bluuebunny/crossref_metadata_2025 huggingface dataset:
Interrelationships between Light and Phytoplankton in the Sea
Authors: Kishino Motoaki
Published: November 2020

Light energy penetrating the sea is diminished almost exponentially with depth with an accompanying drastic change in the energy spectrum as the result of absorption by various components in the seawater. Such a change in the light environment will affect phytoplankton life directly. Accordingly, in the study of light in the sea, much attention has been drawn toward the contribution of phytoplankton to the light field and also how much energy or which parts of the light spectrum are utilized at various depths by phytoplankton. Spectral distribution of underwater irradiance is determined by the processes of absorption and scattering from various components of the seawater. Since absorption plays a much more important role in spectral variation than scattering (Preisendorfer, 1961), the spectral absorption of each component should be studied in order to adequately interpret the variation of spectral irradiance in the sea. The materials absorbing light are phytoplankton, other particles, dissolved organic substances, and the water itself. Spectral characteristics of the light environment in the sea are determined by the variable ratios of these components. Several authors have attempted to measure directly the spectral absorption of individual components in seawater (Kirk, 1980; Okami et al., 1982; Kishino et al., 1984; Carder and Steward, 1985; Weidemann and Bannister, 1986). However, the determination of the absorption coefficient of natural phytoplankton is quite difficult, because no suitable technique is available for the direct measurement of absorption. Accordingly, there is still considerable uncertainty about light absorption by phytoplankton under natural conditions. Phytoplankton photosynthetic efficiency is important for the algae as well as the other organisms in the same ecosystem. Photosynthetic efficiency can be estimated fundamentally from quantum yield, which is obtained by measuring three parameters: photosynthetic rate, spectral downward irradiance, and the spectral absorption coefficient of phytoplankton. The optical system of a recently designed spectral irradiance meter is shown in Fig. 4-1. The meter has two independent cosine collectors that receive downward and upward spectral irradiance, respectively, by rotation of the mirror placed behind the collectors. After collimation, light reflected by the mirror is separated by a beam splitter.
Renewable Energy from the Ocean
Authors: Avery William H. , Wu Chih
Published: November 2020

Scientists and engineers around the world are striving to develop new sources of energy. One source, ocean thermal energy conversion, has virtually unlimited potential. It is based on techniques that exploit heat produced by solar energy that may, in turn, be used to produce fuel and electricity. This book reviews the status and background of this promising technology. William H. Avery is the leading expert in this field, and his co-author Chih Wu is an authority on heat engine performance. Together they describe the workings of an OTEC power plant and how such a system might be implemented as part of a futuristic national energy strategy. The book is the only detailed presentation of basic OTEC technology, its testing and improvement. It is based on extensive development initiatives undertaken internationally during the period from 1974 through 1985. The book offers a thorough assessment of the economics of OTEC in comparison with other energy production methods. It will be of interest to a wide range of professionals in energy research, power and mechanical engineering, and to upper-level undergraduate students taking courses in these fields.
Adolescents at Risk
Authors: Dryfoos Joy G.
Published: November 2020

Seven million youngsters--one in four adolescents--have only limited potential for becoming productive adults because they are at high risk for encountering serious problems at home, in school, or in their communities. This is one of the disturbing findings in this unique overview of what is known about young people aged 10 to 17 growing up in the United States today. The book explores four problem areas that are the subject of a great deal of public interest and social concern: delinquency, substance abuse, teen pregnancy, and school failure. In examining these problem areas, Dryfoos has three objectives: to present a more cogent picture of adolescents who are at risk of problem behaviors and where they fit in society; to synthesize the experience of programs that have been successful in changing various aspects of these behaviors; and to propose strategies for using this knowledge base to implement more effective approaches to helping youngsters succeed. Among the key concepts emerging from this study are the importance of intense individual attention, social skills training, exposure to the world of work, and packaging components in broad, community-wide interventions. Schools are recognized as the focal institution in prevention, not only in regard to helping children achieve academically, but in giving young people access to social support and health programs. The author also proposes comprehensive youth development initiatives at the local, state and national level, based on programs shown to be effective in real practice. This landmark, state-of-the-art study represents an indispensable resource for anyone interested in the welfare and current problems of youth, including psychologists, sociologists, school administrators, state and federal officials, policymakers, and concerned parents.
Water Management in Ancient Greek Cities
Authors: Crouch Dora P.
Published: November 2020

Focusing on the Mediterranean area where water management is crucial, this pioneering study is the first to show how the supply, distribution, and drainage of water contributed to the urbanization of ancient cities. Drawing from classical archaeology, the theory and history of urbanization, geology, and hydraulic engineering, Crouch examines water-system elements, including springs, fountains, wells, channels and drains, latrines, laundry, and dishwashing, as they relate to each other and to the physical, historical, and social bases of ancient Greek cities. Studying numerous sites including Pompeii, Pergamon, Athens, Samos, Delphi, and Corinth, she concludes that increased knowledge and skill in management of water contributed directly to the urbanization of the ancient Greek world. Illustrated with excellent photographs and line drawings, the discussions of supply, distribution, and drainage of water are organized topically, rather than chronologically or by site, offering an excellent example of the interdisciplinary approach. Crouch's study raises stimulating questions for further research, indicates entirely new directions for established academic disciplines, and suggests useful procedures for modern cities facing problems of water supply and management.
Karst: The Hydrogeological Basis of Civilization
Authors: Crouch Dora P.
Published: November 2020

A whole series of questions flows from Loy’s general understanding, such as: Was there a particular sort of land form associated with ancient Greek settlements? Were settlements always located at springs, and did springs always have settlements? Why were there springs in some places and not in others, in what seemed to be the same sort of terrain? How much have the typography and the water resources changed since antiquity? How much did they change in the last 800 years B.C.? What can we tell about the water resources of antiquity from observing the modern situation? What were the relationships between ancient Greek settlements and the occurrence of karst phenomena? Was karst a geological form that had special relevance to water resource management in ancient Greece? Answers to some of these questions will become apparent as we discuss the geological aspects of ancient Greek urban history. Man-environment relations, in the ancient Greek world as elsewhere, were complex interactions of mode, duration, and intensity of human interference with the initial site conditions and with the climatic and biotic flux, affected by the resilience of the ecosystem. To understand these human communities in their physical setting, we need to study a range of features, many complex interactions, and man’s impact on the setting, realizing that our research goals and those of other experts may be widely divergent. Such complex interactions are called socionatural systems by J. W. Bennett (1976, 22). The condition of the watersheds of the hinterlands, in good times and bad, is directly pertinent to the ability of cities to extract water and transport it to municipal users. Hence the problems of erosion are not irrelevant to our topic—the management of water and the process of urbanization (Thrower and Bradbury, 1973, 59 –78; Aschmann, 1973, 362 –66). The thin, barren soil of these rocky peninsulas and islands is the result of climate not man. At the least, the currently observable extensive and permanent deforestation of uplands is locally a very recent phenomena (after the Younger Fill, to be discussed later) and therefore not a cause but a result of existing conditions.
Planning Water Quality: Potable and Subpotable Water at Selinus and Priene
Authors: Crouch Dora P.
Published: November 2020

Today when the rigors of an arid climate (Arabia) or other constraints on water resources press the limits of water supply, hydraulic engineers have to reconsider the nineteenth century answer of one quality of water for all uses. In places where population density far exceeds the supply of potable water—Hong Kong—or where the scanty spring water is not enough to support the massive tourist industry—Bermuda—(Deb, 1987, 222) there is no choice but to use subpotable or nonpotable water whenever feasible. Absolute scarcity of drinking-quality water is the strongest reason for water managers today to consider alternate procedures, but in some situations the quality not quantity of water is the issue. Heavy metals, long-lasting pesticides, or other carcinogens may require separation of the purest supply for drinking and cooking from the less pure supply for other uses, lest the water itself cause disease during a lifetime of use. Since potable water amounts to a small fraction of use in a modern city—6 percent or less (J. Thapa, personal communication)—alternative delivery systems for that small amount may be feasible, with the main systems delivering subpotable water for bathing, cleaning, watering lawns, and so on, and nonpotable water for industry or irrigation. It is easier to contemplate in theory these logical divisions than to make actual plans for altering the delivery system in metropolitan water districts. Political and economic realities restrict change in built-up areas unless the danger is severe, but in some new suburbs in Florida dual pipelines are laid for potable water inside the house and subpotable outside. Drinking bottled water is becoming more common. Many municipal water systems now supply partially purified (nonpotable) water to industry for cooling or other processes. Still, these new ideas have not been widely implemented to date. It is unexpected, then, to find that the ancient Greeks had just such a triple system of water supply and reuse. Each Greek city had both public fountains and springs supplying flowing water of the best quality, and private cisterns in houses and public buildings to supply still water of good quality, plus a drain system that led used water outside the city.
The Academic Vocation
Authors: Schwehn Mark R.
Published: November 2020

In this chapter, I shall try to advance our thinking about college and university education in the United States through a critical study of contemporary conceptions of the academic vocation. Current reflection upon the state of higher learning in America makes this task at once more urgent and more difficult than it has ever been since the rise of the modern research university. Consider, for example, former Harvard President Derek Bok’s 1986–87 report to the Harvard Board of Overseers. On the one hand, Bok repeatedly insists that universities are obliged to help students learn how to lead ethical, fulfilling lives. On the other hand, he admits that faculty are ill-equipped to help the university discharge this obligation. “Professors,” Bok writes, “. . . are trained to transmit knowledge and skills within their chosen discipline, not to help students become more mature, morally perceptive human beings.” Notice Bok’s assumptions. Teaching history or chemistry or mathematics or literature has little or nothing to do with forming students’ characters. Faculty members must therefore be exhorted, cajoled, or otherwise maneuvered to undertake this latter endeavor in addition to teaching their chosen disciplines. The pursuit of knowledge and the cultivation of virtue are, for Bok at least, utterly discrete activities. To complicate matters still further, the Harvard faculty, together with most faculty members at other modern research universities, would very probably resist the notion that their principal vocational obligation is, as Bok suggested, to transmit the knowledge and skills of their disciplines. They believe that their calling primarily involves making or advancing knowledge, not transmitting it. How else could we explain the familiar academic lament “Because this is a terribly busy semester for me, I do not have any time to do my own work”? Among all occupational groups other than the professoriate, such a complaint, voiced under conditions of intensive labor, is inconceivable. Among university faculty members, it is expected. Never mind the number of classes taught, courses prepared, papers graded, and committees convened.
Antiplane Deformations
Authors: Ting T. T. C.
Published: November 2020

As a starter for anisotropic elastostatics we study special two-dimensional deformations of anisotropic elastic bodies, namely, antiplane deformations. Not all anisotropic elastic materials are capable of an antiplane deformation. When they are, the inplane displacement and the antiplane displacement are uncoupled. The deformations due to inplane displacement are plane strain deformations. Associated with plane strain deformations are plane stress deformations. After defining these special deformations in Sections 3.1 and 3.2 we present some basic solutions of antiplane deformations. They provide useful references for more general deformations we will study in Chapters 8, 10, and 11. The derivation and motivation in solving more general deformations in those chapters become more transparent if the reader reads this chapter first. The solutions obtained in those chapters reduce to the solutions presented here when the materials are restricted to special materials and the deformations are limited to antiplane deformations. In a fixed rectangular coordinate system xi (i=1, 2, 3), let ui, σij, and εij be the displacement, stress, and strain, respectively. The strain-displacement relations and the equations of equilibrium are . . .εij = 1/2 (ui,j + uj,i),. . . . . . (3.1 -1) . . . . . .σij,j =0,. . . . . . (3.1 - 2). . . in which repeated indices imply summation and a comma stands for differentiation. The stress-strain laws for an anisotropic elastic material can be written as σij = Cijks εks or εij = Sijksσks, . . .(3.1 - 3). . . where Cijks and Sijks are, respectively, the elastic stiffnesses and
compliances.
Particular Solutions, Stress Singularities, and Stress Decay
Authors: Ting T. T. C.
Published: November 2020

Not all boundary value problems are amenable to a simple analytical solution. This is particularly the case when the geometry of the boundary on which the boundary conditions are specified contains a corner. A crack tip is a special corner. When an analytical solution for the entire region is not available, asymptotic solutions near the corner can be obtained which provide useful information on the nature of stress singularities at the corner. They also provide more accurate numerical solutions by a finite element scheme in which the asymptotic solution at the corner is employed in a special element at the corner with regular elements elsewhere (see, for example, Stolarski and Chiang, 1989). Other information that can be obtained by an asymptotic analysis is the decay factor of stress at a large distance from a point at which a self-equilibrated load is applied (Crafter, et al., 1993). For singularities that arise in non-linear elastic materials the reader is referred to the book by Antman (1995). As in Chapter 8 most solutions can be expressed in a real form with the aid of identities presented in Chapters 6 and 7.
Work at the Interface: Advanced Manufacturing Technology and Job Design
Authors: Martin Corbett J.
Published: November 2020

The currently dominant view among researchers interested in advanced manufacturing technology (AMT) and job design is that an organization’s choice of job design options—whether skill based or management-control oriented—is socially determined and independent of any technological constraint. Technology is seen as effectively neutral. From the perspective of such research, skill-based production system design is achieved through judicial redesign of organizational variables such as supervisory style, training, role, responsibilities, and/or decentralization of decision making. This view, which one may term technological indeterminism, is summed up by Buchanan (1983), who declares that technological imperatives are weak while organizational choice is strong. The aims of this chapter are twofold. The key theoretical aim is to explore the extent to which the development of skill-based production systems may be constrained by the production technology being utilized within a manufacturing organization. Within the social science research literature examining the relationship between AMT and job design, this is a fundamental, yet largely unanswered, question. A second, related aim is more practical: to examine the ways in which social scientists, users, and others can (re)shape the design and implementation of AMT in order to reduce or remove such constraints. This examination is aided by the inclusion of a number of case examples. I will argue that, although organizational variables are undoubtedly important in the development of skill-based production systems, the neglect of technological variables and the reluctance to open the “black box” of technology may seriously undermine the validity of organization-centered research programs in the longer term. Developments in the theory and practice of “human-centered technology” will be used to support this line of argument. The chapter is in five parts. In the first part, the case against technological indeterminism is examined. This is followed by a brief argument to support the case for a “soft” technological determinism that views the relationship between technology and job design as one in which the design of hardware and software technology may constrain key aspects of job design choice. In the third part, the background to two international project case studies is given.
Computer Graphics Modeling for Virtual Environments
Authors: Green Mark , Sun Hanqiu
Published: November 2020

Modelling is currently one of the most important areas in virtual environments research (Bishop et al., 1992). Of all the software areas, this is the area that we know the least about. Modelling has been an active research area in computer graphics for many decades, and is still a major research area. Many of the modelling issues addressed in computer graphics and virtual environments are also of concern to researchers in robotics, mechanical engineering and biomechanics, so progress in modelling can have an impact on many fields. Modelling is difficult since most of the objects that we would like to model, such as people, animals, and airplanes, are quite complex. They have a large amount of geometrical detail and move in complex ways. This difficulty is compounded by the different fields that use modelling techniques, since each field has its own requirements and priorities. For example, it is highly unlikely that the same model of a human figure would be optimal for applications in both virtual environments and biomechanics. The following criteria can be used as a basis for evaluating different modelling techniques. Accuracy. The model should be an accurate representation of the real-world object. Ideally, we would like all of our models to be precise representations of the real-world objects, and not simply approximations to them. But, in reality accuracy comes with a price, usually increased display time or memory usage. The amount of accuracy required often depends upon the application. For example, in some applications it is acceptable to approximate a sphere with a large number of polygons, but for a large number of computer-aided design (CAD) applications the precise mathematical representation of the sphere is required. Since the polygonal representation can be drawn faster, it is often used in applications where display speed is more important than accuracy. Display speed. Many applications place restrictions on the time available to display individual objects. In the case of interactive applications, short display times increase the level of interaction between the user and the model. In large CAD applications there may be many objects, therefore, the time required to display individual objects becomes an important consideration in the usability of the application even if a high level of interactivity is not required.
Multidimensional Programming
Authors: Ashcroft E. A. , Faustini A. A. , Jaggannathan R. , Wadge W. W.
Published: November 2020

This book describes a powerful language for multidimensional declarative programming called Lucid. Lucid has evolved considerably in the past ten years. The main catalyst for this metamorphosis was the discovery that Lucid is based on intensional logic, one commonly used in studying natural languages. Intensionality, and more specifically indexicality, has enabled Lucid to implicitly express multidimensional objects that change, a fundamental capability with several consequences which are explored in this book. The author covers a broad range of topics, from foundations to applications, and from implementations to implications. The role of intensional logic in Lucid as well as its consequences for programming in general is discussed. The syntax and mathematical semantics of the language are given and its ability to be used as a formal system for transformation and verification is presented. The use of Lucid in both multidimensional applications programming and software systems construction (such as a parallel programming system and a visual programming system) is described. A novel model of multidimensional computation--education--is described along with its serendipitous practical benefits for harnessing parallelism and tolerating faults. As the only volume that reflects the advances over the past decade, this work will be of great interest to researchers and advanced students involved with declarative language systems and programming.
Thermally Driven Flows
Authors: Furbish David Jon
Published: November 2020

Recall that we briefly examined the stability of thermally stratified fluids in Chapter 6. Our essential conclusion was that a condition in which hot, light fluid resides beneath cooler, heavier fluid is a potentially unstable configuration, inasmuch as gravitational forces are no longer balanced by forces associated with the vertical pressure gradient. In this regard we obtained a necessary (but insufficient) condition for instability, which stated that the magnitude of the vertical temperature gradient must exceed the adiabatic lapse rate. Further recall, however, that such a condition does not necessarily lead spontaneously to overturning (convection). It is possible for a fluid to possess a steady temperature gradient over its vertical extent, in excess of the adiabatic rate, such that the fluid remains static and merely acts like a thermally conducting solid, and we concluded that this static conduction state represents an unstable equilibrium. We then characterized the tendency for instability in terms of the Rayleigh number Ra. Let us now extend our treatment to a description of thermally driven convection motions. We will concentrate on Rayleigh-Bénard and Hele-Shaw configurations (Chapter 6), and the buoyancy-driven flows that occur within these configurations due to steady heating and cooling of the boundaries. In such configurations, convective motions typically occupy the full region between the boundaries, and vary from steady two-dimensional rolls at small Rayleigh numbers to complex turbulent motions at large Rayleigh numbers. In addition, we will briefly consider buoyancy driven flows that arise from localized temperature and compositional variations near a single solid boundary. Envision, for example, the roof of a magma chamber. For a sufficient contrast in temperature between the magma and country rock, melting of the magma roof occurs. If the density of the melt that is produced is less than that of the underlying magma, thermally driven convection may begin within the buoyant layer of melt, which in turn advects heat upward from the underlying hot magma to the roof. Alternatively, if the density of the melt is greater than that of the underlying magma, compositionally driven convection may occur, which in turn brings hot magma to the roof.
Cognitive Variability: The Ubiquity of Multiplicity
Authors: Siegler Robert S.
Published: November 2020

No one doubts that immense variability exists at the neural level. Even when the identical stimulus is presented repeatedly within a single experimental session, the response of an individual neuron varies from trial to trial. Similarly, with lowlevel cognitive processes such as association, there is no disagreement concerning the existence of competing units. Models of associative memory, both symbolic (e.g., Gillilund & Shiffrin, 1984) and subsymbolic (e.g., Seidenberg & McClelland, 1990), are predicated on the assumptions that stimuli have multiple associations and that these varying associations influence the way in which we remember. Higher level cognition, however, has been treated differently. Many models are universalist: Everyone is depicted as proceeding in the same way when relevant stimuli are presented. Other models are comparative; they hypothesize different ways of thinking among groups defined on the basis of such characteristics as age, expertise, or aptitudes, but hypothesize a single consistent kind of reasoning within each group. Thus, 8-year-olds might be depicted as performing in one way and 5-year-olds in another, experts in one way and novices in another, people with high spatial ability in one way and those with low spatial ability in another, and so on. The finest differentiations that are typically made within these comparative approaches examine individual differences within people of a single age; for example, reflective 8-year-olds are described as taking a long time but answering accurately on the Matching Familar Figures Test, and impulsive 8-year-olds are described as answering more quickly but less accurately (Kogan, 1983). The main purpose of this chapter is to summarize the rapidly growing body of research suggesting that variability is actually a pervasive reality in high-level, as well as low-level, cognition. To place this work in context, however, it seems useful first to briefly consider some prominent examples of universalist and comparative models of cognition and then to consider why they might be proposed and widely accepted even if thinking is far more variable than they depict it as being. A great deal of cognitive research has been devoted to identifying the processing approach that people use on a particular task. This universalist approach has led to many influential models and theories.
Trying to Escape Malthus
Authors: Hardin Garrett
Published: November 2020

Before Malthus appeared on the scene, William Godwin recognized that the expanding population might ultimately produce an unfavorable ratio of population to resources which could create a problem. Five years later Malthus viewed this problem as an inevitable result of human nature reacting to a world of limits. Godwin, however (in the passage previously quoted at the end of Box 3-1) had proposed to solve the population by changing human nature. He suggested that some day our species might "cease to propagate." Since this was written in England two hundred years ago, in the absence of contradictory evidence we can only assume that Godwin was postulating an end to human sexual activity. He no doubt thought the sacrifice would be worthwhile because, in his Utopia, there would be "no war, no crimes, no administration of justice, as it is called, and no government. Besides this, there will be neither disease, anguish, melancholy, nor resentment." Most of Godwin's suppositions are too ridiculous to linger over, but one of them deserves an extended analysis because it touches on a general principle that will be called upon repeatedly as we continue to look for ways to avoid overpopulation. There is not the ghost of a chance that the human species will ever "cease to propagate." The reason is found in the great discovery made by Charles Darwin sixty years later: selection. Suppose, following Godwin, that the natural fertility of our species evolves almost all the way to zero. Then what? Initially, fertile individuals might be but a tiny minority of the whole; but, over time, selection would ensure the dominance of the fertile fraction. If there were even the slightest genetic basis for fecundity in human beings (as indeed there is in other animals) then fertile human beings would in time replace the infertile. To postulate a selection for universal sterility (as Godwin's scheme would require) is to perpetrate an oxymoron. Nature does not work with oxymorons. We who are alive now are the descendents of an unbroken line of fertile ancestors. This line extends back millions of years to the first humanoids—indeed, billions of years to the beginning of sexual life of any kind. Powerful though she is, Nature cannot create a self-sustaining, totally infertile, sexual species.
John Tyndall, Svante Arrhenius, and Early Research on Carbon Dioxide and Climate
Authors: Fleming James R.
Published: November 2020

In the second half of the nineteenth century two prominent scientists, working in two distinct specialties, identified the importance of atmospheric trace constituents as efficient absorbers of long-wave radiation and as factors in climatic control. John Tyndall conducted the first convincing experiments on the radiative properties of gases, demonstrating that “perfectly colorless and invisible gases and vapours” were able to absorb and emit radiant heat. Svante Arrhenius, in pursuing his interests in meteorology and cosmic physics, demonstrated that variations of atmospheric CO2 concentration could have a very great effect on the overall heat budget and surface temperature of the planet. It would be a mistake, however, to consider either of these individuals as direct forerunners or prophets of contemporary climate concerns. Each of them had extremely broad scientific interests and pursued climate-related research as one interest among many. Tyndall worked on absorption in the near infrared at temperatures far above those of the terrestrial environment. Arrhenius, who has recently gained renewed attention as the “father” of the theory of the greenhouse effect, held assumptions and produced results that are not continuous with present-day climate research. . . . The solar heat possesses, in a far higher degree than that of lime light, the power of crossing an atmosphere; but, when the heat is absorbed by the planet, it is so changed in quality that the rays emanating from the planet cannot get with the same freedom back into space. Thus the atmosphere admits of the entrance of the solar heat, but checks its exit; and the result is a tendency to accumulate heat at the surface of the planet. —John Tyndall (1859). . . John Tyndall was born in Leighlin Bridge, County Carlow, Ireland, on August 2, 1820, the son of a part-time shoemaker and constable. He attended the national school in Carlow and, at the age of eighteen, joined the Irish Ordnance Survey as a draftsman and surveyor. In 1842, as the Irish survey neared completion, Tyndall was transferred to the English Survey at Preston, Lancashire, but due to his protests against the survey’s oppressive policies and incompetent management, he was dismissed.
Bulk Ultrasonic Techniques for Evaluation of Elastic Properties
Authors: Chimenti Dale , Rokhlin Stanislav , Nagy Peter
Published: November 2020

Currently, the design of most composite components is based on stiffness, and therefore methods for static measurement of stiffness are in wide use. The disadvantages of these methods lie in their destructive nature (the samples must be cut from parts of different orientations), in the difficulty of measuring shear properties, and in the need for extra care when measuring Young’s modulus in off-axis directions. Ultrasonic methods are more accurate and have higher spatial resolution than static measurements. As we showed in Chapter 2, by measuring ultrasonic velocities in several predefined directions, all elastic constants can be determined. The generic method described there is also destructive, however, requiring cutting numerous samples with appropriate fiber orientation. Specialized nondestructive methods for determining the elastic moduli of composite materials are more powerful and they can be applied to composite coupons before, during, and after strength or fatigue testing. It is important to have a fast and inexpensive technique to estimate input parameters for composite design. It is even more important to have a technique to evaluate composites during service to verify that the manufactured elastic stiffnesses match those assumed in the design. Several methods that utilize bulk ultrasonic waves for measurement of composite elastic constants are considered in this chapter. By bulk wave methods, we mean quasilongitudinal and quasitransverse ultrasonic wave velocity measurement methods that are applicable when the sample thickness h is larger than both the ultrasonic pulse space length τV and the wavelength λ (τ is the ultrasonic pulse length in time, and V is the wave speed). Other methods, which are applicable in the range h < τV and which account for wave interference with the boundaries of the specimen, will be considered in the following chapters. The most promising way to evaluate composite elastic properties nondestructively is to measure ultrasonic velocities in different directions in the composite material and reconstruct the elastic constants from these values using some kind of an inversion technique. One possible method has been suggested by Markham in the 1970s, who used ultrasonic waves obliquely incident from water onto a composite plate to measure ultrasonic velocities in various directions and evaluated the results to determine elastic constants.
Guided Waves in Plates and Rods
Authors: Chimenti Dale , Rokhlin Stanislav , Nagy Peter
Published: November 2020

In this chapter we consider elastic wave modes which propagate in composites with finite boundaries. There are those waves that exist between the two plane parallel boundaries of a homogeneous anisotropic solid. We consider that well-known problem, as well as waves in an elastic anisotropic rod, specifically an individual graphite fiber. Composite laminates seen in applications are essentially all multilayered structures, and in many cases can be considered periodically layered. So, we also take up the subject of guided waves in layered plates in later chapters. In a plate geometry, as illustrated in Fig. 5.1, we choose the propagation direction to be parallel to the x1 axis and the x3 axis to be normal to the plate surfaces. This geometry is particularly significant for composite materials since, by design, laminates are often locally planar in nature. While the solutions we find are appropriate for flat plates, with some modifications they describe wave motion in gently curved structures as well. Clear and mathematically straightforward descriptions of the characteristics of plate waves exist for isotropic media. The results obtained for isotropic media are not, however, directly applicable to most composites. We begin by considering the behavior of waves in a uniaxial composite laminate. In later chapters we generalize the calculation to layered orthotropic media, concentrating on the results and physical interpretation rather than the algebraic details. To begin a description of waves in plates, let us consider the possible polarizations of particle motion. Let the plate surfaces lie in the (x1, x2) plane of mirror symmetry with the origin dividing the plate thickness in half, as shown in Fig. 5.1. Then, we will at first assume the wave to be uniform in the x2 direction and propagating in the x1 direction, and (x1, x3) is the plane of symmetry. Particle motion can occur along any axis. Note that in this restricted symmetry, shear partial waves polarized along the x2 axis will have no component of particle motion normal to the plate surfaces. Partial waves are a concept introduced by Rayleigh to acknowledge that a superposition of both shear and longitudinal particle motion is generally needed to produce plate waves polarized in the vertical plane.
Measurement of Scattering Coefficients
Authors: Chimenti Dale , Rokhlin Stanislav , Nagy Peter
Published: November 2020

In the previous chapters, we saw how waves in composites behaved under various circumstances, depending on material anisotropy and wave propagation direction. The most important function that describes guided wave propagation, and the plate elastic behavior on which propagation depends, is the reflection coefficient (RC) or transmission coefficient (TC). More generally, we can call either one simply, the scattering coefficient (SC). It is clear that the elastic properties of the composite are closely tied to the SC, and in turn the scattering coefficient determines the dispersion spectrum of the composite plate. Measuring the SC provides a route to the inference of the elastic properties. To measure the SC, we need only observe the reflected or transmitted ultrasonic field of the incident acoustic energy. In doing so, however, the scattered ultrasonic field is influenced by several factors, both intrinsic and extrinsic. Clearly, the scattered ultrasonic field of an incident acoustic beam falling on the plate from a surrounding or contacting fluid will be strongly influenced by the RC or TC of the plate material. The scattering coefficients are in turn dependent on the plate elastic properties and structural composition: fiber and matrix properties, fiber volume fraction, layup geometry, and perhaps other factors. These elements are not, however, the only ones to determine the amplitude and spatial distribution of energy in the scattered ultrasonic field. Extrinsic factors such as the finite transmitting and receiving transducers, their focal lengths, and their placement with respect to the sample under study can make contributions to the signal as important as the SC itself. Therefore, a systematic study of the role of the transducer is essential for a complete understanding and correct interpretation of acoustic signals in the scattered field. The interpretation of these signals leads ultimately to the inference of composite elastic properties. As we pointed out in Chapter 5, the near coincidence under some conditions of guided plate wave modes with the zeroes of the reflection coefficient (or peaks in the transmission coefficient) has been exploited many times to reveal the plate’s guided wave mode spectrum.
Optimal Approximation Methods
Authors: Kowalski Marek A. , Sikorski Krzystof A. , Stenger Frank
Published: November 2020

In this chapter we outline a theory of optimal computational methods for general, nonlinear approximation problems. We define the notions of optimal algorithms and information, and we analyze the classes of parallel and sequential methods. We put special emphasis on linear problems as well as linear and spline algorithms. Several relationships between optimal methods and n-widths and s-numbers are also exhibited.
Algebraic Theory of Molecules
Authors: Iachello F. , Levine R. D.
Published: November 2020

Algebraic Theory of Molecules presents a fresh look at the mathematics of wave functions that provide the theoretical underpinnings of molecular spectroscopy. Written by renowned authorities in the field, the book demonstrates the advantages of algebraic theory over the more conventional geometric approach to developing the formal quantum mechanics inherent in molecular spectroscopy. Many examples are provided that compare the algebraic and geometric methods, illustrating the relationship between the algebraic approach and current experiments. The authors develop their presentation from a basic level so as to enable newcomers to enter the field while providing enough details and concrete examples to serve as a reference for the expert. Chemical physicists, physical chemists, and spectroscopists will want to read this exciting new approach to molecular spectroscopy.
The Wave Mechanics of Diatomic Molecules
Authors: Iachello F. , Levine R. D.
Published: November 2020

The spectroscopy of diatomic molecules (Herzberg, 1950) serves as a paradigm for the study of larger molecules. In our presentation of the algebraic approach we shall follow a similar route. An important aspect of that presentation is the discussion of the connection to the more familiar geometrical approach. In this chapter we survey those elements of quantum mechanics that will be essential in making the connection. At the same time we also discuss a number of central results from the spectroscopy of diatomic molecules. Topics that receive particular attention include angular momentum operators (with a discussion of spherical tensors and the first appearance of the Wigner-Eckart theorem which is discussed in Appendix B), transition intensities for rovibrational and Raman spectroscopies, the Dunham expansion for energy levels, and the Herman- Wallis expansion for intensities. Two-body quantum mechanical systems are conveniently discussed by transforming to the center-of-mass system. The momentum (differential) operator for the relative motion is . . .p = − iħ∇ . . . . . .(1.1). . . where ∇ is the gradient operator whose square ∇ • ∇ is the Laplacian and, as usual, i2 = − 1 and ħ is Planck’s constant/2π.
Three-body Algebraic Theory
Authors: Iachello F. , Levine R. D.
Published: November 2020

In the previous chapter we discussed the usual realization of many-body quantum mechanics in terms of differential operators (Schrödinger picture). As in the case of the two-body problem, it is possible to formulate many-body quantum mechanics in terms of algebraic operators. This is done by introducing, for each coordinate r1,r2,... and momentum p1, p2, . . . , boson creation and annihilation operators, b†iα, biα. The index i runs over the number of relevant degrees of freedom, while the index α runs from 1 to n + 1, where n is the number of space dimensions (see note 3 of Chapter 2). The boson operators satisfy the usual commutation relations, which are for i ≠ j, . . . [biα, b†jα´] = 0, [biα, bjα´] = 0,. . . . . .[bjα, b†iα´] = 0, [b†jα, b†iα´] = 0,. . . . . . [biα, b†iα´] = ẟαα´, [biα, b†iα´] = 0, [b†iα, b†iα´] = 0. . . .
Multiphase Systems
Authors: Erman Burak , Mark James E.
Published: November 2020

One class of multiphase elastomers are those capable of undergoing strain-induced crystallization, as was discussed separately in chapter 12. In this case, the second phase is made up of the crystallites thus generated, which provide considerable reinforcement. Such reinforcement is only temporary, however, in that it may disappear upon removal of the strain, addition of a plasticizer, or increase in temperature. For this reason, many elastomers (particularly those which cannot undergo strain-induced crystallization) are generally compounded with a permanent reinforcing filler. The two most important examples are the addition of carbon black to natural rubber and to some synthetic elastomers, and the addition of silica to siloxane rubbers. In fact, the reinforcement of natural rubber and related materials is one of the most important processes in elastomer technology. It leads to increases in modulus at a given strain, and improvements of various technologically important properties, such as tear and abrasion resistance, resilience, extensibility, and tensile strength. There are also disadvantages, however, including increases in hysteresis (and thus of heat buildup) and compression set (permanent deformation). Another problem in this area is the absence of a reliable molecular theory for filler reinforcement, in general, and even simple molecular pictures of the origin of the reinforcement are lacking. The subject is not even discussed in what has long been the standard reference book on rubberlike elasticity! On the other hand, there is an incredible amount of relevant experimental data available, with most of these data relating to reinforcement of natural rubber by carbon black. Recently, however, other polymers such as poly(dimethylsiloxane), and other fillers, such as precipitated silica, metallic particles, and even glassy polymers, have become of interest. These studies have shown that materials which act as fillers can vary substantially with respect to the chemical nature of their surfaces, and probably most solid, finely divided materials may advantageously be incorporated into an elastomer. In fact, this is one of the ways the crystallites discussed in chapter 12 improve the mechanical properties of an elastomer. Experimental evidence indicates that the extent of the reinforcement depends strongly on particle size.