bluuebunny/crossref_metadata_2025 huggingface dataset:
The teachable language comprehender
Authors: Quillian M. Ross
Published: July 2002

The Teachable Language Comprehender (TLC) is a program designed to be capable of being taught to “comprehend” English text. When text which the program has not seen before is input to it, it comprehends that text by correctly relating each (explicit or implicit) assertion of the new text to a large memory. This memory is a “semantic network” representing factual assertions about the world.

The program also creates copies of the parts of its memory which have been found to relate to the new text, adapting and combining these copies to represent the meaning of the new text. By this means, the meaning of all text the program successfully comprehends is encoded into the same format as that of the memory. In this form it can be added into the memory.

Both factual assertions for the memory and the
capabilities
for correctly relating text to the memory's prior content are to be taught to the program as they are needed. TLC presently contains a relatively small number of examples of such assertions and capabilities, but within the system, notations for expressing either of these are provided. Thus the program now corresponds to a general process for comprehending language, and it provides a methodology for adding the additional information this process requires to actually comprehend text of any particular kind.

The memory structure and comprehension process of TLC allow new factual assertions and capabilities for relating text to such stored assertions to generalize automatically. That is, once such an assertion or capability is put into the system, it becomes available to help comprehend a great many other sentences in the future. Thus the addition of a single factual assertion or linguistic capability will often provide a large increment in TLC's effective knowledge of the world and in its overall ability to comprehend text.

The program's strategy is presented as a general theory of
Further remarks on line segment curve-fitting using dynamic programming
Authors: Gluss Brian
Published: July 2002

In a recent paper, Bellman showed how dynamic programming could be used to determine the solution to a problem previously considered by Stone. The problem comprises the determination, given
N
, of the
N
points of subdivision of a given interval (
α
,
β
and the corresponding line segments, that give the best least squares fit to a function
g
(
x
) in the interval. Bellman confined himself primarily to the analytical derivation, suggesting briefly, however, how the solution of the equation derived for each particular point of subdivision

u
i

could be reduced to a discrete search. In this paper, the computational procedure is considered more fully, and the similarities to some of Stone's equations are indicated. It is further shown that an equation for

u
2

involving no minimization may be found. In addition, it is shown how Bellman's method may be applied to the curve-fitting problem when the additional constraints are added that the ends of the line segments must be on the curve.
Company profile of the frequent internet user
Authors: Stanton Jeffrey M.
Published: July 2002

Web addict or happy employee?
Humanoid robots
Authors: Brooks Rodney
Published: July 2002

The future promises lots of robots in our everyday lives; some, perhaps many, of them could look and behave like people but only if being humanoid represents a technological advantage over their relatively utilitarian counterparts.
How to construct random functions
Authors: Goldreich Oded , Goldwasser Shafi , Micali Silvio
Published: July 2002

A constructive theory of randomness for functions, based on computational complexity, is developed, and a pseudorandom function generator is presented. This generator is a deterministic polynomial-time algorithm that transforms pairs (
g
,
r
), where
g
is
any
one-way function and
r
is a random
k
-bit string, to polynomial-time computable functions ƒ

r

: {1, … , 2

k

} → {1, … , 2

k

}. These ƒ

r

's cannot be distinguished from
random
functions by any probabilistic polynomial-time algorithm that asks and receives the value of a function at arguments of its choice. The result has applications in cryptography, random constructions, and complexity theory.
Renaming in an asynchronous environment
Authors: Attiya Hagit , Bar-Noy Amotz , Dolev Danny , Peleg David , Reischuk Rüdiger
Published: July 2002

This paper is concerned with the solvability of the problem of processor renaming in unreliable, completely asynchronous distributed systems. Fischer et al. prove in [8] that “nontrivial consensus” cannot be attained in such systems, even when only a single, benign processor failure is possible. In contrast, this paper shows that problems of processor renaming can be solved even in the presence of up tot<n/2 faulty processors, contradicting the widely held belief that no nontrivial problem can be solved in such a system. The problems deal withrenaming processorsso as to reduce the size of the initial name space. When only uniqueness of the new names is required, we present a lower bound ofn+ 1 on the size of the new name space, and a renaming algorithm that establishes an upper bound onn+t. If the new names are required also to preserve the original order, a tight bound of 2′(n-t+ 1) - 1 is obtained.
Heterogeneous distributed database systems for production use
Authors: Thomas Gomer , Thompson Glenn R. , Chung Chin-Wan , Barkmeyer Edward , Carter Fred , Templeton Marjorie , Fox Stephen , Hartman Berl
Published: July 2002

It is increasingly important for organizations to achieve additional coordination of diverse computerized operations. To do so, it is necessary to have database systems that can operate over a distributed network and can encompass a heterogeneous mix of computers, operating systems, communications links, and local database management systems. This paper outlines approaches to various aspects of heterogeneous distributed data management and describes the characteristics and architectures of seven existing heterogeneous distributed database systems developed for production use. The objective is a survey of the state of the art in systems targeted for production environments as opposed to research prototypes.
THE MOLECULAR-GENETICS OF NITROGEN ASSIMILATION INTO AMINO ACIDS IN HIGHER PLANTS
Authors: Lam H.-M. , Coschigano K. T. , Oliveira I. C. , Melo-Oliveira R. , Coruzzi G. M.
Published: July 2002

▪ Abstract  Nitrogen assimilation is a vital process controlling plant growth and development. Inorganic nitrogen is assimilated into the amino acids glutamine, glutamate, asparagine, and aspartate, which serve as important nitrogen carriers in plants. The enzymes glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), aspartate aminotransferase (AspAT), and asparagine synthetase (AS) are responsible for the biosynthesis of these nitrogen-carrying amino acids. Biochemical studies have revealed the existence of multiple isoenzymes for each of these enzymes. Recent molecular analyses demonstrate that each enzyme is encoded by a gene family wherein individual members encode distinct isoenzymes that are differentially regulated by environmental stimuli, metabolic control, developmental control, and tissue/cell-type specificity. We review the recent progress in using molecular-genetic approaches to delineate the regulatory mechanisms controlling nitrogen assimilation into amino acids and to define the physiological role of each isoenzyme involved in this metabolic pathway.
AGROBACTERIUM AND PLANT GENES INVOLVED IN T-DNA TRANSFER AND INTEGRATION
Authors: Gelvin Stanton B.
Published: July 2002

▪ Abstract  The phytopathogenic bacterium Agrobacterium tumefaciens genetically transforms plants by transferring a portion of the resident Ti-plasmid, the T-DNA, to the plant. Accompanying the T-DNA into the plant cell is a number of virulence (Vir) proteins. These proteins may aid in T-DNA transfer, nuclear targeting, and integration into the plant genome. Other virulence proteins on the bacterial surface form a pilus through which the T-DNA and the transferred proteins may translocate. Although the roles of these virulence proteins within the bacterium are relatively well understood, less is known about their roles in the plant cell. In addition, the role of plant-encoded proteins in the transformation process is virtually unknown. In this article, I review what is currently known about the functions of virulence and plant proteins in several aspects of the Agrobacterium transformation process.
ISOPRENE EMISSION FROM PLANTS
Authors: Sharkey Thomas D , Yeh Sansun
Published: July 2002

▪ Abstract  Very large amounts of isoprene are emitted from vegetation, especially from mosses, ferns, and trees. This hydrocarbon flux to the atmosphere, roughly equal to the flux of methane, has a large effect on the oxidizing potential of the atmosphere. Isoprene emission results from de novo synthesis by the deoxyxylulose phosphate/methyl erythritol 4-phosphate pathway in plastids. Dimethylallyl pyrophosphate made by this pathway is converted to isoprene by isoprene synthase. Isoprene synthase activity in plants has a high pH optimum and requirement for Mg2+ that is consistent with its location inside chloroplasts. Isoprene emission costs the plant significant amounts of carbon, ATP, and reducing power. Researchers hypothesize that plants benefit from isoprene emission because it helps photosynthesis recover from short high-temperature episodes. The evolution of isoprene emission may have been important in allowing plants to survive the rapid temperature changes that can occur in air because of the very low heat capacity of isoprene relative to water.
STAR FORMATION IN GALAXIES ALONG THE HUBBLE SEQUENCE
Authors: Kennicutt Robert C.
Published: July 2002

▪ Abstract  Observations of star formation rates (SFRs) in galaxies provide vital clues to the physical nature of the Hubble sequence and are key probes of the evolutionary histories of galaxies. The focus of this review is on the broad patterns in the star formation properties of galaxies along the Hubble sequence and their implications for understanding galaxy evolution and the physical processes that drive the evolution. Star formation in the disks and nuclear regions of galaxies are reviewed separately, then discussed within a common interpretive framework. The diagnostic methods used to measure SFRs are also reviewed, and a self-consistent set of SFR calibrations is presented as an aid to workers in the field.
The HR Diagram and the Galactic Distance Scale After Hipparcos
Authors: Reid I. Neill
Published: July 2002

▪ Abstract  The completion and publication of the Hipparcos astrometric catalogue has revitalized studies in many fundamental areas of Galactic structure and stellar evolution. This article reviews the impact of the new parallax results on our understanding of the location of the main-sequence as a function of abundance, of the luminosity calibration of primary distance indicators and of the Galactic distance scale. Many of these issues remain to be resolved.
TGF-β SIGNAL TRANSDUCTION
Authors: Massagué J.
Published: July 2002

The transforming growth factor β (TGF-β) family of growth factors control the development and homeostasis of most tissues in metazoan organisms. Work over the past few years has led to the elucidation of a TGF-β signal transduction network. This network involves receptor serine/threonine kinases at the cell surface and their substrates, the SMAD proteins, which move into the nucleus, where they activate target gene transcription in association with DNA-binding partners. Distinct repertoires of receptors, SMAD proteins, and DNA-binding partners seemingly underlie, in a cell-specific manner, the multifunctional nature of TGF-β and related factors. Mutations in these pathways are the cause of various forms of human cancer and developmental disorders.
Two-Component Signal Transduction
Authors: Stock Ann M. , Robinson Victoria L. , Goudreau Paul N.
Published: July 2002

▪ Abstract  Most prokaryotic signal-transduction systems and a few eukaryotic pathways use phosphotransfer schemes involving two conserved components, a histidine protein kinase and a response regulator protein. The histidine protein kinase, which is regulated by environmental stimuli, autophosphorylates at a histidine residue, creating a high-energy phosphoryl group that is subsequently transferred to an aspartate residue in the response regulator protein. Phosphorylation induces a conformational change in the regulatory domain that results in activation of an associated domain that effects the response. The basic scheme is highly adaptable, and numerous variations have provided optimization within specific signaling systems. The domains of two-component proteins are modular and can be integrated into proteins and pathways in a variety of ways, but the core structures and activities are maintained. Thus detailed analyses of a relatively small number of representative proteins provide a foundation for understanding this large family of signaling proteins.
FOCAL ADHESIONS, CONTRACTILITY, AND SIGNALING
Authors: Burridge Keith , Chrzanowska-Wodnicka Magdalena
Published: July 2002

▪ Abstract  Focal adhesions are sites of tight adhesion to the underlying extracellular matrix developed by cells in culture. They provide a structural link between the actin cytoskeleton and the extracellular matrix and are regions of signal transduction that relate to growth control. The assembly of focal adhesions is regulated by the GTP-binding protein Rho. Rho stimulates contractility which, in cells that are tightly adherent to the substrate, generates isometric tension. In turn, this leads to the bundling of actin filaments and the aggregation of integrins (extracellular matrix receptors) in the plane of the membrane. The aggregation of integrins activates the focal adhesion kinase and leads to the assembly of a multicomponent signaling complex.
RGD AND OTHER RECOGNITION SEQUENCES FOR INTEGRINS
Authors: Ruoslahti Erkki
Published: July 2002

▪ Abstract  Proteins that contain the Arg-Gly-Asp (RGD) attachment site, together with the integrins that serve as receptors for them, constitute a major recognition system for cell adhesion. The RGD sequence is the cell attachment site of a large number of adhesive extracellular matrix, blood, and cell surface proteins, and nearly half of the over 20 known integrins recognize this sequence in their adhesion protein ligands. Some other integrins bind to related sequences in their ligands. The integrin-binding activity of adhesion proteins can be reproduced by short synthetic peptides containing the RGD sequence. Such peptides promote cell adhesion when insolubilized onto a surface, and inhibit it when presented to cells in solution. Reagents that bind selectively to only one or a few of the RGD-directed integrins can be designed by cyclizing peptides with selected sequences around the RGD and by synthesizing RGD mimics. As the integrin-mediated cell attachment influences and regulates cell migration, growth, differentiation, and apoptosis, the RGD peptides and mimics can be used to probe integrin functions in various biological systems. Drug design based on the RGD structure may provide new treatments for diseases such as thrombosis, osteoporosis, and cancer.
Geologic Evolution of the Himalayan-Tibetan Orogen
Authors: Yin An , Harrison T. Mark
Published: July 2002

A review of the geologic history of the Himalayan-Tibetan orogen suggests that at least 1400 km of north-south shortening has been absorbed by the orogen since the onset of the Indo-Asian collision at about 70 Ma. Significant crustal shortening, which leads to eventual construction of the Cenozoic Tibetan plateau, began more or less synchronously in the Eocene (50–40 Ma) in the Tethyan Himalaya in the south, and in the Kunlun Shan and the Qilian Shan some 1000–1400 km in the north. The Paleozoic and Mesozoic tectonic histories in the Himalayan-Tibetan orogen exerted a strong control over the Cenozoic strain history and strain distribution. The presence of widespread Triassic flysch complex in the Songpan-Ganzi-Hoh Xil and the Qiangtang terranes can be spatially correlated with Cenozoic volcanism and thrusting in central Tibet. The marked difference in seismic properties of the crust and the upper mantle between southern and central Tibet is a manifestation of both Mesozoic and Cenozoic tectonics. The former, however, has played a decisive role in localizing Tertiary contractional deformation, which in turn leads to the release of free water into the upper mantle and the lower crust of central Tibet, causing partial melting in the mantle lithosphere and the crust.
Partial Melting Experiments on Peridotite and Origin of Mid-Ocean Ridge Basalt
Authors: Kushiro Ikuo
Published: July 2002

▪ Abstract  Recent partial melting experiments on peridotite indicate that mantle peridotites with Mg# < 88 can produce primitive mid-ocean ridge basalt by 15–25% partial melting at 1.0–1.5 GPa followed by small amounts (a few to 10%) of olivine fractionation, whereas those with Mg# > 89 can produce primitive mid-ocean ridge basalt by partial melting at pressures greater than 1.5 GPa followed by extensive olivine fractionation. Polybaric incremental batch melting or stepwise fractional melting experiments indicate that the compositions of accumulated incremental melts formed along a mantle adiabat in the pressure range 2.0–1.0 and 2.0–0.5 GPa are close to, but slightly more olivine-rich than, those of primitive mid-ocean ridge basalt, and that the amount of accumulated incremental melts is significantly smaller than that of batch partial melts formed for the same potential temperature. The melting in adiabatically ascending mantle beneath mid-ocean ridges would cease at depths >15 km because of the inflection of the solidus of mantle peridotite.
ROADS AND THEIR MAJOR ECOLOGICAL EFFECTS
Authors: Forman Richard T. T. , Alexander Lauren E.
Published: July 2002

▪ Abstract  A huge road network with vehicles ramifies across the land, representing a surprising frontier of ecology. Species-rich roadsides are conduits for few species. Roadkills are a premier mortality source, yet except for local spots, rates rarely limit population size. Road avoidance, especially due to traffic noise, has a greater ecological impact. The still-more-important barrier effect subdivides populations, with demographic and probably genetic consequences. Road networks crossing landscapes cause local hydrologic and erosion effects, whereas stream networks and distant valleys receive major peak-flow and sediment impacts. Chemical effects mainly occur near roads. Road networks interrupt horizontal ecological flows, alter landscape spatial pattern, and therefore inhibit important interior species. Thus, road density and network structure are informative landscape ecology assays. Australia has huge road-reserve networks of native vegetation, whereas the Dutch have tunnels and overpasses perforating road barriers to enhance ecological flows. Based on road-effect zones, an estimated 15–20% of the United States is ecologically impacted by roads.
Evolution of Eastern Asian and Eastern North American Disjunct Distributions in Flowering Plants
Authors: Wen Jun
Published: July 2002

▪ Abstract  The disjunct distributions of morphologically similar plants between eastern Asia and eastern North America have fascinated botanists and biogeographers since the Linnaean era. This biogeographic pattern is currently recognized by the disjunct distributions of some species, approximately 65 genera, and a few closely related genera in these two widely separated areas. Early workers treated many disjuncts as conspecific, but most were later recognized as intercontinental species pairs. Recent phylogenetic studies confirm affinities between many of the disjunct taxa but also indicate that the disjunct pairs of species are rarely each other's closest relatives. Instead, a pattern of further diversification of species on one or both continents is commonly found. Phylogenetic, molecular, geologic, and fossil data all support the hypothesis that the eastern Asian and eastern North American disjunct distributions are relicts of the maximum development of temperate forests in the northern hemisphere during the Tertiary. Fossil and geologic evidence supports multiple origins of this pattern in the Tertiary, with both the North Atlantic and the Bering land bridges involved. In many genera of flowering plants, current estimates of divergence times using molecular and fossil data suggest that the disjunct patterns were established during the Miocene. Morphological stasis, evidenced by the minimal morphological divergence of species after a long time of separation, must have occurred in some of the disjunct groups in the north temperate zone.
Diversification of Rainforest Faunas: An Integrated Molecular Approach
Authors: Moritz C. , Patton J. L. , Schneider C. J. , Smith T. B.
Published: July 2002

▪ Abstract  Understanding the evolutionary processes that generate and sustain diversity in tropical faunas has challenged biologists for over a century and should underpin conservation strategies. Molecular studies of diversity within species and relationships among species, when integrated with more traditional approaches of biogeography and paleoecology, have much to contribute to this challenge. Here we outline the current major hypotheses, develop predictions relevant to integrated molecular approaches, and evaluate the current evidence, focusing on central African, Australian, and South American systems. The available data are sparse relative to the scale of the questions. However, the following conclusions can be drawn: (a) in most cases, the divergence of extant sister taxa predates the Pleistocene; (b) areas with high habitat heterogeneity and recent climatic or geological instability appear to harbor more species of recent origin; (c) there is support for both allopatric and gradient models of diversification and more attention should be given to the role of diversifying selection regardless of geographic context; and (d) conservation strategies should seek to protect heterogeneous landscapes within and adjacent to large rainforest areas, rather than rainforests alone.
The Evolution of Predator-Prey Interactions: Theory and Evidence
Authors: Abrams Peter A.
Published: July 2002

▪ Abstract  Recent theories regarding the evolution of predator-prey interactions is reviewed. This includes theory about the dynamics and stability of both populations and traits, as well as theory predicting how predatory and anti-predator traits should respond to environmental changes. Evolution can stabilize or destabilize interactions; stability is most likely when only the predator evolves, or when traits in one or both species are under strong stabilizing selection. Stability seems least likely when there is coevolution and a bi-directional axis of prey vulnerability. When population cycles exist, adaptation may either increase or decrease the amplitude of those cycles. An increase in the defensive ability of prey is less likely to produce evolutionary counter-measures in its partner than is a comparable increase in attack ability of the predator. Increased productivity may increase or decrease offensive and defensive adaptations. The apparent predominance of evolutionary responses of prey to predators over those of predators to prey is in general accord with equilibrium theory, but theory on stability may be difficult to confirm or refute. Recent work on geographically structured populations promises to advance our understanding of the evolution of predator-prey interactions.
Urban Ecological Systems: Linking Terrestrial Ecological, Physical, and Socioeconomic Components of Metropolitan Areas
Authors: Pickett S. T. A. , Cadenasso M. L. , Grove J. M. , Nilon C. H. , Pouyat R. V. , Zipperer W. C. , Costanza R.
Published: July 2002

▪ Abstract  Ecological studies of terrestrial urban systems have been approached along several kinds of contrasts: ecology in as opposed to ecology of cities; biogeochemical compared to organismal perspectives, land use planning versus biological, and disciplinary versus interdisciplinary. In order to point out how urban ecological studies are poised for significant integration, we review key aspects of these disparate literatures. We emphasize an open definition of urban systems that accounts for the exchanges of material and influence between cities and surrounding landscapes. Research on ecology in urban systems highlights the nature of the physical environment, including urban climate, hydrology, and soils. Biotic research has studied flora, fauna, and vegetation, including trophic effects of wildlife and pets. Unexpected interactions among soil chemistry, leaf litter quality, and exotic invertebrates exemplify the novel kinds of interactions that can occur in urban systems. Vegetation and faunal responses suggest that the configuration of spatial heterogeneity is especially important in urban systems. This insight parallels the concern in the literature on the ecological dimensions of land use planning. The contrasting approach of ecology of cities has used a strategy of biogeochemical budgets, ecological footprints, and summaries of citywide species richness. Contemporary ecosystem approaches have begun to integrate organismal, nutrient, and energetic approaches, and to show the need for understanding the social dimensions of urban ecology. Social structure and the social allocation of natural and institutional resources are subjects that are well understood within social sciences, and that can be readily accommodated in ecosystem models of metropolitan areas. Likewise, the sophisticated understanding of spatial dimensions of social differentiation has parallels with concepts and data on patch dynamics in ecology and sets the stage for comprehensive understanding of urban ecosystems. The linkages are captured in the human ecosystem framework.
OPPORTUNITIES FOR POLLUTION PREVENTION AND ENERGY EFFICIENCY ENABLED BY THE CARBON DIOXIDE TECHNOLOGY PLATFORM
Authors: Taylor Darlene K. , Carbonell Ruben , DeSimone Joseph M.
Published: July 2002

▪ Abstract  Various applications using carbon dioxide (CO2) have developed within the last decade and, if current trends continue, the CO2 technology platform could emerge as the most commonly used solvent in the twenty-first century. An environmentally friendly platform that is wrapped in a successful business format with apparent implications for people and their communities is most likely to endure. Does the CO2 technology platform meet the criteria for becoming a sustainable enterprise? Utilizing CO2 as an alternative solvent in conventional processes has the potential to favorably impact the environment and our communities. There are, however, several barriers to adopting CO2-based applications. Several concepts as well as obstacles to adopting the carbon dioxide technology platform are highlighted in this chapter.
CulicoidesBiting Midges: Their Role as Arbovirus Vectors
Authors: Mellor P. S. , Boorman J. , Baylis M.
Published: July 2002

▪ Abstract  Culicoides biting midges are among the most abundant of haematophagous insects, and occur throughout most of the inhabited world. Across this broad range they transmit a great number of assorted pathogens of human, and domestic and wild animals, but it is as vectors of arboviruses, and particularly arboviruses of domestic livestock, that they achieve their prime importance. To date, more than 50 such viruses have been isolated from Culicoides spp. and some of these cause diseases of such international significance that they have been allocated Office International des Épizooties (OIE) List A status. Culicoides are world players in the epidemiology of many important arboviral diseases. In this context this paper deals with those aspects of midge biology facilitating disease transmission, describes the factors controlling insect-virus interactions at the individual insect and population level, and illustrates the far-reaching effects that certain components of climate have upon the midges and, hence, transmission potential.
Pest Management Strategies in Traditional Agriculture: An African Perspective
Authors: Abate T. , van Huis A. , Ampofo J. K. O.
Published: July 2002

▪ Abstract  African agriculture is largely traditional—characterized by a large number of smallholdings of no more than one ha per household. Crop production takes place under extremely variable agro-ecological conditions, with annual rainfall ranging from 250 to 750 mm in the Sahel in the northwest and in the semi-arid east and south, to 1500 to 4000 mm in the forest zones in the central west. Farmers often select well-adapted, stable crop varieties, and cropping systems are such that two or more crops are grown in the same field at the same time. These diverse traditional systems enhance natural enemy abundance and generally keep pest numbers at low levels. Pest management practice in traditional agriculture is a built-in process in the overall crop production system rather than a separate well-defined activity. Increased population pressure and the resulting demand for increased crop production in Africa have necessitated agricultural expansion with the concomitant decline in the overall biodiversity. Increases in plant material movement in turn facilitated the accidental introduction of foreign pests. At present about two dozen arthropod pests, both introduced and native, are recognized as one of the major constraints to agricultural production and productivity in Africa. Although yield losses of 0% to 100% have been observed on-station, the economic significance of the majority of pests under farmers’ production conditions is not adequately understood. Economic and social constraints have kept pesticide use in Africa the lowest among all the world regions. The bulk of pesticides are applied mostly against pests of commercial crops such as cotton, vegetables, coffee, and cocoa, and to some extent for combating outbreaks of migratory pests such as the locusts. The majority of African farmers still rely on indigenous pest management approaches to manage pest problems, although many government extension programs encourage the use of pesticides. The current pest management research activities carried out by national or international agricultural research programs in Africa focus on classical biological control and host plant resistance breeding. With the exception of classical biological control of the cassava mealybug, research results have not been widely adopted. This could be due to African farmers facing heterogeneous conditions, not needing fixed prescriptions or one ideal variety but a number of options and genotypes to choose from. Indigenous pest management knowledge is site-specific and should be the basis for developing integrated pest management (IPM) techniques. Farmers often lack the biological and ecological information necessary to develop better pest management through experimentation. Formal research should be instrumental in providing the input necessary to facilitate participatory technology development such as that done by Farmer Field Schools, an approach now emerging in different parts of Africa.
Arthropods on Islands: Colonization, Speciation, and Conservation
Authors: Gillespie Rosemary G. , Roderick George K.
Published: July 2002

▪ Abstract  Islands have traditionally been considered to be any relatively small body of land completely surrounded by water. However, their primary biological characteristic, an extended period of isolation from a source of colonists, is common also to many situations on continents. Accordingly, theories and predictions developed for true islands have been applied to a huge array of systems, from rock pools, to single tree species in forests, to oceanic islands. Here, we examine the literature on islands in the broadest sense (i.e., whether surrounded by water or any other uninhabitable matrix) as it pertains to terrestrial arthropods. We categorize islands according to the features they share. The primary distinction between different island systems is “darwinian” islands (formed de novo) and “fragment” islands. In the former, the islands have never been in contact with the source of colonists and have abundant “empty” ecological niche space. On these islands, species numbers will initially increase through immigration, the rate depending on the degree of isolation. If isolation persists, over time species formation will result in “neo-endemics.” When isolation is extreme, the ecological space will gradually be filled through speciation (rather than immigration) and adaptive radiation of neo-endemics. Fragment islands are fundamentally different. In these islands, the ecological space will initially be filled as a consequence of connection to the source of colonists prior to insularization. Species numbers will decrease following fragmentation through the process of relaxation. If these islands become more isolated, species will eventually arise through relictualization with the formation of “paleo-endemics.” Given sufficient time, this process can result in generic level endemism on ancient fragment islands, a phenomenon well illustrated in Madagascar and New Zealand. Recognizing the distinction between the different kinds of islands is fundamental for understanding emerging patterns on each, in particular speciation, biodiversity (e.g., neo-endemics versus paleo-endemics), and conservation (e.g., naiveté in interactions with alien species).
THE FLUID MECHANICS OF NATURAL VENTILATION
Authors: Linden P. F.
Published: July 2002

▪ Abstract  Natural ventilation of buildings is the flow generated by temperature differences and by the wind. The governing feature of this flow is the exchange between an interior space and the external ambient. Although the wind may often appear to be the dominant driving mechanism, in many circumstances temperature variations play a controlling feature on the ventilation since the directional buoyancy force has a large influence on the flow patterns within the space and on the nature of the exchange with the outside. Two forms of ventilation are discussed: mixing ventilation, in which the interior is at an approximately uniform temperature, and displacement ventilation, where there is strong internal stratification. The dynamics of these buoyancy-driven flows are considered, and the effects of wind on them are examined. The aim behind this work is to give designers rules and intuition on how air moves within a building; the research reveals a fascinating branch of fluid mechanics.
ON THE FLUID MECHANICS OF FIRES
Authors: Tieszen Sheldon R
Published: July 2002

▪ Abstract  Fluid mechanics research related to fire is reviewed with a focus on canonical flows, multiphysics coupling aspects, and experimental and numerical techniques. Fire is a low-speed, chemically reacting flow in which buoyancy plays an important role. Fire research has focused on two canonical flows, the reacting boundary layer and the reacting free plume. There is rich, multilateral, bidirectional coupling among fluid mechanics and scalar transport, combustion, and radiation. There is only a limited experimental fluid mechanics database for fire owing to measurement difficulties in the harsh environment and to the focus within the fire community on thermal/chemical consequences. Increasingly, computational fluid dynamics techniques are being used to provide engineering guidance on thermal/chemical consequences and to study fire phenomenology.
The Genetics of Aging
Authors: Finch Caleb E. , Ruvkun Gary
Published: July 2002

The genetic analysis of life span has only begun in mammals, invertebrates, such as Caenorhabditis elegans and Drosophila, and yeast. Even at this primitive stage of the genetic analysis of aging, the physiological observations that rate of metabolism is intimately tied to life span is supported. In many examples from mice to worms to flies to yeast, genetic variants that affect life span also modify metabolism. Insulin signaling regulates life span coordinately with reproduction, metabolism, and free radical protective gene regulation in C. elegans. This may be related to the findings that caloric restriction also regulates mammalian aging, perhaps via the modulation of insulin-like signaling pathways. The nervous system has been implicated as a key tissue where insulin-like signaling and free radical protective pathways regulate life span in C. elegans and Drosophila. Genes that determine the life span could act in neuroendocrine cells in diverse animals. The involvement of insulin-like hormones suggests that the plasticity in life spans evident in animal phylogeny may be due to variation in the timing of release of hormones that control vitality and mortality as well as variation in the response to those hormones. Pedigree analysis of human aging may reveal variations in the orthologs of the insulin pathway genes and coupled pathways that regulate invertebrate aging. Thus, genetic approaches may identify a set of circuits that was established in ancestral metazoans to regulate their longevity.
TRANSCRIPTION FACTORS OF THE NFAT FAMILY:Regulation and Function
Authors: Rao Anjana , Luo Chun , Hogan Patrick G.
Published: July 2002

▪ Abstract  As targets for the immunosuppressive drugs cyclosporin A and FK506, transcription factors of the NFAT (nuclear factor of activated T cells) family have been the focus of much attention. NFAT proteins, which are expressed in most immune-system cells, play a pivotal role in the transcription of cytokine genes and other genes critical for the immune response. The activity of NFAT proteins is tightly regulated by the calcium/calmodulin-dependent phosphatase calcineurin, a primary target for inhibition by cyclosporin A and FK506. Calcineurin controls the translocation of NFAT proteins from the cytoplasm to the nucleus of activated cells by interacting with an N-terminal regulatory domain conserved in the NFAT family. The DNA-binding domains of NFAT proteins resemble those of Rel-family proteins, and Rel and NFAT proteins show some overlap in their ability to bind to certain regulatory elements in cytokine genes. NFAT is also notable for its ability to bind cooperatively with transcription factors of the AP-1 (Fos/Jun) family to composite NFAT:AP-1 sites, found in the regulatory regions of many genes that are inducibly transcribed by immune-system cells. This review discusses recent data on the diversity of the NFAT family of transcription factors, the regulation of NFAT proteins within cells, and the cooperation of NFAT proteins with other transcription factors to regulate the expression of inducible genes.
IgG Fc Receptors
Authors: Ravetch Jeffrey V. , Bolland Silvia
Published: July 2002

Since the description of the first mouse knockout for an IgG Fc receptor seven years ago, considerable progress has been made in defining the in vivo functions of these receptors in diverse biological systems. The role of activating FcγRs in providing a critical link between ligands and effector cells in type II and type III inflammation is now well established and has led to a fundamental revision of the significance of these receptors in initiating cellular responses in host defense, in determining the efficacy of therapeutic antibodies, and in pathological autoimmune conditions. Considerable progress has been made in the last two years on the in vivo regulation of these responses, through the appreciation of the importance of balancing activation responses with inhibitory signaling. The inhibitory FcR functions in the maintenance of peripheral tolerance, in regulating the threshold of activation responses, and ultimately in terminating IgG mediated effector stimulation. The consequences of deleting the inhibitory arm of this system are thus manifested in both the afferent and efferent immune responses. The hyperresponsive state that results leads to greatly magnified effector responses by cytotoxic antibodies and immune complexes and can culminate in autoimmunity and autoimmune disease when modified by environmental or genetic factors. FcγRs offer a paradigm for the biological significance of balancing activation and inhibitory signaling in the expanding family of activation/inhibitory receptor pairs found in the immune system.
The B7 Family of Ligands and Its Receptors: New Pathways for Costimulation and Inhibition of Immune Responses
Authors: Carreno Beatriz M. , Collins Mary
Published: July 2002

T cell activation is dependent upon signals delivered through the antigen-specific T cell receptor and accessory receptors on the T cell. A primary costimulatory signal is delivered through the CD28 receptor after engagement of its ligands, B7-1 (CD80) or B7-2 (CD86). Engagement of CTLA-4 (CD152) by the same B7-1 or B7-2 ligands results in attenuation of T cells responses. Recently, molecular homologs of CD28 and CTLA-4 receptors and their B7-like ligands have been identified. ICOS is a CD28-like costimulatory receptor with a unique B7-like ligand. PD-1 is an inhibitory receptor, with two B7-like ligands. Additional members of B7 and CD28 gene families have been proposed. Integration of signals through this family of costimulatory and inhibitory receptors and their ligands is critical for activation of immune responses and tolerance. Understanding these pathways will allow development of new strategies for therapeutic intervention in immune-mediated diseases.
CHARACTERIZATION OF POLYMER SURFACES WITH ATOMIC FORCE MICROSCOPY
Authors: Magonov Sergei N. , Reneker Darrell H.
Published: July 2002

▪ Abstract  Applications of state-of-the-art atomic force microscopy methods to the elucidation of the surface and near-surface structure of polymeric solids are described. Contact, tapping, force modulation, frictional force, and other modes of atomic force microscopy are described, and recent results are summarized. Conformational and chain order, crystalline order, polymer crystals, lamellar structures, lamellar surfaces, fold surfaces, and fibers and films with highly oriented molecules all yield important information. Controlled deformation of polymer surfaces, both reversible and irreversible, with the atomic force microscope, provides a wealth of information about mechanical properties on a nanometer scale. The observation of phase-separated regions and of polymer crystals lying below a smooth surface shows that not only topography but also elastic inhomogeneity can be observed in great detail with the atomic force microscope. This is a rapidly developing field, and some indications of future developments are presented.
Photorefractive Liquid Crystals
Authors: Wiederrecht Gary P
Published: July 2002

▪ Abstract  A review of the field of photorefractive liquid crystals is presented. The first reports of photorefractive liquid crystals occurred in 1994, and the performance of these materials has dramatically improved since that time. Liquid crystalline materials have proven to be highly versatile, showing photorefractive character under a wide range of conditions. For example, new composites based on high-molar-mass liquid crystals are now capable of forming volume (Bragg) gratings with high photorefractive gain coefficients of >600 cm−1. Formation times for photorefractive Bragg gratings of 15 ms with applied fields of only 0.1 V/μm have been reported. Low-molar-mass liquid crystals continue to be developed and show their largest photorefractive character in the thin (Raman-Nath) grating regime. Composites of nonmesogenic polymers and liquid crystals are also discussed. The experiments and theoretical work that have been used to characterize these materials are reviewed.
HYPERCALCEMIA OF MALIGNANCY: The Central Role of Parathyroid Hormone-Related Protein
Authors: Wysolmerski John J. , Broadus Arthur E.
Published: July 2002

▪ Abstract  Hypercalcemia is the most common metabolic complication of cancer. Malignancy-associated hypercalcemia (MAHC) can be divided into two syndromes, humoral hypercalcemia of malignancy (HHM) and local osteolytic hypercalcemia (LOH), based on whether a circulating hormone or local paracrine factors mediate accelerated bone resorption. Over the past decade, studies have shown that parathyroid hormone-related protein is the cause of the HHM syndrome, and recent data suggest that this protein may also play a paracrine role in some patients with local osteolytic hypercalcemia. Study of the regulation of parathyroid hormone-related protein gene expression is beginning to shed some light on the molecular mechanisms responsible for this common clinical problem.
BASIC DETERMINANTS OF MYOCARDIAL HYPERTROPHY: A Review of Molecular Mechanisms
Authors: Cooper George
Published: July 2002

▪ Abstract  The essential cardiac response to a fixed increase in hemodynamic load is an increase in cardiac mass. If the load increase is neither too severe initially nor indefinitely progressive, cardiac stress is renormalized, and compensated hypertrophy ensues. But hypertrophic compensation is often abrogated by progressively abnormal contractile performance per unit mass of myocardium, even when function at the organ level is maintained by the mass increase itself. That is, even when hypertrophy is appropriate to the load imposed, and in a manner analogous to dystrophic growth of skeletal muscle, specific phenotypic changes occurring during this growth response render compensation imperfect such that congestive heart failure ensues. This fact, and the fact that the presence of deleterious phenotypic changes in hypertrophied myocardium is critically dependent on the type of hemodynamic load imposed, mandates that cardiac hypertrophy be understood on the most basic level as a growth process if early, definitive interventions to prevent congestive heart failure following pathological hemodynamic overloads are to be realized.
Rational Approach to AIDS Drug Design Through Structural Biology
Authors: Wlodawer Alexander
Published: July 2002

▪ Abstract  The discovery and development of more than a dozen drugs in the past 15 years for the treatment of AIDS offer an excellent example of progress in the field of rational drug design. At this time, the principal targets are reverse transcriptase and protease, enzymes encoded by the human immunodeficiency virus. The introduction of protease inhibitors, in particular, has drastically decreased the mortality and morbidity associated with AIDS. This review presents the methods used to develop such drugs and discusses the remaining problems, such as the rapid emergence of drug resistance.
THE F0F1-TYPE ATP SYNTHASES OF BACTERIA: Structure and Function of the F0 Complex
Authors: Deckers-Hebestreit Gabriele , Altendorf Karlheinz
Published: July 2002

Membrane-bound ATP synthases (F0F1-ATPases) of bacteria serve two important physiological functions. The enzyme catalyzes the synthesis of ATP from ADP and inorganic phosphate utilizing the energy of an electrochemical ion gradient. On the other hand, under conditions of low driving force, ATP synthases function as ATPases, thereby generating a transmembrane ion gradient at the expense of ATP hydrolysis. The enzyme complex consists of two structurally and functionally distinct parts: the membrane-integrated ion-translocating F0 complex and the peripheral F1 complex, which carries the catalytic sites for ATP synthesis and hydrolysis. The ATP synthase of Escherichia coli, which has been the most intensively studied one, is composed of eight different subunits, five of which belong to F1, subunits α, β, γ, δ, and ε (3:3:1:1:1), and three to F0, subunits a, b, and c (1:2:10 ± 1). The similar overall structure and the high amino acid sequence homology indicate that the mechanism of ion translocation and catalysis and their mode of coupling is the same in all organisms.