Power semiconductor devices are distinguishedby the high current densities at which theyoperate while on, and the high voltages they mustwithstand when off. These requirements haveserious consequences for both their physicalstructure and electrical behavior. In this chapterwe consider their structural and behavioraldepartures from the ideal devices studied inChapter 16.

In Chapter 12 we introduced the process oflinearization for certain classes of nonlinearaveraged-circuit models. This allowed us to obtainLTI circuit models for small perturbations ofaveraged values from their constant values innominal, steady-state operating conditions. TheseLTI models then served as the basis for stabilityevaluation and control design in the examplesconsidered in Chapter 12.

A rectifier converts ac to dc. A basicrectifier circuit produces dc in the electricalengineering sense, that is, unipolar current flow.It does not produce dc in the mathematical sense,that is, a waveform that is constant in time andwhose spectrum consists of a single zero-frequencycomponent. A rectifier’s output containsconsiderable ac content. These ac componentsresult in fluctuations, called ripple, about the averagevalue of the dc output. Eliminating this rippleand obtaining an approximation to “pure” dcrequires insertion of a filtering process afterthe basic rectification function.

All the preceding chapters have led to this one fundamental question: can intelligence be increased? It is a simple question, but what exactly does it mean? As discussed in Chapters 2 and 3, from a scientific standpoint, intelligence can mean an assessment score (from a reliable and valid standardized test), a broad factor (like verbal, visuospatial, or perceptual ability), and the general factor common to all mental abilities (the g-factor). The measured performance on any given cognitive test results from the contribution of g, the specific ability tapped by the test, and the specific skills required for such a test. Therefore, when we observe an increase in the measures we administer, the change can be at the test, the ability, or the g level. An increase can be small, albeit statistically significant, or large enough to have a measurable effect on a relevant outcome variable like educational achievement or job performance. An increase can be temporary or long-lasting. In this chapter, we mean something potentially more interesting than an increase in IQ scores, something that is more permanent, and something that impacts g. As you were reading other chapters, perhaps you considered questions like the following:

• Is there anything I can do to be more intelligent?

• Can intelligence be increased beyond a person’s genetic potential?

• Is there a theoretical limit on just how smart any individual can become?

• Do children and adults have an inner genius that can be unlocked?

We begin our study of rotational motion with the definitions and detailed examination of the fundamental quantities which we will use throughout this book. We then proceed with a description of kinematics in rotational motion by drawing analogies from our knowledge of one-dimensional kinematics in linear motion.

In this chapter, we address several fundamental issues that are important for learning about the scientific concept of intelligence. Many of the arguments about intelligence are less informative than they might be. Often, disagreements are misdirected because concepts of intelligence differ, and there is confusion about the relation between test scores and intelligence. Here we provide a framework for constructively discussing theories, models, and facts about intelligence.

Many of the facts discussed in this book may come as a surprise or even a shock, given that there is so much misinformation about intelligence in high school courses, among teaching faculties in colleges and universities, in the workplace, and in the media. It is quite all right to be skeptical, and we encourage it for every page of this book, but the weight of evidence presented in each chapter supports the following basic statements, which have been replicated across decades and reinforced by recent research:

1. 1. Intelligence can be defined for scientific investigations.

2. 2. Standard measures of intelligence provide quantitative assessments of individual differences for rigorous statistical analyses despite acknowledged limitations.

3. 3. Standard intelligence tests have the required reliability and validity for scientific study.

4. 4. Standard tests of mental ability, including IQ tests, are not biased against any population when administered and interpreted properly.

5. 5. The general factor of intelligence (g), especially when assessed by a diverse battery of mental ability tests, is the single most predictive construct in psychology for a wide variety of real-world relevant social outcomes.

6. 6. Measures of g are related to a number of quantifiable brain features that appear to have developmental sequences.

7. 7. Individual differences in intelligence are influenced by genetics, although details at the molecular level are just beginning to be investigated. Nongenetic factors are also relevant, but there also is no clear model of the mechanics of their impact (although the mechanisms must be biological and ultimately influence the brain).

8. 8. The sources of average population differences for IQ and other measures of mental ability remain unknown, but science is making progress disentangling purported influences.

9. 9. So far, there is no proven way to increase the general ability to integrate cognitive abilities (the g-factor), but the possibility is at an exciting frontier of neuroscience and molecular genetic research.

10. 10. More intelligence is no guarantee of being a better person in any sense, but perhaps enhanced intelligence will help our species solve long-standing global problems.

The preceding chapter presented severalexamples of perturbations from nominal operationof power electronic systems. These examplesmotivated the need for dynamic modeling of powerconverters, in order to understand suchperturbations and to design appropriatecontrollers. We introduced the idea of circuitaveraging as a means of obtaining simple andinformative dynamic models in circuit form.

Angular displacements that occur about the same axis or parallel axes, on the other hand, do follow the commutative law. Also, infinitesimally small angular displacements are commutative. To avoid confusion, we will treat all finite angular displacements as scalar quantities. However, we will have occasion to treat infinitesimal angular displacements as vectors.

The journey through rotational motion is not quite done. In fact, we are just beginning. This chapter introduces a few topics which would be covered in an intermediate-level mechanics course. The topics include more advanced physical phenomena, such as gyroscopic precession, and the mathematical formalism of parameterizing rotations using matrices.

This book is about the nature of intelligence, its causes and uses, and why it differs among people. Scientific psychology has much to say about intelligence, but unfortunately, much that has been said is misunderstood.

These are statements about the importance of intelligence for everyday life. They seem consistent with our own experiences, but they also could imply a cognitive elitism that many find uncomfortable. Nonetheless, compelling data support these statements and imply that everyday life can be seen as one long continuous intelligence test, and that the test is getting harder as modern life becomes more complex (Gottfredson, 1997; Gordon, 1997; Hunt, 1995).