bluuebunny/crossref_metadata_2025 huggingface dataset:
Introduction to Virtual Environments and Advanced Interface Design
Authors: Furness III Thomas A. , Barfield Woodrow
Published: November 2020

We understand from the anthropologists that almost from the beginning of our species we have been tool builders. Most of these tools have been associated with the manipulation of matter. With these tools we have learned to organize or reorganize and arrange the elements for our comfort, safety, and entertainment. More recently, the advent of the computer has given us a new kind of tool. Instead of manipulating matter, the computer allows us to manipulate symbols. Typically, these symbols represent language or other abstractions such as mathematics, physics, or graphical images. These symbols allow us to operate at a different conscious level, providing a mechanism to communicate ideas as well as to organize and plan the manipulation of matter that will be accomplished by other tools. However, a problem with the current technology that we use to manipulate symbols is the interface between the human and computer. That is, the means by which we interact with the computer and receive feedback that our actions, thoughts, and desires are recognized and acted upon. Another problem with current computing systems is the format with which they display information. Typically, the computer, via a display monitor, only allows a limited two-dimensional view of the three-dimensional world we live in. For example, when using a computer to design a three dimensional building, what we see and interact with is often only a two-dimensional representation of the building, or at most a so-called 2½D perspective view. Furthermore, unlike the sounds in the real world which stimulate us from all directions and distances, the sounds emanating from a computer originate from a stationary speaker, and when it comes to touch, with the exception of a touch screen or the tactile feedback provided by pressing a key or mouse button (limited haptic feedback to be sure), the tools we use to manipulate symbols are primitive at best. This book is about a new and better way to interact with and manipulate symbols. These are the technologies associated with virtual environments and what we term advanced interfaces. In fact, the development of virtual environment technologies for interacting with and manipulating symbols may represent the next step in the evolution of tools.
The Design of Multidimensional Sound Interfaces
Authors: Cohen Michael , Wenzel Elizabeth M.
Published: November 2020

Early computer terminals allowed only textual I/O. Because the user read and wrote vectors of character strings, this mode of I/O (character-based user interface, or “CUI”) could be thought of as one-dimensional, 1D. As terminal technology improved, users could manipulate graphical objects (via a graphical user interface, or “GUI”) in 2D. Although the I/O was no longer unidimensional, it was still limited to the planar dimensionality of a CRT or tablet. Now there exist 3D spatial pointers and 3D graphics devices; this latest phase of I/O devices (Blattner, 1992; Blattner and Dannenberg, 1992; Robinett, 1992) approaches the way that people deal with “the real world.” 3D audio (in which the sound has a spatial attribute, originating, virtually or actually, from an arbitrary point with respect to the listener) and more exotic spatial I/O modalities are under development. The evolution of I/O devices can be roughly grouped into generations that also correspond to the number of dimensions. Representative instances of each technology are shown in Table 8-1. This chapter focuses on the italicized entries in the third-generation aural sector. Audio alarms and signals of various types have been with us since long before there were computers, but even though music and visual arts are considered sibling muses, a disparity exists between the exploitation of sound and graphics in interfaces. (Most people think that it would be easier to be hearing- than sight-impaired, even though the incidence of disability-related cultural isolation is higher among the deaf than the blind.) For whatever reasons, the development of user interfaces has historically been focused more on visual modes than aural. This imbalance is especially striking in view of the increasing availability of sound in current technology platforms. Sound is frequently included and utilized to the limits of its availability or affordability in personal computers. However, computer-aided exploitation of audio bandwidth is only beginning to rival that of graphics. General sound capability is slowly being woven into the fabric of applications. Indeed, some of these programs are inherently dependent on sound—voicemail, or voice annotation to electronic mail, teleconferencing, audio archiving—while other applications use sound to complement their underlying functionality.
Unifying Urban Land Use and Land Value Theories
Authors: Thrall Grant Ian
Published: November 2020

The market analysis report that is submitted to the decision maker (see chapter 4) should include a descriptive, qualitative overview of the context the real estate project has to the existing and changing urban environment. To better accomplish this task, one should have knowledge of the general theory regarding the market processes that bring about land use and urban form. This chapter presents three relevant general theories of land use and land value. Together, these general theories provide a general qualitative understanding of how the existing urban environment came to be and allows the analyst to prognosticate the trajectory of change of urban land uses and land values. The first two of the general theories presented here arose out of an attempt to explain agricultural land values and land uses. Why should a discussion of the agronomy sector be included in a book on urban real estate analysis? First, all the general theories relevant to land values and land use, and their spatial distribution within a city, are part of an intellectual heritage that dates from general theories of agricultural land values and land use. Second, much of new urban development occurs at those suburban margins. To understand development at the suburban margins, there must be an understanding of the nonurban land uses and land values at those locations. The third general theory explains spatial equilibrium and its role in shaping urban land values and land uses. Two eighteenth-century theorists, David Ricardo and Johann Heinrich von Thünen, are credited for having created a vast and sometimes opposing literature on land valuation. Ricardo’s economic theory was based upon the relative productivity of sites. In contrast, von Thünen’s geographic theory was focused on the locational component of land values and land use. The juxtaposition of these two competing giants of land theory in many respects still differentiates economists and geographers even today. After the theories of Ricardo and von Thünen are presented, an overview of the consumption theory of land rent (CTLR) is provided. The CTLR is my general theory and methodology for evaluating urban housing land use, land values, and urban form (Thrall 1980, 1987, and see 1991).
Hotel and Motel
Authors: Thrall Grant Ian
Published: November 2020

The key concepts, proceeding top-down, for market analysis for the hospitality industry are market segmentation, demand, and supply. Location or trade area comes into the analysis as an umbrella over these three concepts. Market niche and segmentation, demand, and supply are primary determinants to establishing the criteria for locating hospitality facilities. Whenever there have been sufficient numbers of travelers in search of food and shelter, some form of hostelry industry has arisen.1 The Code of Hammurabi (1800 B.C.E) referred to innkeeping (Winfree 1996). In the western countries, as the Romans established an extensive roadway system, taverns and inns followed at strategically spaced locations. The Roman roads were used for military travel, trade and commerce, and pilgrimage and tourism. These are the primary reasons we use roads today. The early inns were largely run by religious orders. However, in Europe, as commerce grew in the fifteenth century, lodging as a commercial activity began to replace innkeeping as a charitable activity. In the American colonial period during the seventeenth and eighteenth centuries, inns and taverns were an important part of commerce and cultural exchange. These facilities were designed after the inns and taverns of England, which were closely integrated into their communities. Inns and taverns did not intrude or disrupt the neighborhood; instead, they were thought of as being an integral part of the culture and activities of the neighborhood. Architecturally, early inns and taverns conformed to the look and feel of the surrounding neighborhood environment. Survivors of these early inns are the contemporary bed-and-breakfasts (B&Bs). The term hotel arose early in the nineteenth century and was used to distinguish a greater level of commercial activity than an inn. Hotels offered food, drink, retail shopping, and lodging. Hotels were also more intrusive in their neighborhoods. Instead of less than 10 rooms that typified many inns of the era, early hotels contained as many as 200 rooms, and rose to 6 floors in height. Many nineteenth-century hotels were the tallest buildings in town. Thus, the hospitality industry began its first cautious attempts at market segmentation and diversification. Inns remained, but hotels offered an alternative experience via amenity differentiation.
Introduction
Authors: Beris Antony N. , Edwards Brian J.
Published: November 2020

The investigation of dynamical phenomena in gases, liquids, and solids has attracted the interest of physicists, chemists, and engineers from the very beginning of the modern science. The early work on transport phenomena focussed on the description of ideal flow behavior as a natural extension to the dynamical behavior of a collection of discrete particles, which dominated so much of the classical mechanics of the last century. As far back as 1809, the mathematical techniques which later came to be known as Hamiltonian mechanics began to emerge, as well as an appreciation of the inherent symmetry and structure of the mathematical forms embodied by the Poisson bracket. It was in this year that S. D. Poisson introduced this celebrated bracket [Poisson, 1809, p. 281], and in succeeding years that such famous scholars as Hamilton, Jacobi, and Poincaré laid the foundation for classical mechanics upon the earlier bedrock of Euler, Lagrange, and d'Alembert. This surge of interest in Hamiltonian mechanics continues well into the waning years of the twentieth century, where scholars are just beginning to realize the wealth of information to be gained through the use of such powerful analytic tools as the Hamiltonian/Poisson formalism and the development of symplectic methods on differential manifolds. Specifically, the study of the dynamics of ideal continua, which is analogous to the discrete particle dynamics studied by Hamilton, Jacobi, and Poisson, has recently benefited significantly by the adaptation of the equations of motion into Hamiltonian form. The inherent structure and symmetry of this form of the equations is particularly well suited for many mathematical analyses which are extremely difficult when conducted in terms of the standard forms of the dynamical equations, for instance, stability and perturbation analyses of ideal fluid flows. Thus, classical mechanics and its outgrowth, continuum mechanics, seem to be on the verge of some major developments. Yet, further progress in this area was hindered by the fact that the traditional form of the Hamiltonian structure can only describe conservative systems, thus placing a severe constraint on the applicability of these mathematically elegant and computationally powerful techniques to real systems.
Hamiltonian Mechanics of Discrete Particle Systems
Authors: Beris Antony N. , Edwards Brian J.
Published: November 2020

In the previous chapter, we discussed briefly the fundamental nature of the symplectic structure of theories in optics in order to illustrate the underlying uniformity, physical consistency, and mathematical simplicity inherent to a symplectic mathematical formulation of the governing equations. Hence the main emphasis of chapter 2 was to “discover” the symplectic structure in the physical theories of optics and to see how this structure is interconnected with and implies fundamental theorems in optics, such as Fermat's principle and Hamilton's equations. In the present chapter, we continue our efforts to present a coherent description of symplectic transformations and their applications to physical systems; however, here we switch our emphasis from the underlying symplectic structure of the dynamical equations to the physical integrity of the Poisson bracket and the canonical equations which find their roots in Hamilton's principle of least action and the calculus of variations. Hence we intend to cover ground in this chapter which we neglected in the previous one, and, in so doing, to gradually begin to move towards the applications of the extended bracket formalism at which this book is aimed. In order to apply Hamilton's principle of least action, we first need to study a simple problem of the calculus of variations, following Bedford [1985, §1.1]. Let x be a real variable (x∊ R) on the closed interval x1≤ x≤ x2, denoted [x1 ,x2] .
The Dissipation Bracket
Authors: Beris Antony N. , Edwards Brian J.
Published: November 2020

In the opening chapters of the book, we saw how a variety of conservative phenomena could be described through the Poisson bracket of classical physics. As already mentioned, the majority of systems with which engineers and physicists must deal reveal dissipative phenomena inherent to their nature. In the last chapter we offered a concise overview of nonequilibrium thermodynamics as traditionally applied to describe, close to equilibrium, dissipative dynamic phenomena. In this chapter, we lay the groundwork for the incorporation of non-conservative effects into an equation of Hamiltonian form, and show several well-known examples in way of proof that such a thesis is, in fact, tenable. The unified formulation of conservative and dissipative processes based on the fundamental equations of motion is not a new idea. Among the most complete treatments is the one offered by the Brussels school of thermodynamics [Prigogine et al., 1973; Prigogine, 1973; Henin, 1974] based on a modified Liouville/von Neumann equation. This is a seminal work where, using the mathematical approach of projection operators and relying only on first principles, it is demonstrated how large isolated dynamic systems may present dissipative properties in some asymptotic limit. A key characteristic of their theory is that dissipative phenomena arise spontaneously without the need of any macroscopic assumptions, including that of local equilibrium [Prigogine et al., 1973, p. 6]. The main value, however, is mostly theoretical, demonstrating the compatibility of dissipative, irreversible, processes with the reversible dynamics of elemental processes through a “symmetry-breaking process.” The value of the theory in applications is limited since it relies on a quantum mechanical equation for the density matrix ρ which is, in general, very difficult to solve except for highly simplified problems [Henin, 1974]. In a nutshell, we hope to offer with the present work a macroscopic equivalent of the Brussels school theory which, at the expense of the introduction of the local equilibrium assumption, attempts to unify the description of dynamic and dissipative phenomena from a continuum, macroscopic viewpoint. The main tool to achieve that goal is the extension of the Poisson bracket formalism, analyzed in chapter 5, to dissipative continua.
Mechanical Properties of Fluids and Porous Media
Authors: Furbish David Jon
Published: November 2020

Fluids possess characteristic physical properties that govern how they behave when forces are applied to them. Of particular interest are properties that govern fluid responses to ordinary mechanical forces; thus we will not consider electrical and magnetic phenomena, and we will defer treating thermodynamical properties of fluids to the next chapter. Further, we will adopt a classic treatment of bulk behavior, as opposed to fluid behavior below the continuum scale. For example, we will examine how a Newtonian fluid deforms (in bulk) in a systematic way when it is subjected to shear stress, such that the rate of strain is proportional to the stress. In contrast, the same nominal fluid very close to a rock surface within a small pore may exhibit a much more complicated rheological behavior, from which we can infer that surface phenomena fundamentally alter the behavior of the fluid from that observed in bulk. We also will see how different types of real fluids respond differently to an applied shear stress, including how the rate of strain of certain fluids varies with the duration of stress as well as other factors. In this regard we will distinguish between time-independent and time-dependent behaviors; in the latter case the behavior of a fluid depends on its history of strain. These basic ideas of fluid behavior are a foundation for most of the material covered in the remainder of the text. Nonetheless, this initial treatment of fluid properties will provide sufficient insight to fluid behavior to begin using simple mathematical analyses to examine several important fluid-flow problems. Likewise, the description here of mechanical properties of porous media also is a foundation for later use. Coverage of this topic, however, is restricted to items that will be useful to understanding fluid behavior. Certain mechanical properties of fluids are defined in terms of the forces acting on them. In this context, it is useful to distinguish two types of forces: body forces and surface forces. A body force is one whose magnitude is proportional to the volume or mass of a fluid parcel.
Fluid Kinematics
Authors: Furbish David Jon
Published: November 2020

Let us momentarily recall an elementary problem from physics: describing the motion of a ballistic particle. To do this in a formal way first required developing expressions for the geometry of motion, independently of any treatment of the forces producing the motion. One may recall that this task involved defining expressions for the speed, velocity, and acceleration of the particle with respect to a specified coordinate system. In fact, a clear geometrical description of particle motion was essential for understanding its cause. We require similar, explicit descriptions for fluid motion to later relate this motion to the forces involved. Fluid kinematics thus involves the description of flow without explicit treatment of the forces producing motion. In this regard, our treatment of fluid kinematics actually is a pedagogical step toward the topic of fluid dynamics, wherein forces are explicitly treated. Our essential objective is to derive an expression that describes how the velocity of a fluid is changing. A change in velocity implies that the fluid is accelerating and, therefore, that a net force is acting on the fluid. Consider Newton’s second law, F = ma, which states that the net force F acting on a particle of mass m equals the product of this mass and the acceleration a. We thus seek an explicit expression for the acceleration a. We will supplement this later with an expression for F to obtain a full dynamical description of fluid motion. This chapter will introduce the idea of a substantive derivative, which will be used numerous times in subsequent chapters. In developing this idea, we will distinguish between Eulerian and Lagrangian views of fluid motion, and introduce the important concept of a convective acceleration. In most situations of interest in geology, convective accelerations arise when a real boundary induces a change in the direction or magnitude of the velocity of nearby flow; convective accelerations therefore typically involve converging or diverging flow. A good example is flow in a river channel whose bed is irregular due to bedform topography, for example, due to a point bar in a meander bend.
Viscous Flows
Authors: Furbish David Jon
Published: November 2020

Most flow problems in geology involve viscous fluids which exhibit resistance to shearing motions. Mechanical treatments of such flows therefore must involve a consideration of frictional forces associated with this viscous behavior. Our first objective is to obtain a general equation of motion based on Newton’s second law that involves body and surface forces acting on a fluid element, regardless of the specific fluid involved. The steps in this development are similar to those leading to Euler’s equation for inviscid flows (Chapter 10); the difference is that tangential stresses acting on a fluid element, in addition to normal stresses, are included in the description of surface forces. It will be necessary, when describing normal forces, to distinguish between the thermodynamic pressure p, as used in treating inviscid flows, and a mechanical pressure σ0, which arises in treating viscous effects associated with compressible flows, and flows that simultaneously involve chemical reactions and possibly other phenomena. The second step in obtaining an equation of motion is determined by the specific fluid involved. Here we require a supplemental set of equations that describe the relation between surface forces and rates of fluid strain, as defined by the rate-of-strain tensor examined in Chapter 11. This set of equations, referred to as the constitutive equations of a fluid, varies with fluid rheology. The emphasis of this chapter is on Newtonian fluids. The set of constitutive equations in this case, when coupled with the general equation of motion obtained in the first step, lead to the well known Navier-Stokes equations. In addition, we will briefly examine the case of glacier ice as an example of a non-Newtonian fluid whose rheology is described by Glen’s law (Chapter 3). Treatments of viscous flows that incorporate conservation of energy similarly must involve a consideration of work performed against the frictional effects of viscosity. This performance of work against friction is nonconservative. Its effect therefore is to continuously extract mechanical energy from the main fluid motion, dissipating it in the form of heat. Our treatment of this irreversible conversion of energy will lead to a dissipation function that is added to the energy equation developed in Chapter 9.
Emerging Minds
Authors: Siegler Robert S.
Published: November 2020

How do children acquire the vast array of concepts, strategies, and skills that distinguish the thinking of infants and toddlers from that of preschoolers, older children, and adolescents? In this new book, Robert Siegler addresses these and other fundamental questions about children's thinking. Previous theories have tended to depict cognitive development much like a staircase. At an early age, children think in one way; as they get older, they step up to increasingly higher ways of thinking. Siegler proposes that viewing the development within an evolutionary framework is more useful than a staircase model. The evolution of species depends on mechanisms for generating variability, for choosing adaptively among the variants, and for preserving the lessons of past experience so that successful variants become increasingly prevalent. The development of children's thinking appears to depend on mechanisms to fulfill these same functions. Siegler's theory is consistent with a great deal of evidence. It unifies phenomena from such areas as problem solving, reasoning, and memory, and reveals commonalities in the thinking of people of all ages. Most important, it leads to valuable insights regarding a basic question about children's thinking asked by cognitive, developmental, and educational psychologists: How does change occur?
Birth Control versus Population Control
Authors: Hardin Garrett
Published: November 2020

In 1956 an association of lay Catholics in Europe announced an international essay contest, the object of which was to find a solution to overpopulation in the underdeveloped nations. The solution, they said, would "have to comply with the requirements of Catholic principles and at the same time must be effective from a positive point of view." In words plainer than the proposers were willing to use: the solution must not resort to abortion, sterilization, or contraception. A substantial prize awaited the winner. Four years later the committee announced that no entry had been found worthy of the prize: the contest was now closed. "After a number of entries had been eliminated because they did not satisfy the material conditions laid down in the rules, five manuscripts remained to be judged. Four of these had to be considered as not dealing with the question as formulated." The fifth entry, the committee decided, presented "no real solution." From this failure the committee extracted the following moral: what was required was team research. "When the fundamental problems of modern science require highly coordinated team work based on carefully planned programmes, it cannot be expected that the fundamental world-wide problems of those branches of science dealing with human beings and society would be solved by individual endeavours." The committee's statement sounds very open-minded; but is their analysis sound? Suppose a contest had the following objective: To find two different odd integers lying between the numbers 7 and 9. What good would it do to appoint a multidisciplinary committee to work on that problem? None. The very method of stating the problem ensures that it has no solution in the real world. Our knowledge of human behavior is not as securely based as our knowledge of mathematics, but the gap between the two is not overwhelming. Natural selection rewards the kind of human behavior that mocks the ideals of the Roman Catholic Church. In a community that cherishes the lives of all fetuses and children, how can functional sterility, whether partial (continence) or total (celibacy) be selected for? More than thirty years have passed since this call for an interdisciplinary committee to work on a Catholic solution, but the committee has apparently never been formed. Who would serve on it? Don Quixote, perhaps; who else?
Recapitulation and a Look Ahead
Authors: Hardin Garrett
Published: November 2020

The cosmopolitan approach is required for some worldwide problems, such as ozone depletion, acid rain, and the exhaustion of oceanic fisheries. By contrast, potholes and population call for a parochial orientation. But if local "laissez-faire" in population matters is interpreted to mean no borders, a suicidal commons results. To survive, rich nations must refuse immigration to people who are poor because their governments are unable or unwilling to stop population growth. With its borders secured, how is a nation to control its own population growth? In one sense population control is inevitable; in another problematical. If the citizens of a nation pay absolutely no attention to their numbers, population will eventually be controlled by "nature"—by disease, starvation, and the social disorders that follow from too many people fighting for limited resources. But when wellwishers call for "population control" they mean something gentler than nature's ultimate response. Can we now predict what form successful human measures will take? I don't think we can, because the question demands that we successfully predict human history. Who, in the year 1700, could have predicted the Constitution of the United States? Who, in 1900, could have predicted Chernobyl? What happens in history is the result of the interaction of (first) the dependable "Laws of Nature" with (second) the apparent capriciousness of human nature. As concerns the first component, Francis Bacon should be our guide: "Nature to be commanded must be obeyed." Coming to the second factor we turn to the inventor of the holograph, the Nobelist Dennis Gabor: "The future cannot be predicted, but futures can be invented." Ignorance of this insight leads the public to take too seriously the projections of demographers (who rightly insist that they cannot predict the future). Demographers merely project curves—present trends—into the unknown future, all the while knowing—as Rene Dubos said-—that trend is not destiny. This book has been one long dissertation on the laws of nature that must be obeyed, namely: the properties of exponential growth; limits generally; the properties of usury; the significance of human unreliability; and the consequences of reproductive competition (including natural selection). But within these limitations lie many possibilities of population control. Some controls are kinder than others.
The Great Climate Debate in Colonial and Early America
Authors: Fleming James R.
Published: November 2020

Enlightenment ideas of climate and culture, developed in an era of European expansion, were stimulated by the writings of explorers, colonists, and travelers. Initially, colonists were confused and confounded by the cold winters and harsh storms. The New World was the object of considerable disdain for many European elites. Convincing them that the North American continent was not a frozen, primitive, or degenerate wasteland became a crucial element in American apologetics. The notion that a harsh climate could be improved by human activity—draining the marshes, clearing the forests, and cultivating the soil—was a major issue in colonial and early America and remained so until the middle of the nineteenth century. If the climate could truly be transformed, the implications were enormous, involving the health, wellbeing, and prosperity of all. There were contrarians, however, who called these ideas just so much wishful thinking. Early settlers in North America found the climate harsher, the atmosphere more variable, and the storms both more frequent and more violent than in similar latitudes in the Old World. In 1644–45, the Reverend John Campanius of Swedes’ Fort (Delaware) described mighty winds, unknown in Europe, which “came suddenly with a dark-blue cloud and tore up oaks that had a girt of three fathoms.” Another colonist in New Sweden, Thomas Campanius Holm, noted that when it rains “the whole sky seems to be on fire, and nothing can be seen but smoke and flames.” James MacSparran, a missionary to Rhode Island for thirty-six years until his death in 1757, spent considerable energy warning colonists against emigrating to America. He found the American climate “intemperate,” with excessive heat and cold, sudden violent changes of weather, terrible and mischievous thunder and lightning, and unwholesome air—all “destructive to human bodies.” While new settlers in all countries and climates are subject to many hardships, Dr. Alexander Hewatt observed that the hardships experienced by the first settlers of Carolina “must have equalled, if not surpassed, everything of the kind to which men in any age have been exposed. . . . During the summer months the climate is so sultry, that no European, without hazard, can endure the fatigues of labouring in the open air.”
Elastic Waves in Anisotropic Media
Authors: Chimenti Dale , Rokhlin Stanislav , Nagy Peter
Published: November 2020

In this chapter, we provide a brief introduction to ultrasonic wave propagation in unbounded anisotropic solids with emphases on examples suitable for ultrasonics of composites. Many excellent books are relevant to the subject addressed in this chapter. Some of them broadly discuss elastic waves in anisotropic solids, including waves in layered anisotropic media. In-depth theoretical description of elastic waves in anisotropic media is given in classical texts, which have influenced and provided guidance to our treatment of some aspects of the theory. Beautiful visualization of ultrasonic waves in crystals (often obtained by laser excitation) is given in reference. The equations of motion for the vibration of an elastic medium are extensions of Newton’s second law for particles. Treating the elastic continuum as a collection of particles, each of which is assumed to obey Newton’s laws, leads to a particularly straightforward argument. We begin by considering a short segment of a bar with length Δx and cross-sectional area S0 as is illustrated in Fig. 2.1. The material is assumed to be linear and elastic, and its deformations can be described by constitutive equations derived in the previous chapter. For simplicity, we assume only uniaxial stress in the x-direction of the continuum.
Elastic Waves in Multilayer Composites
Authors: Chimenti Dale , Rokhlin Stanislav , Nagy Peter
Published: November 2020

Expanding on the theme of bulk waves from the previous chapters, we will examine the problem of plane wave sound propagation in layered media. We assume we have an finite stack of planar layers with perfect, rigidly bonded planar interfaces, but infinite in their lateral extent. The problem has significant industrial interest. Most practical composite laminates are composed of layers of uniaxial fibers and plastic, i.e., plies, whose fiber orientation directions vary from ply to ply through the thickness of the laminate. The mechanical purpose of this directional variation is to render the product stiff and strong in all in-plane directions, much as plywood is layered in cross-grain fashion. Almost no practical composite would be fabricated as a uniaxial product, because of the low bending strength normal to the fiber direction. Instead, various types of layering have been devised to give either tailored stiffness for a specific purpose or approximate in-plane isotropy, also known colloquially as a “quasi-isotropic” laminate. In fact, the approximate isotropy is achieved only in the plane of the plies, because the out-of-plane direction still has significant and unavoidable stiffness differences, since it contains no fibers. The scale of the layering is also important. When the laminations are fine, i.e., when each directional lamina is no thicker than an individual ply as we go through the thickness, only acoustic waves of relatively short wavelength will be able to discern the effect of the layering. At longer wavelengths, the laminate may behave more like an effective medium, still anisotropic, but with averaged elastic properties. On the other hand, if each lamina contains multiple numbers of individual 1/8-mm plies, then the frequency at which an acoustic wavelength approaches the layer thickness will be proportionately lower. This is an important distinction, because it suggests the point at which the layering must be treated as a discrete substructure in order to develop an accurate description of waves in a layered medium. The situation is illustrated schematically in Fig. 6.1. The figure illustrates laminations for a quasi-isotropic composite.
Phospholipid(s) Associations in Cellular Structures
Authors: Hanahan Donald J.
Published: November 2020

In the preceding chapter, the intent was to provide the reader with a broad perspective on the chemical characteristics of cellular phospholipids. At the same time, emphasis was placed on the potential usefulness of this information in dissecting the importance of phospholipids in cellular events, such as signal transduction. There is no doubt that the large number of observations reported on the close relationship of phospholipids to the transduction process has stimulated a widespread (and gratifying) interest in these compounds. Certainly it is very clear now that stimulus-induced activation of cells leads to the turnover of specific membrane phospholipids. The following diagram reemphasizes several, but not all, possible reaction pathways that can be invoked during an agonist (stimulus)–induced activation of a cell and gives the possible sequelae: In each of the above reactions, the substrates phosphatidylcholine and phosphatidylinositol bisphosphate normally are considered biologically inactive in membranes. Then, subsequent to activation of cellular phospholipases by a stimulus, biologically active products are formed from these compounds. Thus, inositol bisphosphate triggers the release of calcium ions from intracellular stores, diacylglycerol is implicated in the translocation and activation of protein kinase C, arachidonic acid can be converted to biologically active prostaglandins, and phosphatidic acid can be an agonist in its own right. The major point to be stressed here is that phospholipid turnover is intimately associated with the signal transduction pathway in cells. Hence an understanding of the chemistry of these phospholipids is of major relevance to delineating the complicated process of signal transduction. While investigation of the behavior of phospholipids in this pathway in platelets has been a consuming interest of this author, the main thrust in this book will be simply to acquaint the reader with the chemistry of phospholipids of major importance in signal transduction and also to discuss other phospholipids found in mammalian membranes. Inasmuch as most investigations on stimulus response in cells utilize quite small numbers of cells—for example, a typical experiment on human platelets might use 1 x 109 cells, which would yield ∼50 μg of total lipid—this poses a challenge to an investigator to be able to isolate and identify these lipids.
Non-Choline-Containing Phospholipids: Diacyl-, Alkylacyl-, Alkenylacyl-Ethanolaminephosphoglycerides, Phosphatidylinositols, and Phosphatidylserine
Authors: Hanahan Donald J.
Published: November 2020

The diversity of phospholipids present in the mammalian cell membranes continues to titillate one’s scientific senses. In addition to the presence of at least 12 different structural types of phospholipids in a cell that serve to complicate the picture, there are species within species. If one considers the diacyl, alkylacyl, and alkenylacyl variants, plus the number of different fatty acyl and fatty ether combinations, there can be several hundred different species present. Certainly progress is being made in relating certain species with a particular cellular process, and this is no doubt an exciting and important area of study. However, this is only the tip of the “cellular iceberg,” since there is little or no information on the biological role of the majority (certainly over 75%) of the phospholipids. Questions to be asked center on the need for such a spectrum of phospholipids. Are some structural components only, are some vestigial remnants, or do they play a crucial role in biological reactions yet to be discovered? There is no simple answer as yet, but this trend of thought should be kept in mind in any investigation on membrane lipid behavior. An important route to interpreting the role of various phospholipids in a biological milieu is to be certain of the chemical structure and identification of the molecules under study. So in continuation of the general format used in Chapter 4, the chemistry of the ethanolamine-, inositol-, and serine-containing phosphoglycerides will be explored at this point. A limited excursion will be made as to their participation in biological reactions. Though the above three classes of compounds share certain common structural features, there are sufficient differences to warrant separate treatment of each group of compounds. For example, the ethanolamine-containing phosphoglycerides can contain, in addition to the diacyl form, an alkylacyl and/or alkenylacyl form. Inositol-containing phosphoglycerides other than the diacyl type have not been reported, but several other phosphorylated species have been detected. The serine-containing phosphoglycerides have been found only as diacyl derivatives.
Shepherdson Revisited
Authors: Smullyan Raymond M
Published: November 2020

Theorems A and B of the last chapter were proved using previous results about generativity, Kleene pairs, complete effective inseparability, and double generativity. Yet the two theorems made no mention of these notions; they referred only to the notions of universality, double universality and semi-double universality. [These three notions, by the way, unlike the four notions mentioned above, were denned without reference to any indexing; they are what we would call index-free.] Is it not possible to give more direct proofs of Theorems A and B that do not require all the antecedent machinery of Chapters 4 and 5? We are about to show that it is possible; we will simply transfer Shepherdson’s arguments about first-order systems to recursion theory itself. We shall prove some “recursive function-theoretic” analogues of Shepherdson’s theorems which will provide new proofs of Theorems A and B (in fact, a strengthening of Theorem A will result).
Symmetric and Double Recursion Theorems
Authors: Smullyan Raymond M
Published: November 2020

We have proved that every completely E.I. pair of r.e. sets is D.U. In the next chapter we will show the stronger result that every E.I. pair of r.e. sets is D.U. The proof of this is based on the double recursion theorem of this chapter. Our original formulation of the double recursion theorem (T.F.S.) required the recursive pairing function J(x,y), not only for its proof, but for its very statement. In this chapter, we give an improved version whose statement and proof are independent of J, K and L. In Part III of this chapter, we compare our new version with the original J, K and L version and show that they are easily interderivable. §1. The Weak Double Recursion Theorem. Consider two r.e. relations, M1(x,y, z) and M2(x, y, z). For any number b, the relation M1(x,y,b) is an r.e. relation between x and y, and so by the weak recursion theorem (Theorem 1, Chapter 8), there is a number a such that ωa = x : M1(x, a, b). Likewise, for any number a, the relation M2(x,a,y) is an r.e. relation between x and y, and so there is a number b such that ωb, = x : M2(x,a,b). Our next theorem tells us that we can choose a and b so that both these conditions hold simultaneously.
Intermolecular Effects: I. The Constrained-Junction Model
Authors: Erman Burak , Mark James E.
Published: November 2020

The classical theories of rubber elasticity presented in chapter 2 are based on a hypothetical chain which may pass freely through its neighbors as well as through itself. In a real chain, however, the volume of a segment is excluded to other segments belonging either to the same chain or to others in the network. Consequently, the uncrossability of chain contours by those occupying the same volume becomes an important factor. This chapter and the following one describe theoretical models treating departures from phantom-like behavior arising from the effect of entanglements, which result from this uncrossability of network chains. The chains in the un-cross-linked bulk polymer are highly entangled. These entanglements are permanently fixed once the chains are joined during formation of the network. The degree of entanglement, or degree of interpenetration, in a network is proportional to the number of chains sharing the volume occupied by a given chain. This is quite important, since the observed differences between experimental results on real networks and predictions of the phantom network theory may frequently be attributed to the effects of entanglements. The decrease in network modulus with increasing tensile strain or swelling is the best-known effect arising from deformation-dependent contributions from entanglements. The constrained-junction model presented in this chapter and the slip-link model presented in chapter 4 are both based on the postulate that, upon stretching, the space available to a chain along the direction of stretch is increased, thus resulting in an increase in the freedom of the chain to fluctuate. Similarly, swelling with a suitable diluent separates the chains from one another, decreasing their correlations with neighboring chains. Experimental data presented in figure 3.1 show that the modulus of a network does indeed decrease with both swelling and elongation, finally becoming independent of deformation, as should be the case for the modulus of a phantom network. Rigorous derivation of the modulus of a network from the elastic free energy for this case will be given in chapter 5. The starting point of the constrained-junction model presented in this chapter is the elastic free energy.
Critical Phenomena and Phase Transitions in Gels
Authors: Erman Burak , Mark James E.
Published: November 2020

The term “gel” has been used in a wide variety of contexts, and there have been difficulties in reaching an all-inclusive, workable definition for it. Perhaps the simplest way to proceed is to list some of its most important characteristics: It is a solidlike material that when deformed responds in the manner of a typical elastic body, but generally with a very small modulus. If it does show plastic flow, then this occurs above a threshold value of the stress, with full recoverability below this limit. It typically consists of two or more components: one a liquid in substantial quantity, and the other generally a polymeric network. One of the most direct ways of obtaining a gel is to place a network into a solvent known to be capable of dissolving the network chains in the absence of cross-links. In fact, a unique property of a highly extensible elastomer (resulting from a low degree of cross-linking) is its ability to swell greatly when exposed to a good solvent. A gel with less than 10-6 mol cm-3 of cross-links, for example, may increase its volume more than thousandfold when immersed in a suitable solvent. The extent to which such a network will swell depends specifically not only on the degree of cross-linking, but also on the interactions between the chains and the solvent. While the degree of cross-linking is established during the preparation of a network, the extent of the interaction of chains and solvent may be modified as desired, and therefore the degree of swelling may be controlled. A gel can be made to swell or shrink continuously by changing the quality of the solvent with which it is in contact. Alternatively, it may go through critical conditions and, in fact, can exhibit phase transitions, depending on the type of the polymer-solvent interaction and the extent of cross-linking. The discrete shrinkage of the gel, by changing the polymer-solvent interaction parameter, is a volume phase transition similar to the gas-liquid transition of a condensing gas. The possibility of such phase transitions was, notably, first discussed by Dusek and collaborators many years ago. Their treatment was confined to nonionic networks.