bluuebunny/crossref_metadata_2025 huggingface dataset:
LOOP EQUATIONS AND KDV HIERARCHY IN 2-D QUANTUM GRAVITY
Authors: FUCITO F. , MARTELLINI M.
Published: November 2004

A derivation of the loop equation for two-dimensional quantum gravity from the KdV equations and the string equation of the one-matrix model has been recently given. The loop equation was found to be equivalent to an infinite set of linear constraints on the square root of the partition function satisfying the Virasoro algebra. Starting from the equations expressing these constraints, we are able to rederive the equations of the KdV hierarchy using the vertex operator construction of the [Formula: see text] infinite dimensional twisted Kac-Moody algebra. From these considerations it follows that the solutions of the string equation of the one-matrix model are given by a subset of the solutions of the KdV hierarchy.
THE TIME-EVOLUTION OPERATOR FOR HIGHER-ORDER SINGULAR LAGRANGIANS
Authors: CARIÑENA JOSÉ F. , LÓPEZ CARLOS
Published: November 2004

A generalization of the time-evolution operator for higher-order singular-Lagrangian systems is developed and used for the study of the relations between Lagrangian and Hamiltonian formalisms, and, more specifically, for establishing the classification of constraints on both systems.
VIRASORO OPERATORS FOR ARBITRARILY TWISTED KAC–MOODY ALGEBRAS
Authors: MCGETTRICK M. , MCGLINN W. , GORMAN N. , O'RAIFEARTAIGH L.
Published: November 2004

A generalization of the Sommerfield–Sugawara formula which applies to the Virasoro operators for an arbitrarily twisted Kac–Moody algebra is given. It requires a novel but interesting modification of the normal-ordering function. The results are compared with those given previously for inner and canonical outer twists.
MATRIX MODELS AND GAUGE-INVARIANT FIELD THEORY OF SUBCRITICAL STRINGS
Authors: SEN ASHOKE
Published: November 2004

A gauge-invariant interacting field theory of subcritical closed strings is constructed. It is shown that for d ≤ 1 this field theory reproduces many of the features of the corresponding matrix model. Among them are the scaling dimensions of the relevant primary fields, identities involving the correlation functions of some of the redundant operators in the matrix model, and the flow between different matrix models under appropriate perturbation. In particular, it is shown that some of the constraints on the partition function derived recently by Dijkgraaf et al. and Fukuma et al. may be interpreted as Ward identities in string field theory.
FROM LOOPS TO FIELDS IN 2D QUANTUM GRAVITY
Authors: MOORE GREGORY , SEIBERG NATHAN
Published: November 2004

We discuss a target space field theory of macroscopic loops W(ℓ,…) in two-dimensional gravity. The propagator  and topology-changing amplitudes  (string interactions) are considered as off-shell Euclidean Green's functions in this field theory. In the course of the analysis, we identify a new set of operators in the c = 1 system and interpret them in two-dimensional gravity. We also identify an infinite set of new conserved charges in the c = 1 system which are associated with the special states in the theory. The analysis also shows that the eigenvalue coordinate of the matrix model and a zero mode of the Liouville field are not functionally related but are conjugate variables in an integral transform.
INTERACTING INSTANTONS FOR TeV PHYSICS
Authors: AOYAMA HIDEAKI , KIKUCHI HISASHI
Published: November 2004

Multi-instanton effect in the standard electroweak model for baryon and lepton number violation is discussed. Instanton interaction is shown to play a major role in the TeV range. First, the validity of the treatment of the interaction is explicitly checked in the quantum-mechanical case. Then interactions induced by both bosons and fermons are examined in the SU(2) Yang–Mills–Higgs model. They are shown to lead to an effective theory which is manifestly unitary. This results in an estimate that the relevant cross section saturates the unitary bound at the TeV scale, indicating the possibility of detecting baryon- and lepton-number-violating phenomena.
THE FADDEEV–POPOV METHOD FOR THE RELATIVISTIC LANDAU PROBLEM
Authors: FARINA C. , GAMBOA J.
Published: November 2004

We use the Faddeev–Popov method to calculate explicitly the path integral propagator for a relativistic spinless charged particle in the presence of a constant magnetic field. We obtain the conservation laws in the path integral approach. We also establish the equivalence between the Faddeev–Popov method and the Fock–Schwinger proper time approach. Finally, after proposing a suitable regularization prescription for the non-relativistic problem, we obtain the Landau levels directly from the path integral result.
A QUARK-MODEL FIT FOR THE ELECTROMAGNETIC PROPERTIES OF OCTET BARYONS
Authors: JENA S. N. , PANDA S.
Published: November 2004

A simple independent-quark model based on the Dirac equation with an equally mixed scalar–vector linear confining potential model is used to obtain a fit for the electromagnetic properties — like the magnetic moments, charge radii and axial-vector coupling-constant ratios — of octet baryons, taking into account the appropriate center-of-mass corrections. This fit is extended to include the quark-core contributions to the nucleon electromagnetic form factors [Formula: see text], [Formula: see text], [Formula: see text] and the axial-vector form factor GA(q2). The respective root-mean-square radii associated with [Formula: see text] and GA(q2) come out as [Formula: see text] and [Formula: see text]. The possibility of restoring in this model the chiral symmetry in the usual way is discussed and the pion-nucleon coupling constant is found as gπ NN = 13.72 as compared to (gπ NN ) exp ≃ 13.
COVARIANT OPERATOR FORMALISM OF TWO-DIMENSIONAL TOPOLOGICAL GRAVITY
Authors: IKEDA NORIAKI
Published: November 2004

The manifestly covariant canonical operator formalism of two-dimensional topological gravity is formulated. Its unitarity is confirmed by means of constructing the Kugo–Ojima's quartets. A number of new symmetries are found by adopting a particular gauge fixing condition. These symmetries correspond to the "choral symmetry" generated by the 4N-dimensional Poincaré-like superalgebra in the ordinary N-dimensional quantum gravity.
A GENERALIZED METRIC OF GRAVITATION
Authors: EL-TAHIR ALI
Published: November 2004

Useful expressions relating the metric components grr and gtt of the static isotropic space–time, and the scalar curvature R, with the general Lagrangian are obtained. A generalized metric of gravity is introduced, which is essentially nonsingular, and reducible to cosmological and hence Schwarzschild geometries by imposing a weak-field constraint.
THE RELATIVISTIC MODEL OF THE ORBITAL EXCITATIONS OF HADRONS
Authors: BERDNIKOV E. B. , PRON'KO G. P.
Published: November 2004

The relativistic model describing orbital excitations of hadrons composed of light quarks is considered. All the hadrons are treated in a uniform way as the states of a straight-line string with spinors at its ends. There are a quark and antiquark at the ends in the case of mesons, and a quark and diquark for baryons. The model has an additional symmetry, which allows one to describe the exact LS degeneracy. Although the model proposed is essentially relativistic, the states of its spectrum are classified as in nonrelativistic potential models. The spectrum consists of the family of trajectories arising from splitting the leading Regge trajectory due to the spin of quarks.
LOCAL WORLD SHEET WEYL-INVARIANCE IN THE PRESENCE OF BACKGROUND CHARGES
Authors: ELLWANGER U. , SCHNITTGER J.
Published: November 2004

We derive the consistency conditions that follow from imposing local Weyl-invariance on the Polyakov path integral in a general background. In contrast to previous attempts our approach allows for the inclusion of curvature-dependent couplings like the dilaton and in particular of background charges. The resulting equation displays explicitly the corresponding modifications of the trace anomaly and the scale dimensions of vertex operators. A special class of solutions is discussed which, in particular, allows one to interpret the screening operators of Fateev and Dotsenko as an interaction Lagrangian.
ZERO CURVATURE CONDITION AND 2D GRAVITY THEORIES
Authors: DAS A. , HUANG W.-J. , ROY S.
Published: November 2004

We propose interpreting the zero curvature condition associated with an integrable model as an anomaly equation. This can lead to the WZWN action and the associated current algebra quite readily and clarifies further the connections found between the integrable models and 2D gravity theories. We analyze, in detail, the cases SL (2, R) (KdV hierarchy), OSp (2/1) (sKdV hierarchy) and SL (3, R) (Boussinesq hierarchy) and obtain the operator product expansions of the appropriate fields. We also make some observations on the generalization of our method to SL (n, R).
QUANTUM YANG-MILLS THEORY ON ARBITRARY SURFACES
Authors: BLAU MATTHIAS , THOMPSON GEORGE
Published: November 2004

We study quantum Maxwell and Yang-Mills theory on orientable two-dimensional surfaces with an arbitrary number of handles and boundaries. Using path integral methods we derive general and explicit expressions for the partition function and expectation values of contractible and noncontractible Wilson loops on closed surfaces of any genus, as well as for the kernels on manifolds with handles and boundaries. In the Abelian case we also compute correlation functions of intersecting and self-intersecting loops on closed surfaces, and discuss the role of large gauge transformations and topologically nontrivial bundles.
t-J MODEL FOR TRIPLET HOLES
Authors: Oleś Andrzej M. , Zaanen Jan , Drchal Vaclav
Published: November 2004

If a t—J model applies, conventional wisdom tells that the vacancies are singlets in the high-Tc superconductors. Recent experiments indicate, however, that doping induces significant amounts of 3d3z2 - 1 holes character and this should be attached to the vacancies because of Hund’s rule coupling. This motivates us to consider the motion of a triplet hole in a spin S=1/2 background. We analyze this problem on the level of the nonretracable path approximation and we find that also for J=0 coherent motion is possible. The triplet hole has a branched hopping history. This weakens the band singularities in a ferromagnetic background, while in an antiferromagnetic back-ground this adds nearly an additional dimension to the effective electronic dimensionality.
LARGE N EXPANSION FOR FRUSTRATED AND DOPED QUANTUM ANTIFERROMAGNETS
Authors: Sachdev Subir , Read N.
Published: November 2004

A large N expansion technique, based on symplectic (Sp(N)) symmetry, for frustrated magnetic systems is studied. The phase diagram of a square lattice, spin S, quantum antiferromagnet with first, second and third neighbor antiferromagnetic coupling (the J1-J2-J3 model) is determined in the large-N limit and consequences of fluctuations at finite N for the quantum disordered phases are discussed. In addition to phases with long range magnetic order, two classes of disordered phases are found: (i) states similar to those in unfrustrated systems with commensurate, collinear spin correlations, confinement of spinons, and spin-Peierls or valence-bond-solid order controlled by the value of 2S (mod 4) or 2S (mod 2) ; (ii) states with incommensurate, coplanar spin correlations, and unconfined bosonic spin-1/2 spinon excitations. The occurrence of “order from disorder” at large S is discussed. Neither chirally ordered nor spin nematic states are found. Initial results on superconductivity in the t—J model at N=∞ and zero temperature are also presented.
RANDOMLY DECORATED ISING MODEL
Authors: GONÇALVES L.L.
Published: November 2004

A study of the two-dimensional (square lattice) randomly decorated Ising model is presented. The bonds are decorated with Ising spins of magnitude s and an annealed discrete distribution [Formula: see text] for the exchange interaction of the decorating bonds is considered. The phase diagram is exactly obtained and for the case where competition is present there are two percolation thresholds, namely, [Formula: see text] which are independent of s. Reentrant behaviour is presented by the system and the region in the space parameters where it occurs is discussed.
OXYGEN CONTENT AND CRYSTAL FIELD EFFECTS IN RBa2Cu3Ox
Authors: PODLESNYAK A. A. , MIRMELSTEIN A. V. , BOBROVSKII V. I. , ZHDAHIN I. L. , BLINOVSKOV YA. N. , KOZHENVNIKOV V. L. , GOSHCHITSKII B. N.
Published: November 2004

Effects of crystal electrical field (CEF) in the orthorhombic phase of RBa 2 Cu 3 O x( R = Ho , Er ; x = 6.9, 6.4) are investigated by inelastic magnetic neutron scattering (IMNS). The level schemes of the lowest multiplet of 4f-shell of the rare-earth ion are found. It is shown that the experimental scattering spectra and their variation depending on the oxygen content may be explained by spacial distribution of the negative charge within the unit cell.
THEORY OF DYNAMIC RESPONSE FUNCTIONS OF PERIODICALLY MODULATED PHYSICAL SYSTEMS
Authors: LOVESEY STEPHEN W. , WATSON G. I. , WESTHEAD DAVID R.
Published: November 2004

Dynamical properties of models of physical systems distinguished in having two essential length scales are derived. The method used is non-perturbative. It is cast in terms of systems of orthogonal polynomials, whose properties are reviewed together with recent work on the spectrum and algebraic curves associated with periodic difference operators. Response functions observed in experiments, which can probe spatial and temporal features, are calculated for several models of current interest, including spin excitations in a modulated magnet and the vibrations of a modulated harmonically coupled chain of atoms.
REPRODUCIBLE TUNNELING MEASUREMENTS IN CERAMIC Y1Ba2Cu3O7−x SAMPLES WITH DIFFERENT OXYGEN CONTENT
Authors: GONNELLI R. S. , DURIN G. F. , ANDREONE D. , LACQUANITI V. , APPINO C. , VALLINO M.
Published: November 2004

A large number of tunneling measurements on ceramic monophasic Y 1 Ba 2 Cu 3 O 7−x samples with different oxygen content using the point-contact geometry was performed. After a deconvolution procedure for removing the thermal broadening, experimental data were analyzed by means of a model of the total tunneling current which contains two terms: A background "normal" tunneling current and a quasi-particle tunneling one. The quasi-particle current was expressed in terms of the lifetime broadening model. The dependence of the energy gap Δ and of the lifetime broadening parameter Γ, as determined by the model, on the temperature of the sample is discussed. A linear behaviour in the dependence of the gap on the critical temperature of the sample has been found. The ratio 2Δ/kT c varies between 4.3 and 7.2 depending on the value of T c which can be attributed to the sample surface. The possible presence of proximity effect in our tunneling experiments is also discussed.
DOSE-RATE EFFECT IN HIGHLY CORRELATED SOLIDS
Authors: ANDREEV BORIS V. , KOSTRUBOV YURY N.
Published: November 2004

The concept of the dose-rate effect in highly correlated solids (HCS) is presented. The effect consists in the experimentally observed dependence of efficiency of processes stipulated by excitations of electron subsystem of solids upon the dose rate of high-energy radiation. Results of the dose-rate effect investigations in soft-mode (ferroelectric) crystals and chalcogenide glassy semiconductors are presented and discussed. A possibility of revealing the dose-rate effect in such HCS as high-temperature superconductors and compounds with metal-insulator (semiconductor) transition is also discussed.
THEORIES OF THE MODULATED ‘RIPPLE’ PHASE OF LIPID BILAYERS
Authors: SCOTT H.L. , McCULLOUGH W. SCOTT
Published: November 2004

The ripple, or Pβ′ phase of lipid bilayers, which occurs in bimolecular layers of certain phospholipid molecules, exhibits long range periodic intermolecular correlations. These correlations manifest themselves in the form of periodic undulations, or “ripples” in the topography of the layer. In this paper we review theoretical models for this phase.
PIEZOELECTRICITY IN INSULATORS
Authors: MAHAN G.D.
Published: November 2004

A microscopic theory is presented for the piezoelectric constants of zincblende. The theory is valid for ionic crystals. The constants have several contributions: one from long-range Coulomb interactions, and several from short range forces. The long-range term is given only by the dielectric function. The short-range terms are also large and nearly cancel the long-range terms: the largest is from the deformation-dipole term. The agreement between theory and experiment is a sensitive test of theories of short-range polarization in solids.
Current Status of Semionic Pairing Theory of High–Tc Superconductors
Authors: Laughlin R. B.
Published: November 2004

The existence of fractional statistics in nature and the ability of 1/2 statistics to cause superconductivity are now both firmly established. The more difficult question of whether fractional statistics accounts for high– T c behavior is still unclear. The current status of semionic pairing theory is reviewed, and the case made that the situation is encouraging, notwithstanding the slowness of our progress in developing appropriate mathematical tools. Several key questions are identified and strategies for answering them suggested.
OPTICAL PROBES OF ANYON PHYSICS: EXPERIMENTAL STATUS REPORT
Authors: LYONS K. B. , DILLON J. F.
Published: November 2004

A complete review is given of polar Kerr rotation measurements on samples of superconducting cuprates and related materials. We discuss the details of the experimental technique we have employed to discriminate against linear polarization effects, and we compare our results to those of related experiments, We show that there are possible ways to reconcile all of the experimental data available at this time, and we suggest additional crucial experiments needed to make progress towards a definitive identification of the origin of the effect.
Superconductivity of an interacting anyon system
Authors: Yang J. , Su W. P. , Ting C. S.
Published: November 2004

A study of the Meissner effect and the plasmon spectrum for an interacting anyon system is presented. It is shown that the Meissner effect is not sensitive to, and still persists in, the presence of repulsive Coulomb interaction among anyons. Within the random phase approximation we show that the collective excitation of the system in the long-wavelength limit corresponds to the plasmon mode of a two dimensional interacting electron gas and it does not depend on the statistics associated with the anyons. There is a roton minimum of the collective mode at a finite value of the wavevector. A similar analysis on an array of layered anyon systems is also reported.
Anyons: a possible mechanism for binding charged particles
Authors: Schmeltzer D. , Bishop A. R.
Published: November 2004

The hard core boson gas in (2+1)-dimensions in the presence of a Chern-Simons term is considered, we find that the long wave description is given in terms of Coulomb (longitudinal) and transversal electrodynamics. The longitudinal part is described in terms of electric charges which carry vorticity. When binding of electrical charges occurs the transversal part is described by a photon field and corresponds to a superfluid. Using the same language we find that a spinless fermion is described by a massive photon. We use these concepts to understand the relation between the negative-U Hubbard model in the presence of a magnetic field, and vortices which carry electric charge induced by doping in the repulsive Hubbard model.
EXISTENCE OF INFINITE NETWORKS WITHOUT SPECTRAL DIMENSION
Authors: CASSI DAVIDE
Published: November 2004

It is shown that for Bethe lattices is impossible to define a spectral dimension, since a gaussian field theory defined on it is out of criticality even when all the masses are set to zero.
RECENT DEVELOPMENTS OF ALGEBRAIC METHODS IN QUANTUM FIELD THEORIES
Authors: SCHROER B.
Published: November 2004

Recent results obtained by modular methods concerning the algebraic origin of spacetime covariance from modular and dual properties of causal nets are presented. Particular emphasis is given to one-dimensional nets which are important in the classification of chiral conformal field theories.
CRITICAL TEMPERATURES AND MEAN-FIELD CRITICAL COEFFICIENTS FOR THE HEISENBERG MODEL BASED ON CVM
Authors: TANAKA GIICHI , KIMURA MINORU
Published: November 2004

Critical temperatures T c and mean-field critical coefficients [Formula: see text] for susceptibilities are calculated by a cluster-variation method (CVM) for a three-dimensional Heisenberg model on a simple cubic lattice. Both the full CVM based on a 4-spin cluster and the SCVM are applied and the same values for T c and [Formula: see text] are obtained by three different approximation in the SCVM. The results are compared with those obtained by the same approach for the three-dimensional Ising model on the simple cubic lattice.
FRUSTRATED TRANSVERSE ISING MODELS: A CLASS OF FRUSTRATED QUANTUM SYSTEMS
Authors: SEN P. , CHAKRABARTI B. K.
Published: November 2004

The analytical and numerical (Monte Carlo and exact diagonalisation) estimates of phase diagrams of frustrated Ising models in transverse fields are discussed here. Specifically we discuss the Sherrington–Kirkpatrick model in transverse field and the Axial Next-Nearest Neighbour Ising (ANNNI) model in transverse field. The effects of quantum fluctuations (induced by the transverse field) on the ground and excited states of such systems with competing interactions (frustration) are also discussed. The results are compared to those available for other frustrated quantum systems.
SIMPLE ATTEMPT TO OBSERVE SUPERCONDUCTIVITY ON ANTIFERROMAGNETIC BACKGROUND IN THE t-J MODEL
Authors: KALINAY PAVOL
Published: November 2004

Having treated the t-J Hamiltonian in the mean-field approximation on basis generated by the Hubbard operators [Formula: see text], we tried to find the superconductive phase on the antiferromagnetic background. The pairing of the d-wave symmetry appeared to coexist well with the AF long-range order.
WEAK FIELD NONLINEAR OPTICAL RESPONSE OF FERMIONS IN FRENKEL EXCITON CHAINS
Authors: SPANO FRANK C.
Published: November 2004

In this paper the third order nonlinear optical response of a Frenkel chain composed of N dipole-dipole coupled two-level molecules is reviewed. The fundamental electronic excitations of such a system are, in fact, fermions, a property which greatly simplifies the eigenspectrum for multiexciton states. The introduction of site disorder does not disrupt the fermion nature and is therefore easily incorporated into a general expression of the third order nonlinear optical susceptibility.
CLUSTERS WITH NOVEL PROPERTIES
Authors: Jena P. , Khanna S.N. , Rao B.K.
Published: November 2004

The size specific nature of the electronic and structural properties of small metal clusters is reviewed. Three specific examples are illustrated: the nature of hydrogen interaction with neutral and charged metal clusters, the stability and electronic properties of metal-carbon complexes and the role of electron shell filling and close atomic packing on synthesizing very stable and chemically inert clusters.
STRUCTURES AND STABILITIES OF CARBON FULLERENES
Authors: Wang C.Z. , Zhang B.L. , Xu C.H. , Chan C.T. , Ho K.M.
Published: November 2004

The structures and stabilities of carbon fullerenes C n( n =20–94) are studied with tight-binding molecular dynamics in combination with a new scheme for generating energetically favorable fullerene networks. Magic numbers for fullerene formation energy are observed at n =60, 70 and 84. The experimental observation of the more abundant fullerenes is related to the fragmentation stabilities and chemical reactivities of the fullerenes obtained from our calculations.
THEORETICAL DETERMINATION OF THE ELECTRIC DIPOLE AND QUADRUPOLE RESPONSE PROPERTIES OF C60
Authors: Fowler P.W. , Kelly H.M. , Lazzeretti P. , Malagoli M. , Zanasi R.
Published: November 2004

The electronic structures of the fullerenes, characterized by π-electron systems spread over a closed surface, may exhibit novel responses to external electric and magnetic fields. Accurate theoretical determination of such properties is made difficult by the large number of electrons, but for some systems, in particular C 60, the molecular symmetry can be taken into account to achieve significant reduction in computer effort. A method has been developed that permits the use of the full molecular point group symmetry in the calculation of perturbed electron. density matrices transforming as second-rank tensors. In this note preliminary coupled Hartree-Fock results in a minimal basis for static electric response properties of C 60 (the second electric dipole hyperpolarizability γ, the electric quadrupole polarizability C and the first electric (mixed) dipole-quadrupole hyperpolarizability B) are presented.
Polaron Excitations in Buckminsterfullerenes: Doped C60 and C70
Authors: Harigaya Kikuo
Published: November 2004

We propose a Su-Schrieffer-Heeger type electron-phonon model for buckminsterfullerenes: C 60 and C 70. The model is solved by a numerical iteration method with applying the adiabatic approximation to phonons. When the system ( C 60 or C 70) is doped with one or two electrons (or holes), the additional charges accumulate almost along an equatorial line of the molecule. The dimerization becomes weaker almost along the same line. Two energy levels intrude largely in the gap; one is the occupied state and the other is the empty state. The intrusion is larger in C 70 than in C 60. These are “polarons” in doped buckminsterfullerenes. It is also found that C 60 and C 70 are related mutually with respect to electronical structures as well as lattice geometries. We also calculate optical properties of C 60. In optical absorption of the doped C 60, there is a new peak at the lower energy than those of the intergap transition peaks. The third harmonic generation in low frequencies agrees with experiments. Relations of polarons with recent experiments are pointed out.
PHONONS AND NON-LINEAR DYNAMIC EXCITATIONS AT THE SURFACE OF SOLIDS
Authors: SCHOMMERS W. , VON BLANCKENHAGEN P. , SYROS C.
Published: November 2004

In this paper we report molecular dynamics (MD) results for the surface dynamics of realistic model systems (krypton, lead). It turned out that the layers at the surface perform an unusual center-of-mass motion perpendicular to the surface; this new excitation should be due to the anharmonicities at the surface. The generalized phonon density of states has been studied in the bulk as well as at the surface of the crystal. The MD results are discussed in connection with dynamical-matrix solutions.
THERMALLY ACTIVATED DISSIPATION IN WEAK LINKS OF SINTERED Tl4Ba3Ca3Cu4Oy
Authors: XIAOWEN CAO , GANJI CHENG , JUNREN FANG
Published: November 2004

The thermally activated dissipation behaviour in weak link region of sintered Tl 4 Ba 3 Ca 3 Cu 4 O y is reported for the temperature below T c and the magnetic field below 1 kOe. Experimental data suggest a power-law dependence of U0(H)∝H−α with α=0.41. We consider that the magnetic-field-dependent dissipation behaviour are related to flux creep in weak link regions.
METAL-SEMICONDUCTOR TRANSITIONS IN THE SUPERSTOICHIOMETRIC DIHYDRIDES YH2+x
Authors: VAJDA P. , DAOU J.N.
Published: November 2004

After a brief review of the structural and electronic properties of the non-stoichiometric rare-earth hydrides, RH 2+x, we discuss metal-semiconductor transitions observed in several β-phase RH 2+x-systems in the temperature range 200 to 300 K for x-values close to the phase boundary to the trihydride γ-phase. The special case of YH 2+x is treated in detail, showing the evolution from a purely metallic case with x=0.085 to a clear M-S transition for x=0.10 (at the β-phase limit), passing through a fluctuating situation for x=0.095. The essential role played by an order — disorder transformation occurring in the octahedral (x) hydrogen sublattice as the driving mechanism for the M-S transition is emphasized. A second M-S transition observed at low temperatures (≲ 80 K ) is attributed to weak carrier localisation due to x-hydrogen disorder.
DIMENSIONAL REDUCTION OF A GENERALIZED FLUX PROBLEM
Authors: MOROZ ALEXANDER
Published: November 2004

A generalized flux problem with Abelian and non-Abelian fluxes is considered. In the Abelian case we shall show that the generalized flux problem for tight-binding models of noninteracting electrons on either 2n- or (2n + 1)-dimensional lattice can always be reduced to an n-dimensional hopping problem. A residual freedom in this reduction enables one to identify equivalence classes of hopping Hamiltonians which have the same spectrum. In the non-Abelian case, the reduction is not possible in general unless the flux tensor factorizes into an Abelian one times an element of the corresponding algebra.
MICROWAVE ABSORPTION STUDIES ON HIGH-TcSUPER CONDUCTORS AND RELATED MATERIALS IX—NON-RESONANT MICROWAVE ABSORPTION IN AN ULTRA-THIN (~100 Å THICK) Bi-Sr-Ca-Cu-O FILM
Authors: SUGAWARA K. , TANAKA S.
Published: November 2004

Non-resonant microwave absorption (NRMA) studies have been done for an ultra-thin (~100 Å thick) Bi-Sr-Ca-Cu-O film fabricated on MgO(100) by MOCVD. The measurements have been done in two cases; either (a) the rear surface of the substrate or (b) the film surface was covered with an aluminum foil to shield microwave radiation. Three types of NRMA signals were observed for the former case, whereas only one type of signals were detected in the latter. The intensities, linewidths and their temperature dependences are qualitatively and quantitatively different in these two cases, possibly indicating a surface effect rather than a volume effect for the NRMA phenomenon.
PREPARATION AND MAGNETIC PROPERTIES OF TERNARY NITRIDES OF Nd2Fe17−xCox
Authors: RADHAKRISHNA P. , UMARJI A.M. , MURTHY V.G. NARASIMHA
Published: November 2004

The preparation and characterization of Nd2Fe17−xCox with x=0 and 2, has been reported. The ferromagnetic Tc increases from 60.5°C for x=0 to 285°C for x=2. Attempts to synthesize nitrided intermetallics between 400 and 600° C produced materials with broad ferromagnetic transitions.
QUANTIZATION RULES FOR STRONGLY CHAOTIC SYSTEMS
Authors: AURICH R. , BOLTE J.
Published: November 2004

We discuss the quantization of strongly chaotic systems and apply several quantization rules to a model system given by the unconstrained motion of a particle on a compact surface of constant negative Gaussian curvature. We study the periodic-orbit theory for distinct symmetry classes corresponding to a parity operation which is always present when such a surface has genus two. Recently, several quantization rules based on periodic orbit theory have been introduced. We compare quantizations using the dynamical zeta function Z(s) with the quantization condition [Formula: see text] where a periodic-orbit expression for the spectral staircase N(E) is used. A general discussion of the efficiency of periodic-orbit quantization then allows us to compare the different methods. The system dependence of the efficiency, which is determined by the topological entropy τ and the mean level density [Formula: see text], is emphasized.
OLFACTORY NEURAL NETWORK MODEL
Authors: KAZAKOVA N. , DOTSENKO VIK.
Published: November 2004

A statistical neural network olfactory model is proposed. The model is a simple generalization of the Hopfield neural network system. Retrieval properties are analysed and the zero temperature mean field phase diagram is obtained.
ELECTRIC FIELD GRADIENTS IN SEMICONDUCTORS AND INSULATORS: EMPIRICAL CORRELATION FOUND IN BINARY OXIDES
Authors: RENTERÍA M. , MASSOLO C.P. , BIBILONI A.G.
Published: November 2004

For the first time a well defined correlation between local and lattice contributions of the electric field gradient in semiconductors and insulators is presented. The local component of the electric field gradient in binary oxides, originated in extraionic contributions, is extracted from all quadrupole coupling constants measured in Perturbed Angular Correlation experiments with 111Cd probes. The resulting systematics reveals a linear dependence of the local component over a wide range of ionic efg values, both contributing with opposite signs. The clustering of the data points is explained in terms of the oxygen near neighbor symmetry.
THE NATURE OF THE IN-GAP STATES IN WEAKLY DOPED La2−x Srx CuO4
Authors: OVCHINNIKOV S.G.
Published: November 2004

A single-particle density of states is calculated in the strong electron correlation limit of the generalized multiband Hubbard model by exact diagonalization for CuO4 cluster. Several in-gap states are induced by hole doping that are mixtures of Cu d(x2−y2) and b1 O states and Cu d(z2), O a1 states and nonbonding O states. The Fermi level depends on the hole concentration nonmonotonically. The critical concentration of the insulator-metal transition of the Anderson type is estimated.
DISORDER AND SUPERCONDUCTIVITY IN CONNECTION WITH HIGH Tc: AN OVERVIEW
Authors: WIECKO C.
Published: November 2004

There is a growing interest in the interplay between disorder and superconductivity in high T c phenomenon. After a short review of the field we discuss the work done both on the Anderson-Hubbard model, (semianalytically and numerically) and in the model which describes both extended and localized excitations. Enhancement of the superconducting pairing with disorder appears in some of the approaches.
INCORPORATING UNCERTAINTY IN NEURAL NETWORKS
Authors: KÄMMERER BERNHARD R.
Published: November 2004

We propose a method to incorporate the uncertainty of data in the computation process of neural networks. A measure of certainty is used on each input element in order to modulate the element's contribution to the whole input activity. The amount of certainty may result from knowledge about sensor data (e.g. detectable hardware faults or information from preprocessing steps) or may be determined in previous neurons. The method is developed and studied within the scope of the perceptron model and tested on an image processing application.
A REAL-TIME CONTROL ARCHITECTURE FOR AN APPROXIMATE PROCESSING BLACKBOARD SYSTEM
Authors: DECKER KEITH , GARVEY ALAN , HUMPHREY MARTY , LESSER VICTOR
Published: November 2004

Approximate processing is an approach to real-time AI problem solving in domains in which compromise is possible between the resources required to generate a solution and the quality of that solution. It is a satisficing approach in which the goal is to produce acceptable solutions within the available time and computational resource constraints. Previous work has shown how to integrate approximate processing knowledge sources within the blackboard architecture. However, in order to solve real-time problems with hard deadlines using a blackboard system, we need to have: (1) a predictable blackboard execution loop, (2) a representation of the set of current and future tasks and their estimated durations, and (3) a model of how to modify those tasks when their deadlines are projected to be missed, and how the modifications will affect the task durations and results.

This paper describes four components for achieving this goal in an approximate processing blackboard system. A parameterized low-level control loop allows predictable knowledge source execution, multiple execution channels allow dynamic control over the computation involved in each task, a meta-controller allows a representation of the set of current and future tasks and their estimated durations and results, and a real-time blackboard scheduler monitors and modifies tasks during execution so that deadlines are met.

An example is given that illustrates how these components work together to construct a satisficing solution to a time-constrained problem in the Distributed Vehicle Monitoring Testbed (DVMT).
ANA: AUTOMATIC NATURAL ACQUISITION
Authors: ENGUEHARD CHANTAL , TRIGANO PHILIPPE , MALVACHE PIERRE
Published: November 2004

Any system for natural language processing must be based on a lexicon. Once a model has been defined, there is the problem of acquiring and inserting words. This task is tedious for a human operator; on the one hand he must not forget any of the words, and on the other the acquisition of a new concept requires the input of a number of parameters.

In view of these difficulties, research work has been undertaken in order to integrate pre-existing “paper” dictionaries. Nevertheless, these are not faultless, and are often incomplete when processing a very specialized technical field. We have therefore searched to mitigate these problems by automating the enrichment of an already partially integrated lexicon.

We work in a technical field on which we have gathered different sorts of texts: written texts, specialist interviews, technical reports, etc. These documents are stored in an object oriented database, and form part of a wider project, called REX (“Retour d’EXpérience” in French, or “Feedback of Experience” in English).

Our system, called ANA, reads the documents, analyses them, and deduces new knowledge, allowing the enrichment of the lexicon. The group of words already integrated into the lexicon form the “Bootstrap” of the discovery process of new words: it collects the instances of the different concepts thought to be interesting, in order to gather the semantic information. A special module makes it possible to avoid an explosion of the size of the database. It is responsible for forgetting certain instances and maintaining the database in such a way that the order in which the texts are introduced bears no influence.
MATCHING OF STRUCTURAL SHAPE DESCRIPTIONS WITH HOPFIELD NET
Authors: BASAK JAYANTA , CHAUDHURY SANTANU , PAL S.K. , MAJUMDER D. DUTTA
Published: November 2004

Structural description of objects comprised descriptions of the parts and spatial relations between the parts. This paper presents a Hopfield net based scheme for matching structural shape descriptions. The current formulation of the matching scheme is general enough to take care of partial mismatch between the individual parts and spatial constraints between these parts. In addition, a transformation of the shape descriptions has been suggested with which shape descriptions containing asymmetrical spatial constraints between the parts can be matched using symmetric interconnection weights for the Hopfield net. The Hopfield net based formulation has been extended to consider the problem of finding the best match of the test shape descriptions with one of the stored prototypes. The matching scheme has been experimentally applied for recognition of hand-tools and symbols. In both cases, the network produced encouraging recognition results.
AN EXTENDED FRAMEWORK FOR EVIDENTIAL REASONING SYSTEMS
Authors: LIU WEIRU , HONG JUN , McTEAR M.F. , HUGHES J.G.
Published: November 2004

Use of the Dempster-Shafer (D-S) theory of evidence to deal with uncertainty in knowledge-based systems has been widely addressed. Several AI implementations have been undertaken based on the D-S theory of evidence or the extended theory. But the representation of uncertain relationships between evidence and hypothesis groups (heuristic knowledge) is still a major problem. This paper presents an approach to representing such knowledge, in which Yen’s probabilistic multi-set mappings have been extended to evidential mappings, and Shafer’s partition technique is used to get the mass function in a complex evidence space. Then, a new graphic method for describing the knowledge is introduced which is an extension of the graphic model by Lowrance et al. Finally, an extended framework for evidential reasoning systems is specified.
DECOMPOSITION OF BELIEF FUNCTION IN HIERARCHICAL HYPOTHESES SPACE
Authors: HAU HAI-YEN
Published: November 2004

Shafer’s theory of evidence has been used to deal with uncertainty in many artificial intelligence applications. In this paper, we will show that in a hierarchically structured hypotheses space, any belief function whose focal elements are nodes in the hierarchy is a separable support function. We propose an algorithm that decomposes such separable support function into simple support functions. It is shown that the computational complexity of this decomposition algorithm is O(N2). Applications of the decomposition of separable support functions to the data fusion problem and reasoning about the control problem is discussed.
LEARNING STEPPINGSTONES FOR PROBLEM SOLVING
Authors: RUBY DAVID , KIBLER DENNIS
Published: November 2004

One goal of Artificial Intelligence is to develop and understand computational mechanisms for solving difficult real-world problems. Unfortunately, domains traditionally used in general problem-solving research lack important characteristics of real-world domains, making it difficult to apply the techniques developed. Most classic AI domains require satisfying a set of Boolean constraints. Real-world problems require finding a solution that meets a set of Boolean constraints and performs well on a set of real-valued constraints. In addition, most classic domains are static while domains from the real world change. In this paper we demonstrate that SteppingStone, a general learning problem solver, is capable of solving problems with these characteristics. SteppingStone heuristically decomposes a problem into simpler subproblems, and then learns to deal with the interactions that arise between the subproblems. In lieu of an agreed upon metric for problem difficulty, we choose significant problems that are difficult for both people and programs as good candidates for evaluating progress. Consequently we adopt the domain of logic synthesis from VLSI design to demonstrate SteppingStone’s capabilities.
A CONNECTIONIST APPROACH TO SPEECH RECOGNITION
Authors: BENGIO YOSHUA
Published: November 2004

The task discussed in this paper is that of learning to map input sequences to output sequences. In particular, problems of phoneme recognition in continuous speech are considered, but most of the discussed techniques could be applied to other tasks, such as the recognition of sequences of handwritten characters. The systems considered in this paper are based on connectionist models, or artificial neural networks, sometimes combined with statistical techniques for recognition of sequences of patterns, stressing the integration of prior knowledge and learning. Different architectures for sequence and speech recognition are reviewed, including recurrent networks as well as hybrid systems involving hidden Markov models.
SIGNATURE VERIFICATION USING A “SIAMESE” TIME DELAY NEURAL NETWORK
Authors: BROMLEY JANE , BENTZ JAMES W. , BOTTOU LÉON , GUYON ISABELLE , LECUN YANN , MOORE CLIFF , SÄCKINGER EDUARD , SHAH ROOPAK
Published: November 2004

This paper describes the development of an algorithm for verification of signatures written on a touch-sensitive pad. The signature verification algorithm is based on an artificial neural network. The novel network presented here, called a “Siamese” time delay neural network, consists of two identical networks joined at their output. During training the network learns to measure the similarity between pairs of signatures. When used for verification, only one half of the Siamese network is evaluated. The output of this half network is the feature vector for the input signature. Verification consists of comparing this feature vector with a stored feature vector for the signer. Signatures closer than a chosen threshold to this stored representation are accepted, all other signatures are rejected as forgeries. System performance is illustrated with experiments performed in the laboratory.
COMPUTING OPTICAL FLOW WITH A RECURRENT NEURAL NETWORK
Authors: LI HUA , WANG JUN
Published: November 2004

Optical flow computation in dynamic image processing can be formulated as a minimization problem by a variational approach. Because solving the problem is computationally intensive, we reformulate the problem suitable for neural computing. In this paper, we propose a recurrent neural network model which may be implemented in hardware with many processing elements (neurons) operating asynchronously in parallel to achieve a possible real-time solution. We derive and prove the properties of the reformulation, as well as analyze the asymptotic stability and convergence rate of the proposed neural network. Experiments using both the test patterns and the real laboratory images are conducted.
INVARIANT OBJECT RECOGNITION BASED ON A NEURAL NETWORK OF CASCADED RCE NETS
Authors: LI WEI , NASRABADI NASSER M.
Published: November 2004

A neural network of cascaded Restricted Coulomb Energy (RCE) nets is constructed for the recognition of two-dimensional objects. A number of RCE nets are cascaded together to form a classifier where the overlapping decision regions are progressively resolved by a set of cascaded networks. Similarities among objects which have complex decision boundaries in the feature space are resolved by this multi-net approach. The generalization ability of an RCE net recognition system, referring to the ability of the system to correctly recognize a new pattern even when the number of learning exemplars is small, is increased by the proposed coarse-to-fine learning strategy. A feature extraction technique is used to map the geometrical shape information of an object into an ordered feature vector of fixed length. This feature vector is then used as an input to the neural network. The feature vector is invariant to object changes such as positional shift, rotation, scaling, illumination variance, variation of camera setup, perspective distortion, and noise distortion. Experimental results for recognition of several objects are also presented. A correct recognition rate of 100% was achieved for both the training and the testing input patterns.
STRUCTURED NETWORKS FOR ADAPTIVE LANGUAGE ACQUISITION
Authors: MILLER LAURA G. , GORIN ALLEN L.
Published: November 2004

We report on progress in understanding how to build machines which adaptively acquire the language for their task. The generic mechanism in our research has been an information-theoretic connectionist network embedded in a feedback control system. In this paper, we investigate the capability of such a network to learn associations between messages and meaningful responses to them as a task increases in size and complexity. Specifically, we consider how one might reflect task structure in a network architecture in order to provide improved generalization capability in language acquisition. We propose a method for constructing networks from component subnetworks, namely a product network, which provides improved generalization by factoring the associations between words and actions through an intermediate layer of semantic primitives. A two-dimensional product network was evaluated in a 1000-action data retrieval system, the object of which is to answer questions about 20 attributes of the 50 states of the USA. The system was tested by 13 subjects over a two-week period, during which over 1000 natural language dialogues were recorded. The experiment was conducted using typed input with unconstrained vocabulary and syntax. During the course of performing its task, the system acquired over 500 words and retained 92% of what it learned. We provide a description of the system and details on the experimental results.