bluuebunny/crossref_metadata_2025 huggingface dataset:
The Physical Environment
Authors: Clark Kenneth L. , Lawton Robert O.
Published: November 2020

Because biological diversity is directly related to diversity of the physical environment, a clear picture of the physical setting of the Cordillera is crucial to understand its ecology and conservation. The physical setting of Monteverde and the Cordillera de Tilarán encompasses a wide range of environmental conditions. The size, position across the trade windflow, geology, erosional dissection, and hydrology of the Cordillera interact to produce extraordinary physical diversity that parallels its great biological diversity. A major difference between tropical montane and lowland regions is the way biological diversity is distributed across the landscape. Montane regions are usually less diverse at the scale of 0.01-0.1 km2 but are as rich in species as nearby lowland areas at scales of 10-100 km2. We have two goals in this chapter. First, we review what is known of the climate and weather, geology and geologic history, geomorphology, soils, and hydrology of Monteverde. Our account focuses on higher elevations in Monteverde and wetter areas on the Caribbean slope, with less attention to the drier environments on the lower Pacific slope. Second, we point out areas where our knowledge is incomplete and suggest promising lines of future research. Although the geology and geomorphology of Monteverde are moderately well known, our knowledge of the rates of many geomorphic processes, particularly erosion, is poor. We also lack information on soils and hydrology, particularly of wind-driven cloud and precipitation inputs, evapotranspiration, and stream outputs from forests and other land-use types in Monteverde. Quantitative information on how variability in the physical environment interacts with biotic processes at the population, community, and ecosystem levels is scant. Most of the climate and weather data were collected at 1450 m at the Pensiόn (1956-1971), at 1520 m at John Campbell's residence (1972 to present), and intermittently throughout or near the Monteverde Cloud Forest Preserve (MCFP; Lawton and Dryer 1980, Crump et al. 1992, Clark 1994, Bohlman et al. 1995, W. Calvert and A. Nelson, unpubl. data).
Ecosystem Ecology and Forest Dynamics
Authors: Nadkarni Nalini M. , Lawton Robert O.
Published: November 2020

The earth’s surface supports living organisms and their environments to form the biosphere, a thin film of life around the planet. Organisms participate in interacting systems or communities, and these communities are coupled to their environments by the transfer of matter and energy and by movements of air, water, and organisms. Human activities in Monteverde and elsewhere can drastically alter forest ecosystems. Textbooks on ecosystem ecology typically include such topics as community structure and composition (including plant growth forms, vertical structure, niche space, species diversity), communities and environments (species distributions along environmental gradients, community classification, succession), production (food chains and webs, decomposition and detritus, photosynthesis), and nutrient cycling (mineral nutrition of organisms, soil development, biogeochemistry). Our understanding of tropical ecosystem ecology generally falls short of what we know of other aspects of tropical biology. There are far more studies concerning population biology, autecology, and life history of tropical organisms than nutrient cycling, productivity, and landscape ecology. This pattern is true in Monteverde and in such well-studied tropical forests as La Selva, Barro Colorado Island (BCI), and the Luquillo National Forest (Lugo and Lowe 1995, McDade et al. 1994). Logistical blocks to ecosystem research exist because collaborating teams of scientists are typically needed to tackle the multiple disciplines that ecosystem-level questions require, which demands a large infrastructure and budget. Temporal problems exist because ecosystem-level phenomena (e.g., tree mortality and forest regeneration) may involve time scales longer than the life of a single granting period or lifetime of a researcher. A strong academic base for ecosystem ecology is lacking because the pool of existing studies is too small to draw patterns and extrapolate trends. These obstacles have not often been overcome in Monteverde. No Monteverde institution has provided the infrastructure to support ecosystem research (e.g., laboratory facilities, meteorological station, technical library). Some community members have negative feelings about experimental manipulations and destructive sampling sometimes needed to answer ecosystem ecology questions. From the 1970s to the 1990s, Organization for Tropical Studies (OTS) courses were in Monteverde and in such well-studied tropical forests as La Selva, Barro Colorado Island (BCI), and the Luquillo National Forest (Lugo and Lowe 1995, McDade et al. 1994).
Agriculture in Monteverde: Moving Toward Sustainability
Authors: Griffith Katherine , Peck Daniel
Published: November 2020

This chapter is an overview of how Monteverde settlers transformed their environment into a diversity of agricultural systems. We first discuss “people living in nature,” how Monteverdans have viewed natural resources and defined sustainability. We describe the environmental and social conditions that determined agronomic options in the area, and outline the area’s major agricultural activities (dairy, coffee, and beef), other crops, and efforts at agricultural diversification. Where possible, we cite published studies, but few exist for some issues. We rely heavily on local experts, including long-term community members, local agronomists, veterinarians, and farmers. We also draw on agricultural production data collected by local organizations. From the earliest indigenous settlers to today’s commercial farmers, biologists, and artists, Monteverde’s inhabitants have exhibited a wide spectrum of approaches to natural resource use. The community’s ongoing debate over the meaning and practice of “sustainability” throws into sharp relief residents’ differing worldviews, kinds of knowledge, and perceptions of constraints and opportunities. People’s decisions on how to use natural resources depend on three factors: their attitudes and beliefs, their knowledge, and the opportunities, constraints, and conditions that they confront. For example, beliefs may demand that people be “stewards” of the land, that they use resources to maximize economic returns during their lifetime, or that they use resources as sparingly as possible. Their knowledge may prepare them to be organic vegetable farmers, traditional dairy farmers, business people, or biologists. The social, environmental, and economic context in which they make decisions further defines which options are available or attractive. As one local farmer stated, “We do the best we can with what we have, based on what we know, and what the circumstances permit or encourage us to do.” Monteverdans generally agree that “sustainable agriculture” is a good thing, but there is less agreement on what it means. Following the taxonomy of Gillespie (1998), three sustainable agriculture “schools of thought” exist in Monteverde. The first group is the “Ecocentric Agriculture” school, whose approach focuses on what is sustainable in a biological/ecological sense. Many local biologists and organic producers espouse this view.
Analysis of Chemical Oscillations
Authors: Epstein Irving R. , Pojman John A.
Published: November 2020

Many of the most remarkable achievements of chemical science involve either synthesis (the design and construction of molecules) or analysis (the identification and structural characterization of molecules). We have organized our discussion of oscillating reactions along similar lines. In the previous chapter, we described how chemists have learned to build chemical oscillators. Now, we will consider how to dissect an oscillatory reaction into its component parts—the question of mechanism. A persuasive argument can be made that it was progress in unraveling the mechanism of the prototype BZ reaction in the 1970s that gave the study of chemical oscillators the scientific respectability that had been denied it since the discovery of the earliest oscillating reactions. The formulation by Field, Körös, and Noyes (Field et al., 1972) of a set of chemically and thermodynamically plausible elementary steps consistent with the observed “exotic” behavior of an acidic solution of bromate and cerium ions and malonic acid was a major breakthrough. Numerical integration (Edelson et al., 1975) of the differential equations corresponding to the FKN mechanism demonstrated beyond a doubt that chemical oscillations in a real system were consistent with, and could be explained by, the same physicochemical principles that govern "normal" chemical reactions. No special rules, no dust particles, and no vitalism need be invoked to generate oscillations in chemical reactions. All we need is an appropriate set of uni- and bimolecular steps with mass action kinetics to produce a sufficiently nonlinear set of rate equations. Just as the study of molecular structure has benefited from new experimental and theoretical developments, mechanistic studies of complex chemical reactions, including oscillating reactions, have advanced because of new techniques. Just as any structural method has its limitations (e.g., x-ray diffraction cannot achieve a resolution that is better than the wavelength of the x-rays employed), mechanistic studies, too, have their limitations. The development of a mechanism, however, has an even more fundamental and more frustrating limitation, sometimes referred to as the fundamental dogma of chemical kinetics. It is not possible to prove that a reaction mechanism is correct. We can only disprove mechanisms.
Asymmetric Synthesis
Authors: Doraiswamy L. K.
Published: November 2020

The manufacture of fine chemicals, particularly drugs, fragrances, and flavors, is undergoing a major revolution now as a result of the capability of chemists to prepare these chemicals, mainly drugs, in their purest isomeric forms (as stereoisomers). This shift to pure forms has been described by Brown in the following words (1990) (see also Deutsch, 1991): “A mixture of stereoisomers in a medicine will (now) need to be justified just the same way as any other mixture of compounds.” Indeed, in the United States today (as in many other advanced countries), the use of pure enantiomeric forms is practically a requirement since extensive justification is needed to continue with racemates (FDA, 1992). As a consequence, the combined sales of the “chiral top ten” drugs (ammoxycillin, enalapril, ampicillin, captopril, pravastatine, diltiazem, ibuprofen, lovastatin, naproxen, and fluoxetine) in 1994 amounted to more than 16 billion dollars (Sheldon, 1996). (Of these, ibuprofen and fluoxetine are still sold as racemates.) Because patent expiry for a racemate tends to proliferate the drug as generics, product line extension for an existing racemate technology can be obtained by switching to a single stereoisomeric form (the racemic switch). This is an incentive to produce the drugs in their pure enantiomeric forms. The use of homogeneous catalysis in organic synthesis and technology was considered in the previous chapter. A particularly useful application of homogeneous catalysis is in the production of stereoisomers in pure forms by a rapidly expanding technique known as chiral (asymmetric) synthesis or chirotechnology. Note, however, that the term asymmetric synthesis is much broader in scope, and the use of homogeneous catalysis to achieve chirality is only one of the methods of doing so. When applied to this specific case, it is generally referred to as chiral or asymmetric catalysis. This again is a much broader term and includes both homogeneous and heterogeneous catalyses. Although chirality is not a prerequisite for biological activity, the presence of stereogenic centers in bioactive molecules gives rise to large differences in the activities of the individual enantiomers. It is this fact that is exploited in the production of the desired pure enantiomers.
Reactor Design for Simple Reactions
Authors: Doraiswamy L. K.
Published: November 2020

Ideal reactors and their design principles were discussed in Chapter 4. In addition to these ideal reactors, there are certain reactors in which a reasonably welldefined measure of mixing can be introduced. These are the recycle plug-flow reactor and a sequence of fully mixed reactors. Many organic reactions are conducted in a stirred reactor containing a batch of the same or a second reactant, and continuously feeding, or withdrawing, or feeding and withdrawing one or more of the reactants and/or products. These are referred to as semibatch reactors. They belong to a more general class of reactors known as variable volume reactors. The design of all of these types of reactors is briefly considered in this chapter. The principle of the recycle-flow reactor (RFR) is sketched in Figure 10.1.
Membrane-Assisted Reactor Engineering
Authors: Doraiswamy L. K.
Published: November 2020

Like zeolites that combine shape selectivity with catalysis, membranes combine separation with catalysis to enhance reaction rates. The dual functionality of zeolites derives from the nature of the catalytic material, whereas that of membranes derives from the nature of the reactor material. The catalyst in the membrane reactor can be a part of the membrane itself or be external to it (i.e., placed inside the membrane tube). The chief property of a membrane is its ability for selective permeation or permselectivity with respect to certain compounds. Organic membrane reactions are best carried out in reactors made of inorganic membranes, such as from palladium, alumina, or ceramics. Good descriptions of these reactions and the membranes used are available in many reviews, for example, Gryaznov (1986, 1992), Stoukides (1988), Armor (1989), Govind and Ilias (1989), Bhave (1991), Zaspalis and Burggraaf (1991), Hsieh (1989, 1991), Shu et al. (1991), Shieh (1991), Gellings and Bouwmeister (1992), Tsotsis et al. (1993b), Harold et al. (1994), Saracco and Specchia (1994), Sanchez and Tsotsis (1996). A recent trend has been to develop polymeric-inorganic composite type membranes formed by the deposition of a thin dense polymeric film on an inorganic support (Kita et al., 1987; Rezac and Koros, 1994, 1995; Zhu et al., 1996). Another class of membranes under development for organic synthesis is the liquid membrane (Marr and Kopp, 1982; Eyal and Bressler, 1993). The permselective barrier in this type of membrane is a liquid phase, often containing a dissolved “carrier” or “transporter” that selectively reacts with a specific permeate to enhance its transport rate through the membrane. Our main concern in this chapter will be with inorganic membrane reactors. We commence our treatment with an introduction to the exploitable features of membrane reactors (with no attempt to describe membrane synthesis). Then we describe the main variations in design and operating mode of these reactors, develop performance equations for the more important designs, and compare the performances of some important designs with those of the traditional mixed- and plug-flow reactors. Finally, we present a summary of the applications of membrane reactors in enhancing the rates of organic reactions.
High-Pressure Effects on the Structure and Phase Behavior of Model Membrane Systems
Authors: Winter Roland , Landwehr Anne
Published: November 2020

Phospholipids, which provide valuable model systems for lipid membranes, display a variety of polymorphic phases, depending on their molecular structure and on environmental conditions. High hydrostatic pressure has been used as a physical parameter to study the thermodynamic properties and phase behavior of these systems. High pressure is also a characteristic feature of certain natural membrane environments. In the first part of this article, we review our recent work on the temperature- and pressure-dependent phase behavior of phospholipid systems differing in lipid conformation and headgroup structure. In the second part, we report on the determination of the (T, x, p) phase diagrams of binary phospholipid mixtures. An additional section deals with effects of incorporating ions, small amphiphilic molecules, and steroids into the bilayer on the experimental temperature- and pressure-dependent phase behavior of lipid systems. Finally, we discuss lamellar to nonlamellar thermotropic and barotropic phase transformations, which occur for a number of lipids, such as phosphatidylethanolamines, monoacylglycerides, and lipid mixtures. It has been suggested that nonlamellar lipid structures might play an important role as transient and local intermediates in a number of biochemical processes. High-pressure smallangle x-ray (SAXS) and neutron (SANS) scattering, differential scanning calorimetry (DSC), high-pressure differential thermal analysis (DTA), and p, V, T measurements have been used as experimental methods for the investigation of these systems. Lipid bilayer dispersions, in particular the phosphatidylcholines and phosphatidylethanolamines, are the workhorses for the investigation of biophysical properties of membrane lipids because they constitute the basic structural component of biological membranes. They exhibit a rich lyotropic and thermotropic phase behavior (Cevc & Marsh, 1987; Marsh, 1991; Yeagle, 1992). Most fully hydrated saturated phospholipid bilayers exhibit two principal thermotropic lamellar phase transitions, corresponding to a gel to gel (Lβ′–Pβ′) transition and a gel to liquid-crystalline (Pβ′–Lα) main transition at a temperature Tm. In the fluid-like La phase, the hydrocarbon chains of the lipid bilayers are conformationally disordered, whereas in the gel phases the hydrocarbon chains are more extended and relatively ordered.
Learning Together
Authors: Rogoff Barbara , Turkanis Carolyn Goodman , Bartlett Leslee
Published: November 2020

This book advances the theoretical account that Barbara Rogoff presented in her highly acclaimed book, Apprenticeship in Thinking. Here, Rogoff collaborates with two master teachers from an innovative school in Salt Lake City, Utah, to examine how students, parents, and teachers learn by being engaged together in a community of learners. Building on observations by participants in this school, this book reveals how children and adults learn through participation in activities of mutual interest. The insights will speak to all those interested in how people learn collaboratively and how schools can improve.
The City in Roman Palestine
Authors: Sperber Daniel
Published: November 2020

This book is a study of the city and urban life in Roman Palestine during the Talmudic period, 100-400 B.C. Rather than focus on a specific city, Daniel Sperber synthesizes what is known about city life in Talmudic Palestine to create a paradigmatic hypothetical Palestinian city. Drawing on numerous literary records for his information, he describes the structure and use of many physical aspects of the city, such as its markets, pubs, streets, bathhouses, roads, walls, toilets, and water supply. Rounding out the study is a chapter describing the archeological evidence, written by Sperber's colleague, Professor Joshua Schwartz. With the recent upsurge of interest in urbanization in the Greco-Roman world, The City in Roman Palestine will attract not only scholars of Judaic literature and history, but also classicists and ancient historians.
On the Edge of Extinction
Authors: Verschuur Gerrit L.
Published: November 2020

On the morning of June 30, 1908, civilization may have suffered the worst piece of luck in its history. A small cometlike object exploded in the atmosphere above the Tunguska river valley in Siberia. It did little more than scorch and flatten trees for 20 kilometers in all directions and kill a thousand reindeer. However, if that object had struck a heavily populated region, we would not now dwell under any illusion concerning how close to the edge of extinction the human species actually hovers. Because the Tunguska missile missed a populated area, the threat of impact did not really begin to enter the public imagination until after the 1980 announcement of the discovery of the iridium in the K/T boundary layer. Had the Tunguska object struck a large city, a million people or more might have perished, and the phenomenon would have raised everyone’s awareness to the threat of comet impact. Instead, nearly a century later, the threat of comet and asteroid impact is regarded as little more than an interesting anecdote. Very slowly the nature of the threat is being recognized, but only because of the somewhat esoteric discovery that the dinosaurs were wiped out by a major impact 65 million years ago. Such huge collisions are infrequent, perhaps about once every 50 to 100 million years. It is the smaller impacts that pose the greatest danger, and they occur far more frequently. About 800 years ago the South Island of New Zealand suffered widespread fires, which leveled the island and led to the extinction of the Moa bird. Maori legend says that a big explosion in the sky was the cause of the strange fire. Duncan Steel of the University of Adelaide and Peter Snow from Otago in New Zealand have pieced together a fascinating scenario that suggests that the Maori were correct. The fireball created by a comet impact may have ignited the forests of South Island. Near the town of Tapanui in the province of Otago there exists a crater that geologists have been slow to identify as extraterrestrial in origin.
Death Star or Coherent Catastrophism?
Authors: Verschuur Gerrit L.
Published: November 2020

Our instinct for survival drives us to learn as much as possible about what goes on around us. The better we understand nature, the better we will be able to predict its vagaries so as to avoid life-threatening situations. Unfortunately, nature is seldom so kind as to arrange for disasters to occur like clockwork, yet that does not dampen our enthusiasm when even a hint of periodicity in a complex phenomenon is spotted. This helps account for the furor that was created when a few paleontologists claimed that mass extinctions of species seemed to recur in a regular manner. A cycle, a periodicity, had been found! That implied that perhaps they might be able to predict nature’s next move. This is how I interpret the extraordinary public interest that was generated by the claims made around 1984 that the mass extinction phenomenon showed a roughly 30-million-year period (others said it was 26 million years). Almost immediately, several books appeared on the subject as well as many, many articles in the popular press and in science magazines. This activity marked the short life of the Death Star fiasco. Given our instinctual urge to look for order in the chaos of existence, the identification of a periodicity in mass-extinction events was a great discovery, if real. What was not highlighted by those who climbed aboard the bandwagon, however, was that the last peak in the pattern occurred about 13 million years ago. If impact-related mass extinction events were produced every 30 million years, there obviously was no cause for concern that we would be hit by a 10-kilometer object in the next 17 million years. Phew! I think that the suggestion that mass extinctions occurred on a regular cycle caused as much interest as it did because we all want to believe that there is no immediate danger to us. The Death Star fiasco began when David Raup and John Sepkowski of the University of Chicago published a report claiming that mass extinction events recurred about every 26 million years. They were followed by Michael Rampino and Richard Stothers of the Goddard Institute for Space Studies in New York who claimed that the period was more like 30 million years, at least during the last 250 million years.
Dendritic Spines
Authors: Koch Christof
Published: November 2020

Dendritic spines, sometimes also called dendritic thorns, are tiny, specialized protoplasmic protuberances that cover the surface of many neurons. First described by Ramón y Cajal (1909; 1991) in light-microscopic studies of Golgi stained tissue, they are among the most striking subneuronal features of many neurons. Indeed, the presence of a high density of dendritic spines allows the unambiguous classification of neuronal types into spiny and aspiny, sparsely spiny, or smooth neurons. Over 90% of all excitatory synapses that occur in the cortex are located on dendritic spines. Spines can be found in all vertebrates as well as in invertebrates (e.g., the dendrites of Kenyon cells in the mushroom bodies in the olfactory system of the insect brain). The intimate association of spines with synaptic traffic suggests some crucial role in synaptic transmission and plasticity. Because of their submicrometer size (see below), physiological hypotheses as to the function of dendritic spines have only very recently become accessible to the experimentalist. For the previous two decades, spine properties have been investigated through analytical and computational studies based on morphological data, providing a very fertile ground for the crosspollination of theory and experiment. (For a very readable historical account of this see Segev et al., 1995.) The recent technical advances in the direct visualization of calcium dynamics in dendrites and spines are now permitting direct tests of some of these theoretical inferences (Guthrie, Segal, and Kater, 1991; Müller and Connor, 1991; Yuste and Denk, 1995; Denk, Sugimori, and Llinás, 1995; Svoboda, Tank, and Denk, 1996). As discussed in this chapter and, more extensively, in Chap. 19, the theoretical models that have endowed spines with active properties giving rise to all-or-none behavior (Perkel and Perkel, 1985; Shepherd et al., 1985; Segev and Rail, 1988; Baer and Rinzel, 1991) have, in general, been confirmed experimentally. Historically, the possibility of implementing synaptic memory by modulating the electroanatomy of spines was recognized early on (Chang, 1952) and was subsequently analyzed in depth by Rail (1970, 1974, 1978) and many others. Because small changes in the spine morphology can lead to large changes in the amplitude of the EPSP induced by the excitatory synapse on the spine, spines have been considered to contribute to the modulation of synaptic “weight” during long-term potentiation (see Chap. 13).
Introduction
Authors: Yung Yuk L. , DeMore William B.
Published: November 2020

It is usual in the study of planets to consider the Earth first, and then the other planets, so that we can better understand how and why the rest of the solar system is different from us. In this book the order of study will be reversed: we shall first try to understand the solar system, and then we will ask why Earth is unique. We adopt this unconventional approach for two reasons. First, Earth's atmosphere today is the end-point of an evolution that started about 4.6 billion years ago. The pristine materials have all been drastically altered. However, by examining other parts of the solar system that have evolved to a lesser degree, we may deduce what the early Earth might have been like. Second, Earth's atmosphere today is largely determined by the complex biosphere, whose evolution has been intimately coupled to that of the atmosphere. In other words, ours is the only atmosphere in the solar system that supports life, and it is in turn modified by life. Therefore, to appreciate the beauty and the intricacy of our planet, we must start with simpler objects without life. Chemical composition is intimately connected to evolution, which in turn is driven by chemical change. In this book we attempt to provide a coherent basis for understanding the planetary atmospheres, to identify the principal chemical cycles that control their present composition and past history. Figure 1.1 gives an illustration of the intellectual framework in which our field of study is embedded. The unifying theme that connects the planets in the solar system is "origin"; that is, all planets share a common origin about 4.6 billion years ago. The subsequent divergence in the solar system may be partly attributed to evolution, driven primarily by solar radiation. The bulk of solar radiation consists of photons in the visible spectrum with a mean blackbody radiation temperature of 5800 K. The part that is responsible for direct atmospheric chemistry is a tiny portion (less than 1% of the total flux) in the ultraviolet. In addition, the sun emits a steady stream of corpuscular particles, known as the solar wind. While the sun provides the principal source of energy for change, the time rate of change is crucial, and that is where chemical kinetics and chemical cycles play pivotal roles.
Satellites and Pluto
Authors: Yung Yuk L. , DeMore William B.
Published: November 2020

The presence of an atmosphere on a small planetary body the size of the Moon is surprising. Loss of material by escape would have depleted the atmosphere over the age of the solar system. Since these objects are not large enough to possess, or to sustain for long, a molten core, continued outgassing from the interior is not expected. However, it is now known that four small bodies in the outer solar system possess substantial atmospheres: lo, Titan, Triton, and Pluto. These atmospheres range from the very tenuous on lo (of the order of a nanobar) to the very massive on Titan (of the order of a bar). The atmospheric pressures on Triton and Pluto are of the order of 10 μbar. Perhaps the most interesting questions about these atmospheres concern their unusual origin and their chemical evolution. lo is the innermost of the four Galilean satellites of Jupiter, the other three being Ganymede, Europa, and Callisto. All the Galilean moons are comparable in size, but there is no appreciable atmosphere on the other moons. The first indications that lo possesses an atmosphere came in 1974 with the discovery of sodium atoms surrounding the satellite and the detection of a well-developed ionosphere from the Pioneer 10 radio occultation experiment. The Voyager encounter in 1979 established the existence of active volcanoes as well as SOa gas. These are the only extraterrestrial active volcanoes discovered to date, and they owe their existence to a curious tidal heating mechanism associated with the 2:1 resonance between the orbits of lo and Europa.
Statistical Fluid Dynamics
Authors: Salmon Rick
Published: November 2020

In the previous chapter, we considered fluid turbulence from a heuristic viewpoint, combining ideas based on fundamental conservation laws with more qualitative ideas about irreversible behavior. However, there have been many attempts to study turbulence in a more quantitative and deductive fashion, beginning with the governing dynamical equations for a fluid. None of these attempts is, or could be, mathematically rigorous; all involve approximations that are difficult to justify and hard to test. In fact, these more deductive theories are perhaps best viewed as approximations in which the exact dynamical equations are replaced by stochastic-model equations having some (but not all) of the same physical properties as the exact equations, in much the same way as the quasigeostrophic equations contain only a part of the physics in the more exact primitive equations. In this chapter, we examine fluid turbulence from the standpoint of equilibrium and nonequilibrium statistical mechanics. This is a complicated and controversial subject, and our discussion will be introductory and elementary. In fact, we shall be much more concerned with the philosophy behind the statistical methods than with the detailed structure of the theory or with its successes and failures at describing real turbulence. This philosophy appears to be applicable to a much wider range of problems than so far considered. Readers who want a more thorough and complete description of statistical turbulence theory should consult more specialized sources. This chapter continues a theme, begun in chapter 4, to be continued in chapter 6, that much of our understanding of turbulence is based on two general principles: the conservation principle, which states that quantities like energy and potential vorticity are conserved (apart from the effects of dissipation), and the irreversibility principle, which holds that a turbulent system tends toward ever greater complexity. In chapter 4, we met the irreversibility principle in the assumptions that a narrow spectral peak spreads out and that nearby fluid particles tend to move apart. In this chapter, we encounter the irreversibility principle again, as a kind of macroscopic form of the Second Law of Thermodynamics.
Soil Properties and Water Movement
Authors: Parlance J.-Y. , Steenhuis T. S.
Published: November 2020

For all spatial scales, from pore through local and field, to a watershed, interaction of the land surface with the atmosphere will be one of the crucial topics in hydrology and environmental sciences over the forthcoming years. The recent lack of water in many parts of the world shows that there is an urgent need to assess our knowledge on the soil moisture dynamics. The difficulty of parameterization of soil hydrological processes lies not only in the nonlinearity of the unsaturated flow equation but also in the mismatch between the scales of measurements and the scale of model predictions. Most standard measurements of soil physical parameters provide information only at the local scale and highlight the underlying variability in soil hydrological characteristics. The efficiency of soil characteristic parameterization for the field scale depends on the clear definition of the functional relationships and parameters to be measured, and on the development of possible methods for the determination of soil characteristics with a realistic use time and effort. The soil’s hydraulic properties that affect the flow behavior can be expressed by a soil water retention curve that describes the relation between volumetric water content, θ(L3L3), and soil water pressure, h(L), plus the relation between volumetric water content and hydraulic conductivity, K(L/T). In the next section, the determination of soil hydraulic parameters is first discussed for local and field scale. Then, we show how the pore-scale processes can be linked to soil hydraulic properties. These properties are then used in some of the modern methods that use integral and superposition solutions of Richards’ equation for infiltration and water flow problems for both stable and preferential types of flows. Finally, some practical aspects for watersheds are discussed to highlight the difficulties encountered when large-scale predictions are needed.
Water and Solute Transport in Arid Vadose Zones : Innovations in Measurement and Analysis
Authors: Tyler Scott W. , Scanlon Bridget R.
Published: November 2020

Understanding the physics of flow and transport through the vadose zone has advanced significantly in the last three decades. These advances have been made primarily in humid regions or in irrigated agricultural settings. While some of the techniques are useful, many are not suited to arid regions. The fluxes of water and solutes typically found in arid regions are often orders of magnitude smaller than those found in agricultural settings, while the time scales for transport can be orders of magnitude larger. The depth over which transport must be characterized is also often much greater than in humid regions. Rather than relying on advances in applied tracers, arid-zone researchers have developed natural-tracer techniques that are capable of quantifying transport over tens to thousands of years. Techniques have been developed to measure the hydraulic properties of sediments at all water contents, including the very dry range and at far greater depths. As arid and semiarid regions come under increased development pressures for such activities as hazardous- and radioactive-waste disposal, the development of techniques and the understanding of water and solute transport have become crucial components in defining the environmental impacts of activities at the landsurface. In the past, the movement of water and solutes through the unsaturated zones of arid and semiarid regions was largely ignored, either for the sake of expediency or from a lack of knowledge or misperceptions regarding the extent of water movement. In the High Plains of the United States, water extraction from the Ogallala aquifer proceeded at a rapid rate throughout the 20th century, with little attention paid to the rate of replenishment from natural recharge. As withdrawals began to exceed recharge, water levels dramatically declined and are now necessitating changes in the economic base for this large portion of the agricultural United States. At Hanford, Washington, large amounts of radioactive waste from nuclear weapons production were disposed of at or near the landsurface under the premise that there was no movement of water within the unsaturated zone to transport the contaminants to the underlying aquifer.
Customizing Soil-Water Expertise for Different Users
Authors: Wagenet R. J. , Bouma J.
Published: November 2020

Our lives depend upon and determine the fluxes of water and chemicals in the environment. Atmospheric, aquatic, and terrestrial systems are all characterized by transfer processes that make our lives possible. Some of these processes deliver the air, water, and nutrients that we need to produce food and fiber. Other transfer processes relocate our wastes as environmental contaminants that must be properly managed. As society grows in absolute numbers, so, too, must our concern for maintaining the balance between the wise use of our natural resources in a sustainable manner on the one hand, and the misuse of these resources through short-sightedness and mismanagement on the other hand. Utilization of our resources must be accompanied by protection of them, and knowledge of the role that transfer processes play in this balancing act is important. Management for the long term means that wise decisions in the short term are based on two key issues. First, there is a crucial need to further understand how natural processes, particularly transfer processes, operate. Without this knowledge base, we are unable to formulate logical and lasting solutions to environmental problems. While soil scientists have always focused on tabulating land characteristics in the form of soil surveys, there now is the need to translate these static characterizations into dynamic land qualities, such as soil transfer processes. As important, but less appreciated, is the fact that scientists are becoming increasingly accountable to our clients, the public, for approaches to solve problems that are important to society. This is particularly true for those scientists knowledgeable in transfer processes, for the obvious reasons of public focus on environmental management and pollution prevention. The decisions regarding the impact of our science will be debated, enacted, and enforced outside the scientific community. As we now realize, this means we must consider solutions to environmental problems that are endorsed not only by the scientific community, but also by the public citizenry and regulatory bodies. Many soil and water scientists are experts on transfer processes in the unsaturated zone of the soil.
What Limits the Efficiency of Photosynthesis, and Can There Be Beneficial Improvements?
Authors: Barber J.
Published: November 2020

Over the past 35 years a great deal has been learned about the mechanisms of photosynthesis, ranging from the ultrafast reactions involved in the initial capture of photons to the slower processes of carbon metabolism. Today our knowledge of photosynthesis and its molecular mechanisms is enormous, so much so that it is difficult for one person to absorb all the information. This is not necessarily a bad thing, since what we have achieved is sufficient information to appreciate the complexity of the “photosynthetic engine” and to identify the main factors that ultimately regulate its efficiency. In this chapter I summarize those areas of photosynthesis research with which I am reasonably familiar and, in so doing, address the question posed by the chapter title. As Blackman (1895a,b) pointed out, the rate of photosynthesis initially rises as the light intensity is increased and then levels off to a plateau. This plot is often referred to as the rate v PFD curve, where PFD stands for Photon Flux Density. Over the years rigorous analyses of the slopes of the rate v PFD curve have been made to obtain a value of the quantum yield (usually expressed as the number of quanta or photons required to produce one molecule of oxygen or to fix one molecule of carbon dioxide). With a few exceptions, the value obtained for a wide range of “non stressed” organisms and plants supplied with excess CO2 is about 9 or a little more (Björkman and Demmig, 1987; Walker, 1992). Bearing in mind that one molecule of oxygen evolved or carbon dioxide fixed is a 4e/4H+ process, then a value of 8 would he consistent with the “Z-scheme” model proposed by Hill and Bendall (1960). In this scheme, each electron is excited twice, first by photosystem two (PSII) and then by photosystem one (PSI). In this way, 8 photons are used to drive 4e/4H+ from water, through PSII and PSI to NADP.
Rubisco, the Key to Improved Crop Production for a World Population of More Than Eight Billion People?
Authors: Long S. P.
Published: November 2020

Despite great advances in understanding of photosynthesis in crops, photosynthesis research has contributed little to improvement of crop production in the past. Does it have a future role in the task of feeding a world of 8 billion? In this chapter I argue that modification of the primary carboxylase of photosynthesis (Rubisco) promises very significant increases in potential crop yields. Plant breeding over the past three decades has produced remarkable worldwide increases in the potential yields of many crops, most notably improvements in the small grain cereals of the “green revolution” (Beadle and Long, 1985; Evans, 1993). Potential yield is defined as the yield that a genotype can achieve under optimal cultivation practice and in the absence of pests and diseases. What are the physiological bases of these increases? Following the principles of Monteith (1977), the potential yield (Y) of a crop at a given location is determined by . . . y = St- εi- εe- η/k (1) . . . where St is the integral of incident solar radiation (MJ m-2), εi the efficiency with which that radiation is intercepted by the crop; εe the efficiency with which the intercepted radiation is converted into biomass; η the harvest index or the efficiency with which biomass is partitioned into the harvested product; and k the energy content of the biomass (MJ g-1). St is determined by the site and year, while k varies very little across higher plant species (Roberts et al., 1993). Potential yield is therefore determined by the combined product of three efficiencies, each describing broad physiological properties of the crop: εi, εe, and η. εi is determined by the speed of canopy development and closure, and by canopy longevity and architecture. εe is a function of the combined photosynthetic rate of all leaves within the canopy less crop respiratory losses. In the context of equation 1, increase in potential yield over the past 30 years has resulted almost entirely from large increases in η.
A Systems Perspective on Postharvest Losses
Authors: Gill M. , Poulter N.
Published: November 2020

The “green revolution,” fathered by the Nobel Laureate Dr. Norman Borlaug, has led to massive yield increases in key crops. Considerable effort continues to be given to the raising of yield plateaux in mainstream as well as minor crops through the application of traditional breeding and more advanced biotechnical methods. However, attention has increasingly been turned to postharvest losses that may impede the realization of the full impact of new varieties, in terms of both food quantity and quality. IFPRI’s “2020 Vision for Food, Agriculture, and the Environment” acknowledges rapid population growth and food productivity as key determinants in the alleviation of poverty, hunger, and malnutrition. Eight billion people in 2020 will require more than twice the current output of the major food items, but this projection assumes full “utilizable production,” which is far from reality. A 1996 CGIAR review of postharvest activities concluded that if the full benefits of productivity research are to be realized, there must be a complementary attention to efficiency in product utilization. Our aim in this chapter is to analyze the process of setting a research agenda that will maximize the potential for increasing food availability through reduced postharvest losses. We start by considering a commodity systems approach (producer to consumer), followed by discussion of what is meant by “loss” in this wider context and the presentation of data giving the rationale for focusing on tropical systems. We then discuss the particular needs of tropical systems, namely, the issues of food security and the sustainability of renewable natural resources, and describe some of the attributes of the approach proposed. Finally, we present six brief case studies to illustrate the potential contribution that science can make in the research to development continuum and reiterate the need to address postharvest losses in the wider social economic and policy context. The definition of the “postharvest system” to be used in this discussion starts with the harvesting of a crop, the slaughter of an animal, or the capture of fish and proceeds through the stages of their processing, storage, handling, marketing, and utilization.
Late Cretaceous and Cenozoic History of North American Vegetation (North of Mexico)
Authors: Graham Alan
Published: November 2020

This book is a unique and integrated account of the history of North American vegetation and paleoenvironments over the past 70 million years. It includes discussions of the modern plant communities, causal factors for environmental change, biotic response, and methodologies. The history reveals a North American vegetation that is vast, immensely complex, and dynamic.