bluuebunny/crossref_metadata_2025 huggingface dataset:
Twentieth-Century Rumblings
Authors: Verschuur Gerrit L.
Published: November 2020

During the first century B.C., Lucretius wrote, “Legend tells of one occasion when fire got the upper hand. The victory of fire when the earth felt its withering blast, occurred when the galloping steeds that draw the chariot of the sun swept Phaeton from the true course right out of the zone of the ether and far over all lands.” He knew about comets, which is why he said, “There is no lack of external bodies to rally out of infinite space and blast [the world] with a turbulent tornado or inflict some other mortal disaster.” This awareness made him think that the world was newly made, and perhaps in some sense it is. The wheel has come full circle. We now appreciate that the threat of comets and asteroids is real, although the distinction between comets and asteroids has grown blurred. What is no longer in doubt is that catastrophic impacts have occurred in the past, and that they will happen again. At the same time, the hypothesis that impacts and flood legends are related is beginning to experience a revival. A chink in the dam of prejudice against the idea actually began to appear in the 1940’s when two astronomers, Fletcher Watson and Ralph Baldwin, in separate books considered the implications of the discovery of near-earth asteroids (NEAs) and concluded that impacts were likely every million years or so. They were all but ignored. In 1942 H. H. Nininger, the famous meteorite researcher, gave a talk to the Society for Research on Meteorites entitled “Cataclysm and Evolution.” Because of his highly specialized forum, his remarks also went unheard in the wider astronomical community. He considered the danger following the close encounter with Hermes, the NEA discovered in October 1937 that passed within 670,000 kilometers of our planet, which can be compared with the moon’s distance of 384,000 kilometers. (Oddly, Hermes has never been found again. Its rediscovery is one of the prizes that asteroid hunters strive for.) If, instead, it had “smacked the earth in a single lump,” the consequences would “constitute a catastrophe of a magnitude never yet witnessed by man,” said Nininger.
Traditional Exploitation Methods, Efficiency, and Consequences for River Turtles
Authors: Moll Don , Moll Edward O.
Published: November 2020

A wide variety of ingenious methods for collecting river turtles have been developed over time. None requires a particularly high level of technology but many require a great deal of skill, patience, and sometimes physical ability by the collectors, as well as a detailed knowledge of the ecology of the species being sought. Many parallel collecting methods have developed independently in turtle-dependent cultures around the world, leading Nicholls (1977) to state in regard to Bates’s (1863) description of an Amazonian turtle hunt, “With some allowance for small differences in technique, his descriptions provide an accurate image of turtle hunting as it was practiced anytime, anywhere, during the past thousands of years.” We thought that a summary of these techniques with comment upon their variation in different areas and with different species, their effects on populations when this can be ascertained, and examples of their practitioners would be an appropriate addition to our treatment of river turtle exploitation patterns. We will limit our discussion mainly to techniques employed by subsistence and commercial turtlers for obtaining animals and largely omit reference to the growing body of information concerning the collection of turtles for scientific purposes (many of which are largely modifications of the former techniques). For information concerning the latter category the reader is referred to the excellent summary of equipment and techniques by Plummer (1979) and papers by Carr and Marchand (1942), Chaney and Smith (1950), Legler (1960b), Ream and Ream (1966), Wahlquist (1970), Bider and Hoek (1971), Braid (1974), Robinson and Murphy (1975), MacCulloch and Gordon (1978), Iverson (1979), Petokas and Alexander (1979), Vogt (1980b), Frazer et al. (1990), Kennett (1992), Graham and Georges (1996), Jensen (1998), and Kuchling (2003b). Free diving for turtles is of course a time-honored, effective, and nearly cosmopolitan approach to collecting turtles that requires little or no equipment. While diving mask, fins and sophisticated breathing gear certainly enhance the process, they are not required by skilled divers in order to harvest large numbers of turtles.
Linear Cable Theory
Authors: Koch Christof
Published: November 2020

In the previous chapter, we briefly met some of the key actors of this book. In particular, we introduced the RC model of a patch of neuronal membrane and showed an instance where such a “trivial” model accounts reasonably well for the input-output properties of a neuron, as measured at its cell body. However, almost none of the excitatory synapses are made onto the cell body, contacting instead the very extensive dendritic arbor. As we will discuss in detail in Chap. 3, dendritic trees can be quite large, containing up to 98% of the entire neuronal surface area. We therefore need to understand the behavior of these extended systems having a cablelike structure. The basic equation governing the dynamics of the membrane potential in thin and elongated neuronal processes, such as axons or dendrites, is the cable equation. It originated in the middle of the last century in the context of calculations carried out by Lord Kelvin, who described the spread of potential along the submarine telegraph cable linking Great Britain and America. Around the turn of the century, Herman and others formulated the concept of Kemleitermodel, or core conductor model, to understand the flow of current in nerve axons. Such a core conductor can be visualized as a thin membrane or sheath surrounding a cylindrical and electrically conducting core of constant cross section placed in a solution of electrolytes. The study of the partial differential equations describing the evolution of the electrical potential in these structures gave rise to a body of theoretical knowledge termed cable theory. In the 1930s and 1940s concepts from cable theory were being applied to axonal fibers, in particular to the giant axon of the squid (Hodgkin and Rushton, 1946; Davis and Lorente de No, 1947). The application of cable theory to passive, spatially extended dendrites started in the late 1950s and blossomed in the 1960s and 1970s, primarily due to the work of Rail (1989). In an appropriate gesture acknowledging his role in the genesis of quantitative modeling of single neurons, Segev, Rinzel, and Shepherd (1995) edited an annotated collection of his papers, to which we refer the interested reader. It also contains personal recollections from many of Rail's colleagues as well as historical accounts of the early history of this field.
Ionic Channels
Authors: Koch Christof
Published: November 2020

In the previous chapters, we studied the spread of the membrane potential in passive or active neuronal structures and the interaction among two or more synaptic inputs. We have yet to give a full account of ionic channels, the elementary units underlying all of this dizzying variety of electrical signaling both within and between neurons. Ionic channels are individual proteins anchored within the bilipid membrane of neurons, glia, or other cells, and can be thought of as water-filled macromolecular pores that are permeable to particular ions. They can be exquisitely voltage sensitive, as the fast sodium channel responsible for the sodium spike in the squid giant axon, or they can be relatively independent of voltage but dependent on the binding of some neurotransmitter, as is the case for most synaptic receptors, such as the acetylcholine receptor at the vertebrate neuromuscular junction or the AMPA and GABA synaptic receptors mediating excitation and inhibition in the central nervous system. Ionic channels are ubiquitous and provide the substratum for all biophysical phenomena underlying information processing, including mediating synaptic transmission, determining the membrane voltage, supporting action potential initiation and propagation, and, ultimately, linking changes in the membrane potential to effective output, such as the secretion of a neurotransmitter or hormone or the contraction of a muscle fiber. Individual ionic channels are amazingly specific. A typical potassium channel can distinguish a K+ ion with a 1.33 Å radius from a Na+ ion of 0.95 Å radius, selecting the former over the latter by a factor of 10,000. This single protein can do this selection at a rate of up to 100 million ions each second (Doyle et al, 1998). At the time of Hodgkin and Huxley’s seminal study in the early 1950s, two broad classes of transport mechanisms were competing as plausible ways for carrying ionic fluxes across the membrane: carrier molecules and pores. At the time, no direct evidence for either one existed. It was not until the early 1970s that the fast ACh synaptic receptor and the Na channel were chemically isolated and purified and identified as proteins.
Synaptic Plasticity
Authors: Koch Christof
Published: November 2020

Animals live in an ever-changing environment to which they must continuously adapt. Adaptation in the nervous system occurs at every level, from ion channels and synapses to single neurons and whole networks. It operates in many different forms and on many time scales. Retinal adaptation, for example, permits us to adjust within minutes to changes of over eight orders of magnitude of brightness, from the dark of a moonless night to high noon. High-level memory—the storage and recognition of a person's face, for example—can also be seen as a specialized form of adaptation (see Squire, 1987). The ubiquity of adaptation in the nervous system is a radical but often underappreciated difference between brains and computers. With few exceptions, all modern computers are patterned according to the architecture laid out by von Neumann (1956). Here the adaptive elements—the random access memory (RAM)—are both physically and conceptually distinct from the processing elements, the central processing unit (CPU). Even proposals to incorporate massive amounts of so-called intelligent RAM (IRAM) directly onto any future processor chip fall well short of the degree of intermixing present in nervous systems (Kozyrakis et al., 1997). It is only within the last few years that a few pioneers have begun to demonstrate the advantages of incorporating adaptive elements at all stages of the computation into electronic circuits (Mead, 1990; Koch and Mathur, 1996; Diorio et al.,1996). For over a century (Tanzi, 1893; Ramón y Cajal, 1909, 1991), the leading hypothesis among both theoreticians and experimentalists has been that synoptic plasticity underlies most long-term behavioral plasticity. It has nevertheless been extremely difficult to establish a direct link between behavioral plasticity and its biophysical substrate, in part because most biophysical research is conducted with in vitro preparations in which a slice of the brain is removed from the organism, while behavior is best studied in the intact animal. In mammalian systems the problem is particularly acute, but combined pharmacological, behavioral, and genetic approaches are yielding promising if as yet incomplete results (Saucier and Cain, 1995; Cain, 1997; Davis, Butcher, and Morris, 1992; Tonegawa, 1995; McHugh et al., 1996; Rogan, Stäubli, LeDoux, 1997).
Stochastic Models of Single Cells
Authors: Koch Christof
Published: November 2020

The majority of experiments in neurophysiology are based upon spike trains recorded from individual or multiple nerve cells. If all the action potentials are taken to be identical and only the times at which they are generated are considered, the experimentalist obtains a discrete series of time events {t1,···, tn}, where t¡ corresponds to the occurrence of the i th spike, characterizing the spike train. This spike train is transmitted down the axon to all of the target cells of the neuron, and it is this spike train that contains all of the relevant information that the cell is representing (assuming no dendro-dendritic connections). As alluded to in the preceding chapter, there are two opposing views of neuronal coding, with many interim shades. One view holds that it is the firing rate, averaged over a suitable temporal window (Eqs. 14.1 or 14.2), that is relevant for information processing. The dissenting view, correlation coding, argues that the interactions among spikes, at the single cell as well as between multiple cells, encodes information. A key property of spike trains is their seemingly stochastic or random nature, quite in contrast to switching in digital computers. This randomness is apparent in the highly irregular discharge pattern of a central neuron to a sensory stimulus whose details are rarely reproducible from one trial to the next. The apparent lack of reproducible spike patterns has been one of the principal arguments in favor of the hypothesis that neurons only care about the firing frequency averaged over very long time windows. Such a mean rate code is very robust to “sloppy” hardware but is also relatively inefficient in terms of transmitting the maximal amount of information per spike. Encoding information in the intervals between spikes is obviously much more efficient, in particular if correlated across multiple neurons. Such a scheme does place a premium on postsynaptic neurons that can somehow decode this information. Because little or no information can be encoded into a stream of regularly spaced action potentials, this raises the question of how variable neuronal firing really is.
Solar Flux and Molecular Absorption
Authors: Yung Yuk L. , DeMore William B.
Published: November 2020

In this book we are concerned primarily with disequilibrium chemistry, of which the sun is the principal driving force. The sun is not, however, the only source of disequilibrium chemistry in the solar system. We briefly discuss other minor energy sources such as the solar wind, starlight, precipitation of energetic particles, and lightning. Note that these sources are not independent. For example, the ultimate energy source of the magnetospheric particles is the solar wind and planetary rotation; the energy source for lightning is atmospheric winds powered by solar irradiance. Only starlight and galactic cosmic rays are completely independent of the sun. While the sun is the energy source, the atoms and molecules in the planetary atmospheres are the receivers of this energy. For atoms the interaction with radiation results in three possibilities: (a) resonance scattering, (b) absorption followed by fluorescence, and (c) ionization. lonization usually requires photons in the extreme ultraviolet. The interaction between molecules and the radiation field is more complicated. In addition to the above (including Rayleigh and Raman scattering) we can have (d) dissociation, (e) intramolecular conversion, and (f) vibrational and rotational excitation. Note that processes (a)-(e) involve electronic excitation; process (f) usually involves infrared radiation that is not energetic enough to cause electronic excitation. The last process is important for the thermal budget of the atmosphere, a subject that is not pursued in this book. Scattering and fluorescence are a source of airglow and aurorae and provide valuable tools for monitoring detailed atomic and molecular processes in the atmosphere. Processes (c) and (d) are most important for determining the chemical composition of planetary atmospheres. Interesting chemical reactions are initiated when the absorption of solar energy leads to ionization or the breaking of chemical bonds. In this chapter we provide a survey of the absorption cross sections of selected atoms and molecules. The selection is based on the likely importance of these species in planetary atmospheres.
Geostrophic Turbulence
Authors: Salmon Rick
Published: November 2020

Strongly nonlinear, rapidly rotating, stably stratified flow is called geostrophic turbulence. This subject, which blends ideas from chapters 2,4, and 5, is relevant to the large-scale flow in the Earth’s oceans and atmosphere. The quasigeostrophic equations form the basis of the study of geostrophic turbulence. We view the quasigeostrophic equations as a generalization of the vorticity equation for two-dimensional turbulence to include the important effects of stratification, bottom topography, and varying Coriolis parameter. Thus the theory of geostrophic turbulence represents an extension of the theory of two dimensional turbulence. However, its richer physics and greater applicability to real geophysical flows make geostrophic turbulence a much more interesting and important subject. This chapter offers a very brief introduction to the theory of geostrophic turbulence. We illustrate the principal ideas by separately considering the effects of bottom topography, varying Coriolis parameter, and density stratification on highly nonlinear, quasigeostrophic flow. We make no attempt at a comprehensive review. In every case, the theory of geostrophic turbulence relies almost solely on two now-familiar components: a conservation principle that energy and potential vorticity are (nearly) conserved and an irreversibility principle in the form of an appealing assumption that breaks the time-reversal symmetry of the exact (inviscid) dynamics. This irreversibility assumption takes a great many superficially dissimilar forms, fostering the misleading impression of a great many competing explanations for the same phenomena. However, broadminded analysis inevitably reveals that these competing explanations are virtually equivalent. We begin by considering the quasigeostrophic flow of a single layer of homogeneous fluid over a bumpy bottom. No case better illustrates how diverse forms of the irreversibility principle lead to the same conclusions.
Hamiltonian Fluid Dynamics
Authors: Salmon Rick
Published: November 2020

In this final chapter, we return to the subject of the first: the fundamental principles of fluid mechanics. In chapter 1, we derived the equations of fluid motion from Hamilton’s principle of stationary action, emphasizing its logical simplicity and the resulting close correspondence between mechanics and thermodynamics. Now we explore the Hamiltonian approach more fully, discovering its other advantages. The most important of these advantages arise from the correspondence between the symmetry properties of the Lagrangian and the conservation laws of the resulting dynamical equations. Therefore, we begin with a very brief introduction to symmetry and conservation laws. Noether’s theorem applies to the equations that arise from variational principles like Hamilton’s principle. According to Noether’s theorem : If a variational principle is invariant to a continuous transformation of its dependent and independent variables, then the equations arising from the variational principle possess a divergence-form conservation law. The invariance property is also called a symmetry property. Thus Noether’s theorem connects symmetry properties and conservation laws. We shall neither state nor prove the general form of Noether’s theorem; to do so would require a lengthy digression on continuous groups. Instead we illustrate the connection between symmetry and conservation laws with a series of increasingly complex and important examples. These examples convey the flavor of the general theory. Our first example is very simple. Consider a body of mass m moving in one dimension. The body is attached to the end of a spring with spring-constant K. Let x(t) be the displacement of the body from its location when the spring is unstretched.
Microwave Observations of Soil Hydrology
Authors: Jackson T. J. , Engman E. T.
Published: November 2020

The upper few centimeters of the soil are extremely important because they are the interface between soil science and land-atmosphere research and are also the region of the greatest amount of organic material and biological activity (Wei, 1995). Passive microwave remote sensing can provide a measurement of the surface soil moisture for a range of cover conditions within reasonable error bounds (Jackson and Schmugge, 1989). Since spatially distributed and multitemporal observations of surface soil moisture are rare, the use of these data in hydrology and other disciplines has not been fully explored or developed. The ability to observe soil moisture frequently over large regions could significantly improve our ability to predict runoff and to partition incoming radiant energy into latent and sensible heat fluxes at a variety of scales up to those used in global circulation models. Temporal observation of surface soil moisture may also provide the information needed to determine key soil parameters, such as saturated conductivity (Ahuja et al., 1993). These sensors provide a spatially integrated measurement that may aid in understanding the upscaling of essential soil parameters from point observations. Some specific issues in soil hydrology that could be addressed with remotely sensed observations as described above include (Wei, 1995): (1) criteria for soil mapping based on spatial and temporal variance structures of state variables, (2) identifying scales of observation, (3) determining soil physical properties within profiles based on surface observations, (4) quantifying correlation lengths of soil moisture in time and space relative to precipitation and evaporation, (5) examining the covariance structure between soil water properties and those associated with water and heat fluxes at the land-atmosphere boundary at various scales, and (6) determining if vertical and horizontal fluxes of energy and matter below the surface can be ascertained from surface soil moisture distributions. In this chapter, the basis of microwave remote sensing of soil moisture will be presented along with the advantages and disadvantages of different techniques. Currently available sensor systems will be described.
The Rockefeller Foundation in Mexico : The New International Politics of Plant Breeding, 1941-1945
Authors: Perkins John H.
Published: November 2020

Events during World War I and in the years between the two world wars demonstrated that agricultural production was essential for the security of individual nations. No country could afford to neglect its food supply if it wished to maintain its status as a major military power. In addition, pressures from technically sophisticated farmers and industrialists, both interested in efficient agricultural production, solidified the use of scientific research in reforming the agricultural economy. Underlying the drive for both military power and efficient agricultural production was a powerful vision of the nation-state as an industrial economy in which all natural resources, including agriculture, were marshaled by the rational control of modern science. Both people and nature were subservient to the imperatives of power and rationalism in the new scheme of things. What was largely missing from the pre-1939 vision, however, was a sense of how nations might interact to address issues of industrialization and agricultural modernization. By 1939 industrial states like the United Kingdom and the United States developed a sense of how individually they should manage their industrial and agricultural resources, and the British government certainly had a clear sense of how the Indian economy should be controlled. Outside of the realms of direct imperialism, however, industrial countries had only vague notions about how to use scientific and economic policy to foster their aims internationally. Furthermore, no country had any profound sense, incorporated into policy, that rich and powerful countries should assist the poor countries to achieve a better standard of living for humanitarian reasons. Aside from imperialism, therefore, in 1939 no analytical framework existed to see how agricultural science and technology and modernization of agriculture fit into the overall scheme of international relations and power. Perhaps the only exception to this situation was a small program of the Rockefeller Foundation in China. In 1924 the International Education Board of the Rockefeller Foundation began to assist the University of Nanking with wheat improvement, economic issues, and other projects. In addition, during the 1920s, the foundation supported medical reform in China.
Marooned in the Workers’ Paradise: Cold War Catechetics, 1951–61
Authors: Rodden John G.
Published: November 2020

August 12, 1951. It’s a brilliant Sunday afternoon in the eastern sector of Berlin, the DDR’s capital, now an urban showplace of 1.7 million residents and proudly known on road signs as Berlin, Hauptstadt der DDR—a simple declaration of the SED’s ongoing claim to the entire city as DDR territory. The boulevards are clean and neat in Alexanderplatz, the downtown area of East Berlin. Windows are bedecked with flowers, and flags from every nation of the globe festoon the buildings, which are draped with tapestries displaying the goal of world socialism in dozens of languages: Friede, Pokoj, Paix, Beke, Pax, Pace, Peace. But a walk off the main drag casts doubt on whether there is much cause to preen: six years after the war’s close, block after block of row houses are still gutted. The decrepit trolley cars are slow-moving war survivors; postwar automobiles are nowhere to be seen, except for a few “official” vehicles of the government and People’s Police. Rubble lines every side street. The National Reconstruction Program, a much-publicized campaign to repair the DDR’s war-scarred cities, is not slated to begin until late fall. Economic reconstruction is barely under way. But ideological reconstruction is well advanced. Waves of Blueshirts, 100 abreast, pass at the rate of 30 ranks per minute in the gala marking the climax of the two-week World Festival of Youth and Students for Peace. Sponsored by the international Communist Youth Organization, this year’s festival dwarfs its predecessors in Prague (1947) and Budapest (1949), as well as the “Storm Berlin” Deutschlandtreffen (German rally) of 500,000 youth in May 1950. The theme for the 1951 festival is “Stalin’s Call to Arms for Peace.” The vast majority of the participants belong to the FDJ and JP, which together boast almost three million members. Down the treeless center parkway of Unter den Linden—the lime trees were cut down years ago—and from the side streets filled with debris sweep one million East Germans, along with 26,000 foreign guests from 104 countries.
Plauen, 1990/1992/1994 From Schoolmarm to Revolutionary: Annaliese Saupe, Old “New Teacher” and Local Heroine
Authors: Rodden John G.
Published: November 2020

“Oma der Revolution,” a neighborhood child calls her. “Grandmother of the Revolution.” And that she is: a revolutionary in love with the past, a revolutionary in love with a bygone Germany. When I first met Annaliese Saupe in 1987, I had no idea that she had been such a hell-raiser: blacklisted by the Nazis, vocal critic of SED educational policies, fired for insubordination by SED school authorities. Nor could I have guessed what would lay ahead for her only two years in the future, when she would be lionized by neighbors for her derring-do against the SED during the Revolution of the Candles. With her hair coiled into a huge white bun on top of her head, her large brown eyes and quick smile, her slight limp and walking cane, her encyclopedic knowledge of grocery prices past and present, her antiquarian’s passion for the history of her native region, her enduring love affair with Goethe and Schiller: Annaliese Saupe seems much like a Hausfrau and history schoolmarm—which is also just what she has been. I met Frau Saupe in 1987 at a Goethe Institute talk near Freiburg, where she gave a presentation on Goethe’s daily routine in Weimar. Struck by Frau Saupe’s vibrance and energy, I struck up an acquaintance with her. Already 75 years old, she was a dynamo who could easily pass for a woman in her early 60s. She invited me to visit her in her hometown of Plauen, a small Saxony city of 85,000 in the old German region of Vogtland. But the paperwork for my tourist visa to East Germany dragged on beyond my six-week visit in West Germany, and I returned to the United States disappointed. Nonetheless, we wrote each other, and in early December 1990, during the week of the first free elections in eastern Germany since 1933—in which Frau Saupe voted, now as then, for the Social Democrats—I finally had an opportunity to visit Plauen. “Please don’t leave Germany this time without coming to see me!” she had written me.
How and When Will Plant Biotechnology Help?
Authors: Van Montagu Marc
Published: November 2020

It is not difficult to understand why organizers and managers of international agriculture research have doubts about whether plant biotechnology will deliver the promises they have been hearing about in due time. The population pressure is ever increasing, and conferences such as Rio 92 and FAO’s World Food Summit in November 1996 stress for everybody that the limits of expandibility of agriculture has been reached and emphasis is on the limits of the planet itself. Therefore, it is important to look at the population curve and to realize that this increase is very recent. It is really only in the first half of the twentieth century that the exponential growth took off. We should be well aware that our behavior, our societal rules, and our laws were shaped by the wisdom of philosophers and religious and political leaders who were living before this period, or, in other words, by people who were living on a very different planet. In the 1960s, the so-called green revolution was able to thoroughly intensify the agricultural output, and for some crops the production was doubled, but at the cost of a heavy input of chemicals as fertilizers, herbicides, and pesticides and soil deterioration. We have a responsibility to assume that the next doubling of food and feed production should occur in a less polluting way. Moreover, society has to be warned that this unprecedented increase in the population of developing countries will result in unequaled ecological disasters. Indeed, while it is already difficult to ask of emerging economies to respect the environment, it is almost impossible to ask the same of the roughly 1 billion people who barely can survive on the products of their “economic activities.” Activities have to be created to assist them to industrialize. However, the industrial activities we offer them will have to be very different from those we have known in the North. They will have to be low-energy-input, nonpolluting activities. To devise them, we can rely only on our inventiveness and capacity to develop new technologies.
Increasing Rice Productivity by Manipulation of Starch Biosynthesis during Seed Development
Authors: Choi Sang-Bong , Zhang Yunsun
Published: November 2020

The small-grain cereals, wheat and rice, are two of the major crops grown in the world and are used mainly as food. As the world population is projected to increase by 40% by the year 2020, these cereals can be expected to assume a much larger role in providing the basic daily dietary requirements required for human growth and development. This is especially true for rice where this cereal provides many of the dietary calories for about 50% of the world’s population, most of whom live in Asia. In view of constraints caused by the amount of available arable land and the limitations in chemical inputs in the environment imposed by the increasing use of sustainable agricultural practices, new approaches to increase the genetic yield potential of crop plants must be developed and implemented. Although dramatic improvements in the genetic yield potentials of wheat and rice were achieved during the so-called green revolution, only relatively small annual increases (1-2%) in the genetic yield potential have been attained in recent years. This trend is even true for maize (Duvick, 1992), despite the employment of the most modern biotechnological tools and resources available to the maize plant breeder. If we are to meet the challenge of feeding 8 billion people in the year 2020, it is clear that a major increase in genetic yield potential of cereal crops must be achieved. In very general terms, the genetic yield potential is dependent on source-sink relationships (Ho, 1988; Turgeon, 1989). Source leaves capture light energy and fix carbon dioxide to produce sugars and other metabolites. These organic compounds are exported from the source leaves and transported to developing sink tissues, for example, young developing leaves and new root tissue, which utilize these basic precursors for growth and development. Because of the importance of the primary processes of photosynthesis in controlling plant productivity, considerable research effort has been directed to increasing the efficiency of the source leaves. Plant productivity is also influenced by the capacity of sink tissues to uptake and assimilate photosynthate produced by source leaves or reconverted from storage reserves (Ho, 1988).
General Characteristics and Variability of Climate in the Amazon Basin and its Links to the Global Climate System
Authors: Marengo Jose A. , Nobre Carlos A.
Published: November 2020

The Amazon region is of particular interest because it represents a large source of heat in the tropics and has been shown to have a significant impact on extratropical circulation, and it is Earth’s largest and most intense land-based convective center. During the Southern Hemisphere summer when convection is best developed, the Amazon basin is one of the wettest regions on Earth. Amazonia is of course not isolated from the rest of the world, and a global perspective is needed to understand the nature and causes of climatological anomalies in Amazonia and how they feed back to influence the global climate system. The Amazon River system is the single, largest source of freshwater on Earth. The flow regime of this river system is relatively unimpacted by humans (Vörösmarty et al. 1997 a, b) and is subject to interannual variability in tropical precipitation that ultimately is translated into large variations in downstream hydrographs (Marengo et al. 1998a, Vörösmarty et al. 1996, Richey et al. 1989a, b). The recycling of local evaporation and precipitation by the forest accounts for a sizable portion of the regional water budget (Nobre et al. 1991, Eltahir 1996), and as large areas of the basin are subject to active deforestation there is grave concern about how such land surface disruptions may affect the water cycle in the tropics (see reviews in Lean et al. 1996). Previous studies have emphasized either how large-scale atmospheric circulation or land surface conditions can directly control the seasonal changes in rainfall producing mechanisms. Studies invoking controls of convection and rainfall by large-scale circulation emphasize the relationship between the establishment of upper-tropospheric circulation over Bolivia and moisture transport from the Atlantic ocean for initiation of the wet season and its intensity (see reviews in Marengo et al. 1999). On the other hand, Eltahir and Pal (1996) have shown that Amazon convection is closely related to land surface humidity and temperature, while Fu et al. (1999) indicate that the wet season in the Amazon basin is controlled by both changes in land surface temperature and the sea surface temperature (SST) in the adjacent oceans, depending if the region is north-equatorial or southern Amazonia.
Extractive Reserves and Participatory Research as Factors in the Biogeochemistry of the Amazon Basin
Authors: Brown Foster , Kainer Karen
Published: November 2020

The word Amazonia conjures up diverse images, ranging from an exotic jungle to resources for development to a vast web of ecosystems that interact with global element cycles-the focus of this book. This chapter examines the biogeochemical role of extractive reserves, a relatively new land use type within Amazonia in which nontimber forest extraction is the defining human activity. The chapter also provides examples of how participatory research with local communities can enhance the quality of the results and improve their transmission to society. Humans have been a part of the Amazon for the past several thousand years. Amerindian activities have affected forest structure in significant manners by selective planting and clearing (Balée 1989) and by increasing fire frequency, particularly during mega-El Niño events (Meggers 1994). During the last few centuries, neo-Europeans have tragically reduced native indigenous populations by several million and made wide-scale transformations in the tropics of the Americas (Crosby 1993, Ribeiro 1996). The booms in rubber extraction in the late 1800s and during World War II brought waves of nonindigenous migrants to Brazilian Amazonia (Dean 1989). More recently, large-scale implantation of cattle ranching and colonization projects, and to a lesser degree, mining activity, have accelerated change in Amazonian landscapes (Schmink and Wood 1992). In addition, the ensuing road network and infrastructure left in the wake of these recent activities increased access to primary forest, precipitating further deforestation. By 1996, about 52 million hectares, nearly the size of France, had been deforested in Brazilian Amazonia (INPE 1998). At the average rate of deforestation from 1992 to 1996 (1.9 million hectares per year), another area equivalent to this figure will be added by the year 2025, a time frame within the career of many reading this book. Continuation of the present trends will result in an increasing savannization of the Amazonian region, with pastures, secondary forests, and crop lands expanding into areas once occupied by closed-canopy forests. This phenomenon may also be called the “Africanization” of Amazonia because most of the pastures are planted with grasses imported from Africa, such as Bracharia brisanthum, which are notably different in their response to rainfall patterns and to fire than the forests that they replace.
The Recovery of Biomass, Nutrient Stocks, and Deep-Soil Functions in Secondary Forests
Authors: Nepstad Daniel , Moutinho Paulo R. S.
Published: November 2020

Secondary forests cover approximately one third of the 0.5 million km2 of the Brazilian Amazon that have been cleared for agriculture (Houghton et al. 2000, Fearnside and Guimarães 1996). These forests counteract many of the deleterious impacts of forest conversion to agriculture and cattle pasture. They absorb carbon from the atmosphere, they reestablish hydrological functions performed by mature forests, and they reduce the flammability of agricultural landscapes. Secondary forests transfer nutrients from the soil to living biomass, thereby reducing the potential losses of nutrients from the land through leaching and erosion. They also allow the expansion of native plant and animal populations from mature forest remnants back into agricultural landscapes. The study of forest recovery has focused on aboveground processes, primarily biomass accumulation. The few studies that have examined the recovery of belowground functions in Amazon secondary forests have been restricted to the upper meter or less of soil (e.g. Buschbacher et al. 1988). A review of our knowledge of secondary forest recovery is needed that incorporates accumulating evidence that approximately half of the region’s forests rely upon root systems extending to depths of several meters to maintain evapotranspiration during prolonged seasonal drought (Nepstad et al. 1994, Jipp et al. 1998, Nepstad et al. 1999a, Hodnett et al. 1997; see also Richter and Markewitz 1995). This discovery demands a conceptual shift in our approach to forest recovery on abandoned land. Are secondary forests capable of regrowing deep root systems, thereby recovering hydrologic functions and fire resistance of the mature forest? At what rate does this recovery take place? How does this ability to tap a large soil volume change our thinking about the role that nutrient shortages play in restricting secondary forest recovery? In this chapter, we begin to address these questions with the goal of furthering a mechanistic understanding of forest recovery on abandoned Amazonian lands. Our analysis focuses on three measures of secondary forest development: biomass accumulation, nutrient accumulation, and hydrological recovery. We choose biomass accumulation, because it is the best integrative measure of secondary forest development, it is the basis for estimates of carbon sequestration by secondary forests, and it is the most frequently measured secondary forest parameter.
Biogeochemistry of Amazon Floodplain Lakes and Associated Wetlands
Authors: Melack John M. , Forsberg Bruce R.
Published: November 2020

Floodplains and associated lakes are important components of the biogeochemistry, ecology, and hydrology of the Amazon basin. Amazon floodplains contain thousands of lakes and associated wetlands linked to each other and to the many rivers of the immense basin. These floodplain lakes modify the passage of flood waves (Richey et al. 1989a), increase nutrient retention and recycling (Melack and Fisher 1990), and influence the chemistry of the rivers (Devol et al. 1995). The mosaic of flooded forests, open water, and floating macrophytes in the central Amazon floodplain makes a significant contribution of methane to the troposphere (Bartlett et al. 1988, Devol et al. 1990). The fishery potential of the large river systems is closely tied to the area of floodplain and the magnitude and duration of inundation (Welcomme 1979, Bayley and Petrere 1989). The majority of fishes harvested in the Amazon basin obtain nutrition in flooded forests (Goulding 1980) or from organic matter derived from floodplain algae (Araujo-Lima et al. 1986, Forsberg et al. 1993). Much progress has been made during the last fifty years toward understanding the lakes of the Amazon floodplain. Still, the vast size of the Amazon basin poses challenges to limnologists working in the region. Recent research has been enhanced by the maintenance of functional floating laboratories in several areas, use of modern ships capable of regional surveys and equipped for hydrographic studies, and applications of remote sensing. Our objective in this chapter is to examine the role of lakes in the hydrology of the floodplain and in the biogeochemistry of carbon, nitrogen, and phosphorous within the central Amazon basin. Particular emphasis is placed on how inundation patterns interplay with carbon balance and nutrient limitation. By combining numerous measurements of primary productivity with recent results from studies using isotopes of carbon, we will examine the contribution of the major plant groups to aquatic foodwebs, and offer a new paradigm for the processing of organic carbon on the Amazon floodplain. The interplay between the Amazon River and local catchments as sources of nutrients to the floodplain indicates the potential sensitivity of the lakes to basin-wide and local disturbances.
Trace Elements in the Mainstem Amazon River
Authors: Seyler Patrick T. , Boaventura Gerald R.
Published: November 2020

Measurements of trace metals in rivers are of substantial interest for researchers examining basic scientific questions related to geochemical weathering and transport and to scientists involved in pollution control evaluation. Trace metals in natural waters include essential elements such as cobalt, copper, zinc, manganese, iron, molybdenum, nickel, which may also be toxic at higher concentrations, and nonessential elements, which are toxic, such as cadmium, mercury and lead. Recent findings indicate that iron and, to a lesser extent, zinc and manganese play an important role in regulating the growth and ecology of phytoplankton (Martin et al. 1991), while in contrast, cadmium, arsenic, and mercury have long been recognized as poisonous to living organisms (see Pfeiffer et al. 1993, for a description of mercury problem in the Amazon basin). The release of potentially large quantities of these toxic metals, particularly in the river systems of industrialized countries, but also in tropical rivers, is an acute problem of great environmental concern. An understanding of the weathering and transport processes controlling the fate and flux of trace metals in pristine environments is important in evaluating the capacity of receiving waters to accommodate wastes without detrimental effects. The Amazon River system, which is relatively free of industrial and agricultural interference, represents an ideal case for the investigation of the origin and transport of trace metals. This understanding may also provide a scientific basis for the anticipated development of the Amazon basin. With regard to trace metals, Amazon River is still poorly documented. Martin and Meybeck (1979) and Martin and Gordeev (1986) presented a global tabulation of trace metal concentrations in particulate matter of major rivers including the Amazon, and Palmer and Edmond (1992) measured dissolved Fe, Al, and Sr concentrations in the Amazon mainstream and a number of its tributaries. Boyle et al. (1982) and Gordeev et al. (1990) published some data on Cu, Ni, Cd, and Ag dissolved concentrations at the mouth of the Amazon River and in its oceanic plume. Konhauser et al. (1994) reported the trace and rare earth elemental composition of sediments, soils and waters, mainly in the region of Manaus.
The Great Population Spike and After
Authors: Rostow W. W.
Published: November 2020

Midway through the eighteenth century, the rate of growth for the world's population was roughly at zero. Immediately after World War II, it was just above 2 percent. Ever since, it has fallen steadily. This new book, the latest offering from a distinguished expert on international economics, tells readers what this stagnation or fall in population will mean--economically, politically, and historically--for the nations of the world. W. W. Rostow not only traces the whole global arc of this "great population spike"--he looks far beyond it. What he sees will interest anyone curious about what is in store for the world's financial and governmental systems. The Great Population Spike and After: Reflections on the 21st Century contends that, as the decline in population now occurring in the industrialized world spreads to all of the presently developing countries, the global rate of population will fall to the "zero" level circa 2100. (Indeed, with the exception of Africa south of the Sahara, it could reach "zero" long before then.) This being so, how will it be possible to maintain full employment and social services with a decelerating population? What will societies do when the proportion of the working force (as now defined) diminishes radically in relation to the population of poor or elderly dependents? How will the countries of the world confront subsequent decreases in population-related investment? In answering these queries, this bold study asserts that the United States is not the "last remaining superpower" but the "critical margin" without whose support no constructive action on the world scene can succeed. Rostow takes the view that world peace will depend on our government's ability to assume responsibly this "critical margin" role. Further, he argues that, over a period of time, the execution of this strategy on the international scene will require a bipartisan, relentless effort to solve the combustible social problems that weaken not only our cities but our whole society.