bluuebunny/crossref_metadata_2025 huggingface dataset:
CONTENT-BASED IMAGE RETRIEVAL SYSTEM USING NEURAL NETWORKS
Authors: IKEDA TAKASHI , HAGIWARA MASAFUMI
Published: April 2003

An effective image retrieval system is developed based on the use of neural networks (NNs). It takes advantages of association ability of multilayer NNs as matching engines which calculate similarities between a user's drawn sketch and the stored images. The NNs memorize pixel information of every size-reduced image (thumbnail) in the learning phase. In the retrieval phase, pixel information of a user's drawn rough sketch is inputted to the learned NNs and they estimate the candidates. Thus the system can retrieve candidates quickly and correctly by utilizing the parallelism and association ability of NNs. In addition, the system has learning capability: it can automatically extract features of a user's drawn sketch during the retrieval phase and can store them as additional information to improve the performance. The software for querying, including efficient graphical user interfaces, has been implemented and tested. The effectiveness of the proposed system has been investigated through various experimental tests.
DYNAMICAL PROPERTIES OF MIN-MAX NETWORKS
Authors: GOLES ERIC , MATAMALA MARTÍN , ESTÉVEZ PABLO A.
Published: April 2003

In this paper we study the dynamical behavior of a class of neural networks where the local transition rules are max or min functions. We prove that sequential updates define dynamics which reach the equilibrium in O(n2) steps, where n is the size of the network. For synchronous updates the equilibrium is reached in O(n) steps. It is shown that the number of fixed points of the sequential update is at most n. Moreover, given a set of p≤n vectors, we show how to build a network of size n such that all these vectors are fixed points.
LOCAL LINEAR INDEPENDENT COMPONENT ANALYSIS BASED ON CLUSTERING
Authors: KARHUNEN JUHA , MĂlĂROIU SIMONA , ILMONIEMI MIKA
Published: April 2003

In standard Independent Component Analysis (ICA), a linear data model is used for a global description of the data. Even though linear ICA yields meaningful results in many cases, it can provide a crude approximation only for general nonlinear data distributions. In this paper a new structure is proposed, where local ICA models are used in connection with a suitable grouping algorithm clustering the data. The clustering part is responsible for an overall coarse nonlinear representation of the data, while linear ICA models of each cluster are used for describing local features of the data. The goal is to represent the data better than in linear ICA while avoiding computational difficulties related with nonlinear ICA.

Several data grouping methods are considered, including standard K-means clustering, self-organizing maps, and neural gas. Connections to existing methods are discussed, and experimental results are given for artificial data and natural images. Furthermore, a general theoretical framework encompassing a large number of methods for representing data is introduced. These range from global, dense representation methods to local, very sparse coding methods. The proposed local ICA methods lie between these two extremes.
A LOCAL TRAINING AND PRUNING APPROACH FOR NEURAL NETWORKS
Authors: CHANG SHENG-JIANG , LEUNG CHI-SING , WONG KWOK-WO , SUM JOHN
Published: April 2003

The training of neural networks using the extended Kalman filter (EKF) algorithm is plagued by the drawback of high computational complexity and storage requirement that may become prohibitive even for networks of moderate size. In this paper, we present a local EKF training and pruning approach that can solve this problem. In particular, the by-products obtained along with the local EKF training can be utilized to measure the importance of the network weights. Comparing with the original global approach, the proposed local EKF training and pruning approach results in a much lower computational complexity and storage requirement. Hence, it is more practical in solving real world problems. The performance of the proposed algorithm is demonstrated on one medium- and one large-scale problems, namely, sunspot data prediction and handwritten digit recognition.
IMPROVING ARTMAP LEARNING THROUGH VARIABLE VIGILANCE
Authors: CANUTO ANNE , FAIRHURST MICHAEL , HOWELLS GARETH
Published: April 2003

This paper presents a mechanism to vary the vigilance parameter in the RePART fuzzy neural network. This mechanism helps to smooth out the problem of category proliferation which affects ARTMAP-based networks. Empirical experiments show that the use of variable vigilance improves the performance of the RePART model while, at the same time, requiring a less complex structure.
METAL INDUCED CRYSTALLIZATION OF AMORPHOUS SILICON
Authors: JANG JIN , YOON SOO YOUNG
Published: April 2003

Metal induced crystallization of amorphous silicon (a-Si) has been studied for a thin Ni layer on the a-Si. The NiSi2 precipitates, nuclei for the crystallization, can be formed at less than 400°C on the a-Si. The growth of the needlelike crystallites, as a result of the migration of NiSi2 precipitates through a-Si, proceeds to <111> directions with <110> normal to the film surface. The crystallization velocity of a-Si is greatly enhanced and thus the crystallization temperature is lowered by applying an electric field to the a-Si. High-quality polycrystalline silicon having needlelike crystallites can be formed at temperatures as low as 400°C.
SUPERLATTICE MATERIALS FOR THE NEXT GENERATION OF LONG WAVELENGTH INFRARED DETECTORS
Authors: BROWN G. J. , SZMULOWICZ F. , MAHALINGAM K. , SAXLER A. , LINVILLE R. , ELHAMRI S. , LIN CHIH-HSIANG , KUO C. H. , HWANG W. Y.
Published: April 2003

New infrared (IR) detector materials with high sensitivity, multi-spectral capability, improved uniformity and lower manufacturing costs are required for numerous space-based infrared imaging applications. To meet these stringent requirements, new materials must be designed and grown using semiconductor heterostructures, such as quantum wells and superlattices, to tailor new optical and electrical properties unavailable in the current generation of materials. One of the most promising materials is a strained layer supperlattice (SLS) composed of thin InAs and GaInSb layers. While this material shows theoretical and early experimental promise, there are still several materials growth and processing issues to be addressed before this material can be transitioned to the next generation of infrared detector arrays. Our research is focused on addressing the basic materials design, growth, optical properties, and electronic transport issue of these superlattices.
THE ROLE OF BALLISTIC ELECTRON EMISSION MICROSCOPY FOR CHARACTERIZATION OF PHYSICAL PHENOMENA IN SEMICONDUCTOR ALLOYS AND QUANTUM STRUCTURES
Authors: NARAYANAMURTI VENKATESH , KOZHEVNIKOV MICHAEL
Published: April 2003

The measurement of the physical properties of individual semiconductor quantum objects at a length scale corresponding to the de Broglie wavelength of electrons in most semiconductors (a few mm) is a difficult challenge. Determination of spectroscopic properties of individual quantum objects buried below the surface is particularly daunting. In this paper we will review briefly recent progress in the use of BEEM (ballistic electron emission microscopy) for the study of semiconductor alloys and novel quantum objects. We will also discuss general aspects of BEEM experiment and theory in true ballistic and quasi-ballistic hot carrier transport. Examples of the use of this technique for studying buried heterojunctions will be presented. Potential modifications of the technique for imaging the optical emission under conditions of ballistic electron injection will also be discussed.
CAD TOOLS AND OPTICAL DEVICE MODELS FOR MIXED ELECTRONIC/PHOTONIC VLSI
Authors: DENG J. , SHUR M. S. , FJELDLY T. A. , BAIER S.
Published: April 2003

This work addresses the issue of circuit simulation and photonic device modeling for mixed electronic/photonic VLSI. We present a basic approach to establishing the mixed electronic/photonic circuit simulator Photonic SPICE, where optical devices and interconnects are represented in terms of electrical equivalents. We also present results on the compact models of vertical-cavity surface emitting lasers (VCSELs) implemented in AIM-Spice. The VCSEL model is based on first-order rate equations that are expressed in terms of an electrical equivalent circuit. The model accounts for the VCSEL self-heating effects.
850-NM VERTICAL-CAVITY SURFACE-EMITTING LASERS ON SI SUBSTRATES
Authors: ZHOU Y. , XIONG Y. , LO Y.-H. , JI C. , ZHU Z. H. , BASHAR S. A. , ALLERMAN A. A. , HARGETT T. , SIEG R. , CHOQUETTE K. D.
Published: April 2003

By employing a reactive low temperature wafer bonding technique, we have demonstrated oxide-defined 850 nm vertical-cavity surface-emitting lasers (VCSEL's) on Si substrates. Devices reach a differential quantum efficiency of 53% and a light output power of 7.1 mW under room temperature and continuous-wave operation without a heat sink.
HIGH SPEED RESONANT-CAVITY InGaAs/InAlAs AVALANCHE PHOTODIODES
Authors: CAMPBELL J. C. , NIE H. , LENOX C. , KINSEY G. , YUAN P. , HOLMES A. L. , STREETMAN B. G.
Published: April 2003

The evolution of long-haul optical fiber telecommunications systems to bit rates greater than 10 GB/s has created a need for avalanche photodiodes (APDs) with higher bandwidths and higher gain-bandwidth products than are currently available. It is also desirable to maintain good quantum efficiency and low excess noise. At present, the best performance (f3dB ~ 15 GHz at low gain and gain-bandwidth product ~ 150 GHz) has been achieved by AlInAs/InGaAs(P) multiple quantum well (MQW) APDs. In this paper we report a resonant-cavity InAlAs/InGaAs APD that operates near 1.55 μm. These APDs have achieved very low noise (k equivalent to 0.18) as a result of the very thin multiplication regions that were utilized. The low noise is explained in terms of a new model that accounts for the non-local nature of impact ionization. A unity-gain bandwith of 24 GHz and a gain-bandwidth-product of 290 GHz were achieved.
PHOTONIC CRYSTAL NANOCAVITY LASERS
Authors: SCHERER A. , PAINTER O. , HUSAIN A. , VUCKOVIC J. , DAPKUS D. , O'BRIEN J.
Published: April 2003

When combined with high index constrast slabs in which light can be efficiently guided, microfabricated two-dimensional photonic bandgap mirrors provide us with the geometries needed to confine light into extremely small volumes. We show that these high Q cavities now make it possible to define microcavity lasers which function at room temperature and have mode volumes as small as 2.5 (λ/2nslab)3 or 0.03 μm3 in InGaAsP emitting at 1.55μm.
THEORY AND APPLICATIONS OF GREEN'S FUNCTIONS
Authors: BAGHAI-WADJI ALI R.
Published: April 2003

In this chapter it is shown that three dimensional governing- and constitutive equations in transversally inhomogeous piezoelectric media can be diagonalized. A symbolic notation has been introduced which allows to perform the diagonalization simply by inspection. Diagonalized differential equations transform into eigenvalue forms in Fourier domain. Solving for the corresponding eigenpairs, the construction of various Green's functions has been demonstrated by several examples. In addition novel ideas for the calculation of self-actions in the boundary element method have been discussed. The work consists of four sections. Following a brief introduction in the first section, the diagonalization procedure is described in the second section. The presented methodology is a refinement of the author's ideas which were presented in various short courses. The third section on Green's function theory and the calculation of self-actions in the boundary element builds upon the author's lecture notes. The fourth section briefly summarizes our discussion and suggests directions for possible future research.
PSEUDO AND HIGH VELOCITY PSEUDO SAWs
Authors: CUNHA MAURICIO PEREIRA DA
Published: April 2003

This article discusses the characteristics of pseudo surface waves (PSAWs) and high velocity pseudo surface waves (HVPSAWs). The fundamental properties of these waves, the matrix method formulation, the different solution types due to crystal symmetry, early experiments on HVPSAWs, and practical applications of pseudo surface acoustic waves serve as an introduction. The solutions to the pseudo modes are discussed by analyzing the boundary condition function for several orientations. The relation between the radiating partial modes and the sagittal plane bulk slowness reveals new characteristics of the different symmetry types of HVPSAW, and helps classify and understand the pseudo modes. The acoustoelectric Poynting vector is used along different crystal symmetry orientations to reveal and discuss the pseudo SAW characteristics: penetration depth, declination of the power vector, and an estimation of power flow angle. Experimental data and numerical solutions of HVPSAW and PSAW along selected planes and orientations are discussed. This article concludes with a brief analysis of layered structures on different symmetry type substrates and a discussion of the layered pseudo surface wave properties.
HIGH-SPEED AND HIGH-DATA-BANDWIDTH TRANSMITTER AND RECEIVER FOR MULTI-CHANNEL SERIAL DATA COMMUNICATION WITH CMOS TECHNOLOGY
Authors: FUKAISHI MUNEO , NAKAMURA KAZUYUKI , YOTSUYANAGI MICHIO
Published: April 2003

This paper briefly reviews recent research on CMOS gigahertz-rate communication circuits and design innovations for overcoming device performance limitations. A multi-channel transmitter and receiver chip set operating at 5 Gb/s has been developed using 0.25-μm CMOS technology. To achieve high-speed operation, the chip set features: (1) a tree-type demultiplexer and frequency conversion architecture, (2) a self-aligning phase detector for clock and data recovery circuit, and (3) a fully pipelined 8-bit to 10-bit encoder. The features contributing to the achievement of high-data bandwidth for multi-channel transmission include circuits for compensating for the phase difference between multiple receiver chips and for the frequency difference between the system clocks of the transmitter and receiver chips. These techniques for high-speed operation and multi-channel transmission are supported by the high level of integration possible with CMOS technology compared with non-CMOS technology.
Progress toward 100 GHz Logic in InP HBT IC Technology
Authors: FIELDS C. H. , SOKOLICH M. , THOMAS S. , ELLIOT K. , JENSEN J.
Published: April 2003

Future wideband communications, mm-wave digital synthesis, and digital beam-steering will benefit from digital operation at clock frequencies between 50 and 100 GHz at reasonable power levels. HRL has developed InP-based HBT technology that is capable of supporting these needs. We have demonstrated InP HBTs with cutoff frequencies, ft, over 200 GHz and with f max over 300 GHz as well as fully static dividers operating at 72.8 GHz.
CANTILEVERED BASE InP DHBT FOR HIGH SPEED DIGITAL APPLICATIONS
Authors: GUTIERREZ-AITKEN AUGUSTO L. , KANESHIRO ERIC N. , MATSUI JAMES H. , SAWDAI DONALD J. , NOTTHOFF JOHANNES K. , CHIN PATRICK T. , OKI AARON K.
Published: April 2003

High speed digital logic is essential in diverse applications such as optical communication, frequency synthesizers, and analog-digital conversion. Current research efforts indicate that technologies utilizing heterojunction bipolar transistors (HBT) are the preferred approach for systems operating at clock frequencies of 40 GHz and above (1-6). In this paper we report a novel InAIAs/InGaAs/InP double-HBT (DHBT) with a cantilevered base layer and undercut collector. We fabricated and demonstrated an 80 GHz 2:1 digital frequency divider, and a 5 GHz 8-bit phase/7-bit magnitude Direct Digital Synthesizer (DDS) chip with approximately 3000 transistors using this technology.
RF CMOS NOISE CHARACTERIZATION AND MODELING
Authors: CHEN CHIH-HUNG , DEEN M. JAMAL
Published: April 2003

This paper presents a through description of radio frequency (RF) noise characterization and modeling of CMOS transistors. It begins with the definition of the four noise parameter of a two-port network - minimum noise figure (NFmin), equivalent noise resistance (Rn), optimized source impedance (Ropt) and optimized source reactance (Xopt). These four parameters are used in device characterization and it is shown how they can be calculated by using the noise two-port network theory and a circuit simulator. Then two de-embedding procedures are discussed in detail for noise and scattering parameter de-embedding to get rid of the parasitic effects from the probe pads and interconnections in the device-under-test (DUT). Ideally there is no frequency and geometry limitation for the method based on a cascade configuration. Methods to directly extract the channel noise, induced gate noise and their correlation from the RF and noise measurements are developed and the extracted noise sources as a function of frequency and bias condition for different channel lengths a presented. Some design consideration for the design of low noise circuits - how to select the device size, choice of DC bias conditions and design device layout, are presented. Finally, some published noise models for the channel noise, induced gate noise and their correlation are discussed.
AN ALGEBRAIC DUALITY THEORY FOR MULTIPLICATIVE UNITARIES
Authors: DOPLICHER SERGIO , PINZARI CLAUDIA , ROBERTS JOHN E.
Published: April 2003

Multiplicative unitaries are described in terms of a pair of commuting shifts of relative depth two. They can be generated from ambidextrous Hilbert spaces in a tensor C*-category. The algebraic analogue of the Takesaki–Tatsuuma Duality Theorem characterizes abstractly C*-algebras acted on by unital endomorphisms that are intrinsically related to the regular representation of a multiplicative unitary. The relevant C*-algebras turn out to be simple and indeed separable if the corresponding multiplicative unitaries act on a separable Hilbert space. A categorical analogue provides internal characterizations of minimal representation categories of a multiplicative unitary. Endomorphisms of the Cuntz algebra related algebraically to the grading are discussed as is the notion of braided symmetry in a tensor C*-category.
GLASS TRANSITION TEMPERATURE AND FRACTAL DIMENSION OF PROTEIN FREE ENERGY LANDSCAPES
Authors: ALVES NELSON A. , HANSMANN ULRICH H. E.
Published: April 2003

The free-energy landscape of two peptides is evaluated at various temperatures and an estimate for its fractal dimension at these temperatures calculated. We show that monitoring this quantity as a function of temperature allows to determine the glass transition temperature.
ACOUSTIC LOGGING MODELING BY REFINED BIOT'S EQUATIONS
Authors: PLYUSHCHENKOV BORIS D. , TURCHANINOV VICTOR I.
Published: April 2003

An explicit uniform completely conservative finite difference scheme for the refined Biot's equations is proposed. This system is modified according to the modern theory of dynamic permeability and tortuosity in a fluid-saturated elastic porous media. The approximate local boundary transparency conditions are constructed. The acoustic logging device is simulated by the choice of appropriate boundary conditions on its external surface. This scheme and these conditions are satisfactory for exploring borehole acoustic problems in permeable formations in a real axial-symmetrical situation. The developed approach can be adapted for a nonsymmetric case also.
EFFECTS OF TECHNICAL TRADERS IN A SYNTHETIC STOCK MARKET
Authors: BERNASCHI M. , CASTIGLIONE F.
Published: April 2003

In Ref. 1, a new model for the description of the financial markets dynamics has been proposed. Traders move on a two dimensional lattice and interact by means of mechanisms of mutual influence. In the present paper, we present results from large-scale simulations of the same model enhanced by the introduction of rational traders modeled as moving-averages followers. The dynamics now accounts for log-normal distribution of volatility which is consistent with some observation of real financial indexes7 at least for the central part of the distribution.
ON THE DYNAMICS OF SOME NUMERICAL METHODS
Authors: AHMED E. , HEGAZI A. S.
Published: April 2003

From numerical methods point of view of dynamical systems, we have determined dynamical behaviors of the corresponding systems (i.e., chaotic, stable, bifurcations possibility, etc.). New versions of numerical methods are derived and we have compared the dynamical behaviors of the continuous dynamical systems with their corresponding discrete dynamical systems. An application of partial differential equations is given for reaction-diffusion and telegraph equations.
AN ADAPTED SYMPLECTIC INTEGRATOR FOR HAMILTONIAN PROBLEMS
Authors: VIGO-AGUIAR JESÚS , SIMOS T. E. , TOCINO A.
Published: April 2003

In this paper, a new procedure for deriving efficient symplectic integrators for Hamiltonian problems is introduced. This procedure is based on the combination of the trigonometric fitting technique and symplecticness conditions. Based on this procedure, a simple modified Runge–Kutta–Nyström second algebraic order trigonometrically fitted method is developed. We present explicity the symplecticity conditions for the new modified Runge–Kutta–Nyström method. Numerical results indicate that the new method is much more efficient than the "classical" symplectic Runge–Kutta–Nyström second algebraic order method introduced in Ref. 1.
FINITE SIZE SCALING BY USING SCALING FUNCTIONS IN TWO-DIMENSIONAL q = 2 AND 7 STATE POTTS MODELS
Authors: DEMIRTÜRK SEMRA , SEFEROĞLU NURGÜL , AYDIN MERAL , GÜNDÜÇ YIĞIT
Published: April 2003

The scaling behaviors of the percolation cumulant and the surface renormalization are studied on q = 2 and 7 state Potts models. The results show that the scaling functions can be safely used to determine infinite lattice transition points and the thermal and magnetic exponents indicating that these functions have very small correction to scaling contributions.
OFF-AXIAL DYNAMIC SYMMETRY BREAKING IN UNIAXIALLY ANISOTROPIC HEISENBERG FERROMAGNET
Authors: ACHARYYA MUKTISH
Published: April 2003

The dynamics of uniaxially (along the z direction) anisotropic Heisenberg ferromagnets (in three dimensions) in the presence of a magnetic field varying sinusoidally in time (along the x-direction only) is studied by Monte Carlo method using Metropolis rate. The time averaged (over a complete cycle of the oscillating field) value of z component of the magnetization continuously vanishes at a particular transition temperature associated with a dynamic symmetry breaking of mz-hx loop. The temperature variation of dynamic order parameter and the dynamic specific heat for different values of the anisotropy show that the transition temperature increases as the strength of anisotropy increases.
MEDICAL IMAGES REMOTE CONSULTATION
Authors: FERRARIS MAURIZIO , FRIXIONE PAOLO , SQUARCIA SANDRO
Published: April 2003

Teleconsultation of digital images among different medical centers is now a reality. The problem to be solved is how to interconnect all the clinical diagnostic devices in a hospital in order to allow physicians and health physicists, working in different places, to discuss on interesting clinical cases visualizing the same diagnostic images at the same time. Applying World Wide Web technologies, the proposed system can be easily used by people with no specific computer knowledge providing a verbose help to guide the user through the right steps of execution. Diagnostic images are retrieved from a relational database or from a standard DICOM-PACS through the DICOM-WWW gateway allowing connection of the usual Web browsers to DICOM applications via the HTTP protocol. The system, which is proposed for radiotherapy implementation, where radiographies play a fundamental role, can be easily converted to different field of medical applications where a remote access to secure data are compulsory.
DIDACTIC TOOLS ON THE WEB FOR STUDENTS AND TEACHERS: THE ISHTAR SERVER
Authors: LEONE DANIELA , NAVARRIA FRANCESCO-LUIGI , ROVELLI TIZIANO
Published: April 2003

A didactic project is being developed using multimedia techniques at the Physics Department of the University of Bologna to help both students and teachers. The ISHTAR WWW server comprises several courses on different chapters of physics and a set of tools for helping with the didactical activities. The level of the courses is adapted for students in their last years at high school and in their first years at university, and it is especially designed for students of the life sciences.
BROADBAND NETWORKS FOR DISTANCE EDUCATION AND TRAINING: SOME RESULTS AND PRACTICAL SOLUTIONS FROM A HUMAN FACTORS INVESTIGATION
Authors: PAPA FILOMENA
Published: April 2003

Distance education and training is one of the most promising application fields of broadband networks. The present contribution is focused on one of the main opportunities provided by broadband communication networks for distance education: advanced and interactive virtual classroom situations. In particular a virtual classroom field experiment, which employs broadband cellular radio telecommunication technologies is described. The investigation was realised, in cooperation, by Fondazione Ugo Bordoni (FUB) and RAI (Italian Public TV), using the tools made available by the human factors discipline. Some results of the investigation are presented concerning learners' performance and usability of the multimedia tele-education system including factors such as: ease of use usefulness; telepresence efficiency; users' satisfaction. Furthermore, operational results and practical solution coming out of the experiment are shown as well. They include the basic features of multimedia systems used in virtual classroom and the correct procedures for training teachers and learners in the equipment use.
DEPLOYMENT OF NATIVE IP MULTICAST ROUTING SERVICES ON THE ITALIAN ACADEMIC AND RESEARCH NETWORK
Authors: FERRARI TIZIANA , PINIZZOTTO ANTONIO , SOMMANI MARCO , POBRIC DAMIR
Published: April 2003

In 1993 the GARR (Italian Academic and Research Network) was connected to MBONE (worldwide IP multicast enabled network backbone). Since then, and especially in the last few years, this network has been used to test and develop new IP multicast routing protocols and applications. However it was a tunnel-based solution, not suitable for taking advantage of the new potential of IP multicast nor for use by a large community.

This paper describes the work done for a migration to a native IP multicast routing deployment, highlighting the solutions adopted when dealing with the implementation problems and the complex wide area network management. The aim of this work is also to ensure a native IP multicast connection with the other Research Networks and the rest of Internet.
ASPECTS OF VIRTUAL REALITY AND VISUALISATION
Authors: MCDONNELL CIARAN , MCATAMNEY HUGH , KEEGAN CATHAL , MCMAHON CATHERINE
Published: April 2003

The paper describes the development of some VR models for educational use and explores some of the technical and practical issues in the development of the models.
OPTIMALITY AND SELF-STABILIZATION IN ROOTED TREE NETWORKS
Authors: PETIT FRANCK , VILLAIN VINCENT
Published: April 2003

In this paper, we consider arbitrary tree networks where every processor, except one, called the root, executes the same program. We show that, to design a depth-first token circulation protocol in such networks, it is necessary to have at least [Formula: see text] configurations, where n is the number of processors in the network and Δi is the degree of processor pi.

We then propose a depth-first token circulation algorithm which matches the above minimal number of configurations. We show that the proposed algorithm is self-stabilizing, i.e., the system eventually recovers itself to a legitimate state after any perturbation modifying the state of the processors. Hence, the proposed algorithm is optimal in terms of the number of configurations and no extra cost is involved in making it stabilizing.
Load Balancing Using Processor Groups
Authors: GUYENNET Hervé , TREHEL Michel
Published: April 2003

This paper defines a group partitioning model with the view to improving the load balancing in a distributed system. Using modelling and simulation, we analyze the impact of this new partitioning technique on load balancing strategies. We show that a strategy based on group preference gives efficient results.
Using duplication for the multiprocessor scheduling problem with hierarchical communications
Authors: Bampis Evripidis , Giroudeau Rodolphe , König Jean-Claude
Published: April 2003

We propose a two-step algorithm that efficiently constructs a schedule of minimum makespan for the precedence multiprocessor constrained scheduling problem in the presence of hierarchical communications and task duplication. We consider the case where all the tasks of the precedence graph have unit execution times, and the multiprocessor is composed by an unbounded number of clusters with two identical processors each. The communication delay for transferring the data between a predecessor-task and a successor-task executed on processors of different clusters take a unit of time, while this cost becomes null whenever these tasks are executed on the same processor or on different processors of the same cluster. The first step of the algorithm computes for each task an earliest starting time of any of its copies and constructs a critical graph whereas the second step uses the obtained critical graph and task duplication to build up an earliest optimal schedule.
A Parallel Algorithm for Planar Orthogonal Grid Drawings
Authors: TAMASSIA ROBERTO , TOLLIS IOANNIS G. , VITTER JEFFREY SCOTT
Published: April 2003

In this paper we consider the problem of constructing planar orthogonal grid drawings (or more simply, layouts) of graphs, with the goal of minimizing the number of bends along the edges. We present optimal parallel algorithms that construct graph layouts with O(n) maximum edge length, O(n2) area, and at most 2n+4 bends (for biconnected graphs) and 2.4n+2 bends (for simply connected graphs). All three of these quality measures for the layouts are optimal in the worst case for biconnected graphs. The algorithm runs on a CREW PRAM in O( log n) time with n/ log n processors, thus achieving optimal time and processor utilization. Applications include VLSI layout, graph drawing, and wireless communication.
SYMMETRIC COMMUNICATION IN ALL-OPTICAL TREE NETWORKS
Authors: CARAGIANNIS IOANNIS , KAKLAMANIS CHRISTOS , PERSIANO PINO
Published: April 2003

We address the problem of allocating optical bandwidth to a set of communication requests in a tree-shaped all-optical network that utilizes Wavelength Division Multiplexing (WDM) technology. WDM technology establishes communication between pairs of nodes of the network by establishing tranceiver–receiver paths and assigning wavelengths to each path so that no two paths going through the same link use the same wavelength. Optical bandwidth is the number of distinct wavelengths. The important engineering problem to be solved is to establish communication between pairs of nodes so that the total number of wavelengths used is minimized.

In this paper, we focus on a special case of the problem considering patterns of requests that are symmetric, i.e. for any transmitter–receiver pair of nodes (v1, v2) there also exists its symmetric (v2, v1). Our motivation lies in the fact that many services that are expected to be supported by high performance optical networks in the future, require bidirectional reservation of bandwidth. We prove that the problem of optimizing the number of wavelengths used is NP-hard even when the underlying network is a binary tree. We also present two interesting lower bounds.
A HYPERCUBE ALGORITHM FOR SLIDING WINDOW COMPRESSION
Authors: KAKLAMANIS CHRISTOS , KONSTANTOPOULOS CHARALAMPOS , SVOLOS ANDREAS
Published: April 2003

Dictionary compression belongs to the class of lossless compression methods and is mainly used for compressing text files. The most known examples of this technique are the algorithms of the LZ coding family whose common feature is the use of an adaptive dictionary which is dynamically adjusting during the algorithm execution. In this paper, we present a parallel algorithm for one of these coding algorithms, namely the LZ77 coding algorithm also known as a sliding-window coding algorithm. We also present a parallel algorithm for the corresponding LZ77 decoding algorithm. Although there exist PRAM algorithms for various dictionary compression methods, their rather irregular structure has discouraged their implementation on practical interconnection networks such as the mesh and hypercube. However in the case of LZ77 coding/decoding, we show how to exploit the specific properties of the algorithm in order to achieve an efficient implementation on the hypercube. Specifically, we show how to encode a N-character string on a N-node hypercube in only O( log 2N) time. In contrast, a naive simulation of a PRAM algorithm of the LZ77 coding on the hypercube would have O( log 3N) complexity. In addition, we further enhance the performance of our parallel algorithms by using some known heuristics from the field of text compression.
AN ANALYTICAL METHOD FOR PARALLELIZATION OF RECURSIVE FUNCTIONS
Authors: AHN JOONSEON , HAN TAISOOK
Published: April 2003

Programming with parallel skeletons is an attractive framework because it encourages programmers to develop efficient and portable parallel programs. However, extracting parallelism from sequential specifications and constructing efficient parallel programs using the skeletons are still difficult tasks. In this paper, we propose an analytical approach to transforming recursive functions on general recursive data structures into compositions of parallel skeletons. Using static slicing, we have defined a classification of subexpressions based on their data-parallelism. Then, skeleton-based parallel programs are generated from the classification. To extend the scope of parallelization, we have adopted more general parallel skeletons which do not require the associativity of argument functions. In this way, our analytical method can parallelize recursive functions with complex data flows.
TUNING TASK GRANULARITY AND DATA LOCALITY OF DATA PARALLEL GPH PROGRAMS
Authors: LOIDL HANS-WOLFGANG , TRINDER PHILIP W. , BUTZ CARSTEN
Published: April 2003

The performance of data parallel programs often hinges on two key coordination aspects: the computational costs of the parallel tasks relative to their management overhead — task granularity; and the communication costs induced by the distance between tasks and their data — data locality. In data parallel programs both granularity and locality can be improved by clustering, i.e. arranging for parallel tasks to operate on related sub-collections of data.

The GPH parallel functional language automatically manages most coordination aspects, but also allows some high-level control of coordination using evaluation strategies. We study the coordination behavior of two typical data parallel programs, and find that while they can be improved by introducing clustering evaluation strategies, further performance improvements can be achieved by restructuring the program.

We introduce a new generic Cluster class that allows clustering to be systematically introduced, and improved by program transformation. In contrast to many other parallel program transformation approaches, we transform realistic programs and report performance results on a 32-processor Beowulf cluster. The cluster class is highly-generic and extensible, amenable to reasoning, and avoids conflating computation and coordination aspects of the program.
SCHRÖDINGER QUANTUM MODES ON THE TAUB–NUT BACKGROUND
Authors: COTĂESCU ION I. , VISINESCU MIHAI
Published: April 2003

The Schrödinger equation is investigated in the Euclidean Taub–NUT geometry. The bound states are degenerate and an extra degeneracy is due to the conserved Runge–Lenz vector. The existence of the extra conserved quantities, quadratic in four-velocities implies the possibility of separating variables in two different coordinate systems. The eigenvalues and eigenvectors are given in both cases in explicit, closed form.
A NEW SINGULARITY THEOREM IN RELATIVISTIC COSMOLOGY
Authors: RAYCHAUDHURI A. K.
Published: April 2003

It is shown that if the time-like eigenvector of the Ricci tensor is hypersurface orthogonal so that the space–time allows a foliation into space sections, then the space average of each of the scalars that appears in the Raychaudhuri equation vanishes provided that the strong energy condition holds good. This result is presented in the form of a singularity theorem.
THE CHIRALLY SPLIT DIFFEOMORPHISM ANOMALY AND THE μ-HOLOMORPHIC PROJECTIVE CONNECTION
Authors: KACHKACHI M. , DAFOUNANSOU O. , RHALAMI A. El
Published: April 2003

The relationship between the μ-holomorphic projective connection and the action ΓII necessary to write down the chirally split diffeomorphism anomaly when it is shifted to the Weyl anomaly is given. Then, using the [Formula: see text]-Cauchy kernel on the complex plane to solve the μ-holomorphic projective connection equation, we get the general expression for this type of projective connection. This enables us to compute the Green's functions contribution of the action ΓII to the shifting scheme.
PROMOTING FINITE TO INFINITE SYMMETRIES: THE (3 + 1)-DIMENSIONAL ANALOGUE OF THE VIRASORO ALGEBRA AND HIGHER-SPIN FIELDS
Authors: CALIXTO M.
Published: April 2003

Infinite enlargements of finite pseudo-unitary symmetries are explicitly provided in this letter. The particular case of u (2, 2) ≃ so (4, 2) ⊕ u (1) constitutes a (Virasoro-like) infinite-dimensional generalization of the (3 + 1) -dimensional conformal symmetry, in addition to matter fields with all conformal spins. These algebras provide a new arena for integrable field models in higher dimensions; for example, anti-de Sitter and conformal gauge theories of higher-so(4, 2)-spin fields. A proposal for a noncommutative geometrical interpretation of space is also outlined.
LOOP VARIABLES AND GLOBAL CHARACTERIZATION OF CONICAL SPACE–TIMES
Authors: DE ASSIS J. G. , BEZERRA V. B. , DE OLIVEIRA SILVANIO B.
Published: April 2003

Using the loop variable approach we describe the global aspects of the space–time of N parallel chiral cosmic strings with one of them moving relative to the others. Particular results in the framework of (2 + 1)-dimensional gravity are given.
CONSTRAINING MODELS WITH SUPERLIGHT GRAVITINO, SCALAR AND PSEUDOSCALAR PARTICLES
Authors: MORI F. , NATALE A. A.
Published: April 2003

In some supergravity models there are light weakly coupled scalar (S) and pseudoscalar (P) particles. These particles arise following a superlight gravitino. In these models the decay S/P→γγ exists. We examine constraints on this process considering these photons as responsible by the extragalactic background light. We also consider the amount of S/P particles produced through the fusion of the cosmic background photons and contributing to the effective number of light neutrino species during primordial nucleosynthesis. We obtain bounds on the gravitino mass complementary to the existing ones.
TWISTED BOUNDARY CONDITIONS AND MATCHING TO THE EFFECTIVE FOUR-DIMENSIONAL THEORY
Authors: CLARK T. E. , LOVE S. T.
Published: April 2003

Nontrivial twisted boundary conditions associated with extra compact dimensions can produce an ambiguity in the value of the four-dimensional coupling constants of the renormalizable interactions of the twisted fields' zero-modes. Resolving this indeterminacy would require a knowledge of the exact form of the higher dimensional action including the coefficients of higher-dimensional operators. For the case of moderately sized extra dimensions, the uncertainty in the coupling constants can be of order one and may lead to modifications in the stability of the model.
BIEXCITON kth POWER AMPLITUDE SQUEEZING DUE TO OPTICAL EXCITON–BIEXCITON CONVERSION
Authors: TINH VO , AN NGUYEN BA
Published: April 2003

We extend a previous paper on biexciton normal squeezing to the case of k th power amplitude squeezing in a quantum interacting system of photons, excitons and biexcitons. We find that the k th power amplitude squeezing depends on the characteristics of the initial coherent biexciton while the normal squeezing does not. Both the direction of maximal squeezing and the squeezing degree are derived as explicit functions of k. Especially, the squeezing degree always decreases with increasing k regardless of the initial conditions. All these properties are examined numerically.
EFFECT OF SPIN-FLIP SCATTERING ON CURRENT-IN-PLANE MAGNETO-TRANSPORT IN MAGNETIC MULTILAYERED STRUCTURES WITH ARBITRARY MAGNETIZATION ALIGNMENTS
Authors: TAO Y. C. , WANG J. , HU J. G.
Published: April 2003

By a quantization-axis transformation, we derive an extended equation which Green's function satisfies in the presence of spin-flip scattering, and then apply the Kubo formula to study the variation of the giant magnetoresistance (GMR) in magnetic multilayered structures with the angle θ between the magnetizations of succesive magnetic films. It is found that in the presence of spin-flip scattering and spin-dependent potential barriers, the linear dependence of GMR on sin 2(θ/2) can be approximately obtained, which is qualitatively consistent with the experimental result.
DISSIPATIVE DYNAMICS OF A SINGLE PARTICLE IN AN ION TRAP
Authors: LO C. F. , KIANG D.
Published: April 2003

In this paper we have investigated the time evolution of a dissipative quantum time-dependent oscillator which can be used to model particle trapping in an ion trap. Our analysis shows that the nonadiabatic changes in the oscillator mass and/or frequency as well as the dissipation constitute two competing forces on the squeezing properties of the system — the former helps generate the squeezing effect whereas the latter tries to destroy it.
QUANTUM EFFECTS OF A PARTICLE IN AN INFINITE SQUARE WELL WITH A MOVING WALL
Authors: ZOU JIAN , SHAO BIN
Published: April 2003

The quantum behavior of a particle in a one-dimensional infinite square well potential with a moving wall is studied. The particle is assumed to be initially prepared in the coherent state (Gaussian wave packet) and although the boundary is far from the particle, it is shown that the changing of the boundary conditions can instantaneously affect the dynamical behavior of the particle. It is also shown that the initial state can evolve into a squeezed state, and in some cases the spreading of the wavepacket could be suppressed. Finally the Pancharatnam phase is also discussed.
ELECTRICAL AND MAGNETIC PROPERTIES OF BULK (Bi1.6Pb0.4)(Sr1.8Ba0,2)(Ca1-xErx)2Cu3Oy SUPERCONDUCTING SYSTEM
Authors: POP A. V. , DEAC I. G. , ILONCA GH. , DELTOUR R.
Published: April 2003

The effects of partial substitution of Ca by Er on the superconductivity and normal state properties of the bulk superconductor ( Bi 1.6 Pb 0.4)( Sr 1.8 Ba 0.2)( Ca 1-x Er x)2 Cu 3 Oy (0≤x≤0.2) have been investigated using electrical resistivity, a.c. and d.c. magnetic susceptibility measurements.

Above the excess conductivity region, all samples are characterised by a linear temperature dependence of the electrical resistivity. The analysis of the resistivity data in the normal state reveal that the residual resistivity and the parameter p (related to the percolation path in granular samples) increase with increasing x. The critical transition temperature determined from resistivity data, T c and T c (ρ=0), are identical to intra-and intergrain critical temperatures derived from the a.c. susceptibility measurements. These temperatures decreases linearly with increasing Er content. For samples with x≤0.005 a temperature independent susceptibility was evidenced and for x>0.005 the susceptibility data as a function of temperature is well described by a Curie-Weiss law with an effective magnetic moment corresponding to the Er3+ ion.
O-LATTICES FOR RANK-DEFICIENT DISPLACEMENT FIELD MATRICES
Authors: GÓMEZ ALFREDO , ROMEU DAVID
Published: April 2003

In this work the properties of O-lattices are investigated in the case where the rank of the displacement field matrix is less than three. The approaches due to Bollmann are reviewed and it is shown that one of them is equivalent to the use of the Moore–Penrose pseudo-inverse of the displacement field matrix instead of its (in this case inexistent) inverse.

The geometry of the pseudo-inverse approach is discussed and a general solution in terms of the singular value decomposition is proposed.
RAMAN STUDY OF THE SUPERCONDUCTING ORDER PARAMETER IN PURE AND DISORDERED Bi2Sr2CaCu2O8+δ SINGLE CRYSTALS
Authors: MISOCHKO O. V.
Published: April 2003

Low-energy electronic Raman continua (15–1000 cm-1) have been explored in pure and disordered Bi 2 Sr 2 CaCu 2 O 8+δ superconducting crystals with an emphasis on both pair-breaking peaks and low-frequency slopes. In this study we are primarily interested in the relative intensity and line shape of the spectra in different symmetry channels, and the magnitude of the superconducting gap and its anisotropy in k-space deduced from the different features of Raman spectra.
AB INITIO TREATMENTS OF THE ISING MODEL IN A TRANSVERSE FIELD
Authors: BISHOP R. F. , FARNELL D. J. J. , RISTIG M. L.
Published: April 2003

In this article new results are presented for the zero-temperature ground-state properties of the spin-half transverse Ising model on various lattices using three different approximate techniques. These are, respectively, the coupled cluster method, the correlated basis function method, and the variational quantum Monte Carlo method. The methods, at different levels of approximation, are used to study the ground-state properties of these systems, and the results are found to be in excellent agreement both with each other and with results of exact calculations for the linear chain and results of exact cumulant series expansions for lattices of higher spatial dimension. The different techniques used are compared and contrasted in the light of these results, and the constructions of the approximate ground- state wave functions are especially discussed.
A STUDY OF DISORDERED SYSTEMS WITH GAIN: STOCHASTIC AMPLIFICATION
Authors: JOSHI SANDEEP K. , JAYANNAVAR A. M.
Published: April 2003

A study of statistics of transmission and reflection from a random medium with stochastic amplification as opposed to coherent amplification is presented. It is found that the transmission coefficient t, for sample length L less than the critical length L c grows exponentially with L. In the limit L→∞ transmission decays exponentially as < ln t>=-L/ξ where ξ is the localization length. In this limit reflection coefficient r saturates to a fixed value which shows a monotonic increase as a function of strength of amplification α. The stationary distribution of super-reflection coefficient agrees well with the analytical results obtained within the random phase approximation (RPA). Our model also exhibits the well known duality between absorption and amplification. We emphasize the major differences between coherent amplification and stochastic amplification where-ever appropriate.
ON THE IN-PLANE SEEBECK COEFFICIENT IN YBa2Cu3O7-δ
Authors: FUJITA F. , HO H. C. , MORABITO D. L.
Published: April 2003

The measured in-plane Seebeck coefficient Sab in single-crystal YBa 2 Cu 3 O 7-δ is negative and temperature (T)-independent. This behavior is shown to arise from the thermal diffusion of "electrons", which are the minority carriers in the ab-plane conduction. The majority carriers in the plane are "holes", judged from the measured positive Hall coefficient [Formula: see text].