bluuebunny/crossref_metadata_2025 huggingface dataset:
Prey processing in lizards: behavioral variation in sit-and-wait and widely foraging taxa
Authors: McBrayer Lance D , Reilly Stephen M
Published: July 2002

We determined the degree to which lizards process (i.e., chew) and manipulate their prey, using a phylogenetically broad sample of 12 species. Two transport and two chewing behaviors were identified. The transport behaviors included side-to-side movements and lingually mediated posterior movements of the prey. Chewing behaviors included puncture crushing and a previously undescribed behavior we term palatal crushing. Iguanian lizards (sit-and-wait predators) engaged in more palatal-crushing behaviors than autarchoglossans (widely foraging predators) did. However, iguanians also engaged in fewer cycles of chewing and transport behaviors per feeding bout. Autarchoglossan lizards used puncture crushing extensively and exhibited more variability in the sequence of behaviors used within a bout ( interspersion of transport behaviors among chewing behaviors). Three behaviors (puncture crushing, interspersion, total) were shown to be coevolving after the effects of phylogeny were removed. The variation in feeding behavior we observed between iguanian and autarchoglossan lizards parallels patterns in tongue morphology and foraging mode in these large groups. Thus, it seems likely that each represents a component of a highly integrated character complex linking feeding morphology, behavior, and ecology.
SPARSE COMPUTATION WITH PEI
Authors: VOISIN FRÉDÉRIQUE , PERRIN GUY-RENÉ
Published: July 2002

PEI formalism has been designed to reason and develop parallel programs in the context of data parallelism. In this paper, we focus on the use of PEI to transform a program involving dense matrices into a new program involving sparse matrices, using the example of the matrix-vector product.
ENERGY STATES IN QUANTUM DOTS
Authors: WILLIAMSON ANDREW J.
Published: July 2002

We describe a procedure for calculating the electronic structure of semiconductor quantum dots containing over one million atoms. The single particle electron levels are calculated by solving a Hamiltonian constructed from screened atomic pseudopotentials. Effects beyond the single particle level such as electron and hole exchange and correlation interactions are described using a configuration interaction (CI) approach. Application of these methods to the calculation of the optical absorption spectrum, Coulomb repulsions and multi-exciton binding energies of InGaAs self-assembled quantum dots are presented.
SELF-ORGANIZED QUANTUM DOTS
Authors: WOLL A. R. , RUGHEIMER P. , LAGALLY M. G.
Published: July 2002

We review the concepts and principal experimental results pertaining to the self-assembly and self-ordering of quantum dots in semiconductor systems. We focus on the kinetics and thermodynamics of the formation and evolution of coherently strained 3D islands, and the effects of strain on nucleation, growth, and island shape. We also discuss ongoing research on methods to control the density, size, and size distributions of strained islands, both within a single strained layer and in quantum dot (QD) multilayers.
NATURAL BILINEAR FORMS, NATURAL SESQUILINEAR FORMS AND THE ASSOCIATED DUALITY ON NON-COMMUTATIVE Lp-SPACES
Authors: IZUMI HIDEAKI
Published: July 2002

In the author's previous paper, he constructed a complex one-parameter family of non-commutative Lp-spaces [Formula: see text], [Formula: see text], 1 < p < ∞, for a von Neumann algebra ℳ with respect to a fixed faithful normal semi-finite weight φ on ℳ by using Calderón's complex interpolation method. In this paper, we will construct bounded non-degenerate bilinear forms < , >p,(α)on [Formula: see text], [Formula: see text], 1 < p <∞, 1/p + 1/q = 1, and bounded non-degenerate sesquilinear forms ( | )p,(α)on [Formula: see text], [Formula: see text], 1 < p < ∞, 1/p + 1/q = 1, and by using general theory of the complex interpolation method we show the reflexivity of [Formula: see text] and the duality between [Formula: see text] and [Formula: see text] via < , >p,(α)(or the duality between [Formula: see text] and [Formula: see text] via ( | )p,(α)). Moreover, we discuss bimodule properties of [Formula: see text].
MICROCANONICAL SIMULATION OF COMPLEX ACTIONS: THE WESS–ZUMINO–WITTEN CASE
Authors: BAAQUIE BELAL E. , SENG Y. S.
Published: July 2002

We present the main results of our microcanonical simulation of the Wess–Zumino–Witten action functional. This action, being highly nontrivial and capable of exhibiting many different phase transitions, is chosen to be representative of general complex actions. We verify the applicability of microcanonical simulation by successfully obtaining two of the many critical points of the Wess–Zumino–Witten (WZW) action. The microcanonical algorithm has the additional advantage of exhibiting critical behavior for a small 8 × 8 lattice. We also briefly discuss the subtleties that, in general, arise in simulating a complex action. Our algorithm for complex actions can be extended to the study of D-branes in the WZW action.
SCALING IN A SIMPLE MODEL FOR SURFACE GROWTH IN A RANDOM MEDIUM
Authors: AHARONY AMNON , STAUFFER DIETRICH
Published: July 2002

Surface growth in random media is usually governed by both the surface tension and the random local forces. Simulations on lattices mimic the former by imposing a maximum gradient m on the surface heights, and the latter by site-dependent random growth probabilities. Here we consider the limit m → ∞, where the surface grows at the site with minimal random number, independent of its neighbors. The resulting height distribution obeys a simple scaling law, which is destroyed when local surface tension is included. Our model is equivalent to Yee's simplification of the Bak–Sneppen model for the extinction of biological species, where the height represents the number of times a biological species is exchanged.
A SIMPLE MODEL FOR STOCKS MARKETS
Authors: SANCHEZ JUAN R.
Published: July 2002

A new model for stock markets using integer values for each stock price is presented. In contrast with previously reported models, the variables used in the model are not of binary type, but of more general integer type. It is shown how the behavior of the noise and fundamentalists traders can be taken into account simultaneously in the time evolution of each stock price. The simulated time series generated by the model is analyzed in different ways order to compare parameters with those of real markets.
FUZZY REINFORCEMENT LEARNING
Authors: ANDRECUT M. , ALI M. K.
Published: July 2002

Fuzzy logic represents an extension of classical logic, giving modes of approximate reasoning in an environment of uncertainty and imprecision. Fuzzy inference systems incorporates human knowledge into their knowledge base on the conclusions of the fuzzy rules, which are affected by subjective decisions. In this paper we show how the reinforcement learning technique can be used to tune the conclusion part of a fuzzy inference system. The fuzzy reinforcement learning technique is illustrated using two examples: the cart centering problem and the autonomous navigation problem.
LOOP VARIABLES AND GAUGE INVARIANCE IN (OPEN) BOSONIC STRING THEORY
Authors: SATHIAPALAN B.
Published: July 2002

We give a simplified and more complete description of the loop variable approach for writing down gauge-invariant equations of motion for the fields of the open string. A simple proof of gauge invariance to all orders is given. In terms of loop variables, the interacting equations look exactly like the free equations, but with a loop variable depending on an extra parameter, thus making it a band of finite width. The arguments for gauge invariance work exactly as in the free case. We show that these equations are Wilsonian RG equations with a finite worldsheet cutoff and that in the ir limit, equivalence with the Callan–Symanzik β-functions should ensure that they reproduce the on-shell scattering amplitudes in string theory. It is applied to the tachyon–photon system and the general arguments for gauge invariance can be easily checked to the order calculated. One can see that when there is a finite worldsheet cutoff in place, even the U(1) invariance of the equations for the photon, involves massive mode contributions. A field redefinition involving the tachyon is required to get the gauge transformations of the photon into the standard form.
IS GRAVITY AN INTRINSICALLY QUANTUM PHENOMENON? DYNAMICS OF GRAVITY FROM THE ENTROPY OF SPACE–TIME AND THE PRINCIPLE OF EQUIVALENCE
Authors: PADMANABHAN T.
Published: July 2002

The two surprising features of gravity are (a) the principle of equivalence and (b) the connection between gravity and thermodynamics. Using principle of equivalence and special relativity in the local inertial frame, one could obtain the insight that gravity must possess a geometrical description. We show that, using the same principle of equivalence, special relativity and quantum theory in the local Rindler frame one can obtain the Einstein–Hilbert action functional for gravity and thus the dynamics of the space–time. This approach, which essentially involves postulating that the horizon area must be proportional to the entropy, uses the local Rindler frame as a natural extension of the local inertial frame and leads to the interpretation that the gravitational action represents the free energy of the space–time geometry. As an aside, one also obtains a natural explanation as to: (i) why the covariant action for gravity contains second derivatives of the metric tensor and (ii) why the gravitational coupling constant is positive. The analysis suggests that gravity is intrinsically holographic and even intrinsically quantum mechanical.
RADIATION FROM A CHARGE CIRCULATING INSIDE A WAVEGUIDE WITH DIELECTRIC FILLING
Authors: KOTANJYAN ANNA S. , SAHARIAN ARAM A.
Published: July 2002

The emitted power of the radiation from a charged particle moving uniformly on a circle inside a cylindrical waveguide is considered. The expressions for the energy flux of the radiation passing through the waveguide cross-section are derived for both TE and TM waves. The results of the numerical evaluation are presented for the number of emitted quanta depending on the waveguide radius, the radius of the charge rotation orbit and dielectric permittivity of the filling medium. These results are compared with the corresponding quantities for the synchrotron radiation in a homogeneous medium.
A NOTE ON THE osp(1|2s) THERMODYNAMIC BETHE ANSATZ EQUATION
Authors: TSUBOI ZENGO
Published: July 2002

A Bethe ansatz equation associated with the Lie superalgebra osp(1|2s) is studied. A thermodynamic Bethe ansatz (TBA) equation is derived by the string hypothesis. The high temperature limit of the entropy density is expressed in terms of the solution of the osp(1|2s) version of the Q-system. In particular for the fundamental representation case, we also derive a TBA equation from the osp(1|2s) version of the T-system and the quantum transfer matrix method. This TBA equation is identical to the one from the string hypothesis. The central charge is expressed by the Rogers dilogarithmic function and identified to s.
1/N CORRECTIONS TO ANOMALIES AND THEAdS/CFTCORRESPONDENCE FOR ORIENTIFOLDED ${\mathcal N} = 2$ ORBIFOLD AND ${\mathcal N} = 1$ CONIFOLD MODELS
Authors: NACULICH STEPHEN G. , SCHNITZER HOWARD J. , WYLLARD NICLAS
Published: July 2002

We show that for a large class of [Formula: see text] conformal field theories the 1/N correction to the chiral anomaly of the U(1) R-current can be shown to arise from the D7-branes present in the dual orientifolded orbifold string theories, generalizing a result in the literature for the simplest case. We also study the U(1)Ranomaly for [Formula: see text] conformal field theories that arise from orientifolds of the conifold. We find agreement between the field- and string-theoretic calculations, confirming a prediction of the AdS/CFT correspondence at order 1/N for string theories on AdS5× T11/ℤ2.
LEPTONS WITH E > 200 MEV TRAPPED IN THE SOUTH ATLANTIC ANOMALY
Authors: FIANDRINI E. , ESPOSITO G.
Published: July 2002

For the first time accurate measurements of electron and positron fluxes in the energy range 0.2 ÷ 10 GeV have been performed with the Alpha Magnetic Spectrometer (AMS) at altitudes of 370 ÷ 390 km in the geographic latitude interval ±51.7°. We focused on the under-cutoff lepton fluxes inside the region of the South Atlantic Anomaly (SAA), defined as region where the local magnetic field B ≤ 0.26 G.

A clear transtion region from stably-trapped flux typical of the lnner Van Allen Belts to quasi-trapped flux typical underneath the Van Allen Belts is observed in the SAA up to energies O(Gev).

The observations strongly support positrons abundance in the Inner Van Allen Belts, both in the stably trapped component and in the quasi-trapped one.

The flux maps as a function of the canonical adiabatic variables L, αo are presented for the intervval 0.95 < L < 3, 0° < αo < 90° for electrons (E < 10 GeV) and positrons (E < 3 GeV). The results are compared with existing data at lower energies.
LOW ENERGY ELECTRON AND POSITRON SPECTRA IN THE EARTH ORBIT MEASURED BY MARIA-2 INSTRUMENT
Authors: MIKHAILOV V. V.
Published: July 2002

Results of study of secondary electrons and positrons in the energy range 15–150 MeV in the earth space-orbit are reviewed.
COSMIC PHOTON AND POSITRON SPECTRA MEASUREMENTS MODELLING WITH THE AMS-02 DETECTOR AT ISS
Authors: CHOUTKO VITALI , LAMANNA GIOVANNI , MALININ ALEXANDER
Published: July 2002

The results of the MC feasibility study of the AMS-02 Detector cosmic-ray γ and e+ spectra measurement capabilities are presented. AMS will be able to provide accurate measurements of the above spectra in a broad energy range (up to hundreds of GeV) with energy resolution of a few percent and angular resolution of 0.01-1°. The acceptance of 0.05-0.15 m2sr has been estimated both for e+ and γ, with maximal opening angle being 20° to 45°. The systematic study of the background events has been done, the irreducible background to signal ratio below a few percent being obtained.
Some of the Early History of Exactly Soluble Models
Authors: Lieb Elliott H.
Published: July 2002

The early history of exactly soluble models in statistical mechanics and the quantum-mechanical many-body problem, especially in the 1960's, is briefly reviewed.
Star-Star Relation for the Potts Model
Authors: King C. , Wu F. Y.
Published: July 2002

A star-star transformation is introduced for the Potts model as a generalization of the Onsager star-triangle relation. By considering a special limit of the star-star relation, we deduce a dual transformation relation for the Potts model on the 3-12 lattice. We also obtain numerical bounds on the critical point of the Potts model on the kagomé lattice, a long unsolved problem.
Computer Simulation Study of a Disordered Two-Dimensional Nematogenic Lattice Model with Long-Range Interactions Isotropic in Spin Space
Authors: Romano S.
Published: July 2002

We have considered a classical spin system, consisting of 3-component unit vectors, associated with a two-dimensional lattice {uk, k∈ Z2}, and interacting via translationally invariant pair potentials, isotropic in spin space, and of the long-range form [Formula: see text] Here ∊ is a positive constant setting energy and temperature scales (i.e. T*=k B T /∊), P2 denotes the second Legendre polynomial, and xj are dimensionless coordinates of the lattice sites. Available theorems entail the existence of an ordering transition at finite temperature when 0 < σ < 2, and its absence when σ ≥ 2. We have studied the border case σ=2, by means of computer simulation. Similarly to the nearest-neighbour counterpart of the present model, and to other long-range models, we found evidence suggesting a transition to a low-temperature phase with slow decay of correlations and infinite susceptibility, i.e. a Berezhinski[Formula: see text]–Kosterlitz–Thouless-like transition; the transition temperature was estimated to be Θ=1.112 ± 0.005.
Boundary Critical Behaviour of Two-Dimensional Layered Ising Models
Authors: Pelizzola Alessandro
Published: July 2002

Layered models are models in which the coupling constants depend in an arbitrary way on one spatial coordinate, usually the distance from a free surface or boundary. Here the theory of the boundary critical behaviour of two-dimensional layered Ising models, including the Hilhorst–van Leeuwen model and models for aperiodic systems, is reviewed, with a particular attention to exact results for the critical behaviour and the boundary order parameter.
Quantized Density Response in Three Dimensions
Authors: Wu-Morrow Xiao-Rong
Published: July 2002

Niu's notion of particle density response,1 which provides a unifying framework for a number of interesting physical results including the quantum Hall effect and quantum adiabatic charge transport, is applied to a three-dimensional noninteracting electron system. It is shown that the average particle density response to a dilation of a periodic potential in an insulator, with or without an additional background potential, is quantized. This quantum number is a high order topological invariant.
Pairing in the Bogoliubov–de Gennes Equations
Authors: Kim Yong-Jihn
Published: July 2002

It is shown that the Bogoliubov–de Gennes equations pair the electrons in states which are linear combinations of the normal states. Accordingly, the BCS-like reduction procedure is required to choose a correct pairing. For a homogeneous system, we point out that the kernel of the self-consistency equation derived from the Bogoliubov–de Gennes equations needs to be constrained by the BCS pairing condition. In the presence of ordinary impurities, on the other hand, the Bogoliubov–de Gennes equations should be supplemented by Anderson's pairing condition to obtain the correct vacuum state by the corresponding unitary transformation. This results in localization correction to the phonon-mediated interaction.
Homodyne Photocurrent, Symmetries in Photon Mixing and Number State Synthesis
Authors: Paris Matteo G. A.
Published: July 2002

Lossless beam splitter has been studied by the exact diagonalization of the homodyne photocurrent. The probability of totally symmetric and totally antisymmetric output from a balanced beam splitter fed by arbitrary number states has been evaluated. Efficiency of photon mixing to synthesize highly excited number states has been also discussed.
Spin and Charge Density Waves in the Extended Hubbard Model: A Slave Boson Approach
Authors: Caprara S. , Avignon M. , Sarma D. D.
Published: July 2002

We use the extended Hubbard model to investigate the properties of the charge- and spin-density-wave phases in the presence of a nearest-neighbors repulsion term in the framework of the slave-boson technique. We show that, contrary to Hartree–Fock results, an instablity may occur for sufficiently high values of the Hubbard repulsion, both in the spin- and charge-density-wave phase, which makes the system discontinuously jump to a phase with a smaller or zero wave amplitude. The limits of applicability of our approach are discussed and our results are compared with previous numerical analysis. The phase diagram of the model at half-filling is determined.
Physics of the Extended Neuron
Authors: Bressloff P. C. , Coombes S.
Published: July 2002

We review recent work concerning the effects of dendritic structure on single neuron response and the dynamics of neural populations. We highlight a number of concepts and techniques from physics useful in studying the behaviour of the spatially extended neuron. First we show how the single neuron Green's function, which incorporates details concerning the geometry of the dendritic tree, can be determined using the theory of random walks. We then exploit the formal analogy between a neuron with dendritic structure and the tight-binding model of excitations on a disordered lattice to analyse various Dyson-like equations arising from the modelling of synaptic inputs and random synaptic background activity. Finally, we formulate the dynamics of interacting populations of spatially extended neurons in terms of a set of Volterra integro-differential equations whose kernels are the single neuron Green's functions. Linear stability analysis and bifurcation theory are then used to investigate two particular aspects of population dynamics (i) pattern formation in a strongly coupled network of analog neurons and (ii) phase-synchronization in a weakly coupled network of integrate-and-fire neurons.
A POSSIBLE CORRELATION BETWEEN SUPPRESSION OF SUPERCONDUCTIVITY, MAGNETIC ORDERING AND NORMAL STATE RESISTIVITY PARAMETERS IN THE Yb1-xPrxBa2Cu3O7-δ SYSTEM
Authors: GUPTA ANURAG , NARAYAN H. , LISBOA-FILHO P. N. , CARDOSO C. A. , ARAUJO MOREIRA FERNANDO M. , DE LIMA O. F. , NARLIKAR A. V.
Published: July 2002

Polycrystalline samples of the Pr doped Yb 1-x Pr x Ba 2 Cu 3 O 7-δ (i.e. Yb(Pr)-123) system for 0≤x≤1 have been investigated for resistivity ρ and magnetization M as a function of temperature in normal and superconducting states. The gradual decrease in superconducting critical temperature T c (x) is found to be correlated with the x-dependent ratio of resistivity slope (dρ/dT) cc (corresponding to the linear ρ(T) region) and residual resistivity ρ0. In particular, the observed difference of critical Pr concentration where superconductivity is destroyed (x c ) in Yb(Pr)-123 (x c ≈ 0.65) and Y(Pr)-123 (x c ≈ 0.55) matches with the difference in the value of Pr concentration where the ratio (dρ/dT) cc /ρ0 tends to go to zero in them. The M(T) data of the Yb(Pr)-123 samples show magnetic ordering for x > x c at characteristic temperatures, Tn, that increase with x. Interestingly, the Yb(Pr)-123 sample with Pr content (x = 0.6) near x c reveals several anomalous features like transition from metallic to semiconducting-like ρ(T), an excessive broadening of the diamagnetic transition and weakening of the M(T) signal related to antiferromagnetic ordering of Pr ions. These observations can be consistently interpreted by assuming the presence of dynamically fluctuating striped phase in these systems.
COMPLEX DYNAMICS IN NEARLY SYMMETRIC THREE-CELL CELLULAR NEURAL NETWORKS
Authors: DI MARCO M. , FORTI M. , TESI A.
Published: July 2002

The paper introduces a class of third-order nonsymmetric Cellular Neural Networks (CNNs), and shows through computer simulations that they undergo a cascade of period doubling bifurcations which leads to the birth of a large-size complex attractor. A major point is that these bifurcations and complex dynamics happen in a small neighborhood of a particular CNN with a symmetric interconnection matrix.
TARGETING OF CHAOTIC DYNAMICAL SYSTEMS USING NONLINEAR APPROXIMATIONS
Authors: Hill D. L.
Published: July 2002

The ideas underpinning a technique of using nonlinear approximations to control chaotic dynamical systems are shown to be useful as a basis for the development of effective methods for targeting these systems. The inverses of the maps under consideration are not required. The methods are applied to the Hénon and Ikeda maps and also to an Ikeda-like map.
ON THE TRACTION PROBLEM FOR THE STOKES SYSTEM
Authors: STARITA GIULIO , TARTAGLIONE ALFONSINA
Published: July 2002

The traction problem for the Stokes system is studied in the framework of the theory of the hydrodynamical potentials. Existence theorems and integral representations of classical solutions are given for domains having not connected boundary of class C1,α in both the bounded and exterior cases. Finally, a maximum modulus theorem is derived for the traction field in the direction of the normal to the boundary.
FROM THE NONLOCAL TO THE LOCAL DISCRETE DIFFUSIVE COAGULATION EQUATIONS
Authors: LAURENÇOT PHILIPPE , WRZOSEK DARIUSZ
Published: July 2002

We consider the connection between two mean-field models describing the binary coagulation of discrete clusters moving by spatial diffusion. Both models are generalizations of Smoluchowski's infinite system of coagulation equations. In the first (local) model, the coagulation rates are proportional to the concentrations of the interacting clusters as a consequence of the assumption that two clusters coalesce only if they meet at the same point. In the second (nonlocal) one, the coagulation rates contain integral terms which reflect the nonlocal character of interactions between clusters, the intensity of clusters' encounters depending on the distance between them and being measured by means of some positive parameter ε. It is proved that weak solutions to the nonlocal discrete diffusive coagulation equations converge to that of the local one as ε → 0.
COMPARING KEYWORD EXTRACTION TECHNIQUES FOR WEBSOM TEXT ARCHIVES
Authors: AZCARRAGA ARNULFO P. , YAP TEDDY , CHUA TAT SENG
Published: July 2002

The WEBSOM methodology for building very large text archives has a very slow method for extracting meaningful unit labels. This is due to the fact that the method computes for the relative frequencies of all the words of all the documents associated to each unit and then compares these to the relative frequencies of all the words of other units in the map. Since maps may have more than 100,000 units and the archieve may contain up to 7 million documents, the existing WEBSOM method is not practical. A fast alternative method, referred to as the liGHtSOM method, is based on the distribution of weights in the weight vectors of the trained map, plus a simple manipulation of the random projection matrix used for input data compression. Comparison made using a WEBSOM archieve of the Reuters text collection reveal that a high percentage of keywords extracted using this method match the keywords extracted for the same map units using the original WEBSOM method. A detailed time complexity analysis of the two methods is also provided.
GUIDING CONSTRUCTIVE SEARCH WITH STATISTICAL INSTANCE-BASE LEARNING
Authors: TELELIS ORESTIS , STAMATOPOULOS PANAGIOTIS
Published: July 2002

Several real world applications involve solving combinatorial optimization problems. Commonly, existing heuristic approaches are designed to address specific difficulties of the underlying problem and are applicable only within its framework. We suspect, however, that search spaces of combinatorial problems are rich in intuitive statistical and numerical information, which could be exploited heuristically in a generic manner, towards achievement of optimized solutions. Our work presents such a heuristic methodology, which can be adequately configured for several types of optimization problems. Experimental results are discussed, concerning two widely used problem models, namely the Set Partitioning and the Kanpsack problems. It is shown that, by gathering statistical information upon previously found solutions to the problems, the heuristic is able to incrementally adapt its behaviour and reach high quality solutions, exceeding the ones obtained by commonly used greedy heuristics.
DELTA AND CLASP-PASS DISTANCES AND VASSILIEV INVARIANTS OF KNOTS
Authors: OHYAMA YOSHIYUKI , YAMADA HARUMI
Published: July 2002

In this paper, we show that when any nonnegative integer n and any knot K are given, there exist infinitely many unknotting number one knots Jm (m = 1,2, ⋯) such that their Vassiliev invariants of order less than or equal to n coincide with those of K and each Jm satisfies the following: The delta unknotting number of Jm is determined by the order two Vassiliev invariant of K and for almost cases, the clasp-pass distance between Jm and the twist knot with the same order two invariant is determined by the order three invariant of K.
SOLVING THE INVERSE PROBLEM FOR FUNCTION/IMAGE APPROXIMATION USING ITERATED FUNCTION SYSTEMS I: THEORETICAL BASIS
Authors: FORTE BRUNO , VRSCAY EDWARD R.
Published: July 2002

We are concerned with function approximation and image representation using Iterated Function Systems (IFS) over ℒp (X, µ): An N-map IFS with grey level maps (IFSM), to be denoted as (w, Φ), is a set w of N contraction maps wi: X → X over a compact metric space (X, d) (the "base space") with an associated set Φ of maps ϕi: R → R. Associated with each IFSM is a contractive operator T with fixed point [Formula: see text]. We provide a rigorous solution to the following inverse problem: Given a target υ ∈ ℒp(X, µ) and an ∊ > 0, find an IFSM whose attractor satisfies [Formula: see text].
DETERMINATION OF FRACTAL SCALES ON TRABECULAR BONE X-RAY IMAGES
Authors: HARBA R. , JACQUET G. , JENNANE R. , LOUSSOT T. , BENHAMOU C. L. , LESPESSAILLES E. , TOURLIÈRE D.
Published: July 2002

A fractal analysis based on the Fractional Brownian Motion is proposed to characterize the architecture of the trabecular bone network. This analysis is applied on digital image lines of X-ray views. The study of self-similarity on images of calcaneus radiographs allows the determination of two length scales where the fractal hypothesis is verified. The first one is ranging from about 100 to 550 µm. This area is used to characterize the bone structure at the trabecular thickness scale. The second one starts about above 900 µm, it can be related to the trabecular spacing. A statistical approach allow to choose the fractal area given a level of significance.
FRACTAL DOMAIN WALLS IN ISING SPIN GLASSES
Authors: CIEPLAK MAREK , LI MAI SUAN
Published: July 2002

Local mean field studies of domain walls in Ising spin glasses yield the fractal dimensionalities of 1.27 ± 0.04 and 2.57 ± 0.07 for two and three dimensions, respectively.
SIMULATED CROSSBREEDING: A CASE OF HYBRIDIZED FRACTALS
Authors: CHUA MEI CHEN , HSU WEN JING
Published: July 2002

The Lindenmayer-system formalism is extended to model the hybridization of plant forms. Several algorithms are developed and tested. Pictures illustrating these algorithms are generated by using computer graphics. The preliminary results suggest that the proposed new approach may be useful for combining fractals that are generated iteratively.
THE FRACTAL DIMENSION OF THE APOLLONIAN SPHERE PACKING
Authors: BORKOVEC M. , DE PARIS W. , PEIKERT R.
Published: July 2002

The fractal dimension of the Apollonian sphere packing has been computed numerically up to six trusty decimal digits. Based on the 31 944 875 541 924 spheres of radius greater than 2−19 contained in the Apollonian packing of the unit sphere, we obtained an estimate of 2.4739465, where the last digit is questionable. Two fundamentally different algorithms have been employed. Outlines of both algorithms are given.
RELATING THIN AND FAT-FRACTAL SCALING OF RIVER-NETWORK MODELS
Authors: KARLINGER M. R. , OVER T. M. , TROUTMAN B. M.
Published: July 2002

The fractal scaling of river networks has been described in the context of both thin and fat fractals. Whereas the thin-fractal characterization is presented as a fractal dimension, D, derived from the length properties of the river channels, a fat-fractal characterization is given as a scaling exponent, β, derived from the behavior of river-channel area. Several authors have related D to the bifurcation ratio, Rb, and length ratio, Rl, of idealized Hortonian-network trees. Here, for these types of trees, we asymptotically relate β to Rb, Rl, and to a diameter exponent, Δ, which governs the downstream channel-widening process. Using this result, we present a linkage of D to β and discuss the implications of the relative values of Rb, Rl, and Δ on this linkage and on network channel behavior. Finally, we illustrate bias in the estimation of β from preasymptotic trees.
ANALYSES OF ACCELERATED LIFE TEST DATA UNDER TWO FAILURE MODES
Authors: KIM C. M. , BAI D. S.
Published: July 2002

This paper proposes a method of estimating the lifetime distribution at use condition for constant stress accelerated life tests when an extrinsic failure mode as well as intrinsic one exists. A mixture of two distributions is introduced to describe these failure modes. It is assumed that the log lifetime of each failure mode follows a location-scale distribution and a linear relation exists between the location parameter and the stress. An estimation procedure using the expectation and maximization algorithm is proposed and specific formulas for Weibull distribution are obtained. Simulation studies are performed to investigate the properties of the estimates and the effects of stress level. Numerical comparisons with the masked data model are also performed.
A 3-DIMENSIONAL CONSECUTIVE-k-OUT-n: F MODELS
Authors: BOUSHABA M. , GHORAF N.
Published: July 2002

A consecutive-k-out-of-n: F system is an ordered linear sequence of n components that fails if and only if at least k consecutive components fail. The objective of this paper is the generalization of this system to the 3-dimensional case, which we call a "3-dimensional consecutive-k-out- of-n: F model". We first derive upper and lower reliability bounds of our model with independent but not necessarily identical components (Theorem 1). A Weibull limit theorem is also proved for system's time to failure in the case of i.i.d. components.
EFFECT OF ASSET VALUE CORRELATION ON CREDIT-LINKED NOTE VALUES
Authors: HUI C. H. , LO C. F.
Published: July 2002

This paper develops a simple model to study the credit risk premiums of credit-linked notes using the structural model. Closed-form solutions of credit risk premiums of the credit-linked notes derived from the model as functions of firm values and the short-term interest rate, with time-dependent model parameters governing the dynamics of the firm values and interest rate. The numerical results show that the credit spreads of a credit-linked note increase non-linearly with the decrease in the correlation between the asset values of the note issuer and the reference obligor when the final payoff condition depends on the asset values of the note issuer and the reference obligor. When the final payoff condition depends on the recovery rate of the note issuer upon default, the credit spreads could increase with the correlation. In addition, the term structures of model parameters and the correlations involving interest rate are clearly the important factors in determining the credit spreads of the notes.
DIRICHLET PROBLEMS IN A HALF-SPACE OF A HILBERT SPACE
Authors: PRIOLA ENRICO
Published: July 2002

We study a homogeneous infinite dimensional Dirichlet problem in a half-space of a Hilbert space involving a second-order elliptic operator with Hölder continuous coefficients. Thanks to a new explicit formula for the solution in the constant coefficients case, we prove an optimal regularity result of Schauder type. The proof uses nonstandard techniques from semigroups and interpolation theory and involves extensive computations on Gaussian integrals.
FERMI CONVOLUTION
Authors: ORAVECZ FERENC
Published: July 2002

Below a new kind of convolution is introduced for probability measures, whose combinatorics is related to non-crossing partitions without inner blocks other than singletons — the partitions corresponding to the fermionic creation and annihilation operators and Pauli's principle.
VIBRATION EFFECTS OF LIGHT-RAIL TRAIN-VIADUCT SYSTEM ON SURROUNDING ENVIRONMENT
Authors: XIA HE , CAO YANMEI , ZHANG NAN , QU JINGJIAN
Published: July 2002

The objective of this paper is to study the dynamic impacts of moving light-rail trains on viaduct bridges and the vibrations induced on the surrounding ground. The study is based on theoretical analysis and field experiment. The theoretical study is performed in two stages using a 2D interaction model of "train-bridge" system for obtaining the dynamic loads of moving trains on the bridge piers, and a 2D dynamic model of "pier-foundation-ground" system for analyzing the vibration responses of the surrounding ground. In the field experiment, the dynamic responses of bridge piers and the ground accelerations are measured at different distances under different train speeds.
SIMPLIFIED APPROACH FOR SEISMIC ANALYSIS OF STRUCTURES
Authors: VARMA VETO , REDDY G. R. , VAZE K. K. , KUSHWAHA H. S.
Published: July 2002

The seismic analysis of a structure using continuum mechanics approach may yield good results. However, this approach is difficult to apply for complex geometrical problems such as nuclear reactor containment building. To incorporate the entire structural behaviour, a full 3D model is best suited. However, a large number of modes are required to achieve at least 90% mass participation or frequency content up to 33 Hz. This consumes a large computational time due to large number of local modes present. Therefore, an equivalent lumped mass beam model, which as compared to 3D model, is much simpler and produces conservative global responses, has been considered in analysis. The lumped mass equivalent beam model of the system can be prepared after carrying out static analysis of 3D model using static energy equivalence approach. Forces and moments obtained by the seismic analysis of this beam model can be applied on the 3D model in order to obtain stresses in each element. It was found that the results obtained by this approach gives higher results because of higher mass participation. Experimental investigation is also performed on one of the case study to support the analysis. Hence it is concluded that analysis using beam model based on strain energy equivalence, in combination with 3D model is much simpler, economic and gives conservative results.
FLUCTUATION-ENHANCED GAS SENSING BY SURFACE ACOUSTIC WAVE DEVICES
Authors: SCHMERA GABOR , KISH LASZLO B.
Published: July 2002

This paper presents a new method for the detection, identification and quantitative analysis of gas molecules and their mixtures. The enhanced sensitivity and selectivity of this method allows the detection and identification of gases in amounts not previously detectable. This method is based on the spectral analysis of the dynamics of adsorbed molecules on surface acoustic wave (SAW) delay lines and resonators.
FRACTIONAL BROWNIAN MOTION AND STOCHASTIC EQUATIONS IN HILBERT SPACES
Authors: DUNCAN T. E. , PASIK-DUNCAN B. , MASLOWSKI B.
Published: July 2002

In this paper, stochastic differential equations in a Hilbert space with a standard, cylindrical fractional Brownian motion with the Hurst parameter in the interval (1/2,1) are investigated. Existence and uniqueness of mild solutions, continuity of the sample paths and state space regularity of the solutions, and the existence of limiting measures are verified. The equivalence of the probability laws for the solution evaluated at different times and different initial conditions and the convergence of these probability laws to the limiting probability are verified. These results are applied to specific stochastic parabolic and hyperbolic differential equations. The solution of a specific parabolic equation with the fractional Brownian motion only in the boundary condition is shown to have many results that are analogues of the results for a fractional Brownian motion in the domain.
Polynomial-time approximation schemes for geometric min-sum median clustering
Authors: Ostrovsky Rafail , Rabani Yuval
Published: July 2002

The Johnson--Lindenstrauss lemma states that
n
points in a
high-dimensional Hilbert space can be embedded with small
distortion of the distances into an
O
(log
n
)
dimensional space by applying a random linear transformation. We
show that similar (though weaker) properties hold for certain
random linear transformations over the Hamming cube. We use these
transformations to solve NP-hard clustering problems in the cube as
well as in geometric settings.More specifically, we address the
following clustering problem. Given
n
points in a larger set
(e.g., ℝ
d
) endowed with a distance function (e.g.,
L
2
distance), we would like to partition the data
set into
k
disjoint clusters, each with a "cluster center,"
so as to minimize the sum over all data points of the distance
between the point and the center of the cluster containing the
point. The problem is provably NP-hard in some high-dimensional
geometric settings, even for
k
= 2. We give polynomial-time
approximation schemes for this problem in several settings,
including the binary cube {0,1}
d
with Hamming distance,
and ℝ
d
either with
L
1
distance,
or with
L
2
distance, or with the square of
L
2
distance. In all these settings, the best
previous results were constant factor approximation guarantees.We
note that our problem is similar in flavor to the
k
-median
problem (and the related facility location problem), which has been
considered in graph-theoretic and fixed dimensional geometric
settings, where it becomes hard when
k
is part of the input.
In contrast, we study the problem when
k
is fixed, but the
dimension is part of the input.
How bad is selfish routing?
Authors: Roughgarden Tim , Tardos Éva
Published: July 2002

We consider the problem of routing traffic to optimize the performance of a congested network. We are given a network, a rate of traffic between each pair of nodes, and a latency function for each edge specifying the time needed to traverse the edge given its congestion; the objective is to route traffic such that the sum of all travel times---the total latency---is minimized.In many settings, it may be expensive or impossible to regulate network traffic so as to implement an optimal assignment of routes. In the absence of regulation by some central authority, we assume that each network user routes its traffic on the minimum-latency path available to it, given the network congestion caused by the other users. In general such a "selfishly motivated" assignment of traffic to paths will not minimize the total latency; hence, this lack of regulation carries the cost of decreased network performance.In this article, we quantify the degradation in network performance due to unregulated traffic. We prove that if the latency of each edge is a linear function of its congestion, then the total latency of the routes chosen by selfish network users is at most 4/3 times the minimum possible total latency (subject to the condition that all traffic must be routed). We also consider the more general setting in which edge latency functions are assumed only to be continuous and nondecreasing in the edge congestion. Here, the total latency of the routes chosen by unregulated selfish network users may be arbitrarily larger than the minimum possible total latency; however, we prove that it is no more than the total latency incurred by optimally routingtwiceas much traffic.
Personalized hypermedia and international privacy
Authors: Kobsa Alfred
Published: July 2002

Personalized hypermedia systems may be in conflict with privacy concerns of computer users, and with privacy laws that are in effect in many countries.
Culture class vs. culture clash
Authors: Marcus Aaron
Published: July 2002

The events of September 11, 2001, changed the perceptions of many people in the United States. One good result of this terrible day was people's increased awareness of and interest in other cultures, religions, and ways of thinking. In this process, user-interface development was catalyzed toward further maturity of its philosophy, principles, and techniques. We can't go back. Many people who are living outside the United States, or Americans who have traveled extensively abroad, are thankful for an increased global awareness of connectivity, conflicts, and possibilities of mutual cooperation. Much of their hope stems from understanding other cultures better and communicating with people better. User-interface developers may need to go to "culture class" in order to minimize culture clashes in their designs.
Regenerative steady-state simulation of discrete-event systems
Authors: Henderson Shane G. , Glynn Peter W.
Published: July 2002

The regenerative method possesses certain asymptotic properties that dominate those of other steady-state simulation output analysis methods, such as batch means. Therefore, applying the regenerative method to steady-state discrete-event system simulations is of great interest. In this paper, we survey the state of the art in this area. The main difficulty in applying the regenerative method in our context is perhaps in identifying regenerative cycle boundaries. We examine this issue through the use of the "smoothness index." Regenerative cycles are easily identified in systems with unit smoothness index, but this is typically not the case for systems with nonunit smoothness index. We show that "most" (in a certain precise sense) discrete-event simulations will have nonunit smoothness index, and extend the asymptotic theory of regenerative simulation estimators to this context.
Capacity and performance analysis of distributed enterprise systems
Authors: Aries James A. , Banerjee Subhankar , Brittan Marc S. , Dillon Eric , Kowalik Janusz S. , Lixvar John P.
Published: July 2002

Analytic and simulation models enhance the reengineering and tuning of large client/server distributed systems.
Flatlined
Authors: Denning Peter J.
Published: July 2002

Our propensity to create linear scales between opposing alternatives creates false dichotomies that hamper our thinking and limit our action.
Broadband to go
Authors: McGinity Meg
Published: July 2002

Providers know once customers go broadband, they'll never go back to the dark days of dialup.
Building big reliable web sites, (part 2)
Authors: Treese Win
Published: July 2002

In the last issue, we talked about the challenges of building big reliable Web sites. In this column, we'll look at the basics of how one actually goes about doing it.
A parts breakdown technique using list structures
Authors: Brian W. J.
Published: July 2002

List structured parts breakdown is proposed and discussed. Implementation facts are presented on operating program using these techniques.
The usability of everyday technology
Authors: Petersen Marianne Graves , Madsen Kim Halskov , Kjær Arne
Published: July 2002

Current work in the field of usability tends to focus on snapshots of use as the basis for evaluating designs. However, giving due consideration to the fact that everyday use of technology involves a process of evolution, we set out to investigate how the design of the technology may be used to support this. Based on a long-term empirical study of television use in the homes of two families, we illustrate how use continuously develops in a complex interplay between the users' expectations---as they are formed and triggered by the design---and the needs and context of useper se. We analyze the empirical data from the perspective of activity theory. This framework serves to highlight how use develops, and it supports our analysis and discussion about how design, the users' backgrounds, previous experience, and needs, and the specific context of use supports or hinders the development of use. Moreover, we discuss how the characteristics of the home settings, in which the televisions studied were situated, represent a challenge to usability work. The concluding discussion leads to a set of hypotheses relevant to designers and researchers who wish to tackle some of the aspects of usability of particular importance to development in the use of home technology.
Using the Alfa-1 simulated processor for educational purposes
Authors: Wainer Gabriel A. , Daicz Sergio , De Simoni Luis F. , Wassermann Demian
Published: July 2002

Alfa-1 is a simulated computer designed for computer organization courses. Alfa-1 and its accompanying toolkit allow students to acquire practical insights into developing hardware by extending existing components. The DEVS formalism is used to model individual components and to integrate them into a hierarchy that describes the detailed behavior of different levels of a computer's architecture. We introduce Alfa-1 and the toolkit, show how to extend existing components, and describe how to use Alfa-1 for educational purposes. We also explain how to assemble, link, and execute applications and how to test new extensions usingthe testing tools.