bluuebunny/crossref_metadata_2025 huggingface dataset:
A window-based graphics frame store architecture
Authors: Westmore Richard J.
Published: July 2002

A proposal for a scalable frame store architecture for a hardware-based window graphics system is described. The architecture is based on a distributed linear array of common elements called microframe stores. Each window and viewport can be independently configured in size and color depth. Unlike the strip-based hardware window systems referenced, this system places no restrictions on the number of transitions that can be accommodated on each scanline. The approach described allows real-time window graphics to be achieved on a variety of full-color, high-resolution, high-refresh-rate, raster-scan displays with pixel rates of up to 400 MHz.
Improved implementations of binary universal operations
Authors: Attiya Hagit , Dagan Eyal
Published: July 2002

We present an algorithm for implementing binary operations (of any type) from unary
load-linked
(LL) and
store-conditional
(SC) operations. The performance of the algorithm is evaluated according to its
sensitivity
, measuring the distance between operations in the graph induced by conflicts, which guarantees that they do not influence the step complexity of each other. The sensitivity of our implementation is
O
(log
*
n
), where
n
is the number of processors in the system. That is, operations that are Ω(log
*
n
) apart in the graph induced by conflicts do not delay each other. Constant sensitivity is achieved for operations used to implement heaps and array-based linked lists.We also prove that there is a problem which can be solved in
O
(1) steps using binary LL/SC operations, but requires
O
(log log
*
n
) operations if only unary LL/SC operations are used. This indicates a non-constant gap between unary and binary, LL/SC operations.
Diagnostic simulation of stuck-at faults in sequential circuits using compact lists
Authors: Hartanto Ismed , Venkataraman Srikanth , Fuchs W. Kent , Rudnick Elizabeth M. , Patel Janak H. , Chakravarty Sreejit
Published: July 2002

This article describes a diagnostic fault simulator for stuck-at faults in sequential circuits that is both time and space efficient. The simulator represents indistinguishable classes of faults as memory efficient lists. The use of lists reduces the number of output response comparisons between faults and hence speeds up the simulation process. The lists also make it easy to drop faults when they are fully distinguished from other faults. Experimental results on the ISCAS89 circuits show that the simulator runs significantly faster than an earlier work based on distinguishability matrices, and for large circuits is faster and more memory efficient than a recent method based on lists of indistinguishable faults. The paper provides the first reports on pessimistic and optimistic diagnostic measures for all faults of the large ISCAS circuits with known deterministic tests. The diagnostic fault simulator has also been modified to diagnose defects, given the output responses of failing devices. Results on simulated bridging defects show that the diagnosis time is comparable to the time for fault simulation with fault dropping.
Designing the PDA of the future
Authors: Marcus Aaron , Chen Eugene
Published: July 2002

In this article, Aaron Marcus and Associates (AM+A) describes a project with Samsung Electronics to design user-interface concepts for the future of wireless devices. AM+A conducted extensive research, including contextual observation, then designed a suite of product ideas that Samsung could incorporate into specific products over the next few years. Samsung also acquired knowledge about the user-interface development process. AM+A sought to design usable as well as useful mobile devices that could overcome extreme input and output challenges and become true personal companions.
Robotics and interactive simulation
Authors: Khatib Oussama , Brock Oliver , Chang Kyong-Sok , Conti Francois , Ruspini Diego , Sentis Luis
Published: July 2002

As applications of robots extend into everyday human life, new approaches to simulating interactions between them and their environments are emerging at the intersection of the physical and virtual worlds.
Computers, complexity, and the Statue of Liberty restoration
Authors: Frenkel Karen A.
Published: July 2002

Twentieth-century techniques such as computer-aided engineering and finite-element analysis were used to restore the nineteenth-century monument.
A block 6(4) Runge-Kutta formula for nonstiff initial value problems
Authors: Cash J. R.
Published: July 2002

A new selection is made for an efficient two-step block Runge-Kutta formula of order 6. The new formula is developed using some of the efficiency criteria recently investigated by Shampine, and as a result, a block formula with much improved performance is obtained. An important property of this new formula is that there is a “natural” interpolating polynomial available. This can be used to compute approximate solution values at off-step points without the need to compute any additional function evaluations. The quality of this interpolant is examined, and it is shown to have certain desirable properties. The performance of the new block Runge-Kutta formula is evaluated using the DETEST test set and is shown to be more efficient than certain other standard Runge-Kutta formulas for this particular test set.
Computer graphics tools for the study of minimal surfaces
Authors: Callahan M. J. , Hoffman D. , Hoffman J. T.
Published: July 2002

Recent research indicates machine computation and mathematical theory have proceeded hand in hand and have proved to be of great benefit to one another.
An algorithm for generating interpolatory quadrature rules of the highest degree of precision with preassigned nodes for general weight functions
Authors: Patterson T. N. L.
Published: July 2002

The construction of an algorithm is described for generating interpolatory quadrature rules of the highest degree of precision with arbitrarily preassigned nodes for general constant signed weight functions. It is of very wide application in that to operate, only the definition of the 3-term recurrence relation for the orthogonal polynomials associated with the weight function need be supplied. The algorithm can be used to produce specific individual quadrature rules or sequences of rules by iterative application.
Coding image sequences for interactive retrieval
Authors: Lippman Andrew , Butera William
Published: July 2002

An image coding technique for digital storage of motion picture information is presented that is optimated for use in interactive systems where high quality still frames, random access, and database linkages are required.
A finite and real-time processor for natural language
Authors: Blank Glenn D.
Published: July 2002

People process natural language in real time and with very limited short-term memories. This article describes a computational architecture for syntactic performance that also requires fixed finite resources.
Improving a human-computer dialogue
Authors: Molich Rolf , Nielsen Jakob
Published: July 2002

A survey of seventy-seven highly motivated industrial designers and programmers indicates that the identification of specific, potential problems in a human-computer dialogue design is difficult.
Algorithm 679: A set of level 3 basic linear algebra subprograms: model implementation and test programs
Authors: Dongarra J. J. , Cruz Jermey Du , Hammarling Sven , Duff I. S.
Published: July 2002

This paper describes a model implementation and test software for the Level 3 Basic Linear Algebra Subprograms (Level3 BLAS). The Level3 BLAS are targeted at matrix-matrix operations with the aim of providing more efficient, but portable, implementations of algorithms on high-performance computers. The model implementation provides a portable set of Fortran 77 Level 3 BLAS for machines where specialized implementations do not exist or are not required. The test software aims to verify that specialized implementations meet the specification of the Level 3 BLAS and that implementations are correctly installed.
Physical design equivalencies in database conversion
Authors: Gillenson Mark L.
Published: July 2002

As relational technology becomes increasingly accepted in commercial data processing, conversion of some of the huge number of existing navigational databases to relational databases is inevitable. It is thus important to understand how to recognize physical design modifications and enhancements in the navigational databases and how to convert them to equivalent relational terms as applicable.
Toward a unified framework for version modeling in engineering databases
Authors: Katz Randy H.
Published: July 2002

Support for unusual applications such as computer-aided design data has been of increasing interest to database system architects. In this survey, we concentrate on one aspect of such support, namely,
version modeling
. By this, we mean the concepts suitable for structuring a database of complex engineering artifacts that evolve across multiple representations and over time and the operations through which such artifact descriptions are created and modified. There have been many proposals for new models and mechanisms to support such concepts within database data models in general and engineering data models in particular; here we not only describe such proposals; we also unify them. We do not propose yet another model but provide a common terminology and collection of mechanisms that underlie any approach for representing engineering design information in a database. The key remaining challenge is to construct a single framework, based on these mechanisms, which can be tailored for the needs of a given version environment.
The UAN: a user-oriented representation for direct manipulation interface designs
Authors: Hartson H. Rex , Siochi Antonio C. , Hix D.
Published: July 2002

Many existing interface representation techniques, especially those associated with UIMS, are constructional and focused on interface implementation, and therefore do not adequately support a user-centered focus.
But it is in the behavioral domain of the user that interface designers and evaluators do their work
. We are seeking to complement constructional methods by providing a tool-supported technique capable of specifying the
behavioral aspects
of an interactive system–the tasks and the actions a user performs to accomplish those tasks. In particular, this paper is a practical introduction to use of the User Action Notation (UAN), a task- and user-oriented notation for behavioral representation of asynchronous, direct manipulation interface designs. Interfaces are specified in UAN as a quasihierarchy of asynchronous tasks. At the lower levels, user actions are associated with feedback and system state changes. The notation makes use of visually onomatopoeic symbols and is simple enough to read with little instruction. UAN is being used by growing numbers of interface developers and researchers. In addition to its design role, current research is investigating how UAN can support production and maintenance of code and documentation.
Linguistic Relativity
Authors: Lucy John A.
Published: July 2002

The linguistic relativity hypothesis, the proposal that the particular language we speak influences the way we think about reality, forms one part of the broader question of how language influences thought. Despite long-standing historical interest in the hypothesis, there is relatively little empirical research directly addressing it. Existing empirical approaches are classified into three types. 1. Structure-centered approaches begin with language differences and ask about their implications for thought. 2. Domain-centered approaches begin with experienced reality and ask how different languages encode it. 3. Behavior-centered approaches begin with some practical concern and seek an explanation in language. These approaches are compared, and recent methodological improvements highlighted. Despite empirical advances, a theoretical account needs to articulate exactly how languages interpret experiences and how those interpretations influence thought. This will entail integrating theory and data concerning both the general relation of language and thought and the shaping influence of specific discursive structures and practices.
Nutrition and Politics in Prehistory
Authors: Danforth Marie Elaine
Published: July 2002

▪ Abstract  The interaction of nutritional status with political structure in prehistoric New World societies is examined through bioarchaeological analysis. Overall, a general correlation is seen between political complexity and patterns of morbidity among various subsegments of the population. This relationship is strongest among egalitarian societies, in which few differences exist, and state-level societies, in which differences are readily apparent and appear to widen over time. At intermediate levels of political complexity, a less consistent picture emerges; various explanations are considered as to why the dietary differences predicted by the ethnohistorical and archaeological records are not reflected in the osteological record. Also addressed are patterns of differences in access to nutritional resources by gender at the various levels of political organization, as well as patterns of access between rural and urban centers. Future directions of study are suggested.
Africa, Empire, and Anthropology: A Philological Exploration of Anthropology's Heart of Darkness
Authors: Apter Andrew
Published: July 2002

▪ Abstract  As an artifact of imperial culture, Africanist anthropology is historically associated with the colonization of Africa in ways that undermine the subdiscipline's claims of neutrality and objectivity. A critical literature on the ideological and discursive inventions of Africa by the West challenges the very possibility of Africanist anthropology, to which a variety of responses have emerged. These range from historical reexaminations of imperial discourses, colonial interactions, and fieldwork in Africa, including dialogical engagements with the very production of ethnographic texts, to a more dialectical anthropology of colonial spectacle and culture as it was coproduced and reciprocally determined in imperial centers and peripheries. Understood philologically, as an imperial palimpsest in ethnographic writing, the colonial legacy in Africanist ethnography can never be negated, but must be acknowledged under the sign of its erasure.
WHAT CHIMERAS CAN TELL US ABOUT PLANT DEVELOPMENT
Authors: Szymkowiak Eugene J. , Sussex Ian M.
Published: July 2002

▪ Abstract  The generation and analysis of plant chimeras and other genetic mosaics have been used to deduce patterns of cell division and cell fate during plant development and to demonstrate the existence of clonally distinct cell lineages in the shoot meristems of higher plants. Cells derived from these lineages do not have fixed developmental fates but rely on positional information to determine their patterns of division and differentiation. Chimeras with cells that differ genetically for specific developmental processes have been experimentally generated by a variety of methods. This review focuses on studies of intercellular interactions during plant development as well as of the coordination of cells during meristem function and organogenesis. Recent experiments combining mosaic analysis with molecular analysis of developmental mutants have begun to shed light on the nature of the signals involved in these processes and the mechanisms by which they are transmitted and received among cells.
BIOCHEMISTRY AND MOLECULAR BIOLOGY OF WAX PRODUCTION IN PLANTS
Authors: Post-Beittenmiller Dusty
Published: July 2002

▪ Abstract  The aerial surfaces of plants are covered with a wax layer that is primarily a waterproof barrier but that also provides protection against environmental stresses. The ubiquitous presence of cuticular wax is testimony to its essential function. Genetic and environmental factors influence wax quantity and composition, which suggests that it is an actively regulated process. The basic biochemistry of wax production has been elucidated over the past three decades; however, we still know very little about its regulation. This review presents a discussion along with new perspectives on the regulatory aspects of wax biosynthesis. Among the topics discussed are the partitioning of fatty acid precursors into wax biosynthesis and the elongation of fatty acids with particular emphasis on the nature of the acyl primer, and the role of ATP in fatty acid elongation. The recent cloning of wax biosynthetic genes and the transport of wax to plant surfaces are also discussed.
BIOSYNTHESIS AND FUNCTION OF THE SULFOLIPID SULFOQUINOVOSYL DIACYLGLYCEROL
Authors: Benning Christoph
Published: July 2002

▪ Abstract  The sulfolipid sulfoquinovosyl diacylglycerol is an abundant sulfur-containing nonphosphorous glycerolipid that is specifically associated with photosynthetic membranes of higher plants, mosses, ferns, algae, and most photosynthetic bacteria. The characteristic structural feature of sulfoquinovosyl diacylglycerol is the unique head group constituent sulfoquinovose, a derivative of glucose in which the 6-hydroxyl is replaced by a sulfonate group. While there is growing evidence for the final assembly of the sulfolipid by the transfer of the sulfoquinovosyl moiety from UDP-sulfoquinovose to the sn-3 position of diacylglycerol, very little is known about the biosynthesis of the precursor UDP-sulfoquinovose. Recently, a number of mutants deficient in sulfolipid biosynthesis and the corresponding sqd genes have become available from different organisms. These provide novel tools to analyze sulfolipid biosynthesis by a combination of molecular and biochemical approaches. Furthermore, the analysis of sulfolipid-deficient mutants has provided novel insights into the function of sulfoquinovosyl diacylglycerol in photosynthetic membranes.
THE MOLECULAR STRUCTURE OF CELL ADHESION MOLECULES
Authors: Chothia Cyrus , Jones E. Yvonne
Published: July 2002

Considerable advances have been made in our knowledge of the molecular structure of cell adhesion molecules, their binding sites, and adhesion complexes. For the cadherins, protein zero, and CD2, additional experimental data support the insights obtained from structural analysis of their domains and molecular models of their adhesion complexes. For neural cell adhesion molecules, L1, fibronectin, tenascin-C, integrins, and vascular cell adhesion molecules, the molecular structure of domains, and in most cases their binding sites, have been elucidated. The substrate recognition sites in some of these molecules possess rate constants for association and dissociation that permit both rapid cell migration and, through avidity, high-affinity cell-cell interactions.
Protein Glucosylation and Its Role in Protein Folding
Authors: Parodi Armando J.
Published: July 2002

▪ Abstract  An unconventional mechanism for retaining improperly folded glycoproteins and facilitating acquisition of their native tertiary and quaternary structures operates in the endoplasmic reticulum. Recognition of folding glycoproteins by two resident lectins, membrane-bound calnexin and its soluble homolog, calreticulin, is mediated by protein-linked monoglucosylated oligosaccharides. These oligosaccharides contain glucose (Glc), mannose (Man), and N-acetylglucosamine (GlcNAc) in the general form Glc1Man7-9GlcNAc2. They are formed by glucosidase I- and II-catalyzed partial deglucosylation of the oligosaccharide transferred from dolichol diphosphate derivatives to Asn residues in nascent polypeptide chains (Glc3Man9GlcNAc2). Further deglucosylation of the oligosaccharides by glucosidase II liberates glycoproteins from their calnexin/calreticulin anchors. Monoglucosylated glycans are then recreated by the UDP-Glc:glycoprotein glucosyltransferase (GT), and thus recognized again by the lectins, only when linked to improperly folded protein moieties, as GT behaves as a sensor of glycoprotein conformations. The deglucosylation-reglucosylation cycle continues until proper folding is achieved. The lectin-monoglucosylated oligosaccharide interaction is one of the alternative ways by which cells retain improperly folded glycoproteins in the endoplasmic reticulum. Although it decreases the folding rate, it increases folding efficiency, prevents premature glycoprotein oligomerization and degradation, and suppresses formation of nonnative disulfide bonds by hindering aggregation and thus allowing interaction of protein moieties of folding glycoproteins with classical chaperones and other proteins that assist in folding.
Mediator of Transcriptional Regulation
Authors: Myers Lawrence C. , Kornberg Roger D.
Published: July 2002

▪ Abstract  Three lines of evidence have converged on a multiprotein Mediator complex as a conserved interface between gene-specific regulatory proteins and the general transcription apparatus of eukaryotes. Mediator was discovered as an activity required for transcriptional activation in a reconstituted system from yeast. Upon resolution to homogeneity, the activity proved to reside in a 20-protein complex, which could exist in a free state or in a complex with RNA polymerase II, termed holoenzyme. A second line of evidence came from screens in yeast for mutations affecting transcription. Two-thirds of Mediator subunits are encoded by genes revealed by these screens. Five of the genetically defined subunits, termed Srbs, were characterized as interacting with the C-terminal domain of RNA polymerase II in vivo, and were shown to bind polymerase in vitro. A third line of evidence has come recently from studies in mammalian transcription systems. Mammalian counterparts of yeast Mediator were shown to interact with transcriptional activator proteins and to play an essential role in transcriptional regulation.

Mediator evidently integrates and transduces positive and negative regulatory information from enhancers and operators to promoters. It functions directly through RNA polymerase II, modulating its activity in promoter-dependent transcription. Details of the Mediator mechanism remain obscure. Additional outstanding questions include the patterns of promoter-specificity of the various Mediator subunits, the possible cell-type–specificity of Mediator subunit composition, and the full structures of both free Mediator and RNA polymerase II holoenzyme.
Folding of Newly Translated Proteins In Vivo: The Role of Molecular Chaperones
Authors: Frydman Judith
Published: July 2002

▪ Abstract  Recent years have witnessed dramatic advances in our understanding of how newly translated proteins fold in the cell and the contribution of molecular chaperones to this process. Folding in the cell must be achieved in a highly crowded macromolecular environment, in which release of nonnative polypeptides into the cytosolic solution might lead to formation of potentially toxic aggregates. Here I review the cellular mechanisms that ensure efficient folding of newly translated proteins in vivo. De novo protein folding appears to occur in a protected environment created by a highly processive chaperone machinery that is directly coupled to translation. Genetic and biochemical analysis shows that several distinct chaperone systems, including Hsp70 and the cylindrical chaperonins, assist the folding of proteins upon translation in the cytosol of both prokaryotic and eukaryotic cells. The cellular chaperone machinery is specifically recruited to bind to ribosomes and protects nascent chains and folding intermediates from nonproductive interactions. In addition, initiation of folding during translation appears to be important for efficient folding of multidomain proteins.
MITOTIC CHROMOSOME CONDENSATION
Authors: Koshland Douglas , Strunnikov Alexander
Published: July 2002

▪ Abstract  In this chapter, we review the structure and composition of interphase and mitotic chromosomes. We discuss how these observations support the model that mitotic condensation is a deterministic process leading to the invariant folding of a given chromosome. The structural studies have also placed constraints on the mechanism of condensation and defined several activities needed to mediate condensation. In the context of these activities and structural information, we present our current understanding of the role of cis sites, histones, topoisomerase II, and SMC proteins in condensation. We conclude by using our current knowledge of mitotic condensation to address the differences in chromosome condensation observed from bacteria to humans and to explore the relevance of this process to other processes such as gene expression.
TRANSPORT VESICLE DOCKING: SNAREs and Associates
Authors: Pfeffer Suzanne R.
Published: July 2002

▪ Abstract  Proteins that function in transport vesicle docking are being identified at a rapid rate. So-called v- and t-SNAREs form the core of a vesicle docking complex. Additional accessory proteins are required to protect SNAREs from promiscuous binding and to deprotect SNAREs under conditions in which transport vesicle docking should occur. Because access to SNAREs must be regulated, other proteins must also contain specificity determinants to accomplish delivery of transport vesicles to their distinct and specific membrane targets.
THE ORIGIN AND EVOLUTION OF DINOSAURS
Authors: Sereno Paul C.
Published: July 2002

▪ Abstract  Phylogenetic studies and new fossil evidence have yielded fundamental insights into the pattern and timing of dinosaur evolution and the emergence of functionally modern birds. The dinosaurian radiation began in the Middle Triassic, significantly predating the global dominance of dinosaurs by the end of the period. The phylogenetic history of ornithischian and saurischian dinosaurs reveals evolutionary trends such as increasing body size. Adaptations to herbivory in dinosaurs were not tightly correlated with marked floral replacements. Dinosaurian biogeography during the era of continental breakup principally involved dispersal and regional extinction.
DEBRIS-FLOW MOBILIZATION FROM LANDSLIDES
Authors: Iverson Richard M. , Reid Mark E. , LaHusen Richard G.
Published: July 2002

▪ Abstract  Field observations, laboratory experiments, and theoretical analyses indicate that landslides mobilize to form debris flows by three processes: (a) widespread Coulomb failure within a sloping soil, rock, or sediment mass, (b) partial or complete liquefaction of the mass by high pore-fluid pressures, and (c) conversion of landslide translational energy to internal vibrational energy (i.e. granular temperature). These processes can operate independently, but in many circumstances they appear to operate simultaneously and synergistically. Early work on debris-flow mobilization described a similar interplay of processes but relied on mechanical models in which debris behavior was assumed to be fixed and governed by a Bingham or Bagnold rheology. In contrast, this review emphasizes models in which debris behavior evolves in response to changing pore pressures and granular temperatures. One-dimensional infinite-slope models provide insight by quantifying how pore pressures and granular temperatures can influence the transition from Coulomb failure to liquefaction. Analyses of multidimensional experiments reveal complications ignored in one-dimensional models and demonstrate that debris-flow mobilization may occur by at least two distinct modes in the field.
ISOTOPIC RECONSTRUCTION OF PAST CONTINENTAL ENVIRONMENTS
Authors: Koch Paul L.
Published: July 2002

▪ Abstract  Vertebrate fossils and continental sediments provide a rich record of variations in the isotopic composition of surface environments. To interpret these records, a greater understanding of isotopic sources, as well as fractionations associated with animal physiology, soil geochemistry, and diagenesis, has been essential. Tooth enamel and fish otoliths yield subannual records of surface environments, whereas soil minerals may integrate signals over many thousands of years. Carbon isotope variations in fossil vertebrates and soils record changes in the structure of vegetation and the isotope composition and concentration of atmospheric CO2. Oxygen isotope variations may be indirectly related to climate, through reconstruction of the oxygen isotope composition of meteoric water, or directly related to temperature, through application of oxygen isotope paleothermometry to soil minerals or otoliths. In Africa, nitrogen isotope variations show promise as a proxy for rainfall abundance, though the generality of this association elsewhere has not been demonstrated.
K-Ar AND 40Ar/39Ar GEOCHRONOLOGY OF WEATHERING PROCESSES
Authors: Vasconcelos P. M.
Published: July 2002

▪ Abstract  Recent developments in the application of K-Ar and 40Ar/39Ar dating of continental weathering process demonstrate the method's suitability for dating minerals present in weathering profiles. Alunite-group sulfates and hollandite-group manganese oxides, which often precipitate through weathering reactions, were first analyzed by the K-Ar method 30 years ago. Recently these minerals were shown to be suitable to 40Ar/39Ar geochronology, despite their fine-grained habits. The bulk nature of the K-Ar technique and the complex mineral assemblages in weathering profiles restrict K-Ar dating of weathering processes. The single-crystal approach possible with the 40Ar/39Ar method allows the study of weathering profiles where alunite- and hollandite-group minerals occur as minor phases. Step-heating analysis possible with the 40Ar/39Ar method provides information about the Ar and K retention histories, the presence of hypogene contaminants, and possible 39Ar recoil during sample irradiation. Fully automated, modern 40Ar/39Ar systems enable analysis of several samples, providing a comprehensive weathering database. These results are useful in the study of continental paleoclimates and the geochemical, geomorphological, and tectonic histories of an area.
THE GLOBAL STRATIGRAPHY OF THE CRETACEOUS-TERTIARY BOUNDARY IMPACT EJECTA
Authors: Smit J.
Published: July 2002

▪ Abstract  The Chicxulub crater ejecta stratigraphy is reviewed, in the context of the stratigraphy of underlying and overlying rock sequences. The ejecta sequence is regionally grouped in (a) thick polymict and monomict breccia sequences inside the crater and within 300 km from the rim of the crater known from drill holes in and close to the breater, and exposures near the border of Yucatan and Belize; (b) Gulf of Mexico region, <2500 m from the crater, with up to 9 m thick, complex, tsunami-wave influenced, tektite-bearing sequences in shallow marine (<500 m deep) environments and tektite bearing, decimeter thick gravity-flow deposits in deep water sites; (c) an intermediate region between 2500 and 4000 km from the crater where centimeter thick, tektite-bearing layers occur, and (d) a global distal region with a millimeter thin ejecta layer. The distal ejecta layer is characterized by sub-millimeter sized microkrystites, often rich in Ni-rich spinels and (altered) clinopyroxene. Wherever present, the ejecta layers mark exactly the sudden mass-mortality horizon of the K/T boundary. What exactly caused the mass mortality is still uncertain, but it appears the main event leading to the K/T mass extinctions.
Palynology after Y2K—Understanding the Source Area of Pollen in Sediments
Authors: Davis M. B.
Published: July 2002

Pollen grains preserved in lake and bog sediment provide a record of past vegetation that has been an important source of information about climate and land cover during the Quaternary Period. Yet from the beginning, questions have been raised about the source area of pollen in sediment. Interpretation has been hampered by the lack of well-developed theory treating the relationship between the spatial distribution of trees on the landscape and the percentages of pollen in sediment. Within the past decade, however, new theory, models, and empirical data show how heterogeneous vegetation is represented by pollen. The distinction between “local” and “regional” pollen is explained by the Prentice-Sugita dispersal/deposition models, which predict how the ratio of regional to local pollen changes with lake size. Sugita’s model simulating a landscape with heterogeneous vegetation predicts the size of the relevant source area—the area of vegetation reflected in between-lake variations in pollen loading—while demonstrating that regional pollen from beyond this distance is homogeneous at all lakes of similar size. By predicting the way landscape patterns will be reflected in pollen records, simulation models can improve research design and lead to more detailed and spatially precise records of past vegetation, enhancing continental-scale climate reconstructions.
Chemical Weathering, Atmospheric CO2, and Climate
Authors: Kump Lee R. , Brantley Susan L. , Arthur Michael A.
Published: July 2002

There has been considerable controversy concerning the role of chemical weathering in the regulation of the atmospheric partial pressure of carbon dioxide, and thus the strength of the greenhouse effect and global climate. Arguments center on the sensitivity of chemical weathering to climatic factors, especially temperature. Laboratory studies reveal a strong dependence of mineral dissolution on temperature, but the expression of this dependence in the field is often obscured by other environmental factors that co-vary with temperature. In the field, the clearest correlation is between chemical erosion rates and runoff, indicating an important dependence on the intensity of the hydrological cycle. Numerical models and interpretation of the geologic record reveal that chemical weathering has played a substantial role in both maintaining climatic stability over the eons as well as driving climatic swings in response to tectonic and paleogeographic factors.
Tree-Grass Interactions in Savannas
Authors: Scholes R. J. , Archer S. R.
Published: July 2002

Savannas occur where trees and grasses interact to create a biome that is neither grassland nor forest. Woody and gramineous plants interact by many mechanisms, some negative (competition) and some positive (facilitation). The strength and sign of the interaction varies in both time and space, allowing a rich array of possible outcomes but no universal predictive model. Simple models of coexistence of trees and grasses, based on separation in rooting depth, are theoretically and experimentally inadequate. Explanation of the widely observed increase in tree biomass following introduction of commercial ranching into savannas requires inclusion of interactions among browsers, grazers, and fires, and their effects on tree recruitment. Prediction of the consequences of manipulating tree biomass through clearing further requires an understanding of how trees modify light, water, and nutrient environments of grasses. Understanding the nature of coexistence between trees and grass, which under other circumstances are mutually exclusive or unequal partners, yields theoretical insights and has practical implications.
The Role of Hybridization and Introgression in the Diversification of Animals
Authors: Dowling Thomas E. , Secor Carol L.
Published: July 2002

Although hybridization and introgression have been considered important in generation of plant diversity, their role in evolutionary diversification of animals remains unclear. In this review, we reconsider the significance of introgressive hybridization in evolution and diversification of animals to determine if the generally negative assessment of these processes is warranted. Unlike the situation for plants, hybrid animal taxa appear to be relatively rare. This could, however, be due to negative attitudes toward hybridization and difficulty in detecting such forms. Hybridization has been responsible for instantaneous creation of several unique complexes of polyploid and unisexual animals. Allopolyploidy has allowed for diversification, whereas unisexual taxa have acted as conduits of gene exchange among related sexual species. Many instances of diploid, bisexual taxa of hybrid origin have been put forward, but few have been carefully tested. Changing attitudes toward hybrids and technological advances should allow for careful consideration of hypothesized hybrid taxa and will undoubtedly increase the number of known animal hybrid taxa.
MATINGBEHAVIOR ANDCHEMICALCOMMUNICATION IN THEORDERHYMENOPTERA
Authors: Ayasse M. , Paxton R. J. , Tengö J.
Published: July 2002

▪ Abstract  Insects of the order Hymenoptera are biologically and economically important members of natural and agro ecosystems and exhibit diverse biologies, mating systems, and sex pheromones. We review what is known of their sex pheromone chemistry and function, paying particular emphasis to the Hymenoptera Aculeata (primarily ants, bees, and sphecid and vespid wasps), and provide a framework for the functional classification of their sex pheromones. Sex pheromones often comprise multicomponent blends derived from numerous exocrine tissues, including the cuticle. However, very few sex pheromones have been definitively characterized using bioassays, in part because of the behavioral sophistication of many Aculeata. The relative importance of species isolation versus sexual selection in shaping sex pheromone evolution is still unclear. Many species appear to discriminate among mates at the level of individual or kin/colony, and they use antiaphrodisiacs. Some orchids use hymenopteran sex pheromones to dupe males into performing pseudocopulation, with extreme species specificity.
Mixing and Segregation of Granular Materials
Authors: Ottino J. M. , Khakhar D. V.
Published: July 2002

▪ Abstract  Granular materials segregate. Small differences in either size or density lead to flow-induced segregation, a complex phenomenon without parallel in fluids. Modeling of mixing and segregation processes requires the confluence of several tools, including continuum and discrete descriptions (particle dynamics, Monte Carlo simulations, cellular automata computations) and, often, considerable geometrical insight. None of these viewpoints, however, is wholly satisfactory by itself. Moreover, continuum and discrete descriptions of granular flows are regime dependent, and this fact may require adopting different subviewpoints. This review organizes a body of knowledge that forms—albeit imperfectly—the beginnings of an expandable continuum framework for the description of mixing and segregation of granular materials. We focus primarily on noncohesive particles, possibly differing in size, density, shape, etc. We present segregation mechanisms and models for size and density segregation and introduce chaotic advection, which appears in noncircular tumblers. Chaotic advection interacts in nontrivial ways with segregation in granular materials and leads to unique equilibrium structures that serve as a prototype for systems displaying organization in the midst of disorder.
The Motion of High-Reynolds-Number Bubbles in Inhomogeneous Flows
Authors: Magnaudet J. , Eames I.
Published: July 2002

▪ Abstract  Predicting the motion of bubbles in dispersed flows is a key problem in fluid mechanics that has a bearing on a wide range of applications from oceanography to chemical engineering. In this review we synthesize the recent progress made in describing bubble motion in inhomogeneous flow. A trident approach consisting of experimental, analytical, and numerical work has given a clearer description of the hydrodynamic forces experienced by isolated bubbles moving either in inviscid flows or in slightly viscous laminar flows. A significant part of the paper is devoted to a discussion of drag, added-mass force, and shear-induced lift experienced by spheroidal bubbles moving in inertially dominated, time-dependent, rotational, nonuniform flows. The important influence of surfactants and shape distortion on bubble motion in a quiescent liquid is highlighted. Examples of bubble motion in inhomogeneous flows combining several of the effects mentioned above are discussed.
WALL-LAYER MODELS FOR LARGE-EDDY SIMULATIONS
Authors: Piomelli Ugo , Balaras Elias
Published: July 2002

▪ Abstract  Because the cost of large-eddy simulations (LES) of wall-bounded flows that resolve all the important eddies depends strongly on the Reynolds number, methods to bypass the wall layer are required to perform high-Reynolds-number LES at a reasonable cost. In this paper the available methodologies are reviewed, and their ranges of applicability are highlighted. Various unresolved issues in wall-layer modeling are presented, mostly in the context of engineering applications.
EARLY PATTERNING OF THE C. ELEGANS EMBRYO
Authors: Rose Lesilee S. , Kemphues Kenneth J.
Published: July 2002

▪ Abstract  Studies of about 20 maternally expressed genes are providing an understanding of mechanisms of patterning and cell-fate determination in the early Caenorhabditis elegans embryo. The analyses have revealed that fates of the early blastomeres are specified by a combination of intrinsically asymmetric cell divisions and two types of cell-cell interactions: inductions and polarizing interactions. In this review we summarize the current level of understanding of the molecular mechanisms underlying these processes in the specification of cell fates in the pregastrulation embryo.
Animal Models of Tumor-Suppressor Genes
Authors: Hakem Razqallah , Mak Tak W.
Published: July 2002

▪ Abstract  The development of cancer requires multiple genetic alterations perturbing distinct cellular pathways. In human cancers, these alterations often arise owing to mutations in tumor-suppressor genes whose normal function is to either inhibit the proliferation, apoptosis, or differentiation of cells, or maintain their genomic integrity. Mouse models for tumor suppressors frequently provide definitive evidence for the antitumorigenic functions of these genes. In addition, animal models permit the identification of previously unsuspected roles of these genes in development and differentiation. The availability of null and tissue-specific mouse mutants for tumor-suppressor genes has greatly facilitated our understanding of the mechanisms leading to cancer. In this review, we describe mouse models for tumor-suppressor genes.
Apolipoprotein E: Far More Than a Lipid Transport Protein
Authors: Mahley Robert W. , Rall Stanley C.
Published: July 2002

First recognized as a major determinant in lipoprotein metabolism and cardiovascular disease, apolipoprotein (apo) E has emerged as an important molecule in several biological processes not directly related to its lipid transport function, including Alzheimer's disease and cognitive function, immunoregulation, and possibly even infectious diseases. ApoE is a polymorphic protein arising from three alleles at a single gene locus. The three major isoforms, apoE4, apoE3, and apoE2, differ from one another only by single amino acid substitutions, yet these changes have profound functional consequences at both the cellular and molecular levels. ApoE3 seems to be the normal isoform in all known functions, while apoE4 and apoE2 can each be dysfunctional. Isoform (allele)-specific effects include the association of apoE2 with the genetic disorder type III hyperlipoproteinemia and with both increased and decreased risk for atherosclerosis and the association of apoE4 with increased risk for both atherosclerosis and Alzheimer's disease, impaired cognitive function, and reduced neurite outgrowth; isoform-specific differences in cellular signaling events may also exist. Functional differences in the apoE isoforms that affect (or did affect) survival before the reproductive years probably account, at least in part, for the allele frequencies of the present day.
IMMUNE REGULATION BY CD40 AND ITS LIGAND GP39
Authors: Foy Teresa M. , Aruffo Alejandro , Bajorath Jürgen , Buhlmann Janet E. , Noelle Randolph J.
Published: July 2002

▪ Abstract  Over the past three years, CD40 and its ligand (gp39, CD40L, TBAM) have been shown to be essential for humoral immune responses to thymus-dependent antigens. However, as the tissue distribution widens for those cells that express CD40 and gp39, we can now show that this ligand-receptor pair also plays an important role in the selection of self-reactive T cells in the thymus (central tolerance) and the regulation of tolerance in mature T cells (peripheral tolerance). Advances in our understanding of the molecular basis for CD40 biology is based in two areas of research. First, a major breakthrough in our understanding of how CD40 transduces biological events centers on the identification of a novel protein that binds to the cytoplasmic tail of CD40 and may act as a signal transducing molecule. Secondly, advances in molecular modeling and mutagenesis of this ligand-receptor pair have helped to identify the critical receptor/ligand contacts in the gp39/CD40 complex. Advances in each of these areas are discussed.
INITIATION AND PROCESSING OF SIGNALS FROM THE B CELL ANTIGEN RECEPTOR
Authors: Reth Michael , Wienands J.
Published: July 2002

Current models of signal transduction from the antigen receptors on B and T cells still resemble equations with several unknown elements. Data from recent knock-out experiments in cell lines and mice contradict the assumption that Src-family kinase and tyrosine kinases of the Syk/Zap-70 family are the transducer elements that set signaling from these receptors in motion. Using a functional definition of signaling elements, we discuss the current knowledge of signaling events from the BCR and suggest the existence of an as-yet-unknown BCR transducer complex.
Immunobiology of Dendritic Cells
Authors: Banchereau Jacques , Briere Francine , Caux Christophe , Davoust Jean , Lebecque Serge , Liu Yong-Jun , Pulendran Bali , Palucka Karolina
Published: July 2002

Dendritic cells (DCs) are antigen-presenting cells with a unique ability to induce primary immune responses. DCs capture and transfer information from the outside world to the cells of the adaptive immune system. DCs are not only critical for the induction of primary immune responses, but may also be important for the induction of immunological tolerance, as well as for the regulation of the type of T cell–mediated immune response. Although our understanding of DC biology is still in its infancy, we are now beginning to use DC-based immunotherapy protocols to elicit immunity against cancer and infectious diseases.
SiGe Technology: Heteroepitaxy and High-Speed Microelectronics
Authors: Mooney P. M. , Chu J. O.
Published: July 2002

▪ Abstract  We review recent advances in our understanding of the epitaxial growth and properties of SiGe/Si heterostructures for applications in high-speed field-effect transistors. Improvements in computing power and experimental methods have led to new calculations and experiments that reveal the complexity of 60° misfit dislocations and their interactions, which ultimately determine the characteristics of strain-relaxed SiGe films serving as a buffer layer for strained-layer devices. Novel measurements of the microstructure of relaxed SiGe films are discussed. We also present recent work on the epitaxial growth of SiGe/Si heterostructures by ultra-high-vacuum chemical vapor deposition. This growth method not only provides device quality buffer layers, but abrupt, high-concentration phosphorous-doping profiles, and high-mobility S0.20Ge0.80/Ge composite hole channels have also been grown. These achievements enabled the fabrication of outstanding n- and p-channel modulation-doped field-effect transistors that show enormous promise for a variety of applications.