bluuebunny/crossref_metadata_2025 huggingface dataset:
Language and Agency
Authors: Ahearn Laura M.
Published: July 2002

▪ Abstract  This review describes and critiques some of the many ways agency has been conceptualized in the academy over the past few decades, focusing in particular on practice theorists such as Giddens, Bourdieu, de Certeau, Sahlins, and Ortner. For scholars interested in agency, it demonstrates the importance of looking closely at language and argues that the issues surrounding linguistic form and agency are relevant to anthropologists with widely divergent research agendas. Linguistic anthropologists have made significant contributions to the understanding of agency as it emerges in discourse, and the final sections of this essay describe some of the most promising research in the study of language and gender, literacy practices, and the dialogic construction of meaning and agency.
The Anthropology of Afro-Latin America and the Caribbean: Diasporic Dimensions
Authors: Yelvington Kevin A.
Published: July 2002

▪ Abstract  The contributions of a number of First and Third World scholars to the development of the anthropology of the African diaspora in Latin America and the Caribbean have been elided from the core of the discipline as practiced in North America and Europe. As such, the anthropology of the African diaspora in the Americas can be traced to the paradigmatic debate on the origins of New World black cultures between Euro-American anthropologist Melville J. Herskovits and African American sociologist E. Franklin Frazier. The former argued for the existence of African cultural continuities, the latter for New World culture creations in the context of discrimination and deprivation characteristic of the experiences of peoples of African descent, in light of slavery, colonialism, and postcolonial contexts. As a result, subsequent positions have been defined by oppositions in every subdisciplinary specialization and area of interest. Creolization models try to obviate this bifurcation, and newer dialogical theoretical perspectives build upon such models by attempting to combine revisionist historiography with social/cultural constructionist approaches to identity, especially around the concept of blackness understood in the context of cultural identity politics.
PATHWAYS ANDREGULATION OFSULFURMETABOLISMREVEALEDTHROUGHMOLECULAR ANDGENETICSTUDIES
Authors: Leustek Thomas , Martin Melinda N. , Bick Julie-Ann , Davies John P.
Published: July 2002

▪ Abstract  Sulfur is essential for life. Its oxidation state is in constant flux as it circulates through the global sulfur cycle. Plants play a key role in the cycle since they are primary producers of organic sulfur compounds. They are able to couple photosynthesis to the reduction of sulfate, assimilation into cysteine, and further metabolism into methionine, glutathione, and many other compounds. The activity of the sulfur assimilation pathway responds dynamically to changes in sulfur supply and to environmental conditions that alter the need for reduced sulfur. Molecular genetic analysis has allowed many of the enzymes and regulatory mechanisms involved in the process to be defined. This review focuses on recent advances in the field of plant sulfur metabolism. It also emphasizes areas about which little is known, including transport and recycling/degradation of sulfur compounds.
PARSEC-SCALE JETS IN EXTRAGALACTIC RADIO SOURCES
Authors: Zensus J. Anton
Published: July 2002

▪ Abstract  Observations of parsec-scale radio jets associated with active galactic nuclei are reviewed, with a particular emphasis on high-luminosity core-dominated sources where the most detailed information on individual objects exists. Extensive imaging surveys with very long baseline interferometry (VLBI) have made possible a morphologic classification of compact radio sources and systematic studies of the statistics of apparent (often faster-than-light) motions found in an increasing number of sources. VLBI monitoring studies at centimeter and millimeter wavelengths, enhanced by spectral and polarization imaging, of representative types of AGN can discriminate detailed physical models. The observations are especially discussed in light of the variant of the relativistic beaming model that explains kinematic, spectral, and polarization properties of parsec-scale jets through shocks in an underlying continuous jet flow.
The Reionization of the Universe by the First Stars and Quasars
Authors: Loeb Abraham , Barkana Rennan
Published: July 2002

▪ Abstract  The formation of the first stars and quasars marks the transformation of the universe from its smooth initial state to its clumpy current state. In popular cosmological models, the first sources of light began to form at a redshift z = 30 and reionized most of the hydrogen in the universe by z = 7. Current observations are at the threshold of probing the hydrogen reionization epoch. The study of high-redshift sources is likely to attract major attention in observational and theoretical cosmology over the next decade.
Optical Interferometry
Authors: Quirrenbach Andreas
Published: July 2002

▪ Abstract  The field of optical and infrared (IR) interferometry has seen rapid technical and scientific progress over the past few years. A number of instruments capable of precise visibility measurements have been built, and closure-phase imaging with multitelescope arrays has been demonstrated. Astronomical results from these instruments include measurements of stellar diameters and their wavelength dependence, limb darkening, stellar surface structure, and distances of Cepheids and of Nova Cygni 1992. Precise stellar masses have been obtained from interferometric observations of spectroscopic binaries, and circumstellar disks and shells have been resolved. Searches for substellar companions and extrasolar planets with interferometric astrometry will begin soon. Nulling interferometry will enable studies of exozodiacal disks from the ground and the detection and characterization of terrestrial extrasolar planets from space. These developments are reviewed, as well as progress in some key technological areas.
STRUCTURE-BASED PERSPECTIVES ON B12-DEPENDENT ENZYMES
Authors: Ludwig Martha L. , Matthews Rowena G.
Published: July 2002

Two X-ray structures of cobalamin (B12) bound to proteins have now been determined. These structures reveal that the B12cofactor undergoes a major conformational change on binding to the apoenzymes of methionine synthase and methylmalonyl–coenzyme A mutase: The dimethylbenzimidazole ligand to the cobalt is displaced by a histidine residue from the protein. Two methyltransferases from archaebacteria that catalyze methylation of mercaptoethanesulfonate (coenzyme M) during methanogenesis have also been shown to contain histidine-ligated cobamides. In corrinoid iron-sulfur methyltransferases from acetogenic and methanogenic organisms, benzimidazole is dissociated from cobalt, but without replacement by histidine. Thus, dimethylbenzimidazole displacement appears to be an emerging theme in cobamide-containing methyltransferases. In methionine synthase, the best studied of the methyltransferases, the histidine ligand appears to be required for competent methyl transfer between methyl- tetrahydrofolate and homocysteine but dissociates for reductive reactivation of the inactive oxidized enzyme. Replacement of dimethylbenzimidazole by histidine may allow switching between the catalytic and activation cycles.

The best-characterized B12-dependent mutases that catalyze carbon skeleton rearrangement, for which methylmalonyl–coenzyme A mutase is the prototype, also bind cobalamin cofactors with histidine as the cobalt ligand, although other cobalamin-dependent mutases do not appear to utilize histidine ligation. It is intriguing to find that mutases, which catalyze homolytic rather than heterolytic cleavage of the carbon-cobalt bond, can use this structural motif. In methylmalonylCoA mutase a significant feature, which may be important in facilitating homolytic cleavage, is the long cobalt-nitrogen bond linking histidine to the cofactor. The intermediate radical species generated in catalysis are sequestered in the relatively hydrophilic core of an α/β barrel domain of the mutase.
Imaging Transgenic Animals
Authors: Budinger T. F. , Benaron D. A. , Koretsky A. P.
Published: July 2002

▪ Abstract  Transgenic and eugenic animals as small as 30 g can be studied noninvasively by radionuclides with resolutions of 1–2 mm, by MRI with resolution of 100 μm and by light fluorescence and bioluminescence with high sensitivities. The technologies of radionuclide emission, magnetic resonance imaging, magnetic resonance spectroscopy, optical tomography, optical fluorescence and optical bioluminescence are currently being applied to small-animal studies. These technologies and examples of their applications are reviewed in this chapter.
THE LIN-12/Notch SIGNALING PATHWAY AND ITS REGULATION
Authors: Kimble Judith , Simpson Pat
Published: July 2002

▪ Abstract  Notch, LIN-12, and GLP-1 are receptors that mediate a broad range of cell interactions during Drosophila and nematode development. Signaling by these receptors relies on a conserved pathway with three core components: DSL ligand, LNG receptor, and a CSL effector that links the receptor to its transcriptional response. Although key functional regions have been identified in each class of proteins, the mechanism for signal transduction is not yet understood. Diverse regulatory mechanisms influence signaling by the LIN-12/Notch pathway. Inductive signaling relies on the synthesis of ligand and receptor in distinct but neighboring cells. By contrast, lateral signaling leads to the transformation of equivalent cells that express both ligand and receptor into nonequivalent cells that express either ligand or receptor. This transformation appears to rely on regulatory feedback loops within the LIN-12/Notch pathway. In addition, the pathway can be regulated by intrinsic factors that are asymmetrically segregated during cell division or by extrinsic cues via other signaling pathways. Specificity in the pathway does not appear to reside in the particular ligand or receptor used for a given cell-cell interaction. The existence of multiple ligands and receptors may have evolved from the stringent demands placed upon the regulation of genes encoding them.
CONTROL OF TRANSLATION INITIATION IN ANIMALS
Authors: Gray Nicola K. , Wickens Marvin
Published: July 2002

▪ Abstract  Regulation of translation initiation is a central control point in animal cells. We review our current understanding of the mechanisms of regulation, drawing particularly on examples in which the biological consequences of the regulation are clear. Specific mRNAs can be controlled via sequences in their 5′ and 3′ untranslated regions (UTRs) and by alterations in the translation machinery. The 5′UTR sequence can determine which initiation pathway is used to bring the ribosome to the initiation codon, how efficiently initiation occurs, and which initiation site is selected. 5′UTR-mediated control can also be accomplished via sequence-specific mRNA-binding proteins. Sequences in the 3′ untranslated region and the poly(A) tail can have dramatic effects on initiation frequency, with particularly profound effects in oogenesis and early development. The mechanism by which 3′UTRs and poly(A) regulate initiation may involve contacts between proteins bound to these regions and the basal translation apparatus. mRNA localization signals in the 3′UTR can also dramatically influence translational activation and repression. Modulations of the initiation machinery, including phosphorylation of initiation factors and their regulated association with other proteins, can regulate both specific mRNAs and overall translation rates and thereby affect cell growth and phenotype.
Viral Entry into the Nucleus
Authors: Whittaker Gary R. , Kann Michael , Helenius Ari
Published: July 2002

▪ Abstract  Because many viruses replicate in the nucleus of their host cells, they must have ways of transporting their genome and other components into and out of this compartment. For the incoming virus particle, nuclear entry is often one of the final steps in a complex transport and uncoating program. Typically, it involves recognition by importins (karyopherins), transport to the nucleus, and binding to nuclear pore complexes. Although all viruses take advantage of cellular signals and factors, viruses and viral capsids vary considerably in size, structure, and in how they interact with the nuclear import machinery. Influenza and adenoviruses undergo extensive disassembly prior to genome import; herpesviruses release their genome into the nucleus without immediate capsid disassembly. Polyoma viruses, parvoviruses, and lentivirus preintegration complexes are thought to enter in intact form, whereas the corresponding complexes of onco-retroviruses have to wait for mitosis because they cannot infect interphase nuclei.
Biological Basket Weaving: Formation and Function of Clathrin-Coated Vesicles
Authors: Brodsky Frances M. , Chen Chih-Ying , Knuehl Christine , Towler Mhairi C. , Wakeham Diane E.
Published: July 2002

▪ Abstract  There has recently been considerable progress in understanding the regulation of clathrin-coated vesicle (CCV) formation and function. These advances are due to the determination of the structure of a number of CCV coat components at molecular resolution and the identification of novel regulatory proteins that control CCV formation in the cell. In addition, pathways of (a) phosphorylation, (b) receptor signaling, and (c) lipid modification that influence CCV formation, as well as the interaction between the cytoskeleton and CCV transport pathways are becoming better defined. It is evident that although clathrin coat assembly drives CCV formation, this fundamental reaction is modified by different regulatory proteins, depending on where CCVs are forming in the cell. This regulatory difference likely reflects the distinct biological roles of CCVs at the plasma membrane and trans-Golgi network, as well as the distinct properties of these membranes themselves. Tissue-specific functions of CCVs require even more-specialized regulation and defects in these pathways can now be correlated with human diseases.
Cellular Function of Phosphoinositide 3-Kinases: Implications for Development, Immunity, Homeostasis, and Cancer
Authors: Katso Roy , Okkenhaug Klaus , Ahmadi Khatereh , White Sarah , Timms John , Waterfield Michael D.
Published: July 2002

▪ Abstract  The phosphoinositide 3-kinase (PI3K) family of enzymes is recruited upon growth factor receptor activation and produces 3′ phosphoinositide lipids. The lipid products of PI3K act as second messengers by binding to and activating diverse cellular target proteins. These events constitute the start of a complex signaling cascade, which ultimately results in the mediation of cellular activities such as proliferation, differentiation, chemotaxis, survival, trafficking, and glucose homeostasis. Therefore, PI3Ks play a central role in many cellular functions. The factors that determine which cellular function is mediated are complex and may be partly attributed to the diversity that exists at each level of the PI3K signaling cascade, such as the type of stimulus, the isoform of PI3K, or the nature of the second messenger lipids. Numerous studies have helped to elucidate some of the key factors that determine cell fate in the context of PI3K signaling. For example, the past two years has seen the publication of many transgenic and knockout mouse studies where either PI3K or its signaling components are deregulated. These models have helped to build a picture of the role of PI3K in physiology and indeed there have been a number of surprises. This review uses such models as a framework to build a profile of PI3K function within both the cell and the organism and focuses, in particular, on the role of PI3K in cell regulation, immunity, and development. The evidence for the role of deregulated PI3K signaling in diseases such as cancer and diabetes is reviewed.
GPS APPLICATIONS FOR GEODYNAMICS AND EARTHQUAKE STUDIES
Authors: Segall Paul , Davis James L.
Published: July 2002

▪ Abstract  Geodetic measurements obtained with the Global Positioning System (GPS) are increasingly more widely applied in geophysical studies. In this paper, we review the changes to the technology of GPS geodesy over the last five years that are responsible for this increased applicability. We survey geophysical investigations employing GPS to measure coseismic, postseismic, and interseismic deformation; plate motion and crustal deformation at plate boundaries; volcano deformation; and the deformation associated with glacial isostatic adjustment and its application to sea-level studies. We emphasize the use of GPS determinations for the modeling of this wide variety of geophysical phenomena. We also discuss the recent advent of permanent GPS networks for regional geophysical studies, as well as the possible future of GPS surveying in light of the recent advances.
Seismic Imaging of Mantle Plumes
Authors: Nataf Henri-Claude
Published: July 2002

The mantle plume hypothesis was proposed thirty years ago by Jason Morgan to explain hotspot volcanoes such as Hawaii. A thermal diapir (or plume) rises from the thermal boundary layer at the base of the mantle and produces a chain of volcanoes as a plate moves on top of it.

The idea is very attractive, but direct evidence for actual plumes is weak, and many questions remain unanswered. With the great improvement of seismic imagery in the past ten years, new prospects have arisen. Mantle plumes are expected to be rather narrow, and their detection by seismic techniques requires specific developments as well as dedicated field experiments. Regional travel-time tomography has provided good evidence for plumes in the upper mantle beneath a few hotspots (Yellowstone, Massif Central, Iceland). Beneath Hawaii and Iceland, the plume can be detected in the transition zone because it deflects the seismic discontinuities at 410 and 660 km depths. In the lower mantle, plumes are very difficult to detect, so specific methods have been worked out for this purpose. There are hints of a plume beneath the weak Bowie hotspot, as well as intriguing observations for Hawaii. Beneath Iceland, high-resolution tomography has just revealed a wide and meandering plume-like structure extending from the core-mantle boundary up to the surface. Among the many phenomena that seem to take place in the lowermost mantle (or D″), there are also signs there of the presence of plumes.

In this article I review the main results obtained so far from these studies and discuss their implications for plume dynamics. Seismic imaging of mantle plumes is still in its infancy but should soon become a turbulent teenager.
Spreading Volcanoes
Authors: Borgia Andrea , Delaney Paul T. , Denlinger Roger P.
Published: July 2002

As volcanoes grow, they become ever heavier. Unlike mountains exhumed by erosion of rocks that generally were lithified at depth, volcanoes typically are built of poorly consolidated rocks that may be further weakened by hydrothermal alteration. The substrates upon which volcanoes rest, moreover, are often sediments lithified by no more than the weight of the volcanic overburden. It is not surprising, therefore, that volcanic deformation includes—and in the long term is often dominated by—spreading motions that translate subsidence near volcanic summits to outward horizontal displacements around the flanks and peripheries. We review examples of volcanic spreading and go on to derive approximate expressions for the time volcanoes require to deform by spreading on weak substrates. We also demonstrate that shear stresses that drive low-angle thrust faulting from beneath volcanic constructs have maxima at volcanic peripheries, just where such faults are seen to emerge. Finally, we establish a theoretical basis for experimentally derived scalings that delineate volcanoes that spread from those that do not.
TROUBLE ON OILED WATERS: Lessons from theExxon ValdezOil Spill
Authors: Paine R. T. , Ruesink Jennifer L. , Sun Adrian , Soulanille Elaine L. , Wonham Marjorie J. , Harley Christopher D. G. , Brumbaugh Daniel R. , Secord David L.
Published: July 2002

▪ Abstract  The Exxon Valdez oil spill was the largest in US maritime history. We review post-spill research and set it in its legal context. The Exxon Corporation, obviously responsible for the spill, focused on restoration, whereas the Trustees, a coalition of state and federal entities, focused on damage and its assessment. Despite billions of dollars expended, little new understanding was gained about the recovery dynamics of a high latitude marine ecosystem subject to an anthropogenic pulse perturbation. We discuss a variety of case studies that highlight the limitations to and shortcomings of the research effort. Given that more spills are inevitable, we recommend that future studies address spatial patterns in the intertidal, and focus on the abundances of long-lived species and on organisms that preserve a chronological record of growth. Oil spills, while tragic, represent opportunities to gain insight into the dynamics of marine ecosystems and should not be wasted.
Evolutionary Genetics of Life Cycles
Authors: Kondrashov Alexey S.
Published: July 2002

The life cycles of cellular species are reviewed from the genetic perspective. Almost all life cycles include stages during which only one genome is transmitted from a parent to its offspring. This, together with interorganismal gene exchange, which occurs regularly in at least some prokaryotes and in the majority of eukaryotes, allows selection to evaluate different alleles more or less independently. Regular genetic changes due to intraorganismal ploidy cycles or recombination may also be important in life cycles of many unicellular forms. Eukaryotic amphimixis is generally similar in all taxa, but the current data on the phylogeny and reproduction of unicellular eukaryotes are insufficient to determine whether it evolved several times or just once. Theoretically, gradual origin of amphimixis from apomixis, with each step favored by natural selection, is feasible. However, we still do not know how this process occurred nor what selection caused it. For reasons not entirely clear, some properties of amphimictic life cycles are much less variable and more conservative than the others. Evolution of many aspects of reproduction requires more theoretical studies, while the existing data are insufficient to choose among the currently competing hypotheses.
Biospheric Trace Gas Fluxes and Their Control Over Tropospheric Chemistry
Authors: Monson Russell K. , Holland Elisabeth A.
Published: July 2002

▪ Abstract  Terrestrial and marine ecosystems function as sources and sinks for reactive trace gases, and in doing so, profoundly influence the oxidative photochemistry in the troposphere. Principal biogenic processes include microbial methane production and oxidation, the emission of volatile organic compounds from forest ecosystems, the emission of nitric oxide from soils, the emission of reactive sulfur compounds and carbon monoxide from marine ecosystems, control over the production of hydroxyl radical concentration by regional hydrologic processes, and deposition of ozone and nitrogen oxides to ecosystems. The combined influence of these processes is to affect the tropospheric concentrations of ozone, hydroxyl radicals, reactive nitrogen oxides, carbon monoxide, and inorganic acids, all of which constitute fundamental components of oxidative photochemistry. In this review we discuss the recent literature related to the primary controls over the biosphere-atmosphere exchange of reactive trace gases, and also to efforts to model the dominant biospheric influences on oxidative dynamics of the troposphere. These studies provide strong support for the paradigm that biospheric processes exert the dominant control over oxidative chemistry in the lower atmosphere. Improvements in our ability to model biospheric influences on tropospheric chemistry, and its susceptibility to global change, will come from inclusion of more explicit information on the processes that control the emission and uptake of reactive trace gases and the impact of changes in ecosystem cover and land-use change.
HOWMUCH ISENERGYRESEARCH& DEVELOPMENTWORTH ASINSURANCE?
Authors: Schock Robert N. , Fulkerson William , Brown Merwin L. , San Martin Robert L. , Greene David L. , Edmonds Jae
Published: July 2002

▪ Abstract  In this paper, we estimate the value of energy technology research and development (R&D) as an insurance investment to reduce four risks to the United States. These four risks are (a) the costs of climate stabilization, (b) oil price shocks and cartel pricing, (c) urban air pollution, and (d) other energy disruptions. The total value is estimated conservatively to be >$12 billion/year. However, only about half of this total may be warranted because some R&D is applicable to more than one risk. Nevertheless, the total Department of Energy investment in energy technology R&D [∼$1.5 billion/year in fiscal year 1999 (FY99)] seems easily justified by its insurance value alone. In fact, a larger investment might be justified, particularly in the areas related to climate change, oil price shock, and urban air pollution. This conclusion appears robust even if the private sector is assumed to be investing a comparable amount relevant to these risks. No additional benefit is credited for the value to the economy and to the competitiveness of the U.S. from better energy technologies that may result from the R&D; only the insurance value for reducing the potential cost of these four risks to society was estimated.
MODELING TECHNOLOGICAL CHANGE: Implications for the Global Environment
Authors: Grübler Arnulf , Nakićenović Nebojša , Victor David G.
Published: July 2002

▪ Abstract  Technology largely determines economic development and its impact on the environment; yet technological change is one of the least developed parts of existing global change models. This paper reviews two approaches developed at the International Institute for Applied Systems Analysis, both of which use the concept of technological learning and aid modeling of technological change. The first approach is a micromodel (“bottom-up”) of three electricity generation technologies that rigorously endogenizes technological change by incorporating both uncertainty (stochasticity) and learning into the model's decision rules. This model, with its endogenous technological change, allows radical innovations to penetrate the energy market and generates S-shaped patterns of technological diffusion that are observed in the real world. The second approach is a macro (“top-down”) model that consists of coupled economic- and technological-system models. Although more stylistic in its representation of endogenous technological change, the macro model can be applied on a worldwide scale and can generate long-term scenarios that are critical for policy analysis. Both the micro- and macro models generate radical departures from currently dominant technological systems (“surprises”), including long-term scenarios with low carbon and sulfur emissions. Our focus is modeling, but for policy, the work underscores the need for huge investments before environmentally superior technologies can compete in the market.
CAPACITYDEVELOPMENT FOR THEENVIRONMENT: A View for the South, A View for the North
Authors: Sagar Ambuj D.
Published: July 2002

▪ Abstract  The notion of capacity development (CD) has been receiving increasing attention as a way to assist the South in its environmental management. Consequently, there has been an exploration of various facets of the capacity issue in the literature and an incorporation of CD in environmental programs of donor agencies. Yet, many of these discussions have remained rather broad, and efforts to develop environmental capacity have shown only limited success. Based on an examination of the capacity needs for environmental management in agriculture and industry, and for dealing with climate change, this review suggests that strengthening domestic capabilities for policy research and innovation as well as for managing technological change may be particularly critical to allow for adaptation of policies and technologies for local conditions and needs. Examination of innovative local experiments on environmental management in developing countries can also provide useful lessons on how to develop and utilize capacity that works under the constrained conditions often found in developing countries. Furthermore, it is important to stress that improving the environment in developing countries also requires capacity in the North to examine and reorient Northern policies that impact the environment, as well as capacity for the environment, in the poorer parts of the world. Ultimately, though, the development of sustainable and appropriate capacity for the environment will require not merely donor-driven programs but a systematic effort driven by Southern governments and organizations.
PHOTOPERIODIC TIME MEASUREMENT AND RELATED PHYSIOLOGICAL MECHANISMS IN INSECTS AND MITES
Authors: Takeda Makio , Skopik Steven D.
Published: July 2002

▪ Abstract  For over 60 years, many species of insects and mites have been known to respond in an adaptive way to seasonal changes in daylength. Responses to photoperiod allow them to survive periods of unfavorable environmental conditions. Since the early 1950s, light-sensitive and temperature-compensated circadian clocks have also been known to regulate the timing of many events (behavioral, physiological, biochemical) in all eukaryotic organisms, including insects and mites. Over the past 30 years, considerable effort has been directed at elucidation of the nature of the clock mechanism that underlies photoperiodism. Mathematical models using a number of insect systems have been developed that attempt to causally relate the circadian clock to photoperiodic time measurement. Although some experimental evidence supports these circadian-based models, some insects and mites appear to utilize a non-periodic hourglass timer as the photoperiodic clock. Future work in this field would benefit by following the approach that has proven to be very successful in identifying genes and gene products that regulate circadian rhythmicity in Drosophila melanogaster.
THE BIOLOGY, ECOLOGY, AND MANAGEMENT OF THE CAT FLEA
Authors: Rust Michael K. , Dryden Michael W.
Published: July 2002

▪ Abstract  The cat flea, Ctenocephalides felis felis, is the most important ectoparasite of domestic cats and dogs worldwide. In addition to its annoyance to pets and humans, C. felis felis is responsible for flea bite allergy dermatitis and the transmission of dog tapeworm. The abiotic and biotic factors that affect the development of immature stages are reviewed with special emphasis given to those aspects directly affecting control. Factors influencing host selection and feeding by adults are summarized. Recent studies concerning mating and oviposition, especially as they impact the likelihood of survival by immatures, are discussed. There has been an increase in the number of reports of insecticide resistance in the past ten years. Greater attention has been placed on disrupting larval development in modern IPM programs. The immature stages of the cat flea are extremely susceptible to environmental factors such as temperature and relative humidity and insect growth regulators (IGRs). In recent years, the control of cat fleas has increasingly relied on the use of IGRs applied to the host or to the indoor environment. Finally, we discuss advances in pesticide chemistry that provide tools for better control of adult fleas on the host.
Life On the Edge: Insect Ecology in Arctic Environments
Authors: Strathdee A. T. , Bale J. S.
Published: July 2002

▪ Abstract  The restricted Arctic insect fauna is usually explained by a lack of recolonization since the last glacial period, inadequate supply of suitable resources, or insufficient adaptation to such a harsh environment. These hypotheses and others that attempt to explain the latitudinal gradient of species distributions and abundance are reviewed. Arctic habitats available to insects are strongly heterogeneous, requiring a similarly diverse array of adaptive responses, characteristic of those species that have colonized and survived in such a stressful climate. Important adaptations in morphology (size, wings), behavior (activity patterns, thermoregulation), life cycles, and ecophysiology (cold hardiness, anaerobiosis, desiccation resistance) are discussed. The current focus of global climate change research on polar regions is identifed, particularly the opportunity to study fundamental ecological processes and spatial dynamics in the relatively simple Arctic ecosystems.
CONGRUENCE AND CONTROVERSY: Toward a Higher-Level Phylogeny of Diptera
Authors: Yeates D. K. , Wiegmann B. M.
Published: July 2002

▪ Abstract  The order Diptera (true flies) is one of the most species-rich and ecologically diverse clades of insects. The order probably arose in the Permian, and the main lineages of flies were present in the Triassic. A novel recent proposal suggests that Strepsiptera are the sister-order to Diptera. Within Diptera, evidence is convincing for the monophyly of Culicomorpha, Blephariceromorpha, and Tipulomorpha but weak for the monophyly of the other basal infraorders and for the relationships among them. The lower Diptera (Nematocera) is paraphyletic with respect to Brachycera, and morphological evidence suggests the sister-group of Brachycera lies in the Psychodomorpha. Recent analyses suggest Tipulomorpha are closer to the base of Brachycera than to the base of Diptera. Brachycera are undoubtedly monophyletic, but relationships between the basal lineages of this group are poorly understood. The monophyly of Stratiomyomorpha, Xylophagomorpha, Tabanomorpha, and Muscomorpha is well supported. Eremoneura, and its constituent clades Empidoidea and Cyclorrhapha, are monophyletic. The sister-group of Eremoneura is likely to be part or all of Asiloidea. Several viewpoints on the homology of the male genitalia of eremoneuran flies are discussed. Phylogenetic analyses suggest that lower Cyclorrhapha (Aschiza) are paraphyletic; however, schizophoran monophyly is well supported. The monophyly of Acalyptratae is not well-founded and the relationships between acalyptrate superfamilies remain obscure. Recent advances document the monophyly of the families of Calyptratae and the relationships among them. Areas critical to future advances in understanding dipteran phylogeny include the relationships among the basal infraorders of Diptera and Brachycera and the relationships between the superfamilies of acalyptrates. Progress in dipteran phylogenetics will accelerate with the exploration of novel data sources and the formulation of hypotheses in an explicitly quantitative framework.
GERMLINE CYST FORMATION IN DROSOPHILA
Authors: de Cuevas M , Lilly MA , Spradling AC
Published: July 2002

▪ Abstract  In a wide variety of organisms, gametes develop within clusters of interconnected germline cells called cysts. Four major principles guide the construction of most cysts: synchronous division, a maximally branched pattern of interconnection between cells, specific changes in cyst geometry, and cyst polarization. The fusome is a germline-specific organelle that is associated with cyst formation in many insects and is likely to play an essential role in these processes. This review examines the cellular and molecular processes that underlie fusome formation and cyst initiation, construction, and polarization in Drosophila melanogaster. The studies described here highlight the importance of cyst formation to the subsequent development of functional gametes.
Methods to Detect Selection in Populations with Applications to the Human
Authors: Kreitman Martin
Published: July 2002

The development of statistical tests of natural selection at the DNA level in population samples has been ongoing for the past 13 years. The current state of the field is reviewed, and the available tests of selection are described. All tests use predictions from the theory of neutrally evolving sites as a null hypothesis. Departures from equilibrium-neutral expectations can indicate the presence of natural selection acting either at one or more of the sites under investigation or at a sufficiently tightly linked site. Complications can arise in the interpretation of departures from neutrality if populations are not at equilibrium for mutation and genetic drift or if populations are subdivided, both of which are likely scenarios for humans. Attempts to understand the nonequilibrium configuration of silent polymorphism in human mitochondrial DNA illustrate the difficulty of distinguishing between selection and alternative demographic hypotheses. The range of plausible alternatives to selection will become better defined, however, as additional population genetic data sets become available, allowing better null models to be constructed.
THE MALE-SPECIFIC HISTOCOMPATIBILITY ANTIGEN, H-Y:A History of Transplantation, Immune Response Genes, Sex Determination and Expression Cloning
Authors: Simpson Elizabeth , Scott Diane , Chandler Phillip
Published: July 2002

▪ Abstract  H-Y was originally discovered as a transplantation antigen. In vivo primary skin graft responses to H-Y are controlled by immune response (Ir) genes mapping to the MHC. In vitro T cell responses to H-Y are controlled by MHC class I and II Ir genes, which-respectively, restrict CD8 and CD4 T cells: These can be isolated as T cell clones in vitro. T cell receptor (TCR) transgenic mice have been made from the rearranged TCR genes of several of these, of which that specific for H-Y/Dbis the best studied. Non-MHC Ir genes also contribute to the control of in vitro CTL responses to H-Y. The Hya/HYA gene(s) encoding H-Y antigen have been mapped using translocations, mutations, and deletions to Yq in humans and to the short arm of the Y chromosome in mice, where they lie in the deletion defined by the Sxrbmutation between Zfy-1 and Zfy-2. Hya/HYA has been separated from the testis-determining gene, Sry/SRY, in both humans and mice and in humans the azoospermia factor AZF has been separated from HYA. In mice transfection of cosmids and cDNAs mapping to the Sxrbdeletion has identified two genes encoding H-Y peptide epitopes. Two such epitopes, H-Y/Kkand H-Y/Dk, are encoded within different exons of Smcy and a third, H-Y/Db, by a novel gene, Uty. Peptide elution approaches have isolated a human H-Y epitope, H-Y/HLA-B7, and identified it as a product of SMCY. Each of the Hya genes in mice is ubiquitously expressed but of unknown function. Their X chromosome homologues do not undergo X inactivation.
Human Chemokines: An Update
Authors: Baggiolini Marco , Dewald Beatrice , Moser Bernhard
Published: July 2002

Interleukin 8, the first chemokine to be characterized, was discovered nearly ten years ago. Today, more than 30 human chemokines are known. They are often upregulated in inflammation and act mainly on leukocytes inducing migration and release responses. The present review deals largely with the new developments of the last three years. Several structural studies have shown that most chemokines form dimers. The dimers, however, dissociate upon dilution, and the monomers constitute the biologically active form. Chemokine activities are mediated by seven-transmembrane-domain, G protein coupled receptors, five of which were discovered in the past three years. The primary receptor-binding domain of all chemokines is near the NH2terminus, and antagonists can be obtained by truncation or substitutions in this region. Major progress has been made in the understanding of chemokine actions on T lymphocytes that respond to several CC chemokines but also to IP10 and Mig, two CXC chemokines that selectively attract Tcells via a novel receptor. Effects of chemokines on angiogenesis and tumor growth have been reported, but the data are still contradictory and the mechanisms unknown. Of considerable interest is the recent discovery that some chemokines function as HIV-suppressive factors by interacting with chemokine receptors which, together with CD4, were recognized as the binding sites for HIV-1.
SCANNING THERMAL MICROSCOPY
Authors: Majumdar A.
Published: July 2002

▪ Abstract  This chapter presents a review of the technology of scanning thermal microscopy (SThM) and its applications in thermally probing micro- and nanostructured materials and devices. We begin by identifying the parameters that control the temporal and temperature resolution in thermometry. The discussion of SThM research is divided into three main categories: those that use (a) thermovoltage-based measurements, (b) electrical resistance techniques, and (c) thermal expansion measurements. Within each category we describe numerous techniques developed for (a) the method of probe fabrication, (b) the experimental setup used for SThM, (c) the applications of that technique, and (d) the measurement characteristics such as tip-sample heat transfer mechanism, spatiotemporal resolution, and interpretation of data for property measurements. Because most of the SThM techniques require fundamental knowledge of tip-sample heat transfer, all possible heat transfer mechanisms are discussed in depth, and relations for estimating the tip-sample conductance for each mechanism are provided. This is critical because tip-sample heat transfer controls spatial resolution, temperature accuracy and resolution, and imaging artifacts. Based on this discussion, a simple model is given for future design of SThM probes. The review concludes by describing some new developments on the applications of near-field optical microscopy for temperature measurements.
Extremely High-Density Longitudinal Magnetic Recording Media
Authors: Weller Dieter , Doerner Mary F.
Published: July 2002

▪ Abstract  Areal density progress in magnetic recording is largely determined by the ability to fabricate low-noise, granular thin lm media with sufficient stability against thermal agitation to warrant long-term data storage. A key requirement is a medium microstructure with small, magnetically isolated grains to establish optimal macro- and micro-magnetic properties. A lower bound for the minimal average grain diameter, compatible with thermal stability, is imposed by the write field capability of the recording head. It is 10–12 nm assuming maximal writeable coercivities of 400 kA/m (5000 Oe). These are already achieved in today's state-of-the-art CoCr-based thin lm alloy media, leaving little room for further improvements and density gains based on continued grain size reduction. A threefold reduction in grain diameter, however, translating into a tenfold increase in areal density is theoretically possible if write field constraints can be overcome, allowing utilization of magnetically harder alloys. This review emphasizes materials and fabrication aspects behind media for extremely high-density longitudinal magnetic recording. Special attention is paid to thermal stability and write coercivity constraints. Various alternative media designs for extremely high-density recording beyond 40–100 Gbits/inch2 are reviewed.
VIRULENCE GENES OFCLOSTRIDIUM PERFRINGENS
Authors: Rood Julian I.
Published: July 2002

▪ Abstract  Clostridium perfringens causes human gas gangrene and food poisoning as well as several enterotoxemic diseases of animals. The organism is characterized by its ability to produce numerous extracellular toxins including α-toxin or phospholipase C, θ-toxin or perfringolysin O, κ-toxin or collagenase, as well as a sporulation-associated enterotoxin. Although the genes encoding the α-toxin and θ-toxin are located on the chromosome, the genes encoding many of the other extracellular toxins are located on large plasmids. The enterotoxin gene can be either chromosomal or plasmid determined. Several of these toxin genes are associated with insertion sequences. The production of many of the extracellular toxins is regulated at the transcriptional level by the products of the virR and virS genes, which together comprise a two-component signal transduction system.
THE COMPARTMENTALIZATION OF THE CEREBELLUM
Authors: Herrup Karl , Kuemerle Barbara
Published: July 2002

▪ Abstract  The concept of developmental compartments originated in studies of Drosophila embryogenesis. This review examines the hypothesis that the modular structure of the vertebrate cerebellum is strongly analogous to this earlier scheme. The pattern of cerebellar development, the adult circuitry, a variety of molecular markers expressed in specific subdivisions, and the phenotypes of several neurological mutations all provide abundant evidence that the vertebrate cerebellum is organized into modules. We present the case that, as a group, these markers reveal distinct boundaries that partition the cerebellum into true developmental compartments. Although this reductionist viewpoint advances our understanding of cerebellar organization, the relationship between these compartments and the functional behavior of the cerebellum remains a mystery.
HIGH-INTENSITY ELECTRON STORAGE RINGS
Authors: S. Zisman Michael
Published: July 2002

▪ Abstract  In recent years a new generation of electron-positron colliders that will have 10–100 times the luminosity of today's machines has started construction. In a similar time frame, a new generation of high-brightness synchrotron light sources has become operational. The scientific goals for these “particle factories” and light sources are explained briefly, and the machine parameters required to achieve them are indicated. Both the accelerator physics and technology issues that result from the required parameters are discussed to show the challenges involved in such significant extensions of accelerator performance. Examples taken from representative projects are used to illustrate the types of solutions adopted to meet these challenges.
On the Production of Superheavy Elements
Authors: Armbruster P.
Published: July 2002

▪ Abstract  In the first century of nuclear physics, 31 radioactive elements were added to the periodic system of elements. In 1996, at GSI, element 112 was synthesized by fusion of70Zn with208Pb, and its atomic number was established by a decay chain linked to known isotopes. Relativistic mean field calculations of the ground-state stability of nuclei predict the next spherical proton shell not as previously assumed at Z = 114 but at Z = 120 for304184120. Moreover, a region of spherical nuclei with depleted central density is predicted at N = 172 for292172120 by mean field calculations. New elements are established today using recoil separators combined with decay-chain analysis. Three new elements, Z = 110–112, and 18 transactinide isotopes have been discovered since 1985, all assigned by genetical linkage to known isotopes. The production cross sections decrease exponentially going to higher elements and now have reached the 1-pb limit. Fusion aiming at higher and higher atomic numbers is a self-terminated process because of constantly increasing disruptive Coulomb forces. The limitations in the formation and deexcitation stages are presented. The rapid drop to smaller cross sections (“Coulomb falls”) is modified by nuclear structure not only in the ground state of the final product (superheavy element) but also in the collision partners and during the amalgamation process (closed shells and clusters). The prospects to produce higher elements and new isotopes by extrapolating the physics learned from reaching Z = 112 are283114, which might be found in76Ge/208Pb at a level of 0.1 pb and linked to259No. At this level, about 30 transactinide isotopes are still in reach. To explain the stabilization of production cross sections in the pb range claimed in 1999 experiments, new physics delaying the descent in the “Coulomb falls” is to appear. For the FLNR experiments claiming Z = 114, no explanation is offered. For the LBL experiment claiming Z = 118, an explanation from new physics is presented. All experiments need confirmation. Verifying the centrally depleted, spherical nuclei around292172120 would be a victory for nuclear structure physics, much more interesting than the trivial case of another doubly closed shell nucleus.