bluuebunny/crossref_metadata_2025 huggingface dataset:
COMPUTER ALGEBRA, SYMMETRY ANALYSIS AND INTEGRABILITY OF NONLINEAR EVOLUTION EQUATIONS
Authors: GERDT VLADIMIR P.
Published: November 2004

A computer algebra-aided symmetry approach to investigating integrability of polynomial-nonlinear evolution equations in one-temporal and one-spatial dimensions is presented. The approach is based on verifying the existence of higher conservation laws and symmetries. If the equations contain arbitrary numerical parameters, the problem of selection of all the integrable cases is reduced to the solving polynomial equations in those parameters. The Gröbner basis technique is used in order to simplify and to solve such polynomial systems which typically have infinitely many solutions.
THE PATH-INTEGRAL QUANTUM SIMULATION OF HYDROGEN IN METALS
Authors: GILLAN M. J. , CHRISTODOULOS F.
Published: November 2004

The path-integral method for simulating quantum many-body systems is outlined, emphasising the recently developed quantum transition state theory (QTST) for calculating transition rates. Recent applications of path-integral simulation to metal-hydrogen systems are described. It is shown how QTST applied through path-integral simulation allows the calculation of the temperature-dependent diffusion coefficient of hydrogen and its isotopes in metals. The new methods show that the change of activation energy experimentally observed in some systems arises from the cross-over between quantum and classical behaviour.
PHYSICS EDUCATION: A SURVEY OF PROBLEMS AND POSSIBLE SOLUTIONS
Authors: VELARDE MANUEL G.
Published: November 2004

How is it that education all levels is apparently and objectively so bad today? I recall a few provocative opinions on the matter of physics education together with possible solutions.
ALGORITHMS FOR MONTE CARLO SIMULATIONS OF THE ISING MODELS ON A SIMPLE CUBIC LATTICE
Authors: KAWASHIMA NAOKI , ITO NOBUYASU , KANADA YASUMASA
Published: November 2004

The vectorized Monte Carlo algorithm by multi-spin coding is extended to the ±J Ising spin glass model on a simple cubic lattice in a magnetic field. Explicit logical expression is given for this algorithm. In addition, shorter logical expressions are found in some special cases.

They are given for the heat-bath method under the general condition and for the Metropolis method under the condition, H = 0.
ORDERING KINETICS BY VACANCIES
Authors: VIVES EDUARD , PLANES ANTONI
Published: November 2004

Domain growth dynamics in binary alloys undergoing an order-disorder phase transition is revised. After a summary of the state-of-the-art of the problem, we focus on the Monte Carlo simulation results. The usual atom-exchange dynamics is compared with a more realistic vacancy driven dynamics. Results suggest that the expected Allen-Cahn growth law might be modified by this more realistic dynamics.
A VECTORIZED ALGORITHM FOR MOLECULAR DYNAMICS OF SHORT RANGE INTERACTING PARTICLES
Authors: BUCHHOLTZ VOLKHARD , PÖSCHEL THORSTEN
Published: November 2004

We report on a lattice based algorithm, completely vectorized for molecular dynamics simulations. Its algorithmic complexity is of the order O(N), where N is the number of particles. The algorithm works very effectively when the particles have short range interaction, but it is applicable to each kind of interaction. The code was tested on a CRAY YMP EL in a simulation of flowing granular material.
FLUCTUATIONS OF CHERN-SIMONS NUMBERS IN THE SU(2) HIGGS MODEL
Authors: KARSCH F. , LAURSEN M. L. , NEUHAUS T. , PLACHE B.
Published: November 2004

We investigate vacuum transitions in lattice higgs models at finite temperature. The 2 dimensional U(1) Higgs model is used as a toy model. In the 4 dimensional SU(2) Higgs model the region of the phase transition and temperatures above it are considered. The couplings (β, κ, λ) = (2.25, 0.27, 0.5) and (8.0, 0.12996, 0.0017235) correspond to masses in lattice units (aσmH, aσmw) of (0.02, 0.05) and (0.2,0.2), respectively. The algorithm is described and a parallelized version is proposed. Taking the influence of the finite lattice into account we discuss temperature effects. We compare our results with perturbative estimates and claim that they link low and high temperature approximations.
UKQCD — RECENT RESULTS AND FUTURE PROSPECTS
Authors:   UKQCD COLLABORATION, KENWAY RICHARD
Published: November 2004

After a brief description of the UKQCD Project, I review some of our recent results for quenched QCD and conclude with some remarks about our future plans and prospects.
AN IMPROVEMENT OF MAEKAWA'S MUTUAL EXCLUSION ALGORITHM TO MAKE IT FAULT-TOLERANT
Authors: BOUABDALLAH ABDELMADJID , KÖNIG JEAN-CLAUDE
Published: November 2004

In this paper, we present an algorithm to achieve mutual exclusion in distributed systems. Our algorithm tolerates up to t − 1 arbitrary node failures without executing any recovery procedure and requires [Formula: see text] messages in a network of n nodes.
ON ASYNCHRONOUS AVOIDANCE OF DEADLOCKS IN PARALLEL PROGRAMS
Authors: DOROSHENKO A. E.
Published: November 2004

A number of approaches to asynchronous communication in parallel programs based on both data dependence analysis and buffering techniques are briefly described. A criterion for automatically resolving some classes of deadlocks by means of asynchronous data exchanges is established and examples showing the comparative power of the approaches for deadlock avoidance are presented.
COLLECTING INFORMATION IN GRADED ORDERED SETS
Authors: FON-DER-FLAASS DMITRI , RIVAL IVAN
Published: November 2004

We consider a set of computers with precedence constraints (an ordered set) in which stored information can be passed, serially or in parallel, from one computer to any other which is an immediate successor. When is it possible to organize information transmission so that each computer receives all information from its predecessors, without duplication?
A LOWER BOUND FOR ORDER-PRESERVING BROADCAST IN THE POSTAL MODEL
Authors: MACKENZIE PHILIP D.
Published: November 2004

In the postal model of message passing systems, the actual communication network between processors is abstracted by a single communication latency factor, which measures the inverse ratio of the time it takes for a processor to send a message and the time that passes until the recipient receives the message. In this paper we examine the problem of broadcasting multiple messages in an order-preserving fashion in the postal model. We prove lower bounds for all parameter ranges and show that these lower bounds are within a factor of seven of the best upper bounds. In some cases, our lower bounds show significant asymptotic improvements over the previous best lower bounds.
EFFICIENT MULTIPLE-ITEM BROADCAST IN THE LogP MODEL
Authors: SUBRAMONIAN RAMESH , VENKATASUBRAMANYAN NARAYAN
Published: November 2004

A common arising problem in many parallel algorithms is broadcast. Many multiprocessors do not have dedicated hardware for this purpose. In this paper, we address the problem of simulating multiple-item broadcast by point-to-point message transmission, where a source processor has many messages which it wishes to disseminate to P−1 other processors. In a step, a processor can send at most one item from among those in its possession and receive at most one item. An item is received at most L steps after it is sent. The goal is to find a schedule that achieves the broadcast in minimum time. We improve on previous results by developing a simpler and almost optimal solution which makes no assumptions about L or P. We also provide a bound on the performance degradation when the latency, L, is allowed to vary.
DEGREE-BOUNDED SPANNERS
Authors: CAI LEIZHEN , KEIL J. MARK
Published: November 2004

Given a graph G, a spanning subgraph H of G is a t-spanner if for every edge xy of G, the distance in H between x and y is at most t. Spanners have applications in communication networks, distributed systems, parallel computation, and other areas. This paper is concerned with the complexity of determining whether a graph contains a t-spanner whose maximum degree is at most Δ, where Δ, t≥2 are fixed integers. The problem is shown to be NP-complete for any fixed Δ≥4 and t≥2, and linear for Δ=2 and any fixed t≥2. The problem for Δ=3 is open. Furthermore, if the t-spanner in the problem is required to be a tree, then the problem becomes linear. The problem also becomes linear when input graphs are partial k-trees for some fixed integer k.
A PERFORMANCE EVALUATION OF ADAPTIVE ROUTING IN BIDIMENSIONAL CUT-THROUGH NETWORKS
Authors: ARRUABARRENA A. , BEIVIDE R. , IZU C. , MIGUEL J.
Published: November 2004

The performance of the communication network of a massively parallel processor depends, among other parameters, on the network topology, the message flow control and the routing mechanisms. This paper analyses the gains in average message latency and maximum sustained throughput that can be achieved using an adaptive routing strategy instead of an oblivious one. Two different bidimensional topologies have been studied, mesh and torus, using cut-through message flow control. First, we have simulated an ideal case in which there is no limit to the temporary storage capacity of the routing node. Then, a more realistic design, that implies the implementation of a deadlock avoidance technique, is analysed. To assure deadlock-free routing, the network is split into several virtual networks. Results show that adaptive routing is not a good election with this kind of networks. The torus topology shows potentially better results than the mesh. In any case, a different deadlock avoidance technique should be implemented if these potential gains are to be exploited.
QUANTUM GEOMETRY OF DIRAC FERMIONS
Authors: KORCHEMSKY G. P.
Published: November 2004

A bosonic path integral formalism is developed for Dirac fermions interacting with a non-Abelian gauge field in D-dimensional Euclidean space–time. The representation for the effective action and correlation functions of interacting fermions as sums over all bosonic paths on the complex projective space CP2d−1 (2d = 2[D/2]) is derived where the whole of the spinor structure is absorbed by the one-dimensional Wess–Zumino term. It is the Wess–Zumino term that ensures all necessary properties of Dirac fermions under quantization, i.e. quantized values of the spin, Dirac equation, and Fermi statistics.
THE CUBIC MATRIX MODEL WITH IMAGINARY COUPLING AND 2D GRAVITY
Authors: SAADI MAHA , ZEMBA GUILLERMO
Published: November 2004

We study the continuum properties of the Hermitian one-matrix model defined by a cubic potential with imaginary coupling, using the orthogonal polynomials and loop-equation approaches. The model is well defined mathematically and has a continuum limit which cannot be naively interpreted as pure gravity since each term of the sum over surfaces is not positive-definite. Nevertheless, the model may be considered as an analytic continuation of the standard matrix-model formulation of gravity. We study in detail the conditions under which the analytic continuation may be performed. In particular, the specific heat is found to obey a Painlevé equation. Although we find a solution that is compatible, as far as global stability is concerned, with the one proposed by David, it is not completely clear that the two solutions are the same.
THE CONFORMAL BOOTSTRAP AND SUPER W ALGEBRAS
Authors: FIGUEROA-O'FARRILL JOSÉ M. , SCHRANS STANY
Published: November 2004

We undertake a systematic study of the possible extensions of the N = 1 super Virasoro algebra by a superprimary field of spin [Formula: see text]. Besides new extensions, which exist only for specific values of the central charge, we find a new nonlinear algebra (super W2) generated by a spin 2 superprimary which is associative for all values of the central charge. Furthermore, the spin 3 extension is argued to be the symmetry algebra of the m = 6 super Virasoro unitary minimal model, by exhibiting the (A7, D4)-type modular invariant as diagonal in terms of extended characters.
TARGET-SPACE PROPERTIES OF TOPOLOGICAL CONFORMAL FIELD THEORIES
Authors: GIVEON AMIT , SMIT DIRK-JAN
Published: November 2004

Target-space properties of string backgrounds corresponding to topological conformal field theories are discussed. The topological string background is obtained from a "twisting" of an N = 2 superconformal field theory describing an ordinary background of the superstring. Thus, we are able to relate the duality symmetries of topological backgrounds with N = 2 backgrounds.
RENORMALIZATION GROUP FLOWS IN NONPERTURBATIVE 2D QUANTUM GRAVITY
Authors: FUCITO F. , MARTELLINI M.
Published: November 2004

We study the existence of solutions of the string equations which are pole-free on the positive real axis and exhibit such a solution following the work of Boutroux. We further study, using perturbation theory, the flows among different models and we find that there is no flow between the k=2 and k=3 theories. Moreover, we develop a nonperturbative renormalization-group scheme to extract the scaling behavior of the partition function of the k=2 model under perturbations. The key idea is to reinterpret the recent formulation, as Virasoro constraints, of the string-loop equations as generalized Callan-Symanzik renormalization-group equations.
WEYL ANOMALY AND CURCI-PAFFUTI THEOREM FOR σ MODELS ON MANIFOLDS WITH BOUNDARY
Authors: BEHRNDT K. , DORN H.
Published: November 2004

We generalize the relation of the Weyl-anomaly coefficients to renormalization-group functions, and the Curci-Paffuti relation to the case of two-dimensional σ models on manifolds with boundary. The analysis is based on the use of minimal subtraction in a regularization with a dimensional cutoff. The renormalization-group functions are different on and off the boundary. This explicit dependence on the position in two-dimensional space raises serious problems for a straightforward string interpretation of the model if fields corresponding to excitations of both open and closed strings are involved.
QUANTUM BUNDLES AND THEIR SYMMETRIES
Authors: BALACHANDRAN A.P. , MARMO G. , SIMONI A. , SPARANO G.
Published: November 2004

Wave functions in the domain of observables such as the Hamiltonian are not always smooth functions on the classical configuration space Q. Rather, they are often best regarded as functions on a G bundle EG over Q or as sections of an associated bundle. If H is a classical group which acts on Q, its quantum version HG, which acts on EG, is not always H, but an extension of H by G. A powerful and physically transparent construction of EG and HG, where G= U(1) and H1(Q, Z)=0, has been developed using the path space [Formula: see text]. ([Formula: see text] consists of paths on Q from a fixed point.) In this paper we show how to construct EG and HG when G is U(1) or U(1)×π1(Q) and there is no restriction on H1(Q, Z). The method is illustrated with concrete examples, such as a system of charges and monopoles. We argue also that [Formula: see text] is a sort of superbundle from which a large variety of bundles can be obtained by imposing suitable equivalence relations.
NONLINEAR EVOLUTION EQUATIONS AND THE PAINLEVÉ TEST
Authors: STEEB W.-H. , EULER N.
Published: November 2004

A survey is given of new results of the Painlevé test and nonlinear evolution equations where ordinary- and partial-differential equations are considered. We study the semiclassical Jaynes-Cumming model, the energy-eigenvalue-level-motion equation, the Kadomtsev-Petviashvili equation, the nonlinear Klein-Gordon equation and the self-dual Yang-Mills equation.
GAUGE-COVARIANT WESS-ZUMINO ACTIONS FOR SUPER p-BRANES IN SUPERSPACE
Authors: IVANOV E.A. , KAPUSTNIKOV A.A.
Published: November 2004

We present a general method of constructing manifestly world-volume supersymmetric actions of super p-branes, starting from some higher-dimensional field theories in which the partial breaking of global supersymmetry (PBGS) comes about. Our approach is based upon a substitution of the superspace coordinates which relates linear and nonlinear realizations of PBGS. As instructive examples we consider the massive d=2 superparticle (p=0) and d=4 superstring (p=1). The relevant world-line and world-sheet superfied actions naturally appear as a long-wavelength limit of the superfield actions of some two- and four-dimensional supersymmetric field theories possessing topologically nontrivial soliton solutions. The corresponding topological charges prove to enter the super p-brane actions as the coupling constants. We also give a new general Wess-Zumino-type representation of the d=2 superparticle action via the world-line superfields. It respects invariances both under the target space Poincaré supersymmetry and the gauge group of general reparametrizations of the world-line superspace. In one gauge, it is reduced to the standard PBGS form while in another, it gives rise to a very simple action which displays manifest world-line superconformal symmetry and is directly related to the familiar component action of the superparticle. The fermionic κ-symmetry of the latter can be identified with the odd sector of superconformal symmetry. This identity suggests a simple recipe for building higher-order κ-invariant corrections to the minimal superparticle action.
EIGENVALUE TUNNELING IN MATRIX MODELS
Authors: LECHTENFELD OLAF
Published: November 2004

We investigate the nonperturbative physics of the zero-dimensional random Hermitian matrix model, using semiclassical analysis as well as orthogonal polynomials. Finite-N tunneling leads to a unique equilibration of the Dyson gas of eigenvalues and dissolves a fictitious family of N=∞ saddle points. We present a mean-field potential for the limiting multiple-arc eigenvalue distribution. The sequence of the orthogonal-polynomial recursion coefficients Rk is characterized by the critical points of the matrix potential. Its large-N limit can show regions of smooth, quasi-periodic and seemingly chaotic behavior. The tunneling competition between nondegenerate potential wells is the origin of the unpredictability.
FUNCTIONAL DIFFERENTIAL REALIZATION OF THE SU(2) KAC–MOODY ALGEBRA
Authors: BAAQUIE B. E.
Published: November 2004

We derive an explicit realization of the SU(2) Kac–Moody algebra based on the bosonic coordinates of the Kac–Moody group manifold. Kac–Moody commutation equations are exactly evaluated for the SU(2) case. Normal-ordering is not used in these derivations.
TEMPERATURE EFFECT AND COHERENT EFFECT IN SUPERSYMMETRY
Authors: XU CAI , ZHOU ZHUOMEI
Published: November 2004

By using thermo-field dynamics, the temperature effect in supersymmetry is discussed. The supercoherent states at zero temperature, which are determined as the eigenstates of a supersymmetric annihilation operator, are formalized. However, the finite-temperature effect can destroy the coherent behavior of the supersymmetry system whose Hamiltonian is invariant under the Bogoliubov transformations.
AN OVERVIEW OF THE APPLICATION OF THE LANGEVIN EQUATION TO THE DESCRIPTION OF BROWNIAN AND QUANTUM MOTIONS OF A PARTICLE
Authors: NAMSRAI KH. , HULREE YA. , NJAMTSEREN N.
Published: November 2004

A simple scheme of unified description of different physical phenomena by using the Langevin type equations is reviewed. Within this approach much attention is being paid to the study of Brownian and quantum motions. Stochastic equations with a white noise term give all characteristics of the Brownian motion. Some generalization of the Langevin type equations allows us to obtain nonlinear equations of particles' motion, which are formally equivalent to the Schrödinger equation. Thus, we establish Nelson's stochastic mechanics on the basis of the Langevin equation.
AN EXPLICIT FORMULA FOR SOME SINGULAR VECTORS OF THE NEVEU–SCHWARZ ALGEBRA
Authors: BENOIT LOUIS , SAINT-AUBIN YVAN
Published: November 2004

Similarly to the Virasoro algebra, the Neveu–Schwarz algebra has a discrete series of unitary irreducible highest weight representations. These are labeled by the values of [Formula: see text] (the central charge) and of the highest weight hpq = [(p (m + 2) − qm)2 − 4]/(8m (m + 2)) where m, p, q are some integers. The Verma modules constructed with these values (c, h) are not irreducible, however, as they contain two Verma submodules, each generated by a singular vector ψp,q (of weight hpq + pq/2) and ψm−p, m+2−q (of weight hpq + (m−p)(m+2−q)/2), respectively. We give an explicit expression for these singular vectors whenever one of its indices is 1.
DIMENSIONAL REGULARIZATION IN THE 1/N EXPANSION
Authors: CAMPOSTRINI MASSIMO , ROSSI PAOLO
Published: November 2004

Two classes of renormalizable 1/N expandable two-dimensional models are analyzed to O(1/N) and the asymptotic behavior of the renormalized two-point functions is nonperturbatively evaluated.

These results are taken as a benchmark to study the applicability of dimensional regularization and perturbative minimal subtraction renormalization to the context of the 1/N expansion. Perturbation theory is applied to O(1/N) diagrams to all orders in the weak coupling constant and, after resummation, the same finite renormalization group invariant asymptotic amplitudes are obtained.

As a byproduct, the O(1/N) contributions to renormalization group Z functions in the minimal subtraction scheme are extracted and the critical index η is evaluated and compared to previous nonperturbative results, finding complete agreement.

The appendix is devoted to the extension of these results to a supersymmetric version of the models.
A MODEL FOR SIMPSON’S 17 keV NEUTRINO
Authors: RAJPOOT SUBHASH
Published: November 2004

Recent studies of β-decay spectra seem to confirm Simpson’s earlier findings that the electron neutrinos contain a small (1%) admixture of a 17 keV Dirac neutrino. An unconventional model with SU(2)L×SU(2)R×U(1)B−1 gauge interactions is presented in which all neutrinos are Dirac particles. Electron and muon neutrinos acquire seesaw Dirac masses of order 10−3eV for the MSW solution for the solar neutrino problem. The τ neutrino is identified as Simpson’s 17 keV neutrino. Constraints coming from cosmology and particle physics are shown to be satisfied.
PHASE STRUCTURE OF THREE- AND FOUR-DIMENSIONAL ϕ4 FIELD THEORY
Authors: EFIMOV G.V. , NEDELKO S.N.
Published: November 2004

The strong coupling regime of gϕ4 theory in space-time Rd for d=3, 4 is investigated by the methods of canonical transformations and the renormalization group. It is shown that the model describes a system symmetric under transformation ϕ→−ϕ both at small and large coupling constant g. Comparison with the case d=2 shows a crucial influence of the renormalization structure of the theory on its phase structure.
ON THE COVARIANT QUANTIZATION OF THE SECOND-ILK SUPERPARTICLE
Authors: VÁZQUEZ-BELLO J.L.
Published: November 2004

This paper is devoted to the quantization of the second-ilk superparticle using the Batalin-Vilkovisky method. We show the full structure of the master action. By imposing gauge conditions on the gauge fields rather than on coordinates we find a gauge-fixed quantum action which is free. The structure of the BRST charge is exhibited, and the BRST cohomology yields the same physical spectrum as the light-cone quantization of the usual superparticle.
NEUTRAL PION PHOTOPRODUCTION ON THE PROTON AND THE CLOUDY-BAG MODEL
Authors: TABACHENKO A.N.
Published: November 2004

In the cloudy-bag model, the value of the electric dipole amplitude of the photoproduction of neutral pions off protons at threshold connected with the additional contribution from the chiral symmetry breaking interaction is evaluated. If this additional contribution is included in the amplitude of the photoproduction of neutral pions off protons at threshold, the discrepancy between the LET predictions and the measured value of the electric dipole amplitude [Formula: see text] can be resolved for the values of quark masses and bag radii which are close to the generally used values.
ON THE IMPLICATIONS OF CONFINEMENT
Authors: ROBERTS C.D. , WILLIAMS A.G. , KREIN G.
Published: November 2004

We consider some implications of confinement starting from the basic observation that cross-sections for the production of colored asymptotic states, such as free quarks and gluons, from color singlet initial states must be zero if QCD is to be confining. We discuss two pictures of confinement: the failure of the cluster decomposition property and the absence of a pole at timelike momenta in the propagator of a confined particle. We use QCD-based models as a framework to relate the failure of the cluster decomposition property to other ideas, such as the role of a nonzero gluon condensate. Our primary interest is to address the question of the absence of a mass pole through a study of model Schwinger-Dyson equations. These equations contain some of the dynamical information that is present in the study of the cluster decomposition property. We discuss the problems with this idea and its study using the Schwinger-Dyson equations.
EXTRINSIC GEOMETRY OF WORLD-SHEET SUPERSYMMETRY THROUGH GENERALIZED SUPER-GAUSS MAPS
Authors: VISWANATHAN K.S. , PARTHASARATHY R.
Published: November 2004

The extrinsic geometry of N=1 world-sheet supersymmetry is studied through generalized super-Gauss map. The world sheet, realized as a conformally immersed super-Riemann surface S in Rn (n=3 is studied for simplicity) is mapped into the supersymmetric Grassmannian G2,3. In order for the Grassmannian fields to form (super) tangent planes to S, certain integrability conditions are satisfied by G2,n fields. These conditions are explicitly derived. The supersymmetric invariant action for the Kähler σ-model G2,3 is reexpressed in terms of the world-sheet coordinates, thereby an off-shell supersymmetric generalization of the action proportional to the extrinsic curvature of the immersed surface is obtained.
POLARIZED DEEP INELASTIC SCATTERING FROM PHOTON TARGETS AND AXIAL ANOMALIES
Authors: BASS STEVEN D.
Published: November 2004

We discuss the polarized photon structure function [Formula: see text] and focus on the first moment of [Formula: see text], where we explore the role of the axial QED and strong U(1) anomalies. Electromagnetic gauge invariance determines an exact sum rule for the first moment of [Formula: see text]. If we accept a recently proposed definition of “spin content” then we must also accept a polarized gluon component of Δgγ=2π/αs in the spin-one photon.
CORRELATION FUNCTIONS FOR TOPOLOGICAL LANDAU-GINZBURG MODELS WITH c≤3
Authors: KLEMM ALBRECHT , THEISEN STEFAN , SCHMIDT MICHAEL G.
Published: November 2004

We discuss c≤3 topological Landau-Ginzburg models. In particular we give the potential for the three exceptional models E6,7,8 in the constant metric coordinates of coupling constant space and derive the generating function F for correlation functions. For the c=3 torus cases with one marginal deformation and relevant perturbations, we derive and solve the differential equation resulting from flatness of coupling constant space. We perform the transformation to constant metric coordinates and calculate the generating function F. Comparing the three-point correlation functions with those of orbifold superconformal field theory, we find agreement. We finally demonstrate that the differential equations derived from flatness of coupling constant space are the same as the ones satisfied by the periods of the tori.
AFFINE KAC-MOODY ALGEBRAS AT THE CRITICAL LEVEL AND GELFAND-DIKII ALGEBRAS
Authors: FEIGIN BORIS , FRENKEL EDWARD
Published: November 2004

We prove Drinfeld's conjecture that the center of a certain completion of the universal enveloping algebra of an affine Kac-Moody algebra at the critical level is isomorphic to the Gelfand-Dikii algebra, associated to the Langlands dual algebra. The center is identified with a limit of the W-algebra, defined by means of the quantum Drinfeld-Sokolov reduction.
QUANTIZATION ENFORCES INTERACTION: QUANTUM MECHANICS OF TWO PARTICLES ON A QUANTUM SPHERE
Authors: PODLEŚ PIOTR
Published: November 2004

The particles interchanging operator and hamiltonian for two particles on a quantum sphere are constructed. Though there is no interaction hamiltonian, "interaction energy" occurs. It suggests a possibility that in a future quantum theory, all particles might be free.
HEADS, EYES AND HEAD-EYE SYSTEMS
Authors: PAHLAVAN KOUROSH , EKLUNDH JAN-OLOF
Published: November 2004

Active vision systems can be considered as systems that integrate visual sensing and action. Sensing includes detection of actions/events and results also in specific actions/manipulations.

This paper mainly addresses the basic issues in the design of a head-eye system for the study of active-purposive vision. The design complexity of such a head is defined by the activeness of the visual system. Although we have not had the motivation to exactly reproduce the biological solutions in a robot, we claim that the designer should carefully consider the solutions offered by evolution.

The flexibility of the behavioral pattern of the system is constrained by the mechanical structure and the computational architecture used in the control system of the head. The purpose of the paper is to describe the mechanical structure as well as the computational architecture of the KTH-head from this perspective.
ACTIVE AVOIDANCE: ESCAPE AND DODGING BEHAVIORS FOR REACTIVE CONTROL
Authors: ARKIN RONALD C. , CARTER WILLIAM M. , MACKENZIE DOUGLAS C.
Published: November 2004

New methods for producing avoidance behavior among moving obstacles within the context of reactive robotic control are described. These specifically include escape and dodging behaviors. Dodging is concerned with the avoidance of a ballistic projectile while escape is more useful within the context of chase. The motivation and formulation of these new reactive behaviors are presented. Both simulation and experimental results using a robot in a cluttered and moving world are provided.
HYPOTHESIS GENERATION IN CONFLICT-BASED DIAGNOSIS
Authors: CHEN JIAH-SHING , SRIHARI SARGUR N.
Published: November 2004

The goal of diagnostic reasoning is to identify malfunction (disease) that best accounts for the observed discrepancies (symptoms) in system behavior. Model-based diagnosis emerges as an alternative to both the empirical symptom-based and traditional fault-model-based approaches. Within the model-based paradigm, there is an important approach which bases its reasoning on conflicts for diagnosing multiple failures. We refer to such an approach as conflict-based diagnosis in this work. Previous conflict-based diagnostic systems resort to some objective notion of parsimony, e.g. nonredundancy, to reduce the exponential search space of hypotheses. Instead of using subjective measures, a probabilistic model is developed which provides an objective measure for ranking hypotheses. Based on the probabilistic model, an algorithm which generates plausible diagnostic hypotheses in decreasing order of their probabilities is presented. Some possible uses of the algorithm are discussed.
BOOSTING PERFORMANCE IN NEURAL NETWORKS
Authors: DRUCKER HARRIS , SCHAPIRE ROBERT , SIMARD PATRICE
Published: November 2004

A boosting algorithm, based on the probably approximately correct (PAC) learning model is used to construct an ensemble of neural networks that significantly improves performance (compared to a single network) in optical character recognition (OCR) problems. The effect of boosting is reported on four handwritten image databases consisting of 12000 digits from segmented ZIP Codes from the United States Postal Service and the following from the National Institute of Standards and Technology: 220000 digits, 45000 upper case letters, and 45000 lower case letters. We use two performance measures: the raw error rate (no rejects) and the reject rate required to achieve a 1% error rate on the patterns not rejected. Boosting improved performance significantly, and, in some cases, dramatically.
MULTI-MODULAR NEURAL NETWORK ARCHITECTURES: APPLICATIONS IN OPTICAL CHARACTER AND HUMAN FACE RECOGNITION
Authors: SOULIE FRANÇOISE FOGELMAN , VIENNET EMMANUEL , LAMY BERTRAND
Published: November 2004

In practical applications, recognition accuracy is sometimes not the only criterion; capability to reject erroneous patterns might also be needed. We show that there is a trade-off between these two properties. An efficient solution to this trade-off is brought about by the use of different algorithms implemented in various modules, i.e. multi-modular architectures.

We present a general mechanism for designing and training multi-modular architectures, integrating various neural networks into a unique pattern recognition system, which is globally trained. It is possible to realize, within the system, feature extraction and recognition in successive modules which are cooperatively trained. We discuss various rejection criteria for neural networks and multi-modular architectures.

We then give two examples of such systems, study their rejection capabilities and show how to use them for segmentation. In handwritten optical character recognition, our system achieves performances at state-of-the-art level, but is eight times faster. In human face recognition, our system is intended to work in the real world.
TIME-WARPING NETWORK: A NEURAL APPROACH TO HIDDEN MARKOV MODEL BASED SPEECH RECOGNITION
Authors: LEVIN ESTHER , PIERACCINI ROBERTO , BOCCHIERI ENRICO
Published: November 2004

Recently, much interest has been generated regarding speech recognition systems based on Hidden Markov Models (HMMs) and neural network (NN) hybrids. Such systems attempt to combine the best features of both models: the temporal structure of HMMs and the discriminative power of neural networks. In this work we establish one more relation between the HMM and the NN paradigms by introducing the time-warping network (TWN) that is a generalization of both an HMM-based recognizer and a backpropagation net. The basic element of such a network, a time- warping neuron, extends the operation of the formal neuron of a backpropagation network by warping the input pattern to match it optimally to its weights. We show that a single-layer network of TW neurons is equivalent to a Gaussian density HMM-based recognition system. This equivalent neural representation suggests ways to improve the discriminative power of this system by using backpropagation discriminative training, and/or by generalizing the structure of the recognizer to a multi-layer net. The performance of the proposed network was evaluated on a highly confusable, isolated word, multi-speaker recognition task. The results indicate that not only does the recognition performance improve, but the separation between classes is enhanced, allowing us to set up a rejection criterion to improve the confidence of the system.
A NEURAL SYSTEM FOR THE RECOGNITION OF PARTIALLY OCCLUDED OBJECTS IN CLUTTERED SCENES: A PILOT STUDY
Authors: WISKOTT LAURENZ , MALSBURG CHRISTOPH VON DER
Published: November 2004

We present a system for the interpretation of camera images of scenes composed of several known objects with mutual occlusion. The scenes are analyzed by the recognition of the objects present and by the determination of their occlusion relations. Objects are internally represented by stored model graphs. These are formed in a semi-automatic way by showing objects against a varying background. Objects are recognized by dynamic link matching. Our experiments show that our system is very successful in analyzing cluttered scenes. The system architecture goes beyond classical neural networks by making extensive use of flexible links between units, as proposed in the dynamic link architecture. The present implementation is, however, rather algorithmic in style and is to be regarded as a pilot study that is preparing the way for a detailed implementation of the architecture.
BINARY AND GREY-VALUE SKELETONS: METRICS AND ALGORITHMS
Authors: VERWER BEN J.H. , VAN VLIET LUCAS J. , VERBEEK PIET W.
Published: November 2004

A metric defines the distance between any two points. The “natural” metrics of the digital world do not approximate the Euclidean metric of the continuous world well. Skeletonization (sometimes named topology preserving shrinking or homotopic thinning) is one example in which this leads to unacceptable results. In the present work we propose and demonstrate skeletonization using path-based metrics which are a better approximation of the Euclidean metric. Moreover, we achieve a good performance on sequential processors by processing each pixel only once in the calculations of binary (Hilditch) and grey-value (upper) skeletons.
CHUA'S CIRCUIT WITH A DISCONTINUOUS NONLINEARITY
Authors: MAHLA ADELHEID I. , BADAN PALHARES ÁLVARO G.
Published: November 2004

A discrete map can be obtained from Chua's circuit1 with a discontinuous nonlinearity. Chaotic behavior is observed in the simulation of Chua's circuit with a discontinuous piecewise-linear element. The Poincaré map can be used to study the stability behavior and opens the possibility for analyzing the chaotic behavior by determining the existence of a snap-back repeller.
N-DIMENSIONAL CANONICAL CHUA'S CIRCUIT
Authors: KOCAREV LJ. , KARADZINOV LJ. , CHUA L. O.
Published: November 2004

In this paper we present an n-dimensional canonical piecewise-linear electrical circuit. It contains 2n two-terminal elements: n linear dynamic elements (capacitors and inductors), n - 1 linear resistors and one nonlinear (piecewise-linear) resistor. This circuit can realize any prescribed eigenvalue pattern, except for a set of measure zero, associated with (i) any n-dimensional two-region continuous piecewise-linear vector fields and (ii) any n-dimensional three-region symmetric (with respect to the origin) piecewise-linear continuous vector fields. We also proved a theorem that specifies the conditions for a vector field, realized with our canonical circuit, to have two or three equilibrium points.
THE EFFECT OF DAMPING ON THE STEADY STATE AND BASIN BIFURCATION PATTERNS OF A NONLINEAR MECHANICAL OSCILLATOR
Authors: SOLIMAN MOHAMED S. , THOMPSON J.M.T.
Published: November 2004

This paper examines the role of damping on both the steady state and basin behavior of a periodically driven damped oscillator with the ability to escape from a potential well. We examine the effect of damping on both the qualitative and quantitative resonance response of the system. Particular attention is paid to how the damping scales the main steady state bifurcations; saddle-nodes, period-doubling flips, cascades to chaos, boundary crises, etc. We also investigate how the damping level effects the main homoclinic and heteroclinic basin bifurcations that may result in a rapid erosion and stratification of the basin of attraction and hence a loss of engineering integrity of the system.
APPLICATION OF GLOBAL METHODS FOR ANALYZING DYNAMICAL SYSTEMS TO SHIP ROLLING MOTION AND CAPSIZING
Authors: FALZARANO JEFFREY M. , SHAW STEVEN W. , TROESCH ARMIN W.
Published: November 2004

Ship capsizing is a highly nonlinear dynamic phenomenon where global system behavior is dominant. However the industry standards for analysis are limited to linear dynamics or nonlinear statics. Until recently, most nonlinear dynamic analysis relied upon perturbation methods which are severely restricted both with respect to the relative size of the nonlinearity and the region of consideration in the phase space (i.e., they are usually restricted to a small local region about a single equilibrium), or on numerical studies of idealized system models.

In this work, recently developed global analysis techniques (e.g., those found in Guckenheimer and Holmes [1986], and Wiggins [1988, 1990]) are used to study transient rolling motions of a small ship which is subjected to a periodic wave excitation. This analysis is based on determining criteria which can predict the qualitative nature of the invariant manifolds which represent the boundary between safe and unsafe initial conditions, and how these depend on system parameters for a specific ship model. Of particular interest is the transition which this boundary makes from regular to fractal, implying a loss in predictability of the ship’s eventual state. In this paper, actual ship data is used in the development of the model and the effects of various ship and wave parameters on this transition are investigated. Finally, lobe dynamics are used to demonstrate how unpredictable capsizing can occur.
HOMOCLINIC BIFURCATION TO INFINITY IN A MODEL OF THE ECONOMIC LONG WAVE
Authors: BRØNS MORTEN , STURIS JEPPE
Published: November 2004

In a homoclinic bifurcation to infinity, a limit cycle blows up to infinite amplitude and disappears. Based on linearizations at infinity, we argue that this bifurcation occurs in models of the Kondratieff economic long wave. A formal proof of the existence of stable and unstable manifolds at infinity is given. A numerical method is proposed and applied to a new model in which regulation of consumer goods production is taken into account. The economic implications of the analysis are discussed.
A MATRIX METHOD FOR APPROXIMATING FRACTAL MEASURES
Authors: BOYARSKY A. , LOU Y.S.
Published: November 2004

Let X be a bounded subset of Rn and let A be the Lebesgue measure on X. Let {X:τ1,…, τN} be an iterated function system (IFS) with attractor S. We associate probabilities p1,…, pN with τ1,…, τN, respectively. Let M(X) be the space of Borel probability measures on X, and let M: M(X)→M(X) be the Markov operator associated with the IFS and its probabilities given by: [Formula: see text] where A is a measurable subset of X. Then there exists a unique µ∈M (A) such that Mµ=µ; µ is referred to as the measure invariant under the iterated function system with the associated probabilities. The support of μ is the attractor S. We prove the existence of a sequence of step functions {fi}, which are the eigenvectors of matrices {Mi}, such that the measures {fidλ} converge weakly to µ. An algorithm is presented for the construction of Mi and an example is given.
SOME CHARACTERISTIC FEATURES IN THE PATTERN OF BIFURCATING STEADY STATES IN COUPLED REACTION-DIFFUSION SYSTEMS
Authors: Yan Joseph G.-G.
Published: November 2004

We study, in this paper, the spatial pattern of nonuniform steady states bifurcated from a constant steady state in coupled reaction-diffusion systems. These solutions bifurcate under a Hopf bifurcation at 1:1 resonance in the state space, and they emerge as stable solutions when the constant steady state loses stability [Yan, 1992b]. We investigate some special features in the pattern exhibited by such solutions in several models. Mathematical proofs of these features are presented, in which we have used the theories of reversible systems, perturbation analysis and linear approximation. Numerical approximations of such solutions are obtained from these models. All of these solutions exhibit the characteristic features described by our analysis.
INSTABILITIES AND METASTABLE CHAOS IN A TWO-MODE LASER
Authors: NIYAZOV B.A. , SHAROV M.V. , SULTANOVA F.R.
Published: November 2004

The dynamics of homogeneously broadened ring lasers supporting two transverse modes is numerically studied. The regimes with periodic and chaotic intensity pulsations have been obtained for lasers having both fast and slow-response relaxation of the population inversion. A phenomenon of metachaos has been found and statistical properties of metastable chaotic states and their dependence on system parameters have been studied.
ON BIFURCATIONS OF SEPARATRIX CONTOURS WITH TWO SADDLES
Authors: SHASHKOV M.V.
Published: November 2004

Bifurcations in two-parameter families containing a dynamical system having a heteroclinic orbit connecting type-a saddle equilibrium points are investigated. The existence of a countable set of bifurcation curves corresponding to saddle connections is discussed.
COMPUTERS AND CHAOS: AN EXAMPLE
Authors: TROPAREVSKY MARÍA INÉS
Published: November 2004

In this work, an example of the difficulties that may arise when exploring dynamical systems with a digital computer, is presented. It is the case of a linear piecewise function with a period −3 orbit. Computational simulations move us to believe that this orbit is an attracting one, but a theoretical analysis demonstrates that what the computer shows is not, in this case, the real behavior of the system.
TIME-DELAYED MAP PHENOMENOLOGICAL EQUIVALENCY WITH A COUPLED MAP LATTICE
Authors: WILLEBOORDSE FREDERICK H.
Published: November 2004

It is shown that, what so far were considered to be purely spatiotemporal, phenomena in a model for a Coupled Map Lattice can be obtained through a newly introduced Time-Delayed Map with only one chaotic element, thereby effectively eliminating the spatial dimension.
META-ENVIRONMENTS FOR SOFTWARE PRODUCTION
Authors: KARRER ANTHONY S. , SCACCHI WALT
Published: November 2004

Researchers who create software production environments face considerable problems. Software production environments are large systems that are very costly to develop. Furthermore, software production environments which support particular software engineering methods may not be applicable to a large number of software production projects. These conditions have formed a trend towards research into ways which will lessen the cost of developing software production environments. In particular, the trend has been towards the construction of meta-environments. In this paper, we attempt to categorize current meta-environment approaches. For each of the categories, we review research efforts which illustrate different approaches within that category. We conclude by presenting an emerging common thread of requirements which links this field together.
A SURVEY AND ASSESSMENT OF SOFTWARE PROCESS REPRESENTATION FORMALISMS
Authors: ARMENISE PASQUALE , BANDINELLI SERGIO , GHEZZI CARLO , MORZENTI ANGELO
Published: November 2004

Process modeling is a rather young and very active research area. During the last few years, new languages and methods have been proposed to describe software processes. In this paper we try to clarify the issues involved in software process modeling and identify the main approaches. We start by motivating the use of process modeling and its main objectives. We then propose a list of desirable features for process languages. The features are grouped as either already provided by languages from other fields or as specific features of the process domain. Finally, we review the main existing approaches and propose a classification scheme.
LINEAR PROGRAMMING CUTTING PROBLEMS
Authors: MUKHACHIOVA E.A. , ZALGALLER V.A.
Published: November 2004

Different optimal cutting problems are considered in this paper. Among them are cutting forming problems (closed packing problems) and problems of cutting totality planning with intensities of their application. For solving these planning problems, linear or integer programming is used. Furthermore, different cutting technological and organizational situations are considered. Different optimal criteria and a compromise solution choice procedure are presented. All the statements are illustrated by numerical examples from a guillotine cutting area. The possibility of linear cutting approximation for a non-guillotine (closed packing) cutting stock problem is shown. Rectangular packing algorithms based on this approximation can be built. These algorithms form the basis of special software. Their characteristics are presented in the conclusion of the paper.
AN INCREMENTAL ALGORITHM FOR CONSTRUCTING SHORTEST WATCHMAN ROUTES
Authors: TAN XUEHOU , HIRATA TOMIO , INAGAKI YASUYOSHI
Published: November 2004

The problem of finding the shortest watchman route in a simple polygon P through a point s on its boundary is considered. A route is a watchman route if every point inside P can be seen from at least one point along the route. We present an incremental algorithm that constructs the shortest watchman route in O(n3) time for a simple polygon with n edges. This improves the previous O(n4) bound.