bluuebunny/crossref_metadata_2025 huggingface dataset:
CRYSTALLINE SILICON BASED PHOTOVOLTAICS: TECHNOLOGY AND MARKET TRENDS
Authors: NIJS J. F. , SZLUFCIK J. , POORTMANS J. , MERTENS R. P.
Published: July 2002

An overview is given concerning industrial technologies, IMECS's advanced pilot line crystalline silicon solar cell technologies and medium term developments for industrial crystalline silicon terrestrial solar cell fabrication. Also IMEC's work on thin film crystalline silicon solar cells is shortly presented, all of this taking into account the existing market and technology trends.
PHOTOLUMINESCENCE FROM AMORPHOUS SILICON OXIDE FILMS PREPARED BY HFCVD TECHNIQUE
Authors: SALAZAR P. , CHÁVEZ F. , SILVA-ANDRADE F. , ILINSKII A. V. , MORALES N. , PEÑA-SIERRA R.
Published: July 2002

The photoluminescence (PL) properties of hydrogen (H) rich silicon oxide films prepared by hot filament enhanced chemical vapor deposition (HFCVD) have been studied. The observed PL change follow the change in the hydrogen incorporation, detected by transmission Fourier transfonn spectroscopy (FTIR). FTIR spectra show that the oxygen and hydrogen atoms are bonded to the same silicon atom. There is no evidence from the formation of OH groups.
Perturbative Evidence of Nonuniversality in the Quantized Hall Conductivity of A Disordered Relativistic 2D Electron Gas
Authors: Balić N. , de Carvalho C. A. A. , Cavalcanti R. M. , Donatis P.
Published: July 2002

We study a relativistic two-dimensional electron gas in the presence of a uniform external magnetic field and a random static scalar potential. We compute, in first order perturbation theory, the averages of the charge density and of the transverse conductivity for a white-noise potential, and show that, within this treatment, their quantized values are modified by the disorder.
ELECTRONIC STRUCTURES OF ENDOHEDRAL Sr@C60, Ba@C60, Fe@C60 and Mn@C60
Authors: LU JING , GE LIXIN , ZHANG XINWEI , ZHAO XIANGENG
Published: July 2002

Discrete-variational local density functional calculations on endoheral Sr @ C 60, Ba @ C 60, Fe @ C 60 and Mn @ C 60 are performed. The Sr (5s2) and Ba (6s2) atoms denote their two s valence electrons to the C 60 cage, described as [Formula: see text] and [Formula: see text]. The Fe (3d64s2) and Mn (3d54s2) atom are in only +1 valence, rather small oxidation number. The electron affinities and ionization potentials of the four endohedral fullerenes are given.
SHORT-RANGE CORRELATION EFFECTS IN A POLARON GAS IN GaAs–AlGaAs QUANTUM WELL WIRES
Authors: BORGES ANTÔNIO NEWTON , OSÓRIO FRANCISCO A. P. , MACHADO PAULO CÉSAR MIRANDA , HIPÓLITO OSCAR
Published: July 2002

We investigate the short-range correlation effects of plasmon–phonon collective excitations in a quantum well wire by using the self-consistent field approximation theory proposed by Singwi, Tosi, Land and Sjolander [Phys. Rev.176, 589 (1968)]. In our calculation model, we consider a three-subband model with only one populated, for a rectangular cross-section quantum well wire with infinite height for the potential barrier. We have verified that by decreasing the wire width (and/or decreasing the electronic density), the local field correction effects are increased. We compare the present results with those obtained within the Random Phase Approximation throughout the paper and found that the differences between the two calculation methods are more significant for the intrasubband plasmon.
ATTRACTORS FOR LATTICE DYNAMICAL SYSTEMS
Authors: BATES PETER W. , LU KENING , WANG BIXIANG
Published: July 2002

We study the asymptotic behavior of solutions for lattice dynamical systems. We first prove asymptotic compactness and then establish the existence of global attractors. The upper semicontinuity of the global attractor is also obtained when the lattice differential equations are approached by finite-dimensional systems.
VIBRATING QUANTUM BILLIARDS ON RIEMANNIAN MANIFOLDS
Authors: PORTER MASON A. , LIBOFF RICHARD L.
Published: July 2002

Quantum billiards provide an excellent forum for the analysis of quantum chaos. Toward this end, we consider quantum billiards with time-varying surfaces, which provide an important example of quantum chaos that does not require the semiclassical (ℏ → 0) or high quantum-number limits. We analyze vibrating quantum billiards using the framework of Riemannian geometry. First, we derive a theorem detailing necessary conditions for the existence of chaos in vibrating quantum billiards on Riemannian manifolds. Numerical observations suggest that these conditions are also sufficient. We prove the aforementioned theorem in full generality for one degree-of-freedom boundary vibrations and briefly discuss a generalization to billiards with two or more degrees-of-vibrations. The requisite conditions are direct consequences of the separability of the Helmholtz equation in a given orthogonal coordinate frame, and they arise from orthogonality relations satisfied by solutions of the Helmholtz equation. We then state and prove a second theorem that provides a general form for the coupled ordinary differential equations that describe quantum billiards with one degree-of-vibration boundaries. This set of equations may be used to illustrate KAM theory and also provides a simple example of semiquantum chaos. Moreover, vibrating quantum billiards may be used as models for quantum-well nanostructures, so this study has both theoretical and practical applications.
BIFURCATION ANALYSIS OF THE KURAMOTO–SIVASHINSKY EQUATION IN ONE SPATIAL DIMENSION
Authors: LI CHANGPIN , CHEN GUANRONG
Published: July 2002

In this Letter, we study the bifurcation of the Kuramoto–Sivashinsky (K–S) equation in one-spatial dimension with three kinds of boundary value conditions. Using the Liapunov–Schmidt reduction technique, the original equation is first reduced to one or two bifurcation equations, so that bifurcation analysis of the original equation can be transformed to that of the reduced-order systems, and can therefore be carried out in detail.
FAMILIES OF SCROLL GRID ATTRACTORS
Authors: YALÇIN MÜŞTAK E. , SUYKENS JOHAN A. K. , VANDEWALLE JOOS , ÖZOĞUZ SERDAR
Published: July 2002

In this paper a new family of scroll grid attractors is presented. These families are classified into three called 1D-, 2D- and 3D-grid scroll attractors depending on the location of the equilibrium points in state space. The scrolls generated from 1D-, 2D- and 3D-grid scroll attractors are located around the equilibrium points on a line, on a plane or in 3D, respectively. Due to the generalization of the nonlinear characteristics, it is possible to increase the number of scrolls in all state variable directions. A number of strange attractors from the scroll grid attractor families are presented. They have been experimentally verified using current feedback opamps. Also Lur'e representations are given for the scroll grid attractor families.
MULTI-USER RECEIVERS FOR SPREAD SPECTRUM COMMUNICATIONS BASED ON CHAOTIC SEQUENCES
Authors: ARGÜELLO FRANCISCO , BUGALLO MANUEL , AMOR MARGARITA
Published: July 2002

Spread spectrum based on chaotic sequences is an alternative to spread spectrum based on pseudo-noise sequences. In this letter we present the application of two multi-user detection methods (parallel and successive interference cancellation schemes) to this type of code division multiple access. We demonstrate that, also for chaotic sequence-based communications, multi-user receivers significantly improve the BER with respect to single-user receivers, and that their use is practically essential with a high number of users.
ON THE MATHEMATICAL CLARIFICATION OF THE SNAP-BACK-REPELLER IN HIGH-DIMENSIONAL SYSTEMS AND CHAOS IN A DISCRETE NEURAL NETWORK MODEL
Authors: LIN WEI , RUAN JIONG , ZHAO WEIRUI
Published: July 2002

We investigate the differences among several definitions of the snap-back-repeller, which is always regarded as an inducement to produce chaos in nonlinear dynamical system. By analyzing the norms in different senses and the illustrative examples, we clarify why a snap-back-repeller in the neighborhood of the fixed point, where all eigenvalues of the corresponding variable Jacobian Matrix are absolutely larger than 1 in norm, might not imply chaos. Furthermore, we theoretically prove the existence of chaos in a discrete neural networks model in the sense of Marotto with some parameters of the systems entering some regions. And the following numerical simulations and corresponding calculation, as concrete examples, reinforce our theoretical proof.
APPLICATION OF DISCRETE CHAOTIC DYNAMICAL SYSTEMS IN CRYPTOGRAPHY — DCC METHOD
Authors: KOTULSKI ZBIGNIEW , SZCZEPAŃSKI JANUSZ , GÓRSKI KAROL , PASZKIEWICZ ANDRZEJ , ZUGAJ ANNA
Published: July 2002

In the paper we propose a method of constructing cryptosystems, utilizing a nonpredictability property of discrete chaotic systems. We point out the requirements for such systems to ensure their security. The presented algorithms of encryption and decryption are based on multiple iteration of a certain dynamical chaotic system coming from gas dynamics models. A plaintext message specifies a part of the initial condition of the system (a particle's initial position). A secret key specifies the remaining part of initial condition (the particle's initial angle) as well as a sequence of discrete choices of the pre-images in the encryption procedure. We also discuss problems connected with the practical realization of such chaotic cryptosystems. Finally we demonstrate numerical experiments illustrating the basic properties of the proposed cryptosystem.
FRACTALIZATION OF BASIN BOUNDARY IN TWO-DIMENSIONAL NONINVERTIBLE MAPS
Authors: CATHALA J. C.
Published: July 2002

Properties of the basins of a two-dimensional noninvertible degenerated map is studied using the method of critical curves. More precisely, this paper considers a cubic map that belongs to the class of maps having the plane subdivided by the branches of the critical curve in three regions, two nonconnected with one preimage, the other with three distinct preimages. The fractalization of the basin of such an endomorphism is described.
PROFINITE METHODS IN SEMIGROUP THEORY
Authors: WEIL PASCAL
Published: July 2002

Many recent results in finite semigroup theory make use of profinite methods, that is, they rely on the study of certain infinite, compact semigroups which arise as projective limits of finite semigroups.

These ideas were introduced in semigroup theory in the 1980s, first to describe pseudovarieties in terms of so-called pseudo-identities: this is Reiterman's theorem, which can be viewed as the (much more complex) finite algebra analogue of Birkhoff's variety theorem. Soon, these methods were used in conjunction with virtually all the other approaches of finite semigroups, notably to study the decidability of product pseudovarieties.

This paper surveys the contribution of profinite methods and the way they enriched and modified finite semigroup theory.
GEODESIC DEVIATION IN THE BLACK STRING SPACETIME
Authors: CULETU H.
Published: July 2002

The equation of motion of test particles in the geometry of a black string trapped on a domain wall embedded in a five-dimensional AdS spacetime is studied. With an inversion transformation on the fifth coordinate "w," we obtain a simple form of the geodesics and the geodesics deviation. The equations for the separation vector ξα between two nearby geodesics are found, with ξ5(λ)=ξ(0)5 sin (λ/l), where l is the AdS radius, independent of the Schwarzschild potential U(r).
HYPERON-NUCLEON INTERACTIONS IN THE pp→K+Λp REACTION
Authors: KELKAR N. G. , JAIN B. K.
Published: July 2002

We present calculations of the invariant mass spectra of the Λp system for the exclusive pp→K+Λp reaction with the aim of studying the final state interaction between the Λ-hyperon and the proton. The reaction is described within a meson exchange framework and the final state Λp interaction is incorporated through an off-shell t-matrix for the Λp→Λp scattering, constructed using the available hyperon-nucleon (YN) potentials. The cross sections are found to be sensitive to the type of YN potential used especially at the Λ and Σ production thresholds. Hence, data on this exclusive reaction, which can be used to constrain the YN potentials are desirable.
MODEL OF THE DYNAMICS OF A BRANCHING SYSTEM OF THE GLIAL CELL LINEAGESIN VITRO
Authors: NOVAK J. P. , FEDOROFF S.
Published: July 2002

A genealogical model describing the dynamics of a binary branching system of astrocytes and microglia which takes into account a developmental hierarchy, is proposed. The model consists of a scheme of developmental pathways interconnecting the elements at various stages of development from a common progenitor to a nonproliferating end stage. To the elements at each stage are attributed probabilities of division, differentiation and quiescence. The pathway of any particular element at the end of each cycle is determined by a random-number generator according to the predetermined probabilities. The model is applied to colony formation in vitro. The development of each colony is followed for several cycles of division and theoretical results are compared to experimental values. Comparison of values obtained from several variants of the theoretical model with experimental data is then used to derive the most plausible scheme of branching pathways under given experimental conditions. The model is defined as follows: a common unlabeled progenitor with a high self-renewal potential differentiates into unlabeled monopotential precursors which further develop into astrocytes and microglia, identified experimentally as GFAP-positive cells and CR3-positive cells, respectively. Both the monopotential unlabeled cells and the identifiable progeny also have the capability of self-renewal.
DATA INTEGRATION IN DATA WAREHOUSING
Authors: CALVANESE DIEGO , DE GIACOMO GIUSEPPE , LENZERINI MAURIZIO , NARDI DANIELE , ROSATI RICCARDO
Published: July 2002

Information integration is one of the most important aspects of a Data Warehouse. When data passes from the sources of the application-oriented operational environment to the Data Warehouse, possible inconsistencies and redundancies should be resolved, so that the warehouse is able to provide an integrated and reconciled view of data of the organization. We describe a novel approach to data integration in Data Warehousing. Our approach is based on a conceptual representation of the Data Warehouse application domain, and follows the so-called local-as-view paradigm: both source and Data Warehouse relations are defined as views over the conceptual model. We propose a technique for declaratively specifying suitable reconciliation correspondences to be used in order to solve conflicts among data in different sources. The main goal of the method is to support the design of mediators that materialize the data in the Data Warehouse relations. Starting from the specification of one such relation as a query over the conceptual model, a rewriting algorithm reformulates the query in terms of both the source relations and the reconciliation correspondences, thus obtaining a correct specification of how to load the data in the materialized view.
The Boston Trading and Manufacturing Co. Ltd. (HK): Hemp, Fashion and the Environment
Authors: Fryxell Gerald E. , Kimbro Marinilka , Mottershead Terri
Published: July 2002

The Boston Trading and Manufacturing Company (Hong Kong) or (BTC-HK) highlights some of the dilemmas facing an entrepreneur who is operating in a multinational and multicultural context and who is differentiating a major product as being environmentally-friendly. The core idea behind the Boston Trading Company was simply to access low-cost labour and materials in Mainland China in order to manufacture backpacks for sale within Germany. Later, Andree conceived the idea of using hemp material and designs that would reduce waste and permit the products to be marketed as being environmentally-friendly. This "PURE®" product line timed the market well and has been very successful — allowing much higher mark ups than had been possible with the more traditional nylon product line. However, the hemp content in this product line had been permitted to drop to questionable levels and it was clear that its appeal had as much to do with its relationship with marijuana as its ecological advantages. Andree is also aware that his products are being marketed to two very different types of customers — environmentalists and marijuana users. The case touches on multiple themes, but is probably best used either in a business ethics subject or to highlight international management issues in an entreprenuership subject.
CONCURRENT VALIDITY OF PATIENT RATING SCALES IN ASSESSMENT OF OUTCOME AFTER ROTATOR CUFF REPAIR
Authors: Getahun Tajedin Y. , MacDermid Joy C. , Patterson Stuart D.
Published: July 2002

The purpose of this study was to compare the concurrent validity of four questionnaires in the assessment of outcome after rotator cuff repair. Sixty-two patients, who were at least two years post-rotator-cuff repair, completed three upper extremity scales: the Western Ontario Rotator Cuff (WORC) index, the Disabilities of the Arm, Shoulder and Hand (DASH) and the Simple Shoulder Test (SST), and a measure of general health status (SF-36). Internal and external rotation ranges of motion and isometric strength were measured. Pearson correlations were used to evaluate the construct whereby scores should be related to the severity of measured impairments. One-way ANOVA was used to determine the ability of the questionnaires to discriminate between groups expected to have different outcomes based on measured impairment or worker's compensation status. The upper extremity questionnaires demonstrated similar response distributions and were highly correlated (0.88 < r < 0.91). The response distribution of the SF-36 was different from the other scales and its correlation with them was moderate (0.58 < r < 0.75). The upper extremity measures demonstrated better correlations with measured impairments (0.18 < r < 0.56) than the SF-36 (0 < r < 0.40). All the questionnaires were able to discriminate between levels of impairment and worker's compensation status. This study supported the validity of upper extremity scales to measure cuff-related disability and suggests that the use of both specific and general health measures provides a more comprehensive evaluation of patient outcome.
MANAGING BOTH SIGN AND SIZE OF FLUCTUATIONS WITHIN THE n-ZIPF FRAMEWORK
Authors: VANDEWALLE N. , BRISBOIS F. , LEFEBVRE P. H.
Published: July 2002

We have performed a Zipf-like analysis of financial data. We emphasize new results: (i) the existence of long-range correlations for the sign of daily fluctuations of selected size; (ii) the existence of patterns and correlations in the world major trading places. The Zipf analysis allows also to measure the "domino effect" between trading places in the world.
OPTIMAL PORTFOLIOS UNDER THE THREAT OF A CRASH
Authors: KORN RALF , WILMOTT PAUL
Published: July 2002

We consider the determination of optimal portfolios under the threat of a crash. Our main assumption is that upper bounds for both the crash size and the number of crashes occurring before the time horizon are given. We make no probabilistic assumption on the crash size or the crash time distribution. The optimal strategies in the presence of a crash possibility are characterized by a balance problem between insurance against the crash and good performance in the crash-free situation. Explicit solutions for the log-utility case are given. Our main finding is that constant portfolios are no longer optimal ones.
HYPERCONTRACTIVITY VIA SPECTRAL THEORY
Authors: BODINEAU T. , ZEGARLINSKI B.
Published: July 2002

We prove hypercontractivity via spectral theory in a number of infinite dimensional models including the one-dimensional Ising model with nearest neighbours interaction and some non-commutative spin systems.
POISSON MEASURE AS THE SPECTRAL MEASURE OF JACOBI FIELD
Authors: BEREZANSKY YURIJ M.
Published: July 2002

A direct proof of the assertion that the spectral measure of a Poisson field of self-adjoint commuting operators is a Poisson measure is presented. This proof gives a possibility to generalize such a fact to more general situations.
Emerging Economies and International Financial Centers
Authors: Kaufman George G.
Published: July 2002

A number of emerging economies are considering directing public resources to developing an international financial center (IFC). They are doing so because of the perceived advantages of IFCs, including high value added, quick development, and low fixed-cost plant and equipment. But being an IFC also has costs, including high fragility, spillover of problems from the center to the domestic economy, and quick departure of footloose human capital. This paper evaluates the benefits and costs of becoming an IFC, enumerates the characteristics of IFCs, traces the history of IFCs, and describes recent changes in the ranking of major IFCs. It concludes that this may not be an opportune time for emerging economies to devote public resources to developing an IFC.
MULTI-PARTICLE STRUCTURES IN NON-SEQUENTIALLY REORGANIZED HARD SPHERE DEPOSITS
Authors: PUGNALONI LUIS A. , BARKER G. C. , MEHTA ANITA
Published: July 2002

We have examined extended structures, bridges and arches, in computer generated, non-sequentially stabilized, hard sphere deposits. The bridges and arches have well-defined distributions of sizes and shapes. The distribution functions reflect the contraints associated with hard particle packing and the details of the restructuring process. A subpopulation of string-like bridges has been identified. Bridges are fundamental microstructural elements in real granular systems and their sizes and shapes dominate considerations of structural properties and flow instabilities such as jamming.
USING CASE RETRIEVAL TO SEED GENETIC ALGORITHMS
Authors: OMAN STEPHEN , CUNNINGHAM PÁDRAIG
Published: July 2002

In this paper we evaluate the usefulness of seeding genetic algorithms (GAs) from a case-base. This is motivated by the expectation that the seeding will speed up the GA by starting the search in promising regions of the search space. We evaluate this case-based seeding on popular GA solutions to the Travelling Salesman Problem (TSP) and the Job-Shop Scheduling Problem (JSSP). We find that seeding the initial population gives the GA a head start and that this advantage is maintained to the end of the GA in both problem domains. In addition, we have also found that the scale of the initial advantage can be greatly improved through the introduction of problem specific information in the seeding process. Finally, the improvements of the seeded GA over the random GA can be used to reduce the number of generations required to find suitably fit solutions.
Towards a semantic view of an extended entity-relationship model
Authors: Gogolla Martin , Hohenstein Uwe
Published: July 2002

Nearly all query languages discussed recently for the Entity-Relationship (ER) model do not possess a formal semantics. Languages are often defined by means of examples only. The reason for this phenomenon is the essential gap between features of query languages and theoretical foundations like algebras and calculi. Known languages offer arithmetic capabilities and allow for aggregates, but algebras and calculi defined for ER models do not.

This paper introduces an extended ER model concentrating nearly all concepts of known so-called semantic data models in a few syntactical constructs. Moreover, we provide our extended ER model with a formal mathematical semantics. On this basis a well-founded calculus is developed taking into account data operations on arbitrary user-defined data types and aggregate functions. We pay special attention to arithmetic operations, as well as multivalued terms allowing nested queries, in a uniform and consistent manner. We prove our calculus only allows the formulation of safe terms and queries yielding a finite result, and to be (at least) as expressive as the relational calculi.
Computer system reliability and nuclear war
Authors: Borning Alan
Published: July 2002

Given the devastating consequences of nuclear war, it is appropriate to look at current and planned uses of computers in nuclear weapons command and control systems, and to examine whether these systems can fulfill their intended roles.
Update on National Science Foundation funding of the “Collaboratory”
Authors: Rosenberg Laurence C.
Published: July 2002

NSF-funded collaboratories are experimental and empirical research environments in which domain scientist work with computer, communications, behavioral and social scientists to design systems, participate in collaborative science, and conduct experiments to evaluate and improve the systems. These research projects are concerned with distributed and collaborative research that requires intense reliance on wide-area networks and the Internet, to bring together instruments, laboratories and researchers.
Representing extended entity-relationship structures in relational databases
Authors: Markowitz Victor M. , Shoshani Arie
Published: July 2002

A common approach to database design is to describe the structures and constraints of the database application in terms of a semantic data model, and then represent the resulting schema using the data model of a commercial database management system. Often, in practice,
Extended Entity-Relationship
(EER) schemas are translated into equivalent relational schemas. This translation involves different aspects: representing the EER schema using relational constructs, assigning names to relational attributes, normalization, and merging relations. Considering these aspects together, as is usually done in the design methodologies proposed in the literature, is confusing and leads to inaccurate results. We propose to treat separately these aspects and split the translation into four stages (modules) corresponding to the four aspects mentioned above. We define criteria for both evaluating the correctness of and characterizing the relationship between alternative relational representations of EER schemas.
Shortening the
OED
Authors: Blake G. Elizabeth , Bray Tim , Tompa Frank Wm.
Published: July 2002

Textual databases with highly variable structure can be usefully described by a grammar-defined model. One example of such a text is the
Oxford English Dictionary
. This paper describes a first attempt to apply technology based on this model to a real problem. A language called GOEDEL, which is a partial implementation of a set of grammar-defined database operators, was used to extract and alter a subset of the OED in order to assist the editors in their production of
The Shorter Oxford English Dictionary
. The implementation of the pstring data structure to describe a piece of text and the functions that operate on this pstring are illustrated with some detailed examples. The project was judged a success and the resulting program used in production by the Oxford University Press.
Consistency and orderability
Authors: Agrawal Divyakant , El Abbadi Amr , Singh Ambuj K.
Published: July 2002

The semantics of objects and transactions in database systems are investigated. User-defined predicates called
consistency assertions
are used to specify user programs. Three new correctness criteria are proposed. The first correctness criterion
consistency
is based solely on the users' specifications and admit nonserializable executions that are acceptable to the users. Integrity constraints of the database are maintained through consistency assertions. The second correctness criterion
orderability
is a generalization of view serializability and represents a weak notion of equivalence to a serial schedule. Finally, the third correctness criterion
strong order-ability
is introduced as a generalization of conflict serializability. Unlike consistency, the notions of orderability allow users to operate an isolation as maintenance of the integrity constrainst now becomes the responsibility of the database system.
GFUN
Authors: Salvy Bruno , Zimmermann Paul
Published: July 2002

We describe the GFUN package which contains functions for manipulating sequences, linear recurrences, or differential equations and generating functions of various types. This article is intended both as an elementary introduction to the subject and as a reference manual for the package.
An example-based mapping method for text categorization and retrieval
Authors: Yang Yiming , Chute Christopher G.
Published: July 2002

A unified model for text categorization and text retrieval is introduced. We use a training set of manually categorized documents to learn word-category associations, and use these associations to predict the categories of arbitrary documents. Similarly, we use a training set of queries and their related documents to obtain empirical associations between query words and indexing terms of documents, and use these associations to predict the related documents of arbitrary queries. A Linear Least Squares Fit (LLSF) technique is employed to estimate the likelihood of these associations. Document collections from the MEDLINE database and Mayo patient records are used for studies on the effectiveness of our approach, and on how much the effectiveness depends on the choices of training data, indexing language, word-weighting scheme, and morphological canonicalization. Alternative methods are also tested on these data collections for comparison. It is evident that the LLSF approach uses the relevance information effectively within human decisions of categorization and retrieval, and achieves a semantic mapping of free texts to their representations in an indexing language. Such a semantic mapping lead to a significant improvement in categorization and retrieval, compared to alternative approaches.
A taxonomy of computer program security flaws
Authors: Landwehr Carl E. , Bull Alan R. , McDermott John P. , Choi William S.
Published: July 2002

An organized record of actual flaws can be useful to computer system designers, programmers, analysts, administrators, and users. This survey provides a taxonomy for computer program security flaws, with an Appendix that documents 50 actual security flaws. These flaws have all been described previously in the open literature, but in widely separated places. For those new to the field of computer security, they provide a good introduction to the characteristics of security flaws and how they can arise. Because these flaws were not randomly selected from a valid statistical sample of such flaws, we make no strong claims concerning the likely distribution of actual security flaws within the taxonomy. However, this method of organizing security flaw data can help those who have custody of more representative samples to organize them and to focus their efforts to remove and, eventually, to prevent the introduction of security flaws.
Monte Carlo summation and integration applied to multiclass queuing networks
Authors: Ross Keith W. , Tsang Danny H. K. , Wang Jie
Published: July 2002

Although many closed multiclass queuing networks have a product-form solution, evaluating their performance measures remains nontrivial due to the presence of a normalization constant. We propose the application of Monte Carlo summation in order to determine the normalization constant, throughputs, and gradients of throughputs. A class of importance-sampling functions leads to a decomposition approach, where separate single-class problems are first solved in a setup module, and then the original problem is solved by aggregating the single-class solutions in an execution model. We also consider Monte Carlo methods for evaluating performance measures based on integral representations of the normalization constant; a theory for optimal importance sampling is developed. Computational examples are given that illustrate that the Monte Carlo methods are robust over a wide range of networks and can rapidly solve networks that cannot be handled by the techniques in the existing literature.
Reaching for objects in VR displays
Authors: Ware Colin , Balakrishnan Ravin
Published: July 2002

This article reports the results from three experimental studies of reaching behavior in a head-coupled stereo display system with a hand-tracking subsystem for object selection. It is found that lag in the head-tracking system is relatively unimportant in predicting performance, whereas lag in the hand-tracking system is critical. The effect of hand lag can be modeled by means of a variation on Fitts' Law with the measured system lag introduced as a multiplicative variable to the Fitts' Law index of difficulty. This means that relatively small lags can cause considerable degradation in performance if the targets are small. Another finding is that errors are higher for movement in and out of the screen, as compared to movements in the plane of the screen, and there is a small (10%) time penalty for movement in the Z direction in all three experiments. Low frame rates cause a degradation in performance; however, this can be attributed to the lag which is caused by low frame rates, particularly if double buffering is used combined with early sampling of the hand-tracking device.
Software trustability analysis
Authors: Howden W. E. , Huang Yudong
Published: July 2002

A measure of software dependability called trustability is described. A program p has trustability T if we are at least T confident that p is free of faults. Trustability measurement depends on detectability. The detectability of a method is the probability that it will detect faults, when there are faults present. Detectability research can be used to characterize conditions under which one testing and analysis method is more effective than another. Several detectability results that were only previously described informally, and illustrated by example, are proved. Several new detectability results are also proved. The trustability model characterizes the kind of information that is needed to justify a given level of trustability. When the required information is available, the trustability approach can be used to determine strategies in which methods are combined for maximum effectiveness. It can be used to determine the minimum amount of resources needed to guarantee a required degree of trustability, and the maximum trustability that is achievable with a given amount of resources. Theorems proving several optimization results are given. Applications of the trustability model are discussed. Methods for the derivation of detectability factors, the relationship between trustability and operational reliability, and the relationship between the software development process and trustability are described.
A time-sensitive object model for real-time systems
Authors: Callison H. Rebecca
Published: July 2002

Process-oriented models for real-time systems focus on the timing constraints of
processes
, a focus that can adversely affect resulting designs. Data dependencies between processes create scheduling interactions that limit the times at which processes may execute. Processes are then designed to fit available windows in the overall system schedule. “Fitting in” frequently involves fragmenting processes to fit scheduling windows and/or designing program and data structures for speed rather than for program comprehension. The result is often a system with very sensitive timing that is hard to understand and maintain. As an alternative to process-oriented design, we present time-sensitive objects: a data-oriented model for real-time systems. The time-sensitive object (TSO) model structures systems as time-constrained data, rather than time constrained processing. Object values are extended to object histories in which a sequence of time constrained values describe the evolution of the object over time. Systems comprise a set of objects and their dependencies. The TSO model describes the effects of object operations and the propagation of change among related objects. Periodic objects, a class of objects within the TSO model, are described in detail in this article and compared with traditional periodic processes. Advantages of time-sensitive objects are identified, including greater scheduling independence when processes have data dependencies, more opportunity for concurrency, and greater inherent capability for detection of and tolerance to timing errors.
Arithmetic coding for data compression
Authors: Witten Ian H. , Neal Radford M. , Cleary John G.
Published: July 2002

The state of the art in data compression is arithmetic coding, not the better-known Huffman method. Arithmetic coding gives greater compression, is faster for adaptive models, and clearly separates the model from the channel encoding.
Pracniques: Meansort
Authors: Motzkin Dalia
Published: July 2002

This paper presents an efficient algorithm based on Quicksort. The Quicksort algorithm is known to be one of the most efficient sorting techniques; however, one of the drawbacks of this method is its worst case situation of 0 (n
2
) comparisons. The algorithm presented here improves the average behavior of Quicksort and reduces the occurrence of worst case situations.
Efficient vector and parallel manipulation of tensor products
Authors: Buis Paul E. , Dyksen Wayne R.
Published: July 2002

We present efficient vector and parallel methods for manipulating tensor products of matrices. We consider both computing the matrix-vector product (A
1
Ä¼ÄA
K
)x and solving the system of linear equations (A
1
Ä¼ÄA
K
)x=b. The methods described are independent of
K
. We accompany this article with a companion algorithm which describes an implementation of a complete set of tensor product routines based on LAPACK and the Level 2 and 3 Basic Linear Algebra Subprograms (BLAS) which provide vectorization and parallelization.
Algorithm 755: ADOL-C
Authors: Griewank Andreas , Juedes David , Utke Jean
Published: July 2002

The C++ package ADOL-C described here facilitates the evaluation of first and higher derivatives of vector functions that are defined by computer programs written in C or C++. The resulting derivative evaluation routines may be called from C/C++, Fortran, or any other language that can be linked with C. The numerical values of derivative vectors are obtained free of truncation errors at a small multiple of the run-time and randomly accessed memory of the given function evaluation program. Derivative matrices are obtained by columns or rows. For solution curves defined by ordinary differential equations, special routines are provided that evaluate the Taylor coefficient vectors and their Jacobians with respect to the current state vector. The derivative calculations involve a possibly substantial (but always predictable) amount of data that are accessed strictly sequentially and are therefore automatically paged out to external files.
Note on the end game in homotopy zero curve tracking
Authors: Sosonkina Maria , Watson Layne T. , Stewart David E.
Published: July 2002

Homotopy algorithms to solve a nonlinear system of equations
f(x)
= 0 involve tracking the zero curve of a homotopy map
p(a, λ, x)
from λ = 0 until λ = 1. When the algorithm nears or crosses the hyperplane λ = 1, an “end game” phase is begun to compute the solution
x¯
satisfying
p(a, λ, x¯) = f(x¯)
= 0. This note compares several end game strategies, including the one implemented in the normal flow code FIXPNF in the homotopy software package HOMPACK.
Continuous profiling
Authors: Anderson Jennifer M. , Berc Lance M. , Dean Jeffrey , Ghemawat Sanjay , Henzinger Monika R. , Leung Shun-Tak A. , Sites Richard L. , Vandevoorde Mark T. , Waldspurger Carl A. , Weihl William E.
Published: July 2002

This article describes the Digital Continuous Profiling Infrastructure, a sampling-based profiling system designed to run continuously on production systems. The system supports multiprocessors, works on unmodified executables, and collects profiles for entire systems, including user programs, shared libraries, and the operating system kernel. Samples are collected at a high rate (over 5200 samples/sec. per 333MHz processor), yet with low overhead (1–3% slowdown for most workloads). Analysis tools supplied with the profiling system use the sample data to produce a precise and accurate accounting, down to the level of pipeline stalls incurred by individual instructions, of where time is bring spent. When instructions incur stalls, the tools identify possible reasons, such as cache misses, branch mispredictions, and functional unit contention. The fine-grained instruction-level analysis guides users and automated optimizers to the causes of performance problems and provides important insights for fixing them.
Efficient clipping of arbitrary polygons
Authors: Greiner Günther , Hormann Kai
Published: July 2002

Clipping 2D polygons is one of the basic routines in computer graphics. In rendering complex 3D images it has to be done several thousand times. Efficient algorithms are therefore very important. We present such an efficient algorithm for clipping arbitrary 2D-polygons. The algorithm can handle arbitrary closed polygons, specifically where the clip and subject polygons may self-intersect. The algoirthm is simple and faster that Vatti's (1992) algorithm, which was designed for the general case as well. Simple modifications allow determination of union and set-theoretic differences of two arbitrary polygons.
Project Nick: meetings augmentation and analysis
Authors: Cook Peter , Ellis Clarence , Graf Mike , Rein Gail , Smith Tom
Published: July 2002

The Software Technology Program of MCC is investigating the early part of the design process, before requirements are established, for large-scale distributed systems. Face-to-face meetings are an important activity during this phase of a project since they provide a medium for direction, exploration, and consensus building. Project Nick is attempting to apply automated facilities to the process, conduct, and semantic capture of design meetings. Primary topics covered in this paper are meeting analysis, meeting augmentation, and a model of meeting progression that serves as the framework for our work.
Crowds
Authors: Reiter Michael K. , Rubin Aviel D.
Published: July 2002

In this paper we introduce a system called Crowds for protecting users' anonymity on the world-wide-web. Crowds, named for the notion of “blending into a crowd,” operates by grouping users into a large and geographically diverse group (crowd) that collectively issues requests on behalf of its members. Web servers are unable to learn the true source of a request because it is equally likely to have originated from any member of the crowd, and even collaborating crowd members cannot distinguish the originator of a request from a member who is merely forwarding the request on behalf of another. We describe the design, implementation, security, performance, and scalability of our system. Our security analysis introduces
degrees of anonymity
as an important tool for describing and proving anonymity properties.
Optimization techniques for queries with expensive methods
Authors: Hellerstein Joseph M.
Published: July 2002

Object-relational database management systems allow knowledgeable users to define new data types as well as new methods (operators) for the types. This flexibility produces an attendant complexity, which must be handled in new ways for an object-relational database management system to be efficient. In this article we study techniques for optimizing queries that contain time-consuming methods. The focus of traditional query optimizers has been on the choice of join methods and orders; selections have been handled by “pushdown” rules. These rules apply selections in an arbitrary order before as many joins as possible, using th e assumption that selection takes no time. However, users of object-relational systems can embed complex methods in selections. Thus selections may take significant amounts of time, and the query optimization model must be enhanced. In this article we carefully define a query cost framework that incorporates both selectivity and cost estimates for selections. We develop an algorithm called Predicate Migration, and prove that it produces optimal plans for queries with expensive methods. We then describe our implementation of Predicate Migration in the commercial object-relational database management system Illustra, and discuss practical issues that affect our earlier assumptions. We compare Predicate Migration to a variety of simplier optimization techniques, and demonstrate that Predicate Migration is the best general solution to date. The alternative techniques we present may be useful for constrained workloads.
Self-adapting Fortran 77 machine constants
Authors: Gay David M. , Grosse Eric
Published: July 2002

This note discusses user dissatisfaction with the need to uncomment data statements in Algorithm 528, comments on alternative approaches tried by the community, and proposes a solution that is both automatic and safe.
Active database systems
Authors: Paton Norman W. , Díaz Oscar
Published: July 2002

Active database systems support mechanisms that enable them to respond automatically to events that are taking place either inside or outside the database system itself. Considerable effort has been directed towards improving understanding of such systems in recent years, and many different proposals have been made and applications suggested. This high level of activity has not yielded a single agreed-upon standard approach to the integration of active functionality with conventional database systems, but has led to improved understanding of active behavior description languages, execution models, and architectures. This survey presents the fundamental characteristics of active database systems, describes a collection of representative systems within a common framework, considers the consequences for implementations of certain design decisions, and discusses tools for developing active applications.
Database hosting in strongly-typed programming languages
Authors: Bever Martin , Lockemann Peter C.
Published: July 2002

Database system support has become an essential part of many computer applications, which have extended beyond the more traditional commercial applications to, among others, engineering applications. Correspondingly, application programming with the need to access databases has progressively shifted to scientifically oriented languages.

Modern developments in these languages are characterized by advanced mechanisms for the liberal declaration of data types, for type checking, and facilities for modularization of large programs. The present paper examines how a DBMS can be accessed from such a language in a way that conforms to its syntax and utilizes its type-checking facilities, without modifying the language specification itself, and hence its compilers. The basic idea is to rely on facilities for defining modules as separately compilable units, and to use these to declare user-defined abstract data types.

The idea is demonstrated by an experiment in which a specific DBMS (ADABAS) is hosted in the programming language (LIS). The paper outlines a number of approaches and their problems, shows how to embed the DML into LIS, and how a more user-oriented DML can be provided in LIS.
Formal semantics for time in databases
Authors: Clifford James , Warren David S.
Published: July 2002

The concept of a historical database is introduced as a tool for modeling the dynamic nature of some part of the real world. Just as first-order logic has been shown to be a useful formalism for expressing and understanding the underlying semantics of the relational database model, intensional logic is presented as an analogous formalism for expressing and understanding the temporal semantics involved in a historical database. The various components of the relational model, as extended to include historical relations, are discussed in terms of the model theory for the logic IL
s
, a variation of the logic IL formulated by Richard Montague. The modal concepts of intensional and extensional data constraints and queries are introduced and contrasted. Finally, the potential application of these ideas to the problem of natural language database querying is discussed.