bluuebunny/crossref_metadata_2025 huggingface dataset:
Attributes of the performance of central processing units: a relative performance prediction model
Authors: Ein-Dor Phillip , Feldmesser Jacob
Published: July 2002

Using readily available data on CPU characteristics—main memory size, cache memory size, number of channels, and machine cycle time—it is possible to predict relative CPU performance for a wide range of machines. Statistical analyses indicate that these characteristics explain virtually all the variance in relative performance.
Real-time simulation of dust behavior generated by a fast traveling vehicle
Authors: Chen Jim X. , Fu Xiadong , Wegman J.
Published: July 2002

Simulation of physically realistic complex dust behavior is very useful in training, education, art, advertising, and entertainment. There are no published models for real-time simulation of dust behavior generated by a traveling vehicle. In this paper, we use particle systems, computational fluid dynamics, and behavioral simulation techniques to simulate dust behavior in real time. First, we analyze the forces and factors that affect dust generation and the behavior after dust particles are generated. Then, we construct physically-based empirical models to generate dust particles and control the behavior accordingly. We further simplify the numerical calculations by dividing dust behavior into three stages, and establishing simplified particle system models for each stage. We employ motion blur, particle blending texture mapping, and other computer graphics techniques to achieve the final results. Our contributions include constructing physically-based empirical models to generate dust behavior and achieving simulation of the behavior in real time.
Radiance interpolants for accelerated bounded-error ray tracing
Authors: Bala Kavita , Dorsey Julie , Teller Seth
Published: July 2002

Ray tracers, which sample radiance, are usually regarded as offline rendering algorithms that are too slow for interactive use. In this article we present a system that exploits object-space, ray-space, image-space, and temporal coherence to accelerate ray tracing. Our system uses
per-surface interpolants
to approximate radiance both interactive and batch ray tracers.
Our approach explicity decouples the two primary operations of a ray tracer—shading and visibility determination—and accelerates each of them independently. Shading is accelerated by quadrilinearily interpolating lazily acquired radiance samples. Interpolation error does not exceed a user-specified bound, allowing the user to control performance/quality tradeoffs.
Error is bounded by adaptive sampling at discontinuities and radiance nonlinearities.
Visibility determination at pixels is accelerated by
reprojecting
interpolants as the user's viewpoint changes. A fast scan-line alogoithm then achieves high performance without sacrificing image quality. For a smoothly varying viewpoint, the combination of lazy interpolants and projection substantially accelerates the ray tracer. Additionally, an efficient cache management algorithm keeps the memory footprint of the system small with negilgible overhead.
ADMIT-1
Authors: Coleman Thomas F. , Verma Arun
Published: July 2002

ADMIT-1 enables the computation of
sparse
Jacobian and Hessian matrices, using automatic differentiation technology, from a MATLAB environment. Given a function to be differentiated, ADMIT-1 will exploit sparsity if present to yield sparse derivative matrices (in sparse MATLAB form). A generic automatic differentiation tool, subject to some functionality requirements, can be plugged into ADMIT-1; examples include ADOL-C (C/C++ target functions)and ADMAT (MATLAB target funcitons). ADMIT-1 also allows for the calculation of gradients and has several other related functions. This article provides an introduction to the design and usage of ADMIT-1.
Password authentication with insecure communication
Authors: Lamport Leslie
Published: July 2002

A method of user password authentication is described which is secure even if an intruder can read the system's data, and can tamper with or eavesdrop on the communication between the user and the system. The method assumes a secure one-way encryption function and can be implemented with a microcomputer in the user's terminal.
The impact and use of computer technology by the police
Authors: Colton Kent W.
Published: July 2002

Over the past decade there has been a significant growth in the use of computer technology by U.S. police departments. This growth, however, has been at a slower rate than predicted in the early 1970's. Further, when computer applications extend beyond “routine” uses to “nonroutine” efforts, such as resource allocation or computer-aided-dispatch systems where the machine begins to become a tool for decision making, strategic planning and person/machine interaction, the results of the technology to date have been mixed. This paper reports on case studies and surveys which provide insights on the implementation and impact of police computer technology and the relationship of this technology to law enforcement and society.
Logical analysis of programs
Authors: Katz Shmuel , Manna Zohar
Published: July 2002

Most present systems for verification of computer programs are incomplete in that intermediate inductive assertions must be provided manually by the user, termination is not proven, and incorrect programs are not treated. As a unified solution to these problems, this paper suggests conducting a logical analysis of programs by using invariants which express what is actually occurring in the program.

The first part of the paper is devoted to techniques for the automatic generation of invariants. The second part provides criteria for using the invariants to check simultaneously for correctness (including termination) or incorrectness. A third part examines the implications of the approach for the automatic diagnosis and correction of logical errors.
Hierarchical geometric models for visible surface algorithms
Authors: Clark James H.
Published: July 2002

The geometric structure inherent in the definition of the shapes of three-dimensional objects and environments is used not just to define their relative motion and placement, but also to assist in solving many other problems of systems for producing pictures by computer. By using an extension of traditional structure information, or a geometric hierarchy, five significant improvements to current techniques are possible. First, the range of complexity of an environment is greatly increased while the visible complexity of any given scene is kept within a fixed upper limit. Second, a meaningful way is provided to vary the amount of detail presented in a scene. Third, “clipping” becomes a very fast logarithmic search for the resolvable parts of the environment within the field of view. Fourth, frame to frame coherence and clipping define a graphical “working set,” or fraction of the total structure that should be present in primary store for immediate access by the visible surface algorithm. Finally, the geometric structure suggests a recursive descent, visible surface algorithm in which the computation time potentially grows linearly with the visible complexity of the scene.
Control structures in Illiac IV Fortran
Authors: Millstein Robert E.
Published: July 2002

As part of an effort to design and implement a Fortran compiler on the ILLIAC IV, an extended Fortran, called IVTRAN, has been developed. This language provides a means of expressing data and control structures suitable for exploiting ILLIAC IV parallelism. This paper reviews the hardware characteristics of the ILLIAC and singles out unconventiona features which could be expected to influence langluage (and compiler) design. The implications of these features for data layout and algorithm structure are discussed, and the conclusion is drawn that data allocation rather than code structuring is the crucial ILLIAC optimization problem. A satisfactory method of data allocation is then presented. Language structures to utilize this storage method and express parallel algorithms are described.
Graph-based code selection techniques for embedded processors
Authors: Leupers Rainer LEUPERS , Bashford Steven
Published: July 2002

Code selection is an important task in code generation for programmable processors, where the goal is to find an efficient mapping of machine-independent intermediate code to processor-specific machine instructions. Traditional approaches to code selection are based on tree parsing which enables fast and optimal code selection for intermediate code given as a set of data-flow trees. While this approach is generally useful in compilers for general-purpose processors, it may lead to poor code quality in the case of embedded processors. The reason is that the special architectural features of embedded processors require performing code selection on data-flow graphs, which are a more general representation of intermediate code. In this paper, we present data-flow graph-based code selection techniques for two architectural families of embedded processors: media processors with support for SIMD instructions and fixed-point DSPs with irregular data paths. Both techniques exploit the fact that, in the area of embedded systems, high code quality is a much more important goal than high compilation speed. We demonstrate that certain architectural features can only be utilized by graph-based code selection, while in other cases this approach leads to a significant increase in code quality as compared to tree-based code selection.
Generating binary trees using rotations
Authors: Zerling David
Published: July 2002

A new algorithm that, for the first time, exploits the rotational geometry of binary trees is developed in order to allow for the lexicographic generation of computer representations of these trees in average time
O
(1) per tree. “Rotation” codewords for these trees (in average time
O
(1) per tree) are also generated. It is shown how these codewords relate to lattice paths, and, using this relationship, that
n
(
n
- 1)/(
n
+ 2) is the average number of rotations needed to generate a binary tree on
n
nodes. Finally, a necessary and sufficient condition that a codeword represent a full binary tree (each node has 0 or 2 sons) on
n
= 2
m
+ 1 nodes is given and how to contract this codeword to obtain the codeword for the binary tree on
m
nodes for which this full tree is the extended binary tree is shown.
Active zones in CSG for accelerating boundary evaluation, redundancy elimination, interference detection, and shading algorithms
Authors: Rossignac Jaroslaw R. , Voelcker Herbert B.
Published: July 2002

Solids defined by Boolean combinations of solid primitives may be represented in constructive solid geometry (CSG) as binary trees. Most CSG-based algorithms (e.g., for boundary evaluation, graphic shading, interference detection) do various forms of set-membership classification by traversing the tree associated with the solid. These algorithms usually generate intermediate results that do not contribute to the final result, and hence may be regarded as redundant and a source of inefficiency. To reduce such inefficiencies, we associate with each primitive
A
in a tree
S
an
active zone Z
that represents the region of space where changes to
A
affect the solid represented by
S
, and we use a representation of
Z
instead of
S
for set-membership classification. In the paper we develop a mathematical theory of active zones, prove that they correspond to the intersection of certain nodes of the original trees, and show how they lead to efficient new algorithms for boundary evaluation, for detecting and eliminating redundant nodes in CSG trees, for interference (null-set) detection, and for graphic shading.
Introspection
Authors: Karri Ramesh , Iyer Balakrishnan
Published: July 2002

We report a register transfer level technique for concurrent error detection and diagnosis in data dominated designs called
Introspection
. Introspection uses idle computation cyles in the data path and idle data transfer cycles in the interconnection network in a synergistic fashion for concurrent error detection and diagnosis (CEDD). The resulting on-chip fault latencies are one ten-thousandth (10
-4
) of previously reported system level concurrent error detection and diagnosis latencies. The associated area overhead and performance penalty are negligible. We derive a cost function that considers introspection constraints such as (i) executing an operation on three disjoint function units for diagnosis and (ii) promoting function units to participate in at least one CEDD operation. We formulate integration of introspection constraints into the operation-to-operator binding phase of high-level synthesis as a weighted bipartite matching problem. The effectiveness of introspection and its implementation are illustrated on numerous industrial strength benchmarks.
The Cassowary linear arithmetic constraint solving algorithm
Authors: Badros Greg J. , Borning Alan , Stuckey Peter J.
Published: July 2002

Linear equality and inequality constraints arise naturally in specifying many aspects of user interfaces, such as requiring that one window be to the left of another, requiring that a pane occupy the leftmost third of a window, or preferring that an object be contained within a rectangle if possible. Previous constraint solvers designed for user interface applications cannot handle simultaneous linear equations and inequalities efficiently. This is a major limitation, as such systems of constraints arise often in natural declarative specifications. We describe Cassowary---an incremental algorithm based on the dual simplex method, which can solve such systems of constraints efficiently. We have implemented the algorithm as part of a constraint-solving toolkit. We discuss the implementation of the toolkit, its application programming interface, and its performance.
Partitioning a polygonal region into trapezoids
Authors: Asano Takao , Asano Tetsuo , Imai Hiroshi
Published: July 2002

The problem of partitioning a polygonal region into a minimum number of trapezoids with two horizontal sides is discussed. A triangle with a horizontal side is considered to be a trapezoid with two horizontal sides one of which is degenerate. First, a method of achieving a minimum partition is presented. The number
M
* of the trapezoids in the minimum partition of a polygonal region
P
is shown to be
M
*
=
n
+
w
-
h
-
d
- 1, where
n
,
w
, and
h
are the number of vertices, windows (holes), and horizontal edges of
P
, respectively, and
d
is the cardinality of a maximum independent set of the straight-lines-in-the-plane graph associated with
P
. Next, this problem is shown to be polynomially equivalent to the problem of finding a maximum independent set of a straight-lines-in-the-plane graph, and consequently, it is shown to be NP-complete. However, for a polygonal region without windows, an
O
(
n
2
)-time algorithm for partitioning it into a minimum number of trapezoids is presented. Finally, an
O
(
n
log
n
)-time approximation algorithm with the performance bound 3 is presented.
Reaching approximate agreement in the presence of faults
Authors: Dolev Danny , Lynch Nancy A. , Pinter Shlomit S. , Stark Eugene W. , Weihl William E.
Published: July 2002

This paper considers a variant of the Byzantine Generals problem, in which processes start with arbitrary real values rather than Boolean values or values from some bounded range, and in which approximate, rather than exact, agreement is the desired goal. Algorithms are presented to reach approximate agreement in asynchronous, as well as synchronous systems. The asynchronous agreement algorithm is an interesting contrast to a result of Fischer et al, who show that exact agreement with guaranteed termination is not attainable in an asynchronous system with as few as one faulty process. The algorithms work by successive approximation, with a provable convergence rate that depends on the ratio between the number of faulty processes and the total number of processes. Lower bounds on the convergence rate for algorithms of this form are proved, and the algorithms presented are shown to be optimal.
Efficient dispersal of information for security, load balancing, and fault tolerance
Authors: Rabin Michael O.
Published: July 2002

An Information Dispersal Algorithm (IDA) is developed that breaks a file
F
of length
L
= ↿
F
↾ into
n
pieces

F
i

, l ≤
i
≤
n
, each of length ↿

F
i

↾ =
L
/
m
, so that every
m
pieces suffice for reconstructing
F
. Dispersal and reconstruction are computationally efficient. The sum of the lengths ↿
F
i
↾ is (
n
/
m
) ·
L
. Since
n
/
m
can be chosen to be close to l, the IDA is space efficient. IDA has numerous applications to secure and reliable storage of information in computer networks and even on single disks, to fault-tolerant and efficient transmission of information in networks, and to communications between processors in parallel computers. For the latter problem provably time-efficient and highly fault-tolerant routing on the
n
-cube is achieved, using just constant size buffers.
Semantic data models
Authors: Peckham Joan , Maryanski Fred
Published: July 2002

Semantic data models have emerged from a requirement for more expressive conceptual data models. Current generation data models lack direct support for relationships, data abstraction, inheritance, constraints, unstructured objects, and the dynamic properties of an application. Although the need for data models with richer semantics is widely recognized, no single approach has won general acceptance. This paper describes the generic properties of semantic data models and presents a representative selection of models that have been proposed since the mid-1970s. In addition to explaining the features of the individual models, guidelines are offered for the comparison of models. The paper concludes with a discussion of future directions in the area of conceptual data modeling.
Virtual video editing in interactive multimedia applications
Authors: Mackay Wendy E. , Davenport Glorianna
Published: July 2002

Drawing examples from four interrelated sets of multimedia tools and applications under development at MIT, the authors examine the role of digitized video in the areas of entertainment, learning, research, and communication.
Stochastic sampling in computer graphics
Authors: Cook Robert L.
Published: July 2002

Ray tracing, ray casting, and other forms of point sampling are important techniques in computer graphics, but their usefulness has been undermined by aliasing artifacts. In this paper it is shown that these artifacts are not an inherent part of point sampling, but a consequence of using regularly spaced samples. If the samples occur at appropriate nonuniformly spaced locations, frequencies above the Nyquist limit do not alias, but instead appear as noise of the correct average intensity. This noise is much less objectionable to our visual system than aliasing. In ray tracing, the rays can be stochastically distributed to perform a Monte Carlo evaluation of integrals in the rendering equation. This is called
distributed ray tracing
and can be used to simulate motion blur, depth of field, penumbrae, gloss, and translucency.
Interpolants for Runge-Kutta formulas
Authors: Enright W. H. , Jackson K. R. , Nørsett S. P. , Thomsen P. G.
Published: July 2002

A general procedure for the construction of interpolants for Runge-Kutta (RK) formulas is presented. As illustrations, this approach is used to develop interpolants for three explicit RK formulas, including those employed in the well-known subroutines RKF45 and DVERK. A typical result is that no extra function evaluations are required to obtain an interpolant with
O
(
h
5
) local truncation error for the fifth-order RK formula used in RKF45; two extra function evaluations per step are required to obtain an interpolant with
O
(
h
6
) local truncation error for this RK formula.
A model for naming, addressing and routing
Authors: Hauzeur Bernard M.
Published: July 2002

Naming and addressing are areas in which there is still a need for clarification. Many definitions for names, addresses, and routes have been proposed, but the exact relations among these concepts are obscure. A taxonomy of names, addresses, and routes is presented. First, we identify names and routes as the essential concepts of communication. Then, addresses are introduced as an intermediate form that eases the process of mapping between names and routes; an original definition of an address is thus proposed. Relations among names, addresses, and routes are explained with the concept of mapping. On this basis, a general model relating names, addresses, and routes is built and then applied recursively throughout a layered architecture, leading to a layered naming and addressing model which may play the same role for naming and addressing features that the OS1 reference model plays for the definition of services and protocols. Finally, the model is particularized to a typical network architecture. The model may also be applied to non-OSI layered systems; naming, addressing, and routing issues in any network architecture could be a particular instance of this layered model.
NATIONALISM AND ARCHAEOLOGY: On the Constructions of Nations and the Reconstructions of the Remote Past
Authors: Kohl Philip L.
Published: July 2002

▪ Abstract  Nationalism requires the elaboration of a real or invented remote past. This review considers how archaeological data are manipulated for nationalist purposes, and it discusses the development of archaeology during the nineteenth and early twentieth centuries and the relationship of archaeology to nation-building, particularly in Europe. Contrastive conceptions of nationality and ethnicity are presented, and it is argued that adoption of modern constructivist perspectives is incompatible with attempting to identify ethnic/national groups solely on the basis of archaeological evidence. The political uses of archaeology are also reviewed for the construction of national identities in immigrant and postcolonial states. The problematic nature of nationalistic interpretations of the archaeological record is discussed, and the essay concludes with a consideration of the professional and ethical responsibilities of archaeologists confronted with such interpretations.
Archaeological Textiles: A Review of Current Research
Authors: Good Irene
Published: July 2002

▪ Abstract  Archaeological textile studies are now recognized as a robust source of information for anthropological inquiry. Over the past two decades several important developments have taken place, enabling a more integrated approach to their study than in the past. Topics addressed range from the development of methods for analyzing degraded fibers to the comparative study of specific histories of textile and clothing traditions. Archaeological textile studies address relevant issues ranging from aesthetics and style to gender; from technological development to production and exchange economics. This chapter presents an overview of current research in the growing field of archaeological textile studies.
Kuru, Prions, and Human Affairs: Thinking About Epidemics
Authors: Lindenbaum Shirley
Published: July 2002

▪ Abstract  The study of epidemics provides a unique point of entry for examining the relationships among cultural assumptions, institutional forms, and states of mind. The Black Death is said to have contributed to the emergence of nation states, the rise of mercantile economies, and the religious movements that led to the Reformation. It may also have brought about new ways of understanding God, the meaning of death, and the role of authority in religious and social life. Cholera induced a public health approach that stressed quarantine, and venereal diseases led to contact tracing. Western medicine, however, failed to cure the epidemics that resulted from imperial expansion into the Americas, Asia, Africa, and Europe. The focus of this essay is on the impact of two contemporary epidemics considered to be caused by prions, a newly recognized infectious agent: kuru in Papua New Guinea and bovine spongiform encephalopathy (associated with variant Creutzfeldt-Jakob disease) in Europe. A close look at epidemics constitutes a sampling device for illuminating relationships among illness, social forms, and social thought. Theories of disease causation provide ways of thinking about the world and sets of directions for acting in it.
BIOTIN METABOLISM IN PLANTS
Authors: Alban Claude , Job Dominique , Douce Roland
Published: July 2002

▪ Abstract  Biotin is an essential cofactor for a small number of enzymes involved mainly in the transfer of CO2 during HCO−3-dependent carboxylation reactions. This review highlights progress in plant biotin research by focusing on the four major areas of recent investigation: the structure, enzymology, and localization of two important biotinylated proteins (methylcrotonoyl-CoA carboxylase involved in the catabolism of leucine and noncyclic isoprenoids; acetyl-CoA carboxylase isoforms involved in a number of biosynthetic pathways); the biosynthesis of biotin; the biotinylation of biotin-dependent carboxylases, including the characterization of biotin holocarboxylase synthetase isoforms; and the detailed characterization of a novel, seed-specific biotinylated protein. A central challenge for plant biotin research is to determine in molecular terms how plant cells regulate the flow of biotin to sustain the biotinylation of biotin-dependent carboxylases during biosynthetic reactions.
MOLECULAR ENGINEERING OF C4 PHOTOSYNTHESIS
Authors: Matsuoka Makoto , Furbank Robert T , Fukayama Hiroshi , Miyao Mitsue
Published: July 2002

▪ Abstract  The majority of terrestrial plants, including many important crops such as rice, wheat, soybean, and potato, are classified as C3 plants that assimilate atmospheric CO2 directly through the C3 photosynthetic pathway. C4 plants such as maize and sugarcane evolved from C3 plants, acquiring the C4 photosynthetic pathway to achieve high photosynthetic performance and high water- and nitrogen-use efficiencies. The recent application of recombinant DNA technology has made considerable progress in the molecular engineering of C4 photosynthesis over the past several years. It has deepened our understanding of the mechanism of C4 photosynthesis and provided valuable information as to the evolution of the C4 photosynthetic genes. It also has enabled us to express enzymes involved in the C4 pathway at high levels and in desired locations in the leaves of C3 plants for engineering of primary carbon metabolism.
VARIATIONS IN THE BIOSYNTHESIS OF SEED-STORAGE LIPIDS
Authors: Voelker Toni , Kinney Anthony J
Published: July 2002

▪ Abstract  In many plants lipids represent up to 80% of dry weight of storage tissues. In seeds, lipids accumulate as triacylglycerols (TAGs), which are formed by an extension of the membrane-lipid biosynthetic pathway common to all plant tissues. In contrast to the conserved fatty acid (FA) composition of membrane lipids, the observed divergence in seed oil acyl chains among different species is very high. The acyl groups of seed TAGs can vary in their chain length (from 8 to 24) as well as in their degree of unsaturation. In addition to methylene-interrupted double bonds, many seeds contain TAGs that have unusual functional groups in their FAs, such as hydroxyl, oxirane, or acetylene groups. All of the major steps in the biosynthetic pathway to TAG are now known and sequence information for genes encoding most of the enzymes involved is available. Here we present the current knowledge of the metabolic mechanisms involved in the divergence from the membrane-lipid biosynthetic pathway during storage lipid formation.
STELLAR PULSATIONS ACROSS THE HR DIAGRAM: Part II
Authors: Gautschy Alfred , Saio Hideyuki
Published: July 2002

▪ Abstract  Stars over essentially the whole mass domain can become pulsationally unstable during various stages of their evolution. They will appear as variable stars with characteristics that are of much diagnostic value to astronomers. The analysis of such observations provides a challenging and unique approach to study aspects of the internal constitution and evolutionary status of these objects that are not accessible otherwise. This review touches on most classes of known pulsating variable stars and tries to elucidate connections to stellar physical aspects. To aid future investigations, we stress questions and problems that we believe are yet to be resolved satisfactorily.
Rotation Curves of Spiral Galaxies
Authors: Sofue Yoshiaki , Rubin Vera
Published: July 2002

▪ Abstract  Rotation curves of spiral galaxies are the major tool for determining the distribution of mass in spiral galaxies. They provide fundamental information for understanding the dynamics, evolution, and formation of spiral galaxies. We describe various methods to derive rotation curves and review the results obtained. We discuss the basic characteristics of observed rotation curves in relation to various galaxy properties, such as Hubble type, structure, activity, and environment.
REGULATION OF PHOSPHOENOLPYRUVATE CARBOXYKINASE (GTP) GENE EXPRESSION
Authors: Hanson Richard W. , Reshef Lea
Published: July 2002

Phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) (PEPCK) is a key enzyme in the synthesis of glucose in the liver and kidney and of glyceride-glycerol in white adipose tissue and the small intestine. The gene for the cytosolic form of PEPCK (PEPCK-C) is acutely regulated by a variety of dietary and hormonal signals, which result in alteration of synthesis of the enzyme. Major factors that increase PEPCK-C gene expression include cyclic AMP, glucocorticoids, and thyroid hormone, whereas insulin inhibits this process. PEPCK-C is absent in fetal liver but appears at birth, concomitant with the capacity for gluconeogenesis. Regulatory elements that control transcription of the PEPCK-C gene in liver, kidney, and adipose tissue have been delineated, and many of the transcription factors that bind to these elements have been identified. Transgenic mice have been especially useful in elucidating the physiological roles of specific sequence elements in the PEPCK-C gene promoter and in demonstrating the key role played at these sites by the isoforms of CAAT/enhancer binding protein in patterning of PEPCK-C gene expression during the perinatal period. The PEPCK-C gene provides a model for the metabolic control of gene transcription.
NUCLEOCYTOPLASMIC TRANSPORT: The Soluble Phase
Authors: Mattaj Iain W. , Englmeier Ludwig
Published: July 2002

Active transport between the nucleus and cytoplasm involves primarily three classes of macromolecules: substrates, adaptors, and receptors. Some transport substrates bind directly to an import or an export receptor while others require one or more adaptors to mediate formation of a receptor-substrate complex. Once assembled, these transport complexes are transferred in one direction across the nuclear envelope through aqueous channels that are part of the nuclear pore complexes (NPCs). Dissociation of the transport complex must then take place, and both adaptors and receptors must be recycled through the NPC to allow another round of transport to occur. Directionality of either import or export therefore depends on association between a substrate and its receptor on one side of the nuclear envelope and dissociation on the other. The Ran GTPase is critical in generating this asymmetry. Regulation of nucleocytoplasmic transport generally involves specific inhibition of the formation of a transport complex; however, more global forms of regulation also occur.
MATRIX PROTEOGLYCANS: From Molecular Design to Cellular Function
Authors: Iozzo Renato V.
Published: July 2002

The proteoglycan superfamily now contains more than 30 full-time molecules that fulfill a variety of biological functions. Proteoglycans act as tissue organizers, influence cell growth and the maturation of specialized tissues, play a role as biological filters and modulate growth-factor activities, regulate collagen fibrillogenesis and skin tensile strength, affect tumor cell growth and invasion, and influence corneal transparency and neurite outgrowth. Additional roles, derived from studies of mutant animals, indicate that certain proteoglycans are essential to life whereas others might be redundant.

The review focuses on the most recent genetic and molecular biological studies of the matrix proteoglycans, broadly defined as proteoglycans secreted into the pericellular matrix. Special emphasis is placed on the molecular organization of the protein core, the utilization of protein modules, the gene structure and transcriptional control, and the functional roles of the various proteoglycans. When possible, proteoglycans have been grouped into distinct gene families and subfamilies offering a simplified nomenclature based on their protein core design. The structure-function relationship of some paradigmatic proteoglycans is discussed in depth and novel aspects of their biology are examined.
The Signal Recognition Particle
Authors: Keenan Robert J. , Freymann Douglas M. , Stroud Robert M. , Walter Peter
Published: July 2002

▪ Abstract  The signal recognition particle (SRP) and its membrane-associated receptor (SR) catalyze targeting of nascent secretory and membrane proteins to the protein translocation apparatus of the cell. Components of the SRP pathway and salient features of the molecular mechanism of SRP-dependent protein targeting are conserved in all three kingdoms of life. Recent advances in the structure determination of a number of key components in the eukaryotic and prokaryotic SRP pathway provide new insight into the molecular basis of SRP function, and they set the stage for future work toward an integrated picture that takes into account the dynamic and contextual properties of this remarkable cellular machine.
Microengineering of Cellular Interactions
Authors: Folch Albert , Toner Mehmet
Published: July 2002

▪ Abstract  Tissue function is modulated by an intricate architecture of cells and biomolecules on a micrometer scale. Until now, in vitro cellular interactions were mainly studied by random seeding over homogeneous substrates. Although this strategy has led to important discoveries, it is clearly a nonoptimal analog of the in vivo scenario. With the incorporation—and adaptation—of microfabrication technology into biology, it is now possible to design surfaces that reproduce some of the aspects of that architecture. This article reviews past research on the engineering of cell-substrate, cell-cell, and cell-medium interactions on the micrometer scale.
Structures and Proton-Pumping Strategies of Mitochondrial Respiratory Enzymes
Authors: Schultz Brian E. , Chan Sunney I.
Published: July 2002

▪ Abstract  Enzymes of the mitochondrial respiratory chain serve as proton pumps, using the energy made available from electron transfer reactions to transport protons across the inner mitochondrial membrane and create an electrochemical gradient used for the production of ATP. The ATP synthase enzyme is reversible and can also serve as a proton pump by coupling ATP hydrolysis to proton translocation. Each of the respiratory enzymes uses a different strategy for performing proton pumping. In this work, the strategies are described and the structural bases for the action of these proteins are discussed in light of recent crystal structures of several respiratory enzymes. The mechanisms and efficiency of proton translocation are also analyzed in terms of the thermodynamics of the substrate transformations catalyzed by these enzymes.
AH RECEPTOR SIGNALING PATHWAYS
Authors: Schmidt Jennifer V. , Bradfield Christopher A.
Published: July 2002

▪ Abstract  The aryl hydrocarbon (Ah) receptor has occupied the attention of toxicologists for over two decades. Interest arose from the early observation that this soluble protein played key roles in the adaptive metabolic response to polycyclic aromatic hydrocarbons and in the toxic mechanism of halogenated dioxins and dibenzofurans. More recent investigations have provided a fairly clear picture of the primary adaptive signaling pathway, from agonist binding to the transcriptional activation of genes involved in the metabolism of xenobiotics. Structure-activity studies have provided an understanding of the pharmacology of this receptor; recombinant DNA approaches have identified the enhancer sequences through which this factor regulates gene expression; and functional analysis of cloned cDNAs has allowed the characterization of the major signaling components in this pathway. Our objective is to review the Ah receptor's role in regulation of xenobiotic metabolism and use this model as a framework for understanding the less well-characterized mechanism of dioxin toxicity. In addition, it is hoped that this information can serve as a model for future efforts to understand an emerging superfamily of related signaling pathways that control biological responses to an array of environmental stimuli.
Animal Cell Cytokinesis
Authors: Glotzer Michael
Published: July 2002

▪ Abstract  Cytokinesis creates two daughter cells endowed with a complete set of chromosomes and cytoplasmic organelles. This conceptually simple event is mediated by a complex and dynamic interplay between the microtubules of the mitotic spindle, the actomyosin cytoskeleton, and membrane fusion events. For many decades the study of cytokinesis was driven by morphological studies on specimens amenable to physical manipulation. The studies led to great insights into the cellular structures that orchestrate cell division, but the underlying molecular machinery was largely unknown. Molecular and genetic approaches have now allowed the initial steps in the development of a molecular understanding of this fundamental event in the life of a cell. This review provides an overview of the literature on cytokinesis with a particular emphasis on the molecular pathways involved in the division of animal cells.
Using Springs to Study Groundwater Flow and Active Geologic Processes
Authors: Manga Michael
Published: July 2002

▪ Abstract  Spring water provides a unique opportunity to study a range of subsurface processes in regions with few boreholes or wells. However, because springs integrate the signal of geological and hydrological processes over large spatial areas and long periods of time, they are an indirect source of information. This review illustrates a variety of techniques and approaches that are used to interpret measurements of isotopic tracers, water chemistry, discharge, and temperature. As an example, a set of springs in the Oregon Cascades is considered. By using tracers, temperature, and discharge measurements, it is possible to determine the mean-residence time of water, infer the spatial pattern and extent of groundwater flow, estimate basin-scale hydraulic properties, calculate the regional heat flow, and quantify the rate of magmatic intrusion beneath the volcanic arc.
Shrub Invasions of North American Semiarid Grasslands
Authors: Van Auken O. W.
Published: July 2002

▪ Abstract  The composition and structure of the semiarid or desert grasslands of southwestern North America have changed over the past 150 y. Brushy or woody species in these communities have increased in density and cover. This increase in density of woody species is called brush encroachment because most of these species have been present in these communities at lower densities for thousands of years. The brushy or woody species were not introduced from other continents or from great distances. They are indigenous species that have increased in density or cover because of changes in local abiotic or biotic conditions. The brushy and woody plants are not the cause of these changes, but their increase is the result of other factors. The causes of changes that have led to the present woody-brushy composition of these semiarid grasslands has been difficult to determine. Warming of the climate seems to be a background condition, but the driving force seems to be chronic, high levels of herbivory by domestic animals. This herbivory has reduced the aboveground grass biomass, leading to the reduction of fine fuel and a concomitant reduction or complete elimination of grassland fires. This combination of factors favors the encroachment, establishment, survival and growth of woody plants. Less competition from grasses, dispersal of seeds of woody plants by domestic animals, and changes in rodent, lagomorph, and insect populations seem to modify the rate of change. Elevated levels of atmospheric CO2are not necessary to explain shrub encroachment in these semiarid grasslands. The direction of future change is difficult to predict. The density of brushy and woody plants will probably increase as will the stature and number of species. However, if soil nutrients increase, woody legumes may be replaced by other brushy or woody species. Reversing the changes that have been going on for 150 y will be a difficult, long-term, and perhaps impossible, task.
Integrating Function and Ecology in Studies of Adaptation: Investigations of Locomotor Capacity as a Model System
Authors: Irschick Duncan J. , Garland Theodore
Published: July 2002

▪ Abstract  Understanding adaptation in morphological and physiological traits requires elucidation of how traits relate to whole-organism performance and how performance relates to fitness. A common assumption is that performance capacities are utilized by and important to organisms. For some systems, it is assumed that high levels of physical fitness, as indexed by measures of locomotor performance, lead to high fitness levels. Although biologists have appreciated this, little attention has been paid to quantifying how organisms use their performance capacities in nature. We argue that for the study of adaptation to proceed, greater integration of laboratory studies of performance and behavioral/ecological studies is needed, and we illustrate this approach by examining two questions. First, how does the environment affect locomotor function in nature? Second, what percentage of locomotor capacities do animals use in nature? A review of studies in several animal groups shows widespread effects of the environment on measures of locomotor function.
SECURITY OF FISSILE MATERIALS IN RUSSIA
Authors: Bukharin Oleg
Published: July 2002

▪ Abstract  The problem of security of huge stocks of weapons-usable highly enriched uranium and plutonium in Russia against theft or diversion remains a serious nonproliferation concern. During the Cold War, the security of Soviet nuclear materials was based on centralization and discipline, protection by the military, and intrusive political oversight of the people. The recent fundamental societal changes have rendered these arrangements inadequate, and the security of nuclear materials has decreased. Safeguarding nuclear materials in Russia is particularly difficult because of their very large inventories and the size and complexity of the nation's nuclear infrastructure. Russia needs a reliable and more objective technology-based system of nuclear safeguards designed to control nuclear materials. The Russian government and the international community are working towards this goal.
INTEGRATED ASSESSMENT MODELS OF GLOBAL CLIMATE CHANGE
Authors: Parson Edward A. , Fisher-Vanden and Karen
Published: July 2002

▪ Abstract  We review recent work in the integrated assessment modeling of global climate change. This field has grown rapidly since 1990. Integrated assessment models seek to combine knowledge from multiple disciplines in formal integrated representations; inform policy-making, structure knowledge, and prioritize key uncertainties; and advance knowledge of broad system linkages and feedbacks, particularly between socioeconomic and biophysical processes. They may combine simplified representations of the socioeconomic determinants of greenhouse gas emissions, the atmosphere and oceans, impacts on human activities and ecosystems, and potential policies and responses. We summarize current projects, grouping them according to whether they emphasize the dynamics of emissions control and optimal policy-making, uncertainty, or spatial detail. We review the few significant insights that have been claimed from work to date and identify important challenges for integrated assessment modeling in its relationships to disciplinary knowledge and to broader assessment seeking to inform policy- and decision-making.
MIGRATORY ECOLOGY OF THE BLACK CUTWORM
Authors: Showers William B.
Published: July 2002

▪ Abstract  The long-range migration of insects in general is briefly discussed here and serves as an introduction for in-depth inquiry into the migratory ecology of Agrotis ipsilon, the black cutworm. Zoogeography, pest status and injury, and seasonal occurrence of the species are reviewed. Circumstantial evidence of long-range movement of A. ipsilon moths within both hemispheres is presented, followed by experimental evidence of long-range movement of A. ipsilon moths in China and North America. Based upon experimental evidence published by several investigators, a theory is proposed of the existence of a thermal range (0–36°C) for A. ipsilon pupae that acts as the precursor for adult (moth) migration. This theory should help explain the circumstantial and empirical evidence gathered upon the annual appearance and disappearance of this species over large geographic areas.
BIOLOGY OF WOLBACHIA
Authors: Werren John H.
Published: July 2002

▪ Abstract  Wolbachia are a common and widespread group of bacteria found in reproductive tissues of arthropods. These bacteria are transmitted through the cytoplasm of eggs and have evolved various mechanisms for manipulating reproduction of their hosts, including induction of reproductive incompatibility, pathenogenesis, and feminization. Wolbachia are also transmitted horizontally between arthropod species. Significant recent advances have been made in the study of these interesting microorganisms. In this paper, Wolbachia biology is reviewed, including their phylogeny and distribution, mechanisms of action, population biology and evolution, and biological control implications. Potential directions for future research are also discussed.
The Biology of the Dance Language
Authors: Dyer Fred C.
Published: July 2002

▪ Abstract  Honey bee foragers dance to communicate the spatial location of food and other resources to their nestmates. This remarkable communication system has long served as an important model system for studying mechanisms and evolution of complex behavior. I provide a broad synthesis of recent research on dance communication, concentrating on the areas that are currently the focus of active research. Specific issues considered are as follows: (a) the sensory and integrative mechanisms underlying the processing of spatial information in dance communication, (b) the role of dance communication in regulating the recruitment of workers to resources in the environment, (c) the evolution of the dance language, and (d) the adaptive fine-tuning of the dance for efficient spatial communication.
COMPRESSIONSYSTEMSTABILITY ANDACTIVECONTROL
Authors: Paduano JD , Greitzer EM , Epstein AH
Published: July 2002

▪ Abstract  The compression system instabilities known as surge and rotating stall are natural limits to the performance of all compressors and are especially troubling in gas turbine engines. In the last 15 years, rapid progress has been made in understanding this complex problem through the application of control technology; in particular, system identification techniques have proven to be useful. New findings include the roles of compressibility and nonlinearity in the stall-inception process. These findings have been used to implement feedback control schemes that have achieved increased stability in a variety of compressors and engines. Approaches fall into one of two categories: (a) operating range extension through active damping of linear disturbances, or (b) manipulation of the nonlinear system dynamics to maintain the operating point close to the instability boundary in the presence of disturbances seen in operation.