bluuebunny/crossref_metadata_2025 huggingface dataset:
Rheological Properties of an Electrorheological Fluid in Original Transition Zone
Authors: Zhikang Fan , Shuhua Liang , Xu Xue , Gang Wang
Published: July 2002

The rheological properties of an electrorheological(ER) fluid have been studied in a modified concentric cylinder viscometer. The results show that the relation of shear rate and shear stress is non-linear at certain shear rate defined as an original transition zone. Regressive analysis reveals that the ER fluid is of yield-pseudoplastic fluid in the transition zone. With increase in applied fields, the rheological properties of the ER fluid deviates from Newtonian fluid and the length of the transition zone becomes longer.
SELF-CONSISTENT NUMERICAL STUDIES OF MAGNETIC IMPURITIES IN HUBBARD ANTIFERROMAGNET
Authors: SEN PRASENJIT
Published: July 2002

Effects of magnetic impurities on a two-dimensional Hubbard antiferromagnet are treated self-consistently within a numerical Hartree–Fock approximation. Both kinds of impurities — those with spin equal to the host spin (S′=S); and those with spin different from the host spin (S′≠S) — have been studied. In this approach, S′=S impurities lead to momentum (Q) dependent renormalization of the long wavelength magnon energies, unlike in the previous perturbative calculations where the renormalization was found to be Q-independent. S′≠S impurities, however, give Q-dependent logarithmically diverging corrections. Both kinds of impurities leave the gapless Goldstone mode in the spin excitations unaffected.
IRRADIATION-INDUCED INTER- AND INTRA-GRANULAR MODIFICATIONS BY 120 MeV S IONS IN YBa2Cu3O7 THICK FILMS
Authors: BEHERA D. , PATNAIK K. , MISHRA N. C.
Published: July 2002

The evolution of microstructure under swift heavy ion (SHI) irradiation is probed in a granular medium such as YBCO thick films prepared through diffusion reaction technique. From the temperature-dependent in situ resistivity measurement during ion irradiation, we have been able to isolate the irradiation induced modifications at the grain boundaries and the grains. With 120 MeV S ion irradiation, we show that in addition to damaging the insulating grain boundaries and hence destroying superconducting phase coherence, ion irradiation brings about an improvement in the microstructure of the cuprates. Irradiation is shown to induce alignment of the grains in an otherwise randomly oriented granular superconductor.
TWO-STEP ELECTRON BEAM EXCITATION OF Al2O3:Cr BY GALLIUM NITRIDE RECOMBINATION RADIATION
Authors: ZEHE A. , RAMÍrez A. , SEIFERT W.
Published: July 2002

We report on a two-step excitation process of a GaN/A 2 O 3: Cr specimen by an external electron beam of 30 keV. The epitaxial growth of GaN on the (0001) faces of ruby is described, as well as the experimental technique applied in the excitation and recording of the combined luminescence spectrum.

It is known that the spinel and ruby are frequently used as substrate materials for the epitaxial deposition of GaN. At the same time is ruby one of the most useful layer materials with a red emission line λ = 694 nm. Due to its dielectric character, the pumping of ruby is performed usually subjecting it to the light of an intense flash lamp. Electron beam excitation, on the other hand, which could be more powerful, is impaired with electrical insulator material. This discrepancy can be removed by a two-step excitation, where at first the semiconducting GaN-layer, epitaxially grown on a (0001)Al 2 O 3: Cr (ruby) crystal is excited to radiation emission by an external electron beam. The following internal absolption process, by the ruby crystal, of the GaN luminescence radiation provides for the characteristic 2 E to 4 A 2-transition at 1.786 eV. We found a strong and sharp emission line of that photon energy, which additionally displays polarization, typical for the anisotropic uniaxial ruby crystal.

Such an indirect electron-beam excitation of ruby allows to generate almost monochromatic red light, and might point into a direction of interesting practical applications.
SHORT TIME CORRELATIONS IN A TWO-DIMENSIONAL ISING MODEL WITH A LINE OF DEFECTS
Authors: TOMÉ T. , SIMÕES C. S. , DE FELÍCIO J. R. DRUGOWICH
Published: July 2002

We study the short time dynamics of a two-dimensional Ising model with a line of defects. The dynamical critical exponent θ associated to the early time regime at the critical temperature was obtained by Monte Carlo simulations. The exponent θ was estimated by a method where the quantity of interest is the time correlation of the magnetization.
STABLE PHOTOLUMINESCENCE IN LOW-TEMPERATURE ANNEALED POROUS SILICON
Authors: ZHU DELIANG , CHEN QIANWANG , ZHANG YUHENG
Published: July 2002

The low-temperature annealing of porous silicon (PS) has been studied in ambient air and vacuum. After air-annealed samples were again stored in air for a period of time, their luminescence exhibited improved stability in comparison to fresh samples. But their luminescence intensity is much weaker than that of fresh samples, and their peak position moves to shorter wavelengths. A stoichiometric oxide SiO2 can easily be formed on PS surfaces if the annealing is performed in vacuum. The SiO2 layer prevents nc-Si from further oxidation and guarantees the luminescence intensity and that peak position remains unchanged with air storage.
TUNNELING ASYMMETRY IN SUPERCONDUCTING Nd1Ba2Cu3Oy SINGLE CRYSTALS
Authors: WU A. T. , KOSHIZUKA N. , TANAKA S.
Published: July 2002

Clean, stable, and atomically flat (001) surfaces of the as-prepared Nd 1 Ba 2 Cu 3 O y (Nd123) single crystals have been investigated using a Low Temperature UltraHigh Vacuum Scanning Tunneling Microscope/Spectroscopy (STM/STS) system at 10 K. Several sets of highly reproducible STS data show the existence of an asymmetry in the tunneling spectra in superconducting Nd123 single crystals. The asymmetry is found to be intrinsic and can be explained by assuming that the pairing potential is a function of the kinetic energy of the charge carriers. The STS data are compared with the predictions of different theoretical models. The data on the (001) surfaces may be better fitted by assuming an S wave symmetry. Pure d(x2-y2) symmetry is ruled out.
PARTICLE–HOLE SYMMETRY IN QUANTUM HALL EFFECT
Authors: SHRIVASTAVA KESHAV N.
Published: July 2002

We report that the masses of two quasiparticles can be equal only when they are particle–hole conjugates. We suggest several particle–hole conjugate pairs and discuss the role of spin.
ARTIFICIAL LIFE FOR IMAGE SEGMENTATION
Authors: HE HAO , CHEN YAN QIU
Published: July 2002

Artificial life has been successfully used for understanding biological systems and in many applications in robotics, computer graphics, etc. In this paper, we pioneer the use of artificial life for image segmentation, a challenging area in image processing. Our method associates each pixel in an image with a life and it evolves according to a system of rules. The segmented partitions emerge when the state of the lives reaches an equilibrium. The artificial life approach is promising in image processing because it is inherently parallel and coincides with the self-governing biological process. In addition, it has the advantage of the integration of both detail preservation and noise removal. The experiments demonstrate the feasibility of the artificial life approach on both intensity images and color images. We also compared the approach with other four commonly used methods for three different kinds of noise corrupted images.
A COMPARATIVE ANALYSIS OF RÖSSLER TYPE DYNAMICS AND LASER SYSTEMS
Authors: TERRY JOHN R.
Published: July 2002

We introduce the standard Rössler oscillator and extend it from a system defined on ℝ3 to a system defined on [Formula: see text]. We extend the system in such a way that the simple Rössler type dynamics are preserved, whilst introducing an additional symmetry to the system such that when the oscillators are linearly coupled, there exists an embedding of symmetry forced invariant manifolds. We contrast our results with a previously considered model for a linearly coupled solid-state laser system which possessed a similar embedding of invariant manifolds. We discuss whether the mechanisms for loss of synchronization are system dependent or a more generic property of systems with embedded invariant manifolds.
AUTOMATICITY OF COARSE-GRAINING INVARIANT ORBITS OF ONE-DIMENSIONAL LINEAR CELLULAR AUTOMATA
Authors: BARBÉ ANDRÉ , PEITGEN HEINZ-OTTO , SKORDEV GENCHO
Published: July 2002

We consider one-dimensional linear cellular automata whose states are the integers modulo a prime power pd and their orbital patterns. We are particulary interested in initial states and their orbital patterns which are invariant under a certain coarse-graining operation. We show that these coarse-graining invariant initial states are p-automatic. The relationship between the solutions of a certain family of coarse-graining invariant problems concerning linear cellular automata over the integers modulo pn is investigated.
CHUA SYSTEMS WITH DISCONTINUITIES
Authors: LAMARQUE C.-H. , JANIN O. , AWREJCEWICZ J.
Published: July 2002

We present a special class of mechanical systems that could be written as Chua circuits with discontinuities. We recall the general frame for the study of such models. Results of existence and uniqueness are given. Then numerical results obtained via piecewise analytical expressions are presented. We discuss some bifurcation diagrams, phase portraits. Chaos is characterized by computing Lyapunov exponents. We analyze the global behavior in a special case where discontinuity stabilizes the trivial equilibrium solution.
STATISTICAL ESTIMATION OF THE EMBEDDING DIMENSION OF A DYNAMICAL SYSTEM
Authors: BOSQ D. , GUÉGAN D. , LÉORAT G.
Published: July 2002

We consider a dynamical ergodic system defined as: [Formula: see text] where m0 is supposed to be unknown. X1,…, Xn being observed, we construct and study an estimate of m0 based on X1,…, XN, using the fact that m0 is a breaking point for the regularity of the distribution of (Xt-1,…, Xt-m), m=1, 2,…. We present some simulations to illustrate our method and we discuss the computing problems.
LYAPUNOV EXPONENTS FOR THE INTERMITTENT TRANSITION TO CHAOS
Authors: HANSSEN JAMES , WILCOX WALTER
Published: July 2002

The dependence of the Lyapunov exponent on the closeness parameter, ε, in tangent bifurcation systems is investigated. We study and illustrate two averaging procedures for defining Lyapunov exponents in such systems. First, we develop theoretical expressions for an isolated tangency channel in which the Lyapunov exponent is defined on single channel passes. Numerical simulations were done to compare theory to measurement across a range of ε values. Next, as an illustration of defining the Lyapunov exponent on many channel passes, a simulation of the intermittent transition in the logistic map is described. The modified theory for the channels is explained and a simple model for the gate entrance rates is constructed. An important correction due to the discrete nature of the iterative flow is identified and incorporated in an improved model. Realistic fits to the data were made for the Lyapunov exponents from the logistic gate and from the full simulation. A number of additional corrections which could improve the treatment of the gates are identified and briefly discussed.
MULTIDIMENSIONAL PERTURBATIONS OF ONE-DIMENSIONAL MAPS AND STABILITY OF SARKOVSKĬ ORDERING
Authors: ZGLICZYŃSKI PIOTR
Published: July 2002

In this paper we present Sarkovskĭ theorem for multidimensional perturbations of one-dimensional maps. We outline a proof that if the unperturbed one-dimensional map has a point of period n, then sufficiently close multidimensional perturbations of this map have periodic points of all periods which are allowed by Sarkovskĭ theorem. We describe also how the approach from the proof of this theorem is used to show the existence of an infinite number of periodic points for Rössler equations.
AN ALGORITHM TO COMPUTE THE TOPOLOGICAL ENTROPY OF A UNIMODAL MAP
Authors: BRUIN HENK
Published: July 2002

We describe an algorithm, due to F. Hofbauer, to compute the topological entropy of a unimodal interval map.
ℓ1-HOMOLOGY OF COMBABLE GROUPS AND 3-MANIFOLD GROUPS
Authors: MINEYEV IGOR
Published: July 2002

S. Gersten asked whether the reduced ℓ1-homology of a group of type ℱn vanishes in all dimensions up to n - 1. We prove this for combable groups and for the fundamental groups of closed 3-manifolds. This means that the ℓ1-homology in these cases can be interpreted as "an amount of non-linearity" for the isoperimetric functions.
REMARKS ON THE BLOW-UP CRITERION FOR THE 3-D BOUSSINESQ EQUATIONS
Authors: ISHIMURA NAOYUKI , MORIMOTO HIROKO
Published: July 2002

We consider the problem of blow-up of smooth solutions for the 3-D Boussinesq equations. Owing to the viscosity, we prove that the maximum norm of the gradient of vorticity controls the breakdown of the solutions; the scalar temperature function is shown to be irrelevant to the breakdown.
A HYBRID SEARCH ALOGRITHM FOR THE VEHICLE ROUTING PROBLEM WITH TIME WINDOWS
Authors: HO WEE-KIT , ANG JUAY CHIN , LIM ANDREW
Published: July 2002

The vehicle routing problem with time windows (VRPTW) is an extension of the well-known vehicle routing problem (VRP). It involves a fleet of homogeneous vehicles, originating and terminating at a central depot, with limited capacity and maximum travel time to service a set of customers with known demands and service-time windows. The objective is to find a set of feasible routes that minimizes the total costs using some measures of solution quality. This paper focuses on the study of a hybrid of two search heuristics, Tabu Search (TS) and Genetic Algorithm (GA) on VRPTW. TS is a local search technique that has been successfully applied to many NP-complete problems. On the other hand, GA which is capable of searching multiple search areas in a search space is good in diversification. In this paper, we create a hybrid that combines the strengths of the two search heuristics. Experimental results indicate that such a hybrid outperforms the individual heuristics alone.
SCHRÖDINGER–WHEELER–DEWITT EQUATION IN MULTIDIMENSIONAL COSMOLOGY
Authors: BISWAS S. , SHAW A. , BISWAS D.
Published: July 2002

We study multidimensional cosmology to obtain the wavefunction of the universe using wormhole dominance proposal. Using a prescription for time we obtain the Schrödinger–Wheeler–DeWitt equation without any reference to WD equation and WKB ansatz for WD wavefunction. It is found that the Hartle–Hawking or wormhole-dominated boundary conditions serve as a seed for inflation as well as for Gaussian type ansatz to Schrödinger–Wheeler–DeWitt equation.
THE COSMOLOGICAL CONSTANT PROBLEM AND KALUZA–KLEIN THEORY
Authors: WESSON PAUL S. , LIU HONGYA
Published: July 2002

We present technical results which extend previous work and show that the cosmological constant of general relativity is an artefact of the reduction to 4D of 5D Kaluza–Klein theory (or 10D superstrings and 11D supergravity). We argue that the distinction between matter and vacuum is artificial in the context of ND field theory. The concept of a cosmological "constant" (which measures the energy density of the vacuum in 4D) should be replaced by that of a series of variable fields whose sum is determined by a solution of ND field equations in a well-defined manner.
CAN MODULI FIELDS PARAMETRIZE THE COSMOLOGICAL CONSTANT?
Authors: DE LA MACORRA A.
Published: July 2002

We study the cosmological evolution of string/M moduli fields T. We use T-duality to fix the potential and show that the superpotential W is a function of the duality invariant function j(T) only. If W is given as a finite polynomial of j then the moduli fields do not give an accelerating universe, i.e. they cannot be used as quintessence. Furthermore, at T ≫ 1 the potential is given by a double exponential potential [Formula: see text] leading to a fast decaying behavior at large times. For moduli potentials with a finite v.e.v. of T the energy density redshift is model dependent but if T has a finite mass, m < ∞, then the moduli energy density redshifts faster or equal to matter. Only if the moduli mass is infinite can the moduli energy density dominate the universe independently of the initial conditions.
COMMENTS ON "REMARKS ON A DECRUMPLING MODEL OF THE UNIVERSE"
Authors: VISHWAKARMA R. G.
Published: July 2002

A recent paper by Lima and Mohazzab has been examined and it is found that their results, that the Einstein field equations are consistent only for a dust and a turning point in the dynamics of the evolution is possible, are erroneous. This is due to their ignorance of the fact that the field equations and the energy conservation equation are not independent.
PHOTOELECTRON DIFFRACTION STUDY OF THE INITIAL-STAGE GROWTH OF Cu ON Ge(111)-c(2×8)
Authors: OMORI S. , NARIMATSU A. , SUZUKI T. , NIHEI Y.
Published: July 2002

Two phases in the initial stages of Cu growth on Ge(111) have been investigated by using X-ray photoelectron diffraction (XPED). Multiple-scattering analysis showed that the surface layer of the discommensurate phase consists of almost the same amount of two kinds of domains with regular and fault stackings. Furthermore, it was found that the ordered overlayer was formed after annealing the discommensurate phase and that the XPED pattern from the annealed phase cannot be explained by the simple models such as bulklike Cu and stoichiometric germanide Cu 3 Ge .
ANGLE-RESOLVED PHOTOEMISSION STUDIES OF THE 3C–SiC(001)(2×1) SURFACE
Authors: DUDA L. , JOHANSSON L. S. O. , REIHL B. , YEOM H. W. , HARA S. , YOSHIDA S.
Published: July 2002

We have investigated the electronic structure of the single-domain 3C–SiC(001)(2×1) using angle-resolved photoemission and synchrotron radiation. Two different surface-state bands are clearly identified within the bulk bandgap. The upper band has a binding energy of 1.4 eV at the center of the surface Brillouin zone (SBZ) and shows a weak dispersion of 0.3 eV in the [Formula: see text] direction, but is nondispersive in the perpendicular direction. It has a polarization dependence suggesting a pz character, as expected for a Si dangling-bond state. The second band is located at 2.4 eV binding energy and is nondispersive. The weak or nonexistent dispersions suggest very localized electronic states at the surface and show poor agreement with calculated dispersions for the proposed models for the 2×1 and c(4×2) reconstructions.
THE WRIST AND THE METACARPAL ARCH IN RHEUMATOID ARTHRITIS: The Supination Collapse of the Hand
Authors: Zancolli E.A. , Zancolli E.R. , Kohut G.N. , Cagnone J.C.
Published: July 2002

This paper first describes the usual sequence of the structural changes affecting the wrist and the matacarpal arch in rheumatoid arthritis. Acccording to this sequence, four different types of wrist deformities and two different types of metacarpal arch deformities are determined and their specific features are presented. Treatment options are mentioned for each type, and the author’s preferred treatment is discussed in more detail.
THE USE OF CARIN LANGUAGE AND ALGORITHMS FOR INFORMATION INTEGRATION: THE PICSEL SYSTEM
Authors: GOASDOUÉ FRANÇOIS , LATTÈS VÉRONIQUE , ROUSSET MARIE-CHRISTINE
Published: July 2002

PICSEL is an information integration system over sources that are distributed and possibly heterogeneous. The approach which has been chosen in PICSEL is to define an information server as a knowledge-based mediator in which CARIN is used as the core logical formalism to represent both the domain of application and the contents of information sources relevant to that domain. In this paper, we describe the way the expressive power of the CARIN language is exploited in the PICSEL information integration system, while maintaining the decidability of query answering. We illustrate it on examples coming from the tourism domain, which is the first real case that we have to consider in PICSEL, in collaboration with the travel agency Degriftour. see
INVESTIGATION OF ENDOTHELIAL CONTROL OF BONE BLOOD FLOW: DEVELOPMENT OF A RABBIT TIBIA EX VIVO PERFUSION MODEL
Authors: Tu Yuan-Kun , Kato Teiji , Bishop Allen T.
Published: July 2002

An ex vivo rabbit tibia perfusion model was developed to investigate the vascular reactivity and vascular endothelial function of bone tissue. The tibiae of 36 adult New Zealand rabbits were isolated and perfused through the cannulated nutrient artery at a constant flow rate in an organ chamber. The increase in perfusion pressure caused by graded doses of norepinephrine produced a dose response curve, which was first recorded under control condition, and then during perfusion with acetylcholine (ACh), N G -monomethyl-L-arginine acetate (L-NMMA), and/or L-arginine (nitric oxide precursor) infusion. The optimal flow rate for rabbit tibia was 0.3 to 0.4 ml/min, depending on the weight of the tibia. The perfusion baseline and the norepinephrine dose-response curve (NEDRC) remained stable for at least eight hours. Acetylcholine (1 × 10-5 M ) infusion attenuated the NEDRC (33 ± 5%) for 1.5 hours. Thereafter, the vasorelaxant effect of ACh diminished due to depletion of nitric oxide, and ultimately caused an increase in the NEDRC due to a vasoconstrictive action. The rebound vasoconstriction did not occur in the presence of constant L-arginine infusion, which maintained nitric oxide production, and ACh continued to attenuate the NEDRC (36 ± 4.5%) for at least eight hours. L-NMMA, which inhibits the synthesis of nitric oxide, increased the vasoconstrictive effect of norepinephrine significantly (155 ± 16%). The rabbit tibia ex vivo model seems ideal for the study of bone vascular bed activity, due to its stable baseline, reliable NEDRC and cost efficiency. We have further demonstrated that the intraosseous vascular endothelium of rabbit tibia produces nitric oxide as one method of regulating bone perfusion.
PERIARTICULAR GENE EXPRESSION OF OSTEOPONTIN AND PROGRESSION IN OSTEOPENIA FOLLOWING JOINT IMMOBILIZATION
Authors: MIYAMA TAKAHIDE , NAKAMURA NORIMASA , NAKASE TAKANOBU , TORITSUKA YUKIYOSHI , MYOUI AKIRA , TOMITA TETSUYA , HAMADA MASAYUKI , YOSHIKAWA HIDEKI
Published: July 2002

In order to elucidate the molecular events involved in periarticular osteopenia following joint immobilization, we investigated the temporal and spatial gene expression of one of the major non-collagenous bone matrix proteins, osteopontin (OPN), in periarticular regions, after immobilizing rat knee joints. Significant decreases in total BMD was observed in the immobilized limbs after 2 weeks of immobilization. Histologically, multinucleated cells with positive staining for tartrate resistant acid phosphatase (TRAP) were significantly increased in the metaphyseal regions, 1 to 4 weeks following immobilization. In situ hybridization studies revealed that OPN mRNA was present in a significantly larger number of cells in the metaphysial regions of joints immobilized for 1 to 3 weeks; compared with those levels detected in the control limbs, OPN mRNA was mainly detected in osteoblast/osteocyte-lineage cells of the spongiosa. Such temporal and spatial similarities in the expression of TRAP-positive multinucleated cells and OPN transcripts suggest the possible involvement of OPN in the periarticular osteoclastogenesis, leading to the activation of regional bone resorption following joint immobilization.
PHASE TRANSITION IN A TOY MARKET
Authors: CHALLET DAMIEN , MARSILI MATTEO , ZECCHINA RICCARDO
Published: July 2002

We review recent exact analytical results on Minority Game — a binary exactly solvable El Farol's bar problem. Inductive agents minimize the available information, not their losses, thus the stationary state differs from a Nash equilibrium. On the other hand, the same learning dynamics leads to a Nash equilibrium when agents take into account their impact on the market.
MICROWAVE FLUCTUATIONS IN ELECTRON GAS WITH PAIR COLLISIONS
Authors: KATILIUS R. , MATULIONIS A.
Published: July 2002

The paper overviews recent progress in the field of hot-electron microwave noise and fluctuations with an emphasis on contribution due to inter-electron collisions that are inevitable in doped semi-conductors at a relatively high density of mobile electrons. A special attention is paid to the problem of hot-electron diffusion in the range of electric fields where inter-electron collisions are important and Price's relation connecting diffusion and noise characteristics is not necessarily valid. The basic and up-to-date information is presented on methods and advances in the field where combined analytic and Monte Carlo methods of investigation are indispensable while seeking coherent understanding of experimental results.
FLUX-FLOW NOISE IN THE VICINITY OF THE PEAK EFFECT
Authors: PALTIEL Y. , JUNG G. , MYASOEDOV Y. , RAPPAPORT M. L. , ZELDOV E. , BHATTACHARYA S. , HIGGINS M. J.
Published: July 2002

Strong flux-flow voltage noise, commonly observed in the vicinity of the peak effect in superconductors, is ascribed to a novel noise mechanism. Random injection of the strongly pinned metastable disordered vortex phase through the sample edges and its subsequent random annealing into the weakly pinned ordered phase in the bulk result in large critical current fluctuations causing large vortex velocity fluctuations. In the Corbino disk configuration vortices do not cross sample edges, the injection of the metastable phase is prevented, and accordingly the excess noise is absent.
VIOLATION-GUIDED NEURAL-NETWORK LEARNING FOR CONSTRAINED FORMULATIONS IN TIME-SERIES PREDICTIONS
Authors: WAH BENJAMIN W. , QIAN MINGLUN
Published: July 2002

Time-series predictions by artificial neural networks (ANNs) are traditionally formulated as unconstrained optimization problems. As an unconstrained formulation provides little guidance on search directions when a search gets stuck in a poor local minimum, we have proposed to use a constrained formulation in order to use constraint violations to provide additional guidance. In this paper, we formulate ANN learning with cross-validations for time-series predictions as a non-differentiable nonlinear constrained optimization problem. Based on our theory of Lagrange multipliers for discrete constrained optimization, we propose an efficient learning algorithm, called violation guided back-propagation (VGBP), that computes an approximate gradient using back-propagation (BP), that introduces annealing to avoid blind acceptance of trial points, and that applies a relax-and-tighten (R&T) strategy to achieve faster convergence. Extensive experimental results on well-known benchmarks, when compared to previous work, show one to two orders-of-magnitude improvement in prediction quality, while using less weights.
An experimental study of fault detection in user requirements documents
Authors: Schneider G. Michael , Martin Johnny , Tsai W. T.
Published: July 2002

This paper describes a software engineering experiment designed to confirm results from an earlier project which measured fault detection rates in
user requirements documents
(URD). The experiment described in this paper involves the creation of a standardized URD with a known number of injected faults of specific type. Nine independent inspection teams were given this URD with instructions to locate as many faults as possible using the N-fold requirements inspection technique developed by the authors. Results obtained from this experiment confirm earlier conclusions about the low rate of fault detection in requirements documents using formal inspections and the advantages to be gained using the N-fold inspection method. The experiment also provides new results concerning variability in inspection team performance and the relative difficulty of locating different classes of URD faults.
Interprocedural constant propagation
Authors: Metzger Robert , Stroud Sean
Published: July 2002

Constant propagation is an optimization that substitutes values for names. Interprocedural constant propagation performs this substitution throughout an entire program, propagating constant values across procedure boundaries. CONVEX Computer Corporation has developed an interprocedural optimizer for imperative languages, which is available to users of its C-series supercomputers. An aggressive interprocedural constant propagation algorithm, such as the one implemented in this optimizer, can find many constants to propagate into procedures in scientific FORTRAN applications. Detailed statistics derived from compiling a large set of real scientific applications characterize both the opportunities for interprocedural constant propagation in these codes and the effectivenss of algorithm described. These statistics include the frequency of interprocedural constant propagation, the different types of interprocedural constant propagation, which constants are most frequently propagated, and the relationship between interprocedural constant propagation and other interprocedural optimizations.
Height distributional distance transform methods for height field ray tracing
Authors: Paglieroni David W. , Petersen Sidney M.
Published: July 2002

Height distributional distance transform (HDDT) methods are introduced as a new class of methods for height field ray tracing. HDDT methods utilize results of height field preprocessing. The preprocessing involves computing a height field transform representing an array of cone-like volumes of empty space above the height field surface that are as wide as possible. There is one cone-like volume balanced on its apex centered above each height field cell. Various height field transforms of this type are developed. Each is based on distance transforms of height field horizontal cross-sections. HDDT methods trace rays through empty cone-like volumes instead of through successive height field cells. The performance of HDDT methods is evaluated experimentally against existing height field ray tracing methods.
Effective cache prefetching on bus-based multiprocessors
Authors: Tullsen Dean M. , Eggers Susan J.
Published: July 2002

Compiler-directed cache prefetching has the potential to hide much of the high memory latency seen by current and future high-performance processors. However, prefetching is not without costs, particularly on a shared-memory multiprocessor. Prefetching can negatively affect bus utilization, overall cache miss rates, memory latencies and data sharing. We simulate the effects of a compiler-directed prefetching algorithm, running on a range of bus-based multiprocessors. We show that, despite a high memory latency, this architecture does not necessarily support prefetching well, in some cases actually causing performance degradations. We pinpoint several problems with prefetching on a shared-memory architecture (additional conflict misses, no reduction in the data-sharing traffic and associated latencies, a multiprocessor's greater sensitivity to memory utilization and the sensitivity of the cache hit rate to prefetch distance) and measure their effect on performance. We then solve those problems through architectural techniques and heuristics for prefetching that could be easily incorporated into a compiler: (1) victim caching, which eliminates most of the cache conflict misses caused by prefetching in a direct-mapped cache, (2) special prefetch algorithms for shared data, which significantly improve the ability of our basic prefetching algorithm to prefetch individual misses, and (3) compiler-based shared-data restructuring, which eliminates many of the invalidation misses the basic prefetching algorithm does not predict. The combined effect of these improvements is to make prefetching effective over a much wider range of memory architectures.
Envision
Authors: Heath Lenwood S. , Hix Deborah , Nowell Lucy T. , Wake William C. , Averboch Guillermo A. , Labow Eric , Guyer Scott A. , Brueni Dennis J. , France Robert K. , Dalal Kaushai , Fox Edward A.
Published: July 2002

Project Envision is an early NSF-funded digital library effort to develop a multimedia collection of computer science literature with full-text searching and full-content retrieval capabilities. Envision was launched in 1991 in accordance with the ACM Publications Board's plans for encouraging research studies to develop an electronic archive for computer science.
A modification of Talbot's method for the simultaneous approximation of several values of the inverse Laplace transform
Authors: Rizzardi Mariarosaria
Published: July 2002

In recent years many results have been obtained in the field of the numerical inversion of Laplace transforms. Among them, a very accurate and general method is due to Talbot: this method approximates the value of the inverse Laplace transform
f(t)
, for
t
fixed, using the complex values of the Laplace transform
F(s)
sampled on a suitable contour of the complex plane. On the basis of the interest raised by Talbot's method implementation, the author has been induced to investigate more deeply the possibilities of this method and has been able to generalize Talbot's method, to approximate simultaneously several values of
f(t)
using the same sampling values of the Laplace transform. In this way, the only unfavorable aspect of the classical Talbot method, that is, that of recomputing all of the samples of
F(s)
for each
t
, has been eliminated.
Some characterizations of families of surfaces using functional equations
Authors: Castillo Enrique , Iglesias Andrés
Published: July 2002

In this article functional equations are used to characterize some families of surfaces. First, the most general surfaces in implicit form
f
(
x, y, z
) = 0, such that any arbitrary intersection with the planes
z
=
z
0
,
y
=
y
0
, and
x
=
x
0
are linear combinations of sets of functions of the other two variables, are characterized. It is shown that only linear combinations of tensor products of univariate functions are possible for
f
x
,
y
,
z
). Second, we obtain the most general families of surfaces in explicit form such that their intersections with planes parallel to the planes
y
= 0 and
x
= 0 belong to two, not necessarily equal, parametric families of curves. Finally, functional equations are used to analyze the uniqueness of representation of Gordon-Coon surfaces. Some practical examples are used to illustrate the theoretical results.
Evaluation of an algorithm for finding a match of a distorted texture pattern in a large image database
Authors: Vujovic N. , Brzakovic D.
Published: July 2002

Evaluation of an algorithm for finding a match for a random texture pattern in a large image database is presented. The algorithm was designed assuming that the random pattern may be subject to misregistration relative to its representation in the database and assuming that it may have missing parts. The potential applications involve authentication of legal documents, bank notes, or credit cards, where thin fibers are embedded randomly into the document medium during medium fabrication. The algorithm achieves image matching by a three-step hierarchical procedure, which starts by matching parts of fiber patterns while solving the misregistration problem and ends up by matching complete fiber patterns. Performance of the algorithm is studied both theoretically and experimentally. Theoretical analysis includes the study of the probability that two documents have the same pattern, and the probability of the algorithm establishing a wrong match, as well as the algorithm's performance in terms of processing time. Experiments involving over 250,000 trials using databases of synthetic documents, containing up to 100,000 documents, were used to confirm theoretical predictions. In addition, experiments involving a database containing real images were conducted in order to confirm that the algorithm has potential in real applications.
Cluster-cover
Authors: Shi C.-J. , Brzozowski J. A.
Published: July 2002

This article introduces a mathematical framework called cluster-cover. We show that this framework captures the combinatorial structure of a class of VLSI design optimization problems, including two-level logic minimization, constrained encoding, multilayer topological planar routing, application timing assignment for delay-fault testing, and minimization of monitoring logic for BIST enchancement. These apparently unrelated problems can all be cast into two metaproblems in our framework: finding a maximum cluster and finding a minimum cover. We describe paradigms for developing algorithms for these problems. First, a simple heuristic called greedy peeling is presented and characterized. We derive sufficient conditions that guarantee optimum solutions by greedy peeling. We generalize the performance analysis of a multilayer topological planar routing heuristic to greedy peeling for the general cluster-cover problems. We propose a performance bound of greedy set covering that can be computed efficiently for a given problem instance; this bound is much tighter than the previously known bounds. Second, prime covering—orignally developed for logic minimization—is generalized to finding exact solutions for cluster-cover problems. Previously, only the connection between logic minimizaton and constrained encoding was known.
Laws of programming
Authors: Hoare C. A. R. , Hayes I. J. , Jifeng He , Morgan C. C. , Roscoe A. W. , Sanders J. W. , Sorensen I. H. , Spivey J. M. , Sufrin B. A.
Published: July 2002

A complete set of algebraic laws is given for Dijkstra's nondeterministic sequential programming language. Iteration and recursion are explained in terms of Scott's domain theory as fixed points of continuous functionals. A calculus analogous to weakest preconditions is suggested as an aid to deriving programs from their specifications.
On the decidability and axiomatization of query finiteness in deductive databases
Authors: Kifer Michael
Published: July 2002

A database query is
finite
if its result consists of a finite sets tuples. For queries formulated as sets of pure Horn rules, the problem of determining finiteness is, in general, undecidable.

In this paper, we consider
superfiniteness
—a stronger kind of finiteness, which applies to Horn queries whose function symbols are replaced by the abstraction of
infinite relations
with
finiteness constraints
(abbr., FC's). We show that superfiniteness is not only decidable but also
axiomatizable
, and the axiomatization yields an effective decision procedure. Although there are finite queries that are not superfinite, we demonstrate that superfinite queries represent an interesting and nontrivial subclass within the class of all finite queries.

The we turn to the issue of inference of finiteness constraints—an important practical problem that is instrumental in deciding if a query is evaluable by a bottom-up algorithm. Although it is not known whether FC-entailment is decidable for sets of function-free Horn rules, we show that
super-entailment
, a stronger form of entailment, is decidable. We also show how a decision procedure for super-entailment can be used to enhance tests for query finiteness.
Errata
Authors: Allen Robert , Garlan David
Published: July 2002

We present corrections to a previously published article which appeared in
ACM Transaction on Software Engineering and Methodology
6, 3 (July 1997), pp. 213–249
The existence and density of generalized complexity cores
Authors: Book Ronald V. , Du Ding-Zhu
Published: July 2002

If
C
is a class of sets and
A
is not in
C
, then an infinite set
H
is a
proper hard core for A with respect to C
, if
H
⊆
A
and for every
C
ε
C
such that
C
⊆
A
,
C
⋒
H
is finite. It is shown that if
C
is a countable class of sets of strings that is closed under finite union and finite variation, then every infinite set not in
C
has a proper hard core with respect to
C
. In addition, the density of such generalized complexity cores is studied.
Functional test generation for delay faults in combinational circuits
Authors: Pomeranz Irith , Reddy Sudhakar M.
Published: July 2002

We propose a functional fault model for delay faults in combinational circuits and describe a functional test generation procedure based on this model. The proposed method is most suitable when a gate-level description of the circuit-under-test, necessary for employing existing gate-level delay fault test generators, is not available or does not accurately describe the circuit. It is also suitable for generating tests in early design stages of a circuit, before a gate-level implementation is selected. In addition, it can potentially be employed to supplement conventional test generators for gate-level circuits to reduce the cost of handling large numbers of paths. A parameter called Δ is used to control the number of funtional faults targeted and thus the number of tests generated. If Δ is unlimited, the functional test set detects every robustly testable path delay fault in any gate-level implementation of the given ciruit. An appropriate subset of tests can be selected once the implentation is known. The test sets generated for various values of Δ are fault simulated on gate-level realizations to demonstrate their effectiveness. The experiments indicate that functional test sets may be able to identify functions whose realizations have low path delay fault coverage.
Structural diagnosis of interconnects by coloring
Authors: Chen X. T. , Meyer F. J. , Lombardi F.
Published: July 2002

This paper presents a new approach for diagnosing shorts in interconnects in which the adjacencies between nets are known. This structural approach exploits different graph coloring techniques to generate a test set with no aliasing and confounding, i.e., full diagnosis (detection and location) is accomplished. Initially, a simple coloring approach based on a greedy condition of the adjacency graph is proposed for fault detection. Then, the conditions for aliasing and confounding are analyzed with respect to the sizes of the possible shorts. These results are used to generate new colors using a process called color mixing. Color mixing guarantees that additional tests, required in order to avoid aliasing/confounding, will use appropriate codes. The characteristics of unbalanced/balanced codes for encoding the colors in the vector-generation process of interconnect diagnosis are discussed and are proved to yield full diagnosis using a novel method. An algorithm for full diagnosis is then presented; this algorithm has an execution complexity of
O
(
max
{
N
2
,
N
×
D
3
}) where
N
is the number of nets and
D
is the maximum degree of the nodes in the adjacency graph. Simulation results show that the proposed approach requires a smaller number of test vectors than previous approaches.
Effects of resource sharing on circuit delay
Authors: Bhattacharya Subhrajit , Dey Sujit , Breglez Franc
Published: July 2002

This paper analyzes the effect of resource sharing and assignment on the clock period of the synthesized circuit. The assignment phase assigns or binds operations of the scheduled behavioral description to a set of allocated resources. We focus on control-flow intensive descriptions, characterized by the presence of mutually exclusive paths due to the presence of nested conditional branches and loops.

We show that clustering multiple operations in the same state of the schedule, possibly leading to chaining of functional units (FUs) in the RTL circuit, is an effective way to minimize the total number of clock cycles, and hence total execution time. We present an assignment algorithm that is particularly effective for such design styles by minimizing data chaining and hence the clock period of the circuit, thereby leading to further reduction in total execution time.

Existing resource sharing and assignment approaches for reducing the clock period of the resulting circuit either increase the resource allocation or use faster modules, both leading to leading to larger area requirements. In this paper we show that even when the type of available resource units and the number of resource units of each type is fixed, different assignments may lead to circuits with significant differences in clock period.

We provide a comprehensive analysis of how resource sharing and assignment introduces long paths in the circuit. Based on the analysis, we develop an assignment algorithm that uses a high-level delay estimator to asign operations to a fixed set of available resources so as to minimize the clock period of the resultant circuit, with no or minimal effect on the area of the circuit. Experimental results on several conditional-intensive designs demonstrate the effectiveness of the assignment algorithm.
Wormhole routing techniques for directly connected multicomputer systems
Authors: Mohapatra Prasant
Published: July 2002

Wormhole routing has emerged as the most widely used switching technique in massively parallel computers. We present a detailed survey of various techniques for enhancing the performance and reliability of wormhole-routing schemes in directly connected networks. We start with an overview of the direct network topologies and a comparison of various switching techniques. Next, the characteristics of the wormhole routing mechanism are described in detail along with the theory behind deadlock-free routing. The performance of routing algorithms depends on the selection of the path between the source and the destination, the network traffic, and the router design. The routing algorithms are implemented in the router chips. We outline the router characteristics and describe the functionality of various elements of the router. Depending on the usage of paths between the source and the destination, routing algorithms are classified as deterministic, fully adaptive, and partially adaptive. We discuss several representative algorithms for all these categories. The algorithms within each category vary in terms of resource requirements and performance under various traffic conditions. The main difference among various adaptive routing schemes is the technique used to avoid deadlocks. We also discuss a few algorithms based on deadlock recovery techniques. Along with performance, fault tolerance is essential for message routing in multicomputers, and we thus discuss several fault-tolerant wormhole routing algorithms along with their fault-handling capabilities. These routing schemes enable a message to reach its destination even in the presence of faults in the network. The implementation details of wormhole routing algorithms in contemporary commercial systems are also discussed. We conclude by itemizing several future directions and open issues.
Ensuring consistency in multidatabases by preserving two-level serializability
Authors: Mehrotra Sharad , Rastogi Rajeev , Korth Henry F. , Silberschatz Abraham
Published: July 2002

The concept of serializability has been the traditionally accepted correctness criterion in database systems. However in multidatabase systems (MDBSs), ensuring global serializability is a difficult task. The difficulty arises due to the
heterogeneity
of the concurrency control protocols used by the participating local database management systems (DBMSs), and the desire to preserve the
autonomy
of the local DBMSs. In general, solutions to the global serializability problem result in executions with a low degree of concurrency. The alternative, relaxed serializability, may result in data inconsistency.

In this article, we introduce a systematic approach to relaxing the serializability requirement in MDBS environments. Our approach exploits the structure of the integrity constraints and the nature of transaction programs to ensure consistency without requiring executions to be serializable. We develop a simple yet powerful classification of MDBSs based on the nature of integrity constraints and transaction programs. For each of the identified models we show how consistency can be preserved by ensuring that executions are
two-level serializable
(2LSR). 2LSR is a correctness criterion for MDBS environments weaker than serializability. What makes our approach interesting is that unlike global serializability, ensuring 2LSR in MDBS environments is relatively simple and protocols to ensure 2LSR permit a high degree of concurrency. Furthermore, we believe the range of models we consider cover many practical MDBS environments to which the results of this article can be applied to preserve database consistency.