bluuebunny/crossref_metadata_2025 huggingface dataset:
A DYNAMICAL MODEL OF THE BEHAVIOR OF HADRONIC AND FUNDAMENTAL STRINGS AT FINITE DENSITIES
Authors: LIZZI F. , SENDA I. , VISWANATHAN R.R.
Published: November 2004

A dynamical model of interacting strings with fixed total energy and finite energy density is studied. Results previously obtained for the case when the kinetic energy is small are extended by means of a full relativistic analysis. The nonlinear dynamical equations of the model are solved numerically and the equilibrium configurations for the case of both fundamental strings and the flux tube model of hadrons are investigated as a function of the energy density. Our results strongly suggest the formation of a resonance dominated phase for sufficiently large energy densities. The model is applied to the study of the evolution of hadronic matter produced in ion collision experiments. where the formation of a resonance dominated phase is noted immediately after the collision. Our results indicate that this nonequilibrium state decays rapidly and relaxes to equilibrium very soon after the collision, with a typical time scale of T~1/mπ~5−10−24 s.
A TEMPLATE FOR QUANTUM SPIN CHAIN SPECTRA
Authors: MARTIN PAUL , RITTENBERG VLADIMIR
Published: November 2004

We consider a series of N-state L(≥N) site quantum spin chains, characterised by the ordered partition of N into 2 parts, N=P+M. These (P/M) chains are invariant under an action of UqSU(P/M), and are built from a representation of the Hecke algebra HL-1(q). We establish that the intersection of the spectra of a (P/M) and (P'/M') chain of fixed length L is the spectrum of the (min(P,P')/min(M,M')) chain of that length. We establish that the spectrum of the (P/M) chain breaks into blocks corresponding to irreducible representations of HL-1(q) (or equivalently irreducible representations of UqSU(P/M)) characterised by Young diagrams with no rectangular subdiagrams of dimension (P+1)×(M+1) (height × width resp.). We give the corresponding quotient relations for the Hecke algebra. We discuss several implications of these results.
THE FREE–FERMION MODEL IN PRESENSE OF FIELD RELATED TO THE QUANTUM GROUP ${\mathcal U}_q(\widehat{sl}_2)$ OF AFFINE TYPE AND THE MULTI–VARIABLE ALEXANDER POLYNOMIAL OF LINKS
Authors: Murakami Jun
Published: November 2004

The free–fermion model in presense of fields discussed by Felderhof is reformulated as a solution of the Yang–Baxter equation associated with a family of 2–dimensional vector spaces. The trigonometric limit of this solution is equal to the Yang–Baxterization of the state model related to the multi–variable Alexander polynomial of links. This trigonometric limit is also equal to the R–matrix with respect to a family of representations of [Formula: see text] at [Formula: see text] of affine type.
MAGNETIZATION ANISOTROPY OF URANIUM CHALCOGENIDES
Authors: WESSELINOWA J. M. , GENCHEVA I. S.
Published: November 2004

A Green function technique is used to study the static properties of U-chalcogenides. Taking into account the spin-phonon interaction we obtain a strong magnetization anisotropy for UTe, in agreement with the experimental data.
ELECTRONIC SPECTRAL AND WAVEFUNCTION PROPERTIES OF ONE-DIMENSIONAL QUASIPERIODIC SYSTEMS: A SCALING APPROACH
Authors: HIRAMOTO HISASHI , KOHMOTO MAHITO
Published: November 2004

We review the results of the scaling and multifractal analyses for the spectra and wave-functions of the finite-difference Schrödinger equation: [Formula: see text] Here V is a function of period 1 and ω is irrational. For the Fibonacci model, V takes only two values (it is constant except for discontinuities) and the spectrum is purely singular continuous (critical wavefunctions). When V is a smooth function, the spectrum is purely absolutely continuous (extended wavefunctions) for λ small and purely dense point (localized wavefunctions) for λ large. For an intermediate λ, the spectrum is a mixture of absolutely continuous parts and dense point parts which are separated by a finite number of mobility edges. There is no singular continuous part. (An exception is the Harper model V (x) = cos (2πx), where the spectrum is always pure and the singular continuous one appears at λ = 2.)
MAGNETIC FLUCTUATIONS IN METALLIC AND SUPERCONDUCTING La2−xSrxCuO4
Authors: AEPPLI G.
Published: November 2004

The full momentum and energy dependent magnetic susceptibility χ(Q, ω) is a fundamental quantity which determines many readily measured properties, such as bulk susceptibilities and nuclear magnetic relaxation rates. Because there is still no agreement on the origin of the many anomalous properties of the high-Tc compounds, we have used inelastic neutron scattering to establish χ(Q, ω) in insulating metallic and superconducting samples of La 2−x Sr x CuO 4, arguably the simplest of the layered cuprous oxides. For the (x=0) insulator χ(Q, ω) has been determined throughout the Brioullin zone. At ω/ T >1, it is dominated by spin waves with a zone edge energy of 0.312±0.005 eV. (1,2) As x is increased and the metallic phase approached, the long wavelength anitiferromagnetic fluctuations become more rapid in a manner consistent with the marginal Fermi liquid Ansatz.(3) Finally, for the most metallic samples, the peak in the magnetic response found in the insulator at (π,π) (the antiferromagnetic ordering vector of pure La 2 CuO 4) splits into four maxima.(4) The correlation length at (π,π)±(π,0)δ and (π,π)±(0,π)δ does not depend strongly on x, and for x=0.14, is considerably longer than the spacing between holes in the CuO2 planes. However, ξ is strongly temperature-dependent, in contrast to what occurs for more insulating (lower x) crystals. Taken together, the results can be taken as evidence for the emergence of a Fermi surface, with the incommensurabilities corresponding to nesting vectors, and ξ corresponding to a mean free path for the carriers. In other words, the neutron scattering measurement is giving information of a type ordinarily yielded by de Haas van Alphen data. While the relatively large values for δ are inconsistent with single-band models for the CuO 2 planes, P. Littlewood and collaborators(5) have shown that Fermi surface nesting in a multiband model with reasonable hopping parameters can account for the observations at low temperatures.
The Phase Diagram of the Two-Dimensional t-J Model from High Temperature Expansions
Authors: Putikka W.O. , Luchini M.U. , Rice T.M.
Published: November 2004

The phase diagram of the 2D t-J model has been investigated using high temperature expansions. Series for the Helmholtz free energy, the inverse compressibility, the chemical potential and the uniform spin susceptibility through tenth order on a square lattice have been calculated using the finite cluster method.1 The series are analytically continued beyond their radius of convergence by Padé and integral approximants. The most accurate extrapolations can be made for the Helmholtz free energy where for J/t≈0.3 and n≈0.9 we can reach T~t/5. We can test the accuracy of the continuation methods by comparing with the 1D results for the boundary of phase separation of Ogata et al.2

In 2D a region of phase separation was found at T=0 for J/t lying above a line extending from J/t=3.8 at zero filling to J/t=1.2 at half filling. No phase separation was found at very small J/t contrary to the earlier suggestion of Emery et al3 which was based on results from exact diagonalisation on 4×4 clusters but in agreement with Quantum Monte Carlo (QMC) calculations on the Hubbard model.4

For very small J/t near half filling where the Nagaoka effect is possible, we find a region of divergent uniform magnetic susceptibility at T=0. However the divergence is very weak when compared with the exponential behaviour expected from a 2D ferromagnet. This might imply a substantially reduced moment which is consistent with the recent QMC estimates of Zhang et al.5
Spin Singlet Quantum Hall Effect and Nonabelian Landau-Ginzburg Theory
Authors: Balatsky Alexander
Published: November 2004

In this paper we present a theory of Singlet Quantum Hall Effect (SQHE). We show that the Halperin-Haldane SQHE wave function can be written in the form of a product of a wave function for charged semions in a magnetic field and a wave function for the Chiral Spin Liquid of neutral spin-½ semions. We introduce field-theoretic model in which the electron operators are factorized in terms of charged spinless semions (holons) and neutral spin-½ semions (spinons). Broken time reversal symmetry and short ranged spin correlations lead to SU(2)k=1 Chern-Simons term in Landau-Ginzburg action for SQHE phase. We construct appropriate coherent states for SQHE phase and show the existence of SU(2) valued gauge potential. This potential appears as a result of “spin rigidity” of the ground state against any displacements of nodes of wave function from positions of the particles and reflects the nontrivial monodromy in the presence of these displacements. We argue that topological structure of SU(2)k=1 Chern-Simons theory unambiguously dictates semion statistics of spinons.
Nonequilibrium Green’s Function Approach to Dynamic Properties of Resonant-Tunneling through Double-Barrier Structures
Authors: Chen L.Y. , Ting C.S.
Published: November 2004

In this paper, we review a recently developed approach to the dynamic properties of double barrier resonant tunneling systems, based on the nonequilibrium Green’s function technique and the Feynman path integral theory. The transient behavior of tunneling current, immediately after the switch-on of a dc bias voltage, is characterized by the building up process of tunneling electrons in the quantum well. The novel negative differential conductance demonstrates itself as a function of frequency of the small ac signal imposed upon a dc bias. The imaginary part of admittance is shown to be related to the conductance via a Kronig-Kramers relation. The noise characteristics clearly demonstrate a strong time correlation derived from the Pauli exclusion principle and have evident dependence upon the structure parameters and the bias voltage. All those theoretical results are compared with experiments and numerical simulations.
THE EDWARDS MODEL: DYNAMICAL EXTENSIONS OF THE EDWARDS MODEL
Authors: EDWARDS S.F.
Published: November 2004

A simple random walk in space if given a dynamical life is described by the Rouse model. The two extensions required to represent the movement of a macromolecule in solution are interactions, and hydrodynamic effects. It is argued that these can be incorporated into equations which then show, as a bonus, that the dynamics fully honours the topological integrity of the molecules. These ideas can be extended to suspensions of liquid drops, for which exact, topologically correct equations can be written down.
QUANTUM GROUP AND TWO-DIMENSIONAL GRAVITY
Authors: GERVAIS JEAN-LOUP
Published: November 2004

Current progress in understanding quantum gravity from the operator viewpoint are reviewed. They are based on the Uq(sl(2))-quantum-group structure recently put forward,1,2 for the chiral components of the metric in the conformal gauge.
GEOMETRY OF DIFFERENTIAL EQUATIONS AND PROJECTIVE REPRESENTATIONS OF THE WITT ALGEBRA
Authors: ITZYKSON C.
Published: November 2004

We give explicit expressions for the singular vectors in highest weight representations of the Virasoro algebra using a precise definition of fusion.
SELECTED PROPERTIES OF Y-Ba-Cu-O IN CONNECTION WITH THE PROPERTIES OF Cu-O CHAINS
Authors: UIMIN G.
Published: November 2004

Here we discuss some experimental evidence which supports a significant role of …-Cu-O…chain fragments, situated in oxygen deficient planes, in the doping of carriers into CuO 2 planes, in structural phase transitions and in many other normal and superconducting properties of Y-Ba-Cu-O . The relevant experiments are associated with the structural, magnetic, XAS, NMR/NQR investigations. The well-established phase diagram of YBa 2 Cu 3 O 6+x, i-e., the Néel, T N , and superconducting, T c , transition temperatures versus the oxygen content x, is the basis of the theory which should explain the structural phase transitions as well as the charge transfer mechanism. It appears that lattice-gas models do not answer all the requirements, particularly, concerned with the intrinsic chain fragments. Although the theory of the oxygen deficient plane, sharing quantum mechanics of finite chain fragments, statistical mechanics of the chain fragment ensemble as well as Monte Carlo simulations, is in its formative stage yet, it can readily apply to quantitative interpretation of selected experiments.
TDPAC STUDY OF COMPLEX STRUCTURE SEMICONDUCTOR COMPOUNDS — THE CASE OF NIOBIUM PENTOXIDE
Authors: SHITU J. , RENTERÍA M. , MASSOLO C.P. , BIBILONI A.G. , DESIMONI J.
Published: November 2004

A new method for analysing Time-Differential Perturbed Angular Correlation spectra is presented and applied to study the hyperfine interaction of 100 Rh in the high temperature modification of niobium pentoxide.

The measured quadrupole interactions are assigned to about 80% of the radiactive probes replacing niobium atoms in the lattice and about 20% located in perturbed sites. The origin of this perturbation, producing a high frequency component in the measured spectra is discussed and temptatively assigned to remaining radiation damage in the compound.

The hyperfine interaction of 111 Cd probes, introduced through thermal diffusion into niobium pentoxide, is also presented. The temperature dependence of the hyperfine parameters in this case is studied in the temperature range RT-800°C.

The spectral analysing method employed allows a direct comparison of experimental data with point charge model calculations and a simultaneous evaluation of the antishielding factor β. The obtained values (27 for 100 Rh and 15 for 111 Cd ) are discussed in terms of the compound and probe’s characteristics.
SUPERCONDUCTIVITY AND SUPERFLUIDITY IN FERMI SYSTEMS WITH REPULSIVE INTERACTIONS
Authors: BARANOV M. A. , CHUBUKOV A. V. , YU. KAGAN M.
Published: November 2004

We study the possibility of a pairing instability in Fermi systems with a purely repulsive interaction potential. The effective interaction between particles at the Fermi surface is shown to contain a contribution from the fermionic background. This contribution is attractive and in many cases it overshadows the interactive potential in the pairing channels with nonzero orbital angular momenta. In particular, we show that 3D Fermi gas with repulsive interaction is unstable against p-pairing. Both the value of T c and its field dispersion are consistent with the experimental data for pure 3 He . It is also shown that in a magnetic field and in the two-band model there is the possibility of a significant mcrease of T c . We also consider the situation in two dimensions, where the effect of the fermionic background is much weaker than in the 3D case. Nevertheless, we show that the positive-U Hubbard model may have an intrinsic instability at arbitrarily small carrier densities. In particular, the Hubbard model with hopping between nearest neighbors is unstable against d-wave pairing with dxy symmetry of the gap wave function. The superconducting states we study correspond to the actual minima of the Free energy.
DESIGN AND DEVELOPMENT OF FLOW BASED ELECTRO-RHEOLOGICAL DEVICES
Authors: BROOKS D. A.
Published: November 2004

The foundations for the design of electro-rheological (ER) actuating devices that use Poiseuille flow are laid. Systems of measurement to assess ER fluids are described including a high pressure flow apparatus. This was used to examine alternative valve geometries and fluids. A method is shown for the reduction of basic flow data to excess shear stress and shear rate.

Standard actuator arrangements are reviewed before the design of a flying control surface servomechanism is discussed. The evaluation of this validates the methods and indicates that the forces developed are within striking distance of those required for operational systems.
DISTRIBUTED ANECHOIC SYSTEM USING ELECTRICALLY ACTIVE FLUID
Authors: BHADRA D. K. , THOMPSON W. B.
Published: November 2004

A novel application of electrorheological fluid as a potential candidate for externally controllable anechoic material is discussed. The mechanism postulated is a resonant interaction of the incident compressional waves with the subsonic shear modes of the system. The energy dissipation is expected due to the existence of a loss modulus of the system.
SQUEEZING AND QUASIPROBABILITIES FOR A TWO-PHOTON JAYNES-CUMMINGS MODEL WITH ATOMIC MOTION
Authors: JOSHI AMITABH , LAWANDE SURESH V.
Published: November 2004

We study the squeezing and the quasiprobability distribution Q-function for an extended two-photon Jaynes-Cummings model (JCM) that includes atomic motion and the field mode structure. A comparative study of this model with respect to the standard model (in which the atom is at rest) has been presented here to isolate the effect of limited atom-radiation interaction time.
EXACT MANY BODY FERMI-BOSE TRANSMUTATION IN 2+1 DIMENSIONS
Authors: GAITONDE D.M. , RAO SUMATHI
Published: November 2004

We show that the low energy limit of relativistic fermions interacting with a statistical gauge field also includes a scalar interaction. When the Chern-Simons (CS) parameter µ=e2/2π and the scalar interaction is precisely that which is obtained through relativistic reduction, the many-body Hamiltonian can be solved exactly, directly in the fermion gauge, for the ground state energy which is zero and the ground state wavefunction which is gauge equivalent to one, characteristic of free bosons. Conversely, for N bosons interacting with a CS gauge field with µ=e2/2π, the mean-field ground state energy is πN2/m, which is characteristic of N free fermions.
ELECTROMETRIC SENSITIVITY OF THE SINGLE ELECTRON TRANSISTOR
Authors: KRECH WOLFRAM , HÄDICKE ANDREAS , MÜLLER HEINZ-OLAF
Published: November 2004

The essential part of the SET electrometer is the so-called SET transistor which consists of two serially coupled SET junctions driven by an external voltage. An external charge is influenced on the island between the two junctions. Furthermore, the influence of the electromagnetic environment is modelled by an additional impedance in the circuit. Using as well the two-state as the three-state approach, the mean-current through the double-junction, the shot-noise parameters and the charge sensitivity are calculated as a function of the driving voltage and the external charge on the island.
FULLERENE DERIVATIVES: STRUCTURES AND STABILITIES OF C60O AND C70O
Authors: RAGHAVACHARI KRISHNAN
Published: November 2004

Semi-empirical (MNDO) and ab-initio Hartree-Fock (3–21G) calculations on the structures and stabilities of C 60 O and C 70 O are reported. Two low energy isomers of C 60 O , formed by an oxygen atom bridging the two different C–C bonds in C 60, have been found. The first isomer has an epoxide structure with a bridging oxygen across the bond between two fused six-membered rings in C 60 (bridging C–C≈1.6 Å). Its 13 C NMR and infrared spectra are consistent with those seen for the experimentally isolated form of C 60 O . However, the second isomer containing a bridging oxygen across the bond between a five- and a six-membered ring is slightly more stable and appears to be the ground state of C 60 O . The bridging C–C bond opens out to a distance of ≈2.1 Å in this isomer. Endohedral isomers of C 60 O are calculated to be very high in energy. For C 70 O , we have characterized eight isomers formed by an oxygen atom bridging each of the eight distinct C–C bonds in C 70. The ground state isomer corresponds to oxygen bridging across an equatorial C–C bond in C 70 which opens out to a distance of ≈2.2 Å. This structure is different from the bridged paracyclene-like isomer proposed previously for C 70 O . Comparison is made between C 60 O and C 70 O .
SYNCHROTRON RADIATION AND LOW ENERGY ELECTRON DIFFRACTION STUDIES OF ULTRATHIN C60 FILMS DEPOSITED ON Cu(100), Cu(111) AND Cu(110)
Authors: Rowe J.E. , Rudolf P. , Tjeng L.H. , Malic R.A. , Meigs G. , Chen C.T. , Chen J. , Plummer E.W.
Published: November 2004

High resolution K-edge photoemission and X-ray absorption spectroscopies have been used to study the chemical properties of the interface formed with C 60 and Cu . We find that for very thin (0.24–1 monolayers) C 60 films, deposited in ultrahigh vacuum, the Cu substrate plays a role similar to that of K in K 3 C 60 films. Thus Cu donates charge to partially fill the π* LUMO band, and the C (1s) core level shifts due to charge transfer. For monolayer coverage the C (1s) core-level line shape is broad. Low energy electron diffraction studies of C 60 on Cu (100), Cu (111) and Cu (110) show that well ordered overlayers of thickness >2 monolayers can be formed on all three Cu surfaces, but single-domain epitaxy is achieved only on Cu (111). The substrate temperature during C 60 deposition is critical for the ordering of the film.
EVIDENCE FOR JAHN-TELLER COUPLING AND FANO RESONANCE OF LOWER Hg MODES IN K3C60 AND Rb3C60 FILMS FROM RAMAN SCATTERING
Authors: Denisov V.N. , Zakhidov A.A. , Danieli R. , Ruani G. , Zamboni R. , Taliani C. , Imaeda K. , Yakushi K. , Inokuchi H. , Achiba Y.
Published: November 2004

The Raman scattering study of superconducting thin films of A 3 C 60 (A=K,Rb) carried out upon laser excitations at 1.16 and 2.41 eV have revealed the significant broadening and Fano-lineshapes of several low energy H g intramolecular modes with relative intensities and widths depending on excitation energies. The most interesting feature of the 1.16 eV excited spectrum is the wide asymmetric band at 400 cm −1 which can be assigned by Fano-shape fitting to enormously broadened H g (2) mode red shifted compared to its bare frequency of 408 cm −1. The narrowing of all lower H g modes in insulating A 6 C 60 phase indicates strong electron-phonon coupling of this Jahn-Teller modes in x =3 phase and suggests that this low energy vibrations are contributing to superconducting pairing. However the possibility to interpret the wide band at 400 cm −1 as the maximum of electronic background can not be ruled out yet and is supported by our preliminary observations of its disappearance at low temperature below T c .
SUPERCONDUCTING PROPERTIES OF Sn ADDED (BiPb)2Sr2Ca1Cu2Oy
Authors: SEKHAR B. R. , SRIVASTAVA P. , ASOKAN K. , SAINI N. L. , GARG K. B.
Published: November 2004

The addition of Sn in two layered bismuthate superconductors has been investigated using EDAX and SEM. The addition of Sn was found to enhance Tc from 88 K( Sn =0) to 95 K ( Sn =0.3). The possible increase in oxygen content may be the reason for the increase in Tc.
MUTUAL STATISTICS, BRAID GROUP, AND THE FRACTIONAL QUANTUM HALL EFFECT
Authors: TING CHRISTOPHER
Published: November 2004

We show that the notion of mutual statistics arises naturally from the representation theory of the braid group over the multi-sheeted surface. A Hamiltonian which describes particles moving on the double-sheeted surface is proposed as a model for the bilayered fractional quantum Hall effect (FQHE) discovered recently. We explicitly show that the quasi-holes of the bilayered Hall fluid display fractional mutual statistics. A model for 3-dimensional FQHE using the multi-layered sample is suggested.
EXCITONIC CHARGE-DENSITY WAVE: A NOVEL PHASE OF DOUBLE QUANTUM WELL SYSTEMS
Authors: CHEN X.M. , QUINN J.J.
Published: November 2004

Theoretical studies of collective excitations of double quantum wells (DQW’s) in a strong magnetic field indicate that the systems undergo a phase transition when the well separation is larger than a critical value. For electron-hole DQW’s, we find that in the Hartree-Fock approximation this transition generates a novel excitonic density wave state, which has a lower energy than either a homogeneous excitonic fluid or a double charge-density wave state.
SYMMETRY BREAKING AND ORDER PARAMETERS OF THE HUBBARD MODEL
Authors: LIVI ROBERTO , MONTORSI ARIANNA , RASETTI MARIO
Published: November 2004

The effects of different linearization procedures as breaking of the global symmetry of the Hubbard model recently discovered by Yang and Zhang are discussed, together with the ensuing order parameters. In particular it is pointed out how only the Fermi linearization technique allows us both to restore the complete symmetry in the disordered phase, and to describe an ordered phase characterized by an order parameter associated with the breaking of the superconductive symmetry.
MAGNETIC FIELD DEPENDENCE OF CRITICAL CURRENTS IN SUPERCONDUCTING POLYCRYSTALS
Authors: KUGEL K.I. , LISOVSKAYA T. YU. , MINTS R.G.
Published: November 2004

We study the dependence of critical current j c on magnetic field H in superconducting polycrystals which are considered as systems of superconducting crystallites (isotropic or anisotropic) with Josephson contacts between them. Isotropy or anisotropy of contacts depends on the orientation of their crystallographic axes relatively to edges of contact planes. It is shown that for a system of randomly oriented isotropic contacts, the dependence j c (H) in a relatively wide field range has the asymptotic form j c ~( ln H)/H2. This differs drastically from j c (H) for single contacts. Anisotropy effects due to large differences in London penetration depth λ values corresponding to external magnetic field directed along different axes are analyzed in detail. It is shown that for uniaxal crystals with λ1=λ2≪λ3, this anisotropy leads to the relation [Formula: see text] for chaotic orientation of crystallites. The form of j c (H) curves for two different orientations of the magnetic field relatively to the transport current through the sample is found.
X-RAY-IRRADIATED KTiOPO4: ESR STUDIES
Authors: ANDREEV BORIS V. , EFIMOV VLADIMIR N.
Published: November 2004

The study of radiation paramagnetic centres (RPC) arising in flux-grown KTiOPO 4 (KTP) single crystals at X-ray-irradiation at 300 K was conducted by the ESR-method in the temperature range of 3.7÷300 K . For the first time in X-ray-irradiated KTP there were found electron and hole RPC stable at room temperature and related to Ti 3+ and Al 3+ impurity, respectively.
HALL EFFECT IN THIN FILMS WITH ROUGH SURFACE AND IMPURITY SCATTERING
Authors: QIU SHI-YUE
Published: November 2004

The result of microscopic, quantum calculations of one-electron conductivities, σxx (ω) and σxy (ω), in thin films with rough surface and impurity scattering, is reported. Although electronic conductivities have logarithmic singularity at low frequency within the weak localization regime, no such singularity is found for the Hall constant just like in the strictly two-dimensional disordered systems.
SPONTANEOUS MAGNETIZATION OF THE ISING MODEL ON THE ASANOHA LATTICE
Authors: LIN K. Y. , TSAI T. R.
Published: November 2004

We have derived exactly the spontaneous magnetization of the Ising model on the Asanoha (hemp leaf) lattice with nine two-spin coupling constants, two four-spin coupling constants, and three magnetic moments. The dual lattice of the 3–12 lattice is the Asanoha lattice which includes the triangular lattice and the diced lattice as special cases.
NEW EXACT TRANSFORMATIONS FOR HUBBARD OPERATORS
Authors: MARKELOV A. V.
Published: November 2004

In this work we present new exact transformations for Hubbard operators which reduce the problem of strong correlations to that of interacting Bose and Fermi gases. Some peculiarities of the phase diagram of t-J model are discussed.
EFFECT OF STRAIN ON Tl-Ba-Ca-Cu-O SUPERCONDUCTING FILMS FROM ION-BEAM SPUTTERED PRECURSORS ON FLEXIBLE SUBSTRATES
Authors: NAZIRIPOUR A. , KUWAHARA H. , NAKAMURA N. , DUAN H. M. , TIGGES C. P. , GINLEY D. S. , HERMANN A. M.
Published: November 2004

We have synthesized 1.5 micron thick superconducting Tl - Ba - Ca - Cu (TBCCO) films from ion-beam sputtered Ba - Ca - Cu - O precursors on yttria stabilized zirconia flexible substrates. The films have been characterized before and after thallium post-deposition annealing. Our initial data demonstrates that high quality films are produced by heat-treatment in a two-stage annealing. We show from bending experiments that mechanical strain in the films has little effect on the critical current density up to fracture.
NEGATIVE RESISTANCE IN AN ORGANIC THIN FILM
Authors: EHARA S. , TAKAGI T. , YOSHIDA T. , INABA H. , NAITO H. , OKUDA M.
Published: November 2004

The negative resistance of the tunneling currents was observed in a semiconducting organic thin film on a graphite substrate by an STM (Scanning Tunneling Microscopy). This negative resistance may be understood by the theory of a molecular resonance tunneling effect.
ON PARALLEL RECOGNITION OF TWO CLASSES OF 2-D ARRAY PATTERNS
Authors: RYTTER WOJCIECH , SAOUDI AHMED
Published: November 2004

We investigate the parallel complexity of recognition problems for context-free and regular array (image) sets. We show that the sequential time complexity of the recognition of an n × n image is O(n5). The space required for these recognition problems is O(n5). We prove that there are log 2n time parallel algorithms with BM (n4) and n2 BM (n) processors for the recognition of context-free and regular array sets, respectively, where BM (n) is the number of processors sufficient to multiply two boolean n × n matrices in logarithmic time. We develop also a methodology for processing images using composition systems.
IMPLEMENTATION OF THE Z-BUFFER ALGORITHM ON A RECONFIGURABLE NETWORK OF PROCESSORS
Authors: LI JIAN-JIN , MIGUET SERGE , ROBERT YVES
Published: November 2004

This paper describes the parallel implementation of the Z-Buffer algorithm on a distributed memory machine. The Z-Buffer is one of the most popular techniques used to generate a representation of a scene consisting of objects in a three-dimensional world. We propose and compare two different parallel implementations on a reconfigurable network of Transputers. In the first approach, the description of the scene is distributed among the processors configured as a tree. The picture is processed in a pipelined fashion, in order to output parts of the image during the computation of the remainder. We show the influence of the degree and the height of the tree on the global performance of the algorithm. In a second approach, both the picture and the scene description are distributed to the processors. We have therefore to redistribute dynamically the tiles among the processors at the beginning of the computation. To perform this redistribution, a special algorithm is designed for the case where the processors are configured as a unidirectional or bidirectional ring. Then we implement a greedy algorithm that enables us to perform the redistribution on an arbitrary interconnection network. We show that the two approaches are complementary: for small pictures or large scenes, a tree-based algorithm performs better than a redistribution-based algorithm, but for large pictures or smaller scenes, it is the other way round. We obtain substantial speedups over the sequential implementation, with up to 32 processors.
AN EFFICIENT HEURISTIC METHOD FOR STATE ASSIGNMENT OF LARGE SEQUENTIAL MACHINES
Authors: JÓŹWIAK LECH
Published: November 2004

VLSI circuit design is a “trial and error” process that consists of solving a number of design problems. An optimal state assignment is one of the most important problems in the logic synthesis for sequential machines and it consists of choosing a binary representation for symbolic internal states of a sequential machine, so that the resulting logic is optimal for a given objective. This problem belongs to the class of most complex computational problems in VLSI design – it is NP hard. In a strict sense, it has never been solved, except for exhaustive search, which is impossible for large machines even with a computer.

A structural heuristic approach uses specific knowledge about the structure of a given problem in order to reduce the search space to a manageable size and to maintain high quality solutions at the same time.

Using the state assignment problem as an example, we determined the importance of the structural heuristic approach in CAD for VLSI and we showed how to search for suitable heuristics. We discussed a new heuristic method for state assignments concentrating on heuristic aspects such as: the solution space, the generation procedure and its operators, the evaluation functions etc. We provided some experimental results to show that the new method is very efficient.

The structural heuristic search can be highly efficient. Its efficiency is limited more by the capacity of the human brain to think heuristically than by the complexity of the problem itself.
PLANAR ROUTING AROUND A RECTANGLE
Authors: LOU RUEY-DER , LIAO KUO-FENG , SARRAFZADEH MAJID
Published: November 2004

The problem of planar (single-layer) routing, of two- and multi-terminal nets, around a rectangle is considered. Necessary and sufficient conditions for the existence of a solution is presented. An O(n) time algorithm for obtaining a minimum-area planar routing, if one exists, is proposed, where n is the number of terminals.
IMAP: INTEGRATED MEMORY ARRAY PROCESSOR
Authors: FUJITA YOSHIHIRO , YAMASHITA NOBUYUKI , OKAZAKI SHIN-ICHIRO
Published: November 2004

This paper presents architectural features and performances for an Integrated Memory Array Processor (IMAP) LSI, which integrates a large capacity memory and a one-dimensional SIMD processor array on a single chip. The IMAP has a conventional memory interface, almost the same as a dual port video RAM with operational input extension. SIMD processing is carried out on the IMAP chip, using an internal processor array, while other higher level processing is concurrently accomplished with external processors through the random access memory port. In addition to the basic IMAP architecture, this paper describes orthogonal IMAP, which has an extended IMAP architecture. The basic IMAP uses a conventional memory cell, while the orthogonal IMAP uses an orthogonal memory for holding images.
A RECONFIGURATION TECHNIQUE FOR RELIABLE VLSI DSP ARRAY PROCESSORS
Authors: POPLI SANJAY P. , BAYOUMI MAGDY A. , TYAGI AKASH
Published: November 2004

Real-time digital signal processing (DSP) applications require high performance parallel architectures that are also reliable. VLSI arrays are good candidates for providing the required high throughput for these applications. These arrays which consist of a number of regularly interconnected processing elements (PEs) will not function correctly in the presence of even a single fault in any of the PEs. Fault tolerance has therefore become a vital design criterion for VLSI arrays. In this paper, a fault tolerance strategy for VLSI arrays is proposed, which significantly improves the reliability of the system. The fault tolerance scheme is composed of two phases: testing and locating faults (fault detection and diagnosis), and reconfiguration. The first phase employs an on-line error detection technique which achieves a compromise between the space and time redundancy approaches. This concurrent error detection technique reduces the rollback time considerably. The reconfiguration phase is achieved by using a global control responsible for changing the states of the switches in the interconnection network. Backtracking is introduced into the algorithm for maximizing the processor utilization, at the same time keeping the complexity of the interconnection network as simple as possible. Finally, a reliability analysis of this scheme using a Markov model and a comparison with some previous schemes are given.
PRACTICAL CONSIDERATIONS ON THE CALCULATION OF THE UNCERTAINTY EXPONENT AND THE FRACTAL DIMENSION OF BASIN BOUNDARIES
Authors: ANDROULAKAKIS STAVROS P. , HARTLEY TOM T. , GREENSPAN BERNARD , QAMMAR HELEN
Published: November 2004

The calculation of the uncertainty exponent as defined in Grebogi et al. [1983] is examined in detail, and it is modified to provide a more robust estimate of the fractal dimension of basin boundaries. Practical considerations of using the uncertainty exponent method are provided.
ON DETECTING STATIONARY BIFURCATIONS
Authors: SEYDEL R.
Published: November 2004

Locating stationary bifurcations amounts to measuring the singularity of parameter-dependent Jacobian matrices. A well-known example of a measure of singularity is the determinant, requiring O(n) operations to calculate when a decomposition of the matrix is available. This paper discusses an alternative for the case of rank-deficiency one. An algorithm will be based on elements of the inverse Jacobian. The alternative has useful scaling properties, providing estimates of a sensitivity analysis.
UNIVERSAL BEHAVIOR OF COUPLED NONLINEAR OSCILLATORS
Authors: LING F. H. , SCHMIDT G. , KOOK H.
Published: November 2004

Many coupled damped driven oscillator systems exhibit universal scaling behavior in the strength and coupling parameters. These scaling laws are those found in coupled one-dimensional maps, if the damping is sufficiently strong.
NUMERICAL ANALYSIS AND CONTROL OF BIFURCATION PROBLEMS (I): BIFURCATION IN FINITE DIMENSIONS
Authors: DOEDEL EUSEBIUS , KELLER HERBERT B. , KERNEVEZ JEAN PIERRE
Published: November 2004

A number of basic algorithms for the numerical analysis and control of bifurcation phenomena are described. The emphasis is on algorithms based on pseudoarclength continuation for algebraic equations. Several illustrative examples computed with the AUTO software package are included. Part II of this paper deals with ordinary differential equations and will appear in the next issue.
PREDICTING ATTRACTING OUT-OF-PHASE STATES IN COUPLED JOSEPHSON JUNCTIONS
Authors: SCHWARTZ IRA B. , TSANG KWOK YEUNG
Published: November 2004

Recent progress in understanding the dynamics and bifurcation of two coupled Josephson Junctions is numerically presented. The dependencies of the in-phase (IP) states and the anti-phase (AP) states on the parameters are shown when the coupling is symmetric. The connecting branches between the IP and AP are computed, and are found to be saddles which form the basin boundaries between the IP and AP states. A framework is presented based on a two oscillator model with asymmetric coupling which can predict the dynamics of higher dimensional systems. The behavior of out-of-phase (OP) states of n-junctions is examined using this asymmetric model when the oscillators are organized into two distinct groups.
FERN-LIKE STRUCTURES IN THE WILD SET OF THE STANDARD AND SEMISTANDARD MAPS IN C2
Authors: GELFREICH VASILY G. , LAZUTKIN VLADIMIR F. , SIMÓ CARLES , TABANOV MICHAEL B.
Published: November 2004

The standard and semistandard maps are considered in C2 and the behavior of the iterates on complex invariant manifolds of them is studied. This is an attempt to understand complicated real dynamics by looking at the enlarged complex dynamics. Expansions of the manifolds are given as well as criteria for escaping points and hyperbolicity. Some numerical explorations suggest the presence of fractal structures of fern type. Several conjectures suggested by these preliminary explorations are stated.
STOCHASTIC RESONANCE IN CHUA’S CIRCUIT
Authors: ANISHCHENKO V.S. , SAFONOVA M.A. , CHUA L.O.
Published: November 2004

In this paper, we report numerical observations of the stochastic resonance (SR) phenomenon in a bistable chaotic electronic circuit (namely, Chua’s circuit) driven simultaneously by noise and a sinusoidal signal. It is shown that the noise-induced “chaos-chaos” type intermittency is a physical mechanism of the SR-phenomenon in chaotic systems. The resulting amplification of the sinusoidal signal intensity is due to a coherent interaction of three characteristic frequencies of the system. The SR-phenomenon can be controlled by a variation of either the noise intensity or the system parameters in the absence of noise.
RIDDLED BASINS
Authors: ALEXANDER J.C. , YORKE JAMES A. , YOU ZHIPING , KAN I.
Published: November 2004

Theory and examples of attractors with basins which are of positive measure, but contain no open sets, are developed; such basins are called riddled. A theorem is established which states that riddled basins are detected by normal Lyapunov exponents. Several examples, both mathematically rigorous and numerical, motivated by applications in the literature, are presented.
TUTORIAL ON NEUROBIOLOGY: FROM SINGLE NEURONS TO BRAIN CHAOS
Authors: FREEMAN WALTER J.
Published: November 2004

Those classical models are reviewed that are most widely used by neurobiologists to explain the dynamics of neurons and neuron populations, and by modelers to implement artificial neural networks. Each neuron has input fibers called dendrites that integrate and an axon that transmits the output. The differing fiber architectures reflect these dissimilar dynamic operations. The basic tools to describe them are the RC model of the membrane, the core conductor model of the fibers, the Hodgkin–Huxley model of the trigger zone, and the modifiable synapse. Populations additionally require description of macroscopic state variables, the types of nonlinearity (most importantly the sigmoid curve and the dynamic range compression at the input to the cortex), and the types and strengths of connections. The properties of these neural masses can be characterized with the tools of nonlinear dynamics. These include description of point, limit cycle, and chaotic attractors for the cerebal cortex, as well as the types and mechanisms for the state transitions between basins of attraction during learning and perception.
A CATALYTIC SURFACE REACTION MODEL: ANALYSIS AND NUMERICAL SIMULATION
Authors: ZHANG WEN , GLADWELL IAN
Published: November 2004

We investigate a reaction-diffusion-convection model describing a catalyzed surface reaction. The model consists of parabolic partial differential equations involving non-diffusive and non-convective variables where the steady state is the solution of a system of ordinary differential algebraic equations. We analyze solution behavior through perturbation methods and exhibit a linear instability induced by the algebraic equations. Also we find multiple front solutions resulting from a jump discontinuity in the algebraic components. Numerical simulations are performed on the original system as well as the reduced system resulting from the singular perturbation technique. In addition to the stationary front solutions and multiple steady states, we find oscillations which closely relate to the stability at the equilibrium of the algebraic manifold of solutions. Experimentally we observe a regular oscillation when there is one Hopf point on the algebraic manifold, a period-doubling when two Hopf points bifurcate from one Hopf point and a chaotic oscillation when two Hopf points separate (in this last case an unstable segment occurs between the Hopf points).
FRACTAL BOUNDARIES IN PARTIAL DIFFERENTIAL EQUATIONS AND IN PHYSICS
Authors: PIACQUADIO LOSADA M.
Published: November 2004

We will say that Nature reads an object as fractal when the object's physical properties depend upon its – not necessarily integral – fractal dimension df. We will review a number of problems in physics in which an object is thus recognized as a fractal, annotating the corresponding laws L=L(df) of dependence on df. Next we will find that, although these problems are obviously not related, many such laws L(df) have a certain common structure, which we will identify, and denote with Ldf. Finally, we will solve some problems in pure mathematics – P.D.E. in regions with fractal boundaries – finding again and again, our function Ldf. Again, these pure-math problems are not related… what is the significance of Ldf? Our conjecture: such strong formulistic connections are due to profound underlying yet-to-be-studied relationships – for which Ldf is the clue – among the experimental problems, among the various pure math problems, and between the latter and the former.
EXPERIMENTAL CHAOS SYNCHRONIZATION IN CHUA'S CIRCUIT
Authors: CHUA LEON O. , KOCAREV LJUPCO , ECKERT KEVIN , ITOH MAKOTO
Published: November 2004

Several recent papers have investigated the feasibility of synchronization of chaotic systems. Experimentally one of the easiest systems to control and synchronize is the electronic circuit. This paper examines synchronization in Chua's Circuit, proven to be the simplest electronic circuit to exhibit chaotic behavior.
CRITERIA FOR COMPARING REUSE-ORIENTED DOMAIN ANALYSIS APPROACHES
Authors: WARTIK STEVEN , PRIETO-DÍAZ RUBÉN
Published: November 2004

Domain analysis, while still relatively new, has matured to the point where it is beginning to appear in production settings. This raises the problem of how to select among proposed approaches. Domain analysis approaches possess some similarities but differ in many ways — some subtle, some significant, some uninteresting. Comparing them is not simple.

This paper presents criteria for comparing and contrasting domain analysis approaches. The criteria were derived by studying five approaches that seem representative. The criteria attempt to provide a common conceptual ground for comparing and contrasting different ways to undertake domain analysis. The criteria are studied in terms of external factors that determine how and why an organization should use domain analysis. The criteria are first presented independent of any approach. They are then applied to the five approaches, to illustrate characteristics the approaches possess, and to show what some of the approaches' merits are. The paper concludes with some thoughts on the implications of the criteria for the future of domain analysis, considering in particular the likelihood of a single, unified approach emerging.
PARALLEL COMPUTATION OF INTERNAL AND EXTERNAL FARTHEST NEIGHBORS IN SIMPLE POLYGONS
Authors: GUHA SUMANTA
Published: November 2004

We present efficient parallel algorithms for two problems in simple polygons: the all-farthest neighbors problem and the external all-farthest neighbors problem. The all-farthest neighbors problem is that of computing, for each vertex p of a simple polygon P, a point ψ(p) in P farthest from p when the distance between p and ψ(p) is measured by the shortest path between them constrained to lie inside P. The external all-farthest neighbors problem is that of computing, for each vertex p of a simple polygon P, a point ϕ(p) on (the boundary of) P farthest from p when the distance between p and ϕ(p) is measured by the shortest path between them constrained to lie outside (the interior of) P. Both our algorithms run in O( log 2 n) time on a CREW PRAM with O(n) processors. Our divide-and-conquer method for the external all-farthest neighbors problem, in fact, leads to a new O(n log n) time serial algorithm that matches the currently best serial algorithm for this problem, but is simpler.
COMPUTATIONAL GEOMETRY COLUMN 16
Authors: O’Rourke Joseph
Published: November 2004

The papers presented at the Eighth ACM Symposium on Computational Geometry (June 1992) are summarized.
OPTICAL NONLINEARITIES IN SEMICONDUCTOR LASERS AND THEIR APPLICATIONS FOR FUNCTIONAL DEVICES
Authors: KAWAGUCHI HITOSHI
Published: November 2004

Optical functional devices based on the nonlinearities of laser diodes (LDs) are expected to be key components in future optical communications and switching systems, because of advantages such as the existence of optical gain and low optical switching power. This paper briefly summarizes optical nonlinearities in LDs and overviews the state-of-the-art active semiconductor photonic functional devices, such as bistable LDs and filters, and their applications to optical communications and photonic switching. Possibilities for improvements in switching speed, one of the biggest remaining problems, are also discussed.