bluuebunny/crossref_metadata_2025 huggingface dataset:
SOLUTIONS TO CONGRUENCES USING SETS WITH THE PROPERTY OF BAIRE
Authors: DOUGHERTY RANDALL
Published: July 2002

Hausdorff's paradoxical decomposition of a sphere with countably many points removed (the main precursor of the Banach–Tarski paradox) actually produced a partition of this set into three pieces A,B,C such that A is congruent to B (i.e. there is an isometry of the set which sends A to B), B is congruent to C, and A is congruent to B ∪ C. While refining the Banach–Tarski paradox, R. Robinson characterized the systems of congruences like this which could be realized by partitions of the sphere with rotations witnessing the congruences: the only nontrivial restriction is that the system should not require any set to be congruent to its complement. Later, J. F. Adams showed that this restriction can be removed if one allows arbitrary isometries of the sphere to witness the congruences.

The purpose of this paper is to characterize those systems of congruences which can be satisfied by partitions of the sphere or related spaces into sets with the property of Baire. A paper of Dougherty and Foreman gives a proof that the Banach–Tarski paradox can be achieved using such sets, and gives versions of this result using open sets and related results about partitions of spaces into congruent sets. The same method is used here; it turns out that only one additional restriction on a system of congruences is needed to make it solvable using subsets of the sphere with the property of Baire (or solvable with open sets if one allows meager exceptions to the congruences and the covering of the space) with free rotations witnessing the congruences. Actually, the result applies to any complete metric space acted on in a sufficiently free way by a free group of homeomorphisms. We also characterize the systems solvable on the sphere using sets with the property of Baire but allowing all isometries.
Marriages between Asian, American, and Dutch Corporations: A Matter of Cultural Fit?
Authors: Grotenhuis Frits D. J.
Published: July 2002

In this paper two studies about the impact of cultural differences on corporate marriages are discussed. Very often it is hypothesized that culture has a large impact on joint ventures and mergers, however, few studies come up with empirical evidence. To explore such culture's consequences two studies were conducted, where different research approaches were used. In the first study into Japanese and American joint ventures in Indonesia, an etic research approach was chosen. Leadership styles and stress were examined in particular, as effects of differences in national cultures. On most of the concepts we measured, Japanese managers seem to fit better in an Indonesian context than American managers do. In the second study into Japanese-Dutch and American-Dutch mergers, an emic research approach is used. Two American-Dutch mergers and one Japanese-Dutch merger are currently the subject of research. The focus of the second study is on the acculturation process of the two merging entities. Based on the preliminary results and an extensive literature review, it is concluded that Japanese-Dutch companies are more difficult to combine than American-Dutch companies, although culture clashes also occur in American-Dutch combinations.
Getting around the task-artifact cycle
Authors: Carroll John M. , Rosson Mary Beth
Published: July 2002

We are developing an “action science” approach to human-computer interaction (HCI), seeking to better integrate activities directed at understanding with those directed at design. The approach leverages development practices of current HCI with methods and concepts to support a shift toward using broad and explicit design rationale to reify where we are in a design process, why we are there, and to guide reasoning about where we might go from there. We represent a designed artifact as the set of user scenarios supported by that artifact and more finely by causal schemas detailing the underlying psychological rationale. These schemas, called
claims
, unpack wherefores and whys of the scenarios. In this paper, we stand back from several empirical projects to clarify our commitments and practices.
What's in a region?
Authors: Ball Thomas
Published: July 2002

Regions of control dependence identify the instructions in a program that execute under the same control conditions. They have a variety of applications in parallelizing and optimizing compilers. Two vertices in a control-flow graph (which may represent instructions or basic blocks in a program) are in the same region if they have the same set of control dependence predecessors. The common algorithm for computing regions examines each control dependence at least once. As there may be O(V x E) control dependences in the worst case, where V and E are the number of vertices and edges in the control-flow graph, this algorithm has a worst-case running time of O(V x D). We present algorithms for finding regions in reducible control-flow graphs in near-linear time, without using control dependence. These algorithms are based on alternative definitions of regions, which are easier to reason with than the definitions based on control dependence.
An exploratory evaluation of three interfaces for browsing large hierarchical tables of contents
Authors: Chimera Richard , Shneiderman Ben
Published: July 2002

Three different interfaces were used to browse a large (1296 items) table of contents. A fully expanded stable interface, expand/contract interface, and multipane interface were studied in a between-groups experiment with 41 novice participants. Nine timed fact retrieval tasks were performed; each task is analyzed and discussed separately. We found that both the expand/contract and multipane interfaces produced significantly faster times than the stable interface for many tasks using this large hierarchy; other advantages of the expand/contract and multipane interfaces over the stable interface are discussed. The animation characteristics of the expand/contract interface appear to play a major role. Refinements to the multipane and expand/contract interfaces are suggested. A predictive model for measuring navigation effort of each interface is presented.
Templar
Authors: Tuzhilin Alexander
Published: July 2002

A software specification language Templar is defined in this article. The development of the language was guided by the following objectives: requirements specifications written in Templar should have a clear syntax and formal semantics, should be easy for a systems analyst to develop and for an end-user to understand, and it should be easy to map them into a broad range of design specifications. Templar is based on temporal logic and on the Activity-Event-Condition-Activity model of a rule which is an extension of the Event-Condition-Activity model in active databases. The language supports a rich set of modeling primitives, including rules, procedures, temporal logic operators, events, activities, hierarchical decomposition of activities, parallelism, and decisions combined together into a cohesive system.
Optimal register assignment to loops for embedded code generation
Authors: Kolson David J. , Nicolau Alexandru , Dutt Nikil , Kennedy Ken
Published: July 2002

One of the challenging tasks in code generation for embedded systems is register assignment. When more live variables than registers exist, some variables will necessarily be accessed from data memory. Because loops are typically executed many times and are often time-critical, good register assignment in loops is exceedingly important as accessing data memory can degrade performance. The issue of finding an optimal register assignment to loops has been open for some time. In this article, we present a technique for optimal (i.e., spill minimizing) register assignment to loops. First we present a technique for register assignment to architecture styles that are characterized by a consolidated register file. Then we extend the technique to include architecture styles that are characterized by distributed memories and/or a combination of general- and special-purpose registers. Experimental results demonstrate that although the optimal algorithm may be computationally prohibitive, heuristic versions obtain results with performance better than that of an existing graph coloring approach.
Image shading taking into account relativistic effects
Authors: Chang Meng-Chou , Lai Feipei , Chen Wei-Chao
Published: July 2002

This article is concerned with creating more realistic images of 3D scenes which are moving relative to the viewer at such high speeds that the propagation delay of light signals and other relativistic effects can not be neglected. Creating images of 3D scenes in relativistic motion might have important applications to science-fiction films, computer games, and virtual environments. We shall discuss the following problems: (1) how to determine the visual appearance of a rapidly moving object, (2) how to determine the apparent radiance of a scene point on a moving object, (3) how to determine the incident irradiance at a scene point coming from a moving light source, (4) how to determine the color of a rapidly moving object, and (5) how to generate shadows when there are relative motions between the viewer, the scenes, and the light sources. Detailed examples are also given to show the result of shading with the relativistic effects taken into account.
Mersenne twister
Authors: Matsumoto Makoto , Nishimura Takuji
Published: July 2002

A new algorithm called Mersenne Twister (MT) is proposed for generating uniform pseudorandom numbers. For a particular choice of parameters, the algorithm provides a super astronomical period of 2
19937
−1 and 623-dimensional equidistribution up to 32-bit accuracy, while using a working area of only 624 words. This is a new variant of the previously proposed generators, TGFSR, modified so as to admit a Mersenne-prime period. The characteristic polynomial has many terms. The distribution up to
v
bits accuracy for 1 ≤
v
≤ 32 is also shown to be good. An algorithm is also given that checks the primitivity of the characteristic polynomial of MT with computational complexity

O(p
2
)

where
p
is the degree of the polynomial.

We implemented this generator in portable C-code. It passed several stringent statistical tests, including diehard. Its speed is comparable to other modern generators. Its merits are due to the efficient algorithms that are unique to polynomial calculations over the two-element field.
Formalizing space shuttle software requirements
Authors: Crow Judith , Di Vito Ben
Published: July 2002

This article describes four case studies in which requirements for new flight software subsystems on NASA's Space Shuttle were analyzed using mechanically supported formal methods. Three of the studies used standard formal specification and verification techniques, and the fourth used state exploration. These applications illustrate two thesis: (1) formal methods complement conventional requirements analysis processes effectively and (2) formal methods confer benefits even when only selectively adopted and applied. The studies also illustrate the interplay of application maturity level and formal methods strategy, especially in areas such as technology transfer, legacy applications, and rapid formalization, and they raise interesting issues in problem domain modeling and in tailoring formal techniques to applications.
Metric details for natural-language spatial relations
Authors: Egenhofer Max J. , Shariff A. Rashid B. M.
Published: July 2002

Spatial relations often are desired answers that a geographic information system (GIS) should generate in response to a user's query. Current GIS's provide only rudimentary support for processing and interpreting natural-language-like spatial relations, because their models and representations are primarily quantitative, while natural-language spatial relations are usually dominated by qualitative properties. Studies of the use of spatial relations in natural language showed that topology accounts for a significant portion of the geometric properties. This article develops a formal model that captures
metric details
for the description of natural-language spatial relations. The metric details are expressed as refinements of the categories identified by the 9-intersection, a model for topological spatial relations, and provide a more precise measure than does topology alone as to whether a geometric configuration matches with a spatial term or not. Similarly, these measures help in identifying the spatial term that describes a particular configuration. Two groups of metric details are derived:
splitting ratios
as the normalized values of lengths and areas of intersections; and
closeness measures
as the normalized distances between disjoint object parts. The resulting model of topological and metric properties was calibrated for 64 spatial terms in English, providing values for the best fit as well as value ranges for the significant parameters of each term. Three examples demonstrate how the framework and its calibrated values are used to determine the best spatial term for a relationship between two geometric objects.
A decision-theoretic approach to database selection in networked IR
Authors: Fuhr Norbert
Published: July 2002

In networked IR, a client submits a query to a broker, which is in
contact with a large number of databases. In order to yield a maximum number of documents at minimum cost, the broker has to make estimates about the retrieval cost of each database, and then decide for each database whether or not to use it for the current query, and if, how many documents to retrieve from it. For this purpose, we develop a general decision-theoretic model and discuss different cost structures. Besides cost for retrieving relevant versus nonrelevant documents, we consider the following parameters for each database: expected retrieval quality, expected number of relevant documents in the database and cost factors for query processing and document delivery. For computing the overall optimum, a divide-and-conquer algorithm is given. If there are several brokers knowing different databases, a preselection of brokers can only be performed heuristically, but the computation of the optimum can be done similarily to the single-broker case. In addition, we derive a formula which estimates the number of relevant documents in a database based on dictionary information.
Radix Exchange—An Internal Sorting Method for Digital Computers
Authors: Hildebrandt Paul , Isbitz Harold
Published: July 2002

This note describes a new technique—Radix Exchange—for sorting data internal to the high speed memory of an electronic binary digital computer. The technique is faster than Inserting by the ratio (log
2
n
)/
n
for sorting
n
= 2
c
items with values distributed evenly in the range 0 to 2
c
— 1. Its speed compares favorably with internal merging and it has the significant advantage of requiring essentially no working area in addition to that storage for the data being sorted and the instructions comprising the Radix Exchange routine itself. The nomenclature used is, in most cases, that of E. H. Friend [1].
A Comparison of Methods for Generating Normal Deviates on Digital Computers
Authors: Muller Mervin E.
Published: July 2002

Two methods recently developed for generating normal deviates within a computer are reviewed along with earlier proposals. A comparison of the various methods for application on an IBM 704 is given. The new direct method gives higher accuracy than previous methods of comparable speed. The detailed inverse technique proposed yields accuracy comparable with, or better than, most previous proposals using about one-quarter the computing time.
A Family of Quadrature Formulas Which Achieve High Accuracy in Composite Rules
Authors: Ralston A.
Published: July 2002

A class of quadrature formulas is derived which achieve higher accuracy in composite rules (i.e., where the interval of integration is broken up into a number of subintervals) than analogous Newton-Cotes or Gaussian formulas. The cost of this higher accuracy is the computation of one or two more ordinates over the whole interval of integration.

The high accuracy is obtained by using Gaussian techniques in the interior of each subinterval and by using the endpoints of each subinterval as abscissas with weights of equal magnitude and opposite sign. In this way when the subintervals are put together only the endpoints of the whole interval of integration remain. It is proved that the abscissas are all real and interior to the subinterval and that the weights corresponding to the interior abscissas are positive.

Since the abscissas are not equally spaced, the method is not suited to tabular functions but rather to analytically given functions. The roundoff properties of the formulas are discussed and are shown to be quite good.
The Use of Information in Sorting
Authors: Beus H. Lynn
Published: July 2002

The information-gathering aspect of sorting is considered from a theoretical viewpoint. A large class,
R,
of sorting algorithms is defined, based on the idea of information use. Properties of this algorithm class are developed, and it is noted that several well-known sorting algorithms are closely related to algorithms in
R
. The Binary Tree Sort is shown to be in
R
and to have unique properties in this class. A vector is defined which characterizes the information-gathering efficiency of the algorithms of
R
. Finally, a more general class of algorithms is defined, and some of the definitions extended to this class. Two intriguing conjectures are given which appear to require graph theory or combinatorial topology for their solution.
An Efficient Parallel Algorithm for the Solution of a Tridiagonal Linear System of Equations
Authors: Stone Harold S.
Published: July 2002

Tridiagonal linear systems of equations can be solved on conventional serial machines in a time proportional to
N
, where
N
is the number of equations. The conventional algorithms do not lend themselves directly to parallel computation on computers of the ILLIAC IV class, in the sense that they appear to be inherently serial. An efficient parallel algorithm is presented in which computation time grows as log
2
N
. The algorithm is based on recursive doubling solutions of linear recurrence relations, and can be used to solve recurrence relations of all orders.
Monitors
Authors: Hoare C. A. R.
Published: July 2002

This paper develops Brinch-Hansen's concept of a monitor as a method of structuring an operating system. It introduces a form of synchronization, describes a possible method of implementation in terms of semaphores and gives a suitable proof rule. Illustrative examples include a single resource scheduler, a bounded buffer, an alarm clock, a buffer pool, a disk head optimizer, and a version of the problem of readers and writers.
Some realities of data administration
Authors: Kahn Beverly K.
Published: July 2002

Little information exists on the practice of data administration, i.e., the management of data as an enterprise resource. A survey of data administrators at predominantly large enterprises was conducted to determine the extent of the existence of data administration and to assess its effectiveness as implemented. New insight into the realities of data administration, including its real-world objectives and perceived effectiveness, is presented.
The Manchester Mark I and atlas
Authors: Lavington S. H.
Published: July 2002

In 30 years of computer design at Manchester University two systems stand out: the Mark I (developed over the period 1946-49) and the Atlas (1956-62). This paper places each computer in its historical context and then describes the architecture and system software in present-day terminology. Several design concepts such as address-generation and store management have evolved in the progression from Mark I to Atlas. The wider impact of Manchester innovations in these and other areas is discussed, and the contemporary performance of the Mark I and Atlas is evaluated.
The development of the MU5 computer system
Authors: Ibbett R. N. , Capon P. C.
Published: July 2002

Following a brief outline of the background of the MU5 project, the aims and ideas for MU5 are discussed. A description is then given of the instruction set, which includes a number of features conducive to the production of efficient compiled code from high-level language source programs. The design of the processor is then traced from the initial ideas for an associatively addressed “name store” to the final multistage pipeline structure involving a prediction mechanism for instruction prefetching and a function queue for array element accessing. An overall view of the complete MU5 complex is presented together with a brief indication of its performance.
Covering edges by cliques with regard to keyword conflicts and intersection graphs
Authors: Kou L. T. , Stockmeyer L. J. , Wong C. K.
Published: July 2002

Kellerman has presented a method for determining keyword conflicts and described a heuristic algorithm which solves a certain combinatorial optimization problem in connection with this method. This optimization problem is here shown to be equivalent to the problem of covering the edges of a graph by complete subgraphs with the objective of minimizing the number of complete subgraphs. A relationship between this edge-clique-cover problem and the graph coloring problem is established which allows algorithms for either one of these problems to be constructed from algorithms for the other. As consequences of this relationship, the keyword conflict problem and the edge-clique-cover problem are shown to be NP-complete, and if
P
≠
NP
then they do not admit polynomial-time approximation algorithms which always produce solutions within a factor less than 2 from the optimum.
On the stability of Gauss-Jordan elimination with pivoting
Authors: Peters G. , Wilkinson J. H.
Published: July 2002

The stability of the Gauss-Jordan algorithm with partial pivoting for the solution of general systems of linear equations is commonly regarded as suspect. It is shown that in many respects suspicions are unfounded, and in general the absolute error in the solution is strictly comparable with that corresponding to Gaussian elimination with partial pivoting plus back substitution. However, when A is ill conditioned, the residual corresponding to the Gauss-Jordan solution will often be much greater than that corresponding to the Gaussian elimination solution.
Interpolation with rounded ramp functions
Authors: Lagerlöf Rolf O.
Published: July 2002

A new interpolation function is introduced. It has infinitely many continuous derivatives and is a composition of ramp functions with smoothed bends called Rounded Ramp Functions. How the interpolation function can be extended to more than one variable is shown. An efficient Fortran program is given by which the interpolation function can be obtained for a given point set.
A study of storage partitioning using a mathematical model of locality
Authors: Coffman E. G. , Ryan Thomas A.
Published: July 2002

Both fixed and dynamic storage partitioning procedures are examined for use in multiprogramming systems. The storage requirement of programs is modeled as a stationary Gaussian process. Experiments justifying this model are described. By means of this model dynamic storage partitioning is shown to provide substantial increases in storage utilization and operating efficiency over fixed partitioning.
Properties of the working-set model
Authors: Denning Peter J. , Schwartz Stuart C.
Published: July 2002

A program's working set
W
(
t, T
) at time
t
is the set of distinct pages among the
T
most recently referenced pages. Relations between the average working-set size, the missing-page rate, and the interreference-interval distribution may be derived both from time-average definitions and from ensemble-average (statistical) definitions. An efficient algorithm for estimating these quantities is given. The relation to LRU (lease recently used) paging is characterized. The independent-reference model, in which page references are statistically independent, is used to assess the effects of interpage dependencies on working-set size observations. Under general assumptions, working-set size is shown to be normally distributed.
File structures using hashing functions
Authors: Coffman E. G. , Eve J.
Published: July 2002

A general method of file structuring is proposed which uses a hashing function to define tree structure. Two types of such trees are examined, and their relation to trees studied in the past is explained. Results for the probability distributions of path lengths are derived and illustrated.
SABRAC, a time-sharing low-cost computer
Authors: Lehman M. , Netter Z. , Eshed R.
Published: July 2002

The serial SABRAC computer designed and built in the Scientific Department of the Israel Defence Ministry has a 5000-location magnetic drum, main store. To avoid a need to resort to optimum programming techniques and to increase its overall efficiency the computer has also been given a 224-word ferrite core store from which the program is obeyed.

Transfers between the core and drum stores and to and from the twin paper-tape input and output channels are all available autonomously (concurrently, time-shared). Multiplication and division orders are also autonomous, so that the machine may be executing up to three orders simultaneously. All functions naturally are interlocked.

A number of other advanced orders and facilities are also incorporated. In particular, an “Execute” order permits a temporary jump for up to four orders and a second modifier register permits double modification in general and relative addressing of subroutines in particular. Thus the overall effective speed of the machine is much higher than its basic specification would lead one to expect and its design indicates one way in which the concepts of time sharing may be incorporated in “low-cost” computers.
Character manipulation in 7090 FORTRAN
Authors: Smith D. D.
Published: July 2002

The IBM 7090 FORTRAN II language requires that a programmer desiring toa mnipulate characters or strings of characters either assign each character to a separate 7090 word or write special subroutines for handling packed words containing 6 characters. The one-character-per-word approach is superior in most cases due to the much smaller machine time it requires. One pays for this speed advantage in additional core requirements, however, plus more complex logic requirements in some cases. Applications exist where considerations of storage and logic make a packed-word approach competitive. One such application, and the one which led to the work described here, was the desire to manipulate information sent via telephone lines by a remote 7090 user to and from the central computer. The results of this work are not completed, but the methods used for manipulating character strings were felt to be of sufficient interest to warrant a report. The following paragraphs describe the approach taken.
Automated deductive requirements analysis of critical systems
Authors: Gargantini Angelo , Morzenti Angelo
Published: July 2002

We advocate the need for automated support to System Requirement Analysis in the development of time- and safety-critical computer-based systems. To this end we pursue an approach based on deductive analysis: high-level, real-world entities and notions, such as events, states, finite variability, cause-effect relations, are modeled through the temporal logic TRIO, and the resulting deductive system is implemented by means of the theorem prover PVS. Throughout the paper, the constructs and features of the deductive system are illustrated and validated by applying them to the well-known example of the Generalized Railway Crossing.
Multivariate interpolation of large sets of scattered data
Authors: Renka Robert J.
Published: July 2002

This paper presents a method of constructing a smooth function of two or more variables that interpolates data values at arbitrarily distributed points. Shepard's method for fitting a surface to data values at scattered points in the plane has the advantages of a small storage requirement and an easy generalization to more than two independent variables, but suffers from low accuracy and a high computational cost relative to some alternative methods. Localizations of this method have reasonably low computational costs, but remain relatively inaccurate. We describe a modified Shepard's method that, without sacrificing the advantages, has accuracy comparable to other local methods. Computational efficiency is also improved by using a cell method for nearest-neighbor searching. Test results for two and three independent variables are presented.
What makes learning networks effective?
Authors: Hiltz Starr Roxanne , Turoff Murray
Published: July 2002

Asynchronous Learning Networks are providing a strong online option to the learning process. Effective ALNs promote student-instructor interaction, emphasize student-to-student collaboration, and generate active participation with appropriate software.
TEXTNET: a network-based approach to text handling
Authors: Trigg Randall H. , Weiser Mark
Published: July 2002

Textnet is a new system for structuring text. The Textnet approach uses one uniform data structure to capture graphlike pools of text, as well as embedded hierarchical structures. By using a semantic network formalism of nodes connected by typed links, the relationships between neighboring pieces of text are made explicit. Also described is our partial implementation of the Textnet approach, which makes use of an object-oriented window/menu-driven user interface. Users peruse the network by moving among object menus or by reading text along a path through the network. In addition, critiquing, reader linking, searching, and jumping are easily accessible operations. Finally, the results of a short trial with users are presented.
Using dual approximation algorithms for scheduling problems theoretical and practical results
Authors: Hochbaum Dorit S. , Shmoys David B.
Published: July 2002

The problem of scheduling a set of
n
jobs on
m
identical machines so as to minimize the makespan time is perhaps the most well-studied problem in the theory of approximation algorithms for NP-hard optimization problems. In this paper the strongest possible type of result for this problem, a polynomial approximation scheme, is presented. More precisely, for each ε, an algorithm that runs in time
O
((
n
/ε)

1/ε
2

) and has relative error at most ε is given. In addition, more practical algorithms for ε = 1/5 + 2

-
k

and ε = 1/6 + 2

-
k

, which have running times
O
(
n
(
k
+ log
n
)) and
O
(
n
(
km
4
+ log
n
)) are presented. The techniques of analysis used in proving these results are extremely simple, especially in comparison with the baroque weighting techniques used previously.

The scheme is based on a new approach to constructing approximation algorithms, which is called dual approximation algorithms, where the aim is to find superoptimal, but infeasible, solutions, and the performance is measured by the degree of infeasibility allowed. This notion should find wide applicability in its own right and should be considered for any optimization problem where traditional approximation algorithms have been particularly elusive.
Parallel free-text search on the connection machine system
Authors: Stanfill Craig , Kahle Brewster
Published: July 2002

A new implementation of free-text search using a new parallel computer—the Connection Machine®—makes possible the application of exhaustive methods not previously feasible for large databases.
A bridging model for parallel computation
Authors: Valiant Leslie G.
Published: July 2002

The success of the von Neumann model of sequential computation is attributable to the fact that it is an efficient bridge between software and hardware: high-level languages can be efficiently compiled on to this model; yet it can be effeciently implemented in hardware. The author argues that an analogous bridge between software and hardware in required for parallel computation if that is to become as widely used. This article introduces the bulk-synchronous parallel (BSP) model as a candidate for this role, and gives results quantifying its efficiency both in implementing high-level language features and algorithms, as well as in being implemented in hardware.
International perspectives: The globalization of computing
Authors: Goodman S. E.
Published: July 2002

Are the computing and telecommunications technologies making the entire world a better place in which to live?
POLLEN GERMINATION AND TUBE GROWTH
Authors: Taylor Loverine P. , Hepler Peter K.
Published: July 2002

▪ Abstract  Many aspects of Angiosperm pollen germination and tube growth are discussed including mechanisms of dehydration and rehydration, in vitro germination, pollen coat compounds, the dynamic involvement of cytoskeletal elements (actin, microtubules), calcium ion fluxes, extracellular matrix elements (stylar arabinogalactan proteins), and control mechanisms of gene expression in dehydrating and germinating pollen. We focus on the recent developments in pollen biology that help us understand how the male gamete survives and accomplishes its successful delivery to the ovule of the sperm to effect sexual reproduction.
GAMETOPHYTE DEVELOPMENT IN FERNS
Authors: Banks Jo Ann
Published: July 2002

▪ Abstract  The fern gametophyte has interested plant biologists for the past century because its structure and development is simple and amenable to investigation. Past studies have described many aspects of its development, including germination of the spore, patterns of cell division and differentiation, photomorphogenic or light-regulated responses, sex determination and differentiation of gametangia, hormone and pheromone responses, and fertilization. Several genes that are predicted to regulate some of these processes have been recently cloned, making it possible to analyze how these processes are controlled at a molecular level. The emergence of the fern Ceratopteris richardii as a model organism for readily identifying and characterizing mutations that affect key developmental processes in gametophytes makes it a powerful tool for dissecting the molecular mechanisms underlying these processes. If advances in gene cloning techniques and transformation are forthcoming in Ceratopteris, it is likely that the study of developmental processes in ferns will significantly contribute to our understanding of plant development and evolution beyond that which can be learned solely from studying angiosperms.
CELLULOSE BIOSYNTHESIS: Exciting Times for A Difficult Field of Study
Authors: Delmer Deborah P.
Published: July 2002

▪ Abstract  The past few decades have witnessed exciting progress in studies on the biosynthesis of cellulose. In the bacterium Acetobacter xylinum, discovery of the activator of the cellulose synthase, cyclic diguanylic acid, opened the way for obtaining high rates of in vitro synthesis of cellulose. This, in turn, led to purification of the cellulose synthase and for the cloning of genes that encode the catalytic subunit and other proteins that bind the activator and regulate its synthesis and degradation, or that control secretion and crystallization of the microfibrils. In higher plants, a family of genes has been discovered that show interesting similarities and differences from the gene in bacteria that encodes the catalytic subunit of the synthase. Genetic evidence now supports the concept that members of this family encode the catalytic subunit in these organisms, with various members showing tissue-specific expression. Although the cellulose synthase has not yet been purified to homogeneity from plants, recent progress in this area suggests that this will soon be accomplished.
PHOTOPROTECTION REVISITED:Genetic and Molecular Approaches
Authors: Niyogi Krishna K.
Published: July 2002

▪ Abstract  The involvement of excited and highly reactive intermediates in oxygenic photosynthesis poses unique problems for algae and plants in terms of potential oxidative damage to the photosynthetic apparatus. Photoprotective processes prevent or minimize generation of oxidizing molecules, scavenge reactive oxygen species efficiently, and repair damage that inevitably occurs. This review summarizes several photoprotective mechanisms operating within chloroplasts of plants and green algae. The recent use of genetic and molecular biological approaches is providing new insights into photoprotection, especially with respect to thermal dissipation of excess absorbed light energy, alternative electron transport pathways, chloroplast antioxidant systems, and repair of photosystem II.
NONPHOTOSYNTHETICMETABOLISM INPLASTIDS
Authors: Neuhaus H. E. , Emes M. J.
Published: July 2002

▪ Abstract  Nonphotosynthetic plastids are important sites for the biosynthesis of starch, fatty acids, and the assimilation of nitrogen into amino acids in a wide range of plant tissues. Unlike chloroplasts, all the metabolites for these processes have to be imported, or generated by oxidative metabolism within the organelle. The aim of this review is to summarize our present understanding of the anabolic pathways involved, the requirement for import of precursors from the cytosol, the provision of energy for biosynthesis, and the interaction between pathways that share common intermediates. We emphasize the temporal and developmental regulation of events, and the variation in mechanisms employed by different species that produce the same end products.
GUARDCELLSIGNALTRANSDUCTION
Authors: Schroeder Julian I , Allen Gethyn J , Hugouvieux Veronique , Kwak June M , Waner David
Published: July 2002

▪ Abstract  Guard cells surround stomatal pores in the epidermis of plant leaves and stems. Stomatal pore opening is essential for CO2influx into leaves for photosynthetic carbon fixation. In exchange, plants lose over 95% of their water via transpiration to the atmosphere. Signal transduction mechanisms in guard cells integrate hormonal stimuli, light signals, water status, CO2, temperature, and other environmental conditions to modulate stomatal apertures for regulation of gas exchange and plant survival under diverse conditions. Stomatal guard cells have become a highly developed model system for characterizing early signal transduction mechanisms in plants and for elucidating how individual signaling mechanisms can interact within a network in a single cell. In this review we focus on recent advances in understanding signal transduction mechanisms in guard cells.
TRANSPORTERS RESPONSIBLE FOR THE UPTAKE AND PARTITIONING OF NITROGENOUS SOLUTES
Authors: Williams LE , Miller AJ
Published: July 2002

▪ Abstract  The acquisition and allocation of nitrogenous compounds are essential processes in plant growth and development. The huge economic and environmental costs resulting from the application of nitrogen fertilizers make this topic very important. A diverse array of transporters varying in their expression pattern and also in their affinity, specificity, and capacity for nitrogenous compounds has been identified. Now the future challenge is to define their individual contribution to nitrogen nutrition and signalling processes. Here we have reviewed recent advances in the identification and molecular characterization of these transporters, concentrating on mechanisms existing at the plasma membrane. The review focuses on nitrate, ammonium, and amino acid transporter familes, but we also briefly describe what is known at the molecular level about peptide transporters and a recently identified family implicated in the transport of purines and their derivatives.
A Critical Review of Galactic Dynamos
Authors: Kulsrud Russell M.
Published: July 2002

▪ Abstract  I present the general picture of how galactic magnetic fields grow in disks according to the alpha-Omega dynamo theory. Emphasis is placed on following the lines of force during the dynamo process. The dynamo equation is presented together with a simple growing solution for the galactic disk. Then I take up the various critical questions that have been raised concerning the galactic dynamo theory. These are (1) the importance of the escape of flux from the disk in order for the magnetic field to grow; (2) the physics of turbulent diffusion and its mixing of field lines together so that the rms field is possibly greater than the mean field; (3) whether magnetic reconnection plays a role in the galactic dynamo; (4) whether small-scale fields can grow large enough to swamp the dynamo. Then I discuss the possible seed fields from which the dynamo starts and their relation to the primordial hypothesis. Finally I take up the question of the final evolution of the galactic field after the alpha effect saturates. My conclusion is that all these problems warrant attention but none of them seem to be serious enough to cast any real doubt on the dynamo as the most likely generator of galactic fields.
PHOSPHOINOSITIDE KINASES
Authors: Fruman David A. , Meyers Rachel E. , Cantley Lewis C.
Published: July 2002

Phosphatidylinositol, a component of eukaryotic cell membranes, is unique among phospholipids in that its head group can be phosphorylated at multiple free hydroxyls. Several phosphorylated derivatives of phosphatidylinositol, collectively termed phosphoinositides, have been identified in eukaryotic cells from yeast to mammals. Phosphoinositides are involved in the regulation of diverse cellular processes, including proliferation, survival, cytoskeletal organization, vesicle trafficking, glucose transport, and platelet function. The enzymes that phosphorylate phosphatidylinositol and its derivatives are termed phosphoinositide kinases. Recent advances have challenged previous hypotheses about the substrate selectivity of different phosphoinositide kinase families. Here we re-examine the pathways of phosphoinositide synthesis and the enzymes involved.
THE DNA REPLICATION FORK IN EUKARYOTIC CELLS
Authors: Waga Shou , Stillman Bruce
Published: July 2002

Replication of the two template strands at eukaryotic cell DNA replication forks is a highly coordinated process that ensures accurate and efficient genome duplication. Biochemical studies, principally of plasmid DNAs containing the Simian Virus 40 origin of DNA replication, and yeast genetic studies have uncovered the fundamental mechanisms of replication fork progression. At least two different DNA polymerases, a single-stranded DNA-binding protein, a clamp-loading complex, and a polymerase clamp combine to replicate DNA. Okazaki fragment synthesis involves a DNA polymerase-switching mechanism, and maturation occurs by the recruitment of specific nucleases, a helicase, and a ligase. The process of DNA replication is also coupled to cell-cycle progression and to DNA repair to maintain genome integrity.
Structural Insights into Microtubule Function
Authors: Nogales Eva
Published: July 2002

▪ Abstract  Microtubules are polymers that are essential for, among other functions, cell transport and cell division in all eukaryotes. The regulation of the microtubule system includes transcription of different tubulin isotypes, folding of α/β-tubulin heterodimers, post-translation modification of tubulin, and nucleotide-based microtubule dynamics, as well as interaction with numerous microtubule-associated proteins that are themselves regulated. The result is the precise temporal and spatial pattern of microtubules that is observed throughout the cell cycle. The recent high-resolution analysis of the structure of tubulin and the microtubule has brought new insight to the study of microtubule function and regulation, as well as the mode of action of antimitotic drugs that disrupt normal microtubule behavior. The combination of structural, genetic, biochemical, and biophysical data should soon give us a fuller understanding of the exquisite details in the regulation of the microtubule cytoskeleton.
Mechanisms And Control Of mRNA Decapping in Saccharomyces cerevisiae
Authors: Tucker Morgan , Parker Roy
Published: July 2002

▪ Abstract  The process of mRNA turnover is a critical component of the regulation of gene expression. In the past few years a discrete set of pathways for the degradation of polyadenylated mRNAs in eukaryotic cells have been described. A major pathway of mRNA degradation in yeast occurs by deadenylation of the mRNA, which leads to a decapping reaction, thereby exposing the mRNA to rapid 5′ to 3′ exonucleolytic degradation. A critical step in this pathway is decapping, since it effectively terminates the existence of the mRNA and is the site of numerous control inputs. In this review, we discuss the properties of the decapping enzyme and how its activity is regulated to give rise to differential mRNA turnover. A key point is that decapping appears to be controlled by access of the enzyme to the cap structure in a competition with the translation initiation complex. Strikingly, several proteins required for mRNA decapping show interactions with the translation machinery and suggest possible mechanisms for the triggering of mRNA decapping.
Critical Analysis of Antibody Catalysis
Authors: Hilvert Donald
Published: July 2002

▪ Abstract  Antibody molecules elicited with rationally designed transition-state analogs catalyze numerous reactions, including many that cannot be achieved by standard chemical methods. Although relatively primitive when compared with natural enzymes, these catalysts are valuable tools for probing the origins and evolution of biological catalysis. Mechanistic and structural analyses of representative antibody catalysts, generated with a variety of strategies for several different reaction types, suggest that their modest efficiency is a consequence of imperfect hapten design and indirect selection. Development of improved transition-state analogs, refinements in immunization and screening protocols, and elaboration of general strategies for augmenting the efficiency of first-generation catalytic antibodies are identified as evident, but difficult, challenges for this field. Rising to these challenges and more successfully integrating programmable design with the selective forces of biology will enhance our understanding of enzymatic catalysis. Further, it should yield useful protein catalysts for an enhanced range of practical applications in chemistry and biology.
USE OF SURFACE PLASMON RESONANCE TO PROBE THE EQUILIBRIUM AND DYNAMIC ASPECTS OF INTERACTIONS BETWEEN BIOLOGICAL MACROMOLECULES
Authors: Schuck Peter
Published: July 2002

▪ Abstract  Surface plasmon resonance biosensors have become increasingly popular for the qualitative and quantitative characterization of the specific binding of a mobile reactant to a binding partner immobilized on the sensor surface. This article reviews the use of this new technique to measure the binding affinities and the kinetic constants of reversible interactions between biological macromolecules. Immobilization techniques, the most commonly employed experimental strategies, and various analytical approaches are summarized. In recent years, several sources of potential artifacts have been identified: immobilization of the binding partner, steric hindrance of binding to adjacent binding sites at the sensor surface, and finite rate of mass transport of the mobile reactant to the sensor surface. Described here is the influence of these artifacts on the measured binding kinetics and equilibria, together with suggested control experiments.
SIGNALING BY EXTRACELLULAR NUCLEOTIDES
Authors: Brake Anthony J. , Julius David
Published: July 2002

▪ Abstract  ATP and other nucleotides can be released from cells through regulated pathways, or following the loss of plasma membrane integrity. Once outside the cell, these compounds take on new roles as intercellular signaling molecules that elicit a broad spectrum of physiological responses through the activation of numerous cell surface receptor subtypes. This review summarizes recent advances in the molecular characterization of ATP receptors and discusses roles for cloned receptors in established and novel physiological processes.