bluuebunny/crossref_metadata_2025 huggingface dataset:
Voltage-Dependent Events in the Dendritic Tree
Authors: Koch Christof
Published: November 2020

So far, we worked under the convenient fiction that active, voltage-dependent membrane conductances are confined to the spike initiation zone at or close to the cell body and that the dendritic tree is essentially passive. Under the influence of one-dimensional passive cable theory, as refined by Rail and his school (Chaps. 2 and 3), the passive model of dendritic integration of synaptic inputs has become dominant and is taught in all the textbooks. Paradoxically, from the earliest days of intracellular recordings from the fat dendrites of spinal cord motoneurons with the aid of glass microelectrodes, active dendritic responses had been witnessed (Brock, Coombs, and Eccles, 1952; Eccles, Libet, and Young, 1958). Today, there exists overwhelming evidence for a host of voltage-dependent sodium and calcium-conductances in the dendritic tree. In the following section we summarize the experimental evidence and discuss current biophysical modeling efforts focusing on the question of the existence and genesis of fast all-or-none electrical events in the dendrites. We then turn toward possible functional roles of active dendritic processing. One word of advice. It has been argued that linear cable theory as applied to dendrites and taught in the first chapters of this book is irrelevant in the face of all this evidence for active processing and can be relegated to the dustbin. However, this would be a mistake. Under many physiological conditions these nonlinearities will not be relevant. Even if they are, the resistive and capacitive cable properties of the dendrites profoundly influence the initiation and propagation of dendritic action potentials and other active phenomena. Thus, for a complete understanding of the events in active dendritic trees we need to be thoroughly versed in cable theory. The issue of dendritic all-or-none electrical events must be seen as separate from the broader question of the existence and nature of active, that is, voltage-dependent, membrane conductances in the dendritic tree.
Computing with Neurons: A Summary
Authors: Koch Christof
Published: November 2020

We now have arrived at the end of the book. The first 16 chapters dealt with linear and nonlinear cable theory, voltage-dependent ionic currents, the biophysical origin of spike initiation and propagation, the statistical properties of spike trains and neural coding, bursting, dendritic spines, synaptic transmission and plasticity, the types of interactions that can occur among synaptic inputs in a passive or active dendritic arbor, and the diffusion and buffering of calcium and other ions. We attempted to weave these disparate threads into a single tapestry in Chaps. 17-19, demonstrating how these elements interact within a single neuron. The penultimate chapter dealt with various unconventional biophysical and biochemical mechanisms that could instantiate computations at the molecular and the network levels. It is time to summarize. What have we learned about the way brains do or do not compute? The brain has frequently been compared to a universal Turing machine (for a very lucid account of this, see Hofstadter, 1979). A Turing machine is a mathematical abstraction meant to clarify what is meant by algorithm, computation, and computable. Think of it as a machine with a finite number of internal states and an infinite tape that can read messages composed with a finite alphabet, write an output, and store intermediate results as memory. A universal Turing machine is one that can mimic any arbitrary Turing machine. We are here not interested in the renewed debate as to whether or not the brain can, in principle, be treated as such a machine (Lucas, 1964; Penrose, 1989), but whether this is a useful way to conceptualize nervous systems in this manner. Because brains have limited precision, only finite amounts of memory and do not live forever, they cannot possibly be like “real” Turing machines. It is therefore more appropriate to ask: to what extent can brains be treated as finite state machines or automata! Such a machine only has finite computational and memory resources (Hopcroft and Ullman, 1979). The answer has to be an ambiguous “it depends.”
Optimal Solution of Nonlinear Equations
Authors: Sikorski Krzysztof A.
Published: November 2020

Optimal Solution of Nonlinear Equations is a text/monograph designed to provide an overview of optimal computational methods for the solution of nonlinear equations, fixed points of contractive and noncontractive mapping, and for the computation of the topological degree. It is of interest to any reader working in the area of Information-Based Complexity. The worst-case settings are analyzed here. Several classes of functions are studied with special emphasis on tight complexity bounds and methods which are close to or achieve these bounds. Each chapter ends with exercises, including companies and open-ended research based exercises.
Nonlinear Equations
Authors: Sikorski Krzysztof A.
Published: November 2020

In this chapter we address the problem of approximationg zeros ∝ of nonlinear function f, f (∝ ) = 0, where f ϵ F ⊂ {f : D ⊂ Rd →Rl}. In order to define our solution operators, we first review several error criteria that are commonly used to measure the quality of approximations to zeros of nonlinear equations. This is done for univariate function f : [a, b] → R. Straightforward generalizations to the mulivariate case are based on replacing the magnitude function by a specific norm. These are considered in section 2.2 when we review multivariate problems. A number of error criteria are used in practice for approximation of a zero ∝ of f.
History and Momentum
Authors: Pool Robert
Published: November 2020

It was New Year’s Eve 1879, and the small community of Menlo Park, New Jersey, was overrun. Day after day the invaders had appeared, their numbers mounting as the new decade approached. When the New York Herald dispatched a man into the New Jersey countryside to report on the scene, he described a spectacle somewhere between a county fair and an inauguration: “They come from near and far, the towns for miles around sending them in vehicles of all kinds—farmers, mechanics, laborers, boys, girls, men and women—and the trains depositing their loads of bankers, brokers, capitalists, sightseers, hungry agents looking for business.” At first it had been hundreds, but by the last evening of the year, some 3,000 had gathered. They were here to see the future. Thomas Alva Edison, inventor of the phonograph, master of the telephone and telegraph, was said to have a new marvel, and it was his most amazing yet. If the newspapers could be believed, the Wizard of Menlo Park was lighting up the night with a magic lamp that ran on electricity. The news had first broken ten days earlier. A reporter from the Herald had spoken with Edison, who showed off his latest success: a light bulb that would glow for dozens of hours without burning out. On December 21, the Herald trumpeted the achievement, taking an entire page plus an extra column to describe the bulb (“Complete Details of the Perfected Carbon Lamp”) as well as Edison’s trial-and-error search for it (“Fifteen Months of Toil”) and the electrical system that would power it (“Story of His Tireless Experiments with Lamps, Burners and Generators”). Other newspapers soon picked up the story, and Edison, never one to pass up good publicity, announced he would open his laboratory after Christmas. Members of the public could come see the marvel for themselves. And what a marvel it was. Perhaps in this age, when city folk must travel miles into the country to not see an electric light, it’s hard to appreciate the wonder of that night.
Choices
Authors: Pool Robert
Published: November 2020

During the 1940s and early 1950s, when atomic energy was new, it was common to hear reactors described as nuclear “furnaces.” They “burned” their nuclear fuel and left behind nuclear “ash.” Technically, of course, none of these terms made sense, since burning is a chemical process and a reactor gets its energy from fission, but journalists liked the terminology because it was easy and quick. One loaded fuel into the reactor, flipped a switch, and things got very hot. If that wasn’t exactly a furnace, it was close enough. And actually, the metaphor was pretty good—up to a point. The basement furnace burns one of several different fuels: natural gas or fuel oil or even, in some ancient models, coal. Nuclear reactors can be built to use plutonium, natural uranium, or uranium that has been enriched to varying degrees. Home furnaces have a “coolant”—the air that is circulated through the furnace and out through the rest of the house, carrying heat away from the fire. Reactors have a coolant, too—the liquid or gas that carries heat away from the reactor core to another part of the plant, where heat energy is transformed into electrical energy. There, however, the metaphor sputters out. In a nuclear reactor, the coolant not only transfers heat to a steam generator or a turbine, but it also keeps the fuel from overheating. The coolant in a furnace does nothing of the sort. And most reactors use a moderator to speed up the fission reaction. The basement burner has nothing similar. But the most importance weakness of the furnace metaphor is that it obscured just how many varieties of reactors were possible—and, consequently, obscured the difficult choice facing the early nuclear industry: Which reactor type should become the basis for commercial nuclear power? The possibilities were practically unlimited. The fuel selection was wide. The coolant could be nearly anything that has good heat-transfer properties: air, carbon dioxide, helium, water, liquid metals, organic liquids, and so on.
Control
Authors: Pool Robert
Published: November 2020

Texas Utilities is a big company. Through its subsidiary, TU Electric, it provides electric service to a large chunk of Texas, including the Dallas- Fort Worth metropolitan area. It employs some 10,000 people. Its sales are around $5 billion a year. It has assets near $20 billion. Yet this corporate Goliath was brought to its knees by a single determined woman, a former church secretary named Juanita Ellis. For nearly a decade, Ellis fought Texas Utilities to a standstill in its battle to build the Comanche Peak nuclear power plant. During that time the cost of the plant zoomed from an original estimate of $779 million to nearly $11 billion, with much of the increase attributable, at least indirectly, to Ellis. Company executives, who had at first laughed at the thought of a housewife married to a lawn-mower repairman standing up to their covey of high-priced lawyers and consultants, eventually realized they could go neither around her nor through her. In the end, it took a negotiated one-on-one settlement between Ellis and a TU Electric executive vice president to remove the roadblocks to Comanche Peak and allow it to begin operation. No one was really happy with the outcome. Antinuclear groups denounced the settlement as a sellout and Ellis as a traitor. Texas Utilities bemoaned the years of discord as time wasted on regulatory nit-picking with no real improvement in safety. And the utility’s customers were the most unhappy of all, for they had to pay for the $11 billion plant with large increases in their electric bills. So it was natural to look for someone to blame. The antinuclear groups pointed to the utility. TU Electric, they said, had ignored basic safety precautions and had built a plant that was a threat to public health, and it had misled the public and the Nuclear Regulatory Commission. The utility, in turn, blamed the antinuclear groups that had intervened in the approval process and a judge who seemed determined to make TU Electric jump through every hoop he could imagine. The ratepayers didn’t know what to believe.
Technical Fixes, Technological Solutions
Authors: Pool Robert
Published: November 2020

The past couple of decades have been a confusing, frustrating period for engineers. With their creations making the world an ever richer, healthier, more comfortable place, it should have been a time of triumph and congratulation for them. Instead, it has been an era of discontent. Even as people have come to rely on technology more and more, they have liked it less. They distrust the machines that are supposedly their servants. Sometimes they fear them. And they worry about the sort of world they are leaving to their children. Engineers, too, have begun to wonder if something is wrong. It is not simply that the public doesn’t love them. They can live with that. But some of the long-term costs of technology have been higher than anyone expected: air and water pollution, hazardous wastes, the threat to the Earth’s ozone layer, the possibility of global warming. And the drumbeat of sudden technological disaster over the past twenty years is enough to give anyone pause: Three Mile Island, Bhopal, the Challenger, Chernobyl, the Exxon Valdez, the downing of a commercial airliner by a missile from the U.S.S. Vincennes. Is it time to rethink our approach to technology? Some engineers believe that it is. In one specialty after another, a few prophets have emerged who argue for doing things in a fundamentally new way. And surprisingly, although these visionaries have focused on problems and concerns unique to their own particular areas of engineering, a single underlying theme appears in their messages again and again: Engineers should pay more attention to the larger world in which their devices will function, and they should consciously take that world into account in their designs. Although this may sound like a simple, even a self-evident, bit of advice, it is actually quite a revolutionary one for engineering. Traditionally, engineers have aimed at perfecting their machines as machines. This can be seen in the traditional measures of machines: how fast they are, how much they can produce, the quality of their output, how easy they are to use, how much they cost, how long they last.
The Effect of Context
Authors: Kukulska-Hulme Agnes
Published: November 2020

• In what way does formatting a table resemble passing a ball? • Is “Press X” a definition of X? • Does it matter whether we know how to talk about maps? • Does learning always affect one’s language? • When should users hide something that does not exist? . . . “Context” is a word that is used freely and has many meanings. This chapter describes some of the different immediate contexts that apply to language. It shows the links between social conventions and meanings and how meaning is inferred. Visual and conceptual metaphors are investigated here, with emphasis on how we talk about metaphors. Context is then further explored in relation to professional preoccupations, situations, and tasks. This leads up to an important final section on verbal context, in which we look at how words form bonds with other words that surround them. . . . What Is Meant by “Context”? . . . The idea of context and its effect on meaning was briefly introduced in chapter 2, where the point was made that, out of context, a word may have a range of possible meanings, but that within a specific setting, one “actualized” meaning emerges. Put another way, context can help to resolve the ambiguity of word meaning. But it does not always resolve ambiguity. This is partly because there are typically a number of contexts to consider simultaneously. One perspective on this, which has been mentioned earlier, is to see context (in the sense of “reality”) as a set of concentric circles, with personal context at the center, surrounded by social, cultural, and intercultural contexts. Our main concern in this chapter is what might be referred to as the immediate context, which can be said to fall into three categories: situational, verbal, and visual. Visual context is treated again in chapter 7. Sometimes, if aspects of the immediate context are ill-defined or missing, ambiguity can persist. Halliday (1978) has written about the “context of situation” in these terms: . . . Language comes to life only when functioning in some environment. . . .
Labeling and Abbreviation
Authors: Kukulska-Hulme Agnes
Published: November 2020

So many user interfaces have the appearance of a collection of labels, stuck onto invisible boxes whose contents remain a mystery to users until they have made the effort of opening up each box in turn and sifting through its contents. In order to explore what might be called “the language of labeling,” we must first make some observations about the relationship between terms and concepts. Terms are words with special subject meanings; a term may consist of one or more “units” (e.g., user interface). As has been pointed out by Sager (1990), concepts are notoriously difficult to define; it is, however, possible to group them into four basic types: • class concepts or entities, generally corresponding to nouns • property concepts or qualities, for the most part corresponding to adjectives • relation concepts realized though various parts of speech, such as prepositions • function concepts or activities, corresponding to nouns and verbs Looking at the relationship between terms and concepts will help us to think about whether terms can be used to label various types of knowledge and also whether they can properly represent users’ knowledge needs. The present book is structured around linguistic “concepts” in the broad sense, whereas in this chapter, when we refer to concepts, it is in the narrower terminological sense indicated above. “We can use any names we wish as labels for concepts so long as we use them consistently. The only other criterion is convenience” In special subject areas, these same criteria apply, except that communication of specialized knowledge obliges us to take account of how concepts have been labeled by others and how the concepts we are handling fit into a wider scheme. We can draw up systems of concepts and try to specify relationships between them, uncovering along the way the knowledge structures that bind them together. However, we cannot do the same with terms. Terms are existential in nature, that is to say, they signal the existence of an entity, a relationship, an activity, or a quality.
Evaporation : Use of Fast-Response Turbulence Sensors, Raman Lidar, and Passive Microwave Remote Sensing
Authors: Parlance Marc B. , Albertson John D.
Published: November 2020

Since evaporation represents some 60% of precipitation over land surfaces, it is crucial for hydrologic purposes to know with some degree of certainty the magnitude of the water vapor flux into the atmosphere. Actual evaporation (E) from drying land surfaces is often formulated, in hydrology, as a fraction of some measure of potential evaporation (Ep), which can be written as a bulk transfer relationship: . . . Ep =CE up(qs* -q) (10.1) . . . where CE is the bulk mass transfer coefficient for water vapor, u is the mean wind speed at reference height z above the surface, r is the density of the air, q is the mean specific humidity at z, and q*s is the saturation specific humidity at the temperature of the surface (Ts) (Brutsaert, 1982, 1986).
Wheat Breeding and the Reconstruction of Postimperial Britain, 1935-1954
Authors: Perkins John H.
Published: November 2020

Most discussions about the green revolution focus on it as a package of technologies used to increase cereals production in the less industrialized world. Adoption of this package is generally asserted to stem from a crisis of overpopulation. The argument of chapters 6 through 8 was that a better understanding of the green revolution comes from recognition of deeper political questions, particularly those centered around national security issues. The United States promoted highyielding agriculture in countries such as Mexico and India for reasons of its own perception of national security. Mexico and India, similarly, were driven to adopt the technologies in order to foster their own processes of industrialization and preservation of national security. These last two chapters bring forth yet another dimension: adoption of highyielding practices was by no means confined to the less industrialized countries. Both Britain and the United States also had a green revolution. Moreover, industrialized countries adopted the high-yielding practices for reasons related to questions of national security. Revitalization of the British countryside, especially in its ability to produce wheat, had been a fond dream of many agriculturalists and agricultural scientists since the 1870s. Although the food emergency of the First World War temporarily rekindled an interest in British wheat production, its effects did not last after 1920. In contrast, the events during and after the Second World War sparked a rebirth of production and the construction of an integrated agricultural research system. Wheat breeding was a key component of the postwar agricultural reconstruction in the United Kingdom. This chapter focuses on why and how Britain decided to adopt the technology package of the green revolution on a timetable that paralleled events in India. “Dismal” is probably the adjective best suited to describe agriculture and agricultural science in the 1930s, at least among those British who supported more domestic production of foodstuffs. Price guarantees in the Wheat Act of 1932 encouraged British wheat farmers to increase their production, but the increase was not enough to affect imports significantly. In 1939, for example, wheat was grown on 1.76 million acres, up from about 1.2 million acres in 1931.
Extinction Patterns in the Herpetofauna of the Pleistocene of Britain and Europe
Authors: Holman J. Alan
Published: November 2020

As we have seen in Chapter 4, many invalid European Pleistocene amphibian and reptile species were named on the basis of insufficient and inadequately described fossils (e.g., Estes, 1981, 1983; Rage, 1984c; Sanchiz, in press). Some of these forms have been synonymized with modern species, but others are in taxonomic limbo because of the international rules of zoological nomenclature. We now turn to a consideration of the few European Pleistocene fossil herpetological species that have been recognized as valid in recent years. These taxa fit into three catagories: (1) an extinct Pliocene anuran taxon that extended into the Pleistocene, (2) large Lacerta species that lived on oceanic islands, and (3) Pleistocene species that are probably morphological variants of living forms. All of the following taxa are addressed in Chapter 4. No extinct species of Pleistocene salamanders are currently recognized in Britain or Europe. The genus * Pliobatrachus from the Pliocene of eastern Europe extended into the Lower Pleistocene of Poland and the Middle Pleistocene of Germany in the form of * Pliobatrachus cf. Pliobatrachus langhae. The *Palaeobatrachidae, the only family in the history of the Anura that became totally extinct (Roček, 1995), represents the only extinct herpetological family known in the Pleistocene of Britain and Europe, and *Pliobalrachus represents the only extinct herpetologcal genus known in the Pleistocene of the region. Rocck (1995) suggested that the *Palaeobatrachidae did not survive the Pleistocene cooling because of their prevailingly aquatic mode of life, unlike, for instance, the Ranidac and Bufonidae that were able to withdraw from iceobliterated areas and return when climatic conditions improved. *Lacerta goliath is a Pleistocene or Holocene species that is known only from two localities in the Canary islands (see Chapters 4 and 5). It is twice the size of Lacerta lepida, the largest modern European Lacerta. *Lacerta maxima is another very large Pleistocene or Holocene Lacerta that is endemic to the Canary Islands. This species is known from a single fossil locality (see Chapters 4 and 5) and is differentiated from * Lacerta goliath on the basis of several trenchant osteological characters.
Berlin, 1994: Bridge over Broken Glass? A Journey to Germany’s Sole Jewish High School
Authors: Rodden John G.
Published: November 2020

In the beginning was the memory. “I’m still hesitant even to mention it,” the young woman says in a low voice. We huddle closer together. “East Berlin was, after all, the capital of our ‘anti-fascist’ state.” She pauses. “And I’m even more anxious talking about it here—in this Oberschule.” She pauses again, then sets her shoulders and shakes her head impatiently. “But, on the other hand, it is my family history—I can’t do anything about that,” she continues. “I don’t believe in hiding it or repressing it—there’s been too much of that down through the years. And so I do tell people about it. Because it’s precisely my determination to confront my history that has brought me here.” Here: where—in a visceral, sometimes gut-wrenching way—past meets present, native meets foreigner, East meets West, Jew meets Gentile. And, above all, here: where—with as much good will and naturalness (and even a semblance of normalcy) as such an encounter can occur—Jew meets German. For we are sitting in the first—and still only—Jewish Oberschule in Germany in more than 50 years. We are talking in a corner in Room 212, the cramped teacher’s conference room through which her colleagues pass as they leave to teach their classes. Frau Ulla Berhau, 33, has the morning free and is willing to talk to me. A slight woman with short black hair cut in a close crop, Frau Berhau speaks in even tones and in a sharp Saxon accent about her past. Like many eastern German women, she wears no makeup, but her face lights up with animated expression as she tells her story, whose newest chapter has much to do with the historical challenges facing the Jewish Oberschule at Great Hamburg Street 27 in eastern Berlin. “To build a school is hard,” says Frau Berhau, “especially here in this street, especially for . . . us.” She gestures toward the center of Room 212 and her colleagues as she pauses, then shakes her head again.
The Economies of Food
Authors: Dasgupta Partha
Published: November 2020

People expressing concern about the environmental resource basis of human life often take a global, futuristic view (see, e.g., Kennedy, 1993). They emphasize the deleterious effects that growing population and rising consumption would have on our planet in the future. They express worry that the increasing demand for environmental resources (such as agricultural land, forests, fisheries, fresh water, the atmosphere, and the oceans) and the resulting impacts on ecosystem services (such as regenerating soils, recycling nutrients, filtering pollutants, assimilating waste, pollinating crops, and operating the hydrological cycle) would make civilization unsustainable. This book is, at least in part, a response to this thought. Although the global, futuristic emphasis has proved useful, it has had two unfortunate consequences: it has encouraged us to adopt an all-or-nothing position (the future will be either catastrophic or rosy), and it has drawn attention away from the economic misery that is endemic in large parts of the world today. Disaster is not something for which the poorest have to wait: they face it right now, and nearly 1 billion people go to bed hungry each night, having been unable to escape from something that can be called a poverty trap. Moreover, in poor countries, decisions on fertility and on allocations concerning education, child care, food, work, health care, and the use of the local environmental resource base are in large measure reached and implemented within households. In earlier work (Dasgupta, 1993, 1995a, 1995b, 1996, 1997), I have tried to show that the interface that connects the problems of population growth, poverty environmental degradation, food insecurity, and civic disconnection should ideally be studied with reference to myriad communitarian, household, and individual decisions, or, in other words, that if we are to reach a global, futuristic vision of the human dilemma, we need to adopt a local, contemporary lens.
Greater Crop Production Whence and Whither?
Authors: Evans L. T.
Published: November 2020

Crop physiology has been called “the retrospective science” by one plant breeder because we physiologists elucidate what the breeders have already achieved. Indeed, such explanations occupy the first part of this chapter, the whence of greater crop production. We shall also peer ahead, the whither in my title. But physiologists have learned that past increases in crop productivity have often come from unexpected and initially unrecognized directions, in many cases driven by developments in agronomy, mechanization, and demand. The integrating power of empirical selection for yield potential has, so far, proved more effective than ideological selection for specific physiological characteristics, presumably because yield is the integrated end result of a great variety of processes that must act in a balanced and coordinated way. Crop production can be increased in several ways, such as by extending the arable area, by increasing yield per hectare per crop or the number of crops per hectare per year (called intensification), by displacement of lower by higher yielding crops, and by reducing postharvest losses. Until the 1960s the major contribution for the world as a whole came from increases in the area of arable land and in the proportion of it under crop. Since then, however, the limited increases in arable area, in South America and Africa mostly, have largely been matched —though not in land quality —by losses to urbanization, transport, and degradation. The proportion of rainfed arable land under crop continues to increase slowly, currently being about three quarters for the developing countries as a whole. The intensification of arable land use is most important in warmer and wetter climates, particularly under irrigation. Double cropping of rice has been prominent in China since Sung times. Cropping intensity in the Punjab now approaches 200%, and FAO projects that 13% of the increase in crop production in developing countries by A.D. 2010 will come from intensification, compared with 21% from extension of the arable (Alexandratos, 1995). Further intensification will depend heavily on extension of the irrigated area, but much can also be achieved by the breeding of earlier maturing varieties coupled with improvements in fertilizer use and minimum tillage procedures.
Improving Yield Potential by Modifying Plant Type and Exploiting Heterosis
Authors: Khush G. S. , Peng S.
Published: November 2020

World food crops have been improved progressively since their domestication about 10,000 years ago. Progress was especially rapid after the rediscovery of Mendel’s laws of inheritance, when scientific principles could be applied to crop improvement. Modern varieties of wheat and rice, which ushered the so-called green revolution and led to the doubling of cereal production in a 25-year period, are examples of recent achievements in increasing crop productivity. The present world population of 5.8 billion is likely to reach 7 billion in 2010 and 8 billion in 2025. Per caput food intake will increase due to improved living standards. It is estimated that we will have to produce 50% more food by 2025. Food grain production in Africa will have to increase almost 400%, in Latin America 200%, and in Asia 60%. In the past, food production grew as a result of increased yield potential of new crop varieties, as well as increases in cropped area. In the future, major increases in cropped area are unlikely. In fact, in most Asian countries the cultivated area is declining due to pressures of urbanization and industrialization. Pesticide use is dropping as a result of concerns about their harmful effects on the environment and on human health. Increasingly, the industrial base is competing with agriculture for water and labor. Thus, we will have to produce more food from less land, with less pesticides, less labor, and less water. Increases in crop productivity are therefore essential to feed the world in the next century. One way to increase crop productivity is to develop crop cultivars with higher yield potential. Of the various strategies for increasing the yield potential, two are reviewed in this chapter. Selection for semidwarf stature in the late 1950s for rice (Oryza sativa L.) and wheat (Triticum aestivum L.) is the most striking example of a successful improvement in plant type. Although selections were guided by short stature, resistance to lodging, and efficient biomass partitioning between grain and straw, breeders were unintentionally selecting for improved canopy architecture, light penetration, and other favorable agronomic characteristics (as reviewed by Takeda, 1984).
Practical innovation: Partnerships between Scientists and Farmers
Authors: Conway G.
Published: November 2020

Farmers have been experimenters since the beginning of agriculture. Hunters and gatherers had long since learned to use fire as a means of stimulating the growth of tubers and other food plants, and of grass to attract game. Plant selection began when people found they could encourage favored fruiting trees by clearing their competitive neighbors, but the first steps toward intensive plant breeding were taken when an individual, probably a woman rather than a man, deliberately sowed a seed from a high-yielding plant somewhere near the dwelling and observed it grow to maturity. In Europe and Asia, wheat and rice naturally attracted experimental attention. Because they are predominantly self-pollinating, selection produces rapid improvements and the rare crosses provide new material, often with exciting potential. The first bread wheat, a natural cross between emmer wheat and a wild goat grass, was noticed by farmers as early as 8,000 years ago; it was the kind of exotic cross that modern genetic engineers strive for and that is announced in the press, today, as a miracle variety. Farmers continued to domesticate new species, but most attention was devoted to the local selection and adaptation of the existing relatively small number of cereals and livestock. Experimentation also resulted in new whole systems of agriculture— swidden, rice terracing, home gardens, irrigated agriculture, the Mediterranean Trio of wheat, olives, and vines, the Latin American multiple cropping of maize, beans, and squashes, and, in many parts of the world, various forms of integrated crop-livestock agriculture. As is evident from their writings, the Romans analyzed the structure and functions of agricultural systems in a scientific manner. They also described the process of experimentation. Marcus Terentius Varro, who wrote a treatise on agriculture in the 1st century BC, urged farmers to both “imitate others and attempt by experiment to do some things in a different way. Following not chance but some system: as, for instance, if we plough a second time, more or less deeply than others, to see what effect this will have” (Hooper and Ash, 1935). The great agricultural revolution of Britain in the late 18th century was led by farmers.
Setting the Goal: Modern Vegetation of North America Composition and Arrangement of Principal Plant Formations
Authors: Graham Alan
Published: November 2020

Vegetation is the plant cover of a region, which usually refers to the potential natural vegetation prior to any intensive human disturbance. The description of vegetation for an extensive area involves the recognition and characterization of units called formations, which are named with reference to composition (e.g., coniferous), aspect of habit (deciduous), distribution (western North America), and climate, either directly (tropical) or indirectly (tundra). Further subdivisions are termed associations or series, such as the beech-maple association or series within the deciduous forest formation. Formations and associations constitute a convenient organizational framework for considering the development of vegetation through Late Cretaceous and Cenozoic time. For this purpose seven extant plant formations are recognized for North America: (1) tundra, (2) coniferous forest, (3) deciduous forest, (4) grassland, (5) shrubland/chaparral- woodland- savanna, (6) desert, and (7) elements of a tropical formation. Several summaries are available for the modern vegetation of North America, including Barbour and Billings (1988), Barbour and Christensen, Kuchler (1964), and Vankat (1979). The following discussions are based primarily on these surveys. Tundra (Fig. 1.2) is a treeless vegetation dominated by shrubs and herbs, and it is characteristic of the cold climates of polar regions (Arctic tundra) and high-altitude regions (alpine tundra). In the Arctic tundra a few isolated trees or small stands may occur locally, such as Picea glauca (white spruce), but these are always in protected habitats. The Arctic region experiences nearly continuous darkness in midwinter, and nearly continuous daylight in midsummer. There is a short growing season of only 6-24 weeks; this accounts, in part, for the fact that 98% of all Arctic tundra plants are perennials (Vankat, 1979). Strong winds are another feature of the Arctic landscape, often exceeding 65 km/h for 24 h or more. They likely account for the frequency of rosettes, persistent dead leaves, and the cushion growth form, in the center of which wind velocities may be reduced by 90%. The harsh growing conditions also result in leaves of the microphyllous size class being comparable to those of desert plants. Vegetative reproduction and self-pollination is common, and phenotypic plasticity is high among Arctic tundra plants.
Approximate String Searching
Authors: Landau G.M. , Vishkin U.
Published: November 2020

Consider the string searching problem, where differences between characters of the pattern and characters of the text are allowed. Each difference is due to either a mismatch between a character of the text and a character of the pattern, or a superfluous character in the text, or a superfluous character in the pattern. Given a text of length n, a pattern of length m and an integer k, serial and parallel algorithms for finding all occurrences of the pattern in the text with at most k differences are presented. For completeness we also describe an efficient algorithm for preprocessing a rooted tree, so that queries requesting the lowest common ancestor of every pair of vertices in the tree can be processed quickly. Input form. Two arrays: A = a1., ...,am - the pattern, T = t1, ...,tn - the text and an integer k (≥ 1). In the present chapter we will be interested in finding all occurrences of the pattern string in the text string with at most k differences. Three types of differences are distinguished: (a) A character of the pattern corresponds to a different character of the text - a mismatch between the two characters. (Item 2 in Example 1, below.) (b) A character of the pattern corresponds to “no character” in the text. (Item 4). (c) A character of the text corresponds to “no character” in the pattern. (Item 6). Example 1. Let the text be abcdefghi , the pattern bxdyegh and k = 3. Let us see whether there is an occurrence with ≤ k differences that ends at the eighth location of the text. For this the following correspondence between bcdefgh and bxdyegh is proposed. 1. b (of the text) corresponds to b (of the pattern). 2. c to x. 3. d to d. 4. Nothing to y. 5. e to e. 6. f to nothing. 7. g to g. 8. h to h.
Dynamic Programming: Special Cases
Authors: Giancarlo R.
Published: November 2020

In this Chapter we present some general algorithmic techniques that have proved to be useful in speeding up the computation of some families of dynamic programming recurrences which have applications in sequence alignment, paragraph formation and prediction of RNA secondary structure. The material presented in this chapter is related to the computation of Levenshtein distances and approximate string matching that have been discussed in the previous three chapters. Dynamic programming is a general technique for solving discrete optimization (minimization or maximization) problems that can be represented by decision processes and for which the principle of optimality holds. We can view a decision process as a directed graph in which nodes represent the states of the process and edges represent decisions. The optimization problem at hand is represented as a decision process by decomposing it into a set of subproblems of smaller size. Such recursive decomposition is continued until we get only trivial subproblems, which can be solved directly. Each node in the graph corresponds to a subproblem and each edge (a, b) indicates that one way to solve subproblem a optimally is to solve first subproblem b optimally. Then, an optimal solution, or policy, is typically given by a path on the graph that minimizes or maximizes some objective function. The correctness of this approach is guaranteed by the principle of optimality which must be satisfied by the optimization problem: An optimal policy has the property that whatever the initial node (state) and initial edge (decision) are, the remaining edges (decisions) must be an optimal policy with regard to the node (state) resulting from the first transition. Another consequence of the principle of optimality is that we can express the optimal cost (and solution) of a subproblem in terms of optimal costs (and solutions) of problems of smaller size. That is, we can express optimal costs through a recurrence relation. This is a key component of dynamic programming, since we can compute the optimal cost of a subproblem only once, store the result in a table, and look it up when needed.
The Atmospheric Component of Biogeochemical Cycles in the Amazon Basin
Authors: Artaxo Paulo
Published: November 2020

Tropical forests, with their high biological activity, have the potential to emit large amounts of trace gases and aerosol particles to the atmosphere. The accelerated development and land clearing that is occurring in large areas of the Amazon basin suggest that anthropogenic effects on natural biogeochemical cycles are already occurring (Gash et al. 1996). The atmosphere plays a key role in this process. The tropics are the part of the globe with the most rapidly growing population, the most dramatic industrial expansion and the most rapid and pervasive change in land use and land cover. Also the tropics contain the largest standing stocks of terrestrial vegetation and have the highest rates of photosynthesis and respiration. It is likely that changes in tropical land use will have a profound impact on the global atmosphere (Andreae 1998, Andreae and Crutzen 1997). A significant fraction of nutrients are transported or dislocated through the atmosphere in the form of trace gases, aerosol particles, and rainwater (Keller et al. 1991). Also the global effects of carbon dioxide, methane, nitrous oxide, and other trace gases have in the forest ecosystems a key partner. The large emissions of isoprene, terpenes, and many other volatile organic compounds could impact carbon cycling and the production of secondary aerosol particles over the Amazon region. Vegetation is a natural source of many types of aerosol particles that play an important role in the radiation budget over large areas (Artaxo et al. 1998). There are 5 major reservoirs in the Earth system: atmosphere, biosphere (vegetation, animals), soils, hydrosphere (oceans, lakes, rivers, groundwater), and the lithosphere (Earth crust). Elemental cycles of carbon, oxygen, nitrogen, sulfur, phosphorus, and other elements interact with the different reservoirs of the Earth system. The carbon cycle has important aspects in tropical forests due to the large amount of carbon stored in the tropical forests and the high rate of tropical deforestation (Jacob 1999). In Amazonia there are two very different atmospheric conditions: the wet season (mostly from November to June) and the dry season (July-October) (see Marengo and Nobre, this volume). Biomass burning emissions dominate completely the atmospheric concentrations over large areas of the Amazon basin during the dry season (Artaxo et al. 1988).
Terrestrial Inputs to Amazon Streams and Internal Biogeochemical Processing
Authors: McClain Michael E. , Elsenbeer Helmut
Published: November 2020

Enormous meandering rivers are the most remarkable fluvial feature of the Amazon landscape, but these rivers are only the largest component of a much denser network of streams which finely dissects and drains the basin. In terms of combined length and total amount of lotic habitat, streams dominate over their more visible downstream counterparts; this dominance is especially dramatic for first- and second-order streams which alone may account for greater than 80% of total channel length in meso-scale Amazon drainag basins. The flow of Amazon streams emerges directly from the extensive forests and savannas that compose the basin. Biogeochemical cycles in streams are thus intricately associated with processes operating in adjoining riparian and upland ecosystems. Terrestrial processes regulate the input of organic and inorganic species to stream systems, and the chemistry of inflowing waters determines, to some extent, the nature of subsequent reactions and even the composition of the stream’s biological community (Fittkau 1971). Undisturbed Amazon streams are thought to experience virtually no primary production (Walker 1995), thus most inputs of energy, as well as nutrients, must ultimately derive from terrestrial sources. This connection is particularly acute in first-order streams where there is no upstream input and all water, particulates, and solutes derive from immediately adjacent to the stream. Pathways linking the two systems include groundwater runoff, surface and subsurface storm runoff, wetland seepage, direct litterfall, and litter blow-in. These pathways are active across the entire Amazon basin, but their relative importance may vary regionally (McClain and Richey 1996, Elsenbeer and Lack 1996). Riparian ecosystems continue to influence the biogeochemistry of downstream reaches, but as streams become rivers upstream and in-channel influences become increasingly dominant. Streams and the corridors through which they flow also play a crucial role in regional-scale biogeochemical cycles. Greater than 90% of all terrestrial to lotic transfers in the Amazon basin occur in streams of order 6 and less. Thus, organic and inorganic species moving from terrestrial systems to large rivers and ultimately to the ocean must first pass through streams, where rates of material cycling and processing are rapid.