bluuebunny/crossref_metadata_2025 huggingface dataset:
Deformation and Diffusion Compared
Authors: Bayly Brian
Published: November 2020

The suggestion in view is that when volume is lost by diffusive mass transfer, the consequent shortening rate along some direction n is controlled by ∇2σnn regardless of the spatial variations in other stress components. The nature of the argument advanced is comparable with the one on which the theory of relativity is based: “At two separate points in a universe, it is not reasonable to suppose that the fundamental laws of behavior will be different at one point from the other.” If it is only in respect to some reference frame set up by an observer that point P differs from point Q, one should not expect behavior at P to differ from behavior at Q. It is convenient to use anthropomorphic phrasing: “If there is nothing intrinsic about point P to tell the material there to behave differently, the material at P will behave in the same way as the material at Q.” The theme of this chapter is that the material process for diffusive mass transfer is almost indistinguishable from the process for volume-conserving viscous change of shape at a point. In fact it will be argued that the two processes are so similar that it is not reasonable to suppose that behavior will be governed by different laws in the two modes: only an observer can distinguish one process from the other. Again anthropomorphically, “The moving material itself has no means of knowing which process it is involved in. Hence, if it is direction-dependent quantities such as σnn that control behavior in change of shape at a point, it must also be direction-dependent quantities such as σnn that control diffusive mass transfer.” In presenting the argument, it is convenient to imagine an atomic material for purposes of example, and for the sake of concreteness; but it is emphasized at the outset that the atoms are of minimal significance—the objective is a theory for a continuum. We wish to treat a continuum in which diffusion occurs, and even a continuum with only one component in which self-diffusion occurs, and most people find that this requires imagining division of the continuum into particles on some scale: but we need this division only in the most abstract sense, just enough to permit the idea that the continuum is self-diffusive.
Space, Time and Multi-time
Authors: Gelernter David
Published: November 2020

we move now to the world of asynchronous ensembles. we’ve discussed information machines. Now imagine a lot of them zipping around separately, each piloted by its own Actor—communicating occasionally, getting born and self-destructing spontaneously—all converging like a swarm of space-scooters or electronic piranhas on some lurking huge problem in the near distance. Now this is computing! A group of objects that interact; a group, accordingly, that is more than the sum of its parts. If you assemble a hundred toasters side-by-side and turn each one loose on a slice of bread, what you’ve got is a hundred toasters, toasting their hearts out. If you assemble a hundred monkeys side by side, what you’ve got is not merely a hundred monkeys. You have a monkey community of some kind, an ensemble and not simply one hundred separate parts. Toasters don’t interact, but monkeys do. One hundred information machines working on the same problem also form an ensemble, an entity that is more, in some sense, than the sum of its parts. Like monkeys, these information machines interact. They must communicate and coordinate with each other in order to make progress as a group on the same problem. An ensemble is asynchronous if each part is independent, ticking along at its own pace. In the ensembles we’re talking about, each information machine is encased in its own little piece of spacetime. The machines are unsynchronized: No machine can predict exactly what any other machine is doing at any given time, because each Actor runs his own show, executes his own script. Nothing outside the machine beats time or constrains the Actor in any way: He barrels along at his own speed. Asynchronous ensembles (ensembles for short) are a major topic for software in general. They are the crucial Mirror world technology. Mirror worlds would be unthinkable without them. But here’s another interesting thing about ensembles: They are also the “crucial technology” of nature and mankind. That’s a biggish statement. But a bit of thought makes it clear that physical, chemical, biological and sociological systems are virtually all asynchronous ensembles of one kind or another.
Polarization of Light in the Ocean
Authors: Kattawar George W.
Published: November 2020

The effects of polarization on our perception of the environment about us have been recognized for at least 1000 years. The earliest reports were in response to the polarization in blue skylight as observed through various polarizing crystals. Since blue skylight is a source of polarized light, and atmospheric observations are a quite natural part of our daily routine, it is not surprising that an extraordinary amount of research on the polarization of skylight has been undertaken. Study of the polarization properties of the ocean and the hydrosols contained therein has, unfortunately been very limited, perhaps because man has not been a natural resident of the sea. This chapter will introduce a description of the polarized light field beneath the sea by first providing a brief history of polarization. This will familiarize the reader with its rather ubiquitous presence in our environment, even though our visual perception of it is very weak. Finally, a method is presented (Mueller matrices) to fully characterize the polarization properties of the submarine light field and the polarized effects that various hydrosols have on the light field. For a collection of the many diverse applications of polarization, the reader is referred to the excellent book by Gehrels (1974) About 1000 years ago, the Vikings discovered the dichroic properties of crystals such as cordierite. This property of exhibiting various colors when viewed from different directions is due to the selective absorption of waves oscillating along a particular plane of the crystal. When Vikings viewed the blue skylight through such crystals held in a certain orientation, they located portions of the sky relative to the solar position that seemed to disappear. With this discovery of the polarization of the blue sky, they learned to navigate even in the absence of the sun (e.g., when it was below the horizon). It was another six and one-half centuries before other polarization properties were reported (see Table 11-1 taken from Gehrels, 1974, and Können, 1985).
Open-Cycle OTEC
Authors: Avery William H. , Wu Chih
Published: November 2020

The historical development leading to the proposal by Claude to generate power by producing steam in flash evaporation of warm seawater has been discussed in Chapter 2. In this chapter, the thermodynamic fundamentals of the open-cycle concepts are discussed, leading to a detailed review of state of the art and commercial prospects of the process. There are several variations on the standard OTEC open-cycle (OC) system. The three major variations are “hybrid cycle” (Bartone, 1978), “mist lift cycle” (Ridgway, 1977), and “foam lift cycle” (Beck, 1975; Zener et al., 1975). These are advanced concepts that offer certain attractive features and are being investigated. The three cycles will be discussed in Sections 5.3, 5.4, and 5.5, respectively. The standard OTEC open cycle is discussed in the following. The modest but nearly steady temperature difference that exists between the warm surface water and the much colder water at great depth in some tropical regions of the world has attracted the attention of many thermodynamicists from the time that these temperature differences were first observed. From the thermodynamicist’s view, any significant temperature difference can be used to produce power. The open or Claude cycle is the forerunner of various OTEC cycles. The open cycle refers to the use of seawater as the working fluid. A schematic diagram of the system, which comprises a flash evaporator, vapor expansion turbine and generator, steam condenser, noncondensables-removing equipment, and deaerator, is shown in Fig. 5-1 (Chen, 1979). The cycle is a basic Rankine cycle for converting thermal energy of the warm surface water into electrical energy. In the cycle, the warm seawater is deaerated and then passed into a flash evaporation chamber, where a fraction of the seawater is converted into low-pressure steam. The steam is passed through a turbine, which extracts energy from it, and then exits into a condenser. This cycle derives the name “open” from the fact that the condensate is not returned to the evaporator as in the “closed” cycle. Instead, the condensate can be used as desalinated water if a surface condenser is used, or the condensate is mixed with the cooling water and the mixture is discharged back into the ocean.
OTEC Economics
Authors: Avery William H. , Wu Chih
Published: November 2020

The economic contribution that OTEC will make to the solution of the nation’s energy problems depends on its perceived merits relative to existing and alternative sources of energy and fuels. The previous chapters have shown that OTEC technology is ready for large-scale demonstrations that will provide a firm basis for commercial development. OTEC can have a large impact on U.S. energy needs by supplying liquid fuels for direct use in transportation, or for electric power production via fuel cells. Its commercial development will depend finally on political and other factors that cannot be assessed quantitatively. The national security and environmental impacts of continuing dependence on oil should receive major emphasis in decisions to implement new processes for fuel production. In this chapter we review the estimated sales prices of fuels and electric power from existing and proposed sources and compare them with OTEC prices. Actual manufacturing costs are generally unavailable and are highly dependent on the financing methods and resources of the individual producer. However, an objective comparison of the sales prices of fuels produced by proposed processes can be made by using the Mossman financial analysis method to estimate the sales price of fuel or electric power that must be charged for profitable operation. This requires only information on the plant investment, input fuel costs, and operation and maintenance costs. The sensitivity of the product costs to changes in the estimates in plant investment can then be displayed in a suitable graph. With this procedure the alternatives can be equitably compared from a uniform point of view. This includes costs of related facilities as well as the plant investment. See the discussion in Section 7.3. These costs vary with time in an unpredictable manner. Past forecasts have been in error by large factors. These costs are a small part of the total, typically a few percent of plant investment for capital-intensive projects. Environmental impact costs have usually been ignored. These items are a few percent of plant investment. State and local property taxes will be zero for sea-based OTEC systems.
The Setting: A Description of Adolescents in the United States
Authors: Dryfoos Joy G.
Published: November 2020

Before problem behaviors are examined in detail, it is important to understand the current status of American youth and what comprises so-called “normative” behaviors. It is not sufficient to describe the situation only in aggregate terms; there are such vastly different life scripts that are being experienced by the subgroups in this complex and diverse society. Many books on adolescents solve this problem by presenting an array of vignettes from children’s lives with detailed accounts of individuals and quotations from them. This makes more interesting reading than statistics, but vignettes are not necessarily generalizable to the whole society. For an overview of the “setting,” describing the youth population and the social and economic characteristics of various subpopulations, we turn largely to census data. For a look at health status, we rely on national health statistics. However, to gain an understanding of adolescent developmental issues, different kinds of information are required. For these insights, the works of social and behavioral scientists based on small samples of subjects and personal observations will be explored. In 1987, there were about 28 million 10- to 17-year-olds in the United States, with half a million more boys than girls. More males are born than females, but the sex ratio reverses as populations grow older. This becomes an important factor when individuals reach the age of marriage (about 23 for females and 25 for males) because it controls the pool of partners, a particular problem for marriage-age black females, who outnumber marriage-age black males. The number of young people will increase over the next decade by about 10 percent because the number of births has increased every year since 1973, when the current 15-year-olds were born. One way to understand the expected change is to compare the number of births in 1986, almost 3.76 million, with the number in 1973, 3.13 million. By the year 2000, babies born in 1986 will be 14 years old, right in the center of our population of interest. This group will be enlarged by immigrants as well as by increased numbers of births.
A Firm Archaeological Base for Urban History? Difficulties of Cross-Disciplinary Research
Authors: Crouch Dora P.
Published: November 2020

For those who posit that cities began in the nineteenth century, an appropriate methodology for studying them is to run insurance data through computers, generating statistics and calling the results history. But if our interest extends deep into the past, to Roman or Greek cities or to the first cities of the Yucatan, Mesopotamia, or China, then we are forced to find ways to deal with quite different sorts of evidence. In the Old World there are deciphered or decipherable written records in many cases; in the New World little written evidence. In both the Old and New Worlds, the chief evidence for ancient urbanism is the physical remains of the city, with the paraphernalia of daily life. Like other forms of human knowledge, archaeology over the past thirty years has become increasingly conscious of its methodology, goals, biases, and problems. The questions being asked and the solutions being sought today reflect some shifts in consciousness and in method. The identification of one's assumptions and biases is part of the new mode of research. Nowhere is this shift better revealed than at a site like Morgantina, Sicily, where excavation has extended over more than thirty years, as frequently reported in the American Journal of Archaeology since 1957. This site represents an opportunity for studying ordinary urban settlements of the Greek world, just as a modern sociologist might prefer to study Dayton, Ohio, rather than Los Angeles, as a typical American city. Morgantina is a fine test case for the use of archaeological data as the basis of urban history. Some general conclusions may be drawn from this evidence about the problems and opportunities of cross-disciplinary investigation. Since 1977, I have hunted through thirty years of excavation records from Morgantina, looking for the occasional fact about water system elements. Gradually I have come to realize that the data from Morgantina were gathered to verify certain written records from ancient times. The data collected would be very different if at the beginning the excavators had asked more anthropological or geographical questions, such as, “Since water is essential for human settlement, what features of this site provide for that need? And what human interventions were made; that is, what structures were built?”
Morgantina's Agora—Design and Drains
Authors: Crouch Dora P.
Published: November 2020

The agora fulfilled a complex role in the life of Greek cities. In Greek agoras, nearly the whole range of public activities was accommodated: governmental, religious, commercial, military, and social. The market function of the agora was essential to the survival of the city, with the availabilty of everything from imported grain to locally grown lettuce. Services, from haircutting to the teaching of Stoic philosophy, were available. Government offices and officers were readily at hand. Temples, shrines, and monuments to heroes iterated religious, cultural, and moral values from every corner. The agora at Athens is probably the most thoroughly studied of the early ones. In shape it is an irregular quadrilateral, eventually monumentalized with stoas and other public buildings along all four sides. The buildings were placed at the edges of the large open space which therefore was available for many activities. Cisterns and wells of the pre- and postclassical periods were scattered over the surface. Only one well is known, however, from the classical period, that in the shrine in the northwest corner (Athenian Agora Guide,3) suggesting that the sixth century aqueduct was supplying enough water for the population during the fifth and early fourth centuries. Fountains marked important points of entry, and drains led the excess water northwestward toward the city gates (Figs. 16.15, 17.11). As the agora changed over time, being filled in with additional structures, the sources of water and the drains were continually adapted to the new demands. The organic form at Athens contrasts with the more regular but even earlier surviving form—eighth or seventh century B.C.—at Posidonia (Paestum), where a broad strip of public space for temples and agora was set aside at the center of the town (Fig. 5.1B). On this flat site, two sacred precincts flanked the agora (later Forum). The long and varied history of the site precludes our easy understanding of the design of the Greek agora here. Regularity at Posidonia is a function of its status as a colonial city—a city that was planned and laid out all at one time. Careful attention was given to the provision and use of water.
Epilogue
Authors: Badler Norman I. , Phillips Cary B. , Webber Bonnie Lynn
Published: November 2020

To define a future for the work described in this book, it is essential to keep in mind the broad goals which motivated the efforts in the first place. Useful and usable software is desired, to be sure, but the vision of manipulating and especially instructing a realistically behaved animated agent is the greater ambition. Some of our visions for the near future are presented, not just for the sake of prognostication, but for its exciting prospects and possibilities. Any discussion of the future of software must take into account the extraordinary pace of developments in the hardware arena. Even conservative predictions of hardware capabilities such as speed and capacity over the five year term lead one perilously close to science fiction. Accordingly, predictions of “better, faster, cheaper, more reliable, more fault tolerant, more highly parallel computers” are easy to make but do little to inform us of the applications these fantastic machines will facilitate. Rather, as general purpose computers improve in all these ways, specialized hardware solutions will decrease in importance and robust, usable software and symbiotic human-computer interfaces will remain the crucial link between a task and a solution. Transforming research into practice is a lengthy process, consisting of a flow of concepts from ideas through algorithms to implementations, from testing and analysis through iterated design, and finally transfer of demonstratably workable concepts to external users and actual applications. This entire process may span years, from the initial description of the concept to a fielded system. The publication of initial results often breeds over-optimism and has been known to lead researchers to allow false expectations to arise in the minds of potential users, with unfortunate results. (Automatic machine translation of text, speech understanding, and early promises of Artificial Intelligence problem solving are good examples of premature speculations.) At the other end of the spectrum, however, are concepts which take a long time to work their way into mainstream technological consciousness. (3D computer graphics is a good example where concepts and even working systems pre-dated widespread commercial availability by more than a decade.) So we will attempt to strike a balance in making speculations: while looking toward a long term research plan we will generally consider technology transfer to occur when serious but sympathetic users can experiment and accomplish real work with it.
Linear Anisotropic Elastic Materials
Authors: Ting T. T. C.
Published: November 2020

The relations between stresses and strains in an anisotropic elastic material are presented in this chapter. A linear anisotropic elastic material can have as many as 21 elastic constants. This number is reduced when the material possesses a certain material symmetry. The number of elastic constants is also reduced, in most cases, when a two-dimensional deformation is considered. An important condition on elastic constants is that the strain energy must be positive. This condition implies that the 6×6 matrices of elastic constants presented herein must be positive definite. Referring to a fixed rectangular coordinate system x1, x2, x3, let σij and εks be the stress and strain, respectively, in an anisotropic elastic material. The stress-strain law can be written as . . . σij = Cijksεks . . . . . .(2.1-1). . . in which Cijks are the elastic stiffnesses which are components of a fourth rank tensor. They satisfy the full symmetry conditions . . . Cijks = Cjiks, Cijks = Cijsk, Cijks = Cksij. . . . . . .(2.1-2). . .
The Lekhnitskii Formalism
Authors: Ting T. T. C.
Published: November 2020

A two-dimensional deformation means that the displacements ui, (i= 1,2,3) or the stresses σij depend on x1 and x2 only. Among several formalisms for two-dimensional deformations of anisotropic elastic materials the Lekhnitskii (1950, 1957) formalism is the oldest, and has been extensively employed by the engineering community. The Lekhnitskii formalism essentially generalizes the Muskhelishvili (1953) approach for solving two-dimensional deformations of isotropic elastic materials. The formalism begins with the stresses and assumes that they depend on x1 and x2 only. The Stroh formalism, to be introduced in the next chapter, starts with the displacements and assumes that they depend on x1 and x2 only. Therefore the Lekhnitskii formalism is in terms of the reduced elastic compliances while the Stroh formalism is in terms of the elastic stiffnesses. It should be noted that Green and Zerna (1960) also proposed a formalism for two-dimensional deformations of anisotropic elastic materials. Their approach however is limited to materials that possess a symmetry plane at x3=0. The derivations presented below do not follow exactly those of Lekhnitskii.
Transformation of the Elasticity Matrices and Dual Coordinate Systems
Authors: Ting T. T. C.
Published: November 2020

When the elasticity matrices are referred to a rotated coordinate system their elements change and assume different values. We will show in this chapter that, under rotations about the x3-axis, the matrices A and B are tensors of rank one while S, H, L, and M are tensors of rank two. These properties are important in establishing certain invariants that are physically interesting and puzzling. We will also present the amazing Barnett-Lothe integral formalism that allows us to determine S, H, and L without computing the eigenvalues and eigenvectors of elastic constants. New tensors Ni(θ) (i=l,2,3), S(θ), H(θ), L(θ), and Gi(θ) (i=1,3) are introduced, and their properties as well as identities relating them are presented. Also introduced is the idea of dual coordinate systems where the position of a point is referred to one coordinate system while the displacement components are referred to another coordinate system. These will be useful in applications. As in Chapter 6 readers may skip this chapter in the first reading. They can return to this chapter later for specific information.
Introduction
Authors: Baer Tomas , Hase William L.
Published: November 2020

The field of unimolecular reactions has witnessed impressive advances in both experimental and theoretical techniques during the past 20 years. These developments have resulted in experimental measurements that finally permit critical tests of the major assumptions made more than 60 years ago when Rice and Ramsperger (1927, 1928) and Kassel (1928) first proposed their statistical RRK theory of unimolecular decay. At the heart of these advances is our ability to prepare molecules in narrow ranges of internal energy, even in single quantum states, at energies below and above the dissociation limit. This has led to detailed spectroscopic studies of intramolecular vibrational energy redistribution (IVR), a process that is intimately related to the assumption of random energy flow in the statistical theory of unimolecular decay. This book is devoted exclusively to the study of state- or energy-selected systems. However, in order to place these studies in the context of the much larger field of unimolecular reactions in general, we provide a brief background of the field up to about 1970. The experimental studies of unimolecular reactions developed in three stages. The early studies involved strictly thermal systems in which molecules were energized by heating the sample either in a bulb (Chambers and Kistiakowsky, 1934; Schlag and Rabinovitch, 1960; Flowers and Frey, 1962; Schneider and Rabinovitch, 1962), or by more sophisticated methods such as shock tubes which were applied to unimolecular reactions by Tsang (1965, 1972, 1978, 1981) and others (Astholz et al., 1979; Brouwer et al.,1983). The drawback of these studies is that molecules were prepared in a very broad (albeit well characterized) distribution of internal energy states. A major advance was the use of chemical activation in the early 1960s in which a species such as CH2 reacted with a molecule, thereby forming an energized species which could either isomerize or be stabilized by collisions (Rabinovitch and Flowers, 1964; Rabinovitch and Setser, 1964; Kirk et al., 1968; Hassler and Setser, 1966; Simons and Taylor, 1969). This approach permitted the reacting species to be prepared in a narrow range of internal energies.
Theory of Unimolecular Decomposition— The Statistical Approach
Authors: Baer Tomas , Hase William L.
Published: November 2020

The partition function and the sum or density of states are functions which are to statistical mechanics what the wave function is to quantum mechanics. Once they are known, all of the thermodynamic quantities of interest can be calculated. It is instructive to compare these two functions because they are closely related. Both provide a measure of the number of states in a system. The partition function is a quantity that is appropriate for thermal systems at a given temperature (canonical ensemble), whereas the sum and density of states are equivalent functions for systems at constant energy (microcanonical ensemble). In order to lay the groundwork for an understanding of these two functions as well as a number of other topics in the theory of unimolecular reactions, it is essential to review some basic ideas from classical and quantum statistical mechanics. As discussed in chapter 2, the classical Hamiltonian, H(p,q), is the total energy of the system expressed in terms of the momenta (p) and positions (q) of the atoms in the system.
Origins and Elements of Virtual Environments
Authors: Ellis Stephen R.
Published: November 2020

Virtual environments created through computer graphics are communications media (Licklider et al., 1978). Like other media, they have both physical and abstract components. Paper, for example, is a medium for communication. The paper is itself one possible physical embodiment of the abstraction of a two-dimensional surface onto which marks may be made. The corresponding abstraction for head-coupled, virtual image, stereoscopic displays that synthesize a coordinated sensory experience is an environment. These so-called “virtual reality” media have only recently caught the international public imagination (Pollack, 1989; D’Arcy, 1990; Stewart, 1991; Brehde, 1991), but they have arisen from continuous development in several technical and non-technical areas during the past 25 years (Brooks Jr., 1988; Ellis, 1990; Ellis, et al., 1991, 1993; Kalawsky, 1993). A well designed computer interface affords the user an efficient and effortless flow of information to and from the device with which he interacts. When users are given sufficient control over the pattern of this interaction, they themselves can evolve efficient interaction strategies that match the coding of their communications to the characteristics of their communication channel (Zipf, 1949; Mandelbrot, 1982; Ellis and Hitchcock, 1986; Grudin and Norman, 1991). But successful interface design should strive to reduce this adaptation period by analysis of the user’s task and performance limitations. This analysis requires understanding of the operative design metaphor for the interface in question. The dominant interaction metaphor for the computer interface changed in the 1980’s. Modern graphical interfaces, like those first developed at Xerox PARC (Smith et al., 1982) and used for the Apple Macintosh, have transformed the “conversational” interaction from one in which users “talked” to their computers to one in which they “acted out” their commands in a “desk-top” display. This so called desk-top metaphor provides the users with an illusion of an environment in which they enact wishes by manipulating symbols on a computer screen. Virtual environment displays represent a three-dimensional generalization of the two-dimensional “desk-top” metaphor. These synthetic environments may be experienced either from egocentric or exocentric viewpoints. That is to say, the users may appear to actually be in the environment or see themselves represented as a “You are here” symbol (Levine, 1984) which they can control.
VEOS: The Virtual Environment Operating Shell
Authors: Bricken William , Coco Geoffrey
Published: November 2020

Computer technology has only recently become advanced enough to solve the problems it creates with its own interface. One solution, virtual reality (VR), immediately raises fundamental issues in both semantics and epistcmology. Broadly, virtual reality is that aspect of reality which people construct from information, a reality which is potentially orthogonal to the reality of mass. Within computer science, VR refers to interaction with computer-generated spatial environments, environments constructed to include and immerse those who enter them. VR affords non-symbolic experience within a symbolic environment Since people evolve in a spatial environment, our knowledge skills are anchored to interactions within spatial environments. VR design techniques, such as scientific visualization, map digital information onto spatial concepts. When our senses are immersed in stimuli from the virtual world, our minds construct a closure to create the experience of inclusion. Participant inclusion is the defining characteristic of VR. (Participation within information is often called immersion.) Inclusion is measured by the degree of presence a participant experiences in a virtual environment. We currently use computers as symbol processors, interacting with them through a layer of symbolic mediation. The computer user, just like the reader of books, must provide cognitive effort to convert the screen’s representations into the user’s meanings. VR systems, in contrast, provide interface tools which support natural behavior as input and direct perceptual recognition of output. The idea is to access digital data in the form most easy for our comprehension; this generally implies using representations that look and feel like the thing they represent. A physical pendulum, for example, might be represented by an accurate three-dimensional digital model of a pendulum which supports direct spatial interaction and dynamically behaves as would an actual pendulum. Immersive environments redefine the relationship between experience and representation, in effect eliminating the syntax-semantics barrier. Reading, writing, and arithmetic are cast out of the computer interface, replaced by direct, non-symbolic environmental experience. Before we can explore the deeper issues of experience in virtual environments, we must develop an infrastructure of hardware and software to support “tricking the senses” into believing that representation is reality. The VEOS project was designed to provide a rapid prototyping infrastructure for exploring virtual environments.
Visually Coupled Systems Hardware and the Human Interface
Authors: Kocian Dean F. , Lee Task H.
Published: November 2020

A visually coupled system (VCS) has been defined as “ . . . a special ‘subsystem’ which integrates the natural visual and motor skills of an operator into the system he is controlling” (Birt and Task, 1973). A basic VCS consists of three major components: (1) a head- or helmet-mounted (or head-directed) visual display, (2) a means of tracking head and/or eye pointing direction, and (3) a source of visual information which is dependent on eye/head viewing direction. The concept of a VCS is relatively simple: an operator looks in a particular direction, the head or eye tracker determines what that direction is, and the visual information source produces appropriate imagery to be viewed on the display by the operator. In this manner the operator is visually coupled to the system represented by the visual information source. The visual information source could be a physical imaging sensor such as a television camera or it could be a synthetic source such as computer-generated imagery (the basis for a virtual reality (VR) or virtual environment system). Thus, a VR system is really a subset of a VCS which can present both real-world and virtual information to an operator, often on a see-through display. The display is usually a helmet/head-mounted display (HMD) but it could also be the interior of a dome capable of displaying a projected image or it could be a mechanically mounted display that is not supported by the head but is attached to the head which in recent times has been referred to as a binocular omni-oriented monitor (BOOM) display. Both eye-tracking and head-tracking devices have been developed but by far the least expensive and most widely used is head tracking (this is based on the reasonable assumption that the eyes will be looking in the general direction that the head is pointing). Figures 6-1 through 6-4 are photographs of some early helmet-mounted and BOOM displays. In this chapter we will concentrate primarily on helmet/head-mounted displays and helmet/head trackers. This section describes each of the three main components of a visually coupled system and defines characteristics that are used in the specification of these components.
Kinesthetic Displays for Remote and Virtual Environments
Authors: Hannaford Blake , Venema Steven
Published: November 2020

Humans perceive their surrounding environment through five sensory channels, popularly labeled “sight,” “sound,” “taste,” “smell,” and “touch.” All of these modalities are fused together in our brains into an apparently seamless perception of our world. While we typically place the most importance on our visual sense, it is our sense of touch which provides us with much of the information necessary to modify and manipulate the world around us. This sense can be divided into two categories: the kinesthetic sense, through which we sense movement or force in muscles and joints; and the tactile sense, through which we sense shapes and textures. This chapter will focus on the use of kinesthetic sense in realistic teleoperation and virtual environment simulations. Artificial kinesthetic feedback techniques were first developed in the field of teleoperation—robot manipulators remotely controlled by human operators. In teleoperation, the perceptions from a physically remote environment must be conveyed to the human operator in a realistic manner. This differs from virtual reality in which the perceptions from a simulated environment are conveyed to the user. Thus, teleoperation and virtual environments communities share many of the same user interface issues but in teleoperation the need for detailed world modeling is less central. The earliest remote manipulation systems were operated by direct mechanical linkages and the operator viewed the workspace directly through windows (Goertz, 1964). Perhaps because of their relative simplicity and high performance, little was learned about sensory requirements for remote manipulation from these early devices. When remote manipulation was developed for long distances and mobile platforms, electronic links became mandatory. The earliest attempts drove the remote manipulator with a position signal only and no information was returned to the operator about contact force. In the original mechanical designs, force information was intrinsically available because the linkages (actually metal tape and pulley transmissions) were relatively stiff, low-mass, connections between the operator and the environment. With the shift to electronic links, the loss of kinesthetic information was immediately apparent to the operators. The first artificial kinesthetic displays arose to provide improved functionality for remote manipulators.
Presence and Performance Within Virtual Environments
Authors: Barfield Woodrow , Zeltzer David
Published: November 2020

Recent developments in display technology, specifically head-mounted displays slaved to the user’s head position, techniques to spatialize sound, and computer-generated tactile and kinesthetic feedback allow humans to experience impressive visual, auditory, and tactile simulations of virtual environments. However, while technological advancements in the equipment to produce virtual environments have been quite impressive, what is currently lacking is a conceptual and analytical framework in which to guide research in this developing area. What is also lacking is a set of metrics which can be used to measure performance within virtual environments and to quantify the level of presence experienced by participants of virtual worlds. Given the importance of achieving presence in virtual environments, it is interesting to note that we currently have no theory of presence, let alone a theory of virtual presence (feeling like you are present in the environment generated by the computer) or telepresence (feeling like you are actually “there” at the remote site of operation). This in spite of the fact that students of literature, the graphic arts, the theater arts, film, and TV have long been concerned with the observer’s sense of presence. In fact, one might ask, what do the new technological interfaces in the virtual environment domain add, and how do they affect this sense, beyond the ways in which our imaginations (mental models) have been stimulated by authors and artists for centuries? Not only is it necessary to develop a theory of presence for virtual environments, it is also necessary to develop a basic research program to investigate the relationship between presence and performance using virtual environments. To develop a basic research program focusing on presence, several important questions need to be addressed. The first question to pose is, how do we measure the level of presence experienced by an operator within a virtual environment? We need to develop an operational, reliable, useful, and robust measure of presence in order to evaluate various techniques used to produce virtual environments. Second, we need to determine when, and under what conditions, presence can be a benefit or a detriment to performance.
Eduction
Authors: Ashcroft E. A. , Faustini A. A. , Jaggannathan R. , Wadge W. W.
Published: November 2020

We know what a Lucid program means mathematically (see Chapter 3), yet that in itself does not suggest a particular model of computation for deriving the same meaning operationally. The purpose of this chapter is to consider the various ways that Lucid programs can be evaluated and to describe in detail the most appropriate model of computation, namely, eduction. Previously, we have seen that Lucid programs can be viewed globally in geometrical terms or locally in elemental terms. Both these views are equally valid as mental devices to enable the programmer to conceive and understand Lucid programs. And each view suggests its own family of computing models—extensional models that embody the global geometrical view and intensional models that embody the local elemental view. Before we compare these two approaches to evaluating Lucid programs, it is worth relating the operational semantics given by a model of computation to the mathematical semantics. Since Lucid is purely declarative, the correct meaning of a Lucid program is that which is given mathematically. This is done without appealing to any operational notions [8]. Thus, the mathematical semantics of a Lucid program has primacy over the many operational semantics that can be given to the Lucid program using different models of computations. Consequently, the correctness of a model of computation is determined by its ability to operationally give semantics to Lucid programs that coincide with their mathematical semantics. Let us consider an extensional model of computation called reduction [37]. It is the standard model for evaluating declarative programs, and more specifically, functional programs. In reduction, programs are considered to be expressions, and a program is evaluated by repeatedly transforming, or reducing, the expression into a possibly simpler expression. The original expression must include any data that the program is to work on, so that at every stage we are manipulating both program and data, and the two become intimately entwined. The process stops when no further transformation can be applied. At each stage, several transformations may be possible, but it doesn’t matter which we apply. If we get an answer, we always get the same answer, but it is possible to make choices so that we do not arrive at the answer.
Introduction
Authors: Thrall Grant Ian
Published: November 2020

This book shows how to answer questions that provide guidance to the most important decisions in real estate: Should I buy? Should I build? Will the market support the decision? Before developers or investors commit to a project, they must have answers to these questions if they are to remain profitable in the long run. No generic answers will fit all real estate decisions at all times, because the circumstances differ so much between projects. Therefore, in addition to examples of the methodology that is generally accepted in the industry, this book provides explanations for why the methodology is used. True understanding provides the versatility that is needed in ever-changing markets. May I build a residential subdivision here? May I build a class A office building there? Such questions are important, but are better dealt with by planners, zoning officials, and attorneys. Is appropriate zoning available? If not, what would be involved in changing the present zoning to accommodate the proposed development? Answering “permission” questions often involves political considerations, which reflect the taste preferences of citizens and politicians and are a byproduct of the local power structure. Therefore, real estate development involves political decisions, as well as market analysis. The market analyst addresses a different scope of issues than the permission questions address. The market analyst provides information and guidance to the investor, buyer, seller, financier, and planner (See Pyhrr et al. 1989, Vernor 1986, Fanning et al. 1995, Delisle and Sa-Aadu 1994, Brueggeman and Fisher 1996). Funding for development or purchase usually falls upon lending institutions. Lending institutions require market analysis as input for their consideration before they commit to funding. Otherwise, they are jeopardizing the financial viability of their institution. The decision to lend without appropriate market analysis is no more than gambling. Some projects may be successful, some may not. Banking regulations require due diligence in the lending decision to evaluate the exposure to risk by the lending institution. So business geographic real estate market analysis is central to the risk management of those who carry the burden of responsibility for the investment.
Conducting Real Estate Market Analysis
Authors: Thrall Grant Ian
Published: November 2020

This chapter establishes a general framework for conducting market analysis for all types of real estate. The subsequent chapters show how, with appropriate modifications, this general framework applies to specific real estate product types. The following chapters also include examples of the general approach introduced here. Four general steps must be included in all real estate market analysis. This chapter will progress through each of the four steps. First, a trade area, also known as a market area, must be established from which to draw the data for the real estate market analysis. Explanation is provided on how to delineate a trade area for the project, including how large the trade area is and the geographic delineation of its boundaries. Second, to evaluate the competitive position of the project, competing supply is estimated. Competing supply includes both current and projected supply within the trade area derived in the first step. To identify competitive projects, the market analyst must also determine what segment the real estate project is to compete in. Third, demand must be measured. Demand estimation includes the assembly and use of projections of economic, geographic, and social indicators that together influence the demand for a specific real estate project. Occasionally, data readily available from commercial data vendors are inadequate for specific types of real estate projects. In these circumstances, demand is estimated using primary research, including surveys and focus groups, as well as assembly of primary data. The fourth step is compiling the report and presenting the analysis to client. The report must reconcile the results of the foregoing three steps with the goals and needs of the client. The client may be an investor, a developer, a redevelopment agency, and so on. The objectives of the client might influence how the fundamental first three steps are interpreted. The market analysis report generally concludes with recommendations, as well as a description of the overall project within the wide context of the economic, geographic, and social forces that are shaping the urban built environment. The analyst draws conclusions, including projecting absorption rates and pricing recommendations.