bluuebunny/crossref_metadata_2025 huggingface dataset:
The Indian Monsoon and Its Variability
Authors: Gadgil Sulochana
Published: April 2003

▪ Abstract  For over 300 years, the monsoon has been viewed as a gigantic land-sea breeze. It is shown in this paper that satellite and conventional observations support an alternative hypothesis, which considers the monsoon as a manifestation of seasonal migration of the intertropical convergence zone (ITCZ). With the focus on the Indian monsoon, the mean seasonal pattern is described, and why it is difficult to simulate it is discussed. Some facets of the intraseasonal variation, such as active-weak cycles; break monsoon; and a special feature of intraseasonal variation over the region, namely, poleward propagations of the ITCZ at intervals of 2–6 weeks, are considered. Vertical moist stability is shown to be a key parameter in the variation of monthly convection over ocean and land as well as poleward propagations. Special features of the Bay of Bengal and the monsoon brought out by observations during a national observational experiment in 1999 are briefly described.
Is El Niño Sporadic or Cyclic?
Authors: Philander S. George , Fedorov Alexey
Published: April 2003

▪ Abstract  Is El Niño one phase of a continual, self-sustaining natural mode of the coupled ocean-atmosphere that has La Niña as the complementary phase? Or is El Niño a temporary departure from “normal” conditions “triggered” by a random disturbance such as a burst of westerly winds? A growing body of evidence—stability analyses, studies of the energetics, simulations that reproduce the statistics of sea surface temperature variations in the eastern equatorial Pacific—indicates that reality corresponds to a compromise between these two possibilities: The observed Southern Oscillation between El Niño and La Niña corresponds to a weakly damped mode that is sustained by random disturbances. This means that the predictability of El Niño is limited by the continual presence of “noise” so that forecasts should be probabilistic. The Southern Oscillation is also subject to decadal modulations. How it will be influenced by global warming is a matter of considerable uncertainty.
Tropical Cyclones
Authors: Emanuel Kerry
Published: April 2003

Tropical cyclones encompass virtually every subdiscipline of geophysical fluid dynamics, including cumulus convection, boundary layers, thermodynamic cycles, surface wave dynamics, upper ocean wind-driven circulations, barotropic instability, Rossby waves, and air-sea interaction. After briefly reviewing what is known about the structure, behavior, and climatology of these fascinating storms, the author provides an overview of their physics, focusing on the unique and poorly understood nature of the air-sea interface, and discusses several of the most interesting avenues of ongoing research.
Phylogenetic Approaches Toward Crocodylian History
Authors: Brochu Christopher A.
Published: April 2003

▪ Abstract  A review of crocodylian phylogeny reveals a more complex history than might have been anticipated from a direct reading of the fossil record without consideration of phylogenetic relationships. The three main extant crocodylian lineages—Gavialoidea, Alligatoroidea, Crocodyloidea—are known from fossils in the Late Cretaceous, and the group is found nearly worldwide during the Cenozoic. Some groups have distributions that are best explained by the crossing of marine barriers during the Tertiary. Early Tertiary crocodylian faunas are phylogenetically composite, and clades tend to be morphologically uniform and geographically widespread. Later in the Tertiary, Old World crocodylian faunas are more endemic. Crocodylian phylogeneticists face numerous challenges, the most important being the phylogenetic relationships and time of divergence of the two living gharials (Gavialis gangeticus and Tomistoma schlegelii), the relationships among living true crocodiles (Crocodylus), and the relationships among caimans.
The Effects of Bioturbation on Soil Processes and Sediment Transport
Authors: Gabet Emmanuel J. , Reichman O.J. , Seabloom Eric W.
Published: April 2003

▪ Abstract  Plants and animals exploit the soil for food and shelter and, in the process, affect it in many different ways. For example, uprooted trees may break up bedrock, transport soil downslope, increase the heterogeneity of soil respiration rates, and inhibit soil horizonation. In this contribution, we review previously published papers that provide insights into the process of bioturbation. We focus particularly on studies that allow us to place bioturbation within a quantitative framework that links the form of hillslopes with the processes of sediment transport and soil production. Using geometrical relationships and data from others' work, we derive simple sediment flux equations for tree throw and root growth and decay.
Phanerozoic Atmospheric Oxygen
Authors: Berner Robert A. , Beerling David J. , Dudley Robert , Robinson Jennifer M. , Wildman Richard A.
Published: April 2003

▪ Abstract  Theoretical calculations, based on both the chemical and isotopic composition of sedimentary rocks, indicate that atmospheric O2has varied appreciably over Phanerozoic time, with a notable excursion during the Permo-Carboniferous reaching levels as high as 35% O2. This agrees with measurements of the carbon isotopic composition of fossil plants together with experiments and calculations on the effect of O2on photosynthetic carbon isotope fractionation. The principal cause of the excursion was the rise of large vascular land plants and the consequent increased global burial of organic matter. Higher levels of O2are consistent with the presence of Permo-Carboniferous giant insects, and preliminary experiments indicate that insect body size can increase with elevated O2. Higher O2also may have caused more extensive, possibly catastrophic, wildfires. To check this, realistic burning experiments are needed to examine the effects of elevated O2on fire behavior.
Madagascar: Heads It’s a Continent, Tails It’s an Island
Authors: Wit Maarten J. de
Published: April 2003

▪ Abstract  Neither geologists nor biologists have a definition that is capable of classifying Madagascar unambiguously as an island or a continent; nor can they incorporate Malagasy natural history into a single model rooted in Africa or Asia. Madagascar is a microcosm of the larger continents, with a rock record that spans more than 3000 million years (Ma), during which it has been united episodically with, and divorced from, Asian and African connections. This is reflected in its Precambrian history of deep crustal tectonics and a Phanerozoic history of biodiversity that fluctuated between cosmopolitanism and parochialism. Both vicariance and dispersal events over the past 90 Ma have blended a unique endemism on Madagascar, now in decline following rapid extinctions that started about 2000 years ago.
Rheology of Granitic Magmas During Ascent and Emplacement
Authors: Petford Nick
Published: April 2003

▪ Abstract  Considerable progress has been made over the past decade in understanding the static rheological properties of granitic magmas in the continental crust. Changes in H2O content, CO2 content, and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid/fluid mixture. Although the strengths of granitic magmas over the crystallization interval are still poorly constrained, theoretical investigations suggest that during magma ascent, yield strengths of the order of 9 kPa are required to completely retard the upward flow in meter-wide conduits. In low Bagnold number magma suspensions with moderate crystal contents (solidosities 0.1 ≤ φ ≤ 0.3), viscous fluctuations may lead to flow differentiation by shear-enhanced diffusion. AMS and microstructural studies support the idea that granite plutons are intruded as crystal-poor liquids (φ ≤ 50%), with fabric and foliation development restricted to the final stages of emplacement. If so, then these fabrics contain no information on the ascent (vertical transport) history of the magma. Deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt, resulting in a range of local macroscopic flow structures, including layering, crystal alignment, and other mechanical instabilities such as shear zones. As the suspension viscosity varies with stress rate, it is not clear how the timing of proposed rheological transitions formulated from simple equations for static magma suspensions applies to mixtures undergoing shear. New theories of magmas as multiphase flows are required if the full complexity of granitic magma rheology is to be resolved.
The Role of Decay and Mineralization in the Preservation of Soft-Bodied Fossils
Authors: Briggs Derek E.G.
Published: April 2003

▪ Abstract  Fossil deposits that preserve soft-bodied organisms provide critical evidence of the history of life. Usually, only more decay resistant materials, e.g., cuticles, survive as organic remains as a result of selective preservation and subsequent diagenesis to more resistant biopolymers. Permineralization, the permeation of tissues by mineralizing fluids, may preserve remarkable detail, particularly of plants. However, evidence of more labile tissues, e.g., muscle, normally requires the replication of their morphology by rapid in situ growth of minerals, i.e., authigenic mineralization. This process relies on the steep geochemical gradients generated by decay microbes. The minerals involved, and the level of detail preserved (which may be subcellular), depend on a number of factors, including the nature of microbial activity and amount of decay, availability of ions, and the type of organism that is fossilized. Understanding these controls is essential to determining the conditions that favor exceptional preservation.
Volcanic Activity on Io During the Galileo Era
Authors: Geissler Paul E.
Published: April 2003

▪ Abstract  Galileo's explorations have revealed a remarkable variety of eruptive styles among Io's diverse volcanoes. Activity at hundreds of volcanic centers ranges from dormant through sporadic to continuous over the 20-year period of spacecraft observation. High temperature volcanism is common on Io, suggesting that the lavas are made up of mafic to ultramafic silicates rather than sulfur compounds. Io's largest plumes are driven by SO2and sulfur-rich gasses vented from the silicate interior that produce prominent red pyroclastic deposits. Red deposits flag the source regions of many other ongoing or very recent eruptions. Smaller plumes are produced near the margins of active lava flows by explosive volatilization of the underlying or surrounding SO2. These plumes produce SO2snowflakes that mantle existing topography. Io's volcanism drives significant variations in the atmosphere and plasma torus, yet most of the heat loss occurs through lava flows and by the quiet overturning of lava lakes without large-scale explosive activity. Although only a handful of Io's volcanoes have been directly observed to produce explosive eruptions, volcanic resurfacing is efficient enough to erase even small craters from Io's youthful surface.
Metal-Silicate Partitioning of Siderophile Elements and Core Formation in the Early Earth
Authors: Righter Kevin
Published: April 2003

▪ Abstract  Accretion models for the Earth and terrestrial planets are based on the distribution of siderophile (iron-loving) elements between metal and silicate. Extensive experimental studies of the partitioning of these elements between metallic liquid and silicate melt have led to a better understanding and a more sophisticated application to planetary problems. Siderophile element metal/silicate partition coefficients are a function of temperature, pressure, oxygen fugacity, and metal and silicate composition. Quantification of these effects for a limited subset of siderophile elements has led to the idea that early Earth had a 700-km or deeper magma ocean. This new understanding of siderophile element partitioning has also led to applications to the kinetics of metal-silicate equilibrium, links to the timing of core formation, and a better understanding of core formation and metal-silicate equilibrium in the Moon and Mars. Key issues for future consideration include the role of water in early Earth, consideration of the core as a reservoir for noble gases and/or traditionally lithophile elements, siderophile element concentrations in the deep mantle, oxygen fugacity at high pressures, and further evaluation of the need for a late accretional veneer. The strongest approach to improving accretion models for the terrestrial planets is one that combines geochemistry, geophysics, and planetary dynamics.
Recognizing Mantle Plumes in the Geological Record
Authors: Ernst Richard E. , Buchan Kenneth L.
Published: April 2003

▪ Abstract  Mantle plumes are recognized by domal uplift, triple junction rifting, and especially the presence of a large igneous province (LIP), dominated in the Phanerozoic by flood basalts, and in the Proterozoic by the exposed plumbing system of dykes, sills, and layered intrusions. In the Archean, greenstone belts that contain komatiites have been linked to plumes. In addition, some carbonatites and kimberlites may originate from plumes that have stalled beneath thick lithosphere. Geochemistry and isotopes can be used to test and characterize the plume origin of LIPs. Seismic tomography and geochemistry of crustal and subcrustal xenoliths in kimberlites can identify fossil plumes. More speculatively, plumes (or clusters of plumes) have been linked with variation in the isotopic composition of marine carbonates, sea-level rise, iron formations, anoxia events, extinctions, continental breakup, juvenile crust production, magnetic superchrons, and meteorite impacts. The central region of a plume is located using the focus of a radiating dyke swarm, the distribution of komatiites and picrites, etc. The outer boundary of a plume head circumscribes the main flood basalt distribution and approximately coincides with the edge of domal uplift that causes shoaling and offlap in regional sedimentation.
BIOFLUID MECHANICS IN FLEXIBLE TUBES
Authors: Grotberg James B. , Jensen Oliver E.
Published: April 2003

▪ Abstract Almost all vessels carrying fluids within the body are flexible, and interactions between an internal flow and wall deformation often underlie a vessel's biological function or dysfunction. Such interactions can involve a rich range of fluid-mechanical phenomena, including nonlinear pressure-drop/flow-rate relations, self-excited oscillations of single-phase flow at high Reynolds number and capillary-elastic instabilities of two-phase flow at low Reynolds number. We review recent advances in understanding the fundamental mechanics of flexible-tube flows, and discuss physiological applications spanning the cardiovascular system (involving wave propagation and flow-induced instabilities of blood vessels), the respiratory system (involving phonation, the closure and reopening of liquid-lined airways, and Marangoni flows on flexible surfaces), and elsewhere in the body (involving active peristaltic transport driven by fluid-structure/muscle interactions).
SHAPE OPTIMIZATION IN FLUID MECHANICS
Authors: Mohammadi Bijan , Pironneau Olivier
Published: April 2003

▪ Abstract This paper is a short and nonexhaustive survey of some recent developments in optimal shape design (OSD) for fluids. OSD is an interesting field both mathematically and for industrial applications. Existence, sensitivity, and compatibility of discretizations are important theoretical issues. Efficient algorithmic implementations with low complexity are also critical. In this paper we discuss topological optimization, algorithmic differentiation, gradient smoothers, Computer Aided Design (CAD)-free platforms and shock differentiation; all these are applied to a multicriterion optimization for a supersonic business jet.
MODELING ARTIFICIAL BOUNDARY CONDITIONS FOR COMPRESSIBLE FLOW
Authors: Colonius Tim
Published: April 2003

▪ Abstract We review artificial boundary conditions (BCs) for simulation of inflow, outflow, and far-field (radiation) problems, with an emphasis on techniques suitable for compressible turbulent shear flows. BCs based on linearization near the boundary are usually appropriate for inflow and radiation problems. A variety of accurate techniques have been developed for this case, but some robustness and implementation issues remain. At an outflow boundary, the linearized BCs are usually not accurate enough. Various ad hoc models have been proposed for the nonlinear case, including absorbing layers and fringe methods. We discuss these techniques and suggest directions for future modeling efforts.
FLOW-RATE MEASUREMENT IN TWO-PHASE FLOW
Authors: Oddie Gary
Published: April 2003

▪ Abstract Online, continuous, two-phase flow measurement is often necessary, particularly in the oil and gas industry. In this article, we describe some of the commercially most important techniques for gas-liquid, gas-solid, liquid-solid, and liquid-liquid flows, and provide associated illustrative sketches and regime maps. These techniques involve Venturi pressure drop, Coriolis, electromagnetic, and cross-correlation flow meters, gamma-ray absorption and gradio-manometer densitometers, and local electrical and fiber-optic sensors, for which we describe the principles of operation and interpretation. References are given to more comprehensive texts and papers; these are representative rather than exhaustive. It is emphasized that empirical calibration is the norm and that detailed fluid-mechanical analysis has so far played little part in instrument design and operation.
DISSECTING INSECT FLIGHT
Authors: Wang Z. Jane
Published: April 2003

▪ Abstract  “What force does an insect wing generate?” Finding answers to this enduring question is an essential step toward our understanding of interactions of moving objects with fluids that enable most living species such as insects, birds, and fish to travel efficiently and us to follow similar suit with sails, oars, and airfoils. We give a brief history of research in insect flight and discuss recent findings in unsteady aerodynamics of flapping flight at intermediate range Reynolds numbers ([Formula: see text]). In particular, we examine the unsteady mechanisms in uniform and accelerated motions, forward and hovering flight, as well as passive flight of free-falling objects. The results obtained by “taking the insects apart” helped us to resolve previous puzzles about the force estimates in hovering insects, to ellucidate basic mechanisms essential to flapping flight, and to gain insights about the efficieny of flight.
EXPERIMENTAL ANDCOMPUTATIONALMETHODS INCARDIOVASCULARFLUIDMECHANICS
Authors: Taylor Charles A. , Draney Mary T.
Published: April 2003

▪ Abstract The characterization of blood flow is important for understanding the function of the cardiovascular system under normal and diseased conditions, designing cardiovascular devices, and diagnosing and treating congenital and acquired cardiovascular disease. Experimental methods, especially magnetic resonance imaging techniques can be used to noninvasively quantify blood flow for diagnosing cardiovascular disease, researching disease mechanisms, and validating assumptions and predictions of mathematical models. Computational methods can be used to simulate blood flow and vessel dynamics, test hypotheses of disease formation under controlled conditions, and evaluate devices that have not yet been built and treatments that have not yet been implemented. In this article we review experimental and computational methods for quantifying blood flow velocity and pressure fields in human arteries. We place particular emphasis on providing an introduction to the physics and applications of magnetic resonance imaging, and surveying lumped parameter, one-dimensional, and three-dimensional numerical methods used to model blood flow.
ADVANCED CFD AND MODELING OF ACCIDENTAL EXPLOSIONS
Authors: Cant R.S. , Dawes W.N. , Savill A.M.
Published: April 2003

▪ Abstract This paper reviews the current state of the art in accidental explosion modeling using methods based on computational fluid dynamics (CFD) in the petrochemical process industries. We discuss the problem in terms of its industrial importance and its technical difficulty, which stems mainly from the large range of length and timescales that must be represented. Explicit representation of all scales is not feasible due to limitations of computational cost, and modeling of unresolved physical features is required. We also discuss geometry modeling using the porosity/distributed resistance (PDR) method and review relevant combustion modeling. We describe an advanced CFD approach using unstructured adaptive gridding and discuss its usefulness in the context of results obtained for both two dimensional and three dimensional simulations of gas explosion phenomena in complex geometries.
SHOCK WAVE/GEOPHYSICAL AND MEDICAL APPLICATIONS
Authors: Takayama Kazuyoshi
Published: April 2003

▪ Abstract Shock wave research was traditionally developed as an element of high-speed gas dynamics supporting supersonic flights and atmospheric reentry of space vehicles. However, recently its scope has expanded to the comprehensive interpretation of shock wave phenomena in nature and the artificial world. In particular, many aspects of volcanoes's explosive eruptions are closely related to shock wave dynamics. One hypothesis proposes that during asteroid impact events that took place millions of years ago underwater shock waves played a decisive role in mass extinction of marine creatures. Shock waves have been successfully applied to medical therapy. Extracorporeal shock wave lithotripsy (ESWL) was a wonderful success in noninvasive removal of urinary tract stones. Recently, shock wave therapy was further developed for the revascularization of cerebral embolism, drug delivery, and other interesting therapeutic methods. This review provides an overview of the state-of-the-art interdisciplinary applications of shock wave research to geophysics and medicine.
RAY METHODS FOR INTERNAL WAVES IN THE ATMOSPHERE AND OCEAN
Authors: Broutman Dave , Rottman James W. , Eckermann Stephen D.
Published: April 2003

▪ Abstract We review the use of ray models for internal waves, particularly formulations for calculating wave amplitudes along the ray. These are expressed in spatial, wave number, and phase-space coordinates. The choice of formulation affects not only the difficulty of the calculations for rays and caustics but also the degree to which the waves satisfy slowly varying assumptions. We describe several examples taken from atmospheric and oceanic applications that illustrate the variety of options for ray models.
FEEDBACK CONTROL OF COMBUSTION OSCILLATIONS
Authors: Dowling Ann P. , Morgans Aimee S.
Published: April 2003

▪ Abstract  Early work and recent advances in feedback control of combustion oscillations are described. The physics of combustion oscillations, most commonly caused by a coupling between acoustic waves and unsteady heat release, are discussed, and the concept of using feedback control to interrupt these interactions is introduced. Factors affecting practical implementation of feedback control, including sensors, actuators, and controller design are described, and the historical development of control strategy for combustion oscillations is reviewed. Finally, demonstrations of feedback control on full-scale combustion systems are described, and it is concluded that there is potential to apply more systematic controller designs at full scale.
COATING FLOWS
Authors: Weinstein Steven J.
Published: April 2003

▪ Abstract Coating is the process of applying thin liquid layers to a substrate, often a moving web. Complex coating processes can be approached through examination of their fluid mechanical components. The flow elements reviewed in this article include the boundary layer along a moving wall, the dynamic wetting line, withdrawal from a pool, flow metered by a narrow channel, die flow, flow on an incline, the freely falling liquid curtain, premetered coating with a small gap, and flow after coating. Although some flow elements are well studied and understood, others require additional investigation. Genuinely predictive modeling of complex coating processes is not yet possible and coating practice remains largely empirical. Nonetheless, coating science is sufficiently advanced that physical insights and mathematical models greatly benefit design and practice.
TURBULENT FLOWS OVER ROUGH WALLS
Authors: Jiménez Javier
Published: April 2003

▪ Abstract We review the experimental evidence on turbulent flows over rough walls. Two parameters are important: the roughness Reynolds number [Formula: see text], which measures the effect of the roughness on the buffer layer, and the ratio of the boundary layer thickness to the roughness height, which determines whether a logarithmic layer survives. The behavior of transitionally rough surfaces with low [Formula: see text] depends a lot on their geometry. Riblets and other drag-reducing cases belong to this regime. In flows with δ/k ≲ 50, the effect of the roughness extends across the boundary layer, and is also variable. There is little left of the original wall-flow dynamics in these flows, which can perhaps be better described as flows over obstacles. We also review the evidence for the phenomenon of d-roughness. The theoretical arguments are sound, but the experimental evidence is inconclusive. Finally, we discuss some ideas on how rough walls can be modeled without the detailed computation of the flow around the roughness elements themselves.
Shock Wave Drag Reduction
Authors: Bushnell Dennis M.
Published: April 2003

▪ Abstract Early concepts in shock wave drag reduction enabled modern aeronautical systems, and continuing research progress in this arena is crucial for significant improvements in long haul transports and various military platforms and weapons. The research area is rich in concepts/approaches, but many of these have not progressed into the realm of application. This is due in part to a lack of knowledge on the part of the fluids research community concerning the multidisciplinary “real-world” design space/metrics and a consequent lack of the requisite breadth and depth of research information required to evaluate/apply the concept. The article reviews the extant wave drag reduction approaches that are (a) well understood/applied, (b) under active study/indicate considerable promise, and (c) those in the nascent stage only.
THE ORIGINS OF WATER WAVE THEORY
Authors: Craik Alex D.D.
Published: April 2003

▪ Abstract After early work by Newton, the eighteenth and early nineteenth century French mathematicians Laplace, Lagrange, Poisson, and Cauchy made real theoretical advances in the linear theory of water waves; in Germany, Gerstner considered nonlinear waves, and the brothers Weber performed fine experiments. Later in Britain during 1837–1847, Russell, Green, Kelland, Airy, and Earnshaw all made substantial contributions, setting the scene for subsequent work by Stokes and others.
VERTICAL MIXING, ENERGY, AND THE GENERAL CIRCULATION OF THE OCEANS
Authors: Wunsch Carl
Published: April 2003

▪ Abstract The coexistence in the deep ocean of a finite, stable stratification, a strong meridional overturning circulation, and mesoscale eddies raises complex questions concerning the circulation energetics. In particular, small-scale mixing processes are necessary to resupply the potential energy removed in the interior by the overturning and eddy-generating process. A number of lines of evidence, none complete, suggest that the oceanic general circulation, far from being a heat engine, is almost wholly governed by the forcing of the wind field and secondarily by deep water tides. In detail however, the budget of mechanical energy input into the ocean is poorly constrained. The now inescapable conclusion that over most of the ocean significant “vertical” mixing is confined to topographically complex boundary areas implies a potentially radically different interior circulation than is possible with uniform mixing. Whether ocean circulation models, either simple box or full numerical ones, neither explicitly accounting for the energy input into the system nor providing for spatial variability in the mixing, have any physical relevance under changed climate conditions is at issue.
Engineering Flows in Small Devices: Microfluidics Toward a Lab-on-a-Chip
Authors: Stone H.A. , Stroock A.D. , Ajdari A.
Published: April 2003

Microfluidic devices for manipulating fluids are widespread and finding uses in many scientific and industrial contexts. Their design often requires unusual geometries and the interplay of multiple physical effects such as pressure gradients, electrokinetics, and capillarity. These circumstances lead to interesting variants of well-studied fluid dynamical problems and some new fluid responses. We provide an overview of flows in microdevices with focus on electrokinetics, mixing and dispersion, and multiphase flows. We highlight topics important for the description of the fluid dynamics: driving forces, geometry, and the chemical characteristics of surfaces.
VORTEX-INDUCED VIBRATIONS
Authors: Williamson C.H.K. , Govardhan R.
Published: April 2003

▪ Abstract This review summarizes fundamental results and discoveries concerning vortex-induced vibration (VIV), that have been made over the last two decades, many of which are related to the push to explore very low mass and damping, and to new computational and experimental techniques that were hitherto not available. We bring together new concepts and phenomena generic to VIV systems, and pay special attention to the vortex dynamics and energy transfer that give rise to modes of vibration, the importance of mass and damping, the concept of a critical mass, the relationship between force and vorticity, and the concept of “effective elasticity,” among other points. We present new vortex wake modes, generally in the framework of a map of vortex modes compiled from forced vibration studies, some of which cause free vibration. Some discussion focuses on topics of current debate, such as the decomposition of force, the relevance of the paradigm flow of an elastically mounted cylinder to more complex systems, and the relationship between forced and free vibration.
FLUID MECHANICS AND RHEOLOGY OF DENSE SUSPENSIONS
Authors: Stickel Jonathan J. , Powell Robert L.
Published: April 2003

▪ Abstract  We review the fluid mechanics and rheology of dense suspensions, emphasizing investigations of microstructure and total stress. “Dense” or “highly concentrated” suspensions are those in which the average particle separation distance is less than the particle radius. For these suspensions, multiple-body interactions as well as two-body lubrication play a significant role and the rheology is non-Newtonian. We include investigations of multimodal suspensions, but not those of suspensions with dominant nonhydrodynamic interactions. We consider results from both physical experiments and computer simulations and explore scaling theories and the development of constitutive equations.
THENEUROBIOLOGY OFVISUAL-SACCADICDECISIONMAKING
Authors: Glimcher Paul W.
Published: April 2003

▪ Abstract  Over the past two decades significant progress has been made toward understanding the neural basis of primate decision making, the biological process that combines sensory data with stored information to select and execute behavioral responses. The most striking progress in this area has been made in studies of visual-saccadic decision making, a system that is becoming a model for understanding decision making in general. In this system, theoretical models of efficient decision making developed in the social sciences are beginning to be used to describe the computations the brain must perform when it connects sensation and action. Guided in part by these economic models, neurophysiologists have been able to describe neuronal activity recorded from the brains of awake-behaving primates during actual decision making. These recent studies have examined the neural basis of decisions, ranging from those made in predictable sensorimotor tasks to those unpredictable decisions made when animals are engaged in strategic conflict. All of these experiments seem to describe a surprisingly well-integrated set of physiological mechanisms that can account for a broad range of behavioral phenomena. This review presents many of these recent studies within the emerging neuroeconomic framework for understanding primate decision making.
THE BIOLOGY OF EPILEPSY GENES
Authors: Noebels Jeffrey L.
Published: April 2003

▪ Abstract  Mutations in over 70 genes now define biological pathways leading to epilepsy, an episodic dysrhythmia of the cerebral cortex marked by abnormal network synchronization. Some of the inherited errors destabilize neuronal signaling by inflicting primary disorders of membrane excitability and synaptic transmission, whereas others do so indirectly by perturbing critical control points that balance the developmental assembly of inhibitory and excitatory circuits. The genetic diversity is now sufficient to discern short- and long-range functional convergence of epileptogenic molecular pathways, reducing the broad spectrum of primary molecular defects to a few common processes regulating cortical synchronization. Synaptic inhibition appears to be the most frequent target; however, each gene mutation retains unique phenotypic features. This review selects exemplary members of several gene families to illustrate principal categories of the disease and trace the biological pathways to epileptogenesis in the developing brain.
NOVELNEURALMODULATORS
Authors: Boehning Darren , Snyder Solomon H.
Published: April 2003

▪ Abstract  The discovery that nitric oxide (NO) is produced by neurons and regulates synaptic activity has challenged the definition of a neurotransmitter. NO is not stored in synaptic vesicles and does not act at conventional receptors on the surface of adjacent neurons. The toxic gases carbon monoxide (CO) and hydrogen sulfide (H2S) are also produced by neurons and modulate synaptic activity. D-serine synthesis and release by astrocytes as an endogenous ligand for the “glycine” site of N-methyl D-aspartate (NMDA) receptors defy the concept that a neurotransmitter must be synthesized by neurons. We review the properties of these “atypical” neural modulators.
CODING OF AUDITORY SPACE
Authors: Konishi Masakazu
Published: April 2003

▪ Abstract  Behavioral, anatomical, and physiological approaches can be integrated in the study of sound localization in barn owls. Space representation in owls provides a useful example for discussion of place and ensemble coding. Selectivity for space is broad and ambiguous in low-order neurons. Parallel pathways for binaural cues and for different frequency bands converge on high-order space-specific neurons, which encode space more precisely. An ensemble of broadly tuned place-coding neurons may converge on a single high-order neuron to create an improved labeled line. Thus, the two coding schemes are not alternate methods. Owls can localize sounds by using either the isomorphic map of auditory space in the midbrain or forebrain neural networks in which space is not mapped.
GENERATING THE CEREBRAL CORTICAL AREA MAP
Authors: Grove Elizabeth A. , Fukuchi-Shimogori Tomomi
Published: April 2003

▪ Abstract  The view that the cortical primordium is initially patterned in similar ways to the rest of the embryo has been a conceptual breakthrough. We now have a new starting point for understanding how the cortical area map is established and how maps may change and evolve. Here we review findings that signaling molecules secreted from distinct cortical signaling centers establish positional information in the cortical primordium and regulate regional growth. In other embryonic systems, positional signals would regulate the patterned expression of transcription factors, leading, in a gene regulatory cascade, to the patterned differentiation of the tissue. We discuss candidate transcription factors with respect to such a model of cortical patterning. Finally, embryonic structures interact to pattern one another. We review data suggesting that the thalamus and cortex are patterned independently then interact to generate the final cortical area map.
PROGRESS TOWARD UNDERSTANDING THE GENETIC AND BIOCHEMICAL MECHANISMS OF INHERITED PHOTORECEPTOR DEGENERATIONS
Authors: Pacione Laura R. , Szego Michael J. , Ikeda Sakae , Nishina Patsy M. , McInnes Roderick R.
Published: April 2003

▪ Abstract  More than 80 genes associated with human photoreceptor degenerations have been identified. Attention must now turn toward defining the mechanisms that lead to photoreceptor death, which occurs years to decades after the birth of the cells. Consequently, this review focuses on topics that offer insights into such mechanisms, including the one-hit or constant risk model of photoreceptor death; topological patterns of photoreceptor degeneration; mutations in ubiquitously expressed splicing factor genes associated only with photoreceptor degeneration; disorders of the retinal pigment epithelium; modifier genes; and global gene expression analysis of the retina, which will greatly increase our understanding of the downstream events that occur in response to a mutation.
CELLBIOLOGY OF THEPRESYNAPTICTERMINAL
Authors: Murthy Venkatesh N. , Camilli Pietro De
Published: April 2003

▪ Abstract  The chemical synapse is a specialized intercellular junction that operates nearly autonomously to allow rapid, specific, and local communication between neurons. Focusing our attention on the presynaptic terminal, we review the current understanding of how synaptic morphology is maintained and then the mechanisms in synaptic vesicle exocytosis and recycling.
EPIDEMIOLOGY AND MANAGEMENT OF TOMATO SPOTTED WILT IN PEANUT
Authors: Culbreath A.K. , Todd J.W. , Brown S.L.
Published: April 2003

▪ Abstract  Tomato spotted wilt caused by thrips-vectored tomato spotted wilt virus (TSWV) is a very serious problem in peanut (Arachis hypogaea L.) production. TSWV and the thrips Frankliniella fusca and Frankliniella occidentalis, which vector the virus, present a difficult and complicated challenge from the perspectives of both epidemiology and disease management. Simply controlling the vector typically has not resulted in control of spotted wilt. No single measure can currently provide adequate control of spotted wilt where severe epidemics occur. However, interdisciplinary investigations have resulted in development of integrated management systems that make use of moderately resistant cultivars and chemical and cultural practices, each of which helps to suppress spotted wilt epidemics. Such systems have been successfully deployed in many areas for minimizing losses to this disease. The development of a spotted wilt risk index has aided greatly in relaying information on the importance of using an integrated approach for managing this disease.
Visual Thalamotelencephalic Pathways in the Sturgeon Acipenser, a Non-Teleost Actinopterygian Fish
Authors: Albert James S. , Yamamoto Naoyuki , Yoshimoto Masami , Sawai Nobuhiko , Ito Hironobu
Published: April 2003

Terrestrial vertebrates (amphibians, reptiles, birds, and mammals) possess two visual systems, the geniculate and extrageniculate pathways to the telencephalon. In cartilaginous fishes (e.g. sharks) both retinal and tectal neurons project to neurons in the thalamus, which themselves project to a single area in the telencephalon. The condition in ray-finned fishes (Actinopterygii) is ambiguous. In many teleosts there is a well developed extrageniculate pathway but no obvious geniculate system. This study reports on the thalamotelencephalic projections of a sturgeon, a non-teleost ray-finned fish. Several tract tracing methods (e.g., HRP, WGA-HRP, biocytin, BDA, DiI) were employed in conjunction with normal techniques for identifying neural structures (e.g., Nissl, Golgi). After injections of tracer into retinal and tectal recipient areas of the thalamus, labeled terminals were observed in the ventrolateral region of the caudal telencephalon, an area referred to as the thalamic projection area. After injections of tracer into the telencephalon, populations of retrogradely filled neurons were located in both the dorsal and ventral thalamus. These data demonstrate that thalamic neurons in both retinal and tectal pathways project directly to the telencephalon. These results support the view that two visual pathways are a primitive feature of vertebrate brain organization. These results are also consistent with the hypothesis that the ancestor of Acipenser and Teleostei (Actinopteri) acquired a novel visual pathway to the telencephalon through the ventral portion of the thalamus.
Multimicrobial Sepsis Including Clostridium perfringens after Chemoembolization of a Single Liver Metastasis from Common Bile Duct Cancer
Authors: Eckel Florian , Lersch Christian , Huber Wolfgang , Weiss Wolfgang , Berger Hermann , Schulte-Frohlinde Ewert
Published: April 2003

A 65-year-old woman underwent resection of a distal common bile duct carcinoma (Whipple’s procedure). Twelve months later a single hepatic metastasis was detected and a chemoembolization was performed. Immediately after chemoembolization the patient developed a multimicrobial sepsis including Clostridium perfringens. CT scans depicted pathognomonic signs of gas-containing abscess in the necrotic liver metastasis. She was subsequently treated with broad-spectrum antibiotics, abscess drainage and hyperbaric oxygen therapy. We conclude that antibiotic prophylaxis is recommendable for chemoembolization of liver metastasis in patients with risk factors like intestinal biliary reflux (bilioenteric anastomosis or papillotomy and biliary stenting) and bile duct cancer, otherwise severe sepsis including clostridium bacteremia may occur.
Immunological Time-Course of Gadolinium-Enhancing MRI Lesions in Patients with Multiple Sclerosis
Authors: Giovannoni G. , Silver N.C. , Good C.D. , Miller D.H. , Thompson E.J.
Published: April 2003

In multiple sclerosis (MS) gadolinium (Gd)-enhanced MRI activity correlates weakly with immunological markers of disease activity. We, therefore, tested the hypothesis that the poor correlation could be partly explained by the temporal profile of Gd enhancement. We measured urinary neopterin:creatinine ratios (neopt.:creat.urine) in 5 patients with active MS undergoing weekly Gd-enhanced MRI studies of the brain. The neopt.:creat.urine associated with new Gd-enhancing lesions (<8 days) was significantly higher than the ratio not associated with new Gd-enhancing lesions [meangeometric neopt.: creat.urine = 413 μmol/mol (range = 207–521) vs. 250 μmol/mol (range = 132–492), p = 0.03]. Pro-inflammatory immunological markers, which are probably produced early on in the life cycle of an active MS lesion, should preferably be correlated with newly enhancing lesions (<8 days). Failure to do this may explain the poor and unpredictable correlations between immunological markers and Gd-enhanced MRI activity, which cannot be accurately aged in cross-sectional and serial monthly MRI studies.
Preconditioning with Short Cycles Improves Ischemic Tolerance in Rat Fast- and Slow-Twitch Skeletal Muscle
Authors: Mattei A. , Sutter P.M. , Marx A. , Stierli P. , Heberer M. , Gürke L.
Published: April 2003

Aim: The aim of this study was to investigate whether the efficacy of ischemic preconditioning (IP) in rat skeletal muscle depends on the duration of the preconditioning cycles. Methods: Rats were divided into four groups (n = 10 each). The right hindlimb of rats in group A were subjected to 2.5 h of tourniquet ischemia followed by 2 h of reperfusion (I-R). Thereafter, muscular function was analyzed in vitro and high-energy phosphates (HEP) were determined by HPLC. Before I-R, right hindlimbs of rats in groups B–D subjected to IP with three cycles each consisting of 2.5, 5 or 10 min of ischemia followed by reperfusion for the same duration. Results: Postischemic function of the extensor muscle was significantly improved with all three preconditioning protocols. Postischemic function of the soleus muscle was only improved by IP with three cycles of 5 min of ischemia and 5 min of reperfusion. Postischemic HEP tissue levels were not influenced by IP. Conclusion: This study shows for the first time that IP increases ischemic tolerance not only of fast-twitch but also of slow-twitch skeletal muscle. The efficacy of IP seems to be less dependent on the duration of the single preconditioning cycle than on the number of cycles performed. Three cycles each of 2.5, 5 or 10 min ischemia and reperfusion significantly improved postischemic skeletal muscle function. Tissue levels of HEPs, however, were not influenced by IP indicating that preservation of HEPs does not play a major role in the effects of IP on rodent skeletal muscle.
Effect of Sigmoid Colon Distension on the Rectosigmoid Junction
Authors: Shafik A. , El-Sibai O.
Published: April 2003

Purpose The sigmoid colon (SC) is the site of stool storage. The stools accumulate in the SC until, at a certain volume, the mechanoreceptors in the SC wall are stimulated, evoking the sigmoidorectal junction inhibitory reflex with a resulting SC contraction, rectosigmoid junction (RSJ) relaxation and passage of the stools to the rectum. However, the RSJ status during stool accumulation in the SC has been scarcely addressed in the literature. The current study investigated this point. Methods: A balloon-ended tube was introduced into the SC of 21 healthy volunteers [mean age (± SD) 36.8 ± 10.3 years; 15 men and 6 women]. The pressures in the SC and RSJ were measured by means of a perfused tube, at rest and during balloon inflation with carbon dioxide at two rates: slow (3 ml/min) and rapid (150 ml/min). The tests were repeated after individual anesthetization of the SC and RSJ. Results: During slow SC distension up to 80 ml included, the RSJ pressure progressively increased while the SC exhibited no pressure response (p > 0.05). At a distending volume of 100 ml, the pressure in the SC rose (p < 0.01) and declined in the RSJ (p < 0.05), and the balloon was dispelled to the rectum. Rapid SC distension up to 40 ml included, effected no SC pressure response (p > 0.05) while the RSJ showed progressive pressure elevation. At 60 ml distension, the SC recorded a pressure rise (p < 0.001) and the RSJ a pressure decrease (p < 0.05); the balloon was dispelled to the rectum. The pressure in the RSJ did not respond to distension of the anesthetized SC. Conclusion: The study has shown that, during accumulation of stools in the SC, leakage to the rectum seems to be prevented by a reflex action which we call ‘rectosigmoid junction tightening reflex’. This reflex probably acts to control both storage and emptying of the SC contents. Reflex dysfunction might lead to defecation disorders. We suggest that the RSJ tightening reflex be included as an investigative tool in the diagnosis of defecation disorders.