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Summary

The strongest trend in consumer electronics at present is to encode analog signals to digital and record and process them digitally. The consumer unit must then decode the recorded digital data to output what is in most respects an excellent approximation to the original analog signal.

Video discs

Unlike magnetic tape technology, which began with audio machines (Chapter 5) and was extensively upgraded to accommodate video (Chapter 8), digital discs began with video and were then downscaled to audio.

The first digital video disc player hit the market in 1978. There were two main technologies available in the players. Each of them required its own type of disc. Each type of disc had pits on it to differentiate between logic “ 1 ” and “0.” Some of the players had the pits embedded in a groove to facilitate reading by a stylus, whereas others used a dynamic tracking technique that required no grooves.

The two main technologies were the optical pickup system and the capacitance pickup system. Optical pickups use a dynamic tracking laser system to read an ungrooved disc. The “read” mechanism never touches the disc. Capacitance pickups sensed the change in capacitance between a conductive pickup element and a slightly conductive record surface. When the pickup element was over a pit, there was less capacitance. This changed the frequency of an oscillator. The frequency changes were discriminated to produce logic levels. The discs for this type of system might or might not have grooves, but the “read” mechanism did contact the disc surface.

In the U.S. market, the main contenders were the Philips (optical) and the RCA Selectavision (grooved-capacitance). Both produced excellent quality pictures. The RCA system had the advantages of lower price (about half that of optical systems) and an aggressive marketing of low-cost (<$20) video discs. The Philips system, which was produced by others as well, benefited from a public perception that discs read by a laser should last forever. Practically, this may be of little importance except to rental businesses. RCA tests showed that they could play a disc 100 times with no visible picture degradation. This is probably well over the lifetime enjoyment threshold for most people for most movies.

As it turned out, however, all of the video disc technologies were pretty well overshadowed by the VCR (Chapter 8).

Summary

When designing houses, architects frame their design according to conceptual architectures that capture the physiological and cultural aspects of human life relevant to the construction of dwellings. Architects know about sizes, shapes, colors, temperatures, and lighting. They think about issues such as open versus divided spaces or functionality versus aesthetics. They include basic components of living quarters such as facilities for physiological functions (eating, resting, bathing), social activities (congregating, playing, working), and storage (food, clothing, vehicles). When designing an office space, however, they frame their design according to a different architecture.

In other fields as well, designers usually have at their disposal some conceptual architectures reflecting the theories and perspectives that their professional communities have developed through conceptual analyses of their domain of design. The purpose of a conceptual architecture is to lay down the general elements of design. It is not a recipe; it does not tell a designer how to perform a specific design. But it does state what needs to be in place. It is a tool that can guide a design by outlining:

1) the general questions, choices, and trade-offs to address – these define the dimensions of a design “space”
2) the general shape of what needs to be achieved – the basic components and facilities to provide.

Conceptual architectures can exist at different levels of analysis. For instance, designers of computer systems base their designs on conceptual architectures at different levels, with different components and trade-offs.

Summary

In some circumstances, a person is covered by more than one health insurance plan. For instance, children may be covered under the plans of both parents. Similarly, retired workers may be eligible for Medicare, but may still be on the plan of their former employer. If each plan paid the usual 80% of medical expenses for a given service, a patient would receive benefits in excess of the actual bills. But U.S. insurance companies that provide group coverage have signed a nationwide agreement to coordinate the benefits received under multiple coverages. Coordination of benefits (COB) is a fairly common task. In the most common case, the primary carrier covers the first 80%, and then the secondary carrier takes care of the remaining 20%. But coordination clauses can become rather complicated, sometimes leaving both customers and processors confused.

Especially confusing was a new plan for retired employees covered by both Alinsu, through their former employer, and Medicare. This plan is known as coordination of benefit “by reduction” because Alinsu reduces its liability by the amount of Medicare payments. In other words, rather than filling the gap between Medicare payments and the actual bills, as in regular coordination, Alinsu merely fills the gap between Medicare's coverage and its own. So if a treatment is covered by Medicare at 70% and by Alinsu at 80%, Alinsu pays only 10%. If Medicare coverage is equal to or higher than its own, Alinsu pays nothing.

Summary

The mix of participation and non-participation that shapes our identities has to do with communities in which we become invested, but it also has to do with our ability to shape the meanings that define these communities. Each member of a couple, for instance, may identify very deeply with their being a couple. They may also be viewed and identified as a couple by all their friends and relatives. It may be an unquestionable part of who they are. Yet there may still be substantial argument about what it means to be a couple as a way of living together, and who can determine at any given time how being a couple is to be implemented. The fact that they care enough about being a couple to argue about it reflects the degree to which they identify with the relationship. Their identification holds them together enough to debate the question, but the question is not resolved by identification itself. Working out what it means to be together and how to go about living as a couple is an additional dimension of their relationship that contributes in its own right to shaping the kinds of identity that belonging to that couple will produce.

More generally, our identities form in this kind of tension between our investment in various forms of belonging and our ability to negotiate the meanings that matter in those contexts. Identity formation is thus a dual process.

Summary

The main issue at the inception of color TV broadcasting was again one of compatibility. The requirement that the color signal be usable by black-andwhite TV sets led to a system in which additional information was broadcast along with the previously used signals. This additional information was simply not processed by monochrome receivers. Compatibility also requires that a color set be able to receive a monochrome picture properly.

To understand the characteristics that the color signal must have, it will help to digress and take a look at the color cathode-ray tube (CRT).

The color CRT

Even though the predominant color reproduction method used today is pretty much a “brute force” solution, it is at the same time, a testimonial to modern manufacturing techniques that it can be mass produced with the high degree of precision required to make it work.

In the back of the neck of the CRT, arranged as shown in Fig. 7.1, are three electron guns instead of the single on-axis gun used in a B/W set. Even though these guns obviously don't shoot electrons of various colors, they are identified by the color they will cause on the screen. Instead of having a single (white) phosphor as in monochrome TV, the color CRT has three different phosphor colors on the inside face of the CRT. They are, in most cases, arranged in a dot pattern as shown in Fig. 7.2. The sets of dots enclosed in the triangular outlines include one of each color and are called triads. On a 19” (diagonal measurement) color CRT, the dots are about .38 mm in diameter. Between the dots and the gun assembly and close to the dots lies a sheet of metal called the shadow mask. There are holes in the shadow mask, positioned over the center of each triad of dots. The function of this mask is illustrated by Fig. 7.3, which shows only two guns and two dots. It can be readily perceived how the concept could be extended to three of each if the third spatial dimension were added.

Note that although the vertical scale shown is the same for the dots and the guns, it is not the same as the horizontal scale.

Summary

As far as this author is aware, this book blazes new ground. It covers a subject that has been much neglected in traditional electrical engineering education. As such, it may have value as a professional book, as well as serving its original purpose as a text. For such a book, it is mandatory that both the purpose of writing the book and the philosophy governing its structure be articulated.

When I was in high school, I had a home-based business of repairing stereos, radios, and televisions. The knowledge to do this was obtained by reading various technician-level books and magazines on the subject and by experience obtained in the field.

Upon beginning college as an electrical engineering (EE) major, I had eager expectations that the curriculum would teach the principles upon which the equipment worked. Alas, those expectations remained unfulfilled. The “real world” circuits, whose schematics a service technician is used to seeing, are generally far more complex than those in the electronics textbooks. I had a certain sense of having been cheated. Not until later did I realize that presenting simplified circuits in the electronics textbooks was thought of as an act of mercy by the textbook authors. It is obviously easier to understand a simplified circuit than a “real-world” one.

This led to Phase II of this book's origins. After graduation I realized that an EE education at least provided the tools needed to understand consumer electronic circuits at a more advanced level. Commencing a career in college teaching gave additional impetus. A survey of seniors showed a great deal of interest in a course in consumer electronics. This led to a search for books that would give the information needed at the level of understanding desired. This search engendered disappointment of a different sort. The available materials, without exception, fell into three categories:

Summary

The negotiation of meaning, I have argued, is the level of discourse at which the concept of practice should be understood. The second piece of necessary groundwork is to associate practice with the formation of communities. By associating practice with community, I am not arguing that everything anybody might call a community is denned by practice or has a practice that is specific to it; nor that everything anybody might call practice is the defining property of a clearly specifiable community. A residential neighborhood, for instance, is often called “the community” but it is usually not a community of practice. Playing scales on the piano is often called practice – as in “practice makes perfect” – but it does not define what I would call a community of practice. Rather, I am claiming that associating practice and community does two things.

1) It yields a more tractable characterization of the concept of practice – in particular, by distinguishing it from less tractable terms like culture, activity, or structure.
2) It defines a special type of community – a community of practice.

Because its constituent terms specify each other in this way, the term community of practice should be viewed as a unit. In Part I, when I use the term community or the term practice by itself, it is just an abbreviation to make the text less cumbersome.

Summary

Our institutions, to the extent that they address issues of learning explicitly, are largely based on the assumption that learning is an individual process, that it has a beginning and an end, that it is best separated from the rest of our activities, and that it is the result of teaching. Hence we arrange classrooms where students – free from the distractions of their participation in the outside world – can pay attention to a teacher or focus on exercises. We design computer-based training programs that walk students through individualized sessions covering reams of information and drill practice. To assess learning we use tests with which students struggle in one-on-one combat, where knowledge must be demonstrated out of context, and where collaborating is considered cheating. As a result, much of our institutionalized teaching and training is perceived by would-be learners as irrelevant, and most of us come out of this treatment feeling that learning is boring and arduous, and that we are not really cut out for it.

So, what if we adopted a different perspective, one that placed learning in the context of our lived experience of participation in the world? What if we assumed that learning is as much a part of our human nature as eating or sleeping, that it is both life-sustaining and inevitable, and that – given a chance – we are quite good at it? And what if, in addition, we assumed that learning is, in its essence, a fundamentally social phenomenon, reflecting our own deeply social nature as human beings capable of knowing?

Summary

Education, in its deepest sense and at whatever age it takes place, concerns the opening of identities – exploring new ways of being that lie beyond our current state. Whereas training aims to create an inbound trajectory targeted at competence in a specific practice, education must strive to open new dimensions for the negotiation of the self. It places students on an outbound trajectory toward a broad field of possible identities. Education is not merely formative – it is transformative.

In this chapter, I will argue that issues of education should be addressed first and foremost in terms of identities and modes of belonging (as discussed in Part II), and only secondarily in terms of skills and information. To make this argument, I will adopt much the same structure as in the previous chapter. Again, I will have two main sections that apply the framework of Chapter 10.

1) I will first use the four dimensions of design introduced there to discuss issues of educational design.
2) I will then use the framework of the three modes of belonging and of learning communities to discuss education as a process of identity transformation.

This discussion assumes neither that education takes place in schools as we know them nor that education is for children. In fact, once education is understood in terms of identity, it may no longer seem such a good idea to front-load “education” at the beginning of a life.

Summary

Endocrine glands and tissues display a diversity in their gross morphological and histological patterns. This is particularly apparent when comparing species from phyletically distant groups. In some instances the physiological significance of these differences has been recognized but in most this is not so and may be related to the initial pattern of embryonic growth. If, however, one intuitively suspects a close relationship between structure and function, then the lack of a known correlation may merely reflect our ignorance.

The endocrines may display several different types of morphological Variation (see, for instance, Pang and Schreibman, 1986; Matsumoto and Ishii, 1992). The positions of the endocrine glands in the body may not be the same. The Variation can be of a minor nature, such as that seen with the ultimobranchial bodies, which can be situated near the heart or the thyroid gland. In some fish, however, thyroid tissue may vary in position from the branchial region to the kidney. Endocrine cells may show varying degrees of association and be scattered as individual cells, in small segments, or “islets.” or be closely associated as a compact gland enclosed in a capsule. Such aggregation of an endocrine tissue is commonly seen as one ascends the evolutionary (or the phyletic) scale. In addition, different endocrine tissues may display diverse associations with each other, as for instance the conglomeration of chromaffin and interrenal (or adrenocortical) tissue in the adrenal gland. Their relationship to the neural and vascular tissues can be very important. Pituitary tissues usually cannot function properly if they are transplanted to other parts of the body (ectopic transplant) or if the small blood vessels between the gland and the brain are cut. The major blood vessels not only carry hormones away from endocrine tissues but also supply them with nutrients and Controlling Stimuli. The pattern of the vasculature within the gland can also be important for its correct functioning.

The types of cell that make up an endocrine gland are, not surprisingly, similar in homologous glands among the vertebrates. Such similarities, as reflected by their microscopic anatomy (size, shape, the presence of inclusions, granules, etc.) and their reactions with dyes (tinctorial relationships), serve to aid in their identification. Antibodies to specific hormones are used to identify the cells where they are formed.

Summary

The reproductive process is not essential for the life of the individual, though it may make it more interesting, but it is necessary for the perpetuation of the species. In many so-called lower forms of life, reproduction may be an asexual process. A notable disadvantage of this type of reproduction is a diminution in the chances of genetic variability, and the transmission of such inherited changes to other individuals, so that evolutionary adaptation is hampered. Reproduction is a complex process and this is especially true in species that occupy environments where the conditions are variable and large physicochemical changes occur. The young, developing animal is not usually as adaptable as the adult to such changes in the environment, and so must either be protected from these deviations by the parents or be produced on occasions that are most suitable to its more limited physiological capabilities. In vertebrates both conditions usually prevail; the embryo may develop to a quite advanced stage before becoming independent of the parent and it is usually produced during a season when such conditions as the temperature and food and water supply are favorable.

Reproduction in vertebrates, therefore, involves considerable physiological coordination. The sexual process that requires the union of the sperm and ova necessitates complex physiological, social, and morphological arrangements to ensure that these gametes each ripen at a similar time, and that the two sexes then meet and effect their union. The growth and differentiation of the fertilized egg often involve complex parental care, which may occur in utero, within the parent itself, or in an egg that is specially produced to meet the potential needs of the embryo. Care of the young often continues for a period of time following such initial development in the egg or in utero. The foregoing events may not be possible, or successfully accomplished, except during certain seasons of the year when the conditions are favorable.

In vertebrates, the coordination of all the processes outlined above involves hormones and the degree of complexity in their actions directly reflects the intricacies of the reproductive processes in a particular species. The endocrine control of reproduction in humans is therefore more involved than in a jawless fish, like the lamprey.

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Figure credits

9 - Digital audio

Summary

Chapter 10 - Learning architectures

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Contents

Vignette II: The “C, F, and J” thing

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Chapter 9 - Identification and negotiability

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Prologue: Contexts

7 - Color TV

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Preface

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Bibliography

Notes

Chapter 2 - Community

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Introduction: A social theory of learning

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Chapter 12 - Education

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Part II - Identity

Frontmatter

2 - Comparative morphology of the endocrine tissues

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9 - Hormones and reproduction

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Index

References

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