations of these systems can be characterized by a power spectrum density S(f) decaying as f−b at low frequencies with an exponent b<1.5. We present a new approach to describe the individual biorhythm of humans using data from a colleague who has kept daily records for two years of his state of well-being applying a fifty-point magnitude category scale. This time series was described as a point process by introducing two discriminating rating levels R for the occurrence of R≥40 and R≤10.

For b<1 a new method to estimate the low frequency part of S(f) was applied using counting statistics without applying Fast Fourier Transform. The method applied reliably discriminates these types of fluctuations from a random point process, with b=0.0. It is very tempting to speculate that the neural mechanisms at various levels of the nervous system underlying the perception of different values of the subjective state of well-being, are expressions of a self-organized critical state.
INFLUENCE OF CHEMICAL PERTURBATIONS ON THE SURFACE ROUGHNESS OF THIN LAYER ELECTRODEPOSITS
Authors: KUHN A. , ARGOUL F.
Published: November 2004

We have studied the origin of macroscopic and microscopic changes of the morphology of metal electrodeposits in thin layer cells. We concentrate on zinc electrodeposition to show that a part of the variety of growth patterns reported in the literature (dense radial, stringy, dendritic and DLA-like fractal morphologies) is probably due to pollution of the electrolyte. One common pollution in these experiments is molecular oxygen, which is dissolved in the electrolyte during its preparation and conservation in contact with air. Its cathodic reduction can seriously perturb the metallic host lattice by formation and intercalation of metal oxide. Other perturbations with equal dramatic effects on the morphology and the roughness of the deposit are alkali cations. By well-controlled addition of one of these ions or molecules, we are able to generate a wide variety of morphologies, from highly ordered dendritic growth to completely disordered growth. Other metals such as copper or tin are shown to be also highly sensitive towards impurities. Based on this sensitivity upon chemical perturbation, we finally propose a new explanation for the morphological changes, called Hecker effect, which can occur during the growth process.
INTERFACIAL AGGREGATION OF FLOATING MICROPARTICLES UNDER THE CONTROL OF SHORT-RANGE COLLOID AND VERY LONG-RANGE CAPILLARY FORCES
Authors: HÓRVÖLGYI Z. , ZRINYI M.
Published: November 2004

Interfacial aggregation of surface modified glass beads (62–74 μm diameter) at water/air interface was carried out by using two differently hydrophobic samples, respectively. The effect of aggregation time on the self-similar structure of forming aggregates was studied comparing the actual results to those obtained previously.1

The time dependence of restructuring from the point of view of fractal geometry has been proved but the results call attention to another time dependent process— orientation of growing clusters during their collisions due to anisotropy of cluster-cluster interactions.
FRACTAL TECTONICS AND EROSION
Authors: TURCOTTE DONALD L.
Published: November 2004

Tectonic processes build landforms that are subsequently destroyed by erosional processes. Landforms exhibit fractal statistics in a variety of ways; examples include (1) lengths of coast lines; (2) number-size statistics of lakes and islands; (3) spectral behavior of topography and bathymetry both globally and locally; and (4) branching statistics of drainage networks. Erosional processes are dominant in the development of many landforms on this planet, but similar fractal statistics are also applicable to the surface of Venus where minimal erosion has occurred. A number of dynamical systems models for landforms have been proposed, including (1) cellular automata; (2) diffusion limited aggregation; (3) self-avoiding percolation; and (4) advective-diffusion equations. The fractal statistics and validity of these models will be discussed. Earthquakes also exhibit fractal statistics. The frequency-magnitude statistics of earthquakes satisfy the fractal Gutenberg-Richter relation both globally and locally. Earthquakes are believed to be a classic example of self-organized criticality. One model for earthquakes utilizes interacting slider-blocks. These slider block models have been shown to behave chaotically and to exhibit self-organized criticality. The applicability of these models will be discussed and alternative approaches will be presented. Fragmentation has been demonstrated to produce fractal statistics in many cases. Comminution is one model for fragmentation that yields fractal statistics. It has been proposed that comminution is also responsible for much of the deformation in the earth’s crust. The brittle disruption of the crust and the resulting earthquakes present an integrated problem with many fractal aspects.
FRACTAL ANALYSES OF ANISOTROPIC FRACTURE SURFACES
Authors: COX B.L. , WANG J.S.Y.
Published: November 2004

Natural surfaces of rock fractures often have anisotropic asperity distributions, especially for shear fractures or faults. The asperity distributions could be treated as self-affine fractals with directional dependent scaling in the plane of the rock surfaces. Different fractal analyses (divider, slit-island, variogram) are applied to surface distributions of asperity data (topography): (1) a granitic fracture from the Stripa mine in Sweden; (2) a faulted and geothermally altered fracture from Dixie Valley, Nevada, USA. The cutoff patterns (indicator maps) of the granitic fracture show a radial pattern, while those of the faulted fracture show a very anisotropic stretched pattern of shapes. Different cutoff patterns of the same surface generally yield the same fractal dimension with the slit-island technique. The slit-island technique assumes that the cut-off patterns are self-similar in the plane of the surface, with the perimeter versus area analyzed for the entire population of contours, regardless of aspect ratio. We measure the variance in the two coordinate directions as a function of perimeter/area ratio for the anisotropic fracture from Dixie Valley to determine a self-affine scaling ratio for the slit-island analysis. We compare this ratio with anisotropy ratios obtained from simulated flow models based on channeling of flow through the largest openings. The possible applications of fractal analyses to both the geometry and flow are evaluated.
SOME LONG-RUN PROPERTIES OF CLIMATIC RECORDS
Authors: BODRI L.
Published: November 2004

Fractal analysis allows for a mathematical comparison of climatic changes obtained from a variety of observations and recorded at different time scales. Analysis of the oxygen isotope curve of Pacific core V28–239 indicated fractal geometry of the oxygen isotope record for time scales 5000 to 2000000 years, with a fractal dimension of 1.22. On a time scale of some hundred years, tree ring index values yield an average fractal dimension of 1.32±0.02. For annual precipitation records from between 1817 and 1963 at nine major cities in the United States, a mean fractal dimension of 1.26±0.03 was found. Analysis of the annual mean surface air temperatures at seven meteorological stations in Hungary for the period of 1901–1991, indicates that the considered temperatures are fractals with a mean fractal dimension of 1.23±0.01. For the global surface air temperature change estimated from meteorological station records from 1880 to 1985, we derive in the present study a fractal dimension of 1.21.

It is reasonable therefore to assume that climatic changes are characterized by one general fractal dimension over the spectral range 10 to 106 years. Records with such values of fractal dimension have some long-term persistence: even observations sufficiently distant from each other are not completely independent. If these conclusions become confirmed through analysis of a wider set of climatic records, long-run climatic prediction (in statistical sense) on different time scales will appear feasible.
UNDERSTANDING COMPLEXITY IN THE STRUCTURE OF RAINFALL
Authors: RAJAGOPALAN BALAJI , TARBOTON DAVID G.
Published: November 2004

This paper aims at understanding the structure of high resolution storm rainfall rates. Scale invariance property has been observed from the distribution function. Departures from simple scaling (i.e., multiscaling) have been noted, suggesting a cascade phenomenon. Close agreement of theoretical and estimated singularity spectra indicates the plausibility of modeling rainfall process by random cascades. Connections between multiscaling and the singularity spectrum have been identified.
USE OF MULTIFRACTAL ANALYSIS IN THE CHARACTERIZATION OF GEOLOGICAL FORMATIONS
Authors: SAUCIER ANTOINE , MULLER JIRI
Published: November 2004

We use multifractal analysis as a tool for the characterization of geological well log signals. The signals investigated come from dipmeter microresistivity log devices. It is suggested that the multifractal spectra computed from these signals could be used to distinguish geological formations and lithofacies containing different types of oil reservoir heterogeneities.
THE FIXED SCALE TRANSFORMATION: STATUS AND PERSPECTIVES
Authors: PIETRONERO L.
Published: November 2004

Irreversible fractal growth models like DLA and DBM have confronted us with theoretical problems of a new type that cannot be described in terms of the standard concepts like field theory and the renormalization group. The Fixed Scale Transformation is a theoretical scheme of a new type that is able to treat these problems in a reasonably systematic way. The idea is to focus on the dynamics at a given scale and to compute accurately the correlations at this scale by suitable lattice path integrals. The use of scale invariant growth rules then allows the generalization of these correlations to coarse-grained cells of any size and therefore to obtain the fractal dimension. We summarize the present status of the FST approach by focusing on the most recent results about the scale invariant dynamics of DLA/DBM. The possible extensions to other problems like the sand pile model (self-organized-criticality) and simplified models of turbulence will also be considered.
MEMORY EFFECTS ON FRACTAL DIMENSION
Authors: OTERO D. , BOLLINI C.
Published: November 2004

We present a version of the Eden model which uses a memory Markov constraint and shows a clear fractal growth. The rules of growing are very simple. Two probabilities must be selected: one corresponds to the latest step of growth and the other one to the old steps. The growing cluster recognizes the latest occupied site and around it the probability of selecting a new site is highest than around the old sites.
NUMERICAL ESTIMATES OF THE FRACTAL DIMENSION D AND THE LACUNARITY L BY THE MASS RADIUS RELATION
Authors: OBERT MARTIN
Published: November 2004

The mass radius relation (mrr) allows the estimation of a local fractal dimension Dl, which depends on a chosen site l of a set, taken as center position for the mrr. We find an unexpected wide range of Dl-values for a numerically analyzed Sierpinski triangle. The analysis of a computer simulation of a biological branching pattern shows rather small Dl-values at the border lines to major empty areas and rather high Dl-values in densely grown regions. The local impression by many Dl of a growth pattern can be interpreted biologically as an inverse measure of, for example, the local immune activity in a living object.

We also apply the mrr to investigate the lacunarity L of Cantor dusts. Since numerical difficulties to obtain L are based on the finiteness of a set, we analyze projections of fractals on the unit circle, such that a well-defined largest possible gap size is introduced. The first preliminary results imply rather stable numerical values for L and D for many sets, where D is the average over many Dl. L depends on the size of the smallest details in a set. L is larger if many different gap sizes are given in a generator for a fractal curve as opposed to curves, where only one gap size is given. We assume that a totally different approach has to be set up to obtain L numerically of sets of finite size, since projections of sets or the introduction of periodic boundaries seem inadequate.
TIME-DEPENDENT CRITICAL PROPERTIES FROM “DAMAGE SPREADING”
Authors: JAN NAEEM
Published: November 2004

“Damage spreading” is a useful tool for determining equilibrium thermal properties from Monte Carlo simulations of Ising models. Formal exact relations relate static equilibrium properties, e.g. the correlation function, to the equilibrium damage. Similar exact relations also relate the time-dependent correlation function to the time-dependent damage. However, some results such as the direct determination of the characteristic time, τ, from damage spreading appear to be at odds with that reported in the literature by more traditional models. We show that some of these discrepancies, but not all, may be resolved by taking the appropriate scaling function into account.
VIBRATIONAL PROBLEM OF FRACTAL NETWORKS
Authors: NAKAYAMA TSUNEYOSHI
Published: November 2004

This paper describes the recent progress in our understanding of the dynamical properties of fractal percolating networks via large-scale computer simulations.
SURFACE ROUGHENING WITH QUENCHED DISORDER IN d-DIMENSIONS
Authors: BULDYREV SERGEY V. , HAVLIN SHLOMO , KERTÉSZ JANOS , SHEHTER ARKADY , STANLEY H. EUGENE
Published: November 2004

We review recent numerical simulations of several models of interface growth in d- dimensional media with quenched disorder. These models belong to the universality class of anisotropic diode-resistor percolation networks. The values of the roughness exponent α=0.63±0.01 (d=1+1) and α=0.48±0.02 (d=2+1) are in good agreement with our recent experiments. We study also the diode-resistor percolation on a Cayley tree. We find that [Formula: see text] thus suggesting that the critical exponent for [Formula: see text]βp=∞ and that the upper critical dimension in this problem is d=dc=∞. Other critical exponents on the Cayley tree are: τ=3,ν||=ν⊥=γ=σ=0. The exponents related to roughness are: α=β=0, z=2.
CAPILLARY DISPLACEMENT ON DETERMINISTIC AND RANDOM FRACTALS
Authors: PAREDES R.
Published: November 2004

Capillary displacement in deterministic and random fractals is explored numerically and analytically using Invasion Percolation (IP) and Eden growth (EG) models. Both compressible and incompressible native fluid cases are studied. It is found that capillary displacements are markedly different for supports having or lacking singly connected links at all scales. It is shown that IP and EG models fill the support if there are links at all scales, for the compressible case. For the incompressible case, on the other hand, a formula is derived which relates the fractal dimension of EG cluster and the dimension of the minimal path and other non-universal quantities. Numerical estimates of the fractal dimension of IP clusters in several supports with links are obtained, and are shown to be different from the corresponding EG values for the incompressible case.
ON THE DYNAMICAL EVOLUTION OF THE FRACTAL STRUCTURE OF INTERSTELLAR MEDIUM
Authors: YUE Z.Y. , ZHANG B. , WINNEWISSER G. , STUTZKI J.
Published: November 2004

Two-dimensional compressible turbulence in a self-gravitating, magnetic interstellar medium is calculated as an initial value problem. It is shown that even if the initial density distribution is homogeneous and the initial velocity distribution contains only a few Fourier components, the nonlinear interaction among the Fourier components will generate more and more Fourier components and lead to a turbulent and fractal structure in the interstellar medium. The calculations are carried out for three different initial states. In order to see the time evolution, detailed density distributions and fractal dimensions of the density contours are calculated at three moments of time for each of the initial states. The results show that the fractal dimension remains almost the same (~1.4–1.5), although the detailed density distribution has changed considerably. The insensibility of the fractal dimension of density contours to both the initial conditions and the evolution time is in good agreement with observations of molecular clouds in the interstellar medium.
DYNAMICAL STRUCTURE FACTOR OF HEISENBERG ANTIFERROMAGNETS WITH FRACTAL STRUCTURES
Authors: TERAO TAKAMICHI , YAKUBO KOUSUKE , NAKAYAMA TSUNEYOSHI
Published: November 2004

The dynamical structure factor S(q, ω) of Heisenberg antiferromagnets with random fractal structures is investigated in terms of a dynamical scaling argument. It is found that the asymptotic behavior of S(q, ω) can be characterized by the dynamic exponent za and a new exponent y. We have performed numerical calculations of S(q, ω) in order to confirm its predicted scaling behaviors for d=2 percolating antiferromagnets. The calculated values for the exponents y and za are consistent with our theoretical prediction.
EFFECTS OF FREE-END BOUNDARY CONDITION ON THE FREQUENCY SPECTRUM OF A VICSEK FRACTAL
Authors: WU SHI-YU , JAYANTHI C.S.
Published: November 2004

In this paper, we investigate the effects of free-end boundary condition on the transverse vibrations of a Vicsek fractal. The unique feature of the eigenvalue spectrum corresponding to this case is that both non-degenerate and degenerate modes of a given generation are present in all subsequent generations, whereas in the case of fixed-end boundary condition only the degenerate modes persist. In the first case, the nature of the persistent degenerate modes is found to be either edge-localized or localized in the region between two adjacent clusters or adjacent sub-clusters, whereas in the second case the persistent modes are found to be edge-confined superlocalized modes. In both cases one finds that: (i) the frequency spectrum consists of atomic-like levels superimposed on a point-dense, cantor-set-like background; and (ii) there is side-by-side coexistence of the extended non-degenerate modes and superlocalized degenerate persistent modes.
INTERFACE INSTABILITY IN DRIVEN LATTICE GASES
Authors: SZABÓ G. , SZOLNOKI A. , ANTAL T. , BORSOS I.
Published: November 2004

In driven lattice-gas models, the enhanced material transport along the interfaces results in an instability of the planar interfaces and leads to the formation of multistrip states. To study the interfacial instability, Monte Carlo simulations are performed on different square lattice-gas models. The amplification rate of a periodic perturbation depends on the wave number k; it has a positive maximum at a characteristic value of k on the analogy of the Mullins-Sekerka instability. Significant differences have been found in the dependence of amplification rate on k when comparing the systems with nearest neighbor repulsive and nearest and next-nearest neighbor attractive interactions. The results agree qualitatively with theories neglecting the fluctuations.
A NEW TYPE OF DYNAMICAL EXCITATIONS FOR PERCOLATION CLUSTERS
Authors: KOLB M.
Published: November 2004

By increasing the local connectivity of percolation clusters, structures with different scaling properties are generated. Both the topology, characterized by the chemical distance, and the dynamics, measured by the spectral dimension, change. For bond percolation in two (three) dimensions, new exponents have been determined by means of numerical simulations: dmin=1.02(4) (1.09(6)) and, for the scalar model, ds=1.56(7) (1–76(8)).
PATTERN FORMATION IN NONCOHESIVE AND COHESIVE GRANULAR MEDIA
Authors: LEMAIRE E. , ABDELHAYE Y. OULD MOHAMED , LARUE J. , BENOIT R. , LEVITZ P. , DAMME H. VAN
Published: November 2004

We studied pattern formation in granular media in two distinct states: in the dry and non-cohesive (powder) state, on the one hand, and in the wet and cohesive (paste) state, on the other. In the first case, we have shown that gas injection in a thin layer of powder within a Hele Shaw cell leads to fractal patterns remarkably similar to viscous fingering patterns obtained with complex fluids. In the second case, we have shown that the tensile cohesive viscoplastic fracture of a layer of paste leads to self-affine rough surfaces with a Hurst exponent close to 0.88, very close to the value obtained for fragile fracture by other authors.18 Our observations reinforce the universality of two fractal growth processes and add a new element to the ambivalent nature of the granular state of matter.
SELF ORGANIZATION IN A FOREST-FIRE MODEL
Authors: DROSSEL B. , SCHWABL F.
Published: November 2004

We generalize the forest-fire model of P. Bak et al., which contains a tree nearest growth probability p and fire spreading to the neighbors, by including a lightning probability f and an immunity g which is the probability that a tree catches no fire although one of its neighbors is burning. The model becomes self-organized critical in the limit f/p→0, provided the time scales of tree growth and burning down of forest clusters are separated. The size distribution of forest clusters obeys a power law. We calculate the critical exponents in one dimension. A continuous phase transition is observed in the general forest-fire model when g reaches its critical value. We determine the critical line gC(p) and show that the critical fire propagation represents a new type of percolation. Finally, we point out similarities between the forest-fire model and excitable media, which comprise such different systems as chemical reactions, spreading of diseases and populations, and propagation of electrical activity in neurons.
THE STATISTICS OF CRACK BRANCHING DURING FAST CRACK PROPAGATION
Authors: BOUCHAUD E. , BOUCHAUD J.-P. , PLANÈS J. , LAPASSET G.
Published: November 2004

We present simple theoretical ideas which allow an understanding of part of the scaling laws recently observed on branched fracture surfaces. Some of these are argued to be common to all critical branched structures, which barely survive when propagating. This is exemplified by numerical results on the directed percolation cluster, which serves as a good toy-model. Finally, we propose a Langevin equation for unbranched cracks in three dimensions, which naturally leads to self-affine structures.
AN APPROXIMATE BOUNDARY INTEGRAL METHOD FOR ACOUSTIC SCATTERING IN SHALLOW OCEANS
Authors: XU YONGZHI , YAN YI
Published: November 2004

The problem of a time-harmonic acoustic wave scattering from a cylindrical object in shallow oceans is solved by an approximate boundary integral method. In the method we employ a Green's function of the Helmholtz equation with sound soft sea level and sound hard sea bottom conditions, and reformulate the problem into a boundary integral equation on the surface of the scattering object. The kernel of the integral equation is given by an infinite series, and is approximated by an appropriate truncation. The integral equation is then fully discretized by applying a quadrature rule. The method has an O(N−3) rate of convergence. Various numerical examples are presented.
ACOUSTIC TRAVEL TIME COMPUTATION BASED ON PE SOLUTION
Authors: SHANG E. C. , WANG Y. Y.
Published: November 2004

We propose the modal spectrum of the PE field (MOSPEF) method for computing modal travel time under strong mode coupling environments. Instead of dealing with the coupled equations governing the complex modal amplitudes, the coupled modal amplitudes and phases are obtained from the spectral expansion of the full wave field given by the PE solution. Consequently, the method is very efficient and is free of problems at critical coupling points. Numerical simulations for computing modal travel time perturbations caused by a mesoscale eddy are conducted. A case which illustrates the failure of the adiabatic mode theory is also presented, the result of which raises an important issue for ocean acoustic tomography schemes.
NUMERICAL INTERFACES IN FINITE DIFFERENCE METHODS FOR HYPERBOLIC EQUATIONS WITH DISCONTINUOUS COEFFICIENTS
Authors: LIN TAO
Published: November 2004

In this paper, we discuss the interface problems arising in using finite difference methods to solve hyperbolic equations with discontinuous coefficients. The schemes developed here can be used to handle four important types of numerical interfaces due to: (1) the discontinuity of the coefficients of the PDE, (2) using artificial boundary, (3) using different finite difference formulae in different areas, and (4) using different grid sizes in different areas. Stability analysis for these schemes is carried out in terms of conventional l1, l2, and l∞ norms so that the convergence rates of these schemes are obtained. Several numerical examples are supplied to demonstrate properties of these schemes.
TWO VERSIONS OF QUASI-NEWTON METHOD FOR MULTIDIMENSIONAL INVERSE SCATTERING PROBLEM
Authors: GUTMAN SEMION , KLIBANOV MICHAEL
Published: November 2004

Suppose that a medium with slowly changing spatial properties is enclosed in a bounded 3-dimensional domain and is subjected to a scattering by plane waves of a fixed frequency. Let measurements of the wave scattering field induced by this medium be available in the region outside of this domain. We study how to extract the properties of the medium from the information contained in the measurements. We are concerned with the weak scattering case of the above inverse scattering problem (ISP), that is, the unknown. spatial variations of the medium are assumed to be close to a constant. Examples can be found in the studies of the wave propagation in oceans, in the atmosphere, and in some biological media.

Since the problems are nonlinear, the methods for their linearization (the Born approximation) have been developed. However, such an approach often does not produce good results. In our method, the Born approximation is just the first iteration and further iterations improve the identification by an order of magnitude. The iterative sequence is defined in the framework of a Quasi-Newton method. Using the measurements of the scattering field from a carefully chosen set of directions we are able to recover (finitely many) Fourier coefficients of the sought parameters of the model. Numerical experiments for the scattering from coaxial circular cylinders as well as for simulated data are presented.
QUASI-LINEAR ELASTODYNAMIC EQUATIONS FOR FINITE DIFFERENCE SOLUTIONS IN DISCONTINUOUS MEDIA
Authors: FRICKE J. ROBERT
Published: November 2004

The linear elastodynamic equations are ill-posed for models which contain high contrast density discontinuities. This paper presents a quasi-linear superset of the linear equations that is well-posed for this situation. The extended system contains a conservation of mass equation and a quasi-linear convective term in the momentum equation. Density, momentum, and stress are the field variables in the quasi-linear system, which is cast in a first order form. Using a Lax–Wendroff finite difference approximation, the utility of the quasi-linear system is demonstrated by modeling underwater acoustic scattering from a truncated ice sheet. The model contains air, ice, and water with a density contrast between air and ice or water of O(103). Superlinear convergence of the Lax–Wendroff scheme is demonstrated for his heterogeneous medium problem.
BOUNDARY ELEMENT SOLUTION OF A BODY'S EXTERIOR ACOUSTIC FIELD NEAR ITS INTERNAL EIGENVALUES
Authors: MARSCHALL R. A.
Published: November 2004

A relatively straightforward Boundary Element Method (BEM) for the numerical solution of the exterior Helmholtz problem is specified in a tutorial fashion. The algorithm employs the Combined Helmholtz Integral Equation Formulation (CHIEF) and then Singular Value Decomposition (SVD) to solve the resulting system. Its accuracy and convergence characteristics are examined, and compared to the simplest boundary element method for exterior acoustics, the Helmholtz Integral Equation Formulation or HIEF. Boundary element and auxiliary (CHIEF) point requirements to obtain BEM solutions of a desired accuracy are described. This particular CHIEF algorithm is found to largely avoid the numerical difficulties of the HIEF technique while retaining theoretical and practical implementation simplicity.
A NEW LATTICE GAS MODEL FOR 1-D SOUND PROPAGATION
Authors: SUDO YASUSHI , SPARROW VICTOR W.
Published: November 2004

A new lattice gas model for sound propagation in one space dimension is proposed. This model has zero truncation error, and the group velocity is independent of wave number as is required from the continuum limit. Conventional finite difference approaches do not have these properties in general. Boundary condition treatments, applicable to the lattice gas formulation, are also given. Both the boundary between two fluid media and an impedance boundary are considered.
PARAMETER SENSITIVITIES IN TWO-LAYER ISOSPEED MODELS OF SHALLOW WATER CHANNELS
Authors: CEDERBERG R. J. , SIEGMANN W. L. , JACOBSON M. J. , CAREY W. M.
Published: November 2004

Sensitivities of relative intensity, interference wavelength, and horizontal wave number predictions to input parameters in two-layer isospeed models of shallow-water, low-frequency (less than 100 Hz) acoustic propagation problems are examined. The investigation is directed toward environmental parameter values corresponding generally to those near the site of a recent New Jersey shelf experiment. Typical parameter uncertainties in the environment of the experiment site are used to determine effects of parameter sensitivities on the accuracy of propagation model predictions. Also, analytic expressions for rates of change of wave numbers with respect to parameters are used to compute wave number and interference wavelength changes caused by parameter variations corresponding to the uncertainties. It is found that channel depth variations cause the largest change in intensity, while water sound speed variations have the greatest effect on wave numbers. Variabilities of the parameter sensitivities in regions about the base parameter sets are also examined, with the rates of change generally staying of the same order of magnitude throughout the regions considered. However, wave numbers which are close to cutoff can produce rates of change which vary by as much as three orders of magnitude.
ON WEIGHTED MEDIAN AGGREGATION
Authors: YAGER RONALD R.
Published: November 2004

We discuss the issue of weighted Min and Max aggregation. We provide for a formalization of the process of importance weighted transformation. The transformation of zero importance items to the identity element of the aggregation is emphasized. Median type aggregation is discussed and we describe its properties. We suggest a new technique for weighted median aggregation. We show its usefulness as an alternative the weighted average when we are using an ordinal scale.
AN APPROACH TO GOAL-ORIENTED REASONING BASED ON FUZZY SETS
Authors: FATHI MADJID , HÖFFMANN ACHIM
Published: November 2004

In this paper concepts for goal-oriented reasoning within the blackboard development environment QBB are presented. The architecture of QBB supports the selection of problem solving actions with respect to the achivement of quality goals. Furthermore, interactions of goals are explicitly taken into account in action selection.

The features of QBB to support goal-oriented reasoning are presented. Especially, it is described how mutual influence of actions with respect to goal achievement can explicitly modeled as relationships between actions, the so-called compensation relations. The usefullness of compensation relations has been tested by goal-oriented modeling of the travelling salesman problem.
OBJECTIVE-CENTERED FORMULATION OF AN ADAPTIVE FUZZY CONTROL SCHEME
Authors: TAN SHAOHUA , LIN YU , WANG PEI-ZHUANG , HE SHI-ZHONG
Published: November 2004

This paper presents a new adaptive fuzzy control scheme that is formulated and constructed directly in the control objective space. The idea of the objective-centered for-mulism on the basis of decomposition of closed-loop response profile is clarified first followed by a detailed description of the scheme. Unlike the existing adaptive fuzzy control methods, the rules and the membership functions of the fuzzy controller in the new scheme are fixed and the adaptation is done on the input and output weighting factors of the fuzzy controller. A simulation analysis is conducted to evaluate the controller performance in regulating a structure-varying process, and to illustrate the advantage of the scheme in controlling plants that can not be easily handled by other control approaches.
ESTIMATIONS OF EXPECTEDNESS AND POTENTIAL SURPRISE IN POSSIBILITY THEORY
Authors: PRADE HENRI , YAGER RONALD R.
Published: November 2004

This note investigates how various ideas of "expectedness" can be captured in the framework of possibility theory. Particularly, we are interested in trying to introduce estimates of the kind of lack of surprise expressed by people when saying "I would not be surprised that…" before an event takes place, or by saying "I knew it" after its realization. In possibility theory, a possibility distribution is supposed to model the relative levels of possibility of mutually exclusive alternatives in a set, or equivalently, the alternatives are assumed to be rank-ordered according to their level of possibility to take place. Four basic set-functions associated with a possibility distribution, including standard possibility and necessity measures, are discussed from the point of view of what they estimate when applied to potential events. Extensions of these estimates based on the notions of Q-projection or OWA operators are proposed when only significant parts of the possibility distribution are retained in the evaluation. The case of partially-known possibility distributions is also considered. Some potential applications are outlined.
ENCOURAGING ENTREPRENEURSHIP EDUCATION AND DEVELOPMENT IN BAHRAIN
Authors: KHAN GOLAM M
Published: November 2004

The importance of entrepreneurship is now recognized worldwide. This has been reflected in the proliferation of different programs and other related activities aimed at fostering entrepreneurship education and development all over the world during the last two decades. This paper briefly reviews such developments, including those in Bahrain, and suggests that increased efforts are needed to help initiate and launch an effective entrepreneurship development program in the country.
EXPLORING ENTREPRENEURSHIP CULTURES IN SOUTHEAST ASIA
Authors: SWIERCZEK FREDRIC WILLIAM , JATUSRIPATAK SOMKID
Published: November 2004

This paper explores the cultural features of entrepreneurship in Malaysia, the Philippines, Singapore and Thailand. A survey approach is used to assess differences in Entrepreneurial Cultures among managers in these four countries. The findings indicate strong similarities between the samples of managers from the Philippines, Malaysia, and Singapore. Entrepreneurs in these countries emphasize more the personality characteristics of the entrepreneur such as, risk taking, whereas those from Thailand emphasises on innovation.
THE RELATIONSHIP BETWEEN INSTITUTIONS OF HIGHER EDUCATION AND SMALL BUSINESS IN THE UNITED STATES
Authors: SILVA CASTAN JAIME R
Published: November 2004

In recent years, a number of trends have concurrently contributed to promote collaboration between institutions of higher education and small businesses in the United States. These trends include academic institutions’ need for new sources of revenue, students’ growing interest in careers in business, increased media attention to entrepreneurship and small business, and industrialists’ search for a competitively advantageous position. The outcome of these relationships has been positive for both parties. The purpose of this paper, therefore, is to examine the diverse relationships between colleges and universities and the small business sector that currently exist in the United States. The findings of this paper focus on (1) how the relationships between U.S. institutions of higher education and small businesses have been institutionalized, (2) types of research methodologies used in the analysis of these relationships, and (3) the identification of specific areas for further research.
INNOVATION MANAGEMENT IN SOUTH WEST SME SECTOR FIRMS
Authors: CHASTON IAN
Published: November 2004

One response of UK SME sector firms to the competitive threat of the European Single Market is to enhance product performance through product improvement and/or new product development projects. A survey of South West SME firms reveals only a minority had successfully implemented product performance improvement projects. A comparison of successful and unsuccessful programmes confirms the key influence of factors such as acccurate market research, project planning, adequate financial resources and effect internal management systems. Possible actions including Government involvement in building awareness for the importance of innovation in the post-1992 business environment and actions to stimulate greater use of external advisors in areas such as technology transfer are discussed.
USEFULNESS OF TRADITIONAL AND NEW PERFORMANCE MEASURES: SOME EVIDENCE FROM SINGAPORE COMPANIES
Authors: AUN KHOO TENG , YAP TEOH HAI , JOHNSON CHNG
Published: November 2004

This paper reported the findings of a survey study on the usefulness of selected traditional and new performance measures used by Singapore companies that have adopted a flexible manufacturing strategy. The results indicated that the majority of these companies considered the new performance measures useful particularly among the larger companies and among those with 5 years or less of business experience. Traditional measures are still useful, though to a much lesser extent. These results suggested that a combination of both traditional and new measures would be needed especially when Singapore companies are going through the transition of implementing changes to their strategies from cost leadership to flexible manufacturing.
SELF-EMPLOYMENT INITIATIVES IN IRAN—A CASE STUDY
Authors: ALIZADEH YOUNESS
Published: November 2004

A few years after the Islamic Revolution in 1979, the Government of Iran was confronted by a rapid growth in the population, vast migrations from rural areas to urban cities such as Tehran (currently numbering 15 millions), and increasing unemployment. Available statistics, according to sociologists and statisticians, indicate that unemployment in Iran is an “urban” phenomenon affecting high school and university graduates. In an attempt to address the problem of unemployment and the concentration of wealth in the hands of a few individuals in business, the Government decided to introduce several models to promote self-employment enterprises. In order to implement these models the Parliament of the Islamic Republic of Iran has approved several decrees that allow the Government to extend credit to unemployed persons provided they form production co-operatives. There are mainly two self-employment models developed by the Government through the Ministry of Co-operation and the Ministry of Employment and Social Affairs. In order to evaluate these models, this author conducted intensive interviews with a number of staff members in the Ministry of Co-operation and the Ministry of Employment and Social Affairs, reviewed relevant literature, and surveyed 20% of active co-operatives in the Tehran province to gather first-hand information. An important attribute of the scheme is that, through establishing self-employment enterprises for unemployed persons, the Iranian Government attempted to replace mortgages by education or managerial ability as a basis for extending credit. The study revealed that, despite the attractiveness of the models, their success is dependent upon careful implementation and handling of the problems such as management training and the education of self-employed persons.
MOVING SINGAPORE ENTREPRENEURSHIP TO NEW HEIGHTS
Authors: MUN CHEANG BERNARD BOEY , SIEW HOON SUSAN CHIAM-LEE
Published: November 2004

Over the last three decades, Singapore had achieved a rate of economic progress equalled by few countries in the world. From a poor under-developed country with a per capita GNP of less than S$1000 in 1960, Singapore is today a newly industrialised economy with a per capita GNP of about S$24,000 and with full employment.

Since the start of its industrialisation programme, Singapore has pursued actively a strategy to promote foreign investment, and this has been a major factor in its rapid economic growth, to the point that foreign investment policy is almost synonymous with its industrialisation strategy. However, changes in the business climate such as the economic slowdown in the industrialised world, growing global protectionism, spiralling business costs, changes in foreign investment patterns, just to identify some worrying trends, have led the government and the business community to work on developing a “second wing”.

Singapore had leap-frogged the competition in earlier decades by riding piggyback on multinational corporations and this helped Singapore grow “one wing”— its domestic economy. Now the challenge is to nurture a new breed of entrepreneurs who can help Singapore to strengthen its domestic economy and also to seize opportunities to develop the second wing by way of an external economy that will see an increasing number of local companies venturing into the region.
TESTING-COVERAGE DEPENDENT SOFTWARE RELIABILITY GROWTH MODELING
Authors: INOUE SHINJI , YAMADA SHIGERU
Published: November 2004

We discuss software reliability growth modeling considering with testing-coverage. There are several testing-coverage evaluation criteria for the testing thoroughness. As one of them, statement (or block) testing-coverage is measured as the fraction of the total number of statements that have been executed at least once by the test-cases. First, an alternative evaluation metric for the testing-coverage is proposed in this paper. And then, we develop a software reliability growth model by formulating the relationship between the alternative testing-coverage evaluation function and the number of detected faults. Finally, we show numerical examples for software reliability analysis based on the proposed model by using an actual data set.