bluuebunny/crossref_metadata_2025 huggingface dataset:
HTc dc SQUID Magnetometers
Authors: SARNELLI E. , TESTA G. , CAMERLINGO C. , RUSSO M. , PAGANO S.
Published: May 2003

High sensitivity HTc dc-SQUID magnetometers, of bicrystal junction type, have been designed, fabricated and characterized. The magnetometers are characterized by a direct-coupling planar design and their parameters and geometrical dimensions have been optimized in order to achieve the lowest possible noise level. The IV characteristics are RSJ-like and show no excess current. The measured SQUID normalized inductances and magnetic field modulation periods are in good agreement with the expected values. The magnetic field noise spectral densities, measured with a flux locked loop electronic setup, exhibit typical white noise levels of about 150 fT/Hz 1/2 at frequencies above 2 KHz. At lower frequencies a 1/f noise is observed. By employing a bias-reversal electronic readout scheme, the 1/f corner frequency can be reduced to values less than 100 Hz.
JOSEPHSON MESOJUNCTIONS AS DETECTORS OF LOW-INTENSITY QUANTIZED COHERENT FAR-INFRARED FIELDS
Authors: MIGLIORE R. , MESSINA A. , NAPOLI A.
Published: May 2003

We show that the quantum nature of a mesoscopic Josephson junction may be exploited for detecting low-intensity electromagnetic quantized fields. In particular we prove that intensity and phase of single-mode quantized coherent field may be reconstructed measuring amplitude and quantum noise of the first quantum Shapiro step occurring in the I-V characteristic of the ultrasmall Josephson junction.
DEVELOPMENT OF SUPERCONDUCTING Nb/Al DETECTORS
Authors: GRECO M. , MENICHETTI E. , RINAUDO G. , MAGGI S. , LACQUANITI V.
Published: May 2003

We have fabricated superconducting Nb/Al microstrip detectors. The low sensitivity to radiation damage and aging and the high energy resolution make these devices very attractive. The samples are fabricated by superposing a 2 mm × 2 mm Al area on a 5 μm wide, 100 μm long Nb strip. The thickness of each film is between 50 and 200 nm. We present the results both of steady and dynamical tests on Nb/Al bilayers, after irradiation with a 241 Am alpha-source (T = 5.47 MeV ). These devices can operate both in the on-off and in the auto-recovery regimes. We show that the performance of Nb/Al bilayers is better than single Nb strip devices.
DEVELOPMENT OF BUFFER LAYER STRUCTURES FOR YBa2Cu3O7-δ COATED CONDUCTORS ON TEXTURED Ni-V SUBSTRATE
Authors: MANCINI A. , BOFFA V. , CELENTANO G. , CIONTEA L. , DAMASCENI M. , FABBRI F. , GALLUZZI V. , GRIMALDI G. , PETRISOR T. , CERESARA S. , GAMBARDELLA U.
Published: May 2003

Y 2 O 3 and MgO-based buffer layer architectures on non-magnetic cube textured Ni-V substrates were studied for YBa 2 Cu 3 O 7-δ (YBCO) coated conductors fabrication using both pulsed laser deposition and electron beam evaporation. The Y 2 O 3 films exhibited a biaxial texture with φ and ω-scans full width at half maximum (FWHM) of about 11° and 7° and a smooth and continuous surface. YBCO thick films deposited on CeO 2/ Y 2 O 3/ Ni-V and CeO 2/ Y 2 O 3/ NiO/Ni-V architectures were mainly c-axis oriented showing a T C(R=0) above 85 K. MgO films were grown by electron beam evaporation both directly on metallic substrates and with a Pd intermediate layer. The MgO films grown on Ni-V substrates show a good texture and good surface morphological properties. The MgO deposition on Pd buffered Ni-V substrate leads to films with better structural properties with respect to MgO deposition on bare Ni-V substrate, showing φ and ω-scans FWHM up to 8° and 5°, respectively. In spite of the interdiffusion between Pd buffer layer and Ni-V substrate, the MgO films preserve their structural and morphological properties when annealed at typical YBCO deposition temperature.
PREPARATION AND CHARACTERIZATION OF BIAXIALLY TEXTURED METALLIC SUBSTRATES FOR HTS COATED CONDUCTORS
Authors: TUISSI A. , MASINI R. , VILLA E. , EVETTS J. E.
Published: May 2003

CuNi, NiCr, NiV alloys and pure Ni have been processed to obtain metallic substrates for high critical current density YBCO film depositions. High purity alloys were prepared using plasma arc furnace and the material was cold rolled to low thickness tapes. For all the tapes the (100)[001] cube alignment was induced by a primary recrystallization heat treatment after heavy cold rolling (RABITS). Besides the cube texture a good substrate should be smooth, thin, strong, non magnetic, resistant to oxidation, cold workable and low cost. In this work mechanical, magnetic and oxidation resistance properties of the prepared textured substrates were measured and compared.
PHASE DIAGRAMS OF SURFACE HEAVY ION IRRADIATED BI-2223/AG TAPES
Authors: GERBALDO R. , GHIGO G. , GOZZELINO L. , MINETTI B. , MEZZETTI E. , CARACINO P. , MARTINI L. , ZANNELLA S. , CHERUBINI R. , ROVELLI A.
Published: May 2003

Surface columnar defects, SCDs, are produced in high quality (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O y / Ag tapes by irradiating them with 0.25 GeV gold ions only on a top layer up to ≈15% of the full volume. The ion beam is orthogonal to the tape plane. In this paper we report experimental results of the surface implantation of columnar defects both in the high-current and in the low-current regime with a particular emphasis on the influence of SCDs on the anisotropy dependent properties. Some characteristic labels of the SCD implantation are pointed out. A comparison between all the results in the two current regimes is made. A hint is given concerning analogous results obtained by means of transport electrical measurements. The experimental data can be interpreted by assuming that a new confined phase driven by SCDs sets up in both the current regimes. Acting on the dose, it is possible to obtain tunable control of the in-field performance in both regimes.
STUDY OF THE TEXTURING IN BSCCO-AG TAPES THROUGH MAGNETIC MEASUREMENTS
Authors: FERDEGHINI C. , CIMBERLE M. R. , GRASSO G. , GUASCONI P. , MALAGOLI A. , PALLECCHI I.
Published: May 2003

We have developed a method that allows, by a simple set of magnetic measurements, to study the texturing of the grains inside a BSCCO-Ag tape. Because the texture is anisotropic we define the angle ϑ L that identifies the mean grain misalignment angle with respect to the tape surface in longitudinal direction (i.e. rolling direction) and the angle ϑ T in transverse direction. The technique is based on the assumption that, because of the very high anisotropy of the critical current density in BSCCO superconducting compounds, the magnetic moment is essentially generated by the current circulating in the a-b planes of the BSCCO grains. The different magnetisation cycles, measured when the orientation of the magnetic field with respect to the tape surface is changed, depend only on the grain orientation inside the tape, which determines the effective magnetic field component normal to the a-b planes of the grains. Here we present the texture evolution of the BSCCO grains inside silver sheated multifilamentary tape starting from the initial steps of the mechanical deformation up to the final heating stage. The results obtained from the magnetic method are compared with those obtained with other methods, i.e. X-ray diffraction and critical current density anisotropy. Also results obtained on samples prepared in different way will be presented.
NUMERICAL ANALYSIS OF HYSTERETIC LOSSES IN BSCCO/AG TAPES DUE TO TRANSPORT CURRENT AND EXTERNAL MAGNETIC FIELD
Authors: LA CASCIA P. , BIGONI L. , CEREDA E. , NEGRINI F. , OTTOBONI V. , RIBANI P. L.
Published: May 2003

A model to calculate hysteretic and transport losses in multifilamentary BSCCO/Ag tapes is described. The model considers a rectilinear infinitely long tape and is based on the two-dimensional Poisson equation for the magnetic vector potential. The equation is numerically solved by means of the finite element method. The contribution of both transport current and external magnetic field with any orientation with respect to the normal to the wide side of the tape is taken into account. A sinusoidal time dependence of the transport current and of the external magnetic field is considered but the model can analyze any time dependence of both quantities. A comparison between the calculated and experimental data is reported and discussed.
EXPERIMENTAL ANALYSIS AND CIRCUIT MODEL OF AN INDUCTIVE TYPE HIGH TEMPERATURE SUPERCONDUCTING FAULT CURRENT LIMITER
Authors: MORANDI A. , NEGRINI F. , NITTA T. , OSHIMA S. , RIBANI P. L.
Published: May 2003

A basic inductive type high temperature superconducting fault current limiter prototype has been built and tested at the Department of Electrical Engineering of the University of Tokyo. The experimental static V-I characteristics shows a change in the impedance of the device when its limiting current is reached. A circuit model of the fault current limiter is developed by means of a non linear inductor with memory. A good agreement is obtained between numerical and experimental V-I characteristics. Dynamic characteristics are numerically studied by means of the circuit model.
STRUCTURAL AND MAGNETIC PROPERTIES OF Y1-xZrxBa2Cu3O7-δ SUPERCONDUCTING COMPOUNDS
Authors: REDAC R. , SBARCIOG C. , COSMA I. , BORODI G. , POP I.
Published: May 2003

The high-T c Y 1-x Zr x Ba 2 Cu 3 O 7-δ superconductive ceramic material series with x = 0.01, 0.05 and 0.10 was sintered. The system was investigated from the structural and magnetic points of view. The room temperature X-ray pattern shows only orthorhombic reflection and unreacted zirconium oxide reflection. The temperature dependence of the magnetic susceptibility between liquid nitrogen and room temperature reflects a diamagnetic superconductive transition. The zirconium presence in the superconducting compounds determined the approximate linear increase of the critical temperature. The sintering temperature increase between 1200 and 1260 K lowers monotonously the critical temperature between 112 and 91.5 K.
SUPERPOSITION OF THE λ-PARAMETERIZED SQUEEZED STATES
Authors: WANG XIAO-GUANG , FU HONGCHEN
Published: May 2003

The superposition states of the λ-parameterized squeezed states are introduced and investigated. These states are intermediate states interpolating between the number and Schrödinger cat states and admit algebraic characterization in terms of su(1, 1) algebra. It is shown that these states exhibit remarkable nonclassical properties.
SPECIFIC HEAT STUDY OF THE CDW PHASE TRANSITION IN THE DOPED BLUE BRONZESTl0.3-xKxMoO3
Authors: WANG DINGLI , SHI JING , QIN XIAOKUI , TIAN MINGLIANG , XIAO QINGMING , TIAN DECHENG
Published: May 2003

The specific heat of the doped blue bronzes Tl0.3-xKxMoO3(x = 0.06, 0.15) has been measured in the temperature range between 100 and 220 K. Anomalies were observed at 165.7 K and 164.8 K for Tl0.24K0.06MoO3and Tl0.15K0.15MoO3, respectively. The specific heat jump, and the entropy and enthalpy changes associated with the CDW phase transition are estimated. The results suggest that the Peierls phase transition is of second order. By analogy with the behavior of pure Tl0.3-xMoO3, it shows that in the quasi-one-dimensional blue bronze, the perfect order of the interlayer alkali or thallium polyhedral chain plays an important role in the Peierls phase transition.
ELECTROMECHANICAL COEFFICIENTS OF MAGNETOELECTRIC PZT–CoFe2O4 COMPOSITE
Authors: SRINIVAS K. , PRASAD G. , BHIMASANKARAM T. , SURYANARAYANA S. V.
Published: May 2003

The magnetoelectric property of composite materials consisting of piezoelectric and piezomagnetic constituents are of interest since the stresses induced in them on application of an external magnetic field are converted into electrical signals. The electrical output is primarily due to electromagnetic coupling between the two participating phases. The present paper deals with the evaluation of the electromechanical coupling in the magnetoelectric composite consisting of 50% lead zirconate titanate (Pb0.96Sr0.04Ti0.47Zr0.53O3) and 50% CoFe2O4, the composition having maximum magnetoelectric conversion efficiency. A sum rule is proposed to calculate the electromechanical coupling coefficient and the results are correlated with the experimental data.
CONFINED HYDROGEN IN UNIFORM ELECTRIC FIELD
Authors: HUANG YUNG-SHENG , LIAW SY-SANG
Published: May 2003

We calculate the resonant energies and linewidths of hydrogen bounded by a parabolic cavity and exposed to an external uniform electric field. Energies and widths oscillate as a function of the size of the cavity. This interesting property differs from the previous result for the case of spherical cavity without the external field.
EFFECT OF PHASE FLUCTUATIONS OF LASER ON OPTICAL FORCES IN A TWO-LEVEL ATOM
Authors: LAWANDE S. V. , PANAT P. V.
Published: May 2003

An effect of phase fluctuations of a driving laser field on dissipative and dipolar forces of two-level atom is considered. The phase fluctuations are treated by a phase diffusion model where phase fluctuations follow Wiener–Levy process. An exact master equation for the relevant density operator is obtained and solved in the steady state. Optical forces are calculated. The effect of phase fluctuations on angular momentum imparted by a Laguerre–Gaussian beam and an ideal Bessel beam to the atom is investigated.
THE STRUCTURAL STUDY OF Fe2O3–TeO2–B2O3–SrF2 GLASSES BY EPR AND IR SPECTROSCOPIES
Authors: ARDELEAN I. , CIORCAS F. , PETEANU M. , BRATU I. , IONCU V.
Published: May 2003

The local structure of Fe2O3–TeO2–B2O3–SrF2 glasses was studied by recording the EPR and IR absorption spectra. Structural changes and increasing glass stability were evidenced with the addition of Fe2O3 in the sample. The distribution of isolated paramagnetic ions in sites of strongly distorted octahedral symmetry was detected at low concentration (up to 3 mol% Fe2O3) by means of EPR measurements. For x>3 mol% Fe2O3, the clustered iron ions become progressively preponderent in the system. Mixed valence states of iron ions involved in dipole–dipole and superexchange type interactions were also evidenced. The IR spectra analysis revealed the BO3, BO4 and B2O6 units in the structure of tellurite investigated glasses. Among these structural units, those containing the threefold boron atoms are predominant.
PHOTOINDUCED REACTIONS IN COMPLEXES CONSISTING OF A MAGNESIUM CATION AND METHYL HALIDE MOLECULES Mg+(XCH3)n
Authors: YANG S. H.
Published: May 2003

The metal cation Mg + and methyl halide molecules CH 3 X were linked through long-range forces to form Mg +( XCH 3)n. Photoexcitation of Mg + in the complexes gave rise to unusual reactions. We measured the relative yield of the products as a function of the excitation wavelength for several complexes in a broad spectral region. While photoexcitation of the cationic complex Mg + FCH 3 produced exclusively MgF and [Formula: see text], more channels are open in the photoreaction of Mg + ClCH 3. Surprisingly, when n>1, the photoexcitation of Mg +( FCH 3)n led to the predominant formation of the bare MgF + and/or its solvated variant.
ANOMALOUS TEMPERATURE EFFECT ON POINT-CONTACT Ag–LaBa2Cu3O7-x CONDUCTANCE SPECTRA
Authors: HATTA E. , SVISTUNOV V. M. , REVENKO Yu. F. , BELOGOLOVSKII M. A. , DOROSHENKO N. A. , PLITNIK G.
Published: May 2003

The observation of an anomalous temperature behavior of the differential conductance versus voltage curves in contacts formed by an Ag tip and a bulk ceramic LaBa2Cu3O7-x with Tc around 92 K is reported. For a wide range of temperatures from Tc to helium-liquid ones, we have found a crossover from curves typical for a pure conducting normal metal–superconductor interface up to Giaever tunneling characteristics with gap features shifted to high biases. We take into account the existence of a degraded interlayer with suppressed superconducting parameters between a normal injector and a superconducting bulk and interpret qualitatively the data in terms of mesoscopic proximity effects. We argue that as the temperature is decreased, (i) the electron localization in a disordered region is enhanced, and (ii) in the interlayer, inelastic scattering processes become more effective. The latter was considered as a result of the inelastic scattering rate changes for charge carriers interacting with magnetic excitations in the near-interface region of high-Tc compound junctions.
THE INFLUENCE OF MELTING TEMPERATURE ON IRON ION DISTRIBUTION IN Bi2O3·PbO·As2O3 GLASS MATRIX STUDIED BY EPR
Authors: ARDELEAN I. , PETEANU M. , SIMON V. , BORSA C. , CIORCAS F. , IONCU V.
Published: May 2003

Glasses of the system x Fe2O3·(1-x)[Bi2O3·P b O· As 2O3] in the composition range 0.5≤x≤30 mol% were investigated when prepared at 1000°C and 1250°C, respectively. The study was performed by means of EPR of Fe3+ ions. The effects of melting temperature on the valence state and structural distribution of iron ions were shown.
QUANTUM PHASE INTERFERENCE IN MAGNETIC MOLECULAR CLUSTERS
Authors: JIN YAN-HONG , NIE YI-HANG , LI ZHI-JIAN , LIANG J.-Q. , PU F.-C.
Published: May 2003

The oscillation of tunnel splitting in Fe8 molecular clusters is obtained as a function of magnetic field applied along the hard axis by means of the instanton method with both effective potential field description of quantum spin system and the semiclassical treatment. The theoretical splittings of the instanton method are compared with the numerical result by diagonalization of the spin Hamilton operator and experimental observations.
FABRICATION AND CHARACTERIZATION OF AQUEOUS SOL–GEL-DERIVED LaFeO3 THIN FILMS
Authors: RAJENDRAN M. , KRISHNA M. GHANASHYAM , BHATTACHARYA A. K.
Published: May 2003

A novel all-inorganic aqueous sol–gel process has been developed to fabricate LaFeO3 thin films by dip-coating. Stable, positively charged colloidal sol particles of hydrous lanthanum ferrite with an average particle size (Z av ) of 7 nm were prepared and coated onto quartz plates under controlled conditions. The sols have been characterized using photon correlation spectroscopy (PCS) for Z av and size distribution. The redispersible gel was characterized by thermogravimetric and differential thermal analysis (TG-DTA) and also by isothermal heating followed by X-ray diffraction to identify the reaction sequence to form LaFeO 3. The sol–gel films as deposited were X-ray amorphous on heating up to 500°C, partially crystalline at 600°C, fully crystalline and single phase at 650°C and above. These films were continuous, polycrystalline, single phase, had uniform thickness in the range between 180 to 1000 nm, depending on deposition conditions, and showed about 80% optical transmittance. The optical band gap varied from 2.7 to 3.3 eV as a function of the annealing temperature. The refractive index increased with increase in annealing temperature from 1.55 at 500°C to 1.86 at 800°C.
SIMPLE MODEL FOR INTERFACE EXCITON WITH THE ELECTRON-HOLE SEPARATION IN A STRONG MAGNETIC FIELD
Authors: THANH NGO VAN , VIET NGUYEN AI
Published: May 2003

A simple theoretical model for the interface exciton in a strong magnetic field is studied, in which the electrons are confined in the junction plane and the local hole in the quantum well (δ doping3). The main parameter of this model is the separation d between electron and hole, which are assumed to be confined in the two planes. By variational numerical calculations, we obtain its main parameters: binding energies, effective Bohr radius and oscillator strengths, which depend strongly on the magnetic length. We find good agreement with previous results.
FRACTALS FROM GENOMES
Authors: HAO BAI-LIN
Published: May 2003

A visualization scheme of avoided and under-represented strings in complete genomes reveals some nice patterns which become precise fractals in the non-biological limit of infinitely long strings. There arises the problem of calculating the dimensions of these fractals with self-similar and self-overlapping structures. Direct counting of avoided strings in a complete genome raises the problem of distinguishing true and redundant avoided strings of a given length knowing the number of shorter ones. The two problems turn out to be one and are solved exactly by using two different methods: combinatorics and language theory.
THEORETICAL INVESTIGATION ON THE PHASE STABILITY AND SITE PREFERENCE OF R(Co,T)12 AND R(Co,T)12Nx (R = Y, Ce, Pr, Nd, Sm, Gd, Tb, Ho, Er, Dy, T = Mo, Mn, Ni)
Authors: SHEN JIANG , QIAN PING , CHEN NAN-XIAN
Published: May 2003

The phase stability and site preference of some ternary elements of ThMn12 type rare-earth intermetallic compounds R ( Co , T )12 and R ( Co , T )12 N x are evaluated based on ab initio converted interatomic potentials. The calculated results show that adding either Mo or Mn makes the crystal cohesive energy decrease markedly. It proved that these elements can stabilize R ( Co , T )12 with the ThMn12 structure. The systemic energy is the lowest when T atoms occupy symmetrically 8i sites. For T = Mo or Mn, the doped nitrogen atom does not affect the order of site preference of these stabilizing elements. Moreover, the nitrogen atom occupies 2b sites. According to the calculated results, it can be seen that lattice parameters and X-ray patterns are in good agreement with experiment. All the above results indicate that the ab initio converted pair potentials are effective for the calculation of these kinds of anisotropy materials and some related nitrides.
THE USE OF PETRI NETS FOR THE DESIGN AND VERIFICATION OF ASYNCHRONOUS CIRCUITS AND SYSTEMS
Authors: KONDRATYEV ALEX , KISHINEVSKY MICHAEL , TAUBIN ALEXANDER , CORTADELLA JORDI , LAVAGNO LUCIANO
Published: May 2003

Petri nets46,37,45,48 are a powerful formalism for modeling concurrent systems. They are capable of implicitly describing a vast state space by a succinct representation which gracefully captures the notions of causality, concurrency and conflict between events. Petri nets have also been chosen by many authors as a formalism to describe the behavior of asynchronous circuits by interpreting the events as signal transitions, thus coining the term Signal Transition Graph (STG).50,4

A design framework for asynchronous systems involves three main aspects: formal specification, verification and synthesis. In this paper we review the main techniques we have used to cover these aspects in recent years, with a special focus on asynchronous circuits.
A CONSTRUCTIVE METHOD FOR FINDING LEGAL TRANSITION SEQUENCES IN PETRI NETS
Authors: HUANG JENG S. , MURATA TADAO
Published: May 2003

This paper considers the Petri net reachability problem formulated in terms of nonnegative integer solutions of the state equation and their net representation systems. Our main contributions are twofold. First, we show that algorithms for finding legal transition sequences can be easily given for subclasses of Petri nets where reachability criteria are known or can be formulated by our method. Second, for the general reachability problem where reachability theorems or criteria are not known, and thus an exhaustive search for legal transition sequences is inevitable, we introduce the notion of non-crucial sequences to reduce the search effort.
CHEBYSHEV-FAMILY OF TRANSITIONAL FILTERS
Authors: PAI K. R. , MURTHY K. V. V. , RAMACHANDRAN V.
Published: May 2003

The TCC (Transitional-Chebyshev-Chebyshev)-filters are examined in some detail. Closed-form expressions for pole-locations are obtained, where possible. In cases where it is not possible, algorithms or geometrical iterative methods have been enunciated in order to determine the pole-locations. Performance indices for certain low-order transitional filters have been computed and tabulated. These clearly illustrate the transitional nature of these filters.
ON THE CORRECTNESS OF HARDWARE SCHEDULING MECHANISMS FOR OUT-OF-ORDER EXECUTION
Authors: MUELLER SILVIA M. , PAUL WOLFGANG J.
Published: May 2003

Hardware scheduling mechanisms are commonly used in current processors in order to make better use of instruction level parallelism. So far, such a mechanism is considered to be correct, if it avoids the standard structural and data hazards. However, based on two classical scheduling mechanisms, it will be shown that this condition is neither sufficient nor necessary for the correctness of such a mechanism, and that deadlocks are a serious matter in out-of-order execution as well. In addition, the paper provides sufficient conditions for the correctness of scheduling mechanisms.
FILTERING APPLICATIONS OF FIELD PROGRAMMABLE ANALOG ARRAYS
Authors: PALUSINSKI O. A. , GETTMAN D. M. , ANDERSON D. , ANDERSON H. , MARCJAN C.
Published: May 2003

A Field Programmable Analog Array (FPAA), built in CMOS technology, contains uncommitted operational amplifiers, switches, and capacitors. A FPAA containing banks of programmable switched capacitors (SC) can be used to build filters for analog signals as well as a large number of diverse analog applications. The parameters of a given application, such as a filter, are functions of the capacitor values. Manufacturing and quantization errors may result in capacitor values in the FPAA other than those required by the application. For an FPAA to be a viable substitute for dedicated devices we must examine the error performance of the implementation. Such performance analysis can be built into the software to provide circuit designers with additional information. A methodology is described for determining a bound for the filter error as a function of capacitor errors and capacitor sizes. An example of detailed analysis for a low pass filter is included. Measurements of a low-pass filter implemented using Motorola's prototype FPAA compared favorably with the model predictions.
A LOW-VARIATION NONLINEAR NEURON CIRCUIT
Authors: DJAHANSHAHI HORMOZ , AHMADI MAJID , JULLIEN GRAHAM A. , MILLER WILLIAM C.
Published: May 2003

A resistive-type neuron circuit is presented that combines nonlinear characteristics of four MOS transistors to realize a saturating function. Despite circuit simplicity, characteristic variations are found to be small based on circuit analyses and fabrication measurements. Maximum variation between neurons within one chip is 1.3%, while worst-case chip-to-chip variation from 10 fabrications is 2.2%.
MATHEMATICAL MODELING OF ANALOG CONTROLLED VOLTAGE SOURCE CONVERTERS FOR IMPROVED DYNAMIC RESPONSE
Authors: GITAU M. N. , SMITH I. R. , KETTLEBOROUGH J. G.
Published: May 2003

Increases in the occurrence of nonlinear loads have resulted in the need to reduce or minimize the levels of harmonic currents being injected into the power supply. As a consequence, active current waveshaping and pulse-width modulation have now replaced conventional phase-controlled and diode bridge rectifiers in many applications. In this paper, mathematical models are developed for the power circuits of analog controlled single-phase and three-phase voltage source converters, and then used to analyse the performance of current- and voltage-control loops for the converters. Analytical expressions are derived for the gains and time constants of the current and voltage controllers, and it is shown that the bandwidth of the current-loop is a function of the switching frequency, and that of the voltage-loop is a function of the DC-busbar capacitance and the voltage filter cut-off frequency. To illustrate the application of the models, simulation results are presented from investigations into the control of a 5 kW single-phase voltage-source converter and a 100 kW three-phase boost converter.
ARTIFICIAL NEURAL COMPUTATIONS IN DIGITAL ARRAYS
Authors: CARD HOWARD
Published: May 2003

In this paper the properties of artificial neural network computations by digital VLSI systems are discussed. We also comment on artificial computational models, learning algorithms, and digital implementations of ANNs in general. The analysis applies to regular arrays or processing elements performing binary integer arithmetic at various bit precisions. Computation rates are limited by power dissipation which is dependent upon required precision and packaging constraints such as pinout. They also depend strongly on the minimum feature size of the CMOS technology. Custom digital implementations with low bit precision are emphasized, because these circuits require less power and silicon area. This may be achieved using stochastic arithmetic, with pseudorandom number generation using cellular automata.
NEURAL NETWORK INTEGRATED CIRCUITS WITH SINGLE-BLOCK MIXED SIGNAL ARRAYS
Authors: DJAHANSHAHI HORMOZ , AHMADI MAJID , JULLIEN GRAHAM A. , MILLER WILLIAM C.
Published: May 2003

This paper discusses the design and implementation of a family of mixed-signal neural network integrated circuits for general and application-specific purposes. Regular Arrays of a nonlinearly-loaded multiplier block form the core of multi-layer neural networks. Input-output circuitry and network size, however, vary depending on design applications. Salient features of the present architecture, such as modularity and reduced interconnection problems and areas are highlighted and circuit design and improvements are presented for its universal building block. Other design issues such as supply voltage and power reduction and pin limitations are discussed together with experimental results.
NEURAL EXCITABILITY, SPIKING AND BURSTING
Authors: IZHIKEVICH EUGENE M.
Published: May 2003

Bifurcation mechanisms involved in the generation of action potentials (spikes) by neurons are reviewed here. We show how the type of bifurcation determines the neuro-computational properties of the cells. For example, when the rest state is near a saddle-node bifurcation, the cell can fire all-or-none spikes with an arbitrary low frequency, it has a well-defined threshold manifold, and it acts as an integrator; i.e. the higher the frequency of incoming pulses, the sooner it fires. In contrast, when the rest state is near an Andronov–Hopf bifurcation, the cell fires in a certain frequency range, its spikes are not all-or-none, it does not have a well-defined threshold manifold, it can fire in response to an inhibitory pulse, and it acts as a resonator; i.e. it responds preferentially to a certain (resonant) frequency of the input. Increasing the input frequency may actually delay or terminate its firing.

We also describe the phenomenon of neural bursting, and we use geometric bifurcation theory to extend the existing classification of bursters, including many new types. We discuss how the type of burster defines its neuro-computational properties, and we show that different bursters can interact, synchronize and process information differently.
BIFURCATIONS AND OSCILLATORY BEHAVIOR IN A CLASS OF COMPETITIVE CELLULAR NEURAL NETWORKS
Authors: MARCO M. DI , TESI A. , FORTI M.
Published: May 2003

When the neuron interconnection matrix is symmetric, the standard Cellular Neural Networks (CNN's) introduced by Chua and Yang [1988a] are known to be completely stable, that is, each trajectory converges towards some stationary state. In this paper it is shown that the interconnection symmetry, though ensuring complete stability, is not in the general case sufficient to guarantee that complete stability is robust with respect to sufficiently small perturbations of the interconnections. To this end, a class of third-order CNN's with competitive (inhibitory) interconnections between distinct neurons is introduced. The analysis of the dynamical behavior shows that such a class contains nonsymmetric CNN's exhibiting persistent oscillations, even if the interconnection matrix is arbitrarily close to some symmetric matrix. This result is of obvious relevance in view of CNN's implementation, since perfect interconnection symmetry in unattainable in hardware (e.g. VLSI) realizations. More insight on the behavior of the CNN's here introduced is gained by discussing the analogies with the dynamics of the May and Leonard model of the voting paradox, a special Volterra–Lotka model of three competing species. Finally, it is shown that the results in this paper can also be viewed as an extension of previous results by Zou and Nossek for a two-cell CNN with opposite-sign interconnections between distinct neurons. Such an extension has a significant interpretation in the framework of a general theorem by Smale for competitive dynamical systems.
SYNCHRONIZATION OF COUPLED OSCILLATORS THROUGH CONTROLLED ENERGY TRANSFER
Authors: QUINN D. DANE , WANG FANG
Published: May 2003

We study the phenomena of synchronization in a system of two coupled oscillators. The oscillators, identical when decoupled, model forced pendula and are coupled with a linear torsional spring. Using the idea of energy transfer between the two oscillators, we derive nonlinear control laws which stabilize the in-phase motion. Physically, the additional control terms act through a controlled transfer the energy between the two oscillators. Thus the mechanical energy of the system remains constant as the oscillators are synchronized. Trajectories of the controlled system are required to remain on the constant energy surface of the Hamiltonian of the uncontrolled system, which represents the mechanical energy of the coupled oscillator system.
ANALYTICAL PREDICTION OF THE TWO FIRST PERIOD-DOUBLINGS IN A THREE-DIMENSIONAL SYSTEM
Authors: BELHAQ M. , HOUSSNI M. , FREIRE E. , RODRÍGUEZ-LUIS A. J.
Published: May 2003

Analytical study of the two first period-doubling bifurcations in a three-dimensional system is reported. The multiple scales method is first applied to construct a higher-order approximation of the periodic orbit following Hopf bifurcation. The stability analysis of this periodic orbit is then performed in terms of Floquet theory to derive the critical parameter values corresponding to the first and second period-doubling bifurcations. By introducing suitable subharmonic components in the first order of the multiple scale analysis the two critical parameter values are obtained simultaneously solving analytically the resulting system of two algebraic equations. Comparisons of analytic predictions to numerical simulations are also provided.
BIFURCATION TO HIGH-DIMENSIONAL CHAOS
Authors: HARRISON MARY ANN , LAI YING-CHENG
Published: May 2003

High-dimensional chaos has been an area of growing recent investigation. The questions of how dynamical systems become high-dimensionally chaotic with multiple positive Lyapunov exponents, and what the characteristic features associated with the transition are, remain less investigated. In this paper, we present one possible route to high-dimensional chaos. By this route, a subsystem becomes chaotic with one positive Lyapunov exponent via one of the known routes to low-dimensional chaos, after which the complementary subsystem becomes chaotic, leading to additional positive Lyapunov exponents for the whole system. A characteristic feature of this route is that the additional Lyapunov exponents pass through zero smoothly. As a consequence, the fractal dimension of the chaotic attractor changes continuously through the transition, in contrast to the transition to low-dimensional chaos at which the fractal dimension changes abruptly. We present a heuristic theory and numerical examples to illustrate this route to high-dimensional chaos.
ON A NONLOCAL EIGENVALUE PROBLEM AND ITS APPLICATIONS TO POINT-CONDENSATIONS IN REACTION–DIFFUSION SYSTEMS
Authors: WEI JUNCHENG
Published: May 2003

We consider a nonlocal eigenvalue problem which arises in the study of stability of point-condensation solutions in the Gierer–Meinhardt system and generalized Gray–Scott system. We give some sufficient conditions for stability and instability. The conditions are new and can be applied to the study of stability of single point-condensation solutions.
KINETIC COLLISION DETECTION FOR SIMPLE POLYGONS
Authors: KIRKPATRICK DAVID , SNOEYINK JACK , SPECKMANN BETTINA
Published: May 2003

We design a simple and elegant kinetic data structure for detecting collisions between polygonal (but not necessarily convex) objects in motion in the plane. Our structure is compact, maintaining an active set of certificates whose number is proportional to a minimum-size set of separating polygons for the objects. It is also responsive; on the failure of a certificate invariants can be restored in time logarithmic in the total number of object vertices. It is difficult to characterize the efficiency of our structure for lack of a canonical definition of external events. Nevertheless we give an easy upper bound on the worst case number of certificate failures.
POINT SET LABELING WITH SPECIFIED POSITIONS
Authors: DODDI SRINIVAS R. , MARATHE MADHAV V. , MORET BERNARD M.
Published: May 2003

Motivated by applications in cartography and computer graphics, we study a version of the map-labeling problem that we call the k-Position Map-Labeling Problem: given a set of points in the plane and, for each point, a set of up to k allowable positions, place uniform and non-intersecting labels of maximum size at each point in one of the allowable positions. This version combines an aesthetic criterion and a legibility criterion and comes close to actual practice while generalizing the fixed-point and slider models found in the literature.

We present a general heuristic that given an ∊ > 0, runs in time O(n log n + n log (R*/ ∊) log (k)), where R* is the size of the optimal label, and guarantees a constant approximation for any regular labels. For circular labels, our technique yields a (3.6 + ∊)-approximation, improving in the case of arbitrary placement over the previous bound of approximately 19.5 obtained by Strijk and Wolff.28 We then extend our approach to arbitrary positions, obtaining an algorithm that is easy to implement and also substantially improves the best approximation bounds. Our technique combines several geometric and combinatorial properties, which may be of independent interest.
TESTING THE CONGRUENCE OF d-DIMENSIONAL POINT SETS
Authors: BRASS PETER , KNAUER CHRISTIAN
Published: May 2003

This paper presents an algorithm that tests the congruence of two sets of n points in d-dimensional space in [Formula: see text] time. This improves the previous best algorithm for dimensions d≥6.
A SHORTEST PAIR OF PATHS ON THE PLANE WITH OBSTACLES AND CROSSING AREAS
Authors: KUSAKARI YOSHIYUKI , SUZUKI HITOSHI , NISHIZEKI TAKAO
Published: May 2003

Given obstacles and crossing areas together with two pairs of terminals on the plane, our algorithm finds a pair of rectilinear paths which connect the pairs of terminals, neither pass through any obstacle nor cross each other except in the crosssing areas, and minimize the total length, where all obstacles and crossing areas are assumed to be axis-parallel rectangles. The algorithm takes O(n log  n) time and O(n) space, where n is the total number of obstacles and crossing areas.
ISOMORPHIC TRIANGULATIONS WITH SMALL NUMBER OF STEINER POINTS
Authors: KRANAKIS EVANGELOS , URRUTIA JORGE
Published: May 2003

Assume that an isomorphism between two n-vertex simple polygons, P,Q (with k,l reflex vertices, respectively) is given. We present two algorithms for constructing isomorphic (i.e. adjacency preserving) triangulations of P and Q, respectively. The first algorithm computes isomorphic triangulations of P and Q by introducing at most O((k+l)2) Steiner points and has running time O(n+(k+l)2). The second algorithm computes isomorphic traingulations of P and Q by introducing at most O(kl) Steiner points and has running time O(n+kl log n). The number of Steiner points introduced by the second algorithm is also worst-case optimal. Unlike the O(n2) algorithm of Aronov, Seidel and Souvaine1 our algorithms are sensitive to the number of reflex vertices of the polygons. In particular, our algorithms have linear running time when [Formula: see text] for the first algorithm, and kl≤n/ log  n for the second algorithm.
A GRAPH DRAWING AND TRANSLATION SERVICE ON THE WORLD WIDE WEB
Authors: BRIDGEMAN STINA , GARG ASHIM , TAMASSIA ROBERTO
Published: May 2003

Both practitioners and researchers can take better advantage of the latest developments in graph drawing if implementations of graph drawing algorithms are made available on the WWW. We envision a graph drawing and translation service for the WWW with dual objectives: drawing user-specified graphs, and translating graph-descriptions and graph drawings from one format to another. As a first step toward realizing this vision, we have developed a prototype service which is available at .
NONSMOOTH ANALYSIS, CONVEX ANALYSIS, AND THEIR APPLICATIONS TO MOTION PLANNING
Authors: CHOSET HOWIE
Published: May 2003

Nonsmooth analysis of a broad class of functions taking the form F(x)= min ifi(x), where each fi is a convex function. One element of this class of functions is the distance function, which measures the distance between a point and the nearest point on the nearest obstacle. Many motion planning algorithms are based on the distance function, and thus rigorous analysis of the distance function can provide a better understanding of how to implement traditional motion planning algorithms. Finally, this paper enumerates some useful results in convex analysis.
PATH PLANNING IN EXPANSIVE CONFIGURATION SPACES
Authors: HSU DAVID , LATOMBE JEAN-CLAUDE , MOTWANI RAJEEV
Published: May 2003

We introduce the notion of expansiveness to characterize a family of robot configuration spaces whose connectivity can be effectively captured by a roadmap of randomly-sampled milestones. The analysis of expansive configuration spaces has inspired us to develop a new randomized planning algorithm. This new algorithm tries to sample only the portion of the configuration space that is relevant to the current query, avoiding the cost of precomputing a roadmap for the entire configuration space. Thus, it is well-suited for problems where only a single query is submitted for a given environment. The algorithm has been implemented and successfully applied to complex assembly maintainability problems from the automotive industry.
PARALLEL CONSTRUCTION OF QUADTREES AND QUALITY TRIANGULATIONS
Authors: BERN MARSHALL , EPPSTEIN DAVID , Teng Shang-Hua
Published: May 2003

We describe efficient PRAM algorithms for constructing unbalanced quadtrees, balanced quadtrees, and quadtree-based finite element meshes. Our algorithms take time O(log n) for point set input and O(log n log k) time for planar straight-line graphs, using O(n+k/log n) processors, where n measures input size and k output size.
k-PAIRS NON-CROSSING SHORTEST PATHS IN A SIMPLE POLYGON
Authors: PAPADOPOULOU EVANTHIA
Published: May 2003

This paper presents a simple O(n+k) time algorithm to compute the set of knon-crossing shortest paths between k source-destination pairs of points on the boundary of a simple polygon of n vertices. Paths are allowed to overlap but are not allowed to cross in the plane. A byproduct of this result is an O(n) time algorithm to compute a balanced geodesic triangulation which is easy to implement. The algorithm extends to a simple polygon with one hole where source-destination pairs may appear on both the inner and outer boundary of the polygon. In the latter case, the goal is to compute a collection of non-crossing paths of minimum total cost. The case of a rectangular polygonal domain where source-destination pairs appear on the outer and one inner boundary12 is briefly discussed.
COMPUTING HIGHLY ACCURATE SOLUTIONS OF A TUMOUR ANGIOGENESIS MODEL
Authors: VALENCIANO J. , CHAPLAIN M. A. J.
Published: May 2003

In this paper we describe and implement a numerical method which provides highly accurate solutions of a generic two-dimensional model for the formation of capillary networks as a partial process in tumour angiogenesis. The model includes effects due to diffusion, chemotaxis, haptotaxis and cell proliferation. The governing partial differential equation is a diffusion-advection-reaction equation of parabolic type. In order to achieve high accuracy in space, we use a semi-discretisation based on the spectral element method. The resulting system of stiff ordinary differential equations is advanced forward in time using one-step explicit higher order time integrators based on Taylor series expansions. The high accuracy in space is monitored by a residual based a posteriori error indicator while the high accuracy in time is guaranteed by the local and global truncation errors of the higher order Taylor series method.
ON-LINE CONSISTENCY TESTS FOR BAR DETECTORS
Authors: BAGGIO L. , CERDONIO M. , ORTOLAN A. , VEDOVATO G. , MARTINUCCI V. , PRODI G. A. , VITALE S. , TAFFARELLO L. , ZENDRI J.-P.
Published: May 2003

In order to detect gravitational wave signals with resonant bar detectors using Wiener–Kolmogorov (WK) filters, both a model for the power spectrum density (PSD) of the noise and a signal template should be provided. As the analysis is not meant to handle non-gaussian data, we have to discriminate (and constrain to) time periods where the noise follows a quasi-stationary gaussian model. Within these periods, candidate events are selected in the WK filter output, and their fundamental parameters (time of arrival and amplitude) are computed. A necessary and sufficient condition for the reliability of such estimates is the consistency of the signal shape with the template. This is done performing a goodness-of-the-fit test.
A POWER FILTER FOR THE DETECTION OF BURST SOURCES OF GRAVITATIONAL RADIATION IN INTERFEROMETRIC DETECTORS
Authors: ANDERSON WARREN G. , BRADY PATRICK R. , CREIGHTON JOLIEN D. E. , FLANAGAN ÉANNA É.
Published: May 2003

We present a filter for detecting gravitational wave signals from burst sources. This filter requires only minimal advance knowledge of the expected signal: i.e. the signal's frequency band and time duration. It consists of a threshold on the total power in the data stream in the specified signal band during the specified time. This filter is optimal (in the Neyman–Pearson sense) for signal searches where only this minimal information is available.
THE SIGNAL TRACK SEARCH ALGORITHM
Authors: BALASUBRAMANIAN R.
Published: May 2003

In order to detect gravitational waves from partially modelled/unmodelled sources we will need to have in place a group of robust data analysis algorithms. We discuss here, a particular time-frequency strategy, namely the Signal Track Search (STS) strategy, which is both robust and sensitive for a certain class of signals buried in Gaussian noise. We assume that the signal is a a broadband burst containing several cycles. Our basic strategy involves the construction of time-frequency maps of the detector output and subsequently a search for curvilinear structures in the maps. Though this strategy has been found to work extremely well when the noise is Gaussian, it remains to be seen whether the strategy will be effective when the detector output is further contaminated by non Gaussian noise sources. In this article we will discuss various unresolved issues pertaining to the STS algorithm.
DETECTION OF GRAVITATIONAL WAVES FROM INSPIRALING, COMPACT BINARIES USING A NETWORK OF INTERFEROMETRIC DETECTORS
Authors: BOSE SUKANTA , PAI ARCHANA , DHURANDHAR SANJEEV
Published: May 2003

We formulate the data analysis problem for the detection of the Newtonian waveform from an inspiraling, compact binary by a network of arbitrarily oriented and arbitrarily located laser interferometric gravitational-wave detectors. We obtain for the first time the relation between the optimal statistic and the magnitude of the network correlation vector, which is constructed from the matched network-filter.