bluuebunny/crossref_metadata_2025 huggingface dataset:
Feedback Queueing Models for Time-Shared Systems
Authors: Coffman Edward G. , Kleinrock Leonard
Published: July 2002

Time-shared processing systems (e.g. communication or computer systems) are studied by considering priority disciplines operating in a stochastic queueing environment. Results are obtained for the average time spent in the system, conditioned on the length of required service (e.g. message lenght or number of computations). No chage is made for swap time, and the results hold only for Markov assumptions for the arrival and service processes.

Two distinct feedback models with a single quantum-controlled service are considered. The first is a round-robin (RR) system in which the service facility processes each customer for a maximum of
q
sec. If the customer's service is completed during this quantum, he leaves the system; otherwise he returns to the end of the queue to await another quantum of service. The second is a feedback (FB

N

) system with
N
queues in which a new arrival joins the tail of the first queue. The server gives service to a customer from the
n
th queue only if all lower numbered queues are empty. When taken from the
n
th queue, a customer is given
q
sec of service. If this completes his processing requirement he leaves the system; otherwise he joins the tail of the (
n
+ 1)-st queue (
n
= 1, 2, · · ·,
N
- 1). The limiting case of
N
→ ∞ is also treated. Both models are therefore quantum-controlled, and involve feedback to the tail of some queue, thus providing rapid service for customers with short service-time requirements. The interesting limiting case in which
q
→ 0 (a “processor-shared” model) is also examined. Comparison is made with the first-come-first-served system and also the shortest-job-first discipline. Finally the FB
∞
system is generalized to include (priority) inputs at each of the queues in the system.
A Theorem for the Stability of General Predictor-Corrector Methods for the Solution of Systems of Differential Equations
Authors: Karim Abbas I. Abdel
Published: July 2002

Practically, predictor-corrector methods for the solution of differential equations are widely used. In these numerical methods, the question of stability is most important. For a single differential equation Crane and Lambert (1962) studies the stability of a fourth-order generalized corrector formula; Chase (1962) and subsequently Emanuel (1963) demonstrated for particular methods that the overall integration procedure does not generally possess the same stability properties as the corrector except when the step of integration tends to zero. In the present paper it is shown that it is possible to develop a necessary and sufficient condition for the stability of general predictor-corrector methods for the solution of systems of differential equations.
A Policy for JACM
Authors: Salton Gerard
Published: July 2002

When the
Journal of the Association for Computing Machinery
was first issued in 1954, the intention was to make it into the definitive journal in the computer area. This in many ways it has become. Even in some of the applied areas—for example, in information retrieval—many of the articles consistently referred to over the years, and thus considered of fundamental importance, have appeared in the ACM
Journal
.
On the Complexity of Undecidable Problems in Automata Theory
Authors: Hartmanis J.
Published: July 2002

Some general results about hierarchies of undecidable problems in automata theory are given, and studies are described which show how properties of sets accepted by automata (i.e. languages) change from decidable to undecidable problems as the computational power of the automata is increased. This work also yields unified techniques which characterize for different languages large classes of undecidable problems.
Halting Stack Automata
Authors: Ullman J. D.
Published: July 2002

It is shown that every two-way (deterministic) stack automaton language is accepted by a two-way (deterministic) stack automaton which for each input has a bound on the length of a valid computation. As a consequence, two-way deterministic stack languages are closed under complementation.
Computer Time-Sharing Queues with Priorities
Authors: Adiri Igal
Published: July 2002

The paper deals with computer time-sharing disciplines in which external priorities are introduced. For a computer system under a time-sharing discipline, the following priority disciplines are discussed: (a) head-of-the-line; (b) preemptive repeat; and (c) mixed preemptive strategy. All models in question assume that customers arrive according to homogeneous Poisson processes, and that service times are mutually independent exponentially distributed random variables. Results are given in terms of steady-state expectations.
Nonlinear Interpolation of Multivariable Functions by the Monte Carlo Method
Authors: Tsuda Takao , Ichida Kozo
Published: July 2002

The nonlinear interpolation of functions of very many variables is discussed. Deterministic termwise assessment of a prohibitively large number of terms naturally leads to a choice of random sampling from these numerous terms. After introduction of an appropriate higher order interpolation formula, a working algorithm is established by the Monte Carlo method. Numerical examples are also given.
Mathematical Models for Automatic Line Detection
Authors: Griffith Arnold K.
Published: July 2002

A particular decision-theoretic approach to the problem of detecting straight edges and lines in pictures is discussed. A model is proposed of the appearance of scenes consisting of prismatic solids, taking into account blurring, noise, and smooth variations in intensity over faces. A suboptimal statistical decision procedure is developed for the identification of a line within a narrow band in the field of view, given an array of intensity values from within the band. The performance of this procedure is illustrated and discussed.
Efficient Exercising of Switching Elements in Nets of Identical Gates
Authors: Richards Donald L.
Published: July 2002

The problem of finding a minimum number of patterns to exercise the logic elements of a combinational switching net is investigated. Throughout, the word “testing” refers to exercising of this kind; or, equivalently, to fault diagnosis where each line of the net can be directly observed. Any set of permanent faults can be selected to test against, examples of which range from “stuck-at” faults (allowing the most economical test) to “any possible fault” (requiring the most complete test).

The method used depends upon exact structural analysis rather than upon search algorithms or random pattern generation. The types of results presented appear to be fundamentally new. In particular, the maximum number of patterns required to test any one of an infinite class of nets is frequently found to be finite and extremely small. For example, any nontrivial connected tree of 2-input nand gates can be tested for “any possible fault” by exactly five patterns—no more and no less.

The method in brief: Given a set
F
of switching functions and a set of required inputs for each (collectively denoted
T
), a “testing” function is defined for each element of
F
for each positive integer
r
. If the lines of a net can be mapped to the domain of the testing functions
P
(
T, r
) so that the gates perform consistent with these functions, we say the net “accepts”
P
(
T, r
)—and then
r
patterns are sufficient to test the net for
T
.

Only nets in which each logic element is intended to realize the same switching function are discussed here. Trees (nets without fanout) are studied first, and the conditions under which a tree of identical gates “accepts” a partial function on an arbitrary domain is established. Then the common symmetric switching functions are separately investigated to find for each a minimum value of
r
such that all trees composed solely of the function accept
P
(
T, r
) (for various
T
). In most cases, as in the example given, the number of patterns required to test
any
such tree is extremely low.

The conditions under which all nets (nontrees included) accept a set of partial functions with arbitrary domain are then established. These conditions are rarely met in practice, even where
F
consists of a single function. However, many subclasses of nets can be identified which require only a few patterns at most (depending on the function and the class of faults selected). These subclasses often contain nets of arbitrary size and complexity, and frequently consist of exactly those nets for which a related graph can be “colored” (i.e.,
h
-node colored for some particular
h
) in the classical graph-theoretic sense. For example, any
net
of 2-input nand gates can be tested by five patterns if one of its related graphs is 2-colorable and another one is 3-colorable (!).

The detailed results and methods used to obtain them are summarized, and in conclusion coloring problems and test construction are commented upon.
Z-Resolution: Theorem-Proving with Compiled Axioms
Authors: Dixon John K.
Published: July 2002

An improved procedure for resolution theorem proving, called Z-resolution, is described. The basic idea of Z-resolution is to “compile” some of the axioms in a deductive problem. This means to automatically transform the selected axioms into a computer program which carries out the inference rules indicated by the axioms. This is done automatically by another program called the specializer. The advantage of doing this is that the compiled axioms run faster, just as a compiled program runs faster than an interpreted program.

A proof is given that the inference rule used in Z-resolution is complete, provided that the axioms “compiled” have certain properties.
A Path Entropy Function for Rooted Trees
Authors: Green Christopher D.
Published: July 2002

The class of rooted trees or arborescences used for modeling hierarchical classification and indexing procedures is considered. An entropy function measuring the complexity of the paths from the root to the terminal vertices is defined. Upper and lower bounds are found for the values of this function, and it is shown to be additive with respect to a tree product operation defined here. The results are extended to the case when the terminal vertices are weighted, and the path entropy function is compared to the information function defined by C. Picard for questionnaires.
Grammar Schemata
Authors: Gabrielian Armin , Ginsburg Seymour
Published: July 2002

A solution is presented for the following problem: Determine a procedure that produces, for each full trio L of context-free languages (more generally, each trio of r.e. languages), a family of context-free (phrase structure) grammars which (a) defines L, (b) is simple enough for practical and theoretical purposes, and (c) in most cases is a subfamily of a well-known family of context-free (phrase structure) grammars for L if such a well-known family exists. (A full trio (trio) is defined to be a family of languages closed under homomorphism (ε-free homomorphism), inverse homomorphism, and intersection with regular sets.)

The key notion in the paper is that of a grammar schema. With each grammar schema there is associated a family of interpretations. In turn, each interpretation of a grammar schema gives rise to a phrase structure grammar. Given a full trio (trio) L of context-free (r.e.) languages, one constructs a grammar schema whose interpretations (ε-limited interpretations) then give rise to the desired family of grammars for L.
Efficiency of Chebyshev Approximation on Finite Subsets
Authors: Dunham Charles B.
Published: July 2002

Chebyshev approximation on an interval and closed subsets by a Haar subspace are considered. The closeness of best approximations on subsets to the best approximation on the interval is examined. It is shown that under favorable conditions the difference is
O
((density of the subset)
2
), making it unnecessary to use very large finite subsets to get good approximations on the interval.
An Analysis of Some Relationships Between Post and Boolean Algebras
Authors: Wojcik Anthony S. , Metze Gernot
Published: July 2002

The fundamentals of Post algebras are presented and Post and Boolean functions are examined. A functional representation is developed that facilitates the comparison of Post and Boolean algebras. Based on this representation, relationships between finite, higher-order (that is, more than 2-valued) Boolean algebras and functions in these algebras and finite, higher-order Post algebras and their corresponding functions are develop.
Accelerated Iterative Methods for the Solution of Tridiagonal Systems on Parallel Computers
Authors: Heller D. E. , Stevenson D. K. , Traub J. F.
Published: July 2002

Iterative methods for the solution of tridiagonal systems are considered, and a new iteration is presented, whose rate of convergence is comparable to that of the optimal two-cyclic Chebyshev iteration but which does not require the calculation of optimal parameters. The convergence rate depends only on the magnitude of the elements of the tridiagonal matrix and not on its dimension or spectrum. The theory also has a natural extension to block tridiagonal systems. Numerical experiments suggest that on a parallel computer this new algorithm is the best of the iterative algorithms considered.
Covering Points of a Digraph with Point-Disjoint Paths and Its Application to Code Optimization
Authors: Boesch F. T. , Gimpel J. F.
Published: July 2002

A point-disjoint path cover of a directed graph is a collection of point-disjoint paths (some paths possibly having zero length) which covers all the points. A path cover which minimizes the number of paths corresponds to an optimal sequence of the steps of a computer program for efficient coding and documentation. The minimization problem for the general directed graph is hard in the sense of being NP-complete. In the case of cycle-free digraphs, however, the problem is polynomial, for it is shown that it can be reduced to the maximum-matching problem. A heuristic given here for finding a near optimal path cover for the general case is based upon applying the maximum-matching algorithm to the subgraphs of an interval decomposition.
Re-configurable distributed scripting
Authors: Ranganathan M. , Andrey Laurent , Schaal Virginie , Favreau Jean-Philippe
Published: July 2002

Several distributed testing, control and collaborative applications are reactive or event driven in nature. Such applications can be structured as a set of handlers that react to events and that in turn can trigger other events. We have developed an application building toolkit that facilitates development of such applications. Our system is based on the concept of Mobile Streams. Applications developed in our system are dynamically extensible and re-configurable and our system provides the application designer a mechanism to control extension and re-configuration. We describe our system model and give examples of its use.
SMC
Authors: Sistla A. Prasad , Gyuris Viktor , Emerson E. Allen
Published: July 2002

The article presents the SMC system. SMC can be used for checking safety and liveness properties of concurrent programs under different fairness assumptions. It is based on explicit state enumeration. It combats the state explosion by exploiting symmetries of the input concurrent program, usually present in the form of identical processes, in two different ways. Firstly, it reduces the number of explored states by identifying those states that are equivalent under the symmetries of the system; this is called
process symmetry
. Secondly, it reduces the number of edges explored from each state, in0
the reduced state graph, by exploiting the symmetry of a single state; this is called
state symmetry
. SMC works in an
on-the-fly
manner; it constructs the reduced state graph as and when it is needed. This method facilitates early termination, speeds up model checking, and reduces memory requirements. We employed SMC to check the correctness of, among other standard examples, the Link Layer part of the IEEE Standard 1394 “Firewire” high-speed serial bus protocol. SMC found deadlocks in the protocol. SMC was also to check certain liveness properties. A report on the case study is included in the article.
The natural language of interactive systems
Authors: Ledgard Henry , Whiteside John A. , Singer Andrew , Seymour William
Published: July 2002

The work reported here stems from our deep belief that improved human engineering can add
significantly
to the acceptance and use of computer technology.

In particular, this report describes an experiment to test the hypothesis that certain features of natural language provide a useful guide for the human engineering of interactive command languages. The goal was to establish that a syntax employing familiar, descriptive, everyday words and well-formed English phrases contributes to a language that can be easily and effectively used. Users with varying degrees of interactive computing experience used two versions of an interactive text editor; one with an English-based command syntax in the sense described above, the other with a more notational syntax. Performance differences strongly favored the English-based editor.
An improved algorithm for decentralized extrema-finding in circular configurations of processes
Authors: Chang Ernest , Roberts Rosemary
Published: July 2002

This note presents an improvement to LeLann's algorithm for finding the largest (or smallest) of a set of uniquely numbered processes arranged in a circle, in which no central controller exists and the number of processes is not known a priori. This decentralized algorithm uses a technique of selective message extinction in order to achieve an average number of message passes of order (
n
log
n
) rather than
O
(
n
2
).
Rejuvenating experimental computer science: a report to the National Science Foundation and others
Authors: Feldman Jerome A. , Sutherland William R.
Published: July 2002

This report is based on the results of an NSF sponsored workshop held in Washington, D.C. on November 2, 1978. The co-authors of the report are: Gordon Bell, Digital Equipment Corporation; Bernard A. Galler, University of Michigan; Patricia Goldberg, IBM Corporation; John Hamblen, University of Missouri at Rolla; Elliot Pinson, Bell Telephone Laboratories; and Ivan Sutherland, California Institute of Technology. Also participating in the workshop were representatives of NSF and other government agencies. In addition to the authors, a number of other people have contributed to the contents of this report. In preparation for the original workshop, all doctorate-granting computer science departments in the nation were asked for comments and suggestions on the problems of experimental computer science. A version of the current report dated January 15 was circulated to these departments and to a number of industrial and government groups for criticism. The editors and authors of this final version gratefully acknowledge the contribution of a large number of other people at all stages in the preparation of the report. [Note: Following this presentation of the report, there is a position paper on the crisis in experimental computer science written by the ACM Executive Committee.]
Approximation of polygonal maps by cellular maps
Authors: Nagy George , Wagle Sharad G.
Published: July 2002

The approximation of polygonal thematic maps by cellular maps, an important operation in geographical data processing, is analyzed. The data organization used for representing the polygonal maps is a widely used segment-based data structure, where class labels identify the regions bordering each segment on either side. The approximation algorithm presented operates on such an organization, eliminating the need for the recognition of region boundaries. Each segment is examined only once. The versatility of the new organization is further illustrated by the outline of algorithms for area computation and point inclusion. The algorithm is applied to a set of soil maps converted to computer-readable form by means of a coordinate digitizer.
An ACM executive committee position on the crisis in experimental computer science
Authors: McCracken Daniel D. , Denning Peter J. , Brandin David H.
Published: July 2002

The following is the text of a letter commenting on the Feldman Report sent to Dr. Richard C. Atkinson, Director of the National Science Foundation, and other Administration and Congressional officials.
Breaking substitution ciphers using a relaxation algorithm
Authors: Peleg Shmuel , Rosenfeld Azriel
Published: July 2002

Substitution ciphers are codes in which each letter of the alphabet has one fixed substitute, and the word divisions do not change. In this paper the problem of breaking substitution ciphers is represented as a probabilistic labeling problem. Every code letter is assigned probabilities of representing plaintext letters. These probabilities are updated in parallel for all code letters, using joint letter probabilities. Iterating the updating scheme results in improved estimates that finally lead to breaking the cipher. The method is applied successfully to two examples.
Insertions and deletions in one-sided height-balanced trees
Authors: Kosaraju S. Rao
Published: July 2002

Recently Hirschberg has established that insertions into one-sided height-balanced trees can be done in O(log
2
N) steps. It is proved here that deletions can also be performed in O(log
2
N) steps, which answers the open problem posed by Hirschberg.
Right brother trees
Authors: Ottmann Th. , Six H. W. , Wood D.
Published: July 2002

Insertion and deletion algorithms are provided for the class of right (or one-sided) brother trees which have O (log n) performance. The importance of these results stems from the close relationship of right brother trees to one-sided height-balanced trees which have an insertion algorithm operating in O (log
2
n). Further, although both insertion and deletion can be carried out in O (log n) time for right brother trees, it appears that the insertion algorithm is inherently much more difficult than the deletion algorithm—the reverse of what one usually obtains.
Analysis of an algorithm for real time garbage collection
Authors: Wadler Philip L.
Published: July 2002

A real time garbage collection system avoids suspending the operations of a list processor for the long times that garbage collection normally requires by performing garbage collection on a second processor in parallel with list processing operations, or on a single processor time-shared with them. Algorithms for recovering discarded list structures in this manner are presented and analyzed to determine sufficient conditions under which the list processor never needs to wait on the collector. These techniques are shown to require at most twice as much processing power as regular garbage collectors, if they are used efficiently. The average behavior of the program is shown to be very nearly equal to the worst-case performance, so that the sufficient conditions are also suitable for measuring the typical behavior of the algorithm.
The parallel execution of DO loops
Authors: Lamport Leslie
Published: July 2002

Methods are developed for the parallel execution of different iterations of a DO loop. Both asynchronous multiprocessor computers and array computers are considered. Practical application to the design of compilers for such computers is discussed.
Remark on stably updating mean and standard deviation of data
Authors: Cotton Ira W.
Published: July 2002

Although not published as a numbered algorithm, Hanson's article “Stably Updating Mean and Standard Deviation of Data” in the January, 1975, issue of
Communications
, [1] describes an algorithm for sequentially recomputing the mean and standard deviation of a weighted series of numbers when new numbers are added to the series. The procedure requires that only a summary matrix of data be retained, not the entire series, for the new mean and standard deviation to be computed.
Practical syntactic error recovery
Authors: Graham Susan L. , Rhodes Steven P.
Published: July 2002

This paper describes a recovery scheme for syntax errors which provides automatically-generated high quality recovery with good diagnostic information at relatively low cost. Previous recovery techniques are summarized and empirical comparisons are made. Suggestions for further research on this topic conclude the paper.
Hidden lines elimination for a rotating object
Authors: Matsushita Yutaka
Published: July 2002

A method is presented of determining which parts of three-dimensional objects are visible and which are invisible when the objects are rotated about some axis. This paper describes a polygon comparison scheme in which the relationships of two polygons can be classified into tree types, and also discusses how the relationship is changed for each pair of polygons under rotation about some axis. A rotation table is defined for each pair of polygons, which remains fixed as long as rotation is about one axis and provides a means of rapidly determining the visible and hidden line relationship between two polygons. Additional work must be done to extend this approach to simultaneous rotation about several axes.
A generational perspective of information system development
Authors: Benjamin Robert I.
Published: July 2002

System development is categorized from a generational point of view that parallels the commonly described computing system generations. For each generation, the scope of development projects and the technological world view of the system developer are examined.
Logic programming
Authors: Genesereth Michael R. , Ginsberg Matthew L.
Published: July 2002

Logic programming is programming by description. The programmer describes the application area and lets the program choose specific operations. Logic programs are easier to create and enable machines to explain their results and actions.
Composing Bézier simplexes
Authors: DeRose Tony D.
Published: July 2002

This paper describes two algorithms for solving the following general problem: Given two polynomial maps f: R

n

↦ R

N

and S R

N

↦ R

d

in Bézier simplex form, find the composition map S = S ° f in Bézier simplex form (typically,
n
≤
N
≤
d
≤ 3). One algorithm is more appropriate for machine implementation, while the other provides somewhat more geometric intuition. The composition algorithms can be applied to the following problems: evaluation, subdivision, and polynomial reparameterization of Bézier simplexes; joining Bézier curves with geometric continuity of arbitrary order; and the determination of the control nets of Bézier curves and triangular Bézier surface patches after they have undergone free-form deformations.
Practical safety in flexible access control models
Authors: Jaeger Trent , Tidswell Jonathon E.
Published: July 2002

Assurance that an access control configuration will not result in the leakage of a right to an unauthorized principal, called
safety
, is fundamental to ensuring that the most basic of access control policies can be enforced. It has been proven that the safety of an access control configuration cannot be decided for a general access control model, such as Lampson's access matrix, so safety is achieved either through the use of limited access control models or the verification of safety via constraints. Currently, almost all safety critical systems use limited access control models, such as Bell--LaPadula or Domain and Type Enforcement, because constraint expression languages are far too complex for typical administrators to use properly. However, researchers have identified that most constraints belong to one of a few basic types, so our goal is to develop a constraint expression model in which these constraints can be expressed in a straightforward way and extensions can be made to add other constraints, if desired. Our approach to expressing constraints has the following properties: (1) an access control policy is expressed using a graphical model in which the nodes represent sets (e.g., of subjects, objects, etc.) and the edges represent binary relationships on those sets and (2) constraints are expressed using a few, simple set operators on graph nodes. The basic graphical model is very simple, and we extend this model only as necessary to satisfy the identified constraint types. Since the basic graphical model is also general, further extension to support other constraints is possible, but such extensions should be made with caution as each increases the complexity of the model. Our hope is that by keeping the complexity of constraint expression in check, flexible access control models, such as role-based access control, may also be used for expressing access control policy for safety-critical systems.
Supercomputer languages
Authors: Perrott R. H. , Zarea-Aliabadi A.
Published: July 2002

The high-level languages proposed for supercomputers, such as vector and array processors, have been designed using one of the following two approaches: (1) an existing sequential language is adapted, (2) a new language based on the hardware is developed. Recently, there has emerged a third approach, which does not require the programmer to be aware of the sequential nature of the language or the hardware characteristics.

Examples of these language groups are examined to illustrate their main features and what is required of a programmer when using such languages. The study therefore enables a comparison of the different language approaches to be made.
Simple constant-time consensus protocols in realistic failure models
Authors: Chor Benny , Merritt Michael , Shmoys David B.
Published: July 2002

Using simple protocols, it is shown how to achieve consensus in constant expected time, within a variety of fail-stop and omission failure models. Significantly, the strongest models considered are completely asynchronous. All of the results are based on distributively flipping a coin, which is usable by a significant majority of the processors. Finally, a nearly matching lower bound is also given for randomized protocols for consensus.
Design of the Mneme persistent object store
Authors: Moss J. Eliot B.
Published: July 2002

The Mneme project is an investigation of techniques for integrating programming language and database features to provide better support for cooperative, information-intensive tasks such as computer-aided software engineering. The project strategy is to implement efficient, distributed, persistent programming languages. We report here on the Mneme persistent object store, a fundamental component of the project, discussing its design and initial prototype. Mneme storesobjectsin a simple and general format, preserving object identity and object interrelationships. Specific goals for the store include portability, extensibility (especially with respect to object management policies), and performance. The model of memory that the store aims at is a single, cooperatively-shared heap, distributed across a collection of networked computers. The initial prototype is intended mainly to explore performance issues and to support object-oriented persistent programming languages. We include performance measurements from the prototype as well as more qualitative results.
Pastoralism: Governance and Development Issues
Authors: Fratkin Elliot
Published: July 2002

Pastoralist societies face more threats to their way of life now than at any previous time. Population growth; loss of herding lands to private farms, ranches, game parks, and urban areas; increased commoditization of the livestock economy; out-migration by poor pastoralists; and periodic dislocations brought about by drought, famine, and civil war are increasing in pastoralist regions of the world. Mongolia and China, however, have seen a revitalization of pastoral production with decollectivization. This review examines problems of pastoral governance and development including the “tragedy of the commons” debate, threats to common property rights, the effects of commercial ranching on pastoral economies, decollectivization in the former socialist countries, and the current state of development policies of Western donor countries. Case examples from the Maasai and Barabaig of East Africa and pastoralists of Mongolia and China illustrate these changes.
CHEMICAL CONTROL OF GENE EXPRESSION
Authors: Gatz C.
Published: July 2002

▪ Abstract  Promoters that respond to otherwise inactive chemicals will enhance the tools available for analyzing gene function in vivo and for altering defined traits of plants at will. Approaches to provide such tools have yielded plant promoters that respond to compounds activating defense genes. In addition, the transfer of regulatory elements from prokaryotes, insects, and mammals has opened new avenues to construct chemically inducible promoters that respond to signals normally not recognized by plants. This review describes results and applications of these two approaches.
Inner-Core Anisotropy and Rotation
Authors: Tromp Jeroen
Published: July 2002

▪ Abstract  This paper reviews recent research focused on the Earth's inner core. Large inner-core traveltime anomalies and the anomalous splitting of core-sensitive free oscillations strongly suggest that the inner core is anisotropic. Initial models involved a simple, constant or depth-dependent cylindrical anisotropy at a level less than a few percent. Recent observations suggest that its eastern hemisphere is largely isotropic, whereas its western hemisphere is highly anisotropic, and there are indications that its top 100 km may be isotropic. The coda of inner-core reflected phases has been used to infer strong heterogeneities with a length scale of just a few kilometers. Thus, a complicated three-dimensional picture of the inner core is beginning to emerge, although it has been suggested that much of this complexity may be the misinterpretation of signals that have their origin in the lowermost mantle. Numerical models of the geodynamo suggest that the inner core may rotate at a slightly different rate than the mantle. Recent seismological estimates based upon traveltime and normal-mode data limit inner-core differential rotation to less than +0.2 degrees per year.
The Units of Selection on Mitochondrial DNA
Authors: Rand David M.
Published: July 2002

▪ Abstract  Mitochondrial DNA (mtDNA) exists in a nested hierarchy of populations. There are multiple mtDNAs within each mitochondrion, a population of mitochondria in each cell, multiple oocytes within each reproductive female, multiple females in each population, and so on up through species and higher clades. The metabolic properties of mitochondria make them highly mutagenic environments for the naked, circular mtDNAs that lie within them. This mutational pressure introduces mtDNA variation (i.e., heteroplasmy) into the cytoplasmic population of cell lineages that are particularly prone to mutational decay and Muller's ratchet owing to the asexual, maternal inheritance of mtDNA. Neutrality tests show that deleterious mutations are common in mtDNA evolution. Population cage experiments further show that mtDNA fitnesses are influenced by nuclear-mitochondrial interactions. These selective processes are pervasive despite the long-standing use of mtDNA as a neutral marker in population and evolutionary biology. These evolutionary dynamics are also unique in the nested hierarchy of mtDNA populations because mutation, selection, and drift can act—and interact—at multiple levels. Multi-level selection can facilitate the escape from Muller's ratchet and help resolve intragenomic conflicts. This review addresses recent advances in the transmission genetics, population genetics, and evolution of mtDNA. A primary goal of the review is to motivate additional empirical studies that might clarify the many units of selection acting on mtDNA.
ENERGY ANDMATERIALFLOWTHROUGH THEURBANECOSYSTEM
Authors: Decker Ethan H. , Elliott Scott , Smith Felisa A. , Blake Donald R. , Rowland F. Sherwood
Published: July 2002

▪ Abstract  This paper reviews the available data and models on energy and material flows through the world's 25 largest cities. Throughput is categorized as stored, transformed, or passive for the major flow modes. The aggregate, fuel, food, water, and air cycles are all examined. Emphasis is placed on atmospheric pathways because the data are abundant. Relevant models of urban energy and material flows, demography, and atmospheric chemistry are discussed. Earth system–level loops from cities to neighboring ecosystems are identified. Megacities are somewhat independent of their immediate environment for food, fuel, and aggregate inputs, but all are constrained by their regional environment for supplying water and absorbing wastes. We elaborate on analogies with biological metabolism and ecosystem succession as useful conceptual frameworks for addressing urban ecological problems. We conclude that whereas data are numerous for some individual cities, cross-cutting compilations are lacking in biogeochemical analysis and modeling. Synthesis of the existing information will be a crucial first step. Cross-cutting field research and integrated, multidisciplinary simulations will be necessary.
The Design of Vaccines AgainstHelicobacter Pyloriand Their Development
Authors: Del Giudice Giuseppe , Covacci Antonello , Telford John L. , Montecucco Cesare , Rappuoli Rino
Published: July 2002

Helicobacter pylori is a gram negative, spiral, microaerophylic bacterium that infects the stomach of more than 50% of the human population worldwide. It is mostly acquired during childhood and, if not treated, persists chronically, causing chronic gastritis, peptic ulcer disease, and in some individuals, gastric adenocarcinoma and gastric B cell lymphoma. The current therapy, based on the use of a proton-pump inhibitor and antibiotics, is efficacious but faces problems such as patient compliance, antibiotic resistance, and possible recurrence of infection. The development of an efficacious vaccine against H. pylori would thus offer several advantages. Various approaches have been followed in the development of vaccines against H. pylori, most of which have been based on the use of selected antigens known to be involved in the pathogenesis of the infection, such as urease, the vacuolating cytotoxin (VacA), the cytotoxin-associated antigen (CagA), the neutrophil-activating protein (NAP), and others, and intended to confer protection prophylactically and/or therapeutically in animal models of infection. However, very little is known of the natural history of H. pylori infection and of the kinetics of the induced immune responses. Several lines of evidence suggest that H. pylori infection is accompanied by a pronounced Th1-type CD4+T cell response. It appears, however, that after immunization, the antigen-specific response is predominantly polarized toward a Th2-type response, with production of cytokines that can inhibit the activation of Th1 cells and of macrophages, and the production of proinflammatory cytokines. The exact effector mechanisms of protection induced after immunization are still poorly understood. The next couple of years will be crucial for the development of vaccines against H. pylori. Several trials are foreseen in humans, and expectations are that most of the questions being asked now on the host-microbe interactions will be answered.
PATHOGENESIS AND HOST RESPONSE INPneumocystis cariniiPNEUMONIA
Authors: Su, M.D Tony H. , Martin II, M.D William J.
Published: July 2002

▪ Abstract  Pneumocystis carinii (PC) pneumonia is recognized as the leading cause of opportunistic pulmonary infections in immunocompromised hosts during the past decade. Although much remains unknown about pathogenesis and host response in PC, in recent years, studies of PC have provided us with an increasing base of knowledge about this organism and its relationship to the host. These studies have led to a better understanding of mechanisms of PC attachment and injury to host cells. New information about the interaction of PC with pulmonary surfactant provides insight about the pathophysiology of PC pneumonia. The interplay of the organism, host inflammatory cells, release of cytokines, generation of toxic metabolites, and involvement of both cellular and humoral immunity is complex, but understanding the pathogenesis of PC pneumonia is necessary in order to develop new therapies for this disorder.
MODULATION OF THE IONIC MILIEU OF THE AIRWAY IN HEALTH AND DISEASE
Authors: Noone, M.D P.G. , Olivier, M.D K.N. , Knowles, M.D M.R.
Published: July 2002

▪ Abstract  Airway surface liquid (ASL) is an integral part of lung defense mechanisms. Ion transport by airway epithelia regulates the volume and composition of this fluid. A better understanding of the mechanisms of ion transport will enable the development of new therapies for airway diseases associated with defects in these mechanisms. A useful model of a disease with abnormal airway epithelial ion transport is cystic fibrosis (CF), a distinct genetic syndrome of altered lung defense mechanisms characterized by chronic bacterial infection and a steady decline in lung function. Traditional therapies for CF include antibacterial drugs and augmentation of clearance of secretions, but investigators are now studying pharmacological approaches to target the more basic defect of the disease, i.e. abnormal sodium and chloride ion transport. Early treatment in childhood, prior to lung damage, might prevent or at least retard the decline in pulmonary function that remains the hallmark of CF. Ion transport dysfunction may also contribute to other airway diseases such as asthma and chronic bronchitis. Pharmacological intervention at this level may prove beneficial in these common lung diseases as well.
INFLAMMATORY HEART DISEASE: Pathogenesis, Clinical Manifestations, and Treatment of Myocarditis
Authors: Olinde, M.D Kurt D. , O'Connell, M.D John B.
Published: July 2002

▪ Abstract  Myocarditis is an uncommon cause of cardiac disease that can result in arrhythmia, congestive heart failure, and death. Myocardial injury in myocarditis is due in part to activated cellular and humoral immune components directed toward normal cardiac tissue. Although numerous therapies for myocarditis, including corticosteroids and immunosuppressive agents, have been applied in animal experiments and in human studies, none have demonstrated survival benefit over untreated controls. In many patients, myocarditis may spontaneously resolve. Information about myocarditis pathogenesis, manifestations, and treatment has been useful in disease management. Further research into the inflammatory nature of myocarditis may provide the basis for more favorable outcomes of intervention in this disease.
THE SIGNIFICANCE OF NEURAL ENSEMBLE CODES DURING BEHAVIOR AND COGNITION
Authors: Deadwyler Sam A. , Hampson Robert E.
Published: July 2002

▪ Abstract  The development of techniques to record from populations of neurons has made it possible to ask questions concerning the encoding of task-relevant information in awake, behaving animals. The issue of how groups of neurons within different brain structures register and retrieve representations of behaviorally significant events can now be addressed using multineuron-recording techniques. This review examines recent studies employing simultaneous recording of ten or more individual neurons in the mammalian brain. A major issue discussed is whether ensemble information content reconstructed from single-neuron recordings may be underestimated if compared to ensembles where those same neurons were recorded simultaneously. The mechanics of ensemble information encoding in the hippocampus is illustrated from population statistical analyses of ensemble activity during performance of a delay task. Detailed descriptions of methods of extracting ensemble information, as well as cross-correlational analyses, are discussed in the context of emergent issues regarding interpretation of ensemble data.
CELL CYCLE REGULATION AND APOPTOSIS
Authors: King K. L. , Cidlowski J. A.
Published: July 2002

▪ Abstract  Tissue homeostasis requires a balance between cell proliferation and death. Apoptosis and proliferation are linked by cell cycle regulators, and apoptotic stimuli affect both cell proliferation and death. Glucocorticoids induce G1 arrest and apoptosis in transformed lymphoid cells. Decreased expression of the cell cycle components c-myc and cyclin D3 is essential for glucocorticoid-induced growth arrest and death in dividing cells. Other G1 regulators, such as p53, pRb, and E2F, have also been implicated in apoptosis. Mice lacking either p53 or E2F display aberrant cell proliferation and tumor formation, suggesting that these proteins are involved in the elimination of abnormal cells through apoptosis. In contrast, pRb induces G1 arrest and suppresses apoptosis in cultured cells. Mice that lack pRb are nonviable and show ectopic mitosis and massive cell death, suggesting that pRb is an apoptotic suppressor. Further analysis of common components of apoptotic and cell cycle machinery may provide insight into the coordinated regulation of these antagonistic processes.
Dynamic Signaling Between Astrocytes and Neurons
Authors: Araque Alfonso , Carmignoto Giorgio , Haydon Philip G
Published: July 2002

▪ Abstract  Astrocytes, a sub-type of glia in the central nervous system, are dynamic signaling elements that integrate neuronal inputs, exhibit calcium excitability, and can modulate neighboring neurons. Neuronal activity can lead to neurotransmitter-evoked activation of astrocytic receptors, which mobilizes their internal calcium. Elevations in astrocytic calcium in turn trigger the release of chemical transmitters from astrocytes, which can cause sustained modulatory actions on neighboring neurons. Astrocytes, and perisynaptic Schwann cells, by virtue of their intimate association with synapses, are strategically positioned to regulate synaptic transmission. This capability, that has now been demonstrated in several studies, raises the untested possibility that astrocytes are an integral element of the circuitry for synaptic plasticity. Because the highest ratio of glia-to-neurons is found at the top of the phylogenetic tree in the human brain, these recent demonstrations of dynamic bi-directional signaling between astrocytes and neurons leave us with the question as to whether astrocytes are key regulatory elements of higher cortical functions.
RECONCILING PROCESSING DYNAMICS AND PERSONALITY DISPOSITIONS
Authors: Mischel Walter , Shoda Yuichi
Published: July 2002

▪ Abstract  Developments in personality-social psychology, in social cognition, and in cognitive neuroscience have led to an emerging conception of personality dynamics and dispositions that builds on diverse contributions from the past three decades. Recent findings demonstrating a previously neglected but basic type of personality stability allow a reconceptualization of classic issues in personality and social psychology. It reconstrues the nature and role of situations and links contextually sensitive processing dynamics to stable dispositions. It thus facilitates the reconciliation within a unitary framework of dispositional (trait) and processing (social cognitive–affective–dynamic) approaches that have long been separated. Given their history, however, the realization of this promise remains to be seen.
Glycogen Synthase Kinase-3β
Authors: Hardt Stefan E. , Sadoshima Junichi
Published: July 2002

Glycogen synthase kinase-3β (GSK-3β) is a ubiquitously expressed constitutively active serine/threonine kinase that phosphorylates cellular substrates and thereby regulates a wide variety of cellular functions, including development, metabolism, gene transcription, protein translation, cytoskeletal organization, cell cycle regulation, and apoptosis. The activity of GSK-3β is negatively regulated by protein kinase B/Akt and by the Wnt signaling pathway. Increasing lines of evidence show that GSK-3β is an essential negative regulator of cardiac hypertrophy and that the inhibition of GSK-3β by hypertrophic stimuli is an important mechanism contributing to the development of cardiac hypertrophy. GSK-3β also plays an important role in regulating cardiac development. In this review, the role of GSK-3β in cardiac hypertrophy and development and the potential underlying mechanisms are discussed.