bluuebunny/crossref_metadata_2025 huggingface dataset:
AREA EFFICIENT LAYOUT OF BALANCED HYPERCUBES
Authors: HUANG KE , WU JIE
Published: November 2004

As a multicomputer structure, the balanced hypercube is a variant of the standard hypercube for multicomputers, with desirable properties of strong connectivity, regularity, and symmetry. This structure is a special type of load balanced graph designed to tolerate processor failure. In balanced hypercubes, each processor has a backup (matching) processor that shares the same set of neighboring nodes. Therefore, tasks that run on a faulty processor can be reactivated in the backup processor to provide efficient system reconfiguration. In this paper, we study the implementation of balanced hypercubes in VLSI using the Wafer Scale Integration (VLSI/WSI) technology. Emphasis is on VLSI/WSI layout and area estimates. Our results show that the balanced hypercube can be implemented at least as efficient as the standard hypercube in an area layout and more efficient in a linear layout.
PREFIX-SUMS ALGORITHMS ON RECONFIGURABLE MESHES
Authors: NAKANO KOJI
Published: November 2004

This paper shows that the prefix-sums of n binary values can be computed in [Formula: see text] time on an n × m reconfigurable mesh of the word model. It also shows that prefix-sums of n binary values can be computed in [Formula: see text] time on an n × m reconfigurable mesh of the word model if the reconfigurable mesh has communication capability that allows simultaneous sending to the same bus.
THE STATIC NETWORK: A HIGH PERFORMANCE RECONFIGURABLE COMMUNICATION NETWORK
Authors: GERMAIN CECILE , CAPPELLO FRANCK
Published: November 2004

This paper presents a new interconnection network for a massively parallel architecture based on the static model of communication. The principle of the model is to schedule at run time, on a circuit switching hardware, the off-line routed circuits computed at compile time. Designing a network especially for the compiled model can take full benefit of the current interconnection technology. The static network is intended to a synchronised MIMD distributed memory machine, based on high performance processing nodes including microprocessors. The application scope is numerical computation, where all communication patterns may occur. The hardware issues are the various synchronisations inside the network, which need a sophisticated switch design to keep pace with 1.33 Gbit/s links. The network is designed to reach a sustained aggregate bandwidth of more than 500GBytes/s, and provide an overall latency less than 270ns, up to 4K inputs. The network is fully pipelined and can be reconfigured each 60ns.
A BIBLIOGRAPHY OF PUBLISHED PAPERS ON DYNAMICALLY RECONFIGURABLE ARCHITECTURES
Authors: NAKANO KOJI
Published: November 2004

A dynamically reconfigurable architecture is a parallel computer architecture that supports a physical switching of communication patterns during a computation. Basically, the dynamically reconfigurable architecture consists of locally controllable switches, which enables flexible-connection patterns of the network. The bibliography attempts to classify published papers on dynamically reconfigurable architectures according to the problems that are dealt with.
MAX SAT AND MIN SET COVER APPROXIMATION ALGORITHMS ARE $\mathcal P$-COMPLETE
Authors: BONGIOVANNI GIANCARLO , CRESCENZI PIERLUIGI , DE AGOSTINO SERGIO
Published: November 2004

We prove that the sequential approximation algorithms for the problems [Formula: see text] and [Formula: see text] proposed in [9] are [Formula: see text]-hard with respect to the logarithmic space reducibility. As a corollary, these two algorithms cannot be implemented efficiently in parallel unless [Formula: see text].
DO FIXED-PROCESSOR COMMUNICATION-TIME TRADEOFFS EXIST?
Authors: LUTZ DAVID R. , JAYASIMHA D. N.
Published: November 2004

A parallel algorithm exhibits a fixed-processor communication-time tradeoff if lower bounds on communication and time cannot be simultaneously realized by any schedule using p processors. For unrestricted schedules, lower bounds on communication are trivial, so all researchers in this area have made assumptions about what kinds of schedules to consider. The usual restriction is that all processors perform approximately equal work. The problem with this restriction is that it can overstate the number of processors that are needed to realize the claimed time and communication bounds. Since the communication and time bounds are expressed as a function of p, using an inflated value for p can lead us to believe that there is a tradeoff when none exists. In this paper we reexamine previously published communication results for several algorithms and show that the existence of tradeoffs is still an open question. We also introduce the concept of effective schedules, and argue that both tight communication bounds and fixed-processor communication-time tradeoffs are only meaningful for effective schedules.
PERFORMANCE BOUNDS FOR STATIC MULTIPROCESSOR SCHEDULING OF MULTI-TASK JOBS
Authors: MAHESH S. , MURTHY C. SIVA RAM , RANGAN C. PANDU
Published: November 2004

Job scheduling on multiprocessor systems is studied here as a special case of oriented two-dimensional orthogonal bin packing. Each job has subtasks which can be processed in parallel, requiring multiple processors to be allocated to each job. Then each job corresponds to a rectangle with sides equal to the processor requirement and the processing time. We study two classes of algorithms: (i) Longest processing time first (LPT) algorithms, and (ii) Largest processor requirement first (LPR) algorithms. We obtain improved asymptotic upper bounds for these algorithms compared to the bounds of the corresponding algorithms for the general two-dimensional packing problem. This is due to the discrete nature of the processor requirement (dimension) of jobs. We find that the LPR algorithms have better asymptotic upper bound on the makespan compared to the LPT algorithms. Specifically, the bound is 7/4 for the LPR algorithms whereas it is 2 for the LPT algorithms. Moreover, LPR algorithms are found to be more suited for dynamic job scheduling.
CONSTRUCTION OF DO LOOPS FROM SYSTEMS OF AFFINE CONSTRAINTS
Authors: COLLARD JEAN-FRANÇOIS , RISSET TANGUY , FEAUTRIER PAUL
Published: November 2004

Most parallelization techniques for [Formula: see text] loop nests are based on reindexation. Reindexation yields a new iteration space, which is a convex integer polyhedron defined by a set of affine constraints. Parallel code generation thus needs to scan all the integer points of this convex, thereby requiring the construction of a new [Formula: see text] loop nest. We detail an algorithm to this purpose, which relies on a parametrized version of the Dual Simplex. We show how the resulting loop nest and especially the loop bounds can be kept simple, thus reducing the control overhead of parallelization to a minimum.
ON DESIGNING COMMUNICATION-INTENSIVE ALGORITHMS FOR A SPANNING OPTICAL BUS BASED ARRAY
Authors: QIAO CHUNMING
Published: November 2004

The Reconfigurable Array with Spanning Optical Buses (or RASOB) architecture provides flexible reconfiguration and strong connectivities with low hardware and control complexities. We use a parallel implementation of the matrix transposition as well as multiplication algorithms as an example to show how the architectural capabilities can be taken advantage of in designing efficient parallel algorithms.
A STRATEGY FOR SCHEDULING PARTIALLY ORDERED PROGRAM GRAPHS ONTO MULTICOMPUTERS
Authors: LEE BEN , HURSON ALI R.
Published: November 2004

The issue of scalability is key to the success of massively parallel processing. Due to their distributed nature, message-passing multicomputers are appropriate for achieving scalar performance. However, the message-passing model lacks programmability due to difficulties encountered by the programmers to partition and schedule the computation over the processors and to establish efficient inter-processor communication in the user code. Therefore, this paper presents a compile-time scheduling heuristic, called BLS, that maps programs onto the processors of a message-passing multicomputer. In contrast to other methods proposed, BLS takes a more global approach in attempt to balance the tradeoff between exploiting parallelism and reducing communication overhead. To evaluate the effectiveness of BLS, simulation studies of scheduling SISAL programs are presented.
DISTRIBUTED SCHEDULING OF UNSTRUCTURED COLLECTIVE COMMUNICATION ON THE CM-5
Authors: WANG JHY-CHUN , LIN TSENG-HUI , RANKA SANJAY
Published: November 2004

Parallelization of scientific applications often results in unstructured collective communication. In this paper, we present a distributed algorithm for scheduling such communication on parallel machines. We describe the performance of this algorithm on the CM-5 and show that the scheduling algorithm gives a significant improvement over naive methods.
LATTICE DYNAMICS OF THE BINARY APERIODIC CHAINS OF ATOMS III: PROPERTIES OF VIBRATIONAL EIGENVECTORS
Authors: SALEJDA WŁODZIMIERZ
Published: November 2004

We numerically study the localization and multifractal properties of normalized vibrational eigenvectors (NVEV), denoted by U, of the microscopic harmonic model of lattice dynamics in Thue-Morse (TM), generalized Fibonacci, octagonal, dodecagonal, Severin, circle and Rudin-Shapiro (RS) binary chain of atoms. Eigenvalues and NVEV are determined with the help of the Dean and Wu-Zheng algorithm, respectively, with free end boundary conditions for chains containing 103<N<104 atoms. The first FM(L) and second SM(L) moment, and the reduced participation ratios Λ red (L) are derived at 1≤L≤N for varying model parameters. All the chains studied show sinusoidal-like and packet-like extended NVEV with Λred(L)≃1, FM(L)≃N/2 and [Formula: see text] The new extended eigenstates called dimmerized NVEV have been found out in the case of the TM chain. The surface localized NVEV with Λred(L)≪1, FM(L)≃1 or FM(L)≃N and the strong tendency to localization of NVEV in RS chain have been observed. The critical NVEV, which dominate in the optical region of phonon spectra, are objects with a broad multifractal (αmin, αmax) spectra. If magnitudes of model parameters are increased then, first, [Formula: see text] and [Formula: see text] at L≪N and, second, [Formula: see text] and [Formula: see text] at L≃N. It is numerically shown that the multifractal spectra α′—f′ characterizing the curdling of the elastic energy field ε(L) are in excellent qualitative and quantitative agreement with the multifractal spectra of the critical NVEV.
DISLOCATIONS IN UNIAXIAL LAMELLAR PHASES OF LIQUID CRYSTALS, POLYMERS AND AMPHIPHILIC SYSTEMS
Authors: HOŁYST ROBERT , OSWALD PATRICK
Published: November 2004

Dislocations in soft condensed matter systems such as lamellar systems of polymers, liquid crystals and ternary mixtures of oil, water and surfactant (amphiphilic systems) are described in the framework of continuum elastic theory. These systems are the subject of studies of physics, chemistry and biology. They also find applications in industry. Here we will discuss in detail the influence of dislocations on the bulk and surface properties of these lamellar phases. Especially the latter properties have only been recently studied in detail. We will present the experimental evidence of the existence of screw and edge dislocations in the systems and study their static properties such as: energy, line tension and core structure. Next we will show how the surface influences the equilibrium position of dislocations in the system. We will give the theoretical predictions and present the experimental results on thin copolymer films, free standing films of liquid crystals and smectic droplets shapes. In semi-infinite lamellar systems characterized by small surface tension the dislocation is stabilized at a finite distance, heq, from the surface, due to the surface bending elastic constant, Ks (for zero surface tension heq≈Ks/2K, where K is the bulk bending elastic constant). For large surface tension the edge dislocations are strongly repelled by the surface and the equilibrium location for finite symmetric systems such as free standing liquid crystal films shifts towards the center of the system. The surface is deformed by dislocations. These deformations are known as edge profiles. They will be discussed for finite systems with small and large surface tension. Surface deformations induce elastic interactions between edge dislocations, which decay exponentially with distance with decay length proportional to [Formula: see text] where D is the size of the system normal to lamellas. Two screw dislocations in finite system interact with the logarithmic potential, which is proportional to the surface tension and inversly proportional to D. The surface induced elastic interactions will be compared to, well-known, bulk deformation induced interactions. A new phenonenon discussed in our paper is the fluctuations induced interactions between edge dislocations, which follows from the Helfrich mechanism for flexible objects. At suitable conditions, edge dislocations can undergo an unbinding transition. Also a single dislocation loop can undergo an unbinding transition. We will calculate the properties of the loop inside finite system and discuss in particular the unbinding transition in freely suspended smectic films. We shall also compute the equilibrium size of the loop contained between two hard walls. Finally we will discuss the dynamical bulk properties of dislocations such as: mobility (climb and glide), permeation, and helical instability of screw dislocations. Lubrication theory will also be discussed.
THE UNIVERSAL EQUATIONS OF MOTION FOR NONLINEAR FIELDS IN DIFFERENT BASES DESCRIBING STRONGLY INTERACTING MANY-BODY SYSTEMS WITH TWO-BODY INTERACTIONS
Authors: DIXON J.M. , TUSZYŃSKI J.A.
Published: November 2004

A brief account of the Method of Coherent Structures (MCS) is presented using a plane-wave basis to define a quantum field. It is also demonstrated that the form of the quantum field equations, obtained by MCS, although highly nonlinear for many-body systems with two-body interactions, is independent of the basis of states used for the definition of the field.
QED COHERENCE AND THE THERMODYNAMICS OF WATER
Authors: ARANI RAFFAELLA , BONO IVAN , GIUDICE EMILIO DEL , PREPARATA GIULIANO
Published: November 2004

It is shown that when the density becomes larger than a critical density an ensemble of water molecules evolves towards a coherent ground state, where molecules oscillate in phase with the e.m. field. At each temperature, liquid water is found to consist of a coherent phase of molecules in such a ground state and of a normal phase, whose population is determined by thermal excitations. The observed thermodynamical quantities as well as their wellknown anomalous behaviors are satisfactorily described by our theory.
MEMORY-DEPENDENT CONSTITUTIVE EQUATIONS IN INFORMATIONAL STATISTICAL THERMODYNAMICS
Authors: VASCONCELLOS ÁUREA ROSAS , LUZZI ROBERTO , GARCIA-COLIN LEOPOLDO S.
Published: November 2004

The nonequilibrium Statistical Operator Method, seemingly contained within the scope of Jaynes’ Predictive Statistical Mechanics, provides a foundation for irreversible thermodynamics in what is called Informational Statistical Thermodynamics, and within it a way of deriving generalized constitutive equations which contain non-localities on space. Here we present a derivation of these equations of evolution describing how memory effects are incorporated into the theory. We show that the memory kernels in the kinetic coefficients and relaxation times can be expressed in terms of an infinite series of instantaneous collisions integrals, of ever increasing order in the interaction strengths that are related to the slow relaxation processes that develop in the system. The kinetic coefficients are derived on the basis of the Hamiltonian dynamics of the system accompanied by appropriate averages over the nonequilibrium informational statistical ensemble.
DYNAMICS OF INTERACTING ALGEBRAIC SOLITONS
Authors: MATSUNO YOSHIMASA
Published: November 2004

A survey is made which highlights recent topics on the dynamics of algebraic solitons, which are exact solutions to a certain class of nonlinear integrodifferential evolution equations. The model equations that we consider here are the Benjamin-Ono (BO) and its higher-order equations together with the BO-Burgers equation, a model equation for deep-water waves, the sine-Hilbert (sH) equation and a damped sH equation. While these equations have their origin either in physics or in mathematics, each equation exhibits a novel type of algebraic soliton solution and hence its characteristic is worth studying in its own right. After deriving these equations, we are concerned with each equation separately. We first present explicit N-soliton solutions and then summarize related mathematical properties of the equation. Subsequently, a detailed description is given to the interaction process of two algebraic solitons using the pole expansion of the solution. Particular attention is paid to investigating the effects of small perturbations on the overtaking collision of two BO solitons by employing a direct multisoliton perturbation theory. It is shown that the dynamics of interacting algebraic solitons reveal new aspects which have never been observed in the interaction process of usual solitons expressed in terms of exponential functions.
NUMERICAL STUDIES OF PHASE TRANSITIONS AND CRITICAL PHENOMENA IN LIQUID CRYSTALS
Authors: DASGUPTA CHANDAN
Published: November 2004

This article contains an overview of numerical simulations of phase transitions and critical phenomena in liquid crystals. After a brief description of the models studied in simulations and an elementary introduction to commonly used numerical methods, results obtained from existing numerical studies of phase transitions and critial phenomena in liquid crystals are reviewed and some directions for future work are suggested.
PHYSICAL PROPERTIES OF THIN SUBSTRATE-FREE LIQUID-CRYSTAL FILMS
Authors: STOEBE T. , HUANG C.C.
Published: November 2004

Free-standing liquid-crystal films constitute a unique and phenomenally rich system in which a number of physical phenomena may be carefully studied. In particular, they provide an ideal system in which the novel theories of defect-mediated melting in two-dimensions (2D) may be tested. Calorimetric data is presented that indicate that such theories cannot adequately account for phase transitions in effectively 2D free-standing liquid-crystal films only two molecular layers in thickness. Extensive Monte Carlo simulation studies have therefore been performed on a trial Hamiltonian that couples herringbone order to the hexatic order. In a relatively large region of parameter space, the simulation yields heat-capacity consistent with our calorimetric data. These results are discussed in the context of existing data on the structural, optical, and mechanical properties of free-standing films.
PATTERNS IN THIN LIQUID CRYSTAL FILMS AND THE DIVERGENCE (“SURFACELIKE”) ELASTICITY
Authors: LAVRENTOVICH O.D. , PERGAMENSHCHIK V.M.
Published: November 2004

Thin submicron and micron films of liquid crystals placed between two isotropic media represent a particular example of confined systems. Such films can be prepared on the surface of glycerin or other liquids, In comparison with Langmuir monolayers, these films are macroscopically thick to involve the liquid crystalline order in the interplay between molecular structure and macroscopic organization. At the same time, the films are thin enough for such a strong competition between surface and bulk properties that transitional in-plane symmetry is spontaneously violated and a number of patterns appear: stripe domains, square lattices, strings, high strength defects and so on. We show that these structures are governed by the divergence (or “sufacelike”) K13 and K24 terms in the nematic free energy which have been ignored for decades. We also show that both terms can be included in the standard elasiticty theory without contradictions with the basic idea of the nematic phase. The one-dimensional confinement makes the films a unique object of investigation: although the phenomena observed are attributed to the vertical confinement, their manifestation is detected in a non-restricted film plane.
LIQUID CRYSTAL DEFECTS IN A MAGNETIC FIELD
Authors: RANGANATH G.S.
Published: November 2004

In a magnetic field, a liquid crystal exhibits many interesting defect configurations arising due to the diamagnetic anisotropy of the molecules. In this article the structure and properties of some defect states, in the presence of a magnetic field, will be reviewed.
MATHEMATICAL ASPECTS OF QUANTUM PHASE
Authors: DUBIN D.A. , HENNINGS M.A. , SMITH T.B.
Published: November 2004

We consider the current state of the quest for a quantum phase operator, which started in the earliest days of quantum mechanics.4–7 Particular emphasis has been placed on analysis of the structure of the several distinct theories, both physical and mathematical, which has led us from classical function theory to the quantum theory of measurement.
GENERALIZED VARIATIONAL PRINCIPLE IN QUANTUM MECHANICS
Authors: SOLDATOV A.V.
Published: November 2004

An algorithm is proposed that allows us to derive the convergent sequence of upper bounds for the ground state energy of a quantum system. The algorithm generalizes the well-known variational principle of quantum mechanics and moreover provides qualitative, and under some additional conditions even quantitative, characteristics of the spectrum of a quantum system as a whole.
BRIGHT AND DARK GAP SOLITONS GOVERNED BY QUADRATIC NONLINEARITIES
Authors: KIVSHAR YURI S. , CHUBYKALO OKSANA A. , USATENKO OLEG V. , GRINYOFF DMITRI V.
Published: November 2004

It is shown that localized nonlinear modes associated with a gap in the frequency spectrum of linear waves, i.e. the so-called gap solitons, can be supported by purely quadratic nonlinearities. Using the asymptotic expansion technique, a system of coupled nonlinear equations describing interaction between two conter-propagating waves of the same frequency is derived and its spatially localized solutions are found in an explicit form. In some cases the equations and their localized solutions are similar to those known for cubic nonlinearities [see e.g. Yu. S. Kivshar and N. Flytzanis, Phys. Rev.A46, 7972 (1992)] but in other cases they differ very much, being described by a novel type of the couple-mode equations. Particular examples of the physical systems considered include localized gap modes in a diatomic chain on a nonlinear substrate (on-site) potential, a diatomic lattice with anharmonic interaction between nearest-neighbor particles, and spatial gap solitons due to cascaded second-order processes in an optical medium with χ(2) nonlinear susceptibility in the presence of grating. Alternative approaches for deriving the couple-mode equations of the theory of gap solitons as well as parametric stabilization of gap solitons in a lossy medium are also discussed.
DETERMINING EQUATIONS FOR HIGHER-ORDER DECOMPOSITIONS OF EXPONENTIAL OPERATORS
Authors: TSUBOI ZENGO , SUZUKI MASUO
Published: November 2004

The general decomposition theory of exponential operators is briefly reviewed. A general scheme to construct independent determining equations for the relevant decomposition parameters is proposed using Lyndon words. Explicit formulas of the coefficients are derived.
ANTIFERROMAGNETIC ISING MODEL DECORATED WITH D-VECTOR SPINS: TRANSVERSAL AND LONGITUDINAL LOCAL FIELDS EFFECTS
Authors: VASCONCELOS DOS SANTOS R. J. , COUTINHO S.
Published: November 2004

The effect of a local field acting on decorating classical D-vector bond spins of an antiferromagnetic Ising model on the square lattice is studied for both the annealed isotropic and the axial decorated cases. In both models the effect on the phase diagrams of the transversal and the longitudinal components of the local field acting on the decorating spins are fully analyzed and discussed.
INFRARED PROPERTIES OF AN ANISOTROPICALLY DRIVEN MHD TURBULENCE
Authors: Ts. ADZHEMYAN L. , HNATICH M. , HORVÁTH D. , STEHLIK M.
Published: November 2004

The model of anisotropic magnetohydrodynamic turbulence is investigated by the renormalization group approach. It is demonstrated that the inclusion of small anisotropy into the model leads to increasing of the Lorentz force influence. This effect is especially important in the kinetic regime in which the Kolmogorov spectrum of pulsation energy takes place. It is quite different from the isotropic case where the Lorentz force has no influence on large scale properties of magnetohydrodynamic turbulence, even if the external injection of energy is very intensive. Therefore, the magnetic field behaves like a passive admixture. In the anisotropic MHD, nonlinear interactions generate modified "anisotropic Lorentz forces". These forces are relevant for certain values of dimensionless parameter a, which describes the spectrum of the magnetic noise, and the magnetic field ceases to be a passive admixture. In particular, this statement is true for the most realistic value of a = 1 when the random magnetic force amplitude has the same dimensionality as the energy injection rate.
SELF-CONSISTENT THEORY OF ELASTIC PROPERTIES OF STRONGLY ANHARMONIC CRYSTALS II: PROPERTIES OF HEAVY RARE GAS SOLIDS
Authors: ZUBOV V. I. , TRETIAKOV N. P. , SANCHEZ J. F.
Published: November 2004

The method developed in the preceding papers has been used to calculate the full set of equilibrium thermodynamic properties of solid Ar, Kr and Xe at normal pressure. We have used various pairwise interatomic potentials taking into account the three-body Axilrod–Teller forces. For Ar and Kr the multiparameter potentials proposed by Barker et al. provide the best fit to available experimental data, and for Xe the old Lennard–Jones potential does this. Deviations from the Cauchy relations are discussed. Temperature dependencies of the stability coefficients and anisotropy have received much attention. In the unstable point that is about 1.35–1.45 times larger than the experimental melting temperature of each crystal, the isothermal bulk modulus goes to zero (and the thermal expansion coefficient and the isobaric specific heat tend to infinity). Other stability coefficients remain finite and positive.
A LINEAR-TIME ALGORITHM FOR TESTING THE INSCRIBABILITY OF TRIVALENT POLYHEDRA
Authors: DILLENCOURT MICHAEL B. , SMITH WARREN D.
Published: November 2004

We present an algorithm for testing the inscribability of a trivalent polyhedron or, equivalently, testing the circumscribability of a simplicial polyhedron. Our algorithm, which runs in linear time and uses only low-precision integer arithmetic, is based on a purely combinatorial characterization of inscribable trivalent polyhedra.
TRANSLATION QUERIES FOR SETS OF POLYGONS
Authors: BERG MARK DE , EVERETT HAZEL , WAGENER HUBERT
Published: November 2004

Let S be a set of m polygons in the plane with a total of n vertices. A translation order for S in direction [Formula: see text] is an order on the polygons such that no collisions occur if the polygons are moved one by one to infinity in direction [Formula: see text] according to this order. We show that S can be preprocessed in O(n log n) time into a data structure of size O(m) such that a translation order for a query direction can be computed in O(m) time, if it exists. It is also possible to test in O(log n) time whether a translation order exists, with a structure that uses O(n) storage. These results are achieved using new results on relative convex hulls and on embeddings with few vertices. Translation orders correspond to valid displaying orders for hidden surface removal with the painter’s algorithm. Our technique can be used to generate displaying orders for polyhedral terrains, for parallel as well as perspective views.
FINITE REPRESENTATIONS OF REAL PARAMETRIC CURVES AND SURFACES
Authors: BAJAJ CHANDRAJIT L. , ROYAPPA ANDREW V.
Published: November 2004

Global parameterizations of parametric algebraic curves or surfaces are defined over infinite parameter domains. Considering parameterizations in terms of rational functions that have real coefficients and vary over real parameter values, we show how to replace one global parameterization with a finite number of alternate bounded parameterizations, each defined over a fixed, bounded part of the real parameter domain space. The new bounded parameterizations together generate all real points of the old one and in particular the points corresponding to infinite parameter values in the old domain. We term such an alternate finite set of bounded parameterizations a finite representation of a real parametric curve or surface. Two solutions are presented for real parametric varieties of arbitrary dimension n. In the first method, a real parametric variety of dimension n is finitely represented in a piecewise fashion by 2n bounded parameterizations with individual pieces meeting with C∞ continuity; each bounded parameterization is a map from a unit simplex of the real parameter domain space. In the second method, only a single bounded parameterization is used; it is a map from the unit hypersphere centered at the origin of the real parameter domain space. Both methods start with an arbitrary real parameterization of a real parametric variety and apply projective domain transformations of different types to yield the new bounded parameterizations. Both these methods are implementable in a straightforward fashion. Applications of these results include displaying entire real parametric curves and surfaces (except those real points generated by complex parameter values), computing normal parameterizations of curves and surfaces (settling an open problem for quadric surfaces).
ON COMPUTING VORONOI DIAGRAMS FOR SORTED POINT SETS
Authors: DJIDJEV HRISTO N. , LINGAS ANDRZEJ
Published: November 2004

We show that the Voronoi diagram of a finite sequence of points in the plane which gives sorted order of the points with respect to two perpendicular directions can be computed in linear time. In contrast, we observe that the problem of computing the Voronoi diagram of a finite sequence of points in the plane which gives the sorted order of the points with respect to a single direction requires Ω(n log n) operations in the algebraic decision tree model. As a corollary from the first result, we show that the bounded Voronoi diagrams of simple n-vertex polygons which can be efficiently cut into the so called monotone histograms can be computed in o(n log n) time.
ON A CLASS OF SEMIGROUP PSEUDOVARIETIES WITHOUT FINITE PSEUDOIDENTITY BASIS
Authors: VOLKOV M.V.
Published: November 2004

We show that every semigroup pseudovariety [Formula: see text] containing a group not in the subpseudovariety generated by all idempotent generated members of [Formula: see text] has no finite basis of pseudoidentities provided the five-element idempotent generated 0-simple semigroup lies in [Formula: see text]. This gives, in particular, a counterexample to a conjecture by J. Almeida.
FREE SPECTRA GAPS AND TAME CONGRUENCE TYPES
Authors: BERMAN JOEL
Published: November 2004

Chapter 12 of "The Structure of Finite Algebras" by D. Hobby and R. McKenzie contains theorems revealing how the set of types appearing in a locally finite variety [Formula: see text] influences the size of the free algebra in [Formula: see text] freely generated by n elements. We provide more results in this vein. If A is a subdirectly irreducible algebra of size k, then a lower bound on the number of n-ary polynomials of A is obtained for each case that the monolith of A has type 3, 4, or 5. Examples for every k show that in each case the lower bound is the best possible. As an application of these results we show that for every finite k if all k-element simple algebras are partitioned into five classes according to their type, then algebras in each class have a sharply determined band of possible values for their free spectra. These five bands are disjoint except for some overlap on simple algebras of types 2 and 5.
ON SEPARABILITY PROPERTIES OF GROUPS
Authors: GITIK RITA , RIPS ELIYAHU
Published: November 2004

It is shown that if a double F*H F of a free group F along a finitely generated malnormal subgroup H has f.g.i.p., then it is LERF. We also introduce a notion of double coset separability and show that a free group is double coset separable.
EXISTENCE AND UNIQUENESS OF THE SOLUTION TO THE EDGE PROBLEM IN A TWO-DIMENSIONAL REACTIVE BOUNDARY LAYER
Authors: BOILLAT ERIC
Published: November 2004

We prove an existence and uniqueness theorem for the ordinary differential problem which characterizes the profiles of the different physical quantities at the edge of two-dimensional reactive boundary layer. The main difficulties to be circumvented are the nonlinearities due to the different thermodynamical functions involved in the reactive boundary layer equations and the degeneracy caused by the natural initial conditions, where the tangential velocity has to vanish.

We conclude by making some mathematical considerations about the relations that exist between the reactive boundary layer equations and the corresponding equations which describe the boundary layer in chemical equilibrium.
MATHEMATICAL ANALYSIS OF A REACTIVE-DIFFUSIVE MODEL OF THE DISPERSAL OF A CHEMICAL TRACER WITH NONLINEAR CONVECTION
Authors: COHN STEVE , LOGAN J. DAVID
Published: November 2004

We formulate and analyze a nonlinear reaction-convection-diffusion system that models the dispersal of solutes, or chemical tracers, through a one-dimensional porous medium. A similar set of model equations also arises in a weakly nonlinear limit of the combustion equations. In particular, we address two fundamental questions with respect to the model system: first, the existence of wavefront type traveling wave solutions, and second, the local existence and uniqueness of solutions to the pure initial value problem. The solution to the wavefront problem is obtained by showing the existence of a heteroclinic orbit in a two-dimensional phase space. The existence argument for the initial value problem is based on the contraction mapping theorem and Sobolev embedding. In the final section we prove non-negativity of the solution.
QUASIANALYTIC FUNCTION CLASSES AND THE COMPLEX-TIME DIFFUSION GROUP - I
Authors: GULISASHVILI A. , SANDRI G.H.
Published: November 2004

In this paper necessary and sufficient conditions are given for quasianalytic function classes D({Mk}) and the corresponding classes of distributions D′({Mk}) to be invariant with respect to the diffusion group Ut where −∞<t<∞. In addition, the properties of hyperdistributions [Formula: see text] are studied, where δ0 denotes the δ-function at 0. It is shown that hyperdistributions Γ from the class D′({Mk}) are completely characterized by the rate of decay of the moments μk(Γ) = Γ(xk), k≥0.
MINIMAL STABILIZATIONS OF THE Pk+1-Pk APPROXIMATION OF THE STATIONARY STOKES EQUATIONS
Authors: BOFFI D.
Published: November 2004

The triangular finite element approximation of the Stokes problem is analyzed by means of piecewise polynomials of degree k+1 for the velocity and discontinuous of degree k for the pressure. The known results are recalled, with particular interest in the restrictions required for the triangulation and in the stabilization procedures. A new less expensive stabilization method is proposed.
EXISTENCE OF A SOLUTION IN AN AGE-DEPENDENT TRANSPORT-DIFFUSION PDE: A MODEL OF SETTLER
Authors: CHANCELIER J. PH. , LARA M. COHEN DE , PACARD F.
Published: November 2004

The modeling of sludge particles settling in the final stage of a waste water treatment plant may include both transport and diffusion. When the residence time of sludge particles in the settler is considered, this leads to a nonlinear age-dependent transport-diffusion partial differential equation (PDE) with nonlocal condition. We investigate the question of existence of a solution.
A NONCONSERVATIVE HYPERBOLIC SYSTEM MODELING SPRAY DYNAMICS. PART I: SOLUTION OF THE RIEMANN PROBLEM
Authors: RAVIART PIERRE-ARNAUD , SAINSAULIEU LIONEL
Published: November 2004

The flow of a spray of liquid droplets in a gas is modeled by a convection-diffusion system whose convection part is hyperbolic and written in nonconservation form. As a first step towards the numerical solution of the second order system, we solve Riemann problem for the convection part: the shock waves solutions of the latter system are defined as the limit of traveling waves solution of the whole system when the diffusion is neglected. The structure of the first order system allows to define discontinuous solutions associated with the linearly degenerate fields. The definition of rarefaction waves solution of the latter system is standard and we solve Riemann problems at least for initial data with small variation.
HYDRODYNAMICS OF A MODEL GAS IN A SLAB
Authors: SOCIO L. de , IANIRO N.
Published: November 2004

The stationary Boltzmann equation is considered for the Lebowitz model gas of sticks in a slab in the presence of a nonconstant external field. It is proved that the solution is close in L∞ norm to a local “Maxwellian” distribution, the “parameters” of which satisfy the equations of hydrodynamics.
ELEMENT REMOVAL METHOD FOR SINGULAR MINIMIZERS IN PROBLEMS OF HYPERELASTICITY
Authors: LI ZHIPING
Published: November 2004

A numerical method called element removal method is applied to calculate singular minimizers in problems of hyperelasticity. The method overcomes the difficulty in finite element approximations caused by restrictions, such as det (I+∇u)>0, on admissible functions and can avoid Lavrentiev phenomenon if it does occur in the problem. The convergence of the method is proved.
NULL LAGRANGIANS IN LINEAR ELASTICITY
Authors: LANCIA M.R. , CAFFARELLI G. VERGARA , PODIO-GUIDUGLI P.
Published: November 2004

The concept of null Lagrangian is exploited in the context of linear elasticity. In particular, it is shown that the stored energy functional can always be split into a null Lagrangian and a remainder; the null Lagrangian vanishes if and only if the elasticity tensor obeys the Cauchy relations, and is therefore determined by only 15 independent moduli (the so-called “rari-constant” theory of elasticity).
SECOND ORDER BOUNDARY CONDITIONS FOR THE DRIFT-DIFFUSION EQUATIONS OF SEMICONDUCTORS
Authors: YAMNAHAKKI A.
Published: November 2004

By an asymptotic analysis of the Boltzmann equation of semiconductors, we prove that Robin boundary conditions for drift-diffusion equations provide a more accurate fluid model than Dirichlet conditions. The Robin conditions involve the concept of the extrapolation length which we compute numerically. We compare the two-fluid models for a test problem. The numerical results show that the current density is correctly computed with Robin conditions. This is not the case with Dirichlet conditions.
ELASTIC THIN SHELLS: ASYMPTOTIC THEORY IN THE ANISOTROPIC AND HETEROGENEOUS CASES
Authors: CAILLERIE D. , SANCHEZ-PALENCIA E.
Published: November 2004

Asymptotic (two-scale) methods are used to derive thin shell theory from three-dimensional elasticity. The asymptotic process is done directly for the variational formulations, and existence and uniqueness theorems are given for the shell problem. The asymptotic behavior is the same as that recently derived by the authors using classical hypotheses of shell theory. The role of the subspace G of pure bendings (inextensional motions) appears in a natural way. The asymptotic is basically described by a leading order term contained in G and a lower order term contained in the orthogonal to G. As in anisotropic heterogeneous plates, which exhibit a coupling between flexion and traction, in heterogeneous shells there is coupling between the terms in G and in its orthogonal.
HOMOGENIZATION OF PERIODIC NONLINEAR MEDIA WITH STIFF AND SOFT INCLUSIONS
Authors: BRAIDES ANDREA , GARRONI ADRIANA
Published: November 2004

We study the asymptotic behavior as ε→0 of highly oscillating periodic nonlinear functionals of the form [Formula: see text] defined on a Sobolev space W1,p(Ω; ℝm). We characterize their variational limit under the hypotheses that there exists a c such that the region where f(x, ξ)≤c(1+|ξ|p) does not hold for all matrices ξ is composed of well-separated sets, and the condition f(x, ξ)≥|ξ|p for all matrices ξ is verified on a connected open set with Lipschitz boundary.
NUMERICAL SIMULATIONS OF CLUSTER FORMATION USING A DISCRETE VELOCITY KINETIC THEORY OF GASES
Authors: SLEMROD MARSHALL , QI ANMIN
Published: November 2004

Cluster formation is simulated numerically with discrete velocity Boltzmann model in two space dimensions. The model exhibits cluster coagulation, fragmentation and transport. It evolves two different scales obtained from an elastic and inelastic collision Knudsen numbers ε and µ respectively. For flow impinging on a wall with specularly reflective boundary condition these scales appear both analytically and numerically.
A STREAMLINE-UPWINDING/PETROV-GALERKIN METHOD FOR THE HYDRODYNAMIC SEMICONDUCTOR DEVICE MODEL
Authors: JIANG XUNLEI
Published: November 2004

It is well known that the hydrodynamic model of the semiconductor device equations may have solutions with discontinuities or shocks. To solve such problems numerically, a non-symmetric streamline-upwinding/Petrov-Galerkin finite element approach is presented for the simulation of the two-dimensional, time-dependent hydrodynamic model. For the silicon diode, numerical experiments are carried out for both subsonic and transonic electron flows. Shocks of the transonic flow are captured.
SOME RECTANGULAR FINITE ELEMENT METHODS FOR REISSNER-MINDLIN PLATES
Authors: LOVADINA C.
Published: November 2004

A new class of rectangular finite elements for Reissner-Mindlin plate problem is presented. The family is based on a modified mixed formulation recently introduced by Arnold and Brezzi. A result of stability and uniform convergence in the thickness is provided.
EXISTENCE AND REGULARITY OF SOLUTIONS AND THE STABILITY OF THE REST STATE FOR FLUIDS WITH SHEAR DEPENDENT VISCOSITY
Authors: MÁLEK J. , RAJAGOPAL K.R. , RŮŽIČKA M.
Published: November 2004

In this paper we clarify and discuss some subtle features concerning the non-Newtonian fluid models which were considered by Málek, Nečas and Růžička.19 We establish new results regarding the stability of the rest state of mechanically isolated flows of such non-Newtonian fluids for arbitrary initial disturbances. We also discuss some results concerning the existence and regularity of solutions for small data. These results are based on a new method, giving convergence almost everywhere of approximations of gradients from boundedness of fraction of the L2-norm of the second and first derivatives, developed by Nečas to study existence of solutions (global in time) to a class of partial differential equations.
A MARKOVIAN MODEL FOR COOPERATIVE INTERACTIONS IN PROTEINS
Authors: ABUNDO M. , ACCARDI L. , ROSATO N.
Published: November 2004

A stochastic model for cooperative interactions in proteins is proposed. The description is based on the theory of Markov’s chains and of birth-and-death processes. Even if the model depends only on two parameters: the mean probability p and the coupling capacity∆p, it presents a surprising wealth of qualitative behaviors when the two parameters are varied. In particular we provide numerical evidence of change of concavity of the stationary distribution at a critical value of the coupling capacity ∆p. The main mathematical feature is that the probability of creating a new chemical bond depends on the total number of bonds already present in the system. In this sense, we speak of a cooperative behavior.
THE DESCRIPTION OF MANY-PARTICLE SYSTEMS BY THE EQUATIONS FOR A VISCOUS, COMPRESSIBLE, BAROTROPIC FLUID
Authors: OELSCHLÄGER KARL
Published: November 2004

We consider many-particle systems with a Hamiltonian dynamics supplemented by a friction term. Both the interaction potential and the additional friction force are supposed to be long range in comparison with the typical distance between neighboring particles. It is shown that in a zero-temperature situation the empirical processes of the positions and the velocities converge to solutions of the continuity equation and the compressible, barotropic Navier-Stokes equation, respectively, in the limit as the particle number tends to infinity.
ASYMPTOTICAL AND NUMERICAL ANALYSIS OF DEGENERACY EFFECTS ON THE DRIFT-DIFFUSION EQUATIONS FOR SEMICONDUCTORS
Authors: FUCHS F. , POUPAUD F.
Published: November 2004

A current approximation for modeling electron transport in semiconductor devices is to assume small electron density. Through this method nondegenerate models are obtained. Here we present an asymptotical analysis of that approximation on the drift-diffusion equation. The numerical approximations of the degenerate and nondegenerate equations are then compared. A modified Scharfetter-Gummel scheme which integrates the degenerate drift-diffusion equation is proposed for comparison.
A FOUR-NODE QUADRILATERAL MIXED-INTERPOLATED ELEMENT FOR SOLIDS AND FLUIDS
Authors: PANTUSO DANIEL , BATHE KLAUS-JÜRGEN
Published: November 2004

A four-node quadrilateral element is presented which shows promise for general compressible and incompressible two-dimensional analysis of solids and fluids. The element is based on a mixed interpolation of displacements (velocities), pressure and strains (velocity strains). We show that the element satisfies a numerical inf-sup test, and give results of some analysis problems that demonstrate the capabilities of the element.
A FRAMEWORK FOR INTEGRATING ARTIFICIAL NEURAL NETWORKS AND LOGIC PROGRAMMING
Authors: LEE J.H.M. , TAM V.W.L.
Published: November 2004

Many real-life problems belong to the class of constraint satisfaction problems (CSP’s), which are NP-complete, and some NP-hard, in general. When the problem size grows, it becomes difficult to program solutions and to execute the solution in a timely manner. In this paper, we present a general framework for integrating artificial neural networks and logic programming so as to provide an efficient and yet expressive programming environment for solving CSP’s. To realize this framework, we propose PROCLANN, a novel constraint logic programming language. The PROCLANN language retains the simple and elegant declarative semantics of constraint logic programming. Operationally, PROCLANN uses the standard goal reduction strategy in the frontend to generate constraints, and an efficient backend constraint-solver based on artificial neural networks. Its operational semantics is probabilistic in nature. We show that PROCLANN is sound and weakly complete. A novelty of PROCLANN is that while it is a committed-choice language, PROCLANN supports non-determinism, allowing the generation of multiple answers to a query. An initial prototype implementation of PROCLANN is constructed and demonstrates empirically that PROCLANN out-performs the state of art in constraint logic programming implementation on certain hard instances of CSP’s.
HYDRA-MM: LEARNING MULTIPLE DESCRIPTIONS TO IMPROVE CLASSIFICATION ACCURACY
Authors: ALI KAMAL , PAZZANI MICHAEL
Published: November 2004

For learning tasks with few examples, greater classification accuracy can be achieved by learning several concept descriptions for each class in the data and producing a classification that combines evidence from multiple descriptions. Stochastic (randomized) search can be used to generate many concept descriptions for each class. Here we use a tractable approximation to the optimal Bayesian method for combining evidence from multiple descriptions. Learning multiple descriptions is very useful when additional data is difficult to obtain. The primary result of this paper is that multiple concept descriptions are particularly helpful for improving accuracy in hypothesis spaces in which there are many equally good rules to learn. Another result is experimental evidence that learning multiple rule sets yields more accurate classifications than learning multiple rules for concepts containing many disjuncts.