bluuebunny/crossref_metadata_2025 huggingface dataset:
Applied Geography
Authors: Torrieri Nancy K. , Ratcliffe Michael R.
Published: November 2020

Applied geographers solve problems that inform decision-making and policy. The problems most often arise in government or the private sector, require practical, rapid, and cost-effective solutions, and are usually client-driven. Often, government or the private sector funds the research of applied geographers, and the research results have specific and usually current implications for government policies and programs or business strategies. Applied geographers use techniques, tools, methods, and concepts from the discipline of geography, but borrow liberally from other disciplines as necessary. This approach is well suited to solving problems that have multiple, not merely spatial, dimensions. As a subdiscipline of geography, applied geography has an ill-defined niche. Is applied geography a subdiscipline similar to biogeography, geomorphology, or economic geography? Or does it occupy an intermediary position within the discipline, synthesizing concepts from various subdisciplines? A certain ambiguity exists as to the point of origin of applied geography as a subdiscipline as well as whether it is even a distinct subdiscipline within geography (Hart 1989). The nature of applied geography has been a staple topic of discussion in professional papers and applied geography texts. Such discussions tend to focus on applied geography’s role within the discipline and what differentiates applied geographers from other geographers. Kenzer (1989) provides an excellent and lively account, in part noting that aspects of the discussion are bound up in the historic differences between academic and non-academic (professional) geographers. Kenzer and the contributors to the volume he edited provide plenty of grist for discussion. Over the past twenty years considerable interest has been attracted toward this discussion. In particular, we draw attention to work by Frazier (1982), Kenzer (1989), Hart (1989), Palm and Brazel (1992), Johnston (1993); Frazier et al. (1995), Harvey (1997), and Golledge et al. (1997) for discussions of the origins, purpose, and focus of applied geography. For the purposes of this review, applied geography is treated as one of many subdisciplines or specialties. Notwithstanding attaining the status of a subdiscipline, however, there is no single body of research that applied geographers can point to as clearly their own.
Geography of China
Authors: Cindy Fan C. , Ma Laurence J. C.
Published: November 2020

The pioneering work of North American geographers in the 1970s and early 1980s has laid a sound foundation for research and fieldwork opportunities in China (Karan et al. 1989), a nation largely closed to academics and others until the late 1970s. Building on this foundation, research on China geography since the last decade or so has witnessed phenomenal achievements in mass, diversity, and intellectual depth. Geographers have for a long time been captivated by China’s sheer size. But their recent scholarship must also be understood against the backdrop of that nation’s groundbreaking reforms and transformations since the late 1970s. China’s decisive integration into the world economy, in conjunction with its sweeping processes of socialist transition, has fascinated geographers all over the world. As this review will show, these changes have indeed defined the priorities and research agendas of many North American geographers. Their research has been significantly facilitated and stimulated by extensive and increasing contacts with scholars in China, through long-standing collaborations, fieldwork, and international conferences especially since 1979 when exchange of ideas and visits among North American and Chinese geographers have flourished. China’s opening its doors has also motivated a large number of excellent Chinese students to pursue advanced training in North American institutions, who have added considerably to the human resources of China geography there. The research output of North American China geographers is outstanding, which parallels the growth of China geography in general (Selya 1992b). The scope of their attention, however, is also uneven. In this review, we attempt to highlight achievements and dominant themes of inquiry since the late 1980s, as well as areas for future improvement. Recent research on China’s economic geography has concentrated on two substantive foci: regional development and foreign investment-induced growth. Both are rooted in China’s economic transformations and have far-reaching spatial implications.
Bombe and Spider (1940)
Authors: Turing Alan
Published: November 2020

This material forms chapter 6 of Turing’s Treatise on the Enigma (known at Bletchley Park as ‘Prof ’s Book’). The text has been prepared by Ralph Erskine, Philip Marks and Frode weierud from the two known surviving copies of Turing’s original typescript. The pagination of Turing’s typescript indicates that the chapter may possibly have continued for a further four pages; however, these pages are not to be found in either of the archived copies. When one has asteckered Enigma to deal with one’s problems naturally divide themselves into what is to be done to find the Stecker, and what is to be done afterwards. Unless the indicating system is very well designed there will be no problem at all when the Stecker have been found, and evenwith a good indicating system we shall be able to apply the methods of the last two chapters [of Turing’s Treatise] to the individual messages. The obvious example of a good indicating system is the German Naval Enigma cipher, which is dealt with in Chapter VII [of the Treatise]. This chapter is devoted to methods of finding the Stecker. Naturally enough we never find the Stecker without at the same time finding much other information. The most obvious kind of data for finding the keys is a ‘crib’, i.e. a message of which a part of the decode is known. fie shall mostly assume that our data is a crib, although actually it may be a number of constatations arising from another source, e.g. a number of CILLIs or a Naval Banburismus. It is sometimes possible to find the keys by pencil and paper methods when the number of Stecker is not very great, e.g. 5 to 7. One would have to hope that several of the constatations of the crib were ‘unsteckered’. The best chance would be if the same pair of letters occurred twice in the crib (a ‘half-bombe’). In this case, assuming 6 or 7 Stecker there would be a 25% chance of both constatations being unsteckered. The positions at which these constatations occurred could be found by means of the Turing sheets (if there were three wheels) or the Jeffreys sheets.
Starting lives, saving lives, screwing up lives: An exhibition of molecules that can help and harm the young
Authors: Emsley John
Published: November 2020

In this gallery we will look at the portraits of molecules which can affect us very profoundly, and not only ourselves, but also the life we carry inside us, or the life we would like to create. In a private room at the end of the gallery are a few portraits that were not thought suitable for public exhibition, but which selected individuals will be allowed to view. These are molecules that are deemed undesirable, but their eradication is proving difficult, if not impossible. Few things are more important than creating new life, and yet nature has an almost cavalier attitude to the process, investing in gross overproduction of the raw materials necessary. Women have the ability to produce around three hundred eggs in a lifetime, and men to manufacture three hundred million sperm a week. Despite this abundance the human population has been kept in check in many ways—high infant mortality, famine, disease, war; but even so, today we have a world that is overpopulated with humans. This has come about through the success of science, which has lifted the first three of these natural scourges, although it has made the fourth much worse. Sadly science has so far not elicited the response of better birth control in many parts of the world, but it has made it possible to plan parenthood carefully. Science has also made it possible to ensure that if you decide to have a baby, then the baby you bring into the world should be perfect. The only prayer that potential parents in developed nations deem necessary is ‘please let our baby be all right.’ There are a few simple precautions that a woman can take to ensure her baby has a good chance of avoiding some risks that would seriously affect it. In this part of the gallery there are two molecules that she needs to think about. Folic acid is found in plants, animals and microorganisms such as fungi and yeasts. It is present in grass, butterflies’ wings and fish scales. Humans need it also, as an essential component for several metabolic processes.
Chemical Evolution
Authors: Maynard Smith John , Szathmary Eors
Published: November 2020

Even if we take a ‘replicators first’ view of the origin of life, we still have to explain how a chemical environment arose that was sufficiently diverse for such replicators to be formed. As a minimum, we must explain the abiotic formation of sugars and amino acids, and of nucleotides or of some simpler molecules capable of base pairing, and hence of template reproduction. Lipids would not be needed for the first appearance of replicating molecules, but were crucial if evolution was to proceed further. Their importance is apparent from the chemoton model: by forming membranes, they make possible the formation of protocells, and hence of a unit of selection more complex than a replicating molecule. In turn, this encourages the evolution of cooperation between replicators, as discussed in the next chapter. This chapter describes how such a diverse chemical environment could arise. In section 3.2, we introduce the familiar idea of a ‘primitive soup’, and review the experimental evidence concerning what compounds can, and cannot, be formed. Although a surprising array of organic compounds have been synthesized in such experiments, there are some awkward gaps. Section 3.3 describes the more recent, and more promising, idea that the crucial chemical events took place between compounds bonded to a charged surface. There are several reasons why the idea is attractive. Chemical reactions will be both more frequent and more specific if the reacting molecules are moving on a surface, rather than in three dimensions. Also, some reactions will be energetically favoured. In particular, the formation of biological polymers (proteins, nucleic acids) requires the removal of a molecule of water: this is difficult for molecules in solution in water, but easier on a surface. The chemoton model incorporates an autocatalytic cycle, producing two molecules of a compound where one existed before. Such cycles are discussed in section 3.4. They are an essential feature of metabolism. It is important, however, to remember that autocatalytic cycles are not replicators: this distinction is made clearer in Chapter 4. Section 3.5 discusses whether chemical ‘evolution’, in the primitive soup or on a surface, is really evolution. In our view, evolution requires heritable variation: this property is lacking from the reactions discussed in this chapter.
Development in simple organisms
Authors: Maynard Smith John , Szathmary Eors
Published: November 2020

Complex multicellular organisms, whose bodies consist of differentiated cells of many kinds, have evolved independently on three occasions—animals, higher plants and fungi. In addition, multicellular organisms with a lesser degree of cellular differentiation have evolved on a number of occasions. For example, the algae have given rise to ‘seaweeds’ several times. In this and the next three chapters, we discuss the origin and subsequent evolution of such organisms. Some 540 million years ago, at the beginning of the Cambrian, there appeared an array of multicellular marine animals, including the major phyla that exist today—coelenterates, platyhelminths, annelids, arthropods, molluscs, echinoderms and others. Chordates are also present in the Cambrian: they are not known from the earliest deposits, in which only hard parts are preserved, but are present in the slightly later Burgess Shale, in which soft-bodied forms are preserved. Forty years ago, this sudden appearance of metazoan fossils was not only a puzzle but something of an embarassment: the absence of any known fossils from earlier rocks was a weapon widely used by creationists. Today, the fossil evidence for prokaryotes goes back 3000 million years, and for protists some 1000 million years. The Cambrian explosion remains a puzzle, however, which has been only fitfully illuminated by the discovery of the enigmatic soft-bodied Ediacaran fauna, which had a worldwide distribution between 580 and 560 million years ago. There are still doubts about how these fossils should be interpreted (Conway Morris, 1993). The orthodox, and more plausible, view is that the fauna is dominated by coelenterates, with some specimens identified as echinoderms and annelids. An alternative interpretation (Seilacher, 1992) is that they belong to an extinct clade of multicellular eukaryotes, the ventobionts, probably lacking an alimentary canal, muscles and nervous system. Although such organisms may have existed, at least some of the Ediacaran fauna have been successfully compared to recent metazoans. If the interpretation of most of these fossils as coelenterates proves to be correct, it would fit in well with the morphological and molecular evidence. The molecular data suggest that coelenterates arose early, but probably not independently of other metazoans. Morphologically they are simple in being diploblastic (formed from two cell layers), in contrast to the triploblastic animals that predominate in the Cambrian.
General procedures in chain-growth polymerization
Authors: Aragrag Najib , Castiglione Dario C.
Published: November 2020

This chapter is intended to provide a general introduction to the laboratory techniques used in polymer synthesis, by focusing on some relatively well-known polymerizations that occur by chain-growth processes. In this way some of the more commonly used procedures in polymer chemistry are described. Due to the nature of the intermediates produced, such as free radicals, carbanions, carbocations, together with a range of organometallic species, the techniques often involve handling compounds in the complete absence of oxygen and moisture. Because of this the best results may require quite sophisticated equipment and glassware; however, it is our intention to show that the general procedures are accessible to any reasonably equipped laboratory, and indeed some of the techniques are suitable for use in an undergraduate teaching laboratory. Chain-growth polymerization involves the sequential step-wise addition of monomer to a growing chain. Usually, the monomer is unsaturated, almost always a derivative of ethene, and most commonly vinylic, that is, a monosubstituted ethane, 1 particularly where the growing chain is a free radical. For such monomers, the polymerization process is classified by the way in which polymerization is initiated and thus the nature of the propagating chain, namely anionic, cationic, or free radical; polymerization by coordination catalyst is generally considered separately as the nature of the growing chain-end may be less clear and coordination may bring about a substantial level of control not possible with other methods. Ring-opening polymerizations exhibit many of the features of chain-growth polymerization, but may also show some of the features expected from stepgrowth polymerizations. However, it is probably fair to say that from a practical point of view the techniques involved are rather similar or the same as those used in chain-growth processes and consequently some examples of ring-opening processes are provided here. It is particularly instructive to consider the requirements of chain-growth compared to step-growth processes in terms of the demands for reagent purity and reaction conditions.
Liquid crystalline polymers
Authors: Patel Sangdil I. , Davis Fred J.
Published: November 2020

The idea of combining the anisotropic behaviour of liquid crystalline materials with the properties of macromolecular systems was first suggested by Onsanger and subsequently Flory. The actual realization that such systems could exist came from studies of natural polymers such as the tobacco mosaic virus. Interest in these systems intensified with the development of highstrength systems, based on rigid-rod systems, notably the aramid fibres, however, liquid crystallinity in such systems occurs only at high temperatures, usually close to the decomposition point of the polymer. It was only in the late 1970s that the design criteria for liquid crystalline polymers became apparent, the secret being largely in the decoupling of the rigid aromatic groups which give rise to the anisotropic behaviour. As a result of these ideas two classifications of liquid crystalline materials were described. Main-chain liquid crystalline polymers, are those in which rigid aromatic molecules form part of the polymer backbone, either as a continuous chain or separated by a series of methylene groups in order to lower temperature at which liquid crystalline phase behaviour is observed. Side-chain systems resemble the comb-like systems studied by Shibaev and Plate, and have the rigid aromatic groups attached as a side-chain. In general, the monomer systems required for main-chain liquid crystalline polymers are relatively simple; synthetically these systems are prepared by step-growth methods and the main challenge is often maintaining sufficient solubility to allow suitable chain-lengths to be grown (an example of how such problems might be overcome is given in Chapter 4). Side-chain systems tend to be produced from more complex structural sub-units, and may be produced either by polymerization of the appropriate monomer or by functionalization of a preformed polymer backbone. Examples of both approaches are given in this chapter. From a practical viewpoint, the advantage of side-chain systems is that they tend to be much more soluble in common organic solvents and also that thermal phase transitions occur at reasonable temperatures (reasonable being well below the temperature at which the polymer decomposes). A further advantage of such side-chain systems is that the phase behaviour can be effectively tuned through the chemical modifications of the three components, namely the side-group, the flexible coupling chain and the polymer backbone.
Markov Random Fields on Undirected Graphs
Authors: Grenander Ulf , Miller Michael I.
Published: November 2020

This chapter focuses on random fields on lattices and undirected graphs. Discrete finite state spaces are examined in the context of Markov and Gibbs fields. The subsequent chapter studies state spaces on the continuum through Gaussian fields. This chapter examines texture representation and segmentation, exploring the Gibbs random fields. For dealing with the partition function asymptotics are derived allowing for the explicit calculation of the asymptotic approximation to the log-normalizer required for the Bayes solution. Zhu’s maximum-entropy model is explored for representing random field textures.
The Canonical Representations of General Pattern Theory
Authors: Grenander Ulf , Miller Michael I.
Published: November 2020

Pattern theory is combinatory in spirit or, to use a fashionable term, connectionist: complex structures are built from simpler ones. To construct more general patterns, we will generalize from combinations of sites to combinations of primitives, termed generators, which are structured sets. The interactions between generators is imposed via the directed and undirected graph structures, defining how the variables at the sites of the graph interact with their neighbors in the graph. Probabilistic structures on the representations allow for expressing the variation of natural patterns. Canonical representations are established demonstrating a unified manner for viewing DAGs, MRFs, Gaussian random fields and probabilistic formal languages.
Computational Anatomy: Shape, Growth and Atrophy Comparison via Diffeomorphisms
Authors: Grenander Ulf , Miller Michael I.
Published: November 2020

Computational Anatomy (CA) is the study of human anatomy I ∈ I = Iα ◦G, an orbit under groups of diffeomorphisms of anatomical exemplars Iα ∈ I. The observable images ID ∈ ID are the output of medical imaging devices. There are three components CA examines: (i) constructions of the anatomical submanifolds under study in anatomy, (ii) estimation of the underlying diffeomorphisms g ∈G defining the shape or geometry of the anatomical manifolds, and (iii) generation of probability laws of anatomical variation P(·) on the images I for inference and disease testing within the anatomical models. This chapter focuses on the metric comparison of anatomical manifolds.
Markov Processes and Random Sampling
Authors: Grenander Ulf , Miller Michael I.
Published: November 2020

The parameter spaces of natural patterns are so complex that inference must often proceed compositionally, successively building up more and more complex structures, as well as back-tracking, creating simpler structures from more complex versions. Inference is transformational in nature. The philosophical approach studied in this chapter is that the posterior distribution that describes the patterns contains all of the information about the underlying regular structure. Therefore, the transformations of inference are guided via the posterior in the sense that the algorithm for changing the regular structures will correspond to the sample path of a Markov process. The Markov process is constructed to push towards the posterior distribution in which the information about the patterns are stored. This provides the deepconnection between the transformational paradigm of regular structure creation, and random sampling algorithms.
Orthogonal Polynomials
Authors: Gautschi Walter
Published: November 2020

This is the first book on constructive methods for, and applications of orthogonal polynomials, and the first available collection of relevant Matlab codes. The book begins with a concise introduction to the theory of polynomials orthogonal on the real line (or a portion thereof), relative to a positive measure of integration. Topics which are particularly relevant to computation are emphasized. The second chapter develops computational methods for generating the coefficients in the basic three-term recurrence relation. The methods are of two kinds: moment-based methods and discretization methods. The former are provided with a detailed sensitivity analysis. Other topics addressed concern Cauchy integrals of orthogonal polynomials and their computation, a new discussion of modification algorithms, and the generation of Sobolev orthogonal polynomials. The final chapter deals with selected applications: the numerical evaluation of integrals, especially by Gauss-type quadrature methods, polynomial least squares approximation, moment-preserving spline approximation, and the summation of slowly convergent series. Detailed historic and bibliographic notes are appended to each chapter. The book will be of interest not only to mathematicians and numerical analysts, but also to a wide clientele of scientists and engineers who perceive a need for applying orthogonal polynomials.
The Origin and Evolution of Mammals
Authors: Kemp T.S.
Published: November 2020

Mammals are the dominant large animals of today, occurring in virtually every environment. This book is an account of the remarkable fossil records that document their origin since the extinction of the dinosaurs. Tracing their evolution over the last 35 million years. For the first time presented in one single volume Kemp unveils the exciting DNA sequence evidence which coupled with fossil evidence challenges current thinking on the relationships amongst mammal and their inferred history.
Anomalous scattering
Authors: Blow David
Published: November 2020

X-rays set the electronic charges around atoms vibrating, and these vibrations generate radiation of the same frequency, which is propagated in all directions. This is the coherent scattering that gives rise to diffraction effects. Normally, the electrons vibrate in step with the incident beam. If, however, the incident photons have an energy close to a transition energy which can bring the atom to an excited state, the electronic vibration gets out of step. Instead of re-radiating in phase with the incident beam, the radiated energy has a different phase. Also, the intensity of coherent scattering is reduced, because some energy is absorbed to bring about the transition. This effect is called anomalous scattering. More detail is given in Box 8.1. Figure 8.1 shows how X-ray absorption varies with wavelength near the transition energy. X-rays become rapidly less penetrating as wavelength increases, but this trend is interrupted by a sharp ‘edge’ at a wavelength that corresponds to an electronic transition. In practice, at the wavelengths of X-rays convenient for diffraction experiments (less than 1.6 Å) atoms lighter than phosphorus or sulphur behave as normal scatterers because they have no transitions of corresponding energy. At wavelengths very near the energy of an electronic transition, anomalous scattering can become a significant fraction of the total scattering. In this chapter the atoms which are scattering anomalously are referred to as heavy atoms, H. Useful anomalous scatterers can be far lighter than the heavy elements needed for macromolecular isomorphous replacement. From iron (Z=26) to palladium (Z = 46) the K absorption edges are at convenient wavelengths. Much heavier atoms (the lanthanides and beyond) give strong anomalous effects from the L edges, at useful wavelengths. Remember that the X-ray scattering power of an atom is measured by comparison with the scattering of an electron. At low scattering angle and ‘normal’ wavelengths, an atom scatters according to the number of electrons it contains (Box 5.2). At wavelengths close to the absorption edge, the atomic scattering factor includes an ‘anomalous’ component, shown in Fig. 8.2, and presented in algebraic form in Box 8.2.
Shared Memory Parallelism
Authors: Petersen Wesley , Arbenz Peter
Published: November 2020

Shared memory machines typically have relatively few processors, say 2–128. An intrinsic characteristic of these machines is a strategy for memory coherence and a fast tightly coupled network for distributing data from a commonly accessible memory system. Our test examples were run on two HP Superdome clusters: Stardust is a production machine with 64 PA-8700 processors, and Pegasus is a 32 CPU machine with the same kind of processors. The HP9000 is grouped into cells, each with 4 CPUs, a common memory/cell, and connected to a CCNUMA crossbar network. The network consists of sets of 4×4 crossbars and is shown in Figure 4.2. An effective bandwidth test, the EFF_BW benchmark [116], groups processors into two equally sized sets. Arbitrary pairings are made between elements from each group, Figure 4.3, and the cross-sectional bandwidth of the network is measured for a fixed number of processors and varying message sizes. The results from the HP9000 machine Stardust are shown in Figure 4.4. It is clear from this figure that the cross-sectional bandwidth of the network is quite high. Although not apparent from Figure 4.4, the latency for this test (the intercept near Message Size = 0) is not high. Due to the low incremental resolution of MPI_Wtime, multiple test runs must be done to quantify the latency. Dr Byrde’s tests show that minimum latency is ≳ 1.5μs. A clearer example of a shared memory architecture is the Cray X1 machine, shown in Figures 4.5 and 4.6. In Figure 4.6, the shared memory design is obvious. Each multi-streaming processor (MSP) shown in Figure 4.5 has 4 processors (custom designed processor chips forged by IBM), and 4 corresponding caches. Although not clear from available diagrams, vector memory access apparently permits cache by-pass; hence the term streaming in MSP. That is, vector registers are loaded directly from memory: see, for example, Figure 3.4. On each board (called nodes) are 4 such MSPs and 16 memory modules which share a common (coherent) memory view. Coherence is only maintained on each board, but not across multiple board systems.
The Classical World
Authors: Penrose Roger , Gardner Martin
Published: November 2020

What need we know of the workings of Nature in order to appreciate how consciousness may be part of it? Does it really matter what are the laws that govern the constituent elements of bodies and brains? If our conscious perceptions are merely the enacting of algorithms, as many AI supporters would have us believe, then it would not be of much relevance what these laws actually are. Any device which is capable of acting out an algorithm would be as good as any other. Perhaps, on the other hand, there is more to our feelings of awareness than mere algorithms. Perhaps the detailed way in which we are constituted is indeed of relevance, as are the precise physical laws that actually govern the substance of which we are composed. Perhaps we shall need to understand whatever profound quality it is that underlies the very nature of matter, and decrees the way in which all matter must behave. Physics is not yet at such a point. There are many mysteries to be unravelled and many deep insights yet to be gained. Yet, most physicists and physiologists would judge that we already know enough about those physical laws that are relevant to the workings of such an ordinary-sized object as a human brain. While it is undoubtedly the case that the brain is exceptionally complicated as a physical system, and a vast amount about its detailed structure and relevant operation is not yet known, few would claim that it is in the physical principles underlying its behaviour that there is any significant lack of understanding. I shall later argue an unconventional case that, on the contrary, we do not yet understand physics sufficiently well that the functioning of our brains can be adequately described in terms of it, even in principle. To make this case, it will be necessary for me first to provide some overview of the status of present physical theory. This chapter is concerned with what is called ‘classical physics’, which includes both Newton’s mechanics and Einstein’s relativity.
Quantum Magic and Quantum Mystery
Authors: Penrose Roger , Gardner Martin
Published: November 2020

In classical physics there is, in accordance with common sense, an objective world ‘out there’. That world evolves in a clear and deterministic way, being governed by precisely formulated mathematical equations. This is as true for the theories of Maxwell and Einstein as it is for the original Newtonian scheme. Physical reality is taken to exist independently of ourselves; and exactly how the classical world ‘is’ is not affected by how we might choose to look at it. Moreover, our bodies and our brains are themselves to be part of that world. They, also, are viewed as evolving according to the same precise and deterministic classical equations. All our actions are to be fixed by these equations - no matter how we might feel that our conscious wills may be influencing how we behave. Such a picture appears to lie at the background of most serious 1 philosophical arguments concerned with the nature of reality, of our conscious perceptions, and of our apparent free will. Some people might have an uncomfortable feeling that there should also be a role for quantum theory - that fundamental but disturbing scheme of things which, in the first quarter of this century, arose out of observations of subtle discrepancies between the actual behaviour of the world and the descriptions of classical physics. To many, the term ‘quantum theory’ evokes merely some vague concept of an ‘uncertainty principle’, which, at the level of particles, atoms or molecules, forbids precision in our descriptions and yields merely probabilistic behaviour. Actually, quantum descriptions are very precise, as we shall see, although radically different from the familiar classical ones. Moreover, we shall find, despite a common view to the contrary, that probabilities do not arise at the minute quantum level of particles, atoms, or molecules - those evolve deterministically - but, seemingly, via some mysterious larger-scale action connected with the emergence of a classical world that we can consciously perceive. We must try to understand this, and how quantum theory forces us to change our view of physical reality.
Dispersion and absorption
Authors: Newnham Robert E.
Published: November 2020

In this chapter we discuss dispersion, the dependence of the refractive index on wavelength, and absorption that is related to the imaginary part of the refractive index. The variation of the refractive index with temperature (thermo-optic effect) is also described. In terms of their directional behavior, all three of these effects can be represented by second rank tensors because of their relationship to the optical dielectric constant K. The thermo-optic coefficients relate ΔKij to a temperature change
Impact by comets and asteroids
Authors: Hallam Tony
Published: November 2020

Although Norman Newell’s pioneering research was published in 1967, general interest in mass extinctions provoked by catastrophic changes in the environment was not aroused until 1980, when a paper appeared in the journal Science proposing that the end-Cretaceous extinction was caused by the impact of a huge asteroid. Before this time several people had suggested an extra-terrestrial cause for particular mass extinctions. Thus, in the middle of the twentieth century, the German palaeontologist Otto Schindewolf, who had long been preoccupied with the marine mass extinction at the end of the Palaeozoic era, concluded on the evidence of fieldwork in the Salt Range of Pakistan that the event must have been a catastrophic one for which he could literally conceive no earthly explanation. He was consequently led to speculate that the causal factor was a nearby supernova explosion. The increased cosmic radiation impinging on the Earth could, he thought, have destroyed the ozone shield and have led to lethal exposure of numerous organisms. A few other such speculations invoking some kind of extraterrestrial factor were put forward at about the same time, and in 1970 Digby McLaren, an expatriate British palaeontologist who had risen to become Director of the Canadian Geological Survey, made a startling proposal. He was an expert on the late Devonian marine mass extinction at the end of the penultimate, Frasnian, stage. Like Schindewolf, he agreed that the event was much too wide spread, dramatic, and ‘geologically instantaneous’ to have been caused by a merely terrestrial process, and he speculated that the world’s ocean of the time had been severely disturbed by the impact of a giant meteorite. Three years later, the American chemist Harold Urey, a Nobel Prize-winner, published a paper in the journal Nature in which he argued that several extinction events within the past 50 million years had been caused by the impact of comets. These various suggestions, together with a few others invoking increases in radiation from outer space, either in the form of cosmic radiation or solar protons, were virtually ignored. This is unsurprising in view of the almost total absence at that time of any supporting evidence, with the possible exception of a few tektite layers in Tertiary deposits.
Climate change
Authors: Hallam Tony
Published: November 2020

Unlike the other factors that have been invoked to account for mass extinctions, climate change is manifest to us all, whether we travel from the tropics to the poles or experience the seasonal cycle. Over a longer timescale, the issue of global warming in the recent past and likely future, and its probable consequences for other aspects of the environment, has occupied a considerable amount of media attention. Those people who are unaware of the likely consequences of the burning of fossil fuels cannot count themselves as well educated. Over a longer timescale, geologists have been aware for many decades of significant climatic changes on a global scale leading to the appearance and disappearance of polar ice caps on a number of occasions. Steve Stanley, the distinguished palaeobiologist at Johns Hopkins University in Baltimore, has actively promoted the view that episodes of climatic cooling are the most likely cause of mass extinctions. However, we must consider also the significance of global warming, and for the continents, at any rate, the possible effects of changes in the humidity–aridity spectrum. Before examining the relationships between climatic change and mass extinctions we need to examine the criteria from the stratigraphic record that geologists use to determine ancient climates, or palaeo-climates. The most obvious way of detecting cold conditions in the past is to find evidence of the presence of ice. At the present day the sedimentary deposits associated with glaciers and ice sheets, which occur where melting ice dumps its rock load, range in grain size from boulders and pebbles to finely ground rock flour. Such deposits are known as boulder clay or till, and ancient examples consolidated into resistant rock as tillites. The surfaces of hard rock that have underlain substantial ice sheets bear characteristic linear striations indicating the former direction of ice movement, such as glaciers moving up or down a U-shaped valley. The striations are produced by pebbles embedded in the ice, and are a unique marker for glacial action. In the 1830s Louis Agassiz, the great Swiss naturalist, extrapolated from his knowledge of the margins of Alpine glaciers to propose that the whole of northern Europe had been covered by one or more ice sheets in the recent geological past.
Probability and information
Authors: Barnett Stephen
Published: November 2020

The science of information theory begins with the observation that there is a fundamental link between probabilities and information. As early as the mid eighteenth century, Bayes recognized that probabilities depend on what we know; if we acquire additional information then this modifies the probability. For example, the probability that it is raining when I leave for work in the morning is about 0.2, but if I look out of the window ten minutes before leaving and see that it is raining then this additional information adjusts the probability to in excess of 0.9. Information is a function of probabilities: it is the entropy associated with the probability distribution. This conclusion grew out of investigations into the physical nature of entropy by Boltzmann and his followers. The full power of entropy as the quantity of information was revealed by Shannon in his mathematical theory of communication. This work laid the foundations for the development of information and communications theory by proving two powerful theorems which limit our ability to communicate information. The link between probability and information has far wider application than just communications. Indeed, we can expect the ideas of information theory to be applicable to any statistical or probabilistic problem. Quantum mechanics is a probabilistic theory and so it was inevitable that a quantum information theory would be developed. In quantum theory, probabilities are secondary quantities calculated by taking the squared modulus of probability amplitudes and this gives rise to interference effects. Consider, for example, the famous two-slit experiment depicted in Fig. 1.1. A single particle launched at the slits can arrive at a point P on the screen by passing either through slit 1 or through slit 2. In classical statistical mechanics this leads to a probability . . . P = P1 + P2, (1.1) . . . where P1 and P2 are, respectively, the probabilities that the particle passed through slit 1 or slit 2 and went on to arrive at the point P.
Quantum computation
Authors: Barnett Stephen
Published: November 2020

In the preceding chapter we established that a suitable set of quantum gates, complemented by quantum error correction, allows us to produce a desired multiqubit unitary transformation. This transformation is one of the three steps in a quantum computation; the others, of course, are the preparation of the qubits in their initial state and the measurement of them after the transformation has been implemented. A quantum computation is designed to solve a problem or class of problems. The power of quantum computers is that they can do this, at least for some problems, very much more efficiently and quickly than any conventional computer based on classical logic operations. If we can build a quantum computer then a number of important problems which are currently intractable will become solvable. The potential for greatly enhanced computational power is, in itself, reason enough to study quantum computers, but there is another. Moore’s law is the observation that the number of transistors on a chip doubles roughly every eighteen months. A simple corollary is that computer performance also doubles on the same timescale. Associated with this exponential improvement is a dramatic reduction in the size of individual components. If the pace is to be kept up then it is inevitable that quantum effects will become increasingly important and ultimately will limit the operation of the computer. In these circumstances it is sensible to consider the possibility of harnessing quantum effects to realize quantum information processors and computers. We start with a brief introduction to the theory of computer science, the principles of which underlie the operation of what we shall refer to as classical computers. These include all existing machines and any based on the manipulation of classical bits. The development of computer science owes much to Turing, who devised a simple but powerful model of a computing device: the Turing machine. It its most elementary form, this consists of four elements. (i) A tape for data storage, which acts as a memory. This tape has a sequence of spaces, each of which has on it one of a finite set of symbols. (ii) A processor, which controls the operations of the machine.
Linear Response Theory
Authors: Nitzan Abraham
Published: November 2020

Equilibrium statistical mechanics is a first principle theory whose fundamental statements are general and independent of the details associated with individual systems. No such general theory exists for nonequilibrium systems and for this reason we often have to resort to ad hoc descriptions, often of phenomenological nature, as demonstrated by several examples in Chapters 7 and 8. Equilibrium statistical mechanics can however be extended to describe small deviations from equilibrium in a way that preserves its general nature. The result is Linear Response Theory, a statistical mechanical perturbative expansion about equilibrium. In a standard application we start with a system in thermal equilibrium and attempt to quantify its response to an applied (static- or time-dependent) perturbation. The latter is assumed small, allowing us to keep only linear terms in a perturbative expansion. This leads to a linear relationship between this perturbation and the resulting response. Let us make these statements more quantitative. Consider a system characterized by the Hamiltonian Ĥ0.
Electron Transfer Processes
Authors: Nitzan Abraham
Published: November 2020

Electron transfer processes are at the core of all oxidation–reduction reactions, including those associated with electrochemistry and corrosion. Photoelectrochemistry and solar energy conversion, organic light emitting diodes, and molecular electronic devices, all dominated by electron transfer and electron transmission in molecular systems, are presently subjects of intensive research at the interface of science and technology. Similarly, electron transfer processes constitute fundamental steps in important biological phenomena such as photosynthesis and vision. This chapter is an introduction to the general phenomenology and theoretical concepts associated with these processes. Electron transfer is one of the most important, and most studied, elementary chemical processes. This most fundamental oxidation–reduction process lies at the core of many chemical phenomena ranging from photosynthesis to electrochemistry and from the essential steps governing vision to the chemical processes controlling corrosion. As other molecular phenomena that involve charges and charged particles, the natural environment for such processes is a polar solution; the solvation energy associated with the polarization of the environment is a major component in the energetics of such processes. Noting that in vacuum typical molecular ionization potentials are of the order of (100–400)kBT for T = 300 K, it appears that the stabilization of ionic species by the solvent environment is the reason why electron transfer processes in solution can take place at room temperature. When we try to go beyond this general statement, questions arise.
Electron Transfer and Transmission at Molecule–Metal and Molecule–Semiconductor Interfaces
Authors: Nitzan Abraham
Published: November 2020

This chapter continues our discussion of electron transfer processes, now focusing on the interface between molecular systems and solid conductors. Interest in such processes has recently surged within the emerging field of molecular electronics, itself part of a general multidisciplinary effort on nanotechnology. Notwithstanding new concepts, new experimental and theoretical methods, and new terminology, the start of this interest dates back to the early days of electrochemistry, marked by the famous experiments of Galvani and Volta in the late eighteenth century. The first part of this chapter discusses electron transfer in what might now be called “traditional” electrochemistry where the fundamental process is electron transfer between a molecule or a molecular ion and a metal electrode. The second part constitutes an introduction to molecular electronics, focusing on the problem of molecular conduction, which is essentially electron transfer (in this context better termed electron transmission) between two metal electrodes through a molecular layer or sometimes even a single molecule. In Chapter 16 we have focused on electron transfer processes of the following characteristics: (1) Two electronic states, one associated with the donor species, the other with the acceptor, are involved. (2) Energetics is determined by the electronic energies of the donor and acceptor states and by the electrostatic solvation of the initial and final charge distributions in their electronic and nuclear environments. (3) The energy barrier to the transfer process originates from the fact that electronic and nuclear motions occur on vastly different timescales. (4) Irreversibility is driven by nuclear relaxation about the initial and final electronic charge distributions. How will this change if one of the two electronic species is replaced by a metal? We can imagine an electron transfer process between a metal substrate and a molecule adsorbed on its surface, however the most common process of this kind takes place at the interface between a metal electrode and an electrolyte solution, where the molecular species is an ion residing in the electrolyte, near the metal surface. Electron transfer in this configuration is the fundamental process of electrochemistry.