bluuebunny/crossref_metadata_2025 huggingface dataset:
Least-Squares Methods and Their Use in Charge Density Analysis
Authors: Coppens Philip
Published: November 2020

The number of reflection intensities measured in a crystallographic experiment is large, and commonly exceeds the number of parameters to be determined. It was first realized by Hughes (1941) that such an overdetermination is ideally suited for the application of the least-squares methods of Gauss (see, e.g., Whittaker and Robinson 1967), in which an error function S, defined as the sum of the squares of discrepancies between observation and calculation, is minimized by adjustment of the parameters of the observational equations. As least-squares methods are computationally convenient, they have largely replaced Fourier techniques in crystal structure refinement. In addition to the positional and thermal parameters of the atoms, least-squares procedures are used to determine the scale of the data, and parameters such as mosaic spread or particle size, which influence the intensities through multiple-beam effects (Becker and Coppens 1974a, b, 1975). It is not an exaggeration to say that modern crystallography is, to a large extent, made possible by the use of least-squares methods. Similarly, least-squares techniques play a central role in the charge density analysis with the scattering formalisms described in the previous chapter. The following description follows closely the treatment given by Hamilton (1964).
Rationalizing the Catholic System
Authors: Gleason Philip
Published: November 2020

Catholic colleges reacted as individual institutions to the turn-of-the-century challenge, but there was also a collective dimension to their response. It is most directly observable in the activities of the Catholic Educational Association (CEA) and in self-studies undertaken by the Jesuits. It is also extremely revealing, for here we can observe Catholic educators taking counsel together, informing themselves of current developments, and forging the conceptual and organizational tools they needed to bring their institutions more nearly into line with ongoing developments in American higher education. We shall look first at the CEA, but to appreciate its significance we must begin by reviewing the reasons for the fragmentation that put Austin O’Malley in mind of a boiler explosion, and caused Bishop John Lancaster Spalding to exclaim: “We Catholics are united in the faith, but are infinitely disunited in almost everything else. The Lord have mercy on us! We want some point of union.” The disunity that plagued Catholic educators as the new century opened did not arise from ethnic diversity or ideological cleavages, although both were significant features of the larger Catholic scene. Their basic problem was structural, and its key element was the existence in Catholic education of two overlapping, but largely autonomous, chains of command: the episcopal, centered in the bishop of the diocese (known technically as the “ordinary”); and that of the religious community. Reinforcing the disjunctive tendency inherent in this parallel authority structure was an ecclesiastical localism that left each ordinary without effective supervision from higher authority, and made each religious community a kind of realm unto itself. A cursory sketch of the Catholic educational scene will suggest why these circumstances made it so difficult to coordinate all the elements involved. Catholic elementary education was carried on under the authority and supervision of the bishops, but the parochial schools—of which there were in 1900 about 3800, enrolling upwards of 900,000 students—were staffed almost exclusively by nuns. A community of teaching sisters (and there were scores of them) might or might not be under the direct ecclesiastical authority of the bishop.
The Catholic Revival Reaches Full Flood
Authors: Gleason Philip
Published: November 2020

Around 1930 the impulses previously at work among an elite of educators and publicists broadened out to energize American Catholics more generally, especially young people, and the Catholic Revival became a full-fledged movement. It was self-consciously countercultural in the sense that it proclaimed and attempted to actualize the ideal of a Catholic culture set over against and in opposition to modern culture. Since it was so distinctly an intellectual movement, institutions of higher education were of course integrally involved. On the one hand, the revival shaped the mentality that dominated them; on the other hand, they served as focal points for its diffusion among the Catholic population and as a cultural force in American public life. Although the influence of the revival carried over into the post-World War II era, we will concentrate in this chapter on the 1930s. Al Smith’s campaign for the presidency brought the “Catholic question” of the twenties to its ugly climax. Even Catholics who could understand the reasons for their fellow citizens’ uneasiness on the church-state issue were disheartened and embittered by the tidal wave of crude no-popery that engulfed the Smith campaign. Thus Peter Guilday, who was privately troubled by traditional Catholic teaching on church-state and religious freedom, denounced those who had carried on “a studied propaganda o f . . . damnable, obscene and calumnious lies” against the church. But the excesses of bigotry also disturbed many fair minded Protestants, Jews, and non-religious liberals. As a result, the outbursts of 1928 spurred efforts to ameliorate interreligious feeling and the public attitude toward Catholicism improved considerably over the next half a dozen years. Father James M. Gillis, C.S.P., spoke for American Catholics in saying “We shall not wither up and blow away,” but their leaders also felt the need for new apologetical and public-relations efforts. Thus Carlton J. H. Hayes of Columbia University served as the first Catholic co-chairman of the newly formed National Conference of Christians and Jews, which initiated its systematic promotion of interreligious brotherhood in the immediate aftermath of the Smith campaign.
An Introduction to the Theoretical Basis of Semi-Empirical Quantum-Mechanical Methods for Biological Chemists
Authors: Richards Nigel G. J.
Published: November 2020

Computational methods that can be employed to investigate fundamental questions concerning the complex chemical and structural behavior of biological molecules such as proteins, carbohydrates, and nucleic acids have been traditionally limited by the large number of atoms that comprise even the simplest system of biochemical interest. As a consequence, highly parameterized, empirical force field methods have been developed that describe the energy of macromolecular structures as a function of the spatial locations of the atomic nuclei. In combination with algorithms for simulating molecular dynamics, these classical models allow relatively accurate calculations of the structural and thermodynamic properties associated with proteins and nucleic acids. On the other hand, empirical approaches cannot be used to model molecular behavior that is directly dependent on electrons and their energies. For example, no information can be obtained concerning the electronic spectra of macromolecule/ligand complexes, electron transfer reactions such as those that occur within the photosynthetic reaction center, nitrogenase, an enzyme involved in nitrogen fixation, or cytochrome c oxidase which catalyzes the reduction of oxygen in the last step of aerobic respiration. Accurate modeling of transition states, excited states, and intermediates in biological catalysis requires application of quantummechanical (QM) representations since all of these phenomena depend on the distribution and/or excitation of electrons. At present, the most accurate ab initio algorithms for calculating electronic structure cannot be applied to systems comprised of hundreds of atoms, as such calculations scale as N4–N7 on most workstations, where N is the number of functions used in constructing the many-electron, molecular wavefunction. Even with the implementation of ab initio codes optimized for use on parallel computing engines, and density functional approaches, it is likely that high-accuracy QM calculations in the near future will remain limited to systems that comprise tens, rather than hundreds, of nonhydrogen atoms. Semi-empirical quantum-mechanical methods combine fundamental theoretical treatments of electronic behavior with parameters obtained from experiment to obtain approximate wavefunctions for molecules composed of hundreds of atoms.
Water Supply, Sewage, and Drainage
Authors: Sperber Daniel
Published: November 2020

It is well known that Erez Yisrael was not blessed with a plentiful supply of water. Other than the narrow winding Jordan, there are few rivers in the country and hardly any fresh water lakes, other than the Sea (!) of Galilee and Huleh Lake (which virtually no longer exists). Consequently, the cities, which required an abundant and regular flow of water, relied mostly on wells and on rainwater trapped in numerous small private and public cisterns. Fountains (springs) might have been situated at considerable distances from the city, and water would have been transported via an open canal (such as in present-day Wadi Kelt between Jerusalem and Jericho), through a closed piping system, which sometimes spanned hills and valleys for many miles, or by aqueducts (such as those near Caesarea). There were also large underground water systems with vent pipes surfacing at regular intervals to relieve water and air pressure and to enable workers to inspect and clear out the silt deposits and other obstructions (witness the magnificent complex bringing water to Jerusalem through the adjacent Armon ha-Naẓiv). There were also overhead pipes made of lead, earthenware, or at times even wood that were laid out carefully above ground, taking advantage of the lay of the land and using gravitational force to transport water over a great distance from a source high in the hills to a city situated low on the plains. Such piping systems required considerable sophistication in planning and construction, not only in choosing optimal routes but also in calculating water pressures and the strengths and diameters of piping units, in placing air vents to relieve excessive pressure, and in installing sludgecocks for removing silt deposits and for filtering the water. A detailed description of different water-supply systems can be found in the work of the great first century C.E. Roman architect Vitruvius in his De Architectura.
Artificial Landscapes
Authors: Bäck Thomas
Published: November 2020

In order to facilitate an empirical comparison of the performance of Evolution Strategies, Evolutionary Programming, and Genetic Algorithms, a test environment for these algorithms must be provided in the form of several objective functions f : IRn → IR. Finding an appropriate and representative set of test problems is not an easy task, since any particular combination of properties represented by a test function does not allow for generalized performance statements. However, there is evidence from a vast number of applications that Evolutionary Algorithms are robust in the sense that they give reasonable performance over a wide range of different topologies. Here, a set of test functions that are completely artificial and simple is used, i.e., they are stated in a closed, analytical form and have no direct background from any practical application. Instead, they allow for a detailed analysis of certain special characteristics of the topology, e.g. unimodality or multimodality, continuous or discontinuous cases, and others. If any prediction is drawn up for the behavior of Evolutionary Algorithms depending on such strong topological characteristics, the appropriate idealized test function provides a good instrument to test such hypotheses. Furthermore, since many known test sets have some functions in common, at least a minimal level of comparability of results is often guaranteed. Finally, before we can expect an algorithm to be successful in the case of hard problems, it has to demonstrate that it does not fail to work on simple problems. On the other hand, the (public relations) effect of using artificial topologies is vanishingly small, since the test functions used are of no industrial relevance. This way, researchers working with such test functions can never rest on their industrial laurels. A more legitimate objection against artificial topologies may be that they are possibly not representative of the “average complexity” of real-world problems, and that some regularity features of their topology may inadmissibly speed up the search. However, most test function sets incorporate even multimodal functions of remarkable complexity, such that only the regularity argument counts against using an artifical function set.
Mutation
Authors: Bäck Thomas
Published: November 2020

In section 1.1.3 it was clarified that a variety of different, more or less drastic changes of the genome are summarized under the term mutation by geneticists and evolutionary biologists. Several mutation events are within the bounds of possibility, ranging from single base pair changes to genomic mutations. The phenotypic effect of genotypic mutations, however, can hardly be predicted from knowledge about the genotypic change. In general, advantageous mutations have a relatively small effect on the phenotype, i.e., their expression does not deviate very much (in phenotype space) from the expression of the unmutated genotype ([Fut90], p. 85). More drastic phenotypic changes are usually lethal or become extinct due to a reduced capability of reproduction. The discussion, to which extent evolution based on phenotypic macro-mutations in the sense of “hopeful monsters” is important to facilitate the process of speciation, is still ongoing (such macromutations have been observed and classified for the fruitfly Drosophila melangonaster, see [Got89], p. 286). Actually, only a few data sets are available to assess the phylogenetic significance of macro-mutations completely, but small phenotypical effects of mutation are clearly observed to be predominant. This is the main argument justifying the use of normally distributed mutations with expectation zero in Evolutionary Programming and Evolution Strategies. It reflects the emphasis of both algorithms on modeling phenotypic rather than genotypic change. The model of mutation is quite different in Genetic Algorithms, where bit reversal events (see section 2.3.2) corresponding with single base pair mutations in biological reality implement a model of evolution on the basis of genotypic changes. As observed in nature, the mutation rate used in Genetic Algorithms is very small (cf. section 2.3.2). In contrast to the biological model, it is neither variable by external influences nor controlled (at least partially) by the genotype itself (cf. section 1.1.3). Holland defined the role of mutation in Genetic Algorithms to be a secondary one, of little importance in comparison to crossover (see [Hol75], p. 111): . . . Summing up: Mutation is a “background” operator, assuring that the crossover operator has a full range of alleles so that the adaptive plan is not trapped on local optima. . . .
Summary and Outlook
Authors: Bäck Thomas
Published: November 2020

Within the total of seven chapters presented here on the topic of Evolutionary Algorithms there are a number of crude but nevertheless powerful simplifications of the model of organic evolution. Chapter 1 clarified that Evolutionary Algorithms, if they are interpreted as global optimization algorithms, are not to be confused with the oversimplified concept of uniform random search. Instead, they rely on keeping the history insofar as the subsequent generation is created at each step of the evolution process from the current generation maintained by the algorithm. In other words: Evolutionary Algorithms are representatives of the mathematical concept of a Markov process (respectively chain, in discrete spaces). Concerning the convergence reliability of Evolutionary Algorithms, the theoretical property of global convergence with a probability of one holds for all variants that use an elitist selection method and guarantee a reachability property of mutation which is basically assured by working with nonzero mutation rate in Genetic Algorithms (respectively with nonzero standard deviation in Evolution Strategies and Evolutionary Programming). These results are summarized in theorem 7, 10, and 13, which are based on the general convergence theorem 3 for global random search algorithms respectively on well-known results on absorbing Markov chains. In contrast to convergence reliability investigations where the focus is on the explorative character of the search, convergence velocity analysis emphasizes the exploitation of information collected about a promising region or point in the search space. Both properties are contradictory and cause a trade-off that dominates behavior and control of Evolutionary Algorithms. Nevertheless, convergence velocity investigations so far were known only for Evolution Strategies (see section 2.1.7) but can easily be transferred to standard Evolutionary Programming as demonstrated in section 2.2.7. The result provides a clear indication that the step-size control of standard EP is useless for even moderately large dimensions of the search space and for objective functions that possess a non-vanishing global optimum. More advanced versions of Evolutionary Programming overcome this problem by a self-adaptive control of strategy parameters quite similar to the technique used in Evolution Strategies.
Averaging and Simple Models
Authors: Polyak Ilya
Published: November 2020

Simple linear procedures for processing correlated observations are considered and interpreted in this chapter. Primarily, they present different schemes for averaging data. These procedures are important because climatology has historically dealt with spatial and temporal averaging of statistically dependent meteorological observations. The accuracy of such averaging is determined by the volume of data arid by its correlation structure. The examples presented in this chapter illustrate the level of accuracy that can be achieved within the framework of some assumptions about such correlation structure. Let us consider the principal relationships of the least squares method for the statistically dependent observations (see Rao, 1973). The basic assumptions are as follows.
Variability of ARMA Processes
Authors: Polyak Ilya
Published: November 2020

In this chapter, the numerical and pictorial interpretation of the dependence of the standard deviation of the forecast error for the different types and orders of univariate autoregressive-moving average (ARMA) processes on the lead time and on the autocorrelations (in the domains of the permissible autocorrelations) are given. While the convenience of fitting a stochastic model enables us to estimate its accuracy for the only time series under consideration, the graphs in this chapter demonstrate such accuracy for all possible models of the first and second order. Such a study can help in evaluating the appropriateness of the presupposed model, in earring out the model identification procedure, in designing an experiment, and in optimally organizing computations (or electing not to do so). A priori knowledge of the theoretical values of a forecast’s accuracy indicates the reasonable limits of complicating the model and facilitates evaluation of the consequences of certain preliminary decisions concerning its application. The approach applied is similar to the methodology developed in Chapters 1 and 2. Because the linear process theory has been thoroughly discussed in the statistical literature (see, for example, Box and Jenkins, 1976; Kashyap and Rao, 1976; and so on), its principal concepts are presented in recipe form with the minimum of details necessary for understanding the computational aspects of the subject. Consider a discrete stationary random process zt with null expected value [E(zt) = 0] and autocovariance function . . . M(T) = σ2 ρ(T), (4.1) . . . where σ2 is the variance and ρ(T) is the autocorrelation function of zt. Let at be a discrete white noise process with a zero mean and a variance σ2a. Let us assume that processes zt and at are normally distributed and that their cross-covariance function Mza(T) = 0 if T > 0.
The GCM Validation
Authors: Polyak Ilya
Published: November 2020

In this chapter the observed and simulated (by the Hamburg GCM) Northern Hemisphere monthly surface air temperatures, averaged within different latitude bands, are statistically analyzed and compared. The objects used for the analysis are the two-dimensional spatial-temporal spectral and correlation characteristics, the multivariate autoregressive and linear regression model parameters, and the diffusion equation coefficients. A comparison shows that, generally, the shapes of the corresponding spectra and correlation functions are quite similar, but their numerical values and some features differ markedly, especially for the tropical regions. The spectra reveal a few randomly distributed maxima (along the frequency axis), the periods of which were not identical for both types of data. A comparative study of the estimates of the diffusion equation coefficients shows a significant distinction between the character of the meridional circulations of the observed and simulated systems. The approach developed gives approximate stochastic models and reasonable descriptions of the temperature processes and fields, thereby providing an opportunity for solving some of the vital problems of theoretical and practical aspects surrounding validation, diagnosis, and application of the GCM. The methodology and results presented make it clear that formalization of the statistical description of the surface air temperature fluctuations can be achieved by applying the standard techniques of multivariate modeling and multidimensional spectral and correlation analysis to the data which have been averaged spatially and temporally. The idea of the statistical approach to the problems of GCM variability validation is contained in the comparison (observed vs. modeled) of the probability distributions of the different atmospheric and ocean processes and fields. At first, such a statement sounds like a standard statistical approach, and its solution would be obvious and simple if the number of climate processes taking place jointly were not huge and if they did not present a tremendously complicated (in its interrelationships and feedbacks) deterministic-stochastic system. As is known, the Stochastic System Identification Theory (see Eikhoff, 1983) deals mostly with the methodology for identifying linear systems, The interdependences of climatic processes and fields are not linear, and the application of this theory can give only highly approximate results.
Our Place in Space
Authors: Verschuur Gerrit L.
Published: November 2020

Finding asteroids and comets that may someday slam into our planet is the first step. What do we do then? This question is being given a whole lot of attention. In early 1993 NASA and the U.S. Congress received a report of the Near-Earth-Objects Interception Workshop (Spaceguard), the first step toward creating a program for pushing aside approaching asteroids. The report stated that “There is a clear need for continuing national and international scientific investigation and political leadership to establish a successful and broadly acceptable policy.” There are two or three options open to us to avoid being wiped out. The first is to step out of the way. This may not sound very practical, and it isn’t, at least not for a planet-load of people. However, if we plan ahead we could ship a few thousand human beings to other parts of the solar system so that if the earth were to be struck, they, at least, would survive. This would only be a privilege for a few, and getting back to earth after the cataclysm could be a rather large problem in itself. Who will welcome them back upon their return? Where would they land? If we could afford to set up colonies on the moon or Mars, the colonists could wait until after the dust had settled before attempting to return. The problem with this option is that, after a really healthy thwack, the earth’s environment would be so altered that returning human beings might find this to be an alien planet. The second way in which we could avoid getting hit would be to place an object between the onrushing comet or asteroid and ourselves. For such an emergency it might pay to place a few asteroids in geocentric orbit to be maneuvered when we need them. Then we could watch the spectacle as one asteroid slams into another, possibly showering the planet with small bits of debris that might do no more than create a spectacular display of fireballs—if we get it right, of course.
Reading Warm-Ups
Authors: Wiener Harvey S.
Published: November 2020

I've told you that this book will help you help your child be a better reader. After our discussion of the power and glory of words, you're probably expecting me to gun the accelerator across the vast reading roadways beckoning your son or daughter. But no, not yet. We're still not ready to talk about reading as you probably think of it, the moment that your youngster opens a science or social studies or "reading" book and starts her journey through the pages. Why the delay? We have some troubleshooting to do. You have to be able to prepare for those times at home when your guidance can improve comprehension dramatically. You have to stimulate your child to read with the highest possible degree of attention and to get the most from his or her print experience with minimal frustration. To reach those goals, before we do anything else we need to talk about warm-up activities, essential but often neglected areas of reading's domain. Warm-up is a familiar phrase: When you warm up, you prepare to achieve something you want to do well. Runners push against a fence or wall to stretch their muscles before an early morning jog. Pitchers toss a few practice shots before flinging the first ball to the opposing batter. On land swimmers shake their arms and wriggle their legs before taking the big plunge. Mentally, competitive athletes warm up by "imaging," a technique in which they picture all the details of the upcoming meet, project themselves into it, and try to feel all the attendant sensory responses. Warming up is as important and as useful an activity for readers as it is for exercisers and athletes. The warmup session is one that teachers pay little attention to at school; although they may show the whole class some of the strategies I'm about to recommend, they don't often help children apply some of these warm-up techniques on their own.
Exploiting the Potential of Diagrams in Guiding Hardware Reasoning
Authors: Fisler Kathi D.
Published: November 2020

. . .Formal methods offer much more to computer science than just “proofs of correctness” for programs and digital circuits. Many of the problems in software and hardware design are due to imprecision, ambiguity, incompleteness, misunderstanding, and just plain mistakes in the statement of top-level requirements, in the description of intermediate designs, or in the specification of components and interfaces. Rushby [1993] . . .Desire for correctness proofs of systems spawned the research area known as “formal methods”. Today’s systems are of sufficient complexity that testing is infeasible, both computationally and financially. As an alternative, formal methods promote mathematical analysis of a system as a means of locating inconsistencies and other design errors. Techniques used can range from writing system descriptions in a formal notation to verification that the designed system satisfies a particular behavioral specification. A good general introduction to formal methods appears in Rushby [1993]. Ideally, using formal methods increases our assurance in and understanding of our designs. Assurance results from proof, while understanding results from the process of producing the proof. Successful use of formal methods therefore requires powerful proof techniques and clear logical notations. The verification research community has paid considerable attention to the former. Current techniques, many of which can be fully automated, handle sufficiently complex systems that formal methods are now being adopted (albeit slowly) in industry. In our drive to provide powerful proof methods, however, we have overlooked the latter requirement. Research has focused on proof without paying sufficient attention to reasoning. Current tools are often criticized as too hard to use, despite their computational power. Most designers, not having been trained as logicians, find the methodologies and notations very unnatural. Industrial sites, starting out with formal methods, must often rely on external verification professionals to help them use these tools effectively (NASA [1995]). Tools that are not supportive of reasoning therefore fail to provide the full benefits of formal methods. We can augment our current methodologies to address this problem, but we first need to understand reasoning and its role in hardware design.
The Membrane Equation
Authors: Koch Christof
Published: November 2020

Any physical or biophysical mechanism instantiating an information processing system that needs to survive in the real world must obey several constraints: (1) it must operate at high speeds, (2) it must have a rich repertoire of computational primitives, with the ability to implement a variety of linear and nonlinear, high-gain, operations, and (3) it must interface with the physical world—in the sense of being able to represent sensory input patterns accurately and translate the result of the computations into action, that is motor output (Keyes, 1985). The membrane potential is the one physical variable within the nervous system that fulfills these three requirements: it can vary rapidly over large distances (e.g., an action potential changes the potential by 100 mV within 1 msec, propagating up to 1 cm or more down an axon within that time), and the membrane potential controls a vast number of nonlinear gates—ionic channels—that provide a very rich substrate for implementing nonlinear operations. These channels transduce visual, tactile, auditory, and olfactory stimuli into thanges of the membrane potential, and such voltage changes back into the release of neurotransmitters or the contraction of muscles. This is not to deny that ionic fluxes, or chemical interactions of various substances with each other, are not crucial to the working of the brain. They are, and we will study some of these mechanisms in Chap. 11. Yet the membrane potential is the incisive variable that serves as primary vehicle for the neuronal operations underlying rapid computations—at the fraction of a second time scale—in the brain. We will introduce the reader in a very gentle manner to the electrical properties of nerve cells by starting off with the very simplest of all neuronal models, consisting of nothing more than a resistance and a capacitance (a so-called RC circuit). Yet endowed with synaptic input, this model can already implement a critical nonlinear operation, divisive normalization and gain control. As a starting point, we choose a so-called point representation of a neuron. Here, the spatial dependency of the neuron is reduced to a single point or compartment.
Synaptic Input
Authors: Koch Christof
Published: November 2020

How information circulates in the brain was the subject of a heated debate lasting a decade or more among anatomists in the closing years of the last century. One camp argued that neural tissue consisted of a continuum, a syncytium, with no discernible functional units while the opposing view held that the brain consisted of discrete units, the nerve cells, communicating through point-to-point contacts that Sherrington dubbed synapses. Although in principle both views can be supported, in practice the majority of rapid communication occurs via specific point-to-point contacts, at either chemical and electrical synapses. Ephaptic transmission refers to nonsynaptic, electrical interactions between neurons. While such interactions do occur, for instance, among adjacent, parallel axons across the extracellular space, they are, by their very nature, neither very strong among any one pair of processes nor very specific. Their functional significance—if any—is currently not known, and we will not discuss them here (Traub and Miles, 1991; Jefferys, 1995). In the beginning chapter, we introduced the action of fast, chemical synapses. Given their importance, we will now return to this topic in greater depth. We first overview the pertinent biophysical events underlying chemical synaptic transmission and some of the vital statistics of synapses before we come to the mathematical treatment of synaptic input. In the last section, we will summarize our knowledge of electrical synapses and their computational role. Most typically, a synapse consists of a presynaptic axonal terminal and a postsynaptic process that can be located on a dendritic spine, on the trunk of a dendrite, or on the cell body. Figure 4.1 shows some examples of synapses among cortical cells as seen through a high-powered electron microscope. It is not easy at first to identify the synapses amid all the curved, irregular, and densely packed structures making up the neuronal tissue. In a number of locations, such as the retina or the thalamus, a synaptic connection is made between two dendrites, rather than between an axon and a dendrite. These synapses are called dendrodendritic synapses; they are believed to be relatively rare in the adult cortex. Most synapses are small and highly specialized features of the nervous system. As we will see, a chemical synapse converts a presynaptic electrical signal into a chemical signal and back into a postsynaptic electrical signal.
Synaptic Input to a Passive Tree
Authors: Koch Christof
Published: November 2020

Now that we have quantified the behavior of the cell in response to current pulses and current steps as delivered by the physiologist's microelectrode, let us study the behavior of the cell responding to a more physiological input. For instance, a visual stimulus in the environment will activate cells in the retina and its target, neurons in the lateral geniculate nucleus. These, in turn, make on the order of 50 excitatory synapses onto the apical tree of a layer 5 pyramidal cell in primary visual cortex such as the one we use throughout the book, and about 100-150 synapses onto a layer 4 spiny stellate cell (Peters and Payne, 1993; Ahmed et al., 1994, 1996; Peters, Payne, and Rudd, 1994). All of these synapses will be triggered within a fraction of a millisecond (Alonso, Usrey, and Reid, 1996). Thus, any sensory input to a neuron is likely to activate on the order of 102 synapses, rather than one or two very specific synapses as envisioned in Chap. 5 in the discussion of synaptic AND-NOT logic. This chapter will reexamine the effect of synaptic input to a realistic dendritic tree. We will commence by considering a single synaptic input as a sort of baseline condition. This represents a rather artificial condition; but because the excitatory postsynaptic potential and current at the soma are frequently experimentally recorded and provide important insights into the situation prevailing in the presence of massive synaptic input, we will discuss them in detail. Next we will treat the case of many temporally dispersed synaptic inputs to a leaky integrate-and-fire model and to the passive dendritic tree of the pyramidal cell. In particular, we are interested in uncovering the exact relationship between the temporal input jitter and the output jitter. The bulk of this chapter deals with the effect of massive synaptic input onto the firing behavior of the cell, by making use of the convenient fiction that the detailed temporal arrangement of action potentials is irrelevant for neuronal information processing. This allows us to derive an analytical expression relating the synaptic input to the somatic current and ultimately to the output frequency of the cell.
Large Eddy Simulation
Authors: Ferziger Joel H.
Published: November 2020

Over a decade ago, the author (Ferziger, 1983) wrote a review of the then state-of-the-art in direct numerical simulation (DNS) and large eddy simulation (LES). Shortly thereafter, a second review was written by Rogallo and Moin (1984). In those relatively early days of turbulent flow simulation, it was possible to write comprehensive reviews of what had been accomplished. Since then, the widespread availability of supercomputers has led to an explosion in this field so, although the subject is undoubtedly overdue for another review, it is not clear that the task can be accomplished in anything less than a monograph. The author therefore apologizes in advance for omissions (there must be many) and for any bias toward the accomplishments of people on the west coast of North America. In the earlier review, the author listed six approaches to the prediction of turbulent flow behavior. The list included: correlations, integral methods, single-point Reynolds-averaged closures, two-point closures, large eddy simulation and direct numerical simulation. Even then the distinction between these methods was not always clear; if anything, it is less clear today. It was possible in the earlier review to give a relatively complete overview of what had been accomplished with simulation methods. Since then, simulation techniques have been applied to an ever expanding range of flows so a thorough review of simulation results is no longer possible in the space available here. Simulation techniques have become well established as a means of studying turbulent flows and the results of simulations are best presented in combination with experimental data for the same flow. There is also a danger that the success of simulation methods will lead to attempts to apply them too soon to flows which the models and techniques are not ready to handle. To some extent, this is already happening. Direct numerical simulation (DNS) is a method in which all of the scales of motion of a turbulent flow are computed. A DNS must include everything from the large energy-containing or integral scales to the dissipative scales; the latter is usually taken to be the viscous or Kolmogoroff scales.
Language Varieties
Authors: Kukulska-Hulme Agnes
Published: November 2020

• Is jargon meaningless? • Is a “requirement” the same as a “need”? • Why might we never know that we failed to put across a message? • Are user manuals ever “too chatty”? • Do all speakers of English think alike? . . . This chapter addresses these questions and others. It is the first in a series of chapters that present various language concepts and show the ways they are applicable to user interface and documentation design. This part of the book is oriented toward developing a deeper understanding of language and a better appreciation of the needs of users as language learners, as explained in chapter 1. Here we explore the concept of variety in language and look at the reasons or motivations behind variety. Distinctions are drawn between colloquial and formal and between general and professional language. Special consideration is given to scientific and technical language and to jargon and slang. The requirements of international communication are discussed with reference to English, and finally, we look at how variety is related to writing style. “Creatures of habit” is a label that seems to apply to a great majority of human beings. Language habits, acquired through everyday practice in speaking, ensure that in adulthood most people reach a level of fluency in their native language that allows them to use the language to get things done, without needing to reflect on the tool itself. Occasionally, we may become aware of our individual habits—our spelling difficulties, for instance, or the fact that we tend to use certain turns of phrase, which others may laugh at or fail to understand. Collective habits, patterns of speech attributable to a community, serve a particular purpose in that they help to define a group’s identity; the protection of a language is then a means of safeguarding that identity. This can be seen to operate on a national and regional basis, in national languages and regional dialects, but it can also be observed on a smaller scale, in professional circles, and when friends or partners communicate in a way that only they can understand.
Making It Work
Authors: Kukulska-Hulme Agnes
Published: November 2020

This chapter summarizes the main points of the communicative approach to user interface and documentation design. The term “designer” is used here to refer to anyone who designs and develops a user interface or writes user documentation. As stated at the beginning, the main ambition of this book is to further our understanding of the nature of the problems observed and to establish the language concepts (rather than guidelines) that will help designers when thinking about solutions to problems. Of course, the practical side is very important and must be further developed by those whose job it is to create design methodologies, standards, and guidelines. The present chapter highlights elements of practical advice given in earlier chapters and states the implications of what has been said. Accordingly, the style of presentation is different: everything is contained in bullet lists. It is assumed that previous chapters have been read, or will be read, as the supporting arguments are not developed here. The view expressed by Smith (1990) seems fitting: . . . Guidelines cannot replace task analysis. Indeed many guidelines, when considered along with their associated commentary, imply the need for careful task analysis to determine design requirements. Guidelines will not necessarily save work in user interface design, but in fact may entail extra work, at least in the initial stage of establishing design rules. If that initial work is well done, however, then subsequent software design should be more efficient and, of course, should produce a better user interface. . . . What needs to be added is that the initial stage that comprises audience and task analysis [e.g., as described by Bradford (1988) and Brockmann (1986)] must include language requirements analysis if successful communication with users is envisaged in the interface. • The concept of computer literacy creates a barrier to effective communication— people literacy and language literacy are much better concepts to work with. • Communication is language in action: Both spoken and written language must be seen in this light. • Communication involves people, which means that its cultural, social, and psychological contexts must be considered.
Persistence and Interphase Mass Transfer of Liquid Organic Contaminants in the Unsaturated Zone : Experimental Observations and Mathematical Modeling
Authors: Abriola Linda M. , Pennell Kurt D.
Published: November 2020

Surface and subsurface releases of organic chemicals have resulted in widespread contamination of groundwaters and soils. Frequently, such chemicals are introduced into the subsurface as nonaqueous-phase liquids (NAPLs), which are only slightly miscible with water. These organic liquids tend to migrate downward through the unsaturated soil zone, displacing the pore gases under the action of gravitational forces. During its migration, a portion of the NAPL will become entrapped in the soil pores due to capillary forces, creating zones of persistent contamination in the soil matrix. Organic liquid saturation in such zones may range from approximately 4% to 10% of the pore space (Wilkins et al., 1995). This entrapped NAPL may serve as a long-term source of contamination to the aqueous and gaseous pore fluids through subsequent dissolution and volatilization. Soil vapor extraction (SVE) has evolved over the past decade as an attractive in situ remediation technology for unsaturated soils contaminated by entrapped volatile organic compounds (VOCs). This technology involves the induction of gas flow within the porous medium to enhance volatilization of entrapped contaminants (Hutzler et al., 1989). Based upon the success of a number of feasibility studies and the ease of implementation, SVE remediation technologies are currently employed at approximately 18% of Superfund sites (Travis and Macinnis, 1992). An extensive review of the literature pertaining to SVE and related technologies is given in Rathfelder et al. (1995). Although widely implemented, SVE systems are typically designed and installed with limited understanding of the processes that control their effectiveness. Clearly, the performance of SVE will be strongly influenced by contaminant volatility and effective gas-phase permeability (Pedersen and Curtis, 1991). Relatively little is known, however, about the physical and chemical processes that control contaminant vapor-phase mass transfer. The SVE systems characteristically exhibit large initial VOC recovery rates, followed by a rapid decline in effluent gas concentrations to a persistent low level (e.g., Crow et al., 1987; DiGiulio, 1992). Furthermore, a temporary increase in the produced gas organic concentration has often been observed following SVE shutdown periods (McClellan and Gilham, 1992). Such behavior suggests the presence of mass transfer limitations.
Wheat Breeding : Coalescence of a Modern Science, 1900-1939
Authors: Perkins John H.
Published: November 2020

Plant breeding in general and wheat breeding specifically were rudimentary activities on many grounds in the nineteenth century. Not many people engaged in the activity. Those who did were self-taught. because no formal educational programs existed in the subject. For the most part, they had only a few very modest institutional bases within which to work. Many farmers paid them little or no attention, and governments usually ignored their contributions and gave them next to no support. They had no organized way of broadly disseminating their results, which in any case were few in number. By 1970, wheat and other plant breeders occupied a very different position within both the scientific and political economic landscapes. Many people worked as breeders. They were highly trained in educational programs dedicated to the reproduction of plant breeders. Elaborate networks of institutions gave them employment. A substantial proportion of farmers cared very much what they did, and governments gave substantial, sometimes lavish, support. They had means of communicating their work that included both scientific and popular outlets. And they had substantial results to convey to farmers and the general public, some of them remarkable either for their scientific cleverness or for their broad political, economic, and ecological impacts, or both. Another way of gaining perspective on the change in status of wheat and other plant breeders is to suggest that their absence might not have been noticed by anybody but their families had they suddenly disappeared in the nineteenth century. In contrast, the twentieth century came increasingly to depend upon the plant breeders. Cessation of wheat breeding after 1970, for example, would have put some agricultural systems in distinct danger of slow decline or even collapse and failure. In both political economic and ecological terms, an increasing portion of the global human community became absolutely dependent upon wheat breeders and other plant scientists, certainly for prosperity as we now know it and possibly for survival and security. The transformation of wheat breeding from nearly invisible to virtually indispensable resulted from two mutually interacting events: a commercial-industrial revolution in agriculture and construction of a new science of plant breeding.