bluuebunny/crossref_metadata_2025 huggingface dataset:
M-FURCATIONS IN COUPLED MAPS
Authors: KIM SANG-YOON
Published: November 2004

We study the scaling behavior of M-furcation (M=2, 3, 4,…) sequences of Mn-periodic(n=1, 2, …) orbits in two coupled one-dimensional (1D) maps. Using a renormalization method, how the scaling behavior depends on M is particularly investigated in the zero-coupling case in which the two 1D maps become uncoupled. The zero-coupling fixed map of the M-furcation renormalization transformation is found to have three relevant eigenvalues δ, α, and M (δ and α are the parameter and orbital scaling factors of 1D maps, respectively). Here the second and third ones, a and M, called the “coupling eigenvalues”, govern the scaling behavior of the coupling parameter, while the first one δ governs the scaling behavior of the nonlinearity parameter like in the case of 1D maps. The renormalization results are also confirmed by a direct numerical method.
BANDSTRUCTURE EFFECTS IN VeryLEED
Authors: STROCOV V.N.
Published: November 2004

In VeryLEED regime (below 30 eV) the spectra of electron reflection on the surfaces of crystals are dominated by the elastic effects of bulk E(k) above the vacuum level. This is revealed when the reflected intensity is found by matching on the surface the wave-function in vacuum (plane waves) and in the solid (Bloch waves). Following reflectivity features versus energy and incidence angle, one can extract accurate and explicit information on upper E(k): the energies of extremes of bands along any Brillouin zone direction, and even whole bands along symmetry lines. This is illustrated with a profusion of experimental examples. The theoretical background and the experimental technique are surveyed. Capabilities of VeryLEED to generate the upper bands for PES (IPES) are outlined.
EXCITATION SPECTRUM OF QUANTUM DOT IN STRONG MAGNETIC FIELD
Authors: ANDREEV AL. A. , BLANTER YA. M. , LOZOVIK YU. E.
Published: November 2004

Microscopic theory of collective excitations of a quantum dot in a strong magnetic field is proposed. A complete analysis of diagrams in the perturbation theory over the Coulomb interaction is performed. The spectrum of low-lying excitations is calculated for the case of a parabolic quantum dot. It is shown to consist of three terms: single-particle drift, magnetoplasma and exciton ones, with the exciton term dominating the magnetoplasma one. In the framework of the semi-classical approach, the case of a non-parabolic quantum dot is also discussed. The experimental manifestations of the effects under investigation are discussed.
LOCAL ANALYSIS VIA THE REAL SPACE GREEN’S FUNCTION METHOD
Authors: WU SHI-YU , JAYANTHI CHAKRAM S.
Published: November 2004

A complete account of the development of the method of real space Green’s function is given in this review. The emphasis is placed on the calculation of the local Green’s function in a real space representation. The discussion is centered on a list of issues particularly relevant to the study of properties of complex systems with reduced symmetry.They include:

(i) the convergence procedure for calculating the local Green’s function of infinite systems without any boundary effects associated with an arbitrary truncation of the system;

(ii) a general recursive relation which streamlines the calculation of the local Green’s function;

(iii) the calculation of the eigenvector of selected eigenvalues directly from the Green’s function.

An example of the application of the method to carry out a local analysis of dynamics of the Au(511) surface is also presented.
DISORDER IN THE DISCRETE NONLINEAR SCHRÖDINGER EQUATION
Authors: MOLINA M.I. , TSIRONIS G.P.
Published: November 2004

We study the interplay of disorder and nonlinearity in condensed matter systems modeled by the paradigmatic discrete nonlinear Schrödinger equation and focus on selftrapping and transport properties. We start by analyzing the two most simple nonlinear disordered systems, viz. a nondegenerate nonlinear dimer and a perturbed degenerate dimer. We then consider the case of few nonlinear impurities embedded in a linear host and treat the stationary problem analytically. We conclude by examining the case of a one-dimensional nonlinear random binary alloy where we find absence of quasiparticle localization, except for large nonlinearity parameter values. The transmission of plane’ waves across a disordered nonlinear segment of this type shows a power-law decay as a function of the segment size.
TWO PARTICLE CORRELATIONS AND ORTHOGONALITY CATASTROPHE IN INTERACTING FERMI SYSTEMS
Authors: METZNER WALTER , CASTELLANI CLAUDIO
Published: November 2004

The wave function of two fermions, repulsively interacting in the presence of a Fermi sea, is evaluated in detail. We consider large but finite systems in order to obtain an unambiguous picture of the two-particle correlations. As recently pointed out by Anderson, in d≤2 dimensions the particles may be correlated even when situated on the Fermi surface. The “partial exclusion principle” for two particles with opposite spin on the same Fermi point is discussed, and related to results from the T-matrix approximation. Particles on different Fermi points are shown to be uncorrelated in d>1. Using the results for the two-particle correlations we find that the orthogonality effect induced by adding an extra particle to a (tentative) two-dimensional Fermi liquid is finite.
NON-HERMITIAN TUNNELING OF OPEN QUANTUM SYSTEMS
Authors: ANGELOPOULOU P. , BASKOUTAS S. , JANNUSSIS A. , MIGNANI R. , PAPATHEOU V.
Published: November 2004

We discuss some aspects of the time picture of tunneling for open quantum systems described by non-Hermitian (NH) Hamiltonians. The concept of sojourn time for such systems is introduced in the framework of the biorthonormal formalism. Due to the various definitions of probability density in the non-Hermitian case, we get three different sojourn times, two real and one complex. We consider as model of a dissipative NH system the complex, generalized parametric oscillator, for which we derive the exact expressions of the three sojourn times in terms of the Wei-Norman characteristic functions entering the non-unitary evolution operators. The special case of the inverted Caldirola-Kanai oscillator with complex friction parameter is investigated for an initial extended wavepacket. We also discuss the Landau-Zener-like transitions of the NH parametric oscillator, i.e. the dissipative tunneling through a dynamical barrier due to the perturbative effect of the damping.
FERROELECTRIC LIQUID CRYSTALS: FROM THE PLANE WAVE TO THE MULTISOLITON LIMIT
Authors: MUŠEVIČ I. , ŽEKŠ B. , BLINC R. , RASING TH.
Published: November 2004

In the presence of external fields or in restricted geometries, the originally continuous helical symmetry of the Sm C* phase is broken by the appearence of field- or geometry-induced soliton-like domain walls. As a result of this symmetry breaking, a crossover between the plane-wave-like and soliton-like regime occurs in both static and dynamic properties which is responsible for some remarkable phenomena such as field-induced optical biaxiality or a field-induced band structure of collective excitations. Whereas we find in the plane-wave-like regime a degenerate soft mode which splits below the Sm A→Sm C* transition into a symmetry recovering Goldstone-phason-mode and an amplitudon mode, we find in the soliton regime a splitting of the phason mode into acoustic and optic-like branches separated by a band gap. Within the same framework we also discuss other remarkable and extraordinary properties such as reentrant phases, Lifshitz points, one dimensional photonic band gaps and thickness dependent phase diagrams.
SADDLE-SPLAY ELASTICITY IN NEMATIC LIQUID CRYTALS
Authors: CRAWFORD GREGORY P. , ŽUMER SLOBODAN
Published: November 2004

The effect of the saddle-splay elastic constant K24 on nematic director-fields is a topic of fundamental interest for the elastic theory of liquid crystals and plays a vital role in device applications where nematic liquid crystals are confined to a curved geometry. The first measurement of K24 came more than sixty years after the pioneering work of Oseen, who made first steps toward the elastic theory of liquid crystals. Today the study of saddle-splay elasticity has become an important topic in liquid crystal physics. In this review we summarize the various methods used to measure K24 in curved geometries and present the detailed theory behind the measurements.
RECENT ADVANCES AND FUTURE DIRECTIONS OF NMR SPECTROSCOPY OF MOLECULES ORIENTED IN LIQUID CRYSTALS
Authors: KHETRAPAL C.L.
Published: November 2004

Recent interests in NMR spectroscopy of molecules oriented in liquid crystal solvents predominantly revolve around the developments of methods for (1) spectral simplification, (2) novel applications and (3) understanding of the solvent effects on molecular structure and function. A number of such results and their critical evaluations are presented, with emphasis on mixed liquid crystals of opposite diamagnetic susceptibility anisotropies, metal ion-ligand and weak molecular interactions and the discovery of novel liquid crystalline phase. Future directions of research, such as the use of ultra high magnetic fields, partially and perdeuterated samples and near magic angle spinning experiments, are highlighted.
A GENERAL VIEW OF METAL CLUSTERS AND ICOSAHEDRAL ALLOYS IN THE APERIODIC MULTIPLE TWINNING MODEL: CHEMICAL CONCENTRATION GRADIENTS, GROWTH RULE, INTERATOMIC DISTANCES AND NUCLEAR MAGNETIC RESONANCE
Authors: CONTI LUIGI G.
Published: November 2004

Recent experiments by electron diffraction and nuclear magnetic resonance (NMR) reported in the literature are consistent with the defective structure inherent to the aperiodic multiple twinning model proposed some years ago by the author for inhomogeneous metal clusters. A similar structural model is suggested for icosahedral (i) alloys, represented in this paper by i-Al—Mn, a binary system formally analogous to the metal-vacancy i-cluster. Determination of the mass density and interatomic distances for i-Al—Mn is easily accomplished from the strain distribution and the stoichiometric composition. A discussion of the nonzero nuclear quadrupole interaction of dilute quadrupolar nuclei in cubic crystals leads to a reexamination of Bloembergen and Rowland’s theory of NMR in cubic alloys and to a computation of the second-order quadrupole broadening of the 55 Mn NMR line in i-Al—Mn according to the model. Skin-depth effects are invoked in order to explain the observed variable intensity ratio of 55 Mn to 27 Al NMR lines in i-Al—Mn, as due to inhomogeneous quasicrystals differing in grain size.
ABELIAN HALL FLUIDS AND EDGE STATES: A CONFORMAL FIELD THEORY APPROACH
Authors: MARTINO A. DE , MUSTO R.
Published: November 2004

We show that a Coulomb gas Vertex Operator representation of 2D Conformal Field Theory gives a complete description of Abelian Hall fluids: as a Euclidean theory in two space dimensions leads to the construction of the ground state wave functions for planar and toroidal geometry and characterizes the spectrum of low energy excitations; as a 1+1 Minkowski theory gives the corresponding dynamics of the edge states. The difference between a generic Hall fluid and states of the Jain’s sequences is emphasized. In particular, the different structure of the lattice characterizing the indipendent Vertex Operators is exhibited; the presence, in Jain’s case, of of an [Formula: see text] extended algebra and the consequent propagation on the edges of a single charged mode and n−1 neutral modes is discussed.
PERTURBATION THEORY FOR THE ALFVÉN WAVE
Authors: YOSHIDA Z. , MAHAJAN S.M.
Published: November 2004

The Alfvén wave is the dominant low frequency transverse mode of a magnetized plasma. The Alfvén wave propagates along the magnetic field, and displays a continuous spectrum even in a bounded plasma. This is essentially due to the degeneracy of the wave characteristics, i.e. the frequency (ω) is primarily determined by the wave number in the direction parallel to the ambient magnetic field (k||) and is independent of the perpendicular wavenumbers. The characteristics, that are the direction along which the wave energy propagates, are identical to the ambient magnetic field lines. Therefore, the spectral structure of the Alfvén wave has a close relationship with the geometric structure of the magnetic field lines. In an inhomogeneous plasma, the Alfvén resonance (ω−cAk||=0; cA is the phase velocity of the Alfvén wave) constitutes a singularity for the defining wave equation; this results in a singular eigenfunction corresponding to the continuous spectrum. The aim of this review is to present an overview of the perturbation theory for the Alfvén wave. Emphasis is placed on those perturbations of the continuous spectrum which lead to the creation of point spectra. Such qualitative changes in the spectrum are relevant to many plasma phenomena. The first category of perturbations consists of nonideal effects such as the finite conductivity, kinetic effects arising from the finite electron inertia, and finite gyroradius. These effects add singular perturbations to the mode equation, and modify the spectrum dramatically. These modification, viz. the conversion of the continuous to the point spectrum, can lead to interesting physical phenomenon. A case in point is that of an electron beam propagating in a plasma which Cherenkov emits a left-hand circularly polarized Alfvén wave. The helicity of the ambient magnetic field imparts a frequency shift to the eigenmodes changing the critical velocity for Cherenkov emission. It, then, becomes possible for a sub-Alfvénic electron beam to excite a nonsingular Alfvén wave corresponding to a point spectrum. The second category comprises of geometric perturbations associated with higher dimensional inhomogeneity of the ambient field. Forbidden bands occur when a periodic modulation is applied. In a chaotic magnetic field, the weak localization of the wave occurs, resulting in a point spectrum.
IMPROVED PERFORMANCE OF THE HOPFIELD AND LITTLE NEURAL NETWORK MODELS WITH TIME DELAYED DYNAMICS
Authors: MAITI PRABAL K , DASGUPTA PRABIR K , CHAKRABARTI BIKAS K
Published: November 2004

We report the results of simulation of neural network models with the synaptic connections constructed using the Hebb’s rule and the dynamics determined by the internal field, which has a weighted contribution from the time delayed signals. We consider both the asynchronous (or Glauber; Hopfield) and synchronous (Little) dynamics. Our numerical results and the finite size variation study (for sizes N within the range 250 ≤N≤4000) support the previous indication [Sen and Chakrabarti, Phys. Lett.A162, 327 (1992)] of improved performance in the recall and overlap properties in the thermodynamic limit. It is identified that the time delayed term in the dynamics allows the network to come out of the spurious valleys in the “energy landscape” (defined without the delay term; Hopfield model). In an approximate analytical study of such models in the extreme dilution limit, the role of the time delayed term to suppress the (spin glass-like) noise is also indicated.
THERMAL CURRENTS FROM UNDOPED SEMI-INSULATING GaAs MONITORED BY CHARGE DEEP-LEVEL TRANSIENT SPECTROSCOPY
Authors: THURZO I. , GMUCOVÁ K. , DUBECKÝ F. , DARMO J.
Published: November 2004

Metal-semiconductor-metal (MSM) devices prepared from crystalline undoped semi-insulating GaAs were investigated by charge deep-level transient spectroscopy (QDLTS), while exciting the devices by electrical bias pulses in dark. Unlike current concepts of the QDLTS response, thermally stimulated currents were integrated from devices with GaAs crystals thinned down to or below 200 µm and equipped with Au electrodes. Au-GaAs-Au structures on 230 µm thick crystals exhibited standard QDLTS response on either cooling or heating between 100 K and 250 K. It is concluded that a macroscopic space charge region of width ≈10−7 m is formed at the Au/GaAs interface, as the dominant energy levels became ionized. Obtained results on the peaks of the thermally stimulated charge were correlated with those of potentially identical peaks observed via optical admittance transient spectroscopy (OATS).
SERIES EXPANSIONS FOR THE ISING MODEL COUPLED TO TWO HEAT BATHS
Authors: BAKAEV A. V. , KABANOVICH V. I.
Published: November 2004

We present an algorithm for generating high- and low-temperature expansions for non-equilibrium steady states in lattice spin models coupled to two thermal baths at different temperatures. For the Ising model on a square lattice with the sublattice temperature ratio α = Ta/Tb we construct the high-temperature expansion of energy to order eleven. The estimates of T c are in good agreement with the exact equilibrium result (at α = 1) and the existing Monte-Carlo simulations in non equilibrium cases (α = 2 and α = ∞).
SPACE–TIME ASPECTS OF QUASIPARTICLE PROPAGATION
Authors: LEVIEN RICHARD , NAYAK CHETAN , WILCZEK FRANK
Published: November 2004

We discuss how spin–charge separation is realized in a simple double-layer geometry, how mass renormalization affects time-of-flight in compressible Hall states, and how quantum drifts can reveal the effective charge, mass and quantum statistics in incompressible Hall states. We also discuss the possibility of observing the effect of fractional statistics directly in scattering. Finally we propose that, as a result of incompressibility and reflecting the fundamental charge–flux relation, charged probes induce macroscopic rotation of Hall fluids.
EXTINCTION OF SPIN INTERACTIONS IN THE 2D KONDO LATTICE
Authors: PAUL PRABASAJ , MATTIS DANIEL C.
Published: November 2004

A two-dimensional Kondo lattice with inter-site interaction is studied using a canonical transformation to eliminate interactions. Our approach is patterned on Bardeen and Pines' elimination of electron–phonon interaction. It is shown that interactions are eliminated at nonzero temperatures in the thermodynamic limit, in a manner differing radically from the case of phonons.
RELATIVE STABILITY OF SINGLE GRAPHITE SHEETS OF POSITIVE, NEGATIVE AND ZERO CURVATURE
Authors: BOURGEOIS L. N. , BURSILL L. A.
Published: November 2004

The relative stability of single graphite sheets of zero, positive and negative curvature is investigated through a simple model where both strain and dangling bond energy are taken into account. Although it is found that flat sheets are always more stable than negatively curved ones, calculations show that above a critical radius of curvature there is a crossover from positive to negative curvature as the more stable geometry for a single sheet. A maximum size for a negatively curved sheet is also predicted. Similarly, positive curvature is found to be energetically favored over zero curvature below some value of the curvature radius and above a certain number of atoms of the sheet. These results are discussed in view of available transmission electron microscopy observations of sp2 amorphous carbon.
COMPUTER SIMULATION STUDY OF A DISORDERED ONE-DIMENSIONAL NEMATOGENIC LATTICE MODEL WITH LONG-RANGE INTERACTIONS ISOTROPIC IN SPIN SPACE
Authors: ROMANO S.
Published: November 2004

We have considered a classical spin system, consisting of 3-component unit vectors, associated with a one-dimensional lattice {uk, k ∈ Z}, and interacting via translationally invariant pair potentials, isotropic in spin space, and of the long-range form [Formula: see text] where ∊ is a positive constant setting energy and temperature scales (i.e. T* = kBT/∊). Extending previous rigorous results, one can prove the existence of an ordering transition at finite temperature when 0 < σ < 1, and its absence when σ ≥ 1. We have studied the border case σ = 1, by means of computer simulation. Similarly to the magnetic counterparts of the present model, we found evidence suggesting a transition to a low-temperature phase with slow decay of correlations and infinite susceptibility, i.e. a Berezhinskiǐ–Kosterlitz–Thouless-like transition; the transition temperature was estimated to be Θ = 0.475 ± 0.005.
LOW NOISE PHOTON NUMBER MANIPULATION USING SEMICONDUCTOR LIGHT EMITTERS AND RECEIVERS
Authors: GOOBAR EDGARD , KARLSSON ANDERS , BJÖRK GUNNAR , NILSSON OLLE , RIGOLE PIERRE-JEAN
Published: November 2004

The photon number (intensity) of a light beam can be read out and amplified essentially without adding any noise. In this article we will describe recent proof-of-principle experiments using simple optoelectronic circuits. We also discuss the significance of these results with respects to applications in communication and quantum optics. The relation to quantum non-demolition measurement (QND) strategies is also discussed.
A SYMMETRY BASED STUDY OF POSITRON ANNIHILATION SPECTRA
Authors: ADAM GH. , ADAM S.
Published: November 2004

We describe a method for off-line analysis of spectra measured by two-dimensional angular correlation of annihilation radiation [Formula: see text] positron spectroscopy. The method takes into account, at all its stages, two salient data features: the piecewise constant discretization of the [Formula: see text] physical momentum distribution into square pixels, performed by the setup, and the occurrence of a characteristic [Formula: see text] projected symmetry of the positron–electron pair momentum distribution. Several validating criteria are derived which secure significantly increased reliability of the output.

The method is tested on [Formula: see text] spectra measured on (R)Ba 2 Cu 3 O 7−δ( R123 ; R= Y, Dy) single crystals. It resolves ridge Fermi surfaces [Formula: see text] up to 3rd Umklapp components on both kinds of R123 spectra. Moreover, on a c-axis-projected Y123 spectrum, measured at 300 K, it resolves a small but clear signature of the pillbox [Formula: see text] at the S point of the first Brillouin zone as well.
LONGITUDINAL FORCES IN WEBER'S ELECTRODYNAMICS
Authors: ASSIS A. K. T. , BUENO MARCELO
Published: November 2004

We analyze the existence of longitudinal forces with Weber's electrodynamics. We show that they exist. But they cannot explain the exploding wire phenomena due to their order of magnitude.
OPTIMAL PARALLEL ALGORITHMS FOR TRIANGULATED SIMPLE POLYGONS
Authors: HERSHBERGER JOHN
Published: November 2004

We provide optimal parallel solutions to several shortest path and visibility problems set in triangulated simple polygons. Let P be a triangulated simple polygon with n vertices, preprocessed to support shortest path queries. We can find the shortest path tree from any point inside P in O(log n) time using O(n/log n) processors. In the game bounds, we can preprocess P for shooting queries (a query can be answered in O(log n) time by a uniprocessor). Given a set S of m points inside P, we can find an implicit representation of the relative convex hull of S in O(log(nm)) time with O(m) processors. If the relative convex hull has k edges, we can explicitly produce these edges in O(log(nm)) time with O(k/log(nm)) processors. All of these algorithms are deterministic and use the CREW PRAM model.
MINIMUM POLYGON TRANSVERSALS OF LINE SEGMENTS
Authors: RAPPAPORT DAVID
Published: November 2004

Let S be used to denote a finite set of planar geometric objects. Define a polygon transversal of S as a closed simple polygon that simultaneously intersects every object in S, and a minimum polygon transversal of S as a polygon transversal of S with minimum perimeter. If S is a set of points then the minimum polygon transversal of S is the convex hull of S. However, when the objects in S have some dimension then the minimum polygon transversal and the convex hull may no longer coincide. We consider the case where S is a set of line segments. If the line segments are constrained to lie in a fixed number of orientations we show that a minimum polygon transversal can be found in O(n log n) time. More explicitely, if m denotes the number of line segment orientations, then the complexity of the algorithm is given by O(3mn+log n). The general problem for line segments is not known to be polynomial nor is it known to be NP-hard.
COMPLEXITY ASPECTS OF VISIBILITY GRAPHS
Authors: LIN YAW-LING , SKIENA STEVEN S.
Published: November 2004

In this paper, we consider two distinct problems related to complexity aspects of the visibility graphs of simple polygons. Recognizing visibility graphs is a long-standing open problem. It is not even known whether visibility graph recognition is in NP. That visibility graph recognition is in NP would be established if we could demonstrate that any n vertex visibility graph is realized by a polygon which can be drawn on an exponentially-sized grid. This motivates a study of the area requirements for realizing visibility graphs. In this paper, we prove:

• Θ(n3) area is necessary and sufficient to realize the complete visibility graph Kn.

• There exist visibility graphs which require exponential area to realize.

• Any maximal outerplanar graph of diameter d can be realized in O(d2 · 2d) area, which can be as small as O(n log2 n) for a balanced mop. Linear maximal outer-planar graphs can be realized in O(n8) area.

The second part of this paper considers the complexity of specific optimization problems on visibility graphs. Given a polygon P, we show that finding a maximum independent set, minimum vertex cover, or maximum dominating set in the visibility graph of P are all NP-complete. Further we show that for polygons P1 and P2, the problem of testing if they have isomorphic visibility graphs is isomorphism-complete. These problems remain hard when given the visibility graphs as input.
COMPUTATIONAL GEOMETRY COLUMN 26
Authors: O’ROURKE JOSEPH
Published: November 2004

An advance on Conway’s thrackle conjecture is described.
COMPUTATIONAL ASPECTS OF HELLY’S THEOREM AND ITS RELATIVES
Authors: AVIS DAVID , HOULE MICHAEL E.
Published: November 2004

This paper investigates computational aspects of the well-known convexity theorem due to Helly, which states that the existence of a point in the common intersection of n convex sets is guaranteed by the existence of points in the common intersection of each combination of d+1 of these sets. Given an oracle which accepts d+1 convex sets and either returns a point in their common intersection, or reports its non-existence, we give two algorithms which compute a point in the common intersection of n such gets. The first algorithm runs in O(nd+1T) time and O(nd) space, where T is the time required for a single call to the oracle. The second algorithm is a multi-stage variant of the first by which the space complexity may be reduced to O(n) at the expense of an increase in the time complexity by a factor independent of n. We also show how these algorithms may be adapted to construct linear and spherical separators of a collection of sets, and to construct a translate of a given object which either contains, is contained by, or intersects a collection of convex sets.
QUASI-ISOMETRIES AND AMALGAMATIONS OF TAME COMBABLE GROUPS
Authors: BRICK STEPHEN G.
Published: November 2004

We study the property of tame combability for groups. We show that quasi-isometries preserve this property. We prove that an amalgamation, A *C B, where C is finitely generated, is tame combable iff both A and B are. An analogous result is obtained for HNN extensions. And we show that all one-relator groups are tame combable.
PRESENTATION FOR THE VIRASORO ALGEBRA
Authors: GRAGERT P.K.H. , MARTINI R.
Published: November 2004

It is proved that the Virasoro algebra can be constructed starting with only two generators L3, L−2 subjected to 5 relations without neither introducing a central element c (charge) nor assuming any symmetry relation. Our proof is supported by substantial symbolic computations in REDUCE.
INDUCED AUTOMORPHISMS AND p-ELLIPTIC HYPERMAPS
Authors: BESSIS LAURENCE
Published: November 2004

The purpose of this paper is to describe the relationship between a given automorphism ψ of a hypermap (α, σ) and its projection (or induced automorphism) [Formula: see text] on the hypermap [Formula: see text], the latter being the quotient hypermap of (α, σ) by an automorphism group G. Moreover, we propose a generalization of the notion of hyperelliptic hypermaps by defining p-elliptic hypermaps.
DECAY BOUNDS FOR SOLUTIONS OF SECOND ORDER PARABOLIC PROBLEMS AND THEIR DERIVATIVES
Authors: PAYNE L.E. , PHILIPPIN G.A.
Published: November 2004

For a class of quasilinear parabolic equations, we derive in this paper a new maximum principle for the derivatives of solutions of homogeneous Dirichlet and Neumann initial boundary value problems. In the linear heat equation this principle is used to derive new explicit decay bounds for the absolute value of the gradient of the solution, and in the quasilinear problems, criteria are determined which imply that solutions decay exponentially. Explicit decay bounds are then established.
STABILITY OF SHOCK PROFILES FOR NONCONVEX SCALAR VISCOUS CONSERVATION LAWS
Authors: MEI MING
Published: November 2004

This paper is to study the stability of shock profiles for nonconvex scalar viscous conservation laws with the nondegenerate and the degenerate shock conditions by means of an elementary energy method. In both cases, the shock profiles are proved to be asymptotically stable for suitably small initial disturbances. Moreover, in the case of nondegenerate shock condition, time decay rates of asymptotics are also obtained.
QUALITATIVE BEHAVIOR OF SOLUTIONS OF A DEGENERATE NONLINEAR DRIFT-DIFFUSION MODEL FOR SEMICONDUCTORS
Authors: JÜNGEL ANSGAR
Published: November 2004

We are concerned with qualitative properties of transient solutions of a degenerate multi-dimensional quasi-hydrodynamic model for semiconductors with nonlinear diffusivities. For small time and sufficiently small initial and boundary data we show a local vanishing property of a solution. Furthermore it is shown that the carrier densities are bounded uniformly in time and are strictly positive uniformly in time if the recombination-generation rate satisfies some structural assumption. Finally we construct a Lyapunov functional in order to show convergence of the carrier distributions to the thermal equilibrium state as the time tends to infinity.
VIBRATIONS OF A MEMBRANE WITH MANY CONCENTRATED MASSES NEAR THE BOUNDARY
Authors: LOBO MIGUEL , PÉREZ EUGENIA
Published: November 2004

We consider the asymptotic behavior of the vibrations of a membrane occupying a domain Ω ⊂ ℝ2. The density, which depends on a small parameter ε, is of order O(1) out of certain regions where it is O(ε−m) with m>0. These regions, the concentrated masses with diameter O(ε), are located near the boundary, at mutual distances O(η), with η=η(ε)→0. We impose Dirichlet (respectively Neumann) conditions at the points of ∂Ω in contact with (respectively, out of) the masses. Depending on the value of the parameter m(m>2, m=2 or m<2) we describe the asymptotic behavior of the eigenvalues. Small eigenvalues, of order O(εm−2) for m>2, are approached via those of a local problem obtained from the micro-structure of the problem, while the eigenvalues of order O(1) are approached through those of a homogenized problem, which depend on the relation between ε and η. Techniques of boundary homogenization and spectral perturbation theory are used to study this problem.
EVOLUTION OF A SELF-GRAVITATING ROSSELAND GAS IN ONE DIMENSION
Authors: DUCOMET B.
Published: November 2004

We prove the existence of a global solution, for the evolution of a self-gravitating radiative gas (Rosseland’s model) in one space dimension. We then show that, for large time, the solution converges to the isothermal solution of the corresponding stationary problem.
WAVE PROPAGATION, UNIQUENESS AND SINGULARITIES AT INFINITY FOR AN UNBOUNDED LINEARLY VISCOELASTIC MATERIAL
Authors: CARBONARO BRUNO
Published: November 2004

Following a method used in two earlier papers,2,3 a general domain of dependence in equality is proved for inhomogeneous and anisotropic linearly viscoelastic solids, which furnishes the explicit link between the maximum propagation speed of disturbances in the body and the behavior at infinity of the acoustic tensor and the memory functions of the material, and allows to prove a global uniqueness theorem for the mixed problem of viscoelasticity in an unbounded reference configuration Ω. The method of proof applies regardless of whether the memory functions are assumed or not: moreover, no boundedness assumption is made on the material data.
SYSTEM MODELING BY A NEO-FUZZY-NEURON WITH APPLICATIONS TO ACOUSTIC AND CHAOTIC SYSTEMS
Authors: UCHINO EIJI , YAMAKAWA TAKESHI
Published: November 2004

This paper describes a new approach to system modeling by using a neo-fuzzy-neuron. The target system is modeled adaptively by simply feeding its input and output data to the neo-fuzzy-neuron, whose basic principle was proposed by the authors in 1992. Firstly, the neo-fuzzy-neuron is applied to the restoration of a saturated and/or intermittent speech or chaotic signal to show its actual effectiveness. It is then enhanced in order to get a better generalization capability. The enhanced version of the neo-fuzzy-neuron could facilitate to identify clearly the nonlinear chaotic system, and could most likely predict the future behavior of the system. The neo-fuzzy-neuron was further applied to the identification of actual sound insulation systems. The application was a success and provided promising results.
A DISTRIBUTED COOPERATING CONSTRAINTS SOLVING SYSTEM
Authors: MARTI PHILIPPE , RUEHER MICHEL
Published: November 2004

An appropriate combination of symbolic and numeric solvers often makes it possible to solve problems that none of these solvers can tackle alone. In this paper, we specify a cooperative architecture which allows using concurrently heterogeneous solvers when handling constraints over the reals. This architecture is based upon agents that communicate via asynchronous message passing. Agents are synchronized when a failure or a success occurs. Disjunctive constraints are handled by backtracking. Operational semantics and terminating conditions of such systems are discussed. Implementation issues are addressed. We end the presentation by several examples and give some computational results from a first prototype.
ECSIM: DISCRETE EVENT SIMULATION USING EVENT CALCULUS
Authors: MISSIAEN LODE R.
Published: November 2004

This paper presents the theory and implementation of a logic based discrete event simulation system ECSIM, Event Calculus SIMulation. ECSIM’s representation language is PROLOG extended with temporal predicates derived from the event calculus. The theory defines the truth value of a property given a history of events. ECSIM can represent actions that happen at a particular point in time, and activities that happen over a period of time; it can represent properties that change discretely and continuously over time. ECSIM’s scheduling algorithm uses activity scanning to generate event notices for all future activities. ECSIM’s major distinction with other simulation systems is its reference to the complete history of simulated time. A given event schedule can be analyzed by deriving the properties of the world at any time in the simulated history. ECSIM’s logic programming framework enables classical simulation to be extended with explanation generation, inductive learning, planning, decision support, simulation of intelligent agents, and symbolic simulation.
A DEVELOPMENT FRAMEWORK AND VERIFICATION METHODOLOGIES FOR KNOWLEDGE-BASED SYSTEMS
Authors: JANG H.-C.
Published: November 2004

In this paper, we present a development framework and verification methodologies for knowledge-based systems (KBSs) with real-time systems as our target system. The framework originates from an integration of three software development paradigms: rapid prototyping, operational specification, and transformational implementation. Based on this framework, we present RT-FRORL as a formal requirements specification language which exploits knowledge representation techniques as an aid in the specification, development, and verification of a KBS for real-time systems. RT-FRORL uses a combination of resolution refutation, anomaly detection matrix, and algorithms methods to verify a number of properties which might exist in KBSs. By incorporating RT-FROHL and its verification methods with the underlying framework, it lays a very strong foundation to deal with the current issues in KBSs verification.
KYDON VISION SYSTEM: THE ADAPTIVE LEARNING MODEL
Authors: MERTOGUNO J.S. , BOURBAKIS N.G.
Published: November 2004

In this paper, an adaptive learning model for an autonomous vision system multi-layers architecture, called Kydon, are presented, modeled, and analyzed. In particular two critical (deletion and saturation) points on the learning curve are evaluated. These points represent two extreme states on the learning process. The Kydon architecture consists of ‘k’ layers array processors. The lowest layers consists of lower-level processing layers, and the rest consists of higher-level processing layers. The interconnectivity of the PEs in each array is based on a full hexagonal mesh structure. Kydon uses graph models to represent and process the knowledge, extracted from the image. The knowledge base of Kydon is distributed among its PE’s. A unique model for evolving knowledge base has been developed especially for Kydon in order to provide it with some intelligence properties.
DYNAMICS FOR A FUNDAMENTAL PROBLEM OF BIOLOGICAL INFORMATION PROCESSING
Authors: STARK W. RICHARD
Published: November 2004

This paper presents results on the dynamics of asynchronous irregular cellular automata (as representations of natural information-processing systems). It is an approach to explaining global dynamics from local dynamics without the use of unrealistic intermediate structure (i.e., without synchronization or regular communication). The unrealistic intermediate structure is replaced by the the realistic assumption that local behavior is entropy reducing (an idea of E. Schrödinger).

It has been shown that, for systems composed of cells programmed as cyclic finite-state automata, the observed global oscillation can be explained in terms of the structure of attractors in the global state space. The degree of local connectivity (i.e., of communication between cells) is shown here to determine the size of global attractors, and in turn the sharpness of global behavior. However, the primary result here is the extension of these results to systems whose cells are programmed as arbitrary strongly connected automata. Finally, these phenomena are demonstrated by the simulations.
GENE CLASSIFICATION ARTIFICIAL NEURAL SYSTEM
Authors: WU CATHY H. , CHEN HSI-LIEN , CHEN SHENG-CHIH
Published: November 2004

A gene classification artificial neural system has been developed for rapid annotation of the molecular sequencing data being generated by the Human Genome Project. Three neural networks have been implemented, one full-scale system to classify protein sequences according to PIR (Protein Identification Resources) superfamilies, one system to classify ribosomal RNA sequences into RDP (Ribosomal Database Project) phylogenetic classes, and one pilot system to classify proteins according to Blocks motifs. The sequence encoding schema involved an n-gram hashing method to convert molecular sequences into neural input vectors, a SVD (singular value decomposition) method to compress vectors, and a term weighting method to extract motif information. The neural networks used were three-layered, feed-forward networks that employed back-propagation or counter-propagation learning paradigms. The system runs faster by one to two orders of magnitude than existing method and has a sensitivity of 85 to 100%. The gene classification artificial neural system is available on the Internet, and may be extended into a gene identification system for classifying indiscriminately sequenced DNA fragments.
A String Theory for 3-Manifolds with a Kleinian Action
Authors: Lins Sóstenes L.
Published: November 2004

In this paper we show that a class of orientable 3-manifolds can arise as (and be presented by) the “interaction of charged strings”. The presentation is very concise and it encodes complete information for producing the manifold as the union of closed balls, by providing instructions on how to identify the boundaries of these balls.

The central issue of considering this class of manifolds is that (often) the string presentation is capable of revealing the structure of the manifolds in the sense of displaying ways to form them as the “interaction of smaller” closed manifolds in the class.

We also prove some Theorems on the recognition of sufficiently large 3-manifolds. The essential torus, which characterizes such manifolds arises simply as an special pair of “segments” (which are special connected substrings). Cutting along such torus, is internal to the the string presentation and it suggests a natural way to close the boundary of the resulting manifold.

Finally, we use the string presentation theory to display a complete catalogue of closed orientable 3-manifolds whose fundamental groups are not cyclic nor free products and which have “gem-complexity” at most 13.
A HIERARCHICAL DECOMPOSITION OF CHOQUET INTEGRAL MODEL
Authors: SUGENO MICHIO , FUJIMOTO KATSUSHIGE , MUROFUSHI TOSHIAKI
Published: November 2004

In this paper we give a nesessary and sufficient condition for a Choquet integral model to be decomposable into an equivalent hierarchical Choquet integral model constructed by hierarchical combinations of some ordinary Choquet integral models. The condition is obtained by Inclution-Exclusion Covering (IEC). Moreover we show some properties on the set of IECs.
ON THE MAXIMUM-ENTROPY PROBABILITY WHICH IS CONSISTENT WITH A CONVEX CAPACITY
Authors: JAFFRAY JEAN-YVES
Published: November 2004

The solution of Meyerowitz, Richman and Walker to the problem of determining the maximum-entropy probability consistent with a belief function (an ∞-monotone capacity) is shown to remain valid in the case of a convex (i.e., 2-monotone) capacity.
APPROXIMATE REASONING ABOUT PRIORITIES OF IMPRECISE CONFLICTING REQUIREMENTS
Authors: YEN JOHN , LIU XIAOQING
Published: November 2004

Elasticity in an imprecise requirement needs to be captured to enable the trade-off analysis of conflicting requirements. One of the most important issues in the trade-off analysis of conflicting requirements is to understand their priorities. Requirement analysts need to know not only the relative ordering of requirements based on their importance but also how much a requirement is more important than another requirement in order to achieve an effective trade-off between conflicting requirements. Existing formal methods for requirement engineering are limited in addressing these issues. This paper presents a formal methodology for reasoning about their priority by analyzing the customer’s trade-off preference among imprecise conflicting requirements. The elasticity in imprecise requirements is captured using fuzzy logic. Conflicting and cooperative relationships are classified to detect the conflicts between requirements. Multiple requirements are combined based fuzzy multi-criteria decision making techniques. We have also developed a possibilistic reasoning framework for inferring the lower bound of relative priority from case analysis. Consistency and nonredundancy criteria are established to facilitate the aggregation of possibilistic statement on the lower bounds of relative priority. Finally, we describe a process for transforming the lower bounds of relative priority into weights of importance so that they can be used in the aggregation of conflicting requirements to resolve conflicts.
TOWARDS THEORETICAL FOUNDATIONS OF SOFT COMPUTING APPLICATIONS
Authors: NGUYEN HUNG T. , KREINOVICH VLADIK
Published: November 2004

The original idea of fuzzy logic and other soft computing methodologies was to handle the situations in which our knowledge is not precise. Usually, real numbers are used to describe degrees of belief. In practice, only approximate values of the degrees of belief are known, while the existing soft computing formalisms are usually based on the assumption that we know the exact values of these degrees. This difference creates a gap between the theory and applications. In this paper, we outline the theoretical foundations aimed at bridging this gap.
TEXTURE SEGMENTATION: AN UNSUPERVISED APPROACH
Authors: SHIRVAIKAR MUKUL V. , TRIVEDI MOHAN M.
Published: November 2004

The segmentation of scenes into perceptually meaningful partitions has been a basic problem in image understanding, especially when unsupervised methodology has been desired. A novel unsupervised segmentation approach based on texture is developed. The texture model is based on sets of gray level cooccurence (GLC) matrices rather than measures extracted from them. The algorithmic constituents for the segmentation scheme: choice of seed regions, normalized match distances between texture models, region homogeneity, and aggregation criteria are systematically developed. The unsupervised algorithm works so that “seed” regions are discovered by an image search process. Initial estimates of the texture model prototypes are automatically computed for each “seed” region, and classification thresholds are based on the variance of the model over the “seed” region. An aggregation process then results in regions being successively classified and segmented “out” of the image. This recursive process of segmentation is continued until all pixels are classified. The segmentation strategy was tested successfully on natural texture mosaics. The results are analytically presented. These experiments demonstrate that the unsupervised process can correctly identify the perceptual constituents of the image based on texture.
MODELING BUSINESS PROCESSES OVER OBJECT
Authors: HARTEL PETER , JUNGCLAUS RALF
Published: November 2004

The focus of this paper is on the modeling of application and business process in Cooperative Information Systems. Such processes use several resources and services to achieve a common, global system goal. We integrate the proposed concepts into the framework of a formal object-oriented specification language (TROLL). The goals of our approach are to provide additional modeling support for business and application processes, to explain these processes in the underlying framework and to couple tightly the modeling of global processes and the modeling of structural aspects of the system.
AGENT ORGANIZATION AND COMMUNICATION WITH MULTIPLE ONTOLOGIES
Authors: TAKEDA HIDEAKI , IINO KENJI , NISHIDA TOYOAKI
Published: November 2004

In this paper, we discuss how ontology plays roles in building a distributed and heterogeneous knowledge-base system. First, we discuss relationship between ontology and agents in the [Formula: see text] which is a framework of knowledge sharing and reuse based on a multi-agent architecture. Ontology is a minimum requirement for each agent to join the [Formula: see text]. Second, we explain mediation by ontology to show how ontology is used in the [Formula: see text]. A special agent called mediator analyzes undirected messages and infer candidates of recipient agents by consulting ontology and relationship between ontology and agents. Third, we model ontology as combination of aspects each of which can represent a way of conceptualization. Aspects are combined either as combination aspect which means integration of aspects or category aspect which means choice of aspects. Since ontology by aspect allows heterogeneous and multiple descriptions for phenomenon in the world, it is appropriate for heterogeneous knowledge-base systems. We also show translation of messages as a way of interpreting multiple aspects. A translation agent can translate a message with some aspect to one with another aspect by analyzing dependency of aspects. Mediation and translation of messages are important to build agents easily and naturally because less knowledge on other agents is requested for each agent.