bluuebunny/crossref_metadata_2025 huggingface dataset:
Deadlock detection in distributed databases
Authors: Knapp Edgar
Published: July 2002

The problem of deadlock detection in distributed systems has undergone extensive study. An important application relates to distributed database systems. A uniform model in which published algorithms can be cast is given, and the fundamental principles on which distributed deadlock detection schemes are based are presented. These principles represent mechanisms for developing distributed algorithms in general and deadlock detection schemes in particular. In addition, a hierarchy of deadlock models is presented; each model is characterized by the restrictions that are imposed upon the form resource requests can assume. The hierarchy includes the well-known models of resource and communication deadlock. Algorithms are classified according to both the underlying principles and the generality of resource requests they permit. A number of algorithms are discussed in detail, and their complexity in terms of the number of messages employed is compared. The point is made that correctness proofs for such algorithms using operational arguments are cumbersome and error prone and, therefore, that only completely formal proofs are sufficient for demonstrating correctness.
Many hard examples for resolution
Authors: Chvátal Vašek , Szemerédi Endre
Published: July 2002

For every choice of positive integers
c
and
k
such that
k
≥ 3 and
c
2

-
k

≥ 0.7, there is a positive number ε such that, with probability tending to 1 as
n
tends to ∞, a randomly chosen family of
cn
clauses of size
k
over
n
variables is unsatisfiable, but every resolution proof of its unsatisfiability must generate at least (1 + ε)

n

clauses.
A fast approach to computing exact solutions to the resource-constrained scheduling problem
Authors: Narasimhan M. , Ramanujam J.
Published: July 2002

This article presents an algorithm that substantially reduces the computational effort required to obtain the exact solution to the Resource Constrained Scheduling (RCS) problem. The reduction is obtained by (a) using a branch-and-bound search technique, which computes both upper and lower bounds, and (b) using efficient techniques to accurately estimate the possible time-steps at which each operation can be scheduled and using this to prune the search space. Results on several benchmarks with varying resource constraints indicate the clear superiority of the algorithm presented here over traditional approaches using integer linear programming, with speed-ups of several orders of magnitude.
A case study in the performance and scalability of optimization algorithms
Authors: Benson Steven J. , McInnes Lois Curfman , Moré Jorge J.
Published: July 2002

We analyze the performance and scalabilty of algorithms for the solution of large optimization problems on high-performance parallel architectures. Our case study uses the GPCG (gradient projection, conjugate gradient) algorithm for solving bound-constrained convex quadratic problems. Our implementation of the GPCG algorithm within the Toolkit for Advanced Optimization (TAO) is available for a wide range of high-performance architectures and has been tested on problems with over 2.5 million variables. We analyze the performance as a function of the number of variables, the number of free variables, and the preconditioner. In addition, we discuss how the software design facilitates algorithmic comparisons.
Knowledge encapsulation for focused search from pervasive devices
Authors: Aridor Yariv , Carmel David , Maarek Yoelle S. , Soffer Aya , Lempel Ronny
Published: July 2002

Mobile knowledge seekers often need access to information on the Web during a meeting or on the road, while away from their desktop. A common practice today is to use pervasive devices such as Personal Digital Assistants or mobile phones. However, these devices have inherent constraints (e.g., slow communication, form factor) which often make information discovery tasks impractical.In this paper, we present a new focused-search approach specifically oriented for the mode of work and the constraints dictated by pervasive devices. It combines focused search within specific topics with encapsulation of topic-specific information in a persistent repository. One key characteristic of these persistent repositories is that their footprint is small enough to fit on local devices, and yet they are rich enough to support many information discovery tasks in disconnected mode. More specifically, we suggest a representation for topic-specific information based on "knowledge-agent bases" that comprise all the information necessary to access information about a topic (under the form of key concepts and key Web pages) and assist in the full search process from query formulation assistance to result scanning on the device itself. The key contribution of our work is the coupling of focused search with encapsulated knowledge representation making information discovery from pervasive devices practical as well as efficient. We describe our model in detail and demonstrate its aspects through sample scenarios.
The impact of robotics on computer science
Authors: Hopcroft John E.
Published: July 2002

The rapid development of robotics and the resulting need for computer scientists to be better trained in traditional mathematics necessitate changes in computer science curricula.
GERTIS: a Dempster-Shafer approach to diagnosing hierarchical hypotheses
Authors: Yen John
Published: July 2002

Gertis—a prototype expert system—not only demonstrates the feasibility of applying the Dempster-Shafer-based reasoning model to diagnosing hierarchically related hypotheses, but also suggests ways to generate better explanations by using knowledge about the structure of the hypothesis space and knowledge about the intended effects of the rules.
Efficient optimization of simple chase join expressions
Authors: Atzeni Paolo , Chan Edward P. F.
Published: July 2002

Simple chase join expressions are relational algebra expressions, involving only projection and join operators, defined on the basis of the functional dependencies associated with the database scheme. They are meaningful in the weak instance model, because for certain classes of schemes, including independent schemes, the total projections of the representative instance can be computed by means of unions of simple chase join expressions. We show how unions of simple chase join expressions can be optimized efficiently, without constructing and chasing the corresponding tableaux. We also present efficient algorithms for testing containment and equivalence, and for optimizing individual simple chase join expressions.
GRAP—a language for typesetting graphs
Authors: Bentley Jon L. , Kernighan Brian W.
Published: July 2002

The authors describe a system that makes it easy and convenient to describe graphs and to include them as an integral part of the document formatting process.
The combinatorics of local constraints in model-based recognition and localization from sparse data
Authors: Grimson W. Eric L.
Published: July 2002

The problem of recognizing
what
objects are
where
in the workspace of a robot can be cast as one of searching for a consistent matching between sensory data elements and equivalent model elements. In principle, this search space is enormous, and to control the potential combinatorial explosion, constraints between the data and model elements are needed. A set of constraints for sparse sensory data that are applicable to a wide variety of sensors are derived, and their characteristics are examined. Known bounds on the complexity of constraint satisfaction problems are used, together with explicit estimates of the effectiveness of the constraints derived for the case of sparse, noisy, three-dimensional sensory data, to obtain general theoretical bounds on the number of interpretations expected to be consistent with the data. It is shown that these bounds are consistent with empirical results reported previously. The results are used to demonstrate the graceful degradation of the recognition technique with the presence of noise in the data, and to predict the number of data points needed, in general, to uniquely determine the object being sensed.
Preserving and using context information in interprocess communication
Authors: Peterson Larry L. , Buchholz Nick C. , Schlichting Richard D.
Published: July 2002

When processes in a network communicate, the messages they exchange define a partial ordering of externally visible events. While the significance of this partial order in distributed computing is well understood, it has not been made an explicit part of the communication substrate upon which distributed programs are implemented. This paper describes a new interprocess communication mechanism, calledPsync, that explicitly encodes this partial ordering with each message. The paper shows how Psync can be efficiently implemented on an unreliable communications network, and it demonstrates how conversations serve as an elegant foundation for ordering messages exchanged in a distributed computation and for recovering from processor failures.
Computer accessibility for federal workers with disabilities: it's the law
Authors: Ladner Richard E.
Published: July 2002

In 1986, Congress passed Public Law 99-506, the "Rehabilitation Act Amendments of 1986." This law, amending the famous Rehabilitation Act of 1973, contains a small section, titled "Electronic Equipment Accessibility," Section 508, which may have significant impact on the design of computer systems and their accessibility by workers with disabilities. The bill became law when it was signed by former President Reagan on October 21, 1986.

The purpose of this article is to inform concerned computer professionals of Section 508, outline the guidelines and regulations pursuant to the law, describe some of the reaction to the guidelines and regulations, and describe some of the challenges for the future in meeting the computer accessibility needs of users with disabilities.

Section 508 was developed because it was realized that government offices were rapidly changing into electronic offices with microcomputers on every desk. In order for persons with disabilities to keep their jobs or gain new employment in the government, Congress decided it was necessary to make provisions to guarantee accessibility to microcomputers and other electronic office equipment. The driving principle behind Section 508 can be found in Section 504 of the Rehabilitation Act of 1973 which states:

No otherwise qualified handicapped individual in the United States . . . shall, solely by reason of his handicap, be excluded from the participation in, be denied the benefits of, or be subjected to discrimination under any program or activity receiving Federal financial assistance.

It should be stated off the top that the scope of Section 508 is not as broad as Section 504. In particular, Section 508 only applies to direct purchases by the federal government and
not
to purchases made by all programs receiving government funding.

Section 508 does not specify what the guidelines should be nor does it delineate a philosophy on which to base the guidelines. A committee established by the National Institute on Disability and Rehabilitation Research (NIDRR) and the General Services, Administration (GSA), in consultation with the electronics industry, rehabilitation engineers, and disabled computer professionals worked for a year developing the philosophy and guidelines which will significantly affect the purchase of electronic office equipment, including computers and software, by the federal government, the largest computer customer in the world.
Some negative results concerning prime number generators
Authors: Pritchard Paul
Published: July 2002

Programs attributed to Wirth and Misra for generating the prime numbers up to a specified limit are investigated. It is shown that Wirth's program is incorrect according to three increasingly weak criteria, and a composite number is exhibited that the program accepts as prime. This is the smallest known counterexample, and could not have been found by the usual method of program testing—the program would run for trillions of years on the fastest computer before reaching it! Closely related counterexamples are given to a conjecture of Misra concerning his program. An appendix gives a particularly simple algorithmic proof of the Chinese remainder theorem.
Congress tackless computer abuse
Authors: Steier Rosalie
Published: July 2002

Congress has been taking an active interest in protecting information stored in computers. Congressional investigations and media reports have highlighted the vulnerability of computer systems to abuse and mis-use. Recent accounts of “system hackers” describe young students and others who gain illegal access to systems, thereby obtaining information and services, as well as disrupting systems.
MIS in Soviet industrial enterprise: the limits of reform from above
Authors: McHenry William K. , Goodman Seymour E.
Published: July 2002

The USSR has carried out a large-scale program to bring computer-based information systems, called Automated Enterprise Management Systems (ASUPs), to industrial enterprises. This program illustrates the extent to which computer-based information systems are inextricably embedded in the surrounding social, economic, and political systems.
The report of the ACM Longe-Range Planning Committee: a summary
Authors: Deringer Dorothy , Brandin David , Fletcher Dexter , Jacobstein Neil
Published: July 2002

The Committee evaluates ACM as it exists today, and makes recommendations for the future.
DATAPLEX: an access to heterogeneous distributed databases
Authors: Chung Chin-Wan
Published: July 2002

Diverse database management systems are used in large organizations. The heterogeneous distributed database system (DDS) can provide a flexible intergration of diverse databases for users and applications. This is because it allows for retrieval and update of distributed data under different data systems giving the illusion of accessing a single centralized database system.
Phoenix: a safe in-memory file system
Authors: Gait Jason
Published: July 2002

Phoenix contains two timestamped versions of the in-memory file system allowing for a reserve version that ensures safety for diskless computers with battery-powered memeory.
The semiconductor market in the European community
Authors: Chiarodo Roger A. , Mussehl Judee M.
Published: July 2002

The authors discuss the impact of three EC rules of origin on printed circuit boards and on the United States semiconductor industry, which has been the largest exporter to Europe.
Cost-error relationships in A* tree-searching
Authors: Davis Henry W.
Published: July 2002

Pearl has shown that, in admissible A* tree-searching, the expected number of nodes expanded is bounded above and below by exponential functions of heuristic error. An additional assumption required for the validity of Pearl's argument is given. The assumption's significance and interpretation are discussed.
Performing geometric transformations by program transformation
Authors: Nicholl Robin A. , Nicholl Tina M.
Published: July 2002

Problems in geometry often possess symmetry properties that may be exploited in order to develop solutions. Algorithms based on these symmetry properties will frequently use geometric transformations to transform one case into another (symmetric) case. One advantage of this approach is that the algorithm avoids enumeration of cases and thus is shorter and generally easier to read. One disadvantage is that some additional execution time is required to perform these transformations. We describe how simple program equivalences may be used as program transformations to eliminate this additional execution time from programs that use geometric transformations. This approach has been used to develop an efficient implementation of a new algorithm for the two-dimensional line-clipping problem.
Self-assessment procedure XXI: a self-assessment procedure on concurrency
Authors: Rudolph Brain A.
Published: July 2002

A self-assessment procedure on concurrency
Explaining ambiguity in a formal query language
Authors: Wald Joseph A. , Sorenson Paul G.
Published: July 2002

The problem of generating reasonable natural language-like responses to queries formulated in nonnavigational query languages with logical data independence is addressed. An extended ER model, the Entity-Relationship-Involvement model, is defined which assists in providing a greater degree of logical data independence and the generation of natural language explanations of a query processor's interpretation of a query. These are accomplished with the addition of the concept of an involvement to the model. Based on involvement definitions in a formally defined data definition language, DDL, an innovative strategy for generating explanations is outlined and exemplified. In the conclusion, possible extensions to the approach are given.
Nondeterministic polynomial-time computations and models of arithmetic
Authors: Máté Attila
Published: July 2002

A semantic, or model theoretic, approach is proposed to study the problems P =? NP and NP =? co-NP. This approach seems to avoid the difficulties that recursion-theoretic approaches appear to face in view of the result of Baker et al. on relativizations of the P =? NP question; moreover, semantical methods are often simpler and more powerful than syntactical ones. The connection between the existence of certain partial extensions of nonstandard models of arithmetic and the question NP =? co-NP is discussed. Several problems are stated about nonstandard models, and a possible link between the Davis-Matijasevi@@@@-Putnam-Robinson theorem on Diophantine sets and the NP =? co-NP question is mentioned.
Nondeterministic linear-time tasks may require substantially nonlinear deterministic time in the case of sublinear work space
Authors: Gurevich Yuri
Published: July 2002

A technique is developed for establishing lower bounds on the computational complexity of certain natural problems. The results have the form of time-space trade-off and exhibit the power of nondeterminism. In particular, a form of the clique problem is defined, and it is proved that:

a nondeterministic log-space Turing machine solves the problem in linear time, but

no deterministic machine (in a very general use of this term) with sequential-access input tape and work space
n
σ
solves the problem in time
n
1+τ
if σ + 2τ < 1/2.
Legally speaking: should program algorithms be patented
Authors: Samuelson Pamela
Published: July 2002

In the Legally Speaking column last May [6], we reported on a survey conducted at last year's ACM-sponsored Conference on Computer-Human Interaction in Austin, Tex. Among the issues about which the survey inquired was whether the respondents thought patent protection should be available for various aspects of computer programs. The 667 respondents overwhelmingly supported copyright protection for source and object code although they strongly opposed copyright or patent protection for “look and feel” and most other aspects of programs. Algorithms were the only aspect of programs for which there was more than a small minority of support for patent protection. Nevertheless, more than half of the respondents I opposed either copyright or patent protection for algorithms. However, nearly 40 percent of the respondents regarded algorithms as appropriately protected by patents. (Another eight percent would have copyright law protect them.)

We should not be surprised that these survey findings reflect division within the technical community about patents as a form of protection for this important kind of computer program innovation. A number of prominent computer professionals who have written or spoken about patent protection for algorithms or other innovative aspects of programs have either opposed or expressed reservations about this form of protection for software [2, 4, 5].

This division of opinion, of course, has not stopped many firms and some individuals from seeking patent protection for algorithms or other software innovations [8]. Although the Refac Technology patent infringement lawsuit against Lotus and other spreadsheet producers may be in some jeopardy, it and other software patent lawsuits have increased awareness of the new availability of software patents. This situation, in turn, has generated some heated discussion over whether this form of legal protection will be in the industry's (and society's) long-term best interests.

The aim of this column is to acquaint readers with the legal debate on patent protection for algorithms and other computer program innovations, an issue which seems to be as divisive among lawyers as those in the computer field. [3, 9].
Natural language understanding and speech recognition
Authors: White George M.
Published: July 2002

Natural language understanding must be an integral part of any automatic speech recognition system that attempts to deal with interactive problem solving. The methods for representing and integrating knowledge from different sources may be valuable for the understanding process as well as speech recognition.
Algorithm 646
Authors: Crawford Charles R.
Published: July 2002

PDFIND is a FORTRAN-77 implementation of an algorithm that finds a positive definite linear combination of two symmetric matrices, or determines that such a combination does not exist. The algorithm is designed to be independent of the data structures used to store the matrices. The user must provide a subroutine, CHLSKY, which acts as an interface between PDFIND and the matrix data structures. CHLSKY also provides the user control over the number of iterations of the algorithm. Implementations of CHLSKY are included which call LINPAC routines for full matrices as well as symmetric banded matrices.
Accurate and efficient testing of the exponential and logarithm functions
Authors: Tang Ping-Tak Peter
Published: July 2002

Table-driven techniques can be used to test highly accurate implementation of EXP LOG. The largest error observeed in EXP and LOG accurately to within 1/500 unit in the last place are reported in our tests. Methods to verify the tests' reliability are discussed. Results of applying the tests to our own as well as to a number of other implementations of EXP and LOG are presented.
A study of scalar compilation techniques for pipelined supercomputers
Authors: Weiss Shlomo , Smith James E.
Published: July 2002

This paper studies two compilation techniques for enhancing scalar performance in high-speed scientific processors: software pipelining and loop unrolling. We study the impact of the architecture (size of the register file) and of the hardware (size of instruction buffer) on the efficiency of loop unrolling. We also develop a methodology for classifying software pipelining techniques. For loop unrolling, a straightforward scheduling algorithm is shown to produce near-optimal results when not inhibited by recurrences or memory hazards. Our study indicates that the performance produced with a modified CRAY-1S scalar architecture and a code scheduler utilizing loop unrolling is comparable to the performance achieved by the CRAY-1S with a vector unit and the CFT vectorizing compiler.

Finally, we show that the combination of loop unrolling and dynamic software pipelining, as implemented by a decoupled computer, substantially outperforms the vector CRAY-1S.
Inside risks: ghosts, mysteries and uncertainty
Authors: Neumann Peter G.
Published: July 2002

Background: Perhaps the most frustrating of all the Risks Forum cases are those in which uncertainty and doubts remain to spook us long after the event.
A decision theoretic approach to information retrieval
Authors: Moore James C. , Richmond William B. , Whinston Andrew B.
Published: July 2002

We present the file search problem in a decision-theoretic framework, and discuss a variation of it that we call the common index problem. The goal of the common index problem is to return the best available record in the file, where
best
is in terms of a class of user preferences. We use dynamic programming to construct an optimal algorithm using two different optimality criteria, and we develop sufficient conditions for obtaining complete information.
Legally speaking: how to interpret the Lotus decision (and how not to)
Authors: Samuelson Pamela
Published: July 2002

On June 28, 1990, a federal court judge in Boston made public his decision in favor of Lotus Development Corporation in its software copyright lawsuit against Paperback Software. People in the software industry had been waiting for this decision since the lawsuit was first filed in January 1987, certain that it would be a landmark case and would resolve many vexing questions about copyright protection for user interfaces.

The trade press has abounded with varying interpretations of Judge Keeton's opinion in the Lotus case: Some have said the decision is a narrow one, making illegal only the direct copying of another firm's interface [9]; Some have seen it has a much broader ruling—one that will have a chilling effect on development of competitive software products [5]; Others have asserted the case draws a reasonable line, and will have a positive effect overall [4]; Several have argued the ruling will be harmful because it ignores the interests of users of software, and will make standardization of user interfaces impossible to achieve. [3] Still others perceive the opinion as only setting the stage for a new confrontation over the issues in the appellate courts. [1] Lotus has given some indication of how broadly it interprets the Paperback decision by filing a new round of user interface copyright lawsuits against two of its other spreadsheet competitors.

his column, rather than just adding one more interpretation of the Lotus decision to the bin of those already expressed, will give the reader a glimpse of the nature of the legal process and of judicial opinions so he or she can see why people can interpret the Lotus opinion differently. The following three factors make it difficult to know what the Lotus decision means: 1) The legal process is not yet over, and the meaning of the case will depend in part on the outcome of this further process. 2) While Judge Keeton makes some statements that seem to suggest his ruling is a narrow one, some of his other statements could be interpreted much more broadly. 3) Even from unambiguous statements Judge Keeton makes, different people can draw reasonable but nonetheless differing inferences about what the judge would do in similar (though somewhat different) cases. For these reasons, it is impossible to know with any certainty what the law concerning copyright protection for user interfaces is in the aftermath of the Lotus decision.
Efficient Delaunay triangulation using rational arithmetic
Authors: Karasick Michael , Lieber Derek , Nackman Lee R.
Published: July 2002

Many fundamental tests performed by geometric algorithms can be formulated in terms of finding the sign of a determinant. When these tests are implemented using fixed precision arithmetic such as floating point, they can produce incorrect answers; when they are implemented using arbitrary-precision arithmetic, they are expensive to compute. We present adaptive-precision algorithms for finding the signs of determinants of matrices with integer and rational elements. These algorithms were developed and tested by integrating them into the Guibas-Stolfi Delaunay triangulation algorithm. Through a combination of algorithm design and careful engineering of the implementation, the resulting program can triangulate a set of random rational points in the unit circle only four to five times slower than can a floating-point implementation of the algorithm. The algorithms, engineering process, and software tools developed are described.
FLEXIBILITY OF RNA
Authors: Hagerman Paul J.
Published: July 2002

▪ Abstract  One of the fundamental properties of the RNA helix is its intrinsic resistance to bend- or twist-deformations. Results of a variety of physical measurements point to a persistence length of 700–800 Å for double-stranded RNA in the presence of magnesium cations, approximately 1.5–2.0-fold larger than the corresponding value for DNA. Although helix flexibility represents an important, quantifiable measure of the forces of interaction within the helix, it must also be considered in describing conformational variation of nonhelix elements (e.g. internal loops, branches), since the latter always reflect the properties of the flanking helices; that is, such elements are never completely rigid. For one important element of tertiary structure, namely, the core of yeast tRNAPhe, the above consideration has led to the conclusion that the core is not substantially more flexible than an equivalent length of pure helix.
Stress-Induced Structural Transitions in DNA and Proteins
Authors: Strick T. R. , Allemand J.-F. , Bensimon D. , Croquette V.
Published: July 2002

▪ Abstract  The ability to manipulate, stretch and twist biomolecules opens the way to an understanding of their structural transitions. We review some of the recently discovered stress-induced structural transitions in DNA as well as the application of single molecule manipulation techniques to DNA unzipping and to the study of protein folding/unfolding transitions.
FUEL CELLS: Reaching the Era of Clean and Efficient Power Generation in the Twenty-First Century
Authors: Srinivasan Supramaniam , Mosdale Renaut , Stevens Philippe , Yang Christopher
Published: July 2002

▪ Abstract  This chapter on fuel cells covers the following topics: (a) fundamental electrochemical aspects and performance analysis; (b) technology research and development and demonstrations of fuel cell power sources for power generation, transportation, portable power, and space applications; (c) the role of fuel cells vs competing technologies, and (d) prospects for the applications and commercialization of fuel cell technologies in the twenty-first century. Although the fuel cell was invented in the nineteenth century, the twentieth century has been the period for technology development rather than widespread use. The fuel cell faces a great deal of competition in the proposed applications of power generation, transportation, and portable power. Significant work is still necessary, but intensified research and development activities could lead to the dawn of fuel cell commercialization and widespread use in the early part of the twenty-first century.
MODERN HELICOPTER AERODYNAMICS
Authors: Conlisk A. T.
Published: July 2002

▪ Abstract  Modern helicopter aerodynamics is challenging because the flow field generated by a helicopter is extremely complicated and difficult to measure, model, and predict; moreover, experiments are expensive and difficult to conduct. In this article we discuss the basic principles of modern helicopter aerodynamics. Many sophisticated experimental and computational techniques have been employed in an effort to predict performance parameters. Of particular interest is the structure of the rotor wake, which is highly three-dimensional and unsteady, and the rotor-blade pressure distribution, which is significantly affected by the strength and position of the wake. We describe the various modern methods of computation and experiment which span the range from vortex techniques to full three-dimensional Navier-Stokes computations, and from classical probe methods to laser velocimetry techniques. Typical results for the structure of the wake and the blade pressure distribution in both hover and forward flight are presented Despite the complexity of the helicopter flow, significant progress has been made within the last ten years and the future will likely bring marked advances.
Genetics of Hemochromatosis
Authors: Cullen, BSc L.M. , Anderson, PhD G.J. , Ramm, PhD G.A. , Jazwinska, PhD E.C. , Powell, MD, PhD, DUniv, FRCP, FRACP, FRCPT L.W.
Published: July 2002

Hereditary hemochromatosis (HHC) is a common autosomal recessive disorder of iron metabolism that results in progressive iron overload and can be fatal if untreated. The hemochromatosis gene (HFE) was identified by positional cloning in 1996. Two missense mutations have been described in HFE. The majority of HHC patients are homozygous for a cysteine-to-tyrosine substitution (C282Y); however, a small number are homozygous for a histidine-to-aspartic-acid substitution (H63D) or are heterozygous for both of these mutations. Mechanisms by which C282Y and H63D may disrupt the normal functioning of HFE have been suggested, but the role of HFE in the process of normal iron metabolism has yet to be clearly defined.
Catheter Ablation for Atrial Fibrillation
Authors: Jaïs Pierre , Shah Dipen C. , Haïssaguerre Michel , Hocini Meleze , Peng Jing Tian , Clémenty Jacques
Published: July 2002

▪ Abstract  Atrial fibrillation is frequently disabling and resistant to antiarrhythmic drugs. Curative treatment by catheter-based ablation has been shown to be feasible either by achieving long linear lesions, mainly in the left atrium, or by targeting the initiating focus, most frequently in the pulmonary veins. This paper reviews the different ablation approaches, their results, potential complications, and relative merits.
CHROMOPHORE-SOLVENT DYNAMICS
Authors: Fleming Graham R. , Cho Minhaeng
Published: July 2002

▪ Abstract  Experimental and theoretical studies of polar solvation dynamics and spectral line broadening are described. Photon echo and fluorescence Stokes shift experiments are discussed, and the relationship between the information content of the two techniques clarified. The interaction of the chromophore with its solvent bath is described by a spectral density, and the connection of this spectral density with the liquid's instantaneous normal modes discussed. The ubiquity of the ultrafast phase of solvation dynamics is demonstrated, and a discussion of its physical origin given. The slower phases of solvation vary strongly from solvent to solvent. Molecular theories of liquid dynamics are able to rationalize such variations over at least a 2000-fold range of time scale. The review concludes with a brief discussion of the relevance of ultrafast solvation to chemical dynamics.
Monte Carlo Methods in Electronic Structures for Large Systems
Authors: Lüchow Arne , Anderson James B.
Published: July 2002

Quantum Monte Carlo methods have recently made it possible to calculate the electronic structure of relatively large molecular systems with very high accuracy. These large systems range from positron complexes [NH2,Ps] with ∼10 electrons to C20 isomers with 120 electrons, to silicon crystal structures of 250 atoms and 1000 valence electrons. The techniques for such calculations and a sampling of applications are reviewed.
SYNAPTIC MECHANISMS FOR CODING TIMING IN AUDITORY NEURONS
Authors: Trussell Laurence O.
Published: July 2002

▪ Abstract  Neurons in the cochlear ganglion and auditory brain stem nuclei preserve the relative timing of action potentials passed through sequential synaptic levels. To accomplish this task, these neurons have unique morphological and biophysical specializations in axons, dendrites, and nerve terminals. At the membrane level, these adaptations include low-threshold, voltage-gated potassium channels and unusually rapid-acting transmitter-gated channels, which govern how quickly and reliably action potential threshold is reached during a synaptic response. Some nerve terminals are remarkably large and release large amounts of excitatory neurotransmitter. The high output of transmitter at these terminals can lead to synaptic depression, which may itself be regulated by presynaptic transmitter receptors. The way in which these different cellular mechanisms are employed varies in different cell types and circuits and reflects refinements suited to different aspects of acoustic processing.
CONSUMER BEHAVIOR: A Quadrennium
Authors: Jacoby J. , Johar G. V. , Morrin M.
Published: July 2002

▪ Abstract  Consumer behavior continued to attract additional researchers and publication outlets from 1993 through 1996. Both general interest and domain-specific scholarly contributions are discussed, along with limitations and suggested areas for future research. A concluding section observes that the integrity of consumer research is unnecessarily compromised by the failure of the major scholarly association in the field to develop and adopt a code of researcher ethics.
Retaliation, Bargaining, and the Pursuit of “Free and Fair” Trade
Authors: Gawande Kishore , Hansen Wendy L.
Published: July 2002

That domestic political economic factors are important determinants of a nation's trade barriers has been empirically well established. However, the question of how effective strategically retaliatory trade barriers are in deterring foreign protectionism has received far less systematic empirical attention. In this article we use bilateral nontariff barrier (NTB) data between the United States and five developed partner countries (Japan, France, Germany, Italy, and the United Kingdom) to systematically examine the effectiveness of strategic retaliation. We employ a simultaneous Tobit model where the home and foreign NTB levels are determined endogenously in a bilateral game. The model provides estimates of deterrence coefficients, that is, the reduction in foreign trade barriers as a result of U.S. retaliation, which we use to characterize the nature of bilateral NTB games. Our hope is that the empirical results presented here, which have realistic though controversial implications, will inform U.S. trade policy.
Anthropic Cyberspace: Defining Electronic Space from First Principles
Authors: Anders Peter
Published: July 2002

This article proposes principles for the design of human-centered, anthropic cyberspaces. Starting with a brief examination of our cognitive use of space, it suggests that we address cyberspace as an extension of our mental space. The article proceeds to state 12 principles based on scientific and cultural observations regarding individual cognition and social interaction. These concepts are general–not specific to any culture or technology. In the accom-panying arguments, the author expands on these concepts, illustrating them with examples taken from conventional and electronic media, space and cyberspace. With these conjectures, the author hopes to begin a discussion on the anthropology of space and its emulation.
Synthetic Harmonies: An Approach to Musical Semiosis by Means of Cellular Automata
Authors: Bilotta Eleonora , Pantano Pietro
Published: July 2002

The authors explore the creation of artificial universes that are expressible through music and internally comprehensible as complex systems. The semiotic approach this paper presents could also allow the development of new tools of investigation into the complexity of artificial-life systems. Through codification systems using musical language, it is possible to understand the patterns that the global dynamics of cellular automata produce and to use the results in the musical domain. In the authors' approach, music can be considered the semantics of complexity. The authors identify analogies between elements of cellular automata and elements of musical form, creating a narrative musical framework that has allowed them to develop a productive, computational and semantic methodology. Music fosters an increased capability for analyzing and reconstructing complexity, providing unexpected insight into its organization.
A Model that Accounts for Activity Prior to Sensory Inputs and Responses During Matching-to-Sample Tasks
Authors: Moody Sohie Lee , Wise Steven P.
Published: July 2002

Neural network models were examined during delayed matching-to-sample tasks (DMS), and neurons in a monkey's prefrontal cortex were studied during the performance of comparable tasks. In DMS, various input stimuli follow a sample stimulus, and an output should occur whenever the sample reappears. Our previous models have been restricted to certain kinds of inputs, outputs, and temporal patterns. Here, we generalized the models by training them on both spatial and nonspatial inputs, spatial and nonspatial outputs, and both fixed and variable interstimulus intervals. Two versions of DMS were presented to both the model and the monkey, both involving nonspatial samples: (1) Two stimuli simultaneously appeared at a variable interval after the sample; and (2) A series of single stimuli appeared at fixed intervals after the sample. Both versions required identical spatial responses, reflecting the direction (left or right) of the matching stimulus relative to a central origin. Thus, these two versions of DMS involved the same samples, memory, and responses, but established different response contexts. Our analysis focused on unit activity prior to stimuli, as well as that prior to responses, termed anticipatory and response-related activity, respectively. In both the model and the monkey, anticipatory activity occurred only for fixed interstimulus intervals. In the model, we could determine that anticipatory activity acted either like a filter to suppress inappropriate responses or it served to enhance the network's general readiness to respond. As for response-related activity, units in both the model and the monkey showed directional selectivity and had a strong dependence on response context. In the model, we could show that this activity contributed both to the suppression of inappropriate responses and to the generation of correct ones. None of the model's hidden units contributed exclusively to computing the direction of match output. Instead, their response-related activity contributed to the computation of both the match decision and the correct response direction.
Object Activation from Features in the Semantic System
Authors: Kraut Michael A. , Kremen Sarah , Segal Jessica B. , Calhoun Vincent , Moo Lauren R. , Hart John
Published: July 2002

The human brain is thought to elicit an object representation via co-activation of neural regions that encode various object features. The cortical regions and mechanisms involved in this process have never been elucidated for the semantic system. We used functional magnetic resonance imaging (fMRI) to evaluate regions activated during a task designed to elicit object activation within the semantic system (e.g., presenting the words “desert” and “humps” with the task to determine if they combine to form an object, in this case a “camel”). There were signal changes in the thalamus for word pairs that activated an object, but not for pairs that (a) failed to activate an object, (b) were simply semantically associated, or (c) were members of the same category. These results suggest that the thalamus has a critical role in coordinating the cortical activity required for activating an object concept in the semantic system.
Effects of Spike Timing on Winner-Take-All Competition in Model Cortical Circuits
Authors: Lumer Erik D.
Published: July 2002

Synaptic interactions in cortical circuits involve strong recurrent excitation between nearby neurons and lateral inhibition that is more widely spread. This architecture is commonly thought to promote a winner-takeall competition, in which a small fraction of neuronal responses is selected for further processing. Here I report that such a competition is remarkably sensitive to the timing of neuronal action potentials. This is shown using simulations of model neurons and synaptic connections representing a patch of cortical tissue. In the simulations, uncorrelated discharge among neuronal units results in patterns of response dominance and suppression, that is, in a winner-take-all competition. Synchronization of firing, however, prevents such competition. These results demonstrate a novel property of recurrent cortical-like circuits, suggesting that the temporal patterning of cortical activity may play an important part in selection among stimuli competing for the control of attention and motor action.
Dynamical Stability Conditions for Recurrent Neural Networks with Unsaturating Piecewise Linear Transfer Functions
Authors: Wersing Heiko , Beyn Wolf-Jürgen , Ritter Helge
Published: July 2002

We establish two conditions that ensure the nondivergence of additive recurrent networks with unsaturating piecewise linear transfer functions, also called linear threshold or semilinear transfer functions. As Hahn-loser, Sarpeshkar, Mahowald, Douglas, and Seung (2000) showed, networks of this type can be efficiently built in silicon and exhibit the coexistence of digital selection and analog amplification in a single circuit. To obtain this behavior, the network must be multistable and nondivergent, and our conditions allow determining the regimes where this can be achieved with maximal recurrent amplification. The first condition can be applied to nonsymmetric networks and has a simple interpretation of requiring that the strength of local inhibition match the sum over excitatory weights converging onto a neuron. The second condition is restricted to symmetric networks, but can also take into account the stabilizing effect of nonlocal inhibitory interactions. We demonstrate the application of the conditions on a simple example and the orientation-selectivity model of Ben-Yishai, Lev Bar-Or, and Sompolinsky (1995). We show that the conditions can be used to identify in their model regions of maximal orientation-selective amplification and symmetry breaking.
Retrieval Dynamics in Oscillator Neural Networks
Authors: Aoyagi Toshio , Kitano Katsunori
Published: July 2002

We present an analytical approach that allows us to treat the long-time behavior of the recalling process in an oscillator neural network. It is well known that in coupled oscillatory neuronal systems, under suitable conditions, the original dynamics can be reduced to a simpler phase dynamics. In this description, the phases of the oscillators can be regarded as the timings of the neuronal spikes. To attempt an analytical treatment of the recalling dynamics of such a system, we study a simplified model in which we discretize time and assume a synchronous updating rule. The theoretical results show that the retrieval dynamics is described by recursion equations for some macroscopic parameters, such as an overlap with the retrieval pattern. We then treat the noise components in the local field, which arise from the learning of the unretrieved patterns, as gaussian variables. However, we take account of the temporal correlation between these noise components at different times. In particular, we find that this correlation is essential for correctly predicting the behavior of the retrieval process in the case of autoassociative memory. From the derived equations, the maximal storage capacity and the basin of attraction are calculated and graphically displayed. We also consider the more general case that the network retrieves an ordered sequence of phase patterns. In both cases, the basin of attraction remains sufficiently wide to recall the memorized pattern from a noisy one, even near saturation. The validity of these theoretical results is supported by numerical simulations. We believe that this model serves as a convenient starting point for the theoretical study of retrieval dynamics in general oscillatory systems.
Pruning Using Parameter and Neuronal Metrics
Authors: Laar Piërre van de , Heskes Tom
Published: July 2002

In this article, we introduce a measure of optimality for architecture selection algorithms for neural networks: the distance from the original network to the new network in a metric defined by the probability distributions of all possible networks. We derive two pruning algorithms, one based on a metric in parameter space and the other based on a metric in neuron space, which are closely related to well-known architecture selection algorithms, such as GOBS. Our framework extends the theoretically range of validity of GOBS and therefore can explain results observed in previous experiments. In addition, we give some computational improvements for these algorithms.
To Prison
Authors: Tatsumi Hijikata
Published: July 2002

For the first time in English, we present many of Hijikata's aesthetic and poetic texts. These texts are put into context by Kurihara Nanako's introductory essay. The section includes an interview with Hijikata and a conversation between Hijikata and Japanese experimental theatre innovator Suzuki Tadashi.