bluuebunny/crossref_metadata_2025 huggingface dataset:
Input Resistance, Time Constants, and Spike Initiation
Authors: Koch Christof
Published: November 2020

This chapter represents somewhat of a tephnical interlude. Having introduced the reader to both simplified and more complex compartmental single neuron models, we need to revisit terrain with which we are already somewhat familiar. In the following pages we reevaluate two important concepts we defined in the first few chapters: the somatic input resistance and the neuronal time constant. For passive systems, both are simple enough variables: Rin is the change in somatic membrane potential in response to a small sustained current injection divided by the amplitude of the current injection, while τm is the slowest time constant associated with the exponential charging or discharging of the neuronal membrane in response to a current pulse or step. However, because neurons express nonstationary and nonlinear membrane conductances, the measurement and interpretation of these two variables in active structures is not as straightforward as before. Having obtained a more sophisticated understanding of these issues, we will turn toward the question of the existence of a current, voltage, or charge threshold at which a biophysical faithful model of a cell triggers action potentials. We conclude with recent work that suggests how concepts from the subthreshold domain, like the input resistance or the average membrane potential, could be extended to the case in which the cell is discharging a stream of action potentials. This chapter is mainly for the cognoscendi or for those of us that need to make sense of experimental data by comparing therp to theoretical models that usually fail to reflect reality adequately. In Sec. 3.4, we defined Kii (f) for passive cable structures as the voltage change at location i in response to a sinusoidal current injection of frequency f at the same location. Its dc component is also referred to as input resistance or Rin. Three difficulties render this definition of input resistance problematic in real cells: (1) most membranes, in particular at the soma, show voltage-dependent nonlinearities, (2) the associated ionic membrane conductances are time dependent and (3) instrumental aspects, such as the effect of the impedance of the recording electrode on Rin, add uncertainty to the measuring process.
In the Wake of the Yellowstone Hotspot
Authors: Smith Robert B. , Siegel Lee J.
Published: November 2020

Anyone who drives through southern Idaho on Interstates 84 or 15 must endure hours and hundreds of miles of monotonous scenery: the vast, flat landscape of the Snake River Plain. In many areas, sagebrush and solidified basalt lava flows extend toward distant mountain ranges, while in other places, farmers have cultivated large expanses of volcanic soil to grow Idaho’s famous potatoes. Southern Idaho’s topography was not always so dull. Mountain ranges once ran through the region. Thanks to the Yellowstone hotspot, however, the pre-existing scenery was destroyed by several dozen of the largest kind of volcanic eruption on Earth—eruptions that formed gigantic craters, known as calderas, measuring a few tens of miles wide. Some 16.5 million years ago, the hotspot was beneath the area where Oregon, Nevada, and Idaho meet. It produced its first big caldera-forming eruptions there. As the North American plate of Earth’s surface drifted southwest over the hotspot, about 100 giant eruptions punched through the drifting plate, forming a chain of giant calderas stretching almost coo miles from the Oregon—Nevada—Idaho border, northeast across Idaho to Yellowstone National Park in northwest Wyoming. Yellowstone has been perched atop the hotspot for the past 2 million years, and a 45-by-30-mile-wide caldera now forms the heart of the national park. After the ancient landscape of southern and eastern Idaho was obliterated by the eruptions, the swath of calderas in the hotspot’s wake formed the eastern two-thirds of the vast, 50-mile-wide valley now known as the Snake River Plain. The calderas eventually were buried by basalt lava flows and sediments from the Snake River and its tributaries, concealing the incredibly violent volcanic history of the Yellowstone hotspot. Yet we now know that the hotspot created much of the flat expanse of the Snake River Plain. Like a boat speeding through water and creating an arc-shaped wave in its wake, the hotspot also left in its wake a parabola-shaped pattern of high mountains and earthquake activity flanking both sides of the Snake River Plain.
Ice over Fire: Glaciers Carve the Landscape
Authors: Smith Robert B. , Siegel Lee J.
Published: November 2020

Yellowstone, the Tetons, and Jackson Hole were shaped by multiple catastrophes. Huge volcanic eruptions and powerful earthquakes played major roles. Finishing touches were added by another kind of calamity: A rare global Ice Age produced gigantic glaciers that buried the landscape with ice two-thirds of a mile thick in places. The glaciers carved mountains, canyons, and lake basins. They dumped large piles of debris and redirected the flow of rivers. The Yellowstone—Teton region is a world-class example of how land was reshaped by glaciers during what is known as the Pleistocene Ice Age. The Ice Age was not a single glacial period, but many intermittent cold spells interspersed with warmer periods during which the ice melted. The timing of major glacial periods is notoriously uncertain. Although continental ice sheets did not quite reach as far south as Yellowstone, a regional icecap and large glaciers covered the Yellowstone—Teton country during three major episodes of at least the past 300,000 years—and perhaps the past 2 million years. The last of these big glaciers retreated about 14,000 years ago, although some argue they did not recede until 10,000 to 12,000 years ago. Today, small glaciers in the Teton Range are found only above 10,000 feet. During each major episode, most of Yellowstone National Park was buried beneath an icecap as much as 3,500 feet thick, among the largest in the ancient Rocky Mountains. Gigantic masses of ice flowed down from the high Yellowstone Plateau, carving and scouring the Earth’s surface, diverting and damming rivers into their present forms, steepening mountain fronts, and deepening lakes. The ice helped sculpt the Grand Canyon of the Yellowstone. More than anything, the thick ice scraped Yellowstone’s volcanic topography, further smoothing the plateau and helping to excavate the basin occupied by Yellowstone Lake. Jackson Hole became a rendezvous of glaciers converging from the north, north-east, and west. Ice up to 2,000 feet thick scooped out the valley floor. The glaciers left tall ridges of rocky debris now covered by lush conifer forests. Such ridges, called moraines, helped shape Jackson Lake.
Direct Numerical Simulation Of Turbulent Flows
Authors: Leonard Anthony
Published: November 2020

The numerical simulation of turbulent flows has a short history. About 45 years ago von Neumann (1949) and Emmons (1949) proposed an attack on the turbulence problem by numerical simulation. But one could point to a beginning 20 years later when Deardorff (1970) reported on a large-eddy simulation of turbulent channel flow on a 24x20x14 mesh and a direct simulation of homogeneous, isotropic turbulence was accomplished on a 323 mesh by Orszag and Patterson (1972). Perhaps the arrival of the CDC 6600 triggered these initial efforts. Since that time, a number of developments have occurred along several fronts. Of course, faster computers with more memory continue to become available and now, in 1994, 2563 simulations of homogeneous turbulence are relatively common with occasional 5123 simulations being achieved on parallel supercomputers (Chen et al., 1993) (Jimenez et al., 1993). In addition, new algorithms have been developed which extend or improve capabilities in turbulence simulation. For example, spectral methods for the simulation of arbitrary homogeneous flows and the efficient simulation of wall-bounded flows have been available for some time for incompressible flows and have recently been extended to compressible flows. In addition fast, viscous vortex methods and spectral element methods are now becoming available, suitable for incompressible flow with complex geometries. As a result of all these developments, the number of turbulence simulations has been increasing rapidly in the past few years and will continue to do so. While limitations exist (Reynolds, 1990; Hussaini et al., 1990), the potential of the method will lead to the simulation of a wide variety of turbulent flows. In this chapter, we present examples of these new developments and discuss prospects for future developments.
Fixed Points- Noncontractive Functions
Authors: Sikorski Krzysztof A.
Published: November 2020

In this chapter we consider the approximation of fixed points of noncontractive functions with respect to the absolute error criterion. In this case the functions may have multiple and/or whole manifolds of fixed points. We analyze methods based on sequential function evaluations as information. The simple iteration usually does not converge in this case, and the problem becomes much more difficult to solve. We prove that even in the two-dimensional case the problem has infinite worst case complexity. This means that no methods exist that solve the problem with arbitrarily small error tolerance for some “bad” functions. In the univariate case the problem is solvable, and a bisection envelope method is optimal. These results are in contrast with the solution under the residual error criterion. The problem then becomes solvable, although with exponential complexity, as outlined in the annotations. Therefore, simplicial and/or homotopy continuation and all methods based on function evaluations exhibit exponential worst case cost for solving the problem in the residual sense. These results indicate the need of average case analysis, since for many test functions the existing algorithms computed ε-approximations with polynomial in 1/ε cost.
The Statistical Physics of Subsurface Solute Transport
Authors: Sposito Garrison
Published: November 2020

The first detailed study of solute movement through the vadose zone at field scales of space and time was performed by Biggar and Nielsen (1976). Their experiment was conducted on a 150-ha agricultural site located at the West Side Field Station of the University of California, where the soil (Panoche series) exhibits a broad range of textures. Twenty well-separated, 6.5-m-square plots, previously instrumented to monitor matric potential and withdraw soil solution for chemical analysis, were ponded with water containing low concentrations of the tracer anions chloride and nitrate. After about 1 week, steady-state infiltration conditions were established, and 0.075 m of water containing the two anions at concentrations between 0.1 and 0.2 mol L-1 was leached through each plot at the local infiltration rate, which varied widely from 0.054 to 0.46 m day-1, depending on plot location. Once this solute pulse had infiltrated (< 1.5 days), leaching under ponded conditions was recommenced with the water low in chloride and nitrate. Solution samples were extracted before and after the solute pulse input at six depths up to 1.83 m below the land surface in each plot. Analyses of these samples for chloride and nitrate produced a broad range of concentration data which nonetheless showed an excellent linear correlation between the concentrations of the two anions (R2= 0.975), with a proportionality coefficient equal to that expected on the basis of the composition of the input pulse. Values of the measured solute concentrations at each sampling depth were tabulated as functions of the leaching time. Biggar and Nielsen (1976) decided to fit their very large concentration-depth-time database to a finite-pulsc-input solution of the one-dimensional advection-dispersion equation, leaving both the dispersion coefficient D and advection velocity u as adjustable parameters. The 359 field-wide values of u obtained in this way were highly variable (CV ≈ 200%), but also highly correlated (R2 = 0.84) and proportional to values of the advection velocity calculated directly as the ratio of water flux density to water content in each field plot (Biggar and Nielsen, 1976, figure 4).
Water Flow in Desert Soils Near Buried Waste Repositories
Authors: Warrick A. W. , Pan L.
Published: November 2020

Desert soils are frequently considered the safest choice for storing radioactive and chemical wastes (Winograd, 1974; National Research Council, 1976, 1995; Gee et al., 1992; IT Corporation, 1994). The reason is that nearly all rainwater that percolates into a desert soil is assumed to be taken up by plant roots and transpired back into the atmosphere. However, there is still recharge occurring in desert areas, although the magnitude of this recharge can vary greatly from one area to another (Rockhold et al., 1995). Therefore, proper siting of waste-disposal facilities is extremely important. This requires a good understanding of the factors that affect recharge and that minimize water flow through the waste layer. For a brief discussion of recharge in arid and semiarid regions, as well as an introduction to eight comprehensive papers on the topic, see Gee and Tyler (1994). This chapter has two major thrusts. The first part examines field measurements that have been made of the amounts of water that pass below the root zone to deeper depths in arid (and semiarid) environments. Also, some historical precipitation records are examined. The second part deals with modeling water flow in sloping, layered soils as might occur naturally or in cover designs that use capillary barriers. A simple analytical expression is presented for pressure-head distribution and diversion. This is followed by results from numerical modeling in order to test the effects of more complex boundary conditions, including steady versus nonsteady rainfall. Most rainwater that percolates into a desert soil is taken up by plant roots and transpired back into the atmosphere (Phillips, 1994). In addition, there is considerable surface evaporation. The combined processes of transpiration and evaporation, plus the lack of rainfall, cause desert soils to be dry most of the time. Furthermore, many of these soils are dry to great depths. However, not all desert soils are dry. Soils with minimal or no vegetation may contain considerably more water than soils with vegetation. Shifting sand dunes with deep, uniform sandy soils and minimal vegetation are often quite moist (Berndtsson and Chen, 1994).
Site-Specific Management of Flow and Transport in Homogeneous and Structured Soils
Authors: Mulla D. J. , Mallawatantri A. P.
Published: November 2020

Among research publications in soil science, few have had a greater impact than those by Nielsen et al. (1973) or Biggar and Nielsen (1976). According to Science Citation Index, the former paper, entitled “Spatial variability of field-measured soilwater properties,” has been cited by scientific peers over 390 times. The 1976 paper, entitled “Spatial variability of the leaching characteristics of a field soil,” has been cited over 232 times. Experimental work presented in both papers represents the first-ever attempt at a large field-scale study of steady-state water and solute transport (Wagenet, 1986). Among the seminal findings of these two papers were as follows: (1) extensive spatial variability existed in soil hydraulic and solute transport properties within a relatively homogeneous field (important in the work of Pilgrim et al., 1982; Addiscott and Wagenet, 1985; Feddes et al., 1988; van dcr Molen and van Ommen, 1988); (2) soil water content, bulk density, and soil particle size exhibited normal frequency distributions, while distributions for hydraulic conductivity, hydraulic diffusivity, pore water velocity, and hydrodynamic dispersion were lognormal (work extended by van der Pol et al.. 1977; Rao et al., 1979); (3) frequency distributions were far superior to field-average parameter values (especially for lognormally distributed properties) in describing field transport behavior (demonstrated by Rao et al., 1979; Trangmar et al., 1985); (4) a simple unit hydraulic gradient method was shown to estimate saturated hydraulic conductivity accurately (results extended by Libardi et al., 1980; van Genuchten and Leij, 1992); (5) good correspondence was found between solute velocity and pore water velocity (key assumption in Jury and Fluhler, 1992); (6) and theoretical predictions of a linear relation between hydrodynamic dispersion and pore water velocity were shown to be obeyed at the field scale (result used widely by solute transport modelers, as discussed in Nielsen et al., 1986). The seminal works by Nielsen et al. (1973) and Biggar and Nielsen (1976) produced several new directions in soil science and vadose zone hydrology research. The most interesting was a series of papers that rejected the theoretical basis and practicality of using deterministic equations, and instead introduced stochastic approaches to describe field-scale water and solute fluxes.
Plant Breeding in Its Institutional and Political Economic Setting, 1900-1940
Authors: Perkins John H.
Published: November 2020

Geneticists such as Liberty Hyde Bailey and Rowland Harry Biffen were prominent leaders in the new science of plant breeding. By 1940 they and their successors had constructed an elaborate body of theory and methods and had acquired a working collection of plant germ plasm. Plant breeding was an ongoing enterprise in a few countries, and production of such crops as wheat and maize already showed the commercial importance of the science. As noted in chapter 3, the promotion of plant breeding and other agricultural science was part of the industrial revolution and stemmed from (1) the repeal of the Corn Laws in Britain, (2) the development of international markets for wheat and other grains, (3) the population growth and emigration of European peoples to many other parts of earth, (4) the subsequent expansion of land in agriculture, and (5) the increasing mechanization of agriculture. Each of these interlinked factors reflected that the growing of wheat and other grains was increasingly a commercial matter and enhanced the role of science. Conditions conducive to the use of plant breeding also spawned organizations to train plant breeders, support their research, and provide easy access to their results. Agriculture, in turn, came increasingly to depend on a steady stream of new varieties from plant-breeding research. Institutional development in plant breeding did not occur in neat synchrony with the conceptual and methodological breakthroughs outlined in chapter 3. Instead, the growth of organizations depended upon (1) the promotion of the science by scientists, (2) the stresses imposed on farmers by market competition in agricultural products, (3) the perils nations faced in war, and (4) in the case of India, efforts by the British to alleviate famine so that India would remain profitable and governable. Both the organizational infrastructure created by 1940 and the conceptual developments were critically important to the subsequent transformation of wheat yields that occurred between 1940 and 1970. This chapter explores the institutional developments to 1940. Britain, America, and India each started to organize agricultural science before 1900 by forming scientific societies, agricultural improvement associations, private and public experiment stations, educational institutions, and government ministries to promote science.
Herpetological Species as Paleoenvironmental Indicators
Authors: Holman J. Alan
Published: November 2020

In Chapter 5 we have seen that Pleistocene herpetofaunas are often used to suggest paleoenvironmental conditions. The present chapter discusses the validity of this use. With the exception of behavioral responses (and a few quasi-physiological adaptations in reptiles), herpetological species are poorly adapted to resist temperature changes. Or, to put it another way, amphibians and reptiles lack the complex internal physiological mechanisms that interact to regulate temperature in endotherms. This has led to the assumption by many that herpetological species, because of their supposed greater sensitivity to temperature changes, arc much better indicators of local thermal conditions than are birds and mammals. Moreover, most Quaternary amphibians and reptiles represent extant species whose ecological tolerances and habitat preferences are well known, whereas many Pleistocene endotherms, especially large mammals, are extinct species whose ecological traits and specific habitat requirements are not totally understood. This suggests that Pleistocene herpetofaunas should give more refined information about specific habitats than endothermic faunas. Also, it can be argued that most amphibian and reptile species are more spatially confined than endothermic ones (especially birds and large mammals) and that Pleistocene herpetological species indicate paleoenvironmental conditions of more restricted areas. Bailón and Rage (1992) address this subject in the light of their European experience: "They (amphibians and reptiles] arc unable to compensate for large climatic variations as endotherms (birds and mammals) can; therefore each amphibian and reptile species can live only in a definite climate." (p. 95). Moreover,… Amphibians and reptiles present another advantage: whereas endotherm vertebrates are represented in Quaternary fossiliferous localities by a not negligible percentage of extinct species, practically all fossil amphibians and reptiles of that age belong to extant species. If a species is extinct its ecological requirements cannot be known with certainty and arc open to speculation whereas living species present in fossiliferous assemblages afford accurate information, (p. 95)… They also state that the size of reptile home ranges is small, and that as these species are not the preferred prey of predaccous birds, they are probably not an admixture of species that live in a wide area around the locality. Let us examine these assumptions.
From Brown to Red: The Fall and Rise of an Educational System, 1945–51
Authors: Rodden John G.
Published: November 2020

October 1945. It is a testament to the determination of Soviet and German education officials that the schools and universities east of the Elbe have opened at all this fall. Just as in the western occupation zones of the Americans, French, and British, school staff in the SBZ labor under appalling conditions. Although the SBZ is better off in some ways than the western zones—it has more food, coal, newsprint—its major cities, such as Dresden and Leipzig, sustained greater physical damage during the war. And now the eastern zone is suffering massive Soviet dismantling of its factories and railroads. In several cities, devastated by heavy bombing, some school buildings are partially or totally destroyed. Only 20 of Leipzig’s 105 schools have been spared; 95 percent of the school buildings in Frankfurt an der Oder are in ruins. Even in the undamaged schools, central heating is impossible: there is no fuel. And virtually no books, no pencils, no crayons, no paper. But there are children everywhere, 100 or more per classroom in some urban school districts, huddled together on the floor for warmth. For while there are many fewer schools open, there are many more children to educate. The SBZ is overflowing with more than three million refugees who have fled before the advances of the Red Army or have been forcibly expelled from German-speaking areas of eastern Europe. Month after month for the last year the DPs (Displaced Persons) have been pouring into the SBZ. And still they come: the SBZ contains 500,0000 more children in 1945 than in 1939; an additional 319,000 will come in 1946. Far worse, hundreds of thousands of children are orphaned and literally starving. In Berlin alone, the emergency relief program Rescue the Children will distribute food, clothing, shoes, and other articles to 364,000 children in the coming harsh winter of 1945/ 46. The University of Jena is also open, and the other five universities of the SBZ—in Berlin, Leipzig, Halle, Greifswald, and Rostock—will reopen in the winter.
Animals and the Human Food Chain
Authors: Heap R. B.
Published: November 2020

The argument that the population explosion presents a serious challenge to the ability of the world to feed itself and a serious threat for the recovery potential of the planet has been well rehearsed. The Reverend Thomas Malthus, an ordained minister of the Anglican church and a Fellow of Jesus College, Cambridge, stated in his famous essay nearly 200 years ago that “population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio” (Malthus, 1798). Since 1950 the human population has doubled, and U.N. projections indicate that it is set to reach about 8 billion by the year 2020 and 9.5 billion in 2050. The trajectory of the sigmoid model predicts that the current exponential increase will stabilize around a figure of 10 billion by 2100. A different model is the J-shaped curve, in which exponential growth during favorable conditions is followed by a dramatic, if recoverable, crash resulting from density-dependent destruction of the environment. Whichever model will apply in future, population growth will be checked somehow, depending on the influence of food security, fertility control, and socioeconomic factors. Many of the chapters in this book have focused on land resources and the opportunities that exist for improvements in crop production. While a substantial component of the planet’s biomass consists of vegetation, it would be unwise to underestimate the direct and indirect contributions of livestock to food security. In this chapter I consider the impact of scientific advances on animal production and the human food chain and examine the reasons there are strong dissenting voices raised against the adoption of some technologies and to what extent such concerns affect progress. The Brundtland Commission (1987) defined food security as secure ownership of, or access to resources, assets, and income-earning activities to offset risks, ease shocks, and meet contingencies. In other words, not everyone is intended to be a subsistence fanner, but everyone must possess the means to acquire an adequate diet. For most of the world’s population this is a rational interpretation of food security, with the prosperous producing that which is surplus to indigenous needs and the less developed areas benefiting from that surplus’s distribution to areas of scarcity.
Origins of North American Biogeographic Affinities
Authors: Graham Alan
Published: November 2020

An aspect of plant distribution that has intrigued biogeographers for over 200 years is the occurrence of similar biotas in widely separated regions. The North American flora has affinities with several such areas: the Mediterranean, the dry regions of South America, eastern Asia, and eastern Mexico. The origin of some patterns is relatively clear, while for others hypotheses are just now being formulated. During times when the dogma of permanence of continents and ocean basins held sway, explanations for these disjunctions required imaginative thinking that often bordered on the bizarre. The pendulum or schwingpolen hypothesis was offered to explain the perceived bipolar distribution of several taxa (Gnetum, Magnolia, Pinus section Taeda; Simroth, 1914). By this view, the Earth swings in space like a pendulum, creating regular fluctuations in environments and often causing the symmetrical placement of taxa at two points on opposite sides of the Earth. Other disjunctions were explained by casually placing geophysically impossible land bridges at any point in time between any two sites where the presence of similar communities seemed to call for land connections (see review in Simpson, 1943). The presence of teeth of Hipparion, an ungulate related to the horse, in Europe and South Carolina-Florida prompted French geologist Leonce Joleaud to propose a land bridge extending from Florida through the Antilles to North Africa and Spain. Subsequently, to accommodate eight new passengers, it was broadened to encompass the entire region from Maryland and Brazil across to France and Morocco and its life was prolonged to include virtually all of the Tertiary. With the later discovery that there were periodicities in similarity between Old World and New World Cenozoic faunas, the continents were envisioned as moving back and forth like an accordion. George Gaylord Simpson, who favored the North Atlantic land bridge to connect North America and Europe, was beside himself with these theories and characterized Joelaud’s as “the climax of all drift theories.” The bridge became well established in the literature even though it never existed in the Atlantic Ocean (Marvin, 1973). Udvardy (1969) plotted all the Cretaceous and Tertiary land bridges postulated for the South Pacific up to 1913.
Biogeochemical Processes on the Amazon Shelf: Changes in Dissolved and Paniculate Fluxes During River/Ocean Mixing
Authors: DeMaster David J. , Aller Robert C.
Published: November 2020

The immense discharge of the Amazon River causes river/ocean mixing to take place out on the continental shelf instead of within a drowned river valley, as in many smaller dispersal systems (Nittrouer and DeMaster, 1996). The magnitude of this discharge can be appreciated by recognizing that the Amazon River supplies approximately 20% (6 x 1015 L yr−1) of the freshwater reaching the oceans via fluvial transport and roughly 6% (1.2 x 1015 g yr−1, Meade et al. 1985) of the global riverine sediment discharge. Chemical, physical, and biological processes occurring in the river/ocean mixing zone control the fates of these riverine materials, as well as the fates of substances brought onto the shelf from offshore as a result of the estuarine-like circulation. Depending on balances between transport, reaction rates, and sedimentation, the mixing zone may act as a net source, sink, or bypass conduit for chemical species in the coastal environment. For example, if Amazon River nutrients such as silicate, phosphate, or nitrate are simply removed from solution and buried as particulate biogenic debris on the adjacent shelf, the river would have little influence on global ocean nutrient budgets. In contrast, if nutrients coming down the river are not efficiently buried nearshore (as a result of minimal biological uptake or efficient recycling), then they may contribute to larger scale oceanic or atmospheric budgets of Si, P, and N (Treguer et al. 1995; Delaney, 1998). The Amazon River transports ~1015 moles yr−1 of particulate organic carbon from the terrestrial environment to the ocean (Degens et al. 1991). The fate of this material (some of it from leaf litter and some of it from older, more refractory soils) is important to understand because the Amazon River/ocean mixing zone comprises a significant fraction of all deltaic depositional environments, where ~50% of the marine burial of organic matter occurs (Berner 1982, 1989, Hedges and Keil 1995; Devol et al. this volume). The Amazon River also discharges an equivalent amount of dissolved organic carbon (~1012 moles yr−1), much of which is in the form of high molecular weight organic compounds (Sholkovitz et al. 1978, Degens et al. 1991).
Cycles
Authors: Rostow W. W.
Published: November 2020

The reason for tracing in this chapter the history of cycles, as a prelude to speculating about the future, lies in two features of cyclical history: the fact that this history includes the global depression of the 1930s that helped trigger World War II and the fact that a number of economists have underlined the role of population increase, stagnation, or decline in determining the length and amplitude of depressions and of cycles themselves. Cycles viewed historically, then, are not irrelevant to the issues of the next century. Trend periods, treated in Chapter 4, have a rhythm that runs through a series of business cycles. Trend periods affect the price level, interest rates, terms of trade, capital movements, and direction of migration. Business cycles, unlike trend periods, consist of fluctuations in employment and output. The length and intensity of businesscycle upswings —and the extent of overshooting they yield —are partially determined by the time lags involved in the particular leading sectors of the boom. The shortness of the inventory cycle—about three years — is related to the simple fact that inventories have a short life. Unlike a factory, a road, or a house, they are used up rather promptly in the production process. Inventory overshooting, therefore, tends to be capable of correction fairly soon. Housing stands at the other extreme. Houses last a generation, and their replacement (relative to inventories) is more postponable. Against this brief background, the character and timing of businesscycle patterns are examined in four periods: the 18th century, 1783— 1914, the interwar years, and post-1945. Then the cyclical problem as now foreseen for 1996-2050 will be discussed. Britain is the only country where business fluctuations in the 18th century have been examined in a reasonably systematic, if still exploratory, way. Moreover, Britain gained primacy in the course of the 18th century and remained at the heart of global cyclical fluctuations through about 1914. T. S. Ashton's chronology of turning points in British business fluctuations of the 18th century is given in Table 5.1.
Environmental Change and Future Directions in Alpine Research
Authors: Welker Jeffrey M. , Bowman William D.
Published: November 2020

Alpine tundra is an important indicator system of environmental change (Grabherr et al. 1996; Beniston and Fox 1996). This ecosystem occurs at all latitudes, with its lower altitudinal limit at timberline inversely related to latitude (Woodward 1993). Thus, the global distribution of alpine tundra and the fact that this system exists near the limits of vascular plant tolerance to temperature, moisture, and growing season duration makes it an excellent system for monitoring environmental change across the globe (e.g., Körner and Larcher 1988). In addition, the functional integrity of this system is critical to lower elevation ecosystems because substantial amounts of water and elements are intercepted by the alpine, filtered, and transported to lower elevations (Williams et al. 1996; chapter 4). Alpine tundra has been spared most of the large-scale disturbances associated with human development and resource extraction that have occurred in lower altitudinal ecosystems. This is probably due to its climatic severity and lack of renewable resources that can be exploited (e.g., trees, fast-growing forage for grazing). Some high-altitude sites have been impacted by recreational development (e.g., ski areas, trails, roads), mining, and grazing. In addition, changes in native herbivore populations, particularly elk and deer, due to extirpation of predators by humans (chapter 12), may have significantly influenced tundra vegetation (chapter 14). However, the indirect effects of human activities associated with the burning of fossil fuels are of greater current and future concern as the dominant anthropogenic influences on alpine tundra ecosystems. At a global scale, climate change is of concern for all ecosystems, whereas at a more-regional scale, there is concern for the impact of N and acid deposition near centers of industrial and urban growth (Galloway et al. 1995). Niwot Ridge, and possibly much of the Colorado Front Range, has experienced significant increases in the rate of N deposition (Sievering et al. 1996; chapter 3) and precipitation (Fig. 16.1; chapter 2) in the past several decades. Local sources of NOX compounds that potentially contribute to the elevated rates of N deposition in the Front Range include power plants in western Colorado and automobile and industrial emissions in the urban corridor at the base of the mountains (Fort Collins-Boulder-Denver-Colorado Springs megalopolis), which is home to around four million people.
Two Visions of the Earth
Authors: Oreskes Naomi
Published: November 2020

Plate tectonics is the unifying theory of modern geology. This theory, which holds that the major features of the earth’s surface are created by horizontal motions of the continents, has been hailed as the geological equivalent of the “theory of the Bohr atom in its simplicity, its elegance, and its ability to explain a wide range of observation,” in the words of A. Cox. Developed in the mid-1960s, plate tectonics rapidly took hold, so that by 1971, Gass, Smith, and Wilson could say in their introductory textbook in geology: . . . During the last decade, there has been a revolution in earth sciences . . . which has led to the wide acceptance that continents drift about the face of the earth and that the sea-floor spreads, continually being created and destroyed. Finally in the last two to three years, it has culminated in an all-embracing theory known as “plate tectonics.” The success of plate tectonics theory is not only that it explains the geophysical evidence, but that it also presents a framework within which geological data, painstakingly accumulated by land-bound geologists over the past two centuries, can be fitted. Furthermore, it has taken the earth sciences to the stage where they can not only explain what has happened in the past, and is happening at the present time, but can also predict what will happen in the future. . . . Today moving continents are a scientific fact. But some forty years before the advent of the theory of plate tectonics, a very similar theory, initially known as the “displacement hypothesis,” was proposed and rejected by the geological fraternity. In 1912, a German meteorologist and geophysicist, Alfred Wegener, proposed that the continents of the earth were mobile; in the decade that followed he developed this idea into a full-fledged theory of tectonics that was widely discussed and debated and came to be known as the theory of continental drift. To a modern geologist, raised in the school of plate tectonics, Wegener’s book, The Origin of Continents and Oceans, appears an impressive and prescient document that contains many of the essential features of plate tectonic theory.
The “Short Step Backward”
Authors: Oreskes Naomi
Published: November 2020

In 1922, Harry Fielding Reid, a founder of American seismology, encapsulated the American perspective on scientific method in a review of Wegener’s Origin of Continents and Oceans. “There have been many attempts to deduce the characteristics of the Earth from a hypothesis,” he wrote, “but they have all failed. There is the pentagonal system of Elie de Beaumont, the tetrahedral system of Green . . . [continental drift] is another of the same type.” The history of hypothetico-deductive reasoning in geology was a history of failure; progress was to be made another way. “Science has developed,” Reid concluded, “by the painstaking comparison of observations and, through close induction, by taking one short step backward to their cause; not by first guessing at the cause and then deducing the phenomena.” An obvious reading of Reid’s comment is that Wegener’s faulty methodology led him to faulty conclusions. No doubt Reid thought so. But another reading is the implicit suggestion that a different approach —a different presentation —might have elicited a more favorable response. Charles Schuchert’s comment that it was “wrong lor a stranger to the facts to generalize from them to other generalizations” suggested that if evidential support for drift could come from someone who was not a “stranger to the facts,” then Americans might be more disposed to entertain the theory. This thought had occurred a few years earlier to Reginald Daly and Frederick Wright. When Daly and Wright returned from South Africa in the autumn of 1922, each pondered the question of continental drift. Daly, whose proclivities ran to theory, developed a mechanical account of drift; Wright, an experimentalist, began to think about a possible test. The key empirical evidence was the alleged similarities between the Karroo formations in South Africa and age-equivalent rocks elsewhere in the world — evidence that had earlier motivated Suess’s idea of Gondwanaland and now supported Wegener’s theory of drift. But how similar were these rocks, really? Suess and Wegener had based their ideas on compilations of published literature; neither man had studied any of these rocks in person. In fact, there had never been a direct comparative study of the so-called Gondwana beds.
Nutrient Cycling within an Arid Ecosystem
Authors: Schlesinger William H. , Tartowski Sandy L.
Published: November 2020

Low quantities of soil nitrogen limit plant growth in the Chihuahuan Desert (Ettershank et al. 1978; Fisher et al. 1988; Lajtha and Whitford 1989; Mun and Whitford 1989) and in other deserts of the world (Wallace et al. 1980; Breman and de Wit 1983; Sharifi et al. 1988; Link et al. 1995). Indeed, although deserts are often regarded as water-limited systems, colimitation by water and N may be the more general rule (Hooper and Johnson 1999; Austin and Sala 2002). In a broad survey of desert ecosystems, Hooper and Johnson (1999) found evidence for colimitation by water and N even at the lowest levels of rainfall. In arid ecosystems, water is delivered in discrete events separated by drier periods, which restrict biological activity and uncouple plant uptake of nutrients from decomposition. Local variations in net primary production in arid and semiarid ecosystems are largely determined by processes that control the redistribution of water and soil nutrients across the landscape (Noy-Meir 1985; Schlesinger and Jones 1984; Wainwright et al. 2002; see also chapter 11). In this chapter we focus on the N cycle in different plant communities of the Jornada Basin with the recognition that after water, N is the most likely resource to determine the plant productivity of this ecosystem. Where arid environments are dominated by shrubby vegetation, the distribution of soil properties is markedly patchy with strong accumulations of plant nutrients under shrubs and relatively infertile soils in the intershrub spaces (Noy-Meir 1985). These islands of fertility are particularly well described in the Chihuahuan Desert and other areas of the American Southwest. Local accumulations of nutrients under vegetation are also documented for desert habitats on other continents, including Europe (Gallardo et al. 2000), Africa (Gerakis and Tsangarakis 1970; Belsky et al. 1989; Wezel et al. 2000), Australia (Tongway and Ludwig 1994; Facelli and Brock 2000), and South America (Rostagno et al. 1991; Mazzarino et al. 1991, 1998; Gutierrez et al. 1993). In the Jornada Basin, Schlesinger et al. (1996) used geostatistics to compare the scale of soil heterogeneity in arid habitats dominated by shrubs and in adjacent areas of arid grassland.
A Holistic View of an an Arid Ecosystem: A Synthesis of Research and Its Applications
Authors: Bestelmeyer Brandon T. , Brown Joel R.
Published: November 2020

A primary objective of the Jornada Basin research program has been to provide a broad view of arid land ecology. Architects of the program, more recently scientists with the Jornada Basin Long-Term Ecological Research (LTER) program, felt that existing ecological data sets were usually of too short a duration and represented too few ecosystem components to provide a foundation for predicting dynamics in response to disturbances (NSF 1979). This recognition gave rise to the approach of using long-term and multidisciplinary research at particular places to advance a holistic and broad-scale but also mechanistic view of ecological dynamics. Such a view is essential to applying ecological research to natural resources management (Golley 1993; Li 2000). In this synthesis chapter we ask: What has this approach taught us about the structure and function of an arid ecosystem? How should this knowledge change the way we manage arid ecosystems? What gaps in our knowledge still exist and why? The Jornada Basin LTER was established in 1981 with the primary aim of using ecological science to understand the progressive loss of semiarid grasslands and their replacement with shrublands. This motivation echoed that which initiated the Jornada Experimental Range (JER) 69 years earlier. The combined, century-long body of research offers a unique perspective on several core ideas in ecology, including the existence of equilibria in ecosystems, the role of scale, landscape heterogeneity and historic events in ecosystem processes and trajectories, and the linkage between ecosystem processes and biodiversity. From this perspective, we examine key assumptions of this research tradition, including the value of the ecosystem concept and the ability to extrapolate site-based conclusions across a biome. The Jornada Basin research program is also uncommon in its close ties to long-term, management-oriented research. The research questions first asked by the U.S. Forest Service and later by the Agricultural Research Service (ARS), such as how to manage livestock operations, frame much of the Jornada Basin research. This allows us to consider the contributions of this research and synthesis toward answering management questions.
Mean-Field Theories
Authors: Chimowitz Eldred H.
Published: November 2020

The most widely used analytic models for representing thermodynamic behavior in supercritical ßuids are of the mean-Þeld variety. In addition to the practical interest in studying this topic, this class of models is also the conceptual starting point for any microscopic discourse on critical phenomena. In this chapter we take up the basic ideas behind this approach, studying different physical models, showing how their mean-Þeld approximations can be constructed as well as investigating their critical behavior. A useful conceptual model for understanding mean-Þeld ideas is the Ising model whose properties we consider in some detail, especially its mean-Þeld approximation. The Ising model has the advantage of belonging to the same critical universality class as so-called simple fluids, deÞned as ßuids with short-range intermolecular potentials. Most supercritical ßuid solvent systems of practical interest fall within this class; hence results developed using the Ising model have important implications for understanding the critical behavior of this entire universality class. While we discuss universality and related ideas in more detail in subsequent chapters, sufÞce it to say here that the Ising system belongs to arguably the most important critical universality class from a process engineering standpoint. In its simplest form, the Ising model considers N spins arranged on a lattice structure (of 1, 2, or 3 dimensions) with each spin able to adopt one of two (up or down) orientations in its lattice position. A speciÞc state of the system is determined by a given conÞguration of all the spins. The model can be made more complex by considering additional degrees of freedom to the spin orientations. For example, the Heisenberg model considers a 3-dimensional lattice with the spin orientation at each lattice site described by a 3-dimensional vector quantity. All that is required to facilitate the use of statistical mechanics with this model is the deÞnition of the Hamiltonian (the systemÕs energy function) associated with a particular lattice state υ. This Hamiltonian usually consists of spinÐspin interaction terms, as well as a term representing the presence of a magnetic Þeld, which serves to orient the spins in its direction.