bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of mammalian receptors for lactoferrin
Authors: Suzuki Yasushi A , Lönnerdal Bo
Published: July 2002

Lactoferrin (Lf) has been suggested to have several physiological functions. Specific binding of Lf, indicating the presence of Lf receptors (LfRs), has been observed in various types of mammalian cells such as lymphocytes, hepatocytes, and enterocytes. These LfRs are considered to function as a mediator for some of the functions of Lf. We here review current knowledge of mammalian LfRs characterized in different tissues. We also briefly present evidence for the existence of an LfR provided by our cloning of a human intestinal LfR (HLfR). The entire coding region of the HLfR was cloned by polymerase chain reaction (PCR), and a recombinant HLfR (rHLfR) was expressed in a baculovirus system. The rHLfR was purified by immobilized human Lf (HLf) affinity chromatography, indicating that the rHLfR retained the capacity to bind HLf. The gene was expressed at high levels in fetal small intestine and in adult heart but at lower levels in Caco-2 cells. In summary, we demonstrate the presence of a unique receptor-mediated mechanism for Lf, functioning in the small intestine of the newborn infant and possibly in other tissues of human adults.Key words: lactoferrin, lactoferrin receptor, mammalian receptor, human, mouse.
Performance of suction caissons in sand and clay
Authors: Iskander Magued , El-Gharbawy Sherif , Olson Roy
Published: July 2002

The use of suction caissons (suction piles) in marine environments has been increasing in the last decade. A suction caisson is a steel pipe with an open bottom and a closed top that is inserted into the ground by pumping water out of it. Pumping creates a differential pressure across the caisson's top that pushes it into place, thus eliminating the need for pile driving. There are a number of uncertainties in the design of suction caissons. First, the state of stress and soil conditions adjacent to a suction caisson differs from those around typical driven piles or drilled shafts. Second, the axial load capacity of suction caissons depends on the rate of loading, hydraulic conductivity, drainage length, as well as the shearing strength properties of the foundation material. Finally, during pullout, volume change characteristics of the surrounding soils may change the theoretical suction pressures. A review of the existing knowledge relating to the design and construction of suction caissons is presented in this paper along with the results of a laboratory study on model caissons in sand and clay. Test results indicate that the use of suction pressure for installation of caissons is a viable alternative to conventional methods. Suction was also shown to resist some axial tensile loads.Key words: suction, pile, bucket, foundation, anchor, capacity.
DYNAMIC SCHEDULING OF MANUFACTURING SYSTEMS WITH MACHINE LEARNING
Authors: PRIORE PAOLO , DE LA FUENTE DAVID , GOMEZ ALBERTO , PUENTE JAVIER
Published: July 2002

A common way of scheduling jobs dynamically in a manufacturing system is by means of dispatching rules. The drawback of this method is that the performance of these rules depends on the state the system is in at each moment, and no one rule exists that overrules the rest in all the possible states that the system may be in. It would therefore be interesting to use the most appropriate rule at each moment. To achieve this goal, a scheduling approach which uses machine learning is presented in this paper. The methodology proposed in this paper may be divided into five basic steps. Firstly, definition of the appropriate control attributes for identifying the relevant manufacturing patterns. In second place, creation of a set of training examples using different values of the control attributes. Subsequently, acquiring of heuristic rules by means of a machine learning program. Then, using of the previously calculated heuristic rules to select the most appropriate dispatching rules, and finally testing of the performance of the approach. The approach that we propose is applied to a flow shop system and to a classic job shop configuration. The results demonstrate that this approach produces an improvement in the performance of the system when compared to the traditional method of using dispatching rules.
THE DISCRETE BOLTZMANN EQUATION: A REVIEW OF THE MATHEMATICAL ASPECTS OF THE INITIAL AND INITIAL-BOUNDARY VALUE PROBLEMS
Authors: BELLOMO N. , GUSTAFSSON T.
Published: July 2002

This paper provides a review of the various results available in the mathematical literature on the solution to the initial and initial-boundary value problem for the discrete Boltzmann equation, a nonlinear mathematical model of the kinetic theory of gases. References include papers published until 1990. The aim of this survey paper is to provide a detailed picture of the state of the art in the field and some necessary information for future research in the field.
TOPOLOGICAL QUANTUM FIELD THEORIES FROM GENERALIZED 6J-SYMBOLS
Authors: DURHUUS BERGFINNUR , JAKOBSEN HANS PLESNER , NEST RYSZARD
Published: July 2002

Given an associative algebra with a distinguished finite set of representations that is closed under a (deformed) tensor product, and satisfies some technical assumptions, we define generalized 6j-symbols, and show that they can be associated, in a natural way, with certain labeled tetrahedra.

Given a 3-dimensional compact oriented manifold M with boundary ∂M = Σ we choose an arbitrary triangulation [Formula: see text] of M and exploit the above correspondence between 6j-symbols and labeled tetrahedra to construct a vectorspace UΣ and a vector Z(M) ∈ UΣ, independent of [Formula: see text], and fulfilling the axioms of a topological quantum field theory as formulated by Atiyah [11].

Examples covered by our approach are quantum groups corresponding to the classical simple Lie algebras as well as, expectedly, chiral algebras of 2-dimensional rational conformal field theories.
Geometry of Quantum Principal Bundles II
Authors: Đurđević Mićo
Published: July 2002

A general non-commutative-geometric theory of principal bundles is developed. Quantum groups play the role of structure groups and general quantum spaces play the role of base manifolds. A general conceptual framework for the study of differential structures on quantum principal bundles is presented. Algebras of horizontal, verticalized and "horizontally vertically" decomposed differential forms on the bundle are introduced and investigated. Constructive approaches to differential calculi on quantum principal bundles are discussed. The formalism of connections is developed further. The corresponding operators of horizontal projection, covariant derivative and curvature are constructed and analyzed. In particular the analogs of the basic classical algebraic identities are derived. A quantum generalization of classical Weil's theory of characteristic classes is sketched. Quantum analogs of infinitesimal gauge transformations are studied. Interesting examples are presented.
SIMULATION OF SZNAJD SOCIOPHYSICS MODEL WITH CONVINCING SINGLE OPINIONS
Authors: OCHROMBEL R.
Published: July 2002

The Sznajd model is modified such that a single person convinces the neighbors of his/her opinion.
ON MODELS OF GAUGE FIELD LOCALIZATION ON A BRANE
Authors: DUBOVSKY S. L. , RUBAKOV V. A.
Published: July 2002

We argue that any viable mechanism of gauge field localization should automatically imply charge universality on the brane. We study whether this condition is satisfied in the two known proposals aimed to localize vector field in flat bulk space. We construct a simple calculable model with confinement in the bulk and deconfinement on the brane, as in the Shifman–Dvali set-up. We find that in our model the four-dimensional Coulomb law is indeed reproduced on the brane due to the massless localized photon mode. The charge universality is enforced by the presence of "confining strings." On the other hand, charge universality condition is not satisfied in another, brane-induced localization mechanism when the number of extra dimensions d is larger than two. We demonstrate that in the non-Abelian case the gauge fields inside the brane are never four-dimensional and their self-interaction is strong at all distances of interest. Hence this mechanism does not work for d > 2. At d = 2 the charge universality is still a problem, but it holds automatically at d = 1. At d = 1, however, the bulk gauge fields are strongly coupled in the non-Abelian case.
High Performance Electro-Rheological Dampers
Authors: Brooks Douglas A
Published: July 2002

With the proprietary ER fluids available today it is not a viable proposition to develop a high force damper within the available space envelope. ER fluids are simply not strong enough and attempts to overcome this limitation by increasing the size of the damper result in excessive power demands.

A bi-directional controllable damper has been developed that overcomes the limitations of available ER fluids and allows the development of exceptionally high forces with low control power. The forces generated by the damper are not directly linked to the performance of the ER fluid and both very low un-energised and very high energised forces can be developed. The nature of the design permits a wide range of controllable forces and force profiles.

The main limitations of existing ER fluids, that of low excess shear stress, has been overcome with a novel and unique damper design. The performance of the damper is not limited by the performance of the ER fluid and controllable dampers can be developed that are able to generate almost unlimited forces. Two versions, for specific niche markets, have been fully developed to the preproduction stage.
FORM FACTORS IN OFF-CRITICAL SUPERCONFORMAL MODELS
Authors: MUSSARDO G.
Published: July 2002

We discuss the determination of the lowest Form Factors relative to the trace operators of N = 1 Super Sinh-Gordon Model. Analytic continuations of these Form Factors as functions of the coupling constant allows the study of interesting models in a uniform way, among these the latest model of the Roaming Series and a class of minimal supersymmetric models.
A SPIN CHAIN PRIMER
Authors: NEPOMECHIE RAFAEL I.
Published: July 2002

This is a very elementary introduction to the Heisenberg (XXX) quantum spin chain, the Yang–Baxter equation, and the algebraic Bethe Ansatz.
MASTER–SLAVE SYNCHRONIZATION OF LUR'E SYSTEMS WITH TIME-DELAY
Authors: YALÇIN M. E. , SUYKENS J. A. K. , VANDEWALLE J.
Published: July 2002

In this paper time-delay effects on the master–slave synchronization scheme are investigated. Sufficient conditions for master–slave synchronization of Lur'e systems are presented for a known time-delay in the master and slave systems. A delay-dependent synchronization criterion is given based upon a new Lyapunov–Krasovskii function. The derived criterion is a sufficient condition for global asymptotic stability of the error system, expressed by means of a matrix inequality. The feedback matrix follows from solving a nonlinear optimization problem. The method is illustrated for the synchronization of Chua's circuits, 5-scroll attractors and hyperchaotic attractors.
ON ASYMPTOTIC ERROR EXPANSIONS FOR SINGULAR BOUNDARY VALUE PROBLEMS
Authors: FROMMLET FLORIAN , WEINMÜLLER EWA B.
Published: July 2002

The existence of an asymptotic expansion for the global error of a standard three-point finite difference scheme applied to solve BVPs for ordinary differential equations of second order with a singularity of the first kind is considered. It turns out that even for very smooth problem data such asymptotic expansion does not exist, in general. More precisely, its length is restricted by unbounded inhomogeneities occurring in variational equations due to the singularity.
NUMERICAL BIFURCATION OF EQUILIBRIA OF NEMATIC CRYSTALS BETWEEN NON-CO-AXIAL CYLINDERS
Authors: ALOUGES FRANÇOIS , COLEMAN BERNARD D.
Published: July 2002

Calculations are presented giving the stable equilibrium states of nematic liquid crystals confined between non-co-axial circular cylinders subject to the condition that the director be normal to the bounding surfaces. The one-constant theory of nematics is employed and emphasis is laid on cases for which the minimizing director field does not lie in the plane perpendicular to the cylinders. Calculations are made of the force that the nematic exerts on the cylinders, tending to make them co-axial. The numerical problem faced is that of finding, for the Dirichlet energy, minimizing maps to S2, from a region in ℝ2 bounded by non-concentric circles. The method employed is a finite-element implementation of a projected gradient method for which the energy decreases at each iteration.
GRADIENT RECOVERY FOR SINGULARLY PERTURBED BOUNDARY VALUE PROBLEMS II: TWO-DIMENSIONAL CONVECTION–DIFFUSION
Authors: ROOS HANS-GÖRG , LINß TORSTEN
Published: July 2002

We consider a Galerkin finite element method that uses bilinear elements on a class of Shishkin-type meshes for a model singularly perturbed convection–diffusion problem. The recovered gradient is itself piecewise bilinear, with values at the nodes obtained by first interpolating the gradient of the finite element approximation at the centroids of the elements sharing the node. We prove a superconvergence estimate for the recovered gradient uniformly with respect to the singular perturbation parameter. Numerical experiments support our results.
METASTABLE STATES IN A MODEL OF NUCLEAR PAIRING
Authors: DUCOMET B.
Published: July 2002

We consider a simplified linearized quantum mechanical description of pairing in atomic nuclei. The model is given by the Hamiltonian: Hε= H(0)+εH(1), where H(j), for j=0,1, are two 2×2 symmetric operator valued matrices, and ε>0. Physically, H(0) and H(1) represent respectively the density matrix and the pairing contribution to the Hamiltonian. We study this model for small ε. If E0 is an embedded eigenvalue of H0, then the corresponding eigenstate Φ becomes unstable when ε≠0, and we give an asymptotic estimate for the time evolution of Φ under Hε, in terms of the coupling strength ε. We illustrate this result on the case of a solvable model with point interaction, and show that the above asymptotic result is, at least for some matrix elements, almost optimal.
BALANCE LAWS IN CHARGED CONTINUOUS SYSTEMS WITH AN INTERFACE
Authors: MARASCO A. , ROMANO A.
Published: July 2002

The general integral equations used to formulate all the balance laws of thermodynamics of charged continuous systems are analyzed. In particular, simpler (with respect to those known in the literature) procedures are proposed for the localization process leading from the integral balance laws to differential equations and jump conditions.
ON THE STABILIZATION OF A VISCOUS BAROTROPIC SELF-GRAVITATING MEDIUM WITH A NONMONOTONE EQUATION OF STATE
Authors: DUCOMET B. , ZLOTNIK A. A.
Published: July 2002

We consider the compressible barotropic Navier–Stokes system in one dimension, with a nonmonotone equation of state and self-gravitation. We solve an associated "fixed-free" boundary problem and prove asymptotic properties of the unique globally defined solution for large time. We also comment on a related model of quantum fluid describing the dynamics of nuclear matter with zero temperature and Coulomb effects.
THE INFLUENCE OF SLIP AND JUMP BOUNDARY CONDITIONS ON THE CYLINDRICAL COUETTE FLOW
Authors: CUMIN LILIANA M. GRAMANI , KREMER GILBERTO M. , SHARIPOV FELIX
Published: July 2002

The solution of the field equations of the cylindrical Couette flow problem for a rarefied gas is found when the state of equilibrium between the cylinders is perturbed by the following small thermodynamic forces: (i) a pressure difference; (ii) an angular velocity difference; and (iii) a temperature difference. The flow is analyzed within the framework of continuum mechanics by using the field equations that follow from the balance equations of mass, momentum and energy of a viscous and heat conducting gas. These equations are solved analytically by considering slip and jump boundary conditions. The fields of density, velocity, temperature, heat flux vector and viscous stress tensor are calculated as functions of the Knudsen number and of the angular velocity of the rotating cylinders for each thermodynamic force. The asymptotic behaviors of these fields are compared with those obtained from a kinetic model of the Boltzmann equation. The influence of the slip and jump boundary conditions on the solutions is also discussed.
SIMILARITY SOLUTIONS IN A CLASS OF THAWING PROCESSES
Authors: FASANO A. , PRIMICERIO M. , TARZIA D.
Published: July 2002

A study on similarity solutions for a mathematical model for thawing in a saturated porous medium is considered when change of phase induces a density jump and the influence of pressure on the melting temperature is considered. The mathematical analysis is made for different cases, depending on the sign of the three physical parameters.
A FINITE ELEMENT APPROXIMATION OF AN IMAGE SEGMENTATION PROBLEM
Authors: CORTESANI G.
Published: July 2002

We study a numerical discretization scheme for the Mumford–Shah functional, which is introduced to give a variational formulation of image segmentation problems, based on the nonlocal approximation proposed by Braides–Dal Maso.
CONTROL OF QUANTUM SYSTEMS
Authors: PÉREZ R. B. , PROTOPOPESCU V. , MUÑOZ-COBO J. L.
Published: July 2002

We propose a new control method for systems whose evolution is described by Schrödinger's equation (quantum dynamics). The goal of the control is to induce modifications of observable quantities — with possible effects at mesoscopic or macroscopic levels — by modifying the potential at the microscopic level. We illustrate the feasibility of the approach on a harmonic oscillator system.
HOMOGENIZATION OF ELECTRICAL NETWORKS INCLUDING VOLTAGE-TO-VOLTAGE AMPLIFIERS
Authors: LENCZNER MICHEL , SENOUCI-BEREKSI GHOUTI
Published: July 2002

We derive the homogenized model of periodic electrical networks which includes resistive devices, voltage-to-voltage amplifiers, sources of tension and sources of current. On the one hand, in considering the homogenized problem, general conditions are stated insuring the existence and uniqueness of the solution. They are formulated in function of the network topology. On the other hand, the two-scale transformation introduced by Arbogast, Douglas and Hornung is adapted to the context of electrical networks. New two-scale. convergence results, inspired by the principle of Allaire's two-scale convergence, are shown in this context. In particular, the two-scale convergence for the tangential derivative on a network is established. Following these results, two models of homogenized networks are derived. The first one belongs to a general framework whereas the second one does not.
LOCAL APPROXIMATION FOR THE HARTREE–FOCK EXCHANGE POTENTIAL: A DEFORMATION APPROACH
Authors: BOKANOWSKI OLIVIER , MAUSER NORBERT J.
Published: July 2002

We present a method for deriving local approximations of the exchange-term in the Hartree–Fock equation for a system of fermions interacting with a Coulomb-force. Within our model, we give a justification of the Slater-approximation where the exchange-term is replaced by the third root of the local density. Our approach is based on deformations, i.e. local scaling transformations of a constant density, combined with the "high density limit" of infinite number of particles.
THE DYNAMICS OF THE NASH CORRESPONDENCE AND n-PLAYER STOCHASTIC GAMES
Authors: SOLAN EILON
Published: July 2002

A quitting game is a sequential game where each player has two actions: to continue or to quit, and the game continues as long as no player quits.

For every continuation payoff x we assign a one-shot game, where the payoff if everyone continues is x. We study the dynamics of the correspondence that assigns to every continuation payoff the set of equilibrium payoffs in the corresponding one shot game.

The study presented here has an implication on the approach one should take in trying to prove, or disprove, the existence of an equilibrium payoff in n-player stochastic games. It also shows that the minimal length of the period of a periodic δ-equilibrium in three-player quitting games needs not be uniformly bounded for δ>0.
ASYMPTOTIC SELF-SIMILAR BEHAVIOR OF SOLUTIONS FOR A SEMILINEAR PARABOLIC SYSTEM
Authors: SNOUSSI SEIFEDDINE , TAYACHI SLIM
Published: July 2002

This paper studies the global existence and the asymptotic self-similar behavior of solutions of the semilinear parabolic system ∂tu=Δu+a1|u|p1-1u+b1|v|q1-1v, ∂tv=Δv+a2|v|p2-1v+b2|u|q2-1u, on (0,∞)×ℝn, where a1, bi∈ℝ and pi, qi>1. Let p= min {p1,p2, q1(1+q2)/(1+q1), q2(1+q1)/(1+q2)}. Under the condition p>1+2/n we prove the existence of globally decaying mild solutions with small initial data. Some of them are asymptotic, for large time, to self-similar solutions of appropriate asymptotic systems having each one a self-similar structure. All possible asymptotic self-similar behaviors are discussed in terms of exponents pi, qi, the space dimension n and the asymptotic spatial profile of the related initial data.
A MODEL OF LARGE-SCALE PROTEOME EVOLUTION
Authors: SOLÉ RICARD V. , PASTOR-SATORRAS ROMUALDO , SMITH ERIC , KEPLER THOMAS B.
Published: July 2002

The next step in the understanding of the genome organization, after the determination of complete sequences, involves proteomics. The proteome includes the whole set of protein-protein interactions, and two recent independent studies have shown that its topology displays a number of surprising features shared by other complex networks, both natural and artificial. In order to understand the origins of this topology and its evolutionary implications, we present a simple model of proteome evolution that is able to reproduce many of the observed statistical regularities reported from the analysis of the yeast proteome. Our results suggest that the observed patterns can be explained by a process of gene duplication and diversification that would evolve proteome networks under a selection pressure, favoring robustness against failure of its individual components.
FABRICATION OF Si NANOCOLUMNS AND Si SQUARE SPIRALS ON SELF-ASSEMBLED MONOLAYER COLLOID SUBSTRATES
Authors: ZHAO Y.-P. , YE D.-X. , WANG PEI-I , WANG G.-C. , LU T.-M.
Published: July 2002

Amorphous silicon nanocolumns, square nanospirals, and multilayer spiral/column rods are fabricated on bare Si substrates and monolayer colloid substrates by glancing angle deposition. The grown films are studied by scanning electron microscopy and transmission electron microscopy. The size of the deposited Si columns and spirals increases with the size of colloid particles for fixed incident angle of deposition flux. The feasibility of fabricating separated, well-ordered square spirals provides a cost effective and simple way to fabricate photonic crystals.
Reasoning about systems with many processes
Authors: German Steven M. , Sistla A. Prasad
Published: July 2002

Methods are given for automatically verifying temporal properties of concurrent systems containing an arbitrary number of finite-state processes that communicate using CCS actions. TWo models of systems are considered. Systems in the first model consist of a unique
control
process and an arbitrary number of
user
processes with identical definitions. For this model, a decision procedure to check whether all the executions of a process satisfy a given specification is presented. This algorithm runs in time double exponential in the sizes of the control and the user process definitions. It is also proven that it is decidable whether all the fair executions of a process satisfy a given specification. The second model is a special case of the first. In this model, all the processes have identical definitions. For this model, an efficient decision procedure is presented that checks if every execution of a process satisfies a given temporal logic specification. This algorithm runs in time polynomial in the size of the process definition. It is shown how to verify certain global properties such as mutual exclusion and absence of deadlocks. Finally, it is shown how these decision procedures can be used to reason about certain systems with a communication network.
Groupwork close up
Authors: Olson Judith S. , Olson Gary M. , Storrøsten Marianne , Carter Mark
Published: July 2002

A simple collaborative tool, a shared text editor called ShrEdit, changed the way groups of designers performed their work, and changed it for the better. First, the designs produced by the 19 groups of three designers were of higher quality than those of the 19 groups who worked with conventional whiteboard, paper and pencil. The groups with the new tool reported liking their work process a little less, probably because they had to adapt their work style to a new tool. We expected, from the brainstorming literature and recent work on Group Support Systems, that the reason the designs were of better quality was that the supported groups generated
more ideas
. To our surprise, the groups working with ShrEdit generated
fewer design ideas
, but apparently
better
ones. It appears that the tool helped the supported groups keep more focused on the
core
issued in the emerging design, to waste less time on less important topics, and to capture what was said as they went. This suggests that small workgroups can capitalize on the free access they have to a shared workspace, without requiring a facilitator or a work process embedded in the software.
Split menus
Authors: Sears Andrew , Shneiderman Ben
Published: July 2002

When some items in a menu are selected more frequently than others, as is often the case, designers or individual users may be able to speed performance and improve preference ratings by placing several high-frequency items at the top of the menu. Design guidelines for
split menus
were developed and applied. Split menus were implemented and tested in two in situ usability studies and a controlled experiment. In the usability studies performance times were reduced by 17 to 58% depending on the site and menus. In the controlled experiment split menus were significantly faster than alphabetic menus and yielded significantly higher subjective preferences. A possible resolution to the continuing debate among cognitive theorists about predicting menu selection times is offered. We conjecture and offer evidence that, at least when selecting items from pull-down menus, a logarithmic model applies to familiar (high-frequency) items, and a linear model to unfamiliar (low-frequency) items.
The integration of computing and routine work
Authors: Gasser Les
Published: July 2002

Most computing serves as a resource or tool to support other work: performing complex analyses for engineering projects, preparing documents, or sending electronic mail using office automation equipment, etc. To improve the character, quality, and ease of computing work, we must understand how automated systems actually are integrated into the work they support. How do people actually adapt to computing as a resource? How do they deal with the unreliability in hardware, software, or operations; data inaccuracy; system changes; poor documentation; inappropriate designs; etc.; which are present in almost every computing milieu, even where computing is widely used and considered highly successful? This paper presents some results of a detailed empirical study of routine computer use in several organizations. We present a theoretical account of computing work and use it to explain a number of observed phenomena, such as:

How people knowingly use “false” data to obtain desired analytical results by tricking their systems.

How organizations come to rely upon complex, critical computer systems despite significant, recurrent, known errors and inaccurate data.

How people work around inadequate computing systems by using manual or duplicate systems, rather than changing their systems via maintenance or enhancement.

In addition, the framework for analyzing computing and routine work presented here proves useful for representing and reasoning about activity in multiactor systems in general, and in understanding how better to integrate organizations of people and computers in which work is coordinated.
Applications of machine learning and rule induction
Authors: Langley Pat , Simon Herbert A.
Published: July 2002

M
achine learning
is the study of computational methods for improving performance by mechanizing the acquisition of knowledge from experience. Expert performance requires much domain-specific knowledge, and knowledge engineering has produced hundreds of AI expert systems that are now used regularly in industry. Machine learning aims to provide increasing levels of automation in the knowledge engineering process, replacing much time-consuming human activity with automatic techniques that improve accuracy or efficiency by discovering and exploiting regularities in training data. The ultimate test of machine learning is its ability to produce systems that are used regularly in industry, education, and elsewhere.
State event location in differential-algebraic models
Authors: Park Taeshin , Barton Paul I.
Published: July 2002

An efficient discontinuity handling algorithm for initial value problems in differential-algebraic equations is presented. The algorithm supports flexible representation of state conditions in propositional logic, and guarantees the location of all state events in strict time order. The algorithm consists of two phases:(1) event detection and(2) consistent event location. In the event detection phase, the entire integration step is searched for the state event by solving the interpolation polynomials for the discontinuity functions generated by the BDF method. An efficient hierarchical polynomial root-finding procedure based upon interval arithmetic guarantees detection of the state event even if multiple state condition transitions exist in an integration step, in which case many existing algorithms may fail. As a second phase of the algorithm, a consistent even location calculation is developed that accurately locates the state event detected earlier while completely eliminating incorrect reactivation of the same state event immediately after the consistent initialization calculation that may follow. This numerical phenomenon has not been explained before and is termed
discontinuity sticking
. Results from various test problems are presented to demonstrate the correctness and efficiency of the algorithm.
Lightweight lexical source model extraction
Authors: Murphy Gail C. , Notkin David
Published: July 2002

Software engineers maintaining an existing software system often depend on the mechanized extraction of information from system artifacts. Some useful kinds of information—source models—are well known: call graphs, file dependences, etc. Predicting every kind of source model that a software engineer may need is impossible. We have developed a lightweight approach for generating flexible and tolerant source model extractors from lexical specifications. The approach is lightweight in that the specifications are relatively small and easy to write. It is flexible in that there are few constraints on the kinds of artifacts from which source models are extracted (e.g., we can extract from source code, structured data files, documentation, etc.). It is tolerant in that there are few constraints on the condition of the artifacts. For example, we can extract from source that cannot necessarily be compiled. Our approach extended the kinds of source models that can be easily produced from lexical information while avoiding the constraints and brittleness of most parser-based approaches. We have developed tools to support this approach and applied the tools to the extraction of a number of different source models (file dependences, event interactions, call graphs) from a variety of system artifacts (C, C++, CLOS, Eiffel. TCL, structured data). We discuss our approach and describe its application to extract source models not available using existing systems; for example, we compute the implicitly-invokes relation over Field tools. We compare and contrast our approach to the conventional lexical and syntactic approaches of generating source models.
Hanging on the ‘wire
Authors: Ackerman Mark S. , Starr Brian , Hindus Debby , Mainwaring Scott D.
Published: July 2002

The primary focus of this article is an analysis of an audio-only media space from a computer-supported cooperative work (CSCW) perspective. To explore whether audio by itself is suitable for shared media systems, we studied a workgroup using an audio-only media space. This media space, called Thunderwire, combined high-quality audio with open connec-tions to create a shared space for its users. The two-month field study provided a richly nuanced understanding of this audio spaces social use. The system afforded rich sociable interactions. As well, users were able to create a useful, usable social space; however, through an analysis of the social norms that the participants formulated, we show that they had to take into account being in an audio-only environment. Within the field study, then, audio by itself was sufficient for a usable media space and a useful social space, but users were forced to adapt to many audio-only and system conditions. The article also considers audios implications for privacy.
Bounds on information exchange for Byzantine agreement
Authors: Dolev Danny , Reischuk Rüdiger
Published: July 2002

Byzantine Agreement has become increasingly important in establishing distributed properties when errors may exist in the systems. Recent polynomial algorithms for reaching Byzantine Agreement provide us with feasible solutions for obtaining coordination and synchronization in distributed systems. In this paper the amount of information exchange necessary to ensure Byzantine Agreement is studied. This is measured by the total number of messages the participating processors have to send in the worst case. In algorithms that use a signature scheme, the number of signatures appended to messages are also counted.

First it is shown that Ω(
nt
) is a lower bound for the number of signatures for any algorithm using authentication, where
n
denotes the number of processors and
t
the upper bound on the number of faults the algorithm is supposed to handle. For algorithms that reach Byzantine Agreement without using authentication this is even a lower bound for the total number of messages. If
n
is large compared to
t
, these bounds match the upper bounds from previously known algorithms. For the number of messages in the authenticated case we prove the lower bound Ω(
n
+
t
2
). Finally algorithms that achieve this bound are presented.
Trace-driven memory simulation
Authors: Uhlig Richard A. , Mudge Trevor N.
Published: July 2002

As the gap between processor and memory speeds continues to widen, methods for evaluating memory system designs before they are implemented in hardware are becoming increasingly important. One such method, trace-driven memory simulation, has been the subject of intense interest among researchers and has, as a result, enjoyed rapid development and substantial improvements during the past decade. This article surveys and analyzes these developments by establishing criteria for evaluating trace-driven methods, and then applies these criteria to describe, categorize, and compare over 50 trace-driven simulation tools. We discuss the strengths and weaknesses of different approaches and show that no single method is best when all criteria, including accuracy, speed, memory, flexibility, portability, expense, and ease of use are considered. In a concluding section, we examine fundamental limitations to trace-driven simulation, and survey some recent developments in memory simulation that may overcome these bottlenecks.
Consistency maintenance in multiresolution simulation
Authors: Reynolds Paul F. , Natrajan Anand , Srinivasan Sudhir
Published: July 2002

Simulations that run at multiple levels of resolution often encounter consistency problems because of insufficient correlation between the attributes at multiple levels of the same entity. Inconsistency may occur despite the existence of valid models at each resolution level. Cross-Resolution Modeling (CRM) attempts to build effective multiresolution simulations. The traditional approach to CRM—aggregation-disaggregation—causes chain disaggregation and puts an unacceptable burden on resources. We present four fundamental observations that would help guide future approaches to CRM. These observations form the basis of an approach we propose that involves the design of Multiple Resolution Entities (MREs). MREs are the foundation of a design that incorporates maintaining internal consistency. We also propose maintenance of core attributes as an approach to maintaining internal consistency within an MRE..
A cost-benefit decision model: analysis, comparison amd selection of data management
Authors: Su Stanley Y. W. , Dujmovic Jozo , Batory D. S. , Navathe S. B. , Elnicki Richard
Published: July 2002

This paper describes a general cost-benefit decision model that is applicable to the evaluation, comparison, and selection of alternative products with a multiplicity of features, such as complex computer systems. The application of this model is explained and illustrated using the selection of data management systems as an example.

The model has the following features: (1) it is mathematically based on an extended continuous logic and a theory of complex criteria; (2) the decision-making procedure is very general yet systematic, well-structured, and quantitative; (3) the technique is based on a comprehensive cost analysis and an elaborate analysis of benefits expressed in terms of the decision maker's preferences. The decision methodology, when applied to the problem of selecting a data management system, takes into consideration the life cycle of a DMS and the objectives and goals for the new systems under evaluation. It allows the cost and preference analyses to be carried out separately using two different models. The model for preference analysis makes use of comprehensive performance (or preference) parameters and allows what we call a “logic scoring of preferences” using continuous values between zero and one, to express the degree with which candidate systems satisfy stated requirements. It aggregates preference parameters based on their relative weights and logical relationships to compute a global performance (preference) score for each system. The cost model incorporates an aggregation of costs which may be estimated over different time horizons and discounted at appropriate discount rates. A procedure to establish an overall ranking of alternative systems based on their global preference scores and global costs is also discussed.
A specification language to assist in analysis of discrete event simulation models
Authors: Overstreet C Michael , Nance Richard E.
Published: July 2002

Effective development environments for discrete event simulation models should reduce development costs and improve model performance. A model specification language used in a model development environment is defined. This approach is intended to reduce modeling costs by interposing an intermediate form between a conceptual model (the model as it exists in the mind of the modeler) and an executable representation of that model. As a model specification is constructed, the incomplete specification can be analyzed to detect some types of errors and to provide some types of model documentation. The primitives used in this specification language, called a condition specification (CS), are carefully defined. A specification for the classical patrolling repairman model is used to illustrate this language. Some possible diagnostics and some untestable model specification properties, based on such a representation, are summarized.
Generation of high-order interpolants for explicit Runge-Kutta pairs
Authors: Sharp P. W. , Verner J. H.
Published: July 2002

Explicit Runge-Kutta pairs can be enhanced by providing them with interpolants. Enhancements include the ability to estimate and control the defect, to produce dense output, and to calculate past values in delay differential equations. The coefficients of an interpolant are easily generated by bootstripping on the order conditions. However, the generation of high-order interpolants requires a large number of arithmetic operations. We describe an efficient algorithm for the generation of high-order interpolants and illustrate the use of the algorithm with three applications.
Using metalevel techniques in a flexible toolkit for CSCW applications
Authors: Dourish Paul
Published: July 2002

Ideally, software toolkits for collaborative applications should provide generic, reusable components, applicable in a wide range of circumstances, which software developers can assemble to produce new applications. However, the nature of CSCW applications and the mechanics of group interaction present a problem. Group interactions are significantly constrained by the structure of the underlying infrastructure, below the level at which toolkits typically offer control. This article describes the design features of Prospero, a prototype CSCW toolkit designed to be much more flexible than traditional toolkit techniques allow. Prospero uses a metalevel architecture so that application programmers can have control over not only how toolkit components are combined and used, but also over aspects of how they are internally structured and defined. This approach allows programmers to gain access to “internal” aspects of the toolkit's operation that affect how interaction and collaboration proceed. This article explains the metalevel approach and its application to CSCW, introduces two particular metalevel techniques for distributed data management and consistency control, shows how they are realized in Prospero, and illustrates how Prospero can be used to create a range of collaborative applications.
Garbage collecting the Internet
Authors: Abdullahi Saleh E. , Ringwood Graem A.
Published: July 2002

Internet programming languages such as Java present new challenges to garbage-collection design. The spectrum of garbage-collection schema for linked structures distributed over a network are reviewed here. Distributed garbage collectors are classified first because they evolved from single-address-space collectors. This taxonomy is used as a framework to explore distribution issues: locality of action, communication overhead and indeterministic communication latency.
Conceptual schema analysis
Authors: Castano S. , De Antonellis V. , Fugini M. G. , Pernici B.
Published: July 2002

The problem of analyzing and classifying conceptual schemas is becomig increasingly important due to the availability of a large number of schemas related to existing applications. The purposes of schema analysis and classification activities can be different: to extract information on intensional properties of legacy systems in order to restructure or migrate to new architectures; to build libraries of reference conceptual components to be used in building new applications in a given domain; and to identify information flows and possible replication of data in an organization. This article proposes a set of techniques for schema analysis and classification to be used separately or in combination. The techniques allow the analyst to derive significant properties from schemas, with human intervention limited as far as possible. In particular, techniques for associating descriptors with schemas, for abstracting reference conceptual schemas based on schema clustering, and for determining schema similarity are presented. A methodology for systematic schema analysis is illustrated, with the purpose of identifying and abstracting into reference components the similar and potentially reusable parts of a set of schemas. Experiences deriving from the application of the proposed techniques and methodology on a large set of Entity-Relationship conceptual schemas of information systems in the Italian Public Administration domain are described
Algorithm 795
Authors: Verschelde Jan
Published: July 2002

Polynomial systems occur in a wide variety of application domains. Homotopy continuation methods are reliable and powerful methods to compute numerically approximations to all isolated complex solutions. During the last decade considerable progress has been accomplished on exploiting structure in a polynomial system, in particular its sparsity. In this article the structure and design of the software package PHC is described. The main program operates in several modes, is menu driven, and is file oriented. This package features great variety of root-counting methods among its tools. The outline of one black-box solver is sketched, and a report is given on its performance on a large database of test problems. The software has been developed on four different machine architectures. Its portability is ensured by the gnu-ada compiler.
Extendible hashing—a fast access method for dynamic files
Authors: Fagin Ronald , Nievergelt Jurg , Pippenger Nicholas , Strong H. Raymond
Published: July 2002

Extendible hashing is a new access technique, in which the user is guaranteed no more than two page faults to locate the data associated with a given unique identifier, or key. Unlike conventional hashing, extendible hashing has a dynamic structure that grows and shrinks gracefully as the database grows and shrinks. This approach simultaneously solves the problem of making hash tables that are extendible and of making radix search trees that are balanced. We study, by analysis and simulation, the performance of extendible hashing. The results indicate that extendible hashing provides an attractive alternative to other access methods, such as balanced trees.
A Complete Mechanization of Second-Order Type Theory
Authors: Pietrzykowski Tomasz
Published: July 2002

A generalization of the resolution method for higher order logic is presented. The languages acceptable for the method are phrased in a theory of types of order
w
(all finite types)—including the λ-operator, propositional functors, and quantifiers. The resolution method is, of course, a machine-oriented theorem search procedure based on refutation. In order to make this method suitable for higher order logic, it was necessary to overcome two sorts of difficulties. The first is that the unifying substitution procedure—an essential feature of the classic first-order resolution—must be generalized (it is noted that for the higher order unification the proper notion of substitution will include λ-normalization). A general unification algorithm is produced and proved to be complete for second-order languages. The second difficulty arises because in higher order languages, semantic intent is essentially more “interwoven” in formulas than in first-order languages. Whereas quantifiers could be eliminated immediately in first-order resolution, their elimination must be deferred in the higher order case. The generalized resolution procedure which the author produces thus incorporates quantifier elimination along with the familiar features of unification and tautological reduction. It is established that the author's generalized resolution procedure is complete with respect to a natural notion of validity based on Henkin's general validity for type theory. Finally, there are presented examples of the application of the method to number theory and set theory.
A Transformation System for Developing Recursive Programs
Authors: Burstall R. M. , Darlington John
Published: July 2002

A system of rules for transforming programs is described, with the programs in the form of recursion equations. An initially very simple, lucid, and hopefully correct program is transformed into a more efficient one by altering the recursion structure. Illustrative examples of program transformations are given, and a tentative implementation is described. Alternative structures for programs are shown, and a possible initial phase for an automatic or semiautomatic program-manipulation system is indicated.