bluuebunny/crossref_metadata_2025 huggingface dataset:
Prevention of Delinquency
Authors: Dryfoos Joy G.
Published: November 2020

As we have seen in Chapter 3 (Prevalence of Delinquency), the phrase “juvenile delinquency” may refer to the “continuum of behavior that transgresses social norms,” ranging from socially unacceptable behavior (acting out in school) to status offenses (running away) to criminal acts (burglary). This broad definition sets wide boundaries on a discussion of prevention. Preventing disruptive behavior in the early elementary grades is quite a different task from preventing major criminal acts among high-school-age gangs. The former focuses more on altering individual and family functioning, while the latter involves alterations in the peer culture, the school experience, and the broader social environment. In any case, a review of the literature on prevention of delinquency produces few programs that can be cited as models of primary prevention at early or late stages. A very small number of programs could generate evidence that they stopped the onset of delinquent behavior. Interventions were cited, however, that have an indirect effect on later delinquency by modifying “acting out” and conduct disorders at very early ages. Many of the programs discussed in the literature focus on secondary prevention, working with adjudicated juvenile delinquents to lower the rates of recidivism (repeat offenses), and almost none of those appear to meet with great success. The dearth of successful prevention programs in the area of delinquency is not surprising in light of the complexity of the problem and its deep-seated causes. The usual difficulties with evaluation design are compounded in this field by murky definitions. Repeated reviews of literally thousands of studies have produced almost none with adequate evaluations. Leitenberg’s commentary on the “state-of-the-art” is not very encouraging: . . . My thoughts about primary prevention programs in delinquency tend to be pessimistic. Unless the larger political, organizational, economic and social issues are addressed . . . we will make small headway. . . . I think the most productive area is not within the realm of psychology, sociology, psychiatry, social work, or criminology—it is within the area of politics. . .
Prevention of Adolescent Pregnancy
Authors: Dryfoos Joy G.
Published: November 2020

The literature on prevention of adolescent pregnancy has a somewhat different tone than the two sets of literature we have just reviewed on delinquency and substance abuse prevention. While those fields were dominated by psychiatric studies (delinquency) and psychologically oriented school-based interventions (substance abuse), the discussion of teen pregnancy tends to focus much more on broader sociological and moral issues. During the past decade, a great deal has been said in the press and on TV specials about preventing teen pregnancy; the subject has been aired at endless conferences and in Congressional Committee hearings. A number of books have been published on the subject, typically collections of previously published articles or chapters provided by authorities. In this literature, certain strategies appear to have been accepted among most of the commentators: that the major focus of prevention should be sex education in the schools and access to contraceptive methods, with little mention of evaluation of these approaches. It would be a gross overstatement to imply that there is a consensus in the United States about what to do about adolescent pregnancy. As in every other facet of American life, there is a significant difference between “liberals” and “conservatives” about appropriate interventions. The conservatives take the position that only abstention will solve the problem, and it is up to families to produce the moral climate necessary to help their children maintain their virginity until marriage. Mosbacher, in a report for the Family Research Council of America, calls for molding children to “reflect virtue, self-control, and self-sacrifice in services to others.” Clearly, when sex enters the scene, the situation becomes complicated. Scholars may be frightened away. Universities do not have departments and big names associated with the evaluation of pregnancy prevention interventions. There is, however, extensive “population research,” focusing on demographic studies of changes in vital rates, with some work on the determinants and consequences of adolescent pregnancy (see Chapter 5). Evaluations of family planning programs are mostly being conducted overseas in developing countries.
Greek Urbanization — Theoretical Issues
Authors: Crouch Dora P.
Published: November 2020

Urbanization is a process that can be studied both historically and philosophically. The examination by case studies in these pages draws on architectural and art historical insights to illuminate the term “urbanization” as a process. Some theories of great current interest to classicists and ancient history experts are ignored here lest the digression into their arguments impede our concentration on evidence for water management. Rather, we may generalize in very simple terms from accumulated examples. A family selects a site and builds a house. Their grown sons and daughters form households and settle nearby. Friends come to live there too, and strangers arrive to trade or worship, and stay on. Gradually a small settlement with advantageous resources—human, physical, and cultural—prospers and becomes a town, even a city. It forms ties with other settlements and increases its prosperity by trade and cultural interaction. The city’s need for food, raw materials, and population has a strong impact on the countryside, so that other hamlets become towns in response to urban demands for their goods. Thus urbanization may be said to be a process. Growth and decay of urban centers are part of the same process. Once the process of city building is well underway, the resulting “package” of knowledge and behavior can be exported as a product. Greek colonization of the Mediterranean area was done by means of cities, a group of settlers carrying with them to the new place both the concept of city and the technological and political means to bring it into existence (see Fig. 3.1, selected Greek sites). Colonists were organized in one of several standard ways, to make a new urban place without going through a gradual process of social evolution and physical agglomeration. This set of activities is well described in A. J. Graham, Colony and Mothercity in Ancient Greece (1983), and in N. H. Demand, Urban Relocation in Archaic and Classical Greece (1990). In the general field of urban history and theory, we have the works of Vance, Hohenberg and Lees, Wheatley, and Pirenne. From them we learn how urbanization has been understood in the last two centuries.
Exiles from Eden
Authors: Schwehn Mark R.
Published: November 2020

In this thoughtful and literate study, Schwehn argues that Max Weber and several of his contemporaries led higher education astray by stressing research--the making and transmitting of knowledge--at the expense of shaping moral character. Schwehn sees an urgent need for a change in orientation and calls for a "spiritually grounded education in and for thoughtfulness." The reforms he endorses would replace individualistic behavior, the "doing my own work" syndrome derived from the Enlightenment, with a communitarian ethic grounded in Judeo-Christian spirituality. Schwehn critiques philosophies of higher education he considers misguided, from Weber and Henry Adams to Derek Bok, Allan Bloom, and William G. Perry Jr. He draws out valid insights, always showing the theological underpinnings of the so-called secular thinkers. He emphasizes the importance of community, drawing on both the secular communitarian theory of Richard Rorty and that of the Christian theorist Parker Palmer. Finally, he outlines his own prescription for a classroom-centered spiritual community of scholars. Schwehn's study will interest all those concerned with higher education in America today: faculty, students, parents, alumni, administrators, trustees, and foundation officers.
Behavioral Control
Authors: Badler Norman I. , Phillips Cary B. , Webber Bonnie Lynn
Published: November 2020

The behaviors constitute a powerful vocabulary for postural control. The manipulation commands provide the stimuli; the behaviors determine the response. The rationale for using behavioral animation is its economy of description: a simple input from the user can generate very complex and realistic motion. By defining a simple set of rules for how objects behave, the user can control the objects through a much more intuitive and efficient language because much of the motion is generated automatically. Several systems have used the notion of behaviors to describe and generate motion [Zel91]. The most prominent of this work is by Craig Reynolds, who used the notion of behavior models to generate animations of flocks of birds and schools of fish [Rey87]. The individual birds and fish operate using a simple set of rules which tell them how to react to the movement of the neighboring animals and the features of the environment. Some global parameters also guide the movement of the entire flock. William Reeves used the same basic idea but applied it very small inanimate objects, and he dubbed the result particle systems [Ree83]. Behaviors have also been applied to articulated figures. McKenna and Zeltzer [MPZ90] describe a computational environment for simulating virtual actors, principally designed to simulate an insect (a cockroach in particular) for animation purposes. Most of the action of the roach is in walking, and a gait controller generates the walking motion. Reflexes can modify the basic gait patterns. The stepping reflex triggers a leg to step if its upper body rotates beyond a certain angle. The load bearing reflex inhibits stepping if the leg is supporting the body. The over-reach reflex triggers a leg to move if it becomes over-extended. The system uses inverse kinematics to position the legs. Jack controls bipedal locomotion in a similar fashion (Section 5), but for now we focus on simpler though dramatically important postural behaviors. The human figure in its natural state has constraints on its toes, heels, knees, pelvis, center of mass, hands, elbows, head and eyes. They correspond loosely to the columns of the staff in Labanotation, which designate the different parts of the body.
Anisotropic Elasticity
Authors: Ting T. T. C.
Published: November 2020

Anisotropic Elasticity offers for the first time a comprehensive survey of the analysis of anisotropic materials that can have up to twenty-one elastic constants. Focusing on the mathematically elegant and technically powerful Stroh formalism as a means to understanding the subject, the author tackles a broad range of key topics, including antiplane deformations, Green's functions, stress singularities in composite materials, elliptic inclusions, cracks, thermo-elasticity, and piezoelectric materials, among many others. Well written, theoretically rigorous, and practically oriented, the book will be welcomed by students and researchers alike.
Matrix Algebra
Authors: Ting T. T. C.
Published: November 2020

We will present in this chapter some aspects of matrix algebra that are needed in this book. Most results presented here can be found in standard books on matrix algebra. Proofs are provided for those results that are either easily derived or not readily available elsewhere. For readers who have no knowledge of matrix algebra, this chapter is essential for the rest of the book. They may find the one-chapter treatment of matrix algebra in the book by Hildebrand (1954) helpful and informative. For readers who have some knowledge of matrix algebra this chapter can be skimmed or skipped altogether, depending on how familiar they are with the subject. If they want to find the proofs omitted in this chapter or want to devote more time on the subject, the books by Hohn (1965) and Pease (1965) are recommended. The notations employed in this chapter have no relations, in most cases, with the notations adopted in the rest of the book. This point should be kept in mind in referring back to this chapter.
Green's Functions for Infinite Space, Halfspace, and Composite Space
Authors: Ting T. T. C.
Published: November 2020

One of the basic solutions for anisotropic elasticity, and for other subject for that matter, is the Green's function. The importance of Green's functions in constructing solutions to boundary value problems has been well recognized. We will study in this chapter Green's functions for infinite spaces, half-spaces, and bimaterials that consist of two half-spaces of dissimilar materials bonded together. Also studied are a composite space that consists of wedges of dissimilar materials and an angularly inhomogeneous space. Green's functions for the infinite space with the presence of a crack, an elliptic hole, or an elliptic inclusion will be studied in separate chapters. We will be concerned mainly with Green's functions due to a line of concentrated forces and a line dislocation that have the r-1 stress singularity where r is the radial distance from the line of forces or the line dislocation. Green's functions due to a concentrated couple, a double force, a center of dilatation, etc., that provide the r-2 stress singularities will be discussed in Section 8.12. We will see that most solutions can be expressed in a real form with the identities presented in Chapters 6 and 7. The Green's function for two-dimensional deformations of an infinite anisotropic elastic material subject to a line dislocation has been obtained by Eshelby et al. (1953), Stroh (1958), Willis (1970), Malen and Lothe (1970), and Malen (1971). Further developments of the Green's function to include a line force was given by Barnett and Lothe (1975a). The solution was in a complex form. A real form solution using an integral representation was derived by Barnett and Swanger (1971) and Asaro et al. (1973) (see also Mura, 1975). Most of the real form solutions obtained by these authors were for the displacement gradient, and hence for the strain. The stress was then obtained indirectly through the stress-strain relations. Chadwick and Smith (1977) did present real form solutions for the displacement as well as the stress directly. The solutions required the inverse of the 6x6 matrix (x1I + x2N) which can be achieved by employing (7.9-17).
Anisotropic Materials with an Elliptic Boundary
Authors: Ting T. T. C.
Published: November 2020

The determination of stress distribution in a solid with the presence of a hole or an inclusion has been a mathematically interesting and challenging problem. It is also an important problem in applications. The simplest geometry of the hole is a circle. For isotropic materials a hole of arbitrary shape can be transformed, in theory, to a circle by a conformal mapping (Muskhelishvili, 1953; see also Section 3.12). Therefore a circular hole is all one needs to study for isotropic materials. For anisotropic materials there are three complex variables ɀα=x1+pαx2 (α=1,2,3). It is in general not possible to transform a hole of given shape to the same circle for all three complex variables. An exception is the ellipse (Lekhnitskii, 1950; Savin, 1961). In this chapter we study various problems involving an elliptic boundary. The ellipse can be a hole, a rigid body, or an inclusion of different anisotropic materials. We will also consider an elliptic body subjected to external forces. For anisotropic elastic materials even the circular hole needs a transformation. There is practically no difference in the analysis if the ellipse is replaced by a circle. We may employ dual coordinate systems. One coordinate system is chosen to coincide with a symmetry plane of the material when such a plane exists. The other coordinate system is to coincide with the principal axes of the ellipse. The analysis is no more complicated than when a single coordinate system is employed. For some problems employment of dual coordinate systems reveal that certain aspects of the solutions are invariant with the orientation of the ellipse in the material.
Degenerate and Near Degenerate Materials
Authors: Ting T. T. C.
Published: November 2020

The Stroh formalism presented in Sections 5.3 and 5.5 assumes that the 6×6 fundamental elasticity matrix N is simple, i.e., the three pairs of eigenvalues pα are distinct. The eigenvectors ξα (α=l,2,3) are independent of each other, and the general solution (5.3-10) consists of three independent solutions. The formalism remains valid when N is semisimple. In this case there is a repeated eigenvalue, say p2=p1 ,but there exist two independent eigenvectors ξ2 and ξ1 associated with the repeated eigenvalue. The general solution (5.3-10) continues to consist of three independent solutions. Moreover one can always choose ξ2 and ξ1 such that the orthogonality relations (5.5-11) and the subsequent relations (5.5-13)-(5.5- 17) hold. When N is nonsemisimple with p2=p1, there exists only one independent eigenvector associated with the repeated eigenvalue. The general solution (5.3-10) now contains only two independent solutions. The orthogonality relations (5.5-11) do not hold for α,β=l,2 and 4,5, and the relations (5.5-13)-(5.5-17) are not valid. Anisotropic elastic materials with a nonsemisimple N are called degenerate materials. They are degenerate in the mathematical sense, not necessarily in the physical sense. Isotropic materials are a special group of degenerate materials that happen to be degenerate also in the physical sense. There are degenerate anisotropic materials that have no material symmetry planes (Ting, 1994). It should be mentioned that the breakdown of the formalism for degenerate materials is not limited to the Stroh formalism. Other formalisms have the same problem. We have seen in Chapters 8 through 12 that in many applications the arbitrary constant q that appears in the general solution (5.3-10) can be determined analytically using the relations (5.5-13)-(5.5- 17). These solutions are consequently not valid for degenerate materials. Alternate to the algebraic representation of S, H, L in (5.5-17), it is shown in Section 7.6 that one can use an integral representation to determine S, H, L without computing the eigenvalues pα and the eigenvectors ξα. If the final solution is expressed in terms of S, H, and L the solution is valid for degenerate materials.
Three-Dimensional Deformations
Authors: Ting T. T. C.
Published: November 2020

There appears to be very little study, if any, on the extension of Stroh's formalism to three-dimensional deformations of anisotropic elastic materials. In most three-dimensional problems the analyses employ approaches that are remotely related to Stroh's two-dimensional formalism. This is not unexpected, since this has been the situation between two-dimensional and three-dimensional isotropic elasticity. However it needs not be the case for three-dimensional anisotropic elasticity. Much can be gained if a connection to the Stroh formalism can be established. Barnett and Lothe (1975a) appeared to be the only ones who made a connection between a three-dimensional solution and Stroh's two-dimensional formalism. Earlier, several investigators obtained the Green's function for the infinite anisotropic medium in term of a line integral on an oblique plane in the three-dimensional space. That line integral, as we will see here, is one of Barnett-Lothe tensors on an oblique plane. We propose in this chapter extensions and applications of Stroh's two-dimensional formalism to certain three-dimensional deformations of anisotropic elastic solids.
The Dissociation of Small and Large Clusters
Authors: Baer Tomas , Hase William L.
Published: November 2020

Clusters are aggregates of loosely bonded molecules, in which each of the units retains the structure that it has as a free molecule. Because of the weak interactions among the molecules, clusters are stable only in cold environments such as are found in molecular beams. The weak intermolecular bonds provide an interesting testing ground for theories of intramolecular vibrational energy redistribution (IVR) and thus for theories of unimolecular dissociation. In addition, clusters constitute the bridge between the gas and liquid phases. Such phenomena as solvation, heat capacity, and phase transitions, which are ill defined for small clusters, become progressively more precise as the cluster size increases. Typical binding energies for neutral clusters are below 1000 cm-1. Ionic clusters, because of their ion-induced dipole forces, tend to be more strongly bonded with binding energies in excess of 5000 cm-1. Not infrequently, a neutral van der Waals dimer such as Ar2 with its binding energy of about 100 cm-1 (Tang and Toennies, 1986) changes its character upon ionization. The equilibrium bond distance is reduced from about 4 Å to 2.43 Å (Huber and Herzberg, 1979; Ma et al., 1993) and the binding energy increases to 10,000 cm-1 (Norwood et al., 1989; Furuya and Kimura, 1992). Clearly, the Ar2+ ion no longer meets our definition of a dimer. Rather, the neutral dimer is converted into a stable ion with a bond order of 1/2. A molecule that is frequently referred to as a cluster is C60. However, it is held together neither by weak bonds, nor is it composed of a collection of monomers. It is thus better classified as a large covalently bonded molecule. Table 10.1 summarizes some binding energies for various classes of dimers. When clusters comprise several loosely bound molecules, the atoms within each molecule are held together by strong bonds while the molecules themselves are attracted to neighboring molecules by weak bonds. This discrepancy in forces translates into disparities in the respective vibrational frequencies.
Designing Effective Systems: A Tool Approach
Authors: Kukla Charles D. , Morse Robert S.
Published: November 2020

Successfully designing large, complex systems requires including people and organization as elements in the system. Many current design approaches consider only the system’s technical aspects. We need an expanded approach to system design that incorporates the insights from each of three disciplines: system engineering, human factors, and organizational design. Only in this way can we address the dynamics of technology, people, and organizations in a single, coherent approach. The need for a new design strategy is magnified by the accelerating rate of change in the business and technology environment. System design efforts are often stymied by the fact that manufacturing businesses have constantly changing needs and requirements. Companies constantly need to shift the balance between quality, cost, and manufacturing capacity to meet evolving market goals. Moreover, these operations have to consider competitive pressures for the control of cost and schedule, rapidly changing product technology, changes in worker demographics, worker skill, and education, and regulatory pressures. The mission of a plant changes over time. Based on the notion that truly effective systems must offer tools for skilled work, our approach to system design offers an alternative to standard automation strategies, one better able to deal with this context of change. Systems designed as tools for skilled work can help organizations take full advantage of the investment they have already made in people, preserve the tacit knowledge and judgment that cannot be automated, and enable workers to solve problems and improve operations. These tools can help to expand the way existing data are used to help identify and solve problems. They can optimize the effectiveness of existing production processes. They do not constrain the workers by demanding that they follow strictly prescribed sequences, but instead enhance the workers’ ability to respond quickly and effectively to constantly changing combinations of events, to allocate and coordinate limited human resources and materials, and to work together more effectively through ongoing, company-wide collaboration. The purpose of this chapter is to describe some key elements of an expanded approach to system design. We first discuss the foundations, perspective, and techniques of our approach to system design.
Human Stereopsis, Fusion, and Stereoscopic Virtual Environments
Authors: Davis Elizabeth Thorpe , Hodges Larry F.
Published: November 2020

Two fundamental purposes of human spatial perception, in either a real or virtual 3D environment, are to determine where objects are located in the environment and to distinguish one object from another. Although various sensory inputs, such as haptic and auditory inputs, can provide this spatial information, vision usually provides the most accurate, salient, and useful information (Welch and Warren, 1986). Moreover, of the visual cues available to humans, stereopsis provides an enhanced perception of depth and of three-dimensionality for a visual scene (Yeh and Silverstein, 1992). (Stereopsis or stereoscopic vision results from the fusion of the two slightly different views of the external world that our laterally displaced eyes receive (Schor, 1987; Tyler, 1983).) In fact, users often prefer using 3D stereoscopic displays (Spain and Holzhausen, 1991) and find that such displays provide more fun and excitement than do simpler monoscopic displays (Wichanski, 1991). Thus, in creating 3D virtual environments or 3D simulated displays, much attention recently has been devoted to visual 3D stereoscopic displays. Yet, given the costs and technical requirements of such displays, we should consider several issues. First, we should consider in what conditions and situations these stereoscopic displays enhance perception and performance. Second, we should consider how binocular geometry and various spatial factors can affect human stereoscopic vision and, thus, constrain the design and use of stereoscopic displays. Finally, we should consider the modeling geometry of the software, the display geometry of the hardware, and some technological limitations that constrain the design and use of stereoscopic displays by humans. In the following section we consider when 3D stereoscopic displays are useful and why they are useful in some conditions but not others. In the section after that we review some basic concepts about human stereopsis and fusion that are of interest to those who design or use 3D stereoscopic displays. Also in that section we point out some spatial factors that limit stereopsis and fusion in human vision as well as some potential problems that should be considered in designing and using 3D stereoscopic displays. Following that we discuss some software and hardware issues, such as modelling geometry and display geometry as well as geometric distortions and other artifacts that can affect human perception.
Retail
Authors: Thrall Grant Ian
Published: November 2020

Retail real estate analysis is the most well developed, complex and technological of any of the other real estate product categories. This chapter begins with a review of the background literature. Real estate market analysis has been performed for retail longer than for any other category. Unlike medicine, in which some practices, such as bleeding a patient, have become obsolete, no major method that has been widely adopted by the industry during the past 100 years has subsequently gone out of use. Instead, these methods have been modified and incorporated into contemporary analysis and technology. This chapter next proceeds to the macro level with a presentation of how a real estate location strategy is developed for a large, multibranch retail chain. Afterward, a brief discussion of the micro-level strategy is presented following the four steps introduced in the preceding chapters. The methods, technology, and analysis of the four steps for retail real estate have already been presented in chapter 4. Because the retail side has been such a pioneer, methods developed for retail ultimately find use, with some modification, in real estate market analysis of all the other real estate product categories; hence, the four steps were presented as part of the general methods of chapter 4. It has always been the case that certain locations for retail activities offer distinct advantages over other locations. But knowing which locations were best has not al-ways been the complex task it is today. Until the late nineteenth century, the retail location decision was quite simple: always locate at the downtown commercial node. Changes in transportation technology increased the geographic range of the individual household. Each successive transportation era brought increasing geodemographic complexity to the city. The eras of transportation can be broken down by transportation mode: . . . First, households relied primarily on walking from home to work to shopping. Second, for some of the larger cities, the trolley car and other innovations in public transit brought an increased geographic reach of the average household. Third, the personal automobile allowed many households to move beyond the limited corridors of public transit.
Thermodynamics of Flowing Systems: with Internal Microstructure
Authors: Beris Antony N. , Edwards Brian J.
Published: November 2020

This much-needed monograph presents a systematic, step-by-step approach to the continuum modeling of flow phenomena exhibited within materials endowed with a complex internal microstructure, such as polymers and liquid crystals. By combining the principles of Hamiltonian mechanics with those of irreversible thermodynamics, Antony N. Beris and Brian J. Edwards, renowned authorities on the subject, expertly describe the complex interplay between conservative and dissipative processes. Throughout the book, the authors emphasize the evaluation of the free energy--largely based on ideas from statistical mechanics--and how to fit the values of the phenomenological parameters against those of microscopic models. With Thermodynamics of Flowing Systems in hand, mathematicians, engineers, and physicists involved with the theoretical study of flow behavior in structurally complex media now have a superb, self-contained theoretical framework on which to base their modeling efforts.
Introduction
Authors: Furbish David Jon
Published: November 2020

Fluids are involved in virtually all geological processes. Obvious examples are phenomena occurring at Earth’s surface in which fluid flow is a highlight: the flow of a lava stream, the play of a geyser, river flow and wind currents, the swash and backswash on a beach. Also obvious are phenomena that occur in the presence of fluid flows, such as sediment motion. Less obvious, but readily imaginable in terms of their behaviors, are fluid motions occurring within Earth’s crust: flows of magma and ground water, and expulsion of brines from sediments during compaction. In addition, a bit of reflection will recall a host of phenomena in which fluid behavior, although not the highlight, may nonetheless take on a significant role: initiation of landslides, seismic activity, glacier movement, taphonomic organization, and fracture mechanics. With these should be considered instances in which the geological material containing a fluid can influence its fundamental behavior at a molecular scale. An example is flow through very small rock pores, where molecular forces interacting among fluid molecules and pore surfaces can lead to a structural arrangement of the fluid molecules such that their mechanical behavior is unlike that which occurs in large pores, where the bulk of the fluid is “far” from pore surfaces. It is thus understandable that to describe many geologic phenomena requires knowing how fluids work. It is also natural to begin by considering how fluids behave in a general way, then in turn, how they are involved in specific geological processes. There are several approaches for describing fluids and their motions, and the choice of one, or some combination, depends on the sort of insight desired as well as the specific problem being considered. Fluid statics, as the name implies, involves considering the properties of fluids that are at rest in some inertial frame of reference. Note that this frame of reference may actually be moving relative to the Earth frame of reference, so long as the fluid motion is like that of a rigid body. An important example of our use of fluid statics will be in developing the hydrostatic equation, which formalizes how fluid pressure varies with depth.
Conservation of Mass
Authors: Furbish David Jon
Published: November 2020

The concept of conservation of mass holds a fundamental role in most problems in fluid physics. For a given problem this concept is cast in the form of an equation of continuity. Such an equation describes a condition—conservation of mass—that must be satisfied in any formal analysis of a problem. Thus an equation of continuity often is one of several complementary equations that are solved simultaneously to arrive at a solution to a flow problem, for example, the flow velocity as a function of coordinate position in a flow field. (Typically these complementary equations, as we will see in later chapters, involve conservation of momentum or energy, or both.) Although we did not explicitly use this idea in analyzing the one-dimensional flow problems at the end of Chapter 3, it turns out that continuity was implicitly satisfied in setting up each problem. We will return to these problems to illustrate this point. We will develop equations of continuity for three general cases: purely fluid flow, saturated single-phase flow in porous media, and unsaturated flow in porous media. The most general of the three equations is that for unsaturated flow, where pores are partially filled with the fluid phase of interest, such that the degree of saturation with respect to that phase is less than one. We will then show that this equation reduces, in the special case in which the degree of saturation equals one, to a simpler form appropriate for saturated single-phase flow. Then, this equation for saturated flow could be reduced further, in the special case in which the porosity equals one, to a form appropriate for purely fluid flow. For pedagogical reasons, however, we shall reverse this order and consider purely fluid flow first. In addition we will consider conservation of a solid or gas dissolved in a liquid, and take this opportunity to introduce Fick’s law for molecular diffusion. For simplicity we will consider only species that do not react chemically with the liquid, nor with the solid phases of a porous medium. Most of the derivations below are based on the idea of a small control volume of specified dimensions embedded within a fluid or porous medium.
Turbulent Flows
Authors: Furbish David Jon
Published: November 2020

Many geological flows involve turbulence, wherein the velocity field involves complex, fluctuating motions superimposed on a mean motion. Flows in natural river channels are virtually always turbulent. Magma flow in dikes and sills, and lava flows, can be turbulent. Atmospheric flows involving eolian transport are turbulent. The complex, convective overturning of fluid in a magma chamber or geyser is a form of turbulence. Thus, a description of the basic qualities of these complex flows is essential for understanding many geological flow phenomena. Turbulent flows generally are associated with large Reynolds numbers. Recall from Chapter 5 that the Reynolds number Re is a measure of the ratio of inertial to viscous forces acting on a fluid element, . . . Re = ρUL/μ . . . . . . (14.1) . . . where the characteristic velocity U and length L are defined in terms of the particular flow system. Thus, turbulence is typically associated, for given fluid density ρ and viscosity μ, with high-speed flows (although we must be careful in applying this generality to thermally driven convective motions; see Chapter 16). A simple, visual illustration of this occurs when smoke rises from a cigar within otherwise calm, surrounding air. The smoke acts as a flow tracer. Smoke molecules at the cigar tip start from rest, since they are initially attached to the cigar. Upward fluid motion, as traced by the smoke, initially is of low speed, and viscous forces have a relatively important influence on its behavior. The flow is laminar; smoke streaklines are smooth and locally parallel. But as the flow accelerates upward, it typically reaches a point where viscous forces are no longer sufficient to damp out destabilizing effects of growing inertial forces, and the flow becomes turbulent, manifest as whirling, swirling fluid motions (see Tolkien [1937]). Throughout this chapter we will consider only incompressible Newtonian fluids. Unfortunately, the complexity of turbulent fluid motions precludes directly using the Navier–Stokes equations to describe them. Instead, we will adopt a procedure whereby the Navier–Stokes equations are recast in terms of temporally averaged or spatially averaged values of velocity and pressure, and fluctuations about these averages.
Strategic Development: Trudging up the Staircase or Swimming with the Tide?
Authors: Siegler Robert S.
Published: November 2020

As described in the previous chapter, children’s thinking is highly variable. The present chapter focuses on implications of this variability for understanding development. Thinking about a pair of visual metaphors may help facilitate recognition of these implications. The first, which I believe underlies most depictions of development, is the staircase metaphor. The second, which I believe offers a superior alternative, is the overlapping waves metaphor. Cognitive developmentalists have often phrased their models in terms that suggest that children of a given age think about a given task in a single way. W-year-olds are said to have a particular mental structure, a particular processing limit, a particular theory, strategy, or rule that gives rise to a single type of behavior. Change involves a substitution of one mental entity (and accompanying behavior) for another. The basic conceptualization that seems to underlie these models is aptly captured in the title of Robbie Case’s (1992) recent book The Mind’s Staircase. The visual metaphor that this title evokes is, I believe, central to most cognitive-developmental treatments of change: Children are depicted as thinking in a given way for an extended period of time (a tread on the staircase); then their thinking undergoes a sudden, vertical shift (a riser on the staircase); then they think in a different, higher way for another extended period of time (the next tread); and so on. This view of development is most closely identified with Piagetian and neo-Piagetian approaches, such as those of Piaget and Case. Thus, as shown in Figure 4.1, we see development depicted within Piaget’s theory as involving sensorimotor activities from birth to about 2 years; preoperational thinking from 2 to 7 years; concrete operational thinking from 7 to 12 years; and formal operational thinking from 12 years onward. Within Case’s theory, we see thinking depicted as advancing from the sensorimotor level between birth and 18 months, to the relational level from 18 months to 5 years, to the dimensional level between 5 and 11 years, and to the formal level at age 11 and beyond. Although this view of development is associated with the Piagetian and neo-Piagetian traditions, it is far from unique to them.
The Challenge of Limits
Authors: Hardin Garrett
Published: November 2020

A funny thing happened on the way to the second nationwide Earth Day in 1990. Twenty years earlier the first Earth Day had been saluted with much talk about population problems. At that time world population stood at 3.6 billion. But when the second Earth Day rolled around, the topic of population was almost completely ignored. Was that because world population had stopped growing? Hardly: in the intervening two decades it had increased 47 percent to an estimated 5.3 billion— an increase of 1.7 billion (more than six times the present population of the United States). Common sense tells us that the per capita share of environmental riches must decrease as population numbers increase, and waste disposal necessarily becomes an ever greater problem. Of course common sense is sometimes wrong. But if that is so in this instance, the celebrants of the 1990 Earth Day should have been shouting, "We've found the secret of perpetual growth!" A few incurable optimists did defend this position, but most people lumped their claims with those of the flat earthers, ignoring both. The celebrants were generally silent about the 47 percent increase in population. Why? The answer comes in two parts, the first being historical. It is now known that the planners of Earth Day 1990 were under economic pressure to leave population out of the picture. When directors of philanthropic foundations and business concerns were solicited for financial support they let it be known that they would not look kindly on a population emphasis. Money talks, silence can be bought. (Why the bankrollers shied at population will become clear later.) The second aspect of the answer is more subtle. It has long been recognized that some of our most deeply held views are not neat, precise propositions but broadly "global" attitudes that act as the gatekeepers of the mind, letting in only those propositions that do not challenge the dominant picture of reality. Germans call such gatekeeper attitudes Weltanschauungen, an impressive mouthful that is quite adequately translated as "worldviews." For all but the last few hundred years of human history the dominant worldview was a limited view: resources were limited, human nature was fixed, and spending beyond one's income was a sin. This essentially conservative perception prevailed until about 1600.
Carrying Capacity
Authors: Hardin Garrett
Published: November 2020

An often quoted passage of Arthur Conan Doyle's story "Silver Blaze" makes the point that the absence of data can be a datum. When the mystery of the purloined racehorse seems insoluble, Police Inspector Gregory asks Sherlock Holmes:… "Is there any point to which you would wish to draw my attention?" "To the curious incident of the dog in the night-time." "The dog did nothing in the night-time." "That was the curious incident," remarked Sherlock Holmes…. The dog that does not bark attracts no attention to itself. It takes insight to recognize that a nonhappening can be an alarm. Herman Daly showed a Holmeslike insight when he called attention to the bark that was absent from a would-be authoritative study made by a group of economists reporting to the prestigious National Research Council in 1986 on population growth and economic development. In 108 pages of text there is not a single mention of carrying capacity, a concept that should be central to all discussions of population and environment. It is as though gravity were left out of a treatise on the dynamics of the solar system; or assets and liabilities were left out of a textbook on business accounting. If civilization survives another century, and if there are still economists, a history of what will then be called "modern economics" may well begin with a belittling account of the "premodern" economics of the twentieth century in which carrying capacity plays no role. Nothing shows so well the impermeability of the barriers between academic disciplines as the silence of economists about a concept that dominates discussions of game management, a discipline concerned with population and environment problems as they affect animals other than Homo sapiens. Economists, dealing only with human populations, probably unconsciously embrace the human exemptionist doctrine (Chapter 15), though their commitment is seldom no more than implicit in their statements (Box 20-1). Two serious criticisms can be leveled against most of the authors quoted in the box. First, it is obvious that they desperately yearn for a world without limits. This is particularly evident in the last quotation, by Gro Harlem Brundtland, who chaired the United Nations commission that issued this statement. One can praise the heart of the commission without agreeing with the head.
The Necessity of Immigration Control
Authors: Hardin Garrett
Published: November 2020

Every American schoolchild knows about the Statue of Liberty and the accompanying poem, "Give me your tired, your poor, / Your huddled masses yearning to be free . . .". Implicitly, our children are doubly deceived. In the first place the official name of the statue is "Liberty Enlightening the World"—that is, bringing light to the world, educating it: not inviting the whole world to come in. In the second place there is the implication that the poetry on the base expresses official policy. It does not. Emma Lazarus's words were added to the base seventeen years after the statue was erected, and without the blessing of Congress, much less of the multitudes of Americans who might be asked to make room for all the huddled masses. It is only human to want to share with the needy, but the sharing impulse must be curbed to some extent, for the goods of this world are limited. Whenever either matter or energy is redistributed, the consequence is a zero-sum game: that which one person (or group) gains is lost by others. Information, however, is different: sharing it can lead to a plus-sum game. When I give you a bit of information I do not thereby lose it. Indeed, after absorbing this information you may send it back to me in improved form. We both gain. The lady in New York Harbor promises only to enlighten the world, not to feed and clothe it. She proposes to make other people more independent, not less. Only America has a statue that is presumed to welcome immigrants; other nations know better. Their traditions are exclusionary. Or so it seemed until 1989, when political troubles in eastern Europe led to massive movements of people, thus forcing a reassessment of policies. From now on, more and more people throughout the world will be asking Cain's question: "Am I my brother's keeper?" They will have to remember that the singular brother has expanded to become hundreds of millions of brothers and sisters—who are continuing to increase. In the face of exponential growth, a zero-sum game can end fatally in a commons. Yet the opposite extreme, complete isolationism, has its dangers too.