ALBERT

Notes: There is a pressing need for cleaner fuels (free or aromatics and of minimal sulfur content) or ones that convert chemical energy directly to electricity, silently and without production of noxious oxides and particulates; chemical, petrochemical and pharmaceutical processes that may be conducted in a one-step, solvent-free manner and that use air as the preferred oxidant; and industrial processes that minimize consumption of energy, production of waste, or the use of corrosive, explosive, volatile, and nonbiodegradable materials. All these needs and other desiderata, such as the in situ production and containment of aggressive and hazardous reagents, and the avoidance of use of ecologically harmful elements, may be achieved by designing the appropriate heterogeneous inorganic catalyst, which ideally should be cheap, readily preparable and fully characterizable, preferably under in situ reaction conditions. A range of nanoporous and nanoparticle catalysts that meet most of the stringent demands of sustainable development and responsible (clean) technology is described. Specific examples that are highlighted include the production of adipic acid (precursor of polyamides and urethanes) without the use of concentrated nitric acid nor the production of greenhouse gases such as nitrous oxide; the production of caprolactam (precursor of nylon) without the use of oleum and hydroxylamine sulfate; and the terminal oxyfunctionalization of linear alkanes in air. The topic of biocatalysis and sustainable development is also briefly discussed for the epoxidation of terpenes and fatty acid methyl esters; for the generation of polymers, polylactides, and polyesters; and for the production of 1,3-propanediol from corn.

Notes: The review highlights the state-of-the-art research regarding the application of modern in situ spectroscopic, microscopic, and electrochemical techniques to improve the understanding of the interaction of organic molecules with metal surfaces. We also consider the chemical and electrochemical processes that lead to a de-adhesion of polymers from metal surfaces. Spectroscopic techniques such as surface-enhanced infrared or Raman spectroscopy provide molecular understanding of organic molecules and water at buried metal surfaces. This information is complementary to adhesion studies by means of atomic force microscopy and de-adhesion studies of polymer layers from metals by means of a scanning Kelvin probe. Adhesion and de-adhesion mechanisms are discussed, especially those involving humid and corrosive environments, which are the predominant and most important for metal/polymer composites in engineering applications.

Notes: Chemical analysis at high spatial resolution is the domain of analytical transmission electron microscopy. Owing to rapid instrumental developments during the past decade, electron energy-loss spectroscopy offers now a spatial resolution close to 0.1 nm and an energy resolution close to 0.1 eV. This development has been accompanied by the introduction of numerous new techniques and methods for data acquisition and analysis, which are outlined in the present article. Recent results for a wide range of material systems are addressed. These comprise first-principles calculations, which have contributed to enormous progress in the calculation of near-edge fine structures, and fingerprinting methods, which are still important for the interpretation of experimental data.

Notes: The objective of this review is to critically assess the different approaches developed in recent years to understand the dynamics of open flows such as mixing layers, jets, wakes, separation bubbles, boundary layers, and so on. These complex flows develop in extended domains in which fluid particles are continuously advected downstream. They behave either as noise amplifiers or as oscillators, both of which exhibit strong nonlinearities ( Huerre & Monkewitz 1990 ). The local approach is inherently weakly nonparallel and it assumes that the basic flow varies on a long length scale compared to the wavelength of the instability waves. The dynamics of the flow is then considered as a superposition of linear or nonlinear instability waves that, at leading order, behave at each streamwise station as if the flow were homogeneous in the streamwise direction. In the fully global context, the basic flow and the instabilities do not have to be characterized by widely separated length scales, and the dynamics is then viewed as the result of the interactions between Global modes living in the entire physical domain with the streamwise direction as an eigendirection. This second approach is more and more resorted to as a result of increased computational capability. The earlier review of Huerre & Monkewitz (1990) emphasized how local linear theory can account for the noise amplifier behavior as well as for the onset of a Global mode. The present survey first adopts the opposite point of view by demonstrating how fully global theory accounts for the noise amplifier behavior of open flows. From such a perspective, there is strong emphasis on the very peculiar nonorthogonality of linear Global modes, which in turn allows a novel interpretation of recent numerical simulations and experimental observations. The nonorthogonality of linear Global modes also imposes severe constraints on the extension of linear global theory to the fully nonlinear re??gime. When the flow is weakly nonparallel, this limitation is so severe that the linear Global mode theory is of little help. It is then much more appropriate to develop a fully nonlinear formulation involving the presence of a front separating the base state region from the bifurcated state region.

Notes: The flow in turbomachines is unsteady due to the relative motion of the rows of blades. In the low-pressure turbine, the wakes from the upstream bladerows provide the dominant source of unsteadiness. Because much of the blade-surface boundary-layer flow is laminar, one of the most important consequences of this unsteadiness is the interaction of the wakes with the suction-side boundary layer of a downstream blade. This is important because the blade suctionĐ??side boundary layers are responsible for most of the loss of efficiency and because the combined effects of random (wake turbulence) and periodic disturbances (wake velocity defect and pressure fields) cause the otherwise laminar boundary layer to undergo transition and eventually become turbulent. This article summarizes the process of wake-induced boundary-layer transition in low-pressure turbines and the loss generation processes that result. Particular emphasis is placed on how the effects of wakes may be exploited to control loss generation and how this has enabled successful development of ultra-high-lift low-pressure turbines.

Notes: Chaotic advection and, more generally, ideas from dynamical systems, have been fruitfully applied to a diverse, and varied, collection of mixing and transport problems arising in engineering applications over the past 20 years. Indeed, the "dynamical systems approach" was developed, and tested, to the point where it can now be considered a standard tool for understanding mixing and transport issues in many disciplines. This success for engineering-type flows motivated an effort to apply this approach to transport and mixing problems in geophysical flows. However, there are fundamental difficulties arising in this endeavor that must be properly understood and overcome. Central to this approach is that the starting point for analysis is a velocity field (i.e., the "dynamical system"). In many engineering applications this can be obtained sufficiently accurately, either analytically or computationally, so that it describes particle trajectories for the actual flow. However, in geophysical flows (and we concentrate here almost exclusively on oceanographic flows), the wide range of dynamically significant time and length scales makes the justification of any velocity field, in the sense of reproducing particle trajectories for the actual flow, a much more difficult matter. Nevertheless, the case for this approach is compelling due to the advances in observational capabilities in oceanography (e.g., drifter deployments, remote sensing capabilities, satellite imagery, etc.), which reveal space-time structures that are highly suggestive of the structures one visualizes in the global, geometrical study of dynamical systems theory. This has been pursued in recent years through a combination of laboratory studies, kinematic models, and dynamically consistent models that have all been compared with observational data. During the course of these studies it has become apparent that a new type of dynamical system is necessary to consider in these studies (i.e., a finite time, aperiodically time-dependent velocity field defined as a data set), which requires the development of new analytical and computational tools, as well as the necessity to discard some of the standard ideas and results from dynamical systems theory. In this article we review a number of the key developments to date in this young, but rapidly developing, area at the interface between geophysical fluid dynamics and applied and computational mathematics. We also describe the wealth of new directions for research that this approach unlocks.

Notes: The gas-lift technique comprises the injection of gas bubbles in vertical oil wells to increase production. It is based on a reduction of the tubing gravitational pressure gradient. Several fluid-flow phenomena influencing such vertical gas-liquid flows are discussed. These effects include the radial distribution of void fraction and of gas and liquid velocity, flow regime changes, and system stability problems. Associated consequences for gas-lift performance and related optimization approaches are also discussed.

Notes: What mechanisms of flow control do animals use to enhance hydrodynamic performance? Animals are capable of manipulating flow around the body and appendages both passively and actively. Passive mechanisms rely on structural and morphological components of the body (i.e., humpback whale tubercles, riblets). Active flow control mechanisms use appendage or body musculature to directly generate wake flow structures or stiffen fins against external hydrodynamic loads. Fish can actively control fin curvature, displacement, and area. The vortex wake shed by the tail differs between eel-like fishes and fishes with a discrete narrowing of the body in front of the tail, and three-dimensional effects may play a major role in determining wake structure in most fishes.

Notes: Brooke Benjamin's original theories of fluid mechanical phenomena changed our basic understanding of cavitation bubbles, surface and internal waves, gravity currents, instabilities of shear flow over flexible surfaces, and swirling flows. For some types of finite-amplitude wave phenomena, he generated integral constraints and derived new partial differential equations; by establishing their general properties he showed how they have wide application. He developed a complementary approach based on functional analysis that was quite new to fluid mechanics. He demonstrated methods for deriving, without detailed calculation, the essential features of nonlinear and indeterminate flow problems that are otherwise intractable.

Notes: The fluid mechanics of artificial blood pumps has been studied since the early 1970s in an attempt to understand and mitigate hemolysis and thrombus formation by the device. Pulsatile pumps are characterized by inlet jets that set up a rotational "washing" pattern during filling. Strong regurgitant jets through the closed artificial heart valves have Reynolds stresses on the order of 10,000 dynes/cm2 and are the most likely cause of red blood cell damage and platelet activation. Although the flow in the pump chamber appears benign, low wall shear stresses throughout the pump cycle can lead to thrombus formation at the wall of the smaller pumps (10Đ??50 cc). The local fluid mechanics is critical. There is a need to rapidly measure or calculate the wall shear stress throughout the device so that the results may be easily incorporated into the design process.

Notes: Electrophoretic separation of a mixture of chemical species is a fundamental technique of great usefulness in biology, health care, and forensics. In capillary electrophoresis (which has evolved from its predecessor, slab-gel electrophoresis), the sample migrates through a single microcapillary instead of through the network of pores in a gel. A fundamental design problem is to minimize dispersion in the separation direction. Molecular diffusion is inevitable and sets a theoretical limit on the best separation that can be achieved. But in practice, there are a number of effects arising out of the interplay between fluid flow, chemistry, thermal effects, and electric fields that result in enhanced dispersion. This paper reviews the subject of fluid flow in such capillary microchannels and examines the various causes of enhanced dispersion that limit the efficiency of separation.

Notes: Large-eddy simulation (LES) of turbulent combustion is a relatively new research field. Much research has been carried out over the past years, but to realize the full predictive potential of combustion LES, many fundamental questions still have to be addressed, and common practices of LES of nonreacting flows revisited. The focus of the present review is to highlight the fundamental differences between Reynolds-averaged Navier-Stokes (RANS) and LES combustion models for nonpremixed and premixed turbulent combustion, to identify some of the open questions and modeling issues for LES, and to provide future perspectives.

Notes: The preparation of skeletal catalysts is considered, with particular reference to the preparation of skeletal nickel and skeletal copper. Skeletal catalysts have physical properties that are highly desired for some industrial processes, and the means of controlling these properties to optimize performance is reviewed. The preparation can be affected by the initial alloy composition, the quenching process, the leaching procedure, aging and by the addition of promoters. These processes may affect either or both the chemical and physical characteristics of the catalysts. Preparation procedures need to be adjusted for individual reactions if optimal performance is required. The effect of the preparation conditions on the structure and catalytic performance of these systems is reviewed.

Notes: It has recently become possible to measure the anisotropic distribution of interfaces in polycrystals and composites. Because classical theories for grain growth and coarsening assume isotropic interface properties, they are incapable of explaining how these distributions arise. The purpose of this paper is to review the results of recent experiments, simulations, and theories that document the effects of anisotropy on the capillarity-driven evolution of granular systems. The results suggest that meaningful predictions of evolving microstructural characteristics can be made using models that incorporate the anisotropy of the interfacial energy and mobility.

Notes: This review is an introduction to the problem of determining the nature of the diffraction spectra of ordered solids. After explicit computation examples of Bragg diffraction spectra of quasicrystals (bulk, surface) in kinematical and dynamical (high-resolution electron microscopy) situations, we show on simple toy models that long-range order does not necessarily lead to Bragg peaks which, in turn, are not necessarily the signature of the unique long-range periodic order.

Notes: Recent research trends of the preparation and characterization of highly efficient titanium oxideĐ??based photocatalysts are reviewed on the basis of studies done in our laboratory. Special attention is focused on the preparation and characterization of active sites of highly dispersed titanium oxide species within mesoporous matrices and on titanium oxideĐ??based binary catalysts such as Ti/Si and Ti/B oxides and unique visible light-responsive second-generation TiO2 photocatalysts prepared by an advanced metal-ion-implantation and RF magnetron sputtering deposition method. Highly dispersed titanium oxide species within mesoporous frameworks and titanium oxideĐ??based binary catalysts exhibit high and unique photocatalytic activities for various reactions, such as the direct decomposition of NOx. These species also have photo-induced superhydrophiric properties. It is of significance that visible light-responsive TiO2 photocatalysts can be applied to the decomposition of NOx in air and the degradation of pollutants in water, as well as to the splitting of water under UV and visible light irradiation.

Notes: Heterogeneous asymmetric catalysis remains a topic of intense research interest because control of enantioselectivity represents one of the major synthetic challenges today. Successful strategies to achieve high enantioselection have been developed using three key approaches: (a) adsorption of chiral modifiers onto an active metal surface, which is found to be particularly effective for enantioselective hydrogenation; (b) covalent tethering of homogeneous catalysts; and (c) electrostatic interaction between a negatively charged framework and a cation. Other approaches have been advocated, e.g., encapsulation, but in general these lead to lower enantioselectivity for these heterogeneous asymmetric systems when compared with the equivalent homogeneous catalyst. This review covers the strategies for achieving high enantioselection as well as recent interesting features concerning confinement effects, the inversion of enantioselectivity, and specific cases in which enantioselection increases with conversion, all being factors that can guide researchers to identifying improved systems.

Notes: This review covers the synthesis, characterization, and physico-chemical properties of microporous and mesoporous aluminophosphates and silicoaluminophosphates molecular sieves. Particular emphasis is given to the materials that have found applications as acid catalysts. We consider the evolution of the synthesis procedures from the first discoveries to the current methodologies and give perspectives for new possible synthesis strategies. Emphasis is given to the use of specially prepared precursors/reactants designed for the use as molecular sieves. Experimental (especially MAS-NMR and FTIR spectroscopy) and theoretical approaches to the description of the Si insertion into the ALPO framework and to the acidic properties of SAPOs and MeAPSOs materials are discussed.

Notes: The diffusion-multiple approachĐ??the creation of composition gradients and intermetallic phases by long-term annealing of junctions of three or more phases/alloysĐ??enables the generation of a large number of phases and compositions for efficient mapping of phase diagrams, phase properties, and kinetics. With an efficiency much higher than that of a conventional approach, many critical materials data, which otherwise would be too time-consuming and expensive to acquire, can be obtained and employed to accelerate alloy design. The critical data for structural materials design include phase diagrams, diffusion coefficients, precipitation kinetics, solution-strengthening effects, and precipitation-strengthening effects. All these data can be obtained from diffusion multiples. The combination of the diffusion-multiple approach with the CALPHAD approach can impact computational design of structural materials. The diffusion-multiple approach can also be applied to combinatorial screening of functional materials having unique physical, chemical, or other properties when micro-scale measurement techniques are available for these properties. Examples are shown to illustrate the progress made to date on applying the diffusion-multiple approach to accelerated design/discovery of materials.

Notes: Efficiently and accurately solving the equations governing fluid flow in oil reservoirs is very challenging because of the complex geological environment and the intricate properties of crude oil and gas at high pressure. We present these challenges and review successful and promising solution approaches. We discuss in detail the modeling of fluid flow in reservoirs with strongly varying rock properties. This requires subgrid-scale models that accurately represent the flow physics due to fine-scale fluctuations. A second focus is on the complex multiphase, multicomponent systems that describe miscible gas injection processes for enhanced oil recovery and CO2 sequestration.

Notes: Mammalian fertilization requires the coordinated activity of motile spermatozoa, muscular contractions of the uterus and oviduct, as well as ciliary beating. These elastic structures generate forces that drive fluid motion, but their configurations are, in turn, determined by the fluid dynamics. We review the basic fluid mechanical aspects of reproduction, including flagellar/ciliary beating and peristalsis. We report on recent biological studies that have shed light on the relative importance of the mechanical ingredients of reproduction. In particular, we examine sperm motility in the reproductive tract, ovum pickup and transport in the oviduct, as well as sperm-egg interactions. We review recent advances in understanding the internal mechanics of cilia and flagella, flagellar surface interaction, sperm motility in complex fluids, and the role of fluid dynamics in embryo transfer. We outline promising computational fluid dynamics frameworks that may be used to investigate these complex, fluid-structure interactions.

Notes: His contemporaries saw R.T. Jones as one of the notably creative aerodynamicists of the twentieth century. This essay reviews his remarkable life and career, including his years as a farm-country boy, college dropout, and fledgling airplane designer in Missouri, his time as an elevator operator and self-directed student in Washington, D.C., and his long professional career as an aerodynamicist at the Langley and Ames Aeronautical Laboratories and Stanford University. The focus in his career is on his fundamental discovery of the benefits of sweepback for the wings of high-speed airplanes. This includes speculation about his highly intuitive thought processes in arriving at his creative ideas. I also give an account of his work on blood flow and the mechanical heart, his avocational accomplishments as a maker of telescopes and violins, and his philosophical interest in human affairs.

Notes: We review recent advances in understanding, modeling, and controlling oscillations in the flow past a cavity. The fundamental mechanisms underlying cavity flow oscillations have been known for at least 40 years, but suppressing these oscillations in a reliable and robust way is still a challenge today. Interest in controlling the flow past a cavity is motivated by aerospace applications, but in addition, cavity flows provide an attractive canonical problem for exploring general flow control techniques. The focus is on recent advances in modeling these flows, and in controlling them, using both open-loop and closed-loop techniques. A relatively new perspective is that cavity oscillations may not always be self-sustained, but under some flow conditions may be lightly damped resonances, sustained by external disturbances such as boundary layer turbulence. Areas in which our understanding is incomplete, and which deserve further study, are discussed, in particular the effects of high-frequency open-loop forcing, fundamental limitations of feedback control for a given configuration of sensors and actuators, and the development of a feedback design methodology that respects the limited range of validity of the available dynamical models.

Notes: When the free surfaces of most solids approach their bulk melting temperatures from below, the molecular structure of the material gives way to a disordered structure with some attributes of both the solid and liquid phases. When the temperature is sufficiently close to that of bulk transition, the surface melts and literally flows as a viscous fluid. This phenomenon, called interfacial premelting, lies at the heart of the microscopic theory of melting of solid matter, and captures the interest of condensed matter physicists and physical chemists alike. The process is ubiquitous and responsible for a wide range of consequences in materials with biological, geophysical, and technological significance. Because such systems are often exposed to spatial or temporal variations in thermodynamic forcing, there are a host of fluid mechanical phenomena that result from this underlying melting behavior. The fluid dynamics of unfrozen surfaces holds clues for understanding the bulk behavior of polycrystalline materials, from Earth's mantle to the stratosphere and beyond. In this review we focus on the fluid dynamical consequences of the premelting of solids.

Notes: Homeland security involves many applications of fluid mechanics and offers many opportunities for research and development. This review explores a wide selection of fluids topics in counterterrorism and suggests future directions. Broad topics range from preparedness and deterrence of impending terrorist attacks to detection, response, and recovery. Specific topics include aircraft hardening, blast mitigation, sensors and sampling, explosive detection, microfluidics and labs-on-a-chip, chemical plume dispersal in urban settings, and building ventilation. Also discussed are vapor plumes and standoff detection, nonlethal weapons, airborne disease spread, personal protective equipment, and decontamination. Involvement in these applications requires fluid dynamicists to think across the traditional boundaries of the field and to work with related disciplines, especially chemistry, biology, aerosol science, and atmospheric science.

Notes: Catalyst life (with activity and selectivity) is one of the three essential properties of a practical catalyst, both in laboratory and industrial usage. For most catalysts in which the active phase is a metal, high activity requires a high metal surface area. In all cases, for long life, the metal surface area has to be maintained. The various modes of catalyst deactivation leading to loss of metal surface area are described (sintering, poisoning, coking, etc.). The choice of catalyst components for both active metal phases and for support phases is shown to be subject to thermodynamic and kinetic limits. Routes for the preparation of catalysts need to be and can be designed to give not only active, but also stable catalysts. Examples described include copper/zinc catalysts for hydrogenation/dehydrogenation reactions, iron catalysts for ammonia synthesis, nickel catalysts for hydrogenation reactions, automobile exhaust catalysts, and Raney catalysts.

Notes: The key role of electron microscopy in understanding and creating advanced catalyst materials and processes in selective alkane oxidation, environmental control, and alternative energy sources is reviewed. In many technological processes, catalysts are increasingly nanoscale heterogeneous materials. With growing regulatory guidelines requiring efficient and environmentally compatible catalytic processes, it is crucial to have a fundamental understanding of the catalyst nanostructure and modes of operation under reaction conditions to design novel catalysts and processes. The review highlights the pioneering development and applications of atomic resolution in situ-environmental transmission electron microscopy (ETEM) for probing dynamic catalysis directly at the atomic level, high-resolution electron microscopy, and analytical spectroscopic methods in the development of alkane catalyzation, environmental protection, and new energy sources.

Notes: This article reviews our current understanding of the physical mechanisms governing the movement of a tropical cyclone. In a barotropic framework, a tropical cyclone is basically "steered" by the surrounding flow but its movement is modified by the Coriolis force (referred to as the beta effect) and the horizontal vorticity gradient of the surrounding flow. In the presence of vertical wind shear and latent heat release, a tropical cyclone tends to move toward an area with a maximum in the time tendency of potential vorticity, which is mainly contributed by two processes: (a) advection that depends on the structures of the vortex and the environment surrounding the vortex in terms of their flow speed and vorticity gradient (including the beta effect), and (b) heating that results from a coupling between the latent heat released in the clouds and the vertical wind shear.

Notes: The large-scale dynamics of the extratropical stratosphere are reviewed. The role of Rossby waves and vortex dynamics in shaping the winter stratospheric circulation and the dynamics of the longitudinal mean flow are first discussed separately. The important effects of two-way interaction between waves and mean flow are then described, with emphasis on how mechanisms discovered in simple models can be followed through to models that are closer to the real stratosphere. A final topic is the possible effect of the stratosphere on the troposphere, with emphasis on dynamical mechanisms for such an effect.

Notes: Flow simulations are one of the archetypal multiscale problems. Simulations of turbulent and unsteady separated flows have to resolve a multitude of interacting scales, whereas molecular phenomena determine the structure of shocks and the validity of the no-slip boundary condition. Particle simulations of continuum and molecular phenomena can be formulated by following the motion of interacting particles that carry the physical properties of the flow. In this article we review Lagrangian, multiresolution, particle methods such as vortex methods and smooth particle hydrodynamics for the simulation of continuous flows and molecular dynamics for the simulation of flows at the atomistic scale. We review hybrid molecular-continuum simulations with an emphasis on the computational aspects of the problem. We identify the common computational characteristics of particle methods and discuss their properties that enable the formulation of a systematic framework for multiscale flow simulations.

Notes: 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.

Notes: George Gabriel Stokes died just over 100 years ago, and it has been more than 150 years since he published his great 1847 paper on water waves. The work of Stokes' precursors, which informed his early publications of 1842Đ??50, is described in the previous volume of the Annual Review of Fluid Mechanics ( Craik 2004 ). Here I examine Stokes' papers and letters concerning water waves.

Notes: We review major experimental and theoretical studies on microcirculation and hemorheology, focusing on mechanics of blood flow and the vascular wall. We discuss flow of the blood formed elements [red blood cells (RBCs), white blood cells or leukocytes (WBCs) and platelets] in individual arterioles, capillaries, and venules, and in microvascular networks. We also review mechanical and rheological properties of the formed elements and their interactions with the vascular wall. We discuss short-term and long-term regulation of the microvasculature; the modes of regulation include metabolic, myogenic, and shear-stress-dependent mechanisms as well as vascular adaptation such as angiogenesis and vascular remodeling.

Notes: This article provides a critical review of computational techniques for flow-noise prediction and the underlying theories. Hybrid approaches, in which the turbulent noise source field is computed and/or modeled separately from the far-field calculation, are afforded particular attention. Numerical methods and modern flow simulation techniques are discussed in terms of their suitability and accuracy for flow-noise calculations. Other topics highlighted include some important formulation and computational issues in the application of aeroacoustic theories, generalized acoustic analogies with better accounts of flow-sound interaction, and recent computational investigations of noise-control strategies. The review ends with an analysis of major challenges and key areas for improvement in order to advance the state of the art of computational aeroacoustics.

Notes: We consider the hydrodynamics of creatures capable of sustaining themselves on the water surface by means other than flotation. Particular attention is given to classifying water walkers according to their principal means of weight support and lateral propulsion. The various propulsion mechanisms are rationalized through consideration of energetics, hydrodynamic forces applied, or momentum transferred by the driving stroke. We review previous research in this area and suggest directions for future work. Special attention is given to introductory discussions of problems not previously treated in the fluid mechanics literature, with hopes of attracting physicists, applied mathematicians, and engineers to this relatively unexplored area of fluid mechanics.

Notes: We review mathematical models of confined bubbles, emphasizing physical mechanisms as expressed in simple geometries. Molecular interactions between liquid, gas, and the confining solid are all important and are described through the disjoining pressure concept. Methods for finding static shapes are considered. The static solution is a springboard for discussing pressure-driven and surface-tension-driven flows, both of which involve viscous effects and macroscopic films entrained near apparent contact lines. We next discuss vapor bubbles produced by thermal effects. Vaporization localized near contact lines and condensation distributed in colder parts of the interface lead to steady vapor bubbles. Their size is determined through global constraints. Unsteady vapor bubbles are discussed and we end with thoughts on open problems.

Notes: The review deals with drop impacts on thin liquid layers and dry surfaces. The impacts resulting in crown formation are referred to as splashing. Crowns and their propagation are discussed in detail, as well as some additional kindred, albeit nonsplashing, phenomena like drop spreading and deposition, receding (recoil), jetting, fingering, and rebound. The review begins with an explanation of various practical motivations feeding the interest in the fascinating phenomena of drop impact, and the above-mentioned topics are then considered in their experimental, theoretical, and computational aspects.

Notes: Orogenic collapse is a process that transfers gravitational potential energy from regions of high potential energy to regions of lower potential energy. This transfer is classically considered to be accomplished by extension in the orogenic core and by synchronous shortening in foreland regions of the orogen. Not all extensional features in collisional mountain belts need, however, reflect orogenic collapse. Normal faulting, thrust faulting, and strike-slip faulting are all active in different parts of the Alps today and reflect complex local responses to ongoing Europe-Adria convergence. The Western Alps is the only area today where extension and shortening radial to orogen trend occur synchronously and where orogenic collapse may be an important process. Elsewhere in the Alps, normal faults are oriented at a high angle to orogen trend and were primarily active in Oligocene and Miocene time. Most present-day activity in the Central and Eastern Alps is on strike-slip faults that are accommodating lateral extrusion of material rather than orogenic collapse.

Notes: The bulk of the Đ♯50-km-thick Martian crust formed at Đ♯4.5 Gyr B.P., perhaps from a magma ocean. This crust is probably a basaltic andesite or andesite and is enriched in incompatible and heat-producing elements. Later additions of denser basalt to the crust were volumetrically minor, but resurfaced significant portions of the Northern hemisphere. A significant fraction of the total thickness of the crust was magnetized prior to 4 Gyr B.P., with the magnetization later selectively removed by large impacts. Early large impacts also modified the hemispheric contrast in crustal thickness (the dichotomy), which was possibly caused by long-wavelength mantle convection. Subsequent Noachian modification of the crust included further impacts, significant fluvial erosion, and volcanism associated with the formation of the Tharsis rise. Remaining outstanding questions include the origin of the dichotomy and the nature of the magnetic anomalies.

Notes: Recent fossil discoveries from Early Cretaceous rocks of Liaoning Province, China, have provided a wealth of spectacular specimens. Included in these are the remains of several different kinds of small theropod dinosaurs, many of which are extremely closely related to modern birds. Unique preservation conditions allowed soft tissues of some of these specimens to be preserved. Many dinosaur specimens that preserve feathers and other types of integumentary coverings have been recovered. These fossils show a progression of integumentary types from simple fibers to feathers of modern aspect. The distribution of these features on the bodies of these animals is surprising in that some show large tail plumes, whereas others show the presence of wing-like structures on both fore and hind limbs. The phylogenetic distribution of feather types is highly congruent with models of feather evolution developed from developmental biology.

Notes: We know that giant planets played a crucial role in the making of our Solar System. The discovery of giant planets orbiting other stars is a formidable opportunity to learn more about these objects, what their composition is, how various processes influence their structure and evolution, and most importantly how they form. Jupiter, Saturn, Uranus, and Neptune can be studied in detail, mostly from close spacecraft flybys. We can infer that they are all enriched in heavy elements compared to the Sun, with the relative global enrichments increasing with distance to the Sun. We can also infer that they possess dense cores of varied masses. The intercomparison of presently characterized extrasolar giant planets shows that they are also mainly made of hydrogen and helium, but that they either have significantly different amounts of heavy elements, have had different orbital evolutions, or both. Hence, many questions remain and need to be answered to make significant progress on the origins of planets.

Notes: Airborne geophysics has been used to identify more than 100 lakes beneath the ice sheets of Antarctica. The largest, Lake Vostok, is more than 250 km in length and 1 km deep. Subglacial lakes occur because the ice base is kept warm by geothermal heating, and generated meltwater collects in topographic hollows. For lake water to be in equilibrium with the ice sheet, its roof must slope ten times more than the ice sheet surface. This slope causes differential temperatures and melting/freezing rates across the lake ceiling, which excites water circulation. The exploration of subglacial lakes has two goals: to find and understand the life that may inhabit these unique environments and to measure the climate records that occur in sediments on lake floors. The technological developments required for in situ measurements mean, however, that direct studies of subglacial lakes may take several years to happen.

Notes: The Ediacara biota (575Đ??542 Ma) marks the first appearance of large, architecturally complex organisms in Earth history. Present evidence suggests that the Ediacara biota included a mixture of stem- and crown-group radial animals, stem-group bilaterian animals, "failed experiments" in animal evolution, and perhaps representatives of other eukaryotic kingdoms. These soft-bodied organisms were preserved under (or rarely within) event beds of sand or volcanic ash, and four distinct preservational styles (Flinders-, Fermeuse-, Conception-, and Nama-style) profoundly affected the types of organisms and features that could be preserved. Even the earliest Ediacaran communities (575Đ??565 Ma) show vertical and lateral niche subdivision of the sessile, benthic, filter-feeding organisms, which is strikingly like that of Phanerozoic and modern communities. Later biological and ecological innovations include mobility (〉555 Ma), calcification (550 Ma), and predation (〈549 Ma). The Ediacara biota abruptly disappeared 542 million years ago, probably as a consequence of mass extinction andor biological interactions with the rapidly evolving animals of the Cambrian explosion.

Notes: Contrary to Earth, the interior of terrestrial planets is poorly known. This is mainly related to the lack of seismic data and of planetary seismic networks on these planets. So far, despite several attempts, only the Apollo Seismic Network has returned seismic information from the Moon. But even in this case, very few seismic signals were recorded after a propagation path through the deep interior and core owing to a hemispheric distribution of the stations on the near side and to a probably strongly attenuating lower mantle. This review presents the main results achieved by the analysis of the Apollo seismic data and the associated constraints on the internal structure of the Moon. It then presents the current knowledge on the Martian interior, the seismic activity of the planet, and possible source of seismic noise. This information can be used for preparing future Martian seismic network missions. A short review on existing space-qualified instruments and on possible seismic missions toward other telluric bodies, such as Venus, the giant planets' satellites, or small bodies, is then given.