bluuebunny/crossref_metadata_2025 huggingface dataset:
QUANTIZATION OF KINEMATICS ON CONFIGURATION MANIFOLDS
Authors: DOEBNER H.-D. , ŠŤOVÍČEK P. , TOLAR J.
Published: July 2002

This review paper is devoted to topological global aspects of quantal description. The treatment concentrates on quantizations of kinematical observables — generalized positions and momenta. A broad class of quantum kinematics is rigorously constructed for systems, the configuration space of which is either a homogeneous space of a Lie group or a connected smooth finite-dimensional manifold without boundary. The class also includes systems in an external gauge field for an Abelian or a compact gauge group. Conditions for equivalence and irreducibility of generalized quantum kinematics are investigated with the aim of classification of possible quantizations. Complete classification theorems are given in two special cases. It is attempted to motivate the global approach based on a generalization of imprimitivity systems called quantum Borel kinematics. These are classified by means of global invariants — quantum numbers of topological origin. Selected examples are presented which demonstrate the richness of applications of Borel quantization. The review aims to provide an introductory survey of the subject and to be sufficiently selfcontained as well, so that it can serve as a standard reference concerning Borel quantization for systems admitting localization on differentiable manifolds.
JACOBI MATRICES WITH RANDOM POTENTIALS TAKING FINITELY MANY VALUES
Authors: KOTANI SHINICHI
Published: July 2002

It is proved that Jacobi matrices with random potentials taking finitely many values have no absolutely continuous spectrum unless the potentials are periodic.
GAP LABELLING THEOREMS FOR ONE DIMENSIONAL DISCRETE SCHRÖDINGER OPERATORS
Authors: BELLISSARD JEAN , BOVIER ANTON , GHEZ JEAN-MICHEL
Published: July 2002

We study one dimensional tight binding hamiltonians with potentials given by automatic sequences. By means of Shubin’s formula, we show how K-theory allows to prove gap labelling theorems for their spectrum. We apply them to some examples, for which we compare their predictions to previous results.
FROM QUANTUM FIELDS TO LOCAL VON NEUMANN ALGEBRAS
Authors: BORCHERS H.J. , YNGVASON JAKOB
Published: July 2002

The subject of the paper is an old problem of the general theory of quantized fields: When can the unbounded operators of a Wightman field theory be associated with local algebras of bounded operators in the sense of Haag? The paper reviews and extends previous work on this question, stressing its connections with a noncommutive generalization of the classical Hamburger moment problem. Necessary and sufficient conditions for the existence of a local net of von Neumann algebras corresponding to a given Wightman field are formulated in terms of strengthened versions of the usual positivity property of Wightman functionals. The possibility that the local net has to be defined in an enlarged Hilbert space cannot be ruled out in general. Under additional hypotheses, e.g., if the field operators obey certain energy bounds, such an extension of the Hilbert space is not necessary, however. In these cases a fairly simple condition for the existence of a local net can be given involving the concept of “central positivity” introduced by Powers. The analysis presented here applies to translationally covariant fields with an arbitrary number of components, whereas Lorentz covariance is not needed. The paper contains also a brief discussion of an approach to noncommutative moment problems due to Dubois-Violette, and concludes with some remarks on modular theory for algebras of unbounded operators.
Liver Regeneration Enhanced by Orally Administered Ursodesoxycholic Acid is Mediated by Immunosuppression in Partially Hepatectomized Rats
Authors: Liu Lili , Sakaguchi Takeo , Cui Xing , Shirai Yoshio , Nishimaki Tadashi , Hatakeyama Katsuyoshi
Published: July 2002

The relationship of liver regeneration to immunoactivity was examined after ursodesoxycholic acid (UDCA) administration to partially (about 66%) hepatectomized rats. The UDCA was given orally. Liver regeneration was evaluated by the hepatocyte mitotic index (MI) and immunoactivity by natural killer cell (NK) activity in the blood. When UDCA 12.5 mg/kg/day was administered, a significant increase in the MI was observed 2 and 3 days after hepatectomy, and the MI response 2 days after hepatectomy tended to be dose-dependent in the range of 0–25 mg/kg/day. NK activity was decreased 2 days after hepatectomy when UDCA was given, and a significant correlation between MI and NK activity was obtained. The increase in MI and decrease in NK activity was blocked completely or partially (respectively) by interleukin-2 administration. It was also noted that UDCA did not affect serum parameters indicating liver and kidney function.

These findings suggest that liver regeneration can be modified by orally administered UDCA through a change in immunoactivity.
TWO-DIMENSIONAL DILATONIC BLACK HOLES AND HAWKING RADIATION
Authors: VAGENAS ELIAS C.
Published: July 2002

Hawking radiation emanating from two-dimensional charged and uncharged dilatonic black holes — dimensionally reduced from (2+1) spinning and spinless, respectively, BTZ black holes — is viewed as a tunneling process. Two-dimensional dilatonic black holes (AdS(2) included) are treated as dynamical background in contrast to the standard methodology where the background geometry is fixed when evaluating Hawking radiation. This modification to the geometry gives rise to a nonthermal part in the radiation spectrum. Nonzero temperature of the extremal two-dimensional charged black hole is found. The Bekenstein–Hawking area formula is easily derived for these dynamical geometries.
DEFORMATION QUANTIZATION OF CLASSICAL FIELDS
Authors: GARCÍA-COMPEÁN H. , PLEBAŃSKI J. F. , PRZANOWSKI M. , TURRUBIATES F. J.
Published: July 2002

We study the deformation quantization of scalar and Abelian gauge classical free fields. Stratonovich–Weyl quantizer, star products and Wigner functionals are obtained in field and oscillator variables. The Abelian gauge theory is particularly intriguing since the Wigner functional is factorized into a physical part and the other one containing the constraints only. Some effects of nontrivial topology within the deformation quantization formalism are also considered.
HYPERBOLIC STRUCTURE ARISING FROM A KNOT INVARIANT
Authors: HIKAMI KAZUHIRO
Published: July 2002

We study the knot invariant based on the quantum dilogarithm function. This invariant can be regarded as a noncompact analog of Kashaev's invariant, or the colored Jones invariant, and is defined by an integral form. The three-dimensional picture of our invariant originates from the pentagon identity of the quantum dilogarithm function, and we show that the hyperbolicity consistency conditions in gluing polyhedra arise naturally in the classical limit as the saddle point equation of our invariant.
TRILINEAR NEUTRAL GAUGE BOSON COUPLINGS
Authors: CHOUDHURY DEBAJYOTI , DUTTA SUKANTA , RAKSHIT SUBHENDU , RINDANI SAURABH
Published: July 2002

We study the CP even trilinear neutral gauge boson vertices at one-loop in the context of the Standard Model and the Minimal Supersymmetric Standard Model, assuming two of the vector bosons are on-shell. We also study the changes in the form-factors when these two bosons are off-shell.
RANDOM VALUES OF THE PHYSICAL PARAMETERS
Authors: DONOGHUE JOHN F.
Published: July 2002

I briefly describe two motivations, two mechanisms and two possible tests of the hypothesis that the physical parameters of the ground state of a theory can vary in different rerions of the universe.
CORRELATION FUNCTIONS FOR MN/SN ORBIFOLDS
Authors: LUNIN OLEG , MATHUR SAMIR D.
Published: July 2002

We consider a bosonic CFT on a noncommutative orbifold Mn/Sn. To calculate three and four point functions of the twist operators on such an orbifold we perform a conformal map to the covering space and evaluate an appropriate Liouville action. We give an expression for the three point function for the case when the covering space is a sphere.
The CDF Run II Upgrade
Authors:   Representing the CDF Collaboration., HUGHES RICHARD E.
Published: July 2002

The status of the Run II upgrade to the CDF detector will be reviewed and the future schedule summarized.
PIN PHOTODIODES FOR RADIATION MONITORING AND PROTECTION IN THE BABAR SILICON VERTEX TRACKER
Authors:   Representing the BaBar Collaboration., Meyer T. I.
Published: July 2002

We discuss the design, implementation and performance of the radiation monitoring and protection system used by the Silicon Vertex Tracker (SVT) in the BaBar detector. Using 12 reverse-biased PIN photodiodes mounted around the beampipe near the IP, we are able to provide instantaneous radiation dose rates, absorbed dose integrals, and active protection that aborts the circulating beams in the PEP-II storage ring when radiation levels exceed user-defined thresholds. The systems has reliably protected the SVT from excessive radiation damage and has also served as a key diagnostic tool in understanding radiation backgrounds at PEP-II.
THE CMS MICRO-STRIP GAS CHAMBER — A HIGH RESOLUTION DETECTOR FOR TRACKING AT VERY HIGH RATES
Authors:   For the CMS MSGC Collaboration., LATRONICO LUCA
Published: July 2002

Results from a large scale test performed on the Micro-Strip Gas Chambers developed for the CMS experiment are reported. Irradiation, close to the expected LHC background, was provided by a low energy (350MeV), high rate (6kHz/mm2) pion beam at PSI. Excellent performance of the detectors was obtained using solutions specific to the demanding radiation environment.
HERA-B REAL-TIME TRIGGER FOR J/ψ → μ+ μ-
Authors:   For the HERA-B Muon Collaboration., Nam Shinwoo , Karchin Paul E.
Published: July 2002

The decay J/ψ → μ+ μ- is one of the main trigger channels in the HERA-B experiment. The muon deterctor and the trigger hardware are described. Results are reported from the initial trigger commissioning that includes the Muon Pretrigger and Second Level Trigger. A J/ψ mass peak with good signal to background ratio is obtained.
THE $D\emptyset$ LEVEL 1 TRIGGER SYSTEM
Authors:   For the Collaboration., McCROSKEY ROB
Published: July 2002

We describe the Level 1 muon trigger system for Run II of the [Formula: see text] colliding beam experiment at the Fermilab Tevatron. The muon trigger logic makes use of tracks from the central fiber tracker and hits from muon detector elements which include both scintillator and drift tube arrays. Details of the FPGA trigger logic and trigger simulation results are given. Extensive use is made of Gbit/s serial links in order to transmit data to the Level 1 muon trigger system. Results on error rates from these Gbit/s serial links using up to 200 feet of coaxial cable are presented.
Dense Optical-electrical Interface Module
Authors:   For the CDF Collaboration., Chang Paul
Published: July 2002

The DOIM (Dense Optical-electrical Interface Modules) is a custom-designed optical data transmission module employed in the upgrade of Silicon Vertex Detector of CDF experiment at Fermilab. Each DOIM module consists a transmitter(TX) converting electrical differential input signals to optical outputs, a middle segment of jacketed fiber ribbon cable, and a receiver (RX) which senses the light inputs and converts them back to electrical signals. The targeted operational frequency is 53 MHz, and higher rate is achievable. This article outlines the design goals, implementation methods, production test results, and radiation hardness tests of these modules.
RELAXING NEAR THE CRITICAL POINT
Authors: SIMIONATO M.
Published: July 2002

I present an analysis of the relaxation rate for long-wavelength fluctuations of the order parameter in an O(N) scalar theory near the critical point. Our motivation is to model the non-equilibrium dynamics of critical fluctuations near the chiral phase transition in QCD. In the next-to-leading order in the large N expansion we find a critical slowing down regime, i.e. an increasing of the relaxation time of long wavelengths fluctuations. This result suggests, for near critical systems, relevant deviations from thermal equilibrium for the distribution functions of low-energy particles and could have important phenomenological consequences in Heavy Ions Collision and in the Early Universe Cosmology.
BUNDLES OF LIE ALGEBRAS AND COMPATIBLE POISSON BRACKETS
Authors: YANOVSKI A. B.
Published: July 2002

We consider the mechanism of obtaining compatible Poisson-Lie tensors, based on the existence of some special algebraic structures - families of Lie brackets defined on one and the same space.
DECOHERENCE AND GRAVITATIONAL BACKGROUDS
Authors: REYNAUD SERGE , LAMINE BRAHIM , LAMBRECHT ASTRID , NETO PAUOLO MAIA , JAEKEL MARC-THIERRY
Published: July 2002

We study the decoherence process associated with the scattering of stochastic gravitational waves. We discuss the case of macroscopic systems, such as the planetary motion of the Moon around the Earth, for which gravitational scattering is found to dominate decoherence though it has a negligible influence on damping. This contrast is due to the very high effective temperature of the background of gravitational waves in our galactic environment.
VACUUM-VACUUM AMPLITUDES IN THE THEORY OF QUANTUM RADIATION BY MIRRORS IN 1+1-SPACE AND CHARGES IN 3+1-SPACE
Authors: RITUS VLADIMIR I.
Published: July 2002

The symmetry between the creation of pairs of massless bosons or fermions by accelerated mirror in 1+1 space and the emission of single photons or scalar quanta by electric or scalar charge in 3+1 space is deepened in this paper. The relation of Bogoliubov coefficients, describing the processes generated by the mirror, with Fourier's components of current or charge density leads to the coicidence of the spin of any disturbances bilinear in scalar or spinor field with the spin of quanta emitted by the electric or scalar charge. The mass and invariant momentum transfer of these disturbances are essential for the relation of Bogoliubov coefficients with invariant singular solutions and Green's functions of wave equations both for 1+1 and 3+1 spaces and especially for the integral relation (20) between these solutions. Namely the last relation leads to the coincidence of the self-action changes and vacuum-vacuum amplitudes for the accelerated mirror in two-dimentional space-time and charge in four-dimentional space-time. Thus, both invariants of the Lorentz group, spin and mass, perform intrinsic role in established symmetry.
IMPEDANCE SPECTROSCOPIC STUDIES ON GdBi5Fe2Ti3O18 CERAMIC
Authors: PRASAD N. V. , PRASAD G. , BHIMASANKARAM T. , SURYANARAYANA S. V. , KUMAR G. S.
Published: July 2002

GdBi 5 Fe 2 Ti 3 O 18 (GBFT), a compound of Aurivillius family, was prepared by solid state reaction method. Complex impedance measurement was made on these samples from room temperature to 500°C in the frequency range of 1 kHz–1 MHz. Cole–Cole plots were found to become very broad near 400°C. Dielectric and dc conductivity measurements were made on these samples. The results are analysed to understand the conductivity mechanism.
CHANGES OF X-RAY DIFFRACTION PATTERN IN FERROELECTRICS DUE TO THE FIELD-INDUCED PHASE TRANSITION
Authors: Wang J. T. , Tang F. , Jones P. , Chen T.-P.
Published: July 2002

Recently the remarkable discovery of field-induced phase transition from antiferroelectric (AFE) to Ferroelectric (FE) in ferroelectrics excited the scientific community in this field. This finding has both scientific and technological implications to us. In this paper, we studied the changes of the crystal structure when an electrical field is applied to it. The X-ray diffraction pattern reflecting these changes was discussed by theoretical calculation.
RECENT ADVANCES IN STRUCTURE SOLUTION FROM POWDER DIFFRACTION DATA
Authors: NEUMANN M. A. , LEUSEN F. J. J. , ENGEL G. E. , WILKE S. , CONESA-MORATILLA C.
Published: July 2002

Crystal structure determination frequently is a prerequisite for the rational understanding of the solid state properties of new materials. Even though single crystal diffractometry is the method of choice when it comes to crystal structure determination, this approach is often impractical because of the difficulties involved in growing single crystals of appropriate size. High quality powder samples, on the other hand, are much easier to obtain. Using direct-space structure solution techniques, increasingly complex crystal structures can nowadays be solved directly from powder diffraction data. Combined with easy-to-use tools for model building and visualization as well as molecular mechanics and first principles Density Functional Theory (DFT) calculations, crystal structure solution from powder diffraction data is becoming a routine task. To illustrate the applicability of direct-space Monte Carlo techniques to the crystal structure solution of organic and inorganic compounds, a variety of structure solutions with the Powder Solve algorithm are presented.

Recent advances include the determination of a preferred orientation correction during the structure solution search and the use of parallel tempering, a newly implemented global search algorithm. As a complementary technique, first principles DFT calculations have been used successfully to validate structure solutions and to aid the subsequent Rietveld refinement.
Performing Effective YBCO Grain Alignment and Growth by Silver and Spurious Phase Addition
Authors: Costa Giorgio A. , Mele Paolo
Published: July 2002

The effect of silver and the so-called green phase, Y 2 BaCuO 5 (211), on YBa 2 Cu 3 O x (123) melt textured samples has been investigated to check whether better grain alignment is possible in shorter times. We demonstrate that the addition of silver to YBCO always led to enhanced texturing in short times, while not disturbing the typical microstructure of the composite 123 plus 211, that is believed essential for high critical currents in these high Tc superconductors.
Methodology, Performance and Problems in ER Clutch Based Positioning Mechanisms
Authors: Bullough W. A. , Johnson A. R. , Tozer R. , Makin J.
Published: July 2002

Progress and problems encountered in the development of a demonstrator of the fast switching, digital motion profile generator based on the electro-rheological catch/brake are set down. Limiting accelerations of ~ 50g have been obtained but with inadequate reliability - evidenced by the onset of avalanche current at high duty loadings.
THE INFLUENCE OF A CRITICAL SIZE ON THE SCALING BEHAVIOR OF CLUSTERS COALESCENCE
Authors: ZHUANG GUOCE , ZHU XIAOBIN , WANG WEI
Published: July 2002

By introducing a critical cluster size N c , the irreversible and reversible cluster–cluster aggregation are studied with Monte Carlo simulation method. In a long time limit the average size of cluster ∞ reaches its stationary value which depends on the critical size N c and the breakup constant k. Our results indicate that in the presence of critical size the critical exponent y, which is defined as ~k-y, increases as the critical size increases and is lower than the value of (α+ξ+2)-1, where the exponents α and ξ associate with the detachment and attachment of clusters.
NANOCRYSTALLINE FORMATION IN AMORPHOUS Fe79B16Si5 AND Fe78B13Si9 RIBBONS
Authors: THONGMEE S. , ISSRO C. , ROONGKEADSAKOON S. , WINOTAI P. , TANG I. M.
Published: July 2002

Nanocrystalline formation in the amorphous ribbons, Fe 79 B 16 Si 5 and Fe 78 B 13 Si 9, resulting from annealing the ribbons at temperatures below their crystalline temperature is followed by Mossbauer spectroscopy. It is seen that in the B-rich Fe 78 B 16 Si 5 ribbons, the crystallization is a two stage process: amorphous →α-Fe(Si) nanocrystalline formation → (α-Fe, Fe 2 B ) nanocrystalline formation while the crystallization in the B-poor Fe 78 B 13 Si 9 ribbons is a three stage process: amorphous → Fe 3 B nanocrystalline formation → α-Fe(Si) nanocrystalline formation → (α-Fe, Fe 2 B ) nanocrystalline formation. These direct observation confirms the inferred formation of nanocrystallites obtained from magnetization measurements of similar type Fe-Si-B amorphous alloys. Our study also indicated that the α-Fe(Si) nanocrystallites survives at the higher temperatures.
COLLAPSE AND REVIVAL IN VORTEX INTERFERENCE IN THE PRESENCE OF NONCLASSICAL ELECTROMAGNETIC FIELD
Authors: ZOU JIAN , SHAO BIN
Published: July 2002

Interference of vortex winding around electric charges induced by nonclassical electromagnetic field is considered. It is shown that collapse and revival can exist in such a system, which is the effect of the quantum noise of the nonclassical electromagnetic field on the dynamic behavior of the vortex interference.
NONLINEAR PREDICTION AND COMPLEXITY OF ALPHA EEG ACTIVITY
Authors: BRANDT MICHAEL E. , ADEMOĞLU AHMET , PRITCHARD WALTER S.
Published: July 2002

Two prediction techniques were used to investigate the dynamical complexity of the alpha EEG; a nonlinear method using the K-nearest-neighbor local linear (KNNLL) approximation, and one based on global linear autoregressive (AR) modeling. Generally, KNNLL has more ability to predict nonlinearity in a chaotic time series under moderately noisy conditions as demonstrated by using increasingly noisy realizations of the Hénon (a low-dimensional chaotic) and Mackey–Glass (a high-dimensional chaotic) maps. However, at higher noise levels KNNLL performs no better than AR prediction. For linear stochastic time series, such as a sine wave with added Gaussian noise, prediction using KNNLL is no better than AR even at very low signal-to-noise ratios. Both prediction techniques were applied to resting EEGs (O2 scalp recording site, 10–20 EEG system) from ten normal adult subjects under eyes-closed and eyes-open conditions. In all recordings tested, KNNLL did not yield a lower root mean squared error (RMSE) than AR prediction. This result more closely resembles that obtained for noisy sine waves as opposed to chaotic time series with added noise. This lends further support to the notion that these EEG signals are linear-stochastic in nature. However, the possibility that some EEG signals, particularly those with high prediction errors produced by a noisy nonlinear system cannot be ruled out in this study.
SIMULATION AND VISUALIZATION OF CNN DYNAMICS
Authors: HÄNGGI MARTIN , MOSER SIMON , PFAFFHAUSER ERIC , MOSCHYTZ GEORGE S.
Published: July 2002

A new simulator for Cellular Neural Networks (CNNs) is presented. In contrast to other simulators, the CNN cells are visualized in a grid structure, the values of input and states being represented by colors. Input and initial images can easily be generated and changed even while the integration of the system is in progress, and an oscilloscope function allows the quantitative study of CNN transients, thus providing insight into the dynamics of the network.

For those who are new to the world of CNNs, a series of predefined templates set and demonstrations are available, which makes the simulator a valuable educational tool. Advanced users and CNN expert can examine manually-entered and parametrized templates and carry out experiments in a very broad spectrum of CNN theory and applications, including quantitative behavior, robustness aspects, settling time, state limitations, different output functions and numerical integration methods.

The simulator is written in Java and publicly available on WWW and will run on any Web browser of the newer generations.
THE PSEUDOVARIETY GENERATED BY ALL SEMIGROUPS OF ORIENTATION-PRESERVING TRANSFORMATIONS ON A FINITE CYCLE
Authors: CATARINO P. M. , HIGGINS P. M.
Published: July 2002

We continue the study of OPn, the monoids of orientation-preserving mappings on a chain, leading to the study of the semigroup pseudovariety [Formula: see text] generated by all monoids OPn, showing among other results that [Formula: see text] is self-dual and contains all commutative semigroups.
A METHOD FOR THE FORWARD MODELLING OF 3-D ELECTROMAGNETIC QUASI-STATIC PROBLEMS
Authors: ARULIAH D. A. , ASCHER U. M. , HABER E. , OLDENBURG D.
Published: July 2002

We present a solution method for solving electromagnetic problems in three dimensions in parameter regimes where the quasi-static approximation applies and the permeability is constant. Firstly, by using a potential formulation with a Coulomb gauge, we circumvent the ill-posed problem in regions of vanishing conductivity, obtaining an elliptic, weakly coupled system of differential equations. The system thus derived is strongly elliptic, which leads to reliable discretizations. Secondly, we derive a robust finite-volume discretization. Thirdly, we solve the resulting large, sparse algebraic systems using preconditioned Krylov-space methods. A particularly efficient algorithm results from the combination of BICGSTAB and a block preconditioner using an incomplete LU-decomposition of the dominant system blocks only. We demonstrate the efficacy of our method in several numerical experiments.
MATHEMATICAL MODELLING OF MACROPHAGE DYNAMICS IN TUMOURS
Authors: OWEN MARKUS R. , SHERRATT JONATHAN A.
Published: July 2002

Macrophages form an important part of the immune response to cancer. In this paper, we present a mathematical model of reaction–diffusion form, which represents the influx of macrophages into a small avascular tumour, and their dynamics within the tumour as it grows. The model predicts that, despite their ability to selectively kill tumour cells, macrophages are unable to prevent tumour growth. However, significant effects on the form of the tumour are predicted, including in particular the formation of spatial patterns. When the model is extended to include macrophage chemotaxis, these patterns can in some cases bifurcate to give irregular spatiotemporal oscillations, and the authors present a detailed numerical bifurcation study which suggests a novel dynamical origin for these oscillations. Finally, we present results of model simulations in two spatial dimensions.
SINGULARITY AVOIDANCE BY COLLAPSING SHELLS IN QUANTUM GRAVITY
Authors: HÁJÍČEK PETR , KIEFER CLAUS
Published: July 2002

We discuss a model describing exactly a thin spherically symmetric shell of matter with zero rest mass. We derive the reduced formulation of this system in which the variables are embeddings, their conjugate momenta, and Dirac observables. A nonperturbative quantum theory of this model is then constructed, leading to a unitary dynamics. As a consequence of unitarity, the classical singularity is fully avoided in the quantum theory.
STUDY OF FORWARD–BACKWARD SHOWER PARTICLE AND SLOW PROTON PRODUCTION FROM THE INTERACTIONS OF7LiWITH EMULSION NUCLEI AT 3A GeV/c
Authors: ABD-ALLAH N. N.
Published: July 2002

The correlations between the multiplicities of secondary charged particles emitted in collisions of 3 A GeV/c7Li with emulsion have been studied. The dependence of the correlation strength on the mass number of the projectile has been analyzed. Moreover, the dependence of the average multiplicities of shower particle emitted in the forward and backward hemispheres on the number of target fragments has been investigated. The study of the number of backward slow protons (black and grey particles) indicates that, while the number of backward particles is a good factor representing the purely target fragments, the number of backward grey particles can be considered an accurate experimental factor for the impact parameter dependence of the collision.
PUPILLARY HIPPUS: AN UNRECOGNIZED EXAMPLE OF BIOLOGIC CHAOS
Authors: ROSENBERG MICHAEL L. , KROLL MARTIN H.
Published: July 2002

We analyzed the pupil size vs time from six subjects using pupilography and nonlinear techniques. The correlation dimensions ranged from 4.08 to 5.7. The Hurst exponents ranged from 0.132 to 0.546. All data sets contained at least one positive Lyapunov exponent. The use of surrogate yielded statistically significant differences for the correlation dimension. Phase space analysis yields a definite flow, and in subject two, period-doubling is evident. The accumulated evidence supports the notion that dynamics of pupil size are governed by deterministic chaos rather than a stochastic or linear process. This implies that one might discern between well and disease states using pupillography and that the dynamics can be mechanistically modeled.
NUMERICAL SIMULATION OF LOW-FREQUENCY AEROACOUSTICS OVER IRREGULAR TERRAIN USING A FINITE ELEMENT DISCRETIZATION OF THE PARABOLIC EQUATION
Authors: KAMPANIS NIKOLAOS A.
Published: July 2002

Environmental noise raises serious concerns in modern industrial societies. As a result, the study of sound propagation in the atmosphere over irregular terrain is a subject of current interest in aeroacoustics. We use the standard parabolic approximation of the Helmholtz equation to simulate the far-field, low-frequency sound propagation in a refracting atmosphere, over terrains with mild range-varying topography. At an artificial upper boundary of the computational domain, described in range and height coordinates, a nonlocal boundary condition is used to model the effect of a homogeneous, semi-infinite atmosphere. We define a curvilinear coordinate system fitting the irregular topography. We discretize the transformed initial-boundary value problem with a finite element technique in height and a conservative Crank–Nicolson scheme for marching in range. The underlying transformation of coordinates allows the effective coupling with the nonlocal boundary condition. The resulting discretization method is accurate and efficient for the numerical prediction of noise levels in the atmosphere.
RELATIVISTIC TREATMENT OF PHOTOEMISSION INCORPORATING THE SPATIALLY DEPENDENT PHOTON FIELD
Authors: THAPA R. K. , GURUNG SHIVRAJ , PACHUAU ZAITHANZAUVA , KHATING D. T.
Published: July 2002

We discuss a simple theory of photoemission incorporating the relativistically defined initial state wave function for the electronic states. The photocurrent data are calculated in the case of tungsten and silicon.
VARIETIES OF METABELIAN LEIBNIZ ALGEBRAS
Authors: DRENSKY VESSELIN , PIACENTINI CATTANEO GIULIA MARIA
Published: July 2002

In this paper we commence the systematic study of T-ideals of the free Leibniz algebra or, equivalently, varieties of Leibniz algebras, over a field of characteristic 0. We give a description of the free metabelian (i.e. solvable of class 2) Leibniz algebras, a complete list of all left-nilpotent of class 2 varieties and the asymptotic description of the metabelian varieties.
COMPACTION AND DENSITY FLUCTUATIONS IN VIBRATED GRANULAR MEDIA
Authors: BARNUM A. C. B. , OZBAY ARIF , NOWAK E. R.
Published: July 2002

We report measurements of the density of a vibrated granular material as a function of time or taps. The material studied consists of monodisperse spherical glass beads confined to a long, thin cylindrical tube. Changes in vibration intensity are used to induce transitions between two steady state densities that depend on the intensity of the vibrations. We find a complex time evolution similar to previous work on the irreversible relaxation from a loose state toward a steady state. In addition, frequency dependent third order moments of the density fluctuations are measured. The data indicate a coupling between large variations in density on one time scale and noise power over a broad range of higher-frequency scales.
A GENERAL UPDATING RULE FOR DISCRETE HOPFIELD-TYPE NEURAL NETWORK WITH TIME-DELAY AND THE CORRESPONDING SEARCH ALGORITHM
Authors: YEUNG DANIEL S. , QIU SHENSHAN , TSANG ERIC C. C. , WANG XIZHAO
Published: July 2002

In this paper, the Hopfield neural network with delay (HNND) is studied from the standpoint of regarding it as an optimizing computational model. Two general updating rules for networks with delay (GURD) are given based on Hopfield-type neural networks with delay for optimization problems and characterized by dynamic thresholds. It is proved that in any sequence of updating rule modes, the GURD monotonously converges to a stable state of the network. The diagonal elements of the connection matrix are shown to have an important influence on the convergence process, and they represent the relationship of the local maximum value of the energy function to the stable states of the networks. All the ordinary discrete Hopfield neural network (DHNN) algorithms are instances of the GURD. It can be shown that the convergence conditions of the GURD may be relaxed in the context of applications, for instance, the condition of nonnegative diagonal elements of the connection matrix can be removed from the original convergence theorem. A new updating rule mode and restrictive conditions can guarantee the network to achieve a local maximum of the energy function with a step-by-step algorithm. The convergence rate improves evidently when compared with other methods. For a delay item considered as a noise disturbance item, the step-by-step algorithm demonstrates its efficiency and a high convergence rate. Experimental results support our proposed algorithm.
LEARNING ITERATIVE IMAGE RECONSTRUCTION IN THE NEURAL ABSTRACTION PYRAMID
Authors: BEHNKE SVEN
Published: July 2002

Successful image reconstruction requires the recognition of a scene and the generation of a clean image of that scene. We propose to use recurrent neural networks for both analysis and synthesis.

The networks have a hierarchical architecture that represents images in multiple scales with different degrees of abstraction. The mapping between these representations is mediated by a local connection structure. We supply the networks with degraded images and train them to reconstruct the originals iteratively. This iterative reconstruction makes it possible to use partial results as context information to resolve ambiguities.

We demonstrate the power of the approach using three examples: superresolution, fill-in of occluded parts, and noise removal/contrast enhancement. We also reconstruct images from sequences of degraded images.
Authentication in distributed systems
Authors: Lampson Butler , Abadi Martín , Burrows Michael , Wobber Edward
Published: July 2002

We describe a theory of authentication and a system that implements it. Our theory is based on the notion of principal and a “speaks for” relation between principals. A simple principal either has a name or is a communication channel; a compound principal can express an adopted role or delegated authority. The theory shows how to reason about a principal's authority by deducing the other principals that it can speak for; authenticating a channel is one important application. We use the theory to explain many existing and proposed security mechanisms. In particular, we describe the system we have built. It passes principals efficiently as arguments or results of remote procedure calls, and it handles public and shared key encryption, name lookup in a large name space, groups of principals, program loading, delegation, access control, and revocation.
Monotone circuits for matching require linear depth
Authors: Raz Ran , Wigderson Avi
Published: July 2002

It is proven that monotone circuits computing the perfect matching function on
n
-vertex graphs require Ω(
n
) depth. This implies an exponential gap between the depth of monotone and nonmonotone circuits.
Integrality and separability of input devices
Authors: Jacob Robert J. K. , Sibert Linda E. , McFarlane Daniel C. , Mullen M. Preston
Published: July 2002

Current input device taxonomies and other frameworks typically emphasize the mechanical structure of input devices. We suggest that selecting an appropriate input device for an interactive task requires looking beyond the physical structure of devices to the deeper perceptual structure of the task, the device, and the interrelationship between the perceptual structure of the task and the control properties of the device. We affirm that perception is key to understanding performance of multidimensional input devices on multidimensional tasks. We have therefore extended the theory of processing of percetual structure to graphical interactive tasks and to the control structure of input devices. This allows us to predict task and device combinations that lead to better performance and hypothesize that performance is improved when the perceptual structure of the task matches the control structure of the device. We conducted an experiment in which subjects performed two tasks with different perceptual structures, using two input devices with correspondingly different control structures, a three-dimensional tracker and a mouse. We analyzed both speed and accuracy, as well as the trajectories generated by subjects as they used the unconstrained three-dimensional tracker to perform each task. The result support our hypothesis and confirm the importance of matching the perceptual structure of the task and the control structure of the input device.
Explaining type errors in polymorphic languages
Authors: Beaven Mike , Stansifer Ryan
Published: July 2002

Strongly-typed languages present programmers with compile-time feedback about the type correctness of programs. Errors during polymorphic type checking take the form of a unification failure for two types. Finding the source of the type error in the code is often difficult because the error may occur far from the spot where the inconsistency is detected. As functional languages use more and more complex type systems, the difficulty of interpreting and locating these errors will increase. To locate the source of type errors the programmer must unravel the long chain of deductions and type instantiations made during type reconstruction. This paper describes an approach that maintains the deductive steps of type inference and the reasons for type instantiations. The approach could be used in an interactive system to guide the programmer to the source of a type error or to explain why the compiler assigned a particular type to an expression.
On the lower degree intersections of two natural quadrics
Authors: Shene Ching-Kuang , Johnstone John K.
Published: July 2002

In general, two quadric surface intersect in a space quartic curve. However, the intersection frequently degenerates to a collection of plane curves. Degenerate cases are frequent in geometric/solid modeling because degeneracies are often required by design. Their detection is important because degenerate intersections can be computed more easily and allow simpler treatment of important problems. In this paper, we investigate this problem for natural quadrics. Algorithms are presented to detect and compute conic intersections and linear intersections. These methods reveal the relationship between the planes of the degenerate intersections and the quadrics. Using the theory developed in the paper, we present a new and simplified proof of a necessary and sufficient condition for conic intersection. Finally, we present a simple method for determining the types of conic in a degenerate intersection without actually computing the intersection, and an enumeration of all possible conic types. Since only elementary geometric routines such as line intersection are used, all of the above algorithms are intuitive and easily implementable.
Secure communications in ATM networks
Authors: Stevenson Daniel , Hillery Nathan , Byrd Greg
Published: July 2002

High-speed networking technology and standards have progressed dramatically in the past few years and much attention is now focused on deployment efforts, such as the North Carolina Information Highway (NCIH) [7], and applications. With this shift in emphasis, concerns have been raised about information security. Examples of abuse of the Internet abound and unfortunately ATM networks are subject to many of these same abuses. This is of subtanstial concern when thinking about extending the reach of public data networking to broad segments of society.
Transaction chopping
Authors: Shasha Dennis , Llirbat Francois , Simon Eric , Valduriez Patrick
Published: July 2002

Chopping transactions into pieces is good for performance but may lead to nonserializable executions. Many researchers have reacted to this fact by either inventing new concurrency-control mechanisms, weakening serializability, or both. We adopt a different approach. We assume a user who

—has access only to user-level tools such as (1) choosing isolation degrees 1ndash;4, (2) the ability to execute a portion of a transaction using multiversion read consistency, and (3) the ability to reorder the instructions in transaction programs; and

—knows the set of transactions that may run during a certain interval (users are likely to have such knowledge for on-line or real-time transactional applications).

Given this information, our algorithm finds the finest chopping of a set of transactions TranSet with the following property:
If the pieces of the chopping execute serializably, then TranSet executes serializably
. This permits users to obtain more concurrency while preserving correctness. Besides obtaining more intertransaction concurrency, chopping transactions in this way can enhance intratransaction parallelism.

The algorithm is inexpensive, running in
O(n×(e+m))
time, once conflicts are identified, using a naive implementation, where
n
is the number of concurrent transactions in the interval,
e
is the number of edges in the conflict graph among the transactions, and
m
is the maximum number of accesses of any transaction. This makes it feasible to add as a tuning knob to real systems.
Combinational logic synthesis for LUT based field programmable gate arrays
Authors: Cong Jason , Ding Yuzheng
Published: July 2002

The increasing popularity of the field programmable gate-array (FPGA) technology has generated a great deal of interest in the algorithmic study and tool development for FPGA-specific design automation problems. The most widely used FPGAs are LUT based FPGAs, in which the basic logic element is a
K
-input one-output lookup-table (LUT) that can implement any Boolean function of up to
K
variables. This unique feature of the LUT has brought new challenges to logic synthesis and optimization, resulting in many new techniques reported in recent years. This article summarizes the research results on combinational logic synthesis for LUT based FPGAs under a coherent framework. These results were dispersed in various conference proceedings and journals and under various formulations and terminologies. We first present general problem formulations, various optimization objectives and measurements, then focus on a set of commonly used basic concepts and techniques, and finally summarize existing synthesis algorithms and systems. We classify and summarize the basic techniques into two categories, namely,
logic optimization
and
technology mapping
, and describe the existing algorithms and systems in terms of how they use the classified basic techniques. A comprehensive list of references is compiled in the attached bibliography.
Constructing deterministic finite-state automata in recurrent neural networks
Authors: Omlin Christian W. , Giles C. Lee
Published: July 2002

Recurrent neural networks that are
trained
to behave like deterministic finite-state automata (DFAs) can show deteriorating performance when tested on long strings. This deteriorating performance can be attributed to the instability of the internal representation of the learned DFA states. The use of a sigmoidel discriminant function together with the recurrent structure contribute to this instability. We prove that a simple algorithm can
construct
second-order recurrent neural networks with a sparse interconnection topology and sigmoidal discriminant function such that the internal DFA state representations are stable, that is, the constructed network correctly classifies strings of
arbitrary length
. The algorithm is based on encoding strengths of weights directly into the neural network. We derive a relationship between the weight strength and the number of DFA states for robust string classification. For a DFA with
n
state and
m
input alphabet symbols, the constructive algorithm generates a “programmed” neural network with
O
(
n
) neurons and
O
(
mn
) weights. We compare our algorithm to other methods proposed in the literature.
Model and verification of a data manager based on ARIES
Authors: Kuo Dean
Published: July 2002

In this article, we model and verify a data manager whose algorithm is based on ARIES. The work uses the I/O automata method as the formal model and the definition of correctness is defined on the interface between the scheduler and the data manager.
An efficient surface intersection algorithm based on lower-dimensional formulation
Authors: Krishnan Shankar , Manocha Dinesh
Published: July 2002

We present an efficient algorithm to compute the intersection of algebraic and NURBS surfaces. Our approach is based on combining the marching methods with the algbraic formulation. In particular, we propose and matrix computations. We present algorithms to compute a start point on each component of the intersection curve (both open and closed components), detect the presence of singularities, and find all the curve branches near the singularity. We also suggest methods to compute the step size during tracing to prevent component jumping. The algorithm runs an order of magnitude faster than previously published robust algorithms. The complexity of the algorithm is output sensitive.
A survey of approximately optimal solutions to some covering and packing problems
Authors: Paschos Vangelis T.
Published: July 2002

We survey approximation algorithms for some well-known and very natural combinatorial optimization problems, the minimum set covering, the minimum vertex covering, the maximum set packing, and maximum independent set problems; we discuss their approximation performance and their complexity. For already known results, any time we have conceived simpler proofs than those already published, we give these proofs, and, for the rest, we cite the simpler published ones. Finally, we discuss how one can relate the approximability behavior (from both a positive and a negative point of view) of vertex covering to the approximability behavior of a restricted class of independent set problems.
Predictive engineering models based on the EPIC architecture for a multimodal high-performance human-computer interaction task
Authors: Kieras David E. , Wood Scott D. , Meyer David E.
Published: July 2002

Engineering models of human performance permit some aspects of usability of interface designs to be predicted from an analysis of the task, and thus they can replace to some extent expensive user-testing data. We successfully predicted human performance in telephone operator tasks with engineering models constructed in the EPIC (
E
xecutive
P
rocess-
I
nteractive
C
ontrol) architecture for human information processing, which is especially suited for modeling multimodal, complex tasks, and has demonstrated success in other task domains. Several models were constructed on an
a priori
basis to represent different hypotheses about how operators coordinate their activities to produce rapid task performance. The models predicted the total time with useful accuracy and clarified some important properties of the task. The best model was based directly on the GOMS analysis of the task and made simple assumptions about the operator's task strategy, suggesting that EPIC models are a feasible approach to predicting performance in multimodal high-performance tasks.