bluuebunny/crossref_metadata_2025 huggingface dataset:
TIME AVERAGING OF IRREGULAR SPATIOTEMPORAL PATTERNS OF A LARGE APERTURE LASER IN TRANSITORY REGIME
Authors: ENCINAS-SANZ F. , LEYVA I. , GUERRA J. M.
Published: July 2002

By means of a new experimental technique, we measure quasi-intantaneous transverse intensity patterns in the gain-switch peak of a transversely excited atmospheric CO 2 laser with large aperture. The patterns recorded with a 2 ns resolution show a completely irregular spatiotemporal behavior, but when the exposure time of the measurements increases, boundary-determined ordered structures can be observed. As a quantification of this averaging process, the contrast of the intensity distributions decreases as the time integration grows. The results are numerically reproduced by integration of the full Maxwell–Bloch equations.
STATISTICS OF SOME LOW-DIMENSIONAL CHAOTIC FLOWS
Authors: DIMITROVA ELENA S. , YORDANOV OLEG I.
Published: July 2002

As a result of the recent finding that the Lorenz system exhibits blurred self-affinity for values of its controlling parameter slightly above the onset of chaos, we study other low-dimensional chaotic flows with the purpose of providing an approximate description of their second-order, two-point statistical functions. The main pool of chaotic systems on which we focus our attention is that reported by Sprott [1994], generalized however to depend on their intrinsic number of parameters. We show that their statistical properties are adequately described as processes with spectra having three segments all of power-law type. On this basis we identify quasi-periodic behavior pertaining to the relatively slow process in the attractors and approximate self-affine statistical symmetry characterizing the fast processes.
THE PENDULUM AUTOMATON
Authors: LINDNER JOHN F. , WIESENFELD KURT
Published: July 2002

As dynamical models, cellular automata sometimes provide compelling alternatives to differential equations. In addition to rapid simulations, their stylized dynamics may elucidate the essence of the underlying physics. In this Letter, we demonstrate the efficacy with which cellular automata can model spatiotemporal nonlinear dynamics. We explicitly construct and carefully test an automaton that faithfully simulates an array of slowly torqued, heavily damped pendulums. This example is representative of a variety of systems having two time scales (slow driving followed by fast readjustment) that naturally discretize in the singular limit where the ratio of the time scales vanishes.
ON THE CENTER PROBLEM FOR DEGENERATE SINGULAR POINTS OF PLANAR VECTOR FIELDS
Authors: MAÑOSA VÍCTOR
Published: July 2002

The center problem for degenerate singular points of planar systems (the degenerate-center problem) is a poorly-understood problem in the qualitative theory of ordinary differential equations. It may be broken down into two problems: the monodromy problem, to decide if the singular point is of focus-center type, and the stability problem, to decide whether it is a focus or a center.

We present an outline on the status of the center problem for degenerate singular points, explaining the main techniques and obstructions arising in the study of the problem. We also present some new results. Our new results are the characterization of a family of vector fields having a degenerate monodromic singular point at the origin, and the computation of the generalized first focal value for this family V1. This gives the solution of the stability problem in the monodromic case, except when V1 = 1. Our approach relies on the use of the blow-up technique and the study of the blow-up geometry of singular points. The knowledge of the blow-up geometry is used to generate a bifurcation of a limit cycle.
RECOVERING STATE TRAJECTORIES FROM OUTPUT MEASUREMENTS AND DYNAMIC MODELS: A COMPUTATIONAL COMPLEXITY POINT OF VIEW
Authors: MAREELS IVEN
Published: July 2002

Prediction, smoothing, filtering and synchronization or observer design given finitely many measurements and a given (possibly nonlinear) dynamical map are discussed from a computational complexity point of view. All these problems are particular instances of finding a zero of an appropriately defined function. The recognition of this fact enables one to approach these questions from a computational complexity point of view. For polynomial maps the computational complexity of a global Newton algorithm adapted to identify the finite trajectory of the dynamical system's state over the desired window scales in a polynomial manner with the condition number (an invariant for the problem at hand) and the degree of the polynomials required to describe the models. The computational complexity analysis allows one to identify the most efficient manner to approach synchronization (prediction, smoothing, filtering) problems. Moreover differences between adaptive and nonadaptive formulations are revealed based on the condition number of the associated zero finding problem. The advocated formulation, with the associated global Newton algorithm has good robustness properties with respect to measurement errors and model errors for both adaptive and nonadaptive problems. These aspects are illustrated through a simulation study based around the Hénon map.
SYNCHRONIZING HIGH DIMENSIONAL CHAOTIC SYSTEMS VIA EIGENVALUE PLACEMENT WITH APPLICATION TO CELLULAR NEURAL NETWORKS
Authors: GRASSI GIUSEPPE , MASCOLO SAVERIO
Published: July 2002

In this paper a method for synchronizing high dimensional chaotic systems is developed. The objective is to generate a linear error dynamics between the master and the slave systems, so that synchronization is achievable by exploiting the controllability property of linear systems. The suggested approach is applied to Cellular Neural Networks (CNNs), which can be considered as a tool for generating complex hyperchaotic behaviors. Numerical simulations are carried out for synchronizing CNNs constituted by Chua's circuits.
CONTROLLING CHAOTIC DYNAMICS USING BACKSTEPPING DESIGN WITH APPLICATION TO THE LORENZ SYSTEM AND CHUA'S CIRCUIT
Authors: MASCOLO SAVERIO , GRASSI GIUSEPPE
Published: July 2002

In this Letter backstepping design is proposed for controlling chaotic systems. The tool consists in a recursive procedure that combines the choice of a Lyapunov function with the design of feedback control. The advantages of the method are the following: (i) it represents a systematic procedure for controlling chaotic or hyperchaotic dynamics; (ii) it can be applied to several circuits and systems reported in literature; (iii) stabilization of chaotic motion to a steady state as well as tracking of any desired trajectory can be achieved. In order to illustrate the general applicability of backstepping design, the tool is utilized for controlling the chaotic dynamics of the Lorenz system and Chua's circuit. Finally, numerical simulations are carried out to show the effectiveness of the technique.
DEGENERATE BIFURCATIONS WITH Z2⊕Z2-SYMMETRY
Authors: MANOEL MIRIAM , STEWART IAN
Published: July 2002

Bifurcation problems with the symmetry group Z2⊕Z2 of the rectangle are common in applied science, for example, whenever a Euclidean invariant PDE is posed on a rectangular domain. In this work we derive normal forms for one-parameter bifurcations of steady states with symmetry of the group Z2⊕Z2. We study degeneracies of Z2⊕Z2-codimension 3 and modality 1. We also deduce persistent bifurcation diagrams when the system is subject to symmetry-preserving perturbations.
ON SOME SIDON SEQUENCES
Authors: KRZYŻEWSKI K.
Published: July 2002

We study sequences (f ◦ φn), where φ is an ergodic continuous endomorphism of a compact nontrivial Abelian group G with the probability Haar measure μ and f has an absolutely summable Fourier series. We prove that if (f ◦ φn) is a Sidon sequence (i.e. the uniform norm and l1-norm are equivalent on the linear space spanned by f ◦ φn, n≥ 0), then the spectral density of f-μ(f) with respect to the dynamical system (G, μ, φ) is positive. The converse of the theorem holds under an additional assumption on f. For f being a trigonometric polynomial, this characterization is complete and can be reformulated in terms of unsolvability of a generalized cohomology equation for f with respect to the dynamical system (G, μ, φ). It turns out that the set of those f∈ C(G) for which (f ◦ φn) is a Sidon sequence is open and dense in C(G).
A FINITE-VOLUME PARTICLE METHOD FOR COMPRESSIBLE FLOWS
Authors: HIETEL DIETMAR , STEINER KONRAD , STRUCKMEIER JENS
Published: July 2002

We derive a new class of particle methods for conservation laws, which are based on numerical flux functions to model the interactions between moving particles. The derivation is similar to that of classical finite-volume methods; except that the fixed spatial mesh in a finite-volume method is substituted by so-called mass packets of particles. We give some numerical results on a shock wave solution for Burgers equation as well as the well-known one-dimensional shock tube problem.
APPLYING π-CALCULUS TO DYNAMICALLY-CHANGING PLAN FOR AGENT MODEL
Authors: IWATA KAZUNORI , ITO NOBUHIRO , DU XIAOYONG , ISHII NAOHIRO
Published: July 2002

In this paper, we apply π-calculus1,2 to the planning for agents. First, we have proposed a new language for describing agent plans based on π-calculus, called PDL (Plan Description Language), and the model to execute them. The plans described in PDL can be changed dynamically while they are executing, because π-calculus provides dynamically-changing structures. By using this property, agents can change their plans to adapt to the environment around them by themselves in executing their plans. This property called reflection is very important to agents. We state the properties as theorems and prove them. Second, we have implemented an interpreter for PDL. In order to implement the system, we propose a primitive language, called PiL (Pi-calculus Language). PiL can be used on computers more easily than using the mathematical notations of π-calculus. We have shown that this system executes programs correctly and a plan written in PDL can be executed on the system. Finally, we have proved that the PDL is useful in the dynamically-changing environment by experiments.
ADAPTIVE FUZZY SLIDING MODE CONTROL FOR BASE-ISOLATED BUILDINGS
Authors: CHIANG WEI-LING , YEH KEN , LIU MING-YI
Published: July 2002

The purpose of this paper is to apply adaptive fuzzy sliding mode control for the structural control of base-isolated buildings. Combining the fuzzy control and sliding mode control one can reduce the complexity of fuzzy rule bases. It also ensures the stability and robustness. The Lyapunov theory is used to develop the adaptive law. In addition to full-state-feedback controller, an estimator using only the measured information from a few sensors is presented. Finally, the adaptive sliding mode control is applied to two types of base-isolated building, with LRB, and sliding bearing isolators. Stiffness uncertainty and time delay is utilized to illustrate the robustness of this proposed algorithm. The effectiveness of this algorithm is demonstrated by simulation results for a long period, a wide-pass white noise artificial earthquake and Taiwan Chi Chi earthquake occurred in 1999. The simulations show that adaptive sliding mode control can achieve satisfactory results in the application of structural control for base-isolated buildings.
EASE-OF-USE, IMPLEMENTATION AND PERFORMANCE OF HEURISTICS FOR OPTIMIZATION — A COMPARISON OF EVOLUTIONARY AND ITERATIVE IMPROVEMENT METHODS
Authors: SINGH K. , KURBEL K.
Published: July 2002

Many new approaches to solve optimization problems have been proposed with the appearance of methods based on analogies to natural processes. For the user in practice, it is not only difficult to assess which method is the "best" one but also to judge how easy or complicated it is to implement and apply the methods. This is mainly due to the fact that most methods have interacting parameters which need to be tuned before a method can be used. The paper discusses ease of use and implementation as well as performance aspects based on computational tests. Thre iterative improvement methods (simulated annealing, tabu search, threshold accepting) and two evolutionary methods (genetic algorithms, PRSA) are compared with regard to an optimization problem (standard cell placement in chip design). Based on results from a large number of test runs, we discuss how easy or difficult it is to prepare the methods for a specific application. In summary, iterative improvement methods were found easier to implement and to use than evolutionary methods. They also outperformed the latter ones in terms of solution quality and computing time.
INTERACTIVE GENERALIZATION OF A TRANSLATION EXAMPLE USING QUERIES BASED ON A SEMANTIC HIERARCHY
Authors: AKIBA YASUHIRO , NAKAIWA HIROMI , OOYAMA YOSHIFUMI , SHIRAI SATOSHI
Published: July 2002

This article addresses the issue of acquiring translation rules for machine translation (MT) systems that adopt a transfer approach. These rules aer semantic pattern pairs (SPPs) of the source and target languages. Practical MT systems must additionally contain a huge number of SPPs corresponding to rarely-used predicates and predicate usages. Such SPPs are difficult to automatically acquire with corpus-based methods. To solve this difficulty, this article proposes a method to acquire SPPs by using queries based on a semantic hierarchy. The proposed method asks a lexicographer for the necessary information in order to generalize the conditions of SPPs and then gradually generalizes these conditions. Experimental results show that the proposed method allows the acquisition of more plausible conditions within almost the same time spent for manual generalization.
EXTENSIBLE INFORMATION BROKERS
Authors: LU JIANGUO , MYLOPOULOS JOHN
Published: July 2002

The number and size of information services available on the internet has been growing exponentially over the past few years. This growth has created an urgent need for information agents that act as brokers in the sense that they can autonomously search, gather, and integrate information on behalf of a user. To remain useful, such brokers will have to evolve throughout their lifetime to keep up with evolving and ever-changing information services. This paper proposes a framework named XIB (eXtensible Information Brokers) for building and evolving information brokers.

The XIB takes as input a description of required information services and supports the interactive generation of an integrated query interface. It also generates wrappers for each information service dynamically. Once the query interface and wrappers are in place, the user can specify a query and get back a result which integrates data from all wrapped information sources. The XIB depends heavily on XML-related techniques. More specifically, we use DTDs to model the input and output of each service, and XML to represent both input and output values. Based on such representations, the paper investigates service integration in the form DTD integration, and studies query decomposition in the form of XML element decomposition. Within the proposed framework, it is easy to add or remove information services to a broker, thereby facilitating maintenance, evolution and customization of information brokers.
KNOTS OF TEN OR FEWER CROSSINGS OF ALGEBRAIC ORDER 2
Authors: TAMULIS ANDRIUS
Published: July 2002

The concordance orders of many algebraic order two knots of ten or fewer crossings have been heretofore unknown. We use Casson-Gordon invariants and twisted Alexander polynomials to find that, in all but one case, these knots do not have concordance order two. We also find that a certain family of algebraic order two twisted doubles of the unknot have infinite concordance order.
ON THE NUMERICAL STUDY OF THE COMPLEXITY AND FRACTAL DIMENSION OF CMB ANISOTROPIES
Authors: ALLAHVERDYAN A. E. , GURZADYAN V. G. , SOGHOYAN A. A.
Published: July 2002

We consider the problem of numerical computation of the Kolmogorov complexity and the fractal dimension of the anisotropy spots of Cosmic Microwave Background (CMB) radiation. Namely, we describe an algorithm of estimation of the complexity of spots given by certain pixel configuration on a grid and represent the results of computations for a series of structures of different complexity. Thus, we demonstrate the calculability of such an abstract descriptor as the Kolmogorov complexity for CMB digitized maps. The correlation of complexity of the anisotropy spots with their fractal dimension is revealed as well. This technique can be especially important while analyzing the data of the forthcoming space experiments.
STUDY OF THE EXCITED STATE OF DOUBLE-Λ HYPERNUCLEI BY HYPERSPHERICAL SUPERSYMMETRIC APPROACH
Authors: KHAN MD. ABDUL , DAS TAPAN KUMAR , CHAKRABARTI BARNALI
Published: July 2002

Hyperspherical harmonics expansion (HHE) method has been applied to study the structure and ΛΛ dynamics for the ground and first excited states of low and medium mass double-Λ hypernuclei in the framework of core+Λ+Λ three-body model. The ΛΛ potential is chosen phenomenologically while core-Λ potential is obtained by folding the phenomenological Λ N interaction into the density distribution of the core. The parameters of this effective Λ N potential is obtained by the condition that they reproduce the experimental (or empirical) data for core-Λ subsystem. The three-body (core+Λ+Λ) Schrödinger equation is solved by hyperspherical adiabatic approximation (HAA) to get the ground state energy and wave function. This ground state energy and wave function are used to construct a partner potential. The three-body Schrödinger equation is solved once again for this partner potential. According to supersymmetric quantum mechanics, the ground state energy of this potential is exactly the same as that of the first excited state of the potential used in the first step. In addition to the two-Λ separation energy for the ground and first excited state, some geometrical quantities for the ground state of double-Λ hypernuclei [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] are computed. These include the ΛΛ bond energy and various r.m.s. radii.
SYSTEMATIC COMPARISON OF THE EXPERIMENTAL DATA WITH THE FRITIOF MODEL IN NUCLEUS–NUCLEUS INTERACTIONS WITH LIGHT AND HEAVY TARGET NUCLEI IN NUCLEAR EMULSION AT 4.5A Gev/c
Authors: MOHERY M. , ABD-ALLAH N. N.
Published: July 2002

The characteristics of the interactions of 4.5 A GeV/c 28 Si nuclei with emulsion have been investigated. The method of separating interactions into those with hydrogen, light and heavy target nuclei has been discussed. The multiplicity distribution, average multiplicities, multiplicity correlation and the angular distributions of the secondary particles emitted in 28 Si -emulsion are calculated according to the Modified Fritiof Model and compared with the experimental data and with other available data for p, 12 C , 24 Mg at the same energy. It has been found that the modified Fritiof model can describe the multiplicity characteristics of the different emitted particles in the above-mentioned interaction with different target groups. The comparison of the experimental data with the modified Fritiof model shows no clear preference for the case of the light target while it seems to be nearer to the experimental data in the case of the heavy target and the emulsion
CROSS-FERTILIZATION BETWEEN MODELS IN PHYLLOTAXIS
Authors: JEAN ROGER V.
Published: July 2002

There are many models in phyllotaxis concerned with optimality principles which are apparently equivalent. The important problem of showing the equivalence of the models has been underlined but not addressed yet. This paper addresses the general problem of determining up to which point we have equivalence. The viewpoint adopted is the one of the outcomes of the models, of what they generate, and of what they don't, at least in their actual states. It will be emphasized too that models in phyllotaxis can be compared at many different levels, and that their biological supports can spring from many of these levels.
ACOUSTIC SCATTERING FROM A 2-D FLUID WAVEGUIDE WITH AN IRREGULAR FLOOR VIA THE BEM
Authors: TADEU ANTÓNIO J. B. , GODINHO LUÍS M. C. , BRANCO FERNANDO J. F. G.
Published: July 2002

This work focuses on the way the pressure field generated by a dilatational load changes inside a channel waveguide filled with a homogeneous fluid, in the presence of an irregular floor. The problem is solved in the frequency domain using the boundary element method. The Green's functions used are obtained by superposing virtual acoustic sources defined so as to generate the free or rigid surfaces of the fluid channel. The responses in the time domain are obtained by means of Fourier transforms, using complex frequencies. Irregular floors of varying sizes are modeled. The main features and spectral representation of the signals scattered by these inclusions are described. They are used to elucidate the most important aspect of wave acoustics, which can be used as the basis for the development of nondestructive testing and imaging methods.
ON PROOFS IN SYSTEM P
Authors: PARSONS SIMON , BOURNE RACHEL A.
Published: July 2002

This paper investigates how the rules of System P might be used in order to construct proofs for default consequences which take into account the bounds on the probabilities of the consequents of the defaults. Using a knowledge base of default rules which are considered to be constraints on a probability distribution, the result of applying the rules of P gives us new constraints that were implicit in the knowledge base and their associated lower bounds. The paper defines a proof system for such constraints, shows that it is sound, and then discusses at length the completeness of the system and the kind of proofs that it can generate.
ON PRESELECTION OF RULES IN FUZZY LOGIC DEDUCTION
Authors: DVOŘÁK ANTONÍN
Published: July 2002

Preselection of rules is an algorithm which chooses one rule from linguistic description of some process. This rule is then used for inference instead of the whole description. This article studies properties of preselection and proposes use of measures of resemblance for choosing the rule which best fits the observation.
TREATMENT OF HAND DEFORMITIES IN A LONG-TERM SURVIVOR WITH DERMOLYTIC BULLOUS DERMATOSIS-RECESSIVE (DBD-R)
Authors: Sugawara Shinobu , Kusunose Kouichi , Kaneko Kazuo
Published: July 2002

Treatment of hand deformities in a long-term survivor with dermolytic bullous dermatosis-recessive is described. An "open method" is sufficient for dealing with volar skin defects. There is still no effective treatment for perfect control of blister formation. But appropriate surgery, followed by careful post-operative rehabilitation can give reasonable hand function.
THE ARIADNE APPROACH TO WEB-BASED INFORMATION INTEGRATION
Authors: KNOBLOCK CRAIG A. , MINTON STEVEN , AMBITE JOSE LUIS , ASHISH NAVEEN , MUSLEA ION , PHILPOT ANDREW G. , TEJADA SHEILA
Published: July 2002

The Web is based on a browsing paradigm that makes it difficult to retrieve and integrate data from multiple sites. Today, the only way to do this is to build specialized applications, which are time-consuming to develop and difficult to maintain. We have addressed this problem by creating the technology and tools for rapidly constructing information agents that extract, query, and integrate data from web sources. Our approach is based on a uniform representation that makes it simple and efficient to integrate multiple sources. Instead of building specialized algorithms for handling web sources, we have developed methods for mapping web sources into this uniform representation. This approach builds on work from knowledge representation, databases, machine learning and automated planning. The resulting system, called Ariadne, makes it fast and easy to build new information agents that access existing web sources. Ariadne also makes it easy to maintain these agents and incorporate new sources as they become available.
PORTFOLIO OPTIMIZATION, HIDDEN MARKOV MODELS, AND TECHNICAL ANALYSIS OF P&F-CHARTS
Authors: ELLIOTT ROBERT , HINZ JURI
Published: July 2002

In this work we introduce an adaptive method of portfolio optimization. The basic idea is to describe essential movements of the stock price using a hidden Markov model and to calculate the optimal portfolio using a recursive algorithm. The portfolio optimization is adaptive in the sense that the standard EM-algorithm fits the model to historical data, which improves the portfolio performance.
HOCHSCHILD COHOMOLOGY OF POLYNOMIAL ALGEBRAS
Authors: PENKAVA MICHAEL , VANHAECKE POL
Published: July 2002

In this paper we investigate the Hochschild cohomology groups H2(A) and H3(A) for an arbitrary polynomial algebra A. We also show that the corresponding cohomology groups which are built from differential operators inject in H2(A) and H3(A) and we give an application to deformation theory.
BEHAVIOUR OF SILOS SUPPORTED ON DISCRETE BRACKETS
Authors: GILLIE M. , HOLST J. M. F. G. , MÜNCH M. , ROTTER J. M.
Published: July 2002

The controlling design condition in thin metal silos is generally buckling under axial compression. This compression is often assumed to be uniform but in many practical cases several failure modes interact as a result of a rather more complex pattern of stresses. Small silos are often supported on several columns with local brackets attached to the sides of the shell. Failure occurs with an interaction between buckling and yielding under a stress regime involving a combination of membrane and bending stresses developed by the applied loads. This paper firstly reviews the literature relevant to bracket supported silos and exposes the limitations in the available design guidance. The results of a series of finite element analyses are then presented to describe the underlying structural behaviour. It is shown that material and geometric non-linearity both play an important role in the behaviour of discretely supported silos. It is also established that the degree of bracket eccentricity is an important factor in determining the mechanism of failure and the associated strength of the silo. Finally, comparison is made between the numerical results and existing design guidelines.
EXACT VIBRATION FREQUENCIES AND MODES OF BEAMS WITH INTERNAL RELEASES
Authors: EISENBERGER M.
Published: July 2002

The exact vibration frequencies of continuous beams with internal releases are found using the dynamic stiffness method. Two types of releases are considered: hinge and sliding discontinuities. First, the exact dynamic stiffness matrix for a beam element with a release is derived and then used in the assembly of the structure dynamic stiffness matrix. The natural frequencies are found as the values of frequency that make this matrix singular. Then the mode shapes are found exactly. Examples are given for continuous beams with different releases.
GRADIENT-ORIENTED PROFILES FOR BOUNDARY PARAMETERIZATION AND THEIR APPLICATION TO CORE ATOMS TOWARDS SHAPE ANALYSIS
Authors: TAMBURO ROBERT J. , STETTEN GEORGE D.
Published: July 2002

Gradient-oriented profiles are presented as a novel method for boundary parameterization and unsupervised boundary classification. Each profile is created at locations of high gradient magnitude by sampling an ellipsoidal neighborhood of voxels oriented along the image gradient. Every profile is analyzed via nonlinear optimization to fit the best cumulative Gaussian, directly parameterizing the boundary to yield estimates of (1) extrapolated intensity values for voxels located far inside and outside of the boundary and (2) boundary location and width. For these parameter estimates, intrinsic measures of confidence are established to eliminate the low-confidence parameters. Gradient-oriented profiles are demonstrated on artificially generated three-dimensional test data and shown to accurately parameterize and classify the boundary, establishing them as a high-quality replacement for simpler methods of boundary detection. Towards shape analysis gradient-oriented profiles are applied to medial primitives known as core atoms. The additional intensity information delivered by gradient-oriented profiles improves the function of core atoms by eliminating dependence on the absolute direction of the local image gradient and the background intensity. The performance of core profiles is demonstrated on test data simulating a three-dimensional ultrasound scan of the heart improving the previous capabilities of core atoms.
CONTROLLING ACTIVATED PROCESSES
Authors: DYKMAN M. I. , GOLDING BRAGE
Published: July 2002

The rates of activated processes, such as escape from a metastable state and nucleation, are exponentially sensitive to an externally applied field. We describe how this applies to modulation by high-frequency fields and illustrate it with experimental observations. The results may lead to selective control of diffusion in periodic potentials, novel control mechanisms for crystal growth, and new separation techniques.
OPTIMAL DESIGN OF ARTERIAL BYPASS PROSTHESES DIAMETER
Authors: STOYTCHEV S. , PALLOTTI G. , PETTAZZONI P.
Published: July 2002

The objectives of this paper are: (1) to analyze how the bypass diameter and the degree of the stenosis affect the flow-induced wall shear stresses in the stenotic and bypass vessels and (2) to propose a clinically usable method for a proper selection of the bypass diameter. The problem is solved in the following stages: First, the steady pressure and flow within the vessels are obtained using general laws of mass and energy conservation. Then, on the basis of modified Womersley's theory to take into account the nonlinear mechanical properties of the vessels, the oscillating pressure and flow within the vessels are calculated. They are used to derive expressions for the reflection coefficients at the distal (converging) bifurcation and to calculate wall shear stresses.

We hypothesize that the minimal differences in the wall shear stresses of the normal artery, stenotic artery and the bypass graft mitigate the development of anastomotic neointimal hyperplasia and graft pseudo intima. Using cost functions, based on steady and mean wall shear stresses, we calculated the optimal value of the undeformed bypass diameter for various degrees of stenosis. We found that the sum of cross-sectional areas of the optimal graft and the stenotic artery (normalized with respect to the cross-sectional area of the normal artery) varies between 1.14 and 1.28, an interval, which is consistent with the findings of McDonald (1974) for the area of the major branches in the body. Thus we conclude that the results obtained are consistent with the stated hypothesis.
NANOBELTS OF SEMICONDUCTIVE OXIDES: A STRUCTURALLY AND MORPHOLOGICALLY CONTROLLED NANOMATERIALS SYSTEM
Authors: WANG ZHONG LIN , PAN ZHENGWEI
Published: July 2002

We have developed a simple and economic technique for synthesis of one-dimensional nanobelt structures of semiconductive oxides such as ZnO, SnO 2, In 2 O 3, CdO, Ga 2 O 3 and PbO 2. The as-synthesized oxide nanobelts are pure, structurally uniform, single crystalline and most of them free from dislocations; they have a rectangular-like cross-section with typical widths of 30–300 nanometers, width-to-thickness ratios of 5–10 and lengths of up to a few millimeters. The belt-like morphology appears to be a unique and common structural characteristic for the family of semiconducting oxides with cations of different valence states and materials of distinct crystallographic structures. The nanobelts are structurally and morphologically controlled and they are intrinsic semiconductors, providing a new system after carbon nanotubes for a systematic understanding on dimensionally confined transport phenomena in functional oxides. They are also ideal building blocks for fabrication of nanoscale devices based on the integrity of individual nanobelts.
ASSESSMENT OF AIR QUALITY AT THE EUROPEAN SCALE: EXISTING STATUS, RECOMMENDATIONS AND PRIORITIES
Authors: CARTALIS CONSTANTINOS , PETRAKIS MICHAEL
Published: July 2002

The scope of this paper is to describe the existing problems with respect to the lack of a harmonised assessment approach for air quality, and to provide general recommendations and priorities for an assessment approach at the European scale. Taken that the approach for assessment may diverge among the European countries and the players involved, recommendations are general and aim at providing the overall framework on the basis of which the formulation of specific assessment approaches could be worked out. The starting point for the paper is a synopsis of the characteristics of air quality assessments, as well as of the drawbacks for a harmonised assessment approach at the European scale. The assessment of air quality is then described in relation to sources as well as to effects. At a final stage the assessment goals are recognised and the link between air quality assessment and integrated assessment is also discussed.
Finite state verifiers II
Authors: Dwork Cynthia , Stockmeyer Larry
Published: July 2002

The zero knowledge properties of interactive proof systems (IPSs) are studied in the case that the verifier is a 2-way probabilistic finite state automaton (2pfa). The following results are proved:

A new definition of zero knowledge is introduced. This definition captures a concept of “zero knowledge” for IPSs that are used for language recognition.
The generalized tree quorum protocol
Authors: Agrawal D. , El Abbadi A.
Published: July 2002

In this paper, we present a low-cost fault-tolerant protocol for managing replicated data. We impose a logical tree structure on the set of copies of an object and develop a protocol that uses the information available in the logical structure to reduce the communication requirements for read and write operations. The tree quorum protocol is a generalization of the static voting protocol with two degrees of freedom for choosing quorums. In general, this results in significantly lower communication costs for comparable data availability. The protocol exhibits the property of graceful degradation, i.e., communication costs for executing operations are minimal in a failure-free environment but may increase as failures occur. This approach in designing distributed systems is desirable since it provides fault-tolerance without imposing unnecessary costs on the failure-free mode of operations.
Computing selected eigenvalues of sparse unsymmetric matrices using subspace iteration
Authors: Duff I. S. , Scott J. A.
Published: July 2002

This paper discusses the design and development of a code to calculate the eigenvalues of a large sparse real unsymmetric matrix that are the rightmost, leftmost, or are of the largest modulus. A subspace iteration algorithm is used to compute a sequence of sets of vectors that converge to an orthonormal basis for the invariant subspace corresponding to the required eigenvalues. This algorithm is combined with Chebychev acceleration if the rightmost or leftmost eigenvalues are sought, or if the eigenvalues of largest modulus are known to be the rightmost or leftmost eigenvalues. An option exists for computing the corresponding eigenvectors. The code does not need the matrix explicitly since it only requires the user to multiply sets of vectors by the matrix. Sophisticated and novel iteration controls, stopping criteria, and restart facilities are provided. The code is shown to be efficient and competitive on a range of test problems.
An execution model for limited ambiguity rules and its application to derived data update
Authors: Chen I.-Min A. , Hull Richard , McLeod Dennis
Published: July 2002

A novel execution model for rule application in active databases is developed and applied to the problem of updating derived data in a database represented using a semantic, object-based database model. The execution model is based on the use of “limited ambiguity rules” (LARs), which permit disjunction in rule actions. The execution model essentially performs a breadth-first exploration of alternative extensions of a user-requested update. Given an object-based database schema, both integrity constraints and specifications of derived classes and attributes are compiled into a family of limited ambiguity rules. A theoretical analysis shows that the approach is sound: the execution model returns all valid “completions” of a user-requested update, or terminates
with an appropriate error notification. The complexity of the approach in connection with derived data update is considered.
Smalltalk in the telecommunications industry
Authors: Grochow Jerrold M.
Published: July 2002

In a world where global partnerships and rapidly shifting business environments will be the norm, the telecommunications industry stands out for the speed with which both its technology and business processes are being transformed. Beginning with the breakup of AT&T, the industry has been lurching toward worldwide competition, and a blurring of the lines between local, interexchange, cellular, value-added network, and even cable carriers.
Algorithm 762: LLDRLF, log-likelihood and some derivatives for log-F models
Authors: Brown Barry W. , Levy Lawrence B. , Lovato James , Russell Kathy , Spears Floyd M.
Published: July 2002

The flexible statistical models incorporating the log-F distribution are little used because of numeric difficulties. We describe a method for calculating the log-likelihood and two derivatives with respect to the data argument. Fortran subroutines incorporating these calculations are provided.
Bounding errors introduced by clustering of customers in closed product-form queuing networks
Authors: Cheng William C. , Muntz Richard R.
Published: July 2002

Product-form queuing network models have been widely used to model systems with shared resources such as computer systems (both centralized and distributed), communication networks, and flexible manufacturing systems. Closed multichain product-form networks are inherently more difficult to analyze than open networks, due to the effect of normalization. Results in workload characterization for closed networks in the literature are often for networks having special structures and only specific performance measures have been considered.

In this article, we drive certain properties (insensitivity of conditional state probability distributions and fractional-linearity of Markov reward functions) for a broad class of closed multichain product-form networks. These properties are derived using the most basic flow balance conditions of product-form networks. Then we show how these basic properties can be applied in obtaining error bounds when similar customers are clustered together to speed up computation.
Model refinement for hardware-software codesign
Authors: Gong Jie , Gajski Daniel D. , Bakshi Smita
Published: July 2002

Hardware-software codesign, which implements a given specification with a set of system components such as ASICs and processors, includes several key tasks such as system component allocation, functional partitioning, quality metrics estimation, and model refinement. In this work, we focus on the model refinement task which transforms a specification from an original functional model to a refined implementation model. First, we categorize several commonly used implementation models and describe a set of refinement procedures to transform a specification to each of these implementation models. We also present a set of experimental results to compare the implementation models and to demonstrate how the proposed approach can be used to explore different implementation styles.
Comments on “a reduced test suite for protocol conformance testing”
Authors: Petrenko Alexandre
Published: July 2002

A previous
ACM TOSEM
article of Ph. Bernhard (“A Reduced Test Suite of Protocol Conformance Testing,”
ACM Transactions on Software Engineering and Methodology,
Vol. 3, No. 3, July 1994, pages 201-220) describes three new versions of the so-called W-method for solving the protocol-testing problem, i.e., solving the Mealy machine equivalence problem. The author claims that these versions all have the same fault detection capability as the original W-method. In this correspondence we prove that the results of that article are incorrect.
Reconfiguration for fault tolerance using graph grammars
Authors: Derk M. D. , DeBrunner L. S.
Published: July 2002

Reconfiguration for fault tolerance is a widely studied field, but this work applies graph grammars to this discipline for the first time. Reconfiguration Graph Grammars (RGG) are defined and applied to the definition of processor array reconfiguration algorithms. The nodes of a graph are associated with the processors of a processor array, and the edges are associated with those interprocessor communication lines that are active. The resulting algorithms for dynamic (run-time) reconfiguration are efficient and can be implemented distributively.
Computing homology groups of simplicial complexes in
R
3
Authors: Dey Tamal K. , Guha Sumanta
Published: July 2002

Recent developments in analyzing molecular structures and representing solid models using simplicial complexes have further enhanced the need for computing structural information about simplicial complexes in
R
3
. This paper develops basic techniques required to manipulate and analyze structures of complexes in
R
3
.

A new approach to analyze simplicial complexes in Euclidean 3-space
R
3
is described. First, methods from topology are used to analyze triangulated 3-manifolds in
R
3
. Then, it is shown that these methods can, in fact, be applied to arbitrary simplicial complexes in
R
3
after (simulating) the process of thickening a complex to a 3-manifold homotopic to it. As a consequence considerable structural information about the complex can be determined and certain discrete problems solved as well. For example, it is shown how to determine homology groups, as well as concrete representations of their generators, for a given complex in
R
3
Performance of a database manager in a virtual memory system
Authors: Sherman Stephen W. , Brice Richard S.
Published: July 2002

Buffer space is created and managed in database systems in order to reduce accesses to the I/O devices for database information. In systems using virtual memory any increase in the buffer space may be accompanied by an increase in paging. The effects of these factors on system performance are quantified where system performance is a function of page faults and database accesses to I/O devices. This phenomenon is examined through the analysis of empirical data gathered in a multifactor experiment. The factors considered are memory size, size of buffer space, memory replacement algorithm, and buffer management algorithm. The improvement of system performance through an increase in the size of the buffer space is demonstrated. It is also shown that for certain values of the other factors an increase in the size of the buffer space can cause performance to deteriorate.
Database buffer paging in virtual storage systems
Authors: Lang Tomás , Wood Christopher , Fernández Eduardo B.
Published: July 2002

Three models, corresponding to different sets of assumptions, are analyzed to study the behavior of a database buffer in a paging environment. The models correspond to practical situations and vary in their search strategies and replacement algorithms. The variation of I/O cost with respect to buffer size is determined for the three models. The analysis is valid for arbitrary database and buffer sizes, and the I/O cost is obtained in terms of the miss ratio, the buffer size, the number of main memory pages available for the buffer, and the relative buffer and database access costs.
An Algorithm for Reconstructing Protein and RNA Sequences
Authors: Shapiro Marvin B.
Published: July 2002

An algorithm for deriving the primary sequence of a protein or RNA is presented. The data is in the form of short sequences of letters which must be fitted together to form the unknown complete sequence. A computer program for carrying out the steps is described, with an example. It is shown that the algorithm cannot make an error and empirical results are given which illustrate the successful use of the algorithm in reconstructing complete sequences known to be solvable.
A Cycle Generation Algorithm for Finite Undirected Linear Graphs
Authors: Gibbs Norman E.
Published: July 2002

When the algorithms of J. T. Welch, Jr. were implemented it was discovered that they did not perform as described. The generation of all cycles from a basis is faulty. The generation of the basis is apparently correct. A modified version of Welch's Algorithm 3 is presented. The reasons for modifying Welch's algorithms are presented with examples.
On secure and pseudonymous client-relationships with multiple servers
Authors: Gabber Eran , Gibbons Phillip B. , Kristol David M. , Matias Yossi , Mayer Alain
Published: July 2002

This paper introduces a cryptographic engine, Janus, which assists clients in establishing and maintaining secure and pseudonymous relationships with multiple servers. The setting is such that clients reside on a particular subnet (e.g., corporate intranet, ISP) and the servers reside anywhere on the Internet. The Janus engine allows each client-server relationship to use either weak or strong authentication on each interaction. At the same time, each interaction preserves privacy by neither revealing a clients true identity (except for the subnet) nor the set of servers with which a particular client interacts. Furthermore, clients do not need any secure long-term memory, enabling scalability and mobility. The interaction model extends to allow servers to send data back to clients via e-mail at a later date. Hence, our results complement the functionality of current network anonymity tools and remailers. The paper also describes the design and implementation of the Lucent Personalized Web Assistant (LPWA), which is a practical system that provides secure and pseudonymous relations with multiple servers on the Internet. LPWA employs the Janus function to generate site-specific personæ, which consist of alias usernames, passwords, and e-mail addresses.
Practical data-swapping: the first steps
Authors: Reiss Steven P.
Published: July 2002

The problem of statistical database confidentiality in releasing microdata is addressed through the use of approximate data-swapping. Here, a portion of the microdata is replaced with a database that has been selected with approximately the same statistics. The result guarantees the confidentiality of the original data, while providing microdata with accurate statistics. Methods for achieving such transformations are considered and analyzed through simulation.
Character manipulation in 1620 FORTRAN II
Authors: Poore Jesse H.
Published: July 2002

The suggested method of manipulating alphabetic characters in FORTRAN which appeared in this section of the August, 1962, issue of the
Communications of the ACM
has been incorporated into the IBM 1620 FORTRAN II system.
Fixed-word-length arrays in variable-word-length computers
Authors: Sonquiest John A.
Published: July 2002

Scientific users of small-scale variable-word-length computers, such as the IBM 1401, may frequently have the occasion to use fixed-word-length arrays. For instance, it is common practice to store matrices row-wise in linear arrays. A linear array whose elements are addresses is a common storage allocation scheme for handling pushdown lists.