bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of a restricted natural language interface on ease of learning and productivity
Authors: Napier H. Albert , Batsell Richard R. , Guadango Norman S. , Lane David M.
Published: July 2002

People process natural language in real time and with very limited short-term memories. This article describes a computational architecture for syntactic performance that also requires fixed finite resources.
Memory coherence in shared virtual memory systems
Authors: Li Kai , Hudak Paul
Published: July 2002

The memory coherence problem in designing and implementing a shared virtual memory on loosely coupled multiprocessors is studied in depth. Two classes of algorithms, centralized and distributed, for solving the problem are presented. A prototype shared virtual memory on an Apollo ring based on these algorithms has been implemented. Both theoretical and practical results show that the memory coherence problem can indeed be solved efficiently on a loosely coupled multiprocessor.
On the construction of surfaces interpolating curves. I. A method for handling nonconstant parameter curves
Authors: Ferguson David R. , Grandine Thomas A.
Published: July 2002

In industrial design, the tool of choice for constructing surfaces that interpolate curves is the Boolean sum surface technique. However, if curves do not lie on constant parameter lines, reparametrizations will be needed, and this may introduce derivative discontinuities. A new technique which shows promise in overcoming this problem is described here. The method is based on describing the interpolation problem directly as a system of linear equations rather than as a curve-blending problem. The resulting system of equations is usually underdetermined and can be solved using numerical linear algebra methods without the a priori determination of certain parameters. The “free” parameters can be used to control the shape of the resulting surface. Two examples of the procedure are given.
Approximate mean value analysis algorithms for queuing networks
Authors: Pattipati K. R. , Kostreva M. M. , Teele J. L.
Published: July 2002

This paper is concerned with the properties of nonlinear equations associated with the Scheweitzer-Bard (S-B) approximate mean value analysis (MVA) heuristic for closed product-form queuing networks. Three forms of nonlinear S-B approximate MVA equations in multiclass networks are distinguished: Schweitzer, minimal, and the nearly decoupled forms. The approximate MVA equations have enabled us to: (a) derive bounds on the approximate throughput; (b) prove the existence and uniqueness of the S-B throughput solution, and the convergence of the S-B approximation algorithm for a wide class of monotonic, single-class networks; (c) establish the existence of the S-B solution for multiclass, monotonic networks; and (d) prove the asymptotic (i.e., as the number of customers of each class tends to ∞) uniqueness of the S-B throughput solution, and (e) the convergence of the gradient projection and the primal-dual algorithms to solve the asymptotic versions of the minimal, the Schweitzer, and the nearly decoupled forms of MVA equations for multiclass networks with single server and infinite server nodes. The convergence is established by showing that the approximate MVA equations are the gradient vector of a convex function, and by using results from convex programming and the convex duality theory.
Likelihood ratio gradient estimation for stochastic systems
Authors: Glynn Peter W.
Published: July 2002

Consider a computer system having a CPU that feeds jobs to two input/output (I/O) devices having different speeds. Let θ be the fraction of jobs routed to the first I/O device, so that 1 - θ is the fraction routed to the second. Suppose that α = α(θ) is the steady-sate amount of time that a job spends in the system. Given that θ is a decision variable, a designer might wish to minimize α(θ) over θ. Since α(·) is typically difficult to evaluate analytically, Monte Carlo optimization is an attractive methodology. By analogy with deterministic mathematical programming, efficient Monte Carlo gradient estimation is an important ingredient of simulation-based optimization algorithms. As a consequence, gradient estimation has recently attracted considerable attention in the simulation community. It is our goal, in this article, to describe one efficient method for estimating gradients in the Monte Carlo setting, namely the likelihood ratio method (also known as the efficient score method). This technique has been previously described (in less general settings than those developed in this article) in [6, 16, 18, 21]. An alternative gradient estimation procedure is infinitesimal perturbation analysis; see [11, 12] for an introduction. While it is typically more difficult to apply to a given application than the likelihood ratio technique of interest here, it often turns out to be statistically more accurate.

In this article, we first describe two important problems which motivate our study of efficient gradient estimation algorithms. Next, we will present the likelihood ratio gradient estimator in a general setting in which the essential idea is most transparent. The section that follows then specializes the estimator to discrete-time stochastic processes. We derive likelihood-ratio-gradient estimators for both time-homogeneous and non-time homogeneous discrete-time Markov chains. Later, we discuss likelihood ratio gradient estimation in continuous time. As examples of our analysis, we present the gradient estimators for time-homogeneous continuous-time Markov chains; non-time homogeneous continuous-time Markov chains; semi-Markov processes; and generalized semi-Markov processes. (The analysis throughout these sections assumes the performance measure that defines α(θ) corresponds to a terminating simulation.) Finally, we conclude the article with a brief discussion of the basic issues that arise in extending the likelihood ratio gradient estimator to steady-state performance measures.
NATIVE AMERICANS AND THE PRACTICE OF ARCHAEOLOGY
Authors: Ferguson T. J.
Published: July 2002

▪ Abstract  Archaeologists are in the midst of restructuring their relationship with Native Americans. The legal, political, social, and intellectual ramifications of this process are reviewed to examine the fundamental changes occurring in the way archaeology is conducted in the Americas. Much of the impetus for this change resulted from the criticism of archaeology by Native Americans, which led to passage of the Native American Graves Protection and Repatriation Act of 1990 (NAGPRA). NAGPRA has indelibly changed how archaeologists will work in the United States. The issues raised by Native Americans about why and how archaeological research is conducted, however, go beyond NAGPRA to the paradigmatic basis of archaeology. Archaeologists will have new opportunities available to them if they work in partnership with Native Americans in studying the rich archaeological record in the Americas.
Capitalisms in Late Modernity
Authors: Blim Michael
Published: July 2002

▪ Abstract  This article reviews neo-Weberian, neo-institutionalist economic, and neo-Marxian approaches to the analysis of capitalism in late modern societies. It argues that all make important contributions to the understanding of the increasing economic variability reported in capitalist societies. The approaches also may be profitably combined to assess the degree to which specific cases identified deviate in significant ways from current hegemonic patterns of capitalist development. Finally, consumption theory is assessed for its value in revising standard capitalist development theory.
Locations for South Asian Diasporas
Authors: Shukla Sandhya
Published: July 2002

▪ Abstract  This review explores the cultural consequences of migrations from the Indian subcontinent for interdisciplinary inquiries into difference and belonging. It poses the question of whether the constructed term South Asian can adequately bridge the divide between more internationalist conceptions of diaspora and nationalist accounts of racial and ethnic formation, and if so, whether it creates new epistemologies for the consideration of migration in highly globalized political and economic arrangements. In arguing that multiple formations of nationality take place in diasporic culture, this review also intervenes in debates in anthropology about the geographical and conceptual boundaries of community. Finally, in suggesting that gender, sexuality, and generation might profoundly fissure South Asian and other diasporas, the article raises the question of the implicit limits of any category of location or identity.
A Bioarchaeological Perspective on the History of Violence
Authors: Walker Phillip L.
Published: July 2002

▪ Abstract  Traumatic injuries in ancient human skeletal remains are a direct source of evidence for testing theories of warfare and violence that are not subject to the interpretative difficulties posed by literary creations such as historical records and ethnographic reports. Bioarchaeological research shows that throughout the history of our species, interpersonal violence, especially among men, has been prevalent. Cannibalism seems to have been widespread, and mass killings, homicides, and assault injuries are also well documented in both the Old and New Worlds. No form of social organization, mode of production, or environmental setting appears to have remained free from interpersonal violence for long.
XYLOGENESIS: INITIATION, PROGRESSION, AND CELL DEATH
Authors: Fukuda Hiroo
Published: July 2002

▪ Abstract  Xylem cells develop from procambial or cambial initials in situ, and they can also be induced from parenchyma cells by wound stress and/or a combination of phytohormones in vitro. Recent molecular and biochemical studies have identified some of the genes and proteins involved in xylem differentiation, which have led to an understanding of xylem differentiation based on comparisons of events in situ and in vitro. As a result, differentiation into tracheary elements (TEs) has been divided into two processes. The “early” process involves the origination and development of procambial initials in situ. In vitro, the early process of transdifferentiation involves the dedifferentiation of cells and subsequent differentiation of dedifferentiated cells into TE precursor cells. The “late” process, observed both in situ and in vitro, involves a variety of events specific to TE formation, most of which have been observed in association with secondary wall thickenings and programmed cell death. In this review, I summarize these events, including coordinated expression of genes that are involved in secondary wall formation.
GENES AND ENZYMES OF CAROTENOID BIOSYNTHESIS IN PLANTS
Authors: Cunningham F. X. , Gantt E.
Published: July 2002

▪ Abstract  Carotenoids are integral and essential components of the photosynthetic membranes in all plants. Within the past few years, genes encoding nearly all of the enzymes required for the biosynthesis of these indispensable pigments have been identified. This review focuses on recent findings as to the structure and function of these genes and the enzymes they encode. Three topics of current interest are also discussed: the source of isopentenyl pyrophosphate for carotenoid biosynthesis, the progress and possibilities of metabolic engineering of plants to alter carotenoid content and composition, and the compartmentation and association of the carotenogenic enzymes. A speculative schematic model of carotenogenic enzyme complexes is presented to help frame and provoke insightful questions leading to future experimentation.
SPLICE SITE SELECTION IN PLANT PRE-mRNA SPLICING
Authors: Brown J. W. S. , Simpson C. G.
Published: July 2002

▪ Abstract  The purpose of this review is to highlight the unique and common features of splice site selection in plants compared with the better understood yeast and vertebrate systems. A key question in plant splicing is the role of AU sequences and how and at what stage they are involved in spliceosome assembly. Clearly, intronic U- or AU-rich and exonic GC- and AG-rich elements can influence splice site selection and splicing efficiency and are likely to bind proteins. It is becoming clear that splicing of a particular intron depends on a fine balance in the “strength” of the multiple intron signals involved in splice site selection. Individual introns contain varying strengths of signals and what is critical to splicing of one intron may be of less importance to the splicing of another. Thus, small changes to signals may severely disrupt splicing or have little or no effect depending on the overall sequence context of a specific intron/exon organization.
Common Envelope Evolution of Massive Binary Stars
Authors: Taam Ronald E. , Sandquist Eric L.
Published: July 2002

▪ Abstract  The common envelope phase of binary star evolution plays an essential role in the formation of short period systems containing a compact object. In this process, significant mass and angular momentum are lost, transforming a wide progenitor system into a close remnant binary. The pathways leading to this phase and the outcomes are described. Emphasis is placed on the conditions that are required for survival of the binary according to the results of three-dimensional hydrodynamics calculations. The evolution of high-mass systems containing neutron stars is discussed, including double neutron stars, binary pulsars, Thorne-Zytkow objects, and high- and low-mass X-ray binaries.
TRANSPORTERS OF NUCLEOTIDE SUGARS, ATP, AND NUCLEOTIDE SULFATE IN THE ENDOPLASMIC RETICULUM AND GOLGI APPARATUS
Authors: Hirschberg Carlos B. , Robbins Phillips W. , Abeijon Claudia
Published: July 2002

The lumens of the endoplasmic reticulum and Golgi apparatus are the subcellular sites where glycosylation, sulfation, and phosphorylation of secretory and membrane-bound proteins, proteoglycans, and lipids occur. Nucleotide sugars, nucleotide sulfate, and ATP are substrates for these reactions. ATP is also used as an energy source in the lumen of the endoplasmic reticulum during protein folding and degradation. The above nucleotide derivatives and ATP must first be translocated across the membrane of the endoplasmic reticulum and/or Golgi apparatus before they can serve as substrates in the above lumenal reactions. Translocation of the above solutes is mediated for highly specific transporters, which are antiporters with the corresponding nucleoside monophosphates as shown by biochemical and genetic approaches. Mutants in mammals, yeast, and protozoa showed that a defect in a specific translocator activity results in selective impairments of the above posttranslational modifications, including loss of virulence of pathogenic protozoa. Several of these transporters have been purified and cloned. Experiments with yeast and mammalian cells demonstrate that these transporters play a regulatory role in the above reactions. Future studies will address the structure of the above proteins, how they are targeted to different organelles, their potential as drug targets, their role during development, and the possible occurrence of specific diseases.
Regulation of the Cytoskeleton and Cell Adhesion by the Rho Family GTPases in Mammalian Cells
Authors: Kaibuchi K. , Kuroda S. , Amano M.
Published: July 2002

▪ Abstract  Members of the Rho family of small Ras-like GTPases—including RhoA, -B, and -C, Rac1 and -2, and Cdc42—exhibit guanine nucleotide-binding activity and function as molecular switches, cycling between an inactive GDP-bound state and an active GTP-bound state. The Rho family GTPases participate in regulation of the actin cytoskeleton and cell adhesion through specific targets. Identification and characterization of these targets have begun to clarify how the Rho family GTPases act to regulate cytoskeletal structure and cell-cell and cell-substratum contacts in mammalian cells. The Rho family GTPases are also involved in regulation of smooth muscle contraction, cell morphology, cell motility, neurite retraction, and cytokinesis. However, the molecular mechanisms by which the Rho family GTPases participate in the regulation of such processes are not well established.
De Novo Design and Structural Characterization of Proteins and Metalloproteins
Authors: DeGrado William F. , Summa Christopher M. , Pavone Vincenzo , Nastri Flavia , Lombardi Angela
Published: July 2002

▪ Abstract  De novo protein design has recently emerged as an attractive approach for studying the structure and function of proteins. This approach critically tests our understanding of the principles of protein folding; only in de novo design must one truly confront the issue of how to specify a protein's fold and function. If we truly understand proteins, it should be possible to design receptors, enzymes, and ion channels from scratch. Further, as this understanding evolves and is further refined, it should be possible to design proteins and biomimetic polymers with properties unprecedented in nature.
Structure and Function of Hexameric Helicases
Authors: Patel S. S. , Picha K. M.
Published: July 2002

▪ Abstract  Helicases are motor proteins that couple the hydrolysis of nucleoside triphosphate (NTPase) to nucleic acid unwinding. The hexameric helicases have a characteristic ring-shaped structure, and all, except the eukaryotic minichromosomal maintenance (MCM) helicase, are homohexamers. Most of the 12 known hexameric helicases play a role in DNA replication, recombination, and transcription. A human genetic disorder, Bloom's syndrome, is associated with a defect in one member of the class of hexameric helicases. Significant progress has been made in understanding the biochemical properties, structures, and interactions of these helicases with DNA and nucleotides. Cooperativity in nucleotide binding was observed in many, and sequential NTPase catalysis has been observed in two proteins, gp4 of bacteriophage T7 and rho of Escherichia coli. The crystal structures of the oligomeric T7 gp4 helicase and the hexamer of RepA helicase show structural features that substantiate the observed cooperativity, and both are consistent with nucleotide binding at the subunit interface. Models are presented that show how sequential NTP hydrolysis can lead to unidirectional and processive translocation. Possible unwinding mechanisms based on the DNA exclusion model are proposed here, termed the wedge, torsional, and helix-destabilizing models.
Implanted Electrochemical Glucose Sensors for the Management of Diabetes
Authors: Heller Adam
Published: July 2002

▪ Abstract  By maintaining a near normal (70–120 mg/dL) glucose concentration, diabetic patients can drastically reduce the likelihood of the occurrence of diabetes complications. In the near future, subcutaneously implanted electrochemical glucose sensors will be available to provide frequent or continuous information on which timely treatment decisions, such as insulin injection or glucose source intake, can be based, as well as timely alarm signals. The currently engineered devices are of three types: (a) innocuous microsensors, with actively mass-transporting areas <10−3 cm2, replaced twice a week by the patient; (b) self-contained, surgeon-implanted, transmitter-containing packages of >1 cm2 area, operating for >100 days; and (c) devices transporting subcutaneous fluid to an external sensor, based on implanted microfiltration or microdialysis fibers or on iontophoretic transport of the subcutaneous fluid through the skin.
Engineering Design of Optimal Strategies for Blood Clot Dissolution
Authors: Diamond Scott L.
Published: July 2002

▪ Abstract  Blood clots form under hemodynamic conditions and can obstruct flow during angina, acute myocardial infarction, stroke, deep vein thrombosis, pulmonary embolism, peripheral thrombosis, or dialysis access graft thrombosis. Therapies to remove these clots through enzymatic and/or mechanical approaches require consideration of the biochemistry and structure of blood clots in conjunction with local transport phenomena. Because blood clots are porous objects exposed to local hemodynamic forces, pressure-driven interstitial permeation often controls drug penetration and the overall lysis rate of an occlusive thrombus. Reaction engineering and transport phenomena provide a framework to relate dosage of a given agent to potential outcomes. The design and testing of thrombolytic agents and the design of therapies must account for (a) the binding, catalytic, and systemic clearance properties of the therapeutic enzyme; (b) the dose and delivery regimen; (c) the biochemical and structural aspects of the thrombotic occlusion; (d) the prevailing hemodynamics and anatomical location of the thrombus; and (e) therapeutic constraints and risks of side effects. These principles also impact the design and analysis of local delivery devices.
Current Methods in Medical Image Segmentation
Authors: Pham Dzung L. , Xu Chenyang , Prince Jerry L.
Published: July 2002

▪ Abstract  Image segmentation plays a crucial role in many medical-imaging applications, by automating or facilitating the delineation of anatomical structures and other regions of interest. We present a critical appraisal of the current status of semiautomated and automated methods for the segmentation of anatomical medical images. Terminology and important issues in image segmentation are first presented. Current segmentation approaches are then reviewed with an emphasis on the advantages and disadvantages of these methods for medical imaging applications. We conclude with a discussion on the future of image segmentation methods in biomedical research.
Respiratory Fluid Mechanics and Transport Processes
Authors: Grotberg James B.
Published: July 2002

▪ Abstract  The field of respiratory flow and transport has experienced significant research activity over the past several years. Important contributions to the knowledge base come from pulmonary and critical care medicine, surgery, physiology, environmental health sciences, biophysics, and engineering. Several disciplines within engineering have strong and historical ties to respiration including mechanical, chemical, civil/environmental, aerospace and, of course, biomedical engineering. This review draws from a wide variety of scientific literature that reflects the diverse constituency and audience that respiratory science has developed. The subject areas covered include nasal flow and transport, airway gas flow, alternative modes of ventilation, nonrespiratory gas transport, aerosol transport, airway stability, mucus transport, pulmonary acoustics, surfactant dynamics and delivery, and pleural liquid flow. Within each area are a number of subtopics whose exploration can provide the opportunity of both depth and breadth for the interested reader.
SINGLE-PARTICLE TRACKING:Applications to Membrane Dynamics
Authors: Saxton Michael J. , Jacobson Ken
Published: July 2002

▪ Abstract  Measurements of trajectories of individual proteins or lipids in the plasma membrane of cells show a variety of types of motion. Brownian motion is observed, but many of the particles undergo non-Brownian motion, including directed motion, confined motion, and anomalous diffusion. The variety of motion leads to significant effects on the kinetics of reactions among membrane-bound species and requires a revision of existing views of membrane structure and dynamics.
Comparative Protein Structure Modeling of Genes and Genomes
Authors: Martí-Renom Marc A. , Stuart Ashley C. , Fiser András , Sánchez Roberto , Melo Francisco , Šali Andrej
Published: July 2002

▪ Abstract  Comparative modeling predicts the three-dimensional structure of a given protein sequence (target) based primarily on its alignment to one or more proteins of known structure (templates). The prediction process consists of fold assignment, target–template alignment, model building, and model evaluation. The number of protein sequences that can be modeled and the accuracy of the predictions are increasing steadily because of the growth in the number of known protein structures and because of the improvements in the modeling software. Further advances are necessary in recognizing weak sequence–structure similarities, aligning sequences with structures, modeling of rigid body shifts, distortions, loops and side chains, as well as detecting errors in a model. Despite these problems, it is currently possible to model with useful accuracy significant parts of approximately one third of all known protein sequences. The use of individual comparative models in biology is already rewarding and increasingly widespread. A major new challenge for comparative modeling is the integration of it with the torrents of data from genome sequencing projects as well as from functional and structural genomics. In particular, there is a need to develop an automated, rapid, robust, sensitive, and accurate comparative modeling pipeline applicable to whole genomes. Such large-scale modeling is likely to encourage new kinds of applications for the many resulting models, based on their large number and completeness at the level of the family, organism, or functional network.
MITOCHONDRIAL PREPROTEIN TRANSLOCASE
Authors: Pfanner Nikolaus , Craig Elizabeth A. , Hönlinger Angelika
Published: July 2002

▪ Abstract  Mitochondria import most of their proteins from the cytosol. Dynamic protein complexes in the mitochondrial outer and inner membranes are responsible for the specific recognition and membrane translocation of preproteins. The preprotein translocase of the outer mitochondrial membrane contains several import receptors and a general import pore. The preprotein translocase of the inner membrane consists of a channel interacting with preproteins in transit and an import motor that includes the matrix heat shock protein Hsp70. Acidic patches of import components are thought to guide the import of positively charged signal sequences (acid chain hypothesis). Energy input is derived from the inner membrane potential and ATP. Proteins in the mitochondrial matrix are required for proteolytic processing and folding of imported proteins. The dynamic nature of the membrane translocase permits sorting of preproteins at distinct stages of the import pathway.
STRUCTURE, FUNCTION AND REGULATION OF THE VACUOLAR (H+)-ATPase
Authors: Stevens Tom H. , Forgac Michael
Published: July 2002

▪ Abstract  The vacuolar (H+)-ATPases (or V-ATPases) function in the acidification of intracellular compartments in eukaryotic cells. The V-ATPases are multisubunit complexes composed of two functional domains. The peripheral V1 domain, a 500-kDa complex responsible for ATP hydrolysis, contains at least eight different subunits of molecular weight 70-13 (subunits A-H). The integral V0 domain, a 250-kDa complex, functions in proton translocation and contains at least five different subunits of molecular weight 100-17 (subunits a-d). Biochemical and genetic analysis has been used to identify subunits and residues involved in nucleotide binding and hydrolysis, proton translocation, and coupling of these activities.

Several mechanisms have been implicated in the regulation of vacuolar acidification in vivo, including control of pump density, regulation of assembly of V1 and V0 domains, disulfide bond formation, activator or inhibitor proteins, and regulation of counterion conductance. Recent information concerning targeting and regulation of V-ATPases has also been obtained.
Embryo-Derived Stem Cells: Of Mice and Men
Authors: Smith Austin G.
Published: July 2002

▪ Abstract  Mouse embryonic stem cells are continuous cell lines derived directly from the fetal founder tissue of the preimplantation embryo. They can be expanded in culture while retaining the functional attributes of pluripotent early embryo cells. In particular, they can participate fully in fetal development when reintroduced into the embryo. The capacity for multilineage differentiation is reproduced in culture where embryonic stem cells can produce a wide range of well-defined cell types. This has stimulated interest in the isolation of analogous cells of human origin. Such human pluripotent stem cells could constitute a renewable source of more differentiated cells that could be employed to replace diseased or damaged tissue by cellular transplantation. In this review, the relationships between mouse embryonic stem cells, resident pluripotent cells in the embryo, and human embryo-derived cell lines are evaluated, and the prospects and challenges of embryo stem cell research are considered.

This review is dedicated to Rosa Beddington FRS, a great developmental biologist, a wonderful colleague, and an inspirational advocate of human stem cell research.
The Southern Conifer Family Araucariaceae: History, Status, and Value for Paleoenvironmental Reconstruction
Authors: Kershaw Peter , Wagstaff Barbara
Published: July 2002

▪ Abstract  The Araucariaceae are important to biogeography because they have an ancient origin and are a distinctive and sometimes dominant component of southern hemisphere forest communities. This paper examines recent information on ecology and phylogeny and on pollen and macrofossil assemblages to assess the history and present-day status of the family and its potential for refinement of past environmental, particularly climatic, conditions. From an origin in the Triassic, the family expanded and diversified in both hemispheres in the Jurassic and Early Cretaceous and remained a significant component of Gondwanan vegetation until the latter part of the Cenozoic. The development of angiosperms in the Middle Cretaceous probably assisted in the demise of some araucarian components but there was also evolution of new genera. Recorded diversity in the early Cenozoic of Australia is as high as it was in the Early Cretaceous. Continental separation and associated climatic drying, cooling, and increased variability progressively reduced the ranges of conifers to moist, predominantly mesothermal climates on continents. However, tectonic and volcanic activity, partially associated with Australia's collision with Southeast Asia, provided new opportunities for some araucarian components on Asia-Pacific islands. Araucarians provide information on climatic conditions suitable for rainforest vegetation throughout their recorded period, even prior to the recognition or even existence of these forests in the fossil record. High pollen abundance is also indicative of marginal rainforest environments where these canopy emergents can compete effectively with angiosperm forest taxa. Despite their apparent relictual status in many areas, they provide precise paleoclimatic estimates in late Quaternary pollen records and have particular value in providing evidence of climatic variability that has otherwise been difficult to detect.
ECONOMIC GROWTH, LIBERALIZATION, AND THE ENVIRONMENT: A Review of the Economic Evidence
Authors: Chua Swee
Published: July 2002

▪ Abstract  This paper reviews the empirical evidence for the following five hypotheses from the economic growth-liberalization-pollution debate: (a) economic growth will lead to a worsening pollution problem; (b) tighter environmental regulation will reduce economic growth; (c) trade liberalization will exacerbate environmental degradation, especially in developing countries with weak environmental protection; (d) tighter environmental protection in the developed countries will lead to a loss of competitiveness compared with that of countries with lower standards, especially in polluting industries; and (e) tighter environmental protection in the developed countries will lead to relocation of investment to developing countries with lax regulation, especially in polluting industries (the pollution haven hypothesis). Overall, the evidence for these hypotheses is found to be ambiguous and weak. It is further suggested that the growth-liberalization-environment empirical literature has neglected three important elements: (a) environmental innovation, (b) the international diffusion of environmental technologies, and (c) the economic benefits of a cleaner environment. Future research should integrate these elements into the debate. Analyses of endogenous environmental innovation in response to environmental policy, the tradable nature of environmental technologies, the role of trade and foreign direct investment as channels of environmental-technology transfer to developing countries, the effects of local environmental policies in encouraging the adoption of such technologies in developing countries, and the economic benefits of a cleaner environment would contribute to the development of sound, well-coordinated economic and environmental policies.
Nutritional Interactions in Insect-Microbial Symbioses: Aphids and Their Symbiotic BacteriaBuchnera
Authors: Douglas A. E.
Published: July 2002

▪ Abstract  Most aphids possess intracellular bacteria of the genus Buchnera. The bacteria are transmitted vertically via the aphid ovary, and the association is obligate for both partners: Bacteria-free aphids grow poorly and produce few or no offspring, and Buchnera are both unknown apart from aphids and apparently unculturable. The symbiosis has a nutritional basis. Specifically, bacterial provisioning of essential amino acids has been demonstrated. Nitrogen recycling, however, is not quantitatively important to the nutrition of aphid species studied, and there is strong evidence against bacterial involvement in the lipid and sterol nutrition of aphids. Buchnera have been implicated in various non-nutritional functions. Of these, just one has strong experimental support: promotion of aphid transmission of circulative viruses. It is argued that strong parallels may exist between the nutritional interactions (including the underlying mechanisms) in the aphid-Buchnera association and other insect symbioses with intracellular microorganisms.
Amino Acid Transport in Insects
Authors: Wolfersberger Michael G.
Published: July 2002

▪ Abstract  Most insect cell membranes seem to contain uniporters that facilitate the diffusion of amino acids into and out of the cells. In addition to these passive diffusion systems, all but one of the insect tissues studied to date seem to contain at least one amino acid–cation symport system that allows their cells to accumulate certain amino acids from the extracellular medium. cDNAs encoding three such symporters have very recently been cloned and sequenced. The deduced amino acid sequence of each insect symporter was determined to be homologous to that of symporters mediating the transport of the same or related substrates in mammalian tissues.
Methods for Marking Insects: Current Techniques and Future Prospects
Authors: Hagler James R. , Jackson Charles G.
Published: July 2002

▪ Abstract  Tracking the movement of insects in their natural habitat is essential for understanding their basic biology, demography, and ethology. A wide variety of markers have been used to assess insect population dynamics, dispersal, territoriality, feeding behavior, trophic-level interactions, and other ecological interactions. The ideal marker should persist without inhibiting the insect's “normal” biology. Furthermore, the marker should be environmentally safe, cost–effective, and easy to use. In this article, we review the current state of knowledge regarding insect marking, document the advantages and limitations of each marking technique, and discuss advances made in marking insects over the past decade.
PRECONDITIONING TECHNIQUES IN COMPUTATIONAL FLUID DYNAMICS
Authors: Turkel E.
Published: July 2002

▪ Abstract  An overview of preconditioning for the steady-state compressible inviscid fluid dynamic equations is presented. Extensions to the Navier-Stokes equations are also considered. These preconditioners are necessary for many algorithms in order to have the correct behavior at low speeds and to converge to the solution of the incompressible equations as the Mach number goes to zero. In addition, the preconditioning accelerates the convergence to a steady state for problems in which a significant portion of the flow is low speed. This low speed preconditioner can be combined with Jacobi and line preconditioners to damp high frequencies at all speeds. This is necessary for use with multigrid methods. Such combined methods are also better at accelerating problems with high aspect ratios. Details of the implementation are presented including several different variants for the preconditioning matrix.
THE RICHTMYER-MESHKOV INSTABILITY
Authors: Brouillette Martin
Published: July 2002

▪ Abstract  The Richtmyer-Meshkov instability arises when a shock wave interacts with an interface separating two different fluids. It combines compressible phenomena, such as shock interaction and refraction, with hydrodynamic instability, including nonlinear growth and subsequent transition to turbulence, across a wide range of Mach numbers. This review focuses on the basic physical processes underlying the onset and development of the Richtmyer-Meshkov instability in simple geometries. It examines the principal theoretical results along with their experimental and numerical validation. It also discusses the different experimental approaches and techniques and how they can be used to resolve outstanding issues in this field.
PROCESSING OF RECOMBINATION INTERMEDIATES BY THE RuvABC PROTEINS
Authors: West Stephen C.
Published: July 2002

▪ Abstract  The RuvA, RuvB, and RuvC proteins in Escherichia coli play important roles in the late stages of homologous genetic recombination and the recombinational repair of damaged DNA. Two proteins, RuvA and RuvB, form a complex that promotes ATP-dependent branch migration of Holliday junctions, a process that is important for the formation of heteroduplex DNA. Individual roles for each protein have been defined, with RuvA acting as a specificity factor that targets RuvB, the branch migration motor, to the junction. Structural studies indicate that two RuvA tetramers sandwich the junction and hold it in an unfolded square-planar configuration. Hexameric rings of RuvB face each other across the junction and promote a novel dual helicase action that “pumps” DNA through the RuvAB complex, using the free energy provided by ATP hydrolysis. The third protein, RuvC endonuclease, resolves the Holliday junction by introducing nicks into two DNA strands. Genetic and biochemical studies indicate that branch migration and resolution are coupled by direct interactions between the three proteins, possibly by the formation of a RuvABC complex.
GENOMIC IMPRINTING IN MAMMALS
Authors: Bartolomei Marisa S. , Tilghman Shirley M.
Published: July 2002

▪ Abstract  A handful of autosomal genes in the mammalian genome are inherited in a silent state from one of the two parents, and in a fully active form from the other, thereby rendering the organism functionally hemizygous for imprinted genes. To date 19 imprinted genes have been identified; 5 are expressed from the maternal chromosome while the rest are expressed from the paternal chromosome. Allele-specific methylation of CpG residues, established in one of the germlines and maintained throughout embryogenesis, has been clearly implicated in the maintenance of imprinting in somatic cells. Although the function of imprinting remains a subject of some debate, the process is thought to have an important role in regulating the rate of fetal growth.
X-CHROMOSOME INACTIVATION IN MAMMALS
Authors: Heard Edith , Clerc Philippe , Avner Philip
Published: July 2002

▪ Abstract  The inactive X chromosome differs from the active X in a number of ways; some of these, such as allocyclic replication and altered histone acetylation, are associated with all types of epigenetic silencing, whereas others, such as DNA methylation, are of more restricted use. These features are acquired progressively by the inactive X after onset of initiation. Initiation of X-inactivation is controlled by the X-inactivation center (Xic) and influenced by the X chromosome controlling element (Xce), which causes primary nonrandom X-inactivation. Other examples of nonrandom X-inactivation are also presented in this review. The definition of a major role for Xist, a noncoding RNA, in X-inactivation has enabled investigation of the mechanism leading to establishment of the heterochromatinized X-chromosome and also of the interactions between X-inactivation and imprinting as well as between X-inactivation and developmental processes in the early embryo.
Ribosome Synthesis in Saccharomyces cerevisiae
Authors: Venema Jaap , Tollervey David
Published: July 2002

▪ Abstract  The synthesis of ribosomes is one of the major metabolic pathways in all cells. In addition to around 75 individual ribosomal proteins and 4 ribosomal RNAs, synthesis of a functional eukaryotic ribosome requires a remarkable number of trans-acting factors. Here, we will discuss the recent, and often surprising, advances in our understanding of ribosome synthesis in the yeast Saccharomyces cerevisiae. These will underscore the unexpected complexity of eukaryotic ribosome synthesis.
HUMAN T CELL LEUKEMIA VIRUS TYPE I (HTLV-I) AND HUMAN DISEASES
Authors: Uchiyama Takashi
Published: July 2002

▪ Abstract  HTLV-I infection is causally associated with a variety of human diseases including leukemia/lymphoma, myelopathy, uveitis, and arthropathy. Tax protein of HTLV-I, which is considered oncogenic, binds to transcription factors or other cytoplasmic cellular molecules involved in the fundamental cell function and thereby induces cellular changes. The interaction between HTLV-I–infected cells with dysregulated function and different kinds of cells in the host, such as lymphocytes and vascular endothelial cells through viral peptides, antigen receptors, cell adhesion molecules, and cytokines, appears to be one of the basic mechanisms underlying the development of HTLV-I–associated diseases. This interaction may play a major role in determining tumorigenicity and in forming clinical features of the diseases. The in vivo cell proliferation model of HTLV-I–infected cells using severe combined immunodeficient (SCID) mice can differentiate tumorigenicity from cell immortalization in vitro. The OX40 and its ligand gp34, which are induced by HTLV-I infection and directly mediate the adhesion between HTLV-I–infected T cells and vascular endothelial cells, may be critically involved in the localization and proliferation of HTLV-I–infected cells in vivo.
NF-κB AND REL PROTEINS: Evolutionarily Conserved Mediators of Immune Responses
Authors: Ghosh Sankar , May Michael J. , Kopp Elizabeth B.
Published: July 2002

▪ Abstract  The transcription factor NF-κB, more than a decade after its discovery, remains an exciting and active area of study. The involvement of NF-κB in the expression of numerous cytokines and adhesion molecules has supported its role as an evolutionarily conserved coordinating element in the organism's response to situations of infection, stress, and injury. Recently, significant advances have been made in elucidating the details of the pathways through which signals are transmitted to the NF-κB:IκB complex in the cytosol. The field now awaits the discovery and characterization of the kinase responsible for the inducible phosphorylation of IκB proteins. Another exciting development has been the demonstration that in certain situations NF-κB acts as an anti-apoptotic protein; therefore, elucidation of the mechanism by which NF-κB protects against cell death is an important goal. Finally, the generation of knockouts of members of the NF-κB/IκB family has allowed the study of the roles of these proteins in normal development and physiology. In this review, we discuss some of these recent findings and their implications for the study of NF-κB.
EVOLUTION OF ANTIGEN BINDING RECEPTORS
Authors: Litman Gary W. , Anderson Michele K. , Rast Jonathan P.
Published: July 2002

▪ Abstract  This review addresses issues related to the evolution of the complex multigene families of antigen binding receptors that function in adaptive immunity. Advances in molecular genetic technology now permit the study of immunoglobulin (Ig) and T cell receptor (TCR) genes in many species that are not commonly studied yet represent critical branch points in vertebrate phylogeny. Both Ig and TCR genes have been defined in most of the major lineages of jawed vertebrates, including the cartilaginous fishes, which represent the most phylogenetically divergent jawed vertebrate group relative to the mammals. Ig genes in cartilaginous fish are encoded by multiple individual loci that each contain rearranging segmental elements and constant regions. In some loci, segmental elements are joined in the germline, i.e. they do not undergo genetic rearrangement. Other major differences in Ig gene organization and the mechanisms of somatic diversification have occurred throughout vertebrate evolution. However, relating these changes to adaptive immune function in lower vertebrates is challenging. TCR genes exhibit greater sequence diversity in individual segmental elements than is found in Ig genes but have undergone fewer changes in gene organization, isotype diversity, and mechanisms of diversification. As of yet, homologous forms of antigen binding receptors have not been identified in jawless vertebrates; however, acquisition of large amounts of structural data for the antigen binding receptors that are found in a variety of jawed vertebrates has defined shared characteristics that provide unique insight into the distant origins of the rearranging gene systems and their relationships to both adaptive and innate recognition processes.
TUMOR NECROSIS FACTOR RECEPTOR AND Fas SIGNALING MECHANISMS
Authors: Wallach D. , Varfolomeev E. E. , Malinin N. L. , Goltsev Yuri V. , Kovalenko A. V. , Boldin M. P.
Published: July 2002

▪ Abstract  Four members of the tumor necrosis factor (TNF) ligand family, TNF-α, LT-α, LT-β, and LIGHT, interact with four receptors of the TNF/nerve growth factor family, the p55 TNF receptor (CD120a), the p75 TNF receptor (CD120b), the lymphotoxin beta receptor (LTβR), and herpes virus entry mediator (HVEM) to control a wide range of innate and adaptive immune response functions. Of these, the most thoroughly studied are cell death induction and regulation of the inflammatory process. Fas/Apo1 (CD95), a receptor of the TNF receptor family activated by a distinct ligand, induces death in cells through mechanisms shared with CD120a. The last four years have seen a proliferation in knowledge of the proteins participating in the signaling by the TNF system and CD95. The downstream signaling molecules identified so far—caspases, phospholipases, the three known mitogen activated protein (MAP) kinase pathways, and the NF-κB activation cascade—mediate the effects of other inducers as well. However, the molecules that initiate these signaling events, including the death domain- and TNF receptor associated factor (TRAF) domain-containing adapter proteins and the signaling enzymes associated with them, are largely unique to the TNF/nerve growth factor receptor family.
GENETIC ANALYSIS OF B CELL ANTIGEN RECEPTOR SIGNALING
Authors: Kurosaki Tomohiro
Published: July 2002

▪ Abstract  In B lymphocytes, a signaling complex that contributes to cell fate decisions is the B cell antigen receptor (BCR). Data from knockout experiments in cell lines and mice have revealed distinct functions for the intracellular protein tyrosine kinases (Lyn, Syk, Btk) in BCR signaling and B cell development. Combinations of intracellular signaling pathways downstream of these PTKs determine the quality and quantity of BCR signaling. For example, concerted actions of the PLC-γ2 and PI3-K pathways are required for proper calcium responses. Similarly, the regulation of ERK and JNK responses involves both PLC-γ2 and GTPases pathways. Since the immune response in vivo is regulated by alteration of these signaling outcomes, achieving a precise understanding of intracellular molecular events leading to B lymphocyte proliferation, deletion, anergy, receptor editing, and survival still remains a challenge for the future.